Analog VLSI model of binaural hearing

The stereausis model of biological auditory processing is proposed as a representation that encodes both binaural and spectral information in a unified framework. A working analog VLSI chip that implements this model of early auditory processing in the brain is described. The chip is a 100000-transistor integrated circuit that computes the stereausis representation in real time, using continuous-time analog processing. The chip receives two audio inputs, representing sound entering the two ears, computes the stereausis representation, and generates output signals that can directly drive a color CRT display. Outputs from the chips for a variety of artificial and speech stimuli are shown.     

A Low-Power Wide-Dynamic-Range Analog VLSI Cochlea

Low-power wide-dynamic-range systems are extremely hard to build. The biological cochlea is one of the most awesome examples of such a system: It can sense sounds over 12 orders of magnitude in intensity, with an estimated power dissipation of only a few tens of microwatts. In this paper, we describe an analog electronic cochlea that processes sounds over 6 orders of magnitude in intensity, and that dissipates 0.5 mW. This 117-stage, 100 Hz to 10 KHz cochlea has the widest dynamic range of any artificial cochlea built to date. The wide dynamic range is attained through the use of a wide-linear-range transconductance amplifier, of a low-noise filter topology, of dynamic gain control (AGC) at each cochlear stage, and of an architecture that we refer to as overlapping cochlear cascades. The operation of the cochlea is made robust through the use of automatic offset-compensation circuitry. A BiCMOS circuit approach helps us to attain nearly scale-invariant behavior and good matching at all frequencies. The synthesis and analysis of our artificial cochlea yields insight into why the human cochlea uses an active traveling-wave mechanism to sense sounds, instead of using bandpass filters. The low power, wide dynamic range, and biological realism make our cochlea well suited as a front end for cochlear implants.     

Diffusion in gold and Au-Ag alloys

The self-diffusion coefficients of gold in pure gold and alloys of gold and silver have been measured over a range of temperatures. Chemical interdiffusion coefficients have been measured on pure metal and incremental couples, but are of lower accuracy because of the development of porosity. The results are compared with earlier work and internally on the basis of Darken’s equations.     

Autonomic correlates of attention-deficit/hyperactivity disorder and oppositional defiant disorder in preschool children.

Numerous studies have revealed autonomic underarousal in conduct-disordered adolescents and antisocial adults. It is unknown, however, whether similar autonomic markers are present in at-risk preschoolers. In this study, the authors compared autonomic profiles of 4- to 6-year-old children with attention-deficit/hyperactivity disorder (ADHD) and oppositional defiant disorder (ODD; n = 18) with those of age-matched controls (n = 20). Children with ADHD and ODD exhibited fewer electrodermal responses and lengthened cardiac preejection periods at baseline and during reward. Although group differences were not found in baseline respiratory sinus arrhythmia, heart rate changes among ADHD and ODD participants were mediated exclusively by parasympathetic withdrawal, with no independent sympathetic contribution. Heart rate changes among controls were mediated by both autonomic branches. These results suggest that at-risk preschoolers are autonomically similar to older externalizing children. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Applications drive VR interface selection

Physical interfaces to virtual environments fall into two broad categories: devices for navigation and physical interaction (such as deskbound and flying “mice”, gestural devices and navigation controls built into viewing devices); and viewing devices (such as head-mounted displays, counterbalanced displays, shutter glasses and a new class of immersive “desktop” viewers). The visual image is critical to creating an effective virtual experience. Beginning with immersive displays, this survey describes the range of available devices and discusses how application considerations affect the selection of components when configuring a virtual reality (VR) system     

Evaluation of toxicity indicators in rat primary astrocytes, C6 glioma and human 1321N1 astrocytoma cells: can gliotoxicity be distinguished from cytotoxicity?

A comparison was made of rat primary astrocytes, C6 glioma cells pre-treated with dibutyryl cyclic AMP, and the human astrocyte 132N1 cell line using a range of 40 compounds and the neutral red (NR) assay. The 40 chemicals included substances known to be toxic to astrocytes or neurons, to be generally cytotoxic or not thought to be toxic to nervous tissue. For those compounds which were toxic, changes in glial fibrillary acidic protein (GFAP) levels were measured in the primary and C6 cultures, and changes in vimentin and S-100 measured in the C6 cells. The number of compounds with EC50 values < 2000 microg/ml for the NR assay for the different cell cultures were as follows: primary astrocytes, 19; C6 cells, 15; and 1321N1 cells, 11. The log of the EC50 values for the NR assay for the test compounds between the three cell types was not significantly different at the 5% level by paired Student's t-test. For the toxic substances the correlation coefficients of the EC50 values between primary cells and the C6 or 1321N1 cells were r > 0.5, and between the C6 and 1321N1 cells r > 0.9. For GFAP there was a similar degree of correlation in EC50 values between the different cell types. The GFAP, vimentin and S-100 levels showed similar EC50 values for the toxicants, but were not as sensitive as the NR assay. The toxic substances caused altered morphology in the primary, C6 and 1321N1 cells, with increased branching of cell processes. The combined astrocyte systems identified 8 out of 9 substances reported to be toxic to astrocytes in vivo, together with substances which have general cytotoxic properties. A number of substances (including the 1 out of 9 reported gliotoxic substances), which may primarily affect neurons, which may affect nervous tissue after long-term exposure, or which are not thought to be toxic to nervous tissue, were not detected. The astrocyte systems positively identify gliotoxic and cytotoxic substances and will allow detailed mechanistic studies to be made on the different underlying mechanisms.     

The far infrared complex reflectivity of GaTe

The room temperature polarized complex (amplitude and phase) infra-red reflection spectra of single crystal monoclinic GaTe have been measured between 20 and 400 cm^?1 using a dispersive Fourier transform spectrometer. The measurements allow the experimental zone centre transverse and longitudinal phonon modes and optical constants to be determined without recourse to oscillator fit models or Kramers-Kronig analysis. Infrared power transmission measurements have allowed all fifteen predicted modes to be identified and the results are compared to recent Raman work.