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Three heats in a strongly coupled system and bath
Chulan Kwon1, Jaegon Um2, Joonhyun Yeo3
1Department of Physics, Myongji University, Yongin, Gyeonggi-Do 17058, Korea.
Physical Review. E
|December 25, 2019
Summary
We rigorously define three types of heat (Q_{S}, Q_{B}, and Q_{SB}) in strongly coupled systems. Unlike weak-coupling assumptions, these heats exhibit distinct fluctuations, even when averaging to energy steady states.
Area of Science:
- Thermodynamics
- Statistical Mechanics
- Physical Chemistry
Background:
- The equivalence of heat exchanged by a system (Q_{S}) and its bath (Q_{B}) is commonly assumed under weak coupling.
- Understanding heat flow in strongly coupled systems is crucial for non-equilibrium thermodynamics.
Purpose of the Study:
- To rigorously define and differentiate three types of heat (Q_{S}, Q_{B}, Q_{SB}) in a strongly coupled system-bath model.
- To investigate the validity of heat equivalence assumptions beyond the weak-coupling regime.
- To derive and analyze fluctuation theorems for these distinct heat definitions.
Main Methods:
- Analysis of energy flows between a system, a thermostat-equipped bath, and a superbath.
- Derivation of fluctuation theorems (FTs) for system variables and heat flows.
- Application to a model system: a Brownian particle in a fluid with a sliding harmonic potential.
Main Results:
- Rigorous definitions for system heat (Q_{S}), bath heat (Q_{B}), and superbath heat (Q_{SB}) were established.
- The common assumption of Q_{S} = Q_{B} was shown to be invalid in the strong-coupling regime.
- All three heat definitions were found to fluctuate differently over time, despite averaging to the same value in energy steady states.
Conclusions:
- Strong coupling introduces distinct heat definitions and behaviors not observed in weak-coupling approximations.
- Fluctuation theorems provide a framework for analyzing non-equilibrium heat dynamics.
- The study highlights the importance of precise heat definitions in understanding complex thermodynamic systems.
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