860 research outputs found
Derivation of the Gutenberg-Richter Empirical Formula from the Solution of the Generalized Logistic Equation
We have written a new equation to study the statistics of earthquake
distributions. We call this equation "the generalized logistic equation". The
Gutenberg-Richter frequency-magnitude formula was derived from the solution of
the generalized logistic equation as an asymptotic case in approximation of
large magnitudes. To illustrate how the found solution of the generalized
logistic equation works, it was used to approximate the observed cumulative
distribution of earthquakes in four different geological provinces: the Central
Atlantic (40N-25N, 5W-35W), Canary Islands, Magellan Mountains (20N-9S,
148E-170E), and the Sea of Japan. This approximation showed the excellent fit
between the theoretical curves and observed data for earthquake magnitudes
1<m<9.Comment: 10 pages, 2 figures, 1 table, 8 references. Submitted to Natural
Science, Earthquakes special issu
On the phonon-induced superconductivity of disordered alloys
A model of alloy is considered which includes both quenched disorder in the
electron subsystem (``alloy'' subsystem) and electron-phonon interaction. For
given approximate solution for the alloy part of the problem, which is assumed
to be conserving in Baym's sense, we construct the generating functional and
derive the Eliashberg-type equations which are valid to the lowest order in the
adiabatic parameter.The renormalization of bare electron-phonon interaction
vertices by disorder is taken into account consistently with the approximation
for the alloy self-energy. For the case of exact configurational averaging the
same set of equations is established within the usual T-matrix approach. We
demonstrate that for any conserving approximation for the alloy part of the
self-energy the Anderson's theorem holds in the case of isotropic singlet
pairing provided disorder renormalizations of the electron-phonon interaction
vertices are neglected. Taking account of the disorder renormalization of the
electron-phonon interaction we analyze general equations qualitatively and
present the expressions for for the case of weak and intermediate
electron-phonon coupling. Disorder renormalizations of the logarithmic
corrections to the effective coupling, which arise when the effective
interaction kernel for the Cooper channel has the second energy scale, as well
as the renormalization of the dilute paramagnetic impurity suppression are
discussed.Comment: 59 pages, 10 Eps figures, LaTe
Electric-field-induced monoclinic phase in (Ba,Sr)TiO thin film
We have studied electric-field-induced symmetry lowering in the tetragonal
(001)-oriented heteroepitaxial (BaSr)TiO thin film
deposited on (001)MgO substrate. Polarized micro-Raman spectra were recorded
from the film area in between two planar electrodes deposited on the film
surface. Presence of \textit{c}-domains with polarization normal to the
substrate was confirmed from polarized Raman study under zero field, while
splitting and hardening of the \textit{E}(TO) soft mode and polarization
changes in the Raman spectra suggest monoclinic symmetry under external
electric field
On the relevance of quantum corrections to the matter stress-energy tensor in eternally expanding universes
We study a toy-model of continuous infinite expansion of space-time with the
flat start. We use as the gravitational background a conformaly flat metric
with an exponentially growing factor in conformal time. We aim to clarify some
properties of quantum fields in such a gravitational background. In particular,
we calculate one-loop corrections to the Keldysh propagator to verify the fact
of secular growth of the occupation number and anomalous quantum average in the
massless scalar field theory with selfinteractions. We perform the calculation
in arbitrary dimensions with the use of the Schwinger-Keldysh technique. We get
a secular growth which is not of a kinetic type. We provide some results for
the case of generic interaction .Comment: 21 pages, 2 figure
First-principles Calculations of the Electronic Structure and Spectra of Strongly Correlated Systems: Dynamical Mean-field Theory
A recently developed dynamical mean-field theory in the iterated perturbation
theory approximation was used as a basis for construction of the "first
principles" calculation scheme for investigating electronic structure of
strongly correlated electron systems. This scheme is based on Local Density
Approximation (LDA) in the framework of the Linearized Muffin-Tin-Orbitals
(LMTO) method. The classical example of the doped Mott-insulator
La_{1-x}Sr_xTiO_3 was studied by the new method and the results showed
qualitative improvement in agreement with experimental photoemission spectra.Comment: 11 pages, 3 Postscript figures, LaTeX, submit in Journal of Physics:
Condensed Matte
Mapping the Neural Substrates of Recent and Remote Visual Imprinting Memory in the Chick Brain
Social attachment formed by filial imprinting in newborn chicks undergoes a process of memory consolidation that involves rearrangement of its neural storage substrates. In the first 3 h after imprinting it depends on the integrity of the intermediate medial mesopallium (IMM) and beyond that time on unidentified memory storage structures dubbed S’. To search for the S’ memory system in the chick brain, we mapped and compared patterns of activity induced by retrieval of filial attachment memory before and after this critical transition. Chicks were trained in the visual imprinting task, and their memory was reactivated by imprinting stimulus either 1 h (recent memory retrieval) or 24 h (remote memory retrieval) after the completion of training. Patterns of brain activity were mapped by in situ hybridization to mRNA of an immediate early gene c-fos. We also mapped c-fos expression induced by the first presentation of the imprinting stimulus. Memory retrieval triggered massive c-fos expression in the chick brain both 1 and 24 h after the end of training. These activity patterns mostly coincided with the c-fos expression induced by the first presentation of imprinting stimulus. However, in the hippocampus c-fos induction was observed only after the first exposure to imprinting stimulus but not after memory retrieval. In the IMM, medio-rostral nidopallium/mesopallium, and hyperpallium densocellulare c-fos activation was induced by retrieval of only the remote but not of the recent memory. These c-fos mapping data point to the candidate brain structures for systems reorganization of imprinting memory in chicks
The nature of the ferromagnetic ground state in the Mn4 molecular magnet
Using ab initio band structure and model calculations we studied magnetic
properties of one of the Mn molecular magnets (Mn4(hmp)6), where two types
of the Mn ions exist: Mn3+ and Mn2+. The direct calculation of the exchange
constants in the GGA+U approximation shows that in contrast to a common belief
the strongest exchange coupling is not between two Mn3+ ions (J_{bb}), but
along two out of four exchange paths connecting Mn3+ and Mn2+ ions (J_{wb}).
The microscopic analysis performed within the perturbation theory allowed to
establish the mechanism for this largest ferromagnetic exchange constant. The
charge ordering of the Mn ions results in the situation when the energy of the
excited state in the exchange process is defined not by the large on-site
Coulomb repulsion U, but by much smaller energy V, which stabilizes the charge
ordered state. Together with strong Hund's rule coupling and specific orbital
order this leads to a large ferromagnetic exchange interaction for two out of
four Mn2+ --Mn3+ pairs.Comment: 12 pages, 10 figure
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