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Faris G.W.,SRI International | Markosyan A.,Stanford University | Porter C.L.,Engineering Quadrangle | Doshay S.,Stanford University
Optics Letters | Year: 2014

We have demonstrated two-tone frequency-modulation (FM) stimulated Rayleigh spectroscopy. This method can provide high spectral resolution (∼1 MHz), excellent pump/probe detuning accuracy, and near-shot-noise-limited signal-to-noise ratios using a single narrowband laser as the master oscillator. Pump/probe detuning and FM sideband generation are produced with an electro-optic modulator. A double-pass two-rod Nd:YAG amplifier provides peak powers near 1 kW for the pump beam. Unlike with two-tone FM absorption spectroscopy, the phase signal is retained for two-tone FM Rayleigh spectroscopy. Measurements confirm that the shape of the phase component of the stimulated thermal Rayleigh peak agrees with theory. © 2014 Optical Society of America. Source

Mochizuki B.,201 N. Goodwin Avenue | Kiyak F.,201 N. Goodwin Avenue | Keller E.,Engineering Quadrangle | Caesar M.,201 N. Goodwin Avenue
Computer Networks | Year: 2011

Higher-level Internet protocols are typically designed to be implemented in software. As scaling challenges increase, however, conventional software-based protocol processor architectures start to hit performance walls. Recent advances in programmable hardware and high-level hardware description languages provide the opportunity to implement some of these protocols directly in hardware. Such implementations allow designs to take advantage of the parallelization and customizability of the underlying hardware to improve performance, however, these potential performance gains are reliant on being able to efficiently and effectively process the protocol in hardware. In this paper, we suggest that hardware-based implementations should be considered while designing such protocols. To demonstrate the benefits in this, we study Internet routing, using BGP as a case study. We propose an architecture and logical design for processing BGP in hardware and enumerate sources of complexity and performance bottlenecks. We then compare this to our modified version of BGP which retains the features of BGP but is designed with a hardware implementation in mind. We show that a few changes to the protocol improve processing time and throughput by an order of magnitude. © 2010 Elsevier B.V. All rights reserved. Source

Ombrello T.,Engineering Quadrangle | Won S.H.,Engineering Quadrangle | Ju Y.,Engineering Quadrangle | Williams S.,Air Force Research Lab
Combustion and Flame | Year: 2010

The thermal and kinetic effects of O3 on flame propagation were investigated experimentally and numerically by using C3H8/O2/N2 laminar lifted flames. Ozone produced by a dielectric barrier plasma discharge was isolated and measured quantitatively by using absorption spectroscopy. Significant kinetic enhancement by O3 was observed by comparing flame stabilization locations with and without O3 production. Experiments at atmospheric pressures showed an 8% enhancement in the flame propagation speed for 1260ppm of O3 addition to the O2/N2 oxidizer. Numerical simulations showed that the O3 decomposition and reaction with H early in the pre-heat zone of the flame produced O and OH, respectively, from which the O reacted rapidly with C3H8 and produced additional OH. The subsequent reaction of OH with the fuel and fuel fragments, such as CH2O, provided chemical heat release at lower temperatures to enhance the flame propagation speed. It was shown that the kinetic effect on flame propagation enhancement by O3 reaching the pre-heat zone of the flame for early oxidation of fuel was much greater than that by the thermal effect from the energy contained within O3. For non-premixed laminar lifted flames, the kinetic enhancement by O3 also induced changes to the hydrodynamics at the flame front which provided additional enhancement of the flame propagation speed. The present results will have a direct impact on the development of detailed plasma-flame kinetic mechanisms and provided a foundation for the study of combustion enhancement by O2(a1Δg) in part II of this investigation. © 2010 The Combustion Institute. Source

Ombrello T.,Engineering Quadrangle | Won S.H.,Engineering Quadrangle | Ju Y.,Engineering Quadrangle | Williams S.,Air Force Research Lab
Combustion and Flame | Year: 2010

The isolated effect of O2(a1Δg) on the propagation of C2H4 lifted flames was studied at reduced pressures (3.61kPa and 6.73kPa). The O2(a1Δg) was produced in a microwave discharge plasma and was isolated from O and O3 by NO addition to the plasma afterglow in a flow residence time on the order of 1s. The concentrations of O2(a1Δg) and O3 were measured quantitatively through absorption by sensitive off-axis integrated-cavity-output spectroscopy and one-pass line-of-sight absorption, respectively. Under these conditions, it was found that O2(a1Δg) enhanced the propagation speed of C2H4 lifted flames. Comparison with the results of enhancement by O3 found in part I of this investigation provided an estimation of 2-3% of flame speed enhancement for 5500ppm of O2(a1Δg) addition from the plasma. Numerical simulation results using the current kinetic model of O2(a1Δg) over-predicts the flame propagation enhancement found in the experiments. However, the inclusion of collisional quenching rate estimations of O2(a1Δg) by C2H4 mitigated the over-prediction. The present isolated experimental results of the enhancement of a hydrocarbon fueled flame by O2(a1Δg), along with kinetic modeling results suggest that further studies of CnHm+O2(a1Δg) collisional and reactive quenching are required in order to correctly predict combustion enhancement by O2(a1Δg). The present experimental results will have a direct impact on the development of elementary reaction rates with O2(a1Δg) at flame conditions to establish detailed plasma-flame kinetic mechanisms. © 2010 The Combustion Institute. Source

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