Energy resolution of the CdTe‐XPAD detector: calibration and potential for Laue diffraction measurements on protein crystals

The XPAD3S‐CdTe, a CdTe photon‐counting pixel array detector, has been used to measure the energy and the intensity of the white‐beam diffraction from a lysozyme crystal. A method was developed to calibrate the detector in terms of energy, allowing incident photon energy measurement to high resolution (approximately 140 eV), opening up new possibilities in energy‐resolved X‐ray diffraction. In order to demonstrate this, Laue diffraction experiments were performed on the bending‐magnet beamline METROLOGIE at Synchrotron SOLEIL. The X‐ray energy spectra of diffracted spots were deduced from the indexed Laue patterns collected with an imaging‐plate detector and then measured with both the XPAD3S‐CdTe and the XPAD3S‐Si, a silicon photon‐counting pixel array detector. The predicted and measured energy of selected diffraction spots are in good agreement, demonstrating the reliability of the calibration method. These results open up the way to direct unit‐cell parameter determination and the measurement of high‐quality Laue data even at low resolution. Based on the success of these measurements, potential applications in X‐ray diffraction opened up by this type of technology are discussed.     

Controlling X‐ray deformable mirrors during inspection

The X‐ray deformable mirror (XDM) is becoming widely used in the present synchrotron/free‐electron laser facilities because of its flexibility in correcting wavefront errors or modification of the beam size at the sample location. Owing to coupling among the N actuators of an XDM, (N + 1) or (2N + 1) scans are required to learn the response of each actuator one by one. When the mirror has an important number of actuators (N) and the actuator response time including stabilization or the necessary metrology time is long, the learning process can be time consuming. In this work, a fast and accurate method is presented to drive an XDM to a target shape usually with only three or four measurements during inspection. The metrology data are used as feedback to calculate the curvature discrepancy between the current and the target shapes. Three different derivative estimation methods are introduced to calculate the curvature from measured data. The mirror shape is becoming close to the target through iterative compensations. The feasibility of this simple and effective approach is demonstrated by a series of experiments.     

Influence of the local absorber layer thickness on the performance of ZnO nanorod solar cells

The local absorber layer thickness (d_local) of solar cells with extremely thin absorber was changed between 10 nm and 70 nm. As a model system, ZnO nanorod arrays (electron conductor) with fixed internal surface area coated with In₂S₃ (absorber) and impregnated with CuSCN (transparent hole conductor) were applied. The performance of the small area solar cells depended critically on d_local. The highest short circuit current density was reached for the lowest d_local. In contrast, the highest open circuit voltage was obtained for the highest d_local. A maximum energy conversion efficiency of 3.4% at AM1.5 was achieved. Limiting factors are discussed.(© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of olive mill wastewater and gamma irradiation effects on some parameters of its composition

Journal of Radioanalytical and Nuclear Chemistry - Gamma irradiation was applied to olive mill wastewater and synthetic samples prepared from Gallic acid. The effects, generated on the...     

Observation of diffusion and tunneling recombination of dye-photoinjected electrons in ultrathin TiO2 layers by surface photovoltage transients

Surface photovoltage transients were used to monitor both the short time dynamics (>10 ns) and the spatial distribution of electrons photoinjected in thin (2-20 nm) TiO2 layers from dye molecules adsorbed at the surface. At low temperatures (100-250 K), the dynamics are governed exclusively by spatially dependent tunneling recombination, with a rate that varies with the distance from the surface x as exp(-2x/a), and an initial exponential distribution of photoinjected electrons, n0 exp(-x/b). This model is confirmed by the observation of power law decay in time t(-a/2b) with a ratio a/b = 0.28 +/- 0.04. The stability of cis-di(isothiocyanato)-N-bis(2,2'-bipyridine-4,4'-dicarboxy) ruthenium(II) (N3) dye molecules on TiO2 during treatment in a vacuum at high temperatures was proven. For high temperatures (250-540 K), the thickness dependence of the decays indicates that the dynamics of surface recombination are retarded by the diffusion of electrons toward the interior of the film. The implications for thin layer coating in dye-sensitized solar cells are discussed.     

An Original L‐shape,Tunable N‐Heterocyclic Carbene Platform for Efficient Gold(I) Catalysis

The synthesis and characterization of original NHC ligands based on an imidazo[1,5‐a]pyridin‐3‐ylidene (IPy) scaffold functionalized with a flanking barbituric heterocycle is described as well as their use as tunable ligands for efficient gold‐catalyzed C?N, C?O, and C?C bond formations. High activity, regio‐, chemo‐, and stereoselectivities are obtained for hydroelementation and domino processes, underlining the excellent performance (TONs and TOFs) of these IPy‐based ligands in gold catalysis. The gold‐catalyzed domino reactions of 1,6‐enynes give rise to functionalized heterocycles in excellent isolated yields under mild conditions. The efficiency of the NHC gold 5^Me complex is remarkable and mostly arises from a combination of steric protection and stabilization of the cationic Au^I active species by ligand 1^Me .     

Clique inference process for solving Max-CSP

Few works on problems CSP, Max-CSP and weighted CSP was carried out in the field of Combinatorial Optimization, whereas this field contains many algorithmic tools which can be used for the resolution of these problems.In this paper, we introduce the binary clique concept: clique which expresses incompatibilities between values of two CSP variables. We propose a linear formulation for any binary clique and we present several ways to exploit it in order to compute lower bounds or to solve Max-CSP. We also show that the binary clique concept can be exploited in the weighted CSP framework.The obtained theoretical and experimental results are very interesting and they open new prospects to exploit the Combinatorial Optimization algorithmic tools for the resolution of CSP, Max-CSP and weighted CSP.     

Effect of surface activation on charge and mass transfer rates of the hexacyanoferrate(III)/(II) redox probe at fibrinogen-modified carbon paste electrodes

The electron transfer and mass transport properties of fibrinogen-modified carbon paste surfaces, following preliminary activation for various duration, has been studied using cyclic voltammetry (CV) and chronoamperomety. Activation was carried out by subjecting the surface, exposed to a solution-containing oxidant species, to positive polarization of increasing duration. Modification was subsequently achieved following spontaneous adsorption of fibrinogen on exposure to a solution containing the protein. To investigate the electrochemical properties of this surface, the variations in the charge-transfer and mass-transport kinetics of hexacyanoferrate(III)/(II) ions, used as a redox probe, were analyzed separately. The results showed the favorable effect of activation on electrocatalysis and charge-transport properties through the coating. Relative to pretreated bare surfaces, however, the presence of fibrinogen induced opposed variations, thus explaining unchanged CV peak currents. These features were essentially attributed to morphological changes promoted by activation in the protein layer.     

Absolute OH concentration profiles measurements in high pressure counterflow flames by coupling LIF, PLIF, and absorption techniques

A high-pressure combustion chamber enclosing counterflow burners was set-up at ICARE-CNRS laboratory. It allows the stabilization of flat twin premixed flames at atmospheric and high pressure. In this study, lean and stoichiometric methane/air counterflow premixed flames were studied at various pressures (0.1?MPa to 0.7?MPa). Relative OH concentration profiles were measured by Laser Induced Fluorescence. Great care was attached to the determination of the fluorescence signal by taking into account the line broadening and deexcitation by quenching which both arise at high pressure. Subsequently, OH profiles were calibrated in concentration by laser absorption technique associated with planar laser induced fluorescence. Results are successfully compared with literature. The good quality of the results attests of the experimental set-up ability to allow the study of flame structure at high pressure.