106 research outputs found
On the non-equilibrium thermodynamics of quantum systems
No full textA consistent theory of non-equilibrium thermodynamics for Markovian open quantum systems has been developed in the late seventies in analogy with Classical Irreversible Thermodynamics. The time-evolution of these open systems is usually described by means of effective master equations in Lindblad form, that turn out to be reliable when there is a separation of time-scales between system and environment, such that memory effects are negligible and the so-called Markovian approximation is justified. In this framework, the variations of energy and entropy in the system are consistently described, distinguishing between heat and work contributions and providing a statement of the second law of thermodynamics as positivity of the entropy production.
However, there is empirical evidence that many physical systems like photosynthetic complexes,
opto-mechanical resonators and superconducting qubits, just to mention a few, experience more general non-Markovian dynamics. The formulation of the laws of thermodynamics in a non-Markovian setting is matter of current research and represents the main topic of the present work. As a first step, we show that the entropy production defined as in the Markovian case can be negative for a class of non-Markovian dynamics. We argue that this outcome should not be interpreted as a violation of the second law of thermodynamics because the environment must be explicitly taken into account in the balance of entropy in the non-Markovian setting. In order to justify this claim we adopt a more general point of view, studying a closed bipartite quantum system, such that each of the two subsystems plays the role of a finite environment out of equilibrium for the other one. We concentrate on the balance of energy first and construct an effective Hamiltonian for each subsystem using physically reasonable requirements; then we define heat and work as in the standard Markovian treatment, with the effective Hamiltonian replacing the free Hamiltonian. It turns out that, in our framework, the work power is perfectly balanced between subsystems, while the correlations can store a part of energy locally inaccessible and exchange it with both subsystems in the form of heat.
Concerning the balance of entropy, a quite general formulation of the second law of thermodynamics can be given as follows: under the assumption of a factorized initial state for the compound system, the sum of the total variations of the entropies in the two subsystems is always nonnegative. We show with an explicit example that this general formulation does not correspond to the statement presented in the framework of Markovian master equations, which should not be considered a priori the second law of thermodynamics.
In the last part of the thesis we concentrate of the so-called fluctuation relations, that are results extending the thermodynamic formalism beyond the behavior of average quantities. After reviewing the main theoretical outcomes, such as the Jarzynski equality and the Crooks fluctuation theorem, we describe a proposal to access experimentally the work performed on an ensemble of diatomic molecules by a time-dependent electric field coupled with their vibrational degree of freedom. This procedure could then be used to test the quantum Jarzynski equality. With respect to the results so far appeared in the literature, in which the left-hand side of the equality is inferred from an experiment and the right-hand side is computed according to a model, in our proposed setting we should be able to estimate from the experiment both the left-hand side and the right-hand side of the equality, independently
Thermodynamics of a qubit undergoing dephasing
No full textThe thermodynamics of a qubit undergoing dephasing due to the coupling with the external environment is discussed. First of all, we assume the dynamics of the system to be described by a master equation in Lindblad form. In this framework, we review a standard formulation of the first and second law of thermodynamics that has been known in literature for a long time. After that, we explicitly model the environment with a set of quantum harmonic oscillators choosing the interaction such that the global dynamics of system and bath is analytically solvable and the Lindblad master equation is recovered in the weak-coupling limit. In this generalized setting, we can show that the correlations between system and bath play a fundamental role in the heat exchange. Moreover, the internal entropy production of the qubit is proven to be positive for arbitrary coupling strength
Stochastic entropy production: Fluctuation relation and irreversibility mitigation in non-unital quantum dynamics
No full textIn this work, we study the stochastic entropy production in open quantum
systems whose time evolution is described by a class of non-unital quantum
maps. In particular, as in [Phys. Rev. E 92, 032129 (2015)], we consider Kraus
operators that can be related to a nonequilibrium potential. This class
accounts for both thermalization and equilibration to a non-thermal state.
Unlike unital quantum maps, non-unitality is responsible for an unbalance of
the forward and backward dynamics of the open quantum system under scrutiny.
Here, concentrating on observables that commute with the invariant state of the
evolution, we show how the non-equilibrium potential enters the statistics of
the stochastic entropy production. In particular, we prove a fluctuation
relation for the latter and we find a convenient way of expressing its average
solely in terms of relative entropies. Then, the theoretical results are
applied to the thermalization of a qubit with non-Markovian transient, and the
phenomenon of irreversibility mitigation, introduced in [Phys. Rev. Research 2,
033250 (2020)], is analyzed in this context.Comment: 17 pages, v2 close to published versio
Understanding democracy in Contemporary China: the Whole-Process people’s democracy of Xi Jinping (Political Discourse, Debates and New Challenges)
No full textStarting from the Chinese willingness to think democracy outside the Western conceptual framework, this research aims to reflect on the meaning of the concept of democracy in China (minzhu民主), avoiding the two extremes of Western imitation and Eastern exceptionalism. This is a necessary operation that allows first of all to contextualize the many debates on democracy in today's China, and then to grasp the meanings and the prospects for the development of the so-called “whole process-people democracy” (WPPD) of Xi Jinping. The research assumes the methodological perspective of conceptual history adopted by Melvin Richter's proposal, that seeks to bring conceptual history and the history of political discourse into dialogue to consider also the “history of debates”. Tracing the genealogy of the development of the concept of democracy, from the fall of the Empire, through the birth of the Republic of China, the founding of the People's Republic (PRC), and arriving at the New Millennium, the various ideological trends concerning democracy are highlighted. This enables an analysis of the fundamental Maoist ideas of “new democracy”, “people's democratic dictatorship”, “great democracy”, “consultative democracy”, and the principles of “democratic centralism” and “mass line” underlying PRC’s political theory. The same is done for the decades afterwards, going through the ideas of Political Reform and “socialist democracy”, as well as through the practical and theoretical development of “grassroot democracy” and intra-party democracy to that of “democracy with Chinese characteristics”. This reconstruction makes it possible to highlight how the advent of Xi Jinping brought profound changes to the structure supporting Chinese democracy as developed over the previous three decades. The research analyzes the internal and external motivations behind the leader's choices, also reading them in relation to the global process of depoliticization and the need to create a strong discourse community. Since 2012 Xi placed limitations on the old structures by placing great emphasis on the role of ideology, a strong centralization of power, and increased social and ideological control; but he also proposed innovations, conceiving and creating new structures for popular participation on the various levels of governance (e.g. Local Legislative Outreach Offices), and new official formulations around democracy. Through the analysis of the leader's thought, at the level of political theory and political discourse, the various directions on which the new discourse on democracy in China is developed (e.g., the ideas of “Chinese Democracy,” “direct democracy,” “true democracy”, and “democracy that works”) are traced and the illiberal implications highlighted. This has made it possible to understand the meaning of the WPPD, to reflect on the implications and pitfalls of this new official formulation, and to clarify the forms that the Chinese democratization process has taken.Starting from the Chinese willingness to think democracy outside the Western conceptual framework, this research aims to reflect on the meaning of the concept of democracy in China (minzhu民主), avoiding the two extremes of Western imitation and Eastern exceptionalism. This is a necessary operation that allows first of all to contextualize the many debates on democracy in today's China, and then to grasp the meanings and the prospects for the development of the so-called “whole process-people democracy” (WPPD) of Xi Jinping. The research assumes the methodological perspective of conceptual history adopted by Melvin Richter's proposal, that seeks to bring conceptual history and the history of political discourse into dialogue to consider also the “history of debates”. Tracing the genealogy of the development of the concept of democracy, from the fall of the Empire, through the birth of the Republic of China, the founding of the People's Republic (PRC), and arriving at the New Millennium, the various ideological trends concerning democracy are highlighted. This enables an analysis of the fundamental Maoist ideas of “new democracy”, “people's democratic dictatorship”, “great democracy”, “consultative democracy”, and the principles of “democratic centralism” and “mass line” underlying PRC’s political theory. The same is done for the decades afterwards, going through the ideas of Political Reform and “socialist democracy”, as well as through the practical and theoretical development of “grassroot democracy” and intra-party democracy to that of “democracy with Chinese characteristics”. This reconstruction makes it possible to highlight how the advent of Xi Jinping brought profound changes to the structure supporting Chinese democracy as developed over the previous three decades. The research analyzes the internal and external motivations behind the leader's choices, also reading them in relation to the global process of depoliticization and the need to create a strong discourse community. Since 2012 Xi placed limitations on the old structures by placing great emphasis on the role of ideology, a strong centralization of power, and increased social and ideological control; but he also proposed innovations, conceiving and creating new structures for popular participation on the various levels of governance (e.g. Local Legislative Outreach Offices), and new official formulations around democracy. Through the analysis of the leader's thought, at the level of political theory and political discourse, the various directions on which the new discourse on democracy in China is developed (e.g., the ideas of “Chinese Democracy,” “direct democracy,” “true democracy”, and “democracy that works”) are traced and the illiberal implications highlighted. This has made it possible to understand the meaning of the WPPD, to reflect on the implications and pitfalls of this new official formulation, and to clarify the forms that the Chinese democratization process has taken
Stochastic entropy production: Fluctuation relation and irreversibility mitigation in non-unital quantum dynamics
No full textIn this work, we study the stochastic entropy production in open quantum systems whose time evolution is described by a class of non-unital quantum maps. In particular, as in [Phys. Rev. E 92, 032129 (2015)], we consider Kraus operators that can be related to a nonequilibrium potential. This class accounts for both thermalization and equilibration to a non-thermal state. Unlike unital quantum maps, non-unitality is responsible for an unbalance of the forward and backward dynamics of the open quantum system under scrutiny. Here, concentrating on observables that commute with the invariant state of the evolution, we show how the non-equilibrium potential enters the statistics of the stochastic entropy production. In particular, we prove a fluctuation relation for the latter and we find a convenient way of expressing its average solely in terms of relative entropies. Then, the theoretical results are applied to the thermalization of a qubit with non-Markovian transient, and the phenomenon of irreversibility mitigation, introduced in [Phys. Rev. Research 2, 033250 (2020)], is analyzed in this context.N
A Base-Mediated Mild Sulfenylation of Indoles and Pyrrole with α-Acylthiones
No full textA new procedure for the sulfenylation of indoles and pyrroles based on an aromatic substitution with α-acylthiones used as electrophiles is described. The sulfenylating species were obtained, under very mild reaction conditions, from N-thiophthalimides, using a weak base (pyridine or triethylamine) as promoter. The overall yields obtained are comparable with those obtained by other known sulfenylation protocols, which typically require harsher reaction conditions and/or metal-containing Lewis acids as promoters.
Impact of the Mediterranean fruit fly (Medfly) Ceratitis capitata on different peach cultivars: The possible role of peach volatile compounds
No full textThe relationship between susceptibility of different peach cultivars (cvs) to the Mediterranean fruit fly (medfly), Ceratitis capitata, and the volatile composition of ripe fruit of each cv has been investigated, since understanding the fruit-insect interaction mechanism is crucial for developing control strategies for such a pest. Volatile compounds were analyzed by SPME-GC-MS in three cvs highly susceptible to medfly attack (Fair Time, Flaminia, Sicilia Piatta), and in two less susceptible cvs (Percoca Romagnola 7 and Doctor Davis). Among the volatile compounds detected, 88 could be identified. The main differences found in the volatile composition of the cvs, concerned the relative abundance of esters. The least susceptible cvs, above all Percoca Romagnola 7, contained the higher amounts of hexenyl, hexyl, 3-methylbutyl, butyl and 2-methylpropyl esters; among these, some C-6 derivatives detected, such as (Z)-3-hexenyl acetate, are known to act as priming agents, enhancing plant defence response to insects. Instead, a lower relative content of methyl esters, such as methyl hexanoate and methyl octanoate, known to act as medfly pheromone and attractant respectively, was found in the least susceptible cvs. (c) 2013 Elsevier Ltd. All rights reserved
Milk Yield, Major Milk Components and Macro Minerals in Blood Serum of Lactating Donkeys, as Affected by Dietary Trace Element Supplementation and Stage of Lactation
No full textThe aim of this experiment was to test the effects of both dietary trace element supplementation and the stage of lactation on the milk yield per milking and the major milk components, as well as the blood concentrations of total Ca, P, Mg, Na, and K in lactating donkeys. Over a 3-month period, 16 clinically healthy lactating donkeys were used to collect milk and blood samples and to evaluate the milk yield per milking. The experimental subjects were randomly divided into two homogeneous groups, control (CTL) and trace element (TE). The donkeys in the TE group were fed a diet supplemented with Zn, Fe, Cu, Mn, Se, Co, and I. The dietary treatment did not significantly affect neither the milk yield per milking nor the milk macro ingredients. However, these variables were significantly affected by the stage of lactation. The serum concentrations of total Ca, P, Na, and K were not affected by the dietary treatment, but the serum Mg level in the TE group was significantly higher than that in the CTL group (26.6 vs. 25.0 mg/L). The effect of stage of lactation was found to be significant for all the investigated minerals in the blood serum, and negative trends were observed for serum Ca, P, Mg, Na, and K during the experimental period
Correlations in quantum thermodynamics: Heat, work, and entropy production
No full textWe provide a characterization of energy in the form of exchanged heat and work between two interacting constituents of a closed, bipartite, correlated quantum system. By defining a binding energy we derive a consistent quantum formulation of the first law of thermodynamics, in which the role of correlations becomes evident, and this formulation reduces to the standard classical picture in relevant systems. We next discuss the emergence of the second law of thermodynamics under certain—but fairly general—conditions such as the Markovian assumption. We illustrate the role of correlations and interactions in thermodynamics through two examples
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