Search results for "Entropy"

Quantum fluctuations and correlations in equilibrium and nonequilibrium thermodynamics

2014

Assessing Complexity in Physiological Systems through Biomedical Signals Analysis

2020

The idea that most physiological systems are complex has become increasingly popular in recent decades [...]

Discretising Keyfitz' entropy for studies of actuarial senescence and comparative demography

2023

1. Keyfitz’ entropy is a widely used metric to quantify the shape of the survivorship curve of populations, from plants, to animals, and microbes. Keyfitz’ entropy values 1 correspond to species with a decreasing mortality rate with age (negative senescence), and a Keyfitz entropy of exactly 1 corresponds to a constant mortality rate with age. Keyfitz’ entropy was originally defined using a continuous-time model, and has since been discretised to facilitate its calculation from discrete-time demographic data. 2. Here, we show that the previously used discretisation of the continuous-time metric does not preserve the relationship with increasing, decreasing, or constant mortality rates. To r…

A fast and simple spectrofluorometric method for the determination of alendronate sodium in pharmaceuticals

2014

Introduction: Alendronate sodium enhances bone formation and increases osteoblast proliferation and maturation and leads to the inhibition of osteoblast apoptosis. Therefore, a rapid and simple spectrofluorometric method has been developed and validated for the quantitative determination of it. Methods: The procedure is based on the reaction of primary amino group of alendronate with o-phthalaldehyde (OPA) in sodium hydroxide solution. Results: The calibration graph was linear over the concentration range of 0.0-2.4 μM and limit of detection and limit of quantification of the method was 8.89 and 29 nanomolar, respectively. The enthalpy and entropy of the reaction between alendronate sodium …

Compensated transfer entropy as a tool for reliably estimating information transfer in physiological time series

2013

We present a framework for the estimation of transfer entropy (TE) under the conditions typical of physiological system analysis, featuring short multivariate time series and the presence of instantaneous causality (IC). The framework is based on recognizing that TE can be interpreted as the difference between two conditional entropy (CE) terms, and builds on an efficient CE estimator that compensates for the bias occurring for high dimensional conditioning vectors and follows a sequential embedding procedure whereby the conditioning vectors are formed progressively according to a criterion for CE minimization. The issue of IC is faced accounting for zero-lag interactions according to two a…

Best Practices in Constant pH MD Simulations: Accuracy and Sampling

2022

Various approaches have been proposed to include the effect of pH in molecular dynamics (MD) simulations. Among these, the λ-dynamics approach proposed by Brooks and co-workers [Kong, X.; Brooks III, C. L. J. Chem. Phys.1996, 105, 2414−2423] can be performed with little computational overhead and hfor each typeence be used to routinely perform MD simulations at microsecond time scales, as shown in the accompanying paper [Aho, N. et al. J. Chem. Theory Comput.2022, DOI: 10.1021/acs.jctc.2c00516]. At such time scales, however, the accuracy of the molecular mechanics force field and the parametrization becomes critical. Here, we address these issues and provide the community with guidelines on…

Analisi sperimentale di laboratorio sulla stima della velocità media del flusso mediante la teoria entropica

2014

Information-theoretic assessment of cardiovascular-brain networks during sleep

2015

This study was aimed at detecting the structure of the physiological network underlying the regulation of the cardiovascular and brain systems during normal sleep. To this end, we measured from the polysomnographic recordings of 10 healthy subjects the normalized spectral power of heart rate variability in the high frequency band (HF) and the EEG power in the δ, θ, α, σ, and β bands. Then, the causal statistical dependencies within and between these six time series were assessed in terms of internal information (conditional self entropy, CSE) and information transfer (transfer entropy, TE) computed via a linear method exploiting multiple regression models and a nonlinear method combining ne…

Measuring Functional Connectivity of Human Intra-Cortex Regions with Total Correlation

2021

The economy of brain organization makes the primate brain consume less energy but efficiency. The neurons densely wired each other dependent on both anatomy structure connectivity and functional connectivity. Here, I only describe functional connectivity with Functional Magnetic Resonance Imaging (fMRI) data. Most importantly, how to quantitative measure information share or separate among functional brain regions, what’s worse, fMRI data exist large dimensional problems or “curse dimensionality” [1]. However, the multivariate total correlation method can perfectly address the above problems. In this paper, two things measured with the information-theoretic technique - total correlation [2,…

Causal linear parametric model for baroreflex gain assessment in patients with recent myocardial infarction

2001

Spectral and cross-spectral analysis of R-R interval and systolic arterial pressure (SAP) spontaneous fluctuations have been proposed for noninvasive evaluation of baroreflex sensitivity (BRS). However, results are not in good agreement with clinical measurements. In this study, a bivariate parametric autoregressive model with exogenous input (ARXAR model), able to divide the R-R variability into SAP-related and -unrelated parts, was used to quantify the gain (αARXAR) of the baroreflex regulatory mechanism. For performance assessing, two traditional noninvasive methods based on frequency domain analysis [spectral, baroreflex gain by autogressive model (αAR); cross-spectral, baroreflex gain…