11,320 research outputs found

    Finite Element Solution of Axisymmetrical Dynamic Problems of Shells of Revolution

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    Finite element solution for natural frequencies and mode shapes of free axisymmetrical vibrations and dynamic response of arbitrary rotationally symmetric shell

    Distributed Random Process for a Large-Scale Peer-to-Peer Lottery

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    Most online lotteries today fail to ensure the verifiability of the random process and rely on a trusted third party. This issue has received little attention since the emergence of distributed protocols like Bitcoin that demonstrated the potential of protocols with no trusted third party. We argue that the security requirements of online lotteries are similar to those of online voting, and propose a novel distributed online lottery protocol that applies techniques developed for voting applications to an existing lottery protocol. As a result, the protocol is scalable, provides efficient verification of the random process and does not rely on a trusted third party nor on assumptions of bounded computational resources. An early prototype confirms the feasibility of our approach

    Radiative spacetimes approaching the Vaidya metric

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    We analyze a class of exact type II solutions of the Robinson-Trautman family which contain pure radiation and (possibly) a cosmological constant. It is shown that these spacetimes exist for any sufficiently smooth initial data, and that they approach the spherically symmetric Vaidya-(anti-)de Sitter metric. We also investigate extensions of the metric, and we demonstrate that their order of smoothness is in general only finite. Some applications of the results are outlined.Comment: 12 pages, 3 figure

    Understanding Computer Forensics Requirements in China via the “Panda Burning Incense” Virus Case

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    In March 2012, Mainland China has amended its Criminal Procedure Law, which includes the introduction of a new type of evidence, i.e., digital evidence, to the court of law. To better understand the development of computer forensics and digital evidence in Mainland China, this paper discusses the Chinese legal system in relation to digital investigation and how the current legal requirements affect the existing legal and technical usage of digital evidence at legal proceedings. Through studying the famous “Panda Burning Incense (Worm.WhBoy.cw)” virus case that happened in 2007, this paper aims to provide a better understanding of how to properly conduct computer forensics examination and present digital evidence at court of law in Mainland China

    Star-Formation in the Ultraluminous Infrared Galaxy F00183-7111

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    We report the detection of molecular CO(1-0) gas in F00183-7111, one of the most extreme Ultra-Luminous Infrared Galaxies known, with the Australia Telescope Compact Array. We measure a redshift of 0.3292 for F00183-7111 from the CO(1-0) line and estimate the mass of the molecular gas in 00183 to be 1 ×\times 1010^{10} M_{\odot}. We find that F00183-7111 is predominately powered by the AGN and only \sim14 per cent of the total luminosity is contributed by star-formation (SFR \sim220 M_{\odot} yr1^{-1}). We also present an optical image of F00183-7111, which shows an extension to the East. We searched for star-formation in this extension using radio continuum observations but do not detect any. This suggests that the star-formation is likely to be predominately nuclear. These observations provide additional support for a model in which the radio emission from ULIRGs is powered by an intense burst of star-formation and by a radio-loud AGN embedded in its nucleus, both triggered by a merger of gas-rich galaxies.Comment: 5 pages, 2 figures, Accepted for publication in MNRAS Letters Accepted 2014 January 19. Received 2013 December 30; in original form 2013 November 2

    Macroscopic objects in quantum mechanics: A combinatorial approach

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    Why we do not see large macroscopic objects in entangled states? There are two ways to approach this question. The first is dynamic: the coupling of a large object to its environment cause any entanglement to decrease considerably. The second approach, which is discussed in this paper, puts the stress on the difficulty to observe a large scale entanglement. As the number of particles n grows we need an ever more precise knowledge of the state, and an ever more carefully designed experiment, in order to recognize entanglement. To develop this point we consider a family of observables, called witnesses, which are designed to detect entanglement. A witness W distinguishes all the separable (unentangled) states from some entangled states. If we normalize the witness W to satisfy |tr(W\rho)| \leq 1 for all separable states \rho, then the efficiency of W depends on the size of its maximal eigenvalue in absolute value; that is, its operator norm ||W||. It is known that there are witnesses on the space of n qbits for which ||W|| is exponential in n. However, we conjecture that for a large majority of n-qbit witnesses ||W|| \leq O(\sqrt{n logn}). Thus, in a non ideal measurement, which includes errors, the largest eigenvalue of a typical witness lies below the threshold of detection. We prove this conjecture for the family of extremal witnesses introduced by Werner and Wolf (Phys. Rev. A 64, 032112 (2001)).Comment: RevTeX, 14 pages, some additions to the published version: A second conjecture added, discussion expanded, and references adde

    Low-Power, High Data Rate Transceiver System for Implantable Prostheses

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    Wireless telemetry is crucial for long-term implantable neural recording systems. RF-encoded neurological signals often require high data-rates to transmit information from multiple electrodes with a sufficient sampling frequency and resolution. In this work, we quantify the effects of interferers and tissue attenuation on a wireless link for optimal design of future systems. The wireless link consists of an external receiver capable of demodulating FSK/OOK transmission at speeds up to 8 Mbps, with <1e-5 bit-error rate (BER) without error correction, and a fully implanted transmitter consuming about 1.05 mW. The external receiver is tested with the transmitter in vivo to show demodulation efficacy of the transcutaneous link at high data-rates. Transmitter/Receiver link BER is quantified in typical and controlled RF environments for ex vivo and in vivo performance

    Absence of Magnetism in Hcp Iron-Nickel at 11 K

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    Synchrotron Mössbauer spectroscopy (SMS) was performed on an hcp-phase alloy of composition Fe92Ni8 at a pressure of 21 GPa and a temperature of 11 K. Density functional theoretical calculations predict antiferromagnetism in both hcp Fe and hcp Fe-Ni. For hcp Fe, these calculations predict no hyperfine magnetic field, consistent with previous experiments. For hcp Fe-Ni, however, substantial hyperfine magnetic fields are predicted, but these were not observed in the SMS spectra. Two possible explanations are suggested. First, small but significant errors in the generalized gradient approximation density functional may lead to an erroneous prediction of magnetic order or of erroneous hyperfine magnetic fields in antiferromagnetic hcp Fe-Ni. Alternately, quantum fluctuations with periods much shorter than the lifetime of the nuclear excited state would prohibit the detection of moments by SMS
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