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The Cassini spacecraft observed electromagnetic ion cyclotron waves in Saturn's inner magnetosphere. EMIC waves have frequencies close to the frequency of water-group ions, they are left-handed, and, in most areas, they propagate to the ambient magnetic field at small angles. Their origins are explained by the ion cyclotron instability generated by the water group ions extracted from Saturn's neutral clouds. These waves propagate no more than 5° at an oblique angle to the magnetic field. These fluctuations can be identified as the n = 2 mode resulting from the ring distribution of the picked-up ions. In this work, we studied the characteristics of these waves. We also use kinetic method analysis to assess growth rates. The results obtained for the demonstration values of the parameters suitable for the Saturn magnetosphere have been calculated and discussed. It is assumed that temperature anisotropy is an additional free energy source for ion cyclotron instability. Regardless of the magnitude, the AC frequency can significantly affect the growth rate. The drift velocity also seems to affect the growth rate. This result is important to explain the VLF emissions observed over a wide frequency range. [ABSTRACT FROM AUTHOR]

The present study investigates the traversal of torsional wave at a corrugated interface between viscoelastic sandy medium and inhomogeneous half-space. In the lower half-space, the inhomogeneity has been assumed as an exponential variation in density and rigidity with respect to depth. We have taken the method of variable separation to obtain analytical solution of displacement components for layer and half-space. Consequently, we have obtained the wave velocity equation of torsional wave using sufficient boundary conditions. Moreover, the wave velocity equation has been reduced to the pre-established classical relationship of Love wave, when both the media are isotropic and homogeneous, as shown in special case. The comparative study of the influence of various parametric traits viz. sandiness, viscoelasticity, corrugated and inhomogeneity associated with the studied model on the traversal characteristics of torsional wave is one of the salient feature of the current investigation. The study may find its possible applications in various seismic prospecting techniques to analyse the nature of torsional wave propagation in the considered layered media. [ABSTRACT FROM AUTHOR]

The present research work elucidates the characteristics of Love waves propagating through a prestressed non-homogeneous orthotropic medium overlying a heterogeneous half-space. It has been considered here that the properties of the layer vary in the direction of thickness with the help of suitable boundary conditions. The dispersion relation has been obtained by variable separable method. A special case has been undertaken in which due to homogeneity of half-space and layer, the dispersion relation satisfies the classical equation of Love waves. To show the nature of Love waves, dispersion curves have been plotted by taking variation in initial stress and inhomogeneities of layer and half-space. This problem may find its applications in various geophysical prospects. [ABSTRACT FROM AUTHOR]

We present and compare once and twice subtracted dispersion relations including crossing symmetry constraints in order to test the S- and P-wave ππ amplitudes below 1100 MeV. We show that twice subtracted dispersion relations provide stringent constraints on the ππ amplitudes below about 400 MeV than those with one subtraction. Above this energy GKPY eqs. become, however, a more demanding test of ππ amplitudes, thus providing a new tool for the precise determination of ππ scattering. We also show that due to strong constraints imposed by the GKPY eqs. they are useful for the determination of the f((600) pole position with high accuracy. [ABSTRACT FROM AUTHOR]

The effect of dust charge fluctuations on the existence and propagation of dust acoustic waves in unmagnified dusty plasma is studied. Dispersion relation for the dust acoustic waves with temporal dust charge fluctuations is calculated based on the reductive perturbation technique. It is shown that when the dust charging frequency is comparable to the dust acoustic wave frequency, the condition give rise to collision less damping of two existing normal modes and one purely damped mode. In the limit when the charging frequency is very much higher than the wave frequency, it is then possible to derive a nonlinear Schrödinger type equation with envelope soliton as solution. [ABSTRACT FROM AUTHOR]

The propagation of mechanical waves, such as sound, through granular materials is important in many disciplines of engineering. Here wave propagation is studied from the micromechanical viewpoint, in which relationships are investigated between macroscopic wave propagation characteristics and microscopic particle and interparticle characteristics. The interparticle interaction is described by linear elastic springs in directions normal and tangential to interparticle contacts. Dispersion relations are formulated theoretically, in terms of the micromechanical quantities, using three-dimensional lattice-based approaches. In these approaches the rotational degrees of freedom of the particles are explicitly accounted for. This leads to the presence of ‘optical’ branches in the dispersion relations. Dispersion relations for various three-dimensional lattices (simple cubic, body centred cubic, face centred cubic) are given. The resulting dispersion relations are sensitive to the lattice structure and do not show true isotropic behaviour (at larger wave numbers), i.e. they depend on the direction of the wave vector. Therefore, a statistical formulation of the lattice theory is developed, which does result in isotropic behaviour for all wave numbers. The corresponding dispersion relations show ‘optical’ branches, just like the lattice theories. The influence on these dispersion relations of the stiffness ratio of tangential over normal stiffness at the contacts is investigated. [ABSTRACT FROM AUTHOR]

We investigate the validity of using thermal masses in the kinematics of final states in the decay rate of heavy neutrinos in leptogenesis calculations. We find that using thermal masses this way is a reasonable approximation, but corrections arise through quantum statistical distribution functions and leptonic quasiparticles. [ABSTRACT FROM AUTHOR]

Within the framework of a generic generally covariant quantum theory we introduce the logarithmic correction to the quantum wave equation. We demonstrate the emergence of the evolution time from the group of automorphisms of the von Neumann algebra governed by this non-linear correction. It turns out that such time parametrization is essentially energy-dependent and becomes global only asymptotically—when the energies get very small comparing to the effective quantum gravity scale. We show how the logarithmic non-linearity deforms the vacuum wave dispersion relations and explains certain features of the astrophysical data coming from recent observations of high-energy cosmic rays. In general, the estimates imply that ceteris paribus the particles with higher energy propagate slower than those with lower one, therefore, for a high-energy particle the mean free path, lifetime in a high-energy state and, therefore, travel distance from the source can be significantly larger than one would expect from the conventional theory. [ABSTRACT FROM AUTHOR]

Exclusive pi0 electroproduction from nucleons at large photon virtuality can be described in terms of Generalized Parton Distributions, particularly the chiral odd subset. Chiral odd GPDs are related to transversity and can be accessed experimentally for various special choices of observables. This is accomplished by choosing C-parity odd and chiral odd combinations of t-channel exchange quantum numbers. These GPDs are calculated in a spectator model, and are constrained by boundary functions. Alternatively, the production amplitudes correspond to C-odd Regge exchanges with final state interactions. The helicity structure of the virtual photoproduction amplitudes provides relations between the partonic description via GPDs and the hadronic, Regge description of C-odd processes, all via quark helicity flip. GPDs, in general, are analytic functions of energy variables. Their integrals over unobservable parton momenta thereby satisfy Dispersion Relations (DR). Using DR’s could allow the real part of the amplitudes, the integrated GPDs, to be extracted from the more easily measured imaginary parts. However, at non-zero momentum transfer DRs require integration over unphysical regions of the variables. We show that the relevant unphysical region of the non-forward DRs is considerable. This will vitiate the efforts to avoid the actual measurement of the real parts more directly. [ABSTRACT FROM AUTHOR]

We study a non-Hermitian generalization of quantum systems in which an imaginary vector potential is added to the momentum operator. In the tight-binding approximation, we make the hopping energy asymmetric in the Hermitian Hamiltonian. We conjecture that the non-Hermitian critical point where the energy gap vanishes is equal to the inverse correlation length of the Hermitian system. We confirm the conjecture for three exactly solved models analytically and for an unsolved model numerically. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We describe a schematic coupled channels transfer calculation for the reaction 6He + 238U at near-barrier energies. We also present a simple semiclassical DWBA calculation of the 2n-transfer. Both calculations are meant to supply the conditions under which the transfer cross section becomes much larger than the complete fusion one at sub-barrier energies. It seems that a feasible mechanism is the incoherent contribution of two or more processes with quite different Q-values. We also discuss the operation of the dispersion relation in low-energy collisions of loosely bound nuclei. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Pion-pion scattering amplitude is obtained from Chiral Perturbation Theory at one- and two-loop approximations. Dispersion relation formalism provides a more economic method, which was proved to reproduce the analytical structure of that amplitude at both approximation levels. This work extends the use of the formalism in order to compute further unitarity corrections to partial waves, including the D-wave amplitude. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Taking into account the random charge fluctuation on embedded micro spheres in low pressure gas discharge two differential equation for two-dimensional dust lattice wave is derived. 2D hexagonal crystal is investigated in this paper. The dispersion relation for both longitudinal and transverse waves in different direction is studied as well. It is in agreement between analytical results and the experimental ones reported previously. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Nonlinear stability analysis shows that there exists a series of dimensionless breakup point parameters, (ωr/Re)b, (ωr/We)b, (ωr/Eu)b, at any axial location, under certain injected velocity and liquid sheet thicknesses. The liquid sheet will breakup when conditions of ωr/Re>=(ωrRe)b, (ωr/We>=(ωr/We)b, and ωr/Eu<=(ωr/Eu)b are satisfied. There exists a transition region, liquid wave instability from a sinuous wave to a varicose mode, and breakup lengths from a decreasing trend to an increasing one as increased injected velocity, when aspect ratio of nozzle exit is changed from larger to smaller values. [ABSTRACT FROM AUTHOR]

Thermal effects on the properties of the electromagnetic waves propagating in an electron gas have not been fully investigated. The finite temperature effects appear through the dielectric function of the electrons in the Maxwell equation that describes the electromagnetic field. Recently we calculated the dispersion relation of the electromagnetic wave propagating in an ideal electron gas at low temperatures using the self-consistent linear response approximation and the Sommerfeld expansion. We shall discuss the implications of our results on various experimental situations including optical properties of plasma. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]