The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Christophe Bailly - One of the best experts on this subject based on the ideXlab platform.
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Broadband Shock-Associated Noise in Screeching and Non-Screeching Underexpanded Supersonic Jets
2016Co-Authors: Benoit Andre, Thomas Castelain, Christophe BaillyAbstract:The effect of screech tones on the Broadband shock-associated noise of underexpanded jets is investigated experimentally. Screech is removed by means of a notched nozzle, and the properties of the Broadband shock-associated noise in the screech-free configuration are compared to that in a screeching flow. It is first demonstrated that the suppressing technique used is nonintrusive in that it does not alter the shock-cell structure of the jet plume. It is then shown that screech has an effect on the aerodynamics of the jet, which induces changes in the Broadband shock-associated noise. Indeed, screech accelerates the damping of the shock-cell pattern, leading to an attenuation of the Broadband shock-associated noise and a shifting of this noise component to higher frequencies. Moreover, a tuning between the peak frequency of the Broadband shock-associated noise and the screech frequency is observed. It is also deduced from the directivity of the Broadband shock-associated noise in the far field that the convective velocity in the shear layer is modified in the presence of screech tones. I
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Broadband shock associated noise in screeching and non screeching underexpanded supersonic jets
AIAA Journal, 2013Co-Authors: Benoit Andre, Thomas Castelain, Christophe BaillyAbstract:The effect of screech tones on the Broadband shock-associated noise of underexpanded jets is investigated experimentally. Screech is removed by means of a notched nozzle, and the properties of the Broadband shock-associated noise in the screech-free configuration are compared to that in a screeching flow. It is first demonstrated that the suppressing technique used is nonintrusive in that it does not alter the shock-cell structure of the jet plume. It is then shown that screech has an effect on the aerodynamics of the jet, which induces changes in the Broadband shock-associated noise. Indeed, screech accelerates the damping of the shock-cell pattern, leading to an attenuation of the Broadband shock-associated noise and a shifting of this noise component to higher frequencies. Moreover, a tuning between the peak frequency of the Broadband shock-associated noise and the screech frequency is observed. It is also deduced from the directivity of the Broadband shock-associated noise in the far field that the co...
Christine Silberhorn - One of the best experts on this subject based on the ideXlab platform.
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a quantum pulse gate based on spectrally engineered sum frequency generation
Optics Express, 2011Co-Authors: Andreas Eckstein, Benjamin Brecht, Christine SilberhornAbstract:We introduce the concept of a quantum pulse gate (QPG), a method for accessing the intrinsic Broadband spectral mode structure of ultrafast quantum states of light. This mode structure can now be harnessed for applications in quantum information processing. We propose an implementation in a PPLN waveguide, based on spectrally engineered sum frequency generation (SFG). It allows us to pick well-defined spectral Broadband modes from an ultrafast multi-mode state for interconversion to a Broadband mode at another frequency. By pulse-shaping the bright SFG pump beam, different orthogonal Broadband modes can be addressed individually and extracted with high fidelity.
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a quantum pulse gate based on spectrally engineered sum frequency generation
arXiv: Quantum Physics, 2010Co-Authors: Andreas Eckstein, Benjamin Brecht, Christine SilberhornAbstract:We introduce the concept of a quantum pulse gate (QPG), a method for accessing the intrinsic Broadband spectral mode structure of ultrafast quantum states of light. This mode structure can now be harnessed for applications in quantum information processing. We propose an implementation in a PPLN waveguide, based on spectrally engineered sum frequency generation (SFG). It allows us to pick well-defined spectral Broadband modes from an ultrafast multi-mode state for interconversion to a Broadband mode at another frequency. By pulse-shaping the bright SFG pump beam, different orthogonal Broadband modes can be addressed individually and extracted with near unit efficiency.
E Grabbe - One of the best experts on this subject based on the ideXlab platform.
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Broadband ultrasound attenuation in the diagnosis of osteoporosis correlation with osteodensitometry and fracture
Radiology, 1995Co-Authors: M Funke, L Kopka, R Vosshenrich, Uwe Fischer, A Ueberschaer, J W Oestmann, E GrabbeAbstract:PURPOSE: To evaluate the usefulness of Broadband ultrasound attenuation in the prediction of osteoporosis. MATERIALS AND METHODS: Broadband ultrasound attenuation measurements of the calcaneus and dual x-ray absorptiometry (DXA) measurements of the lumbar spine and the femoral neck were obtained in 400 patients (295 female and 105 male), 135 of whom were classified as having osteoporosis. Correlation coefficients between Broadband ultrasound attenuation and DXA were calculated. RESULTS: Patients with osteoporosis showed a statistically significant decrease in Broadband ultrasound attenuation compared with healthy patients (59.7 dB/MHz +/- 1.3 [standard deviation] vs 75.1 dB/MHz +/- 0.8). Broadband ultrasound attenuation correlated statistically significantly with vertebral bone density (r = .49) and femoral neck density (r = .52). At a Broadband ultrasound attenuation index of 64 dB/MHz, the sensitivity and specificity were both 85% for patients with osteoporotic fractures. CONCLUSION: Broadband ultrasoun...
Haim Suchowski - One of the best experts on this subject based on the ideXlab platform.
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pulse shaping of Broadband adiabatic shg in ti sapphire oscillator
arXiv: Optics, 2018Co-Authors: Assaf Levanon, Asaf Dahan, Achiya Nagler, Erga Lifshitz, Eyal Bahar, Michael Mrejen, Haim SuchowskiAbstract:We experimentally demonstrate an efficient Broadband second harmonic generation process with tunable mode-locked Ti: sapphire oscillator. We have achieved a robust Broadband and efficient flat conversion of more than 35nm wavelength, by designing an adiabatic aperiodically poled potassium titanyl phosphate (KTP) crystal. Moreover, we have shown that with such efficient flat conversion, we can shape and control Broadband second harmonic pulses. More specifically, we assign spectral-phase of abs-value and {\pi}-step, which allows wavelength tunable intense pump-probe and amplitude modulation of the Broadband second harmonic output. Such spectral phases serve as a proof of concept for other pulse-shaping application for nonlinear spectroscopy and imaging.
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pulse shaping of Broadband adiabatic shg from a ti sapphire oscillator
Optics Letters, 2017Co-Authors: Assaf Levanon, Asaf Dahan, Achiya Nagler, Erga Lifshitz, Eyal Bahar, Michael Mrejen, Haim SuchowskiAbstract:We experimentally demonstrate an efficient Broadband second-harmonic generation (SHG) process with a tunable mode-locked Ti:sapphire oscillator. We have achieved a robust Broadband and efficient flat conversion of more than 35 nm wavelength by designing an adiabatic aperiodically poled potassium titanyl phosphate crystal. Moreover, we have shown that with such efficient flat conversion, we can shape and control Broadband second-harmonic pulses. More specifically, we assign a spectral phase of absolute value and π-step, which allows wavelength tunable intense pump-probe and amplitude modulation of the Broadband second-harmonic output. Such spectral phases serve as a proof of concept for other pulse-shaping applications for nonlinear spectroscopy and imaging.
Daniel T Baran - One of the best experts on this subject based on the ideXlab platform.
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ultrasound attenuation of the calcaneus a sensitive and specific discriminator of osteopenia in postmenopausal women
Calcified Tissue International, 1991Co-Authors: Mats Agren, Andrew Karellas, Daniel Leahey, Sandy C Marks, Daniel T BaranAbstract:Recent studies have evaluated techniques for estimating bone mass without radiation. The present study compares Broadband ultrasound attenuation of the calcaneus and bone densities of the femoral neck and the lumbar spine in 17 normal women and 41 women with osteoporosis. Twenty of the osteoporotic women had spine (n=16) or femoral neck (n=4) fractures. There was a significant decrease in the Broadband ultrasound attenuation (P<0.001) in women with osteoporosis compared with normal women. The osteoporotic women also showed a decrease in vertebral (P<0.0001) and femoral neck (P<0.0001) densities compared with normal women. At 63 dB/MHz, the sensitivity and specificity of Broadband ultrasound attenuation for decreased bone mineral density with or without fractures were 76%. All women with fractures had a Broadband ultrasound attenuation less than 72 dB/MHz. This corresponded to a specificity of 41%. To determine whether Broadband ultrasound attenuation correlated with trabecular bone volume, samples of cadaver calcaneus were analyzed. The histologic determination showed a significant correlation between Broadband ultrasound attenuation and trabecular bone volume (r=0.992,P=0.008). These results suggest Broadband ultrasound attenuation of the calcaneus reflects bone mass and can be used as a safe and sensitive indicator for decreased axial bone density.
