Preparation of (CdO)1−x(PbO)x and (CdS)1−x(PbS)x thin films by spray pyrolysis technique and their characterization

Mixed thin films of (CdO)_1−x(PbO)_x and (CdS)_1−x(PbS)_x (x=0.25) were prepared on glass substrates by spray pyrolysis technique for various substrate temperatures 300, 320 and 340 °C. Structural and optical properties were studied. XRD studies reveal the formation of mixed films. The substrate temperature of 340 °C seems to be critical for the formation of CdO-PbO mixed films. It is observed that (CdS)_1−x(PbS)_x mixed films were formed at all the three substrate temperatures. The direct band gap value of (CdO)_1−x(PbO)_x and (CdS)_1−x(PbS)_x mixed films is about 2.6 and 2.37 eV, respectively.     

Study of interactions of various ionic species with solvents toward the design of receptors

In earlier studies, the interactions of isolated ionic species with various solvents were investigated using ab initio calculations. The ionic species investigated included cations (proton, hydronium, ammonium, and metal cations) and anions (single electron, hydroxide, and halide anions). However in the present study, we investigate the interactions of these ionic species with the solvent in the presence of other competing ionic species. We also elaborate on how the information obtained from these extensive studies have been employed in designing and synthesizing various kinds of novel ionophores and receptors.     

Design,synthesis, and characterization of main‐chain,aromatic polyesters based on 3,4‐ethylenedioxythiophene

A series of new thermoplastic polyesters based on 3,4‐ethylenedioxythiophene (EDOT) with flexible aliphatic spacers have been synthesized and characterized for the first time. The thermal properties of these polyesters based on EDOT are comparable to those of conventional polyesters based on the 1,4‐phenyl unit, indicating that EDOT is a viable replacement for the phenyl units. The glass‐transition and melting‐transition temperatures decrease monotonically with an increase in the spacer length. Theoretical calculations have revealed that the core angle for EDOT is comparable to that of unsubstituted thiophene and hence should be compatible with the formation of the mesophase. This has been confirmed experimentally by the synthesis of a main‐chain, thermotropic, liquid‐crystalline polyester based on EDOT that exhibits fluid birefringence. In fact, this is the first report in which a main‐chain, liquid‐crystalline polymer based on 3,4‐disubstituted thiophene has been successfully designed and synthesized. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3479–3486, 2006     

Structure–activity studies on the fungitoxicity of some triorganotin(IV) compounds

Seventeen triorganotin(IV) compounds, with the general formula R₃SnX, containing symmetrical and unsymmetrical combinations of alkyl and aryl groups on tin and with a wide variation in the non-carbon-bonded anionic (X) residues, were examined along with three formally pentacoordinated adducts of triaryltin chlorides with triphenylphosphine oxide for their antifungal activity against nine plant pathogenic and saprophytic fungi. The in vitro tests included inhibitory studies on radial growth, mycelial growth, spore germination, and germ tube elongation. A significant finding was the dependence of fungitoxicity on the nature of the X group in both the tributyltin and triaryltin series, in contrast to earlier published reports on the negligible influence of the X groups on overall toxicity relative to the R group. This suggests that the X group is significantly involved in transporting the biocide to the reactive sites, and that the X group which tends to confer increased solubility to the triorganotin compound gives rise to increased activity. In studies of R group variations, tri-iso-butyltin bromide was found to be much less fungitoxic than tri-n-butyltin compounds, a result which is reconcilable in terms of increased steric encumbrance at the tin site in the former case. The steric factor is also implicated in the reduced activities observed for tris(p-tolyl)tin and tris(p-chlorophenyl)tin compounds relative to (Ph₃SnX) towards most of the fungi screened in this study. In general, it was also noted that the triaryltins were more selective in their antifungal action than the trialkyltins, which exhibited broad spectral activity when applied at the concentration level of 10 μg cm^?3.     

Dielectric spectroscopy of a smectic liquid crystal

Complex dielectric spectroscopy (frequency range 5 Hz-13 MHz) has been used to analyse the frequency, temperature and bias-field dependences of the molecular dynamics of a very high-spontaneous-polarization ferroelectric liquid crystalline material exhibiting SmA, SmC* and unknown SmX smectic phases. Different smectic phase transition temperatures have been observed from the study of the temperature dependence of the dielectric strength and the relaxation frequency. The phase transition temperatures (crystalline to isotropic phases) have also been described very accurately from the temperature-dependent symmetric and asymmetric shape parameters of the relaxation function and also the dc conductivity. In a planar aligned cell, two symmetric modes (Goldstone mode and domain mode) have been observed in both the SmX and SmC* phases. One asymmetric mode (X-mode) observed in the SmC* and SmA phases could be related to the interaction of dipoles of the ferroelectric liquid crystals being affected by the surface of the cell. The soft mode, which usually appears very close to the SmC*-SmA phase transition was not observed until the bias field was applied. The second order nature of the SmC*-SmA phase transition was revealed.     

ENSTAR detector forη- mesic studies

We have initiated a search for a new type of nuclear matter, theη-mesic nucleus, using beams from the multi-GeV hadron facility, COSY at Juelich, Germany. A large acceptance scintillator detector, ENSTAR has been designed and built at BARC, Mumbai and fully assembled and tested at COSY. A test run for calibration and evaluation has been completed. In this contribution we present the design and technical details of the ENSTAR detector and how it will be used to detect protons and pions (the decay products ofη-mesic bound state). The detector is made of plastic scintillators arranged in three concentric cylindrical layers. The readout of the detectors is by means of optical fibres. The layers are used to generate ΔE –E spectra for particle identification and total energy information of stopped particles. The granularity of the detector allows for position (θ and ?ø determination making the event reconstruction kinematically complete     

Partitioning multi-edge graphs

We introduce a new kind of graph called multi-edge graph which arises in many applications such as finite state Markov chains and broadcasting communication networks. A cluster in such a graph is a set of nodes such that for any ordered pair of nodes, there is a path of multi-edges from one to the other such that these edges remain within the same set. We give two algorithms to partition a multi-edge graph into maximal clusters. Both these algorithms are based on the depth-first search algorithm to find strongly connected components of the directed graph. We also discuss some applications of clustering in multi-edge graphs.