26,741 research outputs found
The absolute radiometric calibration of the advanced very high resolution radiometer
The early results of an absolute radiometric calibration of the NOAA-9 AVHRR sensor indicate significant degradations in the response of bands 1 and 2 compared to prelaunch values. The results are currently in the process of being verified and it may be that refinements of the methodology will be in order as additional data sets are analyzed. The LANDSAT TM calibration used in this approach is known to be very precise and the Herman radiative transfer code, supplemented by the 5-S code for gaseous transmission, is reliable as well. The extent to which other steps in the analysis procedure give rise to uncertainties in the results is currently under investigation. Particular attention is being given to the geometric matching of the AVHRR and TM imagery, as well as to the spectral redistribution procedure. By taking advantage of a reasonably precise calibration of TM imagery acquired on the same day as the AVHRR data at White Sands, a promising approach to the in-orbit calibration of AVHRR sensors is being developed. Current efforts involve primarily the examination of additional test cases and the investigation of possible simplifications in the procedure through judicious use of atmospheric models
Lattice dynamics and electron-phonon coupling in Sr2RuO4
The lattice dynamics in SrRuO has been studied by inelastic neutron
scattering combined with shell-model calculations. The in-plane bond-stretching
modes in SrRuO exhibit a normal dispersion in contrast to all
electronically doped perovskites studied so far. Evidence for strong electron
phonon coupling is found for c-polarized phonons suggesting a close connection
with the anomalous c-axis charge transport in SrRuO.Comment: 11 pages, 8 figures 2 table
Imprinted Networks as Chiral Pumps
We investigate the interaction between a chirally imprinted network and a
solvent of chiral molecules. We find, a liquid crystalline polymer network is
preferentially swollen by one component of a racemic solvent. This ability to
separate is linked to the chiral order parameter of the network, and can be
reversibly controlled via temperature or a mechanical deformation. It is
maximal near the point at which the network loses its imprinted structure. One
possible practical application of this effect would be a mechanical device for
sorting mixed chiral molecules.Comment: 4 pages, 5 figure
Is the Number of Giant Arcs in LCDM Consistent With Observations?
We use high-resolution N-body simulations to study the galaxy-cluster
cross-sections and the abundance of giant arcs in the CDM model.
Clusters are selected from the simulations using the friends-of-friends method,
and their cross-sections for forming giant arcs are analyzed. The background
sources are assumed to follow a uniform ellipticity distribution from 0 to 0.5
and to have an area identical to a circular source with diameter 1\arcsec. We
find that the optical depth scales as the source redshift approximately as
\tau_{1''} = 2.25 \times 10^{-6}/[1+(\zs/3.14)^{-3.42}] (0.6<\zs<7). The
amplitude is about 50% higher for an effective source diameter of 0.5\arcsec.
The optimal lens redshift for giant arcs with the length-to-width ratio ()
larger than 10 increases from 0.3 for \zs=1, to 0.5 for \zs=2, and to
0.7-0.8 for \zs>3. The optical depth is sensitive to the source redshift, in
qualitative agreement with Wambsganss et al. (2004). However, our overall
optical depth appears to be only 10% to 70% of those from previous
studies. The differences can be mostly explained by different power spectrum
normalizations () used and different ways of determining the
ratio. Finite source size and ellipticity have modest effects on the optical
depth. We also found that the number of highly magnified (with magnification
) and ``undistorted'' images (with ) is comparable to the
number of giant arcs with and . We conclude that our
predicted rate of giant arcs may be lower than the observed rate, although the
precise `discrepancy' is still unclear due to uncertainties both in theory and
observations.Comment: Revised version after the referee's reports (32 pages,13figures). The
paper has been significantly revised with many additions. The new version
includes more detailed comparisons with previous studies, including the
effects of source size and ellipticity. New discussions about the redshift
distribution of lensing clusters and the width of giant arcs have been adde
Theoretical studies of the local structures and EPR parameters for Cu center in Cd(NH)(SO) single crystal
The electron paramagnetic resonance (EPR) parameters ( factors and
the hyperfine structure constants , ) are
interpreted by using the perturbation formulae for a ion in
rhombically ({D}) elongated octahedra. In the calculated formulae, the
crystal field parameters are set up from the superposition model, and the
contribution to the EPR parameters from the admixture of -orbitals in the
ground state wave function of the Cu ion was taken into account. Based
on the calculation, local structural parameters of the impurity Cu
center in Cd(NH)(SO) (CAS) crystal were obtained
(i.e., {\AA}, {\AA},
{\AA}). The theoretical EPR parameters based on the
above Cu-O bond lengths in CAS crystal show a good agreement with
the observed values. The results are discussed.Comment: 5 page
Microlensing of collimated Gamma-Ray Burst afterglows
We investigate stellar microlensing of the collimated gamma-ray burst
afterglows. A spherical afterglow appears on the sky as a superluminally
expanding thin ring (``ring-like'' image), which is maximally amplified as it
crosses the lens. We find that the image of the collimated afterglow becomes
quite uniform (``disk-like'' image) after the jet break time (after the Lorentz
factor of the jet drops below the inverse of the jet opening angle).
Consequently, the amplification peak in the light curve after the break time is
lower and broader. Therefore detailed monitoring of the amplification history
will be able to test whether the afterglows are jets or not, i.e.,
``disk-like'' or not, if the lensing occurs after the break time. We also show
that some proper motion and polarization is expected, peaking around the
maximum amplification. The simultaneous detection of the proper motion and the
polarization will strengthen that the brightening of the light curve is due to
microlensing.Comment: 16 pages, 6 figures, accepted for publication in Ap
Solvable senescence model with positive mutations
We build upon our previous analytical results for the Penna model of
senescence to include positive mutations. We investigate whether a small but
non-zero positive mutation rate gives qualitatively different results to the
traditional Penna model in which no positive mutations are considered. We find
that the high-lifespan tail of the distribution is radically changed in
structure, but that there is not much effect on the bulk of the population. Th
e mortality plateau that we found previously for a stochastic generalization of
the Penna model is stable to a small positive mutation rate.Comment: 3 figure
Ontology mapping neural network: An approach to learning and inferring correspondences among ontologies
An ontology mapping neural network (OMNN) is proposed in order to learn and infer correspondences among ontologies. It extends the Identical Elements Neural Network (IENN)'s ability to represent and map complex relationships. The learning dynamics of simultaneous (interlaced) training of similar tasks interact at the shared connections of the networks. The output of one network in response to a stimulus to another network can be interpreted as an analogical mapping. In a similar fashion, the networks can be explicitly trained to map specific items in one domain to specific items in another domain. Representation layer helps the network learn relationship mapping with direct training method. OMNN is applied to several OAEI benchmark test cases to test its performance on ontology mapping. Results show that OMNN approach is competitive to the top performing systems that participated in OAEI 2009
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