60,228 research outputs found
Relativistic Effects in Extrasolar Planetary Systems
This paper considers general relativistic (GR) effects in currently observed
extrasolar planetary systems. Although GR corrections are small, they can
compete with secular interactions in these systems and thereby play an
important role. Specifically, some of the observed multiple planet systems are
close to secular resonance, where the dynamics is extremely sensitive to GR
corrections, and these systems can be used as laboratories to test general
relativity. For the three-planet solar system Upsilon Andromedae, secular
interaction theory implies an 80% probability of finding the system with its
observed orbital elements if GR is correct, compared with only a 2% probability
in the absence of GR. In the future, tighter constraints can be obtained with
increased temporal coverage.Comment: Accepted for publication in International Journal of Modern Physics
D; this paper received ``Honorable Mention'' in the 2006 Essay Competition of
the Gravity Research Foundation; 9 pages including 1 figur
Possible Suppression of Resonant Signals for Split-UED by Mixing at the LHC?
The mixing of the imaginary parts of the transition amplitudes of nearby
resonances via the breakdown of the Breit-Wigner approximation has been shown
to lead to potentially large modifications in the signal rates for new physics
at colliders. In the case of suppression, this effect may be significant enough
to lead to some new physics signatures being initially missed in searches at,
e.g., the LHC. Here we explore the influence of this `width mixing' on the
production of the nearly degenerate, level-2 Kaluza-Klein (KK) neutral gauge
bosons present in Split-UED. We demonstrate that in this particular case large
cross section modifications in the resonance region are necessarily absent and
explain why this is so based on the group theoretical structure of the SM.Comment: 10 pages, 2 figures; discussion and references adde
Production mechanisms and single-spin asymmetry for kaons in high energy hadron-hadron collisions
Direct consequences on kaon production of the picture proposed in a recent
Letter and subsequent publications are discussed. Further evidence supporting
the proposed picture is obtained. Comparison with the data for the inclusive
cross sections in unpolarized reactions is made. Quantitative results for the
left-right asymmetry in single-spin processes are presented.Comment: 10 pages, 2 Postscript figure
Nondestructive testing of brazed rocket engine components
Report details study made of nondestructive radiographic, ultrasonic, thermographic, and leak test methods used to inspect and evaluate the quality of the various brazed joints in liquid-propellant rocket engine components and assemblies. Descriptions of some of the unique equipment and methods developed are included
Evidence for parallel elongated structures in the mesosphere
The physical cause of partial reflection from the mesosphere is of interest. Data are presented from an image-forming radar at Brighton, Colorado, that suggest that some of the radar scattering is caused by parallel elongated structures lying almost directly overhead. Possible physical sources for such structures include gravity waves and roll vortices
Strong electron correlations in cobalt valence tautomers
We have examined cobalt based valence tautomer molecules such as
Co(SQ)(phen) using density functional theory (DFT) and variational
configuration interaction (VCI) approaches based upon a model Hamiltonian. Our
DFT results extend earlier work by finding a reduced total energy gap (order
0.6 eV) between high temperature and low temperature states when we fully relax
the coordinates (relative to experimental ones). Futhermore we demonstrate that
the charge transfer picture based upon formal valence arguments succeeds
qualitatively while failing quantitatively due to strong covalency between the
Co 3 orbitals and ligand orbitals. With the VCI approach, we argue that
the high temperature, high spin phase is strongly mixed valent, with about 30 %
admixture of Co(III) into the predominantly Co(II) ground state. We confirm
this mixed valence through a fit to the XANES spectra. Moreover, the strong
electron correlations of the mixed valent phase provide an energy lowering of
about 0.2-0.3 eV of the high temperature phase relative to the low temperature
one. Finally, we use the domain model to account for the extraordinarily large
entropy and enthalpy values associated with the transition.Comment: 10 pages, 4 figures, submitted to J. Chem. Phy
Does Positronium Form in the Universe ?
Positronium (the bound state of electron and positron) has been thought to be
formed after proton decay (yr) through collisional recombination and
then decays by pair annihilation, thereby changing the matter content of the
universe. We revisit the issue of the formation of positronium in the long-term
future of the universe in light of recent indication that the universe is
dominated by dark energy and dark matter. We find that if the equation of state
of dark energy is less than -1/3 (including the cosmological constant
), then the formation of positronium would not be possible, while it is
possible through bound-bound transitions for -1/3\siml w\siml-0.2, or through
collisional recombination for w\simg-0.2. The radiation from \epm pair
annihilation cannot dominate over \epm, while that from proton decay will
dominate over baryon and \epm for a while but not over dark matter.Comment: 13 pages, to appear in JCA
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