Structure and magnetic properties of the Al1−xGaxFeO3 family of oxides: A combined experimental and theoretical study

Magnetic properties of the Al_1−xGa_xFeO₃ family of oxides crystallizing in a non-centrosymmetric space group have been investigated in detail along with structural aspects by employing X-ray and neutron diffraction, Mössbauer spectroscopy and other techniques. The study has revealed the occurrence of several interesting features related to unit cell parameters, site disorder and ionic size. Using first-principles density functional theory based calculations, we have attempted to understand how magnetic ordering and related properties in these oxides depend sensitively on disorder at the cation site. The origin and tendency of cations to disorder and the associated properties are traced to the local structure and ionic sizes.     

On Dual Invex Ky Fan Inequalities

In this paper, we obtain some new results for the dual invex Ky Fan inequalities in topological vector spaces. These results can be viewed as an extension and refinement of the previously known results of Noor and others.     

Wiener-Hopf equations technique for variational inequalities

In recent years, the theory of Wiener-Hopf equations has emerged as a novel and innovative technique for developing efficient and powerful numerical methods for solving variational inequalities and complementarity problems. In this paper, we provide an account of some of the fundamental aspects of the Wiener-Hopf equations with major emphasis on the formulation, computational algorithms, various generalizations and their applications. We also suggest some open problems for further research with sufficient information and references.     

Tunable infrared laser instruments for airborne atmospheric studies

Tunable infrared laser-based instruments on airborne platforms have provided invaluable contributions to atmospheric studies over the past several decades. This paper presents an overview of some recent studies and developments using this approach that were presented at the 2007 Field Laser Applications in Industry and Research (FLAIR, http://www.inoa.it/flair/) conference in Florence, Italy. The present overview only covers select in situ absorption-based instruments that were presented in the airborne session at this conference. In no case are comprehensive details presented. These details can be found in the numerous references given. Additional approaches based upon cavity-enhanced and photoacoustic measurements, which are also making invaluable contributions in airborne atmospheric studies, are not discussed in this brief overview. PACS  07.88.+y; 07.57.Ty; 42.60.-v; 42.60.By; 42.62.Fi     

Modified variational iteration method for solving Helmholtz equations

In this paper, we apply the modified variational iteration method (MVIM) for solving the Helmholtz equations. The proposed modification is made by introducing He's polynomials in the correction functional. The suggested algorithm is quite efficient and is practically well suited for use in these problems. The proposed iterative scheme finds the solution without any discretization, linearization, or restrictive assumptions. Several examples are given to verify the reliability and efficiency of the method. The fact that the proposed technique solves nonlinear problems without using the Adomian's polynomials can be considered as a clear advantage of this algorithm over the decomposition method.     

Double yield in tensile deformation of high-density polyethylene fiber

Fiber-grade high-density polyethylene (HOPE) was melt spun into a multifilament yam that, after quenching in air, was wound at speeds in the range 450 m/min to 1000 m/min. Tensile tests on these anisotropic yarns showed two yield points of varying intensity, similar to those reported in the literature for compression molded, isotropic HOPE sheets and films. However, unlike the sheets, the second yield in the case of fibers always occurred at a stress higher than that for the first yield. More detailed studies on the yam spun at 450 m/ min showed that these characteristics persisted at different strain rates and test temperatures and were also present in the heat-set as-spun samples. The applicability of the existing models to explain the double-yield phenomenon has been critically examined in the light of the results obtained. For this, the necessary structural and morphological characterization of the samples was also done.     

Global-local methodologies and their application to nonlinear analysis

An assessment is made of the potential of different global-local analysis strategies for predicting the nonlinear and postbuckling responses of structures. Two postbuckling problems of composite panels are used as benchmarks and the application of different global-local methodologies to these benchmarks is outlined. The key elements of each of the global-local strategies are discussed and future research areas needed to realize the full potential of global-local methodologies are identified.     

Synthesis of poly(butyl acrylate)/sodium silicate nanocomposite fire retardant

Poly(butyl acrylate) (PBA)/sodium silicate (SS) nanocomposites were prepared via emulsifier-free emulsion technique in presence of Cu(II)/glycine chelate complex and ammonium persulfate (APS) initiator. The strongly hydrophobic PBA was intercalated into the hydrophilic SS layer. Since the interlayers of silicate were filled with sodium cations, the hydrophilic properties were enhanced and lead to high degree of swelling. The formation of the PBA/SS nanocomposite was confirmed by infrared spectra (IR). Furthermore, as evidenced by transmission electron microscopy (TEM), the composite so obtained was found to have nanoscale structure. X-ray diffraction (XRD) was used to characterize the nanoscale dispersion of the layer silicate and useful for measurement of d-spacing in interlayer system. It was found from thermogravimetric analysis that PBA/SS nanocomposites had more thermal stability as compared to raw PBA due to intercalation. Burning test of the nanocomposites performance exhibited a flame retardant property, which was also verified from cone calorimeter analysis. For its commercialization, the ecological friendly nature was studied via biodegradation and was found to have better biodegradability than the raw PBA.     

Vibration analysis of quasi-symmetric structures

An efficient computational procedure is presented for the free vibration analysis of structures with unsymmetric geometry. The procedure is based on approximating the unsymmetric vibrational response of the structure by a linear combination of a few symmetric and antisymmetric modes (global approximation vectors), each obtained using approximately half the degrees of freedom of the original model. The three key elements of the procedure are: (a) use of mixed finite element models having independent shape functions for the internal forces (stress resultants) and generalized displacements, with the internal forces allowed to be discontinuous at interelement boundaries, (b) operator splitting, or additive decomposition of the different arrays in the governing finite element equations to delineate the contributions to the symmetric and antisymmetric response vectors, and (c) use of a reduction method through successive application of the finite element method and the classical Bubnov-Galerkin technique. The finite element method is first used to generate a few symmetric and antisymmetric global approximation response vectors. Then, the classical Bubnov-Galerkin technique is used to substantially reduce the size of the eigenvalue problem.

An initial set of global approximation vectors is selected to be a few symmetric and antisymmetric eigenvectors, and their various-order derivatives with respect to a tracing parameter identifying all the correction terms to the symmetric (and antisymmetric) eigenvectors. A modified (improved) set of approximation vectors is obtained by using the inverse iteration procedure. The effectiveness of the proposed procedure is demonstrated by means of a numerical example.     

Design of donor–acceptor–donor (D–A–D) type small molecule donor materials with efficient photovoltaic parameters

Four Donor–Acceptor–Donor (D–A–D) type of donor molecules (M1‐M4) with triphenylamine (TPA) as donor moiety, thiophene as bridge, and thiazolothiazole as acceptor unit were designed and its photovoltaic parameters were equated with reference molecule “R.” DFT functional CAM‐B3LYP/6‐31G (d,p) was found best for geometry optimization and TD‐CAM‐B3LYP/6‐31G (d,p) was found suitable for excited state calculations. Among designed donor molecules, M4 manifests suitable lowest band gap of 4.73 eV, frontier molecular orbital energy levels as well as distinctive broad absorption of 455.3 nm due to the stronger electron withdrawing group. The electron‐withdrawing substituents contribute to red shifts of absorption spectra and better stabilities for designed molecules. The theoretically determined reorganization energies of designed donor molecules suggested excellent charge mobility property. The lower λ_e values in comparison with λ_h illustrated that these four donor materials would be ideal for electron transfer and M4 would be best amongst the investigated molecules with lowest λ_e of 0.0177. Furthermore, the calculated Voc of M4 is 2.04 V with respect to PC₆₀BM (phenyl‐C61‐butyric acid methyl ester). This study revealed that the designed donor materials are suitable and recommended for high performance organic solar cell devices.