Nonlinear generation of vorticity by surface waves
We demonstrate that waves excited on a fluid surface produce local surface rotation owing to hydrodynamic nonlinearity. We examine theoretically the effect and obtain an explicit formula for the vertical vorticity in terms of the surface elevation. Our theoretical predictions are confirmed by measurements of surface motion in a cell with water where surface waves are excited by vertical and harmonic shaking the cell. The experimental data are in good agreement with the theoretical predictions. We discuss physical consequences of the effect.
This edition presents abstracts of the reports of the Meeting and Youth Conference on Neutron Scattering and Synchrotron Radiationin Condensed Matte (NSSR-CM-2014)r
Diffusion transport of material sputtered from the surface of the powered electrode in the asymmetric alternating current discharge is theoretically studied. It is shown that amplitudes of the non-stationary component of the sputtered atom (SA) flow densities at the electrodes depend on the discharge frequency and two dimensionless parameters, which are functions of the SA mass, its mean free path length in the background gas and the distance between the electrodes. It is found that diffusion damping of the time-varying component of the SA number density takes place in the discharge volume under certain conditions and their flows at the electrodes can be considered as time-independent.
The ability of phase mixing to provide eﬃcient damping of Alfvén waves even in weakly dissipative plasmas made it a popular mechanismforexplainingthesolarcoronalheating.Initiallyitwasstudiedintheequilibriumconﬁgurationswiththestraightmagnetic ﬁeldlinesandtheAlfvénspeedonlyvaryinginthedirectionperpendiculartothemagneticﬁeld.LatertheanalysisoftheAlfvénwave phase mixing was extended in various directions. In particular it was studied in two-dimensional planar magnetic plasma equilibria. Analytical investigation was carried out under the assumption that the wavelength is much smaller than the characteristic scale of the background quantity variation. This assumption enabled using the Wentzel, Kramers, and Brillouin (WKB) method. When it is not satisﬁed the study was only carried out numerically. In general, even the wave propagation in a one-dimensional inhomogeneous equilibrium can be only studied numerically. However there is one important exception, so-called non-reﬂective equilibria. In these equilibria the wave equation with the variable phase speed reduces to the Klein-Gordon equation with constant coeﬃcients. In this paper we apply the theory of non-reﬂective wave propagation to studying the Alfvén wave phase mixing in two-dimensional planar magnetic plasma equilibria. Using curvilinear coordinates we reduce the equation describing the Alfvén wave phase mixing to the equationthatbecomesaone-dimensionalwaveequationintheabsenceofdissipation.Thisequationisfurtherreducedtotheequation which is the one-dimensional Klein-Gordon equation in the absence of dissipation. Then we show that this equation has constant coeﬃcients when a particular relation between the plasma density and magnetic ﬁeld magnitude is satisﬁed. Using the derived Klein- Gordon-type equation we study the phase mixing in various non-reﬂective equilibria. We emphasise that our analysis is valid even when the wavelength is comparable with the characteristic scale of the background quantity variation. In particular, we study the Alfvén wave damping due to phase mixing in an equilibrium with constant plasma density and exponentially divergent magnetic ﬁeld lines. We conﬁrm the result previously obtained in the WKB approximation that there is enhanced Alfvén wave damping in this equilibrium with the damping length proportional to ln(Re), where Re is the Reynolds number. Our theoretical results are applied to heating of coronal plumes. We show that, in spite of enhanced damping, Alfvén waves with periods of the order of one minute can be eﬃciently damped in the lower corona, at the height about 200 Mm, only if the shear viscosity is increased by about 6 orders of magnitude in comparison with its value given by the classical plasma theory. We believe that such increase of the shear viscosity can be provided by the turbulence.
In his reasoning concerning the relationship between surface or visible superficies (understood as the boundary or the limit of a body) and color (De sensu 439a19–b17), Aristotle asserts that the Pythagoreans called the surface (ἐπιφάνεια) color (χροιά), i.e. that they made no terminological difference between the former and the latter. In the scholarship on early Pythagoreans, this passage has been usually used as an indirect proof for the inaccuracy of attribution to the early Pythagoreans (1) of the abstract notion of surface (as found in Plato and Euclid), and thereby (2) of various forms of “derivation theory”. We argue that the colour-surface-limit doctrine has great significance for the understanding of the early Pythagorean concept of a number, since they articulated it, in various ways, precisely through the notion of a limit.
The book is an introduction to the qualitative theory of dynamical systems on manifolds of low dimension (on the circle and on surfaces). Along with classical results, it reflects the most significant achevements in this area obtained in recent times. The reader of this book need to be familiar only with basic courses in differential equations and smooth manifolds.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.