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81.
Miyamoto R.Y. Leong K.M.K.H. Seong-Sik Jeon Yuanxun Wang Yongxi Qian Itoh T. 《Vehicular Technology, IEEE Transactions on》2003,52(5):1181-1188
A wireless sensor server is developed based on a reconfigurable active smart-antenna/retrodirective array. The system can serve as both a retrodirective array transponder and a smart-antenna receiver simply by changing the frequency of the local oscillator applied to the mixers, enabling it to utilize its hardware best to suit its communication environment. When operating as a direct-conversion receiver, the receiver array successfully demodulates a quaternary phase-shift keying (QPSK) modulated signal with circuit gain of 7 dB, and E/sub b//N/sub 0/ for BER=10/sup -4/ is approximately 12 dB without any error correction. In the retrodirective array mode, the system provides 20 dB circuit gain and 20 dB radio-frequency/intermediate-frequency isolation at the center frequency as well as phase conjugation, exhibiting excellent retrodirectivity. The mixers perform phase conjugation and modulation simultaneously, enabling the transmission of locally stored data. The local data is successfully extracted by an interrogator. 相似文献
82.
Dielectric loss tangent and permittivity of polytetrafluoroethylene (Teflon), high-density (HD) polyethylene, and cross-linked polystyrene (Rexolite) were measured at temperature range from 28 to 84 K and frequency of approximately 18 GHz. The material properties were determined by measurements of the resonant frequency and the Q factor of a TE011 mode cylindrical superconducting cavity containing a sample under test. It has been demonstrated that these materials exhibit very low losses at cryogenic temperatures (2×10-6 for Teflon, 5×10-5 for HD polyethylene and 1.1×10-4 for Rexolite). Due to low losses, these materials can be useful in construction of various high-Q factor microwave devices for operation at cryogenic temperatures 相似文献
83.
BACKGROUND: This study was a prospective randomized comparison of healing following open and closed haemorrhoidectomy. METHODS: Sixty-seven consecutive patients (mean(s.e.m.) age 45(1.7) years; 35 men, 32 women) with three prolapsed piles were randomized to open haemorrhoidectomy (n = 34) or closed haemorrhoidectomy (n = 33). RESULTS: Mean(s.e.m.) follow-up was 8.7(0.2) months. There were no differences in the linear analogue pain scores, analgesic requirements and length of hospitalization after open haemorrhoidectomy and closed haemorrhoidectomy. Complete wound healing took significantly longer after closed haemorrhoidectomy (mean(s.e.m.) 6.9(0.7) weeks) compared with open haemorrhoidectomy (4.9(0.4)weeks) (P < 0.05). This was related to wound dehiscence in eight patients. Complication rates, however, were similar except for prolonged serous discharge from unhealed wounds. The anal manometry findings after both procedures were equivalent. CONCLUSION: Open haemorrhoidectomy leads to faster and more reliable wound healing, although this did not result in less pain or fewer complications. 相似文献
84.
A review of the effect of stitching on the in-plane mechanical properties of fibre-reinforced polymer composites 总被引:16,自引:0,他引:16
This paper reviews over fifty studies into the effect of through-the-thickness stitching on the in-plane mechanical properties of fibre-reinforced polymer composites. Reviewed are the in-plane tensile, compressive, flexure, interlaminar shear, creep, fracture and fatigue properties, although little work has been undertaken on the last three properties. When comparing studies it is apparent that many contradictions exist: some studies reveal that stitching does not affect or may improve slightly the in-plane properties while others find that the properties are degraded. In reviewing these studies it is demonstrated that predicting the influence of stitching on the in-plane properties is difficult because it is governed by a variety of factors, including the type of composite (eg. type of fibre, resin, lay-up configuration), the stitching conditions (eg. type of thread, stitch pattern, stitch density, stitch tension, thread diameter), and the loading condition. The implications of these findings for the use of stitching in lightweight engineering structures are discussed. 相似文献
85.
Le-Wei Li Mui-Seng Yeo Mook-Seng Leong 《Antennas and Propagation, IEEE Transactions on》2004,52(9):2391-2402
This paper presents derivation and computation of electromagnetic (EM) fields inside a dielectric prolate spheroid radiated by a loop antenna. The dielectric spheroid is considered to be multilayered, and a thin circular loop antenna that is loaded by a voltage source radiates on the top of the prolate spheroid. The multiple interaction of transmitted and reflected waves with the spheroid is characterized by applying the method of moments (MoM) to both the circular loop antenna wire and the stratified spheroidal interfaces. The dyadic Green's function in the expansion form of eigenvector wave functions is used to derive the EM fields, so the formulation is quite compact. Different basis and weighting functions are used inside the method of moments procedure for obtaining in an efficient way the unknown current distributions along the antenna wire and the unknown expansion coefficients of their resulted EM fields. Current distributions and the transmitted fields inside the spheroidal model are computed numerically and the convergence issues are discussed. 相似文献
86.
Y. W. Leong S. Yamaguchi M. Mizoguchi H. Hamada U. S. Ishiaku T. Tsujii 《Polymer Engineering and Science》2004,44(12):2327-2334
An extensive study on the peel strength between a polypropylene (PP) film and PP substrate fabricated using film insert injection molding technique was carried out through a 180° peel test. Injection molding conditions such as barrel temperature, injection speed and holding pressure were varied to gauge their effects on the mechanical and morphological properties. Morphological observations were made at the film‐substrate interfacial regions by means of transmission electron microscopy (TEM). The injection molded products, with the films still attached, were subjected to bending and impact tests to determine if there is any relationship between film‐substrate adhesion and bulk properties. Observation of the load‐displacement curves during the peel test revealed three unique and interesting curves, corresponding to different peeling and film fracture mechanisms. Increases in injection speed, barrel temperature and holding pressure lead to increased bonding between the film and substrate surfaces. The enhancement of bonding between these two polymer surfaces could be attributed to polymer‐polymer interdiffusion. Substantiating evidence from TEM, which shows the fading of the interface as the bond strengthens, further boosts the accuracy of this assumption. The hope that the films could contribute to enhancing bulk properties has been diminished since the bending properties appeared to be similar with or without the film attached. Polym. Eng. Sci. 44:2327–2334, 2004. © 2004 Society of Plastics Engineers. 相似文献
87.
Writing Psychology of reading has given John Downing and this writer a great deal of self-doubts and self-criticisms. This is particularly so in a field which is so vast and complex and where there is a high level of productivity. We are thus appreciative of the insightful review of our volume by Linda Siegel (Canadian Psychology, 1985, 26, pp. 300-301, see record 2007-08971-001). We agree with the comments on the "complexities of definitional issues" and the need to amplify on comprehending. This latter endeavour, to misquote Edmund Huey, "would almost be the acme of a psychologist's achievements." Lest Downing and Leong be misunderstood, I would like to clarify one main point raised in the review. We state that "the discredited achievement or learning quotient should be laid to rest" (p. 306). If some psychometric tests must be used, they must meet all the technical requirements. In particular, these screening devices need to be "supplemented by individual diagnosis of children for appropriate educational placement and programming" (p. 306). Elsewhere I have elaborated on this two-tier approach of the more quantitative psychometric assessment followed by the more qualitative cognitive-developmental diagnosis (Leong, 1985, in press). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
88.
Ding Yu Heh Eng Leong Tan Wei Choon Tay 《International Journal of Numerical Modelling》2016,29(1):93-108
This paper presents fast alternating direction implicit (FADI) method for efficient transient thermal simulation of integrated circuits. The FADI method is formulated from Peaceman–Rachford's ADI and Douglas–Gunn's ADI methods. The update procedure of the proposed method has basic implicit form that features derivative‐free right‐hand side and hence, better efficiency and conciseness. Subsequently, through the basic implicit form of FADI method, the relationship between classical Peaceman–Rachford's and Douglas–Gunn's ADI methods can be clarified and elucidated in detail. A unified boundary condition that can cater to common kinds of boundary conditions in thermal simulation is also introduced. To further accelerate FADI method, the graphics processing unit is also utilized through Compute Unified Device Architecture implementation. It is shown that high efficiency gain can be achieved using the proposed FADI method through large time step size and data parallelism, while maintaining stability and good accuracy. As numerical illustration, an integrated circuit structure with microchannel cooling is demonstrated. Numerical results further ascertain the cooling effect of the microchannels. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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