水泵吸水池不对称流动的自由液面测量试验

水泵吸水池内的流动状况严重影响着水泵的运行,特别是某些流动形式如不均匀流、流速梯度较大的剪切流等会导致水泵进水口各种旋涡的生成,甚至产生空化、振动现象,从而降低泵站效率。本文用2D-PIV系统对水泵吸水池的不对称流动进行了测量,通过图像处理技术的分析,得到了吸水池自由液面高度的平均分布,揭示了不对称流动等因素对吸水池内流动状况的影响。

中国股指期货日内不对称流动性调整VaR度量

本文在考虑买卖双方间不对称流动性及其不对称程度大小的基础上,计算买卖双方的流动性成本,对已有的流动性调整收益率方法进行扩展,提出日内不对称流动性调整VaR计算方法,并计算中国沪深300股指期货不同头寸下的不对称流动性调整VaR。研究结果表明,市场存在的不对称流动性及其程度大小会导致买卖双方面临不同流动性风险。相比传统VaR度量方法以及简单加总市场风险和流动性风险的方法等,不对称流动性调整VaR模型能更好地反映日内市场风险。

不对称流动对航道中航行船舶的影响(英文)

A modified Dawson's method that deals with asymmetric free-surface flow is applied to investigate the effect of the channel walls and water depth on the hydrodynamics of a ship running off the eenterline of a restricted waterway. The comparison of the numerical results with the experimental results shows that the method and the computer program are valid to predict the hydrodynamic forces and ship waves when the under keel clearance is not extremely small.The numerical results also demonstrate how the flow and pressure vary unsymmetriely on both sides of the ship and how the water depth and bank distance influence the hydrodynamic forces and ship waves.

中国股指期货市场的日内不对称波动性研究

股指期货市场由于频繁的交易,具有独特的日内波动性和流动性特征。通过构造日内超高频数据买方、卖方深度,买方、卖方发起比例,渴望度等流动性指标,从不对称流动性的角度对中国沪深300股指期货市场的日内不对称波动进行实证研究,并对比分析2015年9月期货交易新规前后市场波动性的变化。研究发现中国股指期货市场中,卖方发起交易和连续单向交易情况下的不对称流动性更加显著;股指期货市场存在日内不对称波动性,并且能够被日内不对称流动性所解释;期货新规实施导致流动性恶化,增加了日内不对称波动性。

微重力环境下的不对称内角流动研究

研究了用解析计算方法分析液体在线段和圆弧构成的不对称内角的流动.提出了等效内角的概念,把复杂的不对称内角模型转化为对称内角模型,并建立内角流动控制方程,对内角流动过程进行了计算.通过利用该方法,对带有外侧导流板的板式表面张力贮箱内的内角流动过程进行了分析.本文的工作将对板式表面张力贮箱的设计提供有益的参考.

Average Cycle Period in Asymmetrical Flashing Ratchet

The directed motion of a Brownian particle in a Bashing potential with various transition probabilities and waiting times in one of two states is studied. An expression for the average cycle period is proposed and the steady current J of the particle is calculated via Langevin simulation. The results show that the optimal cycle period (Tm), which takes the maximum of J, is shifted to a small value when the transition probability A from the potential on to the potential off decreases, the maximal current appears in the case of the average waiting time in the potential on being longer than in the potential off, and the direction of current depends on the ratio of the average times waiting in two states.

After-market liquidity and IPOs underpricing： Evidence from Shari＇ah and non Shari＇ah-based firms

The underpricing of initial public offerings （IPOs） is generally explained with asymmetric information and risk. We complement these traditional explanations with a new theory proposed by Ellul and Pagano （2006） where investors worry also about the after-market illiquidity that may result from asymmetric information after the IPO. The less liquid the after-market is expected to be, the larger will be the IPO underpricing. The samples are the 41 IPOs carried out between 2001-2005. The samples are 7 Shari＇ah-based firms and 34 non Shariah-based firms. Shariah-based firms are those included in Jakarta Islamic Index （JII）, at least one period （one semester）. Regression results show that the relationship between after-market liquidity and underpricing is insignificant unless we use trading frequency as proxy for liquidity for non Shariah-based firms.

Asymmetric breakup of a droplet in an axisymmetric extensional flow

The asymmetric breakups of a droplet in an axisymmetric cross-like microfluidic device are investigated by using a three-dimensional volume of fluid(VOF) multiphase numerical model. Two kinds of asymmetries(droplet location deviation from the symmetric geometry center and different flow rates at two symmetric outlets) generate asymmetric flow fields near the droplet, which results in the asymmetric breakup of the latter. Four typical breakup regimes(no breakup, one-side breakup, retraction breakup and direct breakup) have been observed.Two regime maps are plotted to describe the transition from one regime to another for the two types of different asymmetries, respectively. A power law model, which is based on the three critical factors(the capillary number,the asymmetry of flow fields and the initial volume ratio), is employed to predict the volume ratio of the two unequal daughter droplets generated in the direct breakup. The influences of capillary numbers and the asymmetries have been studied systematically in this paper. The larger the asymmetry is, the bigger the oneside breakup zone is. The larger the capillary number is, the more possible the breakup is in the direct breakup zone. When the radius of the initial droplet is 20 μm, the critical capillary numbers are 0.122, 0.128, 0.145,0.165, 0.192 and 0.226 for flow asymmetry factor AS= 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5, respectively, in the flow system whose asymmetry is generated by location deviations. In the flow system whose asymmetry is generated by two different flow rates at two outlets, the critical capillary numbers are 0.121, 0.133, 0.145, 0.156 and 0.167 for AS= 1/21, 3/23, 1/5, 7/27 and 9/29, respectively.

Mixed convective heat and mass transfer analysis for peristaltic transport in an asymmetric channel with Soret and Dufour effects

The present investigation addresses the simultaneous effects of heat and mass transfer in the mixed convection peristaltic flow of viscous fluid in an asymmetric channel. The channel walls exhibit the convective boundary conditions. In addition, the effects due to Soret and Dufour are taken into consideration. Resulting problems are solved for the series solutions. Numerical values of heat and mass transfer rates are displayed and studied. Results indicate that the concentration and temperature of the fluid increase whereas the mass transfer rate at the wall decreases with increase of the mass transfer Biot number. Furthermore, it is observed that the temperature decreases with the increase of the heat transfer Biot number.

基于格式塔心理学的手写识别及MatLab仿真

文章从格式塔心理学的角度提出了核函数的设计方法。该方法强调:数字不等于像素点的组合,主张从整体出发,理解每个像素部分。依据这个原理,本文对图像及像素进行了两项有创新的抽象和假设。此外,由于使用了独创的不对称流动核函数和"二次学习"算法并借鉴了图论的思想,此核有很强的适应能力,能自动调整自身以适应:识别阶段(粗识别和细识别阶段)、图像内容(如:识别1和9时核的形态不同)和图像质量(数字扭曲变形程度)。以上这些,解决了传统核方法在参数调整和核函数选择上的一些困难。本文从信息论、反馈和经验校正系数的角度分析了该核的优势,并使用MatLab对所提出的算法进行了测试。结果表明,识别率比普通方法有显著提高。

Control of the Asymmetric Flow in Rocket Nozzles

In some rocket nozzle flows, the existence of the transition from FSS to RSS and the occurrence of asymmetric flow are known in previous researches. As a result, the transition causes excessive side-loads that may damage the nozzle. Thus, it is important to investigate the method in order to control the asymmetric flow separation. In the present study, the relationship between the asymmetric separation and the rate of change of the pressure ratio with time was investigated from the point of view of the transition from FSS to RSS in the supersonic nozzle experimentally. Further, change of the flow separation by using step and cavity, and the possibility of the control was demonstrated. As a result, it was shown that the method using a cavity was effective for the control of the separation pattern.

Numerical Investigation of Pressure Distribution in a Low Specific Speed Centrifugal Pump

To study the pressure distribution of the volute casing, front casing and back casing in a prototype centrifugal pump, the pressure experiments and numerical simulations are carried out at six working conditions in this paper. The experimental results shows that the asymmetry of static pressure distribution on volute casing and front cavity is caused by the tongue of the volute and it may result in high radial and axial resultant force which can cause vibration and noise in the centrifugal pump. With the increasing of flow rote, the asymmetry of static pressure distribution and the magnitude of static pressure values reduce. The numerical results indicate that the pressure fluctuation near the tongue is strongest and it becomes slighter at point away from the tongue. With the increasing of flow rote, the local high=pressure region in impeller passage reduces and the flow becomes smoother accordingly, whereas the fluid speed becomes much higher which may cause further flow losses. The results predicted by numcrical simulation are in coincident with the experimental ones. It shows that the turbulence model for simulating the flow field in centrifugal pumps is feasible.

Convective heat transfer analysis for MHD peristaltic flow in an asymmetric channel

Magnetohydrodynamic peristaltic flow of Jeffery fluid in an asymmetric channel is addressed. The channel walls satisfy the convective conditions. Asymmetry here is con- sidered due to wave trains of different amplitudes and phases. Solutions for the velocity, temperature and pressure gradient are obtained using long wavelength approximation. Plots reflecting the impact of various parameters of interest are shown and examined.

Analytical solutions for MHD flow at a rectangular duct with unsymmetrical walls of arbitrary conductivity

For MHD flows in a rectangular duct with unsymmetrical walls, two analytical solutions have been obtained by solving the gov- erning equations in the liquid and in the walls coupled with the boundary conditions at fluid-wall interface. One solution of ＇Case I＇ is for MHD flows in a duct with side walls insulated and unsymmetrical Hartmann walls of arbitrary conductivity, and another one of ＇Case II＇ is for the flows with unsymmetrical side walls of arbitrary conductivity and Hartmann walls perfectly conductive. The walls are unsymmetrical with either the conductivity or the thickness different from each other. The solutions, which include three parts, well reveal the wall effects on MHD. The first part represents the contribution from insulated walls, the second part represents the contribution from the conductivity of the walls and the third part represents the contribution from the unsymmetri- cal walls. The solution is reduced to the Hunt＇s analytical solutions when the walls are symmetrical and thin enough. With wall thickness runs from 0 to co, there exist many solutions for a fixed conductance ratio. The unsymmetrical walls have great effects on velocity distribution. Unsymmetrical jets may form with a stronger one near the low conductive wall, which may introduce stronger MHD instability. The pressure gradient distributions as a function of Hartmann number are given, in which the wall effects on the distributions are well illustrated.

Peristaltic transport of a conducting Jeffrey fluid in an inclined asymmetric channel

Peristaltic flow of a conducting Jeffrey fluid in an inclined asymmetric channel is investigated. The channel asymmetry is produced by considering a peristaltic wave train on the flexible walls of the channel with different amplitudes and phases. The nonlinear governing equations are solved analytically by a perturbation technique. The expressions for the stream function, axial velocity and the pressure rise per wavelength are determined in terms of the Jeffrey number λ1, the Froude number Fr, the perturbation parameter 5, the angle of inclination θ and the phase difference Ф. Effects of the physical parameters on the velocity field and the pumping characteristics are discussed. It is observed that the size of the trapping bolus increase with an increase in the magnetic parameter and the volume flow rate. That is, the magnetic parameter and the volume flow rate have strong influence on the trapping bolus phenomenon.

Continuous-flow,one-pot synthesis of asymmetrical aromatic ureas from acids and amines via curtius rearrangement

In the present study,we described a continuous-flow,one-pot synthesis of asymmetrical ureas using nucleophilic addition reaction of amines to isocyanates derived from acids’Curtius rearrangement.The advantages of this method included broad substrate scope,high yields,rapid reaction,simplicity,extraordinary safety,and easy scale-up.

Hall effects on peristaltic flow of couple stress fluid in an inclined asymmetric channel

Effect of Hall current on peristaltic transport of couple stress fluid in an inclined asymmetric channel is investigated. An incompressible fluid is conducting in the pres- ence of inclined magnetic field. Problem formulation is developed through heat and mass transfer aspects. Soret and Dufour effects are present. Long wavelength and low Reynolds number approaches are adopted. Closed form expression for longitudinal velocity, pres- sure gradient, temperature and concentration are presented. Important results reflecting the influence of embedded parameters in the problems have been pointed out. Pumping and trapping phenomena are especially focused.

Peristaltic transport of a MHD Carreau fluid in a tapered asymmetric channel with permeable walls

The effect of permeable walls and magnetic field on the peristaltic flow of a Carreau fluid in a tapered asymmetric channel is studied. The tapered asymmetric channel is normally created due to the intra-uterine fluid flow induced by myometrial contractions and it was simulated by asymmetric peristaltic fluid flow in a two-dimensional infinite non-uniform channel. The analysis has been performed under long wavelength and low- Reynolds number assumptions to linearize the governing flow equations. A series solution in respect of a small Weissenberg number is obtained for the stream function, axial pressure gradient and shear stress. Time average of pressure rise and frictional force on the upper wall has also been computed using numerical integration. The results have been presented graphically for the various interested physical parameters. It is observed that for Carreau fluids the peristalsis works as a pump against a greater pressure rise compared with a Newtonian fluid, while there exists no significant difference in free pumping flux for Newtonian and Carreau fluids in the tapered asymmetric channel.