2,332 research outputs found
Varying leptonic chemical potentials and spatial variation of primordial deuterium at high z
We try to explain the spatial variation of primordial deuterium suggested by
some observations by varying leptonic chemical potentials. The variation of the
latter may take place in some scenarios of leptogenesis. The model predicts a
large mass fraction of (35-60%) and (up to ) in
deuterium-rich regions. Because of lepton family symmetry, the angular
variations of cosmic microwave background radiation can be sufficiently small
although still observable in future measurements.Comment: 16 pages, late
Spatial Variations of Fundamental Constants
We show that observational limits on the possible time variation of constants
of Nature are significantly affected by allowing for both space and time
variation. Bekenstein's generalisation of Maxwell's equations to allow for
cosmological variation of is investigated in a universe containing
spherically symmetric inhomogeneities. The time variation of is
determined by the local matter density and hence limits obtained in
high-density geophysical enviroments are far more constraining than those
obtained at high redshift. This new feature is expected to be a property of a
wide class of theories for the variation of constants.Comment: 4 page
Design and fabrication of a radiative actively cooled honeycomb sandwich structural panel for a hypersonic aircraft
The panel assembly consisted of an external thermal protection system (metallic heat shields and insulation blankets) and an aluminum honeycomb structure. The structure was cooled to temperature 442K (300 F) by circulating a 60/40 mass solution of ethylene glycol and water through dee shaped coolant tubes nested in the honeycomb and adhesively bonded to the outer skin. Rene'41 heat shields were designed to sustain 5000 cycles of a uniform pressure of + or - 6.89kPa (+ or - 1.0 psi) and aerodynamic heating conditions equivalent to 136 kW sq m (12 Btu sq ft sec) to a 422K (300 F) surface temperature. High temperature flexible insulation blankets were encased in stainless steel foil to protect them from moisture and other potential contaminates. The aluminum actively cooled honeycomb sandwich structural panel was designed to sustain 5000 cycles of cyclic in-plane loading of + or - 210 kN/m (+ or - 1200 lbf/in.) combined with a uniform panel pressure of + or - 6.89 kPa (?1.0 psi)
Nonequilibrium quantum fluctuation relations for harmonic systems in nonthermal environments
We formulate exact generalized nonequilibrium fluctuation relations for the
quantum mechanical harmonic oscillator coupled to multiple harmonic baths. Each
of the different baths is prepared in its own individual (in general
nonthermal) state. Starting from the exact solution for the oscillator dynamics
we study fluctuations of the oscillator position as well as of the energy
current through the oscillator under general nonequilibrium conditions. In
particular, we formulate a fluctuation-dissipation relation for the oscillator
position autocorrelation function that generalizes the standard result for the
case of a single bath at thermal equilibrium. Moreover, we show that the
generating function for the position operator fullfills a generalized
Gallavotti-Cohen-like relation. For the energy transfer through the oscillator,
we determine the average energy current together with the current fluctuations.
Finally, we discuss the generalization of the cumulant generating function for
the energy transfer to nonthermal bath preparations.Comment: 21 page
The Metallicity of the Red Giant Branch in the Disk of NGC 6822
Deep J, H, and K' images obtained with the Canada-France-Hawaii Telescope
adaptive optics system are used to investigate the metallicity of red giant
branch (RGB) stars in three fields in the disk of the Local Group dwarf
irregular galaxy NGC 6822. The slope of the RGB on the (K, J-K) color-magnitude
diagrams indicates that = -1.0 +/- 0.3. The locus of the RGB is bluer
than that of globular clusters with the same RGB slope, by an amount that is
consistent with the majority of RGB stars in these fields having an age near 3
Gyr. It is demonstrated that if RGB stars in NGC 6822 are this young then the
metallicity computed from the RGB slope may be ~ 0.05 dex too low.Comment: 19 pages of text; 10 figures; to appear in the PAS
How to Avoid Common Pitfalls of Health IT Implementation
The stories in this guide were based on case studies about a specific intensive care IT system that integrates information from bedside monitors into a single intuitive display to provide better real-time information for clinicians
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Ultraconserved words point to deep language ancestry across Eurasia
The search for ever deeper relationships among the Worldâs languages is bedeviled by the fact that most words evolve too rapidly to preserve evidence of their ancestry beyond 5,000 to 9,000 y. On the other hand, quantitative modeling indicates that some âultraconservedâ words exist that might be used to find evidence for deep linguistic relationships beyond that time barrier. Here we use a statistical model, which takes into account the frequency with which words are used in common everyday speech, to predict the existence of a set of such highly conserved words among seven language families of Eurasia postulated to form a linguistic superfamily that evolved from a common ancestor around 15,000 y ago. We derive a dated phylogenetic tree of this proposed superfamily with a time-depth of âŒ14,450 y, implying that some frequently used words have been retained in related forms since the end of the last ice age. Words used more than once per 1,000 in everyday speech were 7- to 10-times more likely to show deep ancestry on this tree. Our results suggest a remarkable fidelity in the transmission of some words and give theoretical justification to the search for features of language that might be preserved across wide spans of time and geography
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