89,994 research outputs found
Coal-rock interface detector
A coal-rock interface detector is presented which employs a radioactive source and radiation sensor. The source and sensor are separately and independently suspended and positioned against a mine surface of hydraulic pistons, which are biased from an air cushioned source of pressurized hydraulic fluid
An analytical law for size effects on thermal conductivity of nanostructures
The thermal conductivity of a nanostructure is sensitive to its dimensions. A
simple analytical scaling law that predicts how conductivity changes with the
dimensions of the structure, however, has not been developed. The lack of such
a law is a hurdle in "phonon engineering" of many important applications. Here,
we report an analytical scaling law for thermal conductivity of nanostructures
as a function of their dimensions. We have verified the law using very large
molecular dynamics simulations
Effects of Cutoff Functions of Tersoff Potentials on Molecular Dynamics Simulations of Thermal Transport
Past molecular dynamics studies of thermal transport have predominantly used
Stillinger-Weber potentials. As materials continuously shrink, their properties
increasingly depend on defect and surface effects. Unfortunately,
Stillinger-Weber potentials are best used for diamond-cubic-like bulk crystals.
They cannot represent the energies of many metastable phases, nor can they
accurately predict the energetics of defective and surface regions. To study
nanostructured materials, where these regions can dominate thermal transport,
the accuracy of Tersoff potentials in representing these structures is more
desirable. Based upon an analysis of thermal transport in a GaN system, we
demonstrate that the cutoff function of the existing Tersoff potentials may
lead to problems in determining the thermal conductivity. To remedy this issue,
improved cutoff schemes are proposed and evaluated
Transverse Asymmetry A_T′ from the Quasielastic ^3He(e,e′) Process and the Neutron Magnetic Form Factor
We have measured the transverse asymmetry A_T′ in ^3He(e,e′) quasielastic scattering in Hall A at Jefferson Laboratory with high precision for Q^2 values from 0.1 to 0.6 (GeV/c)^2. The neutron magnetic form factor GMn was extracted based on Faddeev calculations for Q^2 = 0.1 and 0.2 (GeV/c)^2 with an experimental uncertainty of less than 2%
Plane-wave impulse approximation extraction of the neutron magnetic form factor from quasielastic ^3He(e,e') at Q^2=0.3 to 0.6 (GeV/c)^2
A high precision measurement of the transverse spin-dependent asymmetry A_T' in ^3He(e,e') quasielastic
scattering was performed in Hall A at Jefferson Lab at values of the squared four-momentum transfer, Q^2,
between 0.1 and 0.6 (GeV/c)^2. A_(T') is sensitive to the neutron magnetic form factor, G_M^n . Values of G_M^n at
Q^2 = 0.1 and 0.2 (GeV/c)^2, extracted using Faddeev calculations, were reported previously. Here, we report
the extraction of G_M^n for the remaining Q^2 values in the range from 0.3 to 0.6 (GeV/c)^2 using a plane-wave
impulse approximation calculation. The results are in good agreement with recent precision data from experiments
using a deuterium target
Water-propellant resistojets for man-tended platforms
The selection of a propulsion system for a man-tended platform has been influenced by the planned use of resistojets for drag make-up on the manned space station. For that application a resistojet has been designed that is capable of operation with a wide variety of propellants, including water. The reasons for the selection of water as the propellant and the performance of water as a propellant are discussed. The man-tended platform and its mission requirements are described
Letter between E. S. Jones and W. J. Kerr
Letters concerning a position in botany at Utah Agricultural College
Active and passive microwave measurements in Hurricane Allen
The NASA Langley Research Center analysis of the airborne microwave remote sensing measurements of Hurricane Allen obtained on August 5 and 8, 1980 is summarized. The instruments were the C-band stepped frequency microwave radiometer and the Ku-band airborne microwave scatterometer. They were carried aboard a NOAA aircraft making storm penetrations at an altitude of 3000 m and are sensitive to rain rate, surface wind speed, and surface wind vector. The wind speed is calculated from the increase in antenna brightness temperature above the estimated calm sea value. The rain rate is obtained from the difference between antenna temperature increases measured at two frequencies, and wind vector is determined from the sea surface normalized radar cross section measured at several azimuths. Comparison wind data were provided from the inertial navigation systems aboard both the C-130 aircraft at 3000 m and a second NOAA aircraft (a P-3) operating between 500 and 1500 m. Comparison rain rate data were obtained with a rain radar aboard the P-3. Evaluation of the surface winds obtained with the two microwave instruments was limited to comparisons with each other and with the flight level winds. Two important conclusions are drawn from these comparisons: (1) the radiometer is accurate when predicting flight level wind speeds and rain; and (2) the scatterometer produces well behaved and consistent wind vectors for the rain free periods
The survival and destruction of X-ray coronae of early-type galaxies in the rich cluster environments: a case study of Abell 1367
A new Chandra observation of the northwest region of the galaxy cluster A1367
reveals four cool galaxy coronae (0.4 - 1.0 keV) embedded in the hot
intracluster medium (ICM) (5 - 6 keV). While the large coronae of NGC 3842 and
NGC 3837 appear symmetric and relaxed, the galaxy coronae of the \lsim L*
galaxies (NGC 3841 and CGCG 97090) are disturbed and being stripped. Massive
galaxies, with dense cooling cores, are better able to resist ram pressure
stripping and survive in rich environments than \lsim L* galaxies whose
galactic coronae are much less dense. The survival of these cool coronae
implies that thermal conduction from the hot surrounding ICM has to be
suppressed by a factor of at least 60, at the corona boundary. Within the
galaxy coronae of NGC 3842 and NGC 3837, stellar mass loss or heat conduction
with the Spitzer value may be sufficient to balance radiative cooling. Energy
deposition at the ends of collimated jets may heat the outer coronae, but allow
the survival of a small, dense gas core (e.g., NGC 3842 in A1367 and NGC 4874
in Coma). The survived X-ray coronae become significantly smaller and fainter
with the increasing ambient pressure.Comment: 11 pages, 7 figures, emulateapj5, accepted by Ap
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