利用推迟势求解费曼的行移场问题

本文利用推迟势求解了费曼在其物理学讲义中提出的行移场问题,相比于一般的电磁辐射问题,推迟势解法在本问题中具有以下特点:推迟势积分运算简单,可得到精确解析解;物理思想清晰,推迟势公式中蕴含的“电磁作用以有限速度c传播”这一物理观念在求解过程中得以充分展现.

Study on the Flow Field around Two Parallel Moving Bubbles and Interaction Between Bubbles Rising in CMC Solutions by PIV

The flow fields surrounding two parallel moving bubbles rising from two identical orifices submerged in non-Newtonian fluid of carboxymethylcellulose （CMC） solution of three different mass concentration were measured experimentally by the use of particle image velocimetry （PIV）. The influences of gas flowrate, solution mass concentration, orifice interval and the angle between two bubble centers line and vertical direction on the flow field surrounding bubbles were discussed respectively by analyzing the velocity vector, velocity contours as well as individual velocity components. The results show that the liquid velocity both in front of two bubbles and behind increases with gas flowrate duo to shear-thinning effect of previous bubbles, whereas decreases with the increase of CMC concentration due to the increase of drag force acting on bubbles. The effect of the orifice interval on the flow field around two moving bubbles becomes gradually obvious as the interval becomes closer. Moreover, two adjacent side-by-side bubbles repulse each other during rising, leading to the practical interval between them increased somewhat above the orifice interval. When the distance between bubbles is less than the orifice interval 10 mm, the interaction between two neighboring bubbles changed from mutual repellence to attraction with the decrease of the angle of the line of linking two bubble centers to the vertical direction.

Logistic Model for Customer Dynamics in the Mobile Telecommunication Sector

Starting from the last decade of the 90＇s mobile phone makes its appearance in the world markets, in Mexico it＇s also on that date that the first companies are formed, today there are only four mobile companies that compete strongly for the Mexican market, In this article we use the logistic model （S - shaped logistic curve）, which describes competitive environments, especially for the popularization of new technologies, to describe the dynamics of the telecommunications sector in Mexico and the probability of the companies to fail and disappear in the market. In economic articles, we see more attention to the dynamics of monopolistic competition and power companies, but it is less used the study of the sales dynamics of the sector and the curves that represent it. The proposed model uses as data the total number of subscribers to mobile phone lines to generate the logistic curves of each company and the total market, in search of main points singularities and stability conditions as predictors of the extinction of technologies and the shot-down of companies in the sector.

Applying the Modified Perturbation Theory to High Energy Scattering in the Quasi-Potential Approach

Asymptotic behavior of the scattering amplitude for two scalar particles at high energy and fixed momentum transfer is reconsidered in quantum field theory. In the framework of the quasi-potential approach and the modified perturbation theory, a systematic scheme for finding the leading eikonal scattering amplitudes and its corrections are developed and constructed. The differential cross section is also discussed.

Dayside poleward moving auroral forms and ionospheric convection under stable interplanetary magnetic field (IMF) conditions

Using high temporal resolution optical data obtained from three-wavelength all-sky imagers over six winters continuously at Yellow River Station （78.92°N,11.93°E） in Arctic,we statistically investigated the dependence of location of poleward moving auroral forms （PMAFs） on the interplanetary magnetic field （IMF） B z and B y components as a function of MLT and MLAT under stable IMF conditions.It is found that more PMAFs occurred in lower latitude for Bz＆lt;0 and there was less evident IMF B y-related prenoon-postnoon asymmetry for Bz＆lt;0 than for Bz＆gt;0.We found that the PMAFs were distributed over a wide range of MLT when Bz＆lt;0,which indicates that the reconnection X-line might spread like an ’S’ shape.However,during northward IMF,PMAFs were observed predominantly prenoon for IMF By＆gt;0 and postnoon for IMF By＆lt;0 associating with the effect of the high-latitude reconnection,which is largely consistent with the theoretical model of the convection flow.

Computation of the Viscous Hydrodynamic Forces on a KVLCC2 Model Moving Obliquely in Shallow Water

The viscous hydrodynamic force and moment on ships moving obliquely in shallow water are important for ship navigation safety.In the paper,the viscous flow field around a KVLCC2 model moving obliquely in shallow water is simulated and the hydrodynamic drag,lateral force and yaw moment acting on the hull are obtained by a general purpose computational fluid dynamics(CFD) package FLUENT with shear-stress transport(SST) k—ωturbulence model.The numerical computation is performed at different drift angels and water depths.The numerical results are compared with experimental results,and a good agreement is demonstrated.