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Mon

29
Apr

Seminars

Period doubling as an early warning signal for desertification

Omer Tzuk
Seminars
Period doubling as an early warning signal for desertification
Omer Tzuk
Edna and K.B. Weissman Building of Physical Sciences

Room Room A 14:15 The predictions for a warmer and drier climate and for increased likelihood of climate extremes raise high concerns about the possible collapse of dryland ecosystems, and about the formation of new drylands where native species are less tolerant to water stress. Using a dryland-vegetation model for plant species that display different tradeoffs between fast growth and tolerance to droughts, we find that ecosystems subjected to strong seasonal variability, typical for drylands, exhibit a period-doubling route to chaos that results in early collapse to bare soil. We further find that fast-growing plants go through period doubling sooner and span wider chaotic ranges than stress-tolerant plants. We propose the detection of period-doubling signatures in power spectra as early indicators of ecosystem collapse that outperform existing indicators in their ability to warn against climate extremes and capture the heightened vulnerability of newly-formed drylands.

Room Room A 14:15 The predictions for a warmer and drier climate and for increased likelihood of climate extremes raise high concerns about the possible collapse of dryland ecosystems, and about the formation of new drylands where native species are less tolerant to water stress. Using a dryland-vegetation model for plant species that display different tradeoffs between fast growth and tolerance to droughts, we find that ecosystems subjected to strong seasonal variability, typical for drylands, exhibit a period-doubling route to chaos that results in early collapse to bare soil. We further find that fast-growing plants go through period doubling sooner and span wider chaotic ranges than stress-tolerant plants. We propose the detection of period-doubling signatures in power spectra as early indicators of ecosystem collapse that outperform existing indicators in their ability to warn against climate extremes and capture the heightened vulnerability of newly-formed drylands.

Mon

15
Apr

Seminars

Growth dynamics and complexity of national economies in the

A.L. Stella
Seminars
Growth dynamics and complexity of national economies in the
A.L. Stella
Edna and K.B. Weissman Building of Physical Sciences

Room Room A 14:15 Methods of statistical physics allow to explore the quantitative nexus among economic growth of a country, diversity of its productions, and evolution in time of its export basket(*). A stochastic model of evolution, calibrated on data for 1238 exports from 223 countries in 21 years, enables counterfactual analyses based on estimates of the part of growth due to resource transfers between different productions. Original use of the Boltzmann-Shannon entropy function leads to the construction of consistent measures of the efficiency of national economies and of the specialization of productions. Comparisons with dynamical and GDP pc data lead to clear distinctions among developed, developing, underdeveloped and risky countries. Perspective applications of the entropic measures in other fields (ecology, microbiology,..) where diversity has to be estimated from bipartite networks will be shortly outlined. (Work in collaboration with G. Teza, University of Padova, and M. Caraglio, Katholieke Universiteit Leuven.)

Room Room A 14:15 Methods of statistical physics allow to explore the quantitative nexus among economic growth of a country, diversity of its productions, and evolution in time of its export basket(*). A stochastic model of evolution, calibrated on data for 1238 exports from 223 countries in 21 years, enables counterfactual analyses based on estimates of the part of growth due to resource transfers between different productions. Original use of the Boltzmann-Shannon entropy function leads to the construction of consistent measures of the efficiency of national economies and of the specialization of productions. Comparisons with dynamical and GDP pc data lead to clear distinctions among developed, developing, underdeveloped and risky countries. Perspective applications of the entropic measures in other fields (ecology, microbiology,..) where diversity has to be estimated from bipartite networks will be shortly outlined. (Work in collaboration with G. Teza, University of Padova, and M. Caraglio, Katholieke Universiteit Leuven.)

Mon

08
Apr

Seminars

Emergence and stability of a Brownian motor

Alex Feigel
Seminars
Emergence and stability of a Brownian motor
Alex Feigel
Edna and K.B. Weissman Building of Physical Sciences

Room Room A 14:15 A Brownian motor rectifies thermal noise and creates useful work. Here we address how this machine can emerge without predefined energy minimum in a system out of thermal equilibrium. Intuitively, Brownian motor as any artificial or biological machine should degrade with time. I will show that on contrary, a system with multiple degrees of freedom out of thermal equilibrium can be stable at a state that generates useful work. It is demonstrated with the help of ab initio analysis of a modified Feynman-Smoluchowski ratchet with two degrees of freedom. Out of thermal equilibrium, an environment imposes effective mechanical forces on nano-fabricated devices as well as on microscopic chemical or biological systems. Thus out of thermal equilibrium environment can enforce a specific steady state on the system by creating effective potentials in otherwise homogeneous configuration space. I present an ab initio path from the elastic scattering of a single gas particle by a mechanical system to the transition rate probability between the states of the system with multiple degrees of freedom, together with the corresponding Masters-Boltzmann equation and the average velocities of the system’s degrees of freedom as functions of the macroscopic parameters of the out-of-equilibrium environment. It results in Onsager relations that include the influence of the different degrees of freedom on each other. An interesting finding is that some of these forces persist even in a single temperature environment if the thermodynamic limit does not hold. In addition, the spatial asymmetry of the system’s stable state, together with the corresponding directed motion, may possess preferred chiral symmetry.

Room Room A 14:15 A Brownian motor rectifies thermal noise and creates useful work. Here we address how this machine can emerge without predefined energy minimum in a system out of thermal equilibrium. Intuitively, Brownian motor as any artificial or biological machine should degrade with time. I will show that on contrary, a system with multiple degrees of freedom out of thermal equilibrium can be stable at a state that generates useful work. It is demonstrated with the help of ab initio analysis of a modified Feynman-Smoluchowski ratchet with two degrees of freedom. Out of thermal equilibrium, an environment imposes effective mechanical forces on nano-fabricated devices as well as on microscopic chemical or biological systems. Thus out of thermal equilibrium environment can enforce a specific steady state on the system by creating effective potentials in otherwise homogeneous configuration space. I present an ab initio path from the elastic scattering of a single gas particle by a mechanical system to the transition rate probability between the states of the system with multiple degrees of freedom, together with the corresponding Masters-Boltzmann equation and the average velocities of the system’s degrees of freedom as functions of the macroscopic parameters of the out-of-equilibrium environment. It results in Onsager relations that include the influence of the different degrees of freedom on each other. An interesting finding is that some of these forces persist even in a single temperature environment if the thermodynamic limit does not hold. In addition, the spatial asymmetry of the system’s stable state, together with the corresponding directed motion, may possess preferred chiral symmetry.

Mon

25
Mar

Seminars

Hyperuniformity of driven suspensions

Haim Diamant
Seminars
Hyperuniformity of driven suspensions
Haim Diamant
Edna and K.B. Weissman Building of Physical Sciences

Room Room A 14:15 An arrangement of particles is said to be "hyperuniform" if its density fluctuations over large distances are strongly suppressed relative to a random configuration. Crystals, for example, are hyperuniform. Recently, several disordered materials have been found to be hyperuniform. Examples are sheared suspensions and emulsions, and, possibly, random close packings of particles. We show that externally driven particles in a liquid suspension (as in sedimentation, for example) self-organize hyperuniformly in certain directions relative to the external force. This dynamic hyperuniformity arises from the long-range coupling, induced by the force and carried by the fluid, between the concentration of particles and their velocity field. We obtain the general requirements, which the coupling should satisfy in order for this phenomenon to occur. Under other conditions (e.g., for certain particle shapes), the coupling can lead to the opposite effect -- enhancement of density fluctuations and instability. We confirm these analytical results in a simple two-dimensional simulation.

Room Room A 14:15 An arrangement of particles is said to be "hyperuniform" if its density fluctuations over large distances are strongly suppressed relative to a random configuration. Crystals, for example, are hyperuniform. Recently, several disordered materials have been found to be hyperuniform. Examples are sheared suspensions and emulsions, and, possibly, random close packings of particles. We show that externally driven particles in a liquid suspension (as in sedimentation, for example) self-organize hyperuniformly in certain directions relative to the external force. This dynamic hyperuniformity arises from the long-range coupling, induced by the force and carried by the fluid, between the concentration of particles and their velocity field. We obtain the general requirements, which the coupling should satisfy in order for this phenomenon to occur. Under other conditions (e.g., for certain particle shapes), the coupling can lead to the opposite effect -- enhancement of density fluctuations and instability. We confirm these analytical results in a simple two-dimensional simulation.

Mon

04
Feb

Seminars

Towards a new understanding of disorder and dissipation in solids

Alessio Zaccone
Seminars
Towards a new understanding of disorder and dissipation in solids
Alessio Zaccone
Edna and K.B. Weissman Building of Physical Sciences

Room Room A 14:15 Solid-state theory has been formulated in the 20th century on the assumptions of regular crystalline lattices where linear dynamics holds at both classical and quantum levels, while dissipative effects are taken into account to perturbative order. While considerable success has been achieved in the further understanding of disorder effects on the electronic properties of solids, the same is not true for the thermal, vibrational and mechanical properties due to the difficulty of reformulating the whole body of lattice dynamics in a non-perturbative way for disordered systems. I will present a formulation of lattice dynamics extended (in a non-perturbative way) to disordered systems, called Nonaffine Lattice Dynamics (NALD), successfully tested on different systems [1-3]. I will then consider the effect of viscous dissipation on the lattice dynamics of crystalline solids and show how dissipation can lead, in perfectly ordered crystals, to effects very similar to disorder-induced effects in glasses. Theory can explain all these surprising effects in perfect crystals as a result of anharmonic damping inducing diffusive modes that compete with propagating modes [4], and also predicts similar effects resulting from low-lying soft optical phonons (experimentally confirmed). This framework may lead to a new quantitative connection between lattice/atomic parameters, electron-phonon coupling and the Tc of superconductors with the possibility, in future work, of rationalizing a variety of experimental data and to provide a more quantitative (less empirical) understanding of how Tc can be varied in conventional and perhaps also more exotic superconductors. [1] A. Zaccone and E. Scossa-Romano, Phys. Rev. B 83, 184205 (2011). [2] R. Milkus and A. Zaccone, Phys. Rev. B 93, 094204 (2016). [3] V.V. Palyulin, C. Ness, R. Milkus, R.M. Elder, T.W. Sirk, A. Zaccone, Soft Matter 14, 8475 (2018). [4] M. Baggioli and A. Zaccone, arXiv:1810.09516v1 [cond-mat.soft].

Room Room A 14:15 Solid-state theory has been formulated in the 20th century on the assumptions of regular crystalline lattices where linear dynamics holds at both classical and quantum levels, while dissipative effects are taken into account to perturbative order. While considerable success has been achieved in the further understanding of disorder effects on the electronic properties of solids, the same is not true for the thermal, vibrational and mechanical properties due to the difficulty of reformulating the whole body of lattice dynamics in a non-perturbative way for disordered systems. I will present a formulation of lattice dynamics extended (in a non-perturbative way) to disordered systems, called Nonaffine Lattice Dynamics (NALD), successfully tested on different systems [1-3]. I will then consider the effect of viscous dissipation on the lattice dynamics of crystalline solids and show how dissipation can lead, in perfectly ordered crystals, to effects very similar to disorder-induced effects in glasses. Theory can explain all these surprising effects in perfect crystals as a result of anharmonic damping inducing diffusive modes that compete with propagating modes [4], and also predicts similar effects resulting from low-lying soft optical phonons (experimentally confirmed). This framework may lead to a new quantitative connection between lattice/atomic parameters, electron-phonon coupling and the Tc of superconductors with the possibility, in future work, of rationalizing a variety of experimental data and to provide a more quantitative (less empirical) understanding of how Tc can be varied in conventional and perhaps also more exotic superconductors. [1] A. Zaccone and E. Scossa-Romano, Phys. Rev. B 83, 184205 (2011). [2] R. Milkus and A. Zaccone, Phys. Rev. B 93, 094204 (2016). [3] V.V. Palyulin, C. Ness, R. Milkus, R.M. Elder, T.W. Sirk, A. Zaccone, Soft Matter 14, 8475 (2018). [4] M. Baggioli and A. Zaccone, arXiv:1810.09516v1 [cond-mat.soft].

Mon

04
Feb

Seminars

Towards a new understanding of disorder and dissipation in solids

Alessio Zaccone
Seminars
Towards a new understanding of disorder and dissipation in solids
Alessio Zaccone
Edna and K.B. Weissman Building of Physical Sciences

Room Room A 14:15 Solid-state theory has been formulated in the 20th century on the assumptions of regular crystalline lattices where linear dynamics holds at both classical and quantum levels, while dissipative effects are taken into account to perturbative order. While considerable success has been achieved in the further understanding of disorder effects on the electronic properties of solids, the same is not true for the thermal, vibrational and mechanical properties due to the difficulty of reformulating the whole body of lattice dynamics in a non-perturbative way for disordered systems. I will present a formulation of lattice dynamics extended (in a non-perturbative way) to disordered systems, called Nonaffine Lattice Dynamics (NALD), successfully tested on different systems [1-3]. I will then consider the effect of viscous dissipation on the lattice dynamics of crystalline solids and show how dissipation can lead, in perfectly ordered crystals, to effects very similar to disorder-induced effects in glasses. Theory can explain all these surprising effects in perfect crystals as a result of anharmonic damping inducing diffusive modes that compete with propagating modes [4], and also predicts similar effects resulting from low-lying soft optical phonons (experimentally confirmed). This framework may lead to a new quantitative connection between lattice/atomic parameters, electron-phonon coupling and the Tc of superconductors with the possibility, in future work, of rationalizing a variety of experimental data and to provide a more quantitative (less empirical) understanding of how Tc can be varied in conventional and perhaps also more exotic superconductors. [1] A. Zaccone and E. Scossa-Romano, Phys. Rev. B 83, 184205 (2011). [2] R. Milkus and A. Zaccone, Phys. Rev. B 93, 094204 (2016). [3] V.V. Palyulin, C. Ness, R. Milkus, R.M. Elder, T.W. Sirk, A. Zaccone, Soft Matter 14, 8475 (2018). [4] M. Baggioli and A. Zaccone, arXiv:1810.09516v1 [cond-mat.soft].

Room Room A 14:15 Solid-state theory has been formulated in the 20th century on the assumptions of regular crystalline lattices where linear dynamics holds at both classical and quantum levels, while dissipative effects are taken into account to perturbative order. While considerable success has been achieved in the further understanding of disorder effects on the electronic properties of solids, the same is not true for the thermal, vibrational and mechanical properties due to the difficulty of reformulating the whole body of lattice dynamics in a non-perturbative way for disordered systems. I will present a formulation of lattice dynamics extended (in a non-perturbative way) to disordered systems, called Nonaffine Lattice Dynamics (NALD), successfully tested on different systems [1-3]. I will then consider the effect of viscous dissipation on the lattice dynamics of crystalline solids and show how dissipation can lead, in perfectly ordered crystals, to effects very similar to disorder-induced effects in glasses. Theory can explain all these surprising effects in perfect crystals as a result of anharmonic damping inducing diffusive modes that compete with propagating modes [4], and also predicts similar effects resulting from low-lying soft optical phonons (experimentally confirmed). This framework may lead to a new quantitative connection between lattice/atomic parameters, electron-phonon coupling and the Tc of superconductors with the possibility, in future work, of rationalizing a variety of experimental data and to provide a more quantitative (less empirical) understanding of how Tc can be varied in conventional and perhaps also more exotic superconductors. [1] A. Zaccone and E. Scossa-Romano, Phys. Rev. B 83, 184205 (2011). [2] R. Milkus and A. Zaccone, Phys. Rev. B 93, 094204 (2016). [3] V.V. Palyulin, C. Ness, R. Milkus, R.M. Elder, T.W. Sirk, A. Zaccone, Soft Matter 14, 8475 (2018). [4] M. Baggioli and A. Zaccone, arXiv:1810.09516v1 [cond-mat.soft].

Mon

28
Jan

Seminars

Stochastic pulse dynamics in a laser cavity

Omri Gat
Seminars
Stochastic pulse dynamics in a laser cavity
Omri Gat
Edna and K.B. Weissman Building of Physical Sciences

Room Room A 14:15 The interplay of nonlinear absorption and noise in mode locked lasers turns the process of pulse formation into a non-equilibrium phase transition. The pulses can be regarded as liquid drops immersed in vapor of low intensity quasi-continuum light. The pulses have well-defined shape and amplitude, and diffuse by interaction with the noisy continuum. Subtle effects of gain dynamics bias the diffusion, inducing a long-range noise-mediated interaction that is reminiscent of the Casimir effect in quantum electrodynamics. The noise-mediated interaction are shown to underpin the spectacular complex pulse motion in the ‘soliton rain’ laser operating regime.

Room Room A 14:15 The interplay of nonlinear absorption and noise in mode locked lasers turns the process of pulse formation into a non-equilibrium phase transition. The pulses can be regarded as liquid drops immersed in vapor of low intensity quasi-continuum light. The pulses have well-defined shape and amplitude, and diffuse by interaction with the noisy continuum. Subtle effects of gain dynamics bias the diffusion, inducing a long-range noise-mediated interaction that is reminiscent of the Casimir effect in quantum electrodynamics. The noise-mediated interaction are shown to underpin the spectacular complex pulse motion in the ‘soliton rain’ laser operating regime.

Mon

14
Jan

Seminars

Transport and condensation in the quantum-classical limit of open quantum systems

Ohad Shpilberg
Seminars
Transport and condensation in the quantum-classical limit of open quantum systems
Ohad Shpilberg
Edna and K.B. Weissman Building of Physical Sciences

Room Room A 14:15 The Lindblad equation allows to explore general properties of open quantum systems. Whenever strong decoherence processes are present, one expects the system to become classical. Namely, the evolution of the surviving diagonal terms of the density matrix is Markovian. Surprisingly enough, many interesting aspects of the quantum system can be inferred from the classical limit. Among which we will explore some transport properties as well as a condensation transition for interacting quantum particles. Moreover, we will be interested in the quantum corrections to Fick’s law in diffusive systems

Room Room A 14:15 The Lindblad equation allows to explore general properties of open quantum systems. Whenever strong decoherence processes are present, one expects the system to become classical. Namely, the evolution of the surviving diagonal terms of the density matrix is Markovian. Surprisingly enough, many interesting aspects of the quantum system can be inferred from the classical limit. Among which we will explore some transport properties as well as a condensation transition for interacting quantum particles. Moreover, we will be interested in the quantum corrections to Fick’s law in diffusive systems

Mon

07
Jan

Seminars

Universal features in disordered solids: Implications for directed aging and the creation of non-linear metamaterials

Daniel Hexner
Seminars
Universal features in disordered solids: Implications for directed aging and the creation of non-linear metamaterials
Daniel Hexner
Edna and K.B. Weissman Building of Physical Sciences

Room Auditorium 14:15 The most obvious and distinctive feature of an amorphous solid is its heterogeneous microscopic structure. A central issue is how such disorder governs the elastic properties of an amorphous solid so that it has different behavior from its crystalline counterpart. I will show how such disorder on the microscale determines the elastic properties on long length scales. This theoretical approach ultimately allows us to control a material’s elastic properties and to understand how a material ages and stores memories. I start by studying the change in an amorphous solid’s elastic properties upon the removal of a single bond. I show that the change in moduli, which has a broad and universal shape, is uncorrelated for different imposed strains. Thus, by selectively removing a small number of bonds, the precise global and local elastic behavior of the solid can be controlled. This in turn suggests that small changes in bond properties, which occur naturally as a solid ages, can dramatically alter the solid’s elastic response; the history of imposed strains is encoded in the non-linear response and the aging process, usually considered to be detrimental, can be harnessed to design materials with novel desired properties.

Room Auditorium 14:15 The most obvious and distinctive feature of an amorphous solid is its heterogeneous microscopic structure. A central issue is how such disorder governs the elastic properties of an amorphous solid so that it has different behavior from its crystalline counterpart. I will show how such disorder on the microscale determines the elastic properties on long length scales. This theoretical approach ultimately allows us to control a material’s elastic properties and to understand how a material ages and stores memories. I start by studying the change in an amorphous solid’s elastic properties upon the removal of a single bond. I show that the change in moduli, which has a broad and universal shape, is uncorrelated for different imposed strains. Thus, by selectively removing a small number of bonds, the precise global and local elastic behavior of the solid can be controlled. This in turn suggests that small changes in bond properties, which occur naturally as a solid ages, can dramatically alter the solid’s elastic response; the history of imposed strains is encoded in the non-linear response and the aging process, usually considered to be detrimental, can be harnessed to design materials with novel desired properties.

Mon

10
Dec

Seminars

Against the flow: a colloidal Maxwell demon

Saar Rahav
Seminars
Against the flow: a colloidal Maxwell demon
Saar Rahav
Edna and K.B. Weissman Building of Physical Sciences

Room Room A 14:15 The connection between information and thermodynamics has been fascinating scientists ever since Maxwell envisioned his celebrated demon. Technological progress now allows realizing in the lab this celebrated idea that was originally conceived as a thought experiment. Indeed, recent years have seen experimental realizations of several types of information engines. In this talk, I will describe a realization of Maxwell’s demon in which a colloidal particle is “pushed” against a fluid flow. Beyond its appealing simplicity, our experimental setup also exhibits an almost full conversion of information to useful work, since it allows to control how much work is applied directly on the particle. Another feature of the setup is a frequent repeated measurement of the particle location, resulting in nontrivial correlations between the outcomes of consecutive measurements. The effect of these correlations on the useful information acquired is investigated with the help of computer simulations. · Joint work with Tamir Admon and Yael Roichman

Room Room A 14:15 The connection between information and thermodynamics has been fascinating scientists ever since Maxwell envisioned his celebrated demon. Technological progress now allows realizing in the lab this celebrated idea that was originally conceived as a thought experiment. Indeed, recent years have seen experimental realizations of several types of information engines. In this talk, I will describe a realization of Maxwell’s demon in which a colloidal particle is “pushed” against a fluid flow. Beyond its appealing simplicity, our experimental setup also exhibits an almost full conversion of information to useful work, since it allows to control how much work is applied directly on the particle. Another feature of the setup is a frequent repeated measurement of the particle location, resulting in nontrivial correlations between the outcomes of consecutive measurements. The effect of these correlations on the useful information acquired is investigated with the help of computer simulations. · Joint work with Tamir Admon and Yael Roichman