Αντικείμενο της παρούσας διπλωματικής εργασίας είναι η μελέτη μεθόδων διαφορισμού και πολύπλεξης που μπορούν να χρησιμοποιηθούν στα ασύρματα δίκτυα επικοινωνιών. Αρχικά, γίνεται μια ανασκόπηση της βασικής θεωρίας με τη ντετερμινιστική και στοχαστική μοντελοποίηση του ασύρματου τηλεπικοινωνιακού καναλιού. Αφού παρουσιάζονται οι βασικές τεχνικές διαμόρφωσης, ακολουθεί η σύγκριση του καναλιού Λευκού Προσθετικού Γκαουσιανού Θορύβου (AWGN) με το κανάλι επίπεδων διαλείψεων (flat fading) Rayleigh. Στη συνέχεια, μελετάται ο διαφορισμός στο χώρο με χρήση πολλαπλών κεραιών στον πομπό ή/και στο δέκτη και παρουσιάζονται βασικές τεχνικές μετάδοσης και ανίχνευσης. Ξεκινώντας από συστήματα SIMO και MISO με διαφορισμό μόνο στο δέκτη και στον πομπό, αντίστοιχα, καταλήγουμε στο σύστημα MIMO που εμφανίζει το μεγαλύτερο ενδιαφέρον. Τέλος, τα θεωρητικά αποτελέσματα που προκύπτουν επαληθεύονται με τη χρήση προσομοιώσεων, για τις οποίες εφαρμόζεται η τεχνική σημαίνουσας δειγματοληψίας (Importance Sampling). / The main goal of this diploma thesis is the study of diversity and multiplexing techniques which are employed in wireless communication systems. First of all, the deterministic and stochastic model of the wireless channel are introduced. After the presentation of the basic modulation techniques, the Additive White Gaussian Noise (AWGN) channel is compared with the Flat Fading Rayleigh channel. Space diversity aims at improving the performance of wireless systems in fading environments. More precisely, basic transmission and detection techniques are analyzed for systems with multiple antennas at the transmitter or/and the receiver. Beginning from SIMO and MISO systems the thesis concludes with the study of MIMO systems which are the most interesting. Finally, the theoretical results are confirmed with simulations developed with a fast simulation method called importance sampling.

In order to meet the different public needs and requirements of contemporary urban society, a better understanding of public perceptions, appreciation and knowledge of the assorted values derived from urban trees is beneficial for improved urban greening. Thus, this study carried out an assessment of urban residents’ knowledge and appreciation of the benefits of trees and the role they play in enhancing the quality of life in urban systems. The study primarily focused on the intangible benefits (also referred to as cultural and regulating services) of urban trees, because most research to date in South Africa on trees and the benefits derived from them is biased towards the provisioning services of trees in rural areas. The significance and contribution of the intangible benefits of trees in urban systems is often underestimated and not seriously taken into account by urban planners, policy makers and other key decision makers. The study was conducted in three different residential settlement types (formal townships, RDP settlements and informal settlements) in two towns in the Limpopo Province in South Africa, namely Bela-Bela and Tzaneen. Findings revealed that the intangible benefits of trees are seen to play a significant role in improving both residents’ quality of life and the environmental conditions in cities, including the preservation of biodiversity. Findings also showed that urban residents had strong spiritual connections with trees and placed considerable cultural and historical importance on specific tree species and individual trees. Urban residents in both towns had moderate knowledge of the intangible benefits of trees based on the knowledge score that was created for the purposes of this study. Fifty seven percent of the residents had ‘reasonable’ knowledge of some of the intangible benefits of trees, while 43% had low levels of knowledge. That said, the majority of residents demonstrated high appreciation (98%) of the intangible benefits of trees (especially social and cultural values), with few residents not recognising these, suggesting that knowledge does not necessarily lead to appreciation. Age and level of education were found to influence knowledge of the intangible benefits of trees. A large proportion (86%) of residents who possessed tertiary level qualifications had more knowledge of the intangible benefits of trees as compared to residents with no formal education. Findings also revealed that younger respondents (60%) had more knowledge of the intangible benefits of trees. Factors that influenced appreciation of the intangible benefits of trees included links to crime, peoples’ value systems (their pro-environmental and altruistic values) and residential settlement type. Sixty five percent of residents in both towns felt that urban street trees and trees in public spaces attract criminals and promote crime, while 67% of RDP and 96% of informal township residents did not use or appreciate the social and recreational benefits of trees mainly because of the absence or long distances to public parks. A Willingness To Pay (WTP) survey revealed that a high proportion of residents in Bela-Bela (86%) were WTP a small annual fee in order to sustain greening initiatives in their communities compared to the residents in Tzaneen (53%). In terms of the planting and retention of trees, it was found that 300 households in both study towns had planted and retained a total of 1 615 trees in spite of the various factors that negatively influenced planting and retention of trees such as residency time and tenure security. The majority (66%) of informal township residents said tenure security was an important factor to consider when making tree planting decisions, while this was not an issue for formal township and RDP residents. Policy implications and recommendations are presented to help municipalities and urban planners improve and develop effective policies and programmes that will enable implementation of sustainable urban greening programmes

This thesis makes a number of contributions in the derivative pricing and risk management literature and to the growing literature that exploits information embedded in option prices. First, it develops an effective numerical scheme for importance sampling scheme of Fouque and Tullie (2002) based on a 2-dimensional lookup table of stock price and time to maturity that dramatically improves the speed of this importance sampling scheme. Second, the thesis presents an application of this importance sampling scheme in a Multi-Level Monte Carlo simulation. Such combination yields greater variance reduction compared to Multi-Level Monte Carlo or importance sampling alone. Third, it demonstrates how the Greeks can be computed using the Likelihood Ratio Method based on characteristic function, and how combining it with importance sampling leads to a significant variance reduction for the Greeks. Finally, it documents the positive relationship between the risk-neutral skewness (RNS) and future realized stock returns that is driven by the underperformance of highly negative RNS portfolio. The results provide strong evidence that the underperformance of stocks with the lowest RNS is driven by those stocks that are associated with a higher hedging demand, relative overvaluation and are also too costly or too risky to sell short. Moreover, by decomposing RNS into its systematic and idiosyncratic components, this thesis shows that the latter drives the positive relationship with future realized stock returns.

Effective leadership can and does influence organizational performance. The Executive Success Profile, a multi-rater feedback instrument, was used to gather perception data on 51 executives and 310 senior managers of a large Fortune 500 electronics manufacturing company in regards to three critical leadership dimensions: visionary thinking, empowering others, and global perspective. Paired t-tests were run to compare the means of the two samples. Significant differences were found between executives and senior managers on the perceived importance of and ability to perform on the empowering others dimension. Additionally, correlational measures indicate a statistically significant relationship between importance and competence ratings on the empowering others and global perspective dimensions for executives, and on the empowering others dimension for senior managers.

Research in the field of retention has been dominated by studies focused on retention of highly talented employees or A players. Organisations for many years have overlooked, misunderstood and to a large degree ignored the contributions of the steady and capable performers, the B players. Understanding the retention needs of B players has become critical in ensuring organisational success in the short and long term. The purpose of the research aimed to identify the key factors influencing the retention of B players across generations and ethnic groups, and thereby develop a retention framework that will contribute towards the improved retention of B players. The study adopted a dual approach, incorporating a qualitative and quantitative methodology. Interviews were conducted with key stakeholders to validate the questionnaire and gain insights regarding the key retention variables that influence B players. A questionnaire was then distributed to respondents to obtain their views. Data was gathered electronically and analysed against the research objectives defined. The key findings indicated that B players are most influenced by Financial Reward&Recognition, Independence&Freedom and Leadership& Management factors. A Factor Significance and Variable Importance Retention Framework was developed to assist organisations to develop dynamic multidimensional strategies. Copyright / Dissertation (MBA)--University of Pretoria, 2010. / Gordon Institute of Business Science (GIBS) / unrestricted

Magister Artium - MA / The greater part of the analysis relates to the needs of the Third World, with an emphasis on Africa (as opposed to the entire Third World). Within the African context, these needs should be seen against a background created by political, economic and demographic changes. Throughout the educational process the concept of education as learning, and not simply as schooling, has had important implications for development, in particular rural development.

The purpose of this study was to evaluate a family camp's performance from a consumer (parent) perspective. An Importance-Performance Analysis was used. Responses averages were plotted on a grid of importance versus performance with the overall means used as cross-hairs to create an action grid of four quadrants: keep-up-the-good-work (high importance/high performance), concentrate-here (high importance/low performance), possible-overkill (low importance/high performance), and low-priority (low importance/low performance). Findings indicated that parents are in large part receiving good performance on the factors that are important to them. Findings identified factors that were important to parents including some factors that camp directors were not previously aware of. Three of the five highest importance factor scores were regarding accommodations (clean facility, restrooms provided, and showers provided). All five of the top performance factor scores were regarding programming details. Implications for family camp providers and recommendations for future research are discussed.

The purpose of this study was to discover the various meanings that the Pulaski Theatre held for the residents of Pulaski and the theatre's social importance to the town. The following research objectives directed this study: 1) to document the theatre's history from the time it was built in 1911 until the present day, 2) to uncover memories or feelings associated with the theatre, and 3) to determine if design features of the theatre building influenced those feelings/memories. In documenting the history of the theatre, design features of the original 1911 building were examined as well as changes over time. To determine if design features of the building influenced the feelings/memories that were associated with the structure it was important first to discover which architectural and design features people remembered, if any, and then to determine if these design features reflected a meaningful association, i.e. sense of place to participants. Also of interest was whether this association or sense of place would be similar or different for all. Participants were fifteen males and females aged 43 to 82 who had attended the theatre over time. All participants grew up in Pulaski and six had lived there their entire lives. Both African Americans and Caucasians participated. Subjects were asked to draw a picture of the theatre that expressed their experience of the space. After the drawing, they were asked to discuss the picture and its meaning to them. Clare Cooper Marcus and others used this environmental autobiography technique as a method to bring a person's experiences of a place to a conscious level. Tape-recorded interviews were conducted and transcribed by the researcher to discover memories of the theatre and the meaning of the theatre to the participants. Data were analyzed by coding to look for emerging themes or categories that relate to the research question. Of interest was whether or not the Pulaski Theatre represented a sense of place to residents and if that sense of place varied for different participants. Document research was conducted through old newspapers and artifacts in the Raymond Ratcliffe Museum (the historic museum in Pulaski), documents from scrapbooks, architectural plans, and the files of the Town of Pulaski. Themes that were identified from the research were (1) the structure was an integral part of the community, (2) the theatre was a reflection of the community's social norms and roles, such as segregation, and (3) the theatre interior contributed to the social atmosphere of the space. The theatre building, while transformed over time, retained a presence in the town and memories associated with it across time were significant in creating a sense of place in the community. The theatre was remembered as a setting that brought excitement and stimulation to children and adults for many years. Participants felt "at home" in the theatre, having favored sections of the theatre where they routinely sat. School children attending the weekly matinees in the summer and African Americans sitting in their special section of the balcony developed a special identity with that particular space within the theatre. Even after segregation, many African Americans continued to sit in the balcony where they had sat for many years and felt at home. The unique characteristics of these spaces were dependent on the people that frequented them rather than the architecture of the building. The sense of place was one of personal relationships and emotional attachments rather than of bricks and mortar. Memories of the theatre were stories of groups or individuals and their interactions in the space. The building represented these individuals and what they brought to this place and time. The Pulaski Theatre played a great role in interactions with friends and neighbors and was significant in reflecting a sense of place in this community. / Ph. D.

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