4,772 research outputs found
Infrared Astronomical Satellite (IRAS) analysis of the transmittance of off-axis energy due to scattering and diffraction
Stray light transmittance is analyzed. Mathematical models are evaluated. The results of scatter and diffraction are considered separately, and the combined transmittance values evaluated
The Distribution of Metallicity in the IGM at z~2.5: OVI and CIV Absorption in the Spectra of 7 QSOs
We present a direct measurement of the metallicity distribution function for
the high redshift intergalactic medium. We determine the shape of this function
using survival statistics, which account for both detections and non-detections
of OVI and CIV associated with HI absorption in quasar spectra. Our OVI sample
probes the metal content of ~50% of all baryons at z~2.5. We find a median
intergalactic abundance of [O,C/H]=-2.82; the differential abundance
distribution is approximately lognormal with mean ~-2.85 and
\sigma=0.75 dex. Some 60-70% the Lya forest lines are enriched to observable
levels ([O,C/H]>-3.5) while the remaining ~30% of the lines have even lower
abundances. Thus we have not detected a universal metallicity floor as has been
suggested for some Population III enrichment scenaria. In fact, we argue that
the bulk of the intergalactic metals formed later than the first stars that are
thought to have triggered reionization. We do not observe a significant trend
of decreasing metallicity toward the lower density IGM, at least within regions
that would be characterized as filaments in numerical simulations. However, an
[O/H] enhancement may be present at somewhat high densities. We estimate that
roughly half of all baryons at these redshifts have been enriched to
[O/H]>=-3.5. We develop a simple model for the metallicity evolution of the
IGM, to estimate the chemical yield of galaxies formed prior to z~2.5. We find
that the typical galaxy recycled 0.1-0.4% of its mass back into the IGM as
heavy elements in the first 3 Gyr after the Big Bang.Comment: 23 pages in emulateapj, 19 figures. Accepted to ApJ, pending review
of new changes. Revised comparison between our results and Schaye et al
(2003
Evidence for Rotation in the Galaxy at z=3.15 Responsible for a Damped Lyman-alpha Absorption System in the Spectrum of Q2233+1310
Proof of the existence of a significant population of normal disk galaxies at
redshift z>2 would have profound implications for theories of structure
formation and evolution. We present evidence based on Keck HIRES observations
that the damped Lyman-alpha absorber at z=3.15 toward the quasar Q2233+1310 may
well be such an example. Djorgovski et al have recently detected the
Lyman-alpha emission from the absorber, which we assume is at the systemic
redshift of the absorbing galaxy. By examining the profiles of the metal
absorption lines arising from the absorbing galaxy in relation to its systemic
redshift, we find strong kinematical evidence for rotation. Therefore the
absorber is likely to be a disk galaxy. The inferred circular velocity for the
galaxy is >200 km/s. With a separation of ~17 kpc between the galaxy and the
quasar sightline, the implied dynamic mass for the galaxy is >1.6x10(11) solar
mass. The metallicity of the galaxy is found to be [Fe/H]=-1.4, typical of
damped Lyman-alpha galaxies at such redshifts. However, in another damped
galactic rotation is evident. In the latter case, the damped Lyman-alpha
absorber occurs near the background quasar in redshift so its properties may be
influenced by the background quasar. These represent the only two cases at
present for which the technique used here may be applied. Future applications
of the same technique to a large sample of damped Lyman-alpha galaxies may
allow us to determine if a significant population of disk galaxies already
existed only a few billion years after the Big Bang.Comment: AASTEX, 2 PS figures, accepted by ApJ, 6 pages total, replaced on
1-22-97, the only change is the enlarged figure
Numerical investigation of the quantum fluctuations of optical fields transmitted through an atomic medium
We have numerically solved the Heisenberg-Langevin equations describing the
propagation of quantized fields through an optically thick sample of atoms. Two
orthogonal polarization components are considered for the field and the
complete Zeeman sublevel structure of the atomic transition is taken into
account. Quantum fluctuations of atomic operators are included through
appropriate Langevin forces. We have considered an incident field in a linearly
polarized coherent state (driving field) and vacuum in the perpendicular
polarization and calculated the noise spectra of the amplitude and phase
quadratures of the output field for two orthogonal polarizations. We analyze
different configurations depending on the total angular momentum of the ground
and excited atomic states. We examine the generation of squeezing for the
driving field polarization component and vacuum squeezing of the orthogonal
polarization. Entanglement of orthogonally polarized modes is predicted. Noise
spectral features specific of (Zeeman) multi-level configurations are
identified.Comment: 12 pages 9 figures. Submitted to Physical Review
Steady-state Ab Initio Laser Theory: Generalizations and Analytic Results
We improve the steady-state ab initio laser theory (SALT) of Tureci et al. by
expressing its fundamental self-consistent equation in a basis set of threshold
constant flux states that contains the exact threshold lasing mode. For
cavities with non-uniform index and/or non-uniform gain, the new basis set
allows the steady-state lasing properties to be computed with much greater
efficiency. This formulation of the SALT can be solved in the single-pole
approximation, which gives the intensities and thresholds, including the
effects of nonlinear hole-burning interactions to all orders, with negligible
computational effort. The approximation yields a number of analytic
predictions, including a "gain-clamping" transition at which strong modal
interactions suppress all higher modes. We show that the single-pole
approximation agrees well with exact SALT calculations, particularly for high-Q
cavities. Within this range of validity, it provides an extraordinarily
efficient technique for modeling realistic and complex lasers.Comment: 17 pages, 11 figure
Orientation of Nd dipoles in yttrium aluminum garnet: A simple yet accurate model
We report an experimental study of the 1064nm transition dipoles in neodymium
doped yttrium aluminum garnet (Nd-YAG) by measuring the coupling constant
between two orthogonal modes of a laser cavity for different cuts of the YAG
gain crystal. We propose a theoretical model in which the transition dipoles,
slightly elliptic, are oriented along the crystallographic axes. Our
experimental measurements show a very good quantitative agreement with this
model, and predict a dipole ellipticity between 2% and 3%. This work provides
an experimental evidence for the simple description in which transition dipoles
and crystallographic axes are collinear in Nd-YAG (with an accuracy better than
1 deg), a point that has been discussed for years.Comment: Accepted for publication in Physical Review
Theory of the spatial structure of non-linear lasing modes
A self-consistent integral equation is formulated and solved iteratively
which determines the steady-state lasing modes of open multi-mode lasers. These
modes are naturally decomposed in terms of frequency dependent biorthogonal
modes of a linear wave equation and not in terms of resonances of the cold
cavity. A one-dimensional cavity laser is analyzed and the lasing mode is found
to have non-trivial spatial structure even in the single-mode limit. In the
multi-mode regime spatial hole-burning and mode competition is treated exactly.
The formalism generalizes to complex, chaotic and random laser media.Comment: 4 pages, 3 figure
Large-Scale Correlations in the Lyman-alpha Forest at z = 3-4
We present a study of the spatial coherence of the intergalactic medium
toward two pairs of high-redshift quasars with moderate angular separations
observed with Keck/ESI, Q1422+2309A/Q1424+2255 (z_em = 3.63, theta = 39") and
Q1439-0034A/B (z_em = 4.25, theta = 33"). The crosscorrelation of transmitted
flux in the Lyman-alpha forest shows a 5-7 sigma peak at zero velocity lag for
both pairs. This strongly suggests that at least some of the absorbing
structures span the 230-300/h_70 proper kpc transverse separation between
sightlines. We also statistically examine the similarity between paired spectra
as a function of transmitted flux, a measure which may be useful for comparison
with numerical simulations. In investigating the dependence of the correlation
functions on spectral characteristics, we find that photon noise has little
impact for S/N >~ 10 per resolution element. However, the agreement between the
autocorrelation along the line sight and the crosscorrelation between
sightlines, a potential test of cosmological geometry, depends significantly on
instrumental resolution. Finally, we present an inventory of metal lines. These
include a a pair of strong C IV systems at z ~ 3.4 appearing only toward
Q1439B, and a Mg II + Fe II system present toward Q1439 A and B at z = 1.68.Comment: 33 pages, 13 figures, submitted to Ap
V819 Tau: A Rare Weak-Lined T Tauri Star with a Weak Infrared Excess
We use Spitzer data to infer that the small infrared excess of V819 Tau, a
weak-lined T Tauri star in Taurus, is real and not attributable to a
"companion" 10 arcsec to the south. We do not confirm the mid-infrared excess
in HBC 427 and V410 X-ray 3, which are also non-accreting T Tauri stars in the
same region; instead, for the former object, the excess arises from a red
companion 9 arcsec to the east. A single-temperature blackbody fit to the
continuum excess of V819 Tau implies a dust temperature of 143 K; however, a
better fit is achieved when the weak 10 and 20 micron silicate emission
features are also included. We infer a disk of sub-micron silicate grains
between about 1 AU and several 100 AU with a constant surface density
distribution. The mid-infrared excess of V819 Tau can be successfully modeled
with dust composed mostly of small amorphous olivine grains at a temperature of
85 K, and most of the excess emission is optically thin. The disk could still
be primordial, but gas-poor and therefore short-lived, or already at the debris
disk stage, which would make it one of the youngest debris disk systems known.Comment: 7 pages, 7 figures; accepted for publication in Ap
One dimensional chain of quantum molecule motors as a mathematical physics model for muscle fibre
A quantum chain model of many molecule motors is proposed as a mathematical
physics theory on the microscopic modeling of classical force-velocity relation
and tension transients of muscle fibre. We proposed quantum many-particle
Hamiltonian to predict the force-velocity relation for the slow release of
muscle fibre which has no empirical relation yet, it is much more complicate
than hyperbolic relation. Using the same Hamiltonian, we predicted the
mathematical force-velocity relation when the muscle is stimulated by
alternative electric current. The discrepancy between input electric frequency
and the muscle oscillation frequency has a physical understanding by Doppler
effect in this quantum chain model. Further more, we apply quantum physics
phenomena to explore the tension time course of cardiac muscle and insect
flight muscle. Most of the experimental tension transients curves found their
correspondence in the theoretical output of quantum two-level and three-level
model. Mathematically modeling electric stimulus as photons exciting a quantum
three-level particle reproduced most tension transient curves of water bug
Lethocerus Maximus.Comment: 16 pages, 12 figures, Arguments are adde
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