This thesis comprises four essays in the economics of networks and market design. The common thread in all these essays is the presence of complementarities or externalities. Chapter 2 presents a unified model of networks and matching markets. We build on a contribution by Pycia (2012). We show that strong pairwise alignment of agents’ preferences is a necessary and sufficient condition for the existence of strongly stable networks and strongly stable allocations in multilateral matching markets with finite contracts. Strongly stable networks are not necessarily efficient. Although we use a demanding stability concept, strong pairwise alignment allows for complementarities and externalities. In Chapter 3, we generalise the gross substitutes and complements condition introduced by Sun and Yang (2006). Our new condition guarantees the existence of competitive equilibrium in economies with indivisible goods. Competitive equilibrium can be found using an extension of the double-track adjustment process (Sun and Yang, 2009). In this chapter, we also study contract networks (Ostrovsky, 2008). We show that chain-stable contract allocations can exist even in cyclical contractual networks, such as electricity markets, as long as they are appropriately segmented. In Chapter 4, we run a series of experiments to compare the performance of four auctions – first-price, Vickrey, Vickrey-Nearest Rule (Day and Cramton, 2008), and Reference Rule (Erdil and Klemperer, 2010). In our setting, there are two items and three bidders. Two local bidders want an item each, but the global bidder wants both items. We introduce various exposure and package-bidding treatments. We find that the first-price auction always revenue-dominates all the other auctions without any loss in efficiency, strengthening the results of Marszalec (2011). Exposure affects global bidders only in the first-price auction. In other auctions, global bidders often do not take into account the effect of their own bids on their payments. We find no evidence of threshold effects. Finally, in Chapter 5, we develop a new model of online social network formation. In this model, agents belong to many overlapping social groups. We derive analytical solutions for the macroscopic properties of the network, such as the degree distribution. We study the dynamics of homophily – the tendency of individuals to associate with those similar to themselves. We calibrate our model to Facebook data from ten American colleges.

All people experience pain and for some people, acute pain may over time develop into long-term disabling problems. Already at an early stage, it is possible to identify people at risk for long-term problems and psychologically oriented interventions have been shown to successfully prevent future disability. However, not all people are helped by treatment and there is room for improvement. Moreover, subgroups of people suffering from pain, with different profiles of psychological factors have been identified, indicating that people with pain problems differ. The first aim of this dissertation was to improve the understanding of how people differ. The second aim was to use these individual differences and to match people to psychological treatment based on their psychological profile. The third aim was to explore what happens during treatment that might be important for treatment outcome. The findings show that people who belonged to subgroups with elevated levels of psychological factors had less favorable outcomes over time, despite treatment, than people with no elevations. Moreover, people with elevations in several psychological factors had even less favorable outcomes. Psychological treatments aimed at preventing future disability performed well, but using profiles to match people to treatment did not improve outcomes further; people who were matched to a treatment and people who were unmatched had similar outcomes. However, the profiles used for matching were unstable over time and there is need to improve the identification of psychological variables used for treatment matching. Finally, a number of psychological factors were shown to be valuable targets for treatment; if the treatments successfully produced change in people’s thoughts and emotions related to pain the treatment outcomes were better. The findings were summarized in a flow chart showing the recommended clinical approach to people seekinghealth care for acute pain problems.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / Map matching method plays an important role in vehicle location and navigation systems. It employs the information in a digital map to compensate the positioning error. This paper presents a fuzzy-logic-based probabilistic map-matching algorithm used in GPS/INS integrated navigation systems, in which the reliability degree of map matching resolution is given explicitly as the decision basis in selecting matching road segment by utilizing the fuzzy comprehensive judgement. The results of experimental simulations have shown that the system performance gained significant enhancement by introducing this algorithm.

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / In this paper, a devising scheme of Autonomous Vehicle Location and Navigation System is introduced firstly. Then, several key technologies used in the devising scheme are presented, which includes a data fusion method based on extended decentralized kalman filter technology, a map-matching method used to compensate the positioning error, and a digital map data processing method used to realize route planning algorithm. By this time, a sample machine based on the devising scheme introduced in this paper has already been worked out successfully. The availability and the advantages of these technologies have been demonstrated.

Thesis (PhD) -- Stellenbosch University, 2001. / Some digitised pages may appear illegible due to the condition of the original hard copy. / ENGLISH ABSTRACT: A new technique for the design of multimode devices in overmoded waveguide is presented. The technique applies the principle of growth-based design and uses a conceptual functional block representation of the design structure to provide necessary flexibility to the design algorithms. Two growth based design strategies are proposed and evaluated. The first uses a generalized synthesis-oriented scanning technique, and the second uses an evolutionary strategy. The techniques provide reliable solutions to a variety of multimode design problems. In order to facilitate sufficiently fast numerical analysis, novel enhancements of the mode matching technique are developed and the use of surrogate models is investigated. In addition, to allow physical evaluation of the finished devices, original techniques of measuring multimode devices are formulated and utilised. Two practical problems are used to evaluate the performance of the design procedures. The first is the design of overmoded waveguide chokes for microwave heating facilities, and the second is the design of multimode horns for antenna and spatial power combining applications. Various examples of each type of problem are presented with measurements of manufactured solutions. / AFRIKAANSE OPSOMMING: ’n Nuwe tegniek vir die ontwerp van multimodusstelsels binne multimodus golfleier word voorgestel. Die tegniek maak gebruik van die beginsel van groei-georienteerde ontwerp en ontgin ’n konsepsuele funksionele module-voorstelling van die ontwerpstruktuur om die nodige buigsaamheid aan die ontwerpsalgoritmes te verleen. Twee groei-georienteerde ontwerpstrategiee word aangebied en geevalueer. Die eerste is gebasseer op ’n veralgemeende sintese-georienteerde skandeertegniek, en die tweede maak gebruik van ’n evolusie-strategie. Die tegniek verskaf betroubare oplossings vir ’n verskeidenheid van multimodusontwerpsprobleme. Ten einde ’n numeriese analise-tegniek daar te stel wat vinnig genoeg is, word oorspronklike verbeterings van die modal-pas metode ontwikkel en surrogaatmodelle is ook ondersoek. Verder, vir fisiese evaluasie, word oorspronklike meettegnieke vir multimodusstelsels geformuleer en gebruik. Twee praktiese probleme word gebruik om die ontwerpprosedures te evalueer. Die eerste is die ontwerp van multimodus golfleierdrywingsdempers vir mikrogolfverhitting, en die tweede is die ontwerp van multimodus horings vir antenna- en ruimtelike drywingskombineerdertoepasings. Verskeie voorbeelde van elke tipe probleem word gegee met metings van gei'mplementeerde oplossings.

There has been an increasing interest in Semantic Web services (SWS) as a proposed solution to facilitate automatic discovery, composition and deployment of existing syntactic Web services. Successful implementation and wider adoption of SWS by research and industry are, however, profoundly based on the existence of effective and easy to use methods for service semantic description. Unfortunately, Web service semantic annotation is currently performed by manual means. Manual annotation is a difficult, error-prone and time-consuming task and few approaches exist aiming to semi-automate that task. Existing approaches are difficult to use since they require ontology building. Moreover, these approaches employ ineffective matching methods and suffer from the Low Percentage Problem. The latter problem happens when a small number of service elements - in comparison to the total number of elements – are annotated in a given service. This research addresses the Web services annotation problem by developing a semi-automatic annotation approach that allows SWS developers to effectively and easily annotate their syntactic services. The proposed approach does not require application ontologies to model service semantics. Instead, a standard query template is used: This template is filled with data and semantics extracted from WSDL files in order to produce query instances. The input of the annotation approach is the WSDL file of a candidate service and a set of ontologies. The output is an annotated WSDL file. The proposed approach is composed of five phases: (1) Concept extraction; (2) concept filtering and query filling; (3) query execution; (4) results assessment; and (5) SAWSDL annotation. The query execution engine makes use of name-based and structural matching techniques. The name-based matching is carried out by CN-Match which is a novel matching method and tool that is developed and evaluated in this research. The proposed annotation approach is evaluated using a set of existing Web services and ontologies. Precision (P), Recall (R), F-Measure (F) and Percentage of annotated elements are used as evaluation metrics. The evaluation reveals that the proposed approach is effective since - in relation to manual results - accurate and almost complete annotation results are obtained. In addition, high percentage of annotated elements is achieved using the proposed approach because it makes use of effective ontology extension mechanisms.

Adolescence is characterized by systematic and dramatic physical and behavioural changes, the most noticeable physical growth is the rapid increase in stature marked by peak height velocity (PHV). Anecdotally, many people are aware that as youth pass through their adolescent growth spurt there is a perceived period of physical awkwardness; however, there is no scientific agreement as to whether a period of awkwardness associated with the adolescent growth actually exists. Previous research has focused on the development of general motor performance or gross motor coordination. Increases in strength during adolescence may mask the effect of a stage of adolescent awkwardness on general motor performance tasks. To detect adolescent awkwardness it is necessary to measure either performance of skills that specifically do not depend on strength, or body awareness. The purpose of this study was to investigate whether female adolescents’ awareness of their body size and movement was influenced by biological maturation, and whether adolescent awkwardness could be detected in performance of sport specific skills independent of strength. An endpoint matching task was used to measure awareness of foot position in space by measuring the distance (mm) between a reference and matching endpoint position (endpoint matching error (EME)) with eyes either open or closed. The Johnson wall volley and a ball juggling task were used to measure soccer specific skill and coordination. Thirty six female youth soccer players, aged 10-14 years, were recruited. Age at PHV was predicted from measures of age, height, leg length and weight. Three groups were identified: pre-PHV (n=6), PHV (n=5) and post –PHV (n=25). Mean group differences were assessed using ANOVA. It was found that when the endpoint matching task was performed with eyes open there was no significant difference in mean EME between groups (p > 0.05). With eyes closed the PHV group performed worse than the pre-PHV and post-PHV groups. The Post-PHV group significantly (p < 0.05) decreased their EME (22.2 ± 13.9) compared to the PHV group (32.8 ± 17.6) but no difference was found with the Pre-PHV group (27.5 ± 15.7). On the wall volley test the Post-PHV group performed significantly (p < 0.05) better compared to the PHV group but not the Pre-PHV group. The Post-PHV group performed significantly (p < 0.05) better on the ball juggling task compared to both the Pre-PHV and the PHV groups. In conclusion, the results suggest that in the year around PHV body awareness, as measured by EME, may plateau or decrease and that soccer skill performance plateaus. This plateau or decrease in body awareness and soccer skills involving coordination is likely temporary; participants in this study who were > 6 months past PHV had significantly better body awareness and soccer skill performance than those participants who were within 6 months of PHV. The results from the endpoint matching task also indicate that a measure of body size and movement awareness has the potential to be used to measure changes in body awareness during the adolescent growth spurt. The results of this study suggest that teenage clumsiness could exists. However, a definitive study with larger maturity groups followed over time is required to confirm this statement.

This dissertation addresses the problem of inferring scene depth information from a collection of calibrated images taken from different viewpoints via stereo matching. Although it has been heavily investigated for decades, depth from stereo remains a long-standing challenge and popular research topic for several reasons. First of all, in order to be of practical use for many real-time applications such as autonomous driving, accurate depth estimation in real-time is of great importance and one of the core challenges in stereo. Second, for applications such as 3D reconstruction and view synthesis, high-quality depth estimation is crucial to achieve photo realistic results. However, due to the matching ambiguities, accurate dense depth estimates are difficult to achieve. Last but not least, most stereo algorithms rely on identification of corresponding points among images and only work effectively when scenes are Lambertian. For non-Lambertian surfaces, the "brightness constancy" assumption is no longer valid. This dissertation contributes three novel stereo algorithms that are motivated by the specific requirements and limitations imposed by different applications. In addressing high speed depth estimation from images, we present a stereo algorithm that achieves high quality results while maintaining real-time performance. We introduce an adaptive aggregation step in a dynamic-programming framework. Matching costs are aggregated in the vertical direction using a computationally expensive weighting scheme based on color and distance proximity. We utilize the vector processing capability and parallelism in commodity graphics hardware to speed up this process over two orders of magnitude. In addressing high accuracy depth estimation, we present a stereo model that makes use of constraints from points with known depths - the Ground Control Points (GCPs) as referred to in stereo literature. Our formulation explicitly models the influences of GCPs in a Markov Random Field. A novel regularization prior is naturally integrated into a global inference framework in a principled way using the Bayes rule. Our probabilistic framework allows GCPs to be obtained from various modalities and provides a natural way to integrate information from various sensors. In addressing non-Lambertian reflectance, we introduce a new invariant for stereo correspondence which allows completely arbitrary scene reflectance (bidirectional reflectance distribution functions - BRDFs). This invariant can be used to formulate a rank constraint on stereo matching when the scene is observed by several lighting configurations in which only the lighting intensity varies.

This is a study in two parts. In part-1, I identify several methods of estimating long-run abnormal returns prevalent in the finance literature and present an alternative using propensity score matching. I first demonstrate the concept with a simple simulation using generated data. I then employ historical returns from CRSP and randomly select events from the dataset using various alternating criteria. I test the efficacy of different methods in terms of type-I and type-II errors in detecting abnormal returns over 12- 36- and 60- month periods. I use various forms of propensity score matching: 1--5 Nearest Neighbors in Caliper using distance defined alternatively by Propensity Scores and the Mahalanobis Metric, and Caliper Matching. I show that overall, Propensity Score Matching with two nearest neighbors provides much better performance than traditional methods, especially when the occurence of events is dictated by the presence of certain firm characteristics. In part-2, I demonstrate an application of Propensity Score Matching in the context of open-market share repurchase announcements. I show that traditional methods are ill-suited for the calculation of long-run abnormal returns following such events. Consequently, I am able to improve upon such methods on two fronts. First, I improve upon traditional matching methods by providing better matches on multiple dimensions and by being able to retain a larger sample of firms from the dataset. Second, I am able to eliminate much of the bias inherent in the Fama-French type methods for this particular application. I show this using simulations on samples based on firms that resemble a typical repurchasing firm. As a result, I obtain a statistically significant 1-, 3-, and 5- year abnormal return of about 2%, 5%, and 10% respectively, which is much lower than what prior literature has shown using traditional methods. Further investigation revealed that much of these returns are unique to small and unprofitable firms.

This Thesis is an embodiment of some research work carried out towards achieving faster and more reliable handover techniques in a Mobile WiMAX (Worldwide Interoperability for Microwave Access) network. Handover, also called handoff, is the critical mechanism that allows an ongoing session in a cellular mobile network like WiMAX to be seamlessly maintained without any call drop as the Mobile Station (MS) moves out of the coverage area of one base station (BS) to that of another. Mobile WiMAX supports three different types of handover mechanisms, namely, the hard handover, the Fast Base Station Switching (FBSS) and the Micro-Diversity Handover (MDHO). Out of these, the hard handover is the default handover mechanism whereas the other two are the optional schemes. Also, FBSS and MDHO provide better performance in comparison to hard handover, when it comes to dealing with the high-speed multimedia applications. However, they require a complex architecture and are very expensive to implement. So, hard handover is the commonly used technique accepted by the mobile broadband wireless user community including Mobile WiMAX users. The existing Mobile WiMAX hard handover mechanism suffers from multiple shortcomings when it comes to providing fast and reliable handovers. These shortcomings include lengthy handover decision process, lengthy and unreliable procedure of selecting the next BS, i.e., the target BS (TBS) for handover, occurrence of frequent and unwanted handovers, long connection disruption times (CDT), wastage of channel resources, etc. Out of these, reducing the handover latency and improving the handover reliability are the two issues that our present work has focused on. While the process of selecting the TBS for handover adds to the overall delay in completing the process of handover, choosing a wrong TBS for handover increases the chance of further unwanted handovers to occur or even a call drop to occur. The latter greatly hampers the reliability of a handover. In order to contribute to the solution of the above two problems of slow handover and unreliable handover, this Thesis proposes and investigates three handover techniques, which have been called Handover Techniques 1, 2 and 3, respectively. Out of these three techniques, the first two are fully MS-controlled while the third one is a dominantly serving BS-controlled. In Handover Techniques 1 and 2, which share between them some amount of commonness of ideas, the MS not only itself determines the need for a handover but also self-tracks its own independent movement with respect to the location of the (static) neighboring BSs (NBS). N both these handover techniques, the MS performs distance estimation of the NBSs from the signal strength received from the NBSs. But they (the two handover techniques) employ different kinds of “lookahead” techniques to independently choose, as the TBS, that NBS to which the MS is most likely to come nearest in the future. Being MS-controlled, both Handover Technique 1 and Handover Technique 2 put minimal handover-related workload on their respective SBSs who thus remain free to offer services to many more MSs. This interesting capability of the two handover techniques can increase the scalability of the WiMAX network considerably. In Handover Technique 3, which is a BS-controlled one with some assistance received from the MS, the SBS employs three different criteria or parameters to select the TBS. The first criterion, a novel one, is the orientation matching between the MS’s direction of motion and the geolocation of each NBS. The other two criteria are the current load of each NBS (the load provides an indication of a BS’s current QoS capabilities) and the signal strength received by the MS from each NBS. The BS assigns scores to each NBS against each of the three independent parameters and selects the TBS, which obtains the highest weighted average score among the NBSs. All three handover techniques are validated using simulation methods. While Handover Techniques 1 and 2 are simulated using Qualnet network simulator, for Handover Technique 3, we had to design, with barest minimum capability, our own simulation environment, using Python. Results of simulation showed that for Handover Techniques 1 and 2, it is possible to achieve around 45% improvement (approx) in the overall handover time by using the two proposed handover techniques. The emphasis in the simulation of the Handover Technique 3 was on studying its reliability in producing correct handovers rather than how fast handovers are. Five different arbitrary pre-defined movement paths of the MS were studied. Results showed that with orientation matching or orientation matching together with signal strength, reliability was extremely good, provided the pre-defined paths were reasonably linear. But reliability fell considerably when relatively large loads were also considered along with orientation matching and signal strength. Finally, the comparison between the proposed handover techniques in this Thesis and few other similar techniques in Mobile WiMAX proposed by other researchers showed that our techniques are better in terms providing fast, reliable and intelligent handovers in Mobile WiMAX networks, with scalability being an added feature.