Abstract We propose an extended formalism for the spectral broadening function (BF) based on the multiplication rule of block matrices. The formalism, which we named the binary BF (BBF), can produce ...decomposed BFs for individual components of a binary star system by using two spectral templates. The decomposed BFs can be used to derive precise rotational profiles and radial velocities for individual components. We test the BBF on simulated spectra and actual observational spectra to show that the method is feasible on spectroscopic binaries, even when the spectral lines of two stellar components are heavily blended. To demonstrate the capability of the method, we conduct a simulation of “sketching” (imaging) a transiting circumbinary exoplanet using the BBF. We also discuss issues of implementation such as the variation of BBF with biased templates, the pros and cons of BBF, and cases when the method is not applicable.
Sequence generative adversarial networks (SeqGAN) have been used to improve conditional sequence generation tasks, for example, chit-chat dialogue generation. To stabilize the training of SeqGAN, ...Monte Carlo tree search (MCTS) or reward at every generation step (REGS) is used to evaluate the goodness of a generated subsequence. MCTS is computationally intensive, but the performance of REGS is worse than MCTS. In this paper, we propose stepwise GAN (StepGAN), in which the discriminator is modified to automatically assign scores quantifying the goodness of each subsequence at every generation step. StepGAN has significantly less computational costs than MCTS. We demonstrate that StepGAN outperforms previous GAN-based methods on both synthetic experiment and chit-chat dialogue generation.
Luck in the Life of a Geographer Tuan, Yi-Fu
The Geographical bulletin (Ypsilanti, Mich.),
05/2021, Letnik:
62, Številka:
1
Journal Article
Recenzirano
Luck plays a far greater role in people's lives than they are willing to acknowledge, for the obvious reason that it detracts from the role as agents. Tuan used to see himself as planning his career ...path and then following it. Only now, in extreme old age, do he finds the idea of that planned life untenable. Looking back, at critical points, it was not the wisdom of his planning, but rather happenstance that took him to the more fruitful way.
Abstract
According to the number of detected bursts, fast radio bursts (FRBs) can be classified into two categories, i.e., one-off FRBs and repeating ones. We make a statistical comparison of these ...two categories based on the first FRB catalog of the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst Project. Using the Anderson–Darling, Kolmogorov–Smirnov, and Energy statistic tests, we find significant statistical differences (
p
-value < 0.001) in the burst properties between the one-off FRBs and the repeating ones. More specifically, after controlling for distance, we find that the peak luminosities of one-off FRBs are, on average, higher than the repeating ones; the pulse temporal widths of repeating FRBs are, on average, longer than the one-off ones. The differences indicate that these two categories could have distinct physical origins. Moreover, we discuss the subpopulations of FRBs and provide statistical evidence to support the existence of subpopulations in one-off FRBs and in repeating ones.
Abstract
The time-domain (TD) surveys of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) yield high-cadence radial velocities, paving a new avenue to study binary systems ...including compact objects. In this work, we explore LAMOST TD spectroscopic data of four K2 plates and present a sample of six single-lined spectroscopic binaries that may contain compact objects. We conduct analyses using phase-resolved radial velocity measurements of the visible star to characterize each source and to infer the properties of invisible companion. By fitting the radial velocity curves for the six targets, we obtain accurate orbital periods, ranging from ∼(0.6 to 6) days, and radial velocity semiamplitudes, ranging from ∼(50 to 130) km s
−1
. We calculate the mass function of the unseen companions to be between 0.08 and 0.17
M
⊙
. Based on the mass function and the estimated stellar parameters of the visible star, we determine the minimum mass of the hidden star. Three targets—J034813, J063350, and J064850—show ellipsoidal variability in the light curves from K2, ZTF, and TESS surveys. Therefore, we can put constraints on the mass of the invisible star using the ellipsoidal variability. We identify no X-ray counterparts for these targets except for J085120, of which the X-ray emission can be ascribed to stellar activity. We note that the nature of these six candidates is worth further characterization utilizing multiwavelength follow-up observations.
Abstract
Finding nearby neutron stars can probe the supernova and metal-enrichment histories near our solar system. Recently, Lin et al. reported an exciting neutron star candidate, Two Micron All ...Sky Survey J15274848+3536572 (hereafter J1527), with a small Gaia distance of 118 pc. They claim that J1527 harbors an unseen neutron star candidate with an unusually low mass of 0.98 ± 0.03
M
⊙
. In this work, we use the Canada–France–Hawaii Telescope high-resolution spectrum to measure J1527's orbital inclination independently. Our spectral fitting suggests an orbital inclination of 63° ± 2°. Instead, by fitting a complex hybrid variability model consisting of the ellipsoidal-variation component and the starspot modulation to the observed light curve, Lin et al. obtain an orbital inclination of
45.2
−
0.20
+
0.13
degrees. We speculate that the orbital inclination obtained by the light-curve fitting is underestimated since J1527's light curves are obviously not pure ellipsoidal variations. According to our new inclination (
i
∼ 63°), the mass of the unseen compact object is reduced to 0.69 ± 0.02
M
⊙
, which is as massive as a typical white dwarf.
Geography is useful, indeed necessary, to survival. Everyone must know where to find food, water, and a place of rest, and, in the modern world, all must make an effort to make the Earth—our ...home—habitable. But much present-day geography lacks drama, with its maps and statistics, descriptions and analysis, but no acts of chivalry, no sense of quest. Not long ago, however, geography was romantic. Heroic explorers ventured to forbidding environments—oceans, mountains, forests, caves, deserts, polar ice caps—to test their power of endurance for reasons they couldn't fully articulate. Why climb Everest? "Because it is there."             Yi-Fu Tuan has established a global reputation for deepening the field of geography by examining its moral, universal, philosophical, and poetic potentials and implications. In his twenty-second book, Romantic Geography , he continues to engage the wide-ranging ideas that have made him one of the most influential geographers of our time. In this elegant meditation, he considers the human tendency—stronger in some cultures than in others—to veer away from the middle ground of common sense to embrace the polarized values of light and darkness, high and low, chaos and form, mind and body. In so doing, venturesome humans can find salvation in geographies that cater not so much to survival needs (or even to good, comfortable living) as to the passionate and romantic aspirations of their nature. Romantic Geography is thus a paean to the human spirit, which can lift us to the heights but also plunge us into the abyss.
The decellularization of long segments of tubular tissues such as blood vessels may be improved by perfusing decellularization solution into their lumen. Particularly, transmural flow that may be ...introduced by the perfusion, if any, is beneficial to removing immunogenic cellular components in the vessel wall. When human umbilical arteries (HUAs) were perfused at a transmural pressure, however, very little transmural flow was observed. We hypothesized that a watertight lining at the abluminal surface of HUAs hampered the transmural flow and tested the hypothesis by subjecting the abluminal surface to enzyme digestion. Specifically, a highly viscous collagenase solution was applied onto the surface, thereby restricting the digestion to the surface. The localized digestion resulted in a water-permeable vessel without damaging the vessel wall. The presence of the abluminal lining and its successful removal were also supported by evidence from SEM, TEM, and mechanical testing. The collagenase-treated HUAs were decellularized with 1% sodium dodecyl sulfate (SDS) solution under either rotary agitation, simple perfusion, or pressurized perfusion. Regardless of decellularization conditions, the decellularization of HUAs was significantly enhanced after the abluminal lining removal. Particularly, complete removal of DNA was accomplished in 24 h by pressurized perfusion of the SDS solution. We conclude that the removal of the abluminal lining can improve the perfusion-assisted decellularization.
Abstract The Gaia Data Release 3 (DR3) mission has identified and provided about 440,000 binary systems with orbital solutions, offering a valuable resource for searching binaries including a compact ...component. By combining the Gaia DR3 data with radial velocities from the LAMOST spectroscopic survey, we identify three wide binaries possibly containing a compact object. For two of these sources with a main-sequence companion, no obvious excess is observed in the blue/red band of the Gaia DR3 XP spectra, and the LAMOST medium-resolution spectra exhibit clear single-lined features. The absence of an additional component from spectral disentangling analysis further suggests the presence of compact objects within these systems. On the other hand, the visible star of the third source is a stripped giant star. In contrast to most binaries including stripped stars, no emission line is detected in the optical spectra. The unseen star could potentially be a massive white dwarf or neutron star, but the possibility of an F-type dwarf star scenario cannot be ruled out. An examination of about 10 binaries containing white dwarfs or neutron stars using both kinematic and chemical methods suggests most of these systems are located in the thin disk of the Milky Way.
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