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Pressure Perturbations (pressure + perturbation)
Selected AbstractsFlexibility of the Cu,Zn superoxide dismutase structure investigated at 0.57,GPaACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2010Isabella Ascone The 2,Å resolution crystal structure of bovine erythrocyte Cu,Zn superoxide dismutase (CuZnSOD) has been determined by X-ray diffraction at high pressure (0.57,GPa) and room temperature. At 0.57,GPa the secondary, tertiary and quaternary structures are similar to other previously determined bovine erythrocyte CuZnSOD structures. Nevertheless, pressure has a localized impact on the atomic coordinates of C, atoms and on side chains. The compression of the crystal and of the protein backbone is anisotropic. This anisotropy is discussed, taking into account intermolecular contacts and protein conformation. Pressure perturbation highlights the more flexible zones in the protein such as the electrostatic loop. At 0.57,GPa, a global shift of the dimetallic sites in both subunits and changes in the oxidation state of Cu were observed. The flexibility of the electrostatic loop may be useful for the interaction of different metal carriers in the copper-uptake process, whereas the flexibility of the metal sites involved in the activity of the protein could contribute to explaining the ubiquitous character of CuZnSODs, which are found in organisms living in very different conditions, including the deep-sea environment. This work illustrates the potential of combining X-ray crystallography with high pressure to promote and stabilize higher energy conformational substates. [source] Pressure-Induced Emission Enhancement of a Series of Dicyanovinyl-Substituted Aromatics: Pressure Tuning of the Molecular Population with Different ConformationsCHEMPHYSCHEM, Issue 8 2008Qian Wang Dr. Abstract A series of dicyanovinyl-substituted aromatic compounds (Ar-DCV; Ar=9-anthracenyl, 1-naphthyl, 1-pyrenyl) with dual fluorescence are prepared, and their emission properties,when molecularly dispersed in a polymer medium,are investigated under pressure perturbation. The total emission intensity is enhanced drastically from ambient pressure up to 70 kbar. Emission 30,107 times more intense than that at ambient pressure is observed at higher pressure. In dual emission, the enhancement of the local excited state (LE state) is significantly different from that of the intramolecular charge-transfer state (ICT state). The intensity of the ICT emission increases faster (30,370 times) than that of the LE emission (less than 20 times). In accordance with spectroscopic data, emission dynamics at different pressures, and computational studies on the molecular conformations of these compounds, a kinetic model is proposed to explain the effect of pressure on the emissive properties of the Ar-DCV compounds from the point of view of pressure-dependent populations of the species in the ground state. [source] Probing of Thin Slipping Films by Persistent External DisturbancesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2007N. Alleborn Abstract This paper investigates the propagation of thickness disturbances on the free surface of a thin viscous liquid film on a solid substrate. On the free surface of the film the disturbances are induced by moving local external pressure perturbations acting on the surface. The analysis is performed by the Fourier-Laplace transform applied to the linearized perturbation equations for small amplitudes. The amplitude of the interface deflection caused by the disturbance, is reconstructed by the inverse Fourier-Laplace transform and numerically evaluated in the long time limit in long wave approximation. The proposed technique appears promising for probing the slip length of a thin film by recording its free surface response to a moving perturbation. On étudie dans cet article la propagation des perturbations d'épaisseur à la surface libre d'un film liquide visqueux sur un substrat solide. Sur la surface libre du film, les perturbations sont provoquées en déplaçant des perturbations de pression externes locales agissant sur la surface. L'analyse est effectuée par l'application de la transformée de Fourier-Laplace aux équations de perturbation linéarisées pour des petites amplitudes. L'amplitude de la déviation de surface causée par la perturbation est reconstruite par la transformée de Fourier-Laplace inverse et évaluée numériquement pour un temps très long par l'approximation des ondes longues. La technique proposée apparaît prometteuse pour sonder la longueur de glissement d'un film mince en enregistrant la réponse de sa surface libre à une perturbation mobile. [source] Analytical models for the mean flow inside dense canopies on gentle hilly terrainTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 634 2008D. Poggi Abstract Simplifications and scaling arguments employed in analytical models that link topographic variations to mean velocity perturbations within dense canopies are explored using laboratory experiments. Laser Doppler anemometry (LDA) measurements are conducted in a neutrally-stratified boundary-layer flow within a large recirculating flume over a train of gentle hills covered by a dense canopy. The hill and canopy configuration are such that the mean hill slope is small and the hill is narrow in relation to the canopy (H/L , 1 and Lc/L , 1, where H is the hill height, L the half-length, and Lc the canopy adjustment length-scale). The LDA data suggest that the often-criticized linearizations of the advective terms, turbulent-shear-stress gradients and drag force appear reasonable except in the deep layers of the canopy. As predicted by a previous analytical model, the LDA data reveal a recirculation region within the lower canopy on the lee slope. Adjusting the outer-layer pressure perturbations by a virtual ground that accounts for the mean streamline distortions induced by this recirculation zone improves this model's performance. For the velocity perturbations in the deeper layers of the canopy, a new analytical model, which retains a balance between mean horizontal advection, mean pressure gradient and mean drag force but neglects the turbulent-shear-stress gradient, is developed. The proposed model reproduces the LDA measurements better than the earlier analytical model, which neglected advection but retained the turbulent-shear-stress gradient in the lower layers of the canopy and near the hill top. This finding is consistent with the fact that the earlier model was derived for tall hills in which advection inside the canopy remains small. In essence, the newly-proposed model for the narrow hill studied here assumes that in the deeper layers of the canopy the spatial features of the mean flow perturbations around their background state can be approximated by the inviscid mean-momentum equation. We briefly discuss how to integrate all these findings with recent advances in canopy lidar remote-sensing measurements of general topography and canopy height. Copyright © 2008 Royal Meteorological Society [source] | ||||||||||