Vinyl acetate monomer—a pilot plant study

The kinetics of the reaction of acetic acid and acetylene over zinc acetate-activated carbon catalyst was investigated over a wide range of process variables in a pilot reactor. Although various catalytic reaction mechanisms were postulated, the rate of reaction was most satisfactorily correlated by a mechanism of surface reaction between charged adsorbed acetic acid and acetylene, which assumes that the rate controlling step was the irreversible charged adsorption of acetylene and acetic acid.     

Two-tier architecture for unconstrained handwritten character recognition

In this paper, we propose an approach that combines the unsupervised and supervised learning techniques for unconstrained handwritten numeral recognition. This approach uses the Kohonen self-organizing neural network for data classification in the first stage and the learning vector quantization (LVQ) model in the second stage to improve classification accuracy. The combined architecture performs better than the Kohonen self-organizing map alone. In the proposed approach, the collection of centroids at different phases of training plays a vital role in the performance of the recognition system. Four experiments have been conducted and experimental results show that the collection of centroids in the middle of the training gives high performance in terms of speed and accuracy. The systems developed also resolve the confusion between handwritten numerals.     

Investigations of surface characterization of silicone rubber due to tracking phenomena under a.c. and d.c. voltages

In the present work, tracking phenomena has been studied with silicone rubber material under the a.c. and d.c. voltages following IEC-587 standards. The surface condition of the tracked zone was analysed using wide angle X-ray diffraction (WAXD) and thermogravimetric differential thermal analysis (TG-DTA) studies. The tracking time was different for a.c. and d.c. voltages.     

Modeling of optical low coherence reflectometry recorded Braggreflectograms: evidence to a decisive role of Bragg spectral selectivity

This paper draws attention to the basic principles governing reflections in uniform Bragg reflectors (BR) when measured employing optical low coherence reflectometry (OLCR) technique. Using computations based on transfer matrix method (TMM), we first showed a strong spectral dependence of Bragg reflectograms on an OLCR probe spectrum. Later, this dependence is exploited to evaluate, for the first time, the coupling coefficient κ of a Bragg grating in a distributed Bragg reflector (DBR) laser on InP     

Thoria doped with cations of group VB–synthesis and sintering

The cations M⁵⁺ (M=V, Nb and Ta) were doped in thoria through gel-combustion synthesis using citric acid as fuel. Thorium dioxide feed powders thus prepared were cold compacted without binder or lubricant and sintered to a high density (9.5 Mg m⁻³) at relatively low temperatures (1623 K). The powders were characterised for the residual carbon, crystallite size, specific surface area, particle size distribution and bulk density. The distribution of the dopant in the thoria matrix was analyzed by electron probe microanalysis. The reactivity of the calcined powders was determined by measuring the density of the sintered compacts prepared from them. For the first time it is demonstrated that apart from niobia, even tantala and vanadia can bring about accelerated sintering in thoria if they are doped through a wet chemical route viz., the gel-combustion procedure. The maximum densities obtained by doping with vanadia (0.02 mol%), niobia (0.50 mol%) and tantala (0.50 mol%) were 9.8 Mg m⁻³ (1573 K), 9.68 Mg m⁻³ (1423 K) and 9.69 Mg m⁻³ (1623 K), respectively.     

Ion implantation doping of OMCVD grown GaN

Doping by ion implantation using Si, O, Mg, and Ca has been studied in single crystal semi-insulating and n-type GaN grown on a-sapphire substrates. The n-and p-type dopants used in this study are Si and O; Mg and Ca, respectively. Room temperature activation of Si and O donors has been achieved after 1150°C annealing for 120 s. The activation of Mg and Ca acceptors is too low to measure at both room temperature and 300°C. Using higher doses to achieve a measurable p-type conduction increases the amount of damage created by the implantation. Rutherford back scattering measurements on this material indicate that the damage is still present even after the maximum possible heat treatment. Secondary ion mass spectrometry measurements have indicated a redistribution in the measured profiles of Mg due to annealing.     

Ductile-phase toughening and Fatigue-Crack Growth in Nb-Reinforced Molybdenum Disilicide Intermetallic Composites

A study has been made of the role of ductile-phase toughening on the ambient temperature fracture toughness and fatigue-crack propagation behavior of a molybdenum disilicide intermetallicmatrix composite reinforced with 20 vol pct niobium spheres. Using disk-shaped compact DC(T) samples, only moderate improvements (∼24 pct) in fracture toughnessK _lcvalues were found for the composite compared to the unreinforced MoSi₂ matrix material. Moreover, (cyclic) fatigue- crack propagation was seen at stress intensities as low as 75 to 90 pct ofK _Ic, with growth rates displaying a high dependency (∼14) on the applied stress-intensity range. The lack of significant toughening due to the incorporation of ductile Nb particles is associated with an absence of crack/particle interactions. This is attributed to the formation of a weak reaction-layer interface and elastic mismatch stresses at the crack tip between the Nb and MoSi₂, both factors which favor interfacial debonding; moreover, the spherical morphology of Nb phase stabilizes cracking around the particle. Results suggest that increasing the aspect ratio of the distributed Nb rein- forcement phase with attendant interfacial debonding and eliminating possible Nb-phase em- brittlement due to interstitial impurity contamination are critical factors for the successful development of tougher Nb/MoSi₂ structural composites. Formerly with McDonnell Formerly with McDonnell     

Properties of ligno‐cellulose fiber Hildegardia

Studies on some properties such as the density, the degradation temperatures, the morphology and the spectral features of the ligno‐cellulose fiber Hildegardia were carried out in both untreated and alkali treated form. The fibers are found to have good morphology and moderate initial and final degradation temperatures. On alkali treatment, the lignin was found to be eliminated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2216–2221, 2002