240,190 research outputs found
An Experimental Investigation of the Performance of the Nitrogen Tetroxide-Hydrazine System in the Oxidizer-Rich and Fuel-Rich Regions
The results of an experimental program directed toward determining some of the operational characteristics of the nitrogen tetroxide-hydrazine propellant system under oxidizer-rich and fuel-rich conditions are reported. Data are presented for the mixture-ratio ranges of 0 to 0.55 at a nominal chamber pressure of 300 psia and characteristic chamber length of 250 in., and at mixture ratios of 5.9 to 13.0 at nominal chamber pressures of 400 and 500 psia and characteristic chamber lengths of 100 and 3900 in. The relationship of the actual performance data obtained in each region with those predicted from thermochemical performance calculations is presented. From this comparison, it is concluded that in neither region are equilibrium conditions obtained and that utilization of performance data obtained from assumptions of equilibrium will lead to serious errors. In the oxidizer-rich region investigated, temperatures considerably below those predicted occur throughout the range of mixture ratios investigated because of the lack of exothermic dissociation of the nitrogen oxides. In the fuel-rich region, below a mixture ratio of 0.3, temperatures considerably higher than those predicted occur because of the lack of endothermic dissociation of ammonia
Conductance Correlations Near Integer Quantum Hall Transitions
In a disordered mesoscopic system, the typical spacing between the peaks and
the valleys of the conductance as a function of Fermi energy is called
the conductance energy correlation range . Under the ergodic hypothesis,
the latter is determined by the half-width of the ensemble averaged conductance
correlation function: . In
ordinary diffusive metals, , where is the diffusion constant
and is the linear dimension of the phase-coherent sample. However, near a
quantum phase transition driven by the location of the Fermi energy , the
above picture breaks down. As an example of the latter, we study, for the first
time, the conductance correlations near the integer quantum Hall transitions of
which is a critical coupling constant. We point out that the behavior of
is determined by the interplay between the static and the dynamic
properties of the critical phenomena.Comment: 4 pages, 4 figures, minor corrections, to appear in Phys. Rev. Let
Pion-Exchange and Fermi-Motion Effects on the Proton-Deuteron Drell-Yan Process
Within a nuclear model that the deuteron has NN and \pi NN components, we
derive convolution formula for investigating the Drell-Yan process in
proton-deuteron (pd) reactions. The contribution from the \pi NN component is
expressed in terms of a pion momentum distribution that depends sensitively on
the \pi NN form factor. With a \pi NN form factor determined by fitting the \pi
N scattering data up to invariant mass W = 1.3 GeV, we find that the
pion-exchange and nucleon Fermi-motion effects can change significantly the
ratios between the proton-deuteron and proton-proton Drell-Yan cross sections,
R_{pd/pp} = \sigma^{pd}/(2\sigma^{pp}), in the region where the partons emitted
from the target deuteron are in the Bjorken x_2 > 0.4 region. The calculated
ratios R_{pd/pp} at 800 GeV agree with the available data. Predictions at 120
GeV for analyzing the forthcoming data from Fermilab are presented.Comment: 27 pages, 10 figures. A couple of new numerical results are added.
arXiv admin note: substantial text overlap with arXiv:1106.556
Temperature Effects on Development of Three Cereal Aphid Parasitoids (Hymenoptera: Aphidiidae)
Temperature is an important climatological variable that influences the biology and ecology of insects. Poor climatic adaptation can limit the effectiveness of parasitic insects in biological control. Two exotic parasites (Syrian Diaeretiella rapae (M\u27Intosh) and Argentinean Aphidius colemani Viereck) imported for biological control of the Russian wheat aphid, Diuraphis noxia (Mordvilko), and one native parasite (Diaeretiella rapae) were reared in growth chambers in three fluctuating temperature regimes with average daily temperatures of 12, 18, and 24°C. Estimates of temperature thresholds for immature development were 3.3, 3.5, and 2.8°C, for Oklahoman D. rapae, Syrian D. rapae, and A. colemani, respectively. Estimates of thermal require- ments for development from egg to adult were 297, 278, and 301 degree-days for the three parasitoids. Dry weights of adults reared in different fluctuating temperature regimes did not differ significantly among sexes, but adults from regimes with low average temperatures of 12 and 18°C had significantly greater weights than those reared in a regime with an average temperature of 24°C. Results suggest that developmental response to temperature will not limit the effectiveness of the exotic parasites in biological control
Complementary algorithms for graphs and percolation
A pair of complementary algorithms are presented. One of the pair is a fast
method for connecting graphs with an edge. The other is a fast method for
removing edges from a graph. Both algorithms employ the same tree based graph
representation and so, in concert, can arbitrarily modify any graph. Since the
clusters of a percolation model may be described as simple connected graphs, an
efficient Monte Carlo scheme can be constructed that uses the algorithms to
sweep the occupation probability back and forth between two turning points.
This approach concentrates computational sampling time within a region of
interest. A high precision value of pc = 0.59274603(9) was thus obtained, by
Mersenne twister, for the two dimensional square site percolation threshold.Comment: 5 pages, 3 figures, poster version presented at statphys23 (2007
Metallic characteristics in superlattices composed of insulators, NdMnO3/SrMnO3/LaMnO3
We report on the electronic properties of superlattices composed of three
different antiferromagnetic insulators, NdMnO3/SrMnO3/LaMnO3 grown on SrTiO3
substrates. Photoemission spectra obtained by tuning the x-ray energy at the Mn
2p -> 3d edge show a Fermi cut-off, indicating metallic behavior mainly
originating from Mn e_g electrons. Furthermore, the density of states near the
Fermi energy and the magnetization obey a similar temperature dependence,
suggesting a correlation between the spin and charge degrees of freedom at the
interfaces of these oxides
Nuclear and Particle Physics applications of the Bohm Picture of Quantum Mechanics
Approximation methods for calculating individual particle/ field motions in
spacetime at the quantum level of accuracy (a key feature of the Bohm Picture
of Quantum Mechanics (BP)), are studied. Modern textbook presentations of
Quantum Theory are used throughout, but only to provide the necessary, already
existing, tested formalisms and calculational techniques. New coherent
insights, reinterpretations of old solutions and results, and new (in principle
testable) quantitative and qualitative predictions, can be obtained on the
basis of the BP that complete the standard type of postdictions and
predictions.Comment: 41 page
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