The Man Inthe Black Suit – Presence of Evil

Stephen King's â€Å"The Man in the Black Suit† is a short story that makes us think. Who are we in this world? Is our destiny in our hands or is it already written? Can we avoid being in contact with evil? â€Å"The Man in the Black Suit† proves that evil is omnipresent in our world and that there is no way to avoid it. It does not matter who you are, where you are and when you are there, if evil wants to meet you, it will wind a way to do so. We would not be shocked so much if an adult has met the Devil, because we all know that adults are more likely to commit sins. But what when a child meet the Devil?What would a child do wrong to be punished by the Devil? It is difficult to say. â€Å".. This is something that happened to me when I was very young, only nine years old. â€Å"(page 821) Our main character Gary was a young child when he saw the Devil for a reason he has never understood â€Å"Until that Saturday in 1914, I had thought that bears were the worst thi ng the forest could hold. â€Å"(page 831) Kids think that bears are the most terrific creatures in the forest. We can see their huge innocence. Why does evil attack those innocent children? Because evil can attack anybody.Our nine-year old character Gary meets the Devil in the town of Motton as he defines like this : â€Å"The town of Motton was a different world in those day – more different then I could ever tell you. That was a world without airplanes droning overhead, a world almost without cars. † (page 821) As he talks about Motton, we learn that it is a little rural town in western Maine. There was no phone, no doctors, no paved roads and not more than a dozen of houses. All those little things make Motton a completely innocent place. Why would the Devil attack a little innocent farmer town?It does not seem so attractive†¦ But evil does not have any criteria, it is omnipresent. In â€Å"The Man in the Black Suit†, Gary's meeting with evil happens d uring the summer of 1914. â€Å"†¦ one afternoon in the summer of 1914. † (page 821). As we all know, the begging of the 20th century is a very religious period of time in the United States. Also, religion has a lot of power especially in the small rural communities like in the town of Motton. People back then believed in God, and that God will protect them from the Devil if they were good believers. Also the part of pagans was really slim in the society.We could call that period of time an innocent period of time that should have not met the Devil in any case. If the 1910s have not been â€Å"saved† from evil, how could our generation be? We can see that any period of time can be in contact with evil. In conclusion, we can see that in â€Å"The Man in the Black Suit†, evil attacks an innocent child, in an innocent place during an innocent period of time. What can we find more innocent than that to avoid evil?. With those three things combined, we can concl ude that there is not a way to avoid evil in our world, it is absolutely omnipresent.

Gender Stereotypical Attitudes Past Essay

It has been generally observed that workplace attitudes on gender have continued to influence decisions and direct actions in organizations. These attitudes have tended to be directed more at women than men. The result has been a hindrance in the effective participation of women in decision-making at the workplace. Most men, and sadly women, have had the opinion that women lack the ability to function in management positions that require strategic decision making within the organization. They are said to lack the ability to decide on their feet, as somebody would put it. Research findings unfortunately seem to point at the existence of this sad scenario in most organizations. A research carried out by Wood (2008) provides a lot of insightful information on the effect of gender stereotyping of women at the work place. Out of a total of 30 respondents selected for this study, there were 19 men and 11 women, who happened to be in various management positions in their organizations. It is interesting to note the gender stereotyping began right from the sampling. One wonders why the researchers decided to use 19 male and 11 female managers and not 15 male and 15 female managers. A good number of the female managers in the US felt it would take over 10 years for women to achieve equal representation with men in terms of job placement. A number of male respondents from the US shared a similar view and supported his position by submitting that in the organisation where he works, there are very few women, and even then most of them take long durations in lower positions. Some female respondents were of the opinion that it would take more than a decade for women to realize 50% representation in senior management positions. A female respondent was of the opinion that 50% representation might not be realized. She however opined that this was not because women lacked the ability to perform in these high positions, but because they were not simply interested in taking up such positions. This position is tandem with the respondents who were asked if they aspired to be promoted. Whereas 68% of the men said they aspired for promotion, only 55% of the women were willing to be promoted. It is however unclear whether their lack of aspiration is due to lack of skills, knowledge and abilities. Whereas 58% of the men said that they had successfully achieved promotion, only 27% of the women shared this position. It is however debatable whether their failure to secure promotion was based on their lack of interest, lack of ability or because of their smaller number in organizations. It would appear that children hinder women from aspiring for management positions because one respondent said that women who wish to get these positions put off bearing children. Some respondents said that senior management positions are not open to everybody, but to a small clique of old boys who operate like a closed shop. Breaking into this network requires people with unique abilities, and not many women have the stamina to push through. The few who have been able constitute the small percentage. Some managers were of the view that achieving 40/60 percent representation for women and men respectively in more than 10 years could be more realistic than 50/50 percent representation. They argue that it takes time to develop somebody to management level, which not many women are willing to wait for patiently. Even when they reach the top, some of them opt out and might not be replaced by other women, but by men. It was also felt by some respondents that management positions require performers, which not many women might be. They feel that 50% representation at any time might be quite ambitious, but 10% would be realistic. Cumulatively, out of the female respondents, 1 felt that it would take 5 – 10 years to have 50% female representation, 2 said it would take more than 10 years while 4 said it would take 10 years or more. Only one female respondent said women will never achieve 50% representation. 1 said it would take another 5-10 years, while two said it would take more than 10 years from that time. 1 out of the 19 male respondents said it would take between 5-10 years to achieve 5% female representation, while 1 said it would take more than 10 years. 6 said it would take another 10 years or more. 5 male respondents said women will never achieve 50% representation, while one said it would take them more than ten years to achieve a paltry 10% representation. The results from this research could have major implications in the actual working environment as far as female aspirations for higher managerial positions are concerned. The first implication which is more theoretical in nature is that women are being negatively influenced as far as their career advancement is concerned. When the results make it abundantly clear that chances of achieving a 50% female representation on the workplace are slim, most of the female employees will get demotivated and will find no reason to aspire for high managerial positions. Such a decision is likely to keep them at the lower level of then organization hence inhibiting their career advancement. Making top management positions appear like a private members’ club which requires connections before joining could easily scare away women from venturing. Not many women are able to weave their way through male dominated networks. The few who are able are possibly the ones who share such positions with men. Some women would like to be mothers as well as career women. Making it appear as if advancing in one’s career can only take place at the expense of family life is enough deterrent to a woman’s career advancement. The practical implication of the research findings is that organizations might fail to sufficiently utilize the skills, knowledge and talents possessed by women. It is known that women have some unique abilities which could be harnessed and utilized in the organization. Scaring them away from management positions where important decision making is done denies the organization opportunity to benefit from their input. Apart from being scared by the attitude of men, fellow women also play a role. References Wood, Glence. 2008. Gender Stereotypical Attitudes Past, Present and Future Influences on Women’s Career Advancement. Equal Opportunities International, Vol. 27 No. 7, pp. 613-628

Compromising Development: the Language of Instruction Dilemma

Tayebwa Morris Compromising development: The Language of Instruction dilemma in Tanzania. Introduction Following release of the Tanzania 2012 Form IV results by the Ministry of Education and Vocational Training on February 18, the media and the general public have been frantically discussing the fact that up to 60 % of the students who sat last years’ ‘O' level final failed the exam. i This has once again raised a lot of concern in and around Tanzania from educators, parents and policy makers.Among many reasons given for the failure, that has in fact been increasing every year are factors like; shortage of quality teachers, poor infrastructure and study tools. The reason that stands out however, is the poor proficiency of secondary school students in English, the language of instruction. In fact studies have shown that the same students do much better in primary school where they are taught and examined in Kiswahili, the national language.The Tanzanian Dilemma Inspite of incessant advice by policy makers and educators for a complete adoption of Kiswahili as the only medium of instruction at all levels, the Tanzanian government has upheld the bilingual education system and English is continually used as a language of instruction for all post-primary school education. In fact early research agrees with the promotion of Kiswahili as the appropriate choice as a language of instruction.However, going by the advances of education worldwide where especially tertiary education is becoming more globalised, wouldn’t it be regressive to adopt a language of instruction that is limited to just one country? Unless we of course consider that the returns from quality secondary education would be sufficient for Tanzania without regarding the effect on tertiary education. Or maybe higher education would also have to adopt Kiswahili as a language of instruction.This is before we consider the feasibility of such a transformation most importantly in terms of pre sence and quality of secondary school and higher education tools such as curricula, textbooks, teaching guides and manuals and obviously teachers trained to instruct post – primary levels. Or maybe the country should take the bitter pill and adopt English as a language of instruction on all levels. In this paper, I will try to delve into previous research on this matter and find a relation etween the language of instruction and effect on developmental outcomes of Tanzania both in terms of human capital growth and general wellbeing of citizens. Does the language of instruction really matter? From the human capital rationale, language does matter. â€Å"Human capital† refers to the set of skills a person acquires mainly through education and training to aid his/her productivity and attain greater compensation in the labour market (Becker 1964).Proficiency in a language of instruction (reading, writing, oral expression) is a skill vital to the development of human capital . As explained by Chiswick and Miller (1995), the language skill â€Å"satisfies the three criteria that define human capital,† that is, the costs involved in the creation of language skills, the skills that serve a productive purpose relevant to economic activity in the labour market; and the fact that all that is embodied in a person. As demonstrated by Samuel O.Ortiz (2004) in his assessment of culturally and linguistically diverse students, language of instruction also determines the competence of students in relation to the improvement of their cognitive skills, a means and end to the means of quality education. By discussing cognitive skills and quality education, we get closer to the effect of language of instruction on the development of individuals and societies, both socio-economic and general well-being. According to Hanushek and Kim (1995) and Hanushek and Woessmann (2007), quality of education is a measure of labour force quality based on the cognitive skills att ained.Therefore, such big failure rates, and reports that most students failed to write anything in last year’s exam, and either resorted to cheating, writing funny verses and abuses spells a bad image for the Tanzanian education system and leaves us to wonder what kind skills are the students getting anyway. Undeniably, research over the years has shown that standards of English education are inadequate thus affecting the general performance of most post-primary students (Mlama and Matteru 1977, Criper and Dodd 1984, Roy-Campbell 1997, Martha Quorro (2013).In fact it was found that students perform much better under the medium of Swahili and that nearly 75 percent of teaching, especially in the early stages of secondary education, was being done in Swahili rather than English or sometimes with massive code switching involved (Rugemalira et al 1990). ii Students therefore receive a large part of their education in the local language yet assignments, tests and even national ex ams are written in English. This, as a result handicaps students with low proficiency and leads such to high failure rates.This goes on to not only affect the education system but the students as well. For example, after such failure, most students drop out of schools even without qualifications, girls are married off at an early age by parents who are not seeing direct returns from the education, boys resort to lower income jobs for survival and this ultimately also affects the motivation of other students to join secondary school. As a result, Tanzania has the lowest secondary school enrolment in the region (World Bank, 2009).The government has however ignored research findings and the sociolinguistic reality by maintaining a weak bilingual instruction format. It makes no sense teaching in a language that children are not understanding. In fact the Ministry of Education and Vocational Training has in the past proposed starting English as Language of Instruction from nursery school all through to tertiary education (MoEVT, 2009). Tangled in this predicament, there is also an inequality dimension.Studies have shown that many wealthy Tanzanian parents send their children to better performing private schools, as well as to schools in the neighbouring countries, in order to have their children exposed to English-medium education in primary school (Mazrui 1997, Cox and Jimenez 1991). In a country where there are better opportunities for the English proficient workforce, the foreign trained students consequently have more valuable capital and better potential to get better paying jobs and thus opportunities are still in the hands of the already privileged. The uncertain futureFrom the aforementioned studies, it is clear that adoption of Swahili as the language of instruction in secondary schools, will lead to better outcomes in terms of effective transfer of information, legibility, improved education and a more productive population. On the other hand, emphasis on English, just like in other neighbouring countries will likewise improve the skills needed to compete globally especially in tourism and other export-oriented investments, broaden other labour- market opportunities, and close the socioeconomic classes’ gap that exists between the English currently proficient labour force and the general public.In my opinion and as discussed by Batibo (1990) a bilingual system can still be maintained but the government will need to invest more in promoting the learning of English at pre- primary level to better prepare the students to the reality of an English post primary education. However as this paper has shown, even with a plethora of research on this matter, the Tanzanian government is faced with the dilemma of choosing a curriculum policy that should emphasize a well understood and better performing language or one that is used widely around the world especially in economic, scientific and technological circles.NOTES i The breakdowns b y divisions are as follows: division 1-1,641; division 2-6,453; division 3- 15,426; division 4103,327, and division 0-240,903. By gender for those who passed i. e. received divisions 1-3: girls =7, 178 and boys = 16, 342. That means 5. 6% of those who sat for this exam passed (divisions 1-3), it only when division 4 (the worst possible grade) is included that failure rate reduces to 60% otherwise with division 4 included, failure rate is actually 94. 4%. ii Code switching is the practice of alternating between two languages to ease communication.References Barro R (1999). Human Capital and Growth in Cross Country Regressions, Swedish Economic Policy Review, 6, 237-77. Barry R. Chiswick and Paul W. Miller (1995). The Endogeneity between Language and Earnings, Journal of Labor Economics, 13, 248. Batibo, H. M. (1990). English language teaching and learning in Tanzanian primary schools. Language in Education in Africa: A Tanzanian Perspective. Ed. C. M. Becker, Gary. (1964). Human Capi tal: A Theoretical and Empirical Analysis with Special Reference to Education. Chicago: University of Chicago Press.Cox, Donald and Emmanuel Jimenez. (1991). The Relative Effectiveness of Private and Public Schools: Evidence from Two Developing Countries. Journal of Development Economics 34:99-121. Criper, C. and William Dodd (1984). Report on the Teaching of English and its Use as a Medium of Instruction in Tanzania, ODA/ British Council. Education in Africa: A Tanzanian Perspective. Ed. C. M. Rubagumya. Philadelphia: Multilingual Matters, 1990. Hanushek E and Kim D (1995), Schooling Labour Force Quality and Economic Growth, National Bureau of Economic Research Working Paper No. 399, Cambridge, MA. Hanushek E and Woessmann L (2008). The Role of Cognitive Skills in Economic Development, Journal of Economic Literature, 46, 607-668. Martha A. S. Qorro, (2013). Language of instruction in Tanzania: Why are research findings not heeded? International Review of Education Mazrui, Alamin. T he World Bank, the language question and the future of African education. Race and Class 38. 3 (1997): 35-48. Mlama, Penina na May Matteru (1977). Haja ya kutumia Kiswahili kufundishia elimu ya juu, a research report commissioned by BAKITA, Dar es Salaam, Tanzania.MoEVT (2009). Sera ya Elimu na Mafunzo (2009), Rasimu ya I. Toleo Jipya, Juni, 2009. Ortiz O. Samuel, Comprehensive Assessment of Culturally and Linguistically Diverse Student: A Systematic, Practical Approach for Non-discriminatory Assessment Washington, DC: National Association of School Psychologists. Qorro (eds. ): Language of Instruction in Tanzania and South Africa. (LOITASA) Dar es Salaam: E & D Limited. pp. 149 – 170. Roy-Campbell, Zaline Makini and Martha. Qorro, (1997). The Language Crisis in Tanzania: the Myth of English versus Education, DSM: Mkuki na Nyota Publishers.Rubagumya, Casmir (2003). English medium primary schools in Tanzania: a new â€Å"linguistic market† in education? In: Brock-Utne, Birgit, Zubeida Desai and Martha Rubagumya. Philadelphia: Multilingual Matters. Rugemalira, J. M, C. M. Rubagumya, M. K. Kapinga, A. F. Lwaitama and J. G. Tetlow. Reflections on recent developments in language policy in Tanzania. Language in World Bank, (2009) World Bank Indicators – Tanzania accessed on 15. 03. 2013 from http://www. tradingeconomics. com/tanzania/school-enrollment-secondary-femalepercent-gross-wb-data. html

Global Marketing Assignment Essay Example | Topics and Well Written Essays - 3500 words

Global Marketing Assignment - Essay Example Macro environment is the larger societal forces that affect the microenvironment- demographic, economic, natural, technological, political, and cultural forces. The SLEPT Analysis is a useful starting point for the analysis of an organizations external environment and the forces at which it works like Hennes & Mauritz. The aim of any SWOT analysis is to identify the key internal and external factors that are important to achieve the objective of an organization. H&M faces challenges in Japanese market in selling goods. H & M has collaborated with Madonna 3 for their promotion, which is a good decision, and for being a famous singer in all over the world as well as Japan and a symbol of fashion and style; Hennes would gain vast and successful market in Japan. H & M Hennes & Mauritz AB is a Swedish clothing company with outlets in different market of Europe and the U.S. The principal activity of this company is retailing of fashion clothing. The products of the Group are sold through a chain of stores, by mail order and through the Internet. They offer their products in different concepts for women, men, teenagers and children. They also retail sportswear, accessories and cosmetics. The product range includes body and care and hair care products and make-up accessories for men, women and teenagers. This Group has 22 production offices in Europe, Asia, and in Africa 4. Hennes & Mauritz targets the Hip & Modish. They design cheap but chic clothing, mainly for men and women 18 to 45, children's apparel, and its own brands of cosmetics. It operates more than 1,200 stores in 24 countries with direct sales operations in selected areas. Stefan Persson, the billionaire son of founder Erling Persson is the Chairman of 'H&M'. The family has a good controlled over the company and they own nearly 37% 5. 1-2: Problem Statement: 1. In regards to Hennes & Mauritz (H&M), we have to undertake a critical assessment of the Global Marketing and organisational procedures adopted by the

The influence of technology on modernist and avant-garde architecture Essay

The influence of technology on modernist and avant-garde architecture - Essay Example After the liberal-national revolutions of 1848, there was the need to expand the economy of the colonial territories and to fill the political, military and economic conditions with the traditional European. This led to the development of cities in its suburbs. In addition, the decrease in mortality because of the improved standards of living in terms of nutrition and medical techniques in urban areas resulted in urbanisation. The increase in population in urban areas led to transformation of old neighbourhoods into slums as well as entry of jerry-built houses that would provide shelter to people working in the factories. However, the Housing of the Working Classes Act of 1890 and the slum clearance Acts of 1868 and 1875 were established to provide quality housing. As the construction of new houses for workers began, several architectural designs developed in order to produce engaging and beautiful buildings and improve the overall appearance of the urban centres. According to Conrad s (25), in organic architecture, the building, its furnishings and its setting and environment are considered as one thing. Furnishings such as tables, chairs, musical instruments and cabinets are said to be part of the buildings, as well. However, the heating, lighting or ventilation can be incorporated together with other features in the building or excluded. Conrads (25) argues that a human dwelling place should be a complete work of art that is closely related to modern life and fit for people to live. It should include harmonious entity, which is beautiful and suitable in providing the needs of the dwellers. An example of such a building is shown below. Winslow House in Chicago (1893) Conrads (95) states it is through the new evolving techniques that people are able to discover new materials and new ways to construct objects; hence, enabling individuals to learn how to design objects and develop a new attitude towards design. This includes the living environment of vehicles and machines, limitation of certain characteristics such as colours and they should be readily accessible to all. Additionally, they should be economical in terms of space used, time, materials and money. This can be seen in Gropius office (1932) as shown below. Bauhaus argues that the necessities of life are the same for most people. Additionally, he states that the home and its furnishings are mass consumer goods and their design is as a result of reason other than a matter of passion. Machines that produce such products use steam and electricity in order to help people from working manually when producing their daily needs as well as to provide them with cheap products that are better than those produced by hand. According to Conrads (96), Bauhaus workshops are laboratories that are suitable for production of mass products, which are well developed and can be improved with time. An illustration of Bauhaus workshop is as shown below. According to Conrads (96), the Bauhaus represents that the contrast between the industry and the crafts is less marked by the difference in tools used than by the division of labor in the industry, as well as the quality of the work in the crafts. The past crafts have changed, and new ones are expected to emerge in a new and productive industry in which they will carry out work for industrial production. The experiments in the laboratory workshops will produce models and prototypes that will be implemented in the factories to produce quality work. Moreover, the products that have been produced in the Bauhaus are also been produced in other firms with are closely related to Bauhaus. Some of the architectural features that describe a new building according to Le Corbusier houses designs include the supports, the roof gardens, the free designing of the plan, the free design of the facade and the horizontal window. For the supports, it is necessary to distinguish between the non-supporting and the supporting elements,

Financial Performance Assignment Example | Topics and Well Written Essays - 3000 words

Financial Performance - Assignment Example It is an important section of the companies' annual report, which contains acknowledgement from the external auditors that the company's accounts and financial statements reported present a true and fair view of the company's affairs. This satisfies the government about the accuracy of financial information presented in the Tesco and Sainsbury's financial statements. This section represents the financial performance of both the companies for the current year and also the previous year. This section helps the investors, lenders, employees and general public to compare the companies' income and expense condition of the current year against the previous year and predict the future of the company. This reveals the companies' financial position for the current year-end. It shows the companies' asset and equity position for the current and previous year. This contains the information on companies' liquidity, solvency, efficiency and investment prospects. This is helpful for investors, lenders, suppliers, employees, customers and general public. This section reveals the companies' position in terms of availability of cash and shows the cash inflow and outflow for the current and previous years. Again, this section is very important for various stakeholders of the company. The Operating and Financial Review (OFR) statement of both the companie... This section contains information necessary to read between the lines of financial statements. This section is very important for a true and complete analysis of the companies' financial statements. THE OPERATING AND FINANCIAL REVIEW (OFR) STATEMENT The Operating and Financial Review (OFR) statement of both the companies show the summary of the companies' financial statements, their financial performance, their segmented financial results and the profitability of the companies reflecting their financial statements. Both the companies have provided a thorough analysis of their company's major operations and results obtained from these operations. The statement also emphasises the major risks faced by the company, which enables a reader to get an insight of the companies' present condition and evaluate any future risks. TESCO PLC-- RATIO ANALYSIS The financial performance and position of Tesco Plc can be assessed with the help of ratio analysis for the last three years. This analysis is broken down into sections so as to be helpful for all the groups interested in the financial performance of the company i.e., the management, the investors, the lenders, the analysts etc. PERFORMANCE The performance of Tesco Plc over the last three years can be assessed by the following ratio: Return on Investment (ROI) 2005 2004 2003 14.95% 14.04% 13.85% The Return on Investment ratio is used to analyse a company's position in terms of the return or profit it gains on the funds invested. It shows the effectiveness and performance of the company's management to obtain more returns on the company's investment. Tesco Ltd's Return on Investment ratio has almost been stable over the last three years, showing that the company's management has been utilising its

The Effectiveness of Relaxtion Therapy in the Reduction of Anxiety Article

The Effectiveness of Relaxtion Therapy in the Reduction of Anxiety Related Symptoms (A Case Study) - Article Example Results were gathered using the application of different relaxation techniques for twelve months and administration of both the scales again after the end of the therapy. There was a significant decrease in the level of anxiety and depression. Heading: The Effectiveness of Relaxation Therapy in the Reduction of Anxiety Related Symptoms (A Case Study) Authors: Uzma Ali and Shazia Hassan Journal: International Journal of Psychological Studies Year: 2010 Location: http://ezproxy.hacc.edu/login?url=http://search.proquest.com.ezproxy.hacc.edu/docview/840751128?accountid=11302 Hypotheses: There is a significant positive impact of relaxation therapy in reduction of anxiety related symptoms. Method: This study used the case study approach. A 20-year-old girl suffering from fatigue and pain was selected as a subject. Identifying Information, family history, medical history, personal and occupation history along with information regarding sleep, orientation, behavior, and affect was gathered u sing Intake Card and Case History Sheet. IPAT Anxiety Scale (King, Scheier & Cattell, 1976) and IPAT Depression Scale (Krug & Laughlin, 1976) were administered to gauge the level of anxiety and depression, respectively, prior to the therapy. Afterwards, 15 sessions were conducted, out of which 12 sessions were dedicated to the application of relaxation therapy.

Breast Cancer Research Paper Example | Topics and Well Written Essays - 500 words

Breast Cancer - Research Paper Example Morphologically breast cancer is divided into two basic types depending on the anatomic site affected by the tumor cells; Ductal and lobular carcinoma. As the name indicates, the ductal type originates form the ducts or lactiferous tubes of the breast while the lobular carcinoma originates from the stroma or lobules of the breast responsible for lactation. On the basis of penetration through the limiting basement membrane, the breast cancers are divided into two basic subtypes; Invasive and non-invasive. The non-invasive types are classified into two types which include ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS) on the basis that tumor cells have not invaded the adjacent tissues (Chen 2010; McPherson et al 2000). The causes or risk factors of breast cancer can be divided into two major categories which are modifiable and non-modifiable. Non-modifiable risk factors are age, geographical variations, family history, menstrual history, associated familial syndromes and genetics. The increase in the age of a woman is also a risk factor for breast cancer. Women who fall between the age group of 40-50 are at the highest risk of getting this malignancy. Moreover, if family history shows positive cases especially in first degree relatives like mother, daughter or sister, then it also increases the chances to develop breast cancer. Breast cancer has been associated with genes which include BRCA1 and BRCA2 which have been linked to the causation of familial breast cancer. These are genes located on chromosome 17 which undergo autosomal dominant mutations and are responsible for 5% to 10% inherited cases of breast cancer. The sporadic breast cancer is considered to be caused by mutations in several tumo r suppressor and oncogenes like p53, c-myc, c-myb and bcl-2. Moreover, the over expression of HER2/neu also has a very strong relation to breast cancer. The age of menarche and menopause also plays an important role in the incidence of breast

Dakota men and the Pictographic Style Essay Example | Topics and Well Written Essays - 500 words

Dakota men and the Pictographic Style - Essay Example Dakota men had painted in what is called the pictographic style for centuries, usually to record tribal histories and personal exploits. The arrangement of these points was usually according to one of a few traditional designs, one of the most popular being the Tahokmu or spider-web design. The Museum’s collection of over 6000 objects consists of paintings, drawings, prints, photographs, textiles, sculptures, and Native American artifacts and art. The objects are a cultural reflection of the work of local, national, and international artists. The emphasis however, is on the work of artists from South Dakota and the surrounding region. Dakota men had painted in what is called the pictographic style for centuries, usually to record tribal histories and personal exploits. Howe learned that Dakota artists frequently contemplated the painting surface, often for days, until and arrangement of â€Å"aesthetic points† appeared, the intersections for all lines subsequently drawn or painted in making the picture. The arrangement of these points was usually according to one of a few traditional designs, one of the most popular being the Tahokmu or spider-web design. (South Dakota Art Museum. Oscar Howe. Oscar Howe Biography. South Dakota State University).

Evaluative Review Assignment Essay Example | Topics and Well Written Essays - 750 words

Evaluative Review Assignment - Essay Example Recommendations Organize with parents to address ways to identify if their child has destructive tendencies According to Jimerson and Furlong (2006), this is a better way of dealing with a student’s aggressive behavior. Parents are better positioned to evaluate their children mannerisms and take the necessary measures. Education about the signs of this behavior will assist parents in taming their misdemeanor. Application of this will streamline a student’s morals and methods of associating with others. Parents are occasionally determinants of a child’s character development. Therefore, their children are more likely to take heed of their advice. Metal Detectors According to Jimerson and Furlong (2006), the employment of a metal detector in searches is highly advisable. It is in the interest of all students that this practice is approved. Some students who have malicious intentions towards the teaching staff or fellow comrades are capable of carrying weapons to th is effect. However, persons who do it should not abuse this activity. This measure will definitely discourage students from transporting harmful objects to schools. Metal detectors have proven effective in sectors such as airports and highly guarded government institutions. It has reduced potential threats such as terrorism and smuggling. Follow the law The law is a guideline of limitations and freedoms we should exercise. Teachers are to exercise acceptable disciplining methods of students who have behavioral cases (Conoley and Goldstein 2004). Disciplinary punishment should be implemented to the extent instructed by law. Excessive use of force in disciplinary cases often initiates some violent and rude behaviors from students. This can have extensive consequences as the student can resort to unconventional ways of coming even. Conoley also suggests that statistically, in many cases students win legal cases concerning discipline and the institution suffers the embarrassment. Teache rs should be more cautious on this issue. Training School Staff The schools staff both administrative and non-administrative is instrumental in ensuring proper safety precautions are adhered to (Conoley and Goldstein, 2004).Violence is impartial and occurs randomly in view of the supposition that it is intricate to determine a person’s intentions. Students have developed clever ways to conceal their intentions. Therefore, the staff including teachers, train guards and drivers should focus on violence prevention. The staff should be trained to take steps promptly when violence occurs. This will help them mitigate the adverse effects that associate to this vice. They should also be trained to detect destructive behavior in the initial stages thus enabling them prevents unavoidable that was to happen. According to Daniels and Bradley (2011), ignorance of the staff of growing tensions between students is what leads to the columbine High school riot. Violent incidences were ignore d based on the perpetrators social status in the institution. This allowed the popular and senior students assault their fellow junior scholars uncontrollably. The intimidated student’s collective anger led to the rampage. The staff was vindicated on their negligence of the spiteful activities that were occurring in that institution. Establishment of Good Trust relationship with Students According to Daniels and Bradley (2011), most of the students who partake in these acts have

Oscar Wilde’s The Importance of Being Earnest Essay Example for Free

Oscar Wilde’s The Importance of Being Earnest Essay 1. What does the play say about marriage? The play says many things about marriage.   One is that marriage can be quite complicated when there is deceit even if the feelings involved are genuine.   Another is that there are so many trivial things that society considers â€Å"important† that disregards the true meaning of marriage.   Another is that parental consent and money still play an important role in matrimony. 2. What is the significance of the names? The word Earnest means sincere. However, the play showed how that sincerity is downplayed by the many trivial things that society expects from individuals.    Ms. Prism’s name is also significant because it was her character that finally shed light on the true background of Jack – who later became truly Earnest. 3. Suggest some of the things that Wilde is poking fun at in this play. Wilde made fun of the way women can be so assuming of relationships as can be seen with Cecily’s account of how she and Algy became engaged and how Gwendolyn fled from her mother to go to Jack.   The author also made fun of the way society can be deceived by many aspects of a person beside his true self (e.g. names and money).   This was especially evident in the way the name Earnest became so important that Algy and Jack had wanted to be re-baptized with it. Marriage was also funny because it gave too much importance on money and family background before it considers the true person. 4. What is your favorite character and why? I loved the character of Ms. Prism because at first she seemed to be only a minor character but in the end, the story actually centered on her misgivings.

Shyness refers to anxiety Essay Example for Free

Shyness refers to anxiety Essay I believe millions of people are suffering from shyness. â€Å"Shyness refers to anxiety and excessive caution in interpersonal relationship† (Corey 2009). We have learnt that shyness is actually social anxiety in which the individual tries to avoid eye contact with people, making it difficult to communicate effectively. I am an outgoing person when interacting with my family or close friends, however, when it comes to someone I don’t really know, I am very shy. However, the anxiety and shyness disappears little by little after I have gotten along with such person, I also have a fear of public speaking especially if I am in the center of attention. I consider myself as being too shy, so I am always willing to get over my shyness and trying to build confidence. Since I am a student, I have a lot of opportunities to interact with other people. I put myself in situations where I forced to make contact with people, like speech class and engaging in social activities, even though I find doing these stressful and uncomfortable. However, these didn’t work well and my shyness actually gets worse. After all attempts to get over my shyness fails, I have no choice than to live with it. However, Prof. Occhiato mentioned in class that shyness is the same as selfishness, I had to face this trait of mine again since I concur with what the professor said Before getting into the theme of the book I chose, I would like to talk on how my shyness/ fear of public speaking developed. When I was in elementary school in Switzerland, I was prudent but energetic and outgoing person. During lectures, I usually ask question without thinking of embarrassment that might result from my inquisitive character. Even though I was only seven or eight years old, I knew that I need to perform and produce good results. I received my teacher’s and peer’s praise for my good work and I was encouraged to keep the flag flying. I became industrious and tried to accomplish my task successfully, I also wanted to gain recognition for creating new things. In general, children’s efforts to master their school work help them to grow and form a positive self-concept a sense of who they really are. However, after I moved to Asia, I changed a lot, although in negative ways. In Korea, it is considered rude for a student to ask questions during class, such act is regarded as interruption to the flow of the lesson, whereas, in Swiss classrooms children are encouraged to ask questions. It is all about culture so that moving to a new school abroad means I have adjusting to the new culture. However, since I am used to taking classes either in the United States or in Europe, I felt uncomfortable with being in this environment. Older children may find it hard to adapt, both to a new culture and a new language, but since I was still ten years old, I settled in quickly. Once I get used to being in Korean culture, I started to feel embarrassed asking questions in the class, but I also felt a sense of shame that I am different. This feeling became worse after moving to Japan. Even though I have lived in abroad for most of my life, I consider myself as a very Japanese since my parents taught me a lot of things about Japanese culture, morals, injunctions and many other things. One day, my teacher asked me the meaning of famous Japanese proverb and I was floored by that question. She said â€Å"This question is actually quite easy and a kind of common sense. † And she pointed at me and said â€Å"However, even you are not able to answer the question; this is understandable to me since you are from the different culture. † My face was flushed with shame that I couldn’t answer the easiest and a kind of common sense question. At that moment, I felt I had been stupid all the while and that I am and failure in everything. However, anytime I think of it now, I didn’t have to be panic any longer since I know I wasn’t old enough to think logically and subjectively during those periods. As a result of the embracement that I experienced in my childhood, those negative feelings are firmly planted in my mind. This is the reason why I develop extreme shyness/ fear of public speaking. Well, I would like to go into the main theme which is about the book I chose. The author, Leil Lowndes was able to produce a magnificent book that can counter shyness and workout confidence among people. The book â€Å"Goodbye to Shy: 85 Shy Busters†, helps readers to face everyday lives with full confidence and brighter perspectives. It determines the source of shyness, the effects of being shy and introduces possible remedies to achieve a shy free life. Each chapter focuses on a particular step that shy individual can use. Then at the end of each chapter, it is summarize the discussion in a little gray box called a `Shy Buster. ` The first part of the book tackles proper way of dealing with people nowadays even in the presence of shyness in one’s personality. The goal of attaining a shy free life is never an easy task; it will take time to gain a complete confidence. The other day, I told people that I am shy, however, they didn’t even believe me. †Oh I don’t think you are, since you are talking to me. † They don’t know how much I am suffering inside. Since then, I have been thinking it is not a proper idea telling people that I am shy. Surprisingly, the author recommends telling other people that you are shy (Lowndes 3). In most situations, shy people try to hide their condition to avoid being humiliated. People will only laugh at an individual whoadmitted that he/she is shy and may say things like â€Å"Oh, not you! You’ve got to be kidding† (Lowndes 3). According to the book, shy people are classified to three different types: born shy, situational shy and traumatic experience shy. The first type of shy people is a natural shy from birth. The sensitivity of born shy people is extremely high and they try to avoid socialization as much as possible. The second type of shy is usually affected by certain events that expose them to others. One great example of situational shyness is during class discussions. Lastly, traumatic experiences make someone shy because of too much humiliation or failure. This can also be viewed as people who are usually well taken care of right from their childhood days. It produces traumatic shyness because they will keep on depending and talking to close family members rather than exposing themselves to people that they barely know. In my case, my shyness comes under either the second or the third one. Once a person is already aware of the type of shyness he/she possess, it is the time for him/her to get out of the situation (Lowndes 7). There are discussions made in the book about battling with blushing, sweating and other signs of shyness (Lowndes 10). The author also encourages shy people to talk about their condition (Lowndes 12). This will make them face the tough situation that they are and step by step settle the problem with their personality (Lowndes 15). The book is indeed helpful for shy people because they will be aware of the things that they need to do to counter shyness. It is one way of showing readers how life will be more meaningful with the right confidence and sociable personality. Another good part of the book is the second chapter which discusses different point of views of people about the shy person. Either the shy person says that he/she is shy or not, other people can notice it even without even telling them (Lowndes 21). The author also based her findings on studies that prove how shy people view themselves worse than what they really are. The â€Å"mud colored glasses† hinders people from growing up and showing off their proud personality (Lowndes 25). Shy readers will find themselves whispering â€Å"Yes that’s me! † upon encountering several discussions in the book when the discussions are really similar to their life experiences. This is a good way of making people aware of their weaknesses so that they can work it out and transform it into strengths. Reading the book serves as a self discovery for shy people. after they have already gathered pertinent information about their condition, the author then lead them to more juicy chapters that will make them finish with confidence. As mentioned before, there are shy busters’ techniques identified by the author which can be easily applied to the lives of shy people. There is a three-step game plan given by the author, so that shy people will unhook themselves from the terrible condition (Lowndes 43). It includes chapters about hooking hide and seek, shaving off the years of suffering from shyness and how to warm up one’s wacky confidence (Lowndes 45- 58). For beginners, there are shy buster techniques that will improve shyness little by little. From simple eye to eye contact to giving out a perfect smile and eliminating snob mannerism were discussed in the chapter titled† The seven best beginner’s shy busters† (Lowndes 61). Rare shy busters were also given by the author that will allow shy people contemplate on things that made them shy. It will also encourage them that the only people who can help them from recovering are their own selves. Big time sufferers were also tackled in the book, but eventually there is still a hope for them to recover. Crowd behaviors were also cited in the book and how shyness is available on almost every place like parties and other places. Shy people often treat crowded people as hell but the book will make them change this kind of orientation. The book is great for both the shy and people that are not shy, the author outlines many aspects of personal relations that will be beneficial to everyone. In a humorous way, she sites real-life examples (many of her own) that point out where a shy person may have shortcomings. She then explains why they may behave the way they do and offers alternatives to overcome the shy behavior. Also, it manifests the author’s willingness to help out and change the lifestyle of shy people. Fearless conversation will be made available for shy people after reading this book. Family and sexual relationship problem which are affected by shyness will also be resolved through several shy busters given in the book. Getting to know one’s self is the best way to get out of a shy life. Loving yourself is the main message of this book because it assures shy people that life is a priceless gift especially for those who extends themselves to others. Again, each shy buster introduced by the author allows shy people to practice and apply it in their lives. Every accomplished shy buster technique leads them closer to graduation day. By the end of the book, shy people will find themselves successful and free from painful shyness experiences. It will give shy people the chance to look attractive and feel more comfortable whenever other people are around them. In conclusion, this is an excellent step by step guide to getting over our shyness. I found many of the author’s suggestions and words very helpful. Honestly, I initially resist buying this book because the cover is so local. It looks like some 1980s book that I usually find in my mothers closet. But then, I bought it anyway. I am glad I did. It is quite funny and entertaining to read. As I read the book, it eases away from its clinical insights and moves more towards the practical. And the practical offers tips that I think would help most people regardless of how shy they are. (Chances are good that most people have some shyness in them based on how the author defines `shyness. ) The exercises help to give me some confidence and it really helps me realize that people are not as critical as we think they are. Besides, she opened my eyes to a lot of things. For example, I’ve heard before that people considered me to an arrogant person for avoiding them, and I was just shy. I had no idea that they did not understand it. I always thought that there is no hope for my shyness. Reading this book doesn’t mean I can get over my shyness completely. I know I have to put theories into practice. But at least, this book gives me some hope. I want to thank Prof. Occhiato for mentioning that â€Å"shyness = selfishness. † It could be a life changing book that will reshape and reconstruct the lives of many shy people.

Underwater Acoustic Sensor Network (UASN)

Underwater Acoustic Sensor Network (UASN) CHAPTER1: Introduction Most of the earth surface is composed of water including fresh water from river, lakes etc and salt water from the sea. There are still many un-explored areas for such places. This needs significant research efforts and good communication systems. Wireless sensor network in aqueous medium has the ability to explore the underwater environment in details. For all applications of underwater, a good communication system as well as an effective routing protocol is needed. This will enable the underwater devices to communicate precisely. Underwater propagation speed varies with temperature, salinity and depth. By varying the underwater propagation speed at different depth, two scenarios can be achieved accurately namely: shallow and deep water. Shallow water consists of depth less than 200m and cylinder spreading. Deep water consists of depth greater or equal to 200 m and spherical spreading. In both shallow and deep water, different ambient noise and different spreading factor is applied. CHAPTER 2: Study of Underwater Acoustic Sensor Network (UASN) Application of UASN Wireless sensor network in aqueous medium also known as underwater sensor network has enabled a broad range of applications including: Environmental Monitoring Underwater sensor network can be used to monitor pollution like chemical, biological such as tracking of fish or micro-organisms, nuclear and oil leakage pollutions in bays, lakes or rivers [1]. Underwater sensor network can also be used to improve weather forecast, detect climate change, predict the effect of human activities on marine ecosystems, ocean currents and temperature change e.g. the global warming effect to ocean. Under Ocean Exploration Exploring minerals, oilfields or reservoir, determine routes for laying undersea cables and exploration valuable minerals can be done with such underwater sensor network. Disaster Prevention Sensor network that measure seismic activity from remote locations can provide tsunami warning to coastal areas, or study the effects of submarine earthquakes (seaquakes) [2] Equipment Monitoring Long-term equipment monitoring may be done with pre-installed infrastructure. Short-term equipment monitoring shares many requirements of long-term seismic monitoring, including the need for wireless (acoustic) communication, automatic configuration into a multihop network, localization (and hence time synchronization), and energy efficient operation Mine Reconnaissance By using acoustic sensors and optical sensors together, mine detection can be accomplished quickly and effectively. Assisted Monitoring Sensor can be used to discover danger on the seabed, locate dangerous rocks or shoals in shallow waters, mooring position, submerged wrecks and to perform bathymetry profiling. Information collection The main goal of communication network is the exchange of information inside the network and outside the network via a gateway or switch center. This application is used to share information among nodes and autonomous underwater vehicles. Characteristic of UASN Underwater Acoustic Networks (UANs), including but not limited to, Underwater Acoustic Sensor Networks (UASNs) and Autonomous Underwater Vehicle Networks (AUVNs) , are defined as networks composed of more than two nodes, using acoustic signals to communicate, for the purpose of underwater applications. UASNs and AUVNs are two important kinds of UANs. The former is composed of many sensor nodes, mostly for a monitoring purpose. The nodes are usually without or with limited capacity to move. The latter is composed of autonomous or unmanned vehicles with high mobility, deployed for applications that need mobility, e.g., exploration. An UAN can be an UASN, or an AUVN, or a combination of both. Acoustic communications, on the other hands, is defined as communication methods from one point to another by using acoustic signals. Network structure is not formed in acoustic point-to-point communications. Sound travels best through the water in comparison with electromagnetic waves and optical signals. Acoustic signal is sound signal waveform, usually produced by sonar for underwater applications. Acoustic signal processing extracts information from acoustic signals in the presence of noise and uncertainty. Underwater acoustic communications are mainly influenced by path loss, noise, multi-path, Doppler spread, and high and variable propagation delay. All these factors determine the temporal and spatial variability of the acoustic channel, and make the available bandwidth of the Underwater Acoustic channel (UW-A) limited and dramatically dependent on both range and frequency. Long-range systems that operate over several tens of kilometers may have a bandwidth of only a few kHz, while a short-range system operating over several tens of meters may have more than a hundred kHz bandwidth. These factors lead to low bit rate. Underwater acoustic communication links can be classified according to their range as very long, long, medium, short, and very short links. Acoustic links are also roughly classified as vertical and horizontal, according to the direction of the sound ray. Their propagation characteristics differ consistently, especially with respect to time dispersion, multi-path spreads, and delay variance. Acoustic signal is the only physical feasible tool that works in underwater environment. Compared with it, electromagnetic wave can only travel in water with short distance due to the high attenuation and absorption effect in underwater environment. It is found that the absorption of electromagnetic energy in sea water is about 45Ãâ€" ?f dB per kilometer, where f is frequency in Hertz; In contrast, the absorption of acoustic signal over most frequencies of interest is about three orders of magnitude lower [40]. Hereafter the factors that influence acoustic communications is analyzed in order to state the challenges posed by the underwater channels for underwater sensor networking. These include: Path loss Attenuation is mainly provoked by absorption due to conversion of acoustic energy into heat, which increases with distance and frequency. It is also caused by scattering a reverberation (on rough ocean surface and bottom), refraction, and dispersion (due to the displacement of the reflection point caused by wind on the surface). Water depth plays a key role in determining the attenuation. Geometric Spreading is the spreading of sound energy as a result of the expansion of the wavefronts. It increases with the propagation distance and is independent of frequency. There are two common kinds of geometric spreading: spherical (omni-directional point source), and cylindrical (horizontal radiation only). Noise Man made noise is mainly caused by machinery noise (pumps, reduction gears, power plants, etc.), and shipping activity (hull fouling, animal life on hull, cavitations), especially in areas encumbered with heavy vessel traffic. Ambient Noise is related to hydrodynamics (movement of water including tides, current, storms, wind, rain, etc.), seismic and biological phenomena. Multi-path Multi-path propagation may be responsible for severe degradation of the acoustic communication signal, since it generates Inter-Symbol Interference (ISI). The multi-path geometry depends on the link configuration. Vertical channels are characterized by little time dispersion, whereas horizontal channels may have extremely long multi-path spreads. The extent of the spreading is a strong function of depth and the distance between transmitter and receiver. High delay and delay variance The propagation speed in the UW-A channel is five orders of magnitude lower than in the radio channel. This large propagation delay (0.67 s/km) can reduce the throughput of the system considerably. The very high delay variance is even more harmful for efficient protocol design, as it prevents from accurately estimating the round trip time (RTT), which is the key parameter for many common communication protocols. Doppler spread The Doppler frequency spread can be significant in UW-A channels, causing degradation in the performance of digital communications: transmissions at a high data rate because many adjacent symbols to interfere at the receiver, requiring sophisticated signal processing to deal with the generated ISI. The Doppler spreading generates: a simple frequency translation, which is relatively easy for a receiver to compensate for a continuous spreading of frequencies, which constitutes a non-shifted signal, which is more difficult for a receiver to compensate for. If a channel has a Doppler spread with bandwidth B and a signal has symbol duration T, then there are approximately BT uncorrelated samples of its complex envelope. When BT is much less than unity, the channel is said to be under spread and the effects of the Doppler fading can be ignored, while, if greater than unity, it is overspread. Most of the described factors are caused by the chemical-physical properties of the water medium such as temperature, salinity and density, and by their spatio-temporal variations. These variations, together with the wave guide nature of the channel, because the acoustic channel to be temporally and spatially variable. In particular, the horizontal channel is by far more rapidly varying than the vertical channel, in both deep and shallow water. CHAPTER 3: Network Architecture Underwater sensor nodes: The underwater sensor nodes are deployed on the sea floor anchored to the ocean bottom [32]. The sensors are equipped with floating buoys to push the nodes upwards, thus they are relatively stationary nodes [3]. Using acoustic links, they relay data to underwater sink directly or via multi-hop path. Underwater sink nodes: Underwater sink nodes take charge of collecting data of underwater sensors deployed on the ocean bottom and then send to the surface sink node. They may be equipped with vertical and horizontal acoustic transducers. The horizontal transceiver is used to collect the sensors data and the vertical transceiver provides transmitting link between underwater sink and the surface sink node. Surface sink node: Surface sink node is attached on a floating buoy with satellite, radio frequency (RF) or cell phone technology to transmit data to shore in real time. 2D Model A reference architecture for two-dimensional underwater networks is shown in Figure. 1. A group of sensor nodes are anchored to the deep of the ocean. Underwater sensor nodes are interconnected to one or more underwater gateways by means of wireless acoustic links. Underwater-gateways are network devices in charge of relaying data from the ocean bottom network to a surface station. To achieve this objective, they are equipped with two acoustic transceivers, namely a vertical and a horizontal transceiver. The horizontal transceiver is used by the underwater-gateway to communicate with the sensor nodes in order to: send commands and configuration data to the sensors (underwater -gateway to sensors); collect monitored data (sensors to underwater -gateway). The vertical link is used by the underwater -gateways to relay data to a surface station. In deep water applications, vertical transceivers must be long range transceivers. The surface station is equipped with an acoustic transceiver that is able to handle multiple parallel communications with the deployed underwater -gateways. It is also endowed with a long range RF and/or satellite transmitter to communicate with the onshore sink (os-sink) and/or to a surface sink (s-sink). In shallow water, bottom-deployed sensors/modems may directly communicate with the surface buoy, with no specialized bottom node (underwater -gateway). 3D Model Three-dimensional underwater networks are used to detect and observe phenomena that cannot be adequately observed by means of ocean bottom sensor nodes, i.e., to perform cooperative sampling of the 3D ocean environment. In three-dimensional underwater networks, sensor nodes float at different depths to observe a phenomenon. In this architecture, given in Figure 2, each sensor is anchored to the ocean bottom and equipped with a floating buoy that can be inflated by a pump. The buoy pushes the sensor towards the ocean surface. The depth of the sensor can then be regulated by adjusting the length of the wire that connects the sensor to the anchor, by means of an electronically controlled engine that resides on the sensor. Sensing and communication coverage in a 3D environment are rigorously investigated in [8]. The diameter, minimum and maximum degree of the reachability graph that describes the network are derived as a function of the communication range, while different degrees of cov erage for the 3D environment are characterized as a function of the sensing range. 3D Model with AUV The above figure represents the third type of network architecture which consist of sensor nodes and Autonomous Underwater Vehicles (AUV) which act as mobile sensor nodes for ocean monitoring, underwater resource study, etc. CHAPTER 4: Differences between underwater and terrestrial Sensor Network An underwater acoustic channel is different from a ground-based radio channel from many aspects, including: Bandwidth is extremely limited. The attenuation of acoustic signal increases with frequency and range [6] [10]. Consequently, the feasible band is extremely small. For example, a short range system operating over several tens of meters may have available bandwidth of a hundred kHz; a medium-range system operating over several kilometers has a bandwidth on the order of ten kHz; and a long-range system operating over several tens of kilometers is limited to only a few kHz of bandwidth [11]. Propagation delay is long. The transmission speed of acoustic signals in salty water is around 1500 meter/s [22], which is a difference of five orders of magnitude lower than the speed of electromagnetic wave in free space. Correspondently, propagation delay in an underwater channel becomes significant. This is one of the essential characteristics of underwater channels and has profound implications on localization and time synchronization. The channel impulse response is not only spatially varied but also temporarily varied. The channel characteristics vary with time and highly depend on the location of the transmitter and receiver. The fluctuation nature of the channel causes the received signals easily distorted. There are two types of propagation paths: macro-multipaths, which are the deterministic propagation paths; and micro-multipath, which is a random signal fluctuation. The macro-multipaths are caused by both reflection at the boundaries (bottom, surface and any object in the water) and bending. Inter- Symbol Interference (ISI) thus occurs. Compared with the spread of its ground-based counterpart, which is on the order of several symbol intervals, ISI spreading in an underwater acoustic channel is several tens or hundred of symbol intervals for moderate to high data rate in the horizontal channel. Micro-multipath fluctuations are mainly caused by surface wave, which contributes the most to the time variability of shallow water channel. In deep water, internal waves impact the single-path random fluctuations [12][13]. Probability of bit error is much higher and temporary loss of connectivity (shadow zone) sometimes occurs, due to the extreme characteristics of the channel. Cost. While terrestrial sensor nodes are expected to become increasingly inexpensive, underwater sensors are expensive devices. This is especially due to the more complex underwater transceivers and to the hardware protection needed in the extreme underwater environment. Also, because of the low economy of scale caused by a small relative number of suppliers, underwater sensors are characterized by high cost. Deployment. While terrestrial sensor networks are densely deployed, in underwater, the deployment is generally more sparse. Power. The power needed for acoustic underwater communications is higher than in terrestrial radio communications because of the different physical layer technology (acoustic vs. RF waves), the higher distances, and more complex signal processing techniques implemented at the receivers to compensate for the impairments of the channel. Memory. While terrestrial sensor nodes have very limited storage capacity, underwater-sensors may need to be able to do some data caching as the underwater channel may be intermittent. Spatial Correlation. While the readings from terrestrial sensors are often correlated, this is more unlikely to happen in underwater networks due to the higher distance among sensors. CHAPTER 5: Layered of UASN The underwater architecture network consists of five layers, application, transport, network, data link and physical layer as shown in the figure below. As typical underwater systems have limited processing capability, the protocol has been kept as simple as possible without significantly compromising performance. The underwater sensor network specifications currently do not include any recommendations for authentication and encryption. These may be easily implemented at the application layer or via a spreading scheme at the physical layer. Each layer is described by a SAPI. The SAPI is defined in terms of messages being passed to and from the layer. The clients (usually higher layers) of a layer invoke the layer via a request (REQ). The layer responds to each REQ by a response (RSP). Errors are reported via an ERR RSP with error codes. If the layer needs to send unsolicited messages to the client, it does so via a notification (NTF). A layer communicates logically with its peer layer via protocol data units (PDU). As the peer-to-peer communication is symmetric, a layer may send a REQ PDU to its peer layer at any time. It would optionally respond to such a PDU with a RSP PDU. This is logically depicted in Figure below It may be desirable in some cases, that non-neighboring layers communicate with each other to achieve cross-layer optimization. This may be implemented by allowing REQ and RSP PDUs between any two layers in the protocol stack. The underwater sensor network specifications define detailed message structures for all SAPI messages. These message structures include message identifiers, data formats to be used, parameters and their possible values Physical layer The physical layer provides framing, modulation and error correction capability (via FEC). It provides primitives for sending and receiving packets. It may also provide additional functionality such as parameter settings, parameter recommendation, carrier sensing, etc. At first underwater channel development was based on non-coherent frequency shift keying (FSK) modulation, since it relies on energy detection. Thus, it does not require phase tracking, which is a very difficult task mainly because of the Doppler-spread in the underwater acoustic channel. Although non-coherent modulation schemes are characterized by high power efficiency, their low bandwidth efficiency makes them unsuitable for high data rate multiuser networks. Hence, coherent modulation techniques have been developed for long-range, high-throughput systems. In the last years, fully coherent modulation techniques, such as phase shift keying (PSK) and quadrature amplitude modulation (QAM), have become practical due to the availability of powerful digital processing. Channel equalization techniques are exploited to leverage the effect of the inter-symbol interference (ISI), instead of trying to avoid or suppress it. Decision-feedback equalizers (DFEs) track the complex, relatively slowly varying channel response and thus provide high throughput when the channel is slowly varying. Conversely, when the channel varies faster, it is necessary to combine the DFE with a Phase Locked Loop (PLL) [9], which estimates and compensates for the phase offset in a rapid, stable manner. The use of decision feedback equalization and phase-locked loops is driven by the complexity and time variability of ocean channel impulse responses. Differential phase shift keying (DPSK) serves as an intermediate solution between incoherent and fully coherent systems in terms of bandwidth efficiency. DPSK encodes information relative to the previous symbol rather than to an arbitrary fixed reference in the signal phase and may be referred to as a partially coherent modulation. While this strategy substantially alleviates carrier phase-tracking requirements, the penalty is an increased error probability over PSK at an equivalent data rate. Another promising solution for underwater communications is the orthogonal frequency division multiplexing (OFDM) spread spectrum technique, which is particularly efficient when noise is spread over a large portion of the available bandwidth. OFDM is frequently referred to as multicarrier modulation because it transmits signals over multiple sub-carriers simultaneously. In particular, sub-carriers that experience higher SNR, are allotted with a higher number of bits, whereas less bits are allotted to sub-carriers experiencing attenuation, according to the concept of bit loading, which requires channel estimation. Since the symbol duration for each individual carrier increases, OFDM systems perform robustly in severe multi-path environments, and achieve a high spectral efficiency. Many of the techniques discussed above require underwater channel estimation, which can be achieved by means of probe packets [17]. An accurate estimate of the channel can be obtained with a high probing rate and/or with a large probe packet size, which however result in high overhead, and in the consequent drain of channel capacity and energy. Data link layer (MAC layer) The data link layer provides single hop data transmission capability; it will not be able to transmit a packet successfully if the destination node is not directly accessible from the source node. It may include some degree of reliability. It may also provide error detection capability (e.g. CRC check). In case of a shared medium, the data link layer must include the medium access control (MAC) sub-layer. Frequency division multiple access (FDMA) is not suitable for underwater sensor network due to the narrow bandwidth in underwater acoustic channels and the vulnerability of limited band systems to fading and multipath. Time division multiple access (TDMA) shows limited bandwidth efficiency because of the long time guards required in the underwater acoustic channel. In fact, long time guards must be designed to account for the large propagation delay and delay variance of the underwater channel in order to minimize packet collisions from adjacent time slots. Moreover, the variable delay makes it very challenging to realize a precise synchronization, with a common timing reference, which is required for TDMA. Carrier sense multiple access (CSMA) prevents collisions with the ongoing transmission at the transmitter side. To prevent collisions at the receiver side, however, it is necessary to add a guard time between transmissions dimensioned according to the maximum propagation delay in the network. This makes the protocol dramatically inefficient for underwater acoustic sensor network. The use of contention-based techniques that rely on handshaking mechanisms such as RTS/ CTS in shared medium access is impractical in underwater, for the following reasons: large delays in the propagation of RTS/CTS control packets lead to low throughput; due to the high propagation delay of underwater acoustic channels, when carrier sense is used, as in 802.11, it is more likely that the channel be sensed idle while a transmission is ongoing, since the signal may not have reached the receiver yet; the high variability of delay in handshaking packets makes it impractical to predict the start and finish time of the transmissions of other stations. Thus, collisions are highly likely to occur. Code division multiple access (CDMA) is quite robust to frequency selective fading caused by underwater multi-paths, since it distinguishes simultaneous signals transmitted by multiple devices by means of pseudo-noise codes that are used for spreading the user signal over the entire available band. CDMA allows reducing the number of packet retransmissions, which results in decreased battery consumption and increased network throughput. In conclusion, although the high delay spread which characterizes the horizontal link in underwater channels makes it difficult to maintain synchronization among the stations, especially when orthogonal code techniques are used [17], CDMA is a promising multiple access technique for underwater acoustic networks. This is particularly true in shallow water, where multi-paths and Doppler- spreading plays a key role in the communication performance. Network layer (Routing) The network layer is in charge of determining the path between a source (the sensor that samples a physical phenomenon) and a destination node (usually the surface station). In general, while many impairments of the underwater acoustic channel are adequately addressed at the physical and data link layers, some other characteristics, such as the extremely long propagation delays, are better addressed at the network layer. Basically, there are two methods of routing. The first one is virtual circuit routing and the second one is packet-switch routing. In virtual circuit routing, the networks use virtual circuits to decide on the path at the beginning of the network operation. Virtual-circuit-switch routing protocols can be a better choice for underwater acoustic networks. The reasons are: Underwater acoustic networks are typical asymmetric instead of symmetric. However, packet switched routing protocols are proposed for symmetric network architecture; Virtual-circuit-switch routing protocols work robust against link failure, which is critical in underwater environment; and Virtual-circuit-switch routing protocols have less signal overhead and low latency, which are needed for underwater acoustic channel environment. However, virtual-circuit-switch routing protocols usually lack of flexibility. In packet-switch routing, every node that is part of the transmission makes its own routing decision, i.e., decides its next hop to relay the packet. Packet-switch routing can be further classified into Proactive routing, Reactive and geographical routing protocols. Most routing protocols for ground-based wireless networks are packet-switch based. Proactive routing protocols attempt to minimize the message latency by maintaining up-to-date routing information at all times from each node to any other node. It broadcasts control packets that contain routing table information. Typical protocols include Destination Sequence Distance Vector (DSDV) [28] and Temporally Ordered Routing Algorithm (TORA). However, proactive routing protocols provoke a large signaling overhead to establish routes for the first time and each time the network topology changes. It may not be a good fit in underwater environment due to the high probability of link failure and extremely limited bandwidth there. Reactive routing protocols only initiate a route discovery process upon request. Correspondently, each node does not need to maintain a sizable look-up table for routing. This kind of routing protocols is more suitable for dynamic environment like ad hoc wireless networks. Typical protocol examples are Ad hoc On-demand Distance Vector (AODV) [23], and Dynamic Source Routing (DSR) [27]. The shortage of reactive routing protocols is its high latency to establish routing. Similar to its proactive counterpart, flooding of control packets to establish paths is needed, which brings significant signal overhead. The high latency could become much deteriorated in underwater environment because of the much slower propagation speed of acoustic signal compared with the radio wave in the air. Geographic routing (also called georouting or position-based routing) is a routing principle that relies on geographic position information. It is mainly proposed for wireless networks and based on the idea that the source sends a message to the geographic location of the destination instead of using the network address. Geographic routing requires that each node can determine its own location and that the source is aware of the location of the destination. With this information a message can be routed to the destination without knowledge of the network topology or a prior route discovery. Transport layer A transport layer protocol is needed in underwater sensor network not only to achieve reliable collective transport of event features, but also to perform flow control and congestion control. The primary objective is to save scarce sensor resources and increase the network efficiency. A reliable transport protocol should guarantee that the applications be able to correctly identify event features estimated by the sensor network. Congestion control is needed to prevent the network from being congested by excessive data with respect to the network capacity, while flow control is needed to avoid that network devices with limited memory are overwhelmed by data transmissions. Most existing TCP implementations are unsuited for the underwater environment, since the flow control functionality is based on a window- based mechanism that relies on an accurate esteem of the round trip time (RTT), which is twice the end-to-end delay from source to destination. Rate-based transport protocols seem also unsuited for this challenging environment. They still rely on feedback control messages sent back by the destination to dynamically adapt the transmission rate, i.e., to decrease the transmission rate when packet loss is experienced or to increase it otherwise. The high delay and delay variance can thus cause instability in the feedback control. Furthermore, due to the unreliability of the acoustic channel, it is necessary to distinguish between packet losses due to the high bit error rate of the acoustic channel, from those caused by packets being dropped from the queues of sensor nodes due to network congestion. In terrestrial, assume that congestion is the only cause for packet loss and the solution lies on decreasing the transmission rate, but in underwater sensor network if the packet loss is due to bad channel then the transmission rate should not be decreased to preserve throughput efficiency. Transport layer functionalities can be tightly integrated with data link layer functionalities in a cross-layer module. The purpose of such an integrated module is to make the information about the condition of the variable underwater channel available also at the transport layer. In fact, usually the state of the channel is known only at the physical and channel access sub-layers, while the design principle of layer separation makes this information transparent to the higher layers. This integration allows maximizing the Underwater Acoustic Sensor Network (UASN) Underwater Acoustic Sensor Network (UASN) CHAPTER1: Introduction Most of the earth surface is composed of water including fresh water from river, lakes etc and salt water from the sea. There are still many un-explored areas for such places. This needs significant research efforts and good communication systems. Wireless sensor network in aqueous medium has the ability to explore the underwater environment in details. For all applications of underwater, a good communication system as well as an effective routing protocol is needed. This will enable the underwater devices to communicate precisely. Underwater propagation speed varies with temperature, salinity and depth. By varying the underwater propagation speed at different depth, two scenarios can be achieved accurately namely: shallow and deep water. Shallow water consists of depth less than 200m and cylinder spreading. Deep water consists of depth greater or equal to 200 m and spherical spreading. In both shallow and deep water, different ambient noise and different spreading factor is applied. CHAPTER 2: Study of Underwater Acoustic Sensor Network (UASN) Application of UASN Wireless sensor network in aqueous medium also known as underwater sensor network has enabled a broad range of applications including: Environmental Monitoring Underwater sensor network can be used to monitor pollution like chemical, biological such as tracking of fish or micro-organisms, nuclear and oil leakage pollutions in bays, lakes or rivers [1]. Underwater sensor network can also be used to improve weather forecast, detect climate change, predict the effect of human activities on marine ecosystems, ocean currents and temperature change e.g. the global warming effect to ocean. Under Ocean Exploration Exploring minerals, oilfields or reservoir, determine routes for laying undersea cables and exploration valuable minerals can be done with such underwater sensor network. Disaster Prevention Sensor network that measure seismic activity from remote locations can provide tsunami warning to coastal areas, or study the effects of submarine earthquakes (seaquakes) [2] Equipment Monitoring Long-term equipment monitoring may be done with pre-installed infrastructure. Short-term equipment monitoring shares many requirements of long-term seismic monitoring, including the need for wireless (acoustic) communication, automatic configuration into a multihop network, localization (and hence time synchronization), and energy efficient operation Mine Reconnaissance By using acoustic sensors and optical sensors together, mine detection can be accomplished quickly and effectively. Assisted Monitoring Sensor can be used to discover danger on the seabed, locate dangerous rocks or shoals in shallow waters, mooring position, submerged wrecks and to perform bathymetry profiling. Information collection The main goal of communication network is the exchange of information inside the network and outside the network via a gateway or switch center. This application is used to share information among nodes and autonomous underwater vehicles. Characteristic of UASN Underwater Acoustic Networks (UANs), including but not limited to, Underwater Acoustic Sensor Networks (UASNs) and Autonomous Underwater Vehicle Networks (AUVNs) , are defined as networks composed of more than two nodes, using acoustic signals to communicate, for the purpose of underwater applications. UASNs and AUVNs are two important kinds of UANs. The former is composed of many sensor nodes, mostly for a monitoring purpose. The nodes are usually without or with limited capacity to move. The latter is composed of autonomous or unmanned vehicles with high mobility, deployed for applications that need mobility, e.g., exploration. An UAN can be an UASN, or an AUVN, or a combination of both. Acoustic communications, on the other hands, is defined as communication methods from one point to another by using acoustic signals. Network structure is not formed in acoustic point-to-point communications. Sound travels best through the water in comparison with electromagnetic waves and optical signals. Acoustic signal is sound signal waveform, usually produced by sonar for underwater applications. Acoustic signal processing extracts information from acoustic signals in the presence of noise and uncertainty. Underwater acoustic communications are mainly influenced by path loss, noise, multi-path, Doppler spread, and high and variable propagation delay. All these factors determine the temporal and spatial variability of the acoustic channel, and make the available bandwidth of the Underwater Acoustic channel (UW-A) limited and dramatically dependent on both range and frequency. Long-range systems that operate over several tens of kilometers may have a bandwidth of only a few kHz, while a short-range system operating over several tens of meters may have more than a hundred kHz bandwidth. These factors lead to low bit rate. Underwater acoustic communication links can be classified according to their range as very long, long, medium, short, and very short links. Acoustic links are also roughly classified as vertical and horizontal, according to the direction of the sound ray. Their propagation characteristics differ consistently, especially with respect to time dispersion, multi-path spreads, and delay variance. Acoustic signal is the only physical feasible tool that works in underwater environment. Compared with it, electromagnetic wave can only travel in water with short distance due to the high attenuation and absorption effect in underwater environment. It is found that the absorption of electromagnetic energy in sea water is about 45Ãâ€" ?f dB per kilometer, where f is frequency in Hertz; In contrast, the absorption of acoustic signal over most frequencies of interest is about three orders of magnitude lower [40]. Hereafter the factors that influence acoustic communications is analyzed in order to state the challenges posed by the underwater channels for underwater sensor networking. These include: Path loss Attenuation is mainly provoked by absorption due to conversion of acoustic energy into heat, which increases with distance and frequency. It is also caused by scattering a reverberation (on rough ocean surface and bottom), refraction, and dispersion (due to the displacement of the reflection point caused by wind on the surface). Water depth plays a key role in determining the attenuation. Geometric Spreading is the spreading of sound energy as a result of the expansion of the wavefronts. It increases with the propagation distance and is independent of frequency. There are two common kinds of geometric spreading: spherical (omni-directional point source), and cylindrical (horizontal radiation only). Noise Man made noise is mainly caused by machinery noise (pumps, reduction gears, power plants, etc.), and shipping activity (hull fouling, animal life on hull, cavitations), especially in areas encumbered with heavy vessel traffic. Ambient Noise is related to hydrodynamics (movement of water including tides, current, storms, wind, rain, etc.), seismic and biological phenomena. Multi-path Multi-path propagation may be responsible for severe degradation of the acoustic communication signal, since it generates Inter-Symbol Interference (ISI). The multi-path geometry depends on the link configuration. Vertical channels are characterized by little time dispersion, whereas horizontal channels may have extremely long multi-path spreads. The extent of the spreading is a strong function of depth and the distance between transmitter and receiver. High delay and delay variance The propagation speed in the UW-A channel is five orders of magnitude lower than in the radio channel. This large propagation delay (0.67 s/km) can reduce the throughput of the system considerably. The very high delay variance is even more harmful for efficient protocol design, as it prevents from accurately estimating the round trip time (RTT), which is the key parameter for many common communication protocols. Doppler spread The Doppler frequency spread can be significant in UW-A channels, causing degradation in the performance of digital communications: transmissions at a high data rate because many adjacent symbols to interfere at the receiver, requiring sophisticated signal processing to deal with the generated ISI. The Doppler spreading generates: a simple frequency translation, which is relatively easy for a receiver to compensate for a continuous spreading of frequencies, which constitutes a non-shifted signal, which is more difficult for a receiver to compensate for. If a channel has a Doppler spread with bandwidth B and a signal has symbol duration T, then there are approximately BT uncorrelated samples of its complex envelope. When BT is much less than unity, the channel is said to be under spread and the effects of the Doppler fading can be ignored, while, if greater than unity, it is overspread. Most of the described factors are caused by the chemical-physical properties of the water medium such as temperature, salinity and density, and by their spatio-temporal variations. These variations, together with the wave guide nature of the channel, because the acoustic channel to be temporally and spatially variable. In particular, the horizontal channel is by far more rapidly varying than the vertical channel, in both deep and shallow water. CHAPTER 3: Network Architecture Underwater sensor nodes: The underwater sensor nodes are deployed on the sea floor anchored to the ocean bottom [32]. The sensors are equipped with floating buoys to push the nodes upwards, thus they are relatively stationary nodes [3]. Using acoustic links, they relay data to underwater sink directly or via multi-hop path. Underwater sink nodes: Underwater sink nodes take charge of collecting data of underwater sensors deployed on the ocean bottom and then send to the surface sink node. They may be equipped with vertical and horizontal acoustic transducers. The horizontal transceiver is used to collect the sensors data and the vertical transceiver provides transmitting link between underwater sink and the surface sink node. Surface sink node: Surface sink node is attached on a floating buoy with satellite, radio frequency (RF) or cell phone technology to transmit data to shore in real time. 2D Model A reference architecture for two-dimensional underwater networks is shown in Figure. 1. A group of sensor nodes are anchored to the deep of the ocean. Underwater sensor nodes are interconnected to one or more underwater gateways by means of wireless acoustic links. Underwater-gateways are network devices in charge of relaying data from the ocean bottom network to a surface station. To achieve this objective, they are equipped with two acoustic transceivers, namely a vertical and a horizontal transceiver. The horizontal transceiver is used by the underwater-gateway to communicate with the sensor nodes in order to: send commands and configuration data to the sensors (underwater -gateway to sensors); collect monitored data (sensors to underwater -gateway). The vertical link is used by the underwater -gateways to relay data to a surface station. In deep water applications, vertical transceivers must be long range transceivers. The surface station is equipped with an acoustic transceiver that is able to handle multiple parallel communications with the deployed underwater -gateways. It is also endowed with a long range RF and/or satellite transmitter to communicate with the onshore sink (os-sink) and/or to a surface sink (s-sink). In shallow water, bottom-deployed sensors/modems may directly communicate with the surface buoy, with no specialized bottom node (underwater -gateway). 3D Model Three-dimensional underwater networks are used to detect and observe phenomena that cannot be adequately observed by means of ocean bottom sensor nodes, i.e., to perform cooperative sampling of the 3D ocean environment. In three-dimensional underwater networks, sensor nodes float at different depths to observe a phenomenon. In this architecture, given in Figure 2, each sensor is anchored to the ocean bottom and equipped with a floating buoy that can be inflated by a pump. The buoy pushes the sensor towards the ocean surface. The depth of the sensor can then be regulated by adjusting the length of the wire that connects the sensor to the anchor, by means of an electronically controlled engine that resides on the sensor. Sensing and communication coverage in a 3D environment are rigorously investigated in [8]. The diameter, minimum and maximum degree of the reachability graph that describes the network are derived as a function of the communication range, while different degrees of cov erage for the 3D environment are characterized as a function of the sensing range. 3D Model with AUV The above figure represents the third type of network architecture which consist of sensor nodes and Autonomous Underwater Vehicles (AUV) which act as mobile sensor nodes for ocean monitoring, underwater resource study, etc. CHAPTER 4: Differences between underwater and terrestrial Sensor Network An underwater acoustic channel is different from a ground-based radio channel from many aspects, including: Bandwidth is extremely limited. The attenuation of acoustic signal increases with frequency and range [6] [10]. Consequently, the feasible band is extremely small. For example, a short range system operating over several tens of meters may have available bandwidth of a hundred kHz; a medium-range system operating over several kilometers has a bandwidth on the order of ten kHz; and a long-range system operating over several tens of kilometers is limited to only a few kHz of bandwidth [11]. Propagation delay is long. The transmission speed of acoustic signals in salty water is around 1500 meter/s [22], which is a difference of five orders of magnitude lower than the speed of electromagnetic wave in free space. Correspondently, propagation delay in an underwater channel becomes significant. This is one of the essential characteristics of underwater channels and has profound implications on localization and time synchronization. The channel impulse response is not only spatially varied but also temporarily varied. The channel characteristics vary with time and highly depend on the location of the transmitter and receiver. The fluctuation nature of the channel causes the received signals easily distorted. There are two types of propagation paths: macro-multipaths, which are the deterministic propagation paths; and micro-multipath, which is a random signal fluctuation. The macro-multipaths are caused by both reflection at the boundaries (bottom, surface and any object in the water) and bending. Inter- Symbol Interference (ISI) thus occurs. Compared with the spread of its ground-based counterpart, which is on the order of several symbol intervals, ISI spreading in an underwater acoustic channel is several tens or hundred of symbol intervals for moderate to high data rate in the horizontal channel. Micro-multipath fluctuations are mainly caused by surface wave, which contributes the most to the time variability of shallow water channel. In deep water, internal waves impact the single-path random fluctuations [12][13]. Probability of bit error is much higher and temporary loss of connectivity (shadow zone) sometimes occurs, due to the extreme characteristics of the channel. Cost. While terrestrial sensor nodes are expected to become increasingly inexpensive, underwater sensors are expensive devices. This is especially due to the more complex underwater transceivers and to the hardware protection needed in the extreme underwater environment. Also, because of the low economy of scale caused by a small relative number of suppliers, underwater sensors are characterized by high cost. Deployment. While terrestrial sensor networks are densely deployed, in underwater, the deployment is generally more sparse. Power. The power needed for acoustic underwater communications is higher than in terrestrial radio communications because of the different physical layer technology (acoustic vs. RF waves), the higher distances, and more complex signal processing techniques implemented at the receivers to compensate for the impairments of the channel. Memory. While terrestrial sensor nodes have very limited storage capacity, underwater-sensors may need to be able to do some data caching as the underwater channel may be intermittent. Spatial Correlation. While the readings from terrestrial sensors are often correlated, this is more unlikely to happen in underwater networks due to the higher distance among sensors. CHAPTER 5: Layered of UASN The underwater architecture network consists of five layers, application, transport, network, data link and physical layer as shown in the figure below. As typical underwater systems have limited processing capability, the protocol has been kept as simple as possible without significantly compromising performance. The underwater sensor network specifications currently do not include any recommendations for authentication and encryption. These may be easily implemented at the application layer or via a spreading scheme at the physical layer. Each layer is described by a SAPI. The SAPI is defined in terms of messages being passed to and from the layer. The clients (usually higher layers) of a layer invoke the layer via a request (REQ). The layer responds to each REQ by a response (RSP). Errors are reported via an ERR RSP with error codes. If the layer needs to send unsolicited messages to the client, it does so via a notification (NTF). A layer communicates logically with its peer layer via protocol data units (PDU). As the peer-to-peer communication is symmetric, a layer may send a REQ PDU to its peer layer at any time. It would optionally respond to such a PDU with a RSP PDU. This is logically depicted in Figure below It may be desirable in some cases, that non-neighboring layers communicate with each other to achieve cross-layer optimization. This may be implemented by allowing REQ and RSP PDUs between any two layers in the protocol stack. The underwater sensor network specifications define detailed message structures for all SAPI messages. These message structures include message identifiers, data formats to be used, parameters and their possible values Physical layer The physical layer provides framing, modulation and error correction capability (via FEC). It provides primitives for sending and receiving packets. It may also provide additional functionality such as parameter settings, parameter recommendation, carrier sensing, etc. At first underwater channel development was based on non-coherent frequency shift keying (FSK) modulation, since it relies on energy detection. Thus, it does not require phase tracking, which is a very difficult task mainly because of the Doppler-spread in the underwater acoustic channel. Although non-coherent modulation schemes are characterized by high power efficiency, their low bandwidth efficiency makes them unsuitable for high data rate multiuser networks. Hence, coherent modulation techniques have been developed for long-range, high-throughput systems. In the last years, fully coherent modulation techniques, such as phase shift keying (PSK) and quadrature amplitude modulation (QAM), have become practical due to the availability of powerful digital processing. Channel equalization techniques are exploited to leverage the effect of the inter-symbol interference (ISI), instead of trying to avoid or suppress it. Decision-feedback equalizers (DFEs) track the complex, relatively slowly varying channel response and thus provide high throughput when the channel is slowly varying. Conversely, when the channel varies faster, it is necessary to combine the DFE with a Phase Locked Loop (PLL) [9], which estimates and compensates for the phase offset in a rapid, stable manner. The use of decision feedback equalization and phase-locked loops is driven by the complexity and time variability of ocean channel impulse responses. Differential phase shift keying (DPSK) serves as an intermediate solution between incoherent and fully coherent systems in terms of bandwidth efficiency. DPSK encodes information relative to the previous symbol rather than to an arbitrary fixed reference in the signal phase and may be referred to as a partially coherent modulation. While this strategy substantially alleviates carrier phase-tracking requirements, the penalty is an increased error probability over PSK at an equivalent data rate. Another promising solution for underwater communications is the orthogonal frequency division multiplexing (OFDM) spread spectrum technique, which is particularly efficient when noise is spread over a large portion of the available bandwidth. OFDM is frequently referred to as multicarrier modulation because it transmits signals over multiple sub-carriers simultaneously. In particular, sub-carriers that experience higher SNR, are allotted with a higher number of bits, whereas less bits are allotted to sub-carriers experiencing attenuation, according to the concept of bit loading, which requires channel estimation. Since the symbol duration for each individual carrier increases, OFDM systems perform robustly in severe multi-path environments, and achieve a high spectral efficiency. Many of the techniques discussed above require underwater channel estimation, which can be achieved by means of probe packets [17]. An accurate estimate of the channel can be obtained with a high probing rate and/or with a large probe packet size, which however result in high overhead, and in the consequent drain of channel capacity and energy. Data link layer (MAC layer) The data link layer provides single hop data transmission capability; it will not be able to transmit a packet successfully if the destination node is not directly accessible from the source node. It may include some degree of reliability. It may also provide error detection capability (e.g. CRC check). In case of a shared medium, the data link layer must include the medium access control (MAC) sub-layer. Frequency division multiple access (FDMA) is not suitable for underwater sensor network due to the narrow bandwidth in underwater acoustic channels and the vulnerability of limited band systems to fading and multipath. Time division multiple access (TDMA) shows limited bandwidth efficiency because of the long time guards required in the underwater acoustic channel. In fact, long time guards must be designed to account for the large propagation delay and delay variance of the underwater channel in order to minimize packet collisions from adjacent time slots. Moreover, the variable delay makes it very challenging to realize a precise synchronization, with a common timing reference, which is required for TDMA. Carrier sense multiple access (CSMA) prevents collisions with the ongoing transmission at the transmitter side. To prevent collisions at the receiver side, however, it is necessary to add a guard time between transmissions dimensioned according to the maximum propagation delay in the network. This makes the protocol dramatically inefficient for underwater acoustic sensor network. The use of contention-based techniques that rely on handshaking mechanisms such as RTS/ CTS in shared medium access is impractical in underwater, for the following reasons: large delays in the propagation of RTS/CTS control packets lead to low throughput; due to the high propagation delay of underwater acoustic channels, when carrier sense is used, as in 802.11, it is more likely that the channel be sensed idle while a transmission is ongoing, since the signal may not have reached the receiver yet; the high variability of delay in handshaking packets makes it impractical to predict the start and finish time of the transmissions of other stations. Thus, collisions are highly likely to occur. Code division multiple access (CDMA) is quite robust to frequency selective fading caused by underwater multi-paths, since it distinguishes simultaneous signals transmitted by multiple devices by means of pseudo-noise codes that are used for spreading the user signal over the entire available band. CDMA allows reducing the number of packet retransmissions, which results in decreased battery consumption and increased network throughput. In conclusion, although the high delay spread which characterizes the horizontal link in underwater channels makes it difficult to maintain synchronization among the stations, especially when orthogonal code techniques are used [17], CDMA is a promising multiple access technique for underwater acoustic networks. This is particularly true in shallow water, where multi-paths and Doppler- spreading plays a key role in the communication performance. Network layer (Routing) The network layer is in charge of determining the path between a source (the sensor that samples a physical phenomenon) and a destination node (usually the surface station). In general, while many impairments of the underwater acoustic channel are adequately addressed at the physical and data link layers, some other characteristics, such as the extremely long propagation delays, are better addressed at the network layer. Basically, there are two methods of routing. The first one is virtual circuit routing and the second one is packet-switch routing. In virtual circuit routing, the networks use virtual circuits to decide on the path at the beginning of the network operation. Virtual-circuit-switch routing protocols can be a better choice for underwater acoustic networks. The reasons are: Underwater acoustic networks are typical asymmetric instead of symmetric. However, packet switched routing protocols are proposed for symmetric network architecture; Virtual-circuit-switch routing protocols work robust against link failure, which is critical in underwater environment; and Virtual-circuit-switch routing protocols have less signal overhead and low latency, which are needed for underwater acoustic channel environment. However, virtual-circuit-switch routing protocols usually lack of flexibility. In packet-switch routing, every node that is part of the transmission makes its own routing decision, i.e., decides its next hop to relay the packet. Packet-switch routing can be further classified into Proactive routing, Reactive and geographical routing protocols. Most routing protocols for ground-based wireless networks are packet-switch based. Proactive routing protocols attempt to minimize the message latency by maintaining up-to-date routing information at all times from each node to any other node. It broadcasts control packets that contain routing table information. Typical protocols include Destination Sequence Distance Vector (DSDV) [28] and Temporally Ordered Routing Algorithm (TORA). However, proactive routing protocols provoke a large signaling overhead to establish routes for the first time and each time the network topology changes. It may not be a good fit in underwater environment due to the high probability of link failure and extremely limited bandwidth there. Reactive routing protocols only initiate a route discovery process upon request. Correspondently, each node does not need to maintain a sizable look-up table for routing. This kind of routing protocols is more suitable for dynamic environment like ad hoc wireless networks. Typical protocol examples are Ad hoc On-demand Distance Vector (AODV) [23], and Dynamic Source Routing (DSR) [27]. The shortage of reactive routing protocols is its high latency to establish routing. Similar to its proactive counterpart, flooding of control packets to establish paths is needed, which brings significant signal overhead. The high latency could become much deteriorated in underwater environment because of the much slower propagation speed of acoustic signal compared with the radio wave in the air. Geographic routing (also called georouting or position-based routing) is a routing principle that relies on geographic position information. It is mainly proposed for wireless networks and based on the idea that the source sends a message to the geographic location of the destination instead of using the network address. Geographic routing requires that each node can determine its own location and that the source is aware of the location of the destination. With this information a message can be routed to the destination without knowledge of the network topology or a prior route discovery. Transport layer A transport layer protocol is needed in underwater sensor network not only to achieve reliable collective transport of event features, but also to perform flow control and congestion control. The primary objective is to save scarce sensor resources and increase the network efficiency. A reliable transport protocol should guarantee that the applications be able to correctly identify event features estimated by the sensor network. Congestion control is needed to prevent the network from being congested by excessive data with respect to the network capacity, while flow control is needed to avoid that network devices with limited memory are overwhelmed by data transmissions. Most existing TCP implementations are unsuited for the underwater environment, since the flow control functionality is based on a window- based mechanism that relies on an accurate esteem of the round trip time (RTT), which is twice the end-to-end delay from source to destination. Rate-based transport protocols seem also unsuited for this challenging environment. They still rely on feedback control messages sent back by the destination to dynamically adapt the transmission rate, i.e., to decrease the transmission rate when packet loss is experienced or to increase it otherwise. The high delay and delay variance can thus cause instability in the feedback control. Furthermore, due to the unreliability of the acoustic channel, it is necessary to distinguish between packet losses due to the high bit error rate of the acoustic channel, from those caused by packets being dropped from the queues of sensor nodes due to network congestion. In terrestrial, assume that congestion is the only cause for packet loss and the solution lies on decreasing the transmission rate, but in underwater sensor network if the packet loss is due to bad channel then the transmission rate should not be decreased to preserve throughput efficiency. Transport layer functionalities can be tightly integrated with data link layer functionalities in a cross-layer module. The purpose of such an integrated module is to make the information about the condition of the variable underwater channel available also at the transport layer. In fact, usually the state of the channel is known only at the physical and channel access sub-layers, while the design principle of layer separation makes this information transparent to the higher layers. This integration allows maximizing the