Two-gap superconductivity in MgB2_{2}: clean or dirty?

A large number of experimental facts and theoretical arguments favor a two-gap model for superconductivity in MgB$_{2}$. However, this model predicts strong suppression of the critical temperature by interband impurity scattering and, presumably, a strong correlation between the critical temperature and the residual resistivity. No such correlation has been observed. We argue that this fact can be understood if the band disparity of the electronic structure is taken into account, not only in the superconducting state, but also in normal transport

Effect of strain aging on physical and mechanical properties of austenitic chromium-nickel steel

The processes occurring in chromium-nickel steel 08Kh18N10T due to strain aging are studied. The tensile mechanical properties are determined. Relaxation tests and metallographic and x-ray diffraction analyses are performed. The internal energy state of the steel is estimated with the help of acoustic emissionyesBelgorod State Universit

Mechanical properties of mass-produced nanostructured titanium

The structure and mechanical properties of nanostructured titanium VT1-0 derived using an ingenious method which combines helical and longitudinal rolling are studied in comparison with the properties of commercial titanium alloys VT6 and VT16, as well as VT1-0 in a coarse-grained stateye

Magnetic Field Effects on the Far-Infrared Absorption in Mn_12-acetate

We report the far-infrared spectra of the molecular nanomagnet Mn_12-acetate (Mn_12) as a function of temperature (5-300 K) and magnetic field (0-17 T). The large number of observed vibrational modes is related to the low symmetry of the molecule, and they are grouped together in clusters. Analysis of the mode character based on molecular dynamics simulations and model compound studies shows that all vibrations are complex; motion from a majority of atoms in the molecule contribute to most modes. Three features involving intramolecular vibrations of the Mn_12 molecule centered at 284, 306 and 409 cm-1 show changes with applied magnetic field. The structure near 284 cm$^{-1}$ displays the largest deviation with field and is mainly intensity related. A comparison between the temperature dependent absorption difference spectra, the gradual low-temperature cluster framework distortion as assessed by neutron diffraction data, and field dependent absorption difference spectra suggests that this mode may involve Mn motion in the crown.Comment: 5 pages, 4 figures, PRB accepte

Infrared optical properties of Pr2CuO4

The ab-plane reflectance of a Pr2CuO4 single crystal has been measured over a wide frequency range at a variety of temperatures, and the optical properties determined from a Kramers-Kronig analysis. Above ~ 250 K, the low frequency conductivity increases quickly with temperature; the resistivity follows the form e^(E_a/k_BT), where E_a ~ 0.17 eV is much less than the inferred optical gap of ~ 1.2 eV. Transport measurements show that at low temperature the resistivity deviates from activated behavior and follows the form e^[(T_0/T)^1/4], indicating that the dc transport in this material is due to variable-range hopping between localized states in the gap. The four infrared-active Eu modes dominate the infrared optical properties. Below ~ 200 K, a striking new feature appears near the low-frequency Eu mode, and there is additional new fine structure at high frequency. A normal coordinate analysis has been performed and the detailed nature of the zone-center vibrations determined. Only the low-frequency Eu mode has a significant Pr-Cu interaction. Several possible mechanisms related to the antiferromagnetism in this material are proposed to explain the sudden appearance of this and other new spectral features at low temperature.Comment: 11 pages, 7 embedded EPS figures, REVTeX

Enhancement of the upper critical field by nonmagnetic impurities in dirty two-gap superconductors

Quasiclassic Uzadel equations for two-band superconductors in the dirty limit with the account of both intraband and interband scattering by nonmagnetic impurities are derived for any anisotropic Fermi surface. From these equations the Ginzburg-Landau equations, and the critical temperature $T_c$ are obtained. An equation for the upper critical field, which determines both the temperature dependence of $H_{c2}(T)$ and the orientational dependence of $H_{c2}(\theta)$ as a function of the angle $\theta$ between ${\bf H}$ and the c-axis is obtained. It is shown that the shape of the $H_{c2}(T)$ curve essentially depends on the ratio of the intraband electron diffusivities $D_1$ and $D_1$, and can be very different from the standard one-gap dirty limit theory. In particular, the value $H_{c2}(0)$ can considerably exceed $0.7T_cdH_{c2}/dT_c$, which can have important consequences for applications of $MgB_2$. A scaling relation is proposed which enables one to obtain the angular dependence of $H_{c2}(\theta)$ from the equation for $H_{c2}$ at ${\bf H}\| c$. It is shown that, depending on the relation between $D_1$ and $D_2$, the ratio of the upper critical field $H_{c2}^\|/H_{c2}^\perp$ for ${\bf H}\| ab$ and ${\bf H}\perp ab$ can both increase and decrease as the temperature decreases. Implications of the obtained results for $MgB_2$ are discussed

Solar flare-related eruptions followed by long-lasting occultation of the emission in the He II 304 A line and in microwaves

Plasma with a temperature close to the chromospheric one is ejected in solar eruptions. Such plasma can occult some part of emission of compact sources in active regions as well as quiet solar areas. Absorption phenomena can be observed in the microwave range as the so-called 'negative bursts' and also in the He II 304 A line. The paper considers three eruptive events associated with rather powerful flares. Parameters of absorbing material of an eruption are estimated from multi-frequency records of a 'negative burst' in one event. 'Destruction' of an eruptive filament and its dispersion like a cloud over a huge area observed as a giant depression of the 304 A line emission has been revealed in a few events. One such event out of three ones known to us is considered in this paper. Another event is a possibility.Comment: 23 pages, 8 figures, submitted for publication in Astronomy Report

The Tc amplification by quantum interference effects in diborides

The model of two (s and p) channel superconductivity known to be necessary to explain the superconductivity in MgB2 has been applied to the Al1-xMgxB2 diborides by tuning x from MgB2 to AlMgB4. The evolution of the interband coupling parameter (probing the strength of the interchannel pairing due to quantum interference effects) and the two gaps in the s and p channel as a function of x have been calculated. While in MgB2 the quantum interference effects give an amplification of Tc by a factor of 1.5 in comparison with the dominant intra s band single channel pairing, in AlMgB4 the amplification is about 100, in comparison with the dominant intra p band single channel pairing.Comment: 7 pages, 6 figure

Особенности ДНК-идентификации потожировых следов на кожных покровах трупов

The paper presents the results of a pilot molecular genetic study of sweat and oil residue left by the fingertips and hand palms of male volunteers (donors) on various regions of the skin surface of dead bodies (recipients) of both sexes. In cases of contact with female recipients donor-specific allele combinations were obtained for only 11.6% of autosomal loci and 12.9% of Y-chromosomal loci. Donor-specific traits were absent in 68.4% of autosomal loci and 87.1% of Y-chromosomal loci. In cases of contact with male recipients the full genetic profile was obtained for 18.6% of autosomal loci, and 64.2% of loci showed a lack of donor-specific alleles. Meanwhile, allelic combinations specific to female recipients were encountered in 40.5% of autosomal loci, and to male recipients – in 34.2% of autosomal loci. Results demonstrate poor adhesion of sweat and oil compounds from donors’ hands to the corpses’ skin, probably due to significant temperature differences between contact surfaces. Представлены результаты экспериментального молекулярно-генетического исследования следов потожирового вещества, оставленного подушечками пальцев рук и ладонями добровольцев (доноров) мужского пола на кожных покровах различных частей тел трупов (реципиентов) обоего пола. Аллельные комбинации, свойственные донорам, при контакте с реципиентами женского пола получены только для 11,6 % аутосомных локусов и 12,9 % локусов Y-хромосомы. В 68,4 % аутосомных и 87,1 % локусов Y-хромосомы отсутствовали генетические признаки, присущие донорам. В случае контакта доноров с реципиентами мужского пола полный генетический профиль получен для 18,6 % аутосомных локусов, а в 64,2 % отсутствовали свойственные донорам аллели. При этом аллельные комбинации, свойственные реципиентам женского пола, встречались в 40,5 %, а реципиентам мужского пола – в 34,2 % аутосомных локусов. Полученные результаты могут свидетельствовать о слабой адгезии потожирового вещества доноров на кожных покровах трупов, вероятно, из-за высокой разницы температур контактирующих поверхностей

Resetting single nanoparticle structural phase with nanosecond pulses

The authors demonstrate that transitions from high temperature phases to low temperature phases in a gallium nanoparticle can be stimulated by nanosecond optical pulses, and explain how this phenomenon could be used in a single nanoparticle all-optical memory