Influences of triblock-copolymer interfacial-modifiers on fracture and yielding behaviors of polystyrene/ethylene-propylene-rubber blends

Au cours des dernières années, plusieurs travaux ont été réalises dans Ie domaine des mélanges de polymères. Ceci est un des moyens efficaces et peu couteux pour améliorer les propriétés mécaniques des polymères. Dans une étude précédente [I], deux copolymères de triblock de styrène/éthylène - butylène/styrène (SEBS), de différents poids moléculaires, ont été utilises pour compatibiliser un mélange contenant en volume 80 % de polystyrènes (PS) et 20 % de caoutchouc-éthylène-propylène (CEP). Les résultats montrent, premièrement, une augmentation significative de la résistance aux chocs lorsque les concentrations d'agents interfaciaux sont au-dessus de la concentration critique en émulsification pour des mélanges compatibilises par Ie copolymère ayant une masse moléculaire faible (K2) et, deuxièmement, qu'une transition fragile-ductile de rupture se produit. À partir de ces résultats, l'objectif de cette étude est d'améliorer la compréhension des effets des deux copolymères de triblock ci-dessus sur la rupture et Ie comportement des mélanges sur un intervalle étendu des taux de chargement et des températures. A cette fin, les mélanges de différentes concentrations de ces copolymères out été étudiés dans de diverses conditions d'essai. L'attention est mise sur la corrélation entre temps-température et la résistance de rupture ainsi que Ie comportement d'écoulement de ces mélanges. L'ajout du copolymère de triblock, connu sous Ie nom d'agent interfacial, permet au mélange fragile de PS/CEP de devenir plus ductile. La dépendance temps-température de la transition fragile-ductile a la rupture des mélanges est contrôlée par un processus d'énergie d'activation et peut être prédit par l'équation d'Arrhenius. Ajouter un agent interfacial abaisse la température a la transition fragile-ductile et réduit la barrière d'énergie contrôlant Ie processus de rupture. Cet effet, cependant, est beaucoup plus prononce pour l'agent interfacial de poids moléculaire inferieur, K2. La résistance de rupture pendant la propagation de fissure des mélanges est déterminée en utilisant la méthode de R-courbe et elle présente une contribution distincte aux mélanges K2-20 et K2-30 pour la résistance la plus élevée de rupture du mélange de PS/CEP.Abstract: In a previous study two triblock copolymers of styrene/ethylene - butylene/styrene (SEBS), of different molecular weights, were used to compatibilize a blend of 80 volume % of polystyrene (PS) and 20 volume % of ethylene - propylene rubber (EPA). The aim of this work is to foster the understanding of the effects of the two triblock copolymers on fracture and yielding behavior of the blends over a large range of loading rates and temperatures. For this purpose, the blends of different concentrations of these two triblock copolymers were studied at various test conditions. The focus is put on the time - temperature dependence of fracture performance and yielding behavior of these blends. The addition of the triblock copolymer, known as an interfacial modifier, allows the brittle PS/EPR blend to become more ductile. The time-temperature dependence of the brittle-ductile transition in fracture performance of the blends is controlled by an energy activation process and can be predicted by the Arrhenius equation."--Résumé abrégé par UM

Sampling strategies for forest aerial detection survey in Colorado

2015 Summer.Aerial detection survey (ADS) has been commonly employed in forest surveys in the United States for detecting forest damage and monitoring forest health. In Colorado, ADS by USDA Forest Service has conducted annual 100% census of government forested land for more than 20 years with the goal of achieving information about forest damage due to different causal agents and disorders. Sketchmapping has been commonly employed in ADS with the goal of detecting and documenting on maps mortality, defoliation and other visible forest change from aircraft. At medium and large scale, sketchmapping is a suitable technique for forest monitoring that provides valuable information in forest health. This dissertation deals with data of forest area damaged by five causal agents mountain pine beetle, spruce beetle, western spruce budworm, pin engraver, and Douglas fir beetle and two disorders subalpine fir mortality and sudden aspen decline. The combined areas damaged by all causes were also considered. Data were downloaded from ADS in Colorado from 1994 to 2013 as polygon shapefiles with associated information such as causal agents or disorders, area damaged, and type of forest. The goal of my dissertation was to identify an appropriate sampling strategies to archive good estimates of total area damaged, to decrease survey cost, and to increase safety by reducing the amount of flights. To approach this goal, four sample designs for estimating total area damaged caused by various causal agent were evaluated: simple random sampling, stratified random sampling, probability proportional to size, and non-alignment systematic sampling. A GIS layer of 150 transects covering Colorado’s forestlands was developed and represented the sample unit for my study. Each transect was 3.2 km wide and 625 km long and was numbered from 1 to 150 from south to north. Each sample design was evaluated using eight sample sizes (10, 15, 20, 25,30, 35, 50, and 70) and applied to the seven damages and the combined damaged area. The statistical properties were evaluated to determine the optimal sample design for estimating area damaged caused by different causal agents. The spatio-temporal characteristics of area damaged that influence precision and accuracy of estimate were considered. Most of the damaged forest areas by single causal agents and disorders showed aggregated spatial patterns; whereas the combined damaged areas were uniformly distributed across the landscape. A loss plus cost function was employed to determine the optimal sample size for each sample design and analyzed for the cost advantage of alternative sample designs. We found that stratified random sampling was the most optimal sample design by producing the highest percentage of unbiased estimates of total area damaged and the smallest variances. The next best sampling designs were simple random sampling and probability proportional to size. The non-alignment systematic sampling was the worst for estimating total area damaged both for individual causal agents and disorders and all causal agents combined. The optimal sample size varied by sample design and causal agents and disorders as well as the level of confidence. Optimal sample size increased with increasing variability in the population and as the desired level of confidence increased. Larger samples were required to simultaneously provide estimates for multiple causal agents and disorder with reasonable levels of precision when compared to a single causal agent. Stratified random sampling was the most cost effective when compared with other sample designs. For example, the cost advantage of stratified sampling over random sampling for estimating the damage from subalpine-fir mortality was $85,000 per year. In contrast, PPS sampling had a cost disadvantage of -$13,000 per year when compared with simple random sampling and -$95,000 per year when compared with stratified sampling for estimating the total damage from all causal agents combined at the 0.95 level of confidence

Influence of the "second gap" on the transparency-conductivity compromise in transparent conducting oxides: an ab initio study

Transparent conducting oxides (TCOs) are essential to many technologies. These materials are doped (\emph{n}- or \emph{p}-type) oxides with a large enough band gap (ideally $>$3~eV) to ensure transparency. However, the high carrier concentration present in TCOs lead additionally to the possibility for optical transitions from the occupied conduction bands to higher states for \emph{n}-type materials and from lower states to the unoccupied valence bands for \emph{p}-type TCOs. The "second gap" formed by these transitions might limit transparency and a large second gap has been sometimes proposed as a design criteria for high performance TCOs. Here, we study the influence of this second gap on optical absorption using \emph{ab initio} computations for several well-known \emph{n}- and \emph{p}-type TCOs. Our work demonstrates that most known \emph{n}-type TCOs do not suffer from second gap absorption in the visible even at very high carrier concentrations. On the contrary, \emph{p}-type oxides show lowering of their optical transmission for high carrier concentrations due to second gap effects. We link this dissimilarity to the different chemistries involved in \emph{n}- versus typical \emph{p}-type TCOs. Quantitatively, we show that second gap effects lead to only moderate loss of transmission (even in p-type TCOs) and suggest that a wide second gap, while beneficial, should not be considered as a needed criteria for a working TCO.Comment: 6 pages, 4 figures, APS March Meetin

Topological Lifshitz phase transition in effective model of QCD with chiral symmetry non-restoration

The topological Lifshitz phase transition is studied systematically within an effective model of QCD, in which the chiral symmetry, broken at zero temperature, is not restored at high temperature and/or baryon chemical potential. It is found that during phase transition the quark system undergoes a first-order transition from low density fully-gapped state to high density state with Fermi sphere which is protected by momentum-space topology. The Lifshitz phase diagram in the plane of temperature and baryon chemical potential is established. The critical behaviors of various equations of state are determined.Comment: 8 pages, 10 figure

A Prospective Cohort Study of Gestational Weight Gain, Postpartum Weight Retention, and Maternal Health in Vietnam

The studies presented in this thesis are the first published investigations of physical activity on maternal weight changes, postpartum low back pain and on periconceptional folic acid supplementation in Vietnam. Prenatal and postnatal physical activity are protective factors for excessive gestational weight gain, postpartum weight retention, and low back pain. Folic acid supplementation in the periconceptional period is recommended to prevent neural tube defects, but the rate of correct use in Vietnam is too low

Cost-effectiveness analysis of interventions to prevent cardiovascular disease in Vietnam

Background Vietnam is in the process of an epidemiological transition, with cardiovascular disease (CVD) now ranked as the leading cause of death. The burden of CVD will continue to rise unless effective interventions for addressing its underlying risk factors are put in place. Objectives To assess the costs, health effects and cost-effectiveness of a set of personal and non-personal prevention strategies to reduce CVD in Vietnam, including mass media campaigns for reducing consumption of salt and tobacco, drugs for lowering blood pressure or cholesterol, and combined pharmacotherapy for people at varying levels of absolute risk of a cardiovascular event. Methods WHO-CHOICE methods and analytical models were employed, using local data to estimate the costs, effects and cost-effectiveness of 12 population and individual interventions implemented singly or in combination. Costs were measured in Vietnamese Dong for the year 2007 (discounted at a rate of 3% per year), while health effects were expressed in age-weighted and discounted disability-adjusted life years (DALYs) averted. Results A health education programme to reduce salt intake (VND 1 945 002 or US$118 per DALY averted) and individual treatment of systolic blood pressure above 160 mmHg (VND 1 281 596 or US$78 per DALY averted) were found to be the most cost-effective measures for population- and individual-based approaches, respectively. Where budget is very limited, a mass media education programme on salt intake and a combination mass media programme addressing salt intake, cholesterol and tobacco should be selected first. If more resources become available, greatest population health gains can be achieved via individual treatment of systolic blood pressure and the absolute risk approach to CVD prevention. Conclusions Contextualization of WHO-CHOICE using local data provides health decision-makers with more sound economic evidence for policy debates on prioritizing health interventions to reduce cardiovascular diseases in Vietnam. When used, cost-effectiveness analysis could increase efficiency in allocating scare resource