Axisymmetric solitary waves on the surface of a ferrofluid

We report the first observation of axisymmetric solitary waves on the surface of a cylindrical magnetic fluid layer surrounding a current-carrying metallic tube. According to the ratio between the magnetic and capillary forces, both elevation and depression solitary waves are observed with profiles in good agreement with theoretical predictions based on the magnetic analogue of the Korteweg-deVries equation. We also report the first measurements of the velocity and the dispersion relation of axisymmetric linear waves propagating on the cylindrical ferrofluid layer that are found in good agreement with theoretical predictions.Comment: to be published in Phys. Rev. Let

Elongation of confined ferrofluid droplets under applied fields

Ferrofluids are strongly paramagnetic liquids. We study the behavior of ferrofluid droplets confined between two parallel plates with a weak applied field parallel to the plates. The droplets elongate under the applied field to reduce their demagnetizing energy and reach an equilibrium shape where the magnetic forces balance against the surface tension. This elongation varies logarithmically with aspect ratio of droplet thickness to its original radius, in contrast to the behavior of unconfined droplets. Experimental studies of a ferrofluid/water/surfactant emulsion confirm this prediction.Comment: 12 pages, 7 figures. Submitted to Phys. Rev.

SPECIFIC FEATURES OF ELECTROENCEPHALOGRAPHIC PAROXYSMAL ACTIVITY REGISTRATION IN OLD AGE GROUP PATIENTS

The differential diagnosis of epilepsy and other paroxysmal states mimicking this condition is very important in the daily activity of a neurologist (an epileptologist) since diagnostic accuracy directly ensures the efficacy and safety of treatment. According the data available in the literature, both overdiagnosis of epilepsy (20–25 % of all new diagnosed cases) and its underdiagnosis (as high as 10 %) are frequent diagnostic errors. Such errors are most commonly related to the misinterpretation of electrophysiological evidence in both young patients (in whom paroxysmal phenomena are a result of functional immaturity of brain structures) and elderly patients (in whom paroxysmal activity is a consequence of the development of degenerative processes in the neurons).Objective: to show examples of electroencephalographic (EEG) paroxysmal activity in old age group patients suffering from non-epileptic paroxysms.Now EEG investigation is a highly sensitive technique that requires a physician’s knowledge of neuroanatomy and neurophysiology to correct interpretation of the findings. Non-epileptiform paroxysmal events may be detected not only in children who have immature cerebral cortical neurons and median brainstem structures, but also in the elderly in whom their emergence is due to the development of degenerative processes in the neurons. The similarity of these phenomena with typical EEG epileptiform patterns is not coincidental. The basis for their occurrence is the similar mechanism for glutamate excitotoxicity, but, unlike epilepsy, which is triggered by ischemic and hypoxic processes, rather than by the exhausted reserve abilities of nerve cells during overstimulation. Therefore the detection of this pathological EEG paroxysmal activity calls for careful differential diagnosis

Instability of the origami of a ferrofluid drop in a magnetic field

Capillary origami is the wrapping of an usual fluid drop by a planar elastic membrane due to the interplay between capillary and elastic forces. Here, we use a drop of magnetic fluid whose shape is known to strongly depend on an applied magnetic field. We study the quasi-static and dynamical behaviors of such a magnetic capillary origami. We report the observation of an overturning instability that the origami undergoes at a critical magnetic field. This instability is triggered by an interplay between magnetic and gravitational energies in agreement with the theory presented here. Additional effects of elasticity and capillarity on this instability are also discussed.Comment: in press in PRL (2011

Cathode fall characteristics in a dc atmospheric pressure glow discharge

Copyright 2003 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the authors and the American Institute of Physics. This article appeared in the Journal of Applied Physics and may be found at: http://link.aip.org/link/?JAPIAU/94/5504/1Atmospheric pressure glow discharges are attractive for a wide range of material-processing applications largely due to their operation flexibility afforded by removal of the vacuum system. These relatively new atmospheric plasmas are nonequilibrium plasmas with gas temperature around 100 °C and electron temperature in the 1–10 eV range. Their appearance is characteristically diffuse and uniform, and their temporal features are repetitive and stable. Of the reported numerical studies of atmospheric glow discharges, most are based on the hydrodynamic approximation in which electrons are assumed to be in equilibrium with the local electric field. Spectroscopic and electrical measurements suggest however that the cathode fall region is fundamentally nonequilibrium. To this end we consider a hybrid model that treats the cathode fall region kinetically but retains a hydrodynamic description for the region between the thin cathode fall layer and the anode. Using this hybrid model, a helium discharge system excited at dc is studied numerically for a very wide current density range that spans from Townsend dark discharge, through normal glow discharge, to abnormal glow discharge. Numerical results confirm many distinct characteristics of glow discharges and compare well with that of low-pressure glow discharges. Generic relationships, such as that between the electric field and the current density, are also established and are in good agreement with experimental data. This hybrid model is simple and insightful as a theoretical tool for atmospheric pressure glow discharges

ЧИСЛЕННЫЕ РЕШЕНИЯ ДЛЯ СОБСТВЕННЫХ МОД АБСОЛЮТНОЙ ПАРАМЕТРИЧЕСКОЙ РАСПАДНОЙ НЕУСТОЙЧИВОСТИ НЕОДНОРОДНОЙ ПЛАЗМЫ НА НЕЛИНЕЙНОЙ СТАДИИ

A mathematical model for the nonlinear absolute decay parametric instability of inhomogeneous plasma is developed. Decay of the Langmuir pump wave on the Langmuir and ion-acoustic waves is considered in detail. The numerical solutions describing the eigen modes of the instability are obtained. It is shown that at the nonlinear stage of the instability, a depletion of a pump wave and a broadening of an ion-acoustic wave spectrum are observed. The simulation results are in agreement with the experimental ones.Создана математическая модель, описывающая нелинейную абсолютную параметрическую неустойчивость в неоднородной плазме. Подробно рассмотрен распад ленгмюровской волны накачки на ленгмюровскую и ионно- звуковую волны. Получены численные решения, описывающие собственные моды неустойчивости. Показано, чтов нелинейной стадии неустойчивости наблюдается истощение накачки и уширение спектра ионно-звуковой волны. Результаты численных расчетов согласуются с экспериментальными результатами

БАКТЕРИЦИДНЫЕ КОМПОНЕНТЫ В ВОЗДУШНОЙ ПЛАЗМЕННОЙ СТРУЕ ПРИ ПОСТОЯННОМ И ИМПУЛЬСНО-ПЕРИОДИЧЕСКОМ ТОКОВЫХ РЕЖИМАХ

Atmospheric pressure air plasma jets within dc, pulsed and self-oscillatory current regimes are realized. It is shown that the main mechanism of inactivation of bacteria Staphylococcus aureus is the effect of chemically active molecules of NO, NO2 and HNO2. The method of IR absorption spectroscopy is used to investigate chemical active component concentrations. The optimal regime of discharge inducing plasma jets, which is more suitable for production of bactericidal components, is found. Получены воздушные плазменные струи атмосферного давления на постоянном, импульсно-периодическом и автоколебательном токовых режимах. Показано, что основным механизмом инактивации бактерий Staphylococcus aureus является воздействие химически активных молекул NO, NO2 и HNO2. Методом ИК-абсорбционной спектроскопии определены их концентрации. Выявлен оптимальный режим разряда, индуцирующий плазменные струи, наиболее подходящий для получения бактерицидных компонент.