Conductivity of materials made of aluminum nitride and silicon nitride mixtures

To establish the possible mechanism for conductivity in aluminum nitride a study was made of the electric conductivity of pure AlN and its mixtures with silicon nitride at different temperatures and partial pressures of nitrogen in the gas phase. The thermoelectromotive force was also measured. The experiments used polycrystalline samples of cylindrical shape 18 mm in diameter made of powders by hot pressing in graphite press molds at a temperature of 1973-2273 K and pressure 1,470,000 n/sqm. The items obtained by this method had porosity not over 5%. After pressing, the samples were machined to remove carbon from the surface, and were annealed in a stream of dry ammonia for 10 h at a temperature of 1273-1373 K. Electric conductivity was measured according to the bridge scheme on an alternating current of frequency 10 kHz. In order to guarantee close contact of the platinum electrodes with the surface of the samples, a thin layer of platinum was sprayed on them. Experiments were conducted in the temperature interval 1273-1573 K with a half hour delay at each assigned temperature with heating and cooling

Gauged D=7 Supergravity on the S**1/Z_2 Orbifold

We construct the most general couplings of a bulk seven-dimensional Yang-Mills-Einstein N=2 supergravity with a boundary six-dimensional chiral N=(0,1) theory of vectors and charged hypermultiplets. The boundary consists of two brane worlds sitting at the fixed points of an S^1/Z_2 compactification of the seven-dimensional bulk supergravity. The resulting 6D massless spectrum surviving the orbifold projection is anomalous. By introducing boundary fields at the orbifold fixed points, we show that all anomalies are cancelled by a Green-Schwarz mechanism. In addition, all couplings of the boundary fields to the bulk are completely specified by supersymmetry. We emphasize that there is no bulk Chern-Simons term to cancel the anomalies. The latter is traded for a Green-Schwarz term which emerges in the boundary theory after a duality transformation implemented to construct the bulk supergravity.Comment: LaTeX, 42 pages; typos corrected, reference added, version to appear in Phys. Rev.

Superconductivity in Ropes of Single-Walled Carbon Nanotubes

We report measurements on ropes of Single Walled Carbon Nanotubes (SWNT) in low-resistance contact to non-superconducting (normal) metallic pads, at low voltage and at temperatures down to 70 mK. In one sample, we find a two order of magnitude resistance drop below 0.55 K, which is destroyed by a magnetic field of the order of 1T, or by a d.c. current greater than 2.5 microA. These features strongly suggest the existence of superconductivity in ropes of SWNT.Comment: Accepted for publication in Phys. Rev. Let

Solid solution decomposition and Guinier-Preston zone formation in Al-Cu alloys: A kinetic theory with anisotropic interactions

Using methods of statistical kinetic theory parametrized with first-principles interatomic interactions that include chemical and strain contributions, we investigated the kinetics of decomposition and microstructure formation in Al-Cu alloys as a function of temperature and alloy concentration. We show that the decomposition of the solid solution forming platelets of copper, known as Guinier-Preston (GP) zones, includes several stages and that the transition from GP1 to GP2 zones is determined mainly by kinetic factors. With increasing temperature, the model predicts a gradual transition from platelet-like precipitates to equiaxial ones and at intermediate temperatures both precipitate morphologies may coexist.Comment: 9 pages, 8 figure

Sub-threshold resonances in few-neutron systems

Three- and four-neutron systems are studied within the framework of the hyperspherical approach with a local S-wave nn-potential. Possible bound and resonant states of these systems are sought as zeros of three- and four-body Jost functions in the complex momentum plane. It is found that zeros closest to the origin correspond to sub-threshold (nnn) (1/2-) and (nnnn) (0+) resonant states. The positions of these zeros turned out to be sensitive to the choice of the $nn$--potential. For the Malfliet- Tjon potential they are E(nnn)=-4.9-i6.9 (MeV) and E(nnnn)=-2.6-i9.0 (MeV). Movement of the zeros with an artificial increase of the potential strength also shows an extreme sensitivity to the choice of potential. Thus, to generate ^3n and ^4n bound states, the Yukawa potential needs to be multiplied by 2.67 and 2.32 respectively, while for the Malfliet-Tjon potential the required multiplicative factors are 4.04 and 3.59.Comment: Latex, 22 pages, no PS-figures, submitted to J.Phys.

Conductivity and Atomic Structure of Isolated Multiwalled Carbon Nanotubes

We report associated high resolution transmission electron microscopy (HRTEM) and transport measurements on a series of isolated multiwalled carbon nanotubes. HRTEM observations, by revealing relevant structural features of the tubes, shed some light on the variety of observed transport behaviors, from semiconducting to quasi-metallic type. Non Ohmic behavior is observed for certain samples which exhibit "bamboo like" structural defects. The resistance of the most conducting sample, measured down to 20 mK, exhibits a pronounced maximum at 0.6 K and strong positive magnetoresistance.Comment: 4 pages, 4 eps figure

ETEKOS experimental ecological system

The problem of changes in the ecology resulting, for example, in increases in water temperature because of discharges from large thermal power plants is considered. An experiment creating a model of such an ecological system is described

Orthodox Communities and Partisan Movement in Kuzbass in 1919

The results of the analysis of the tragic stage in the history of the Russian Orthodox Church during the civil war in the Kemerovo region are presented. Based on materials from periodicals and archives, as well as on the research of secular and church historians, the partisan pogroms of 1919 are considered as events that had a negative impact on the life of the church as a social institution. It is noted that pogroms and murders of believers and clergy took place everywhere in the territory of Kuzbass. It was revealed on the basis of documentary evidence that the main target of the attack of the red partisans was the clergy. Punitive operations continued throughout 1919, but the peak of the pogroms is associated with the activities of the united detachment under the command of G. F. Rogov and I. P. Novoselov in December in the Kuznetsk district. It is shown that the Russian Orthodox Church was seized by an institutional crisis, the parish life of the counties was upset, the number of clergy decreased, and some of the clergy left the region