109 research outputs found

    Steering efficiency of a ultrarelativistic proton beam in a thin bent crystal

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    Crystals with small thickness along the beam exhibit top performance for steering particle beams through planar channeling. For such crystals, the effect of nuclear dechanneling plays an important role because it affects their efficiency. We addressed the problem through experimental work carried out with 400 GeV/c protons at fixed-target facilities of CERN-SPS. The dependence of efficiency vs. curvature radius has been investigated and compared favourably to the results of modeling. A realistic estimate of the performance of a crystal designed for LHC energy including nuclear dechanneling has been achieved.Comment: 16 pages, 6 figure

    The AGILE Mission

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    AGILE is an Italian Space Agency mission dedicated to observing the gamma-ray Universe. The AGILE's very innovative instrumentation for the first time combines a gamma-ray imager (sensitive in the energy range 30 MeV-50 GeV), a hard X-ray imager (sensitive in the range 18-60 keV), a calorimeter (sensitive in the range 350 keV-100 MeV), and an anticoincidence system. AGILE was successfully launched on 2007 April 23 from the Indian base of Sriharikota and was inserted in an equatorial orbit with very low particle background. Aims. AGILE provides crucial data for the study of active galactic nuclei, gamma-ray bursts, pulsars, unidentified gamma-ray sources, galactic compact objects, supernova remnants, TeV sources, and fundamental physics by microsecond timing. Methods. An optimal sky angular positioning (reaching 0.1 degrees in gamma- rays and 1-2 arcmin in hard X-rays) and very large fields of view (2.5 sr and 1 sr, respectively) are obtained by the use of Silicon detectors integrated in a very compact instrument. Results. AGILE surveyed the gamma- ray sky and detected many Galactic and extragalactic sources during the first months of observations. Particular emphasis is given to multifrequency observation programs of extragalactic and galactic objects. Conclusions. AGILE is a successful high-energy gamma-ray mission that reached its nominal scientific performance. The AGILE Cycle-1 pointing program started on 2007 December 1, and is open to the international community through a Guest Observer Program

    Measurement of inclusive π0\pi^{0} production in hadronic Z0Z^{0} decays

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    An analysis is presented of inclusive \pi^0 production in Z^0 decays measured with the DELPHI detector. At low energies, \pi^0 decays are reconstructed by \linebreak using pairs of converted photons and combinations of converted photons and photons reconstructed in the barrel electromagnetic calorimeter (HPC). At high energies (up to x_p = 2 \cdot p_{\pi}/\sqrt{s} = 0.75) the excellent granularity of the HPC is exploited to search for two-photon substructures in single showers. The inclusive differential cross section is measured as a function of energy for {q\overline q} and {b \bar b} events. The number of \pi^0's per hadronic Z^0 event is N(\pi^0)/ Z_{had}^0 = 9.2 \pm 0.2 \mbox{(stat)} \pm 1.0 \mbox{(syst)} and for {b \bar b}~events the number of \pi^0's is {\mathrm N(\pi^0)/ b \overline b} = 10.1 \pm 0.4 \mbox{(stat)} \pm 1.1 \mbox{(syst)} . The ratio of the number of \pi^0's in b \overline b events to hadronic Z^0 events is less affected by the systematic errors and is found to be 1.09 \pm 0.05 \pm 0.01. The measured \pi^0 cross sections are compared with the predictions of different parton shower models. For hadronic events, the peak position in the \mathrm \xi_p = \ln(1/x_p) distribution is \xi_p^{\star} = 3.90^{+0.24}_{-0.14}. The average number of \pi^0's from the decay of primary \mathrm B hadrons is found to be {\mathrm N} (B \rightarrow \pi^0 \, X)/\mbox{B hadron} = 2.78 \pm 0.15 \mbox{(stat)} \pm 0.60 \mbox{(syst)}

    Search for Lepton Flavour Number violating Z0Z^0-Decays

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    A search for lepton flavour number violating Z0Z^0 decays in the channels \begin{center} Z0μτZ^0\rightarrow \mu\tau,\\ Z0eτZ^0\rightarrow e\tau, \\ Z0eμZ^0\rightarrow e\mu, \\ \end{center} using the DELPHI detector with data collected during the 1991--94 LEP runs, is described. No signal was found. Upper limits at 95\% confidence level for the respective branching fractions of 1.2×1051.2\times 10^{-5}, 2.2×1052.2\times 10^{-5}, and 0.25×1050.25\times 10^{-5}, were obtained

    The Influence of Political Connection and Institutions to the Performance and Bank Loans of Private Listed Companies

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    我国有着不同于西方发达国家的制度背景和政治制度,政府对市场的管制力度较大,上市公司的高管具有一定的政治背景,其中国有企业本身大股东的政府背景性质,其政治关联很可能是与生俱来的,而民营企业政治关联的形成则具有主动性。改革开放以来,民营经济不断发展壮大,己成为我国经济增长的主要推动力量,因此,研究政治关联对民营公司的影响这一问题在中国更具有现实启发意义。 本文以民营上市公司的高级管理人员是否是前任或现任的政府官员、人大代表或政协委员来衡量公司是否具有政治关联,选取2004年—2008年中国沪深两市所有A股民营上市公司为样本,实证研究了政治关联与制度环境对民营上市公司经营绩效和银行贷款的影响。研究...Chinese current institution and political system are different from the Western developed countries. Under this system, many executives of private listed companies are relevant to politics. Therefore the study of political influence of private companies related to this issue in China is more realistic instructive. This paper focuses on whether the company has the political connection, which measu...学位:管理学硕士院系专业:管理学院财务学系_财务学学号:1762007115174