Alfven surface waves along cylindrical plasma columns

The properties of Alfven surface waves along a cylindrical plasma column surrounded by vacuum or by another plasma medium are discussed. Both symmetric (m=0) and asymmetric (m=+or-1) modes are found to be dispersive in nature. The interfacial symmetric modes propagate in a certain frequency window ( omega A1, omega As), where omega As is the Alfven surface wave frequency along the interface of two semi-infinite media; when nu A1> nu A2 these modes propagate as backward waves and when nu A1< nu A2 as forward waves. The asymmetric modes change from backward to forward waves at a critical wave number kTr approximately=1.59/a when nu A1< nu A2 or vice versa when nu A1> nu A2.

Propagating waves in polar coronal holes as seen by SUMER and EIS

Context. To study the dynamics of coronal holes and the role of waves in the acceleration of the solar wind, spectral observations were performed over polar coronal hole regions with the SUMER spectrometer on SoHO and the EIS spectrometer on Hinode. Aims. Using these observations, we aim to detect the presence of propagating waves in the corona and to study their properties. Methods. The observations analysed here consist of SUMER spectra of the Ne VIII 770 angstrom line (T = 0.6 MK) and EIS slot images in the Fe XII 195 angstrom line (T = 1.3 MK). Using the wavelet technique, we study line radiance oscillations at different heights from the limb in the polar coronal hole regions. Results. We detect the presence of long period oscillations with periods of 10 to 30 min in polar coronal holes. The oscillations have an amplitude of a few percent in radiance and are not detectable in line-of-sight velocity. From the time distance maps we find evidence for propagating velocities from 75 km s(-1) (Ne VIII) to 125 km s(-1)(Fe XII). These velocities are subsonic and roughly in the same ratio as the respective sound speeds. Conclusions. We interpret the observed propagating oscillations in terms of slow magneto-acoustic waves. These waves can be important for the acceleration of the fast solar wind.

Normal-mode sound propagation in an ocean with sinusoidal surface waves

The normal-mode solution to the problem of acoustic wave propagation in an isovelocity ocean with a wavy surface is considered. The surface wave amplitude is assumed to be small compared to the acoustic wavelength, and the method of multiple scales is employed to study the interaction between normal-mode acoustic waves and the surface waves. A nonresonant interaction causes small fluctuations of the amplitude and phase of the acoustic wave at a rate dependent on the frequency of the surface wave. Backscatter occurs if the wavenumber of the surface wave is larger than that of the acoustic wave. The interaction becomes resonant if appropriate phase-matching conditions are satisfied. In this case, two acoustic normal modes get coupled, resulting in a large-scale periodic exchange of energy from one mode to another.

Characteristics of Alfven surface waves along moving cylindrical plasma columns

The dispersive and stability characteristics of Alfven surface waves (ASW) along the boundary of the moving cylindrical plasma column, surrounded by a stationary medium embedded in a parallel magnetic field is studied. The nature of the symmetric and asymmetric modes on the interface parameters is also discussed.

Surface acoustic waves of finite amplitude excited by a monochromatic line source

A technique for obtaining a uniformly valid solution to the problem of nonlinear propagation of surface acoustic waves excited by a monochromatic line source is presented. The method of solution is an extension of the method of strained coordinates wherein both the dependent and independent variables are expanded in perturbation series. A special transformation is proposed for the independent variables so as to make the expansions uniformly valid and also to satisfy all the boundary conditions. This perturbation procedure, carried out to the second order, yields a solution containing a second harmonic surface wave whose amplitude and phase exhibit an oscillatory variation along the direction of propagation. In addition, the solution also contains a second harmonic bulk wave of constant amplitude but varying phase propagating into the medium.

Alfven surface waves along a cylindrical plasma column surrounded by neutral gas

The dispersion characteristics of Alfven surface waves along a cylindrical plasma column insulated by a neutral gas are discussed. There is no qualitative change in the characteristic curves below the critical magnetic field, given by vA approximately=s, as compared to the propagation of surface waves along the plasma-plasma interface. For magnetic fields above this critical value, there exists a cut-off wave number kc, which depends upon the azimuthal wave number, the radius of the cylinder, the strength of the magnetic field above the critical value and the gas pressure, such that surface waves do not exist for kwaves, which exist only in the presence of magnetic fields with a strength greater than the critical value, will therefore have restricted wavelength range 0< lambda < lambda c, when propagating along a cylindrical plasma column.

Effect of density discontinuity on Alfvén internal gravity waves

The stability characteristics of Alfvén Internal gravity waves for an inviscid, nondissipative, Boussinesq fluid undergoing shear in the presence of a density discontinuity with and without a rigid boundary is studied.

Analysis of flange joints with elastic bolt

The contact zone and pressure distribution between two elastic plates joined by an elastic bolt and nut are estimated using finite element analysis. Smooth interfacial conditions are assumed in all the regions of contact. Eight node axisymmetric ring elements are used to model the structure. The matrix solution is obtained through frontal technique and this solution technique is shown to be very efficient for the iterative scheme adopted to determine the extent of contact. A parametric study is conducted varying the elastic properties of bolt and plate materials, bolt head diameter and thickness of the plates. The method of approach presented in this paper provides a solution with a realistic idealization of tension flange joints.

A note on the existence of Alfvén surface waves

The Alfvén surface waves can arise due to the discontinuity in the Alfvén speed across the interface along which these waves propagate. This note studies the relationship between v A1 and v A2 which is required for the existence of Alfvén surface waves in low-beta.

Load Transfer from a Smooth Elastic Pin to a Large Sheet

The plane problem of load transfer from an elastic interference or clearance fit pin to a large elastic sheet with a perfectly smooth interface is solved. As the load on the pin is monotonically increased, the pin-hole interface is in partial contact above certain critical load in interference fit and throughout the loading range in clearance fit.Such situations result in mixed boundary-value problems with moving boundaries and the arc of contact varies nonlinearly with applied load. These problems are analyzed by an inverse technique in which the arcs of contact/separation are prescribed and the causative loads are evaluated. A direct method of analysis is adopted using biharmonic polar trigonometric stress functions and a simple collocation method for satisfying the boundary conditions. A unified analytical formulation is achieved for interference and clearance fits. The solutions for the linear problem of push fits are inherent in the unified analysis. Numerical results highlighting the effects of pin and sheet elasticity parameters are presented.

On the Landau damping of sound waves in a plasma with magnetic flux tubes

The Landau damping of sound wave in a plasma consisting of an ensemble of magnetic flux tubes with reference to the work by Ryutov and Ryutova (1976) is discussed. Sound waves cannot be Landau damped in general but under certain restriction conditions on plasma parameters the possibility of absorption of these waves can exist.

Stress-induced phase transformation and pseudo-elastic/pseudo-plastic recovery in intermetallic Ni-Al nanowires

Extensive molecular dynamics (MD) simulations have been performed in a B2-NiAl nanowire using an embedded atom method (EAM) potential. We show a stress induced B2 -> body-centered-tetragonal (BCT) phase transformation and a novel temperature and cross-section dependent pseudo-elastic/pseudo-plastic recovery from such an unstable BCT phase with a recoverable strain of similar to 30% as compared to 5-8% in polycrystalline materials. Such a temperature and cross-section dependent pseudo-elastic/pseudo-plastic strain recovery can be useful in various interesting applications of shape memory and strain sensing in nanoscale devices. Effects of size, temperature, and strain rate on the structural and mechanical properties have also been analyzed in detail. For a given size of the nanowire the yield stress of both the B2 and the BCT phases is found to decrease with increasing temperature, whereas for a given temperature and strain rate the yield stress of both the B2 and the BCT phase is found to increase with increase in the cross-sectional dimensions of the nanowire. A constant elastic modulus of similar to 80 GPa of the B2 phase is observed in the temperature range of 200-500 K for nanowires of cross-sectional dimensions in the range of 17.22-28.712 angstrom, whereas the elastic modulus of the BCT phase shows a decreasing trend with an increase in the temperature.

Surface explosive instability for high frequency waves

High frequency three-wave nonlinear 'explosive' interaction of the surface modes of a semi-infinite beam-plasma system under no external field is investigated. The conditions that favour nonlinear instability, keep the plasma linearly stable. The beam runs parallel to the surface. If at least one of the three wave vectors of the surface modes is parallel to the beam, explosive interaction at the surface takes place after it has happened in the plasma bulk, provided the bulk waves propagate almost perpendicular to the surface and are of short wavelength. On the other hand if the bulk modes have long wavelength and propagate almost parallel to the surface, the surface modes can 'explode' first.

Alfven Surface-Waves Along Coronal Streamers

The dispersive characteristics of Alfvdn Surface Waves (ASW) along a moving plasma surrounded by a stationary plasma is discussed. The stability curves for the symmetric and the asymmetric modes are also discussed.

Oscillatory flow in an elastic tube of variable cross-section

An oscillatory flow of a viscous incompressible fluid in an elastic tube of variable cross section has been investigated at low Reynolds number. The equations governing, the flow are derived under the assumption that the variation of the cross-section is slow in the axial direction for a tethered tube. The problem is then reduced to that of solving for the excess pressure from a second order ordinary differential equation with complex valued Bessel functions as the coefficients. This equation has been solved numerically for geometries of physiological interest and a comparison is made with some of the known theoretical and experimental results.