Abstract
This work presents the initial results of the drift-scan observation for the neutral hydrogen (
Hi
) intensity mapping survey with the Five-hundred-meter Aperture Spherical radio Telescope ...(FAST). The data analyzed in this work were collected in night observations from 2019 through 2021. The primary findings are based on 28 hr of drift-scan observation carried out over 7 nights in 2021, which covers 60 deg
2
sky area. Our main findings are, first, our calibration strategy can successfully correct both the temporal and bandpass gain variation over the 4 hr drift-scan observation. Second, the continuum maps of the surveyed region are made with frequency resolution of 28 kHz and pixel area of
2.95
arcmin
2
. The pixel noise levels of the continuum maps are slightly higher than the forecast assuming
T
sys
= 20 K, which are 36.0 mK (for 10.0 s integration time) at the 1050–1150 MHz band, and 25.9 mK (for 16.7 s integration time) at the 1323–1450 MHz band, respectively. Third, the flux-weighted differential number count is consistent with the NRAO-VLA Sky Survey (NVSS) catalog down to the confusion limit ∼7 mJy beam
−1
. Finally, the continuum flux measurements of the sources are consistent with those found in the literature. The difference in the flux measurement of 81 isolated NVSS sources is about 6.3%. Our research offers a systematic analysis for the FAST
Hi
intensity mapping drift-scan survey and serves as a helpful resource for further cosmology and associated galaxies sciences with the FAST drift-scan survey.
ABSTRACT
fink is a broker designed to enable science with large time-domain alert streams such as the one from the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). It ...exhibits traditional astronomy broker features such as automatized ingestion, annotation, selection, and redistribution of promising alerts for transient science. It is also designed to go beyond traditional broker features by providing real-time transient classification that is continuously improved by using state-of-the-art deep learning and adaptive learning techniques. These evolving added values will enable more accurate scientific output from LSST photometric data for diverse science cases while also leading to a higher incidence of new discoveries which shall accompany the evolution of the survey. In this paper, we introduce fink, its science motivation, architecture, and current status including first science verification cases using the Zwicky Transient Facility alert stream.
The Tianlai dish array low-z surveys forecasts Perdereau, Olivier; Ansari, Réza; Stebbins, Albert ...
Monthly Notices of the Royal Astronomical Society,
11/2022, Letnik:
517, Številka:
3
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
We present the science case for surveys with the Tianlai dish array interferometer tuned to the 1300, 1400 MHz frequency range. Starting from a realistic generation of mock visibility data ...according to the survey strategy, we reconstruct maps of the sky and perform foreground subtraction. We estimate the level of residuals from imperfect subtraction, mostly due to mode mixing, i.e. distortions in the reconstructed 3D maps due to frequency-dependent instrument response. We show that a survey of the North Celestial Polar cap during a year of observations, covering an area of $150 \, \mathrm{deg^2}$, would reach a sensitivity of $1.5-2 \, \mathrm{mK}$ per $1 \, \mathrm{MHz} \times 0.25^2 \, \mathrm{deg^2 }$ voxel and be marginally impacted by mode mixing. Tianlai would be able to detect ∼10 nearby massive H i clumps as well as a very strong cross-correlation signal of 21 cm intensity maps with the North Celestial Cap Survey optical galaxies. We also studied the performance of a mid-latitude survey, covering $\sim 1500 \, \mathrm{deg^2}$ overlapping the SDSS footprint. Despite a higher noise level for the mid-latitude survey, as well as significant distortions due to mode mixing, Tianlai would be able to detect a highly significant cross-correlation between the 21 cm signal and the Sloan spectroscopic galaxy sample. Using the extragalactic signals measured from either or both of these surveys, and comparing them with simulations such as those presented here will make it possible to assess the impact of various instrumental imperfections on the Tianlai dish array performance. This would pave the way for future intensity mapping surveys with higher sensitivity.
In the next decade, the Large Synoptic Survey Telescope (LSST) will become a major facility for the astronomical community. However, accurately determining the redshifts of the observed galaxies ...without using spectroscopy is a major challenge. Reconstruction of the redshifts with high resolution and well-understood uncertainties is mandatory for many science goals, including the study of baryonic acoustic oscillations (BAO). We investigate different approaches to establish the accuracy that can be reached by the LSST six-band photometry. We construct a realistic mock galaxy catalog, based on the Great Observatories Origins Deep Survey (GOODS) luminosity function, by simulating the expected apparent magnitude distribution for the LSST. We demonstrate that the photometric redshifts will be accurately estimated with the LSST if a Bayesian prior probability and a calibration sample are used.
•The complex single heater is designed and developed or VGF process.•The control system of VGF process is simplified and now production cost can be decreased.•Full process transient optimization ...method is proposed and developed.
A complex single heater is designed for a VGF process to decrease process complexity caused by the use of a multi-heater system. To do this, a set of design criteria is selected to ensure that the final quality of the crystal is acceptable. Then a 3D transient finite element model is coupled with a new optimization procedure. All important physical phenome a such as temperature distribution, turbulent melt flow, thermal stress and crystal front shape are monitored and controlled during crystal growth. Using these, a single heater is designed for 4″ InP VGF crystal growth which meets all design criteria. It is concluded that using the complex single heater, high quality InP crystal growth by VGF process is possible.
The purpose of this article is the comprehensive analysis of free vibration of beam-type liquid micro-pump with a free boundary approach. Besides the liquid loading on the micro-beam, the kinematic ...compatibility between liquid and micro-beam is modeled according to the free boundaries. Galerkin and separation of variables methods are employed to solve these equations. Based on the nonlinear nature of the equations, the Newmark method is applied to obtain the normal frequencies, mode shapes, and the fluid oscillation of the coupled system. The aim of this model is to achieve the exact results for the small oscillations of micro-beam in the liquid container. Comparing the free and fixed boundary method reveals that for small oscillation of Euler–Bernoulli micro-beam, there is a slight deviation on the natural frequency, which can be negligible.
A new HTUC model with AC constraints is presented. A new decomposition strategy for HTUC problem is suggested. A new Benders decomposition method is proposed. Effectiveness of the proposed solution ...strategy is extensively tested.
This paper presents a new approach based on Benders decomposition (BD) to solve hydrothermal unit commitment problem with AC power flow and security constraints. The proposed method decomposes the problem into a master problem and two sets of sub-problems. The master problem applies integer programming method to solve unit commitment (UC) while the sub-problems apply nonlinear programming solution method to determine economic dispatch for each time period. If one sub-problem of the first set becomes infeasible, the corresponding sub-problem of the second set is called. Moreover, strong Benders cuts are proposed that reduce the number of iterations and CPU time of the Benders decomposition method. All constraints of the hydrothermal unit commitment problem can be completely satisfied with zero penalty terms by the proposed solution method. The methodology is tested on the 9-bus and IEEE 118-bus test systems. The obtained results confirm the validity of the developed approach.
Room-temperature accumulative roll bonding was employed to refine the grain structure in commercial pure titanium. The microstructural evaluations show reduction in the grain size from about 45µm to ...about 90nm upon six cycles of accumulative roll bonding while increase in the degree of deformation inhomogeneity, measured through micro-hardness testing. The yield stress and tensile strength of the nano-grained commercial pure titanium after the sixth cycle, 799MPa and 989MPa, were about 180% and 140% increase as compared with the as-received sample, 284MPa and 415MPa. A remarkable grain refinement during the initial cycles of accumulative roll bonding resulted in increasing strain hardening rate and decreasing strain hardening exponent. However, upon the initial cycles, the saturation in hardening led to nearly constant strain hardening rate and exponent.
In the current study, the elastic and plastic properties of the 2 × 2 and 3 × 3 pristine and transition metal (TM)-doped antimonene are studied through DFT calculations. Sc, Ti, V, Cr, Fe, Co, Ni, ...Cu, and Zn atoms are selected as the doping atoms. It was observed that Young’s and bulk moduli of both 2 × 2 and 3 × 3 pristine structure would decrease while affected by the doping atoms. The highest reduction in the Young’s and bulk moduli of the 2 × 2 nanosheets has occurred in the Cr- and Ti-doped structures, respectively, while the same reduction was observed in the V- and Ti-doped structures in the 3 × 3 nanosheets. In addition, it was shown that all of the investigated structures express isotropic behavior since the obtained Young’s moduli of these nanostructures have negligible difference along armchair and zigzag directions. Finally, the loading is further increased to investigate the plastic behavior of these structures. The results showed that except for 2 × 2 Sc-doped structure under biaxial loading, the yield strain of all doped nanosheets would decrease under uniaxial and biaxial loadings. The highest reduction in the yield strain of the 2 × 2 nanosheets under biaxial loading has been observed in Cu-doped nanosheet while in 3 × 3 nanosheets, the highest reduction has occurred in Cu-, Fe-, and Zn-doped nanosheets under the same condition. As for the yield strain of the doped 2 × 2 nanosheets while affected by the uniaxial loading, Cu- and Zn-doped nanosheets experienced the highest reduction while in 3 × 3 nanosheets, the highest reduction has been observed for Cr-doped nanosheet under the same condition.
Context. In the next decade, the Large Synoptic Survey Telescope (LSST) will become a major facility for the astronomical community. However, accurately determining the redshifts of the observed ...galaxies without using spectroscopy is a major challenge. Aims. Reconstruction of the redshifts with high resolution and well-understood uncertainties is mandatory for many science goals, including the study of baryonic acoustic oscillations (BAO). We investigate different approaches to establish the accuracy that can be reached by the LSST six-band photometry. Methods. We construct a realistic mock galaxy catalog, based on the Great Observatories Origins Deep Survey (GOODS) luminosity function, by simulating the expected apparent magnitude distribution for the LSST. To reconstruct the photometric redshifts (photo-z’s), we consider a template-fitting method and a neural network method. The photo-z reconstruction from both of these techniques is tested on real Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) data and also on simulated catalogs. We describe a new method to improve photometric redshift reconstruction that efficiently removes catastrophic outliers via a likelihood ratio statistical test. This test uses the posterior probability functions of the fit parameters and the colors. Results. We show that the photometric redshift accuracy will meet the stringent LSST requirements up to redshift ~2.5 after a selection that is based on the likelihood ratio test or on the apparent magnitude for galaxies with signal-to-noise ratio S/N > 5 in at least 5 bands. The former selection has the advantage of retaining roughly 35% more galaxies for a similar photo-z performance compared to the latter. Photo-z reconstruction using a neural network algorithm is also described. In addition, we utilize the CFHTLS spectro-photometric catalog to outline the possibility of combining the neural network and template-fitting methods. Conclusions. We demonstrate that the photometric redshifts will be accurately estimated with the LSST if a Bayesian prior probability and a calibration sample are used.
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