7,228 research outputs found
What is the number of spiral galaxies in compact groups
The distribution of morphological types of galaxies in compact groups is studied on plates from the 6 m telescope. In compact groups there are 57 percent galaxies of late morphological types (S + Irr), 23 percent lenticulars (SO) and 20 percent elliptical galaxies. The morphological content of compact groups is very nearly the same as in loose groups. There is no dependence of galaxy morphology on density in all compact groups (and possibly in loose groups). Genuine compact groups form only 60 percent of Hickson's list
Charge-exchange resonances and restoration of the Wigner SU(4)-symmetry in heavy and superheavy nuclei
Energies of the giant Gamow-Teller and analog resonances - and
, are presented, calculated using the microscopic theory of finite
Fermi system. The calculated differences go to zero in heavier nuclei indicating the restoration of Wigner
SU(4)-symmetry. The calculated values are in good
agreement with the experimental data. The average deviation is 0.30 MeV for the
33 considered nuclei for which experimental data is available. The values were calculated for heavy and superheavy nuclei up to the
mass number = 290. Using the experimental data for the analog resonances
energies, the isotopic dependence of the difference of the Coulomb energies of
neighboring nuclei isobars analyzed within the SU(4)-approach for more than 400
nuclei in the mass number range of = 3 - 244. The Wigner SU(4)-symmetry
restoration for heavy and superheavy nuclei is confirmed. It is shown that the
restoration of SU(4)-symmetry does not contradict the possibility of the
existence of the "island of stability" in the region of superheavy nuclei.Comment: 5 pages, 2 figure
DFT Study of Nitroxide Radicals. 1. Effects of solvent on structural and electronic characteristics of 4-amino-2,2,5,5-tetramethyl-3-imidazoline-N-oxyl
Imidazoline-based nitroxide radicals are often used as spin probes for medium
acidity and polarity in different systems. In this work, using the density
functional theory (DFT) approach, we have studied how physico-chemical
characteristics (geometry, atomic charges and electron spin density
distribution) of pH-sensitive spin label
4-amino-2,2,5,5-tetramethyl-3-imidazoline-N-oxyl (ATI) depend on protonation
and aqueous surroundings. Our calculations demonstrate that ATI protonation
should occur at the nitrogen atom of the imidazoline ring rather than at the
amino group. Protonation of ATI leads to a decrease in a spin density on the
nitrogen atom of the nitroxide fragment >N-O. For simulation of ATI hydration
effects, we have constructed a water shell around a spin label molecule by
means of gradual (step-by-step) surrounding of ATI with water molecules (n =
2-41). Calculated spin density on the nitrogen atom of the nitroxide fragment
increased with an extension of a water shell around ATI. Both protonation and
hydration of ATI caused certain changes in calculated geometric parameters
(bond lengths and valence angles). Investigating how structural and energy
parameters of a system ATI-(H2O)n depend on a number of surrounding water
molecules, we came to the conclusion that a hydrogen-bonded cluster of n
≥ 41 water molecules could be considered as an appropriate model for
simulation of ATI hydration effects.Comment: 30 pages, 11 figures, 6 table
Parabolic equations with the second order Cauchy conditions on the boundary
The paper studies some ill-posed boundary value problems on semi-plane for
parabolic equations with homogenuous Cauchy condition at initial time and with
the second order Cauchy condition on the boundary of the semi-plane. A class of
inputs that allows some regularity is suggested and described explicitly in
frequency domain. This class is everywhere dense in the space of square
integrable functions.Comment: 7 page
On the Mapping of Time-Dependent Densities onto Potentials in Quantum Mechanics
The mapping of time-dependent densities on potentials in quantum mechanics is
critically examined. The issue is of significance ever since Runge and Gross
(Phys. Rev. Lett. 52, 997 (1984)) established the uniqueness of the mapping,
forming a theoretical basis for time-dependent density functional theory. We
argue that besides existence (so called v-representability) and uniqueness
there is an important question of stability and chaos. Studying a 2-level
system we find innocent, almost constant densities that cannot be constructed
from any potential (non-existence). We further show via a Lyapunov analysis
that the mapping of densities on potentials has chaotic regions in this case.
In real space the situation is more subtle. V-representability is formally
assured but the mapping is often chaotic making the actual construction of the
potential almost impossible. The chaotic nature of the mapping, studied for the
first time here, has serious consequences regarding the possibility of using
TDDFT in real-time settings
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