3D stochastic interferometer detects picometer deformations and minute dielectric fluctuations of its optical volume Graciani, G., M. Filoche, and F. Amblard Communications Physics 5, no. 1 (2022)


The Landscape Law for Tight Binding Hamiltonians Arnold, D., M. Filoche, S. Mayboroda, W. Wang, and S. Zhang Communications in Mathematical Physics 396, no. 3, 13391391 (2022)


WignerWeyl description of light absorption in disordered semiconductor alloys using the localization landscape theory Banon, J.P., P. Pelletier, C. Weisbuch, S. Mayboroda, and M. Filoche Physical Review B 105, no. 12 (2022)


Spectral functions and localizationlandscape theory in speckle potentials Pelletier, P., D. Delande, V. Josse, A. Aspect, S. Mayboroda, D. N. Arnold, and M. Filoche Physical Review A 105, no. 2 (2022)


The landscape law for the integrated density of states David, G., M. Filoche, and S. Mayboroda Advances in Mathematics 390, 107946 (2021)


Sharp estimates for the integrated density of states in Anderson tightbinding models Desforges, P., S. Mayboroda, S. Zhang, G. David, D. N. Arnold, W. Wang, and M. Filoche Physical Review A 104, no. 1 (2021)


The effective potential of an Mmatrix Filoche, M., S. Mayboroda, and T. Tao Journal of Mathematical Physics 62, no. 4 (2021)


Piezoresistance in DefectEngineered Silicon Li, H., A. Thayil, C. T. K. Lew, M. Filoche, B. C. Johnson, J. C. Mccallum, S. Arscott, and A. C. H. Rowe Physical Review Applied 15, no. 1 (2021)


Reply Filoche, M., D. Arnold, G. David, D. Jerison, and S. Mayboroda Physical Review Letters 124, no. 21 (2020)


Functional and structural consequences of epithelial cell invasion by Bordetella pertussis adenylate cyclase toxin Angely, C., D. Ladant, E. Planus, B. Louis, M. Filoche, A. Chenal, and D. Isabey PLOS ONE 15, no. 5, e0228606 (2020)


Pathogenesis of chronic rhinosinusitis with nasal polyps: role of IL6 in airway epithelial cell dysfunction Bequignon, E., D. Mangin, J. Bécaud, J. Pasquier, C. Angely, M. Bottier, E. Escudier, D. Isabey, M. Filoche, B. Louis, J.F. Papon, and A. Coste Journal of Translational Medicine 18, no. 1 (2020)


Deep phenotyping, including quantitative ciliary beating parameters, and extensive genotyping in primary ciliary dyskinesia Blanchon, S., M. Legendre, M. Bottier, A. Tamalet, G. Montantin, N. Collot, C. Faucon, F. Dastot, B. Copin, A. Clement, M. Filoche, A. Coste, S. Amselem, E. Escudier, J.F. Papon, and B. Louis Journal of Medical Genetics 57, no. 4, 237244 (2019)


Surfactant delivery in rat lungs: Comparing 3D geometrical simulation model with experimental instillation Kazemi, A., B. Louis, D. Isabey, G. F. Nieman, L. A. Gatto, J. Satalin, S. Baker, J. B. Grotberg, and M. Filoche PLOS Computational Biology 15, no. 10, e1007408 (2019)


Universality of foldencoded localized vibrations in enzymes Chalopin, Y., F. Piazza, S. Mayboroda, C. Weisbuch, and M. Filoche Scientific Reports 9, no. 1 (2019)


Localization of eigenfunctions via an effective potential Arnold, D. N., G. David, M. Filoche, D. Jerison, and S. Mayboroda Communications in Partial Differential Equations 44, no. 11, 11861216 (2019)


Computing Spectra without Solving Eigenvalue Problems Arnold, D. N., G. David, M. Filoche, D. Jerison, and S. Mayboroda SIAM Journal on Scientific Computing 41, no. 1, B69B92 (2019)


Evidence of nanoscale Anderson localization induced by intrinsic compositional disorder in InGaN/GaN quantum wells by scanning tunneling luminescence spectroscopy Hahn, W., J.M. Lentali, P. Polovodov, N. Young, S. Nakamura, J. S. Speck, C. Weisbuch, M. Filoche, Y.R. Wu, M. Piccardo, F. Maroun, L. Martinelli, Y. Lassailly, and J. Peretti Physical Review B 98, no. 4 (2018)


Perfluorocarbon induces alveolar epithelial cell response through structural and mechanical remodeling André Dias, S., E. Planus, C. Angely, L. Lotteau, R. Tissier, M. Filoche, B. Louis, G. Pelle, and D. Isabey Biomechanics and Modeling in Mechanobiology 17, no. 4, 961973 (2018)


IFPA meeting 2017 workshop report: Clinical placentology, 3D structurebased modeling of placental function, placental bed, and treating placental dysfunction Acharya, G., J. Aplin, P. Brownbill, J. Bulmer, G. Burton, L. Chamley, I. Chernyavsky, A. Clark, S. Collins, E. Cottrell, M. Dilworth, D. Elad, M. Filoche, N. Hannan, A. E. P. Heazell, O. Jensen, E. D. Johnstone, L. Leach, R. Lewis, T. Morgan, J. Myers, G. Nye, M. Oyen, C. Salafia, H. Schneider, O', and P. tierneyGinn Placenta 64, S4S8 (2018)


Exposure to <i>Bordetella pertussis</i> adenylate cyclase toxin affects integrin‐mediated adhesion and mechanics in alveolar epithelial cells Angely, C., N. Nguyen, S. Andre Dias, E. Planus, G. Pelle, B. Louis, M. Filoche, A. Chenal, D. Ladant, and D. Isabey Biology of the Cell 109, no. 8, 293311 (2017)


A new index for characterizing microbead motion in a flow induced by ciliary beating: Part I, experimental analysis Bottier, M., S. Blanchon, G. Pelle, E. Bequignon, D. Isabey, A. Coste, E. Escudier, J. B. Grotberg, J.F. Papon, M. Filoche, and B. Louis PLOS Computational Biology 13, no. 7, e1005605 (2017)


A new index for characterizing microbead motion in a flow induced by ciliary beating: Part II, modeling Bottier, M., M. Peña Fernández, G. Pelle, D. Isabey, B. Louis, J. B. Grotberg, and M. Filoche PLOS Computational Biology 13, no. 7, e1005552 (2017)


Characterisation of cellular adhesion reinforcement by multiple bond force spectroscopy in alveolar epithelial cells Nguyen, N., C. Angely, S. Andre Dias, E. Planus, M. Filoche, G. Pelle, B. Louis, and D. Isabey Biology of the Cell 109, no. 7, 255272 (2017)


Localization landscape theory of disorder in semiconductors. I. Theory and modeling Filoche, M., M. Piccardo, Y.R. Wu, C.K. Li, C. Weisbuch, and S. Mayboroda Physical Review B 95, no. 14 (2017)


Localization landscape theory of disorder in semiconductors. II. Urbach tails of disordered quantum well layers Piccardo, M., C.K. Li, Y.R. Wu, J. S. Speck, B. Bonef, R. M. Farrell, M. Filoche, L. Martinelli, J. Peretti, and C. Weisbuch Physical Review B 95, no. 14 (2017)


Localization landscape theory of disorder in semiconductors. III. Application to carrier transport and recombination in light emitting diodes Li, C.K., M. Piccardo, L.S. Lu, S. Mayboroda, L. Martinelli, J. Peretti, J. S. Speck, C. Weisbuch, M. Filoche, and Y.R. Wu Physical Review B 95, no. 14 (2017)


Did Reduced Alveolar Delivery of Surfactant Contribute to Negative Results in Adults with Acute Respiratory Distress Syndrome? Grotberg, J. B., M. Filoche, D. F. Willson, K. Raghavendran, and R. H. Notter American Journal of Respiratory and Critical Care Medicine 195, no. 4, 538540 (2017)


A Macroscopic Model for Simulating the Mucociliary Clearance in a Bronchial Bifurcation: The Role of Surface Tension Manolidis, M., D. Isabey, B. Louis, J. B. Grotberg, and M. Filoche Journal of Biomechanical Engineering 138, no. 12 (2016)


One Single Static Measurement Predicts Wave Localization in Complex Structures Lefebvre, G., A. Gondel, M. Dubois, M. Atlan, F. Feppon, A. Labbe, C. Gillot, A. Garelli, M. Ernoult, S. Mayboroda, M. Filoche, and P. Sebbah Physical Review Letters 117, no. 7 (2016)


Studies of the B‐Z transition of DNA: The temperature dependence of the free‐energy difference, the composition of the counterion sheath in mixed salt, and the preparation of a sample of the 5′‐d[T‐(m<sup>5</sup>C‐G)<sub>12</sub>‐T] duplex in pure B‐DNA or Z‐DNA form Guéron, M., P. Plateau, and M. Filoche Biopolymers 105, no. 7, 369384 (2016)


Effective Confining Potential of Quantum States in Disordered Media Arnold, D. N., G. David, D. Jerison, S. Mayboroda, and M. Filoche Physical Review Letters 116, no. 5 (2016)


The role of morphology in mathematical models of placental gas exchange Serov, A. S., C. Salafia, D. S. Grebenkov, and M. Filoche Journal of Applied Physiology 120, no. 1, 1728 (2016)


Unsteady diffusional screening in 3D pulmonary acinar structures: from infancy to adulthood Hofemeier, P., L. ShacharBerman, J. TenenbaumKatan, M. Filoche, and J. Sznitman Journal of Biomechanics 49, no. 11, 21932200 (2016)


Multiscale evaluation of cellular adhesion alteration and cytoskeleton remodeling by magnetic bead twisting Isabey, D., G. Pelle, S. André Dias, M. Bottier, N.M. Nguyen, M. Filoche, and B. Louis Biomechanics and Modeling in Mechanobiology 15, no. 4, 947963 (2015)


Threedimensional model of surfactant replacement therapy Filoche, M., C.F. Tai, and J. B. Grotberg Proceedings of the National Academy of Sciences 112, no. 30, 92879292 (2015)


A microfluidic model to study fluid dynamics of mucus plug rupture in small lung airways Hu, Y., S. Bian, J. Grotberg, M. Filoche, J. White, S. Takayama, and J. B. Grotberg Biomicrofluidics 9, no. 4 (2015)


ABYSS: Therapeutic hypothermia by total liquid ventilation following cardiac arrest and resuscitation André Dias, S., A. Berdeaux, L. Darrasse, M. Demanesse, L. De Rochefort, M. Filoche, B. Ghaleh, A. Hutin, D. Isabey, T. Kunc, F. Lidouren, L. Lotteau, B. Louis, and R. Tissier IRBM 36, no. 2, 110117 (2015)


Dual landscapes in Anderson localization on discrete lattices Lyra, M. L., S. Mayboroda, and M. Filoche EPL (Europhysics Letters) 109, no. 4, 47001 (2015)


Analytical theory of oxygen transport in the human placenta Serov, A. S., C. M. Salafia, M. Filoche, and D. S. Grebenkov Journal of Theoretical Biology 368, 133144 (2015)


Optimal villi density for maximal oxygen uptake in the human placenta Serov, A. S., C. M. Salafia, P. Brownbill, D. S. Grebenkov, and M. Filoche Journal of Theoretical Biology 364, 383396 (2015)


Maximal efficiency of convective mixing occurs in mid acinus: A 3Dnumerical analysis by an Eulerian approach Muller, P.A., M. Pichelin, G. Apiou, B. Louis, I. Katz, G. Caillibotte, M. Filoche, and D. Isabey Journal of Aerosol Science 76, 163174 (2014)


Magic trees in mammalians respiration or when evolution selected clever physical systems Sapoval, B., and M. Filoche Fractals 21, no. 03n04, 1350024 (2013)


Optimisations and evolution of the mammalian respiratory system Sapoval, B., and M. Filoche The European Physical Journal E 36, no. 9 (2013)


A first principles calculation of the oxygen uptake in the human pulmonary acinus at maximal exercise Foucquier, A., M. Filoche, A. A. Moreira, J. S. Andrade, G. Arbia, and B. Sapoval Respiratory Physiology & Neurobiology 185, no. 3, 625638 (2013)


Universal mechanism for Anderson and weak localization Filoche, M., and S. Mayboroda Proceedings of the National Academy of Sciences 109, no. 37, 1476114766 (2012)


An asymptotic model of particle deposition at an airway bifurcation Zierenberg, J. R., D. Halpern, M. Filoche, B. Sapoval, and J. B. Grotberg Mathematical Medicine and Biology 30, no. 2, 131156 (2012)


The stationary flow in a heterogeneous compliant vessel network Filoche, M., and M. Florens Journal of Physics: Conference Series 319, 012008 (2011)


Optimal Branching Asymmetry of Hydrodynamic Pulsatile Trees Florens, M., B. Sapoval, and M. Filoche Physical Review Letters 106, no. 17 (2011)


Numerical study of flow fields in an airway closure model Tai, C.F., S. Bian, D. Halpern, Y. Zheng, M. Filoche, and J. B. Grotberg Journal of Fluid Mechanics 677, 483502 (2011)


Particle capture into the lung made simple? De Vasconcelos, T. F., B. Sapoval, J. S. Andrade, J. B. Grotberg, Y. Hu, and M. Filoche Journal of Applied Physiology 110, no. 6, 16641673 (2011)


An anatomical and functional model of the human tracheobronchial tree Florens, M., B. Sapoval, and M. Filoche Journal of Applied Physiology 110, no. 3, 756763 (2011)


The optimal branching asymmetry of a bidirectional distribution tree Florens, M., B. Sapoval, and M. Filoche Computer Physics Communications 182, no. 9, 19321936 (2011)


Strong Localization Induced by One Clamped Point in Thin Plate Vibrations Filoche, M., and S. Mayboroda Physical Review Letters 103, no. 25 (2009)


Enhanced wave absorption through irregular interfaces Félix, S., B. Sapoval, M. Filoche, and M. Asch EPL (Europhysics Letters) 85, no. 1, 14003 (2009)
Résumé: The diffraction and absorption of waves by a system with both absorbing properties and irregular geometry is an open physical problem. A more reachable and closely related question is the understanding of wave oscillations in confined systems containing an absorbing material with an irregular shape. This has to be solved to understand why anechoic chambers (electromagnetic or acoustic) do work better with irregular absorbing walls. The answer to this question could also be used in other fields such as light or microwave absorption, or also to improve the performances of breakwaters in order to damp seawaves. It is found here that, in resonators containing an irregular shaped absorbent material, there appears a new type of mode localization. This phenomemon, that we call “astride” localization, describes the fact that these modes exist in both the lossless and the lossy regions. It is these modes that are particularly efficient in dissipating the energy of waves excited in the nonabsorbing region.


Diffusion of gases into the lung: How physics can help to understand physiology Filoche, M., and B. Sapoval Pramana 71, no. 2, 245251 (2008)
Résumé: In the human lung, the gas transfer between air and blood is achieved in terminal units that are called ‘acini’. Whereas convection is still the predominant trans port phenomenon at the acinus entrance, most of the acinar surface is in fact accessed by diffusion. The transition between convection and diffusion, and thus the size of the diffusion unit, depends on the air velocity at the acinus entrance. In this paper, we present a gas transport model which takes into account both the diffusion into the acinus and the diffusion across the alveolar membrane. It is shown that the physiological sizes of the diffusion unit in the lung, at rest or at exercise, can be explained by physical arguments. In that sense, diffusion is the ‘dimensioning criterion’ of the lung at the acinar level. This approach shows that, due to diffusional screening at inspiration and at rest, there exists a permanent spatial inhomogeneity of oxygen and carbon dioxide partial pressure which reduces the effective surface efficiency of the human acinus to a value of only 30 to 40%. This model casts a new light on the properties of this physiological transport system. It permits in particular to understand how several diseases among which pulmonary edema may remain asymptomatic in their early stages.


Localisation and damping in resonators with complex geometry Sapoval, B., S. Félix, and M. Filoche The European Physical Journal Special Topics 161, no. 1, 225232 (2008)
Résumé: Based on numerical studies, we show that localisation is a common phenomenon in resonators exhibiting some kind of geometrical complexity. In two dimensional (2d) shallow cavities of irregular shape, localisation effects are due to spatial decoherence in a major fraction of the volume. In 2d shallow cavities of regular geometry with embedded absorbing material of irregular shape, one observes the appearance of eigenmodes localised in both, the absorbing and the nonabsorbing media. Those modes are thought to be responsible for increased dissipation. These results may be a hint to understand why natural or practical systems absorbing wave energy are found, or built, with complex geometry.


Passivation of irregular surfaces accessed by diffusion Filoche, M., D. S. Grebenkov, J. S. Andrade, and B. Sapoval Proceedings of the National Academy of Sciences 105, no. 22, 76367640 (2008)
Résumé: We investigate the process of progressive passivation of irregular surfaces accessed by diffusion. More precisely, we quantify through numerical simulations how the activity of the von Koch surface is gradually transferred from its initially active (or absorb ing) regions to its less accessible regions. We show that in three dimensions, in sharp contrast with the twodimensional case, the size of the successive active zones steadily decreases during the passivation process, even though a large quantity of alive surface remains available. As a consequence, in three dimensions, the evolution of the efficiency of a surface accessed by diffusion (i.e., by a Laplacian field) can exhibit longtail behaviors that, unlike in two dimensions, strongly depend on its specific geometry. This fact has important implications for the design of heterogeneous cata lysts under deactivation conditions, for the performance of heat exchangers subjected to passivation by ‘‘fouling,’’ and for changes in the behavior of the digestive system, where the activity of the absorbing intestinal membrane can be substantially affected by inflammatory disorders.


The toposcopy, a new tool to probe the geometry of an irregular interface by measuring its transfer impedance Filoche, M., and D. S. Grebenkov EPL (Europhysics Letters) 81, no. 4, 40008 (2008)
Résumé: Semipermeable interfaces of irregular geometry accessed by diffusion exhibit complex transfer properties. In particular, their transfer impedance is the nontrivial result of the interplay between their geometry and their physical properties. In this paper, we present a new method that we call toposcopy. Its aim is to solve the “inverse impedance spectroscopy problem”, namely to retrieve the geometrical features of an irregular interface from a “black box” measurement of its transfer impedance only. From previous studies, one knows that all the possible information about the geometry of an interface that can be extracted from a measurement of its impedance consists in its harmonic geometrical spectrum, a set of spectral characteristics of the Dirichlet toNeumann operator of the same interface. Here, we first describe how the toposcopy technique permits to retrieve the main components of the harmonic geometrical spectrum and to deduce from them characteristic geometrical features of the interface. The toposcopy is then tested numerically for several irregular interfaces of either simple or complex shape. It is finally shown that this method gives access to the characteristics lengths of these interfaces and, when these lengths are sufficiently different, allows to separate and quantify their respective contributions to the interface impedance.


Screening Effects in Flow through Rough Channels Andrade, J. S., A. D. Araújo, M. Filoche, and B. Sapoval Physical Review Letters 98, no. 19 (2007)
Résumé: A surprising similarity is found between the distribution of hydrodynamic stress on the wall of an irregular channel and the distribution of flux from a purely Laplacian field on the same geometry. This finding is a direct outcome of numerical simulations of the NavierStokes equations for flow at low Reynolds numbers in twodimensional channels with rough walls presenting either deterministic or random selfsimilar geometries. For high Reynolds numbers, the distribution of wall stresses on deterministic and random fractal rough channels becomes substantially dependent on the microscopic details of the walls geometry. Finally, the effects on the flow behavior of the channel symmetry and aspect ratio are also investigated.


Localization and increased damping in irregular acoustic cavities Félix, S., M. Asch, M. Filoche, and B. Sapoval Journal of Sound and Vibration 299, no. 45, 965976 (2007)
Résumé: The present study is concerned with the properties of 2D shallow cavities having an irregular boundary. The eigenmodes are calculated numerically on various examples, and it is shown first that, whatever the shape and characteristic sizes of the boundary, irregularity always induces an increase of localized eigenmodes and a global decrease of the existence surface of the eigenmodes. Besides, irregular cavities are shown to exhibit specific damping properties. As expected, the increased damping, compared to a regular cavity, is related first to the larger perimeter to surface ratio. But more interestingly, there is a specific enhancement of the dissipation for those modes that are localized near the boundary, modes which are favored by the geometric irregularity.


A simplified analytical model for laplacian transfer across deterministic prefractal interfaces Grebenkov, D. S., M. Filoche, and B. Sapoval Fractals 15, no. 01, 2739 (2007)
Résumé: The role of the geometry of prefractal interfaces in Laplacian transport is analyzed through its “harmonic geometrical spectrum.” This spectrum summarizes the properties of the Dirichlet toNeumann operator associated with these geometries. Numerical analysis shows that very few eigenmodes contribute significantly to the macroscopic response of the system. The hierarchical spatial frequencies of these particular modes correspond to the characteristic length scales of the interface. From this result, a simplified analytical model of the response of selfsimilar interfaces is developed. This model reproduces the classical low and high frequency asymptotic limits and gives an approximate constant phase angle behavior for the intermediate frequency region. It also provides an analytical description for the crossovers between these regimes and for their dependency on the order of the prefractal interface. In this frame, it is shown that the properties of any generation prefractal can be deduced from the properties of the fractal generator, which are easy to reach numerically.


Mathematical basis for a general theory of Laplacian transport towards irregular interfaces Grebenkov, D. S., M. Filoche, and B. Sapoval Physical Review E 73, no. 2 (2006)
Résumé: The theory of Laplacian transport towards and across irregular surfaces is reformulated in terms of the DirichlettoNeumann operator and its spectral characteristics. This permits us to obtain an exact equivalent circuit for the impedance of a working interface of arbitrary shape. The important result is that only very few eigenmodes of this operator do govern the entire response of a macroscopic system. This property drastically simplifies the understanding of irregular or prefractal interfaces. The results can be applied in electrochemistry, physiology and chemical engineering, fields where exchange processes across surfaces with complex geometry are ubiquitous.


Renormalized random walk study of oxygen absorption in the human lung Filoche, M., M. Felici, and B. Sapoval Physica A: Statistical Mechanics and its Applications 357, no. 1, 2735 (2005)
Résumé: Gas exchange at the acinar level involves several physicochemical phenomena within a complex geometry. A gas transport model, which takes into account both the diffusion into the acinus and the diffusion across the alveolar membrane, is used to understand gas mixing in realistic systems. The behaviour of the system, first computed on model geometries in 3D finite elements method, can in fact be derived from the topological structure of the acinus only. A new efficient method based on random walks on a lattice is thus used to compute gas diffusion in structures taken from real morphological data. This approach shows that, at rest, the human acinus efficiency is only of 30–40%. These results provide a new evidence of the existenceofdiffusionalscreeningattheacinarlevel,whichmeanspermanentspatial inhomogeneity of oxygen and carbon dioxide partial pressure. Application of these results to CO2 clearance provides for the first time a theoretical support to the empirical relation between the O2 and CO2 partial pressures.


New simple properties of a few irregular systems Sapoval, B., J. S. Andrade, A. Baldassarri, A. Desolneux, F. Devreux, M. Filoche, D. Grebenkov, and S. Russ Physica A: Statistical Mechanics and its Applications 357, no. 1, 117 (2005)
Résumé: This paper presents seven results on irregular systems that are both new and can be described simply. The first three results are related to dynamical and static properties of gradient percolation. Firstly, it is shown that the transient regimes which lead to selforganized gradient percolation due to corrosion do not scale like gradient percolation itself. Secondly, it is shown that there is no diffusion front in 1D but there exists a zone of fluctuations with a size of the order of the system size. Thirdly, the geometry of realistic intermetallic contacts in 3D is shown to be closely related to that of diffusion fronts, but different. The two next results are related to reactive irregular surfaces. Firstly, molecular dynamics results indicates that, in 2D, the size of the active zone of purely absorptive surfaces in the Knudsen diffusion regime is larger than that found in the molecular diffusion regime. Secondly, it is then shown that, in this last regime, the particles that really interacts with the surface, remains near the surface within a distance equal to the unscreened perimeter length. The following topic is related to the vibrations of deterministic surface fractals: with very good approximation, the extended disordered modes can be described as a superposition of regular (nonlocalized) trivial modes of the initiator of the fractal morphology. Finally, it is shown that the diffusion reorganized This paper presents seven results on irregular systems that are both new and can be described simply. The first three results are related to dynamical and static properties of gradient percolation. Firstly, it is shown that the transient regimes which lead to selforganized gradient percolation due to corrosion do not scale like gradient percolation itself. Secondly, it is shown that there is no diffusion front in 1D but there exists a zone of fluctuations with a size of the order of the system size. Thirdly, the geometry of realistic intermetallic contacts in 3D is shown to be closely related to that of diffusion fronts, but different. The two next results are related to reactive irregular surfaces. Firstly, molecular dynamics results indicates that, in 2D, the size of the active zone of purely absorptive surfaces in the Knudsen diffusion regime is larger than that found in the molecular diffusion regime. Secondly, it is then shown that, in this last regime, the particles that really interacts with the surface, remains near the surface within a distance equal to the unscreened perimeter length. The following topic is related to the vibrations of deterministic surface fractals: with very good approximation, the extended disordered modes can be described as a superposition of regular (nonlocalized) trivial modes of the initiator of the fractal morphology. Finally, it is shown that the diffusion reorganized


Multifractal properties of the harmonic measure on Koch boundaries in two and three dimensions Grebenkov, D. S., A. A. Lebedev, M. Filoche, and B. Sapoval Physical Review E 71, no. 5 (2005)
Résumé: The multifractal properties of the harmonic measure on quadratic and cubic Koch boundaries are studied with the help of a new fast random walk algorithm adapted to these fractal geometries. The conjectural logarithmic development of local multifractal exponents is guessed for regular fractals and checked by exten sive numerical simulations. This development allows one to compute the multifractal exponents of the har monic measure with high accuracy, even with the first generations of the fractal. In particular, the information dimension in the case of the concave cubic Koch surface embedded in three dimensions is found to be slightly higher than its value D =2 for a smooth boundary.


Design of peripheral airways for efficient gas exchange Weibel, E. R., B. Sapoval, and M. Filoche Respiratory Physiology & Neurobiology 148, no. 12, 321 (2005)
Résumé: Peripheral airways combine branched tubes for ventilation with the gas exchanging alveoli in the pulmonary acini, defined as the complex of airways supplied by one first order respiratory or transitional bronchiole. In this part, the replenishment of oxygen at the alveolar surface occurs by a combination of convective air flow with diffusion of oxygen in the air. The transition between convection and diffusion depends on the morphometric properties of the airways. The design of the peripheral airways in the acinus of the human lung is described quantitatively on the basis of measurements obtained on casts of the acinar airways. Comparable data for rat and rabbit are also discussed. On the basis of this morphometric information, a typical path model for human acinar airways is derived. These studies also form the basis for advanced modeling studies of gas exchange and ventilation. In particular the problems occurring because of diffusional screening and the design conditions for minimizing this effect are discussed.


Deactivation dynamics of rough catalytic surfaces Filoche, M., B. Sapoval, and J. S. Andrade AIChE Journal 51, no. 3, 9981008 (2005)
Résumé: The dynamics of deactivation due to parallel fouling is investigated in the case of a rough reactive interface under diffusionlimited conditions. For a firstorder reaction, a mathematical method is introduced that permits to analyze the response of the system for any type of interface geometry or input condition. Exact analytical results, such as the lifetime of the catalyst or its total production are calculated. The deactivation dynamics in specific geometries, such as a flat catalytic surface, an infinite pore or a rough surface, are examined. Through these three examples, a general picture of the role of the morphology on the system response is provided. Even more, this approach shows that the determination of a single time response function of a catalyst of unknown morphology provides a means to control the dynamics of the production process.


DiffusionReaction in Branched Structures: Theory and Application to the Lung Acinus Grebenkov, D. S., M. Filoche, B. Sapoval, and M. Felici Physical Review Letters 94, no. 5 (2005)
Résumé: An exact ‘‘branch by branch’’ calculation of the diffusional flux is proposed for partially absorbed random walks on arbitrary tree structures. In the particular case of symmetric trees, an explicit analytical expression is found which is valid whatever the size of the tree. Its application to the respiratory phenomena in pulmonary acini gives an analytical description of the crossover regime governing the human lung efficiency.


Diffusional screening in real 3D human acini—a theoretical study Felici, M., M. Filoche, C. Straus, T. Similowski, and B. Sapoval Respiratory Physiology & Neurobiology 145, no. 23, 279293 (2005)
Résumé: Gas exchange at the acinar level involves several physicochemical phenomena within a complex geometry. A gas transport model, which takes into account both the diffusion into the acinus and the diffusion across the alveolar membrane, is used to understand gas mixing in realistic systems. It is first shown that the behaviour of the system, computed on model geometries in 3D, only depends on the topological structure of the acinus. Taking advantage of this property, a new efficient method based on random walks on a lattice is used to compute gas diffusion in structures taken from real morphological data. This approach shows that, at rest, the human acinus efficiency is only 30–40%. These results provide a new evidence of the existence of diffusional screening at the acinar level. This implies permanent spatial inhomogeneity of oxygen and carbon dioxide partial pressure. The notion of an “alveolar gas” is reinterpreted as a spatial average of the gas distribution. This model casts new light on the respiratory properties of other gas mixtures, such as helium–oxygen.


Reply Mauroy, B., M. Filoche, J. Andrade, and B. Sapoval Physical Review Letters 93, no. 4 (2004)


Laplacian transport towards partially passivated 2D irregular interfaces: A conjectural extension of the Makarov theorem Sapoval, B., M. H. A. S. Costa, J. S. Andrade, and M. Filoche Fractals 12, no. 04, 381387 (2004)
Résumé: In several phenomena of practical interest, such as catalyst deactivation, fouling in heat transfer and other systems of technological and scientific relevance, an irregular surface accessed by diffusion can be progressively passivated. In a diffusion limited situation, an interface that works unevenly due to Laplacian screening is simultaneously and unevenly passivated. To study this phenomenon, we describe a process in which the regions of the surface that are initially working, are transformed into passive, reflecting zones. As a consequence, at each step, a new part of the interface becomes active. In turn, this new active zone is passivated, and so on. It is found that the length of the successive active zones remains approximately constant for a prefractal interface. The concept of active zone in Laplacian transport can then be successfully extended to elucidate this selflimiting behavior of the passivation process. A conjecture is then proposed which states that, in D = 2, the information dimension of the harmonic measure on a fractal supporting a “passivated or reflecting subfractal” (of smaller dimension) is equal to 1. This constitutes an extension of Makarov theorem. From our results, fractal geometry is revealed as a potential candidate to engineer substrate morphologies that are robust to Laplacian passivation.


Mathematical aspects of deactivation processes of rough catalytic surfaces Filoche, M., J. S. Andrade, and B. Sapoval Physica A: Statistical Mechanics and its Applications 342, no. 12, 395401 (2004)
Résumé: The progressive deactivation of catalytic surfaces, either by parallel or serial fouling, is a key problem in heterogeneous catalysis. A mathematical model of the deactivation of a catalytic reactor is presented. It is shown that this dynamical model can be turned into the study of the steadystate nonlinear response of the same system but for a virtual species. This mapping of the problem permits to obtain analytical results such as the duration of the reactor or its total production. As an example, one shows how a fractal surface would respond in such a deactivation process. Finally, a way to control the time dependency of the reactor production is suggested.


An optimal bronchial tree may be dangerous Mauroy, B., M. Filoche, E. R. Weibel, and B. Sapoval Nature 427, no. 6975, 633636 (2004)
Résumé: The geometry and dimensions of branched structures such as blood vessels or airways are important factors in determining the efficiency of physiological processes. It has been shown that fractal trees can be space filling1 and can ensure minimal dissipation2–4. The bronchial tree of most mammalian lungs is a good example of an efficient distribution system with an approximate fractal structure5,6. Here we present a study of the compatibility between physical optimization and physiological robustness in the design of the human bronchial tree. We show that this physical optimization is critical in the sense that small variations in the geometry can induce very large variations in the net air flux. Maximum physical efficiency therefore cannot be a sufficient criterion for the physiological design of bronchial trees. Rather, the design of bronchial trees must be provided with a safety factor and the capacity for regulating airway calibre. Paradoxically, our results suggest that bronchial malfunction related to asthma is a necessary consequence of the optimized efficiency of the tree structure.


Renormalized Random Walk Study of Oxygen Absorption in the Human Lung Felici, M., M. Filoche, and B. Sapoval Physical Review Letters 92, no. 6 (2004)
Résumé: The possibility to renormalize random walks is used to study numerically the oxygen diffusion and permeation in the acinus, the diffusion cell terminating the mammalian airway tree. This is done in a 3D tree structure which can be studied from its topology only. The method is applied to the human acinus real morphology as studied by HaefeliBleuer and Weibel in order to compute the respiratory efficiency of the human lung. It provides the first quantitative evidence of the role of diffusion screening in real 3D mammalian respiration. The net result of this study is that, at rest, the efficiency of the human acinus is only of order 33%. Application of these results to CO2 clearance provides for the first time a theoretical support to the empirical relation between the O2 and CO2 partial pressures in blood.


Cancer death statistics: analogy between epidemiology and critical systems in physics Filoche, M., and L. Schwartz Medical Hypotheses 62, no. 5, 704709 (2004)
Résumé: The determination of risk factors in carcinogenesis is said to be an essential step towards the understanding of this disease. Most mathematical models describing the evolution of mortality figures use the concept of death probability (or “force of mortality” or “hazard of death”). When summarizing the death statistics through this unique parameter, one implicitly makes the assumption that the death events are independent from one individual to another. In this paper, we show that this hypothesis has profound consequences as it implies a “Gaussian” behavior of the death statistics fluctuations. In order to verify the validity of this assumption, French cancer death statistics between the years 1978–1996 are examined. Their fluctuations, for every age bracket, are computed and then compared to the expected gaussian fluctuations that should emerge from a model of death probability. We show that the observed fluctuations are in close agreement with a Gaussian model up to 35–40 years. After 40 years, the fluctuations are much higher and cannot be explained by a model where every individual would have a given “probability of death”. These
observations may produce a new insight into oldage cancer mortality. It suggests that there could exist a major difference between cancers in young or older organisms: cancer developed in young organisms are the consequence of a specific attack against an organ (essentially originated from a single cause, like a virus or a genetic deficiency). On the other hand, older organism are closer to a “critical state” and, as such, the outcome of a cancer in a given organ could be the consequence of a chain of “malfunctions” (analogous to an avalanch in physical systems) in the entire organism.


Spectral properties of the Brownian selftransport operator Grebenkov, D. S., M. Filoche, and B. Sapoval The European Physical Journal B  Condensed Matter 36, no. 2, 221231 (2003)
Résumé: The problem of the Laplacian transfer across an irregular resistive interface (a membrane or an electrode) is investigated with use of the Brownian selftransport operator. This operator describes the transfer probability between two points of a surface, through Brownian motion in the medium neighbour ing the surface. This operator governs the flux across a semipermeable membrane as diffusing particles repetitively hit the surface until they are finally absorbed. In this paper, we first give a theoretical study of the properties of this operator for a planar membrane. It is found that the net effect of a decrease of the surface permeability is to induce a broadening of the region where a particle, first hitting the surface on one point, is finally absorbed. This result constitutes the first analytical justification of the Land Surveyor Approximation, a formerly developed method used to compute the overall impedance of a semipermeable membrane. In a second step, we study numerically the properties of the Brownian selftransport operator for selected irregular shapes.


Diffusional screening in the human pulmonary acinus Felici, M., M. Filoche, and B. Sapoval Journal of Applied Physiology 94, no. 5, 20102016 (2003)
Résumé: In the mammalian lung acini, O2 diffuses into quasistatic air to ward the alveolar membrane, where the gas exchange with blood takes place. The O2 flux is then influenced by the O2 diffusivity, the membrane permeability, and the acinus geo metric complexity. This phenomenon has been recently stud ied in an abstract geometric model of the acinus, the Hilbert acinus (Sapoval B, Filoche M, and Weibel ER, Proc Natl Acad Sci USA 99: 10411, 2002). This is extended here to a more realistic geometry originated from the morphological model of Kitaoka et al. (Kitaoka K, Tamura S, and Takaki R, J Appl Physiol 88: 2260–2268, 2000). Twodimensional numerical simulations of the steadystate diffusion equation with mixed boundary conditions are used to quantify the process. The alveolar O2 concentration, or partial pressure, and the O2 flux are computed and show that diffusional screening exists at rest. These results confirm that smaller acini are more efficient, as suggested for the Hilbert acini.


Interplay between Geometry and Flow Distribution in an Airway Tree Mauroy, B., M. Filoche, J. S. Andrade, and B. Sapoval Physical Review Letters 90, no. 14 (2003)
Résumé: Uniform flow distribution in a symmetric volume can be realized through a symmetric branched tree. It is shown here, however, by 3D numerical simulation of the NavierStokes equations, that the flow partitioning can be highly sensitive to deviations from exact symmetry if inertial effects are present. The flow asymmetry is quantified and found to depend on the Reynolds number. Moreover, for a given Reynolds number, we show that the flow distribution depends on the aspect ratio of the branching elements as well as their angular arrangement. Our results indicate that physiological variability should be severely restricted in order to ensure adequate fluid distribution through a tree.


Smaller is better—but not too small: A physical scale for the design of the mammalian pulmonary acinus Sapoval, B., M. Filoche, and E. R. Weibel Proceedings of the National Academy of Sciences 99, no. 16, 1041110416 (2002)
Résumé: The transfer of oxygen from air to blood in the lung involves three processes: ventilation through the airways, diffusion of oxygen in the air phase to the alveolar surface, and finally diffusion through tissue into the capillary blood. The latter two steps occur in the acinus, where the alveolar gasexchange surface is arranged along the last few generations of airway branching. For the acinus to work efficiently, oxygen must reach the last branches of acinar airways, even though some of it is absorbed along the way. This ‘‘screening effect’’ is governed by the relative values of physical factors like diffusivity and permeability as well as size and design of the acinus. Physics predicts that efficient acini should be space filling surfaces and should not be too large. It is shown that the mammalian acini fulfill these requirements, small mammals being more efficient than large ones both at rest and in exercise.


Analytical approximation for diffusionreaction processes in rough pores Andrade, J. S., M. Filoche, and B. Sapoval Europhysics Letters (EPL) 55, no. 4, 573579 (2001)
Résumé: The concept of an active zone in Laplacian transport is used to obtain an ana lytical approximation for the reactive effectiveness of a pore with an arbitrary rough geometry. We show that this approximation is in very good agreement with direct numerical simulations performed over a wide range of diffusionreaction conditions (i.e., with or without screening effects). In particular, we find that in most practical situations, the effect of roughness is to increase the intrinsic reaction rate by a geometrical factor, namely the ratio between the real and the apparent surface area. We show that this simple geometrical piece of information is suf ficient to characterize the reactive effectiveness of a pore, in spite of the complex morphological features it might possess.


Catalytic effectiveness of irregular interfaces and rough pores: the “land surveyor approximation” Sapoval, B., J. S. Andrade, and M. Filoche Chemical Engineering Science 56, no. 17, 50115023 (2001)
Résumé: We apply the concept of active zone in Laplacian transport to investigate the steady state mass transfer ofa diffusive species
towards an arbitrarily irregular catalytic interface. By means of a recently proposed coarsegraining technique, it is possible to
compute the reactive flux on the catalytic interface from its geometry alone, without solving the general Laplace problem. As a
result,we demonstrate by direct numerical simulation of molecular diffusion and firstorder reaction that this method allows one to
predict the catalytic effectiveness of a slitshaped pore with an arbitrary rough geometry and over a wide range of diffusion–reaction
conditions. It is found that, contrary to the traditional pseudohomogeneous approach, the effect of the irregular morphology at
the mesoscopic pore level is to modify the reaction rate and not the effective diffusion coefficient. We show that, for all practical
situations where the reactant penetration in the pore is significant, a simplified picture of a smooth pore with an effective reactivity
Keff can be used to describe the efficiency of a rough pore. Remarkably, Keff is the product of the intrinsic reactivity by a screening factor S, which has an elementary geometrical meaning, namely, the ratio between the real and the apparent surface area.


Devreux, F., P. Barboux, M. Filoche, and B. Sapoval Journal of Materials Science 36, no. 6, 13311341 (2001)
Résumé: Numerical simulations of the water dissolution of a random ternary solid are presented. The three elements represent silica, soluble oxides (alkalis and boron) and quasiinsoluble oxides (Al2O3, ZrO2, Fe2O3, . . .). The soluble species are dissolved immediately when they are in contact with the solution. Their proportion is kept below the percolation threshold. For the other species, one introduces a model of dissolutionrecondensation. It is shown that the dissolution rate constants should be dependent on the bonding environment in order to include surface tension. The condensation fluxes are proportional to the concentration of each species in solution. In the dynamic regime (no recondensation), one observes the congruent dissolution of silica and soluble species, after a short initial phase of selective extraction of the soluble species. The common rate of dissolution decreases with the proportion of insoluble species and increases sharply with that of soluble species. This is mainly due to the formation of a porous hydrated layer whose active surface area increases markedly with the proportion of soluble species. In the static regime (finite solution volume), the equilibrium solubility of silica decreases with the proportion of insoluble species and is practically independent of the proportion of soluble species. The porous hydrated layer is rearranged and almost free of soluble species. The ripening of the surface layer makes it protective and inhibits further extraction of the soluble species. These results are in general agreement with the experimental observations on the dissolution of durable glasses.


DiffusionReorganized Aggregates: Attractors in Diffusion Processes? Filoche, M., and B. Sapoval Physical Review Letters 85, no. 24, 51185121 (2000)
Résumé: A process based on particle evaporation, diffusion, and redeposition is applied iteratively to a twodimensional object of arbitrary shape. The evolution spontaneously transforms the object morphol ogy, converging to branched structures. Independently of initial geometry, the structures found after a long time present fractal geometry with a fractal dimension around 1.75. The final morphology, which constantly evolves in time, can be considered as the dynamic attractor of this evaporationdiffusionredeposition operator. The ensemble of these fractal shapes can be considered to be the dynamical equilibrium geometry of a diffusioncontrolled selftransformation process.


Shapedependency of current through nonlinear irregular electrodes Filoche, M., and B. Sapoval Electrochimica Acta 46, no. 23, 213220 (2000)
Résumé: We describe a simple way to understand the nonlinear response of an irregular resistive electrode in d=2. It is based on the concept of an active zone in the Laplacian transfer to and across irregular interfaces. It applies to arbitrary electrode geometry and permits to compute the flux across an irregular electrode from its geometry without solving the Laplace problem. The simplifying arguments that are used are tested numerically on prefractal models of the geometrical irregularity. One finds that, for electrodes following a local Butler–Volmer response, the Tafel slope depends on the geometry. It is shown that the measure of the cell impedance leads to the determination of the actual active potential. It also gives the mean size of a part of the electrode with a surface impedance equal to the electrolyte bulk resistivity


Transfer Across Random versus Deterministic Fractal Interfaces Filoche, M., and B. Sapoval Physical Review Letters 84, no. 25, 57765779 (2000)
Résumé: A numerical study of the transfer across random fractal surfaces shows that their responses are very close to the response of deterministic model geometries with the same fractal dimension. The simulations of several interfaces with prefractal geometries show that, within very good approximation, the flux depends only on a few characteristic features of the interface geometry: the lower and higher cutoffs and the fractal dimension. Although the active zones are different for different geometries, the electrode responses are very nearly the same. In that sense, the fractal dimension is the essential “universal” exponent which determines the net transfer.


A Unified Theory of the BZ Transition of DNA in High and Low Concentrations of Multivalent Ions Guéron, M., J.P. Demaret, and M. Filoche Biophysical Journal 78, no. 2, 10701083 (2000)
Résumé: We showed recently that the highsalt transition of poly[d(GC)] z poly[d(GC)] between BDNA and ZDNA (at [NaCl] 5 2.25 M or [MgCl2] 5 0.7 M) can be ascribed to the lesser electrostatic free energy of the B form, due to better immersion of the phosphates in the solution. This property was incorporated in cylindrical DNA models that were analyzed by PoissonBoltzmann theory. The results are insensitive to details of the models, and in fair agreement with experiment. In contrast, the Z form of the poly[d(Gm5C)] duplex is stabilized by very small concentrations of magnesium. We now show that this striking difference is accommodated quantitatively by the same electrostatic theory, without any adjustable parameter. The different responses to magnesium of the methylated and nonmethylated polymers do not come from stereospecific cationDNA interactions: they stem from an experimentally derived, modest difference in the nonelectrostatic component of the free energy difference (or NFED) between the Z and B forms. The NFED is derived from circular DNA measurements. The differences between alkaline earth and transition metal ions are explained by weak coordination of the latter. The theory also explains the induction of the transition by micromolar concentrations of cobalt hexammine, again without specific binding or adjustable parameters. Hence, in the case of the BZ transition as in others (e.g., the folding of tRNA and of ribozymes), the effect of multivalent cations on nucleic acid structure is mediated primarily by nonspecific ionpolyelectrolyte interactions. We propose this as a general rule for which convincing counterexamples are lacking.


Dynamical fractal equilibrium in diffusion limited reorganization Filoche, M., and B. Sapoval Comptes Rendus de l'Académie des Sciences  Series IIB  MechanicsPhysicsAstronomy 327, no. 10, 10711076 (1999)
Résumé: The evolution of a compact structure under surface evaporation,diffusion and subsequent redeposition is studied numerically in d=2. After a transitory regime, the evolution leads to the spontaneous apparition of a dynamic fractal morphology exhibiting a dimension of order D=1.6. The final morphology plays the role of a statistical dynamic attractor. This effect indicates that fractal structures can result from the irreversible evolution of dynamical processes towards internal equilibrium.


Can one hear the shape of an electrode? II. Theoretical study of the Laplacian transfer Filoche, M., and B. Sapoval The European Physical Journal B 9, no. 4, 755763 (1999)
Résumé: The flux across resistive irregular interfaces driven by a force deriving from a Laplacian potential is computed on a rigorous basis. The theory permits one to relate the size of the active zone Aact. to the derivative of the spectroscopic impedance Zspect.(r) with respect to the surface resistivity r through:
d(Zspect.)/dr = A_act^−1 . It is shown that the macroscopic transfer properties through a system of arbitrary shape are determined by the characteristics of a firstpassage interfaceinterface random walk operator. More precisely, it is the distribution of the harmonic measure (or normalized primary current) on the eigenmodes of this linear operator that controls the transfer. In addition, it is also shown that, whatever the dimension, the impedance of a weakly polarizable electrode for any irregular geometry scales under a homothety transformation as L^d−1, L being the size of the system and d its topological dimension. In this new formalism, the question addressed in the title is transformed in a open mathematical question: “Knowing the distribution of the harmonic measure on the eigenmodes of the selftransport operator, can one retrieve the shape of the interface?”


Can one hear the shape of an electrode? I. Numerical study of the active zone in Laplacian transfer Sapoval, B., M. Filoche, K. Karamanos, and R. Brizzi The European Physical Journal B 9, no. 4, 739753 (1999)
Résumé: The concept of active zone in the Laplacian transport to and across irregular interfaces is rigorously introduced. It applies to arbitrary geometries and uses the coarsegraining method proposed by Sapoval to compute the flux across an irregular interface from its geometry without solving the general Laplace problem. Such transport play a dominant role in electrochemistry, heterogeneous catalysis and physiological diffusion processes. In the field of electrochemistry, the method permits one to predict the impedance of an electrode of arbitrary geometry for any value of the frequency. It shows that, for systems with aspect ratios of the order of a few times unity or less, impedance spectroscopy yields in principle a reliable approximate measure of the length of the chord corresponding to a perimeter length inversely proportional to the interface capacitance and frequency. For these cases, impedance spectroscopy can determine the shape of an electrode to the extent that the knowledge of the average chord length as a function of the perimeter determines the shape. For systems of arbitrary geometry, it is shown that impedance spectroscopy permits a measure of the size of the active zone. These results can be transposed to several problems related to Laplacian transfer, such as etching of irregular solids and catalysis in the EleyRideal regime.


Gain modeling of strained InGaAsP based MQW optical amplifiers Debaisieux, G., M. Guemmouri, S. Chelles, A. Ougazzaden, G. HerveGruyer, M. Filoche, and J.Y. Martin IEEE Photonics Technology Letters 9, no. 11, 14751477 (1997)
Résumé: This paper presents a selfconsistent 1D multiquantumwell laser simulation in which, for the ®rst time, the SchroÈ dinger equation is solved over the whole quantumwell zone, taking into account welltowell coupling. The computed lightintensity curve is com pared with experimental results for an InGaAs/InGaAsP multiquantumwell laser and also with simpli®ed models. The quantum calculation has an important in ̄uence on the carrier density pro®le in the active region. This results in a signi®cant difference in the estimation of the threshold current with respect to other simpli®ed models.


Gain modeling of strained InGaAsP based MQW optical amplifiers Debaisieux, G., G. Herve´Gruyer, M. Filoche, S. Bouchoule, and J. F. Palmier Optical and Quantum Electronics 29, no. 6, 651660 (1997)


A Simple Method to Compute the Response of NonHomogeneous and Irregular Interfaces: Electrodes and Membranes Filoche, M., and B. Sapoval Journal de Physique I 7, no. 11, 14871498 (1997)
Résumé: We present a detailed numerical test of the coarsegraining method proposed by Sapoval to compute the flux through an irregular interface in the case where the local response is inhomogeneously distributed. It is shown, through comparison with detailed finite elements simulations, that this method permits to deduce the flux across an irregular interface from its topography only, as for example in the case of nonuniform polarizability in electrochemistry. The interest of the method lies in its computational simplicity. It then constitutes an essential step towards the understanding of the flux across irregular interfaces in nonlinear regimes.


Folded and confined onedimensional plasmons in modulated wires Perez, F., B. Jusserand, C. Dahl, and M. Filoche Superlattices and Microstructures 22, no. 2, 257260 (1997)
Résumé: We demonstrate theoretically and experimentally that onedimensional plasmons of doped wires are either extended or longitudinally confined when the lateral width of the wires is periodically modulated. Theoretical dispersion curves, calculated within a classical framework, reproduce well the experimental dispersion deduced from Raman scattering on deep etched modulated wires. Zoneedge gap openings, increasing with the modulation amplitude, are exhibited. We show that deep etching allows a good control of complex geometries and provides quasiabrupt boundary conditions.


Folded and confined onedimensional plasmons in modulated wires Perez, F., B. Jusserand, C. Dahl, M. Filoche, L. FerlazzoManin, and B. Etienne Physical Review B 54, no. 16, R11098R11101 (1996)
Résumé: We demonstrate theoretically and experimentally that onedimensional plasmons confined in doped wires are either extended or longitudinally confined when the lateral width of the wires is periodically modulated. Theoretical dispersion curves, calculated within a classical framework, reproduce well the experimental dis persion deduced from Raman scattering on deep etched modulated wires. Zoneedge gap openings, increasing with the modulation amplitude, are exhibited. We show that deep etching allows good control of complex geometries and provides quasiabrupt boundary conditions.


Horizontal directional coupler filter suitable for integration in a 1.3+/1.3µm duplexer Francois, S., N. Bouadma, J. Brandon, M. Filoche, A. Carenco, A. Ougazzaden, G. HervéGruyer, M. Carré, S. Fouchet, and F. Huet Electronics Letters 31, no. 23, 20022003 (1995)
Résumé: The authors report the design and first realisation of a grating assisted honzontal directional coupler filter exibiting a highly reduced polansation sensitivity (below 1dB on the filtered channel) and a high sidelobe suppression ratio (>25dB for both polansations). This filter is particulary suitable for integration in a 1.3+/1.3µm duplexer


Polarizationindependent filtering in a gratingassisted horizontal directional coupler Francois, S., S. Fouchet, N. Bouadma, A. Ougazzaden, M. Carre, G. HerveGruyer, M. Filoche, and A. Carenco IEEE Photonics Technology Letters 7, no. 7, 780782 (1995)
Résumé: We report here on the design and the first realization of a gratingassisted horizontal directional coupler filter exhibiting a highly reduced polarization sensitivity. The filter, which is based on InPInGaAsP materials, is particularly suitable for integration in a 1.3/spl plusmn/1.3 μm duplexer. A polarization dependence below 1 dB has been measured for the separation of two 10 nm wide channels, respectively centered at 1.28 μm and 1.32 μm, for a rejection ratio of 10 dB.


1.5μm DFB lasers with new currentinduced gain gratings Kazmierski, C., D. Robein, D. Mathoorasing, A. Ougazzaden, and M. Filoche IEEE Journal of Selected Topics in Quantum Electronics 1, no. 2, 371374 (1995)
Résumé: We introduce a new concept for gratings, based on a spatial carrier modulation, induced by current for optoelectronic devices. The concept is experimentally tested on gain coupled lasers, showing predicted features as highpower, lowlinewidth, and lengthindependent coupling length product.


Spot size transformer with a periodically segmented waveguide based on InP Dorgeuille, F., B. Mersali, S. François, G. HervéGruyer, and M. Filoche Optics Letters 20, no. 6, 581 (1995)
Résumé: We report what is to our knowledge the first optimization of a spot size transformer by use of a periodically segmented waveguide for photonic integrated circuits based on InP. It is shown that a nonlinear variation of the segmentation ratio along the propagation direction allows one to make an adiabatic transition of a short length. A simple method based on the study of a beveled edge transition is presented for the optimization of such a device. Internal losses in the transition region as low as 1.2 dB are obtained between a coupling waveguide and a simple heterostructure waveguide, with a very high transition spot size expansion factor.


Semiconductor device modelling for heterojunctions structures with mixes finite elements Hecht, F., A. Marrocco, E. Caquot, and M. Filoche COMPEL  The international journal for computation and mathematics in electrical and electronic engineering 10, no. 4, 425438 (1991)
Résumé: Numerical simulation of the static semiconductor device equations using mixed finite element for the approximation and A.D.I. techniques (Douglas‐Rachford with local time steps) for the solution is presented in this paper. The formulation with electrostatic potential φ and quasi‐Fermi levels φn,φp is used.


Electrical characterisation of the ptype dopant diffusion of highly doped AlGaAs/GaAs heterojunction bipolar transistors grown by MOCVD Dangla, J., C. DubonChevallier, M. Filoche, and R. Azoulay Electronics Letters 26, no. 14, 1061 (1990)
Résumé: The emitter base threshold voltage is found to be a very effcient method of characterising ptype dopant diffusionin highly doped heterojunction bipolar transistors. Simulated curves have been successfully used to determine the amount of diffusion at different doping levels, showing the ability of MOCVD to achieve a high base doping level without any dopant diffusion.

