Enzymatic glyceride synthesis in a foam reactor

We report the results of our study on Rhizomucor miehei lipase-catalyzed lauric acid-glycerol esterification in a foam reactor. A satisfactory yield of glyceride synthesis can be achieved with an unusually high initial water content (50% w/w). We found that product formation could be regulated by controlling foaming. Foaming was a function of the air flow rate, reaction temperature, pH value, ionic strength, and substrate molar ratio. Monolaurin and dilaurin, which constituted nearly 80% of the total yield, were the two dominant products in this reaction; trilaurin was also formed at the initial stages of the reaction. A study of pH and ionic strength effects on an independent basis revealed that they affect the interfacial mechanism in different manners. On varying the ratio of lauric acid and glycerol, only a slight change in the degree of conversion was detected and the consumption rate of fatty acid was approximately the same.     

Improved adhesion of PMSQ hard coatings on polymer substrates

Various surface treatment methods were investigated to improve the adhesion of abrasion-resistant polymethylsilsesquioxane (PMSQ) coatings on the optical resins. The adhesion of PMSQ films was improved on polymethylmethacrylate (PMMA), polycarbonate (PC), and PC/acrylonitrile butadiene styrene (ABS) by pretreating their surface with O₂ plasma or chromic acid followed by surface grafting with trimethyl ethoxysilane (TMES). After the O₂ plasma and the subsequent TMES treatments, the adhesion of PMSQ coating on PMMA substrate was significantly enhanced by the reduction of the percentage of peeling area from ~100% to <1% in cross cut tests. After the chromic acid and the subsequent TMES treatments of PC and PC/ABS substrates, the adhesion of PMSQ coatings was also significantly enhanced by reducing the percentages of peeling areas from nearly 100% to 50% and <1%, respectively, for PC and PC/ABS. The PMSQ coating might increase the hardness of the polymer by two to three levels.     

Effects of RF power and pressure on performance of HF-PECVD silicon thin-film solar cells

High-frequency plasma-enhanced chemical vapor deposition (HF-PECVD) is a widely applicable method of deposition over a large area at a high rate for fabricating silicon thin-film solar cells. This investigation presents the properties of hydrogenated amorphous silicon (a-Si:H) films and the preparation of highly-efficient p-i-n solar cells using an RF (27.1 MHz) excitation frequency. The influence of the power (10-40 W) and pressure (20-50 Pa) used during the deposition of absorber layers in p-i-n solar cells on the properties and mechanism of growth of the a-Si:H thin films and the solar cells is studied. The a-Si:H thin films prepared under various deposition conditions have widely varying deposition rates, optical-electronic properties and microstructures. When the deposition parameters were optimized, amorphous silicon-based thin-film silicon solar cells with efficiency of 7.6% were fabricated by HF-PECVD. These results are very encouraging for the future fabrication of highly-efficient thin-film solar cells by HF-PECVD.     

Direct printing of silver nanoparticles by an agarose stamp on planar and patterned substrates

In this study, we have used an agarose stamp to conduct direct printing of silver nanoparticles, nanowires and nanoplates on both planar and structured substrates. Nanoparticle solution could be first coated on an agarose stamp, and then transferred to a planar substrate. Micro-patterns comprising metal nanoparticles could be printed on planar substrates without the formation of residual layers. Thus a three-dimensional metal microstructure could be easily fabricated. The patterning of electrodes by printing Ag nanowires directly on TiO(2) was also demonstrated to fabricate resistive random access memory (RRAM) devices by all-solution-processing methods. By using a flat agarose stamp, the patterns printed on the microstructured substrates were quite different from those on the nanostructured substrates. On the microstructured substrates, direct printing could print silver nanoparticles onto the protrusion surface, and could print silver layers as thick as several microns, useful for high conductivity electrodes. On the substrates with nanostructures such as photonic crystals or nano-gratings, direct printing could transfer nanoparticles into the grooves or cavities only due to the contact of the agarose stamp with the groove or concavity surface. A new approach to fabricate metal wire grid polarizers was further demonstrated. A nanoporous agarose stamp has a good potential for printing using nanoparticle suspension.     

pISRA: privacy considered information security risk assessment model

The Journal of Supercomputing - The security threats related to personally identifiable information are increasing dramatically. In addition to government agencies, large international companies...     

Simultaneous Analysis of Free/Bound Phytosterols and Diosgenin in Taiwanese Yams

Gas chromatography (GC) and high performance liquid chromatography (HPLC) methods were developed for the simultaneous analysis of phytosterols and diosgenin in two representative Taiwanese yams, Dioscorea pseudojaponica Yamamoto and Dioscorea alata L. The major phytosterols found were β-sitosterol, stigmasterol, and campesterol. GC afforded good separation of phytosterols and diosgenin, with the diosgenin peak appearing between stigmasterol and β-sitosterol. For HPLC, UV detection had higher sensitivity (detection limits 0.03–0.09 μg); however, evaporative light scattering detection (ELSD) achieved higher noise tolerance and did not show baseline interference from solvent gradients. In addition, mixed solvents for extraction before acid hydrolysis, which is necessary to avoid fibers and acid hydrolysates binding to the target compounds, were evaluated. Phytosterol contents of 30.1 and 9.9 mg/100 g were found in D. pseudojaponica Yamamoto and D. alata L., respectively. Diosgenin was only found in D. pseudojaponica Yamamoto at a content of 15.2 mg/100 g.     

A procedural semantics for stratified database updates

This paper investigates efficient evaluation of database updates and presents a procedural semantics for stratified update programs that extend stratified logic programs with bulk updates and hypothetical reasoning. Bulk rules with universal quantification in the body allow an arbitrary update to be applied simultaneously for every answer of an arbitrary query. Hypothetical reasoning is supported by testing the success or failure of an update. The procedural semantics offers efficient goal-oriented tabled evaluation of database updates. It guarantees termination for function-free stratified update programs and avoids repeated computation of identical subgoals. This revised version was published online in June 2006 with corrections to the Cover Date.     

Kinetic studies on electrochemical stripping of CrN films

Chromium nitride (CrN) films deposited on silicon substrates by a cathodic arc plasma technique were electrochemically stripped off in KOH alkaline electrolytes. Current densities and electrolyte concentrations were varied to investigate their influences on the stripping process. By analyzing the relation between the potential and reaction time, it is possible to determine the optimal time for terminating the stripping process because of the different resistivities of the substrates and overlayers. The critical stripping times were defined from the potential−time relation and were observed to be inversely proportional to the current density. The total required charge/unit volume was also determined. The relationship between the thickness of the residual films after stripping and the reaction time at various current densities and KOH concentrations was analyzed using a kinetic model. Moreover, CrN films deposited by another method, namely, unbalanced magnetron sputtering, were also tested for comparison. The stripping process was apparently influenced by the microstructure of the films.     

Effect of diameter variation in a large set of carbon nanotube transistors

A study involving a large number of carbon nanotube transistors reveals that the nanotube diameter and the metal contact material play key roles in determining the on- and off-state currents of these devices. The results are discussed in terms of the Schottky barrier at the metal-semiconductor junction and the variation of this barrier relative to the alignment of energy levels between the carbon nanotube and the metal.