Cyclic axial response and energy dissipation of cold-formed steel framing members

This paper summarizes results from an experimental program that investigated the cyclic axial behavior and energy dissipation of cold-formed steel C—sections structural framing members. Fully characterized cyclic axial load–deformation response of individual members is necessary to facilitate performance-based design of cold-formed steel building systems. Specimen cross-section dimensions and lengths were selected to isolate specific buckling modes (i.e., local, distortional or global buckling). The cyclic loading protocol was adapted from FEMA 461 with target displacements based on elastic buckling properties. Cyclic response showed large post-buckling deformations, pinching, strength and stiffness degradation. Damage accumulated within one half-wave after buckling. The total hysteretic energy dissipated within the damaged half-wave decreased with increasing cross-section slenderness. More energy dissipation comes at the cost of less cumulative axial deformation before tensile rupture.     

Impact of gypsum supersaturated process water on the interactions between silica and zinc sulphide minerals

Flotation recovery and selectivity problems have been reported in the flotation of fine sulphide minerals in gypsum supersaturated process water. In this study, the effect of gypsum supersaturated solution on the interactions between silica and sphalerite (ZnS) minerals was examined by observing deposition behaviour of silica nanoparticles on sphalerite surface using a quartz crystal microbalance with dissipation (QCM-D). Significant deposition of silica nanoparticles on ZnS coated sensor surface was observed in the gypsum supersaturated solution, indicating consequential slime coating of silica fines on sphalerite mineral surface. Substantial deposition of silica nanoparticles on SiO₂ coated surface was also observed suggesting strong homo-aggregation of silica fines in the gypsum supersaturated solution. The interaction behaviour between silica–sphalerite and silica–silica is mainly attributed to the high calcium concentration of the gypsum supersaturated solution. Similar deposition behaviour of silica nanoparticles onto ZnS or SiO₂ coated sensor surface was observed in 800 ppm calcium solution, which is similar to the calcium concentration of the gypsum supersaturated solution. Colloidal force measurement between a silica particle and a fractured sphalerite surface or a silica wafer surface by an atomic force microscopy (AFM) revealed attractive van der Waals force between the mineral particles in both gypsum supersaturated solution and 800 ppm calcium solution. The high calcium concentration of the gypsum supersaturated solution induced the hetero-aggregation between silica and sphalerite, accounting for the observed decrease in flotation selectivity.     

Evaluating the potential for energy extraction from turbines in the gulf stream system

Increasing energy consumption and decreasing reserves of fossil fuels have led to growing interest in renewable energy from the ocean. Ocean currents are an alternative source of clean energy due to their inherent reliability, persistence and sustainability. General ocean circulations exist in the form of large rotating ocean gyres, and feature extremely rapid current flow in the western boundaries due to the Coriolis effect. The Gulf Stream system is formed by the western boundary current of the North Atlantic Ocean that flows along the east coastline of the United States, and therefore is of particular interest as a potential energy resource for the United States. The theoretical energy balance in the Gulf Stream system is examined using the two-dimensional ocean circulation equations based on the assumptions of the Stommel model for subtropical gyres with the quasi-geostrophic balance between pressure gradient, Coriolis force, wind stress and friction driving the circulation. To represent flow dissipation due to turbines a spatially varying turbine drag coefficient is formulated and a finite difference numerical approach is utilized to obtain an implicit solution of the model. The results show that considering extraction over a region representing the entire Florida Current portion of the Gulf Stream system, the average power dissipated ranges between 4 and 6 GW with a mean around 5.1 GW. This corresponds to an average of approximately 45 TWh/yr. However, if the extraction area approximates the entire portion of the Gulf Stream within 200 miles of the US coastline, the average power dissipated becomes 18.6 GW or 163 TWh/yr. The impact of the localized turbine drag on the hydrodynamics is primarily within the turbine region. The extra drag force from turbines slows down the current velocity and leads to redirection of the Gulf Stream flow. It also results in a sea surface drop in the turbine region. Localized turbine drag significantly reduces residual kinetic energy flux in the circulation. However, its influence on the residual volume flux depends on the area of the turbine region.     

海拔高度对计算机散热影响的研究

中国海拔1 km以上地区占全国总面积65％，属于高原国家．计算机等电子设备的散热能力受海拔高度的影响很大，电器的散热的好坏直接影响元器件的寿命、运算速度和使用的稳定性等．为了研究海拔高度对电子设备的散热的影响，依据热力学的基本理论，引入了海拔高度参数，对建立在海平面基础上的茹卡乌斯数学模型、Chilton-Colburn方程等传热计算模型进行了修正，建立了一套不同海拔高度电器热分析计算方法，解决了海拔高度参数和电器散热关系的问题．其分析结果符合国际电工委员会实验标准，并用Ansys．Icepak14.5电子热设计专用软件进行了验证．为不同海拔高度地区计算机等电器设备热设计和寿命评估提供了理论基础．     

淋溪河水电站溢洪道泄洪消能形式研究

鉴于淋溪河水电站溢洪道原设计方案的种种缺陷,基于弗劳德准则,采用1∶60的模型比尺,通过设置表孔和深孔出口体型,研究了不同体型参数下泄流能力和水流对水垫塘底板的冲击压力。试验结果表明,优化后的底板冲击压力由14.50kPa降至11.44kPa,脉压均方根由95.67kPa降至45.55kPa,同时水垫塘长度由269.5m减小至169.5m,仍满足泄洪消能要求。研究成果可为同类工程提供参考。     

A DRBEM model for harbor oscillation with the effect of energy dissipation

Abstract

In this study, the numerical scheme of dual reciprocity boundary element method (DRBEM) is adopted to investigate the resonant problem in a harbor while considering the effect of energy dissipation. The numerical model employed the mild slope equation as a basic equation. To avoid complicated procedures for solving the equation, DRBEM is used to improve numerical efficiency. Computation results are compared with the existing experimental data and other theoretical results. It shows that the present model is valid and effective to solve the harbor oscillation problem.     

Solution of low péclet number heat transfer with viscous dissipation in the semi‐infinite axial region of a tube via functional analytic methods

Abstract

A solution of the extended Graetz problem with prescribed wall heat flux and viscous dissipation in a semi‐infinite axial region of a tube is obtained by functional analytic methods. The energy equation is split into a set of partial differential equations to obtain a self‐adjoint formulism. Then, an algebraic characteristic equation of the eigenvalue problem for an arbitrary velocity profile is obtained by an approximation method in L ₂[0, 1]. In addition, a backward recursive formula for calculating the expansion coefficients of the solution is developed.     

Time evolution of entanglement and bistability of two coupled quantum dots in a driven cavity

Abstract

The time evolution of entanglement between two quantum dots (QDs) trapped inside a cavity driven by a coherent quantized field is studied. In the presence of dissipation, entanglement shows many interesting features such as sudden death and revival, and finite steady state value after sudden death. We also investigate dependence of entanglement on dot variables and its relation to bistability. It is found that entanglement vanishes when the cavity field intensity approaches the upper branch of the bistability curve. When the cavity is driven by a modulated field in the presence of dissipation, it can periodically generate entanglement, which is much larger than the maximum value attained in the steady-state for this system but the dots are never fully entangled.     

Modified Lim-Lee Combing Using Signed Window and Direct Doublings

ABSTRACT

The fast exponentiation is a crucial one in any kind of public key cryptosystem. Lim-Lee proposed a method for an efficient exponentiation in elliptic curve by dividing n-bit scalar into equal length of simple scalars. In this paper, the general Lim-Lee method is further improved by using the signed binary window method and direct doublings.