8,159 research outputs found
A summary of research on the NASA-Global Atmospheric Sampling Program performed by the Atmospheric Sciences Research Center
The annual variations of ozone near the tropopause are derived from aircraft exhibit year-to-year differences which are not explicitly accounted for by the simple, classical ozone transport theory. Phenomena such as tropopause lifting, interannual variations in the rates of stratospheric-tropospheric exchange and meridional mixing, contribute differently to the distribution of ozone in this altitude region. Ozone encounter climatologies have been represented by global maps which show the probabilities of exceeding ambient ozone levels of 200, 300, and 400 ppbV along flight routes during the year. Continuous ozone records obtained from the GASP system revealed the presence of gravity waves whose wavelength is of the order 20 km. The GASP data cannot, however, be utilized for the evaluation of horizontal fluxes of such quantities as ozone, sensible heat, and zonal momentum; the data are too sparsely and irregularly distributed for the computation of stable correlations. Multiple species data from the unique circumglobal flight of a Pan American airliner on 28-30 October 1977 are discussed with particular regard to the apparent interhemispheric differences in tropospheric species concentrations, variation between the Arctic and Antarctic stratospheres, to possible covariations between species, and to potential source regions for various constituents
Advanced analog television study final report, 4 nov. - 19 dec. 1963
Information bandwidth reduction for analog television signals - Description of multiple interlace syste
Pairing of 1-hexyl-3-methylimidazolium and tetrafluoroborate ions in n-pentanol
Molecular dynamics simulations are obtained and analyzed to study pairing of
1-hexyl-3-methylimidazolium and tetrafluoroborate ions in n-pentanol, in
particular by evaluating the potential-of-mean-force between counter ions. The
present molecular model and simulation accurately predicts the dissociation
constant Kd in comparison to experiment, and thus the behavior and magnitudes
for the ion-pair pmf at molecular distances, even though the dielectric
constant of the simulated solvent differs from the experimental value by about
30%. A naive dielectric model does not capture molecule structural effects such
as multiple conformations and binding geometries of the Hmim+ and BF4-
ion-pairs. Mobilities identify multiple time-scale effects in the
autocorrelation of the random forces on the ions, and specifically a slow,
exponential time-decay of those long-ranged forces associated here with
dielectric friction effects.Comment: 5 pages, 7 figures. V2: Figs. 4 & 7 redrawn for better visual clarity
with log-scales. No change in results. In press J. Chem. Phys. 201
Tsunamis, Viscosity and the HBT Puzzle
The equation of state and bulk and shear viscosities are shown to be able to
affect the transverse dynamics of a central heavy ion collision. The net
entropy, along with the femtoscopic radii are shown to be affected at the
10-20% level by both shear and bulk viscosity. The degree to which these
effects help build a tsunami-like pulse is also discussed.Comment: Contribution to SQM 2007 in Levoca, Slovaki
Hydrogen Dissociation and Diffusion on Ni and Ti -doped Mg(0001) Surfaces
It is well known, both theoretically and experimentally, that alloying
MgH with transition elements can significantly improve the thermodynamic
and kinetic properties for H desorption, as well as the H intake by Mg
bulk. Here we present a density functional theory investigation of hydrogen
dissociation and surface diffusion over Ni-doped surface, and compare the
findings to previously investigated Ti-doped Mg(0001) and pure Mg(0001)
surfaces. Our results show that the energy barrier for hydrogen dissociation on
the pure Mg(0001) surface is high, while it is small/null when Ni/Ti are added
to the surface as dopants. We find that the binding energy of the two H atoms
near the dissociation site is high on Ti, effectively impeding diffusion away
from the Ti site. By contrast, we find that on Ni the energy barrier for
diffusion is much reduced. Therefore, although both Ti and Ni promote H
dissociation, only Ni appears to be a good catalyst for Mg hydrogenation,
allowing diffusion away from the catalytic sites. Experimental results
corroborate these theoretical findings, i.e. faster hydrogenation of the Ni
doped Mg sample as opposed to the reference Mg or Ti doped Mg.Comment: 17 pages, 15 figures, to appear in Journal of Chemical Physic
Early evolution of electron cyclotron driven current during suppression of tearing modes in a circular tokamak
When electron cyclotron (EC) driven current is first applied to the inside of
a magnetic island, the current spreads throughout the island and after a short
period achieves a steady level. Using a two equation fluid model for the EC
current that allows us to examine this early evolution in detail, we analyze
high-resolution simulations of a 2/1 classical tearing mode in a low-beta large
aspect-ratio circular tokamak. These simulations use a nonlinear 3D reduced-MHD
fluid model and the JOREK code. During the initial period where the EC driven
current grows and spreads throughout the magnetic island, it is not a function
of the magnetic flux. However, once it has reached a steady-state, it should be
a flux function. We demonstrate numerically that if sufficiently resolved
toroidally, the steady-state EC driven current becomes approximately a flux
function. We discuss the physics of this early period of EC evolution and its
impact on the size of the magnetic island.Comment: 12 pages, 7 figure
Thermodynamic and magnetic properties of the layered triangular magnet NaNiO2
We report muon-spin rotation, heat capacity, magnetization, and ac magnetic
susceptibility measurements of the layered spin-1/2 antiferromagnet NaNiO2.
These show the onset of long-range magnetic order below T_N = 19.5K. Rapid muon
depolarization persisting to about 5K above T_N is consistent with the presence
of short-range magnetic order. The temperature and frequency dependence of the
ac susceptibility suggests that magnetic clusters persist above 25K in the
paramagnetic state and that their volume fraction decreases with increasing
temperature. A frequency dependent peak in the ac magnetic susceptibility at
T_sf = 3K is observed, consistent with a slowing of spin fluctuations at this
temperature. A partial magnetic phase diagram is deduced.Comment: 4 pages, 4 figure
Personal Pedagogical Systems: Core Beliefs, Foundational Knowledge, and Informal Theories of Teaching
This case study describes a personal pedagogical system that acts a guide for adult educators in their practice. The system reflects core beliefs (assumptions about truth or propriety), foundational knowledge (essential knowledge for effective teaching of adults) and an informal theory of teaching (a theory of what works and what doesn\u27t work), all of which interact dialectically. Implications for further research and practice are discussed
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