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- 주제어 : Fluctuation theorem (검색결과 6 건)
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Fluctuation of the Electric Field in a Plasma
Hee J. Lee 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.8
The theory of electric field fluctuations in a plasma is reviewed. The fluctuations of an electric field can be assumed to be due to the Cerenkov radiation, which is emitted by single particles that satisfy the Landau wave-particle resonance conditions. This view naturally agrees with the picture that a plasma can be considered to be an aggregate of non-interacting dressed particles. A simple classical derivation of the fluctuation-dissipation theorem is presented to show that the fluctuations of the Cerenkov electric field agree with the fluctuation-dissipation theorem. A quasilinear-like solution of the Liouville equation is shown to derive an electric field fluctuation with the same form as that obtained by using the dressed particle approach. We suggest that the fluctuation can be traced to the causality that gives rise to collisionless dissipation (imaginary part of the dielectric function). Therefore, the fluctuation in a plasma has a philosophical implication in that its existence is fundamentally due to the causal principle that the effect cannot be precedent to the cause, thus defining the direction of time.
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박형규 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.12
Recently, there has been a considerable progress on the issue of the thermodynamic second law, which is known as the law of entropy increase or irreversibility. In particular, a novel symmetry known as the Gallavotti-Cohen symmetry is found in nonequilibrium (NEQ) fluctuations, which leads to so-called fluctuation theorems. The thermodynamic second law is a simple corollary of fluctuation theorems, from which one can predict quantitatively how often NEQ processes violate the law of entropy increase. Violations disappear in the thermodynamic limit, but can be observed reasonably well in small systems. In this article, we will briefly introduce the stochastic thermodynamics and derive various fluctuation theorems, including the total entropy production (EP), the work-free-energy relation, the excess and house-keeping EP, and the information entropy.
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고밀도 연성 콜로이드 안의 추적입자의 동력학: 밀도 요동 및 수송특성
김봉수 한국물리학회 2016 New Physics: Sae Mulli Vol.66 No.9
The dynamics and the transport properties of a tracer particle embedded in highly-dense soft colloids is studied through a new field theoretic perturbation method. Dictated by the time-reversal symmetry of the action, the perturbation preserves the fluctuation-dissipation theorem (FDT) order by order. Out of the second-order perturbation calculation, the bare version of the mode-coupling theory emerges for the tracer density correlation function. The long-time tracer diffusion coefficient is reduced in proportion to the density of the bath's liquid, and the velocity correlation function of the tracer exhibits a long-time tail behavior; $i.e.$, it shows a power-law relaxation in time in the long-time region. 밀도가 아주 높은 연성 콜로이드 액체 안의 추적입자의 밀도 요동의 동력학 및 수송특성을 새로운 장이론적 섭동이론을 통해 연구한다. 이 섭동이론은 해당 액션의 시간 반전 대칭성에 의해 각 전개 차수마다 요동-소모 정리를 보전해 준다. 여기서는 상호작용의 세기의 2차까지의 섭동 계산을 통해 추적입자의 밀도 상관함수의 동력학 방정식이 모드 결합이론에서와 같은 꼴을 가진다는 것을 보여준다. 다만, 기억적분 안의 상관 및 반응함수가 영차의 함수들이라는 점이 다르다. 기억함수로 부터 얻어지는 추적입자의 긴 시간 확산계수는 열원 콜로이드 액체의 평균밀도에 비례하여 줄어든다. 또한 추적입자의 속도 상관함수는 긴 시간 영역에서 시간에 따라 급수적으로 완화하는 긴 시간 꼬리 거동을 보인다.
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Path-dependent Entropy Production
권철안 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.5
A rigorous derivation of nonequilibrium entropy production via the path-integral formalism is presented. Entropy production is defined as the entropy change piled in a heat reservoir as a result of a nonequilibrium thermodynamic process. It is a central quantity by which various forms of the fluctuation theorem are obtained. The two kinds of the stochastic dynamics are investigated: the Langevin dynamics for an even-parity state and the Brownian motion of a single particle. Mathematical ambiguities in deriving the functional form of the entropy production, which depends on path in state space, are clarified by using a rigorous quantum mechanical approach.
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Optimal Protocol for Maximum Work Extraction in a Feedback Process with a Time-varying Potential
권철안 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.71 No.12
The nonequilibrium nature of information thermodynamics is characterized by the inequality or non-negativity of the total entropy change of the system, memory, and reservoir. Mutual information change plays a crucial role in the inequality, in particular if work is extracted and the paradox of Maxwell’s demon is raised. We consider the Brownian information engine where the protocol set of the harmonic potential is initially chosen by the measurement and varies in time. We confirm the inequality of the total entropy change by calculating, in detail, the entropic terms including the mutual information change. We rigorously find the optimal values of the time-dependent protocol for maximum extraction of work both for the finite-time and the quasi-static process.
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Nonequilibrium thermodynamics for a harmonic potential moving in time
Lee Hyun Keun,Kwon Youngchae,권철안 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.83 No.5
We investigate non-equilibrium thermodynamics externally driven by moving the center of harmonic potential in time. We present the theoretical formalism for an arbitrary motion in underdamped dynamics. We provide the formulas to find thermodynamic quantities such as work, heat and entropy production produced for time period, which are main quantities in non-equilibrium studies. For sinusoidal driving with external frequency Ω, we observe a resonance for work production where the average rate for infinite period is maximized at Ω = ω0 that is the internal frequency of the harmonic oscillator. It may be used for an alternative way to measure the stiffness of an optical trap potential. We confirm the thermodynamic uncertainty relation newly found for underdamped dynamics subject to general time-dependent protocols for a specific example of driving.
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