1,109 research outputs found
A Search for Small-Scale Clumpiness in Dense Cores of Molecular Clouds
We have analyzed HCN(1-0) and CS(2-1) line profiles obtained with high
signal-to-noise ratios toward distinct positions in three selected objects in
order to search for small-scale structure in molecular cloud cores associated
with regions of high-mass star formation. In some cases, ripples were detected
in the line profiles, which could be due to the presence of a large number of
unresolved small clumps in the telescope beam. The number of clumps for regions
with linear scales of ~0.2-0.5 pc is determined using an analytical model and
detailed calculations for a clumpy cloud model; this number varies in the
range: ~2 10^4-3 10^5, depending on the source. The clump densities range from
~3 10^5-10^6 cm^{-3}, and the sizes and volume filling factors of the clumps
are ~(1-3) 10^{-3} pc and ~0.03-0.12. The clumps are surrounded by inter-clump
gas with densities not lower than ~(2-7) 10^4 cm^{-3}. The internal thermal
energy of the gas in the model clumps is much higher than their gravitational
energy. Their mean lifetimes can depend on the inter-clump collisional rates,
and vary in the range ~10^4-10^5 yr. These structures are probably connected
with density fluctuations due to turbulence in high-mass star-forming regions.Comment: 23 pages including 4 figures and 4 table
Security Challenges and Development of Seaports: Educational Context
The paper deals with implementation of the function of ensuring economic security by seaports. In the absence of a generally accepted statistical basis for the analysis of seaports, the experience of countries is used as arguments. The logic of the research involved the construction and analysis of a competitive map of the world port market. World trends show a reduction in place states play in decision-making related to the development of ports and the expansion of composition and role of other stakeholders. The main challenges to the development of seaports are identified: focus and consistency of countries’ activities; implementation of international infrastructure projects; dependence on trade flows, development of logistics chains; willingness of countries to make long-term investments; improvement of the quality of port ties with the system of professional and higher education, scientific and analytical organizations
The biology of Simulium erythrocephalum and S. chelevini (Diptera, Simuliidae): Morpho-logical, ecological and molecular data
The subgenus Boophthora is a typical Palearctic taxon, which includes only 6 species, among them. Simulium erythrocephalum has a transpalearctic distribution. In Europe, Adler notes only the species S. erythrocephalum, and Yankovsky – two species S. (Boophthora) erythrocephalum and S. (Boophthora) chelevini. According to morphological characteristics, these species differ in their life stages. We have studied the development of S. erythrocephalum and S. chelevini from three rivers of Volyn region, Ukraine (Styr, Chornoguzka, Putylivka) from 2017 to 2019. We used the EPPO PM7 / 129 standard. Collected samples, 615-bp fragments of the COI gene were sequenced from five individuals of S. erythrocephalum and five individuals of S. chelevini and compared with four samples of S. erythrocephalum from the GenBank. We obtained the nucleotide sequence of S. chelevini. All of the S. erythrocephalum samples from Ukraine had 692 bases, the S. erythrocephalum samples from Armenia had 673 bases. S. erythrocephalum and S. chelevini did not have any intraspecific variations. These intraspecific variations were not larger than the interspecific variations. It has been proved that the populations of S. erythrocephalum and S. chelevini from medium and small rivers of Volyn do not differ in biological, behavioural and genetic characteristics. Comparison of S. erythrocephalum and S. chelevini life stages showed clear differences in 20 morphological features, which are probably manifestations of phenotypic variability. Comparison of species with data from the GenBank from Spain and Armenia on the mitochondrial cytochrome c oxidase subunit I (COI) gene confirmed the opinion that S. erythrocephalum and S. chelevini are one species. On the phylogenetic tree, the data are not grouped, there is no clear separation of the clades. Bootstrap values are 95–100%, which may indicate a significant similarity of all studied samples and the lack of isolation of individual morphotypes from Volyn, Spain and Armenia. To finally confirm the taxonomic position of these two species, additional research is needed covering more individuals from different parts of Europe and analysis of more genes
Molecular abundance ratios as a tracer of accelerated collapse in regions of high mass star formation?
Recent observations suggest that the behaviour of tracer species such as
N_2H+ and CS is significantly different in regions of high and low mass star
formation. In the latter, N_2H+ is a good tracer of mass, while CS is not.
Observations show the reverse to be true in high-mass star formation regions.
We use a computational chemical model to show that the abundances of these and
other species may be significantly altered by a period of accelerated collapse
in high mass star forming regions. We suggest these results provide a potential
explanation of the observations, and make predictions for the behaviour of
other species.Comment: 5 pages, 3 figures To be published in the Astrophysical Journa
Review of scientific topics for Millimetron space observatory
This paper describes outstanding issues in astrophysics and cosmology that
can be solved by astronomical observations in a broad spectral range from far
infrared to millimeter wavelengths. The discussed problems related to the
formation of stars and planets, galaxies and the interstellar medium, studies
of black holes and the development of the cosmological model can be addressed
by the planned space observatory Millimetron (the "Spectr-M" project) equipped
with a cooled 10-m mirror. Millimetron can operate both as a single-dish
telescope and as a part of a space-ground interferometer with very long
baseline.Comment: The translation of the original article in Physics Uspekhi
http://ufn.ru/ru/articles/2014/12/c
Two 2MASS-Selected Young Stellar Clusters: Photometry, Spectroscopy, and the IMF
We present near-infrared J, H, and K_s images and K-band spectroscopy of two
newly discovered stellar clusters at different stages of evolution. Our spectra
suggest the presence of massive YSOs in the heavily embedded cluster in the
star-forming region near radio source G353.4-0.4 and an O5-O6V star in the
cluster near radio source G305+00.2. We determine a K-band luminosity function
(KLF) for both clusters and an initial mass function (IMF) for the cluster near
G305+00.2. The derived IMF slope is -1.5 if the KLF is used to derive the IMF
and is -0.98 if the color-magnitude diagram and spectra are used. The more
reliable CMD-based slope is flatter than the Salpeter value usually found for
stellar clusters. We find that using the KLF alone to derive an IMF is likely
to produce an overly steep slope in stellar clusters subject to variable
extinction.Comment: 16 pages, 18 figures, accepted to A
Mopra line survey mapping of NGC6334I and I(N) at 3mm
A 5'x5' region encompassing NGC6334I and I(N) has been mapped at a wavelength
of 3mm (from 83.5 to 115.5GHz) with the Mopra telescope at an angular
resolution between 33 arcsec and 36 arcsec. This investigation has made use of
the recently installed 3mm MMIC receiver and the Mopra Spectrometer (MOPS) with
broadband capabilities permitting total coverage of the entire frequency range
with just five different observations. In total, the spatial distribution of
nineteen different molecules, ions and radicals, along with additional selected
isotopologues have been studied. Whilst most species trace the sites of star
formation, CH_3CN appears to be most closely associated with NGC6334I and I(N).
Both CN and C_2H appear to be widespread, tracing gas that is not associated
with active star formation. Both N_2H^+ and HC_3N closely resemble dust
continuum emission, showing they are reliable tracers of dense material, as
well as the youngest stages of high mass star formation. Hot (E_u/k>100K)
thermal CH_3OH emission is preferentially found towards NGC6334I, contrasting
with I(N), where only cold (E_u/k<22K) thermal CH_3OH emission is found.Comment: Accepted by MNRA
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