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At least 631 records · Page 35Linked to original sources
PubMed1999

Fisher-based thermodynamics: its Legendre transform and concavity properties.

It is shown that the Legendre-transform structure of thermodynamics can be replicated without any change if one replaces the entropy S by Fisher's information measure I. Also, the important thermodynamic property of concavity is shown to be obeyed by I. By this use of the Fisher information measure we develop a thermodynamics that seems to be able to treat equilibrium and nonequilibrium situations in a manner entirely similar to the conventional one.

Journal Article↗
PubMed1999

Irreversible thermodynamics of Poisson processes with reaction.

A kinetic model is derived to study the successive movements of particles, described by a Poisson process, as well as their generation. The irreversible thermodynamics of this system is also studied from the kinetic model. This makes it possible to evaluate the differences between thermodynamical quantities computed exactly and up to second-order. Such differences determine the range of validity of the second-order approximation to extended irreversible thermodynamics.

Journal Article↗
PubMed2000

Canonical deformations of surfaces of equilibrium states in thermodynamic phase space

Deformations of submanifolds of thermodynamic equilibrium states introduced by continuous contact maps on a phase-space manifold are considered in terms of the geometrical formulation of thermodynamics. The notion of a contact Hamiltonian is recalled in order to give some possible physical interpretations of such a function in terms of statistical quantities describing initial and deformed systems. Using contact flows we propose a very efficient method for constructing continuous families of thermodynamic systems. A few examples show the possible advantages of using contact Hamiltonians.

Journal Article↗
PubMed2001

Fluctuations in the presence of fields: phenomenological Gaussian approximation and a class of thermodynamic inequalities.

The fluctuations of thermodynamic systems in the presence of the fields are considered. The approach is of phenomenological nature and developed in a Gaussian approximation. The cases of a magnetizable continuum in a magnetoquasistatic field, as well as the so called discrete systems are used to exemplify the study. In the latter case one finds that the fluctuation estimators depend both on the intrinsic properties of the system and on the characteristics of the environment. Following earlier ideas of one of the authors we present a class of thermodynamic inequalities for the systems investigated in this paper. In the case of two variables these inequalities are nonquantum analogs of the well known quantum Heisenberg "uncertainty" relations. In this context, the fluctuation estimators support the idea that Boltzmann's constant k has the signification of a generic indicator of stochasticity for thermodynamic systems.

Journal Article↗
PubMed2002

Generalized thermodynamics of q-deformed bosons and fermions.

We study the thermostatistics of q-deformed bosons and fermions obeying the symmetric (q<-->q(-1)) algebra and show that it can be built on the formalism of q calculus. The entire structure of thermodynamics is preserved if ordinary derivatives are replaced by an appropriate Jackson derivative. In this framework, we derive the most important thermodynamic functions describing the q-boson and q-fermion ideal gases in the thermodynamic limit. We also investigate the semiclassical limit and the low-temperature regime and demonstrate that the nature of the q deformation gives rise to pure quantum statistical effects stronger than undeformed boson and fermion particles.

Journal Article↗
PubMed2002

Out-of-equilibrium thermodynamic relations in systems with aging and slow relaxation.

The experimental time scale dependence of thermodynamic relations in out-of-equilibrium systems with aging phenomena is investigated theoretically by using only aging properties of the two-time correlation functions and the generalized fluctuation-dissipation theorem. We show that there are two experimental time regimes characterized by different thermal properties. In the first regime where the waiting time is much longer than the measurement time, the principle of minimum work holds even though a system is out of equilibrium. In the second regime where both the measurement time and the waiting time are long, the thermal properties are completely different from properties in equilibrium. For the single-correlation-scale systems such as p-spin spherical spin glasses, contrary to a fundamental assumption of thermodynamics, the work done in an infinitely slow operation depends on the path of change of the external field even when the waiting time is infinite. On the other hand, for the multi-correlation-scale systems such as Sherrington-Kirkpatrick model, the work done in an infinitely slow operation is independent of the path. Our results imply that in order to describe thermodynamic properties of systems with aging it is essential to consider the experimental time scales and history of a system as a state variable is necessary.

Journal Article↗
PubMed2003

Dynamic mean-field models from a nonequilibrium thermodynamics perspective.

Complicated dynamic models are often approximated by introducing mean-field approximations and closures. The focus here is on examining such mean-field models using nonequilibrium thermodynamics. Two illustrative examples are studied in terms of the double-generator general equation for the nonequilibrium reversible-irreversible coupling (GENERIC) framework. First, it is shown that a model for the coil-stretch transition of long chains in strong elongation flows as proposed by de Gennes is thermodynamically admissible. In the second example, we study a Gaussian approximation, which is used to simplify the effect of hydrodynamic interactions in polymer solutions. This approximation, which is known to be in conflict with the fluctuation-dissipation theorem, is identified as defective directly when formulated in the thermodynamic formalism.

Journal Article↗
PubMed2004

Statistical thermodynamics of adsorbates with nonsymmetrical lateral interactions.

The exact adsorption thermodynamics of particles with nonsymmetrical ad-ad interactions on a one-dimensional space is presented. The asymmetry is introduced by considering the lateral interactions depending on the orientation of the adsorbed molecules. The adsorption process is monitored by following the adsorption isotherm, the thermodynamic factor, the differential heat of adsorption, and the configurational entropy of the adlayer. A rich variety of different behaviors is found with respect to the standard lattice gas of interacting monomers. The resulting thermodynamic description may also be applicable to adsorption and transport of nonspherical molecules in low-dimensional systems such as carbon nanotubes.

Journal Article↗
PubMed2005

Riemannian geometry of thermodynamics and systems with repulsive power-law interactions.

A Riemannian geometric theory of thermodynamics based on the postulate that the curvature scalar R is proportional to the inverse free energy density is used to investigate three-dimensional fluid systems of identical classical point particles interacting with each other via a power-law potential energy gamma r(-alpha) . Such systems are useful in modeling melting transitions. The limit alpha-->infinity corresponds to the hard sphere gas. A thermodynamic limit exists only for short-range (alpha>3) and repulsive (gamma>0) interactions. The geometric theory solutions for given alpha>3 , gamma>0 , and any constant temperature T have the following properties: (1) the thermodynamics follows from a single function b (rho T(-3/alpha) ) , where rho is the density; (2) all solutions are equivalent up to a single scaling constant for rho T(-3/alpha) , related to gamma via the virial theorem; (3) at low density, solutions correspond to the ideal gas; (4) at high density there are solutions with pressure and energy depending on density as expected from solid state physics, though not with a Dulong-Petit heat capacity limit; (5) for 3 3.7913 a phase transition is required to go between these regimes; (7) for any alpha>3 we may include a first-order phase transition, which is expected from computer simulations; and (8) if alpha-->infinity, the density approaches a finite value as the pressure increases to infinity, with the pressure diverging logarithmically in the density difference.

Journal Article↗
PubMed2006

Nonequilibrium thermodynamics of highly charged ion plasmas.

Thermodynamics of irreversible processes is applied to study the interaction of matter and radiation field in nonlocal thermodynamic equilibrium. The rate of entropy production of matter and radiation field, in contact with a free electron reservoir in local thermodynamic equilibrium, is obtained using the conjugate variables of the state variables. When approximating the electronic configuration populations by an effective Boltzmann law, the corresponding effective temperature is determined by minimizing the rate of entropy production at fixed electronic density, electronic temperature, and radiation field. Numerical results and comparisons with recent experiment for photoionized iron plasma are presented and discussed.

Journal Article↗
PubMed2006

Linear irreversible thermodynamics and coefficient of performance.

Following the recent proposal by Van den Broeck for a heat engine [Phys. Rev. Lett. 95, 190602 (2005)], we analyze the coefficient of performance of a refrigerator in two working regimes using the tools of linear irreversible thermodynamics. In particular, one of the analyzed regimes gives a coefficient of performance which could be considered as the equivalent to the Curzon-Ahlborn efficiency. Also we consider the relation with the Clausius inequality, and some results for the relevant thermodynamic magnitudes in this formalism are confronted with those obtained using the finite-time thermodynamics framework.

Journal Article↗
PubMed2004

Eigenmodes and thermodynamics of a Coulomb chain in a harmonic potential.

The density of ions trapped in a harmonic potential in one dimension is not uniform. Consequently the eigenmodes are not phononlike waves. We calculate the long-wavelength modes in the continuum limit, and evaluate the density of states in the short-wavelength limit for chains of N>>1 ions. Remarkably, the results that are found analytically in the thermodynamic limit provide a good estimate of the spectrum of excitations of small chains down to few tens of ions. The spectra are used to compute the thermodynamic functions of the chain. Deviations from the extensivity of the thermodynamic quantities are found. An analytic expression for the critical transverse frequency determining the stability of a linear chain is derived.

Journal Article↗
PubMed1997

Analysis and quantification of mental stress and fatigue using Maxwell relations from thermodynamics.

Several experimental and theoretical techniques have been developed to analyze both physical and psychological stresses. These techniques have relied mainly on certain parameters based on physiological, behavioral, and performance related data. This study is based on a thought experiment which describes the technique to quantify mental stress based on physiological responses using the entropy concept. It relates different physiological parameters using the Maxwell relations of thermodynamics with a systems approach. Data for testing this analytical approach were obtained from an experimental study which was conducted to determine the effects of a mentally stressful situation (final examination) on the common physiological responses (blood pressure, pulse rate, and oral body temperature) of students. The results indicated that the imposed mental stress causes significant changes in physiological responses. The Maxwell relations of thermodynamics were used to quantify the level of stress under different conditions. The results obtained from these relations validated the principles of thermodynamics as applied to the human system.

Adolescent↗
PubMed2000

Retention and Thermodynamic Properties of Three Insulin Variants on the Reversed-phase Liquid Chromatography.

The retention and thermodynamic behaviour of three insulin variants, bovine, human and porcine insulins, in reversed-phase high-performance liquid chromatography were studied over a range of temperatures between 10 and 65 degrees and a range of methanol concentrations between 53 and 59%(v/v). The results demonstrated that the slight difference of three insulins in the amino acid sequence could be resolved significantly in C(8)-hydrophobic ligand. Values for the relative changes in enthalpy (deltaH deg;/R) and entropy (deltaS deg;*) associated with the interaction process were also determined. These values of thermodynamic parameters would provide further insight into the factors involved in the stabilization of protein conformation and the mechanism of the interaction of peptides with hydrophobic surfaces. The experimental results also demonstrated that the determination of thermodynamic parameters of interactions between peptides and hydrophobic surfaces would provide an alternative approach for the investigation of mechanisms of protein folding and of interaction between proteins.

Journal Article↗
PubMed1996

Effect of the Counterion on Thermodynamic Properties of Aqueous Micellar Solutions of 1-(3,3,4,4,5,5,6,6,6-Nonafluorohexyl) Pyridinium Halides

We report a thermodynamic study of the aqueous solutions of 1-(3,3,4,4,5,5,6,6,6-nonafluorohexyl) pyridinium chloride, bromide, and iodide and N-octyl pyridinium iodide. Dilution enthalpies and osmotic coefficients of the aqueous solutions of these cationic surfactants have been measured at 313 K as a function of the concentration. The experimental data are expressed in terms of apparent and partial molar quantities. The changes in thermodynamic properties upon micellization have been obtained from the experimental data by using a pseudo phase transition approach. The cmc at 313 K have been evaluated from the plot of the milliosmolality, the measured quantity, vs molality. From the comparison with the trends of the enthalpies at 298 K of the same set of compounds, the effect of temperature on the energetics of their solutions can be derived. The trends of thermodynamic properties vs molality and the micellization parameters confirm that the effect of the counterions, however strong and inversely proportional to the radius of the hydrated counterion, seems to be reduced with respect to the hydrogenated analogs. The curves of the apparent and partial molar enthalpies vs m for the bromide and the iodide are lowered, with respect to the curve of the chloride, by an amount comparable to that at 298 K. This observation suggests that the changes in the absolute trends of the curves and in the micellization enthalpies are due to the modification of the more mobile hydrophobic hydration shell of the perfluoroalkyl chain, whereas the hydration sphere of the counterions is practically unaffected. The heat capacity data and the comparison with the behaviour of hydrogenated analogs is in agreement with the above observation. The trends of the free energies confirm that the degree of counterion binding, beta, and the aggregation number, n, increase with the increasing of the radius of the hydrated counterion.

Journal Article↗
PubMed1999

Non-Boltzmann thermodynamic integration (NBTI) for macromolecular systems: relative free energy of binding of trypsin to benzamidine and benzylamine.

The relative free energies of binding of trypsin to two amine inhibitors, benzamidine (BZD) and benzylamine (BZA), were calculated using non-Boltzmann thermodynamic integration (NBTI). Comparison of the simulations with the crystal structures of both complexes, trypsin-BZD and trypsin-BZA, shows that NBTI simulations better sample conformational space relative to thermodynamic integration (TI) simulations. The relative binding free energy calculated using NBTI was much closer to the experimentally determined value than that obtained using TI. The error in the TI simulation was found to be primarily due to incorrect sampling of BZA's conformation in the binding pocket. In contrast, NBTI produces a smooth mutation from BZD to BZA using a surrogate potential, resulting in a much closer agreement between the inhibitors' conformations and the omit electron density maps. This superior agreement between experiment and simulation, of both relative binding free energy differences and conformational sampling, demonstrates NBTI's usefulness for free energy calculations in macromolecular simulations.

Benzamidines↗
PubMed1999

Nucleation and growth of hydroxyapatite on titanium pretreated in NaOH solution: experiments and thermodynamic explanation.

Titanium was submitted to chemical attack with sodium hydroxide solution under hydrothermal (SBF) conditions and then kept for 4 weeks in simulated body fluid after heat treatment. The resultant coating titanium samples were characterized regarding nucleation and growth of hydroxyapatite on their surfaces using scanning electron microscopy and energy dispersive spectroscopy, as well as low angle X-ray diffraction. In order to obtain a thermodynamic explanation of same results, Eh-pH diagrams of Na-Ti-H2O and Ca-Ti-H2O systems at 25, 100, 200, and 300 degrees C were built for selected activities of the species in aqueous solutions. Values of pairs corresponding to the predominance limit of the species in solution at equilibrium with 0.21 atm of oxygen pressure were taken from these Eh-pH diagrams for subsequent building of the pNa-pH and pCa-pH diagrams of the same systems at each referred temperature (pi = -log10ai). In addition, the titanate-apatite free energy of formation was estimated and then a pCa-pH diagram of the Ca-P-Ti-H2O system at 25 degrees C was built. Examination of the resultant diagrams could elucidate the thermodynamic viability of the process.

Coated Materials, Biocompatible↗
PubMed2000

Determination of apparent thermodynamic parameters for adsorption of a midchain peptidyl residue onto a glass surface.

Protein adsorption onto the surface of an implanted material is widely recognized as an important factor controlling the biological response. Although numerous studies have been conducted to investigate protein adsorption behavior, very little is actually understood regarding the specific molecular events involved in protein-surface adsorption processes. As a basic science approach to investigate protein-surface interactions, an experimental method is developed and applied to determine apparent thermodynamic parameters for the adsorption of a single midchain peptidyl residue onto a glass surface. This article presents the results of adsorption studies for four molecular weight ranges of poly-L-lysine onto glass microspheres in physiologic saline at four temperatures. Isotherm data plots are constructed and the apparent changes in enthalpy (DeltaH degrees ), entropy (DeltaS degrees ), and Gibbs' free energy (DeltaG degrees ) are calculated assuming a Langmuir-like model for adsorption. Estimates of apparent DeltaH degrees, DeltaS degrees, and DeltaG degrees for the adsorption of a single midchain lysine residue are determined from the initial slopes of the plots of the apparent thermodynamic parameters versus the degree of polymerization of the adsorbed poly-L-lysine. It is proposed that the generation of such molecular-level adsorption data is a necessary step toward the goal of understanding, predicting, and controlling protein-surface interactions.

Adsorption↗