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Effect of Ni:Al blending ratio on porous structure of porous nickel aluminides fabricated through reactive synthesis with space holder particles were investigated. Fabricated porous nickel aluminides had large pores derived from NaCl space holder particles and small pores derived from reactions between Ni and Al. Porosity and size of the small pores increased with increasing Al content in the raw powder mixture. Compressive property of porous NiAl are also investigated. porous NiAl exhibited good energy-absorption properties with relatively high plateau stress, high plateau end strain, and relatively flat plateau stress. This study suggests the possibility of intermetallic-based porous materials as high-performance energy absorber.
We have examined tensile properties of a novel heat-resistant aluminium (Al)-based alloy (with a composition of Al-5Mg-3.5Zn (at%)) strengthened by the T-Al6Mg11Zn11 (cubic) intermetallic phase at various temperatures. The tested specimens of the present alloy were solution-treated at 450°C for 24 h and subsequently aged at 200 or 300 oC for 1 h. The granular precipitates of the T phase were dispersed rather homogenously in the grain interior in the specimen aged at 300°C. In the specimen aged at 200°C, numerous fine precipitates with a mean size of ∼20 nm were observed in the α-Al matrix. The specimen pre-aged at 200°C for 1 h exhibited a superior strength to the conventional Al alloys at elevated temperatures ranging from 150 to 200°C (corresponding to service temperatures for compressor impellers in turbochargers).
The stability of stably stratified vortices is studied by local stability analysis. Three base flows that possess hyperbolic stagnation points are considered: the two-dimensional (2-D) Taylor–Green vortices, the Stuart vortices and the Lamb–Chaplygin dipole. It is shown that the elliptic instability is stabilized by stratification; it is completely stabilized for the 2-D Taylor–Green vortices, while it remains and merges into hyperbolic instability near the boundary or the heteroclinic streamlines connecting the hyperbolic stagnation points for the Stuart vortices and the Lamb–Chaplygin dipole. More importantly, a new instability caused by hyperbolic instability near the hyperbolic stagnation points and phase shift by the internal gravity waves is found; it is named the strato-hyperbolic instability; the underlying mechanism is parametric resonance as unstable band structures appear in contours of the growth rate. A simplified model explains the mechanism and the resonance curves. The growth rate of the strato-hyperbolic instability is comparable to that of the elliptic instability for the 2-D Taylor–Green vortices, while it is smaller for the Stuart vortices and the Lamb–Chaplygin dipole. For the Lamb–Chaplygin dipole, the tripolar instability is found to merge with the strato-hyperbolic instability as stratification becomes strong. The modal stability analysis is also performed for the 2-D Taylor–Green vortices. It is shown that global modes of the strato-hyperbolic instability exist; the structure of an unstable eigenmode is in good agreement with the results obtained by local stability analysis. The strato-hyperbolic mode becomes dominant depending on the parameter values.
To determine annual layers for reconstructing the past environment at annual resolution from ice cores, we employed snow-stake data back to 1972, tritium content, solid electrical conductivity measurements (ECM) and stratigraphic properties for the 73m ice core at the H72 site, east Dronning Maud Land, Antarctica. the average annual surface mass balance at H72 is 307 mma–1w.e. during the last 27 years from continuous accumulation data, 317 mma–1 w.e. according to the densification model and 311 mma–1 w.e. according to the average surface mass balance for 167 years based on annual-layer counting. the ECM age is closely coincident with tritium age, and corresponds with the snow-stake record back to AD 1972 from the surface to 15 m depth. the H72 ice core is dated as AD 1831by ECMat 73.16 mdepth.The time series of yearly surface mass balance at H72 shows an almost constant 311 mm a–1 w.e. for the last 167 years. the oxygen-isotope records indicate a significant trend to lower values, with negative gradient of 1.7% (100 years)–1.
This note demonstrates analytically that a persistent catastrophic shock on endowment growth, even if moderate, yields negative equity premiums when a representative agent is relatively prudent. In particular, it derives the minimum persistence necessary to have zero equity premiums.
The organic highly conducting Langmuir-Blodgett (LB) film formed by a molecular association of BEDO-TTF and stearic acid shows the logarithmic decrease of DC conductivity and negative magnetoresistance at low temperature. These data are interpreted by the weak localization of two-dimensional (2D) electronic system inside the homogeneous conducting layer of BEDO-TTF molecules. The electronic length with phase memory has a mesoscopic scale. Strong evidence of the 2D coherent charge transport in the conducting LB film is provided for the first time.
We present a high-current reliability study of carbon nanofibers (CNFs) for interconnect applications. In situ scanning transmission electron microscopy (STEM) reveals structural damage to CNFs after current stress. The effect of heat dissipation on the current capacity is also discussed by using different experimental configurations. Long-time reliability tests are performed with a vertical via interconnect structure, showing promising high reliability of CNF interconnects for future electronic devices.
Recent studies in nanostructural characterization for on-chip interconnect applications using carbon nanofibers (CNFs) are presented. In this paper, we propose a novel technique, for the purpose of characterizing interfacial structures of vertically aligned CNFs for cross-sectional imaging with scanning transmission electron microscopy (STEM). In this technique, vertically aligned CNFs are selectively grown, by plasma-enhanced chemical vapor deposition (PECVD), on a substrate comprising a narrow strip (width ~100nm) fabricated by focused ion beam (FIB). Using high-resolution STEM, we show that CNFs with diameters ranging from 10 -100 nm exhibit very similar graphitic layer morphologies at the base contact interface.
Scanning electron microscopy (SEM) for imaging the interface between carbon nanofibers (CNFs) and the underlying substrate is presented. By irradiating the electron beam perpendicular to the substrate, bright contrast is observed at the region where a small gap exists between the CNF and substrate. The energy-diameter diagram for the observation of the bright contrast is derived, which can be understood by using the theory of electron penetration into solid. Monte Carlo simulation is performed to reproduce the experimental observation based on our model, and the contrast sensitivity to the gap height is discussed.
We studied the crystallization mechanism of ultra-fast phase change optical disks with recording layers made of GaSb material for digital versatile disk (DVD) systems. The results of a static recording test and an amorphous mark formation simulation suggest that GaSb maintains a high crystal growth rate even at temperatures 150 degrees lower than the material's melting point. Disks with recording layers made of this material have a write speed margin ranging from DVD 3× to 8× or more.
To evaluate the antibody response to influenza vaccines in nursing home residents and healthcare workers (HCWs) and its relation to residents' functional and chronic disease status during four successive seasons.
Nine nursing homes during the 1998-1999 season and two during the 1999-2000, 2000-2001, and 2001-2002 seasons.
Two hundred fifty-nine residents and 79 HCWs during the 1998-1999 season; 180 and 71, respectively, during the 1999-2000 season; 162 and 71, respectively, during the 2000-2001 season; and 153 and 79, respectively, during the 2001-2002 season.
Multivariate analysis indicated that the mean fold increase in the geometric mean titers (GMTs) of hemagglutination inhibition (HI) antibodies and the response rate (the proportion of vaccinées resulting in a significant, at least fourfold increase in antibody titer) were good and no significant differences occurred for almost all strains in both residents and HCWs. The GMTs of HI antibodies and the protection rate (the proportion of participants with HI antibody titers & 40) were increased in both residents and HCWs, but were significantly lower for almost all strains in residents than in HCWs. Furthermore, multivariate analysis indicated that subdivision of residents into three groups by level of daily activities and into four groups according to underlying diseases revealed only minor differences in immune responses.
Antibody responses to the influenza vaccine were lower in residents than in HCWs. However, residents showed similar antibody responses regardless of their level of daily activity or underlying diseases.
Chromium aluminum oxynitride (Cr-Al-N-O) thin films have been successfully prepared by pulsed laser deposition (PLD). Experiments were carried out by changing surface area ratio of the targets (SR = SAlN / (S +SAlN)) from 0 to 100 %. The composition of the thin film prepared at SR = 75 % was determined to be Cr0.11Al0.39N0.25O0.25 by Rutherford backscattering spectroscopy (RBS). The hardness of the Cr-Al-N-O thin film was found to be above HV 4000 when the aluminum content in cations (x) was 25 at. %. The high hardness can be explained by solid solution hardening and/or increasing bulk modulus. The oxidation of the Cr-Al-N-O thin film occurred above 900°C. From the result of grazing angle X-ray diffractometry (GXRD), the oxidation resistance of the Cr-Al-N-O thin film was found to be improved due to the fact that Cr2O3 and -Al2O3 grains are formed at the outermost surface of the thin film.