Electrothermal characterization and nonlinear modelling of GaN transistors for telecommunication circuit design

This thesis starts showing the main characteristics and application fields of the AlGaN/GaN HEMT technology, focusing on reliability aspects essentially due to the presence of low frequency dispersive phenomena which limit in several ways the microwave performance of this kind of devices. Based on an equivalent voltage approach, a new low frequency device model is presented where the dynamic nonlinearity of the trapping effect is taken into account for the first time allowing considerable improvements in the prediction of very important quantities for the design of power amplifier such as power added efficiency, dissipated power and internal device temperature. An innovative and low-cost measurement setup for the characterization of the device under low-frequency large-amplitude sinusoidal excitation is also presented. This setup allows the identification of the new low frequency model through suitable procedures explained in detail. In this thesis a new non-invasive empirical method for compact electrothermal modeling and thermal resistance extraction is also described. The new contribution of the proposed approach concerns the non linear dependence of the channel temperature on the dissipated power. This is very important for GaN devices since they are capable of operating at relatively high temperatures with high power densities and the dependence of the thermal resistance on the temperature is quite relevant. Finally a novel method for the device thermal simulation is investigated: based on the analytical solution of the tree-dimensional heat equation, a Visual Basic program has been developed to estimate, in real time, the temperature distribution on the hottest surface of planar multilayer structures. The developed solver is particularly useful for peak temperature estimation at the design stage when critical decisions about circuit design and packaging have to be made. It facilitates the layout optimization and reliability improvement, allowing the correct choice of the device geometry and configuration to achieve the best possible thermal performance.

A moment symbolic representation of Lévy processes with applications

By using a symbolic method, known in the literature as the classical umbral calculus, a symbolic representation of Lévy processes is given and a new family of time-space harmonic polynomials with respect to such processes, which includes and generalizes the exponential complete Bell polynomials, is introduced. The usefulness of time-space harmonic polynomials with respect to Lévy processes is that it is a martingale the stochastic process obtained by replacing the indeterminate x of the polynomials with a Lévy process, whereas the Lévy process does not necessarily have this property. Therefore to find such polynomials could be particularly meaningful for applications. This new family includes Hermite polynomials, time-space harmonic with respect to Brownian motion, Poisson-Charlier polynomials with respect to Poisson processes, Laguerre and actuarial polynomials with respect to Gamma processes , Meixner polynomials of the first kind with respect to Pascal processes, Euler, Bernoulli, Krawtchuk, and pseudo-Narumi polynomials with respect to suitable random walks. The role played by cumulants is stressed and brought to the light, either in the symbolic representation of Lévy processes and their infinite divisibility property, either in the generalization, via umbral Kailath-Segall formula, of the well-known formulae giving elementary symmetric polynomials in terms of power sum symmetric polynomials. The expression of the family of time-space harmonic polynomials here introduced has some connections with the so-called moment representation of various families of multivariate polynomials. Such moment representation has been studied here for the first time in connection with the time-space harmonic property with respect to suitable symbolic multivariate Lévy processes. In particular, multivariate Hermite polynomials and their properties have been studied in connection with a symbolic version of the multivariate Brownian motion, while multivariate Bernoulli and Euler polynomials are represented as powers of multivariate polynomials which are time-space harmonic with respect to suitable multivariate Lévy processes.

Friend of the police: Polizei in Nord-Ghana (Upper West Region) /// Arbeitspapiere / Institut für Ethnologie und Afrikastudien ; 93

Korruption, Gewalt, Machtmissbrauch – im medialen, aber auch im wissenschaftlichen Diskurs wird die afrikanische Polizei oft als dysfunktionale staatliche Institution dargestellt. Dabei erscheinen Polizisten und zivile Akteure als klar voneinander abgegrenzte Akteursgruppen, wobei die Polizisten einseitig das staatliche Gewaltmonopol durchsetzen. Ein Blick auf den Alltag polizeilichen Handelns in Nordghana eröffnet jedoch eine andere Perspektive: Wegen der niedrigen Legitimität, konkurrierenden alternativen Rechtsinstanzen und den Widersprüchen innerhalb ihrer Institution sind Polizisten mit massiven Unsicherheiten konfrontiert. Ihre Praktiken können als situative Anpassungen der Polizeiarbeit an dieses Umfeld verstanden werden. Dabei übertragen Polizisten oft Kernaufgaben ihrer Institution an zivile Akteure, die sogenannten „friends of the police“. Auch zivile Akteure verfügen jedoch durch physischen Widerstand, Beziehungen, Status und Geld über beträchtliche Beeinflussungsmöglichkeiten. Die öffentliche Ordnung ergibt sich erst aus den Verhandlungen zwischen den Polizisten und unterschiedlichen zivilen Akteuren unter Einbeziehung ihrer sozialen Ressourcen und moralischer Vorstellungen.

Celestial Church of Christ in Italia. Percorsi, Spazi e Pratiche Rituali

Il lavoro che presento propone un’analisi di una chiesa africana indipendente in Italia, la Celestial Church Of Christ Worldwide (CCCW), cercando di mettere in luce il nesso tra religione, migrazione e il processo di ‘plunting churches’ (Kooning 2009) nel contesto italiano. Attraverso una ricerca sul campo, sono stati indagati i percorsi personali, familiari e comunitari dei membri di una ‘Celestial Parish’ presente nel comune di Brescia, ‘Ileri Oluwa Parish’, al fine di comprendere la natura dei processi identitari coinvolti nell’organizzazione della CCC in Italia. ‘Ileri Oluwa Parish’, in quanto luogo che denota una ‘chiesa individuale collegata ad una Diocesi’ (CCC Constitution (CCC Constitution, 107 (d) si rivela, nella materialità delle sue forme e dei ‘Devotional Services’ che in essa si svolgono, a ‘field of action’ (Lefebvre, 1991). La storia della chiesa, i fondamenti della sua dottrina e i significati comunicati attraverso le forme rituali e religiose che la stessa promuove, sono stati contestualizzati alla luce delle tensioni e delle strategie di potere che strutturano il campo. Le storie dei membri della parrocchia, percorsi di migrazione e mobilità in itinere, rappresentano la lente attraverso cui si è guardato alle relazioni vissute nel nome dello ‘Spirito’, e alla percezione stessa di ciò che gli stessi Celestians definiscono sacro, santo, puro e impuro. Lo sguardo fisso alla vita ordinaria di una Celestial parish in Italia, esteso nell’ultima parte dell’elaborato alla Celestial parish londinese, è stato fondamentale per capire l’intreccio di relazioni spirituali, reti familiari e mobilità degli individui sul territorio italiano ed europeo, processo che ribalta la condizione diasporica della CCC, trasformando una condizione di dispersione in un valore aggiunto, nella possibilità di nuove traiettorie territoriali e spazi di presenza religiosa e socioeconomica.

Vulnerability and robustness indices against blackouts in power grids

In this dissertation some novel indices for vulnerability and robustness assessment of power grids are presented. Such indices are mainly defined from the structure of transmission power grids, and with the aim of Blackout (BO) prevention and mitigation. Numerical experiments showing how they could be used alone or in coordination with pre-existing ones to reduce the effects of BOs are discussed. These indices are introduced inside 3 different sujects: The first subject is for taking a look into economical aspects of grids’ operation and their effects in BO propagation. Basically, simulations support that: the determination to operate the grid in the most profitable way could produce an increase in the size or frequency of BOs. Conversely, some uneconomical ways of supplying energy are shown to be less affected by BO phenomena. In the second subject new topological indices are devised to address the question of "which are the best buses to place distributed generation?". The combined use of two indices, is shown as a promising alternative for extracting grid’s significant features regarding robustness against BOs and distributed generation. For this purpose, a new index based on outage shift factors is used along with a previously defined electric centrality index. The third subject is on Static Robustness Analysis of electric networks, from a purely structural point of view. A pair of existing topological indices, (namely degree index and clustering coefficient), are combined to show how degradation of the network structure can be accelerated. Blackout simulations were carried out using the DC Power Flow Method and models of transmission networks from the USA and Europe.

Power Converters and Electric Drives for Smart Grid Applications

The present dissertation aims to explore, theoretically and experimentally, the problems and the potential advantages of different types of power converters for “Smart Grid” applications, with particular emphasis on multi-level architectures, which are attracting a rising interest even for industrial requests. The models of the main multilevel architectures (Diode-Clamped and Cascaded) are shown. The best suited modulation strategies to function as a network interface are identified. In particular, the close correlation between PWM (Pulse Width Modulation) approach and SVM (Space Vector Modulation) approach is highlighted. An innovative multilevel topology called MMC (Modular Multilevel Converter) is investigated, and the single-phase, three-phase and "back to back" configurations are analyzed. Specific control techniques that can manage, in an appropriate way, the charge level of the numerous capacitors and handle the power flow in a flexible way are defined and experimentally validated. Another converter that is attracting interest in “Power Conditioning Systems” field is the “Matrix Converter”. Even in this architecture, the output voltage is multilevel. It offers an high quality input current, a bidirectional power flow and has the possibility to control the input power factor (i.e. possibility to participate to active and reactive power regulations). The implemented control system, that allows fast data acquisition for diagnostic purposes, is described and experimentally verified.

The role of indigenous people in national development processes: Participation and marginalisation of indigenous Bedouin in South Sinai tourism development

The Bedouin of South Sinai have been significantly affected by the politics of external powers for a long time. However, never had the interest of external powers in Sinai been so strong as since the Israeli-Egyptian wars in the second half of the 20th century when Bedouin interests started to collide with Egypt’s plans for a development of luxury tourism in South Sinai. rnrnThe tourism boom that has started in the 1980s has brought economic and infrastructure development to the Bedouin and tourism has become the most important source of income for the Bedouin. However, while the absolute increase of tourists to Sinai has trickled down to the Bedouin to some extent, the participation of Bedouin in the overall tourism development is under-proportionate. Moreover, the Bedouin have become increasingly dependent on monetary income and consequently from tourism as the only significant source of income while at the same time they have lost much of their land as well as their self-determination.rnrnIn this context, the Bedouin livelihoods have become very vulnerable due to repeated depressions in the tourism industry as well as marginalization. Major marginalization processes the Bedouin are facing are the loss of land, barriers to market entry, especially increasingly strict rules and regulations in the tourism industry, as well as discrimination by the authorities. Social differentiation and Bedouin preferences are identified as further factors in Bedouin marginalization.rnrnThe strategies Bedouin have developed in response to all these problems are coping strategies, which try to deal with the present problem at the individual level. Basically no strategies have been developed at the collective level that would aim to actively shape the Bedouin’s present and future. Collective action has been hampered by a variety of factors, such as the speed of the developments, the distribution of power or the decay of tribal structures.rnWhile some Bedouin might be able to continue their tourism activities, a large number of informal jobs will not be feasible anymore. The majority of the previously mostly self-employed Bedouin will probably be forced to work as day-laborers who will have lost much of their pride, dignity, sovereignty and freedom. Moreover, with a return to subsistence being impossible for the majority of the Bedouin, it is likely that an increasing number of marginalized Bedouin will turn to illegal income generating activities such as smuggling or drug cultivation. This in turn will lead to further repression and discrimination and could escalate in a serious violent conflict between the Bedouin and the government.rnrnDevelopment plans and projects should address the general lack of civil rights, local participation and protection of minorities in Egypt and promote Bedouin community development and the consideration of Bedouin interests in tourism development.rnrnWether the political upheavals and the resignation of president Mubarak at the beginning of 2011 will have a positive effect on the situation of the Bedouin remains to be seen.rn

Hydraulic evaluation of the gyro electric wave energy converter

Motivation Thanks for a scholarship offered by ALma Mater Studiorum I could stay in Denmark for six months during which I could do physical tests on the device Gyro PTO at the Departmet of Civil Engineering of Aalborg University. Aim The goal of my thesis is an hydraulic evaluation of the device: Gyro PTO, a gyroscopic device for conversion of mechanical energy in ocean surface waves to electrical energy. The principle of the system is the application of the gyroscopic moment of flywheels equipped on a swing float excited by waves. The laboratory activities were carried out by: Morten Kramer, Jan Olsen, Irene Guaraldi, Morten Thøtt, Nikolaj Holk. The main purpose of the tests was to investigate the power absorption performance in irregular waves, but testing also included performance measures in regular waves and simple tests to get knowledge about characteristics of the device, which could facilitate the possibility of performing numerical simulations and optimizations. Methodology To generate the waves and measure the performance of the device a workstation was created in the laboratory. The workstation consist of four computers in each of wich there was a different program. Programs have been used : Awasys6, LabView, Wave lab, Motive optitrack, Matlab, Autocad Main Results Thanks to the obtained data with the tank testing was possible to make the process of wave analisys. We obtained significant wave height and period through a script Matlab and then the values of power produced, and energy efficiency of the device for two types of waves: regular and irregular. We also got results as: physical size, weight, inertia moments, hydrostatics, eigen periods, mooring stiffness, friction, hydrodynamic coefficients etc. We obtained significant parameters related to the prototype in the laboratory after which we scale up the results obtained for two future applications: one in Nissun Brending and in the North Sea. Conclusions The main conclusion on the testing is that more focus should be put into ensuring a stable and positive power output in a variety of wave conditions. In the irregular waves the power production was negative and therefore it does not make sense to scale up the results directly. The average measured capture width in the regular waves was 0.21 m. As the device width is 0.63 m this corresponds to a capture width ratio of: 0.21/0.63 * 100 = 33 %. Let’s assume that it is possible to get the device to produce as well in irregular waves under any wave conditions, and lets further assume that the yearly absorbed energy can be converted into electricity at a PTO-efficiency of 90 %. Under all those assumptions the results in table are found, i.e. a Nissum Bredning would produce 0.87 MWh/year and a North Sea device 85 MWh/year.

Strategies of Representation, Relationship, and Resistance: British Women Travelers and Mormon Plural Wives, c. 1870-1890

During the 1870s and 1880s, several British women writers traveled by transcontinental railroad across the American West via Salt Lake City, Utah, the capital of the Church of Jesus Christ of Latter-day Saints, or Mormons. These women subsequently wrote books about their travels for a home audience with a taste for adventures in the American West, and particularly for accounts of Mormon plural marriage, which was sanctioned by the Church before 1890. "The plight of the Mormon woman," a prominent social reform and literary theme of the period, situated Mormon women at the center of popular representations of Utah during the second half of the nineteenth century. "The Mormon question" thus lends itself to an analysis of how a stereotyped subaltern group was represented by elite British travelers. These residents of western American territories, however, differed in important respects from the typical subaltern subjects discussed by Victorian travelers. These white, upwardly mobile, and articulate Mormon plural wives attempted to influence observers' representations of them through a variety of narrative strategies. Both British women travel writers and Mormon women wrote from the margins of power and credibility, and as interpreters of the Mormon scene were concerned to established their representational authority.

'Listen, Rama’s Wife!’: Maithil Women’s Perspectives and Practices in the Festival of Sāmā-Cakevā

As a female-only festival in a significantly gender-segregated society, sāmā cakevā provides a window into Maithil women’s understandings of their society and the sacred, cultural subjectivities, moral frameworks, and projects of self-construction. The festival reminds us that to read male-female relations under patriarchal social formations as a dichotomy between the empowered and the disempowered ignores the porous boundaries between the two in which negotiations and tradeoffs create a symbiotic reliance. Specifically, the festival names two oppositional camps—the male world of law and the female world of relationships—and then creates a male character, the brother, who moves between the two, loyal to each, betraying, in a sense, each, but demonstrating, by his movements, the currents and avenues of power. This article makes available to other scholars of South Asian culture and society an extended description and analysis of this distinctive festival, while also contributing to the scholarly discussion of women’s expressive traditions.

Current Changes in the Lifestyle and Mental Health of Teenagers

The group studied 1,253 students from various types of schools chosen randomly from those in Prague and Budejovice in order to evaluate the life styles, prevailing value standards, attitudes and behavioural patterns of Czech adolescents. The respondents (including 614 men and 639 women with an average age of 16.4 years) completed questionnaires containing standard scales focusing on feelings about social life, conservative and authoritarian tendencies, levels of self-esteem, general health, eating attitudes and behaviour The adolescents showed a relatively high level of conformity with authoritarian, conservative tendencies and with a dictate of power, rigid conventionality, ethnocentrism and low inner tolerance of differences, their scores being higher than those found in Western European countries. These tendencies were stronger among students outside Prague and those attending vocational schools. As the level of education rose, the sense of fatality and social determination decreased, indicating a higher share of responsibility for events in the surrounding world. When changes of life style were considered, adolescents can be expected to adapt more easily to more risky, socially attractive and manifest models of attitudes and behaviour. On the one hand, adolescents were often involved in sports, and young women in particular often showed a extreme concern and care for their own bodies. On the other hand, one quarter of respondents smoked, one fifth reported serious problems with alcohol and one quarter had already had some experience with drugs. One third of young men and one quarter of young women reported regular consumption of alcohol, and 6.5 percent of men and 3.6 percent of women regularly smoked marihuana or hashish. For the majority of adolescents, life conditions and conformity seem to be more important than the sense of active choice and responsibility for one's own life.

Changes in Psychological Characteristics of Working Adults in Different Stages of Economic Transition in Lithuania

Global economic changes have psychological consequences and Mr. Lepeska set out to assess these changes in working adults in Lithuania between 1993 and 1997. He surveyed two groups of working adults, with a total of 200 people, randomly selected and representing different organisations and professions. In both groups around 30% of participants were managers, with the remainder working in non-managerial positions. The participants were surveyed twice, once in 1993 and the second time in 1997,using various psychodiagnostic tools to measure their psychological characteristics. The results showed that strategies for coping with stress have changed, with problem solving strategies being used more often, and avoidance behaviour or seeking social support less. Men tended to have rejected these strategy more radically than women. Attitudes towards work had become more positive, with managers' attitudes having changed more significantly than those of employees from lower levels of organisations. Younger people were more positive towards work-related changes, while situational anxiety tended to increase with age, although overall it remained low. Mr. Lepeska found that while there were some indications of an increasing individualist in relation to peers, the traditional collective orientation of Lithuanian adults had if anything increased. People have become more accepting of an unequal distribution of power, making it difficult to increase the participation of subordinates in decision making. He also noted a tendency for Lithuanians to see their organisations as traditional families, expecting them to take care of them physically and economically in return for loyalty. The strong feminine orientation with its stress on interpersonal relations and overall quality of life has also strengthened, but the ability of Lithuanians to take initiative and control their environment was relatively low. Mr. Lepeska concludes that organisations should seek to recruit people who are able to adjust more easily to changes and consider measuring dominance, individualism, and attitudes to work-related change and situational anxiety in the process of professional selection. There should also be more emphasis on team building and on training managers to maintain closer relationships with their subordinates so as to increase the latter's participation in decision making. Good interpersonal relations can be a strong work motivator, as may be special attention to the security needs of older employees.

The role of genetic polymorphisms in alcoholic liver disease

Chronic alcohol consumption is a major cause of liver cirrhosis which, however, develops in only a minority of heavy drinkers. Evidence from twin studies indicates that genetic factors account for at least 50% of individual susceptibility. The contribution of genetic factors to the development of diseases may be investigated either by means of animal experiments, through linkage studies in families of affected patients, or population based case-control studies. With regard to the latter, single nucleotide polymorphisms of genes involved in the degradation of alcohol, antioxidant defense, necroinflammation, and formation and degradation of extracellular matrix are attractive candidates for studying genotype-phenotype associations. However, many associations in early studies were found to be spurious and could not be confirmed in stringently designed investigations. Therefore, future genotype-phenotype studies in alcoholic liver disease should meet certain requirements in order to avoid pure chance observations due to a lack of power, false functional interpretation, and insufficient statistical evaluation.

Reporting of randomized controlled trials in Hodgkin lymphoma in biomedical journals

BACKGROUND: Randomized controlled trials (RCTs) are the best tool to evaluate the effectiveness of clinical interventions. The Consolidated Standards for Reporting Trials (CONSORT) statement was introduced in 1996 to improve reporting of RCTs. We aimed to determine the extent of ambiguity and reporting quality as assessed by adherence to the CONSORT statement in published reports of RCTs involving patients with Hodgkin lymphoma from 1966 through 2002. METHODS: We analyzed 242 published full-text reports of RCTs in patients with Hodgkin lymphoma. Quality of reporting was assessed using a 14-item questionnaire based on the CONSORT checklist. Reporting was studied in two pre-CONSORT periods (1966-1988 and 1989-1995) and one post-CONSORT period (1996-2002). RESULTS: Only six of the 14 items were addressed in 75% or more of the studies in all three time periods. Most items that are necessary to assess the methodologic quality of a study were reported by fewer than 20% of the studies. Improvements over time were seen for some items, including the description of statistics methods used, reporting of primary research outcomes, performance of power calculations, method of randomization and concealment allocation, and having performed intention-to-treat analysis. CONCLUSIONS: Despite recent improvements, reporting levels of CONSORT items in RCTs involving patients with Hodgkin lymphoma remain unsatisfactory. Further concerted action by journal editors, learned societies, and medical schools is necessary to make authors even more aware of the need to improve the reporting RCTs in medical journals to allow assessment of validity of published clinical research.

Designed Extension of Survival Studies: Application to Clinical Trials with Unrecognized Heterogeneity

It is well known that unrecognized heterogeneity among patients, such as is conferred by genetic subtype, can undermine the power of randomized trial, designed under the assumption of homogeneity, to detect a truly beneficial treatment. We consider the conditional power approach to allow for recovery of power under unexplained heterogeneity. While Proschan and Hunsberger (1995) confined the application of conditional power design to normally distributed observations, we consider more general and difficult settings in which the data are in the framework of continuous time and are subject to censoring. In particular, we derive a procedure appropriate for the analysis of the weighted log rank test under the assumption of a proportional hazards frailty model. The proposed method is illustrated through application to a brain tumor trial.