漂移热流与托卡马克等离子体粒子径向箍缩

利用流体力学模型分析了由漂移热通过磁场不均匀性引的沿磁力线的电场,结合俘获粒子极向分布的不均匀性,计算了这种沿力线电场引起的粒子径向箍缩。这种“新经典”类型的粒子径向箍缩机制,对理解“反常”粒子径向箍缩及某些条件下向内的热输运的有帮助的。     

基于中分辨卫星影像的农用航空喷药效果评估

遥感技术能被用于大尺度作物化学喷药效果检测,这为精准农业航空施药发展提供了重要的技术支撑。利用M-18B农用飞机在4米的飞行高度喷施化学农药混合剂(杀菌剂和植物生长调节剂),去控制水稻爆发性疾病--叶片纹枯病和促进水稻植株的生长。施药一周后,喷药区的卫星影像被获取并计算植被指数,同时采集了地面化学农药的药液沉积量。分析了药液雾滴沉积量和植被指数的关系,结果显示,单相光谱特征(NDVI)和液滴沉积点密度(DDPD点·cm-2) 的相关系数是0.315,p-value为0.035;时间变化特征 (MSAVI)和液滴沉积体积密度(DDVD μL·cm-2)之间的相关系数是0.312,p-value为0.038。另外,水稻生长活力最旺盛的范围都出现在喷洒区域内,植株活力随着药液漂移距离的增加逐步减少。同时,相同的变化趋势也出现在雾滴沉积量与光谱特征的空间变化插值图中。由此得知,从卫星图像中计算的植被指数NDVI和MSAVI,可以用来评估大尺度农田的农用航空药液喷洒效果。     

基于DSP交替式积分器设计

在DSP扣除斜率算法的基础上,设计了一种新型交替式积分器。该积分器利用DSP进行逻辑控制,使两个模拟积分器交替工作,减小两个积分器的积分时间,从而有效克服由于电容和温漂带来的误差,实现了对信号的长时间积分。同时采用Iqmath库函数实现定点处理器的运算来提高实时精度,很方便地实现了实时而准确的积分处理。     

On ballistic transport in carbon nanotubes

We investigate theoretically the ballistic regime exhibited by conduction electrons in multiwalled carbon nanotubes in relation to the conductance quantization in these tubes. Starting from the fact that electron drift mobility is quantized in multiwall tubes, essential aspects related to both ballistic and diffusive regimes are discussed.     

Drift response of a bilinear hysteretic system to periodic excitation under sustained load effects

This paper presents an investigation of response characteristics for hysteretic systems idealized as a bilinear hysteretic model subjected to period excitations composed of a harmonic function and a sustained load. It is shown that the displacement solution can exhibit a drift sequence persistently repeated at a frequency identical to the excitation frequency in the case of zero post-yielding stiffness. The periodic-like drift sequence is further classified into three major types according to their different hysteretic looping behaviors. An approximate solution approach based on the method of weighted residuals is proposed to analyze the drift amplitude per response cycle. The assumed response shape is composed of two concatenated harmonic functions each with a frequency slightly detuned from the excitation frequency. The method is accompanied with a subsequent first-order analysis to obtain a closed-form approximation for the drift response. Good response predictions of the proposed solution method are demonstrated through both undamped and damped drift-frequency analyses.     

Scanning Electron Microscopy for Quantitative Small and Large Deformation Measurements Part I: SEM Imaging at Magnifications from 200 to 10,000

A series of baseline displacement measurements have been obtained using 2D Digital Image Correlation (2D-DIC) and images from Scanning Electron Microscopes (SEM). Direct correlation of subsets from a reference image to subsets in a series of uncorrected images is used to identify the presence of non-stationary step-changes in the measured displacements. Using image time integration and recently developed approaches to correct residual drift and spatial distortions in recorded images, results clearly indicate that the corrected SEM images can be used to extract deformations with displacement accuracy of ±0.02 pixels (1 nm at magnification of 10,000) and mean value strain measurements that are consistent with independent estimates and have point-to-point strain variability of ±1.5 × 10⁻⁴.

Large time behavior and energy relaxation time limit of the solutions to an energy transport model in semiconductors

In this paper, the global existence and the large time behavior of smooth solutions to the initial boundary value problem for the multi-dimensional energy transport model are studied. It is also proved that the solutions of the problem converge to an isothermal drift-diffusion model as energy relaxation time τ goes to 0 by compactness argument with the help of energy estimates and entropy inequality.     

New stochastic model for dispersion in heterogeneous porous media: 1. Application to unbounded domains

A new model of solute dispersion in porous media that avoids Fickian assumptions and that can be applied to variable drift velocities as in non-homogeneous or geometrically constricted aquifers, is presented. A key feature is the recognition that because drift velocity acts as a driving coefficient in the kinematical equation that describes random fluid displacements at the pore scale, the use of Ito calculus and related tools from stochastic differential equation theory (SPDE) is required to properly model interaction between pore scale randomness and macroscopic change of the drift velocity. Solute transport is described by formulating an integral version of the solute mass conservation equations, using a probability density. By appropriate linking of this to the related but distinct probability density arising from the kinematical SPDE, it is shown that the evolution of a Gaussian solute plume can be calculated, and in particular its time-dependent variance and hence dispersivity. Exact analytical solutions of the differential and integral equations that this procedure involves, are presented for the case of a constant drift velocity, as well as for a constant velocity gradient. In the former case, diffusive dispersion as familiar from the advection–dispersion equation is recovered. However, in the latter case, it is shown that there are not only reversible kinematical dispersion effects, but also irreversible, intrinsically stochastic contributions in excess of that predicted by diffusive dispersion. Moreover, this intrinsic contribution has a non-linear time dependence and hence opens up the way for an explanation of the strong observed scale dependence of dispersivity.     

Stochastic Motion Under G-Framework: I. Nelson Stochastic Derivatives

In this article we take the initial step in the study of kinematics of stochastic motion under the sublinear expectation approach, (the so called G-framework). We compute, in this article, the stochastic forward/backward derivatives/drifts of some G-diffusion processes, and calculate the current and osmotic velocities. While the G-framework that we use creates a few technical difficulties, it also rewards us with nice extensions of results corresponding to the linear expectation case.