3,980 research outputs found
Infrared Astronomical Satellite (IRAS) analysis of the transmittance of off-axis energy due to scattering and diffraction
Stray light transmittance is analyzed. Mathematical models are evaluated. The results of scatter and diffraction are considered separately, and the combined transmittance values evaluated
Falloff of the Weyl scalars in binary black hole spacetimes
The peeling theorem of general relativity predicts that the Weyl curvature
scalars Psi_n (n=0...4), when constructed from a suitable null tetrad in an
asymptotically flat spacetime, fall off asymptotically as r^(n-5) along
outgoing radial null geodesics. This leads to the interpretation of Psi_4 as
outgoing gravitational radiation at large distances from the source. We have
performed numerical simulations in full general relativity of a binary black
hole inspiral and merger, and have computed the Weyl scalars in the standard
tetrad used in numerical relativity. In contrast with previous results, we
observe that all the Weyl scalars fall off according to the predictions of the
theorem.Comment: 7 pages, 3 figures, published versio
Fluctuations relations for semiclassical single-mode laser
Over last decades, the study of laser fluctuations has shown that laser
theory may be regarded as a prototypical example of a nonlinear nonequilibrium
problem. The present paper discusses the fluctuation relations, recently
derived in nonequilibrium statistical mechanics, in the context of the
semiclassical laser theory.Comment: 11 pages, 3 figure
One dimensional chain of quantum molecule motors as a mathematical physics model for muscle fibre
A quantum chain model of many molecule motors is proposed as a mathematical
physics theory on the microscopic modeling of classical force-velocity relation
and tension transients of muscle fibre. We proposed quantum many-particle
Hamiltonian to predict the force-velocity relation for the slow release of
muscle fibre which has no empirical relation yet, it is much more complicate
than hyperbolic relation. Using the same Hamiltonian, we predicted the
mathematical force-velocity relation when the muscle is stimulated by
alternative electric current. The discrepancy between input electric frequency
and the muscle oscillation frequency has a physical understanding by Doppler
effect in this quantum chain model. Further more, we apply quantum physics
phenomena to explore the tension time course of cardiac muscle and insect
flight muscle. Most of the experimental tension transients curves found their
correspondence in the theoretical output of quantum two-level and three-level
model. Mathematically modeling electric stimulus as photons exciting a quantum
three-level particle reproduced most tension transient curves of water bug
Lethocerus Maximus.Comment: 16 pages, 12 figures, Arguments are adde
Estimating factor models for multivariate volatilities : an innovation expansion method
We introduce an innovation expansion method for estimation of factor models for conditional variance (volatility) of a multivariate time series. We estimate the factor loading space and the number of factors by a stepwise optimization algorithm on expanding the "white noise space". Simulation and a real data example are given for illustration
Doing more with less: Teacher professional learning communities in resource-constrained primary schools in rural China.
Teacher professional learning communities provide environments in which teachers engage in regular research and collaboration. They have been found effective as a means for connecting professional learning to the day-to-day realities faced by teachers in the classroom. In this article, the authors draw on survey data collected in primary schools serving 71 villages in rural Gansu Province as well as transcripts from in-depth interviews with 30 teachers. Findings indicate that professional learning communities penetrate to some of China’s most resource-constrained schools but that their nature and development are shaped by institutional supports, principal leadership, and teachers’ own initiative
A Search for Ultraviolet Emission from LINERs
We have obtained Hubble Space Telescope WFPC2 2200 A and optical V-band
images of 20 low-luminosity active galactic nuclei, most of which are
spectroscopically classified as LINERs, in order to search for a possible
photoionizing continuum. Six (30%) of the galaxies are detected in the UV. Two
of the detected galaxies (NGC 3642 and NGC 4203) have compact, unresolved
nuclear UV sources, while the remaining four UV sources (in NGC 4569, NGC 5005,
NGC 6500, and NGC 7743) are spatially extended. Combining our sample with that
of Maoz et al. (1995), we find that the probability of detection of a nuclear
UV source is greatest for galaxies having low internal reddening and low
inclination, and we conclude that dust obscuration is the dominant factor
determining whether or not a UV source is detected. Large emission-line
equivalent widths and the presence of broad-line emission also increase the
likelihood of detection of nuclear UV emission. Our results suggest that the
majority of LINERs harbor obscured nuclear UV sources, which may be either
accretion-powered active nuclei or young star clusters. Under the assumption
that the compact UV sources in NGC 3642 and NGC 4203 have nonstellar power-law
spectra extending into the extreme ultraviolet, the extrapolated ionizing
fluxes are sufficiently strong to photoionize the narrow-line regions of these
objects. The V-band images of many galaxies in our sample reveal remarkably
strong dust lanes which may be responsible for obscuring some UV sources.Comment: 25 pages, 4 figures, 3 tables, LaTeX, AASTeX v4.0 style file,
accepted for publication in The Astrophysical Journal, additional figures
available at http://astro.berkeley.edu/~barth/papers/u
A model for the infrared-radio correlation of main-sequence galaxies at GHz frequencies and its dependence on redshift and stellar mass
The infrared-radio correlation (IRRC) of star-forming galaxies can be used to
estimate their star formation rate (SFR) based on the radio continuum
luminosity at MHz-GHz frequencies. For application in future deep radio
surveys, it is crucial to know whether the IRRC persists at high redshift z.
Delvecchio et al. (2020) observed that the 1.4 GHz IRRC correlation of
star-forming galaxies is nearly z-invariant up to z~4, but depends strongly on
the stellar mass M_star. This should be taken into account for SFR calibrations
based on radio luminosity. To understand the physical cause of the
M_star-dependence of the IRRC and its properties at higher z, we construct a
phenomenological model for galactic radio emission involving magnetic fields
generated by a small-scale dynamo, a steady-state cosmic ray population, as
well as observed scaling relations that reduce the number of free parameters.
The best agreement between the model and the characteristics of the IRRC
observed by Delvecchio et al. (2020) is found when the efficiency of the
SN-driven turbulence is 5 % and when saturation of the small-scale dynamo
occurs once 10 % of the kinetic energy is converted into magnetic energy. The
observed dependence of the IRRC on M_star and z can be reproduced with our
model. For galaxies with intermediate to high (M_star ~ 10^9.5 - 10^11 M_sun)
stellar masses, our model results in a IRRC which is nearly independent of z.
For galaxies with lower masses (M_star ~ 10^8.5 M_sun), we find that the
IR-to-radio flux ratio increases with increasing redshift. This matches the
observational data in that mass bin which, however, only extends to z~1.5. The
increase of the IR-to-radio flux ratio for low-mass galaxies at z>1.5 that is
predicted by our model could be tested with future deep radio observations.Comment: 18 pages, 17 figures, submitted to A&
Is there consensus in defining childhood cerebral visual impairment? A systematic review of terminology and definitions
The childhood condition of visual difficulties caused by brain damage, commonly termed cortical or cerebral visual impairment (CVI), is well established but has no internationally accepted definition. Clarification of its core features is required to advance research and clinical practice. This systematic review aimed to identify the definitions of childhood CVI in the original scientific literature to describe and critically appraise a consensual definition of the condition. MEDLINE, EMBASE, PsychINFO, CINAHL and AMED databases were searched in January 2017. Studies were included if they (1) were published original research, (2) contained a childhood CVI sample, (3) contained a definition of CVI and (4) described their CVI identification/diagnostic method. Thematic analysis identified concepts within definitions and narrative synthesis was conducted. Of 1150 articles, 51 met inclusion criteria. Definitions were subdivided according to detail (descriptive definition, description not reaching definition status and diagnostic/operationalising criteria). Three themes concerning visual deficits, eye health and brain integrity were identified (each containing subthemes) and analysed individually across definitions. The most common themes were ‘visual impairment’ (n=20), ‘retrochiasmatic pathway damage’(n=13) and ‘normal/near normal eye health’ (n=15). The most consensual definition identified here may not be the best quality for advancing our understanding of CVI. We argue for the alternative definition: CVI is a verifiable visual dysfunction which cannot be attributed to disorders of the anterior visual pathways or any potentially co-occurring ocular impairment. We propose reporting guidelines to permit comparison across studies and increase the evidence base for more reliable clinical assessment and diagnosis
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