Population Growth Density Dependent Factors Abstract...

Population Growth: Density dependent factors Abstract Sets of experiments were used to assess the growth rate of the Lemna minor, a duckweed population. The growth of Lemna minor was observed and followed by counting and recording the number of thalli on a weekly basis. These experiments were constructed lab models which varied the size of the starting thalli population, and varied the nutrient concentration the thali were placed in. In the first experimental model two plastic cups were prepared with pond water, then two healthy lemna minor plants were placed in the first cup while fifteen healthy lemna minor plants were placed in the second cup. The second experimental model consisted of four nutrient concentrations, a control model of no nutrients, a low nutrient model, a medium nutrient model and a high nutrient model. At high density populations, we observed a nonlinear decreasing growth rate with increasing lemna minor density. At very low densities, as expected, we observed an inverse density dependence. Duckweed reproduces by budding, causing a larger density to reproduce a greater amount of biomass. This would indicate that Duckweed likes overcrowding, and this may be a possible clue to the limiting factor in the growth of Duckweed. Introduction Lemna minor, commonly known as duckweed, is efficient and fast growing, making it an ideal experimental organism. It is known as a small aquatic monocotyledon which can be found floating in ponds, lakes or streams (Harper,Show MoreRelatedThe Effects of Population Density on the Reproduction and Survival of Daphnia Magna2308 Words   |  10 PagesAbstract The population dynamics of Daphnia magna are observed under three different conditions; low, medium, and high density. The effects of different population densities on the survivorship and reproduction of Daphnia are observed over a two-week period within a lab environment. Over the two week period, the numbers of parent Daphnia alive and dead are recorded daily, along with the amount of offspring produced each day. From the main parameter investigated, the net reproductive rate, theRead MoreInstitutions as a Fundamental Cause of Long-Run14323 Words   |  58 PagesAS A FUNDAMENTAL CAUSE OF LONG-RUN GROWTH DARON ACEMOGLU 1 , Department of Economics, MIT, 50 Memorial Drive E52-3806, Cambridge, MA 02142 e-mail: damn@mit.edu SIMON JOHNSON Sloan School o f h f a ~ g e m e n t , MIT, 50 Memorial Drive, Cambridge, MA 02142 e-mail: sjohnson@mit.edu JAMES A. ROBINSON Deparhnent of Government, WCFIA, Harvard University, 1033 Massachusetts Avenue, Cambridge, MA 02138 e-mail: jmbinson@gov.harvard.edu Contents Abstract Keywords 1. Introduction 1.1. TheRead MoreGlobal Climate Change : A Threat Of Aphid Populations Essay8320 Words   |  34 PagesClimate Change: A Threat to Aphid Populations Abstract Global climate change is a matter of grave concern in the present scenario casting its significant and lasting effect on the flora and fauna dwelling over earth. A number of factors such as biotic processes, variations in solar radiation received by earth, plate tectonics, volcanic eruptions certain human activities can be considered as key components responsible for this devastating phenomenon. Aphid populations are also under potential threatRead MoreNihms4511 Words   |  19 PagesNational Institutes of Health, Bethesda, Maryland, 20892–4442, USA. Abstract $watermark-text The skin is the human body’s largest organ, colonized by a diverse milieu of microorganisms, most of which are harmless or even beneficial to their host. Colonization is driven by the ecology of the skin surface, which is highly variable depending on topographical location, endogenous host factors and exogenous environmental factors. The cutaneous innate and adaptive immune responses can modulateRead MoreInstitution as the Fundamental Cause of Long Tern Growth39832 Words   |  160 PagesNBER WORKING PAPER SERIES INSTITUTIONS AS THE FUNDAMENTAL CAUSE OF LONG-RUN GROWTH Daron Acemoglu Simon Johnson James Robinson Working Paper 10481 http://www.nber.org/papers/w10481 NATIONAL BUREAU OF ECONOMIC RESEARCH 1050 Massachusetts Avenue Cambridge, MA 02138 May 2004 Prepared for the Handbook of Economic Growth edited by Philippe Aghion and Steve Durlauf. We thank the editors for their patience and Leopoldo Fergusson, Pablo Querubà ­n and Barry Weingast for their helpful suggestions. TheRead MoreSurvival Strategy for Startup Business10775 Words   |  44 Pagesappreciate the comments of the journal associate editor and reviewers, as well as the financial support of the Ewing Marion Kauffman Foundation. All remaining errors are ours. Product Strategies and Firm Survival in Technologically Dynamic Industries ABSTRACT Studying the US personal computer industry from its inception in 1974 through 1994, we address the following questions. What product strategies increase the survival chances of entrants into new, technologically dynamic industries? Does the effectivenessRead MoreMonte Carlo Simulation218872 Words   |  876 Pages19 21 25 32 36 39 39 39 43 44 47 49 53 54 58 63 63 65 71 79 79 79 90 93 2 3 x Contents 3.3 3.4 3.5 3.6 3.7 3.2.1 Basic Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 3.2.2 Path-Dependent Options . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 3.2.3 Multiple Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 Gaussian Short Rate Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108Read MoreImpact of Globalization and Bangladesh18126 Words   |  73 PagesMONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S) 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION / AVAILABILITY STATEMENT Approved for public release; distribution is unlimited. 13. SUPPLEMENTARY NOTES 14. ABSTRACT Over the past decades, globalization has now become a new world order, which virtually influences everything that comes in our mind. Developing countries like Bangladesh with vulnerable geopolitical locations and weak economies are now lookingRead More4g Communication22481 Words   |  90 Pages4G WIRELESS COMMUNICATIONS Anto vinoth.M, Punith Maharishi.Y.R antovinoth.m@gmail.com maharishipunith@yahoo.com Abstract— Mobile communication is continuously one of the hottest areas that are developing at a booming speed, with advanced techniques emerging in all the fields of mobile and wireless communications. With this rapid development it is expected that fourth generation mobile systems will be launched within decades. 4G mobile systems focus on seamlessly integrating the existingRead MoreRetailing Characteristics of Fast Food Stores and Their Impact on Customer Sales and Satisfaction29639 Words   |  119 Pages Research Framework and Methodology 3.1 Research purpose†¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦ 3.2 Hypothesis†¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦.. 3.3 Data Collection†¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦ 3.4 Methodology†¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦ 3.5 Factor Analysis†¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦ ï  ¶ Chap-4 Result and Interpretation 4.1 Interpretation of Result†¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦..†¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦.. ï  ¶ Chap-5 Suggestions and Managerial Implications ï  ¶ Chap-6 Limitations of the study References†¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦..

Critical Analysis Critical Thinking In The Family Man

Critical thinking is the use of your intelligence, knowledge, and skills to a question, carefully exploring situations to arrive at thoughtful conclusions based on evidence and reason. Critical thinking is used in the movie The Family Man Jack Campbell is a man who works on wall street. Jack Campbell is the top in his company, very professional, and has everything he could possibly want. Jack has thrown himself into work, and is a workaholic, he wonders what his life would be like if he had married his old sweetheart Kate. Jack gets a chance to go back, and see what his life would have been like if he had not accepted broker internship some thirteen years before. Jack falls asleep and awakes to Kate his wife, two kids, and no wall street†¦show more content†¦Workplace conflict should be addressed as quickly as possible to ensure a positive outcome for your organization. There are a lot of ways to deal with conflict in the workplace. Conflict happens in every workplace whether big or small it happens, because you are dealing with a lot of different emotions. By ignoring the conflict this can cause the situation to be more stressful and tension can arise. Leaders can improve the communication levels to build the performance level of their team. Strategies for reducing conflict: Attempt to avoid a conflict is only a fairy tale there will always be conflict within the workplace. By avoiding conflict this strategy can do away with conflict all together and be more profitable for employees. Accommodation can be one way to adjust or lower any differences, and help keep the peace among employees. Friendly competition is another way to get employees involved to help boost the company morale. Compromise is always needed to help each party come up with a positive outcome. Compromise is where both parties give up something to come to an agreement. Competing with the competition is sometimes used as a conflict management strategy. Fifth and final strategy are collaboration a collective effort in which all parties agree on a solution that benefits the entire company. Putting ideas in place could provide positive solutions, and outcomes for your company. Setting conflict guidelines can be very beneficial to yourShow MoreRelatedphi 103 week 1 reading quiz Essay1393 Words   |  6 Pagescriticalthinking.org/pages/critical-thinking-teaching-students-how-to-study-and-learn-part-one/513    Points Received: 1 of 1    Comments: Question  2. Question : Paul and Elder claim that all reasoning:    Student Answer: Seeks to defeat others in arguments    Has assumptions underneath it    Is expressed through ideas and concepts    a and b    b and c    Instructor Explanation: The answer can be found in â€Å"The Analysis and Assessment of Thinking† [Paul and ElderRead MoreInterpretation Of Inferences And Assumptions1512 Words   |  7 PagesINTERPRETATION OF INFERENCES AND ASSUMPTIONS 1 Interpretation of Inferences and Assumptions Diana L. Brown HUM101 – Critical Reasoning Colorado State University: Global Campus Robert Freeborough September 14, 2014 Running head: INTERPRETATION OF INFERENCES AND ASSUMPTIONS 2 Critical thinking is a part of everyday life and does not necessarily mean making a decision in a high pressure or high stakes environment. It can be as simpleRead MoreTransformative Learning : Transformational Learning1585 Words   |  7 Pages Joseph Cardello May 13, 2015 Learning paper Draft Dr. Franklin Tuner Kean University Transformative learning overview Thinking is something we all do on a regular basis. The process of using our minds to create ideas make all of our decisions or to remember our earlier experiences. Our minds are complicated structures that we have yet to understand. One man has a theory of learning as an adult and his name is Jack Mezirow. Mezirow was concerned in adulthood learning and began to interpretRead MoreAnalysis of Sonnys Blues by James Baldwin Essay804 Words   |  4 Pagesnarrator seems to have assimilated into the larger society/culture; he was a school teacher doing generally well in what we call life. Sonny on the other hand turned to drugs (heroin) to escape from the pain and suffering he endured growing up a black man in the 1950’s. â€Å"Sonny’s Blues† also tells the reader about how art and music was a huge part of Black people’s lives in Harlem. Many looked towards music for an escape; Sonny turned towards Jazz to release his pain and anguish. This story does haveRe ad MoreAssignment : Conflict Resolution Interview1264 Words   |  6 Pagessystem; the Department of Family Children, a medical team, clients, and the healthcare business provider. What happened? The healthcare provider was assigned to care for critical disable twenty two year old male. The parents were separated because the mother of the twenty two year threat to kill the father with a daggers. So the courts removed the mother from the home and the father has cared for the son alone for ten years. The court system, the Department of Family Children and a medical teamRead MoreThe Life You Save May Be Your Own1506 Words   |  7 PagesThe Life You Save May Be Your Own. In this story we see that Tom Shiftlet, a man from the story, is very displeased with the state of the world. In one scene of the story, mother Lucynell Crater tells Mr. Shiftlet that her car no longer runs, and Mr. Shiftlet s reply to her is, Nothing is like it used to be, lady... The world is almost rotten. (Flannery O Connor, The Life You Save May Be Your Own) So we can Critical Essay Rojas 2 clearly see here that Mr. Shiftlet is discontent and that he wishesRead MoreDeep Rooted Work On A Hard Man1427 Words   |  6 PagesResearch Paper: Deep Rooted Work on a Hard Man Flannery O’Connor was born March 25, 1925, in Savanah, Georgia. She went to what is, now Iowa University and majored in literature. She’s primarily known for her short stories but was a novelist. Flannery O’Connor passed away in 1964 after losing a battle with lupus. The piece of writing that I will be discussing is titled: â€Å"A Good Man is Hard to Find,† she wrote this work in 1953 along with several other short stories (Biography.com Editors)Read MoreRestraints Review Of Qualitative And Quantitative Studies1517 Words   |  7 Pagesthe research article, Mohler Meyer’s â€Å"Attitude of nurses towards the use of restraints in geriatric care: A systemic review of qualitative and quantitative study 2014. The incident I am going to discuss in this paper is of Mr. P., an 85-year-old man, admitted to this facility about 4 months ago. His history includes coronary heart disease, cataract, dementia, hypertension, macular degeneration and Al zheimer’s. Mr P. scored 28 of 30 on the Folstein Mini-Mental State Test, he missed the date andRead MoreHegemonic Masculinity in the Media1080 Words   |  5 Pageswhich emphasizes the connecting of masculinity to toughness and competitiveness as well as the subordination of women and the marginalization of gay men† (Trujillo, 1991, p. 290). We live society were male dominance is the order of the day, from the family arena to the workplace, and in sports in which individuals with certain characteristics and attributes as seen as normal and the rest are termed as the â€Å"other†. 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Hamlet Soliloquy Analysis free essay sample

The young prince of Denmark, Hamlet has recently lost his father. Right after this depressing event, his uncle, Claudius, takes over the entire property of his past away father: his crown and his wife (Gertrude) who is Hamlets mother. This chain of heartbreaking misfortunes leaves deep wounds on the soul of young Hamlet and his soliloquies, allowing the audience to enter his agitated mind, revealing these spiritual scars. This soliloquy is the closing part of the second act and points out the inner feelings of the prince Hamlet being affected by the tremendous acting of the player which was full of meaning to him. This soliloquy can be divided into two parts: the first part deals with Hamlet being amazed by the passion of the player toward Hecuba The queen of Troy, imagining how he would behave if he were in his situation. The second part of soliloquy deals with Hamlets self censure and his anger headed for his uncle. The tone of this soliloquy is of self criticism and can be sensed from the very first line where Hamlet expresses himself as rouge and peasant salve. Through using different techniques, Shakespeare seeks to maintain this tone from first to last of this soliloquy: One of the tools he uses to achieve this goal is by the means of exclamations made by Hamlet. For instance some of these exclamations are: all for nothing! For Hecuba! , O, vengeance! and What an ass I am! The further skill Shakespeare utilizes in order to accomplish this tone of rebuke is by the means of the rhetorical questions that Hamlet asks himself. Such as: Whats Hecuba to him or, he to Hecuba? , What would he do, had he the motive and the cue of passion that I have? and the series of questions he asks himself in the third paragraph. The last literary device used by Shakespeare to preserve this tone of self-criticisms is through using proper diction or the set of words that reveals this mood. Shakespeare uses a variety of diction on behalf of Hamlet, like dull, muddy-mettled rascal and John-a-dreams in order to tell that he is self criticizing himself . Besides for highlighting the priority of some of Hamlets words, Shakespeare employs a series of sound devices, including: Alliterations and consonances. In this soliloquy there are two alliterations applied by Shakespeare in the words of Hamlet- muddy-mettled and damnd defeat-. The first alliterations muddy-mettled emphasizes the level of Hamlets fault for not putting his thoughts into action (having delay in taking his fathers revenge) and the second one damns defeat points out the tragedy of his fathers murder. There are also some consonants used by Shakespeare while Hamlet is insulting his uncle by means of the adjectives: Remorseless, treacherous, lecherous, kindles villain. The reason that Shakespeare uses consonants for these adjectives is to build up their effect on the audience and to present a clear appearance of the king Claudius in the mind of Hamlet. The word monstrous used by Hamlet to describe the overflowed emotions of the player for Hecuba signifies that Hamlet has been stunned by it. Shakespeare also uses the world pride while Hamlet describes the emotions of player to Hecuba in favor of revealing the high imaginative power of the player. In the second paragraph Shakespeare uses a set of hyperboles while Hamlet is imagining how the player would react if he had the melancholy and the duty of taking revenge as he has. He would drown the stage with tears and cleave the general ear, with horrid speech, make mad the guilty and appall the free, confound the ignorant, and amaze indeed the very faculties of eyes and ears. Hamlet uses such shocking Hyperboles for the reason of motivating himself to perform the duty assigned for him by the ghost of his father. Introducing Hecuba as the main emphasis of the opening part of Hamlets soliloquy, Shakespeare seeks to demonstrate that Hamlet wished her mother to act similar to Hecuba after the death of his father by not marrying his uncle and keeping this sorrow forever in her heart. In this soliloquy Shakespeare also takes the advantage of figures of speech to exaggerate Hamlets self criticism. The first metaphor deals with Hamlet comparing his dilemma and melancholy to a pregnancy. This is revealed when he mentions unpregnant of my cause This statement by Hamlet can also be considered as foreshadowing in view of the fact that pregnancy is a period full of difficulty, however when its over, it brings joy and happiness. The other metaphor used by Hamlet is when he calls himself pigeon livered for not being brave enough to take revenge. The final metaphor deals with Hamlet introducing himself as an ass; when he says: What an ass I am! this metaphor, in my opinion, is the climax of self criticism in this soliloquy. There are, also two similes used in the closing part when Hamlet compares the way he conduct himself toward his situation to a whore and a scullion. Once finishing criticizing himself, Hamlet starts passing the judgment on his thoughts as he knows them as the root cause of his delay in taking revenge. This part of soliloquy, in my judgment, is a turning point in Hamlets character since it is at this stage that his personality alters from a head to a heart character. This fact can be clearly sensed as it is right after this soliloquy that he starts taking the first serious steps of revenging his uncle, Cladius.

The Effects Of HIV Mutations On The Immune System Science C.J. Stimson Essay Example For Students

The Effects Of HIV Mutations On The Immune System Science C.J. Stimson Essay INTRODUCTIONThe topic of this paper is the human immunodeficiency virus, HIV, and whether or not mutations undergone by the virus allow it to survive in the immune system. The cost of treating all persons with AIDS in 1993 in the United States was $7.8 billion, and it is estimated that 20,000 new cases of AIDS are reported every 3 months to the CDC. This question dealing with how HIV survives in the immune system is of critical importance, not only in the search for a cure for the virus and its inevitable syndrome, AIDS (Acquired Immunodeficiency Syndrome), but also so that over 500,000 Americans already infected with the virus could be saved. This is possible because if we know that HIV survives through mutations then we might be able to come up with a type of drug to retard these mutations allowing the immune system time to expunge it before the onset of AIDS. BACKGROUNDIn order to be able to fully comprehend and analyze this question we must first ascertain what HIV is, how the body attempts to counter the effects of viruses in general, and how HIV infects the body. DefinitionHIV is the virus that causes AIDS. We will write a custom essay on The Effects Of HIV Mutations On The Immune System Science C.J. Stimson specifically for you for only $16.38 $13.9/page Order now HIV is classified as a RNA Retrovirus. A retrovirus uses RNA templates to produce DNA. For example, within the core of HIV is a double molecule of ribonucleic acid, RNA. When the virus invades a cell, this genetic material is replicated in the form of DNA . But, in order to do so, HIV must first be able to produce a particular enzyme that can construct a DNA molecule using an RNA template. This enzyme, called RNA-directed DNA polymerase, is also referred to as reverse transcriptase because it reverses the normal cellular process of transcription. The DNA molecules produced by reverse transcription are then inserted into the genetic material of the host cell, where they are co-replicated with the hosts chromosomes; they are thereby distributed to all daughter cells during subsequent cell divisions. Then in one or more of these daughter cells, the virus produces RNA copies of its genetic material. These new HIV clones become covered with protein coats and leave the cell to find other host cells where they can repeat the life cycle. The Body Fights BackAs viruses begin to invade the body, a few are consumed by macrophages, which seize their antigens and display them on their own surfaces. Among millions of helper T cells circulating in the bloodstream, a select few are programmed to ?read? that antigen. Binding the macrophage, the T cell becomes activated. Once activated, helper T cells begin to multiply. They then stimulate the multiplication of those few killer T cells and B cells that are sensitive to the invading viruses. As the number of B cells increases, helper T cells signal them to start producing antibodies. Meanwhile, some of the viruses have entered cells of the body the only place they are able to replicate. Killer T cells will sacrifice these cells by chemically puncturing their membranes, letting the contents spill out, thus disrupting the viral replication cycle. Antibodies then neutralize the viruses by binding directly to their surfaces, preventing them from attacking other cells. Additionally, they precipitate chemical reactions that actually destroy the infected cells. As the infection is contained, suppresser T cells halt the entire range of immune responses, preventing them from spiraling out of control. Memory T and B cells are left in the blood and lymphatic system, ready to move quickly should the same virus once again invade the body. HIVs Life CycleIn the initial stage of HIV infection, the virus colonizes helper T cells, specifically CD4+ cells, and macrophages, while replicating itself relatively unnoticed. As the amount of the virus soars, the number of helper cells falls; macrophages die as well. The infected T cells perish as thousands of new viral particles erupt from the cell membrane. Soon, though, cytotoxic T and B lymphocytes kill many virus-infected cells and viral particles. These effects limit viral growth and allow the body an opportunity to temporarily restore its supply of helper cells to almost normal concentrations. It is at this time the virus enters its second stage.Throughout this second phase the immune system functions well, and the net concentration of measurable virus remains relatively low. .uaa17ec01275f8cf402c7fd6b77b00f40 , .uaa17ec01275f8cf402c7fd6b77b00f40 .postImageUrl , .uaa17ec01275f8cf402c7fd6b77b00f40 .centered-text-area { min-height: 80px; position: relative; } .uaa17ec01275f8cf402c7fd6b77b00f40 , .uaa17ec01275f8cf402c7fd6b77b00f40:hover , .uaa17ec01275f8cf402c7fd6b77b00f40:visited , .uaa17ec01275f8cf402c7fd6b77b00f40:active { border:0!important; } .uaa17ec01275f8cf402c7fd6b77b00f40 .clearfix:after { content: ""; display: table; clear: both; } .uaa17ec01275f8cf402c7fd6b77b00f40 { display: block; transition: background-color 250ms; webkit-transition: background-color 250ms; width: 100%; opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; background-color: #95A5A6; } .uaa17ec01275f8cf402c7fd6b77b00f40:active , .uaa17ec01275f8cf402c7fd6b77b00f40:hover { opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; background-color: #2C3E50; } .uaa17ec01275f8cf402c7fd6b77b00f40 .centered-text-area { width: 100%; position: relative ; } .uaa17ec01275f8cf402c7fd6b77b00f40 .ctaText { border-bottom: 0 solid #fff; color: #2980B9; font-size: 16px; font-weight: bold; margin: 0; padding: 0; text-decoration: underline; } .uaa17ec01275f8cf402c7fd6b77b00f40 .postTitle { color: #FFFFFF; font-size: 16px; font-weight: 600; margin: 0; padding: 0; width: 100%; } .uaa17ec01275f8cf402c7fd6b77b00f40 .ctaButton { background-color: #7F8C8D!important; color: #2980B9; border: none; border-radius: 3px; box-shadow: none; font-size: 14px; font-weight: bold; line-height: 26px; moz-border-radius: 3px; text-align: center; text-decoration: none; text-shadow: none; width: 80px; min-height: 80px; background: url(https://artscolumbia.org/wp-content/plugins/intelly-related-posts/assets/images/simple-arrow.png)no-repeat; position: absolute; right: 0; top: 0; } .uaa17ec01275f8cf402c7fd6b77b00f40:hover .ctaButton { background-color: #34495E!important; } .uaa17ec01275f8cf402c7fd6b77b00f40 .centered-text { display: table; height: 80px; padding-left : 18px; top: 0; } .uaa17ec01275f8cf402c7fd6b77b00f40 .uaa17ec01275f8cf402c7fd6b77b00f40-content { display: table-cell; margin: 0; padding: 0; padding-right: 108px; position: relative; vertical-align: middle; width: 100%; } .uaa17ec01275f8cf402c7fd6b77b00f40:after { content: ""; display: block; clear: both; } READ: George Bush Essay Paper But after a period of time, the viral level rises gradually, in parallel with a decline in the helper population. These helper T and B lymphocytes are not lost because the bodys ability to produce new helper cells is impaired, but because the virus and cytotoxic cells are destroying them. This idea that HIV is not just evading the immune system but attacking and disabling it is what distinguishes HIV from other retroviruses.THE THEORIESThe hypothesis in question is whether or not the mutations undergone by HIV allow it to survive in the immune system. This idea was conceived by Martin A. Nowak, an immunologist at the University of Oxford, and his coworkers when they considered how HIV is able to avoid being detected by the immune system after it has infected CD4+ cells. The basis for this hypothesis was excogitated from the evolutionary theory and Nowaks own theory on HIV survival. Evolutionary TheoryThe evolutionary theory states that chance mutation in the genetic material of an individual organism sometimes yields a trait that gives the organism a survival advantage. That is, the affected individual is better able than its peers to overcome obstacles to survival and is also better able to reproduce prolifically. As time goes by, offspring that share the same trait become most abundant in the population, outcompeting other members until another individual acquires a more adaptive trait or until environmental conditions change in a way that favors different characteristics. The pressures exerted by the environment, then, determine which traits are selected for spread in a population. Nowaks Theory on HIV SurvivalWhen Nowak considered HIVs life cycle it seemed evident that the microbe was particularly well suited to evolve away from any pressures it confronted (this idea being derived from the evolutionary theory). For example, its genetic makeup changes constantly; a high mutation rate increases the probability that some genetic change will give rise to an advantageous trait. This great genetic variability stems from a property of the viral enzyme reverse transcriptase. As stated above, in a cell, HIV uses reverse transcriptase to copy its RNA genome into double-strand DNA. The virus mutates rapidly during this process because reverse transcriptase is rather error prone. It has been estimated that each time the enzyme copies RNA into DNA, the new DNA on average differs from that of the previous generation in one site. This pattern makes HIV one of the most variable viruses known.HIVs high replication rate further increases the odds that a mutation useful to the virus will arise. To fully appreciate the extent of HIV multiplication, look at the numbers published on it; a billion new viral particles are produced in an infected patient each day, and in the absence of immune activity, the viral population would on average double every two days. With the knowledge of HIVs great evolutionary potential in mind, Nowak and his colleagues conceived a scenario they thought could explain how the virus resists complete eradication and thus causes AIDS, usually after a long time span. Their proposal assumed that constant mutation in viral genes would lead to continuous production of viral variants able to evade the immune defenses operating at any given time. Those variants would emerge when genetic mutations led to changes in the structure of viral peptides recognized by the immune system. Frequently such changes exert no effect on immune activities, but sometimes they can cause a peptide to become invisible to the bodys defenses. The affected viral particles, bearing fewer recognizable peptides, would then become more difficult for the immune system to detect. The ModelUsing the theory that he had developed on the survival of HIV, along with the evolutionary theory, Nowak devised a model to simulate the dynamics and growth of the virus. The equations that formed the heart of the model reflected features that Nowak and his colleagues thought were important in the progression of HIV infection: the virus impairs immune function mainly by causing the death of CD4+ helper T cells, and higher levels of virus result in more T cell death. Also, the virus continuously produces escape mutants that avoid to some degree the current immunologic attack, and these mutants spread in the viral population. .ued1dd219f99f8d885e44bd354a99cb83 , .ued1dd219f99f8d885e44bd354a99cb83 .postImageUrl , .ued1dd219f99f8d885e44bd354a99cb83 .centered-text-area { min-height: 80px; position: relative; } .ued1dd219f99f8d885e44bd354a99cb83 , .ued1dd219f99f8d885e44bd354a99cb83:hover , .ued1dd219f99f8d885e44bd354a99cb83:visited , .ued1dd219f99f8d885e44bd354a99cb83:active { border:0!important; } .ued1dd219f99f8d885e44bd354a99cb83 .clearfix:after { content: ""; display: table; clear: both; } .ued1dd219f99f8d885e44bd354a99cb83 { display: block; transition: background-color 250ms; webkit-transition: background-color 250ms; width: 100%; opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; background-color: #95A5A6; } .ued1dd219f99f8d885e44bd354a99cb83:active , .ued1dd219f99f8d885e44bd354a99cb83:hover { opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; background-color: #2C3E50; } .ued1dd219f99f8d885e44bd354a99cb83 .centered-text-area { width: 100%; position: relative ; } .ued1dd219f99f8d885e44bd354a99cb83 .ctaText { border-bottom: 0 solid #fff; color: #2980B9; font-size: 16px; font-weight: bold; margin: 0; padding: 0; text-decoration: underline; } .ued1dd219f99f8d885e44bd354a99cb83 .postTitle { color: #FFFFFF; font-size: 16px; font-weight: 600; margin: 0; padding: 0; width: 100%; } .ued1dd219f99f8d885e44bd354a99cb83 .ctaButton { background-color: #7F8C8D!important; color: #2980B9; border: none; border-radius: 3px; box-shadow: none; font-size: 14px; font-weight: bold; line-height: 26px; moz-border-radius: 3px; text-align: center; text-decoration: none; text-shadow: none; width: 80px; min-height: 80px; background: url(https://artscolumbia.org/wp-content/plugins/intelly-related-posts/assets/images/simple-arrow.png)no-repeat; position: absolute; right: 0; top: 0; } .ued1dd219f99f8d885e44bd354a99cb83:hover .ctaButton { background-color: #34495E!important; } .ued1dd219f99f8d885e44bd354a99cb83 .centered-text { display: table; height: 80px; padding-left : 18px; top: 0; } .ued1dd219f99f8d885e44bd354a99cb83 .ued1dd219f99f8d885e44bd354a99cb83-content { display: table-cell; margin: 0; padding: 0; padding-right: 108px; position: relative; vertical-align: middle; width: 100%; } .ued1dd219f99f8d885e44bd354a99cb83:after { content: ""; display: block; clear: both; } READ: Kaiser William II - Cause of World War I Essay After awhile, the immune system finds the mutants efficiently, causing their population to shrink.The simulation managed to reproduce the typically long delay between infection by HIV and the eventual sharp rise in viral levels in the body. It also provided an explanation for why the cycle of escape and repression does not go on indefinitely but culminates in uncontrolled viral replication, the almost complete loss of the helper T cell population and the onset of AIDS.After the immune system becomes more active, survival becomes more complicated for HIV. It is no longer enough to replicate freely; the virus also has to be able to ward off immune attacks. Now is when Nowak predicts that selection pressure will produce increasing diversity in peptides recognized by immune forces. Once the defensive system has collapsed and is no longer an obstacle to viral survival, the pressure to diversify evaporates. In patients with AIDS, we would again anticipate selection for the fastest-growing variants and a decrease in viral diversity. Long-term studies involving a small number of patients have confirmed some of the modeling predictions. These investigations, conducted by several researchersincluding Andrew J. Leigh Brown of the University of Edinburgh, et al.tracked the evolution of the so-called V3 segment of a protein in the outer envelop of HIV for several years. V3 is a major target for antibodies and is highly variable. As the computer simulation predicted, viral samples obtained within a few weeks after patients become infected were alike in the V3 region. But during subsequent years, the region diversified, thus causing a rapid increase in the amount of V3 variants and a progressive decrease in the CD4+ cell count.The model presented by Nowak is extremely difficult to verify with clinical tests alone, largely because the diversified interactions between the virus and the immune system are impossible to monitor in detail. Consequently, Nowak turned to a computer simulation in which an initially homogeneous viral population evolved in response to immunologic pressure. He reasoned that if the mathematical model produced the known patterns of HIV progression, he could conclude the evolutionary scenario had some merit. To verify his model, he turned to the experiments done on the V3 protein segment in HIV. These experiments demonstrated that the peptides were mutating and that these mutations were leading to a decline in helper lymphocytes. CONCLUSIONBefore we begin to answer the question that this paper is investigating, an evaluation of our primary experiment source is necessary, this being a publication of Nowaks model. Upon evaluation of this source, a problem is exposed, this being that because there was no experiment performed to substantiate this model, we have no idea if the modeling predictions are true. Although there were previous non-directly related experiments ( i.e. , V3 experiment) that Nowak referred to to rationalize his model there was never an experiment done solely based on the model. Because the V3 findings were in accord with the findings of Nowaks model, we can assume that the model has some merit.This absence of an experiment is what leads to the boundaries that one encounters when experimenting with HIV mutations. These boundaries being that because HIV replicates and mutates non-linearly, it is impossible to chronicle all its viral dynamics scrupulously. The lack of experimental data based on Nowaks model along with the inadequacy of experiments dealing with HIV mutations leads to the conclusion that at present, there is no answer to this question. Although, other questions have been exposed, including: does the virus mutate at random or is it systematic? And how does the virus know where to mutate in order to continue surviving undetected?These are all questions that must first be answered before we even begin to try to determine if viral mutations are what allows HIV to survive in the immune system.