275 research outputs found
The critical binary star separation for a planetary system origin of white dwarf pollution
The atmospheres of between one quarter and one half of observed single white
dwarfs in the Milky Way contain heavy element pollution from planetary debris.
The pollution observed in white dwarfs in binary star systems is, however, less
clear, because companion star winds can generate a stream of matter which is
accreted by the white dwarf. Here we (i) discuss the necessity or lack thereof
of a major planet in order to pollute a white dwarf with orbiting minor planets
in both single and binary systems, and (ii) determine the critical binary
separation beyond which the accretion source is from a planetary system. We
hence obtain user-friendly functions relating this distance to the masses and
radii of both stars, the companion wind, and the accretion rate onto the white
dwarf, for a wide variety of published accretion prescriptions. We find that
for the majority of white dwarfs in known binaries, if pollution is detected,
then that pollution should originate from planetary material.Comment: Accepted for publication in MNRA
Texture Segmentation using LBP embedded Region Competition
In this paper, we modify the region competition method to segment textures. First, local Binary pattern (LBP) histogram is adopted to capture the texture information. Then, considering the specific goal of texture segmentation, we propose new assumption about region competition and rewrite the energy function based on LBP histograms. We also develop the two-stage iterative algorithm to make our energy converge to a local minimum. Because of the fast LBP operator and nonparametric histogram model, we can simplify the step of parameter estimating, which is always the most time-consuming. Besides, LBP' s high performance for texture characterization helps to make our method more suitable for texture segmentation problem. Experiments show that the performance of our proposed method is promising, and a robust and fast segmentation of texture images is obtained
Chemical composition of the outer halo globular cluster Palomar 15
Globular clusters (GCs) in the outer Milky Way halo are important tracers of
the assembly history of our Galaxy. Only a few of these objects show spreads in
heavier elements beyond the canonical light-element variations that have
essentially been found throughout the entire Galactic GC system, suggesting a
more complex origin and evolution of these objects. Here, we present the first
abundance analysis of three red giants in the remote ( kpc)
outer halo GC Palomar 15, based on medium-resolution spectra obtained with the
Keck/ESI instrument. Our results ascertain a low iron abundance of
1.940.06 dex with no evidence of any significant abundance spreads,
although this is based on low number statistics. Overall, abundance ratios of
16 species were measured, including carbon, Na, Al, -peak (Mg,Si,Ca,Ti)
and Fe-peak (Sc,V,Cr,Fe,Co,Ni) elements, and the three neutron-capture elements
Sr, Ba, and Eu. The majority of abundances are compatible with those of halo
field stars and those found in other GCs in the outer and inner halos at
similar metallicity. Pal 15 is enhanced to [Mg/Fe]=0.45 dex, while other
-elements, Ca and Ti, are lower by 0.3 dex. Taking Mg as a
representative for [/Fe], and coupled with the lack of any significant
spread in any of the studied elements we conclude that Pal 15 is typical of the
outer halo, as is bolstered by its chemical similarity to the benchmark outer
halo cluster NGC 7492. One star shows evidence of elevated Na and Al
abundances, hinting at the presence of multiple stellar populations in this
cluster.Comment: 9 pages, 8 figures, published in Astronomy & Astrophysics (July 2019
Perturbative Unitarity and NEC Violation in Genesis Cosmology
Explorations of the violation of null energy condition (NEC) in cosmology could enrich our understanding of the very early universe and the related gravity theories. Although a fully stable NEC violation can be realized in the âbeyond Horndeskiâ theory, it remains an open question whether a violation of the NEC is allowed by some fundamental properties of UV-complete theories or the consistency requirements of effective field theory (EFT). We investigate the tree-level perturbative unitarity for stable NEC violations in the contexts of both Galileon and âbeyond Horndeskiâ genesis cosmology, in which the universe is asymptotically Minkowskian in the past. We find that the constraints of perturbative unitarity imply that we may need some unknown new physics below the cut-off scale of the EFT other than that represented by the âbeyond Horndeskiâ operators
Efficient Offline Policy Optimization with a Learned Model
MuZero Unplugged presents a promising approach for offline policy learning
from logged data. It conducts Monte-Carlo Tree Search (MCTS) with a learned
model and leverages Reanalyze algorithm to learn purely from offline data. For
good performance, MCTS requires accurate learned models and a large number of
simulations, thus costing huge computing time. This paper investigates a few
hypotheses where MuZero Unplugged may not work well under the offline RL
settings, including 1) learning with limited data coverage; 2) learning from
offline data of stochastic environments; 3) improperly parameterized models
given the offline data; 4) with a low compute budget. We propose to use a
regularized one-step look-ahead approach to tackle the above issues. Instead of
planning with the expensive MCTS, we use the learned model to construct an
advantage estimation based on a one-step rollout. Policy improvements are
towards the direction that maximizes the estimated advantage with
regularization of the dataset. We conduct extensive empirical studies with
BSuite environments to verify the hypotheses and then run our algorithm on the
RL Unplugged Atari benchmark. Experimental results show that our proposed
approach achieves stable performance even with an inaccurate learned model. On
the large-scale Atari benchmark, the proposed method outperforms MuZero
Unplugged by 43%. Most significantly, it uses only 5.6% wall-clock time (i.e.,
1 hour) compared to MuZero Unplugged (i.e., 17.8 hours) to achieve a 150% IQM
normalized score with the same hardware and software stacks. Our implementation
is open-sourced at https://github.com/sail-sg/rosmo.Comment: ICLR202
Physiological Function of Fermented Modified Dietary Fiber and Its Application in Food
Soluble dietary fiber has small molecular weight, disordered structure and good physicochemical properties. However, natural dietary fiber possesses low bioavailability due to the low content of soluble dietary fiber, so it is essential to modify it. Traditional modification methods such as physical and chemical methods have the disadvantages of high cost, high energy consumption and environmental pollution. Enzymes produced by microorganisms are able to break the glycosidic bond of macromolecules and convert insoluble macromolecules into soluble dietary fiber. Therefore, fermentation is a low-cost, low energy consumption, green and pollution-free new modification method. This article systematically explains the principle of fermentation modification and the factors that affect the modification effect, such as inoculation amount, temperature, pH and so on, then it introduces the physiological function of dietary fiber by fermentation modification and its application in food products such as flour products, dairy products, meat products, providing theoretical basis for further development and utilization of dietary fiber in the future
Near-Infrared Variability in Dusty White Dwarfs: Tracing the Accretion of Planetary Material
The inwards scattering of planetesimals towards white dwarfs is expected to be a stochastic process with variability on human time-scales. The planetesimals tidally disrupt at the Roche radius, producing dusty debris detectable as excess infrared emission. When sufficiently close to the white dwarf, this debris sublimates and accretes on to the white dwarf and pollutes its atmosphere. Studying this infrared emission around polluted white dwarfs can reveal how this planetary material arrives in their atmospheres. We report a near-infrared monitoring campaign of 34 white dwarfs with infrared excesses with the aim to search for variability in the dust emission. Time series photometry of these white dwarfs from the United Kingdom Infrared Telescope (Wide Field Camera) in the J, H and K bands were obtained over baselines of up to three years. We find no statistically significant variation in the dust emission in all three near-infrared bands. Specifically, we can rule out variability at ⌠1.3% for the 13 white dwarfs brighter than 16th mag in K band, and at ⌠10% for the 32 white dwarfs brighter than 18th mag over time-scales of three years. Although to date two white dwarfs, SDSS J095904.69â020047.6 and WD 1226+110, have shown K band variability, in our sample we see no evidence of new K band variability at these levels. One interpretation is that the tidal disruption events which lead to large variabilities are rare, occur on short time-scales
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