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Simultaneous two cross-sectional measurements of NH<sub>3</sub> concentration in bent pipe flow using CT-tunable diode laser absorption spectroscopy
摘要： Urea Selective Catalytic Reduction (urea SCR) system is widely used for diesel engine to reduce the emission of NOx by NH3 which is provided by a hydrolysis of urea water. Concentration distribution of NH3 in an exhaust pipe is an important factor for improvement of the SCR efficiency and prevention of NH3 slip and urea deposit. Therefore, it is necessary to measure two-dimensional (2D) concentration of NH3 in detail. The purpose of this study is to develop the real-time two cross-sectional measurements technology of NH3 concentration using the computed tomography-tunable diode laser absorption spectroscopy (CT-TDLAS). Theoretical NH3 concentration distribution which was reconstructed by CT agreed to CFD results and quadruple pipe’s results showed good resolution by 14th order reconstruction. Therefore, this method has enough resolution and accuracy for measuring the concentration distribution of NH3. And this method was employed in a bent pipe model demonstrated a urea SCR system. The experimental results of two cross-sectional 2D concentration of NH3 show differences of the concentration distribution of NH3 each cross-section and flow pattern like swirl flow. It was found that CT-TDLAS was an effective method to measure concentration distribution of NH3 and observe characteristics of flow. In addition, observing flow pattern enable to validate CFD results, and it helps to improve efficiency of after treatment system.
关键词： Urea selective catalytic reduction,NH3 concentration measurement,Exhaust aftertreatment,CT tunable diode laser absorption spectroscopy,Measurement and instrumentation
更新于2025-09-11 14:15:04
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Efficient Spectroscopy of Exoplanets at Small Angular Separations with Vortex Fiber Nulling
摘要： Instrumentation designed to characterize potentially habitable planets may combine adaptive optics and high-resolution spectroscopy techniques to achieve the highest possible sensitivity to spectral signs of life. Detecting the weak signal from a planet containing biomarkers will require exquisite control of the optical wavefront to maximize the planet signal and significantly reduce unwanted starlight. We present an optical technique, known as vortex fiber nulling (VFN), that allows polychromatic light from faint planets at extremely small separations from their host stars (～λ/D) to be efficiently routed to a diffraction-limited spectrograph via a single-mode optical fiber, while light from the star is prevented from entering the spectrograph. VFN takes advantage of the spatial selectivity of a single-mode fiber to isolate the light from close-in companions in a small field of view around the star. We provide theoretical performance predictions of a conceptual design and show that VFN may be utilized to characterize planets detected by radial velocity (RV) instruments in the infrared without knowledge of the azimuthal orientation of their orbits. Using a spectral template-matching technique, we calculate an integration time of ～400, ～100, and ～30 hr for Ross 128 b with Keck, the Thirty Meter Telescope, and the Large Ultraviolet/Optical/Infrared Surveyor, respectively.
关键词： techniques: spectroscopic,instrumentation: adaptive optics,instrumentation: high angular resolution
更新于2025-09-10 09:29:36
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A Study of the Point-spread Function in SDSS Images
摘要： We use SDSS imaging data in the ugriz passbands to study the shape of the point-spread function (PSF) pro?le and the variation of its width with wavelength and time. We ?nd that the PSF pro?le is well described by theoretical predictions based on von Kármán’s turbulence theory. The observed PSF radial pro?le can be parameterized by only two parameters, the pro?le’s full width at half maximum (FWHM) and a normalization of the contribution of an empirically determined “instrumental” PSF. The pro?le shape is very similar to the “double Gaussian plus power-law wing” decomposition used by the SDSS image-processing pipeline, but here it is successfully modeled with two free model parameters, rather than six as in the SDSS pipeline. The FWHM variation with wavelength follows the λ α power law, where α?≈??0.3 and is correlated with the FWHM itself. The observed behavior is much better described by von Kármán’s turbulence theory, with the outer-scale parameter in the range of 5–100 m, than by Kolmogorov’s turbulence theory. We also measure the temporal and angular structure functions for FWHM and compare them to simulations and results from the literature. The angular structure function saturates at scales beyond 0°. 5?1°. 0. The power spectrum of the temporal behavior is found to be broadly consistent with a damped random-walk model with a characteristic timescale in the range of ～5–30 minutes, though the data show a shallower high-frequency behavior. The latter is well ?t by a single power law with an index in the range of ?1.5 to ?1.0. A hybrid model is likely needed to fully capture both the low-frequency and high-frequency behavior of the temporal variations of atmospheric seeing.
关键词： surveys,atmospheric effects,stars: imaging,methods: observational,instrumentation: detectors
更新于2025-09-10 09:29:36
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A VERSATILE TECHNIQUE TO ENABLE SUB-MILLI-KELVIN INSTRUMENT STABILITY FOR PRECISE RADIAL VELOCITY MEASUREMENTS: TESTS WITH THE HABITABLE-ZONE PLANET FINDER
摘要： Insufficient instrument thermomechanical stability is one of the many roadblocks for achieving 10 cm s?1 Doppler radial velocity precision, the precision needed to detect Earth-twins orbiting solar-type stars. Highly temperature and pressure stabilized spectrographs allow us to better calibrate out instrumental drifts, thereby helping in distinguishing instrumental noise from astrophysical stellar signals. We present the design and performance of the Environmental Control System (ECS) for the Habitable-zone Planet Finder (HPF), a high-resolution (R = 50,000) fiber-fed near-infrared (NIR) spectrograph for the 10 m Hobby–Eberly Telescope at McDonald Observatory. HPF will operate at 180 K, driven by the choice of an H2RG NIR detector array with a 1.7 μm cutoff. This ECS has demonstrated 0.6 mK rms stability over 15 days at both 180 and 300 K, and maintained high-quality vacuum (<10?7 Torr) over months, during long-term stability tests conducted without a planned passive thermal enclosure surrounding the vacuum chamber. This control scheme is versatile and can be applied as a blueprint to stabilize future NIR and optical high-precision Doppler instruments over a wide temperature range from ～77 K to elevated room temperatures. A similar ECS is being implemented to stabilize NEID, the NASA/NSF NN-EXPLORE spectrograph for the 3.5 m WIYN telescope at Kitt Peak, operating at 300 K. A [full SolidWorks 3D-CAD model] and a comprehensive parts list of the HPF ECS are included with this manuscript to facilitate the adaptation of this versatile environmental control scheme in the broader astronomical community.
关键词： instrumentation: spectrographs,techniques: radial velocities,techniques: spectroscopic
更新于2025-09-10 09:29:36
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The UVES Spectral Quasar Absorption Database (SQUAD) data release 1: the first 10 million seconds
摘要： We present the first data release (DR1) of the UVES Spectral Quasar Absorption Database (SQUAD), comprising 467 fully reduced, continuum-fitted high-resolution quasar spectra from the Ultraviolet and Visual Echelle Spectrograph (UVES) on the European Southern Observatory's Very Large Telescope. The quasars have redshifts z = 0–5, and a total exposure time of 10 million seconds provides continuum-to-noise ratios of 4–342 (median 20) per 2.5 km s?1 pixel at 5500 ?. The SQUAD spectra are fully reproducible from the raw, archival UVES exposures with open-source software, including our UVES POPLER tool for combining multiple extracted echelle exposures which we document here. All processing steps are completely transparent and can be improved upon or modified for specific applications. A primary goal of SQUAD is to enable statistical studies of large quasar and absorber samples, and we provide tools and basic information to assist three broad scientific uses: studies of damped Lyman-α systems (DLAs), absorption-line surveys, and time-variable absorption lines. For example, we provide a catalogue of 155 DLAs whose Lyman-α lines are covered by the DR1 spectra, 18 of which are reported for the first time. The H I column densities of these new DLAs are measured from the DR1 spectra. DR1 is publicly available and includes all reduced data and information to reproduce the final spectra.
关键词： instrumentation: spectrographs,line: profiles,quasars: absorption lines,cosmology: observations,cosmology: miscellaneous
更新于2025-09-10 09:29:36
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Frequency pair model for selection of signal spectral components to determine position of zero optical-path difference in a pulse-train interferometer
摘要： High-accuracy measurement using phase information of fringe patterns – that is not much affected by amplitude noises – than amplitude information, in a pulse-train interferometer is demonstrated in this study. However, the selection criteria for spectral components of the measured interferogram for regeneration of phase information are not obvious. In this work, a frequency pair model is proposed. The experimental work demonstrates the model’s ability to optimally select signal components. The application field of pulse-train or white-light interferometers may be extended by associating them with the proposed method.
关键词： Metrology,Fringe analysis,Interferometry,Fourier optics and signal processing,Instrumentation, measurement, and metrology
更新于2025-09-10 09:29:36
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Daytime optical turbulence and wind speed distributions at the Baikal Astrophysical Observatory
摘要： Atmospheric turbulence limits the angular resolution of ground-based optical telescopes. The daytime turbulence conditions for solar observations are stronger and more complicated than the turbulence observed at night. The Baikal Astrophysical Observatory is the site of the 1-m Large Solar Vacuum Telescope (LSVT) located near Lake Baikal (East Siberia, Russia), which is the largest freshwater lake in the world. The region hosts unique weather regimes and natural phenomena, including local winds and giant ice rings. Because the LSVT has ongoing and planned programmes in adaptive optics (AO), statistical knowledge of atmospheric turbulence and wind speed distributions is essential for designing and optimizing AO systems. We present the first seasonal study of the vertical distribution of wind speed and daytime optical turbulence conditions at the Baikal Astrophysical Observatory. Site measurements of the daytime Fried parameter were collected using the Shack–Hartmann wavefront sensor in the LSVT AO system. Reanalysis data from the National Centers for Environmental Prediction (NCEP) and the National Centers for Atmospheric Research (NCAR) were used to characterize the wind speed distribution. The results demonstrate seasonal variation in both solar seeing and wind speed profile. The strongest wind speed was detected in winter and in November, while the weakest wind speed occurred during summer. The strongest daytime turbulence conditions were observed in the winter. The best solar seeing β0 ≈ 1 arcsec was detected in the summer.
关键词： site testing,atmospheric effects,instrumentation: adaptive optics
更新于2025-09-10 09:29:36
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Application of the gas-discharge surge arresters in X-ray devices and low voltage instrumentation
摘要： Usage of the gas discharge in science and engineering is discussed. Application examples of the compact gas-discharge tubes in the X-ray devices and low voltage instrumentation appliances for the surge protection are presented.
关键词： low voltage instrumentation,gas-discharge,X-ray devices,surge arresters
更新于2025-09-10 09:29:36
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A new infrared Fabry-Pérot-based radial-velocity-reference module for the SPIRou radial-velocity spectrograph
摘要： Context. The ?eld of exoplanet research is moving towards the detection and characterization of habitable planets. These exo-Earths can be easily found around low-mass stars by using either photometric transit or radial-velocity (RV) techniques. In the latter case the gain is twofold because the signal induced by the planet of a given mass is higher due to the more favourable planet-star mass ratio and because the habitable zone lies closer to the star. However, late-type stars emit mainly in the infrared (IR) wavelength range, which calls for IR instruments. Aims. SPIRou is a stable RV IR spectrograph addressing these ambitious scienti?c objectives. As with any other spectrograph, calibration and drift monitoring is fundamental to achieve high precision. However, the IR domain su?ers from a lack of suitable reference spectral sources. Our goal was to build, test and ?nally operate a Fabry-Pérot-based RV-reference module able to provide the needed spectral information over the full wavelength range of SPIRou. Methods. We adapted the existing HARPS Fabry-Pérot calibrator for operation in the IR domain. After manufacturing and assembly, we characterized the FP RV-module in the laboratory before delivering it to the SPIRou integration site. In particular, we measured ?nesse, transmittance, and spectral ?ux of the system. Results. The measured ?nesse value of F = 12.8 corresponds perfectly to the theoretical value. The total transmittance at peak is of the order of 0.5%, mainly limited by ?bre-connectors and interfaces. Nevertheless, the provided ?ux is in line with the the requirements set by the SPIRou instrument. Although we could test the stability of the system, we estimated it by comparing the SPIRou Fabry-Pérot with the already operating HARPS system and demonstrated a stability of better than 1 m s?1 during a night. Conclusions. Once installed on SPIRou, we will test the full spectral characteristics and stability of the RV-reference module. The goal will be to prove that the line position and shape stability of all lines is better than 0.3 m s?1 between two calibration sequences (typically 24 h), such that the RV-reference module can be used to monitor instrumental drifts. In principle, the system is also intrinsically stable over longer time scales such that it can also be used for calibration purposes.
关键词： instrumentation: spectrographs,telescopes,instrumentation: interferometers,techniques: radial velocities
更新于2025-09-09 09:28:46
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The hard X-ray Photon Single-Shot Spectrometer of SwissFEL—initial characterization
摘要： SwissFEL requires the monitoring of the photon spectral distribution at a repetition rate of 100 Hz for machine optimization and experiment online diagnostics. The Photon Single Shot Spectrometer has been designed for the photon energy range of 4 keV to 12 keV provided by the Aramis beamline. It is capable of measuring the spectrum in a non-destructive manner, with an energy resolution of ?E/E = (2–5) × 10?5 over a bandwidth of 0.5% on a shot-to-shot basis. This article gives a detailed description about the technical challenges, structures, and considerations when building such a device, and to further enhance the performance of the spectrometer.
关键词： Beam-line instrumentation (beam position and pro?le monitors; beam-intensity monitors; bunch length monitors),Instrumentation for FEL
更新于2025-09-09 09:28:46