This study examines a specific application of button-head type twist-off bolts. Currently, the Research Council on Structural Connections Specification (2000) removes the requirement for ASTM F436 washers (ASTM 2000a) under the bolt head of twist-off bolts where the head diameter equals or exceeds that of an ASTM F436 washer when oversized and slotted holes are used. The need for washers is also removed for A490 strength bolts used on steels with specified yield strengths less than 40 ksi provided that the head diameter equals or exceeds an ASTM F436 washer. The ASTM F1852 Specification (ASTM 2000b) allows for head diameter dimensions that are slightly smaller than an ASTM F436 washer. Following the RCSC Specification, manufacturers that produce bolts using the ASTM F1852 dimensions are required to use ASTM F436 washers under the bolt head. The discrepancies between the specifications lead to this study, which involved the testing of button-head type twist-off bolts with two different head diameters, both of which were smaller than an ASTM F436 washer. Five bolt diameters between 5/8 in and 1-1/8 in. were tested in standard, oversized, and long-slotted holes. The performance of the twist-off bolts was determined by measuring and comparing the achieved relaxed pretension force in the bolt after tightening. It was found that twist-off bolts with head diameters less than an ASTM F436 washer had no trouble attaining their required minimum pretension force. Bolt head diameter and hole size were found to have no significant influence on the pretension force that was achieved for all bolts tested. / Master of Science

This thesis examined the effect of heat stress, dehydration and exercise on global left ventricular (LV) function and LV twist, untwisting and strain (LV mechanics) in healthy individuals. The primary aim was to identify whether the different haemodynamics induced by heat stress, dehydration and exercise would be associated with alterations in systolic and diastolic LV mechanics as assessed by two-dimensional speckle tracking echocardiography. Study one showed that enhanced systolic and diastolic LV mechanics during progressively increasing heat stress at rest likely compensate in part for a lower venous return, resulting in a maintained stroke volume (SV). In contrast, heat stress during knee-extensor exercise did not significantly increase LV twist, suggesting that exercise attenuates the increase in LV mechanics seen during passive heat stress. Study two revealed that dehydration enhances systolic LV mechanics whilst diastolic mechanics remain unaltered at rest, despite pronounced reductions in preload. The maintenance of systolic and diastolic LV mechanics with dehydration during knee-extensor exercise further suggests that the large decline in SV with dehydration and hyperthermia is caused by peripheral cardiovascular factors and not impaired LV mechanics. During both, heat stress and dehydration, enhanced systolic mechanics were achieved solely by increases in basal rotation. In contrast, the third study demonstrated that when individuals are normothermic and euhydrated, systolic and diastolic basal and apical mechanics increase significantly during incremental exercise to approximately 50% peak power. The subsequent plateau suggests that LV mechanics reach their peak at sub-maximal exercise intensities. Together, the present findings emphasise the importance of acute adjustments in both, basal and apical LV mechanics, during periods of increased cardiovascular demand.

This thesis presents a new approach to the hardware test environment for a twist reflector monopulse antenna system with a radome extending current measurement practice. New research is presented on the optimisation of the design of a twist reflector monopulse antenna system with a radome, significantly improving the design and the design process. A unique extension to current measurement practice, for single channel antennas, is presented to determine the best practice method on phase stable measurements of a multi-channel antenna on a moving positioner. A novel axis transform for a 3 axis positioner system located within an anechoic chamber is derived. It allows for true performance measurement of a twist reflector antenna with a radome. This progresses the field of antenna measurement as, uniquely, this axis transform allows the aberration caused by the antenna radome to be measured and included. Design improvements have been made on polarisation selective grids, the matched thickness of the radome and a new software method that removes the need for a comparator and increases the robustness of the antenna system. Polarisation selective grids, constructed from a set of parallel conductors, have a wide range of uses in antenna systems. This thesis shows that the depth of a copper grid line can be reduced to 15 m and still provide better than -25 dB cross-polar isolation. This is contrary to current understanding at 30 times the skin depth. A new combined approach to radome thickness optimisation is presented that reduces the time taken to calculate the optimal thickness by over 3 orders of magnitude and the computer memory by over 2 orders of magnitude without compromising accuracy. The use of a digital comparator is described and leads to a novel method to compensate for a failed feed element, verifified in both simulation and anechoic chamber measurements.

Thesis (doctoral)--Utrecht, 1939. / Published also as Utrechtsche bijdragen tot de geschiedenis, het staatsrecht en de economie van Nederlandsch-Indië, v. 16. "Stellingen": [2] leaves inserted. Includes bibliographical references (p. 406-407) and index.

Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 81-82).

Thesis (doctoral)--Bonn, 1998. / Includes bibliographical references (p. 111-112).

An investigation has been carried out into the twist blockage which may occur when yarns pass over guides or other surfaces. The influence of primary physical parameters such as surface curvature, are and length of contact, yarn twist level and tension and yarn/surface friction have been investigated together with secondary parameters such as yarn surface, pressure, angle of approach etc. As a result of these investigations, three mechanisms of blockage have been identified. The first of these occurs especially with doubled yarn in which the components lie side by side on the guide surface and blocked twist builds up until sufficient torque is developed to turn the yarn over against the couple generated by the components of yarn tension and reaction on the guide surface. In the second mechanism blocking torque is generated by components of friction on the yarn surface at right angles to the yarn axis. These orthogonal friction components may arise from interaction between the topography of the twisted yarn surface and the guide surface or may be generated by forces arising from an angular orientation of yarn to guide. The third mechanism is intermediate between the other two where a singles yarn (or its equivalent) is flattened on the surface and resistance to twist transmission is generated partly by internal friction within the yarn and partly by yarn/guide frictional forces. The main circumstances under which these different mechanisms may operate, have been identified and suggestions made for minimising the blockage of twist.

No description available.

No description available.

"Single Photon Emission Computed Tomography (SPECT) is a medical imaging modality that allows us to visualize functional information about a patient's specific organ or body systems. During 20 minute scan, patients may move. Such motion will cause misalignment in the reconstruction, degrade the quality of 3D images and potentially lead to errors in diagnosis. Body bend and twist are types of patient motion that may occur during SPECT imaging and which has been generally ignored in SPECT motion correction strategies. To correct for these types of motion we propose a deformation model and its inclusion within an iterative reconstruction algorithm. One simulation and three experiments were conducted to investigate the applicability of our model. The simulation employed simulated projections of the MCAT phantom formed using an analytical projector which includes attenuation and distance-dependent resolution to investigate applications of our model in reconstruction. We demonstrate in the simulation studies that twist and bend can significantly degrade SPECT image quality visually. Our correction strategy is shown to be able to greatly diminish the degradation seen in the slices, provided the parameters are estimated accurately. To verify the correctness of our deformation model, we design the first experiment. In this experiment, the return of the post-motion-compensation locations of markers on the body-surface of a volunteer to approximate their original coordinates is used to examine our method of estimating the parameters of our model and the parameters' use in undoing deformation. Then, we design an MRI based experiment to validate our deformation model without any reconstruction. We use the surface marker motion to alter an MRI body volume to compensate the deformation the volunteer undergoes during data acquisition, and compare the motion-compensated volume with the motionless volume. Finally, an experiment with SPECT acquisitions and modified MLEM algorithm is designed to show the contribution of our deformation correction for clinical SPECT imaging. We view this work as a first step towards being able to estimate and correct patient deformation based on information obtained from marker tracking data."