6,490 research outputs found
Are polar rings indeed polar?
We have considered polar ring galaxy candidates, the images of which can be
found in the SDSS. The sample of 78 galaxies includes the most reliable
candidates from the SPRC and PRC catalogs, some of which already have kinematic
confirmations. We analyze the distributions of studied objects by the angle
between the polar ring and the central disk, and by the optical diameter of the
outer ring structures. In the vast majority of cases, the outer structures lie
in the plane close to polar (within 10-20 deg) which indicates the stability of
the corresponding orbits in the gravitational potential of the halo. Moderately
inclined outer structures are observed only in about 6% of objects which
probably indicates their short lifetime. In such an unstable configuration, the
polar ring would often cross the disk of the galaxy, being smaller than it in
the diameter. We show that the inner polar structures and outer large-scale
polar rings form a single family in the distribution of diameters normalized to
the optical size of the galaxy. At the same time, this distribution is bimodal,
as the number of objects with d_ring= (0.4-0.7)*d_disk is negligible. Such a
shape of size distribution is most likely due to the fact that the stability of
polar orbits in the inner regions of galaxies is maintained by the bulge or the
bar, while in the outer regions it is provided by the spheroidal (or triaxial)
halo.Comment: Corrected version accepted in Astrophysical Bulletin, 8 pages, 5 EPS
figure
Evolution of adaptation mechanisms: adaptation energy, stress, and oscillating death
In 1938, H. Selye proposed the notion of adaptation energy and published
"Experimental evidence supporting the conception of adaptation energy".
Adaptation of an animal to different factors appears as the spending of one
resource. Adaptation energy is a hypothetical extensive quantity spent for
adaptation. This term causes much debate when one takes it literally, as a
physical quantity, i.e. a sort of energy. The controversial points of view
impede the systematic use of the notion of adaptation energy despite
experimental evidence. Nevertheless, the response to many harmful factors often
has general non-specific form and we suggest that the mechanisms of
physiological adaptation admit a very general and nonspecific description.
We aim to demonstrate that Selye's adaptation energy is the cornerstone of
the top-down approach to modelling of non-specific adaptation processes. We
analyse Selye's axioms of adaptation energy together with Goldstone's
modifications and propose a series of models for interpretation of these
axioms. {\em Adaptation energy is considered as an internal coordinate on the
`dominant path' in the model of adaptation}. The phenomena of `oscillating
death' and `oscillating remission' are predicted on the base of the dynamical
models of adaptation. Natural selection plays a key role in the evolution of
mechanisms of physiological adaptation. We use the fitness optimization
approach to study of the distribution of resources for neutralization of
harmful factors, during adaptation to a multifactor environment, and analyse
the optimal strategies for different systems of factors
Relation between parameters of dust and parameters of molecular and atomic gas in extragalactic star-forming regions
The relationships between atomic and molecular hydrogen and dust of various
sizes in extragalactic star-forming regions are considered, based on
observational data from the Spitzer and Herschel infrared space telescopes, the
Very Large Array (atomic hydrogen emission) and IRAM (CO emission). The source
sample consists of approximately 300 star-forming regions in 11 nearby
galaxies. Aperture photometry has been applied to measure the fluxes in eight
infrared bands (3.6, 4.5, 5.8, 8, 24, 70, 100, and 160m), the atomic
hydrogen (21cm) line and CO (2--1) lines.
The parameters of the dust in the starforming regions were determined via
synthetic-spectra fitting, such as the total dust mass, the fraction of
polycyclic aromatic hydrocarbons (PAHs), etc. Comparison of the observed fluxes
with the measured parameters shows that the relationships between atomic
hydrogen, molecular hydrogen, and dust are different in low- and
high-metallicity regions. Low-metallicity regions contain more atomic gas, but
less molecular gas and dust, including PAHs. The mass of dust constitutes about
of the mass of molecular gas in all regions considered. Fluxes produced
by atomic and molecular gas do not correlate with the parameters of the stellar
radiation, whereas the dust fluxes grow with increasing mean intensity of
stellar radiation and the fraction of enhanced stellar radiation. The ratio of
the fluxes at 8 and 24m, which characterizes the PAH content, decreases
with increasing intensity of the stellar radiation, possibly indicating
evolutionary variations of the PAH content. The results confirm that the
contribution of the 24m emission to the total IR luminosity of
extragalactic star-forming regions does not depend on the metallicity.Comment: Published in Astronomy Reports, 2017, vol. 61, issue
The effect of the relative nuclear size on the nucleus-nucleus interactions
The experimental data on the interactions of light nuclei (d, He(4), C(12)) at the momentum 4.2 GeV/cA with the carbon nuclei were taken in the 2-m propane bubble chamber. The distributions in the number of interacting nucleons, the spectra of protons, the mean energies of secondary pions and protons, the mean fractions of energy transferred to the pion and nucleon components are presented. The results of the investigation of the mechanism of nucleus-nucleus interactions can be used to calculate the nuclear cascades in the atmosphere
On the T-Odd Quark Fragmentation Function and on Transversal Handedness
The first probe of the correlation of the T-odd one-particle fragmentation
function responsible for the left--right asymmetry of fragmentation of a
transversely polarized quark is done by using the 1991-95 DELPHI data for -jet decay. Integrated over the fraction of longitudinal and transversal
momenta, this correlation is of 1.5% order, which means order of 13% for the
analyzing power.
A rather large () handedness transversal to the production plane
was observed in the diffractive production of () triples from
nuclei by the --beam. It was shown that the phenomenon has a
clear dynamic origin and resembles the single spin asymmetry behavior. All this
makes us hope to use this effects in polarized DIS experiments for transversity
measurement.Comment: 10 pp, 5 epsfig, Latex 2e, szjp.cls, epsfig.sty, wrapfig.sty
included. Talk in "Spin and Symmetry - Praha98". To be published in
Czechoslovak Journal of Physics, Supp
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