A glutamate-sensitizing activity in conditioned media derived from rat cerebellar granule cells

When cerebellar granule cells that had been cultured in vitro for 8 days were subjected to a cytotoxic glutamate pulse (100 microM, 30 min incubation), the response varied according to cell density and the volume of medium in which cells were grown. Thus, lowering the cell density by a factor of 4 compared with usual conditions (2.6 x 10(5) cells/cm2) or increasing the volume by an identical 4-fold factor reduced cell death from 90-95% to 20-30%. Addition of a conditioned medium derived from high-density to low-density cultures or to high-volume cultures markedly increased the sensitivity of the cells to glutamate. This glutamate-sensitizing activity, which accelerated by several days the onset of the response of cerebellar cultures to glutamate, was inhibited by actinomycin D and was not detectable in conditioned medium derived from confluent cultures of cerebellar astroglia, or from cell lines such as PC12, GT1-7, 3T3 and CHP 100. Glutamate-sensitizing activity was not mimicked by trilodo-L-thyronine, insulin-like growth factor-I (IGF-I), truncated IGF-I, GPE [a tripeptide (gly-pro-glu) derived from IGF-I], brain-derived neurotrophic factor (BDNF), basic fibroblast growth factor or tumour necrosis factor-alpha. However, IGF-I added to cultures of granule cells plated at high density and grown in basal medium Eagle's without serum or any other constituent of chemically defined media was capable of supporting production of glutamate-sensitizing activity to an extent similar to that shown by whole fetal calf serum. Under the same conditions triiodo-L-thyronine and BDNF did not support the production of glutamate-sensitizing activity. Glutamate-sensitizing activity was not mimicked by glutamate, NMDA, glycine or lactate, and was not inhibited by glucose, haemoglobin or N-omega-nitro-L-arginine methyl ester. At variance with the response of granule cells, the response to glutamate of GABAergic cells present in the same culture was not affected by cell density or by glutamate-sensitizing activity.     

On resistor-induced thermal noise in linear circuits

In a previous correspondence, M. Vargas and R. Pallas-Areny [ibid., vol. 45, p. 345, 1996] showed that the thermal noise introduced by a resistor in any linear circuit will ultimately decrease with the value of the resistance R, to explain some paradoxical behavior on certain active circuits. Here it is shown how this result, although correct for every physical network, has some noticeable breakdowns for ideal networks and, consequently, in some limit conditions that are worthwhile considering. Moreover, with the same hypothesis needed for the theoretical correctness of the results, more general considerations are possible and have been investigated     

Remarks on models for prediction of radiated fields in electricaldischarge events

Ambiguities have appeared in the literature on the role of the arc in the electromagnetic radiation associated with electrostatic discharges. The authors discuss the contribution of the arc channel to the total emission and present experimental evidence that this contribution is negligible compared to that of the rest of the circuit     

Chip-level differential encoding/detection of spread-spectrumsignals for CDMA radio transmission over fading channels

This paper is concerned with the design and performance evaluation of a direct-sequence spread-spectrum transmission and signal-detection technique for application to code-division multiple-access mobile radio networks. Unlike the conventional differential encoding/detection of data symbols, such a technique envisages differential encoding/detection of the spreading code chips to counteract the fast time-selective fading encountered in mobile radio transmissions. Binary PSK modulation on a Rician frequency-flat-fading channel is assumed, with Gaussian and Rayleigh channels as particular cases. The bit-error rate performance of the receiver is analytically evaluated as a function of the relevant system parameters, and the impact on the receiver performance of a carrier frequency offset is also investigated     

Film formation and surface growth on tin electrodes in bicarbonate solutions: an impedance spectroscopy study

The electrochemical behaviour of potentiodynamically formed thin anodic films of polycrystalline tin in aqueous sodium bicarbonate solutions (pH ≈ 8.3) were studied using cyclic voltammetry and electrochemical impedance spectroscopy. Different equivalent circuits corresponding to various potential regions were employed to account for the electrochemical processes taking place under each condition.     

Simple carrier frequency rate-of-change estimators

This paper is concerned with the estimation of the rate-of-change of the instantaneous frequency of an unmodulated carrier. Such an issue arises, for instance, in satellite communication systems based on a low-Earth-orbit constellation, wherein the speed of each satellite relative to earth is rapidly time-varying, and consequently, the received carrier is affected by nonnegligible Doppler shift and Doppler rate. First, we present simple yet efficient estimators of the Doppler rate derived from maximum-likelihood estimation theory. Next, we investigate their performance in terms of bias and estimation error variance. Finally, we compare our variance results with the relevant modified Cramer-Rao bound     

Mobile and Personal Communications in the 60 GHz Band: A Survey

This paper intends to present a summary of the technical issues arising in the exploitation of the 60 GHz mm-wave band for mobile and personal communications. The most significant applications proposed so far are surveyed, with particular emphasis placed on recent experimentation about millimeter-wave propagation for road/railway transportation as well as indoor scenarios. As a case study, the capacity of a (micro-)cellular Code Division Multiple Access (CDMA) network in the 60-GHz band is also evaluated in detail.     

Echographic evaluation with image analysis of normal skin: variations according to age and sex

In order to identify and characterize the sonographic variations between different age groups, 48 subjects, 24 aged 27-30, and 24 over 60, were studied with a 20-MHz B scanner on six skin sites. Images were evaluated by the instrument's standard programme and by a new image analysis software package enabling the characterization of steady structures or transitory functional aspects of skin reactions, by highlighting areas in which the echo amplitudes are included within selected values, and by calculating their extension. Three bands were selected as intervals of interest, respectively, highlighting hyporeflecting parts of the dermis, tissue reflecting with intermediate amplitude values and hyperreflecting epidermis and dermis. This method was employed to assess skin thickness, demonstrating its decrease in elderly skin, to characterize and quantify the hypoechogenic subepidermal band appearing in the elderly at volar and dorsal forearm skin, and to evaluate echogenicity of the upper and lower dermis. Our data show that there is a great regional variation in the behaviour of ultrasound reflection of elderly skin in respect to the skin of young subjects. However, a general trend can be identified, consisting in a shift from low-intensity ultrasound echoes, characteristic in the dermis of young subjects, to intermediate or high reflection amplitudes, which are more frequent in elderly skin. Thus, the echographic method provides two parameters for the evaluation of skin aging.(ABSTRACT TRUNCATED AT 250 WORDS)     

High resolution silicon detectors for colliding beam physics

Resolution and linearity of the position measurement of Pisa multi-electrode silicon detectors are presented. The detectors are operated in slightly underdepleted mode and take advantage of their intrinsic resistivity for resistive charge partition between adjacent strips. 22 μm resolution is achieved with readout lines spaced 300 μm. Possible applications in colliding beam experiments for the detection of secondary vertices are discussed.