# Seminars

Regular seminars are held on Thursdays in the Kapitza Institute in Moscow and on Fridays at the scientific council of the Landau Institute in Chernogolovka.

Departments of the institute hold their own seminars; the topic are determined by the scientific orientation of the related department.

Seminars information is also sent via e-mail. If you want to receive seminar announcements, please subscribe.

## Zeros of Riemann’s Zeta Functions in the Line z=1/2+it_{0}

18 September in 11:30 at scientific council

Yu.N. Ovchinnikov

Investigation of Josephson effect, current flow in narrow superconducting stripes, dynamical states in superconductors lead to the necessity to deal with an important phenomenon: phase slip events. The study of the distribution of zeros for Riemann's Zeta function also requires an analisis of the same phenomenon.

It was found that, in addition to trivial zeros in points ($ z = -2N, N = 1, 2, ... $, natural numbers), the Riemann’s zeta function $\zeta(z)$ has zeros only on the line {$z = 1/2 + i t_0$, $t_0$ is real}. All zeros are numerated, and for each number, N, the positions of the non-overlap intervals with one zero inside are found. The simple equation for the determination of centers of intervals is obtained. The analytical function $\eta(z)$), leading to the possibility fix the zeros of the zeta function $\zeta(z)$, was estimated. To perform the analysis, the well-known phenomenon, phase-slip events, is used. This phenomenon is the key ingredient for the investigation of dynamical processes in solid-state physics, for example, if we are trying to solve the TDGLE (time-dependent Ginzburg-Landau equation).

J. Supercond. Novel Magn., 32(11), 3363-3368 (2019)

It was found that, in addition to trivial zeros in points ($ z = -2N, N = 1, 2, ... $, natural numbers), the Riemann’s zeta function $\zeta(z)$ has zeros only on the line {$z = 1/2 + i t_0$, $t_0$ is real}. All zeros are numerated, and for each number, N, the positions of the non-overlap intervals with one zero inside are found. The simple equation for the determination of centers of intervals is obtained. The analytical function $\eta(z)$), leading to the possibility fix the zeros of the zeta function $\zeta(z)$, was estimated. To perform the analysis, the well-known phenomenon, phase-slip events, is used. This phenomenon is the key ingredient for the investigation of dynamical processes in solid-state physics, for example, if we are trying to solve the TDGLE (time-dependent Ginzburg-Landau equation).

J. Supercond. Novel Magn., 32(11), 3363-3368 (2019)

## Coalescence of isotropic droplets in overheated free standing smectic films

2 October in 11:30 at scientific council

Elena S. Pikina, Boris I. Ostrovskii and Sergey A. Pikin

A theoretical study of the interaction and coalescence of isotropic droplets in overheated free-standing
smectic films (FSSF) is presented. Experimentally it is clear that merging of such droplets is extremely
rare. On the basis of the general thermodynamic approach to the stability of FSSF, we determined the
energy gains and losses involved in the coalescence process. The main contributions to the critical work
of drop coalescence are due to the gain related to the decrease of the surface energy of the merging
drops, which is opposed by the entropic repulsions of elementary steps at the smectic interface
between them. To quantify the evolution of the merging drops, we use a simple geometrical model in
which the volume of the smectic material, rearranged in the process of coalescence, is described by an
asymmetrical pyramid at the intersection of two drops. In this way, the critical work for drop
coalescence and the corresponding energy barrier have been calculated. The probability of the thermal
activation of the coalescence process was found to be negligibly small, indicating that droplet merging
can be initiated by only an external stimulus. The dynamics of drop merging was calculated by equating the capillary force driving the coalescence, and the Stokes viscous force slowing it down. For the latter, an approximation of moving oblate spheroids permitting exact calculations was used. The time evolution of the height of the neck between the coalescing drops and that of their lateral size are in good agreement with experiments.