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1.
The paper presents some two-dimensional simulation results of granular vortex-structures in cohesionless initially dense sand during a quasi-static passive wall translation. The sand behaviour was simulated using the discrete element method (DEM). Sand grains were modelled by spheres with contact moments to approximately capture the irregular grain shape. In order to detect vortex-structures, the Helmholtz–Hodge decomposition of a vector field from DEM calculations was used. This approach enabled us to distinguish both incompressibility and vorticity in the granular displacement field. In addition the predominant periods of vortices during horizontal wall movement were determined. The vortices were strongly connected to shear localization. They localized in locations where shear zones ultimately developed. In addition, the vortex-structures were calculated during plane strain compression. 相似文献
2.
The coupling of 1-naphthol with diazotised sulphanilic acid produces by competitive, consecutive reactions two dyestuffs, whose concentrations can readily be measured spectrophotometrically. The reaction kinetics have been measured using the stopped-flow method and the reaction mechanism is known. Using mild reaction conditions (room temperature, aqueous solution of pH = 10, concentrations of order 0.1 mol m?3), the product mixture always contained more disubstituted and therefore less monosubstituted dyestuff than would have been formed in the chemically controlled regime. (In these experiments the stoichiometric and volumetric ratios of the reagents were varied and the 0.063 m3 reactor was operated semi-continuously, as well as continuously using various turbine speeds). The reactions were fast enough to produce inhomogeneity at the molecular scale (segregation) and are shown to possess highly convenient properties for studying such segregation. 相似文献
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D. Henscheid M. N. Kozicki G. W. Sheets M. Mughal I. Zwiebel R. J. Graham 《Journal of Electronic Materials》1989,18(2):99-104
An alternative to SiO2 for gate dielectric applications in MIS devices is nitrided silicon dioxide. A study of this material is presented in this
paper. Thin SiO2 layers (10 nm minimum thickness) were grown on silicon substrates and subsequently nitrided in ammonia at 1 atm using a rapid
thermal processing system. Nitridation times ranged from 3 sec to 60 sec at temperatures from 900 to 1200‡ C. The resulting
films were then characterized using a variety of techniques including high resolution TEM, XPS, AES, SIMS, and electrical
measurements (C-V). Higher temperatures and longer processing times resulted in the accumulation of nitrogen at the film surface
and at the Si/SiO2 interface. As expected, the electrical characteristics of the nitrided films were strongly influenced by the processing conditions.
The morphology of the interface, as revealed by high-resolution TEM, was also altered by the nitridation process, especially
for high processing temperatures (>1000° C). 相似文献
6.
A general method is proposed for prediction of the flow rate and maximum velocity in the isothermal, steady, uniform, laminar flow of any incompressible, time-independent non-Newtonian fluid in straight open channels of arbitrary cross section. The method requires only a knowledge of two geometric coefficients and a function of shear stress, used to characterize the behavior of the fluid model. The slip effect at the solid boundary has been taken into consideration. Numerical values of the geometric parameters have been determined for flow through an inclined plane of infinite width, semi-circular, semi-elliptical, rectangular, and 90° and 60° symmetric triangular open channels. Applications have been made to various non-Newtonian fluid models such as the power-law, Bingham, Ellis, Meter and the Reiner-Rivlin general model. Numerical examples are presented. A generalization of the Fanning friction factor — Reynolds number is also presented. The problem of determining the point of transition from laminar to turbulent flow in the general case is examined, as is the problem of prediction of the friction factor in turbulent flow. 相似文献
7.
Forecasts by rational agents contain embedded initial and terminal boundary conditions. Standard time series models generate two types of long-run boundary values or steady-state 'endpoints' – fixed endpoints and moving average endpoints. Neither can explain the shifting endpoints implied by postwar movements in the cross-section of forward rate forecasts in the term structure or by post-1979 changes in survey estimates of expected long-run inflation. Multiperiod forecasts by a broader class of 'moving endpoint' time series models provide substantially improved tracking of the historical term structure and generally support the internal consistency of the ex ante long-run expectations of bond traders and survey respondents. 相似文献
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This review focuses on electrochemical metallization memory cells (ECM), highlighting their advantages as the next generation memories. In a brief introduction, the basic switching mechanism of ECM cells is described and the historical development is sketched. In a second part, the full spectra of materials and material combinations used for memory device prototypes and for dedicated studies are presented. In a third part, the specific thermodynamics and kinetics of nanosized electrochemical cells are described. The overlapping of the space charge layers is found to be most relevant for the cell properties at rest. The major factors determining the functionality of the ECM cells are the electrode reaction and the transport kinetics. Depending on electrode and/or electrolyte material electron transfer, electro-crystallization or slow diffusion under strong electric fields can be rate determining. In the fourth part, the major device characteristics of ECM cells are explained. Emphasis is placed on switching speed, forming and SET/RESET voltage, R(ON) to R(OFF) ratio, endurance and retention, and scaling potentials. In the last part, circuit design aspects of ECM arrays are discussed, including the pros and cons of active and passive arrays. In the case of passive arrays, the fundamental sneak path problem is described and as well as a possible solution by two anti-serial (complementary) interconnected resistive switches per cell. Furthermore, the prospects of ECM with regard to further scalability and the ability for multi-bit data storage are addressed. 相似文献
10.
An alternative method for determination of intrinsic viscosities is described which evolves from the application of l'Hǒpital's rule to the expression defining the intrinsic viscosity. The method yields independent evaluations of the intrinsic viscosity and does not involve extrapolation beyond the range of experimental data or rely on a theoretical expression associated with such extrapolations. The application of the method is illustrated and comparisons are included with the results obtained by traditional approaches. 相似文献