External Dissipation Research Articles

Emergence of order from turbulence in an isolated planar superfluid.

We study the relaxation dynamics of an isolated zero temperature quasi-two-dimensional superfluid Bose-Einstein condensate that is imprinted with a spatially random distribution of quantum vortices. Following a period of vortex annihilation the remaining vortices self-organize into two macroscopic coherent "Onsager vortex" clusters that are stable indefinitely--despite the absence of driving or external dissipation in the dynamics. We demonstrate that this occurs due to a novel physical mechanism--the evaporative heating of the vortices--that results in a negative-temperature phase transition in the vortex degrees of freedom. At the end of our simulations the system is trapped in a nonthermal state. Our computational results provide a pathway to observing Onsager vortex states in a superfluid Bose gas.

Influence of Insert Structure on Hollow Cathode Discharge Characteristics

A new structure of lanthanum hexaboride (LaB 6 ) hollow cathode insert, which has a cylindrical core, is studied in this paper. The cylindrical core is inserted into and connected at the back of the traditional hollow cylinder part. Two inserts with core and one traditional insert are tested. The new structure can largely reduce the cathode temperature, the gas flow rate of discharge mode transition, and the discharge voltage. The insert, the core of which is closer to the orifice, has the best performance. Larger electron emission area and poor heat dissipation of the core with unchanged external heat dissipation area should be the reason. The core closer to the orifice receives more power deposition and thus results in better cathode performance. Lower temperature and extra material can extend the insert life. Overall, the new insert structure with core is better than the traditional structure.

Nonlinear analysis of cylindrical and conical hysteretic whirl motions in rotor-dynamics

The internal friction of a rotor–shaft-support system is mainly due to the shaft structural hysteresis and to some possible shrink-fit release of the assembly. The experimentation points out the destabilizing effect of the internal friction in the over-critical rotor running. Nevertheless, this detrimental influence may be efficiently counterbalanced by other external dissipative sources located in the supports or by a proper anisotropic configuration of the support stiffness. The present analysis considers a rotor–shaft system which is symmetric with respect to the mid-span and is constrained by viscous-flexible supports with different stiffness on two orthogonal planes. The cylindrical and conical whirling modes are easily uncoupled and separately analysed. The internal dissipation is modelled by nonlinear Coulombian forces and moments, which counteract the translational and rotational motion of the rotor relative to a frame rotating with the shaft ends. The nonlinear equations of motion are solved by averaging approaches of the Krylov–Bogoliubov type. In both the over-critical whirling motions, cylindrical and conical, stable limit cycles may be attained whose amplitude is as large as the external dissipation applied by the supports is low. The stiffness anisotropy of the supports may be recognised as quite beneficial for the cylindrical whirl.

25aKJ-2 弾性薄板における強・弱乱流スペクトルに対する外力・散逸の影響(剛体・弾性体,複雑流体,非圧縮性流体,領域11(統計力学,物性基礎論,応用数学,力学,流体物理))

25aKJ-2 弾性薄板における強・弱乱流スペクトルに対する外力・散逸の影響(剛体・弾性体,複雑流体,非圧縮性流体,領域11(統計力学,物性基礎論,応用数学,力学,流体物理))

Quantum Stochastic Dynamics in the Presence of a Time-Periodic Rapidly Oscillating Potential: Nonadiabatic Escape Rate

Escape from a metastable state in the presence of a high-frequency field (where the driving becomes nonadiabatic) underlies a broad range of phenomena of physics and chemistry, and thus its understanding is of paramount importance. We study the problem of intermediate-to-high-damping escape from a metastable state of a dissipative system driven by a rapidly oscillating field, one of the most important classes of nonequilibrium systems, in a broad range of field driving frequencies (ω) and amplitudes (a). We construct a Langevin equation using quantum gauge transformation in the light of Floquet theorem and exploiting a systematic perturbative expansion in powers of 1/ω using "Kapitza-Landau time window". The quantum dynamics in a high-frequency field are found to be described by an effective time-independent potential. The temperature dependence of escape rate and the change of its form with varying parameters of the field have been analyzed. It may decrease upon increasing the temperature which is contingent on the effects of intricate interplay between external modulation and dissipation. The crossover temperature between tunnelling and thermal hopping increases with an increase in external modulation so that quantum effects in the escape are relevant at higher temperatures. These observations are uncommon and counterintuitive and, therefore, of considerable interest. Our results might be valuable for the exploration of the dynamics of cold atoms in electromagnetic fields.

Excitation modes of vortices in submicron magnetic disks

Classical and quantum theory of spin waves in the vortex state of a mesoscopic sub-micron magnetic disk has been developed with account of the finite mass density of the vortex. Oscillations of the vortex core resemble oscillations of a charged string in a potential well in the presence of the magnetic field. Conventional gyroscopic frequency appears as a gap in the spectrum of spin waves of the vortex. The mass of the vortex has been computed that agrees with experimental findings. Finite vortex mass generates a high-frequency branch of spin waves. Effects of the external magnetic field and dissipation have been addressed.

Intracavity Tunneling Introduced Transparency in Ultrastrong-coupling Regime

Intracavity tunneling induced transparency in asymmetric double-quantum wells embedded in a microcavity in the ultrastrong-coupling regime is investigated by the input-output theory developed by Ciuti and Carusotto. In this system a narrow spectra can be realized under anti-resonant terms of the external dissipation. Fano-interference asymmetric line profile is found in the absorption spectra.

Algebraic Rossby Solitary Waves Excited by Non-Stationary External Source

The paper deals with the effects of non-stationary external source forcing and dissipation on algebraic Rossby solitary waves. From quasi-geostrophic potential vorticity equation, basing on the multiple-scale method, an inhomogeneous Korteweg-de Vries—Benjamin—Ono—Burgers (KdV-B-O-Burgers) equation is obtained. This equation has not been previously derived for Rossby waves. By analysis and calculation, four conservation laws associated with the above equation are first obtained. With the help of pseudo-spectral method, the waterfall plots are obtained and the evolutional characters of algebraic Rossby solitary waves are studied. The results show that non-stationary external source and dissipation have great effect on the generation and evolution of algebraic solitary Rossby waves.

Irreversibilities and efficiency at maximum power of heat engines: The illustrative case of a thermoelectric generator

Energy conversion efficiency at maximum output power, which embodies the essential characteristics of heat engines, is the main focus of the present work. The so-called Curzon and Ahlborn efficiency η(CA) is commonly believed to be an absolute reference for real heat engines; however, a different but general expression for the case of stochastic heat engines, η(SS), was recently found and then extended to low-dissipation engines. The discrepancy between η(CA) and η(SS) is here analyzed considering different irreversibility sources of heat engines, of both internal and external types. To this end, we choose a thermoelectric generator operating in the strong-coupling regime as a physical system to qualitatively and quantitatively study the impact of the nature of irreversibility on the efficiency at maximum output power. In the limit of pure external dissipation, we obtain η(CA), while η(SS) corresponds to the case of pure internal dissipation. A continuous transition between from one extreme to the other, which may be operated by tuning the different sources of irreversibility, also is evidenced.

Recycling Energy to Restore Impaired Ankle Function during Human Walking

BackgroundHumans normally dissipate significant energy during walking, largely at the transitions between steps. The ankle then acts to restore energy during push-off, which may be the reason that ankle impairment nearly always leads to poorer walking economy. The replacement of lost energy is necessary for steady gait, in which mechanical energy is constant on average, external dissipation is negligible, and no net work is performed over a stride. However, dissipation and replacement by muscles might not be necessary if energy were instead captured and reused by an assistive device.Methodology/Principal FindingsWe developed a microprocessor-controlled artificial foot that captures some of the energy that is normally dissipated by the leg and “recycles” it as positive ankle work. In tests on subjects walking with an artificially-impaired ankle, a conventional prosthesis reduced ankle push-off work and increased net metabolic energy expenditure by 23% compared to normal walking. Energy recycling restored ankle push-off to normal and reduced the net metabolic energy penalty to 14%.Conclusions/SignificanceThese results suggest that reduced ankle push-off contributes to the increased metabolic energy expenditure accompanying ankle impairments, and demonstrate that energy recycling can be used to reduce such cost.

Modulation of the velocity of soliton-like perturbations for the sine–Gordon equation with external force and dissipation

An analytical expression of the function modulating the amplitude of soliton velocity perturbations for the sine-Gordon equation with a uniform external harmonic force and dissipation is derived. The evolution of the soliton velocity for the external force in the form of a step function of time is examined. An analytical expression for the time-averaged soliton velocity is obtained.

Three-dimensional thermal finite element modeling of lithium-ion battery in thermal abuse application

In order to better understand the thermal abuse behavior of high capacities and large power lithium-ion batteries for electric vehicle application, a three-dimensional thermal model has been developed for analyzing the temperature distribution under abuse conditions. The model takes into account the effects of heat generation, internal conduction and convection, and external heat dissipation to predict the temperature distribution in a battery. Three-dimensional model also considers the geometrical features to simulate oven test, which are significant in larger cells for electric vehicle application. The model predictions are compared to oven test results for VLP 50/62/100S-Fe (3.2 V/55 Ah) LiFePO 4/graphite cells and shown to be in great agreement.

Движение кинка под действием переменной внешней силы в среде с диссипацией

Движение кинка под действием переменной внешней силы в среде с диссипацией

Steady-state work fluctuations of a dragged particle under external and thermal noise

We consider a particle, confined to a moving harmonic potential, under the influence of friction and external asymmetric Poissonian shot noise (PSN). We study the fluctuations of the work done to maintain this system in a nonequilibrium steady state. PSN generalizes the usual Gaussian noise and can be considered to be a paradigm of external noise, where fluctuation and dissipation originate from physically independent mechanisms. We consider two scenarios: (i) the noise is given purely by PSN and (ii) in addition to PSN the particle is subject to white Gaussian noise. In both cases we derive exact expressions for the large deviation form of the work distribution, which are characterized by the time scales of the system. We show that the usual steady-state fluctuation theorem does not apply in our model and that in a certain parameter regime large negative work fluctuations are more likely to occur than the corresponding positive ones, though the average work is always positive.

Dissipative instability under weak beam–plasma coupling in finite magnetic field

Beam–plasma interaction is considered in a model of plasma microwave generator: cylindrical waveguide with thin annular plasma and spatially separated thin annular e-beam. Finite external longitudinal magnetic field and dissipation are assumed. Such a configuration is favorable to trigger a new type of dissipative beam instability with more critical, as compared to conventional, inverse proportional dependence of the growth rate on the dissipation.

Exact dynamics of driven Brownian oscillators

Exact quantum master equation for a driven Brownian oscillator system is constructed via a Wigner phase-space Gaussian wave packet approach. The interplay between external field and dissipation leads to this system an effective field correction that enhances the polarization. This cooperative property is resulted from an effective bath response to the external field applied on the system. It is important in the low-frequency driving and intermediate bath memory region. We demonstrate this non-Markovian effect on the linear response and nonlinear dynamics and analyze the results together with analytical asymptotic expressions.

Kink dynamics in the medium with a random force and dissipation in the sine-Gordon model

Within the formalism of the Fokker-Planck equation, the influence of nonstationary external force, random force, and dissipation effects on the kink dynamics is investigated in the sine-Gordon model. The equation of evolution of the kink momentum is obtained in the form of the stochastic differential equation in the Stratonovich sense within the framework of the well-known McLaughlin and Scott energy approach. The corresponding Fokker-Planck equation for the momentum distribution function coincides with the equation describing the Ornstein-Uhlenbek process with a regular nonstationary external force. The influence of the nonlinear stochastic effects on the kink dynamics is considered with the help of the Fokker-Planck nonlinear equation with the shift coefficient dependent on the first moment of the kink momentum distribution function. Expressions are derived for average value and variance of the momentum. Examples are considered which demonstrate the influence of the external regular and random forces on the evolution of the average value and variance of the kink momentum.

Adiabatic approximations for Landau-Lifshitz equations

The asymptotics with respect to a small parameter for solutions of a system of Landau-Lifshitz equations with slowly varying coefficients and small dissipative terms is investigated. These equations are a mathematical model of a uniaxial ferromagnet in a time-dependent magnetic field. The asymptotics constructed make it possible to describe the magnetization reversal effect and to reveal the influence of the parameters of the external magnetic field and dissipation on the stability of this process.

Power squeeze [Portable system energy budget

Careful thought is needed to design portable systems that have a strong mixed-signal component. The need to power a system purely from batteries puts severe constraints on the design in terms of energy consumption. We are seeing more portable systems appear, particularly in the medical, industrial and consumer markets. Cost and size considerations mean they often need custom silicon designing for them. But there are different trade-offs needed depending on where the bulk of the energy is consumed. For energy efficient designs, it is important to calculate the energy budget of a system including internal and external power dissipation, and also to consider the energy budget summed over the full operating cycle or lifetime.

Fast transition between classical and weak lined T Tauri stars due to external UV dissipation

The discovery of optical jets immersed in the strong UV radiation field of the Rosette Nebula sheds new light on, but meanwhile poses challenges to, the study of externally irradiated jets. The jet systems in the Rosette are found to have a high state of ionization and show unique features. In this paper, we investigate the evolutionary status of the jet-driving sources for young solar-like stars. To our surprise, these jet sources indicate unexpected near infrared properties with no excess emission. They are bathed in harsh external UV radiation such that evaporation leads to a fast dissipation of their circumstellar material. This could represent a transient phase of evolution of young solar-like stars between classical and weak lined T Tauri stars. Naked T Tauri stars formed in this way have indistinguishable evolutionary ages from those of classical T Tauri stars resulting from the same episode of star formation. However, it would be hard for such sources to be identified if they are not driving an irradiated jet in a photoionized medium.