Thermo‐mechanical Properties of PEO‐PU/PAN Semi‐Interpenetrating Polymer Networks and their LiClO4 Salt‐Complexes

This paper is an investigation on the thermo‐mechanical properties of a new class of materials, which holds promise for its potential use as solid polymer electrolytes, i.e., SPE material. A series of poly(ethylene oxide)‐polyurethane/poly(acrylonitrile) (PEO‐PU/PAN) semi‐IPNs, along with their LiClO₄ salt complexes, were characterized for their thermal, mechanical and dimensional stability using DSC, TG‐DTA, UTM and DMTA. The glass transition temperature (T_g) of both the undoped and doped semi‐IPNs, obtained by DSC, remained well below room temperature (～?50°C to ?35°C), satisfying one of the essential requirements to serve as a SPE host matrix. The crystallization process in the PEO segments of the PEO‐PU/PAN semi‐IPNs was prevented at higher salt concentrations, which is attributed to the Li⁺ ion mediated pseudo‐crosslinks. Good thermal stability of the semi‐IPNs was evident from the degradation onset temperature (T₀～240°C) with a three‐stage degradation process, which is independent of the PAN content as observed from differential thermogravimetric studies. The incorporation of PAN in the PEO‐PU networks results in improved mechanical properties, such as tensile strength and modulus while retaining the flexibility of the semi‐IPNs. The peak temperatures and storage modulus obtained from DMTA correlates well with the observations of DSC and tensile measurements.     

Charge‐Transfer Complex Formation in Gelation: The Role of Solvent Molecules with Different Electron‐Donating Capacities

A naphthalenediimide (NDI)‐based synthetic peptide molecule forms gels in a particular solvent mixture (chloroform/aromatic hydrocarbon, 4:1) through charge‐transfer (CT) complex formation; this is evident from the corresponding absorbance and fluorescence spectra at room temperature. Various aromatic hydrocarbon based solvents, including benzene, toluene, xylene (ortho, meta and para) and mesitylene, have been used for the formation of the CT complex. The role of different solvent molecules with varying electron‐donation capacities in the formation of CT complexes has been established through spectroscopic and computational studies.     

Magnetoelectric effect in cobalt ferrite-barium titanate composites and their electrical properties

CoFe₂O₄-BaTiO₃ composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric conversion factor has been studied as a function of magnetic field.     

Energy dependence of multiplicity in proton-nucleus collisions and models of multiparticle production

This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR _em = 〈n _s〉/〈n _ch〉, where 〈n _ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R _em = 1·71 implies an effectiveA-dependence ofR _A =A ^0.18,i.e., a very weak dependence. Predictions ofR _em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production.     

Design, synthesis and DNA-cleaving efficiency of photoswitchable dimeric azobenzene-based C2-symmetric enediynes

Designed azobenzene-based enediyne-amino acid C(2)-symmetric hybrids have been synthesized and the role of amino acid linker in stabilizing the Z form has been demonstrated; DNA-binding and cleavage studies have established higher reactivity of the Z-isomers.     

Synthesis, structure, and spectroscopic properties of chiral oxorhenium(V) complexes incorporating polydentate ligands derived from L-amino acids: a density functional theory/time-dependent density functional theory investigation

The oxorhenium(V) complexes [Re (V)O(L A)Cl 2] bearing the (N-2-pyridylmethyl) of l-valine (HL A (1)), l-leucine (HL A (2)), and l-phenylalanine (HL A (3)) and [Re (V)O(L B)Cl] containing the {(N-2pyridylmethyl)-(N-(5-nitro-2-hydroxybenzyl)} of l-valine (H 2L B (1)), l-leucine (H 2L B (2)), and l-phenylalanine (H 2L B (3)) are presented in this article. The complexes are isolated in enantiomeric pure form examined from X-ray structure determination. The complexes are characterized by spectroscopic and electrochemical methods. The molecular structures observed in the solid state are grossly preserved in solution ( (1)H, (13)C, and circular dichroism spectra). Gas-phase geometry optimization and the electronic structures of [Re (V)O(L A (1))Cl 2], [Re (V)O(L A (2))Cl 2], and [Re (V)O(L B (2))Cl] have been investigated with the framework of density functional theory. The absorption and circular dichroism spectra of the complexes were also calculated applying time-dependent density functional theory (TDDFT) using the conductor-like polarizable continuum solvent model to understand the origin of the electronic excitations. The chemical shift ( (1)H and (13)C) as well as (1)H- (1)H spin-spin coupling constant were also computed by the gauge-independent atomic orbital method, and the computed values are consistent with the experimental data.     

Langevin type limiting processes for adaptive MCMC

Adaptive Markov Chain Monte Carlo (AMCMC) is a class of MCMC algorithms where the proposal distribution changes at every iteration of the chain. In this case it is important to verify that such a Markov Chain indeed has a stationary distribution. In this paper we discuss a diffusion approximation to a discrete time AMCMC. This diffusion approximation is different when compared to the diffusion approximation as in Gelman et al. [5] where the state space increases in dimension to ∞. In our approach the time parameter is sped up in such a way that the limiting process (as the mesh size goes to 0) approaches to a non-trivial diffusion process.