Wireless telecommunication + matlab program Assignment

Wireless telecommunication + matlab program - Assignment Example Then Angle modulation is discussed with its two types i.e. frequency modulation and phase Modulation. Advantages and disadvantages of each technique are discussed. Generation of modulated signals is also discussed briefly along with useful equations and figures. In the end an appendix is presented in which MATLAB program is presented for Amplitude Modulation with the snapshot of the resulting graphs of signals. A similar program for Frequency Modulation is presented with resulting graphs of signals. In today’s communication, wireless communication has become the main area for researchers and has become an industry and also the governments of different countries are interested in it as wireless sensors have an enormous range of both commercial and military applications. Commercial applications include monitoring of fire hazards, stress and strain in building, carbon dioxide movement and gases at a disaster side. Military application includes identification and tracking of enemies target, direction of chemical and biological attacks, support of unmanned robotic vehicles, and counter-terrorism. There are many factors of growing of this field. One of which is the tremendous increase in demand for tether less connectivity, driven so far mainly by cellular telephony but is expected to be soon eclipsed by wireless data applications. Wireless communication has also captured the attention of media and imagination of the public. Not only this, the Cellular systems have experienced exponential growth over last decade and there are currently about two billion subscribers around the world and cellular phones have become critical business tool and part of everyday life and are rapidly replacing the wired systems in many developing countries. In addition, wireless local area networks are currently replacing the wired networks in many homes, businesses and campuses. This is because by using wireless things it is easy to move and to get

Designs of Heat Exchangers Essay Example for Free

Designs of Heat Exchangers Essay Heat transfer from one substance to another plays a major role in the process of some commonly use technology today. The heat transfer is done to control temperature, to heat up a cooler substance, or to cool down a hotter substance. This process is done by a machine called the heat exchanger. The heat exchanger is commonly used in the space heating, in cooling of engines, refrigeration and other processes which need temperature control. They are classified according to their flow arrangement design. One is the parallel-flow design which the two substance flow from the same direction and exit at the same direction also. The other one is the counter-flow design on which the fluids flow on opposite direction. The last one is the cross-flow heat exchanger where the fluids flow perpendicular to each other (Heat Exchanger Design, Inc. 2009). Figure 1. Parallel-flow and Counter-flow Design (Engineering Edge 2009) There are also several types of heat exchangers depending on its design. Some are shell and tube heat exchangers, plate heat exchangers, Regenerative heat exchangers and many others. The shell and tube design of the heat-exchanger consists of two sets of tubes. The first set of tubes is where the cooled or heated fluid flows and on the other set of tubes is the fluid that needed to be heated or cooled. The fluids are separated by the tube’s wall. This design ensures a better protection from leakage because of the tube design. So this design is ideal for the treatment of highly pressurize fluids (Kakac Liu 2002:8). The plate heat exchanger is consisting of multiple, thin and slightly separated plates which allow a larger fluid flow area fro heat transfer. It is said to be more effective than the shell and tube design because it provides more surface area for heat transfer. Additionally, the plate heat exchangers have recent developments on its brazing and gasket that makes it practical to use than other heat exchangers. However, the plate heat exchanger is needs a lot of space and it is more susceptible to leakage (Wang, Sunden Manglik 2007). The regenerative heat exchangers are heat exchangers that make use of the heated fluid after a process to be the heating fluid for the next process. This design can be on a plate or shell and tube structure. The advantages of this type are adapted from the design it is structured. Furthermore, this design brought an economical perspective to the first two designs. On the other hand, this design is only intended for the use of gas substances as fluids (Saunders 1988). Figure 4. Regenerative Heat Exchanger (Defense Research Development Organization 2004) The adiabatic wheel heat exchanger is a machine which uses a third substance, fluid or solid, to transfer heat between the streams. The disadvantage of this design is that there will be a small mixing of the two streams in the process of heat transfer (Saunders 1988). The plate fin heat exchanger is highly used in different industries. The plate-fin heat exchangers utilize plates and finned chambers for relatively high heat transfer. It is preferred by other industries because of its ability to transfer heat with to small difference between the streams. Additionally, it has a compact design and is very lightweight (Kakac Liu 2002:17). Another type is the fluid heat exchangers. The process being done is by showering fluids to a gas stream in an upward direction. The process is used in machines that needed gas cooling and purification at the same time (Saunders 1988). Figure 6. Thermal Fluid Heat Exchanger (Thermotech Industries n. d. ) A waste heat recovery unit is a heat exchanger that recovers waste heat from other mechanism and uses it to transfer heat the fluid being heating. This design is very desirable for refineries and plants since they have an abundant amount of waste heat from their machineries. This design is very economical since waste recycled to something useful (Saunders 1988). Figure 7. Waste Heat Recovery Unit (Turner 2005) Dynamic or scraped surface heat exchangers are heat exchangers that have high maintenance cost because of the constant surface scraping. The scraping is due to the process these machines are used. Such processes are heating and cooling of high-viscosity fluids and other highly fouling substance. However, this design has a sustainable heat transfer and it avoids fouling of the surface of transfer (Saunders 1988). Figure 8. Scraped Surface Heat Exchanger (GEA Niro 2008) The phase-change heat exchangers are machines that utilizes liquid and gas phase in heat transfer. These heat exchangers either heat a liquid to boil and evaporate or cool hot gases to condense. This process is common in distillation set ups. The distillation is a process of which a liquid is heated up and cooled down to remove impurities. It is also used in power plants such as nuclear power plants and fossil fuel plants. These power plants usually use steam driven turbines to generate electricity. In which the steam came from the heat exchange between the heater and the liquid (Saunders 1988). The heat exchangers above are heat exchangers which utilizes a wall to separate the two streams of liquids. The classifications above are based on the design of which how the two streams are separated. However, there are other heat exchangers that do not use walls or separators. These are called direct contact heat exchangers. These heat exchangers use two different phases in heat transfer (Saunders 1988). Figure 9. Phase-changed Heat Exchanger (NationMaster. com 2003) There are other heat exchangers in the market today. Some of these are the multi-phase heat exchangers and spiral heat exchangers. Selecting a proper heat exchanger can be a challenging task. It requires technical knowledge about the designs since there are many factors to be taken into consideration. Some are temperature ranges, the composition of the substance to be heated and pressure limits. That is why the decision about the design is made by a computer program or an engineer. Additionally, large companies and corporations tend to design their own heat exchanger to tend to their needs (Wang, Sunden Manglik 2007). Heat exchangers are seen everywhere without you noticing that they are there. The advances in the technology of heat exchangers can produce better results for engineers, researcher and many industrialists since it will increase the efficiency of the process which common machines have today. List of References Defense Research Development Organization (2004). Mechanical Propulsion System. Technology Focus [online] available from http://www. drdo. org/pub/techfocus/oct04/welcomeoct04. html [17 April 2009] Engineering Edge. (2009). Heat Transfer. [online] available from http://www. engineersedge. com/heat_transfer/parallel_counter_flow_designs. htm [17 April 2009] GEA Niro. (2008). Preheating System. [online] available from http://www. niro. com/niro/CMSDoc. nsf/WebDoc/ndkw5y7gby [17 April 2009] Heat Exchanger Design, Inc. (2009). Shell and Tube Heat Exchanger. [online] available from http://www. hed-inc. com/shell-tube. html [17 April 2009] Kakac, S. Liu, H. (2002). Heat Exchangers: Selection, Rating and Thermal Design (2nd Edition). CRC Press Linde Engineering Division (2005). Plate Fin Heat Exchangers. [online] available from http://www. linde-engineering. com/plant_components/plateheatexchanger_aluminium. php [17 April 2009] NationMaster. com (2003). Heat Exchanger. [online] available from http://www. nationmaster. com/encyclopedia/Heat-exchanger [17 April 2009] Saunders, E. A. (1988). Heat Exchanges: Selection, Design and Construction. New York: Longman Scientific and Technical Thermotech Industries (n. d. ) Products. [online] available from http://www. thermotech-finnedtubes. com/products. htm [17 April 2009] Turner, J. (2005). Making the Most of Waste Energy. Science and Technical Information- National Aeronautics Space Administration [online] available from http://www. sti. nasa. gov/tto/Spinoff2005/er_7. html [17 April 2009] Wang, L. , Sunden, B. , Manglik R. M. (2007). Plate Heat Exchangers: Design, Applications and Performance. Southamton, Boston: WIT Press

The Advantages Of Renewable Energy Resources Environmental Sciences Essay

The Advantages Of Renewable Energy Resources Environmental Sciences Essay The rapid growth of the world population leads to energy demand on a rise especially in developing countries. In addition, due to the limited ability to supply of non-renewable there are a number of huge challenges that are posed to the population of the world. This situation leads to the risk of depletion of cheap fossil energy and environmental pollution as well as climate change. According to Loir, there will probably be sufficient oil and gas for this century, and coal for 2 or more (Loir .N 2007, p.843). Or Edwin Cartlidge reports the annual total consumption of energy sources by the world population is about 1.41017 kWh, of which the proportion of the fossil energy has accounted for 90% of the energy sources used (Physics World 7/2007). Therefore, researchers around the world have been constantly trying to find solutions to diversify energy sources and reduce harmful emissions and greenhouse emissions into the environment and renewable energy sources have taken the spotlight. T hus, what is the renewable energy? The Oxford Dictionary () defines renewable energy as natural energy that can be used again and again and will never run out. There are four major types of renewable energy: solar, hydro, wind and geothermal energy. This paper will discuss advantages and disadvantages that renewable energy resource (RES) brings, as well as analysis the importance of RES to the worlds future. 2. Discussion of findings 2.1 Advantages of renewable energy resources (RES) The use of renewable energy has many potential benefits, including human beings and environment. Firstly, one of the most important  advantages of renewable energy  is that it is renewable. Essence of RES is derivation from natural processes so the energy is sustainable and never run out. Truly, renewable energy is really important and necessary to human beings when fossil fuels are more and more exhausted. With the never-ending supply of renewables, we would feel secure when having abundant supply of energy to last our planet, our human race and our economies, for generations and ever. Khemani (2011) says: As long as human life is there, there will be earth, sun, wind and water, and the energy from these sources will also be available as long as they are there. With the abundance from many renewable resources and development of science and technology, he strongly believes that renewable energy can meet the worlds energy needs today and tomorrow. Secondly, another benefit of renewable energy technologies is that ability of providing a measure of assurance of continued electricity supply at times when it otherwise might be threatened. In some circumstances, renewable energy technologies can be more reliable than other forms of electricity. For example, solar electricity systems can be used after storms for response and recovery. Renewable energy technologies such as generators powered by photovoltaics (PV) can supply electricity if the grid fails. Often the sun comes out in the immediate aftermath of a devastating storm. It can take weeks to repair the electricity grid and restore power to all customers. If battery storage is added to the system, it can supply electricity even after the sun goes down or through several cloudy or stormy days. Energy is needed to provide lighting, heating, air conditioning, cooking, transport and to  power  all the technologies in the family home or business premises (Parker 2010) Moreover, renewable energy not only is regarded as an unlimited resource but also plays an important role to regional development. Renewable energy and energy efficiency can help revitalize rural communities. For example, Wind turbines and solar panel systems can provide energy and provide rural communities with new tax revenue. Farmers on windy lands can lease space to wind developers, earning thousands of dollars for each turbine every year. One of the greatest alternative energy benefits is that it is so much better for environment than the use of  fossil fuels that contribute heavily to issues such as acid rain, smog and global warming. On the contrary, renewable energy has little or no waste products such as carbon dioxide or other chemical pollutants. Renewable energy systems produce much lower carbon dioxide emissions as opposed to carbon-intensive fossil fuels such as oil, coal and natural gas while they are being used only a small amount of fuel during the manufacturing of equipment (Walser 2012). With renewable energies, energy is usually converted from one form to another without the creation of pollutants. Chandler (2006) takes solar energy as example, light energy from the sun can be converted directly to electricity using photovoltaic without the production of any pollutants like carbon dioxide or other greenhouse gasses. Similarly, wind power energy relies on moving air and converts it into electricity wit hout polluting the environment. Therefore, it is obvious that the non-pollution or minimal impacts on environment are the positive advantages of renewable energy. 2.2 Disadvantages of renewable energy resources (RES) Although it is obvious to recognize the human as well as environmental advantages of utilizing renewable forms of energy, we must also consider some limiting sides from the energy. The biggest disadvantage of renewable energy is that the cost of the energy is relatively higher than non-renewable energy. The initial costs of renewable energy still make many people ignore it completely when comparing it with fossil fuel on two aspects: total cost and over the same time period. For example, installation of solar energy water heater costs many times in comparison with a heater, so they decided to buy heaters for hot water solution. According Global Wind Energy Council (GWEC) (2008) reported that turbine installation costs $ 47.5 billion; by contrast, we only have to spend a much smaller amount of money to build thermal power station about $ 2,25 billion (Shah 2011). He also pointed that other incidental costs such as maintenance costs and production costs cause price increasing. Generally, it is price that the reason has prevented approaching and using clean energy as compared to the fossil fuel sources of energy. Another distinct disadvantage is relying too much on weather conditions and geographic locations to create energy (Sinclair 2011). Each types of renewable sources is just better suited to some places. This means that you cannot use each of these renewable sources in all locations. For instance, when using geo-thermal energy, you must be in a location that provides the environment for geo-thermal energy to be produced. Likewise, we cannot generate hydro-electric power without having a fast-flowing water source, such as a river or waterfall. In addition, the energy also brings some inconvenient problems. Take solar energy water heater as an example, it is inefficient because in summer ambient temperature are high and the use of hot water is not needed; however, in the winter we could not have hot water due to low light of the sun. Shah (2011) claimed that despite the fact that most renewable energy sources are more environmentally friendly they may still have a negative impact on the environment. He stated that hydroelectricity projects can cause a dramatic change in the development of wildlife and ecosystem along the river and flood risks. 2.3 Can renewable energy supply the Worlds energy needs? With the significant benefits from renewable energy, we cant deny that roles of it are more and more important. Nowadays, by advances and achievements of science and technology scientists are having every confidence in bright future of renewable energy. According to the report of The  Intergovernmental Panel on Climate Change (IPCC) in 2011, renewable sources occupied about 13 percent of the worlds energy in 2008 and the proportion likely to have risen. The report also point out that within four decades renewable energy  could account for almost 80% of the worlds  energy supply. The statistics are completely appeared in the near future if we combine four main alternative resources and use hydroelectric to fill in gaps, which makes easier to match demand. The most important thing is to combine renewable energy sources into a bundle (cited in BERGERON 2011). Particularly, in research (Edenhofer et al. 2011) shows that by 2050, geothermal energy could meet more than 3 percent of global electricity demand and about 5 percent of the global heat demand, hydropower will contribute about 30 percent of worldwide electricity supply, wind power will grow to more than 20 percent and solar energy becomes one of the major sources of energy supply with about 15 percent.

Will Jamaica Self-Destruct? Essay -- essays papers

Will Jamaica Self-Destruct? Jamaica is an island paradise, located in the northern Caribbean, approximately 145 km south of Cuba and 160 km west of Haiti, with a population of about 2,553,600 million people in 1997 and a land area of 11,000 km/sq. The country has had a low and steady population growth rate of 1.0 percent in 1997. Tourism is Jamaica’s most important industry besides the mining of bauxite (accounts for more than half of exports). It is the country’s largest foreign exchange earner, (generating approximately US$965 million annually) and is still one of its fastest growing industries. These profitable service industries depend on the island and its natural beauty–pure air, abundant sunshine, and clean sandy beaches. This industry is evidence to the close relationship between economic well being and the quality of the natural environment. "You ain’t gonna miss your water, until your well runs dry. No matter how you treat him, The man will never be satisfied." (Bob Marley, 1980) Tourism is both Jamaica’s largest foreign exchange earner and one of its fastest growing industries. A recent environmental study commissioned by the Organization of American States (OAS) surveyed the natural resource base (which supports tourism) and concluded that this base is "heavily stressed" in and around the three main tourist centers (Negril, Montego Bay, and Ocho Rios). The problem is that these areas now support large populations of tourists with high-income lifestyles and these impacts harm both the environment and the people of Jamaica. It could also spoil Jamaica and lead to its own destruction of the land and its deeply engrained culture and roots. Jamaica’s natural resources–tropical temperatures, unspoiled beaches, clear C... ...conomy, R 062059Z, July 1994. Government of Jamaica, Organization of American States, Economic Analysis of Tourism in Jamaica, September 1994. Also, visit the web sight http://www.oas.org Health Analysis, Country Health Data of Jamaica, last revised10/19/99, http://www.paho.org/english/sha/prifljam.html. Myers, Fletcher & Morgan, A lawyers Guide to Jamaica, no date, http://hg.org/guide-jamaica.html , 4/2/00. Seagrasses Policy and Regulation natural Resources Conservation Authority Coastal Zone Management Division, April, 1996, http://www.nrca.org, 4/6/00. Water Resources Authority, March 10, 2000, http://www.wra-ja.org/index.htm , 4/2/00. U.S. Department of State, Background Notes: Jamaica, March 1998. Released by the Bureau of Inter-American Affairs. No author, U.S. Department of State, March 1998, http://www.state.gov/www/background_notes/jamaica_0398_bgn.html

Research Paper on Stereotype Threat

Stereotype Threat in a High Stakes Testing Environment Jennifer J. Krebs Wilkes University Abstract Given the rapidly changing demographics of today’s classrooms combined with the high-stakes testing environment created by the passage of No Child Left Behind, it is important to understand potential explanations for the persistence of achievement gaps. Explanations for the achievement gap have included high populations of English Language Learners (ELLs), socioeconomic issues, lack of resources at the school, teacher, and student levels, and even inherent differences in the intellectual abilities of stereotyped and non-stereotyped groups.A theory developed by Steele and Aronson, called stereotype threat, provided a radical view into how knowledge of stereotypes affects performance (McKown & Strambler, 2009). Stereotype threat is the experience of anxiety or concern in a situation where a person has the potential to confirm a negative stereotype about their social group. The pur pose of this research was to determine how and when children begin to develop knowledge of stereotypes and how stereotype threat affects academic performance. IntroductionThe diversity of student demographics increases every day. Therefore, teachers must be increasingly more aware of the cultural differences and challenges that students from diverse backgrounds bring to school. Not only are these students likely to learn differently based on their cultural expectations, but these students are also likely to possess knowledge of commonly held social stereotypes which can negatively impact their performance (McKown & Strambler, 2009). The current emphasis on high-stakes testing makes the achievement of all students extremely important.Experimental research into performance gaps was limited prior to a groundbreaking study that focused on the possibility of stereotype threat. First described by social psychologist Claude Steele and his colleagues, stereotype threat (ST) has been shown t o reduce the performance of individuals who belong to negatively stereotyped groups (McKown & Strambler, 2009). Since its introduction into the academic literature in 1995, stereotype threat has become one of the most widely studied topics in the field of psychology.However, a major assumption of this theory was that children possess knowledge of commonly held social stereotypes. In order to address this assumption, the following qualitative studies were implemented to determine how and when children begin to develop knowledge of stereotypes. This research is combined with quantitative studies to determine how ST affects academic performance. Method Schaffer and Skinner (2009) examined student interactions within four fourth grade classrooms at a diverse public school in the southeastern United States.Upon observing student interactions and conducting interviews, the researchers discovered several patterns. First, white children were less likely to engage in explicit race talk, whil e black students frequently engaged in openly racial discussions and often used commonly held stereotypes to identify themselves. Second, most minority students who performed at the high end of the class and participated in challenging academic programs relied heavily on racial stereotypes to bridge the social gap between themselves and their racial peers.These students sought to distance themselves from the white students with whom they took advanced classes. Third, white students were more likely to describe students of other races as â€Å"loud† or â€Å"troublemaking† (Schaffer & Skinner, 2009). These observations suggest that students were not only aware of commonly held stereotypes, but strategically used them to organize their social world and dictate social functions. Another study, which examined high school students, suggested that these trends continue as students mature rather than diminish. Lisa M.Nunn (2011) observed six classrooms across three different high schools, and conducted 57 interviews with students to determine the ways in which students’ classroom interactions reflected ideas about commonly held stereotypes. In one school, nearly half of the students interviewed said that race matters for school success. At another school, students expressed frustration with being racial targets and felt they had done nothing to provoke degrading views from their classmates. Furthermore, in a remedial English classroom consisting of eight students, the researcher noticed a ommon occurrence. Five of the students in this classroom were Latino, and three were white. The white students all had learning disabilities which hindered their language usage, while the Latino students’ only handicap was that English was not their native language (Nunn, 2011). Combining ELLs with students with disabilities effectively treats the native language of ELLs as a learning disability. Between the racial views of the students and the systematic reinforcement of prejudices, it is easy to understand why students tend to hold views that race matters for success.The question that remains is how does this knowledge of stereotypes affect student academic performance? McKown and Strambler (2009) conducted a study of 124 students ranging in age from grades K-4 in a suburban Chicago area. The students were given a series of vignettes to determine their ability to identify stereotypes and then placed in diagnostic or non-diagnostic groups to complete performance tasks. Consistent with prior research, minority participants in the diagnostic group performed worse than in the non-diagnostic group; and majority participants performed equally well in both groups (McKown & Strambler, 2009).Desert, Preaux, and Jund (2009) administered Raven’s APM to 153 children within first and third grades. In the diagnostic group, students were given the standard administration instructions as provided in the Raven’s APM Administration Ma nual. In the non-diagnostic group, students were given instructions explaining that the test was actually a series of games that the researchers developed and were testing to determine their appropriateness for the students’ age groups.Researchers stratified the results based on socioeconomic status, arguing that negative stereotypes about the performance of low-SES students could result in ST. The results of the study showed that low-SES students in the diagnostic group performed significantly worse than those in the non-diagnostic group. The performance of high SES students did not differ significantly among the two groups (Desert, Preaux, & Jund, 2009). These results suggested that children in the early elementary years are not immune to ST, even on a test that is supposed to be culture free. While all of these experiments support he theory of ST, one of the strongest arguments to date relies heavily on developing technologies. Derks, Inzlicht, and Kang (2008) offered an o verview of breakthroughs in social neuroscience research that highlighted biological factors underlying conditions of stereotype threat. The researchers discussed several experiments that used functional magnetic resonance imagining (fMRI), electroencephalography (EEG), and event-related potentials (ERP) to measure the neurological activities of participants when asked to perform tasks under diagnostic and non-diagnostic conditions.One study tested women under mathematical performance stereotypes and found that the conflict monitoring systems of the brain showed a mis-regulation of neural responses. This information supported the hypothesis that emotions aroused by ST conditions lead to a decrease in cognitive ability. The decrease in ability occurred because emotion-regulation centers of the brain experienced increased activity while areas of the brain associated with academic performance and cognition experienced decreased activity. The researchers cautioned that neuroscience expe riments in the area are too new to allow for generalizations and definitive findings.However, they argued that development of this area is crucial to the study and understanding of stereotype threat (Derks, Inzlicht, & Kang, 2008). Results The assumption that the performance gap between stereotyped and non-stereotyped groups is solely rooted in cultural differences and limitations of students’ background is restrictive. Research has shown that there is also a factor of social psychological threat related to knowledge and perceptions of stereotypes, which can depress test scores of stereotyped individuals.The use of high-stakes testing in an overall environment of racial inequality perpetuates that inequality through the emotional and psychological power of the tests over the test-takers. While researchers have begun to delve into the intricacies as to how stereotype threat causes decreases in performance and other negative effects, there is still much research that needs to b e conducted in order to completely understand the mechanisms that underlie the performance deficits that occur as a result of stereotype threat. ConclusionIn conclusion, stereotype threat is a pervasive phenomenon that has the ability to impact a variety of individuals in a number of ways. Current research offers us insight as to what stereotype threat is, how it impacts individuals, what mechanisms drive the relationship between stereotype threat and performance, and how we can begin to remediate some of the damaging impacts of this threat. Since the current emphasis on high-stakes testing does not appear to be diminishing, teachers and mentors should at a minimum equip students with knowledge about the possible effects of stereotype threat.In this way, proactive strategies might transform a powerless situation into one where students are actively participating in discussions that illuminate the complexities and strengths of their educational futures. Teacher education programs sho uld review their course curriculum and address any gaps in the discussion of standardized testing and methods to improve test scores. Changing test directions from diagnostic to non-diagnostic, educating students in malleable intelligence theories, and reducing the general stress of the testing environment are all methods which could be implemented.References Derks, B. , Inzlicht, M. , & Kang, S. (2008). The neuroscience of stigma and stereotype threat. Group Processes & Intergroup Relations, 11(2), 163-181. Desert, M. , Preaux, M. , & Jund, R. (2009). So young and already victims of stereotype threat: Socio-economic status and performance of 6 to 9 years old children on Raven’s progressive matrices. European Journal of Psychology of Education, 24, 207-218. McKown, C. & Strambler, M. J. (2009).Developmental antecedents and social academic consequences of stereotype-consciousness in middle childhood. Child Development, 80, 1643-1659. Nunn, L. (2011). Classrooms as racialized s paces: Dynamics of collaboration, tension, and student attitudes in urban and suburban high schools. Urban Education, 46, 1226-1255. Schaffer, R. & Skinner, D. G. (2009). Performing race in four culturally diverse fourth grade classrooms: Silence, race talk, and the negotiation of social boundaries. Anthropology & Education Quarterly, 40, 277-296.

Placenta Previa Essays

Placenta Previa Essays Placenta Previa Essay Placenta Previa Essay Abstract The paper discussion is about Placenta Previa a medical condition observed, and that occurs in women during birth. The paper begins b giving an introduction of the term Placenta Previa sampling the data survey together with the degree of the disease. The paper further presents a credible discussion on the pathology discussing some of the causes and risks. Diagnosis is also looked it with the article pointing out some of the significant procedures and care taken to help in prevention and treatment of Placenta Previa. Prognosis and management outline some of the primary managerial procedures to be taken and observed to prevent and help one with Placenta Previa. Finally, the paper gives a conclusion of the recap of all the discussion in the article. Introduction Placenta Previa is a condition in which the placenta implants in the lower portion of the uterus and covers all or part of the internal cervical os. The incidence according to the survey is that 1 out of 200 women giving birth. The major difficulty with classification system is accounting for the potentially changing relationship between the placenta and cervix during the third trimester, especially as labor progresses (Nyberg, 2003). Degrees of Placenta Previa are described concerning the internal os prior or the onset of labor. There are four types or degree of Placenta Previa: Total Placenta Previa is where the internal os is entirely covered by the placenta Marginal Placenta Previa is whereby the edging of the placenta is close to the internal os. Partial Placenta Previa is where the internal os is partly sheltered by the placenta. Low lying Placenta Previa is where lower uterine segment has a placenta implant such that the placental edging has a proximity of the internal os. The incidence of Placenta Previa varies widely with gestational age at diagnosis and the criteria used. The impact at the term of clinically significant Placenta Previa is approximately 0.5% (Nyberg, 2003). Placenta Previa is diagnosed in about 5% of second-trimester pregnancies before genetic amniocentesis. At least 90% of Placenta Previa, therefore, resolves to a standard position by the term. Possible reasons for this improvement are discussed in the following pathology section. Pathology Placenta Previa results from implantation of the blastocyst in the lower uterine segment. Some factors appear to increase the risk of this occurrence, including advancing age, multi-parity, smoking, cocaine use, prior Placenta Previa and parity, previous cesarean delivery and suction curettage related to pregnancy. The firm association between Placenta Previa and parity previous cesarean delivery and curettage suggests that endometrial damage is an etiologic factor. Subsequent pregnancies are more likely to implant in the lower uterine segment by a process of elimination (Mishell, Goodwin Brenner, 2002). Multiple pregnancies are at higher risk because of the reduced surface area of the endometrial available. Improvement in Placenta Previa with gestational age primarily reflects marketed growth of the lower uterine segment during pregnancy which pulls the placenta superiorly. At 20 weeks, the placenta covers approximately one-fourth of the myometrium surface area, but near term the placenta covers one-eighth the myometrial surface. Improvement may also be partly secondary to trophotropism in which the placenta atrophies at suboptimal sites of implantation and hypertrophies at more optimal sites. Diagnosis Placenta Previa is most often diagnosed by routine sonography. In other cases, the initial diagnosis is made at the time of presentation for vaginal bleeding through the second part of pregnancy. In these cases, sonographic confirmation of placental location is recommended before the digital cervical examination. The trans-abdominal ultrasound may confirm the suspicion of Placental Previa (Krishna, Daftary Tank, 1995). When sufficient visualization of the affiliation between the placenta and the internal cervical os is not possible with trans-abdominal ultrasound, the transperineal or transvaginal approach may be beneficial. Careful transvaginal may be beneficial. Careful sonography does not appear to increase the risk of hemorrhage in Placenta Previa. In general, prenatal ultrasound is highly sensitive but not specific for the diagnosis of placenta previa. Therefore, while false negative diagnoses are rare, false positive diagnoses are common depending on the gestational age, the sonographic technique used. This is especially true before the third trimester because of differential growth of the lower segment of the uterus in the second half of pregnancy. Placental Previa is readily diagnosed by the location of the placenta over the cervix. Placenta localization by trans-vaginal examination complements trans-abdominal scans and provides good visualization of the internal os and its relationship to the location of the placenta. Thus, may help to decrease the number of false positive diagnosed with Placenta Previa during early pregnancy (Nyberg, 2003). Prognosis and management Krishna, Daftary and Tank (1995) indicate that patients with a lower lying identify at mid-trimester should be observed with further ultrasound examination until at least 34 weeks, or unequivocal conversion has occurred. Placenta Previa diagnosed by custom second-trimester sonography is managed expectancy. The patient can be a measure that the likelihood of spontaneous resolution is greater than 90%. It is reasonable to recommend avoidance of strenuous activity, but further limitations probably are not necessary early in pregnancy. The placental location should be re-evaluated at 28-30 weeks (Mishell, Goodwin Brenner, 2002). If Placenta Previa persists, the patient should be cautioned that rigorous activity and intercourse might provoke bleeding. Cesarean delivery should be scheduled at a gestational age that will exploit the probability of fetal maturity and diminish the risk of hemorrhage that may effect from the standard commencement of uterine abbreviations. According to Mishell, Goodwin and Brenner (2002) the management of Placenta Previa complicated by acute hemorrhage is directed at optimizing the outcomes of the mother and the fetus. In many cases, bleeding resolves spontaneously and the patient may be managed expectantly. In other cases, severe hemorrhage may require intervention. The management varies dramatically with the severity of the condition. Through ultrasound with color and duplex Doppler should be performed. MRI should be considered. Mild cases of placenta accrete may be treated with hemostatic cultures and removal of the placenta or observation alone. Patients may also be treated with methotrexate (Nyberg, 2003). For more classic, severe cases the usual treatment is hysterectomy at the time of delivery. If the placenta also invades the urinary bladder, however, this may be insufficient to control the hemorrhage. Adequate blood for transfusion must be available at the time of delivery. The goal is to deliver a live, healthy baby and maintain the health of the mother. Conclusion In concluding Placenta Previa is a stipulation whereby the placenta implants in the lower portion of the uterus and covers all or part of the internal cervical. Degrees of Placenta Previa are described concerning the internal os prior or the onset of labor. It results from implantation of the blastocyst in the lower uterine segment. Some factors appear to increase the risk of this occurrence, including advancing age, multi-parity, smoking, cocaine use, prior Placenta Previa and parity, previous cesarean delivery and suction curettage related to pregnancy. Placental Previa is readily diagnosed by the location of the placenta over the cervix. Placenta localization by trans-vaginal examination complements trans-abdominal scans and provides good visualization of the internal os and its relationship to the location of the placenta. the management of Placenta Previa complicated by acute hemorrhage is directed at optimizing the outcomes of the mother and the fetus. References Krishna, U., Daftary, S., Tank, D. K. (1995).Pregnancy at risk: Current concepts. New Delhi, India: Jaypee Bros. Medical Publishers. Mishell, D. R., Goodwin, T. M., Brenner, P. F. (2002).Management of common problems in obstetrics and gynecology. Malden, Mass., USA: Blackwell. Nyberg, D. A. (2003).Diagnostic imaging of fetal anomalies. Philadelphia: Lippincott Williams Wilkins.