Response of protonic acid‐doped poly(o‐anisidine)/poly(vinyl alcohol) composites to relative humidity and role of dopant anions

Various protonated poly(o‐anisidine) (PoAN)/poly(vinyl alcohol) (PVA) composites were prepared with different types of acids: sulfuric (SA), p‐toluene sulfonic (TSA), camphor sulfonic (CSA), and p‐dodecylbenzene sulfonic (DBSA). In the visible spectrum of each composite in dimethyl sulfoxide, three absorption peaks were observed at 440, 620, and 860 nm. The peaks at 440 and 860 nm, which were enhanced with the increasing content of acid‐doped PoAN in the PVA matrix, were attributed to the radical cation and localized polaron generated in the conducting polymer. However, the peak at 620 nm was ascribed to the emeraldine base (EB) form of PoAN; that is, a portion of the acid was detached from the conducting polymer to form EB‐PoAN and free acid. The linear dependence of the logarithmic electrical conductivity on the variation of humidity, which was observed for all the composites, was caused by the salt–base transition of the conducting polymer, that is, by the movement of free acid between the active sites of the conducting polymer and the strongly bound water existing in PVA, which in turn depended directly on the environmental humidity. The response time of the composites to humidity was shortened with a decrease in the size of the dopant anions: DBSA > CSA > TSA > SA. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4343–4352, 2000     

Nonlinear state feedback control design to eliminate subcritical limit cycle oscillations in aeroelastic systems

A strictly nonlinear state feedback control law is designed for an aeroelastic system to eliminate subcritical limit cycle oscillations. Numerical continuation techniques and harmonic balance methods are employed to generate analytical estimates of limit cycle oscillation commencement velocity and its sensitivity with respect to the introduced control parameters. The obtained estimates are used in a multiobjective optimization framework to generate optimal control parameters which maximize the limit cycle oscillation commencement velocity while minimizing the control cost. Numerical simulations are used to show that the assumed nonlinear state feedback law with the optimal control parameters successfully eliminates any existing subcritical limit cycle oscillations by converting it to supercritical limit cycle oscillations, thereby guaranteeing safe operation of the system in its flight envelope.     

Experimental study of heat transfer characteristics in oscillating fluid flow in tube

In the present work, an experimental investigation of heat transfer enhancement parameters of the oscillating flow heat exchanger under different frequencies, tidal displacement, and heat fluxes is carried out. The effect of different parameters on experimental effective thermal conductivity and convective heat transfer coefficient in cooling region is studied using correlations given by different researchers. A correlation for experimental effective thermal conductivity in terms of S²√ω is derived based on experimental data. This correlation is useful for predicting the optimum value of S²√ω before onset of turbulence.     

Structural,optical and electrical properties of post annealed Mg doped ZnO films for optoelectronics applications

Mg _x Zn_1-x O films with 0.15 mole composition of Magnesium were successfully deposited by the spin coating sol–gel method. Zinc acetate dihydrate and Magnesium acetate were used as starting precursors to prepare the solution in ethanol solvent. The MgZnO films were deposited on microscopic glass substrates and post annealed at three different temperatures. X-ray Diffractometer (XRD), Scanning Electron Microscopy (SEM) and UV–VIS Spectrophotometer were used to characterize the deposited films for studying structural and optical properties. Energy dispersive analysis by X-ray (EDAX) was used to determine incorporation of Mg content in ZnO films. XRD spectrum reveals that, the deposited Mg doped ZnO films were polycrystalline in nature. The intensity of c-axis in the XRD spectrum goes on decreasing as Mg composition slightly increasing corresponding to increase in annealing temperature. EDAX spectra clearly showed the incorporation of Mg into the ZnO films. Semiconductor characterization system was used for the I–V characterization of MgZnO films. I–V characteristics show decrease in current as increase in the biased voltage. Optical band gap of MgZnO films was found to be increased from 3.2 to 3.38 eV as estimated from the absorption coefficients.     

Nano-graphitic clustering and break down of phonon selection rule in diamond-like carbon films

Diamond-like carbon films are deposited on silicon substrates at different substrate bias using ECR-CVD technique. Raman spectroscopic studies show the presence of broad G and D peaks. In contrast to the position of D peak, the G peak shows a systematic red-shift with increase in the bias voltage. From the analysis it is found that an increase in bias voltage decreases the sp² cluster diameter. Furthermore, two additional Raman peaks at around 690 and 880 cm^?1 are also observed. These peaks, forbidden in the first order Raman scattering, arise due to the breakdown of phonon selection rule in graphitic nanoclusters.     

Facile one-pot synthesis of α-bromoketones from olefins using bromide/bromate couple as a nonhazardous brominating agent

A new method for the preparation of α-bromoketones from olefins using bromide/bromate couple as a nonhazardous brominating agent has been developed. Several α-bromoketones were successfully prepared from a variety of olefins by this method. This procedure is an alternative to conventional molecular bromine.