Fast evaluation of time domain fields in sub-wavelength source/observer distributions using accelerated Cartesian expansions (ACE)

Time domain integral equation solvers for transient scattering from electrically large objects have benefitted significantly from acceleration techniques like the plane wave time domain (PWTD) algorithm; these techniques reduce the asymptotic CPU and memory cost. However, PWTD breaks down when used in the analysis of structures that have subwavelength features or features whose length scales are orders of magnitude smaller than the smallest wavelength in the incident pulse. Instances of these occurring in electromagnetics range from antenna topologies, to feed structures, etc. In this regime, it is the geometric constraints that dictate the computational complexity, as opposed to the wavelength of interest. In this work, we present an approach for efficient analysis of such sub-wavelength source/observer distributions in time domain. The methodology that we seek to exploit is the recently developed algorithm based on Cartesian expansions for accelerating the computation of potentials of the form R^ν. In this paper, we present an efficient methodology for computing these polynomials for two different scenarios; where the size of the domain spans the distance travelled by light in (i) one time step and (ii) multiple time steps. These algorithms are cast within the framework of both uniform and non-uniform distributions. Results that demonstrate the efficiency and convergence of the proposed algorithm are presented.     

Analysis of crystal binding of ammonium halides

Electronic polarizabilities and sizes of ions in NH₄Cl, NH₄Br and NH₄I crystals are calculated using Ruffa's theory and an empirical relation between polarizability and radius. Using the electronic polarizabilities we have estimated the van der Waals dipole-dipole and dipole-quadrupole potentials following the Slater-Kirkwood varitional method. These potentials and ionic radii are then used to calculate the cohesive energies of ammonium halides. The results are discussed and compared with those of other investigators.     

Effect of surface-topology on magnetic properties in (La0.6Eu0.4)0.67Ca0.33MnO3 of anisotropic shape of nanoplates

(La_0.6Eu_0.4)_0.67Ca_0.33MnO₃ has been prepared in the shape of nanoplates of single crystallites (an orthorhombic structure) through polymer templates. HRTEM images reveal 18, 25, and 30 nm thicknesses of plates after heating a precursor powder at 873, 1073, and 1273 K in air for 2 h. These values present average crystallite size determined from broadening of the X-ray diffraction peaks. A spin-glass-like surface (GS) overlayer (3-5 nm thickness) in such plates facilitates a ferromagnetic→ferrimagnetic reordering with markedly suppressed Curie point T_C, i.e., as small as 90 K in a 873 K heated sample, from the parent value 268 K. The T_C point increases to 103 K (or 120 K) when heating at higher temperature 1073 (or 1273 K), during which the core grows at the expense of the overlayer. The GS tailors as high coercivity H_c as 617 Oe in the zero field cooled (ZFC) sample that is decreased to 500 Oe in the field cooled (FC) sample in the surface spin-freezing along the field direction. The H_c-value (ZFC) that steps down successively to 252 Oe on the overlayer is thinned down by heating at 1273 K. Samples heated at 873, 1073, or 1273 K have regularly increased saturation magnetization 35.3, 63.9, or 69.6 emu/g in ZFC, while 43.7, 70.2, or 75.5 emu/g in FC measured at 10 K. The ferrimagnetic reordering are described based on the scenario of an antiferromagnetic exchange coupling between the Eu³⁺ and Mn³⁺ (or Mn⁴⁺) sublattices.     

High-spin states in odd-odd 168Lu

High-spin states in the odd-odd ¹⁶⁸Lu nucleus, populated in the ¹⁵⁴Sm(¹⁹F,5n) reaction at a beam energy of 96 MeV, were investigated using in-beam γ-ray spectroscopy techniques. The BC neutron crossing in the yrast band, based on πg _7/2[404]7/2⁺⊗νi _13/2[642]5/2⁺ configuration, occurs at ħω= 0.31 MeV. The two side bands, based on πh _11/2[514]9/2⁻⊗νi _13/2[642]5/2⁺ and πh _9/2[541]1/2⁻⊗νi _13/2[642]5/2⁺ configurations, show anomalous signature-splitting and signature-inversion in the first one, to occur at ħω= 0.24 MeV. A moderately delayed BC-crossing is anticipated in the second one. Received: 15 June 1998 / Revised version: 11 January 1999     

Volume dependence of the dielectric constants and the effective charge parameter in alkali halides under hydrostatic pressure

The method often used for evaluating the strain derivatives of the effective charge parameter in ionic crystals is based on the deformation dipole model. In the present communication we show that the strain derivatives of the effective charge parameter calculated from the Phillips-Lawaetz ionicity model are closer to the recent experimental data on the volume dependence of dielectric constants.     

Structural stability of alkaline earth oxide crystals

Using recemtly developed interionic potentials we have studied the structural stability problem of MgO, CaO, SrO and BaO crystals. The observed crystal structure for the alkaline earth oxides viz. NaCl structure is found to be stable only when Lundqvist's three body potential is taken into account along with Madelung's potential, overlap repulsive potential and van der Waals potentials.     

Electronic polarizabilities of ions in transition metal oxides

A method for evaluating the electronic polarizabilities from ionic radii in transition metal oxides has been suggested. The ionic radii used in the present calculations are those deduced from the electron density measurements. The calculated polarizabilities agree closely with the experimental values obtained from the electronic dielectric constant.     

Chemistry of metal (benzylidene) picramates. Part II. Benzylene picramates of copper and silver

Summary Benzylidene picramates of copper and silver have been prepared by treating the corresponding aqueous acetate and nitrate solutions with the sodium salt of 4dimethylamino-benzylidene-2-hydroxy-3,5-dinitroaniline. 1 : 2 and 1 : 1 Metal: ligand ratios have been established for copper and silver benzylidene picramates respectively with the help of microanalysis and have been confirmed by spectrophotometric, potentiometric and conductometric measurements. The i.r. studies of the metal benzylidene picramates show N M coordination, M = Cu or Ag. Explosive properties of these benzylidene picramates have also been studied and it was found that the thermal stability increases as the atomic radius of the metal decreases.Part I,Propellants and Explosives 2, 74 (1977).Deceased.