[en] The effectiveness of evoked potentials, cerebral spinal fluid analysis and MRI compared in establishing diagnosis of MS. (author). 6 refs.; 8 tabs

[en] We report Ru K-edge extended X-ray absorption fine structure (EXAFS) measurements on the Ce_1-xLa_xRu₂ superconducting system with variable La concentration. The correlated Debye-Waller factor of the Ru-Ru bonds follows the T_c of the system. This remarkable T_c dependence indicates the key role of local atomic displacements in the anomalous superconductivity of the system at small La concentration

[en] Document available in extended abstract form only. In the framework of the research program on nuclear waste repository in deep geological formation, TED in-situ experiment was performed by ANDRA in Meuse/Haute Marne underground research laboratory to determine THM behaviour of Callovo-Oxfordian clay, and more precisely to identify thermal characteristics of the host rock: thermal conductivity and specific heat capacity. clay-stone thermal characteristics are obtained by an inverse method : comparison numerical process between calculated temperature from physical modelling and experiment temperature from in situ sensors. First of all a thermal modelling of TED experiment is performed. Here the main physical process taken into account is transient heat transfer by conduction from hot packer to host rock. A single diffusion partial differential equation is used. This equation is solved by linear Finite Element Method implemented in CAST3M code with unstructured three-dimensional mesh and Crank-Nicolson time discretization. The diffusion tensor is function of two thermal conductivity; one (λ_l) characterizes thermal diffusion parallel to the bedding plane, the other (λ_t) perpendicularly. Packers heating is represented by source term r. A first sensitivity analysis completes the implementation of direct method. The inverse method modelling is then applied: - three input thermal parameters are identified: longitudinal (λ_l), transversal (λ_t) thermal conductivity, and specific heat capacity (C_p); experimental variables are represented by 108 sensors temperatures in host rock, during more than two years of packers heating; - a meta-model is built with the help of neural network, to replace CAST3M modelling, too time consuming; the methods employed, like LHS experiment plan performance, come from URANIE platform; - a minimization of objective function, depending on experimental and calculated temperatures, is realized to determine thermal parameters; - solution parameters confidence domain is obtained by taking into account experimental temperature uncertainties

[en] The Gradient Refocusing Technique, which seppresses the influence of cerebrospinal fluis (GSF) and vascular motion artifact on MRI sensitivity, is applied combined with Brainstem Auditory Evoked Potentials (BAEPs) and median Somatosensory Evoked Potentials (SEPs) in the evaluation of the brainstem in 30 MS patients with clinical signs of involvement of this structure in order to reevaluate the sensitivity of these techniques. (Author). 2 refs.; 1 tab

[en] Document available in extended abstract form only. In the framework of the research program on nuclear waste repository in deep geological formation, among others two in situ experiments were performed by ANDRA in Meuse/Haute Marne underground research laboratory to determine the callovo-Oxfordian argillite characteristics: TER and DIR experiments. TER experiment was designed to determine THM behaviour of the host rock and thermal characteristics: thermal conductivity and specific heat capacity. DIR experiment was performed to characterize diffusion and retention of inert and reactive tracers in the host rock. We determine the argillite thermal and diffusion characteristics by a numerical approach based on inverse method. First of all a direct method is applied by performing a physical modelling of the experiments. A single diffusion partial differential equation is used for the two experiments. The diffusion equation is numerically solved by Finite Element Method implemented in CAST3M code; an unstructured mesh is used. The diffusion tensor is function of two coefficients; one characterizes diffusion parallel to the bedding plane, the other perpendicularly. A first sensitivity analysis is made by direct modelling. The same inverse method process is applied for the two sets TER and DIR experiment/modelling: - a response surface (neural network) is made from CAST3M code: LHS experiment plan, composed by Kalif code, give a examples base used by Nemo neural network generator; - thermal or diffusion parameters identification is obtained by a minimization of objective function depending on experimental and calculated variables; - sensitivity analyses are done in order to evaluate the confidence domain for parameters determination in function of data uncertainties. In TER experiment, argillite characteristics to identify are longitudinal (λ_l) and transversal (λ_t) thermal conductivity, respectively along and perpendicular to the bedding plane, and specific heat capacity. The experimental variables are temperatures in the host rock at different locations and times. A 3D CAST3M model is used; the packer heat source is represented by a source term in the equation. All experimental data are available and TER is in dismantling phase. Back analysis of TER is difficult due to experimental uncertainties, mainly error on error location. Typical analysis of confident domain of parameters identification is given. In DIR experiment, argillite parameters to identify are longitudinal (D_l) and transversal (D_t) effective diffusion coefficients, and accessible porosity. The experimental and calculated variables are tracer normalized activities (or concentrations) in the diffusion chamber, and tracer specific activities (or concentrations) in argillite profiles over-cored. Three zones are modelled: diffusion chamber, E.d.Z around the chamber and undisturbed argillite. Radioactive decay, dilution in the diffusion chamber and eventually sorption in the solid phase are taken into account. A 2D(r,z) axisymmetric CAST3M model is used. Two tracers are monitored in DIR2001 borehole, four tracers HTO, ³⁶Cl, ²²Na, ¹³³Cs in DIR2003 borehole. Direct and inverse methods are under progress. (authors)

[en] Full text of publication follows: The Mont Terri underground laboratory supports a part of the research program on nuclear waste repository in deep geological formation. Among the in-situ experiments, two of them (HE-C and HED) take part to the thermal hydraulic mechanical program. In fact, the storage of high level radioactive waste induces a coupling process between the thermal field, the water content and the velocity field, then the mechanical stress of the host rock. These experiments are designed to provide data base for Opalinus clay characterization. In HE-C experiment, a central borehole is drilled at a 2 m depth, fitted with a temperature controlled heating source. The temperature field among the source is continuously monitored using thermocouples, still reaching a steady state. In a first phase, thermal conductivity is still to be accurately defined. The solution presented here, uses numerical inverse method. This requires first a direct modelling, in 3 dimensional geometry, since in fact, the rock bedding plane, as well as the thermal conductivity anisotropy greatly affect the temperature field. Variable boundary conditions, meaning to the atmospheric variation in the gallery all over the monitoring, stand as an other arising difficulty. In the examples, the numerical resolution uses a Finite Element model implemented in Cast3m, applied to a 60 000-element meshing. Inverse method proceeds then by minimizing the cost function, expressed as the quadratic difference between calculated and measured temperatures. The KALIF code developed in CEA defines different parameter sets for the direct modelling. As direct calculations needs 3 hours CPU time, the neural network method provides a good approximation of the solution for short CPU time, allowing then more than 500 000 calculations. Then the best set of parameters means to the minimization of the cost function. The following example deals with the numerical estimation of the longitudinal and transverse thermal conductivities: λ_L and λ_T that have different values according to the geological anisotropy. These parameters are estimated with a rather good confidence, exhibiting a dissymmetry for the two instrumented boreholes: Borehole C2: λ_L = 1.84 +/- 6% W/K.m and λ_T 0.55 +/- 9% W/K.m Borehole C3: λ_L = 1.90 +/- 7% W/K.m and λ_T 1.07 +/- 11% W/K.m First interpretations conclude to a probable effect of the geological surrounding heterogeneity. (authors)

[en] Magnetic resonance imaging (MRI) is highly sensitive to pathological tissue changes in multiple sclerosis (MS) patients. It demonstrates the frequently subclinical disease activity and follow-up examinations regularly show the accumulation of new lesions and the development of atrophy. The increasing importance of follow-up examinations in MS patients makes it necessary to provide comparable MRI data even over long observation periods. This review article focusses on critical variables in this regard and technical issues; practical guidelines for MRI protocols in MS patients are presented. The influence of field strenght, MR systems from different manufacturers, and new software releases is described. Guidelines concerning the graphic planning of the examination, sequence protocols, documentation and reporting of cranial MR studies in MS patients are presented. (orig.)

[en] We report low-temperature Raman measurements under hydrostatic pressure in Pr_0.6Ca_0.4MnO₃ thin films grown on LaAlO₃ substrate. Certain phonons attributed to metallic rhombohedral phase become narrower with pressure and coexist with broad bands characteristic of spectra from the insulating paramagnetic orthorhombic phase. This behavior is similar with the changes induced from the chemical pressure (Ca substitution) and has been attributed to ferromagnetic metallic clusters formed in the insulating phase. Our data indicate that the Jahn-Teller distortion of the octahedra and the transition temperature is reduced under pressure

[en] We report a systematic study of Pr_1-xCa_xMnO₃ (x=0.4 and 0.6) thin films grown on LaAlO₃(LAO) substrate (PCMO/LAO). X-ray diffraction measurements have shown that the PCMO/LAO film is[101]-oriented and under compressive strain due to the lattice mismatch. According to Raman spectroscopy the Jahn-Teller modes are suppressed under the application of pressure in the PCMO (x=0.4) thin film. In particular, it was found that a pressure of 2 GPa suppresses the charge ordered state. Further high pressure measurements have confirmed that resistivity decreases linearly up to 2.4 GPa corresponding to a total reduction of about 35% in resistivity leading to a more conductive state on both concentrations. The temperature dependence of the resistivity has shown that the samples under pressure retain their semiconducting behavior. At ambient pressure the PCMO (x=0.6) film shows a moderate magnetoresistance in the range 0-7 T and no metal to insulator transition (MIT). Raman spectroscopy confirmed that the application of a magnetic field of 1 T does not induce any remarkable changes on the electron-phonon interaction. Although, the hydrostatic pressure is not enough to induce a macroscopic metallic state, its effect is much greater than the one of the magnetic field. In addition, the effect of the 7 T magnetic field appears the same at ambient pressure and 2.5 GPa. Therefore the two effects of hydrostatic pressure and magnetic field do not seem to be coupled, at least up to the magnitudes studied. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] Functional MRI (fMRI) of the spinal cord is able to provide maps of neuronal activity. Spinal fMRI data have been analyzed in previous studies by calculating the cross-correlation (CC) between the stimulus and the time course of every voxel and, more recently, by using the general linear model (GLM). The aim of this study was to compare three different approaches (CC analysis, GLM and independent component analysis (ICA)) for analyzing fMRI scans of the cervical spinal cord. We analyzed spinal fMRI data from healthy subjects during a proprioceptive and a tactile stimulation by using two model-based approaches, i.e., CC analysis between the stimulus shape and the time course of every voxel, and the GLM. Moreover, we applied independent component analysis, a model-free approach which decomposes the data in a set of source signals. All methods were able to detect cervical cord areas of activity corresponding to the expected regions of neuronal activations. Model-based approaches (CC and GLM) revealed similar patterns of activity. ICA could identify a component correlated to fMRI stimulation, although with a lower statistical threshold than model-based approaches, and many components, consistent across subjects, which are likely to be secondary to noise present in the data. Model-based approaches seem to be more robust for estimating task-related activity, whereas ICA seems to be useful for eliminating noise components from the data. Combined use of ICA and GLM might improve the reliability of spinal fMRI results. (orig.)