5,330 research outputs found
Spectral longwave emission in the tropics - FTIR measurement at the sea-surface and comparison with fast radiation codes
Longwave emission by the tropical western Pacific atmosphere has been measured at the ocean surface by a Fourier Transform Infrared (FTIR) spectroradiometer deployed aboard the research vessel John Vickers as part of the Central Equatorial Pacific Experiment. The instrument operated throughout a Pacific Ocean crossing, beginning on 7 March 1993 in Honiara, Solomon Islands, and ending on 29 March 1993 in Los Angeles, and recorded longwave emission spectra under atmospheres associated with sea surface temperatures ranging from 291.0 to 302.8 K. Precipitable water vapor abundances ranged from 1.9 to 5.5 column centimeters. Measured emission spectra (downwelling zenith radiance) covered the middle infrared (5-20 mu m) with one inverse centimeter spectral resolution. FTIR measurements made under an entirely clear field of view are compared with spectra generated by LOWTRAN 7 and MODTRAN 2, as well as downwelling flux calculated by the NCAR Community Climate Model (CCM-2) radiation code, using radiosonde profiles as input data for these calculations. In the spectral interval 800-1000 cm(-1), these comparisons show a discrepancy between FTIR data and MODTRAN 2 having an overall variability of 6-7 mW m(-2) sr(-1) cm and a concave shape that may be related to the representation of water vapor continuum emission in MODTRAN 2. Another discrepancy appears in the spectral interval 1200-1300 cm(-1), where MODTRAN 2 appears to overestimate zenith radiance by 5 mW m(-2) sr(-1) cm. These discrepancies appear consistently; however, they become only slightly larger at the highest water vapor abundances. Because these radiance discrepancies correspond to broadband (500-2000 cm(-1)) flux uncertainties of around 3 W m(-2), there appear to be no serious inadequacies with the performance of MODTRAN 2 or LOWTRAN 7 at high atmospheric temperatures and water vapor abundances. On average, CCM-2 flux calculations agree to within 1 W m(-2) with downwelling flux estimates from the FTIR data over all sea surface temperatures, although this result has a scatter of +/-12 W m(-2) at high sea surface temperatures
Processing of temporal duration information in working memory after frontodorsal tumour excisions
This study aimed to test the hypothesis that impairments of temporal duration processing after frontal lobe lesions reflect deficits in executive monitoring functions rather than a domain-specific deficit in the maintenance of duration information in working memory. Patients with frontodorsal lesions, clinical controls with post-central lesions, and healthy controls performed recognition and classification tasks, which should allow for testing maintenance and monitoring functions, respectively. Results showed mild non-selective impairments of the frontal patients on both temporal and spatial recognition tasks, but a marked selective degradation on temporal classification while performance on spatial classification was unimpaired. This suggests that maintenance of duration information in working memory after frontal lesions is basically preserved but that, depending on executive task characteristics, there is a specific deficit in the strategic organization of this type of information
Two-component Bose gas in an optical lattice at single-particle filling
The Bose-Hubbard model of a two-fold degenerate Bose gas is studied in an
optical lattice with one particle per site and virtual tunneling to empty and
doubly-occupied sites. An effective Hamiltonian for this system is derived
within a continued-fraction approach. The ground state of the effective model
is studied in mean-field approximation for a modulated optical lattice. A
dimerized mean-field state gives a Mott insulator whereas the lattice without
modulations develops long-range correlated phase fluctuations due to a
Goldstone mode. This result is discussed in comparison with the superfluid and
the Mott-insulating state of a single-component hard-core Bose.Comment: 11 page
Quasiparticle Lifetime in a Finite System: A Non--Perturbative Approach
The problem of electron--electron lifetime in a quantum dot is studied beyond
perturbation theory by mapping it onto the problem of localization in the Fock
space. We identify two regimes, localized and delocalized, corresponding to
quasiparticle spectral peaks of zero and finite width, respectively. In the
localized regime, quasiparticle states are very close to single particle
excitations. In the delocalized state, each eigenstate is a superposition of
states with very different quasiparticle content. A transition between the two
regimes occurs at the energy , where is
the one particle level spacing, and is the dimensionless conductance. Near
this energy there is a broad critical region in which the states are
multifractal, and are not described by the Golden Rule.Comment: 13 pages, LaTeX, one figur
Two interacting quasiparticles above the Fermi sea
We study numerically the interaction and disorder effects for two
quasiparticles in two and three dimensions. The dependence of the
interaction-induced Breit-Wigner width on the excitation energy above the Fermi
level, the disorder strength and the system size is determined. A regime is
found where the width is practically independent of the excitation energy. The
results allow to estimate the two quasiparticle mobility edge.Comment: revtex, 4 pages, 4 figure
Compact Frontend-Electronics and Bidirectional 3.3 Gbps Optical Datalink for Fast Proportional Chamber Readout
The 9600 channels of the multi-wire proportional chamber of the H1 experiment
at HERA have to be read out within 96 ns and made available to the trigger
system. The tight spatial conditions at the rear end flange require a compact
bidirectional readout electronics with minimal power consumption and dead
material.
A solution using 40 identical optical link modules, each transferring the
trigger information with a physical rate of 4 x 832 Mbps via optical fibers,
has been developed and commisioned. The analog pulses from the chamber can be
monitored and the synchronization to the global HERA clock signal is ensured.Comment: 13 pages, 10 figure
Pores in Bilayer Membranes of Amphiphilic Molecules: Coarse-Grained Molecular Dynamics Simulations Compared with Simple Mesoscopic Models
We investigate pores in fluid membranes by molecular dynamics simulations of
an amphiphile-solvent mixture, using a molecular coarse-grained model. The
amphiphilic membranes self-assemble into a lamellar stack of amphiphilic
bilayers separated by solvent layers. We focus on the particular case of
tension less membranes, in which pores spontaneously appear because of thermal
fluctuations. Their spatial distribution is similar to that of a random set of
repulsive hard discs. The size and shape distribution of individual pores can
be described satisfactorily by a simple mesoscopic model, which accounts only
for a pore independent core energy and a line tension penalty at the pore
edges. In particular, the pores are not circular: their shapes are fractal and
have the same characteristics as those of two dimensional ring polymers.
Finally, we study the size-fluctuation dynamics of the pores, and compare the
time evolution of their contour length to a random walk in a linear potential
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