Two-particle-shift Monte-Carlo method for simulating the composition of solvated complexes

We propose a modified Monte-Carlo method for studying the solvation of ions in a mixed solvent. We include two-particle shifts in the algorithm along with oneparticle shifts. Some of the two-particle shifts end with exchange of adjacent molecules. We have carried out calculations for the system Na⁺-N₁·H₂O-N₂·MeOH for N₁=N₂=6 and N₁=N₂=9. We have concluded that there is preferential hydration of the Na⁺ ion in an equimolar water-methanol mixture.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 2, pp. 218–222, March–April 1988.     

Ultrafast changes in the optical properties of a titanium surface and femtosecond laser writing of one-dimensional quasi-periodic nanogratings of its relief

One-dimensional quasi-periodic nanogratings with spacings in the range from 160 to 600 nm are written on a dry or wet titanium surface exposed to linearly polarized femtosecond IR and UV laser pulses with different surface energy densities. The topological properties of the obtained surface nanostructures are studied by scanning electron microscopy. Despite the observation of many harmonics of the one-dimensional surface relief in its Fourier spectra, a weak decreasing dependence of the first-harmonic wavenumber (nanograting spacing) on the laser fluence is found. Studies of the instantaneous optical characteristics of the material during laser irradiation by measuring the reflection of laser pump pulses and their simulation based on the Drude model taking into account the dominant interband absorption allowed us to estimate the length of the excited surface electromagnetic (plasmon-polariton) wave for different excitation conditions. This wavelength is quantitatively consistent with the corresponding nanograting spacings of the first harmonic of the relief of the dry and wet titanium surfaces. It is shown that the dependence of the first-harmonic nanograting spacing on the laser fluence is determined by a change in the instantaneous optical characteristics of the material and the saturation of the interband absorption along with the increasing role of intraband transitions. Three new methods are proposed for writing separate subwave surface nanogratings or their sets by femtosecond laser pulses using the near-threshold nanostructuring, the forced adjustment of the optical characteristics of the material or selecting the spectral range of laser radiation, and also by selecting an adjacent dielectric.     

Giant spin-Hall effect induced by the Zeeman interaction in graphene

We propose a new approach to generate and detect spin currents in graphene, based on a large spin-Hall response arising near the neutrality point in the presence of an external magnetic field. Spin currents result from the imbalance of the Hall resistivity for the spin-up and spin-down carriers induced by the Zeeman interaction, and do not involve a spin-orbit interaction. Large values of the spin-Hall response achievable in moderate magnetic fields produced by on-chip sources, and up to room temperature, make the effect viable for spintronics applications.     

Diffusion coefficients of vacancies and interstitials along tilt grain boundaries in molybdenum

The diffusion coefficients of vacancies and interstitials along symmetrical tilt grain boundaries in molybdenum have been calculated using the molecular dynamics method. The migration energies of defects have been obtained. The activation energy and coefficients of grain boundary self-diffusion have been deter-mined. A comparison of the obtained results with the studies of other authors indicates that boundaries formed between particles in the powder in sintering experiments have a higher diffusion activity as compared to stable grain boundaries in polycrystals.     

Formation of a 4c tetraquark in J/ψ-meson pair production at LHC

Cross sections for J??-meson pair production in proton-proton interaction at the c.m. collision energy of $\sqrt s = 7$ TeV were theoretically predicted under conditions of various kinematical cuts. The possible contribution to this process from the decays of 4c tetraquarks, new hypothetic particles consisting of two valence c quarks and two valence $\bar c$ antiquarks, was studied. It is shown that at least one such state (tensor 4c tetraquark) can in principle be observed experimentally under conditions of the LNCb experiment.     

Fabrication of graphene nanostructures by probe nanoablation

We present the results of the study of graphene nanoablation under mechanical stress of an ultrasharp (the rounding radius is ～2 nm) tip of a scanning probe microscope (SPM)). It was found that the SPM probe contact with graphene results in average removal of 7 · 10^?3?5 · 10^?2 nm of film per scan, i.e., only a few carbon atoms or clusters, in the impact area. The capability of this precision nanoablation process was shown in developing graphene nanoislands and nanoribbons ～1 µm long and ～10 nm wide.