State analysis related to zinc and manganese components in hopeite crystals of zinc phosphate films by XANES and EXAFS

Using Hopeite crystals as zinc phosphate films formed on zinc coated steel sheets of automobile body, EXAFS methods were applied to analyze the local structure of heavy metal components contained in these crystals. The relationship between these spectral data and the modified crystal structure of Hopeite was discussed. Analysis was done by observing XANES spectra and Fourier transformation of EXAFS for two kinds of powdered Hopeite crystals formed in zinc phosphating bath. XANES and EXAFS spectra for Zn-K and Mn-K absorption edge of the Hopeite containing a manganese component were compared with those of the manganese free sample. Both spectra showed almost the same value of the absorption edge with 9.662–9.663 keV, but the amplitude of XANES and EXAFS spectra for the former was smaller than that for the latter. And, though Mn-K absorption edges were 6.545–6.546 keV for the modified Hopeite crystals and MnO, that of MnO₂ showed a higher value by 5–6eV than the former samples. The peak position of EXAFS relating to first neighbouring atom showed the same difference as in XANES. These facts support that manganese exists as Mn²⁺ in the modified Hopeite crystals. XANES spectra and Fourier transformation of EXAFS provided a conclusion that the modified Hopeite crystal has a structure of Zn_3–xMn_x(PO₄)₂ · 4H₂O.     

Local Order and Structure in Mn-Substituted Manganites Studied by EXAFS

We report extended X-ray absorption fine structure measurements at the Mn K edge on La_0.25Ca_0.75Mn_0.92Cr_0.08O₃ samples. Macroscopically, the Mn substitution induces a short-range charge-ordered state in spite of the long-range one present in the parent manganite La_0.25Ca_0.75MnO₃. We show how on a local scale the structural EXAFS parameters still confirm the presence, with only a slight reduction, of the features characteristic of the charge ordered un-substituted compounds.     

Displacement incrementation in non-linear structural analysis by the self-correcting method

The prediction of non-linear structural behaviour by the finite element method wherein buckling does not occur has received considerable attention and, with it, reasonable success has been achieved. However, the post-buckling problem has been less actively pursued probably because of the inherent numerical difficulties encountered. This Technical Note reviews very briefly the numerical methods currently being used for pre- and post-buckling analysis and presents a self-correcting approach based on load and displacement incrementation which is shown to be efficient, reliable, and easy to program. Numerical solutions are presented which demonstrate the effectiveness of the method.     

Variational principle in the EXAFS analysis

A new method has been developed for separating the smooth and oscillating components in extended X-ray absorption fine structure (EXAFS) spectra. The form of a functional, which is minimized by the smooth function, is proposed. This method is applied to an analysis of the EXAFS spectrum of copper. A method of solution optimization is described. The results of application of the proposed method to the experimental spectra are presented.     

Crystal growth and structural analysis of zirconium sulphoselenide single crystals

A series of zirconium sulphoselenide (ZrS _x Se_3−x , where x = 0, 0·5, 1, 1·5, 2, 2·5, 3) single crystals have been grown by chemical vapour transport technique using iodine as a transporting agent. The optimum condition for the growth of these crystals is given. The stoichiometry of the grown crystals were confirmed on the basis of energy dispersive analysis by X-ray (EDAX) and the structural characterization was accomplished by X-ray diffraction (XRD) studies. The crystals are found to possess monoclinic structure. The lattice parameters, volume, particle size and X-ray density have been carried out for these crystals. The effect of sulphur proportion on the lattice parameter, unit cell volume and X-ray density in the series of ZrS _x Se_3−x single crystals have been studied and found to decrease in all these parameters with rise in sulphur proportion. The grown crystals were examined under optical zoom microscope for their surface topography study. Hall effect measurements were carried out on grown crystals at room temperature. The negative value of Hall coefficient implies that these crystals are n-type in nature. The conductivity is found to decrease with increase of sulphur content in the ZrS _x Se_3−x series. The electrical resistivity parallel to c-axis as well as perpendicular to c-axis have been carried out in the temperature range 303–423 K. The results obtained are discussed in detail.     

A novel meshless approach – Local Kriging (LoKriging) method with two-dimensional structural analysis

This paper develops a novel meshless approach, called Local Kriging (LoKriging) method, which is based on the local weak form of the partial differential governing equations and employs the Kriging interpolation to construct the meshless shape functions. Since the shape functions constructed by this interpolation have the delta function property based on the randomly distributed points, the essential boundary conditions can be implemented easily. The local weak form of the partial differential governing equations is obtained by the weighted residual method within the simple local quadrature domain. The spline function with high continuity is used as the weight function. The presently developed LoKriging method is a truly meshless method, as it does not require the mesh, either for the construction of the shape functions, or for the integration of the local weak form. Several numerical examples of two-dimensional static structural analysis are presented to illustrate the performance of the present LoKriging method. They show that the LoKriging method is highly efficient for the implementation and highly accurate for the computation.     

Sub-bandgap analysis of boron doped InSe single crystals by constant photocurrent method

Sub-bandgap absorption properties of indium selenide doped with boron atoms within a range of [B] = 0–1.8 at.% have been investigated. From the absorption coefficient spectra measured by using constant photocurrent method (CPM) at 300 K, we observed that the disorder in the structure increases. The calculated Urbach parameters, quantifying the disorder, vary from 17 to 53 meV, as [B] is increased from 0 to 1 at.%. Also the calculated optical gaps decrease from 1.28 eV to 1.17 eV for the same range of [B]. From temperature dependent dark conductivity measurements, the characteristic activation energies are calculated to range from 0.25 to 0.18 eV for vertical (to c-axis) direction; to stay almost constant for parallel (c-axis) direction. At a temperature of 12 K, the absorption coefficient spectra by using CPM and the radiative recombination spectra by photoluminescence (PL) have been taken for the samples with [B] = 0 and 0.5 at.%. Three main PL bands are observed at photon energies of ∼1.24, 1.306 and 1.337 eV. The PL bands are interpreted by corresponding absorption bands detected at 12 K and at the photon energies of ∼1.24, ∼1.31 and ∼1.35 eV.     

EXAFS Study of the Local Order and Structure in Cu Doped Manganites

We report extended X-ray absorption fine structure measurements at the Mn K edge on (La_0.63Ca₀₃₇) (Mn_0.92Cu_0.08)O₃ and (La_0.25Ca₀₇₅)(Mn_0.92Cu_0.08)O₃ samples. We observe that the Cu²⁺ substitution in these two compounds belonging from the opposite sides of the phase diagram induces two very different effects. In the first case, it weakens ferromagnetic ordering, while in the second one, it does not significantly modify the charge ordering present in the system.     

Synthesis of ZnO single crystals by the flux method

Zinc oxide (ZnO) single crystals have been grown at temperatures ranging from 450–900 °C and for 1–12 h, using hydrous KOH and NaOH melts as fluxes. For a KOH flux, brown ZnO single crystals with diameter 0.5 mm × 7.5 mm were grown under conditions of 500 °C for 20 h and white crystals of diameter 0.5 mm × 7 mm were grown at 800 °C for 20 h, using a small crucible (average 50 ml). When a large crucible (average 400 ml) was used, ZnO single crystals with diameter 0.5 mm × 8 mm were formed at 900 °C for 30 h. When using a KOH + NaOH (1∶1) flux, light-brown and long crystals with diameter 1.0 mm × 18 mm could be grown. The grown ZnO single crystals were bounded with only both p- and m-faces. It seems that crystal qualities were good under conditions of 900 °C for 30 h. The following mechanisms of dissociation and formation of ZnO single crystal from KOH (or NaOH) + ZnO melt seemed to occur $$KOH(or{\text{ NaOH}}){\text{ }} \to {\rm K}^ + {\text{ (or Na}}^{\text{ + }} {\text{) + OH}}^ - $$ $$ZnO{\text{ + 2 OH}}^ - \to {\text{ ZnO}}_{\text{2}}^{{\text{2}} - } {\text{ + H}}_{\text{2}} {\text{O,}}$$ $${\text{ZnO}}_{\text{2}}^{{\text{2}} - } {\text{ }} \to {\text{ ZnO + O}}^{{\text{2}} - } .$$      

Nonlinear structural analysis using integrated force method

Though the use of the integrated force method for linear investigations is well-recognised, no efforts were made to extend this method to nonlinear structural analysis. This paper presents the attempts to use this method for analysing nonlinear structures. General formulation of nonlinear structural analysis is given. Typically highly nonlinear bench-mark problems are considered. The characteristic matrices of the elements used in these problems are developed and later these structures are analysed. The results of the analysis are compared with the results of the displacement method. It has been demonstrated that the integrated force method is equally viable and efficient as compared to the displacement method.     

On the method of calibration of the energy dispersive EXAFS beamline at Indus-2 and fitting theoretical model to the EXAFS spectrum

A procedure for calibration of the recently developed energy dispersive EXAFS beamline at the Indus-2 synchrotron source at RRCAT, Indore, India has been described. The procedure involves recording of absorption spectra of two standard samples, whose absorption edge energies are well-established. Two methods have been considered for calibration. In the first method, the position of the first maximum of the derivative of absorption curve is taken as the position of the edge energy. In the second method, the position of the point at half edge step in the absorption curve is taken as the position of the edge energy. It has been shown that only the first method gives same values of dispersion even when the beam current is varied and should be used for calibrating the experimental spectra. Further, it is recommended that the performance of the beamline for a particular setting should be checked by recording and analysing EXAFS of a standard. Hence, the procedure for analysis and extracting information about the various parameters that can be determined by fitting the EXAFS data with a theoretical model has also been described, by taking the example of K-absorption spectra of copper metal foil recorded on this beamline.     

Local deformation in diamond crystals defined by the Fourier transformations of Kikuchi patterns

A new approach has been proposed to determination of local strains in crystals using patterns of electrons backscattering diffraction (Kikuchi patterns) and discrete two-dimensional Fourier transformations. The new approach has been tested in studying diamond samples synthesized under different conditions. The results obtained have been found to agree well with the data obtained by other methods.     

Growth of lead sulfide single crystals by the bridgman method

Large crackfree crystals could be grown by the Bridgman technique using graphite ampoules. Their metallurgical properties are typical for Bridgman crystals. However, a high content of carbon is incorporated into the crystals using this method. The variation of the carrier concentration along the length of the crystal could be deduced from the phase diagram.     

Inelasticity monitoring of structural materials by the resonance method

We have developed a method which provides monitoring of the inelasticity kinetics of polycrystal materials by variation of the stress-strain phase-shift angle in the locally loaded surface zone of the material under study. The proposed method allows one to determine current value of damage of investigated aluminum alloy under laboratory conditions of cyclic deformation by variation of statistical characteristics of phase-shift angle distribution. AMg6N aluminum alloy, which is a cyclically hardening material, was used in this study. Translated from Problemy Prochnosti, No. 3, pp. 124–133, May–June, 2009.     

A new method for the structural analysis of thin island films

Analytical formulas for a systemic analysis of the structural coarsening of an island film on a solid substrate are obtained based on a comparison of the characteristics of theoretical and experimental distributions of the island size. This approach established a correlation between the features of transformation of the experimental distributions (histograms) and the features of processes in the island film material.     

Time analysis of structural concrete elements using the equivalent displacement method

This paper presents a modelling technique referred to as the equivalent displacement method (EDM) which describes the behaviour in time of structural concrete elements, such as reinforced concrete beams and composite beams with full shear interaction, accounting for time effects, such as creep, of the concrete component. The time-dependent behaviour of the concrete is modelled using the algebraic representations, such as the age-adjusted effective modulus method (AEMM), while the steel joist and reinforcement are assumed to behave in a linear-elastic fashion. The main advantage of the EDM method is that it requires only one analysis to obtain the deformation state of the structural system at one step in time based on the AEMM methods, instead of the two required by available modelling techniques (i. e. one performed at timet ₀ and one performed one step in timet). The EDM method is then applied to the analysis of structural concrete elements using the stiffness analysis and the results obtained based on this modelling technique are validated against other modelling methods. The advantages of using the EDM method in design applications are also illustrated.

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Résumé Cet article présente une méthode appelée méthode de déplacement équivalent (EDM), qui décrit le comportement temporel des éléments de béton, par example les poutres en béton armé et les poutres mixtes à interaction complète, tenant compte des effets temporaux, tel que le fluage du béton. Le comportement temporel du béton est modelé par représentation algébrique, tel que la méthode age ajusté du module effectif (AEMM), tandis que la poutre d'acier et les renforts sont supposés linéaire et élastique. L'avantage majeur de la méthode EDM est qu'elle n'exige qu'une seule analyse pour obtenir l'état de déformation du système à un point temporel (méthode EDM), au lieu des deux points exigés par les méthodes courantes, en temps t₀ et l'autre à t. La méthode EDM est ensuite appliquée à l'analyse des éléments structurels en béton, utilisant l'analyse de raideur, et les résultats obtenus par cette méthode sont vérifiés par d'autres méthodes. Les avantages de l'utilisation de la méthode EDM dans les applications du dessein sont aussi illustrés.

     

基于结构动力学方法的气动弹性分析

摘 要：对于气动与弹性的耦合模型,给出气动力的频域公式,并表示成有理多项式,通过等价的变换,能够推导出与结构动力学方程完全相似的、关于求解变量的二阶常微分方程组。于是,可以在计算结构动力学框架下实现气动弹性问题的分析和计算。此方法将通用计算结构动力学程序的功能与试验或数值分析得到的气动力模型相结合,简化了气动弹性的耦合分析、提高计算效率。     

An iterative penalty function method in structural analysis

An iterative solution process combined with the penalty function method employed in constrained variational priciples is described. As an example of the use of the method an axi-symmetric plate with the complementary energy formulation is considered.