Biomedical subjects

L Diambra

Publications and source records attributed to L Diambra.

14 recordsLinked to original sources

PubMed2005

Complex networks approach to gene expression driven phenotype imaging.

MOTIVATION: The need is to visualize and quantify gene expression spatial patterns. Because of their generality for representation of interaction among several elements, complex networks are used to measure the spatial interactions and adjacencies defined by gene expression patterns. RESULTS: Enhanced visualization of spatial interactions between elements where genes are expressed is possible, allowing the identification of structures which would go unnoticed by using conventional imaging. The quantification of the expression intensity in terms of the node degree and clustering coefficient allows the identification of different types of interactions, yielding insights about cell signaling and differentiation, and providing the basis for comparison and discrimination of the patterns along the developmental stages. AVAILABILITY: Supplementary Material, including visualizations as well as the basic routines for translating gene expression images into complex networks and obtaining node degree and clustering coefficient measurements, are provided. CONTACT: luciano@if.sc.usp.br; diambra@univap.br.

Algorithms↗

PubMed2005

Modeling stochastic Ca2+ release from a cluster of IP3-sensitive receptors.

We focused our attention on Ca(2+) release from the endoplasmic reticulum through a cluster of inositol(1,4,5)-trisphosphate (IP(3)) receptor channels. The random opening and closing of these receptors introduce stochastic effects that have been observed experimentally. Here, we present a stochastic version of Othmer-Tang model (OTM) for IP(3) receptor clusters. We address the average behavior of the channels in response to IP(3) stimuli. In our stochastic simulation we found that the fraction of open channels versus [IP(3)] follows a Hill curve, whose associate Hill coefficient increases when intracellular Ca(2+) level increase. This finding suggests that feedback from cytosolic Ca(2+) plays a key role in the channel response to IP(3). We also study several aspects of the stochastic properties of Ca(2+) release and we compare with experimental observations.

Calcium↗

PubMed2004

Infradian rhythmicity in sleep/wake ratio in developing infants.

Although there are several reports on ultradian and circadian rhythms in newborns, we found only one report in which infradian periodicities are described for heart-rate measurements in the early stages of human development. Here, we report infradian rhythms in the monthly range in the sleep/wake cycle of four infants studied along 24 consecutive weeks. Our procedure was applied to sleep diary records from four healthy newborns. The data were arranged in binary time series representing sleep (-1) or wake (1) states. These time series were integrated in order to obtain the cumulative sleep/wake time. A measure of the sleep/wake ratio (SWR) was obtained by computing the average slope of the cumulative sleep/wake time. To extract periodicities we applied the Fourier periodogram to the temporal course of the SWR. We found a notorious difference in the SWR pattern among infants. In two infants the SWR showed a marked linear decay, spending more time asleep than awake, while in the two other infants oscillated near zero. We found robust oscillations in all children. In all cases the Fourier periodogram results present significant power in the infradian range. From these results, we suggest that sleep and wake durations are probably modulated by some internal stimuli.

Circadian Rhythm↗

PubMed2002

Chaos in two-loop negative feedback systems.

Multiloop delayed negative feedback systems, with each feedback loop having its own characteristic time lag (delay), are used to describe a great variety of systems: optical systems, neural networks, physiological control systems, etc. Previous investigations have shown that if the number of delayed feedback loops is greater than two, the system can exhibit complex dynamics and chaos, but in the case of two delayed loops only periodic solutions were found. Here we show that a period-doubling cascade and chaotic dynamics are also found in systems with two coupled delayed negative feedback loops.

Biophysics↗

PubMed2002

Detecting epileptic spikes.

We present a technique for automatic detection of epileptic spikes in electroencephalogram (EEG) recordings. We used a nonlinear modeling method that enables us to detect rapidly and accurately epileptic behavior in the EEG signal. Our approach is illustrated by an application to interictal activity from a patient with focal epilepsy.

Action Potentials↗

PubMed2002

Ciclograma: a tool for detection of rhythmicities in sleep/wake cycles.

The Fourier spectral analysis of binary time series (or rectangular signals) causes methodological problems, due to the fact that it is based on sinusoidal functions. We propose a new tool for the detection of periodicities in binary time series, focusing on sleep/wake cycles. This methodology is based on a weighted histogram of cycle durations. In this paper, we compare our methodology with the Fourier spectral analysis on the basis of simulated and real binary data sets of various lengths. We also provide an approach to statistical validation of the periodicities determined with our methodology. Furthermore, we analyze the discriminating power of both methods in terms of standard deviation. Our results indicate that the Ciclograma is much more powerful than Fourier analysis when applied on this type of time series.

Algorithms↗

PubMed2001

Information theory approach to learning of the perceptron rule.

By recourse to a method based on information theory, we have studied the generalization problem in perceptrons. We considered different a priori distributions about the weights of the teacher perceptron. Our approach allows us to define the information gain from the examples used in the training procedure. The information gain can be used to choose a convenient example set for training the perceptron and to select the transfer function of the student perceptron.

Journal Article↗

PubMed2001

Divergence measure between chaotic attractors.

We propose a measure of divergence of probability distributions for quantifying the dissimilarity of two chaotic attractors. This measure is defined in terms of a generalized entropy. We illustrate our procedure by considering the effect of additive noise in the well known Hénon attractor. Finally, we show how our approach allows one to detect nonstationary events in a time series.

Journal Article↗

PubMed1996