Spin waves in diluted magnetic quantum wells

We study collective spin excitations in two-dimensional diluted magnetic semiconductors, placed into external magnetic field. Two coupled modes of the spin waves (the electron and ion modes) are found to exist in the system along with a number of the ion spin excitations decoupled from the electron system. We calculate analytically the spectrum of the waves taking into account the exchange interaction of itinerant electrons both with each other and with electrons localized on the magnetic ions. The interplay of these interactions leads to a number of intriguing phenomena including tunable anticrossing of the modes and a field-induced change in a sign of the group velocity of the ion mode

Model of Nanostructure Formation on Solid Surface Melted by Laser Pulse

The paper describes the model of nanostructure formation on solid surface by nanosecond laser pulses melting the material. Stefan problem with corresponding boundary conditions is solved in combination with nucleation theory. It is found that typical size of surface nanostructure formed depends on energy and duration of laser pulse. For comparison of theoretic and experimental results titan pieces irradiated by ArF-laser are shown. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3541

REGULATION OF ARABIDOPSIS GDH2 NUCLEAR GENE EXPRESSION DEPENDS ON FUNCTIONAL STATE OF MITOCHONDRIA AND CHLOROPLASTS

The results of recent studies indicate that expression of some plant nuclear genes depends on functional state of mitochondria and chloroplasts. We have demonstrated that expression of gdh2 gene encoding beta-subunit of mitochondrial glutamate dehydrogenase depends on a redox state of mitochondrial respiratory chain. Treatment of Arabidopsis thaliana cell culture with respiratory complex III inhibitor antimycin A or complex IV inhibitor KCN led to rapid increase of gdh2 transcript content. Complex I inhibition by rotenone had no influence on the transcript level. We suggest that gdh2 expression responds to changes of redox state of the respiratory chain segment located between complex I and complex III. We suppose that the revealed effect is not due to elevated generation of reactive oxygen species occurring upon the electron transport chain blockage, because cell treatment with hydrogen peroxide and paraquat did not lead to induction of gdh2 expression. Experiments with Arabidopsis green seedlings have demonstrated that gdh2 gene expression and GDH2 enzyme activity decrease strongly in the normal and high light conditions and increase in darkness. Resuming our experiments on different Arabidopsis organs and cell types we generalize that gdh2 expression is maximal when both respiratory and photosynthetic electron transport chains are inhibited, and minimal when both of the electron transport chains are highly active. There are a number of hypotheses which would explain such a regularity. The first one proposes an energetic deficit as a regulatory factor initiating gdh2 gene induction. We assume, however, that sugar starvation or ATP depletion cannot be the main factors in regulation of gdh2 expression, because oxidative phosphorylation uncoupling by FCCP did not mimic the effects of antimycin A or prolonged dark treatment on the gdh2 gene expression. The second hypothesis is developed for chloroplast-to-nucleus signaling and proposes that the regulatory signal can be initiated by redox state of plastoquinone pool and mediated by thylakoid membrane-bound protein kinases. We assume that similar mechanism would exist also in mitochondria-to-nucleus signaling, so that gdh2 expression would depend on redox state of both ubiquinone and plastoquinone pools. This is confirmed by our experiments, in which the involvement of serine/threonine protein kinases in the antimycin-related gdh2 induction was demonstrated as an ultimate step in transduction of the regulatory signal to the nucleus. Abscisic acid and/or pyridine nucleotides ratio changes can also participate in the retrograde regulation of gdh2 gene expression. Thus, we have demonstrated that regulation of gdh2 gene expression depends on mitochondrial and chloroplast functional state, and it can be considered as another example of retrograde regulation. The redox states of ubiquinone/plastoquinone pools are the most likely primary factors of this regulation type, which also involves serine/threonine protein kinases in signal transduction

Multifragmentation in Collisions of 4.4gev-Deuterons with Gold Target

The relative velocity correlation function of pairs of intermediate mass fragments has been studied for d+Au collitions at 4.4 GeV. Experimental correlation functions are compared to that obtained by multibody Coulomb trajectory calculations under the assumption of various decay timees of the fragmenting system. The combined approach with the empirically modified intranuclear cascade code followed by the statistical multifragmentation model was used to generate the starting conditions for these calculations. The fragment emossion time is found to be less than 40 fm/c.Comment: Accepted for publication in Bulletin of the Russian Academy of Sciences. Physic

Condensation of a tetrahedra rigid-body libration mode in HoBaCo4O7 : the origin of phase transition at 355 K

Rietveld profiles, Moessbauer spectra and x-ray absorption fine structure (XAFS) were analyzed through the structural phase transition at Ts = 355 K in HoBaCo4O7. Excess of the oxygen content over O7 was avoided via annealing the samples in argon flow at 600 degree C. Space groups (S.G.) Pbn21c and P63mc were used to refine the structure parameters in the low- and high-temperature phases, respectively. Additionally, the Cmc21 symmetry was considered as a concurrent model of structure of the low-temperature phase. In the high-temperature phase, severe anisotropy of thermal motion of the major part of the oxygen atoms was observed. This anisotropic motion turns to be quenched as the sample is cooled below Ts. The variation of quadrupole splitting near Ts is not similar to a steplike anomaly frequently seen at the charge-ordering transition. We observe instead a dip-like anomaly of the average quadrupole splitting near Ts. Narrow distribution of the electric field gradient (EFG) over different cobalt sites is observed and explained on the basis of point-charge model. XAFS spectra show no evidence of significant difference between YBaCo4O7 (T > Ts) and HoBaCo4O7 (T < Ts). The origin of the transition at Ts is ascribed to the condensation of the libration phonon mode associated with the rigid-body rotational movements of the starlike tetrahedral units, the building blocks of kagome network. It is shown that the condensation of the libration mode is not compatible with translation symmetry for the hexagonal S.G., but compatible for the orthorhombic S.G. The orthorhombic lattice parameters and EFG components (Vxx, Vyy, Vzz) vary smoothly with temperature at approaching Ts and closely follow each other.Comment: 13 figure

Comparative Study of Multifragmentation of Gold Nuclei Induced by Relativistic Protons, 4^4He, and 12^{12}C

Multiple emission of intermediate-mass fragments has been studied for the collisions of p, $^4$He and $^{12}$C on Au with the $4\pi$ setup FASA. The mean IMF multiplicities (for the events with at least one IMF) are saturating at the value of $2.2\pm0.2$ for the incident energies above 6 GeV. The observed IMF multiplicities cannot be described in a two-stage scenario, a fast cascade followed by a statistical multifragmentation. Agreement with the measured IMF multiplicities is obtained by introducing an intermediate phase and modifying empirically the excitation energies and masses of the remnants. The angular distributions and energy spectra from the p-induced collisions are in agreement with the scenario of ``thermal'' multifragmentation of a hot and diluted target spectator. In the case of $^{12}$C+Au(22.4 GeV) and $^4$He(14.6 GeV)+Au collisions, deviations from a pure thermal break-up are seen in the energy spectra of the emitted fragments, which are harder than those both from model calculations and from the measured ones for p-induced collisions. This difference is attributed to a collective flow.Comment: 33 pages 15 figures, accepted in Nucl. Phys.