Damping effects and the metal-insulator transition in the two-dimensional electron gas

The damping of single-particle degrees of freedom in strongly correlated two-dimensional Fermi systems is analyzed. Suppression of the scattering amplitude due to the damping effects is shown to play a key role in preserving the validity of the Landau-Migdal quasiparticle picture in a region of a phase transition, associated with the divergence of the quasiparticle effective mass. The results of the analysis are applied to elucidate the behavior of the conductivity $\sigma(T)$ of the two-dimensional dilute electron gas in the density region where it undergoes a metal-insulator transition.Comment: 7 pages, 6 figures. Improved and slightly extended version: new paragraph about Hall effect + new Fig.

Physical and mechanical properties and thermal protection efficiency of intumescent coatings

The new engineering technique for the experimental investigation of physical and mechanical characteristics of thermal protective intumescent coatings is offered. A mathematical model is proposed for predicting the thermal behavior of structures protected by coatings; the model is closed by the studied material characteristics. The heating of a metal plate under standard thermal loading conditions is modeled mathematically. The modeling results are in good agreement with bench test results for metal temperature under the coating. The proposed technique of studying physical and mechanical characteristics can be applied to identify and monitor the state of thermal protective intumescent coatings in the long-term operation

Normal state resistivity of Ba1−x_{1-x}Kx_xFe2_2As2_2: evidence for multiband strong-coupling behavior

We present theoretical analysis of the normal state resistivity in multiband superconductors in the framework of Eliashberg theory. The results are compared with measurements of the temperature dependence of normal state resistivity of high-purity Ba$_{0.68}$K$_{0.32}$Fe$_{2}$As$_{2}$ single crystals with the highest reported transition temperature $T_c$ = 38.5 K. The experimental data demonstrate strong deviations from the Bloch-Gr\"{u}neisen behavior, namely the tendency to saturation of the resistivity at high temperatures. The observed behavior of the resistivity is explained within the two band scenario when the first band is strongly coupled and relatively clean, while the second band is weakly coupled and is characterized by much stronger impurity scattering.Comment: 4 pages, 3 figures, to be published in JETP Letters Vol.94, N

ATP as modulator of carbacholine effect on contractility of rat myocardium in postnatal ontogeny

We studied combined effect of 2-m-ATP, P 2 receptor agonist, and carbacholine, muscarinic M 2 cholinoreceptor agonist, on contractility of rat myocardium during the postnatal ontogeny. Activation of P 2 receptors can stimulate or attenuate the effects of carbacholine depending on animal age. 2-m-ATP potentiates the inhibitory effect of carbacholine on myocardial contractility in 14- and 100-day-old rats. In 21-day-old rats, activation of P 2 receptors prevented the negative effect of carbacholine on myocardial contractility. Activation of muscarinic M 2 receptors inhibited the inotropic effect of purine in all age groups. © 2009 Springer Science+Business Media, Inc

Role of P2X receptors in positive inotropic effect of rat myocardium during ontogeny

Experiments with selective agonists and antagonists of purinoceptors allowed us to evaluate the subtype of P2X receptors. We showed that the myocardium of 14-100-day-old rats contains functionally active P2X 1 receptors. These receptors are involved in the realization of the positive inotropic effect of the atria and ventricles. Selective P2X 1 receptor agonist β,γ-methylene-ATP induced a dose-dependent increase in the strength of atrial and ventricular contractions. P2X 1 receptor antagonist TNP-ATP abolished the effect of the agonist in rats of all age groups. © Springer Science+Business Media, Inc. 2008

Magnetic and spectral properties of multi-sublattice oxides SrY2O4:Er3+ and SrEr2O4

SrEr2O4 is a geometrically frustrated magnet which demonstrates rather unusual properties at low temperatures including a coexistence of long- and short-range magnetic order, characterized by two different propagation vectors. In the present work, the effects of crystal fields (CF) in this compound containing four magnetically inequivalent erbium sublattices are investigated experimentally and theoretically. We combine the measurements of the CF levels of the Er3+ ions made on a powder sample of SrEr2O4 using neutron spectroscopy with site-selective optical and electron paramagnetic resonance measurements performed on single crystal samples of the lightly Er-doped nonmagnetic analogue, SrY2O4. Two sets of CF parameters corresponding to the Er3+ ions at the crystallographically inequivalent lattice sites are derived which fit all the available experimental data well, including the magnetization and dc susceptibility data for both lightly doped and concentrated samples.Comment: 14 pages, 9 figure

Robustness of the van Hove scenario for high-Tc superconductors

The pinning of the Fermi level to the van Hove singularity and the formation of flat bands in the two-dimensional t-t' Hubbard model is investigated by the renormalization group technique. The "van-Hove" scenario of non-Fermi-liquid behavior for high-Tc compounds can take place in a broad enough range of the hole concentrations. The results are in qualitative agreement with the recent ARPES data on La2CuO4.Comment: 4 pages, LaTeX, 3 figure

Theoretical Aspects of Science with Radioactive Nuclear Beams

Physics of radioactive nuclear beams is one of the main frontiers of nuclear science today. Experimentally, thanks to technological developments, we are on the verge of invading the territory of extreme N/Z ratios in an unprecedented way. Theoretically, nuclear exotica represent a formidable challenge for the nuclear many-body theories and their power to predict nuclear properties in nuclear terra incognita. It is important to remember that the lesson learned by going to the limits of the nuclear binding is also important for normal nuclei from the neighborhood of the beta stability valley. And, of course, radioactive nuclei are crucial astrophysically; they pave the highway along which the nuclear material is transported up in the proton and neutron numbers during the complicated synthesis process in stars.Comment: 26 ReVTeX pages, 11 Postscript figures, uses epsf.sty, to be published in: Theme Issue on Science with Beams of Radioactive Nuclei, Philosophical Transactions, ed. by W. Gelletl

Effect of ATP and its analogs on contractility of rat myocardium during ontogeny

The effects of P2-receptor agonists on myocardial contractility were examined in rats aging 14-100 days. ATP and its stable analog 2-methylthio-ATP potentiated the contraction force of isolated myocardial strips in a dose-dependent manner. The agonist concentrations producing the positive inotropic effect increased from days 14 to 100 of life. The efficiency of extracellular purines depends on animal age: in 14-and 56-day rats the positive inotropic effects of ATP and 2-methylthio-ATP were similar, while in 100-day rats ATP produced more pronounced effect than 2-methylthio-ATP. © Springer Science+Business Media, Inc. 2007