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排序方式: 共有960条查询结果,搜索用时 15 毫秒
881.
882.
Ya-Ju Lee Hao-Chung Kuo Tien-Chang Lu Shing-Chung Wang Kar Wai Ng Kei May Lau Zu-Po Yang Chang A.S.-P. Shawn-Yu Lin 《Lightwave Technology, Journal of》2008,26(11):1455-1463
We investigate the mechanism responding for performance enhancement of gallium nitride (GaN)-based light-emitting diode (LED) grown on chemical wet-etching-patterned sapphire substrate (CWE-PSS) with V-Shaped pit features on the top surface. According to temperature-dependent photoluminescence (PL) measurement and the measured external quantum efficiency, the structure can simultaneously enhance both internal quantum efficiency and light extraction efficiency. Comparing to devices grown on planar sapphire substrate, the threading dislocation defects of LED grown on CWE-PSS are reduced from 1.28 times 109/cm2 to 3.62 times 108/cm2, leading to a 12.5% enhancement in internal quantum efficiency. In terms of the theoretical computing of radiation patterns, the V-Shaped pits roughening surface can be thought of as a strong diffuser with paraboloidal autocorrelation function, increasing the escape probability of trapped photons and achieving a 20% enhancement in light extraction efficiency. Moreover, according to the measurement of optical diffraction power, CWE-PSS demonstrated superior guided light extraction efficiency than that of planar sapphire substrate, thus an extra 7.8% enhancement in light extraction efficiency was obtained. Therefore, comparing to the conventional LED, an overall 45% enhancement in integrated output power was achieved. 相似文献
883.
Digital signatures for flows and multicasts 总被引:2,自引:0,他引:2
We present chaining techniques for signing/verifying multiple packets using a single signing/verification operation. We then present flow signing and verification procedures based upon a tree-chaining technique. Since a single signing/verification operation is amortized over many packets, these procedures improve signing and verification rates by one to two orders of magnitude, compared to the approach of signing/verifying packets individually. Our procedures do not depend upon reliable delivery of packets. They also provide delay-bounded signing, and are thus suitable for delay-sensitive flows and multicast applications. To further improve our procedures, we propose several extensions to the Feige-Fiat-Shamir (1987) digital signature scheme to substantially speed up both the signing and verification operations, as well as to allow “adjustable and incremental” verification. The extended scheme, called eFFS, is compared to four other digital signature schemes (RSA, DSA, ElGamal (1985), and Rabin). We compare their signing and verification times, as well as key and signature sizes. We observe that: (1) eFFS is the fastest in signing (by a large margin over any of the other four schemes) and as fast as RSA in verification (tie for a close second behind Rabin (1979)); (2) eFFS allows a tradeoff between memory and signing/verification time; and (3) eFFS allows adjustable and incremental verification by receivers 相似文献
884.
Hiroaki Kotani Kei Ohkubo Shunichi Fukuzumi 《Applied catalysis. B, Environmental》2008,77(3-4):317-324
Visible light irradiation of an O2-saturated acetonitrile (MeCN) solution containing 9-mesityl-10-methylacridinium ion (Acr+–Mes) and MeCN-extracted coal tar results in formation of hydrogen peroxide (H2O2). Anthracene and other aromatic hydrocarbons contained in coal tar act as hydrogen sources in the photocatalytic reduction of O2 to produce H2O2. The photocatalytic formation of H2O2 is initiated by photoexcitation of Acr+–Mes, which results in formation of the electron-transfer state: Acr–Mes+, followed by electron-transfer from coal tar to the Mes+ moiety and electron-transfer from the Acr moiety to O2. 相似文献
885.
886.
887.
Toda M. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2001,48(6):1568-1574
A new type of large area PVDF film air transducer is proposed. The transducer features a high power output and a sharp beam angle. Conventionally known curved length mode resonators with two clamps at both ends have a resonance frequency determined by the curvature. In the present work, PVDF was formed into alternating concave and convex multiple curved sections, eliminating clamps, i.e., a periodic corrugation structure using a single PVDF film. Each convex and concave section has a common resonance frequency. A common excitation voltage induces vibration for each section, and the vibration direction is normal to the film surface. The vibration phase of convex section is shifted 180 degrees from the concave section. These waves add constructively to form a strong acoustic beam when corrugation height is approximately one-half of the wavelength. The corrugation height controls propagation path difference, canceling excitation phase difference. The design principle based on a uniform vibration mode is presented. Experimental investigations using 8.8×2.5-, 10×5-, and 20×20-cm2 transducers are presented. Side lobes unique to this corrugation structure have been observed. A theoretical analysis of the side lobes is also presented. According to the theory, choosing the corrugation height appropriately will reduce side lobes to -15 dB with regard to the main lobe, and the observed side lobe height agreed with the theoretical result 相似文献
888.
Vegas Olmos J.J. Kuri T. Sono T. Tamura K. Toda H. Kitayama K.-I. 《Photonics Technology Letters, IEEE》2008,20(13):1127-1129
We show a bidirectional optical access network with dynamic channel allocation capability of decimeter-wave band optical radio-over-fiber (RoF) and baseband signals. The network can be configured enabling peer-to-peer connectivity, and is based on a simple access point (AP) unit. The proposed RoF architecture is highly scalable, both in terms of channels and APs. 相似文献
889.
Kei Shimoda Naoji Kubota Yoko Kondo Daisuke Sato Hiroki Hamada 《International journal of molecular sciences》2009,10(5):1942-1949
Fluoroaromatic compounds are used as agrochemicals and released into environment as pollutants. Glycosylation of 2-, 3-, and 4-fluorophenols using plant cell cultures of Nicotiana tabacum was investigated to elucidate their potential to metabolize these compounds. Cultured N. tabacum cells converted 2-fluorophenol into its β-glucoside (60%) and β-gentiobioside (10%). 4-Fluorophenol was also glycosylated to its β-glucoside (32%) and β-gentiobioside (6%) by N. tabacum cells. On the other hand, N. tabacum glycosylated 3-fluorophenol to β-glucoside (17%). 相似文献
890.
Hiroyuki Shimada Yuichi Kimura Takao Suzuki Takashi Hirata Miho Sugiura Yosuke Endo Ken Yasuhara Kei Shimada Keishiro Kikuchi Masaya Hashimoto Masatomo Ishikawa Keiichi Oda Kenji Ishii Kiichi Ishiwata 《IEEE transactions on neural systems and rehabilitation engineering》2007,15(3):442-448
The aim of this study was to investigate the use of [18F]fluorodeoxyglucose and positron emission tomography (FDG PET) for quantitative evaluation of glucose metabolism in skeletal muscle during walking. Ten young males underwent FDG PET twice during walks, which were done with or without an automated stride assistance system (SAS). Walk ratios were significantly increased by the SAS in seven subjects. Regional glucose metabolism in muscles between the crista iliaca and the planta was clearly visualized in all ten subjects. Glucose utilization increased significantly in the tibialis posterior and medial gastrocnemius muscles of the seven subjects in whom walk ratios were increased by the SAS. FDG PET is useful for analysis of muscle activity during exercise and rehabilitation. 相似文献