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101.
Vladimir Petukhov John Stoemenos Johan Rothman Andrey Bakin Andreas Waag 《Applied Physics A: Materials Science & Processing》2011,102(1):161-168
In order to interpret results of temperature dependent Hall measurements in heteroepitaxial ZnO-thin films, we adopted a multilayer
conductivity model considering carrier-transport through the interfacial layer with degenerate electron gas as well as the
upper part of ZnO layers with lower conductivity. This model was applied to the temperature dependence of the carrier concentration
and mobility measured by Hall effect in a ZnO-layer grown on c-sapphire with conventional high-temperature MgO and low-temperature
ZnO buffer. We also compared our results with the results of maximum entropy mobility-spectrum analysis (MEMSA). The formation
of the highly conductive interfacial layer was explained by analysis of transmission electron microscopy (TEM) images taken
from similar layers. 相似文献
102.
103.
Eric Johnsen Johan Larsson Ankit V. Bhagatwala William H. Cabot Parviz Moin Britton J. Olson Pradeep S. Rawat Santhosh K. Shankar Bj?rn Sj?green H.C. Yee Xiaolin Zhong Sanjiva K. Lele 《Journal of computational physics》2010,229(4):1213-1237
Flows in which shock waves and turbulence are present and interact dynamically occur in a wide range of applications, including inertial confinement fusion, supernovae explosion, and scramjet propulsion. Accurate simulations of such problems are challenging because of the contradictory requirements of numerical methods used to simulate turbulence, which must minimize any numerical dissipation that would otherwise overwhelm the small scales, and shock-capturing schemes, which introduce numerical dissipation to stabilize the solution. The objective of the present work is to evaluate the performance of several numerical methods capable of simultaneously handling turbulence and shock waves. A comprehensive range of high-resolution methods (WENO, hybrid WENO/central difference, artificial diffusivity, adaptive characteristic-based filter, and shock fitting) and suite of test cases (Taylor–Green vortex, Shu–Osher problem, shock-vorticity/entropy wave interaction, Noh problem, compressible isotropic turbulence) relevant to problems with shocks and turbulence are considered. The results indicate that the WENO methods provide sharp shock profiles, but overwhelm the physical dissipation. The hybrid method is minimally dissipative and leads to sharp shocks and well-resolved broadband turbulence, but relies on an appropriate shock sensor. Artificial diffusivity methods in which the artificial bulk viscosity is based on the magnitude of the strain-rate tensor resolve vortical structures well but damp dilatational modes in compressible turbulence; dilatation-based artificial bulk viscosity methods significantly improve this behavior. For well-defined shocks, the shock fitting approach yields good results. 相似文献
104.
105.
106.
For the analysis of protein digests, the peak capacity in reversed-phase liquid chromatography is of paramount importance. A univariate method to maximize the peak capacity as developed by Wang et al. (Anal Chem 78:3406–3416, 20) has been applied and tested for a monolithic RP-18 silica capillary column. In their method, using model peptides representing a bovine serum albumin digest, the gradient time and temperature are kept constant while the flow rate and eluent strength are varied. Despite our criticism on the fixed starting conditions, a long gradient time leading to an unnecessary long analysis time and a high temperature leading to possible degradation products in the chromatogram, and the peak capacity as the only optimization parameter this fast and simple optimization strategy turns out to be applicable to capillary monolithic columns. Furthermore, the influence of the peak capacity on a second optimization parameter, the MS protein identification score, is examined. The procedure is also used to enhance the performance of two popular types of monolithic capillary LC columns (silica-C18 and poly(styrene–divinylbenzene)) of the same length for the analysis of protein digests. Comparison of both columns show that the calculated chromatographic parameters, like productivity and peak capacity, and identification score for both columns are about the same. For a more complicated nine-protein digest the performance of the silica monolith is slightly better. 相似文献
107.
An efficient method was developed for the synthesis of the ketoamino acid 2, a key intermediate in the synthesis of the novel sweet compound, monatin 1. Preparation of 2 entails coupling of a suitably protected indole acetate anion to an aspartic acid derivative. 相似文献
108.
109.
Alejandro Benítez Johan J. SánchezMaría L. Arnal Alejandro J. Müller 《Polymer Degradation and Stability》2013
The mechanical properties of two linear low density and low density polyethylenes containing a pro-oxidant additive were monitored during accelerated aging (60 °C in a convection oven) and weather exposure. Tearing tests (trouser) were performed for the first time in polyethylenes subjected to oxo-degradation revealing a transition from an extensible to a non-extensible material, at exposure times when standard tensile tests were not able to detect any changes in the materials. The essential work of fracture (EWF) technique was also applied and the results were in agreement with those of trouser tests. The specific essential work of fracture first increased with exposure time until the sample experienced a transition to a less ductile state where EWF was no longer applicable. EWF and trouser tear tests were more sensitive detecting the onset of degradation probably because they employ notched specimens that impose more critical stress concentration conditions than conventional tensile tests. 相似文献
110.
Anne Silset Pål Viggo Hemmingsen Johan Sjöblom 《Journal of Dispersion Science and Technology》2013,34(10):1432-1445
The stability of 30 heavy crude oil emulsions was studied in a parallel-plate laboratory coalescer (DC field). Particularly, viscous responses and their influence on the emulsion stability measurements were investigated. In addition to highlighting previous results from the same experimental setup and discussing these based on recent experience, new results at different temperatures and volume fractions of water were presented. A new semi-empirical model for the characteristic time of the destabilization process was presented. The electrical forces were modelled with a point-dipole approximation and the hydrodynamic resistance to droplet transport was modelled with an empirical term including the logarithmic viscosity of the oil phase. The new model clearly performed much better than the previous model, particularly for very viscous crude oils. Studies of the performance of industrial electrocoalescers have showed that simple electrostatic theory can potentially explain complex separation phenomena when the resistance to the coalescence step is reduced by an efficient demulsifier. The ultimate goal is to build a model for both the laboratory setup and the industrial coalescer so that laboratory experiments can be used to predict the behavior of the industrial process. 相似文献