Boundary conditions for stokes flows near a porous membrane

A theoretical development is carried out to model the boundary conditions for Stokes flows near a porous membrane, which, in general, allows non-zero slip as well as normal flow at the surface. Two types of models are treated: an infinitesimally thin plate with a periodic array of circular apertures and a series of parallel slits. For Stokes flows, the mean normal flux and slip velocity are proportional to the pressure difference across the membrane and the average shear stress at the membrane, respectively. The appropriate proportionality constants which depend on the membrane geometry are calculated as functions of the porosity. An interesting feature of the results is that the slip at the membrane has, in general, a direction different from that of the applied shear for these models.     

ISTBC: A spectrally efficient distributed transmission scheme using incremental redundancy with space–time block coding

Cooperative communication is a promising paradigm that could address many of the challenges encountered in the development of future mobile communication systems. With multiple wirelessly communicating devices that cooperate with each other, a network of wireless nodes with virtual antenna arrays is created. This emulates a MIMO system and mimics most of its benefits. However bandwidth efficiency is a major issue in cooperative communication. Incremental-redundancy based techniques can be employed in cooperating nodes to minimize the bandwidth penalty but lacks error protection capability against unreliable decoding. Motivated by such shortcomings, a technique that combines the concept of incremental redundancy with space–time block coding (STBC) is proposed in this paper. The proposed scheme retains spatial diversity and bandwidth efficiency advantage offered by normal incremental redundancy based systems, in addition to offering guard against error propagation due to imperfect decoding at the relay. The theoretical framework is also developed to provide an understanding on the fundamental performance characteristics of the system. Two parameters such as Error Propagation Quotient (EPQ) and Spectral Efficiency Gain (SEG) are proposed to gauge the benefits offered by the proposed technique.     

Carbonyl addition reaction by means of β-silylphosphorous ylide. -diastereoselective vinylation of α-alkoxy aldehydes.

β-Silylphosphorous ylide reacts with α-alkoxy aldehydes to give exclusively vinylation product , with high -diastereoselectivity.     

Thermal analysis of micro heat pipes using a porous-medium model

Using Darcy's equation for two-phase flows in porous media and Laplace's capillary equation, a one-dimensional model of a micro heat pipe is developed to investigate its thermal and fluid-mechanical behaviors within its capillary limitation. The effects of various parameters are incorporated into the analysis. These parameters are: the capillary number, the charge level of the working fluid, the vapor-liquid viscosity ratio, contact angle, the relative lengths of the evaporator and condenser sections, the orientation of the micro heat pipe, and the Bond number. Furthermore, comparisons with existing experimental results show that the porous-medium model is reasonably adequate for the prediction of the capillary performance limit of a micro heat pipe. Received on 26 October 1998