303 research outputs found
Dust emission in star-forming dwarf galaxies: General properties and the nature of the sub-mm excess
We studied the global characteristics of dust emission in a large sample of
emission-line star-forming galaxies. The sample consists of two subsamples. One
subsample (SDSS sample) includes ~4000 compact star-forming galaxies from the
SDSS, which were also detected in all four bands at 3.4, 4.6, 12, and 22 mum of
the WISE all-sky survey. The second subsample (Herschel sample) is a sample of
28 compact star-forming galaxies observed with Herschel in the FIR range. Data
of the Herschel sample were supplemented by the photometric data from the
Spitzer observations, GALEX, SDSS, WISE, 2MASS, NVSS, and FIRST surveys, as
well as optical and Spitzer spectra and data in sub-mm and radio ranges. It is
found that warm dust luminosities of galaxies from the SDSS sample and cold and
warm dust luminosities of galaxies from the Herschel sample are strongly
correlated with Hbeta luminosities, which implies that one of the main sources
of dust heating in star-forming galaxies is ionising UV radiation of young
stars. Using the relation between warm and cold dust masses for estimating the
total dust mass in star-forming galaxies with an accuracy better than ~0.5 dex
is proposed. On the other hand, it is shown for both samples that dust
temperatures do not depend on the metallicities. The dust-to-neutral gas mass
ratio strongly declines with decreasing metallicity, similar to that found in
other studies of local emission-line galaxies, high-redshift GRB hosts, and
DLAs. On the other hand, the dust-to-ionised gas mass ratio is about one
hundred times as high implying that most of dust is located in the neutral gas.
It is found that thermal free-free emission of ionised gas in compact
star-forming galaxies might be responsible for the sub-mm emission excess. This
effect is stronger in galaxies with lower metallicities and is also positively
affected by an increased star-formation rate.Comment: 22 pages, 15 figures, accepted for publication in Astronomy and
Astrophysic
Kharkiv region of Ukraine in the aspect of a polycentric development model
This article is devoted to the analysis of a model of regional
development of Kharkiv region of Ukraine, which is monocentric, and the rationale for
the formation of polycentrism in the region. The city of Kharkiv and urban areas as
centers of growth in the region are considered in the articl
Numerical simulation of a turbulent wake subjected to adverse pressure gradient
Results are presented of high-fidelity scale-resolving simulations of the wake flow exposed to adverse pressure gradient (APG). Specifically, zonal RANS-IDDES computations are performed of the flow model designed and manufactured at the Technische Universität Braunschweig in the framework of a joint German-Russian project "Wake in Adverse Pressure gradient". The model includes a flat plate as the wake generator and two pairs of thin liner foils creating APG. Results of the computations of mean flow characteristics agree with currently available experimental data and differ from those of the RANS predictions. This suggests the necessity of RANS models improvement which is planned to be done with the use of the combined experimental/numerical database on the mean flow and turbulence statistics of the wake accumulated in the course of the project
The Effect of pre-incubation duration of soil-biochar model mixtures on the results of determination the intensity of substrate-induced respiration (Methodological aspects of study)
Was studied in laboratory experiments the effect of short term (3 days) and long term (95 and 187 days) pre-incubation of soil-biochar model mixes (ratio 20:1) in optimal conditions for the microorganisms on the results of definition the intensity of substrate induced respiration. For experiments 10 biochar samples were used. The biochars were produced from the woody and herbaceous materials under different pyrolysis conditions. Is revealed the heterogeneous influence of biochar by direction and dynamics on the rate of substrate induced respiration depending on the pre-incubation time of model mixtures. It is shown that the prolonged pre-incubation of biochar with soil material under optimal levels of moisture and temperature is a prerequisite for the correct formulation of laboratory experiments and provides a reliable assessment of the impact of biochar on a soil respiration. We can recommend the duration of pre-incubation 3-5 months
On a possibility of inelasticity partial coefficient K sub gamma determination in pi C and pi Pb interactions at 10 to the 14th power eV (experiment PAMIR 1)
The investigation of hadron-nuclear interactions in Pamir experiment is carried out by means of X-ray emulsion chambers of two types: carbon (C) and lead (Pb). While comparing the results from the chambers of both types it was found a discrepancy in n sub h and E sub h(1)R values. The observed discrepancy in C and Pb chambers is connected with the difference in values of effective coefficients of energy transfer to the soft component K sub eff for C and Pb chambers
"Counterpart" method for abundance determinations in HII regions
We suggest a new way of the determining abundances and electron temperatures
in HII regions from strong emission lines. Our approach is based on the
standard assumption that HII regions with similar intensities of strong
emission lines have similar physical properties and abundances. A "counterpart"
for a studied HII region may be chosen among HII regions with well-measured
abundances (reference HII regions) by comparison of carefully chosen
combinations of strong line intensities. Then the abundances in the
investigated HII region can be assumed to be the same as that in its
counterpart. In other words, we suggest to determine the abundances in HII
regions "by precedent". To get more reliable abundances for the considered HII
region, a number of reference HII regions is selected and then the abundances
in the target HII region is estimated through extra-/interpolation. We will
refer to this method of abundance determination as the counterpart method or,
for brevity, the C method. We define a sample of reference HII regions and
verify the validity of the C method. We find that this method produces reliable
abundances. Finally, the C method is used to obtain the radial abundance
distributions in the extended discs of the spiral galaxies M83, NGC4625 and NGC
628.Comment: 21 pages, 11 figures, accepted for publication in the MNRA
An imaging and spectroscopic study of the very metal-deficient blue compact dwarf galaxy Tol 1214--277
We present a spectrophotometric study based on VLT/FORS I observations of one
of the most metal-deficient blue compact dwarf (BCD) galaxies known, Tol
1214-277 (Z ~ Zsun/25). The data show that roughly half of the total luminosity
of the BCD originates from a bright and compact starburst region located at the
northeastern tip of a faint dwarf galaxy with cometary appearance. The
starburst has ignited less than 4 Myr ago and its emission is powered by
several thousands O7V stars and ~ 170 late-type nitrogen Wolf-Rayet stars
located within a compact region with < 500 pc in diameter. For the first time
in a BCD, a relatively strong [Fe V] 4227 emission line is seen which together
with intense He II 4686 emission indicates the presence of a very hard
radiation field in Tol 1214-277. We argue that this extraordinarily hard
radiation originates from both Wolf--Rayet stars and radiative shocks in the
starburst region. The structural properties of the low-surface-brightness (LSB)
component underlying the starburst have been investigated by means of surface
photometry down to 28 B mag/sq.arcsec. We find that, for a surface brightness
level fainter than ~ 24.5 B mag/sq.arcsec, an exponential fitting law provides
an adequate approximation to its radial intensity distribution. The broad-band
colors in the outskirts of the LSB component of Tol 1214-277 are nearly
constant and are consistent with an age below one Gyr. This conclusion is
supported by the comparison of the observed spectral energy distribution (SED)
of the LSB host with theoretical SEDs.Comment: 17 pages, 11 Postscript figures, uses emulateapj.sty, to appear in
Astronomical Journa
Synaptic Remodeling Depends on Signaling between Serotonin Receptors and the Extracellular Matrix
Rewiring of synaptic circuitry pertinent to memory formation has been associated with morphological changes in dendritic spines and with extracellular matrix (ECM) remodeling. Here, we mechanistically link these processes by uncovering a signaling pathway involving the serotonin 5-HT7 receptor (5-HT7R), matrix metalloproteinase 9 (MMP-9), the hyaluronan receptor CD44, and the small GTPase Cdc42. We highlight a physical interaction between 5-HT7R and CD44 (identified as an MMP-9 substrate in neurons) and find that 5-HT7R stimulation increases local MMP-9 activity, triggering dendritic spine remodeling, synaptic pruning, and impairment of long-term potentiation (LTP). The underlying molecular machinery involves 5-HT7R-mediated activation of MMP-9, which leads to CD44 cleavage followed by Cdc42 activation. One important physiological consequence of this interaction includes an increase in neuronal outgrowth and elongation of dendritic spines, which might have a positive effect on complex neuronal processes (e.g., reversal learning and neuronal regeneration)
Helium abundance in the most metal-deficient blue compact galaxies: I Zw 18 and SBS 0335-052
We present high-quality spectroscopic observations of the two most-metal
deficient blue compact galaxies known, I Zw 18 and SBS 0335-052 to determine
the helium abundance. The underlying stellar absorption strongly influences the
observed intensities of He I emission lines in the brightest NW component of I
Zw 18, and hence this component should not be used for primordial He abundance
determination. The effect of underlying stellar absorption, though present, is
much smaller in the SE component. Assuming all systematic uncertainties are
negligible, the He mass fraction derived in this component is Y =
0.243+/-0.007. The high signal-to-noise ratio spectrum (> 100 in the continuum)
of SBS 0335-052 allows us to measure the helium mass fraction with a precision
better than 2% -- 5% in nine different regions along the slit. Assuming all
systematic uncertainties are negligible, the weighted mean He mass fraction in
SBS 0335-052 is Y = 0.2437+/-0.0014 when the three He I 4471, 5876 and 6678
emission lines are used, and is 0.2463+/-0.0015 when the He I 4471 emission
line is excluded. The weighted mean helium mass fraction in the two most
metal-deficient BCGs I Zw 18 and SBS 0335-052, Y=0.2462+/-0.0015, after
correction for the stellar He production results in a primordial He mass
fraction Yp = 0.2452+/-0.0015. The derived Yp leads to a baryon-to-photon ratio
of (4.7+/-1.0) 10^{-10}, consistent with the values derived from the primordial
D and 7Li abundances, and supporting the standard big bang nucleosynthesis
theory. For the most consistent set of primordial D, 4He, and 7Li abundances we
derive an equivalent number of light neutrino species 3.0+/-0.3 (95% C.L.).Comment: 28 pages, 10 figures. To appear in Ap
Analysis of the Foundation of National Standards for the Use of Information Technologies
В данной статье представлена информация о действующих национальных стандартах на информационные технологии. Рассмотрена структура фонда стандартов на информационные технологии по временным интервалам их принятия и классификация по тематике действующих стандартов.This article provides information about the current national standards for information technology. The structure of the fund of information technology standards by time intervals of their adoption and classification by the subject of existing standards are considered
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