The influence of superficial conduction on the magnetoresistivity of antimony

The difference between adiabatic- and isothermal-magnetoresistivity has been used to study the dependence of the superficial current in antimony monocrystals upon the condition of the surfaces of the sample.     

Crack Initiation in Brittle Materials

In this paper we study the crack initiation in a hyper-elastic body governed by a Griffith-type energy. We prove that, during a load process through a time-dependent boundary datum of the type t → t g(x) and in the absence of strong singularities (e.g., this is the case of homogeneous isotropic materials) the crack initiation is brutal, that is, a big crack appears after a positive time t _i > 0. Conversely, in the presence of a point x of strong singularity, a crack will depart from x at the initial time of loading and with zero velocity. We prove these facts for admissible cracks belonging to the large class of closed one-dimensional sets with a finite number of connected components. The main tool we employ to address the problem is a local minimality result for the functional where , k > 0 and f is a suitable Carathéodory function. We prove that if the uncracked configuration u of Ω relative to a boundary displacement ψ has at most uniformly weak singularities, then configurations (uΓ, Γ) with small enough are such that .     

Charge order as seen by resonant (elastic) X-ray scattering

We review the main features of charge order observation by means of Resonant (Elastic) X-ray Scattering. Different cases have been studied during the past 12 years (NaV₂O₅, NdNiO₃, Fe₃O₄, BaVS₃, manganites, ...) that have allowed us to develop a systematic approach for data collection, correction and data analysis.     

Determination of liquid water content and dielectric constant in porous media by the capacitive methodDétermination,par la méthode capacitive,de la teneur en eau liquide et de la constante diélectrique dans un milieu poreux

A capacitive sensor-based apparatus has been settled to determine the liquid water amount and dielectric constant in consolidated porous media. This technique relies on the dielectric properties of water, air, and mineral substrate. The experimental procedure is described for successively oven-dried samples at 323 K. It allows us to determine the sample dielectric constant as a function of the sample water amount. For limestones from Caen region, an affine relationship is found at 293 K. This is then compared with other empirical soils data and with existing homogeneisation techniques applied to undeformable heterogeneous dielectrics. To cite this article: T. Fen-Chong et al., C. R. Mecanique 332 (2004).     

Fourier transform spectroscopy around 3 μm with a broad difference frequency comb

We characterize a new mid-infrared frequency comb generator based on difference frequency generation around 3.1 μm. High power per comb mode (>10^?7 W/mode) is obtained over a broad spectral span (>750 nm, >790 cm^?1). The source is used for direct absorption spectroscopy with a Michelson-based Fourier transform interferometer.     

Innovative technique for the direct determination of proteins in calcified aortic valves

Aortal valve mineralization very frequently causes a genesis of aortic stenosis, which is the most often surgically treated heart disease. Hydroxyapatite deposits have been identified as one of the causes leading to the loss of elasticity of the aortic valves. It is known that phosphates/calcium is accumulated in valve tissues during mineralization, but the mechanism of this process remains unclear. The work is focused mainly on the study of protein composition of mineralized aortic valves by nano-liquid chromatography electrospray ionization in a quadrupole orthogonal acceleration time-of-flight mass spectrometry. New methodological approach based on direct enzymatic digestion of proteins contained in hydroxyapatite deposits was developed for the study of pathological processes connected with osteogenesis. Our objectives were to simplify the traditional analytical protocols of sample preparation and to analyze the organic components of the explanted aortic valves for significant degenerative aortic stenosis. The study of aortic valve mineralization on the molecular level should contribute to understanding this process, which should consequently lead to effective prevention as well as to new ways of treatment of this grave disease.

Ultra-high-contrast few-cycle pulses for multipetawatt-class laser technology

We report the generation of few-cycle multiterawatt light pulses with a temporal contrast of 10(10), when measured as close as 2 ps to the pulse's peak. Tens of picoseconds before the main pulse, the contrast value is expected to spread much beyond the measurement limit. Separate measurements of contrast improvement factors at different stages of the laser system indicate that real contrast values may reach 10(19) and 10(14), when measured 50 and 25 ps before the pulse's peak, respectively. The combination of the shortest pulse duration and the highest contrast renders our system a promising front-end architecture for future multipetawatt laser facilities.     

Transport properties and in-situ Raman spectroscopy study of BaCe0.9Y0.1O3 − δ as a function of water partial pressures

The total conductivity of BaCe_0.9Y_0.1O_3 − δ material was measured under air, in a large p(H₂O) range up to 0.30 bar. The defect concentrations (OH_O^·, V_O^· · and h^·) and electrical conductivities were calculated on the basis of chemical constants (diffusion coefficients and equilibrium constants reported in the past literature) and compared to the experimental data. Protonic transport number as high as 0.8 was found at 700 °C, under air containing 0.30 bar of water, which allows a possible extension of the protonic temperature range of this material using water rich atmosphere. In-situ Raman spectroscopy under wet and dry air was performed from room temperature up to 700 °C in two wavenumber ranges. At low wavenumber, characteristic of lattice vibrations, this study clearly shows that no significant changes occur upon water insertion while at high wavenumbers, characteristic of OH vibrations, two contributions to the OH vibrations were found. This is discussed in terms of proton environment and transient hydrogen bonds. Moreover, this in situ study confirms that, at moderate p(H₂O), water insertion becomes significant at temperature below 650 °C.     

Phase relations and binary clathrate hydrate formation in the system H2-THF-H2O

Experimentally determined equilibrium phase relations are reported for the system H2-THF-H2O as a function of aqueous tetrahydrofuran (THF) concentration from 260 to 290 K at pressures up to 45 MPa. Data are consistent with the formation of cubic structure-II (CS-II) binary H2-THF clathrate hydrates with a stoichiometric THF-to-water ratio of 1:17, which can incorporate modest volumes of molecular hydrogen at elevated pressures. Direct compositional analyses of the clathrate phase, at both low (0.20 mol %) and stoichiometric (5.56 mol %) initial THF aqueous concentrations, are consistent with observed phase behavior, suggesting full occupancy of large hexakaidecahedral (51264) clathrate cavities by THF, coupled with largely complete (80-90%) filling of small dodecahedral (512) cages by single H2 molecules at pressures of >30 MPa, giving a clathrate formula of (H2) < or =2.THF.17H2O. Results should help to resolve the current controversy over binary H2-THF hydrate hydrogen contents; data confirm recent reports that suggest a maximum of approximately 1 mass % H2, this contradicting values of up to 4 mass % previously claimed for comparable conditions.