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Entropy, Volume 14, Issue 4 (April 2012), Pages 599-847

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Open AccessArticle Thermodynamic Modelling of an Ejector with Compressible Flow by a One-Dimensional Approach
Entropy 2012, 14(4), 599-613; doi:10.3390/e14040599
Received: 10 January 2012 / Revised: 9 March 2012 / Accepted: 12 March 2012 / Published: 23 March 2012
Cited by 1 | PDF Full-text (363 KB) | HTML Full-text | XML Full-text
Abstract
The purpose of this study is the dimensioning of the cylindrical mixing chamber of a compressible fluid ejector used in particular in sugar refineries for degraded vapor re‑compression at the calandria exit, during the evaporation phase. The method used, known as the [...] Read more.
The purpose of this study is the dimensioning of the cylindrical mixing chamber of a compressible fluid ejector used in particular in sugar refineries for degraded vapor re‑compression at the calandria exit, during the evaporation phase. The method used, known as the “integral” or “thermodynamic model”, is based on the model of the one‑dimensional isentropic flow of perfect gases with the addition of a model of losses. Characteristic curves and envelope curves are plotted. The latter are an interesting tool from which the characteristic dimensions of the ejector can be rapidly obtained for preliminary dimensioning (for an initial contact with a customer for example). These ejectors, which were specifically designed for the process rather than selected from a catalog of standard devices, will promote energy saving. Full article
Open AccessArticle Modeling Time’s Arrow
Entropy 2012, 14(4), 614-629; doi:10.3390/e14040614
Received: 2 February 2012 / Revised: 13 March 2012 / Accepted: 19 March 2012 / Published: 23 March 2012
Cited by 3 | PDF Full-text (236 KB) | HTML Full-text | XML Full-text
Abstract
Quantum gravity, the initial low entropy state of the Universe, and the problem of time are interlocking puzzles. In this article, we address the origin of the arrow of time from a cosmological perspective motivated by a novel approach to quantum gravitation. [...] Read more.
Quantum gravity, the initial low entropy state of the Universe, and the problem of time are interlocking puzzles. In this article, we address the origin of the arrow of time from a cosmological perspective motivated by a novel approach to quantum gravitation. Our proposal is based on a quantum counterpart of the equivalence principle, a general covariance of the dynamical phase space. We discuss how the nonlinear dynamics of such a system provides a natural description for cosmological evolution in the early Universe. We also underscore connections between the proposed non-perturbative quantum gravity model and fundamental questions in non-equilibrium statistical physics. Full article
(This article belongs to the Special Issue Arrow of Time)
Open AccessArticle Effect of Gold Nanoparticle Conjugation on Peptide Dynamics and Structure
Entropy 2012, 14(4), 630-641; doi:10.3390/e14040630
Received: 31 January 2012 / Revised: 10 March 2012 / Accepted: 19 March 2012 / Published: 23 March 2012
Cited by 13 | PDF Full-text (383 KB) | HTML Full-text | XML Full-text
Abstract
Molecular dynamics simulations were used to characterize the structure and dynamics for several peptides and the effect of conjugating them to a gold nanoparticle. Peptide structure and dynamics were compared for two cases: unbound peptides in water, and peptides bound to the [...] Read more.
Molecular dynamics simulations were used to characterize the structure and dynamics for several peptides and the effect of conjugating them to a gold nanoparticle. Peptide structure and dynamics were compared for two cases: unbound peptides in water, and peptides bound to the gold nanoparticle surface in water. The results show that conjugating the peptides to the gold nanoparticle usually decreases conformational entropy, but sometimes increases entropy. Conjugating the peptides can also result in more extended structures or more compact structures depending on the amino acid sequence of the peptide. The results also suggest that if one wishes to use peptide-nanoparticle conjugates for drug delivery it is important that the peptides contain secondary structure in solution because in our simulations the peptides with little to no secondary structure adsorbed to the nanoparticle surface. Full article
Open AccessArticle Association of Finite-Time Thermodynamics and a Bond-Graph Approach for Modeling an Endoreversible Heat Engine
Entropy 2012, 14(4), 642-653; doi:10.3390/e14040642
Received: 16 January 2012 / Revised: 13 March 2012 / Accepted: 23 March 2012 / Published: 28 March 2012
Cited by 3 | PDF Full-text (175 KB) | HTML Full-text | XML Full-text
Abstract
In recent decades, the approach known as Finite-Time Thermodynamics has provided a fruitful theoretical framework for the optimization of heat engines operating between a heat source (at temperature ) and a heat sink (at temperature ). The aim of this paper [...] Read more.
In recent decades, the approach known as Finite-Time Thermodynamics has provided a fruitful theoretical framework for the optimization of heat engines operating between a heat source (at temperature ) and a heat sink (at temperature ). The aim of this paper is to propose a more complete approach based on the association of Finite-Time Thermodynamics and the Bond-Graph approach for modeling endoreversible heat engines. This approach makes it possible for example to find in a simple way the characteristics of the optimal operating point at which the maximum mechanical power of the endoreversible heat engine is obtained with entropy flow rate as control variable. Furthermore it provides the analytical expressions of the optimal operating point of an irreversible heat engine where the energy conversion is accompanied by irreversibilities related to internal heat transfer and heat dissipation phenomena. This original approach, applied to an analysis of the performance of a thermoelectric generator, will be the object of a future publication. Full article
(This article belongs to the Special Issue Concepts of Entropy and Their Applications)
Open AccessArticle A Rotated Quasi-Orthogonal Space-Time Block Code for Asynchronous Cooperative Diversity
Entropy 2012, 14(4), 654-664; doi:10.3390/e14040654
Received: 16 February 2012 / Revised: 4 March 2012 / Accepted: 22 March 2012 / Published: 29 March 2012
Cited by 2 | PDF Full-text (119 KB) | HTML Full-text | XML Full-text
Abstract
The rotated quasi-orthogonal space-time block code (RQSTBC) for asynchronous cooperative diversity is proposed in this paper. The source selects half of the symbols from a signal constellation set and the other half of them from that constellation rotated with the optimum angle. [...] Read more.
The rotated quasi-orthogonal space-time block code (RQSTBC) for asynchronous cooperative diversity is proposed in this paper. The source selects half of the symbols from a signal constellation set and the other half of them from that constellation rotated with the optimum angle. Meanwhile, it constructs orthogonal frequency division multiplexing (OFDM) frames to counterbalance time delays of the signals. Then, relays create the frequency domain quasi-orthogonal space-time block transmitted signals matrix in such a way that its items are staggered to take on the Jafarkhani code structure or time-reversion of it. These three stages let the received signals at the destination take on RQSTBC structure with diversity order 4, which results in the fast symbol-pair-wise maximum likelihood (ML) decoder. Simulation results have shown that the proposed scheme outperforms the other asynchronous cooperative diversity schemes considered in this paper. Full article
(This article belongs to the Special Issue Information Theory Applied to Communications and Networking)
Open AccessArticle Experimental Test of the “Special State” Theory of Quantum Measurement
Entropy 2012, 14(4), 665-686; doi:10.3390/e14040665
Received: 25 December 2011 / Revised: 21 March 2012 / Accepted: 26 March 2012 / Published: 2 April 2012
Cited by 3 | PDF Full-text (335 KB) | HTML Full-text | XML Full-text
Abstract
An experimental test of the “special state” theory of quantum measurement is proposed. It should be feasible with present-day laboratory equipment and involves a slightly elaborated Stern–Gerlach setup. The “special state” theory is conservative with respect to quantum mechanics, but radical with [...] Read more.
An experimental test of the “special state” theory of quantum measurement is proposed. It should be feasible with present-day laboratory equipment and involves a slightly elaborated Stern–Gerlach setup. The “special state” theory is conservative with respect to quantum mechanics, but radical with respect to statistical mechanics, in particular regarding the arrow of time. In this article background material is given on both quantum measurement and statistical mechanics aspects. For example, it is shown that future boundary conditions would not contradict experience, indicating that the fundamental equal-a-priori-probability assumption at the foundations of statistical mechanics is far too strong (since future conditioning reduces the class of allowed states). The test is based on a feature of this theory that was found necessary in order to recover standard (Born) probabilities in quantum measurements. Specifically, certain systems should have “noise” whose amplitude follows the long-tailed Cauchy distribution. This distribution is marked by the occasional occurrence of extremely large signals as well as a non-self-averaging property. The proposed test is a variant of the Stern–Gerlach experiment in which protocols are devised, some of which will require the presence of this noise, some of which will not. The likely observational schemes would involve the distinction between detection and non-detection of that “noise”. The signal to be detected (or not) would be either single photons or electric fields (and related excitations) in the neighborhood of the ends of the magnets. Full article
(This article belongs to the Special Issue Arrow of Time)
Open AccessArticle Protein Loop Dynamics Are Complex and Depend on the Motions of the Whole Protein
Entropy 2012, 14(4), 687-700; doi:10.3390/e14040687
Received: 16 February 2012 / Revised: 27 March 2012 / Accepted: 29 March 2012 / Published: 10 April 2012
Cited by 7 | PDF Full-text (493 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We investigate the relationship between the motions of the same peptide loop segment incorporated within a protein structure and motions of free or end-constrained peptides. As a reference point we also compare against alanine chains having the same length as the loop. [...] Read more.
We investigate the relationship between the motions of the same peptide loop segment incorporated within a protein structure and motions of free or end-constrained peptides. As a reference point we also compare against alanine chains having the same length as the loop. Both the analysis of atomic molecular dynamics trajectories and structure-based elastic network models, reveal no general dependence on loop length or on the number of solvent exposed residues. Rather, the whole structure affects the motions in complex ways that depend strongly and specifically on the tertiary structure of the whole protein. Both the Elastic Network Models and Molecular Dynamics confirm the differences in loop dynamics between the free and structured contexts; there is strong agreement between the behaviors observed from molecular dynamics and the elastic network models. There is no apparent simple relationship between loop mobility and its size, exposure, or position within a loop. Free peptides do not behave the same as the loops in the proteins. Surface loops do not behave as if they were random coils, and the tertiary structure has a critical influence upon the apparent motions. This strongly implies that entropy evaluation of protein loops requires knowledge of the motions of the entire protein structure. Full article
(This article belongs to the Special Issue Loop Entropy)
Figures

Open AccessArticle Tsallis Relative Entropy and Anomalous Diffusion
Entropy 2012, 14(4), 701-716; doi:10.3390/e14040701
Received: 1 March 2012 / Revised: 19 March 2012 / Accepted: 30 March 2012 / Published: 10 April 2012
Cited by 18 | PDF Full-text (182 KB) | HTML Full-text | XML Full-text
Abstract
In this paper we utilize the Tsallis relative entropy, a generalization of the Kullback–Leibler entropy in the frame work of non-extensive thermodynamics to analyze the properties of anomalous diffusion processes. Anomalous (super-) diffusive behavior can be described by fractional diffusion equations, where [...] Read more.
In this paper we utilize the Tsallis relative entropy, a generalization of the Kullback–Leibler entropy in the frame work of non-extensive thermodynamics to analyze the properties of anomalous diffusion processes. Anomalous (super-) diffusive behavior can be described by fractional diffusion equations, where the second order space derivative is extended to fractional order α ∈ (1, 2). They represent a bridging regime, where for α = 2 one obtains the diffusion equation and for α = 1 the (half) wave equation is given. These fractional diffusion equations are solved by so-called stable distributions, which exhibit heavy tails and skewness. In contrast to the Shannon or Tsallis entropy of these distributions, the Kullback and Tsallis relative entropy, relative to the pure diffusion case, induce a natural ordering of the stable distributions consistent with the ordering implied by the pure diffusion and wave limits. Full article
(This article belongs to the Special Issue Tsallis Entropy)
Open AccessArticle Entropy Generation During the Interaction of Thermal Radiation with a Surface
Entropy 2012, 14(4), 717-735; doi:10.3390/e14040717
Received: 15 February 2012 / Revised: 27 March 2012 / Accepted: 27 March 2012 / Published: 11 April 2012
Cited by 5 | PDF Full-text (809 KB) | HTML Full-text | XML Full-text
Abstract
The entropy calculation for radiation fluxes is reviewed and applied to simple radiation-surface interactions. A plate interacting with radiation from a hot object in the zenith of the hemisphere surrounded by a colder atmosphere is analyzed in detail. The entropy generation rate [...] Read more.
The entropy calculation for radiation fluxes is reviewed and applied to simple radiation-surface interactions. A plate interacting with radiation from a hot object in the zenith of the hemisphere surrounded by a colder atmosphere is analyzed in detail. The entropy generation rate upon absorption and reflection of the incoming radiation is calculated and discussed. The plate is adiabatic in a first version (thermal equilibrium), then its temperature is fixed by allowing a heat flux to or from the plate. This analysis prepares the way towards an entropy generation minimization analysis of more complex radiation settings. Full article
(This article belongs to the Special Issue Entropy Generation Minimization)
Open AccessArticle Computing the Topological Entropy of Multimodal Maps via Min-Max Sequences
Entropy 2012, 14(4), 742-768; doi:10.3390/e14040742
Received: 9 February 2012 / Revised: 30 March 2012 / Accepted: 2 April 2012 / Published: 18 April 2012
Cited by 6 | PDF Full-text (353 KB) | HTML Full-text | XML Full-text
Abstract
We derive an algorithm to recursively determine the lap number (minimal number of monotonicity segments) of the iterates of twice differentiable l-modal map, enabling to numerically calculate the topological entropy of these maps. The algorithm is obtained by the min-max sequences—symbolic sequences [...] Read more.
We derive an algorithm to recursively determine the lap number (minimal number of monotonicity segments) of the iterates of twice differentiable l-modal map, enabling to numerically calculate the topological entropy of these maps. The algorithm is obtained by the min-max sequences—symbolic sequences that encode qualitative information about all the local extrema of iterated maps. Full article
Open AccessArticle Self-Energy Closure for Inhomogeneous Turbulent Flows and Subgrid Modeling
Entropy 2012, 14(4), 769-799; doi:10.3390/e14040769
Received: 14 March 2012 / Revised: 10 April 2012 / Accepted: 11 April 2012 / Published: 18 April 2012
Cited by 7 | PDF Full-text (221 KB) | HTML Full-text | XML Full-text
Abstract
A new statistical dynamical closure theory for general inhomogeneous turbulent flows and subgrid modeling is presented. This Self-Energy (SE) closure represents all eddy interactions through nonlinear dissipation or forcing ‘self-energy’ terms in the mean-field, covariance and response function equations. This makes the [...] Read more.
A new statistical dynamical closure theory for general inhomogeneous turbulent flows and subgrid modeling is presented. This Self-Energy (SE) closure represents all eddy interactions through nonlinear dissipation or forcing ‘self-energy’ terms in the mean-field, covariance and response function equations. This makes the renormalization of the bare dissipation and forcing, and the subgrid modeling problem, transparent. The SE closure generalizes the quasi-diagonal direct interaction closure to allow for more complex interactions. The SE closure is applicable to flows in different geometries, is exact near maximum entropy states corresponding to canonical equilibrium, and provides a framework for deriving simpler realizable closures. Full article
(This article belongs to the Special Issue Concepts of Entropy and Their Applications)
Open AccessArticle Entropies and Scaling Exponents of Street and Fracture Networks
Entropy 2012, 14(4), 800-833; doi:10.3390/e14040800
Received: 23 March 2012 / Revised: 7 April 2012 / Accepted: 10 April 2012 / Published: 19 April 2012
Cited by 16 | PDF Full-text (1771 KB) | HTML Full-text | XML Full-text
Abstract
Many natural and man-made lineaments form networks that can be analysed through entropy and energy considerations. Here we report the results of a detailed study of the variations in trends and lengths of 1554 named streets and 6004 street segments, forming a [...] Read more.
Many natural and man-made lineaments form networks that can be analysed through entropy and energy considerations. Here we report the results of a detailed study of the variations in trends and lengths of 1554 named streets and 6004 street segments, forming a part of the evolving street network of the city of Dundee in East Scotland. Based on changes in the scaling exponents (ranging from 0.24 to 3.89), the streets can be divided into 21 populations. For comparison, we analysed 221 active crustal fractures in Iceland that (a) are of similar lengths as the streets of Dundee; (b) are composed of segments; and (c) form evolving networks. The streets and fractures follow power-law size distributions (validated through various statistical tests) that can be partly explained in terms of the energies needed for their formation. The entropies of the 21 street populations and 9 fracture populations show strong linear correlations with (1) the scaling exponents (R2 = 0.845–0.947 for streets, R2 = 0.859 for fractures) and with (2) the length ranges, that is, the differences between the longest and shortest streets/fractures, (R2 = 0.845–0.906 for streets, R2 = 0.927 for fractures). Full article
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Open AccessArticle Open Problems on Information and Feedback Controlled Systems
Entropy 2012, 14(4), 834-847; doi:10.3390/e14040834
Received: 16 January 2012 / Revised: 28 March 2012 / Accepted: 12 April 2012 / Published: 19 April 2012
Cited by 11 | PDF Full-text (119 KB) | HTML Full-text | XML Full-text
Abstract
Feedback or closed-loop control allows dynamical systems to increase their performance up to a limit imposed by the second law of thermodynamics. It is expected that within this limit, the system performance increases as the controller uses more information about the system. [...] Read more.
Feedback or closed-loop control allows dynamical systems to increase their performance up to a limit imposed by the second law of thermodynamics. It is expected that within this limit, the system performance increases as the controller uses more information about the system. However, despite the relevant progresses made recently, a general and complete formal development to justify this statement using information theory is still lacking. We present here the state-of-the-art and the main open problems that include aspects of the redundancy of correlated operations of feedback control and the continuous operation of feedback control. Complete answers to these questions are required to firmly establish the thermodynamics of feedback controlled systems. Other relevant open questions concern the implications of the theoretical results for the limitations in the performance of feedback controlled flashing ratchets, and for the operation and performance of nanotechnology devices and biological systems. Full article
(This article belongs to the Special Issue Advances in Applied Thermodynamics)

Other

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Open AccessLetter Radiation Entropy Bound from the Second Law of Thermodynamics
Entropy 2012, 14(4), 736-741; doi:10.3390/e14040736
Received: 14 February 2012 / Revised: 22 March 2012 / Accepted: 6 April 2012 / Published: 13 April 2012
PDF Full-text (67 KB) | HTML Full-text | XML Full-text
Abstract
It has been suggested heuristically by Unruh and Wald, and independently by Page, that at given energy and volume, thermal radiation has the largest entropy. The suggestion leads to the corresponding universal bound on entropy of physical systems. Using a gedanken experiment [...] Read more.
It has been suggested heuristically by Unruh and Wald, and independently by Page, that at given energy and volume, thermal radiation has the largest entropy. The suggestion leads to the corresponding universal bound on entropy of physical systems. Using a gedanken experiment we show that the bound follows from the Second Law of Thermodynamics if the CPT symmetry is assumed and a general condition on matter holds. The experiment suggests that a wide class of Lorentz invariant local quantum field theories obeys a bound on the density of states. Full article

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