A multielectrode array system has been developed to study how the retina processes and encodes visual images. This system can simultaneously record the extracellular electrical activity from hundreds of retinal output neurons as a dynamic visual image is focused on the input neurons. The retinal output signals detected can be correlated with the visual input to study the neural code used by the eye to send information about the visual world to the brain. The system consists of the following components: 1) a 32 16 rectangular array of 512 planar microelectrodes with a sensitive area of 1.7 mm2 ; the electrode spacing is 60 m and the electrode diameter is 5 m (hexagonal arrays with 519 electrodes are under development); 2) eight 64-channel custom-designed integrated circuits to platinize the electrodes and ac couple the signals; 3) eight 64-channel integrated circuits to amplify, band-pass filter, and analog multiplex the signals; 4) a data acquisition system; and 5) data processing software. This paper will describe the design of the system, the experimental and data analysis techniques, and some first results with live retina. The system is based on techniques and expertise acquired in the development of silicon microstrip detectors for high-energy physics experiments

Abstract. We present results of the monitoring of the black hole candidate 1E 1740.7-2942 with INTEGRAL, in combination with simultaneous observations by RXTE. We concentrate on broad-band spectra from INTEGRAL/IBIS and RXTE/PCA instruments. During our observations, the source spent most of its time in the canonical low/hard state with the measured flux variation within a factor of two. In 2003 September the flux started to decline and in 2004 February it was below the sensitivity level of the INTEGRAL and RXTE instruments. Notably, during the decline phase the spectrum changed, becoming soft and typical of black-hole binaries in the intermediate/soft state.

The Galactic Center black hole candidate (BHC) GRS 1758−258 has been observed extensively within INTEGRAL's Galactic Center Deep Exposure (GCDE) program in 2003 and 2004, while also being monitored with RXTE. We present quasi-simultaneous PCA, ISGRI, and SPI spectra from four GCDE observation epochs as well as the evolution of energy-resolved PCA and ISGRI light curves on time scales of days to months. We find that during the first epoch GRS 1758−258 displayed another of its peculiar dim soft states like the one observed in 2001, increasing the number of observed occurrences of this state to three. During the other epochs the source was in the hard state. The hard X-ray emission component in the epoch-summed spectra can be well described either by phenomenological models, namely a cutoff power law in the hard state and a pure power law in the dim soft state, or by thermal Comptonization models. A soft thermal component is clearly present in the dim soft state and might also contribute to the softer hard state spectra. We argue that in the recently emerging picture of the hardness-intensity evolution of black hole transient outbursts in which hard and soft states are observed to occur in a large overlapping range of luminosities (hysteresis), the dim soft state is not peculiar. As noted before for the 2001 dim soft state, these episodes seem to be triggered by a sudden decrease (within days) of the hard emission, with the soft spectral component decaying on a longer time scale (weeks). We discuss this behavior as well as additional flux changes observed in the light curves in terms of the existence of two accretion flows characterized by different accretion time scales, the model previously suggested for the 2001 episode.

Two multichannel Application Specific Integrated Circuits (ASICs) for extracellular recording of neuronal signals from live retinal tissues using microelectrode arrays have been developed. In this paper we discuss the requirements concerning the IC parameters and characteristics as well as present the designs and the test results. The required electronic functionality has been divided into two ASICs: PLAT-64 and NEURO-64 realized in a 0.7 µ µ µ µm CMOS process. The PLAT-64 chip comprises 64 capacitors of 150 pF each, and 64 addressable and controlled DC current sources for platinization of electrodes. The NEURO-64 chip comprises 64 channels of low noise amplifiers and bandpass filters and an analog multiplexer. The low noise performance of the preamplifier has been achieved by careful selection of a CMOS process and by proper sizing and biasing of the input devices. The required lower cut-off frequency of 20 Hz has been obtained by employing a novel RC filter structure. ).A. A. Grillo is with the UCSC, ). A. M. Litke is with the UCSC,