1,511 research outputs found
Stark broadening data for spectral lines of rare-earth elements: Nb III
The electron-impact widths for 15 doubly charged Nb ion lines have been
theoretically determined by using the modified semiempirical method. Using the
obtained results, we considered the influence of the electron-impact mechanism
on line shapes in spectra of chemically peculiar stars and white dwarfs.Comment: 10 pages, 2 figures, 1 table, accepted in Advances in Space Researc
Emission Lines in X-ray Spectra of Clusters of Galaxies
Emission lines in X-ray spectra of clusters of galaxies reveal the presence
of heavy elements in the diffuse hot plasma (the Intra Cluster Medium, or ICM)
in virial equilibrium in the dark matter potential well. The relatively simple
physical state of the ICM allows us to estimate, with good accuracy, its
thermodynamical properties and chemical abundances. These measures put strong
constraints on the interaction processes between the galaxies and the
surrounding medium, and have significant impact on models of galaxy formation
as well. This field is rapidly evolving thanks to the X-ray satellites Chandra
and XMM-Newton. Among the most relevant progresses in the last years, we
briefly discuss the nature of cool cores and the measure of the Iron abundance
in high redshift clusters. Future X-ray missions with bolometers promise to
provide a substantial step forward to a more comprehensive understanding of the
complex physics of the ICM.Comment: 8 pages, 3 figures, Proceedings of the VI Serbian Conference on
Spectral Line Shapes in Astrophysics, Sremski Karlovci, Serbia June 11-15
200
Radial Dependence of Extinction in Parent Galaxies of Supernovae
The problem of extinction is the most important issue to be dealt with in the
process of obtaining true absolute magnitudes of core-collapse supernovae
(SNe). The plane-parallel model which gives absorption dependent on galaxy
inclination, widely used in the past, was shown not to describe extinction
adequately. We try to apply an alternative model which introduces radial
ependence of extinction. A certain trend of dimmer SNe with decreasing radius
from the center of a galaxy was found, for a chosen sample of stripped-envelope
SNe.Comment: 4 pages, 1 table, 2 figures, 6th SCSLSA Pro
Alkali Line Profiles in Degenerate Dwarfs
Ultracool stellar atmospheres show absorption by alkali resonance lines
severely broadened by collisions with neutral perturbers. In the coolest and
densest atmospheres, such as those of T dwarfs, Na I and K I broadened by
molecular hydrogen and helium can come to dominate the entire optical spectrum.
Their profiles have been successfully modelled with accurate interaction
potentials in the adiabatic theory, computing line profiles from the first few
orders of a density expansion of the autocorrelation function. The line shapes
in the emergent spectrum also depend on the distribution of absorbers as a
function of depth, which can be modelled with improved accuracy by new models
of dust condensation and settling.
The far red K I wings of the latest T dwarfs still show missing opacity in
these models, a phenomenon similar to what has been found for the Na I line
profiles observed in extremely cool, metal-rich white dwarfs. We show that the
line profile in both cases is strongly determined by multiple-perturber
interactions at short distances and can no longer be reproduced by a density
expansion, but requires calculation of the full profile in a unified theory.
Including such line profiles in stellar atmosphere codes will further improve
models for the coolest and densest dwarfs as well as for the deeper atmosphere
layers of substellar objects in general.Comment: VI Serbian Conference on Spectral Line Shapes in Astrophysics; to be
published by the American Institute of Physics, eds. Milan S. Dimitrijevic
and Luka C. Popovic; 6 pages, 6 figure
Growth Response and Serum Biochemistry of Growing Rabbits Fed Graded Levels of Baobab (Adansonia digitata L.) Seed Kernel Meal
The study was conducted for fifty-six (56) days to investigate the effects of feeding baobab seed kernel meal on growth and serum biochemical indices of grower rabbits. Five isonitrogenous, isocaloric and isofibrous rabbit grower diets were formulated to contain 0, 2.5, 5.0, 7.5 and 10.0% baobab seed kernel meal. Twenty (20) cross bred grower rabbits with mean initial live weight of 916±233.04 grams were randomly distributed to five treatments, each replicated four times in a completely randomized design. Final weight, weight gain, feed intake, feed conversion ratio and protein efficiency ratio were not significantly (P>0.05) different. Serum biochemical indices showed that albumin and alanine aminotransferase values were significantly (P<0.05) elevated by additional inclusion of baobab seed kernel. However, this elevation was not out of normal range reported for healthy rabbits. Creatinine was significantly (P<0.05) reduced at up to 5.0% baobab seed kernel inclusion level, but elevated at higher levels of inclusion. Serum biochemistry values for the experimental groups were within normal range, implying healthy nutrition. Baobab seed kernel meal can be fed to grower rabbits up to 10.0% of the diet without deleterious effect on growth and serum biochemistry.Key Words: Grower rabbits, baobab seed kernel, growth, serum biochemistr
Using genotype abundance to improve phylogenetic inference
Modern biological techniques enable very dense genetic sampling of unfolding
evolutionary histories, and thus frequently sample some genotypes multiple
times. This motivates strategies to incorporate genotype abundance information
in phylogenetic inference. In this paper, we synthesize a stochastic process
model with standard sequence-based phylogenetic optimality, and show that tree
estimation is substantially improved by doing so. Our method is validated with
extensive simulations and an experimental single-cell lineage tracing study of
germinal center B cell receptor affinity maturation
Properties and characterization of ALD grown dielectric oxides for MIS structures
We report on an extensive structural and electrical characterization of
under-gate dielectric oxide insulators Al2O3 and HfO2 grown by Atomic Layer
Deposition (ALD). We elaborate the ALD growth window for these oxides, finding
that the 40-100 nm thick layers of both oxides exhibit fine surface flatness
and required amorphous structure. These layers constitute a base for further
metallic gate evaporation to complete the Metal-Insulator-Semiconductor
structure. Our best devices survive energizing up to ~3 MV/cm at 77 K with the
leakage current staying below the state-of-the-art level of 1 nA. At these
conditions the displaced charge corresponds to a change of the sheet carrier
density of 3 \times 1013 cm-2, what promises an effective modulation of the
micromagnetic properties in diluted ferromagnetic semiconductors.Comment: 8 pages, 5 figures, 14 reference
Existence and Non-Existence of Doubly Heavy Tetraquark Bound States
In this work we investigate the existence of bound states for doubly heavy tetraquark systems Q¯Q¯′qq′ in a full lattice-QCD computation, where heavy bottom quarks are treated in the framework of non-relativistic QCD. We focus on three systems with quark content b¯b¯ud, b¯b¯us and b¯c¯ud. We show evidence for the existence of b¯b¯ud and b¯b¯us bound states, while no binding appears to be present for b¯c¯ud. For the bound four-quark states we also discuss the importance of various creation operators and give an estimate of the meson-meson and diquark-antidiquark percentages
Faceted wrinkling by contracting a curved boundary
Single-mode deformations of two-dimensional materials, such as the Miura-ori
fold, are important to the design of deployable structures because of their
robustness, but usually require careful pre-patterning of the material. Here,
we show that inward contraction of a curved boundary produces a novel
single-mode deformation without any pre-patterning. Using finite-element
simulations of the contraction of a thin circular annular sheet, we show that
these sheets wrinkle into a structure with negligible stretching energy, in
which the contracted boundary forms spontaneous facets. We construct a strictly
isometric wrinkled surface formed of triangles and cones that matches geometric
and energy features closely, suggesting that this class of partly-faceted
wrinkled deformations is isometric. Isometry favours the restriction of such
deformations to a robust low-bending energy channel that avoids stretching.
This class of buckling also offers a novel way to manipulate sheet morphology
via boundary forces. Finally, it serves as a minimal model for illustrating the
strong constraints imposed by geometry in elastic pattern formation.Comment: V3. Double column. 6 pages, 5 figures + S
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