The purpose of this study has been to construct two accelerating tubes with small beam apertures for the Van de Graaff, modifying the prototype tube designed and tested by Wiley (20), to design and construct a vacuum system for evacuating the tubes, and to determine the characteristics of the tube under operating conditions while installed in the generator.

Neural tube defects are a set of developmental malformations which can be highly debilitating, with limited treatment available. Mouse mutants exhibiting neural tube defects are studied to identify processes promoting proper neural tube closure, and potential points of intervention for future therapies. This thesis characterises the mouse mutant hitchhiker (hhkr), a hypomorphic allele of Tulp3 which presents with neural tube defects and polydactyly. The spina bifida and exencephaly observed in hhkr mutants are demonstrated to be consequences of failure of neural tube closure, and excessive proliferation is identified in the hindbrain neuroepithelium of mutant embryos. Intriguingly, increases apoptosis was reported for the Tulp3tmlJng mutant (lkeda et aI., 2001), and this increase is not conserved in Tulp3hhkr. Further support is provided for the role of Tulp3 as a negative regulator of Sonic hedgehog (Shh) signalling, confirming such a role in the limb, while preliminary data from genetic interaction studies between hhkr and Tectonic-/- are presented to suggest Tulp3 may exert a positive influence on Shh signalling in cranial regions. The molecular function of the Tulp3 protein is investigated, revealing an interaction between Tulp3 and Alx1, a transcription factor involved in skeletal patterning. An interaction between Tulp3 and Trim71, an E3 ubiquitin ligase is also demonstrated and supported by the eo- localisation of the proteins in transfected cells. Tulp3 is shown to be ubiquitinated in vivo, although this modification does not appear to be dependent on Trim7!. This thesis provides evidence that Tulp3 is likely to be involved in diverse protein-protein interactions around the cell, and some of these interactions may be crucial in promoting the proper closure of the neural tube.

Silty soils are a common occurrence and can exhibit low strengths, and minimal bearing capacity, causing widespread construction and performance problems. These soils are highly moisture-sensitive and their stability is greatly influenced by the degree of densification achieved during compaction. The strength and stiffness of silty-subgrade soils is also greatly reduced when moisture infiltrates the compacted soil during post construction period. This investigation concentrated on further developing the description of the pumping problem for soils with high silt content and the development of guidelines for stabilization of problematic silts. Using documented field experiences of the DOTD districts, the study presents a testing program to investigate the nature of the problem, the character of the silt materials, and their performance with modifying/stabilizing agents. Seven representative silt soil samples were used in the laboratory program. The unique characteristics that identify a soil with a high potential to pump were determined with standard laboratory tests. The response and stability of the silts under compaction and loading with various moisture levels and compaction efforts was also tested. The susceptibility to pumping of the different samples was reviewed in terms of their physical characteristics. In addition to the silt content percentage, the plasticity character was noted as being significant. The potential for the modification/stabilization of the problem silt soils was also studied. The laboratory tests were selected with respect to construction needs and possible post construction conditions. A limited number of specific additives were proposed with consideration for their ability to dry the subgrade silts sufficiently to be compacted and with the strength to provide a "working table" for the construction of the base and pavement. The additives selected included hydrated lime, portland cement, and class c fly ash. A unitary set of guidelines for stabilizing problematic silts is proposed.

Vita. / Digitized by Kansas Correctional Industries

Measurement of lava effusion rates is a key objective for monitoring basaltic eruptions because it helps constrain geophysical models of magma dynamics, conduit geometry, and both deep and shallow volcano processes. During these eruptions, lava frequently travels through a single "master" lava tube. A new method and instrument for continuously monitoring the crosssectional area of lava streams in tubes and estimating the instantaneous effusion rate (IER) is described. The method uses 2 stationary very low frequency (VLF) radio receivers to measure an unperturbed VLF signal and the influence of highly conductive molten lava on that signal. The difference between these signals is a function of the cross-sectional area of molten lava and the IER. Data from a short test of the instrument are described. This methodology represents a breakthrough in the continuous monitoring of IER because it provides higher temporal resolution than competing methods at a fraction of the cost.

L'implantation de parois végétalisées dans les zones urbaines est encouragée par les pouvoirs publics car elle contribue à l'amélioration de la qualité de l'air, favorise la biodiversité et atténue les effets d'îlot de chaleur urbain. L'apport acoustique de ces parois végétalisées est mis en évidence par des études récentes. Les phénomènes physiques à l’origine de leur propriétés acoustiques restent cependant insuffisamment compris et font l'objet de ce travail de thèse. Dans ce but, un dispositif expérimental original couplant mesures acoustiques via un tube à impédance et mesures vibratoires à l'aide d’un vibromètre laser à balayage est développé pour caractériser simultanément les propriétés acoustiques et vibratoires des feuillages et substrats qui composent ces parois dans la gamme 100 Hz-1000 Hz. Ce dispositif caractérise les coefficients acoustiques (absorption, réflexion, transmission...), les propriétés physiques effectives (célérité, impédance caractéristique...) et la réponse vibratoire d'échantillons de feuillages (fusain et laurier) et de substrats (perlite, fibre de coco, tourbe de coco). Les résultats obtenus mettent en évidence les propriétés acoustiques de chaque milieu et soulignent le lien étroit entre résonances vibratoires et propriétés acoustiques des parois. Enfin, l'étude acoustique d'échantillons superposant les couches de feuillage et de substrat montre une augmentation du coefficient d'absorption due aux résonances en épaisseur de la paroi et à l'adaptation d'impédance entre l'air et le substrat apportée par la couche de feuillage. Une stratégie d'optimisation de l'absorption acoustique dans une bande de fréquence donnée est également proposée. / Establishment of green walls in urban areas is supported by the public administration as it improves air quality, fosters biodiversity and mitigates urban heat island effects. Contribution of green walls to urban soundscape due to their acoustic properties has also been demonstrated by recent works. However, physical phenomena behind these acoustical properties are not yet fully understood and constitutes the purpose of this thesis. In this work, a new experimental setup coupling acoustical measurements with an impedance tube and vibration measurements with a scanning laser vibrometer is developped to characterize simultaneously acoustical and vibrational properties of foliages and substrates used in green walls in the 100 Hz-1000 Hz frequency range. This setup is used to characterize acoustic coefficients (absorption, reflection, transmission...), effective physical properties (speed of sound, characteristic impedance...) and vibrational response of foliage (spindle and bay) substrate (perlite, coco fiber, coco peat) samples. Results reveal acoustic properties of each medium and highlight the close link between vibrational resonances and acoustic coefficients of walls. Acoustic properties of samples constituted by the superposition of foliage and substrate layers are finally studied. Results demonstrate that the increase of absorption coefficient comes from both wall thickness resonances and impedance matching between air and substrate provided by the foliage layer. A method for optimizing acoustic absorption in a given frequency range is also proposed.

Thesis (M.S.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (February 26, 2007) Includes bibliographical references.

Thesis (M. Ing.)--University of Stellenbosch, 1997. / Bibliography. Also available via the Internet.

The tube hydroforming process has gained increasing attention in recent years. Coordination of the internal pressurization and axial feeding curves is critical in the tube hydroforming process to generate successful parts without fracture or wrinkling failure. The stress state at a given time and location varies with the process history and the design and control of the load paths. A new process parameter, counter-pressure, is introduced to achieve a favorable tri-axial stress state during the deformation process. The new process is referred to as dual hydroforming. The benefits offered by dual hydroforming will be characterized based upon the amount of wall thinning, plastic instability limit and final bulged configuration. An analytical model is developed to analyze the stress and strain state in the part (tube) during the dual hydroforming process. The stress-strain condition analyzed will be used to evaluate and compare thinning for tube hydroforming and dual hydroforming. The effect of applying counter-pressure on the plastic instability of thin-walled tubes with only internal pressure and combination of internal pressure and independent axial loading is considered. Finite element analysis is used to quantify the merits of dual hydroforming in terms of final bulged configuration. A parametric study has been conducted to investigate the effectiveness of dual hydroforming based on the various material properties and process conditions. Dual hydroforming results in different stress and strain states compared to tube hydroforming. The counter-pressure enabled favorable tri-axial stress state during deformation that resulted in different thickness and percentage thinning. Finite element analysis showed that for a particular amount of wall thinning there is an increase of around 8% in bulge height for dual hydroforming. Dual hydroforming delays the onset of plastic instability. This increase in the value of effective strain to failure results in an increase of around 12% in bulge height for dual hydroforming as shown by finite element simulations. Results of this study indicate that dual hydroforming can increase expansion i.e. more difficult parts can be designed and manufactured. Also, for a given part geometry, higher strength and less formable materials can be used.

Magnesium alloy tubes have good formability at elevated temperatures. In this paper, firstly, uniaxial tensile tests are conducted to evaluate the flow stress of AZ61 magnesium alloy at different temperatures and strain rates. Secondly, a hydraulic warm forming machine with axial feeding, counter punch and internal pressure is designed and manufactured. Using this testing machine with the FEM results, experiments of hydraulic forming of AZ61 magnesium alloy tubes at different temperatures are carried out. The effect of loading paths on the product shape and formability at different temperature are discussed.