65,592 research outputs found
Size effects and dislocation patterning in two-dimensional bending
We perform atomistic Monte Carlo simulations of bending a Lennard-Jones
single crystal in two dimensions. Dislocations nucleate only at the free
surface as there are no sources in the interior of the sample. When
dislocations reach sufficient density, they spontaneously coalesce to nucleate
grain boundaries, and the resulting microstructure depends strongly on the
initial crystal orientation of the sample. In initial yield, we find a reverse
size effect, in which larger samples show a higher scaled bending moment than
smaller samples for a given strain and strain rate. This effect is associated
with source-limited plasticity and high strain rate relative to dislocation
mobility, and the size effect in initial yield disappears when we scale the
data to account for strain rate effects. Once dislocations coalesce to form
grain boundaries, the size effect reverses and we find that smaller crystals
support a higher scaled bending moment than larger crystals. This finding is in
qualitative agreement with experimental results. Finally, we observe an
instability at the compressed crystal surface that suggests a novel mechanism
for the formation of a hillock structure. The hillock is formed when a high
angle grain boundary, after absorbing additional dislocations, becomes unstable
and folds to form a new crystal grain that protrudes from the free surface.Comment: 15 pages, 8 figure
A short, cylindrical antenna as a diagnostic probe for measuring collision frequencies in a collision-dominated, non-Maxwellian plasma
Effects of particle collisions on antiresonant characteristics of cylindrical antennas used in electron plasma temperature and density measurement
Precision Electro-Weak and Hadronic Luminosity Calculations
We have used YFS Monte Carlo techniques to obtain per-mil level accuracy for
the Bhabha scattering cross section used in the luminosity monitor in
electro-weak scattering experiments. We will describe techniques for extending
these methods for use in the W production luminosity cross section for hadron
colliders.Comment: 8 pages (LaTex) with 5 figures (EPS). Presented by S.A. Yost at the
Third International Symposium on Quantum Theory and Symmetries, Cincinnati,
Sept. 10 - 14, 200
Differential localization of glutamate receptor subunits at the drosophila neuromuscular junction
The subunit composition of postsynaptic neurotransmitter receptors is a key determinant of synaptic physiology. Two glutamate receptor subunits, Drosophila glutamate receptor IIA (DGluRIIA) and DGluRIIB, are expressed at the Drosophila neuromuscular junction and are redundant for viability, yet differ in their physiological properties. We now identify a third glutamate receptor subunit at the Drosophila neuromuscular junction, DGluRIII, which is essential for viability. DGluRIII is required for the synaptic localization of DGluRIIA and DGluRIIB and for synaptic transmission. Either DGluRIIA or DGluRIIB, but not both, is required for the synaptic localization of DGluRIII. DGluRIIA and DGluRIIB compete with each other for access to DGluRIII and subsequent localization to the synapse. These results are consistent with a model of a multimeric receptor in which DGluRIII is an essential component. At single postsynaptic cells that receive innervation from multiple motoneurons, DGluRIII is abundant at all synapses. However, DGluRIIA and DGluRIIB are differentially localized at the postsynaptic density opposite distinct motoneurons. Hence, innervating motoneurons may regulate the subunit composition of their receptor fields within a shared postsynaptic cell. The capacity of presynaptic inputs to shape the subunit composition of postsynaptic receptors could be an important mechanism for synapse-specific regulation of synaptic function and plasticity
The Rise of Accelerated Seasoned Equity Underwritings
Seasoned equity offerings (SEOs) executed through accelerated underwritings have increased global market share recently, raising over 2.9 trillion for firms and selling shareholders. Compared to fully marketed deals, accelerated offerings occur more rapidly, raise more money, and require fewer underwriters. Importantly, accelerated deals reduce total issuance cost by about 250 basis points. Accelerated deals sell equal fractions of primary and secondary shares, whereas in traditional SEOs primary shares dominate. Announcement period returns are comparable for traditional and accelerated offerings, while secondary and mixed offerings trigger more negative market responses than do primary offerings. We conclude that this rapid, worldwide shift towards accelerated underwriting creates a spot market for SEOs, and represents the long-predicted shift towards an auction model for seasoned equity sales.Equity Offerings, Underwriting, Investment Banking
Spectral Line Removal in the LIGO Data Analysis System (LDAS)
High power in narrow frequency bands, spectral lines, are a feature of an
interferometric gravitational wave detector's output. Some lines are coherent
between interferometers, in particular, the 2 km and 4 km LIGO Hanford
instruments. This is of concern to data analysis techniques, such as the
stochastic background search, that use correlations between instruments to
detect gravitational radiation. Several techniques of `line removal' have been
proposed. Where a line is attributable to a measurable environmental
disturbance, a simple linear model may be fitted to predict, and subsequently
subtract away, that line. This technique has been implemented (as the command
oelslr) in the LIGO Data Analysis System (LDAS). We demonstrate its application
to LIGO S1 data.Comment: 11 pages, 5 figures, to be published in CQG GWDAW02 proceeding
Diurnal variation in harbour porpoise detection â potential implications for management
Peer reviewedPublisher PD
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