The optimal filters for the construction of the ensemble pulsar time

The algorithm of the ensemble pulsar time based on the optimal Wiener filtration method has been constructed. This algorithm allows the separation of the contributions to the post-fit pulsar timing residuals of the atomic clock and pulsar itself. Filters were designed with the use of the cross- and autocovariance functions of the timing residuals. The method has been applied to the timing data of millisecond pulsars PSR B1855+09 and PSR B1937+21 and allowed the filtering out of the atomic scale component from the pulsar data. Direct comparison of the terrestrial time TT(BIPM06) and the ensemble pulsar time PT$_{\rm ens}$ revealed that fractional instability of TT(BIPM06)--PT$_{\rm ens}$ is equal to $\sigma_z=(0.8\pm 1.9)\cdot 10^{-15}$. Based on the $\sigma_z$ statistics of TT(BIPM06)--PT$_{\rm ens}$ a new limit of the energy density of the gravitational wave background was calculated to be equal to $\Omega_g h^2 \sim 3\cdot 10^{-9}$.Comment: 6 pages, 5 figure

On The Existence of Planets Around the Pulsar PSR B0329+54

Results of timing measurements of the pulsar PSR B0329+54 obtained in 1968--2012 using the Big Scanning Antenna of the Pushchino Radio Astronomy Observatory (at 102 and 111 MHz), the DSS 13 and DSS 14 telescopes of the Jet Propulsion Laboratory (2388 MHz), and the 64 m telescope of the Kalyazin Radio Astronomy Observatory (610 MHz) are presented. The astrometric and rotational parameters of the pulsar are derived at a new epoch. Periodic variations in the barycentric timing residuals have been found, which can be explained by the presence of a planet orbiting the pulsar, with an orbital period $P_{1}$ = 27.8 yr, mass \textit{$m_{c}$}sin\textit{i} = 2$M_{\oplus}$, and orbital semi-major axis $a$ = 10.26 AU. The results of this study do not confirm existence of a proposed second planet with orbital period $P_{2}$ = 3 yr.Comment: 11 pages, 3 figures, to be published in Astronomy Reports, Nov. 201

On the nuclear symmetry energy and the neutron skin in neutron-rich nuclei

The symmetry energy for nuclear matter and its relation to the neutron skin in finite nuclei is discussed. The symmetry energy as a function of density obtained in a self-consistent Green function approach is presented and compared to the results of other recent theoretical approaches. A partial explanation of the linear relation between the symmetry energy and the neutron skin is proposed. The potential of several experimental methods to extract the neutron skin is examined.Comment: to appear in Phys. Rev.

E1 transitions between spin-dipole and Gamow-Teller giant resonances

The branching ratios for E1 transitions between the spin-dipole (SD) and Gamow-Teller (GT) giant resonances in $^{90}$Nb and $^{208}$Pb are evaluated. Assuming the main GT-state has the wave function close to that for the "ideal" GT-state, we reduced the problem to calculate the SD and GT strength functions. These strength functions are evaluated within an extended continuum-RPA approach.Comment: 8 pages, submitted to Phys. Rev.

On stochastic switching of bistable resonant-tunneling structures via nucleation

We estimate the critical size of the initial nucleus of the low current state in a bistable resonant tunneling structure which is needed for this nucleus to develop into a lateral switching front. Using the results obtained for deterministic switching fronts, we argue that for realistic structural parameters the critical nucleus has macroscopic dimensions and therefore is too large to be created by stochastic electron noise.Comment: the extended version of the Comment on "Lifetime of metastable states in resonant-tunneling structures" to appear in Phys. Rev.

Theoretical studies of the kinetics of mechanical unfolding of cross-linked polymer chains and their implications for single molecule pulling experiments

We have used kinetic Monte Carlo simulations to study the kinetics of unfolding of cross-linked polymer chains under mechanical loading. As the ends of a chain are pulled apart, the force transmitted by each crosslink increases until it ruptures. The stochastic crosslink rupture process is assumed to be governed by first order kinetics with a rate that depends exponentially on the transmitted force. We have performed random searches to identify optimal crosslink configurations whose unfolding requires a large applied force (measure of strength) and/or large dissipated energy (measure of toughness). We found that such optimal chains always involve cross-links arranged to form parallel strands. The location of those optimal strands generally depends on the loading rate. Optimal chains with a small number of cross-links were found to be almost as strong and tough as optimal chains with a large number of cross-links. Furthermore, optimality of chains with a small number of cross-links can be easily destroyed by adding cross-links at random. The present findings are relevant for the interpretation of single molecule force probe spectroscopy studies of the mechanical unfolding of load-bearing proteins, whose native topology often involves parallel strand arrangements similar to the optimal configurations identified in the study

Nuclear Structure Aspects of the Neutrinoless Double Beta Decay

In this article, we analyze some nuclear structure aspects of the neutrinoless double beta decay nuclear matrix elements (NME), in the framework of the Interacting Shell Model. We give results for the decays of 48Ca, 76Ge, 82Se, 124Sn, 128Te, 130Te, and 136Xe, using improved effective interactions and valence spaces. We examine the dependence of the NME's on the effective interaction and the valence space, and analyze the effects of the short range correlations and the finite size of the nucleon. Finally we study the influence of the deformation on the values of the NME's.Comment: To appear in EJP-

Lateral current density fronts in asymmetric double-barrier resonant-tunneling structures

We present a theoretical analysis and numerical simulations of lateral current density fronts in bistable resonant-tunneling diodes with Z-shaped current-voltage characteristics. The bistability is due to the charge accumulation in the quantum well of the double-barrier structure. We focus on asymmetric structures in the regime of sequential incoherent tunneling and study the dependence of the bistability range, the front velocity and the front width on the structure parameters. We propose a sectional design of a structure that is suitable for experimental observation of front propagation and discuss potential problems of such measurements in view of our theoretical findings. We point out the possibility to use sectional resonant-tunneling structures as controllable three-terminal switches.Comment: to appear in J.Appl.Phy