13,943 research outputs found
Development and fabrication of radiation resistant high efficiency solar cells Final periodic report, 24 Aug. 1966 - 24 Feb. 1967
Diffusion process for lithium doping of solar cells, and electrical characteristics and radiation resistance of solar cell
New Consequences of Induced Transparency in a Double-Lambda scheme: Destructive Interference In Four-wave Mixing
We investigate a four-state system interacting with long and short laser
pulses in a weak probe beam approximation. We show that when all lasers are
tuned to the exact unperturbed resonances, part of the four-wave mixing (FWM)
field is strongly absorbed. The part which is not absorbed has the exact
intensity required to destructively interfere with the excitation pathway
involved in producing the FWM state. We show that with this three-photon
destructive interference, the conversion efficiency can still be as high as
25%. Contrary to common belief,our calculation shows that this process, where
an ideal one-photon electromagnetically induced transparency is established, is
not most suitable for high efficiency conversion. With appropriate
phase-matching and propagation distance, and when the three-photon destructive
interference does not occur, we show that the photon flux conversion efficiency
is independent of probe intensity and can be close to 100%. In addition, we
show clearly that the conversion efficiency is not determined by the maximum
atomic coherence between two lower excited states, as commonly believed. It is
the combination of phase-matching and constructive interference involving the
two terms arising in producing the mixing wave that is the key element for the
optimized FWM generation. Indeed, in this scheme no appreciable excited state
is produced, so that the atomic coherence between states |0> and |2> is always
very small.Comment: Submitted to Phys. Rev. A, 7 pages, 4 figure
A second eigenvalue bound for the Dirichlet Schroedinger operator
Let be the th eigenvalue of the Schr\"odinger
operator with Dirichlet boundary conditions on a bounded domain and with the positive potential . Following the spirit of the
Payne-P\'olya-Weinberger conjecture and under some convexity assumptions on the
spherically rearranged potential , we prove that . Here denotes the ball, centered at the
origin, that satisfies the condition .
Further we prove under the same convexity assumptions on a spherically
symmetric potential , that decreases
when the radius of the ball increases.
We conclude with several results about the first two eigenvalues of the
Laplace operator with respect to a measure of Gaussian or inverted Gaussian
density
Vibrational modes of circular free plates under tension
The vibrational frequencies of a plate under tension are given by the
eigenvalues of the equation . This
paper determines the eigenfunctions and eigenvalues of this bi-Laplace problem
on the ball under natural (free) boundary conditions. In particular, the
fundamental modes --- the eigenfunctions of the lowest nonzero eigenvalue ---
are identified and found to have simple angular dependence.Comment: 17 pages. To be submitted for publication shortly
Carbon recombination lines between 34.5 and 770 MHz toward Cassiopeia A
We present observations of low-frequency recombination lines of carbon toward Cas A near 34.5 MHz (n ~ 575) using the Gauribidanur radio telescope and near 560 MHz (n ~ 225) and 770 MHz (n ~ 205) using the NRAO 140 foot (43 m) telescope in Greenbank. We also present high angular resolution (1') observations of the C270α line near 332 MHz using the Very Large Array in B-configuration. A high signal-to-noise ratio spectrum is obtained at 34.5 MHz, which clearly shows a Voigt profile with distinct Lorentzian wings, resulting from significant pressure and radiation broadening at such high quantum numbers. The emission lines detected near 332, 550, and 770 MHz, on the other hand, are narrow and essentially Doppler-broadened. The measured Lorentzian width at 34.5 MHz constrains the allowed combinations of radiation temperature, electron density, and electron temperature in the line-forming region. Radiation broadening at 34.5 MHz places a lower limit of 115 pc on the separation between Cas A and the line-forming clouds. Modeling the variation in the integrated line-to-continuum ratio with frequency indicates that the region is likely to be associated with the cold atomic hydrogen component of the interstellar medium, and the physical properties of this region are likely to be Te = 75 K, ne = 0.02 cm-3, TR100 = 3200 K, and nHTe = 10,000 cm-3 K. Comparison of the distribution of the C270α recombination line emission across Cas A with that of 12CO and H I also supports the above conclusion
Charge-Symmetry-Breaking Three-Nucleon Forces
Leading-order three-nucleon forces that violate isospin symmetry are
calculated in Chiral Perturbation Theory. The effect of the
charge-symmetry-breaking three-nucleon force is investigated in the trinucleon
systems using Faddeev calculations. We find that the contribution of this force
to the 3He - 3H binding-energy difference is approximately 5 keV.Comment: 14 pages, 3 figure
Wind measurements from an array of oceanographic moorings and from F/SMeteor during JASIN 1978
During the Joint Air-Sea Interaction (JASIN) experiment conducted in the northern Rockall Trough in the summer of 1978, oceanographic moorings with surface buoys carrying wind recorders were deployed in an array designed to investigate the variability of the near-surface wind field at scales of from 2 to 200 km. The wind records together with observations taken on board the research vessels participating in JASIN have provided ground truth measurements for the sea surface wind velocity sensors on the Seasat satellite. During most of the experiment the wind field was characterized by spatial scales large in comparison with the separations between the buoys. On several occasions, spatial differences associated with cold fronts were identified, and it was possible to track the passage of the front through the array. However, quantitative analysis of the variability of the wind field was complicated both by a lack of data due to mechanical failures of some instruments and by significant differences in the performance of the diverse types of wind recorders. Reevaluation of the instruments used in JASIN and recent comparison of some of these instruments with more conventional sets of wind sensors confirm the possibility that there is significant error in the JASIN wind measurements made from the buoys. In particular, the vector-averaging wind recorder on W2, which was one of the few instruments to recover a full length record and which was chosen during a Seasat-JASIN workshop as the JASIN standard, had performance characteristics that were among the most difficult to explain
Observation of a red-blue detuning asymmetry in matter-wave superradiance
We report the first experimental observations of strong suppression of
matter-wave superradiance using blue-detuned pump light and demonstrate a
pump-laser detuning asymmetry in the collective atomic recoil motion. In
contrast to all previous theoretical frameworks, which predict that the process
should be symmetric with respect to the sign of the pump-laser detuning, we
find that for condensates the symmetry is broken. With high condensate
densities and red-detuned light, the familiar distinctive multi-order,
matter-wave scattering pattern is clearly visible, whereas with blue-detuned
light superradiance is strongly suppressed. In the limit of a dilute atomic
gas, however, symmetry is restored.Comment: Accepted by Phys. Rev. Let
Shell-model calculations for the three-nucleon system
We use Faddeev's decomposition to solve the shell-model problem for three
nucleons. The dependence on harmonic-oscillator excitations allowed in the
model space, up to in the present calculations, and on the
harmonic-oscillator frequency is studied. Effective interactions derived from
Nijmegen II and Reid93 potentials are used in the calculations. The binding
energies obtained are close to those calculated by other methods. The structure
of the Faddeev equations is discussed and a simple formula for matrix elements
of the permutation operators in a harmonic-oscillator basis is given. The Pauli
principle is properly treated in the calculations.Comment: 11 pages. REVTEX. 6 PostScript figure
Atlantis II : cruise 102 : moored and shipboard surface meteorological measurements during JASIN 1978
During cruise 102 of the R/V Atlantis-II in the Joint Air-Sea Interaction
Project (JASIN), surface meteorological data were gathered by Woods Hole
Oceanographic Institution personnel from two moored buoys and from the ship.
One buoy (JASIN W2/WHOI 651) carried a Vector Averaging Wind Recorder
(VAWR) and a Vector Measuring Wind Recorder (VMWR); these instruments provided
18 days of intercomparison data and 38 days of meteorological data from 30 July
to 6 September 1978. The other buoy (JASIN H2) carried a VMWR and gave 25
total days of data from 16 July to 10 August, and from 26 August to
1 September.
A PET computer, hardwired to sensors positioned on the ship, displayed
data that were logged during both legs of the cruise. Manual data were
gathered by the science watches.
This report describes the PET system, and displays and compares all the
data. VAWR hourly meteorological data are listed for the 38 day period.
Scientific interpretation of these data, such as calculations of heat
fluxes, will be published separately.Prepared for the National Science Foundation under
Grants OCE77-25803 and OCE76-80174, and for the Office
of Naval Research under Contract N00014-76-C-0197;
NR 083-400 to the Woods Hole Oceanographic Institution
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