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排序方式: 共有160条查询结果,搜索用时 31 毫秒
1.
M. Muhr ÖVE S. Pack ÖVE H. Haidvogl F. Kreyca 《e & i Elektrotechnik und Informationstechnik》1997,114(11):680-686
Recently appeared defects on high voltage cables have required an urgent evaluation of the impact of lightning strikes necessary. In some cases overvoltages between the copper wire screen of the cable and earth may appear which cause damages of the cablesheath. Field measurements with a classification of the voltage impulses at the copper wire screen have been made to evaluate the number of events. Additionally a numerical model was developed to study the effects of atmospheric discharges on underground cables with emphasis to the influence on the cablesheath. This numeric method was also applied to estimate the effectiveness of different protection arrangements. This contribution presents evaluation methods for overvoltages of cables and a model used firstly for calculating the stress caused by differential voltages and secondly to determinate the influence of protection measures. 相似文献
2.
M. Muhr S. Pack S. Jaufer H. Lugschitz 《e & i Elektrotechnik und Informationstechnik》2006,123(12):537-543
New developments in diagnostic tools and systems are necessary for a reliable and economic evaluation of the condition of
equipment in power systems. In a research project a tool for the condition of contacts of centre break disconnector, which
is used under normal operation by the aid of a thermography measurement system, has been developed. In this paper, an overview
about the laboratory investigation of the temperature load behaviour and the environmental influence on-site for new and aged
disconnector contacts are given. A condition evaluation tool for contacts, which was the aim of the project, has been created.
The basic method for the evaluation is presented, and also two additional easements for a fast identification of suspect contacts
are presented. With this evaluation tool and the usage of a thermography based measuring system, a condition based maintenance
strategy can be applied, whereby an early detection of damages is possible and so power quality and reliability increase.
相似文献
3.
DK Robbins MA Castles DJ Pack VO Bhargava SJ Weir 《Canadian Metallurgical Quarterly》1998,19(7):455-463
The pharmacokinetics and dose proportionality of fexofenadine, a new non-sedating antihistamine, and its enantiomers were characterized after single and multiple-dose administration of its hydrochloride salt. A total of 24 healthy male volunteers (31 +/- 8 years) received oral doses of 20, 60, 120 and 240 mg fexofenadine HCl in a randomized, complete four-period cross-over design. Subjects received a single oral dose on day 1, and multiple oral doses every 12 h on day 3 through the morning on day 7. Treatments were separated by a 14-day washout period. Serial blood and urine samples were collected for up to 48 h following the first and last doses of fexofenadine HCl. Fexofenadine and its R(+) and S(-) enantiomers were analysed in plasma and urine by validated HPLC methods. Fexofenadine pharmacokinetics were linear across the 20-120 mg dose range, but a small disproportionate increase in area under the plasma concentration-time curve (AUC) (< 25%) was observed following the 240 mg dose. Single-dose pharmacokinetics of fexofenadine were predictive of steady-state pharmacokinetics. Urinary elimination of fexofenadine played a minor role (10%) in the disposition of this drug. A 63:37 steady-state ratio of R(+) and S(-) fexofenadine was observed in plasma. This ratio was essentially constant across time and dose. R(+) and S(-) fexofenadine were eliminated into urine in equal rates and quantities. All doses of fexofenadine HCl were well tolerated after single and multiple-dose administration. 相似文献
4.
Ho-Yong Lee Yeong-Kyeun Pack Byoung-Ki Lee Suk-Joong L. Kang 《Journal of the American Ceramic Society》1995,78(8):2149-2152
When sintered 85Al2 O3 –15Fe2 O3 (in wt%) specimens consisting of corundum grains and spinel particles were annealed at temperature where only a corundum phase was stable, phase transformation of spinel into metastable FeAIO3 and subsequently complete dissolution of the metastable phase occurred together with the migration of grain boundaries at the surface of the specimens. Since the grain boundary migration was induced by grain boundary diffusion of Fe2 O3 from the transforming and dissolving particles, the boundary migration by temperature decrease corresponds to a discontinuous dissolution of the spinel particles and a chemically induced grain boundary migration by temperature change. Inside the specimens, however, the transformation—dissolution and the grain boundary migration were suppressed because of unavailable accommodation of the volume expansion due to the transformation. 相似文献
5.
Recently, there have been a lot of research efforts on peer-to-peer (P2P) live streaming services. P2P systems can be easily deployed since a participating peer’s resources (i.e., upload link bandwidth) can be exploited to distribute contents. However, how to adapt to leaving peers and how to encourage peers to contribute resources voluntarily are still challenging issues. In this paper, we propose Climber, an adaptive P2P live streaming system with incentives for resilience. Climber is based on the hybrid structure of a tree and a mesh, so as to achieve self-improvement and adaptation to users’ dynamic joining and leaving. Moreover, Climber substantiates an incentive mechanism that provides better resilience for peers with more upload bandwidth allocated. Simulation results reveal that Climber significantly reduces the topology maintenance cost compared to SplitStream and NICE-PRM. Also, simulation and analytical results verify that Climber can bound the level of disruption by dynamically adapting to the user churning rate. 相似文献
6.
7.
In the future, most mobile nodes will have multiple radio interfaces, and this feature can be exploited to reduce the transmission cost in wireless data access applications. In this work, we propose cooperative poll-each-read (CoopPER) and cooperative callback (CoopCB) wireless data access algorithms with strong consistency in multi-radio wireless networks. In addition, we investigate CoopPER and CoopCB in heterogeneous wireless networks where CoopPER and CoopCB nodes are mixed. Extensive simulations are done to show the effects of access-to-update ratio, data access pattern, cache size, and cooperation range. Simulation results demonstrate that CoopPER and CoopCB can significantly reduce the expensive transmission cost over wireless links. 相似文献
8.
WiMedia MAC is an attractive transmission technology for high rate multimedia streaming and high quality consumer electronic devices in wireless personal area networks. In this paper, we propose a deterministic channel access (DCA), where all the devices determine their transmission orders in a distributed manner by exchanging beacon frames in the beacon period. Since all of the devices follow a deterministic transmission order, collision-free channel access can be achieved and thus the throughput can be significantly improved. In addition, the DCA addresses unfairness problems found in channel access by using circulating reference points. The trace-driven simulation results demonstrate that the DCA outperforms the existing channel access schemes in WiMedia MAC under different situations, especially under bursty traffic. 相似文献
9.
Hierarchical Mobile IPv6 (HMIPv6) is an enhanced version of Mobile IPv6 designed to reduce signaling overhead and to support
seamless handoff in IP-based wireless/mobile networks. To support more scalable services, HMIPv6 networks can be organized
as the form of a multi-level hierarchy architecture (i.e., tree structure). However, since multi-level HMIPv6 networks incur
additional packet processing overhead at multiple mobility agents, it is important to find the optimal hierarchy level to
minimize the total cost, which consists of the location update cost and the packet delivery cost. In this paper, we investigate
this problem, namely the design of an optimal multi-level HMIPv6 (OM-HMIPv6) network. To accomplish this, we design a function
to represent the location update cost and the packet delivery cost in multi-level HMIPv6 networks. Based on these formulated
cost functions, we calculate the optimal hierarchy level in multi-level HMIPv6 networks, in order to minimize the total cost.
In addition, we investigate the effects of the session-to-mobility ratio (SMR) on the total cost and the optimal hierarchy.
The numerical results, which show various relationships among the network size, optimal hierarchy, and SMR, can be utilized
to design an optimal HMIPv6 network. In addition, the analytical results are validated by comprehensive simulations.
Sangheon Pack received his B.S. (2000, magna cum laude) and Ph.D. (2005) degrees from Seoul National University, both in computer engineering.
He is a post doctor fellow in the School of Computer Science and Engineering at the Seoul National University, Korea. He is
a member of the IEEE and ACM. During 2002–2005, he was a recipient of the Korea Foundation for Advanced Studies (KFAS) Computer
Science and Information Technology Scholarship. He has been also a member of Samsung Frontier Membership (SFM) from 1999.
He received a student travel grant award for the IFIP Personal Wireless Conference (PWC) 2003. He was a visiting researcher
to Fraunhofer FOKUS, German in 2003. His research interests include mobility management, wireless multimedia transmission,
and QoS provision issues in the next-generation wireless/mobile networks.
Yanghee Choi received B.S. in electronics engineering from Seoul National University, M.S. in electrical engineering from Korea advanced
Institute of Science, and Doctor of Engineering in Computer Science from Ecole Nationale Superieure des Telecommunications
(ENST) in Paris, in 1975, 1977 and 1984 respectively. Before joining the School of Computer Engineering, Seoul National University
in 1991, he has been with Electronics and Telecommunications Research Institute (ETRI) during 1977–1991, where he served as
director of Data Communication Section, and Protocol Engineering Center. He was research student at Centre National d'Etude
des Telecommunications (CNET), Issy-les-Moulineaux, during 1981–1984. He was also Visiting Scientist to IBM T.J. Watson Research
Center for the year 1988–1989. He is now leading the Multimedia Communications Laboratory in Seoul National University. He
is also director of Computer Network Research Center in Institute of Computer Technology (ICT). He was editor-in-chief of
Korea Information Science Society journals. He was chairman of the Special Interest Group on Information Networking. He has
been associate dean of research affairs at Seoul National University. He was president of Open Systems and Internet Association
of Korea. His research interest lies in the field of multimedia systems and high-speed networking.
Minji Nam received her B.S. and M.S degrees in Computer Science and Engineering from Seoul National University in 2003 and 2005, respectively.
From 2005, she has worked on Portable Internet Development Team for Korea Telecom. Her research interests are mobile networks,
portable internet technology (IEEE 802.16) and Mobile IPv6. 相似文献
10.