6,482 research outputs found
High efficiency thermionic converter studies
The objective is to improve thermionic converter performance by means of reduced interelectrode losses, greater emitter capabilities, and lower collector work functions until the converter performance level is suitable for out-of-core space reactors and radioisotope generators. Electrode screening experiments have identified several promising collector materials. Back emission work function measurements of a ZnO collector in a thermionic diode have given values less than 1.3 eV. Diode tests were conducted over the range of temperatures of interest for space power applications. Enhanced mode converter experiments have included triodes operated in both the surface ionization and plasmatron modes. Pulsed triodes were studied as a function of pulse length, pulse potential, inert gas fill pressure, cesium pressure, spacing, emitter temperature and collector temperature. Current amplifications (i.e., mean output current/mean grid current) of several hundred were observed up to output current densities of one amp/sq cm. These data correspond to an equivalent arc drop less than 0.1 eV
CONSUMER HOME-USE EVALUATION OF A DEVELOPED LEAN GROUND BEEF PRODUCT
This study reports findings on the acceptance of a new lean ground beef product. Tested products involved 1) a Developed Lean product (less than 10% fat plus quality enhancers), 2) a Lean product (less than 10% fat without quality enhancers), and 3) a Market product (slightly more than 20% fat). These products were home delivered on a rotating basis to a random sample of 91 households, one product each week for three weeks. Product traits were evaluated by the household meal preparer at three stages of home use: preparing (5 traits), cooking (3 traits), and eating (4 traits), and by other household members at the final consumption stage of eating. More favorable ratings were observed for both Developed Lean and Lean products over the Market product at the preparing and cooking stages. Ratings at the eating stage were similar between the Developed Lean and the Market products indicating a favorable response to the Developed Lean product.Consumer/Household Economics,
High efficiency thermionic converter studies
Research in thermionic energy conversion technology is reported. The objectives were to produce converters suitable for use in out of core space reactors, radioisotope generators, and solar satellites. The development of emitter electrodes that operate at low cesium pressure, stable low work function collector electrodes, and more efficient means of space charge neutralization were investigated to improve thermionic converter performance. Potential improvements in collector properties were noted with evaporated thin film barium oxide coatings. Experiments with cesium carbonate suggest this substance may provide optimum combinations of cesium and oxygen for thermionic conversion
Testing T Invariance in the Interaction of Slow Neutrons with Aligned Nuclei
The study of five-fold (P even, T odd) correlation in the interaction of slow
polarized neutrons with aligned nuclei is a possible way of testing the time
reversal invariance due to the expected enhancement of T violating effects in
compound resonances. Possible nuclear targets are discussed which can be
aligned both dynamically as well as by the "brute force" method at low
temperature. A statistical estimation is performed of the five-fold correlation
for low lying p wave compound resonances of the Sb, Sb and
I nuclei. It is shown that a significant improvement can be achieved
for the bound on the intensity of the fundamental parity conserving time
violating (PCTV) interaction.Comment: 22 pages, 5 figures, published versio
Lossy data compression with random gates
We introduce a new protocol for a lossy data compression algorithm which is
based on constraint satisfaction gates. We show that the theoretical capacity
of algorithms built from standard parity-check gates converges exponentially
fast to the Shannon's bound when the number of variables seen by each gate
increases. We then generalize this approach by introducing random gates. They
have theoretical performances nearly as good as parity checks, but they offer
the great advantage that the encoding can be done in linear time using the
Survey Inspired Decimation algorithm, a powerful algorithm for constraint
satisfaction problems derived from statistical physics
Longitudinal and lateral-directional static aerodynamic characteristics of an unpowered escape system extraction rocket model
An escape system extraction rocket proposed for use on the Rotor Systems Research Aircraft was tested at Mach numbers of 0.1 and 0.3 through an angle of attack range from -2 deg to 102 deg and an angle of sideslip range from 0 deg to 15 deg in the Langley 7- by 10-foot high speed tunnel
Constraints on a Parity-Conserving/Time-Reversal-Non-Conserving Interaction
Time-Reversal-Invariance non-conservation has now been unequivocally
demonstrated in a direct measurement at CPLEAR. What about tests of
time-reversal-invariance in systems other than the kaon system? Tests of
time-reversal-invariance belong to two classes: searches for parity violating
(P-odd)/time-reversal-invariance-odd (T-odd) interactions, and for P-even/T-odd
interactions (assuming CPT conservation this implies C-conjugation
non-conservation). Limits on a P-odd/T-odd interaction follow from measurements
of the electric dipole moment of the neutron (with a present upper limit of 6 x
10^-26 e.cm [95% C.L.]). It provides a limit on a P-odd/T-odd pion-nucleon
coupling constant which is less than 10^-4 times the weak interaction strength.
Experimental limits on a P-even/T-odd interaction are much less stringent.
Following the standard approach of describing the nucleon-nucleon interaction
in terms of meson exchanges, it can be shown that only charged rho-meson
exchange and A_1 meson exchange can lead to a P-even/T-odd interaction. The
better constraints stem from measurements of the electric dipole moment of the
neutron and from measurements of charge-symmetry breaking in neutron-proton
elastic scattering. The latter experiments were executed at TRIUMF (497 and 347
MeV) and at IUCF (183 MeV). Weak decay experiments may provide limits which
will possibly be comparable. All other experiments, like gamma decay
experiments, detailed balance experiments, polarization - analyzing power
difference determinations, and five-fold correlation experiments with polarized
incident nucleons and aligned nuclear targets, have been shown to be at least
an order of magnitude less sensitive.Comment: 15 pages LaTeX, including 5 PostScript figures. Uses ijmpe1.sty. To
appear in International Journal of Modern Physics E (IJMPE). Slight change in
short abstrac
Anisotropic infrared response of vanadium dioxide microcrystals
Vanadium dioxide (VO2) undergoes a phase transition at a temperature of 340 K between an insulating monoclinic M-1 phase and a conducting rutile phase. Accurate measurements of possible anisotropy of the electronic properties and phonon features of VO2 in the insulating monoclinic M-1 and metallic rutile phases are a prerequisite for understanding the phase transition in this correlated system. Recently, it has become possible to grow single domain untwinned VO2 microcrystals, which makes it possible to investigate the true anisotropy of VO2. We performed polarized transmission infrared micro-spectroscopy on these untwinned microcrystals in the spectral range between 200 cm(-1) and 6000 cm(-1) and have obtained the anisotropic phonon parameters and low frequency electronic properties in the insulating monoclinic M-1 and metallic rutile phases. We have also performed ab initio GGA+U total energy calculations of phonon frequencies for both phases. We find our measurements and calculations to be in good agreement. DOI: 10.1103/PhysRevB.87.11512
A Microscopic T-Violating Optical Potential: Implications for Neutron-Transmission Experiments
We derive a T-violating P-conserving optical potential for neutron-nucleus
scattering, starting from a uniquely determined two-body -exchange
interaction with the same symmetry. We then obtain limits on the T-violating
-nucleon coupling from neutron-transmission
experiments in Ho. The limits may soon compete with those from
measurements of atomic electric-dipole moments.Comment: 8 pages, 2 uuencoded figures in separate files (replaces version sent
earlier in the day with figures attached), in RevTeX 3, submitted to PR
Far-Infrared Blocked Impurity Band Detector Development
DRS Sensors & Targeting Systems, supported by detector materials supplier Lawrence Semiconductor Research Laboratory, is developing far-infrared detectors jointly with NASA Langley under the Far-IR Detector Technology Advancement Partnership (FIDTAP). The detectors are intended for spectral characterization of the Earth's energy budget from space. During the first year of this effort we have designed, fabricated, and evaluated pilot Blocked Impurity Band (BIB) detectors in both silicon and germanium, utilizing pre-existing customized detector materials and photolithographic masks. A second-year effort has prepared improved silicon materials, fabricated custom photolithographic masks for detector process, and begun detector processing. We report the characterization results from the pilot detectors and other progress
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