22,507 research outputs found
Duties of Members, Directors, and Managers of Cooperative Associations
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Effects of spacecraft reflections on RF interferometer position location accuracy
This report describes one of three study tasks related to the application of an RF interferometer aboard a low-orbiting spacecraft to determine the location of ground-based transmitters. Computer modeling was used to estimate the error in the measured signal angle-of-arrival caused by reflection and diffraction off the spacecraft. Existing computer codes (NEC-BSC) were modified and used to determine the perturbation, due to the spacecraft, in the phase difference between two interferometer antennas, suspended on either side of the spacecraft. This phase perturbation was found as a function of the angle-of-arrival of the signal from a far-field source. The spacecraft antennas were assumed to be circularly polarized with a cardioid pattern. It was found that the perturbation was as much 12.4 deg within the + or - 60 deg field-of-view. This suggests that phase calibration and correction of phase measurements are essential for precision position location using this technique
Strainrange partitioning behavior of an automotive turbine alloy
This report addresses Strainrange Partitioning, an advanced life prediction analysis procedure, as applied to CA-101 (cast IN 792 + Hf), an alloy proposed for turbine disks in automotive gas turbine engines. The methodology was successful in predicting specimen life under thermal-mechanical cycling, to within a factor of + or - 2
Observation of Single Transits in Supercooled Monatomic Liquids
A transit is the motion of a system from one many-particle potential energy
valley to another. We report the observation of transits in molecular dynamics
(MD) calculations of supercooled liquid argon and sodium. Each transit is a
correlated simultaneous shift in the equilibrium positions of a small local
group of particles, as revealed in the fluctuating graphs of the particle
coordinates versus time. This is the first reported direct observation of
transit motion in a monatomic liquid in thermal equilibrium. We found transits
involving 2 to 11 particles, having mean shift in equilibrium position on the
order of 0.4 R_1 in argon and 0.25 R_1 in sodium, where R_1 is the nearest
neighbor distance. The time it takes for a transit to occur is approximately
one mean vibrational period, confirming that transits are fast.Comment: 19 pages, 8 figure
Adiabatic and Non-Adiabatic Contributions to the Free Energy from the Electron-Phonon Interaction for Na, K, Al, and Pb
We calculate the adiabatic contributions to the free energy due to the
electron--phonon interaction at intermediate temperatures, for the elemental metals Na, K, Al, and Pb. Using our
previously published results for the nonadiabatic contributions we show that
the adiabatic contribution, which is proportional to at low
temperatures and goes as at high temperatures, dominates the
nonadiabatic contribution for temperatures above a cross--over temperature,
, which is between 0.5 and 0.8 , where is the melting
temperature of the metal. The nonadiabatic contribution falls as for
temperatures roughly above the average phonon frequency.Comment: Updated versio
Did Neoliberalizing West African Forests Produce a New Niche for Ebola?
A recent study introduced a vaccine that controls Ebola Makona, the Zaire ebolavirus variant that has infected 28,000 people in West Africa. We propose that even such successful advances are insufficient for many emergent diseases. We review work hypothesizing that Makona, phenotypically similar to much smaller outbreaks, emerged out of shifts in land use brought about by neoliberal economics. The epidemiological consequences demand a new science that explicitly addresses the foundational processes underlying multispecies health, including the deep-time histories, cultural infrastructure, and global economic geographies driving disease emergence. The approach, for instance, reverses the standard public health practice of segregating emergency responses and the structural context from which outbreaks originate. In Ebola's case, regional neoliberalism may affix the stochastic "friction" of ecological relationships imposed by the forest across populations, which, when above a threshold, keeps the virus from lining up transmission above replacement. Export-led logging, mining, and intensive agriculture may depress such functional noise, permitting novel spillovers larger forces of infection. Mature outbreaks, meanwhile, can continue to circulate even in the face of efficient vaccines. More research on these integral explanations is required, but the narrow albeit welcome success of the vaccine may be used to limit support of such a program.SCOPUS: re.jinfo:eu-repo/semantics/publishe
An \emph{ab initio} method for locating characteristic potential energy minima of liquids
It is possible in principle to probe the many--atom potential surface using
density functional theory (DFT). This will allow us to apply DFT to the
Hamiltonian formulation of atomic motion in monatomic liquids [\textit{Phys.
Rev. E} {\bf 56}, 4179 (1997)]. For a monatomic system, analysis of the
potential surface is facilitated by the random and symmetric classification of
potential energy valleys. Since the random valleys are numerically dominant and
uniform in their macroscopic potential properties, only a few quenches are
necessary to establish these properties. Here we describe an efficient
technique for doing this. Quenches are done from easily generated "stochastic"
configurations, in which the nuclei are distributed uniformly within a
constraint limiting the closeness of approach. For metallic Na with atomic pair
potential interactions, it is shown that quenches from stochastic
configurations and quenches from equilibrium liquid Molecular Dynamics (MD)
configurations produce statistically identical distributions of the structural
potential energy. Again for metallic Na, it is shown that DFT quenches from
stochastic configurations provide the parameters which calibrate the
Hamiltonian. A statistical mechanical analysis shows how the underlying
potential properties can be extracted from the distributions found in quenches
from stochastic configurations
Excited state baryon spectroscopy from lattice QCD
We present a calculation of the Nucleon and Delta excited state spectrum on
dynamical anisotropic clover lattices. A method for operator construction is
introduced that allows for the reliable identification of the continuum spins
of baryon states, overcoming the reduced symmetry of the cubic lattice. Using
this method, we are able to determine a spectrum of single-particle states for
spins up to and including J = 7/2, of both parities, the first time this has
been achieved in a lattice calculation. We find a spectrum of states
identifiable as admixtures of SU(6) x O(3) representations and a counting of
levels that is consistent with the non-relativistic constituent quark
model. This dense spectrum is incompatible with quark-diquark model solutions
to the "missing resonance problem" and shows no signs of parity doubling of
states.Comment: 29 pages, 18 figure
On the accuracy of the melting curves drawn from modelling a solid as an elastic medium
An ongoing problem in the study of a classical many-body system is the
characterization of its equilibrium behaviour by theory or numerical
simulation. For purely repulsive particles, locating the melting line in the
pressure-temperature plane can be especially hard if the interparticle
potential has a softened core or contains some adjustable parameters. A method
is hereby presented that yields reliable melting-curve topologies with
negligible computational effort. It is obtained by combining the Lindemann
melting criterion with a description of the solid phase as an elastic
continuum. A number of examples are given in order to illustrate the scope of
the method and possible shortcomings. For a two-body repulsion of Gaussian
shape, the outcome of the present approach compares favourably with the more
accurate but also more computationally demanding self-consistent harmonic
approximation.Comment: 25 pages, 7 figure
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