Si, CdTe and CdZnTe radiation detectors for imaging applications

The structure and operation of CdTe, CdZnTe and Si pixel detectors based on crystalline semiconductors, bump bonding and CMOS technology and developed mainly at Oy Simage Ltd. And Oy Ajat Ltd., Finland for X- and gamma ray imaging are presented. This detector technology evolved from the development of Si strip detectors at the Finnish Research Institute for High Energy Physics (SEFT) which later merged with other physics research units to form the Helsinki Institute of Physics (HIP). General issues of X-ray imaging such as the benefits of the method of direct conversion of X-rays to signal charge in comparison to the indirect method and the pros and cons of photon counting vs. charge integration are discussed. A novel design of Si and CdTe pixel detectors and the analysis of their imaging performance in terms of SNR, MTF, DQE and dynamic range are presented in detail. The analysis shows that directly converting crystalline semiconductor pixel detectors operated in the charge integration mode can be used in X-ray imaging very close to the theoretical performance limits in terms of efficiency and resolution. Examples of the application of the developed imaging technology to dental intra oral and panoramic and to real time X-ray imaging are given. A CdTe photon counting gamma imager is introduced. A physical model to calculate the photo peak efficiency of photon counting CdTe pixel detectors is developed and described in detail. Simulation results indicates that the charge sharing phenomenon due to diffusion of signal charge carriers limits the pixel size of photon counting detectors to about 250 μm. Radiation hardness issues related to gamma and X-ray imaging detectors are discussed.

Multilevel Dodecagonal Space Vector Generation for Open-end Winding Induction Motor Drive Using Conventional Three Level Inverters

A novel dodecagonal space vector structure for induction motor drive is presented in this paper. It consists of two dodecagons, with the radius of the outer one twice the inner one. Compared to existing dodecagonal space vector structures, to achieve the same PWM output voltage quality, the proposed topology lowers the switching frequency of the inverters and reduces the device ratings to half. At the same time, other benefits obtained from existing dodecagonal space vector structure are retained here. This includes the extension of the linear modulation range and elimination of all 6+/-1 harmonics (n=odd) from the phase voltage. The proposed structure is realized by feeding an open-end winding induction motor with two conventional three level inverters. A detailed calculation of the PWM timings for switching the space vector points is also presented. Simulation and experimental results indicate the possible application of the proposed idea for high power drives.

Providing QoS to Real and Data Applications in WiMAX Mesh Networks

We consider the problem of centralized routing and scheduling for IEEE 802.16 mesh networks so as to provide Quality of Service (QoS) to individual real and interactive data applications. We first obtain an optimal and fair routing and scheduling policy for aggregate demands for different source- destination pairs. We then present scheduling algorithms which provide per flow QoS guarantees while utilizing the network resources efficiently. Our algorithms are also scalable: they do not require per flow processing and queueing and the computational requirements are modest. We have verified our algorithms via extensive simulations.

Applications of Gauge/Gravity Duality to QCD and Heavy Ion Collisions

The description of quarks and gluons, using the theory of quantum chromodynamics (QCD), has been known for a long time. Nevertheless, many fundamental questions in QCD remain unanswered. This is mainly due to problems in solving the theory at low energies, where the theory is strongly interacting. AdS/CFT is a duality between a specific string theory and a conformal field theory. Duality provides new tools to solve the conformal field theory in the strong coupling regime. There is also some evidence that using the duality, one can get at least qualitative understanding of how QCD behaves at strong coupling. In this thesis, we try to address some issues related to QCD and heavy ion collisions, applying the duality in various ways.

Applications of dimensional reduction to electroweak and QCD matter

When heated to high temperatures, the behavior of matter changes dramatically. The standard model fields go through phase transitions, where the strongly interacting quarks and gluons are liberated from their confinement to hadrons, and the Higgs field condensate melts, restoring the electroweak symmetry. The theoretical framework for describing matter at these extreme conditions is thermal field theory, combining relativistic field theory and quantum statistical mechanics. For static observables the physics is simplified at very high temperatures, and an effective three-dimensional theory can be used instead of the full four-dimensional one via a method called dimensional reduction. In this thesis dimensional reduction is applied to two distinct problems, the pressure of electroweak theory and the screening masses of mesonic operators in quantum chromodynamics (QCD). The introductory part contains a brief review of finite-temperature field theory, dimensional reduction and the central results, while the details of the computations are contained in the original research papers. The electroweak pressure is shown to converge well to a value slightly below the ideal gas result, whereas the pressure of the full standard model is dominated by the QCD pressure with worse convergence properties. For the mesonic screening masses a small positive perturbative correction is found, and the interpretation of dimensional reduction on the fermionic sector is discussed.

An agent based adaptive bandwidth allocation scheme for multimedia applications

Bandwidth allocation for multimedia applications in case of network congestion and failure poses technical challenges due to bursty and delay sensitive nature of the applications. The growth of multimedia services on Internet and the development of agent technology have made us to investigate new techniques for resolving the bandwidth issues in multimedia communications. Agent technology is emerging as a flexible promising solution for network resource management and QoS (Quality of Service) control in a distributed environment. In this paper, we propose an adaptive bandwidth allocation scheme for multimedia applications by deploying the static and mobile agents. It is a run-time allocation scheme that functions at the network nodes. This technique adaptively finds an alternate patchup route for every congested/failed link and reallocates the bandwidth for the affected multimedia applications. The designed method has been tested (analytical and simulation)with various network sizes and conditions. The results are presented to assess the performance and effectiveness of the approach. This work also demonstrates some of the benefits of the agent based schemes in providing flexibility, adaptability, software reusability, and maintainability. (C) 2004 Elsevier Inc. All rights reserved.

Toiminta, valta ja kokemus organisaation muutoksessa : Tutkimus kolmesta suuryrityksestä

Action, Power and Experience in Organizational Change - A Study of Three Major Corporations This study explores change management and resistance to change as social activities and power displays through worker experiences in three major Finnish corporations. Two important sensitizing concepts were applied. Firstly, Richard Sennett's perspective on work in the new form of capitalism, and its shortcomings - the lack of commitment and freedom accompanied by the disruption to lifelong career planning and the feeling of job insecurity - offered a fruitful starting point for a critical study. Secondly, Michel Foucault's classical concept of power, treated as anecdotal, interactive and nonmeasurable, provided tools for analyzing change-enabling and resisting acts. The study bridges the gap between management and social sciences. The former have usually concentrated on leadership issues, best practices and goal attainment, while the latter have covered worker experiences, power relations and political conflicts. The study was motivated by three research questions. Firstly, why people resist or support changes in their work, work environment or organization, and the kind of analyses these behavioural choices are based on. Secondly, the kind of practical forms which support for, and resistance to change take, and how people choose the different ways of acting. Thirdly, how the people involved experience and describe their own subject position and actions in changing environments. The examination focuses on practical interpretations and action descriptions given by the members of three major Finnish business organizations. The empirical data was collected during a two-year period in the Finnish Post Corporation, the Finnish branch of Vattenfal Group, one of the leading European energy companies, and the Mehiläinen Group, the leading private medical service provider in Finland. It includes 154 non-structured thematic interviews and 309 biographies concentrating on personal experiences of change. All positions and organizational levels were represented. The analysis was conducted using the grounded theory method introduced by Straus and Corbin in three sequential phases, including open, axial and selective coding processes. As a result, there is a hierarchical structure of categories, which is summarized in the process model of change behaviour patterns. Key ingredients are past experiences and future expectations which lead to different change relations and behavioural roles. Ultimately, they contribute to strategic and tactical choices realized as both public and hidden forms of action. The same forms of action can be used in both supporting and resisting change, and there are no specific dividing lines either between employer and employee roles or between different hierarchical positions. In general, however, it is possible to conclude that strategic choices lead more often to public forms of action, whereas tactical choices result in hidden forms. The primary goal of the study was to provide knowledge which has practical applications in everyday business life, HR and change management. The results, therefore, are highly applicable to other organizations as well as to less change-dominated situations, whenever power relations and conflicting interests are present. A sociological thesis on classical business management issues can be of considerable value in revealing the crucial social processes behind behavioural patterns. Keywords: change management, organizational development, organizational resistance, resistance to change, change management, labor relations, organization, leadership

A Success Story or a Failure? : Representing the European Integration in the Curricula and Textbooks of Five Countries

The economic, political and social face of Europe has been changing rapidly in the past decades. These changes are unique in the history of Europe, but not without challenges for the nation states. The support for the European integration varies among the countries. In order to understand why certain developments or changes are perceived as threatening or as desired by different member countries, we must consider the social representations of the European integration on the national level: how the EU is represented to its citizens in media and in educational systems, particularly in the curricula and textbooks. The current study is concerned with the social representations of the European integration in the curricula and school textbooks in five European countries: France, Britain, Germany, Finland and Sweden. Besides that, the first volume of the common Franco-German history textbook was analyzed, since it has been seen as a model for a common European history textbook. As the collective representations, values and identities are dominantly mediated and imposed through media and educational systems, the national curricula and textbooks make an interesting starting point for the study of the European integration and of national and European identities. The social representations theory provides a comprehensive framework for the study of the European integration. By analyzing the curricula and history and civics textbooks of major educational publishers, the study aimed to demonstrate what is written on the European integration and how it is portrayed how the European integration is understood, made familiar and concretized in the educational context in the five European countries. To grasp the phenomenon of the European integration in the textbooks in its entirety, it was investigated from various perspectives. The two analysis methods of content analysis, the automatic analysis with ALCESTE and a more qualitative theory-driven content analysis, were carried out to give a more vivid and multifaceted picture of the object of the research. The analysis of the text was complemented with the analysis of visual material. Drawing on quantitative and qualitative methods, the contents, processes, visual images, transformations and structures of the social representations of European integration, as well as the communicative styles of the textbooks were examined. This study showed the divergent social representations of the European integration, anchored in the nation states, in the five member countries of the European Union. The social representations were constructed around different central core elements: French Europe in the French textbooks, Ambivalent Europe in the British textbooks, Influential and Unifying EU in the German textbooks, Enabling and Threatening EU in the Finnish textbooks, Sceptical EU in the Swedish textbooks and EU as a World Model in the Franco-German textbook. Some elements of the representations were shared by all countries such as peace and economic aspects of the European cooperation, whereas other elements of representations were found more frequently in some countries than in others, such as ideological, threatening or social components of the phenomenon European integration. The study also demonstrated the linkage between social representations of the EU and national and European identities. The findings of this study are applicable to the study of the European integration, to the study of education, as well as to the social representation theory.

Hybrid learning scheme for data mining applications

Classification of large datasets is a challenging task in Data Mining. In the current work, we propose a novel method that compresses the data and classifies the test data directly in its compressed form. The work forms a hybrid learning approach integrating the activities of data abstraction, frequent item generation, compression, classification and use of rough sets.