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Journal articles on the topic 'Analyse des perturbations'

Author: Grafiati

Published: 4 June 2021

Last updated: 6 February 2022

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1

Tsizh, M., and B. Novosyadlyj. "Evolution of density and velocity profiles of matter in large voids." Advances in Astronomy and Space Physics 6, no. 1 (2016): 28–33. http://dx.doi.org/10.17721/2227-1481.6.28-33.

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We analyse the evolution of cosmological perturbations which leads to the formation of large voids in the distribution of galaxies. We assume that perturbations are spherical and all components of the Universe - radiation, matter and dark energy - are continuous media with ideal fluid energy-momentum tensors, which interact only gravitationally. Equations of the evolution of perturbations in the comoving to cosmological background reference frame for every component are obtained from equations of conservation and Einstein's ones and are integrated by modified Euler method. Initial conditions a

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2

Urbina, A. M., M. Cañas, G. León de la Barra, and M. León de la Barra. "Perturbations of a Hamiltonian family of cubic vector fields." Bulletin of the Australian Mathematical Society 44, no. 1 (1991): 139–47. http://dx.doi.org/10.1017/s0004972700029531.

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This paper is related with the configurations of limit cycles for cubic polynomial vector fields in two variables (χ3).It is an open question to decide whether every limit cycle configuration in χ3 can be obtained by perturbation of a corresponding Hamiltonian configuration of centres and graphs.In this work, by considering perturbations of the Hamiltonian vector field XH = (Hy, − Hx), where H(x, y) = [a(x + h)2 + by2 − 1] [a(x − h)2 + by2 − 1], we make a global analysis of the possible cases.The vector field XH has three centres (C−, C+ and the origin) and two saddles. By means of quadratic p

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3

Volkova, Victoria. "On perturbations in Horndeski theories." EPJ Web of Conferences 182 (2018): 02127. http://dx.doi.org/10.1051/epjconf/201818202127.

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This research has been carried out in collaboration with R. Kolevatov, S. Mironov, V. Rubakov and N. Sukhov. We study the approach suggested by Deffayet et al. for obtaining a derivative part of the quadratic action for scalar perturbations in the cubic Horndeski theory. We analyse the validity of the approach and generalize it for the complete Horndeski theory. We explicitly check that the generalized method gives the correct result.

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Faure, R. M. "Analyse des contraintes dans un talus par la méthode des perturbations." Revue Française de Géotechnique, no. 33 (1985): 49–59. http://dx.doi.org/10.1051/geotech/1985033049.

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CLARISSE, J. M., C. BOUDESOCQUE-DUBOIS, and S. GAUTHIER. "Linear perturbation response of self-similar ablative flows relevant to inertial confinement fusion." Journal of Fluid Mechanics 609 (July 31, 2008): 1–48. http://dx.doi.org/10.1017/s0022112008002279.

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A family of exact similarity solutions for inviscid compressible ablative flows in slab symmetry with nonlinear heat conduction is proposed for studying unsteadiness and compressibility effects on the hydrodynamic stability of ablation fronts relevant to inertial confinement fusion. Dynamical multi-domain Chebyshev spectral methods are employed for computing both the similarity solution and its time-dependent linear perturbations. This approach has been exploited to analyse the linear stability properties of two self-similar ablative configurations subjected to direct laser illumination asymme

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6

Cheng, Chuan, Chengpeng Wang, and Keming Cheng. "Response of an oblique shock train to downstream periodic pressure perturbations." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, no. 1 (2017): 57–70. http://dx.doi.org/10.1177/0954410017727028.

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An experimental investigation of the response of an oblique shock train to downstream periodic pressure perturbations was conducted. The oblique shock train is generated in a Mach 2.7 ducted flow and controlled by a downstream elliptical shaft. Cyclic rotating of the shaft leads to a periodic oscillatory motion of the oblique shock train. Six cases of perturbation frequency are studied. The results indicate that the downstream pressure perturbations propagate upstream to cause the oblique shock train to oscillate with a translational motion back and forth and the wall pressure to fluctuate wit

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ZHAO, M., M. S. GHIDAOUI, and A. A. KOLYSHKIN. "Perturbation dynamics in unsteady pipe flows." Journal of Fluid Mechanics 570 (January 3, 2007): 129–54. http://dx.doi.org/10.1017/s0022112006003193.

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This paper deals with perturbed unsteady laminar flows in a pipe. Three types of flows are considered: a flow accelerated from rest; a flow in a pipe generated by the controlled motion of a piston; and a water hammer flow where the transient is generated by the instantaneous closure of a valve. Methods of linear stability theory are used to analyse the behaviour of small perturbations in the flow. Since the base flow is unsteady, the linearized problem is formulated as an initial-value problem. This allows us to consider arbitrary initial conditions and describe both short-time and long-time e

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FONTANE, J., P. BRANCHER, and D. FABRE. "Stochastic forcing of the Lamb–Oseen vortex." Journal of Fluid Mechanics 613 (October 1, 2008): 233–54. http://dx.doi.org/10.1017/s002211200800308x.

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The aim of the present paper is to analyse the dynamics of the Lamb–Oseen vortex when continuously forced by a random excitation. Stochastic forcing is classically used to mimic external perturbations in realistic configurations, such as variations of atmospheric conditions, weak compressibility effects, wing-generated turbulence injected into aircraft wakes, or free-stream turbulence in wind tunnel experiments. The linear response of the Lamb–Oseen vortex to stochastic forcing can be decomposed in relation to the azimuthal symmetry of the perturbation given by the azimuthal wavenumber m. In t

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9

Wang, Shixiao, Zvi Rusak, Rui Gong, and Feng Liu. "On the three-dimensional stability of a solid-body rotation flow in a finite-length rotating pipe." Journal of Fluid Mechanics 797 (May 18, 2016): 284–321. http://dx.doi.org/10.1017/jfm.2016.223.

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The three-dimensional, inviscid and viscous flow instability modes that appear on a solid-body rotation flow in a finite-length straight, circular pipe are analysed. This study is a direct extension of the Wang & Rusak (Phys. Fluids, vol. 8 (4), 1996a, pp. 1007–1016) analysis of axisymmetric instabilities on inviscid swirling flows in a pipe. The linear stability equations are the same as those derived by Kelvin (Phil. Mag., vol. 10, 1880, pp. 155–168). However, we study a general mode of perturbation that satisfies the inlet, outlet and wall conditions of a flow in a finite-length pipe wi

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10

Anastasio, Thomas J., Andrea K. Barreiro, and Jared C. Bronski. "A geometric method for eigenvalue problems with low-rank perturbations." Royal Society Open Science 4, no. 9 (2017): 170390. http://dx.doi.org/10.1098/rsos.170390.

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We consider the problem of finding the spectrum of an operator taking the form of a low-rank (rank one or two) non-normal perturbation of a well-understood operator, motivated by a number of problems of applied interest which take this form. We use the fact that the system is a low-rank perturbation of a solved problem, together with a simple idea of classical differential geometry (the envelope of a family of curves) to completely analyse the spectrum. We use these techniques to analyse three problems of this form: a model of the oculomotor integrator due to Anastasio & Gad (2007 J. Compu

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11

Delcey, Lucie, and Mariana Haraguss. "Periodic waves of the Lugiato–Lefever equation at the onset of Turing instability." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 376, no. 2117 (2018): 20170188. http://dx.doi.org/10.1098/rsta.2017.0188.

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We study the existence and the stability of periodic steady waves for a nonlinear model, the Lugiato–Lefever equation, arising in optics. Starting from a detailed description of the stability properties of constant solutions, we then focus on the periodic steady waves which bifurcate at the onset of Turing instability. Using a centre manifold reduction, we analyse these Turing bifurcations, and prove the existence of periodic steady waves. This approach also allows us to conclude on the nonlinear orbital stability of these waves for co-periodic perturbations, i.e. for periodic perturbations wh

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12

MASUDA, S., S. FUKUDA, and M. NAGATA. "Instabilities of plane Poiseuille flow with a streamwise system rotation." Journal of Fluid Mechanics 603 (April 30, 2008): 189–206. http://dx.doi.org/10.1017/s0022112008000943.

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We analyse the stability of plane Poiseuille flow with a streamwise system rotation. It is found that the instability due to two-dimensional perturbations, which sets in at the well-known critical Reynolds number, Rc = 5772.2, for the non-rotating case, is delayed as the rotation is increased from zero, showing a stabilizing effect of rotation. As the rotation is increased further, however, the laminar flow becomes most unstable to perturbations which are three-dimensional. The critical Reynolds number due to three-dimensional perturbations at this higher rotation case is many orders of magnit

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Koroteev, M. V., and I. I. Lipatov. "Local temperature perturbations of the boundary layer in the regime of free viscous–inviscid interaction." Journal of Fluid Mechanics 707 (July 24, 2012): 595–605. http://dx.doi.org/10.1017/jfm.2012.312.

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AbstractWe analyse the disturbed flow in the subsonic laminar boundary layer, disturbances being generated by local heating elements, which are placed on the surface. It is exhibited that these flows are described in terms of free interaction theory for specific sizes of thermal sources. We construct the numerical solution for the case of a flat subsonic stream in the viscous asymptotic layer, in which the flow is described by nonlinear equations for vorticity, temperature and an interaction condition which provides the influence of perturbations to the pressure in the main order. The obtained

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14

Martin, Franck, Agnès Morcillo, and Jean-François Blin. "Le vécu émotionnel des enseignants confrontés à des perturbations scolaires." Revue des sciences de l'éducation 30, no. 3 (2006): 579–604. http://dx.doi.org/10.7202/012083ar.

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Résumé Notre étude concerne le personnel éducatif des établissements du secondaire. Elle se centre sur la prise en compte des émotions dans l’activité réelle de ce personnel. Ces émotions interviennent lors de perturbations scolaires. Elles enclenchent une dynamique cognitivo-émotionnelle qui gère des comportements réponses. Ces comportements ne s’inscrivent pas dans des pratiques professionnelles réfléchies. La problématique posée et les résultats obtenus, grâce à une analyse de similitude, incitent à proposer une réflexion sur l’inscription méthodologique, dans les programmes de formation, d

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Strube, Cornelia, Manfred Ern, Peter Preusse, and Martin Riese. "Removing spurious inertial instability signals from gravity wave temperature perturbations using spectral filtering methods." Atmospheric Measurement Techniques 13, no. 9 (2020): 4927–45. http://dx.doi.org/10.5194/amt-13-4927-2020.

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Abstract. Gravity waves are important drivers of dynamic processes in particular in the middle atmosphere. To analyse atmospheric data for gravity wave signals, it is essential to separate gravity wave perturbations from atmospheric variability due to other dynamic processes. Common methods to separate small-scale gravity wave signals from a large-scale background are separation methods depending on filters in either the horizontal or vertical wavelength domain. However, gravity waves are not the only process that could lead to small-scale perturbations in the atmosphere. Recently, concerns ha

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16

Ammari, Habib, Doo Sung Choi, and Sanghyeon Yu. "A mathematical and numerical framework for near-field optics." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 474, no. 2217 (2018): 20180150. http://dx.doi.org/10.1098/rspa.2018.0150.

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This paper is concerned with the inverse problem of reconstructing small and local perturbations of a planar surface using the field interaction between a known plasmonic particle and the planar surface. The aim is to perform a super-resolved reconstruction of these perturbations from shifts in the plasmonic frequencies of the particle-surface system. In order to analyse the interaction between the plasmonic particle and the planar surface, a well-chosen conformal mapping, which transforms the particle-surface system into a coated structure, is used. Then the even Fourier coefficients of the t

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17

Mekideche, Siham, Lila Brakchi-Ouakour, and Leila Kadik. "Impact des perturbations anthropiques sur la diversité végétale de la subéraie de Chréa, au nord de l’Algérie." BOIS & FORETS DES TROPIQUES 337 (November 26, 2018): 53. http://dx.doi.org/10.19182/bft2018.337.a31633.

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La subéraie de la réserve de biosphèrede Chréa, au nord de l’Algérie, révèle une action anthropique ayant profondément modifié le paysage végétal. Les feux récurrents et le surpâturage sont les principales perturbations des formations forestières présentes, s’agissant de perte de surface et de biomasse végétale. Notre objectif était de savoir comment, au sein de cette réserve, réagit la végétation de l’écosystème à Quercus suber L. aux conditions de milieu et aux perturbations liées à l’activité humaine. Pour y répondre, nous avons adopté une approche synchronique en réalisant 124 relevés phyt

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Birmelé, Etienne, François Delbot, Christian Laforest, and Nicolas Thibault. "Analyse du nombre de perturbations lors du maintien d’un arbre de connexion de faible diamètre." Techniques et sciences informatiques 30, no. 7 (2011): 781–808. http://dx.doi.org/10.3166/tsi.30.781-808.

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19

Capettini, H., M. Cécere, A. Costa, G. Krause, and O. Reula. "Slow and sausage loop mode excitation due to local and global spontaneous perturbations." Astronomy & Astrophysics 644 (December 2020): A106. http://dx.doi.org/10.1051/0004-6361/202039023.

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Aims. We analyse the capability of different types of perturbations associated with usual environment energy fluctuations of the solar corona to excite slow and sausage modes in solar flaring loops. Methods. We performed numerical simulations of magnetohydrodynamic ideal equations with a consideration of straight plasma magnetic tubes subject to local and global energy depositions. Results. We find that local loop energy depositions of typical microflares [∼(1027 − 1030) erg] are prone to driving slow shock waves that induce slow-mode patterns. The slow-mode features are obtained for every tes

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20

Decaluwé, Bernard, and Jagdeep S. Bhandari. "Le régime du double marché des changes sous les Tropiques : une analyse théorique." Articles 61, no. 4 (2009): 428–52. http://dx.doi.org/10.7202/601346ar.

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RÉSUMÉ Dans cet article, nous présentons un modèle de double marché des changes. La principale innovation de notre étude est l’inclusion de transactions croisées, ou de liaisons légales ou illégales entre les deux compartiments du marché des changes. L’existence de liaisons entre les marchés complique sensiblement le fonctionnement d’une telle économie car les résidents nationaux peuvent acquérir des actifs financiers étrangers alors qu’ils ne le peuvent pas lorsque les deux compartiments du marché sont parfaitement cloisonnés. En faisant la distinction entre des liaisons « à l’importation » o

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21

Bondarev, Vsevolod, and Vasily Vedeneev. "Short-wave instability of an elastic plate in supersonic flow in the presence of the boundary layer." Journal of Fluid Mechanics 802 (August 5, 2016): 528–52. http://dx.doi.org/10.1017/jfm.2016.482.

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Panel flutter is a dangerous aeroelastic instability of the skin panels of supersonic flight vehicles. Though the linear stability of panels in uniform flow has been studied in detail, the influence of the boundary layer is still an open question. Most studies of panel flutter in the presence of the boundary layer are devoted to the ($1/7$)th-power velocity law and yield a stabilising effect of the boundary layer. Recently, Vedeneev (J. Fluid Mech., vol. 736, 2013, pp. 216–249) considered arbitrary velocity and temperature profiles and showed that, for a generalised convex boundary layer profi

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LINDSAY, A. E., and M. J. WARD. "Asymptotics of some nonlinear eigenvalue problems modelling a MEMS Capacitor. Part II: multiple solutions and singular asymptotics." European Journal of Applied Mathematics 22, no. 2 (2010): 83–123. http://dx.doi.org/10.1017/s0956792510000318.

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Some nonlinear eigenvalue problems related to the modelling of the steady-state deflection of an elastic membrane associated with a Micro-Electromechanical System capacitor under a constant applied voltage are analysed using formal asymptotic methods. These problems consist of certain singular perturbations of the basic membrane nonlinear eigenvalue problem Δu = λ/(1 + u)2 in Ω with u = 0 on ∂Ω, where Ω is the unit ball in 2. It is well known that the radially symmetric solution branch to this basic membrane problem has an infinite fold-point structure with λ → 4/9 as ϵ ≡ 1 − ||u||∞ → 0+. One

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Lotz, Martin, and Vanni Noferini. "Wilkinson’s Bus: Weak Condition Numbers, with an Application to Singular Polynomial Eigenproblems." Foundations of Computational Mathematics 20, no. 6 (2020): 1439–73. http://dx.doi.org/10.1007/s10208-020-09455-y.

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AbstractWe propose a new approach to the theory of conditioning for numerical analysis problems for which both classical and stochastic perturbation theories fail to predict the observed accuracy of computed solutions. To motivate our ideas, we present examples of problems that are discontinuous at a given input and even have infinite stochastic condition number, but where the solution is still computed to machine precision without relying on structured algorithms. Stimulated by the failure of classical and stochastic perturbation theory in capturing such phenomena, we define and analyse a wea

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Tousignant, Michel. "La santé mentale des migrants : analyse de son contexte social et longitudinal." Santé mentale au Québec 17, no. 2 (2008): 35–45. http://dx.doi.org/10.7202/502069ar.

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RÉSUMÉ La santé mentale des migrants est affectée par plusieurs facteurs qui relèvent à la fois des expériences pré-migratoires et des conditions d'adaptation au pays hôte. L'interaction entre ces deux niveaux de facteurs évolue cependant en fonction du temps, marqué tantôt de périodes de relatif équilibre, tantôt de perturbations inattendues comme si le processus de migration n'était jamais complété. L'âge d'arrivée dans un nouveau pays est aussi fort important, les adolescents ayant à affronter plusieurs demandes simultanées et les personnes aînées n'ayant plus les ressources personnelles po

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Ávila-Aroche, A., P. F. Velázquez, A. Camps-Fariña, J. C. Toledo-Roy, and A. Esquivel. "Young bilateral supernova remnants evolving into a turbulent interstellar magnetic field." Monthly Notices of the Royal Astronomical Society 495, no. 2 (2020): 2112–24. http://dx.doi.org/10.1093/mnras/staa1301.

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ABSTRACT We employ 3D magnetohydrodynamic simulations to study the morphology and synchrotron emission of young supernova remnants evolving in a turbulent interstellar magnetic field, seeking to shed new light on to the polarization structure of the emission and on the debate concerning the quasi-parallel and quasi-perpendicular acceleration mechanisms. In the simulations, we consider a non-homogeneous interstellar medium magnetic field by introducing small random perturbations in the direction and intensity of the field. In order to analyse the dependence of the radio morphology on the degree

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ABDESSEMED, N., S. J. SHERWIN, and V. THEOFILIS. "Linear instability analysis of low-pressure turbine flows." Journal of Fluid Mechanics 628 (June 1, 2009): 57–83. http://dx.doi.org/10.1017/s0022112009006272.

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Three-dimensional linear BiGlobal instability of two-dimensional states over a periodic array of T-106/300 low-pressure turbine (LPT) blades is investigated for Reynolds numbers below 5000. The analyses are based on a high-order spectral/hpelement discretization using a hybrid mesh. Steady basic states are investigated by solution of the partial-derivative eigenvalue problem, while Floquet theory is used to analyse time-periodic flow set-up past the first bifurcation. The leading mode is associated with the wake and long-wavelength perturbations, while a second short-wavelength mode can be ass

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VOROBEV, A., and O. ZIKANOV. "Instability and transition to turbulence in a free shear layer affected by a parallel magnetic field." Journal of Fluid Mechanics 574 (February 15, 2007): 131–54. http://dx.doi.org/10.1017/s002211200600423x.

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Instability and transition to turbulence in a temporally evolving free shear layer of an electrically conducting fluid affected by an imposed parallel magnetic field is investigated numerically. The case of low magnetic Reynolds number is considered. It has long been known that the neutral disturbances of the linear problem are three-dimensional at sufficiently strong magnetic fields. We analyse the details of this instability solving the generalized Orr–Sommerfeld equation to determine the wavenumbers, growth rates and spatial shapes of the eigenmodes. The three-dimensional perturbations are

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Hota, Tapan Kumar, and Manoranjan Mishra. "Non-modal stability analysis of miscible viscous fingering with non-monotonic viscosity profiles." Journal of Fluid Mechanics 856 (October 12, 2018): 552–79. http://dx.doi.org/10.1017/jfm.2018.674.

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A non-modal linear stability analysis (NMA) of the miscible viscous fingering in a porous medium is studied for a toy model of non-monotonic viscosity variation. The onset of instability and its physical mechanism are captured in terms of the singular values of the propagator matrix corresponding to the non-autonomous linear equations. We discuss two types of non-monotonic viscosity profiles, namely, with unfavourable (when a less viscous fluid displaces a high viscous fluid) and with favourable (when a more viscous fluid displaces a less viscous fluid) endpoint viscosities. A linear stability

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Bonnet, Nicolas. "Résilience d’un territoire face au chômage : les réseaux d’entreprises innovantes sur Montpellier." Nouvelles perspectives en sciences sociales 5, no. 1 (2009): 97–115. http://dx.doi.org/10.7202/038625ar.

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Résumé L’objectif de l’article est d’évaluer la résilience d’un territoire face à des perturbations économiques, ici l’aire urbaine de Montpellier, au travers de l’étude de la morphologie des réseaux d’entreprises locales. Pour réaliser cette analyse, nous avons mené un recensement des dépôts communs de brevets des entreprises innovantes locales. Cette approche a permis une modélisation de ces réseaux avec la théorie des graphes sur plusieurs plages temporelles. Au final, cette analyse permet de mettre en évidence au sein de ces réseaux locaux d’innovation le rôle joué par des entreprises-pivo

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Bechchari, A., A. El Aich, H. Mahyou, M. Baghdad, and M. Bendaou. "Analyse de l’évolution du système pastoral du Maroc oriental." Revue d’élevage et de médecine vétérinaire des pays tropicaux 67, no. 4 (2015): 151. http://dx.doi.org/10.19182/remvt.20557.

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Le système pastoral des hauts plateaux du Maroc oriental est caractérisé par l’étendue des parcours (3,2 millions d’hectares) et la dominance de l’élevage ovin (1,2 million de têtes). Ce travail, mené à Béni Mathar au nord et à Maâtarka au sud, traite la question des changements d’occupation des terres de parcours et de conduite des troupeaux, à partir de l’hypothèse d’une dégradation des parcours suivie d’une baisse de la pression de pâturage. Cette dynamique est perçue par l’étude de l’occupation des sols en 1970, 1988 et 2013. Les modes de conduite sont identifiés au travers d’enquêtes (85)

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LAM, M. A., L. J. CUMMINGS, T. S. LIN, and L. KONDIC. "Three-dimensional coating flow of nematic liquid crystal on an inclined substrate." European Journal of Applied Mathematics 26, no. 5 (2015): 647–69. http://dx.doi.org/10.1017/s0956792515000091.

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We consider a coating flow of nematic liquid crystal (NLC) fluid film on an inclined substrate. Exploiting the small aspect ratio in the geometry of interest, a fourth-order nonlinear partial differential equation is used to model the free surface evolution. Particular attention is paid to the interplay between the bulk elasticity and the anchoring conditions at the substrate and free surface. Previous results have shown that there exist two-dimensional travelling wave solutions that translate down the substrate. In contrast to the analogous Newtonian flow, such solutions may be unstable to st

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Turconi, M., M. Giudici, and S. Barland. "Response of laser-localized structures to external perturbations in coupled semiconductor microcavities." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, no. 2027 (2014): 20140004. http://dx.doi.org/10.1098/rsta.2014.0004.

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Laser-localized structures have been observed in several experiments based on broad-area semiconductor lasers. They appear as bounded regions of laser light emission which can exist independently of each other and are expected to be commuted via external optical perturbations. In this work, we perform a statistical analysis of time-resolved commutation experiments in a system of coupled lasers and show the role of wavelength, polarization and pulse energy in the switching process. Furthermore, we also analyse the response of the system outside of the stability region of laser-localized states

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Benedick, Paul-Lou, Jérémy Robert, and Yves Le Traon. "A Systematic Approach for Evaluating Artificial Intelligence Models in Industrial Settings." Sensors 21, no. 18 (2021): 6195. http://dx.doi.org/10.3390/s21186195.

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Artificial Intelligence (AI) is one of the hottest topics in our society, especially when it comes to solving data-analysis problems. Industry are conducting their digital shifts, and AI is becoming a cornerstone technology for making decisions out of the huge amount of (sensors-based) data available in the production floor. However, such technology may be disappointing when deployed in real conditions. Despite good theoretical performances and high accuracy when trained and tested in isolation, a Machine-Learning (M-L) model may provide degraded performances in real conditions. One reason may

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Albert, C., A. Tezuka, and D. Bothe. "Global linear stability analysis of falling films with inlet and outlet." Journal of Fluid Mechanics 745 (March 24, 2014): 444–86. http://dx.doi.org/10.1017/jfm.2014.57.

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AbstractIn this paper, the stability of falling films with different flow conditions at the inlet is studied. This is done with an algorithm for the numerical investigation of stability of steady-state solutions to dynamical systems, which is based on an Arnoldi-type iteration. It is shown how this algorithm can be applied to free boundary problems in hydrodynamics. A volume-of-fluid solver is employed to predict the time evolution of perturbations to the steady state. The method is validated by comparison to data from temporal and spatial stability theory, and to experimental results. The alg

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NOVIKOV, ALEXEI, and GEORGE PAPANICOLAOU. "Eddy viscosity of cellular flows." Journal of Fluid Mechanics 446 (October 23, 2001): 173–98. http://dx.doi.org/10.1017/s0022112001005730.

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We analyse modulational (large-scale) perturbations of stationary solutions of the two-dimensional incompressible Navier–Stokes equations. The stationary solutions are cellular flows with stream function ϕ = sin y1 sin y2 + δ cos y1 cos y2, 0 [les ] δ [les ] 1. Using multiscale techniques we derive effective coefficients, including the eddy viscosity tensor, for the (averaged) modulation equations. For cellular flows with closed streamlines we give rigorous asymptotic bounds at high Reynolds number for the tensor of eddy viscosity by means of saddle-point variational principles. These results

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Prat, Pau, Lorenzo Benedetti, Lluís Corominas, Joaquim Comas, and Manel Poch. "Model-based knowledge acquisition in environmental decision support system for wastewater integrated management." Water Science and Technology 65, no. 6 (2012): 1123–29. http://dx.doi.org/10.2166/wst.2012.759.

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The main goal of the Water Framework Directive is to achieve good chemical and ecological status of water bodies by 2015. The implementation of integrated river basin management, including sewer systems, wastewater treatment plants and receiving water bodies, is essential to accomplishing this objective. Integrated management is complex and therefore the implementation of control systems and the development of decision support systems are needed to facilitate the work of urban wastewater system (UWS) managers. Within this context, the objective of this paper is to apply integrated modelling of

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Driessen, F. A., N. D. Kee, J. O. Sundqvist, and S. P. Owocki. "Line-drag damping of Alfvén waves in radiatively driven winds of magnetic massive stars." Monthly Notices of the Royal Astronomical Society 499, no. 3 (2020): 4282–92. http://dx.doi.org/10.1093/mnras/staa3196.

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ABSTRACT Line-driven stellar winds from massive (OB) stars are subject to a strong line-deshadowing instability. Recently, spectropolarimetric surveys have collected ample evidence that a subset of Galactic massive stars hosts strong surface magnetic fields. We investigate here the propagation and stability of magnetoradiative waves in such a magnetized, line-driven wind. Our analytic, linear stability analysis includes line-scattering from the stellar radiation, and accounts for both radial and non-radial perturbations. We establish a bridging law for arbitrary perturbation wavelength after w

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Maceda, Marco, and Sergio Patiño-López. "Holographic superconductor from a noncommutative-inspired anti-de Sitter–Einstein–Born–Infeld black hole." International Journal of Modern Physics D 29, no. 01 (2019): 2050003. http://dx.doi.org/10.1142/s0218271820500030.

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Using a noncommutative-inspired anti-de Sitter–Einstein–Born–Infeld black hole with both noncommutative mass and charge distributions, we analyse a holographic superconductor in the context of the AdS/CFT correspondence. We show that the coupling of the Born–Infeld parameter and the noncommutative perturbations provides an enhancing mechanism for higher values of the expectation value of the condensate. Furthermore, we remark that noncommutativity counter-balances the nonlinearity of the electrodynamics to maintain the universal ratio of [Formula: see text].

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Śladowski, Grzegorz. "Using meta-networks to analyse the impact of adverse random events on the time and cost of completing." Przegląd Naukowy Inżynieria i Kształtowanie Środowiska 28, no. 2 (2019): 192–202. http://dx.doi.org/10.22630/pniks.2019.28.2.18.

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According to the concept of a system-based approach, a construction project can be treated as a complex system composed of various elements, such as human, equipment and material resources, as well as knowledge and tasks that are mutually interlinked. In the classical approach to construction project risk assessment, the impact of the “system” in the analysis of relationships between risk sources and their consequences has so far been neglected. The concept of construction project vulnerability and its adaptability has appeared in literature in recent years. It is analysed on the basis of a pr

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RADKO, TIMOUR. "Mechanics of thermohaline interleaving: beyond the empirical flux laws." Journal of Fluid Mechanics 675 (March 10, 2011): 117–40. http://dx.doi.org/10.1017/s0022112011000061.

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An analytical theory is developed which illustrates the dynamics of the spontaneous generation of thermohaline intrusions in the stratified ocean with density compensated lateral temperature and salinity gradients. Intrusions in the model are driven by the interaction with the initially homogeneous field of salt fingers, whose amplitude and spatial orientation is weakly modulated by the long wavelength perturbations introduced into the system. The asymptotic multiscale analysis makes it possible to identify intrusive instabilities resulting from the positive feedback of salt fingers on large-s

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Lee, Edward D., Daniel M. Katz, Michael J. Bommarito, and Paul H. Ginsparg. "Sensitivity of collective outcomes identifies pivotal components." Journal of The Royal Society Interface 17, no. 167 (2020): 20190873. http://dx.doi.org/10.1098/rsif.2019.0873.

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A social system is susceptible to perturbation when its collective properties depend sensitively on a few pivotal components. Using the information geometry of minimal models from statistical physics, we develop an approach to identify pivotal components to which coarse-grained, or aggregate, properties are sensitive. As an example, we introduce our approach on a reduced toy model with a median voter who always votes in the majority. The sensitivity of majority–minority divisions to changing voter behaviour pinpoints the unique role of the median. More generally, the sensitivity identifies piv

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Amaral, Marco A., and Marco A. Javarone. "Heterogeneity in evolutionary games: an analysis of the risk perception." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 476, no. 2237 (2020): 20200116. http://dx.doi.org/10.1098/rspa.2020.0116.

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In this study, we analyse the relationship between heterogeneity and cooperation. Previous investigations suggest that this relation is non-trivial, as some authors found that heterogeneity sustains cooperation, while others obtained different results. Among the possible forms of heterogeneity, we focus on the individual perception of risks and rewards related to a generic event, which can appear in a number of social and biological systems. The modelling approach is based on the framework of evolutionary game theory. To represent this kind of heterogeneity, we implement small and local pertur

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Kotani, Kiyoshi, Ikuhiro Yamaguchi, Lui Yoshida, Yasuhiko Jimbo, and G. Bard Ermentrout. "Population dynamics of the modified theta model: macroscopic phase reduction and bifurcation analysis link microscopic neuronal interactions to macroscopic gamma oscillation." Journal of The Royal Society Interface 11, no. 95 (2014): 20140058. http://dx.doi.org/10.1098/rsif.2014.0058.

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Gamma oscillations of the local field potential are organized by collective dynamics of numerous neurons and have many functional roles in cognition and/or attention. To mathematically and physiologically analyse relationships between individual inhibitory neurons and macroscopic oscillations, we derive a modification of the theta model, which possesses voltage-dependent dynamics with appropriate synaptic interactions. Bifurcation analysis of the corresponding Fokker–Planck equation (FPE) enables us to consider how synaptic interactions organize collective oscillations. We also develop the adj

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Casas, F. R. "Stabilité des marchés de change au comptant et à terme : une approche d’équilibre simultané." Articles 59, no. 2 (2009): 240–65. http://dx.doi.org/10.7202/601215ar.

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L’article analyse la relation entre les marchés de change à terme et au comptant. On obtient les conditions de stabilité statique et dynamique de l’équilibre simultané à court terme des deux marchés à partir de l’étude de l’effet des variations des taux de change au comptant et à terme sur les décisions des participants dans les deux marchés, directement et à travers l’impact de telles variations sur les anticipations. Ces conditions sont requises pour l’évaluation des effets de perturbations d’origine domestique ou étrangère et de ceux des politiques fiscales et monétaires.

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MATHUNJWA, JOCHONIA S., and ANDREW J. HOGG. "Freely draining gravity currents in porous media: Dipole self-similar solutions with and without capillary retention." European Journal of Applied Mathematics 18, no. 3 (2007): 337–62. http://dx.doi.org/10.1017/s0956792507006985.

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We analyse the two-dimensional, gravitationally-driven spreading of fluid through a porous medium overlying a horizontal impermeable boundary from which fluid can drain freely at one end. Under the assumption that none of the intruding fluid is retained within the pores in the trail of the current, the motion of the current is described by the dipole self-similar solution of the first kind derived by Barenblatt and Zel'dovich (1957). We show that small perturbations of arbitrary shape imposed on this solution decay in time, indicating that the self-similar solution is linearly stable. We use t

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Protas, Bartosz, and Takashi Sakajo. "Harnessing the Kelvin–Helmholtz instability: feedback stabilization of an inviscid vortex sheet." Journal of Fluid Mechanics 852 (August 3, 2018): 146–77. http://dx.doi.org/10.1017/jfm.2018.523.

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In this investigation, we use a simple model of the dynamics of an inviscid vortex sheet given by the Birkhoff–Rott equation to obtain fundamental insights about the potential for stabilization of shear layers using feedback control. As actuation, we consider two arrays of point sinks/sources located a certain distance above and below the vortex sheet and subject to the constraint that their mass fluxes separately add up to zero. First, we demonstrate using analytical computations that the Birkhoff–Rott equation linearized around the flat-sheet configuration is in fact controllable when the nu

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REINAUD, JEAN N., and XAVIER CARTON. "The stability and the nonlinear evolution of quasi-geostrophic hetons." Journal of Fluid Mechanics 636 (September 25, 2009): 109–35. http://dx.doi.org/10.1017/s0022112009007812.

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We analyse the linear stability and nonlinear evolutions of circular hetons under the quasi-geostrophic approximation. We compare results obtained with a three-layer model and with a model based on a continuous density stratification. Though the models also differ by the vertical boundary conditions, they show a remarkable similarity in the stability properties of the hetons (threshold values of vortex radius for baroclinic instability, dominant modes, growth rates, etc.), and in their nonlinear evolutions (spatial reorganization of potential vorticity by nonlinear processes, end-states of the

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Heikenfeld, Max, Bethan White, Laurent Labbouz, and Philip Stier. "Aerosol effects on deep convection: the propagation of aerosol perturbations through convective cloud microphysics." Atmospheric Chemistry and Physics 19, no. 4 (2019): 2601–27. http://dx.doi.org/10.5194/acp-19-2601-2019.

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Abstract. The impact of aerosols on ice- and mixed-phase processes in deep convective clouds remains highly uncertain, and the wide range of interacting microphysical processes is still poorly understood. To understand these processes, we analyse diagnostic output of all individual microphysical process rates for two bulk microphysics schemes in the Weather and Research Forecasting model (WRF). We investigate the response of individual processes to changes in aerosol conditions and the propagation of perturbations through the microphysics all the way to the macrophysical development of the con

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Pilat-Lohinger, Elke. "The role of dynamics on the habitability of an Earth-like planet." International Journal of Astrobiology 14, no. 2 (2014): 145–52. http://dx.doi.org/10.1017/s1473550414000469.

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AbstractFrom the numerous detected planets outside the Solar System, no terrestrial planet comparable with our Earth has been discovered so far. The search for an Exo-Earth is certainly a big challenge which may require the detections of planetary systems resembling our Solar System in order to find life like on Earth. However, even if we find Solar System analogues, it is not certain that a planet in Earth position will have similar circumstances as those of the Earth. Small changes in the architecture of the giant planets can lead to orbital perturbations which may change the conditions of h

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SHTERN, VLADIMIR, and FAZLE HUSSAIN. "Instabilities of conical flows causing steady bifurcations." Journal of Fluid Mechanics 366 (July 10, 1998): 33–85. http://dx.doi.org/10.1017/s002211209800891x.

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A new stability approach is developed for a wide class of strongly non-parallel axisymmetric flows of a viscous incompressible fluid. This approach encompasses all conical flows, and all steady and weakly unsteady disturbances, while prior studies were limited to specific flows and particular disturbances. A specially derived form of the Navier–Stokes equations allows the exact reduction of the linear stability problem to a system of ordinary differential equations. We found that disturbances originating at the boundaries of a similarity region cause a variety of steady bifurcations. Considera

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