2,637 research outputs found
Synthetic spectra of H Balmer and HeI absorption lines. I: Stellar library
We present a grid of synthetic profiles of stellar H Balmer and HeI lines at
optical wavelengths with a sampling of 0.3 A. The grid spans a range of
effective temperature 4000 K < Teff < 50000 K, and gravity 0.0 < log g < 5.0 at
solar metallicity. For Teff > 25000 K, NLTE stellar atmosphere models are
computed using the code TLUSTY (Hubeny 1988). For cooler stars, Kurucz (1993)
LTE models are used to compute thesynthetic spectra. The grid includes the
profiles of the high-order hydrogen Balmer series and HeI lines for effective
temperatures and gravities that have not been previously synthesized. The
behavior of H8 to H13 and HeI 3819 with effective temperature and gravity is
very similar to that of the lower terms of the series (e.g. Hb) and the other
HeI lines at longer wavelengths; therefore, they are suited for the
determination of the atmospheric parameters of stars. These lines are
potentially important to make predictions for these stellar absorption features
in galaxies with active star formation. Evolutionary synthesis models of these
lines for starburst and post-starburst galaxies are presented in a companion
paper. The full set of the synthetic stellar spectra is available for retrieval
at our website http://www.iaa.es/ae/e2.html and
http://www.stsci.edu/science/starburst/ or on request from the authors at
[email protected]: To be published in ApJS. 28 pages and 12 figure
Thermodynamics and magnetic field profiles in low-kappa type-II superconductors
Two-dimensional low-kappa type-II superconductors are studied numerically
within the Eilenberger equations of superconductivity. Depending on the
Ginzburg-Landau parameter \kappa=\lambda/\xi vortex-vortex interaction can be
attractive or purely repulsive. The sign of interaction is manifested as a
first (second) order phase transition from Meissner to the mixed state.
Temperature and field dependence of the magnetic field distribution in
low-kappa type-II superconductors with attractive intervortex interaction is
calculated. Theoretical results are compared to the experiment.Comment: 4 pages, 3 figure
The Zeeman effect in the G band
We investigate the possibility of measuring magnetic field strength in G-band
bright points through the analysis of Zeeman polarization in molecular CH
lines. To this end we solve the equations of polarized radiative transfer in
the G band through a standard plane-parallel model of the solar atmosphere with
an imposed magnetic field, and through a more realistic snapshot from a
simulation of solar magneto-convection. This region of the spectrum is crowded
with many atomic and molecular lines. Nevertheless, we find several instances
of isolated groups of CH lines that are predicted to produce a measurable
Stokes V signal in the presence of magnetic fields. In part this is possible
because the effective Land\'{e} factors of lines in the stronger main branch of
the CH A--X transition tend to zero rather quickly for
increasing total angular momentum , resulting in a Stokes spectrum of
the G band that is less crowded than the corresponding Stokes spectrum. We
indicate that, by contrast, the effective Land\'{e} factors of the and
satellite sub-branches of this transition tend to for increasing .
However, these lines are in general considerably weaker, and do not contribute
significantly to the polarization signal. In one wavelength location near 430.4
nm the overlap of several magnetically sensitive and non-sensitive CH lines is
predicted to result in a single-lobed Stokes profile, raising the
possibility of high spatial-resolution narrow-band polarimetric imaging. In the
magneto-convection snapshot we find circular polarization signals of the order
of 1% prompting us to conclude that measuring magnetic field strength in
small-scale elements through the Zeeman effect in CH lines is a realistic
prospect.Comment: 22 pages, 6 figures. To be published in the Astrophysical Journa
Non-LTE Models and Theoretical Spectra of Accretion Disks in Active Galactic Nuclei
We present self-consistent models of the vertical structure and emergent
spectrum of AGN accretion disks. The central object is assumed to be a
supermassive Kerr black hole. We demonstrate that NLTE effects and the effects
of a self-consistent vertical structure of a disk play a very important role in
determining the emergent radiation, and therefore should be taken into account.
In particular, NLTE models exhibit a largely diminished H I Lyman discontinuity
when compared to LTE models, and the He II discontinuity appears strongly in
emission for NLTE models. Consequently, the number of ionizing photons in the
He II Lyman continuum predicted by NLTE disk models is by 1 - 2 orders of
magnitude higher than that following from the black-body approximation. This
prediction has important implications for ionization models of AGN broad line
regions, and for models of the intergalactic radiation field and the ionization
of helium in the intergalactic medium.Comment: 11 pages; 2 postscript figures; LaTeX, AASPP4 macro; to appear in the
Astrophysical Journal (Letters
Application of Volcano Plots in Analyses of mRNA Differential Expressions with Microarrays
Volcano plot displays unstandardized signal (e.g. log-fold-change) against
noise-adjusted/standardized signal (e.g. t-statistic or -log10(p-value) from
the t test). We review the basic and an interactive use of the volcano plot,
and its crucial role in understanding the regularized t-statistic. The joint
filtering gene selection criterion based on regularized statistics has a curved
discriminant line in the volcano plot, as compared to the two perpendicular
lines for the "double filtering" criterion. This review attempts to provide an
unifying framework for discussions on alternative measures of differential
expression, improved methods for estimating variance, and visual display of a
microarray analysis result. We also discuss the possibility to apply volcano
plots to other fields beyond microarray.Comment: 8 figure
Radiative Transfer in Obliquely Illuminated Accretion Disks
The illumination of an accretion disk around a black hole or neutron star by
the central compact object or the disk itself often determines its spectrum,
stability, and dynamics. The transport of radiation within the disk is in
general a multi-dimensional, non-axisymmetric problem, which is challenging to
solve. Here, I present a method of decomposing the radiative transfer equation
that describes absorption, emission, and Compton scattering in an obliquely
illuminated disk into a set of four one-dimensional transfer equations. I show
that the exact calculation of the ionization balance and radiation heating of
the accretion disk requires the solution of only one of the one-dimensional
equations, which can be solved using existing numerical methods. I present a
variant of the Feautrier method for solving the full set of equations, which
accounts for the fact that the scattering kernels in the individual transfer
equations are not forward-backward symmetric. I then apply this method in
calculating the albedo of a cold, geometrically thin accretion disk.Comment: 16 pages, 3 figures; to appear in The Astrophysical Journa
Protein sequence and structure: Is one more fundamental than the other?
We argue that protein native state structures reside in a novel "phase" of
matter which confers on proteins their many amazing characteristics. This phase
arises from the common features of all globular proteins and is characterized
by a sequence-independent free energy landscape with relatively few low energy
minima with funnel-like character. The choice of a sequence that fits well into
one of these predetermined structures facilitates rapid and cooperative
folding. Our model calculations show that this novel phase facilitates the
formation of an efficient route for sequence design starting from random
peptides.Comment: 7 pages, 4 figures, to appear in J. Stat. Phy
Multi-Resolution Radiative Transfer for Line Emission
We present describe a new computer code that solves the radiative transfer
problem on multi-resolution grids. If the cloud model is from an MHD simulation
on a regular cartesian grid, criteria based for example on local density or
velocity gradients are used to refine the grid by dividing selected cells into
sub-cells. Division can be repeated hierarchically. Alternatively, if the cloud
model is from an MHD simulations with adaptive mesh refinement, the same
multi-resolution grid used for the MHD simulation is adopted in the radiative
transfer calculations. High discretization is often needed only in a small
fraction of the total volume. This makes it possible to simulate spectral line
maps with good accuracy, also minimizing the total number of cells and the
computational cost (time and memory). Multi-resolution models are compared with
models on regular grids. In the case of moderate optical depths (tau ~ a few)
an accuracy of 10% can be reached with multi-resolution models where only 10%
of the cells of the full grid are used. For optically thick species (tau~100),
the same accuracy is achieved using 15% of the cells. The relation between
accuracy and number of cells is not found to be significantly different in the
two MHD models we have studied. The new code is used to study differences
between LTE and non-LTE spectra and between isothermal and non-isothermal cloud
models. We find significant differences in line ratios and individual spectral
line profiles of the isothermal and LTE models relative to the more realistic
non-isothermal case. The slope of the power spectrum of integrated intensity is
instead very similar in all models.Comment: Submitted to ApJ, 34 pages, 14 figure
An analysis of consumer protection for gamblers across different online gambling operators in Ireland: a descriptive study
The aim of the present study was to evaluate the responsible gambling tools which are available to online gamblers at Irish online gambling websites. The present study used a similar methodology to a recent study carried out on the worldâs most popular websites (Bonello and Griffiths Gaming Law Review and Economics, 21, 278â285, 2017), where 50 of the most advertised online gambling websites were evaluated in relation to their responsible gambling (RG) practices. The present study evaluated 39 gambling websites with either a â.ieâ or â.com/ieâ domain. Each website was evaluated by checking for a number of RG practices, including presence of a dedicated RG page; age verification; access to gambling account history; the availability of RG tools, such as limit setting facilities and exclusion settings; and links to limit-setting options on the deposit page. Descriptive statistics were then performed on the results from each website. Of the 39 online gambling operators identified, 22 redirected gamblers to a â.comâ domain, while 17 operators remained as a â.ieâ domain. Thirty-five websites (89.7%) visited had a dedicated RG page. Responsible gambling features were evaluated and demonstrated to be available in an inconsistent manner across online gambling websites. Irish websites were shown to perform poorly in comparison with non-Irish counterparts in the provision of RG tools. The researchers of the present study are not aware of any similar studies conducted to date in Ireland
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