Measurement of effective permeability of reinforcement mats using sensitivity analysis

A methodology using sensitivity analysis is proposed to measure the effective permeability which includes the interaction of the resin and the reinforcement. Initially, mold‐filling experiments were performed at isothermal conditions on the test specimen and the positions of the flow front were tracked with time using a flow visualization method. Following this, mold‐filling experiments were simulated using a commercial software to obtain the positions of the flow front with time at the process conditions used for experiments. Several iterations were performed using different trial values of the permeability until the experimentally tracked and simulated positions of the flow front with time were matched. Finally, the value of the permeability thus obtained was validated by comparing the positions obtained by performing the experiments at different process conditions with the positions obtained by simulating the experiments. In this study, woven roving and chopped strand mats of E‐class glass fiber and unsaturated polyester resin were used for the experiments. From the results, it was found that the measured permeabilities were consistent with varying process conditions. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Optical properties of the c-axis oriented LiNbO3 thin film

C-axis oriented Lithium Niobate (LiNbO₃) thin films have been deposited onto epitaxially matched (001) sapphire substrate using pulsed laser deposition technique. Structural and optical properties of the thin films have been studied using the X-ray diffraction (XRD) and UV-Visible spectroscopy respectively. Raman spectroscopy has been used to study the optical phonon modes and defects in the c-axis oriented LiNbO₃ thin films. XRD analysis indicates the presence of stress in the as-grown LiNbO₃ thin films and is attributed to the small lattice mismatch between LiNbO₃ and sapphire. Refractive index (n = 2.13 at 640 nm) of the (006) LiNbO₃ thin films was found to be slightly lower from the corresponding bulk value (n = 2.28). Various factors responsible for the deviation in the refractive index of (006) LiNbO₃ thin films from the corresponding bulk value are discussed and the deviation is mainly attributed to the lattice contraction due to the presence of stress in deposited film.     

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%.     

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%).     

Synthesis and characterization of terephthalamides from poly(ethylene terephthalate) waste

Poly(ethylene terephthalate) (PET) waste flakes (blow‐molded‐grade industrial waste) were degraded with aqueous methylamine and ammonia at room temperature in the presence and absence of quaternary ammonium salt as a catalyst for various times. The catalyst reduced the time required for the degradation of the PET waste. The degraded products were analyzed with IR, nuclear magnetic resonance, mass spectrometry, and differential thermal analysis and were characterized as N,N′‐dimethylterephthalamide and terephthalamide in the case of methylamine and ammonia, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1515–1528, 2005     

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