711 research outputs found
A First-Quantized Formalism for Cosmological Particle Production
We show that the amount of particle production in an arbitrary cosmological
background can be determined using only the late-time positive-frequency modes.
We don't refer to modes at early times, so there is no need for a Bogolubov
transformation. We also show that particle production can be extracted from the
Feynman propagator in an auxiliary spacetime. This provides a first-quantized
formalism for computing particle production which, unlike conventional
Bogolubov transformations, may be amenable to a string-theoretic
generalization.Comment: 18 pages, LaTeX; v2: significantly revised for clarity; conclusions
unchange
Analytical solution of a generalized Penna model
In 1995 T.J.Penna introduced a simple model of biological aging. A modified
Penna model has been demonstrated to exhibit behaviour of real-life systems
including catastrophic senescence in salmon and a mortality plateau at advanced
ages. We present a general steady-state, analytic solution to the Penna model,
able to deal with arbitrary birth and survivability functions. This solution is
employed to solve standard variant Penna models studied by simulation.
Different Verhulst factors regulating both the birth rate and external death
rate are considered.Comment: 6 figure
Coulomb gap in a model with finite charge transfer energy
The Coulomb gap in a donor-acceptor model with finite charge transfer energy
describing the electronic system on the dielectric side of the
metal-insulator transition is investigated by means of computer simulations on
two- and three-dimensional finite samples with a random distribution of equal
amounts of donor and acceptor sites. Rigorous relations reflecting the symmetry
of the model presented with respect to the exchange of donors and acceptors are
derived. In the immediate neighborhood of the Fermi energy the the
density of one-electron excitations is determined solely by
finite size effects and further away from is described by
an asymmetric power law with a non-universal exponent, depending on the
parameter .Comment: 10 pages, 6 figures, submitted to Phys. Rev.
Spin polarization and spin-dependent scattering of holes observed in transverse magnetic focusing
In two-dimensional systems with a spin-orbit interaction, magnetic focusing can be used to create a spatial separation of particles with different spin. Here we measure hole magnetic focusing for two different magnitudes of the Rashba spin-orbit interaction. We find that when the Rashba spin-orbit magnitude is large there is significant attenuation of one of the focusing peaks, which is conventionally associated with a change in the spin polarization. We instead show that in hole systems with a k3 spin-orbit interaction, this peak suppression is due to a change in the scattering of one spin state, not a change in spin polarization. We also show that the change in scattering length extracted from magnetic focusing is consistent with results obtained from measurements of Shubnikov-de Haas oscillations. This result suggests that scattering must be considered when relating focusing peak amplitude to spin polarization in hole systems
Methodology: Systematic Review and Meta-analysis of the AAC Literature for People with Autism Spectrum Disorder or Intellectual Disabilities who have Complex Communication Needs through 2020
A comprehensive meta-analysis examining the impacts of augmentative and alternative communication for individuals with complex communication needs was conducted, examining the relationship between social-communicative and educational outcomes and use of augmentative and alternative communication devices and across potential moderating variables. This document reports the methodology of the project as a whole, describing overarching procedures. Given the comprehensiveness of the review and meta-analysis, results of this review are reported in digestible groupings of types of research designs, types of research questions, and moderator groupings. Each of the resulting papers cite this primary document, as do additional reviews derived from the assembled data set.
The documents herewith report the overarching methodology of the project, including the following. The document searches occurred in 2018 and 2020, resulting in 7,327 documents reviewed for title/abstract indication of meeting inclusion criteria. Full text document review was conducted for 1,758 documents for the next inclusion/exclusion gate. Documents were divided into group design (n = 132) and single-case experimental design (SCED) documents (n = 547) and reviewed for basic design criteria, resulting in 59 group design documents and 257 SCED documents. Lead project authors conducted screening remaining documents for false positives, resulting in 20 group and 176 SCED documents remaining for further analysis. Data extraction and potential moderator variable coding procedures are described in detail, with relevant coding manuals and other materials attached. Effect size metrics used for meta-analytic procedures are detailed.The research described here is supported by the Institute of Education Sciences, U.S. Department of Education, through Grant R324A180110 to Texas A&M University. The opinions expressed are those of the authors and do not represent views of the Institute or the U.S. Department of Educatio
Mutual Events in the Cold Classical Transneptunian Binary System Sila and Nunam
Hubble Space Telescope observations between 2001 and 2010 resolved the binary
components of the Cold Classical transneptunian object (79360) Sila-Nunam
(provisionally designated 1997 CS29). From these observations we have
determined the circular, retrograde mutual orbit of Nunam relative to Sila with
a period of 12.50995 \pm 0.00036 days and a semimajor axis of 2777 \pm 19 km. A
multi-year season of mutual events, in which the two near-equal brightness
bodies alternate in passing in front of one another as seen from Earth, is in
progress right now, and on 2011 Feb. 1 UT, one such event was observed from two
different telescopes. The mutual event season offers a rich opportunity to
learn much more about this barely-resolvable binary system, potentially
including component sizes, colors, shapes, and albedo patterns. The low
eccentricity of the orbit and a photometric lightcurve that appears to coincide
with the orbital period are consistent with a system that is tidally locked and
synchronized, like the Pluto-Charon system. The orbital period and semimajor
axis imply a system mass of (10.84 \pm 0.22) \times 10^18 kg, which can be
combined with a size estimate based on Spitzer and Herschel thermal infrared
observations to infer an average bulk density of 0.72 +0.37 -0.23 g cm^-3,
comparable to the very low bulk densities estimated for small transneptunian
binaries of other dynamical classes.Comment: In press in Icaru
Obesity and Breast Cancer Metastasis across Genomic Subtypes
Background: Obese women have higher risk of aggressive breast tumors and distant metastasis. However, obesity has rarely been assessed in association with metastasis in diverse populations. Methods: In the Carolina Breast Cancer Study Phase 3 (2008–2013), waist-to-hip ratio (WHR), body mass index (BMI), and molecular subtype [PAM50 risk-of-recurrence (ROR) score] were assessed. Obesity measures were evaluated in association with metastasis within five years of diagnosis, overall and stratified by race and ROR score. Absolute risk of metastasis and risk differences between strata were calculated using the Kaplan–Meier estimator, adjusted for age, grade, stage, race, and ER status. Relative frequency of metastatic site and multiplicity were estimated in association with obesity using generalized linear models. Results: High-WHR was associated with higher risk of metastasis (5-year risk difference, RD, 4.3%; 95% confidence interval, 2.2–6.5). It was also associated with multiple metastases and metastases at all sites except brain. The 5-year risk of metastasis differed by race (11.2% and 6.9% in Black and non-Black, respectively) and ROR score (19.5% vs. 6.6% in high vs. low-to-intermediate ROR-PT). Non-Black women and those with low-to-intermediate ROR scores had similar risk in high- and low-WHR strata. However, among Black women and those with high ROR, risk of metastasis was elevated among high-WHR (RDBlack/non-Black = 4.6%, RDHigh/Low-Int = 3.1%). Patterns of metastasis were similar by BMI. Conclusions: WHR is associated with metastatic risk, particularly among Black women and those with high-risk tumors. Impact: Understanding how risk factors for metastasis interact may help in tailoring care plans and surveillance among patients with breast cancer
Large-scale periodicity in the distribution of QSO absorption-line systems
The spatial-temporal distribution of absorption-line systems (ALSs) observed
in QSO spectra within the cosmological redshift interval z = 0.0--4.3 is
investigated on the base of our updated catalog of absorption systems. We
consider so called metallic systems including basically lines of heavy
elements. The sample of the data displays regular variations (with amplitudes ~
15 -- 20%) in the z-distribution of ALSs as well as in the eta-distribution,
where eta is a dimensionless line-of-sight comoving distance, relatively to
smoother dependences. The eta-distribution reveals the periodicity with period
Delta eta = 0.036 +/- 0.002, which corresponds to a spatial characteristic
scale (108 +/- 6) h(-1) Mpc or (alternatively) a temporal interval (350 +/- 20)
h(-1) Myr for the LambdaCDM cosmological model. We discuss a possibility of a
spatial interpretation of the results treating the pattern obtained as a trace
of an order imprinted on the galaxy clustering in the early Universe.Comment: AASTeX, 13 pages, with 9 figures, Accepted for publication in
Astrophysics & Space Scienc
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