An analytic model for the performance evaluation of space-division asynchronous transfer mode (ATM) switches is presented. This model assumes that the switch has a fixed capacity of m, where 1/spl les/m/spl les/N (N i...
详细信息
An analytic model for the performance evaluation of space-division asynchronous transfer mode (ATM) switches is presented. This model assumes that the switch has a fixed capacity of m, where 1/spl les/m/spl les/N (N is the number of trunks). Other important parameters include arrival rate and buffer sizes. Numerical solutions for the maximum throughput, cell delay, and cell loss probability are given with simulation being utilized in order to validate the analytic model. For independent and identical Bernoulli arrivals, the study shows that the contention processes can be modeled as discrete M/D/m (FIFO or Random) queues, while input queues can be modeled by Geom/G/1 queues, and the output queues are G/sup [X]//D/1 queues. A closed-form approximation for cell delay when m>2 is given. The result shows that the performance of switches with a small capacity can approach that of output queueing. The model and result can be used for switch design analysis and higher layer performance models.
Fiber optic oblique incidence reflectometry has been demonstrated to be a simple and accurate method for measuring the optical properties, μa and μs', of turbid media such as biological tissues [1,2]. After samp...
详细信息
We present a comparative analysis of bandwidth access control schemes under nonstationary traffic conditions for heterogeneous circuit-mode traffic offered to a B-ISDN network link. A unified model for analysing the b...
详细信息
We present a comparative analysis of bandwidth access control schemes under nonstationary traffic conditions for heterogeneous circuit-mode traffic offered to a B-ISDN network link. A unified model for analysing the behavior of several bandwidth access control schemes is developed using a Markov process model with acceptance functions. Numerical techniques are used to solve the associated Chapman-Kolmogorov equations and determine the nonstationary behavior. Performance results are given for several common bandwidth access control schemes, namely: complete sharing, complete partitioning, partial sharing, classical trunk reservation, and the probabilistic reservation policy. It is shown that the use of the average arrival rate to estimate the average connection blocking rate may be an underestimate for a system with a time varying arrival process. Also, it is found that a nonstationarity in one traffic class arrival process can impact other stationary traffic classes and the degree of variability depends on the particular access control scheme.
The advantages of single electron devices with asymmetrical tunnel barriers (ATBs), proposed by the authors, over conventional single electron devices with symmetrical tunnel barriers (STBs) are discussed by referring...
详细信息
The advantages of single electron devices with asymmetrical tunnel barriers (ATBs), proposed by the authors, over conventional single electron devices with symmetrical tunnel barriers (STBs) are discussed by referring to the features of ATBs and the results of computer simulation of the performance of tunnel-junction-load SET logic and turnstile devices. Experimental observation of a Coulomb staircase and asymmetrical tunnel characteristics in ATBs fabricated with GaAs/AlGaAs heterostructures are also reported.
The progress in understanding wafer-fused vertical-cavity lasers and improvements in fabrication techniques have led to the realization of the first room-temperature continuous-wave operating 1.54-/spl mu/m vertical-c...
详细信息
The progress in understanding wafer-fused vertical-cavity lasers and improvements in fabrication techniques have led to the realization of the first room-temperature continuous-wave operating 1.54-/spl mu/m vertical-cavity lasers. By demonstrating continuous-wave operation at room temperature using vertical-cavity lasers fabricated by two wafer fusion steps, we have shown that wafer fusion is a viable technique. The lasers comprise strain compensated InGaAsP quantum-well active layers sandwiched between two AlGaAs/GaAs quarter-wave mirrors. Characteristics discussed include cavity losses, the gain-current density relationship, and voltage-current characteristics.
作者:
Kihara, HHiyama, TMiyauchi, HOrtmeyer, THKumamoto UniversityB.E. and M.S. degrees in Electrical Engineering from Kumamoto University in 1986 and 1988
respectively and is currently in the doctoral program at the university. In 1988 he joined Kyushu Electric Power Co. and is working in the Research Division. B.E.
M.S. and Ph.D. degrees in Electrical Engineering from Kyoto University Japan in 1969 1971 and 1980 respectively. He joined Kumamoto University in 1971 and he has been a Professor of Electrical Engineering and Computer Science since 1989. During the period of June 1985 through September 1986 he was at Clarkson University and was involved with power system harmonics research. His current interests include intelligent control of electric power systems using fuzzy logic control scheme and neural network measurement and real time control of photovoltaic systems and harmonic analysis in distribution systems. He is a senior member of IEEE SICE of Japanand Japan Solar Energy Society.B.E.
M.S. and Ph.D. degrees in Electrical Engineering from Kyoto University in 1981 1983 and 1991 respectively. He joined Kyoto University in 1985. Since 1993 he has been at Kumamoto University and currently is an Associate Professor of Electrical Engineering and Computer Science. His current interests include stabilizing control of electric power system and applications of the Superconducting Magnetic Energy Storage (SMES) to electric power systems. He is a member of IEEE and Institute of Systems Control and Information Engineers of Japan. B.S.E.E. degree in 1972
his M.S.E.E. degree in 1977 and Ph.D. degree in 1980 all from Iowa State University. From 1972 to 1976 he worked in the Operational Analysis Department Commonwealth Edison Company Chicago Illinois. Since 1979 he has been at Clarkson University Potsdam N.Y. where he is a Professor of Electrical Engineering. During the period of July 1993 to June 1994 he was also a Visiting Professor at Kumamoto University Kumamoto Japan. His current interests include harmonic performance po
This paper presents a new switching control scheme for static var compensator (SVC) using fuzzy logic control rules to enhance the overall stability of electric power systems. In addition, the coordination with power ...
详细信息
This paper presents a new switching control scheme for static var compensator (SVC) using fuzzy logic control rules to enhance the overall stability of electric power systems. In addition, the coordination with power system stabilizers (PSS) is also considered to achieve a wider stable region. An SVC is set on one of the busbars in the transmission system, where the real power flow signal is utilized at the location of the SVC to determine the firing angle of the thyristor switch. The switching control scheme is simple so as not to require heavy computation on the microcomputer based switching controller. The PSSs are also set on the generators in the study system. Simulation results show the effectiveness of the proposed fuzzy logic switching control scheme for the SVC. The coordination between SVC and PSS is also effective to enlarge the stable region.
Iterative methods for tomographic image reconstruction often converge slowly. Preconditioning methods can often accelerate gradient-based iterations. Previous preconditioning methods for PET reconstruction have used e...
详细信息
Iterative methods for tomographic image reconstruction often converge slowly. Preconditioning methods can often accelerate gradient-based iterations. Previous preconditioning methods for PET reconstruction have used either diagonal or Fourier-based preconditioners. Fourier-based preconditioners are well suited to problems with near-circulant Hessian matrices. However, due to the nonuniform Poisson noise variance in PET, the circulant approximation to the Hessian is suboptimal. This paper shows that a particular combined diagonal/Fourier preconditioner yields a more accurate approximation to the Hessian and gives significantly faster convergence rates than does either preconditioner used alone.
A versatile signal processor has been designed that can perform multiple rotations, multiplications and additions within one clock cycle. The computational elements of this processor include four pipelined CORDIC rota...
详细信息
A versatile signal processor has been designed that can perform multiple rotations, multiplications and additions within one clock cycle. The computational elements of this processor include four pipelined CORDIC rotators, two pipelined fast multipliers and two adders. A combination of register files, SRAM, and ROM provides on chip storage for coefficients, running sums and programs. The chip architecture and its applicability to complex valued signal processing tasks are discussed.
Catheter based ablation of cardiac tissue has been shown to provide an immediate and long lasting cure for cardiac arrhythmia. However, the procedure does not always allow placing the catheter in close proximity to th...
详细信息
Catheter based ablation of cardiac tissue has been shown to provide an immediate and long lasting cure for cardiac arrhythmia. However, the procedure does not always allow placing the catheter in close proximity to the pathological tissues requiring ablation. Use of non-invasive focused ultrasound ablation in the moving heart is an attractive potential alternative to catheter based ablative therapy. In this paper, initial studies have been performed to explore the feasibility of using ultrasound phased array technology for this application. A 3-D treatment planning software package was developed to study the available acoustic windows allowing ultrasound to be focused on the myocardium. Numerical simulation studies of the feasibility of precise beam forming by propagating ultrasound around the ribs shows that the beam, even though formed by an irregularly shaped subset of phased array elements not blocked by ribs and air, was very sharply focused at the target. Using invasive phase aberration correction algorithms developed in the authors' lab, experiments with pork and human rib phantoms confirm the ability to precisely form beams with phased array through the available noncontiguous windows.
暂无评论