Scattering of electromagnetic wave by perfect electromagnetic conductor (PEMC) sphere placed in chiral media

A theoretical investigation has been carried out for electromagnetic waves scattering from a perfect electromagnetic conductor (PEMC) sphere which is placed in chiral media. The formulation of the problem is realized by expanding the incident as well as the scattered electromagnetic fields in terms of left circularly polarized (LCP) and right circularly polarized (RCP) waves. By applying the boundary conditions at the chiral-PEMC interface, eight simultaneous equations are generated, which yield the scattering coefficients associated with the Left and Right electromagnetic waves. The relative contribution of Co-polarized and Cross-polarized components of fields to the calculations of scattering cross-section is presented. The effect of admittance parameter and the effect of chirality parameter in cases of lossless, lossy permittivity and lossy permeability on Co and Cross components of scattering cross sections are observed. The results are also compared with available published literatures which are in good agreement.     

Gaussian beam scattering by a chiral sphere

Based on the generalized Lorenz–Mie theory that provides the general framework, an analytic solution to Gaussian beam scattering by a chiral sphere is constructed, by expanding the incident Gaussian beam, scattered fields and internal fields in terms of spherical vector wave functions. The unknown expansion coefficients are determined by a system of equations derived from the boundary conditions. For a localized beam model, numerical results of the normalized differential scattering cross section are presented.     

Reflection characteristics of chiral microwave absorbing coatings

The formulations of reflection coefficients for metal-backed one- and multi-layered chiral microwave absorbing coatings are derived in a much straight way in this paper. It is found that the propagation of normally incident plane waves in chiral coatings can be treated as in their achiral counterparts if the intrinsic impedance and wavenumber of the achiral structure are replaced by their associated chiral impedance and average chiral wavenumber, respectively. From a practical point of view, examples of one- and two-layered chiral microwave absorbing coatings are given, and the effects of the real and imaginary parts of the chiral admittance on the antireflection characteristics are examined for the first time, the results show that with a appropriate complex chiral admittance, the reduction in reflection can be enhanced and the minimum-reflection-frequency can be controlled.     

Three-Dimensional FDTD Analysis of Chiral Discontinuities in the Waveguide

A simple finite difference time domain (FDTD) scheme for chiral media is developed for modeling the chiral discontinuities in the waveguide with the aid of the second-order backward finite difference. The accuracy of the FDTD scheme is demonstrated by the comparison between our calculated results and those in the literature for achiral and chiral media. Comparisons of characteristics between chiral and achiral discontinuities in the waveguide are presented at last.     

Self-assembled chiral superstructures composed of rigid achiral molecules and molecular scale chiral induction by dopants

We explore the phase behavior of a rigid achiral bent-core model system. Nematic and smectic phases form at higher densities, whereas micelles and columns composed of chiral clusters of these molecules self-assemble at lower densities. No nucleation mechanism requiring transient chirality is possible in the formation of these chiral superstructures due to the rigid achiral nature of the substituents. We show the chiral micelles are minima of the potential energy surface using energy minimization and parallel tempering simulations. Chiral dopants were found to induce the system to adopt a consistent chiral twist direction, the first molecular scale computer simulation of this effect.     

A multiple sphere T-matrix Fortran code for use on parallel computer clusters

A general-purpose Fortran-90 code for calculation of the electromagnetic scattering and absorption properties of multiple sphere clusters is described. The code can calculate the efficiency factors and scattering matrix elements of the cluster for either fixed or random orientation with respect to the incident beam and for plane wave or localized-approximation Gaussian incident fields. In addition, the code can calculate maps of the electric field both interior and exterior to the spheres. The code is written with message passing interface instructions to enable the use on distributed memory compute clusters, and for such platforms the code can make feasible the calculation of absorption, scattering, and general EM characteristics of systems containing several thousand spheres.     

Molecular structure and chiral liquid crystalline phases

We describe briefly some results obtained on both chiral and achiral compounds exhibiting chiral mesophases. We report the first example of a single component system exhibiting the undulated twist grain boundary C* or UTGB _C* phase. Preliminary results concerning a few achiral compounds composed of banana-shaped molecules exhibiting a mesophase is reported. They have been investigated by polarized light optical microscopy, differential scanning calorimetry and x-ray diffraction studies.     

Optical activity in mixed-ligand terbium complexes containing 1,2-Benzenedicarboxylic acid and chiral carboxylic acids

The optical activity of Tb(PHT)(L) complexes has been studied by means of circularly polarized luminescence (CPL) spectroscopy, where PHT=1,2-benzenedicarboxylic acid (phthalic acid) and L=L-mandelic, L-aspartic, and L-malic acids. The CPL spectra were characteristic of multidentate bonding, and close examination of the spectra revealed the nature of the metal-ligand bonding. The results obtained have demonstrated that the optical activity experienced by the Tb(III) ion is primarily determined by the nature of the chiral ligand, and that this chirality can be affected by the achiral ligands also bound in the metal coordination sphere.     

Exact solution for the scattering and absorption properties of sphere clusters on a plane surface

A formulation and computational scheme are presented for predicting the scattering and absorption cross-sections, and the scattering matrix elements, of clusters of non-intersecting spheres that are lying on or above an infinite plane surface and exposed to plane-wave radiation. The formulation provides an exact solution to Maxwell's equations and the associated boundary conditions on the spheres and the plane surface, and is applicable for arbitrary refractive indices for the spheres and the surface. A simplified strategy is presented for the calculation of the surface reflection matrix, which transforms the reflected scattered field from one sphere into a regular vector spherical harmonic expansion centered about another sphere. The calculation results are presented for the clusters of one, two, and four polystyrene spheres, with size parameters of one and 10, lying on a silicon substrate, and are compared with the predictions from the normal incidence approximation (NIA) in which the reflectance of the surface is assumed constant at the normal incidence value. The results show that the accuracy of the NIA is highly dependent on the extent of the sphere cluster, the angle of incidence, and the particular quantity (cross-sections, scattering matrix elements) under examination.     

Experimental study of the radiation mechanism of the chiral action

The first results of the RAMBAS (Radiation Mechanism of Biomolecular Asymmetry) experiment on the study of the radiation mechanism of the effect on chiral molecules as a factor leading to chiral asymmetry formation are presented. It was found that irradiation with an electron flux from a radioactive source of a mixture of simple achiral materials initiates synthesis of the simplest amino acids; in a racemic mixture of complexes of amino acids and metals irradiation leads to asymmetric decomposition and chrial asymmetry formation. The results obtained can be essential for solving the problem of the origin of life and the formation of chiral asymmetry of the biosphere.     

Acoustic scattering from two spheres,one with a small radius

The scattering of a plane acoustic wave from an acoustically penetrable or impenetrable (soft or hard) sphere separated at a distance from another sphere, also penetrable or impenetrable (soft or hard), of acoustically small radius, is examined. The penetrable spheres and the surrounding medium are fluids or fluidlike; i.e., they do not support shear waves. Separation of variables, in conjunction with translational addition theorems for spherical wave functions, is used. Analytical expressions are obtained for the scattered pressure field and the scattering cross sections. Numerical results are given for penetrable and impenetrable spheres, showing the influence of the small sphere on the scattering cross sections of the other sphere. Published in Russian in Akusticheskiĭ Zhurnal, 2007, Vol. 53, No. 1, pp. 38–49. The text was submitted by the authors in English.     

Experimental method to detect chiral asymmetry in specular light scattering from a naturally optically active medium

An experimental method is described for measuring chiral asymmetries in specular light scattering from a naturally optically active medium with a sensitivity on the order of one part in 10⁶. The chiral asymmetries of interest are the differential reflection of left and right circularly polarised light (circular differential reflection) and the deviation from mutual orthogonality of reflected transverse electric and transverse magnetic polarised light (skewness). The measurement of these chiral asymmetries would permit one to test the recently predicted Fresnel amplitudes for reflection from isotropic optically active transparent and absorving media and thereby to resolved controversial fundamental issues concerning the electrodynamics of chiral media.     

Helical twisting power and circular dichroism in nematic liquid crystals doped with chiral molecules

Explicit expressions for the helical twisting power of a chiral dopant in the nematic phase have been obtained in the mean field approximation taking into account chiral dispersion intermolecular interactions. The results of the theory enable one to explain a correlation between the signs of helical twisting power and circular dichroism of selected electronic transitions which have recently been established experimentally for some mono- and bis-aminoantroquinones. Helical twisting power is proportional to the pseudoscalar parameter that specifies the chirality of the dopant molecule in terms of its dipole and quadrupole matrix elements. This expression is simplified for a special class of molecules in which chirality is induced by a perturbing achiral group into an achiral skeleton. In this case both helical twisting power and circular dichroism are approximately proportional to some simple pseudoscalar functions that specify the location of the achiral perturbing group with respect to the symmetry planes of the unperturbed achiral skeleton. Simple sector rules have been proposed to determine the sign change of the helical twisting power associated with the change of location of the perturbing group.     

Guided and surface modes in chiral nihility fiber

Guided and surface modes in the chiral nihility fiber consisting of a chiral nihility metamaterial core with an achiral cladding have been investigated. The dispersion equations of guided and surface modes in the chiral nihility fiber and their cutoff frequencies are derived. Dispersion curves of guided and surface modes are presented and the effect of chirality parameter on dispersion curves is discussed in detail. Some novel propagation characteristics are found.     

Describing small-scale structure in random media using pulse-echo ultrasound

A method for estimating structural properties of random media is described. The size, number density, and scattering strength of particles are estimated from an analysis of the radio frequency (rf) echo signal power spectrum. Simple correlation functions and the accurate scattering theory of Faran [J.J. Faran, J. Acoust. Soc. Am. 23, 405-418 (1951)], which includes the effects of shear waves, were used separately to model backscatter from spherical particles and thereby describe the structures of the medium. These methods were tested using both glass sphere-in-agar and polystyrene sphere-in-agar scattering media. With the appropriate correlation function, it was possible to measure glass sphere diameters with an accuracy of 20%. It was not possible to accurately estimate the size of polystyrene spheres with the simple spherical and Gaussian correlation models examined because of a significant shear wave contribution. Using the Faran scattering theory for spheres, however, the accuracy for estimating diameters was improved to 10% for both glass and polystyrene scattering media. It was possible to estimate the product of the average scattering particle number density and the average scattering strength per particle, but with lower accuracy than the size estimates. The dependence of the measurement accuracy on the inclusion of shear waves, the wavelength of sound, and medium attenuation are considered, and the implications for describing the structure of biological soft tissues are discussed.     

Theory of chiral imprinting

We present a continuum model for a nematic elastomer network formed in a chiral environment, for instance, in the presence of a chiral solvent. When this environment is removed, the network can retain some memory of its chiral genesis. We predict the residual chiral order for a number of possible scenarios, and examine the robustness (stability) of the imprinted chirality. We show that a twist-untwist transition can take place, which determines whether the imprinting has been successful. A transition is via a coarsening of the helical director pattern and a lengthening of its pitch. Finally, the effect due to a subsequent swelling by an achiral solvent, or by a solvent of differing chirality, is considered.     

Development of highly potent chiral discrimination methods that solve the problems of the diastereomer method

The development of highly potent chiral discrimination methods that solve the problems of the diastereomer method, in which it is impossible to discriminate the diastereomers having chiral centers separated by more than four bonds, is described. On the basis of the results obtained, a new hypothesis, Induced Chiral Fields that the achiral reversed phase can provide chiral fields depending on the structures of the eluents, is proposed to explain the significant results of separation of the diastereomers derived from newly developed chiral and fluorescent labeling reagents and optical isomers by reversed-phase HPLC, which was hitherto impossible.     

Isotropic Maxwell-Garnett model for biisotropic-in-biisotropic mixtures

The Rayleigh scattering response of an electrically small biisotropic sphere immersed in an ambient biisotropic medium has been utilized in constructing a Maxwell-Garnett model of a composite material formed by randomly dispersing biisotropic spheres in a biisotropic host medium. It is anticipated that this work will be of interest for estimating the electromagnetic properties of particulate media.     

Anisotropic spheres with uniform energy density in general relativity

An ansatz is developed to obtain interior solutions of the Einstein field equations for anisotropic spheres. This procedure necessitates a choice for the energy-density and the radial pressure. A class of solutions for a uniform energy-density source is presented. These anisotropic spheres match smoothly to the Schwarzschild exterior and are well-behaved in the interior of the sphere.     

Entropy-driven formation of a chiral liquid-crystalline phase of helical filaments

We study the liquid-crystalline phase behavior of a concentrated suspension of helical flagella isolated from Salmonella typhimurium. Flagella are prepared with different polymorphic states, some of which have a pronounced helical character while others assume a rodlike shape. We show that the static phase behavior and dynamics of chiral helices are very different when compared to simpler achiral hard rods. With increasing concentration, helical flagella undergo an entropy-driven first order phase transition to a liquid-crystalline state having a novel chiral symmetry.