678 research outputs found
Constant Approximation for -Median and -Means with Outliers via Iterative Rounding
In this paper, we present a new iterative rounding framework for many
clustering problems. Using this, we obtain an -approximation algorithm for -median with outliers, greatly
improving upon the large implicit constant approximation ratio of Chen [Chen,
SODA 2018]. For -means with outliers, we give an -approximation, which is the first -approximation for
this problem. The iterative algorithm framework is very versatile; we show how
it can be used to give - and -approximation
algorithms for matroid and knapsack median problems respectively, improving
upon the previous best approximations ratios of [Swamy, ACM Trans.
Algorithms] and [Byrka et al, ESA 2015].
The natural LP relaxation for the -median/-means with outliers problem
has an unbounded integrality gap. In spite of this negative result, our
iterative rounding framework shows that we can round an LP solution to an
almost-integral solution of small cost, in which we have at most two
fractionally open facilities. Thus, the LP integrality gap arises due to the
gap between almost-integral and fully-integral solutions. Then, using a
pre-processing procedure, we show how to convert an almost-integral solution to
a fully-integral solution losing only a constant-factor in the approximation
ratio. By further using a sparsification technique, the additive factor loss
incurred by the conversion can be reduced to any
CO Depletion in Protoplanetary Disks: A Unified Picture Combining Physical Sequestration and Chemical Processing
The gas-phase CO abundance (relative to hydrogen) in protoplanetary disks
decreases by up to 2 orders of magnitude from its ISM value ,
even after accounting for freeze-out and photo-dissociation. Previous studies
have shown that while local chemical processing of CO and the sequestration of
CO ice on solids in the midplane can both contribute, neither of these
processes appears capable of consistently reaching the observed depletion
factors on the relevant timescale of . In this study, we
model these processes simultaneously by including a compact chemical network
(centered on carbon and oxygen) to 2D () simulations of the outer
() disk regions that include turbulent diffusion, pebble
formation, and pebble dynamics. In general, we find that the CO/H abundance
is a complex function of time and location. Focusing on CO in the warm
molecular layer, we find that only the most complete model (with chemistry and
pebble evolution included) can reach depletion factors consistent with
observations. In the absence of pressure traps, highly-efficient planetesimal
formation, or high cosmic ray ionization rates, this model also predicts a
resurgence of CO vapor interior to the CO snowline. We show the impact of
physical and chemical processes on the elemental (C/O) and (C/H) ratios (in the
gas and ice phases), discuss the use of CO as a disk mass tracer, and, finally,
connect our predicted pebble ice compositions to those of pristine
planetesimals as found in the Cold Classical Kuiper Belt and debris disks.Comment: Accepted for publication in The Astrophysical Journa
Alleviating Human-level Shift : A Robust Domain Adaptation Method for Multi-person Pose Estimation
Human pose estimation has been widely studied with much focus on supervised
learning requiring sufficient annotations. However, in real applications, a
pretrained pose estimation model usually need be adapted to a novel domain with
no labels or sparse labels. Such domain adaptation for 2D pose estimation
hasn't been explored. The main reason is that a pose, by nature, has typical
topological structure and needs fine-grained features in local keypoints. While
existing adaptation methods do not consider topological structure of
object-of-interest and they align the whole images coarsely. Therefore, we
propose a novel domain adaptation method for multi-person pose estimation to
conduct the human-level topological structure alignment and fine-grained
feature alignment. Our method consists of three modules: Cross-Attentive
Feature Alignment (CAFA), Intra-domain Structure Adaptation (ISA) and
Inter-domain Human-Topology Alignment (IHTA) module. The CAFA adopts a
bidirectional spatial attention module (BSAM)that focuses on fine-grained local
feature correlation between two humans to adaptively aggregate consistent
features for adaptation. We adopt ISA only in semi-supervised domain adaptation
(SSDA) to exploit the corresponding keypoint semantic relationship for reducing
the intra-domain bias. Most importantly, we propose an IHTA to learn more
domain-invariant human topological representation for reducing the inter-domain
discrepancy. We model the human topological structure via the graph convolution
network (GCN), by passing messages on which, high-order relations can be
considered. This structure preserving alignment based on GCN is beneficial to
the occluded or extreme pose inference. Extensive experiments are conducted on
two popular benchmarks and results demonstrate the competency of our method
compared with existing supervised approaches.Comment: Accepted By ACM MM'202
The emerging structure of the Extended Evolutionary Synthesis: where does Evo-Devo fit in?
The Extended Evolutionary Synthesis (EES) debate is gaining ground in contemporary evolutionary biology. In parallel, a number of philosophical standpoints have emerged in an attempt to clarify what exactly is represented by the EES. For Massimo Pigliucci, we are in the wake of the newest instantiation of a persisting Kuhnian paradigm; in contrast, Telmo Pievani has contended that the transition to an EES could be best represented as a progressive reformation of a prior Lakatosian scientific research program, with the extension of its Neo-Darwinian core and the addition of a brand-new protective belt of assumptions and auxiliary hypotheses. Here, we argue that those philosophical vantage points are not the only ways to interpret what current proposals to āextendā the Modern Synthesis-derived āstandard evolutionary theoryā (SET) entail in terms of theoretical change in evolutionary biology. We specifically propose the image of the emergent EES as a vast network of models and interweaved representations that, instantiated in diverse practices, are connected and related in multiple ways. Under that assumption, the EES could be articulated around a paraconsistent network of evolutionary theories (including some elements of the SET), as well as models, practices and representation systems of contemporary evolutionary biology, with edges and nodes that change their position and centrality as a consequence of the co-construction and stabilization of facts and historical discussions revolving around the epistemic goals of this area of the life sciences. We then critically examine the purported structure of the EESāpublished by Laland and collaborators in 2015āin light of our own network-based proposal. Finally, we consider which epistemic units of Evo-Devo are present or still missing from the EES, in preparation for further analyses of the topic of explanatory integration in this conceptual framework
A proposal for a coordinated effort for the determination of brainwide neuroanatomical connectivity in model organisms at a mesoscopic scale
In this era of complete genomes, our knowledge of neuroanatomical circuitry
remains surprisingly sparse. Such knowledge is however critical both for basic
and clinical research into brain function. Here we advocate for a concerted
effort to fill this gap, through systematic, experimental mapping of neural
circuits at a mesoscopic scale of resolution suitable for comprehensive,
brain-wide coverage, using injections of tracers or viral vectors. We detail
the scientific and medical rationale and briefly review existing knowledge and
experimental techniques. We define a set of desiderata, including brain-wide
coverage; validated and extensible experimental techniques suitable for
standardization and automation; centralized, open access data repository;
compatibility with existing resources, and tractability with current
informatics technology. We discuss a hypothetical but tractable plan for mouse,
additional efforts for the macaque, and technique development for human. We
estimate that the mouse connectivity project could be completed within five
years with a comparatively modest budget.Comment: 41 page
UV-driven Chemistry as a Signpost for Late-stage Planet Formation
The chemical reservoir within protoplanetary disks has a direct impact on
planetary compositions and the potential for life. A long-lived carbon-and
nitrogen-rich chemistry at cold temperatures (<=50K) is observed within cold
and evolved planet-forming disks. This is evidenced by bright emission from
small organic radicals in 1-10 Myr aged systems that would otherwise have
frozen out onto grains within 1 Myr. We explain how the chemistry of a
planet-forming disk evolves from a cosmic-ray/X-ray-dominated regime to an
ultraviolet-dominated chemical equilibrium. This, in turn, will bring about a
temporal transition in the chemical reservoir from which planets will accrete.
This photochemical dominated gas phase chemistry develops as dust evolves via
growth, settling and drift, and the small grain population is depleted from the
disk atmosphere. A higher gas-to-dust mass ratio allows for deeper penetration
of ultraviolet photons is coupled with a carbon-rich gas (C/O > 1) to form
carbon-bearing radicals and ions. This further results in gas phase formation
of organic molecules, which then would be accreted by any actively forming
planets present in the evolved disk.Comment: Accepted to Nature Astronomy, Published Dec 8th 202
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Respective impacts of Arctic sea ice decline and increasing greenhouse gases concentration on Sahel precipitation
The impact of climate change on Sahel precipitation is uncertain and has to be widely documented. Recently, it has been shown that Arctic sea ice loss leverages the global warming effects worldwide, suggesting a potential impact of Arctic sea ice decline on tropical regions. However, defining the specific roles of increasing greenhouse gases (GHG) concentration and declining Arctic sea ice extent on Sahel climate is not straightforward since the former impacts the latter. We avoid this dependency by analysing idealized experiments performed with the CNRM-CM5 coupled model. Results show that the increase in GHG concentration explains most of the Sahel precipitation change. We found that the impact due to Arctic sea ice loss depends on the level of atmospheric GHG concentration. When the GHG concentration is relatively low (values representative of 1980s), then the impact is moderate over the Sahel. However, when the concentration in GHG is levelled up, then Arctic sea ice loss leads to increased Sahel precipitation. In this particular case the ocean-land meridional gradient of temperature strengthens, allowing a more intense monsoon circulation. We linked the non-linearity of Arctic sea ice decline impact with differences in temperature and sea level pressure changes over the North Atlantic Ocean. We argue that the impact of the Arctic sea ice loss will become more relevant with time, in the context of climate change
Tn1546 is part of a larger plasmid-encoded genetic unit horizontally disseminated among clonal Enterococcus faecium lineages
o determine the genetic composition of the first VanA-type plasmid (pIP816) reported, which was isolated from a clinical Enterococcus faecium (BM4147) strain in France in 1986, and to reveal the genetic units responsible for the dissemination of the vanA gene cluster by comparisons with current, published and additionally generated vanA-spanning plasmid sequences obtained from a heterogeneous E. faecium strain collection (nā=ā28).Plasmid sequences were produced by shotgun sequencing using ABI dye chemistry and primer walking, and were subsequently annotated. Comparative sequence analysis of the vanA region was done with published plasmids, with a partial vanA plasmid (pVEF4) reported here and to >140 kb of sequence obtained from a collection of vanA-harbouring plasmid fragments. Bioinformatic analyses revealed that pIP816 from 1986 and contemporary vanA plasmids shared a conserved genetic fragment of 25 kb, spanning the 10.85 kb vanA cluster encoded by Tn1546, and that the larger unit is present in both clinical and animal complexes of E. faecium. A new group II intron in pVEF4 was characterized. Comparative DNA analyses suggest that Tn1546 disseminates in and between clonal complexes of E. faecium as part of a larger genetic unit, possibly as a composite transposon flanked by IS1216 elements
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