Case study Coursework Example | Topics and Well Written Essays - 500 words

Contextual investigation - Coursework Example Rajaratnam had a consistent example of utilizing insider exchanging to make a large number of dollars in benefits. Ordinarily insider exchanging happens as one time tips that an individual endeavors. A keen insider merchant won't misuse his insight to win cash to remain off the radar of the Securities and Exchange Commission (SEC). Covetousness was the essential factor that prompted the end of Raj Rajaratnam. The monetary market endured a hazard with respect to the trustworthiness of Wall Street all in all. The SEC found during its thorough examination of the insider exchanging exercises of Raj Rajaratnam that insider exchanging was more far reaching across America than what the specialists suspected. Raj Rajaratnam had a system of witnesses he paid for the insider data he utilized. During the examination 16 individuals were accused of money related violations. It shows up as though insider exchanging is more boundless than anybody at any point thought. The explanation insider exchanging is illicit is on the grounds that it gives the beneficiary of the data an uncalled for advantage in examination with the commonplace investor2. The financial exchange should have asymmetry and everybody ought to have a similar data. It is my assessment that the adjudicator was totally right in the unforgiving sentence he offered out to Raj Rajaratnam. The appointed authority stated, â€Å"His wrongdoings and the extent of his violations mirror an infection in our business culture that should be eradicated.† Insider exchanging is serious stuff; it harms the trustworthiness of the budgetary market, while simultaneously giving an unscrupulous dealer a bit of leeway which he can underwrite to get an individual advantage. Rich insider brokers can influence the entire market by making colossal purchase or sell arranges on a specific stock. The enormous exchange can modify the day’s value citation on a stock. Raj Rajaratnam was an eager monster that needed to make easy money to the detriment of the financial specialist network. It is somewhat miserable that Raj Rajaratnam turned to the illegal action since he was at that point a mogul and he did

Skoda Case Study Example | Topics and Well Written Essays - 1000 words

Skoda - Case Study Example Volkswagen's experience helped with fixing a large portion of the mechanical issues that Skoda had at first experienced. Skoda UK sells Skoda vehicles through its system of free diversified vendors and its most present well known models are the frabia, octavia, eminent and the roomster. Its' piece of the overall industry is at 1.7% making it a little player in the market for vehicles (The occasions 100 134). Anyway it has figured out how to fit in the profoundly serious market and divided market. It properties this on it's fixation on proprietors experience as opposed to making huge deals. It has respected 'the human touch' from structure through to deal. One of its recognizable and quantifiable quality is the readiness and capacity of the Skoda's driver to prescribe Skoda to a companion. It uses this solidarity to advertise its image picture just as laying plans for future vital turn of events. As indicated by the review report in the occasions 100 (134), Skoda confronted an emergency due to the oudated impression of the brand. The vehicle had a picture of low quality, plan, materials and get together which contrarily influenced its proprietors. This is because of the way that individuals related vehicle possession to the picture. In 1999, Skoda figured out how to change its negative picture and Skoda vehicles were not, at this point considered of low quality. In spite of its exertion of improving its picture, the vehicle didn't have a solid intrigue ot people in general. Examination of case To improve its presentation in the serious vehicle showcase, Skoda UK's administration expected to evaluate its image situating. Brand situating implies building up a particular picture for the brand contrasted with contending brands. Its by so doing that it would figure out how to develop from a little player to a greater player. From the review report it got after a statistical surveying, Skoda UK was placed into a decent positionto make the most of new chances and react to dangers. As indicated by JD Power study, Skoda has been in the best five vehicle producers for as long as thirteen years. In Top Gear's 2007 client satisfactionsurvey, 56,000 watchers offered their thoughts on 152 models and Skoda was casted a ballot as the number 1 vehicle producer (The Times 100 134). Skoda's Octavia model aloso won the 2008 Auto Express Driver Power best vehicle. Skoda ascribes the outcomes to its key administration technique which foccused on building vehicles that their proprietors would appreciate. This was not quite the same as basically expanding deals of an item. Vital administration is a procedure in whih it directs a business with the goal that it can contend and develop in its market. As indicated by the Audit report gave, Skoda has a 1.7% piece of the overall industry making it a little player in the market for vehicles. The shortcoming was mostly because of obsolete impression of the brand. This can be credited to its poor advertising techniques that it utilized. The organization ought to have consequently centered around improving its picture to improve the demographic base. Suggestions Skoda ought to focuss on the Niche portion by building up a B in addition to or prudent vehicles which are monetarily benevolent to clients winning beneath 3000 RMB. This is because of the way that, most clients are not in a situation to bear the cost of the vehicle at its present cost. It is hence fitting that, the organization considers the low salary workers by creating and delivering practical vehicles. Skoda ought to likewise

Philosophy of social science and some problem Essay

Theory of sociology and some issue - Essay Example Let us currently look at Society, which is a whole of people, connecting in limited space in unending assortment of ways. To comprehend the unpredictable society by utilizing exactly detectable objectivity is maybe the center goal of sociology. To normally clarify the unpredictability of subsidiaries that singular associations make in the public arena is the implied order of Social Science. Along these lines Social Science might be characterized as the balanced and efficient investigation of human culture in the entirety of its structures with the point of showing up at a suffering understanding, recognized as such by a wide accord of scientists, of social marvel (Meyer.1999). In inspecting the way of thinking of Social Science, we will endeavor to test behind the cover and take a gander at the center of the conviction framework which administers, directs and characterizes the structure of information exuding from this part of Human request. Judiciousness frames the essential percept of reasoning of Social Science. The 'rationalistic perspective on information depends on reason and reflection' (Johannessen and Olaisen.2005), wherein observationally and dispassionately irrefutable perception is verbalized and thrown in to ideal models and speculations. We might now want to allude to the discussion among naturalist and enemies of naturalists which structure the general contending scholastic gatherings (in the same place) inside the way of thinking of sociology. ... Fundamental methodology anyway looks to see the social world as framework containing sub-frameworks and an 'epistemology consolidating authenticity and reason, expecting to comprehend, anticipate and control' (Johannessen. 1997, cited in Johannessen and Olaisen.2005), an endeavored mixing of objectivity, subjectivity and intersubjectivity. The Naturalist position sharing the 'negligence for abstract understanding'; is developed on the accompanying four columns: 1. Induction 2. Positivism and neo-Positivism (Vienna Circle) 3. Authenticity 4. Logic (Karl Popper) (Bunge.1996 cited in Johannessen and Olaisen.2005 ) Empiricists base their contention on a possible inclination, that 'it is just observation which gives the information' (Turner.1991 cited in Johannessen and Olaisen.2005). They have an obdurate view that information is understanding and ensuing reflection on and about it. The essential concern is discernible. The Positivists and neo-Positivist radiated from Vienna School (1926-1936). These 'Consistent Empiricists' centered around exact testability, certain information and enlistment. They don't perceive non-straight causative elements like feelings and so on and term them as informal and out of logical setting (Von Wright. 1971quoted in Johannessen and Olaisen.2005). It was an endeavor to present scientific exactness in the domain of uncertain social information. Neo-Positivists put together their epistemology with respect to Instrumental Rationality. Authenticity 'is an epistemological teaching that information endeavors to speaks to the real world' (Bunge.1981, p. IX ). Authenticity has additionally expand in to Nave Realism, Critical Realism and Scientific Realism (Johannessen and Olaisen.2005). Realism's most significant sub-regulation is Methodological Individualism, which expresses that social

Nurses' Responsibility During an Emergency Situation Essay

Medical caretakers' Responsibility During an Emergency Situation - Essay Example Their work outside the emergency clinic incorporates giving water, food and sanitation benefits too and conveying the wellbeing suggestions and requirements to the individuals influenced (Stanhope and Lancaster, 2008). This paper takes a gander at what the open attendant work includes when a debacle, for example, a storm hits a populated zone. Medical clinics When a hurricane hits a zone and causes physical wounds and demise, emergency clinics regularly wind up overpowered by the quantity of patients that must be taken care of. Most fiascos that include water, similar to tropical storms are huge because of the degrees of harm and mortality included (Adelman and Legg, 2009). Storms may make individuals get harmed because of the auxiliary harm that it causes. Those harmed may have inside structures that descended when the hurricane struck. Others may have been driving and their vehicles squashed because of the calamity. Others may have been harmed attempting to escape from the resultin g floods and decimation. Storms may likewise cause natural irregular characteristics which may thus expand the danger of ecological perils and transmittable ailments. The probability of illnesses, for example, typhoid and cholera is high when a debacle, for example, this happens (Stanhope and Lancaster, 2008). Medical clinics should consistently be prepared to deal with such crisis circumstances that emerge from characteristic or man made debacles. ... It is the obligation of attendants to guarantee that the death toll because of wounds is kept at a negligible level (Carmona, 2010). The medical attendants should arrange with other emergency clinic staff to guarantee that specialists take care of the individuals who are genuinely harmed as quick as could be expected under the circumstances. The attendants ought to likewise work with specialists in the Intensive Care Unit and crisis focuses to guarantee that there is sufficient gear and clinical material to deal with patients (Gebbie and Qureshi, 2002). On the off chance that there is have to get outside assistance, the medical attendants have the duty of guaranteeing that there is legitimate coordination of exercises with the goal that patients can be given the consideration they need. The attendants working in clinics during crisis circumstances ought to guarantee that all offices accessible are all around used to help spare lives (Stanhope and Lancaster, 2008). Water When a tropic al storm happens, there is ordinarily water all over the place, making it difficult for individuals to get perfect water. In the nursing setting, it is the obligation of the general wellbeing medical attendant to guarantee that individuals influenced by a tropical storm or some other fiasco so far as that is concerned get perfect water, particularly for drinking and cooking. Medical attendants should work connected at the hip with other crisis offices and associations to guarantee that everybody approaches clean water, particularly for drinking (Adelman and Legg, 2009). By giving clean drinking water to the network influenced by a tropical storm, or some other catastrophe so far as that is concerned, he medical caretakers would satisfy hypothesis part of their job of giving essential consideration and life necessities. Water ought to be made accessible to everybody who has been influenced by a fiasco. On account of a storm, it is exceptionally hard to

Lady of Shalott Essay Topics - How to Write an Interesting Essay

Lady of Shalott Essay Topics - How to Write an Interesting EssayHere is a good place to look for Lady of Shalott essay topics. There are many of these sites that are devoted to all sorts of topics and you can find plenty of ideas here.No matter what topic you are looking for, you can find one that will allow you to create an informative article. Many of these are quite detailed and it can be quite helpful to understand the history of the land, the environment and many other things that you may not have considered before. Using these types of essays can help you make your thesis more interesting.You can also find these types of essays for various other thesis subjects as well. Of course, you can always use them for your major. You do not have to stick with one topic and it would not hurt to do so. If you want to go beyond your level of education, you should find some other areas of interests.Another advantage that people take advantage of when they use essay topics such as the Lady of Shalott is that they are very easy to write. No matter what your skill level is, you can find plenty of different topics to write about. When you are learning more about essay writing, this is a perfect thing to take advantage of.You will also learn about the English grammar, which is something that you may not have considered before. There are many people who find grammar difficult to grasp and they are often caught up in words. It is important to understand what grammar means and how it applies to your essay. This can be very helpful to any of the different topics that you write about.Keep in mind that the better the topic you choose, the better the essay topics will be. You should not be trying to write an essay about everything that you read or hear. You should not worry about reading the dictionary every day or even every week. This will only confuse you and could slow you down from writing your essay.When you first start writing a piece of writing, you will realize that you n eed to have a good vocabulary that you can use throughout the essay. You do not have to memorize the meanings of every word that you see. Just keep your words to the point and simple.When you are trying to write an essay that you will be proud of, you will have to make sure that you are comfortable with this process. Once you know what you are doing, you will be able to take advantage of the different essay topics that are available. Of course, you can also create your own topics, but you will learn that this is the best way to go if you are trying to write a different type of essay.

Should Scientists be Allowed to Experiment with Human Cloning - Free Essay Example

Cloning is a biotechnology field that has been under intense protection ever since the cloning of Dolly the sheep in the year 1996. This breakthrough saw Doctor Richard Seed announce that he intends to clone human beings using the technique used by Keith Campbell and Ian Wilmut to create Dolly the sheep (Wilmut, Campbell and Tudge). Human cloning technology is an area that should not be left to develop as it is characterized by multiple ethical issues. With the availability of the cloning technology, Governments globally instituted domestic laws which banned human cloning activities. However, these nations saw that it was paramount to have regulations governing human cloning on a global scale rather than leaving the regulation to independent countries. Due to the serious implication that and life-altering ramifications presented by this area of biotechnology, the debate on human cloning regulations has shift its focus on the concept of human rights. For us to effectively cover the concept of human cloning, it will be imperative to cover the two types of cloning available. Therapeutic and reproductive cloning are the two types of cloning. Reproductive cloning procedure is employed in the production of the same genetic makeup similar to that of another human being. Reproductive cloning technique involves the creation of babies by implanting embryos into the uterus. The resulting product will be a live child. On the other hand, Therapeutic cloning is a form of cloning that deals with the production of embryo for the purpose of research with the aim of production of human embryonic stem cells that can extracted and used for the development of treatment of a number of human diseases and disorders (Jensen 4). The human somatic-cells nuclear are utilized when dealing with therapeutic cloning. This process involves the nucleus of a human somatic cell being transferred into an oocyte where a nucleus has been rendered inert or removed. A cell will then divide and form an embryo after the nucleus transfer. Stem cell possess the ability to develop into any tissue or organ. Important to note is that this process is different from the in vitro fertilization, both processes lead to the development of an embryo which can be used for research. When dealing with invite fertilization, it uses a sperm and an egg when creating an embryo. Scientist globally have supported the idea of therapeutic cloning being contended with the fact that it avails an avenue to study changes in the genetic makeup. By exploiting this area of research, patients who suffer from diseases such as Alzheimer, diabetes and Parkinson diseases can have their genetic makeup studied. According to scientist, there is a belief that embryonic stem cells can be used to facilitate drug development and evaluation (Pham). In addition, it can also be used to diagnose patients and to develop tissues and cells for transplantation. On the other hand, the opponents of therapeutic cloning argue that this process is ethically and morally unacceptable, this is because it necessitates for a scientist to develop an embryo and later terminate it in order to harvest the stem cells. Scientist globally agree that the practice of human reproductive cloning is morally unethical and should be discouraged the Playing God argument is one of the common arguments that objects the idea of reproductive cloning. However, there is little of consensus when it comes to measures that should be taken to regulate therapeutic cloning. There have been some divisions in nations whereby they should complete ban all practices pertaining to cloning or if they should only ban reproductive cloning and let therapeutic cloning to thrive guided with strict regulations. The United nations is one of the global body that has had contribution to this matter .It has tried to remove the confusion that exists in this areas with the adoption of the United Nations Declaration on Human Cloning .The main purpose of the United Nations to highlight on this issues was to establish an international framework that will foster responsibility societal governance on matters pertaining to human genetic technology (Gruskin, Grodin and Annas 161). However, it is important to note that this declaration fell short of implementing the international framework it aimed to develop. Since the agreement was non-binding, the declaration contains ambiguities that leaves nations to have limited guidelines on how they should establish national legislation on matters of human cloning. There are many dangers that might be as a result of human cloning, for instance Ursula Goodenough, who works as a cell biologist from the Washington University did add an application of this technology. She claimed it was a way to reproduce without men. Such as situation can render men superfluous in reproduction and phase out mens role in reproduction or create a world without men. This would lead to the ultimate feminist utopia. According to scientist including the creators of Dolly the sheep they claim that human cloning will only lead to many questions than answers due to the continued animal research. Another potential danger can be as a result of reactivation of cells in a gene. This process is risky. This is because an adult cell is composed of already differentiated genes whereby only a small fraction is activated to perform their specialized tasks. There may be some mutations if scientists activate genes that are not active. In addition, cells that have differentiated can rearrange themselves as a subset of their genes. A good example to illustrate this can be whereby cell that are immune rearranging themselves to form surface molecules. Such a rearrangement can lead to problems for the resulting clone. Also, if the entire set of genes in an adult DNA are not reactivated properly, there may be future problems with a clone during later developmental stages. This claim can be supported by the high levels of death associated with cloning at the laboratory stage due to DNA damage as may be the case during cloning of Dolly the sheep. Furthermore, the inability of scientist to not have a comprehensive understanding of the cellular aging process, they lack the understanding of the genetic clock that will be inherited by the subject (Piazza and Sforza 381). There is compelling evidence that a cloning subject will inherit the generic clock of the nucleus donor. such a situation will greatly undermine developments which have been made supporting cloning. People will view clones as copies of human that are short lived and disposable. From the discussion above, it is evident that human cloning is a controversial issue which is coupled by binding international regulation. There is a general consensus on the issue of reproductive cloning from the general public, scientist and politicians. As illustrated above, there are many motivations that desist scientist from participating in cloning. Some of the concerns include individuality, safety concerns and family integrity among others. However, based on the paper, there is a varied global view when it comes to therapeutic cloning? Critical issues such as moral and ethical issues having been a stumbling block for scientific and medical advancement. Therefore, the issue of human cloning should be avoided as it is subject to controversy and fear of the unknown presents itself to the world. In addition, the existing domestic laws have proven to be inconsistent and have been observed to contradict each other in some cases. This situation presents researches with limited regulation on how to go about human cloning research. Failure for one binding international guideline on cloning allows for researches to move to other countries where they can pursue their research. There is also the problem whereby nations in need of funding can tend to ignore unsafe and unethical research practices to attract researchers conducting their research within their borders. It is unfortunate that the United Nations failed to give offer an international consensus which would regulate activities revolving around human cloning. The adoption of the declaration makes the United Nations not to formally consider this issue until a point in time when it is brought forward by a member state. Lastly, there is need for the United Nations to implement a binding international convention that will regulate human cloning. States need to strike a balance between individual interests and come to a compromise that will lead to a consensus. Human cloning has potential ramification which are both negative and positive. These ramifications necessitate for extreme efforts to lead to a binding international regulation. Nations need to work together and deter developments in human cloning by enforcing the regulations set forth.

Thesaurus History, Definition, and Examples

A thesaurus is a book of synonyms, often including related words and antonyms. Plural is  thesauri or thesauruses. Peter Mark Roget (1779-1869) was a physician, a scientist, an inventor, and a Fellow of the Royal Society. His fame rests on a book that he published in 1852: Thesaurus of English Words and Phrases. Neither Roget nor thesaurus is copyrighted, and several different versions of Rogets work are available today. Etymology:  From the Latin, treasury. Pronunciation:  thi-SOR-us Observations John McPhee: The value of a thesaurus is not to make a writer seem to have a vast vocabulary of recondite words. The value of a thesaurus is in the assistance it can give you in finding the best possible word for the mission that the word is supposed to fulfill. Sarah L. Courteau: A thesaurus can extract that word thats on the tip of your tongue but cant quite reach your lips. It reacquaints you with words youve forgotten and presents ones you dont know. It suggests relationships but usually doesnt spell them out—like a hostess who invites you to a party of well-connected guests where youre expected to circulate and make your own introductions. In our hyper-searchable world, in which shelf browsing and even book skimming are on the wane, the thesaurus reminds us that precision isnt always a matter of predestined calibration. It can still be an informed choice. T. S. Kane: The limitations of most thesauri are revealed in the directions given in one edition of Roget: Turning to No. 866 (the sense required) we read through the varied list of synonyms... and select the most appropriate expression. [Italics added] The matter of selection is critical, and a thesaurus does not offer much help with that. For example, among the synonyms listed in one Roget under the category seclusion/exclusion are solitude, isolation, loneliness, and aloofness. They are merely listed as alternates with no distinctions drawn. but, except in a very loose sense, these words are not completely synonymous and may not be interchanged indiscriminately. To use these synonyms effectively you need to know considerably more about them than a thesaurus is likely to tell you. With many words—those in the example, for instance—a good abridged dictionary is more helpful... [But] used wisely, [a thesaurus] can improve your working vocabulary. Bruce Sterling: Rogets Disease. The ludicrous overuse of farfetched adjectives, piled into a festering, fungal, tenebrous, troglodytic, ichorous, leprous, synonymic heap. (Attr. John W. Campbell) Bill Brohaugh: The word thesaurus has numerous synonyms—so many that you could fill a magazine with them. So many you could fill a warehouse with them. A storehouse, even, or perhaps a treasury, a depository, a repository, an armory, a stockpile, a chest, a compendium, a vault, a hoard, a promptuary, a reservoir... all of which, you have likely guessed by now, are words that you would legitimately find in a thesaurus of thesauri.

Autism The Fastest Growing Disability That Deals With...

In the United States today, the fastest-growing disability that deals with development is autism(Facts). Autism Spectrum Disorder can be described as â€Å"a condition or disorder that begins in childhood and that causes problems in forming relationships and in communicating with other people(Webster).† Although the number of children diagnosed with autism is on the rise, there are many different levels of autism, which can affect how the cases are dealt with. Autism has no cure, but by informing the world, it can help to prepare an autistic child for the future that they hold. Diagnosing and testing for autism isn’t always a crystal clear path. It is common for autism to be tested and diagnosed in children age three or younger. There is not a medical test as of now to test for autism, instead there are analyses done by psychologists and specialists to test a child’s behavioral patterns and actions. By giving an MRI (Magnetic Resonance Imaging), doctors are able to pinpoint spots on a child’s brain â€Å"where the left and right hemispheres of the brains of people with ASD do not communicate properly with one another(Diagnosing).† There is also a study to monitor a pregnant woman’s blood, if her previous child has been diagnosed with autism. After the woman has her baby, the blood is still monitored by more blood tests to see if the autistic symptoms appear in the newborn child. By doing this, there is a hope to find a cause and cure for autism, since there is no definite cure as ofShow MoreRelatedInformational Essay on Autism598 Words   |  3 PagesAutism About 1 percent of the world population has autism spectrum disorder. (CDC, 2014) Autism is the fastest growing developmental disability. Autism is defined by a certain set of behaviors and is a spectrum disorder that effects individuals differently. Autism is a serious and lifelong developmental disability. On its own, autism is not a learning disability or a mental health problem. To go further back into history, autism was first recognized in the early years of the 20th century byRead MoreThe Effects Of Autism On Children And Adults Essay1706 Words   |  7 Pages Autism AP 226 BD 12/06/2016 Elizabeth Kimbrough â€Æ' Imagine how you would feel not being able to express yourself, or not being understood by others. Think of all the struggles you may go through. This is how many children and adults that are living with Autism feel today. Autism is a serious disease that needs a cure to better the lives of children and adults. Autism is the fastest growing disability in the United States. There are many questions being asked about Autism. Is there a cure for AutismRead MoreAutism Spectrum Disorder ( Asd )3918 Words   |  16 Pagesâ€Æ' Once a child is born, the parents may ask questions such as what kind of child he or she will grow up to be. However, when the child is born with a disability, the line of questioning may change to how could this happen to my child or what do we do now? Receiving the news that one’s child has been diagnosed with Autism Spectrum Disorder (ASD) may shatter a parent as their child and family’s life begins to change. These parents are now faced with many obstacles in trying to do what they feel willRead MoreCareer Aspirations of Undergraduate Students in University of Ibadan: an Implication on Their Emotional Health7438 Words   |  30 PagesNature of the Work Special education teachers work with children and youths who have a variety of disabilities. A small number of special education teachers work with students with severe cognitive, emotional, or physical disabilities, primarily teaching them life skills and basic literacy. However, the majority of special education teachers work with children with mild to moderate disabilities, using or modifying the general education curriculum to meet the child s individual needs and providingRead MoreStephen P. Robbins Timothy A. Judge (2011) Organizational Behaviour 15th Edition New Jersey: Prentice Hall393164 Words   |  1573 PagesCharacteristics of the U.S. Workforce 41 †¢ Levels of Diversity 42 †¢ Discrimination 42 Biographical Characteristics 44 Age 44 †¢ Sex 46 †¢ Race and Ethnicity 48 †¢ Disability 48 †¢ Other Biographical Characteristics: Tenure, Religion, Sexual Orientation, and Gender Identity 50 Ability 52 Intellectual Abilities 52 †¢ Physical Abilit ies 55 †¢ The Role of Disabilities 56 Implementing Diversity Management Strategies 56 Attracting, Selecting, Developing, and Retaining Diverse Employees 56 †¢ Diversity in Groups 58 †¢ EffectiveRead MoreGsk Annual Report 2010135604 Words   |  543 Pageslive longer GlaxoSmithKline Annual Report 2010 Contents Business review P08–P57 Governance and remuneration P58–P101 Financial statements P102–P191 Shareholder information P192–P212 Business review 2010 Performance overview Research and development Pipeline summary Products, competition and intellectual property Regulation Manufacturing and supply World market GSK sales performance Segment reviews Responsible business Financial review 2010 Financial position and resources Financial reviewRead MoreMedicare Policy Analysis447966 Words   |  1792 PagesD—Coverage Subtitle E—Financing Subtitle F—Waste, Fraud, and Abuse Subtitle G—Puerto Rico and the Territories Subtitle H—Miscellaneous TITLE VIII—REVENUE-RELATED PROVISIONS TITLE IX—MISCELLANEOUS PROVISIONS DIVISION C—PUBLIC HEALTH AND WORKFORCE DEVELOPMENT TITLE I—COMMUNITY HEALTH CENTERS TITLE II—WORKFORCE Subtitle A—Primary Care Workforce Subtitle B—Nursing Workforce Subtitle C—Public Health Workforce Subtitle D—Adapting Workforce to Evolving Health System Needs TITLE III—PREVENTION AND WELLNESS Read More_x000C_Introduction to Statistics and Data Analysis355457 Words   |  1422 PagesLuis Obispo Australia †¢ Brazil †¢ Canada †¢ Mexico †¢ Singapore †¢ Spain †¢ United Kingdom †¢ United States Introduction to Statistics and Data Analysis, Third Edition Roxy Peck, Chris Olsen, Jay Devore Acquisitions Editor: Carolyn Crockett Development Editor: Danielle Derbenti Assistant Editor: Beth Gershman Editorial Assistant: Ashley Summers Technology Project Manager: Colin Blake Marketing Manager: Joe Rogove Marketing Assistant: Jennifer Liang Marketing Communications Manager: Jessica Perry

Cocoa Production in Ghana A Mechanism for Biodiversity...

Introduction When it comes to intensive farming systems, many rural farmers face a trade-off between agricultural production and biodiversity . In order to protect the biodiversity, farmers must sacrifice agricultural production. Hence, the challenge is to continuously expand food production while bearing no negative effects on biodiversity. These negative effects widely include deforestation, disrupting ecosystem integrity and species viability. In light of these issues, better farming technologies and natural resource management practices along with improved agricultural policies are required. This brings up the question of how to protect wild species and conserve habitat while increasing agricultural production and farmer’s incomes?†¦show more content†¦Cocoa agroforests in particular, can create forest-like habitats, harboring tropical biodiversity in degrading lands . It is claimed that to date, biological diversity in cocoa production has been poorly studied, especially in t he context of ecoagriculture, which is referred to as â€Å"land-use systems managed for both agricultural production and wild biodiversity conservation† . Ecoagriculture can be considered the future of landscape management as it helps to preserve species and increase the productivity of the land while enabling the rural poor. The cocoa sector in Ghana provides livelihoods for over 700,000 farmers in the country . Since 1990s, world cocoa prices have steadily increased (with the exception of 1998 – 2000 and 2003 – 2006) . Hence, the steady increase in prices combined with farmers being paid a higher share of the price, has offered farmers increasing real producer prices. Even so, the ongoing environmental impact of existing farming practices may affect rural livelihoods. Trees have been cut down in large numbers to accommodate the open-field hybrid variety of coca, which grows in full sun conditions . According to Kolavalli and Vigneri (2010), â€Å"the damage to cocoa trees from capsid attacks tends to be higher for cocoa trees growing in full sun than for those in shaded systems† . Hence, the best possible environmental alternative to the

Analysis Of Robert Arrives s A New Vision - 1486 Words

1. When Robert arrives, he visits with the narrator’s wife first; the narrator observes them, but only occasionally joins in on the conversation. They all drink heavily and eat a large dinner. On his first visit to her home, an outgoing blind friend of the narrator s wife interacts with the narrator by having the husband of his friend draw what he sees on the television; in doing so, the narrator allows Robert to share his sight through art; at the same time, the narrator shares Robert s inner vision of beauty and feeling. This act of sharing gives each man meaning, and as such, relieves suffering from the narrator as he obtains new insights. Narrator new vision through the ability to create. A new vision is constructed when the narrator has to sketch the cathedral for Robert. The narrator doesn’t fully understand what happened when he closed his eyes and drew the cathedral, but he knows that it was an important experience, as the narrative opens; the narrator is shown to be one that lacks vision. He closes his eyes and start drawing cathedral with the help of Robert. He realizes the word is way vaster than his perspective. From my point of view life is all about making things happen not to sit by side and try to judge someone else for their look. The modern world made easy to judge and define people among their looks. When he says my eyes were still closed. I was in my house. I knew that. 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They do need it, but often they do not like it, and are prone to believe that when intelligence is not out to get them, it is incompetent.† In order for intelligence to be welcomed and have a significant impact, it must arrive at the right time, which is after the leaders have become seized with the issue but before they have made an overall decision. DNI Vision for the IC The Honorable JamesRead MoreThe Position Of Director Of National Intelligence1669 Words   |  7 Pagesintelligence advisor to the President of the United States (POTUS) and the National Security Council (NSC). The IRTPA of 2004, also established the Office of the Director of National Intelligence (ODNI) as an independent agency to assist the DNI. The ODNI s goal is to effectively integrate foreign, military and domestic intelligence in defense of the homeland and of United States interests abroad. 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The Black Men And Public Space By Brent Staples, The Myth...

Just Walk on By, Myth of a Latin Woman, and Shooting an Elephant; Depression from Stereotyping and Prejudice There has been many years of racial stereotypes and wanting to fit into a group. The essays that show this theme are Just Walk on By: Black Men and Public Space by Brent Staples, The Myth of the Latin Woman by Judith Ortiz Cofer, and Shooting an Elephant by George Orwell. Staples shows his audience the struggles he has gone through as a black male. Cofer shows her audience the stereotypes that surround Latin women. Orwell shows his audience the overwhelming desire of being accepted into a group of people. All three of these authors want to be accepted by the larger group of people. Society needs to empathise and be aware of the silence that surrounds these issues. Otherwise it can create depression amongst minority groups. Brent Staples is a black man in American society who has been exposed to being stereotyped against. He was walking down the street one night and a white woman was walking towards him. She turned around and started quickly walking away from him. She automatically assumed because he was a black man out at night that he would mug her. He was wearing casual street clothes with his hands in his pockets, but he never showed any threat towards her. Sh figured that he was a thug or a threat to her well being. Staples does not openly say this, but it is clear from the way he describes the woman s actions. â€Å"She cast a worried glance. To her, the

Audit and Assurance Successful Audit

Question: Describe about the Audit and Assurance for Successful Audit. Answer: Preamble To start the audit program of M Ltd the need of audit plan is necessary as the first element of such activity. To be a responsible partner of the audit firm, I am appending below the audit plan for performing a successful audit of M Ltd which is involved in the business of wine manufacturing and subsequent sales of the product both in domestic and overseas market. The company has recently enlisted themselves in ASX for their share to be traded in the Australian Share Market(Asx, 2015). This activity increases the number of stakeholders of the company with more responsibilities dawned upon the company to ensure proper financial activities with maintenance of records for justifying their business activities. Being external auditor, the responsibility of the firm is more to the statutory authorities and the external stakeholders. The company had replaced their erstwhile auditor by our firm with the expectation of more accurate and focal activities towards ensuing audit performance. The audit period for M Ltd is for the financial year of 2015 -16 which starts from 1st July 2015 and ends at 30th June 2016. The standard audit plan starts with detection of audit risk along with phase-wise planning with preliminary audit plan, execution of the job and submission of the report to the respective recipients in the form of authorities and the company along with published report in the website of the company to ensure its accessibility to all stakeholders irrespective of nature of internal or external stakeholders. Audit Plan Diagram of audit performance: Detection of audit risk: Normally before starting any audit assignment, audit firm has to analyze the audit risk. Audit risk is broadly divided into three components- Inherent Risk, Control Risk and Detection Risk. Although all the risks are connected with the concept of material misstatement, there are different types of effects getting generated out of these activities which may pose barrier to the audit assignment with not reaching the coveted level of deliverance so far audit process is concerned(Aicpa, 2006). Inherent Risk The inherent risks are material misstatement on the part of the employees involved in the activities of maintenance of financial statements created through omission or errors, which may be deliberate or not. Control Risk The control risks are generated from the practice of internal control through imposition of check in different layer of activities of the company in order to avoid material misstatement. Detection risk Detection risks are for the material misstatement generated on the part of auditors due to their overlooking of any important matter which may cause improper projection of facts of the company by the auditor resulted to proven insignificance of any important factor. In the case of M Ltd, inherent risk is found negligible as the company works on accounting software approved by AASB. As Finance Director is directly involved in finance and accounting activities with initiatives of decision making and setting of accounting and financial framework as per compliance of AASB. The control risk is minimized. Detection risk our area of concern and we will be attentive with all sensitive issues related to financial accounting system to mitigate the same(Accounting-simplified, 2010). Primary Plan Preliminary audit plan is mainly focused on the initial plans which are appended below:- Intimation The first step is to intimate M Ltd about the audit plan with date of initiation, duration of audit work, probable submission date of audit report, details of required financial documents and registers, size of the audit team, name of the team leader. The same is to be forwarded to M Ltd through formal letter through E Mail and hard copy along with quest for the acknowledgement and necessary compliance(Cag, 2011). Audit Team Audit team is to be fixed and my plan is to deploy 8 members out of which 7 members will be deployed in the process of verification and checking with necessary notes to be made on the facts derived from the financial statements for the period. Audit period The audit period is fixed from 10.10.2016 and will end on 31.10.16. The submission of audit report will be made on 5th of November 2016. Execution of Audit Process Verification and investigation The verification process will start from 10.10.2016 with segregation of financial document including registers. To start the verification, few concerns will be kept in mind. It had been noted earlier that there are export discarded inventories for some technical reasons which had caused the doubt in receivables. The receivables are not recovered which made a threat of declaration of bad and doubtful debts for the company effecting current asset and the working capital. The company is involved in the manufacturing process of wine and most of the sales is being made to overseas customers. Hence there is a constant threat of recoverable receivables for fluctuation of currency exchange rate. To cover this risk, the company is insisting on hedging. The bank and cash registers are to be verified as per norms with the statutory compliance towards district and federal taxes are to be verified with utmost care(Auasb, 2009). Preliminary report preparation The preliminary report is to be prepared by me as the audit team leader with highlighting the different issues come through audit process. After preparation of draft report, the same will be given to the management to get the clarification on the issues. It will be done with the head of operations like CEO, Financial Director and other heads of operations like manufacturing, HR and supply chain to earmark the problem areas and probable dates to resolve the issues(Auasb, 2016). Final report submission Final submission report submission will be made on 5th November with signature of CEO and the Audit Team Head and will be submitted to the respective authorities like income tax, ASX and will be published online for the stakeholders to make them understand the financial situation of the company. This will help them to raise questions in the AGM to be announced by the company later. Conclusion This assignment will give our firm enough opportunity to understand the trend of liquor business and enhance our expertise through experience gathered through this assignment. References: Accounting-simplified, 2010. Audit Risk Model Inherent Risk, Control Risk Detection Risk. [Online] Available at: https://accounting-simplified.com/audit/risk-assessment/audit-risk.html [Accessed 20 September 2016]. Aicpa, 2006. Audit Risk and Materiality in Conducting an Audit. Effective for audits of financial statements for periods beginning on or after December 15, 2006. Earlier application is permitted; https://www.aicpa.org/Research/Standards/AuditAttest/DownloadableDocuments/AU-00312.pdf, 47(107), pp.1647-62. Asx, 2015. Asx Listinig Rules. [Online] Available at: https://www.asx.com.au/documents/rules/gn04_foreign_entities.pdf [Accessed 29 September 2016]. Auasb, 2009. Auditing Standard ASA 200 Overall Objectives of the Independent Auditor and the Conduct of an Audit in Accordance with AustralianAuditing Standards. [Online] Available at: https://www.auasb.gov.au/admin/file/content102/c3/asa_200_27-10-09.pdf [Accessed 22 September 2016]. Auasb, 2016. Australian Auditing Standards. [Online] Available at: https://www.auasb.gov.au/Pronouncements/Australian-Auditing-Standards.aspx [Accessed 13 October 2016]. Cag, 2011. Audit Plan. [Online] Available at: https://dgace.cag.gov.in/pdf/AMG-III-Audit-Plan.pdf [Accessed 22 September 2016].

Diagramas de Fases Essay Example For Students

Diagramas de Fases Essay DISCUSION GENERAL SOBRE LOS DIAGRAMAS DE FASE OSCAR JAIME RESTREPO BAENA Doctor en Materiales Universidad de Oviedo Espana UNIVERSIDAD NACIONAL DE COLOMBIA GRUPO DE CERAMICOS Y VITREOS MEDELLIN 1998 Oscar Jaime Restrepo Baena DISCUSION GENERAL SOBRE LOS DIAGRAMAS DE FASE NATURALEZA E IMPORTANCIA DE LOS DIAGRAMAS DE FASE 1. INTRODUCCION Los materiales en estado solido existen en muchas formas diferentes o fases. El numero de tales fases puede ser grande incluso para sustancias puras, por ejemplo el hielo puede existir en varias fases solidas y un metal tan importante como el hierro presenta hasta cuatro fases solidas. En los sistemas que presentan mas de una especie quimica el numero de fases puede igualmente ser grande. Es tambien frecuente, aun en sistemas comerciales importantes, la disponibilidad de datos que cubren solo una parte de los sistemas. En vista del hecho que las propiedades de los materiales dependen significativamente de la naturaleza, numero, cantidad, y forma de las posibles fases que se presentan y pueden cambiarse por alteraciones en dichas cantidades, es vital, en el uso de materiales, conocer las condiciones bajo las cuales cualquier sistema dado puede existir en sus varias formas posibles. A traves de los anos se ha acumulado gran cantidad de informacion de un gran numero de sistemas; para registrar tal enorme cantidad de datos se acostumbra graficar el numero y composicion (e indirectamente las cantidades) de fases presentes como funcion de la temperatura, la presion y sobre todo la composicion. Estas graficas se llaman diagramas de fase, diagramas de constitucion o diagramas de equilibrio. Este ultimo nombre se deriva del hecho de que tales diagramas permiten mostrar la mayoria de las fases estables que se encuentran bajo condiciones de equilibrio. El termino â€Å"condiciones de equilibrio† requiere cierta elaboracion. Estrictamente hablando el estado de equilibrio de un sistema es aquel estado en el cual las propiedades del sistema no cambian con el tiempo, a menos que se ejerza una restriccion. En este ultimo sentido, restriccion significa normalmente una alteracion de la temperatura, la presion o la composicion, pero puede tambien referirse a la aplicacion de fuerzas mecanicas, electricas, magneticas, etc. En la practica, sin embargo, la definicion de equilibrio se modifica teniendo en cuenta las velocidades relativas de los posibles procesos que puedan introducirse en un sistema por cambios en la temperatura, la composicion o la presion. Frecuentemente un sistema es importante solo para ciertos valores de presion, temperatura y composicion; en tales casos las reacciones al interior de los sistemas pueden proceder a velocidades que son: a) tan lentas que producen cambios despreciables en las propiedades para periodos de tiempo lo suficientemente considerables. ) tan rapidas que llegan al equilibrio en menos tiempo que el que se puede registrar de manera practica y c) una magnitud intermedia. Los diagramas de fase 2 Discusion General sobre Diagramas de Fase muestran los reactivos en los procesos tipo a) y los productos de reaccion en los procesos tipo b) y c) como fases en equilibrio. En el tratamiento de los diagramas de fase, tanto en la determinacion, como en el uso se ha hecho un ac ercamiento fundamentalmente empirico, aunque en general ellos poseen una fuerte base termodinamica. En principio, al menos los diagramas de equilibrio, pueden calcularse por relaciones termodinamicas, en la practica, sin embargo, solo se recurre a sustituciones relativamente simples fundamentalmente por dos razones: la teoria exacta para casos generales es bastante compleja y muchos de los datos termodinamicos necesarios no se encuentran disponibles. Otros acercamientos posibles son: a) estudios desde un punto de vista puramente quimico, con lo cual se involucrarian algunos sistemas que no son de interes. ) una vision puramente matematica, haciendo uso de un lenguaje y simbolismos que no se manejan normalmente en ingenieria. c) estudio geometrico y/o aproximacion fenomenologica a los diagramas de fase sin casi ninguna discusion termodinamica. En estas notas se opta por una fundamentacion termodinamica con el fin de sentar las bases de discusion para cualquier otro sistema que se desee afrontar. 2. DEFINICIONES La base de todo el trabajo sobre los diagramas de equilibrio es, por sup uesto, la regla de fases de Willard Gibbs. El diagrama, tambien conocido como diagrama de fase o diagrama de equilibrio es esencialmente una expresion grafica de la regla de fases. La ecuacion siguiente presenta la regla de fases en la forma matematica usual: F+L=C+2 Donde: C: Numero de componentes del sistema F: Numero de fases presentes en el equilibrio L: Varianza del sistema (grados de libertad) Los terminos usados en la expresion anterior asi como otros necesarios para entender los diagramas de fase se definen a continuacion. 2. SISTEMA: cualquier porcion del universo material que pueda aislarse completamente y arbitrariamente del resto, por consideracion de los cambios que puedan ocurrir en su interior y bajo condiciones variantes. Los sistemas que existen dentro de otros sistemas se llaman subsistemas. En el sistema Ca0 Al203 los componentes, cal-alumina, con sus puntos de mezcla congruentes forman sistemas unos con otros, por ejemplo, los sistemas 5Ca0. 3Al203 CaO. Al2O3 y CaO- 3 Oscar Jaime Restrepo Baena CaO. Al2O 3. En el sistema ternario CaO-Al2O3-SiO2 las uniones binarias tales como CaO. SiO2 CaO-Al2O3-2SiO2 son verdaderos sistemas binarios y los tres componentes se mezclan congruentemente, CaO-SiO2, CaO-Al2O3-SiO2 y 2CaO. Al2O3. SiO2 cuya linea de frontera comun se encuentra en un eutectico constituye un verdadero sistema ternario. Los subsistemas en los cuales no se forman componentes se llaman sistemas minimos. 2. 2 FASE: cualquier porcion del sistema fisicamente homogenea consigo misma y separada por una superficie mecanicamente separable de otras porciones. 2. COMPONENTES: el menor numero de variables individuales independientes (vapor, liquido o solido) por medio de los cuales la composicion del sistema puede expresarse cuantitativamente. 2. 4 VARIANZA DEL SISTEMA (GRADOS DE LIBERTAD): es la aplicacion de la regla de fase al tipo de sistemas bajo consideracion; la variable independiente condiciona cuales factores se consideran; usualmente son la temperatura, la presion y la concentracio n. El numero de estas variables, las cuales se fijan de manera arbitraria para definir completamente el sistema, se llama varianza o grados de libertad del istema. 2. 5 EQUILIBRIO: Se dice que el equilibrio existe en cualquier sistema cuando las fases del mismo no conducen a ningun cambio en las propiedades con el paso del tiempo y permite que las fases tengan las mismas propiedades cuando se tienen las mismas condiciones con respecto a las variantes que se han alcanzado por procedimientos diferentes. 2. 6 EQUILIBRIO HETEROGENEO: un sistema es heterogeneo y esta en equilibrio heterogeneo cuando consta de dos o mas porciones homogeneas (fases) en equilibrio entre ellas. 2. EQUILIBRIO HOMOGENEO: un sistema es homogeneo y esta en equilibrio homogeneo cuando consta de una fase y todos los procesos y/o reacciones que ocurren al interior estan en equilibrio reversible. 2. 8 PUNTO DE FUSION CONGRUENTE: la temperatura a la cual un solido cambia a un liquido a la presion especificada, en la cual la fase liquida tiene la misma composicion que la fase solida. 2. 9 PUNTO DE FUSION INCONGRUENTE: la temperatura a la cual una fase solida cambia a una segunda fase solida mas un liquido, ambos de diferente composicion que el solido original. 2. 0 SOLUCION SOLIDA: es una fase cristalina simple la cual puede variar en composicion con limites finitos sin tener la apariencia de una fase adicional. 4 Discusion General sobre Diagramas de Fase 2. 11 POLIMORFISMO: la propiedad que poseen algunas sustancias de existir en mas de una forma cristalina, todas las formas con igual composicion quimica, pero con diferente estructura cristalina y propiedades fisicas e identico comportamiento en las fases liquida o gaseosa, en la fusion o evaporacion. 2. 12 PUNTO DE INVERSION: La temperatura a la cual una forma polimorfica de una sustancia cambia a otra bajo condiciones invariantes. . 13 METAESTABLE: se dice que una forma polimorfica es metaestable cuando existe en equilibrio con vapor en el ra ngo de temperaturas en el cual otra forma polimorfica de menor presion de vapor esta en equilibrio con el mismo vapor. Metaestabilidad no debe confundirse con inestabilidad la cual infiere que una forma polimorfica puede existir a una temperatura por encima o por debajo de su temperatura de transicion debido a la de la inversion. 2. 14 FORMAS ENANTIOTROPICAS: formas polimorficas que poseen un punto de inversion en el cual estan en equilibrio, esto es, que son interconvertibles. Por ejemplo: ? y ? 2CaO. SiO2 y ? y ? cuarzo. En tales casos, las curvas de presion de vapor se interceptan por debajo del punto de fusion de la forma polimorfica de mas alta temperatura. 2. 15 FORMAS MONOTROPICAS: en ciertas instancias de polimorfismo, las curvas de presion de vapor de dos formas no se encuentran por debajo del punto de fusion, por lo tanto carecen de punto de inversion estable y la forma que presenta una presion de vapor mas alta es metaestable con respecto a la otra en todas las temperaturas por debajo del punto de fusion. Tales formas se llaman monotropicas y no son interconvertibles. 2. 16 ESTUDIO ISOTERMICO: el metodo de considerar los cambios que ocurren en un sistema en el cual la variable temperatura se mantiene constante y la composicion (o la presion) se varia. 2. 17 ESTUDIO ISOPLETICO: el metodo de considerar los cambios que ocurren en un sistema en el cual la variable composicion se mantiene constante y la temperatura varia (una isopleta es una linea de composicion constante). 2. 8 EUTECTICO: un eutectico es un punto invariante (temperatura) es el sistema en el cual la fase reacciona, una remocion del calor provoca una desaparicion de la fase liquida sin cambio de temperatura. La composicion eutectica es aquella combinacion de componentes de un sistema minimo que tiene el mas bajo punto de fusion que cualquier otra relacion de componentes y esta en la interseccion de dos curvas de solubilidad en un sistema binario y de tres superficies de solubilidad en un sistema ternario. 2. 9 LIQUIDUS: el limite de puntos invariantes temperatura-composicion que representan la solubilidad maxima (saturacion) de un componente en la fase liquida. En un sistema binario es una linea y en un sistema ternario es una superficie, usualmente curva. 5 Oscar Jaime Restrepo Baena En un estudio isopletico a la temperatura superior a la de liquidus, el sistema es completamente liquido y en la interseccion de liquidus y la isopleta, el liquido esta en equilibrio con una fase cristalina. 2. 20 SOLIDUS: el limite de puntos invariantes temperatura–composicion en un sistema, a temperatura por debajo de la cual solido y liquido estan en quilibrio y por debajo de la cual el sistema es completamente solido. En un sistema binario sin soluciones solidas es una linea recta y con soluciones solidas es una linea curvada o una combinacion de curvas y lineas rectas. De otro lado en un sistema ternario el solido es un plano o una superficie curvada respectivamente. 2. 21 FASE PRIMARIA: en un estudio isoplet ico la primera fase cristalina que aparece en el enfriamiento a una composicion desde el estado liquido (esto es la interseccion entre la isopleta y la linea liquidus). . 22 LINEA DE FRONTERA: la interseccion de las superficies liquidus adyacentes en un diagrama de fases ternario. El area incluida por una serie de lineas de frontera adyacentes se conoce como area de fase primaria. 2. 23 LINEAS DE AMARRE: una linea dibujada desde un punto arbitrario en el liquidus al punto en el solidus correspondiente a la composicion de la fase solida que existe en equilibrio con el liquido a la temperatura del punto arbitrario. Para una temperatura particular, es la linea recta que conecta la composicion de dos fases en equilibrio una con otra. 2. 24 UNIONES: La region de un diagrama de fases que representa todas las mezclas que pueden formarse de un numero dado de composiciones seleccionadas. Una union puede ser binaria (una linea recta), ternaria (un plano), etc. , dependiendo del numero de composiciones seleccionadas, las cuales no necesariamente son compuestas. Debe notarse, sin embargo, que ninguna composicion seleccionada puede formarse a partir de las otras. 2. 5 LINEA ALKEMADA: una union en un diagrama de fases ternario que conecta los puntos de composicion de dos fases primarias cuyas areas de fase son adyacentes y la interseccion de las cuales forman una curva de frontera. 2. 26 TRIANGULO DE COMPOSICION: en sistemas ternarios los tres puntos que conectan las uniones de composicion de tres fases primarias cuyas superficies liquidas se encuentran en un punto. 3. FUNDAMENTOS TERMODINAMICOS La termodi namica es una disciplina cientifica que estudia las relaciones matematicas cuantitativas entre las propiedades mensurables de los sistemas, dando cuenta de leyes y 6 Discusion General sobre Diagramas de Fase principios que estan involucrados en las transformaciones energeticas de la materia. Las relaciones estan expresadas en terminos de cantidades, las cuales pueden designarse como variables de estado y propiedades de estado. En un sentido operativo las variables de estado son los potenciales que pueden manipularse de manera razonable para fijar o alterar la condicion o estado del sistema; esto es, aquellas propiedades a traves de las cuales pueden ejercerse restricciones al sistema. Las variables de estado mas frecuentes son la temperatura, la presion y la composicion; en situaciones especiales pueden ser importantes otras variables como los potenciales mecanico, electrico, magnetico, gravitacional y superficial. En el tratamiento de los diagramas de fase, solo la temperatura, la presion y la composicion se consideran fundamentales, por lo tanto es de ellos que se trata aqui. La fisico-quimica, donde la termodinamica tiene su origen, ha tenido en cuenta tradicionalmente liquidos y gases. La experiencia ha mostrado que cuando se fija el estado del sistema regulando la temperatura, la presion y la composicion, este queda completamente especificado, no importando la historia pasada del sistema. Las propiedades de tales sustancias se conocen como propiedades de estado ya que estas propiedades son las unicas funciones de estado que son tambien funciones de valor singular y por lo tanto pueden manejarse cuantitativamente en las expresiones matematicas de la termodinamica. Cuando se trabaja con materiales, los cuales pueden ser solidos, es frecuente encontrar que las propiedades dependen de la historia pasada tanto como de la temperatura, la presion y la composicion. Esta situacion se debe a dos caracteristicas de los solidos, su capacidad para resistir esfuerzos cortantes y su inercia relativa a reaccionar, comparados con los gases y liquidos. Esta caracteristica de los solidos es la responsable de muchas de sus propiedades y por lo tanto el estudio de los diagramas de equilibrio debe tener en cuenta tales aspectos ya que son limitaciones al aplicar las ecuaciones termodinamicas. . 1 CRITERIO DE EQUILIBRIO La termodinamica ha hecho posible expresar en unos pocos principios, o leyes, la evidencia de innumerables observaciones y experimentos sobre la naturaleza del universo. Estas layes expresadas matematicamente forman un conjunto de ecuaciones extremadamente utiles que relacionan las cantidades de estado de los sistemas. La primera ley de la termodina mica asegura que para un sistema en equilibrio interno, hay una cantidad llamada energia interna E, que es una propiedad de estado del sistema. Mas especificamente, esta ley establece que en cualquier sistema cerrado que pasa de un estado inicial dado a un estado final, por cualquier medio o proceso, si se mide todo el calor, Q, absorbido por el sistema y todo el trabajo, W, hecho por el sistema, la diferencia entre Q y W sera constante para cualquier via utilizada. Esto teniendo en cuenta que las magnitudes Q y W separadamente dependen de la naturaleza del medio. En otras palabras, la diferencia Q-W depende solo de los estados inicial y final del sistema, esto 7 Oscar Jaime Restrepo Baena significa el cambio en una propiedad de estado del sistema. Ya que tanto Q como W son terminos de energia, esta propiedad de estado es tambien un termino de energia, se le ha dado el nombre de energia interna y su simbolo es E; entonces, 1 ?2 E = Q W (1) La energia interna no esta descrita en detalle por la termodinamica clasica. Debe tenerse en cuenta que ni desde un punto de vista termodinamico, ni atomistico, puede considerarse a E, ni ninguna otra forma de energia, como completamente definida. Esto quiere decir que la magnitud del termino energia no puede darse nunca en una base absoluta, sino relativamente a algun sistema arbitrario de referencia; por ejemplo, E solo esta parcialmente definida por la ecuacion (1) o por su equivalente diferencial dE = ? Q ? W (2) El simbolo diferencial d se aplica solo a cambios en las propiedades de estado, es un diferencial exacto. La ecuacion (2) define solo un cambio en E durante un proceso, en terminos de dos cambios medibles ? Q, el calor absorbido por el sistema, y ? W el trabajo hecho por el sistema durante el proceso. Integrando (2) resulta: E2 E1 = ? 2Q ? 12W Esto es, la energia E2 del sistema, en el estado 2, solo puede darse en terminos de la energia E1, en el estado 1, cuando se pasa de un estado al otro. La misma limitacion existe cuando se considera el problema atomisticamente. La segunda ley de la termodinamica asegura que otra propiedad asociada con todos los sistemas llamada entropia, S, es tambien una propiedad de est ado y tiene como caracteristica importante que: a. En cualquier proceso que se lleva a cabo en un sistema en equilibrio con sus alrededores (proceso reversible) la entropia del sistema mas la de los alrededores es constante, esto es: sistrevS + d alrrevS = 0 (3) b. En un proceso espontaneo (irreversible): dsistirrevS + d alrirrevS 0 (4) Esta cantidad, la entropia, esta (parcialmente) definida termodinamicamente como: dS = dQrev 8 Discusion General sobre Diagramas de Fase T (5) Resumiendo (3), (4) y (5) se establece una expresion para la segunda ley dS ? 0 (6) para un sistema y sus alrededores, esto es, un sistema aislado (sistema adiabatico, isometrico y cerrado). De nuevo, la termodinamica no describe la entropia en detalle y el entendimiento de la ecuacion (5) en ocasiones es de una gran dificultad en quien estudia este tema. La entropia como cantidad termodinamica es una expresion del grado de aleatoriedad de un sistema y la segunda ley de la termodinamica es unicamente una expresion que da cuenta de la tendencia hacia la espontaneidad, hacia la completa aleatoriedad o hacia la maxima entropia. Esta claro que el equilibrio real (el mas probable) de cualquier grupo de atomos esta determinado primordialmente por dos factores; la resistencia de las energias potenciales interatomicas y la resistencia de la tendencia a la aleatoriedad. Estos atomos, con las mas altas atracciones mutuas tenderan a juntarse produciendo las mayores energias de interaccion negativa posible. De otro lado, la energia cinetica de los atomos aumentara la aleatoriedad en las posiciones atomicas (entropia positiva). El compromiso optimo entre estas dos tendencias opuestas llevara al estado de equilibrio. Una expresion termodinamica equivalente puede derivarse combinando las ecuaciones (2) y (5), para un proceso reversible; esto es, un sistema en equilibrio: dE = TdS ? W (7) Si se restringe el sistema a una composicion y masa fijas en el cual el unico trabajo hecho por el sistema esta asociado a un cambio de volumen (contra la presion) ? W se convierte en P alr dV y ya que P alr = P sist en un proceso reversible, entonces: dE = TdS Palr dV = TdS PdV (8) Tal y como se plantea la ecuacion (8), no se trata de la forma mas util, ya que el cambio de E esta expresado en terminos de dos variables independientes S y V; las cuales son dificiles de manipular experimentalmente. Esta dificultad puede eliminarse introduciendo una nueva cantidad, G, llamada energia libre de Gibbs y definida como: G ? E + PV -TS diferenciando (9) y sustituyendo en (8) se obtiene: dG = VdP SdT (10) (9) 9 Oscar Jaime Restrepo Baena Aqui la cantidad dependiente G, esta expresada en terminos de dos variables independientes P y T, las cuales pueden controlarse facilmente en el laboratorio. Para procesos llevados a cabo a presion y temperatura constantes, la ecuacion (10) dice que bajo condiciones de equilibrio: dG = 0 (11) Ademas puede mostrarse, de las ecuaciones (4) y (9) que para un proceso espontaneo o irreversible, a presion y temperatura constante: dG 0 (12) Por lo tanto, las dos primeras leyes de la termodinamica revelan que en un proceso espontaneo, a presion y temperatura constante, la energia libre decrece y alcanza un minimo en el equilibrio. 3. 2 EQUILIBRIO EN SISTEMAS DE COMPOSICION VARIABLE. Es importante tratar el problema de los sistemas multicomponentes, multifasicos, esto es, heterogeneos, los cuales pueden presentar variaciones de composicion interna por trasferencia de materia entre las fases. Tal sistema puede estudiarse centrando la atencion primero en una fase simple; por lo tanto puede considerarse cada fase como un sistema y el resto de ellas como los alrededores. Para ser consistentes con la condicion de que el sistema heterogeneo original puede permitir el transporte de materia entre fases, el nuevo sistema de una sola fase debe considerarse como un sistema abierto; esto es, puede intercambiar materia con los alrededores. Cada intercambio de materia lleva a una trasferencia de energia interna, la cual, para un cambio infinitesimal, puede expresarse como: dE = ? ?E dni = ?  µi dni ? ni (13) donde  µi se llama el potencial quimico de i y es la tasa de cambio de la energia interna con el cambio en la cantidad del i-esimo componente, manteniendo constantes todas las otras variables. The Civil War Effects All Americans In Different W EssayEn el diagrama de equilibrio de fases del carbono pueden verse las condiciones de temperatura y presion necesarias para obtener diamante (metaestable a temperatura ambiente) y no grafito que es la otra forma alotropica del carbono. 19 Oscar Jaime Restrepo Baena Figura 3. Diagrama de estabilidad para el carbono Figura 4. Diagrama de estabilidad para el carbono Otro sistema de gran interes para los refractaristas es el de la silice (SiO2). En el hay cinco fases condensadas: cuarzo ? , cuarzo? , tridimita ? 2, cristobalita ? y silice liquida. A una atmosfera de presion las temperaturas de transicion son las que se muestran en la figura. La transicion de cuarzo ? a cuarzo? que tiene lugar a 573 °C es rapida y reversible. Las otras transformaciones son lentas y necesitan largos periodos de tiempo para alcanzar el equilibrio. 20 Discusion General sobre Diagramas de Fase Figura 5. Diagrama de fases del SiO2 Los valores de presion de vapor del diagrama son una medida del potencial quimico de la silice en las diferentes fases. El diagrama de la figura 5 puede extenderse de manera que se incluyan las formas metaestables de la silice. Figura 6. Diagrama de fases del SiO2 incluyendo las fases metaestables Se tiene asi el siguiente diagrama: a una temperatura cualquiera la fase solida estable es aquella que tiene el valor mas pequeno de la presion de vapor (energia libre mas baja). Esto no es estrictamente cierto, ya que por ejemplo a 1100 °C, la silice vitrea podria transformarse en cristobalita ? , cuarzo ? o tridimita ? 2. De esas transformaciones la que tiene lugar viene determinada por la cinetica de los cambios. En la practica cuando la silice vitrea se calienta durante un largo periodo de tiempo a aquella temperatura, cristaliza 1 Oscar Jaime Restrepo Baena o se desvitrifica para formar cristobalita que no es la forma de menor energia libre, pero estructuralmente es la mas similar a la silice vitrea. Enfriando la cristobalita ? se trasforma en cristobalita ?. 5. 2 SISTEMAS DE DOS COMPONENTES Los sistemas de dos componentes tienen tres variables independientes, nominalmente, temperatura, presion y composicion. En los sistemas de importancia en ceramica, donde la presion de vapor permanece muy baja para grandes variaciones en la temperatura, la variable presion y la fase gaseosa pueden eliminarse de consideracion. Por lo tanto los diagramas pueden reducirse a dos dimensiones representando la composicion en las abscisas y la temperatura en las ordenadas. Los sistemas en los cuales se ha eliminado la presion se llaman sistemas condensados; por lo tanto la regla de fases que representa estos sistemas condensados se expresa en la ecuacion (29) donde F se refiere unicamente a las fases solida y liquida. F+L=C+1 (29) En los sistemas binarios bajo estas condiciones pueden coexistir tres fases produciendo una condicion invariante; dos fases producen una condicion univariante y una fase una condicion bivariante. . 2. 1 Insolubilidad total. Se da cuando dos compuestos A y B son totalmente insolubles entre si en estado solido, se pueden considerar los siguientes casos: Si A y B carecen de afinidad entre si: Sean Ta y Tb, las temperaturas de solidificacion de A y B (TaTb). Tomando como punto de partida un fundido homogeneo de A y B a temperatura superior a Ta; si se enfria el fundido los atomos de B obst aculizan la solidificacion de A y hacen necesario un descenso de la temperatura hasta Ta? ara que A pueda comenzar a solidificar. La accion perturbadora de B se debe tanto a la energia cinetica de sus atomos, como al efecto barrera que ellos oponen a los atomos de A para que ellos se adicionen al solido que se esta formando. La temperatura Ta? es tanto menor cuanto mayor sea la proporcion de atomos de B en el liquido. La solidificacion se iniciara con la formacion de algunos cristales de A puro, ya que por no existir afinidad entre A y B en estado solido, ningun atomo de B sera retenido en la red de A. El liquido restante, enriquecido en B, respecto a su composicion inicial, exigira un nuevo descenso de la temperatura para que la solidificacion pueda proseguir. Si el descenso de temperatura se desarrolla de modo continuo y lento (en equilibrio), aumenta la cantidad de A solidificado, hasta que el liquido residual contenga solo atomos de B. Al llegar a la 22 Discusion General sobre Diagramas de Fase temperatura Tb se inicia la solidificacion de B en forma de cristales que, solidificados a temperatura constante, constituyen una especie de matriz en la que se hallan dispersos los granos del compuesto A (constituyente disperso). En la figura 7 se senalan en las abscisas las concentraciones de A y B y en las ordenadas las temperaturas de principio y fin de solidificacion. Figura 7. Diagrama de insolubilidad total A y B forman un compuesto estequiometrico AxBy: cuando entre los dos compuestos existe afinidad quimica para formar otro compuesto A xBy; la red cristalina del compuesto C suele ser distinta a la red de A y de la red de B, y mas estable que estas. Esto se debe a que la agrupacion de atomos de A y B obedece a una atraccion entre ambos, enlace ionico, enlace covalente, etc. uperior a la energia de enlace de los atomos de A entre si y de B entre si. La solidificacion se inicia cuando se ha disminuido suficientemente la temperatura hasta equilibrar la energia cinetica de los atomos (repulsion) con la afinidad quimica (fuerzas de atraccion) que tiende a reagruparlos en forma de red solida del compuesto. Dado que la atraccion de los atomos A y B es superior a la energia de enlace de cada elemento, esa tem peratura de solidificacion Tc, es mas elevada que Ta y Tb. Cuando se ha llegado a Tc, la primera fraccion que solidifica deja al liquido con la misma proporcion de atomos A y B que habia en el liquido inicial y por ello la solidificacion proseguira a temperatura constante dando una estructura constituida por granos del compuesto C. Cuando existe en el liquido un exceso de atomos de A respecto a la composicion estequiometrica AxBy, la solidificacion es similar a la de dos compuestos insolubles A y C (siendo C en este caso el compuesto AxBy). La solidificacion de C se inicia a una temperatura Tc? inferior a Tc (Tc? s tanto menor, cuanto mayor sea el exceso de atomos de A). El liquido restante, enriquecido en A respecto a su composicion inicial, requerira un nuevo descenso de temperatura para que, disminuyendo la energia cinetica de los atomos de A en el liquido, la solidificacion de C pueda seguir. La solidificacion de C tiene lugar en un intervalo de temperatura hasta alcanzar la temperatura Ta, momento en el que el liquido residual, compuest o solo por atomos de A, 23 Oscar Jaime Restrepo Baena solidifica libremente a temperatura constante, como lo hacen los elementos puros. El resultado sera un compuesto constituido por granos de C (constituyente primario), contorneados por una matriz de granos de A, solidificados a temperatura Ta. La naturaleza del constituyente matriz determina siempre el comportamiento termico del compuesto; claro esta, que si la cantidad del compuesto quimico primario fuera tan grande que los granos de C entraran en contacto entre si, podria designarse a este como constituyente matriz. Figura 8. Insolubilidad parcial formando un compuesto estequiometrico. En la figura 8 se presenta el diagrama de solidificacion de dos compuestos nsolubles entre si que forman un compuesto estequiometrico 50%A y 50%B. A y B presentan afinidad eutectica: se presenta cuando A y B tienden a formar un compuesto de composicion A xBy estable en estado liquido hasta temperaturas inferiores a Ta y Tb. Siendo Ta y Tb respectivamente las temperaturas de solidificacion del compuesto A puro y B puro y teniendo la mezcla liquida exactamente a la proporcion AxBy; suponiendo TaTb, si desciende la temperatura hasta Ta, los atomos de A no llegaran a solidificar, pues la afinidad eutectica induce a que en el liquido la proporcion siga siendo de x atomos de A y y atomos de B. Por consiguiente, nada de liquido A solidificara hasta tanto no pueda solidificar tambien B. Pero tampoco se inicia la solidificacion al alcanzar la temperatura Tb. La solidificacion se inicia a una temperatura Te inferior tanto a Ta como a Tb en la que se equilibra el balance entre fuerzas de atraccion y de repulsion. Puesto que a Te el compuesto A se halla en estado liquido, pero notablemente sobre enfriado respecto a la temperatura teorica de solidificacion Ta, en primer lugar comienzan a solidificar, al alcanzarse Te, algunos atomos de A, con gran velocidad de nucleacion y tendiendo por tanto a dar una estructura muy fina. Pero de inmediato, y puesto que en el liquido la proporcion de A y B debe seguir siendo x/y, solidifican tambien atomos de B, proximos, en cantidad proporcional a los de A ya solidificados (y atomos de B por cada x atomos de A). 24 Discusion General sobre Diagramas de Fase Dado que las condiciones de solidificacion del liquido restante a la temperatura Te son identicas a las iniciales, proseguira la solidificacion a temperatura constante. El resultado a escala microscopica sera una mezcla de finos cristales de A puro y B puro (cada uno con su red peculiar propia) intimamente mezclados que dan un agregado complejo de ambos compuestos, que recibe el nombre de estructura eutectica. Cuando la mezcla liquida contiene un exceso de compuesto A, respecto a la composicion eutectica, la solidificacion se inicia a la temperatura Ta? , menor que Ta y tanto mas proxima a ella, cuanto mayor sea el exceso de A que se tenga en la mezcla, con formacion de granos de A. El proceso continua con la formacion de mas cantidad de A solido cuando desciende la temperatura. Al ir solidificando A, el liquido residual se enriquece en B y se va aproximando a la composicion eutectica. Una vez alcanzada la proporcion AxBy, el liquido solidificara a temperatura constante Te cuando el enfriamiento llegue a este valor, a modo de matriz en la que quedan embebidos los granos de A solidificados previamente (en el intervalo de temperatura Ta? -Te). En la figura 9 se indica como ejemplo el diagrama de solidificacion de un sistema formado por dos elementos que cumplen la condicion de ser insolubles en estado solido, pero con afinidad para dar una eutectica de composicion atomica 70%A y 30%B. Figura 9. Afinidad eutectica. Desde un punto de vista termico, no son deseables como materiales solidos este tipo de compuestos cuando se requiera trabajar a temperaturas superiores a la eutectica. 5. 2. 2 Diagramas de equilibrio de solubilidad total. Sistemas Isomorfos. En la solidificacion de compuestos binarios de solucion solida total, supongase el formado por dos compuestos A y B de puntos de fusion respectivos Ta y Tb (TaTb). Durante la solidificacion los atomos de B entran en la red cristalina de A a temperaturas superiores a Tb, ya que entre A y B existe una afinidad de solucion que tiende a apresar los atomos de B en la red de A. 5 Oscar Jaime Restrepo Baena La solidificacion de una solucion solida se inicia a una temperatura Ts, tanto mas baja, cuanto mayor sea la proporcion de atomos de B que presenta inicialmente el liquido. El primer solido formado es mas rico en metal A que la composicion promedia del liquido. En efecto, a la temperatura Ts, se fijan en el solido un numero de ato mos de B menor que el promedio, ya que a dicha temperatura los atomos de B en el liquido estan a temperatura superior a Tb; por lo que, teniendo en cuenta la perturbacion producida por los atomos de B en la solidificacion de A, sera necesario disminuir la emperatura para que la mezcla siga solidificando. La mezcla acabara de solidificar cuando todos los atomos de B se hayan incorporado al solido; esto ocurre (por la afinidad de solucion existente entre B y A) por encima de la temperatura Tb. Para que la solidificacion se realice en condiciones de equilibrio, las velocidades de enfriamiento deben ser lentas, a fin de permitir que en cada momento (antes de descender a una temperatura inferior) se uniformice la composicion del solido por difusion de atomos de B hacia el interior y se permita igualmente la uniformidad del liquido. Aunque en la practica no se consigue la completa uniformidad del solido a cada temperatura, es interesante el estudio de esta solidificacion de equilibrio teorica (ver figura 10). Para un compuesto de m% de composicion, las composiciones de la fase solida en equilibrio con la fase liquida para una cierta temperatura T1, son las que corresponden a las intersecciones con las lineas solidus y liquidus del diagrama de equilibrio, cuando se traza la horizontal correspondiente a la temperatura T1 Isotermica (Regla de la Horizontal). De la figura 10 se pueden deducir las proporciones de la fase solida de composicion s% y la fase liquida de composicion l% a dicha temperatura. Si se llama P1 al peso total de solido a dicha temperatura, P 2 al del liquido y P t al peso total del compuesto, se verificara: P1 + P 2 = P t P1 * s + P 2 * l = P t * m (30) (31) 26 Discusion General sobre Diagramas de Fase Figura 10. Diagrama de equilibrio de solubilidad total. siendo esta ultima expresion el resultado de igualar los porcentajes de atomos B. De las dos igualdades anteriores se deduce la llamada Regla de los Segmentos Inversos, expresada por la relacion: P1 = l m P2 m – s (32) Analogamente pueden deducirse los porcentajes de mezcla solidificada con relacion al total y de mezcla liquida con relacion al total: P1 = l m Pt ls (33) P2 = m s Pt ls (34) 5. 2. 3 Equilibrios invariantes. Reacciones invariantes son aquellos cambios de fase que tienen lugar a temperatura constante. Para que este tipo de reacciones pueda darse en un sistema binario sera preciso que, segun la Ley de Gibbs, haya tres fases en equilibrio. Con anterioridad se ha comentado la constancia de temperatura durante la solidificacion eutectica formada por dos compuestos insolubles entre si. Otro tanto ocurre cuando una 27 Oscar Jaime Restrepo Baena fase liquida reacciona con otra fase solida para producir otra fase solida diferente (reaccion peritectica), o cuando una fase liquida origina otra fase liquida y una solida (reaccion monotectica), o cuando dos liquidos reaccionan para dar un solido (reaccion sintectica). En los sistemas binarios pueden producirse ademas, otros tipos de reaccion invariante, por ejemplo transformaciones en que todas las fases en equilibrio son solidas (reaccion eutectoide, peritectoide, etc. 5. 2. 3. 1 Reaccion eutectica binaria. En general se dice que un sistema binario presenta una reaccion eutectica, cuando un liquido de composicion constante da lugar a dos solidos de composiciones definidas. La reaccion eutectica puede esquematizarse como sigue: Liquido E o Solido 1 + Solido 2 La reaccion eutectica se realiza en su totalidad, es decir, hasta la desaparicion de todo el liquido a temperatura constante. A esta conclusion, empiricamente compro bable, se llega tambien teoricamente, por aplicacion de la Ley de Gibbs. Una de las principales caracteristicas de los sistemas eutecticos es que la temperatura a la que se forma la fase liquida es mas baja que la de los dos componentes puros. Esto puede ser una ventaja o una desventaja, segun las aplicaciones. Para aplicaciones de alta temperatura, como son los materiales refractarios, no interesa que se forme una fase liquida. Asi la formacion de eutecticos de bajo punto de fusion conduce a severas limitaciones en el uso de refractarios como puede verse en el diagrama del CaO-Al2O3 (figura 29). La fase liquida puede aparecer a temperaturas muy bajas debido a la existencia de una serie de eutecticos. En general oxidos fuertemente basicos como el CaO forman eutecticos de bajo punto de fusion con oxidos anfoteros o basicos y ese tipo de compuestos no pueden usarse adyacentemente, aunque ellos independientemente tengan alta refractariedad. Sin embargo, si las aplicaciones de alta temperatura no son las de mayor importancia, puede ser deseable la aparicion de fase liquida como una ayuda para efectuar, por ejemplo, el proceso de coccion a bajas temperaturas, ya que la fase liq uida facilita la densificacion. La efectividad de los sistemas con punto eutectico tambien se usa para la fusion a bajas temperaturas de vidrios. Esto queda patente observando el sistema Na 2OSiO2 (figura 11). De 1710? C para la silice pura, se pasa a 790? C para la composicion eutectica 75% SiO2 -25% Na 2O. 28 Discusion General sobre Diagramas de Fase Figura 11. Sistema SiO2-2Na2O. SiO2 5. 2. 3. 2 Reaccion peritectica binaria. Cuando por reaccion de un liquido y un solido, a temperatura constante, se obtiene otro solido, la reaccion recibe el nombre de peritectica (o periferica). Se trata de un solido con un punto de fusion no congruente. Considerese el diagrama de la figura 12 y dentro de el, la composicion m% de la mencionada curva. Por aplicacion de la Ley de Gibbs, se desprende que a la temperatura Tp, esta se mantiene constante durante la reaccion: Liquido + Solido ? n o Solido ? m El enfriamiento de equilibrio segun la isopleta m% transcurre, al principio, como un sistema de solubilidad total, se van formando cristales de la solucion solida ? n y la composicion del liquido sigue la curva liquidus. Al llegar a la temperatura peritectica Tp, el liquido de composicion p, reacciona con la solucion solida ? n para trasformarse completamente en la solucion solida ? m . 29 Oscar Jaime Restrepo Baena Figura 12. Diagrama peritectico. Cuando comienza la reaccion entre el liquido y ? n, los cristales de la solucion solida Am se forman en la intercara liquido/? n. Esta capa de cristales de ? m actua de barrera e impide la reaccion posterior entre el liquido y ? n. Para que la reaccion sea completa hay que dar tiempo suficiente para la difusion de los atomos del componente A desde Bn hasta ? m . Tal difusion dara lugar al crecimiento de ? m en las intercaras ? n/? m y ? m /liquido hasta que la formacion de ? m sea completa. Como tal tiempo no se alcanza, los cristales primarios de ? n no se trasforman completamente en ? m y persistiran aunque no sea una fase de equilibrio. . 2. 3. 3 Reaccion monotectica binaria. Existen casos en que dos compuestos no forman fase unica en estado fundido. Entre ciertos limites de composicion dan dos capas liquidas cuyas composiciones dependen de la temperatura y su mezcla solo es completa por encima de una cierta temperatura critica Tm, tal como se muestra en la figura 13. Aplicando la regla de fases al compuesto m% se aprecia que al llegar a la temperatura Tm tiene lugar la reaccion invariante: Liquido I o Liquido II + ? esta reaccion recibe el nombre de monotectica. 30 Discusion General sobre Diagramas de Fase Figura 13. Diagrama monotectico. El enfriamiento de una mezcla liquida por la isopleta m% se realiza de un modo similar al de un eutectico, pero dando lugar, a la temperatura Tm, a una sola fase solida y a un liquido de composicion muy diferente de la del inicial. El sistema SiO2-MgO presenta una reaccion invariante del tipo monotectico para un 98% de SiO2. Figura 14. Sistema MgO-SiO2 5. 2. 3. 4 Reaccion sintectica binaria. La reaccion sintectica es una reaccion invariante consistente en la descomposicion, por calentamiento, de una fase solida en dos liquidos inmiscibles: 31 Oscar Jaime Restrepo Baena Liquido I + Liquido II o ? como se ilustra en la figura 15. Figura 15. Reaccion sintectica. Esta reaccion es muy poco frecuente. Del diagrama de equilibrio se desprende que toda mezcla fundida cuya composicion se encuentre dentro del rango de la linea sintectica, se separa en forma de dos liquidos. Reciprocamente, al solidificar, la reaccion sintectica tendra lugar en la superficie o separacion de los liquidos Li y Lii. Esta reaccion se produce en la intercara de los dos liquidos y por tanto la fase B formada actua como una barrera que impide que continue la reaccion entre Li y Lii por lo que, en general, sera muy dificil mantener condiciones de equilibrio en un sistema con punto sintectico. Despues de la formacion de los cristales de la fase ? cada uno de los liquidos solidificara independientemente. Existe otra reaccion invariante conocida como metatectica en la cual un solido A, se encuentra en equilibrio con otra fase solida ? , de composicion diferente y un liquido: ? o ? + Liquido indicando una fusion parcial del solido ? durante la transformacion. 5. 2. 3. 5 Otras reacciones invariantes. Las reacciones invariantes entre tres fases de un sistema binario pueden reducirse a dos tipos. Uno de ellos es la transformacion de una fase en otras dos a temperatura constante: Fase I o Fase II + Fase III 32 Discusion General sobre Diagramas de Fase en este tipo de reaccion quedan encuadradas las eutecticas y monotecticas. El otro tipo corresponde a la reaccion de dos fases para dar una tercera, distinta a las anteriores: Fase I + Fase II o Fase III a este corresponden las reacciones peritecticas y las sintecticas. Cuando las reacciones se dan en estado solido, existen tres posibilidades de gran interes que son: Reaccion eutectoide: Reaccion peritectoide: Reaccion monotectoide: ? ? +? ? +? o ? ?n o ? m + ? Estos equilibrios presentan una velocidad de reaccion mas lenta que sus equivalentes cuando existe una fase liquida. 5. 2. 4 Sistemas binarios complejos. En la figura 16 se presenta un ejemplo de un diagrama binario hipotetico de considerable complejidad el cual permite ilustrar como se realiza la cristalizacion bajo condiciones de equilibrio. Los dos componentes son A y B . El componente A, en el rango de temperaturas que muestra el diagrama, presenta cinco formas enantiotropicas: liquido, ? 1, ? 2, ? 3 y ? 4. El componente B existe en solo dos formas

Senior Essay Topics

Senior Essay TopicsSenior essay topics are generally researched on the internet or any other site. You may have to compose and submit the topic yourself if you do not know how to. Senior essay topics are often of course rejected due to the one-sided and unoriginal content.Instead of writing on senior essay topics, make sure that your research materials are complete and free from any errors before you go about preparing your topics. Remember that any mistake in your senior essay topics will be present to everyone and so you have to make sure that your topic is complete and is not full of mistakes.So if you are to write your senior essay topics, prepare for it with the utmost precision. This will definitely make your topics more unique and interesting to read and you will also know what your senior essay topics are like.Before starting your senior essay topics, make sure that you come up with a plan. Make sure that you can actually sit down and write it all down and make sure that it i s not one-sided. Also think of something to say and write it out.Keep in mind that your topic is a vital part of your senior essay topic. To avoid confusion and also avoid giving too much emphasis to your topic, make sure that you stick to one single topic. At least, a single topic should do it.Before you begin your senior essay topics, choose your topic with care. It is very important that you make the topic to a singular topic so that you will not make the entire essay too long and to work it out of your head. If you make the topic to a singular topic, it will also help in making the essay simpler.Senior essay topics can be shorter and the more the student writes, the easier will be to write the senior essay topics. All senior essay topics should not exceed six hundred words, maximum.Writing senior essay topics should be done in such a way that the student will not realize he has made a mistake. Make sure that you write the essay topics in a style that will look good in the reader 's eyes.

Effects Of Computers And The Internet On Society Essays

Effects Of Computers And The Internet On Society Before we know it, technology is going to pass us by. With the invention of the computer and the Internet, the possibilities are endless. Society is changing by leaps and bounds, with no chance of a stopping point in the near future. All this change is dealing with computers and the effects that it will have on the way we live tomorrow. The Internet affects us in every way, most importantly with our social lives, our jobs, and our entertainment. Our social lives are not just communicating with telephones and mail anymore. Going on-line is the new way we like to communicate with people. Chat rooms on the Internet are open for people to talk and explore with other people who may live on the other side of the world or the other side of the street. E-Mail is also another popular way to correspond with others. Users can electronically send mail to another person with an on-line mailbox, simply by typing in their message and sending it by the click of a button. Two seconds to send e-mail to someone on the other side of the world is much quicker than a week or more through the ordinary mail. The Internet can also affect our jobs. Computers can calculate and figure out things much quicker than the average person. This process cannot only save time, but money too. Stock trading is now on the Internet, along with banking and any other type of business you could imagine. The world wants thing to be quick and easy. The best answer to that is to have a computer do it for you. In the future, hundreds of millions of jobs will be taken away from honest hard-working employees and will be given to computers. No matter what choices we make, or what plans we change, these outcomes are going to become real. Why would a business pay someone to take phone orders, when a computer can do it in less time and make it both cheaper and easier for the business and the buyer? Computers and the Internet are definitely affecting the way we entertain ourselves. The most basic example is card games. If the computer can deal out cards on a screen with the click of a button, why would anyone want to deal out a deck of cards manually and have to clean them up afterwards? On the Internet, you can gamble with on-line casinos, place bets on a horse race, or even watch movies. People can do all of these activities in the comfort of their own home. No gas money is wasted or time spent driving around to find entertainment so people are happy. The inevitable outcome of this magnificent invention is going to change the world. Society is happy about the way things are changing. Cheaper is better, less time consuming is better. With the choice of having a computer and being on-line, there is almost nothing you cannot do. This remarkable idea of the Internet is going to revolutionize the way we live in the future. Technology Essays