Showing papers on "Dissipation published in 2020"

Efficient Light Funneling based on the non-Hermitian Skin Effect

Abstract: In the last two decades, the ubiquitous effect of dissipation has proven to entail astonishing non-Hermitian features, rather than just being an inescapable nuisance. As an alternative route to non-Hermiticity, we tailor the anisotropy of a lattice, which constitutes an, up to now, barely exploited degree of freedom. In this case, the appearance of an interface dramatically alters the entire eigenmode spectrum, leading to the exponential localization of all modes at the interface, which goes beyond the expectations for Hermitian systems. This effect is dubbed "non-Hermitian skin effect". We experimentally demonstrate it by studying the propagation of light in a large scale photonic mesh lattice. For arbitrary excitations, we find that light is always transported to the interface, realizing a highly efficient funnel for light.

Complex Spacing Ratios: A Signature of Dissipative Quantum Chaos

Abstract: Mathematical tools for distinguishing open quantum systems that are chaotic from those that are exactly solvable fill an important gap in understanding dissipation and decoherence in scenarios relevant to quantum-based technologies.

Experimental investigation on dynamic strength and energy dissipation characteristics of gas outburst‐prone coal

Abstract: This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2019 The Authors. Energy Science & Engineering published by the Society of Chemical Industry and John Wiley & Sons Ltd. 1College of Mining, Liaoning Technical University, Fuxin, Liaoning Province, China 2State Key Laboratory for GeoMechanics and Deep Underground Engineering, China University of Mining & Technology, Xuzhou, Jiangsu Province, China 3Energy and Mineral Engineering, Pennsylvania State University, University Park, Pennsylvania, USA

Simulation and modeling of second order velocity slip flow of micropolar ferrofluid with Darcy–Forchheimer porous medium

Abstract: Ferrofluids are made out of nanoscale ferromagnetic particles and known as colloidal liquids suspended on a bearer liquid, normally water (H2O) or an organic solvent i e., kerosene. A typically composition would be 5% magnetic particles, 10% surfactant and 85% bearer liquid. Ferrofluid is utilized in rotary seals in computer hard drives, loudspeakers, and MRI (magnetic resonance imaging). It is trusted this research work may explore the specialist to think of consider new uses for this attractive material. Therefore, such effectiveness in mind, mathematical modeling for the second order velocity slip nonlinear entropy optimized Darcy–Forchheimer flow of ferrofluid (FF) is developed towards a stretched surface. The energy equation is discussed in the presence of heat source/sink, dissipation and Ohmic heating or Joule heating. Numerical solutions for the desired ordinary system are contracted via built-in shooting method. The flow parameters are discussed graphically.

Time–information uncertainty relations in thermodynamics

Abstract: Physical systems powering motion and creating structure in a fixed amount of time dissipate energy and produce entropy. Whether living, synthetic or engineered, systems performing these dynamic functions must balance dissipation and speed. Here, we show that rates of energy and entropy exchange are subject to a speed limit—a time–information uncertainty relation—imposed by the rates of change in the information content of the system. This uncertainty relation bounds the time that elapses before the change in a thermodynamic quantity has the same magnitude as its s.d. From this general bound, we establish a family of speed limits for heat, dissipated/chemical work and entropy depending on the experimental constraints on the system and its environment. In all of these inequalities, the timescale of transient dynamical fluctuations is universally bounded by the Fisher information. Moreover, they all have a mathematical form that mirrors the Mandelstam–Tamm version of the time–energy uncertainty relation in quantum mechanics. These bounds on the speed of arbitrary observables apply to transient systems away from thermodynamic equilibrium, independent of the physical constraints on the stochastic dynamics or their function. A time–information uncertainty relation in thermodynamics has been derived, analogous to the time–energy uncertainty relation in quantum mechanics, imposing limits on the speed of energy and entropy exchange between a system and external reservoirs.

On the relation between enhanced dissipation time-scales and mixing rates

Abstract: We study diffusion and mixing in different linear fluid dynamics models, mainly related to incompressible flows. In this setting, mixing is a purely advective effect which causes a transfer of energy to high frequencies. When diffusion is present, mixing enhances the dissipative forces. This phenomenon is referred to as enhanced dissipation, namely the identification of a time-scale faster than the purely diffusive one. We establish a precise connection between quantitative mixing rates in terms of decay of negative Sobolev norms and enhanced dissipation time-scales. The proofs are based on a contradiction argument that takes advantage of the cascading mechanism due to mixing, an estimate of the distance between the inviscid and viscous dynamics, and of an optimization step in the frequency cut-off. Thanks to the generality and robustness of our approach, we are able to apply our abstract results to a number of problems. For instance, we prove that contact Anosov flows obey logarithmically fast dissipation time-scales. To the best of our knowledge, this is the first example of a flow that induces an enhanced dissipation time-scale faster than polynomial. Other applications include passive scalar evolution in both planar and radial settings and fractional diffusion.

Electromagnetic Interference Shielding of Graphene Aerogel with Layered Microstructure Fabricated via Mechanical Compression.

Abstract: Graphene aerogel is a promising electromagnetic interference (EMI) shielding material because of its light weight, excellent electrical conductivity, uniform three-dimensional (3D) microporous structure, and good mechanical strength. The graphene aerogel with high EMI shielding performance is attracting considerable critical attention. In this study, a novel procedure to fabricate high EMI shielding graphene aerogel was presented, inspired by the irreversible deformation of hydrogels under mechanical pressure. The procedure involved a mechanical compression step on graphene hydrogels for the purpose of altering microstructures followed by freeze-drying and thermal annealing at 900 °C to generate the final products. Because of the flow of internal liquid caused by mechanical compression, the microstructures of hydrogels changed from a cellular configuration to a layered configuration. After a high degree of compression, GAs can be endowed with homogeneous layered structure and high density, which plays a leading role in electromagnetic wave dissipation. Consequently, the aerogels with excellent electrical conductivity (181.8 S/m) and EMI shielding properties (43.29 dB) could be obtained. Besides, the compression process enabled us to form complex hydrogel shapes via different molds. This method enhances the formability of graphene aerogels and provides a robust way to control the microstructure.

Measurement-induced transitions of the entanglement scaling law in ultracold gases with controllable dissipation

Abstract: Recent studies of quantum circuit models have theoretically shown that frequent measurements induce a transition in a quantum many-body system, which is characterized by a change in the scaling law of the entanglement entropy from a volume law to an area law. In order to propose a way to experimentally observe this measurement-induced transition, we present numerical analyses using matrix-product states on the quench dynamics of a dissipative Bose-Hubbard model with controllable two-body losses, which has been realized in recent experiments with ultracold atoms. We find that when the strength of dissipation increases, there occurs a measurement-induced transition from volume-law scaling to area-law scaling with a logarithmic correction in a region of relatively small dissipation. We also find that the strong dissipation leads to a revival of the volume-law scaling due to a continuous quantum Zeno effect. We show that dynamics starting with the area-law states exhibits strong suppression of particle transport stemming from ergodicity breaking, which can be used in experiments to distinguish them from the volume-law states.

Entropy Generation and Consequences of MHD in Darcy–Forchheimer Nanofluid Flow Bounded by Non-Linearly Stretching Surface

Abstract: Present communication aims to inspect the entropy optimization, heat and mass transport in Darcy-Forchheimer nanofluid flow surrounded by a non-linearly stretching surface. Navier-Stokes model based governing equations for non-Newtonian nanofluids having symmetric components in various terms are considered. Non-linear stretching is assumed to be the driving force whereas influence of thermal radiation, Brownian diffusion, dissipation and thermophoresis is considered. Importantly, entropy optimization is performed using second law of thermodynamics. Governing problems are converted into nonlinear ordinary problems (ODEs) using suitably adjusted transformations. RK-45 based built-in shooting mechanism is used to solve the problems. Final outcomes are plotted graphically. In addition to velocity, temperature, concentration and Bejan number, the stream lines, contour graphs and density graphs have been prepared. For their industrial and engineering importance, results for wall-drag force, heat flux (Nusselt) rate and mass flux (Sherwood) rate are also given in tabular data form. Outputs indicate that velocity reduces for Forchheimer number as well as for the porosity factor. However, a rise is noted in temperature distribution for elevated values of thermal radiation. Entropy optimization shows enhancement for larger values of temperature difference ratio. Skin-friction enhances for all relevant parameters involved in momentum equation.

Numerical Study on Hysteretic Behaviour of Horizontal-Connection and Energy-Dissipation Structures Developed for Prefabricated Shear Walls

Abstract: This study proposed a developed horizontal-connection and energy-dissipation structure (HES), which could be employed for horizontal connection of prefabricated shear wall structural system. The HES consists of an external replaceable energy dissipation (ED) zone mainly for energy dissipation and an internal stiffness lifting (SL) zone for enhancing the load-bearing capacity. By the predicted displacement threshold control device, the ED zone made in bolted low-yielding steel plates could firstly dissipate the energy and can be replaced after damage, the SL zone could delay the load-bearing and the load-displacement curves of the HES would exhibit “double-step” characteristics. Detailed finite element models are established and validated in software ABAQUS. parametric analysis including aspect ratio, the shape of the steel plate in the ED zone and the displacement threshold in the SL zone, is conducted. It is found that the HES depicts high energy dissipation ability and its bearing capacity could be obtained again after the yielding of the ED zone. The optimized X-shaped steel plate in the ED zone exhibit better performance. The “double-step” design of the HES is a potential way of improving the seismic and anti-collapsing performance of prefabricated shear wall structures against large and super-large earthquakes.

Dissipation-Time Uncertainty Relation.

Abstract: We show that the entropy production rate bounds the rate at which physical processes can be performed in stochastic systems far from equilibrium. In particular, we prove the fundamental tradeoff ⟨S[over ˙]_{e}⟩T≥k_{B} between the entropy flow ⟨S[over ˙]_{e}⟩ into the reservoirs and the mean time T to complete any process whose time-reversed is exponentially rarer. This dissipation-time uncertainty relation is a novel form of speed limit: the smaller the dissipation, the larger the time to perform a process.

MHD Turbulence: A Biased Review

Abstract: This review puts the developments of the last few years in the context of the canonical time line (Kolmogorov to Iroshnikov-Kraichnan to Goldreich-Sridhar to Boldyrev). It is argued that Beresnyak's objection that Boldyrev's alignment theory violates the RMHD rescaling symmetry can be reconciled with alignment if the latter is understood as an intermittency effect. Boldyrev's scalings, recovered in this interpretation, are thus an example of a physical theory of intermittency in a turbulent system. Emergence of aligned structures brings in reconnection physics, so the theory of MHD turbulence intertwines with the physics of tearing and current-sheet disruption. Recent work on this by Loureiro, Mallet et al. is reviewed and it is argued that we finally have a reasonably complete picture of MHD cascade all the way to the dissipation scale. This picture appears to reconcile Beresnyak's Kolmogorov scaling of the dissipation cutoff with Boldyrev's aligned cascade. These ideas also enable some progress in understanding saturated MHD dynamo, argued to be controlled by reconnection and to contain, at small scales, a tearing-mediated cascade similar to its strong-mean-field counterpart. On the margins of this core narrative, standard weak-MHD-turbulence theory is argued to require adjustment - and a scheme for it is proposed - to take account of the part that a spontaneously emergent 2D condensate plays in mediating the Alfven-wave cascade. This completes the picture of the MHD cascade at large scales. A number of outstanding issues are surveyed, concerning imbalanced MHD turbulence (for which a new theory is proposed), residual energy, subviscous and decaying regimes of MHD turbulence (where reconnection again features prominently). Finally, it is argued that the natural direction of research is now away from MHD and into kinetic territory.

On Green and Naghdi Thermoelasticity Model without Energy Dissipation with Higher Order Time Differential and Phase-Lags

Abstract: In the present work, a modified model of heat conduction including higher order of time derivative is derived by extending Green and Naghdi theory without energy dissipation. We introduce two phase lag times to include the thermal displacement gradient and the heat flux in the heat conduction and depict microscopic responses more precisely. The constructed model is applied to study thermoelastic waves in a homogeneous and isotropic perfect conducting unbounded solid body containing a spherical cavity. We use the Laplace transform method to analyze the problem. The solutions for the field functions are obtained numerically using the numerical Laplace inversion technique. The results are analyzed in different tables and graphs and compared with those obtained earlier in the contexts of some other theories of thermoelasticity.

Velocity and thermal slip effects on MHD nanofluid flow past a stretching cylinder with viscous dissipation and Joule heating

Abstract: The motivation behind the current study is to investigate the flow and heat characteristics of magnetohydrodynamic (MHD) silver–water (Ag/H2O) nanofluid under the influence of Joule heating and viscous dissipation over a stretching cylinder in the presence of suction/injection and slip boundary conditions. Problem formulation is created considering low magnetic Reynolds number subjected to boundary layer theory. Two different models of thermal conductivity and dynamic viscosity based on unlike shapes of nanoparticles, namely spherical and cylindrical (nanotubes), are also considered. The associated PDEs related to conservation terms of hydroflow and hydrothermal are molded to system of non-dimensional ODEs with the help of appropriate similarity transformation. The obtained nonlinear equations are solved with the help of numerical approach Runge–Kutta–Fehlberg (RKF) fourth–fifth order via shooting algorithm. The convergence of its solution profiles has been demonstrated through graphs and numerical data. A detailed parametric study is performed to describe the influences of relevant physical parameters on velocity and temperature profiles. Nusselt number is also tabularized and examined for both models. Some of the results of the investigation are effects of magnetic parameter and thermal slip to decrease the velocity profiles, which in turn causes the increment in temperature profiles. Moreover, temperature fields show a similar behavior for dissipation and heat generation/absorption parameter, but the reverse trend is observed in the case of suction/blowing parameter. The computed results are validated with existing ones for limiting sense and provided excellent agreement.

Energy Transfer from Large to Small Scales in Turbulence by Multiscale Nonlinear Strain and Vorticity Interactions

Abstract: An intrinsic feature of turbulent flows is an enhanced rate of mixing and kinetic energy dissipation due to the rapid generation of small-scale motions from large-scale excitation. The transfer of kinetic energy from large to small scales is commonly attributed to the stretching of vorticity by the strain rate, but strain self-amplification also plays a role. Previous treatments of this connection are phenomenological or inexact, or cannot distinguish the contribution of vorticity stretching from that of strain self-amplification. In this Letter, an exact relationship is derived which quantitatively establishes how intuitive multiscale mechanisms such as vorticity stretching and strain self-amplification together actuate the interscale transfer of energy in turbulence. Numerical evidence verifies this result and uses it to demonstrate that the contribution of strain self-amplification to energy transfer is higher than that of vorticity stretching, but not overwhelmingly so.

Dissipative SymODEN: Encoding Hamiltonian Dynamics with Dissipation and Control into Deep Learning

Abstract: In this work, we introduce Dissipative SymODEN, a deep learning architecture which can infer the dynamics of a physical system with dissipation from observed state trajectories. To improve prediction accuracy while reducing network size, Dissipative SymODEN encodes the port-Hamiltonian dynamics with energy dissipation and external input into the design of its computation graph and learns the dynamics in a structured way. The learned model, by revealing key aspects of the system, such as the inertia, dissipation, and potential energy, paves the way for energy-based controllers.

In situ investigation into temperature evolution and heat generation during additive friction stir deposition: A comparative study of Cu and Al-Mg-Si

Abstract: Additive friction stir deposition is an emerging solid-state additive manufacturing technology that enables site-specific build-up of high-quality metals with fine, equiaxed microstructures and excellent mechanical properties By incorporating proper machining, it has the potential to produce large-scale, complex 3D geometries Still early in its development, a thorough understanding of the thermal process fundamentals, including temperature evolution and heat generation mechanisms, has not been established Here, we aim to bridge this gap through in situmonitoring of the thermal field and material flow behavior using complementary infrared imaging, thermocouple measurement, and optical imaging Two materials challenging to print via beam-based additive technologies, Cu and Al-Mg-Si, are investigated During additive friction stir deposition of both materials, we find similar trends of thermal features (eg, the trends of peak temperature T P e a k , exposure time, and cooling rate) with respect to the processing conditions (eg, the tool rotation rate Ω and in-plane velocity V ) However, there is a salient, quantitative difference between Cu and Al-Mg-Si; T P e a k exhibits a power law relationship with Ω / V in Cu but with Ω 2 / V in Al-Mg-Si We correlate this difference to the distinct interfacial contact states that are observed through in situ material flow characterization In Cu, the interfacial contact between the material and tool head is characterized by a full slipping condition, so interfacial friction is the dominant heat generation mechanism In Al-Mg-Si, the interfacial contact is characterized by a partial slipping/sticking condition, so both interfacial friction and plastic energy dissipation contribute significantly to the heat generation