12,317 research outputs found

    Single-particle and collective excitations in a charged Bose gas at finite temperature

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    The main focus of this work is on the predictions made by the dielectric formalism in regard to the relationship between single-particle and collective excitation spectra in a gas of point-like charged bosons at finite temperature TT below the critical region of Bose-Einstein condensation. Illustrative numerical results at weak coupling (rs=1r_s = 1) are presented within the Random Phase Approximation. We show that within this approach the single-particle spectrum forms a continuum extending from the transverse to the longitudinal plasma mode frequency and leading to a double-peak structure as TT increases, whereas the density fluctuation spectrum consists of a single broadening peak. We also discuss the momentum distribution and the superfluidity of the gas.Comment: 15 pages, 5 figure

    Numerical calculations of a high brilliance synchrotron source and on issues with characterizing strong radiation damping effects in non-linear Thomson/Compton backscattering experiments

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    A number of theoretical calculations have studied the effect of radiation reaction forces on radiation distributions in strong field counter-propagating electron beam-laser interactions, but could these effects - including quantum corrections - be observed in interactions with realistic bunches and focusing fields, as is hoped in a number of soon to be proposed experiments? We present numerical calculations of the angularly resolved radiation spectrum from an electron bunch with parameters similar to those produced in laser wakefield acceleration experiments, interacting with an intense, ultrashort laser pulse. For our parameters, the effects of radiation damping on the angular distribution and energy distribution of \emph{photons} is not easily discernible for a "realistic" moderate emittance electron beam. However, experiments using such a counter-propagating beam-laser geometry should be able to measure such effects using current laser systems through measurement of the \emph{electron beam} properties. In addition, the brilliance of this source is very high, with peak spectral brilliance exceeding 102910^{29} photons \,s−1^{-1}mm−2^{-2}mrad−2(0.1^{-2}(0.1% bandwidth)−1)^{-1} with approximately 2% efficiency and with a peak energy of 10 MeV.Comment: 11 figures, 11 page

    Using White Dish CMB Anisotropy Data to Probe Open and Flat-Lambda CDM Cosmogonies

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    We use data from the White Dish experiment to set limits on cosmic microwave background radiation anisotropies in open and spatially-flat-Lambda cold dark matter cosmogonies. We account for the White Dish calibration uncertainty, and marginalize over the offset and gradient removed from the data. Our 2-sigma upper limits are larger than those derived previously. These upper limits are consistent with those derived from the COBECOBE-DMR data for all models tested.Comment: 17 pages of latex. Uses aasms4.sty. 4 figures included. Submitted to ApJ

    First Results from SPARO: Evidence for Large-Scale Toroidal Magnetic Fields in the Galactic Center

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    We have observed the linear polarization of 450 micron continuum emission from the Galactic center, using a new polarimetric detector system that is operated on a 2 m telescope at the South Pole. The resulting polarization map extends ~ 170 pc along the Galactic plane and ~ 30 pc in Galactic latitude, and thus covers a significant fraction of the central molecular zone. Our map shows that this region is permeated by large-scale toroidal magnetic fields. We consider our results together with radio observations that show evidence for poloidal fields in the Galactic center, and with Faraday rotation observations. We compare all of these observations with the predictions of a magnetodynamic model for the Galactic center that was proposed in order to explain the Galactic Center Radio Lobe as a magnetically driven gas outflow. We conclude that the observations are basically consistent with the model.Comment: 11 pages, 2 figures, 1 table, submitted to ApJ Let

    FFTF Event Fact Sheet root cause analysis calendar year 1985 through 1988

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    The Event Fact Sheets written from January 1985 through mid August 1988 were reviewed to determine their root causes. The review group represented many of the technical disciplines present in plant operation. The review was initiated as an internal critique aimed at maximizing the ``lessons learned`` from the event reporting system. The root causes were subjected to a Pareto analysis to determine the significant causal factor groups. Recommendations for correction of the high frequency causal factors were then developed and presented to the FFTF Plant management. In general, the distributions of the causal factors were found to closely follow the industry averages. The impacts of the events were also studied and it was determined that we generally report events of a level of severity below that of the available studies. Therefore it is concluded that the recommendations for corrective action are ones to improve the overall quality of operations and not to correct significant operational deficiencies. 17 figs
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