Efficient Relaxations for Dense CRFs with Sparse Higher Order Potentials

Dense conditional random fields (CRFs) have become a popular framework for modelling several problems in computer vision such as stereo correspondence and multi-class semantic segmentation. By modelling long-range interactions, dense CRFs provide a labelling that captures finer detail than their sparse counterparts. Currently, the state-of-the-art algorithm performs mean-field inference using a filter-based method but fails to provide a strong theoretical guarantee on the quality of the solution. A question naturally arises as to whether it is possible to obtain a maximum a posteriori (MAP) estimate of a dense CRF using a principled method. Within this paper, we show that this is indeed possible. We will show that, by using a filter-based method, continuous relaxations of the MAP problem can be optimised efficiently using state-of-the-art algorithms. Specifically, we will solve a quadratic programming (QP) relaxation using the Frank-Wolfe algorithm and a linear programming (LP) relaxation by developing a proximal minimisation framework. By exploiting labelling consistency in the higher-order potentials and utilising the filter-based method, we are able to formulate the above algorithms such that each iteration has a complexity linear in the number of classes and random variables. The presented algorithms can be applied to any labelling problem using a dense CRF with sparse higher-order potentials. In this paper, we use semantic segmentation as an example application as it demonstrates the ability of the algorithm to scale to dense CRFs with large dimensions. We perform experiments on the Pascal dataset to indicate that the presented algorithms are able to attain lower energies than the mean-field inference method

Switching waves-induced broadband Kerr frequency comb in fiber Fabry-Perot resonators

We report the generation of broadband frequency combs in fiber Fabry-Perot resonators in the normal dispersion regime enabled by the excitation of switching waves. We theoretically characterise the process by means of a transverse linear stability analysis of the Lugiato-Lefever equation, enabling precise prediction of the switching waves' frequencies. Experimentally, we employed a pulsed-pump fiber Fabry-Perot resonator operating in the normal dispersion regime, integrated into an all-fiber experimental setup. The synchronisation mismatch and the influence of dispersion is thoroughly discussed, unveiling the potential to generate a frequency comb spanning over 15 THz bandwidth, specifically leveraging a flattened low dispersion cavity

Theory of modulation instability in Kerr Fabry-Perot resonators beyond the mean field limit

We analyse the nonlinear dynamics of Fabry-Perot cavities of arbitrary finesse filled by a dispersive Kerr medium, pumped by a continuous wave laser or a synchronous train of flat-top pulses. The combined action of feedback, group velocity dispersion and Kerr nonlinearity leads to temporal instability with respect to perturbations at specified frequencies. We characterise the generation of new spectral bands by deriving the exact dispersion relation and we find approximate analytical expressions for the instabilities threshold and gain spectrum of modulation instability (MI). We show that, in contrast to ring-resonators, both the stationary solutions and the gain spectrum are dramatically affected by the duration of the pump pulse. We derive the extended Lugiato-Lefever equation for the Fabry-Perot resonator (FP-LLE) starting from coupled nonlinear Schr\"odinger equations (rather than Maxwell-Bloch equations) and we compare the outcome of the stability analysis of the two models. While FP-LLE gives overall good results, we show regimes that are not captured by the mean-field limit, namely the period-two modulation instability, which may appear in highly detuned or nonlinear regimes. We report numerical simulations of the generation of MI-induced Kerr combs by solving FP-LLE and the coupled Schr\"odinger equations

28 THz soliton frequency comb in a continuous-wave pumped fiber Fabry-Perot resonator

We report the generation of an optical frequency comb featuring 28 THz bandwidth, sustained by a single 80 fs cavity soliton recirculating in a fiber Fabry-Perot resonator. This large spectrum is comparable to frequency combs obtained with microresonators operating in the anomalous dispersion regime. Thanks to the compact design and the easy coupling of the resonator, cavity solitons can be generated in an all-fiber experimental setup with a continuous wave pumping scheme. We also observe the generation of a dispersive wave at higher frequencies which is supported by higher-order dispersion. These observations align remarkably well with both numerical simulations and the established theory of cavity solitons.Comment: 6 pages, 6 figure

Switching waves-induced broadband Kerr frequency comb in fiber Fabry-Perot resonators

We report the generation of broadband frequency combs in fiber Fabry-Perot resonators in the normal dispersion regime enabled by the excitation of switching waves. We theoretically characterise the process by means of a transverse linear stability analysis of the Lugiato-Lefever equation, enabling precise prediction of the switching waves' frequencies. Experimentally, we employed a pulsed-pump fiber Fabry-Perot resonator operating in the normal dispersion regime, integrated into an all-fiber experimental setup. The synchronisation mismatch and the influence of dispersion is thoroughly discussed, unveiling the potential to generate a frequency comb spanning over 15 THz bandwidth, specifically leveraging a flattened low dispersion cavity

Bench Evaluation of Four Portable Oxygen Concentrators Under Different Conditions Representing Altitudes of 2438, 4200, and 8000 m

International audienceBunel, Vincent, Amr Shoukri, Frederic Choin, Serge Roblin, Cindy Smith, Thomas Similowski, Capucine Morélot-Panzini, and Jésus Gonzalez. Bench evaluation of four portable oxygen concentrators under different conditions representing altitudes of 2438, 4200, and 8000 m. High Alt Med Biol. 17:370–374, 2016.—Air travel is responsible for a reduction of the partial pressure of oxygen (O2) as a result of the decreased barometric pressure. This hypobaric hypoxia can be dangerous for passengers with respiratory diseases, requiring initiation or intensification of oxygen therapy during the flight. In-flight oxygen therapy can be provided by portable oxygen concentrators, which are less expensive and more practical than oxygen cylinders, but no study has evaluated their capacity to concentrate oxygen under simulated flight conditions. We tested four portable oxygen concentrators during a bench test study. The O2 concentrations (FO2) produced were measured under three different conditions: in room air at sea level, under hypoxia due to a reduction of the partial pressure of O2 (normobaric hypoxia, which can be performed routinely), and under hypoxia due to a reduction of atmospheric pressure (hypobaric hypoxia, using a chamber manufactured by Airbus Defence and Space). The FO2 obtained under conditions of hypobaric hypoxia (chamber) was lower than that measured in room air (0.92 [0.89–0.92] vs. 0.93 [0.92–0.94], p = 0.029), but only one portable oxygen concentrator was unable to maintain an FO2 ≥ 0.90 (0.89 [0.89–0.89]). In contrast, under conditions of normobaric hypoxia (tent) simulating an altitude of 2438 m, none of the apparatuses tested was able to achieve an FO2 greater than 0.76. (0.75 [0.75–0.76] vs. 0.93 [0.92–0.94], p = 0.029). Almost all portable oxygen concentrators were able to generate a sufficient quantity of O2 at simulated altitudes of 2438 m and can therefore be used in the aircraft cabin. Unfortunately, verification of the reliability and efficacy of these devices in a patient would require a nonroutinely available technology, and no preflight test can currently be performed by using simple techniques such as hypobaric hypoxia

Laboratoire de Néphrologie Expérimentale de la Faculté de Médecine: Etude de la néphropathie aux plantes chinoises

info:eu-repo/semantics/nonPublishe

Unexpected phase-locked Brillouin Kerr Frequency comb in fiber Fabry Perot resonators

We report the observation of a stable and broadband optical frequency comb in a high-Q fiber Fabry Perot resonator. We evidence it arises from an unexpected mode-locking phenomenon