387 research outputs found
Properties of voids in the Local Volume
Current explanation of the overabundance of dark matter subhalos in the Local
Group (LG) indicates that there maybe a limit on mass of a halo, which can host
a galaxy. This idea can be tested using voids in the distribution of galaxies:
at some level small voids should not contain any (even dwarf) galaxies. We use
observational samples complete to M_B=-12 with distances less than 8 Mpc to
construct the void function (VF): the distribution of sizes of voids empty of
any galaxies. There are ~ 30 voids with sizes ranging from 1 to 5 Mpc. We also
study the distribution of dark matter halos in very high resolution simulations
of the LCDM model. The theoretical VF matches the observations remarkably well
only if we use halos with circular velocities larger than 45 +/- 10 km/s. This
agrees with the Local Group predictions. Small voids look quite similar to heir
giant cousins: the density has a minimum at the center of a void and it
increases as we get closer to the border. Thus, both the Local Group data and
the nearby voids indicate that isolated halos below 45 +/- 10 km/s must not
host galaxies and that small (few Mpc) voids are truly dark.Comment: 5 pages 1 figure. To appear in proceedings of the conference
"Galaxies in the Local Volume", Sydney, 8 to 13 July 200
Formation of Globular Clusters in Hierarchical Cosmology: ART and Science
We test the hypothesis that globular clusters form in supergiant molecular
clouds within high-redshift galaxies. Numerical simulations demonstrate that
such large, dense, and cold gas clouds assemble naturally in current
hierarchical models of galaxy formation. These clouds are enriched with heavy
elements from earlier stars and could produce star clusters in a similar way to
nearby molecular clouds. The masses and sizes of the model clusters are in
excellent agreement with the observations of young massive clusters. Do these
model clusters evolve into globular clusters that we see in our and external
galaxies? In order to study their dynamical evolution, we calculate the orbits
of model clusters using the outputs of the cosmological simulation of a Milky
Way-sized galaxy. We find that at present the orbits are isotropic in the inner
50 kpc of the Galaxy and preferentially radial at larger distances. All
clusters located outside 10 kpc from the center formed in the now-disrupted
satellite galaxies. The spatial distribution of model clusters is spheroidal,
with a power-law density profile consistent with observations. The combination
of two-body scattering, tidal shocks, and stellar evolution results in the
evolution of the cluster mass function from an initial power law to the
observed log-normal distribution. However, not all initial conditions and not
all evolution scenarios are consistent with the observed mass function.Comment: 8 pages, invited review for conference "Globular Clusters, Guide to
Galaxies", 6-10 March 2006, University of Concepcion, Chile, ed. T. Richtler,
et a
Energy level dynamics in systems with weakly multifractal eigenstates: equivalence to 1D correlated fermions
It is shown that the parametric spectral statistics in the critical random
matrix ensemble with multifractal eigenvector statistics are identical to the
statistics of correlated 1D fermions at finite temperatures. For weak
multifractality the effective temperature of fictitious 1D fermions is
proportional to (1-d_{n})/n, where d_{n} is the fractal dimension found from
the n-th moment of inverse participation ratio. For large energy and parameter
separations the fictitious fermions are described by the Luttinger liquid model
which follows from the Calogero-Sutherland model. The low-temperature
asymptotic form of the two-point equal-parameter spectral correlation function
is found for all energy separations and its relevance for the low temperature
equal-time density correlations in the Calogero-Sutherland model is
conjectured.Comment: 4 pages, Revtex, final journal versio
Cosmological perturbations in a family of deformations of general relativity
We study linear cosmological perturbations in a previously introduced family
of deformations of general relativity characterized by the absence of new
degrees of freedom. The homogeneous and isotropic background in this class of
theories is unmodified and is described by the usual Friedmann equations. The
theory of cosmological perturbations is modified and the relevant deformation
parameter has the dimension of length. Gravitational perturbations of the
scalar type can be described by a certain relativistic potential related to the
matter perturbations just as in general relativity. A system of differential
equations describing the evolution of this potential and of the stress-energy
density perturbations is obtained. We find that the evolution of scalar
perturbations proceeds with a modified effective time-dependent speed of sound,
which, contrary to the case of general relativity, does not vanish even at the
matter-dominated stage. In a broad range of values of the length parameter
controlling the deformation, a specific transition from the regime of modified
gravity to the regime of general relativity in the evolution of scalar
perturbations takes place during the radiation domination. In this case, the
resulting power spectrum of perturbations in radiation and dark matter is
suppressed on the comoving spatial scales that enter the Hubble radius before
this transition. We estimate the bounds on the deformation parameter for which
this suppression does not lead to observable consequences. Evolution of scalar
perturbations at the inflationary stage is modified but very slightly and the
primordial spectrum generated during inflation is not noticeably different from
the one obtained in general relativity.Comment: 45 pages, version published in JCAP; minor changes, one section moved
to the appendi
Multifractality and critical fluctuations at the Anderson transition
Critical fluctuations of wave functions and energy levels at the Anderson
transition are studied for the family of the critical power-law random banded
matrix ensembles. It is shown that the distribution functions of the inverse
participation ratios (IPR) are scale-invariant at the critical point,
with a power-law asymptotic tail. The IPR distribution, the multifractal
spectrum and the level statistics are calculated analytically in the limits of
weak and strong couplings, as well as numerically in the full range of
couplings.Comment: 14 pages, 13 eps figure
The Galactic Halo in Mixed Dark Matter Cosmologies
A possible solution to the small scale problems of the cold dark matter (CDM)
scenario is that the dark matter consists of two components, a cold and a warm
one. We perform a set of high resolution simulations of the Milky Way halo
varying the mass of the WDM particle () and the cosmic dark matter
mass fraction in the WDM component (). The scaling ansatz
introduced in combined analysis of LHC and astroparticle searches postulates
that the relative contribution of each dark matter component is the same
locally as on average in the Universe (e.g. ). Here we find however, that the normalised local WDM fraction ( / ) depends strongly on for 1 keV. Using the scaling ansatz can therefore introduce significant
errors into the interpretation of dark matter searches. To correct this issue a
simple formula that fits the local dark matter densities of each component is
provided.Comment: 19 pages, 10 figures, accepted for publication in JCA
Internuclear chromosome bridges in thyrocytes of papillary thyroid cancer in patients, subjected to radioactive iodine isotopes during first months after the accident at the Chernobyl nuclear power plant
Background. Fallout from Chernobyl accident was primarily to iodine radioisotopes, with Iodine-131 (I-131) being the most predominant. Radioiodines accumulated following the accident could induce pathologic changes in thyrocytes. Internuclear chromatine bridges and ‘‘tailed’’nuclei - broken bridge fragments - are considered like cytopathological effects of radiation exposure as these abnormalities are formed from dicentric chromosomes, which are established markers of radiation exposure. Objective. To test the possibility that internuclear bridges and tailed nuclei are cytological markers of radiation exposure of the thyroid. Methods. We investigated thyrocyte nuclear abnormalities in cytological samples from fine-needle aspiration biopsy in papillary thyroid cancer patients exposed to radioiodine after Chernobyl accident (35 subjects from Gomel region, Belarus) and in papillary thyroid cancer of unexposed patients (25 subjects from Leningrad region, Russia). Nuclear abnormalities included internuclear bridges and ‘‘tailed’’ nuclei were examined. Results. Cells in papillary thyroid cancer of irradiated patients are characterized by the high frequency of appearance of hole nucleoplasmic bridges as well as broken bridges in comparison with the control group. The average frequency of thyrocytes with bridges in irradiated patients was almost 4 times higher than that in the unexposed group (4,69±0,69‰ vs. 1,10±0,23 ‰, p<0.001). The same contrast was observed in parameter “frequency of thyrocytes with “tailed” nuclei” (12,40±1,82 ‰ vs 3,68±0,39 ‰, (p<0.001)). Conclusion. Thyrocytes with internuclear bridges may be considered as markers of radiation effects on the thyroid gland.
Citation:
Kravtsov VIu, Ibragimova NV, Nikonovich SN, Nadyrov EA, Rozhko AV. [Internuclear chromosome bridges in thyrocytes of papillary thyroid cancer in patients, subjected to radioactive iodine isotopes during first months after the accident at the Chernobyl nuclear power plant]. Morphologia. 2015;9(4):37-42. Russian
Semiclassical Field Theory Approach to Quantum Chaos
We construct a field theory to describe energy averaged quantum statistical
properties of systems which are chaotic in their classical limit. An expression
for the generating function of general statistical correlators is presented in
the form of a functional supermatrix nonlinear -model where the
effective action involves the evolution operator of the classical dynamics.
Low-lying degrees of freedom of the field theory are shown to reflect the
irreversible classical dynamics describing relaxation of phase space
distributions. The validity of this approach is investigated over a wide range
of energy scales. As well as recovering the universal long-time behavior
characteristic of random matrix ensembles, this approach accounts correctly for
the short-time limit yielding results which agree with the diagonal
approximation of periodic orbit theory.Comment: uuencoded file, 21 pages, latex, one eps figur
Dynamical Dark Energy simulations: high accuracy Power Spectra at high redshift
Accurate predictions on non--linear power spectra, at various redshift z,
will be a basic tool to interpret cosmological data from next generation mass
probes, so obtaining key information on Dark Energy nature. This calls for high
precision simulations, covering the whole functional space of w(z) state
equations and taking also into account the admitted ranges of other
cosmological parameters; surely a difficult task. A procedure was however
suggested, able to match the spectra at z=0, up to k~3, hMpc^{-1}, in
cosmologies with an (almost) arbitrary w(z), by making recourse to the results
of N-body simulations with w = const. In this paper we extend such procedure to
high redshift and test our approach through a series of N-body gravitational
simulations of various models, including a model closely fitting WMAP5 and
complementary data. Our approach detects w= const. models, whose spectra meet
the requirement within 1% at z=0 and perform even better at higher redshift,
where they are close to a permil precision. Available Halofit expressions,
extended to (constant) w \neq -1 are unfortunately unsuitable to fit the
spectra of the physical models considered here. Their extension to cover the
desired range should be however feasible, and this will enable us to match
spectra from any DE state equation.Comment: method definitely improved in semplicity and efficacy,accepted for
publication on JCA
Measurement of and Structure Functions in Low Region with the IHEP-JINR Neutrino Detector
The isoscalar structure functions and are measured as functions
of averaged over all permissible for the range of 6 to 28 GeV of
incident neutrino (anti-neutrino) energy at the IHEP-JINR Neutrino Detector.
The QCD analysis of structure function provides
MeV under the assumption of QCD
validity in the region of low . The corresponding value of the strong
interaction constant agrees with the
recent result of the CCFR collaboration and with the combined LEP/SLC result.Comment: 11 pages, 1 Postscript figure, LaTeX. Talk given at the 7th
International Workshop on Deep Inelastic Scattering and QCD (DIS 99),
Zeuthen, Germany, 19-23 Apr 199
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