African Americans (AA) are at an increased risk for cardio and cerebral vascular disease relative to Caucasians (CA) and the underlying impairments manifest as early as the second generation prior to overt signs of risk. The mechanisms of this increased risk are multifactorial; however, evidence suggests that microvascular dysfunction is a primary contributor. This study tested the hypothesis that microvascular function, indexed by the skin vascular conductance (SkVC) response to local heating, is impaired in young otherwise healthy AAs. Furthermore, we hypothesized that AAs have an attenuated cerebral vasodilator response to hypercapnia. Nineteen healthy young individuals were participated in this study (9 AAs, 10 CAs). SkVC was assessed while the skin was clamped at 34 °C and 40 °C and values were normalized to a maximal value obtained during heating at 43 °C for 30 min. Cerebral vasomotor reactivity (CVMR) was assessed by increases in cerebral vascular conductance (CVC) during a rebreathing protocol. SkVC was lower in the AA group at 34 °C (AA: 10±3 % max vs. CA: 16±7 % max; P < 0.01) In addition, SkVC was reduced in AAs at 40 °C (AA: 56±15 % max vs. CA: 68±12 % max; P=0.03). CVMR was significantly attenuated during hypercapnic rebreathing in AAs relative to CAs (AA: 2.8 ± 1.2 %CVC/Torr vs. CA: 5.7 ±0.9 %CVC/Torr; P < 0.001). Our findings suggest that microvascular function is impaired in young otherwise healthy AAs. / text

Les composites à matrice céramique (CMC) SiCf/SiC sont des matériaux envisagés pour le gainage du combustible des futurs réacteurs à neutrons rapides. Une des problématiques de mise en oeuvre concerne leur assemblage et notamment la fermeture de ces gaines contenant le combustible. A l'heure actuelle, aucune composition de joint d'assemblage suffisamment réfractaire n'est mentionnée dans la littérature. Les objectifs de cette étude sont : (1) la recherche d'un matériau d'assemblage et du procédé associé répondant aux contraintes de mise en oeuvre et de fonctionnement, (2) la validation d'un procédé "nucléarisable" de chauffage localisé et rapide afin de ne pas dégrader le composite lors de l'assemblage et (3) la définition de tests mécaniques pour caractériser ces assemblages. Après une étude bibliographique approfondie des systèmes d'assemblage potentiels et la sélection d'une composition à travers des travaux expérimentaux exploratoires par frittage flash, la solution proposée est de réaliser un brasage à partir d'une composition mixte de disiliciure métallique (MSi2) et de carbure de silicium (SiC). Le choix du brasage a nécessité une étude de mouillabilité et de cinétique d'étalement de la brasure en prenant en compte les aspects réactifs de celle-ci sur le carbure de silicium. Différents procédés de chauffage localisé de la brasure tels que le laser CO2, les micro-ondes ou le chauffage inductif haute fréquence ont été testés. La faisabilité de différents procédés d'élaboration du joint a été montrée, notamment par dépôt physique en phase vapeur (PVD), par projection plasma et par enduction de suspensions de poudres. Un essai de flexion 4-points a également été défini afin d'évaluer la résistance mécanique des assemblage. / The present work is part of the Fourth Generation Fast Reactors program. One of the key issues is the joining of the SiCf/SiC ceramic matrix composites (CMC) to seal the combustible cladding. At the present time, no chemical composition as a joint is refractive enough to face the expected operating temperatures. The aimes of this study are the following : (1) the identification of a joining composition and its associated elaboration process answering the specifications, (2) the validation of a local and fast heating process and (3) the definition of mechanical tests to caracterise these joinings. We describe the methodology and the results for joining SiC and SiCf/SiC substrates at solid and liquid state using metallic silicides. Joint integrity and joint strength can be improved by adding small SiC particles to the silicides powders. Chemical reactivity, wettability tests and thermo-mechanical properties analysis have been carried out on the joints. Cross sections of the assembly were prepared to study the joint/substrate chemical bonding, the cracking and the crack deflection in the vicinity of the interface. Also, one of the challenge consists in using a local heating at a high temperature (around 1800°C) for a short time to avoid the degradation of the composite structure. The assemblies have been then performed in an inductive furnace but in order to prepare the joining technology, trials of local heating have also been investigated with a CO2 laser beam and a microwave generator. Finally, descriptions of the 4-points bending mechanical test used and the associated results are presented.

This master thesis evaluates the spatial variability of concentrations of PM10 on the area of towns Mladá Boleslav, Kosmonosy and small village Plazy during one month in the winter of 2013. Using a network measurements, we tried to determine whether sources of pollution are inside the city, or whether these harmful substances are transferred from the outside of the city to the area of the city. For the measurements we used a set of 9 portable laser nephelometers DustTrak (8520, TSI), which were placed on the roofs of schools. In the same time the device called beta-prachoměr (beta dust-meter) was continuously measuring concentrations of PM10, and we also monitored basic meteorological parameters (temperature, humidity, wind speed and direction). All these parameters were continuously measured at five minutes intervals. Also we did personal walks through the city, during which we measured personal exposure to PM10 concentrations. This exposure was compared with exposure of stationary monitors, and finally the differences were quantified. In Mladá Boleslav and in Kosmonosy, the same trend of concentrations of PM10 was observed at all selected locations in the city. Different trend of PM10 concentrations was observed in the village Plazy, where the peaks were higher and more frequent, especially in...

Hot forming is highly utilized in manufacturing of complex shapes. Relatively low flow stresses of materials at elevated temperatures provide ease of manufacturing. On the other side, the current trend is to replace hot forming with cold forming due to the superior mechanical properties and higher dimensional accuracy of the products and less energy consumption. However, cold forming requires high tooling costs and forming loads. In this study, a new process is proposed for production of complex shaped products where the disadvantages of both of the alternatives are tried to be minimized. The basic idea is to control the mode of deformation by heating the specimen locally prior to forming. Electromagnetic induction is used for local heating. Numerical simulations are carried out by finite element method (FEM) for further investigation on the effect of parameters. Thermo-mechanical analysis of heat diffusion and upsetting is supported by electromagnetic analysis of induction heating. The failure modes and operational window of the novel process is established. Conclusions are drawn on the applicability of the process and the effect of process parameters on the efficiency.