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991.
A general parallel direct simulation Monte Carlo method using unstructured mesh is introduced, which incorporates a multi‐level graph‐partitioning technique to dynamically decompose the computational domain. The current DSMC method is implemented on an unstructured mesh using particle ray‐tracing technique, which takes the advantages of the cell connectivity information. In addition, various strategies applying the stop at rise (SAR) (IEEE Trans Comput 1988; 39: 1073–1087) scheme is studied to determine how frequent the domain should be re‐decomposed. A high‐speed, bottom‐driven cavity flow, including small, medium and large problems, based on the number of particles and cells, are simulated. Corresponding analysis of parallel performance is reported on IBM‐SP2 parallel machine up to 64 processors. Analysis shows that degree of imbalance among processors with dynamic load balancing is about ??½ of that without dynamic load balancing. Detailed time analysis shows that degree of imbalance levels off very rapidly at a relatively low value with increasing number of processors when applying dynamic load balancing, which makes the large problem size fairly scalable for processors more than 64. In general, optimal frequency of activating SAR scheme decreases with problem size. At the end, the method is applied to compute two two‐dimensional hypersonic flows, a three‐dimensional hypersonic flow and a three‐dimensional near‐continuum twin‐jet gas flow to demonstrate its superior computational capability and compare with experimental data and previous simulation data wherever available. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
992.
Sheng-Yi Huang Kun-Ming Chen Guo-Wei Huang Victor Liang Hua-Chou Tseng Hsu T.-L. Chun-Yen Chang 《Device and Materials Reliability, IEEE Transactions on》2005,5(2):183-189
Hot-carrier (HC) effects on high-frequency and RF power characteristics of Si/SiGe HBTs are investigated in this paper. By using the two-tone load-pull measurement, we find that not only the cutoff frequency, but also the output power performances of Si/SiGe HBTs are suffered by the HC stress. In this work, S-parameters and intrinsic elements of an equivalent hybrid-/spl pi/ model were used to validate the HC effects on high-frequency characteristics. With different bias conditions, the degradations of cutoff frequency, power gain, and linearity are found to be worse under constant base-current measurement than that under constant collector-current measurement. The HC-induced degradations on the current gain, transconductance, and ideality-factor of base and collector currents are analyzed to explain the experimental observations. 相似文献
993.
994.
A Seamless Handoff Mechanism for DHCP-Based IEEE 802.11 WLANs 总被引:1,自引:0,他引:1
Jen-Jee Chen Yu-Chee Tseng Hung-Wei Lee 《Communications Letters, IEEE》2007,11(8):665-667
IEEE 802.11 wireless networks have gained great popularity. However, handoff is always a critical issue in this area. In this paper, we propose a novel seamless handoff mechanism for IEEE 802.11 wireless networks which support IEEE 802.11i security standard. Our approach consists of a dynamic tunnel establishing procedure and a seamless handoff mechanism. Both intra- and inter-subnet handoff cases are considered in our seamless handoff approach. Our work focuses on handoffs in DHCP-based IP networks rather than mobile IP-supported networks, but the proposed scheme can be easily tailored to mobile IP-supported networks. 相似文献
995.
Yuh‐Min Tseng 《International Journal of Network Management》2007,17(1):3-15
A mobile ad hoc network does not require fixed infrastructure to construct connections among nodes. Due to the particular characteristics of mobile ad hoc networks, most existing secure protocols in wired networks do not meet the security requirements for mobile ad hoc networks. Most secure protocols in mobile ad hoc networks, such as secure routing, key agreement and secure group communication protocols, assume that all nodes must have pre‐shared a secret, or pre‐obtained public‐key certificates before joining the network. However, this assumption has a practical weakness for some emergency applications, because some nodes without pre‐obtained certificates will be unable to join the network. In this paper, a heterogeneous‐network aided public‐key management scheme for mobile ad hoc networks is proposed to remedy this weakness. Several heterogeneous networks (such as satellite, unmanned aerial vehicle, or cellular networks) provide wider service areas and ubiquitous connectivity. We adopt these wide‐covered heterogeneous networks to design a secure certificate distribution scheme that allows a mobile node without a pre‐obtained certificate to instantly get a certificate using the communication channel constructed by these wide‐covered heterogeneous networks. Therefore, this scheme enhances the security infrastructure of public key management for mobile ad hoc networks. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
996.
Tang C.-W. Shen C.-W. Tseng C.-C. 《Microwave and Wireless Components Letters, IEEE》2007,17(5):340-342
The broadband bandpass filter (BPF) designed with low-temperature co-fired ceramic technology has been proposed in this letter. By adopting a quadruple resonator, the broadband BPF with compact size can be fabricated. A quadruple resonator with metal-insulator-metal capacitors is employed to make inductive and capacitive couplings. The coupling scheme can create two transmission zeros at both sides of passband skirts by appropriately selecting the coupling coefficient. The center frequency and bandwidth ratio of this filter are 3.875 GHz and 50%, respectively. This filter can increase the sensitivity and linearity in the wireless communication system as well 相似文献
997.
Joshi S. Krug C. Heh D. Hoon Joo Na Harris H.R. Jung Woo Oh Kirsch P.D. Majhi P. Byoung Hun Lee Hsing-Huang Tseng Jammy R. Lee J.C. Banerjee S.K. 《Electron Device Letters, IEEE》2007,28(4):308-311
To realize high-mobility surface channel pMOSFETs on Ge, a 1.6-nm-thick SiOX passivation layer between the bulk Ge substrate and HfSiO gate dielectric was introduced. This approach provides a simple alternative to epitaxial Si deposition followed by selective oxidation and leads to one of the highest peak hole mobilities reported for unstrained surface channel pMOSFETs on Ge: 332 cm2 middotV-1middots-1 at 0.05 MV/cm-a 2times enhancement over the universal Si/SiO2 mobility. The devices show well-behaved output and transfer characteristics, an equivalent oxide thickness of 1.85 nm and an ION/IOFF ratio of 3times103 without detectable fast transient charging. The high hole mobility of these devices is attributed to adequate passivation of the Ge surface 相似文献
998.
Shin-Mu Tseng Ching-Fu Tsui 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》2004,34(6):2480-2485
In this correspondence, we address the issue of efficiently mining multilevel and location-aware associated service patterns in a mobile web environment. In terms of multilevel concept, we consider the complex problem that locations and services are of hierarchical structures. We propose a new data mining method named two-dimensional multilevel (2-DML) association rules mining, which can efficiently discover the associated service request patterns by taking into account the multilevel properties of locations and services. The discovered patterns can be effectively utilized in real applications like location-based and personalized services. To the best of our knowledge, this is the first work addressing this research issue. Some variations of the 2-DML method with different properties in terms of execution efficiency and memory efficiency were also developed. Through empirical evaluation, the proposed methods are shown to deliver good performance in terms of efficiency and scalability under various system conditions. 相似文献
999.
1000.
Nonlinear control of interior permanent-magnet synchronous motor 总被引:1,自引:0,他引:1
Rahman M.A. Vilathgamuwa D.M. Uddin M.N. King-Jet Tseng 《Industry Applications, IEEE Transactions on》2003,39(2):408-416
This paper presents a novel speed control technique for an interior permanent-magnet synchronous motor (IPMSM) drive based on newly developed adaptive backstepping technique. The proposed stabilizing feedback law for the IPMSM drive is shown to be globally asymptotically stable in the context of Lyapunov theory. The adaptive backstepping technique takes system nonlinearities into account in the control system design stage. The detailed derivations of the control laws have been given for controller design. The complete IPMSM drive incorporating the proposed backstepping control technique has been successfully implemented in real-time using digital signal processor board DS1102 for a laboratory 1-hp motor. The performance of the proposed drive is investigated both in experiment and simulation at different operating conditions. It is found that the proposed control technique provides a good speed tracking performance for the IPMSM drive ensuring the global stability. 相似文献