4,904 research outputs found
Extrapolation of Galactic Dust Emission at 100 Microns to CMBR Frequencies Using FIRAS
We present predicted full-sky maps of submillimeter and microwave emission
from the diffuse interstellar dust in the Galaxy. These maps are extrapolated
from the 100 micron emission and 100/240 micron flux ratio maps that Schlegel,
Finkbeiner, & Davis (1998; SFD98) generated from IRAS and COBE/DIRBE data.
Results are presented for a number of physically plausible emissivity models.
We find that no power law emissivity function fits the FIRAS data from 200 -
2100 GHz. In this paper we provide a formalism for a multi-component model for
the dust emission. A two-component model with a mixture of silicate and
carbon-dominated grains (motivated by Pollack et al., 1994}) provides a fit to
an accuracy of about 15% to all the FIRAS data over the entire high-latitude
sky. Small systematic differences are found between the atomic and molecular
phases of the ISM.
Our predictions for the thermal (vibrational) emission from Galactic dust at
\nu < 3000 GHz are available for general use. These full-sky predictions can be
made at the DIRBE resolution of 40' or at the higher resolution of 6.1 arcmin
from the SFD98 DIRBE-corrected IRAS maps.Comment: 48 pages, AAS LaTeX, 6 figures, ApJ (accepted). Data described in the
text, as well as 4 additional figures, are available at
http://astro.berkeley.edu/dus
Cold Dust in Kepler's Supernova Remnant
The timescales to replenish dust from the cool, dense winds of Asymptotic
Giant Branch stars are believed to be greater than the timescales for dust
destruction. In high redshift galaxies, this problem is further compounded as
the stars take longer than the age of the Universe to evolve into the dust
production stages. To explain these discrepancies, dust formation in supernovae
(SNe) is required to be an important process but until very recently dust in
supernova remnants has only been detected in very small quantities. We present
the first submillimeter observations of cold dust in Kepler's supernova remnant
(SNR) using SCUBA. A two component dust temperature model is required to fit
the Spectral Energy Distribution (SED) with K and K. The total mass of dust implied for Kepler is -
1000 times greater than previous estimates. Thus SNe, or their progenitors may
be important dust formation sites.Comment: 12 pages, 2 figures, accepted to ApJL, corrected proof
HIV risk among Australian men travelling overseas: networks and context matter
Increasing international mobility presents a risk for communicable disease transmissions. Overseas-acquired HIV infections have been increasingly observed across Australian jurisdictions. This includes a mix of men emigrating from countries with high HIV prevalence and men travelling abroad. There is currently little research exploring international mobility and HIV risk and as a consequence the increase of men acquiring HIV while travelling overseas is poorly understood. This article draws on data from a qualitative study exploring the risk perspectives and experiences of 14 Australian men who acquired HIV while travelling overseas in the years between 2000-2009. Participants articulated a strong desire to distance themselves from the identity of a tourist. Social networks were highlighted as important entry points to engage with other foreign travellers and expatriates. These networks were highly influential and were understood by the participants to provide guidance on how they should negotiate the local scene, including where to meet sex partners. Limited discussion of safe sex and HIV was mentioned in these contexts. The findings suggest that prevalent social norms and social networks play an influential role in how participants negotiate sex and social relations in overseas settings. These networks could potentially provide sites for effective HIV prevention programs.
Keywords: male tourists; HIV transmission; social networks; behaviour; sexual risk; HIV preventio
Far infrared and submillimeter brightness temperatures of the giant planets
The brightness temperatures of Jupiter, Saturn, Uranus, and Neptune in the range 35 to 1000 micron. The effective temperatures derived from the measurements, supplemented by shorter wavelength Voyager data for Jupiter and Saturn, are 126.8 + or - 4.5 K, 93.4 + or - 3.3 K, 58.3 + or - 2.0 K, and 60.3 + or - 2.0 K, respectively. The implications of the measurements for bolometric output and for atmospheric structure and composition are discussed. The temperature spectrum of Jupiter shows a strong peak at approx. 350 microns followed by a deep valley at approx. 450 to 500 microns. Spectra derived from model atmospheres qualitatively reproduced these features but do not fit the data closely
Dust heating by the interstellar radiation field in models of turbulent molecular clouds
We have calculated the radiation field, dust grain temperatures, and far
infrared emissivity of numerical models of turbulent molecular clouds. When
compared to a uniform cloud of the same mean optical depth, most of the volume
inside the turbulent cloud is brighter, but most of the mass is darker. There
is little mean attenuation from center to edge, and clumping causes the
radiation field to be somewhat bluer. There is also a large dispersion,
typically by a few orders of magnitude, of all quantities relative to their
means. However, despite the scatter, the 850 micron emission maps are well
correlated with surface density. The fraction of mass as a function of
intensity can be reproduced by a simple hierarchical model of density
structure.Comment: 32 pages, 14 figures, submitted to Ap
L1551NE - Discovery of a Binary Companion
L1551NE is a very young (class 0 or I) low-mass protostar located close to
the well-studied L1551 IRS5. We present here evidence, from 1.3mm continuum
interferometric observations at ~1'' resolution, for a binary companion to
L1551NE. The companion, whose 1.3mm flux density is ~1/3 that of the primary
component, is located 1.43'' (~230 A.U. at 160pc) to the southeast. The
millimeterwave emission from the primary component may have been just barely
resolved, with deconvolved size ~0.82"x0.70" (~131x112 A.U.). The companion
emission was unresolved (<100 A.U.). The pair is embedded within a flattened
circum-binary envelope of size ~5.4'' x 2.3'' (~860 x 370 A.U.). The masses of
the three components (i.e. from the cicumstellar material of the primary star
and its companion, and the envelope) are approximately 0.044, 0.014 and 0.023
Mo respectively.Comment: 8 pages, 1 figur
The exact evaluation of the corner-to-corner resistance of an M x N resistor network: Asymptotic expansion
We study the corner-to-corner resistance of an M x N resistor network with
resistors r and s in the two spatial directions, and obtain an asymptotic
expansion of its exact expression for large M and N. For M = N, r = s =1, our
result is
R_{NxN} = (4/pi) log N + 0.077318 + 0.266070/N^2 - 0.534779/N^4 + O(1/N^6).Comment: 12 pages, re-arranged section
Mesophase formation in two-component cylindrical bottle-brush polymers
When two types of side chains (A,B) are densely grafted to a (stiff) backbone
and the resulting bottle-brush polymer is in a solution under poor solvent
conditions, an incompatibility between A and B leads to microphase separation
in the resulting cylindrical brush. The possible types of ordering are
reminiscent of the ordering of block copolymers in cylindrical confinement.
Starting from this analogy, Leibler's theory of microphase separation in block
copolymer melts is generalized to derive a description of the system in the
weak segregation limit. Also molecular dynamics simulation results of a
corresponding coarse-grained bead-spring model are presented. Using side chain
lengths up to N = 50 effective monomers, the ratio of the Lennard-Jones energy
parameter between unlike monomers and monomers of the same
kind is varied. Various correlation
functions are analyzed to study the conditions when (local) Janus cylinder-type
ordering and when (local) microphase separation in the direction along the
cylinder axis occurs. Both the analytical theory and the simulations give
evidence for short range order due to a tendency towards microphase separation
in the axial direction, with a wavelength proportional to the side chain
gyration radius, irrespective of temperature and grafting density, for a wide
range of these parameters.Comment: 26 pages, 19 figure
Star Formation in the Northern Cloud Complex of NGC 2264
We have made continuum and spectral line observations of several outflow
sources in the Mon OB1 dark cloud (NGC 2264) using the Heinrich Hertz Telescope
(HHT) and ARO 12m millimeter-wave telescope. This study explores the kinematics
and outflow energetics of the young stellar systems observed and assesses the
impact star formation is having on the surrounding cloud environment. Our data
set incorporates 12CO(3-2), 13CO(3-2), and 12CO(1-0) observations of outflows
associated with the sources IRAS 06382+1017 and IRAS 06381+1039, known as IRAS
25 and 27, respectively, in the northern cloud complex. Complementary 870
micron continuum maps were made with the HHT 19 channel bolometer array. Our
results indicate that there is a weak (approximately less than 0.5%) coupling
between outflow kinetic energy and turbulent energy of the cloud. An analysis
of the energy balance in the IRAS 25 and 27 cores suggests they are maintaining
their dynamical integrity except where outflowing material directly interacts
with the core, such as along the outflow axes.Comment: 28 pages including 6 figures, to be published in ApJ 01 July 2006,
v645, 1 issu
Far-infrared polarimetry from the Stratospheric Observatory for Infrared Astronomy
Multi-wavelength imaging polarimetry at far-infrared wavelengths has proven
to be an excellent tool for studying the physical properties of dust, molecular
clouds, and magnetic fields in the interstellar medium. Although these
wavelengths are only observable from airborne or space-based platforms, no
first-generation instrument for the Stratospheric Observatory for Infrared
Astronomy (SOFIA) is presently designed with polarimetric capabilities. We
study several options for upgrading the High-resolution Airborne Wideband
Camera (HAWC) to a sensitive FIR polarimeter. HAWC is a 12 x 32 pixel bolometer
camera designed to cover the 53 - 215 micron spectral range in 4 colors, all at
diffraction-limited resolution (5 - 21 arcsec). Upgrade options include: (1) an
external set of optics which modulates the polarization state of the incoming
radiation before entering the cryostat window; (2) internal polarizing optics;
and (3) a replacement of the current detector array with two state-of-the-art
superconducting bolometer arrays, an upgrade of the HAWC camera as well as
polarimeter. We discuss a range of science studies which will be possible with
these upgrades including magnetic fields in star-forming regions and galaxies
and the wavelength-dependence of polarization.Comment: 12 pages, 5 figure
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