Investigation of DNA denaturation in Peyrard-Bishop-Dauxois model by molecular dynamics method

The phase transition of $(PolyA/PolyT)_{100}$ duplex into the denaturated state is studied in the Peyrard-Bishop-Dauxois model by the method of direct molecular-dynamical modeling. The temperature dependencies of the total energy and heat capacity of the duplex are calculated. The approach applied can be used to calculate the statistical properties of the duplexes of any length and nucleotide composition.Comment: 6 pages, 4 figure

Review of scientific topics for Millimetron space observatory

This paper describes outstanding issues in astrophysics and cosmology that can be solved by astronomical observations in a broad spectral range from far infrared to millimeter wavelengths. The discussed problems related to the formation of stars and planets, galaxies and the interstellar medium, studies of black holes and the development of the cosmological model can be addressed by the planned space observatory Millimetron (the "Spectr-M" project) equipped with a cooled 10-m mirror. Millimetron can operate both as a single-dish telescope and as a part of a space-ground interferometer with very long baseline.Comment: The translation of the original article in Physics Uspekhi http://ufn.ru/ru/articles/2014/12/c

Pecularities of Hall effect in GaAs/{\delta}<Mn>/GaAs/In\timesGa1-\timesAs/GaAs (\times {\approx} 0.2) heterostructures with high Mn content

Transport properties of GaAs/{\delta}/GaAs/In\timesGa1-\timesAs/GaAs structures containing InxGa1-xAs (\times {\approx} 0.2) quantum well (QW) and Mn delta layer (DL) with relatively high, about one Mn monolayer (ML) content, are studied. In these structures DL is separated from QW by GaAs spacer with the thickness ds = 2-5 nm. All structures possess a dielectric character of conductivity and demonstrate a maximum in the resistance temperature dependence Rxx(T) at the temperature {\approx} 46K which is usually associated with the Curie temperature Tc of ferromagnetic (FM) transition in DL. However, it is found that the Hall effect concentration of holes pH in QW does not decrease below TC as one ordinary expects in similar systems. On the contrary, the dependence pH(T) experiences a minimum at T = 80-100 K depending on the spacer thickness, then increases at low temperatures more strongly than ds is smaller and reaches a giant value pH = (1-2)\cdot10^13 cm^(-2). Obtained results are interpreted in the terms of magnetic proximity effect of DL on QW, leading to induce spin polarization of the holes in QW. Strong structural and magnetic disorder in DL and QW, leading to the phase segregation in them is taken into consideration. The high pH value is explained as a result of compensation of the positive sign normal Hall effect component by the negative sign anomalous Hall effect component.Comment: 19 pages, 6 figure

Structural and transport properties of GaAs/delta<Mn>/GaAs/InxGa1-xAs/GaAs quantum wells

We report results of investigations of structural and transport properties of GaAs/Ga(1-x)In(x)As/GaAs quantum wells (QWs) having a 0.5-1.8 ML thick Mn layer, separated from the QW by a 3 nm thick spacer. The structure has hole mobility of about 2000 cm2/(V*s) being by several orders of magnitude higher than in known ferromagnetic two-dimensional structures. The analysis of the electro-physical properties of these systems is based on detailed study of their structure by means of high-resolution X-ray diffractometry and glancing-incidence reflection, which allow us to restore the depth profiles of structural characteristics of the QWs and thin Mn containing layers. These investigations show absence of Mn atoms inside the QWs. The quality of the structures was also characterized by photoluminescence spectra from the QWs. Transport properties reveal features inherent to ferromagnetic systems: a specific maximum in the temperature dependence of the resistance and the anomalous Hall effect (AHE) observed in samples with both "metallic" and activated types of conductivity up to ~100 K. AHE is most pronounced in the temperature range where the resistance maximum is observed, and decreases with decreasing temperature. The results are discussed in terms of interaction of 2D-holes and magnetic Mn ions in presence of large-scale potential fluctuations related to random distribution of Mn atoms. The AHE values are compared with calculations taking into account its "intrinsic" mechanism in ferromagnetic systems.Comment: 15 pages, 9 figure

Neutrino conversions in random magnetic fields and ν~e\tilde{\nu}_e from the Sun

The magnetic field in the convective zone of the Sun has a random small-scale component with the r.m.s. value substantially exceeding the strength of a regular large-scale field. For two Majorana neutrino flavors $\times$ two helicities in the presence of a neutrino transition magnetic moment and nonzero neutrino mixing we analyze the displacement of the allowed ($\Delta m^2- \sin^22\theta$)-parameter region reconciled for the SuperKamiokande(SK) and radiochemical (GALLEX, SAGE, Homestake) experiments in dependence on the r.m.s. magnetic field value $b$, or more precisely, on a value $\mu b$ assuming the transition magnetic moment $\mu = 10^{-11}\mu_B$. In contrast to RSFP in regular magnetic fields we find an effective production of electron antineutrinos in the Sun even for small neutrino mixing through cascade conversions $\nu_{eL}\to \nu_{\mu L}\to \tilde{\nu}_{eR}$, $\nu_{eL}\to \nu_{\mu R}\to \tilde{\nu}_{eR}$ in a random magnetic field that would be a signature of the Majorana nature of neutrino if $\tilde{\nu}_{eR}$ will be registered. Basing on the present SK bound on electron antineutrinos we have also found an excluded area in the same $\Delta m^2,~\sin^22\theta$-plane and revealed a strong sensitivity to the random magnetic field correlation length $L_0$.Comment: LaTex 36 pages including 14 PostScript figure

Simulations of M87 and Sgr A* imaging with the Millimetron Space Observatory on near-Earth orbits

High resolution imaging of supermassive black holes shadows is a direct way to verify the theory of general relativity at extreme gravity conditions. Very Long Baseline Interferometry (VLBI) observations at millimeter/sub-millimeter wavelengths can provide such angular resolution for supermassive black holes, located in Sgr A* and M87. Recent VLBI observations of M87 with the Event Horizon Telescope (EHT) has shown such capabilities. The maximum obtainable spatial resolution of EHT is limited by Earth diameter and atmospheric phase variations. In order to improve the image resolution longer baselines are required. Radioastron space mission has successfully demonstrated the capabilities of Space-Earth VLBI with baselines much larger than Earth diameter. Millimetron is a next space mission of the Russian Space Agency that will operate at millimeter wavelengths. Nominal orbit of the observatory will be located around Lagrangian L2 point of the Sun-Earth system. In order to optimize the VLBI mode, we consider a possible second stage of the mission that could use near-Earth high elliptical orbit (HEO). In this contribution a set of near-Earth orbits is used for the synthetic space-ground VLBI observations of Sgr A* and M87 in joint Millimetron and EHT configuration. General-relativistic magnetohydrodynamic models (GRMHD) for black hole environment of Sgr A* and M87 are used for static and dynamic imaging simulations at 230 GHz. A comparison preformed between ground and space-ground baselines demonstrates that joint observations with Millimetron and EHT significantly improve the image resolution and allow the EHT+Millimetron to obtain snapshot images of Sgr A* probing dynamics at fast timescales.Comment: 12 pages, 6 figure