Biomedical subjects

M Mezouar

Publications and source records attributed to M Mezouar.

8 recordsLinked to original sources

PubMed2005

Rubberlike dynamics in sulphur above the lambda-transition temperature.

The high-frequency acoustic dynamics of sulfur across the liquid-liquid, lambda transition has been studied using inelastic x-ray scattering. The combination of these high-frequency data with lower frequency, literature data indicates that liquid sulfur develops, in the high-temperature, polymeric solution phase, some characteristic features of a rubber. In particular, entanglement coupling among polymeric chains plays a relevant role in the dynamics of this liquid phase.

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PubMed2005

Development of a new state-of-the-art beamline optimized for monochromatic single-crystal and powder X-ray diffraction under extreme conditions at the ESRF.

A new state-of-the art synchrotron beamline fully optimized for monochromatic X-ray diffraction at high pressure and high (or low) temperature is presented. In comparison with the old high-pressure beamline ID30, this new beamline exhibits outstanding performance in terms of photon flux and focusing capabilities. The main components of this new instrument will be described in detail and compared with the performance of beamline ID30. In particular, the choices in terms of X-ray source, X-ray optics, sample environment and detectors are discussed. The first results of the beamline commissioning are presented.

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PubMed2003

Nature of the first-order phase transition in fluid phosphorus at high temperature and pressure.

An in situ x-ray diffraction experiment has been performed on phosphorus to characterize the liquid-liquid transition which occurs at high temperature and pressure. The transition line has been measured over an extended temperature range up to 2200 degrees C at 0.3 GPa. From the shape of this line, a thermodynamic characterization of the transition is obtained in terms of latent heat and internal energy change. Moreover, the addition of the high-pressure high-temperature data to the known phase diagram of phosphorus allows us to conclude that this is a first-order transition between a dense molecular fluid and a polymeric liquid.

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PubMed2003

Pressure-induced suppression of the diffuse scattering in the model relaxor ferroelectric PbMg(1/3)Nb(2/3)O3.

We report an investigation of the relaxor ferroelectric PbMg(1/3)Nb(2/3)O3 by combining the external parameter high pressure with x-ray diffuse scattering. The observed total suppression of the relaxor-characteristic x-ray diffuse scattering is unusual and points to important pressure-induced changes in the local order. The observed behavior might well be a general feature in relaxor ferroelectrics under high pressure.

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PubMed2001

Breakdown of intermediate-range order in liquid GeSe(2) at high pressure.

Studies of liquids with tetrahedral coordination, particularly during compression or quenching, have indicated the existence of distinct phases in the liquid state, distinguishable by density and local structure. In systems that exhibit critical phenomena in the supercooled state, anomalous behaviour of the compressibility is also anticipated above the critical point, as revealed by simulations of water. Liquid GeSe(2) is a potentially attractive system for studying both types of phenomena, given its two-dimensional tetrahedral structure and anomalous physical properties (including a density minimum near its melting point). Here we report in situ X-ray diffraction measurements of solid and liquid GeSe(2) at high temperature and high pressure, revealing that the structure of the liquid is sensitive to pressure and that anomalous compressibility is expected. During compression of liquid GeSe(2), the connectivity of the liquid changes from two- to three-dimensional, leading to a breakdown of the intermediate-range order. The gradual change in structure above the melting line may develop to a first-order liquid-liquid transition in the supercooled regime.

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PubMed2001

High-pressure protein crystallography (HPPX): instrumentation, methodology and results on lysozyme crystals.

A new set-up and associated methodology for the collection of angle-dispersive diffraction data from protein crystals submitted to high hydrostastic pressure have been developed on beamline ID30 at the ESRF. The instrument makes use of intense X-rays of ultra-short wavelength emitted by two collinear undulators, and combines a membrane-driven diamond-anvil cell mounted on a two-axis goniometer and an imaging-plate scanner. Sharp and clean diffraction pictures from tetragonal crystals of hen egg-white lysozyme (tHEWL) and orthorhombic crystals of bovine erythrocyte Cu, Zn superoxide dismutase (SOD) were recorded at room temperature and pressures up to 0.915 and 1.00 GPa, respectively. The compressibility of tHEWL was determined from unit-cell parameters determined at 24 different pressures up to 0.915 GPa. High-pressure diffraction data sets from several crystals of tHEWL were collected and analyzed. Merging of data recorded on different crystals at 0.30 and 0.58 GPa produced two sets of structure amplitudes with good resolution, completeness, redundancy and R(sym) values. A third set at 0.69 GPa was of a similar quality except a lower completeness. The three structures have been refined. The pressure-induced loss of crystalline order in a tHEWL crystal beyond 0.82 GPa was captured through a series of diffraction pictures.

Crystallization↗

PubMed1999

"Debye-Scherrer Ellipses" from 3D fullerene polymers: An anisotropic pressure memory signature

High-pressure studies on fullerenes have previously shown the existence of one- and two-dimensional (2D) polymerized C60 structures. Synchrotron radiation measurements, performed on C60 samples quenched from 13 gigapascals and 820 kelvin, yield unambiguous proof for the existence of a three-dimensional (3D) polymerized C60 derivative. Moreover, unusual ellipsoidal Debye-Scherrer diffraction patterns are observed, which shows that the giant anisotropic deformation induced by the nonhydrostatic compression is retained in the quenched samples. The multiple bonding possibilities of the highly symmetrical C60 allow the retention (down to ambient pressure) of the deformation, a phenomenon reported previously only under high pressure.

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PubMed1998

Density measurements of liquid under high pressure and high temperature.

A new method for density measurements by means of X-ray absorption under high pressure and high temperature using synchrotron radiation has been developed. The method has been modified for a large-volume Paris-Edinburgh press and combined with intense high-energy X-rays at the ESRF. In order to overcome effects of deformation of sample shape under pressure, a ruby cylinder was used as a sample container. The density was determined from the intensity profile of transmitted X-rays. The densities of crystalline and liquid Bi were successfully measured up to 750 K at 1 GPa.

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