Dynamic channel assignment algorithms allow wireless nodes to switch channels when their traffic loads exceed certain thresholds. These thresholds represent estimations of their throughput capacities. Unfortunately, the threshold estimation may not be accurate due to co-channel interference (CCI) and adjacent-channel interference (ACI), especially with high traffic loads in dense networks. When the link capacity is over-estimated, these channel assignment algorithms are not effective. This is because channel switch is not triggered even with overloaded data traffic and the link quality decreases significantly as the channel is overloaded. When the link capacity is under-estimated, the link is under utilized. Moreover, when link traffic load increases from time to time, channel switch occurs frequently. Such frequent channel switches increase latency and degrade throughput, and can even cause network wide channel oscillations. In this paper, we propose a novel threshold-based control system, called \emph{balanced control system} (BCS). The proposed threshold-based control policy consist of deciding, according to the real time traffic load and interference, whether to switch to another channel,{which channel should be switched to and how to perform the switch. Our control model is based on a fuzzy logic control. The threshold which assists to make the channel switch decisions, could be deduced dynamically according to the real-time traffic of each node. We also design a novel dynamic channel assignment scheme, which is used for the selection of the new channel. The channel switch scheduler is provided to perform channel-switch processing for sender and receiver over enhanced routing protocols. We implement our system in NS2, and the simulation results show that with our proposed system, the performance improves by 12.3\%-72.8\% in throughput and reduces 23.2\%-52.3\% in latency. / Computer and Information Science

Wireless mesh networks have received increasing interest in recent years due to the fast expanding Wi-Fi market. More and more, individual communities and companies are beginning to set up intranets with multiple Wi-Fi access points, so that clients can communicate using wireless connections. Because the traditional IEEE 802.11 standard cannot provide efficient performance for mesh networks, the IEEE set up a task group in 2001 to establish a wireless mesh network standard, IEEE 802.11s. For compatibility, IEEE 802.11s will be an extension of the IEEE 802.11 MAC/PHY, and as a result, the new standard has inherited both the pros and cons of IEEE 802.11. Co-channel and inner-channel interference are the dominant factors affecting the system performance of wireless networks. Since there are a number of available non-overlapping channels one can always use these in order to eliminate inner-channel interference. However, the number of channels is not sufficient for an ESS Mesh if channel reuse is not considered, not only because of the network size, but also because of the non-licensed nature of the IEEE 802.11 PHY ISM band, where the network will suffer interference from other co-located networks. For this reason, channel reuse in an ESS Mesh is essential and reducing co-channel interference is a key issue in channel assignment. In this thesis, we investigate the performance of deterministic traffic scheduling with channel assignment in an ESS Mesh based on a TDMA MAC framework while still using the IEEE 802.11 PHY. We first analyze an upper bound on channel assignment performance, considering both binary interference models and cumulative interference models. Then, a scheduling solution for deterministic traffic is proposed, based on heuristic channel assignment and path selection algorithms. Our simulation results show that the scheduling solution is feasible and the performance is close to the theoretical value. / Thesis / Master of Applied Science (MASc)

A current trend in residential construction is the use of prefabricated wall panels. It is important to carefully establish how panels will be stacked, because an optimal sequence will improve productivity and reduce the possibility of worker injury. Mathematical models and heuristics are proposed for solving the panel stacking problem without consideration of interference. Dissertation work includes a mathematical model of the corresponding panel stacking problems in which the goal is to minimize total weighted panel move distance concurrent with certain construction assumptions. The heuristic method was provided to establish how each panel would be stacked and gave the drop-off location of each stack. The heuristic method was found to be able to reduce the total weighted panel move distance and ensure connectivity was always maintained, meanwhile, interference could also be avoided. In terms of solution speed, the heuristic method can solve real size problems in less than one second. Solutions to such problems can increase productivity. Three improvements to the only known existing panel stacking algorithm with consideration of interference were proposed. The computational results indicate the proposed algorithm performed better than existing algorithm in all experimental cases. Improvement on panel move distance ranged from 1.35-47.93%, and improvement on interfering panels ranged from 20-100%. The proposed algorithm can solve non-rectangular cases (not possible with existing algorithm) and was compared with an experienced panel designer and commercial software. When compared to the proposed algorithm, total weighted panel move distance increased 0.10-85.52% and 0.77-136.23%, respectively, for the panel designer and software. While connectivity was 100% for all cases with the proposed algorithm (the algorithm ensures connectivity is always maintained), it ranged from 69.56-86.95% and 73.33-90.91%, however, for the panel designer and software respectively. Finally, the proposed algorithm can solve the interfering panels in the last stack: this cannot be done with the existing algorithm. Because prefabricated wall panels are typically large and cumbersome to work with, there is a significant probability of worker injury. It is important to carefully establish how each panel will be handled by workers. This is typically the responsibility of field construction foreman, but such personnel are often ill-equipped to make such decisions. An alternative, proactive approach is to establish how each panel will be handled in advance, such that overall ergonomic consequences can be properly considered. This dissertation presents mathematical models of the corresponding construction task scheduling and worker assignment problems, where the goal is to minimize total project completion time (subject to worker quantity constraints) and assign tasks to workers as evenly as possible. The solution of such problems can help residential construction managers better plan construction by establishing the ergonomic impact associated with a given construction plan. A heuristic was also developed to solve large problems by balancing workload between workers. The heuristic was found to be able to provide near-optimal solutions, and can solve large problems in less than one second. / Ph. D.

One of the most popular and useful areas of graph theory is graph colorings. A graph coloring is an assignment of integers to the vertices of a graph so that no two adjacent vertices are assigned the same integer. This problem frequently arises in scheduling and channel assignment applications. A list coloring of a graph is an assignment of integers to the vertices of a graph as before with the restriction that the integers must come from specific lists of available colors at each vertex. For a physical application of this problem, consider a wireless network. Due to hardware restrictions, each radio has a limited set of frequencies through which it can communicate, and radios within a certain distance of each other cannot operate on the same frequency without interfering. We model this problem as a graph by representing the wireless radios by vertices and assigning a list to each vertex according to its available frequencies. We then seek a coloring of the graph from these lists. In this thesis, we give an overview of the last thirty years of research in list colorings. We begin with an introduction of the list coloring problem, as defined by Erdös, Rubin, and Taylor in [6]. We continue with a study of variations of the problem, including cases when all the lists have the same length and cases when we allow different lengths. We will briefly mention edge colorings and overview some restricted list colors such as game colorings and L(p, q)-labelings before concluding with a list of open questions. / Master of Science

Process planning is an important and integral part of operating a printed circuit board (PCB) assembly system effectively. The focus of this research is to develop a new solution approach to determine the component placement sequence and feeder assignment for a turret style Chip Shooter machine often used in PCB assembly systems. This solution approach can be integrated into a process planning system to reduce assembly time and improve productivity. The Chip Shooter machine consists of three primary mechanisms: the turret head, a moving table, and the feeder carriage. These mechanisms move simultaneously in a cyclic manner to mount the components on the PCB. The mechanism with the longest movement time determines the placement time of a component. Therefore, the placement sequence of the components and the arrangement of the feeders in the feeder carriage directly affect the time required to mount all the components on a PCB. A placement time estimator function that accounts for the functional characteristic of the Chip Shooter machine is developed and is used to evaluate the performance of the solution approach presented in this research. The solution approach consists of a construction algorithm that uses a set of knowledge-based rules to construct an initial placement sequence and feeder assignment, and an improvement procedure to improve the initial solution. A case study is presented to validate the proposed solution approach. A Fuji CP4-3 machine and actual PCB data are used to test the performance of the proposed solution approach for different machine setup scenarios. The solutions obtained using the proposed solution approach are compared to those obtained using state of the art PCB assembly process optimization software. For all PCBs in the case study, the proposed solution approach yielded lower placement times than the commercial software, thus generating additional valuable production capacity. / Master of Science

Conference paper assignment---the task of assigning paper submissions to reviewers---is a key step in the management and smooth functioning of conferences. We study this problem as an application of recommender systems research. Besides the traditional goal of predicting `who likes what?', a conference management system must take into account reviewer capacity constraints, adequate numbers of reviews for papers, expertise modeling, conflicts of interest, and an overall distribution of assignments that balances reviewer preferences with conference objectives. Issues of modeling preferences and tastes in reviewing have traditionally been studied separately from the optimization of assignments. In this thesis, we present an integrated study of both aspects. First, due to the sparsity of data (relative to other recommender systems applications), we integrate multiple sources of information to learn reviewer/paper preference models, using methods commonly associated with merging content-based and collaborative filtering in the study of large recommender systems. Second, our models are evaluated not just in terms of prediction accuracy, but also in terms of end-assignment quality, and considering multiple evaluation criteria. Using a linear programming-based assignment optimization formulation, we show how our approach better explores the space of potential assignments to maximize the overall affinities of papers assigned to reviewers. Finally, we demonstrate encouraging results on real reviewer preference data gathered during the IEEE ICDM 2007 conference, a premier international data mining conference. Our research demonstrates that there are significant advantages to applying recommender system concepts to the conference paper assignment problem. / Master of Science

The use of teams and work groups in organizations has become increasingly more popular in the last decade. Within each of these groups, a leadership role must be filled in order for the team to achieve its task. This study posited that the method by which the leader comes into this role may have a direct impact on the group's performance and its perceptions of the group's interpersonal processes and efficiency, satisfaction with the group, satisfaction with the group output, and support for the leader. In addition, the influence of leader assignment was expected to change based on the level of interdependence required by the task. One hundred forty-eight subjects were assigned to one of four conditions in a 2X2 design (appointed vs. elected leaders X high vs. low interdependence task), and were asked to fill out a questionnaire upon completion of their task. Results found that the higher level of interdependence was significantly related to more favorable ratings of Perceived Group Efficiency ( F =6.89, p <.05) and Satisfaction with Group Output ( F =7.69, p <.05). Possible limitations and future research opportunities are addressed. / Master of Science

<p>Since the pactum de non cedendo is prohibitory by its nature and operation, our law should have proceeded with caution when determining its effect. This, unfortunately, is not what transpired in the locus classicus decision. Nor did subsequent cases correct this fatal ratio. The distressing truth is that the old authorities, upon whom the locus classicus judgment is based, were in all probability not writing about pacta de non cedendo. Strangely enough, when this was suggested by an academic in the field, it elicited no response. The lack of response evidences a lack of interest in the topic in general, partly due to the uncertain state of affairs in which the pactum de non cedendo operates, and partly due to the courts&rsquo / unwillingness to rectify the situation. Despite the waning interest, the pactum de non cedendo is prevalent and appears in many types of contracts, most recently in the powerhouse factoring industry, and cannot simply be swept under the rug. This dissertation breathes new life into the pactum de non cedendo and discusses its validity and effect from a fresh perspective: A commercial perspective with a strong influence from American law. Hopefully this re-evaluation of the pactum de non cedendo will re-capture the attention of academics and judges alike, so that those in the position to do so, will re-consider its validity and effect.</p>

This thesis concerns different areas of biomolecular nuclearmagnetic resonance spectroscopy (NMR). In the first part of thethesis a new formalism for simulations of NMR pulse sequencesis introduced. The formalism is derived both from classicalmechanics and quantum mechanics and is presented forhomonuclear and heteronuclear spin systems. The formalism hasalso been adapted to systems in chemical exchange. Simulationsof pulse sequences should be more straightforward using the newformalism. In the second part of the thesis the NMR solution structuresof two ribosomal proteins are described. The ribosome isresponsible for protein production in all living cells and tounderstand the mechanism of the ribosome it is important toknow the three dimensional structure. In this thesis thestructures of S16 and S19, two of the proteins in the smallribosomal subunit, are presented. S16 is a mixed α /βprotein with a five-stranded parallel-antiparallel β-sheetand two α -helices. S19 is s mixed α/β proteinwith a three-stranded parallel-antiparallel β -sheet, oneα -helix and a short 310-helix. In the third part of the thesis a program for semiautomaticassignment of NMR-spectra is presented. Assigning resonances inthe NMR spectrum is a labor-intensive process, which can takelong time. In semiautomatic assignment a computer program aidsthe user in finding assignments but leaves all decisions to theuser, thus speeding up the process. The program described inthis thesis is a new version of ANSIG, called Ansig forWindows. The program runs on PCs under Windows and has severaltools for semiautomatic assignment. <b>Keywords:</b>nuclear magnetic resonance, structuredetermination, ribosomal proteins, NMR simulations, NMR theory,NMR assignment software, semiautomatic assignment

This thesis has focused on an aircraft schedule and network design problem that involves multiple types of aircraft and flight service. First, this thesis expands a business model for integrating on-demand flight services with the traditional scheduled flight services. Then, this thesis proposes a three-step approach to the design of aircraft schedules and networks from scratch. After developing models in the three steps and creating large-scale instances of these models, this dissertation develops iterative algorithms and subproblem approaches to solving these instances, and it presents computational results of these large-scale instances. To validate the models and solution algorithms developed, this thesis compares the daily flight schedules that it designed with the schedules of the existing airlines. In addition, it discusses the implication of using new aircraft in the future flight schedules. Finally, future research in three areas--model, computational method, and simulation for validation--is proposed.