Vol 62, No 5 (2017)

The electric resistance of contacts between superconducting tape conductors on the basis of the GdBa₂Cu₃O_{7 − x} compound (2G) is investigated in an external magnetic field up to 5 T at T = 77 K. The mechanical tensile strength of both the initial conductors and the contacts is measured.

For the variational method of the thermodynamic perturbation theory with the square well reference system to which the semianalytical way of solving the mean spherical approximation is applied, a new way of minimizing the free energy is proposed. The approach is applied to liquid sodium and potassium, the effective pair interaction in which is described within the framework of the pseudopotential theory. For each of the metals under study, the global minimum of the free energy was found as a function of two independent variables (the hard core diameter and the mean atomic volume). In this minimum, a better agreement between the calculation results and the experimental data is obtained than when using the hard sphere reference system.

A theoretical description of the plastic deformation of nanostructured and polycrystalline metals through paired nanotwinning on grain boundaries has been proposed. Within the micromechanical approach developed, deformation nanotwins are formed as a result of successive plastic shears. The energy characteristics and critical stresses of paired twin nucleation in titanium are calculated.

A simple mechanical model illustrates that even very weak vibration or shock impacts can cause a significant displacement of bodies in contact by dry friction. The model is studied using the concepts of effective friction coefficients under vibration and elements of the vibrational displacement theory. The results are compared with those of earlier and new experiments. Their application to the theory of man-made earthquakes and the problem of increasing oil recovery from petroliferous layers through vibration effects is discussed.

The integrability of certain classes of dynamic systems arising in the dynamics of a multidimensional solid and in the dynamics of a point on a tangent bundle of a multidimensional sphere is shown. In this case, the force fields under consideration have the so-called variable dissipation with zero average and generalize previously considered fields.

By the example of a brake pad, a typical error is illustrated, i.e., the fact that the initial conditions should be reconsidered upon finding that there is no solution of the static problem in a certain region of parameters (incorrect in the sense of Hadamard). For example, it turns out that the conditions of disk rotation in the positive direction cannot be implemented in the domain of parameters leading to a “paradox.” In this region, the “brake-pad” mechanism is transformed into the “wedge stopper” mechanism.

The goal of this paper is to construct a 3D model of the surface of a cometary nucleus that allows the irradiance nonuniformity and temperature distribution to be investigated. This is very important, because in zones with a maximum surface temperature chemical and physical transformations of material are possible in subsurface layers. We propose a 3D model of the geometry and dynamics of a cometary nucleus that takes into account the diurnal rotation and orientation of the rotation axis relative to the Sun to simulate the irradiance and temperature distribution for both the surface of the nucleus as a whole and its individual regions.

Actinometric data of World Radiation Data Center and NASA POWER were used to get daily clearness index frequencies for Russia. The results obtained provide the opportunity to estimate more accurately the output of various types of solar power plants. Frequencies determined using the data sources indicated correlate well and differ from universal dependences that were recommended earlier for the entire globe.