Mid-block crosswalks present a challenging detection task when drivers are not familiar with the area, crosswalks are at locations with high traffic volume, or the visibility of the approaching crosswalk is obstructed. A major contributor to crashes at uncontrolled marked mid-block crosswalks on multilane roads is the presence of a motorist who is yielding to a pedestrian in the crosswalk, creating an additional threat from a motorist in the adjacent lane who may not see the pedestrian. Advance yield markings and sign prompts have been shown to be effective when there is no obstruction in either travel lane. The purpose of this research is to evaluate drivers' performance in response to multi-threat (obstruction in travel lane) and sight-limited (obstruction in parking lane) scenarios with and without advance yield markings and sign prompts. No direct evaluations of the effectiveness of this countermeasure in these scenarios have been undertaken. The methods used to evaluate drivers' performance include observations of drivers navigating virtual crosswalks on a driving simulator, field observations of drivers responding to staged pedestrian crossings, and observations of drivers in an actual vehicle on the open roadway navigating marked mid-block crosswalks. Dependent variables include yielding behavior and eye-fixations. It is hypothesized that at multi-threat and sight-limited scenarios drivers approaching a crosswalk are more likely to look for pedestrians, to yield and to yield sooner when advance yield markings and prompt sign are used than when the traditional markings are used. The extent of these benefits is highly dependent on visibility improvements at the site, providing real benefit only when sight distance is adequate. This comprehensive evaluation, limited to low speed approaches in an urban environment, provides data from sight-limited and multi-threat scenarios where the probability of seeing the pedestrian is low. This information can help traffic engineers make informed decisions when implementing pedestrian safety countermeasures. It also provides data from locations in the United States to add to the studies completed in Canada which served as the basis for inclusion of the advance yield markings and related sign as guidance in the Manual on Uniform Traffic Control Devices.

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This research presents the development of a comprehensive and unified solution procedure for solving general problems in mechanism synthesis. The uniqueness of this approach lies in its ability to derive the exact gradient relationships for the purposes of finding optimal solutions to generic mechanism problems. In this approach, mechanism problems are modeled using a generalized matrix-based method and the exact gradients necessary for optimization are systematically generated for any type of mechanism. The availability of these exact gradients eliminates the use of highly time consuming finite difference techniques and the problems associated with gradient approximation. From the application point of view, the use of exact gradients significantly enhances the efficiency of optimization process, improves the accuracy of final solutions, and avoids premature termination of optimization algorithms due to bad gradient approximation. One of the main problems in the synthesis of mechanisms is the occurrence of circuit defects. They occur when the desired orientations of a linkage assembly fall in different mobility regions during its cycle of motion. In this research, a sub-Jacobian based approach has been developed and integrated into the mechanism synthesis process to guarantee circuit free optimal solutions. The systematic development of exact gradients for various design objectives, its integration in the mechanism synthesis process, and the ability of this approach to eliminate circuit defects offer a unified as well as comprehensive approach for general mechanism synthesis. Several examples are presented to illustrate the effectiveness of this approach for designing industrial mechanisms. The generality and efficiency of exact gradient methodology make it the most viable approach for mechanism synthesis. The potential application of this approach to other domains of engineering design with an example from structural shape optimization is presented.

This study investigated (1) the volatilization and biodegradation removal rates of volatile organic compounds (VOCs) in a membrane bioreactor (MBR), and (2) impacts of biomass and soluble organics characteristics on membrane fouling. A laboratory-scale MBR was operated to treat synthetic wastewater containing acetaldehyde, butyraldehyde and vinyl acetate. In Phase I, the organic loading rates were varied from 1.06 to 2.98 kg chemical oxygen demand (COD) m-3 d-1. In Phase II, the dissolved oxygen (DO) concentrations were varied from 0.2 to 5.4 mg L-1. Total VOC removal rates were greater than 99.75 percent at all organic loading rates. Volatilization removal rates were achieved as low as 0.78 percent for acetaldehdyde, 1.27 percent for butyraldehyde, and 0.59 percent for vinyl acetate. Biomass stabilization status had a significant effect on volatilization. Under unstable conditions, 85 percent of vinyl acetate was volatilized. Regardless of the DO concentrations, total and biodegradation removal rates were greater than 99.7 and 95.9 percent. When the DO concentrations were increased, the volatilization rate increased. The experimental data were close to VOC emission modeling results using an analytical model and TOXCHEM+. The biomass showed a non-Newtonian and pseudoplastic flow behavior. The average particle diameter was less than 10 µm. Few filamentous bacteria were observed, leading to weak and fragile microbial flocs. The microorganisms were dispersed freely as small clumps or individual cells. The total organic carbon (TOC) and COD concentration in the bound extracellular polymeric substances (EPS) increased linearly with viscosity. The membrane permeate flux was inversely proportional to mixed liquor volatile suspended solids (MLVSS) concentration, viscosity, and total bound EPS concentration. The cake resistances were approximately 95 percent of the total membrane resistances. Soluble organics had a greater impact on cake layer formation under DO limited conditions, when soluble organics contained a larger amount of high molecular weight compounds. The bound EPS concentration had a greater influence on membrane filtering resistance than the molecular weight fraction of EPS. It is confirmed that confocal laser scanning microscopy (CLSM) could be a promising tool to visualize and map the biofouled membrane.

The objective of a routing algorithm in a network is to provide paths from source to destination for each incoming unit of work so as to optimize some appropriate cost function. Many sophisticated routing algorithms are based on distributional assumptions regarding the underlying arrival and service processes at the network nodes. This dissertation examines the effect of uncertainties in modeling the underlying processes on the optimization process. In addition, it explores answers to a related question: is it at all possible to do optimal routing without any modeling assumptions regarding the underlying processes? The effect of modeling uncertainties on the optimization process is examined for a generic basic routing model where each incoming unit is routed to one of several parallel heterogeneous servers, each associated with a queue of infinite capacity, with a certain probability. It is expected that any error in modeling the underlying processes will result in errors in the optimal routing solution and the optimal cost which is chosen to be the optimal mean system delay. For Poisson arrivals some asymptotic properties of the errors due to uncertainties in modeling the service time distribution are derived for heavy traffic conditions. For exponential service time distributions similar asymptotic characterizations of the errors resulting from modeling uncertainties in a General renewal arrival process are also derived. The differences between the two cases are identified and are numerically illustrated. Several model-based and model-independent gradient-based on-line routing algorithms are proposed for the above basic routing model and their performances are compared through simulations for various underlying arrival and service processes. An estimator for the gradient of mean delay on a tandem link (i.e. several queues in tandem) with respect to the routing probability (admission probability) associated with it is developed and using this a gradient-based algorithm is proposed for routing in a system of parallel tandem links. The performance of this algorithm is compared with that of some other model-based and model-independent algorithms through simulations. Finally the performance of a proposed on-line gradient-based routing algorithm is compared with that of two routing algorithms in practice, namely the CODEX Algorithm and the ARPANET Algorithm, by applying them to a communication network model.

In this dissertation group theory, being the standard mathematical tool for describing symmetry, is used to characterize the symmetries of bodies and features, especially the symmetries relevant to contact between bodies. Such a characterization reveals the necessity of intersecting subgroups of the proper Euclidean group ${\cal E}\sp{+}$. The central theoretical results of this dissertation are to establish this necessity mathematically and to provide a compact representation for the subgroups of ${\cal E}\sp{+}$ that leads an efficient group intersection algorithm. I define a geometric representation in terms of characteristic invariants for an important family of subgroups of ${\cal E}\sp{+}$. Each member of this family is called a $TR$ group since it is a semidirect product of a translation group $T$ and a rotation group $R$. I prove that there is a one-to-one correspondence between $TR$ groups and their characteristic invariants. I also prove that the intersection of $TR$ groups is closed and can be efficiently calculated from their characteristic invariants. A practical issue addressed in this dissertation is the linkage between mechanical design and robotic task-level planning. The formal treatment of $TR$ symmetry groups has been embedded into the implementation of an assembly planning system ${\cal KA}$3, which takes as input the geometric boundary models of assembly components provided by an off-the-shelf geometric solid modeller PADL2, and a set of instructions in the form of 'body A fits body B'. ${\cal KA}$3 finds a set of detailed robotic assembly task specifications in three steps: Step one: ${\cal KA}$3 finds mating features from the boundary models of assembly components using a salient feature library and the symmetry group intersection algorithm. Step two: ${\cal KA}$3 applies techniques used in constraint satisfaction problems (CSP) to satisfy kinematic and spatial constraints for each candidate assembly configuration. Step three: ${\cal KA}$3 generates a partially ordered sequence of contact states for assembly components through an analysis of disassembly via translational motion. The interaction between algebra and geometry within a group theoretic framework and the interaction between CSP techniques and heuristic search strategies provide us with a unified computational treatment of reasoning about how parts with multiple contacting features fit together.

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