The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Ferdi Altintas - One of the best experts on this subject based on the ideXlab platform.
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Construction of a quantum Carnot heat engine cycle
Quantum Information Processing, 2020Co-Authors: Selçuk Çakmak, Mustafa Çandır, Ferdi AltintasAbstract: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.
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Quantum Carnot cycle with inner friction
Quantum Information Processing, 2020Co-Authors: Selçuk Çakmak, Ferdi AltintasAbstract: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.
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quantum Carnot cycle with inner friction
arXiv: Quantum Physics, 2020Co-Authors: Selçuk Çakmak, Ferdi AltintasAbstract: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.
Selçuk Çakmak - One of the best experts on this subject based on the ideXlab platform.
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Construction of a quantum Carnot heat engine cycle
Quantum Information Processing, 2020Co-Authors: Selçuk Çakmak, Mustafa Çandır, Ferdi AltintasAbstract: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.
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Quantum Carnot cycle with inner friction
Quantum Information Processing, 2020Co-Authors: Selçuk Çakmak, Ferdi AltintasAbstract: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.
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quantum Carnot cycle with inner friction
arXiv: Quantum Physics, 2020Co-Authors: Selçuk Çakmak, Ferdi AltintasAbstract: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.
Bernhard K. Meister - One of the best experts on this subject based on the ideXlab platform.
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Entropy and temperature of a quantum Carnot engine
Proceedings of the Royal Society of London. Series A: Mathematical Physical and Engineering Sciences, 2002Co-Authors: Carl M. Bender, Dorje C. Brody, Bernhard K. MeisterAbstract:It is possible to extract work from a quantum–mechanical system whose dynamics is governed by a time–dependent cyclic Hamiltonian. An energy bath is required to operate such a quantum engine in place of the heat bath used to run a conventional classical thermodynamic heat engine. The effect of the energy bath is to maintain the expectation value of the system Hamiltonian during an isoenergetic process. It is shown that the existence of such a bath leads to equilibrium quantum states that maximize the von Neumann entropy. Quantum analogues of certain thermodynamic relations are obtained that allow one to define the temperature of the energy bath.
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Quantum mechanical Carnot engine
Journal of Physics A: Mathematical and General, 2000Co-Authors: Carl M. Bender, Dorje C. Brody, Bernhard K. MeisterAbstract:A cyclic thermodynamic heat engine runs most efficiently if it is reversible. Carnot constructed such a reversible heat engine by combining adiabatic and isothermal processes for a system containing an ideal gas. Here, we present an example of a cyclic engine based on a single quantum-mechanical particle confined to a potential well. The efficiency of this engine is shown to equal the Carnot efficiency because quantum dynamics is reversible. The quantum heat engine has a cycle consisting of adiabatic and isothermal quantum processes that are close analogues of the corresponding classical processes.
Christian Van Den Broeck - One of the best experts on this subject based on the ideXlab platform.
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the unlikely Carnot efficiency
Nature Communications, 2014Co-Authors: Gatien Verley, Massimiliano Esposito, Tim Willaert, Christian Van Den BroeckAbstract:Carnot efficiency is the highest theoretically possible efficiency that a heat engine can have. Verley et al. use the fluctuation theorem to show that the Carnot value is the least likely efficiency in the long time limit.
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Quantum-dot Carnot engine at maximum power
Physical Review E, 2010Co-Authors: Massimiliano Esposito, Ryoichi Kawai, Katja Lindenberg, Christian Van Den BroeckAbstract:We evaluate the efficiency at maximum power of a quantum-dot Carnot heat engine. The universal values of the coefficients at the linear and quadratic order in the temperature gradient are reproduced. Curzon-Ahlborn efficiency is recovered in the limit of weak dissipation.
A D Nobre - One of the best experts on this subject based on the ideXlab platform.
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a critique of some modern applications of the Carnot heat engine concept the dissipative heat engine cannot exist
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2010Co-Authors: A. M. Makarieva, V. G. Gorshkov, A D NobreAbstract:In several recent studies, a heat engine operating on the basis of the Carnot cycle is considered, where the mechanical work performed by the engine is dissipated within the engine at the temperature of the warmer isotherm and the resulting heat is added to the engine together with an external heat input. This internal dissipation is supposed to increase the total heat input to the engine and elevate the amount of mechanical work produced by the engine per cycle. Here it is argued that such a dissipative heat engine violates the laws of thermodynamics. The existing physical models employing the dissipative heat engine concept, in particular the heat engine model of hurricane development, need to be revised.