20,015 research outputs found
An Accurate Method for Computing the Absorption of Solar Radiation by Water Vapor
The method is based upon molecular line parameters and makes use of a far wing scaling approximation and k distribution approach previously applied to the computation of the infrared cooling rate due to water vapor. Taking into account the wave number dependence of the incident solar flux, the solar heating rate is computed for the entire water vapor spectrum and for individual absorption bands. The accuracy of the method is tested against line by line calculations. The method introduces a maximum error of 0.06 C/day. The method has the additional advantage over previous methods in that it can be applied to any portion of the spectral region containing the water vapor bands. The integrated absorptances and line intensities computed from the molecular line parameters were compared with laboratory measurements. The comparison reveals that, among the three different sources, absorptance is the largest for the laboratory measurements
An efficient routine for infrared radiative transfer in a cloudy atmosphere
A FORTRAN program that calculates the atmospheric cooling rate and infrared fluxes for partly cloudy atmospheres is documented. The IR fluxes in the water bands and the 9.6 and 15 micron bands are calculated at 15 levels ranging from 1.39 mb to the surface. The program is generalized to accept any arbitrary atmospheric temperature and humidity profiles and clouds as input and return the cooling rate and fluxes as output. Sample calculations for various atmospheric profiles and cloud situations are demonstrated
Behavior of the sonic boom shock wave near the sonic cutoff altitude
Behavior of sonic boom shock wave near sonic cutoff altitud
A mean-removed variation of weighted universal vector quantization for image coding
Weighted universal vector quantization uses traditional codeword design techniques to design locally optimal multi-codebook systems. Application of this technique to a sequence of medical images produces a 10.3 dB improvement over standard full search vector quantization followed by entropy coding at the cost of increased complexity. In this proposed variation each codebook in the system is given a mean or 'prediction' value which is subtracted from all supervectors that map to the given codebook. The chosen codebook's codewords are then used to encode the resulting residuals. Application of the mean-removed system to the medical data set achieves up to 0.5 dB improvement at no rate expense
Stochastic self-assembly of incommensurate clusters
We examine the classic problem of homogeneous nucleation and growth by
deriving and analyzing a fully discrete stochastic master equation. Upon
comparison with results obtained from the corresponding mean-field
Becker-D\"{o}ring equations we find striking differences between the two
corresponding equilibrium mean cluster concentrations. These discrepancies
depend primarily on the divisibility of the total available mass by the maximum
allowed cluster size, and the remainder. When such mass incommensurability
arises, a single remainder particle can "emulsify" or "disperse" the system by
significantly broadening the mean cluster size distribution. This finite-sized
broadening effect is periodic in the total mass of the system and can arise
even when the system size is asymptotically large, provided the ratio of the
total mass to the maximum cluster size is finite. For such finite ratios we
show that homogeneous nucleation in the limit of large, closed systems is not
accurately described by classical mean-field mass-action approaches.Comment: 5 pages, 4 figures, 1 tabl
Deep shower interpretation of the cosmic ray events observed in excess of the Greisen-Zatsepin-Kuzmin energy
We consider the possibility that the ultra-high-energy cosmic ray flux has a
small component of exotic particles which create showers much deeper in the
atmosphere than ordinary hadronic primaries. It is shown that applying the
conventional AGASA/HiRes/Auger data analysis procedures to such exotic events
results in large systematic biases in the energy spectrum measurement. SubGZK
exotic showers may be mis-reconstructed with much higher energies and mimick
superGZK events. Alternatively, superGZK exotic showers may elude detection by
conventional fluorescence analysis techniques.Comment: 22 pages, 5 figure
Dynamic aperture studies during collisions in the LHC
The dynamic aperture during collisions in the LHC is mainly determined by the beam-beam interactions and by multipole errors of the high gradient quadrupoles in the interaction regions. The computer code JJIP has been modified to accommodate the LHC lattice configuration and parameters and is employed in this study. Simulations over a range of machine parameters are carried out, and results of preliminary investigation are presented
Determining Absorption, Emissivity Reduction, and Local Suppression Coefficients inside Sunspots
The power of solar acoustic waves is reduced inside sunspots mainly due to
absorption, emissivity reduction, and local suppression. The coefficients of
these power-reduction mechanisms can be determined by comparing time-distance
cross-covariances obtained from sunspots and from the quiet Sun. By analyzing
47 active regions observed by SOHO/MDI without using signal filters, we have
determined the coefficients of surface absorption, deep absorption, emissivity
reduction, and local suppression. The dissipation in the quiet Sun is derived
as well. All of the cross-covariances are width corrected to offset the effect
of dispersion. We find that absorption is the dominant mechanism of the power
deficit in sunspots for short travel distances, but gradually drops to zero at
travel distances longer than about 6 degrees. The absorption in sunspot
interiors is also significant. The emissivity-reduction coefficient ranges from
about 0.44 to 1.00 within the umbra and 0.29 to 0.72 in the sunspot, and
accounts for only about 21.5% of the umbra's and 16.5% of the sunspot's total
power reduction. Local suppression is nearly constant as a function of travel
distance with values of 0.80 and 0.665 for umbrae and whole sunspots
respectively, and is the major cause of the power deficit at large travel
distances.Comment: 14 pages, 21 Figure
Ising metamagnets in thin film geometry: equilibrium properties
Artificial antiferromagnets and synthetic metamagnets have attracted much
attention recently due to their potential for many different applications.
Under some simplifying assumptions these systems can be modeled by thin Ising
metamagnetic films. In this paper we study, using both the Wang/Landau scheme
and importance sampling Monte Carlo simulations, the equilibrium properties of
these films. On the one hand we discuss the microcanonical density of states
and its prominent features. On the other we analyze canonically various global
and layer quantities. We obtain the phase diagram of thin Ising metamagnets as
a function of temperature and external magnetic field. Whereas the phase
diagram of the bulk system only exhibits one phase transition between the
antiferromagnetic and paramagnetic phases, the phase diagram of thin Ising
metamagnets includes an additional intermediate phase where one of the surface
layers has aligned itself with the direction of the applied magnetic field.
This additional phase transition is discontinuous and ends in a critical end
point. Consequently, it is possible to gradually go from the antiferromagnetic
phase to the intermediate phase without passing through a phase transition.Comment: 8 figures, accepted for publication in Physical Review
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