35,253 research outputs found
Poly-essential and general Hyperelastic World (brane) models
This article provides a unified treatment of an extensive category of
non-linear classical field models whereby the universe is represented (perhaps
as a brane in a higher dimensional background) in terms of a structure of a
mathematically convenient type describable as hyperelastic, for which a
complete set of equations of motion is provided just by the energy-momentum
conservation law. Particular cases include those of a perfect fluid in
quintessential backgrounds of various kinds, as well as models of the elastic
solid kind that has been proposed to account for cosmic acceleration. It is
shown how an appropriately generalised Hadamard operator can be used to
construct a symplectic structure that controles the evolution of small
perturbations, and that provides a characteristic equation governing the
propagation of weak discontinuities of diverse (extrinsic and extrinsic) kinds.
The special case of a poly-essential model - the k-essential analogue of an
ordinary polytropic fluid - is examined and shown to be well behaved (like the
fluid) only if the pressure to density ratio is positive.Comment: 16 pages Latex, Contrib. to 10th Peyresq Pysics Meeting, June 2005:
Micro and Macro Structures of Spacetim
The use of a simplified structural model as an aid in the strain gage calibration of a complex wing
The use of a relatively simple structural model to characterize the load responses of strain gages located on various spars of a delta wing is examined. Strains measured during a laboratory load calibration of a wing structure are compared with calculations obtained from a simplified structural analysis model. Calculated and measured influence coefficient plots that show the shear, bending, and torsion characteristics of typical strain gage bridges are presented. Typical influence coefficient plots are shown for several load equations to illustrate the derivation of the equations from the component strain gage bridges. A relatively simple structural model was found to be effective in predicting the general nature of strain distributions and influence coefficient plots. The analytical processes are shown to be an aid in obtaining a good load calibration. The analytical processes cannot, however, be used in lieu of an actual load calibration of an aircraft wing
Application of fracture mechanics and half-cycle method to the prediction of fatigue life of B-52 aircraft pylon components
Stress intensity levels at various parts of the NASA B-52 carrier aircraft pylon were examined for the case when the pylon store was the space shuttle solid rocket booster drop test vehicle. Eight critical stress points were selected for the pylon fatigue analysis. Using fracture mechanics and the half-cycle theory (directly or indirectly) for the calculations of fatigue-crack growth ,the remaining fatigue life (number of flights left) was estimated for each critical part. It was found that the two rear hooks had relatively short fatigue life and that the front hook had the shortest fatigue life of all the parts analyzed. The rest of the pylon parts were found to be noncritical because of their extremely long fatigue life associated with the low operational stress levels
Bogomol'nyi Limit For Magnetic Vortices In Rotating Superconductor
This work is the sequel of a previous investigation of stationary and
cylindrically symmetric vortex configurations for simple models representing an
incompressible non-relativistic superconductor in a rigidly rotating
background. In the present paper, we carry out our analysis with a generalized
Ginzburg-Landau description of the superconductor, which provides a
prescription for the radial profile of the normal density within the vortex.
Within this framework, it is shown that the Bogomol'nyi limit condition marking
the boundary between type I and type II behavior is unaffected by the rotation
of the background.Comment: 7 pages, uses RevTeX, submitted to Phys.Rev.
Southwest Research Institute assistance to NASA in biomedical areas of the technology utilization program
The activities are reported of the NASA Biomedical Applications Team at Southwest Research Institute between 25 August, 1972 and 15 November, 1973. The program background and methodology are discussed along with the technology applications, and biomedical community impacts
Quasiequilibrium black hole-neutron star binaries in general relativity
We construct quasiequilibrium sequences of black hole-neutron star binaries
in general relativity. We solve Einstein's constraint equations in the
conformal thin-sandwich formalism, subject to black hole boundary conditions
imposed on the surface of an excised sphere, together with the relativistic
equations of hydrostatic equilibrium. In contrast to our previous calculations
we adopt a flat spatial background geometry and do not assume extreme mass
ratios. We adopt a Gamma=2 polytropic equation of state and focus on
irrotational neutron star configurations as well as approximately nonspinning
black holes. We present numerical results for ratios of the black hole's
irreducible mass to the neutron star's ADM mass in isolation of
M_{irr}^{BH}/M_{ADM,0}^{NS} = 1, 2, 3, 5, and 10. We consider neutron stars of
baryon rest mass M_B^{NS}/M_B^{max} = 83% and 56%, where M_B^{max} is the
maximum allowed rest mass of a spherical star in isolation for our equation of
state. For these sequences, we locate the onset of tidal disruption and, in
cases with sufficiently large mass ratios and neutron star compactions, the
innermost stable circular orbit. We compare with previous results for black
hole-neutron star binaries and find excellent agreement with third-order
post-Newtonian results, especially for large binary separations. We also use
our results to estimate the energy spectrum of the outgoing gravitational
radiation emitted during the inspiral phase for these binaries.Comment: 17 pages, 15 figures, published in Phys. Rev.
Engineering Negative Differential Conductance with the Cu(111) Surface State
Low-temperature scanning tunneling microscopy and spectroscopy are employed
to investigate electron tunneling from a C60-terminated tip into a Cu(111)
surface. Tunneling between a C60 orbital and the Shockley surface states of
copper is shown to produce negative differential conductance (NDC) contrary to
conventional expectations. NDC can be tuned through barrier thickness or C60
orientation up to complete extinction. The orientation dependence of NDC is a
result of a symmetry matching between the molecular tip and the surface states.Comment: 5 pages, 4 figures, 1 tabl
Novel Rbfox2 isoforms associated with alternative exon usage in rat cortex and suprachiasmatic nucleus
Abstract Transcriptome diversity in adult neurons is partly mediated by RNA binding proteins (RBPs), including the RBFOX factors. RBFOX3/NeuN, a neuronal maturity marker, is strangely depleted in suprachiasmatic nucleus (SCN) neurons, and may be compensated by a change in Rbfox2 expression. In this study, we found no superficial changes in Rbfox2 expression in the SCN, but mRNA population analysis revealed a distinct SCN transcript profile that includes multiple novel Rbfox2 isoforms. Of eleven isoforms in SCN and cerebral cortex that exhibit exon variation across two protein domains, we found a 3-fold higher abundance of a novel (‘−12–40’) C-terminal domain (CTD)-variant in the SCN. This isoform embraces an alternative reading frame that imparts a 50% change in CTD protein sequence, and functional impairment of exon 7 exclusion activity in a RBFOX2-target, the L-type calcium channel gene, Cacna1c. We have also demonstrated functional correlates in SCN gene transcripts; inclusion of Cacna1c exon 7, and also exclusion of both NMDA receptor gene Grin1 exon 4, and Enah exon 12, all consistent with a change in SCN RBFOX activity. The demonstrated regional diversity of Rbfox2 in adult brain highlights the functional adaptability of this RBP, enabling neuronal specialization, and potentially responding to disease-related neuronal dysfunction
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