2,857 research outputs found

    Emotional enhancement of memory: how norepinephrine enables synaptic plasticity

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    Changes in synaptic strength are believed to underlie learning and memory. We explore the idea that norepinephrine is an essential modulator of memory through its ability to regulate synaptic mechanisms. Emotional arousal leads to activation of the locus coeruleus with the subsequent release of norepineprine in the brain, resulting in the enhancement of memory. Norepinephrine activates both pre- and post-synaptic adrenergic receptors at central synapses with different functional outcomes, depending on the expression pattern of these receptors in specific neural circuitries underlying distinct behavioral processes. We review the evidence for noradrenergic modulation of synaptic plasticity with consideration of how this may contribute to the mechanisms of learning and memory

    The ACS Nearby Galaxy Survey Treasury

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    The ACS Nearby Galaxy Survey Treasury (ANGST) is a systematic survey to establish a legacy of uniform multi-color photometry of resolved stars for a volume-limited sample of nearby galaxies (D<4 Mpc). The survey volume encompasses 69 galaxies in diverse environments, including close pairs, small & large groups, filaments, and truly isolated regions. The galaxies include a nearly complete range of morphological types spanning a factor of ~10^4 in luminosity and star formation rate. The survey data consists of images taken with ACS on HST, supplemented with archival data and new WFPC2 imaging taken after the failure of ACS. Survey images include wide field tilings covering the full radial extent of each galaxy, and single deep pointings in uncrowded regions of the most massive galaxies in the volume. The new wide field imaging in ANGST reaches median 50% completenesses of m_F475W=28.0 mag, m_F606W=27.3 mag, and m_F814W=27.3 mag, several magnitudes below the tip of the red giant branch (TRGB). The deep fields reach magnitudes sufficient to fully resolve the structure in the red clump. The resulting photometric catalogs are publicly accessible and contain over 34 million photometric measurements of >14 million stars. In this paper we present the details of the sample selection, imaging, data reduction, and the resulting photometric catalogs, along with an analysis of the photometric uncertainties (systematic and random), for both the ACS and WFPC2 imaging. We also present uniformly derived relative distances measured from the apparent magnitude of the TRGB.Comment: 54 pages, including 24 pages of figures and 16 pages of tables. Project website and data available at http://www.nearbygalaxies.org/ . Data is also available through MAST. Scheduled to appear in the Astrophysical Journal Supplements. (Replaced to fix several figures that were damaged during compression

    US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report

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    This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in Dark Matter" held at University of Maryland on March 23-25, 2017.Comment: 102 pages + reference

    Search for Branons at LEP

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    We search, in the context of extra-dimension scenarios, for the possible existence of brane fluctuations, called branons. Events with a single photon or a single Z-boson and missing energy and momentum collected with the L3 detector in e^+ e^- collisions at centre-of-mass energies sqrt{s}=189-209$ GeV are analysed. No excess over the Standard Model expectations is found and a lower limit at 95% confidence level of 103 GeV is derived for the mass of branons, for a scenario with small brane tensions. Alternatively, under the assumption of a light branon, brane tensions below 180 GeV are excluded

    Search for Charginos with a Small Mass Difference with the Lightest Supersymmetric Particle at \sqrt{s} = 189 GeV

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    A search for charginos nearly mass-degenerate with the lightest supersymmetric particle is performed using the 176 pb^-1 of data collected at 189 GeV in 1998 with the L3 detector. Mass differences between the chargino and the lightest supersymmetric particle below 4 GeV are considered. The presence of a high transverse momentum photon is required to single out the signal from the photon-photon interaction background. No evidence for charginos is found and upper limits on the cross section for chargino pair production are set. For the first time, in the case of heavy scalar leptons, chargino mass limits are obtained for any \tilde{\chi}^{+-}_1 - \tilde{\chi}^0_1 mass difference

    Dark sectors 2016 Workshop: community report

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    This report, based on the Dark Sectors workshop at SLAC in April 2016, summarizes the scientific importance of searches for dark sector dark matter and forces at masses beneath the weak-scale, the status of this broad international field, the important milestones motivating future exploration, and promising experimental opportunities to reach these milestones over the next 5-10 years

    Measurement of the Michel Parameters and the Average τ\tau-Neutrino Helicity from τ\tau Decays at LEP

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    Four of the Michel parameters and the average tau-neutrino helicity have been measured by analysing tau decay spectra in 147 \pb ~of data collected by the L3 detector. The decays \tte, ~\ttm, ~\ttp, ~\ttr ~and their charge conjugates were considered. The results: ρ=0.762±0.035\rho = 0.762 \pm 0.035, η=0.27±0.14\eta = 0.27 \pm 0.14, ξ=0.70±0.16\xi = 0.70 \pm 0.16, ξδ=0.70±0.11\xi\delta = 0.70 \pm0.11 and ξh=1.032±0.031\xi_{h} = -1.032 \pm 0.031 are consistent with a V-A structure for the weak charged current and lepton universality

    QCD studies in e+ee^{+}e^{-} annihilation from 30 GeV to 189 GeV

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    We present results obtained from a study of the structure of hadronic events recorded by the L3 detector at various centre-of-mass energies.The distributions of event shape variables and the energy dependence of their mean values are measured from 30 GeV to 189 GeV and compared with various QCD models. The energy dependence of the moments of event shape variables is used to test a power law ansatz for the non-perturbativecomponent. We obtain a universal value of the non-perturbative parameterα0\alpha_{0} = 0.537 ±\pm 0.073. From a comparison with resummedOαs2)\cal{O} \alpha_{\rm s}^{2}) QCD calculations, we determine thestrong coupling constant at each of the selected energies. The measurements demonstrate the running of αs\alpha_{\rm s} as expected in QCD with a value ofαs(mZ)\alpha_{\rm s} (m_{\rm Z}) = 0.1215 ±\pm 0.0012 (exp) ±\pm 0.0061 (th)

    Measurement of the Average Lifetime of b-Hadrons in Z Decays

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    We present a measurement of the average b-hadron lifetime τb{\rm \tau_b} at the e+e\mathrm{e^+e^-} \, collider LEP. Using hadronic Z decays collected in the period from 1991 to 1994, two independent analyses have been performed. In the first one, the b-decay position is reconstructed as a secondary vertex of hadronic b-decay particles. The second analysis is an updated measurement of τb{\rm \tau_b} using the impact parameter of leptons with high momentum and high transverse momentum. The combined result is \begin{center} τb=[1549±9(stat)±15(syst)]  fs{\rm \tau_b= [ 1549 \pm 9 \, (stat) \, \pm 15 \, (syst) ] \; fs \,} . \end{center} In addition, we measure the average charged b-decay multiplicity nb{\rm \langle n_{\rm b}} \rangle and the normalized average b-energy xEb{\rm \langle x_E \rangle_{\rm b}} at LEP to be \begin{center} nb=4.90±0.04 (stat)±0.11(syst){\rm \langle n_{\rm b} \rangle = 4.90 \pm 0.04 \ (stat) \pm 0.11 \, (syst)} , \end{center} \begin{center} xEb=0.709±0.004(stat+syst).{\rm \langle x_E \rangle_{\rm b} = 0.709 \pm 0.004 \, (stat + syst).} \end{center
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