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Evolutionary Synthesis Of Stellar Population In Elliptical Galaxies .1. Ingredients, Broad-Band Colors, And Infrared Features
NSF MPS 73-04673 A01, GP-40482, GP-3143, MPS 75-01398Astronom
Testing protoplanetary disc dispersal with radio emission
We consider continuum free-free radio emission from the upper atmosphere of
protoplanetary discs as a probe of the ionized luminosity impinging upon the
disc. Making use of previously computed hydrodynamic models of disc
photoevaporation within the framework of EUV and X-ray irradiation, we use
radiative transfer post-processing techniques to predict the expected free-free
emission from protoplanetary discs. In general, the free-free luminosity scales
roughly linearly with ionizing luminosity in both EUV and X-ray driven
scenarios, where the emission dominates over the dust tail of the disc and is
partial optically thin at cm wavelengths. We perform a test observation of GM
Aur at 14-18 Ghz and detect an excess of radio emission above the dust tail to
a very high level of confidence. The observed flux density and spectral index
are consistent with free-free emission from the ionized disc in either the EUV
or X-ray driven scenario. Finally, we suggest a possible route to testing the
EUV and X-ray driven dispersal model of protoplanetary discs, by combining
observed free-free flux densities with measurements of mass-accretion rates. On
the point of disc dispersal one would expect to find a M_dot^2 scaling with
free-free flux in the case of EUV driven disc dispersal or a M_dot scaling in
the case of X-ray driven disc dispersal.Comment: Accepted MNRAS, 12 pages, 11 figures, (pdf generation fixed
Gate control of a quantum dot single-electron spin in realistic confining potentials: anisotropy effects
Among recent proposals for next-generation, non-charge-based logic is the
notion that a single electron can be trapped and its spin can be manipulated
through the application of gate potentials. In this paper, we present numerical
simulations of such spins in single electron devices for realistic (asymmetric)
confining potentials in two-dimensional electrostatically confined quantum
dots. Using analytical and numerical techniques we show that breaking the
in-plane rotational symmetry of the confining potential leads to a significant
effect on the tunability of the g-factor with applied gate potentials. In
particular, anisotropy extends the range of tunability to larger quantum dots.Comment: 7 pages, 13 figure
RESPONDING TO FOREIGN MARKET OPPORTUNITIES: A SURVEY OF U.S. DAIRY MANUFACTURERS
International Relations/Trade,
Status of NASA's Stirling Space Power Converter Program
An overview is presented of the NASA-Lewis Free-Piston Stirling Space Power Convertor Technology Program. The goal is to develop the technology base needed to meet the long duration, high capacity power requirements for future NASA space initiatives. Efforts are focused upon increasing system power output and system thermal and electric energy conversion efficiency at least fivefold over current SP-100 technology, and on achieving systems that are compatible with space nuclear reactors. Stirling experience in space and progress toward 1050 and 1300 K Stirling Space Power Converters is discussed. Fabrication is nearly completed for the 1050 K Component Test Power Converters (CTPC); results of motoring tests of cold end (525 K), are presented. The success of these and future designs is dependent upon supporting research and technology efforts including heat pipes, bearings, superalloy joining technologies, high efficiency alternators, life and reliability testing and predictive methodologies. An update is provided of progress in some of these technologies leading off with a discussion of free-piston Stirling experience in space
Particle-in-cell simulations of electron acceleration by a simple capacitative antenna in collisionless plasma
We examine the electron acceleration by a localized electrostatic potential oscillating at high frequencies by means of particleâinâcell (PIC) simulations, in which we apply oscillating electric fields to two neighboring simulation cells. We derive an analytic model for the direct electron heating by the externally driven antenna electric field, and we confirm that it approximates well the electron heating obtained in the simulations. In the simulations, transient waves accelerate electrons in a sheath surrounding the antenna. This increases the Larmor radii of the electrons close to the antenna, and more electrons can reach the antenna location to interact with the externally driven fields. The resulting hot electron sheath is dense enough to support strong waves that produce highâenergy sounderâaccelerated electrons (SAEs) by their nonlinear interaction with the ambient electrons. By increasing the emission amplitudes in our simulations to values that are representative for the ones of the sounder on board the OEDIPUS C (OC) satellites, we obtain electron acceleration into the energy range which is comparable to the 20 keV energies of the SAE observed by the OC mission. The emission also triggers stable electrostatic waves oscillating at frequencies close to the first harmonic of the electron cyclotron frequency. We find this to be an encouraging first step of examining SAE generation with kinetic numerical simulation codes
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