Phase behavior of ternary blends containing dimethylpolycarbonate,tetramethylpolycarbonate and poly[styrene‐co‐(methyl methacrylate)] copolymers (or polystyrene)

The miscibility and phase behavior of ternary blends containing dimethylpolycarbonate (DMPC), tetramethylpolycarbonate (TMPC) and poly[styrene‐co‐(methyl methacrylate)] copolymer (SMMA) have been explored. Ternary blends containing polystyrene (PS) instead of SMMA were also examined. Blends of DMPC with SMMA copolymers (or PS) did not form miscible blends regardless of methyl methacrylate (MMA) content in copolymers. However, DMPC blends with SMMA (or PS) blends become miscible by adding TMPC. The miscible region of ternary blends is compared with the previously determined miscibility region of binary blends having the same chemical components and compositions. The region where the ternary blends are miscible is much narrower than that of binary blends. Based on lattice fluid theory, the observed phase behavior of ternary blends was analyzed. Even though the term representing the Gibbs free energy change of mixing for certain ternary blends had a negative value, blends were immiscible. It was revealed that a negative value of the Gibbs free energy change of mixing was not a sufficient condition for miscible ternary blends because of the asymmetry in the binary interactions involved in ternary blends. Copyright © 2004 Society of Chemical Industry     

Re-inventing the electrical machines curriculum

Undergraduate courses in electromechanical energy conversion are typically oriented toward the steady-state analysis of electrical machines. The advent of low-cost computer power and the availability of numerical software tools provide the opportunity to fundamentally reorient the pedagogical approach to the topic. A new approach is consistent with the developing need to emphasize the study of new machine designs and machines employed for control purposes as well as machines for use in more traditional power applications. This paper presents the results obtained from simulations developed as an integral part of an undergraduate electrical machines course at the University of Dayton, USA. Sample simulation files are presented to demonstrate the ease with which the matrix model of the machine is transferred to the program. The matrix models and simulation results of the following machines are included: the single-phase transformer; the variable-reluctance machine; the cylindrical-rotor dual-winding machine; the symmetrical two-phase induction motor; a PWM-controlled DC machine; and an inverter-driven brushless machine. The selected machines provide a systematic framework for analysis and simulation and present problems of increasing complexity to the student     

Template-based quadrilateral meshing

Generating quadrilateral meshes is a highly non-trivial task, as design decisions are frequently driven by specific application demands. Automatic techniques can optimize objective quality metrics, such as mesh regularity, orthogonality, alignment and adaptivity; however, they cannot make subjective design decisions. There are a few quad meshing approaches that offer some mechanisms to include the user in the mesh generation process; however, these techniques either require a large amount of user interaction or do not provide necessary or easy to use inputs. Here, we propose a template-based approach for generating quad-only meshes from triangle surfaces. Our approach offers a flexible mechanism to allow external input, through the definition of alignment features that are respected during the mesh generation process. While allowing user inputs to support subjective design decisions, our approach also takes into account objective quality metrics to produce semi-regular, quad-only meshes that align well to desired surface features.     

The effect of lipoxygenase action on the mechanical development of doughs from fat-extracted and reconstituted wheat flours

The mechanism by which soya lipoxygenase enzyme action improves the Theological properties of wheat flour doughs during mechanical development in air has been investigated further. Free-lipid extraction, reconstitution and replacement experiments have shown that the rheological effect of lipoxygenase action, which is consistent with an oxidative improvement of the dough proteins and may also result in extended mixing tolerance, only occurred in the presence of an oxidisable, polyunsaturated, free-lipid substrate. Addition of this substrate in an oxidised state (produced either by autoxidation or enzyme-oxidation) to doughs mixed from fat-extracted flour under nitrogen resulted only in a small rheological improvement, greater for the autoxidised than the enzyme-oxidised lipid, but in no way comparable with the large rheological effect of lipoxygenase action during dough mixing in air. Furthermore, the presence of an antioxidant, nordihydroguaiaretic acid (NDGA), during dough development, although greatly inhibiting peroxide formation, only marginally impaired the rheological improvement due to lipoxygenase action. Additional evidence is therefore provided for a coupled oxidation mechanism being responsible for the rheological effect, since lipoxygenase-catalysed oxidation actively occurring in the dough during mixing appears to be the fundamental requirement, irrespective of whether the primary oxidation products lead to lipid peroxides or oxidised NDGA.     

Logic and memory with nanocell circuits

Molecular electronics is an emerging field that seeks to build faster, cheaper, denser computers from nanoscale devices. The nanocell is a molecular electronics design wherein a random, self-assembled array of molecules and metallic nanoparticles is addressed by a relatively small number of input/output pins. The challenge then is to program the nanocell post-fabrication. We have previously demonstrated the ability to program individual simulated nanocells as logic gates. In this paper, we further explore the problem of programming nanocells and consider connecting nanocells into circuits using bistable latches at the interconnects. These latches are critical because they permit signal restoration. Simulated nanocell circuits for logic and memory are presented here.     

Lipid-protein interactions during dough development

Radionuclide-labelled glycerol triolein has been used to follow the fate of triglyceride lipids during the mixing of wheat flour doughs. After removal of residual free lipid by petrol extraction, initial fractionation of freeze-dried dough identified the acetic acid-soluble protein as being the only component involved significantly in work-induced lipid binding during dough development under nitrogen, and also in lipid release on admission of air. Very little labelled lipid was found in either the water-soluble proteins or the starch residue. Sub-fractionation of the acetic acid-soluble protein by ammonium sulphate precipitation from acetic acid-urea-cetyltrimethyl-ammonium bromide (AUC) solvent showed bound lipid to be distributed almost entirely between high-molecular-weight glutenin and protein which remained soluble in the AUC supernatant even in the presence of 20% ammonium sulphate. Precipitated gliadins contained very little labelled lipid. However, significant levels were found in classical ethanol-extracted gliadin, and were traced predominantly to the same supernatant-protein owing to its solubility in aqueous ethanol. Examination of this AUC-supernatant fraction showed it to contain a hitherto unreported protein which had a molecular weight of about 9000, was strongly complexed with tri-glyceride lipid on a 1:1 molar basis and showed a tendency to aggregate in solution. Its amino acid frequency was found to differ significantly from both glutenin and purothionin, the latter containing in particular very much more cysteine than the supernatant-protein. Representing 10% or more of the total gluten, this small, highly interactive protein is responsible for a significant, if not the major, part of lipid binding activity in dough and may well have a fundamental role in the formation of an insoluble glutenin structure through both —SH and hydrophobic interaction. Accordingly, the name ‘Ligolin’ is proposed, from the Latin ligare: to bind, to tie.     

Renaturation of formyltetrahydrofolate synthetase from urea and guanidinium chloride solutions

Formyltetrahydrofolate synthetase from Clostridium cylindrosporum and Clostridium acidi-urici was denatured in 6 M urea and 4 M guanidinium chloride. Viscometric, fluorimetric and ultracentrifugal measurements were used to determine that the protein is completely unfolded under these conditions. The polypeptide chains refold upon dilution of the denaturant-protein solutions to give final concentrations of 0.5 M urea or 0.1 M guanidinium chloride. In the presence of NH4+, but not in its absence, the refolded proteins associate to produce the catalytically active tetramer. Refolding and reassociation were followed by measuring changes in protein fluorescence and by determination of sedimentation constants. Under most conditions 80% of the enzymic activity is recovered.