Yield stress and zeta potential of nanoparticulate silica dispersions under the influence of adsorbed hydrolysis products of metal ions--Cu(II), Al(III) and Th(IV)

The effects of hydrolysable Cu2+, Al3+ and Th4+ ions on the zeta potential and yield stress behaviour of silica dispersions were evaluated as a function of pH and metal ions concentration. Silica dispersion remained dispersed at its point of zero charge (pzc) of pH approximately 2.0 (CR1). Adsorbed hydrolysis products of Cu2+ and Al3+ caused the dispersion to display two further points of charge reversal (CR2 and CR3) at moderate ions concentration. CR2 occurred near the pH for the formation of the first hydrolysis product. This pH is about 2.8 for Al3+ and 5.0 for Cu2+. For all three metal ions, CR3 approached the pzc of the metal hydroxides at complete surface coverage. At CR3, the dispersions displayed a maximum yield stress. As many as three type of attractive forces; bridging, charged patch and van der Waals, may account for the maximum yield stress at low surface coverage. At complete coverage, only the van der Waals force is in play--the adsorbed hydrolysis products must have increased significantly the effective Hamaker constant of silica. With Al3+ the yield stress was absent at CR2 because particle bridging and charged patch attraction are unimportant as the silica surface charge is near zero. Adsorption of strongly hydrolysed Th4+ ions at pH<2.0 caused the dispersion to display only one pzc (CR3).     

A performance adequate computational model for auditory localization

A computational model of auditory localization resulting in performance similar to humans is reported. The model incorporates both the monaural and binaural cues available to a human for sound localization. Essential elements used in the simulation of the processes of auditory cue generation and encoding by the nervous system include measured head-related transfer functions (HRTFs), minimum audible field (MAF), and the Patterson-Holdsworth cochlear model. A two-layer feed-forward back-propagation artificial neural network (ANN) was trained to transform the localization cues to a two-dimensional map that gives the direction of the sound source. The model results were compared with (i) the localization performance of the human listener who provided the HRTFs for the model and (ii) the localization performance of a group of 19 other human listeners. The localization accuracy and front-back confusion error rates exhibited by the model were similar to both the single listener and the group results. This suggests that the simulation of the cue generation and extraction processes as well as the model parameters were reasonable approximations to the overall biological processes. The amplitude resolution of the monaural spectral cues was varied and the influence on the model's performance was determined. The model with 128 cochlear channels required an amplitude resolution of approximately 20 discrete levels for encoding the spectral cue to deliver similar localization performance to the group of human listeners.     

Photoaddition reactions of benzene and related compounds with thiochromone 1,1-dioxide

The photoaddition reactions of benzene and some simple derivatives with thiochromone 1,1-dioxide have been examined in an attempt to correlate the pattern of photochemical behavior with data on ionization potentials.     

Enhancement of the infrared detection efficiency of silicon photon-counting avalanche photodiodes by use of silicon germanium absorbing layers

An enhancement of the infrared detection efficiency of Si photon-counting detectors by inclusion of SiGe absorbing layers has been demonstrated for what is believed to be the first time. An improvement of 30 times in detection efficiency at a wavelength of 1210 nm compared with that of an all-Si structure operated under identical conditions has been measured. The Si/Si(0.7)Ge(0.3) device is capable of room-temperature operation and has a response time of less than 300 ps.     

Organometallic radical-initiated cleavage of the metal chelate and thiazole rings in a cyclopentadienylchromium complex

Extensive ring cleavage in the mercaptobenzothiazole chromium complex CpCr(CO)2(SCSN(C6H4)) (2), initiated by cyclopentadienyl chromium tricarbonyl, produced novel polynuclear complexes 3-5.