49 research outputs found
A comparative analysis of gamma and hadron families at the superhigh energies recorded in experiment Pamir
A comparative analysis of hadron and gamma families which have undergone the decascading procedure is made. Results are compared with different models of interactions. In hadron families with energies Summary E sub H sup gamma 20 TeV as well as in gamma families with energies Summary E sub gamma 70 TeV, increasing azimuthal anisotropy is observed
Stability and electronic structure of the complex KPtCl structure-type hydrides
The stability and bonding of the ternary complex KPtCl structure
hydrides is discussed using first principles density functional calculations.
The cohesion is dominated by ionic contributions, but ligand field effects are
important, and are responsible for the 18-electron rule. Similarities to oxides
are discussed in terms of the electronic structure. However, phonon
calculations for SrRuH also show differences, particularly in the
polarizability of the RuH octahedra. Nevertheless, the yet to be made
compounds PbRuH and BeFeH are possible ferroelectrics. The
electronic structure and magnetic properties of the decomposition product,
FeBe are reported. Implications of the results for H storage are discussed
Mоделирование режимов электрических сетей на основе уравнений установившегося режима и теплового баланса
In the traditional calculations of the steady-state mode of the electrical network, the dependences of the active resistances of the overhead line wire on the ambient temperature and currents in the branches are not taken into account. However, the temperature is a function of the active power losses, the power losses are a function of the resistance and current, and the resistance is temperature dependent. Therefore, these relations should be related to the traditional equations for stationary regimes. In order to increase the accuracy of steady-state calculations, a temperature correction of the resistance of the branches is required. In this paper, we present a method based on the joint solution of nonlinear equations of the steady-state electric network regime and the thermal balance of the wires of overhead lines. The algorithm and the program of calculation of the steady-state mode of an electric network taking into account dependence of active resistances of a wire of an overhead line on ambient temperature and currents in branches have been developed. The quantitative influence of the load current, wire temperature, wind speed, solar radiation on the active resistance of the wires has been estimated, and the errors in calculating annual variable energy losses have been determined. Numerical experiments were carried out for a 6-node modified version of the IEEE test system and equivalent circuit of 110 kV. The results of the calculations of the steady-state regime on various test circuits showed that the non-account of the temperature dependence of the active resistances might cause errors in power loss for individual loaded lines up to 10 %, and for total losses of the system – up to 30 %. This is unacceptable in simulating the modes of the electric network. The results of simulation of steady-state regimes taking into account the temperature dependence of the resistance of the wires are presented on the example of 6-node and 7-node circuits.В традиционных расчетах установившегося режима электрической сети не учитываются зависимости активных сопротивлений провода воздушной линии от температуры окружающей среды и токов в ветвях. Однако температура является функцией потерь активной мощности, потери – функцией сопротивления и тока, а сопротивление зависит от температуры. Поэтому эти соотношения должны быть связаны с традиционными уравнениями для стационарных режимов. Для повышения точности расчетов установившегося режима требуется температурная коррекция сопротивления ветвей. В работе представлен метод, основанный на совместном решении нелинейных уравнений установившегося режима электрической сети и теплового баланса проводов воздушных линий. Разработаны алгоритм и программа расчета установившегося режима электрической сети с учетом зависимости активных сопротивлений провода воздушной линии от температуры окружающей среды и токов в ветвях. Произведена оценка количественного влияния тока нагрузки, температуры провода, скорости ветра, солнечной радиации на активное сопротивление проводов, а также определены погрешности расчета годовых переменных потерь электроэнергии. Проводились численные эксперименты для шестиузловой модифицированной версии тестовой системы IEEE и эквивалентной схемы 110 кВ. Результаты проведенных расчетов установившегося режима на различных тестовых схемах показали, что неучет температурной зависимости активных сопротивлений может привести к ошибкам в потере мощности для отдельных нагруженных линий до 10 % и для суммарных потерь системы до 30 %, что является недопустимым в моделировании режимов электрической сети. Приведены результаты моделирования установившихся режимов с учетом температурной зависимости сопротивлений проводов на примерах шести- и семиузловых схем
Electronic Structure of Sr_2FeMoO_6
We have analysed the unusual electronic structure of Sr_2FeMoO_6 combining
ab-initio and model Hamiltonian approaches. Our results indicate that there are
strong enhancements of the intraatomic exchange strength at the Mo site as well
as the antiferromagnetic coupling strength between Fe and Mo sites. We discuss
the possibility of a negative effective Coulomb correlation strength (U_{eff})
at the Mo site due to these renormalised interaction strengths.Comment: To appear in Phys. Rev. Let
Spin-orbit splitting of image states
We quantify the effect of the spin-orbit interaction on the Rydberg-like
series of image state electrons at the (111) and (001) surface of Ir, Pt and
Au. Using relativistic multiple-scattering methods we find Rashba-like
dispersions with Delta E(K)=gamma K with values of gamma for n=1 states in the
range 38-88 meV Angstrom. Extending the phase-accumulation model to include
spin-orbit scattering we find that the splittings vary like 1/(n+a)^3 where a
is the quantum defect and that they are related to the probability of spin-flip
scattering at the surface. The splittings should be observable experimentally
being larger in magnitude than some exchange-splittings that have been resolved
by inverse photoemission, and are comparable to linewidths from inelastic
lifetimes.Comment: 10 pages, 4 figure
Spin currents and spin dynamics in time-dependent density-functional theory
We derive and analyse the equation of motion for the spin degrees of freedom
within time-dependent spin-density-functional theory (TD-SDFT). Results are (i)
a prescription for obtaining many-body corrections to the single-particle spin
currents from the Kohn-Sham equation of TD-SDFT, (ii) the existence of an
exchange-correlation (xc) torque within TD-SDFT, (iii) a prescription for
calculating, from TD-SDFT, the torque exerted by spin currents on the spin
magnetization, (iv) a novel exact constraint on approximate xc functionals, and
(v) the discovery of serious deficiencies of popular approximations to TD-SDFT
when applied to spin dynamics.Comment: now includes discussion of OEP and GGA; to appear in Phys. Rev. Let
Surface states and their possible role in the superconductivity of MgB2
We report layer-Korringa-Kohn-Rostocker calculations for bulk and surface
states as well as the corresponding angle resolved photoemission (ARPES)
intensities of MgB2. Our theoretical results reproduce very well the recent
ARPES data by Uchiyama et al., cond-mat/0111152. At least two surface states
are assigned. Consequences of SFS on the anisotropy of the upper critical
fields and other properties in the superconducting state of small grains in
micropowder samples are briefly discussed.Comment: 4pages, 6figures, corrected typos, references adde
Importance of Correlation Effects on Magnetic Anisotropy in Fe and Ni
We calculate magnetic anisotropy energy of Fe and Ni by taking into account
the effects of strong electronic correlations, spin-orbit coupling, and
non-collinearity of intra-atomic magnetization. The LDA+U method is used and
its equivalence to dynamical mean-field theory in the static limit is
emphasized. Both experimental magnitude of MAE and direction of magnetization
are predicted correctly near U=4 eV for Ni and U=3.5 eV for Fe. Correlations
modify one-electron spectra which are now in better agreement with experiments.Comment: 4 pages, 2 figure
Linear Response Calculations of Spin Fluctuations
A variational formulation of the time--dependent linear response based on the
Sternheimer method is developed in order to make practical ab initio
calculations of dynamical spin susceptibilities of solids. Using gradient
density functional and a muffin-tin-orbital representation, the efficiency of
the approach is demonstrated by applications to selected magnetic and strongly
paramagnetic metals. The results are found to be consistent with experiment and
are compared with previous theoretical calculations.Comment: 11 pages, RevTex; 3 Figures, postscript, high-resolution printing
(~1200dpi) is desire
One-dimensional dynamics of the d-electrons in -NaVO
We have studied the electronic properties of the ladder compound
-NaVO, adopting a joint experimental and theoretical
approach. The momentum-dependent loss function was measured using electron
energy-loss spectroscopy in transmission. The optical conductivity derived from
the loss function by a Kramers-Kronig analysis agrees well with our results
from LSDA+U band-structure calculations upon application of an
antiferromagnetic alignment of the V~3 spins along the legs and an
on-site Coulomb interaction U of between 2 and 3 eV. The decomposition of the
calculated optical conductivity into contributions from transitions between
selected energy regions of the DOS reveals the origin of the observed
anisotropy of the optical conductivity. In addition, we have investigated the
plasmon excitations related to transitions between the vanadium states within
an effective 16 site vanadium cluster model. Good agreement between the
theoretical and experimental loss function was obtained using the hopping
parameters derived from the tight binding fit to the band-structure and
moderate Coulomb interactions between the electrons within the ab plane.Comment: 23 pages, 8 figures; submitted to PR