La plupart des matériaux étudiés en physique de la matière condensée sont à base de fermions massifs vérifiant les relations de dispersion paraboliques usuelles. Récemment, sont apparus un certain nombre de matériaux dotés de relations de dispersion linéaires : le graphène, système purement bidimensionnel et les isolants topologiques, composés tridimensionnels à base de Bismuth où les fermions de Dirac surfaciques coexistent avec les fermions massifs volumiques. À côté de ces deux grandes familles de matériaux de Dirac, on trouve le composé organique α-(BEDT-TTF)2I3, un système quasi-bidimensionnel du point de vue du transport électronique en raison de sa structure cristalline lamellaire et qui présente une phase de Dirac sous forte pression hydrostatique (P>1,5 GPa). Cette phase de Dirac est singulière puisque ses cônes de Dirac sont inclinés, et donc fortement anisotropes, et qu'ils émergent aux côtés d'une bande de porteurs de charge massifs. Ce travail de thèse porte ainsi sur l'étude, à la fois expérimentale et théorique, des effets des spécificités de la phase de Dirac du α-(BEDT-TTF)2I3 sur son transport électronique en régime quantique. Il examine notamment plusieurs modèles théoriques pour tenter d'interpréter les oscillations quantiques apériodiques mesurées dans le composé organique, ainsi que l'impact de l'inclinaison des cônes de Dirac. Les effets de dopage, surfacique et volumique, sur le α-(BEDT-TTF)2I3 sont également discutés. / The physics of most of the materials studied within condensed matter are based on massive fermions which verify the usual parabolic dispersion relations. Recently, a certain number of materials with linear dispersion relation have appeared: graphene, purely bidimensional and topological insulators, tridimensional compounds based on Bismuth where the surfacic Dirac fermions coexist with bulk massive fermions. Alongside these two families of Dirac materials, there is the organic α-(BEDT-TTF)2I3 compound, a quasi-bidimensional system from an electronic transport point of view because of its lamellar crystalline structure and which exhibits a Dirac phase under high hydrostatic pressure (P>1,5 GPa). This Dirac phase is singular: the Dirac cones are tilted, and highly anisotropic, and they emerge with a massive band. This work is then focus on the study, experimentally and theoretically, of the effects of the α-(BEDT-TTF)2I3 Dirac phase specificities on its electronical transport in quantum regime. It examines particularly several theoretical models to understand the aperiodic quantum oscillations measured in the organic compound, and the impact of Dirac cones tilting. Doping effects, surfacic and in the bulk, on the α-(BEDT-TTF)2I3 are also discussed.

The diploma thesis is focused on the study of pressure-induced changes in a behavior of RECo2-type compounds. HoCo2 and its substitution of Si instead of Co in Ho(Co1-xSix)2, x = 0,025 were chosen as a representative compounds from this family of materials. Measurements of electric resistivity, heat capacity, magnetization and AC magnetic susceptibility under ambient pressure showed presence of three magnetic transitions for both samples: the change of the easy magnetization direction at TR ~ 16 K, the Curie temperature TC ~ 80 K and the flipping of magnetization of Co magnetic moments into the parallel direction with Ho magnetic moments at Tf ~ 125 K for HoCo2. Under hydrostatic pressures up to 3 GPa, the TR shifts to higher temperatures whereas TC and Tf, both decrease. This probably occurs due to the weakening of the Co magnetism and the strength of exchange interaction between Ho-Co sublattices. The experiment of muon spin rotation demonstrates a pressure influence to the decay of Co magnetic clusters, which occurs at lower temperatures with increasing pressure. It is evident that the hydrostatic pressure directly influences the exchange interaction between Co-Co.

This diploma thesis is focused on the study of the structural phase transitions in intermetallic compounds LaPd2(Al,Ga)2 by low-temperature x-ray powder diffraction and macroscopic measurements on single crystals. The results obtained from powder diffraction at room temperature confirm that the compounds crystallize in tetragonal CaBe2Ge2 structure type (space group P4/nmm). At low temperature all the compounds undergo the same structural phase transition by lowering the symmetry to the orthorhombic space group Cmma. Although the structural transformation is of first order, the transition is not-manifested in step-like change of the phase at a certain temperature, but occurs in a broader temperature interval. In this interval the different phases coexist and transform gradually from high- to low- temperature phase. After application of hydrostatic pressure the structural transition is shifted to higher temperatures. Despite that the low temperature structures are of the same type, there is a difference between compounds containing Ga and Al in the discontinuity of the lattice parameters resulting in a distinct anomaly in electrical resistivity. In pressures >0.6 GPa this characteristic anomaly on single crystalline CePd2Al2 is changed, indicating a pressure- induced change of the low-temperature...

Magnetic properties of RCo2 compounds have been studied since the sec- ond half of the last century. However, there was recently observed new mag- netic state, so-called parimagnetism. The aim of this thesis was to find the real behavior of TmCo2, which exhibits many discrepancies in the published results, by means of preparation of high-quality single-crystals, its characteri- zation around the ordering temperature and to study parimagnetic behavior. Obtained results showed differences between the samples, which should be caused by the instability of Co and Tm magnetism. It might be the reason of discrepancies in the literature. The results however show the same struc- ture of measured curves with two present phase transition. We suggest two possible interpretations: a) magnetic reorientation of Tm magnetic moments below the ordering temperature of the Tm sub-lattice or b) consequent or- dering of the rare-earth sub-lattice followed by ordering of the Co sub-lattice at lower temperature, which seems to be more realistic. We observed pari- magnetic anomalies at 38 K, 80 K, 168 K only in the case of single-crystals containing small amount of impurity phase, which probably affects the for- mation of magnetic clusters. 1

Indiana University-Purdue University Indianapolis (IUPUI) / Mesenchymal stem cells (MSCs) are responsive to mechanical stimuli that play an essential role in directing their differentiation to the chondrogenic lineage. A better understanding of the mechanisms that allow MSCs to respond to mechanical stimuli is important to improving cartilage tissue engineering and regenerative medicine. Hydrostatic pressure (HP) in particular is known to be a primary mechanical force in joints. However, little is known about the underlying mechanisms that facilitate HP mechanotransduction. Understanding the signaling pathways in MSCs in transducing HP to a beneficial biologic response and their interrelationship were the focus of this thesis. Studies used porcine marrow-derived MSCs seeded in agarose gel. Calcium ion Ca++ signaling, focal adhesion kinase (FAK) involvement, and sirtuin1 activity were investigated in conjunction with HP application. Intracellular Ca++ concentration was previously shown to be changed with HP application. In our study a bioreactor was used to apply a single application of HP to the MSC-seeded gel structures and observe Ca++ signaling via live imaging of a fluorescent calcium indicator in cells. However, no fluctuations in Ca++ concentrations were observed with 10 minutes loading of HP. Additionally a problem with the biore actor design was discovered. First the gel was floating around in the bioreactor even without loading. After stabilizing the gel and stopping it from floating, there were still about 16 µm of movement and deformation in the system. The movement and deformation was analyzed for the gel structure and different parts of the bioreactor. Furthermore, we investigated the role of FAK in early and late chondrogenesis and also its involvement in HP mechanotransduction. A FAK inhibitor was used on MSCs from day 1 to 21 and showed a dose-dependent suppression of chondrogenesis. However, when low doses of FAK inhibitor added to the MSC culture from day 21 to 42, chondrogenesis was not inhibited. With 4 hour cyclic HP, FAK phosphorylation increased. The beneficial effect of HP was suppressed with overnight addition of the FAK inhibitor to MSC medium, suggesting FAK involvement in HP mechanotransd ucation by MSCs. Moreover, sirtuin1 participation in MSC chondrogenesis and mechanotransduc tion was also explored. The results indicated that overnight sirtuin1 inhibition in creased chondrogenic gene expression (Agc, Col2, and Sox9) in MSCs. Additionally, the activity of sirtuin1 was decreased with both 4 hour cyclic hydrostatic pressure and inhibitor application. These two together demonstrated that sirtuin1 inhibition enhances chondrogenesis. In this research we have investigated the role of Ca++ signaling, FAK involvement, and sirtuin1 activity in the mechanotransduction of HP in MSCs. These understand ings about the mechanisms regulating the chondrogenesis with respect to HP could have important implications for cartilage tissue engineering and regenerative studies.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20264号 / 医博第4223号 / 新制||医||1021(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 椛島 健治, 教授 松田 秀一, 教授 羽賀 博典 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

This study was motivated by a theoretical formulation on mechanobiology of soft and hard skeletal tissue differentiation. To prove this formulation experimentally, I hypothesized that cartilaginous phenotype can be induced in vitro in a seemingly non-cartilaginous cell source from fibrous tissue. In testing this hypothesis, I have focused on cartilage as a target and fibrous tissue as an origin or the source of cell. Four different trials were pursued with one supposition in common, i.e. hydrostatic pressure is one of the main driving forces for chondroinduction in vitro. The first and second trials pertained to the influence of a relatively short and long duration cyclic hydrostatic compression on rat Achilles tendon fibroblasts. The third trial was to examine the effect of two different drugs on cytoskeletal elements of mesenchymal stem cells or mouse embryonic fibroblast lines in pellet cultures combined with the similar duration and/or frequency of cyclic hydrostatic pressure adopted in the aforesaid trials with no pharmacological agents added. Last, attempts were made to implement an advanced technique in molecular biology called 'PCR array' to further quantify expression levels of eighty four pathway-specific genes in mouse TGFbeta/BMP signaling traffic under the same physiological regimen of hydrostatic compression. Results demonstrated that transdifferentation in phenotype from tendon to fibrocartilage may have occurred in vitro in tendon fibroblasts in pellet cultures exposed to hydrostatic pressure. Experiments on the role of the cytoskeleton in mechanotransduction of the applied level of hydrostatic pressure demonstrated that disruption of microfilaments in the presence of cytochalasin-D did not significantly interfere with the anabolic effect of cyclic pressure. However, disruption of microtubule assembly by nocodazole abolished the pressure-induced stimulation in cartilage marker genes. These findings suggest that microtubules, but not microfilaments, are involved in mechanotransduction of hydrostatic pressure by mesenchymal stem cells.

No description available.

Foodborne disease outbreaks associated with the protozoan parasite Cryptosporidium spp. are an emerging public health concern. Shellfish, including Eastern oysters (Crassostrea virginica) in Chesapeake Bay and other Atlantic coastal waters, have been identified as a potential source of Cryptosporidium parvum infection for humans. The inactivation of C. parvum and other pathogens in raw molluscan shellfish would provide increased food safety for normal and at-risk consumers. The objectives of this study were to evaluate the efficacy of three alternative food-processing treatments (e-beam irradiation, microwave energy, and high hydrostatic pressure processing) on the viability of C. parvum oocysts in Eastern oysters. Oysters were artificially infected with the Beltsville strain of C. parvum and subjected to the three treatments in separate experiments. The effects of the treatments were evaluated by inoculation of the processed oyster tissues using the neonatal mouse bioassay. E-beam radiation of in-shell and shucked oysters treated with doses of 1.0, 1.5 or 2.0 kGy produced significant reductions (P < 0.05) in C. parvum mouse infectivity. A dose of 2.0 kGy completely terminated the infectivity of C. parvum and did not adversely affect the visual appearance of the oysters. Microwave treatments of shucked oysters at time (temperature) exposures of 1 sec (43.2°C), 2 sec (54.0°C), and 3 sec (62.5°C) produced a reduction in C. parvum mouse infectivity of 26.7%, 33.3%, and 46.7%, respectively. Microwave treatments at 2 sec (54.0°C) and 3 sec (62.5°C) showed extensive changes in oyster meat texture and color. Thus due to lack of efficacy and unacceptable tissue changes, microwave treatment of oysters is not considered a viable food processing method. High pressure processing of shucked oysters at all pressures tested (305 MPa, 370 MPa, 400 MPa, 480 MPa, 550 MPa) significantly (P < 0.05) reduced infectivity of C. parvum oocysts as measured by the neonatal mouse bioassay. A treatment of 550 MPa at 180 sec produced the maximum decrease of C. parvum infectivity (93.3%). The results indicate that HPP (high pressure processing) can produce significant (P < 0.05) reductions in infectivity of C. parvum oocysts. Measurement of tristimulus color values of pressurized raw oysters at extended processing times from 120 sec to 360 sec at 550 MPa showed an increase (P < 0.05) in whiteness. One (e-beam irradiation) of the three food-processing treatments shows promise for commercial applications to reduce public health risks from cryptosporidiosis in Eastern oysters. / Ph. D.

The Food and Drug Administration has recently expressed concern for the safety of seafood and seafood products. One of the concerns is the presence of Bacillus cereus in fresh blue crab meat. Bacillus cereus is a spore-forming pathogen whose spores survive the customary thermal treatments applied during cooking and pasteurization; therefore it could potentially present a health concern to consumers as the microorganism could increase to pathogenic levels. The objectives of this study were to evaluate the effects of a post-processing method i.e. high hydrostatic pressure treatment on the quality of fresh crab meat and to evaluate the effectiveness of high pressures on the inactivation of B. cereus spores. Fresh blue crab meat was pressurized at 300 and 550 MPa at 25° C for 5 min and stored at 4° C for 31 days to determine the pressurization effects on the microbiological, physical, and sensory quality of the meat. A pressure of 300 MPa caused a 1 log reduction in total aerobic plate count and a 3 day lag period, whereas 550 MPa inactivated 2 logs in total aerobic plate count with no evident lag phase. Physical and sensory qualities of pressurized crab meat were not statistically different from the untreated crab meat (P>0.05). A pressure of 300 MPa extended the shelf-life from 17 to over 24 days with the prevalence of Carnobacterium piscicola at the time of spoilage. Crab meat treated with 550 MPa was not rejected by sensory panels at day 31 and Enterococcus spp. was identified as the predominant microorganism. High hydrostatic pressure (550 MPa at 40° C for 15 min) inactivated less than 1 log (0.66 log) of B. cereus spores inoculated in fresh crab meat. The meat essentially had a protective effect on pressure inactivation of the spores. During storage (31 days), surviving B. cereus was suppressed and outgrown by the other pressure resistant microflora at a storage temperature of 12° C. At 4° C, B. cereus could compete with the other pressure-resistant microflora and was isolated even at the end of the storage period (day 31); however, diarrheal toxin was not detected in any stored samples. / Ph. D.