In this dissertation¡Atwo topics in microbubble systems are investigated¡G1) Pore Formation from Bubble Entrapment by a Solidification Front¡F2) Pore formation in Solid¡C In the first study¡Amechanism of the pore shape in solid resulted from a tiny bubble captured by a solidification front is geometrically and generally investigated¡CPore formation and its shape in solid are one of the most critical factors affecting properties¡Amicrostructure¡Aand stresses in materials¡CFor simplicity without loss of generality, the tiny bubble beyond the solidification front is considered to have a spherical cap in this work¡CIntroducing a geometrical analysis it is found that the contact angle of the bubble cap can be governed by the Abel¡¦s equation of the first kind in terms of displacement of the solidification front¡CThe pore can be elongated, expanded¡Ashrunk and closed¡Adepending on relative variation of the bubble growth rate and solidification rate¡CThe pore can be closed by imposing infinitesimal bubble growth rate-to-solidification rate ratio¡Aand a finite bubble growth-to-solidification rate ratio in order to produce a minimal bubble radius at the contact angle of ¡CA criterion intuitively accepted in the literature¡Astating that closure of a pore is attributed to a greater solidification rate than bubble growth rate¡Ais incorrect¡CThe predicted pore shape and contact angle agree with experimental observations¡CManipulating either bubble growth rate or solidification rate can control pore formation in solid¡C In second study¡Athe shapes of a growing or decaying bubble entrapped by a solidification front are predicted in this work¡CThe bubble results from supersaturation of a dissolved gas in the liquid ahead of the solidification front¡CPore formation and its shape in solid are one of the most critical factors affecting properties¡Amicrostructure, and stresses in materials¡CIn this study¡Athe bubble and pore shapes entrapped in solid can be described by a three-dimensional phase diagram¡Aobtained from perturbation solutions of Young-Laplace equation governing the tiny bubble shape in the literature¡CThe predicted growth and entrapment of a microbubble as a pore in solid are found to agree with experimental data¡CThis work thus provides a realistic prediction of the general growth of the pore shape as a function of different working parameters¡C

This study investigated the effect of chronic alcohol exposure on the responses of the maternal hypothalamus-pituitary adrenal axis (HPA-axis) and thyroid hormones throughout gestation using an ovine model. Maternal plasma concentrations of ACTH, cortisol and the thyroid hormones T3, free T4 and total T4 were determined in response to infusion of 0.75, 1.25 and 1.75 g/kg alcohol. Maternal endocrine responses to alcohol administration have been investigated before in rodent models. However, this is the first study using a large animal model (sheep), in which all three human trimester equivalents occur in utero. Different concentrations of alcohol were administered intermittently from gestational day 4 to 132 in a pattern that modeled human binge drinking during pregnancy. Maternal blood samples were collected on specific days (GD 6, 40, 90, 132) and at multiple time-points (0, 0.5, 1, 1.5, 2, 6, 24 hours) and were analyzed to determine blood alcohol concentrations (BACs) and ACTH, cortisol, free T4, total T4 and T3 plasma concentrations. Alcohol readily permeates the placenta and can directly affect fetal cells and tissues. Alcohol also causes endocrine imbalances in the mother and interferes with maternal-fetal hormonal interactions and the mother’s ability to maintain a healthy pregnancy, thus also indirectly affecting fetal development. Sheep receiving either 0.75, 1.25 or 1.75 g/kg alcohol achieved peak BAC values of 93 + 5, 126 + 5 and 183 + 5 respectively. Alcohol exposure resulted in increased plasma ACTH and cortisol concentrations peaking at 2 hours after beginning of the infusion and returning to baseline values at 6 hours after beginning of the infusion. There was no effect of alcohol on any of the plasma thyroid hormone concentrations. Thyroid hormone concentrations changed as a result of progressing pregnancy. Plasma concentrations of total T4 and free T4 were higher on gestational days 6 and 40 compared to GDs 90 and 132, and plasma T3 concentrations were highest on GD 6. The results of this study show that alcohol stimulates the HPA-axis in a dose dependent fashion in pregnant sheep. The response of the HPA-axis to repeated alcohol exposure throughout gestation remained unchanged. Alcohol exposure did not affect the release of thyroid hormones. Thyroid hormone concentrations changed during pregnancy in sheep in a manner similar to changes observed in pregnant women.

Testing of delay defects is necessary in deep submicron (DSM) technologies. High coverage delay tests produced by automatic test pattern generation (ATPG) can be applied during wafer and package tests, but are difficult to apply during the board test, due to limited chip access. Delay testing at the board level is increasingly important to diagnose failures caused by supply noise or temperature in the board environment. An alternative to ATPG is the built-in self test (BIST). In combination with the insertion of test points, BIST is able to achieve high coverage of stuck-at and transition faults. The quality of BIST patterns on small delay defects is an open question. In this work we analyze the application of BIST to small delay defects using resistive short and open models in order to estimate the coverage and correlate the coverage to traditional delay fault models.

This paper describes a method by means of FE code DEFORMTM-2D to simulate the formation of central bursting defects in extrusion processes; the effect of various extrusion parameters such as half die angle, reduction in area, friction factor, and strain hardening exponent on the maximum damage value is examined. The differences between various ductile fracture criteria are compared and critical damage value(CDV) of the material AA6061 is found. In addition, we get the strength coefficient(K), strain hardening exponent(n), CDV and friction factor(m) by material tests, such as uniform tensile test, notched tensile test, compression test, and ring compression test. Finally, the cold multistage extrusion experiment was conducted to verify the accuracy of the finite element simulations. From the continuous three pass extrusion experimental data, no fracture in the center of the extruded product was found. From the analytical data, it was known that the maximum damage value 1.0479 for third pass extrusion was small than critical damage value 1.068, thus, central bursting defects didn¡¦t occur in extrusion processes.

Eddy current testing is a widely-used examination of the nondestructive testing method. According to the theory of electromagnetic induction, the coil impendence varies with the interaction between the coil magnetic field and the eddy current magnetic field. By observing the variations of the phase angle and the impendence plane diagram, the influence of different defects and factors are evidently presented. The purpose of this study is to analyze the three-dimensional defects of eddy current testing by means of the finite element method. To begin with, a complete 3-D electromagnetic model in eddy current testing by finite element software package COMSOL Multiphysic was created. Then the impendence plane diagram and evaluation curves are drawn by the mathematics software package MATLAB to show the variations of the impendence and the phase angle. Moreover, the results show the effect of reducing testing errors. The simulation of 3-D defect model can provide more comparable data for experimentalists. So that the problem of inappropriate judgement can be prevented, and then the accuracy in eddy current testing can be enhanced.

The prevalence of concrete and cement-based materials in the civil infrastructure plus the risk of failure makes structural health monitoring an important issue in the understanding of the complete life cycle of civil structures. Correspondingly, the field of nondestructive evaluation (NDE) has been maturing and now concentrates on the detection of flaws and defects, as well as material damage in early stages of degradation. This defect detection is typically usually done by looking at the impulse response of the medium in question such as a cement-based material. The impulse response of a solid can be used to image a complex medium. Classically, the waveform is obtained by an active setup: an ultrasonic signal is generated at one location and recorded at another location. The waveform obtained from imaging can be used to quantitatively characterize the medium, for example by calculating the material's diffusivity coefficient or dissipation rate. In recent years, a different monitoring technique has been developed in seismology to measure the velocity of different kinds of waves, the Coda Wave Interferometry (CWI). In this CWI technique, the main focus is given to the late part of the recorded waveform, the coda. CWI is now successfully used in seismology and acoustics. In the current research, CWI is applied on concrete in different damage states to develop basic knowledge of the behavior of the wave velocity, and how it can be used to characterize cement-based materials. By comparing two impulse responses, the relative velocity change between the two impulse responses is used to characterize damage. Because of the stress-dependency of the velocity change, the calculations can also be used to directly calculate the Murnaghan's and Lam´e's coefficients. The newer technique of CWI is applied - the Stretching Technique (ST) [27]. The first goal of this research is to establish the viability of using CWI in cement-based materials. Next, we use the ST in the application of stress as we compress concrete samples for the detection of thermal damage, ASR-damage and mechanical softening.

Congenital heart defects due to the aberrant development of the atrioventricular (AV) valves and septum are among the most common developmental abnormality in newborns and cause significant neonatal morbidity and mortality. A key point in cardiac morphogenesis occurs when cells within the endocardial cushions (ECCs), the precursors for the AV valvoseptal complex, delaminate and undergo an epithelial-to-mesenchymal transformation (EMT). The mesenchymal cells then proliferate and the cushion area elongates to form the AV valves and portions of the AV septae. The signals that initiate region-specific EMT during heart development are unknown. Cilia, known for their role in establishing left-right (LR) asymmetry, function to receive and integrate extracellular signals, including fluid flow, in a range of other organ systems. We hypothesize that cilia could also have a direct role in heart development outside of their role in LR development. Using immunohistochemistry, we demonstrated the presence of cilia on the myocardium, epicardium, and ECCs of wild-type mouse hearts at embryonic day (e) 9.5 and e12.5. To characterize the potential role of these cilia, we compared mice with mutations affecting ciliary biogenesis, motility, and mechanosensation. Using bright field microscopy and in situ hybridization, we analyzed the embryonic heart structure and the expression pattern of Gata4, an EMT transcription factor. We showed that compared to mice with immotile but structurally normal cilia, the mice without cilia had hypocellular ECCs, a thinned compact myocardium (CM), and an up-regulated expression of Gata4. These observations suggest that a subset of cilia called cardiac cilia have a role in cardiogenesis outside of their role in LR development and affect Gata4 expression. One possible function of cardiac cilia is as mechanosensors, integrating fluid flow and influencing cardiac morphogenesis including EMT and development of the CM.

Thesis (M. Sc.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 68-75).

The Ubuntu Linux Distribution represents a massive investment of time and human effort to produce a reliable computing experience for users. To accomplish these goals, software bugs must be tracked and fixed. However, as the number of users increase and bug reports grow advanced tools such as data mining must be used to increase the effectiveness of all contributors to the project. Thus, this report involved collecting a large amount of bug reports into a database and calculating relevant statistics. Because of the diversity and quantity of bug reports, contributors must find which bugs are most relevant and important to work on. One study in this report created an automatic way to determine who is best fit to solve a particular bug by using classification techniques. In addition, this report explores how to initially classify if a bug report will be eventually marked invalid or not. / text

Lead zirconate titantate (PZT) is an electroceramic material with many important technological applications in sensing and computer memory. Some of these applications require the PZT based devices to operate in radiation fields where they will be exposed to a high flux of energetic, heavy and light, charged and uncharged particles. The risk to any device exposed to ionizing radiation is the accumulation of displacement and ionization damage. Significant damage accumulation over time can lead to property drifts and, in some cases, failure of the device to perform properly. The goal of the undertaking recounted in this dissertation was to study changes in the ferroelectric properties of PZT exposed to the neutron field of a research nuclear reactor and to help develop an understanding for the type of radiation induced defects that play a dominant role in the degradation process. Thin film PZT capacitors were prepared using a wet chemical technique. The capacitors were then irradiated in a 1 MW TRIGA research nuclear reactor at the University of Texas at Austin up to a maximum 1 MeV equivalent neutron flux of 5.2 x 10¹⁵ cm⁻². Following irradiation, electronic characterization of polarization-electric field hysteresis loops, first order reversal curves, and small-signal permittivity were performed to ascertain tendencies between irradiation dose and ferroelectric properties. The measurements indicate a drop in remanent polarization, a loss of domain wall mobility, shifts in local switching fields and the formation of dipolar defects. These effects are all attributed to the introduction of defects into the material through displacement damage cascades. Numerical models of the damage cascades were performed to determine the displacement concentration. Comparison of those values and the primary recoil spectrum with typical survival rates found in the literature suggest that both free point defects as well as defect clusters are produced in comparable if not larger concentrations. It is proposed that defect clusters play a more significant role in ferroelectric property change than previously believed. / text