Search results for "THERMODYNAMICS"
showing 10 items of 2774 documents
Tuning active Brownian motion with shot noise energy pulses
2009
The main aim of this work is to explore the possibility of modeling the biological energy support mediated by absorption of ATP (adenosine triphosphate) as an energetic shot noise. We develop a general model with discrete input of energy pulses and study shot-noise-driven ratchets. We consider these ratchets as prototypes of Brownian motors driven by energy-rich ATP molecules. Our model is a stochastic machine able to acquire energy from the environment and convert it into kinetic energy of motion. We present characteristic features and demonstrate the possibility of tuning these motors by adapting the mean frequency of the discrete energy inputs, which are described as a special shot noise…
Thermodynamic approach to vortex production and diffusion in inhomogeneous superfluid turbulence
2014
In this paper, we use a non-equilibrium thermodynamic framework to generalize a previous nonlocal model of counterflow superfluid turbulence to incorporate some new coupled terms which may be relevant in the evolution of inhomogeneous vortex tangles. The theory chooses as fundamental fields the energy density, the heat flux, and the averaged vortex line length per unit volume. The constitutive quantities are assumed to depend on the fundamental fields and on their first spatial derivatives, allowing us to describe thermal dissipation, vortex diffusion and a new contribution to vortex formation. The restrictions on the constitutive relations are deduced from the entropy principle, using the …
Microscopic theory for hopping transport in glass-forming liquids: mode coupling corrections
1999
Abstract By introducing an order parameter that describes the geometry of clusters of particles, Liu and Oppenheim [Physica A 247 (1997) 183] developed a microscopic theory for hopping transport in glass-forming liquids. In this work we bring this theory within the frame of mode coupling theories in the highly viscous regime. We calculate corrections to the effective longitudinal viscosity that affect its long-time dynamical behavior. Nevertheless, the relation between the longitudinal viscosity and the hopping kernel is not qualitatively altered by mode coupling.
Extended irreversible thermodynamics of liquid helium II: boundary condition and propagation of fourth sound
2001
Abstract The work deals with further developments of a study previously initiated, in which a macroscopic monofluid model of liquid helium II, based on extended irreversible thermodynamics, has been formulated. The transversal modes are investigated and a boundary condition, suggested in the natural way by their analysis, is formulated; the existence of the fourth sound is demonstrated too. A possible experimental determination of the coefficients appearing in the theory is proposed: it is shown that the model is able to express the velocities and the attenuations of the two sounds in bulk helium II, in accord with the experimental data, using a number of parameters smaller than those intro…
Global stability of protein folding from an empirical free energy function
2013
The principles governing protein folding stand as one of the biggest challenges of Biophysics. Modeling the global stability of proteins and predicting their tertiary structure are hard tasks, due in part to the variety and large number of forces involved and the difficulties to describe them with sufficient accuracy. We have developed a fast, physics-based empirical potential, intended to be used in global structure prediction methods. This model considers four main contributions: Two entropic factors, the hydrophobic effect and configurational entropy, and two terms resulting from a decomposition of close-packing interactions, namely the balance of the dispersive interactions of folded an…
Geometric Entropies of Mixing (EOM)
2005
Trigonometric and trigonometric-algebraic entropies are introduced. Regularity increases the entropy and the maximal entropy is shown to result when a regular $n$-gon is inscribed in a circle. A regular $n$-gon circumscribing a circle gives the largest entropy reduction, or the smallest change in entropy from the state of maximum entropy which occurs in the asymptotic infinite $n$ limit. EOM are shown to correspond to minimum perimeter and maximum area in the theory of convex bodies, and can be used in the prediction of new inequalities for convex sets. These expressions are shown to be related to the phase functions obtained from the WKB approximation for Bessel and Hermite functions.
Random Boolean networks response to external periodic signals
2002
Random Boolean networks have been proposed as discrete models of genetic networks. Depending on the values of their control parameters, these networks fall by themselves in order or disorder phases. These networks are autonomous systems: no external inputs are considered. Nevertheless, in the real world the genetic networks are in5uenced by external signals. Many biological rhythms have 24-h periods related to sunlight, coupled with molecular clocks. In this work we study the response of Random Boolean Networks to analytical and non-analytical external periodic signals. The relationship between external and internal parameters for the determination of the dynamical behaviour of this network…
Domains of time-dependent density-potential mappings
2011
The key element in time-dependent density functional theory is the one-to-one correspondence between the one-particle density and the external potential. In most approaches this mapping is transformed into a certain type of Sturm-Liouville problem. Here we give conditions for existence and uniqueness of solutions and construct the weighted Sobolev space they lie in. As a result the class of v-representable densities is considerably widened with respect to previous work.
Meta-work and the analogous Jarzynski relation in ensembles of dynamical trajectories
2014
Recently there has been growing interest in extending the thermodynamic method from static configurations to dynamical trajectories. In this approach, ensembles of trajectories are treated in an analogous manner to ensembles of configurations in equilibrium statistical mechanics: generating functions of dynamical observables are interpreted as partition sums, and the statistical properties of trajectory ensembles are encoded in free-energy functions that can be obtained through large-deviation methods in a suitable large time limit. This establishes what one can call a 'thermodynamics of trajectories'. In this paper we go a step further, and make a first connection to fluctuation theorems b…
Monte Carlo simulation of the glass transition in three-dimensional dense polymer melts
1993
Abstract We determine the incoherent intermediate scattering function φsq(t) for a three-dimensional dense polymer melt. This function shows the signature of a two-step process which was quantitatively compared to the idealized mode coupling theory (MCT) within the β-relaxation regime. A major result of this analysis is that the studied temperature interval splits in a high temperature part, where the idealized theory describes φsq(t) over about three decades in time, and a low temperature part, where it strongly overestimates the freezing tendency of the melt. Since one can qualitatively attribute this discrepancy between the idealized MCT and the simulation data to hopping processes, the …