80,775 research outputs found
Comment on ``Stripes and the t-J Model''
This is a comment being submitted to Physical Review Letters on a recent
letter by Hellberg and Manousakis on stripes in the t-J model.Comment: One reference correcte
Cosmology of the Next-to-Minimal Supersymmetric Standard Model
We discuss the domain wall problem in the Next-to-Minimal Supersymmetric
Standard Model, with particular attention to the usual solution of explicit
breaking of the discrete symmetry by non-renormalisable operators. This
``solution'' leads to a contradiction between the requirements of cosmology and
those of avoiding the destabilisation of the hierarchy.Comment: 6 pages LaTeX, needs sprocl.sty (included at end) Talk presented by
P.L. White at Valencia 9
Comment on ``Density-matrix renormalization-group method for excited states''
In a Physical Review B paper Chandross and Hicks claim that an analysis of
the density-density correlation function in the dimerised Hubbard model of
polyacetylene indicates that the optical exciton is bound, and that a previous
study by Boman and Bursill that concluded otherwise was incorrect due to
numerical innacuracy. We show that the method used in our original paper was
numerically sound and well established in the literature. We also show that,
when the scaling with lattice size is analysed, the interpretation of the
density-density correlation function adopted by Chandross and Hicks in fact
implies that the optical exciton is unbound.Comment: RevTeX, 10 pages, 4 eps figures fixed and included now in tex
ALMA imaging of SDP.81 - I. A pixelated reconstruction of the far-infrared continuum emission
We present a sub-50 pc-scale analysis of the gravitational lens system SDP.81
at redshift 3.042 using Atacama Large Millimetre/submillimetre Array (ALMA)
science verification data. We model both the mass distribution of the
gravitational lensing galaxy and the pixelated surface brightness distribution
of the background source using a novel Bayesian technique that fits the data
directly in visibility space. We find the 1 and 1.3 mm dust emission to be
magnified by a factor of u_tot = 17.6+/-0.4, giving an intrinsic total
star-formation rate of 315+/-60 M_sol/yr and a dust mass of 6.4+/-1.5*10^8
M_sol. The reconstructed dust emission is found to be non-uniform, but composed
of multiple regions that are heated by both diffuse and strongly clumped
star-formation. The highest surface brightness region is a ~1.9*0.7 kpc
disk-like structure, whose small extent is consistent with a potential
size-bias in gravitationally lensed starbursts. Although surrounded by extended
star formation, with a density of 20-30+/-10 M_sol/yr/kpc^2, the disk contains
three compact regions with densities that peak between 120-190+/-20
M_sol/yr/kpc^2. Such star-formation rate densities are below what is expected
for Eddington-limited star-formation by a radiation pressure supported
starburst. There is also a tentative variation in the spectral slope of the
different star-forming regions, which is likely due to a change in the dust
temperature and/or opacity across the source.Comment: MNRAS accepted 2015 April 1
Recommended from our members
Flood- and Weather-Damaged Homes and Mental Health: An Analysis Using England's Mental Health Survey
There is increasing evidence that exposure to weather-related hazards like storms and floods adversely affects mental health. However, evidence of treated and untreated mental disorders based on diagnostic criteria for the general population is limited. We analysed the Adult Psychiatric Morbidity Survey, a large probability sample survey of adults in England (n = 7525), that provides the only national data on the prevalence of mental disorders assessed to diagnostic criteria. The most recent survey (2014–2015) asked participants if they had experienced damage to their home (due to wind, rain, snow or flood) in the six months prior to interview, a period that included months of unprecedented population exposure to flooding, particularly in Southern England. One in twenty (4.5%) reported living in a storm- or flood-damaged home in the previous six months. Social advantage (home ownership, higher household income) increased the odds of exposure to storm or flood damage. Exposure predicted having a common mental disorder over and above the effects of other known predictors of poor mental health. With climate change increasing the frequency and severity of storms and flooding, improving community resilience and disaster preparedness is a priority. Evidence on the mental health of exposed populations is key to building this capacity
High frequency, high power capacitor development
A program to develop a special high energy density, high power transfer capacitor to operate at frequency of 40 kHz, 600 V rms at 125 A rms plus 600 V dc bias for space operation. The program included material evaluation and selection, a capacitor design was prepared, a thermal analysis performed on the design. Fifty capacitors were manufactured for testing at 10 kHz and 40 kHz for 50 hours at Industrial Electric Heating Co. of Columbus, Ohio. The vacuum endurance test used on environmental chamber and temperature plate furnished by Maxwell. The capacitors were energized with a special power conditioning apparatus developed by Industrial Electric Heating Co. Temperature conditions of the capacitors were monitored by IEHCo test equipment. Successful completion of the vacuum endurance test series confirmed achievement of the main goal of producing a capacitor or reliable operation at high frequency in an environment normally not hospitable to electrical and electronic components. The capacitor developed compared to a typical commercial capacitor at the 40 kHz level represents a decrease in size and weight by a factor of seven
Testing Cosmological Models With A \lya Forest Statistic: The High End Of The Optical Depth Distribution
We pay particular attention to the high end of the \lya optical depth
distribution of a quasar spectrum. Based on the flux distribution
(Miralda-Escud\'e et al 1996), a simple yet seemingly cosmological model
-differentiating statistic, -- the cumulative probability of
a quasar spectrum with \lya optical depth greater than a high value
-- is emphasized. It is shown that two different models -- the cold dark matter
model with a cosmological constant and the mixed hot and cold dark matter
model, both normalized to COBE and local galaxy cluster abundance -- yield
quite different values of : 0.13 of the former versus 0.058 of
the latter for at . Moreover, it is argued that
may be fairly robust to compute theoretically because it does
not seem to depend sensitively on small variations of simulations parameters
such as radiation field, cooling, feedback process, radiative transfer,
resolution and simulation volume within the plausible ranges of the concerned
quantities. Furthermore, it is illustrated that can be
obtained sufficiently accurately from currently available observed quasar
spectra for , when observational noise is properly taken
into account. We anticipate that analyses of observations of quasar \lya
absorption spectra over a range of redshift may be able to constrain the
redshift evolution of the amplitude of the density fluctuations on
small-to-intermediate scales, therefore providing an independent constraint on
, and .Comment: ApJ Letters, in press, substantial changes have been made from the
last versio
ALMA imaging of SDP.81 - II. A pixelated reconstruction of the CO emission lines
We present a sub-100 pc-scale analysis of the CO molecular gas emission and
kinematics of the gravitational lens system SDP.81 at redshift 3.042 using
Atacama Large Millimetre/submillimetre Array (ALMA) science verification data
and a visibility-plane lens reconstruction technique. We find clear evidence
for an excitation dependent structure in the unlensed molecular gas
distribution, with emission in CO (5-4) being significantly more diffuse and
structured than in CO (8-7). The intrinsic line luminosity ratio is r_8-7/5-4 =
0.30 +/- 0.04, which is consistent with other low-excitation starbursts at z ~
3. An analysis of the velocity fields shows evidence for a star-forming disk
with multiple velocity components that is consistent with a
merger/post-coalescence merger scenario, and a dynamical mass of M(< 1.56 kpc)
= 1.6 +/- 0.6 x 10^10 M_sol . Source reconstructions from ALMA and the Hubble
Space Telescope show that the stellar component is offset from the molecular
gas and dust components. Together with Karl G. Jansky Very Large Array CO (1-0)
data, they provide corroborative evidence for a complex ~2 kpc-scale starburst
that is embedded within a larger ~15 kpc structure.Comment: MNRAS accepted, 6th July 201
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