Thermopower of composites containing metallic cobalt nanoparticles embedded in the Al<Subscript>2</Subscript>O<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> dielectric matrix

The concentration and temperature dependences of the thermopower of composites containing Co nanoparticles embedded in the Al₂O _n dielectric matrix are investigated. Below the percolation threshold, i.e., in the tunneling conduction region, the absolute values of the thermopower of the composites under investigation are less than those above the percolation threshold. It is revealed that, in the tunneling conduction region, the slope of the temperature dependences of the thermopower changes at a temperature of ～205 K. This can indicate that the thermopower is sensitive to a change in the mechanism of conduction from the Mott law ln(σ) ∝ (1/T)^1/4 to a power relation that corresponds to the model of inelastic resonant tunneling through a chain of localized states in the dielectric matrix. The introduction of oxygen in the course of sputtering brings about a decrease in the absolute values of the thermopower; however, the character of variation in the concentration and temperature dependences of the thermopower remains unchanged.     

Isotropic positive magnetoresistance in Co-Al<Subscript>2</Subscript>O<Subscript>n</Subscript> nanocomposites

The magnetotransport properties of Co_x(Al₂O_n)_{100 ? x} nanocomposites were studied in a wide concentration range (34 ≤ x ≤ 74 at %). Negative tunnel magnetoresistance reaching 6.5% in a field of 10 kOe was established. In addition to the negative magnetoresistance, the Co_x(Al₂O_n)_{100 ? x} composites were found to exhibit positive magnetoresistance reaching 1.5% in fields of 10 kOe over the concentration range corresponding to the percolation threshold (54 ≤ x ≤ 67 at %). The positive magnetoresistance is assumed to be due to the simultaneous existence in the composite structure of clusters and individual nanoparticles characterized by different values of the magnetic anisotropy and due to the dipole-dipole interaction between the clusters and nearest neighbor particles.     

Kinetics of D,L–Lactide Polymerization Initiated with Zirconium Acetylacetonate

The kinetic of D,L-lactide polymerization in presence of biocompatible zirconium acetylacetonate initiator was studied by differential scanning calorimetry in isothermal mode at various temperatures and initiator concentrations. The enthalpy of D,L-lactide polymerization measured directly in DSC cell was found to be ΔH=−17.8±1.4 kJ mol⁻¹. Kinetic curves of D,L-lactide polymerization and propagation rate constants were determined for polymerization with zirconium acetylacetonate at concentrations of 250–1000 ppm and temperature of 160–220 °C. Using model or reversible polymerization the following kinetic and thermodynamic parameters were calculated: activation energy E_a=44.51±5.35 kJ mol⁻¹, preexponential constant lnA=15.47±1.38, entropy of polymerization ΔS=−25.14 J mol⁻¹ K⁻¹. The effect of reaction conditions on the molecular weight of poly(D,L-lactide) was shown.     

Measurement of Cross Sections for Inclusive Forward Charged Hadron Production in Carbon–Carbon Collisions at Beam Energy of 19.6 GeV per Nucleon

Physics of Atomic Nuclei - The invariant cross sections for forward charged-hadron production at zero angle in carbon–carbon collisions at a beam kinetic energy of 19.6 GeV per nucleon were...     

Nitraminomethylation of silylated polynitrogen heterocyclic compounds in nonaqueous solutions

Trimethylsilyloxy derivatives of 1,2,4-triazole, 3(5)-nitro-1,2,4-triazole, and tetrazole are inert toward 2-nitro-1-trimethylsilyloxy-2-azapropane, but they react with 1-chloro-2-nitro-2-azapropane to give the corresponding nitraminomethyl derivatives. Silyiated 1,2,4-triazole undergoes bis-nitraminomethylation to give a triazolium salt.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1666–1668, September, 1993.     

Electrical and magnetoresistive properties of nanogranular CoFeB-CaF2

The electrical properties and magnetoresistance of (Co₄₁Fe₃₉B₂₀) _x (CaF₂)_{100 ? x} composite are investigated. The principal mechanisms of electric charge transfer at low temperatures are determined. The effective density of localized states at the Fermi level and the average number of localized states between adjacent granules at various concentrations of the metal phase are estimated.     

A Gorizont neutron reflectometer—small-angle spectrometer based on the IN-06 pulsed neutron source

The Gorizont time-of-flight neutron reflectometer—small-angle spectrometer has been designed, manufactured, and assembled to operate with the IN-0 6 pulsed neutron source. The instrument has a vertical neutron scattering plane enabling research on liquid surfaces and interfaces. Model calculations of neutron spectra, beam profiles, and spectrometer resolutions have been performed via the Monte Carlo method. The spectrometer operates at wavelengths from 1.5 to 9 Å and ensures measurements in the momentum-transfer range of 0.003—1.5 Å^-1.     

Galactic cosmic ray intensity in the inner and outer heliosphere in the epoch of the solar cycle 24 minimum

The behavior of the observed and expected Galactic cosmic ray (GRC) intensity both near the Earth and in the outer heliosphere is considered. The hypothesis is discussed of the strong dependence of the GCR intensity in the interaction region of the solar and interstellar winds on the heliospheric magnetic field polarity in the epoch of a solar activity minimum.