Exactly solvable models in 2D semiclassical dilaton gravity and extremal black holes

Previously known exactly solvable models of 2D semiclassical dilaton gravity admit, in the general case, only non-extreme black holes. It is shown that there exist exceptional degenerate cases, that can be obtained by some limiting transitions from the general exact solution, which include, in particular, extremal and ultraextremal black holes. We also analyze properties of extreme black holes without demanding exact solvability and show that for such solutions quantum backreaction forbids the existence of ultraextreme black holes. The conditions,under which divergencies of quantum stresses in a free falling frame can disappear, are found. We derive the closed equation with respect to the metric as a function of the dilaton field that enables one, choosing the form of the metric, to restore corresponding Lagrangian. It is demonstrated that exactly solvable models, found earlier, can be extended to include an electric charge only in two cases: either the dilaton-gravitation coupling is proportional to the potential term, or the latter vanishes. The second case leads to the effective potential with a negative amplitude and we analyze, how this fact affects the structure of spacetime. We also discuss the role of quantum backreaction in the relationship between extremal horizons and the branch of solutions with a constant dilaton.Comment: 31 pages. In v.2 typo in Ref. [2] corrected, 4 references added. Accepted in Class. Quant. Gra

Ground state wavefunction of the quantum Frenkel-Kontorova model

The wavefunction of an incommensurate ground state for a one-dimensional discrete sine-Gordon model -- the Frenkel-Kontorova (FK) model -- at zero temperature is calculated by the quantum Monte Carlo method. It is found that the ground state wavefunction crosses over from an extended state to a localized state when the coupling constant exceeds a certain critical value. So, although the quantum fluctuation has smeared out the breaking of analyticity transition as observed in the classical case, the remnant of this transition is still discernible in the quantum regime.Comment: 5 Europhys pages, 3 EPS figures, accepted for publication in Europhys. Letter

A study of hydroxyapatite nanocrystals by the multifrequency EPR and ENDOR spectroscopy methods

Specimens of powders of hydroxyapatite (Ca10(PO 4)6(OH)2) with average crystallite sizes in the range of 20-50 nm synthesized by the wet precipitation method have been investigated by the multifrequency (9 and 94 GHz) electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) methods. In specimens subjected to X-ray irradiation at room temperature, EPR signals that are caused by nitrogen compounds have been observed. Numerical calculations performed in terms of the density functional theory show that the observed EPR signal is caused by the occurrence of paramagnetic centers, the structure of which is NO 3 2- and which replace the positions of PO 4 3- in the hydroxyapatite structure. © 2014 Pleiades Publishing, Ltd

Wave transmission, phonon localization and heat conduction of 1D Frenkel-Kontorova chain

We study the transmission coefficient of a plane wave through a 1D finite quasi-periodic system -- the Frenkel-Kontorova (FK) model -- embedding in an infinite uniform harmonic chain. By varying the mass of atoms in the infinite uniform chain, we obtain the transmission coefficients for {\it all} eigenfrequencies. The phonon localization of the incommensurated FK chain is also studied in terms of the transmission coefficients and the Thouless exponents. Moreover, the heat conduction of Rubin-Greer-like model for FK chain at low temperature is calculated. It is found that the stationary heat flux $J(N)\sim N^{\alpha}$, and $\alpha$ depends on the strength of the external potential.Comment: 15 pages in Revtex, 8 EPS figure

A study of hydroxyapatite nanocrystals by the multifrequency EPR and ENDOR spectroscopy methods

Specimens of powders of hydroxyapatite (Ca10(PO 4)6(OH)2) with average crystallite sizes in the range of 20-50 nm synthesized by the wet precipitation method have been investigated by the multifrequency (9 and 94 GHz) electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) methods. In specimens subjected to X-ray irradiation at room temperature, EPR signals that are caused by nitrogen compounds have been observed. Numerical calculations performed in terms of the density functional theory show that the observed EPR signal is caused by the occurrence of paramagnetic centers, the structure of which is NO 3 2- and which replace the positions of PO 4 3- in the hydroxyapatite structure. © 2014 Pleiades Publishing, Ltd

A study of hydroxyapatite nanocrystals by the multifrequency EPR and ENDOR spectroscopy methods

Specimens of powders of hydroxyapatite (Ca10(PO 4)6(OH)2) with average crystallite sizes in the range of 20-50 nm synthesized by the wet precipitation method have been investigated by the multifrequency (9 and 94 GHz) electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) methods. In specimens subjected to X-ray irradiation at room temperature, EPR signals that are caused by nitrogen compounds have been observed. Numerical calculations performed in terms of the density functional theory show that the observed EPR signal is caused by the occurrence of paramagnetic centers, the structure of which is NO 3 2- and which replace the positions of PO 4 3- in the hydroxyapatite structure. © 2014 Pleiades Publishing, Ltd

A study of hydroxyapatite nanocrystals by the multifrequency EPR and ENDOR spectroscopy methods

Specimens of powders of hydroxyapatite (Ca10(PO 4)6(OH)2) with average crystallite sizes in the range of 20-50 nm synthesized by the wet precipitation method have been investigated by the multifrequency (9 and 94 GHz) electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) methods. In specimens subjected to X-ray irradiation at room temperature, EPR signals that are caused by nitrogen compounds have been observed. Numerical calculations performed in terms of the density functional theory show that the observed EPR signal is caused by the occurrence of paramagnetic centers, the structure of which is NO 3 2- and which replace the positions of PO 4 3- in the hydroxyapatite structure. © 2014 Pleiades Publishing, Ltd