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A peer-to-peer (P2P) system is a networked system characterized by the lack of centralized control, in which all or most communication is symmetric. Also, a P2P system is supposed to handle frequent arrivals and departures of nodes, and is expected to scale to very large network sizes. These requirements make the design of P2P systems particularly challenging. We investigate two central issues pertaining to the design of P2P systems: load balancing and routing. In the first part of this thesis, we study the problem of load balancing in the context of Distributed Hash Tables (DHTs). Briefly, a DHT is a giant hash table that is maintained in a P2P fashion: Keys are mapped to a hash space I --- typically the interval [0,1), which is partitioned into blocks among the nodes, and each node stores the keys that are mapped to its block. Based on the position of their blocks in I, the nodes also set up connections among themselves, forming a routing network, which facilitates efficient key location. Typically, in a DHT it is desirable that the nodes' blocks are roughly of equal size, since this usually implies a balanced distribution of the load of storing keys among nodes, and it also simplifies the design of the routing network. We propose and analyze a simple distributed scheme for partitioning I, inspired by the multiple random choices paradigm. This scheme guarantees that, with high probability, the ratio between the largest and smallest blocks remains bounded by a small constant. It is also message efficient, and the arrival or departure of a node perturbs the current partition of I minimally. A unique feature of this scheme is that it tolerates adversarial arrivals and departures of nodes. In the second part of the thesis, we investigate the complexity of a natural decentralized routing protocol, in a broad family of randomized networks. The network family and routing protocol in question are inspired by a framework proposed by Kleinberg to model small-world phenomena in social networks, and they capture many designs that have been proposed for P2P systems. For this model we establish a general lower bound on the expected message complexity of routing, in terms of the average node degree. This lower bound almost matches the corresponding known upper bound.

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Participants were twelve 70+ kg male strength-trained athletes and one passenger child with a mass of 29 kg. The male participants walked three times over a force plate embedded in an eight metre walkway for each of three conditions: carrying no load, a 29 kg backpack, or a 29 kg passenger. Variables were compared using a repeated measures ANOVA test with a Bonferroni correction. Both load conditions produced compensatory trunk flexion; trunk flexion increased from no load to piggybacking to backpacking. Trunk range of motion was similar for no load and piggybacking, but increased to backpacking. The backpack load caused greater resultant and total magnitude of torque than the passenger load. The trunk extensors dominated with no load and piggybacking and the trunk flexors dominated with backpacking. Many of the significant differences between conditions suggest that piggybacking is biomechanically more similar to natural gait than is backpacking.

This study provides the physical, mathematical and numerical basis of analysis work performed for predicting the flow around three-dimensional bluff body configurations. The flow has been treated as steady, incompressible, turbulent. The predictions were made using a two-equation turbulence model, solving transport equations for turbulence kinetic energy K and the turbulence dissipation rate ε, in addition to the partial differential equations for the conservation of mass and momentum. The program used was the well tested computer code "PHOENICS-84" based on work conducted by Prof. D.B. Spalding and Co-workers. Several computations have been performed, for three models: a single cube, a pair of cubes with different spacing, and a rudimentary representation of an offshore oil platform stucture. The prediction procedure was first tested for grid refinement and optimum solution domain size until profiles at several locations for selected variables showed little change with further increase of domain size and grid points. The effect of different wind directions was investigated for the three models; in addition, different pitching conditions of the oncoming flow were also considered for the platform-model configurations. Comparisons were made with wind tunnel test results on the same three models, and some discrepancies are noted, particularly in regions of separated, recirculating flow. Also comparisons were made with certain empirical calculation procedures used for wind load estimation in maritime engineering. Overall wind loading is nevertheless reasonably well predicted. Applications of the method in the area of wind loadings on a full scale offshore oil rig is discussed, and plans for refinement and extension of the present work are outlined. It is concluded that the present method can be used as a suitable starting point for generating a platform aerodynamics simulator. However, more work is required to this end, in order to represent adequately all aspects of platform-aerodynamics phenomena.

The key to the co-rotational (CR) finite element is the separation between the rigid body motion and the deformational motion. It is this separation which makes it superior to other methods in the analysis of large displacement problems. Since the dynamic analysis of a guyed transmission line system contains large displacements from the vibration of the cable, it is considered appropriate to utilize the technique in the analysis. This thesis re-formulates and simplifies the CR method for such a purpose. Numerical tests show that the time step required for convergence in the present technique is ten times less than that is required for convergence in ANSYS. In the construction of the equation for the prediction of the longitudinal load factor (LLF) for the A402-M guyed transmission line due to cable break events, the tower is modelled using a simplified model of a detailed lattice tower. The simplified model considers latticed tower segment as an equivalent beam segment. The use of the simplified model enables to perform the broken wire dynamic analysis of the ten-span transmission line system within a day or two on a personal computer. Two initiating events are considered: all conductors on one arm break and all cables in one span break. Based on the analysis results, it is found that the LLFs for the all cables break event for the A402-M tower are 5% less than that calculated using the EPRI equation. It is therefore recommended that either the LLFs derived from the EPRI equation or from the proposed equation be used in the design of a guyed transmission tower for the broken wire event. The developed procedure can also be used to predict the LLF for the other type transmission line systems.

Piles are engineering structures which are subjected to axial and lateral loading. In this dissertation, pile load tests were performed on a full-scale fabricated pile to understand lateral pile responses under static and cyclic loading. The experiments were performed on a fabricated test pile at the Geo-Engineering Laboratory at Queen's University. Dry loose Olimag Synthetic Olivine sand was used as the test soil. Instrumentation including axial strain gauges, null sensors (earth pressure sensors) and string potentiometers were used to monitor pile responses throughout the tests. What differentiates the current study from previous investigations is direct measurements of lateral earth pressure on a test pile using those null sensors with conventional measurements of curvature and deformation. The null sensors of Talesnick (2005) have ‘infinite stiffness’ and calibration that is almost independent of the soil type, soil condition and stress history, qualities that make the sensor superior to other commercially available sensors. The initial pile response under static loading was examined. Previous laterally loaded pile test programs have utilized curvature measurements to infer moments, and differentiation of moments to determine lateral forces. Comparisons with the directly measured pressures confirmed the effectiveness of differentiated moments. To understand offshore structures, the behaviour of a pile subjected to cyclic loading is examined and explained by elastic soil response at low load levels and the progressive development of inelastic response at higher load levels. In addition, the loading condition (i.e. two-way versus one-way loading) was found to have a substantial effect on pile responses. The pressure distributions for two-way cyclic loading suggest that the lateral pressure is proportional to displacement with peak pressures near the ground surface during elastic responses. The peak lateral pressures move deeper towards the point of rotation with increasing cyclic loads to generate inelastic responses. However, the lateral pressure response is consistently inelastic for one-way loading. / Thesis (Master, Civil Engineering) -- Queen's University, 2014-05-02 20:29:56.489

The aim of this study was to determine the combined effects of high-heeled shoes and load carriage on gait and posture adaptation. Furthermore, the adaptation of gait and posture to the combined two conditions was examined by a comparison of the measured parameters between experienced and novice groups. 30 participants underwent a quantitative measurement of temporospatial, kinematic, and kinetic parameters of hip, knee, and ankle on both loaded and unloaded limbs using 3D motion analysis. Double support time and stride length increased during high-heeled gait and the magnitude of alteration was greater with a load. Increased plantarflexion was main cause of raised heel. Ankle plantarflexor moment increased with high-heeled but decreased with load carriage. As a result, plantarflexor moment diminished, in addition knee extensor moment exaggerated further. Hip extensor moment increased with heel height but not with load weight, however, hip angle was affected only by the load.