Bibliografie tematiche / Dynamical instabilities

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Letteratura scientifica selezionata sul tema "Dynamical instabilities"

Autore: Grafiati
Pubblicato: 22 febbraio 2025

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Articoli di riviste sul tema "Dynamical instabilities"

1

Fuchs, B., e O. Esquivel. "Can Massive Dark Haloes Destroy the Discs of Dwarf Galaxies?" Proceedings of the International Astronomical Union 3, S244 (giugno 2007): 336–40. http://dx.doi.org/10.1017/s1743921307014184.

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AbstractRecent high-resolution simulations together with theoretical studies of the dynamical evolution of galactic disks have shown that contrary to wide-held beliefs a ‘live’, dynamically responsive, dark halo surrounding a disk does not stabilize the disk against dynamical instabilities. We generalize Toomre's Q stability parameter for a disk-halo system and show that if a disk, which would be otherwise stable, is embedded in a halo, which is too massive and cold, the combined disk-halo system can become locally Jeans unstable. The good news is, on the other hand, that this will not happen in real dark haloes, which are in radial hydrostatic equilibrium. Even very low-mass disks are not prone to such dynamical instabilities.
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2

Barnes, Joshua. "Dynamical Instabilities in Spherical Stellar Systems". Symposium - International Astronomical Union 113 (1985): 297–99. http://dx.doi.org/10.1017/s0074180900147461.

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Equlibrium spherical stellar systems exhibiting instabilities on a dynamical timescale were first studied by Henon (1973), using a spherically symmetric N-body code. We have re-examined Henon's models using an improved code which includes non-radial forces to quadrupole order. In addition to the radial instability reported by Henon, two new non-radial instabilities are also observed. In one, found in models with highly circular orbits, the mass distribution exhibits quadrupole-mode oscillations. In the other, seen in models with highly radial orbits, the system spontaneously breaks spherical symmetry and settles into a tri-axial ellipsoid. These instabilities, which are driven by fluctuations of the mean field, offer some analogies to the well-known dynamical instabilities of a cold disk of stars. While our models are rather artificial, they indicate that dynamical instabilities may be more common in spherical systems than had been thought.
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Michtchenko, T. A., S. Ferraz-Mello e C. Beaugé. "Dynamical instabilities in planetary systems". EAS Publications Series 42 (2010): 315–31. http://dx.doi.org/10.1051/eas/1042035.

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4

Ivanov, Yu B. "Dynamical instabilities in hadron plasma:". Nuclear Physics A 474, n. 3-4 (novembre 1987): 693–716. http://dx.doi.org/10.1016/0375-9474(87)90602-6.

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5

West, Bruce J. "Book review:Synergetics and dynamical instabilities". Journal of Statistical Physics 62, n. 1-2 (gennaio 1991): 493–95. http://dx.doi.org/10.1007/bf01020886.

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6

Orellana, P., F. Claro, E. V. Anda e E. S. Rodrigues. "Dynamical Instabilities in Resonant Tunneling". physica status solidi (b) 218, n. 1 (marzo 2000): 303–7. http://dx.doi.org/10.1002/(sici)1521-3951(200003)218:1<303::aid-pssb303>3.0.co;2-f.

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Baier, Gerold, Peter Urban e Klaus Wegmann. "Dynamical Instabilities in a Diffusion Layer". Zeitschrift für Naturforschung A 44, n. 11 (1 novembre 1989): 1107–10. http://dx.doi.org/10.1515/zna-1989-1111.

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We investigate the dynamics of a reaction-diffusion-convection enzyme system as a function of relevant parameters and observe reproducible types of periodic and aperiodic oscillations. These oscillations arise within a narrow diffusion layer only. Some implications for more complex reaction networks are considered
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Tamayo, D., J. A. Burns, D. P. Hamilton e P. D. Nicholson. "DYNAMICAL INSTABILITIES IN HIGH-OBLIQUITY SYSTEMS". Astronomical Journal 145, n. 3 (18 gennaio 2013): 54. http://dx.doi.org/10.1088/0004-6256/145/3/54.

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9

Barnes, J., P. Hut e J. Goodman. "Dynamical instabilities in spherical stellar systems". Astrophysical Journal 300 (gennaio 1986): 112. http://dx.doi.org/10.1086/163786.

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Barnes, Joshua E. "Dynamical Instabilities in Hollow Halo Models". Astrophysical Journal 419 (dicembre 1993): L17. http://dx.doi.org/10.1086/187126.

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Più fonti

Tesi sul tema "Dynamical instabilities"

1

Lin, Min-Kai. "Dynamical instabilities in disc-planet interactions". Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/245135.

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Protoplanetary discs can be dynamically unstable due to structure induced by an embedded giant planet. In this thesis, I discuss the stability of such systems and explore the consequence of instability on planetary migration. I present semi-analytical models to understand the formation of the unstable structure induced by a Saturn mass planet, which leads to vortex formation. I then investigate the effect of such vortices on the migration of a Saturnmass planet using hydrodynamic simulations. I explain the resulting nonmonotonic behaviour in the framework of type III planetary migration. I then examine the role of disc self-gravity on the vortex instabilities. It can be shown that self-gravity has a stabilising effect. Linear numerical calculations confirms this. When applied to disc-planet systems, modes with small azimuthal wavelengths are preferred with increasing disc selfgravity. This is in agreement the observation that more vortices develop in simulations with increasing disc mass. Vortices in more massive discs also resist merging. I show that this is because inclusion of self-gravity sets a minimal vortex separation preventing their coalescence, which would readily occur without self-gravity. I show that in sufficiently massive discs vortex modes are suppressed. Instead, global spiral instabilities develop. They are interpreted as disturbances associated with the planet-induced structure, which interacts with the wider disc leading to instability. I carry out linear calculations to confirm this physical picture. Results from nonlinear hydrodynamic simulations are also in agreement with linear theory. I give examples of the effect of these global modes on planetary migration, which can be outwards, contrasting to standard inwards migration in more typical disc models. I also present the first three-dimensional computer simulations examining planetary gap stability. I confirm that the results discussed above, obtained from two-dimensional disc approximations, persist in three-dimensional discs.
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2

Tomadin, Andrea. "Dynamical instabilities in quantum many-body systems". Doctoral thesis, Scuola Normale Superiore, 2010. http://hdl.handle.net/11384/85874.

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from the introduction: "[...] This thesis addresses the problem of the nonequilibrium time-evolution of many-body sistems realized with quantum simulators. We investigate theoretically the relation between the time-evolution and the equilibrium phase diagram in the presence of a quantum phase transition. The long-time evolution of the systems is investigated, both in the case of conservative dynamics and under the action of dissipative processes. The thesis is organized as follows. Chaps. 1-3 contain theoretical and experimental facts that are relevant to the present work. In the Chap. 1 we describe the quantum simulator realized with fermionic cold atoms in the bulk of an optical trap. In the Chap. 2 we describe the microresonators where light and matter are strongly coupled, and we focus on the implementation of a quantum simulator with defect-cavities in photonic crystals. In Chap. 3 several theoretical works concerning the nonequilibrium dynamics of many-body systems are summarized. Chaps. 4{6 contain the original contributions of this thesis. In Chap. 4 we investigate the time-evolution of an ensemble of fermionic atoms after an abrupt change of the interaction strength from a vanishing to a weak attractive value. In Chap. 5 we demonstrate the possibility to measure the quantum phase transition between a super fluid and a Mott-insulator state in an array of microresonators, in the presence of the leakage of photons out of the cavities. In Chap. 6 we study a system of cold bosonic atoms coupled to a tailored bath that dissipatively drives the system into a super fluid or into a thermal state.
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Persson, Kristin Aslaug. "Thermodynamical and Dynamical Instabilities from Ab initio Electronic-Structure Calculations". Doctoral thesis, KTH, Physics, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3137.

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Persson, Kristin. "Thermodynamical and dynamical instabilities from Ab initio electronic-structure calculations /". Stockholm : Tekniska högsk, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3137.

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5

Madden, Francis. "Dynamical instabilities in a fluid spin-up and in an open flow system". Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293436.

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6

Rostami, Masoud. "Dynamical influence of diabatic processes upon developing instabilities of Earth and planetary jets and vortices". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066186.

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Abstract (sommario):
Le but de la thèse est de comprendre l'influence dynamique des effets diabatiques, comme la convection humide, sur les instabilités des vortex atmosphériques terrestres et planétaires. Un modèle verticalement intégré, avec les paramétrisations type relaxation des transitions de phase et de dégagement de la chaleur latente, le modèle de St-Venant avec la convection humide, a été utilisé. La version précédente du modèle a été améliorée pour inclure l'eau précipitable, sa vaporisation et son entrainement. L'approche consiste en 1) analyse détaillée de stabilité des profils idéalisés, ou extraits des données, des vortex, 2) étude de saturation non-linéaire des instabilités à l'aide de schéma numérique de haute résolution aux volumes finis. Les résultats principaux de la thèse sont : 1. Démonstration et quantification d'une forte influence des effets humides sur les instabilités des vortex synoptiques, y compris asymétrie cyclone-anticyclone des vortex de faible intensité aux latitudes moyennes, et de l'intensification des vortex type cyclones tropicaux, avec formation des nuages caractéristiques. 2. Explication de l'origine dynamique de l'hexagone au pôle Nord de Saturne, et de l'absence de structure similaire au pôle Sud, en termes d'instabilité du système vortex polaire - jet circumpolaire, et sa saturation non-linéaire. 3. Explication de la structure observée du vortex polaire hivernal sur Mars en termes d'instabilité et sa saturation en présence de réchauffement /refroidissement radiatif et de déposition de CO2 (transition de phase gaz - solide). Une nouvelle paramétrisation simple a été proposée pour ce processus, incluant l'influence des noyaux de déposition
The thesis is devoted to understanding dynamical influence of diabatic effects, like moist convection, on instabilities of vortices in Earth and planetary atmospheres. A vertically integrated atmospheric model with relaxational parameterisation of phase transitions and related heat release, and with convective fluxes included in mass and momentum equations, the moist-convective rotating shallow water model, was used for this purpose. The previous version of the model was improved to include precipitable water and its vaporisation and entrainment. The approach consists in 1)detailed stability analysis of idealised, or extracted from the data, vortex profiles, 2)study of nonlinear saturation of the instabilities with the help of finite-volume high-resolution numerical code. The main results of the thesis are: 1. Demonstration and quantification of strong influence of moist effects upon instabilities of synoptic vortices, including cyclone-anticyclone asymmetry of mid-latitude vortices of weak intensity, and intensification of tropical-cyclone like vortices with formation of typical cloud patterns. 2. Explanation of the dynamical origin of the Saturn's North Polar hexagon, and of the lack of similar structure at the South Pole, in terms of instability of the coupled polar vortex and circumpolar jet, and their nonlinear saturation.3. Explanation of the observed structure of Mars' winter polar vortex in terms of instability of the latter, and its saturation in the presence of radiative heating/cooling and CO2 deposition (gas-solid phase transition). A new simple parameterisation of the latter process, including the influence of deposition nuclei, was developed in the thesis
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7

Rostami, Masoud. "Dynamical influence of diabatic processes upon developing instabilities of Earth and planetary jets and vortices". Electronic Thesis or Diss., Paris 6, 2017. http://www.theses.fr/2017PA066186.

Testo completo
Abstract (sommario):
Le but de la thèse est de comprendre l'influence dynamique des effets diabatiques, comme la convection humide, sur les instabilités des vortex atmosphériques terrestres et planétaires. Un modèle verticalement intégré, avec les paramétrisations type relaxation des transitions de phase et de dégagement de la chaleur latente, le modèle de St-Venant avec la convection humide, a été utilisé. La version précédente du modèle a été améliorée pour inclure l'eau précipitable, sa vaporisation et son entrainement. L'approche consiste en 1) analyse détaillée de stabilité des profils idéalisés, ou extraits des données, des vortex, 2) étude de saturation non-linéaire des instabilités à l'aide de schéma numérique de haute résolution aux volumes finis. Les résultats principaux de la thèse sont : 1. Démonstration et quantification d'une forte influence des effets humides sur les instabilités des vortex synoptiques, y compris asymétrie cyclone-anticyclone des vortex de faible intensité aux latitudes moyennes, et de l'intensification des vortex type cyclones tropicaux, avec formation des nuages caractéristiques. 2. Explication de l'origine dynamique de l'hexagone au pôle Nord de Saturne, et de l'absence de structure similaire au pôle Sud, en termes d'instabilité du système vortex polaire - jet circumpolaire, et sa saturation non-linéaire. 3. Explication de la structure observée du vortex polaire hivernal sur Mars en termes d'instabilité et sa saturation en présence de réchauffement /refroidissement radiatif et de déposition de CO2 (transition de phase gaz - solide). Une nouvelle paramétrisation simple a été proposée pour ce processus, incluant l'influence des noyaux de déposition
The thesis is devoted to understanding dynamical influence of diabatic effects, like moist convection, on instabilities of vortices in Earth and planetary atmospheres. A vertically integrated atmospheric model with relaxational parameterisation of phase transitions and related heat release, and with convective fluxes included in mass and momentum equations, the moist-convective rotating shallow water model, was used for this purpose. The previous version of the model was improved to include precipitable water and its vaporisation and entrainment. The approach consists in 1)detailed stability analysis of idealised, or extracted from the data, vortex profiles, 2)study of nonlinear saturation of the instabilities with the help of finite-volume high-resolution numerical code. The main results of the thesis are: 1. Demonstration and quantification of strong influence of moist effects upon instabilities of synoptic vortices, including cyclone-anticyclone asymmetry of mid-latitude vortices of weak intensity, and intensification of tropical-cyclone like vortices with formation of typical cloud patterns. 2. Explanation of the dynamical origin of the Saturn's North Polar hexagon, and of the lack of similar structure at the South Pole, in terms of instability of the coupled polar vortex and circumpolar jet, and their nonlinear saturation.3. Explanation of the observed structure of Mars' winter polar vortex in terms of instability of the latter, and its saturation in the presence of radiative heating/cooling and CO2 deposition (gas-solid phase transition). A new simple parameterisation of the latter process, including the influence of deposition nuclei, was developed in the thesis
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8

Dufour, Oscar. "Enhanced agent-based models for pedestrian crowds : insights from empirical data at the Festival of Lights and refinements of mechanical interactions, pedestrian shapes, and decisional aspects". Electronic Thesis or Diss., Lyon 1, 2024. http://www.theses.fr/2024LYO10338.

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Avec la multiplication des événements de masse, la dynamique des foules est devenue un sujet d’étude de plus en plus important. Comprendre comment les groupes se déplacent et évoluent dans l'espace, en particulier à des densités moyennes et élevées, est crucial pour l'organisation de tels événements. La première section de cette thèse de doctorat présente l'un des premiers ensembles de données de terrain sur les foules denses. Cet ensemble comprend aussi bien des trajectoires de piétons que des données GPS et de contact collectées lors de la Fête des Lumières 2022 à Lyon. Je développe ensuite un cadre théorique de modélisation de la dynamique des foules qui intègre une composante décisionnelle, où les piétons ajustent régulièrement leur vitesse désirée, et une couche mécanique qui confronte ces décisions à la réalité physique environnante. La plupart des modèles existants échouent à reproduire fidèlement les interactions mécaniques, car ils reposent souvent sur des forces d'interaction idéalisées et des formes circulaires simplifiées. En m'inspirant de la littérature scientifique sur la dynamique granulaire, j'intègre aux équations newtoniennes, des interactions mécaniques plus réalistes, en utilisant des ressorts amortis à la fois tangentiels et normaux aux surfaces de contact. J'utilise de plus des données anthropométriques pour représenter le plus fidèlement possible le contour humain, en deux dimensions, plutôt que de recourir à de simples disques. Cela me permet de créer une foule synthétique qui intègre les hétérogénéités individuelles. En ce qui concerne la composante décisionnelle, les piétons s'efforcent de sélectionner une vitesse souhaitée tout en tenant compte de diverses contraintes métaboliques, physiques et psychologiques, la plupart étayées par des données empiriques. Ces contraintes incluent : une contrainte de destination qui prend en compte l'objectif d'atteindre un lieu spécifique ; des limites biomécaniques liées aux capacités musculaires et articulaires des piétons ; un coût lié à la différence d’alignement entre le corps et la direction de mouvement souhaité ; une volonté de préserver sa bulle sociale, une zone que les individus souhaitent maintenir libre de toute intrusion, qu'il s'agisse d'obstacles ou de piétons voisins ; une intention d’éviter les collisions lors d'un déplacement, basée sur des estimations de temps avant collision. Cet espace de confort est modélisé par un champ scalaire d'inconfort dont les courbes de niveau ne sont pas circulaires. Après validation dans des situations simples impliquant des paires de piétons ou un piéton près d'un mur, je compare avec succès les prédictions du modèle à des expériences impliquant la propagation d’une poussée à travers une rangée de personnes, des évacuations, et des mouvements de faufilement entre murs et piétons. J'étudie enfin les phénomènes collectifs qui se manifestent non seulement dans les foules, mais aussi dans le trafic véhiculaire, en particulier les ondes stop-and-go résultant de la croissance d'instabilités dynamiques. Pour mieux comprendre ces phénomènes, je simule un modèle de suivi automobile en file qui repose sur le maintien d'un temps de freinage constant avec le véhicule suivant. Bien que la version déterministe de ce modèle soit inconditionnellement stable, l'ajout de bruit entraîne de manière inattendue l'apparition d’ondes stop-and-go. J'explique cette observation en utilisant une analogie avec le pendule de Kapitza, qui développe un nouvel état stationnaire sous l'effet de fortes vibrations. Plus précisément, une discontinuité d’un paramètre d'ordre apparaît lorsque le niveau de bruit ou la densité dépasse un certain seuil, faisant écho à une transition liquide-gaz. Mes recherches sur la dynamique des foules soulignent l'importance d'intégrer les processus décisionnels aux interactions mécaniques pour approfondir notre compréhension des comportements collectifs complexes, en particulier dans les environnements bondés
With the surge in mass events, crowd dynamics have become an increasingly important subject of study. Understanding how groups move and evolve in space, particularly at medium and high densities, is crucial for organising such events.The first section of this PhD dissertation presents one of the first field datasets on dense crowds. This dataset includes pedestrian trajectories and meta-information collected during the 2022 Festival of Lights in Lyon as part of the Franco-German MADRAS project. It includes up to 7000 trajectories, GPS data, and contact information. In addition, some rare events have been identified, providing an in-depth description of pedestrian dynamics in complex, real-life scenarios. Subsequently, I develop a theoretical framework for modelling crowd dynamics that integrates a decision-making component, where pedestrians regularly adjust their desired speed, and a mechanical layer that confronts these decisions with the surrounding physical reality. Most existing models fail to faithfully reproduce mechanical interactions, often relying on idealised interaction forces and simplified circular shapes. Drawing inspiration from the scientific literature on grain dynamics, I integrate more realistic mechanical interactions into the Newtonian equations, using damped springs that are tangential and normal to the contact surfaces. I also use anthropometric data to represent the human contour as faithfully as possible, in two dimensions, rather than using simple discs. This allows me to create a synthetic crowd that incorporates individual heterogeneity. Regarding decision-making, pedestrians strive to choose a desired speed while adhering to various metabolic, physical, and psychological constraints, largely supported by empirical data. These constraints include:- A destination constraint which considers the goal of reaching a specific location.- Biomechanical limits related to the muscular and articular capacities of pedestrians.- A cost associated with the misalignment between the body and the desired direction of movement.- A desire to preserve one's social bubble, a zone that individuals wish to keep free of any intrusion, whether from obstacles or neighbouring pedestrians.- An intention to avoid collisions or interpenetration of comfort spaces during movement based on the estimation of time to collision.This comfort space is modelled by a scalar field of discomfort whose contours are not simply circular. The model is implemented in C++ and tested in various scenarios. After validation in simple situations involving pairs of pedestrians or a pedestrian near a wall, I successfully compare the model's predictions with experiments involving the propagation of a push through a row of people, evacuations, and weaving movements between walls and pedestrians.Finally, I investigate collective phenomena that occur not only in crowds but also in vehicular traffic, specifically stop-and-go waves resulting from the growth of dynamical instabilities. To better understand these phenomena, I simulate a car-following model that relies on maintaining a constant time gap with the following vehicle. Although the deterministic version of the model is unconditionally stable, introducing noise intriguingly leads to the emergence of stop-and-go waves. I explain this observation using an analogy with the Kapitza pendulum, which develops a new stationary state under strong vibrations. Specifically, discontinuities in a suitably defined order parameter appear when noise or density exceeds a finite threshold, echoing a liquid-gas transition. This noise may stem from inaccuracies in drivers' and pedestrians' observations, difficulties in brain information processing, or unaccounted interactions. My research on crowd dynamics highlights the importance of integrating decision-making processes with mechanical interactions to deepen our understanding of complex collective behaviours, notably in crowded environments
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Cordeiro, Timothy Joseph. "Dynamic instabilities imparted by CubeSat propulsion". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/105612.

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Abstract (sommario):
Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 120-123).
As the role of CubeSats evolves to include more challenging and complex missions in addition to technology demonstrations, the demand for agility have increased. As the technology improves and gains flight heritage, CubeSats are being deployed to accomplish more difficult missions including, but not limited to, large constellations and missions beyond Low Earth Orbit (LEO). To perform missions like station keeping for constellations, and to move beyond LEO, CubeSat developers are increasingly integrating propulsion into the design of their CubeSats. In addition, more complex payloads and communication systems require more power generation, which leads to larger deployed solar arrays. Meanwhile, the limiting factor for the CubeSat remains the size and weight constraints of the containerized launch deployers. In order to meet these constraints, the solar array design has to trade stiffness and strength for size. In this work, we investigate whether designs that use a combination of propulsion and solar arrays stress the dynamics of the solar panels and the hinges that hold them in place. Our approach uses SimXpert to perform dynamic simulations on CubeSat models, both 3U and 6U, with deployable solar panels and propulsion forces. By default, SimXpert treats every part as a rigid body and stress is not calculated. By doing a modal analysis of the panels in Nastran and importing the results into SimXpert, stress on the panels can be tracked during propulsive maneuvers. We determine that Margin of Safety (MoS) for the solar panels analyzed is over 100 when combined with three different COTS propulsion units. We also show the movement induced on the panels from propulsion can cause errors in body attitude ranging from 0.04 to 90 degrees. The worst case showed a difference becoming one degree in five seconds before growing exponentially to 90 degrees in 30 seconds.
by Timothy Joseph Cordeiro.
S.M.
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Nguyen, Thi Thu Tra. "Dynamic instabilities of model granular materials". Thesis, Lyon, 2019. http://www.theses.fr/2019LYSET007/document.

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Abstract (sommario):
Cette thèse étudie les instabilités dynamiques des milieux granulaires modèles saturés à l’aide d’un appareil triaxial classique. Les instabilités englobent la liquéfaction et les effondrements en compression isotrope drainée, les frottements saccadés en compression triaxiale drainée. Ces instabilités apparaissent spontanément à des contraintes effectives de confinement imprévisibles. Elles sont accompagnées de très rapides et très fortes surpressions interstitielles, malgré un drainage approprié; ce que ne présentent pas les milieux granulaires naturels. En compression isotrope drainée (consolidation), des effondrements locaux naissent instantanément. En compression triaxiale drainée, on observe de larges frottements saccadés quasi-périodiques caractérisés par des déformations volumiques et axiales contractantes. De temps en temps, ces effondrements et frottements saccadés locaux peuvent se développer en liquéfaction menant à une destruction complète de la structure granulaire. Les données à haute résolution temporelle issues de ce travail ont permis la découverte d’une nouvelle famille de liquéfaction dynamique et statique. L’étude des émissions acoustiques passives a permis l’identification de signature spectrale caractéristique. Pour les frottements saccadés, la phase de glissement peut être interprétée comme une consolidation dynamique, limitée par l’unique surface en dessous de la ligne critique de rupture dans le plan des contraintes effectives. La séquence temporelle précise des événements exclut que la pression interstitielle soit la cause principale des instabilités. Cependant, le rôle important de la surpression interstitielle est démontré dans des relations quantitatives entre les incréments de contraintes, et de déformations et l’éphémère surpression interstitielle stabilisée développée pendant la phase de glissement. Cela montre finalement la nature quasi-déterministique de ces instabilités dynamiques. Ces relations empiriques sont basées uniquement sur l’amplitude maximale de l’accélération verticale de très courte durée et sont gouvernées indépendamment par la pression de confinement et par l’indice des vides. La similarité de la surpression interstitielle entre différentes instabilités suggère fortement quelques mécanismes similaires de déclenchement, probablement à partir de ré-arrangements de la micro-structure granulaire
This thesis reports a laboratory study on the dynamic instabilities of model saturated granular material using a triaxial apparatus. The term instability consists of isotropic collapse and liquefaction under isotropic compression and of stick-slip under triaxial compression in drained condition. The instabilities spontaneously occur at unpredictable effective stress with unexpected buildup of excess pore pressure irrespective of fully drained condition, contrasting with the instability-free behaviour of natural granular materials. In isotropic compression, instantaneous local collapse happens and in triaxial compression, very large and quasi-periodic stick-slip occurs with sudden volumetric compaction and axial contraction. Sometimes, these local failures (collapse and stick-slip) can develop into total liquefaction failure, destroying completely the granular structure. High time-resolved data permit the discovery of a new family of dynamic and static liquefaction. Passive acoustic measurements allow the identification of typical spectral signature. For stick-slip phenomenon, the slip phase with constant duration of stress drop can be interpreted as dynamic consolidation at constant deviatoric stress, limited by a unique boundary inside the critical state line in the effective stress plane. The precise temporal sequence of mechanical measurements excludes the generated pore pressure as the main cause of the instabilities. However, the role of pore pressure is emphasised by consistent quantitative relations between the amplitude of incremental stresses, incremental strains and the ephemeral stabilised excess pore pressure developed during the dynamic event, leading to the quasi-deterministic nature of granular instabilities. These empirical relations are based only on the short-lived maximum vertical acceleration and governed separately by the confining pressure and the initial void ratio. The similarity of pore pressure evolution for different kinds of instability strongly suggests some common speculative triggering mechanisms, probably originated from different rearrangements of the granular micro-structure
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Libri sul tema "Dynamical instabilities"

1

Enrique, Tirapegui, Villarroel D, Universidad de Chile. Facultad de Ciencias Físicas y Matemáticas., Universidad Técnica Federico Santa María. e International Workshop on Instabilities and Nonequilibrium Structures (2nd : 1987 : Valparaíso, Chile), a cura di. Instabilities and nonequilibrium structures II: Dynamical systems and instabilities. Dordrecht: Kluwer Academic Publishers, 1989.

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Tirapegui, Enrique. Instabilities and Nonequilibrium Structures II: Dynamical Systems and Instabilities. Dordrecht: Springer Netherlands, 1989.

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Collet, Pierre. Instabilities and fronts in extended systems. Princeton, N.J: Princeton University Press, 1990.

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Sergei, Fedotov, e Horsthemke W. (Werner) 1950-, a cura di. Reaction-transport systems: Mesoscopic foundations, fronts, and spatial instabilities. Heidelberg: Springer, 2010.

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Charru, François. Hydrodynamic instabilities. Cambridge: Cambridge University Press, 2011.

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1925-, Knopoff Leon, Keĭlis-Borok Vladimir Isaakovich e Puppi G, a cura di. Instabilities in continuous media. Basel: Birkhäuser, 1985.

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Enrique, Tirapegui, Villarroel D e International Workshop on Instabilities and Nonequilibrium Structures (1st : 1985 : Universidad Técnica Federico Santa María), a cura di. Instabilities and nonequilibrium structures. Dordrecht: D. Reidel Pub. Co., 1987.

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Eckelmann, Helmut, J. Michael R. Graham, Patrick Huerre e Peter A. Monkewitz, a cura di. Bluff-Body Wakes, Dynamics and Instabilities. Berlin, Heidelberg: Springer Berlin Heidelberg, 1993. http://dx.doi.org/10.1007/978-3-662-00414-2.

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IUTAM, Symposium (1992 Göttingen Germany). Bluff-body wakes, dynamics and instabilities. Berlin: Springer-Verlag, 1993.

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Enrique, Tirapegui, e Zeller Walter, a cura di. Instabilities and nonequilibrium structures IV. Dordrecht: Kluwer Academic Publishers, 1993.

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Capitoli di libri sul tema "Dynamical instabilities"

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Kiss, István Z., Timea Nagy e Vilmos Gáspár. "Dynamical Instabilities in Electrochemical Processes". In Solid State Electrochemistry II, 125–78. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA, 2011. http://dx.doi.org/10.1002/9783527635566.ch4.

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Magnani, Loris, e Steven N. Shore. "Dynamical Considerations: Instabilities and Turbulence". In Astrophysics and Space Science Library, 267–94. Berlin, Heidelberg: Springer Berlin Heidelberg, 2017. http://dx.doi.org/10.1007/978-3-662-54350-4_11.

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Walgraef, D. "Flow Field Effects on Dynamical Instabilities". In Instabilities and Nonequilibrium Structures II, 269–83. Dordrecht: Springer Netherlands, 1989. http://dx.doi.org/10.1007/978-94-009-2305-8_21.

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Miguel, M. San, E. Hernández-García, P. Colet, M. O. CáCeres e F. de Pasquale. "Passage Time Description of Dynamical Processes". In Instabilities and Nonequilibrium Structures III, 143–55. Dordrecht: Springer Netherlands, 1991. http://dx.doi.org/10.1007/978-94-011-3442-2_13.

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Barnes, Joshua. "Dynamical Instabilities in Spherical Stellar Systems". In Dynamics of Star Clusters, 297–99. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-5335-2_30.

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Graham, R. "Weak Noise Limit and Nonequilibrium Potentials of Dissipative Dynamical Systems". In Instabilities and Nonequilibrium Structures, 271–90. Dordrecht: Springer Netherlands, 1987. http://dx.doi.org/10.1007/978-94-009-3783-3_12.

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Grimvall, Göran. "Dynamical Lattice Instabilities in Alloy Phase Diagrams". In Properties of Complex Inorganic Solids 2, 473–78. Boston, MA: Springer US, 2000. http://dx.doi.org/10.1007/978-1-4615-1205-9_35.

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Williamson, C. H. K., T. Leweke e G. D. Miller. "Wing Wake Vortices and Temporal Vortex Pair Instabilities". In Fluid Mechanics and the Environment: Dynamical Approaches, 379–400. Berlin, Heidelberg: Springer Berlin Heidelberg, 2001. http://dx.doi.org/10.1007/3-540-44512-9_20.

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Ferrari, P. A., S. Martinez e P. Picco. "Some Properties of Quasi Stationary Distributions in the Birth and Death Chains: A Dynamical Approach". In Instabilities and Nonequilibrium Structures III, 177–87. Dordrecht: Springer Netherlands, 1991. http://dx.doi.org/10.1007/978-94-011-3442-2_16.

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Bourlioux, A., A. Majda e V. Roytburd. "Nonlinear Development of Low Frequency One-Dimensional Instabilities for Reacting Shock Waves". In Dynamical Issues in Combustion Theory, 63–82. New York, NY: Springer New York, 1991. http://dx.doi.org/10.1007/978-1-4612-0947-8_3.

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Atti di convegni sul tema "Dynamical instabilities"

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Burrello, Stefano, Maria Colonna, Francesco Matera e Rui Wang. "Consistent description of mean-field instabilities and clustering phenomena within a unified dynamical approach". In 10th International Conference on Quarks and Nuclear Physics, 179. Trieste, Italy: Sissa Medialab, 2025. https://doi.org/10.22323/1.465.0179.

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Haken, H. "The adiabatic elimination principle in dynamical theories". In Instabilities and Dynamics of Lasers and Nonlinear Optical Systems. Washington, D.C.: Optica Publishing Group, 1985. http://dx.doi.org/10.1364/idlnos.1985.the1.

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Abstract (sommario):
The adiabatic elimination principle or, more generally, the slaving principle play a crucial role in the general strategy of dealing with multicomponent systems. In physics as well as in other branches of science, as chemistry or biology, we have to deal with systems composed of many subsystems. The laser is a typical example. It consists of a great many laser active atoms and the in general quite numerous field modes within the cavity.
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Rosenberger, A. T., L. A. Orozco e H. J. Kimble. "Instrinsic Dynamical Instability in Optical Bistability with Two-Level Atoms". In Instabilities and Dynamics of Lasers and Nonlinear Optical Systems. Washington, D.C.: Optica Publishing Group, 1985. http://dx.doi.org/10.1364/idlnos.1985.wa2.

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Self pulsing due to the single-mode instability has been observed in optical bistability.1 This self-pulsing instability has its roots in corresponding instabilities first analyzed for the homogeneously broadened laser. It shares a common physical origin in the intrinsic mechanism by which a strong intracavity field alters the absorption profile of the intracavity medium to produce amplification at frequencies offset from that of the strong field.
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Fressengeas, Claude, Satya VARADHAN e Armand J. BEAUDOIN. "Coupling the dynamical behavior of compatible/incompatible dislocation distributions". In International conference on Statistical Mechanics of Plasticity and Related Instabilities. Trieste, Italy: Sissa Medialab, 2006. http://dx.doi.org/10.22323/1.023.0004.

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Graham, R. "Quantized Chaotic Systems". In Instabilities and Dynamics of Lasers and Nonlinear Optical Systems. Washington, D.C.: Optica Publishing Group, 1985. http://dx.doi.org/10.1364/idlnos.1985.thc1.

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Abstract (sommario):
Chaos is a typical form of dynamical behavior of classical nonlinear dynamical systems. In conservative Hamiltonian systems with f degrees of freedom chaos appears if the system is not intergrable and in some regions of phase space trajectories are not restricted to f-dimensional smooth manifolds. In dissipative systems chaos in the dynamical steady state appears if the system has a strange attractor in configuration space.
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Nhu, Viet-Hung, Mathieu Renouf, Francesco Massi e Aurélien Saulot. "Wear particles: Influence on local stress and dynamical instabilities". In POWDERS AND GRAINS 2013: Proceedings of the 7th International Conference on Micromechanics of Granular Media. AIP, 2013. http://dx.doi.org/10.1063/1.4812061.

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Kouomou, Y. Chembo, Laurent Larger, Herve Tavernier, Ryad Bendoula, Pere Colet e Enrico Rubiola. "Dynamical instabilities in opto-electronic ultra-pure microwave generators". In 2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference. IEEE, 2007. http://dx.doi.org/10.1109/cleoe-iqec.2007.4386142.

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Casati, Giulio. "Overview Of Classical And Quantum Hamiltonian Chaos". In Instabilities and Dynamics of Lasers and Nonlinear Optical Systems. Washington, D.C.: Optica Publishing Group, 1985. http://dx.doi.org/10.1364/idlnos.1985.wb1.

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New, G. H. C., e J. M. Catherall. "Perturbations and Instabilities in Laser Mode-Locking Dynamics". In Instabilities and Dynamics of Lasers and Nonlinear Optical Systems. Washington, D.C.: Optica Publishing Group, 1985. http://dx.doi.org/10.1364/idlnos.1985.fc1.

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Abstract (sommario):
In this paper, we present a range of theoretical results that relate to the dynamical properties of mode-locked lasers, discussing perturbations induced by stochastic background fluctuations and instabilities arising from self-pulsing effects in hybrid systems.
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Pare, C., M. Piche e P. A. Belanger. "Instabilities of Self-Pumped Phase-Conjugate Laser". In Instabilities and Dynamics of Lasers and Nonlinear Optical Systems. Washington, D.C.: Optica Publishing Group, 1985. http://dx.doi.org/10.1364/idlnos.1985.wd29.

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Optical chaos has recently been observed in a phase-conjugate laser1 (PCL) where phase conjugation was obtained by degenerate four-wave- mixing in BaTiO3. This complex dynamical behaviour is not predicted by a simple third-power law for the phase-conjugate mirror (PCM) reflectivity. A nonlinear theory by Wright et al2 has also confirmed the possibility of optical instabilities in a PCL with external pumps and without a saturable gain medium.
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Rapporti di organizzazioni sul tema "Dynamical instabilities"

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Harrison, Robert G. Dynamical Instabilities, Chaos And Spatial Complexity In Fundamental Nonlinear Optical Interactions. Fort Belvoir, VA: Defense Technical Information Center, maggio 1994. http://dx.doi.org/10.21236/ada291223.

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Stroud, Jr, e Carlos R. Optoelectronic Workshops. Dynamical Instabilities in Homogeneously Broadened Lasers (9th) (23 August 1988). Fort Belvoir, VA: Defense Technical Information Center, agosto 1988. http://dx.doi.org/10.21236/ada213482.

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Williamson, Charles H. Vortex-Surface Interactions: Vortex Dynamics and Instabilities. Fort Belvoir, VA: Defense Technical Information Center, ottobre 2015. http://dx.doi.org/10.21236/ada627306.

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Spong, D. A., K. C. Shaing, B. A. Carreras, J. D. Callen e L. Garcia. Nonlinear dynamics of single-helicity neoclassical MHD tearing instabilities. Office of Scientific and Technical Information (OSTI), ottobre 1988. http://dx.doi.org/10.2172/7079859.

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Liu, Joseph T. C. Vortex Shedding and Vortex Wakes: Dynamics, Instabilities and Modifications,. Fort Belvoir, VA: Defense Technical Information Center, gennaio 1994. http://dx.doi.org/10.21236/ada298840.

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Tajima, T., W. Horton, P. Morrison, J. Schutkeker, T. Kamimura, K. Mima e Y. Abe. Instabilities and vortex dynamics in shear flow of magnetized plasmas. Office of Scientific and Technical Information (OSTI), marzo 1990. http://dx.doi.org/10.2172/7055389.

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Symonds, P. S. Dynamic Plastic Instabilities in Nonlinear Inelastic Response to Pulse Loading. Fort Belvoir, VA: Defense Technical Information Center, novembre 1991. http://dx.doi.org/10.21236/ada244486.

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Blinov, Sergey, Nathan Mackey, Ari Le e Adam Stanier. Dynamics and Instabilities of a Plasma Blob in Curved Magnetic Geometries. Office of Scientific and Technical Information (OSTI), agosto 2022. http://dx.doi.org/10.2172/1883106.

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Hassanein, A., e I. Konkashbaev. Dynamic behavior of plasma-facing materials during plasma instabilities in tokamak reactors. Office of Scientific and Technical Information (OSTI), settembre 1997. http://dx.doi.org/10.2172/563287.

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Bountis, T., e S. Tompaidis. Strong and weak instabilities in a 4-D mapping model of accelerator dynamics. Office of Scientific and Technical Information (OSTI), maggio 1990. http://dx.doi.org/10.2172/6944120.

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