HT-7托卡马克装置纵场超导磁体失超保护可靠性研究

重点介绍 HT- 7超导托卡马克纵场失超保护可靠性措施 ,如双门限信号相与、双通道信号处理、前馈补偿、高频滤波等 ;简明介绍了托卡马克装置运行中失超发生的规律性。     

Cauchy's Theorem on Manifolds

A generalization of the Cauchy theory of forces and stresses to the geometry of differentiable manifolds is presented using the language of differential forms. Body forces and surface forces are defined in terms of the power densities they produce when acting on generalized velocity fields. The normal to the boundary is replaced by the tangent space equipped with the outer orientation induced by outward pointing vectors. Assuming that the dimension of the material manifold is m, stresses are modelled as m − 1 covector valued forms. Cauchy's formula is replaced by the restriction of the stress form to the tangent space of the boundary while the outer orientation of the tangent space is taken into account. The special cases of volume manifolds and Riemannian manifolds are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

波场逆向外推脊小波成像方法

地震偏移波动方程成像问题本质上讲是数学逆问题,传统方法求解采用的基函数具有明显的不足,针对其存在的不足,以及研究对象的地质构造特点,利用最新的具有较好光滑性、紧支性的Ridgelet函数基,以及能较好表征地质构造的平面或平面特征的数学分析工具;Ridgelet变换,提出了相应的改进方法,利用变换后系数的较好稀疏性,建立了多尺度脊小波波场递推成像计算方法。     

Existence and universality of the blow-up profile for the semilinear wave equation in one space dimension

In this paper, we consider the semilinear wave equation with a power nonlinearity in one space dimension. We exhibit a universal one-parameter family of functions which stand for the blow-up profile in self-similar variables at a non-characteristic point, for general initial data. The proof is done in self-similar variables. We first characterize all the solutions of the associated stationary problem, as a one parameter family. Then, we use energy arguments coupled with dispersive estimates to show that the solution approaches this family in the energy norm, in the non-characteristic case, and to a finite decoupled sum of such a solution in the characteristic case. Finally, in the case where this sum is reduced to one element, which is the case for non-characteristic points, we use modulation theory coupled with a nonlinear argument to show the exponential convergence (in the self-similar time variable) of the various parameters and conclude the proof. This step provides us with a result of independent interest: the trapping of the solution in self-similar variables near the set of stationary solutions, valid also for non-characteristic points. The proof of these results is based on a new analysis in the self-similar variable.     

Effect of temperature on the frictional forces between polystyrene brushes

Normal and shear forces between opposing polystyrene (PS) brushes made from preferentially assembled PS–polyvinylpyridine diblock copolymers were measured in toluene and in near‐theta cyclohexane at 32, 40, and 50 °C, using a modified surface forces apparatus. In cyclohexane, over the temperature window probed, the normal forces of interaction are repulsive and the range of those force profiles changes only slightly; however, for both of the PS brushes studied, the onset of shear forces in near‐theta cyclohexane is strongly influenced by changes in temperature: As the temperature is increased, the onset of the frictional interactions between the brushes in cyclohexane shifts to smaller distances, approaching the distances where frictional forces are observed for brushes in the good solvent toluene. The pattern of behavior seen in the frictional response between the limits of good and theta condition is attributed to composition fluctuations, which increase near the theta condition because of the decrease in excluded volume interactions. These fluctuations may give rise to increased drag during shearing motion because of interfacial roughness or interchain coupling across the brush–brush interface. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 649–655, 2006     

Pressure weighted upwinding for flow induced force predictions: application to iced surfaces

This paper addresses two main topics, namely the development of a pressure‐weighted upwinding method and its application to flow induced forces on iced cylinders. Although the near‐wall convective upwinding exhibits special applicability to iced surfaces, its capabilities extend more generally to other applications. By fully linking pressure and velocity at a sub‐element level near the wall, a higher order accuracy can be obtained. Also, a non‐physical de‐coupling between pressure and velocity can be prevented. The method is developed under the context of a control‐volume‐based finite element method for 2‐D, incompressible flows. Drag and lift coefficients are predicted, based on the pressure weighted upwinding near the wall. The numerical predictions are successfully compared against experimental data, including flow induced forces on iced cables. Copyright © 2004 John Wiley & Sons, Ltd.     

Wave propagation analysis in nonlinear curved single-walled carbon nanotubes based on nonlocal elasticity theory

Theoretical predictions are presented for wave propagation in nonlinear curved single-walled carbon nanotubes (SWCNTs). Based on the nonlocal theory of elasticity, the computational model is established, combined with the effects of geometrical nonlinearity and imperfection. In order to use the wave analysis method on this topic, a linearization method is employed. Thus, the analytical expresses of the shear frequency and flexural frequency are obtained. The effects of the geometrical nonlinearity, the initial geometrical imperfection, temperature change and magnetic field on the flexural and shear wave frequencies are investigated. Numerical results indicate that the contribution of the higher-order small scale effect on the shear deformation and the rotary inertia can lead to a reduction in the frequencies compared with results reported in the published literature. The theoretical model derived in this study should be useful for characterizing the mechanical properties of carbon nanotubes and applications of nano-devices.     

Oligosaccharide Shells as a Decisive Factor for Moderate and Strong Ionic Interactions of Dendritic Poly(ethylene imine) Scaffolds under Shear Forces

For better understanding and improving the non‐covalent interactions of dendritic core–shell, we evaluated the interactions of hyperbranched poly(ethylene imine) (PEI) decorated with various oligosaccharide shells with water‐soluble B vitamins, an estradiol derivative and pantoprazole. Depending on the different properties of the analyte molecules, dendritic core–shell glyco architectures showed (very) weak, moderate and strong interactions with the analyte molecules. Thus, ionic interactions are the strongest driving force for the formation of host–guest complexes. The core–shell glyco architecture is a necessary prerequisite for stable analyte/PEI complexes; the pure hyperbranched PEI did not show any sufficiently strong interactions with neutral, cationic or anionic analytes under the shear forces applied during ultrafiltration of pure aqueous solution without an adjusted pH. Thus, only robust non‐covalent interactions between analytes and the dendritic polyamine scaffold of the glycopolymer structure survive this separation step and allow isolation of stable host–guest complexes in aqueous solution.     

Estimate of the travelling wave speed for an integro-differential equation

Travelling waves for nonlocal reaction–diffusion equations are studied. The minimax representation of the wave speed is obtained. It is used to obtain analytical estimates and asymptotic values of the speed. Two regimes of wave propagation are identified. One of them is dominated by diffusion and another one by the nonlocal interaction.     

Wave propagation in advected acoustics within a non-uniform medium under the effect of gravity

We investigate linear wave propagation in non-uniform medium under the influence of gravity. Unlike the case of constant properties medium here the linearized Euler equations do not admit a plane-wave solution. Instead, we find a “pseudo-plane-wave”. Also, there is no dispersion relation in the usual sense. We derive explicit analytic solutions (both for acoustic and vorticity waves) which, in turn, provide some insights into wave propagation in the non-uniform case.