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951.
Chang -Doo Kee Won -Gul Hwang Jong -Yeop Kim 《Journal of Mechanical Science and Technology》1990,4(2):141-149
The so called “Quantitative Pole Placement” (QPP) identified in the context of guaranteed tracking in the sens of spheres is considered. In the prior literature this pole-placement problem was treated in a somewhat adhoc way. The primary purpose of the present work therefore is to propose a systematic procedure for such pole placement. The approach to the problem is based on a generalization of the standard LQ problem formulation. The preferred pole locations that minimize a crucial operator norm needed for the success of the QPP formulation are shown to be a perturbed version of the Butterworth pole configuration. The results are applied to a 3 d.o.f. robotic manipulator for illustrating the evolving methodology. At the center of the overall design philosophy is the need to directly satisfy performance specifications in uncertain. nonlinear systems. 相似文献
952.
953.
Woong Ki Kim Author Vitae Young Woo Lee Ji Yeon Park Jung Byung Park 《Nuclear Engineering and Design》2008,238(12):3285-3291
The TRISO-coated fuel particle for a HTGR (high temperature gas-cooled reactor) is composed of a nuclear fuel kernel and outer coating layers. The coating layers consist of a buffer PyC (pyrolytic carbon) layer, an inner PyC (I-PyC) layer, a SiC layer, and an outer PyC (O-PyC) layer. X-ray radiography is one of the nondestructive alternatives to measure a coating thickness without generating a radioactive waste. Phase contrast X-ray radiography technology is more powerful for acquiring a radiograph with clear boundaries, when compared with a conventional X-ray radiography. The contrast can be enhanced for weakly absorbing materials in a phase contrast X-ray radiograph by detecting an intensity variation due to the variation of a phase of the X-rays in the boundary between two objects. Phase contrast X-ray radiograph was acquired from a simulated TRISO-coated fuel particle with a micro-focus X-ray imaging system. The coating thickness was nondestructively measured from the phase contrast X-ray image for the fuel particle. 相似文献
954.
Direct quantitative comparisons of four different probe methods were performed for determination of local gas holdup, vertical bubble length, bubble rising velocity, and bubble frequency. The methods include vertically projecting electroresistivity, horizontally projecting electroresistivity, U-shape light reflection, and light transmission. The measured bubble properties strongly depended on the size and configuration of the probe tips. The light transmission probe developed in this work can be used to determine the bubble properties effectively. In order to minimize interferences with bubble flow, the size of probe tip should be small as possible and its configuration must be vertically projecting. 相似文献
955.
A self aligned In0.52Al0.48As/In0.53 Ga0.47As double heterojunction bipolar transistor (HBT) with a graded heterointerface has been grown by molecular-beam epitaxy (MBE) and tested. The DC characteristics of HBT structures with a compositionally graded junction using a linear graded In0.53Ga0.47-xAlxAs between two ternary layers were investigated. Typical quaternary graded devices with an emitter dimension of 50×50 μm2 exhibited a current gain as high as 1260, as compared to 800 for abrupt devices, at a collector current density of 2.8×103 A/cm2 相似文献
956.
P. Chauviere K. H. Jung D. K. Kim H. C. Lee S. H. Kang Y. T. Im 《Journal of Mechanical Science and Technology》2008,22(5):924-930
A tip test was developed and used successfully for friction measurement between the billet and dies or punches for the cold
forging process. In the present investigation, the test was downsized and experimentally investigated to find the size effect
on test results. For the test, aluminum alloys of 2024-O and 6061-O were used and the specimen was made into a cylinder of
diameter and height of 10.0mm and 5.0mm, respectively. For lubrications, VG32, VG100, grease, and corn oil were used in experiments
and tests were also carried out with two different humidity conditions. A micro-hardness test was made to compare the hardness
distribution with the strain distribution obtained from the finite element simulation. The load levels and tip distances were
measured for Al6061-O specimen with various lubrication conditions and compared to each other to find any correlation between
the two. The shear friction factors were determined for various lubrications by using the finite element simulation under
the present condition. 相似文献
957.
Mesoporous compound of cobalt-layered manganese oxide was synthesized by self-assembly reaction between 2D manganate nanosheets and cobalt ions. It was found that 2D manganate nanosheets are interstratified with cobalt ions, leading to the formation of porous intercalation heterostructure with expanded surface area of ∼ 44-100 m2/g. The mesopores with the average diameters of ∼ 11-17 nm originate from the house-of-cards type stacking of the layered manganate crystallites. Co K- and Mn K-edge X-ray absorption spectroscopy revealed that both the cobalt and manganese ions are stabilized in octahedral symmetry with the mixed oxidation states of Mn3+/Mn4+ and Co2+/Co3+. Considering high oxidation states of component metal ions, this porous material is expected to be very useful as redox catalysts and/or lithium intercalation electrodes. 相似文献
958.
Summary Miscibility of bisphenol-A polycarbonate, PC, with methyl methacrylate/cyclohexyl methacrylate, PMCHM, copolymers were examined
by glass transition temperature and lower critical solution temperature, LCST, behavior.
PMCHM copolymers were found to be miscible with PC at levels of below 4% or less of CHM in weight. Relatively small amount
of the comonomer markedly raised phase separation temperature on heating. This result can be rationalized by intramolecular
repulsion effect reported earlier. 相似文献
959.
Wen-Lin Jung Jingshown Wu 《Microwave Theory and Techniques》1990,38(8):1079-1085
A modified real-frequency technique for designing a broadband microwave amplifier with guaranteed stability is presented. This method generates the two sets of resistive excursions necessary for synthesizing the source and load admittances of the amplifier concurrently, rather than sequentially, while both the stability and realizability requirements are satisfied simultaneously. Regardless of its constrained nature, the method has been formulated as an unconstrained optimization problem. An 8-12-GHz-band amplifier design example is presented to demonstrate its application. The transducer power gain obtained in the example by this method is 11.3±0.4 dB, which is 2.6-dB higher than that obtained by using the real-frequency technique 相似文献
960.
Silicon dioxide (SiO2) films prepared by plasma‐enhanced atomic‐layer deposition were successfully grown at temperatures of 100 to 250 °C, showing self‐limiting characteristics. The growth rate decreases with an increasing deposition temperature. The relative dielectric constants of SiO2 films are ranged from 4.5 to 7.7 with the decrease of growth temperature. A SiO2 film grown at 250 °C exhibits a much lower leakage current than that grown at 100°C due to its high film density and the fact that it contains deeper electron traps. 相似文献