Wireless Personal Communications special issue on Cellular and Wireless Location Based Technologies and Services

Wireless Personal Communications -     

Time-varying turbo codes

Turbo codes typically utilize time-invariant component codes whose total encoder memory is no greater than 4. In this letter, turbo codes with time-varying component codes are studied via EXIT analysis, distance spectrum analysis and simulation. Turbo codes with time-varying component codes and memory 6 are shown to have similar performance in the waterfall region and superior performance in the error floor region when compared to both the original memory 4 Berrou turbo code and the memory 8 big numerator-little denominator turbo codes.     

Increased response to antigen and histamine release in smaller sensitized canine bronchi

Presynaptic alpha 2-autoreceptors in mouse atria were characterized in terms of the alpha 2A, alpha 2B, alpha 2C and alpha 2D subtypes. Segments of the atria were preincubated with 3H-noradrenaline and then superfused and stimulated electrically. The affinity of up to 16 antagonists for the autoreceptors was assessed as (1) pEC30% values. i.e. concentrations that increased previously autoinhibited release of 3H-noradrenaline (120 pulses, 3 Hz) by 30%, and (2) pKd values against the release-inhibiting effect of 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK 14,304) under conditions of no or little autoinhibition (2 trains of 20 pulses, 50 Hz, train interval 120 s). The pKd values correlated well with the pEC30% values (r = 0.98; P < 0.001; slope of regression line 0.93), indicating that UK 14,304 and released noradrenaline modulated the release of noradrenaline through pharmacologically identical receptors. Comparison with antagonist affinities for (1) prototypic native alpha 2 radioligand binding sites, (2) radioligand binding sites in COS cells transfected with alpha 2 subtype genes, and (3) previously classified presynaptic alpha 2-autoreceptors-all taken from the literature-indicated that the mouse atrial autoreceptors corresponded to the alpha 2D subtype. For example, the pKd values at mouse atrial auto-receptors correlated closely with pKd values at native alpha 2D binding sites in the bovine pineal gland (r = 0.96; P < 0.001); with pKd values at alpha 2D binding sites in COS cells transfected with the rat alpha 2D gene (r = 0.85; P < 0.01); and with pKd values at guinea-pig cerebral and atrial and mouse cerebral alpha 2D-autoreceptors (r = 0.96-0.98; P < 0.001). The antagonist pKd values at mouse atrial autoreceptors correlated less with pKd values at alpha 2A, alpha 2B and alpha 2C sites. It is concluded that the presynaptic alpha 2-autoreceptors in mouse atria are alpha 2D. This identification supports the hypothesis that at least the majority of alpha 2-autoreceptors belong to the alpha 2A/D pair of orthologous alpha 2-adrenoceptors.     

Thermofluid-neutronic stability of the rotating, fluidized bed, space-power reactor

A rotating fluidized bed nuclear reactor has the potential of being a vary attractive option for ultra-high power space systems, especially for propulsion. Research has already examined fuel bed expansion due to variations in state variables, propellant flow rate, and rotational speed, and has also considered problems related to thermal stress. This paper describes the results of a coupled thermofluid-neutronic analysis where perturbations in fuel bed height caused by maneuvering changes in operating conditions alter power levels due to varying absorption of neutrons which would otherwise leak from the system, mainly through the nozzle. This first analysis was not a detailed stability analysis. Rather, it utilized simplified neutronic methods, and was intended to provide an order-of-magnitude assessment of the stability of the reactor with the intention to determine whether or not stability might be a “concept killer”.Stability was compared with a fixed-fuel-bed reactor of identical geometry for three different cases comprising a set of small, medium and large sizes/powers from 250 MW to 5 GW. It was found that power fluctuations in the fluidized bed reactor were larger by 100 db or more than expected in a packed bed reactor of the same geometry, but never resulted in power excursions. Margins to unit gain in some cases, however, were sufficiently small that the approximations in this quasi-2-dimensional model may not be sufficiently accurate to preclude significant excursions.     

Des vigiles invisibles: les administrateursréseaux et la sécurité informatique

The aim of this paper is to describe the activity of Network Administrators, in analyzing the ways used to manage the critical situations and alerts which punctuate the ordinary operations of computer networks. Our empirical material leads us to identify different kinds of risks and the manners to anticipate and manage them. To spot, qualify and make tangible, vulnerabilities, these professionals have to hold inquiries. Their works suffer a lack of gratitude from the other actors who conceive the network as a magical world running without human intervention. Administrators try to convince users of the need for some collective vigilance. By so doing, they hope their activities will be made visible and will appeal to a sense of responsibility towards technical devices. In this way, the Virtual has not killed the Real but, on the contrary, has given a has given a most important substance to it.     

Resolution depths for some transmitter-receiver configurations

Equivalent dipole polarizability matrices and equivalent dipole location are a convenient way to interpret magnetic field data due to currents induced in isolated conductive objects. The uncertainties in polarizability estimates and in the equivalent dipole location provide a quantitative measure of the performance of different configurations of transmitters and receivers. In another paper, we estimate these uncertainties using a linearized inversion. For many systems, consisting of one or more rectangular loop transmitters and a number of dipole receivers, sited on a horizontal grid, equivalent dipole depth is determined to 10% accuracy to depths approximately 20% deeper than the depths at which polarizability matrix elements can be determined to the same precision. Systems that have a lower product of rms polarizability uncertainty and square root of their number of transmitter-receiver pairs are considered more effective for the number of transmitter-receiver pairs. Among the systems studied, a system with three orthogonal transmitter loops and a three-component receiver is the most effective, for objects shallower than 0.6 times the instrument siting grid spacing, yielding an rms polarizability uncertainty 0.04 times that of a single-transmitter single-receiver system. At intermediate depths, a system with two vertical component receivers on the diagonal of a square horizontal transmitter loop is most effective for its number of transmitter-receiver pairs, yielding an rms polarizability uncertainty 0.07 times that of a single receiver system. At depths greater than 2.5 times, the siting grid spacing a three-orthogonal loop transmitter with a single vertical component receiver is about the most effective for its number of transmitter-receiver pairs, yielding an rms polarizability uncertainty 0.08 times that of a single-transmitter system.     

X-masking during logic BIST and its impact on defect coverage

We present a technique for making a circuit ready for logic built-in self test by masking unknown values at its outputs. In order to keep the silicon area cost low, some known bits in output responses are also allowed to be masked. These bits are selected based on a stuck-at n-detection based metric, such that the impact of masking on the defect coverage is minimal. An analysis based on a probabilistic model for resistive short defects indicates that the coverage loss for unmodeled defects is negligible for relatively low values of n.     

Femtosecond laser fabrication of Bragg gratings in borosilicate ion-exchange waveguides

Ultrafast 800-nm radiation from a Ti : sapphire amplifier was used to write high reflectivity Bragg gratings in silver ion-exchange waveguides made in a borosilicate glass substrate. The fabrication and visual/spectral characterization of the grating structures are presented. The measurements show low polarization effects in the grating spectral characteristics.