2,709 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

    Millimeter-wavelengths propagation studies Annual status report, Sep. 1, 1967 - Aug. 31, 1968

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    Millimeter wavelength propagation studies related to ATS-E communication transmission experimen

    Twitter and the US stock market: the influence of micro‑bloggers on share prices

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    With the increased interest in social media over recent years, the role of information disseminated through avenues such as Twitter has become more widely perceived. This paper examines the mention of stocks on the US markets (NYSE and NASDAQ) by a number of financial micro-bloggers to establish whether their posts are reflected in price movements. The Twitter feeds are selected from syndicated and nonsyndicated authors. A substantial number of tweets were linked to the price movements of the mentioned assets and an event study methodology was used to ascertain whether these mentions carry any significant information or whether they are merely noise

    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

    Learning and generation of long-range correlated sequences

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    We study the capability to learn and to generate long-range, power-law correlated sequences by a fully connected asymmetric network. The focus is set on the ability of neural networks to extract statistical features from a sequence. We demonstrate that the average power-law behavior is learnable, namely, the sequence generated by the trained network obeys the same statistical behavior. The interplay between a correlated weight matrix and the sequence generated by such a network is explored. A weight matrix with a power-law correlation function along the vertical direction, gives rise to a sequence with a similar statistical behavior.Comment: 5 pages, 3 figures, accepted for publication in Physical Review

    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

    The detection of single electrons by means of a Micromegas-covered MediPix2 pixel CMOS readout circuit

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    A small drift chamber was read out by means of a MediPix2 readout chip as direct anode. A Micromegas foil was placed 50 μ\mum above the chip, and electron multiplication occurred in the gap. With a He/Isobutane 80/20 mixture, gas multiplication factors up to tens of thousands were achieved, resulting in an efficiency for detecting single electrons of better than 90% . We recorded many frames containing 2D images with tracks from cosmic muons. Along these tracks, electron clusters were observed, as well as delta-rays.Comment: 15 pages, 9 included postscript figures, 5 separate jpeg figures, submitted to Nucl. Instr. and Meth. A. A complete postscript version with high resolution figures 1, 3, 11, 12 and 14 can be found at http://www.nikhef.nl/~i06/RandD/final/letter4.p

    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
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