Growth and characterization of 2-hydroxy-4-methoxybenzophenone single crystal using modified vertical Bridgman technique

The 2-hydroxy-4-methoxybenzophenone single crystal has been grown by the modified vertical Bridgman technique using the double wall ampoule. The grown crystal was confirmed by single and powder X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy analyses. High resolution X-ray diffraction (HRXRD) analysis indicates the crystalline perfection of the grown crystal. The cutoff wavelength of the grown crystal was analyzed by optical studies. The dielectric measurements were carried out and the results indicate an increase in dielectric and conductivity parameters with the increase of temperature at all frequencies. The thermal property of the grown crystal was studied by thermo gravimetric (TG) and differential thermal analyses (DTA).     

A modified evidential methodology of identifying influential nodes in weighted networks

How to identify influential nodes in complex networks is still an open hot issue. In the existing evidential centrality (EVC), node degree distribution in complex networks is not taken into consideration. In addition, the global structure information has also been neglected. In this paper, a new Evidential Semi-local Centrality (ESC) is proposed by modifying EVC in two aspects. Firstly, the Basic Probability Assignment (BPA) of degree generated by EVC is modified according to the actual degree distribution, rather than just following uniform distribution. BPA is the generation of probability in order to model uncertainty. Secondly, semi-local centrality combined with modified EVC is extended to be applied in weighted networks. Numerical examples are used to illustrate the efficiency of the proposed method.     

Size distribution of magnetic iron oxide nanoparticles using Warren–Averbach XRD analysis

We use the Fourier transform based Warren–Averbach (WA) analysis to separate the contributions of X-ray diffraction (XRD) profile broadening due to crystallite size and microstrain for magnetic iron oxide nanoparticles. The profile shape of the column length distribution, obtained from WA analysis, is used to analyze the shape of the magnetic iron oxide nanoparticles. From the column length distribution, the crystallite size and its distribution are estimated for these nanoparticles which are compared with size distribution obtained from dynamic light scattering measurements. The crystallite size and size distribution of crystallites obtained from WA analysis are explained based on the experimental parameters employed in preparation of these magnetic iron oxide nanoparticles. The variation of volume weighted diameter (D_v, from WA analysis) with saturation magnetization (M_s) fits well to a core shell model wherein it is known that M_s=M_bulk(1?6g/D_v) with M_bulk as bulk magnetization of iron oxide and g as magnetic shell disorder thickness.     

Dielectric measurements on urea added ZTS single crystals

Pure and urea added zinc tris(thiourea)sulphate (ZTS) single crystals were grown by the solvent evaporation method from aqueous solutions. The grown crystals were characterized by X-ray powder diffraction, Fourier transform infrared, second harmonic generation and density measurements. The observed results show that the small amount of urea molecules were incorporated in the crystalline matrix of ZTS crystals. Dielectric measurements were carried out along a-, b- and c-directions of the grown crystals at various temperatures by the conventional parallel plate capacitor method with a fixed frequency of 1 kHz. The present study shows that the dielectric parameters (viz. dielectric constant, dielectric loss and a.c. conductivity) increases with the increase in temperature for all the grown crystals. Activation energies were also determined.     

Role of Coulomb interactions in semicore levels Ga d levels of GaX semiconductors: Implication on band offsets

The positions of the semicore Ga d levels in GaX semiconductors (X=N,P, and As) are underestimated in density functional calculations using either the local density approximation LDA or the generalized gradient approximation GGA for the exchange functional. Correcting for this inaccuracy within LDA+U calculations with an on-site Coulumb interaction U on the semicore d-states results in a modest enhancement of the band gap. We show that this modest enhancement of the band-gap energy comes from the movement of the valence-band maximum alone, thus not affecting the conduction-band states. Further, the localization of the charge on Ga d states with U leads to a regulation of charge on Ga. This yields a shift of 1–2 eV of the core levels on the Ga atom while the anion core levels remain unchanged.     

Quasi-bound states, resonance tunnelling, and tunnelling times generated by twin symmetric barriers

In analogy with the definition of resonant or quasi-bound states used in three-dimensional quantal scattering, we define the quasi-bound states that occur in one-dimensional transmission generated by twin symmetric potential barriers and evaluate their energies and widths using two typical examples: (i) twin rectangular barrier and (ii) twin Gaussian-type barrier. The energies at which reflectionless transmission occurs correspond to these states and the widths of the transmission peaks are also the same as those of quasi-bound states. We compare the behaviour of the magnitude of wave functions of quasi-bound states with those for bound states and with the above-barrier state wave function. We deduce a Breit-Wigner-type resonance formula which neatly describes the variation of transmission coefficient as a function of energy at below-barrier energies. Similar formula with additional empirical term explains approximately the peaks of transmission coefficients at above-barrier energies as well. Further, we study the variation of tunnelling time as a function of energy and compare the same with transmission, reflection time and Breit-Wigner delay time around a quasi-bound state energy. We also find that tunnelling time is of the same order of magnitude as lifetime of the quasi-bound state, but somewhat larger.     

Growth and characterization of pure and potassium iodide-doped zinc tris-thiourea sulphate (ZTS) single crystals

Single crystals of pure and potassium iodide (KI)-doped zinc tris-thiourea sulphate (ZTS) were grown from aqueous solutions by the slow evaporation method. The grown crystals were transparent. The lattice parameters of the grown crystals were determined by the single-crystal X-ray diffraction technique. The grown crystals were also characterized by recording the powder X-ray diffraction pattern and by identifying the diffracting planes. The FT-IR spectrum was recorded in the range 400-4500 cm⁻¹. Second harmonic generation (SHG) was confirmed by the Kurtz powder method. The thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) studies reveal that the materials have good thermal stability. Atomic absorption studies confirm the presence of dopant in ZTS crystals. The electrical measurements were made in the frequency range 10²-10⁶ Hz and in the temperature range 40-130 °C along a-, b- and c-directions of the grown crystals. The present study shows that the electrical parameters viz. dc conductivity, dielectric constant, dielectric loss factor and ac conductivity increase with increase in temperature. Activation energy values were also determined for the ac conduction process in grown crystals. The dc conductivity, dielectric constant, dielectric loss factor and ac conductivity of KI-doped ZTS crystal were found to be more than those of pure ZTS crystals.     

Thermo-kinetic studies of NaN3/KNO3 air bag gas generant mixture

Journal of Thermal Analysis and Calorimetry - This paper addresses the thermal behavior of commonly used NaN3/KNO3 gas generant mixtures under different heating rates using simultaneous thermal...     

Formation of multiphased mixed crystals from miscible NaBr,KBr and KCl

Multiphased ternary and quaternary mixed crystals were grown by the melt method, for the first time, using the miscible alkali halides, viz. NaBr, KBr and KCl. X‐ray powder diffraction measurements indicate the existence of multiple phases. Density and refractive index were measured and the composition was determined. The metal atom contents determined through flame photometric measurements confirm the estimated composition of the crystals grown. The present study indicates the possibility of preparing multiphased ternary and quaternary mixed alkali halide crystals using the miscible NaBr, KBr and KCl as the starting materials. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)