Search results for " Entropy"
showing 10 items of 236 documents
I. Glass Transition. Theoretical concepts on the glass transition of polymers and their test by computer simulation
1996
Various organic molecules, in particular polymers, are extremely good glass formers and allow the study of supercooled melts near the glass transition in metastable equilibrium. Theories of the glass transition imply such an equilibrium (e.g. mode-coupling theory, or Gibbs-di Marzio theory) and can hence be tested in these systems. Simplified lattice models for polymer melts (e.g. the bond fluctuation model) have been developed that can very efficiently be studied by Monte-Carlo simulation, and although they fail to accurately describe the local structure, they describe many features of the experiments very well. In this model, the mechanism of the glass transition is a competition between …
Glass transition of polymer melts: Test of theoretical concepts by computer simulation.
2003
Abstract Polymers are good glass formers and allow for the study of melts near the glass transition in (meta-)stable equilibrium. Theories of the glass transition imply such an equilibrium and can, hence, be tested by the study of polymer melts. After a brief summary of the basic experimental facts about the glass transition in polymers, the main theoretical concepts are reviewed: mode coupling theory (MCT), entropy theory, free-volume theory, the idea of a growing length describing the size of cooperative regions, etc. Then, two basic coarse-grained models of polymers are described, which have been developed aiming at a test of these concepts. The first model is the bond-fluctuation model …
Monte carlo simulation of the glass transition of polymer melts
2007
The bond fluctuation model of polymer melts is presented as a reasonable compromise between simulation efficiency and realistic chemical detail. It is shown that inclusion of a potential energy that depends on the length of the effective bonds connecting the effective monomers easily creates a conflict between configurational entropy of dense packing and the energetic tendency of the bonds to stretch. This competition leads to a glass transition of the model, which very well describes many features of real systems.
Unexpectedly normal phase behavior of single homopolymer chains
2006
Employing Monte Carlo simulations, we show that the topology of the phase diagram of a single flexible homopolymer chain changes in dependence on the range of an attractive square well interaction between the monomers. For a range of attraction larger than a critical value, the equilibrium phase diagram of the single polymer chain and the corresponding polymer solution phase diagram exhibit vapor (swollen coil, dilute solution), liquid (collapsed globule, dense solution), and solid phases. Otherwise, the liquid-vapor transition vanishes from the equilibrium phase diagram for both the single chain and the polymer solution. This change in topology of the phase diagram resembles the behavior k…
Information Transfer in Linear Multivariate Processes Assessed through Penalized Regression Techniques: Validation and Application to Physiological N…
2020
The framework of information dynamics allows the dissection of the information processed in a network of multiple interacting dynamical systems into meaningful elements of computation that quantify the information generated in a target system, stored in it, transferred to it from one or more source systems, and modified in a synergistic or redundant way. The concepts of information transfer and modification have been recently formulated in the context of linear parametric modeling of vector stochastic processes, linking them to the notion of Granger causality and providing efficient tools for their computation based on the state&ndash
Feasibility of Ultra-Short-Term Analysis of Heart Rate and Systolic Arterial Pressure Variability at Rest and during Stress via Time-Domain and Entro…
2022
Heart Rate Variability (HRV) and Blood Pressure Variability (BPV) are widely employed tools for characterizing the complex behavior of cardiovascular dynamics. Usually, HRV and BPV analyses are carried out through short-term (ST) measurements, which exploit ~five-minute-long recordings. Recent research efforts are focused on reducing the time series length, assessing whether and to what extent Ultra-Short-Term (UST) analysis is capable of extracting information about cardiovascular variability from very short recordings. In this work, we compare ST and UST measures computed on electrocardiographic R-R intervals and systolic arterial pressure time series obtained at rest and during both post…
Propagation of Bankruptcy Risk over Scale-Free Economic Networks.
2022
The propagation of bankruptcy-induced shocks across domestic and global economies is sometimes very dramatic; this phenomenon can be modelled as a dynamical process in economic networks. Economic networks are usually scale-free, and scale-free networks are known to be vulnerable with respect to targeted attacks, i.e., attacks directed towards the biggest nodes of the network. Here we address the following question: to what extent does the scale-free nature of economic networks and the vulnerability of the biggest nodes affect the propagation of economic shocks? We model the dynamics of bankruptcies as the propagation of financial contagion across the banking sector over a scale-free network…
Application of the entropy model to high-curved turbulent flows
2018
The entropy-based approach allows the estimation of the mean flow velocity in open channel flow by using the maximum flow velocity. The entropy model allows to correlate the mean velocity, um, and the maximum velocity, umax by means of a linear relationship, um, = Φ (M) umax, which depends on the entropy parameter, M, characteristic of the fluvial section ([1]). The present work also focuses on high-curved channels where the secondary motion, which is also induced by the channel’s curvature, evolves along the bend. The study is motivated by the fact that meandering bends have radii of curvature continuously variable in stream-wise direction so that convective flow accelerations occur and th…
ENTROPY PARAMETER ESTIMATION IN A HIGH-CURVATURE CHANNEL: EXPERIMENTAL INVESTIGATION IN A LABORATORY FLUME
2017
The entropy model developed by Chiu (1988) allows to correlate the mean velocity, um, and the maximum velocity, umax by means of a linear relationship, um, = Φ (M) umax, which depends on the entropy parameter, M, characteristic of the fluvial section. This formulation was tested on several natural streams with different hydraulic and geometric characteristics (Ammari et al. 2010, Moramarco et al., 2004; Moramarco and Termini, 2015). In this paper, attention is focused on the verification of the entropic relationship between the mean velocity and maximum velocity in the presence of the forcing action due to the variable channel curvature and for different values of the aspect ratio. The anal…
Geometric Brownian Motion (GBM) of Stock Indexes and Financial Market Uncertainty in the Context of Non-Crisis and Financial Crisis Scenarios
2022
The present article proposes a methodology for modeling the evolution of stock market indexes for 2020 using geometric Brownian motion (GBM), but in which drift and diffusion are determined considering two states of economic conjunctures (states of the economy), i.e., non-crisis and financial crisis. Based on this approach, we have found that the GBM proved to be a suitable model for making forecasts of stock market index values, as it describes quite well their future evolution. However, the model proposed by us, modified geometric Brownian motion (mGBM), brings some contributions that better describe the future evolution of stock indexes. Evidence in this regard was provided by analyzing …