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Artykuły w czasopismach na temat "Non-ergodicity in many body systems"
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De Roeck, Wojciech, i John Z. Imbrie. "Many-body localization: stability and instability". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, nr 2108 (30.10.2017): 20160422. http://dx.doi.org/10.1098/rsta.2016.0422.
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Rare regions with weak disorder (Griffiths regions) have the potential to spoil localization. We describe a non-perturbative construction of local integrals of motion (LIOMs) for a weakly interacting spin chain in one dimension, under a physically reasonable assumption on the statistics of eigenvalues. We discuss ideas about the situation in higher dimensions, where one can no longer ensure that interactions involving the Griffiths regions are much smaller than the typical energy-level spacing for such regions. We argue that ergodicity is restored in dimension d >1, although equilibration should be extremely slow, similar to the dynamics of glasses. This article is part of the themed issue ‘Breakdown of ergodicity in quantum systems: from solids to synthetic matter’.
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Blok, B., i X. G. Wen. "Many-body systems with non-abelian statistics". Nuclear Physics B 374, nr 3 (maj 1992): 615–46. http://dx.doi.org/10.1016/0550-3213(92)90402-w.
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Hess, P. W., P. Becker, H. B. Kaplan, A. Kyprianidis, A. C. Lee, B. Neyenhuis, G. Pagano i in. "Non-thermalization in trapped atomic ion spin chains". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, nr 2108 (30.10.2017): 20170107. http://dx.doi.org/10.1098/rsta.2017.0107.
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Linear arrays of trapped and laser-cooled atomic ions are a versatile platform for studying strongly interacting many-body quantum systems. Effective spins are encoded in long-lived electronic levels of each ion and made to interact through laser-mediated optical dipole forces. The advantages of experiments with cold trapped ions, including high spatio-temporal resolution, decoupling from the external environment and control over the system Hamiltonian, are used to measure quantum effects not always accessible in natural condensed matter samples. In this review, we highlight recent work using trapped ions to explore a variety of non-ergodic phenomena in long-range interacting spin models, effects that are heralded by the memory of out-of-equilibrium initial conditions. We observe long-lived memory in static magnetizations for quenched many-body localization and prethermalization, while memory is preserved in the periodic oscillations of a driven discrete time crystal state. This article is part of the themed issue ‘Breakdown of ergodicity in quantum systems: from solids to synthetic matter’.
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Moore, Joel E. "A perspective on quantum integrability in many-body-localized and Yang–Baxter systems". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, nr 2108 (30.10.2017): 20160429. http://dx.doi.org/10.1098/rsta.2016.0429.
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Two of the most active areas in quantum many-particle dynamics involve systems with an unusually large number of conservation laws. Many-body-localized systems generalize ideas of Anderson localization by disorder to interacting systems. While localization still exists with interactions and inhibits thermalization, the interactions between conserved quantities lead to some dramatic differences from the Anderson case. Quantum integrable models such as the XXZ spin chain or Bose gas with delta-function interactions also have infinite sets of conservation laws, again leading to modifications of conventional thermalization. A practical way to treat the hydrodynamic evolution from local equilibrium to global equilibrium in such models is discussed. This paper expands upon a presentation at a discussion meeting of the Royal Society on 7 February 2017. The work described was carried out with a number of collaborators, including Jens Bardarson, Vir Bulchandani, Roni Ilan, Christoph Karrasch, Siddharth Parameswaran, Frank Pollmann and Romain Vasseur. This article is part of the themed issue ‘Breakdown of ergodicity in quantum systems: from solids to synthetic matter’.
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Ponte, Pedro, C. R. Laumann, David A. Huse i A. Chandran. "Thermal inclusions: how one spin can destroy a many-body localized phase". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, nr 2108 (30.10.2017): 20160428. http://dx.doi.org/10.1098/rsta.2016.0428.
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Many-body localized (MBL) systems lie outside the framework of statistical mechanics, as they fail to equilibrate under their own quantum dynamics. Even basic features of MBL systems, such as their stability to thermal inclusions and the nature of the dynamical transition to thermalizing behaviour, remain poorly understood. We study a simple central spin model to address these questions: a two-level system interacting with strength J with N ≫1 localized bits subject to random fields. On increasing J , the system transitions from an MBL to a delocalized phase on the vanishing scale J c ( N )∼1/ N , up to logarithmic corrections. In the transition region, the single-site eigenstate entanglement entropies exhibit bimodal distributions, so that localized bits are either ‘on’ (strongly entangled) or ‘off’ (weakly entangled) in eigenstates. The clusters of ‘on’ bits vary significantly between eigenstates of the same sample, which provides evidence for a heterogeneous discontinuous transition out of the localized phase in single-site observables. We obtain these results by perturbative mapping to bond percolation on the hypercube at small J and by numerical exact diagonalization of the full many-body system. Our results support the arguments that the MBL phase is unstable in systems with short-range interactions and quenched randomness in dimensions d that are high but finite. This article is part of the themed issue ‘Breakdown of ergodicity in quantum systems: from solids to synthetic matter’.
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Freese, Johannes, Boris Gutkin i Thomas Guhr. "Spreading in integrable and non-integrable many-body systems". Physica A: Statistical Mechanics and its Applications 461 (listopad 2016): 683–93. http://dx.doi.org/10.1016/j.physa.2016.06.008.
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Biehs, Svend-Age. "Thermal radiation in dipolar many-body systems". EPJ Web of Conferences 266 (2022): 07001. http://dx.doi.org/10.1051/epjconf/202226607001.
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The framework of fluctuational electrodynamics for dipolar many-body systems is one of the working horse for theoretical studies of thermal radiation at the nanoscale which includes dissipation and retardation in a naturally way. Based on this framework I will discuss near-field thermal radiation in non-reciprocal and topological many-body systems. The appearance of the Hall and non-reciprocal diode effect for thermal radiation illustrates nicely the interesting physics in such systems as well as the edge mode dominated heat transfer in topological Su-Schrieffer-Heeger chains and a honeycomb lattices of plasmonic nanoparticles. In the latter, the theory allows for quantifying the effciency of the edge-mode dominated heat transfer as function of the dissipation. Finally, I will present how the theoretical framework can be generalized to study far-field thermal emission of many-body systems close to an environment like a substrate, for instance. This theory might be particularly interesting for modelling thermal imaging microscopes.
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Lindgren, Ingvar, Sten Salomonson i Daniel Hedendahl. "New approach to many-body quantum-electrodynamics calculations:merging quantum electrodynamics with many-body perturbation". Canadian Journal of Physics 83, nr 4 (1.04.2005): 395–403. http://dx.doi.org/10.1139/p05-012.
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A new method for bound-state quantum electrodynamics (QED) calculations on many-electron systems is presented that is a combination of the non-QED many-body technique for quasi-degenerate systems and the newly developed covariant-evolution-operator technique for QED calculations. The latter technique has been successfully applied to the fine structure of excited states of medium-heavy heliumlike ions, and it is expected that the new method should be applicable also to light elements, hopefully down to neutral helium. PACS Nos.: 31.30.Jv, 31.15.Md, 31.25.Jf, 33.15.Pw
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Zhang, Xueyue, Eunjong Kim, Daniel K. Mark, Soonwon Choi i Oskar Painter. "A superconducting quantum simulator based on a photonic-bandgap metamaterial". Science 379, nr 6629 (20.01.2023): 278–83. http://dx.doi.org/10.1126/science.ade7651.
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Synthesizing many-body quantum systems with various ranges of interactions facilitates the study of quantum chaotic dynamics. Such extended interaction range can be enabled by using nonlocal degrees of freedom such as photonic modes in an otherwise locally connected structure. Here, we present a superconducting quantum simulator in which qubits are connected through an extensible photonic-bandgap metamaterial, thus realizing a one-dimensional Bose-Hubbard model with tunable hopping range and on-site interaction. Using individual site control and readout, we characterize the statistics of measurement outcomes from many-body quench dynamics, which enables in situ Hamiltonian learning. Further, the outcome statistics reveal the effect of increased hopping range, showing the predicted crossover from integrability to ergodicity. Our work enables the study of emergent randomness from chaotic many-body evolution and, more broadly, expands the accessible Hamiltonians for quantum simulation using superconducting circuits.
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Gritsev, Vladimir, Peter Barmettler i Eugene Demler. "Scaling approach to quantum non-equilibrium dynamics of many-body systems". New Journal of Physics 12, nr 11 (3.11.2010): 113005. http://dx.doi.org/10.1088/1367-2630/12/11/113005.
Pełny tekst źródłaRozprawy doktorskie na temat "Non-ergodicity in many body systems"
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Fusco, Lorenzo. "Non-equilibrium thermodynamics in quantum many-body systems". Thesis, Queen's University Belfast, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.706680.
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Thermodynamics is one of the pillars of modern science. Understanding which are the boundaries for the applicability of a theory is fundamental for every science and thermodynamics makes no exception. This Thesis studied the implications of thermodynamic transformations applied to quantum systems, particularly discussing the limits of a proper thermodynamic interpretation of such a transformation for a quantum many-body system. First a framework is developed to give a physical meaning to the full statistics of the work distributions for a many-body system, with particular emphasis on the quantum Ising model. Signatures of criticality are found at any level of the statistics of the work distribution. Furthermore, a detailed study of cyclic work extraction protocols is reported, for the case of the Dicke model, analysing the interplay between entanglement and phase transition from the point of view of non-equilibrium thermodynamics. Afterwards, a study of non-equilibrium thermodynamics of open quantum systems is reported. The first experimental reconstruction of the irreversible entropy production for a critical quantum manybody system is demonstrated, showing an excellent agreement with the theoretical predictions. Finally, in the framework of thermodynamics of quantum jump trajectories, a novel approach to the resolution of the large-deviation function is derived. Using this method many studies on the thermodynamics of open quantum many-body systems can be realised in the future.
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Henriet, Loïc. "Non-equilibrium dynamics of many body quantum systems". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX036/document.
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Cette thèse porte sur l'étude de propriétés dynamiques de modèles quantiques portés hors équilibre. Nous introduisons en particulier des modèles généraux de type spin-boson, qui décrivent par exemple l'interaction lumière-matière ou certains phénomènes de dissipation. Nous contribuons au développement d'une approche stochastique exacte permettant de d'écrire la dynamique hors équilibre du spin dans ces modèles. Dans ce contexte, l'effet de l'environnement bosonique est pris en compte par l'intermédiaire des degrés de liberté stochastiques supplémentaires, dont les corrélations temporelles dépendent des propriétés spectrales de l'environnement bosonique. Nous appliquons cette approche à l'étude de phénomènes à N-corps, comme par exemple la transition de phase dissipative induite par un environnement bosonique de type ohmique. Des phénomènes de synchronisation spontanée, et de transition de phase topologique sont aussi identifiés. Des progrès sont aussi réalisés dans l'étude de la dynamique dans les réseaux de systèmes lumière-matière couplés. Ces développements théoriques sont motivés par les progrès expérimentaux récents, qui permettent d'envisager une étude approfondie de ces phénomènes. Cela inclut notamment les systèmes d'atomes ultra-froids, d'ions piégés, et les plateformes d'électrodynamique en cavité et en circuit. Nous intéressons aussi à la physique des systèmes hybrides comprenant des dispositifs à points quantiques mésoscopiques couplés à un résonateur électromagnétique. L'avènement de ces systèmes permet de mesures de la formation d'états à N-corps de type Kondo grâce au résonateur; et d'envisager des dispositifs thermoélectriquesThis thesis deals with the study of dynamical properties of out-of-equilibrium quantum systems. We introduce in particular a general class of Spin-Boson models, which describe for example light-matter interaction or dissipative phenomena. We contribute to the development of a stochastic approach to describe the spin dynamics in these models. In this context, the effect of the bosonic environment is encapsulated into additional stochastic degrees of freedom whose time-correlations are determined by spectral properties of the bosonic environment. We use this approach to study many-body phenomena such as the dissipative quantum phase transition induced by an ohmic bosonic environment. Synchronization phenomena as well as dissipative topological transitions are identified. We also progress in the study of arrays of interacting light-matter systems. These theoretical developments follow recent experimental achievements, which could ensure a quantitative study of these phenomena. This notably includes ultra-cold atoms, trapped ions and cavity and circuit electrodynamics setups. We also investigate hybrid systems comprising electronic quantum dots coupled to electromagnetic resonators, which enable us to provide a spectroscopic analysis of many-body phenomena linked to the Kondo effect. We also introducethermoelectric applications in these devices
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Fedorov, Aleksey. "Non-conventional Many-body Phases in Ultracold Dipolar Systems". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS580/document.
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Le problème de la détection et de ladescription des nouveaux états quantiquesmacroscopiques, caractérisées par des propriétésexotiques et non-conventionnelles, estd’importance fondamentale dans la physiquemoderne. Ces états offrent des perspectivesfascinantes dans le domaine de traitementd’information, de simulations quantiques et derecherche des nouveaux types des matériaux.Dans ce travail de thèse nous développons unethéorie qui permet de décrire des phases non conventionnellesdans des systèmes des gazultra-froids dipolaires. Ces systèmes sontactivement étudiés expérimentalement enutilisant des atomes à grand-spins, desmolécules polaires et des excitations dipolairesdans des semi-conducteurs. Nous mettonsl'accent sur la révélation du rôle de l’interactiondipôle-dipôle à long porté.Nous considérons l’effet de rotonization dansun système de gaz des bosons dipolaires «tiltés»aux interactions faibles dans une couchehomogène. Nous prédisons l’effet derotonization pour un gaz de Bose faiblementcorrélé des excitons dipolaires dans une couchede semi-conducteur et nous calculons lediagramme de stabilité. Ensuite, nousconsidérons des superfluides d’onde-p desfermions identiques dans des réseaux 2D.Finalement, nous faisons une discussion sur unautre état superfluide intéressant des moléculespolaires fermioniques, qui devrait apparaitredans des systèmes bicouchesThe problem of revealing anddescribing novel macroscopic quantum statescharacter- ized by exotic and non-conventionalproperties is of fundamental importance formodern physics. Such states offer fascinatingprospects for potential applications in quantumin- formation processing, quantum simulation,and material research. In the present Thesis wedevelop a theory for describing nonconventionalphases of ultracold dipolar gases.The related systems of large-spin atoms, polarmolecules, and dipolar excitons in semiconductorsare actively studied in experiments.We put the main emphasis on revealing the roleof the long-range character of the dipole-dipoleinteraction.We consider the effect of rotonization for a 2Dweakly interacting gas of tilted dipolar bosonsin a homogeneous layer. We predict the effectof rotonization for a weakly correlated Bosegas of dipolar excitons in a semiconductorlayer and calculate the stability diagram. Wethen consider p-wave superfluids of identicalfermions in 2D lattices. Finally, we discussanother interesting novel superfluid offermionic polar molecules
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Gils, Charlotte. "Phases of interacting many-body systems: from classical systems to non-abelian anyons /". Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=18141.
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Moosavi, Per. "Interacting fermions and non-equilibrium properties of one-dimensional many-body systems". Licentiate thesis, KTH, Teoretisk fysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-193330.
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Recent experimental progress on ultracold atomic gases have opened up the possibility to simulate many-body systems out of equilibrium. We consider such a system described by the Luttinger model, which is a model of interacting fermions in one spatial dimension. It is well known that the Luttinger model is exactly solvable using bosonization. This also remains true for certain extensions of the model, e.g., where, in addition, the fermions are coupled to phonons. We give a self-contained account of bosonization, together with complete proofs, and show how this can be used to solve the Luttinger model and the above fermion-phonon model rigorously. The main focus is on non-equilibrium properties of the Luttinger model. We use the exact solution of the Luttinger model, with non-local interactions, to study the evolution starting from a non-uniform initial state with a position-dependent chemical potential. The system is shown to reach a current-carrying final steady state, in which the universal value of the electrical conductance, known from near-to-equilibrium settings, is recovered. We also study the effects of suddenly changing the interactions and show that the final state has memory of the initial state, which is, e.g., manifested by non- equilibrium exponents in its fermion two-point correlation functions.QC 20161003
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Bertini, Bruno. "Non-equilibrium dynamics of interacting many-body quantum systems in one dimension". Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:1e2c50b9-73b3-4ca0-a5f3-276f967c3720.
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In this thesis we study three examples of interacting many-body systems undergoing a non equilibrium time evolution. Firstly we consider the time evolution in an integrable system: the sine-Gordon field theory in the repulsive regime. We will focus on the one point function of the semi-local vertex operator eiβφ(x)/2 on a specific class of initial states. By analytical means we show that the expectation value considered decays exponentially to zero at late times and we determine the decay time. The method employed is based on a form-factor expansion and uses the "Representative Eigenstate Approach" of Ref. [73] (a.k.a. "Quench Action"). In a second example we study the time evolution in models close to "special" integrable points characterised by hidden symmetries generating infinitely many local conservation laws that do not commute with one another, in addition to the infinite commuting family implied by integrability. We observe that both in the case where the perturbation breaks the integrability and when it breaks only the additional symmetries maintaining integrability, the local observables show a crossover behaviour from an initial to a final quasi stationary plateau. We investigate a weak coupling limit, identify a time window in which the effects of the perturbations become significant and solve the time evolution through a mean-field mapping. As an explicit example we study the XYZ spin-1/2 chain with additional perturbations that break integrability. Finally, we study the effects of integrability breaking perturbations on the non-equilibrium evolution of more general many-particle quantum systems, where the unperturbed integrable model is generic. We focus on a class of spinless fermion models with weak interactions. We employ equation of motion techniques that can be viewed as generalisations of quantum Boltzmann equations. We benchmark our method against time dependent density matrix renormalisation group computations and find it to be very accurate as long as interactions are weak. For small integrability breaking, we observe robust prethermalisation plateaux for local observables on all accessible time scales. Increasing the strength of the integrability breaking term induces a "drift" away from the prethermalisation plateaux towards thermal behaviour. We identify a time scale characterising this crossover.
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Buchhold, Michael. "Thermalization and Out-of-Equilibrium Dynamics in Open Quantum Many-Body Systems". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-181786.
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Thermalization, the evolution of an interacting many-body system towards a thermal Gibbs ensemble after initialization in an arbitrary non-equilibrium state, is currently a phenomenon of great interest, both in theory and experiment. As the time evolution of a quantum system is unitary, the proposed mechanism of thermalization in quantum many-body systems corresponds to the so-called eigenstate thermalization hypothesis (ETH) and the typicality of eigenstates. Although this formally solves the contradiction of thermalizing but unitary dynamics in a closed quantum many-body system, it does neither make any statement on the dynamical process of thermalization itself nor in which way the coupling of the system to an environment can hinder or modify the relaxation dynamics.
In this thesis, we address both the question whether or not a quantum system driven away from equilibrium is able to relax to a thermal state, which fulfills detailed balance, and if one can identify universal behavior in the non-equilibrium relaxation dynamics.
As a first realization of driven quantum systems out of equilibrium, we investigate a system of Ising spins, interacting with the quantized radiation field in an optical cavity. For multiple cavity modes, this system forms a highly entangled and frustrated state with infinite correlation times, known as a quantum spin glass. In the presence of drive and dissipation, introduced by coupling the intra-cavity radiation field to the photon vacuum outside the cavity via lossy mirrors, the quantum glass state is modified in a universal manner. For frequencies below the photon loss rate, the dissipation takes over and the system shows the universal behavior of a dissipative spin glass, with a characteristic spectral density $\\mathcal{A}(\\omega)\\sim\\sqrt{\\omega}$. On the other hand, for frequencies above the loss rate, the system retains the universal behavior of a zero temperature, quantum spin glass. Remarkably, at the glass transition, the two subsystems of spins and photons thermalize to a joint effective temperature, even in the presence of photon loss. This thermalization is a consequence of the strong spin-photon interactions, which favor detailed balance in the system and detain photons from escaping the cavity. In the thermalized system, the features of the spin glass are mirrored onto the photon degrees of freedom, leading to an emergent photon glass phase. Exploiting the inherent photon loss of the cavity, we make predictions of possible measurements on the escaping photons, which contain detailed information of the state inside the cavity and allow for a precise, non-destructive measurement of the glass state.
As a further set of non-equilibrium systems, we consider one-dimensional quantum fluids driven out of equilibrium, whose universal low energy theory is formed by the so-called Luttinger Liquid description, which, due to its large degree of universality, is of intense theoretical and experimental interest. A set of recent experiments in research groups in Vienna, Innsbruck and Munich have probed the non-equilibrium time-evolution of one-dimensional quantum fluids for different experimental realizations and are pushing into a time regime, where thermalization is expected. From a theoretical point of view, one-dimensional quantum fluids are particular interesting, as Luttinger Liquids are integrable and therefore, due to an infinite number of constants of motion, do not thermalize. The leading order correction to the quadratic theory is irrelevant in the sense of the renormalization group and does therefore not modify static correlation functions, however, it breaks integrability and will therefore, even if irrelevant, induce a completely different non-equilibrium dynamics as the quadratic Luttinger theory alone. In this thesis, we derive for the first time a kinetic equation for interacting Luttinger Liquids, which describes the time evolution of the excitation densities for arbitrary initial states. The resonant character of the interaction makes a straightforward derivation of the kinetic equation, using Fermi\'s golden rule, impossible and we have to develop non-perturbative techniques in the Keldysh framework. We derive a closed expression for the time evolution of the excitation densities in terms of self-energies and vertex corrections. Close to equilibrium, the kinetic equation describes the exponential decay of excitations, with a decay rate $\\sigma^R=\\mbox\\Sigma^R$, determined by the self-energy at equilibrium. However, for long times $\\tau$, it also reveals the presence of dynamical slow modes, which are the consequence of exactly energy conserving dynamics and lead to an algebraic decay $\\sim\\tau^$ with $\\eta_D=0.58$. The presence of these dynamical slow modes is not contained in the equilibrium Matsubara formalism, while they emerge naturally in the non-equilibrium formalism developed in this thesis.
In order to initialize a one-dimensional quantum fluid out of equilibrium, we consider an interaction quench in a model of interacting, dispersive fermions in Chap.~\\ref. In this scenario, the fermionic interaction is suddenly changed at time $t=0$, such that for $t>0$ the system is not in an eigenstate and therefore undergoes a non-trivial time evolution. For the quadratic theory, the stationary state in the limit $t\\rightarrow\\infty$ is a non-thermal, or prethermal, state, described by a generalized Gibbs ensemble (GGE). The GGE takes into account for the conservation of all integrals of motion, formed by the eigenmodes of the Hamiltonian. On the other hand, in the presence of non-linearities, the final state for $t\\rightarrow\\infty$ is a thermal state with a finite temperature $T>0$. . The spatio-temporal, dynamical thermalization process can be decomposed into three regimes: A prequench regime on the largest distances, which is determined by the initial state, a prethermal plateau for intermediate distances, which is determined by the metastable fixed point of the quadratic theory and a thermal region on the shortest distances. The latter spreads sub-ballistically $\\sim t^$ in space with $0<\\alpha<1$ depending on the quench. Until complete thermalization (i.e. for times $t<\\infty$), the thermal region contains more energy than the prethermal and prequench region, which is expressed in a larger temperature $T_{t}>T_$, decreasing towards its final value $T_$. As the system has achieved local detailed balance in the thermalized region, energy transport to the non-thermal region can only be performed by the macroscopic dynamical slow modes and the decay of the temperature $T_{t}-T_\\sim t^$ again witnesses the presence of these slow modes. The very slow spreading of thermalization is consistent with recent experiments performed in Vienna, which observe a metastable, prethermal state after a quench and only observe the onset of thermalization on much larger time scales. As an immediate indication of thermalization, we determine the time evolution of the fermionic momentum distribution after a quench from non-interacting to interacting fermions. For this quench scenario, the step in the Fermi distribution at the Fermi momentum $k\\sub$ decays to zero algebraically in the absence of a non-linearity but as a stretched exponential (the exponent being proportional to the non-linearity) in the presence of a finite non-linearity. This can serve as a proof for the presence or absence of the non-linearity even on time-scales for which thermalization can not yet be observed.
Finally, we consider a bosonic quantum fluid, which is driven away from equilibrium by permanent heating. The origin of the heating is atomic spontaneous emission of laser photons, which are used to create a coherent lattice potential in optical lattice experiments. This process preserves the system\'s $U(1)$-invariance, i.e. conserves the global particle number, and the corresponding long-wavelength description is a heated, interacting Luttinger Liquid, for which phonon modes are continuously populated with a momentum dependent rate $\\partial_tn_q\\sim\\gamma |q|$. In the dynamics, we identify a quasi-thermal regime for large momenta, featuring an increasing time-dependent effective temperature. In this regime, due to fast phonon-phonon scattering, detailed balance has been achieved and is expressed by a time-local, increasing temperature. The thermal region emerges locally and spreads in space sub-ballistically according to $x_t\\sim t^{4/5}$. For larger distances, the system is described by an non-equilibrium phonon distribution $n_q\\sim |q|$, which leads to a new, non-equilibrium behavior of large distance observables. For instance, the phonon decay rate scales universally as $\\gamma_q\\sim |q|^{5/3}$, with a new non-equilibrium exponent $\\eta=5/3$, which differs from equilibrium. This new, universal behavior is guaranteed by the $U(1)$ invariant dynamics of the system and is insensitive to further subleading perturbations. The non-equilibrium long-distance behavior can be determined experimentally by measuring the static and dynamic structure factor, both of which clearly indicate the exponents for phonon decay, $\\eta=5/3$ and for the spreading of thermalization $\\eta_T=4/5$.
Remarkably, even in the presence of this strong external drive, the interactions and their aim to achieve detailed balance are strong enough to establish a locally emerging and spatially spreading thermal region.
The physical setups in this thesis do not only reveal interesting and new dynamical features in the out-of-equilibrium time evolution of interacting systems, but they also strongly underline the high degree of universality of thermalization for the classes of models studied here. May it be a system of coupled spins and photons, where the photons are pulled away from a thermal state by Markovian photon decay caused by a leaky cavity, a one-dimensional fermionic quantum fluid, which has been initialized in an out-of-equilibrium state by a quantum quench or a one-dimensional bosonic quantum fluid, which is driven away from equilibrium by continuous, external heating, all of these systems at the end establish a local thermal equilibrium, which spreads in space and leads to global thermalization for $t\\rightarrow\\infty$. This underpins the importance of thermalizing collisions and endorses the standard approach of equilibrium statistical mechanics, describing a physical system in its steady state by a thermal Gibbs ensemble.
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Schiulaz, Mauro. "Ideal quantum glass transitions: many-body localization without quenched disorder?" Doctoral thesis, SISSA, 2015. http://hdl.handle.net/20.500.11767/4908.
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In this work the role of disorder, interaction and temperature in the physics of quantum non-ergodic systems is discussed. I first review what is meant by thermalization in closed quantum systems, and how ergodicity is violated in the presence of strong disorder, due to the phenomenon of Anderson localization. I explain why localization can be stable against the addition of weak dephasing interactions, and how this leads to the very rich phenomenology associated with many-body localization. I also briefly compare localized systems with their closest classical analogue, which are glasses, and discuss their similarities and differences, the most striking being that in quantum systems genuine non ergodicity can be proven in some cases, while in classical systems it is a matter of debate whether thermalization eventually takes place at very long times.
Up to now, many-body localization has been studies in the region of strong disorder and weak interaction. I show that strongly interacting systems display phenomena very similar to localization, even in the absence of disorder. In such systems, dynamics starting from a random inhomogeneous initial condition are non-perturbatively slow, and relaxation takes place only in exponentially long times. While in the thermodynamic limit ergodicity is ultimately restored due to rare events, from the practical point of view such systems look as localized on their initial condition, and this behavior can be studied experimentally. Since their behavior shares similarities with both many-body localized and classical glassy systems, these models are termed “quantum glasses”.
Apart from the interplay between disorder and interaction, another important issue concerns the role of temperature for the physics of localization. In non-interacting systems, an energy threshold separating delocalized and localized states exist, termed “mobility edge”. It is commonly believed that a mobility edge should exist in interacting systems, too. I argue that this scenario is inconsistent because inclusions of the ergodic phase in the supposedly localized phase can serve as mobile baths that induce global delocalization. I conclude that true non-ergodicity can be present only if the whole spectrum is localized. Therefore, the putative transition as a function of temperature is reduced to a sharp crossover. I numerically show that the previously reported mobility edges can not be distinguished from finite size effects. Finally, the relevance of my results for realistic experimental situations is discussed.
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Staniscia, Fabio. "Out-of-equilibrium behavior of many-body Hamiltonian systems with different interaction ranges". Doctoral thesis, Università degli studi di Trieste, 2011. http://hdl.handle.net/10077/4972.
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2009/2010In this Thesis we describe the theoretical-computational study performed on the behavior of isolated systems, far from thermodynamic equilibrium. Analyzing models well-known in literature we follow a path bringing to the classification of different behaviors in function of the interaction range of the systems' particles. In the case of systems with long-range interaction we studied the "Quasi-Stationary states" (QSSs) which emerge at short times when the system evolves with Hamiltonian dynamics. Their interest is in the fact that in many physical systems, such as self-gravitating systems, plasmas and systems characterized by wave-particle interaction, QSSs are the only experimentally accessible regime. QSS are defined as stable solutions of the Vlasov equation and, as their duration diverges with the system size, for large systems' size they can be seen as the true equilibria. They do not follow the Boltzmann statistics, and it does not exists a general theory which describes them. Anyway it is possible to give an approximate description using Lynden-Bell theory. One part of the thesis is devoted to shed light on the characteristics of the phase diagram of the "Hamiltonian mean field" model (HMF), during the QSS, calculated with the Lynden-Bell theory. The results of our work allowed to confirm numerically the presence of a phase re-entrance. In the Thesis is present also a detailed description on the system's caloric curves and on the metastability. Still in this context we show an analysis of the equivalence of the statistical ensembles, confirmed in almost the totality of the phase diagram (except for a small region), although the presence of negative specific heat in the microcanonical ensemble, which in Boltzmannian systems implies the non-equivalence of statistical ensembles. This result allowed us to arrive to a surprising conclusion: the presence of negative specific heat in the canonical ensemble. Still in the context of long-range interacting systems we analyze the linear stability of the non-homogeneous QSSs with respect to the Vlasov equation. Since the study of QSS find an application in the Free-electron laser (FEL) and other light sources, which are characterized by wave-particle interaction, we analyze, in the last chapter, the experimental perspectives of our work in this context. The other class of systems we studied are short-range interacting systems. Here the behavior of the components of the system is strongly influenced by the neighbors, and if one takes a system in a disordered state (a zero magnetization state for magnetic systems), which relaxes towards an ordered equilibrium state, one sees that the ordering process first develops locally and then extends to the whole system forming domains of opposed magnetization which grow in size. This process is called "coarsening". Our work in this field consisted in investigating numerically the laws of scale, and in the Thesis we characterize the temporal dependence of the domain sizes for different interaction ranges and we show a comparison between Hamiltonian and Langevin dynamics. This work inserts in the open debate on the equivalence of different dynamics where we found that, at least for times not too large, the two dynamics give different scaling laws.
In questa Tesi è stato fatto uno studio di natura teorico-computazionale sul comportamento dei sistemi isolati lontani dall'equilibrio termodinamico. Analizzando modelli noti in letteratura è stato seguito un percorso che ha portato alla classificazione di differenti comportamenti in funzione del range di interazione delle particelle del sistema. Nel caso di sistemi con interazione a lungo raggio sono stati studiati gli "stati quasi-stazionari" (QSS) che emergono a tempi brevi quando il sistema evolve con dinamica hamiltoniana. Il loro interesse risiede nel fatto che in molti sistemi fisici, come i sistemi auto-gravitanti, plasmi e sistemi caratterizzati da interazione onda-particella, i QSS risultano essere gli unici regimi accessibili sperimentalmente. I QSS sono definiti come soluzioni stabili dell'equazione di Vlasov, e visto che la loro durata diverge con la taglia del sistema, per sistemi di grandi dimensioni possono essere visti come i veri stati di equilibrio. Questi non seguono la statistica di Bolzmann, e non esiste una teoria generale che li descriva. E' tuttavia possibile fare una descrizione approssimata utilizzando la teoria di Lynden-Bell. Una parte della tesi è dedicata alla comprensione delle caratteristiche del diagramma di fase del modello "Hamiltonian mean field" (HMF) durante il QSS, calcolato con la teoria di Lynden-Bell. Il risultato del nostro lavoro ha permesso di confermare numericamente la presenza di fasi rientrati. E' inoltre presente un'analisi dettagliata sulle curve caloriche del sistema e sulla metastabilità. Sempre in questo contesto è stata fatto uno studio sull'equivalenza degli ensemble statistici, confermata nella quasi totalità del diagramma di fase (tranne in una piccola regione), nonostante la presenza di calore specifico negativo nell'insieme microcanonico, che in sistemi Boltzmanniani è sinonimo di non-equivalenza degli ensemble statistici. Questo risultato ci ha permesso di arrivare ad una sorprendente conclusione: la presenza di calore specifico negativo nell'insieme canonico. Sempre nel contesto dei sistemi con interazione a lungo range, è stata analizzata la stabilità lineare rispetto all'equazione di Vlasov degli stati quasi-stazionari non-omogenei. Poiché lo studio dei QSS trova applicazione nel Free-electron laser (FEL) e in altre sorgenti di luce, caratterizzate dall'interazione onda-particella, abbiamo analizzato anche le prospettive sperimentali del nostro lavoro in questo contesto. L'altra classe di sistemi che è stata studiata sono i sistemi con interazione a corto raggio. Qui il comportamento dei componenti del sistema è fortemente influenzato dai vicini, e se si prende un sistema in uno stato disordinato (a magnetizzazione nulla nei sistemi magnetici) che rilassa verso l'equilibrio ordinato, si vede che il processo di ordinamento si sviluppa prima localmente e poi si estende a tutto il sistema formando dei domini di magnetizzazione opposta che crescono in taglia. Questo processo si chiama "coarsening". Il nostro lavoro in questo contesto è consistito in una investigazione numerica delle leggi di scala, e nella tesi è stata caratterizzata la dipendenza temporale della taglia dei domini per differenti range di interazione ed è stato fatto un confronto fra dinamica hamiltoniana e dinamica di Langevin. Questi risultati si inseriscono nel dibattito aperto sull'equivalenza di differenti dinamiche, e si è mostrato che, almeno per tempi non troppo grandi, le due dinamiche portano a leggi di scala differenti.
XXIII Ciclo
1982
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Roggero, Alessandro. "Ground state and dynamical properties of many-body systems by non conventional Quantum Monte Carlo algorithms". Doctoral thesis, Università degli studi di Trento, 2014. https://hdl.handle.net/11572/367745.
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In this work we develop Quantum Monte Carlo techniques suitable for exploring both ground state and dynamical properties of interacting many-body systems. We then apply these techniques to the study of excitations in superfluid He4 and to explore the structure of nuclear systems using chiral effective field theory interactions.
Książki na temat "Non-ergodicity in many body systems"
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NATO Advanced Study Institute on Dynamics : Models and Kinetic Methods for Non-equilibrium Many Body Systems (1998 Lorentz Institute, Leiden University). Dynamics: Models and kinetic methods for non-equilibrium many body systems. Dordrecht: Kluwer Academic Publishers, 2000.
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Karkheck, John. Dynamics: Models and Kinetic Methods for Non-equilibrium Many Body Systems. Dordrecht: Springer Netherlands, 2002.
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Karkheck, John, red. Dynamics: Models and Kinetic Methods for Non-equilibrium Many Body Systems. Dordrecht: Springer Netherlands, 2002. http://dx.doi.org/10.1007/978-94-011-4365-3.
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Dynamics Models and Kinetic Methods for Non- equilibrium Many body Systems. Springer, 2000.
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Karkheck, John. Dynamics: Models and Kinetic Methods for Non-equilibrium Many Body Systems. Springer, 2011.
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Karkheck, John. Dynamics: Models and Kinetic Methods for Non-Equilibrium Many-Body Systems. Springer, 2000.
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Glocker, Christoph. Set-Valued Force Laws: Dynamics of Non-Smooth Systems. Springer, 2012.
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Glocker, Christoph. Set-Valued Force Laws: Dynamics of Non-Smooth Systems. Springer, 2013.
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Glocker, Christoph. Set-Valued Force Laws: Dynamics of Non-Smooth Systems. Springer, 2012.
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Set-Valued Force Laws: Dynamics of Non-Smooth Systems (Lecture Notes in Applied and Computational Mechanics). Springer, 2001.
Znajdź pełny tekst źródłaCzęści książek na temat "Non-ergodicity in many body systems"
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Fransson, Jonas. "Many-Body Representation of Physical Systems". W Non-Equilibrium Nano-Physics, 1–11. Dordrecht: Springer Netherlands, 2010. http://dx.doi.org/10.1007/978-90-481-9210-6_1.
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Blom, Kristian. "Bethe-Guggenheim Approximation for Non-uniform Systems". W Pair-Correlation Effects in Many-Body Systems, 35–56. Cham: Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-29612-3_3.
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Novoselsky, Akiva, i Jacob Katriel. "Non-Spurious Harmonic Oscillator States for Many-Body Systems". W Recent Progress in Many-Body Theories, 175–82. Boston, MA: Springer US, 1990. http://dx.doi.org/10.1007/978-1-4615-3798-4_16.
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Zon, R., H. Beijeren i J. R. Dorfman. "Kinetic Theory of Dynamical Systems". W Dynamics: Models and Kinetic Methods for Non-equilibrium Many Body Systems, 131–67. Dordrecht: Springer Netherlands, 2000. http://dx.doi.org/10.1007/978-94-011-4365-3_8.
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Lindgren, Ingvar. "Relativistic and Non-Relativistic Many-Body Procedure, Applied to Atomic Systems". W Lecture Notes in Chemistry, 367–92. Berlin, Heidelberg: Springer Berlin Heidelberg, 1989. http://dx.doi.org/10.1007/978-3-642-61330-2_20.
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Piasecki, J. "Stationary States in Systems with Dissipative Interactions". W Dynamics: Models and Kinetic Methods for Non-equilibrium Many Body Systems, 279–95. Dordrecht: Springer Netherlands, 2000. http://dx.doi.org/10.1007/978-94-011-4365-3_16.
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Gaspard, Pierre. "Scattering, Transport & Stochasticity in Quantum Systems". W Dynamics: Models and Kinetic Methods for Non-equilibrium Many Body Systems, 425–56. Dordrecht: Springer Netherlands, 2000. http://dx.doi.org/10.1007/978-94-011-4365-3_25.
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Piasecki, J., i Ya G. Sinai. "A Model of Non-Equilibrium Statistical Mechanics". W Dynamics: Models and Kinetic Methods for Non-equilibrium Many Body Systems, 191–99. Dordrecht: Springer Netherlands, 2000. http://dx.doi.org/10.1007/978-94-011-4365-3_10.
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Bocquet, Lydéric, i Jean-Pierre Hansen. "Dynamics of Colloidal Systems: Beyond the Stochastic Approach". W Dynamics: Models and Kinetic Methods for Non-equilibrium Many Body Systems, 1–16. Dordrecht: Springer Netherlands, 2000. http://dx.doi.org/10.1007/978-94-011-4365-3_1.
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Chernov, N. "Statistical Properties of Chaotic Systems in High Dimensions". W Dynamics: Models and Kinetic Methods for Non-equilibrium Many Body Systems, 201–14. Dordrecht: Springer Netherlands, 2000. http://dx.doi.org/10.1007/978-94-011-4365-3_11.
Pełny tekst źródłaStreszczenia konferencji na temat "Non-ergodicity in many body systems"
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Liu, Xueying, Xuezao Ren, Kelin Wang, Xiaohong Li i Xiaoming Lin. "Non-perturbation calculation for the dynamic problem of quantum many-body systems". W CIOP100, redaktor Yue Yang. SPIE, 2018. http://dx.doi.org/10.1117/12.2505698.
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Scherer, Norbert F. "Negative torque and many-body non-conservative dynamics in optical matter systems". W Optical Trapping and Optical Micromanipulation XVII, redaktorzy Kishan Dholakia i Gabriel C. Spalding. SPIE, 2020. http://dx.doi.org/10.1117/12.2568967.
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SEMKAT, D., i M. BONITZ. "NON–LORENTZIAN SPECTRAL FUNCTIONS FOR COULOMB SYSTEMS". W Proceedings of the Conference “Kadanoff-Baym Equations: Progress and Perspectives for Many-Body Physics”. WORLD SCIENTIFIC, 2000. http://dx.doi.org/10.1142/9789812793812_0041.
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ŠPIČKA, V., P. LIPAVSKÝ i K. MORAWETZ. "SPACE–TIME VERSUS PARTICLE–HOLE SYMMETRY OF NON–LOCAL COLLISIONS IN AN KINETIC EQUATION FOR FERMI SYSTEMS". W Proceedings of the Conference “Kadanoff-Baym Equations: Progress and Perspectives for Many-Body Physics”. WORLD SCIENTIFIC, 2000. http://dx.doi.org/10.1142/9789812793812_0009.
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Kusnezov, Dimitri. "Quantum systems, spectrum generating algebras and non-compact lie algebras". W Symmetries and Order: Algebraic Methods in Many Body Systems: A symposium in celebration of the career of Professor Francesco Iachello. AIP Publishing, 2019. http://dx.doi.org/10.1063/1.5124587.
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Tang, Jiping, i Gordon Parker. "Input Shaping Vibration Control for Nonminimum Phase Systems". W ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-37665.
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Many systems exist that contain coupled rigid body and flexible body dynamics. Rigid body repositioning of these systems can be problematic due to unwanted residual vibration of the flexible body degrees of freedom. Input shaping is a method for generating system commands creating desired rigid body motion where the flexible body motion being quiescent at the end of the maneuver. Either operator-in-the-loop or batch commands are convolved with a carefully designed input shaping filter to produce the eventual system input. Systems with minimum phase zeros are easily accommodated using input shaping filters designed for the system without zeros, and then using a secondary pole-zero cancellation filter. This approach cannot be practically applied to nonminimum phase systems since the resulting system input may become unbounded. This paper considers input shaping methods for generating residual vibration-free input time histories for non-minimum phase, oscillatory systems using bounded inputs. An example is presented where the system is an undamped oscillator with a single right plant zero.
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Mukherjee, Rudranarayan M. "Operational Space Algorithm for Flexible Multibody Systems With Generalized Topologies". W ASME 2011 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/detc2011-48657.
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Multibody system with flexible and / or rigid bodies are found in various applications of science and engineering. Many of these systems have topological constraints in the form of kinematically closed loop topologies. Similarly, many of these systems have non-holonomic constraints that are either linear or nonlinear in the system velocities. In this paper, an efficient algorithm is presented for simulating the dynamics of multi-body systems of rigid or flexible bodies in generalized topologies with particular emphasis on treatment of topological and non-holonomic constraints. The flexible bodies are modeled using the small deformation large displacement approach. This algorithm achieve linear and logarithmic complexities in serial and parallel implementation and provides robust performance.
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Van Auken, R. Michael. "Development and Comparison of Laplace Domain Models for Non-Slender Beams and Application to a Half-Car Model With Flexible Body". W ASME 2014 12th Biennial Conference on Engineering Systems Design and Analysis. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/esda2014-20348.
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Math models of flexible dynamic systems have been the subject of research and development for many years. One area of interest is exact Laplace domain solutions to the differential equations that describe the linear elastic deformation of idealized structures. These solutions can be compared to and complement finite order models such as state-space and finite element models. Halevi (2005) presented a Laplace domain solution for a finite length rod in torsion governed by a second order wave equation. Using similar methods Van Auken (2010, 2012) presented a Laplace domain solution for the transverse bending of an undamped uniform slender beam based on the fourth order Euler-Bernoulli equation, where it was assumed that rotary inertia and shear effects were negligible. This paper presents a new exact Laplace domain solution to the Timoshenko model for an undamped uniform non-slender beam that accounts for rotary inertia and shear effects. Example models based on the exact Laplace domain solution are compared to finite element models and to slender beam models in order to illustrate the agreement and differences between the methods and models. The method is then applied to an example model a half-car with a flexible body.
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Khan, Imad M., Woojin Ahn, Kurt Anderson i Suvranu De. "Multi-Flexible-Body Simulations Using Interpolating Splines in a Divide-and-Conquer Scheme". W ASME 2013 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/detc2013-12217.
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A new method for modeling multi-flexible-body systems is presented that incorporates interpolating splines in a divide-and-conquer scheme. This algorithm uses the floating frame of reference formulation and piece-wise interpolation spline functions to construct and solve the non-linear equations of motion of the multi-flexible-body systems undergoing large rotations and translations. We compare the new algorithm with the flexible divide-and-conquer algorithm (FDCA) that uses the assumed modes method and may resort to sub-structuring in many cases [1]. We demonstrate, through numerical examples, that in such cases the interpolating spline-based approach is comparable in accuracy and superior in efficiency to the FDCA. The algorithm retains the theoretical logarithmic complexity inherent to the divide-and-conquer algorithm when implemented in parallel.
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Sado, Danuta. "The Periodic and Chaotic Vibration of Dynamical System With Elastic Pendulum". W ASME 8th Biennial Conference on Engineering Systems Design and Analysis. ASMEDC, 2006. http://dx.doi.org/10.1115/esda2006-95636.
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The nonlinear damping effect on response of coupled three degree-of-freedom autoparametric vibration system with elastic pendulum attached to the main mass is investigated numerically. It was assumed that the main body is suspended by an element characterized by non-linear elasticity and non-linear damping force and is excited harmonically in the vertical direction. The elastic pendulum characterized also by -linear elasticity and non-linear damping. Solutions for the system response are presented for specific values of the uncoupled normal frequency ratios and the energy transfer between modes of vibrations is observed. Curves of internal resonances for free vibrations and external resonances for exciting force are shown. In this type system one mode of vibration may excite or damp another one, and except different kinds of periodic vibration there may also appear chaotic vibration. Various techniques, including chaos techniques such as bifurcation diagrams and: time histories, phase plane portraits, power spectral densities, Poincare` maps and exponents of Lyapunov, are used in the identification of the responses. These bifurcation diagrams show many sudden qualitative changes, that is, many bifurcations in the chaotic attractor as well as in the periodic orbits. The results show that the system can exhibit various types of motion, from periodic to quasi-periodic to chaotic, and is sensitive to small changes of the system parameters.
Raporty organizacyjne na temat "Non-ergodicity in many body systems"
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Zhu, Jianxin, i Benedikt Fauseweh. Digital quantum simulation of non-equilibrium quantum many-body systems. Office of Scientific and Technical Information (OSTI), maj 2022. http://dx.doi.org/10.2172/1868210.
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DeMille, David, i Karyn LeHur. NON-EQUILIBRIUM DYNAMICS OF MANY-BODY QUANTUM SYSTEMS: FUNDAMENTALS AND NEW FRONTIER. Office of Scientific and Technical Information (OSTI), listopad 2013. http://dx.doi.org/10.2172/1108018.
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Lehtimaki, Susanna, Aisling Reidy, Kassim Nishtar, Sara Darehschori, Andrew Painter i Nina Schwalbe. Independent Review and Investigation Mechanisms to Prevent Future Pandemics: A Proposed Way Forward. United Nations University International Institute for Global Health, kwiecień 2021. http://dx.doi.org/10.37941/rr/2021/1.
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The COVID-19 pandemic has created enormous challenges for national economies, livelihoods, and public services, including health systems. In January 2021, the World Health Organization proposed an international treaty on pandemics to strengthen the political commitment towards global pandemic preparedness, control, and response. The plan is to present a draft treaty to the World Health Assembly in May 2021. To inform the design of a support system for this treaty, we explored existing mechanisms for periodic reviews conducted either by peers or an external group as well as mechanisms for in-country investigations, conducted with or without country consent. Based on our review, we summarized key design principles requisite for review and investigation mechanisms and explain how these could be applied to pandemics preparedness, control, and response in global health. While there is no single global mechanism that could serve as a model in its own right, there is potential to combine aspects of existing mechanisms. A Universal Periodic Review design based on the model of human rights treaties with independent experts as the authorized monitoring body, if made obligatory, could support compliance with a new pandemic treaty. In terms of on-site investigations, the model by the Committee on Prevention of Torture could lend itself to treaty monitoring and outbreak investigations on short notice or unannounced. These mechanisms need to be put in place in accordance with several core interlinked design principles: compliance; accountability; independence; transparency and data sharing; speed; emphasis on capabilities; and incentives. The World Health Organization can incentivize and complement these efforts. It has an essential role in providing countries with technical support and tools to strengthen emergency preparedness and response capacities, including technical support for creating surveillance structures, integrating non-traditional data sources, creating data governance and data sharing standards, and conducting regular monitoring and assessment of preparedness and response capacities.
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Lehtimaki, Susanna, Kassim Nishtar, Aisling Reidy, Sara Darehshori, Andrew Painter i Nina Schwalbe. Independent Review and Investigation Mechanisms to Prevent Future Pandemics: A Proposed Way Forward. United Nations University International Institute for Global Health, maj 2021. http://dx.doi.org/10.37941/pb-f/2021/2.
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Based on the proposal by the European Council, more than 25 heads of state and the World Health Organization (WHO) support development of an international treaty on pandemics, that planned to be negotiated under the auspices of WHO, will be presented to the World Health Assembly in May 2021. Given that the treaty alone is not enough to ensure compliance, triggers for a high-level political response is required. To this end, to inform the design of a support system, we explored institutional mechanismsi with a mandate to review compliance with key international agreements in their signatory countries and conduct independent country investigations in a manner that manages sovereign considerations. Based on our review, there is no single global mechanism that could serve as a model in its own right. There is, however, potential to combine aspects of existing mechanisms to support a strong, enforceable treaty. These aspects include: • Periodic review - based on the model of human rights treaties, with independent experts as the authorized monitoring body to ensure the independence. If made obligatory, the review could support compliance with the treaty. • On-site investigations - based on the model by the Committee on Prevention of Torture according to which visits cannot be blocked by state parties. • Non-negotiable design principles - including accountability; independence; transparency and data sharing; speed; emphasis on capabilities; and incentives. • Technical support - WHO can provide countries with technical assistance, tools, monitoring, and assessment to enhance emergency preparedness and response.
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Gothilf, Yoav, Roger Cone, Berta Levavi-Sivan i Sheenan Harpaz. Genetic manipulations of MC4R for increased growth and feed efficiency in fish. United States Department of Agriculture, styczeń 2016. http://dx.doi.org/10.32747/2016.7600043.bard.
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The hypothalamic melanocortin system plays a central role in the regulation of food consumption and energy homeostasis in mammals. Accordingly, our working hypothesis in this project was that genetic editing of the mc4r gene, encoding Melanocortin Receptor 4 (MC4R), will enhance food consumption, feed efficiency and growth in fish. To test this hypothesis and to assess the utility of mc4r editing for the enhancement of feed efficiency and growth in fish, the following objectives were set: Test the effect of the mc4r-null allele on feeding behavior, growth, metabolism and survival in zebrafish. Generate mc4r-null alleles in tilapia and examine the consequences for growth and survival, feed efficiency and body composition. Generate and examine the effect of naturally-occurring mc4r alleles found in swordfish on feeding behavior, growth and survival in zebrafish. Define the MC4R-mediated and MC4R-independent effects of AgRP by crossing mc4r- null strains with fish lacking AgRP neurons or the agrpgene. Our results in zebrafish did not support our hypothesis. While knockout of the agrpgene or genetic ablation of hypothalamic AgRP neurons led to reduced food intake in zebrafish larvae, knockout (KO) of the mc4r gene not only did not increase the rate of food intake but even reduced it. Since Melanocortin Receptor 3 (MC3R) has also been proposed to be involved in hypothalamic control of food intake, we also tested the effectofmc3r gene KO. Again, contrary to our hypothesis, the rate of food intake decreased. The next step was to generate a double mutant lucking both functional MC3R and MC4R. Again, the double KO exhibited reduced food intake. Thus, the only manipulation within the melanocortin system that affected food intake in consistent with the expected role of the system was seen in zebrafish larvae upon agrpKO. Interestingly, despite the apparent reduced food intake in the larval stage, these fish grow to be of the same size as wildtype fish at the adult stage. Altogether, it seems that there is a compensatory mechanism that overrides the effect of genetic manipulations of the melanocortin system in zebrafish. Under Aim 3, we introduced the Xna1, XnB1l, and XnB2A mutations from the Xiphophorus MC4R alleles into the zebrafish MC4R gene. We hypothesized that these MC4R mutations would act as dominant negative alleles to increase growth by suppressing endogenous MC4R activity. When we examined the activity of the three mutant alleles, we were unable to document any inhibition of a co-transfected wild type MC4R allele, hence we did not introduce these alleles into zebrafish. Since teleost fish possess two agrpgenes we also tested the effect of KO of the agrp2 gene and ablation of the AgRP2 cells. We found that the AgRP2 system does not affect food consumption but may rather be involved in modulating the stress response. To try to apply genetic editing in farmed fish species we turned to tilapia. Injection of exogenous AgRP in adult tilapia induced significant changes in the expression of pituitary hormones. Genetic editing in tilapia is far more complicated than in zebrafish. Nevertheless, we managed to generate one mutant fish carrying a mutation in mc4r. That individual died before reaching sexual maturity. Thus, our attempt to generate an mc4r-mutant tilapia line was almost successful and indicate out non-obvious capability to generate mutant tilapia.