263 research outputs found
GRB Redshift Distribution is Consistent with GRB Origin in Evolved Galactic Nuclei
Recently we have elaborated a new cosmological model of gamma-ray burst (GRB)
origin (1998, ApJ 502, 192), which employs the dynamical evolution of central
dense stellar clusters in the galactic nuclei. Those clusters inevitably
contain a large fraction of compact stellar remnants (CSRs), such as neutron
stars (NSs) and stellar mass black holes (BHs), and close encounters between
them result in radiative captures into short-living binaries, with subsequent
merging of the components, thereby producing GRBs (typically at large distances
from the nucleus).
In the present paper, we calculate the redshift distribution of the rate of
GRBs produced by close encounters of NSs in distant galactic nuclei. To this
end, the following steps are undertaken: (i) we establish a connection between
the parameters of the fast evolving central stellar clusters (i.e. those for
which the time of dynamical evolution exceeds the age of the Universe) with
masses of the forming central supermassive black holes (SMBHs) using a
dynamical evolution model; (ii) we connect these masses with the inferred mass
distributions of SMBHs in the galactic nuclei and the redshift distribution of
quasars by assuming a certain `Eddington luminosity phase' in their activity;
(iii) we incorporate available observational data on the redshift distribution
of quasars as well as a recently found correlation between the masses of
galaxies and their central SMBHs. The resulting redshift distribution of the
GRB rate, which accounts for both fast and slowly evolving galactic nuclei is
consistent with that inferred from the BATSE data if the fraction of fast
evolving galactic nuclei is in the range .Comment: LaTeX, 4 pages (incl. 1 figure), to appear in "After the Dark Ages:
When Galaxies Were Young (the Universe at 2<z<5)", eds. S.S. Holt and E.P.
Smit
The Eddington Luminosity Phase in Quasars: Duration and Implications
Non-steady and eruptive phenomena in quasars are thought to be associated
with the Eddington or super-Eddington luminous stage. Although there is no lack
in hypotheses about the total duration of such a stage, the latter remains
essentially unknown. We calculate the duration of quasar luminous phase in
dependence upon the initial mass of a newborn massive black hole (MBH) by
comparing the observed luminosity- and redshift distributions of quasars with
mass distribution of the central MBHs in normal galactic nuclei. It is assumed
that, at the quasar stage, each MBH goes through a single (or recurrent)
phase(s) of accretion with, or close to, the Eddington luminosity. The mass
distributions of quasars is found to be connected with that of MBHs residing in
normal galaxies by a one-to-one corrrespondence through the entire mass range
of the inferred MBHs if the accretion efficiency of mass-to-energy
transformation .Comment: 4 pages, 2 figures, uses aipproc.sty. To appear in "Cosmic
Explosions" (Proc. of the 10th Annual October Conference in Maryland, Eds.
S.S. Holt and W.W. Zhang
Yield, plasticity, stability and homeostasis of spring barley cultivars in the Non-Black Earth Region
Background. The expansion of agrometeorological factors negatively affecting the productivity of spring barley has oriented plant breeders towards developing adaptable forms capable of realizing their genetic potential for higher yield under unfavorable conditions. Applying several methods of statistical data analysis helps to perform a more accurate assessment of the material differentiated according to its adaptability indicators. The objective of this study was to assess the adaptability of spring barley cultivars on the basis of their yield, plasticity, stability and homeostasis.Materials and methods. The resulting data were obtained for ten spring barley cultivars developed at Nemchinovka FRC.Results. High yield potential of more than 8.5 t/ha was disclosed in barley cultivars âYaromirâ, âNurâ, âNadezhnyâ, âSudarâ, âZlatoyarâ and âZnatnyâ. Cvs. âLuboyarâ, âNadezhnyâ and âRafaelâ showed the highest adaptability to the worst growing conditions (4.65â5.04 t/ha) as well as high adaptive and compensatory ability. Cvs. âSudarâ, âNurâ and âZlatoyarâ were identified for high environmental plasticity (Cvi = 24.1â25.9%; bi = 1.02â1.16; Ď = 1.52â1.59), while âLyuboyarâ, âZnatnyâ and âVladimirâ for their stability parameters (S2di = 0.05â0.19; Ď2CACi = 1.60â1.78; Ď2(GĂE)gi = 0.05â0.15). The highest values of homeostasis (BVGi = 3.45â 3.53; CSLi = 138.7â139.4; Homi = 9.02â9.85) were registered for cvs. âRafaelâ and âLyuboyarâ. The calculated rating of the tested cultivars identified âNadezhnyâ as the best in productivity, while âZlatoyarâ was the best in environmental plasticity. The highest levels of stability and homeostasis were recorded for cvs. âRafaelâ and âLyuboyarâ.Conclusion. Comprehensive assessment of productivity and adaptability indicators in the tested spring barley cultivars showed that âLyuboyarâ, âNadezhnyâ, âZlatoyarâ and âRafaelâ were the best under the conditions of the Non-Black Earth Region
Effect of grain refinement on deformation behavior of technical grade titanium under tension
The paper deals with the study on the impact of grain refinement by severe plastic deformation upon the microstructure, as well as deformation and fracture behavior under tensile loading of technical grade titanium. The microstructure of coarse- and ultra-fine grain technical grade titanium was investigated by optical, transmission electron microscopy and X-ray diffraction. In situ monitoring of deformation behavior was conducted by means of acoustic emission and digital image correlation. Scanning electron microscopy was employed for fracture surface observation. The results of the tensile tests have revealed significant growth in ultimate strength and decrease of ductility due to grain-boundary strengthening. The experimental data obtained allow one to get the appropriate understanding of the mechanisms responsible for variation of mechanical properties and fracture patterns as well as to attain quantitative estimation of strain localization induced by the grain refinement
Historical and Modern Classifications of the Plague Agent
The review presents the data on domestic and foreign phenotypic classifications of Yersinia pestis strains developed in the XX century; genetic classifications of the XXI century; as well as on the genealogy of ancient strains of the plague microbe, reconstructed using paleogenomic technologies. Since the discovery of the plague agent in 1894, many classifications were created that corresponded to the level of development of microbiology at that time. The intraspecific classification schemes of the XX century were based on three principles: phenotypic differences between strains, features of the species composition of carriers, and geographical affiliation. With the development of molecular microbiology early on in the XXI century, a genetic nomenclature of the branches of the pathogen evolution was developed and a number of classifications based on the analysis of the population structure of Y. pestis were created. Through the prism of the genetic diversity of Y. pestis strains from natural plague foci in Russia, near and far abroad countries, an improved classification with a division into seven subspecies has been developed: pestis, tibetica, caucasica, qinghaica, angolica, central asiatica, ulegeica, which allocates the subspecies according to the phylogenetic principle and epidemic significance. With the advancements in paleomicrobiology, prehistoric lineages of evolution have been included in the genealogy of Y. pestis, which expand the data on the intraspecific diversity of the plague microbe
Correlation effects during liquid infiltration into hydrophobic nanoporous mediums
Correlation effects arising during liquid infiltration into hydrophobic
porous medium are considered. On the basis of these effects a mechanism of
energy absorption at filling porous medium by nonwetting liquid is suggested.
In accordance with this mechanism, the absorption of mechanical energy is a
result expenditure of energy for the formation of menisci in the pores on the
shell of the infinite cluster and expenditure of energy for the formation of
liquid-porous medium interface in the pores belonging to the infinite cluster
of filled pores. It was found that in dependences on the porosity and,
consequently, in dependences on the number of filled pores neighbors, the
thermal effect of filling can be either positive or negative and the cycle of
infiltration-defiltration can be closed with full outflow of liquid. It can
occur under certain relation between percolation properties of porous medium
and the energy characteristics of the liquid-porous medium interface and the
liquid-gas interface. It is shown that a consecutive account of these
correlation effects and percolation properties of the pores space during
infiltration allow to describe all experimental data under discussion
Gamma Ray Bursts from the Evolved Galactic Nuclei
A new cosmological scenario for the origin of gamma ray bursts (GRBs) is
proposed. In our scenario, a highly evolved central core in the dense galactic
nucleus is formed containing a subsystem of compact stellar remnants (CSRs),
such as neutron stars and black holes. Those subsystems result from the
dynamical evolution of dense central stellar clusters in the galactic nuclei
through merging of stars, thereby forming (as has been realized by many
authors) the short-living massive stars and then CSRs. We estimate the rate of
random CSR collisions in the evolved galactic nuclei by taking into account,
similar to Quinlan & Shapiro (1987), the dissipative encounters of CSRs, mainly
due to radiative losses of gravitational waves, which results in the formation
of intermediate short-living binaries, with further coalescence of the
companions to produce GRBs. We also consider how the possible presence of a
central supermassive black hole, formed in a highly evolved galactic nucleus,
influences the CSR binary formation. This scenario does not postulate ad hoc a
required number of tight binary neutron stars in the galaxies. Instead, it
gives, for the most realistic parameters of the evolved nuclei, the expected
rate of GRBs consistent with the observed one, thereby explaining the GRB
appearance in a natural way of the dynamical evolution of galactic nuclei. In
addition, this scenario provides an opportunity for a cosmological GRB
recurrence, previously considered to be a distinctive feature of GRBs of a
local origin only. We also discuss some other observational tests of the
proposed scenario.Comment: 25 pages, LATEX, uses aasms4.sty, accepted by Ap
Gravitational Wave Bursts from Collisions of Primordial Black Holes in Clusters
The rate of gravitational wave bursts from the mergers of massive primordial
black holes in clusters is calculated. Such clusters of black holes can be
formed through phase transitions in the early Universe. The central black holes
in clusters can serve as the seeds of supermassive black holes in galactic
nuclei. The expected burst detection rate by the LISA gravitational wave
detector is estimated.Comment: 10 pages, 2 figure
- âŚ