992 research outputs found
Control networks for the Galilean satellites, November 1979
Pictures of the four Galilean satellites taken as the two Voyager spacecraft approached Jupiter during March and July 1979 are presented. Control nets of the Galilean satellites, computed photogrammetrically, and measurements of the mean radii are presented. The pictures in the control nets are identified, the coordinates of the control points are given, and identifications of some of the control points are shown on figures. The use of star field pictures to compute the focal lengths of the camera is discussed and the geometric relationship between the narrow and wide and angle cameras is reported. A description of the coordinate systems of the Galilean satellites is presented and the status of the control net computations is reported
Gastroduodenal Morphology and Related Symptoms in Chronic Alcoholics
Twenty-four chronic alcoholics admitted to hospital for detoxification after a drinking
spree were examined by upper gastrointestinal endoscopy. Biopsy specimens were taken
from corpus/fundus, antrum and duodenum for tissue histology (eosin stain). From the
duodenum villus index and ultrastructure (scanning electron microscopy, SEM) were
also performed. As a control group 12 subjectively healthy non-alcoholics referred to
upper gastrointestinal endoscopy mainly for dyspepsia were chosen
Estimation of Buttiker-Landauer traversal time based on the visibility of transmission current
We present a proposal for the estimation of B\"uttiker-Landauer traversal
time based on the visibility of transmission current. We analyze the tunneling
phenomena with a time-dependent potential and obtain the time-dependent
transmission current. We found that the visibility is directly connected to the
traversal time. Furthermore, this result is valid not only for rectangular
potential barrier but also for general form of potential to which the WKB
approximation is applicable . We compared these results with the numerical
values obtained from the simulation of Nelson's quantum mechanics. Both of them
fit together and it shows our method is very effective to measure
experimentally the traversal time.Comment: 12 pages, REVTeX, including 7 eps figure
Stability of 1-D Excitons in Carbon Nanotubes under High Laser Excitations
Through ultrafast pump-probe spectroscopy with intense pump pulses and a wide
continuum probe, we show that interband exciton peaks in single-walled carbon
nanotubes (SWNTs) are extremely stable under high laser excitations. Estimates
of the initial densities of excitons from the excitation conditions, combined
with recent theoretical calculations of exciton Bohr radii for SWNTs, suggest
that their positions do not change at all even near the Mott density. In
addition, we found that the presence of lowest-subband excitons broadens all
absorption peaks, including those in the second-subband range, which provides a
consistent explanation for the complex spectral dependence of pump-probe
signals reported for SWNTs.Comment: 4 pages, 4 figure
Collective Antenna Effects in the Terahertz and Infrared Response of Highly Aligned Carbon Nanotube Arrays
We study macroscopically-aligned single-wall carbon nanotube arrays with
uniform lengths via polarization-dependent terahertz and infrared transmission
spectroscopy. Polarization anisotropy is extreme at frequencies less than
3 THz with no sign of attenuation when the polarization is perpendicular
to the alignment direction. The attenuation for both parallel and perpendicular
polarizations increases with increasing frequency, exhibiting a pronounced and
broad peak around 10 THz in the parallel case. We model the electromagnetic
response of the sample by taking into account both radiative scattering and
absorption losses. We show that our sample acts as an effective antenna due to
the high degree of alignment, exhibiting much larger radiative scattering than
absorption in the mid/far-infrared range. Our calculated attenuation spectrum
clearly shows a non-Drude peak at 10 THz in agreement with the
experiment.Comment: 5 pages, 5 figure
Wetting of Curved Surfaces
As a first step towards a microscopic understanding of the effective
interaction between colloidal particles suspended in a solvent we study the
wetting behavior of one-component fluids at spheres and fibers. We describe
these phenomena within density functional theory which keeps track of the
microscopic interaction potentials governing these systems. In particular we
properly take into account the power-law decay of both the fluid-fluid
interaction potentials and the substrate potentials. The thicknesses of the
wetting films as a function of temperature and chemical potential as well as
the wetting phase diagrams are determined by minimizing an effective interface
potential which we obtain by applying a sharp-kink approximation to the density
functional. We compare our results with previous approaches to this problem.Comment: 54 pages, 17 figures, accepted for publication in Physica
Salecker-Wigner-Peres clock and average tunneling times
The quantum clock of Salecker-Wigner-Peres is used, by performing a
post-selection of the final state, to obtain average transmission and
reflection times associated to the scattering of localized wave packets by
static potentials in one dimension. The behavior of these average times is
studied for a gaussian wave packet, centered around a tunneling wave number,
incident on a rectangular barrier and, in particular, on a double delta barrier
potential. The regime of opaque barriers is investigated and the results show
that the average transmission time does not saturate, showing no evidence of
the Hartman effect (or its generalized version).Comment: 9 pages, 4 figure
Direct Observation of Sub-Poissonian Number Statistics in a Degenerate Bose Gas
We report the direct observation of sub-Poissonian number fluctuation for a
degenerate Bose gas confined in an optical trap. Reduction of number
fluctuations below the Poissonian limit is observed for average numbers that
range from 300 to 60 atoms.Comment: 5 pages, 4 figure
Quantile Motion and Tunneling
The concepts of quantile position, trajectory, and velocity are defined. For
a tunneling quantum mechanical wave packet, it is proved that its quantile
position always stays behind that of a free wave packet with the same initial
parameters. In quantum mechanics the quantile trajectories are mathematically
identical to Bohm's trajectories. A generalization to three dimensions is
given.Comment: 13 pages, LaTeX, elsart, 3 ps figures, submitted to Phys. Lett.
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