Synthesis of Co(II), Ni(II) and Cu(II) Complexes from Schiff base Ligand and Reactivity Studies with Thermosetting Epoxy Resin

A hybrid thermosetting maleimido epoxy compound 4-(N-maleimidophenyl) glycidylether (N-MPGE) containing Co(II), Ni(II) and Cu(II) ions was prepared by curing N-MPGE and tetradentate Schiff base Co(II), Ni(II) and Cu(II) complexes. The curing polymerization reaction of N-MPGE with metal complexes as curing agents was studied. The cured samples were studied for thermal stability, chemical (acid/alkali/solvent) and water absorption resistance and homogeneity of the cured systems. The tetradentate Schiff base, 3-(Z)-2-piperazin-1-yl-ethylimino]-1,3-dihydro indol-2-one was synthesized by the condensation of Isatin (Indole-2, 3-dione) with 1-(2-aminoethyl)piperazine (AEP). Its complexes with Co(II), Ni(II) and Cu(II) have been synthesized and characterized by microanalysis, conductivity, Uv-Visible, FT-IR, TGA and magnetic susceptibility measurements. The spectral data revealed that the ligand acts as a neutral tetradentate Schiff base and coordinating through the azomethine nitrogen, two piperazine nitrogen atoms and carbonyl oxygen.

Solvation dynamics in monohydroxy alcohols: Agreement between theory and different experiments

Recently three different experimental studies on ultrafast solvation dynamics in monohydroxy straight-chain alcohols (C-1-C-4) have been carried out, with an aim to quantify the time constant (and the amplitude) of the ultrafast component. The results reported are, however, rather different from different experiments. In order to understand the reason for these differences, we have carried out a detailed theoretical study to investigate the time dependent progress of solvation of both an ionic and a dipolar solute probe in these alcohols. For methanol, the agreement between the theoretical predictions and the experimental results [Bingemann and Ernsting J. Chem. Phys. 1995, 102, 2691 and Horng et al. J: Phys, Chern, 1995, 99, 17311] is excellent. For ethanol, propanol, and butanol, we find no ultrafast component of the time constant of 70 fs or so. For these three liquids, the theoretical results are in almost complete agreement with the experimental results of Horng et al. For ethanol and propanol, the theoretical prediction for ionic solvation is not significantly different from that of dipolar solvation. Thus, the theory suggests that the experiments of Bingemann and Ernsting and those of Horng et al. studied essentially the polar solvation dynamics. The theoretical studies also suggest that the experimental investigations of Joo et al. which report a much faster and larger ultrafast component in the same series of solvents (J. Chem. Phys. 1996, 104, 6089) might have been more sensitive to the nonpolar part of solvation dynamics than the polar part. In addition, a discussion on the validity of the present theoretical approach is presented. In this theory the ultrafast component arises from almost frictionless inertial motion of the individual solvent molecules in the force field of its neighbors.

Some recent advances in the theory of homogeneous isotropic turbulence

We review some advances in the theory of homogeneous, isotropic turbulence. Our emphasis is on the new insights that have been gained from recent numerical studies of the three-dimensional Navier Stokes equation and simpler shell models for turbulence. In particular, we examine the status of multiscaling corrections to Kolmogorov scaling, extended self similarity, generalized extended self similarity, and non-Gaussian probability distributions for velocity differences and related quantities. We recount our recent proposal of a wave-vector-space version of generalized extended self similarity and show how it allows us to explore an intriguing and apparently universal crossover from inertial- to dissipation-range asymptotics.

Spin distributions in antiferromagnetically coupled Mn2+Cu2+ systems: from the pair to the infinite chain

Probably the most informative description of the ground slate of a magnetic molecular species is provided by the spin density map. Such a map may be experimentally obtained from polarized neutron diffraction (PND) data or theoretically calculated using quantum chemical approaches. Density functional theory (DFT) methods have been proved to be well-adapted for this. Spin distributions in one-dimensional compounds may also be computed using the density matrix renormalization group (DMRG) formalism. These three approaches, PND, DFT, and DMRG, have been utilized to obtain new insights on the ground state of two antiferromagnetically coupled Mn2+Cu2+ compounds, namely [Mn(Me-6-[14]ane-N-4)Cu(oxpn)](CF3SO3)(2) and MnCu(pba)(H2O)(3) . 2H(2)O, with Me-6-[14]ane-N-4 = (+/-)-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, oxpn = N,N'-bis(3-aminopropyl)oxamido and pba = 1,3-propylenebis(oxamato). Three problems in particular have been investigated: the spin distribution in the mononuclear precursors [Cu(oxpn)] and [Cu(pba)](2-), the spin density maps in the two Mn2+Cu2+ compounds, and the evolution of the spin distributions on the Mn2+ and Cu2+ sites when passing from a pair to a one-dimensional ferrimagnet.

Strong shock approximation in the new theory of shock dynamics

This paper investigates the propagation of a strong shock into an inhomogeneous medium using the new theory of shock dynamics. The equations are simple to solve and involve no trial-and-error method commonly used in this case. The results compare favourably with earlier results obtained in the case of self-similar flows, which arise as a special case of this theory.

Studies on age-hardening characteristics of ceramic particle/matrix interfaces in Al-Cu-SiCp composites using ultra low-load-dynamic microhardness measurements

Ultra low-load-dynamic microhardness testing facilitates the hardness measurements in a very low volume of the material and thus is suited for characterization of the interfaces in MMC's. This paper details the studies on age-hardening behavior of the interfaces in Al-Cu-5SiC(p) composites characterized using this technique. Results of hardness studies have been further substantiated by TEM observations. In the solution-treated condition, hardness is maximum at the particle/matrix interface and decreases with increasing distance from the interface. This could be attributed to the presence of maximum dislocation density at the interface which decreases with increasing distance from the interface. In the case of composites subjected to high temperature aging, hardening at the interface is found to be faster than the bulk matrix and the aging kinetics becomes progressively slower with increasing distance from the interface. This is attributed to the dislocation density gradient at the interface, leading to enhanced nucleation and growth of precipitates at the interface compared to the bulk matrix. TEM observations reveal that the sizes of the precipitates decrease with increasing distance from the interface and thus confirms the retardation in aging kinetics with increasing distance from the interface.

X-ray photoelectron spectroscopic investigations of Cu-Ni, Au-Ag, Ni-Pd, and Cu-Pd bimetallic clusters

Core-level binding energies of the component metals in bimetallic clusters of various compositions in the Ni-Cu, Au-Ag, Ni-Pd, and Cu-Pd systems have been measured as functions of coverage or cluster size, after having characterized the clusters with respect to sizes and compositions. The core-level binding energy shifts, relative to the bulk metals, at large coverages or cluster size, Delta E(a), are found to be identical to those of bulk alloys. By substracting the Delta E(a) values from the observed binding energy shifts, Delta E, we obtain the shifts, Delta E(c), due to cluster size. The Delta E(c) values in all the alloy systems increase with the decrease in cluster size. These results establish the additivity of the binding energy shifts due to alloying and cluster size effects in bimetallic clusters.

Mapping adaptive resonance theory onto ring and mesh architectures

In recent years, parallel computers have been attracting attention for simulating artificial neural networks (ANN). This is due to the inherent parallelism in ANN. This work is aimed at studying ways of parallelizing adaptive resonance theory (ART), a popular neural network algorithm. The core computations of ART are separated and different strategies of parallelizing ART are discussed. We present mapping strategies for ART 2-A neural network onto ring and mesh architectures. The required parallel architecture is simulated using a parallel architectural simulator, PROTEUS and parallel programs are written using a superset of C for the algorithms presented. A simulation-based scalability study of the algorithm-architecture match is carried out. The various overheads are identified in order to suggest ways of improving the performance. Our main objective is to find out the performance of the ART2-A network on different parallel architectures. (C) 1999 Elsevier Science B.V. All rights reserved.

Synthesis, spectral characterization and in vitro microbiological evaluation of novel glyoxal, biacetyl and benzil bis-hydrazone macrocyclic Schiff bases and their Co(II), Ni(II) and Cu(II) complexes

A series of binuclear Co(II), Ni(II) and Cu(II) complexes were synthesized by the template condensation of glyoxal, biacetyl or benzil bis-hydrazide, 2,6-diformyl-4-methylphenol and Co(11), Ni(II) or Cu(II) chloride in a 2:2:2 M ratio in ethanol. These 22-membered macrocyclic complexes were characterized by elemental analyses, magnetic, molar conductance, spectral, thermal and fluorescence studies. Elemental analyses suggest the complexes have a 2:1 stoichiometry of the type (M2LX2]center dot nH(2)O and Ni(2)LX(2)2H(2)O]center dot nH(2)O (where M = Co(II) and Cu(II); L = H2L1, H2L2 and H2L3; X = Cl; n = 2). From the spectroscopic and magnetic studies, it has been concluded that the Co(11) and Cu(11) complexes display a five coordinated square pyramidal geometry and the Ni(II) complexes have a six coordinated octahedral geometry. The Schiff bases and their metal complexes have also been screened for their antibacterial and antifungal activities by the MIC method. (C) 2011 Elsevier Ltd. All rights reserved.

Mean-field theory of charge ordering and phase transitions in the colossal-magnetoresistive manganites

We study phase transitions in the colossal-magnetoresistive manganites by using a mean-field theory both at zero and non-zero temperatures. Our Hamiltonian includes double-exchange, superexchange, and Hubbard terms with on-site and nearest-neighbour Coulomb interaction, with the parameters estimated from earlier density-functional calculations. The phase diagrams show magnetic and charge-ordered (or charge-disordered) phases as a result of the competition between the double-exchange, superexchange, and Hubbard terms, the relative effects of which are sensitively dependent on parameters such as doping, bandwidth, and temperature. In accord with the experimental observations, several important features are reproduced from our model, namely, (i) a phase transition from an insulating, charge-ordered antiferromagnetic to a metallic, charge-disordered ferromagnetic state near dopant concentration x = 1/2, (ii) the reduction of the transition temperature TAF-->F by the application of a magnetic field, (iii) melting of the charge order by a magnetic field, and (iv) phase coexistence for certain values of temperature and doping. An important feature, not reproduced in our model, is the antiferromagnetism in the electron-doped systems, e.g., La1-xCaxMnO3 over the entire range of 0.5 less than or equal to x less than or equal to 1, and we suggest that a multi-band model which includes the unoccupied t(2g) orbitals might be an important ingredient for describing this feature.

Microstructural evolution and giant magnetoresistance in melt spun and annealed Cu-85(FeCo)(15) alloy

Granular alloys of Cu with FeCo were prepared by the melt-spinning technique. The alloy was characterized by x-ray, transmission electron microscopy, vibrating sample magnetometer, and magnetoresistance measurements. The alloys were heat treated for different temperatures to optimize the magnetoresistance properties. Structural characterization reveals that the FeCo phase initially precipitates out as fcc and later transforms to the bcc structure by martensitic transformation. It is seen that the trend in the magnetoresistance properties is different for the measurements carried out at room temperature and 4.2 K. This has been attributed to the transformation of fine fcc precipitates to the bcc structure during the low temperature measurements. It is seen that the presence of fine particles causes an increase in the field for saturation and is not suitable for applications where moderate field giant magnetoresistance is required. (C) 1999 American Institute of Physics. [S0021-8979(99)08317-6].

Microstructure and properties of squeeze cast Cu-carbon fibre metal matrix composite

There have been reported attempts of producing Cu based MMCs employing solid phase routes. In this work, copper was reinforced with short carbon fibres by pressure infiltration (squeeze casting) of molten metal through dry-separated carbon fibres. The resulting MMC's microstructure revealed uniform distribution of fibres with minimum amount of clustering. Hardness values are considerably higher than that for the unreinforced matrix. Addition of carbon fibres has brought in strain in the crystal lattice of the matrix, resulting in higher microhardness of MMCs and improved wear resistance. Tensile strength values of MMCs at elevated temperatures are considerably higher than that of the unreinforced matrix processed under identical conditions. (C) 1999 Kluwer Academic Publishers.

Nanoscale embedded alloy particles through rapid solidification: the case of Al-Pb-In and Cu-Fe-Si

Rapid solidification techniques can be used to produce the embedded nanoparticles in a desired matrix. The origin and morphology of these small particles and their transformation behaviour are still not fully understood. In this paper, we discuss the issues involved and present some interesting results in Al-Pb-In and Cu-Fe-Si systems.

Nonresonant edge slot antenna for phased array applications: Theory and experiment

The design and development of nonresonant edge slot antenna for phased array applications has been presented. The radiating element is a slot cut on the narrow wall of rectangular waveguide (edge slot). The admittance characteristics of the edge slot have been rigorously studied using a novel hybrid method. Nonresonant arrays have been fabricated using the present slot characterization data and the earlier published data. The experimentally measured electrical characteristics of the antenna are presented which clearly brings out the accuracy of the present method.