| 1. |
- Petersson, Per, et al.
(författare)
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Simultaneous PIV/PH-PLIF, Rayleigh thermometry/OH-PLIF and stereo PIV measurements in a low-swirl-flame
- 2007
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Ingår i: Applied Optics. - 2155-3165. ; 46:19, s. 3928-3936
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Tidskriftsartikel (refereegranskat)abstract
- The diagnostic techniques for simultaneous velocity and relative OH distribution, simultaneous temperature and relative OH distribution, and three component velocity mapping are described. The data extracted from the measurements include statistical moments for inflow fluid dynamics, temperature, conditional velocities, and scalar flux. The work is a first step in the development of a detailed large eddy simulation (LES) validation database for a turbulent, premixed flame. The low-swirl burner used in this investigation has many of the necessary attributes for LES model validation, including a simplified interior geometry; it operates well into the thin reaction zone for turbulent premixed flames, and flame stabilization is based entirely on the flow field and not on hardware or pilot flames.
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| 2. |
- Bean, Jacob L., et al.
(författare)
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The CRIRES search for planets around the lowest-mass stars. I. High-precision near-infrared radial velocities with an ammonia gas cell
- 2010
-
Ingår i: Astrophysical Journal. - 0004-637X. ; 713:1, s. 410-422
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Tidskriftsartikel (refereegranskat)abstract
- Radial velocities measured from near-infrared (NIR) spectra are a potentially powerful tool to search for planets around cool stars and sub-stellar objects. However, no technique currently exists that yields NIR radial velocity precision comparable to that routinely obtained in the visible. We are carrying out an NIR radial velocity planet search program targeting a sample of the lowest-mass M dwarfs using the CRIRES instrument on the Very Large Telescope. In this first paper in a planned series about the project, we describe a method for measuring high-precision relative radial velocities of these stars from K-band spectra. The method makes use of a glass cell filled with ammonia gas to calibrate the spectrograph response similar to the "iodine cell" technique that has been used very successfully in the visible. Stellar spectra are obtained through the ammonia cell and modeled as the product of a Doppler-shifted template spectrum of the object and a spectrum of the cell, convolved with a variable instrumental profile (IP) model. A complicating factor is that a significant number of telluric absorption lines are present in the spectral regions containing useful stellar and ammonia lines. The telluric lines are modeled simultaneously as well using spectrum synthesis with a time-resolved model of the atmosphere over the observatory. The free parameters in the complete model are the wavelength scale of the spectrum, the IP, adjustments to the water and methane abundances in the atmospheric model, telluric spectrum Doppler shift, and stellar Doppler shift. Tests of the method based on the analysis of hundreds of spectra obtained for late-M dwarfs over 6 months demonstrate that precisions of similar to 5 m s(-1) are obtainable over long timescales, and precisions of better than 3 m s(-1) can be obtained over timescales up to a week. The obtained precision is comparable to the predicted photon-limited errors, but primarily limited over long timescales by the imperfect modeling of the telluric lines.
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| 3. |
- Bean, Jacob L., et al.
(författare)
-
The crires search for planets around the lowest-mass stars. I. High-precision near-infrared radial velocities with an ammonia gas cell
- 2010
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 713:1, s. 410-422
-
Tidskriftsartikel (refereegranskat)abstract
- Radial velocities measured from near-infrared (NIR) spectra are a potentially powerful tool to search for planets around cool stars and sub-stellar objects. However, no technique currently exists that yields NIR radial velocity precision comparable to that routinely obtained in the visible. We are carrying out an NIR radial velocity planet search program targeting a sample of the lowest-mass M dwarfs using the CRIRES instrument on the Very Large Telescope. In this first paper in a planned series about the project, we describe a method for measuring high-precision relative radial velocities of these stars from K-band spectra. The method makes use of a glass cell filled with ammonia gas to calibrate the spectrograph response similar to the "iodine cell" technique that has been used very successfully in the visible. Stellar spectra are obtained through the ammonia cell and modeled as the product of a Doppler-shifted template spectrum of the object and a spectrum of the cell, convolved with a variable instrumental profile (IP) model. A complicating factor is that a significant number of telluric absorption lines are present in the spectral regions containing useful stellar and ammonia lines. The telluric lines are modeled simultaneously as well using spectrum synthesis with a time-resolved model of the atmosphere over the observatory. The free parameters in the complete model are the wavelength scale of the spectrum, the IP, adjustments to the water and methane abundances in the atmospheric model, telluric spectrum Doppler shift, and stellar Doppler shift. Tests of the method based on the analysis of hundreds of spectra obtained for late-M dwarfs over 6 months demonstrate that precisions of ∼ 5 m s−1 are obtainable over long timescales, and precisions of better than 3 m s−1 can be obtained over timescales up to a week. The obtained precision is comparable to the predicted photon-limited errors, but primarily limited over long timescales by the imperfect modeling of the telluric lines.
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| 4. |
- Bean, Jacob L., et al.
(författare)
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The proposed giant planet orbiting VB 10 does not exist
- 2010
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Ingår i: Astrophysical Journal Letters. - 2041-8213. ; 711:1, s. 19-23
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Tidskriftsartikel (refereegranskat)abstract
- We present high-precision relative radial velocities of the very low mass star VB 10 that were obtained over a time span of 0.61 years as part of an ongoing search for planets around stars at the end of the main sequence. The radial velocities were measured from high-resolution near-infrared spectra obtained using the CRIRES instrument on the Very Large Telescope with an ammonia gas cell. The typical internal precision of the measurements is 10 m s(-1). These data do not exhibit significant variability and are essentially constant at a level consistent with the measurement uncertainties. Therefore, we do not detect the radial velocity variations of VB 10 expected due to the presence of an orbiting giant planet similar to that recently proposed by Pravdo & Shaklan based on apparent astrometric perturbations. In addition, we do not confirm the similar to 1 km s(-1) radial velocity variability of the star tentatively detected by Zapatero Osorio and colleagues with lower precision measurements. Our measurements rule out planets with M-p > 3 M-Jup and the orbital period and inclination suggested by Pravdo & Shaklan at better than 5 sigma confidence. We conclude that the planet detection claimed by Pravdo & Shaklan is spurious on the basis of this result. Although the outcome of this work is a non-detection, it illustrates the potential of using ammonia cell radial velocities to detect planets around very low mass stars.
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| 5. |
- Bean, Jacob L., et al.
(författare)
-
The proposed giant planet orbiting VB 10 does not exist
- 2010
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 711:1, s. L19-L23
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Tidskriftsartikel (refereegranskat)abstract
- We present high-precision relative radial velocities of the very low mass star VB 10 that were obtained over a time span of 0.61 years as part of an ongoing search for planets around stars at the end of the main sequence. The radial velocities were measured from high-resolution near-infrared spectra obtained using the CRIRES instrument on the Very Large Telescope with an ammonia gas cell. The typical internal precision of the measurements is 10 m s−1. These data do not exhibit significant variability and are essentially constant at a level consistent with the measurement uncertainties. Therefore, we do not detect the radial velocity variations of VB 10 expected due to the presence of an orbiting giant planet similar to that recently proposed by Pravdo & Shaklan based on apparent astrometric perturbations. In addition, we do not confirm the ∼1 km s−1 radial velocity variability of the star tentatively detected by Zapatero Osorio and colleagues with lower precision measurements. Our measurements rule out planets with Mp > 3 MJup and the orbital period and inclination suggested by Pravdo & Shaklan at better than 5σ confidence. We conclude that the planet detection claimed by Pravdo & Shaklan is spurious on the basis of this result. Although the outcome of this work is a non-detection, it illustrates the potential of using ammonia cell radial velocities to detect planets around very low mass stars.
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| 6. |
- Kaminski, Clemens, et al.
(författare)
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Development of high speed spectroscopic imaging techniques for the time resolved study of spark ignition phenomena
- 2000
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on the development of novel time resolved spectroscopic imaging techniques for the study of spark ignition phenomena in combustion cells and an SI-engine. The techniques are based on planar laser induced fluorescence imaging (PLIF) of OH radicals, on fuel tracer PLIF, and on chemiluminescence. The techniques could be achieved at repetition rates reaching several hundreds of kilo-Hz and were cycle resolved. These techniques offer a new path along which engine related diagnostics can be undertaken, providing a wealth of information on turbulent spark ignition.
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| 7. |
- Kuzuhara, Masayuki, et al.
(författare)
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Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Transmission Spectroscopy
- 2024
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Ingår i: Astrophysical Journal Letters. - 2041-8213 .- 2041-8205. ; 969:1
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Tidskriftsartikel (refereegranskat)abstract
- Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (P(or)b) of 12.76 days. The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous P-orb from TESS data. We confirmed the transit signal and P-orb using ground-based photometry with MuSCAT2 and MuSCAT3, and validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host star is inactive, with an X-ray-to-bolometric luminosity ratio of log L-X/L-bol approximate to - 5.7. Joint analysis of the light curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 +/- 0.05 R-circle plus, a 3 sigma mass upper limit of 3.9M(circle plus), and an equilibrium temperature of 315 +/- 6 K assuming zero albedo. The transmission spectroscopy metric (TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
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| 8. |
- Li, Xun, et al.
(författare)
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Investigation of burning velocity of lean and rich premixed NH3/H2 turbulent flames using multi-scalar imaging
- 2024
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Ingår i: Proceedings of the Combustion Institute. - 1540-7489. ; 40:1-4
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Tidskriftsartikel (refereegranskat)abstract
- Two groups of both lean and rich NH3/H2/O2/N2 turbulent premixed piloted jet flames with the same laminar flame speed are investigated using simultaneous multi-scalar laser diagnostics techniques including NH3/NH/OH planar laser induced fluorescence (PLIF) and Rayleigh scattering. One group uses air as the oxidizer and the other uses an adapted mixture of atomic N-to-H ratio of 1:3 associated with in-situ hydrogen production from ammonia cracking. Turbulent rms velocity uʹ is varied in a wide range by changing the bulk flow velocity. Global consumption speeds ST,G are evaluated by measuring the inlet bulk flow rates of reactants and areas of time-averaged flame fronts extracted using different flame marker contours, i.e., cNH3 = 0.3, cNH = 0.3 (inner contour), and cOH = 0.4, where c designates species number density normalized using its maximum value. The obtained results show the following trends to be emphasized. First, an increase in ST,G,NH3 by uʹ is more pronounced when compared to two other global consumption speeds (ST,G,NHi , where i indicates the inner contour, and ST,G,OH ) and is close to a linear dependence. The adapted mixture shows only a moderate influence on ST,G,NH3 but not on the other two. Second, ST,G,NH3 is weakly affected by variations in Lewis number Le. On the contrary, third, ST,G,NHi is significantly higher in lean mixtures characterized by Le < 1 when compared to rich mixtures characterized by Le > 1. Fourth, these variations in ST,G,NHi are reasonably well approximated introducing an empirical factor of Le−0.9 into fitting ST,G,NHi /SL onto uʹ/SL . The qualitative difference between sensitivities of ST,G,NH3 and ST,G,NHi to variations in Le is attributed to the fact that the NH3 and NH isosurfaces are localized to preheat and reaction zones, respectively, of the laminar flames. The reported experimental data imply different influence of differential diffusion on flame preheat and reaction zones, thus, calling for further research into the issue.
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| 9. |
- Stephan, Michael, et al.
(författare)
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Multiple scattering reduction in instantaneous gas phase phosphor thermometry : Applications with dispersed seeding
- 2019
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Ingår i: Measurement Science and Technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 30:5
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Tidskriftsartikel (refereegranskat)abstract
- In this study the structured laser illumination planar imaging (SLIPI) technique is combined with gas phase phosphor thermometry to measure quasi-instantaneously two-dimensional temperature fields with reduced bias from multiple scattering. Different reconstruction strategies are implemented, evaluated and compared, including a two-pulse and one-pulse SLIPI approach. A gradient-based threshold algorithm for particle detection is applied to conventional planar light sheet imaging as an alternative to reduce the bias caused by multiple scattering in seeding-free regions. As a demonstration, measurements are performed in a canonical flow configuration, consisting of a heated, turbulent, air jet surrounded by an ambient co-flow. Both air flows are seeded with the thermographic phosphor BaMgAl10O17:Eu2+. Conventional light sheet imaging in the context of gas phase phosphor thermometry suffers from multiple scattering causing a significant temperature bias and low temperature sensitivity. Applying the gradient threshold algorithm removes areas without any seeding particles which improves accuracy, precision and temperature sensitivity. However, multiple scattering influences are still present and may cause an increasing bias particularly for higher seeding density. One pulse (1p) SLIPI exhibits high accuracy at intermediate precision. Multiply scattered luminescence is not fully removed and spatial resolution is lowered. Two pulse (2p) SLIPI is recommended for high temperature sensitivity and accuracy, removing impact of multiple scattering furthermost. However, 2p-SLIPI exhibits reduced temperature precision.
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| 10. |
- Wang, Ze, et al.
(författare)
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Experimental investigation of internal structures of NH3/H2/O2/N2 premixed jet flames using multi-scalar imaging
- 2024
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Ingår i: Proceedings of the Combustion Institute. - 1540-7489. ; 40:1-4
-
Tidskriftsartikel (refereegranskat)abstract
- Ammonia-hydrogen (NH3-H2) blends stand as a promising carbon-neutral fuel alternative. This study delves into the variation in the internal structure of NH3-H2 flames with varying Lewis numbers (Le) and turbulence intensities. Simultaneous multi-scalar imaging of NH3/NH/OH was performed to characterize the structures of turbulent jet flames with the same unstretched laminar flame speed (30.8 cm/s) but different H2 contents. Internal flame structures were characterized by isocontours of NH3, NH (both inner and outer edges, NHi and NHo), and OH to delimit the reaction zone. The parallelism of the selected isocontours (i.e., NH3, NHi, and NHo) with the OH baseline was quantified by calculating the probabilities, P(δp), of the selected isocontours overlapping with the OH baseline shifted by a distance of δp along its normal direction. On the one hand, results have revealed that increasing turbulence disrupts the parallelism of the selected isocontours with the OH baseline, leading to a larger and FWHM, as well as a reduced skewness of the P(δp) profiles. On the other hand, flames with higher H2 content and lower Le exhibit great resistance to turbulence but experience enhanced wrinkling due to the differential diffusion effect, which can also cause deviations in scalar parallelism at low turbulence intensity. For flames with reduced Le numbers, the NH3 isocontours are observed to be located even downstream of the NHi isocontours, which belong to the reaction zone. The extent of parallelism for the selected isocontours within the reaction zone is found to respond to turbulence and Le differently, deviating from an idealized picture of the flamelet manifold.
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