Suppression of the Verwey Transition by Charge Trapping

The Verwey transition in Fe₃O₄ nanoparticles with a mean diameter of 6.3 nm is suppressed after capping the particles with a 3.5 nm thick shell of SiO₂. By X‐ray absorption spectroscopy and its associated X‐ray magnetic circular dichroism this suppression can be correlated to localized Fe²⁺ states and a reduced double exchange visible in different site‐specific magnetization behavior in high magnetic fields. The results are discussed in terms of charge trapping at defects in the Fe₃O₄/ SiO₂ interface and the consequent difficulties in the formation of the common phases of Fe₃O₄. By comparison to X‐ray absorption spectra of bare Fe₃O₄ nanoparticles in course of the Verwey transition, particular changes in the spectral shape could be correlated to changes in the number of unoccupied d states for Fe ions at different lattice sites. These findings are supported by density functional theory calculations.     

Fluorescence resonance energy transfer from TX-100 to 3-acetyl-4-oxo-6,7-dihydro-12H-indolo-[2,3-a]quinolizine in premicellar and micellar environments

Fluorescence (Förster) resonance energy transfer (FRET) from the phenyl groups of the non-ionic triton X-100 (TX-100) micelles to a potent bioactive molecule 3-acetyl-4-oxo-6,7-dihydro-12H-indolo-[2,3-a] quinolizine (AODIQ) has been studied using steady state absorption and fluorescence techniques. High values of Stern–Volmer constants (K_SV) suggest that a long-range dipole–dipole interaction is operative for the energy transfer mechanism. From the analysis of the quenching of the donor fluorescence the energy transfer efficiency (E) has been determined in both premicellar and micellar environments. Experimental results reveal that the energy transfer process is more efficient in the micellar environment compared to the premicellar situation.     

Effect of coupling of spontaneous emission to the lasing mode in a two level model of quantum cascade lasers

In this paper, an improved two level model of quantum cascade lasers is extended to include the coupling of the spontaneous emission to the lasing mode. The variation of the electron numbers at the two levels, their difference and the variation of the light output with injected current are examined. The normalized modulation response for different ratios of the injected current to the threshold current is given.     

Properties of Particle Trajectory Around a Weakly Magnetized Black Hole

In this paper, we consider charged accelerating AdS black holes with nonlinear electromagnetic source. The metric chosen by us is of a regular black hole, which shows regular nature at poles and a conical effect, which corresponds to a cosmic string. In such a space time construction of the Lagrangian for a charged particle is done. Cyclic coordinates as well as the corresponding symmetry generators, i.e., the Killing vectors are found. Conservation laws corresponding to the symmetries are counted. Euler-Lagrange equations are found. The orbit is mainly taken to be a circular one and effective potential is found. The minimum velocity obtained by a particle to escape from innermost stable circular orbit is found. The value of this escape velocity is plotted with respect to the radius of the event horizon of the central black hole for different parametric values. The nature of the escape velocity is studied when the central object is working with gravitational force and charge simultaneously. Effective potential and effective force are also plotted. The range of radius of event horizon for which the effective force turns to be positive is found out. A pathway of future studies of accretion disc around such black holes is made.     

Effects of thermal radiation on MHD viscous fluid flow and heat transfer over nonlinear shrinking porous sheet

This paper investigates the effects of thermal radiation on the magnetohy-drodynamic (MHD) flow and heat transfer over a nonlinear shrinking porous sheet. The surface velocity of the shrinking sheet and the transverse magnetic field are assumed to vary as a power function of the distance from the origin. The temperature dependent viscosity and the thermal conductivity are also assumed to vary as an inverse function and a linear function of the temperature, respectively. A generalized similarity transformarion is used to reduce the governing partial differential equations to their nonlinear coupled ordinary differential equations, and is solved numerically by using a finite difference scheme. The numerical results concern with the velocity and temperature profiles as well as the local skin-friction coefficient and the rate of the heat transfer at the porous sheet for different values of several physical parameters of interest.     

Multi-scale Mechanical Characterization of Palmetto Wood using Digital Image Correlation to Develop a Template for Biologically-Inspired Polymer Composites

Palmetto wood is garnering growing interest as a template for creating biologically-inspired polymer composites due to its historical use as an energy absorbing material in protective structures. In this study, quasi-static three-point bend tests have been performed to characterize the mechanical behavior of Palmetto wood. Full-field deformation measurements are obtained using Digital Image Correlation (DIC) to elucidate on the strain fields associated with the mechanical response. By analyzing strain fields at multiple length scales, it is possible to study the more homogeneous mechanical behavior at the macro-scale associated with the global load-deformation response; while at the microscale the mechanical behavior is more inhomogeneous due to microstructural failure mechanisms. Thus, it was possible to determine that, despite the presence of discontinuous macro-fiber reinforcement, at the macro-scale the response is associated with classical bending and progressive failure processes that are adequately described by Weibull statistics proceeding from the tensile side of the specimen. At the microscale, however, the failure mechanisms giving rise to the macroscopic response consist of both shear-dominated debonding between the fiber and matrix, and inter-fiber matrix failure due to pore collapse. These microscale mechanisms are present in both the compressive and tensile regions of the specimen, most likely due to local macro-fiber bending, which is independent of the global bending state. The pore collapse mechanism observed during mechanical loading appears to improve the energy absorption of the matrix material, thereby, transferring less energy and shear strain to the macro-fiber-matrix interface for initiation of debonding. However, the pore collapse mechanism can also accumulate substantial shear strain, which results in matrix shear cracking. Through these complex failure mechanisms, Palmetto wood exhibits a high resistance to catastrophic failure after damage initiation, an observation that can be used as inspiration for creating new polymer composite materials.     

Optimizing the degradation of dichlorvos in aqueous solution using nZVI DTPA+H2O2 and its detection using ac conductivity measurement with the help of response surface methodology

Degradation of organic pollutants in wastewater is a common subject of discussion under advanced oxidation process. To detect the degradation of colourless organic pollutants conventional analytical techniques are available but their sophistication makes it difficult to pursue in all form of chemical laboratories. In the present study it was found that during degradation of Dichlorvos using diethylene triamine pent acetic acid (DTPA) stabilized nano zero valent iron (nZVI), COD removal and ac conductivity change has been done simultaneously. In this degradation study the heterogeneous Fenton type oxidation method was employed and an LCR circuit (which contains inductor, capacitor and resistor) was used to measure the ac conductivity. This study aims to find out a correlation between ac conductivity and COD removal using simple response surface methodology (RSM) so that the degradation of colourless pollutants can be estimated easily and also to identify the best processing parameters to optimise Dichlorvos degradation. It was found that COD removal in most of all cases, was more than 60% when the change in final ac conductivity more than 600% with respect to initial value. All of the experimental results were in good accord with the projected outcome.     

Effect of cyclodextrin nanocavity confinement on the photophysics of a beta-carboline analogue: a spectroscopic study

Interaction of a beta-carboline based biologically active molecule, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), with alpha-, beta-, and gamma-cyclodextrins (CDs) in aqueous solution has been studied using steady state and time-resolved fluorescence and steady-state fluorescence anisotropy techniques. Polarity dependent intramolecular charge transfer (ICT) process is responsible for the remarkable sensitivity of this biological fluorophore to the CD environments. Upon encapsulation, the CT fluorescence exhibits hypsochromic shift along with enhancements in the fluorescence yield, fluorescence anisotropy (r), and fluorescence lifetime. The reduction in the nonradiative deactivation rate of the fluorophore within the CD nanocavities leads to an increase in both fluorescence yield and lifetime. Among the three CDs, gamma-CD shows the most spectacular confinement effect. The results establish the formation of 1:1 AODIQ:CD inclusion complexes in alpha- and beta-CDs. In aqueous gamma-CD solutions, however, depending on the concentration of the gamma-CD, formation of both 1:1 and 1:2 complexes have been revealed. Hydrodynamic radii of the 1:1 and 1:2 probe-gamma-CD supramolecular complexes have also been determined.