Effects of a magnetic field on the free convective flow through a porous medium bounded by an infinite vertical porous plate with constant heat flux

This paper investigates the effects of a magnetic field on the free convective flow of a viscous, incompressible, dissipative fluid through a porous medium, occupying a semi-infinite region of the space bounded by an infinite vertical and porous plate. The plate is subjected to a normal suction velocity and the heat flux at the plate is constant. The magnetic field is of uniform strength and is applied perpendicular to the plate. An analytical solution to the problem is obtained. The influence of the magnetic parameter (M) and permeability parameter (K) is discussed for the case of air (P = 0.71) when the plate is subjected to a constant suction velocity and is being cooled by free convection currents.     

Comparing firms’ triadic patent applications across countries: Is there a gap in terms of R&D effort or a gap in terms of performances?

This paper addresses the question of national differences as regard the number of triadic patents applied for by inventors from several OECD countries. The key idea is to determine whether such differences should be attributed to differences in R&D expenditures or rather to some other reasons, mainly institutional or behavioural ones. With this aim in view, both a macro-economic analysis, based on aggregate data for triadic patent counts and R&D expenditures and a micro-economic analysis based on firms’ data from three selected sectors are performed. In both cases, the methodological focus is made on the introduction, the definition and the estimation of a national index of relative efficiency in standard count data models. The main empirical findings are that there is a strong heterogeneity in terms of performance among European countries and a strong intra-country heterogeneity among sectors. This suggests that, in the field of innovation policies, there is a need for “tailored” solutions reflecting the specificities of each innovation system. Moreover, we show that European countries over-perform the United States in some high-tech sectors where the leadership of American firms is traditionally alleged, whereas European firms fail to keep up in more traditional sectors.     

Analysis of a differential magnetic amplifier with flux reset control

This paper describes in detail the theoretical operation and mathematical analysis of a differential magnetic amplifier circuit operating on the flux reset control principle.Experimental results verify the theoretical operation and the usefulness of the derived gain and output range equations. With the results of this investigation, it is possible to make intelligent use of a simple, yet extremely versatile magnetic amplifier circuit.     

Velocity field control of robot manipulators by using only position measurements

In the velocity field control approach the robot motions are specified through a vectorial function that assigns the desired velocity to each point of the configuration space. In other words, a velocity field defines the robot desired velocity in the operational space as a function of its current position. In this paper is introduced a new algorithm to solve the velocity field control formulation in the robot operational space. The proposed approach assumes only joint position measurements and is based on a hierarchical structure that results of using the kinematic control concept and a joint velocity controller. To estimate the joint velocity, nonlinear filtering of the joint position is used.     

磁场对液态金属粘度的影响

金属熔体的粘滞性是液态金属原子迁徙能力的一种表现,反映了原子间结合能力的大小。理论研究表明:在无磁场的条件下,随着温度的降低金属熔体的粘度增大;在磁场的条件下,金属熔体的粘度随着磁场强度的增加而增大。磁场对粘度的影响是洛伦兹力和磁化能的共同作用的结果。     

Total time for magnetic field penetration into a superconducting strip of type-I material

The field-induced transition of a flat strip of superconducting material is shown to proceed via two dynamically distinct stages. The dynamics of the first stage is well known; however, the existence of a second stage has not previously been recognized. It is shown that the second stage of the transition lasts at least as long as the first one when the applied field exceeds the critical field by about 90%. It is concluded that the second stage plays an important role even when moderate fields are used to induce the transition.     

Distinctive translational and self-rotational motion of lymphoma cells in an optically induced non-rotational alternating current electric field

In this paper, the translational motion and self-rotational behaviors of the Raji cells, a type of B-cell lymphoma cell, in an optically induced, non-rotational, electric field have been characterized by utilizing a digitally programmable and optically activated microfluidics chip with the assistance of an externally applied AC bias potential. The crossover frequency spectrum of the Raji cells was studied by observing the different linear translation responses of these cells to the positive and negative optically induced dielectrophoresis force generated by a projected light pattern. This digitally projected spot served as the virtual electrode to generate an axisymmetric and non-uniform electric field. Then, the membrane capacitance of the Raji cells could be directly measured. Furthermore, Raji cells under this condition also exhibited a self-rotation behavior. The repeatable and controlled self-rotation speeds of the Raji cells to the externally applied frequency and voltage were systematically investigated and characterized via computer-vision algorithms. The self-rotational speed of the Raji cells reached a maximum value at 60 kHz and demonstrated a quadratic relationship with respect to the applied voltage. Furthermore, optically projected patterns of four orthogonal electrodes were also employed as the virtual electrodes to manipulate the Raji cells. These results demonstrated that Raji cells located at the center of the four electrode pattern could not be self-rotated. Instead any Raji cells that deviated from this center area would also self-rotate. Most importantly, the Raji cells did not exhibit the self-rotational behavior after translating and rotating with respect to the center of any two adjacent electrodes. The spatial distributions of the electric field generated by the optically projected spot and the pattern of four electrodes were also modeled using a finite element numerical simulation. These simulations validated that the electric field distributions were non-uniform and non-rotational. Hence, the non-uniform electric field must play a key role in the self-rotation of the Raji cells. As a whole, this study elucidates an optoelectric-coupled microfluidics-based mechanism for cellular translation and self-rotation that can be used to extract the dielectric properties of the cells without using conventional metal-based microelectrodes. This technique may provide a simpler method for label-free identification of cancerous cells with many associated clinical applications.     

硫酸法钛白生产中磷元素的影响及工艺调控手段

论述硫酸法钛白生产中磷元素的影响以及对钛矿含磷量不同时在生产工艺方面的调节手段,达到稳定和提高产品质量的目的。