Finite Element Analysis of Enlarged End Piles Using Frictional Contact

This paper presents a modified finite element formulation of frictional contact for soil-pile interaction. This modified formulation is based on smoothed discretisation of the pile surface using Bézier polynomials. The finite element code based on this formulation is then used to analyse the loading of piles with enlarged ends of different shapes. Very simple material models are used to represent the behaviour of the soil and the pile. The numerical predictions are compared with the laboratory measurements. It is demonstrated that the new finite element formulation can produce reasonable results for the pile loading problem that involves large interfacial sliding and surface separation.     

Defect structures in cosputtered thin films of transition-metal disilicides with C11<Subscript><Emphasis Type="Italic">b</Emphasis></Subscript>, C40 and C54 structures

Defect structures in crystallites of the stable phases in thin films of transition-metal (TM) disilicides (C11 _b MoSi₂, C40 TaSi₂, and C54 TiSi₂) produced by cosputtering and subsequent annealing have been investigated by transmission electron microscopy (TEM). Crystallites in thin films of MoSi₂, TaSi₂, and TiSi₂ all contain planar faults parallel to hexagonally arranged TMSi₂ planes, which are a characteristic feature commonly observed in all three crystal structures. These planar faults are twin boundaries in all cases. Twins in thin films of these disilicides, thus, have a common characteristic that the twin habit plane is parallel to hexagonally arranged TMSi₂ stoichiometric planes. For twins in thin films of C11 _b MoSi₂, and C54 TiSi₂, the twining elements can be deduced and the twin habit plane is found not to be parallel to the twinning (K ₁) plane, but to be perpendicular to it. Twins formed in C40 TaSi₂ thin films are different from those formed in C11 _b MoSi₂ and C54 TiSi₂ thin films, in that the crystal orientation of the twin is exactly the same as that of the matrix, since they are racemic twins that are only enantiomorphically (space groups of P6₂22 or P6₄22) related to each other. This article is based on a presentation in the symposium “Terence E. Mitchell Symposium on the Magic of Materials: Structures and Properties” from the TMS Annual Meeting in San Diego, CA in March 2003.     

Effects of carbon content on microstructures and magnetic properties of annealed or solution treated Fe-Cr-Ni-C alloys

The correlations between microstructures and magnetic properties were studied in four Fe-17.5 mass%Cr-2.0 mass%Ni-Xmass%C (X = 0.3–0.6) alloys. Each alloy consisted of ferromagnetic and M₂₃C₆ carbide phases by step-annealing at 1053 K and 848 K. The number of the M₂₃C₆ carbide particles increased with the carbon content, and this microstructural variation caused a deterioration of the soft magnetic properties. On the other hand, the alloy with 0.3 mass% carbon content consisted of ferromagnetic and paramagnetic retained structures after solution treatment at 1473 K. The amount of the stable structure increased with the carbon content, while the amount of the structure decreased. This microstructural variation caused a decrease in the relative permeability, _r, and the stabilization of the paramagnetic property to low temperatures below room temperature. The temperature stability of the _r values was closely related to the martensite start temperature, M _s. From an equation for the estimation of M _s from the chemical compositions of the phase, the M _s's of the alloys with 0.3, 0.4, 0.5 and 0.6 mass%C were estimated to be 326, 289, 241 and 216 K respectively. These values were consistent with the M _s's expected from the microstructures and temperature dependences of the _r values.     

A liquid-Ga-filled carbon nanotube: a miniaturized temperature sensor and electrical switch

Temperature control on the nanometer scale is a challenging task in many physical, chemical, and material science applications where small experimental volumes with high temperature gradients are used. The crucial difficulty is reducing the size of temperature sensors while keeping their sensitivity, working temperature range, and, most importantly, their simplicity and accuracy of temperature reading. In this work, we demonstrate the ultimate miniaturization of the classic thermometer using an expanding column of liquid gallium inside a multi-walled C nanotube for precise temperature measurements. We report that electrical conductivity through unfilled nanotube regions is diffusive with a resistance per unit length of approximately 10 kOmega microm(-1), whereas Ga-filled segments of the nanotube show metallic behavior with a low resistance of approximately 100 Omega microm(-1). No noticeable Schottky barrier exists between the nanotube carbon shell and the inner Ga filling. Based on these findings, an individual carbon nanotube partially filled with liquid Ga is used as a temperature sensor and/or switch. The nanotube's electrical resistance decreases linearly with increasing temperature as the metallic Ga column expands inside the tube channel. In addition, the tube resistance drops sharply when two encapsulated Ga columns approaching each other meet inside the nanotube, producing a switching action that can occur at any predetermined temperature, as the Ga column position inside the nanotube can be effectively pre-adjusted by nanoindentation using an atomic force microscope.     

Combined carbon‐dioxide‐capturing high‐performance power generation system using a solid oxide fuel cell operating on pressurized fuel/air

The authors recently proposed a high‐performance combined carbon‐dioxide‐capturing power generation system using a solid oxide fuel cell (SOFC) and a closed‐cycle MHD generator, in which pure oxygen is used as the oxidant. This combined system makes the best use of the advantages of combustion with pure oxygen but fails to prevent the efficiency deterioration caused by high power demand for oxygen production. In the present study, the authors modified this previous system and proposed an improved combined carbon‐dioxide‐capturing power generation system using SOFC/MHD characterized by a higher overall thermal efficiency. In this system, pure oxygen is supplied only to the combustor to reduce the power required for the oxygen production, and pressurized air is used as the oxidant gas in the SOFC. The power saving amounts to about 5% of the thermal input, resulting in a very high total thermal efficiency of 67.53% (HHV) or 74.94% (LHV), which is considered to be the highest possible value of the overall thermal efficiency of carbon‐dioxide‐capturing systems. Advantages of the proposed system suggest that it is advisable to continue further research in this direction. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(4): 21–30, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20010     

Central pontine myelinolysis: an immunofluorescent study

A young pregnant woman showing clinical symptoms of numbness, vertigo, diplopia, and amnesia with associated hypernatremia ran a fulminant course. At autopsy, an area or extensive demyelination in the center of the pons was found and a pathological diagnosis of central pontine myelinolysis was made. Since definitive etiology and pathogenesis of the lesion have not been established, we investigated the role of humoral immunity in the pathogenesis of this condition by retrospective immunofluorescent study; the result was negative. Possible factors related to the etiology and pathogenesis of the lesion in this case are discussed.     

Expression of a gene encoding chitinase (pCA 8 ORF) from Aeromonas sp. no. 10S-24 in Escherichia coli and enzyme characterization

A gene encoding chitinase from Aeromonas sp. no. 10S-24 was expressed using pTrc99A in Escherichia coli JM 105 which yielded a 5-fold higher activity than when pUC19 was used. Three different truncated enzymes (SA-1, SA-2 and SA-3) were obtained after purification. Their isoelectric points were 7.0, 6.9, and 6.7, respectively. The enzymes showed two optimum pHs, 4.0 and 7.0, when incubated with ethylene glycol chitin as the substrate, and were stable over a wide pH range (3.0–9.0). The optimum temperature was 60°C and the enzymes were stable up to 50°C. The chitinases exhibited wide substrate specificities for chitin-related compounds.     

Creep deformation of TiAl-Si alloys with aligned γ/α 2 lamellar microstructures

Creep tests were conducted on directionally solidified TiAl-Si alloys to discern the effect of lamellar spacing and lamellar orientation on the high-temperature strength. Directional solidification of a Ti-43Al-3Si alloy was used to produce a model microstructure consisting of a single γ/α ₂ lamellar colony of controlled orientation for creep testing. Different heat treatments were used to vary the lamellar spacing and tensile creep tests were performed at 750 °C using applied stresses of 180, 210, and 240 MPa. In addition, ingots with large columnar grains of various lamellar orientation were also tested. The results clearly show the beneficial effect of microstructural control with the aligned microstructure having a much superior creep resistance. Furthermore, for specimens with aligned lamellar microstructure, decreasing the lamellar spacing greatly improved creep resistance, as both the primary creep strain and secondary creep rate are much smaller for materials with the fine lamellar spacing.