1,909 research outputs found
Altitude dependence of atmospheric temperature trends: Climate models versus observation
As a consequence of greenhouse forcing, all state of the art general
circulation models predict a positive temperature trend that is greater for the
troposphere than the surface. This predicted positive trend increases in value
with altitude until it reaches a maximum ratio with respect to the surface of
as much as 1.5 to 2.0 at about 200 to 400 hPa. However, the temperature trends
from several independent observational data sets show decreasing as well as
mostly negative values. This disparity indicates that the three models examined
here fail to account for the effects of greenhouse forcings.Comment: 9 pages, 3 figure
Characterizing the Galactic Gravitational Wave Background with LISA
We present a Monte Carlo simulation for the response of the Laser
Interferometer Space Antenna (LISA) to the galactic gravitational wave
background. The simulated data streams are used to estimate the number and type
of binary systems that will be individually resolved in a 1-year power
spectrum. We find that the background is highly non-Gaussian due to the
presence of individual bright sources, but once these sources are identified
and removed, the remaining signal is Gaussian. We also present a new estimate
of the confusion noise caused by unresolved sources that improves on earlier
estimates.Comment: 32 pages, 14 figures. Version to appear in PR
Fast two-dimensional model
A two dimensional (altitude and latitude) model of the atmosphere is used to investigate problems relating to the variability of the dynamics and temperature of the atmosphere on the ozone distribution, solar cycle variations of atmospheric constituents, the sensitivity of model results to tropospheric trace gas sources, and assessment computations of changes in ozone related to manmade influences. In a comparison between two dimensional model results in which the odd nitrogen family was transported together and model results in which the odd nitrogen species was transported separately, it was found that the family approximations are adequate for perturbation scenario calculations
A first-principles comparison of the electronic properties of MgC_{y}Ni_{3} and ZnC_{y}Ni_{3} alloys
First-principles, density-functional-based electronic structure calculations
are employed to study the changes in the electronic properties of ZnC_{y}Ni_{3}
and MgC_{y}Ni_{3} using the Korringa-Kohn-Rostoker coherent-potential
approximation method in the atomic sphere approximation (KKR-ASA CPA). As a
function of decreasing C at%, we find a steady decrease in the lattice constant
and bulk modulus in either alloys. However, the pressure derivative of the bulk
modulus displays an opposite trend. Following the Debye model, which relates
the pressure derivative of the bulk modulus with the average phonon frequency
of the crystal, it can thus be argued that ZnCNi_{3} and its disordered alloys
posses a different phonon spectra in comparison to its MgCNi_{3} counterparts.
This is further justified by the marked similarity we find in the electronic
structure properties such as the variation in the density of states and the
Hopfield parameters calculated for these alloys. The effects on the equation of
state parameters and the density of states at the Fermi energy, for partial
replacement of Mg by Zn are also discussed.Comment: 19 pages, 15 figure
Subgap resonant quasiparticle transport in normal-superconductor quantum dot devices
We report thermally activated transport resonances for biases below the superconducting energy gap in a carbon nanotube quantum dot (QD) device with a superconducting Pb and a normal metal contact. These resonances are due to the superconductor`s finite quasi-particle population at elevated temperatures and can only be observed when the QD life-time broadening is considerably smaller than the gap. This condition is fulfilled in our QD devices with optimized Pd/Pb/In multi-layer contacts, which result in reproducibly large and ``clean`` superconducting transport gaps with a strong conductance suppression for subgap biases. We show that these gaps close monotonically with increasing magnetic field and temperature. The accurate description of the subgap resonances by a simple resonant tunneling model illustrates the ideal characteristics of the reported Pb contacts and gives an alternative access to the tunnel coupling strengths in a QD. Published by AIP Publishing
Microwave Spectroscopy
Contains research objectives and reports on two research projects.U.S. Army Signal Corps under Contract DA36-039-sc-87376Lincoln Laboratory, Purchase Order DDL B-00306U. S. ArmyU. S. NavyU. S. Air Force under Air Force Contract AF19(604)-740
Microwave Spectroscopy
Contains reports on five research projects.Signal Corps Contract DA36-039-sc-7489
Microwave Spectroscopy
Contains reports on five research projects.United States Army Signal Corps (Contract DA36-039-sc-74895
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Simultaneous mapping of membrane voltage and calcium in zebrafish heart in vivo reveals chamber-specific developmental transitions in ionic currents
The cardiac action potential (AP) and the consequent cytosolic Ca2+ transient are key indicators of cardiac function. Natural developmental processes, as well as many drugs and pathologies change the waveform, propagation, or variability (between cells or over time) of these parameters. Here we apply a genetically encoded dual-function calcium and voltage reporter (CaViar) to study the development of the zebrafish heart in vivo between 1.5 and 4 days post fertilization (dpf). We developed a high-sensitivity spinning disk confocal microscope and associated software for simultaneous three-dimensional optical mapping of voltage and calcium. We produced a transgenic zebrafish line expressing CaViar under control of the heart-specific cmlc2 promoter, and applied ion channel blockers at a series of developmental stages to map the maturation of the action potential in vivo. Early in development, the AP initiated via a calcium current through L-type calcium channels. Between 90 and 102 h post fertilization (hpf), the ventricular AP switched to a sodium-driven upswing, while the atrial AP remained calcium driven. In the adult zebrafish heart, a sodium current drives the AP in both the atrium and ventricle. Simultaneous voltage and calcium imaging with genetically encoded reporters provides a new approach for monitoring cardiac development, and the effects of drugs on cardiac function
Microwave Spectroscopy
Contains reports on six research projects.Signal Corps Contract DA36-039-sc-7489
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