96,235 research outputs found

    Measurements of alpha_s from hadronic event shapes in e+e- annihilation

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    New studies of hadronic event shape observables in e+ e- collisions between 13 and 183 GeV CM energy have enabled the running of alpha_s to be confirmed and the validity of non-perturbative power-law corrections to be investigated. A more precise value of alpha_s(M_Z) with reduced theoretical errors has been reported from fitting 18 oriented event shape distributions measured in one experiment at the Z.Comment: 3 pages, 2 figures, ICHEP Vancouver, Canada, 199

    The Supernova-Gamma Ray Burst Connection

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    Supernovae 1998bw and its corresponding relativistically expanding radio source are coincident with the \grb source GRB 980425. We show that of six recent SN Ib/c for which an outburst epoch can be estimated with some reliability, four have radio outbursts and all are correlated in time and space with BATSE \grbs. The joint probability of all six correlations is 1.5×105\times10^{-5}. No such correlation exists for SN Ia and SN II. The \gr\ energy associated with the SN/GRB events is 10461048\sim10^{46} - 10^{48} ergs if emitted isotropically. Economy of hypotheses leads us to propose that all \grbs are associated with supernovae and that the \grb events have a quasi-isotropic component that cannot be observed at cosmological distances and a strongly collimated and Doppler-boosted component that can only be seen if looking nearly along the collimation axis. Such collimation requires a high rate of occurrence perhaps consistent with a supernova rate. The collimated flow may be generated by core collapse to produce rotating, magnetized neutron stars. All core collapse events may produce such jets, but only the ones that occur in supernovae with small or missing hydrogen envelopes, Type Ib or Ic, can propagate into the interstellar medium and yield a visible \grb. We suggest that asymmetries in line profiles and spectropolarimetry of SN II and SN Ib/c, pulsar runaway velocities, soft \gr repeaters and \grbs are associated phenomena.Comment: Submitted to ApJL on May 19, 1998. Revised on Jun 15, 199

    Performance of transducers with segmented piezoelectric stacks using materials with high electromechanical coupling coefficient

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    Underwater acoustic transducers often include a stack of thickness polarized piezoelectric material pieces of alternating polarity interspersed with electrodes, bonded together and electrically connected in parallel. The stack is normally much shorter than a quarter wavelength at the fundamental resonance frequency, so that the mechanical behavior of the transducer is not affected by the segmentation. When the transducer bandwidth is less than a half octave, as has conventionally been the case, stack segmentation has no significant effect on the mechanical behavior of the device. However, when a high coupling coefficient material such as PMN-PT is used to achieve a wider bandwidth, the difference between a segmented stack and a similar piezoelectric section with electrodes only at the two ends can be significant. This paper investigates the effects of stack segmentation on the performance of wideband underwater acoustic transducers, particularly tonpilz transducer elements. Included is discussion of transducer designs using single crystal piezoelectric material with high coupling coefficient compared with more traditional PZT ceramics.Comment: 26 pages including 14 figures, one table and one appendi

    Oregon Wine Board Meeting Minutes September 11, 2012

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    These meeting minutes list individuals in attendance and missing at the September 11, 2012 Oregon Wine Board (OWB) meeting, held via conference call. Dewey Weddington provided a marketing update focused on planning for Oregon Wine Month and the Oregon Wine Industry Symposium. The meeting also included discussion of the 2011-2012 year-end financial review and a presentation of the budget for the following year. The meeting lasted 2 hours 6 minutes, and the Board went into Executive Session after the meeting was adjourned

    Sampling strategies and four-dimensional assimilation of altimetric data for ocean monitoring and prediction

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    Numerical experiments using simulated altimeter data were conducted in order to examine the assimilation of altimeter-derived sea surface heights into numerical ocean circulation models. A reduced-gravity, primitive equation circulation model of the Gulf of Mexico was utilized; the Gulf of Mexico was chosen because of its amenability to modeling and the ability of low vertical-mode models to reproduce the observed dynamical features of the Gulf circulation. The simulated data were obtained by flying an imaginary altimeter over the model ocean and sampling the model sea surface just as real altimeter would observe the true ocean. The data were used to initialize the numerical model and the subsequent forecast was compared to the true numerical solution. Results indicate that for a stationary, circular eddy, approximately three to four tracks (either ascending or descending) across the eddy are sufficient to ensure adequate spatial resolution

    Beyond the hybrid library : libraries in a Web 2.0 world

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    Considers the development of social networking and the concept of Web 2.0. Looks at the implications for libraries and how traditional competences remain relevant. Explores what libraries are doing and must do to remain relevan

    SGR 1806-20 Is a Set of Independent Relaxation Systems

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    The Soft Gamma Repeater 1806-20 produced patterns of bursts during its 1983 outburst that indicate multiple independent energy accumulation sites, each driven by a continuous power source, with sudden, incomplete releases of the accumulated energy. The strengths of the power sources and their durations of activity vary over several orders of magnitude.Comment: Accepted ApJLett, 15 pages, 3 figure
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