181 research outputs found
Transmission of matter wave solitons through nonlinear traps and barriers
The transmissions of matter wave solitons through linear and nonlinear
inhomogeneities induced by the spatial variations of the trap and the
scattering length in Bose-Einstein condensates are investigated. New phenomena,
such as the enhanced transmission of a soliton through a linear trap by a
modulation of the scattering length, are exhibited. The theory is based on the
perturbed Inverse Scattering Transform for solitons, and we show that radiation
effects are important. Numerical simulations of the Gross-Pitaevskii equation
confirm the theoretical predictions.Comment: 6 pages, 4 figure
Velocity estimation via model order reduction
A novel approach to full waveform inversion (FWI), based on a data driven
reduced order model (ROM) of the wave equation operator is introduced. The
unknown medium is probed with pulses and the time domain pressure waveform data
is recorded on an active array of sensors. The ROM, a projection of the wave
equation operator is constructed from the data via a nonlinear process and is
used for efficient velocity estimation. While the conventional FWI via
nonlinear least-squares data fitting is challenging without low frequency
information, and prone to getting stuck in local minima (cycle skipping),
minimization of ROM misfit is behaved much better, even for a poor initial
guess. For low-dimensional parametrizations of the unknown velocity the ROM
misfit function is close to convex. The proposed approach consistently
outperforms conventional FWI in standard synthetic tests.Comment: 5 pages, 3 figures, to be presented at IMAGE 202
Estimating the accuracy of satellite ephemerides using the bootstrap method
International audienceContext: The accuracy of predicted orbital positions depends on the quality of the theorical model and of the observations used to fit the model. During the period of observations, this accuracy can be estimated through comparison with observations. Outside this period, the estimation remains difficult. Many methods have been developed for asteroid ephemerides in order to evaluate this accuracy. Aims: This paper introduces a new method to estimate the accuracy of predicted positions at any time, in particular outside the observation period. Methods: This new method is based upon a bootstrap resampling and allows this estimation with minimal assumptions. Results: The method was applied to two of the main Saturnian satellites, Mimas and Titan, and compared with other methods used previously for asteroids. The bootstrap resampling is a robust and practical method for estimating the accuracy of predicted positions
Bayesian ECG reconstruction using denoising diffusion generative models
In this work, we propose a denoising diffusion generative model (DDGM)
trained with healthy electrocardiogram (ECG) data that focuses on ECG
morphology and inter-lead dependence. Our results show that this innovative
generative model can successfully generate realistic ECG signals. Furthermore,
we explore the application of recent breakthroughs in solving linear inverse
Bayesian problems using DDGM. This approach enables the development of several
important clinical tools. These include the calculation of corrected QT
intervals (QTc), effective noise suppression of ECG signals, recovery of
missing ECG leads, and identification of anomalous readings, enabling
significant advances in cardiac health monitoring and diagnosis
Conditional score-based diffusion models for Bayesian inference in infinite dimensions
Since their first introduction, score-based diffusion models (SDMs) have been
successfully applied to solve a variety of linear inverse problems in
finite-dimensional vector spaces due to their ability to efficiently
approximate the posterior distribution. However, using SDMs for inverse
problems in infinite-dimensional function spaces has only been addressed
recently and by learning the unconditional score. While this approach has some
advantages, depending on the specific inverse problem at hand, in order to
sample from the conditional distribution it needs to incorporate the
information from the observed data with a proximal optimization step, solving
an optimization problem numerous times. This may not be feasible in inverse
problems with computationally costly forward operators. To address these
limitations, in this work we propose a method to learn the posterior
distribution in infinite-dimensional Bayesian linear inverse problems using
amortized conditional SDMs. In particular, we prove that the conditional
denoising estimator is a consistent estimator of the conditional score in
infinite dimensions. We show that the extension of SDMs to the conditional
setting requires some care because the conditional score typically blows up for
small times contrarily to the unconditional score. We also discuss the
robustness of the learned distribution against perturbations of the
observations. We conclude by presenting numerical examples that validate our
approach and provide additional insights
Donepezil-based hybrids as multifunctional anti-Alzheimer's disease chelating agents: Effect of positional isomerization
The intricate and multifactorial nature of Alzheimer's disease (AD) requires the development of compounds able to hit different pathophysiological targets, such as cholinergic dysfunction, deposits of amyloid beta (A beta) peptide and metal dyshomeostasis. In order to continue the search for new anti-AD drugs, a design strategy was once more followed based on repositioning donepezil (DNP) drug, by ortho-attaching a benzylpiperidine mimetic of DNP moiety to a hydroxyphenyl-benzimidazole (BIM) chelating unit (compound 1). Herein, compound 1 and a positional isomer 2 are compared in terms of their potential multiple properties: both present good acetylcholinesterase (AChE) inhibition (low mu molar range) and are moderate/good inhibitors of A beta self- and Cu-mediated aggregation, the inhibition process being mainly due to ligand intercalation between the p-sheets of the fibrils; compound 1 has a higher chelating capacity towards Cu2+ and Zn2+ (pCu = 14.3, pZn = 6.4, pH 7.4, C-I/C-M = 10, C-M = 10(-6) M) than 2 (pCu = 10.7, pZn = 6.3), attributed to its ability to establish a tridentate (N,O,O) coordination to the metal ion. Both compounds are eligible as drug candidates for oral administration but compound 1 shows improved neuroprotective role by completely preventing Ali-induced cell toxicity
PrĂ©venir les troubles musculosquelettiques chez les soignants : connaĂźtre les expositions et Ă©tude des outils dâaide Ă la manutention
ObjectifsDans le cadre de la Caisse nationale de retaite des agents des collectivitĂ©s locales (CNRACL), la dĂ©marche dâĂ©valuation et de prĂ©vention des risques vise Ă conduire Ă une dĂ©marche spĂ©cifique au milieu hospitalier et Ă construire des outils dâĂ©valuation des risques dans le rĂ©seau des CHU français. Les Ă©tudes menĂ©es sur la prĂ©vention des troubles musculosquelettiques (TMS) associent principalement les compĂ©tences en ergonomie, Ă©pidĂ©miologie et mĂ©decine du travail des CHU dâAngers et de Grenoble. MĂ©thode Une premiĂšre Ă©tude Ă©pidĂ©miologique a permis dâidentifier les facteurs de risque de TMS et de lombalgie en milieu hospitalier ; une seconde sâest intĂ©ressĂ©e Ă lâĂ©valuation des outils dâaide Ă la manutention des patients en milieu de soins sous un angle ergonomique. RĂ©sultats Les salariĂ©s du secteur santĂ© sont en moyenne exposĂ©s Ă 2,4 facteurs de risque des 19 rĂ©pertoriĂ©s (3,5 pour le reste du rĂ©seau) et ne souffrent pas plus de TMS des membres supĂ©rieurs que les autres salariĂ©s de la rĂ©gion des Pays-de-la-Loire. En revanche, les expositions aux manutentions manuelles de charges lourdes liĂ©es aux soins aux patients sont plus frĂ©quentes. Les aides techniques pour la manutention Ă©tudiĂ©es ne rĂ©pondent pas aux critĂšres de dĂ©pendance du patient ou aux conditions organisationnelles du service. Du point de vue psychologique, le rapport du patient au matĂ©riel ainsi que lâusage du corps du soignant dans la relation aux soins doivent ĂȘtre pris en compte. Conclusion Lâapproche biomĂ©canique a fait lâobjet de cette premiĂšre investigation. Il sâagit dâune dĂ©marche de prĂ©vention pluridisciplinaire intĂ©grĂ©e dans la politique dâĂ©tablissement
HV 11423: The Coolest Supergiant in the SMC
We call attention to the fact that one of the brightest red supergiants in
the SMC has recently changed its spectral type from K0-1 I (December 2004) to
M4 I (December 2005) and back to K0-1 I (September 2006). An archival spectrum
from the Very Large Telescope reveals that the star was even cooler (M4.5-M5 I)
in December 2001. By contrast, the star was observed to be an M0 I in both
October 1978 and October 1979. The M4-5 I spectral types is by far the latest
type seen for an SMC supergiant, and its temperature in that state places it
well beyond the Hayashi limit into a region of the H-R diagram where the star
should not be in hydrostatic equilibrium. The star is variable by nearly 2 mag
in V, but essentially constant in K. Our modeling of its spectral energy
distribution shows that the visual extinction has varied during this time, but
that the star has remained essentially constant in bolometric luminosity. We
suggest that the star is currently undergoing a period of intense instability,
with its effective temperature changing from 4300 K to 3300 K on the time-scale
of months. It has one of the highest 12-micron fluxes of any RSG in the SMC,
and we suggest that the variability at V is due primarily to changes in
effective temperature, and secondly, due to changes in the local extinction due
to creation and dissipation of circumstellar dust. We speculate that the star
may be nearing the end of its life.Comment: Accepted by the Astrophysical Journa
Enhanced statistical stability in coherent interferometric imaging
http://iopscience.iop.org/0266-5611/International audienc
The chemical composition of the circumstellar envelopes around yellow hypergiant stars
The yellow hypergiant stars (YHGs) are extremely luminous and massive objects
whose general properties are poorly known. Only two of this kind of star show
massive circumstellar envelopes, IRC+10420 and AFGL2343. We aim to study the
chemistry of the circumstellar envelopes around these two sources, by
comparison with well known AGB stars and protoplanetary nebulae. We also
estimate the abundances of the observed molecular species. We have performed
single-dish observations of different transitions for twelve molecular species.
We have compared the ratio of the intensities of the molecular transitions and
of the estimated abundances in AFGL2343 and IRC+10420 with those in O-rich and
C-rich AGB stars and protoplanetary nebulae. Both YHGs, AFGL2343, and
IRC+10420, have been found to have an O-rich chemistry similar to that in
O-rich AGB stars, though for AFGL2343 the emission of most molecules compared
with 13CO lines is relatively weak. Clear differences with the other evolved
sources appear when we compare the line intensity corrected for distance and
the profile widths which are, respectively, very intense and very wide in YHGs.
The abundances obtained for IRC+10420 agree with those found in AGB stars, but
in general those found in AFGL2343, except for 13CO, are too low. This
apparently low molecular abundance in AFGL2343 could be due to the fact that
these molecules are present only in an inner region of the shell where the mass
is relatively low.Comment: 14 pages, 12 figure
- âŠ