Tribological properties of aluminum alloy matrix TiB2 composite prepared by in situ processing

An investigation of the wear behavior, in lubricated sliding and rolling of in situ prepared TiB₂ particle-reinforced 2024 T4 Al alloy matrix composites against 52100 steel and hardened pearlitic nodular cast iron, respectively, was undertaken. In sliding contact, the 10 vol pct 0.3-μm TiB₂-metal matrix composite (MMC) showed slightly less wear than the 10 vol pct 1.3-μm TiB₂-MMC. Transmission electron microscopy of cross sections, taken normal to the wear track and parallel to the sliding direction, revealed that the TiB₂ particles on the wear track were polished and particle pullout was largely absent. This was attributed to the strong interfacial bonding between the Al-alloy matrix and the TiB₂ reinforcing phase. The TiB₂ particles on the wear track inhibited spalling. Subsurface damage of the MMC did not occur. The wear of the steel mating surfaces worn against the TiB₂-MMCs was minor and caused by the cutting action of the TiB₂ particles that resided on the MMC wear track. In rolling contact, the 0.3-μm-size TiB₂-MMC showed 5 times higher weight loss than the 1.3-μm TiB₂-MMC for the same content of reinforcement, but the weight loss of the cast iron mating surface was less for the former. For the smaller particle size, the wear of 5 and 10 vol pct TiB₂-MMCs was the same. A high density of surface cracks was present on the wear track of the 0.3-μm TiB₂-MMC but not on the 1.3-μm MMC. The significance of strong particle/matrix interfacial bonding and particle size effect on the wear behavior of ceramic particulate-reinforced MMCs in lubricated sliding and rolling wear is discussed.     

Floor, wall and ceiling approach for ball-end tool pocket machining

This paper presents a floor-wall and ceiling (FWC) approach to determining the tool axes for five-axis pocket machining. The FWC method generates tool axes by simply linking the corresponding points between tool location paths on floor and tool axial paths on ceiling. The geometry of the floor, wall, and ceiling of a pocket are first discussed. The construction and manipulations of the tool location paths and the tool axial paths are then addressed. The relationship between the tool axis variation and the manipulations is analyzed such that the generated tool axes are guaranteed to be smooth, optimized, and collision-free. By using the FWC method, the complexity of determining the tool axes can be significantly reduced. Computer illustrations and example demonstrations are shown in this paper. The results reveal that the FWC method can generate much higher quality tool axes than the traditional methods.     

Cellular thiols as a determinant of responsiveness to menadione in cardiomyocytes

The role of intracellular thiols in menadione-mediated toxicity was studied in neonatal rat cardiomyocytes. The sensitivity of cardiomyocytes to menadione was greater than that of skeletal muscle cells and 3T3 fibroblasts. Before cell degeneration, menadione induced marked depletion of intracellular thiols and an increase of oxidized glutathione. The sensitivity of these cells to menadione correlated with the level of depletion of intracellular thiols. After incubation of cardiomyocytes with menadione, glutathione reductase activity was inhibited and lipid peroxidation was increased. Both dicumarol (an inhibitor of DT-diaphorase) and diethyldithiocarbamate (an inhibitor of superoxide dismutase) enhanced the capacity of menadione to induce cellular damage and to cause depletion of intracellular glutathione. Decreasing intracellular glutathione by pretreatment of cells with N-ethylmaleimide or buthionine sulphoximine also increased menadione-induced cell degeneration. Preincubation with cysteine or dithiothreitol suppressed the capacity of menadione to damage the cells. Menadione-induced lipid peroxidation was also suppressed by the same treatment. These results show that the oxidative stress induced by menadione in cardiomyocytes results in the depletion of glutathione and protein thiols. Both DT-diaphorase and superoxide dismutase can protect cells from the toxicity of menadione. Cellular thiols are determinants of the responsiveness to menadione.     

What do they say about “Friends”? A cross-cultural study on Internet discussion forum

This exploratory study is to analyze the communication differences among viewers of US TV program Friends on Internet discussion forum in the US, Japan, and Taiwan. It intends to establish whether exposure to foreign TV could lead to similar communication content in the context of the virtual community between exporting and importing societies. Content analysis was used in this cross-cultural study, with the aim of understanding the ways in which dialogues posted on various discussion forums differed among the United States, Japan, and Taiwan. The results of this exploratory study support the notion that the process of cultural value influence is more complex than cultural imperialism advocates propose. Audiences respond actively rather than passively to foreign TV programs. Prior information structure of the audience is affecting the interpretation of subsequent information.     

Effect of nitrogen on diamond growth using unconventional gas mixtures

The influence of nitrogen on the growth of diamond using unconventional gas mixtures of CH₄---CO₂ by microwave plasma chemical vapor deposition was investigated. A clear improvement in the surface morphology and quality of the diamond films indicates the beneficial effect of adding nitrogen to CH₄-CO₂ gas mixtures. However, most interestingly, for lower methane concentration, the addition of small amounts of nitrogen resulted in the formation of isolated diamond particles possessing a vacant “cage-like” structure with completed {100} facets This result indicates that the continued addition of nitrogen gives rise to the deterioration of {111} facets and the retention of {100} facets. Analysis using Auger electron spectroscopy and secondary ion mass spectroscopy shows very low and uniform levels of nitrogen in the diamond films. Although the amount of atomic hydrogen in the ground state decreased and CN radicals increased with increasing amounts of added nitrogen, good-quality diamond films were deposited resulting from a larger amount of atomic oxygen and the decrease in the C₂ emissions in the gas phase under optimum conditions.     

Broadband dual-polarized aperture-coupled patch antennas withmodified H-shaped coupling slots

This paper presents a new design of aperture-coupled patch antennas with modified H-shaped coupling slots for achieving dual-polarization radiation with high isolation over a wide bandwidth. By using the proposed coupling slots, whose two upper side arms are bent inward with a proper angle, the isolation between the two feeding ports of the patch antenna can. greatly be improved, compared to the case with conventional H-shaped coupling slots. Also, when using a pair of modified H-shaped coupling slots for each feeding port, the isolation can further be improved; a high degree of isolation (< -34 dB) over the entire impedance bandwidth greater than 15% and good cross-polarization level (> 20 dB) for the two polarizations can be achieved. Details of the proposed design and experimental results are presented and discussed     

Dimension and related anatomical distance of Koch's triangle in patients with atrioventricular nodal reentrant tachycardia

INTRODUCTION: The dimension of Koch's triangle in patients with AV nodal reentrant tachycardia has not been well described. Understanding the dimension and anatomical distance related to Koch's triangle might be useful in avoiding accidental AV block during ablation of the slow pathway. The purposes of this study were to define the dimension of Koch's triangle and its related anatomical distance and correlate these parameters with the successful ablation sites in patients with AV nodal reentrant tachycardia. METHODS AND RESULTS: We studied 218 patients with AV nodal reentrant tachycardia. The distance between the presumed proximal His-bundle area and the base of the coronary sinus orifice (DHis-OS) measured in the right anterior oblique view was used to define the dimension of Koch's triangle. The distance of the proximal His-bundle recording site from the successful ablation site (DHis-Ab) and the distance as a fraction of the entire length of Koch's triangle (DHis-Ab/DHis-Os) were determined. The mean DHis-Os and DHis-Ab were 25.9 +/- 7.9 and 13.4 +/- 3.8 mm, respectively. DHis-Os negatively correlated with patient age (r = -0.41, P < 0.0001) and body mass index (r = -0.18, P = 0.004). Among the patients with successful ablation sites in the medial area, DHis-Os was longer (27.2 +/- 6.6 vs 24.6 +/- 8.4 mm, P < 0.005), DHis-Ab was similar (12.9 +/- 3.1 vs 13.9 +/- 4.0, P > 0.05) and DHis-Ab/DHis-Os was smaller (0.48 +/- 0.04 vs 0.74 +/- 0.11, P < 0.05). Furthermore, the patients with successful ablation sites in the medial location needed more radiofrequency pulse numbers than those in the posterior location (6 +/- 4 vs 4 +/- 3, P < 0.05). CONCLUSION: The site of successful slow pathway ablation was consistently about 13 mm from the site recording the proximal His-bundle deflection in patients with AV nodal reentrant tachycardia despite marked variability in the dimensions of Koch's triangle; therefore, patients with large triangles required ablation in the medial region rather than the posterior region. Care should be taken when delivering radiofrequency energy to the posteroseptal area in patients with shorter DHis-Os to avoid injury to AV node.     

Endothelin receptor antagonists: effect of serum albumin on potency and comparison of pharmacological characteristics

Endothelins (ETs) are 21-amino acid peptides that bind to membrane receptors to initiate pathophysiological effects. Two types of ET receptors, ETA and ETB, have been identified. Various ET receptor antagonists are being developed as therapeutic agents. This report examines the effects of bovine serum albumin (BSA) on the potency of ET receptor antagonists and compares five ET receptor antagonists. Competition studies show that in the absence of BSA, A-127722 and L-749329 inhibited ET-1 binding to ETA receptor with the same IC50 value of 0.09 nM. Addition of increasing concentrations of BSA incrementally decreased the potency of the antagonists: in the presence of 5% BSA, the IC50 values increased to 4.3 and 820 nM, respectively. Similarly, addition of BSA decreased the potency of antagonists in inhibiting ET-1-stimulated phosphatidylinositol hydrolysis. These results suggest that serum albumin has profound effects on the potencies of ET receptor antagonists. FR139317, PD-156707, L-749329, Ro-47-0203 and A-127722 were then selected for direct comparison under identical experimental conditions with 0.2% BSA. The potency of antagonists was assessed by binding studies for the determination of IC50 and Ki values and by ET-1-stimulated phosphatidylinositol hydrolysis and arachidonic acid release for the determination of IC50 and pA2 values. All five antagonists inhibited ET binding and the biological effects exerted by ET in a competitive mode. The Ki values for A-127722, PD-156707, FR139317, Ro-47-0203 and L-749329 for the ETA receptor were 0.07, 0.38, 0.80, 3.67 and 33.6 nM, respectively. A similar hierarchy was revealed by the functional assays. Our results suggest that the rank order of potency of the antagonists is A-127722 > or = PD-156707 > or = FR139317 > Ro-47-0203 > L-749329.     

Vena contracta suppression in dilute polymer solutions

Very small amounts of high molecular weight polymers were found to eliminate vena contracta formation in flow through a circular orifice. This effect was reflected in the decreased efflux time for drainage between two fixed levels in a tank, reductions up to 30% being obtained. Aqueous solutions of seven commercially available polymers were studied, consisting of a poly(acrylic acid), two polyacrylamides of different degrees of hydrolysis, and four poly(ethylene oxides) of widely differing molecular weights. The poly(acrylic acid) and two highest molecular weight poly(ethylene oxides) each caused a sudden drop in efflux time at a “critical concentration”, which was 2, 50, and 90 wppm, respectively, for these three polymers. An explanation of this phenomenon in terms of the high Deborah number flow field existing near the orifice edge is advanced. In the case of the polyacrylamide solutions, a very gradual reduction in efflux time with increasing polymer concentration was observed, beginning at about 3 wppm. Coincident with this was the formation of a wine-glass stem or converging flow field upstream of the orifice. Such a flow field was not observed for the other solutions. It is suggested that vena contracta inhibition with polyacrylamide is simply a manifestation of solution die swell. The reason for the differing efflux time behavior between the various polymers is not known and represents a challenging problem for further study.