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151.
Kinetics of steam gasification of delayed and fluid cokes derived from Athabasca bitumen have been studied in 6.35 cm diameter stirred and fixed bed reactors. Experiments were carried out at atmospheric pressure and at temperatures between 800°C and 930°C. The coke particle size ranged from 0.1 to 3.5 mm, and the steam partial pressure was varied from 15.2 to 60.6 kPa. Scanning electron microscopy, surface area analysis, and mercury porosimetry were employed to relate physical structure changes in the solids to experimental kinetic data. Several kinetic models for gasification were tested with the experimental gasification data. Rate expressions are presented for carbon conversion and for the release of sulphur. 相似文献
152.
Yuzhu Guo L.Z. Guo Daniel Coca Z.Q. Lang 《International journal of systems science》2014,45(10):2133-2144
A new parametric frequency response algorithm is introduced to investigate linear and non-linear dynamic systems with time-varying parameters. In the new algorithm the time-varying parameters are regarded as additional inputs of the systems and the non-linear generalised frequency response functions for multi-input-single-output systems are then employed to obtain Zadeh's system functions from a differential equation representation. The parametric frequency response method reveals how the time-varying parameters affect the behaviour of the systems through a time-varying term. The new method can be applied to both linear and non-linear time-varying systems. 相似文献
153.
In this article, motion/force control problem of a class of constrained mobile manipulators with unknown dynamics is considered. The system is subject to both holonomic and nonholonomic constraints. An adaptive recurrent neural network controller is proposed to deal with the unmodelled system dynamics. The proposed control strategy guarantees that the system motion asymptotically converges to the desired manifold while the constraint force remains bounded. In addition, an adaptive method is proposed to identify the contact surface. Simulation studies are carried out to verify the validation of the proposed approach. 相似文献
154.
X.Y.?Wang J.M.?WangEmail author H.B.?Shao J.Q.?Zhang C.N.?Cao 《Journal of Applied Electrochemistry》2005,35(2):213-216
The corrosion behavior of pure aluminum in inhibited and uninhibited 4 MKOH was investigated by means of hydrogen collection, polarization curve measurement and electrochemical impedance spectroscopy (EIS). The results showed that the corrosion of pure aluminum was greatly inhibited by the addition of ZnO and dimethyl amine epoxy propane (designated as DE). EIS and EDAX analyses revealed that ZnO produces its effect by depositing on the aluminum surface, which increases the overpotential of hydrogen evolution. It was also found that the addition of DE could greatly improve the deposition of zinc layers. 相似文献
155.
Robert P. Kusy James M. Stuart John Q. Whitley Carl R. Saunders 《Journal of the American Ceramic Society》1993,76(2):299-304
Using laser specular reflectance, the optical rms roughnesses (σ0 'S) of 42 polycrystalline aluminas (PCA's) were determined. From these conventional experimental results, a nomogram was constructed so that single grazing angle (α) measurements could be used to predict σ0 . Subsequently, the nomogram was reassessed using five commercially important PCA's and one single-crystal sapphire (SC). The outcomes were twofold: that this nomogram was valid for PCA's over the range of 0.28 σ0 0.10 μm, but that the nomogram was invalid for SC sapphire. When the conventional experimental method was compared with the nomogram method at three different single-angle values, a 1:1 correspondence was observed for α= 78°, 80°, and 82°. The present noncontact method is advocated for speed and cleanliness, particularly when a quality assurance method is desired. 相似文献
156.
William D. Bedard Kenneth Q. Lindahl Jr. Paul E. Tilden David L. Wood 《Journal of chemical ecology》1985,11(9):1249-1261
After living ponderosa pines were baited with either female-infested bolts or synthetic pheromones,Dendroctonus brevicomis were caught on sticky screens throughout trapping periods of 15–46 days; however, large numbers of beetles were trapped during only a small portion (5–10 days) of these trapping periods. The most attractive portions of trees attacked contained 3–6 beetles dm2, in galleries ca. 2 cm long. Catch increased following addition of males to female-infested bolts, supporting the hypothesis that male-produced frontalin is an attractive pheromone of the western pine beetle. Catch at bolts removed from trees under attack was strongly dependent upon levels of boring activity. We found no evidence of interruption of the response to attractants during host colonization.Coleoptera: Scolytidae. Trade names and commercial enterprises or products are mentioned solely for information and do not constitute endorsement by the U.S. Department of Agriculture or University of California. 相似文献
157.
Tungsten oxide (WO3) nanorods array prepared using chemical vapor deposition techniques was studied. The influence of oxygen gas concentration
on the nanoscale tungsten oxide structure was observed; it was responsible for the stoichiometric and morphology variation
from nanoscale particle to nanorods array. Experimental results also indicated that the deposition temperature was highly
related to the morphology; the chemical structure, however, was stable. The evolution of the crystalline structure and surface
morphology was analyzed by scanning electron microscopy, Raman spectra and X-ray diffraction approaches. The stoichiometric
variation was indicated by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. 相似文献
158.
Q. L. Burrell 《Scientometrics》1991,21(2):181-194
It is pointed out that the so-called Bradford distribution derived by Leimkuhler is more properly viewed as the theoretical form of a variant of the Lorenz curve. The equation of this Leimkuhler curve allows an easy calculation of the Gini coefficient of concentration which can be compared with empirical values. 相似文献
159.
Transition temperatures between tetragonal and monoclinic polymorphs of ZrO2 nanoparticles, thin films and nanostructured materials are calculated by considering energetic contributions of surface (interface) energy and surface stress on total Gibbs free energy. The transition temperatures drop as the size of the nanocrystals decreases, which is consistent with available results. 相似文献
160.
G. Q. Zhao R. Hufi A. Hutter R. V. Grandhi 《Journal of Materials Engineering and Performance》1997,6(3):303-310
This paper uses a finite element-based sensitivity analysis method to design the preform die shape for metal forming processes.
The sensitivity analysis was developed using the rigid visco-plastic finite element method. The preform die shapes are represented
by cubic B-spline curves. The control points or coefficients of the B-spline are used as the design variables. The optimization
problem is to minimize the difference between the realized and the desired final forging shapes. The sensitivity analysis
includes the sensitivities of the objective function, nodal coordinates, and nodal velocities with respect to the design variables.
The remeshing procedure and the interpolation/transfer of the history/dependent parameters are considered. An adjustment of
the volume loss resulting from the finite element analysis is used to make the workpiece volume consistent in each optimization
iteration and improve the optimization convergence. In addition, a technique for dealing with fold-over defects during the
forming simulation is employed in order to continue the optimization procedures of the preform die shape design. The method
developed in this paper is used to design the preform die shape for both plane strain and axisymmetric deformations with shaped
cavities. The analysis shows that satisfactory final forging shapes are obtained using the optimized preform die shapes. 相似文献