2,324 research outputs found

    Surface brightness measurements of supernova remanants in the energy band 0.15 - 4 keV and an XUV survey from an altitude controlled rocket

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    Reports are presented concerning the flight of Aerobee 170, 13.063 UG. The papers presented include: soft X-rays for Cygnus X-1 and Cygnus X-2; X-ray spectrum of the entire Cygnus loop; X-ray surface brightness of the Cygnus loop; and observations of He II 304 A and He I 584 a nightglow

    Receiver Architectures for MIMO-OFDM Based on a Combined VMP-SP Algorithm

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    Iterative information processing, either based on heuristics or analytical frameworks, has been shown to be a very powerful tool for the design of efficient, yet feasible, wireless receiver architectures. Within this context, algorithms performing message-passing on a probabilistic graph, such as the sum-product (SP) and variational message passing (VMP) algorithms, have become increasingly popular. In this contribution, we apply a combined VMP-SP message-passing technique to the design of receivers for MIMO-ODFM systems. The message-passing equations of the combined scheme can be obtained from the equations of the stationary points of a constrained region-based free energy approximation. When applied to a MIMO-OFDM probabilistic model, we obtain a generic receiver architecture performing iterative channel weight and noise precision estimation, equalization and data decoding. We show that this generic scheme can be particularized to a variety of different receiver structures, ranging from high-performance iterative structures to low complexity receivers. This allows for a flexible design of the signal processing specially tailored for the requirements of each specific application. The numerical assessment of our solutions, based on Monte Carlo simulations, corroborates the high performance of the proposed algorithms and their superiority to heuristic approaches

    Performance of single photon-counting X-ray charge coupled devices

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    Results of intial performance tests on X-ray sensing properties of charge-coupled devices (CCDs) are presented. CCDs have demonstrated excellent spatial resolution and good spectral resolution, superior to that of non-imaging proportional counters

    Resistive plate chambers for time-of-flight measurements

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    The applications of Resistive Plate Chambers (RPCs) have recently been extended by the development of counters with time resolution below 100 ps sigma for minimum ionising particles. Applications to HEP experiments have already taken place and many further applications are under study. In this work we address the operating principles of such counters along with some present challenges, with emphasis on counter aging.Comment: Presented at "PSD6 - 6th International Conference on Position Sensitive Detectors", 9-13 September 2002, Leicester, UK. Submitted to Nuclear Instruments and Methods

    INTEGRAL/IBIS search for e-e+ annihilation radiation from the Galactic Center Region

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    Electron-positron annihilation radiation from the Galactic Center region has been detected since the seventies, but its astrophysical origin is still a topic of a scientific debate. We have analyzed data of the gamma-ray imager IBIS/ISGRI onboard of ESA's INTEGRAL platform in the e−^{-}e+^{+} line. During the first year of the missions Galactic Center Deep Exposure no evidence for point sources at 511 keV has been found in the ISGRI data; the 2σ2 \sigma upper limit for resolved single point sources is estimated to be 1.6×10−4phcm−2s−11.6\times 10^{-4} ph cm^{-2} s^{-1}.Comment: 6 pages, 3 figures; Cospar 2004. To be published in: Advances in Space Researc

    CARIOCA: a fast binary front-end implemented in 0.25μ0.25\mu CMOS using a Novel current-mode technique for the LHCb muon detector

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    The CARIOCA front-end is an amplifier discriminator chip, using 0.25mm CMOS technology, developed with a very fast and low noise preamplifier. This prototype was designed to have input impedance below 10W. Measurements showed a peaking time of 14ns and noise of 450e- at zero input capacitance, with a noise slope of 37.4 e-/pF. The sensitivity of 8mV/fC remains almost unchanged up to a detector capacitance of 120pF

    Warning System Options for Landslide Risk: A Case Study in Upper Austria

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    This paper explores warning system options in the landslide-prone community of Gmunden/Gschliefgraben in Upper Austria. It describes stakeholder perspectives on the technical, social, economic, legal and institutional characteristics of a warning system. The perspectives differ on issues such as responsibility allocation in decisions regarding warnings, technologies used for monitoring and forecasting, costs and financial aspects, open data policies and the role of the residents. Drawing on the theory of plural rationality and based on a desk study and interviews, stakeholder perspectives and discourses on the warning system problem and its solution were elicited. The perspectives formed the basis for the specification of three technical policy options for a warning system in Gschliefgraben: a minimal-cost and cost-effective system; a technical-expert system; and a resident-centered system. The case demonstrates the importance of accounting for a plurality of values and preferences and of giving voice to competing discourses in communities contemplating warning systems or other public good policies. This paper concludes that understanding the different and often conflicting perspectives and technical policy options is the starting point for formulating an agreed compromise for an effective warning system. We describe the compromise solution in an accompanying paper included in this Special Issue

    On-Line AdaTron Learning of Unlearnable Rules

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    We study the on-line AdaTron learning of linearly non-separable rules by a simple perceptron. Training examples are provided by a perceptron with a non-monotonic transfer function which reduces to the usual monotonic relation in a certain limit. We find that, although the on-line AdaTron learning is a powerful algorithm for the learnable rule, it does not give the best possible generalization error for unlearnable problems. Optimization of the learning rate is shown to greatly improve the performance of the AdaTron algorithm, leading to the best possible generalization error for a wide range of the parameter which controls the shape of the transfer function.)Comment: RevTeX 17 pages, 8 figures, to appear in Phys.Rev.

    Reversible silencing of lumbar spinal interneurons unmasks a task-specific network for securing hindlimb alternation

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    Neural circuitry in the lumbar spinal cord governs two principal features of locomotion, rhythm and pattern, which reflect intra- and interlimb movement. These features are functionally organized into a hierarchy that precisely controls stepping in a stereotypic, speed-dependent fashion. Here, we show that a specific component of the locomotor pattern can be independently manipulated. Silencing spinal L2 interneurons that project to L5 selectively disrupts hindlimb alternation allowing a continuum of walking to hopping to emerge from the otherwise intact network. This perturbation, which is independent of speed and occurs spontaneously with each step, does not disrupt multi-joint movements or forelimb alternation, nor does it translate to a non-weight-bearing locomotor activity. Both the underlying rhythm and the usual relationship between speed and spatiotemporal characteristics of stepping persist. These data illustrate that hindlimb alternation can be manipulated independently from other core features of stepping, revealing a striking freedom in an otherwise precisely controlled system
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