Chilean Copper Mine Collapse Essay Example for Free

Chilean Copper Mine Collapse Essay On August 5, 2010, employees of Minera San Esteban Primera woke up, stretched out, bathed, ate breakfast, and walked around their assuredly modest homes. They said their casual goodbyes to family as they headed off to yet another dark day at work deep in the San Jose copper mine in northern Chile. Little did they know it would be the last time for nearly two months they would see the light of day. These same blessings of life they most likely took for granted earlier that day to be able to stretch out, to bathe, to eat, and to walk around in the comfort of their own homes would be taken from them unexpectedly later that same day. Some time around the miners lunch time on August 5, 2010, the upper galleries of the private copper mine collapsed trapping the miners. Many on the outside feared the worst. After all, when the collapse occurred the miners should have been in or near the hazard zone on their way out for their lunch break. Furthermore, with limited necessities such as food, water, and oxygen it was unknown whether the miners could have survived. Liliana Ramirez, the wife of one of the oldest minders trapped, said she had faith all along that they were still alive and that she knew that her husband would never let his fellow workers perish (Hughes, 2010). Families of the missing miners, like Liliana Ramirez, started gathering and camping out at the mines surface since the collapse was first disclosed. Finally, 17 days after the collapse occurred, on August 22, 2010, the 33 trapped miners were discovered alive and doing considerably well. Drilling probes discovered the refuge area located 2,297 feet underground (Hughes, 2010). At that time loved ones were able to send inspirational, encouraging, and heart-felt messages down through the probes to their trapped miners. The miners were able to inform those above how they were faring. Upon hearing of her husbands well being, Liliana Ramirez said her message was that she wished him the strength to resist until they can be rescued, and that she loved him (Hughes, 2010). Over the next two months, the miners trapped nearly half a mile below the surface endured trying circumstances. Food supply was extremely limited. Water was obtained from the mines storage tanks that survived the collapse. Sugars, water, and liquid nutrients were sent down to the trapped miners from the surface via tiny bore holes (Barrionuevo, 2011). Risks of additional cave-ins were always present. In fact, just days after the initial search and rescue efforts had begun a second cave-in occurred suspending relief efforts for several hours (Weik, 2010). After nearly two months of being fed by a virtual umbilical cord, overcoming claustrophobia, and wondering if theyd ever see their friends and family again, late in the evening of October 12, 2010, the first miner ascended to the surface and to safety. One by one the remaining 32 miners were lifted through the rescue shaft and were greeted by cheers, hugging, crying, and feelings of elation. The story of the trapped Chilean miners (which actually consisted of 32 Chileans and one Bolivian) was a story that gripped the world. More than 1,400 journalists were present to witness the final rescue operation (Barrionuevo, 2011). Seemingly every race, color, tongue, and ethnicity was engaged one way or another, hoping and praying for a positive outcome. Amid all of the news-worthy stories that capture the audiences attention with their negative trauma-like effect the story of the trapped and rescued Chilean miners stands out. This was a story that united nations. This was a story that was bigger than the color of ones skin, the language one speaks, or the country one calls home. This was a story about the love of mankind, about teamwork, about sacrifice, and about the basic struggle for survival. Final score: Mankind-1, Adversity-0. References Barrionuevo, A. (2011). Chile Mining Accident (2010). http://topics. nytimes. com/top/reference/timestopics/subjects/c/chile_mining_accident_2010/index. html Hughes, H. (2010). 33 Trapped Chilean Miners Found Alive, But Could Be Stuck 4 Months. http://abcnews. go. com/International/33-trapped-chilean-miners-found-alive-stu k-months/story? id=11457872 Weik, J. (2010). Over 30 workers trapped after Chilean copper mine collapse. Metal Bulletin Daily, (224), 65. Memo to Families of Employees of Minera San Esteban Primera To Whom It May Concern, As President and CEO of this company I feel a personal responsibility to each and every one of our employees as well as to the welfare of their families. It is with deep concern for each of them and for each of you that I write this memo to inform you of a developing situation. Mid-day today (August 5, 2010) there was an accident in the San Jose mine. The upper galleries of the mine collapsed. 3 of our miners are still unaccounted for. We want to assure you that we are doing everything within our means and ability to expedite relief efforts. At this time of unprecedented disaster we pray for you as well as for the miners. If you have a loved one that may have been stationed in the San Jose mine today we have posted (and will update and maintain) a list of those miners that have been accounted for as well as a list of unaccounted miners on our website. We will not stop, we will not rest, until every miner has been accounted for. Thank you for your prayers and for your cooperation in any relief efforts that are being coordinated.

Effect Of Temperature On The Digestive Enzyme Pepsin Biology Essay

Effect Of Temperature On The Digestive Enzyme Pepsin Biology Essay In this study an experiment was carried out to determine if varied temperatures affect the rate at which enzymes function. Enzymes are biological catalysts; catalysts are substances that increase the rate of chemical reactions without being used up (BBC, 2010), without these catalysts it would take an extremely long time for these reactions to take place. The enzyme used in this particular experiment was pepsin; pepsin is a zymogen of pepsinogen. Pepsinogen is activated by hydrochloric acid, which is released from parietal cells in the stomach lining. The hormone gastrin and the vagus nerve trigger the release of both pepsinogen and hydrochloric acid from the stomach lining when food is ingested. Hydrochloric acid creates an acidic environment, which allows pepsinogen to unfold and cleave itself in an autocatalytic fashion, generating pepsin. (Life Science Network, 2010) A lot can be learnt about enzymes by studying the rate of enzyme catalyzed reactions, these rates of reaction can be studied in various ways. In this experiment, using a range of different temperatures, the enzyme pepsin will be mixed with egg albumen. This is high in protein and bound to the dye Coomassie blue to gain a light absorbance reading using a spectrophotometer and in effect see how much protein has been digested by the pepsin. Egg albumen was used as the protein source in this study as although it is composed mainly of around 80% water it has about 15% of its total mass made up from approximately 40 different types of proteins, mainly Ovalbumin (54%) (Edin Formatics, 1999). A spectrophotometer is a device used for measuring light intensity and will be used to determine the amount of protein in each mixture, it works by measuring the light intensity as a function of the colour or more specifically the wavelength of light (Global Water Instrumentation Inc, 2007) (Appendix 2). Therefore the lower the reading means less light has been absorbed by the solution being tested indicating in this case that more protein (egg albumen) has been digested by the enzyme (pepsin) and the lower the reading the faster the enzyme reaction rate. If enzyme reactions are affected by temperature, then changes in temperature may bring about different absorbances of light readings related to how much protein has been broken down by the enzyme. As pepsin is found in the stomach it would seem only logical to assume the optimum temperature for this particular enzyme would be around 37Â °c, human body temperature. Method A cuvette was filled with 0.5ml of distilled water and placed in a spectrophotometer, then the machine was calibrated by pressing the zero button with the spectrophotometer set to a wavelength of 595nm. After calibration 0.5ml of egg albumen (2mg.cm-Â ³) was added to a test tube using a glass pipette and incubated in a pre heated water bath at a temperature of 10Â °c (then 20Â °c, 30Â °c, 40Â °c, 50Â °c, 60Â °c, 70Â °c) for five minutes. 0.5ml of pepsin (0.1%) was then added to the test tube and incubated at the same temperature for a further ten minutes. After this incubation period 2.0ml of Coomassie blue reagent was added to the test tube and immediately mixed by capping the test tube with parafilm and inverting several times. After the test tubes contents had been mixed they were carefully poured into a cuvette and placed into the spectrophotometer with the light absorbance levels being recorded at a wavelength of 595nm. The experiment was carried out three times at each temperature to achieve reliable data. Results The results documented in Table 1 are the light absorbance reading averages of three separate experiments carried out at each temperature. A full set of results can be seen in Appendix 1. Figure 1 shows the averaged results plotted on a scatter graph. Table 1 Temperature (Degrees Celsius) Average light absorbance at 595nm 10 2.501 20 2.550 30 2.516 40 2.403 50 2.543 60 2.740 70 2.806 Fig 1 Change absorbance Discussion The results in Table 1 as well as the bell curve graph (Fig 1) show that the optimum temperature as predicted in the hypothesis seems to be 40Â °c, close to human body temperature. These results also show that temperature has a definite effect on the rate the enzyme reacts to breakdown the protein in the egg albumen. Table 1 shows that at 10Â °c, 20Â °c and 30Â °c the light absorbed by the solution is more than at 40Â °c, this is because the pepsin has not broken down as much of the egg albumen at lower temperatures as it has at 40Â °c so the spectrophotometer is picking up more undigested protein particles in these readouts. The same applies to the temperatures above 40Â °c and indicates 40Â °c is the best temperature range for pepsin to be active. Enzymes are made up of amino acids; amino acids are the basic building blocks of proteins consisting of a basic amino group, a carboxyl group, a hydrogen atom and an organic side group attached to the carbon atom (Biology Online, 2010). When an enzyme is formed it is made by stringing together between 100 to 1,000 amino acids in a specific and unique order defining the three dimensional shape of the enzyme and its particular chemical reactivity (Brain, M. 2000). The lock and key theory explains how an enzyme may work, it utilizes the concept of an active site on the enzyme. The theory is that a particular part of the enzymes surface has a strong affinity to the substrate (protein). The substrate is held in such a way that its conversion to the reaction products is more favorable. If you consider the enzyme is the lock and the substrate is the key, the key is inserted in the lock and turns it to open the door letting the reaction proceed (Worthington Biochemical Corporation, 2010) (Appendix 3). However, the induced fit theory expands on the rigid lock and key theory. This updated view of enzymology proposes that the substrate causes a conformational change in the enzyme so the active site achieves the exact configuration for a reaction to occur, the overall effect being a tighter binding between the enzyme and substrate (Allaby, M. 1999) (Appendix 4). The benefit of this tighter binding would be a faster reaction rate as more surface area of the enzyme would be in contact with the substrate. The kinetic collision theory describes temperature affects on a system as the amount of kinetic energy it has, a lower temperature will provide less kinetic energy than a higher temperature. When molecules collide the kinetic energy can be converted into chemical potential energy, if the chemical potential is great enough the activation energy or energy required for an enzyme to work can be reached. The more chemical potential energy molecules have when they collide, a greater number of molecules per unit time will reach the activation energy needed to bind the enzymes active site to the protein resulting in a quicker rate of reaction. If the temperature gets too high some of the weak bonds that determine the shape of a protein and its active site could be broken resulting in the enzyme becoming denatured and decreasing the rate of reaction sometimes rendering the enzyme inactive (Brooklyn College, 2010). Figure 1 shows that after 50Â °c the enzyme reaction rate slows down considera bly, the enzyme is denaturising at a faster rate than it is below 30Â °c. This change in enzyme reaction rate may be due to the fact that pepsins are stored at low temperatures to prevent the enzyme destroying itself, therefore pepsin is less active at lower temperatures until it reaches its activation energy around 30Â °c and anything beyond around 50Â °c 55Â °c will rapidly denature the pepsin so the molecules in the active site can no longer bind to the protein and produce a reaction, rendering the enzyme inactive permanently. Once the pepsin has digested the egg albumen it would still be difficult to analyse the amount of protein left at each temperature, this is why Coomassie was added before taking a reading. In an acidic environment the protein will bind to Coomassie causing a spectral shift from a reddish/brown colour with a low absorbance maximum of 465nm to a light blue colour with a higher maximum absorbance of 610nm with the difference of the two colours greatest at 595nm, an optimal wavelength (Thermo Fisher Scientific, 2010). The binding of the Coomassie takes place when the red form donates its free electron to the ionisable groups on the protein causing a disruption of the proteins normal state and revealing its hydrophobic pockets. These pockets, via Van der Waals forces (attractive and repulsive forces between molecules) bind to the non polar region of the dye, putting the positive amine groups close to the negative charge of the dye, creating a strong bond. Binding of the protein stabilizes the blue form of Coomassie dye, thus the amount of complex present in solution is a measure for the protein concentration by use of an absorbance reading. (Bradford M, 1976, P248-254) Although this experiment has produced reliable accurate data that has proven the hypothesis right, many things could affect the results and readings obtained. When using such an accurate way of recording the data such as a spectrophotometer a number of things could affect the reliability of the results. Things like minor differences in volumes of substances added to the test tubes or inattentive timing methods could be damaging to the results obtained. Simple human error could possibly influence any results with any fingerprints or water on the cuvette affecting the absorbance readings. Conclusion In conclusion, the study carried out was adequate for the data required and indicated that temperature definitely affects the rate at which an enzyme reacts. As long as the method is executed well this is a great experiment to look at temperature and its effect on enzyme activity however as with any scientific study human input is a crucial factor and could affect the quality of results. Another experiment may need to be carried out to determine what the optimum temperature is on a more specific scale, something closer to body temperature would help to discover a more precise optimum temperature, 35Â °c 40Â °c for example. As well as finding out an exact optimum temperature a further study to find out the optimum pH of pepsin could be done to further enhance the enzymes rate of reaction, focused around the acidic pH in the human stomach. Appendices Appendix 1 Temperature (Â °c) Absorbance at 595nm (Reading 1) Absorbance at 595nm (Reading 2) Absorbance at 595nm (Reading 3) 10 2.430 2.550 2.520 20 2.480 2.530 2.640 30 2.500 2.510 2.540 40 2.360 2.400 2.450 50 2.520 2.560 2.550 60 2.660 2.780 2.780 70 2.800 2.820 2.800 Appendix 2 http://commons.wikimedia.org/wiki/File:Spetrophotometer-en.svg Appendix 3 http://www.chemistry.wustl.edu/~edudev/LabTutorials/Carboxypeptidase/images/lockkey.jpg Appendix 4 http://wpcontent.answers.com/wikipedia/commons/thumb/2/24/Induced_fit_diagram.svg/450px-Induced_fit_diagram.svg.png

Analysing the Plot and Sub Plot of A Dolls House by Henrik Ibsen Essay

Analysing the Plot and Sub Plot of A Dolls House by Henrik Ibsen As another year goes by I am now writing a piece of coursework for AS drama, this particular piece will be about a not so well known play called ‘A dolls house, written by Henrik Ibsen. In particular I will by studying carefully and analysing the plot and subplot of the play. The play was wrote in the 1800’s and was first performed in Copenhagen during the winter of 1879. Most of Ibsens plays were based around the issues during that era, as was a dolls house covering forgery, feminism, freedom, independence, love?, stereotypes, and duty all in the main plot. The subplot covered issues like; loneliness, widowed, manipulation, deception/secrets and the new woman. To convey the issues there where two characters in the main plot, these were Nora and Torvald (the husband and wife living in the â€Å"dolls house†. As the story unravels we discover many different things but we also find out that Nora is in every scene to show how she has adapted to living her lifestyle and how she is slowly moving out of it and into another. Torvald is also in most scenes but always seems to be in his office hard at work trying to earn money for Nora and the family, as most families would be in this century. Then there are two other characters running the subplot these are Mrs Linde and Krogstad both of these convey how Nora’s life could be if she were to separate from he husband, Torvald, showing how hard it is to be a part of society. Mrs Linde feels that Nora leads the perfect lifestyle with a happy family where as Nora feels that Mrs Linde has the better lifestyle, being free. The features of the subplot are shown via the main plot, this is to show a variety o... ...bsen had to re-write the play with an alternate ending, as they did not want to show that women can be more powerful than men. The ending was that Nora broke down in tears and stayed after Torvald forcing her to see her children. The normal ending was described as an act of barbarous violence. Through researching and thoroughly studying the play act by act I have learnt that not only was the subplot just as important as the main plot but how they were run through each other and the impact it had. I also gathered more information on what life was like during the 1800’s and how controlling the male was over the female during them times. The play also gave a great insight to how widowed and/or single adults were treated back in them days. So if you ever read the play I hope you enjoy it as much as I did and get a good understanding of all the key issues.

Importance of the Meteor in Nathaniel Hawthornes The Scarlet Letter :: Scarlet Letter essays

The Importance of the Meteor in The Scarlet Letter      Ã‚   Nathaniel Hawthorne's novel, The Scarlet Letter, is considered by many to be a masterpiece. It was a culmination of everything Hawthorne experienced in his life. He grew up in a household that held fast to Puritan ideals. This affected him in ways he himself may not have even realized.   â€Å"Nathaniel Hawthorne placed many undercurrents of meaning in this novel†(Tucker 16). At the climax of the story, a meteor flashes through the night sky. The appearance of this meteor at this particular moment in time contributes to the plot in many ways.    First, Reverend Dimsdale thinks the meteor is a message from God specifically for him. "Nothing was more common in those days than to interpret all meteoric appearances, and other natural phenomena that occurred with less regularity than the rise and set of the sun and moon, as so many revelations from a supernatural source"(149). Any person of that day would have assumed that something of that nature applied to some portion of his or her life. "Then, and there, before the judgment seat, thy mother, and thou, and I, must stand together. But the daylight of this world shall not see our meeting"(149)! Just after those words leave Reverend Dimsdale's mouth, the meteor lights up the sky as bright as day. It's as if God is proving Reverend Dimsdale's words to be false. The light of the meteor resembles the letter "A" to Reverend Dimsdale because his conscience is pricking at him. Subconsciencely he wants to punish himself for his sin since the townspeople can't punish him for a sin of whi ch they were unaware. Therefore, his guilty feelings twist a natural part of creation into a punishment of sorts. He believed the meteor resembled the letter "A" to convict him further of his sinfulness. "...a great red letter in the sky-the letter 'A' which we interpret to stand for 'Angel.' For, as our good Governor Winthrop was made an angel this past night, it was doubtless held fit that there should be some notice thereof"(153). The fact that a member of his congregation also believes that the meteor resembles the letter "A" is ironic because of his belief that it stands for "Angel" in honor of the departed governor rather than something with a negative connotation. The mind can make one event appear as something to one person while another person observing the same event will consider it the complete opposite of the first.

Diverse Australian Biomes Adapting :: Adaptation Australia Essays

Diverse Australian Biomes Adapting Australia is a land of rather extreme weather conditions and widely diverse climates that force the vegetation living there to adapt in many interesting ways. Australia is the driest continent, and biomes such as grasslands and savannas are prime sources of widespread catastrophic fires. The plants that grow in the vast arid and semi-arid regions of Australia are prone to fires simply because of the desert climates that they grow in. High temperatures combined with low fuel moisture contents, little humidity and drying winds that sweep across the landscape encourage many of the plants living in these areas to burst into flames at fairly frequent intervals. Serotinous cones, protective bark, intricate underground recovery systems, unique seed distributions and even the necessity of fire for reproduction are just some of the amazing ways that the major plant families which grow in these fire-prone areas have learned to adapt to their environments. History of fires in Australia Australia is currently the driest continent in the world and has a vast history of fire to prove it. Bushfires in the Adelaide Hills were first described and recorded in 1827, and have occurred at frequent intervals since that time. Fire weather can reach extremes in places such as Rudall River National Park in NW Western Australia. Temperatures are often above 40 degrees Celsius (104 degrees Fahrenheit), dew points can drop to —37 degrees Celsius, and the winds, uninhibited by trees, can reach speeds of 50-60 km/h (31-37 mph) at any given time in the year. The fuels there may appear to be completely dead, and gaps between plants may be a meter or more (Gill, 1995). In 1966 a massive fire at Brooyar, Queensland had flame heights of 20-25 meters (65-82 feet). In addition to being devastating, the fires are also very unpredictable. A bushfire in the Baulkham Hills in January of 1975 completely destroyed property and some homes, while leaving others untouched. Serious fires occur in the Dandenog Ranges at frequent intervals, and housing there has always been a difficult problem with fire control [3]. Fire has also been used for centuries as an important tool for land management (O’Neill, 1993). Necessary Conditions For Fire Plants that grow in the vast arid and semi-arid regions of Australia are prone to fires simply because of the desert climate they grow in. High temperatures, low fuel moisture contents, little humidity and drying winds that sweep across the landscape encourage small patches of plants to burst into flames.

English Personal Recount Essay

One of my most recent memories is the authentic experience at the mall with three of my friends, Eunice, Wing Kit and Cheng Ye. We went there to buy a gift for Cheng Ye’s cousin, Claire, from abroad, whom he has not met in a long time. She is aged 14 years old, her favourite foods are ice- cream and sushi, and her hobbies are sleeping, swimming, cycling, running, and listening to music. She is also more of a sporty and hardworking person. She likes playing on her phone, the colour PINK, using social media such as whatsapp, facebook to socialize. She dislikes computer games and the colour blue. Cheng Ye has not seen Claire in quite a while, and Claire has not visited Singapore in ages, we have decided to get Claire a gift to welcome her. Thus we decided to go to Tampines Mall as there is a wide variety of shops there. Our budget is $50. When we reached Tampines mall, it was very packed with shoppers, were lugging huge shopping bags. The mall was filled with the noisy sound of people chattering and laughing. It was so noisy that I had to shout and strain my voice to talk to Eunice, who was just right beside me. Salespersons were announcing the various offers they were having. The smell of curry chicken entered my nostrils as I while gazed at the patrons savouring the mouth-watering curry chicken, causing my mouth to drool as we walked past the restaurant. Finally, after browsing through many electronic stores, we decided upon an pink shiny earpiece from Courts that costs $20. We chose the product based on her preferences as she liked pink and shiny objects and also because it had a reasonable price and was within our budget. After buying the earpiece, we were left with $30. Thus we decided to get her another gift based on her hobby of sports. We wanted it to be within our  budget of $30, the colour pink and it to be useful and long-lasting. Eventually, we headed down to the ‘ Royal Sporting House’ and chose a pair of pink as it would be useful to her as swimming was her favourite hobby which she did pretty often. Thus, she would be able to use it often as well. In conclusion, this experience of going to Tampines Mall on 29 March 2014, was a wonderful experience.We had a lot of considerations at first, such as her personality,likes & dislikes, the budget for the gift and what gift would she really wanted. However, all of us worked together, communicated effectively and overcame the challenges. So, eventually we decided on the gift. I also think that this experience was an educational and enriching one, as we learnt how to decide on things in a group without having any conflicts and how to take things into considerations before making a final decision. In conclusion to this, this experience was a fun, educational and enriching experience.

Business Finance Written Assignment

Q1. Define an â€Å"efficient market† and the three forms of market efficiency. Explain how each of the forms differs from a perfect market. Define arbitrage and explain what kind of information is needed for you to obtain arbitrage in each of the forms of market efficiency. (5 points) Q2. Please compare the advantages and disadvantages of the following investment rules: Net Present Value (NPV), Payback Period, Discounted Payback Period, Average Accounting Return, Internal Rate of Return (IRR) and Profitability Index (PI). You can start by considering the following questions for each investment rule: Does it use cash flows or accounting earnings? Does it consider all cash flows or not? Does it apply a proper discount rate? Whether the acceptance criteria are clear and reasonable? In what situation it can be applied? What kind of weakness does it have? ) (5 points) Question 1 An efficient market is advocated by a hypothesis that under free movement of information, the true valu e of securities are fairly priced, which immediately and accurately reflect all information available to investors.By the assumptions that rational investors evaluate the price by ascertained future cash flows, and are able to learn and react quickly to new information once delivered, investors do not expect to achieve returns in excess of average market returns. The three forms of market efficiency are weak, semi-strong, and strong. Different degree of information is reflected by price in different forms. Under weak form, the prices reflect all past publicly available information, like historical prices movements. Under semi-strong form, the prices reflect all publicly available information, like financial statements and news reports.Under strong form, the prices reflect all public and private information. Generally, because of quick reflection of information in price and quick response of investors to the market, it is impossible for investors to obtain or use new information to f ind undervalued stocks. To illustrate, in weak form, using past prices for technical analysis is useless to predict future trend as past information is irrelevant to the future. In semi-strong form, using fundamental analysis is not useful as the prices are immediately adjusted once the information widely circulated in the market.In strong form, finding undervalued stocks is not consistent as all information is well known. Thus, no investors can earn excess return by trading the information or selling the stocks with too high expected returns. A perfect market is where no arbitrage opportunities occur (i. e. Law of One Price) because complete information is shared among all investors. Compared with efficient market, no distinction in degree of information is reflected in price here. Arbitrage means the practice of buying and selling equivalent goods in different markets to take advantage of a price difference.An arbitrage opportunity occurs if making a profit without taking any risk . An efficient market does not necessarily mean investors cannot yield excess return. Instead, an arbitrage opportunity does exist if they ask for appropriate information quickly. If a market achieves strong form efficiency given that it is mature enough, no investor can yield any excess return in long run. Thus, no more information is needed. On the other hand, private and latest public information are needed to obtain arbitrage in semi-strong and weak form efficiency respectively. (395 words) Question 2 Use of cash flows and discount rateAll investment rules are determined by estimated cash flows but only NPV, IRR and PI consider all cash flows throughout the project’s life. Except payback period, the cash flows are discounted by proper discount rate under each rule. A positive NPV expects the project adding value to firm and shareholders’ wealth. All discounted expected future cash flows are taken into consideration compared with the initial cost. The discount rate estimates the risk level and the return and thus it is appropriate. Thus, NPV is the best because it accounts for time value of money and risk of cash flows.IRR is the return that set NPV to zero. Similarly, the calculation is based on cash flows and discount rate (i. e. same benefit as NPV). It provides a simple tool without estimating all details but intuitively appealing to know. If IRR is high enough, the time spent on estimating a required cost of capital is avoidable. PI measures benefit per unit cost based on time value of money to estimate an additional value to firm. Two versions of PI provide same decision and both are easy to understand and communicate. For calculating PI, NPV calculation is used and thus PI’s advantage is same as NPV’s.Payback period is the amount of time for future cash flows taken to recover the initial investment. It is a scanning tool for uncertain cash flows. However, it ignores cost of capital and time value of money since only cash f lows for that current period are concerned. Also, not all cash flows are considered as cash flows beyond payback period are ignored. Similar to payback period, the only difference is discounted payback period better considers discount rate (i. e. time value of money). Therefore, payback period on a discounted basis will be longer. Clearness and reasonableness of acceptance criteriaNPV, IRR and PI can provide clear and reasonable criteria while only NPV can be applied to all situations. The NPV rule is to accept a stand-alone project with positive NPV or a mutually exclusive project with the highest NPV. As NPV is estimated absolutely, the rule can still be applied despite of different scale of projects. The IRR rule is to accept a stand-alone project with IRR greater than cost of capital or a mutually exclusive project with the highest IRR. However, IRR rule is consistent with NPV rule only if all negative cash flows precede positive cash flows. In other words, the conflict is due t o non-conventional ash flows and change in signs more than once. Thus, non-existent or multiple IRR(s) may cause uncertainty in decision making. IRR is unreliable when mutually exclusive projects are different in scale, risk and time horizon. PI is closely related to NPV, generally leading to identical decisions. PI helps evaluate and identify the optimal combination under resource constraint, especially for limited budget. The project with the highest PI should be chosen first. Nevertheless, it ignores the size factor and thus leads to incorrect decisions among mutually exclusive projects.Moreover, PI cannot be applied during multiple resource constraints. The rule of (discounted) payback period is to accept the project if it is less than a pre-specified length of time. It is easily understood and simply used because of clear acceptance criteria. However, an arbitrary cutoff point is required for determination. It is subjective since ignoring the impact of cash flows after payback period favors short –term projects and biases against long –term projects. Conclusion NPV is the most commonly used investment criteria and true at any time. If any conflicts exist among the investment rules, NPV rule should prevail. 605 words) Reference 1. Hong Kong Institute of Investors (2001), â€Å"Efficient Market Hypothesis†, retrieved 1 April 2012, from http://td. hkii. org/investu/168ch7/7-5. php 2. NYU Stern, â€Å"Market Efficiency – Definition and Tests†, retrieved 1 April 2012, from http://pages. stern. nyu. edu/~adamodar/New_Home_Page/invemgmt/effdefn. htm 3. Wikipedia, â€Å"Efficient-market hypothesis†, retrieved 1 April 2012, from http://en. wikipedia. org/wiki/Efficient-market_hypothesis 4. Wretch (21 February 2006), â€Å"Efficient Market Hypothesis†, retrieved 1 April 2012, from http://www. wretch. cc/blog/jeysafe/3421966