11,409 research outputs found
Automatic estimation of flux distributions of astrophysical source populations
In astrophysics a common goal is to infer the flux distribution of
populations of scientifically interesting objects such as pulsars or
supernovae. In practice, inference for the flux distribution is often conducted
using the cumulative distribution of the number of sources detected at a given
sensitivity. The resulting "-" relationship can be used to
compare and evaluate theoretical models for source populations and their
evolution. Under restrictive assumptions the relationship should be linear. In
practice, however, when simple theoretical models fail, it is common for
astrophysicists to use prespecified piecewise linear models. This paper
proposes a methodology for estimating both the number and locations of
"breakpoints" in astrophysical source populations that extends beyond existing
work in this field. An important component of the proposed methodology is a new
interwoven EM algorithm that computes parameter estimates. It is shown that in
simple settings such estimates are asymptotically consistent despite the
complex nature of the parameter space. Through simulation studies it is
demonstrated that the proposed methodology is capable of accurately detecting
structural breaks in a variety of parameter configurations. This paper
concludes with an application of our methodology to the Chandra Deep Field
North (CDFN) data set.Comment: Published in at http://dx.doi.org/10.1214/14-AOAS750 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Further studies on relic neutrino asymmetry generation II: a rigorous treatment of repopulation in the adiabatic limit
We derive an approximate relic neutrino asymmetry evolution equation that
systematically incorporates repopulation processes from the full quantum
kinetic equations (QKEs). It is shown that in the collision dominant epoch, the
said equation reduces precisely to the expression obtained previously from the
static/adiabatic approximation. The present treatment thus provides a rigorous
justification for the seemingly incongruous assumptions of a negligible
repopulation function and instantaneous repopulation sometimes employed in
earlier works.Comment: RevTeX, 11 pages, no figure
Controlling laser spectra in a phaseonium photonic crystal using maser
We study the control of quantum resonances in photonic crystals with
electromagnetically induced transparency driven by microwave field. In addition
to the control laser, the intensity and phase of the maser can alter the
transmission and reflection spectra in interesting ways, producing hyperfine
resonances through the combined effects of multiple scattering in the
superstructure.Comment: 7 pages, 4 figure
Warm Absorbers and Outflows in the Seyfert-1 Galaxy NGC 4051
We present both phenomenological and more physical photoionization models of
the Chandra HETG spectra of the Seyfert-1 AGN NGC 4051. We detect 40 absorption
and emission lines, encompassing highly ionized charge states from O, Ne, Mg,
Si, S and the Fe L-shell and K-shell. Two independent photoionization packages,
XSTAR and Cloudy, were both used to self-consistently model the continuum and
line spectra. These fits detected three absorbing regions in this system with
densities ranging from 10^{10} to 10^{11} cm^{-3}. In particular, our XSTAR
models require three components that have ionization parameters of log \xi =
4.5, 3.3, & 1.0, and are located within the BLR at 70, 300, and 13,000 R_g,
respectively, assuming a constant wind density. Larger radii are inferred for
density profiles which decline with radius. The Cloudy models give a similar
set of parameters with ionization parameters of log \xi = 5.0, 3.6, & 2.2
located at 40, 200, and 3,300 R_g. We demonstrate that these regions are
out-flowing from the system, and carry a small fraction of material out of the
system relative to the implied mass accretion rate. The data suggest that
magnetic fields may be an important driving mechanism.Comment: 21 pages, 11 Figures, Accepted to Ap
The level structure of Dy160
Gamma rays in Dy160 following beta decay of the 72 day Tb160 have been studied using coincidence and angular correlation methods. The relative intensity and coincidence measurements confirm the principal features of the decay scheme proposed by Nathan1). Angular correlation measurements were made on six cascades. The spin and parity of the 0.087 MeV, 0.964 MeV, and 1.262 MeV levels were found to be 2+, 2+, and 2- respectively. The measurements favour spins of 4 and 3 for the 0.283 MeV and 1.359 MeV levels. These assignments are in agreement with previous assignments by Ofer2).The multi- polarities of the main gamma transitions are given.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32460/1/0000544.pd
Bilateral symmetry breaking in a nonlinear Fabry-Perot cavity exhibiting optical tristability
We show the existence of a region in the parameter space that defines the
field dynamics in a Fabry-Perot cylindrical cavity, where three output stable
stationary states of the light are possible for a given localized incident
field. Two of these states do not preserve the bilateral (i.e. left-right)
symmetry of the entire system. These broken-symmetry states are the
high-transmission nonlinear modes of the system. We also discuss how to excite
these states.Comment: 5 pages, 5 figure
NASA Planetary Mission Concept Study: Assessing: Dwarf Planet Ceres' past and Present Habitability Potential
The Dawn mission revolutionized our understanding of Ceres during the same decade that has also witnessed the rise of ocean worlds as a research and exploration focus. We will report progress on the Planetary Mission Concept Study (PMCS) on the future exploration of Ceres under the New Frontiers or Flagship program that was selected for NASA funding in October 2019. At the time this writing, the study was just kicked off, hence this abstract reports the study plan as presented in the proposal
Identifying critically important vascular access outcomes for trials in haemodialysis : an international survey with patients, caregivers and health professionals
BACKGROUND:
Vascular access outcomes reported across haemodialysis (HD) trials are numerous, heterogeneous and not always relevant to patients and clinicians. This study aimed to identify critically important vascular access outcomes.
METHOD:
Outcomes derived from a systematic review, multi-disciplinary expert panel and patient input were included in a multilanguage online survey. Participants rated the absolute importance of outcomes using a 9-point Likert scale (7-9 being critically important). The relative importance was determined by a best-worst scale using multinomial logistic regression. Open text responses were analysed thematically.
RESULTS:
The survey was completed by 873 participants [224 (26%) patients/caregivers and 649 (74%) health professionals] from 58 countries. Vascular access function was considered the most important outcome (mean score 7.8 for patients and caregivers/8.5 for health professionals, with 85%/95% rating it critically important, and top ranked on best-worst scale), followed by infection (mean 7.4/8.2, 79%/92% rating it critically important, second rank on best-worst scale). Health professionals rated all outcomes of equal or higher importance than patients/caregivers, except for aneurysms. We identified six themes: necessity for HD, applicability across vascular access types, frequency and severity of debilitation, minimizing the risk of hospitalization and death, optimizing technical competence and adherence to best practice and direct impact on appearance and lifestyle.
CONCLUSIONS:
Vascular access function was the most critically important outcome among patients/caregivers and health professionals. Consistent reporting of this outcome across trials in HD will strengthen their value in supporting vascular access practice and shared decision making in patients requiring HD
Targeted Long-Read Bisulfite Sequencing Identifies Differences in the TERT Promoter Methylation Profiles between TERT Wild-Type and TERT Mutant Cancer Cells
Background: TERT promoter methylation, located several hundred base pairs upstream of the transcriptional start site, is cancer specific and correlates with increased TERT mRNA expression and poorer patient outcome. Promoter methylation, however, is not mutually exclusive to TERT activating genetic alterations, as predicted for functionally redundant mechanisms. To annotate the altered patterns of TERT promoter methylation and their relationship with gene expression, we applied a Pacific Biosciences-based, long-read, bisulfite-sequencing technology and compared the differences in the methylation marks between wild-type and mutant cancers in an allele-specific manner. Results: We cataloged TERT genetic alterations (i.e., promoter point mutations or structural variations), allele-specific promoter methylation patterns, and allele-specific expression levels in a cohort of 54 cancer cell lines. In heterozygous mutant cell lines, the mutant alleles were significantly less methylated than their silent, mutation-free alleles (p < 0.05). In wild-type cell lines, by contrast, both epialleles were equally methylated to high levels at the TERT distal promoter, but differentially methylated in the proximal regions. ChIP analysis showed that epialleles with the hypomethylated proximal and core promoter were enriched in the active histone mark H3K4me2/3, whereas epialleles that were methylated in those regions were enriched in the repressive histone mark H3K27me3. Decitabine therapy induced biallelic expression in the wild-type cancer cells, whereas the mutant cell lines were unaffected. Conclusions: Long-read bisulfite sequencing analysis revealed differences in the methylation profiles and responses to demethylating agents between TERT wild-type and genetically altered cancer cell lines. The causal relation between TERT promoter methylation and gene expression remains to be established
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