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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.
221

Flat Virtual Pure Tangles

Chu, Karene Kayin 11 December 2012 (has links)
Virtual knot theory, introduced by Kauffman, is a generalization of classical knot theory of interest because its finite-type invariant theory is potentially a topological interpretation of Etingof and Kazhdan's theory of quantization of Lie bi-algebras. Classical knots inject into virtual knots}, and flat virtual knots is the quotient of virtual knots which equates the real positive and negative crossings, and in this sense is complementary to classical knot theory within virtual knot theory. We classify flat virtual tangles with no closed components and give bases for its ``infinitesimal'' algebras. The classification of the former can be used as an invariant on virtual tangles with no closed components and virtual braids. In a subsequent paper, we will show that the infinitesimal algebras are the target spaces of any universal finite-type invariants on the respective variants of the flat virtual tangles.
222

Signal distortion caused by tree foliage in a 2.5 GHz channel

Pélet, Eric Robert 12 December 2003
A fixed terrestrial wireless system such as the Microwave Multi-channel Distribution Service (MMDS) can be used as the ``last mile' to provide a high speed Internet connection from a base station to a home in a rural or suburban residential area. Such a broadband wireless system works very well under line-of-sight transmission. It works quite well even if the line-of-sight is obstructed with a large number of trees. However, when trees obstruct the line-of-sight, under conditions of wind, the user may experience loss of the RF signal from time to time. This is especially true under gusty conditions. As part of this research a high precision DSP-based measuring system is devised to accurately measure and characterize the distortions caused by tree foliage on the RF line-of-sight signal. The approach is to digitally generate a signal composed of several tones, up-convert the signal to 2.5 GHz and send it through tree foliage to a receiver where the signal is down-converted and sampled for a duration of five seconds. The samples collected are processed using Matlab to compute the temporal amplitude and phase variations of the tones. The measurement system provides estimates of the amplitude and phase of the receive tones with a time resolution of 3.2 ms. The standard deviation of the amplitude estimates is 0.3\% of the actual amplitude of the tones and the standard deviation of the phase estimates is 0.23 degree. This accuracy is obtained when the signal-to-noise ratio of the receive signal is greater than 20 dB. Measurement in the field with tree foliage in the line-of-sight shows that the swaying of the branches in the wind can cause rapid signal fading. This research determines the type of fade, the depth and duration of the fade, as well as the fading rate.
223

Signal distortion caused by tree foliage in a 2.5 GHz channel

Pélet, Eric Robert 12 December 2003 (has links)
A fixed terrestrial wireless system such as the Microwave Multi-channel Distribution Service (MMDS) can be used as the ``last mile' to provide a high speed Internet connection from a base station to a home in a rural or suburban residential area. Such a broadband wireless system works very well under line-of-sight transmission. It works quite well even if the line-of-sight is obstructed with a large number of trees. However, when trees obstruct the line-of-sight, under conditions of wind, the user may experience loss of the RF signal from time to time. This is especially true under gusty conditions. As part of this research a high precision DSP-based measuring system is devised to accurately measure and characterize the distortions caused by tree foliage on the RF line-of-sight signal. The approach is to digitally generate a signal composed of several tones, up-convert the signal to 2.5 GHz and send it through tree foliage to a receiver where the signal is down-converted and sampled for a duration of five seconds. The samples collected are processed using Matlab to compute the temporal amplitude and phase variations of the tones. The measurement system provides estimates of the amplitude and phase of the receive tones with a time resolution of 3.2 ms. The standard deviation of the amplitude estimates is 0.3\% of the actual amplitude of the tones and the standard deviation of the phase estimates is 0.23 degree. This accuracy is obtained when the signal-to-noise ratio of the receive signal is greater than 20 dB. Measurement in the field with tree foliage in the line-of-sight shows that the swaying of the branches in the wind can cause rapid signal fading. This research determines the type of fade, the depth and duration of the fade, as well as the fading rate.
224

The Mutagenic Activity of High-Energy Explosives; Contaminants of Concern at Military Training Sites

McAllister, Jennifer E. 24 August 2011 (has links)
The genotoxicity of energetic compounds (i.e., explosives) that are known to be present in contaminated soils at military training sites has not been extensively investigated. Thus, the Salmonella mutagenicity and Muta(TM)Mouse assays were employed as in vitro assays to examine the mutagenic activity of twelve explosive compounds, as well as three soil samples from Canadian Forces Base Petawawa. Salmonella analyses employed strains TA98 (frameshift mutations) and TA100 (base-pair substitution mutations), as well as the metabolically-enhanced YG1041 (TA98 background) and YG1042 (TA100 background), with and without exogenous metabolic activation (S9). For Salmonella analyses, the results indicate that ten of the explosive compounds were mutagenic, and consistently elicited direct-acting, base-pair substitution activity. All three soil samples were also observed to be mutagenic, eliciting direct-acting, frameshift activity. Mutagenic potencies were significantly higher on the metabolically-enhanced strains for all compounds and soil samples. For Muta(TM)Mouse analyses on FE1 cells, the results indicate that the majority of explosive compounds did not exhibit mutagenic activity. All three soil samples elicited significant positive responses (PET 1 and PET 3 without S9, and PET 2 with S9), and although there is some evidence of a concentration-related trend, the responses were weak. Correspondence of the mutagenic activity observed with the two assay systems, for both the explosive compounds and soil samples, was negligible. The differential response is likely due to differences in metabolic capacity between the two assay systems. Furthermore, it is likely that there are unidentified compounds present in these soil samples that are, at least in part, responsible for the observed mutagenic activity. Additional testing of other explosive compounds, as well as soil samples from other military training sites, using a variety of in vitro and in vivo assays, is warranted in order to reliably estimate mutagenic hazard and subsequently assess risk to human health.
225

Punching Shear Retrofit Method Using Shear Bolts for Reinforced Concrete Slabs under Seismic Loading

Bu, Wensheng January 2008 (has links)
Reinforced concrete slab-column structures are widely used because of their practicality. However, this type of structures can be subject to punching-shear failure in the slab-column connections. Without shear reinforcement, the slab-column connection can undergo brittle punching failure, especially when the structure is subject to lateral loading in seismic zones. The shear bolts are a new type of transverse reinforcement developed for retrofit of existing structures against punching. This research focuses on how the shear bolts can improve the punching-shear capacity and ductility of the existing slab-column connections under vertical service and lateral seismic loads. A set of nine full-scale reinforced concrete slab-column connection specimens were tested under vertical service and cyclic loads. The vertical (gravity) load for each specimen was kept at a constant value throughout the testing. The cyclic lateral drift with increasing intensity was applied to the columns. The specimens were different in number of bolts, concrete strength, number of openings, and level of gravity punching load. Strains in flexural rebars in the slabs, crack widths, lateral loads, and displacements were obtained. The peak lateral load (moment) and its corresponding drift ratio, connection stiffness, crack width, and ductility were compared among different specimens. The testing results show that shear bolts can increase lateral peak load resisting capacity, lateral drift capacity at peak load, and ductility of the slab-column connections. Shear bolts also change the failure mode of the slab-column connections and increase the energy dissipation capacity. The thesis includes also research on the development of guidelines for shear bolt design for concrete slab retrofitting, including the punching shear design method of concrete slab (with shear bolts), dimensions of bolts, spacing, and influence of bolt layout patterns. Suggestions are given for construction of retrofitting method using shear bolts. Recommendations are also presented for future research.
226

Modeling of Thermal Joint Resistance for Sphere-Flat Contacts in a Vacuum

Bahrami, Majid January 2004 (has links)
As a result of manufacturing processes, real surfaces have roughness and surface curvature. The real contact occurs only over microscopic contacts, which are typically only a few percent of the apparent contact area. Because of the surface curvature of contacting bodies, the macrocontact area is formed, the area where microcontacts are distributed randomly. The heat flow must pass through the macrocontact and then microcontacts to transfer from one body to another. This phenomenon leads to a relatively high temperature drop across the interface. Thermal contact resistance (TCR) is a complex interdisciplinary problem, which includes geometrical, mechanical, and thermal analyses. Each part includes a micro and a macro scale sub-problem. Analytical, experimental, and numerical models have been developed to predict TCR since the 1930's. Through comparison with more than 400 experimental data points, it is shown that the existing models are applicable only to the limiting cases and none of them covers the general non-conforming rough contact. The objective of this study is to develop a compact analytical model for predicting TCR for the entire range of non-conforming contacts, i. e. , from conforming rough to smooth sphere-flat in a vacuum. The contact mechanics of the joint must be known prior to solving the thermal problem. A new mechanical model is developed for spherical rough contacts. The deformation modes of the surface asperities and the bulk material of contacting bodies are assumed to be plastic and elastic, respectively. A closed set of governing relationships is derived. An algorithm and a computer code are developed to solve the relationships numerically. Applying Buckingham Pi theorem, the independent non-dimensional parameters that describe the contact problem are specified. A general pressure distribution is proposed that covers the entire spherical rough contacts, including the Hertzian smooth contact. Simple correlations are proposed for the general pressure distribution and the radius of the macrocontact area, as functions of the non-dimensional parameters. These correlations are compared with experimental data collected by others and good agreement is observed. Also a criterion is proposed to identify the flat surface, where the influence of surface curvature on the contact pressure is negligible. Thermal contact resistance is considered as the superposition of macro and micro thermal components. The flux tube geometry is chosen as the basic element in the thermal analysis of microcontacts. Simple expressions for determining TCR of non-conforming rough joints are derived which cover the entire range of TCR by using the general pressure distribution and the flux tube solution. A complete parametric study is performed; it is seen that there is a value of surface roughness that minimizes TCR. The thermal model is verified with more than 600 data points, collected by many researchers during the last 40 years, and good agreement is observed. A new approach is taken to study the thermal joint resistance. A novel model is developed for predicting the TCR of conforming rough contacts employing scale analysis methods. It is shown that the microcontacts can be modeled as heat sources on a half-space for engineering applications. The scale analysis model is extended to predict TCR over the entire range of non-conforming rough contacts by using the general pressure distribution developed in the mechanical model. It is shown that the surface curvature and contact pressure distribution have no effect on the effective micro thermal resistance. A new non-dimensional parameter is introduced as a criterion to identify the three regions of TCR, i. e. , the conforming rough, the smooth spherical, and the transition regions. An experimental program is designed and data points are collected for spherical rough contacts in a vacuum. The radius of curvature of the tested specimens are relatively large (in the order of m) and can not be seen by the naked eye. However, even at relatively large applied loads the measured joint resistance (the macro thermal component) is still large which shows the importance of surface out-of-flatness/curvature. Collected data are compared with the scale analysis model and excellent agreement is observed. The maximum relative difference between the model and the collected data is 6. 8 percent and the relative RMS difference is approximately 4 percent. Additionally, the proposed scale analysis model is compared/verified with more than 880 TCR data points collected by many researchers. These data cover a wide range of materials, surface characteristics, thermal and mechanical properties, mean joint temperature, directional heat transfer effect, and contact between dissimilar metals. The RMS difference between the model and all data is less than 13. 8 percent.
227

Punching Shear Retrofit Method Using Shear Bolts for Reinforced Concrete Slabs under Seismic Loading

Bu, Wensheng January 2008 (has links)
Reinforced concrete slab-column structures are widely used because of their practicality. However, this type of structures can be subject to punching-shear failure in the slab-column connections. Without shear reinforcement, the slab-column connection can undergo brittle punching failure, especially when the structure is subject to lateral loading in seismic zones. The shear bolts are a new type of transverse reinforcement developed for retrofit of existing structures against punching. This research focuses on how the shear bolts can improve the punching-shear capacity and ductility of the existing slab-column connections under vertical service and lateral seismic loads. A set of nine full-scale reinforced concrete slab-column connection specimens were tested under vertical service and cyclic loads. The vertical (gravity) load for each specimen was kept at a constant value throughout the testing. The cyclic lateral drift with increasing intensity was applied to the columns. The specimens were different in number of bolts, concrete strength, number of openings, and level of gravity punching load. Strains in flexural rebars in the slabs, crack widths, lateral loads, and displacements were obtained. The peak lateral load (moment) and its corresponding drift ratio, connection stiffness, crack width, and ductility were compared among different specimens. The testing results show that shear bolts can increase lateral peak load resisting capacity, lateral drift capacity at peak load, and ductility of the slab-column connections. Shear bolts also change the failure mode of the slab-column connections and increase the energy dissipation capacity. The thesis includes also research on the development of guidelines for shear bolt design for concrete slab retrofitting, including the punching shear design method of concrete slab (with shear bolts), dimensions of bolts, spacing, and influence of bolt layout patterns. Suggestions are given for construction of retrofitting method using shear bolts. Recommendations are also presented for future research.
228

Analys av prispåverkande faktorer på bostadsrättsmarknaden i Uppsala

Karlsson, Mattias, Lövgren, Mats January 2010 (has links)
AimThe purpose of this study is to analyze factors that affect the price on tenant-owner apartments in the central parts of Uppsala. Special attention is put on analyzing how the monthly fee and the location affect the price. The hypotheses are that the monthly fee and the distance to the central part of the city have a negative effect on the price. A number of additional price affecting factors was taken in consideration during this study. Method This study is mainly based on data supplied to us by Mäklarstatistik. The supplied data consists of information about tenant-owner apartment sales in Uppsala during a year under 2008 and 2009. Before the Hedonic method was used in order to get the result, we added information, processed it and eliminated unwanted data. The Hedonic method makes it possible to describe the selling price as a function of several price affective factors. To investigate how the monthly fee affects the selling price, several regression equations were conducted. The data supplied to us was processed with the computer program Microsoft Excel. Result and conclusions The investigation shows that there is a negative correlation both between the monthly fee and the apartments selling price, as well as between the selling price and the distances to the Fyrisån and the Stora torget. Suggestions for future research The interest rate on the housing loan is one of the biggest contributing factors in the total monthly cost for most household owners. In this study we have not taken in consideration the effect of the present interest rate for household loan. Therefore we think it would be interesting to investigate its effects on the market. Contribution of the thesis   This study has strengthened the credibility of earlier studies. It has also given a deeper insight into how the monthly fee affects the price on apartments by using more variables than earlier studies.
229

Seasonal sediment transport pathways and sources in the Jhoushuei river delta and tidal flat complex based on grain-size distributions

Chen, Chun-wei 13 February 2012 (has links)
This study used the sediment samples collected in May (dry season) and September (wet season) 2010 in a river delta and tidal flat complex around Jhoushuei River mouth in Central Taiwan to examine seasonal sediment transport pathways and sources. Four different approaches were used in the analysis of grain-size distribution pattern. They include (1) the McLaren-Bowles method, and (2) the transport vector technique (Gao-Collins method), and (3) a combination of `filtering' and the empirical orthogonal (eigen) function (EOF) analysis technique, and (4) C/N elemental ratios of organic sediments. The results of surface grain size distributions of sediment range from clay to medium sand towards the sea, and very fine sand deposited in the river delta. On the upper tidal flat, mud content of the wet season is higher than dry season due to higher river output of organic sediment and low-energy sediment transport. In wet season, according to the fine-grained sediment from the Jhoushuei River is therefore mainly discharged to the offshore area and little remain around the tidal flat, the influence of river on the grain-size distribution is the least. The results based on McLaren-Bowles method indicate that there were two type sediment transport pathways, (1) the river carried sediment to the coast, then alone the northeast-southwest direction by the longshore current, and (2) during the flood tide, the riverine sediment move to northeast and east through the river delta and tidal creek to the upper tidal flat, respectively. The results based on Gao-Collins method indicate that there was possible seasonal variation of sediment transport pathways on the river delta front, where the significant transport was seaward in the wet season whereas the transport was the opposite in the dry season. On the tidal flat, the model results indicate that seaward transport seems to be controlled by ebb tidal current perhaps due to the sampling at low-tide.
230

Film cooling on a flat plate: investigating density

Grizzle, Joshua Peter Fletcher 15 May 2009 (has links)
This study is an investigation of two specific effects on turbine blade film cooling. The effect of coolant to mainstream density ratio and upstream steps was studied. The studies were conducted on two flat plates with 4mm cylindrical film cooling holes, one with simple angle and the other with compound angle, in a low-speed suction type wind tunnel. Density effect was studied at ratios of 0.93 and 1.47 by using air and CO2 as coolant. An IR camera was used to record the temperature on the plate and T-type thermocouples were used to record the coolant and mainstream temperatures. During the study the nature of the conduction effect from the heated coolant was studied and found to be most prevalent along the plate surface not through the plate from the plenum. A methodology was presented by which conduction error free results were obtained. The results showed an increased effectiveness at higher density ratios, particularly near the holes and for the simple angle plate. Upstream step effect was studied using pressure sensitive paint and a coupled strobe light and camera. Steps of 0.5, 1 and 1.5mm were placed at the upstream edge of the holes. The steps were found to increase effectiveness significantly more than previous studies have shown when placing the step slightly upstream of the holes.

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