Browsing by Author "Bassie, Yigermal"

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    Finite-time Thermodynamic Processes of a Spin-One Quantum Electric Dipole System
    (Addis Ababa University, 2020-09-25) Bassie, Yigermal; Bekele, Mulugeta (PhD)
    We take a collection of large non-interacting spin one particles, each having an electric dipole of magnitude D in contact with a heat reservoir at temperature T . We apply a strong static electric field, E0, to the system along a z-axis causing three level split energy values. In addition to the strong electric field, applying a weak AC electric field in the xy􀀀plane induced transitions between the three levels. Through a given protocol _(t), the system is taken from an initial thermodynamic equilibrium state F(T ;_i ) to a final non-equilibrium state with parameter _f . We analytically obtain the expressions for the probability amplitudes for a transition from one particular initial state to the other two final states. This will enable us to find the work distributions of a finite-time process of taking the system from one initial state to either of the two final states of the three-level system. This finite-time non-equilibrium process will then enable us to extract equilibrium thermodynamic quantities like free energy from non-equilibrium process, which is what we call Jarzanski equality and its relation to the second law of thermodynamics. We obtain the possibilities of work distributions of the three-level system in the optimum condition for non-interacting particles. Besides, we empirically obtain the average work of the three-level system as a function of ! and time around the optimum frequency, where ! is the frequency of AC electric field.
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    Finite-Time Thermodynamic Processes of a Spin-One Quantum Electric Dipole System Department:
    (Addis Ababa University, 2020-09-25) Bassie, Yigermal; Bekele, Mulugeta (PhD)
    We take a collection of large non-interacting spin one particles, each having an electric dipole of magnitude D in contact with a heat reservoir at temperature T . We apply a strong static electric field, E0, to the system along a z-axis causing three level split energy values. In addition to the strong electric field, applying a weak AC electric field in the xy􀀀plane induced transitions between the three levels. Through a given protocol _(t), the system is taken from an initial thermodynamic equilibrium state F(T ;_i ) to a final non-equilibrium state with parameter _f . We analytically obtain the expressions for the probability amplitudes for a transition from one particular initial state to the other two final states. This will enable us to find the work distributions of a finite-time process of taking the system from one initial state to either of the two final states of the three-level system. This finite-time non-equilibrium process will then enable us to extract equilibrium thermodynamic quantities like free energy from non-equilibrium process, which is what we call Jarzanski equality and its relation to the second law of thermodynamics. We obtain the possibilities of work distributions of the three-level system in the optimum condition for non-interacting particles. Besides, we empirically obtain the average work of the three-level system as a function of ! and time around the optimum frequency, where ! is the frequency of AC electric field.
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    Optimized Efficiency of a Stochastically Driven Quantum dot Heat Engine
    (Addis Ababa University, 2012-06) Bassie, Yigermal; Bekele, Mulugeta (PhD)
    In this thesis, we take a stochastically driven single level quantum dot embedded between two metallic leads at di erent temperatures which works as a heat engine. We analytically study the optimized e ciency that lies between the maximum e ciency and minimum e ciencies (e ciency at maximum power and the minimum e ciency) condition. We perform two ways of optimization criteria to nd their corresponding optimized e cien- cies, powers and periods. We study the performance of the heat engine by introducinng a gure of merit as a function of Carnot e ciency