Alpha-decay lifetimes semiempirical relationship including shell effects

A new version of the semiempirical formula based on fission approach of alpha decay is derived, by using the optimum values of the fitting parameters determined for even-even nuclei, combined with hindrance factors for even-odd, odd-even, and odd-odd nuclides. The deviations from experimental data for two regions of nuclear chart (493 alpha emitters with Z=52-118 and 142 transuranium nuclei including superheavies (Z=92-118), respectively) are compared with those obtained by using the universal curve and the Viola-Seaborg semiempirical relationship.Comment: 11 pages, 3 figures, revtex

Nonlinear dynamics of polariton scattering in semiconductor microcavity: bistability vs stimulated scattering

We demonstrate experimentally an unusual behavior of the parametric polariton scattering in semiconductor microcavity under a strong cw resonant excitation. The maximum of the scattered signal above the threshold of stimulated parametric scattering does not shift along the microcavity lower polariton branch with the change of pump detuning or angle of incidence but is stuck around the normal direction. We show theoretically that such a behavior can be modelled numerically by a system of Maxwell and nonlinear Schroedinger equations for cavity polaritons and explained via the competition between the bistability of a driven nonlinear MC polariton and the instabilities of parametric polariton-polariton scattering.Comment: 5 pages, 4 Postscript figures; corrected typo

Efficient fiber coupling of down-conversion photon pairs

We develop and apply an effective analytic theory of a non-collinear, broadband type-I parametric down-conversion to study a coupling efficiency of the generated photon pairs into single mode optical fibers. We derive conditions necessary for highly efficient coupling for single and double type-I crystal producing polarization entangled states of light. We compare the obtained approximate analytic expressions with the exact numerical solutions and discuss the results for a case of BBO crystals.Comment: 15 pages, 4 figure

Transition Radiation by Standard Model Neutrinos at an Interface

We discuss the transition radiation process $\nu \to \nu \gamma$ at an interface of two media. The medium fulfills the dual purpose of inducing an effective neutrino-photon vertex and of modifying the photon dispersion relation. The transition radiation occurs when at least one of those quantities have different values in different media. We present a result for the probability of the transition radiation which is both accurate and analytic. For $E_\nu =1$MeV neutrino crossing polyethylene-vacuum interface the transition radiation probability is about $10^{-39}$ and the energy intensity (deposition) is about $10^{-34}$eV. At the surface of the neutron stars the transition radiation probability may be $\sim 10^{-20}$. Our result on three orders of magnitude is larger than the results of previous calculations.}Comment: invited talk, to appear in the proceedings of the XLVIth Rencontres de Moriond EW 201

BCS approximation to the effective vector vertex of superfluid fermions

We examine the effective interaction of nonrelativistic fermions with an external vector field in superfluid systems. In contrast to the complicated vertex equation, usually used in this case, we apply the approach which does not employ an explicit form of the pairing interaction. This allows to obtain a simple analytic expression for the vertex function only in terms of the order parameter and other macroscopic parameters of the system. We use this effective vertex to analyze the linear response function of the superfluid medium at finite temperatures. At the time-like momentum transfer, the imaginary part of the response function is found to be proportional to the fourth power of small Fermi velocity, i.e. the energy losses through vector currents are strongly suppressed. As an application, we calculate the neutrino energy losses through neutral weak currents caused by the pair recombination in the superfluid neutron matter at temperatures lower than the critical one for S-wave pairing. This approach confirms a strong suppression of the neutrino energy losses as predicted in Ref.[4].Comment: 19 pages, no figure

NiTi shape-memory transformations: minimum-energy pathways between austenite, martensites, and kinetically-limited intermediate states

NiTi is the most used shape-memory alloy, nonetheless, a lack of understanding remains regarding the associated structures and transitions, including their barriers. Using a generalized solid-state nudge elastic band (GSSNEB) method implemented via density-functional theory, we detail the structural transformations in NiTi relevant to shape memory: those between body-centered orthorhombic (BCO) groundstate and a newly identified stable austenite ("glassy" B2-like) structure, including energy barriers (hysteresis) and intermediate structures (observed as a kinetically limited R-phase), and between martensite variants (BCO orientations). All results are in good agreement with available experiment. We contrast the austenite results to those from the often-assumed, but unstable B2. These high- and low-temperature structures and structural transformations provide much needed atomic-scale detail for transitions responsible for NiTi shape-memory effects.Comment: 4 pages, 4 figure