117 research outputs found
Turbulent convection: comparing the moment equations to numerical simulations
The non-local hydrodynamic moment equations for compressible convection are
compared to numerical simulations. Convective and radiative flux typically
deviate less than 20% from the 3D simulations, while mean thermodynamic
quantities are accurate to at least 2% for the cases we have investigated. The
moment equations are solved in minutes rather than days on standard
workstations. We conclude that this convection model has the potential to
considerably improve the modelling of convection zones in stellar envelopes and
cores, in particular of A and F stars.Comment: 10 pages (6 pages of text including figure captions + 4 figures),
Latex 2e with AAS Latex 5.0 macros, accepted for publication in ApJ
Stokes Diagnostis of 2D MHD-simulated Solar Magnetogranulation
We study the properties of solar magnetic fields on scales less than the
spatial resolution of solar telescopes. A synthetic infrared
spectropolarimetric diagnostics based on a 2D MHD simulation of
magnetoconvection is used for this. We analyze two time sequences of snapshots
that likely represent two regions of the network fields with their immediate
surrounding on the solar surface with the unsigned magnetic flux density of 300
and 140 G. In the first region we find from probability density functions of
the magnetic field strength that the most probable field strength at logtau_5=0
is equal to 250 G. Weak fields (B < 500 G) occupy about 70% of the surface,
while stronger fields (B 1000 G) occupy only 9.7% of the surface. The magnetic
flux is -28 G and its imbalance is -0.04. In the second region, these
parameters are correspondingly equal to 150 G, 93.3 %, 0.3 %, -40 G, and -0.10.
We estimate the distribution of line-of-sight velocities on the surface of log
tau_5=-1. The mean velocity is equal to 0.4 km/s in the first simulated region.
The averaged velocity in the granules is -1.2 km/s and in the intergranules is
2.5 km/s. In the second region, the corresponding values of the mean velocities
are equal to 0, -1.8, 1.5 km/s. In addition we analyze the asymmetry of
synthetic Stokes-V profiles of the Fe I 1564.8 nm line. The mean values of the
amplitude and area asymmetry do not exceed 1%. The spatially smoothed amplitude
asymmetry is increased to 10% while the area asymmetry is only slightly varied.Comment: 24 pages, 12 figure
Formation of Li I lines in photospheric granulation
The possibility of significant systematic errors due to the use of 1D
homogeneous atmospheres in lithium-abundance determinations of cool stars
motivates a study of non-local-thermodynamic-equilibrium (NLTE) effects on Li I
line formation in a 3D solar-granulation simulation snapshot. The NLTE effect
on the equivalent width of the 671 nm resonance line is small in 1D models or
in integrated light from the granulation model. The line-strength variations
over the granulation pattern are however markedly different in NLTE compared to
LTE -- observations of this may provide diagnostics to NLTE effects. The
effects of horizontal photon exchange found in the granulation model are
moderate and due entirely to bound-bound processes, ultraviolet overionization
is unimportant.Comment: 9 pages Latex (AASTeX using aaspp4.sty) with 3 figures (PS). The
former EPS figures have been replaced with safer PS due to technical problems
encountered by some users. No change in content. Accepted for publication in
Astrophysical Journal Letter
Horizontal Magnetic Fields in the Solar Photosphere
The results of 2D MHD simulations of solar magnetogranulation are used to
analyze the horizontal magnetic fields and the response of the synthesized
Stokes profiles of the FeI 1564.85 nm line to the magnetic fields. Selected
1.5-h series of the 2D MHD models reproduces a region of the network fields
with their immediate surrounding on the solar surface with the unsigned
magnetic flux density of 192 G. According to the magnetic field distribution
obtained, the most probable absolute strength of the horizontal magnetic field
at an optical depth of tau_5 = 1 (tau_5 denotes tau at lambda = 500 nm) is 50
G, while the mean value is 244 G. On average, the horizontal magnetic fields
are stronger than the vertical fields to heights of about 400 km in the
photosphere due to their higher density and the larger area they occupy. The
maximum factor by which the horizontal fields are greater is 1.5. Strong
horizontal magnetic flux tubes emerge at the surface as spots with field
strengths of more than 500 G. These are smaller than granules in size, and have
lifetimes of 3.6 min. They form in the photosphere due to the expulsion of
magnetic fields by convective flows coming from deep subphotospheric layers.
The data obtained qualitatively agree with observations with the Hinode space
observatory.Comment: 15 pages, 7 figures, published by Astronomicheskii Zhurnal (in
Russian) and Astronomy Reports (in English
Genome-wide association study for frozen-thawed sperm motility in stallions across various horse breeds
Objective: The semen quality of stallions including sperm motility is an important target of selection as it has a high level of individual variability. However, effects of the molecular architecture of the genome on the mechanisms of sperm formation and their preservation after thawing have been poorly investigated. Here, we conducted a genome-wide association study (GWAS) for the sperm motility of cryopreserved semen in stallions of various breeds.
Methods: Semen samples were collected from the stallions of 23 horse breeds. The following semen characteristics were examined: progressive motility (PM), progressive motility after freezing (FPM), and the difference between PM and FPM. The respective DNA samples from these stallions were genotyped using Axiom™ Equine Genotyping Array.
Results: We performed a GWAS search for single nucleotide polymorphism (SNP) markers and potential genes related to motility properties of frozen-thawed semen in the stallions of various breeds. As a result of the GWAS analysis, two SNP markers, rs1141327473 and rs1149048772, were identified that were associated with preservation of the frozen-thawed stallion sperm motility, the relevant putative candidate genes being NME8, OR2AP1 and OR6C4. Potential implications of effects of these genes on sperm motility are herein discussed.
Conclusion: The GWAS results enabled us to localize novel SNPs and candidate genes for sperm motility in stallions. Implications of the study for horse breeding and genetics are a better understanding of genomic regions and candidate genes underlying stallion sperm quality, and improvement in horse reproduction and breeding techniques. The identified markers and genes for sperm cryotolerance and the respective genomic regions are promising candidates for further studying the biological processes in the formation and function of the stallion reproductive system
Spectroscopic Signatures of Convection in the Spectrum of Procyon. Fundamental Parameters and Iron Abundance
We have observed the spectrum of Procyon A (F5IV) from 4559 to 5780 A with a
S/N of ~ 1e3 and a resolving power of 2e5. We have measured the line bisectors
and relative line shifts of a large number of Fe I and Fe II lines, comparing
them to those found in the Sun. A three-dimensional(3D) hydrodynamical model
atmosphere has been computed and is tested against observations. The model
reproduces in detail most of the features observed, although we identify some
room for improvement. At all levels, the comparison of the 3D time-dependent
calculations with the observed spectral lines shows a much better agreement
than for classical homogeneous models, making it possible to refine previous
estimates of the iron abundance, the projected rotational velocity, the
limb-darkening, and the systemic velocity of the Procyon binary system.
The difference between the iron abundance determined with the 3D model and
its
1D counterpart is <~ 0.05 dex. We find consistency between the iron abundance
derived from Fe I and Fe II lines, suggesting that departures from LTE in the
formation of the studied lines are relatively small. The scatter in the iron
abundance determined from different lines still exceeds the expectations from
the uncertainties in the atomic data, pointing out that one or more components
in the modeling can be refined further.Comment: 30 pages, 19 figures; uses emulateapj.sty (included); to appear in
ApJ (Feb 2002
УСПЕШНОЕ ЛЕЧЕНИЕ БОЛЬНОЙ ПЛОСКОКЛЕТОЧНЫМ РАКОМ ПРЯМОЙ КИШКИ. КЛИНИЧЕСКОЕ НАБЛЮДЕНИЕ
Long-term results of conservative squamous-cell rectal cancer treatment (12 cm above anal verge) are presented in the article. Squamous-cell rectal cancer is a rare disease with only 73 cases described in the literature. Patient received a novel chemoradiotherapy scheme. Complete response was achieved and no surgery performed. Patient is disease-free and has good quality of life with 4 years followup.В статье представлены отдаленные результаты консервативного лечения больной, страдающей эктопической формой плоскоклеточного рака, локализовавшегося в верхнеампулярном отделе прямой кишки (на 12 см). Плоскоклеточный рак прямой кишки – редкое заболевание, описано всего 73 наблюдения, и только в англоязычной литературе. Пациентке проводилась разработанная в клинике схема химиолучевого лечения. Удалось достичь полной резорбции опухоли и избежать хирургического лечения. При 4-летнем периоде наблюдения нет данных за прогрессирование заболевания при хорошем качестве жизни пациентки
Experimental Detection of the CNO Cycle
Borexino recently reported the first experimental evidence for a CNO neutrino. Since this process accounts for only about 1% of the Sun’s total energy production, the associated neutrino flux is remarkably low compared to that of the pp chain, the dominant hydrogen-burning process. This experimental evidence for the existence of CNO neutrinos was obtained using a highly radio-pure Borexino liquid scintillator. Improvements in the thermal stabilization of the detector over the last five years have allowed us to exploit a method of constraining the rate of 210Bi background. Since the CNO cycle is dominant in massive stars, this result is the first experimental evidence of a major stellar hydrogen-to-helium conversion mechanism in the Universe
Solar and geoneutrinos
Thanks to the progress of neutrino physics, today we are able of exploiting neutrinos as a tool to study astrophysical objects. The latter in turn serve as unique sources of elusive neutrinos, which fundamental properties are still to be understood. This contribution attempts to summarize the latest results obtained by measuring neutrinos emitted from the Sun and geoneutrinos produced in radioactive decays inside the Earth, with a particular focus on a recent discovery of the CNO-cycle solar neutrinos by Borexino. Comprehensive measurement of the pp-chain solar neutrinos and the first directional detection of sub-MeV solar neutrinos by Borexino, the updated 8B solar neutrino results of Super-Kamiokande, as well as the latest Borexino and KamLAND geoneutrino measurements are also discussed
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