On the cascaded Weibull fading channel model

A new stochastic fading channel model called cascaded Weibull fading is introduced and the associated capacity is derived in closed form. This model is generated by the product of independent, but not necessarily identically distributed, Weibull random variables (RVs). By quantifying the convergence rate of the central limit theorem as pertaining to the multiplication of Weibull distributed RVs, the statistical basis of the lognormal distribution is investigated. By performing Kolmogorov-Smirnov tests, the null hypothesis for this product to be approximated by the lognormal distribution is studied. Another null hypothesis is also examined for this product to be approximated by a Weibull distribution with properly adjusted statistical parameters.     

Maiden voyage of a novel research ship

Shiyan-1, a new research vessel of CAS, recently accomplished its first official journey in South China Sea. CAS leaders, including CAS President LU Yongxiang and CAS Vice President JIANG Mianheng, were present at the ceremony marking its maiden voyage held on 9 May in Sanya City, south China＇s Hainan Province.     

On metrics matched to the discrete memoryless channel

A sequence of metrics {D_N} is said to be additive and matched to a discrete memoryless channel (DMC) if D_N is the sum on its coordinates of N single letter metrics and if the maximum likelihood decoder for sequences of length N is a minimum D_N-distance decoder. Necessary and sufficient conditions on the transition probabilities of a DMC for the existence of a sequence of additive metrics matched to it are given. In the case of the binary channel these are shown to be equivalent to the channel being symmetric. Explicit transition probabilities are given for a large class of ternary DMCs with an associated sequence of additive matched metrics. The problem solved here may be considered a generalization of the problem of finding the DMCs matched to the Lee metric solved by Chiang and Wolf in 1971 (2).     

Mary Somerville: a scientist and her ship

Mary Somerville enjoyed posing for busts and portraits, yet just as in her autobiography, she chose how she wished to be seen. A powerful advocate for scientific progress, Somerville gave her name to a ship that carried British products around the world, and portrayed herself as an ideal role model for women and also an exemplar of European civilisation.     

跨区域流域生态补偿府际间协调机制研究

处理好流域流经各地政府间的利益均衡问题,是我国流域生态补偿研究和实践中的重点.从博弈论的角度探讨了流域生态补偿中流域上下游地方政府与上级政府间的行为和利益问题,建立了跨区域流域生态补偿府际间三方博弈模型.分析表明:跨区域流域生态补偿需要流域上下游地方政府和上级政府的共同参与,并以确保上游地方政府收益为手段推动流域生态补偿全局;上级政府通过建立健全流域生态补偿的准市场机制,使流域上游地方政府的保护行为和下游地方政府的补偿行为成为府际间三方博弈的长期稳定均衡.最后,还对建立流域生态补偿的准市场机制提出了建议.     

Heat transfer in a dipolar flow through a porous channel

The theory of constitutive equations for dipolar fluids, obtained by Bleustein and Green, is applied to investigate the Couette and Poiseuille flows between parallel plates maintained at constant but different temperatures in addition to being subjected to uniform injection and suction. Explicit expressions for the velocity and the temperature fields are obtained. It is found that different sets of conditions imposed on the flow parameters lead to different expressions for the velocity distribution which are valid only for restricted ranges of the cross-flow Reynolds number R. A table showing the various conditions imposed on the parameters, the corresponding solutions and the ranges of R for which the solution exist is presented. Velocity and temperature profiles for the dipolar and the Newtonian flows are drawn and compared to bring out the important differences resulting from the variations in R and B, the Brinkman number. For the dipolar Couette flow it is found that the value of B at which a transition from cooling to heating of the suction wall occurs always exceeds its corresponding value for Newtonian flow. Tables comparing the rates of heat transfer at the walls are provided for several values of R and B.     

Effect of a dual inlet channel on cell loading in microfluidics

Unwanted sedimentation and attachment of a number of cells onto the bottom channel often occur on relatively large-scale inlets of conventional microfluidic channels as a result of gravity and fluid shear. Phenomena such as sedimentation have become recognized problems that can be overcome by performing microfluidic experiments properly, such as by calculating a meaningful output efficiency with respect to real input. Here, we present a dual-inlet design method for reducing cell loss at the inlet of channels by adding a new “ upstream inlet ” to a single main inlet design. The simple addition of an upstream inlet can create a vertically layered sheath flow prior to the main inlet for cell loading. The bottom layer flow plays a critical role in preventing the cells from attaching to the bottom of the channel entrance, resulting in a low possibility of cell sedimentation at the main channel entrance. To provide proof-of-concept validation, we applied our design to a microfabricated flow cytometer system (μFCS) and compared the cell counting efficiency of the proposed μFCS with that of the previous single-inlet μFCS and conventional FCS. We used human white blood cells and fluorescent microspheres to quantitatively evaluate the rate of cell sedimentation in the main inlet and to measure fluorescence sensitivity at the detection zone of the flow cytometer microchip. Generating a sheath flow as the bottom layer was meaningfully used to reduce the depth of field as well as the relative deviation of targets in the z-direction (compared to the x-y flow plane), leading to an increased counting sensitivity of fluorescent detection signals. Counting results using fluorescent microspheres showed both a 40% reduction in the rate of sedimentation and a 2-fold higher sensitivity in comparison with the single-inlet μFCS. The results of CD4⁺ T-cell counting also showed that the proposed design results in a 25% decrease in the rate of cell sedimentation and a 28% increase in sensitivity when compared to the single-inlet μFCS. This method is simple and easy to use in design, yet requires no additional time or cost in fabrication. Furthermore, we expect that this approach could potentially be helpful for calculating exact cell loading and counting efficiency for a small input number of cells, such as primary cells and rare cells, in microfluidic channel applications.     

Mixing enhancement in microfluidic channel with a constriction under periodic electro-osmotic flow

We present a new approach to enhance mixing in T-type micromixers by introducing a constriction in the microchannel under periodic electro-osmotic flow. Two sinusoidal ac electric fields with 180° phase difference and similar dc bias are applied at the two inlets. The out of phase ac electric field induces oscillation of fluid interface at the junction of the two inlet channels and the constriction. Due to the constriction introduced at the junction, fluids from these two inlets form alternative plugs at the constricted channel. These plugs of fluids radiate downstream from the constriction into the large channel and form alternate thin crescent-shaped layers of fluids. These crescent-shaped layers of fluids increase tremendously the contact surface area between the two streams of fluid and thus enhance significantly the mixing efficiency. Experimental results and mixing mechanism analysis show that amplitude and frequency of the ac electric field and the length of the constriction govern the mixing efficiency.     

Density-dependent separation of encapsulated cells in a microfluidic channel by using a standing surface acoustic wave

This study presents a method for density-based separation of monodisperse encapsulated cells using a standing surface acoustic wave (SSAW) in a microchannel. Even though monodisperse polymer beads can be generated by the state-of-the-art technology in microfluidics, the quantity of encapsulated cells cannot be controlled precisely. In the present study, mono-disperse alginate beads in a laminar flow can be separated based on their density using acoustophoresis. A mixture of beads of equal sizes but dissimilar densities was hydrodynamically focused at the entrance and then actively driven toward the sidewalls by a SSAW. The lateral displacement of a bead is proportional to the density of the bead, i.e., the number of encapsulated cells in an alginate bead. Under optimized conditions, the recovery rate of a target bead group (large-cell-quantity alginate beads) reached up to 97% at a rate of 2300 beads per minute. A cell viability test also confirmed that the encapsulated cells were hardly damaged by the acoustic force. Moreover, cell-encapsulating beads that were cultured for 1 day were separated in a similar manner. In conclusion, this study demonstrated that a SSAW can successfully separate monodisperse particles by their density. With the present technique for separating cell-encapsulating beads, the current cell engineering technology can be significantly advanced.