REFLECTIVE INFRARED ELLIPSOMETRY OF PLASTIC FILMS

High resolution reflective ellipsometry is used to study freely suspended plastic films. We determine room temperature optical constants in the infrared for a variety of plastics using ellipsometry. The films are typically 6 to 100 μm thick and measurements are performed from near infrared to long wave-IR. The setup includes modeling software to fit the ellipsometric data to a generalized oscillator model. The films studied include acrylics, fluoropolymers, and variations of polyethylene, polystyrene, and polyvinyl chloride (PVC) among others. We are able to determine in-plane and out-of-plane optical constants. Transmission spectra from FTIR measurements are plotted and compared with ellipsometry results.     

Study of electropolymerised polyaniline films using cyclic voltammetry, atomic force microscopy and optical spectroscopy

Electropolymerisation of polyaniline (PANI) has been investigated using cyclic voltammetry in aqueous bath. The effect of dopant on the structure, morphology & optical properties of electrodeposited PANI has also been studied using x-ray diffraction (XRD), atomic force microscopy (AFM), optical absorbance & luminescence spectroscopy. It is shown that the presence of a neutral salt (KI) in the deposition matrix imparts enhanced crystallinity to PANI films.     

Modeling Rainwater Storage in Distributed Reservoir Systems in Humid Subtropical and Tropical Savannah Regions

Using a hydrologic model this study estimated rainwater storages in field-scale on-farm reservoir (OFR) systems at two locations: (1) Fort Worth, Texas, US; (2) Kharagpur, West Bengal, India. The water storages were estimated for variable OFR sizes: 1%, 5%, 10%, 15%, and 25% of the farm area. Water losses through seepage and evaporation were estimated using variable saturated hydraulic conductivity conditions: 0.33, 0.64, 1.3, 5 cm/h, which corresponded to the ranges of hydraulic conductivity of loam, sandy loam, loamy sand, and sandy soils, respectively. Results indicated that the water loss through evaporation was dominant at the first location, while seepage was at the second location. Changing the OFR sizes captured 5 to 28% of the total rainfall received in the farm area of the first location and 20–40% at the second location. Finally, a comparative economic analysis was made between a distributed OFR system and a centralized large reservoir that indicated that the distributed OFR system benefits exceeded the benefits of a large reservoir.     

Characteristics of atmospheric divergence and convergence in the Indian Ocean inferred from scatterometer winds

Large-scale surface atmospheric convergence and divergence patterns in the Indian Ocean are mapped using high-spatial resolution, merged scatterometer wind vectors during 1991-2000. The convergence zone evolves to north of 15°S as a result of convection promoted by warm (> 28 °C) equatorial sea surface temperature (SST), and it exhibits strong intensity during boreal summer and winter. A divergence zone evolves to the south of 15°S as a result of subdued convection caused by colder SST (< 24 °C) that reduces outgoing long-wave radiation; it exhibits enhanced intensity in the eastern Indian Ocean during boreal winter. The interannual variability shows that the divergence in the eastern Indian Ocean lags its western counterpart by 5-7 months. The convergence in the eastern Indian Ocean is stronger than its western counterpart during boreal summer. Relationship between Southern Oscillation Index and spatially averaged convergence time series indicate that the latter weakened during strong El Niño years 1994 and 1997. Spatially averaged divergence time series show a near-contemporaneous relationship with all-India rainfall, with a temporal lag of 1∼2 months.     

Enrichment of γ-linolenic acid in the lipid extracted from Mucor zychae MTCC 5420

The aim of this work was to study the enrichment of the Gamma linolenic acid (GLA) content of lipid extracted from Mucor zychae by employing a low-temperature urea crystallization process. GLA, a polyunsaturated fatty acid has been reported to have many health benefits and has potential implications in food and pharmaceutical industry. Lipids extracted from the mycelia of fermented broth were transesterfied and analysed by gas chromatography. Results showed that the fungal oil contained (%) myristic acid (1.2), palmitic acid (35.3), palmitoleic acid (3.7), stearic acid (2.7), oleic acid (39.2), linoleic acid (6.4) and gamma linolenic acid (8.7). After the first step of crystallization, the percentage of GLA enriched in the total lipid was increased to 63.5. The concentration of GLA further increased when the enriched lipid sample was subjected to urea crystallization for the second time. GLA percentage increased from 63.5 to 92.7, and recovery of GLA was 63%. By altering the ratio of fatty acid ethyl ester:urea, the concentration characteristics and the recovery of GLA also varied; highest recovery of GLA (69%) was obtained when, the above ratio was 1:3. Furthermore, GLA recovery was in considerable amounts at 0 °C crystallization.     

Some aspects of workability studies on P/M sintered high strength 4% Titanium carbide composite steel preforms during cold upsetting

Workability is concerned with the extent to which a material can be deformed in a specific metal working process without the initiation of cracks. Ductile fracture is the most common failure in bulk forming process. The formability is a complicated phenomenon which depends on the friction between the preform and the die surface in cold upsetting. A complete experimental investigation on the workability behavior of the steel composite of 4%TiC was performed under different stress states, namely, plane and triaxial stress state conditions. Cold upsetting of the Fe–1.0%C–4%Ti steel composite preforms was carried out applying different lubricants, namely, graphite, zinc stearate and molybdenum disulphide, and without lubricant, and the formability behaviour of the same under plane and triaxial stress state conditions was determined. The curves plotted for different preforms were analysed and relationship was established between the axial strain and the formability stress index under plane and triaxial state conditions. A relationship between the relative density and the axial strain was also established. Various stress ratio parameters, namely, (σ_θ/σ_eff), (σ_m/σ_eff) and (σ_z/σ_eff), under plane and triaxial stress state conditions were determined empirically as a function of the relative density. An attempt is also made to study the variation of slope of the relative density versus stress ratio parameters under plane and triaxial stress conditions with respect to the relative density to identify the pore closure mechanism.     

Performance of superstrate multijunction amorphous silicon-based solar cells using optical layers for current management

The performance of multijunction amorphous silicon-based thin film solar cells has been reported using thin layers of TiO₂ and SiO_x acting as refractive index matching optical layers for different interfaces of the superstrate device structure. Improvement of short-circuit current from the sub-cells of a-Si/μc-Si cells is demonstrated with TiO₂ as anti-reflection layer at TCO/Si interface and SiO_x as intermediate-reflector layer between two sub-cells. An initial efficiency of 11.8% is achieved by applying both the TiO₂ and SiO_x optical layers in a-Si/μc-Si solar cell.     

Simultaneous heat and mass transfer in sphere in presence of phase and chemical transformation under generalised boundary conditions

The present investigation includes a theoretical study of simultaneous heat and mass transfer in a sphere in presence of phase and chemical transformation. The transfer potentials are determined under the influence of most general type of boundary conditions. Approximate solutions of these transfer potentials have also been determined. The whole analysis has been presented in the dimensionless form with the help of similarity criteria.     

A comparative study of analytical squeeze film damping models in rigid rectangular perforated MEMS structures with experimental results

Several analytical models exist for evaluating squeeze film damping in rigid rectangular perforated MEMS structures. These models vary in their treatment of losses through perforations and squeezed film, in their assumptions of compressibility, rarefaction and inertia, and their treatment of various second order corrections. We present a model that improves upon our previously reported work by incorporating more accurate losses through holes proposed by Veijola and treating boundary cells and interior cell differently as proposed by Mohite et al. We benchmark all these models against experimental results obtained for a typical perforated MEMS structure with geometric parameters (e.g., perforation geometry, air gap, plate thickness) that fall well within the acceptable range of parameters for these models (with the sole exception of Blech’s model that does not include perforations but is included for historical reasons). We compare the results and discuss the sources of errors. We show that the proposed model gives the best result by predicting the damping constant within 10% of the experimental value. We study the validity of the proposed model over the entire range of perforation ratios (PR) by comparing its results with numerically computed results from 3D Navier-Stokes equation. These results are also compared with other analytical models. The proposed model shows considerably better results than other models, especially for large values of PR.     

Failure analysis of styrene reactor tubes

The analysis of failure of the styrene reactor tubes made of stainless steel has been reported where the tubes contained catalyst as well as ethyl benzene in vapour form along with superheated steam at 570 °C. The tubes were exposed to flue gases causing heating of tubes to 790 °C in the upper part where cracking and failure were mostly noticed. The studies included microstructural examinations of cracked and uncracked tubes, fracture surface investigations and estimation of creep rupture strength, etc. The degradation in microstructure such as extensive grain coarsening, sigma phase formation, carbide formation along grain boundaries, etc., led to development of cracks/voids within the grains and along the grain boundaries and also excessive oxidation of tubes. Possible chemical attack by the feed on the inner surface of tubes further deteriorated the tube life. Suggestions for avoidance of failure have been listed.