24,889 research outputs found
A computer model of solar panel-plasma interactions
High power solar arrays for satellite power systems are presently being planned with dimensions of kilometers, and with tens of kilovolts distributed over their surface. Such systems face many plasma interaction problems, such as power leakage to the plasma, particle focusing, and anomalous arcing. These effects cannot be adequately modeled without detailed knowledge of the plasma sheath structure and space charge effects. Laboratory studies of 1 by 10 meter solar array in a simulated low Earth orbit plasma are discussed. The plasma screening process is discussed, program theory is outlined, and a series of calibration models is presented. These models are designed to demonstrate that PANEL is capable of accurate self consistant space charge calculations. Such models include PANEL predictions for the Child-Langmuir diode problem
Spontaneous ignition delay characteristics of hydrocarbon fuel-air mixtures
The influence of pressure on the autoignition characteristics of homogeneous mixtures of hydrocarbon fuels in air is examined. Autoignition delay times are measured for propane, ethylene, methane, and acetylene in a continuous flow apparatus featuring a multi-point fuel injector. Results are presented for mixture temperatures from 670K to 1020K, pressures from 1 to 10 atmospheres, equivalence ratios from 0.2 to 0.7, and velocities from 5 to 30 m/s. Delay time is related to pressure, temperature, and fuel concentration by global reaction theory. The results show variations in global activation energy from 25 to 38 kcal/kg-mol, pressure exponents from 0.66 to 1.21, and fuel concentration exponents from 0.19 to 0.75 for the fuels studied. These results are generally in good agreement with previous studies carried out under similar conditions
Simulator test to study hot-flow problems related to a gas cooled reactor
An advance study of materials, fuel injection, and hot flow problems related to the gas core nuclear rocket is reported. The first task was to test a previously constructed induction heated plasma GCNR simulator above 300 kW. A number of tests are reported operating in the range of 300 kW at 10,000 cps. A second simulator was designed but not constructed for cold-hot visualization studies using louvered walls. A third task was a paper investigation of practical uranium feed systems, including a detailed discussion of related problems. The last assignment resulted in two designs for plasma nozzle test devices that could be operated at 200 atm on hydrogen
Focus Point Supersymmetry Redux
Recent results from Higgs boson and supersymmetry searches at the Large
Hadron Collider provide strong new motivations for supersymmetric theories with
heavy superpartners. We reconsider focus point supersymmetry (FP SUSY), in
which all squarks and sleptons may have multi-TeV masses without introducing
fine-tuning in the weak scale with respect to variations in the fundamental
SUSY-breaking parameters. We examine both FP SUSY and its familiar special
case, the FP region of mSUGRA/CMSSM, and show that they are beautifully
consistent with all particle, astroparticle, and cosmological data, including
Higgs boson mass limits, null results from SUSY searches, electric dipole
moments, b -> s gamma, B_s -> mu^+ mu^-, the thermal relic density of
neutralinos, and dark matter searches. The observed deviation of the muon's
anomalous magnetic moment from its standard model value may also be explained
in FP SUSY, although not in the FP region of mSUGRA/CMSSM. In light of recent
data, we advocate refined searches for FP SUSY and related scenarios with heavy
squarks and sleptons, and we present a simplified parameter space to aid such
analyses.Comment: v3: 20 pages, 20 figures, minor numerical error in relic density
calculation corrected, fixed contours in figure
Motif-based communities in complex networks
Community definitions usually focus on edges, inside and between the
communities. However, the high density of edges within a community determines
correlations between nodes going beyond nearest-neighbours, and which are
indicated by the presence of motifs. We show how motifs can be used to define
general classes of nodes, including communities, by extending the mathematical
expression of Newman-Girvan modularity. We construct then a general framework
and apply it to some synthetic and real networks
Network Structure, Topology and Dynamics in Generalized Models of Synchronization
We explore the interplay of network structure, topology, and dynamic
interactions between nodes using the paradigm of distributed synchronization in
a network of coupled oscillators. As the network evolves to a global steady
state, interconnected oscillators synchronize in stages, revealing network's
underlying community structure. Traditional models of synchronization assume
that interactions between nodes are mediated by a conservative process, such as
diffusion. However, social and biological processes are often non-conservative.
We propose a new model of synchronization in a network of oscillators coupled
via non-conservative processes. We study dynamics of synchronization of a
synthetic and real-world networks and show that different synchronization
models reveal different structures within the same network
HI studies of the Sculptor group galaxies. VIII. The background galaxies: NGC 24 and NGC 45
In order to complete our HI survey of galaxies in the Sculptor group area,
VLA observations of NGC 24 and NGC 45 are presented. These two galaxies of
similar magnitude M_B ~ -17.4 lie in the background of the Sculptor group and
are low surface brightness galaxies, especially NGC 45. The HI distribution and
kinematics are regular for NGC 24 while NGC 45 exhibits a kinematical twist of
its major axis. A tilted-ring model shows that the position angle of the major
axis changes by ~25 degrees. A best-fit model of their mass distribution gives
mass-to-light ratios for the stellar disk of 2.5 and 5.2 for NGC 24 and NGC 45
respectively. These values are higher than the ones expected from stellar
population synthesis models. Despite the large dark matter contribution, the
galaxy mass is still dominated by the stellar component in their very inner
regions. These high mass-to-light ratios are typical of what is seen in low
surface brightness galaxies and may indicate that, in those galaxies, disks are
far from the maximum disk case. The halo parameters derived from the best-fit
models are thus lower limits.Comment: 23 pages, 10 figures, accepted for publication in The Astronomical
Journa
Eumops perotis.
Eumops perotis is the largest bat in the United States. The greater mastiff bat resembles other North American free-tailed bats, but is distinguished from other molossids by its large size and lack of long guard hairs on the rump (Barbour and Davis, 1969). E. perotis has the thinnest dentary of any Eumops (Freeman, 1981a).In the United States, E. perotis can be separated from E. underwoodi by its larger size (forearm is 73-83 mm in E. perotis and 65-77 mm in E. underwoodi), darker color, and lack of long guard hairs on the rump. The ears are longer (36-47 mm in E. perotis and 28-32 mm in E. underwoodi), they extend beyond the nose when laid forward, and they are joined at the midline. In E. perotis, the tragus is large, broad, and square, the greatest length of the skull usually is \u3e30 mm rather than less, the basisphenoid pits are large, deep, and not oval shaped, and the third transverse commissure of the M3 hardly is discernible (Barbour and Davis, 1969; Hoffmeister, 1986). Compared with E. perotis, the skull of E. underwoodi (Fig. 2) is shorter, wider, and less robust, and the interorbital region is distinctly hourglass-shaped rather than nearly cylindrical as in E. perotis (Benson, 1947). Compared with E. perotis, E. dabbenei has shorter ears, smaller pointed tragus, more massive skull, and the basisphenoid pits are shallower and less developed (Eger, 1977)
Error tolerance in an NMR Implementation of Grover's Fixed-Point Quantum Search Algorithm
We describe an implementation of Grover's fixed-point quantum search
algorithm on a nuclear magnetic resonance (NMR) quantum computer, searching for
either one or two matching items in an unsorted database of four items. In this
new algorithm the target state (an equally weighted superposition of the
matching states) is a fixed point of the recursive search operator, and so the
algorithm always moves towards the desired state. The effects of systematic
errors in the implementation are briefly explored.Comment: 5 Pages RevTex4 including three figures. Changes made at request of
referees; now in press at Phys Rev
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