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31.
32.
In-situ EXAFS studies of sulphided Mo/TiO2 catalysts have shown that at low Mo loadings (2–4 wt%), an active species with a short Mo-S distance of 2.25 Å is formed, while on Mo/TiO2 with high Mo loadings as well as on Mo/-Al2O3, bulk MoS2 (Mo-S, 2.42 Å) is formed. The species with the short Mo-S distance has Mo in an oxidation state close to 6 + and is likely to result from the sulphidation of the tetrahedral molybdate species present in the oxidic precursor at low Mo loadings. The calcination temperature of the oxidic precursor appears crucial, a high calcination temperature of 973 K favouring the formation of MoS3 on sulphidation, and a low calcination temperature of 623 K favouring MoS2.Contribution No. 790 from the Solid State and Structural Chemistry Unit. 相似文献
33.
G. Moulin C. Mons C. Severac C. Haut G. Rautureau E. Beauprez 《Oxidation of Metals》1993,40(1-2):85-108
Nickel-base alloys, such as Astroloy, used for aeronautical turbine disks, are sensitive to time-dependent cracking in environments containing oxygen. The mosaic structure of the alloy consisting islands (200 nm average size) surrounded by the -phase (100 nm thick) induces complex oxidation phenomena. Various analytical approaches allow the delineation of all the steps from segregation to oxidation occurring on the surface of such a duplex structure. The protection of Astroloy by its outer oxide layer against oxygen penetration was studied also, using alternative
16O2
then
18O2
oxidation. In association with STEM studies, it is shown that the outer oxide scale is not a real barrier against oxygen penetration and that inner precipitation of chronium (+ aluminium and titanium)-enriched oxides, takes place especially in the structure. 相似文献
34.
The design and test of dual/triple‐mode bandpass filter based on temporal coupled‐mode theory 下载免费PDF全文
Hui Xu Jiong‐Jiong Mo Xiu‐Qin Xu Xu Ding Zhi‐Yu Wang Yong‐Heng Shang Li‐Ping Wang Fa‐Xin Yu 《国际射频与微波计算机辅助工程杂志》2016,26(7):609-622
In this article, the design and test of both a K‐band dual‐mode bandpass filter (BPF) pair and a K‐band triple‐mode BPF are presented based on N‐mode temporal coupled‐mode theory (CMT). The expressions of transmission and reflection responses are analytically derived. All the parameters in the expressions have clear physical meanings and are easily optimized to reach the required filter performance. Aided by eigenmode simulations, concrete structures of the three integrated BPFs are designed and optimized to approach the calculated physical parameters. After the fabrications and measurements of the three BPFs, extended upper/lower stopband with high stopband rejections are achieved, and by increasing the number of resonant modes, improved frequency selectivity and better passband flatness are obtained. The analytical analysis well predicts the simulation and measurement results, which provides an efficient way for BPF designs. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:609–622, 2016. 相似文献
35.
On ADRC for non-minimum phase systems: canonical form selection and stability conditions 总被引:1,自引:0,他引:1
Active disturbance rejection control (ADRC), as proposed by Prof. Jingqing Han, reduces first the plant dynamics to its canonical form, normally in the form of cascade integrators, for which the standard controller can be employed to meet the design specifications. This paper concerns with the selection of the canonical form for non-minimum phase systems. In particular, it
is shown that, by employing the well known controllable canonical form, the uncertainties of such systems can be divided into two terms in the state space model, one in the control channel and the other in the output channel. The necessary and sufficient condition is obtained for the stability of the closed-loop system with the proposed canonical form and ADRC. Also, by showing
the necessity of the detectability of the extended system as well as certain information of the systemˉs “zeros”, we present the fundamental guidelines of design ADRC for non-minimum phase uncertain systems. 相似文献
36.
With the rapid deployments of the active disturbance rejection control (ADRC) as a bonafide industrial technology in the background, this paper summarizes some recent results in the analysis of linear ADRC and offers explanations in the frequency response language with which practicing engineers are familiar. Critical to this endeavor is the concept of bandwidth, which has been used in a more general sense. It is this concept that can serve as the link between the otherwise opaque state space formulation of the ADRC and the command design considerations and concerns shared by practicing engineers. The remarkable characteristics of a simple linear ADRC was first shown in the frequency domain, followed by the corresponding analysis in time
domain, where the relationship between the tracking error and the ADRC bandwidth is established. It is shown that such insight is only possible by using the method of solving linear differential equations, instead of the more traditional techniques such as the Lyapunov methods, which tend to be more conservative and difficult to grasp by engineers. The insight obtained from such
analysis is further demonstrated in the simulation validation. 相似文献
37.
Joe Miseli 《Journal of the Society for Information Display》2013,21(6):214-224
On June 1, 2012, the Information Display Measurement Standard version 1 was released. This is the first standard from the worldwide standard group, the International Committee for Display Metrology, a standards committee within SID, and it culminates several years worth of development from many contributors at various levels. It has 26 top‐level chapters and a total over 450 sections of all parts, including over 200 measurement sections and 8 appendices that cover 133 topics of display metrology, tutorials, technical discussions, and references. Herein is an overview of the Information Display Measurement Standard version 1, including the structure of the document, tips, tricks, and hidden features, how it is maintained, support material, a breakdown of its contents, and finally, a sampling of four of the over 200 measurements. The standard is available as a free download and can be found on the International Committee for Display Metrology home page — http://www.icdm‐sid.org . 相似文献
38.
针对基于PI控制器的永磁同步电动机直接转矩控制系统存在转矩波动大、易受负载变化影响的问题,设计了一种基于转速外环的自抗扰控制器,代替PI控制器以改善永磁同步电动机直接转矩控制系统的性能;采用粒子群优化算法对自抗扰控制器的相关参数进行了优化计算,改进了控制器的调节性能。仿真和实验结果表明,基于参数优化自抗扰控制器的永磁同步电动机直接转矩控制系统具有较高的抗负载扰动能力,更快的响应速度和良好的动、静态性能。 相似文献
39.
Chun-Liang Lin Chun-Hsiung Chen Bing-Min Shiu 《Journal of Intelligent Manufacturing》2008,19(4):407-419
In practical electro-pneumatic or hydraulic servo mechanism, there is usually an unavoidable operating delay time in the solenoid
valves. This may sometimes cause closed-loop instability if the time delay is not treated carefully in the control system
designs. Furthermore, pneumatic actuators can offer high performance at low cost, but are often suffered from external disturbances
depending on the operating conditions. This paper proposes a non-model-based design approach for pneumatic actuating systems.
In the proposed control system, a gain scheduled fuzzy-PID controller ensures tracking performance an adaptable wavelet neuro
compensator compensates for time-delay of the control valve, and a disturbance rejecter diminishes influence from load changes.
A condition ensuring the closed-loop stability is derived. The proposed design is experimentally verified to show its effectiveness. 相似文献
40.
Fotis N. Koumboulis Nikolaos D. Kouvakas Paraskevas N. Paraskevopoulos 《中国科学F辑(英文版)》2009,52(7):1084-1094
In the present paper the problem of disturbance rejection of single input-single output neutral time delay systems with multiple
measurable disturbances is solved via dynamic controllers. In particular, the general form of the controller matrices is presented,
while the necessary and sufficient conditions for the controller to be realizable are offered. The proposed technique is applied
to a test case neutral time delay central heating system. In particular, the nonlinear model of the plant and its linearized
approximation are presented. Based on the linearized model, a two-stage controller is designed in order to regulate the room
temperature and the boiler effluent temperature. The performance of the closed loop system is investigated through computational
experiments. 相似文献