墙体对UWB脉冲信号衰减特性的FDTD分析

用时域有限差分法分析墙体对超宽带脉冲信号传播的影响.计算得出脉冲信号穿墙后的时域波形,利用傅里叶变换得出脉冲信号穿墙后的频谱变化.研究了墙体厚度的变化对脉冲信号的影响以及不同的墙体对穿墙脉冲信号的影响,仿真结果与相关理论一致.     

IT服务与有线行业信息化

在完成"双改"后,有线电视行业开始将关注点转向数字电视增值服务,但对于面向互联网的IT增值服务关注不够.事实是IT服务和IT服务外包在迅猛地发展,即使电信行业也开始向"综合信息服务提供商"转型.有线行业在经营好自己"花园围墙"的时候,应该考虑如何将自己传统的业务与新兴的IT服务结合起来,"兼容"互联网,依托开放的技术、丰富的内容、优质的服务谋求更大的发展.     

汤家墩遗址冶炼遗物的科技研究

采用X射线荧光仪、X射线衍射分析仪、扫描电子显微镜及激光剥蚀电感耦合等离子体质谱等现代检测手段对汤家墩遗址的炉壁、炉渣及炉渣中的金属颗粒进行分析,进而探讨汤家墩古铜冶炼技术。结果表明：汤家墩遗址的炉壁为冶炼炉炉壁,炉渣为还原渣;根据铜颗粒中As,Ag,Sb,Bi等微量元素的含量,可以计算出汤家墩遗址炼渣中的铜颗粒来自于硫化铜矿的概率高达87.87%以上,从而表明汤家墩是采用“硫化铜—铜”的冶铜工艺进行冶炼的早期青铜文化遗址。这一研究结果不仅有利于枞阳地区青铜文化遗产的深入研究,而且对于探究枞庐地区青铜冶铸技术的发展与演变具有非常重要的意义。     

建筑朝向对玻璃幕墙建筑空调冷负荷影响的分析

以上海地区为例,采用暖通空调负荷计算及分析软件HDY-SMAD模拟分析了建筑朝向和玻璃幕墙建筑冷热负荷的关系。模拟结果表明,对于玻璃幕墙建筑,合理选择建筑朝向,对玻璃幕墙建筑冷负荷有很大的影响。     

一种铁磁材料探伤的方法

介绍一种利用LC振荡电路的磁回路探测材料表面和内部伤痕的方法．实验证明,该方法能应用于高压容器的深层探伤,且效果很好．     

Analysis of dislocation wall formation in a disclinated nanograin

Disclinations are common defects in nanocrystalline materials processed via the severe plastic deformation technique. A disclination, depending on its strength, may remain stable or partially relax into other structures such as cracks and dislocation walls. This paper develops closed-form analytical expressions for the energy of a nanograin containing a negative wedge disclination and a wall of periodic edge dislocations. Using these expressions, it is found that (1) a critical disclination strength is required for emitting dislocations and that this critical value demonstrates a strong power law dependence on the nanograin size, (2) there exists a favorable dislocation spacing, which decreases with increase in the disclination strength, in the dislocation wall formed by the emitted dislocations, and (3) the misorientation of the dislocation wall lies between 5° and 12° for disclination strength in the range of 15–35°.     

Peculiarities of inversion walls and singular points in oriented textures of nematic mesophase

In this work the nature and peculiarities of the inversion walls and singular points, which can spontaneously arise or can be stimulated in the homeotropic and planar oriented textures of the thermotropic nematogens, have been investigated for large temperature interval. The interaction force and mean approach velocity of the singular points, having opposite optical sign, have been calculated. The optical mappings and sketches of the inversion walls and singularities, taking place in the oriented textures of the nematogens, are presented. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fluid flow driven along microchannel by its upper stretching wall with electrokinetic effects

We develop a mathematical model to describe the flow in a microchannel driven by the upper stretching wall of the channel in the presence of electrokinetic effects. In this model, we avoid imposing any unphysical boundary condition, for instance, the zero electrostatic potential in the middle of the channel. Using the similarity transformation, we employ the homotopy analysis method (HAM) to get the analytical solution of the model. In our approach, the unknown pressure constant and the integral constant related to the electric potential are solved spontaneously by using the proper boundary conditions on the channel walls, which makes our model consistent with the commonly accepted models in the field of fluid mechanics. It is expected that our model can offer a general and proper way to study the flow phenomena in microchannels.     

Local equilibrium in the inertial layer of wall bounded turbulence

Recently Brouwers [Dissipation equals production in the log layer of wall-induced turbulence. Phys Fluids. 2007;19:101702] carried out an asymptotic analysis using the RANS based turbulence energy transport equation and showed that the energy dissipation equals its production in the inertial layer of wall-induced turbulence. Assuming log-law profile to the mean velocity, pressure, viscous and energy diffusion terms were estimated and shown to be negligibly small compared to the production and dissipation terms thereby proving local equilibrium. However, based on scale relations Tennekes and Lumley [A first course in turbulence. Cambridge (MA): MIT Press; 1994] have already established that the pressure and energy diffusion terms appearing in the energy transport equation are of the same order of magnitude especially in the inertial layer thus leading to a contradiction. Hence we have attempted here to re-estimate the turbulence energy budgets in a different way by invoking the Kolomogrov’s similarity hypotheses and (4/5)th law. Magnitudes of pressure and energy diffusion terms are determined explicitly and found to match well with the DNS data. The striking point of the present analysis is that no prior assumption is enforced on the mean velocity profile. Further, two main advantages of the present study are, (i) reasonable estimates for both the diffusion terms are obtained explicitly that were unavailable before and (ii) these estimates help us to tweak the production/dissipation terms to reflect the influence of turbulent diffusion mechanisms without the necessity to model them as in the case of elliptic relaxation and Reynold stress RANS models.     

Electrohydrodynamic transport of non‐symmetric electrolyte through porous wall of a microtube

Transport of salt through the wall of porous microtube is relevant in various physiological microcirculation systems. Transport phenomena based modeling of such system is undertaken in the present study considering a combined driving force consisting of pressure gradient and external electric field. Transport of salt is modeled in two domains, in the flow conduit and in the pores of porous wall of the microtube. The solute transport in the microtube is presented by convective‐diffusive mass balance and it is solved using integral method under the framework of boundary layer analysis. The wall of the microtube is considered to be consisting of series of straight parallel cylindrical pores with charged inner surface. The solute transport through the pores is considered to be composed of diffusive, convective and electric potential gradient governed by Nernst‐Planck equation. Transport in the microtube and pores is coupled through the osmotic pressure model for the solvent and Donnan equilibrium distribution for the solute. The simulated results agree remarkably well with the experimental data conducted by in‐house experimental set up. The charge density of the porous wall is estimated through the minimization of errors involved between the experimental and simulated data for different operating conditions.