1,322 research outputs found
Modeling of optical amplifier waveguide based on silicon nanostructures and rare earth ions doped silica matrix gain media by a finite-difference time-domain method: comparison of achievable gain with Er3+ or Nd3+ ions dopants
A comparative study of the gain achievement is performed in a waveguide
optical amplifier whose active layer is constituted by a silica matrix
containing silicon nanograins acting as sensitizer of either neodymium ions (Nd
3+) or erbium ions (Er 3+). Due to the large difference between population
levels characteristic times (ms) and finite-difference time step (10 --17 s),
the conventional auxiliary differential equation and finite-difference
time-domain (ADE-FDTD) method is not appropriate to treat such systems.
Consequently, a new two loops algorithm based on ADE-FDTD method is presented
in order to model this waveguide optical amplifier. We investigate the steady
states regime of both rare earth ions and silicon nanograins levels populations
as well as the electromagnetic field for different pumping powers ranging from
1 to 10 4 mW.mm-2. Furthermore, the three dimensional distribution of
achievable gain per unit length has been estimated in this pumping range. The
Nd 3+ doped waveguide shows a higher gross gain per unit length at 1064 nm (up
to 30 dB.cm-1) than the one with Er 3+ doped active layer at 1532 nm (up to 2
dB.cm-1). Considering the experimental background losses found on those
waveguides we demonstrate that a significant positive net gain can only be
achieved with the Nd 3+ doped waveguide. The developed algorithm is stable and
applicable to optical gain materials with emitters having a wide range of
characteristic lifetimes.Comment: Photonics West , Feb 2015, San Francisco, United States. S, SPIE
Proceedings, 9357 (935709), 2015, Physics and Simulation of Optoelectronic
Devices XXIII. arXiv admin note: text overlap with arXiv:1405.533
Theoretical investigation of the more suitable rare earth to achieve high gain in waveguide based on silica containing silicon nanograins doped with either Nd3+ or Er3+ ions
We present a comparative study of the gain achievement in a waveguide whose
active layer is constituted by a silica matrix containing silicon nanograins
acting as sensitizer of either neodymium ions (Nd3+) or erbium ions (Er3+). By
means of an auxiliary differential equation and finite difference time domain
(ADE-FDTD) approach that we developed, we investigate the steady states regime
of both rare earths ions and silicon nanograins levels populations as well as
the electromagnetic field for different pumping powers ranging from 1 to 104
mW/mm2. Moreover, the achievable gain has been estimated in this pumping range.
The Nd3+ doped waveguide shows a higher gross gain per unit length at 1064 nm
(up to 30 dB/cm) than the one with Er3+ doped active layer at 1532 nm (up to 2
dB/cm). Taking into account the experimental background losses we demonstrate
that a significant positive net gain can only be achieved with the Nd3+ doped
waveguide
A convex programming approach for discrete-time Markov decision processes under the expected total reward criterion
In this work, we study discrete-time Markov decision processes (MDPs) under constraints with Borel state and action spaces and where all the performance functions have the same form of the expected total reward (ETR) criterion over the infinite time horizon. One of our objective is to propose a convex programming formulation for this type of MDPs. It will be shown that the values of the constrained control problem and the associated convex program coincide and that if there exists an optimal solution to the convex program then there exists a stationary randomized policy which is optimal for the MDP. It will be also shown that in the framework of constrained control problems, the supremum of the expected total rewards over the set of randomized policies is equal to the supremum of the expected total rewards over the set of stationary randomized policies. We consider standard hypotheses such as the so-called continuity-compactness conditions and a Slater-type condition. Our assumptions are quite weak to deal with cases that have not yet been addressed in the literature. An example is presented to illustrate our results with respect to those of the literature
LIA@CLEF 2018: Mining events opinion argumentation from raw unlabeled Twitter data using convolutional neural network
International audienceSocial networks on the Internet are becoming increasingly important in our society. In recent years, this type of media, through communication platforms such as Twitter, has brought new research issues due to the massive size of data exchanged and the important number of ever-increasing users. In this context, the CLEF 2018 Mining opinion argumentation task aims to retrieve, for a specific event (festival name or topic), the most diverse argumentative microblogs from a large collection of tweets about festivals in different languages. In this paper, we propose a four-step approach for extracting argumentative microblogs related to a specific query (or event) while no reference data is provided
Espace virtuel de construction collective
Le présent document présente un projet d'espace virtuel de construction collective sur internet. Débuté il y a maintenant six ans, le contexte social et technologique web qui a servi de base à la conception et la production de ce projet était alors très différent. La montée fulgurante des réseaux sociaux n'avait pas encore commencé et le web social en était encore à ses débuts. Ce projet tire donc ses racines des débuts de l'ascension des réseaux sociaux. S'appuyant sur les principes de cyberculture et de communautés virtuelles, cet espace virtuel cherchait à appuyer le développement d'une démarche artistique virtuelle et collective en permettant aux utilisateurs de construire ensemble des espaces tridimensionnels. Fournissant une interface interactive à l'intérieur d'une page internet, l'application projetée se voulait ouverte à tous et évolutive. C'était les utilisateurs qui en fournissaient le contenu. L'application ne fournissait que les outils de construction afin de bâtir les espaces : objets géométriques, lumières, matériaux, etc. Les utilisateurs travaillaient donc collectivement afin de créer les espaces selon des thématiques qu'ils définissaient eux-mêmes : thématique précise, portfolio, espaces artistiques divers, etc. D'un point de vue pratique, le projet était d'une ampleur démesurée par rapport aux ressources disponibles à la production. La complexité technique du projet ainsi que les limites de ressources ont grandement contribué à réduire l'étendue du projet, le limitant à un prototype fonctionnel. Ces derniers éléments ont également limité l'analyse du prototype dans un contexte d'interaction entre les différents utilisateurs. La phase de test a été effectuée principalement par ceux qui ont contribué à la création du projet, limitant de ce fait les données quant à l'efficacité du système dans la création d'une démarche artistique virtuelle et collective. Le projet se résume donc à un prototype fonctionnel ayant permis d'acquérir des connaissances considérables dans l'univers des réseaux sociaux.\ud
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MOTS-CLÉS DE L’AUTEUR : communauté virtuelle, espace virtuel, construction collective, réseaux sociaux, internet
Optimization of preservation methods allows deeper insights into changes of raw milk microbiota
The temporal instability of raw milk microbiota drastically affects the reliability of
microbiome studies. However, little is known about the microbial integrity in preserved samples.
Raw cow milk samples were preserved with azidiol or bronopol and stored at 4 â—¦C, or with dimethyl
sulfoxide (DMSO) or a mixture of azidiol and DMSO and stored at −20 ◦C for up to 30 days. Aliquots
of 5-, 10-, and 30-day post-storage were treated with propidium monoazide (PMA), then analyzed by
sequencing the 16S rRNA gene V3-V4 and V6-V8 regions. The V6-V8 gave a higher richness and
lower diversity than the V3-V4 region. After 5-day storage at 4 â—¦C, the microbiota of unpreserved
samples was characterized by a drastic decrease in diversity, and a significant shift in community
structure. The treatment with azidiol and DMSO conferred the best community stabilization in
preserved raw milk. Interestingly, the azidiol treatment performed as well for up to 10 days, thus
appearing as a suitable alternative. However, neither azidiol nor bronopol could minimize fungal
proliferation as revealed by PMA-qPCR assays. This study demonstrates the preservative ability of a
mixture of azidiol and DMSO and provides deeper insights into the microbial changes occurring
during the cold storage of preserved raw milk
Particle Size Distribution in a Godbert-Greenwald Furnace: Experiments and Modelling
During a dust dispersion, the particle size distribution (PSD) depends on several factors such as the turbulence, the initial particle size and shape as well as the dust concentration. As a consequence, when determining safety parameters using standard procedures, its potential evolution should be considered. Different powders were chosen: glucose, starch, ascorbic acid, glass beads and cellulose. A Godbert-Greenwald furnace was used to disperse the powders and determine their minimum ignition temperature (MIT) according to ISO/IEC 80079-20-2:2016 standard. The PSD of each powder was determined in-situ at different locations using a laser diffraction sensor. Some powders showed clear signs of breakage, as for glucose whose mean diameter decreases from 166 to 76 µm during its dispersion. On the contrary, many samples tended to agglomerate, e.g. starch and cellulose. For instance, the d90 of starch can even be quadrupled under certain conditions. Agglomeration occurs especially for fine dusts due to strong inter-particles forces (e.g. starch) or for elongated fibres due to entanglement phenomenon (e.g. cellulose). During a powder dispersion in the Godbert-Greenwald furnace, the PSD evolves not only as a function of time but also along with its location. The impact of the glass elbow on PSD variation has notably been highlighted by placing the G-G furnace horizontally. For powders showing strong tendency to agglomeration or breakage, the influence of the dispersion pressure has also been studied. The role of such PSD modification on the MIT has been measured and, depending on the dispersion procedure, temperature differences of more than 50°C have been observed. The agglomerate strength was assessed using three models (from Rumpf, Weiler and Kendall works) and compare to the deagglomeration stress exerted on the powders. In the case of cohesive powders, fibres or brittle dusts, attention should be paid to the PSD evolution during MIT determination
AdaWCT: Adaptive Whitening and Coloring Style Injection
Adaptive instance normalization (AdaIN) has become the standard method for
style injection: by re-normalizing features through scale-and-shift operations,
it has found widespread use in style transfer, image generation, and
image-to-image translation. In this work, we present a generalization of AdaIN
which relies on the whitening and coloring transformation (WCT) which we dub
AdaWCT, that we apply for style injection in large GANs. We show, through
experiments on the StarGANv2 architecture, that this generalization, albeit
conceptually simple, results in significant improvements in the quality of the
generated images.Comment: 4 pages + ref
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