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The surface morphology of hollow silica microspheres has influence on their applications. After a thorough investigation of the deposition of silica nanoparticles on polystyrene (PS) beads and the surface morphology and texture of the resultant hollow silica shells with scanning electron microscopy, transmission electron microscopy, and N2-sorption measurements, the influence of surfactant [cetyltrimethylammonium bromide (CTAB)] concentration on the surface morphology of hollow silica microspheres templated by PS beads is explained. Previously, CTAB was believed to turn the surface charge of PS beads from negative into positive so that negatively charged silica could be deposited on the PS template. Here, we show CTA+ cations preferentially assemble with silica species to form silica-CTA+ composite nanoparticles. Since the zeta potential of silica-CTA+ composite nanoparticles is smaller than that of pure silica nanoparticles, these composite nanoparticles encounter less repulsion when they are deposited on the surface of PS beads and close to each other. As more CTAB is added, the silica-CTA+ nanoparticles are less negatively charged, and more compact and smooth hollow silica microspheres are obtained. [ABSTRACT FROM AUTHOR]

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]

A bis-bisurea receptor (L) based on the R,R-cyclohexane-1,2-diamino scaffold forms an uncommon 2 : 2 complex (1) with the monohydrogen phosphate ion (HPO(4)(2-)) and a 1 : 1 complex (2) with the sulfate ion (SO(4)(2-)). Solution binding properties of the two anions were studied by (1)H NMR, UV-vis, and circular dichroism (CD) methods.

A bis-trisurea ligand assembles with the tetraalkylammonium halides to form the flat 'stave' structures or 'barrels' that encapsulate multiple R(4)N(+) guests, depending on the size of the halide anion (Cl(-) or Br(-)) and the R(4)N(+) cation.