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pulses generated in the visible at the repetition rate 40 kHz using optical parametric amplifiers

By Ernest Rice,2014-01-25 13:44
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pulses generated in the visible at the repetition rate 40 kHz using optical parametric amplifiers...

    planar measurements of transient phenomena in a partially pre-mixed swirl flame in a gas turbine model combustor Original Research Article

    Combustion and Flame

    This paper presents observations and analysis of the time-dependent behavior of a 10 kW partially pre-mixed, swirl-stabilized methaneair flame exhibiting self-excited thermo-acoustic oscillations. This analysis is based on a series of measurements wherein particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) of the OH radical were performed simultaneously at 5 kHz repetition

    *rate over durations of 0.8 s. Chemiluminescence imaging of the OH radical was performed separately,

    also at 5 kHz over 0.8 s acquisition runs. These measurements were of sufficient sampling frequency and duration to extract usable spatial and temporal frequency information on the medium to large-scale flow-field and heat-release characteristics of the flame. This analysis is used to more fully characterize the interaction between the self-excited thermo-acoustic oscillations and the dominant flow-field structure of this flame, a precessing vortex core (PVC) present in the inner recirculation zone. Interpretation of individual measurement sequences yielded insight into various physical phenomena and the underlying mechanisms driving flame dynamics. It is observed for this flame that location of the reaction zone tracks large-scale fluctuations in axial velocity and also conforms to the passage of large-scale vortical structures through the flow-field. Local extinction of the reaction zone in regions of persistently high principal compressive strain is observed. Such extinctions, however, are seen to be self healing and thus do not induce blowout. Indications of auto-ignition in regions of unburned gas near the exit are also observed. Probable auto-ignition events are frequently observed coincident with the centers of large-scale vortical structures, suggesting the phenomenon is linked to the enhanced mixing and longer residence times associated with fluid at the core of the PVC as it moves through the flame. Article Outline

    1. Introduction

    2. Burner and flames

    3. Measurement technique

3.1. Planar laser-induced fluorescence

    3.2. Particle image velocimetry

    4. Results and discussion

    4.0.1. Power spectra

    4.1. POD analysis

    5. Phenomenological data

    5.1. OH-PLIF

    5.2. OH gradient field

    5.3. Flame location

    5.4. Flamevortex Interaction

    5.5. Local extinction

    5.6. Isolated OH pockets

    6. Conclusions

    Acknowledgements

    References

    focusing of acoustical waves generated by a parametric array onto a concave reflecting surface Original Research Article

    Comptes Rendus Mécanique

    The present Note is devoted to the study of the so-called cuspidal caustic at the surface of a hemi-cylindrical reflector illuminated with plane waves. In order to generate low frequency (e.g. in the range of 4 kHz) acoustical plane waves, a commercially available parametric array has been used. It produces powerful ultrasonic carrier waves at 40 kHz which can be electronically modulated between 200 Hz and 10 kHz. Further self-demodulation process during propagation in air generates an ultra-directive acoustical field (i.e. quasi-planar wavefronts) enabling to accurately study the focusing process occurring along the cuspidal caustic. The focusing coefficient can be computed locally by using two numerical tools, on one hand by computing the density of tangent rays to the caustic, and on the other hand by using some numerical results provided by a ray tracing algorithm. Some preliminary

    experimental data are then provided in order to validate the numerical predictions (spatial position of the caustic and focusing coefficient). To cite this article: B. Castagnède et al., C. R. Mecanique 337

    (2009).

    Résumé

    Ce travail est consacré à l'étude de la caustique en ? corne de croissant ? à la surface d'un réflecteur hémi-cylindrique illuminée par des ondes planes. En vue de générer des ondes planes acoustiques de basse fréquence (autour de 4 kHz), une antenne paramétrique disponible commercialement a été utilisée. Elle produit une onde ultrasonore porteuse de forte puissance à 40 kHz qui peut-être modulée en amplitude de façon électronique entre 200 Hz et 10 kHz. Le processus d'auto-démodulation au cours de la propagation dans l'air permet de générer un champ acoustique ultra-directif (c'est-à-dire des ondes quasi-planes) autorisant une étude précise de la focalisation le long de la caustique. Le coefficient de focalisation est alors calculé localement, en utilisant deux approches numériques différentes, d'une part en calculant la densité de rayons tangents à la caustique et d'autre part en mettant en œuvre une méthode de calcul du type tracé de rayons. Des résultats expérimentaux préliminaires sont alors décrits avec l'objectif de valider les prédictions numériques (position spatiale de la singularité et coefficient de focalisation).

    Spatiotemporal reconstruction of the auditory steady-state response to frequency modulation using magnetoencephalography Original Research Article

    NeuroImage

    The aim of this study was to investigate the mechanisms involved in the perception of perceptually salient frequency modulation (FM) using auditory steady-state responses (ASSRs) measured with magnetoencephalography (MEG). Previous MEG studies using frequency-modulated amplitude modulation as stimuli (Luo et al., 2006, 2007) suggested that a phase modulation encoding mechanism exists for low (< 5 Hz) FM modulation frequencies but additional amplitude modulation encoding is required for faster FM modulation frequencies. In this study single-cycle sinusoidal FM stimuli were used to generate the ASSR. The stimulus was either an unmodulated 1-kHz sinusoid or a 1-kHz sinusoid that

    was frequency-modulated with a repetition rate of 4, 8, or 12 Hz. The fast Fourier transform (FFT) of each MEG channel was calculated to obtain the phase and magnitude of the ASSR in sensor-space and

    2multivariate Hotelling's T statistics were used to determine the statistical significance of ASSRs. MEG beamformer analyses were used to localise the ASSR sources. Virtual electrode analyses were used to reconstruct the time series at each source. FFTs of the virtual electrode time series were calculated to obtain the amplitude and phase characteristics of each source identified in the beamforming analyses.

    2Multivariate Hotelling's T statistics were used to determine the statistical significance of these reconstructed ASSRs. The results suggest that the ability of auditory cortex to phase-lock to FM is dependent on the FM pulse rate and that the ASSR to FM is lateralised to the right hemisphere. Article Outline

    Introduction

    Materials and methods

    Participants

    Stimuli

    MEG recording

    Co-registration

    Sensor-space analyses

    Source-space analyses

    Virtual electrode analyses

    2Multivariate Hotelling's T tests

    Results

    Sensor-space results

    Source-space results

    “Whole-head” VLCMV beamformer

    4-Hz FM

    8-Hz FM

    12-Hz FM

    “Half-head” VLCMV beamformer

4-Hz FM

    8-Hz FM

    12-Hz FM

    Virtual electrode results

    “Whole-head” VLCMV beamformer

    “Half-head” VLCMV beamformer

    Discussion

    Evidence of FM processing strategy from sensor-space analyses Possible FM encoding strategies

    Cortical representation of harmonic structure

    Right hemisphere lateralisation of the ASSR for FM

    Choice of FM stimulus

    Comparison of “whole-head” and “half-head” VLCMV beamforming results Failure of the VLCMV beamfomer to localise ASSRs for all FM conditions Choice of statistical thresholding procedure

    Virtual electrode reconstructions of the ASSR

    Summary

    Acknowledgements

    References

6 articles found for: pub-date > 2008 and TITLE-ABSTR-KEY(kHZ and (wind or generate or turbine))

    Electromagnetic cellular interactions Review Article Progress in Biophysics and Molecular Biology

    Chemical and electrical interaction within and between cells is well established. Just the opposite is true

    about cellular interactions via other physical fields. The most probable candidate for an other form of

    cellular interaction is the electromagnetic field. We review theories and experiments on how cells can generate and detect electromagnetic fields generally, and if the cell-generated electromagnetic field can mediate cellular interactions. We do not limit here ourselves to specialized electro-excitable cells. Rather we describe physical processes that are of a more general nature and probably present in almost every type of living cell. The spectral range included is broad; from kHz to the visible part of the electromagnetic spectrum. We show that there is a rather large number of theories on how cells can generate and detect electromagnetic fields and discuss experimental evidence on electromagnetic cellular interactions in the modern scientific literature. Although small, it is continuously accumulating.

    Article Outline

    1. Introduction

    2. Evidence that cells generate electromagnetic fields

    2.1. Type of EMF

    2.2. Measurement of EMF

    2.2.1. History of detection of cellular EMF

    2.2.2. Experimental detection of EMF of biologic origin in infra-red, visible and ultraviolet ranges

    2.2.3. Indirect cellular EMF detection by dielectrophoresis

    2.2.4. Direct electronic detection of cellular EMFs

    2.2.5. Detection of cellular vibration states by spectroscopic techniques

    2.3. Correlation of cellular EMF activity with cellular metabolism, vitality and replication

    2.4. How cells can generate EMFs

    2.4.1. Basis of EMF generation

    2.4.2. Basis for cellular EMF generation

    3. Evidence for cells being affected by electromagnetic fields

    3.1. The effect of EMFs on biological systems

    3.2. How EMFs affect biosystems

    3.2.1. How cells react to non-visible EMFs

    3.2.2. How cells react to EMF in the visible range

    4. Evidence for cells interacting through electromagnetic fields

4.1. Are biological systems really interacting through EMFs?

    4.2. Caveats and obstacles in experiments on cellular EMF interactions

    4.3. How cells interact via EMFs

    5. Conclusion and future prospects

    Acknowledgements

    References

high-repetition rate CH PLIF imaging in turbulent nonpremixed flames Original

    Research Article

    Proceedings of the Combustion Institute

    We report on the development of high-repetition rate planar laser-induced fluorescence (PLIF) imaging of the CH radical in turbulent flames. This paper presents what the authors believe to be the first multi-frame, high-speed CH PLIF image sequences captured in a turbulent nonpremixed jet-flame. The high-repetition rate CH PLIF measurements were made using a combination of a custom pulse burst laser system operating at a 10-kHz repetition rate, an in-house optical parametric oscillator (OPO) with frequency mixing for 390-nm laser pulse generation, and a high-framing rate ICCD camera for high-speed image capture. The 1064-nm output of the pulse burst laser is frequency-tripled (355 nm) and

    ?1used to pump the OPO, which can be operated in a narrow bandwidth (300 MHz) or broadband (4 cm)

    mode. The OPO system produces a burst of laser pulses near 615 nm, which can be subsequently mixed with residual 1064-nm output from the pulse burst laser to generate a series of 390-nm pulses separated by less than 100 μs. The tunable ultraviolet output around 390 nm is then used to excite the BX (0, 0)

    band allowing high-speed image sequences of the CH radical to be acquired from the BX(0, 1),

    AX(1, 1), and AX(0, 0) bands near 430 nm. In this paper, we present results using the narrow bandwidth mode of the laser. By injection seeding the OPO with a single-frequency diode laser, we can obtain spectrally-narrow output at 390-nm, which allows imaging of CH with only 0.4 mJ/pulse of laser energy. Ten-kilohertz-CH PLIF image sequences from a turbulent nonpremixed flame are reported as an example of the potential of this diagnostic system. Although, the signal-to-noise ratio (SNR) is marginal, we discuss future improvements to the system to increase the SNR to levels comparable to that achieved with traditional low-repetition rate systems.

Article Outline

    1. Introduction

    2. Experimental details

    2.1. Pulse burst laser system

    2.2. High-speed CH PLIF imaging

    2.3. Turbulent flame conditions

    3. Results and discussion

    4. Summary and conclusions

    Acknowledgements

    References

Design of high-peak current and narrow pulse driver of laser diode Original

    Research Article

    The Journal of China Universities of Posts and Telecommunications

    This paper presents a laser diode (LD) pulse driving circuit that can generate current pulses of amplitudes range from 6 to 30A, with pulse widths varying from 5 to 100 ns and frequencies varying from 500 Hz to 50 kHz. It is with monostabillity trigger used as pulse shaping component, with power metal-oxide-semiconductor field effect transistors (MOSFETs) as fast switches and power inverter devices, with low voltage power supply that the circuit generates high-peak pulse current. As its structure is simple and easy to understoand and realize, the circuit is of great value to be used to drive pulsed semiconductor laser.

    Air-turbine driven optical low-coherence reflectometry at 28.6-kHz scan repetition rate Original Research Article

    Optics Communications

    An optical low-coherence reflectometer is actuated with an air bearing turbine to show the feasibility of scanning at rates lying typically one order of magnitude above previously reported high-speed scanning systems. The rotation frequency of the air turbine of 427 000 rpm leads to a repetition rate of longitudinal scans of 28.6 kHz. Coherent signals are detected over a distance of 2 mm at a longitudinal scan speed of 175 m/s.

Article Outline

    1. Introduction

    2. Experimental setup

    3. Results and discussion

    4. Conclusions

    Acknowledgements

    References

winter anomaly of 1983/84 as observed in the A3-absorption and 5 kHz

    atmospherics in Central Europe Original Research Article

    Advances in Space Research

    Continuous rubbing between the shaft and surrounding seals or end-glands of electricity generating turbine units can escalate into very severe vibration and costly rotor damage. Therefore such rotorstator

    contacts require early diagnosis so as to minimize the financial consequences of any unplanned shutdowns. Acoustic emissions (AEs) or stress wave monitoring at the bearings has been identified as a sensitive non-destructive monitoring technique for such rub conditions [Electr. Eng. Jpn. 110(2) (1990); IEEE Proc. 6 (2000) 79; Hall and Mba, 14th International Congress on Condition Monitoring and Diagnostic Engineering Management (COMADEM‟2001), Manchester, UK, 2001, p. 21]. However, experimental results from real turbines have been scarce. This paper presents a diagnosis of continuous rotorstator rubbing in an operational 500 MW turbine unit via high frequency AE measurement within a 100 KHz1 MHz ultrasonic band. As detailed by Sato [Electr. Eng. Jpn. 110(2) (1990)] and reported in this paper the onset of a continuous rub contact at a seal/gland was revealed by a sinusoidal modulation within the raw „rf‟ AE response. By synchronous measurement at adjacent bearings, an estimation of the

    location of the rub was calculated using the phase delay between the adjacent AE modulations. Importantly, the AE diagnosis was closely corroborated by post-inspection of the turbine rotor.

Article Outline

    1. Introduction

    2. AE monitoring of rotating machinery

    3. The AE system

    4. Preliminary laboratory experiment

    5. AE diagnosis of operational turbine unit

    6. Conclusions

    Acknowledgements

    References

Reflection and transmission of GMIR shock at the heliopause and their relation to

    the 2- and 3-kHz radio emissions Original Research Article Advances in Space Research

continuous rotorstator rubbing in large scale turbine units using acoustic

    emissions Original Research Article

    Ultrasonics

Methodology for low- and high-cycle fatigue characterization with kHz-frequency

    resonators Original Research Article

    Sensors and Actuators A: Physical

    Arrays for airborne 100 kHz ultrasound Original Research Article Ultrasonics

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