压电类智能层合结构的力学和计算模型综述

综述了压电类智能层合结构的力学和计算模型。基于大量国内外有关压电类智能层合结构的文献 ,根据各自采用的运动学假设、场变量的近似、压电层的表达法以及曲率和温度的影响 ,对压电层合结构的力学和计算模型进行了分类 ,阐述了各种理论的特点及一般形式。     

Computational Models of Combustion of Nonmetallized Heterogeneous Propellant

Physical and chemical models are treated which are employed for numerical analysis of the processes of combustion of nonmetallized sandwich heterogeneous propellants on the basis of ammonium perchlorate and hydroxyl-terminated polybutadiene.     

静电计量检测的研究

本文阐述静电通过静电场对微电子元器件产生危害的途径,总结了静电防护方法.并在此基础上,对静电计量检测的对象及其特点、技术要求和依据的标准进行了较为全面的研究.     

Electrostatics of interdigital transducers

Interdigital transducers are systems of conducting strips on a piezoelectric halfspace; in some systems, the groups of strips repeat periodically over a transducer counting hundreds of strips that can be considered infinite. An infinite planar periodic system of groups of strips with adequate period, sufficiently large if necessary, is considered to model an electric field in the plane of strips. There are electric charge distributions on strips either resulting from an external voltage source applied to the strips or induced by a propagating surface acoustic wave in the piezoelectric substrate. The latter case is equivalent, in the electrostatic approximation applied in this paper, to strips embedded in an already existing, spatially variable electric field. A method is presented for evaluation of the spatial spectrum of charge distribution that is responsible for either the surface wave generation or the scattering by strips in weak piezoelectrics. It overcomes certain numerical difficulties arising when Fourier transform is computed from the already evaluated numerical representation of the square-root singular charge distribution at the strip edges.     

Electrostatics of nanowire transistors

The electrostatics of nanowire transistors are studied by solving the Poisson equation self-consistently with the equilibrium carrier statistics of the nanowire. For a one-dimensional, intrinsic nanowire channel, charge transfer from the metal contacts is important. We examine how the charge transfer depends on the insulator and the metal/semiconductor Schottky barrier height. We also show that charge density on the nanowire is a sensitive function of the contact geometry. For a nanowire transistor with large gate underlaps, charge transferred from bulk electrodes can effectively "dope" the intrinsic, ungated region and allow the transistor to operate. Reducing the gate oxide thickness and the source/drain contact size decreases the length by which the source/drain electric field penetrates into the channel, thereby, improving the transistor characteristics.     

Applications of Chemometrics for Characterization of Macromolecules

The possibilities of employing methods of chemometrics in order to characterize macromolecules are described. The review has been limited to chemometric methods concerning multivariate data analysis. Principal component analysis (PCA) has shown to be very useful for pattern recognition problems arising from chromatographic and spectroscopic data. An example of using a classification technique, SIMCA (Soft Independent Modelling of Class Analogy), as a product control method is presented. The suitability of Partial Least Squares (PLS) for relating data of different natures, e.g. chemical data with biological data, is discussed. Moreover, examples ranging from spectroscopic determinations to QSAR (Quantitative Structure Activity Relationships) are illustrated.     

Applications of Chemometrics for Characterization of Macromolecules

Abstract

The possibilities of employing methods of chemometrics in order to characterize macromolecules are described. The review has been limited to chemometric methods concerning multivariate data analysis. Principal component analysis (PCA) has shown to be very useful for pattern recognition problems arising from chromatographic and spectroscopic data. An example of using a classification technique, SIMCA (Soft Independent Modelling of Class Analogy), as a product control method is presented. The suitability of Partial Least Squares (PLS) for relating data of different natures, e.g. chemical data with biological data, is discussed. Moreover, examples ranging from spectroscopic determinations to QSAR (Quantitative Structure Activity Relationships) are illustrated.     

适用于回流区流体力学模拟计算的三种高雷诺数湍流模型的比较

在数值模拟计算领域,标准k-ε模型、CHEN-KIM k-ε模型和RNG k-ε模型属于两方程的高雷诺数湍流模型,运用这三种模型对暖通空调室内空气回流区进行计算流体力学(CFD)模拟,结果表明采用CHEN-KIM k-ε模型和RNG k-ε模型的模拟结果差别不大,但二者均优于标准k-ε模型.     

Enhanced Electrostatics for Low-Voltage Operations in Nanocrystal Based Nanotube/Nanowire Memories

The metal nanocrystal (NC)/carbon nanotube (CNT) based nonvolatile memory has been proposed recently in comparison to the microfabricated Si channel and Si NCs in ultranarrow channel structure. The electrostatics of metal NC-CNT devices during memory operations differ significantly from the metal NC memory with planar silicon channel. In this paper, we present the theoretical analysis on the three-dimensional (3-D) electrostatics of the NC-CNT device during memory operations, to illustrate the experimentally observed large number of charge storage at low gate bias (5 V) despite a 100-nm-thick bottom-gate control dielectric. NCs are electrostatically more strongly coupled to the two-dimensional (2-D) gate electrode than to the one-dimensional (1-D) channel, even when the NCs are in much closer proximity to the 1-D channel, for efficient tunneling and low-voltage program operation. Under the retention condition, the NC-CNT devices have lower electric field across tunneling oxide than that in the case of a 2-D channel. This increasing electric field difference with respect to program versus retention operations indicates larger ratio between program and retention times. Together with the large number of electrons stored per NC, this enhanced electrostatics can be utilized either to reduce the operating voltage or to reduce statistical fluctuation of the information storage     

Electrostatics of partially gated carbon nanotube FETs

The finite-element method is used to solve Poisson's equation, under equilibrium conditions, for coaxial carbon nanotube field-effect transistors in which the gate electrode does not entirely cover the nanotube channel between the source- and drain-end contacts. A conformal transformation is applied to overcome the problems that arise in this open structure of specifying boundary conditions and of terminating the model space. The effect on the potential distribution within the transistor of changing various geometrical properties of the device is investigated, and some special conditions under which appropriate boundary conditions may be defined a priori are identified. The effects on the potential energy profile along the nanotube of varying the work function of the end contacts, and of introducing charge into the gate dielectric, are also investigated. The latter is shown to be effective in suppressing the otherwise dominant role that the end contacts play in determining the barrier to charge flow in the nanotube, thereby allowing bulk control to occur.     

Electrostatics of coaxial Schottky-barrier nanotube field-effect transistors

Analytical and numerical methods are used to solve Poisson's equation for carbon nanotube field-effect transistors (FETs) with a cylindrical surrounding gate and Schottky-barrier contacts to the source and drain. The effect on the nanotube potential profile of varying the work functions of all the electrodes, and the thickness and permittivity of the gate dielectric, is investigated. From these results, the general trends to be expected in the above-threshold drain current-voltage characteristics of Schottky-barrier nanotube FETs are predicted. The unusual possibility of simultaneous electron and hole contributions to the drain current is revealed. The subthreshold characteristics are computed from a solution to Laplace's equation, and the subthreshold slope is found to depend on gate dielectric thickness in a different manner from that in other FETs.     

A New Measure of Misfit for Covariance Structure Models

Various fit indices exist in structural equation models. Most of these indices are related to the noncentrality parameter (NCP) of the chi-square distribution that the involved test statistic is implicitly assumed to follow. Existing literature suggests that few statistics can be well approximated by chi-square distributions. The meaning of the NCP is not clear when the behavior of the statistic cannot be described by a chi-square distribution. In this paper we define a new measure of model misfit (MMM) as the difference between the expected values of a statistic under the alternative and null hypotheses. This definition does not need to assume that the population covariance matrix is in the vicinity of the proposed model, nor does it need for the test statistic to follow any distribution of a known form. The MMM does not necessarily equal the discrepancy between the model and the population covariance matrix as has been assumed in existing literature. Bootstrap approaches to estimating the MMM and a related quantity are developed. An algorithm for obtaining bootstrap confidence intervals of the MMM is constructed. Examples with practical data sets contrast several measures of model misfit. The quantile-quantile plot is used to illustrate the unrealistic nature of chi-square distribution assumptions under either the null or an alternative hypothesis in practice.

     

广告中女性形象设计的新模式解析

对于广告中女性形象的设计提出了3种模式:传统一致性模式、男性化模式以及双性化模式.传统一致性模式主要反应传统的女性社会角色,新兴起的男性化模式则着力渲染独立、自信的现代女性形象,而双性化模式在男性化模式基础上不仅塑造女性工作中独立、自信的进取精神,还重点刻画女性在生活中的温柔、细腻、精致的休闲风格.并且在文中还进一步指出了这2种新模式出现的原因以及对社会观念转变和个体人格塑造的意义.     

一种新的视觉运动注意力计算方法

由于运动注意力模型不合理、光流估算的局限性和噪声影响,对于复杂运动场景,现有运动注意力计算方法往往不能准确计算出运动显著图。本文提出了一种新的运动注意力计算方法,该方法首先根据注意力形成机理构建运动注意力模型;在可变块大小运动估计的基础上计算运动注意力;最后采用空间多尺度融合得到最终的运动显著图。通过对多个高清视频序列的测试,表明本文提出的方法比现有方法更能准确地计算出运动显著图。     

A New Class of Materials: Sequence‐Defined Macromolecules and Their Emerging Applications

Emerging applications of a new class of materials, sequence‐defined macromolecules, are explored. Such molecularly highly defined macromolecules require stringent synthesis and purification procedures, yet offer unprecedented application possibilities. The first examples of molecular data storage and related technologies are already starting to emerge today. From a more fundamental point of view, such macromolecules offer a unique opportunity to determine quantitative structure–property relationships (QSPR), which critically aids in designing materials with applications ranging from catalysis to artificial enzymes.     

The Effects of Different Property Models in a Computational Fluid Dynamics Simulation of a Reciprocating Compressor

Computational fluid dynamics was applied to model a simple reciprocating compressor using R134a (1,1,1,2-tetrafluoroethane) as the working fluid. The sensitivity of the compressor model to various property models was quantitatively assessed by calculating the work required to carry out several compression cycles. The ideal gas equation, a virial equation using only the second virial coefficient, and the Peng–Robinson equation were compared to a reference-quality Helmholtz energy equation of state. Significant errors, up to 12% in the density of the outflowing gas, can result from the use of the ideal gas model. The Peng–Robinson equation resulted in density errors up to 6.3%. The virial equation gave values closest to those calculated using the Helmholtz energy equation of state, with errors in density up to 4.7%. The results also show that an increase in accuracy in work and mass flow calculations achieved by using the Helmholtz energy equation of state is obtainable without an impractical increase in computation time.     

A New Algorithm for Extreme Vertices Designs for Linear Mixture Models

A new algorithm for obtaining extreme vertices designs for linear mixture models is proposed. The algorithm generally produces designs that are as efficient as those produced by the XVERT algorithm of Snee and Marquardt (1974) but with less computational effort. Use of the algorithm in obtaining designs is also described.