Fatigue Essay Example | Topics and Well Written Essays - 2250 words

Fatigue - Essay Example Because of this subtlety, it is important to develop methods of predicting and controlling fatigue during the design process. The progress of fatigue is categorised into three stages (Budynas and Nisbett, 2006). Stage I is the presence of microcracks, which are the tiny regions of plastic deformation from which the failure process begins. During stage II, these cracks steadily grow and increase in length. It is during this stage that cracks can be detected and measured, and are apparent in post-failure analysis as visible ridges: How quickly a part reaches failure due to fatigue is an important question for mechanical design. It is a complicated process, influenced by many factors. A cornerstone of fatigue behaviour prediction is extensive materials testing. Whatever the mathematical framework used to predict fatigue behaviour, it invariably relies on empirical measurements of representative material samples. Because crack formation and propagation are stochastic processes, these tes ts must be repeated a large number of times and a statistical average used as a guideline. This is particularly true for low cycle fatigue. Characterization of Cyclical Loads In order to discuss fatigue and the types of loading that cause it, some standard terminology needs to first be established. Any cyclical stress can be characterized by the following parameters: ?a Stress amplitude ?r Stress range ?m Mid-range stress ?max Maximum stress ?min Minimum stress Additionally, there is the stress ratio R, and the amplitude ratio A defined by: In contrast to static failure, which occurs when a single threshold value is exceeded, fatigue failure can result from a near-endless combination of the above components. A number of different criteria have been developed to determine which combinations will lead to failure. The following diagram shows some of these criteria, with points on or above each line indicating failure. Some criteria are clearly more conservative than others, from the So derberg line to the Gerber ellipse. These criteria are somewhat crude approaches that do little to describe the physical phenomenon; they are deterministic, whilst the phenomenon itself is stochastic. They were developed early in the study of fatigue, and are primarily useful for quick estimation. The following three sections define more rigorous approaches. Fatigue-Life Methods Stress-Life Method The stress-life method is very convenient and intuitive, and consists of applying repetitive stresses to a sample, then measuring the number of cycles to failure. A sample of material is loaded into a high-speed rotating-beam machine, which places the sample into a state of pure bending, then rotates it to create fully-reversed cyclical axial stresses within it. These samples are very carefully machined and polished to control surface defects that could initiate a crack. Testing begins at near-yield strength, and then gradually reduced in subsequent tests. The result is known as the  "S-N curve† which shows the expected fatigue strength vs. the number of cycles to expected failure. This method of determining material fatigue properties is straightforward to implement, but lacks accuracy, particularly for determining low-cycle endurance. Fatigue failure is stochastic in nature, and even the most carefully-controlled experiments

How to Escape from a Bad Date by Piven et al (297-302)Patterns 11th ed Essay

How to Escape from a Bad Date by Piven et al (297-302)Patterns 11th ed - Essay Example Likely, the idea is that young individuals would want to have the perfect date every time they would get out with someone they treat to be a special someone in their lives. The importance of dating makes a particular developmental impact on the personality of any individual engaging in such social relations. This is why it is important to assure that each one does not bring about shame towards those that are involved in the relationship establishment. However, it could not be denied that there are dates that bring about shame to one. What if it happens that a person dates someone that is the perfect opposite of what he or she expected to be, and somewhat even worse at some point? This is when the need to escape from a bad date comes in. The reading written by Piven, Borgenicht and Worrick provides a proper set of guidelines that would give dating partners the best chance of moving away from bad dates that are bound to bring about particular shameful experiences in the past that would likely give them lesser chances of experiencing better levels of self-confidence later on. Getting away from a bad date experience though need not be harsh on the part of those who would be left alone in the date. The reading on this matter written by the authors mentioned above creatively advices several strategies on the part of the one wanting to end the date to move about the process in a less shaming way with respect to the one that is to be left on. The writers of the book were likely able to find better approaches to provide essential guidelines and points of important issues that need to be given attention to when one naturally wants to move away from a particular dating tragedy. This was likely because of the fact that the writers were able to base their informative advices from their own experiences making the entire reading not only informative but also entertaining in many ways. Certainly,

Building a marketing website for bed & breakfast outline

Building a marketing website for bed & breakfast - Outline Example well structured and probing questions which are asked to various clients and other stakeholders in order to obtain useful information helpful in the development of the system. Questionnaires give the developer a chance to ask his/her respondents questions that are vital for the design of the website but the stakeholders are not aware of. Care should be taken in the construction of the questionnaire to avoid inappropriate questions that may not necessarily show the opinion and views of the stakeholders (Inflectra, 2010). The questionnaire should not be too long or take much of the respondent’s time as this might lead to the respondent to answering superficially. The questions should also flow sensibly in order to make the respondent enjoy answering them. This is the most appropriate way to determine the contents of a website. It involves observing the stakeholders of the business as they engage in their day to day activities and then recording the events. Observing is critical as the developer is able to know what he/she will require in developing the website from first hand information. It also ensures that the stakeholders will be able to use the site with ease. This method also helps in validating information gathered from other methods like interviews. A disguised observation is preferred as the respondents (customers and the management) are unaware that they are being observed and therefore will act in their natural way (Requirements, 2010). An interview is valuable in getting the background information about the business problems and position currently and also to have a wider perspective of what other bed and breakfast websites includes. The interview should be wide enough to cover all the stakeholders of the business so that the website will have all the information required by any stakeholder. Interviews are essential as they will provide the developer with a chance to probe further for more information (Nancy, 2008). Unstructured interview is more

Disaster management assignment Essay Example | Topics and Well Written Essays - 2500 words

Disaster management assignment - Essay Example Why was there such a deficiency in the aid provided? Was there any effect on the extent of Hurricane Katrina of the human activities? Was the catastrophe prompted by the land use practices along the Gulf Coast? Can Global Warming be considered as one of the factors that impelled the storm to such appalling proportions? What effect would it have on the over all nation’s economy? These are just some of the questions that started arising in the utter confusion after the disaster. Since the time that Katrina hit, the tropical storms and hurricane activity in the Atlantic have been well above normal. The arrival of Katrina actually signified a continuation of the trend in 1995 (Hurricane Katrina: A Scientist’s Response). The development of hurricanes had an average of 7.7 hurricanes and 3.6 major hurricanes yearly between 1995 and 2005, while in the previous 25 years the average had been 5 hurricanes and 1.5 major hurricanes. (Hurricane Katrina: A Scientist’s Response 2005) New Orleans, which was directly in the eye of the hurricane, sits in the middle of the flood plain of the Mississippi river. This mighty river like most rivers of such a scale overflowed its banks inundating the surrounding area which threatened the wellbeing of the communities surrounding that area. Katrina arrived in the busiest hurricane seasons of the Atlantic Ocean by the end of which 24 tropical storms had formed. Out of these thirteen became hurricanes including seven classified as being category-3 and higher. (Hurricane Katrina: Possible Causes 2005) Hurricane Katrina was one of the most calamitous hurricanes to have ever hit the American soil. It completely devastated New Orleans, Louisiana and other communities settled on the Gulf Coast when it came ashore on August 29, 2005 (Hurricane Katrina: Possible Causes 2005). It made landfall on Louisiana after crossing South Florida and gaining strength over the Gulf of Mexico at 6:10 A.M local time. At 9:45 A.M, the Katrina centre

Writing the History of the Australian Frontier Essay

Writing the History of the Australian Frontier - Essay Example However, Reynolds denied the claim by Windschuttle and stood by his original estimate. Thus, there started a conflict between the two distinguished figures over the number of Aboriginals killed in the frontier. "This skirmish was the first in what has since become known as the Aboriginal history wars. Windschuttle fired more shots in articles in the last four issues of Quadrant in 2000. Reynolds returned fire in a major article in the March 2001 issue of The Australian Review of Books. And there have been carefully staged verbal skirmishes in venues like Gould's Book Arcade in Sydney, on ABCTV Lateline and at the National Press Club in Canberra." (Ryan 2001, P. 31). Therefore, there has been a significant conflict of ideas and arguments by Henry Reynolds and Keith Windschuttle on the topic of writing the history of the Australian frontier and it is essential to comprehend the main areas of disagreement and agreement between the two. This paper undertakes an exploratory analysis of th e major arguments by Reynolds and Windschuttle in order to identify the major areas of disagreement and agreement between them, the evidence provided by each of them to support his position, and the utility of Ryan’s article to comprehend the realities of this controversy.... h Windschuttle has been their positions on the number of causalities in the Australian frontier and the two proposed significant substantive evidences to argue their positions. According to Reynolds, "It seems reasonable to suggest that Aborigines killed somewhere between 2,000 and 2,500 Europeans in the course of the invasion and settlement of the continent. There were many hundreds of others who were injured and carried both physical and psychological scars for the rest of their lives. Calculating the Aboriginal death toll is much more difficult For the continent as a whole it is reasonable to suppose that at least were killed as a direct result of conflict with the settlers." (Reynolds 1981, P. 99). Therefore, he mainly argues that the casualties can be calculated around 2,000-2,500 Europeans, and it is much more difficult to calculate the Aboriginal death toll. He also ascertains that Tasmania documented the conflict better than anywhere else in the country and Ryan's estimate of 800 is possibly more precise than the other estimations. The secondary effects of the invasion include disease, deprivation, and disruption which were responsible for the premature deaths of many more people and it is not possible to arrive at a realistic figure on the question. Windschuttle confronted the views by Reynolds on the number of deaths in the Australian frontier and his article "The Myths of Frontier Massacres in Australian History," claimed that many massacres of Aborigines in the Australian frontier were fabricated pointing out that the number of casualties in the frontier was far fewer than estimations of Henry Reynolds. He also disagrees with Reynolds' argument that the number of the Aborigines who died defending their territory outnumbers, in both relative and even

Social And Natural Sciences Essay Example | Topics and Well Written Essays - 1250 words

Social And Natural Sciences - Essay Example A great contribution of positivism into philosophical and methodological explorative methods is considered further on the example of social and natural sciences. In sociology, positivism is the core paradigmatic methodology. Science and inquiry are two basic pillars of positivism. Still, it is very important to solve the major problem of social sciences, which concerns results finding on the basis of complex species research and study. The roots of Positivism can be traced in the French Enlightenment. The philosopher suggested combining natural sciences principles with social sciences. Comte claimed that religion was conquered by science. It was much important those times to refer to facts and laws, than to suppositions and considerations. Scientific knowledge is outlined by Comte in the following way: the stage of fictitious, metaphysical and scientific knowledge. The last stage of knowledge, scientific knowledge, is preferential for Comte. The development of all other stages, if su ccessfully implemented, would result in scientific knowledge emergence. These stages of knowledge can be also sought in Empiricism. This science is based on observable facts, claiming that logical and mathematical roots are in the background of the facts. The main principle of positivism should be also found in â€Å"positive† information, which can be obtained from a positive experience. A methodological paradigm of positivism consists of science and inquiry. An empirical exploration is of crucial importance for any science.  ... These stages of knowledge can be also sought in Empiricism. This science is based on observable facts, claiming that logical and mathematical roots are on the background of the facts. The main principle of positivism should be also found in â€Å"positive† information, which can be obtained from a positive experience. Therefore, a methodological paradigm of positivism consists of science and inquiry. An empirical exploration is of crucial importance for any science. Thus, from positivist perspective it can be claimed that social phenomena are not distributed in accordance with certain or specific types, where the members of these types are homogenous (Cassell, 2002). In other words, positivist vision or methodology implemented in social sciences is not relevant to the fullest extent. Sociological phenomena are of inhomogeneous nature. For example, a structure of any sociological object or phenomena cannot be considered in accordance with specific features or characteristics, w hich are relevant at all times. Moreover, social processes and generalizations cannot be characterized simultaneously in accordance with homogenous characteristics. For sociological sciences it is of crucial importance to formulate specific hypotheses focused on special sociological events or imagination. A development of sociological theory is one possible way to develop explanations concerning sociological events or objects. Therefore, positivism is often criticized as irrelevant methodology applied for social inquiry. Social science requires development of special approaches focused on â€Å"contingency, heterogeneity, path-dependence, and particularity corresponding to the plasticity of

History of Electrocardiography Machine Essay Example for Free

History of Electrocardiography Machine Essay History of electrocardiography prevails over two centuries as an intellectual exercise as the process of inventing an electrocardiogram started with the Galvani’s idea of animal electricity. In 1842 this idea was further reinforced by Italian physicist Carlo Matteucci who illustrated by his experiments that electric current could be quantified from inactive heart muscle. German physiologist Emil Dubois-Reymond further explored this phenomenon and confirmed Carlo Matteucci’s conclusion and labeled this changing current in the resting muscle as â€Å"action potential†. He further developed a device that could deliver stimulation pulses to the muscles and was capable of computing discharge current of muscles at short intervals. In 1856 Rudolph von Koelliker and Heinrich Muller recorded an â€Å"action potentialâ€Å"on the spotaneous beating heart. But the major development came in 1872 when French physicist Gabriel Lippmann introduced a capillary electrometer. This capillary electrometer was based on the principle of â€Å"polarization† and â€Å"surface tension†. Structurally it was a slender glass tube with mercury-sulphuric acid base. The mercury meniscus stirred with the influx of electrical potential and was observable by a microscope. In 1893, Willem Einthoven who is considered as the inventor of modern electric cardiogram and its various principles used the term electrocardiogram at a conference of the Dutch Medical Association. But major development occurred during the three years staring from 1901 when Einthoven dissatisfied with capillary electrometer and it slow response, designed a string galvanometer. This galvanometer contained a string eletromagnet to produce a magnetic flux, two piece poles, a quartz string between the two piece poles, peepholes in the two piece poles to observe the position of string. It further contained a lamp and timing systen to examine the shadow of string at different time intervals. The weight of this whole apparatus was about 600 pounds. He further modified the string galvanometer to invent a more effective electrocardiograms. However in 1902, Einthoven brought out the first electrocardiogram that was recorded on his string galvanometer. This was a giant’s leap in the history of bio-medical. In order to produce string galvanometer on commercial level, Einthoven discussed the possibilities with Horace Darwin of Cambridge Scientific Instruments Company of London. So this event made the electrocardiogram to come out of experimentation and to be used in medical profession. Einthoven, in 1906, circulated the first presentation electrocardiograms recorded with a string galvanometer. These electrocardiograms included the specimen of left and right ventricular and atrial, atrial flutter, ventricular premature beats etc. In 1910, Horatio Williams who was professor at Cornell University Medical College, New York issued electrocardiograms of patient that manifest atrial and ventricular ectopics, ventricular hypertrophy, atrial fibrillation and ventricular fibrillation that were recorded in hospital using a complex system of cables. This was first large-scale use of electrocardiograms in the hospitals. With the advent and introduction of vacuum tubes, the electric galvanometer was further modified and improved. In 1926, Ernestine and Levine used these vacuum tubes to produce enlarged images. Cathode rays tube further helped to produce portable electrocardiograms. Today electrocardiograms works on the same principles that were devised Einthoven in the first decade of 20th century. References Burchell HB. A centennial note on Waller and the first human electrocardiogram. Am J Cardiol 1987; 59:979-983 Burch, G.E. A History of Electrocardiography. Chicago. Year Book Medical. 1964. Burnett J. The origins of the electrocardiograph as a clinical instrument. Medical History Supplement 5: 1985, 53-76. Published as a monograph. The emergence of modern cardiology. Bynum WF, Lawrence C, Nutton V, eds. Wellcome Institute for the History of Medicine:1985. Fye WB. A history of the origin, evolution, and impact of electrocardiography. Am J Cardiol 1994;73:937-949 Plonsey, R. Bioelectric Phenomenon. New York. McGraw-Hill. 1972.