Variable toroidal ferrite phase shifter

Careful design of the magnetic bias circuit used in ferrite phase shifters can help to reduce space, weight and energy consumption. Low reluctance circuits must avoid air-gaps and this can be achieved using toroidal-shaped ferrite inserts positioned inside a rectangular waveguide. Here, these ferrite inserts are fabricated using a viscous plastic processing method that avoids machining and produces a continuous magnetic circuit. Finite-element methods are used to initially model the magnetostatic solution for the bias circuit before being used to analyse the microwave performance of a double toroid phase shifter. A closedform technique is introduced to model the dielectric slab waveguide impedance transformer. The final insertion loss was ,1 dB over the 9.5?10.3 GHz band and return loss of 20 dB was achievable. The phase shift calculation agrees to within 10% of the measured values.     

Ab initio and thermodynamic modelling of alloying effects on activity of sacrificial aluminium anodes

This work summarizes the experimental literature to date on Al-alloy sacrificial anodes and shows that the presence of Sn as an alloying element in solid solution form consistently debases the alloy corrosion potential. This study then assesses the lattice expander theory, which states that lattice-expanding dopants can be used to increase Sn solubility in Al and thereby reduce passivation. The thermodynamic effects on Sn solubility of lattice expanders (Ga, Mg, Zr, In and Bi) are predicted with ab-initio methods. Our results support lattice expander theory although we demonstrate that Sn solubility can decrease by alloying with even large dopants if they form compounds with Sn.     

Identification of microglial signal transduction pathways mediating a neurotoxic response to amyloidogenic fragments of beta-amyloid and prion proteins

Microglial interaction with amyloid fibrils in the brains of Alzheimer's and prion disease patients results in the inflammatory activation of these cells. We observed that primary microglial cultures and the THP-1 monocytic cell line are stimulated by fibrillar beta-amyloid and prion peptides to activate identical tyrosine kinase-dependent inflammatory signal transduction cascades. The tyrosine kinases Lyn and Syk are activated by the fibrillar peptides and initiate a signaling cascade resulting in a transient release of intracellular calcium that results in the activation of classical PKC and the recently described calcium-sensitive tyrosine kinase PYK2. Activation of the MAP kinases ERK1 and ERK2 follows as a subsequent downstream signaling event. We demonstrate that PYK2 is positioned downstream of Lyn, Syk, and PKC. PKC is a necessary intermediate required for ERK activation. Importantly, the signaling response elicited by beta-amyloid and prion fibrils leads to the production of neurotoxic products. We have demonstrated in a tissue culture model that conditioned media from beta-amyloid- and prion-stimulated microglia or from THP-1 monocytes are neurotoxic to mouse cortical neurons. This toxicity can be ameliorated by treating THP-1 cells with specific enzyme inhibitors that target various components of the signal transduction pathway linked to the inflammatory responses.     

A simple instructional computer

A fully functional computer is described that is simple enough to be built by junior-level undergraduate computer science students with no electronics experience. Any computable algorithm can be programmed using its tree instructions, which are modelled after Turing's original machine. Building this computer gives the computer science students confidence that computer hardware is real and understandable. Layered enhancements of this basic machine can prove to its builders that it can indeed execute any computable algorithm and provides practical exam questions to motivate the study of all six levels of modern computer systems: hardware, microprogram, instruction set, operating system, assembly language, and problem-oriented language level. Equally important, this computer provides a vehicle for practicing hardware/software tradeoffs at several architectural levels. Assigning computer development to small teams of students provides essential professional experience in solving open-ended design problems, working in teams, and presenting original ideas to their peers     

Rapid,simple, and accurate method for measurement of VFA and carbonate alkalinity in anaerobic reactors

This paper presents a new simple, rapid, and accurate method suitable for on-site measurement of volatile fatty acids (VFA) and carbonate alkalinity in anaerobic reactors. This titrimetric method involves eight pH observations, and typically, the full procedure takes approximately 15 min. An important feature of the method is a built-in quality control mechanism allowing the user a rapid means of assessing the reliability of the experimental procedure. To evaluate the accuracy of the method, both laboratory-made waters and industrial UASB effluent were tested. High accuracy for both VFA and carbonate alkalinity measurements (error within 2% and 1%, respectively) plus good repetition (average standard deviation of 6.7% and 1.45%, respectively) was obtained. The method takes into account the effects of the phosphate, ammonium, and sulfide weak acid subsystems. Appraisal of the effect of an input error in these subsystems revealed that VFA measurement is fairly insensitive to phosphate and ammonium concentrations. It is, however, sensitive to H2S loss during titration where the sulfide concentration is higher than approximately 10 mg/Las S. With regard to the carbonate alkalinity measurement, error in concentration of either phosphate or sulfide or H2S loss might result in a significant error. Short guidelines for correct execution of the method are given in an appendix.     

High density net shape components by direct laser re-melting of single-phase powders

Direct Metal Laser Re-Melting is a variant of the Selective Laser Sintering process, a Rapid Prototyping (RP) technology. This tool-less manufacturing technology has the potential of producing complex, high quality components from single-phase metal powders in short time scales. This is made possible by the production of consecutive two-dimensional layers. Unfortunately, finished components manufactured by this technique have their integrity and material properties dictated by the porosity within the laser re-melted structure. In order to maintain structural integrity comparable to conventionally produced components, metal components produced by the rapid prototyping method should exhibit a porosity of the order of maximum of 2% with corresponding bulk material properties. To achieve these objectives, process and laser parameters require optimisation for maximum densities to be attained. This paper reports on the development of a scanning strategy that produces stainless steel (316L) laser re-melted components which exhibit porosities of <1%, while maintaining the concept of rapid prototyping.     

Cartilage degeneration in relation to repetitive pressure: case study of a unilateral hip hemiarthroplasty patient

The mitochondrial, inner-membrane-associated, reversible NADPH-->NAD transhydrogenase of adult Hymenolepis diminuta physiologically couples matrix-localized, NADP-specific "malic" enzyme with NADH-dependent anaerobic electron transport. Employing submitochondrial particles (SMP) as the source of enzyme activity and both spectrophotometric and fluorometric assessments, the present study made evident that in its catalysis of transhydrogenation between NADPH and NAD, the cestode enzyme engages in the concomitant transmembrane translocation of protons. As assessed spectrophotometrically, the catalysis of NADPH-dependent NAD reduction by H. diminuta SMP was stimulated significantly by carbonyl cyanide 3-chlorophenylhydrazone (CCCP), carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP), as well as by the protonophoric anthelmintic, niclosamide. In addition, N,N'-dicyclohexylcarbodiimide (DCCD) markedly diminished SMP-catalyzed hydride ion transfer between NADPH and NAD. The catalysis by SMP of concomitant, transhydrogenase-mediated proton translocation was evaluated more directly via fluorometric assays using 8-anilino-1-napthalenesulfonic acid (ANS) as the probe. These latter evaluations revealed a transhydrogenase-dependent enhancement of ANS fluorescence in accord with an intravesicular accumulation of protons. ANS fluorescence was quenched rapidly when the assay system was supplemented with CCCP, FCCP, or niclosamide. Consistent with the helminth transhydrogenase acting as a proton pump, transhydrogenase-mediated enhanced fluorescence also was inhibited by DCCD. Considered collectively, these data indicated, apparently for the first time for any invertebrate system, that the transhydrogenase, in catalyzing the NADPH-->NAD reaction, acts in the translocation of protons from the matrix to the intermembrane space mitochondrial compartment.     

Enhancement of the surface expression of tumor necrosis factor alpha (TNFalpha) but not the p55 TNFalpha receptor in the THP-1 monocytic cell line by matrix metalloprotease inhibitors

The monocytic cell line THP-1 can be induced to express and release tumor necrosis factor alpha (TNFalpha) and both TNFalpha receptors (p55 and p75) upon exposure to bacterial lipopolysaccharide (LPS). The broad-spectrum matrix metalloprotease (MMP) inhibitors [4-(N-hydroxyamino)-2R-isobutyl-3S-(phenylthiomethyl)succinyl]-L-p henylalanine-N-methylamide (GI-129471) and marimastat [2S-[N4(R*),2R*,3S*]]-N4[2,2-dimethyl-1-[(methylamino)carbonyl]propyl]-N 1,2-dihydroxy-3-(2-methylpropyl)butanediamide (BB-2516) were effective inhibitors of LPS-induced TNFalpha (soluble) release with IC50 values of 0.2 and 4.0 microM, respectively. Upon LPS stimulation, the expression of pro-TNFalpha (membrane associated) on the cell surface (FACS analysis) could not be observed. However, in the presence of GI-129471, a concentration-dependent increase in TNFalpha surface expression was observed. Peak expression (percentage of cells expressing pro-TNFalpha and mean fluorescence units) in the presence of GI-129471 was at 2 hr, and steadily declined to return to near control levels by 8 hr. This time course was similar to TNFalpha release, which also peaked at 2-4 hr after LPS exposure and then declined. Stimulation of THP-1 cells with LPS + phorbol myristate acetate increased the percentage of cells expressing pro-TNFalpha by 10-fold. In the presence of GI-129471, these increases were augmented further and peaked between 2 and 4 hr, but also returned to near control levels of expression by 24 hr. This was in contrast to the release of soluble TNFalpha, which continued to accumulate over a 24-hr time course. TNFalpha receptor I (p55, TNFRI) and II (p75, TNFRII) shedding was also inhibited by GI-129471 (IC50 = 1.5 and 3.1 microM, respectively) and BB-2516 (IC50 = 14 and 15 microM, respectively). Unlike pro-TNFalpha surface expression, surface expression of both TNFalpha receptors steadily increased over 72 hr. In contrast to pro-TNFalpha surface expression, TNFRI surface expression was not augmented by these MMP inhibitors in THP-1 cells after LPS stimulation. Surface expression of TNFRII was augmented by these MMP inhibitors. These results suggest that even in the continued presence of LPS stimulation and an inhibitor of TNFalpha processing, the augmented surface expression of TNFalpha is transient. The potential "deleterious" implications of high levels of surface pro-TNFalpha expression in the presence of these inhibitors may be lessened by its transient nature.