Showing papers on "Dissipation published in 2012"
TL;DR: Efficiency and, in particular, efficiency at maximum power can be discussed systematically beyond the linear response regime for two classes of molecular machines, isothermal ones such as molecular motors, and heat engines such as thermoelectric devices, using a common framework based on a cycle decomposition of entropy production.
Abstract: Stochastic thermodynamics as reviewed here systematically provides a framework for extending the notions of classical thermodynamics such as work, heat and entropy production to the level of individual trajectories of well-defined non-equilibrium ensembles. It applies whenever a non-equilibrium process is still coupled to one (or several) heat bath(s) of constant temperature. Paradigmatic systems are single colloidal particles in time-dependent laser traps, polymers in external flow, enzymes and molecular motors in single molecule assays, small biochemical networks and thermoelectric devices involving single electron transport. For such systems, a first-law like energy balance can be identified along fluctuating trajectories. For a basic Markovian dynamics implemented either on the continuum level with Langevin equations or on a discrete set of states as a master equation, thermodynamic consistency imposes a local-detailed balance constraint on noise and rates, respectively. Various integral and detailed fluctuation theorems, which are derived here in a unifying approach from one master theorem, constrain the probability distributions for work, heat and entropy production depending on the nature of the system and the choice of non-equilibrium conditions. For non-equilibrium steady states, particularly strong results hold like a generalized fluctuation–dissipation theorem involving entropy production. Ramifications and applications of these concepts include optimal driving between specified states in finite time, the role of measurement-based feedback processes and the relation between dissipation and irreversibility. Efficiency and, in particular, efficiency at maximum power can be discussed systematically beyond the linear response regime for two classes of molecular machines, isothermal ones such as molecular motors, and heat engines such as thermoelectric devices, using a common framework based on a cycle decomposition of entropy production. (Some figures may appear in colour only in the online journal) This article was invited by Erwin Frey.
2,834 citations
TL;DR: Graphene is a two-dimensional (2D) material with over 100-fold anisotropy of heat flow between the in-plane and out-of-plane directions as mentioned in this paper.
Abstract: Graphene is a two-dimensional (2D) material with over 100-fold anisotropy of heat flow between the in-plane and out-of-plane directions. High in-plane thermal conductivity is due to covalent sp2 bonding between carbon atoms, whereas out-of-plane heat flow is limited by weak van der Waals coupling. Herein, we review the thermal properties of graphene, including its specific heat and thermal conductivity (from diffusive to ballistic limits) and the influence of substrates, defects, and other atomic modifications. We also highlight practical applications in which the thermal properties of graphene play a role. For instance, graphene transistors and interconnects benefit from the high in-plane thermal conductivity, up to a certain channel length. However, weak thermal coupling with substrates implies that interfaces and contacts remain significant dissipation bottlenecks. Heat flow in graphene or graphene composites could also be tunable through a variety of means, including phonon scattering by substrates, edges, or interfaces. Ultimately, the unusual thermal properties of graphene stem from its 2D nature, forming a rich playground for new discoveries of heat-flow physics and potentially leading to novel thermal management applications.
1,091 citations
TL;DR: A friction tensor is derived that induces a Riemannian manifold on the space of thermodynamic states that controls the dissipation of finite-time transformations, and bestows optimal protocols with many useful properties within the linear-response regime.
Abstract: A fundamental problem in modern thermodynamics is how a molecular-scale machine performs useful work, while operating away from thermal equilibrium without excessive dissipation. To this end, we derive a friction tensor that induces a Riemannian manifold on the space of thermodynamic states. Within the linear-response regime, this metric structure controls the dissipation of finite-time transformations, and bestows optimal protocols with many useful properties. We discuss the connection to the existing thermodynamic length formalism, and demonstrate the utility of this metric by solving for optimal control parameter protocols in a simple nonequilibrium model.
299 citations
TL;DR: This work gives a systematic method for discretizing Hamiltonian partial differential equations (PDEs) with constant symplectic structure, while preserving their energy exactly.
268 citations
TL;DR: In this article, the authors describe the wave dissipation over a vegetation field by the implementation of the Mendez and Losada formulation in a full spectrum model SWAN, with an extension to include a vertical layer schematization for the vegetation.
223 citations
TL;DR: In this article, the authors give a 2x2 treatment for the creation and evolution of spectral distortions in the CMB, consistently including the effect of polarization and photon mixing in the free streaming regime.
Abstract: Silk damping of primordial small scale perturbations in the photon-baryon fluid due to di ffusion of photons inevitably creates spectral distortions in the CMB. With the proposed CMB experiment PIXIE it might become possible to measure these distortions and thereby constrain the primordial power spectrum at comoving wavenumbers 50 Mpc −1 . k. 10 4 Mpc −1 . Since primordial fluctuations on these scales are completel y erased by Silk damping, these distortions may provide the only way to shed light on otherwise unobservable aspects of inflationary physics. A consistent treatment of the primordial dissipation problem requires going to second order in perturbation theory, while thermalizati on of these distortions necessitates consideration of second order in Compton scattering energy transfer. Here we give a full 2x2 treatment for creation and evolution of spectral distortio ns due to the acoustic dissipation process, consistently including the effect of polarization and photon mixing in the free streaming regime. We show that 1/3 of the total energy (9/4 larger than previous estimate) stored in small scale temperature perturbations imprints observable spectral distortions, while the remaining 2/3 only raise the average CMB temperature, an effect that is unobservable. At high redshift dissipation is mainly mediated through the quadrupole anisotropies, while after recombination peculiar motions are most important. During recombination the damping of the higher multipoles is also significant. We compute the average disto rtion for several examples using CosmoTherm, analyzing their dependence on parameters of the primordial power spectrum. For one of the best fit WMAP7 cosmologies, with nS = 1.027 and nrun =−0.034, the cooling of baryonic matter practically compensates the heating from acoustic dissipation in the µ-era. We also derive the evolution equations in first order pe rturbation theory for the spectral distortions. These first order anisotropies of spectral dis tortions may dominate over the corresponding second order contributions from recombination if an average fractional distortion of ∼ 10 −5 is already present before recombination.
202 citations
TL;DR: In this article, high-resolution kinetic simulations of collisionless plasma driven by shear show the development of turbulence characterized by dynamic coherent sheet-like current density structures spanning a range of scales down to electron scales.
Abstract: High resolution kinetic simulations of collisionless plasma driven by shear show the development of turbulence characterized by dynamic coherent sheetlike current density structures spanning a range of scales down to electron scales. We present evidence that these structures are sites for heating and dissipation, and that stronger current structures signify higher dissipation rates. Evidently, kinetic scale plasma, like magnetohydrodynamics, becomes intermittent due to current sheet formation, leading to the expectation that heating and dissipation in astrophysical and space plasmas may be highly nonuniform and patchy.
197 citations
TL;DR: In this article, an overview of recent advances that have been achieved in understanding the basic physics of friction and energy dissipation in molecularly thin adsorbed films and the associated impact on friction at microscopic and macroscopic length scales.
Abstract: This review provides an overview of recent advances that have been achieved in understanding the basic physics of friction and energy dissipation in molecularly thin adsorbed films and the associated impact on friction at microscopic and macroscopic length scales. Topics covered include a historical overview of the fundamental understanding of macroscopic friction, theoretical treatments of phononic and electronic energy dissipation mechanisms in thin films, and current experimental methods capable of probing such phenomena. Measurements performed on adsorbates sliding in unconfined geometries with the quartz crystal microbalance technique receive particular attention. The final sections review the experimental literature of how measurements of sliding friction in thin films reveal energy dissipation mechanisms and how the results can be linked to film-spreading behavior, lubrication, film phase transitions, superconductivity-dependent friction, and microelectromechanical systems applications. Materials s...
190 citations
01 Sep 2012
TL;DR: In this article, the authors generalized the Wasserstein metric to reaction-diffusion systems with reversible mass-action kinetic and showed that this gradient structure can be generalized to systems including electrostatic interactions and correct energy balance via coupling to the heat equation.
Abstract: In recent years the theory of the Wasserstein metric has opened up new treatments of diffusion equations as gradient systems, where the free energy or entropy take the role of the driving functional and where the space is equipped with the Wasserstein metric. We show on the formal level that this gradient structure can be generalized to reaction–diffusion systems with reversible mass-action kinetic. The metric is constructed using the dual dissipation potential, which is a quadratic functional of all chemical potentials including the mobilities as well as the reaction kinetics. The metric structure is obtained by Legendre transform from the dual dissipation potential.The same ideas extend to systems including electrostatic interactions or a correct energy balance via coupling to the heat equation. We show this by treating the semiconductor equations involving the electron and hole densities, the electrostatic potential, and the temperature. Thus, the models in Albinus et al (2002 Nonlinearity 15 367–83), which stimulated this work, have a gradient structure.
190 citations
TL;DR: In this paper, the authors investigate the long time behavior of the critical mass Patlak-Keller-Segel equation and find basins of attraction for them using an entropy functional.
174 citations
TL;DR: In this article, a new wind-input and wind-breaking dissipation for phase-averaged spectral models of wind-generated surface waves is presented, based on recent field observations in Lake George, New South Wales, Australia, at moderate-to-strong wind-wave conditions.
Abstract: A new wind-input and wind-breaking dissipation for phase-averaged spectral models of wind-generated surface waves is presented. Both are based on recent field observations in Lake George, New South Wales, Australia, at moderate-to-strong wind-wave conditions. The respective parameterizations are built on quantitative measurements and incorporate new observed physical features, which until very recently were missing in source terms employed in operational models. Two novel features of the wind-input source functionarethosethataccountfortheeffectsoffullairflowseparation(andthereforerelativereductionofthe input at strongwindforcing) andfor nonlinear behaviorofthis term. Thebreakingtermalsoincorporatestwo new features evident from observational studies; the dissipation consists of two parts—a strictly local dissipation term and a cumulative term—and there is a threshold for wave breaking, below which no breaking occurs. Four variants of the dissipation term are selected for evaluation, with minimal calibration to each. These fourmodels areevaluatedusing simplecalculationsherein.Resultsaregenerallyfavorable.Evaluation for more complex situations will be addressed in a forthcoming paper.
TL;DR: In this paper, the authors provide a framework for extending the notions of classical thermodynamics like work, heat and entropy production to the level of individual trajectories of well-defined non-equilibrium ensembles.
Abstract: Stochastic thermodynamics as reviewed here systematically provides a framework for extending the notions of classical thermodynamics like work, heat and entropy production to the level of individual trajectories of well-defined non-equilibrium ensembles. It applies whenever a non-equilibrium process is still coupled to one (or several) heat bath(s) of constant temperature. Paradigmatic systems are single colloidal particles in time-dependent laser traps, polymers in external flow, enzymes and molecular motors in single molecule assays, small biochemical networks and thermoelectric devices involving single electron transport. For such systems, a first-law like energy balance can be identified along fluctuating trajectories. Various integral and detailed fluctuation theorems, which are derived here in a unifying approach from one master theorem, constrain the probability distributions for work, heat and entropy production depending on the nature of the system and the choice of non-equilibrium conditions. For non-equilibrium steady states, particularly strong results hold like a generalized fluctuation-dissipation theorem involving entropy production. Ramifications and applications of these concepts include optimal driving between specified states in finite time, the role of measurement-based feedback processes and the relation between dissipation and irreversibility. Efficiency and, in particular, efficiency at maximum power, can be discussed systematically beyond the linear response regime for two classes of molecular machines, isothermal ones like molecular motors, and heat engines like thermoelectric devices, using a common framework based on a cycle decomposition of entropy production.
TL;DR: In this paper, a suite of three-dimensional circulation models with dual-band radiative transfer, exploring a relevant range of irradiation temperatures, both with and without temperature inversions, is presented.
Abstract: Hot Jupiters, due to the proximity to their parent stars, are subjected to a strong irradiating flux that governs their radiative and dynamical properties We compute a suite of three-dimensional circulation models with dual-band radiative transfer, exploring a relevant range of irradiation temperatures, both with and without temperature inversions We find that, for irradiation temperatures T{sub irr} {approx}< 2000 K, heat redistribution is very efficient, producing comparable dayside and nightside fluxes For T{sub irr} Almost-Equal-To 2200-2400 K, the redistribution starts to break down, resulting in a high day-night flux contrast Our simulations indicate that the efficiency of redistribution is primarily governed by the ratio of advective to radiative timescales Models with temperature inversions display a higher day-night contrast due to the deposition of starlight at higher altitudes, but we find this opacity-driven effect to be secondary compared to the effects of irradiation The hotspot offset from the substellar point is large when insolation is weak and redistribution is efficient, and decreases as redistribution breaks down The atmospheric flow can be potentially subjected to the Kelvin-Helmholtz instability (as indicated by the Richardson number) only in the uppermost layers, with a depth that penetrates down to pressures of a few millibars atmore » most Shocks penetrate deeper, down to several bars in the hottest model Ohmic dissipation generally occurs down to deeper levels than shock dissipation (to tens of bars), but the penetration depth varies with the atmospheric opacity The total dissipated Ohmic power increases steeply with the strength of the irradiating flux and the dissipation depth recedes into the atmosphere, favoring radius inflation in the most irradiated objects A survey of the existing data, as well as the inferences made from them, reveals that our results are broadly consistent with the observational trends« less
TL;DR: In this article, the authors estimate energy dissipation rates during ocean wave breaking from high-resolution profiles of turbulent velocities collected within 1 m of the surface using a pulse-coherent acoustic Doppler sonar.
Abstract: Energy dissipation rates during ocean wave breaking are estimated from high-resolution profiles of turbulent velocities collected within 1 m of the surface. The velocity profiles are obtained from a pulse-coherent acoustic Doppler sonar on a wave-following platform, termed a Surface Wave Instrument Float with Tracking (SWIFT), and the dissipation rates are estimated from the structure function of the velocity profiles. The purpose of the SWIFT is to maintain a constant range to the time-varying surface and thereby observe the turbulence in breaking crests (i.e., above the mean still water level). The Lagrangian quality is also useful to prefilter wave orbital motions and mean currents from the velocity measurements, which are limited in magnitude by phase wrapping in the coherent Doppler processing. Field testing and examples from both offshore whitecaps and nearshore surf breaking are presented. Dissipation rates are elevated (up to 10−3 m2 s−3) during strong breaking conditions, which are confir...
TL;DR: In this article, a moment hierarchy is developed to describe the transport of the total energy density in fluctuations, the cross-helicity, the energy difference, and correlation lengths corresponding to forward-and backward-propagating modes.
Abstract: Numerous problems in space physics and astrophysics require a detailed understanding of the transport and dissipation of low-frequency turbulence in an expanding magnetized flow. We employ a scale-separated decomposition of the incompressible MHD equations (based on an Elssasser description) and develop a moment hierarchy to describe the transport of the total energy density in fluctuations, the cross-helicity, the energy difference, and correlation lengths corresponding to forward- and backward-propagating modes and to the energy difference. The dissipation terms for the various transport equations are derived. One-point closure schemes are utilized. The technical elements of this work that distinguish it from previous studies are (1) the inclusion of the large-scale background inhomogeneous Alfvenic velocity V A at a level of detail greater than before, (2) the introduction of a tractable slow timescale closure to eliminate high-frequency interference terms that is likely to prove a useful approximation for practical problems related to the transport of turbulence in an inhomogeneous flow such as the solar wind or solar corona, and finally, (3) we develop a simplified phenomenology for the energy difference or equivalently residual energy that may be useful for practical applications. This yields a coupled system of six equations that describes the transport of turbulence in inhomogeneous sub-Alfvenic and super-Alfvenic flows. The turbulence transport equations are quasi-linear in their spatial evolution operators and nonlinear in the dissipation terms, making the model equations relatively tractable to analysis.
TL;DR: In this article, a novel implementation of smoothed particle hydrodynamics that uses the spatial derivative of the velocity divergence as a higher order dissipation switch is presented, which detects flow convergence before it occurs.
Abstract: We present a novel implementation of smoothed particle hydrodynamics that uses the spatial derivative of the velocity divergence as a higher order dissipation switch. Our switch – which is second order accurate – detects flow convergence before it occurs. If particle trajectories are going to cross, we switch on the usual SPH artificial viscosity, as well as conservative dissipation in all advected fluid quantities (e.g. the entropy). The viscosity and dissipation terms (that are numerical errors) are designed to ensure that all fluid quantities remain single valued as particles approach one another, to respect conservation laws, and to vanish on a given physical scale as the resolution is increased. SPHS alleviates a number of known problems with ‘classic’ SPH, successfully resolving mixing, and recovering numerical convergence with increasing resolution. An additional key advantage is that – treating the particle mass similarly to the entropy – we are able to use multimass particles, giving significantly improved control over the refinement strategy. We present a wide range of code tests including the Sod shock tube, Sedov–Taylor blast wave, Kelvin–Helmholtz Instability, the ‘blob test’ and some convergence tests. Our method performs well on all tests, giving good agreement with analytic expectations.
TL;DR: In this paper, an optical and electrical characterization of plasma sheet formed by applying a pulse of voltage with rising and falling periods of 50 ns for a typical surface DBD geometry is presented.
Abstract: Flow control consists of manipulating flows in an effective and robust manner to improve the global performances of transport systems or industrial processes. Plasma technologies, and particularly surface dielectric barrier discharge (DBD), can be a good candidate for such purpose. The present experimental study focuses on optical and electrical characterization of plasma sheet formed by applying a pulse of voltage with rising and falling periods of 50 ns for a typical surface DBD geometry. Positive and negative polarities are compared in terms of current behavior, deposited energy, fast-imaging of the plasma propagation, and resulting modifications of the surrounding medium by using shadowgraphy acquisitions. Positive and negative pulses of voltage produce streamers and corona type plasma, respectively. Both of them result in the production of a localized pressure wave propagating in the air with a speed maintained at 343 m/s (measurements at room temperature of 20 °C). This suggests that the produced pressure wave can be considered as a propagating sound wave. The intensity of the pressure wave is directly connected to the dissipated energy at the dielectric wall with a linear increase with the applied voltage amplitude and a strong dependence toward the rising time. At constant voltage amplitude, the pressure wave is reinforced by using a positive pulse. The present investigation also reveals that rising and decaying periods of a single pulse of voltage result in two distinct pressure waves. As a result, superposition or successive pressure wave can be produced by adjusting the width of the pulse.
TL;DR: Major physical, chemical and mechanical characteristics of the adaptive coating, which play a significant role in its operating properties, such as enhanced mass transfer, and the ability of the layer to provide dissipation and accumulation of frictional energy during operation are presented.
TL;DR: In this paper, the authors showed that switching a shape-anisotropic 2-phase multiferroic nanomagnet with voltage-generated stress can be performed with ∼100% probability in less than 1
Abstract: Switching the magnetization of a shape-anisotropic 2-phase multiferroic nanomagnet with voltage-generated stress is known to dissipate very little energy (<1 aJ for a switching time of ∼0.5 ns) at 0 K temperature. Here, we show by solving the stochastic Landau-Lifshitz-Gilbert equation that switching can be carried out with ∼100% probability in less than 1 ns while dissipating less than 1.5 aJ at room temperature. This makes nanomagnetic logic and memory systems, predicated on stress-induced magnetic reversal, one of the most energy-efficient computing hardware extant. We also study the dependence of energy dissipation, switching delay, and the critical stress needed to switch, on the rate at which stress on the nanomagnet is ramped up or down.
TL;DR: In this paper, the initial spreading dy-namics, characterized by the radius of the wetted area, for viscous drops, were investigated using high-speed imaging with synchronized bottom and side views, and they showed that short time spreading does not exhibit a pure power-law growth.
Abstract: Liquid drops start spreading directly after coming into contact with a solid sub- strate. Although this phenomenon involves a three-phase contact line, the spread- ing motion can be very fast. We experimentally study the initial spreading dy- namics, characterized by the radius of the wetted area, for viscous drops. Using high-speed imaging with synchronized bottom and side views gives access to 6 decades of time resolution. We show that short time spreading does not exhibit a pure power-law growth. Instead, we find a spreading velocity that decreases logarithmically in time, with a dynamics identical to that of coalescing viscous drops. Remarkably, the contact line dissipation and wetting effects turn out to be unimportant during the initial stages of drop spreading.
TL;DR: It is experimentally shown that the nonclassical high Reynolds number energy dissipation behavior, C(ε)≡εL/u(3)=f(Re(M))/Re(L), observed during the decay of fractal square grid-generated turbulence is also manifested in decaying turbulence originating from various regular grids.
Abstract: It is experimentally shown that the nonclassical high Reynolds number energy dissipation behavior, C(e)≡eL/u(3)=f(Re(M))/Re(L), observed during the decay of fractal square grid-generated turbulence (where Re(M) is a global inlet Reynolds number and Re(L) is a local turbulence Reynolds number) is also manifested in decaying turbulence originating from various regular grids. For sufficiently high values of the global Reynolds numbers Re(M), f(Re(M))~Re(M).
TL;DR: The design of PMA CoFeB racetrack memory and a spice-compatible model to perform mixed simulation with CMOS circuits are presented and its area, speed, and power dissipation performance has been simulated and evaluated based on different technology nodes.
Abstract: Current-induced domain wall motion in magnetic nanowires drives the invention of a novel ultra-dense non-volatile storage device, called “racetrack memory.” Combining with magnetic tunnel junctions write and read heads, CMOS integrability and fast data access speed can also be achieved. Recent experimental progress showed that perpendicular-magnetic anisotropy (PMA) CoFeB could be a good candidate to build up racetrack memory and promise high performance like high-density (e.g., ∼1 F2/bit), fast-speed, and low-power beyond classical spin transfer torque memories. In this paper, we first present the design of PMA CoFeB racetrack memory and a spice-compatible model to perform mixed simulation with CMOS circuits. Its area, speed, and power dissipation performance has been simulated and evaluated based on different technology nodes.
TL;DR: In this paper, the authors considered the tuning of a dynamic vibration absorber such that either the kinetic energy of the host structure is minimised or the power dissipation within the absorber is maximised.
TL;DR: In this article, the performance of numerical models in conditions with strong currents is reviewed, and observed strong effects of opposed currents and modulations of wave heights by tidal currents in several typical situations are interpreted.
Abstract: Currents effects on waves have led to many developments in numerical wave modeling over the past two decades, from numerical choices to parameterizations. The performance of numerical models in conditions with strong currents is reviewed here, and observed strong effects of opposed currents and modulations of wave heights by tidal currents in several typical situations are interpreted. For current variations on small scales, the rapid steepening of the waves enhances wave breaking. Using different parameterizations with a dissipation rate proportional to some measure of the wave steepness to the fourth power, the results are very different, none being fully satisfactory, which points to the need for more measurements and further refinements of parameterizations. For larger-scale current variations, the observed modifications of the sea state are mostly explained by refraction of waves over currents and relative wind effects, that is, the wind speed relevant for wave generation is the speed in the ...
01 Dec 2012
TL;DR: High resolution kinetic simulations of collisionless plasma driven by shear show the development of turbulence characterized by dynamic coherent sheetlike current density structures spanning a range of scales down to electron scales, indicating that kinetic scale plasma, like magnetohydrodynamics, becomes intermittent due to current sheet formation.
Abstract: High resolution kinetic simulations of collisionless plasma driven by shear show the development of turbulence characterized by dynamic coherent sheetlike current density structures spanning a range of scales down to electron scales. We present evidence that these structures are sites for heating and dissipation, and that stronger current structures signify higher dissipation rates. Evidently, kinetic scale plasma, like magnetohydrodynamics, becomes intermittent due to current sheet formation, leading to the expectation that heating and dissipation in astrophysical and space plasmas may be highly nonuniform and patchy.
TL;DR: A porphyrin aggregate is reported that exhibits novel exciton state properties for light-harvesting applications and enables control of energy dissipation of coherent excited states by changing the self-assembly pattern.
Abstract: A porphyrin aggregate is reported that exhibits novel exciton state properties for light-harvesting applications. This porphyrin aggregate enables control of energy dissipation of coherent excited states by changing the self-assembly pattern. New exciton spectral features create a new route of energy transfer in this porphyrin aggregate. The kinetic model of exciton state decay is addressed in this Perspective by reporting steady-state and transient emission and absorption studies of porphyrin J- and H-aggregates. The porphyrin J-aggregate emerges with better spectral coverage and exciton dynamics, which are suitable for light-harvesting antenna functions. This motif is explored in a photosensitization study of TiO2 semiconductor materials. The transient absorption studies show that the J-aggregate improves the photoinduced charge separation at the porphyrin/TiO2 interface. The higher charge separation is attributed to exciton-coupled charge-transfer processes in porphyrin J-aggregate/TiO2 hybrid material...
TL;DR: In this article, a parametric study was performed to fully investigate the effects of initial specimen density and crushability on the energy allocation of the crushable soil, and the simulation results showed that the initial sample density and the crushability strongly affect the energy consumption of the soil both at small and large strains.
TL;DR: In this article, a numerical simulation of kinetic plasma turbulence is performed to assess the applicability of critical balance to kinetic, dissipation scale turbulence, and the analysis is performed in the frequency domain to obviate complications inherent in performing a local analysis of turbulence.
Abstract: A numerical simulation of kinetic plasma turbulence is performed to assess the applicability of critical balance to kinetic, dissipation scale turbulence. The analysis is performed in the frequency domain to obviate complications inherent in performing a local analysis of turbulence. A theoretical model of dissipation scale critical balance is constructed and compared to simulation results, and excellent agreement is found. This result constitutes the first evidence of critical balance in a kinetic turbulence simulation and provides evidence of an anisotropic turbulence cascade extending into the dissipation range. We also perform an Eulerian frequency analysis of the simulation data and compare it to the results of a previous study of magnetohydrodynamic turbulence simulations.
TL;DR: In this paper, the authors proposed the minimally nonlinear irreversible heat engine as a new general theoretical model to study the efficiency at the maximum power η* of heat engines operating between the hot heat reservoir at the temperature Th and the cold one at Tc (Tc≤Th).
Abstract: We propose the minimally nonlinear irreversible heat engine as a new general theoretical model to study the efficiency at the maximum power η* of heat engines operating between the hot heat reservoir at the temperature Th and the cold one at Tc (Tc≤Th). Our model is based on the extended Onsager relations with a new nonlinear term meaning the power dissipation. In this model, we show that η* is bounded from the upper side by a function of the Carnot efficiency ηC≡1−Tc/Th as η*≤ηC/(2−ηC). We demonstrate the validity of our theory by showing that the low-dissipation Carnot engine can easily be described by our theory.
TL;DR: In this paper, the authors examine the equilibrium tide in the anelastic parts of a planet for every rheology, and by taking into account the presence of a fluid envelope of constant density.
Abstract: Context. Earth-like planets have viscoelastic mantles, whereas giant planets may have viscoelastic cores. The tidal dissipation of these solid regions, which are gravitationally perturbed by a companion body, strongly depends on their rheology and the tidal frequency. Therefore, modeling tidal interactions provides constraints on planets’ properties and helps us to understand their history and evolution, in either our solar system or exoplanetary systems. Aims. We examine the equilibrium tide in the anelastic parts of a planet for every rheology, and by taking into account the presence of a fluid envelope of constant density. We show how to obtain the different Love numbers describing its tidal deformation, and discuss how the tidal dissipation in the solid parts depends on the planet’s internal structure and rheology. Finally, we show how our results may be implemented to describe the dynamical evolution of planetary systems. Methods. We expand in Fourier series the tidal potential exerted by a point mass companion, and express the dynamical equations in the orbital reference frame. The results are cast in the form of a complex disturbing function, which may be implemented directly in the equations governing the dynamical evolution of the system. Results. The first manifestation of the tide is to distort the shape of the planet adiabatically along the line of centers. The response potential of the body to the tidal potential then defines the complex Love numbers, whose real part corresponds to the purely adiabatic elastic deformation and the imaginary part accounts for dissipation. The tidal kinetic energy is dissipated into heat by means of anelastic friction, which is modeled here by the imaginary part of the complex shear modulus. This dissipation is responsible for the imaginary part of the disturbing function, which is implemented in the dynamical evolution equations, from which we derive the characteristic evolution times.Conclusions. The rate at which the system evolves depends on the physical properties of the tidal dissipation, and specifically on (1) how the shear modulus varies with tidal frequency, (2) the radius, and (3) the rheological properties of the solid core. The quantification of the tidal dissipation in the solid core of giant planets reveals a possible high dissipation that may compete with dissipation in fluid layers.