In this paper, several new MOSFET devices, vertical MOSFET with L-shaped internal block layers (bVMOS), planar MOSFET with self-aligned internal block layers (bMOS), and Silicon-Germanium MOSFET with self-aligned internal block layers (bSGMOS) are presented. We use the sidewall spacer and etch back techniques to form the L-shaped internal block layers of bVMOS. They can suppress the short channel effects, diminish the parasitic capacitance, and reduce the leakage current cause by P-N junction between source/drain and body regions. They also provide a pass way to eliminate carriers and heat which generated by impact ionization resulting in suppression of floating-body effect and self-heating effect. In addition, we use Si3N4 cap layer upon gate as a hard mask, combining self-aligned and sidewall spacer techniques to fabricate the internal block layers under the both sides of channel end to form bMOS. The depleted region between source/drain and body is shielded and so the short channel effects and the controllability of gate to channel are improved. The internal block layers not only maintain the character of internal block layers but also ameliorate the drawback of bVMOS. The ISE TCAD simulation results show the short channel effect is suppressed and the thermal instability is improved by the internal block layers effectively in each device. Furthermore, we employ the epitaxial silicon-germanium thin film process (bSGMOS) to form silicon-germanium thin film at source/drain region to improve the device current drive by the strain thereby enhancing the device performance.

Subject to a sufficiently large compression, materials may undergo mechanical instabilities of various types. When the material is homogeneous, creases set in. When the material is a bilayer consisting of a stiff thin film on a thick compliant substrate, wrinkles set in. Creases are localized self-contact regions with large strain deviating from the smooth state, while wrinkles are undulations finite in space with infinitesimal strain deviating from the smooth state. After the formation of wrinkles, if the compression further increases, wrinkles double their period and form localized folds. If the substrate is subject to a sufficiently large pre-tension, wrinkles transit to ridges. This thesis explores different types of mechanical instabilities: creases, wrinkles, folds, and ridges. We start with studying creases in different materials. Soft tissues growing under constraint often form creases. We adopt the model of growth that factors the deformation gradient into a growth tensor and an elastic deformation tensor, and show that the critical conditions for the onset of creases take a remarkably simple form. We then perform simulations to explore creases in strain-stiffening materials. For a solid that stiffens steeply at large strains, as the compression increases, the surface is initially smooth, then forms creases, and finally becomes smooth again. For a solid that stiffens steeply at small strains, creases never form for all levels of compression. In order to better control the formation and disappearance of creases, we design a soft elastic bilayer with same moduli of the film and substrate but the substrate pre-compressed, and show that the bilayer can snap between the flat and creased states reproducibly with tunable hysteresis in a large strain range. We also show that an interface between two soft materials can form creases under compression. We then investigate the critical conditions for the onset of wrinkles and creases in bilayers with arbitrary thicknesses and moduli of the two layers, and show several new types of bifurcation behavior when the film and substrate have comparable moduli and thicknesses. We study the effect of substrate pre-stretch on post-wrinkling bifurcations, and show that pre-tension stabilizes wrinkles while pre-compression destabilizes wrinkles. When the pre-compression is sufficiently large, `chaotic' morphologies emerge. When the pre-tension is sufficiently large, we realize ridge localizations and networks under an equi-biaxial compression, and study the mechanics of ridge formation and propagation. / Engineering and Applied Sciences

No description available.

Experiments are presented in which the diffuse interface between two gases is made Rayleigh-Taylor unstable by interaction with a rarefaction wave. The apparatus used consists of a test section where the counter-flow of light and heavy gases generates a diffuse, stably stratified interface. A tank attached to the bottom of the apparatus is evacuated, and when an appropriate pressure is reached, the interface is perturbed using either a horizontal or a vertical oscillation technique to produce 2D, 3D, and multi-mode perturbations. A solenoid plunger fires an arrowhead which ruptures a membrane, generating a rarefaction wave that travels upward toward the interface. When the rarefaction wave impacts the interface, the interface accelerates down toward the vacuum tank, and the Rayleigh-Taylor instability and mixing develop in the test section. The instability evolution and mixing are recorded using high-speed CMOS cameras and planar laser Mie scattering of smoke particles seeded in the heavy gas. Additional visualization is undertaken with a high-speed shadowgraph system using three CMOS cameras. Interface diffusion thicknesses are recorded using the Rayleigh scattered light of an unexpanded laser beam. Simulations are conducted using a 1D numerical characteristics code based on the method of Hoskin (Meth. Comp. Physics, 3, 1964), and using the LLNL research hydrodynamics code Miranda (Cook, Phys. Fluids, 19, 2007). This 1D code produces Lagrangian interface trajectories while the 2D and 3D simulations using Miranda calculate the growth of perturbations. The theory of Chandrasekhar (Chandrasekhar, Proc. Camb. Phil. Soc., 51, 1955) is extended to capture the effects of diffuse interfaces while including viscosity, and dispersion curves are solved for numerically using a Riccati technique. These solutions show that the method of Duff et al. (Phys. Fluids, 5, 1962) may not accurately describe the growth of single modes for large wavenumbers. For large wavenumbers, when the interface has a large diffusion thickness, perturbations are found to grow with the linear growth rate n = 2Ag/(√πv₀δk²), where A is the Atwood number, g is the acceleration, v₀ is the average kinematic viscosity, δ is the thickness of the interface, and k is the wavenumber of the perturbation. Flat interface experiments exhibit predictable acceleration profiles, but the tail of the rarefaction wave appears at late times reducing the duration of acceleration. Single-mode experiments are conducted for four Atwood numbers including CO₂/SF₆ with A = 0.49, Air/SF₆ with A = 0.63, He/CO₂ with A = 0.82, and He/SF₆ with A = 0.94. Early time results compare well with linear stability theory when non-constant acceleration and diffusion thickness are accounted for. Simulations show good agreement with experiments into the non-linear growth phase. The CO₂/SF₆ and Air/SF₆ experiments show terminal velocity behavior where buoyancy is balanced by drag, but produce Froude numbers larger than those predicted by the Goncharov model (Phys. Rev. Lett., 88, 2002). Using the Mikaelian model (Phys. Fluids, 21, 2009), improved asymptotic Froude numbers are found. The He/CO₂ and He/SF₆ experiments exhibit free-fall behavior, accelerating freely without external forces, with spike amplitudes proportional to the displacement of the unperturbed interface. Single-mode experiments conducted with 3D perturbations using CO₂/SF₆ and Air/SF₆ show good agreement with linear stability theory when non-constant acceleration and diffusion thickness are accounted for. Simulations and the model of Mikaelian predict the growth of the spikes up until late time, while the 3D bubbles reach a terminal velocity more quickly than in simulations. Multi-mode experiments were conducted using Air/SF₆. Multi-mode experiments exhibit nearly t² growth at early times which decays. Using extraction techniques that account for variable acceleration, alpha values are found between ɑ = 0.02 and ɑ = 0.04. These alpha values are lower than are seen for most experiments, but are similar to ɑ values seen in miscible experiments.

Chromosomal fragile sites are specific loci associated with a high frequency of breakage and recombination. A cell's ability to repair and/or replicate through a lesion is prerequisite to the maintenance of genomic stability. An improved understanding of fragile site biology and its contribution to replication defects and genomic instability is critical for prevention, intervention, and diagnosis of genetic diseases such as cancer. This work seeks to identify and characterize both trans and cis fragile sites associated elements involved in instability onset and progression. An array of Saccharomyces cerevisiae isogenic DNA repair deficient mutants were utilized to identify genes contributing to the stability or instability of a natural fragile site ~ 403 kb from the left telomere on chromosome VII. Findings suggest that the RAD52 epistasis group, the MRX complex, non-homologous end-joining (NHEJ) pathways, MUS81 and SGS1 helicases, translesion polymerases, and a majority of the post replication repair (PRR) proteins are all required for faithful replication of the 403 fragile site and likely other fragile sites as well. In contrast I found that MMS2, previously thought to be specific to the PRR pathway, is required to prevent the fusion of repetitive elements within the 403 site. mgs1 (homolog of the human Werner helicase interacting protein, WHIP) and pol3-13 (a subunit of the DNA polymerase delta) mutants also exhibited reduced instability in checkpoint deficient cells. These findings suggest previously uncharacterized function of Mgs1, Pol3 and Mms2 in regulation of genome regions at risk of replication damage. We further find the presence of inverted repeats (IR) are sufficient to induce instability. Two IR's proximal to the 403 site consistently fuse to generate acentric and dicentric chromosomes involving the 403 fragile site and a newly identified site on chromosome VII as well. The frequency of fusion events is aggravated by chromatin traffic stressors such as tRNA transcription induced fork stalling and replisome termination regions.

It is currently believed that angular momentum transport in accretion disks is mediated by magnetohydrodynamic (MHD) turbulence driven by the magnetorotational instability (MRI). More than 15 years after its discovery, an accretion disk model that incorporates the MRI as the mechanism driving the MHD turbulence is still lacking. This dissertation constitutes the first in a series of steps towards establishing the formalism and methodology needed to move beyond the standard accretion disk model and incorporating the MRI as the mechanism enabling the accretion process. I begin by presenting a local linear stability analysis of a compressible, differentially rotating flow and addressing the evolution of the MRI beyond the weak-field limit when magnetic tension forces due to strong toroidal fields are considered. Then, I derive the first formal analytical proof showing that, during the exponential growth of the instability, the mean total stress produced by correlated MHD fluctuations is positive and leads to a net outward flux of angular momentum. I also show that some characteristics of the MHD stresses that are determined during this initial phase are roughly preserved in the turbulent saturated state observed in local numerical simulations. Motivated by these results, I present the first mean-field MHD model for angular momentum transport driven by the MRI that is able to account for a number of correlations among stresses found in local numerical simulations. I point out the relevance of a new type of correlation that couples the dynamical evolution of the Reynolds and Maxwell stresses and plays a key role in developing and sustaining the MHD turbulence. Finally, I address how the turbulent transport of angular momentum depends on the magnitude of the local shear. I show that turbulent MHD stresses in accretion disks cannot be described in terms of shear-viscosity.

Internal instability of a widely graded cohesionless soil refers to a phenomenon in which its finer particles migrate within the void network of its coarser particles, as a result of seepage flow. Onset of internal instability of a soil is governed by a combination of geometric and hydromechanical constraints. Much concern exists for embankment dams and levees built using soils with a potential for internal instability. Migration of finer particles to a boundary where they can exit, by washing out, may cause erosion or piping failure and, occasionally, induce collapse of these soil structures. There is a need, in professional practice, to better understand the phenomenon and to develop improved methods to evaluate the susceptibility of a soil. A series of permeameter tests was performed on six widely-graded cohesionless materials. The objectives are to assess the geometric indices proposed for evaluation of susceptibility, and examine hydromechanical factors influence the onset of internal instability. A modified slurry mixing technique, with discrete deposition, was found satisfactory for reconstitution of the homogeneous saturated test specimens. The onset of internal instability was founded to be triggered by a combination of effective stress and hydraulic gradient. The finding yields a hydromechanical envelope, unique for a particular gradation shape, at which internal instability initiated. Three commonly used geometric criteria were comprehensively evaluated with reference to these experimental data and also a database compiled from the literature. The relative conservatism of each criterion was examined and a modified semi-empirical geometric rule then proposed based on the capillary tube model. A theoretical framework for plotting the hydromechanical envelope was established based on an extension of the α concept of Skempton and Brogan, and subsequently verified by test data. Finally, a novel unified approach was proposed to assess the onset of internal instability, based on combining geometric and hydromechanical indices of a soil.

The integrity of the genome is critical to organisms and it is affected by many factors. Radiation, for example, poses a serious threat to genome stability of human beings. While physical monitors for radiation hazard are present, the biological consequences of long term exposure to radiation are not well understood. With the opportunity as part of the International Caenorhabditis elegans Experiment-1 flight project, several approaches using C. elegans were taken to measure mutational changes that occurred during the spaceflight. Among these methods, the eT1 balancer system was demonstrated to be well-suited as an integrating biological dosimeter for spaceflight. The dog-1 gene in C. elegans is required to prevent mutations at poly-G/poly-C tracts, and previous work has described that in the absence of DOG-1, small deletions initiate within these tracts, most likely as a consequence of improperly repaired replication blocks. The eT1 balancer system was adapted to investigate the broad mutational spectrum of dog-1 mutants. Using this system, I was able to determine a forward mutation rate of approximately 1 x 10-3, 10 fold higher than spontaneous. Both small deletions as reported previously and unreported large chromosome rearrangements were observed, and most of mutations analyzed are associated with G/C tracts. Thus, I propose that following dog-1-induced replication blocks, repair leads to a wide range of mutational events and chromosomal instabilities, similar to those seen in human cancers. The existence of the G/C tracts in C. elegans creates a fortuitous but perplexing problem. They are hotspots for genome instability and need enzymatic protection. In the genome of C. elegans, approximately 400 G/C tracts exist and are distributed along every chromosome in a non-random pattern. G/C tracts are also over-represented in another Caenorhabditis species, C. briggsae. However, the positions and distribution differ from those in C. elegans. Furthermore, in C. elegans, analysis of SAGE data showed that the position of the G/C tracts correlated with the level of gene expression. Although being a threat to genome stability, the genomic distribution of G/C tracts in C. elegans and their effect on regional transcription levels suggest a role for G/C tracts in chromatin structure.

Background: As the number of smokers in industrialized nations declines the number of smokers in developing countries increases. Many of the nations that are experiencing an increase in smoking prevalence are poor, politically unstable countries. The smoking rates among adolescents are increasing at an especially alarming rate. The tumultuous sociopolitical conditions such as civil unrest, the overthrowing of government regimes and the presence of political violence makes adolescents in these environments susceptible to engagement in high risk behavior such as smoking as a means of self- medicating the symptoms of mental disorder or unhealthy coping mechanisms. The purpose of this study was to analyze the difference in smoking behaviors and beliefs among adolescents in politically unstable countries compared to those in more stable areas. Methods: The West Bank, Gaza Strip, Yemen, Iraq, United Arab Emirates, Oman, Qatar and Kuwait were selected for inclusion in the study based on their World Bank Indicators. Stable countries were defined by their ranking in the 50th percentile or higher on the Political Stability and Absence of Violence Index, whereas unstable countries were defined as being in the 10th percentile or lower. Using secondary data from the 2001, 2002, 2003, 2004, 2005 and 2006 Global Youth Tobacco Survey (GYTS) for eight countries, univariate and multivariate analyses were conducted to assess the factors associated with smoking behaviors. Cases were truncated for 13- 15 year old respondents. A p- value of < .05 and 95% confidence intervals was used to determine statistical significance through the various analyses performed. Results: The univariate and multivariate analysis found that living in an unstable country and being male was associated with increased odds of smoking and experimentation among 13- 15 year old adolescents. Conclusion: The study results suggest that political stability may be associated with smoking behaviors and beliefs among adolescents. Since the factors that create political instability are multi-factorial and beyond the scope of this study, interventions should be designed to address smoking and other risk behaviors within this unique sociopolitical context. Previous interventions in similar settings have found programs integrating mental health dimension and religious leaders have been successful in staving off the onset of smoking among study populations. INDEX WORDS: teens, adolescents, trauma, political instability, risk behavior, tobacco, smoking, interventions,

The overall objective of this thesis was to compare compensatory reactions in young and older adults following unexpected platform perturbations in the frontal and sagittal planes during gait. Eleven young (aged 18-30) and ten community-dwelling older adults (aged 65+) completed a general health questionnaire, Mini BESTest, hip strength tests, and 45 walking trials on a motion platform. The walking trials were completed in a randomized block design on a 5 m pathway that moved following right heel contact after at least two steps. Young adults had stronger hips and performed better on the Mini BESTest than older adults. Compensatory reactions (measured through gait parameters and centre of mass motion) indicated that lateral perturbations were more difficult for both groups. These measures showed that young adults were able to recover more quickly than older adults. This could be attributed to altered base of support changes that occurred immediately following platform motions. / Ontario Graduate Scholarship