Kinetics of the Coordination Transformation for Preparation of Nanosized ZnS in a PVA Film

Abstract

This study was focused on the pervasion process of sulfion in a PVA–Zn²⁺ complex film. A diffusion equation for this process, based on the Fick first diffusion law, is suggested, which was in good agreement with the experimental results. The diffusion constant was 9.92 × 10^?6 cm²/sec, calculated by combining the model and the experimental results.     

The B(3) field: Its role in the Rayleigh-Jeans law,Planck law,and Einstein coefficients

The role of the novel longitudinal vacuum fieldB ⁽³⁾is discussed in relation to fundamental radiation laws: the Rayleigh-Jeans law, the Planck law, and the Einstein coefficients. The circular index (3) ofB ⁽³⁾causes electromagnetic energy density to be redistributed from the other indices (1) and (2) of the circular basis, but the presence ofB ⁽³⁾in the vacuum does not change the value of the Planck constant h. TheB ⁽³⁾field does not affect, furthermore, the understanding of quantized radiation absorption first proposed by Einstein. Therefore, the experimental observableB ⁽³⁾ does not imply modification of these fundamental, radiation laws, and experimental isolation ofB ⁽³⁾ must take place through its characteristic square root power density dependence when used to magnetize an électron plasma.     

Effects of cross correlations between inhomogeneities of the parameters of an isotropic medium on the spectrum and damping of elastic waves

The dispersion and damping laws have been investigated for elastic waves in an isotropic medium with one- and three-dimensional inhomogeneities of the density p(x) of the material and the elastic force constants μ(x) and λ(x) with allowance for the cross correlations between these inhomogeneities. It has been demonstrated that the positive cross correlations between μ(x) and λ(x), as well as the negative cross correlations between p(x) and μ(x) or p(x) and λ(x), lead to an enhancement of the modification of the dispersion law and an increase in the damping of waves. The positive cross correlations between p(x) and μ(x) or p(x) and λ(x), as well as the negative cross correlations between μ(x) and λ(x), result in the opposite effects: a weakening of the modification of the dispersion law and a decrease in the damping. An analysis of the results obtained in this paper and in our recent work [15] has made it possible to formulate the general regularity of the effects of cross correlations, irrespective of the physical nature of the waves: the effects of cross correlations between inhomogeneities of any two parameters of the material on the wave spectrum depend on whether both parameters related by the cross correlations belong to the same part of the Hamiltonian (i.e., if they both belong to either the kinetic part or the potential part of the Hamiltonian) or they belong to different parts of the Hamiltonian. The positive cross correlations lead to a greater modification of the dispersion law and to an increase in the damping of waves in the former case and to a decrease in these characteristics in the latter case. Correspondingly, the negative cross correlations in each of these cases result in the opposite effects. This regularity has been explained qualitatively.     

On the T Bloch law in magnets with fourth-order exchange interaction

For the ferromagnets EuS and GdMg, in which fourth-order exchange interactions (i.e. biquadratic, three-spin and four-spin interactions) have been identified, the deviation of the spontaneous magnetization with respect to the T =0 value is shown to follow a T² law instead of the famous T3/2 law expected for a Heisenberg ferromagnet. Moreover, the observed T² law holds for temperatures as large as 0.8T_C and the extrapolated magnetization value for does not conform to ferromagnetic saturation. This is because the fourth-order exchange interactions generate a second order-parameter which is assumed to govern the order of the transverse moment components. These moment components have a finite expectation value for at the expense of the Heisenberg order parameter. Like the spontaneous magnetization, the critical field curves B c ( T ) of the metamagnet EuSe and the antiferromagnet EuTe also start decreasing with a T² term for . It is argued that the T² law is a consequence of the fourth-order exchange interactions. This is shown experimentally by a study of the critical field curves [0pt] pertinent to the longitudinal (Heisenberg) order-parameter in the diamagnetically diluted antiferromagnets Eu_xSr_1-xTe. In this solid solution series a particular composition of x c =0.85 exists at which the different fourth-order interaction processes compensate each other in the high temperature average. As a consequence, an Eu_xSr_1-xTe sample with x =0.85 meets the requirements of a Heisenberg antiferromagnet at least if a quantity is considered for which the high-temperature average over all fourth-order interactions is decisive. This seems to be the case for the critical field curve [0pt] which gives the phase boundary to the paramagnetic phase. In fact, a crossover from a T² to a T3/2 law is observed for [0pt] on approaching x_c. This, we believe, shows the frequently observed T² law is caused by the fourth-order interactions. Received 23 July 1998 and Received in final form 12 October 1998     

Theoretical and Experimental Study of Long-Period Grating Refractive Index Sensor

Abstract

This article presents the theoretical and experimental investigation of the response of long-period gratings as a refractive index sensor. Cladding modes are calculated, and results are compared with Optigrating 4.2.2 (Optiwave Systems Inc., Ottawa, Canada). The response has been checked for refractive indices ranging from 1 to 1.458. Theoretically simulated results are in accordance with the experimental results. It was found that the software package calculated values correctly up to the seventh decimal point. The ambient refractive index response of a long-period grating over a much wider index range has been modeled for values both less and more than the cladding refractive index.     

All Valence Electron Molecular Orbital Study of Electronic Strture and Spectra of the Three Isometric Xylenes

Abstract

The modified method of Del Bene and Jaffe' (CNDO-CI) has been applied to study the electronic structure and spectra of the three isomeric xylenes taking a three dimensional geometry for the CH₃ group. The spectral transition energies and the corresponding oscillator strengths have been computed and the results are compared with ?-electron calculations and experimental results. Quite satisfactory results have been obtained. Ionization potentials have also been computed by the INDO and extended Hückel methods.     

On the 240 K anomaly in the magnetic properties of LiNiO2

In this work, results of X-band ESR spectroscopy, ac-magnetic susceptibility and X-ray powder diffraction measurements on Li_1-xNi _1+x O₂ (x = 0.02 and x = 0.07) are presented and discussed. While the susceptibility of the compound with x = 0.02 is shown to follow a Curie-Weiss law, with a Weiss temperature of the order of 30 K, the compound with x = 0.07 is found to order ferromagnetically below K. However, an additional anomaly is observed in the magnetic properties of this latter compound at around 240 K. We attribute this anomaly to the presence of macroscopic Ni-rich regions which order ferrimagnetically below this temperature. This phenomenon is different from the bulk ferromagnetism that occurs at much lower temperatures, and allows us to discard earlier suggestions proposed in the literature in which the 240 K anomaly has been considered as denoting an intrinsic phenomenon. Received 14 May 1999 and Received in final form 5 August 1999     

Reanalysis and semi-empirical predictions of the hyperfine structure of in the model space

On the basis of most of the earlier hyperfine-structure (hfs) experimental results, the hfs of the atomic zirconium has been reanalyzed by the simultaneous parameterization of the one- and two-body interactions for the model space (4 d + 5 s ) ⁴ . The values of the one- and two-body hfs parameters have been determined and the nuclear quadrupole moment, free of Sternheimer corrections up to second order, has been evaluated. Moreover, the values of the magnetic-dipole A and the electric-quadrupole B constants for all known levels of this model space have been predicted. Received: 22 December 1997 / Revised: 15 May 1998 / Accepted: 1 July 1998     

First principles study of electronic structure and optical properties of CaTiO3

The electronic-energy band structure, site and angular momentum decomposed density of states (DOS) and charge-density contours of perovskite CaTiO ₃ are calculated by the first principles tight-binding linear muffin-tin orbitals method with atomic sphere approximation using density functional theory in its local density approximation. The calculated band structure shows an indirect (R-Γ) band gap of 1.5 eV. The total DOS as well as the partial density of states (PDOS) are compared with the experimental photoemission spectra. The calculated DOS are in reasonable agreement with the experimental energy spectra and the features in the spectra are interpreted by a comparison of the spectra with the PDOS. The origin of the various experimentally observed bands have been explained. From the DOS analysis, as well as charge-density studies, we conclude that the bonding between Ca and TiO ₃ is mainly ionic and that the TiO ₃ entities bond covalently. Using the projected DOS and band structure we have analyzed the interband contribution to the optical properties of CaTiO ₃ . The real and imaginary parts of the dielectric function and hence the optical constants such as refractive index and extinction coefficient are calculated. The calculated spectra are compared with the experimental results for CaTiO ₃ and are found to be in good agreement with the experimental results. The effective number of electrons per unit cell participating in the interband transitions are calculated. The role of band structure calculation as regards the optical properties of CaTiO ₃ is discussed. Received 1 February 2000 and Received in final form 21 July 2000     

Sub-shell distributions of total electron capture and ionization cross-sections in Bq+ (q = 1−4) + H collisions

The Classical Trajectory Monte-Carlo (CTMC) simulation method has been employed to calculate the total electron capture cross-sections with sub-shell distributions and ionization cross-sections in collision of B ^q+ (q=1-4) with ground state atomic hydrogen in the energy range of 10-200 keV/amu. The computed results have been observed to be in reasonable agreement with other existing theoretical and experimental results over the entire energy region considered. Received 23 February 1999 and Received in final form 23 May 1999     

Beyond modified mean field: a case for a stochastic grain growth model

ABSTRACT

We address the basic mechanism of grain growth in two and three dimensions in single phase metallic systems. It is argued, a comprehensive grain growth model is best based on a stochastic process described by a Fokker Planck equation. This concept is sufficient to determine almost all features of grain growth in general terms. The existence of the von Neumann law and its counterpart in three dimensions enables us to provide an explicit form of the Fokker Planck equation and thus determine many features of grain growth in great detail. Finally, we illustrate this model by determining the salient features of grain growth in three dimensions in the long time limit, and comparing them with experimental and computational results.     

Quantum 1/f noise associated with ionized impurity scattering and electron-phonon scattering in condensed matter

Scattering of charged particles is accompanied by the emission of soft photons. Handel's theory of 1/f noise, based on the infrared quasi-divergent coupling of the system to the electromagnetic field, indicates that the current associated with a beam of scattered particles will exhibit 1/f noise. His derivation is valid in a vacuum. Here we extend his results and obtain the fluctuation spectrum for the fluctuations in cross-section and for the scattering rates w _kk′ in k-space, using the Born approximation. Next we consider mobility fluctuations due to these scattering rates, employing the relaxation time solutions of the Boltzmann transport equation, valid in non-degenerate semiconductors. Explicit results are obtained for the mobility-fluctuation noise caused by ionized impurity scattering, acoustic phonon scattering, optical phonon scattering, polar optical phonon scattering, and intervalley scattering. We derive Hooge's law, and the Hooge parameters for the above-mentioned processes are obtained in detail. This is then applied to n-type silicon and n-type gallium arsenide; the overall Hooge parameter, which is a weighted average of the partial α-parameters, is computed as a function of temperature and compared with experiment. For silicon, good agreement is obtained with available data. As a byproduct we also find the mobilities as function of temperature for these materials. Excellent agreement with the well-known experimental data is observed.

We still note that this is the first theoretical derivation of Hooge's law and that the magnitude of the noise is obtained in detail without adjustable parameters. We believe that quantum 1/f noise gives the limiting value of 1/f noise that can be observed.     

Influence of small-angle scattering on magnetoresistance

Small-angle scattering can produce significant effects when the Fermi surface is able to provide both electron and hole orbits in a magnetic field. These orbits may run close to one another ink-space so that scattering through a small angle is sufficient to change the path of an electron radically. Simple models of the phenomenon will be described and their calculated behaviour compared with experimental results. This work has been published in Proc. Roy. Soc.A 305, 291 (1968).     

Lifetime measurements of some levels belonging to the 3p <Emphasis Type="Bold">5</Emphasis>nd ( , 5, 6, 7) configuration of ArI

Lifetimes of some 3p^5nd (n = 4, 5, 6, 7) levels of neutral argon have been measured by high frequency deflection technique with a delayed coincidence single photon counting arrangement. The measurements have been performed under conditions where pressure dependent effects are negligible. Lifetimes of some of the levels have been measured for the first time. The results have been compared with other experimental and theoretical values. Received 7 August 2002 / Received in final form 20 December 2002 Published online 24 April 2003     

The spectral distribution of light scattered from methyl fluoride in the critical region

Abstract

The experimental data for the spectral distribution of light scattered from methyl fluoride in the critical region are collected and analysed for different polarization directions by means of a Fabry-Pérot etalon. The analysis reveals the presence of an unshifted Rayleigh line and two frequency shifted Brilllouin lines for polarized and depolarized intensities. The intensity ratio of these lines - the so-called Landau-Placzek ratio - is determined along the critical isochore and its divergence near the critical point is described by a power law expression.     

A new constitutive relation for simulating plastic flow involving continuous-shear or shear-localisation during metal cutting

ABSTRACT

A new constitutive relation has been established by modifying Zerilli-Armstrong formulation whose performance is investigated in simulating continuous-shear and shear-localisation during orthogonal machining of a super alloy. Two different procedures in consonance with strains, strain rates, temperatures and thermo-mechanical-coupling encountered during metal cutting were adopted to identify material-constants for continuous-shear and shear-localisation. The constitutive data for continuous-shear is generated by using the distributed- primary-zone-deformation model. In contrast, an inverse methodology is followed to calibrate material-constants for shear-localisation where values were adjusted iteratively until predicted cutting force and chip morphology matched experimental values. The iterative procedure was also used to investigate sensitivity of shear-localisation to constitutive parameters. The constitutive relation was later implemented in two different finite element models to separately simulate serrated- and continuous-chip formation. The proposed constitutive relation successfully captured the underlying physics of continuous-shear and shear-localisation with finite element predictions of cutting force and chip morphology being in good agreement with experimental results over the range of conditions encompassing the two deformation mechanisms. The proposed law was further validated against split-Hopkinson-pressure-bar test-data. Moreover, the proposed relation gave better physics-based predictions when compared to those from the Johnson-Cook model.     

Ultraviolet photoelectron spectroscopy of Si 4 - to Si 1000 -

Using a new experimental setup we have measured UV (h ν = 6.4 eV) photoelectron spectra of cold silicon cluster anions Si _n ^- in a very broad size range. For sizes up to n = 46 the spectra exhibit rich structures. For larger sizes only smooth spectra have been obtained. No trace of a bandgap has been found even for clusters with more than 1000 atoms. Received 30 November 2000     

The fundamental vibrational shift of HCl diluted in dense Ar and Kr

The fundamental infrared band vibrational shifts of HCl diluted in dense Ar and Kr have been calculated by means of molecular dynamics simulation techniques and compared with the experimental data reported by Pérez et al. (J. Chem. Phys. 122, 194507 (2005)). The results have been analysed along the liquid–vapour coexistence line as in several supercritical states, with good agreement between the theoretical and experimental values.     

Systematic row and zone axis STEM defect image simulations

Transmission electron microscopy (TEM) has been instrumental in advancing the field of crystalline defect analysis. Conventional TEM imaging techniques, such as bright field (BF), dark field (DF), and weak beam dark field (WBDF or g–3g) imaging, have been well-documented in the scientific literature, with simulation methods readily available for each. The present contribution highlights the use of a field-emission TEM, operated in scanning transmission electron microscopy mode, as a viable tool for defect analysis. Common techniques such as two-beam diffraction contrast and zone axis imaging are applied to defect analysis; both experimental and computational results are presented. Effects of experimental parameters such as camera length, beam divergence angle, and diffraction aperture placement are also discussed and illustrated by both experimental and computed micrographs of stacking faults.     

Theory of chemical bonds in metalloenzymes XX: magneto-structural correlations in the CaMn4O5 cluster in oxygen-evolving complex of photosystem II

ABSTRACT

Magneto-structural correlations in oxygen-evolving complex (OEC) of photosystem II (PSII) have been elucidated on the basis of theoretical and computational results in combination with available electron paramagnetic resonance (EPR) experimental results, and extended x-ray absorption fine structure (EXAFS) and x-ray diffraction (XRD) results. To this end, the computational methods based on broken-symmetry (BS) UB3LYP solutions have been developed to elucidate magnetic interactions in the active manganese catalyst for water oxidation by sunlight. The effective exchange interactions J for the CaMn(III)Mn(IV)₃O₅(H₂O)₃Y(Y = H₂O or OH^?) cluster (1) model of OEC of PSII have been calculated by the generalised approximate spin projection (GAP) method that eliminates the spin contamination errors of the BS UB3LYP solution. Full geometry optimisations followed by the zero-point energy (ZPE) correction have been performed for all the spin configurations of 1 to improve the J values that are compared with accumulated EPR in the S₂ state of Kok cycle and magnetic susceptibility results of Christou model complex Ca₂Mn(IV)₃O₄ (2). Using the calculated J values, exact diagonalisation of the spin Hamiltonian matrix has been carried out to obtain excitation energies and spin densities of the ground and lower excited states of 1. The calculated excitation energies are consistent with the available experimental results. The calculated spin densities (projection factors) are also compatible with those of the EPR results. The calculated spin densities have been used to calculate the isotropic hyperfine (A_iso) constants of ⁵⁵Mn ions revealed by the EPR experiments. Implications of the computational results are discussed in relation to the structural symmetry breaking (SSB) in the S₁, S₂ and S₃ states, spin crossover phenomenon induced by the near-infrared excitation and the right- and left-handed scenarios for the O–O bond formation for water oxidation.