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81.
Nd-doped bismuth titanate Bi4 − x
Nd
x
Ti3O12 ceramics (x = 0–1.0) were prepared by the solid state reaction method. The temperature dependence of the dielectric dispersion and ferroelectric
properties were investigated. With the increase of the Nd substitution for Bi ion, the Curie temperature decreased and the
corresponding dielectric constant peak broadened. In addition, the strong low-frequency dielectric dispersions were exhibited.
The Nd doping decreases the temperature dependence of the ac conductivity and increases the temperature dependence of the
remanent polarization, which is caused by the induced polarization by defects, such as bismuth and oxygen vacancies. 相似文献
82.
Chul-Ho Park Mi-Sook Won Chul-Su Lee Won-Hyo Cha Young-Gook Son 《Journal of Electroceramics》2006,17(2-4):619-623
PZT thin films and interlayers were fabricated by the radio frequency (r.f.) Magnetron-sputtering from the Pb1.1Zr0.53Ti0.47O3, PbO and TiO2 target. As a result of the XPS depth profile analysis, we can confirm that the substrate temperature affects the oxidation
condition of each element of interlayers and the PZT film. Compared to the PZT/Pt structure, the dielectric and pyroelectric
properties of PZT thin films inserted by interlayers were measured to a relatively high value. In particular, the PZT/PbO
structure had the highest pyroelectric properties (P = 189.4 μC/cm2K; F
D = 12.7×10−6 Pa−1/2; F
V = 0.018 m2/C). 相似文献
83.
Wook Hyun Kwon Jin Won Kang Young Sam Lee Young Soo Moon 《Journal of Process Control》2003,13(6):1080
In this paper, a simple receding horizon (or model predictive) control for state delayed systems is presented and its solution is given in a closed form by a reduction method. While the control for a time-delay system is usually complex, the proposed controller is simple to construct and therefore can be simply implemented in real applications. To check the closed-loop stability of the proposed controller, a sufficient condition is provided by linear matrix inequalities. In addition, a numerical algorithm is presented for computing the eigenvalues of systems with distributed time delays, which can be used as a necessary and sufficient condition to check closed-loop stability. It is shown by simulation that this simple control can be a stabilizing control for time-delay systems. 相似文献
84.
Hybrid accident simulation methodology using artificial neural networks for nuclear power plants 总被引:3,自引:0,他引:3
Young Joon Choi Hyun Koon Kim Won Pil Baek Soon Heung Chang 《Information Sciences》2004,160(1-4):207-224
A hybrid accident simulation methodology for nuclear power plants is proposed to enhance the capabilities of compact simulator by introducing artificial neural networks. Two neural networks are trained with the target values obtained from the analyses of detailed computer codes and trained results are combined with the compact simulator to perform the following roles: (i) compensation for inaccuracies of a compact simulator occurring from simplified governing equation and reduced number of physical control volumes, and (ii) prediction of the critical parameter usually calculated from the sophisticated computer code: the autoassociative neural network improves the computational results of the compact simulator up to the accuracy level of detailed best estimate computer code, while the backpropagation neural network predicts the minimum departure from nucleate boiling ratio (DNBR). Simulations are carried out to verify the applicability of the proposed methodology for the loss of flow accidents and the results show that the neural networks can be used as a complementary tool to improve the results of a compact simulator. 相似文献
85.
Man Gyun Na Sun Ho Shin Dong Won Jung Soong Pyung Kim Ji Hwan Jeong Byung Chul Lee 《Nuclear Engineering and Design》2004,232(3):267-300
In this work, a probabilistic neural network (PNN) that has been applied well to the classification problems is used in order to identify the break locations of loss of coolant accidents (LOCA) such as hot-leg, cold-leg and steam generator tubes. Also, a fuzzy neural network (FNN) is designed to estimate the break size. The inputs to PNN and FNN are time-integrated values obtained by integrating measurement signals during a short time interval after reactor scram. An automatic structure constructor for the fuzzy neural network automatically selects the input variables from the time-integrated values of many measured signals, and optimizes the number of rules and its related parameters. It is verified that the proposed algorithm identifies very well the break locations of LOCAs and also, estimate their break size accurately. 相似文献
86.
In this paper, a novel actuation method for a smooth impact drive mechanism that positions dual-slider by a single piezo-element is introduced and applied to a compact zoom lens system. A mode chart that determines the state of the slider at the expansion or shrinkage periods of the piezo-element is presented, and the design guide of a driving input profile is proposed. The motion of dual-slider holding lenses is analyzed at each mode, and proper modes for zoom functions are selected for the purpose of positioning two lenses. Because the proposed actuation method allows independent movement of two lenses by a single piezo-element, the zoom lens system can be designed to be compact. For a feasibility test, a lens system composed of an afocal zoom system and a focusing lens was developed, and the passive auto-focus method was implemented. 相似文献
87.
Chinwon?LeeEmail author Kukhyun?Ahn Jang?Moo?Lee Won?Sik?Lim 《Journal of Mechanical Science and Technology》2003,17(4):521-527
Modern automatic transmissions equip torque converters with lock-up clutches to reduce the energy loss of hydraulic systems.
Instead of simply engaging the clutch disks, the new technology of clutch slip has been developed to improve the overall efficiency
of power transmission. There are two major problems with the clutch slip system. The first is how to keep the slip between
the two disks within a small range and the second is when to start or stop the slip. In this paper, the second problem is
discussed in view of the vehicle economy. With a simple vehicle dynamic model, the fuel economy is calculated to determine
the lock-up strategy. Then the lock-up strategy is developed for a slip schedule. 相似文献
88.
E. S. Lee J. K. Won Y. J. Chun M. W. Cho W. S. Cho J. H. Lee 《The International Journal of Advanced Manufacturing Technology》2007,31(11-12):1101-1108
The machinable ceramic Si3N4-BN is a material which is increasingly being employed for automobile bearings and machinable ceramics. This material is very hard and has high resistance against volatile temperature and wear. It's efficient quality and accurate surfaces have always been of high demand for many applications in the industrial field. Besides, this material is varied by the percentage of BN contained in it, and the characteristics of lapping also varies according to this percentage of BN. Hence, in-process electrolytic dressing for ultra-precision lapping was introduced and used to experiment with the differing BN percentages in machinable ceramic Si3 N4. Metal-bonded super-abrasive diamond lapping wheels have superior qualities such as high bond strength, high stability and high machinability. The major problems encountered are wheel loading and glazing, which impedes the effectiveness of the cast-iron bonded diamond lapping wheel and, therefore, dressing should be considered. In this respect, in-process electrolytic dressing (IED) is proposed as an effective method regarding continuous protruding abrasives on the surface of wheels, whereby loading and glazing phenomena can apparently disappear. In this paper, the machining characteristics of machinable ceramic Si3N4-BN have been studied by adapting the IED lapping process in terms of the percentage of h-BN material. 相似文献
89.
On social Web sites 总被引:1,自引:0,他引:1
Today hundreds of millions of Internet users are using thousands of social Web sites to stay connected with their friends, discover new “friends,” and to share user-created contents, such as photos, videos, social bookmarks, and blogs. There are so many social Web sites, and their features are evolving rapidly. There is controversy about the benefits of these sites, and there are social issues these sites have given rise to. There are lots of press articles, Wikipedia articles, and blogs—in varying degrees of authoritativeness, clarity and accuracy—about some of the social Web sites, uses of the sites, and some social problems, and business challenges faced by the sites. In this paper, we attempt to organize the status, uses, and issues of social Web sites into a comprehensive framework for discussing, understanding, using, building, and forecasting the future of social Web sites. 相似文献
90.
Guided Evolution of Bulk Metallic Glass Nanostructures: A Platform for Designing 3D Electrocatalytic Surfaces
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