66 research outputs found
On the Submillimeter Opacity of Protoplanetary Disks
Solid particles with the composition of interstellar dust and power-law size
distribution dn/da propto a^{-p} for a 3 lambda and 3 <
p < 4 will have submm opacity spectral index beta(lambda) = dln(kappa)/dln(nu)
approx (p-3) beta_{ism}, where beta_{ism} approx 1.7 is the opacity spectral
index of interstellar dust material in the Rayleigh limit. For the power-law
index p approx 3.5 that characterizes interstellar dust, and that appears
likely for particles growing by agglomeration in protoplanetary disks, grain
growth to sizes a > 3 mm will result in beta(1 mm) < ~1. Grain growth can
naturally account for beta approx 1 observed for protoplanetary disks, provided
that a_{max} > ~ 3 lambda.Comment: Submitted to ApJ. 17 pages, 6 figure
Diffuse interstellar bands in reflection nebulae
A Monte Carlo code for radiation transport calculations is used to compare the profiles of the lambda lambda 5780 and 6613 Angstrom diffuse interstellar bands in the transmitted and the reflected light of a star embedded within an optically thin dust cloud. In addition, the behavior of polarization across the bands were calculated. The wavelength dependent complex indices of refraction across the bands were derived from the embedded cavity model. In view of the existence of different families of diffuse interstellar bands the question of other parameters of influence is addressed in short
Endothelial dysfunction in patients after COVID-19
Relevance: Over the past two years, the COVID-19 infection has gained unprecedented relevance at the global level. All countries are spending significant resources in the fight against COVID-19 [1 2].
The purpose of the work is to clarify the issue of the state of the kidneys in the distant post-covid period (after 2-3 months), we conducted a study of the kidneys simultaneously with the desquamation of the endothelium, as one of the probable mechanisms of the nephrotic effect of the COVID-19 virus.
Materials and methods: 29 people participated in the study. Patients with post-covid syndrome (n=10) were treated on an outpatient basis at the "KNP "Center of primary medical and sanitary (medical and sanitary) care No. 3, Odesa" of the Odesa City Council" in the period from 2020 to 2021. The control group consisted of patients without cardiovascular and endocrine disorders, comparable in terms of gender and age, who were examined in 2018 at the Odesa Regional Clinical Medical Center of the Odesa Regional Council.
Endothelial dysfunction "ED" was determined by the intensity of desquamation of the endothelium according to the method of J. Hladovec as modified by M.M. Petryschev. and other. (2001).
          Statistical analysis was performed using Status software [https://status-please.herokuapp.com/]. Mean values ​​(M) and its standard deviation (SD) were used to describe quantitative data, and percentages were used for qualitative data. For comparison, data were presented as M and standard error of the mean (SEM). Analysis of normality was performed using the Shapiro-Wilk test. Levene's test was used to assess homogeneity of variances. Differences between groups were determined using Student's t-test and one-way analysis of variance (ANOVA). The relationship and presence of correlation between the studied parameters was determined using the Pearson correlation coefficient (r). The correlation coefficient in the range of 0.5≤|r|<1 indicated a strong correlation relationship, 0.3≤|r|<0.5 – a relationship of medium strength, 0<|r|<0.3 – on a weak correlation. Statistical significance was established only at the level of p < 0.05.
Results: 17 men and 12 women aged from 32 to 80 years who suffered from a disease of moderate severity participated in the study. The average age of the group of patients with post-covid syndrome (n=9) is 55.9±14.47 years, the average age of the control group (n=20) is 55.95±14.47 years.
There were no complaints from the urinary system in the examined patients. According to blood serum tests, it was established that the creatinine level among patients with post-covid syndrome was on average 113±11.91 μmol/l, the urea level was 8.11±1.2 mmol/l, the GFR level was 55.06±12, 19 ml/min/1.73. m2.
In the control group, the numbers were as follows: creatinine level was 73.2±8.5 μmol/l, mean urea level was 4.61 mmol/l, GFR was 94.78±13.76 ml/min/1.73 m2.
Conclusions:
2-3 months after the transfer of COVID-19, the examined patients show signs of chronic kidney disease.
After a disease with COVID-19, an increase in CEC is detected, which is a manifestation of endothelial dysfunction
Calculating Cross Sections of Composite Interstellar Grains
Interstellar grains may be composite collections of particles of distinct
materials, including voids, agglomerated together. We determine the various
optical cross sections of such composite grains, given the optical properties
of each constituent, using an approximate model of the composite grain. We
assume it consists of many concentric spherical layers of the various
materials, each with a specified volume fraction. In such a case the usual Mie
theory can be generalized and the extinction, scattering, and other cross
sections determined exactly.
We find that the ordering of the materials in the layering makes some
difference to the derived cross sections, but averaging over the various
permutations of the order of the materials provides rapid convergence as the
number of shells (each of which is filled by all of the materials
proportionately to their volume fractions) is increased. Three shells, each
with one layer of a particular constituent material, give a very satisfactory
estimate of the average cross section produced by larger numbers of shells.
We give the formulae for the Rayleigh limit (small size parameter) for
multi-layered spheres and use it to propose an ``Effective Medium Theory''
(EMT), in which an average optical constant is taken to represent the ensemble
of materials.
Multi-layered models are used to compare the accuracies of several EMTs
already in the literature.Comment: 29 pages, 6 figures, accepted for publication in the Astrophysical
Journal (part 1, scheduled in Vol. 526, #1, Nov. 20
Silicon nanoparticles and interstellar extinction
To examine a recently proposed hypothesis that silicon nanoparticles are the
source of extended red emission (ERE) in the interstellar medium, we performed
a detailed modeling of the mean Galactic extinction in the presence of silicon
nanoparticles. For this goal we used the appropriate optical constants of
nanosized Si, essentially different from those of bulk Si due to quantum
confinement. It was found that a dust mixture of silicon nanoparticles, bare
graphite grains, silicate core-organic refractory mantle grains and three-layer
silicate-water ice-organic refractory grains works well in explaining the
extinction and, in addition, results in the acceptable fractions of UV/visible
photons absorbed by silicon nanoparticles: 0.071-0.081. Since these fractions
barely agree with the fraction of UV/visible photons needed to excite the
observed ERE, we conclude that the intrinsic photon conversion efficiency of
the photoluminescence by silicon nanoparticles must be near 100%, if they are
the source of the ERE.Comment: Latex2e, uses emulateapj.sty (included), multicol.sty, epsf.sty, 6
pages, 3 figures (8 Postscript files), accepted for publication in ApJ
Letters, complete Postscript file is also available at
http://physics.technion.ac.il/~zubko/eb.html#SNP
Recent Results of Solid-State Spectroscopy
Solid state spectroscopy continues to be an important source of information
on the mineralogical composition and physical properties of dust grains both in
space and on planetary surfaces. With only a few exceptions, artificially
produced or natural terrestrial analog materials, rather than 'real' cosmic
dust grains, are the subject of solid state astrophysics. The Jena laboratory
has provided a large number of data sets characterizing the UV, optical and
infrared properties of such cosmic dust analogs. The present paper highlights
recent developments and results achieved in this context, focussing on
'non-standard conditions' such as very low temperatures, very high temperatures
and very long wavelengths.Comment: 15 pages, 10 figures. Contribution to an IAU Conference "The
Molecular Universe" held in Toledo in June 201
The 10 micron amorphous silicate feature of fractal aggregates and compact particles with complex shapes
We model the 10 micron absorption spectra of nonspherical particles composed
of amorphous silicate. We consider two classes of particles, compact ones and
fractal aggregates composed of homogeneous spheres. For the compact particles
we consider Gaussian random spheres with various degrees of non-sphericity. For
the fractal aggregates we compute the absorption spectra for various fractal
dimensions. The 10 micron spectra are computed for ensembles of these particles
in random orientation using the well-known Discrete Dipole Approximation. We
compare our results to spectra obtained when using volume equivalent
homogeneous spheres and to those computed using a porous sphere approximation.
We conclude that, in general, nonspherical particles show a spectral signature
that is similar to that of homogeneous spheres with a smaller material volume.
This effect is overestimated when approximating the particles by porous spheres
with the same volume filling fraction. For aggregates with fractal dimensions
typically predicted for cosmic dust, we show that the spectral signature
characteristic of very small homogeneous spheres (with a volume equivalent
radius r_V<0.5 micron) can be detected even in very large particles. We
conclude that particle sizes are underestimated when using homogeneous spheres
to model the emission spectra of astronomical sources. In contrast, the
particle sizes are severely overestimated when using equivalent porous spheres
to fit observations of 10 micron silicate emission.Comment: Accepted for publication in A&
Infrared extinction by homogeneous particle aggregates of SiC, FeO and SiO2: comparison of different theoretical approaches
Particle shape and aggregation have a strong influence on the spectral
profiles of infrared phonon bands of solid dust grains. Calculating these
effects is difficult due to the often extreme refractive index values in these
bands. In this paper, we use the Discrete Dipole Approximation (DDA) and the
T-matrix method to compute the absorption band profiles for simple clusters of
touching spherical grains. We invest reasonable amounts of computation time in
order to reach high dipole grid resolutions and take high multi-polar orders
into account, respectively. The infrared phonon bands of three different
refractory materials of astrophysical relevance are considered - Silicon
Carbide (SiC), Wustite (FeO) and Silicon Dioxide (SiO2). We demonstrate that
even though these materials display a range of material properties and
therefore different strengths of the surface resonances, a complete convergence
is obtained with none of the approaches. For the DDA, we find a strong
dependence of the calculated band profiles on the exact dipole distribution
within the aggregates, especially in the vicinity of the contact points between
their spherical constituents. By applying a recently developed method to
separate the material optical constants from the geometrical parameters in the
DDA approach, we are able to demonstrate that the most critical material
properties are those where the real part of the refractive index is much
smaller than unity.Comment: Accepted for publication in the Journal of Quantitative Spectroscopy
& Radiative Transfer (JQSRT
New Interstellar Dust Models Consistent with Extinction, Emission, and Abundance Constraints
We present new interstellar dust models which have been derived by
simultaneously fitting the far-ultraviolet to near-infrared extinction, the
diffuse infrared (IR) emission and, unlike previous models, the elemental
abundance constraints on the dust for different interstellar medium abundances,
including solar, F and G star, and B star abundances. The fitting problem is a
typical ill-posed inversion problem, in which the grain size distribution is
the unknown, which we solve by using the method of regularization. The dust
model contains various components: PAHs, bare silicate, graphite, and amorphous
carbon particles, as well as composite particles containing silicate, organic
refractory material, water ice, and voids. The optical properties of these
components were calculated using physical optical constants. As a special case,
we reproduce the Li & Draine (2001) results, however their model requires an
excessive amount of silicon, magnesium, and iron to be locked up in dust: about
50 ppm (atoms per million of H atoms), significantly more than the upper limit
imposed by solar abundances of these elements, about 34, 35, and 28 ppm,
respectively. A major conclusion of this paper is that there is no unique
interstellar dust model that simultaneously fits the observed extinction,
diffuse IR emission, and abundances constraints.Comment: 70 pages, 23 figures, accepted for publication in the Astrophysical
Journal Supplemen
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