1,845 research outputs found
Radiative Transfer Model of Dust Attenuation Curves in Clumpy, Galactic Environments
The attenuation of starlight by dust in galactic environments is investigated
through models of radiative transfer in a spherical, clumpy ISM. Extinction
properties for MW, LMC, and SMC dust types are considered. It is illustrated
that the attenuation curves are primarily determined by the wavelength
dependence of absorption rather than by the underlying extinction
(absorption+scattering) curve. Attenuation curves consistent with the "Calzetti
attenuation curve" are found by assuming the silicate-carbonaceous dust model
for the MW, but with the 2175A absorption bump suppressed or absent. The
discrepancy between our results and previous work that claimed the SMC-type
dust to be the most likely origin of the Calzetti curve is ascribed to the
difference in adopted albedos; this study uses the theoretically calculated
albedos whereas the previous ones adopted empirically derived albedos from
observations of reflection nebulae. It is also found that the model attenuation
curves calculated with the MW dust are well represented by a modified Calzetti
curve with a varying slope and UV bump strength. The strong correlation between
the slope and UV bump strength, with steeper curves having stronger bumps, as
found in star-forming galaxies at 0.5<z<2.0, is well reproduced by our models
if the abundance of the UV bump carriers or PAHs is assumed to be 30% or 40% of
that of the MW-dust. The trend is explained by radiative transfer effects which
lead to shallower attenuation curves with weaker UV bumps as the ISM is more
clumpy and dustier. We also argue that at least some of the IUE local starburst
galaxies may have a UV bump feature in their attenuation curves, albeit much
weaker than that of the MW extinction curve.Comment: 28 pages, 30 figures, submited to ApJ
The Far-Infrared Background Correlation with CMB Lensing
The intervening large--scale structure distorts cosmic microwave background
(CMB) anisotropies via gravitational lensing. The same large--scale structure,
traced by dusty star--forming galaxies, also induces anisotropies in the
far--infrared background (FIRB). We investigate the resulting inter--dependence
of the FIRB and CMB with a halo model for the FIRB. In particular, we calculate
the cross--correlation between the lensing potential and the FIRB. The lensing
potential can be quadratically estimated from CMB temperature and/or
polarization maps. We show that the cross--correlation can be measured with
high signal--to--noise with data from the Planck Surveyor. We discuss how such
a measurement can be used to understand the nature of FIRB sources and their
relation to the distribution of dark matter.Comment: 9 pages, 5 figures, submitted to Ap
Experimental and numerical investigations of flow structure and momentum transport in a turbulent buoyancy-driven flow inside a tilted tube.
Buoyancy-driven turbulent mixing of fluids of slightly different densities [At = ÎÏ/(2ăÏă) = 1.15Ă10â2] in a long circular tube tilted at an angle Ξ = 15° from the vertical is studied at the local scale, both experimentally from particle image velocimetry and laser induced fluorescence measurements in the vertical diametrical plane and numerically throughout the tube using direct numerical simulation. In a given cross section of the tube, the axial mean velocity and the mean concentration both vary linearly with the crosswise distance z from the tube axis in the central 70% of the diameter. A small crosswise velocity component is detected in the measurement plane and is found to result from a four-cell mean secondary flow associated with a nonzero streamwise component of the vorticity. In the central region of the tube cross section, the intensities of the three turbulent velocity fluctuations are found to be strongly different, that of the streamwise fluctuation being more than twice larger than that of the spanwise fluctuation which itself is about 50% larger than that of the crosswise fluctuation. This marked anisotropy indicates that the turbulent structure is close to that observed in homogeneous turbulent shear flows. Still in the central region, the turbulent shear stress dominates over the viscous stress and reaches a maximum on the tube axis. Its crosswise variation is approximately accounted for by a mixing length whose value is about one-tenth of the tube diameter. The momentum exchange in the core of the cross section takes place between its lower and higher density parts and there is no net momentum exchange between the core and the near-wall regions. A sizable part of this transfer is due both to the mean secondary flow and to the spanwise turbulent shear stress. Near-wall regions located beyond the location of the extrema of the axial velocity (|z|âł0.36âd) are dominated by viscous stresses which transfer momentum toward (from) the wall near the top (bottom) of the tube
On the Origins of the High-Latitude H-alpha Background
The diffuse high-latitude H-alpha background is widely believed to be
predominantly the result of in-situ recombination of ionized hydrogen in the
warm interstellar medium of the Galaxy. Instead, we show that both a
substantial fraction of the diffuse high-latitude H-alpha intensity in regions
dominated by Galactic cirrus dust and much of the variance in the high-latitude
H-alpha background are the result of scattering by interstellar dust of H-alpha
photons originating elsewhere in the Galaxy. We provide an empirical relation,
which relates the expected scattered H-alpha intensity to the IRAS 100um
diffuse background intensity, applicable to about 81% of the entire sky. The
assumption commonly made in reductions of CMB observations, namely that the
observed all-sky map of diffuse H-alpha light is a suitable template for
Galactic free-free foreground emission, is found to be in need of
reexamination.Comment: 26 pages, 5 figures, Accepted for publication in Ap
Design and realization of a smart battery management system
Battery management system (BMS) emerges a decisive system component in battery-powered applications, such as (hybrid) electric vehicles and portable devices. However, due to the inaccurate parameter estimation of aged battery cells and multi-cell batteries, current BMSs cannot control batteries optimally, and therefore affect the usability of products. In this paper, we proposed a smart management system for multi-cell batteries, and discussed the development of our research study in three directions: i) improving the effectiveness of battery monitoring and current sensing, ii) modeling the battery aging process, and iii) designing a self-healing circuit system to compensate performance variations due to aging and other variations.published_or_final_versio
A limit on the detectability of the energy scale of inflation
We show that the polarization of the cosmic microwave background can be used
to detect gravity waves from inflation if the energy scale of inflation is
above 3.2 times 10^15 GeV. These gravity waves generate polarization patterns
with a curl, whereas (to first order in perturbation theory) density
perturbations do not. The limiting ``noise'' arises from the second--order
generation of curl from density perturbations, or rather residuals from its
subtraction. We calculate optimal sky coverage and detectability limits as a
function of detector sensitivity and observing time.Comment: 4 pages, 3 figures, submitted to PR
Dielectronic Recombination of Argon-Like Ions
We present a theoretical investigation of dielectronic recombination (DR) of
Ar-like ions that sheds new light on the behavior of the rate coefficient at
low-temperatures where these ions form in photoionized plasmas. We provide
results for the total and partial Maxwellian-averaged DR rate coefficients from
the initial ground level of K II -- Zn XIII ions. It is expected that these new
results will advance the accuracy of the ionization balance for Ar-like M-shell
ions and pave the way towards a detailed modeling of astrophysically relevant
X-ray absorption features. We utilize the AUTOSTRUCTURE computer code to obtain
the accurate core-excitation thresholds in target ions and carry out
multiconfiguration Breit-Pauli (MCBP) calculations of the DR cross section in
the independent-processes, isolated-resonance, distorted-wave (IPIRDW)
approximation. Our results mediate the complete absence of direct DR
calculations for certain Ar-like ions and question the reliability of the
existing empirical rate formulas, often inferred from renormalized data within
this isoelectronic sequence
The Detectability of Departures from the Inflationary Consistency Equation
We study the detectability, given CMB polarization maps, of departures from
the inflationary consistency equation, r \equiv T/S \simeq -5 n_T, where T and
S are the tensor and scalar contributions to the quadrupole variance,
respectively. The consistency equation holds if inflation is driven by a
slowly-rolling scalar field. Departures can be caused by: 1) higher-order terms
in the expansion in slow-roll parameters, 2) quantum loop corrections or 3)
multiple fields. Higher-order corrections in the first two slow-roll parameters
are undetectably small. Loop corrections are detectable if they are nearly
maximal and r \ga 0.1. Large departures (|\Delta n_T| \ga 0.1) can be seen if r
\ga 0.001. High angular resolution can be important for detecting non-zero
r+5n_T, even when not important for detecting non-zero r.Comment: 7 pages, 4 figures, submitted to PR
Can electron distribution functions be derived through the Sunyaev-Zel'dovich effect?
Measurements of the Sunyaev-Zel'dovich (hereafter SZ) effect distortion of
the cosmic microwave background provide methods to derive the gas pressure and
temperature of galaxy clusters. Here we study the ability of SZ effect
observations to derive the electron distribution function (DF) in massive
galaxy clusters.
Our calculations of the SZ effect include relativistic corrections considered
within the framework of the Wright formalism and use a decomposition technique
of electron DFs into Fourier series. Using multi-frequency measurements of the
SZ effect, we find the solution of a linear system of equations that is used to
derive the Fourier coefficients; we further analyze different frequency samples
to decrease uncertainties in Fourier coefficient estimations.
We propose a method to derive DFs of electrons using SZ multi-frequency
observations of massive galaxy clusters. We found that the best frequency
sample to derive an electron DF includes high frequencies =375, 600, 700,
857 GHz. We show that it is possible to distinguish a Juttner DF from a
Maxwell-Bolzman DF as well as from a Juttner DF with the second electron
population by means of SZ observations for the best frequency sample if the
precision of SZ intensity measurements is less than 0.1%. We demonstrate by
means of 3D hydrodynamic numerical simulations of a hot merging galaxy cluster
that the morphologies of SZ intensity maps are different for frequencies
=375, 600, 700, 857 GHz. We stress that measurements of SZ intensities at
these frequencies are a promising tool for studying electron distribution
functions in galaxy clusters.Comment: 11 pages, 12 figures, published in Astronomy and Astrophysic
Prompt atmospheric neutrino fluxes: perturbative QCD models and nuclear effects
We evaluate the prompt atmospheric neutrino flux at high energies using three
different frameworks for calculating the heavy quark production cross section
in QCD: NLO perturbative QCD, factorization including low-
resummation, and the dipole model including parton saturation. We use QCD
parameters, the value for the charm quark mass and the range for the
factorization and renormalization scales that provide the best description of
the total charm cross section measured at fixed target experiments, at RHIC and
at LHC. Using these parameters we calculate differential cross sections for
charm and bottom production and compare with the latest data on forward charm
meson production from LHCb at TeV and at TeV, finding good agreement
with the data. In addition, we investigate the role of nuclear shadowing by
including nuclear parton distribution functions (PDF) for the target air
nucleus using two different nuclear PDF schemes. Depending on the scheme used,
we find the reduction of the flux due to nuclear effects varies from to
at the highest energies. Finally, we compare our results with the
IceCube limit on the prompt neutrino flux, which is already providing valuable
information about some of the QCD models.Comment: 61 pages, 25 figures, 11 table
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