34,786 research outputs found

    Fundamental Plane Distances to Early-type Field Galaxies in the South Equatorial Strip. I. The Spectroscopic Data

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    Radial velocities and central velocity dispersions are derived for 238 E/S0 galaxies from medium-resolution spectroscopy. New spectroscopic data have been obtained as part of a study of the Fundamental Plane distances and peculiar motions of early-type galaxies in three selected directions of the South Equatorial Strip, undertaken in order to investigate the reality of large-scale streaming motion; results of this study have been reported in M\"uller etet al.al. (1998). The new APM South Equatorial Strip Catalog (−17∘.5<ÎŽ<+2∘.5-17^{\circ}.5 < \delta < +2^{\circ}.5) was used to select the sample of field galaxies in three directions: (1) 15h10 - 16h10; (2) 20h30 - 21h50; (3) 00h10 - 01h30. The spectra obtained have a median S/N per A˚{\AA} of 23, an instrumental resolution (FWHM) of ∌\sim 4 A˚{\AA}, and the spectrograph resolution (dispersion) is ∌\sim 100 km~s−1^{-1}. The Fourier cross-correlation method was used to derive the radial velocities and velocity dispersions. The velocity dispersions have been corrected for the size of the aperture and for the galaxy effective radius. Comparisons of the derived radial velocities with data from the literature show that our values are accurate to 40 km~s−1^{-1}. A comparison with results from J\orgensen et al. (1995) shows that the derived central velocity dispersion have an rms scatter of 0.036 in logâĄÏƒ\log \sigma. There is no offset relative to the velocity dispersions of Davies et al. (1987).Comment: accepted for publication in Astronomy & Astrophysics Supplement Serie

    Testing Lorentz invariance by use of vacuum and matter filled cavity resonators

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    We consider tests of Lorentz invariance for the photon and fermion sector that use vacuum and matter-filled cavities. Assumptions on the wave-function of the electrons in crystals are eliminated from the underlying theory and accurate sensitivity coefficients (including some exceptionally large ones) are calculated for various materials. We derive the Lorentz-violating shift in the index of refraction n, which leads to additional sensitivity for matter-filled cavities ; and to birefringence in initially isotropic media. Using published experimental data, we obtain improved bounds on Lorentz violation for photons and electrons at levels of 10^-15 and below. We discuss implications for future experiments and propose a new Michelson-Morley type experiment based on birefringence in matter.Comment: 15 pages, 8 table

    Comment on 'Stability of the semiclassical Einstein equation'

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    Some mathematical errors of the paper commented upon [W.-M. Suen, Phys. Rev. D 40, (1989) 315] are corrected.Comment: 3 pages, LaTeX, reprinted from Phys. Rev. D 50 (1994) 545

    Improving LLR Tests of Gravitational Theory

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    Accurate analysis of precision ranges to the Moon has provided several tests of gravitational theory including the Equivalence Principle, geodetic precession, parameterized post-Newtonian (PPN) parameters Îł\gamma and ÎČ\beta, and the constancy of the gravitational constant {\it G}. Since the beginning of the experiment in 1969, the uncertainties of these tests have decreased considerably as data accuracies have improved and data time span has lengthened. We are exploring the modeling improvements necessary to proceed from cm to mm range accuracies enabled by the new Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) currently under development in New Mexico. This facility will be able to make a significant contribution to the solar system tests of fundamental and gravitational physics. In particular, the Weak and Strong Equivalence Principle tests would have a sensitivity approaching 10−14^{-14}, yielding sensitivity for the SEP violation parameter η\eta of ∌3×10−5\sim 3\times 10^{-5}, v2/c2v^2/c^2 general relativistic effects would be tested to better than 0.1%, and measurements of the relative change in the gravitational constant, G˙/G\dot{G}/G, would be ∌0.1\sim0.1% the inverse age of the universe. Having this expected accuracy in mind, we discusses the current techniques, methods and existing physical models used to process the LLR data. We also identify the challenges for modeling and data analysis that the LLR community faces today in order to take full advantage of the new APOLLO ranging station.Comment: 15 pages, 3 figures, talk presented at 2003 NASA/JPL Workshop on Fundamental Physics in Space, April 14-16, 2003, Oxnard, C

    Faraday waves on a viscoelastic liquid

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    We investigate Faraday waves on a viscoelastic liquid. Onset measurements and a nonlinear phase diagram for the selected patterns are presented. By virtue of the elasticity of the material a surface resonance synchronous to the external drive competes with the usual subharmonic Faraday instability. Close to the bicriticality the nonlinear wave interaction gives rise to a variety of novel surface states: Localised patches of hexagons, hexagonal superlattices, coexistence of hexagons and lines. Theoretical stability calculations and qualitative resonance arguments support the experimental observations.Comment: 4 pages, 4figure
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