The Raven - Edgar Allan Poes Essay Example for Free

The Raven Edgar Allan Poes Essay Edgar Allan Poe was born on January 19, 1809 in Boston, Massachusetts. He is one of the most significant writers in the American history. Well known for its mystery and horror stories he is considered part of the Romantic movement in US and the inventor of detective fiction genre. On January 29, 1845 he publishes his poem The Raven in the Evening Mirror which granted him with immense fame (Edgar Allan Poe: A Critical Biography 1941). The editor of the publishing newspaper wrote: It is the most effective single example of â€Å"fugitive poetry† ever published in this country; and unsurpassed in English poetry for subtle conception, masterly ingenuity of versification, and consistent, sustaining of imaginative lift and â€Å"pokerishness. † It is one of these â€Å"dainties bred in a book† which we feedon. It will stick to the memory of everybody who reads it(Evening Mirror, New York, January 29, 1845). The poem is of great artistic merit, it exudes many emotions and arise many feelings. Every reading of the poem gives new experience and new feelings but when You got familiar with Poes life a inevitable question is arising. Putting together The raven and Poes life we can see that the place where the poem is written corresponds to the room where the action of the story is held in addition the raven represents Poes inner self, furthermore for the image of the narrator Poe uses for prototype himself and all these lead to the conclusion that The Raven is Poes own view about his fate. The correspondence between the time and the settings of the poem and the time and conditions it was written supports the idea of coherence between the story of the poem and the prediction for the future that lies before the author. The Raven was published in January 29, 1845, according to The New York Times at that time Poe and his wife Virginia lived at a farm house in New York. In 1844 the farm house was away from the city. Poes home stood on a rocky and commanding eminence a few hundred feet of 84 Street and St. Nicholas Boulevard, at that time Manhattan was a country north of Greenwich Village otted with tiny hamlets(The New York Times January 1, 1908). This distant and isolated house was his sanctuary giving him solitude from the world outside. We can see quite the same at the opening of the poem with depiction of the room. The room is closed claustrophobic place well furnished with lots of books and heavy curtains which give a sense of isolation And the silken, sad, uncertain rustling of each purple curtain (line 13) Straight I wheeled a cushioned seat in front of bird, and bust and door (line 68) Then, upon the velvet sinking, I betook myself to linking (line 69). Isolation and solitude is was the narrator is seeking in order to surcease the inner pain and sorrow. What is more the time of the action in the poem and the time of its writing is the same winter. The poem was published in January 29 and the process of the writing can take us a month back in December. December is the time in which the action in the poem is held. The view from Poes distant house away from the city during the winter is only bare uplands which co-responds to the description he gave bleak December at the beginning of the second stanza Ah, distinctly I remember it was in the bleak December (line 7). In a nutshell the place, in which he lived at the time of the writing of The Raven, resembles the place in which the action takes place. Another evident in favor of the statement that the poem corresponds exactly to the view about Poes fate is the fact that he uses himself for prototype of the protagonist in the poem. The narrator possess many books which refers that he is well educated and intelligent as Poe himself. The protagonist is suffering from great inner pain and sorrow and vainly hoping for a cure Is there—is there balm in Gilead? —tell me—tell me, I implore! (line 89) as does Poe at the time, according to Arthur Quinn , in which the poem was published his great love Virginia had been sick from Tubercolosis for three years, her death is inevitable and Poe is aware of it (Edgar Allan Poe: A Critical Biography 1941). Another confirmation is the fact that the narrator is using the books for distraction from the painful reality which Poe had been doing for a long time Once upon a midnight dreary, while I pondered, weak and weary / Over many a quaint and curious volume of forgotten lore (lines 1- 2). In brief the narrator is a mirror image of Edgar Allan Poe. The fact that The Raven represents Poes inner personality confirms the statement that the poem is Poe foresight about his fate. We can see the manner in which Poe rites The Raven with capital R which tells us that it is not any raven. Well known for his macabre stories full with horror, this ebony bird is his black soul, his sinister mind. His talk with the bird asking if he will be or will be not again reunited with his beloved Lenore in the after life is a symbol of his inner doubts and desires Tell this soul with sorrow laden if, within the distant Aidenn (line 93) It shall clasp a sainted maiden whom the angels name Lenore— (line 94) Clasp a rare and radiant maiden whom the angels name Lenore. line 95). Another confirmation is the conversation with the bird in which he is begging for nepenthe to release him from sorrow but his request is not fulfilled which represents Poes inner inability to free himself from the pain Respite—respite and nepenthe from thy memories of Lenore; (line 82) Quaff, oh quaff this kind nepenthe and forget this lost Lenore! (line 83)† Quoth the Raven â€Å"Nevermore. †(line 84) An additional element leading to the conclusion that the ominous bird is a personification of Poes inner self is the way how he writes Hope and Hopes with capital H, referring both to the bird and to the narrator On the morrow he will leave me, as my Hopes have flown before. (line 59)/ Till the dirges of his Hope that melancholy burden bore (line 65). In other word the raven is a representation of Poes inner self. To cut a long story short the poem The Raven is Poes view about his own fait. In The Raven the action is held in a place which resembles the house that Poe and his wife Virginia inhabited, also in the story Poe gives life to his dark inner self trough the image of the raven, who took the life of the narrator which prototype is Poe himself. Though the cause of Poes death is unclear, according to Jeffrey Meyers and Charles scriber, Poe had died from Delirium Tremens alcohol poisoning (Edgar Allan Poe Jeffrey Meyers, Charles Scriber, 1992) responsible for which is Poe himself or in particular his inner inability to resist the need of alcohol. In other words the foresight had been fulfilled.

RF Propagation Pathloss Model

RF Propagation Pathloss Model Introduction What is the need of RF Propagation Model? In wireless communication the transmitted signal propagates in space i.e the radio signal. Wireless communication system is the most widely used communication system now a days and communication took place in such system with the help of radiowave in space. Thus a detailed analysis and study of radiowave propagation is required and it is a very important aspect before we finally design and implement a wireless communication system. When we talk about the communication through a wired line medium such as RF Coaxial cable or twisted pair cable or optical fiber provides reliable communication with minimum pathloss as signal is well secured in it from the atmospheric distortions. Though the laying and maintaining of the wired medium takes time and is cost effective as well but it is reliable means of communication. on the other hand communication in such medium i.e. in wireless communication is quite unreliable and unsecured. In wireless communication a limited operating frequency bandwidth is available for communication as it has many other applications of radiowave propagation in space. Every communication system is designed with some specific objectives of providing continuous communication services to mobile subscribers that are present in the service area i.e. the area upto which the operator will provide communication services. But as we studied earlier a good quality service can only be obtained if loss of transmitted signal will be minimum and maximum signal will reach at receiver end. The design can be optimized only when the parameters under which a system has to operate are fully understood whether the frequency band allocated or the height of antenna, distance between transmitter and receiver, and the most important is the pathloss and an estimation of received signal level at the receiver end. If proper radio analysis is done than it will be of great use to design a network and implement it in hardware level with proper and desired results which are expected from a system. The most important design parameter in mobile communication system is to achieve the desired signal coverage as the basic purpose of operator is to serve the subscribers in a specified service area. Whenever a system is designed it is designed for some specific aims and that is to provide a better service to subscribers with in the range for which the services are introduced but if we directly implement the system without checking it whether the system is giving desired output or not and directly implement it than if it is not performing according to ones expectation the system will be wasted and soon our efforts so it is the most important factor to check and calculate the pathloss. Classification of RF Propagation Pathloss model Different models were developed which are empirical in nature that means they are developed based on the collection of data in specific areas. Data must be sufficient enough so as to study the losses that may happen in any specific area, so that on the basis of that data one can come to a conclusion as propagation models does not tell the exact pathloss that may happen but it will tell the most likely behavior of the link under some defined conditions. Mainly RF Propagation Models can be classified as below: Basically RF Propagation models can be classified into three main categories which can be classified as above defined. Empirical models Semi-deterministic models Deterministic models The Basic classification of RF Propagation Pathloss Models can be seen in the above figure 3.1. Three kinds of models Figure 3.1 Classification of RF Propagation Pathloss Model Empirical models : based on measurement data, simple (few parameters), use statistical properties, not very accurate. Semi-deterministic models : based on empirical models + deterministic aspects Deterministic models : site-specific, require enormous number of geometry information about the cite, very important computational effort, accurate. Every Model is defined for a different and a specific environment and for different cells. Cells in a mobile communication is nothing but a geographical area covered by a telephone transmitter. cells can also be divided into three main types and they are as follows: Macrocell Microcell Picocell Macrocell The area of largest coverage. Macrocells are used to described the widest range of cell sizes. Example : An Entire City. It covers the area upto 1-5 km long. Microcell The area of intermediate coverage. Mainly the range of microcell is less than two kilometers. It covers the area upto 100- 1 kilo meters. Pico cell A picocell is a small cellular base station which covers a small station such as in buildings, offices, shopping malls etc. It covers the area upto 500 meters. From the above figure we can understand the concept and coverage area covered by a macrocell, microcell and picocell. Representation of macrocell, microcell, picocell A table is shown where different cells and the area covered by those cells i.e Macrocell, Microcell, and picocell is shown in table 3.1.3. Table 3.1.3 Different cell sites and area they covered. Different RF Propagation Pathloss models are defined for different cells which can better perform on different cells and better results can be obtained. Now the cells and the models defined for it will be described. Okumura-Hata model It is the most popular model which is based on the empirical information obtained from measurements in japan.(okumura 1965). The okumura Hata predicts the Pathloss L between the transmitter and receiver taking into considering the frequency, the distance between transmitter and receiver, height of antenna, terrain type.this model fits best for urban and suburban areas. General formula The general formula for the path loss L according to the Okumura-Hata model is: L = a0 + a4 ·logf a2 ·loghb a ·hm + [a1 – a3 ·loghb] ·logd Lc, where a0, a1, a2, a3, and a4 are adjustable parameters Specific formulas The path loss L can be found by the standard path loss formulas for GSM-900, GSM-1800, and GSM-1900 according to the Okumara-Hata model. GSM–900 formula The path loss formula for GSM-900 is: L = 69.55 + 26.16 ·logf 13.82 ·loght a ·hm + [44.9 – 6.55 ·loght] ·logd Lc. GSM–1800/1900 formula The path loss formula for GSM-1800/1900 is: L = 46.3 + 33.9 ·logf 13.82 ·loght a ·hm + [44.9 – 6.55 ·loght] ·logd -Lc Where, L= Pathloss fc=frequency of transmission ht=antenna height ar=correction factor for effective mobile antenna height which depends on the size of the in area Lc=correction factor for different terrains. Correction factor for different clutter classes is determined according to okumura hata model and following is the table 3.1.4 which shows the clutter classes and correction factor for it. Table 3.1.4 Correction factor defined according to okumura Hata Model Cost 231 Hata Propagation Model A Model that is widely used for predicting pathloss in wireless system operating from 500 MHz to 2000 MHz is the cost 231 Hata Model. It contains correction factor for Urban, suburban and open rural environment. The general expression for calculating pathloss in the urban area as given by COST 231 Hata model is: Lpch(urban)db)=46.3 + 33.9logfc 13.82loght ar + (44.9-6.55loght)logr + Cm where, fc=frequency of transmission ht=antenna height ar=correction factor for effective mobile antenna height which depends on the size of the coverage area. Cm =3db for urban environments and 0db for suburban or open environment Walfisch-Ikegami model The Walfisch-Ikegami model is more recent than the Okumura-Hata model. It is based upon the deterministic models of Walfisch, Ikegami, and Bertoni. It works in 2 cases : LOS and NLOS LOS (Line of sight) LLOS [dB] = 42.6 + 26 log10 d[km] + 20 log10 f [MHz] NLOS (Non line of sight) LNLOS [dB] = LFS + Lrts (wr, f, ΔhMobile , ÃŽ ¦ ) + LMSD (ΔhBase, hBase, d, f, bS ) LFS = free space path loss = 32.4 + 20 log10 d[km] + 20 log10 f [MHz] Lrts= roof-to-street loss LMSD= multi-diffraction loss But it has some restrictions which are as follows: Frequency f between 800 MHz and 2000 Mhz TX height hBase between 4 and 50 m RX height hMobile between 1 and 3 m TX RX distance d between 0.02 and 5 km Longley – Rice Propagation Model The Longley Rice Propagation model also known as irregular terrain model. It basically calculates large scale median propagation loss relative to free space loss propagation loss over irregular terrain. It is mainly applicable for point to point wireless communication system. It operates in the frequency range from 40 MHz to 100 GHz. It is mainly used for frequency planning in television broadcasting. The modified model can also be used for radio wave propagation in urban areas for mobile communication. The Longley – Rice propagation models has two parts: model Area to area prediction model. Point to point prediction model. The area to area is used when path profile is not given but point ot point is used when detailed path profile is given. But, the main drawback of this model is that it doesnot consider the effect of multipath, foliage, buildings and other environment factors. Two Ray Point to Point Propagation model The point to point propagation model is a basic system design tool that is used to generate a signal coverage map, an interference area map, or a handoff occurrence map. In many mobile communication system the maximum distance between the cellsite and the mobile is at the most only a few tens of kilometers and surface is assumed flat. A simple two ray model can be used to predict pathloss and received signal strength. Lpch = 40 log r – 20 log ht – 20 log hr Thus it implies that the propagation pathloss in a mobile communication Lpch increases by 40dB for every increase in distance by 10 times. If the cellsite antenna height is doubled, there will be reduction in pathloss by 6dB. The two ray model is found to be reasonably accurate for predicting the large scale received signal strength over distances of several kilometers for mobile radio communication system that use tall cellsite towers and los microcell application in urban area.

Essay on The Value of Dreams in Hawthornes Young Goodman Brown

Young Goodman Brown: The Value of Dreams Young Goodman Brown The Birthmark Nathaniel Hawthorne's stories "Young Goodman Brown" and "The Birthmark" both make use of dreams to affect the story and reveal the central characters. With each story, the dreams presented are extremely beneficial to the development of the story as they give the reader a new view of the plot itself, or the characters within. At the same time, however, it becomes difficult to determine how much of the dream has been affected by the character, and how much is pure fantasy. This is true with Young Goodman Brown, who cannot determine whether the events in his life actually occurred, or if they simply were created in his troubled mind while he slept. In "The Birthmark," Aylmer too is haunted by his night-time musings as he dreams of mutilating his wife in order to rid her of a small birthmark. This small detail later turns out to foreshadow the conclusion of the story, while giving readers further insight into his diabolical nature. Dreams thusly play an important developmental role in the explica... ...he beauty of his bride, which is, at least, unsettling, until his dream of butchering Georgianna is revealed. Troubled, too is Young Goodman Brown, who can not determine whether or not the incredible visions of the previous night were real. As a precaution, he avoids contact with the dream-related peole and lives the remainder of his life alone, but surrounded by those who were once his friends, associates, and family. As evidenced by these two short stories, we can see the important role that dreams can play in the effective telling of a tale.

Nora Helmer in Ibsens A Doll House Essay -- A Doll’s House Essays

In 1879, Henrik Ibsen published the play A Dolls House. However, to much of his displeasure the portrayal of the third act was considered erroneous to critics and audiences of that time frame. This controversy centered on the play’s conclusion in Nora's decision to leave her marriage and abandon her children. Critics labeled this decision appalling and unrealistic, since at that time in history no true woman would ever make such a choice. This uproar forced Ibsen to write a second ending where Nora instead decides that the children need her more than she needs her freedom. Thus, leaving critics and audiences contently satisfied. Since then, though times have changed and ideas and beliefs of the past have been altered, maybe the critics had it right about Nora’s departure. Perhaps Ibsen’s original ending is better left unsaid. Therefore, other than the alternative ending that Ibsen produced, how might the character of Nora deal with the situation at hand differently, based on what can be determined about her from the text? For starters, how about confronting the title of the story? Just who is the Doll? Many may claim that the doll is automatically Nora, for the reasons that she has been molded by her father and then toyed around with by her husband. To those individuals, Nora may seem like she is the victim, the poor little girl who can not comprehend who she is, the sweet â€Å"sky-lark† who had to leave her family for the findings of her true inner being†¦Or on a different note, Nora is the master and the controller of all that is functioning in the Helmer household. Although her husband, Torvald, may refer to her as a sky-lark, squirrel, or singing bird, it can be viewed in the text that Nora does not object to these remarks but r... ...a man who loves her and abandoning her children. Point in taking: Nora served no sense of accomplishment and only declared her egotism in a single selfish act. In the end, Nora’s greatest strength became her greatest weakness and it lead to her vindicated defeat. If only Nora used her powerful gift of control to step up to society instead of blocking it out, would she been able to save herself, her family, and her characters reputation as a feminine heroine, instead of a controversial role. But perhaps the controversy over Nora’s character is what we cherish so deeply because it is beyond our understanding. The idea that she is someone who is eternally captivating but can never fully be defined completely. Works Cited Kennedy, X.J. and Gioia, Dana. Backpack Literature: An Introduction to Fiction, Poetry, and Drama. New York: Pearson Longman, 2006. 778-843. Nora Helmer in Ibsen's A Doll House Essay -- A Doll’s House Essays In 1879, Henrik Ibsen published the play A Dolls House. However, to much of his displeasure the portrayal of the third act was considered erroneous to critics and audiences of that time frame. This controversy centered on the play’s conclusion in Nora's decision to leave her marriage and abandon her children. Critics labeled this decision appalling and unrealistic, since at that time in history no true woman would ever make such a choice. This uproar forced Ibsen to write a second ending where Nora instead decides that the children need her more than she needs her freedom. Thus, leaving critics and audiences contently satisfied. Since then, though times have changed and ideas and beliefs of the past have been altered, maybe the critics had it right about Nora’s departure. Perhaps Ibsen’s original ending is better left unsaid. Therefore, other than the alternative ending that Ibsen produced, how might the character of Nora deal with the situation at hand differently, based on what can be determined about her from the text? For starters, how about confronting the title of the story? Just who is the Doll? Many may claim that the doll is automatically Nora, for the reasons that she has been molded by her father and then toyed around with by her husband. To those individuals, Nora may seem like she is the victim, the poor little girl who can not comprehend who she is, the sweet â€Å"sky-lark† who had to leave her family for the findings of her true inner being†¦Or on a different note, Nora is the master and the controller of all that is functioning in the Helmer household. Although her husband, Torvald, may refer to her as a sky-lark, squirrel, or singing bird, it can be viewed in the text that Nora does not object to these remarks but r... ...a man who loves her and abandoning her children. Point in taking: Nora served no sense of accomplishment and only declared her egotism in a single selfish act. In the end, Nora’s greatest strength became her greatest weakness and it lead to her vindicated defeat. If only Nora used her powerful gift of control to step up to society instead of blocking it out, would she been able to save herself, her family, and her characters reputation as a feminine heroine, instead of a controversial role. But perhaps the controversy over Nora’s character is what we cherish so deeply because it is beyond our understanding. The idea that she is someone who is eternally captivating but can never fully be defined completely. Works Cited Kennedy, X.J. and Gioia, Dana. Backpack Literature: An Introduction to Fiction, Poetry, and Drama. New York: Pearson Longman, 2006. 778-843.

The Wonderful Bedroom Essays -- Descriptive Essay Examples, Observation

The Wonderful Bedroom Have you ever wondered how something so simple as your bedroom could have so much meaning? How a place where one usually just sleeps and doesn't return until the next night, could be so special to someone? It does make one think, once stopped and thought about. To some, it means as much as a gym does to a basketball player or as much as a tree does to a monkey. But then there are also those who still think of their bedroom as just a place to sleep and prepare themselves. I guess things have different meanings for each person, but for many including myself, their bedroom ranks near the top of the list. A bedroom is meaningful because often it is where one grows up, where lots of time is spent, and where one can bring out there inner-most self. A bedroom is not something that changes from day to day, but rather something that is pretty permanent. Many people grow up in the same room that they spend the first part of their life in. It is something that people grow attached to and become accustomed to, like a college student becomes accustomed to studying. For this factor, change is not so much a good thing but rather a thing of frustration. It is nice to have a place to call home, and better yet, a place to call one's own bedroom. Once one is settled, it is usually of best nature to stay settled. Through this settlement, it is easiest to see how much of importance one's bedroom may mean to them. My bedroom has meant a lot to me due to the fact that I have been in the same place for the majority of my years. Another important reason on this subject is that there is usually a lot of time spent in one's own room Besides the ten hours of sleep everyone gets a night in their room, there is often a gr... ...all sorts of things to do and eventually time slips away along with the boredom. A bedroom is full of wonderful surprises and often has much more meaning than one may imagine. In just a simple little corner of a house, it can tell you so much about a person. Is the person a pack rat, organized, and clean, or are they simple-minded, just waiting to open their eyes and explore? Perhaps there are things that go far and beyond the word "special". A room can tell ones whole life story, but yet again maybe it is just thought of as a place to catch some Z's. No matter what the case, this simple little place they call one's bedroom can and usually does have much meaning. So, next time you're lying in bed trying to fall asleep, ask yourself, does my room really have much meaning to me, and if so, how much, or am I just thankful for this comfortable bed to sleep on? Â   The Wonderful Bedroom Essays -- Descriptive Essay Examples, Observation The Wonderful Bedroom Have you ever wondered how something so simple as your bedroom could have so much meaning? How a place where one usually just sleeps and doesn't return until the next night, could be so special to someone? It does make one think, once stopped and thought about. To some, it means as much as a gym does to a basketball player or as much as a tree does to a monkey. But then there are also those who still think of their bedroom as just a place to sleep and prepare themselves. I guess things have different meanings for each person, but for many including myself, their bedroom ranks near the top of the list. A bedroom is meaningful because often it is where one grows up, where lots of time is spent, and where one can bring out there inner-most self. A bedroom is not something that changes from day to day, but rather something that is pretty permanent. Many people grow up in the same room that they spend the first part of their life in. It is something that people grow attached to and become accustomed to, like a college student becomes accustomed to studying. For this factor, change is not so much a good thing but rather a thing of frustration. It is nice to have a place to call home, and better yet, a place to call one's own bedroom. Once one is settled, it is usually of best nature to stay settled. Through this settlement, it is easiest to see how much of importance one's bedroom may mean to them. My bedroom has meant a lot to me due to the fact that I have been in the same place for the majority of my years. Another important reason on this subject is that there is usually a lot of time spent in one's own room Besides the ten hours of sleep everyone gets a night in their room, there is often a gr... ...all sorts of things to do and eventually time slips away along with the boredom. A bedroom is full of wonderful surprises and often has much more meaning than one may imagine. In just a simple little corner of a house, it can tell you so much about a person. Is the person a pack rat, organized, and clean, or are they simple-minded, just waiting to open their eyes and explore? Perhaps there are things that go far and beyond the word "special". A room can tell ones whole life story, but yet again maybe it is just thought of as a place to catch some Z's. No matter what the case, this simple little place they call one's bedroom can and usually does have much meaning. So, next time you're lying in bed trying to fall asleep, ask yourself, does my room really have much meaning to me, and if so, how much, or am I just thankful for this comfortable bed to sleep on? Â  

Quantitative risk assessment Essay

Monte-Carlo simulation is carried out using a large number of computations, using a computer, with random inputs. This method is particularly useful when it comes to â€Å"predicting† the outcome a complex eventuality. Typically, the Monte-Carlo simulation is useful when predicting the outcome of a large number inter-related factors that are â€Å"uncertain†. Predictivity using Monte-Carlo simulation is far more accurate where variables under consideration are many, uncertain and random. For this particular reason, using Monte-Carlo simulation for this study is the best choice as there are many uncertain factors that need to be analyzed for computing a risk assessment. In this study, the first step begins with the production of meat and ends with health effects that meat can probably induce in consuming subjects. There is a large interplay of uncertain factors, and the entire food chain model proposed in the study has inherent variability across most levels. 2. What comment would you make about the source of data used for the concentration of E. coli in cattle feces? Prevalence and concentration of E. Coli in cattle fecal matter was used to assess the level of contamination of the meat. The level of contamination of the meat is a pointer to the probable exposure that a consuming subject could possibly have, to E. Coli. Concentration of E. Coli in cattle fecal matter is directly related to factors like seasonality, geographical properties, and feeding practices. However, the data related to concentration of E. Coli in the cattle fecal matter was constructed without consideration for these factors. Data used for concentration of E. Coli in fecal matter was obtained using enrichment methods. The results show a wide bipolar variation, from as low as undetectable E. Coli levels to as much as 5. 0 log10 CFU/g. The data for prevalence of E. Coli in cattle fecal matter was obtained from previously held studies. However, only data from those studies was used, that primarily aimed at detecting E. Coli prevalence rates in cattle fecal matter for beef that was supposedly slated for human consumption. 3. What comment would you make about the following: †¢ modeling the distribution of feces on carcass as Uniform? Slaughtering invariably causes the fecal matter to come in contact with the meat. Skinning a carcass will lead to contamination of exposed meat due to contact with the hide. Although, fecal matter is the main source of bacterial reservoir, the nature and number of agents that can directly or indirectly participate as contaminating agents is uncertain. However, the concentration of E. Coli in fecal matter is directly proportional to the extent of meat contamination. The distribution of fecal matter on carcass surface is uneven. A dilution factor was used as a model simplification. †¢ modeling fecal contamination only on the carcass surface? As a fact, E. Coli are present in the fecal matter but not inside red meat. Contamination of red meat, therefore, occurs only when fecal matter comes in contact with it. This will usually happen during slaughtering, and the following processes like packaging and trimming. For this reason fecal contamination has been modeled only on the carcass surface. 4. Briefly (less than 500 words), discuss the practicalities and likely success of implementing each of the proposed hypothetical mitigation strategies in the paper. The author has proposed three hypothetical risk mitigation strategies for risk reduction. However, the strategies have been proposed to reduce risk as per mentioned figures, assuming that the strategy is being implemented and the desired goal is being achieved. For instance, the first strategy of regulating storage temperature control norms shows a reduced risk to over 80%. Practically, this strategy can indeed cause a large risk reduction but a protocol will need to be developed that incorporates all the levels of the proposed beef-cold-chain, starting right from the farm to the retailer. Even with a concrete legislature to make sure this strategy works, it needs to be evaluated how far would this strategy prove to be practically enforceable. With definite legislature, a good compliance can be expected out of this strategy and apparently this strategy is far more practicable, and could prove successful. Pre-slaughter screening proposes to reduce risk by over 46%. However, more variables like feeding practices, geographical locations, and seasonal variation (that affect E. Coli fecal load) need to considered, before a definite â€Å"control† level can be instated to rule out slaughters for animals that have more than a certain level of bacterial fecal concentration. The consumer information program, although with a risk reduction of 16%, is certainly a very important level wherein proper intervention can dramatically decrease E. Coli related health morbidity. Even though anticipated risk reduction is only 16%, simple measures like adequate promotional tools, could significantly increase risk reduction through mass communication; the biggest limitation however, is that compliance in this case cannot be ascertained, nor enforceable. Keeping in mind the practical limitations of each of these strategies, a prudent approach would involve application of all the three strategies in conjunct, to ensure greater risk reduction. A good reason for this approach is that due to the uncertain nature of all the factors involved in E. Coli contamination and delivery to consuming host, it appears quite difficult to determine the individual potency of each of these factors, and they would easily remain relative values. ‘Evaluation of MRSA Select, a new chromogenic medium for the detection of nasal carriage of methicillin-resistant Staphylococcus aureus’ 1. What is the ‘gold standard’ used to assess the sensitivity and specificity etc. of the different diagnostic tests? The sensitivity and specificity of a particular diagnostic test needs to be estimated before the test under consideration can be employed for practical purposes, to ensure that the results obtained are accurate, and of consequence. A â€Å"gold standard†, hence, is an absolute, against which results from a particular diagnostic test are compared. The gold standard, also called as the standard frame of reference, is a perfect test for the given condition, and is 100% sensitive and specific as well. 2. Is the ‘gold standard’ the same for all of the tests? Within the context of this paper, the gold standard used is same for all the tests. The gold standard used is identification of methicillin resistant S. Aureus, from nasal swabs of patients, confirmed for the mecA gene using PCR. 3. Can the tests be compared in this way? Yes, the tests can be compared this way. The same samples (n) were subjected to different growth mediums, to ascertain the presence of MRSA. All these media were specifically designed to promote the growth of MRSA. Hence, depending on the growths shown by these different media, results can be drawn and compared. 4. Are the authors’ conclusions valid? I think that the author’s conclusions are valid. Although, PCR will remain the gold standard in ascertaining presence of MRSA, the application of this procedure, to remain practically enforceable, is quite limiting. For instance, considering the sheer number of samples that an urban community hospital has to handle on a daily basis, using PCR for all instances may not be feasible all the times. In this circumstance, using simple tissue culture techniques would definitely prove to be more desirable, especially with faster results and low costs; like using the MRSA Select that will give results within 24 hours with a sensitivity and specificity over 99%. Moreover, simplicity of the test requires no complex skill set, especially compared with handling PCR techniques. References 1. Fishman, G. S. (1995). Monte Carlo: Concepts, Algorithms, and Applications. New York: Springer 2. Bell, B. P. , Goldoft, M. , Griffin, P. M. , Davis, M. S. , Gordon, D. C. , Tarr, P. I. , Bartleson, C. A. , Lewis, J. H. , Barret, T. J. , Wells, J. G. , Baron, R. , Kobayashi, J. , (1994). A multistate outbreak of Escherichia coli O157:H7-associated bloody diarrhea and hemolytic uremic syndrome from hamburgers: the Washington experience. J. Am. Med. Assoc. 3. Vose, D. , (1996). Quantitative risk analysis: A guide to Monte Carlo simulation modelling. John Wiley and Sons, Chichester England. 4. USDA:APHIS:VS. , 1994a. E. coliO157:H7 issues and ramifications. Centers for Epidemiology and Animal Health, U. S. Department of Agriculture, Fort Collins, CO. 5. Gehlbach SH. (1993) Interpretation: sensitivity, specificity, and predictive value. In: Gehlbach SH, ed. Interpreting the medical literature. New York: McGraw-Hill 6. Apfalter P, Assadian O, Kalczyk A, et al. (2002) Performance of a new chromogenic oxacillin resistance screen medium (Oxoid) in the detection and presumptive identification of methicillin-resistant Staphylococcus aureus. Diagn Microbiol Infect Dis;44:209–11. 7. Murakami K, Minamide W, Wada K, Nakamura E, Teraoka, H, Watanabe S. (1991) Identification of methicillin-resistant strains of staphylococci by polymerase chain reaction. J Clin Microbiol;29:2240–4. 8. Safdar N, Narans L, Gordon B, Maki DG. (2003) Comparison of culture screening methods for detection of nasal carriage of methicillin resistant Staphylococcus aureus: a prospective study comparing 32 methods. J Clin Microbiol;41:3163–6.

Investigation of Magnetic Fields by Search Coil

Physics Lab Report – C15 Title: Investigation of magnetic fields by search coil Objective: To use a search coil and a CRO to investigate the magnetic fields generated by alternating currents through a straight wire and a slinky solenoid. Apparatus: Search coil 1 |Slinky solenoid 1 | |CRO 1 |Slotted bases 2 | |Signal generator 1 |Metre rule 1 | |a. c. mmeter 1 |Crocodile clips 2 | |PVC-covered copper wire 26 s. w. g. 1 m long |Connecting leads. 2 | Theory: When there is a change of the magnetic flux ? linked with a wire loop, it induces an electromotive force (emf) ? between the loop ends, but a constant magnetic flux or a non-linked flux does not. This is the basic fact of electromagnetic induction, expressed by Faraday’s law for a wire loop, ? -d? /dt The induced emf, ? is equal to the negative rate of change of the magnetic flux ? linked with the loop. If we replace the wire loop by a short coil of N turns, the induced voltage is N times that of a single loop, so Far aday’s law becomes ? = -Nd? /dt When loop ends are connected, ? produces a current which yields its own magnetic field. Its direction always opposes the flux change d? /dt. This fact is known as Lenz’s law and is expressed by the negative sign. For a circular loop of radius r and area A = ? r2 in a constant magnetic field B (Fig. 36. ), the magnetic flux linkage ? is ? = B? A = BA cos? B? denotes the field component normal to the loop. The flux linkage is zero when loop and field are parallel. It is highest when the loop is perpendicular to the field, i. e. cos? =1, thus, ? = -NA dB/dt. The search coil is always used to measure the magnetic fields. It consists of N turns of the coil enclosing an area A. When exposed to a changing magnetic field B, an e. m. f. is induced across the ends of the coil. The induced e. m. f. (? ) is directly proportional to the rate of magnetic field, i. e. ? = -NA dB/dt . When the search coil is connected to a CRO, the corresponding induced e. m. f. and hence magnetic field magnitude can be determined. Precautions for magnetic field around straight wire 1. The wire should be long 2. The distance(r) should much smaller than the length of the wire. Procedure A. Magnetic field around straight wire 1. The circuit as shown in Fig. C15. 1 and a lateral type search coil to a CRO was connected. 2. The signal generator was turned on and was set to 0. 5A and 5kHz. 3. The centre of the search coil was placed 1 cm away from the straight wire. The search coil was at the same level and perpendicular to the straight wire. The CRO setting was adjusted to display a whole trace on its screen. 4. The time base of the CRO was switched off. The length of the vertical trace shown on the CRO was recorded, which represents the induced peak-to-peak e. m. f. (V) in the search coil and also the magnetic field around the straight wire. 5. The steps 2 to 4 were repeated with the other values of current (I) from the signal generator in steps of 0. 1A. Then, the results were tabulated. 6. A graph of the induced e. m. f. (V) against the current(I) as plotted. 7. The steps 2 to 4 were repeated with the others values of distances (r) of the search coil away from the straight wire. The results were tabulated. 8. A graph of the induced e. m. f. (V) against the reciprocal of distance([pic]) is plotted. 9. The frequency of the signal generator was varied to change the sensitivity of the search coil. B. Magnetic field around slinky solenoid 10. The circuit as shown in Fig. C15. 2 and a lateral type search coil to a CRO was connected. The stretched length of the solenoid is 1 m. 11. The signal generator was turned on and was set to 0. 5A and 5kHz. 12. The search coil was placed at the centre of the solenoid. Make sure that the search coil was perpendicular to the solenoid. The variation of induced e. m. f. was shown on the CRO. 13. Step 12 was repeated with placing the search coil at the end of the solenoid, across its cross-section and along its length. 14. The search coil was placed at the centre of the solenoid again. The time base of the CRO was switched off. The length of the vertical trace shown on the CRO was recorded, which represents the induced peak-to-peak e. m. f. (V) in the search coil and also the magnetic field around the solenoid. 15. Step 14 was repeated with the other values of currents (I) from the signal generator in steps of 0. 1A. The results were tabulated. 16. A graph of the induced e. m. f. (V) against the current (I) was plotted. 17. Step 14 was repeated with the other stretched lengths (l) of the solenoid. The space between coils must be even. The results were tabulated. 18. A graph of the induced e. m. f. (V) against the reciprocal of the stretched length of the solenoid(1/l ) was plotted. Results A. Magnetic field around straight wire |Current I/A |0 |0. 1 |0. 2 |0. |0. 4 |0. 5 | |Induced e. m. f. (V)/mV |0 |0. 5 |1 |1. 6 |2. 4 |4. 1 | [pic] |Distance (r) / cm |1 |2 |3 |4 |5 | |1/r /cm |1. 00 |0. 50 |0. 33 |0. 25 |0. 20 | |Induced e. m. f. (V)/ mV |4. 2 |3. 2 |2. 6 |2. 3 |2 | [pic] The sensitivity of the search coil can be increased by increasing the frequency. B. Magnetic field around slinky solenoid When placing the search coil at the centre of the solenoid, across its cross-section, the induced e. m. f. shown on the CRO, i. e. the length of the vertical trace is the maximum, that means the magnetic field of the straight wire is the maximum. When placing the search coil at the end of the solenoid, across its cross-section, the induced e. m. f. shown on the CRO, i. e. the length of the vertical trace is nearly half that at the centre of the solenoid, that means the magnetic field of the straight wire is nearly half that at the centre of the solenoid. When placing the search coil along the length of the solenoid, the induced e. m. f. shown on the CRO is quite uniform except near its two ends. |Current I/A |0. 01 |0. 02 |0. 03 |0. 04 |0. 05 |0. 06 | |Induced e. m. f. (V)/mV |1. 4 |2. 8 |3. 4 |4. 2 |6 |6. 6 | [pic]p Stretched length (l ) / m |1 |0. 9 |0. 8 |0. 7 |0. 6 |0. 5 |0. 4 |0. 3 | |1/l /m |1. 00 |1. 11 |1. 25 |1. 43 |1. 7 |2. 00 |2. 50 |3. 33 | |Induced e. m. f. (V)/ mV |1. 6 |1. 8 |2 |2. 2 |2. 4 |2. 8 |3 |3. 2 | |[pic] Discussion 1. From the V-I graph in step 6 (Graph A. 1), the current flowing in the straight wire is directly proportional to the induced e. m. f. (V). As the induced e. m. f. ? = -NA dB/dt, the current flowing in the straight wire increases with the magnetic field produced by the current-carrying straight wire. From the V- graph in step 8 (Graph A. 2), the distance from the straight wire is inversely proportional to the induced e. m. f. (V). As the induced e. m. . ? = -NA dB/dt, the distance from the straight wire decreases with the magnetic field produced by the current-carrying straight wire. Thus, the result agree with the equation [pic], where ? 0 is the permeability of free space. 2. From the V-I graph in step 16 (Graph B. 1), the current flowing in the slinky solenoid is directly proportional to the induced e. m. f. (V). As the induced e. m. f. ? = -NA dB/dt, the current flowing in the slinky solenoid increases with the magnetic field produced by the current-carrying solenoid. From the V- graph in step 18 (Graph B. ), its stretched length is inversely proportional to the induced e. m. f. (V). As the induced e. m. f. ? = -NA dB/dt, its stretched length decreases with the magnetic field produced by the current-carrying solenoid. Thus, the result agree with the equation [pic], where ? 0 is the permeability of free space and is the number of turns of the solenoid. 3. It is necessary to place the search coil at the same level and perpendicular to the straight wire. Otherwise, the magne tic field cannot cut the search coil completely and ideally. Then, the induced e. m. f. is not the maximum and even there is no induced e. . f. shown on the CRO. As a rollecteesult, the data cd is not accurate. 4. There are several sources of error. First, there is reading error, zero error of ammeter. Secondly, the space between coils is not even. Thirdly, the magnetic field around the straight wire and the slinky solenoid is easily disturbed by other apparatus nearby. Finally, the search coil is not at right angles to the straight wire and the solenoid, this make the data collected becomes inaccurate. To avoid disturbance, the set-up should be significantly distant from the return leads and other apparatus. The space between coils is nearly even. The search coil is nearly at right angles to the straight wire and the solenoid Therefore, the experiment can be improved. 5. Reason for the sensitivity of the search coil can be increased by increasing the frequency. First of all, the search coil detects a varying B-field through the current induced in it which is: From the deduction, we can see that with A and B0 held constant, which are the area of search coil and the peak value of the varying B-field respectively, the rate of change of magnetic flux ? ncreases with increasing ? which is the angular frequency with value 2? f, where f is the frequency of the B-field. 6. The Earth’s field can be ignored because it is a steady magnetic field. Conclusion The magnetic field around a long straight wire carrying a current is directly proportional to the current (I) and inversely proportional to the distance(r) from the wire. The magnetic field inside the solenoid carrying a current is direct ly proportional to the current (I) and the number of turns (N) but inversely proportional to the length (l ) of the solenoid.