4,063 research outputs found
Asymptotic expansion of the difference of two Mahler measures
We show that for almost every polynomial P(x,y) with complex coefficients,
the difference of the logarithmic Mahler measures of P(x,y) and P(x,x^n) can be
expanded in a type of formal series similar to an asymptotic power series
expansion in powers of 1/n. This generalizes a result of Boyd. We also show
that such an expansion is unique and provide a formula for its coefficients.
When P has algebraic coefficients, the coefficients in the expansion are linear
combinations of polylogarithms of algebraic numbers, with algebraic
coefficients.Comment: 25 pages. V2: Demoted previous Corollary 1 to a comment, after
realizing that Boyd had already proved that bit. Made small corrections to
Lemma 5, streamlined the proof of Lemma 9, and reworded section 9.
Relation between dust and radio luminosity in optically selected early type galaxies
We have surveyed an optical/IR selected sample of nearby E/S0 galaxies with
and without nuclear dust structures with the VLA at 3.6 cm to a sensitivity of
100 Jy. We can construct a Radio Luminosity Function (RLF) of these
galaxies to ~10^19 W/Hz and find that ~50% of these galaxies have AGNs at this
level. The space density of these AGNs equals that of starburst galaxies at
this luminosity. Several dust-free galaxies have low luminosity radio cores,
and their RLF is not significantly less than that of the dusty galaxies.Comment: 8 pages, 5 figures, accepted for publication in A&
X-ray absorption spectra at the Ca-L-edge calculated within multi-channel multiple scattering theory
We report a new theoretical method for X-ray absorption spectroscopy (XAS) in
condensed matter which is based on the multi-channel multiple scattering theory
of Natoli et al. and the eigen-channel R-matrix method. While the highly
flexible real-space multiple scattering (RSMS) method guarantees a precise
description of the single-electron part of the problem, multiplet-like electron
correlation effects between the photo-electron and localized electrons can be
taken account for in a configuration interaction scheme. For the case where
correlation effects are limited to the absorber atom, a technique for the
solution of the equations is devised, which requires only little more
computation time than the normal RSMS method for XAS. The new method is
described and an application to XAS at the Ca -edge in bulk Ca, CaO
and CaF is presented.Comment: 10 pages, 4 figures, submitted to Phys. Rev.
Status of NASA/Army rotorcraft research and development piloted flight simulation
The status of the major NASA/Army capabilities in piloted rotorcraft flight simulation is reviewed. The requirements for research and development piloted simulation are addressed as well as the capabilities and technologies that are currently available or are being developed by NASA and the Army at Ames. The application of revolutionary advances (in visual scene, electronic cockpits, motion, and modelling of interactive mission environments and/or vehicle systems) to the NASA/Army facilities are also addressed. Particular attention is devoted to the major advances made in integrating these individual capabilities into fully integrated simulation environment that were or are being applied to new rotorcraft mission requirements. The specific simulators discussed are the Vertical Motion Simulator and the Crew Station Research and Development Facility
Resolving the Radio Source Background: Deeper Understanding Through Confusion
We used the Karl G. Jansky Very Large Array (VLA) to image one primary beam
area at 3 GHz with 8 arcsec FWHM resolution and 1.0 microJy/beam rms noise near
the pointing center. The P(D) distribution from the central 10 arcmin of this
confusion-limited image constrains the count of discrete sources in the 1 <
S(microJy/beam) < 10 range. At this level the brightness-weighted differential
count S^2 n(S) is converging rapidly, as predicted by evolutionary models in
which the faintest radio sources are star-forming galaxies; and ~96$% of the
background originating in galaxies has been resolved into discrete sources.
About 63% of the radio background is produced by AGNs, and the remaining 37%
comes from star-forming galaxies that obey the far-infrared (FIR) / radio
correlation and account for most of the FIR background at lambda = 160 microns.
Our new data confirm that radio sources powered by AGNs and star formation
evolve at about the same rate, a result consistent with AGN feedback and the
rough correlation of black hole and bulge stellar masses. The confusion at
centimeter wavelengths is low enough that neither the planned SKA nor its
pathfinder ASKAP EMU survey should be confusion limited, and the ultimate
source detection limit imposed by "natural" confusion is < 0.01 microJy at 1.4
GHz. If discrete sources dominate the bright extragalactic background reported
by ARCADE2 at 3.3 GHz, they cannot be located in or near galaxies and most are
< 0.03 microJy at 1.4 GHz.Comment: 28 pages including 16 figures. ApJ accepted for publicatio
Causal and stable reduced-order model for linear high-frequency systems
With the ever-growing complexity of high-frequency systems in the electronic industry, formation of reduced-order models of these systems is paramount. In this reported work, two different techniques are combined to generate a stable and causal representation of the system. In particular, balanced truncation is combined with a Fourier series expansion approach. The efficacy of the proposed combined method is shown with an example
Alien Registration- Condon, Robert D. (Presque Isle, Aroostook County)
https://digitalmaine.com/alien_docs/33848/thumbnail.jp
ATPMN: accurate positions and flux densities at 5 and 8 GHz for 8,385 sources from the PMN survey
We present a source catalogue of 9,040 radio sources resulting from
high-resolution observations of 8,385 PMN sources with the Australia Telescope
Compact Array. The catalogue lists flux density and structural measurements at
4.8 and 8.6 GHz, derived from observations of all PMN sources in the
declination range -87 deg < delta < -38.5 deg (exclusive of galactic latitudes
|b| 70 mJy (50 mJy south of delta = -73
deg). We assess the quality of the data, which was gathered in 1992-1994,
describe the population of catalogued sources, and compare it to samples from
complementary catalogues. In particular we find 127 radio sources with probable
association with gamma-ray sources observed by the orbiting Fermi Large Area
Telescope.Comment: 20 pages, 21 figure
The higher order C_n dispersion coefficients for the alkali atoms
The van der Waals coefficients, from C_11 through to C_16 resulting from 2nd,
3rd and 4th order perturbation theory are estimated for the alkali (Li, Na, K
and Rb) atoms. The dispersion coefficients are also computed for all possible
combinations of the alkali atoms and hydrogen. The parameters are determined
from sum-rules after diagonalizing the fixed core Hamiltonian in a large basis.
Comparisons of the radial dependence of the C_n/r^n potentials give guidance as
to the radial regions in which the various higher-order terms can be neglected.
It is seen that including terms up to C_10/r^10 results in a dispersion
interaction that is accurate to better than 1 percent whenever the
inter-nuclear spacing is larger than 20 a_0. This level of accuracy is mainly
achieved due to the fortuitous cancellation between the repulsive (C_11, C_13,
C_15) and attractive (C_12, C_14, C_16) dispersion forces.Comment: 8 pages, 7 figure
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