Resonant frequencies of shielded rectangular and circular microstrip resonators

Resonant frequencies of shielded rectangular and circular microstrip patches have been determined using the modified Wolff model (MWM). The model determines effect of top-shield, side-walls, and end-walls on the resonant frequency. Results of the MWM have been compared to those of SDA and FEM. The MWM has an accuracy of 0.2% compared with experimental results. Numerically, the MWM is fast even on a desktop computer. The model is suitable for CAD applications. © 1995 John Wiley & Sons, Inc.     

Thermal aspects of shear localization in microporous viscoplastic solids

A set of phenomenological state variable constitutive equations for large deformations of isotropic, thermo-elasto-viscoplastic, porous materials is considered, and a new semi-implicit, incrementally objective time-integration procedure for these constitutive equations is developed. The constitutive equations and the time-integration procedure are implemented in a finite element program, and used to study the shear band formation and ductile fracture initiation triggered by flow softening due to the combined effects of void growth and deformation heating, in a plane strain tension test.     

Vibrational Technique for Stress Measurement in Films: I, Ideal Membrane Behavior

A vibrational technique for the measurement of stress in films has been developed, based on the theory of membranes. Specimens for vibrational analysis are prepared by removing a circular or square piece of the substrate. It is shown that the error introduced due to substrate removal is negligible except for thin metallic films. The resulting specimen, a film stretched across a hole in the substrate, behaves as a membrane. Since its natural frequencies increase with the square root of in-plane stress, these can be measured to compute the in-plane stress. The only material parameter needed is the density of the film. Because a number of natural frequencies can be measured, each of which can be used to compute the stress, this method has a strong check for internal consistency. Two different techniques have been used to measure natural frequencies: (1) sinusoidal excitation and holographic imaging of the vibration modes, and (2) random excitation and Fourier analysis of measured vibrations. In this, the first part of the study, we discuss cases when ideal membrane behavior is obtained. Three applications of the method are presented: measurement of stress in a filled-glass layer bonded to an aluminum substrate, a study of the effect of temperature and humidity on stress in a thermoset polymer coating, and stress in a silver film during heat treatment. The second part of the study¹ deals with extensions of the technique when complicating effects, such as air loading, bending stiffness, and an aniso-tropic state of stress, are important. In the third part of the study,² the method is used to identify the orthotropic axes and all nine elasticity coefficients of a commercially made film.     

Mild oxidation of hydrocarbons catalyzed by iron corrole with tert-butylhydroperoxide

Catalytic alkane and alkene oxidation by iron complex of 5,10,15 tris-(pentafluorophenyl)corrole, using 70% tert-butyl hydroperoxide as oxidant at room temperature is reported for the very first time. Involvement of freely diffusing radicals in the oxidizing system is observed. A reaction mechanism is proposed based on the experimental results.     

Epoxidation of styrene with TBHP/O2 over ferrierite (FER) type molecular sieves

Epoxidation of styrene over vanadium silicalite with ferrierite (FER) type topology is undertaken. Influence of temperature, pressure, various solvents and solvent to substrate mole ratio was investigated. Conversion increased with increase in temperature and pressure. Solvent to substrate mole ratio is found to play a crucial role in increasing the conversion and selectivity. Catalytic activity of V‐FER was compared with those of Ti‐FER, TS‐1 and Fe‐FER. In the case of V‐ and Ti‐ferrierite analogs, styrene oxide was the major product, whereas phenylacetaldehyde was the major product in the case of TS‐1. The catalyst could be recycled after washing by a suitable solvent such as acetone and showed no significant loss in catalytic activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Exceptionally good,transparent and flexible FeS2/poly(vinyl pyrrolidone) and FeS2/poly(vinyl alcohol) nanocomposite thin films with excellent UV‐shielding properties

Composites of nanocrystalline iron disulfide (FeS₂) coated with poly(vinyl pyrrolidone) (PVP) or poly(vinyl alcohol) (PVA) have been successfully synthesized using a solvothermal process, in which PVP and PVA serve as soft templates. Transparent, flexible thin films of these nanocomposites were prepared from homogeneous solution using a solution‐casting approach. X‐ray diffraction and thermogravimetric analysis and energy‐dispersive X‐ray, Fourier transform infrared and UV‐visible absorption spectroscopic techniques were employed to study the structural and optical properties of these nanocomposite films. UV‐visible spectra in transmission mode reveal the UV‐shielding efficiency of these nanocomposite films and the films are found to be exceptionally good for UV‐shielding applications in the wavelength range 200 to 400 nm. The present work aims at developing transparent and flexible UV‐shielding materials and colour filters using cost‐effective and non‐toxic inorganic–polymer nanocomposites. © 2012 Society of Chemical Industry     

Selective separation of copper (II) and cobalt (II) from wastewater by using continuous cross‐flow micellar‐enhanced ultrafiltration and surfactant recovery from metal micellar solutions

Performance of continuous cross‐flow micellar‐enhanced ultrafiltration (MEUF) method was investigated for the selective separation of copper (Cu²⁺) and cobalt (Co²⁺) from the aqueous phase using sodium dodecyl sulfate (SDS) as an anionic surfactant and iminodiacetic acid (IDA) as a chelating agent. Operating parameters such as operating time (10–120 min), cross‐flow rate (100–250 mL/min), pH of the solution (2.8–5.6), molar concentration ratio of the chelating agent to metals (the C/M ratio, 0.5–2.5), molar concentration ratio of the surfactant to metals (the S/M ratio, 5–8) and mode of operation were studied to investigate the effectiveness of the process on selective separation. At optimal parameters, above 90% selective separation (Cu²⁺ in permeate and Co²⁺ in retentate) was achieved. Two methods were studied for the separation of Co²⁺ and SDS from retentate stream; acidification followed by UF and addition of chelating agent followed by UF with surfactant recovery of 75% and 83%, respectively, and Co going into the permeate.     

Improved optical limiting in dispersible carbon nanotubes and their metal oxide hybrids

The mechanism and performance of optical limiting in carbon nanotubes (CNTs) and their metal oxide hybrids are presented. The mechanism of nonlinear absorption (NLA) in dispersed CNTs was an “effective” three-photon absorption arising due to sequential transitions between the real excited states. The effect of nonlinear scattering was minimal, and it was found that the metal oxide immobilization on the CNT surface does not alter either the mechanism of NLA, or the optical limiting threshold. With limiting thresholds in the range of 0.37–0.46 J/cm², these highly dispersible MWCNTs and their hybrids are excellent optical liming nanocarbons.     

Enzyme‐Based Nanoscale Composites for Use as Active Decontamination Surfaces

Perhydrolase S54V (AcT) effectively catalyzes the perhydrolysis of propylene glycol diacetate (PGD) to generate peracetic acid (PAA). PAA is a potent oxidant used for sanitization and disinfection, with broad effectiveness against bacteria, yeasts, fungi, and spores. In this study, active and stable composites are developed by incorporating AcT–carbon nanotube conjugates into polymer and latex‐based paint. At a conjugate loading of 0.16% (w/v), the composite generated 11 mM PAA in 20 min, capable of killing more than 99% spores initially charged at 10⁶ colony‐forming units per milliliter.