Mid‐node admissible spaces for quadratic triangular 2D finite elements with one edge curved

A robust element distortion metric, based on the new concept of mid‐node admissible spaces, for two‐dimensional quadratic triangular finite elements is developed. The metric is based on the Jacobian determinant over the entire element, without requiring that it actually be computed everywhere on the element. The metric is relatively inexpensive to compute, especially for mildly distoted elements. The metric is able to detect elementsof poor quality that other distortion metrics fall to detect. It also has the ability to approve elements of good quality regardless of the extent to which they may appear geometrically distorted. Copyright © 2001 John Wiley & Sons, Ltd.     

Reconfigurable main‐arm for assembly of all revolute‐only kinematically simple branches

Within previous work by Podhorodeski and Pittens,a class of kinematically simple (KS) joint layouts was defined for spatial serial joint‐assemblies consisting of revolute joints only. The identified KS class of layouts was comprised of main‐arms with three successively parallel and/or perpendicular revolute joints and end located spherical joint groups. Arguments of degeneracy and kinematic equivalency can be used to demonstrate that only five unique main‐arm layouts belong to the KS class. Within the current work, the design of a reconfigurable main‐arm (RMA) allowing the construction of all of the KS branches is examined. Sufficient joints are included within the RMA to allow, by the locking of certain joints and the freeing (actuation) of others, the kinematic attributes of each of the unique KS main‐arm layouts to be acquired. It is concluded that five successively perpendicular revolute joints are required within the RMA to allow such reconfiguration. Inverse kinematic solutions are presented for each of the five layouts. Potential RMA applications, use of the RMA for kinematically redundant layouts, and an RMA prototype are discussed. ©2000 John Wiley & Sons, Inc.     

Propagation characteristics of impulse creepage discharge in perfluorocarbon liquid

In this paper, the propagation characteristics of a creepage discharge on the surface of a solid insulator with a back electrode in perfluorocarbon liquid under an impulse voltage application are investigated. The propagation process is observed in detail by means of a high‐speed schlieren optical technique, and simultaneously waveforms of a current and a charge are also measured. Consequently, the polarity effect of the streamer propagation and the positive streamer which propagates stepwise can be seen. The latter is concurrent with the sparse current pulse which corresponds to the charge step‐variation. These results are compared with ones obtained in transformer oil. © 2000 Scripta Technica, Electr Eng Jpn, 131(4): 19–28, 2000     

Pulsed plasma-enhanced chemical vapor deposition from hexafluoropropylene oxide: Film composition study

Films deposited using pulsed plasma-enhanced chemical vapor deposition (PECVD) from hexafluoropropylene oxide (HFPO) were investigated by X-ray photoelectron spectroscopy (XPS). As compared to continuous rf PECVD, pulsed excitation increases the CF₂ fraction in the film. Film composition was determined as a function of plasma processing conditions including on-time, off-time, pressure, flow rate, substrate temperature, electrode spacing, substrate potential, and input power. Varying the on–off pulsing cycle resulted in compositional control of the deposited films. At a low duty cycle [t_on/(t_on + t_off)], up to 70% CF₂ could be incorporated into the film. The input gas, HFPO, may facilitate greater CF₂ incorporation into the films as this gas thermally decomposes into a difluorocarbene. Both absolute on-time and off-time, rather than simply duty cycle, are important parameters for determining film composition. A simple model was developed to describe the experimentally determined variation %CF₂ as a function of substrate temperature and off-time. This model accounts for changes in film composition due to plasma-surface modification and differences in gas-phase chemistry. The model suggests that surface modification by the plasma is the dominant factor only for long on-times or for low deposition rates. However, the gas-phase concentration of CF₂ relative to other film-forming species is typically the controlling factor under conditions which achieve the high %CF₂ in the film. The gas-phase composition will depend on both abslute on-time and off-time, rather than simply on the duty cycle. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 67:1489–1502, 1998     

Amphipathic polymers with stimuli‐responsive microdomains for water remediation: Binding studies with p‐cresol

Amphipathic, stimuli‐responsive water‐soluble polymers have been investigated as potential remediation agents for micellar enhanced ultrafiltration (MEUF). The systems represent divergent architectural types, a triblock ABA copolymer of PEO‐PPO‐PEO, an n‐octylamide modified poly(sodium maleate‐alt‐ethyl vinyl ether), and the transport protein, bovine serum albumin. Each type exhibits stimuli‐dependent microphase separation or domain formation in response to temperature, pH, and/or ionic strength changes. Segmental associations result in hydrophobic clusters resembling those present in small molecule surfactant micelles. The effects of such segmental aggregation on sequestration of a model hydrophobic foulant, p‐cresol, have been investigated using equilibrium dialysis. The favorable molar binding values, the large hydrodynamic dimensions of the stable polymer aggregates, and potential reversibility of foulant loading could have commercial utility in high flow rate, multiple‐pass remediation processes. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2290–2300, 1999     

Film-forming tendencies of some base fluids and viscosity modifiers

The film-forming tendencies of selected mineral base oils and synthetic base fluids were investigated with and without conventional GL-5 additive packages. A pressurised falling-body viscometer and a concentrated contact simulator were used to measure low-shear viscosities, central film thicknesses, and traction coefficients. Analysis of the mineral—based oils showed that a paraffinic base oil and a naphthenic base oil had similar film thicknesses, even though the naphthenic base oil has higher pressure-viscosity coefficients. A very high viscosity index oil gave thinner film thicknesses and lower pressure—viscosity coefficients than the paraffinic or naphthenic base oils. Analysis of the synthetic base fluids showed that a PAO-4 base fluid gave thicker film thicknesses than an ester base fluid. The analysis of fully-formulated oils showed that the PAO-4 oil containing a proprietary polyolefin provided a similar filnz thickness to the PAO-4 oil containing a more expensive PAO-100.     

Biochemical and molecular biological characterization of a lipase produced by the fungus Rhizopus delemar

The results of a comprehensive biochemical and molecular biological investigation of the lipase produced by the mycelial fungus Rhizopus delemar are described. This enzyme cleaves and synthesizes primary esters and related bonds, exhibits 1,3-positional selectivity in its actions on glycerides, and is a member of a family of enzymes that have been widely used in applied biocatalysis. Use of glycerol as main carbon source rather than glucose or lipid supported mycelial growth and lipase production. The enzyme was purified to homogeneity and characterized. Pure lipase was crystallized and its three-dimensional structure determined. The enzyme was found to adopt a configuration similar to those of other members of its homologous family. The structural data also indicated that lipases possess greater configurational mobility than had been previously appreciated. A complementary DNA clone was isolated that contained the full length lipase gene. The nucleic acid sequence of this cDNA indicated that it was initially synthesized as a preproenzyme, and allowed determination of the complete predicted amino acid sequence of the lipase, and its comparison to the sequences of related enzymes. Truncated forms of the cloned cDNA were produced that encoded either mature or prepro-lipase. These DNAs were introduced into a tightly regulated E. coli expression system, overcoming the toxicity of the enzyme while also allowing overproduction of lipase. Molecular modelling was employed to guide the rational mutagenesis of the enzyme, identifying sites within the substrate binding region that regulated substrate selectivity. Mutant lipases were generated with altered substrate specificities, creating novel enzymes and beginning the definition of structure-function relationships in the lipolytic enzymes.     

Determinant assembled stowage bins—a case study

Most commercial aircraft interior stowage bins are assembled using jigs. These assembly jigs are built to strict tolerances to ensure that the assemblies created in them will perform properly. Over the past decade, commercial aircraft structures assembly has been in transition from a method of assembly jig location to a method of part to part indexing, also known as Determinant Assembly. This method is now being investigated for accurate location of composite sandwich panels and metal attachments for commercial aircraft interiors. A background on Determinant Assembly (DA) as it has developed in structures is introduced. Several methods of coordinating composite sandwich panels to metal parts are discussed. Data that substantiates the use of these methods to maintain the prescribed tolerances is presented graphically. The results of building prototype parts using these techniques are presented. The process capability for DA assembled stowage bins is predicted using Variation Simulation Analysis, and those predictions are compared to results obtained with the current assembly jig method.