Effect of injecting electrodes on TSD behaviour of vacuum deposited PVF films

Depolarization behaviour of vacuum deposited polyvinyl fluoride (PVF) films has been studied as a function of nature of the electrode materials used during polarization such as copper, silver, aluminium and indium using the thermally stimulated discharge current (TSD) technique. TSD spectra of these films show a single relaxation peak centered around 430 ± 1 K with activation energies of ∼ 0.65 eV. The peak current and the charge associated with the relaxation peak depend strongly on the electrode material used. This has been attributed to the electrode-polymer interface barrier controlling the injection of the charge carriers into PVF films that results into space charge effects by subsequent trapping of the injected charge carriers at macroscopic distances. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Synthesis,properties and structural characterization of 4-(2-ammonioethyl)piperazin-1-ium tetrasulfidotungstate hemihydrate and 1-ethylpiperazinediium tetrasulfidotungstate

The reaction of ammonium tetrasulfidotungstate with 2-piperazin-1-ylethanamine or 1-ethylpiperazine results in the formation of 4-(2-ammonioethyl)piperazin-1-ium tetrasulfidotungstate hemihydrate (C₆H₁₇N₃)[WS₄]·½H₂O 1 or 1-ethylpiperazinediium tetrasulfidotungstate (C₆H₁₆N₂)[WS₄] 2. The hemihydrate 1 can be dehydrated to the anhydrous compound (C₆H₁₇N₃)[WS₄] 1a, which can be rehydrated to 1. Both 1 and 2 decompose to amorphous carbon containing tungsten disulphide. Compound 1 crystallizes in the centrosymmetric monoclinic space group C2/c, while compound 2 crystallizes in the centrosymmetric orthorhombic space group Pbca. The structures of 1 and 2 consist of a slightly distorted tetrahedral [WS₄]^2? anion and 4-(2-ammonioethyl)piperazin-1-ium (1) or 1-ethylpiperazinediium dication (2) and additionally a lattice water in 1. In the crystal structure of 1 and 2 the organic cation and the [WS₄]^2? anion are linked to each other via several weak N–H?S and C–H?S bonding interactions. The lattice water serves as a link between pairs of cations and pairs of anions with the aid of O–H?S and N–H?O interactions in compound 1.     

Probability distribution for the number of cycles between successive regime transitions for the Lorenz model

The Lorenz model has been widely used for exploring many real world problems. In this paper we obtain, with the help of an invariant manifold technique, the return map for the maximum value of the variable x of the model and use this return map to derive the simple, empirically obtained, regime transition rules for forecasting regime changes and length in the new regime for the model. The probability distribution for number of cycles between successive regime transitions of the Lorenz model may be of interest in many disciplines. We apply the Perron-Frobenius algorithm over the return map to estimate the probability distribution for the number of cycles between successive regime transitions. These probabilities are also estimated for the forced Lorenz model, which is a conceptual model to explore the effects of sea surface temperature on seasonal rainfall.     

Thermal stresses in an elastic sphere containing a penny-shaped crack

Zusammenfassung Es wird der Spannungszustand in einer elastischen Kugel untersucht, die im Zentrum einen münzenförmigen Riss mit konstanter Oberflächentemperatur besitzt, während die sphärische Oberfläche auf der Temperatur null gehalten wird. Dabei wird angenommen, dass an der Oberfläche a) die Schubspannung und die radiale Verschiebung, b) die Normalspannung und die Schubspannung null sind.

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This work was supported by a C.S.I.R. grant No. 3(277)/69-GAU-II.     

Cobordism independence of Grassmann manifolds

This note proves that, forF = ℝ, ℂ or ℍ, the bordism classes of all non-bounding Grassmannian manifoldsG _k(F ^n+k), withk <n and having real dimensiond, constitute a linearly independent set in the unoriented bordism group N _d regarded as a ℤ₂-vector space.     

Dynamics of texture evolution in face-centered cubic polycrystals

Texturing of polycrystals under slip-dominated plastic deformation is driven by reorientation velocity fields that arise from the lattice spin that accompanies restricted slip. Here, the dynamics of reorientation velocity fields are analyzed to isolate mechanisms by which textures develop and dissipate. Two tools are introduced to enable this analysis: linear stability analysis to assess behavior of equilibrium orientations, and a parametrization of lattice spins to enable analysis of fields without equilibria. This toolkit is applied to face-centered cubic (FCC) polycrystals and sheds new insight into texture development under three representative deformation modes: plane strain compression, pure shear and simple shear.     

Rotational barrier and thermodynamical parameters of furfural,thiofurfural, and selenofurfural in the gas and solution phases: theoretical study based on density functional theory method

This work aims to study the trans and cis conformers of furfural, thiofurfural and selenofurfural in the gas and solution phases. Assuming that there is equilibrium between these conformers, the transition state has also been investigated. All computations have been done using density functional theory method with B3LYP as the functional and 6-311++G(d,p) as the basis sets. The optimized molecular structures and related parameters of these conformers are reported. The infrared wavenumbers and Raman activities of these conformers are also reported with appropriate assignments. The energy differences between the trans and cis conformers, associated barriers and thermodynamical parameters have been derived from the computations. It is found that the structural parameters are not much different in the gas and solution phases. However, in the gas phase, the trans conformer is always more stable, but increasing the polarity of the solvent leads to the cis conformer becoming more stable. The rotational barrier is always larger than the energy difference and both of them increase when the solvent becomes more polar. Some of the results for furfural compare satisfactorily with literature and therefore the data from this work will be useful for thiofurfuraldehyde and selenofurfuraldehyde, as their literature is limited.     

Degradation in polytetrafluoro ethylene by 62 mev protons

The aim of our study is to describe the dose dependent proton induced modifications in Polytetrafluoro ethylene (PTFE) by using Fourier Transform Infra-red spectroscopy (FTIR), Thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC) and X-ray diffraction analysis (XRD). The shifting of the main peak along with a decrease in its intensity, the decrease in thermal stability and melting point and the formation of stable free radicals were observed in the polymer by proton irradiation.