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Related Concept Videos

Entropy02:39

Entropy

Salt particles that have dissolved in water never spontaneously come back together in solution to reform solid particles. Moreover, a gas that has expanded in a vacuum remains dispersed and never spontaneously reassembles. The unidirectional nature of these phenomena is the result of a thermodynamic state function called entropy (S). Entropy is the measure of the extent to which the energy is dispersed throughout a system, or in other words, it is proportional to the degree of disorder of a...
Entropy01:18

Entropy

The first law of thermodynamics is quantitatively formulated via an equation relating the internal energy of a system, the heat exchanged by it, and the work done on it. A quantitative formulation of the second law of thermodynamics leads to defining a state function, the entropy.
When an ideal gas expands isothermally, the disorder in the gas increases. From the molecular perspective, the gas molecules have more volume to move around in.
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Stress: General Loading Conditions01:15

Stress: General Loading Conditions

To grasp the intricacy of real-world conditions where multiple loads are applied simultaneously to a structure, one might visualize a section passing through a specific point within a body, aligned parallel to the xy plane. This section is subjected to various forces, including original loads, normal forces, and shearing forces.
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Stress Concentrations01:24

Stress Concentrations

Stress concentration is when stress intensifies near discontinuities such as holes or abrupt cross-sectional changes in a structural member. This localized stress can often surpass the average stress within the member. The stress distribution in flat bars, either with a circular hole or varying widths connected by fillets, can be determined experimentally using a photoelastic method. The results are based on ratios of geometric parameters like the ratio of the hole's radius to the smaller width...
Stress Concentrations01:13

Stress Concentrations

The concept of stress concentration is crucial for understanding how materials respond under bending stresses, particularly when there are irregularities or discontinuities in the material's geometry. Normally, stress in a symmetric member subjected to pure bending is assumed to be uniformly distributed across the entire cross-section. However, this assumption does not hold when there are variations in the cross-sectional geometry or the presence of notches and holes.
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General State of Stress01:21

General State of Stress

The general state of stress within a material can be accurately depicted using a stress tensor. This tensor encapsulates the internal forces distributed within a material subjected to external forces or deformations.
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Unbiased entropy estimates in stress: a parameter study.

Aleksandar Boskovic1, Tatjana Loncar-Turukalo, Olivera Sarenac

  • 1University of Novi Sad, Department KTIOS-DEET, Trg D. Obradovica 6, 21000 Novi Sad, University of Belgrade, School of Medicine, Serbia.

Computers in Biology and Medicine
|April 4, 2012
PubMed
Summary

This study introduces a stable method for calculating approximate entropy and sample entropy. It corrects thresholding in stress-exposed rat data, improving cardiovascular disease risk assessment.

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Area of Science:

  • Physiology and Biomedical Engineering
  • Cardiovascular Research
  • Data Analysis and Signal Processing

Background:

  • Approximate entropy and sample entropy are vital for analyzing physiological time series.
  • Previous methods for threshold selection in entropy analysis can be unstable.
  • Stress impacts cardiovascular health, necessitating accurate analysis of physiological signals.

Purpose of the Study:

  • To develop a stable method for unbiased estimation of approximate entropy and sample entropy.
  • To investigate the influence of pattern length, threshold, time delay, and series length on entropy estimation.
  • To propose a correction method for threshold levels in entropy analysis.

Main Methods:

  • Utilized pulse interval signals from normal and borderline hypertensive rats under acute and chronic stress.
  • Systematically varied parameters including pattern length, normalized threshold, time delay, and time series length.
  • Developed and applied a novel method for threshold level correction.

Main Results:

  • Identified the normalized threshold level as the primary source of instability in entropy estimation.
  • Demonstrated that common threshold selection methods can lead to misinterpretations of physiological data.
  • The proposed correction method enhances the stability and reliability of entropy estimates.

Conclusions:

  • A stable working point for entropy estimation is achievable through corrected thresholding.
  • Accurate entropy analysis is crucial for understanding stress-induced cardiovascular changes.
  • The proposed method offers improved insights into cardiovascular disease risk assessment.