Abstract Accurately characterizing the intrinsic stellar photometric noise induced by stellar astrophysics, such as stellar activity, granulation, and oscillations, is of crucial importance for ...detecting transiting exoplanets. In this study, we investigate the relation between the intrinsic stellar photometric noise, quantified by the Kepler combined differential photometric precision (CDPP) metric, and the level of stellar chromospheric activity, indicated by the S -index of Ca ii H K lines derived from LAMOST spectra. Our results reveal a clear positive correlation between the S -index and robust rms values of CDPP, with the correlation becoming more significant at higher activity levels and on longer timescales. We have therefore built an empirical relation between the robust rms values of CDPP and the S -index as well as T eff , log g , Fe/H, and the apparent magnitude, with the XGBoost regression algorithm, using the LAMOST–Kepler common star sample as the training set. This method achieves a precision of ∼20 ppm for inferring the intrinsic noise from the S -index and other stellar labels on a 6 hr integration duration. We have applied this empirical relation to the full LAMOST DR7 spectra database and obtained the intrinsic noise predictions for 1,358,275 stars. The resultant catalog is publicly available and expected to be valuable for optimizing target selection for future exoplanet-hunting space missions, such as the Earth 2.0 mission.
Abstract The empirical relations between rotation period, chromospheric activity, and age can be used to estimate stellar age. To calibrate these relations, we present a catalog, including the masses ...and ages of 52,321 FGK dwarfs, 47,489 chromospheric activity index log R HK + , 6077 rotation periods P rot , and variability amplitudes S ph , based on data from LAMOST DR7, Kepler, and Gaia Data Release 3. We find a pronounced correlation among P rot , age, and Fe/H throughout the main-sequence phase for F dwarfs. However, the decrease of log R HK + over time is not significant except for those with Fe/H < −0.1. For G dwarfs, both P rot and log R HK + are reliable age probes in the ranges ∼2–11 Gyr and ∼2–13 Gyr, respectively. K dwarfs exhibit a prominent decrease in log R HK + within the age range of ∼3–13 Gyr when the relation of P rot – τ is invalid. These relations are very important for promptly estimating the age of a vast number of stars, thus serving as a powerful tool in advancing the fields of exoplanet properties, stellar evolution, and Galactic archeology.
Predicting Origin-Destination (OD) flow is a crucial problem for intelligent transportation. However, it is extremely challenging because of three reasons: first, correlations exist between both ...origins and destinations; second, the correlations are dynamic across the time; at last, there are multiple correlations from different aspects. To the best of our knowledge, existing models for OD flow prediction cannot tackle all of these three issues simultaneously. We propose Multi-Perspective Graph Convolutional Networks (MPGCN) to capture the complex dependencies. Our proposed model first utilizes long short-term memory (LSTM) network to extract temporal features for each OD pair and then learns the spatial dependency of origins and destinations by a two-dimensional graph convolutional network. Furthermore, we design a dynamic graph together with two static graphs to capture the complicated spatial dependencies and use an average strategy to obtain the final predicted OD flow. We conduct extensive experiments on two large-scale and real-world datasets, which not only demonstrate our design philosophy but also validate the effectiveness of the proposed model.
•We fabricated reverse ordered Cu2O–ZnO heterojunctions by magnetron sputtering.•An obvious asymmetry was observed in the VBOs of Cu2O/ZnO–ZnO/Cu2O by XPS.•We analyzed the asymmetry by d–p electronic ...repulsion in the valence band of Cu2O.•Growth order can affect crystal structure of the top layer of the heterojunction.
X-ray photoelectron spectroscopy was used to investigate the valence-band offsets (VBOs) of the Cu2O–ZnO heterojunctions fabricated by magnetron sputtering. A significant forward–backward asymmetry was observed in the band alignments of Cu2O/ZnO–ZnO/Cu2O heterojunctions. The valence band offsets of 2.91eV and 2.52eV were achieved in Cu2O/ZnO and ZnO/Cu2O heterojunctions respectively. The asymmetry was attributed to the lattice distortion of the Cu2O at the interface of Cu2O/ZnO heterojunction. The compressed Cu2O lattices lead to the upward shift of the top of the valence-band of Cu2O, and thus the measured VBO of Cu2O/ZnO is larger than that of ZnO/Cu2O. Considering the band alignments, the ZnO/Cu2O structure is expected to have more advantage in photovoltaic application than Cu2O/ZnO structure.
Models dealing with ordinal multinomial(OM) variables have drawn much attention in regression analysis. Studies on the ordinal response variable have been solidly established and widely applied. ...However, few studies have investigated generalized linear models with OM covariates, especially in high-dimensional situations. For this problem, the detection of pseudo categories for the OM covariates and the selection of other important covariates need to be concerned simultaneously. This paper proposes an
-norm penalized estimation procedure to detect pseudo categories of OM covariates in high-dimensional(
) Cox models. The estimation approach is based on the combination of a transformation method of dummy variables and the penalized partial likelihood. Theoretical properties, such as consistency and oracle property of the proposed estimators, are rigorously established under some regularity conditions. The performance of the proposed method is illustrated by analyses on both simulated data and real data.
Abstract
Varying oxygen abundance could impact modeling-inferred ages. This work aims to estimate the ages of dwarfs considering observed oxygen abundance. To characterize 67,503 LAMOST and 4006 ...GALAH FGK-type dwarf stars, we construct a grid of stellar models, which take into account oxygen abundance as an independent model input. Compared with ages determined with commonly used
α
-enhanced models, we find a difference of ∼9% on average when the observed oxygen abundance is considered. The age differences between the two types of models are correlated to Fe/H and O/
α
, and they are relatively significant on stars with Fe/H ≲ −0.6 dex. Generally, varying 0.2 dex in O/
α
will alter the age estimates of metal-rich (−0.2 < Fe/H < 0.2) stars by ∼10% and relatively metal-poor (−1 < Fe/H < −0.2) stars by ∼15%. Of the low-O stars with Fe/H < 0.1 dex and O/
α
∼−0.2 dex, many have fractional age differences of ≥ 10% and even reach up to 27%. The fractional age difference of high-O stars with O/
α
∼0.4 dex reaches up to −33% to −42% at Fe/H ≲ −0.6 dex. We also analyze the chemical properties of these stars. We find a decreasing trend of Fe/H with ages from 7.5–9 Gyr to 5–6.5 Gyr for the stars from the LAMOST and GALAH. The O/Fe of these stars increases with decreasing age from 7.5–9 Gyr to 3–4 Gyr, indicating that the younger population is more O rich.
Novel CoO nanostructure arrays on nickel foam with needle-like and rhombic morphologies have been prepared by using urea and hexamethylenetetramine as hydrolysis agents through fluoride-assisted ...hydrothermal method, respectively. The possible formation mechanism and effect factors of the novel arrays were systematically investigated by X-ray diffraction, scanning and transmission electron microscopies, N2 sorption, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The precursor Co(CO3)0.5(OH)·0.11H2O or Co(OH)F plays a crucial role in the formation of needle-like or rhombic arrays. As-prepared precursor arrays can be further converted to corresponding CoO arrays by annealing at 450 °C for 2 h without signification alteration of one-dimensional (1D) morphology. When tested as anodes for lithium ion batteries (LIBs) without the addition of other ancillary materials (carbon black and binder), the synthesized CoO arrays with needle-like and rhombic morphologies deliver ultrahigh initial discharge capacities of 1973.3 and 1447.9 mAh g–1, respectively. In addition, they also maintain high reversible capacities of 710 and 719 mAh g–1 at 0.2 C after 50 cycles, respectively.
Abstract
This paper presents a correction to the scaling relations for red giant stars using model-based masses and radii. We measure radial-mode frequencies from Kepler observations for 3642 ...solar-like oscillators on the red giant branch and use them to characterize the stars with grid-based modeling. We determine fundamental stellar parameters with good precision: the typical uncertainty is 4.5% for mass, 16% for age, 0.006 dex for surface gravity, and 1.7% for radius. We also achieve good accuracy for estimated masses and radii, based on a comparison with those determined for eclipsing binaries. We find a systematic offset of ∼15% in mass and ∼7% in radius between the modeling solutions and the scaling relations. Further investigation indicates that these offsets are mainly caused by a systematic bias in the Δ
ν
scaling relation: the original scaling relation underestimates the Δ
ν
value by ∼4%, on average, and it is important to correct for the surface term in the calibration. We find no significant offset in the
ν
max
scaling relation, although a clear metallicity dependence is seen and we suggest including a metallicity term in the formulae. Lastly, we calibrate new scaling relations for red giant stars based on observed global seismic parameters, spectroscopic effective temperatures and metallicities, and modeling-inferred masses and radii.
Abstract
The Transiting Exoplanet Survey Satellite (TESS) mission searches for new exoplanets. The observing strategy of TESS results in high-precision photometry of millions of stars across the sky, ...allowing for detailed asteroseismic studies of individual systems. In this work, we present a detailed asteroseismic analysis of the giant star HD 76920 hosting a highly eccentric giant planet (
e
= 0.878) with an orbital period of 415 days, using five sectors of TESS light curve that cover around 140 days of data. Solar-like oscillations in HD 76920 are detected around 52
μ
Hz by TESS for the first time. By utilizing asteroseismic modeling that takes classical observational parameters and stellar oscillation frequencies as constraints, we determine improved measurements of the stellar mass (1.22 ± 0.11
M
⊙
), radius (8.68 ± 0.34
R
☉
), and age (5.2 ± 1.4 Gyr). With the updated parameters of the host star, we update the semimajor axis and mass of the planet as
a
= 1.165 ± 0.035 au and
M
p
sin
i
=
3.57
±
0.22
M
Jup
. With an orbital pericenter of 0.142 ± 0.005 au, we confirm that the planet is currently far away enough from the star to experience negligible tidal decay until being engulfed in the stellar envelope. We also confirm that this event will occur within about 100 Myr, depending on the stellar model used.
Region-level demand forecasting is an essential task in ridehailing services. Accurate ride-hailing demand forecasting can guide vehicle dispatching, improve vehicle utilization, reduce the ...wait-time, and mitigate traffic congestion. This task is challenging due to the complicated spatiotemporal dependencies among regions. Existing approaches mainly focus on modeling the Euclidean correlations among spatially adjacent regions while we observe that non-Euclidean pair-wise correlations among possibly distant regions are also critical for accurate forecasting. In this paper, we propose the spatiotemporal multi-graph convolution network (ST-MGCN), a novel deep learning model for ride-hailing demand forecasting. We first encode the non-Euclidean pair-wise correlations among regions into multiple graphs and then explicitly model these correlations using multi-graph convolution. To utilize the global contextual information in modeling the temporal correlation, we further propose contextual gated recurrent neural network which augments recurrent neural network with a contextual-aware gating mechanism to re-weights different historical observations. We evaluate the proposed model on two real-world large scale ride-hailing demand datasets and observe consistent improvement of more than 10% over stateof-the-art baselines.
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