Fin515 Wk 4

7-2 – Boehm Incorporated is expected to pay a $1. 50 per share dividend at the end of this year (i. e. , D1 = $1. 50). The dividend is expected to grow at a constant rate of 7% a year. The required  rate of return  on the stock, rs, is 15%. What is the value per share of Boehm’s stock? D1= $1. 50 per share g = 7% rs= 15% What is the value of a share of Boehm Stock? P^0 =    D1 /(rs – g) P^0 =    1. 50/(0. 15-0. 07) P^0 =    $18. 75 7-4 – Nick’s Enchiladas Incorporated has preferred stock outstanding that pays a dividend of $5 at the end of each year. The preferred sells for $50 a share.What is the stock’s required rate of return? Dividend = $5 Preferred    = $50 What is the stock’s required rate of return ^P 0 = D/rs rs = D/^P 0 rs = 5/50 rs = 0. 10 or 10% 7-5 – A company currently pays a dividend of $2 per share (D0 = $2). It is estimated that the company’s dividend will grow at a rate of 20% per year for the next 2 years, then at a constant rate of 7% thereafter. The company’s stock has a beta of 1. 2, the risk- free rate is 7. 5%, and the market risk premium is 4%. What is your estimate of the stock’s current price? D0 = $2. 00 g = 20% for 2 years g = 7% there after Bi = 1. 2 Rf = 7. 5%RPm = 4% Rs = Rf +(bi* RPm) Rs = 7. 5 +(1. 2*4) Rs = 12. 3 What is your estimate of the stock’s current price? D0 $2. 00 g0 to 1 20. 0% g1 to 2 20. 0% gn 7. 0% rs 12. 3% Year 1 2 D1 D2 Expected dividends $2. 40 $2. 88 Expected P2 $58. 14 PV of expected dividends $4. 42 PV of expected P2 $46. 10 Expected P0 $50. 53 Problems (p. 371) 9-2 After-Tax Cost of Debt LL Incorporated’s currently outstanding 11% coupon bonds have a yield to maturity of 8%. LL believes it could issue new bonds at par that would provide a similar yield to maturity. If its marginal tax rate is 35%, what is LL’s after-tax cost of debt?After Tax cost of debt = rd * (1- tx rate) 0. 08 * (1 – 0. 35) = 0. 08 * (0. 65) = 0. 052 Answer: 5. 2% 9-4 Cost of Preferred Stock with Flottion Costs Burnwood Tech plans to issue some $60 par preferred stock with a 6% dividend. A similar stock is selling on the market for $70. Burnwood must pay flotation costs of 5% of the issue price. What is the cost of the preferred stock? E= Dividend/ (Market price-Flotation Costs)=(60/6)/(70-(70X0. 05)=0. 0541=5. 41 Answer: 5. 41% 9-5 Cost of Equity – DCF Summerdahl Resorts' common stock is currently trading at $36 a share. The stock is expected to pay a dividend of $3. 0 a share at the end of the year (D1 _ $3. 00), and the dividend is expected to grow at a constant rate of 5% a year. What is the   cost of common equity? P0 = $36; D1 = $3. 00; g = 5%; rs = ? rs = D1/P0+g=(3/36)+0. 05=0. 01333 Answer: 13. 33% 9-6 Cost of Equity – CAPM Booher Book Stores has a beta of 0. 8. The yield on a 3-month T-bill is 4% and the yield on a 10-year T-bond is 6%. The market risk premium is 5. 5%, an d the return on an average stock in the market last year was 15%. What is the estimated cost of common equity using the CAPM? rs = rRF + bi(RPM) = 0. 06 + 0. 8(0. 55) = 0. 14 Answer: 10. 4% 9-7 WACC Shi Importers' balance sheet shows $300 million in debt, $50 million in preferred stock, and $250 million in total common equity. Shi faces a 40% tax rate and the following data: rd _ 6%, rps _ 5. 8%, and rs _ 12%. If Shi has a target capital structure of 30% debt, 5% preferred stock, and 65% common stock, what is Shi's WACC? 30% Debt; 5% Preferred Stock; 65% Equity; rd = 6%; T = 40%; rps = 5. 8%; rs = 12%. WACC = (wd)(rd)(1 – T) + (wps)(rps) + (wce)(rs) WACC = 0. 30(0. 06)(1-0. 40) + 0. 05(0. 058) + 0. 65(0. 12) = 0. 0917 Answer: 9. 17%

In the Romanesque Church the Interior Decoration Was More Important Than the Architecture. Do You Agree

Romanesque art and architecture we can see that there are many points for and against the statement ‘in the Romanesque church the interior decoration was more important than the architecture’. There are many surviving Romanesque churches throughout Europe which we can look to when discussing topics like this particular one. However, many of these churches have been redecorated, restored, extended in later periods or even just left in disrepair, but from looking at a wide range of buildings from different regions and countries we can get a general sense of what the buildings would have looked like at the time.In my essay I will discuss points in favour of the above statement, points against the above statement and also my own opinion on the subject. I will firstly discuss a few of the points in favour of the topic ‘interior decoration was more important than the architecture’. Looking at many Romanesque churches and buildings we can see that the interior deco ration is more important than the architecture. The first point, and example, is that the architecture was plain and basic, more about being structurally sound than aesthetically pleasing the viewers, and we can see this at Cuddesdon Church, in Oxfordshire.This church in England, even though the architecture and interior decoration are both modest compared with many other Romanesque churches, shows us that the interior decoration is more important than the architecture. The exterior stone walls are thick and undecorated. The architecture is exclusively for functional reasons, not decorative. There is a tower, west portal and south portal off this cruciform shaped church.However the interior decoration in this church was more elaborately considered and carried out than the architecture. One example to show this is the tower crossing, which has richly ornamented Norman arches. All the outer faces of the arches have two orders with angle half-rolls, except for the arch facing the nave. This has a hood with doghead stops, an outer order of zigzag, and an inner order with roll-moulding. In many of the Romanesque churches the interior decoration is elaborate, intricate and sophisticated.The patrons, architects and designers in the Romanesque period may have had the notion that the interior decoration was more important as that was where people would have worshipped, prayers would have been said and where ceremonies were held. Examples of this elaborate interior decoration can be seen in places such as the Cappella Palatina (Palermo), the Santa Maria in Trastevere (Rome) and the Eglise Notre-Dame de l'Assomption (Gourdon). These buildings have interior decoration features such as decorated capitals, fluting, vaulting, frescoes, arches, round blind arches and sculptural decoration.There are many other features of Romanesque interior decoration that add to the point that architecture was less important than the interior decoration. Maybe if the architecture really had been more important than the interior decoration, the Gothic style of architecture would have emerged sooner replacing the plain and basic architecture that was associated with the Romanesque style. The second point to discuss is that the interior decoration was not, in truth, more important than the architecture.The architecture of the Romanesque style could also be seen as carefully designed, well thought out and engineered. Even the most architecturally simple buildings would reinforce this point, because if the architecture was not considered as important, the exterior would be plain, different types of stones would not have been used, there would be no vaulting, no arches or any other structurally yet decoratively relevant features. The buildings would not be able to support towers, there would not have more clerestories or upper levels.There are then the Romanesque buildings where the architecture is startlingly intricate, elaborate and detailed. An example of this is the Egli se Notre-Dame-la-Grande, Poitiers. The west front of Notre-Dame-la-Grande is one of the finest Romanesque facades in France. It is flanked by turrets topped with conical spires, which, along with the rich sculpture, are the hallmarks of Poitou Romanesque architecture . The plan of the church consists of a central nave with aisles which is a common plan in Romanesque architecture of the province of Poitou.The sculpture of the West Front depicts many scenes; saints, prophets, creatures, foliage, the story of Jesus, the word of God spread by apostles and Christ in Glory. The inside of the church consists of a dim, barrel-vaulted nave with no clerestory, more narrow side aisles, a transept crossing capped with a tower, a diminutive choir, and a groin-vaulted ambulatory with radiating chapels. Other examples of buildings where the architecture is clearly not less important than the interior decoration are St. Martin's Cathedral (Mainz), Abbaye aux Hommes (Caen), Winchester Cathedral (Ham pshire) and LyonCathedral (Lyon). Some of the architectural features in these buildings include Romanesque towers, vaults, intricate exterior sculpture, high rising towers and outer buildings, ample windows and strong walls capable of reaching significant heights (without the use of buttresses). From looking at several buildings and different points of view regarding the statement ‘in the Romanesque church the interior decoration is more important than the architecture’, I can discuss my ideas and opinions regarding the above statement.In my opinion neither the architecture nor the interior decoration has priority or more importance over the other. I would say there is a parallel between the two aspects. The architecture allows for the interior decoration to be created, as it structurally supports the whole building and constructs features for the interior decoration to be created on, for example sculpture on columns and arches, mosaics and frescoes on ceilings and wall s, and stained glass windows which are structurally able to be placed there because of walls (and later buttresses).An example, in my opinion, of a Romanesque building where architecture and interior decoration are parallel in terms of importance is the Ely Cathedral, Cambridgeshire. Off the south aisle of the nave is the Prior's Door, which has a magnificent example of 12th-century Romanesque carvings. Dating from about 1150, its tympanum depicts Christ in Majesty held aloft by archangels and blessing the creatures of the universe. Two human heads peer down from the corners and the pilasters on the sides have medallions populated by various beasts and humans .This massive scale cathedral shows how both architecture and interior decoration were equally important, as both features were sophisticatedly designed. In conclusion, we can see that there are many different ideas about the statement ‘in the Romanesque church the interior decoration was more important than the architect ure’. In my opinion both features are equal, however the whole subject is open to debate for academics and art historians. Architecture can seem plain and incomplete without interior decoration, and interior decoration cannot exist without architecture.The fact that many buildings still survive help us to understand the Romanesque period and the art and architecture from that time. Yet as we have no firsthand experience with the buildings at that time we cannot characterize what the architects and engineers, or even just the viewers of the buildings, were thinking in regards to architecture versus interior decoration. ?Bibliography †¢http://www. sacred-destinations. com/reference/romanesque-architecture †¢http://www. wordiq. com/definition/Romanesque †¢http://www. sacred-destinations. com/categories/romanesque

The European Chivalry: the Ideals and Practices

The Ideals and Practices Andrew Daniels Strayed University Abstract This paper focuses on the ideals and practices of chivalry, specifically in the Middle Ages. During this time, a list of Ten Commandments pertaining to chivalry existed. Knights were expected to uphold a certain code that impacted their country, church, king, and fellow man. This paper will elaborate on those individual commandments and explore what each mandate meant for a knight, and it will show how those obligations affected various aspects of their lives.Also, the paper will touch on heavily In relation to a knight's demeanor toward a woman, and the rules that were to be followed when engaging in courtly love. Lastly, one will see how some of these ideas have carried into modern day, though they have been altered throughout time. Picture King Arthur, a knight In shining armor, waging war against his former knight Lancelot to prove his love for Guinevere. Most people envision such scenes when they hear the word à ¢â‚¬Å"chivalry. While dragon-slaying knights and tales of rescuing damsels in distress have contributed to our notion of chivalry, many more unifying aspects make up what it means to be chivalrous. I will be delving into the true meaning behind the principles and what it means to be a knight devoted to the ideals of chivalry. Knights first evolved in the eighth century under the direction of the French ruler Charlemagne; It was from this time that the Idea of chivalry arose. Though the code of chivalry was never formally written, it was understood by all as a way of culture and moral conduct.During the Middle Ages, knights upheld the ideals and practices delineated in The Code of Chivalry. These values ranged from dedication to the church, to defending the weak and defending your country, and loading yourself to a higher standard by being faithful to your word and respecting others. The unspoken Ten Commandments revealed the duties a knight was to defend. This paper will further exp and upon the customs of knights and their chivalric ways. One of the major components of chivalry dealt with protecting the church.The first commandment stated, â€Å"thou shall believe all that the church teaches, and shall observe all its directions† (Marshall, 2002). The second commandment simply stated, â€Å"thou shall defend the Church† (Marshall, 2002). In the Middle Ages Christianity in ten Tort AT cottontails was ten only practice religion. I en snuck played a Olsten and dominate role in the majority of people's lives, not only medieval knights. Beginning as free peasants, knights often pillaged churches. Due to such violence, Rome declared knights the protectors of churches starting in the tenth century and threatening sanctions against any who ransacked churches.Later, in the 1 lath century, the Truce of God asserted that knights should not make war on all holy days, all saints days or Thursday through Sunday. Abiding to these rules meant that knights exhibi ted their chivalric duty by observing the churches directions. Not only did the knights protect the church, but the church protected the knights' estate if he embarked on a Crusade to Jerusalem, the supposed burial sight of Jesus. During his time away, the knight was also exempt from paying taxes to the church (Warrior Challenge, 2003).While knights were required to defend the church, they were also expected to defend the weak, according to the Code of Chivalry (Marshall, 2002). Knights were expected to protect the weak and innocent. Given a plot of land for their services, rather than monetary compensation, knights were required to oversee the land in order to keep agricultural procedures running smoothly and to ensure the well-being over their serfs. Another knightly duty was to avenge the wronged. This was possible with extensive training from the age of seven to twenty one.In this fourteen year span, knights learned everything from hunting and falconry to wielding a battle and v aulting on a horse in heavy armor (Martin, 1991). With a repertoire of experiences such as these, knights were surely qualified to shield anyone weaker than them. Moreover, knights â€Å"shall love the country in which thou waist born† (Marshall, 2002). Knights upheld this chivalric code by living to serve their king and country. In the eighth century when Charlemagne ruled over his vast empire he enacted many longstanding ideas both in religion and education.During this period he and his vassals were involved in protecting their borders; without such a charismatic leader knights may not have been so obliged to serve and defend their king and country. In order to exhibit love for his country, the knight was sure to obey the king, country, and Code of Chivalry. The fifth commandment found in the code of chivalry, â€Å"thou shall not recoil before thing enemy' (Marshall, 2002). In a time when battles were common, knights were expected to fight with honor and die with valor. T hese traits would have been taught to these men when they were squires training to be knights.However, knights also established principles of what not to do in battle. It was thought chivalrous to never attack an unarmed foe, never use a weapon on an opponent not equal to the attack, and never attack from behind (Marshall, 2002). By maintaining these principles a knight showed respect to themselves, their king and their country. The next commandment reads, â€Å"thou shall make war against the Infidel without sensation and without mercy,† which relates to the seventh commandment â€Å"thou snail perform scrupulously tiny Teal outlets, IT teen De not contrary to ten laws AT God† (Marshall, 2002).Certain tasks categorized under these two commandments were thought of as chivalrous. One such task stated that knights were to destroy evil in all of its atrocious forms. Knights were required to fight for the ideals of their king, country and chivalry, which meant annihilating all those that attempted to steal land or rob people within the kingdom's borders in which a knight resided. Protection of one's country by destroying the enemy remained a priority for knights, as long as they did not betray any teachings of the church.Knights also abided by the code, â€Å"thou shall never lie, and shall remain faithful to thy pledged word† (Marshall, 2002). It was thought gallant to live a life complete with respect and honor. Knights should not take for granted their freedom or their livelihood, and they must remain thankful for the opportunities provided to them. Of course, if knights kept their word of honor, they must avoid lying or cheating their fellow man. Living an existence abundant of deception would defy the principals hose chivalrous men were to uphold.Just as it was thought unethical to deceive their fellow man, it was also thought improper to desert a friend or ally in need. Likewise, knights were not to relinquish a noble cause, whether it p resented itself in the form of a battle, defending one's church, or protecting one's country (Marshall, 2002). By living a truthful, honest existence, knights became role models of suitable gentlemen, which have contributed to our current view of the word chivalry today. Additionally, the code of chivalry demands, â€Å"thou shall be generous, and give largesse to everyone† (Marshall, 2002).Sir Thomas Malory provides a glimpse into such charitable actions as he recounts a scene between King Arthur and Sir Lancelot in his legend El Mortem d'art. After Arthur learns of Lancelot and Gunrunner's affair, he wages war against Lancet's kingdom, only to find himself at the mercy of Lancelot and his kinsman, Sir Boors' sword Not so hardy, said Sir Lancelot, upon pain of thy head, that thou touch him no more, for I will never see that most noble king that made me knight neither slain en shamed.And therewith Sir Lancelot alighted off his horse and took up the king ND horsed him again, a nd said thus: My lord Arthur, for God's love stint this strife, for ye get here no worship, and I would do mine utterance, but always I forbear you, and ye nor none of yours forbear me; my lord, remember what I have done in many places, and now I am evil rewarded (Taylor, 2010, Para. L). Lancelot spares Urethra's life, remembering when Arthur once placed his faith in Lancelot by making him his knight. Despite the quarrel between the former friends over Guinevere, they still respect one another.In this instance Lancet's generosity outweighs his desire to defeat Arthur. Such demonstrations of largesse, whether legend or not, reveal the true meaning behind this commandment. The final commandment documented in the Code of Chivalry states, â€Å"thou shall be everywhere and always the champion of the Right and the Good against Injustice an Eve â€Å"(Marshall,2 I Nils last commandment Disloyally encapsulates ten tore mentioned orders, reminding knights to live for all that is virtuous and to reinforce the need to respect the authority of country, church and king.Knights were to avoid certain practices such as torture and deceit; they were to remain loyal to their friends ND those who placed their trust in them. Furthermore, the concept of respecting women was considered a significant courtesy, though not directly mentioned in the Ten Commandments of Chivalry. Men were to exhibit manners at all times, and they must be polite and attentive to women. Additionally, gentlemen showed respect to whoever should be their host.Andrea Aquaplanes, a 12th century author, wrote De Amour, known today in English as The Art of Courtly Love. In his work, he addresses the â€Å"twelve chief rules of love,† and elaborates on thirty-one aspect of â€Å"the art of courtly love. Rules that men must abide by consisted of topics such as chastity: â€Å"Thou shall keep thyself chaste for the sake of her whom thou loves† (Marshall, 2002). Within these numerous rules, one can see what was thought of as proper in a relationship and the graciousness that was displayed toward women (Marshall, 2002).Concepts such as this reveal the origins of present day views on chivalry or in some opinions, the lack of chivalry. Overall, I feel the principles that contribute to the idea of chivalry, whether or not construed by legend, are important ones. The codes that knights abided by revealed number of characteristics: faith, loyalty, strength, honesty, generosity and courtesy. I believe living an existence according to these principles, or even attempting to attain such standards, makes a person a superior, well-rounded individual.Incorporating such characteristics into one's everyday life allows a person to be more virtuous, and these values reinforce one's relationship with the church, country and allies. The romanticism of chivalry has survived to present day, though the code is not held to standards nearly as high as in the past with the majority of the ideas fall ing to the wayside. I believe a rejuvenation of several of these notions could benefit factions of society and reinstate principles that should be essential for all mankind.

Assignment 6 Essay Example | Topics and Well Written Essays - 1250 words

Assignment 6 - Essay Example The data obtained reveals that learners are gifted differently, and there is a need to attend to them based on their abilities. This provides a platform for teachers to attend to learners with special needs. Necessary assistance would be extended to such learners. Assessing this type of records would be relatively easy with the assistance from subject teachers and administrators of the school. Working closely with parents would help avail necessary documents of previous performance. The author is involved as a principal in a school in Southern Oregon characterized by transition of leadership, where he replaces a principle that left little to be desired. The school has 86% annual student transient rate with a high teacher turnover. Parents’ involvement is low, and all is left to the teachers. The principal aims to turn things around and pull the high-poverty community together. The new principal is keen to realize the key affected areas in his new school. The teachers are alienated in decision-making, and their opinions are overlooked. The learners are not addressed appropriately, and there is a case of multiage grouping. Such a decision affects the overall performance of the learners, in the long run. Cooperative learning is poorly executed leading to a great deal of â€Å"Davids† in the institutions. Another problem is full class inclusion without paying attention to gifted and learners with special needs. The author further realizes that language learning was a mystery topic. With the involvement of teachers, he engages in an action research with an aim to have things work perfectly. He designs a plan to higher new teachers for the school to meet the demands of the learners. The learners would need instructors competent enough to better them. The principal purposes to meet the key parents for their involvement. They would support teachers establish the most conducive environment in the school. He identified requirements in the new

Gender and the effectiveness of leadership Research Paper

Gender and the effectiveness of leadership - Research Paper Example Leadership is defined as an art and science of influence (Emmerik, 2010). In the past, males were believed that they were blessed with the ability to practice leadership and females were considered ideal for occupying the subordinate roles in the organizations (Jogulu, 2006). Nevertheless, with the passage of time, females’ ability to practice leadership grew and therefore, many of them managed to break the so-called glass ceiling in the organizations that are operating in a vast range of industry (Kolb, 2013). The basic and fundamental purpose of the study is to run a descriptive investigation with reference to males and females’ capability of practicing leadership. The study will be conducted in order to evaluate the presence of the glass ceiling in the local corporate market (Mavin, 2012). Following are the research question and hypotheses respectively (Maleki, 2011). The character of the study will be experimental in nature Literature review Females as Effective Leaders Reports show that male and female leadership styles get influenced for their tasks and considerations based upon the organizational-structure (Maleki, 2011). This structure puts that one’s position in the hierarchy, rather than the gender influences the leadership style. The gender-organization and the gender-organization system develop that gender and organization system combine to influence the leadership behavior in an independent and interactive method (Jogulu, 2006). Major research in the area of gender and leadership stereo typicality show that the workplace is either self -perception centered or subordinate centered, based upon the female or male leadership behavior. ... The character of the study will be experimental in nature Literature review Females as Effective Leaders Reports show that male and female leadership styles get influenced for their tasks and considerations based upon the organizational-structure (Maleki, 2011). This structure puts that one’s position in the hierarchy, rather than the gender influences the leadership style. The gender-organization and the gender-organization system develop that gender and organization system combine to influence the leadership behavior in an independent and interactive method (Jogulu, 2006). Major research in the area of gender and leadership stereo typicality show that the workplace is either self -perception centered or subordinate centered, based upon the female or male leadership behavior. In most of the cases, gender differentiation has been more frequently reported by their subordinates rather than by the leaders themselves (Mavin, 2012). Marissa Mayer who is a CEO of Yahoo proved hersel f as the effective leader as she successfully managed to stimulate growth in the company by taking bold and concrete measures. The removal of policy supporting telecommuting is the most risky decision she took after becoming a leader. The featured lady challenged and nullified the presumption that under her command people can manage to take things easy because female leaders are weak when it comes to implementing discipline. The featured leader proved the common belief wrong by tightening the strings. The females that are leading the show for famous companies are known for their dedication towards discipline whereas; they tend to follow mechanistic philosophy in terms of organizational management. Elena Ford who is Vice President of Consumer Experience

Risk Managment Essay Example | Topics and Well Written Essays - 1500 words

Risk Managment - Essay Example The purpose of risk management centres not in eliminating risk, but to comprehend risk so that the organization can take advantage of the upside and reduce the downside. Risk management cannot be considered as an end in and of itself, but rather forms part of sound organizational practices detailing planning, program appraisal, process improvement, preparedness, and budget priority development. The core principles guiding effective risk management entail transparency, effectiveness, urgency, flexibility, adaptability, practicality, customization, robustness, synergy, and transparency. The key areas in risk management include fund (governance risk); strategy (asset allocation risk); implementation (manager risk and Implementation risk), and review (monitoring risk). Given the uncertainties connected to estimating the costs and benefits, the function of risk management strongly connected to process rather than outcome. Cost benefit analysis is a useful tool for structuring, appraising, and presenting the cost and benefits, as well as the pros and cons on interventions. This demands a coherent methodological, especially in data-restricted environments. In the context of risk management, two prominent issues deserve close attention when undertaking risk management: assessment of risk, whereby the analysis should be undertaken in a â€Å"stochastic way so as to account for the nature of exposure impacts† (Moller 2011, p.2). Second, the assessment of averted risks, whereby benefits represent risks avoided. The core benefits derived from investment in risk management centres on the minimization of future impacts and losses. Risk management plans may detail set functions, areas, activities, projects or processes that are consistent with the organization’s risk management strategy. In order to manage risk, companies should first comprehend the risks that they may be

Sleeping disorders Research Paper Example | Topics and Well Written Essays - 1250 words

Sleeping disorders - Research Paper Example On identifying, the causes of sleeping disorders can help you find solutions and enhance your sleeping patterns (Mayo Foundation par. 1). This is the most common sleep disorder experienced by most people. A person suffering from insomnia does not get the right amount of sleep necessary to keep rested or refreshed. A number of factors including stress, nervousness, depression or any health problem can cause insomnia. In addition, it can also occur because of lack of exercises, lifestyle choices and jet lack or consumption of a given food or drink such as increase in coffee intake (Kalimoet al. 65). A person suffering from insomnia may have difficulty in sleeping during the night or upon waking up during the night he or she will have trouble in resuming back to sleep. The person may also have the problem of waking up very recurrently during the night as well as having a very light sleep. The person may also require something to fall sleep and during the day, he can feel sleepiness and low body strength (Ford and Lisa 3). This causes an irresistible desire to move legs when sleeping. It occurs because of lack of comfort, tingling, ache and creeping sensation (Chervin 1185). The affected person will thus experience scratchy sensations cavernous within the legs and a strong desire to move. The movement of the legs tends to relieve the person from the sensations and the person will be repetitively jerking his legs when asleep (Walterset al. 634). Excessive, unmanned sleepiness during daytime are the common characteristics of this sleep disorder. It comes because of malfunction of the part of the brain that determines sleeping and waking. A person with narcolepsy sees things when starting dream and often feels weak and loses control of his muscles when laughing. He may also experience easy dreams even when he just starts sleeping and

Growth Strategies to Achieve Competitive Advantage Essay

Growth Strategies to Achieve Competitive Advantage - Essay Example Business growth is nothing but a double-edged sword. If it is well managed and properly controlled, it would definitely provide remarkable rewards to the shareholders as well as to the leaders of the emerging organization. But when growth is uncontrolled and poorly planned it might results in financial misery and failure (Sherman, A. J. July 13, 2006). Effective planning and management are crucial for sustaining the growth for a long time. Lack of effective planning and management would result to attack by the creditors, competitors, creative takeover specialists and hostile employees. The central question that needs to be asked regarding this topic is what strategies ought to be followed in facilitating growth. Apart from this central question, there could be various sub-questions which would be associated with the business structure, availability of the capital, time and market condition. The central question focus on the strategies that are required for growth. Without proper stra tegy, no management can keep the organization on the growth track. These strategies would be based on the structure of the organization, availability of the capital, time and market condition. As a result, these factors would be the main focus of the sub-questions. XYZ power utility company is operating in a developing state of Southern Africa. The company is a state-operated company; as a result, there is lack of efficiency in company’s operation. There could be various growth strategies for such a company. Ansoff matrix is one of the most useful growth strategies which are widely used in the industry. There are four strategies in Ansoff matrix. These are market penetration, product development, Market development, and diversification. In market penetration strategy organization tries to grow with its existing product within its existing market. In product development strategy firm introduces a new product in the existing market. In market development strategy firm identifies a new market for its existing product and finally in diversification strategy firm introduce a new product in a totally new market (Valuebasedmanagement.net, n.d.).

President George Washington's Childhood Essay Example | Topics and Well Written Essays - 500 words

President George Washington's Childhood - Essay Example These critical years laid a foundation for the greater tasks that awaited him later. George Washington’s father, Augustine Washington, had high ambitions. He owned slaves, land, practiced tobacco farming, built mills and dealt with iron mines. He married George Washington’s mother, Mary Ball in 1731 after the death of his first wife, Jane Butler in 1729 who had left behind three children. George Washington was the first born of the six children born by Mary Ball. Their family was prosperous, and among the top middle class of Virginia (Freeman, Alexander & Ashworth, 2007). George Washington spent most of his youth on Ferry Farm on the Rappahannock River, Virginia. Little is known about his childhood. However, a widely held notion is that George Washington was home schooled between the ages five and fifteen, and attended sexton classes at a nearby church. Career wise, George Washington first worked as a teacher of Math, Geography, English, and Latin classics. This was important as it prepared him for future leadership roles. His interaction with supervisors in plantations and backwoodsmen made him more knowledgeable. He had learnt surveying, tobacco growing and stock rising by the time he was a teenager. At the age of eleven, he lost his father and so lived with Lawrence, his half-brother, who brought him up in a commendable way. Here, he received schooling in the colonial culture under the directions of Lawrence’s wife, Anne Fairfax. At the age of sixteen, George was part of a surveying group that plotted land in the Western territory of Virginia. In 1749, Lord Fairfax appointed George, to be the official surveyor of Culpeper, Augusta, and Frederick Counties. The two years’ experience as a surveyor made George a strong and resourceful man, both physically and psychologically. This also enhanced his interest in land buying, which prevailed for the rest of his life, as he bought large pieces of land and

Newspaper article Essay Example for Free

Newspaper article Essay The Pirates put out an amazing playoff season, this year having been the first year in the playoffs since 1992, but on October 9, 2013 they lost to the St. Louis Cardinals ending their amazing playoff season. In their last playoff game in St. Louis the Pirates lost 6-1 to the Cardinals, ending the season. In the second inning the Cardinals scored two runs taking the lead over the pirates. There was no more scoring until the sixth inning when the Cardinals scored yet another run, now having a three point lead over the Pirates. In the next inning the Pirates scored their first run. And sadly, the Cardinals scored three more runs in the eighth inning ending the game at a score of 6-1. The Pirates played the best theyve played since 1992, which wasnt enough this time. There was some amazing plays in the game, but I believe an incredible one was in the fourth inning when Starling Marte covered about twenty feet to catch a fly ball and get the second out with his incredible dive catch. An articles read about their season said that they played everything right, it was a amazing season but it wasnt enough this year, they needed a little more. This year the Pirates MVP player is Andrew McCutchen, he put up an OPS+ of 158, and swiped 27 bags this season. The teams LVP was Barmes, who plays shortstop, he hit a measly . 211/. 249/. 309, which is considered quite weak. The Pirates gameplan for next season is to keep the team mostly intact, and to hopefully make it farther into the playoffs next season. According to Christian Hartman The teams MVP should definitely be McCutchen, he hits well, plays amazing center field, and hes just overall great. He is everything a player should be. The Pirates put out an amazing playoff season, this year being their first playoff season since 1992.

Digital Security And Privacy Information Technology Essay

Digital Security And Privacy Information Technology Essay In this essay i will look at the basic fundamentals of security and privacy for users and businesses in the 21st century and what i think the security risks are for them and what the impact the security problems have on our privacy laws, does this controversal access to everybit of information about people actually make system more secure e.g prevent system attacks. I will go indept into what i believe are the main security risks for users and businesses when browsing the internet or shopping and using online banking and also discuse briefly what it would be like to have no privacy. I will also discuses how when a user goes on a scoial networking site or search engine they might be at risk of sharing information unwillingly with the providers. And another topic i will be discussing in this is how humans fail in there bit for security and how to prevent this from happening. Digital security in the 21st century is now more important than ever before, there are many different types of security threats to the average person, business or even government. This is because everything we do on a daily basis can have a security risk, whether it be from online shopping or checking your email. If a users computer has been hacked or has some spyware or malware and they are using it for online shopping, then the attacker may be able to gain access to the users sensitive data which can then be used for fraud or theft or sold on to a third party for marketing data. Shopping in a store using your debit card can also be a risk as debit cards can be cloned by staff and pin numbers stolen using a device that looks the same as the card machine but has been designed or modified to remember pin codes and clone users debit cards/credit card details. Laptops and Mobile phones being stolen can have personal information on them, even losing your universal serial bus storage device or USB pen drive as they are know as for short which can contain all sorts of information because people, businesses and governments all use these devises to move or store data. And if the data is not encrypted then there is always the chance that someone can gain access to it. Security is the main issue when it comes to a persons personal information whether it be from browsing the Internet to online banking there will always be people who want to steal information for an entire range of reasons (eg: phishing and fraud) ! Another thing to be wary of is the topic of Liberty; are security laws infringing on our basic human rights to privacy and our security by allowing corporations and even governments to spy on our Internet communications for what they call  ¿Ã‚ ½anti-piracy ¿Ã‚ ½ or National Security such as the PATRIOT Act in the United Sates of America, and this brings me to conclude, why should the rights of the many suffer because of the actions of a few. And this is being debated everyday of every week by civil rights activists to our own government deciding what they can do and cannot do. Too much information available about anyone to anyone can be dangerous and this topic should be taken extremely seriously. One major impact on privacy is the development of social networking sites and search engine providers that sell the users information to third parties. The quote Privacy is a fundamental human right. It underpins human dignity and other values such as freedom of association and freedom of speech. It has become one of the most important human rights of the modern age. by Marc Rotenberg, Protecting Human Dignity in the Digital Age (UNESCO 2000) 1. And i think that we are heading into a society that does not care about the fundamental human rights we have and how we attained them. For example anti-utopian, dystopian novels of the 20th century, depicted societies where privacy was non existant and an intrusive, oppressive regime denied this fundamental human right as a matter of course. In Yevgeny Zamyatins novel  ¿Ã‚ ½We ¿Ã‚ ½ 2the population lived in buildings constructed of glass, which allowed everyone and anyone to snoop on anyone whom they wished. Opposition is impossible in a society where privacy is non-existant. George Orwells 1984  ¿Ã‚ ½Big Brother ¿Ã‚ ½ and tele-screen are frighteningly similar to todays move towards a 21stcentury society where the Government and corporations have full access to every bit of any citizens digital life. The 19thcentury black champion of civil rights, Frederick Douglass protested that any rights and liberties won by any people were awarded after contesting the power structures of society. He said in 1857 that  ¿Ã‚ ½Power concedes nothing without a demand, it never did and it never will. Find out just what any people will quietly submit to, and you have found out the exact measure of injustice and wrong that will be imposed upon them. ¿Ã‚ ½ 3 Frederick Douglass, speaking on the emancipation of the West Indies, 1857  ¿Ã‚ ½Men may not get all they pay for in this world, but they must certainly pay for all they get. ¿Ã‚ ½ 3 also has meaning to that you can use a search engine for free and also a social networking site, but be careful of your information as they might sell it on to third parties. In the book; The Art of Deception: Controlling the Human Element of Security 4, the authors Kevin D. Mitnick William L. Simon na ¿Ã‚ ½blame the Human individual as the weakest link, the individual is relegated to a position below the security system in question. Page 3, titled in big black letters  ¿Ã‚ ½Securitys Weakest Link ¿Ã‚ ½ states  ¿Ã‚ ½the humanfactor is truly securitys weakest link. ¿Ã‚ ½ In the Computer Security Handbook, John Wiley Sons (2002) 5which some of the top security specialists in the world have contributed to. Donn B. Parker, a retired (1997) senior management consultant at RedSiren Technologies in Menlo Park, Ca, who has specialised in information security for 35 of his 50 years in the computer field and who Information Security Magazinehas identified as one of the five top Infosecurity Pioneers (1998) writes in  ¿Ã‚ ½5.1.3 Functions of Information Security Computer Security Handbook ¿Ã‚ ½ that the complete opposite to the previous paragraph is true, that the current three function security model, (prevention, detection, and recovery) are completely insufficient and that an 11 function model is needed to eliminate or mitigate the security risks in question, which include avoidance, deterrence, detection, prevention, mitigation, transference, investigation, sanctions rewards, recovery, correction, finally; education 5. It is easy to jump to conclusions and intuitively blame the people whom personify  ¿Ã‚ ½hackers ¿Ã‚ ½ or adversaries to computer security professionals, but history shows us that nothing should be taken for granted concerning security. No system will be inherently perfect, and new technologies are continually being created and updated, and most will likely become more secure as time goes on. Human nature on the other hand is a constant and no man or woman should ever denigrate humanity to a role below that of a firewall, for any reason. If a computer security system is vulnerable, patch the system or come up with innovative methods to secure it from outside access, improve on the imperfect and take comfort knowing that you have executed your job successfully, thus without sacrificing your morality. Types of attack  ¿Ã‚ ½ Once a malicious program has been installed on a person or business or governments bodys computer, it can cause harm in many different ways. And the most typical mechanisms for attacks by hackers is:  ¿Ã‚ ½ taking control of a users access and pretending to be that legitimate user. This can be very bad if a hacker gains access to any information as the user might not realise in time for it to be stopped being used eg. bank account or credit card information being stolen.  ¿Ã‚ ½ Stealing or copying secret or confidential data for corporate espionage or other purposes.  ¿Ã‚ ½ Destroying corporate data to do financial damage to a business or government body  ¿Ã‚ ½  ¿Ã‚ ½ Causing network and system shortages to paralyze a company ¿Ã‚ ½s operations eg. Denial of service attack (D.O.S) or Distributed denial of service attack (D.D.O.S). Risks to an Organisation: Security vulnerabilites coming from within an organisation are on the increase in todays businesses and are increasingly the operational risks of any business in todays world, and in a time of recession this is not good because it brings the running costs of the business up and costs to the average person may go up also . so this can lead to a loss of reputation in the regard to customers or partnership in a company or even the share holders of the company. There may also be a risk to the business by interruption to the company and lead to the violation of legal and government reulation requirements to protect sensitive customer information E.G OFCOM if the attack works, some examples are:  ¿Ã‚ ½ Unauthorized access to any information where the access includes disclosure, modification and destruction of any data.  ¿Ã‚ ½ Unauthorized users or hackers, i.e. a person who have not been given the rights by the owner/user to access the system. How do people fail in the line of security? Social Engineering Manipulation: con-artists are being used to acquire confidential information by manipulating genuine users into telling them. It is a new type of insider attack that is on the up trend similar to an attack that is knowm as  ¿Ã‚ ½phishing ¿Ã‚ ½ in which a malicious or hackeris able toget internal access with access to company sensitive information in turn which can lead to other users/customers into providing access to forbiddon information. These con-artists rely and work on the basis that people are kind hearted and not aware of the valuble information they know and are careless about protecting it because they think its irrelevant. These con-artists will search bins or skips or take advantage of people ¿Ã‚ ½s natural ability to choose passwords that are based on what is considered to bemeaningful to the user such as relative ¿Ã‚ ½s, date of birth or pets name etc but can be easily guessed if the hacker learns persoanl information about them. the name they now give the method these con-artists employ is called  ¿Ã‚ ½Social engineering ¿Ã‚ ½ and will always a threat to any security system. More internal threats may be: if there is aloss of data or data is corrupted, and backups fail this will lead to business having a losses of revenu and this in turn may affect the clients and loss of money to a business. There may also be misuse and theft of Call Records and information and also tele-communication center in which, internal breaches my accure by users who sometimes bypass the usage record from billing someone or a subscribers and then bydeleting the call record information from a database or by manipulating a program to overlook simple things to user subscribers. Identity theft: Identity theft of a customer ¿Ã‚ ½s valuable information such as address, security passwords credit card information, and date of birth or in a business ¿Ã‚ ½s sense, ID cards, Access codes . Identity fraud is a term that is used to refer to any type of crime in which any person or business wrongfully gets hold of and uses another person ¿Ã‚ ½s personal data in anyway way that may involves fraud or deception, typically for capital gains eg. giving the business an upper-hand from a competitor. Information used in scanning of biometrics for example of soem (face image scanner, palm print scanner, hand scanner ,handwriting of a person, fingerprints,voice recognition software, iris/retina scaners ) are each unique to every person and cannot be given to another human for their use, but can be faked, well some of them. However, personal data, especially a credit card account or debit card number, and other valuable personal information can be taken advantage of and maybe used by the wrong person for fraudulent purposes and sold to third parties at the cost to the average users. The not so innocent: Browsing the Web and using e-mails can seem a normal exercise in layman terms but may seem na ¿Ã‚ ½ve to the advanced users whom understand the security risks. For the average user however, all their activities can upset business. Some viruses that can do this are ( Worms/trojons/malware/spyware or Choke viruses) that are design and aimed at Instant Messaging systems that people use such as a social networking site and windows live messenger (MSN), the users may use these softwares or websites to talk to their friends online or send information from and each pose their own unique security threats. Anti-virus softwares and other tools may not detect malicious code opening through the font-system 6 or Instant Messaging system, so infected files can infect the desktop and then into the network or a business. If a company ¿Ã‚ ½s usb stick or security cards or notebooks are lost or stolen, important information may be at risk such as id names and Unique Identifier numbers. Outside threats to an organisation: External threats are mixed threats that combine many different ways such as worms, viruss, spam and distributed denial of service (DDOS). Every day, hundreds of new ways are discovered to attack software and security breaches by intruders, hackers and security professionals. There are more than 30k hacking-based Web sites on the internet now so it no longer needs a computer savy person to hack a site, just someone with time and patience. How to keep your computer safe with Virus Counter Measures. Regular Updating of a users Anti-Virus and Anti Spyware Software: This is to protect the user against viruses and malware/spyware and this is why antivirus software should be installed. All user email attachment files should be scanned: This is because computer viruses are most likely to be in an email attachment. just because emails come from your best friends does not mean it is still not important to scan there emails which may contain attachments before opening them as they may contain anything. Key points for handling email attachments:  ¿Ã‚ ½ Be careful when opening email attachments from unknown recipients.  ¿Ã‚ ½  ¿Ã‚ ½ Do not be fooled by the appearance of attachment files always check the extension to make sure its not a .exe, .com or any other  ¿Ã‚ ½executable ¿Ã‚ ½ extension for a word document or image file.  ¿Ã‚ ½  ¿Ã‚ ½ Do not send a plain text that can be included in the body of an email message as an attachment file eg. Encrypt your messages.  ¿Ã‚ ½  ¿Ã‚ ½ Learn about how email attachments are handled by different email programs.  ¿Ã‚ ½  ¿Ã‚ ½ Every file that is should be scanned with a users anti-virus and anti-spyware scanner before opening, because the user will never fully know whats inside.  ¿Ã‚ ½  ¿Ã‚ ½ A lot of files such as image files, .MP3,.MP4 and .avi videos are downloaded from the Internet, but some are notwhat we expect and contain malicious programs embedded in them or in the code of these files to hurt or dammage our computers, and a way to avoid this is to be sure to scan downloaded files before using them or opening them. An example is the font system vulnerability of Windows XP. 6  ¿Ã‚ ½  ¿Ã‚ ½ Take full advantage of the security functions/ settings supplied with any application software  ¿Ã‚ ½  ¿Ã‚ ½ Regulary updates of Security Patches Should be installed: All recent viruses attempt to exploit bug in a software or security holes that a programmer mite not have known about when creating the software to gain access to the operating systems and application software that a current user might be using.  ¿Ã‚ ½  ¿Ã‚ ½ If there is any weakness in your computer it can be and most likely will be infected with viruses or have corporate malware on them and the only way to combat this is by previewing emails or accessing the Internet when all security updates have been applied and clearing your Internet cookies after every session. causes of Virus Infection must not be overlooked. If you have encountered symptoms that you think are a virus you should do a scan, a users computer may have been infected with any sort of virus . so it is very important to watch out for this as it can be a major security flaw and scan your computer for viruses regularly to avoid disapointment. If a users computer system or an application freezes, or the system does not start. Files may be deltes or just become hidden. Unknown icons apear. some programs may make attempts to access the Internet without any notification to the user, this is why a firewall is needed. Emails are sent without the user ¿Ã‚ ½s consent. Scan intuitively to make sure there is no virus or spyware on a users PC. All a users data should backup data regulary in case of of system failure: Data corrupted by a system or hardware failure cannot always be restored by using software. Make the habit of getting use to backing up. Conclusion

Investigating Interference in Response Time

Investigating Interference in Response Time Saran Singh Sound An experiment to investigate Interference in response time Abstract In my investigation I have replicated the Stroop Effect, which is a test for checking interference in response time and processing. This effect has been useful as it helps us understand that brain’s reaction time slows down when there is conflicting stimuli. In my investigation i wanted to check for the difference in the response time participants take when a colored block stimulus is compared to a conflicting stimulus. For the collection of data for this experiment participants were conveniently chosen i.e. the students were sent into the classroom as an when they were free. In the experiment I recorded the response time of each participant until they finished the whole task. For the purpose of this investigation, standard deviation was used as a statistic measure. It was hypothesized that participants would have increased response time in the conflicting stimuli as it had interference. Our replicated study seems to match the same. Word Count: 152 Introduction Automatic processing can be defined as processes that do not require attention; they can often be performed along with other tasks without interference.[1] The Stroop Effect tested how automatic processing works. J. Ridley Stroop (1935) aimed to demonstrate the effect of interference in the reaction time. Stroop used only five colors (red, blue, green, brown, and purple) for his stimuli and conducted three separate experiments. He tested different number of participants for each of his experiments. In his first experiment he made his seventy undergraduate college participants (14 male and 56 female) read two stimuli and call out the color name in both cases. Stimulus-one was a list of color names printed in black ink and stimulus-two was a list of colors written in conflicting/contradictory ink, i.e., blue written in red ink. For the second experiment, Stroop used 100 participants (88 college undergraduates, 29 males and 59 females, and 12 graduate students, all females) who were als o made to read two stimuli. Stimulus-one was a list of colored square boxes and stimulus-two was a list of color names printed in conflicting/contradictory ink. The participants were made to call out the color the words and blocks are printed in. In his last experiment, Stroop replicated experiment two in the same manner except for two things. One he used thirty two undergraduates’ participants from the University of Arizona and second he replaced the colored blocks with colored swastikas. The results of Stroops’ experiment were: Naming of the ink color in the neutral stimuli was faster than in the conflicting stimulus which is semantic interference. When participants were asked to name the word instead of the ink color semantic interference disappeared. In this study we have replicated the Stroop Effect and our aim and hypothesis is that there would be an increase in the response time for the conflicting stimuli Method Design Repeated measures were used for this experiment. Using repeated measures helped us control any effects that might be attributed to personal characteristics of the participants, such as age and gender and if random measures were used we wouldn’t have truly known the effect of interference on response time. The independent variable for my experiment was the two-stimulus and the dependent variable was the response time taken in seconds to identify the color of the ink in both the stimuli; colored block stimuli and contradictory ink stimuli. The instructions and procedure was kept constant for each participant. During the experiment, ethical considerations were made. Participants data was kept anonymous, were given right to withdraw and were debriefed[2] after the experiment. They were also made to sign an informed consent form[3] at their own wish and will before the experiment was conducted. Participants The participants in this experiment were conveniently chosen Jamnabai Narsee School IB Seniors population non psychology students. Convenience sampling was used because at the time of conducting this experiment regular classes were functioning in the School and only the students who were free at that time were chosen to participate. A total of ten participants out of 98 students in the seniors’ population were used for this experiment; 7 male and 3 female. The participants’ age ranged from sixteen to seventeen. All of the participants were fluent with English and were from the same educational and cultural background. Materials Standardized Instructions[4] Informed Consent[5] Matrix of colored blocks printed on blank sheet of paper- Colored block stimulus[6] Matrix of color names printed in contradictory ink on blank sheet of paper-Conflicting stimulus[7] Post task questions[8] Debriefing[9] Digital stopwatch  ±0.01s Pens Procedure The materials for this experiment were prepared using word processing and photo editing software. The steps for carrying out the experiment were as follows: Participants were tested individually in a classroom in Jamnabai Narsee School. The researcher read out the standardized instructions[10] out loud. Then the informed consent[11] was handed out to be signed. Instructions on performing the task first condition (Colored block stimulus)[12]-were read aloud to the participants The participants were then informed to begin the task on the count of 3. After the participant finished speaking out all the color names the stopwatch was stopped and the time was noted. The participants were then instructed on the second condition (Word stimulus)[13]. They were told to begin the new task at the count of 3. The stopwatch was stopped immediately after they finished the task and the time was noted. The post task questions[14] were handed over to the participants after they had finished their tasks. Lastly, the researcher debriefed[15] the participants on the nature of the experiment. Before the participants left they were thanked and instructed not to reveal their participation in this experiment in order to avoid revealing of the aim of this experiment. Results From the mean measure on Table 1, it can be deduced that the conflicting word stimulus had higher response times than the colored block stimulus. The colored block stimulus had response times close to the mean because it has a low standard deviation. The mean was calculated for this experiment as it measures the central tendency for the response time and furthermore, mean encompasses all the data. The standard deviation shows us how far the values tend to be from the mean. Calculations[16] Table 1: Mean response time and standard deviation of Colored Block Stimulus and Conflicting Word Stimulus Figure 1: Comparison of the mean response time for Colored Block Stimulus and Conflicting Word Stimulus. Discussion Colored Block Stimulus and Conflicting Word Stimulus have a mean of 17.0 and 24.8 seconds respectively. The difference in the time for both the stimulus suggests that response time was indeed greater for the conflicting word stimulus than that of the colored block stimulus which supports my hypothesis. This was because of the conflicting factors that caused interference and slowed processing speeds. This study matches the results found from the original Stroop Effect experiment[17]. The standard deviation value indicates that at some point of time there were errors in the experiment. While the execution of the experiment was simple, there were a few improvements which could have been made to ensure better results. The font size of the text was really small which increased the difficulty in reading it. The use of a slightly bigger font size would be beneficial. There were a few noises in the classroom which may have affected the participant’s concentration. Reassuring that there are no disturbances in the classroom during the experiment would be advantageous. There could also be an error in time from the researcher as there is a delay in the time at which the participant finishes the task and the time at which the researcher stops the stopwatch. The gender distribution for the experiment weren’t equal i.e. 7 male and 3 female participants. Some of the factors mentioned above could be the reason for the high standard deviation value. Therefore, after analyzing the data we can conclude that the hypothesis of my experiment was met even though there were some flaws in the experiment. References Stroop R, J. (n.d.), Stroop Effect, STUDIES OF INTERFERENCE IN SERIAL VERBAL REACTIONS. Journal of Experimental Psychology, 18, 643-662. Retrieved August 16, 2014 from http://psychclassics.yorku.ca/Stroop/ Gerrig, R., Zimbardo, P. (2002, January 1). Glossary of Psychological Terms. Retrieved October 30, 2014, from http://www.apa.org/research/action/glossary.aspx Resnik, D. (2011, May 1). National Institute of Environmental Health Sciences. Retrieved October 30, 2014, from http://www.niehs.nih.gov/research/resources/bioethics/whatis Appendices Appendix 1 Standardized Instructions: Appendix 2 Informed Consent: Appendix 3 Stimulus 1: Appendix 4 Stimulus 2 Appendix 5 Post Task Questions: Appendix 6 Debriefing: Appendix 7 Raw Data: Sample Standard Deviation calculation = = 1.7s [1] Gerrig, R., Zimbardo, P. (2002, January 1). Glossary of Psychological Terms. Retrieved October 30, 2014, from http://www.apa.org/research/action/glossary.aspx [2] Appendix 6 [3] Appendix 2 [4] Appendix 1 [5] Appendix 2 [6] Appendix 3 [7] Appendix 4 [8] Appendix 5 [9] Appendix 6 [10] Appendix 1 [11] Appendix 2 [12] Appendix 3 [13] Appendix 4 [14] Appendix 5 [15] Appendix 6 [16] Appendix 7 [17] Stroop R, J. (n.d.), Stroop Effect, STUDIES OF INTERFERENCE IN SERIAL VERBAL REACTIONS. Journal of Experimental Psychology, 18, 643-662. Retrieved August 16, 2014 from http://psychclassics.yorku.ca/Stroop/

where did all the yams go? :: essays research papers fc

What About All Those Yams? After all those stories and discussions about yams, I was curious to see what exactly Nigerians eat. As an agricultural society, most of their food comes from farming. They do have meat, but yams are the main food component of their diet. Most Nigerians eat a light breakfast and have their main meal in the late afternoon (Chroness). For meats, Nigerians have goat, cow, chicken, turkey, geese, guinea fowls, pigeon, fish, shrimp, crab, and other seafood. For fruits and vegetables, they have oranges, bananas, pineapples, tangerines, carrots, watermelons, guava, melons, limes, grape fruits, mangos, apple (tinier than American apples and pink and white in color), peppers, tomatoes, onions, peas, and many other things (Chroness). Yams, cocoyams and sweet potatoes are popular in Nigeria. Ah, those yams, also called isu. The image we, as Americans, conjure up when we think of yams is not the same as Nigerian yams. These yams can grown up to 7 feet long and weigh approximately 150 pounds. They have three (3) types of yams: white, yellow, and à ¢Ã¢â€š ¬Ã‹Å"water yamsà ¢Ã¢â€š ¬Ã¢â€ž ¢ (Gourmet). There are numerous ways to prepare and serve this abundant Nigerian food staple. However, they must be cooked, otherwise they are very toxic. Plain boiled yams, either white or yellow, are peeled, sliced up, usually into pieces about 3 centimeters, and boiled in water with salt. It is accompanied with vegetable oil, palm, oil, eggs, beans, and sometimes soup (Gourmet). Another popular meal is a variation of the above using boiled yams requires pounding the yams and forming small smooth balls with the them, it is eaten with vegetables, meat or fish soup. Nigerians also fry their yams. White or yellow yams are cut up into long thin squares and fried in vegetable oil or palm oil (Lipman). This is usually eaten by itself or occasionally as a side dish. Another dish is ojojo. This dish consists of cut up water yams that are fried in vegetable oil or palm oil. This dish is also usually eaten on its own(Recipes). Asaro is white or yellow yams peeled, sliced, and diced into small cubes, then cooked with ground tomatoes, peppers, sometimes meat, other spices, and comes out reddish in color (Recipes). Ikokore is similar to asaro, but it is made with different yams. Yes, there are different forms of yams! The water yam is softer in texture and, when cooked, it usually comes out a brownish color.

Barbados :: essays research papers

Barbados Barbados is a small country located in the Caribbean Sea. The capital is Bridgetown with a population of about 8,789. The head of state of Barbados is Queen Elizabeth II and she is represented by General Dame Nita Barrow. The total population of the country is around 252,000. The main language is English and the predominant religion is Christianity. Their date of independence was November 30, 1966. Barbados is the eastern most Caribbean Island. It is about 200 miles North-North East of Trinidad and about 100 miles East-South East of St. Lucia. It is the second smallest country in the Western Hemisphere. The major urban centers in the area include Bridgetown, Speightstown, Oistins, and Holetown. The land is mainly flat except for a series of ridges that rise up to about 1,000 feet and then falling towards the sea. The climate of the region consists of tropical temperatures influenced by the Northeast trade winds. The average annual temperature is approximately 77 degrees Fahrenheit. The daily temperatures rarely get above 90 degrees Fahrenheit. The dry season is cool, while the wet season is slightly warmer. The main rains come during the months of July, August, September, October, and November. The annual average rainfall is 40 inches in the coastal areas and 90 inches in the central areas. The net migration into Barbados is 4.82 per 1000. The annual growth rate is 0.4%, which is one of the lowest in the world. The annual birthrate is 15.45 per 1000, and the annual deathrate is 8.27 per 1000. Barbados ranks fourth in the World in population density with the overall density being 1526 per square mile. The whole island is inhabited, leaving no sparsely populated areas. The main race is Negro, which is about 92% of the population. The remainder of the population is consists of Whites (3.8%), Mulattoes (3.8%), and East Indians (0.4%). About 70% of the population is Anglican. The other 30% belong to various denominations such as Moravian, Methodist, and Roman Catholic. Barbados was once under British control from 1624. Its House of Assembly, which began in 1639, is the third oldest legislative body in the Western Hemisphere. By the time Britain left in 1966, the island was completely English in culture. The British influence is still seen today in quaint pubs, cricket games on the village greens, and in the common law. Barbados' government is British Parliament. The queen is the head of state and she is represented by the governor general. The governor general appoints an advisory council. The executive authority is the Prime Minister who is Owen Seymour Arthur which came into power on September 6, 1994.

Schoolbooks and the Female Stereotype

In the United States schoolbooks tend to show females as a passive and dependent creatures, who are used to serve males. A University of California professor claims that the most widely-used textbooks demonstrate girls in an inferior position to boys. Louise White, of the U. S. Office of Education expresses that because of a strong stereotype most girls think themselves as a servant who only does four jobs – nurse, secretary, teacher and mother. Lenore Weitzman points out that different types of texts were examined and the result was the next: boys are shown in a good way with great qualities and the girls play a passive role usually hidden in the house. If they are together, the girls are either watching the boys do something or they are helping them. Adult men are addressed with various skillful jobs. Elementary texts failed to reflect the complexities of the mother and housewife jobs, in spite of the fact that these â€Å"jobs† are simple but time-consuming. A study was done including many books, companies and stories, and this survey shows that the role of a housewife is a burden done by the women, but for them, this is the only source of happiness. In illustrations women are in a hard and unpleasant position while working, but, the typical father is the â€Å"good guy† who is the fount of all happiness. Professor Weitzman says that young girls tend to think themselves to serve others and have a good-look in order to please others. However, they are generally better than boys by the time they reach adolescence they are getting worse than boys.

Case Marriot and Flinder Valves Essay

1. Why is Marriott’s CFO proposing the Project Chariot? To improve the financial performance of the firm, by re-structuring the company in two separating activities to distinguish those that require a large fixed assets (Real estates ownership) and those with relative low amount of assets (Management services and others). By dividing in this way, the large amount of debt will go with the real estates ownership called Host Marriott Corp. (HMC), whereas the rest of activities will go to Marriott International (MII). Doing so, the value of the 2 firms combined will exceed this year’s book value, according to expectations (see appendix 1). 2. Is the proposed restructuring consistent with management’s responsibilities? It is, as it clearly separate the activities and focus on management services rather than owning the hotels. Furthermore, it improves the cash flows from the existing structure (see appendix 1), this improvement will allow HMC to meet its debt responsibilities ( a total cash flow projected of $771 million in 1992 versus $478 million in 1991. The DCF in HMC assuming a worst case scenario will exceed current value of the firm’s assets $5,218 million versus $4,600 million, which indicates that the firm will improve as its assets will appreciate. 3. The case describes two conceptions of managers’ fiduciary duty (page 9). Which do you favor: the shareholder conception or the corporate conception? Does your stance make a difference in this case? We agree upon favoring the shareholder conception, as this provides an improvement on cash flows, as this condition is met, other financial gaps can be covered, plus it revalues the total firm based upon the expected cash flows. In this particular case, by having this improvement on cash flow, debt responsibilities can be covered inside HMC or by using the line of credit guaranteed by MII. On regards of the bondholders, the option is to increase the return as bonds will reduce the grade to junk bonds, for the calculation on DCF we assume a return of 10.81 assuming the highest risk for bonds. This action will compensate bondholders for the action. 4. Should Mr. Marriott recommend the proposed restructuring to the board? Yes, as it increase the value of the combined firms, focus activities per company and provides better cash flows.

English Coursework †Crucible Essay

The Crucible’ is a play, based on a true event in American history. Written by Arthur Miller in 1953, The Crucible was set in the small Puritan village called Salem, Massachusetts in 1692. This town can be seen to be extremely oppressive, and a place in which people had no freedom or individuality.  Miller wrote the play during the period in which McCarthy’s anti-Communist campaign was at its height. Miller saw many parallels between this period and the ‘witch hunts’ in Salem, for example unsupported accusations, fear of individual difference, and people being encouraged to inform on their friends. Senator Joe McCarthy organized a twentieth-century version of ‘witch-hunting’. In the early 1950’s he exploited the US fears about Communism and managed to create a national campaign against Communists. As chairman of the House Un-American Activities Committee, McCarthy interrogated many witnesses and tried to make them inform on their friends. Anyone suspected of communist views was arrested for taking part in ‘Un-American Activities’. Between 1950 and 1954 McCarthy investigated and accused a wide range of famous people such as Walt Disney, John Lennon, and Marilyn Monroe. Even Miller was investigated as many of his plays were seen as an attack on capitalism. This was very similar to what happened in Salem in the 17th century. Salem can be seen as a corrupted society in which people were trapped by the strict rules of Puritanism. The accusations of witchcraft and dealing with the Devil in Salem were all started off by a group of girls who were caught chanting, dancing and conjuring spirits in the woods. Dancing and partying was forbidden at this time, due to the strict puritan rules. The forest was thought to be where the Devil ‘carried out his work’, which led people to believe that the girls were witches. This was a prime example of when people’s longing for individuality and or spiritual freedom was undermined by the rules within society. This can be compared to the anti-communists during the McCarthy years, in which people’s political freedom was undermined. Also in both situations the allegations lead to hysteria.  However, many people may argue that Salem is like any other society, even today, full of good and bad people, the exploited and the exploiters. The plot in the Crucible starts after the girls were found dancing and conjuring spirits in the woods, and there were already suspicions of witchcraft. After being accused of witchcraft the girls begin to accuse other people in the town in order to deflect the attention away from themselves. The court believes these accusations made by the girls, and many are named as witches, and are sentenced to death. This then leads to many hangings of innocent individuals, who would rather die than commit the sin of lying and having their names tarnished. John Proctor and Abigail Williams are two central characters in the play. Their secretive affair results in Abigail conjuring spirits, as she was obsessed with rekindling their relationship. However John rejected her, which led to her becoming even more desperate to be with him. Her desperate act led to a catalogue of events, resulting in the death of many innocent people. John is one of those suspected of witchcraft. When given the opportunity to confess, he does so. However after signing the confession, John suddenly changes his mind. He takes back his confessions as he realises that he could not live with a name associated with witchcraft, and would therefore rather die. This can be linked to the themes of integrity and courage. Both of these themes are explored throughout the play through many different characters. Another central theme within the play is envy, which is mainly shown through the character of Abigail Williams. Tyranny, purification, justice and bigotry are also key themes in the Crucible as they all contribute to the oppressive society in which the play is set. They also show how people at the time felt a deep religious need to cleanse the town of any association with the devil. This was due to fear and intolerance of any cultural or religious difference or spiritual freedom. All of the themes explored are linked to the individual as well as the society.

Reciprocating Engine

224 C H A P T E R 6 RECIPROCATING INTERNAL COMBUSTION ENGINES 6. 1 Introduction Perhaps the best-known engine in the world is the reciprocating internal combustion (IC) engine. Virtually every person who has driven an automobile or pushed a power lawnmower has used one. By far the most widely used IC engine is the spark-ignition gasoline engine, which takes us to school and work and on pleasure jaunts. Although others had made significant contributions, Niklaus Otto is generally credited with the invention of the engine and with the statement of its theoretical cycle.Another important engine is the reciprocating engine that made the name of Rudolf Diesel famous. The Diesel engine, the workhorse of the heavy truck industry, is widely used in industrial power and marine applications. It replaced the reciprocating steam engine in railroad locomotives about fifty years ago and remains dominant in that role today. The piston, cylinder, crank, and connecting rod provide the geometric basis of the reciprocating engine. While two-stroke-cycle engines are in use and of continuing interest, the discussion here will emphasize the more widely applied four-stroke-cycle engine.In this engine the piston undergoes two mechanical cycles for each thermodynamic cycle. The intake and compression processes occur in the first two strokes, and the power and exhaust processes in the last two. These processes are made possible by the crank-slider mechanism, discussed next. 6. 2 The Crank-Slider Mechanism Common to most reciprocating engines is a linkage known as a crank-slider mechanism. Diagramed in Figure 6. 1, this mechanism is one of several capable of producing the straight-line, backward-and-forward motion known as reciprocating.Fundamentally, the crank-slider converts rotational motion into linear motion, or vice-versa. With a piston as the slider moving inside a fixed cylinder, the mechanism provides the vital capability of a gas engine: the ability to compress and expand a gas . Before delving into this aspect of the engine, however, let us examine the crank-slider mechanism more closely. 225 It is evident from Figure 6. 2 that, while the crank arm rotates through 180Â °, the piston moves from the position known as top-center (TC) to the other extreme, called bottom-center (BC).During this period the piston travels a distance, S, called the stroke, that is twice the length of the crank. For an angular velocity of the crank,
, the crank pin A has a tangential velocity component
S/2. It is evident that, at TC and at BC, the crank pin velocity component in the piston direction, and hence the piston velocity, is zero. At these points, corresponding to crank angle  = 0Â ° and 180Â °, the piston reverses direction. Thus as  varies from 0Â ° to 180Â °, the piston velocity accelerates from 0 to a maximum and then returns to 0.A similar behavior exists between 180Â ° and 360Â °. The connecting rod is a two-force member; hence it is evident that there ar e both axial and lateral forces on the piston at crank angles other than 0Â ° and 180Â °. These lateral forces are, of course, opposed by the cylinder walls. The resulting lateral force component normal to the cylinder wall gives rise to frictional forces between the piston rings and cylinder. It is evident that the normal force, and thus the frictional force, alternates from one side of the piston to the other during each cycle.Thus the piston motion presents a challenging lubrication problem for the control and reduction of both wear and energy loss. The position of the piston with respect to the crank centerline is given by x = (S/2)cos + Lcos [ft | m] (6. 1) where yA = (S/2)sin = Lsin can be used to eliminate  to obtain x/L = (S/2L)cos + [1? (S/2L)2 sin2  ]? [dl] (6. 2) Thus, while the axial component of the motion of the crank pin is simple harmonic, xA = (S/2)cos, the motion of the piston and piston pin is more complex. It may be 226 seen from Equation (6. ), however , that as S/L becomes small, the piston motion approaches simple harmonic. This becomes physically evident when it is recognized that, in this limit, the connecting rod angle,  , approaches 0 and the piston motion approaches the axial motion of the crank pin. Equations (6. 1) and (6. 2) may be used to predict component velocities, accelerations, and forces in the engine. The volume swept by the piston as it passes from TC to BC is called the piston displacement, disp. Engine displacement, DISP, is then the product of the piston displacement and the number of cylinders, DISP = (n)(disp).The piston displacement is the product of the piston cross-sectional area and the stroke. The cylinder inside diameter (and, approximately, also the piston diameter) is called its bore. Cylinder bore, stroke, and number of cylinders are usually quoted in engine specifications along with or instead of engine displacement. It will be seen later that the power output of a reciprocating engine is proport ional to its displacement. An engine of historical interest that also used the crank-slider mechanism is discussed in the next section. 6. 3 The Lenoir CycleAn early form of the reciprocating internal combustion engine is credited to Etienne Lenoir. His engine, introduced in 1860, used a crank-slider-piston-cylinder arrangement 227 in which a combustible mixture confined between the piston and cylinder is ignited after TC. The resulting combustion gas pressure forces acting on the piston deliver work by way of the connecting rod to the rotating crank. When the piston is at BC, combustion gases are allowed to escape. The rotational momentum of the crank system drives the piston toward TC, expelling additional gases as it goes.A fresh combustible mixture is again admitted to the combustion chamber (cylinder) and the cycle is repeated. The theoretical Lenoir cycle, shown in Figure 6. 3 on a pressure-volume diagram, consists of the intake of the working fluid (a combustible mixture) fro m state 0 to state 1, a constant-volume temperature and pressure rise from state 1 to state 2, approximating the combustion process, an isentropic expansion of the combustion gases to state 3, and a constant-pressure expulsion of residual gases back to state 0.Note that a portion of the piston displacement, from state 0 to state 1, is used to take in the combustible mixture and does not participate in the power stroke from state 2 to state 3. The engine has been called an explosion engine because the power delivered is due only to the extremely rapid combustion pressure rise or explosion of the mixture in the confined space of the cylinder. Hundreds of Lenoir engines were used in the nineteenth century, but the engine is quite inefficient by todays standards. In 1862, Beau de Rochas pointed out that the 228 fficiency of internal combustion could be markedly improved in reciprocating engines by compression of the air-fuel mixture prior to combustion. In 1876 Niklaus Otto (who is thou ght to have been unaware of Rochas? suggestion) demonstrated an engine that incorporated this important feature, as described next. 6. 4 The Otto Cycle The Otto cycle is the theoretical cycle commonly used to represent the processes in the spark ignition (SI) internal combustion engine. It is assumed that a fixed mass of working fluid is confined in the cylinder by a piston that moves from BC to TC and back, as shown in Figure 6. . The cycle consists of isentropic compression of an air-fuel mixture from state 1 to state 2, constant-volume combustion to state 3, isentropic expansion of the combustion gases to state 4, and a constant-volume heat rejection back to state 1. The constant-volume heat rejection is a simple expedient to close the cycle. It obviates the need to represent the complex expansion and outflow of 229 combustion gases from the cylinder at the end of the cycle. Note that the Otto cycle is not concerned with the induction of the air-fuel mixture or with the expulsion of residual combustion gases.Thus only two mechanical strokes of the crank-slider are needed in the Otto cycle, even when it is used to represent an ideal four-stroke-cycle Otto engine. In this case the remaining strokes are used to execute the necessary intake and exhaust functions. Because it involves only two strokes, the Otto cycle may also represent a two-stroke-cycle engine. The two-stroke-cycle engine is in principle capable of as much work in one rotation of the crank as the four-stroke engine is in two. However, it is difficult to implement because of the necessity of making the intake and exhaust functions a part of those wo strokes. It is therefore not as highly developed or widely used as the four-stroke-cycle engine. We will focus on the fourstroke- cycle here. The simplest analysis of the Otto cycle assumes calorically perfect air as the working fluid in what is called the Air Standard cycle analysis. Following the notation of Figure 6. 4, the compression process can be represented by the isentropic relation for a calorically perfect gas, Equation (1. 21), as p2/p1 = (V1/V2)k [dl] (6. 3) where the compression ratio, CR = V1/V2, is a fundamental parameter of all reciprocating engines.The diagram shows that the expansion ratio for the engine, V4 /V3, has the same value, V1/V2. The clearance volume, V2, is the volume enclosed between the cylinder head and the piston at TC. Thus the compression ratio may be expressed as the ratio of the sum of the clearance and displacement volumes to the clearance volume: CR = [V2 + (V1 ? V2)]/V2 Thus, for a given displacement, the compression ratio may be increased by reducing the clearance volume. The efficiency of the cycle can be most easily determined by considering constantvolume- process heat transfers and the First Law cyclic integral relation, Equation (1. ). The heat transferred in the processes 2
3 and 4
1 are q2
3 = cv (T3 ? T2) [Btu/lbm | kj/kg] (6. 4) and q4
1 = cv (T1 ? T4) [Btu/lbm | kJ/kg] (6. 5) B oth the expansion process, 3
4, and the compression process, 1
2, are assumed to be isentropic. Thus, by definition, they are both adiabatic. From the cyclic integral, the net work per unit mass is then: w = q2
3 + q4
1 = cv (T3 ? T2 + T1 ? T4) [Btu/lbm | kJ/kg] (6. 6) 230 As before, the cycle thermal efficiency is the ratio of the net work to the external heat supplied: Otto = w/q2
3 = cv (T3 ? T2 + T1 ?T4) / [cv (T3 ? T2)] = 1 + (T1 ? T4) / (T3 ? T2) = 1 ? T1/T2 = 1 ? 1 / CR k-1 [dl] (6. 7) where Equation (1. 20) has been used to eliminate the temperatures. Equation (6. 7) shows that increasing compression ratio increases the cycle thermal efficiency. This is true for real engines as well as for the idealized Otto engine. The ways in which real spark ignition engine cycles deviate from the theoretical Otto cycle are discussed later. EXAMPLE 6. 1 An Otto engine takes in an air-fuel mixture at 80Â °F and standard atmosphere presssure. It has a compression ratio of 8.Using Air Stan dard cycle analysis, a heating value of 20,425 Btu/lbm, and A/F = 15, determine: (a) The temperature and pressure at the end of compression, after combustion, and at the end of the power stroke. (b) The net work per pound of working fluid. (c) The thermal efficiency. Solution We use the notation of Figure 6. 4: (a) p2 = p1(V1/V2)k = 1(8)1. 4 = 18. 38 atm T2 = T1(V1/V2)k ? 1 = (540)(8)0. 4 = 1240. 6Â °R T3 = T2 + qa /cv = T2 + (F/A)(HV)k/cp = 1240. 6 + 1. 420,425/150. 24 = 9184Â °R p3 = p2T3 /T2 = 18. 38(9184/1240. 6) = 136. 1 atm T4 = T3 /CRk? 1 = 9184/ 80. 4 = 3997. Â °R p4 = p3 /CRk = 136. 1/81. 4 = 7. 4 atm (b) The constant-volume heat addition is governed by the fuel-air ratio and the fuel heating value: qa = HV(F/A) = 20,425/15 = 1361. 7 Btu/lbm of air 231 qr = cv (T1 ? T4) = (0. 24/1. 4)( 540 ? 3997. 4) = ? 592. 7 Btu/lbm w = qa + qr = 1361. 7 + ( ? 592. 7) = 769 Btu/lbm (c) The cycle termal efficiency may then be determined from the definition of the heat engine thermal efficiency or Equation (6. 7): th = w/qa = 769/1361. 7 = 0. 565 th = 1 ? 1/80. 4 = 0. 565 _____________________________________________________________________ In view f the discussion of gas properties and dissociation in Chapter 3, the values of T3 and T4 in Example 6. 1 are unrealistically high. Much of the energy released by the fuel would go into vibration and dissociation of the gas molecules rather than into the translational and rotational degrees of freedom represented by the temperature. As a result, significantly lower temperatures would be obtained. Thus, while the analysis is formally correct, the use of constant-low-temperature heat capacities in the Air Standard cycle makes it a poor model for predicting temperature extremes when high energy releases occur.Some improvement is achieved by using constant-hightemperature heat capacities, but the best results would be achieved by the use of real gas properties, as discussed in several of the references. 6. 5 Combustion in a Reciprocating Engine The constant-volume heat transfer process at TC in the Otto cycle is an artifice to avoid the difficulties of modeling the complex processes that take place in the combustion chamber of the SI engine. These processes, in reality, take place over a crank angle span of 30Â ° or more around TC.Let us consider aspects of these processes and their implementation in more detail. Normally, the mixture in the combustion chamber must have an air-fuel ratio in the neighborhood of the stoichiometric value for satisfactory combustion. A more or less homogeneous mixture may be produced outside the cylinder in a carburetor, by injection into the intake manifold, or by throttle-body injection into a header serving several intake manifolds. In the case of the carburetor, fuel is drawn into the engine from the carburetor by the low pressure created in a venturi through which the combustion air flows.As a result, increased air flow causes lower venturi pressure and hence in creased fuel flow. The fuel system thus serves to provide an air-fuel mixture that remains close to the stoichiometric ratio for a range of air flow rates. Various devices designed into the carburetor further adjust the fuel flow for the special operating conditions encountered, such as idling and rapid acceleration. Maximum fuel economy is usually attained with excess air to ensure that all of the fuel is burned. A mixture with excess air is called a lean mixture.The carburetor 232 usually produces this condition in automobiles during normal constant-speed driving. On the other hand, maximum power is achieved with excess fuel to assure that all of the oxygen in the air in the combustion chamber is reacted. It is a matter of exploiting the full power-producing capability of the displacement volume. A mixture with excess fuel is called a rich mixture. The automotive carburetor produces a rich mixture during acceleration by supplying extra fuel to the air entering the intake manifold. The equivalence ratio is sometimes used to characterize the mixture ratio, whether rich or lean. The equivalence ratio,
, is defined as the ratio of the actual fuel-air ratio to the stoichiometric fuel-air ratio. Thus
> 1 represents a rich mixture and
< 1 represents a lean mixture. In terms of air-fuel ratio,
= (A/F)stoich /(A/F). Homogeneous air-fuel mixtures close to stoichiometric may ignite spontaneously (that is, without a spark or other local energy source) if the mixture temperature exceeds a temperature called the autoignition temperature.If the mixture is brought to and held at a temperature higher than the autoignition temperature, there is a period of delay before spontaneous ignition or autoignition This time interval is called the ignition delay, or ignition lag. The ignition delay depends on the characteristics of the fuel and the equivalence ratio and usually decreases with increasing temperature. In spark-ignition engines, compression ratios and therefore the temperatures at the end of compression are low enough that the air-fuel mixture is ignited by the spark plug before spontaneous ignition can occur.SI engines are designed so that a flame front will propagate smoothly from the spark plug into the unburned mixture until all of the mixture has been ignitied. However, as the flame front progresses, the temperature and pressure of the combustion gases behind it rise due to the release of the chemical energy of the fuel. As the front propagates, it compresses and heats the unburned mixture, sometimes termed the end-gas. Combustion is completed as planned when the front smoothly passes completely through the end-gas without autoignition. However, if the end-gas autoignites, a pinging or low-pitched sound called knock is heard.The avoidance of knock due to autoignition of the end-gas is a major constraint on the design compression ratio of an SI engine. If hot spots or thermally induced compression of the end-gas ignite it before the flame front does, there is a more rapid release of chemical energy from the end-gas than during normal combustion. Knock is sometimes thought of as an explosion of the end gas that creates an abrupt pulse and pressure waves that race back and forth across the cylinder at high speed, producing the familiar pinging or low-pitched sound associated with knock.Knock not only reduces engine performance but produces rapid wear and objectionable noise in the engine. Thus it is important for a SI engine fuel to have a high autoignition temperature. It is therefore important for SI engine fuel to have a high autoignition temperature. Thus the knock characteristics of commercially available fuels limit the maximum allowable design compression ratio for SI engines and hence limit their best efficiency. The octane number is a measure of a gasoline’s ability to avoid knock. Additives such as tetraethyl lead have been used in the past to suppress engine knock.However, the accumulation of lead in the environment and its penetration into the food cycle has 233 resulted in the phaseout of lead additives. Instead refineries now use appropriate blends of hydrocarbons as a substitute for lead additives in unleaded fuels. The octane number of a fuel is measured in a special variable-compression-ratio engine called a CFR (Cooperative Fuels Research) engine. The octane rating of a fuel is determined by comparison of its knocking characteristics with those of different mixtures of isooctane, C8H18, and n-heptane, C7H16.One hundred percent isooctane is defined as having an octane number of 100 because it had the highest resistance to knock at the time the rating system was devised. On the other hand, n-heptane is assigned a value of 0 on the octane number scale because of its very poor knock resistance. If a gasoline tested in the CFR engine has the same knock threshold as a blend of 90% isooctane and 10% n-heptane, the fuel is assigned an octane rating of 90. In combustion chamber de sign, the designer attempts to balance many factors to achieve good performance.Design considerations include locating intake valves away from and exhaust valves near spark plugs, to keep end-gas in a relatively cool area of the combustion chamber and thereby suppress hot-surface-induced autoignition tendencies. Valves are, of course, designed as large as possible to reduce induction and exhaust flow restrictions. More than one intake and one exhaust valve per cylinder are now used in some engines to improve ? engine breathing.? In some engines, four valves in a single cylinder are employed for this purpose.The valves are also designed to induce swirl and turbulence to promote mixing of fuel and air and to improve combustion stability and burning rate. Pollution and fuel economy considerations have in recent years profoundly influenced overall engine and combustion chamber design. Stratified-charge engines, for example, attempt to provide a locally rich combustion region to control peak temperatures and thus suppress NOx formation. The resulting combustion gases containing unburned fuel then mix with surrounding lean mixture to complete the combustion process, thus eliminating CO and unburned hydrocarbons from the exhaust.These processes occur at lower temperatures than in conventional combustion chamber designs and therefore prevent significant nitrogen reactions. 6. 6 Representing Reciprocating Engine Perfomance In an earlier section, the theoretical work per unit mass of working fluid of the Otto engine was evaluated for a single cycle of the engine, using the cyclic integral of the First Law of Thermodynamics. The work done by pressure forces acting on a piston can also be evaluated as the integral of pdV. It is evident therefore that the work done during a single engine cycle is the area enclosed by the cycle process curves on the pressure-volume diagram.Thus, instead of using the cyclic integral or evaluating pdV for each process of the cycle, the work o f a reciprocating engine can be found by drawing the theoretical process curves on the p? V diagram and graphically integrating them. Such a plot of pressure versus volume for any reciprocating engine, real or theoretical, is called an indicator diagram. 234 In the nineteenth and early twentieth centuries a mechanical device known as an engine indicator was used to produce indicator cards or diagrams to determine the work per cycle for slow-running steam and gas reciprocating ngines. The indicator card was attached to a cylinder that rotated back and forth on its axis as the piston oscillated, thus generating a piston position (volume) coordinate. At the same time a pen driven by a pressure signal from the engine cylinder moved parallel to the cylinder axis, scribing the p-V diagram over and over on the card. The work of high speed engines is still evaluated from traces of pressure obtained with electronic sensors and displayed on electronic monitors and through digital techniques.T he work done per cycle (from an indicator card, for instance) can be represented as an average pressure times a volume. Because the displacement volumes of engines are usually known, an engine performance parameter known as the mean effective pressure, MEP, is defined in terms of the piston displacement. The mean effective pressure is defined as the value of the pressure obtained by dividing the net work per cylinder per cycle at a given operating condition by the piston displacement volume: MEP = W/disp [lbf/ft2 | kPa] (6. 8)Thus the MEP is a measure of the effectiveness of a given displacement volume in producing net work. The power output of an engine with identical cylinders may be represented as the product of the work per cycle and the number of cycles executed per unit time by the engine. Thus if the engine has n cylinders, each executing N identical thermodynamic cycles per unit time, and delivering W work units per cylinder, with a piston displacement, disp, the power outpu t is given by P = n
N
W = n
N MEP  disp [ft-lbf /min | kW] (6. 9)Expressed for the entire engine, the engine displacement is DISP = ndisp and the engine work is MEP DISP. Hence the engine power is: P = N MEPDISP [ft-lbf /min | kW] (6. 10) where N, the number of thermodynamic cycles of a cylinder per unit time, is the number of crank-shaft revolutions per unit time for a two-stroke-cycle engine and one-half of the revolutions per unit time for a four-stroke-cycle engine. The factor of ? for the four-stroke-cycle engine arises because one thermodynamic cycle is executed each time the crank rotates through two revolutions. EXAMPLE 6. 2What is the displacement of an engine that develops 60 horsepower at 2500 rpm in a four-stroke-cycle engine having an MEP of 120 psi? 235 Solution From Equation (6. 10), the displacement of the engine is DISP = P/(N MEP) = (60)(33,000)(12)/[(2500/2)(120)] = 158. 4 in3 Checking units: (HP)(ft-lbf/HP-min)(in/ft)/[(cycles/min)(lbf/in2)] = in3 ________ _____________________________________________________________ If the work is evaluated from an indicator diagram the work is called indicated work; the MEP is called the indicated mean effective pressure, IMEP; and the power is indicated power, IP.Note that the indicated work and power, being associated with the work done by the combustion chamber gases on the piston, do not account for frictional or mechanical losses in the engine, such as piston-cylinder friction or the drag of moving parts (like connecting rods) as they move through air or lubricating oil. Brake Performance Parameters Another way of evaluating engine performance is to attach the engine output shaft to a device known as a dynamometer, or brake. The dynamometer measures the torque, T, applied by the engine at a given rotational speed.The power is then calculated from the relation P = 2rpm T [ft-lbf /min | N-m/min] (6. 11) A simple device called a prony brake, which was used in the past, demonstrates the concept for the measurement of the shaft torque of engines. Figure 6. 5 shows the prony brake configuration in which a stationary metal band wrapped around the rotating flywheel of the engine resists the torque transmitted to it by friction. The product of the force measured by a spring scale, w, and the moment arm, d , gives the resisting torque. The power dissipated is then given by 2(rpm)w d.Modern devices such as water brakes and electrical dynamometers long ago replaced the prony brake. The water brake is like a centrifugal water pump with no outflow, mounted on low-friction bearings, and driven by the test engine. As with the prony brake, the force required to resist turning of the brake (pump) housing provides the torque data. This, together with speed measurement, yields the power output from Equation (6. 11). The power dissipated appears as increased temperature of the water in the brake and heat transfer from the brake. Cool water is circulated slowly through the brake to mainta in a steady operating condition.The torque measured in this way is called the brake torque, BT, and the resulting power is called the brake power, BP. To summarize: while indicated parameters relate to gas forces in the cylinder, brake parameters deal with output shaft forces. Thus the brake power differs from the indicated power in that it accounts for the effect of all of the energy losses in the engine. The difference between the two is referred to as the friction power, FP. Thus FP = IP ? BP. 236 Friction power varies with engine speed and is difficult to measure directly.An engine is sometimes driven without fuel by a motor-dynamometer to evaluate friction power. An alternative to using friction power to relate brake and indicated power is through the engine mechanical efficiency, m: m = BP/IP [dl] (6. 12) Because of friction, the brake power of an engine is always less than the indicated power; hence the engine mechanical efficiency must be less than 1. Clearly, mechanical e fficiencies as close to 1 as possible are desired. The engine indicated power can also be expressed in terms of torque, through Equation (6. 11). Thus an indicated torque, IT, can be defined.Similarly, a brake mean effective pressure, BMEP, may be defined that, when multiplied by the engine displacement and speed, yields the brake power, analogous to Equation (6. 10). Table 6. 1 summarizes these and other performance parameters and relations. The thermal efficiency, as for other engines, is a measure of the fuel economy of a reciprocating engine. It tells the amount of power output that can be achieved for a given rate of heat release from the fuel. The rate of energy release is, in turn, the product of the rate of fuel flow and the fuel heating value.Thus, for a given thermal efficiency, power output can be increased by employing a high fuel flow rate and/or selecting a fuel with a high heat of combustion. If the thermal efficiency is evaluated using the brake power, it is called t he brake thermal efficiency, BTE. If the evaluation uses the indicated power, it is called the indicated thermal efficiency, ITE. 237 It is common practice in the reciprocating engine field to report engine fuel economy in terms of a parameter called the specific fuel consumption, SFC, analogous to the thrust specific fuel consumption used to describe jet engine performance.The specific fuel consumption is defined as the ratio of the fuel-mass flow rate to the power output. Typical units are pounds per horsepower-hour or kilograms per kilowatt-hour. Obviously, good fuel economy is indicated by low values of SFC. The SFC is called brake specific fuel consumption, BSFC, if it is defined using brake power or indicated specific fuel consumption, ISFC, when based on indicated power. The SFC for a reciprocating engine is analogous to the heat rate for a steam power plant in that both are measures of the rate of energy supplied per unit of power output, and in that low values of both are d esirable.Volumetric Efficiency The theoretical energy released during the combustion process is the product of the mass of fuel contained in the combustion chamber and its heating value if the fuel is completely reacted. The more air that can be packed into the combustion chamber, the Table 6. 1 Engine Performance Parameters Indicated Brake Friction Mean effective pressure IMEP BMEP FMEP = IMEP – BMEP
m = BMEP / IMEP Power IP BP FP = IP – BP
m = BHP / IHP Torque IT BT FT = IT – BT
m = BT / IT Thermal efficiency ITE BTE
m = BTE / ITE Specific fuel consumption ISFC BSFC
m = ISFC / BSFC more fuel that can be burned with it.Thus a measure of the efficiency of the induction system is of great importance. The volumetric efficiency, v, is the ratio of the actual mass of mixture in the combustion chamber to the mass of mixture that the displacement volume could hold if the mixture were at ambient (free-air) density. Thus the average mass-flow rate of air through a cylinder is v (disp) aN. Pressure losses across intake and exhaust valves, combustion-chamber clearance volume, the influence of hot cylinder walls on mixture density, valve timing, and gas inertia effects all influence the volumetric efficiency.EXAMPLE 6. 3 A six-cylinder, four-stroke-cycle SI engine operates at 3000 rpm with an indicated mean effective pressure of five atmospheres using octane fuel with an equivalence ratio 238 of 0. 9. The brake torque at this condition is 250 lbf? ft. , and the volumetric efficiency is 85%. Each cylinder has a five inch bore and 6 inch stroke. Ambient conditions are 14. 7 psia and 40Â °F. What is the indicated horsepower, brake horsepower, and friction horsepower; the mechanical efficiency; the fuel flow rate; and the BSFC? Solution The six cylinders have a total displacement ofDISP = 6? 52? 6/4 = 706. 86 in3 Then the indicated horsepower is IP = MEP? DISP? N /[12? 33,000] [lbf /in2][in3][cycles/min]/[in/ft][ft-lbf /HP-min] = (5)(14. 7)(706 . 86)(3000/2)/[12? 33,000] = 196. 8 horsepower The brake horsepower, from Equation (6. 11), is: BP = 2 ? 3000 ? 250 / 33,000 = 142. 8 horsepower Then the friction power is the difference between the indicated and brake power: FP = 196. 8 ? 142. 8 = 54 horsepower and the mechanical efficiency is m = 142. 8/196. 8 = 0. 726 The ambient density is a = 14. 7 ? 144/ [53. 3 ? 500] = 0. 0794 lbm /ft3 nd the mass flow rate of air to the engine is ma = 0. 85? 0. 0794? 706. 86? (3000/2)/1728 = 41. 4 lbm /min For octane the stoichiometric reaction equation is C8H18 + 12. 5O2 + (12. 5? 3. 76)N2
8CO2 + 9H2O + (12. 5? 3. 76)N2 The fuel-air ratio is then F/A = 0. 9? [(8? 12) + (18? 1)]/[12. 5(32 + 3. 76? 28)] = 0. 0598 lbm-fuel /lbm-air 239 The fuel flow rate is mf = ma (F/A) = 41. 4 ? 0. 0598 = 2. 474 lbm /min The brake specific fuel consumption is BSFC = 60 mf /BHP = 60? 2. 474/142. 8 = 1. 04 lbm /BHP-hr ____________________________________________________________________ 6. Spark-Ignition E ngine Performance A typical indicator diagram showing intake and exhaust processes, valve actuation, and spark timing for a four-stroke-cycle SI engine is shown in Figure 6. 6. It is assumed that an appropriate air-fuel mixture is supplied from a carburetor through an intake manifold to an intake valve, IV, and that the combustion gas is discharged through an exhaust valve, EV, into an exhaust manifold. The induction of the air-fuel mixture starts with the opening of the intake valve at point A just before TC.As the piston sweeps to the right, the mixture is drawn into the cylinder through the IV. The pressure in the cylinder is somewhat below that in the intake manifold due to the pressure losses across the intake valve. In order to use the momentum of the mixture inflow through the valve at the end of the intake stroke to improve the volumetric efficiency, intake valve closure is delayed to shortly after BC at point B. Power supplied from inertia of a flywheel (and the other rotat ing masses in the engine) drives the piston to the left, compressing and raising the temperature of the trapped mixture.The combustion process in a properly operating SI engine is progressive in that the reaction starts at the spark plug and progresses into the unburned mixture at a finite speed. Thus the combustion process takes time and cannot be executed instantaneously as implied by the theoretical cycle. In order for the process to take place as near to TC as possible, the spark plug is fired at point S. The number of degrees of crank rotation before TC at which the spark occurs is called the ignition advance. Advances of 10Â ° to 30Â ° are common, depending on speed and load.The spark advance may be controlled by devices that sense engine speed and intake manifold pressure. Microprocessors are now used to control spark advance and other functions, based on almost instantaneous engine performance measurements. Recalling the slider-crank analysis, we observ that the piston vel ocity at top center is momentarily zero as the piston changes direction. Therefore no work can be done at this point, regardless of the magnitude of the pressure force. Thus, to maximize the work output, it is desired to have the maximum cylinder pressure occur at about 20Â ° after TC.Adjustment of the spark advance (in degrees before TC) allows some control of the combustion process and the timing of peak pressure. For a fixed combustion duration, the combustion crank-angle interval must increase with engine speed. As a consequence, the ignition advance must increase with increasing engine speed to 240 maintain optimum timing of the peak pressure. Following combustion, the piston continues toward bottom center as the high pressure gases expand and do work on the piston during the power stroke. As the piston approaches BC, the gases do little work on the piston as its velocity again approaches zero.As a result, not much work is lost by early opening of the exhaust valve before BC ( at point E) to start the blowdown portion of the exhaust process. It is expedient to sacrifice a little work during the end of the power stroke in order to reduce the work needed to overcome an otherwise-high exhaust stroke cylinder pressure. Inertia of the gas in the cylinder and resistance to flow through the exhaust valve opening slow the drop of gas pressure in the cylinder after the valve opens. Thus the gases at point E are at a pressure above the exhaust manifold pressure and, during blowdown, rush out through the EV at high speed.Following blowdown, gases remaining in the cylinder are then expelled as the piston returns to TC. They remain above exhaust manifold pressure until reaching TC because of the flow resistance of the exhaust valve. The EV closes shortly after TC at point C, terminating the exhaust process. The period of overlap at TC between the intake valve opening at point A and exhaust valve closing at point C in Figure 6. 6 allows more time for the intake and exh aust processes at high engine speeds, when about 10 milliseconds may be available for these processes.At low engine speed and at idling there may be some mixture loss through the exhaust valve and discharge into the intake manifold during this valve overlap period. The combined exhaust and induction processes are seen to form a ? pumping loop? that traverses the p-V diagram in a counterclockwise direction and therefore 241 represents work input rather than work production. The higher the exhaust stroke pressure and the lower the intake stroke pressure, the greater the area of the pumping loop and hence the greater the work that must be supplied by the power loop (clockwise) to compensate.Great attention is therefore paid to valve design and other engine characteristics that influence the exhaust and induction processes. Volumetric efficiency is a major parameter that indicates the degree of success of these efforts. Performance Characteristics A given ideal Otto-cycle engine produce s a certain amount of work per cycle. For such a cycle, MEP = W/disp is a constant. Equating the power equations (6. 9) and (6. 11) shows that the average torque is proportional to MEP and independent of engine engine speed.Therefore power output for the ideal engine is directly proportional to the number of cycles executed per unit time, or to engine speed. Thus an Otto engine has ideal torque and power characteristics, as shown by the solid lines in Figure 6. 7. The characteristics of real engines (represented by the dashed lines) tend to be similar in nature to the ideal characteristics but suffer from speed-sensitive effects, particularly at low or high speeds. Torque and power characteristics for a 3. 1 liter V6 engine (ref. 9) are shown by the solid lines in Figure 6. 8.Note the flatness of the torque-speed curve and the expected peaking of the power curve at higher speed than the torque curve. Rather than present graphical characteristics such as this in their 242 brochures, automobile manufacturers usually present only values for the maximum power and torque and the speeds at which they occur. Engine characteristics such as those shown in the figure are invaluable to application engineers seeking a suitable engine for use in a product. 6. 8 The Compression-Ignition or Diesel Cycle The ideal Diesel cycle differs from the Otto cycle in that combustion is at constant pressure rather than constant volume.The ideal cycle, shown in Figure 6. 9, is commonly implemented in a reciprocating engine in which air is compressed without fuel from state 1 to state 2. With a typically high compression ratio, state 2 is at a temperature high enough that fuel will ignite spontaneously when sprayed directly into the air in the combustion chamber from a high-pressure fuel injection system. By controlling the fuel injection rate and thus the rate of chemical energy release in relation to the rate of expansion of the combustion gases after state 2, a constant243 pressure pro cess or other energy release pattern may be achieved as in Figure 6. . For example, if the energy release rate is high, then pressure may rise, as from 2 to 3’, and if low may fall to 3’’. Thus constant-pressure combustion made possible by controlling the rate of fuel injection into the cyclinder implies the use of a precision fuel injection system. Instead of injecting fuel into the high-temperature compressed air, the cycle might be executed by compression of an air-fuel mixture, with ignition occurring either spontaneously or at a hot spot in the cylinder near the end of the compression process.Inconsistency and unpredictability of the start of combustion in this approach, due to variations in fuel and operating conditions, and to lack of control of the rate of heat release with the possibility of severe knock, makes the operation of such an engine unreliable, at the least, and also limits the maximum compression ratio. The Diesel engine therefore usually emp loys fuel injection into compressed air rather than carbureted mixture formation. In the Air Standard cycle analysis of the Diesel cycle, the heat addition process is at constant pressure: q2
3 = cp(T3 ? T2) [Btu/lbm | kJ/kg] (6. 13) nd, as with the Otto cycle, the closing process is at constant volume: q4
1 = cv(T1 ? T4) [Btu/lbm | kJ/kg] (6. 14) 244 The net work and thermal efficiency are then: w = q2
3 + q4
1 = cp(T3 ? T2) + cv(T1 ? T4) = cvT1[k(T3/T1 ? T2/T1) + 1 ? T4/T1] [Btu/lbm | kJ/kg] (6. 15) Diesel = w/q2
3 = 1 + q4-
1/q2
3 = 1 + (cv/cp)(T1 ? T4)/(T3 ? T2) = 1 ? (1/k)(T1/T2)(T4/T1 ? 1)/(T3/T2 ? 1) [dl] (6. 16) The expressions for the net work and cycle efficiency may be expressed in terms two parameters, the compression ratio, CR = V1/V2 (as defined earlier in treating the Otto cycle) and the cutoff ratio, COR = V3/V2.The temperature ratios in Equations (6. 15) and (6. 16) may be replaced by these parameters using, for the constant-pressure process, COR = V3/V2 = T3/T2 an d by expanding the following identity: T4 /T1 = (T4/T3)(T3/T2)(T2 /T1) = (V3 /V4)k-1(V3/V2)(V1/V2)k-1 = [(V3/V4)(V1/V2)]k-1COR = (COR)k-1COR = CORk where the product of the volume ratios was simplified by recognizing that V4 = V1. Thus the nondimensionalized net work and Diesel-cycle thermal efficiency are given by w /cvT1 = kCRk-1(COR ? 1) + (1 ? CORk) [dl] (6. 17) and Diesel = 1 ? (1/k)[(CORk ? 1)/(COR ? 1)]/CRk-1 [dl] (6. 8) where the cutoff ratio, COR, is the ratio of the volume at the end of combustion, V3, to that at the start of combustion, V2. Thus the cutoff ratio may be thought of as a measure of the duration of fuel injection, with higher cutoff ratios corresponding to longer combustion durations. 245 Diesel-cycle net work increases with both compression ratio and cutoff ratio. This is readily seen graphically from Figure 6. 9 in terms of p-V diagram area. As with the Otto cycle, increasing compression ratio increases the Diesel-cycle thermal efficiency. Increasing cutof f ratio, however, decreases thermal efficiency.This may be rationalized by observing from the p-V diagram that much of the additional heat supplied when injection is continued is rejected at increasingly higher temperatures. Another view is that heat added late in the expansion process can produce work only over the remaining part of the stroke and thus adds less to net work than to heat rejection. EXAMPLE 6. 4 A Diesel engine has a compression ratio of 20 and a peak temperature of 3000K. Using an Air Standard cycle analysis, estimate the work per unit mass of air, the thermal efficiency, the combustion pressure, and the cutoff ratio.Solution Assuming an ambient temperature and pressure of 300K and 1 atmosphere, the temperature at the end of the compression stroke is T2 = (300)(20)1. 4 ? 1 = 994. 3K and the combustion pressure is p2 = (1)(20)1. 4 = 66. 3 atm Then the cutoff ratio is V3/V2 = T3/T2 = 3000/994. 3 = 3. 02 The expansion ratio is calculated as follows: V4 /V3 = (V1/V2)/(V 3 /V2) = 20/3. 02 = 6. 62 T4 = T3 (V3 /V4)1. 4 ? 1 = 3000/6. 620. 4 = 1409K w = 1. 005(3000 ? 994. 3) + (1. 005/1. 4)(300 ? 1409) = 1219. 6 kJ/kg qa = 1. 005(3000 ? 994. 3) = 2015. 7 kJ/kg th = w/qa = 1219. /2015. 6 = 0. 605, or 60. 5% _____________________________________________________________________ 246 6. 9 Comparing Otto-Cycle and Diesel-Cycle Efficiencies A reasonable question at this point is: Which cycle is more efficient, the Otto cycle or the Diesel cycle? Figure 6. 10 assists in examining this question. In general notation, the cycle efficiency may be written as th = wnet /qin = wnet /(wnet + |qout|) = 1 /(1 + |qout| /wnet) [dl] (6. 19) Comparing the Otto cycle 1? 2? 3? 4 and the Diesel cycle with the same compression ratio 1? 2? 3’? , we see that both have the same heat rejection but that the Otto cycle has the higher net work. Equation (6. 19) then shows that, for the same compression ratio, the Otto cycle has the higher efficiency. It has been observed that Diesel-cycle efficiency decreases with increasing cutoff ratio for a given compression ratio. Let us examine the limit of the Diesel-cycle efficiency for constant CR as COR approaches its minimum value, 1. We may write Equation (6. 18) as Diesel = 1 ? 1 /(kCRk-1) f (COR) where f(COR) = (CORk ? 1)/(COR ? 1). Applying L’Hospital’s rule, with primes 247 esignating differentiation with respect to COR, to the limit of f(COR) as COR
1, yields lim f(COR) = lim (CORk ? 1)’/ Lim (COR? 1)’ = lim kCORk ? 1 = k COR
1 COR
1 COR
1 and limDiesel = 1 ? 1 /CRk ? 1 COR
1 = Otto Thus the limit of the Diesel-cycle efficiency as COR approaches 1 is the Otto cycle efficiency. Hence Equation (6. 18) shows that the efficiency of the Diesel cycle must be less than or equal to the Otto-cycle efficiency if both engines have the same compression ratio, the same conclusion we reached by examination of the p-V diagram.Suppose, however, that the compression ratios are not the same. Compare the Otto cycle 1? 2’? 3’? 4 with the Diesel cycle 1? 2? 3’? 4 having the same maximum temperature in Figure 6. 10. The Otto cycle has a smaller area, and therefore less work, than the Diesel cycle, but the same heat rejection. Equation (6. 19) demonstrates that the Otto cycle has a lower thermal efficiency than the Diesel cycle with the same maximum temperature. The conclusion that must be drawn from the above comparisons is quite clear. As in most comparative engineering studies, the result depends on the ground ules which were adopted at the start of the study. The Otto cycle is more efficient if the compression ratio is the same or greater than that of the competing Diesel cycle. But knock in spark-ignition (Otto) engines limits their compression ratios to about 12, while Diesel-engine compression ratios may exceed 20. Thus, with these higher compression ratios, the Air Standard Diesel-cycle efficiency can exceed that of the Otto cycle. In practice, Diesel engines tend to have higher efficiencies than SI engines because of higher compression ratios. 6. 0 Diesel-Engine Performance In 1897, five years after Rudolph Diesel’s first patents and twenty-one years after Otto’s introduction of the spark-ignition engine, Diesel’s compression-ignition engine was proven to develop 13. 1 kilowatts of power with an unprecedented brake thermal efficiency of 26. 2% (ref. 7). At that time, most steam engines operated at thermal efficiencies below 10 %; and the best gas engines did not perform much better than the steam machines. Diesel claimed (and was widely believed) to have developed his engine from the principles expounded by Carnot.He had developed â€Å"the rational engine. † Whether his claims were exaggerated or not, Diesel’s acclaim was well deserved. He had developed an engine that operated at unprecedented temperatures and pressures, had proven his concept of ignition of fuel by injection into the c ompressed high-temperature air, and had overcome the formidable problems of injecting a variety of fuels in appropriate 248 amounts with the precise timing required for satisfactory combustion. His is a fascinating story of a brilliant and dedicated engineer (refs. 7, 8).In the Diesel engine, the high air temperatures and pressures prior to combustion are attributable to the compression of air alone rather than an air-fuel mixture. Compression of air alone eliminates the possibility of autiognition during compression and makes high compression ratios possible. However, because of the high pressures and temperatures, Diesel engines must be designed to be structurally more rugged. Therefore, they tend to be heavier than SI engines with the same brake power. The energy release process in the Diesel engine is controlled by the rate of injection of fuel.After a brief ignition lag, the first fuel injected into the combustion chamber autoignites and the resulting high gas temperature susta ins the combustion of the remainder of the fuel stream as it enters the combustion chamber. Thus it is evident that the favorable fuel characteristic of high autoignition temperature for an SI engine is an unfavorable characteristic for a Diesel engine. In the Diesel engine, a low autoignition temperature and a short ignition delay are desirable. Knock is possible in the Diesel engine, but it is due to an entirely different cause than knock in a spark-ignition engine.If fuel is ignited and burns as rapidly as it is injected, then smooth, knock-free combustion occurs. If, on the other hand, fuel accumulates in the cylinder before ignition due to a long ignition lag, an explosion or detonation occurs, producing a loud Diesel knock. The cetane number is the parameter that identifies the ignition lag characteristic of a fuel. The cetane number, like the octane number, is determined by testing in a CFR engine. The ignition lag of the test fuel is compared with that of a mixture of n-ceta ne, C16H34, and heptamethylnonane, HMN (ref. 0). Cetane, which has good ignition qualities, is assigned a value of 100; and HMN, which has poor knock behavior, a value of 15. The cetane number is then given by the sum of the percentage of n-cetane and 0. 15 times the percentage of HMN in the knock-comparison mixture. A cetane number of 40 is the minimum allowed for a Diesel fuel. 6. 11 Superchargers and Turbochargers The importance of the volumetric efficiency, representing the efficiency of induction of the air-fuel mixture into the reciprocating-engine cylinders, was discussed earlier.Clearly, the more mixture mass in the displacement volume, the more chemical energy can be released and the more power will be delivered from that volume. During the Second World War, the mechanical supercharger was sometimes used with SI aircraft engines to increase the power and operational ceiling of American airplanes. Today supercharging is used with both Diesel engines and SI engines. The super charger is a compressor that supplies air to the cylinder at high pressure so that the as density in the cylinder at the start of compression is well above the free-air density. The piston exhaust gases are allowed to expand freely to the atmosphere through the exhaust manifold and tailpipe. The supercharger is usually driven by a belt or gear train from the engine crank shaft. 249 Figure 6. 11 shows a modification of the theoretical Otto cycle to accommodate mechanical supercharging. The supercharger supplies air to the engine cyclinders at pressure p7 in the intake process 7
1. The processes 4
5
6 purge most of the combustion gas from the cylinder.The most striking change in the cycle is that the induction-exhaust loop is now traversed counterclockwise, indicating that the cylinder is delivering net work during these processes as well as during the compressionexpansion loop. It should be remembered, however, that part of the cycle indicated power must be used to drive the ex ternal supercharger. The turbosupercharger or turbocharger, for short, is a supercharger driven by a turbine using the exhaust gas of the reciprocating engine, as shown schematically in Figure 6. 12. A cutaway view of a turbocharger is shown in Figure 6. 3(a). Figure 6. 13(b) presents a diagram for the turbocharger. Compact turbochargers commonly increase the brake power of an engine by 30% or more, as shown in Figure 6. 8, where the performance of an engine with and without turbocharging is compared. There, a substantial increase in peak torque and flattening of the torque-speed curve due to turbocharging is evident. For a supercharged engine, the brake power, BP, is the indicated power (as in Figure 6. 11) less the engine friction power and the supercharger shaft power: BP = DISP  IMEP  N ? Pm ?FP [ft-lbf /min | kJ/s] (6. 15) 250 where Pm is the supercharger-shaft mechanical power supplied by the engine (0 for a turbocharger). The IMEP includes the positive work contribution of the exhaust loop. The exhaust back pressure of the reciprocating engine is higher with a turbocharger than for a naturally aspirated or mechanically supercharged engine because of the drop in exhaust gas pressure through the turbine. The engine brake power increases primarily because of a higher IMEP due to the added mass of fuel and air in the cylinder during combustion.Intercooling between the compressor and the intake manifold may be used to further increase the cylinder charge density. Turbocharging may increase engine efficiency, but its primary benefit is a substantial increase in brake power. In a turbocharged engine, a wastegate may be required to bypass engine exhaust gas around the turbine at high engine speeds. This becomes necessary when the compressor raises the intake manifold pressure to excessively high levels, causing engine knock or threatening component damage. Thirty to forty percent of the exhaust flow may be bypassed around the turbine at maximum speed and load (ref. ). 251 252 6. 12 The Automobile Engine and Air Pollution Since the Second World War, concern for environmental pollution has grown from acceptance of the status quo to recognition and militance of national and international scope. Among other sources, causes of the well-known Los Angeles smog problem were identified as hydrocarbons (HC) and oxides of nitrogen (NOx) in exhaust emissions from motor vehicle reciprocating engines. As a result, national and California automobile air pollution limits for automobiles have been established and toughened.Prior to the Clean Air Act of 1990, the U. S. federal exhaust-gas emissions standards limited unburned hydrocarbons, carbon monoxide, and oxides of nitrogen to 0. 41, 3. 4, and 1. 0 g/mile, respectively. According to reference 12, today it takes 25 autos to emit as much CO and unburned hydrocarbons and 4 to emit as much NOx as a single car in 1960. The reference anticipated that, led by existing California law and other factors, futur e engine designs should be targeted toward satisfying a tailpipe standard of 0. 5, 3. 4, 0. 4 g/mile. Indeed, the 1990 Clean Air Act (refs. 15,16) specified these limits for the first 50,000 miles or five years of operation for all passenger cars manufactured after 1995. In addition to the regulations on gaseous emissions, the Clean Air Act of 1990 adopted the California standard for particulate matter of 0. 08 g/mile for passenger cars. The standards on particulates are particularly difficult for the Diesel engine, because of its of soot-producing tendency.The automobile air pollution problem arises in part because the reactions in the exhaust system are not in chemical equilibrium as the gas temperature drops. Oxides of nitrogen, once formed in the cylinder at high temperature, do not return to equilibrium concentrations of nitrogen and oxygen in the cooling exhaust products. Likewise, CO formed with rich mixtures or by dissociation of CO2 in the cylinder at high temperature does not respond rapidly to an infusion of air as its temperature drops in the exhaust system. Their concentrations may be thought of as constant or frozen.Unburned hydrocarbons are produced not only by rich combustion but also by unburned mixture lurking in crevices (such as between piston and cylinder above the top piston ring), by lubricating oil on cylinder walls and the cylinder head that absorbs and desorbs hydrocarbons before and after combustion, and by transient operating conditions. Starting in 1963, positive crankcase ventilation was used in all new cars to duct fuel-rich crankcase gas previously vented to the atmosphere back into the engine intake system. Later in the ? 0s, various fixes were adopted to comply with regulation of tailpipe unburned hydrocarbons and CO, including lowering compression ratios. In 1973, NOx became federally regulated, and exhaust gas recirculation (EGR) was employed to reduce NOx formation through reduced combustion temperatures. At the same time, HC and CO standards were reduced further, leading to the use of the oxidizing catalytic converter. Introduction of air pumped into the tailpipe provided additional oxygen to assist in completion of the oxidation reactions.In 1981, a reducing catalytic converter came into use to reduce NOx further. This device does not perform well in an oxidizing atmosphere. As a result, two-stage catalytic converters were applied, with the first stage reducing NOx in a near-stoichiometric mixture and the 253 second oxidizing the combustibles remaining in the exhaust with the help of air introduced between the stages. This fresh air does not the increase NOx significantly, because of the relatively low temperature of the exhaust.The three-way catalytic converter using several exotic metal catalysts to reduce all three of the gaseous pollutants was also introduced. The use of catalytic converters to deal with all three pollutants brought about significant simultaneous reductions in the three major ga seous pollutants from automobiles. This allowed fuel-economy-reducing modifications that had been introduced earlier to satisfy emission reduction demands to be eliminated or relaxed, leading to further improvements in fuel economy.Catalytic converters, however, require precise control of exhaust gas oxygen to near-stoichiometric mixtures. The on-board computer has made possible control of mixture ratio and spark timing in response to censor outputs of intake manifold pressure, exhaust gas oxygen, engine speed, air flow, and incipient knock. The oxygen, or lambda, censor located in the exhaust pipe upstream of the three-way converter or between the two-stage converters is very sensitive to transition from rich to lean exhaust and allows close computer control of the mixture ratio to ensure proper operation of the catalytic converter.Computer control of carburetors or fuel injection as well as other engine functions has allowed simultaneous improvement in fuel economy and emissions i n recent years. Thus, while emissions have been drastically reduced since 1974, according to reference 11 the EPA composite fuel economy of the average U. S. passenger car has nearly doubled; although this improvement has not come from the engine alone. Despite the hard-won gains in emissions control and fuel economy, further progress may be expected. EXAMPLE 6. 5 The 1990 NOx emissions standard is 0. grams per mile. For an automobile burning stoichiometric octane with a fuel mileage of 30 mpg, what is the maximum tailpipe concentration of NOx in parts per million? Assume that NOx is represented by NO2 and that the fuel density is 692 kilograms per cubic meter. Solution For the stoichiometric combustion of octane, C8H18, the air-fuel ratio is 15. 05 and the molecular weight of combustion products is 28. 6. The consumption of octane is mf = (692)(1000)(3. 79? 10-3)/ 30 = 87. 4 g/mile [Note: (kg/m3)(g/kg)(m3/gal)/(mile/gal) = g/mile. The concentration of NOx is the ratio of the number of moles of NOx to moles of combustion gas products: mole Nox /mole cg = (mNOx /mf)(mf / mcg)(Mcg /MNOx) = (0. 4/87. 4)(28. 6/46)/ (15. 05 + 1) = 0. 0001773 254 or 177. 3 parts per million (ppm). _____________________________________________________________________ Bibliography and References 1. Heywood, John B. , Internal Combustion Engine Fundamentals. New York: McGraw-Hill, 1988. 2. Ferguson, Colin R. , Internal Combustion Engines. New York: Wiley, 1986. 3. Adler, U. , et al. , Automotive Handbook, 2nd ed. Warrendale, Pa. Society of Automotive Engineers. , 1986. 4. Lichty, Lester C. , Internal Combustion Engines. New York: McGraw Hill, 1951. 5. Crouse, William H. , Automotive Engine Design. New York: McGraw-Hill, 1970. 6. Obert, Edward, Internal Combustion Engines, Analysis and Practice. Scranton, Pa. : International Textbook Co. , 1944. 7. Grosser, Morton, Diesel: The Man and the Engine. New York: Atheneum, 1978. 8. Nitske, W. Robert, and Wilson, Charles Morrow, Rudolph Diesel: Pioneer of the Age of Power. Norman, Okla. : University of Oklahoma Press, 1965. 9. Demmler, Albert W. Jr. , et al. , ? 989 Technical Highlights of Big-three U. S. Manufacturers,? Automotive Engineering. Vol. 96, No. 10, October 1988, p. 81. 10. Anon. , ? Ignition Quality of Diesel Fuels by the Cetane Method,? ASTM D 613-84, 1985 Annual Book of ASTM Standards, Section 5. 11. Amann, Charles A. , ? The Automotive Spark Ignition Engine-A Historical Perspective,? American Society of Mechanical Engineers, ICE-Vol. 8, Book No. 100294, 1989. 12. Amann, Charles A. , ? The Automotive Spark-Ignition Engine-A Future Perspective,? Society of Automotive Engineers Paper 891666, 1989. 13. Amann, Charles A. , ?The Passenger Car and the Greenhouse Effect,? Society of Automotive Engineers Paper, 1990. 14. Taylor, Charles Fayette, The Internal Combustion Engine in Theory and Practice, 2nd ed. , revised. Cambridge, Mass. : MIT Press, 1985. 255 15. Public Law 101-549, ? An Act to Amend the Clean Air Ac t to Provide for Attainment and Maintenance of Health, Protection, National Air Quality Standards, and Other Purposes,? November 15, 1990. 16. Anon. , ? Provisions? Clean Air Amendments,? Congressional Quarterly, November 24, 1990. EXERCISES 6. 1 Plot dimensionless piston position against crank angle for S/2L = 0. , 0. 4, 0. 3, and 0. 2. 6. 2* Obtain expressions for the piston velocity and acceleration as a function of the crank angle, constant angular velocity, and S/2L ratio. Use a spreadsheet to calculate and plot velocity and acceleration against crank angle for S/2L = 0. 5, 0. 4, 0. 3, and 0. 2. 6. 3 Determine the equation for the piston motion for a scotch yoke mechanism in terms of crank angle. Obtain an equation for the piston velocity for a crank that turns with a given angular velocity,
. 6. 4 Derive an equation for the Otto-engine net work by integration of pdV for the Air Standard cycle.Compare with Equation (6. 6). 6. 5* Use a spreadsheet to calculate and plot cycle ef ficiency as a function of compression ratio for the Diesel cycle for cutoff ratios of 1, 2, and 3. Indentify the Otto-cycle efficiency on the plot. Explain and show graphically from the plot how a Diesel engine can be more efficient than an Otto engine. 6. 6 A single-cylinder Air Standard Otto engine has a compression ratio of 8. 5 and a peak temperature of 3500Â °F at ambient conditions of 80Â °F and one atmosphere. Determine the cycle efficiency, maximum cylinder pressure, and mean effective pressure. 6. A six-cylinder engine with a compression ratio of 11 runs at 2800 rpm at 80Â °F and 14. 7 psia. Each cylinder has a bore and stroke of three inches and a volumetric efficiency of 0. 82. Assume an Air Standard, four-stroke Otto cycle _______________________ * Exercise numbers with an asterisk indic