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991.
This study focuses upon the evolution of microstructures during solidification processing of several intermetallic alloys
around the Ll2 phase in the Al-rich corner of the Al-Ti-Ni ternary system. The alloys were produced by double induction melting and subsequent
homogenization followed by furnace cooling. The microstructure was characterized by means of optical and scanning electron
microscopy with energy-dispersive spectroscopy (EDS) analysis and X-ray diffraction. The microstructural evolution in homogenized
alloys was dependent on both nickel and titanium content. Very fine precipitates of Al2Ti were observed within the Ll2 phase in alloys containing 62 to 65 at. pct Al and at least 25 at. pct Ti. The Al2Ti precipitates are stable at least up to 1000 °C and undergo complete dissolution at 1200 °C. In alloys containing around
66 at. pct Al and 25 to 31 at. pct Ti, phases such as Al3Ti, Al5Ti2, and Al11Ti5 were observed. A modified room temperature isotherm in the Al-Ti-Ni ternary system is proposed, taking into account the existence
of Al2Ti, Al11Ti5, Al5Ti2, and Al3Ti in equilibrium with the Ll2 phase. It seems that at room temperature, the Ll2 phase field for homogenized alloys is extremely small. It will be practically impossible to obtain a single-phase microstructure
at room temperature in the Al-Ti-Ni ternary alloys after homogenization at 1000 °C followed by furnace cooling.
S. BISWAS, formerly Graduate Student, Department of Mechanical Engineering, University of Waterloo 相似文献
992.
An experimental and numerical study of necking initiation in aluminium alloy tubes during hydroforming 总被引:2,自引:0,他引:2
A. Kulkarni P. Biswas R. Narasimhan Alan A. Luo Raj K. Mishra Thomas B. Stoughton Anil K. Sachdev 《International Journal of Mechanical Sciences》2004,46(12):1727-1746
In this paper, a combined experimental and numerical investigation of free hydroforming of aluminium alloy tubes is conducted. The tubes are subjected to different loading histories involving axial compression and internal pressure. The circumferential and axial strains experienced by the tubes are continuously recorded along with the pressure and axial load. The numerical simulations are carried out using both 2D axisymmetric and 3D finite-element formulations by applying the experimentally recorded axial load and internal pressure. In the latter, a geometric imperfection is introduced in the form of wall thickness reduction at the tube mid-length in order to trigger necking which happens after significant bulging and beyond the stage of peak pressure. The strain histories and peak pressures obtained from the simulations agree well with those determined from the experiments. Further, the forming limit curve predicted by the simulations as well as from a M–K analysis incorporating the computed strain paths corroborate well with the experimental data. The role of nonproportional straining on the mechanics of failure of the tubes due to bulging and necking is studied in detail. 相似文献
993.
We have assessed the effect of two induction agents on tracheal intubating conditions after rocuronium 0.6 mg.kg-1 in unpremedicated patients undergoing simulated rapid sequence induction. Following pre-oxygenation, anaesthesia was induced with propofol up to 2.5 mg.kg-1 (n = 35) or etomidate 0.3 mg.kg-1 (n = 36), and further increments as required. After loss of verbal contact, cricoid pressure was applied and rocuronium was injected. Laryngoscopy was performed at 45 s and intubation attempted at 60 s after rocuronium had been given. Ninety-four per cent of patients in the propofol group had clinically acceptable (good or excellent) intubating conditions compared to only 75% in the etomidate group (p = 0.025). Owing to coughing, one patient in the etomidate group could not be intubated on the first attempt. A greater pressor response also followed intubation after induction with etomidate. We conclude that etomidate and rocuronium alone cannot be recommended for intubation at 60 s under rapid sequence induction conditions. 相似文献
994.
Water‐dispersible conducting nanocomposites were prepared by precipitating polyaniline (PANI)/polypyrrole (PPY) in an aqueous suspension of polyacrylonitrile–SiO2 (PAN–SiO2) via K2CrO4–NaAsO2 redox polymerization. Incorporation of PANI and PPY in the composites was confirmed by the FTIR spectrum. Scanning electron microscopic analyses for the PANI–(PAN–SiO2) and PPY–(PAN–SiO2) composites indicated formation of lumpy aggregates with irregular sizes. TEM analyses revealed formation of spherical particles with size ranging between 80 and 150 nm for PANI–(PAN–SiO2) nanocomposite and 75–150 nm for PPY‐(PAN‐SiO2) nanocomposites, respectively. Thermal stabilities of the PANI–(PAN–SiO2) and PPY–(PAN–SiO2) nanocomposites were higher than those of the individual base polymers. Conductivity values of PANI–(PAN–SiO2) nanocomposite (10?3 S cm?1) and PPY–(PAN–SiO2) nanocomposite (10?4 S cm?1) were remarkably improved relative to that for PAN homopolymer (>10?11 S cm?1). Both of these composites produced a permanently stable aqueous suspension when the polymerization was conducted in presence of nanodimensional SiO2 as a particulate dispersant. Copyright © 2004 Society of Chemical Industry 相似文献
995.
Aggressive responding was compared between 29 subjects with a history of substance dependence and 24 subjects with no drug use history, using the Point Subtraction Aggression Paradigm. The hypothesis was that subjects from the substance dependence history group would emit more aggressive responses than subjects with no drug use history. The substance dependence history group emitted more aggressive responses per session than the non drug using group (F(1,49) = 14.867, P = 0.032). These results are consistent with previous studies that have reported an association between aggression and drug abuse or dependence. 相似文献
996.
The spatiotemporal organization of the mechanically evoked perioral sensorimotor response was sampled from five normal females using a custom-designed linear motor operating under force feedback. Electromyographic activity was sampled from the superior and inferior segments of the orbicularis oris muscle during the production of a visually guided ramp-and-hold lip-rounding task. Brief mechanical inputs of approximately 0.45 N delivered to the left upper lip during the ramp-and-hold task produced a composite myogenic response characterized by phases of excitation and suppression. Modulation of the primary excitatory component (R1) of the mechanically evoked perioral response was found to be highly dependent upon the rate of force recruitment (1 N/s vs. 4 N/s) and the phase of force recruitment (20% vs. 50% vs. 80% of 1 N end-point force). Modulation of later occurring inhibitory (S1) and excitatory (R2) potentials were also found to be dependent upon differences in the rate and phase of force recruitment. The organization of the perioral sensorimotor response is considered in relation to speech motor control and the dynamic organization of neuronal groups subserving perioral sensorimotor activity. 相似文献
997.
K Kumar SK Sharma KS Gill R Katyal S Biswas S Lal 《Canadian Metallurgical Quarterly》1997,50(6):219-226
Studies carried out on entomological and rodent surveillance in agroclimatic and feral biotopes of five districts of Maharashtra and two districts of Gujarat revealed that the terrain features of the seven districts surveyed were conducive to wild rodent species, Tatera indica, a natural reservoir of plague and vector flea species, Xenopsylla cheopis. A total of 214 Tatera indica and three Bandicoota bengalensis were collected from burrows by the digging method and 89 rat fleas were retrieved. The flea index calculated ranged from 0.26 to 1.0 in different districts. The examination of blood serum samples, contact tissue impression smears and tissue organs (heart, lung, liver and spleen) of these wild rodents did not reveal any evidence of plague activity. The natural harbourages of Tatera indica were found to be elevated land or raised margins of agricultural fields or barren land with thorny bushes/xerophytic plants and parthenium grass. Agricultural fields having wet soil were found to be the preferred harbourages of Bandicoota bengalensis. Movement of wild rodents toward human settlement was observed to be the common phenomenon during the harvesting season which may lead to the creation of favorable conditions for plague outbreaks. 相似文献
998.
To determine the role of enteric pathogens in acute childhood diarrhoea in Hong Kong, 388 children with diarrhoea and 306 children of similar age without diarrhoea were evaluated in a hospital-based study during a one-year period from August 1994 to July 1995. Of the diarrhoeal cases, 55% were under 1 year and 95% were below 5 years of age. On admission, 22% had some dehydration but none was severely dehydrated. All children were well nourished. Oyer 60% of children with diarrhoea had one or more pathogens in their stool. Rotavirus was the most commonly isolated pathogen (34.6%), followed by Salmonella (23.3%), Campylobacter (4.7%) and Shigella (2.1%). Rotavirus was not assessed in the controls and was detected mainly during the winter months December to February. Bacterial pathogens were identified more commonly in diarrhoea patients (30%) than in controls (5.6%) (P < 0.001). Despite rapid recent socioeconomic development in Hong Kong, non-typhoidal Salmonella diarrhoea remains a significant local problem in infants under 1 year. Further detailed assessment of the transmission and prevention of this infection is required. 相似文献
999.
We have studied the biosynthesis and transport of the endogenous caveolins in MDCK cells. We show that in addition to homooligomers of caveolin-1, heterooligomeric complexes of caveolin-1 and -2 are formed in the ER. The oligomers become larger, increasingly detergent insoluble, and phosphorylated on caveolin-2 during transport to the cell surface. In the TGN caveolin-1/-2 heterooligomers are sorted into basolateral vesicles, whereas larger caveolin-1 homooligomers are targeted to the apical side. Caveolin-1 is present on both the apical and basolateral plasma membrane, whereas caveolin-2 is enriched on the basolateral surface where caveolae are present. This suggests that caveolin-1 and -2 heterooligomers are involved in caveolar biogenesis in the basolateral plasma membrane. Anti-caveolin-1 antibodies inhibit the apical delivery of influenza virus hemagglutinin without affecting basolateral transport of vesicular stomatitis virus G protein. Thus, we suggest that caveolin-1 homooligomers play a role in apical transport. 相似文献
1000.