Magnetic ordering and phase separation in high-temperature superconductors

The Monte Carlo method has been used to investigate the magnetic properties of doped copper-oxide high-temperature superconductors and phase separation in La₂CuO₄₊. The calculations were based on a model in accordance with which a hole induced by the dopant or excess oxygen changes the antiferromagnetic interaction between neighboring copper spins to a ferromagnetic interaction in a group of Cu–Cu bonds forming a nest of defect bonds. For copper oxides with impurities in which the nests are distributed in accordance with a random law and frozen the concentration of impurities at which an antiferromagnet—spin-glass phase transition occurs has been calculated. Good agreement with the experimental value is found. A mechanism that explains the phenomenon, of phase separation in La₂CuO₄₊ is found. It is shown that the phase separation is due to magnetic effects. Mobile nests formed with excess oxygen atoms exhibit a clear tendency to clustering forming regions with high oxygen concentration. The clustering is energetically advantageous, since it leads to a decrease of the frustration energy.V. A. Steklov Mathematics Institute, Russian Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 92, No. 2, pp. 344–352, August, 1992.     

Tamm states in zigzag carbon nanotubes: Analytic estimates in the Hückel approximation

The frontier molecular orbitals of [C _n ] _q hydrocarbons, fragments of (n, 0) nanotubes, were considered. Asymptotic estimates for two different sets of frontier molecular orbitals were obtained in the Hückel approximation. The problem was shown to be equivalent to the search for model polyene levels with alternating resonance parameters (β and β′ = γβ). The γ parameter was determined by the symmetry type of molecular orbitals and took on values from 0 to 2. The problem was reduced to an analysis of a regular linear polyene with a modified terminal atom by taking alternant symmetry into account. The states of the system were classified according to quasi-momentum Θ values, which could be complex. Solutions with a complex Θ value were localized at tube ends and could be interpreted as Tamm states. The criterion of the appearance of Tamm solutions for the problem under consideration was formulated, γ < 1 − 1/(q + 2). The conclusion was drawn that these states for an arbitrary [C _n ] _q fragment lied close to the Fermi level, and their energies were described by the asymptotic equation α ± βρ^{(q + 1)}. Delocalized levels were always situated farther from the Fermi level than Tamm states.     

Inhibited Polymerization of N,N,N-Trimethylammonioethyl Methacrylate Methyl Sulfate

The kinetic features of initiation of N,N,N-trimethylammonioethyl methacrylate methyl sulfate polymerization in the presence of manganese(III) bis(acetylacetonate) nitrate and p-nitrosoaniline were studied by the inhibited polymerization method. The kinetic parameters of initiation were calculated, and participation of the monomer in the initiation stage was established.     

Secondary structure of globules of copolymers consisting of amphiphilic and hydrophilic units: Effect of potential range

The relation of the coil-globule transition in macromolecules consisting of amphiphilic and hydrophilic monomer units to the radius of action of the interaction potential is investigated by the method of computer-assisted experiments. The internal structure of globules formed by such macromolecules is significantly dependent on the radius of action of the potential. In the case of the long-range potential, the globule is characterized by the blob structure, while in the case of the short-range potential, a quasi-helical structure forms. In this structure, the skeleton of a macromolecule forms a helical turn, and the direction of twisting may vary from one turn to another. The coil-globule transition in such macromolecules proceeds through formation of the necklace conformation from quasi-helical micelle beads. For sufficiently long macromolecules, the dimensions of such globules are linearly dependent on the degree of polymerization.     

Influence of formulation parameters on the mechanical failure energy of filled elastomers

Ways to increase, by optimizing the formulation, the energy of mechanical failure of filled 3D-crosslinked elastomers intended for application of a frost-resistant and waterproof layer onto road asphalt were examined.     

A mathematical model for the angular motion of large space structures with gyroscopic drive for an active compensation of elastic oscillations

Doklady Mathematics -     

Diffraction dissociation of neutrons into (pπ−) on protons in the momentum range 35 to 65 GeV/c

The diffraction dissociation reaction n + p → (pπ^?) + p was studied at the Serpukhov accelerator neutron beam in the momentum range 35–65 GeV/c in an electronics experiment. The differential cross sections of the reaction are analysed and presented in the five-dimensional phase space $\text{(p}{}_{\mathrm{<mtext>n</mtext>}}\text{, m}{}^1\text{, t,}\text{cos}\text{θ}{}^1\text{, φ}{}^1\text{)}$. The backward peak observed in the distribution over if cosθin GJ ¹ in the Gottfried-Jackson frame of if(pπ) is interpreted as a baryon-exchange effect. The angular distribution of the (pπ^?) system is compared with Deck-type models.     

Neutron-proton elastic scattering from 10 to 70 GeV/c

The neutron-proton elastic differential cross section has been measured for incident momenta between 10 and 70 GeV/c and for values of the momentum transfer squared between 0.1 and 2.8 (GeV/c)². The forward peak and the break at about ∣t∣ = 1 (GeV/c)² are very similar to corresponding pp data.