On frequency response and stability of an optical front–end with variable‐gain current amplifier using a bipolar junction transistor translinear loop

A comparative analysis of implementations of an optical front–end with variable transimpedance intended for optical storage systems in two different BiCMOS technologies is given in this article. The variable‐gain current amplifier within the optical front–end is designed by using a modified balanced type of the bipolar junction transistors translinear loop. The predictions of the optical front–end mathematical models are confirmed by the measured results. They show that a 0.6‐µm BiCMOS silicon technology implementation with worse bipolar junction transistor parameters (unity‐gain frequency, current gain β, and the Early voltage) gives much better stability than a 0.35‐µm BiCMOS silicon‐germanium technology implementation. As a consequence, the useful measured transimpedance dynamic range of the proposed optical front–end is 17.5 times larger in the 0.6‐µm BiCMOS silicon technology than that in the 0.35‐µm BiCMOS silicon‐germanium technology. Copyright © 2012 John Wiley & Sons, Ltd.     

Computer aided estimation of fugitive emission rates and occupational air concentration in process design

European Union directives such as the Integrated Pollution Prevention and Control (IPPC) require inclusion of safety, environmental and health analyses in process design as part of strategies towards achieving sustainable process development. In petrochemical and organic chemical industries, which mostly handle volatile compounds, the most significant contributor to atmospheric releases is fugitive emissions that are mainly contributed by piping fittings and components. Fugitive emissions are not only of economic and environmental concern, but also a major source of background inhalative exposure to workers that may lead to various diseases including cancer. More people die every year from occupational diseases as compared to the number killed in industrial accidents. Therefore the estimation of occupational air concentration due to fugitive emission needs to be done early when developing a new process. Several methods for fugitive emissions estimation have been introduced which mostly involve manual calculations. Computer-based tools for such purpose however, are still lacking. Besides, the current methods mainly focus on the emission rates only but not on the process air concentrations. Computer aided methods for fugitive emissions assessment are highly in need, since now most of the design work is done by using computer aided process engineering (CAPE) tools. Therefore in this paper computer aided methods for quantifying fugitive emission rates and occupational air concentration are presented. Three methods are proposed for early design stages based on data available from simple process flow diagrams (PFDs), detailed PFDs or piping and instrumentation diagrams (P&IDs). The method becomes more comprehensive as it progresses from simple PFDs to P&IDs, since more process data are available later, which include plot plan, coordinates of the emission sources and local wind speed. Users however, can choose which method to use depending on the process information available in hand. The methods are demonstrated in a case study of product distillation system of toluene hydrodealkylation.     

A Study of FTIR,Thermal Properties and Natural Weathering Test on NBRVirgin/Recycled with SBR Blends

The effects of styrene butadiene rubber/virgin acrylonitrile butadiene rubber (SBR/NBRv) blends and styrene butadiene rubber/recycled acrylonitrile butadiene rubber (SBR/NBRr) blends on properties such Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) were carried out. Results indicated that, based on intensity of amine peak from FTIR at 85/15 blend ratio (R15) revealed optimum formation of crosslink between SBR and NBR either using virgin or NBRr. TG thermograms of SBR/NBRv blends of all ratios showed better onset thermal stability than SBR/NBRr blends. The change in the horizontal baseline from high to low energy level occurred in virgin NBR blends because the amount of reactive sites available in virgin NBR is higher compared to NBRr. Meanwhile NBRr blends showed T_c because the amount of crosslink occurred in these blends were slightly lower than NBRv blends. Up to 25 phr of NBRr, the tensile strength and elongation at break (E_b) retention of SBR/NBRv blends was better than SBR/NBRr blends after 6 months' weathering test except for M100. The scanning electron microscopy on the surface of both blends after 6 months exposure indicated that the severity of the crack was minimal for SBR/NBRr blends compared to SBR/NBRv particularly at 50/50 blend ratio designated the SBR/NBRr blends that contained more NBRr particles could reduce the degradation towards natural weathering.     

Water management in a single cell proton exchange membrane fuel cells with a serpentine flow field

Gas and water management is the key to achieving good performance from a polymer electrolyte membrane fuel cell (PEMFC) stack. Imbalance between production and evaporation rates can result in either flooding of the electrodes or membrane dehydration, both of which severely limit fuel cell performance. In the present study, a mathematical model was developed to evaluate moisture profiles of hydrogen and air flows in the flow field channels of both the anode and the cathode. For model validation, a single fuel cell was designed with an active area of 200 cm². Six humidity sensors were installed in the flow fields of both the anode and the cathode at 457 mm, 1266 mm and 2532 mm from the inlets. The experiment was performed using an Arbin Fuel Cell Test Station. The temperature was varied (25 °C, 40 °C, 50 °C and 60 °C), while hydrogen and air velocities were fixed at 3 L min⁻¹ and 6 L min⁻¹, respectively, during the operation of the single cell. The feed relative humidity at the anode was fixed at 1.0, while the feed relative humidity at the cathode was fixed at 0.005 (dry air). All humidity sensor readings were taken at steady state after 2 h of operation. Model predictions were then compared with experimental results by using the least squares algorithm. The moisture content was found to decrease along the flow field at the anode, but to increase at the cathode. The moisture content profile at the anode was shown to depend on the moisture Peclet number, which decreased with temperature. On the other hand, the moisture profile at the cathode was shown to depend on both the Peclet number and the Damkohler number. The trend of the Peclet number in the cathode followed closely that of the anode. The Damkohler number decreased with temperature, indicating increasing moisture mass transfer with temperature. The moisture profile models were successfully validated by the published data of the estimated overall mass transfer coefficient and moisture effective diffusivity of the same order of magnitude. The strategy of saturating the hydrogen feed and using dry air, as in the present work, has been shown to successfully prevent water droplet formation in the cathode, and hence prevent flooding.     

Effect of soy protein subunit composition and processing conditions on stability and particle size distribution of soymilk

The influence of soy protein subunit composition on the particle size distribution and solid content of soymilk and various supernatant fractions was investigated. A well-established seed variety (Harovinton), containing all protein subunits, and eleven null soybean genotypes lacking specific glycinin and β-conglycinin subunits were investigated, to determine the effect of protein composition on the physico-chemical characteristic of soymilk. Soymilk made from Harovinton and soybean lines null in glycinin showed significantly higher total solid yields than the other genotypes evaluated. Soymilks prepared from soybeans null for glycinin or lacking glycinin's group I (A₁, A₂) showed a smaller particle size distribution compared to soybean lines containing glycinin. In general, unheated soymilk made from lines having glycinin showed a bimodal size distribution with large particles, with a decrease in the particle size distribution after heating and heating with homogenization. The results of this work will help in the evaluation of breeding lines with a specific protein composition tailored to a specific processing functionality.     

Effects of supercritical carbon dioxide extraction parameters on virgin coconut oil yield and medium-chain triglyceride content

The extraction of coconut oil has been performed using supercritical carbon dioxide (SC-CO₂). The extractions were performed at pressure and temperature ranges of 20.7–34.5 MPa and 40–80 °C, respectively. It was observed that almost all (more than 99%) of the total oil could be extracted. Response surface methodology (RSM) was applied to evaluate the effects of the parameters (pressure, temperature and CO₂ consumption) on the extraction yield and medium-chain triglycerides (MCTs), in terms of the fatty acid content in the extracted oil. A correlation was established with p-values for both responses significant at the 95% confidence level.     

Progress Towards Metal Additive Manufacturing Standardization to Support Qualification and Certification

As the metal additive manufacturing (AM) industry moves towards industrial production, the need for qualification standards covering all aspects of the technology becomes ever more prevalent. While some standards and specifications for documenting the various aspects of AM processes and materials exist and continue to evolve, many such standards still need to be matured or are under consideration/development within standards development organizations. An important subset of this evolving the standardization domain has to do with critical property measurements for AM materials. While such measurement procedures are well documented, with various legacy standards for conventional metallic material forms such as cast or wrought structural alloys, many fewer standards are currently available to enable systematic evaluation of those properties in AM-processed metallic materials. This is due in part to the current lack of AM-specific standards and specifications for AM materials and processes, which are a logical precursor to the material characterization standards for any material system. This paper summarizes some of the important standardization activities, as well as limitations associated with using currently available standards for metal AM with a focus on measuring mission-critical properties. Technical considerations in support of future standards development, as well as a pathway for qualification/certification of AM parts enabled by the appropriate standardization landscape, are discussed.     

Development and material properties of new hybrid plywood from oil palm biomass

Shortage of wood as a raw material has forced wood-based industries to find alternative local raw materials. Currently, oil palm biomass is undergoing research and development (R & D) and appears to be the most viable alternative. This work examines the conversion of oil palm trunk (OPT) and oil palm empty fruit bunches (OPEFB) into new plywood and analyses its properties. We prepared five-ply veneer hybrid plywood (alternating layers of oil palm trunk veneer and empty fruit bunch mat) with different spread levels (300 g/m² and 500 g/m²) of resins (phenol formaldehyde and urea formaldehyde). We then studied the mechanical and physical properties of the plywood. The results show that hybridisation of EFB with OPT improves some properties of plywood, such as bending strength, screw withdrawal and shear strength. The thermal properties of the plywood panels were studied by thermogravimetric analysis (TGA). The panels glued with phenol formaldehyde with a spread level of 500 g/m² showed better thermal stability than the other panels. Scanning electron microscope (SEM) was used to study the fibre matrix bonding and surface morphology of the plywood at different glue spread levels of the resins. The fibre–matrix bonding showed good improvement for the hybrid panel glued with 500 g/m² phenol formaldehyde.     

Ion imprinted polymers for selective recognition and separation of lanthanum and cerium ions from other lanthanide

The lanthanide-ion-imprinted polymers (L-IIPs) were synthesized from La³⁺ or Ce³⁺ ion and complexing agents either Schiff base or azobenzene with ethylene glycol-dimethylacrylate as cross-linking agent, 4-vinylpyridine monomer and 2,2-azobisisobutyronitrile initiator. After polymerization, cavities in the polymer particles corresponding to the La³⁺/Ce³⁺ ions were created by leaching in 20 mL of HCl solution (2.0 mol L^?1). The maximum sorption capacity is found to be 25.0, 24.3, 24.5 and 24.7 mg g^?1 of La-IIP-Schiff, La-IIP-Azo, Ce-IIP-Schiff, Ce-IIP-Azo polymers, respectively at pH 6. The L-IIPs gave good selectivity to La or Ce ions in the presence of other selected lanthanide cations with close atomic radius. The L-IIPs were reused and regenerated for ten times without a significant decrease in binding affinity.     

Work characteristics and employee well-being within a context of strategic downsizing.

Findings from this 4-year longitudinal study of strategic downsizing suggest that introducing deliberate work organization and change management strategies can combat the negative effects of reduced head count. Results showed that there was no overall decrease in well-being from before to after downsizing for the 139 employees remaining in an organization, despite an increase in work demands. The potential detrimental effect of demands appears to have been offset by improvement in work characteristics arising from initiatives introduced as part of the downsizing strategy. This interpretation is consistent with analyses at the individual level, which showed that high demands were associated with poorer well-being but that increases in control, clarity, and participation were associated with improved well-being. (PsycINFO Database Record (c) 2010 APA, all rights reserved)