In this paper, a new kinetic model for methanol to olefin process (MTO) over SAPO-34 catalyst was developed based on data obtained from a micro catalytic reactor using appropriate reaction network. The reaction rate equation has been introduced with consideration of reaction mechanism and the parameters were optimized on the experimental data by genetic algorithm. Comparing the experimental and predicted data showed that the predicted values from the presented model are well fitted to the experimental data. Using this kinetic model, the effect of most important operating conditions such as temperature, pressure, inlet water to methanol molar ratio and methanol space–time on the product distribution, has been examined. Finally, the optimal operating conditions for maximum production of the ethylene and the propylene were introduced. 相似文献
This paper addresses the two-stage assembly flow-shop problem (TSAFP) with multiple non-identical assembly machines in second stage with the objective function of makespan minimization. This problem is a generalization of previously proposed problems in TSAFP. Mathematical mixed-integer linear programming model of this problem is defined, and for it being NP-hard, a hybrid SA heuristic is proposed. The heuristic is proved to solve the problem in reduced time with negligible error. To validate the proposed method, a real-life example is presented and solved in which the efficiency of the proposed heuristic is shown. 相似文献
Growth pressure has a dramatic influence on the grain size, transport characteristics, optical recombination processes, and
alloy composition of GaN and AlGaN films. We report on systematic studies which have been performed in a close spaced showerhead
reactor and a vertical quartz tube reactor, which demonstrate increased grain size with increased growth pressure. Data suggesting
the compensating nature of grain boundaries in GaN films is presented, and the impact of grain size on high mobility silicon-doped
GaN and highly resistive unintentionally doped GaN films is discussed. We detail the influence of pressure on AlGaN film growth,
and show how AlGaN must be grown at pressures which are lower than those used for the growth of optimized GaN films. By controlling
growth pressure, we have grown high electron mobility transistor (HEMT) device structures having highly resistive (105 Ω-cm) isolation layers, room temperature sheet carrier concentrations of 1.2×1013 cm−2 and mobilities of 1500 cm2/Vs, and reduced trapping effects in fabricated devices. 相似文献
Using plan-view transmission electron microscopy (TEM), we have identified stacking faults (SFs) in 4H-SiC PiN diodes subjected
to both light and heavy electrical bias. Our observations suggest that the widely expanded SFs seen after heavy bias are faulted
dislocation loops that have expanded in response to strain of the 4H-SiC film, while faulted screw or 60° threading dislocations
do not give rise to widely expanded SFs. Theoretical calculations show that the expansion of SFs depends on the Peach-Koehler
(PK) forces on the partial dislocations bounding the SFs, indicating that strain plays a critical role in SF expansion. 相似文献
Mixed-mode loading represents the true loading condition in many practical situations. In addition, most of the fatigue life
of many components is often spent in the short crack growth stage. The study of short crack growth behavior under mixed-mode
loading has, therefore, much practical significance. This work investigated short crack growth behavior under mixed-mode loading
using a common medium carbon steel. The effects of load mixity, crack closure, and load ratio on short crack growth behavior
were evaluated by conducting experiments using four-point bending specimens with several initial KII/KI mixed-mode ratios and two load ratios. Cracks were observed to grow along the paths with very small KII/KI ratios (i.e. mode I). The maximum tangential stress criterion was used to predict the crack growth paths and the predictions
were found to be close to the experimental observations. Several parameters including equivalent stress intensity factor range
and effective stress intensity factor range were used to correlate short crack growth rates under mixed-mode loading. Threshold
values for short cracks were found to be lower than those for long cracks for all the mixed-mode loading conditions. Crack
closure was observed for the entire crack length regime with all load mixity conditions at R ≈ 0.05 and for short crack regime under high load mixity condition at R = 0.5. Several models were used to describe mean stress effects and to correlate crack growth rate data. 相似文献
Bulletin of Engineering Geology and the Environment - Soft rock masses represent a significant percentage of rock material on the earth’s crust. The engineering properties of these rocks are... 相似文献
Multimedia Tools and Applications - This paper presents an area-efficient and multi-sized DCT architecture for HEVC application. We exploit the commonality in the arithmetic units to increase the... 相似文献
Wireless sensor network has special features and many applications, which have attracted attention of many scientists. High energy consumption of these networks, as a drawback, can be reduced by a hierarchical routing algorithm. The proposed algorithm is based on the Low Energy Adaptive Clustering Hierarchy (LEACH) and Quadrant Cluster based LEACH (Q-LEACH) protocols. To reduce energy consumption and provide a more appropriate coverage, the network was divided into several regions and clusters were formed within each region. In selecting the cluster head (CH) in each round, the amount of residual energy and the distance from the center of each node were calculated by the base station (including the location and residual energy of each node) for all living nodes in each region. In this regard, the node with the largest value had the highest priority to be selected as the CH in each network region. The base station calculates the CH due to the lack of energy constraints and is also responsible for informing it throughout the network, which reduces the load consumption and tasks of nodes in the network. The information transfer steps in this protocol are similar to the LEACH protocol stages. To better evaluate the results, the proposed method was implemented with LEACH LEACH-SWDN, and Q-LEACH protocols using MATLAB software. The results showed better performance of the proposed method in network lifetime, first node death time, and the last node death time.
Evidence is presented showing that the presence of the commonly used anti-reflection coating material Ta2O5 on the free surface of contact metallization can either suppress or enhance, depending on the system, the interaction that
takes place at elevated temperatures between the metallization and the underlying Si. The cap layer is shown to suppress both
the generation and annihilation of vacancies at the free surface of the metal which are necessary to support metal-Si interactions.
Evidence is also presented indicating that the mechanical condition of the free metal surface has a significant effect on
the metal-silicon reaction rate. 相似文献