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121.
Antoniades N. Boskovic A. Tomkos I. Madamopoulos N. Lee M. Roudas I. Pastel D. Sharma M. Yadlowsky M.J. 《Selected Areas in Communications, IEEE Journal on》2002,20(1):149-165
This paper demonstrates the use of computer simulation for topological design and performance engineering of transparent wavelength-division multiplexing metropolitan-area networks. Engineering of these networks involves the study of various transport-layer impairments such as amplifier noise, component ripple, chirp/dispersion, optical crosstalk, waveform distortion due to filter concatenation, fiber nonlinearities, and polarization effects. A computer simulation methodology composed of three main simulation steps is derived and implemented. This methodology obtains performance estimations by applying efficient wavelength-domain simulations on the entire network topology, followed by time-/frequency-domain simulations on selected paths of the network and finally Q-budgeting on an identified worst case path. The above technique provides an efficient tool for topological design and network performance engineering. Accurate simulation models are presented for each of the performance impairments, and the computer simulation methodology is used for the design and engineering of a number of actual metro network architectures 相似文献
122.
Cheul-Ro Lee 《Journal of Electronic Materials》2002,31(4):327-331
We have investigated the growth characteristics of n-Al0.15Ga0.85N:Si/GaN and the electronic properties of Au/n-Al0.15Ga0.85N:Si diode structures grown by metal-organic chemical vapor deposition (MOCVD) with various Si incorporations. The Al0.15Ga0.85N:Si layers were grown on undoped GaN/sapphire (0001) epitaxial layers in a horizontal MOCVD reactor at the reduced pressure
of 300 torr. The mirrorlike surface, free of defects, such as cracks or hillocks, can be seen in the undoped Al0.15Ga0.85N epilayer, which was grown without any intentional flow of SiH4. However, many cracks are observed in the n-Al0.15Ga0.85N:Si, which was grown with Si incorporation above 1.0 nmol/min. While Au/n-Al0.15Ga0.85N:Si diodes having low incorporation of Si showed retively good rectifying behavior, the samples having high Si incorporation
exhibited leaky current-voltage (I-V) behavior. Particularly, the Au/n-Al0.15Ga0.85N:Si structure grown with Si incorporation above 1.0 nmol/min cannot be used for electrical rectification. Both added tunneling
components and thermionic emission influence the current transport at the Au/n-Al0.15Ga0.85N:Si barrier when Si incorporation becomes higher. 相似文献
123.
Seong-Ku Kim Joon Kyu Lee Yong-Mo Kim Jae-Hyun Ahn 《Journal of Mechanical Science and Technology》2002,16(7):1009-1018
The Representative Interactive Flamelet (RIF) concept has been applied to numerically simulate the combustion processes and
pollutant formation in the direct injection diesel engine. Due to the ability for interactively describing the transient behaviors
of local flame structures with CFD solver, the RIF concept has the capabilities to predict the auto-ignition and subsequent
flame propagation in the diesel engine combustion chamber as well as to effectively account for the detailed mechanisms of
soot formation, NOX formation including thermal NO path, prompt and nitrous NOX formation, and reburning process. Special emphasis is given to the turbulent combustion model which properly accounts for
vaporization effects on the mixture fraction fluctuations and the pdf model. The results of numerical modeling using the RIF
concept are compared with experimental data and with numerical results of the commonly applied procedure which the low-temperature
and high-temperature oxidation processes are represented by the Shell ignition model and the eddy dissipation model, respectively.
Numerical results indicate that the RIF approach including the vaporization effect on turbulent spray combustion process successfully
predicts the ignition delay time and location as well as the pollutant formation. 相似文献
124.
A mechanistic modeling of critical heat flux (CHF) in upflow boiling at low qualities is performed. The developed model is based on a physical criterion of CHF occurrence and a mechanism limiting the thermal transport between a stagnant bubbly layer and bulk stream. The mechanism can be mathematically formulated by coupling the equation of limiting mixing mass flux, which is derived from momentum balance equations in two regions, with local mass and energy balance equations on the bubbly layer. The resulting form of the model is represented by a general and straightforward CHF formula involving two empirical constants related to the void fraction and the thickness of the bubbly layer. The predictions agree well with the extensive CHF data of water in uniformly heated tubes. 相似文献
125.
Mountfield K. Mitchell P. Lee J.-W. Demczyk B. Artman J. 《IEEE transactions on magnetics》1987,23(5):2037-2039
A sequence of Co78 Cr22 films, 500 nm in thickness, was prepared by deposition on glass in a modified Varian D.C. magnetron S-gun sputtering system. The substrate temperature during deposition, Ts , was fixed at various values with an upper limit of 300°C. Specimens were examined by VSM, TM, FMR and TEM. Ms rises significantly with increasing Ts , peaking at 200°C at 370 emu/cm3. The effective volume-averaged anisotropy drops for Ts >110°C from +1.6 KOe to progressively negative values (-4.3 KOe at 300°C). From FMR we find indications of the presence, in addition to the transition and bulk layers, of a highly negative anisotropy constituent (sim-11.5 KOe anisotropy field). This resonance appears at Ts values of 150°C and above. TEM plane and cross-section views taken on a Ts = 150°C specimen show islands composed of tilted columns within the bulk. For vertical recording, specimens prepared at Ts values between 50 and 100°C are recommended. On the other hand, for longitudinal recording applications, films prepared at Ts values above 250°C would seem to be appropriate. 相似文献
126.
The behavior of two series of concrete slabs exposed to sulfate-bearing soils was investigated by a numerical model called
STADIUM. In addition to the diffusion of ions and moisture, the model also accounts for the effects of dissolution/precipitation
reactions on the transport mechanisms. The simulations yielded by the model were compared to the actual degradation of the
slabs after 8 years of exposure. The microstructural alterations of concrete resulting from the penetration of magnesium,
chloride and sulfate ions were studied by backscatter mode scanning electron microscope observations and energy-dispersive
X-ray analyses. The comparison of both series of data indicates that the model can reliably predict the various features of
the microstructural alterations of concrete.
Editorial Note Laval University (Canada) is a RILEM Titular Member. Prof. J. Marchand was awarded the 2000 Robert L'Hermite Medal. He is Editor in Chief for Concrete Science and Engineering and Associate Editor for Materials and Structures. He participates in RILEM TC 186-ISA ‘Internal Sulfate attack’. 相似文献
Résumé Le comportement de deux séries de dalles sur sol en béton exposées à des sols chimiquement agressifs a été étudié à l'aide d'un code de calcul numérique appelé STADIUM. Ce modèle permet de décrire le transport couplé de l'eau et des ions dans des matériaux poreux non-saturés en prenant en considération l'influence des réactions chimiques. Les résultats des simultations de la dégradation du béton après huit ans d'exposition à des ions chlore, sulfate et magnésium. Les observations ont été réalisées par microscopie électronique à balayage. Des analyses par dispersion des rayons X ont également été effectuées. Les données démontrent clairement que le modèle perment de prédire avec précision le comportement du béton soumis à différents types d'agression chimique.
Editorial Note Laval University (Canada) is a RILEM Titular Member. Prof. J. Marchand was awarded the 2000 Robert L'Hermite Medal. He is Editor in Chief for Concrete Science and Engineering and Associate Editor for Materials and Structures. He participates in RILEM TC 186-ISA ‘Internal Sulfate attack’. 相似文献
127.
Flame structure and NO emission characteristics in counterflow diffusion flame of blended fuel of H2/CO2/Ar have been numerically simulated with detailed chemistry. The combination of H2, CO2 and Ar as fuel is selected to clearly display the contribution of hydrocarbon products to flame structure and NO emission characteristics due to the breakdown of CO2. A radiative heat loss term is involved to correctly describe the flame dynamics especially at low strain rates. The detailed chemistry adopts the reaction mechanism of GRI 2.11, which consists of 49 species and 279 elementary reactions. All mechanisms including thermal, NO2, N2O and Fenimore are taken into account to separately evaluate the effects of CO2 addition on NO emission characteristics. The increase of added CO2 quantity causes flame temperature to fall since at high strain rates a diluent effect is prevailing and at low strain rates the breakdown of CO2 produces relatively populous hydrocarbon products and thus the existence of hydrocarbon products inhibits chain branching. It is also found that the contribution of NO production by N2O and NO2 mechanisms are negligible and that thermal mechanism is concentrated on only the reaction zone. As strain rate and CO2 quantity increase, NO production is remarkably augmented. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
128.
Chang-Ho Lee Sutono A. Sangwoo Han Kyutae Lim Pinel S. Tentzeris E.M. Laskar J. 《Advanced Packaging, IEEE Transactions on》2002,25(3):374-384
Presents design, implementation, and measurement of a three-dimensional (3-D)-deployed RF front-end system-on-package (SOP) in a standard multi-layer low temperature co-fired ceramic (LTCC) technology. A compact 14 GHz GaAs MESFET-based transmitter module integrated with an embedded bandpass filter was built on LTCC 951AT tapes. The up-converter MMIC integrated with a voltage controlled oscillator (VCO) exhibits a measured up-conversion gain of 15 dB and an IIP3 of 15 dBm, while the power amplifier (PA) MMIC shows a measured gain of 31 dB and a 1-dB compression output power of 26 dBm at 14 GHz. Both MMICs were integrated on a compact LTCC module where an embedded front-end band pass filter (BPF) with a measured insertion loss of 3 dB at 14.25 GHz was integrated. The transmitter module is compact in size (400 /spl times/ 310 /spl times/ 35.2 mil/sup 3/), however it demonstrated an overall up-conversion gain of 41 dB, and available data rate of 32 Mbps with adjacent channel power ratio (ACPR) of 42 dB. These results suggest the feasibility of building highly SOP integrated RF front ends for microwave and millimeter wave applications. 相似文献
129.
130.
The Distribution of Active ingredients in Supported Catalysts Prepared by Impregnation 总被引:1,自引:0,他引:1
Supported catalysts, one of the commonest forms of heterogeneous catalysts in practical use, consist of small crystallites of a catalytically active component dispersed in a porous support of high surface area. Impregnation of the support with an aqueous solution of a compound containing the appropriate catalytic component is an important and frequently used method of preparing this type of catalyst. A nonaqueous solution should be used if the sup port surface is hydrophobic or if hydrolysis of the support surface is to be avoided. In its simplest form, this impregnation method involves three steps: (1) contacting the support with impregnating solution for a certain period of time, (2) drying the support to remove the imbibed liquid, and (3) activating the catalyst by calcination, reduction, or other appropriate treatment. 相似文献