75,786 research outputs found
Multi-spectral window radiance observations of Cirrus from satellite and aircraft, November 2, 1986 Project FIRE
High resolution infrared radiance spectra achieved from the NASA ER2 airborne HIS experiment are used to analyze the spectral emissivity properties of cirrus clouds within the 8 to 12 micron atmospheric window region. Observations show that the cirrus emissivity generally decreases with increasing wavenumber (i.e., decreasing wavelength) within this band. A very abrupt decrease in emissivity (increase in brightness temperature) exists between 930/cm (10.8 microns) and 1000/cm (10.0 microns), the magnitude of the change being associated with the cirrus optical thickness as observed by lidar. The HIS observations are consistent with theoretical calculations of the spectral absorption coefficient for ice. The HIS observations imply that cirrus clouds can be detected unambiguously from the difference in brightness temperatures observed within the 8.2 and 11.0 micron window regions of the HIRS sounding radiometer flying on the operational NOAA satellites. This ability is demonstrated using simultaneous 25 km resolution HIRS observations and 1 km resolution AVHRR imagery achieved from the NOAA-9 satellite. Finally, the cirrus cloud location estimates combined with the 6.7 micron channel moisture imagery portray the boundaries of the ice/vapor phase of the upper troposphere moisture. This phase distinction is crucial for infrared radiative transfer considerations for weather and climate models, since upper tropospheric water vapor has little effect on the Earth's outgoing radiation whereas cirrus clouds have a very large attenuating effect
Twisted and Nontwisted Bifurcations Induced by Diffusion
We discuss a diffusively perturbed predator-prey system. Freedman and
Wolkowicz showed that the corresponding ODE can have a periodic solution that
bifurcates from a homoclinic loop. When the diffusion coefficients are large,
this solution represents a stable, spatially homogeneous time-periodic solution
of the PDE. We show that when the diffusion coefficients become small, the
spatially homogeneous periodic solution becomes unstable and bifurcates into
spatially nonhomogeneous periodic solutions.
The nature of the bifurcation is determined by the twistedness of an
equilibrium/homoclinic bifurcation that occurs as the diffusion coefficients
decrease. In the nontwisted case two spatially nonhomogeneous simple periodic
solutions of equal period are generated, while in the twisted case a unique
spatially nonhomogeneous double periodic solution is generated through
period-doubling.
Key Words: Reaction-diffusion equations; predator-prey systems; homoclinic
bifurcations; periodic solutions.Comment: 42 pages in a tar.gz file. Use ``latex2e twisted.tex'' on the tex
files. Hard copy of figures available on request from
[email protected]
CD4+ T-cell responses to Epstein-Barr virus nuclear antigen EBNA1 in Chinese populations are highly focused on novel C-terminal domain-derived epitopes
Epstein-Barr virus nuclear antigen EBNA1, the one viral protein uniformly expressed in nasopharyngeal carcinoma (NPC), represents a prime target for T-cell-based immunotherapy. However, little is known about the EBNA1 epitopes, particularly CD4 epitopes, presented by HLA alleles in Chinese people, the group at highest risk for NPC. We analyzed the CD4 T-cell responses to EBNA1 in 78 healthy Chinese donors and found marked focusing on a small number of epitopes in the EBNA1 C-terminal region, including a DP5- restricted epitope that was recognized by almost half of the donors tested and elicited responses able to recognize EBNA1-expressing, DP5-positive target cells
Correlated particle dynamics in concentrated quasi-two-dimensional suspensions
We investigate theoretically and experimentally how the hydrodynamically
correlated lateral motion of particles in a suspension confined between two
surfaces is affected by the suspension concentration. Despite the long range of
the correlations (decaying as 1/r^2 with the inter-particle distance r), the
concentration effect is present only at short inter-particle distances for
which the static pair correlation is nonuniform. This is in sharp contrast with
the effect of hydrodynamic screening present in unconfined suspensions, where
increasing the concentration changes the prefactor of the large-distance
correlation.Comment: 13 page
Hydrodynamic interaction in quasi-two-dimensional suspensions
Confinement between two parallel surfaces is found, theoretically and
experimentally, to drastically affect the hydrodynamic interaction between
colloid particles, changing the sign of the coupling, its decay with distance
and its concentration dependence. In particular, we show that three-body
effects do not modify the coupling at large distances as would be expected from
hydrodynamic screening.Comment: 8 pages, 2 figure
Graphene microwave transistors on sapphire substrates
We have developed metal-oxide graphene field-effect transistors (MOGFETs) on
sapphire substrates working at microwave frequencies. For monolayers, we obtain
a transit frequency up to ~ 80 GHz for a gate length of 200 nm, and a power
gain maximum frequency of about ~ 3 GHz for this specific sample. Given the
strongly reduced charge noise for nanostructures on sapphire, the high
stability and high performance of this material at low temperature, our MOGFETs
on sapphire are well suited for a cryogenic broadband low-noise amplifier
Effect of Spatial Charge Inhomogeneity on 1/f Noise Behavior in Graphene
Scattering mechanisms in graphene are critical to understanding the limits of
signal-to-noise-ratios of unsuspended graphene devices. Here we present the
four-probe low frequency noise (1/f) characteristics in back-gated single layer
graphene (SLG) and bilayer graphene (BLG) samples. Contrary to the expected
noise increase with the resistance, the noise for SLG decreases near the Dirac
point, possibly due to the effects of the spatial charge inhomogeneity. For
BLG, a similar noise reduction near the Dirac point is observed, but with a
different gate dependence of its noise behavior. Some possible reasons for the
different noise behavior between SLG and BLG are discussed.Comment: 28 pages, 3 figures + 3 supplement figure
Coherent Optimal Control of Multiphoton Molecular Excitation
We give a framework for molecular multiphoton excitation process induced by
an optimally designed electric field. The molecule is initially prepared in a
coherent superposition state of two of its eigenfunctions. The relative phase
of the two superposed eigenfunctions has been shown to control the optimally
designed electric field which triggers the multiphoton excitation in the
molecule. This brings forth flexibility in desiging the optimal field in the
laboratory by suitably tuning the molecular phase and hence by choosing the
most favorable interfering routes that the system follows to reach the target.
We follow the quantum fluid dynamical formulation for desiging the electric
field with application to HBr molecule.Comment: 5 figure
Nucleon, and excited states in lattice QCD
The energies of the excited states of the Nucleon, and are
computed in lattice QCD, using two light quarks and one strange quark on
anisotropic lattices. The calculation is performed at three values of the light
quark mass, corresponding to pion masses = 392(4), 438(3) and 521(3)
MeV. We employ the variational method with a large basis of interpolating
operators enabling six energies in each irreducible representation of the
lattice to be distinguished clearly. We compare our calculation with the
low-lying experimental spectrum, with which we find reasonable agreement in the
pattern of states. The need to include operators that couple to the expected
multi-hadron states in the spectrum is clearly identified.Comment: Revised for publication. References added, Table VI expanded to add
strange baryon multiparticle thresholds and multiparticle thresholds added to
Figs. 4, 5 and 6. 15 pages, 6 figure
Nonlinear propagation of planet-generated tidal waves
The propagation and evolution of planet-generated density waves in
protoplanetary disks is considered. The evolution of waves, leading to the
shock formation and wake dissipation, is followed in the weakly nonlinear
regime. The local approach of Goodman & Rafikov (2001) is extended to include
the effects of surface density and temperature variations in the disk as well
as the disk cylindrical geometry and nonuniform shear. Wave damping due to
shocks is demonstrated to be a nonlocal process spanning a significant fraction
of the disk. Torques induced by the planet could be significant drivers of disk
evolution on timescales of the order 1-10 Myr even in the absence of strong
background viscosity. A global prescription for angular momentum deposition is
developed which could be incorporated into the study of gap formation in a
gaseous disk around the planet.Comment: AASTeX, 26 pages, 4 figures, 1 table, submitted to Ap
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