Absorption of electromagnetic radiation in systems with orientational interactions

Absorption of electromagnetic radiation in ordered ferroelectric and antiferro-electric systems in external electrical fields has been investigated by means of Monte Carlo method. The dependences of the areas of the hysteresis curves on the frequency of the field have been calculated. At the resonance frequency, there is a maximum of the area of the hysteresis curve; the position of this maximum depends weakly on the temperature and the constant of intra- and interchain inte-ractions, and its height increases with decreasing temperature and increasing the interaction energy between molecules.     

Universal properties of lamellar systems under weak shear

We have observed that different lamellar phases (thermotropic, lyotropic of surfactants or blockcopolymers) share the same rheological properties = A(T)σ^m, m = 1.67±0.1, independently of their chemical nature, in a range of shear rates , shear stresses σ, and temperatures T, where the flow is stationary. It is argued that the key phenomenon is the appearance of screw dislocations whose glide under an applied shear counterbalances plastically the applied vorticity, and stabilizes the layers, whose slip past each other is thus made more feasible. The theory, which makes use in other respects of the high-temperature creep model in solids, reproduces correctly the power law behavior and the values of A(T). Received 18 April 2001 and Received in final form 25 October 2001     

Stability properties of beam-plasma systems in strong electromagnetic waves

It is strong that beam-plasma systems can be stabilized if a strong circularly polarized electromagnetic wave is applied. New unstable modes may, however, also be generated.     

Exact groundstates for antiferromagnetic spin-one chains with nearest and next-nearest neighbour interactions

We have found the exact ground state for a large class of antiferromagnetic spin-one chains with nearest and next-nearest neighbour interactions. The ground state is characterized as a matrix product of local site states and has the properties characteristic of the Haldane scenario.Work performed within the research program of the Sonderforschungsbereich 341, Köln-Aachen-Jülich     

Universal properties of the transition from quasi-periodicity to chaos in dissipative systems

An exact renormalization group transformation is developed for dissipative systems which describes how the transition to chaos may occur in a continuous and universal manner if the frequency ratio in the quasi-periodic regime is held at a fixed irrational value. Our approach is a natural extension of K.A.M. theory to strong coupling. Most of our analysis is for analytic circle maps. We have found a strong coupling fixed point where invertibility is lost, which describes the universal features of the transition to chaos. We find numerically that any two such critical maps with the same winding number are C¹ conjugate. It follows that the low frequency peaks in an experimental spectrum are universal and we determine how their envelope scales with frequency.When the winding number has a periodic continued fraction, our renormalization transform has a fixed point and spectra are self similar in addition. For a set of non-periodic winding numbers with full measure our renormalization transformation yields an ergodic trajectory in a sub-space of all critical maps. Physically one finds singular and universal spectra that do not scale.     

Some properties of the thermodynamics of ideal systems with nonlinear interactions

In this work we present a comparative study of the thermodynamic properties of two two-dimensional systems. One of them corresponds to a two-dimensional system of coupled harmonic oscillators, while the second is a nonlinear anharmonic oscillator. We present the spectrum for the harmonic oscillator and we present for the first time a calculation of the WKB spectrum and the wave functions for the nonlinear oscillator. We show that the Ω-potential has significantly different behavior in the high temperature region. This may be noted, for example, in a study of the temperature dependence of the specific heat in planar anisotropic media. State Institute of Radio Technology, Electronics, and Automation, Technical University, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 42, No. 1, pp. 8–17, January, 1999.     

Universal early-time response in high-contrast electromagnetic scattering

The time-domain response of highly conducting targets following a rapidly terminated electromagnetic pulse displays three distinct regimes: early, intermediate, and late time. The intermediate and late times are characterized by a superposition of exponentially decaying eigenmodes. At early time an ever increasing number of rapidly decaying modes contribute, with the result that the scattered electric field displays a universal t(-1/2) power law which emerges from the diffusive decay of a pattern of surface currents induced by the pulse. The power law amplitude reflects the surface geometry of the target, a property that may prove useful in buried target classification in geophysical remote sensing applications.     

Equilibrium and nonequilibrium properties of systems with long-range interactions

We briefly review some equilibrium and nonequilibrium properties of systems with long-range interactions. Such systems, which are characterized by a potential that weakly decays at large distances, have striking properties at equilibrium, like negative specific heat in the microcanonical ensemble, temperature jumps at first order phase transitions, broken ergodicity. Here, we mainly restrict our analysis to mean-field models, where particles globally interact with the same strength. We show that relaxation to equilibrium proceeds through quasi-stationary states whose duration increases with system size. We propose a theoretical explanation, based on Lynden-Bell’s entropy, of this intriguing relaxation process. This allows to address problems related to nonequilibrium using an extension of standard equilibrium statistical mechanics. We discuss in some detail the example of the dynamics of the free electron laser, where the existence and features of quasi-stationary states is likely to be tested experimentally in the future. We conclude with some perspectives to study open problems and to find applications of these ideas to dipolar media.     

Non-eikonal corrections for the scattering of spin-one particles

The Wallace Fourier-Bessel expansion of the scattering amplitude is generalised to the case of the scattering of a spin-one particle from a potential with a single tensor coupling as well as central and spin-orbit terms. A generating function for the eikonal-phase (quantum) corrections is evaluated in closed form. For medium-energy deuteron-nucleus scattering, the first-order correction is dominant and is shown to be significant in the interpretation of analysing power measurements. This conclusion is supported by a numerical comparison of the eikonal observables, evaluated with and without corrections, with those obtained from a numerical resolution of the Schrödinger equation for d-⁵⁸ Ni scattering at incident deuteron energies of 400 and 700 MeV.Received: 4 December 2003, Published online: 10 August 2004PACS: 03.65.Nk Scattering theory - 24.70. + s Polarization phenomena in reactions - 25.10. + s Nuclear reactions involving few-nucleon systems - 25.40.Hs Transfer reactionsM.W. Gaber: Present address: Department of Radiological Sciences, St. Jude Childrens Research Hospital, 332 N. Lauderdale St., Memphis, TN 38105-2794, USA     

Neutrino electromagnetic properties

The main goal of the paper is to give a short review on neutrino electromagnetic properties. In the introductory part of the paper a summary on what we really know about neutrinos is given: we discuss the basics of neutrino mass and mixing as well as the phenomenology of neutrino oscillations. This is important for the following discussion on neutrino electromagnetic properties that starts with a derivation of the neutrino electromagnetic vertex function in the most general form, that follows from the requirement of Lorentz invariance, for both the Dirac and Majorana cases. Then, the problem of the neutrino form factor definition and calculation within gauge models is considered. In particular, we discuss the neutrino electric charge form factor and charge radius, dipole magnetic and electric and anapole form factors. Available experimental constraints on neutrino electromagnetic properties are also discussed, and the recently obtained experimental limits on neutrino magnetic moments are reviewed. The most important neutrino electromagnetic processes involving a direct neutrino coupling with photons (such as neutrino radiative decay, neutrino Cherenkov radiation, spin light of neutrino and plasmon decay into neutrino-antineutrino pair in media) and neutrino resonant spin-flavor precession in a magnetic field are discussed at the end of the paper.     

The spin-one Ising model in the mean-spherical approximation

The spin-one Ising ferromagnet on a simple cubic lattice is treated in the mean-spherical approximation (MSA) for an exchange potentialJ(r) parametrized by a Kac-Baker inverse-range parameter γ. The mean-field result is recovered when γ→ 0; in this limit the result is exact. For γ≠ 0, a detailed analysis is given of the phase separation associated with the tricritical point that occurs. The analysis is made through the relation that gives the internal energy viaJ(r). It shows that the MSA result satisfactorily captures the important thermodynamic features of the tricritical point as long as γ is not too large. The case of CoulombicJ(r) is also considered; hereJ(r) is antiferromagnetic. An argument is given in support of the expectation that on the simple cubic and body-centered cubic lattices the CoulombicJ(r) will give rise to a tricritical point at which a λ-line of Néel points meets a paramagnetic-antiferromagnetic coexistence boundary.     

Universal fluctuations in correlated systems

The probability density function (PDF) of a global measure in a large class of highly correlated systems has been suggested to be of the same functional form. Here, we identify the analytical form of the PDF of one such measure, the order parameter in the low temperature phase of the 2D XY model. We demonstrate that this function describes the fluctuations of global quantities in other correlated equilibrium and nonequilibrium systems. These include a coupled rotor model, Ising and percolation models, models of forest fires, sandpiles, avalanches, and granular media in a self-organized critical state. We discuss the relationship with both Gaussian and extremal statistics.     

Universal properties of growing networks

Networks growing according to the rule that every new node has a probability p_k of being attached to k preexisting nodes, have a universal phase diagram and exhibit power-law decays of the distribution of cluster sizes in the non-percolating phase. The percolation transition is continuous but of infinite order and the size of the giant component is infinitely differentiable at the transition (though of course non-analytic). At the transition the average cluster size (of the finite components) is discontinuous.     

Modelling of electromagnetic wave interactions with the human body

Electromagnetic modelling plays a more and more important role in the study of complex systems involving Maxwell phenomena, such as the interactions of radiowaves with the human body. Simulation then becomes a credible means in decision making, related to the engineering of complex electromagnetic systems. To increase confidence in the models with respect to reality, validation and uncertainty estimation methods are needed. The different dimensions of model validation are illustrated through dosimetry, i.e., quantification of human exposure to electromagnetic waves. To cite this article: M.-F. Wong, J. Wiart, C. R. Physique 6 (2005).