Molding of Pb and Zn with microscale mold inserts

Molding of Pb and Zn metal plates with LiGA (Lithographie, Galvanoformung, Abformung) fabricated Ni microscale mold inserts was carried out at 300 °C. Both as fabricated Ni inserts and Ni inserts conformally coated with Ti-containing hydrocarbon (Ti-C:H) coatings were used. The molding performance was characterized both in terms of feature generation on the metal plates and insert condition after molding. The present results demonstrate that, in cases where significant metal/insert chemical interactions exist, surface engineering of the mold insert is necessary to obtain satisfactory performance, and that conformal deposition of suitably engineered ceramic coatings onto Ni microscale mold inserts is an effective means for achieving high temperature micromolding of reactive metals. WJM gratefully acknowledges partial project support from NSF through grant DMI-0124441, Louisiana Board of Regents through contracts LEQSF(2001–04)-RD-A-07 and LEQSF(2000–03)-RD-B-03, and NASA SBIR contract NAS5–01179 through a subcontract with Mezzo Systems Inc.     

The deposition and analysis of pyrotechnic devices deposited by magnetron sputtering

Powdered mixtures of titanium and boron can undergo a highly exothermic reaction which is virtually gasless. As a result of this Ti-B mixtures find widespread applications in conventional pyrotechnic delays and heat sources. However, the burning rate of such devices can be affected by particle size distribution, degree of blending and the presence of an inhibiting oxide layer on the surface of the reactants.

Pyrotechnic delays composed of multilayer coatings of titanium and boron have been deposited directly by magnetron sputtering. This is a novel application of such techniques and offers solutions to many of the problems encountered with conventional pyrotechnics.

The deposition and analysis of Ti/B multilayer pyrotechnic coatings deposited by magnetron sputtering are described.     

A practical object-oriented analysis engine for CLP

The incorporation of global program analysis into recent compilers for Constraint Logic Programming (CLP) languages has greatly improved the efficiency of compiled programs. We present a global analyser based on abstract interpretation. Unlike traditional optimizers, whose designs tend to be ad hoc, the analyser has been designed with flexibility in mind. The analyser is incremental, allowing substantial program transformations by a compiler without requiring redundant re-computation of analysis data. The analyser is also generic in that it can perform a large number of different program analyses. Furthermore, the analyser has an object-oriented design, enabling it to be adapted to different applications easily and allowing it to be used with various CLP languages with simple modifications. As an example of this generality, we sketch the use of the analyser in two different applications involving two distinct CLP languages: an optimizing compiler for CLP(R) programs and an application for detecting occur-check problems in Prolog programs. © 1998 John Wiley & Sons Ltd.     

Solvent extraction of bacteriocins from model solutions and fermentation broths

A novel method for the extraction and purification of bacteriocins (small peptides with antimicrobial properties) from fermentation broths is described. Model solutions of nisin were prepared from Nisaplin®, a commercial whey‐based powder containing about 2.5% nisin and sold as a food preservative. These model solutions and fermentation broths from a culture of nisin‐producing Lactococcus lactis subsp lactis were cross‐flow filtered and stirred with toluene to obtain a white suspension in the toluene layer, which was back extracted with 10 mmol dm⁻³ HCl. Yields of the order of 90% for a single stage extraction were obtained followed by similar yields on back extraction. Yields dropped with decreasing pH, going through a minimum at pH 2. In larger scale experiments (11 dm³) at pH 6, a gel layer was formed which, on centrifugation and drying, gave a white solid containing about 50% nisin, the remainder being water and salt. Further process development would almost certainly bring this figure closer to the small‐scale value. The phase transfer technique was also applied to solutions containing variacin and carnocin (produced by Micrococcus varians and Carnobacterium piscicola, respectively). The mechanism of bacteriocin extraction probably involves concentration of the peptides, which are surface active, at the interface until their solubility is exceeded and they form reverse submicelles, which aggregate into reverse micelles to give a gel. © 2000 Society of Chemical Industry     

A class of adaptive regulators for robot manipulators

In this paper we propose a framework to adaptive regulator design of robot manipulators. A class of global regulators for robot is characterized for which we provide guidelines to derive adaptive versions. The class of regulators is described by control laws comprising the gradient of an artificial potential energy depending in a linear manner on the robot and payload unknown parameters plus a linear velocity feedback. We provide explicit sufficient conditions on the artificial potential energy which allow to obtain an adaptive regulator which yields a stable closed-loop system and global positioning. Using this framework we revise two previously proposed adaptive regulators and we suggest two new ones. © 1998 John Wiley & Sons, Ltd.     

An improved protocol for the preparation of yeast cells for transformation by electroporation

Pretreatment of yeast cells with lithium acetate (LiAc) and dithiothreitol (DTT) enhances the frequency of transformation by electroporation. The method shows improvements of 6–67-fold in wild-type strains derived from commonly used Saccharomyces cerevisiae genetic backgrounds. In addition, 15–300-fold improvement in transformation frequency was achieved with several mutant strains of S. cerevisiae that transformed poorly by conventional procedures. Both DTT and lithium acetate were necessary for maximal transformation frequencies. Pretreatment with lithium and DTT also resulted in an ∼3·5-fold increase in the electroporation transformation frequency of the pathogenic fungus Candida albicans. © 1998 John Wiley & Sons, Ltd.     

Polymerization of furandicarbonyl chloride with bisphenol A poly(2,5-furandiylcarbonyloxy-1,4-phenylenedimethylmethylene-1,4-phenyleneoxycarbonyl)

Polymerization of 2,5-furandicarbonyl chloride with bisphenol A in four systems was studied. Catalysed polymerizations in tetrachloroethane solution at 155°C using AlCl₃ or Zn dust yielded coloured polymer with intrinsic viscosities of 0.24 and 0.23, respectively in about 80% yield. Uncatalysed solution polymerization in chloroform at ambient temperature using triethylamine as an acid acceptor gave a 90% yield of a white, film-forming polymer with an intrinsic viscosity of 0.5. Interfacial polymerization in benzene yielded a polymer of the same viscosity but in reduced yield (16%). Thermal analysis by differential scanning calorimetry revealed that thermal decomposition begins at about 225°C and is superimposed on an apparent crystallization exotherm at ～250°C and an apparent melting endotherm at ～320°C.     

Investigation of cytochrome P450 mediated benzo(a)pyrene hydroxylation in Aspergillus fumigatus

Microsomal fractions of Aspergillus fumigatus exhibited a reduced carbon monoxide difference spectrum with a maximum at 448 nm and a substrate-induced Type I spectrum on addition of benzo(a)pyrene. Metabolism of benzo(a)pyrene, as measured using the aryl hydrocarbon hydroxylase assay, was found to be P450-dependent and activity was observed to have a K_m of 82 μM and V_max of 33·3 pmol min⁻¹ mg⁻¹ protein. P450 productivity was investigated during growth from spore inocula and observed to be constant until the stationary phase, where the specific content declined to undetectable levels. The specific content of P450 was found to increase in higher concentrations of glucose.