arXiv subjects

Jean-Luc Garden

Publications and source records attributed to Jean-Luc Garden.

18 recordsLinked to original sources

arXiv2026

Nonequilibrium distribution for stochastic thermodynamics

We extend the canonical Gibbs distribution, originally formulated for systems at equilibrium, to systems driven out of equilibrium. The stochastic dynamics of a small system are described by a probability distribution over discrete energy levels. Within this framework, we derive a microscopic expression for work and introduce a microscopic definition of entropy production (defined here in terms of the uncompensated heat of Clausius) during a nonequilibrium stochastic process. Work and entropy production share a common origin arising from variations of the system energy. The proposed framework allows us to recover the nonequilibrium work relation and to establish an equivalent identity for the heat exchanged during a work protocol. Finally, we show that the fluctuations of work and heat governed by the extended canonical distribution follow directly from the fluctuation theorem for entropy production.

cond-mat.stat-mech↗

arXiv2026

Linking the pressure dependence of the structure and thermal stability to α- and \b{eta}-relaxations in metallic glasses

Glasses derive their functional properties from complex relaxation dynamics that remain enigmatic under extreme conditions. While the temperature dependence of these relaxation processes is well-established, their behavior under high-pressure conditions remains poorly understood due to significant experimental difficulties. In this study, we employ cutting-edge experimental techniques to probe the pressure evolution of the relaxation spectrum in a Zr46.8Ti8.2Cu7.5Ni10Be27.5 metallic glass across gigapascal pressure ranges. Our findings reveal two distinct relaxation mechanisms under high pressure: In the \b{eta}-relaxation regime, compression drives the system with reduced atomic mobility and enhanced structural disorder, without significant density changes. Conversely, α-relaxation under pressure promotes density-driven structural ordering that improves thermal stability. Notably, the transition between these regimes occurs at a constant T/Tg,P ratio, independent of applied pressure. These results provide crucial insights for decoupling the competing structural and relaxation contributions to glass stability, establishing a systematic framework for tailoring glass properties through controlled thermo-mechanical processing.

cond-mat.mtrl-sci↗

arXiv2024

Nonequilibrium heat relation

The nonequilibrium work relation, or Jarzynski equality, establishes a statistical relationship between a series of nonequilibrium experiments on a system subjected to thermal fluctuations and a hypothetical experiment at thermodynamic equilibrium. In these experiments, the fluctuating quantity is the work exchanged between the system and its environment, while in the equilibrium scenario, the Helmholtz free energy difference between the system's initial and final states is determined. We inquire about the corresponding associated heat, the contribution of which, when added to the work, yields the change in internal energy. A new equality is presented for the random heat exchanged between the system and its thermal bath during the same protocol as the Jarzynski equality. Guidelines are provided for the experimental conditions required to measure such random heat.

cond-mat.stat-mech↗

arXiv2024

Fluctuations of thermal variables investigated by cross-correlation function

Fluctuations in conjugate thermodynamic variables are studied using the cross-correlation function. A new procedure is given enabling the derivation of fluctuation formulas for a system in equilibrium. Specifically, the cross-correlation function between heat and temperature is employed for thermal variables. Additionally, fluctuation-dissipation relations involving the frequency-dependent specific heat are established. Moreover, a general relation concerning the average entropy production is also given, which is the microscopic analogue of the dissipation formula of the linear response theory. In the case of thermal variables, this formula finds application in various scenarios describing fluctuating thermal systems in equilibrium.

cond-mat.stat-mech↗

arXiv2022

Understanding temperature modulated calorimetry through studies of a model system

Temperature Modulated calorimetry is widely used but still raises some fundamental questions. In this paper we study a model system as a test sample to address some of them. The model has a nontrivial spectrum of relaxation times. We investigate temperature modulated calorimetry at constant average temperature to precise the meaning of the frequency-dependent heat capacity, its relation with entropy production, and how such measurements can observe the aging of a glassy sample leading to a time-dependent heat capacity. The study of the Kovacs effect for an out-of-equilibrium system shows how temperature modulated calorimetry could contribute to the understanding of this memory effect. Then we compare measurements of standard scanning calorimetry and temperature-modulated calorimetry and show how the two methods are complementary because they do not observe the same features. While it can probe the time scales of energy transfers in a system, even in the limit of low frequency temperature modulated calorimetry does not probe some relaxation phenomena which can be measured by scanning calorimetry, as suggested by experiments with glasses.

cond-mat.stat-mech↗

arXiv2020

Memory effects in glasses: insights into the thermodynamics of out of equilibrium systems revealed by a simple model of the Kovacs effect

This paper is an extended version of an article accepted for publication in Physical Review E. Besides its fundamental interest, the model that we investigate in this article is simple enough to be used as a basis for courses or tutorials on the thermodynamics of out of equilibrium systems. It allows simple numerical calculations and analytical analysis which highlight important concepts with an easily workable example. This version includes studies of fast cooling and heating, exhibiting cases with negative heat capacity, and further discussions on the entropy which are not presented in the Physical Review E version. Glasses are interesting materials because they allow us to explore the puzzling properties of out-of-equilibrium systems. One of them is the Kovacs effect in which a glass, brought to an out-of-equilibrium state in which all its thermodynamic variables are identical to those of an equilibrium state, nevertheless evolves, showing a hump in some global variable before the thermodynamic variables come back to their starting point. We show that a simple three-state system is sufficient to study this phenomenon using numerical integrations and exact analytical calculations. It also brings some light on the concept of fictive temperature, often used to extend standard thermodynamics to the out-of-equilibrium properties of glasses. We confirm that the concept of a unique fictive temperature is not valid, an show it can be extended to make a connection with the various relaxation processes in the system. The model also brings further insights on the thermodynamics of out-of-equilibrium systems. Moreover we show that the three-state model is able to describe various effects observed in glasses such as the asymmetric relaxation to equilibrium discussed by Kovacs, or the reverse crossover measured on $B_2O_3$.

cond-mat.stat-mech↗

arXiv2011

Structural correlations and melting of B-DNA fibres

Despite numerous attempts, the understanding of the thermal denaturation of DNA is still a challenge due to the lack of structural data at the transition since standard experimental approaches to DNA melting are made in solution and do not provide spatial information. We report a measurement using neutron scattering from oriented DNA fibres to determine the size of the regions that stay in the double-helix conformation as the melting temperature is approached from below. A Bragg peak from the B-form of DNA has been observed as a function of temperature and its width and integrated intensity have bean measured. These results, complemented by a differential calorimetry study of the melting of B DNA fibres as well as electrophoresis and optical observation data, are analysed in terms of a one-dimensional mesoscopic model of DNA.

cond-mat.stat-mech↗

arXiv2011

The thermal denaturation of DNA studied with neutron scattering

The melting transition of deoxyribonucleic acid (DNA), whereby the strands of the double helix structure completely separate at a certain temperature, has been characterized using neutron scattering. A Bragg peak from B-form fibre DNA has been measured as a function of temperature, and its widths and integrated intensities have been interpreted using the Peyrard-Bishop-Dauxois (PBD) model with only one free parameter. The experiment is unique, as it gives spatial correlation along the molecule through the melting transition where other techniques cannot.

cond-mat.stat-mech↗

arXiv2010

Configurational Prigogine-Defay ratio

Classically, the Prigogine-Defay (PD) ratio involves differences in isobaric volumic specific heat, isothermal compressibility and isobaric thermal expansion coefficient between a super-cooled liquid and the corresponding glass at the glass transition. However, determining such differences by extrapolation of coefficients that have been measured for super-cooled liquid and glassy state, respectively, poses the problem that it does not take into account the non-equilibrium character of the glass transition. In this paper, we asses this old question by taking into account the gradual change of configurational contributions to the three thermodynamic coefficients upon varying temperature and pressure. Macroscopic non-equilibrium thermodynamics is applied to obtain a generalized form of the PD ratio. The classical PD ratio can then be taken as a particular case of this generalization. Under some assumptions, a configurational PD ratio (CPD ratio) can be expressed in terms of fictive temperature and fictive pressure what, hence, provides the possibility to experimentally verify this formalism. Noteworthy and differing from previous approaches towards the PD ratio, here, the glass transition is considered as non-isoaffine.

physics.chem-ph↗

arXiv2009

Thermodynamics of small systems by nanocalorimetry: from physical to biological nano-objects

Membrane based nanocalorimeters have been developed for ac calorimetry experiments. It has allowed highly sensitive measurements of heat capacity from solid state physics to complex systems like polymers and proteins. In this article we review what has been developed in ac calorimetry toward the measurement of very small systems. Firstly, at low temperature ac calorimetry using silicon membrane permits the measurement of superconducting sample having geometry down to the nanometer scale. New phase transitions have been found in these nanosystems illustrated by heat capacity jumps versus the applied magnetic field. Secondly, a sensor based on ultra-thin polymer membrane will be presented. It has been devoted to thermal measurements of nanomagnetic systems at intermediate temperature (20K to 300K). Thirdly, three specific polyimide membrane based sensors have been designed for room temperature measurements. One is devoted to phase transitions detection in polymer, the second one to protein folding/unfolding studies and the third one will be used for the study of heat release in living cells. The possibility of measuring systems out of equilibrium will be emphasized.

cond-mat.mes-hall↗

arXiv2009

Temperature fluctuations in the Ultimate Regime of Convection

A new regime of turbulent convection has been reported nearly one decade ago, based on global heat transfer measurements at very high Rayleigh numbers. We examine the signature of this "Ultimate Regime" from within the flow itself. A systematic study of probe-size corrections shows that the earlier temperature measurements within the flow were altered by an excessive size of thermometer, but not according to a theoretical model proposed in the literature. Using a probe one order of magnitude smaller than the one used previously, we find evidence that the transition to the Ultimate Regime is indeed accompanied with a clear change in the statistics of temperature fluctuations in the flow.

physics.flu-dyn↗

arXiv2008

Entropy production in temperature modulated differential scanning calorimetry

The non-equilibrium process due to irreversible heat exchanges occurring during a temperature modulated differential scanning calorimetry experiment is investigated in detail. This enables us to define an experimental frequency dependent complex heat capacity from this calorimetric method. The physical meaning of this dynamic heat capacity is discussed. A relationship is clearly established between the imaginary part of this complex quantity and the net entropy created during the experimental time-scale.

cond-mat.other↗

arXiv2008

Temperature of systems out of thermodynamic equilibrium

Two phenomenological approaches are currently used in the study of the vitreous state. One is based on the concept of fictive temperature introduced by Tool [Jour. Research Nat. Bur. Standards 34, 199 (1945)] and recently revisited by Nieuwenhuizen [Phys. Rev. Lett. 80, 5580 (1998)]. The other is based on the thermodynamics of irreversible processes initiated by De Donder at the beginning of the last century [L'Affinité (Gauthier-Villars, Paris, 1927)] and recently used by Möller and co-workers for a thorough study of the glass transition [J. Chem. Phys. 125, 094505 (2006)]. This latter approach leads to the possibility of describing the glass transition by means of the freezing-in of one or more order parameters connected to the internal structural degrees of freedom involved in the vitrification process. In this paper, the equivalence of the two preceding approaches is demonstrated, not only for glasses, but in a very general way for any system undergoing an irreversible transformation. This equivalence allows the definition of an effective temperature for all systems departed from equilibrium generating a positive amount of entropy. In fact, the initial fictive temperature concept of Tool leads to the generalization of the notion of temperature for systems out of thermodynamic equilibrium, for which glasses are just particular cases.

cond-mat.soft↗

arXiv2007

Entropy production in ac-calorimetry

In calorimetry and particularly in heat capacity measurements, different characteristic relaxation time constants may perturb the experiment which cannot be considered at thermodynamic equilibrium. In this case, thermodynamics of irreversible processes has to be taken into account and the calorimetric measurements must be considered as dynamic. In a temperature modulated experiment, such as ac-calorimetry, these non-equilibrium experiments give rise to the notion of frequency dependent complex heat capacity. In this paper, it is shown that for each irreversible process an experimental frequency dependent complex heat capacity can be inferred. Furthermore, we demonstrate rigorously that a same equality connects the imaginary part of these different complex heat capacities with the entropy produced during these irreversible processes. Finally, we claim that the presence of an imaginary part in the measured heat capacity always indicates that a certain amount of heat does not participate to the classical equilibrium heat capacity of the sample when measured over the observation time scale.

cond-mat.other↗

arXiv2007

Macroscopic non-equilibrium thermodynamics in dynamic calorimetry

What is really measured in dynamic calorimetric experiments is still an open question. This paper is devoted to this question, which can be usefully envisaged by means of macroscopic non-equilibrium thermodynamics. From the pioneer work of De Donder on chemical reactions and with other authors along the 20th century, the question is tackled under an historical point of view. A special attention is paid about the notions of frequency dependent complex heat capacity and entropy production due to irreversible processes occurring during an experiment. This phenomenological approach based on thermodynamics, not widely spread in the literature of calorimetry, could open significant perspectives on the study of macro-systems undergoing physico-chemical transformations probed by dynamic calorimetry.

cond-mat.soft↗

arXiv2007

Non-equilibrium heat capacity of polytetrafluoroethylene at room temperature

Polytetrafluoroethylene can be considered as a model for calorimetric studies of complex systems with thermodynamics transitions at ambient temperature. This polymer exhibits two phase transitions of different nature at 292 K and 303 K. We show that sensitive ac-calorimetry measurements allow us to study the thermodynamic behaviour of polytetrafluoroethylene when it is brought out of thermodynamic equilibrium. Thanks to the thermal modelisation of our calorimetric device, the frequency dependent complex heat capacity of this polymer is extracted. The temperature and frequency variations of the real and imaginary parts of the complex heat capacity are obtained when polytetrafluoroethylene undergoes its first-order structural phase transition at 292 K.

cond-mat.soft↗

arXiv2007

Simple derivation of the frequency dependent complex heat capacity

This paper gives a simple derivation of the well-known expression of the frequency dependent complex heat capacity in modulated temperature experiments. It aims at clarified again that the generalized calorimetric susceptibility is only due to the non-equilibrium behaviour occurring in the vicinity of thermodynamic equilibrium of slow internal degrees of freedom of a sample when the temperature oscillates at a well determined frequency.

cond-mat.other↗

arXiv2006

New sensor for thermodynamic measurement of magnetization reversal in magnetic nanomaterials

A sensor for thermal and thermodynamic measurements of small magnetic systems have been designed and built. It is based on a 5μm-thick suspended polymer membrane, which has a very low heat capacity (≈ 10-6 J/K at nitrogen temperature), and on which a heater and a highly sensitive thermometer are deposited. The sensor properties have been characterized as a function of temperature and frequency. Energy exchanges as small as 1 picojoule (10-12 Joule) were detected in the 40K- 300K temperature range. Such values correspond to those required for measuring the thermal signatures occurring during magnetization reversal in very thin samples (typically 10 nm thick), which would be deposited on the membrane. It is expected that this method will constitute a powerful tool in view of analyzing magnetization reversal processes in magnetic nanosystems, e.g. exhibiting the exchange-spring and exchange-bias phenomena.

cond-mat.mes-hall↗