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991.
Core-level electronic properties of nanostructured NiO coatings 总被引:1,自引:0,他引:1
Nanostructured NiO films with different thicknesses were grown on nanoporous alumina membrane substrates by reactive evaporation of Ni in an oxygen atmosphere. The reactive deposition process was assisted by a low energy oxygen ion-beam in order to increase the NiO input into the pores. Surface morphology and structure of the films were analyzed by SEM and XPS. SEM observations reveal a well adhered film of NiO on the substrate. This film appears to be uniform and presents a rather irregular nanostructured morphology, built of NiO clusters with sizes ranging between 5 and 30 nm. The core-level electronic properties of this nanostructured NiO film result to be similar to those of an ultrathin film about one monolayer thick. This behaviour can be explained by the large surface to volume ratio of both systems. 相似文献
992.
993.
The one-dimensional totally asymmetric simple exclusion process (TASEP) is considered. We study the time evolution property
of a tagged particle in the TASEP with the step initial condition. Calculated is the multi-time joint distribution function
of its position. Using the relation of the dynamics of the TASEP to the Schur process, we show that the function is represented
as the Fredholm determinant. We also study the scaling limit. The universality of the largest eigenvalue in the random matrix
theory is realized in the limit. When the hopping rates of all particles are the same, it is found that the joint distribution
function converges to that of the Airy process after the time at which the particle begins to move. On the other hand, when
there are several particles with small hopping rate in front of a tagged particle, the limiting process changes at a certain
time from the Airy process to the process of the largest eigenvalue in the Hermitian multi-matrix model with external sources. 相似文献
994.
995.
Enzyme-Inspired Chiral Secondary-Phosphine-Oxide Ligand with Dual Noncovalent Interactions for Asymmetric Hydrogenation
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Caiyou Chen Zhefan Zhang Shicheng Jin Dr. Xiangru Fan Mingyu Geng Yan Zhou Songwei Wen Xinrui Wang Dr. Lung Wa Chung Dr. Xiu-Qin Dong Prof. Xumu Zhang 《Angewandte Chemie (International ed. in English)》2017,56(24):6808-6812
Inspired by the unique character of enzymes, we developed novel chiral SPO (secondary-phosphine-oxide) ligand (SPO-Wudaphos) which can enter into both ion pair and H-bond noncovalent interactions. The novel chiral SPO-Wudaphos exhibited excellent results in the asymmetric hydrogenation of α-methylene-γ-keto carboxylic acids, affording the chiral γ-keto acids with up to over 99 % ee. A series of control experiments and DFT calculations were conducted to illustrate the critical roles of both the ion pair and H-bond noncovalent interactions. 相似文献
996.
Extensive computer simulations of multicomponent ion exchange processes in fixed beds are reported. The simulations are based on the local equilibrium theory developed by Helfferich and Klein. The simulations illustrate through computer graphics how the various ions separate and migrate in a column. Detailed concentration profiles as a function of time are shown for cyclic chromatographic operations such as elution, displacement, and selective displacement processes. The simulations elucidate the main features of the interference phenomena as a result of solute competition for the sorbent sites. These simulations also provide important guidelines for designing bulk separation processes, for example, the strategies of recovery, the choices of cyclic operations, feed size, presaturant, eluant, and displacer. 相似文献
997.
998.
The electrochemical properties of a perfluorosulfonic acid (PFSA) membrane are estimated using a combination of molecular dynamics simulation and statistical thermodynamic model. We obtain all parameters in an ionic conductivity model from an atomistic simulation and remove all adjusted model parameters. From a microscopic point of view, the hydrated PFSA membrane shows micro‐phase segregation which separated into hydrophilic and hydrophobic phases. Our present work originates with this phenomenon and we treat this phase segregation as if it is a continuous phase for each of which the proton (H+) is transported inside the PFSA membrane/solvent (water and alcohols) mixture. The chemical potential for a given system is estimated using a molecular simulation technique to predict the van der Waals interaction energy between the polymer and solvent. In addition, the self diffusion coefficients are calculated from the molecular dynamics simulation. We study various polymer/solvent compositions to understand the concentration dependence of self diffusion coefficient. Our self diffusion coefficients and also the predicted final ionic conductivity agree well with previously reported experimental data. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1455–1463, 2011 相似文献
999.
Ahmet Kusoglu Michael H. Santare Anette M. Karlsson 《Journal of Polymer Science.Polymer Physics》2011,49(21):1506-1517
The swelling‐driven fatigue behavior of polymer fuel cell membranes during relative humidity (RH) cycling is investigated. In particular, swelling‐induced membrane stresses are obtained from a numerical model simulating fuel cell RH cycle tests, and compared to the lifetimes obtained experimentally from tests conducted in the absence of electrochemical effects. A strong correlation between the lifetimes of the membranes in the actual tests and model results is obtained. In general, higher RH (or swelling) amplitude results in larger stress amplitudes and shorter lifetime, that is, fewer cycles to failure. Tensile stresses are needed for forming local cavities in the membrane, which may eventually lead to craze formation. Cavitation is less likely to occur in compressed membrane at high humidities. The stress–lifetime plots for polymer fuel cell membranes exhibit similar features to those observed for other polymers. The crazing criterion for polymers suggests that craze initiation during RH cycling is more likely to occur in the low compression regions, such as under the channels, which is in agreement with experimental observations. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1506–1517, 2011 相似文献
1000.
Uri Yermiyahu Shlomo Nir Gozal Ben-Hayyim Uzi Kafkafi Gunther F. E. Scherer Thomas B. Kinraide 《Colloids and surfaces. B, Biointerfaces》1999,14(1-4):237-249
The hypotheses that genotypic differences in salinity tolerance may result from (i) differences in global surface charge density or (ii) from differences in global Ca2+ binding were tested. An attempt was made to correlate the differing salinity tolerance of four melon cultivars with surface properties of vesicles extracted from the plasma membrane (PM) of their root cells. Surface characterization involved measurements of electrophoretic mobility and sorption of 45Ca2+ to the vesicles in the presence of varying concentrations of Ca2+, Na+ and Mg2+. Irrespective of salinity tolerance, vesicles from the four cultivars yielded similar ζ potentials under similar conditions, indicating similar global surface charge densities. Sorption studies with vesicles from two cultivars differing in salinity tolerance predicted independently this result of equal surface charge density. The estimated global binding affinities of Ca2+, Na+ and Mg2+ to the PM of both cultivars were the same with binding coefficients of 50, 0.8 and 9 M−1, respectively. Consequently, the hypotheses enumerated above to interpret genotypic differences in salinity toxicity are rejected. However, vesicles from the salt-resistant strain sorbed 19% more Ca2+ per given amount of protein in the membrane, indicating the existence of a larger number of negatively charged surface sites per given amount of protein and a smaller amount of protein per given area of membrane. Genotypic differences in site-specific Ca2+-binding affinity (e.g. at ion channels) remain a viable hypothesis for genotypic differences in salinity tolerance. 相似文献