自重对混凝土三点弯曲梁断裂性能的影响

自重对三点弯曲梁试件的断裂性能有重要影响,而以往基于三点弯曲梁研究混凝土的断裂性能时,很少考虑自重引起的试件初始裂缝张口位移（CMOD_ini）的影响。为了研究CMOD_ini对三点弯曲梁断裂性能的影响规律,给出了CMOD_ini及考虑CMOD_ini影响的有效裂缝长度（a_c）和失稳断裂韧度（K_IC^un）的计算公式,并用不同试件尺寸及不同初始缝高比的三点弯曲梁试验数据进行了对比分析。结果表明：当试件初始缝高比为0.4时,CMOD_ini受试件尺寸影响较小,即使试件尺寸达到2200 mm×550 mm×240 mm时,自重对其CMOD_ini、a_c及K_IC^un的影响均小于5%。CMOD_ini受初始缝高比的影响较大,且随着初始缝高比的增大而增大,对于尺寸为1143 mm×305 mm×76 mm,初始缝高比为0.818的三点弯曲梁试件,自重对其CMOD_ini、ac及K_IC^un的影响分别为24.26%、1.73%和17.31%。可见,当三点弯曲梁试件尺寸及初始缝高比均较大时应该考虑自重引起的CMOD_ini的影响。     

传感器温漂对磁悬浮转子控制精度的影响

传感器温漂对磁悬浮转子的控制精度有很大的影响．磁悬浮转子在运转时有较大的温升．磁悬浮转子的结构设计对其工作温度的高低及其分布有很大影响．本文研究了磁悬浮转子实际工作温度场的不均匀性,对涡流传感器的温度特性进行了实验测试,对传感器的布置形式对磁悬浮转子精度的影响进行了分析．研究了磁悬浮转子结构形式、结构参数、传感器的个数及其测试方式等对磁悬浮转子控制精度的影响程度和变化规律．在上述研究的基础上得出了减少传感器温漂对磁悬浮转子控制精度影响的结构设计原则．     

弯曲刚度对斜拉索非线性固有频率的影响

考虑斜拉索的弯曲刚度、垂度及几何非线性,利用Hamilton变分原理推导了斜拉索的三维非线性动力学方程。研究了斜拉索弯曲刚度对面内、面外的一阶及高阶固有频率的影响,并分析了斜拉索长度和初张力等参数对固有频率的影响。结果表明:弯曲刚度对面外固有频率的影响大于面内;随着斜拉索的长度和初张力的增加,弯曲刚度对面外固有频率的影响递减,对面内固有频率的影响呈钟罩型变化;弯曲刚度对固有频率的影响随着振型阶数的增加而变大。     

Effect of gelling conditions and mechanical treatment on drug availability from a lipogel

This study has been conducted to determine whether the rheological differences depending on gelling and treatment conditions could have an influence on drug availability. Lipogels with constant composition were obtained by gelling olive oil with monodiglycerides at rest, under stirring, and milled after gelling. The considerable differences in rheological characteristics produced significant differences on in vitro drug release tests, whereas a lesser influence was observed on in vitro simulated absorption test. The rheological differences appeared not to influence in vivo drug availability. Also, rheological differences owing to the concentration of the gelling agent showed no significant influence on in vivo availability.     

Determination of influence weights for scientific journals

A new citation matrix is proposed for the computation of journal influence weights applying Geller's methodology. Instead of self-citations, references to fringe journals are introduced and the proportions of all references (without self-citations) are used as matrix elements. On the basis of the determined weights, relative weights for fringe journals are calculated, i.e. the initial set (core) of journals is extended and simultaneously a rank order is obtained (by total influence and influence per article). The procedure is examplified on elementary particle physics (EPP) journals. Using first a reference/citation criterion, eight core journals were determined by iteration and then influence weights were calculated. A ranking by total influence and influence per article is presented for core and fringe journals in EPP.     

Influence of perfusion depth on laser Doppler flow measurements with large source-detector spacing

Laser Doppler flowmetry with a large source-detector spacing has been applied to measure blood perfusion in the deeper regions of tissue. The influence of the depth of perfusion on the Doppler spectrum for the large source-detector spacing is likely to be different from that for the conventional laser Doppler instruments with small source-detector spacing. In this study, the light propagation in a tissue model with a blood perfusion layer is predicted by the Monte Carlo simulation to discuss the influence of the depth of perfusion, blood volume, and source-detector spacing on the spectrum of the Doppler signal detected with large source-detector spacing. The influence of the depth of perfusion on the Doppler spectrum for the large source-detector spacing is different from that for the conventional laser Doppler instruments with small source-detector spacing, although the influence of source-detector spacing and blood volume on the Doppler spectrum for large source-detector spacing is almost the same as that for the conventional laser Doppler instruments. The influence of the depth of the perfusion on the Doppler spectrum depends on the path length that the detected light travels at different depths.     

Preparation and hard magnetic properties of Co-Zn-P films for high-density recording

The digital recording density of magnetic media can be improved by the development of thin ferromagnetic coatings having a high coercive force. An experimental study of the influence of zinc on the coercive force of chemically reduced cobalt-phosphorus films is presented. Incorporation of zinc increases the coercive force of cobalt-phosphorus films on Mylar substrates by a factor of 2 to 60. Cobalt-zinc-phosphorus films exhibited coercivities ranging from 300 to 1200 Oe, depending on the preparation conditions. The influence of substrate and solution parameters, such as hypophosphite ion concentration, zinc concentration, and pH are discussed with respect to the hysteresis properties of the films. The influence of zinc on the coercivity is attributed to increased magnetic isolation of the cobalt particles and to a modification of particle size.     

近场项对车用交流发电机气动噪声影响分析

为了探究近场项(反射面、端盖及定子)对车用交流发电机气动噪声的影响,基于Lighthill声比拟理论,大涡模拟(LES)方法及边界元法对交流发电机的气动噪声特性进行研究。结果表明:仿真得到的主要阶次及幅值与实验相比一致性较好,验证了仿真方法的正确性;第4、6、8、9、10及12阶次为该型交流发电机的主要阶次;反射面对各主要阶次皆有影响,端盖主要影响10阶次,定子主要影响6及9阶次;反射面对左、上测点声压级影响较大,端盖对左、右测点影响较大,定子对各测点几乎无影响;近场项对五点平均总声压级的影响大小依次为:反射面>端盖>定子。     

The influence of dissipative heating on active vibration damping of viscoelastic plates

A mathematical formulation of a new nonlinear problem for active vibration damping (ACD) of thin viscoelastic plates by distributed piezoelectric sensors and actuators is given. The influence of dissipative heating on ACD is considered. The nonlinearity of the problem is caused by the temperature dependence of the material properties and the nonlinearity of the dissipative function. The thermomechanical behavior of the materials under harmonic loading is described by the concept of complex characteristics. Numerical and analytical methods are used for solving this problem. As an example, the influence of dissipative heating on damped axisymmetric bending vibrations of a circular viscoelastic plate is investigated. It is shown that this influence can be significant in the case of ACD of polymeric plates.     

Magnetoresistive Effect in Magnetoactive Elastomers

A study of the influence of magnetic field on the resistivity of the magnetoactive (magnetorheological) elastomer has been conducted. The material consisted of a soft polymer matrix and magnetic fillers being powders of Fe, Ni, and the Fe–Nd–B alloy. Under the influence of the field with a value of 300 mT, the elastomer exhibited the magnetoresistive effect: The specific electric resistivity of the material was noticed to decrease by 3 orders. In addition, a significant dependency of the ability to conduct electric current was found on mechanical influence (piezoresistive effect) and combined influence of mechanical force and magnetic field. In the case considered, the behavior of the electroconductivity has a complex character.     

化学镀镍溶液渗透对多孔PTC陶瓷影响的机理研究

通过对比实验研究了化学镀镍溶液渗透对多孔ＰＴＣ陶瓷影响的机理。结果表明，这种影响是由溶液中的还原剂引起的，镀液中的其它物质的渗透对ＰＴＣ陶瓷的性能没有影响或者影响很小。提出了化学镀镍溶液中的还原剂对ＰＴＣ陶瓷的晶界产生还原从而影响ＰＴＣ效应的观点。化学镀镍溶液渗透造成的这种影响可以通过一定温度下的氧化热处理而消除。     

2.1 Metal-semiconductor junctions—related to deposition of thin films

The electrical properties of metal-semiconductor junctions are defined by the barrier height, by interface states, by interfacial layers and by doping and carrier lifetime of the semiconductor. Schottky contacts have a high barrier at the junction which the carriers have to surmount for current transport. Ohmic contacts require a low barrier or a low tunnelling resistance through the barrier.The surface preparation, the choice of the metal, the deposition technique and the post deposition treatment have an influence on the junction properties. The influence, however, is limited by surface states and is modified by the degree to which an interfacial layer is desired or to be eliminated.The heating of the semiconductor by the deposition process and the radiation damage when e-gun evaporation, sputtering or ion implantation is used, must be examined as to their influence on the junction. With most of the semiconductors a thermal treatment is part of the deposition process.     

Effect of deflecting ring on noise generated by outdoor set of a split-unit air conditioner

In order to analyze the influence of the deflecting ring on the noise generated by the outdoor set of a split-unit air conditioner, the flow field in the outdoor set is simulated with the CFD software STAR-CD, the relative turbulent intensities are computed and the influence of the width and contoured duct of the deflecting ring on the noise generated by the outdoor set is analyzed. The results of computation and experiment show that there is an optimal width of the deflecting ring, corresponding to the minimum noise generated by the outdoor set. In addition, the influence of the contoured duct of the deflecting ring on the noise generated by the outdoor set is analyzed and a double contoured duct is designed. The results of computation and experiment verify that the deflecting ring with double contoured duct can improve the aerodynamic performance and reduce the noise generated by the outdoor set.     

Rayleigh波作用下地下结构的动力反应分析

基于粘弹性人工边界提出了Rayleigh波的时域波动输入方法,在此基础上研究了Rayleigh波作用下地下隧道的动力反应特性,重点研究了埋深对结构动力反应的影响。结果表明提出的波动输入方法具有良好的模拟精度;Rayleigh波对浅埋地下结构的动力反应影响显著;存在临界埋深D0,当结构埋深D>D0时,随着埋深的增加,结构动力反应逐渐减小;当D相似文献   

充气薄膜对开敞空间气体爆炸试验的影响分析

为分析充气薄膜对开敞空间中可燃气体爆炸试验结果的影响,该文基于10 m半径的半球形氢气/空气混合气体的爆燃试验,采用AutoReaGas分析软件,建立精细化有限体积分析模型。计算结果与试验结果的对比分析表明,该文建立的有限体积模型能够较为真实地反映充气薄膜对气体爆燃过程的影响;试验中薄膜的破裂超压约为0.5 kPa~3 kPa。进一步分析了充气薄膜对1 m³、8 m³、125 m³和1000 m³的氢气/空气、乙炔/空气和甲烷/空气混合气体爆燃超压的影响。结果表明,充气薄膜对爆燃超压的影响随着气体体积、燃烧速度和传播距离的增加而减弱,并据此给出了不同气体爆炸试验中充气薄膜选择的建议。     

Influence of Acoustic Perturbation and Acoustically Induced Thermal Convection on Premixed Flame Propagation

Interference between an acoustic field and premixed flame is investigated. Two kinds of transport processes are considered to cause combustion promotion in the acoustic field. One is diffusive transport. It has long been considered that the acoustic oscillation promotes diffusion, like turbulence does. The other is convective transport. Acoustically induced thermal convection that is driven by a kind of acoustic radiation force in a standing acoustic field has been previously found (Tanabe et al., Proc Combust Inst 28:1007–1013, 2000). The burning rate of an isolated single droplet is promoted by this thermal convection. In this report, the influence of the acoustic oscillation on the premixed flame propagation was examined through experiment and numerical simulation. The gravitational force was not taken into account since it complicates the combustion phenomena. The experiment and numerical simulation were done in microgravity condition. Each influence of turbulent diffusion and thermal convection were evaluated from the burning velocity, flame shape and flame speed, since the diffusive effect has been considered to have an influence on the burning velocity, while the convective effect has an influence on the flame speed and flame shape. As a result, it was clarified that the diffusive effect has a minor influence on the burning enhancement of the premixed flame in the standing acoustic field. On the contrary, the acoustically induced thermal convection has a significant influence on it. Premixed flame behavior in the standing acoustic field can be explained through the characteristics of the acoustically induced thermal convection.     

流体绕流不同方向振动圆柱换热特性数值分析

基于Fluent动网格及UDF编程技术对二维流场中振动圆柱的换热特性进行了研究,分析了来流速度及圆柱振动方向对其换热特性的影响。数值计算结果表明,相比于静止圆柱换热,当圆柱的最大振动速度远大于来流速度时,其振动强化传热效果显著;随着流速的增大,振动圆柱的强化传热效果降低,当流速为圆柱最大振动速度的4倍时,圆柱传热效果仅增强1.2%。另外,对相等流速下的圆柱沿不同方向的振动换热特性研究表明,振动方向对圆柱强化换热的影响不显著。     

A study on the influence of cohesive zone interface element strength parameters on mixed mode behaviour

This paper presents a detailed study of the influence of maximum interfacial stress on interface element analyses for composites delamination. The development of the non-linear cohesive zone ahead of a crack tip is analysed with respect to length, stress distribution and mode ratio. The energy absorbed by interface elements is compared with the crack tip strain energy release rate from fracture mechanics analyses. These studies are performed initially on standard fracture toughness specimens, where mode-ratio is fixed by the applied displacement constraints. Results show close agreement with linear elastic fracture mechanics solutions. A simple ply drop specimen is then modelled, where the mode ratio is not constrained by the boundary conditions, and results are compared with the Virtual Crack Closure Technique. In this case maximum interfacial stress has a far greater influence on the numerical results, due to its significant influence on cohesive zone length, mode ratio and energy absorbed.     

Compositional influence on toughness of structural acrylic adhesives

The fracture behaviour and toughness of modified acrylic adhesives, based on mixtures of various acrylic monomers and rubbers polymerized by a radical mechanism have been investigated. The influence of the matrix and rubber composition on bulk morphology and mechanical properties is analysed by means of transmission and scanning electron microscopy, and dynamic-mechanical measurements. Both microtexture of the material and resin-rubber compatibility have been found to significantly influence the fracture behaviour in tension-impact tests.     

Structural influence on charge-carrier lifetimes in TiO2 powders studied by microwave absorption

A set-up for contactless transient photoconductivity measurements on powders by the Time Resolved Microwave Photoconductivity (TRMC) method has been realized. These measurements have been used as a tool for the investigation of excess charge-carrier lifetimes in TiO₂ (anatase and rutile) powders. The influence of laser wavelength and intensity on TRMC decay shows the importance of the fast-recombination processes. The presence of a long time tail in the TRMC signals of the anatase modification of TiO₂ is attributed to quenching of this recombination by hole-trapping at the surface. The influence of surface treatment by ethanol and water on TRMC decay evidences that dominant effects are bulk recombination in rutile and surface trapping in anatase. The influence of doping in rutile shows that increasing the doping rate accelerates the decay whatever the doping type is. The doping element acts as an impurity favoring recombination by creation of structural defects. The influence of thermal treatment in anatase shows that increasing the thermal treatment temperature increases the lifetimes. High crystalline quality leads to long charge-carrier lifetimes. The results are discussed in view of their relevance for photocatalysis.