11,040 research outputs found
Supernova Reverse Shocks and SiC Growth
We present new mechanisms by which the isotopic compositions of X-type grains
of presolar SiC are altered by reverse shocks in Type II supernovae. We address
three epochs of reverse shocks: pressure wave from the H envelope near t =
10s; reverse shock from the presupernova wind near 10s; reverse
shock from the ISM near 10s. Using 1-D hydrodynamics we show that the
first creates a dense shell of Si and C atoms near 10s in which the SiC
surely condenses. The second reverse shock causes precondensed grains to move
rapidly forward through decelerated gas of different isotopic composition,
during which implantation, sputtering and further condensation occur
simultaneously. The third reverse shock causes only further ion implantation
and sputtering, which may affect trace element isotopic compositions. Using a
25M supernova model we propose solutions to the following unsolved
questions: where does SiC condense?; why does SiC condense in preference to
graphite?; why is condensed SiC Si-rich?; why is O richness no obstacle
to SiC condensation?; how many atoms of each isotope are impacted by a grain
that condenses at time t at radial coordinate r? These many
considerations are put forward as a road map for interpreting SiC X grains
found in meteorites and their meaning for supernova physics.Comment: 28 pages, 14 figures, animation for Figure 3 and machine-readable
Table 3 can be found at
http://antares.steelangel.com/~edeneau/supernova/DHC_2003, Submitted to Ap
Design and Fabrication of the NASA Decoupler Pylon for the F-16 Aircraft
The NASA Decoupler Pylon is a passive means of suppressing wing-store flutter. The feasibility of demonstrating this concept on the F-16 aircraft was established through model wind tunnel tests and analyses. As a result of these tests and studies a ship set of Decoupler Pylons was designed and fabricated for a flight test demonstration on the F-16 aircraft. Basic design criteria were developed during the analysis study pertaining to pylon pitch stiffness, alignment system requirements, and damping requirements. A design was developed which utilized an electrical motor for the pylon alignment system. The design uses a four pin, two link pivot design which results in a remote pivot located at the center of gravity of the store when the store is in the aligned position. The pitch spring was fabricated from a tapered constant stress cantilevered beam. The pylon has the same external lines as the existing production pylon and is designed to use a MAU-12 ejection rack which is the same as the one used with the production pylon. The detailed design and fabrication was supported with a complete ground test of the pylon prior to shipment to NASA
Variable-Speed-of-Light Cosmology and Second Law of Thermodynamics
We examine whether the cosmologies with varying speed of light (VSL) are
compatible with the second law of thermodynamics. We find that the VSL
cosmology with varying fundamental constant is severely constrained by the
second law of thermodynamics, whereas the bimetric cosmological models are less
constrained.Comment: 15 pages, LaTeX, Revised version with minor corrections to appear in
Phys. Rev.
Vector field mediated models of dynamical light velocity
A vector-tensor theory of gravity that was introduced in an earlier
publication is analyzed in detail and its consequences for early universe
cosmology are examined. The multiple light cone structure of the theory
generates different speeds of gravitational and matter wave fronts, and the
contraction of these light cones produces acausal, superluminary inflation that
can resolve the initial value problems of cosmology.Comment: 16 pages, uses amsar
Unstable Hadrons in Hot Hadron Gas in Laboratory and in the Early Universe
We study kinetic master equations for chemical reactions involving the
formation and the natural decay of unstable particles in a thermal bath. We
consider the decay channel of one into two particles, and the inverse process,
fusion of two thermal particles into one. We present the master equations the
evolution of the density of the unstable particles in the early Universe. We
obtain the thermal invariant reaction rate using as an input the free space
(vacuum) decay time and show the medium quantum effects on reaction relaxation time. As another laboratory example
we describe the process in thermal hadronic gas in
heavy-ion collisions. A particularly interesting application of our formalism
is the process in the early Universe.
We also explore the physics of and freeze-out in the
Universe.Comment: 13 pages, 9 figures, published in Physical Review
Is the iPhone an accurate and useful tool for the monitoring of spinal deformity?
The progression of spinal deformity is traditionally monitored by spinal surgeons using the Cobb method on hardcopy radiographs with a protractor and pencil. The rotation of the spine and ribcage (rib hump) in scoliosis is measured with a simple hand-held inclinometer (Scoliometer). The iPhone and other smart phones have the capability to accurately sense inclination, and can therefore be used to measure Cobb angles and rib hump angulation. The purpose of this study was to quantify the performance of the iPhone compared to a standard protractor for measuring Cobb angles and the Scoliometer for measuring rib humps. The study concluded that the iPhone is a clinically equivalent measuring tool to the traditional protractor and Scoliomete
Magnetically Catalyzed Fusion
We calculate the reaction cross-sections for the fusion of hydrogen and
deuterium in strong magnetic fields as are believed to exist in the atmospheres
of neutron stars. We find that in the presence of a strong magnetic field (B
\gsim 10^{12}G), the reaction rates are many orders of magnitude higher than
in the unmagnetized case. The fusion of both protons and deuterons are
important over a neutron star's lifetime for ultrastrong magnetic fields (G). The enhancement may have dramatic effects on thermonuclear
runaways and bursts on the surfaces of neutron stars.Comment: 13 pages, 6 figure
Chaos driven fusion enhancement factor at astrophysical energies
We perform molecular dynamics simulations to assess the screening effects by
bound target electrons in low energy nuclear reactions in laboratories. Quantum
effects corresponding to the Pauli and Heisenberg principle are enforced by
constraints. We show that the enhancement of the average cross section and of
its variance is due to the perturbations induced by the electrons.This gives a
correlation between the maximum amplitudes of the inter-nuclear oscillational
motion and the enhancement factor. It suggests that the chaotic behavior of the
electronic motion affects the magnitude of the enhancement factor.Comment: 4 pages, 3 figure
Biomechanical performance of polycaprolactone (PCL)-based scaffold with rhBMP-2 in a sheep thoracic spine fusion model
Adolescent idiopathic scoliosis is a complex three dimensional deformity affecting 2-3% of the general population. Resulting spine deformities include progressive coronal curvature, hypokyphosis, or frank lordosis in the thoracic spine and vertebral rotation in the axial plane with posterior elements turned into the curve concavity. The potential for curve progression is heightened during the adolescent growth spurt. Success of scoliosis deformity correction depends on solid bony fusion between adjacent vertebrae after the intervertebral discs have been surgically cleared and the disc spaces filled with graft material. Problems with bone graft harvest site morbidity as well as limited bone availability have led to the search for bone graft substitutes. Recently, a bioactive and resorbable scaffold fabricated from medical grade polycaprolactone (PCL) has been developed for bone regeneration at load bearing sites. Combined with recombinant human bone morphogenic protein–2 (rhBMP-2), this has been shown to be successful in acting as a bone graft substitute in acting as a bone graft substitute in a porcine lumbar interbody fusion model when compared to autologous bone graft. This in vivo sheep study intends to evaluate the suitability of a custom designed medical grade PCL scaffold in combination with rhBMP-2 as a bone graft substitute in the setting of mini–thoracotomy surgery as a platform for ongoing research to benefit patients with adolescent idiopathic scoliosis
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