Low energy universality and scaling of Van der Waals forces

At long distances interactions between neutral ground state atoms can be described by the Van der Waals potential V(r) =-C6/r^6-C8/r^8 - ... . In the ultra-cold regime atom-atom scattering is dominated by s-waves phase shifts given by an effective range expansion p cot d0 (p) = -1/a0 + r0 p^2/2 + ... in terms of the scattering length a0 and the effective range r0. We show that while for these potentials the scattering length cannot be predicted, the effective range is given by the universal low energy theorem r0 = A + B/a0+ C/a0^2 where A,B and C depend on the dispersion coefficients Cn and the reduced di-atom mass. We confront this formula to about a hundred determinations of r0 and a0 and show why the result is dominated by the leading dispersion coefficient C6. Universality and scaling extends much beyond naive dimensional analysis estimates.Comment: 4 pages, 3 figure

Efimov states in asymmetric systems

The conditions for occurrence of the Efimov effect is briefly described using hyperspherical coordinates. The strength of the effective hyperradial $\rho^{-2}$ potential appearing for two or three large scattering lengths is computed and discussed as function of two independent mass ratios of the three constituent particles. The effect is by far most pronounced for asymmetric systems with three very different masses. One Efimov state may by chance appear in nuclei. Many states could be present for systems with one electron and two neutral atoms or molecules. Estimates of the number of states and their sizes and energies are given.Comment: 7 pages, 3 figure

Complex research on the interaction of glass with space debris

This paper discusses the interactions of barriers with a spherical impactor and the character of possible deformation and fragmentation of barriers and impactors. The destruction of glass is considered as a process of destruction of fragile material without a part of plastic deformation characteristic of the deformation metals. To calculate the elastic-plastic flow a technique was used which was implemented on the tetrahedral cells and based on the combined use of the Wilkins method for calculating the interior points of the body and the Johnson method for calculating contact interactions. Methods for accelerating the flow of fine particles and the individual spherical particles have been developed. A series of experiments for usual glass and glass with coatings has been carried out

ПІДЛІТКОВИЙ АЛКОГОЛІЗМ: СОЦІАЛЬНІ ФАКТОРИ РИЗИКУ

The article analyzes the historical aspects of alcoholism; risk factors for alcohol dependence. An investigation statistics on this issue.У статті проаналізовано історичні аспекти проблеми алкоголізму, фактори ризику розвитку алкогольної залежності. Наведено статистичні дані дослідження з даної проблеми