56,136 research outputs found
Influence of the Dirac sea on proton electromagnetic knockout
We use the relativistic distorted-wave impulse approximation (RDWIA) to study
the effects of negative-energy components of Dirac wave functions on the
left-right asymmetry for (e,e'p) reactions on 16-O with 0.2 < Q^2 < 0.8 and
12-C with 0.6 < Q^2 < 1.8 (GeV/c)^2. Spinor distortion is more important for
the bound state than for the ejectile and the net effect decreases with Q^2.
Spinor distortion breaks Godon equivalence and the data favor the CC2 operator
with intermediate coupling to the sea. The left-right asymmetry for Q^2 < 1.2
(GeV/c)^2 is described well by RDWIA calcuations, but at Q^2 = 1.8 (GeV/c)^2
the observed variation with missing momentum is flatter than predicted.Comment: 12 pages, 9 figures, to be submitted to PR
RDWIA analysis of 12C(e,e'p) for Q^2 < 2 (GeV/c)^2
We analyze data for 12C(e,e'p) with Q^2 < 2 (GeV/c)^2 using the relativistic
distorted-wave impulse approximation (RDWIA) based upon Dirac-Hartree wave
functions. The 1p normalization extracted from data for Q^2 > 0.6 (GeV/c)^2 is
approximately 0.87, independent of Q^2, which is consistent with the predicted
depletion by short-range correlations. The total 1p and 1s strength for E_m <
80 MeV approaches 100% of IPSM, consistent with a continuum contribution for 30
< E_m < 80 MeV of about 12% of IPSM. Similarly, a scale factor of 1.12 brings
RDWIA calculations into good agreement with 12C(e,e'p) data for transparency.
We also analyzed low Q^2 data from which a recent NDWIA analysis suggested that
spectroscopic factors might depend strongly upon the resolution of the probe.
We find that momentum distributions for their empirical Woods-Saxon wave
functions fit to low Q^2 data for parallel kinematics are too narrow to
reproduce data for quasiperpendicular kinematics, especially for larger Q^2,
and are partly responsible for reducing fitted normalization factors.Comment: 19 pages, 14 figures, to be submitted to PR
Development of an autonomous video rendezous and docking system
Video control systems using three flashing lights and two other types of docking aids were evaluated through computer simulation and other approaches. The three light system performed much better than the others. Its accuracy is affected little by tumbling of the target spacecraft, and in the simulations it was able to cope with attitude rates up to 20,000 degrees per hour about the docking axis. Its performance with rotation about other axes is determined primarily by the state estimation and goal setting portions of the control system, not by measurement accuracy. A suitable control system, and a computer program that can serve as the basis for the physical simulation are discussed
The Infrared Nucleus of the Wolf-Rayet Galaxy Henize 2-10
We have obtained near-infrared images and mid-infrared spectra of the
starburst core of the dwarf Wolf-Rayet galaxy He 2-10. We find that the
infrared continuum and emission lines are concentrated in a flattened ellipse
3-4'' or 150 pc across which may show where a recent accretion event has
triggered intense star formation. The ionizing radiation from this cluster has
an effective temperature of 40,000 K, corresponding to stars, and
the starburst is years old.Comment: 17 pages Latex, 7 postscript figures, 1 postscript table, accepted to
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Arkansas Small-Grain Cultivar Performance Tests 2004-2005
Small-grain cultivar performance tests are conducted each year in Arkansas by the Arkansas Agricultural Experiment Station, Department of Crop, Soil and Environmental Sciences. The tests provide information to companies developing cultivars and/or marketing seed within the state and aid the Arkansas Cooperative Extension Service in formulating cultivar recommendations for smallgrain producers
Seasonal Price Patterns for Arkansas Soybeans
Seasonality is generally regarded as a major feature in soybean market price variations. Recent years in Arkansas have seen considerable construction of on-farm storage, a move that could mitigate the seasonality effect on price variations. A study comparing cash price indices from the past ten years with results from a 1986 Arkansas study and a recent national-level study found that Arkansas soybean prices appear to have followed a consistent and logical pattern around their national average in spite of increased variability and uncertainty.Seasonality, soybean, cash price index, Demand and Price Analysis, Farm Management, Marketing,
Development of biaxial test fixture includes cryogenic application
Test fixture has the capability of producing biaxial stress fields in test specimens to the point of failure. It determines biaxial stress by dividing the applied load by the net cross section. With modification it can evaluate materials, design concepts, and production hardware at cryogenic temperatures
Flightweight radiantly and actively cooled panel: Thermal and structural performance
A 2- by 4-ft flightweight panel was subjected to thermal/structural tests representative of design flight conditions for a Mach 6.7 transport and to off-design conditions simulating flight maneuvers and cooling system failures. The panel utilized Rene 41 heat shields backed by a thin layer of insulation to radiate away most of the 12 Btu/ft2-sec incident heating. A solution of ethylene glycol in water circulating through tubes in an aluminum-honeycomb-sandwich panel absorbed the remainder of the incident heating (0.8 Btu/sq ft-sec). The panel successfully withstood (1) 46.7 hr of radiant heating which included 53 thermal cycles and 5000 cycles of uniaxial inplane loading of + or - 1200 lfb/in; (2) simulated 2g-maneuver heating conditions and simulated cooling system failures without excessive temperatures on the structural panel; and (3) the extensive thermal/structural tests and the aerothermal tests reported in NASA TP-1595 without significant damage to the structural panel, coolant leaks, or hot-gas ingress to the structural panel
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