The Experts below are selected from a list of 3621 Experts worldwide ranked by ideXlab platform

Pascal Stouffs - One of the best experts on this subject based on the ideXlab platform.

Giulio Casati - One of the best experts on this subject based on the ideXlab platform.

  • thermodynamic bounds on Efficiency for systems with broken time reversal symmetry
    Physical Review Letters, 2011
    Co-Authors: Keiji Saito, Giuliano Benenti, Giulio Casati
    Abstract:

    We show that for systems with broken time-reversal symmetry the maximum Efficiency and the Efficiency at maximum power are both determined by two parameters: a ``figure of merit'' and an asymmetry parameter. In contrast to the time-symmetric case, the figure of merit is bounded from above; nevertheless the Carnot Efficiency can be reached at lower and lower values of the figure of merit and far from the so-called strong coupling condition as the asymmetry parameter increases. Moreover, the Curzon-Ahlborn limit for Efficiency at maximum power can be overcome within linear response. Finally, always within linear response, it is allowed to have Carnot Efficiency and nonzero power simultaneously .

Koji Okuda - One of the best experts on this subject based on the ideXlab platform.

  • compatibility of Carnot Efficiency with finite power in an underdamped brownian Carnot cycle in small temperature difference regime
    arXiv: Statistical Mechanics, 2020
    Co-Authors: Kosuke Miura, Yuki Izumida, Koji Okuda
    Abstract:

    We study the possibility of achieving the Carnot Efficiency in a finite-power Brownian Carnot cycle described by the underdamped Langevin equation in the small temperature-difference regime. A previous study [V. Holubec and A. Ryabov, Phys. Rev. Lett. {\bf 121}, 120601 (2018)] pointed out that it is possible to achieve both the Carnot Efficiency and finite power in an overdamped Brownian Carnot cycle by considering the vanishing limit of the relaxation times of the system. However, an overlooked heat leakage exists at the beginning of the isothermal processes because of the instantaneous adiabatic processes when considering the overdamped limit in an underdamped Brownian Carnot cycle. As heat leakage decreases Efficiency, the compatibility of the Carnot Efficiency and finite power should be reexamined. We study the relaxation-times dependence of the Efficiency and power in the underdamped Brownian Carnot cycle in the small temperature-difference regime where the heat leakage can be neglected. Additionally, we demonstrate that the compatibility of the Carnot Efficiency and finite power is achieved by considering the vanishing limit of the relaxation times of the system. Furthermore, we show that this result is consistent with a trade-off relation between power and Efficiency by explicitly deriving the relation of our cycle in terms of the relaxation times.

  • Efficiency at maximum power of minimally nonlinear irreversible heat engines
    EPL, 2012
    Co-Authors: Yuki Izumida, Koji Okuda
    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.

  • Efficiency at maximum power of minimally nonlinear irreversible heat engines
    arXiv: Statistical Mechanics, 2011
    Co-Authors: Yuki Izumida, Koji Okuda
    Abstract:

    We propose the minimally nonlinear irreversible heat engine as a new general theoretical model to study the Efficiency at the maximum power $\eta^*$ of heat engines operating between the hot heat reservoir at the temperature $T_h$ and the cold one at $T_c$ ($T_c \le T_h $). Our model is based on the extended Onsager relations with a new nonlinear term meaning the power dissipation. In this model, we show that $\eta^*$ is bounded from the upper side by a function of the Carnot Efficiency $\eta_C\equiv 1-T_c/T_h$ as $\eta^*\le \eta_C/(2-\eta_C)$. We demonstrate the validity of our theory by showing that the low-dissipation Carnot engine can easily be described by our theory.

Ferdi Altintas - One of the best experts on this subject based on the ideXlab platform.

  • Construction of a quantum Carnot heat engine cycle
    Quantum Information Processing, 2020
    Co-Authors: Selçuk Çakmak, Mustafa Çandır, Ferdi Altintas
    Abstract:

    The microscopic state description of an irreversible quantum Carnot cycle for a general quantum working medium is investigated. An Efficiency lag term, which quantifies the deviation of the irreversible cycle Efficiency from the classical Carnot Efficiency, is given in terms of the total entropy increase in the universe. The Efficiency lag and the total entropy increase in the universe are directly connected to the quantum relative entropy between the density matrices obtained at the end of the quantum adiabatic and the relaxation steps of the cycle. The total entropy increase and the Efficiency lag are found to be always nonnegative quantities. Our results give a direct proof that the irreversible cycle Efficiency is always smaller than the classical Carnot Efficiency. Two interacting spins under an external magnetic field are proposed as the working medium of the irreversible quantum Carnot cycle. The external magnetic field is considered to be quasistatically changed during the steps of the cycle. The coupling between the spins is found to break down the scale invariance and make the quantum Carnot cycle irreversible. It is shown that while the quantum coupling can lower the cycle Efficiency monotonically to zero, it can make the irreversible cycle to produce more work than the one obtained from the uncoupled spins. The conditions in which one can always construct a reversible Carnot cycle for the coupled spin working medium are also given.

  • Quantum Carnot cycle with inner friction
    Quantum Information Processing, 2020
    Co-Authors: Selçuk Çakmak, Ferdi Altintas
    Abstract:

    A single driven spin is investigated as the working substance of a six-stroke irreversible quantum Carnot cycle. The role of inner friction associated with the finite-time adiabatic transformations on the cycle Efficiency and the harvested work are investigated in detail. The inner friction is found to significantly reduce the work output and the cycle Efficiency which can make the engine incapable to produce positive work for the too fast adiabatic transformations. The ideal Carnot Efficiency is found to be reached only for the quasistatic transformations. A deviation of the cycle Efficiency from the classical Carnot Efficiency has been given by an Efficiency lag which is directly related to the total entropy production due to the inner friction. The released heat in the relaxation processes of the cycle is associated with the entropy production and the inner friction. The extension of the results for a scale-invariant quantum working substance and the possible experimental implementation of the irreversible quantum Carnot cycle in a liquid-state nuclear magnetic resonance setup are also discussed.

  • quantum Carnot cycle with inner friction
    arXiv: Quantum Physics, 2020
    Co-Authors: Selçuk Çakmak, Ferdi Altintas
    Abstract:

    A single driven spin is investigated as the working substance of a six-stroke irreversible quantum Carnot cycle. The role of inner friction associated with the finite-time adiabatic transformations on the cycle Efficiency and the harvested work are investigated in detail. The inner friction is found to significantly reduce the work output and the cycle Efficiency which can make the engine incapable to produce positive work for the too fast adiabatic transformations. The ideal Carnot Efficiency is found to be reached only for the quasi-static transformations. A deviation of the cycle Efficiency from the classical Carnot Efficiency has been given by an Efficiency lag which is directly related to the total entropy production due to the inner friction. The released heat in the relaxation processes of the cycle are associated with the entropy production and the inner friction. The extension of the results for a scale invariant quantum working substance and the possible experimental implementation of the irreversible quantum Carnot cycle in a liquid state nuclear magnetic resonance setup are also discussed.

Yuki Izumida - One of the best experts on this subject based on the ideXlab platform.

  • compatibility of Carnot Efficiency with finite power in an underdamped brownian Carnot cycle in small temperature difference regime
    arXiv: Statistical Mechanics, 2020
    Co-Authors: Kosuke Miura, Yuki Izumida, Koji Okuda
    Abstract:

    We study the possibility of achieving the Carnot Efficiency in a finite-power Brownian Carnot cycle described by the underdamped Langevin equation in the small temperature-difference regime. A previous study [V. Holubec and A. Ryabov, Phys. Rev. Lett. {\bf 121}, 120601 (2018)] pointed out that it is possible to achieve both the Carnot Efficiency and finite power in an overdamped Brownian Carnot cycle by considering the vanishing limit of the relaxation times of the system. However, an overlooked heat leakage exists at the beginning of the isothermal processes because of the instantaneous adiabatic processes when considering the overdamped limit in an underdamped Brownian Carnot cycle. As heat leakage decreases Efficiency, the compatibility of the Carnot Efficiency and finite power should be reexamined. We study the relaxation-times dependence of the Efficiency and power in the underdamped Brownian Carnot cycle in the small temperature-difference regime where the heat leakage can be neglected. Additionally, we demonstrate that the compatibility of the Carnot Efficiency and finite power is achieved by considering the vanishing limit of the relaxation times of the system. Furthermore, we show that this result is consistent with a trade-off relation between power and Efficiency by explicitly deriving the relation of our cycle in terms of the relaxation times.

  • Efficiency at maximum power of minimally nonlinear irreversible heat engines
    EPL, 2012
    Co-Authors: Yuki Izumida, Koji Okuda
    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.

  • Efficiency at maximum power of minimally nonlinear irreversible heat engines
    arXiv: Statistical Mechanics, 2011
    Co-Authors: Yuki Izumida, Koji Okuda
    Abstract:

    We propose the minimally nonlinear irreversible heat engine as a new general theoretical model to study the Efficiency at the maximum power $\eta^*$ of heat engines operating between the hot heat reservoir at the temperature $T_h$ and the cold one at $T_c$ ($T_c \le T_h $). Our model is based on the extended Onsager relations with a new nonlinear term meaning the power dissipation. In this model, we show that $\eta^*$ is bounded from the upper side by a function of the Carnot Efficiency $\eta_C\equiv 1-T_c/T_h$ as $\eta^*\le \eta_C/(2-\eta_C)$. We demonstrate the validity of our theory by showing that the low-dissipation Carnot engine can easily be described by our theory.