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1.
L. Vu‐Quoc V. Srinivas Y. Zhai 《International journal for numerical methods in engineering》2003,58(3):397-461
We establish a systematic methodology to design and analyse electromagnetic components such as advanced multilayer ceramic capacitors (MLCCs) using the finite element (FE) method. We employ a coupled formulation to compute the interaction between the electric and magnetic fields. Unlike a linear distribution of current assumed in the circuit model, an accurate electrostatic solution to model the entire advanced MLCCs (4 × 4 × 27 = 432 cells) is presented. The FE solution is used to compute the lumped parameters for a range of frequencies. These lumped parameters are then used to compute the parasitic elements of the MLCCs. We introduce two algorithms to efficiently analyse the behaviour of a capacitor with changing frequency. The lower frequency (much below the self‐resonant frequency of the capacitor) algorithm separates the effect of the electric and magnetic fields and reduces the computational effort required to solve the FE problem, whereas, the high‐frequency algorithm couples the effect between the electric and the magnetic fields. We use these algorithms in conjunction with a new multiple scale technique to effectively determine the small values of R, L and C in MLCCs. The formulation, the implementation, and the numerical results demonstrate the efficacy of the present FE formulation and establish a systematic methodology to design and analyse advanced electromagnetic components. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
2.
Zukerman M. Wong E.W.M. Rosberg Z. Gyu Myoung Lee Hai Le Vu 《Communications Letters, IEEE》2004,8(2):116-118
We provide teletraffic models for loss probability evaluation of optical burst switching (OBS). We show that the popular Engset formula is not exact for OBS modeling and demonstrate that in certain cases it is not appropriate. A new exact model is provided. The various models are compared using numerical results for various OBS alternatives with and without burst segmentation. 相似文献
3.
The network interconnection and its regulation consist in solving the following dilemma: increase competition and preserve the universal service through access charges, which symbolizes today institutional organization within the telecommunication industry. This paper presents some of the economic and social factors that drive the interconnection policies namely ona (open network architecture) in the United States, or onp (open network provision) in Europe. In the first section, we list some social and economical issues related to open network policies. In the second section, we study the different answers brought up by the regulator through alternative interconnection price formulas. In conclusion, we discuss the stakes and risks of interconnection, while the technological evolution of network introduces intelligent software in switching équipement and implements the tremendous abilities of the digital broadband networks. 相似文献
4.
The authors present an adaptive space-time reduced-length minimum mean-squared error (MMSE) receiver to suppress co-channel interference in the near-far environment for an asynchronous direct-sequence code-division multiple-access (DS/CDMA) system. Simulation results show that better bit-error rate and faster and more stable convergence are achieved over the existing full- and reduced-length MMSE receivers 相似文献
5.
The purpose of the study was to identify psychiatric symptoms, neurological impairments, and situational factors associated with the emergence of violence and with its persistence. Psychiatric symptoms were assessed in newly admitted physically assaultive psychiatric patients and nonviolent controls. Patients were than evaluated for 4 weeks to determine the persistence or resolution of these physical assaults. Patients who showed marked resolution of assaults were classified as transiently violent (n = 41), and those who remained assaultive throughout were categorized as persistently violent (n = 34). At the end of 4 weeks, all patients received a comprehensive psychiatric and neurological assessment. Physical assaults were associated initially with prominent positive psychotic symptoms. Both transiently and persistently violent patients were more psychotic than the nonviolent controls; however transiently violent patients showed better resolution of these symptoms over the 4 weeks. They also evidenced less frontal lobe impairment on the neurological examination than the persistently violent patients. The two violent groups differed in their susceptibility to environmental influences: the surrounding ward agitation fostered physical assaults in transiently but not in persistently violent patients. This differentiation between transiently and persistently violent patients has major implications for the comprehensive treatment of violent behavior. 相似文献
6.
Newlin D.P. Pham A.-V.H. Harriss J.E. 《Components and Packaging Technologies, IEEE Transactions on》2002,25(3):506-510
We present the design and development of an ultra-violet (UV) LIGA (a German acronym for electroplating, lithography and molding) micromachining process on silicon substrates at microwave/millimeter wave frequencies. The process employs an ultra-thick negative photoresist SU-8 that can be spin-coated and processed using conventional lithography techniques. Using this process, we have developed micromachined coplanar waveguide (CPW) interconnects on Si substrates. The conductor-backed micromachined CPW on Si (7.2 /spl Omega/-cm) achieves a measured attenuation of 0.18 dB/cm at 20 GHz. 相似文献
7.
Gerosa G. Gary S. Dietz C. Dac Pham Hoover K. Alvarez J. Sanchez H. Ippolito P. Tai Ngo Litch S. Eno J. Golab J. Vanderschaaf N. Kahle J. 《Solid-State Circuits, IEEE Journal of》1994,29(12):1440-1454
A 28 mW/MHz at 80 MHz structured-custom RISC microprocessor design is described. This 32-b implementation of the PowerPC architecture is fabricated in a 3.3 V, 0.5 μm, 4-level metal CMOS technology, resulting in 1.6 million transistors in a 7.4 mm by 11.5 mm chip size. Dual 8-kilobyte instruction and data caches coupled to a high performance 32/64-b system bus and separate execution units (float, integer, loadstore, and system units) result in peak instruction rates of three instructions per clock cycle. Low-power design techniques are used throughout the entire design, including dynamically powered down execution units. Typical power dissipation is kept under 2.2 W at 80 MHz. Three distinct levels of software-programmable, static, low-power operation-for system power management are offered, resulting in standby power dissipation from 2 mW to 350 mW. CPU to bus clock ratios of 1×, 2×, 3×, and 4× are implemented to allow control of system power while maintaining processor performance. As a result, workstation level performance is packed into a low-power, low-cost design ideal for notebooks and desktop computers 相似文献
8.
An experimental investigation under cold condition was made to study the effects of some operating/design parameters and non-mechanical L valve configuration on the solid circulation rate in a 4.5 m tall, 0.15 m diameter circulating fluidized bed with riser flow rate varying from 1400 litres/min to 2000 litres/min and bed inventory from 15 kg to 25 kg of sand of average sizes 200 μm, 400 μm and 500 μm. Solid circulation rate was estimated by measuring velocity of sand particle travelling through a vertical Perspex tube section at the bottom of the return leg. It was found to be in the range of 2.8 to 12.3kg/m2s, 0.07 to 9.1kg/m2s and 0.12 to 2.23kg/m2s for sand sizes of 200 μm, 400 μm and 500 μm, respectively for a horizontal L valve. Two mathematical correlations have been developed from the experimental results to predict solid circulation rate as a function of riser flow rate, aeration flow rate, total bed inventory and particle size used. 相似文献
9.
Yi Fang Vu Anh Pham Takeshi Matsuura J. P. Santerre Roberto M. Narbaitz 《应用聚合物科学杂志》1994,54(12):1937-1943
Polyethersulfone (PES) membranes using different evaporation periods were fabricated by the phase-inversion method. Pervaporation experiments were conducted for chloroform/water mixtures to determine the selectivity of the PES membranes. It was found that chloroform could be concentrated in the permeate from chloroform/water binary feed mixtures by PES membranes prepared using longer evaporation periods, and that the selectivity of PES membranes in pervaporation could be reversed by shorter evaporation periods. This study also showed that by adding surface-modifying macromolecules (SMM) up to 1 wt % into the casting solution, chloroform enrichment in the permeate could be increased by 50%. Chloroform enrichment increased with increasing SMM concentration until an optimal value, after which the enrichment decreased. © 1994 John Wiley & Sons, Inc. 相似文献
10.
Krivelevich M. Sudakov B. Vu V.H. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(7):1812-1815
We prove a general recursive inequality concerning /spl mu//sup */(R), the asymptotic (least) density of the best binary covering codes of radius R. In particular, this inequality implies that /spl mu//sup */(R)/spl les/e/spl middot/(RlogR+logR+loglogR+2), which significantly improves the best known density 2/sup R/R/sup R/(R+1)/R!. Our inequality also holds for covering codes over arbitrary alphabets. 相似文献