14,337 research outputs found
Causal vs. Noncausal Description of Nonlinear Wave Mixing; Resolving the Damping-Sign Controversy
Frequency-domain nonlinear wave mixing processes may be described either
using response functions whereby the signal is generated after all interactions
with the incoming fields, or in terms of scattering amplitudes where all fields
are treated symetrically with no specific time ordering. Closed Green's
function expressions derived for the two types of signals have different
analytical properties. The recent controversy regarding the sign of radiative
damping in the linear (Kramers Heisenberg) formula is put in a broader context
Enumeration of quarter-turn symmetric alternating-sign matrices of odd order
It was shown by Kuperberg that the partition function of the square-ice model
related to the quarter-turn symmetric alternating-sign matrices of even order
is the product of two similar factors. We propose a square-ice model whose
states are in bijection with the quarter-turn symmetric alternating-sign
matrices of odd order, and show that the partition function of this model can
be also written in a similar way. This allows to prove, in particular, the
conjectures by Robbins related to the enumeration of the quarter-turn symmetric
alternating-sign matrices.Comment: 11 pages, 13 figures; minor correction
A decomposition theorem for compact groups with application to supercompactness
We show that every compact connected group is the limit of a continuous
inverse sequence, in the category of compact groups, where each successor
bonding map is either an epimorphism with finite kernel or the projection from
a product by a simple compact Lie group. As an application, we present a proof
of an unpublished result of Charles Mills from 1978: every compact group is
supercompact.Comment: 12 page
Three-coloring statistical model with domain wall boundary conditions. I. Functional equations
In 1970 Baxter considered the statistical three-coloring lattice model for
the case of toroidal boundary conditions. He used the Bethe ansatz and found
the partition function of the model in the thermodynamic limit. We consider the
same model but use other boundary conditions for which one can prove that the
partition function satisfies some functional equations similar to the
functional equations satisfied by the partition function of the six-vertex
model for a special value of the crossing parameter.Comment: 16 pages, notations changed for consistency with the next part,
appendix adde
Rat mammary carcinogenesis following neutron- or X-radiation
Female 61 to 63 - day - old Sprague-Dawley rats were exposed once to a single dose of either 0.43 - MeV
neutrons or 250 - kVX - rays . For neutrons 23 rats were exposed in plastic tubes rotated around and 31 c m from
a water-cooled tritium impregnated target bombarded with 2.45 - MeV protons from a V a n de Graaff generator.
The mean kerma was measured at the rat location by integrating the response of a rat - sized homogeneous
tissue equivalent ionization chamber of minimum mass. The ratio between absorbed dose and kerma is under
investigation and is anticipated to be approximately 0.7. A compensated GM gamma-ray dosimeter indicated
that the gamma - ray doses were 3.5% of the total dose. All rats were examined weekly for the presence
of breast tumours and these were removed, fixed, stained and verified histologically as mammary neoplasms.
At 10 months after exposure 98<7ο of the rats were a live . The neutron kerma, the per cent of rats with
mammary neoplasia, and the number of rats were, respectively: 0.125 rads, 8.2°}o, 182; 0.5 rads, 9.0^0,
89; 2 rads, 20. 6,68; and 8 rads, 31.1%, 45. The X - ray results were: 30 R, 1.4% 95; 60 R, 27. l°Io, 48;
and 90 R, 35.4%, 48. A 3. O^o incidence was found in 167 control rats. At 10 months after exposure the
mammary neoplastic response after 8 rads of neutrons corresponds approximately to that after 60 - 90 R of
X - rays . Similarly, the response after 2 rads of neutrons was intermediate between 30 and 60 R of X - rays and
the response after 0 . 125 and 0.5 rads of neutrons was similar to that after 30 R of X - rays . This demonstrates
that the RBE for 0.43 - MeV neutrons is much lower at high doses than at low doses. Determination of the
confidence limits for the dose-RBE dependence and dose-incidence relationship will be determined as additional
data are collected
Outcomes of a remote, decentralized health center-based HIV/AIDS antiretroviral program in Zambia, 2003 to 2007
A cross-sectional study of patients living with HIV/ AIDS treated during 2003 to 2007 in decentralized, rural health centers in Zambia was performed to measure virological outcomes after 12 months of antiretroviral therapy and identify factors associated with virological failure. Data from 228 patients who started antiretroviral therapy >12 months prior were analyzed. In all, 93% received stavudine + lamivudine + nevirapine regimens, and median antiretroviral therapy duration was 23.5 months (interquartile range 20-28). Of the 205 patients tested for viral load, 177 (86%) had viral load <1000 copies/mL. Probability of developing virological failure (viral load >1000 copies/mL) was 8.9% at 24 months and 19.6% at 32 months. Predictors for virological failure were <100% adherence, body mass index <18.5 kg/m(2), and women <40 years old. Of those with virological failure who underwent 3 to 6 months of intensive adherence counseling, 45% obtained virological success. In a remote, resource-limited setting in decentralized health centers, virological and immunological assessments of patients on antiretroviral therapy >12 months showed that positive health outcomes are achievable
Exact expressions for correlations in the ground state of the dense O(1) loop model
Conjectures for analytical expressions for correlations in the dense O
loop model on semi infinite square lattices are given. We have obtained these
results for four types of boundary conditions. Periodic and reflecting boundary
conditions have been considered before. We give many new conjectures for these
two cases and review some of the existing results. We also consider boundaries
on which loops can end. We call such boundaries ''open''. We have obtained
expressions for correlations when both boundaries are open, and one is open and
the other one is reflecting. Also, we formulate a conjecture relating the
ground state of the model with open boundaries to Fully Packed Loop models on a
finite square grid. We also review earlier obtained results about this relation
for the three other types of boundary conditions. Finally, we construct a
mapping between the ground state of the dense O loop model and the XXZ
spin chain for the different types of boundary conditions.Comment: 25 pages, version accepted by JSTA
A guided self-help intervention supporting mental health professionals’ decisions regarding sharing of lived experience
Mental health professionals with lived experience often experience heightened stigma and fear that their competency may be questioned. We present a new intervention (HOP-MHP) designed to support them in decisions about sharing their lived experience and preliminary results regarding the intervention’s acceptability and feasibility
ROSAT and ASCA observations of the Crab-Like Supernova Remnant N157B in the Large Magellanic Cloud
We report the results of ROSAT and ASCA X-ray observations of the supernova
remnant N157B (or 30 Dor B, SNR 0539-69.1) in the Large Magellanic Cloud. For
comparison, we also briefly describe the results on SNR 0540-69.3, the only
confirmed Crab-like remnant in the Cloud. The X-ray emission from N157B can be
decomposed into a bright comet-shaped feature, superimposed on a diffuse
emission region of a dimension pc. The flat and nearly featureless
spectrum of the remnant is distinctly different from those of young shell-like
remnants, suggesting a predominantly Crab-like nature of N157B. Characterized
by a power law with an energy slope , the spectrum of N157B above
keV is, however, considerably steeper than that of SNR 0540-69.3,
which has a slope of . At lower energies, the spectrum of N157B
presents marginal evidence for emission lines, which if real most likely arise
in hot gas of the diffuse emission region. The hot gas has a characteristic
thermal temperature of 0.4-0.7 keV. No significant periodic signal is detected
from N157B in the period range of s. The pulsed
fraction is (99% confidence) in the keV range. We discuss
the nature of the individual X-ray components. In particular, we suggest that
the synchrotron radiation of relativistic particles from a fast-moving () pulsar explains the size, morphology, spectrum, and energetics
of the comet-shaped X-ray feature. We infer the age of the remnant as yrs. The lack of radio polarization of the remnant may be due to
Faraday dispersion by foreground \ion{H}{2} gas.Comment: To be published in The Astrophysical Journal, 21 pages, plus 11
images in the PS, GIF, or jpeg format. Postscript files of images are
available at http://www.astro.nwu.edu/astro/wqd/paper/n157b
GR 290 (Romano's Star): 2. Light history and evolutionary state
We have built the historical light curve of the luminous variable GR 290 back
to 1901, from old observations of the star found in several archival plates of
M 33. These old recordings together with published and new data show that for
at least half a century the star was in a low luminosity state, with B ~18.
After 1960, five large variability cycles of visual luminosity were recorded.
The amplitude of the oscillations was seen increasing towards the 1992-1994
maximum, then decreasing during the last maxima. The recent light curve
indicates that the photometric variations have been quite similar in all the
bands, and that the B-V color index has been constant within +/-0.1 m despite
the 1.5m change of the visual luminosity. The spectrum of GR 290 at the large
maximum of 1992-94, was equivalent to late-B type, while, during 2002-2014, it
has varied between WN10h-11h near the visual maxima to WN8h-9h at the
luminosity minima. We have detected, during this same period, a clear
anti-correlation between the visual luminosity, the strength of the HeII 4686 A
emission line, the strength of the 4600-4700 A lines blend and the spectral
type. From a model analysis of the spectra collected during the whole 2002-2014
period we find that the Rosseland radius R_{2/3}, changed between the minimum
and maximum luminosity phases by a factor of 3, while T_eff varied between
about 33,000 K and 23,000 K. The bolometric luminosity of the star was not
constant, but increased by a factor of ~1.5 between minimum and maximum
luminosity, in phase with the apparent luminosity variations. In the light of
current evolutionary models of very massive stars, we find that GR 290 has
evolved from a ~60 M_Sun progenitor star and should have an age of about 4
million years. We argue that it has left the LBV stage and is moving to a
Wolf-Rayet stage of late nitrogen spectral type.Comment: Accepted on The Astronomical Journal, 10 figures. Replaced because
the previous uploaded file was that without the final small corrections
requested by the refere
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