441 research outputs found
Least Squares Subdivision Surfaces
International audienceThe usual approach to design subdivision schemes for curves and surfaces basically consists in combining proper rules for regular configurations, with some specific heuristics to handle extraordinary vertices. In this paper, we introduce an alternative approach, called Least Squares Subdivision Surfaces (LS^3), where the key idea is to iteratively project each vertex onto a local approximation of the current polygonal mesh. While the resulting procedure have the same complexity as simpler subdivision schemes, our method offers much higher visual quality, especially in the vicinity of extraordinary vertices. Moreover, we show it can be easily generalized to support boundaries and creases. The fitting procedure allows for a local control of the surface from the normals, making LS^3 very well suited for interactive freeform modeling applications. We demonstrate our approach on diadic triangular and quadrangular refinement schemes, though it can be applied to any splitting strategies
Heat distribution in the Southeast Pacific is only weakly sensitive to high-latitude heat flux and wind stress.
The Southern Ocean features regionallyâvarying ventilation pathways that transport heat and carbon from the surface ocean to the interior thermocline on timescales of decades to centuries, but the factors that control the distribution of heat along these pathways are not well understood. In this study, we use a global ocean state estimate (ECCOv4) to (1) define the recently ventilated interior Pacific (RVP) using numerical passive tracer experiments over a 10âyear period and (2) use an adjoint approach to calculate the sensitivities of the RVP heat content (RVPh) to changes in net heat flux and wind stress. We find that RVPh is most sensitive to local heat flux and wind stress anomalies north of the sea surface height contours that delineate the Antarctic Circumpolar Current, with especially high sensitivities over the South Pacific Gyre. Surprisingly, RVPh is not especially sensitive to changes at higher latitudes.
We perform a set of step response experiments over the South Pacific Gyre, the subduction region, and the highâlatitude SO. In consistency with the adjoint sensitivity fields, RVPh is most sensitive to wind stress curl over the subtropical gyre, which alter isopycnal heave, and it is only weakly sensitive to changes at higher latitudes. Our results suggest that despite the localized nature of mode water subduction hotspots, changes in basinâscale pressure gradients are an important controlling factor on RVPh. Because basinâscale wind stress is expected to change in the coming decades to centuries, our results may have implications for climate, via the atmosphere/ocean partitioning of heat
Alpha-Stable Multichannel Audio Source Separation
International audienceIn this paper, we focus on modeling multichannel audio signals in the short-time Fourier transform domain for the purpose of source separation. We propose a probabilistic model based on a class of heavy-tailed distributions, in which the observed mixtures and the latent sources are jointly modeled by using a certain class of multivariate alpha-stable distributions. As opposed to the conventional Gaussian models, where the observations are constrained to lie just within a few standard deviations near the mean, the pro- posed heavy-tailed model allows us to account for spurious data or important uncertainties in the model. We develop a Monte Carlo Expectation-Maximization algorithm for making inference in the proposed model. We show that our approach leads to significant improvements in audio source separation under corrupted mixtures and in spatial audio object coding
Coagulation status of critically ill patients with and without liver disease assessed using a novel thrombin generation analyzer
Funding Information: NHS Blood and TransplantPeer reviewedPublisher PD
Alpha-stable low-rank plus residual decomposition for speech enhancement
International audienceIn this study, we propose a novel probabilistic model for separating clean speech signals from noisy mixtures by decomposing the mixture spectrograms into a structured speech part and a more flexible residual part. The main novelty in our model is that it uses a family of heavy-tailed distributions, so called the α-stable distributions, for modeling the residual signal. We develop an expectation-maximization algorithm for parameter estimation and a Monte Carlo scheme for posterior estimation of the clean speech. Our experiments show that the proposed method outperforms relevant factorization-based algorithms by a significant margin
Photon-assisted tunneling at the atomic scale: Probing resonant Andreev reflections from Yu-Shiba-Rusinov states
Tunneling across superconducting junctions proceeds by a rich variety of
processes, which transfer single electrons, Cooper pairs, or even larger
numbers of electrons by multiple Andreev reflections. Photon-assisted tunneling
combined with the venerable Tien-Gordon model has long been a powerful tool to
identify tunneling processes between superconductors. Here, we probe
superconducting tunnel junctions including an impurity-induced Yu-Shiba-Rusinov
(YSR) state by exposing a scanning tunneling microscope with a superconducting
tip to microwave radiation. We find that a simple Tien-Gordon description
describes tunneling of single electrons and Cooper pairs into the bare
substrate, but breaks down for tunneling via YSR states by resonant Andreev
reflections. We develop an improved theoretical description which is in
excellent agreement with the data. Our results establish photon-assisted
tunneling as a powerful tool to analyze tunneling processes at the atomic scale
which should be particularly informative for unconventional and topological
superconductors
The B-Star Exoplanet Abundance Study: a co-moving 16-25 Mjup companion to the young binary system HIP 79098
Wide low-mass substellar companions are known to be very rare among low-mass
stars, but appear to become increasingly common with increasing stellar mass.
However, B-type stars, which are the most massive stars within ~150 pc of the
Sun, have not yet been examined to the same extent as AFGKM-type stars in that
regard. In order to address this issue, we launched the ongoing B-star
Exoplanet Abundance Study (BEAST) to examine the frequency and properties of
planets, brown dwarfs, and disks around B-type stars in the Scorpius-Centaurus
(Sco-Cen) association; we also analyzed archival data of B-type stars in
Sco-Cen. During this process, we identified a candidate substellar companion to
the B9-type spectroscopic binary HIP 79098 AB, which we refer to as HIP 79098
(AB)b. The candidate had been previously reported in the literature, but was
classified as a background contaminant on the basis of its peculiar colors.
Here we demonstrate that the colors of HIP 79098 (AB)b are consistent with
several recently discovered young and low-mass brown dwarfs, including other
companions to stars in Sco-Cen. Furthermore, we show unambiguous common proper
motion over a 15-year baseline, robustly identifying HIP 79098 (AB)b as a bona
fide substellar circumbinary companion at a 345+/-6 AU projected separation to
the B9-type stellar pair. With a model-dependent mass of 16-25 Mjup yielding a
mass ratio of <1%, HIP 79098 (AB)b joins a growing number of substellar
companions with planet-like mass ratios around massive stars. Our observations
underline the importance of common proper motion analysis in the identification
of physical companionship, and imply that additional companions could
potentially remain hidden in the archives of purely photometric surveys.Comment: 9 pages, 6 figures, accepted for publication in A&
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