Investigation of Lattice Boltzmann Methods applied to multiphase flows

The purpose of this thesis is the study of Lattice Boltzmann Methods (LBM), applied to multiphase flows. First, general principles of statistical physics and of Lattice Boltzmann Methods are introduced, followed by a historical review about Lattice Gas Automata. A state of the art of the multiphase flow simulation methods is then proposed, with a particular emphasize on diffuse interface methods. In particular, the phase field methods are introduced, and different methods allowing to numerically simulate surface tension are also presented. A second review concerning multiphase flow simulation in a Lattice Boltzmann framework is presented. More precisely, general principals are presented, and the four major methods, Color Gradient, Pseudo-Potential, Free Energy and HCZ, are successively presented. Lattice Boltzmann Methods advanced notions are then introduced, in particular, a Taylor expansion based method that allows to determine Lattice Boltzmann schemes equivalent macroscopic equation is described. A Gradient Color method theoretical study is proposed. First, an original reformulation of the algorithm allowing an improvement in computational efficiency is proposed. The Taylor expansion method is then applied to Gradient Color Method in order to determine the high order error induced by the numerical scheme. This expression allows to demonstrate how the degree of isotropy is essential to the scheme numerical stability. In particular, a numerical operator allowing to introduce an equation of states that differs from the athermal perfect gas equation is proposed. This operator efficiency is illustrated by being applied to academical testcases. The Taylor expansion method is also applied in order to show how the Color Gradient Method allows to solve an Allen-Cahn phase field equation. This theoretical result is then validated numerically. Finally, an original improved version of the Gradient Color Method is proposed. In this method, the efficient formulation and the isotropic Equation of State operator is used, and an original temporal correction term is proposed. This correction term improves the scheme numerical stability and allows to expands the method application range to higher density ratios. Finally, this method is validated through academical testcases

Part One: The Man Who Loved Cities

Part One: The Man Who Loved Cities -- Whyte on Whyte: A Walk in the City / Eugenie L. Birch -- Holly Whyte’s Journalism of Place / Charles E. Little -- The Energizer / Ann Louise Strong -- Sowing the Seeds / Thomas Balsley -- The Wit and Wisdom of Holly Whyte / Gathered by Albert LaFarge

Smearing of Coulomb Blockade by Resonant Tunneling

We study the Coulomb blockade in a grain coupled to a lead via a resonant impurity level. We show that the strong energy dependence of the transmission coefficient through the impurity level can have a dramatic effect on the quantization of the grain charge. In particular, if the resonance is sufficiently narrow, the Coulomb staircase shows very sharp steps even if the transmission through the impurity at the Fermi energy is perfect. This is in contrast to the naive expectation that perfect transmission should completely smear charging effects.Comment: 4 pages, 3 figure

Acoustic metamaterial for low frequency sound absorption in linear and nonlinear regimes

Acoustic metamaterial absorbers have been built and tested with focus on low frequency airborne sound absorption in linear and nonlinear regimes. The absorbers are made up of a series of piled up flat cavities, separated by thin walls and traversed by a perforation at their centre. A model for absorber effective properties is developed and compared with experimental data. The model is used to derive simple formulae for the frequency and the peak value of the absorption coefficient at the lowest frequency resonance, depending on the geometrical parameters of the structure. Different absorbers have been built with several cavity thicknesses to allow comprehensive comparisons with the model. Nonlinear properties of the absorbers are investigated experimentally using sine wave excitation around the resonance frequency with the amplitude of the incident wave up to 250 Pa. Flow resistivity measurements at low flow rates show that the periodic set of cavities does not modify resistivity significantly when compared to a simple perforated cylinder with same thickness. As flow rate increases, the flow resistivity grows linearly according to Forchheimer's law and has a significant dependence on the absorber thickness. A numerical model is developed accounting for the linear growth of flow resistivity with particle velocity amplitude in the central perforation and compared with the measurements at high amplitudes of the incident wave

Extraordinary absorption of sound in porous lamella-crystals

We present the design of a structured material supporting complete absorption of sound with a broadband response and functional for any direction of incident radiation. The structure which is fabricated out of porous lamellas is arranged into a low-density crystal and backed by a reflecting support. Experimental measurements show that strong all-angle sound absorption with almost zero reflectance takes place for a frequency range exceeding two octaves. We demonstrate that lowering the crystal filling fraction increases the wave interaction time and is responsible for the enhancement of intrinsic material dissipation, making the system more absorptive with less material.The work was supported by the Spanish Ministry of Science and Innovation and European Union FEDER through project FIS2011-29734-C02-01. J.C. gratefully acknowledges financial support from the Danish Council for Independent Research and a Sapere Aude grant (12-134776). V. R. G. gratefully acknowledges financial support from the ''Contratos Post-Doctorales Campus Excelencia Internacional'' UPV CEI-01-11.Christensen, J.; Romero García, V.; Picó Vila, R.; Cebrecos Ruiz, A.; Garcia De Abajo, FJ.; Mortensen, NA.; Willatzen, M.... (2014). Extraordinary absorption of sound in porous lamella-crystals. Scientific Reports. 4(4674). https://doi.org/10.1038/srep04674S44674Mei, J. et al. Dark acoustic metamaterials as super absorbers for low-frequency sound. Nat. Commun. 3, 756 (2012).Leroy, V., Strybulevych, A., Scanlon, M. G. & Page, J. Transmission of ultrasound through a single layer of bubbles. Eur. Phys. J. E 29, 123 (2009).Leroy, V., Bretagne, A., Fink, M. H. W., Tabeling, P. & Tourin, A. Design and characterization of bubble phononic crystals. Appl. Phys. Lett. 95, 171904 (2009).Thomas, E. L. Applied physics: Bubbly but quiet. Nature 462, 990 (2009).Romero-García, V., Sánchez-Pérez, J. V. & Garcia-Raffi, L. M. Tunable wideband bandstop acoustic filter based on two-dimensional multiphysical phenomena periodic systems. J. Appl. Phys. 110, 014904 (2011).Garcia-Chocano, V. M., Cabrera, S. & Sanchez-Dehesa, J. Broadband sound absorption by lattices of microperforated cylindrical shells. Appl. Phys. Lett. 101, 184101 (2012).Kushwaha, M. S., Halevi, P., Dobrzynski, L. & Djafari-Rouhani, B. Acoustic band structure of periodic elastic composites. Phys. Rev. Lett. 71, 2022 (1993).Vasseur, J. O. et al. Experimental and Theoretical Evidence for the Existence of Absolute Acoustic Band Gaps in Two-Dimensional Solid Phononic Crystals. Phys. Rev. Lett. 86, 3012 (2001).Liu, Z. et al. Locally Resonant Sonic Materials. Science 289, 1734 (2000).Christensen, J., Martin-Moreno, L. & Garcia-Vidal, F. J. All-angle blockage of sound by an acoustic double-fishnet metamaterial. Appl. Phys. Lett. 97, 134106 (2010).Botten, L. C., Craig, M. S., McPhedran, R. C., Adams, J. L. & Andrewartha, J. R. The finitely conducting lamellar diffraction grating. Optica Acta 28, 1087 (1981).McPhedran, R. C., Botten, L. C., Craif, M. S., Neviere, M. & Maystre, D. Lossy lamellar gratings in the quasistatic limit. Optica Acta 29, 289 (1982).Kravets, V. G., Schedin, F. & Grigorenko, A. N. Plasmonic blackbody: Almost complete absorption of light in nanostructured metallic coatings. Phys. Rev. B 78, 205405 (2008).Sondergaard, T. et al. Plasmonic black gold by adiabatic nanofocusing and absorption of light in ultra-sharp convex grooves. Nat. Commun. 3, 969 (2012).Clapham, P. B. & Hurtley, M. C. Reduction of Lens Reflexion by the Moth Eye Principle. Nature Vol. 244, 281 (1973).Garcia-Vidal, F. J., Pitarke, J. M. & Pendry, J. B. Effective Medium Theory of the Optical Properties of Aligned Carbon Nanotubes. Phys. Rev. Lett. 78, 4289 (1997).Yang, Z., Ci, L., Bur, J. A., Lin, S. & Ajayan, P. M. Experimental Observation of an Extremely Dark Material Made By a Low-Density Nanotube Array. Nano Lett. 8, 446 (2008).Garcia-Vidal, F. J. Metamaterials: Towards the dark side. Nat. Photonics 2, 215 (2008).Mizunoa, K. et al. A black body absorber from vertically aligned single-walled carbon nanotubes. Proc. Natl. Acad. Sci. USA 106, 6044 (2009).Lidorkis, E. & Ferrari, A. C. Photonics with Multiwall Carbon Nanotube Arrays. ACS Nano 3, 1238 (2009).Beenakker, C. W. J. & Brouwer, P. W. Distribution of the reflection eigenvalues of a weakly absorbing chaotic cavity. Physica E 9, 463 (2001).Lafarge, D., Lemarinier, P., Allard, J. F. & Tarnow, V. Dynamic compressibility of air in porous structures at audible frequencies. J. Acoust. Soc. Am. 102, 1995 (1997), With the macroscopic parameters: ϕ = 0.94, α∞ = 1, σ = 20000 Nm−4s and Λ = Λ′ = 0.41 μm.García de Abajo, F. J. Colloquium: Light scattering by particle and hole arrays. Rev. Mod. Phys. 79, 1267–1290 (2007)

Early Forest Fire Detection Using Radio-Acoustic Sounding System

Automated early fire detection systems have recently received a significant amount of attention due to their importance in protecting the global environment. Some emergent technologies such as ground-based, satellite-based remote sensing and distributed sensor networks systems have been used to detect forest fires in the early stages. In this study, a radio-acoustic sounding system with fine space and time resolution capabilities for continuous monitoring and early detection of forest fires is proposed. Simulations show that remote thermal mapping of a particular forest region by the proposed system could be a potential solution to the problem of early detection of forest fires

Mitosis domain generalization in histopathology images -- The MIDOG challenge

The density of mitotic figures within tumor tissue is known to be highly correlated with tumor proliferation and thus is an important marker in tumor grading. Recognition of mitotic figures by pathologists is known to be subject to a strong inter-rater bias, which limits the prognostic value. State-of-the-art deep learning methods can support the expert in this assessment but are known to strongly deteriorate when applied in a different clinical environment than was used for training. One decisive component in the underlying domain shift has been identified as the variability caused by using different whole slide scanners. The goal of the MICCAI MIDOG 2021 challenge has been to propose and evaluate methods that counter this domain shift and derive scanner-agnostic mitosis detection algorithms. The challenge used a training set of 200 cases, split across four scanning systems. As a test set, an additional 100 cases split across four scanning systems, including two previously unseen scanners, were given. The best approaches performed on an expert level, with the winning algorithm yielding an F_1 score of 0.748 (CI95: 0.704-0.781). In this paper, we evaluate and compare the approaches that were submitted to the challenge and identify methodological factors contributing to better performance.Comment: 19 pages, 9 figures, summary paper of the 2021 MICCAI MIDOG challeng

Epidemiology and outcome predictors in 450 patients with hanging-induced cardiac arrest: a retrospective study

BackgroundCardiac arrest is the most life-threatening complication of attempted suicide by hanging. However, data are scarce on its characteristics and outcome predictors.MethodsThis retrospective observational multicentre study in 31 hospitals included consecutive adults admitted after cardiac arrest induced by suicidal hanging. Factors associated with in-hospital mortality were identified by multivariate logistic regression with multiple imputations for missing data and adjusted to the temporal trends over the study period.ResultsOf 450 patients (350 men, median age, 43 [34–52] years), 305 (68%) had a psychiatric history, and 31 (6.9%) attempted hanging while hospitalized. The median time from unhanging to cardiopulmonary resuscitation was 0 [0–5] min, and the median time to return of spontaneous circulation (ROSC) was 20 [10–30] min. Seventy-nine (18%) patients survived to hospital discharge. Three variables were independently associated with higher in-hospital mortality: time from collapse or unhanging to ROSC>20 min (odds ratio [OR], 4.71; 95% confidence intervals [95%CIs], 2.02–10.96; p = 0.0004); glycaemia >1.4 g/L at admission (OR, 6.38; 95%CI, 2.60–15.66; p < 0.0001); and lactate >3.5 mmol/L at admission (OR, 6.08; 95%CI, 1.71–21.06; p = 0.005). A Glasgow Coma Scale (GCS) score of >5 at admission was associated with lower in-hospital mortality (OR, 0.009; 95%CI, 0.02–0.37; p = 0.0009).ConclusionIn patients with hanging-induced cardiac arrest, time from collapse or unhanging to return of spontaneous circulation, glycaemia, arterial lactate, and coma depth at admission were independently associated with survival to hospital discharge. Knowledge of these risk factors may help guide treatment decisions in these patients at high risk of hospital mortality

ECFS best practice guidelines: the 2018 revision

Developments in managing CF continue to drive dramatic improvements in survival. As newborn screening rolls-out across Europe, CF centres are increasingly caring for cohorts of patients who have minimal lung disease on diagnosis. With the introduction of mutation-specific therapies and the prospect of truly personalised medicine, patients have the potential to enjoy good quality of life in adulthood with ever-increasing life expectancy. The landmark Standards of Care published in 2005 set out what high quality CF care is and how it can be delivered throughout Europe. This underwent a fundamental re-write in 2014, resulting in three documents; center framework, quality management and best practice guidelines. This document is a revision of the latter, updating standards for best practice in key aspects of CF care, in the context of a fast-moving and dynamic field. In continuing to give a broad overview of the standards expected for newborn screening, diagnosis, preventative treatment of lung disease, nutrition, complications, transplant/end of life care and psychological support, this consensus on best practice is expected to prove useful to clinical teams both in countries where CF care is developing and those with established CF centres. The document is an ECFS product and endorsed by the CF Network in ERN LUNG and CF Europe

Investigation de l'utilisation des méthodes Boltzmann sur réseaux appliquées aux écoulements multi-phasiques

L’objectif de cette thèse est l’étude des méthodes Boltzmann sur Réseau (dites LBM) appliquées aux écoulements multiphasiques. Dans un premier temps, des principes généraux concernant la physique statistique ainsi que les méthodes Boltzmann sur Réseaux sont introduites, ainsi qu’une revue historique des automates de gaz sur réseaux. Un état de l’art des méthodes de simulation des écoulement multiphasiques est ensuite proposé avec une intention particulière portée aux méthodes aux interfaces diffuses. En particulier, les méthodes de champs de phases (dites « phase field ») sont introduites, ainsi que les différentes méthodes permettant de simuler la numériquement le phénomène de tension de surface. Une seconde revue bibliographique portant sur la simulation des écoulement multiphasiques dans le contexte des schémas de Boltzmann sur réseau est présentée. Plus précisément, des principes généraux sont présentés, puis les quatre grandes familles de méthodes, gradient de couleur, énergie libre, pseudo-potentielle et HCZ sont détaillées successivement. Des notions avancées concernant les méthodes de Boltzmann sur Réseau sont ensuite introduites, en particulier une méthode basée sur le principe de développement de Taylor permettant de déterminer les équations macroscopiques équivalentes d’un schéma de Boltzmann sur réseau est décrite. Une étude théorique des méthodes du Gradient de Couleur est ensuite proposée. En premier lieu, une reformulation de l’algorithme permettant un gain en efficacité est proposée. La méthode de développement de Taylor est ensuite appliquée à la méthode du Gradient de Couleur afin de déterminer l’expression analytique des erreurs d’ordre élevée induite par le schéma numérique. Cette expression permet de démontrer l’importance du degré d’isotropie sur la stabilité du schéma numérique. En particulier, un opérateur numérique permettant d’introduire une équation d’état différente de l’équation d’état des gaz parfait athermale est proposée. L’efficacité de ce schéma isotropique est illustrée sur des cas académiques. La méthode du développement de Taylor est également appliquée afin de démontrer que la méthode du Gradient de Couleur est équivalent à la résolution d’une équation d’Allen-Cahn ce qui est vérifié numériquement. Enfin, une version améliorée de la méthode du Gradient de Couleur est proposée. En plus d’utiliser la reformulation et l’opérateur isotropique présentés plus haut, un opérateur de correction temporelle est proposé. Ce dernier permet de grandement améliorer la stabilité numérique du schéma et permet d’étendre le domaine d’applicabilité de la méthode à de plus hauts ratio de densité. Enfin, cette méthode est ensuite validée sur différents cas d’applications académiques.The purpose of this thesis is the study of Lattice Boltzmann Methods (LBM), applied to multiphase flows. First, general principles of statistical physics and of Lattice Boltzmann Methods are introduced, followed by a historical review about Lattice Gas Automata. A state of the art of the multiphase flow simulation methods is then proposed, with a particular emphasize on diffuse interface methods. In particular, the phase field methods are introduced, and different methods allowing to numerically simulate surface tension are also presented. A second review concerning multiphase flow simulation in a Lattice Boltzmann framework is presented. More precisely, general principals are presented, and the four major methods, Color Gradient, Pseudo-Potential, Free Energy and HCZ, are successively presented. Lattice Boltzmann Methods advanced notions are then introduced, in particular, a Taylor expansion based method that allows to determine Lattice Boltzmann schemes equivalent macroscopic equation is described. A Gradient Color method theoretical study is proposed. First, an original reformulation of the algorithm allowing an improvement in computational efficiency is proposed. The Taylor expansion method is then applied to Gradient Color Method in order to determine the high order error induced by the numerical scheme. This expression allows to demonstrate how the degree of isotropy is essential to the scheme numerical stability. In particular, a numerical operator allowing to introduce an equation of states that differs from the athermal perfect gas equation is proposed. This operator efficiency is illustrated by being applied to academical testcases. The Taylor expansion method is also applied in order to show how the Color Gradient Method allows to solve an Allen-Cahn phase field equation. This theoretical result is then validated numerically. Finally, an original improved version of the Gradient Color Method is proposed. In this method, the efficient formulation and the isotropic Equation of State operator is used, and an original temporal correction term is proposed. This correction term improves the scheme numerical stability and allows to expands the method application range to higher density ratios. Finally, this method is validated through academical testcases