1,871 research outputs found
Preliminary report on IUE spectra of the Crab Nebula
The Crab Nebula is marginally observable with the IUE. Observations of the optically brightest filamentary regions, made with IUE in August 1979, show the C IV lambda 1549, He II lambda 1640, and C III lambda 1909 emission lines. The intensities of these lines were compared with the visual wavelength data. It appears that carbon is not overabundant in the Crab; carbon/oxygen is approximately normal and oxygen is slightly scarcer than normal as a fraction of the total mass
Core-Collapse Simulations of Rotating Stars
We present the results from a series of two-dimensional core-collapse
simulations using a rotating progenitor star. We find that the convection in
these simulations is less vigorous because a) rotation weakens the core bounce
which seeds the neutrino-driven convection and b) the angular momentum profile
in the rotating core stabilizes against convection. The limited convection
leads to explosions which occur later and are weaker than the explosions
produced from the collapse of non-rotating cores. However, because the
convection is constrained to the polar regions, when the explosion occurs, it
is stronger along the polar axis. This asymmetric explosion can explain the
polarization measurements of core-collapse supernovae. These asymmetries also
provide a natural mechanism to mix the products of nucleosynthesis out into the
helium and hydrogen layers of the star. We also discuss the role the collapse
of these rotating stars play on the generation of magnetic fields and neutron
star kicks. Given a range of progenitor rotation periods, we predict a range of
supernova energies for the same progenitor mass. The critical mass for black
hole formation also depends upon the rotation speed of the progenitor.Comment: 16 pages text + 13 figures, submitted to Ap
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Cyclic Material Properties Test to Determine Hardening/Softening Characteristics of HY-80 Steel
The Cyclic Material Properties Test was structured to obtain and provide experimental data for determining cyclic hardening/softening characteristics of HY-80 steel. The inelastic strain history data generated by this test program and the resulting cyclic stress-strain curve will be used to enhance material models in the finite element codes used to perform nonlinear elastic-plastic analysis
Multiple myeloma presenting as an intracranial plasmacytoma: a case report
Multiple myeloma presenting as an intracranial tumor (plasmacytoma) is very rare. An 81-year-old woman was admitted to our hospital because of gait disturbance. A blood laboratory test revealed a mildly increased lactate dehydrogenase (236 IU/L) and glucose (121 mg/dl). Blood protein fractions were normal. Brain computed tomography and magnetic resonance imaging revealed an intracranial mass (5 × 4 × 3 cm) in the brain base next to the clavus, and it was clinically diagnosed as chordoma. An excision of the brain tumor was performed. Imaging modalities including ultrasound, x-ray, computed tomography, magnetic resonance imaging and positron emission tomography did not reveal any tumors other than the brain tumor. The tumor was soft, fragile, and bloody. Microscopically, a monotonous proliferation of atypical plasma cells with hyperchromatic nuclei was recognized. Histochemically, the tumor cells were pyroninophilic and the congo-red stain revealed amyloidosis. Immunohistochemically, the tumor cells were positive for κ-chain and negative for cytokeratin, epithelial membrane antigen, vimentin, CD45, CD20, CD45RO, λ-chain, IgM, IgA, IgG, synaptophysin, chromogranin, S100 protein, desmin, α-smooth muscle antigen, myoglobin, p53 protein, and glial fibrillary acidic protein. The Ki-67 labeling was 11%. Intracranial plasmacytoma was pathologically diagnosed. The patient was treated by adjuvant chemoradiation, and entered into the complete remission stage. However, multiple metastases emerged in the vertebral bones and ribs six months after the remission. A diagnosis of multiple myeloma was made. The urine revealed Bence-Jones protein of monoclonal IgG κ-chain type, but blood M protein was not recognized. The patient's condition gradually deteriorated. The patient died of respiratory failure due to bronchopneumonia 18 months after the admission. The present case indicates that multiple myeloma may manifest as an intracranial brain tumor (plasmacytoma)
Advanced perception, navigation and planning for autonomous in-water ship hull inspection
Inspection of ship hulls and marine structures using autonomous underwater vehicles has emerged as a unique and challenging application of robotics. The problem poses rich questions in physical design and operation, perception and navigation, and planning, driven by difficulties arising from the acoustic environment, poor water quality and the highly complex structures to be inspected. In this paper, we develop and apply algorithms for the central navigation and planning problems on ship hulls. These divide into two classes, suitable for the open, forward parts of a typical monohull, and for the complex areas around the shafting, propellers and rudders. On the open hull, we have integrated acoustic and visual mapping processes to achieve closed-loop control relative to features such as weld-lines and biofouling. In the complex area, we implemented new large-scale planning routines so as to achieve full imaging coverage of all the structures, at a high resolution. We demonstrate our approaches in recent operations on naval ships.United States. Office of Naval Research (Grant N00014-06-10043)United States. Office of Naval Research (Grant N00014-07-1-0791
A New WIMP Population in the Solar System and New Signals for Dark-Matter Detectors
We describe in detail how perturbations due to the planets can cause a
sub-population of WIMPs captured by scattering in surface layers of the Sun to
evolve to have orbits which no longer intersect the Sun. We argue that such
WIMPs, if their orbit has a semi-major axis less than 1/2 of Jupiter's, can
persist in the solar system for cosmological timescales. This leads to a new,
previously unanticipated WIMP population intersecting the Earth's orbit. The
WIMP-nucleon cross sections required for this population to be significant are
precisely those in the range predicted for SUSY dark matter, lying near the
present limits obtained by direct underground dark matter searches using
cyrogenic detectors. Thus, if a WIMP signal is observed in the next generation
of detectors, a potentially measurable signal due to this new population must
exist. This signal, lying in the keV range for Germanium detectors, would be
complementary to that of galactic halo WIMPs. A comparison of event rates,
anisotropies, and annual modulations would not only yield additional
confirmation that any claimed signal is indeed WIMP-based, but would also allow
one to gain information on the nature of the underlying dark matter model.Comment: Revtex, 37 pages including 6 figures, accepted by Phys. Rev D.
(version to be published, including changes made in response to referees
reports
Molecular Aspects of Secretory Granule Exocytosis by Neurons and Endocrine Cells
Neuronal communication and endocrine signaling are fundamental for integrating
the function of tissues and cells in the body. Hormones released by endocrine
cells are transported to the target cells through the circulation. By contrast, transmitter
release from neurons occurs at specialized intercellular junctions, the synapses.
Nevertheless, the mechanisms by which signal molecules are synthesized,
stored, and eventually secreted by neurons and endocrine cells are very similar.
Neurons and endocrine cells have in common two different types of secretory
organelles, indicating the presence of two distinct secretory pathways. The synaptic
vesicles of neurons contain excitatory or inhibitory neurotransmitters, whereas the
secretory granules (also referred to as dense core vesicles, because of their electron
dense content) are filled with neuropeptides and amines. In endocrine cells, peptide
hormones and amines predominate in secretory granules. The function and content
of vesicles, which share antigens with synaptic vesicles, are unknown for most
endocrine cells. However, in B cells of the pancreatic islet, these vesicles contain
GABA, which may be involved in intrainsular signaling.'
Exocytosis of both synaptic vesicles and secretory granules is controlled by
cytoplasmic calcium. However, the precise mechanisms of the subsequent steps,
such as docking of vesicles and fusion of their membranes with the plasma membrane,
are still incompletely understood. This contribution summarizes recent observations
that elucidate components in neurons and endocrine cells involved in
exocytosis. Emphasis is put on the intracellular aspects of the release of secretory
granules that recently have been analyzed in detail
The Dispersion Velocity of Galactic Dark Matter Particles
The self-consistent spatial distribution of particles of Galactic dark matter
is derived including their own gravitational potential, as also that of the
visible matter of the Galaxy. In order to reproduce the observed rotation curve
of the Galaxy the value of the dispersion velocity of the dark matter
particles, \rmsveldm, should be \sim 600\kmps or larger.Comment: RevTex, 4 pages, 1 ps figure, accepted for publication in Physical
Review Letter
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