Correlation of Back Optic Zone Radius measurement of rigid contact lenses with radiuscope and keratometer

PurposeTo investigate the accuracy of Back Optic Zone Radius (BOZR, base curve) measurements with manual keratometer for spherical polymethylmethacrylate (PMMA) lenses.Methods100 spherical PMMA contact lenses were selected randomly from the trial sets. One investigator measured the BOZR with radiuscope. The second investigator measured the BOZR with keratometer. The two investigators were masked to each other's readings. As the keratometer is designed to measure a convex corneal surface, the BOZR readings are less than actual radii. A correction factor of 0.025 was used to have corrected keratometers readings.ResultsThere was a high correlation between the BOZR measurement with radiuscope and the uncorrected (Pearson's correlation coefficient, r = 0.99) and corrected (r = 0.99) measurements with keratometer. The mean difference between BOZR measurement with radiuscope and the uncorrected and corrected measurements with keratometer were 0.003 mm (p = 0.62) and ?0.024 mm (p < 0.001) respectively. The 95% limits of agreement for the BOZR measurements with radiuscope and the uncorrected and corrected measurements with keratometer were ?0.11 to 0.11 mm and ?0.14 to 0.09 mm respectively.ConclusionWe found that the uncorrected BOZR measurements with keratometer were similar to the BOZR measurements with radiuscope. With unavailability of radiuscope in majority of contact lens practice, keratometer can be used to measure the BOZR of contact lenses.     

Viscosity modeling of a medium reactive unsaturated polyester resin used for liquid composite molding process

The development of new composite product for an application through liquid composite molding (LCM) process simulation requires submodels describing the raw material characteristics. The viscosity during resin cure is the major submodel required for the effective simulation of mold-filling phase of LCM process. The viscosity of the resin system during mold filling changes as the cure reaction progresses. Applied process temperature also affects the viscosity of the resin system. Hence, a submodel describing the resin viscosity as a function of extent of cure and process temperature is required for the LCM process simulation. In this study, a correlation for viscosity during curing of medium reactive unsaturated polyester resin, which is mostly used for the LCM process, has been proposed as a function of temperature and degree of cure. The viscosity and the degree of cure of reacting resin system at different temperatures were measured by performing isothermal rheological and isothermal differential scanning calorimetry experiments, respectively. A nonlinear-regression analysis of viscosity and degree of cure data were performed to quantify the dependence of viscosity on temperature and extent of cure reaction. Comparisons of model solutions with our experimental data showed that the proposed empirical model is capable of capturing resin viscosity as a function of extent of cure and temperature qualitatively as well as quantitatively. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Combining MoS<Subscript>2</Subscript> or MoSe<Subscript>2</Subscript> nanoflakes with carbon by reacting Mo(CO)<Subscript>6</Subscript> with S or Se under their autogenic pressure at elevated temperature

This paper describes a non-aqueous, solvent-free, environmentally friendly, one-pot facile reaction to synthesize inorganic materials inclusion with carbon (MoS₂ or MoSe₂/C) at low temperatures. Nanoflakes of MoS₂ and MoSe₂ inclusion with carbon are prepared by a thermal (750 °C) reaction between Mo(CO)₆ and S or Se at their autogenic pressure in a closed reactor under inert atmosphere. Elemental sulfur or selenium powders are chosen in order to avoid the use of highly toxic H₂S and H₂Se gases. Without further processing of the as-prepared MoS₂/C or MoSe₂/C products, their compositional, morphological and structural characterization are carried out. The possibility of hydrogen storage in as-synthesized MoS₂/C or MoSe₂/C products is examined. A probable reaction mechanism for the formation of MoS₂ or MoSe₂ nanoflakes inclusion with C is discussed.     

A two‐warehouse inventory model for items with three‐parameter Weibull distribution deterioration,shortages and linear trend in demand

Depending on the type of goods and storage facilities available, perishable goods decay in different manners in terms of the initial point and rate of deterioration. The three‐parameter Weibull distribution is an excellent generalization of exponential decay, with the flexibility of modeling various types of deteriorations. Since inventory management of perishable goods involves expensive storage facilities, the retailer with small storage may have to rent a warehouse. In this paper, we discuss a two‐warehouse inventory model where deteriorations in the two warehouses follow independent three‐parameter Weibull distributions. Transfer of units is from the rented warehouse to the own warehouse, and incurs a positive cost per unit. Demand is a non‐decreasing linear function of time, shortages are backlogged and replenishment is instantaneous. A solution procedure for obtaining optimal values of initial inventory level and cycle time is presented. Sensitivity analysis is carried out. The effect of using other related deterioration distributions is illustrated.     

Accelerated degradation in amorphous silicon solar cells by a combination of current injection and light insolation

A new degradation technique for amorphous silicon solar cells comprising of a combination of current injection and insolation has been developed. Compared to the conventional light degradation technique, current-induced degradation which involves forward biased current stress, results in a lower stabilized cell parameters including efficiency. This stabilized efficiency is, however, independent of the amount of current injected. The excess degradation is recovered under light illumination. The stabilized value of the conversion efficiency is within experimental error identical to that observed in long term, illumination only degradation. The method is fast, accurate and reliable. Its reliability has also been tested for single junction solar cells having intrinsic layers of different band gaps, as well.     

Effect of gravure process variables on void area in shrink film

The gravure print quality on shrink film depends on process parameters and is fairly gaged by minimum print defects such as voids. The visibility of these defects is visually disturbing and could result in product rejection. This article investigates the effect of process parameters such as viscosity, speed, hardness, and line screen frequency on ink transfer from recess gravure cells and hence on print voids in an attempt to minimize them. A general full factorial design with the abovementioned four independent variables was analyzed by variance, main, and interaction effects. The results revealed line screen, hardness, and ink viscosity as the most influential factors in minimizing the defect. A regression model was developed to predict void area. The model was validated by conducting an additional 11 runs on the press. The predicted values from the model were in close agreement with the press results. The results showed a commendable decrease in the void area by 65%.     

Casson fluid flow and heat transfer past a symmetric wedge

Boundary‐layer forced convection flow of a Casson fluid past a symmetric wedge is investigated. Similarity transformations are used to convert the governing partial differential equations to ordinary ones and the reduced equations are then solved numerically with the help of the shooting method. Comparisons with various previously published works on special cases are performed and the results are found to be in excellent agreement. A representative set of graphical results is obtained and illustrated graphically. The velocity is found to increase with an increasing Falkner–Skan exponent whereas the temperature decreases. With the rise of the Casson fluid parameter, the fluid velocity increases but the temperature is found to decrease in this case. The skin friction decreases with increasing values of the Casson fluid parameter. It is found that the temperature decreases as the Prandtl number increases and thermal boundary layer thickness decreases with increasing values of the Prandtl number. A significant finding of this investigation is that flow separation can be controlled by increasing the value of the Casson fluid parameter. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 42(8): 665–675, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21065     

Light induced degradation in nanocrystalline Si films and related solar cells: Role of crystalline fraction

Silicon thin films with different crystalline volume fractions have been deposited at different power and pressure conditions. Structural properties of the films have been investigated. The effects of crystalline volume fractions and grain sizes on the degradation of photoconductivity have been studied. Single-junction solar cells have been fabricated with protocrystalline and nanocrystalline Si as absorber layer. Protocrystalline silicon solar cells show less than 1% degradation upto 50 h of light soaking. Then the cells degrade upto 500 h and thereafter become steady. Nanocrystalline solar cells show degradation initially and become steady after 10 h of light soaking. Using protocrystalline silicon as absorber layer the solar cell efficiency degrades 9% before stabilization, whereas using nanocrystalline silicon as absorber layer (X_c～65%) the solar cell efficiency degrades 2.9%. Stabilized efficiency of the second type of cell is better than that of the first cell, but initial efficiency is higher for the first cell (η=7.1%).     

Methylmethacrylate polymerization photoinitiated by 1‐(bromoacetyl)pyrene

The photopolymerization of methylmethacrylate induced by pyrene, 1‐acetylpyrene (AP), and 1‐(bromoacetyl)pyrene (BP) has been investigated. Under all conditions employed, pyrene was completely ineffective. Introduction of a carbonyl and a bromo group in pyrene enhanced the polymerization efficiencies. Efficiency of AP as photoinitiator was very low; however, BP was proved to be a good photoinitiator. The polymerization with BP follows first‐order kinetics with respect to monomer conversion, with a shorter induction period as compared with that of AP. The value of the initiator exponent (0.5) and the linear dependence of reciprocal average degree of polymerization on the square root of the initiator concentration suggest radical polymerization with bimolecular termination. IR and NMR spectra showed the atactic nature of polymethylmethacrylate. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 920–926, 2006     

Studies on a stove for powdery biomass

The sawdust stove, classically known for several decades, is considered here in a scientific study. The poor ignition characteristics and smoky start up are related to improper geometric dimensions. Based on a parametric study, the startup procedure and the dimensions of the stove were modified to achieve a smooth start up. Also, the range of acceptable fuels was enlarged to include tiny unprocessed dry twigs, weeds and wood sticks o the extent of about 50%, with the rest being sawdust-like material. The efficiency of the stove was measured to be 30–40%, depending on the relative size and shape of the vessel and the power level of the stove. A simple procedure for designing this class of stove for various power levels, as well as burning times, is presented. A new concept of multiport design is also discussed.