arXiv subjects
Publications and source records attributed to Mikhail Pekker.
In this paper, the tunneling mechanism of cavitation in liquid helium for 3He and 4He is considered on the basis of the Schr\"odinger-like equation. It is assumed that the pairwise interactions of helium atoms are determined by the Lennard-Jones potential. The kinetics of nucleation and the mechanism that limits the growth of cavitation bubbles in liquid helium are considered, taking into account their growth in a negative pressure field.
In this paper, a simple theoretical model of excitation of action potentials of multiple motor pools by stimulating current pulses over the lumbosacral regions of the spinal cord is presented. The present model is consistent with known experimental data.
This paper considers the structure and physical processes in the transition region at the border between the regions of false and physical vacuums in a cavitation model of the inflationary stage of the Big Bang. It is shown that in the process of the formation of physical vacuum bubbles in a false vacuum, conditions for the formation of a narrow layer filled with matter arise in the transition region, which is the precursor to bridges in the observed large-scale cellular structure of the universe.
In this paper, we propose a model for the initial stage of the development of the Universe, analogous to cavitation in a liquid in a negative pressure field. It is assumed that at the stage of inflation, multiple breaks of the metric occur with the formation of areas of physical vacuum in which the generation of matter occurs. The proposed model explains the large-scale isotropy of the Universe without ultrafast inflationary expansion and the emergence of a large-scale cellular (cluster) structure, as a result of the development of cavitation ruptures of a false vacuum. It is shown that the cavitation model can be considered on par with (or as an alternative to) the generally accepted inflationary multiverse model of the Big Bang.
In this paper, on the basis of the model Schrödinger equation, we consider the tunneling mechanism of cavitation in liquid helium and obtain threshold values of negative pressure as a function of temperature for 3He and 4He. The results of calculating the surface tension coefficients for flat and curved interfaces, obtained in the approximation of the Lenard-Jones interaction potential, are presented. It is shown that the temperature dependence of the critical pressure at which cavitation begins is stepwise in nature. The obtained critical pressure values are in satisfactory agreement with the experimental data.
This paper discusses possible mechanisms for the selective effect of weakly ionized non-equilibrium plasma and currents in electrolyte on healthy and cancerous cells in physiological saline in a Petri dish. The interaction with the plasma source leads to a change in osmotic pressure, which affects the electro-mechanical properties of cell membranes in healthy and cancerous cells in different ways. The currents arising in the electrolyte charge the membranes of healthy and cancerous cells to a different potential difference due to the different values of the membranes' dielectric constant. We hypothesized that the dielectric permeability of cancer cell membranes is lower than that of healthy cells, as is the capacity of a unit of the membrane surface, and therefore, the additional potential difference acquired by the membrane through charging with currents induced in the intercellular electrolyte is greater in cancer cells. This can lead to electroporation of cancer cell membranes, resulting in their apoptosis, but does not effect healthy cells.
In this paper, using an unified approach, estimates are given of the magnitude of the surface tension of water for planar and curved interfaces in the pairwase interaction approximation based on the Lennard-Jones potential. It is shown that the surface tensions of a bubble and droplet have qualitatively different dependences on the curvature of the surface: for the bubble, as the radius of the surface's curvature decreases, the surface tension decreases, whereas it increases on the droplet. The corresponding values of the Tolman corrections are also determined. In addition, it is shown that the dependence of the surface tension on the surface's curvature is important for evaluating the critical negative pressure for the onset of cavitation.
Computationally efficient classification system architecture is proposed. It utilizes fast tensor-vector multiplication algorithm to apply linear operators upon input signals . The approach is applicable to wide variety of recognition system architectures ranging from single stage matched filter bank classifiers to complex neural networks with unlimited number of hidden layers.
A new method of numerical solution for partial differential equations is proposed. The method is based on a fast matrix multiplication algorithm. Two-dimensional Poison equation is used for comparison of the proposed method with conventional numerical methods. It was shown that the new method allows for linear growth in the number of elementary addition and multiplication operations with the growth of grid size, as contrasted with quadratic growth necessitated by the standard numerical methods. The proposed method can be easily generalized for any differential equations.
We consider the development of pre-breakdown cavitation nanopores appearing in the dielectric fluid under the influence of the electrostrictive stresses in the inhomogeneous pulsed electric field. It is shown that three characteristic regions can be distinguished near the needle electrode. In the first region, where the electric field gradient is greatest, the cavitation nanopores, occurring during the voltage nanosecond pulse, may grow to the size at which an electron accelerated by the field inside the pores can acquire enough energy for excitation and ionization of the liquid on the opposite pore wall, i.e., the breakdown conditions are satisfied. In the second region, the negative pressure caused by the electrostriction is large enough for the cavitation initiation (which can be registered by optical methods), but, during the voltage pulse, the pores do not reach the size at which the potential difference across their borders becomes sufficient for ionization or excitation of water molecules. And, in the third, the development of cavitation is impossible, due to an insufficient level of the negative pressure: in this area, the spontaneously occurring micropores do not grow and collapse under the influence of surface tension forces. This paper discusses the expansion dynamics of the cavitation pores and their most probable shape.
In this paper, based on a theoretical model [1], it has been shown experimentally that the initial stage of development of a nanosecond breakdown in liquids is associated with the appearance of discontinuities in the liquid (cavitation) under the influence of electrostriction forces. Comparison of experimentally measured area dimensions and its temporal development were found to be in a good agreement with the theoretical calculations.
This work investigates the development of nanosecond pulsed discharges in water ignited with the application of both positive and negative polarity pulses to submerged pin to plane electrodes. Optical diagnostics are used to study two main aspects of these discharges: the initiation phase, and the development phase. Nanosecond pulses up to 24 kV with 4 ns rise time, 10 ns duration and 5 ns fall time are used to ignite discharges in a 1.5 mm gap between a copper plate and a tungsten needle with radius of curvature of 25 um. Fast ICCD imaging is used to trace the discharge development over varying applied pulse amplitudes for both positively and negatively applied pulses to the pin electrode. The discharge is found to progress similar to that of discharges in long gaps in gases, both in structure and development. The more important initiation phase is investigated via Schlieren transmission imaging. The region near the tip of the electrode is investigated for slightly under-breakdown conditions, and changes in the liquids refractive index and density are observed over the duration of the applied pulse. An attempt to explain the results is made based on the electrostriction model of discharge initiation.
In this study we have studied the initial stage of the nanosecond-pulsed discharge development in liquid phase. Modeling predicts that in the case of fast rising strong nonhomogeneous electric fields in the vicinity of high voltage pin electrode a region saturated with nanoscale non-uniformities may be developed. This phenomenon is attributed to the electrostriction mechanisms and may be used to explain development of breakdown in liquid phase. In this work, schlieren method was used in order to demonstrate formation of negative pressure region in liquids with different dielectric permittivity constants: water, ethanol and ethanol-water mixture. It is shown that this density perturbation, formed at the raising edge of the high voltage pulse, is followed by a generation of a shock wave propagating with the speed of sound away from the electrode, with negative pressure behind it.