63 research outputs found
Coherent Selection of Independent Trackers for Real-time Object Tracking
International audienceThis paper presents a new method for combining several independent and heterogeneous tracking algorithms for the task of online single-object tracking. The proposed algorithm runs several trackers in parallel, where each of them relies on a different set of complementary low-level features. Only one tracker is selected at a given frame, and the choice is based on a spatio-temporal coherence criterion and normalised confidence estimates. The key idea is that the individual trackers are kept completely independent, which reduces the risk of drift in situations where for example a tracker with an inaccurate or inappropriate appearance model negatively impacts the performance of the others. Moreover, the proposed approach is able to switch between different tracking methods when the scene conditions or the object appearance rapidly change. We experimentally show with a set of Online Adaboost-based trackers that this formulation of multiple trackers improves the tracking results in comparison to more classical combinations of trackers. And we further improve the overall performance and computational efficiency by introducing a selective update step in the tracking framework
Combattre l’obsolescence des compétences: Le rôle préventif de l’apprentissage continu
Skill’s obsolescence is a phenomenon that people can cope with during their professional life. It is defined as an important loss of a part of their knowledge and/or an inappropriate updating of it.
The threat of professional obsolescence is impending in the careers of those working in rapidly changing fields of knowledge. Over time, it is most likely that knowledge and skills that turned out to be relevant in the past are no longer imminent with the evolution of new ways of doing things. In short, the age of information has an impact on both the organization and employed people. Thus, new requirements should be taken into account; they should keep updating their knowledge in order to maintain a moral balance. Obsolescence should be the concern of technical professionals, managers and human resources specialists of any organization. If it is neglected, it can have destructive consequences on both the moral and the career of the individual, and if it is apprehended it offers new perspective of development. However, studies in this field are still rare.L’obsolescence des compétences est un phénomène que pourrait connaitre tout individu durant sa vie professionnelle. Elle est définie par une perte significative et/ou une mise à jour inappropriée des connaissances.
La menace de l'obsolescence des compétences est imminente dans la carrière des personnes qui travaillent dans des domaines de connaissances en évolution rapide. Avec le temps, il est tout à fait normal que les connaissances et compétences qui s’avéraient être pertinentes dans le passé cessent de l’être avec l’avènement de nouvelle façon de faire. En résumé, l’ère informationnelle a des conséquences aussi bien sur l’organisation que sur les individus en emploi. De nouvelles exigences voient le jour. Elles se définissent par l’intégration de nouvelles connaissances pour rester à jour et conserver également un équilibre moral.
L’obsolescence devrait être la préoccupation des professionnels techniques, des gestionnaires et des spécialistes en ressources humaines de toute organisation. Car si elle est négligée, elle peut avoir des conséquences néfastes sur le moral et la carrière de l’individu, et si elle est appréhendée elle lui offre de nouvelles perspectives d’évolution. Or, les études à son sujet demeurent rares
Classifying Global Scene Context for On-line Multiple Tracker Selection
International audienceIn this paper, we present a novel framework for combining several independent on-line trackers using visual scene context. The aim of our method is to decide automatically at each point in time which specific tracking algorithm works best under the given scene or acquisition conditions. To this end, we define a set of generic global context features computed on each frame of a set of training videos. At the same time, we record the performance of each individual tracker on these videos in terms of object bounding box overlap with the ground truth. Then a classifier is trained to estimate which tracker gives the best result given the global scene context in a particular frame. We experimentally show that such a classifier can predict the best tracker with a precision of over 80% in unknown videos with unknown environments. The proposed tracking method further filters the classifier responses temporarily using a Hidden Markov Model in order to avoid rapid oscillations between different trackers. Finally, we evaluated the overall tracking system and showed that this scene context-based tracker selection considerably improves the overall robustness and compares favourably with the state-of-the-art
On the evolutionary status of Be stars. I. Field Be stars near the Sun
A sample of 97 galactic field Be stars were studied by taking into account
the effects induced by the fast rotation on their fundamental parameters. All
program stars were observed in the BCD spectrophotometric system in order to
minimize the perturbations produced by the circumstellar environment on the
spectral photospheric signatures. This is one of the first attempts at
determining stellar masses and ages by simultaneously using model atmospheres
and evolutionary tracks, both calculated for rotating objects. The stellar ages
() normalized to the respective inferred time that each rotating star can
spend in the main sequence phase () reveal a mass-dependent
trend. This trend shows that: a) there are Be stars spread over the whole
interval 0 \la \tau/\tau\_{\rm MS} \la 1 of the main sequence evolutionary
phase; b) the distribution of points in the () diagram indicates that in massive stars (M \ga
12M\_{\odot}) the Be phenomenon is present at smaller
age ratios than for less massive stars (M \la 12M\_{\odot}). This
distribution can be due to: ) higher mass-loss rates in massive objets,
which can act to reduce the surface fast rotation; ) circulation time
scales to transport angular momentum from the core to the surface, which are
longer the lower the stellar mass.Comment: 18 pages, 6 figures, A&A, in pres
A study of the B and Be star population in the field of the LMC open cluster NGC2004 with VLT-FLAMES
Observations of hot stars belonging to the young cluster LMC-NGC2004 and its
surrounding region have been obtained with the VLT-GIRAFFE facilities in MEDUSA
mode. 25 Be stars were discovered; the proportion of Be stars compared to
B-type stars is found to be of the same order in the LMC and in the Galaxy
fields. 23 hot stars were discovered as spectroscopic binaries (SB1 and SB2), 5
of these are found to be eclipsing systems from the MACHO database, with
periods of a few days. About 75% of the spectra in our sample are polluted by
hydrogen (Halpha and Hgamma), [SII] and [NII] nebular lines. These lines are
typical of HII regions. They could be associated with patchy nebulosities with
a bi-modal distribution in radial velocity, with higher values (+335 kms^{-1})
preferentially seen inside the southern part of the known bubble LMC4 observed
in HI at 21 cm.Comment: 12 pages, 17 figures, accepted to A&
Physical parameters of IPHAS-selected classical Be stars. (I. Determination procedure and evaluation of the results.)
Reproduced with permission from Astronomy & Astrophysics, © 2016 ESOWe present a semi-automatic procedure to obtain fundamental physical parameters and distances of classical Be (CBe) stars, based on the Barbier-Chalonge-Divan (BCD) spectrophotometric system. Our aim is to apply this procedure to a large sample of CBe stars detected by the IPHAS photometric survey, to determine their fundamental physical parameters and to explore their suitability as galactic structure tracers. In this paper we describe the methodology used and the validation of the procedure by comparing our results with those obtained from different independent astrophysical techniques for subsamples of stars in common with other studies. We also present a test case study of the galactic structure in the direction of the Perseus Galactic Arm, in order to compare our results with others recently obtained with different techniques and the same sample of stars. We did not find any significant clustering of stars at the expected positions of the Perseus and Outer Galactic Arms, in agreement with previous studies in the same area that we used for verification.Peer reviewedFinal Published versio
Fundamental Parameters of He-Weak and He-Strong Stars
We carried out low resolution spectroscopic observations in the wavelength
range 3400-4700 A of 20 He-weak and 8 He-strong stars to determine their
fundamental parameters by means of the Divan-Chalonge-Barbier (BCD)
spectrophotometric system. For a few He-weak stars we also estimate the
effective temperatures and the angular diameters by integrating absolute fluxes
observed over a wide spectral range. Non-LTE model calculations are carried out
to study the influence of the He/H abundance ratio on the emergent radiation of
He-strong stars and on their Teff determination. We find that the effective
temperatures, surface gravities and bolometric absolute magnitudes of He-weak
stars estimated with the BCD system and the integrated flux method are in good
agreement between each other, and they also agree with previous determinations
based on several different methods. The mean discrepancy between the visual
absolute magnitudes derived using the Hipparcos parallaxes and the BCD values
is on average 0.3 mag for He-weak stars, while it is 0.5 mag for He-strong
stars. For He-strong stars, we note that the BCD calibration, based on stars in
the solar environment, leads to overestimated values of Teff. By means of model
atmosphere calculations with enhanced He/H abundance ratios we show that larger
He/H ratios produce smaller BD which naturally explains the Teff
overestimation. We take advantage of these calculations to introduce a method
to estimate the He/H abundance ratio in He-strong stars. The BD of HD 37479
suggests that the Teff of this star remains fairly constant as the star
spectrum undergoes changes in the intensity of H and He absorption lines. Data
for the He-strong star HD 66765 are reported for the first time.Comment: Accepted for publication in A&
Be stars: one ring to rule them all?
Aims. We report theoretical spectral energy distributions (SEDs), Br
line profiles and visibilities for two scenarios that can explain the disk
dissipation of active hot stars an account for the transition from the Be to
the B spectroscopic phase. Methods. We use the SIMECA code to investigate these
two scenarios: the first one where the disk is formed by successive outbursts
of the central star. A low-density region is developing above the star and
slowly grows outward and forms a ring-like structure that will gradually
excavate the disk. The second one, where a slowly decreasing mass loss, for
instance due to a decrease of the radiative force through an opacity change at
the base of the photosphere, may also be responsible for the vanishing of the
circumstellar disk. Results. We obtain that a clear signature of the disk
dissipation following the ring scenario will be the disappearance of the high
velocity tails in the emission lines and a nearly constant peaks separation.
Moreover, we found that following the ring-like scenario the visibilities must
show an increasing second lobe, an increase of the value of the first zero and,
assuming an unresolved central star, a first zero of the visibility curves that
appends at shorter baselines as far as the disk is been excavate. We propose to
use the AMBER instrument on the VLTI to probe if the the ring scenario is the
one that rule the Be phenomenon.Comment: 10 page
Fatty Acids in Waste Tissues: The Nutraceutical Value of Gonads and Livers from the Moroccan Hypophthalmichthys molitrix and Cyprinus carpio Fishes
Fishes are an important component of human nutrition, mainly acting as source of essential fatty acids in the prevention of cardiovascular disorders. The increase in their consumption has led to a growth of fishes waste; therefore, the disposal and recycling of waste has become a key issue to address, in accordance with circular economy principles. The Moroccan Hypophthalmichthys molitrix and Cyprinus carpio fishes, living in freshwater and marine environments, were collected at mature and immature stages. The fatty acid (FA) profiles of liver and ovary tissues were investigated by GC-MS and compared with edible fillet tissues. The gonadosomatic index, the hypocholesterolemic/hypercholesterolemic ratio, and the atherogenicity and thrombogenicity indexes were measured. Polyunsaturated fatty acids were found to be abundant in the mature ovary and fillet of both species, with a polyunsaturated fatty acids/saturated fatty acids ratio ranging from 0.40 to 1.06 and a monounsaturated fatty acids/polyunsaturated fatty acids ratio between 0.64 and 1.84. Saturated fatty acids were found to be highly abundant in the liver and gonads of both species (range 30-54%), as well as monounsaturated fatty acids (range 35-58%). The results suggested that the exploitation of fish wastes, such as the liver and ovary, may represent a sustainable strategy for the achievement of high value-added molecules with nutraceutical potential
Twelve-month observational study of children with cancer in 41 countries during the COVID-19 pandemic
Introduction Childhood cancer is a leading cause of death. It is unclear whether the COVID-19 pandemic has impacted childhood cancer mortality. In this study, we aimed to establish all-cause mortality rates for childhood cancers during the COVID-19 pandemic and determine the factors associated with mortality. Methods Prospective cohort study in 109 institutions in 41 countries. Inclusion criteria: children <18 years who were newly diagnosed with or undergoing active treatment for acute lymphoblastic leukaemia, non-Hodgkin's lymphoma, Hodgkin lymphoma, retinoblastoma, Wilms tumour, glioma, osteosarcoma, Ewing sarcoma, rhabdomyosarcoma, medulloblastoma and neuroblastoma. Of 2327 cases, 2118 patients were included in the study. The primary outcome measure was all-cause mortality at 30 days, 90 days and 12 months. Results All-cause mortality was 3.4% (n=71/2084) at 30-day follow-up, 5.7% (n=113/1969) at 90-day follow-up and 13.0% (n=206/1581) at 12-month follow-up. The median time from diagnosis to multidisciplinary team (MDT) plan was longest in low-income countries (7 days, IQR 3-11). Multivariable analysis revealed several factors associated with 12-month mortality, including low-income (OR 6.99 (95% CI 2.49 to 19.68); p<0.001), lower middle income (OR 3.32 (95% CI 1.96 to 5.61); p<0.001) and upper middle income (OR 3.49 (95% CI 2.02 to 6.03); p<0.001) country status and chemotherapy (OR 0.55 (95% CI 0.36 to 0.86); p=0.008) and immunotherapy (OR 0.27 (95% CI 0.08 to 0.91); p=0.035) within 30 days from MDT plan. Multivariable analysis revealed laboratory-confirmed SARS-CoV-2 infection (OR 5.33 (95% CI 1.19 to 23.84); p=0.029) was associated with 30-day mortality. Conclusions Children with cancer are more likely to die within 30 days if infected with SARS-CoV-2. However, timely treatment reduced odds of death. This report provides crucial information to balance the benefits of providing anticancer therapy against the risks of SARS-CoV-2 infection in children with cancer
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