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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
471

Geometry and mechanics of the human ankle complex, and ankle prosthesis design

Leardini, Alberto January 2000 (has links)
No description available.
472

Eurasian symbols change and stability in Taiwan popular religion: case study of the 18 deities cult

許義國, Sitnikov, Igor Unknown Date (has links)
The case of the “Temple of 18 Deities” (十八王公廟) is an example which shows that the process of changes in religious culture can be both gradual and sudden. From the first glance it seems that the boom of “Temple of 18 Deities” cult suddenly appeared from nowhere. But the analysis of the temple origin mythology and it symbols shows that the opportunities for such sudden changes were created gradually during the long period of religious culture development when fazes of change and conservation were taking turns endlessly in Taiwan societies. Those opportunities traces into more remote times of gradual development of numerous religious cultures which were brought in Taiwan by multitude of migration waves. The “Temple of 18 Deities” cult conserved many stable religious elements which were created in the period of Eurasian cultural unity and bring us to the Neolith and even Paleolithic epoch. One of the most stable elements in the “Temple of 18 Deities cult is the symbol of a dog. The geographical area of the former dog’s worshiping cults distribution is spread all over Eurasia with the most western point in the British Isles and the most eastern point in Taiwan. The dog symbol in mythologies of many various peoples all over Eurasia is connected to another stable religious element – an idea of the life after death and underworld. The underworld conception origin also should be dated by Paleolithic epoch, because it stability occurring everywhere spreading. Paleolithic hunting religious ideas should be common all over the world, because all the societies passed this faze of evolution in their history.
473

Centrifuge Modelling of Instability in Granular Soils under Infinite Slope Conditions

Jacobs, EMILY 04 December 2013 (has links)
Rainfall induced granular flow slides pose a significant risk in many areas of the world. These failures, characterized by the sudden release of material in a fluid-like manner, are the result of static liquefaction occurring in these slopes. The static liquefaction phenomenon has been linked to instability. Instability behaviour is primarily studied under undrained triaxial conditions, and although many instability theories have therefore been defined in this stress space, these have been shown to also extend into plane strain conditions. In order to further investigate this behaviour under these stress conditions, Wolinsky et al. (2013) developed a tilt-table soil box for use in a geotechnical centrifuge to analyze instability in infinite slope soil models. This testing apparatus has been used to simulate instability in plane strain under both dry and saturated soil conditions. Stress-controlled experiments were performed on dry infinite slope soil models to investigate the effects of both void ratio and effective stress on instability behaviour. By performing these tests dry, this test apparatus provides the ability to decouple the triggers of instability from the corresponding response in pore pressure and the consequences. The results of this testing confirmed that the instability line angle is a function of both void ratio and effective stress. As the void ratio decreases and effective stress in the soil model increases, the resulting instability line angle will increase. This testing also demonstrated typical stress-dilatancy behaviour in these infinite slope models, characterized by contractive response in loose soils and dilative response in dense soil subject to increasing shear stress. Secondly, this testing apparatus was used to investigate the effects of seepage force on instability behaviour in granular slopes through the introduction of groundwater seepage in the form of a rising groundwater level. Although the results illustrated shear and volumetric response to these increased pore water pressures, these were not significant enough to initiate instability and the resulting pore water response leading to failure. It has been determined that this apparatus must be further adapted to dissipate the matric suctions developed above the water table during groundwater rise. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-12-03 21:06:56.806
474

Stability and Boundedness of Impulsive Systems with Time Delay

Wang, Qing 27 March 2007 (has links)
The stability and boundedness theories are developed for impulsive differential equations with time delay. Definitions, notations and fundamental theory are presented for delay differential systems with both fixed and state-dependent impulses. It is usually more difficult to investigate the qualitative properties of systems with state-dependent impulses since different solutions have different moments of impulses. In this thesis, the stability problems of nontrivial solutions of systems with state-dependent impulses are ``transferred" to those of the trivial solution of systems with fixed impulses by constructing the so-called ``reduced system". Therefore, it is enough to investigate the stability problems of systems with fixed impulses. The exponential stability problem is then discussed for the system with fixed impulses. A variety of stability criteria are obtained and`numerical examples are worked out to illustrate the results, which shows that impulses do contribute to the stabilization of some delay differential equations. To unify various stability concepts and to offer a general framework for the investigation of stability theory, the concept of stability in terms of two measures is introduced and then several stability criteria are developed for impulsive delay differential equations by both the single and multiple Lyapunov functions method. Furthermore, boundedness and periodicity results are discussed for impulsive differential systems with time delay. The Lyapunov-Razumikhin technique, the Lyapunov functional method, differential inequalities, the method of variation of parameters, and the partitioned matrix method are the main tools to obtain these results. Finally, the application of the stability theory to neural networks is presented. In applications, the impulses are considered as either means of impulsive control or perturbations.Sufficient conditions for stability and stabilization of neural networks are obtained.
475

Central Nervous System Control of Dynamic Stability during Locomotion in Complex Environments

MacLellan, Michael January 2006 (has links)
A major function of the central nervous system (CNS) during locomotion is the ability to maintain dynamic stability during threats to balance. The CNS uses reactive, predictive, and anticipatory mechanisms in order to accomplish this. Previously, stability has been estimated using single measures. Since the entire body works as a system, dynamic stability should be examined by integrating kinematic, kinetic, and electromyographical measures of the whole body. This thesis examines three threats to stability (recovery from a frontal plane surface translation, stepping onto and walking on a compliant surface, and obstacle clearance on a compliant surface). These threats to stability would enable a full body stability analysis for reactive, predictive, and anticipatory CNS control mechanisms. From the results in this study, observing various biomechanical variables provides a more precise evaluation of dynamic stability and how it is achieved. Observations showed that different methods of increasing stability (eg. Lowering full body COM, increasing step width) were controlled by differing CNS mechanisms during a task. This provides evidence that a single measure cannot determine dynamic stability during a locomotion task and the body must be observed entirely to determine methods used in the maintenance of dynamic stability.
476

Locating Instability in the Lumbar Spine: Characterizing the Eigenvector

Howarth, Samuel January 2006 (has links)
Overloading of the back can cause instability such that buttressing the instability is a primary objective of many of the leading edge therapeutic approaches. However, a challenge lies in determining the location of the instability or the least stable vertebral joint. A mathematical analysis, based on a commonly used approach in engineering for determining structural stability, has been developed for the lumbar spine. The purpose of this investigation was to determine the feasibility of a method for mathematically locating potential areas of instability within a computer-based model of the lumbar spine. To validate this method, the eigenvector from the stability analysis was compared to the output from a geometric equation that approximated individual vertebral joint rotational stiffness with the idea that the entry in the eigenvector with the largest absolute value would correspond to the vertebral joint and axis with the lowest stiffness. Validation of the eigenvector was not possible due to computational similarities between the stability analysis and the geometric rotational stiffness method. However, it has been previously demonstrated that the eigenvector can be useful for locating instability, and thus warrants future study. Determining the least stable vertebral joint and axis can be used to guide proper motor pattern training as a clinical intervention. It was also shown in this investigation that an even distribution of fascicle force and stiffness generated stability. This supports the idea that well-coordinated efforts of muscle activation are beneficial for improving stability of the lumbar spine.
477

The influence of woven stretch fabric properties on pattern design

Tsai, I-Chin January 2001 (has links)
Conventional pattern construction and pattern making methods typically require the size measurements of a range of standard mannequins or human bodies in order to construct the varying pattern blocks for garment design. These various methods and skills, in the fashion industry, factory or studio are performed by pattern makers or producers, and are refined through the garment sampling and wearer trial system (an uneconomical trial and error) used on woven garments or on woven stretch garments to produce varying garment designs. This is particularly true when fabric stretch and recovery properties and values are encountered. There is a strong alliance with the heuristic knowledge. The aim of the present work is to investigate the influence of woven stretch fabric properties on pattern construction. The stretch and recovery properties of woven stretch fabrics will be taken account for pattern reduction and alteration for the development of a suitable garment pattern to fit the body shape and to meet the comfort requirement during the body movement. The relationship between the degree of alteration and reduction and the relevant fabric stretch properties is to be established. In this thesis, the stretch and recovery properties of various woven stretch fabrics have been measured. The conventional pattern is reduced and altered based on the comfort requirement for body movement, fit to body shape and the extension and recovery properties of the woven stretch fabric. Wearer trial test of the altered garment pattern of woven stretch fabrics is carried out for subjective and objective evaluation in the reference of the traditional woven garment pattern. Their comfort and garment appearances are evaluated by a panel of judges and the wearer. The size and shape stability of garments after the wearing tests are assessed. The results demonstrated that the new pattern method was significantly better for woven stretch fabric. The garment pattern for fit and comfort can be predicated and produced according to the extension and recovery properties of fabrics.
478

Risk and performance based fire safety design of steel and composite structures

Lange, David January 2009 (has links)
For the development of performance based design on a proper scientific basis the use of the concept of risk is inevitable. However, the application of this concept to actual structural design is not simple because of the large ranges of probability and consequences of events which exist. This is compounded by a plethora of different actions that can be taken to reduce the probabilities of the events and also the magnitude of the consequences. It is the reduction in the magnitude of these consequences which is essentially the goal of design. This work aims to address the challenges posed by the application of the concepts of performance based design for structures in fire. Simple methodologies have been developed for the assessment of the consequences of an extreme event. These methodologies are based upon fundamental behaviour of structures in fire. A methodology has been developed which can be used to assess the capacity/deflection behaviour through the complete thermal deflection of floor slabs. This takes into account positive effects on the capacity of floor slabs of the membrane stress at the slabs boundaries at low deflections as well as the final capacity provided by the tensile membrane action of the reinforcement mesh at high deflections. For vertical stability of structures in fire, analytical equations to describe the behaviour of floor systems at the perimeter of a building are developed. From these equations, the resulting pull-in forces on external columns can be calculated as well as the resulting horizontal load applied to the column. From this, a simple stability assessment is proposed which can be used to assess the consequences of multiple floor fires on tall buildings. These analytical methodologies are brought together in a risk based frame- work for structural design which can be used to identify areas in a building or structural components which pose a high residual risk. These elements can be qualitatively ’ranked’ according to their relative risk and appropriate measures taken to reduce the risk to an acceptable level. The framework is illustrated via 2 case studies. The first is of a typical small office building, and the second is of a prestige office development.
479

The geomorphology of palaeo-ice streams : identification, characterisation and implications for ice stream functioning

Stokes, Christopher Richard January 2001 (has links)
Ice streams are the dominant drainage pathways of contemporary ice sheets and their location and behaviour are viewed as key controls on ice sheet stability. Identifying palaeo-ice streams is of paramount importance if we are to produce accurate reconstructions of former ice sheets and examine their critical role in the oceanclimate system. Many workers have invoked palaeo-ice streams from a variety of former ice sheets, despite a limited understanding of their glacial geomorphology. This thesis addresses the problem by predicting several diagnostic geomorphological criteria indicative of ice stream activity. These are developed objectively from the known characteristics of contemporary ice streams and can be summarised as: large flow-set dimensions (>20 km wide and >150 km long), highly convergent flow patterns, highly attenuated subglacial bedforms (length:width >10: 1), Boothia-type dispersal plumes, abrupt lateral margins «2 km), ice stream marginal moraines, evidence of pervasively deformed till, and submarine sediment accumulations (marine-terminating ice streams only). Collectively, the criteria are used to construct conceptual landsystems of palaeo-ice stream tracks. Using satellite imagery and aerial photography to map glacial geomorphology, identification of the criteria is used to validate the location of a previously hypothesised ice stream and identify a hitherto undetected palaeo-ice stream from the former Laurentide Ice Sheet. Implications for ice stream basal processes are explored and their ice sheet-wide significance is assessed. On Victoria Island (Arctic Canada) five of the geomorphological criteria are identified and the extent of the marine-based M'Clintock Channel Ice Stream is reconstructed at 720 km in length and 140 km in width. The ice stream (operating between 10,400 and 10,000 yr BP) was located within a broad topographic trough, but internal glaciological processes, rather than properties of the bed controlled the margin locations. It eroded into pre-existing unconsolidated sediments and left a spectacular pattern of subglacially-produced landforms, recording a snapshot view of the bed prior to ice stream shut-down. Sediment availability appears critical to its functioning (deformable bed?) and the debris flux of the ice stream is inferred to have been high. Frictional shut-down occurred once down-cutting through sediments reached hard bedrock close to the terminus. The presence of four of the geomorphological criteria are used to identify a terrestrial ice stream which drained the Keewatin Sector of the Laurentide Ice Sheet between ca. 10,000 and 8,500 yr BP. Its size is reconstructed at over 450 km in length and 140 km in width, and it left behind a subglacial bedform pattern consisting of highly attenuated drumlins (length:width ratios up to 48: 1) displaying exceptional parallel conformity. This represents an isochronous bedform pattern and variations in lineament elongation ratio are thought to be a useful proxy for ice velocity. Highest elongation ratios occur immediately downstream of a topographic step where the ice stream entered a sedimentary basin. It is inferred that the ice stream was triggered by climatic warming which altered the ice sheet configuration and the thermal state of the bed. A switch from cold to warm-based conditions probably triggered rapid basal sliding. The ice stream (and a tributary) shut down when it ran out of ice, causing widespread thinning of the ice sheet and subsequent deglaciation. These ice streams denote considerable ice sheet instability over both hard and soft (deformable) beds and emphasise the enormous effects that ice streams had in controlling the deglaciation of the Laurentide Ice Sheet.
480

Viscosity Characterization of 20% Pluronic Lecithin Organogel at varying pHs

Lucht, Julie January 2009 (has links)
Class of 2009 Abstract / OBJECTIVES: The primary objective of this experiment was to characterize the pH stability range of 20% Pluronic lecithin organogel (PLO). We intended to determine the viscosity at varying pHs. We prepared six samples of 20% PLO. METHODS: An initial rheological reading of each sample was recorded by a dynamic stress rheometer. Each sample was titrated drop-wise with citric acid or KOH in 0.5 pH increments. When the desired pH was obtained, a 0.5 mL sample was analyzed with a dynamic stress rheometer, RS-200, using Rheos software. RESULTS: Since PLO is a non-Newtonian substance, viscosity changed relative to shear stress and we were not able to examine a correlation of pH with viscosity. Instead we inputted the data into Microsoft Excel® and plotted a shear stress versus viscosity curve for each sample to identify trends. CONCLUSIONS: We were unable to achieve our primary objective of determining the viscosity characterization of 20% PLO at varying pHs due to the non-Newtonian nature of the material. Subjectively, we determined the viscosity of 20% PLO is not substantially affected by pH. Other factors such as temperature, excess liquid, and surfactant ability may influence viscosity and need to be examined in the future.

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