A Sheath Collision Model with Thermionic Electron Emission and the Schottky Correction Factor for Work Function of Wall Material

This paper proposes a model that expands Godyak's collisional sheath model to the case of hot electrodes (anode or cathode) with thermionic electron emission. In the model, the electrodes are assumed to be made from refractory metals and, consequently, the erosion of the electrodes is small and can be neglected. In the frame of two temperature thermal plasma modeling, this model allows self-consistent calculation of the sheath potential drop, the Schottky correction factor for the work function of the wall material, the thermionic electron current density, and the heat fluxes of the charged particles from the plasma to the wall. The model is applied to the cathode spot at the tungsten cathode in argon. It is shown that the Shottky correction factor plays a crucial role in modeling high-intensity arcs. It is demonstrated that a virtual cathode can be formed in the atmospheric pressure argon plasma at the cathode surface temperature of 4785 K if the cathode current density is sufficiently small. The heat flux to the thermionic cathode due to charged particles and the heat flux to the plasma due to thermionic electrons are calculated. The model can be reduced to the case of cold walls where the thermionic electron emission and the wall erosion processes are small and can be neglected. The sheath potential drop and the heat fluxes calculated by this model can be used as boundary conditions at the wall for the electric potential and for the energy equations for the electrons and heavy particles (ions and neutrals).Comment: 27 pages, 12 figures. arXiv admin note: text overlap with arXiv:1501.0050

Plateau-Rayleigh Instability of a Cylinder of Viscous Liquid (Rayleigh vs. Chandrasekhar)

In 1982, in his classical work, L. Rayleigh considered the instability of a cylinder of viscous liquid under capillary force, the so-called Plateau-Rayleigh instability. In this work, in linear approximation, he obtained a dispersion equation describing the increment of this instability as a function of wavelength, the radius of cylinder, the mass density, surface tension, and viscosity of the liquid. Hundreds of authors referred to this work, but none of them used his dispersion equation in its complete form; they used only the asymptotic solutions of his equation for zero and infinitely large viscousities. A reason for this is, probably, that Rayleigh's writing is very difficult and his dispersion equation is quite complex. Then, in 1961, S Chandrasekhar, in his monograph, also considered the stability of a viscous cylindrical jet and obtained his dispersion equation which is also quite complex and differs from the one obtained by Rayleigh. As in the case of Rayleigh's dispersion equation, other works use only the asymptotic solution of Chandrasekhar's equation that corresponds to the case where the viscosity is very large in comparison to inertia. In this paper, I demonstrate that Chandrasekhar's dispersion equation is equivalent to Rayleigh's and then simplify their dispersion equations to a form which can be easily solved numerically for arbitrary values of viscosity. I also present Mathematica code to calculate the maximum increment of the Plateau-Rayleigh instability for given parameters of the jet. To illustrate how the code works, I apply it to a cylindrical jet to estimate its breakup.Comment: 20 pages, 4 figure

A Calculator for Sediment Transport in Microchannels Based on the Rouse Number

The Rouse number is commonly used to estimate the mode of the sediment transports in turbulent flows with large Reynolds number. However, in microchannels such as in modern inkjet systems, the liquid flows are usually laminar. In this paper, I modify the Rouse number by expanding it to the case of weakly turbulent and laminar flows and construct a calculator to estimate the modes of sediment transport in microchannels. To illustrate the applicability of the modified Rouse number, I apply it to the transport of sediments in an inkjet system and compare theoretical results with experimental observations. The modified Rouse number constructed in this paper can be used in other application as well.Comment: 10 pages, 4 figures, 3 table

A comment on percolation and signatures of superconductivity in Au/Ag nanostructures

In this comment we point out that the experimental evidence for superconductivity presented by Thapa and Pandey in arXiv:1807.08572 is also consistent with a percolation transition. We propose simple follow-up experiments which would help to eliminate percolation as a possible explanation for the observed data.Comment: 2 pages, 3 figure

Boundary Conditions at the Walls with Thermionic Electron Emission in Two Temperature Modeling of "Thermal" Plasmas

In this paper we propose new boundary conditions at the hot walls with thermionic electron emission for two-temperature thermal arc models. In the derived boundary conditions the walls are assumed to be made from refractory metals and that the erosion of the wall is small and, therefore, is not taken into account in the model. In these boundary conditions the plasma sheath formed at the electrode is considered as the interface between the plasma and the wall. The derived boundary conditions allow the calculation of the heat flux to the walls from the plasma and consequently the thermionic electron current that makes the two temperature thermal model self consistent.Comment: 32 pages, 11 page

A general figure of merit for thick and thin transparent conductive carbon nanotube coatings

We suggest a wavelength-dependent figure of merit for transparent conducting nanotube networks, composed of the sheet resistance and the optical density. We argue that this would be more useful than other suggestions prevailing in the literature, because it relies on more realistic assumptions regarding the optical parameters of real nanotubes: it takes into account the fact that the dc resistivity depends on the concentration of free carriers, while the visible absorption is caused by bound carriers. Based on sheet resistance measurements and wide-range transmission spectra, we compare several commercial nanotube types and find correlation between metal enrichment and figure of merit. A simple graphical approach is suggested to determine if the required optical and transport properties can be achieved by varying the thickness of the nanotube layer or a more aggressive treatment is needed. The procedure can be extended to oxide coatings as well.Comment: 17 pages, 7 figure

Initiation and blocking of the action potential in the axon in weak ultrasonic or microwave fields

In this paper, we analyze the effect of the redistribution of the transmembrane ion channels in the axon caused by longitudinal acoustic vibrations of the membrane. These oscillations can be excited by an external source of ultrasound and weak microwave radiation interacting with the charges sitting on the surface of the lipid membrane. It is shown, using the Hodgkin-Huxley model of the axon, that the density redistribution of transmembrane sodium channels may reduce the threshold of the action potential, up to its spontaneous initiation. At the significant redistribution of sodium channels in membrane, the rarefaction zones of the transmembrane channels density are formed, blocking the propagation of the action potential. Blocking the action potential propagation along the axon is shown to cause anestesia in the example case of a squid axon. Various approaches to experimental observation of the effects considered in this paper are discussed

On the possible mechanisms of the selective effect of a non-equilibrium plasma on healthy and cancer cells in a physiological solution

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

Non-thermal influence of a weak microwave on nerve fiber activity

This paper presents a short selective review of the non-thermal weak microwave field impact on a nerve fiber. The published results of recent experiments are reviewed and analyzed. The theory of the authors is presented, according to which there are strongly pronounced resonances in the range of about 30-300 GHz associated with the excitation of ultrasonic vibrations in the membrane as a result of interactions with the microwave radiation. These forced vibrations create acoustic pressure, which may lead to the redistribution of the protein transmembrane channels, thus changing the threshold of the action potential excitation in the axons of the neural network. The problem of surface charge on the bilayer lipid membrane of the nerve fiber is discussed. Various experiments for observing the effects considered are also discussed.Comment: arXiv admin note: text overlap with arXiv:1309.594

Surface tension of small bubbles and droplets and the cavitation threshold

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