Rhodium(III) and cadmium(II) complexes based on the polypyridyl ligand 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz)

Tppz (2,3,5,6-tetrakis(2-pyridyl)pyrazine) complexes [Rh(tppz)(bpy)Cl][PF₆]₂.acetylacetone (bpy = 2,2′-bipyridine) and [{CdCl₂}₂(μ-tppz)].ethylene glycol have been synthesized and characterized by elemental analyses, IR, ¹H NMR, cyclic voltammetry, photoluminescence and electronic spectral studies. Solid state structures of both complexes have been determined by single-crystal X-ray crystallography. The structural determination shows that the dinuclear Cd(II) complex, [{CdCl₂}₂(μ-tppz)], is a 1D coordination polymer. An ORTEP drawing of [Rh(tppz)(bpy)Cl][PF₆]₂.acetylacetone shows that the coordination geometry around the Rh(III) center is a distorted octahedron. [{CdCl₂}₂(μ-tppz)] displays intraligand ¹(π–π^*) fluorescence and can potentially serve as a photoactive material. For the mononuclear Rh(III) complex, only a two-electron reduction process occurs at the metal with the elimination of Cl⁻ ligand. The emission of this complex is assigned as πd^* phosphorescence.     

Effect of thermal annealing of high temperature growth [(GaAs)m(Fe)n]p composite films on GaAs(001) by molecular beam epitaxy

[(GaAs) _m (Fe) _n ] _p composite films on GaAs(001) substrates obtained by molecular beam deposition methods at T _s = 580°C have been thermally annealed, and magnetic/structural changes caused by the annealing have been measured to study the relation between room-temperature photo-magnetic effect and by-products in composite films. Annealing inhomogeneous [(GaAs)₈(Fe)₅]₂₀ film, prepared by alternate beam deposition of Fe and GaAs, results in an increase in saturation magnetization, whereas the room-temperature photo-enhanced magnetization (RT-PEM) vanishes. Metamagnetic Fe₃Ga₄ is suppressed with the formation of ferromagnetic Fe₃Ga_2−x As _x . Observed results suggest two important points: firstly, metamagnetic Fe₃Ga₄ compound is most likely meta-stable bi-product and may play a principle role for RT-PEM, and secondly, ferromagnetic Fe₃GaAs and its derivatives are the stable form in Ga-As-Fe ternary system.     

Axiomatisability problems for S-acts, revisited

This paper discusses necessary and sufficient conditions on a monoid S, such that a class of left S-acts is first order axiomatisable. Such questions have previously been considered by Bulman-Fleming, Gould, Stepanova and others. Let $\mathcal{C}$ be a class of embeddings of right S-acts. A left S-act B is $\mathcal{C}$ -flat if tensoring with B preserves the embeddings in $\mathcal{C}$ . We find two sets (depending on a property of $\mathcal{C}$ ) of necessary and sufficient conditions on S such that the class of all $\mathcal{C}$ -flat left S-acts is axiomatisable. These results are similar to the ??replacement tossings?? results of Gould and Shaheen for S-posets. Further, we show how to axiomatise some classes using both replacement tossings and interpolation conditions, thus throwing some light on the former technique.     

The influence of annealing temperature on the structure,morphologies and optical properties of ZnO nanoparticles

ZnO nanoparticles (NPs) have been successfully synthesized by the simple solution method at low temperature. The effects of annealing temperature on the structure and optical properties of ZnO NPs were investigated in detail by X-ray diffraction, transmission electron microscopy (TEM), ultraviolet–visible (UV–vis) spectroscopy and photoluminescence (PL) measurements. As the annealing temperature was increased above 180 ^°C the particles morphology evolved from spherical to hexagonal shape, indicating that the average particle size increased from 11 nm to 87 nm. The UV-vis and PL spectra showed a red-shift from 3.62 to 3.33 eV when the annealing temperature was increased.     

Lepton polarization asymmetry and forward–backward asymmetry in exclusive B→K<Subscript>1</Subscript>τ<Superscript>+</Superscript>τ<Superscript>-</Superscript> decay in universal extra dimension scenario

Decay rate, forward–backward asymmetry and polarization asymmetries of the final state leptons in B→K₁τ⁺τ^-, where K₁ is the axial vector meson, are calculated in the standard model and in the universal extra dimension (UED) model. The sensitivity of the observables to the compactification radius R, the only unknown parameter in the UED model, is studied. Finally, the helicity fractions of the final state K₁ are calculated and their dependence on the compactification radius is discussed. This analysis of the helicity fraction is briefly extended to B→K^*ℓ⁺ℓ^- (ℓ=e,μ) and compared with the other approaches existing in the literature.     

Dynamics of Particles Around a Regular Black Hole with Nonlinear Electrodynamics

We investigate the dynamics of a charged particle being kicked off from its circular orbit around a regular black hole by an incoming massive particle in the presence of magnetic field. The resulting escape velocity, escape energy and the effective potential are analyzed. It is shown that the presence of even a very weak magnetic field helps the charged particles in escaping the gravitational field of the black hole. Moreover the effective force acting on the particle visibly reduces with distance. Thus particle near the black hole will experience higher effective force as compared to when it is far away.     

Evolution of a Schwarzschild black hole in phantom-like Chaplygin gas cosmologies

In the classical relativistic regime, the accretion of phantom energy onto a black hole reduces the mass of the black hole. In this context, we have investigated the evolution of a Schwarzschild black hole in the standard model of cosmology using the phantom-like modified variable Chaplygin gas and the viscous generalized Chaplygin gas. The corresponding expressions for accretion time scale and evolution of mass have been derived. Our results indicate that the mass of the black hole will decrease if the accreting phantom Chaplygin gas violates the dominant energy condition and will increase in the opposite case. Thus, our results are in agreement with the results of Babichev et al. who first proposed this scenario.     

Vibration modelling of helical springs with non-uniform ends

Helical springs constitute an integral part of many mechanical systems. Usually, a helical spring is modelled as a massless, frequency independent stiffness element. For a typical suspension spring, these assumptions are only valid in the quasi-static case or at low frequencies. At higher frequencies, the influence of the internal resonances of the spring grows and thus a detailed model is required. In some cases, such as when the spring is uniform, analytical models can be developed. However, in typical springs, only the central turns are uniform; the ends are often not (for example, having a varying helix angle or cross-section). Thus, obtaining analytical models in this case can be very difficult if at all possible. In this paper, the modelling of such non-uniform springs are considered. The uniform (central) part of helical springs is modelled using the wave and finite element (WFE) method since a helical spring can be regarded as a curved waveguide. The WFE model is obtained by post-processing the finite element (FE) model of a single straight or curved beam element using periodic structure theory. This yields the wave characteristics which can be used to find the dynamic stiffness matrix of the central turns of the spring. As for the non-uniform ends, they are modelled using the standard finite element (FE) method. The dynamic stiffness matrices of the ends and the central turns can be assembled as in standard FE yielding a FE/WFE model whose size is much smaller than a full FE model of the spring. This can be used to predict the stiffness of the spring and the force transmissibility. Numerical examples are presented.     

Ab-initio calculations of bandgap tuning of In1-xGaxY (Y = N,P) alloys for optoelectronic applications

The Ⅲ-V alloys and doping to tune the bandgap for solar cells and other optoelectronic devices has remained a hot topic of research for the last few decades. In the present article, the bandgap tuning and its influence on optical properties of In_1-xGa_xN/P, where (x = 0.0, 0.25, 0.50, 0.75, and 1.0) alloys are comprehensively analyzed by density functional theory based on full-potential linearized augmented plane wave method (FP-LAPW) and modified Becke and Johnson potentials (TB-mBJ). The direct bandgaps turn from 0.7 eV to 3.44 eV, and 1.41 eV to 2.32 eV for In_1-xGa_xN/P alloys, which increases their potentials for optoelectronic devices. The optical properties are discussed such as dielectric constants, refraction, absorption, optical conductivity, and reflection. The light is polarized in the low energy region with minimum reflection. The absorption and optical conduction are maxima in the visible region, and they are shifted into the ultraviolet region by Ga doping. Moreover, static dielectric constant ε₁(0) is in line with the bandgap from Penn's model.