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The unicasting mode is a natural choice in multi-relay systems to utilize the spatial potential of source and destination nodes. In the unicasting phase, the source node transmits different data streams to several relay nodes with the downlink multi-user precoding; in the multi-accessing phase, relay nodes transmit the received data streams to the destination node simultaneously. In this paper, the received signal-to-noise-ratio (SNR) at the destination node of the unicasting mode is analyzed and derived, which can be calculated with two SNRs related to the two phases as an approximate harmonic mean function. Then, an approximate method for calculating the system ergodic capacity is presented. The inner products between singular vectors are approximately replaced by their expectations and distribution functions of singular values are derived. The numerical and simulation results demonstrate the efficiency of the analysis and the approximate method. Copyright © 2010 John Wiley & Sons, Ltd. The received signal-to-noise-ratio (SNR) at the destination node of the unicasting mode in multi-relay systems is analyzed and derived, which can be calculated with two SNRs related to the two phases as an approximate harmonic mean function. Then, an approximate method for calculating the system ergodic capacity is presented. The inner products between singular vectors are approximately replaced by their expectations and distribution functions of singular values are derived. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The nature of core template has significant influences on the synthesis of hollow silica microspheres via the polystyrene (PS) beads templating route. Our present study indicates that the silica forming medium determines whether a surfactant is needed in the synthesis. It is shown that in a medium which itself gives discrete silica microspheres, hollow silica microspheres can only be templated by PS beads with the addition of cetyltrimethylammonium bromide surfactant. In contrast, in a medium which itself generates highly aggregated silica microspheres, hollow silica microspheres successfully templated by PS beads without any cationic surfactant. A unified mechanism for the formation of hollow silica shells with and without the surfactant is proposed. [ABSTRACT FROM AUTHOR]

Abstract: Cage-like hollow silica microspheres composed of mesoporous silica nanoparticles and macroporous interparticle voids were fabricated via the latex–surfactant dual templates route, simply by controlling the surfactant additions below its critical micelle concentration. The surface area, pore volume increase, and both the mesopore and macropore sizes decrease with the increase in surfactant amount. The surfactant cations preferentially assemble with negatively charged silica species generated by the hydrolysis and condensation of tetraethyl orthosilicate to form composite silica–surfactant nanoparticles. The electrostatic repulsion between the silica–surfactant composite nanoparticles and negatively charged polystyrene (PS) beads is smaller than that between surfactant–free silica and PS, favoring the deposition of composite nanoparticles on the surface of PS template. In the meantime, the deposited nanoparticles also have reduced repulsion from their neighbors, favoring their bridging to form silica shells. The more the surfactant is used, the less the repulsion exists among the composite particles and the smaller the interparticle macroporous voids are. [Copyright &y& Elsevier]