Proefschrift Rijksuniversiteit Groningen. / Met lit.opg. - Met samenvatting in het Nederlands.

After viewing this interactive tutorial a user will be able to login into WebCT 4 and will be able to take a multiple choice quiz.

This paper describes the coupling of contexts and ontologies for semantic integration in the ECOIN semantic interoperability framework. Ontological terms in ECOIN correspond to multiple related meanings in different contexts. Each ontology includes a context model that describes how a generic ontological term can be modified according to contextual choices to acquire specialized meanings. Although the basic ECOIN concepts have been presented in the past, this paper is the first to show how ECOIN addresses the case of "single-ontology with multiple contexts" with an example of semantic integration using our new prototype implementation.

Essays in this dissertation address three research questions. (1) What types of persons hold dual jobs and what are their motives for doing so? In essay 1, I investigate multiple factors that affect the decision to hold more than a single job. Using data from the Current Population Survey (CPS), the first essay documents the characteristics of second jobs and multiple job holders in the U.S. I characterize the types of people who hold dual jobs and use additional information from the BLS to find out workers’ motives for holding multiple jobs. I examine how multiple job holding differs with respect to age, education, race and ethnicity, sex, foreign-born status, marital status, public-private worker status, broad industry and occupation. (2) How does dual job holding vary with the business cycle and state of the labor market? Essay 2 explores a large micro data set for 1998-2013 that covers most U.S. urban labor markets. We find clear-cut evidence that multiple job holding across labor markets and over time is weakly cyclical, thus (slightly) exacerbating rather than mitigating the severity of business cycles. Much of the cyclicality in multiple job holding seen across labor markets, however, is not causal, dropping sharply after accounting for MSA fixed effects. Using longitudinal worker data, there is minimal response to unemployment changes within labor markets over time. Our large CPS sample size produces precise estimates, albeit ones close to zero, helping explain conflicting results in prior studies based on far smaller data sets. (3) How might one explain the persistent geographical differences in multiple job holding? Essay 3 documents what are systematic (i.e., long-run) differences in multiple job holding across labor markets (MSAs) and explores possible explanations for these differences. Geographical differences in multiple job holding rates have received little attention, although the multiple job holding rates in some regions of the country are substantially higher than in other regions, and these differences have been persistent over time. Examining correlates of these labor market differences in multiple job holding provides us with a better understanding of the determinants of labor supply and how local labor markets work.

Cognitive fatigue (CF) presents a considerable challenge for individuals with multiple sclerosis (MS) often negatively impacting quality of life. CF can be defined as a decrease in, or inability to sustain, optimal task performance throughout the duration of a continuous cognitive task. The following dissertation presents three original research reports which evaluate CF in MS in three distinct ways using a multidimensional approach. The objective of this dissertation was to comprehensively evaluate and quantify this frequently misunderstood symptom of the disease. The first report examines four theoretical models of CF in MS which evaluate the interrelatedness of disease severity, fatigue, depression, and sleep quality in order to determine their predictive roles with regard to CF. The second report assesses CF longitudinally by examining whether or not the ability to perform optimally on a continuous cognitive task changes as the disease progresses across a three-year time interval. The final report objectively quantifies CF in MS by evaluating changes in global and regional cerebral blood flow during a task of sustained attention using arterial spin labeling perfusion fMRI. Results of all three reports are further discussed in terms of clinical and research implications. CF is a symptom of MS not readily apparent to outside observers but presents a very real burden for people with the disease that negatively impacts their ability to lead active and productive lives. These individuals may be discriminated against because CF has thus far been a largely unverifiable subjective experience. The totality of these three studies allows for a multidimensional quantification of CF. By providing objective support to the self-reports of individuals with MS, not only can they achieve much needed validation, but this can also lead to interventions that may provide further direct benefit to their health-related quality of life.

Neural stem cell (NSC) transplantation induces recovery in animal models of central nervous system (CNS) diseases, in part by modulating adaptive and innate immune responses. Since metabolism governs the phenotype and function of immune cells, the aim of this thesis was to investigate whether NSCs have the ability to regulate the immunometabolic components underpinning neuroinflammation. Herein I have identified a new mechanism by which transplanted somatic and directly-induced NSCs counteract CNS-compartmentalised chronic inflammation in mice. NSC transplantation reduces the immunometabolite succinate in the cerebrospinal fluid, while decreasing the burden of mononuclear phagocyte (MP) infiltration and secondary CNS damage. Mechanistically, the anti-inflammatory activity of NSCs arises in response to succinate released by inflammatory MPs, which activates succinate receptor 1 (SUCNR1)/GPR91 on NSCs, thus initiating prostaglandin E2 secretion and extracellular succinate scavenging. This work uncovers a succinate-SUCNR1 axis in NSCs that clarifies how stem cells respond to inflammatory metabolic signals to inhibit the activation of pro-inflammatory MPs in the chronically inflamed brain.

The conditions under which stable separate and coalesced multiple parallel arcs can be operated from a common power supply have been investigated and analysed. Results indicate that any number of stable parallel arcs can be maintained provided each arc is individually stabilised. Multiple electrode configurations relevant to industrial plasma processes have been investigated including coalesced discharges with multiple, individually stabilised, anodes and cathodes and discharges with multiple cathodes and a common anode. The results have been applied to a number of plasma processes including a horizontal multiple discharge system, capable of producing large volumes of ionised gas with a high degree of uniformity, a plasma furnace incorporating multiple de plasma torches operating from a single power supply, and a high-current, non-consumable, multiple cathode assembly for use in do arc furnaces. A horizontal multiple arc system and a plasma furnace incorporating three plasma torches have been designed at the University and are in use for processing material at Cambridge University and in industry respectively.

Code division multiple access (CDMA) is a well-known radio communication technique that allows multiple users to share the same spectrum simultaneously. It is an alternative to frequency division and time division multiple access scheme. Its numerous advantages have merited being the main air-interface choice for the third generation (3G) mobile communication system. Nevertheless, due to the use of same frequency, the capacity of CDMA air-interface is interference limited. This problem is minimised by use of power control scheme. Power Control reduces the interference in the system by adjusting the transmitted power according to the received Signal-to-Interference (SIR) ratio. The main difficulty to achieve this scheme is that mobile terminals experience different radio propagation channel. For success completion of this task, two objectives have been identified for power control. First assure that the received signal matches the required SIR at physical layer and secondly adjust the required SIR of users at system layer to an acceptable value so that the terminals in the system are capable of achieving. In this thesis both objectives are discussed and analysed through analytical and simulation methods. At physical layer, two analytical methods based on non-linear control theory are proposed to combat the fast fading channel propagation. The proposed methods are a fast solution to assess the performance of the Closed Loop Power Control compared to the usual lengthy simulation process. At system level, a new distributed power algorithm for reverse link that adjusts the SIR target of the mobile terminal at the base station is proposed. This algorithm brings the performance of the distributed algorithm closer to the optimal solution provided by the non-feasible centralised power control algorithm in current technology.

The goal for the third generation (3G) of mobile communications system is to seamlessly integrate a wide variety of communication services such as high-speed data, video and multimedia traffic as well as voice signals for transmission on a Wideband Code Division Multiple Access (WCDMA) air interface. CDMA suffers from interference and in this thesis multiuser detection for the mobile uplink has been considered. A thorough comparative study for different multiuser detection methods is done. RAKE-IC as an architecture for mixing the ideas of RAKE receiver, and parallel Interference Cancellation, are introduced. The basic concept is to maximize the signal to noise ratio of all users in the system by using adaptive algorithms. The structure of RAKE-IC has been extended to multi-stages and several adaptive algorithms are implemented. An iterative method for interference cancellation has been considered and its convergence issue has been analytically studied. An improvement in convergence using the Rayleigh-Ritz theorem is proposed which in consequence increases the convergence speed in synchronous scenarios. Using analytical methods another improvement using the Gershgorin theorem has been proposed which does not impose a great complexity in the system, yet works well even in asynchronous environments. A suboptimum search algorithm for correcting the reliable detected information has been introduced with the property that its structure can be combined well with the iterative detectors. This combination achieves a better performance than partial parallel interference cancellation method even in rather low interference regions of operation. The structure of the sub-optimum search algorithm has been extended to multiple stages and its performance in terms of bit error rate has been analytically derived in closed form that shows good agreement with the simulation results. Considering the power profile of the users and by sacrificing a little performance, the suboptimum search structure has been further simplified. Key words: Multiuser Detection, WCDMA and Interference Cancellation.

No abstract / Decision Sciences / M. Sc. (Operations Research)