Crystal Structure and Spectroscopic Properties of Bis[trans‐dichlorobis(2,2‐dimethylpropane‐1,3‐diamine)chromium(III)] Tetrachlorozincate

The structure of trans‐[Cr(Me₂tn)₂Cl₂]₂ZnCl₄ (Me₂tn = 2,2‐dimethylpropane‐1,3‐diamine) was determined by a single‐crystal X‐ray diffraction study at 173 K. The analysis reveals that there are three crystallographically independent chromium(III) complex cations in the title compound. The chromium(III) atoms are coordinated by four nitrogen atoms of Me₂tn and two chlorine atoms in a trans arrangement, displaying a distorted octahedral geometry. The two six‐membered chelate rings in three complex cations are oriented in an anti chair–chair conformation with respect to each other. The Cr–N and Cr–Cl bond lengths average 2.0862(2) and 2.3112(6) Å, respectively. The ZnCl₄^2– have slightly distorted tetrahedral arrangement with Zn–Cl lengths and the Cl–Zn–Cl angles are influenced by hydrogen bonding. The resolved absorption maxima in the electronic d–d spectrum were fitted with a secular determinant for a quartet energy state of the d³ configuration in a tetragonal field. It is confirmed that the nitrogen atoms of the Me₂tn ligand are strong σ donors, but the chloro ligands have weak σ‐ and π donor properties toward the chromium(III) ion.     

Studies on purification of plutonium from silver ions

Precipitation and solvent extraction methods have been investigated for the purification of plutonium from silver from the solution generated during oxidative dissolution of plutonium oxide using Ag(II) ions. Initial experiments have been carried out using thorium as representative of plutonium. Selecting the optimum conditions, the experiments were repeated with plutonium. The results revealed that Pu can be purified from silver ions either by precipitating silver as silver chloride or silver metal followed by Pu(IV) oxalate precipitation or by selective extraction of Pu(IV) into 20% Aliquat-336 or 30% TBP.     

Topological estimation of proton-ligand formation constants of potential antitumour agents: Salicylhydroxamic acids

Proton-ligand formation constants of salicylhydroxamic acids (SHA) and their nuclear substituted derivatives have been estimated topologically using the normalized Wiener index, referred to as mean square Wiener index (Wms). Regression analysis of the data indicates that Wms can be used successfully for estimating and monitoring proton-ligand formation constants.     

Influence of covalent and non-covalent modification of graphene on the mechanical,thermal and electrical properties of epoxy/graphene nanocomposites: a review

Abstract

Graphene is emerged as a highly sought after reinforcing filler for epoxy matrix in view of its superior electrical, mechanical and thermal properties. Dispersion of low concentration of graphene can significantly enhance the epoxy/graphene nanocomposites properties. Dispersion of graphene in epoxy matrix depends on processing protocols used, and interfacial interaction between epoxy matrix and graphene. Interfacial interaction between epoxy matrix and graphene can be achieved by covalent and non-covalent modification of graphene. This paper comprehensively review the influence of different processing protocols adopted for the processing of epoxy/graphene nanocomposites, and its effect on mechanical, thermal and electrical properties. In addition, covalent and non-covalent strategies adopted for modification of graphene, and its influence on mechanical, thermal and electrical properties of epoxy/graphene nanocomposites are extensively discussed. The future challenges associated with graphene reinforced epoxy nanocomposites processing have been discussed.     

A Cylindrical Waveguide Structure with Helical Grooves for High Power TWTs

In this work, the field analysis of a cylindrical interaction structure, with helical grooves, and an inner dielectric lining for possible employment in high power TWT amplifiers in the conventional slow-wave regime, is presented. The Ohmic dominance of the microwave power on the walls of this propagating circuit is deduced.     

Photophysics of 9-aminoacridinium hydrochloride

The steady state and time domain spectroscopy of 9-aminoacridinium hydrochloride have been studied. 9-aminoacridine (I), 9-aminoacridinium (II) and the double protonated ion (III) follow Waterman’s principle with respect to their spectra and lifetimes. It is established that the excimer formation in (II) is from the ground state dimers which undergo either thermally-activated radiationless excimer conversion or a geometrical rearrangement in the excited state at room temperature. The quenching of monomer emission by dimers or foreign quenchers (KI) is found to be of transient nature as suggested by the continuum model. The authors felicitate Prof. D S Kothari on his eightieth birthday and dedicate this paper to him on this occasion.     

Influence of donor-donor transport on excitation energy transfer

Energy migration and transfer from acriflavine to rhodamine B and malachite green in poly (methylmethacrylate) have been investigated using the decay function analysis. It is found that the influence of energy migration in energy transfer can be described quite convincingly by making use of the theories of Loring, Andersen and Fayer (LAF) and Huber. At high acceptor concentration direct donor-acceptor transfer occurs through Förster mechanism.     

Studies in spiroheterocycles,Part XV. Investigation of the reaction of 3-(2-oxocycloalkylidene)-indol-2-ones with thiourea and urea derivatives

The reaction of 3-(2-oxocycloalkylidene)indol-2-one 1 with thiourea and urea derivatives has been investigated. Reaction of 1 with thiourea and urea in ethanolic potassium hydroxide media leads to the formation of spiro-2-indolinones 2a-f in 40–50% yield and a novel tetracyclic ring system 4,5-cycloalkyl-1,3-diazepino-[4,5-b]indole-2-thione/one 3a-f in 30–35% yield. 3-(2-Oxocyclopentylidene)indol-2-one afforded 5′,6′-cyclopenta-2′-thioxo/ oxospiro[3H-indole-3,4′(3′H)pyrimidin]-2(1H)-ones 2a,b and 3-(2-oxocyclohexylidene)indol-2-one gave 2′,4′a,5′,6′,7′,8′- hexahydro-2′-thioxo/oxospiro[3H-indole-3,4′ (3′H)-quinazolin]-2(1H)-ones 2c-f . Under exactly similar conditions, reaction of 1 with fluorinated phenylthiourea/cyclohexylthiourea/phenylurea gave exclusively spiro products 2g-1 in 60–75% yield. The products have been characterized by elemental analyses, ir pmr. ¹⁹F nmr and mass spectral studies.     

Quantum effects in a homogeneous dust cloud collapse

The status of a classical space-time singularity, when quantum effects are taken into account, has remained a matter of intense interest ever since the epochmaking paper of DeWitt [1] on quantum gravity. We examine here the evolution of quantum fluctuations in the vicinity of the singularity arising out of the classical collapse of a homogeneous dust cloud. As opposed to the pathintegral method used to quantize the conformal degree of freedom (see, e.g., [3] or [4]), we use here the traditional operator approach to the quantum theory which is much more direct and appealing while achieving an additional generalization that the wave function of the system is assumed to have a completely general form. It is shown that the quantum uncertainty diverges in the limit of approach to the classically singular epoch and that nonsingular, nonclassical states can occur with finite probability.     

Ply-by-Ply Failure Analysis of Laminates Under Dynamic Loading

Ply-by-ply failure analysis of symmetric and anti-symmetric laminates under uniform sinusoidal transverse dynamic loading is performed for a specified duration. The study investigates the first ply failure load, followed by the detection of successive ply failures along with their failure modes using various failure theories. Some of the well-established failure theories, mostly used by the researchers, are considered for the failure prediction in laminates. The finite element computational model based on higher order shear deformation displacement field is used for the failure analysis and the complete methodology is computer coded using FORTRAN. The ply-discount stiffness reduction scheme is employed to modify the material properties of the failed lamina. The failure theories used in the analysis are compared according to their ability to predict failure load, failed ply, failure mode and progression of failure. The failure analysis is performed for both the cross-ply and angle-ply laminates with all edges simply supported and clamped. The significance of fibre orientation and stacking sequence in terms of the strength of a laminate and failure progression is also highlighted.