<p>Pelagic fish distribution and diel behaviour patterns were studied in coastal areas in the north-western Baltic Sea Proper to understand more about how fish distribution and behaviour might affect planning and analyses of results of hydroacoustic surveys (Papers I and II). The vertical distribution of fish at night from spring to autumn showed seasonal and annual trends that could be explained by predictable and consistent seasonal changes, e.g., in temperature and stratification. Horizontal fish distributions did not show any trends probably owing to a lack of such seasonal characteristics. The observed vertical fish distribution over the diel cycle showed that hydroacoustic surveys at night were to be preferred over daytime surveys. At night, fish did not school and were generally less aggregated resulting in less variable hydroacoustic backscattering values and a higher percentage of single echo detections. By starting the surveys one hour after sunset and stopping one hour before sunrise, confusion between day- and nighttime behaviour in fish could be avoided. At night, fish occupied mid-water layers to a higher extent than surface and bottom layers, which was beneficial for the quality of the hydroacoustic data, particularly with respect to the hydroacoustic blind and dead zones (i.e. surface and bottom, respectively).</p><p>To quantify seasonal changes in pelagic fish abundance, densities and size distributions, nighttime hydroacoustic surveys were done every second week from spring through autumn in 2000 and 2001 (Paper III). There was a drastic increase in fish abundance and densities that started in early July and peaked in mid-August in both years. Analyses of the hydroacoustic data in relation to gillnet and trawl catches showed that the increase was caused mainly by young-of-the-year (YOY) herring. This age class is commonly not well represented in catches using traditional sampling methods like gillnets and trawling. Consequently, hydroacoustic data that have high precision and accuracy may improve quantitative estimates and our understanding of the biology in coastal nursery areas.</p><p>Baltic herring spawn in coastal areas and the density of metamorphosed YOY individuals may provide an early estimate of year-class strength. By analysing the relationship between parameters known to affect recruitment success and year-class strength in age 2 herring (YCS) a model that predicted herring recruitment was developed (Paper IV). The model explained 93 % of the variation in the number of age 2 herring over the period 1985-2000 and included the parameters YOY densities, climate (North Atlantic Oscillation index) and spawning stock biomass (SSB). Thus YCS could be predicted two years earlier than today and three years before entering the fishery. Up to the present, three new years (2001-2003) have become available for testing the model. For one of these years the predicted YCS was notably different from the assessed YCS. The reason for this is not fully understood, but for all three years SSB was outside the range used in the original model. Including the three new years into the data series resulted in a poorer explanation of the observed recruitment variation (55 %). A comparison of the standardized regression coefficients of both models showed increased significance for the parameter YOY (from 0.47 to 0.61).</p>

Physical distribution is one of the key functions in logistics systems, involving the flow of products from manufacturing plants or distribution centers through the network of transportation to consumers. The function is very costly, especially for the distribution industries. During the past decades, the significance of physical distribution has increased enormously in both economic and managerial aspects. Several firms have realized that an efficiency improvement and a cost control of physical distribution would provide a potential for cost reduction and hence profit improvement. However, the customer satisfaction cannot be disregarded, since the focus on reducing cost often decreases the customer service level in many cases. A compromised strategy which lowers the cost of physical distribution and accounts for customer satisfaction must be sought. In this research, an effort to improve distribution strategies and reduce the distribution cost for the multi-product, multi-depot periodic distribution problem is made, while maintaining the desired customer service levels. In industry practice, distribution centers typically operate independently within their own territories only. However, it may be beneficial to allow those distribution centers to operate interdependently, particularly when the product supplies are limited at some distribution centers. In such cases, the distributors may satisfy customers' requests by delivering products from other distribution centers that hold more supplies. The interaction of interdependent operations among distribution centers, which have not been used in the industrial applications so far, is investigated. A mixed-integer linear programming model is formulated to represent this multi-product, multi-depot periodic distribution problem. Three tabu-search heuristics with different applications of long-term memory are developed for solving the problem. The performance of the heuristics is evaluated by comparing the solutions obtained with the optimal solutions or lower bounds from the regular branch-and-bound method and fast lower-bound finding techniques developed in this research. The heuristics provide good-quality solutions in a much shorter time than those methods. The performance of the three tabu-search heuristics is compared using statistical experiments based on the randomized complete block design and Tukey's Honestly Significant Differences. The experimental results show that the tabu-search heuristic with the use of long-term memory for diversification process outperforms the others. The heuristic is further applied to investigate the impact of interdependent operations among distribution centers. The results reveal that the interdependent operations among distribution centers provide a significant cost saving over the independent operations among distribution centers, especially for large-size problems. / Graduation date: 2004

Forest carnivores such as the fisher have frequently been the target of conservation concern due to their association with older forests and assumed sensitivity to landscape-level habitat alteration. Although the fisher has been extirpated from most of its former range in the western U.S., it is still found throughout much of northwestern California. However, fisher distribution is still poorly known in the majority of this region where surveys have not been conducted. In order to predict fisher distribution across the region, a multiple logistic regression model was created using data from 682 previously surveyed locations and a GIS vegetation coverage created from satellite imagery. A moving-average function was used to derive landscape level indices of vegetation variables from the GIS layer. Moving averages of canopy closure, tree size class, and percent conifer were found to have strong correlations with fisher presence. Regional gradients as represented by either precipitation or a trend surface derived from spatial coordinates were also significant predictors in the model. The model was validated with new data collected from 240 survey locations and proved to be accurate in predicting fisher presence in unsurveyed areas. The model was used to generate hypotheses as to the mechanisms controlling habitat selection and the scales at which these operate and to evaluate the representation of fisher habitat in existing protected areas. These insights may be valuable in designing conservation reserve networks that insure the long-term viability of forest carnivore populations. / Graduation date: 1998

Graduation date: 1998

The computation of a piecewise smooth function that approximates a finite set of data points is decomposed into two decoupled tasks: first, the computation of the locally smooth models, and hence, the segmentation of the data into classes that consist on the sets of points best approximated by each model, and second, the computation of the normalized discriminant functions for each induced class. The approximating function is then computed as the optimal estimator with respect to this measure field. Applications to image processing and time series prediction are presented as well.

The ability to distribute signals everywhere in a circuit with controlled and known delays is essential in large, high-speed digital systems. We present a technique by which a signal driver can adjust the arrival time of the signal at the end of the wire using a pair of matched variable delay lines. We show an implemention of this idea requiring no extra wiring, and how it can be extended to distribute signals skew-free to receivers along the signal run. We demonstrate how this scheme fits into the boundary scan logic of a VLSI chip.

Thesis (M.B.A.)--North-West University, Potchefstroom Campus, 2009.

The first essay studies the channel relationship between the reseller and the manufacturer based on a social network theory framework. We propose a conceptual model that approaches this topic from a relational embeddedness perspective. Our analysis shows how the reseller can strategically develop relational ties with a manufacturer that transform the latters common marketing mix into unique resources that enhance the resellers own profit. Results from a large scale survey of beer resellers in a local Chinese market suggest that in a channel setting, social norms (e.g. communication effectiveness and conflict resolution) and social relations influence the resellers access to the manufacturers valuable resources. Furthermore, we find that over embeddedness affects the resellers profit in a non-linear manner. That is, a resellers effort to develop a relationship with a particular manufacturer may generate information that lacks freshness, objectivity or usefulness, thereby diminishing the resellers profitability. Theory of social contagion states that individuals adoption of new product depends on the adoption of his immediate neighbors in a social network in addition to the influence from other sources. This research models the dynamic diffusion process of new drug in a social network of physicians. We simulated the information transmission process in a social network, where each network entity repetitively influences the probability of connected entitys new product adoption. The simulation approach integrates two seemingly contradictive concepts of cohesion and structural equivalence into a single modeling framework. Besides, it incorporates a coefficient that describes an individual entitys efficiency of information transmission. On the one extreme it assumes that information transmits to only one of the network neighbors and on the other extreme it assumes that information transmits to all of the network neighbors. We revisited Medical Innovation data and empirically find an optimum point for each of the four cities in this data set, using a discrete time hazard model. The four cities demonstrate different patterns of information transmission. Managerially, we suggest different ways of pinpointing initial adopters in different types of social networks. / Marketing

This study examined fairness in the online society of World of Warcraft(WoW), a society under constraint by game developers but dynamically affected by users. Because the society is voluntary, people have the ability to both effect major change on, and leave, that society at any time. Thus, fairness in this virtual world is an important area for anthropological research. In-game fairness pointed to the organization, distribution, and acquisition of wealth. In particular, I examined player perceptions of real-money trading (RMT) in the context of individual and collective motivations in the endgame. In addition, I considered loot distribution systems as a mode of promoting player-initiated definitions of fairness. I discovered an overall economy of fun in which players act to maximize fun for the majority. Real-money trading was justified by casual players because players require progression as individuals in order to better serve the fun of the collective.

In polymer electrolyte membrane (PEM) fuel cells one of the most important components is the flow field. The flow field distributes reactant gasses to the active area and also delivers electrons from the outer circuit so that the electrochemical reaction may be completed. Optimizing flow field design is extremely important in order to increase the overall power density of the fuel cell. It is particularly important to understand the ways in which the different portions of the flow field, namely the land and channel sections, interact with the gas diffusion layer (GDL), catalyst layer and membrane; this study focuses on those interactions. The most common type of flow field design currently used in PEM fuel cells is the serpentine flow field. It is used for its simplicity of design, its effectiveness in distributing reactants and its water removal capabilities. The knowledge about where current density is higher, under the land or the channel, is critical for flow field design and optimization. Yet, no direct measurement data are available for serpentine flow fields. In this study a fuel cell with a single channel serpentine flow field is used to separately measure the current density under the land and channel, which is either catalyzed or insulated on the cathode. In this manner, a systematic study is conducted under a wide variety of conditions and a series of comparisons are made between land and channel current density. Results show that under most operating conditions, current density is higher under the land than that under the channel. However, at low voltage, a rapid drop off in current density occurs under the land due to concentration losses. The mechanisms for the direct measurement results and general guidelines for serpentine flow field design and optimizations are provided. In addition the same technique is utilized to separately measure current density under the land and channel on a variety of serpentine flow field geometries. Each flow field is tested under a wide variety of operating conditions thereby providing guidance for the optimum design geometry. Experimental results show that generally flow fields with both thinner lands and thinner channels provide better overall performance. However, the optimal flow field designs are highly dependent on fuel cell operating parameters. Finally, it is critical not only to know where the current density is greater, under the land or under the channel, but to understand the fundamental mechanisms driving these differences. Resistance was measured, ex-situ, between the GDE and flow plate under the land of the flow field and under the channel separately. The contact resistance between the gas diffusion electrode (GDE) and the graphite flow plate were measured using an ex-situ technique. The resistance was measured under different land and channel widths. Cyclic Voltammetry tests were also conducted in order to determine if there is any different in electrochemically active area(ECA) under the land and under the channel and what the cause of this difference might be. Results show that the compression of the gas diffusion electrode not only affects the electronic resistance but the ECA as well and that these are key factors in current density variations under the land and channel.