Effect of Dy substitution on structural,magnetic and optical properties of BiFeO3 ceramics

Bi_1−xDy_xFeO₃ (x=0.0, 0.03, 0.05, 0.07, 0.10 and 0.12) ceramics were synthesized by solid state reaction method. Effects of Dy substitution on structural distortion, magnetic and optical properties of BiFeO₃ were examined by X-ray diffraction, Raman and UV–Visible spectroscopy. The samples were found to crystallize in rhombohedral structure of BiFeO₃ with R3c space group. The reduction in lattice parameters and unit cell volume indicate the distortion in FeO₆ octahedra of the rhombohedral structure without any signature of phase transformation up to x=0.12. The predictable weak ferromagnetic hysteresis loops can be observed in the Dy doped samples with maximum remnant magnetization of 0.2103 emu/g for x=0.12. The weak ferromagnetism is ascribed to the suppressed spiral spin structure and magnetically active characteristic of Dy³⁺ ions together with ferromagnetic coupling between Dy³⁺ and Fe³⁺ ions. With optical band gap in visible region, Dy doped BiFeO₃ ceramics are potential material for optoelectronic device and solar cell applications.     

Deep Level Transient Spectroscopy of Defects in High-Energy Light-Particle Irradiated Si

The authors review what has been learned concerning the electrical and annealing properties of point defects in high-energy electron or proton irradiated Si from deep level transient spectroscopy (DLTS). The authors have focused mainly on the properties of electron traps, and to a lesser extent on the properties of hole traps. In addition to an in-depth discussion of hydrogen-related defects in Si, this review article provides a brief tutorial on ion-solid interactions and the theory underlying DLTS. The authors also provide a few examples of the power of high resolution Laplace DLTS in analyzing radiation induced defects. The collection of results gathered in this article may provide the fundamental information for successful defect engineering in light-particle irradiated Si.     

Band gap control and photoluminescence properties of Ba(Co2x Ti1−x )O3 thin films prepared by Sol–gel method

This paper reports on the preparation, characterization and optical properties of transparent Ba(Co_2x Ti_1?x )O₃ (0 ≤ x ≤ 0.06) thin films prepared by sol–gel method and deposited on fused quartz substrate by spin-coating technique. Their formation is confirmed by X-ray diffraction patterns, energy dispersive X-ray spectrometry and Fourier transformed infrared measurements. Hitherto unreported near-band-gap photoluminescence in ultraviolet, at 378 nm (3.28 eV), of exciton origin is observed which remains unaffected with change in excitation wavelength from 320 to 350 nm. A weak defect emission appears in green region. For larger excitation wavelength, i.e., 488 nm, emission arising from localized states again occurs in green region but with lower energy. The occurrence of efficient violet–blue PL emission is related to ‘direct’ band gap and shallow levels with high optical band gap values. Analysis of band gap variation with dopant concentration, determined using Tauc’s plot assuming them both of ‘direct’ and ‘indirect’ nature, also indicates the ‘direct’ nature. Co⁺² ions as dopants promote a decrease of band gap of films linearly. Scanning electron micrographs show the granular and flakes-like surface growth. Atomic force microscopy images show the presence of ribbon-like nanostructured grains throughout the surface of the films which is smooth with small values of surface roughness.     

Flow coupling mechanisms in two-layer Rayleigh–Benard convection

 Rayleigh-Benard convection in two-layer systems is characterized by two distinct modes of flow coupling. These are: thermal coupling and mechanical coupling. Intellegible observations of the temperature field for both coupling mechanisms are provided. The flow coupling mechanisms are experimentally characterized as a function of the contrast in the buoyancy driving forces and in the viscosities of the two layers. Aside from the flow coupling between the layers, flow patterns in each layer, and their corresponding spatial transitions are found to be similar to those reported for single layer convection in rectangular boxes. Received: 7 January 1996/Accepted: 4 February 1997     

A more chaotic and easily hardware implementable new 3-D chaotic system in comparison with 50 reported systems

This paper attempts to construct a new 3-D chaotic system which is easily hardware realisable and fulfil the requirement of a real-life application. The proposed system is relatively more chaotic (based on the first Lyapunov exponent) and has larger bandwidth than 50 available chaotic systems. Lyapunov spectrum and bifurcation diagram of the system reveal that it has chaotic behaviour for a wider range of its parameters. Such characteristic is helpful for an easy hardware realisation of the system. It is to be noted that the reported systems with hidden attractors are not considered here for the comparison. The proposed system has more complexity and disorder due to several unique properties like asymmetry to principle coordinates, dissimilar and asymmetrical equilibria, and non-uniform contraction and expansion of volume in phase space. The proposed system also exhibits asymmetric pairs of coexisting attractors during its operation in two modes. The new system has different routes to chaos including crisis, an inverse crisis, period-doubling and reverse period-doubling routes to chaos with the variation of parameters. MATLAB simulation results confirm the claims, and the results of hardware circuit realisation validate the simulation results. An application of the new system is shown by masking and retrieving an information signal. It is also shown that the proposed system is better than a well-known Lorenz chaotic system for this application. A system with the above unique properties is rare in the literature.     

Unsteady MHD Non-Darcian Flow over a Vertical Stretching Plate Embedded in a Porous Medium with Thermal Non-Equilibrium Model

An analysis is performed to study the influence of local thermal non-equilibrium (LTNE) on unsteady MHD laminar boundary layer flow of viscous, incompressible fluid over a vertical stretching plate embedded in a sparsely packed porous medium in the presence of heat generation/absorption. The flow in the porous medium is governed by Brinkman-Forchheimer extended Darcy model. A uniform heat source or sink is presented in the solid phase. By applying similarity analysis, the governing partial differential equations are transformed into a set of time dependent non-linear coupled ordinary differential equations and they are solved numerically by Runge-Kutta Fehlberg method along with shooting technique. The obtained results are displayed graphically to illustrate the influence of different physical parameters on the velocity, temperature profile and heat transfer rate for both fluid and solid phases. Moreover, the numerical results obtained in this study are compared with the existing literature in the case of LTE and found that they are in good agreement.     

Growth of tetrakis thiourea potassium iodide as new second order optical material

A novel organometallic nonlinear optical (NLO) crystal, namely thiourea complex of tetrakis thiourea potassium iodide (TTPI), has been grown by slow evaporation solution growth technique. The harvested crystal is large in size. To our knowledge there is no report is available for the bulk size single crystal of TTPI. This material has a positive temperature coefficient and has been grown by slow evaporation solution growth technique. The grown crystal have been characterized by employing several techniques such as single crystal and powder X‐ray diffraction, FTIR, UV‐Vis‐NIR spectra, thermo gravimetric analyses respectively. Etching studies have also been carried out in order to know the surface defects on the as grown specimen of TTPI. The relative second harmonic generation efficiency have been tested by using Nd:YAG laser as source. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theory of collective motion of interacting gas of polyvalent Hg atoms at 3.0, 6.3 and 9.0 particles per nm

Collective dynamics of interacting gaseous mercury at high temperatures and pressures having densities of 3.0, 2.1 and 1.0 g cm⁻³, as determined very recently by the measurement of dynamical structure factor using the inelastic X-ray scattering, have been successfully explained, making use of the recently modified microscopic theory of a simple fluid. It also turns out that in determining the collective dynamics of all the three systems of the mercury vapor, the two body interactions, as prevalent in a weakly interacting system, play a dominant role.     

Extracellular Surface Potential Mapping by Scanning Ion Conductance Microscopy Revealed Transient Transmembrane Pore Formation Induced by Conjugated Polymer Nanoparticles

In‐depth understanding of the biophysicochemical interactions at the nano–bio interface is important for basic cell biology and applications in nanomedicine and nanobiosensors. Here, the extracellular surface potential and topography changes of live cell membranes interacting with polymeric nanomaterials using a scanning ion conductance microscopy‐based potential imaging technique are investigated. Two structurally similar amphiphilic conjugated polymer nanoparticles (CPNs) containing different functional groups (i.e., primary amine versus guanidine) are used to study incubation time and functional group‐dependent extracellular surface potential and topographic changes. Transmembrane pores, which induce significant changes in potential, only appear transiently in the live cell membranes during the initial interactions. The cells are able to self‐repair the damaged membrane and become resilient to prolonged CPN exposure. This study provides an important observation on how the cells interact with and respond to extracellular polymeric nanomaterials at the early stage. This study also demonstrates that extracellular surface potential imaging can provide a new insight to help understand the complicated interactions at the nano–bio interface and the following cellular responses.