There are two primary sources of motivation for the contents of this thesis. The first is an effort to generalize classical dilation theory, a brief history of which is given in Section 2.1. The second source of motivation is the study of the representation theory of tensor algebras associated to C*-correspondences; these concepts are discussed in Sections 2.2 and 2.4. Although seemingly unrelated, there is a close connection between these two motivating theories. The link between classical dilation theory and the representation theory of tensor algebras over C*-correspondences was established by Muhly and Solel in their 1998 paper Tensor Algebras over C*-Correspondences: Representations, Dilations, and C*-Envelopes. In that paper, the authors not only introduced the concept of (operator-theoretic) tensor algebras – non-selfadjoint operator algebras that generalize algebraic tensor algebras – but they also developed the representation theory of these algebras. In order to do so, they introduced and made extensive use of a generalized dilation theory for contractions on Hilbert space. In analogy with classical dilation theory, they developed notions of “isometric dilation” and “coisometric extension” for completely contractive representations of the tensor algebra. The process of forming isometric dilations proceeded smoothly, but constructing coisometric extensions proved more problematic. In contrast to the classical case, Muhly and Solel showed that there is a high degree of nonuniqueness involved when building coisometric extensions. This lack of uniqueness proved to be an impediment to developing a full generalization of the dilation and model theories of Sz.-Nagy and Foias. In this thesis, we introduce a way to manage the ambiguities that arise when forming coisometric extensions. More specifically, we show that the notion of a transfer operator from classical dynamics can be adapted to this setting, and we prove that when a transfer operator is fixed in advance, every completely contractive representation of the tensor algebra admits a unique coisometric extension that respects the transfer operator in a fashion that we describe in Chapter 5. We also prove a commutant lifting theorem in the context of coisometric extensions.

Ce document de synthèse résume les travaux de l'auteur sur les extensions et systèmes de Hopf-Galois et leurs applications en théorie des représentations des groupes quantiques, ainsi que sur les constructions d'exemples de groupes quantiques.

Imagine how you would react if you learned that your favorite singer was recording new music in a style far from that which you have come to love. Perhaps you would disapprove. Then you might react like many Porsche consumers did when they learned that “their” brand would start producing sports utility vehicles. They are not without peers. In fact, how would you respond if a favored brand would launch, say, a chain of coffee shops? Some people would resist such an idea. These scenarios illustrate how strong consumer-brand bonds may complicate attempts to extend brands into new businesses. The research presented in the thesis explores this connection, towards a better understanding of the stakes facing both companies and consumers. It is an inquiry into tensions of extensions. The thesis comprises four published studies. Three explore how consumers with close ties to a brand react to brand extension. They acknowledge that consumers who come close to a brand potentially become stakeholders with opinions on efforts to change the products and marketing of that brand. They suggest that the implications of combining brand extension and strong consumer bonds can be substantial. The fourth study considers how the financial implications in particular can be analyzed and communicated within organizations. The findings show how brand extension can be an important event in a longer relationship with core consumers. This perspective is easily obscured when concentrating only on the perceptions of “the average consumer”. The thesis highlights symbolic and experiential aspects. It offers a closer look at such things as consumer identity, emotional reactions, and expression of criticism, and the findings should inform communication strategies and decision-making related to brand extensions. / <p>Diss. Stockholm : Handelshögskolan i Stockholm, 2008. Sammanfattning jämte 4 uppsatser</p>

The growing interest that multimedia processing has experimented during the last decade is motivating processor designers to reconsider which execution paradigms are the most appropriate for general-purpose processors. On the other hand, as the size of transistors decreases, power dissipation has become a relevant limitation to increases in the frequency of operation. Thus, the efficient exploitation of the different sources of parallelism is a key point to investigate in order to sustain the performance improvement rate of processors and face the growing requirements of future multimedia applications. We belief that a promising option arises from the combination of the Very Long Instruction Word (VLIW) and the vector processing paradigms together with other ways of exploiting coarser grain parallelism, such as Chip MultiProcessing (CMP). As part of this thesis, we analyze the problem of memory disambiguation in multimedia applications, as it represents a serious restriction for exploiting Instruction Level Parallelism (ILP) in VLIW architectures. We state that the real handicap for memory disambiguation in multimedia is the extensive use of pointers and indirect references usually found in those codes, together with the limited static information available to the compiler on certain occasions. Based on the observation that the input and output multimedia streams are commonly disjointed memory regions, we propose and implement a memory disambiguation technique that dynamically analyzes the region domain of every load and store before entering a loop, evaluates whether or not the full loop is disambiguated and executes the corresponding loop version. This mechanism does not require any additional hardware or instructions and has negligible effects over compilation time and code size. The performance achieved is comparable to that of advanced interprocedural pointer analysis techniques, with considerably less software complexity. We also demonstrate that both techniques can be combined to improve performance.In order to deal with the inherent Data Level Parallelism (DLP) of multimedia kernels without disrupting the existing core designs, major processor manufacturers have chosen to include MMX-like µSIMD extensions. By analyzing the scalability of the DLP and non-DLP regions of code separately in VLIW processors with µSIMD extensions, we observe that the performance of the overall application is dominated by the performance of the non-DLP regions, which in fact exhibit only modest amounts of ILP. As a result, the performance achieved by very wide issue configurations does not compensate for the related cost. To exploit the DLP of the vector regions in a more efficient way, we propose enhancing the µSIMD -VLIW core with conventional vector processing capabilities. The combination of conventional and sub-word level vector processing results in a 2-dimensional extension that combines the best of each one, including a reduction in the number of operations, lower fetch bandwidth requirements, simplicity of the control unit, power efficiency, scalability, and support for multimedia specific features such as saturation or reduction. This enhancement has a minimal impact on the VLIW core and reaches more parallelism than wider issue µSIMD implementations at a lower cost. Similar proposals have been successfully evaluated for superscalar cores. In this thesis, we demonstrate that 2-dimensional Vector-µSIMD extensions are also effective with static scheduling, allowing for high-performance cost-effective implementations.

ISA extensions are a very powerful approach to implement new hardware techniques that require or benefit from compiler support: decisions made at compile time can be complemented at runtime, achieving a synergistic effect between the compiler and the processor. This thesis is focused on two ISA extensions: predicate execution and register windows. Predicate execution is exploited by the if-conversion compiler technique. If-conversion removes control dependences by transforming them to data dependences, which helps to exploit ILP beyond a single basic-block. Register windows help to reduce the amount of loads and stores required to save and restore registers across procedure calls by storing multiple contexts into a large architectural register file.In-order processors specially benefit from using both ISA extensions to overcome the limitations that control dependences and memory hierarchy impose on static scheduling. Predicate execution allows to move control dependence instructions past branches. Register windows reduce the amount of memory operations across procedure calls. Although if-conversion and register windows techniques have not been exclusively developed for in-order processors, their use for out-of-order processors has been studied very little. In this thesis we show that the uses of if-conversion and register windows introduce new performance opportunities and new challenges to face in out-of-order processors.The use of if-conversion in out-of-order processors helps to eliminate hard-to-predict branches, alleviating the severe performance penalties caused by branch mispredictions. However, the removal of some conditional branches by if-conversion may adversely affect the predictability of the remaining branches, because it may reduce the amount of correlation information available to the branch predictor. Moreover, predicate execution in out-of-order processors has to deal with two performance issues. First, multiple definitions of the same logical register can be merged into a single control flow, where each definition is guarded with a different predicate. Second, instructions whose guarding predicate evaluates to false consume unnecessary resources. This thesis proposes a branch prediction scheme based on predicate prediction that solves the three problems mentioned above. This scheme, which is built on top of a predicated ISA that implement a compare-and-branch model such as the one considered in this thesis, has two advantages: First, the branch accuracy is improved because the correlation information is not lost after if-conversion and the mechanism we propose permits using the computed value of the branch predicate when available, achieving 100% of accuracy. Second it avoids the predicate out-of-order execution problems.Regarding register windows, we propose a mechanism that reduces physical register requirements of an out-of-order processor to the bare minimum with almost no performance loss. The mechanism is based on identifying which architectural registers are in use by current in-flight instructions. The registers which are not in use, i.e. there is no in-flight instruction that references them, can be early released.In this thesis we propose a very efficient and low-cost hardware implementation of predicate execution and register windows that provide important benefits to out-of-order processors.

Nous étudions le comportement des extensions linéaires au travers de deux invariants de comparabilité: le nombre de sauts et la dimension. La reconnaissance des ordres de Dilworth est montrée comme étant NP-complète, nous donnons des algorithmes polynomiaux pour résoudre ce problème sur deux sous-classes. Nous définissons les notions de dimension gloutonne et dimension dfgloutonne et étudions les cas d'égalité avec la dimension classique. Nous montrons la relation très étroite entre les extensions linéaires dfgloutonnes et les parcours en profondeur. Deux problèmes concernant les extensions linéaires dfgloutonnes sont montrés comme étant NP-difficiles.

Det är idag vanligt med företag som använder sitt befintliga varumärke för att nå nya målgrupper för att öka sin lönsamhet. Ett sätt att göra detta är att introducera produkter i en ny prisklass, en så kallad vertikal brand extension. Problemet är det att det är oklart exakt hur detta påverkar konsumenternas uppfattning om varumärket och vilka faktorer som spelar roll. Denna uppsats behandlar prestigens påverkan på konsumenternas uppfattning av varumärket vid en vertikal brand extension för företag inom den högteknologiska sektorn. Anledningen bakom att vi har begränsat oss till den högteknologiska sektorn är att det saknas empiriska undersökningar som behandlat denna bransch. All föregående datainsamling och analysering har tidigare behandlat för många branscher samtidigt vilket lett till ett resultat som inte nödvändigtvis är rättvisande för den högteknologiska. Det finns teori som hävdar att det bör vara skillnad på branscherna men det saknas relevant data för att bekräfta detta. Vi har samlat in egen primärdata genom att hålla öppna gruppintervjuer med två fokusgrupper uppdelade i två ålderssegment. Vi har valt att utgå ifrån två välkända märken som uppfattas har olika hög prestige; Apple och Asus. Vår undersökning kommer fram till att varumärken som är uppfattade att ha hög prestige har lättare att gå upp i prisklass än ett företag som uppfattas ha lägre prestige. Omvänt så har ett företag som har låg prestige lättare att gå ner i prisklass än ett företag som har hög. Dessutom finner vi att fler och fler konsumenter köper datorer baserat på funktion vilket minskar vikten av prestige inom den högteknologiska sektorn. / Every so often companies take use of their brand equity to expand to new markets and target audiences. A common strategy to do so is to introduce products in a different price class, also known as vertical brand extensions. The problem is that it is unknown how this affects the consumer’s evaluation of the brand and which factors that contributes to this effect. This thesis deals with the effects of prestige on consumer’s evaluation of vertical brand extensions in the high-technology sector. The reason for choosing the high-technology sector is that there is a lack of empirical research dealing with it separately. All recent data and analysis includes a wide variety of sectors which has resulted in conclusions that may not be relevant for the sector of our interest. Theory exists that argue that there should be a difference between these sectors but there is no evidence to prove this. We have collected our own primary data by conducting two open group interviews with two focus groups divided into two age segments. The research and questions have been formed around a couple of well-known brands; Apple and Asus. Our conclusion is that highly prestigious brands have a higher probability to succeed at introducing more expensive products than a brand with lower prestige. Brands with lower perceived prestige may likewise have a higher probability to succeed at introducing a cheaper product than their higher-prestige counterparts. Furthermore we find that more consumers base their buying decision on function rather than prestige which reduces prestige’ relevance within the high-technology sector.

In this thesis, we present our approach to add dynamism support to simulation environments, which adopts DEVS-based modeling and simulation approach and builds upon previous work on SiMA, a DEVS-based simulation framework developed at TUBITAK UEKAE. Defining and executing simulation models of complex and adaptive systems is often a non-trivial task. One of the requirements of simulation software frameworks for such complex and adaptive systems is that supporting variable structure models, which can change their behavior and structure according to the changing conditions. In the relevant literature there are already proposed solutions to the dynamism support problem. One particular contribution offered in this study over previous approaches is the systematic and automatic framework support for poststructural-change state synchronization among models with related couplings, in a way that benefits from the strongly-typed execution environment SiMA provides. In this study, in addition to introducing theoretical extensions to classic SiMA, performance comparisons of dynamic version with classic version over a sample Wireless Sensor Network simulation is provided and possible effects of dynamism extensions to the performance are discussed.

Let K/Fq be an algebraic function field with full constant field Fq and genus g. Then the divisor class number hK of K/Fq is the order of the quotient group, D0K /P(K), degree zero divisors of K over principal divisors of K. The classification of the function fields K with hK = 1 is done by MacRea, Leitzel, Madan and Queen and the classification of the extensions with class number two is done by Le Brigand. Determination of the necessary and the sufficient conditions for a function field to have class number three is done by H&uml / ulya T&uml / ore. Let k := Fq(T) be the rational function field over the finite field Fq with q elements. For a polynomial N &isin / Fq[T], we construct the Nth cyclotomic function field KN. Cyclotomic function fields were investigated by Carlitz, studied by Hayes, M. Rosen, M. Bilhan and many other mathematicians. Classification of cyclotomic function fields and subfields of cyclotomic function fields with class number one is done by Kida, Murabayashi, Ahn and Jung. Also the classification of function fields with genus one and classification of those with class number two is done by Ahn and Jung. In this thesis, we classified all algebraic function fields and subfields of cyclotomic function fields over finite fields with class number three.

Refactoring is the process of reorganising or restructuring code by means of behaviour-preserving program transformations, themselves called refactorings. Most modern development environments come with built-in support for refactoring in the form of automated refactorings that the user can perform at the push of a button. Implementing refactorings is notoriously complex, however, and even state-of-the-art implementations have very low standards of correctness and can introduce subtle changes of behaviour into refactored programs. In this thesis, we develop concepts and techniques that make it possible to give concise, modular specifications of refactorings. These specifications are precise enough to cover all details of the object language, and thus give rise to full featured, high-quality refactoring implementations. Their modularity, on the other hand, makes them amenable to formal proof, and hence opens the door to the rigorous verification of refactorings. We discuss a disciplined approach to maintaining name bindings and avoiding name capture by treating the binding from a name to the declaration it refers to as a dependency that the refactoring has to preserve. This approach readily generalises to other types of dependencies for capturing control flow, data flow and synchronisation behaviour. To implement complex refactorings, it is often helpful for the refactoring to internally work on a richer language with language extensions that make the transformation easier to express. We show how this allows the decomposition of refactorings into small microrefactorings that can be specified, implemented and verified in isolation. We evaluate our approach by giving specifications and implementations of many commonly used refactorings that are concise, yet match the implementations in the popular Java development environment Eclipse in terms of features, and outperform them in terms of correctness. We give detailed informal correctness proofs for some of our specifications, which are greatly aided by their modular structure. Finally, we discuss a rigorous formalisation of the central name binding framework used by most of our specifications in the theorem prover Coq, and show how its correctness can be established mechanically.