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71.
This paper describes the swing-up and stabilization of a cart–pendulum system with a restricted cart track length and restricted control force using generalized energy control methods. Starting from a pendant position, the pendulum is swung up to the upright unstable equilibrium configuration using energy control principles. An “energy well” is built within the cart track to prevent the cart from going outside the limited length. When sufficient energy is acquired by the pendulum, it goes into a “cruise” mode when the acquired energy is maintained. Finally, when the pendulum is close to the upright configuration, a stabilizing controller is activated around a linear zone about the upright configuration. The proposed scheme has worked well both in simulation and a practical setup and the conditions for stability have been derived using the multiple Lyapunov functions approach. 相似文献
72.
Chemically deposited zinc oxide thin film gas sensor 总被引:4,自引:0,他引:4
Zinc oxide (ZnO) thin films were prepared by a low cost chemical deposition technique using sodium zincate bath. Structural characterizations by X-ray diffraction technique (XRD) and scanning electron microscopy (SEM) indicate the formation of ZnO films, containing 0.05–0.50 m size crystallites, with preferred c-axis orientation. The electrical conductance of the ZnO films became stable and reproducible in the 300–450 K temperature range after repeated thermal cyclings in air. Palladium sensitised ZnO films were exposed to toxic and combustible gases e.g., hydrogen (H2), liquid petroleum gas (LPG), methane (CH4) and hydrogen sulphide (H2S) at a minimum operating temperature of 150 °C; which was well below the normal operating temperature range of 200–400 °C, typically reported in literature for ceramic gas sensors. The response of the ZnO thin film sensors at 150 °C, was found to be significant, even for parts per million level concentrations of CH4 (50 ppm) and H2S (15 ppm). 相似文献
73.
Annals of Telecommunications - This paper reviews two hybrid (frequency domain) finite element methods for electromagnetic scattering applications. Specifically, the progress over the last five... 相似文献
74.
A K Chatterjee 《Bulletin of Materials Science》1993,16(6):453-464
Three generally accepted generic groups of competitive engineering materials—metals, inorganic ceramics, as well as plastics
and polymers belonging to the organic family—have been comparatively reviewed in the context of raw materials availability,
energy requirements in production, engineering properties, combustibility and environmental friendliness. The intrinsic advantages
of inorganic materials have been discussed. The shortcomings of engineering properties of inorganic materials and the new
technologies of making chemically bonded ceramics or biomimic compounds from inorganic materials with improved toughness have
been dealt with. The expanding application horizons of inorganic materials have been illustrated with the help of several
novel products. 相似文献
75.
76.
The design details of a 0.254 m stainless steel cylindrical fluidized bed pilot plant facility, whose fabrication, installation and testing have been recently completed, are described. It primarily consists of a fluidized-bed reactor, fluidizing air-supply system, solids feeder, off-gas cleaning and exhaust system, and cooling water-supply system for heat-transfer tubes provided in the bed and in the freeboard sections. The plant is operated at ambient pressure in the temperature range 300–600 K, both in the batch and continuous modes for solids feed. Bed-pressure drop measurements as a function of fluidizing velocity for two different bed heights reveal that the quality of fluidization is good. Similar experiments have been conducted with the continuous solids feed. The heat-transfer coefficient between the bed and an immersed stainless steel U-tube is measured as a function of fluidizing air velocity at five different temperatures. The effects on bed-to-tube heat-transfer rate of solids feed rate, bed height, air-flow rate, and bed temperature are examined. All of these observed variations are interpreted in terms of the solids mixing and bubble mechanics in the bed. 相似文献
77.
The system CaO-Al2O3-CaF2 is important in cement and slag technology and in metallurgy. A section of this system, the pseudo-binary join CaO·Al2O3-CaF2, has been studied and the phase diagram established. This join is of particular interest since CaO·Al2O3 is one of the main constituents of high alumina cement.Quenching in sealed platinum capsules followed by microscopic and X-ray examination was the principal method used. The only compound on the join is 3CaO·3Al2O3·CaF2 which melts congruently at 1507±1.5° C and forms one eutectic with CaO·Al2O3 at 11% CaF2 and 1498±5° C and another with CaF2 at 97.5% CaF2 and 1405±10° C. There is a wide zone of liquid immiscibility. The m.p. of CaF2 was determined to be 1422±1° C.Attempts to use high temperature microscopy to study this system are described. 相似文献
78.
Niobic acid of composition H8Nb6O19 has been prepared by thorough drying of the hydrated oxide at 150°C. The mass was heated in stages up to 1200°C and the intermediate products were subjected to 1H NMR measurements for determining their proton content. Infra red spectra indicate the presence of protons which are highly delocalised among different oxygen sites. The electrical conductivity of niobic acid has been interpreted as due to proton-hopping. The ion exchange capacity of the material has also been studied. The data have been used to formulate the structure of niobic acid and to obtain the correct procedure for the gravimetric determination of niobium as oxide. 相似文献
79.
The phase equilibria of the system CaO-Al2O3-CaF2 have been studied by quenching in sealed platinum capsules followed by microscopic and X-ray examination of quenched products. The established phase diagram contains five ternary eutectics, two ternary peritectics and two invariant points of four-phase monotectic transformations. The system Al2O3-CaF2 has been established to be the stable diagonal of the reversible reciprocal system Al2O3 + 3CaF2 = 3CaO + 2AlF3. In the high-fluoride region a wide zone of liquid immiscibility has been found. The system also shows such rarely noticed but theoretically possible phenomena as the transformation of peritecticals into eutecticals and occurrence of three different primary fields under single continuous zone of liquid immiscibility. 相似文献
80.
The influence of sodium silicate on the ability of a diacetylene-containing phospholipid (23:2 diyne PC) to inhibit the oxidation of pyrite at pH 2 and pH 6 was investigated. The phospholipid used has previously been reported to show up to 80% suppression of pyrite oxidation and to show excellent stability down to at least pH 2. Pyrite was leached with a solution containing Fe3+ but no coating agent and three different solutions or treatments: a lipid treatment, a silicate treatment, and a lipid + silicate treatment. Pyrite oxidation was based on iron (Fe3+, Fe2+) leached out of a continuous-flow porous-bed reactor system. The results show that at pH 6 the silicate and lipid both bind strongly to the pyrite surfaces, providing a barrier that inhibits the production and subsequent release of oxidation products. The lipid is superior to the silicate in suppressing pyrite oxidation at both pH 2 and pH 6. Also, the presence of silicates decreased the ability for the lipid to suppress pyrite oxidation, both at pH 2 and pH 6. The reaction mechanism for pyrite oxidation at pH 2 is first order for pyrite leached by solutions containing only ferric, ferric together with silicate, and ferric combined with silicate and lipid. The only treatment that effectively prevented pyrite oxidation at pH 2 was the lipid treatment. The Fe speciation results are supported by both SEM images and EDS calculations. 相似文献