Search results for "Biological system"
showing 10 items of 319 documents
Multivariate and Multiscale Complexity of Long-Range Correlated Cardiovascular and Respiratory Variability Series
2020
Assessing the dynamical complexity of biological time series represents an important topic with potential applications ranging from the characterization of physiological states and pathological conditions to the calculation of diagnostic parameters. In particular, cardiovascular time series exhibit a variability produced by different physiological control mechanisms coupled with each other, which take into account several variables and operate across multiple time scales that result in the coexistence of short term dynamics and long-range correlations. The most widely employed technique to evaluate the dynamical complexity of a time series at different time scales, the so-called multiscale …
Inclusion of Instantaneous Influences in the Spectral Decomposition of Causality: Application to the Control Mechanisms of Heart Rate Variability
2021
Heart rate variability is the result of several physiological regulation mechanisms, including cardiovascular and cardiorespiratory interactions. Since instantaneous influences occurring within the same cardiac beat are commonplace in this regulation, their inclusion is mandatory to get a realistic model of physiological causal interactions. Here we exploit a recently proposed framework for the spectral decomposition of causal influences between autoregressive processes [2] and generalize it by introducing instantaneous couplings in the vector autoregressive model (VAR). We show the effectiveness of the proposed approach on a toy model, and on real data consisting of heart period (RR), syst…
Study on the transient characteristic in the human visual system using masking experiments
1979
In this paper the visual masking effect is interpreted on the basic of the transient characteristic in two dimensional neuronal networks. The study investigates the suitability of the effect for use as a measurement method. It is shown that the stimulus distribution in space can be scanned at different points in time and that various dynamic characteristic values of the system can be measured.
A “Noise Gene” for Econets
1993
Genetically controlled noise is applied to the weights of neural networks trained with a genetic algorithm. Networks simulate simple organisms living in an environment Reproduction is based on the ability of each network, during its life, to respond to sensory information from the environment with appropriate motor action. Each network has an amount of noise which is genetically inherited (in the ‘noise gene’) with mutations and it varies interindividually. Noise modifies the value of a weight differently for each spreading of the activation through the network. Such noise has a positive effect on the evolutionary increase in fitness and it makes fitness less dependent on the initial choice…
On the modeling of nonlinear interactions in large complex systems
2010
Abstract This work deals with the modeling of large systems of interacting entities in the framework of the mathematical kinetic theory for active particles. The contents are specifically focused on the modeling of nonlinear interactions which is one of the most important issues in the mathematical approach to modeling and simulating complex systems, and which includes a learning–hiding dynamics. Applications are focused on the modeling of complex biological systems and on immune competition.
A kriging interpolation strategy for the optimization of Acidithiobacillus ferrooxidans biomass production using fed-batch bioreactors
2008
In this work, a procedure for the optimization of Acidithiobacillus ferrooxidans biomass production in fed-batch reactors using a model based on optimal spatial interpolation of experimental data is proposed. The approach is useful in those cases where specific growth and substrate consumption rates are unknown. Based on interpolation, the optimal values of biomass and substrate concentrations set points are obtained at the minimum of 2-dimensional cost function. In the fed-batch reactor biomass and substrate concentrations are controlled at their set points by changing the input flow and its concentration. We propose a minimum variance control strategy which improves the classical proporti…
Data-independent acquisition strategies for quantitative proteomics
2013
In shotgun proteomics, data-dependent precursor acquisition (DDA) is widely used to profile protein components in complex samples. Although very popular, there are some inherent limitations to the DDA approach, such as irreproducible precursor ion selection, under-sampling and long instrument cycle times. Unbiased ‘data-independent acquisition’ (DIA) strategies try to overcome those limitations. In MSE, which is supported by Waters Q-TOF instrument platforms, such as the Synapt G2-S, a wide band pass filter is used for precursor selection. During acquisition, alternating MS scans are collected at low and high collision energy (CE), providing precursor and fragment ion information, respectiv…
A revised model for lipid-normalizing δ13C values from aquatic organisms, with implications for isotope mixing models
2006
1. Stable isotope analyses coupled with mixing models are being used increasingly to evaluate ecological management issues and questions. Such applications of stable isotope analyses often require simultaneous carbon and nitrogen analyses from the same sample. Correction of the carbon isotope values to take account of the varying content of 13 C-depleted lipids is then frequently achieved by a lipid-normalization procedure using a model describing the relationship between change in δ 13 C following lipid removal and the original C:N ratio of a sample. 2. We evaluated the applicability of two widely used normalization models using empirical data for muscle tissue from a wide range of fish an…
isotracer: An R package for the analysis of tracer addition experiments
2021
AbstractTracer addition experiments, particularly using isotopic tracers, are becoming increasingly important in a variety of studies aiming at characterizing the flows of molecules or nutrients at different levels of biological organization, from the cellular and tissue levels, to the organismal and ecosystem levels.We present an approach based on Hidden Markov Models (HMM) to estimate nutrient flow parameters across a network, and its implementation in the R package isotracer.The isotracer package is capable of handling a variety of tracer study designs, including continuous tracer drips, pulse experiments, and pulse-chase experiments. It can also take into account tracer decay when radio…
Just noticeable differences in component concentrations modify the odor quality of a blending mixture.
2008
International audience; The odors we perceive are mainly the result of mixtures of odorants that, however, are commonly perceived as single undivided entities; nevertheless, the processes involved remain poorly explored. It has been recently reported that perceptual blending based on configural olfactory processing can cause odorant mixtures to give rise to an emergent odor not present in the components. The present study examined whether specific component proportions are required to elicit an emergent odor. Starting from the composition of a ternary target mixture in which an emergent pineapple odor was perceived, 4 concentration levels of each component were chosen to elicit just noticea…