Wave instability of a magnetic fluid surface at the boundary with water in an electric field

Свойства межфазной поверхности магнитной жидкости на границе с водой в электрическом поле изучались во многих работах. Были обнаружено изменение отражательной способности межфазной поверхности вода – магнитная жидкость в электрическом поле, что авторами связывается с образованием на межфазной границе слоя плотноупакованных частиц. По оптическим и электрическим измерениям оценена толщина d этого слоя. Интерес к этим эффектам, помимо чисто академического, связан с возможностью управления поведением межфазной границы раздела магнитного коллоида и гомогенной жидкости внешним электрическим полем, что представляет практический интерес, поскольку слой частиц магнетита на межфазной поверхности может быть интерпретирован как жидкая мембрана с особыми свойствами. Задача настоящего исследования – теоретически показать, что образование слоя частиц дисперсной фазы магнитной жидкости в электрическом поле и связанное с этим уменьшение межфазного натяжения является определяющим фактором для развития волновой неустойчивости. A layer of close-packed particles of a dispersed phase (magnetite) with a protective shell of oleic acid is formed on the interface of a weakly conducting magnetic colloid (magnetic fluid) and water in a perpendicular electric field. The formation of a layer leads to a decrease in the interfacial tension. When the magnetic particles come into contact with the electrode surface, the electrochemical interaction of oleic acid molecules surrounding the particle with water occurs. As a result of the reaction, released ions charge the surface layer. After some time, the particles in the layer get recharged and repelled from the interface. This leads to wave instability. This paper considers the mathematical modeling of instability in the form of a boundary value problem – a dispersion equation. The determining factor in the development of wave instability is the action of the electric field, the formation of the near-electrode layer and, as a consequence, a decrease in the interfacial tension.

Ionization Waves Enhance the Production of X-rays during Streamer Collisions

Experimental data show that in laboratory sparks, X-rays are produced in time synchronization with the meeting of streamers of opposite polarity just before the final breakdown of the discharge gap. It has been suggested that the electric field enhancement created during the collision of streamers could provide the necessary conditions for electron acceleration, even though some of the theoretical studies show that the duration of the electric field is not long enough to do so. The experimental data on laboratory discharges show that. when streamers of opposite polarity meet each other, a potential or ionization wave that renders the streamer channels conducting is initiated. This paper shows that these ionization waves that convert the discharge channels from weakly conducting to highly conducting are associated with electric fields large enough to accelerate electrons to relativistic energies.

The Role of Surface-Charge Transport in Electrohydrodynamics and Electromechanics of a Dielectric Sphere

To simulate the electrokinetic processes in weakly-conducting dielectric media, the Taylor–Melcher leaky-dielectric model is widely used, though its applicability conditions are unknown. To define them, the electric-potential distributions inside and outside a dielectric sphere placed in an electric field are determined, by assuming the sphere and the environment are weakly conducting and by considering the electric and diffusion interfacial currents and the surface-charge decay. Earlier, an electric-field characteristic of a dielectric sphere, for example, the real part of the Clausius–Mossotti factor found for a direct current (DC) field was commonly thought to be a single-valued function of two parameters, the conductivities of the sphere and the environment. Now, it depends on a larger number of parameters and, in the dc case, can range from the perfect-dielectric to perfect-conductor values even for a particle of a good insulator. Using the proposed theory, a variety of the experimental results on the electrohydrodynamic (EHD) fluid circulation and dielectrophoretic (DEP) motion of microparticles in the dielectric drops are explained for the first time or in a new way. The dielectrophoretic inflection and cross-over frequencies are defined allowing for the decay of the surface charge. A dependence of the effective conductivity of a sphere on the angular field distribution is predicted for the first time.

Investigating the effects of the planetary rings on the azimuthal magnetic field at Saturn

<p>Magnetic field observations from the 22 Cassini Grand Finale orbits have shown a mean lagging azimuthal magnetic field configuration on magnetic field lines mapping from Saturn to its main rings in the equatorial plane, with some orbit to orbit variability. A prominent feature is observed in the southern hemisphere on field lines connecting to the B-ring on 70% of the orbits, which is spatially consistent with the location of in-falling dust indicated by the Cosmic Dust Analyser instrument. In our work, we examine the possible connection between the in-falling charged dust and the B-ring magnetic field feature. We also use a simple steady-state model to couple the planetary ionosphere to a weakly conducting ring ionosphere over the main rings, where the model output shows an expected leading field configuration associated with the rings. The discrepancy between the simple theoretical model and the data indicates the presence of additional processes (e.g. departure from Keplerian velocity of the charged ring particles), which will be discussed. We will further discuss the likely connection between the observed lagging field configuration in the middle magnetosphere and in the inner magnetosphere.  </p>

Идентификация дефектов в слоистых композитах с помощью импульсного вихретокового метода

This paper describes the practical possibility of determining the size and depth of the delamination in non-metallic multilayer weakly conducting materials using a unique pulsed eddy-current equipment. The efficiency of the developed methods and technical solutions is confirmed by the results of experimental investigation. The objects of control were carbon fiber reinforced plastic specimens with artificially created delaminations in the material structure. Defects had different sizes and shapes.