14,602 research outputs found

    Future Spin Physics at JLab; 12 GeV and Beyond

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    The project to upgrade the CEBAF accelerator at Jefferson Lab to 12 GeV is presented. Most of the research program supporting that upgrade, will require a highly polarized beam, as will be illustrated by a few selected examples. To carry out that research program will require an extensively upgraded instrumentation in two of the existing experimental halls and the addition of a fourth hall. The plans for a high-luminosity electron-ion collider are briefly discussed.Comment: 6 pages; 2 figures; submitted to the Proceedings of SPIN200

    Nucleon Electromagnetic Form Factors

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    A review of data on the nucleon electromagnetic form factors in the space-like region is presented. Recent results from experiments using polarized beams and polarized targets or nucleon recoil polarimeters have yielded a significant improvement on the precision of the data obtained with the traditional Rosenbluth separation. Future plans for extended measurements are outlined.Comment: 12 pages, 6 figures, Talk presented at the Bates25 Symposiu

    Nucleon Form Factor Experiments and the Pion Cloud

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    The experimental and theoretical status of elastic electron scattering from the nucleon is reviewed. A wealth of new data of unprecedented precision, especially at small values of the momentum transfer, in parallel to new theoretical insights, has allowed sensitive tests of the influence of the pionic cloud surrounding the nucleon.Comment: 9 pages; 4 figures; submitted to the Proceedings of the Shape of the Nucleo

    On the origin of the Korteweg-de Vries equation

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    The Korteweg-de Vries equation has a central place in a model for waves on shallow water and it is an example of the propagation of weakly dispersive and weakly nonlinear waves. Its history spans a period of about sixty years, starting with experiments of Scott Russell in 1834, followed by theoretical investigations of, among others, Lord Rayleigh and Boussinesq in 1871 and, finally, Korteweg and De Vries in 1895. In this essay we compare the work of Boussinesq and Korteweg-de Vries, stressing essential differences and some interesting connections. Although there exist a number of articles, reviewing the origin and birth of the Korteweg-de Vries equations, connections and differences, not generally known, are reported.Comment: minor corrections; 25 pages, 3 figure

    Estimating the birth period of pulsars through GLAST/LAT observations of their wind nebulae

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    In this paper we show that the high energy γ\gamma-ray flux in the GeV domain from mature pulsar wind nebulae (PWN) scales as the change in rotational kinetic energy I(Ω02Ω2)/2I(\Omega_0^2-\Omega^2)/2 since birth, rather than the present day spindown power IΩΩ˙I\Omega\dot{\Omega}. This finding holds as long as the lifetime of inverse Compton emitting electrons exceeds the age of the system. For a typical γ2\gamma^{-2} electron spectrum, the predicted flux depends mostly on the pulsar birth period, conversion efficiency of spindown power to relativistic electrons and distance to the PWN, so that first order estimates of the birth period can be assessed from {\it GLAST/LAT} observations of PWN. For this purpose we derive an analytical expression. The associated (``uncooled'') photon spectral index in the GeV domain is expected to cluster around 1.5\sim 1.5, which is bounded at low energies by an intrinsic spectral break, and at higher energies by a second spectral break where the photon index steepens to 2\sim 2 due to radiation losses. Mature PWN are expected to have expanded to sizes larger than currently known PWN, resulting in relatively low magnetic energy densities and hence survival of GeV inverse Compton emitting electrons. Whereas such a PWN may be radio and X-ray quiet in synchrotron radiation, it may still be detectable as a {\it GLAST/LAT} source as a result of the relic electrons in the PWN.Comment: 10 pages, no figures. To appear in Astrophysical Journal Letter

    The Development of Regulatory Standards for Gene Therapy in the European Union

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    This note examines the EU\u27s efforts to regulate gene therapy, considering the Union\u27s resolve to establish scientifically, economically, and morally sound parameters acceptable to its varied constituency. This includes discussion of legal and ethical considerations, biotechnology goals in the EU, and EU-wide uniform regulations

    Probing the Nature of the Vela X Cocoon

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    Vela X is a pulsar wind nebula (PWN) associated with the active pulsar B0833-45 and contained within the Vela supernova remnant (SNR). A collimated X-ray filament ("cocoon") extends south-southwest from the pulsar to the center of Vela X. VLA observations uncovered radio emission coincident with the eastern edge of the cocoon and H.E.S.S. has detected TeV γ\gamma-ray emission from this region as well. Using XMM-\textit{Newton} archival data, covering the southern portion of this feature, we analyze the X-ray properties of the cocoon. The X-ray data are best fit by an absorbed nonequilibrium plasma model with a powerlaw component. Our analysis of the thermal emission shows enhanced abundances of O, Ne, and Mg within the cocoon, indicating the presence of ejecta-rich material from the propagation of the SNR reverse shock, consistent with Vela X being a disrupted PWN. We investigate the physical processes that excite the electrons in the PWN to emit in the radio, X-ray and γ\gamma-ray bands. The radio and non-thermal X-ray emission can be explained by synchrotron emission. We model the γ\gamma-ray emission by Inverse Compton scattering of electrons off of cosmic microwave background (CMB) photons. We use a 3-component broken power law to model the synchrotron emission, finding an intrinsic break in the electron spectrum at 5×106\sim5 \times 10^{6} keV and a cooling break at \sim 5.5 ×1010\times 10^{10} keV. This cooling break along with a magnetic field strength of 5 ×106\times 10^{-6} G indicate that the synchrotron break occurs at \sim1 keV.Comment: accepted for publication to ApJ
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