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Related Concept Videos

Density00:56

Density

Density is an important characteristic of substances, crucial in determining whether an object sinks or floats in a fluid. Its SI unit is kg/m3, and its cgs unit is g/cm3. The density of an object helps in identifying its composition, and also reveals information about the phase of the matter and its substructure. The densities of liquids and solids are roughly comparable, consistent with the fact that their atoms are in close contact. However, gases have much lower densities than liquids and...
Newtonian Fluid: Problem Solving01:18

Newtonian Fluid: Problem Solving

Newtonian fluids exhibit a constant viscosity, meaning their shear stress and shear strain rate are directly proportional. This property ensures a predictable and stable response to applied forces, maintaining a linear relationship between force and flow. Examples include water, air, and light oils, consistently demonstrating this proportional behavior regardless of external conditions.
A velocity gradient forms within the fluid when a Newtonian fluid is placed between two parallel plates, with...
Linear Approximation in Frequency Domain01:26

Linear Approximation in Frequency Domain

Linear systems are characterized by two main properties: superposition and homogeneity. Superposition allows the response to multiple inputs to be the sum of the responses to each individual input. Homogeneity ensures that scaling an input by a scalar results in the response being scaled by the same scalar.
In contrast, nonlinear systems do not inherently possess these properties. However, for small deviations around an operating point, a nonlinear system can often be approximated as linear.
Types of Fluids01:27

Types of Fluids

Fluids can be classified into Newtonian and non-Newtonian fluids based on their response to shear stress. Newtonian fluids have a linear relationship between shear stress and the shear strain rate, following Newton's law of viscosity. Their viscosity remains constant regardless of the shear rate, making their behavior predictable and easier to analyze. Common examples include water, air, oil, and gasoline.
In contrast, non-Newtonian fluids do not follow Newton's law of viscosity, and their...
Characteristics of Fluids01:20

Characteristics of Fluids

When a force is applied parallel to the top surface of a solid, it resists the applied force due to the internal frictional forces between the layers of the solid known as shearing resistance. However, when the force is removed, the shearing forces restore the original shape of the solid. Other deformation forces also cause temporary changes in shape if the forces are not beyond a threshold magnitude. Solids tend to retain their shape, making the study of their rest and motion easier. Beyond...
Characteristics of Fluids01:31

Characteristics of Fluids

Fluids differ from solids primarily in their molecular structure and stress response. Solids have tightly packed molecules with strong intermolecular forces, maintaining their shape and resisting deformation. In contrast, fluids have molecules spaced farther apart with weaker forces, allowing them to flow and deform easily.
Fluids, which include both liquids and gases, are substances that deform continuously under shearing stress. For example, water and oil are liquids with molecules that can...

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An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
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Linear and nonlinear density response functions for a simple atomic fluid.

Benjamin A Dalton1, Kirill S Glavatskiy, Peter J Daivis

  • 1School of Applied Sciences, RMIT University, GPO Box 2476, Melbourne, Victoria 3001, Australia. benjamin.dalton@rmit.edu.au

The Journal of Chemical Physics
|August 2, 2013
PubMed
Summary
This summary is machine-generated.

Molecular dynamics simulations reveal how fluids respond to external fields. This study quantifies linear and nonlinear density responses, aiding in understanding fluid structure and correlations.

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Area of Science:

  • Computational physics
  • Statistical mechanics

Background:

  • Understanding fluid behavior under external forces is crucial in condensed matter physics.
  • Density response functions characterize how fluids reorganize in response to perturbations.

Purpose of the Study:

  • To investigate linear and nonlinear density response functions in simple fluids using molecular dynamics simulations.
  • To establish a method for determining these response functions from simulations under periodic external fields.

Main Methods:

  • Employing molecular dynamics (MD) simulations.
  • Utilizing direct Fourier space decomposition of microscopic density.
  • Applying single-component sinusoidal longitudinal forces with varying wavelengths and amplitudes.

Main Results:

  • Successfully identified distinct orders of response in the fluid.
  • Demonstrated that linear response analysis can determine key liquid properties like the pair correlation function and static structure factor.
  • Showed that large external field amplitudes allow for the determination of nonlinear response functions.

Conclusions:

  • The study provides a robust simulation-based approach to characterizing fluid responses.
  • This method facilitates the calculation of fundamental liquid properties from both linear and nonlinear response analyses.
  • The findings contribute to a deeper understanding of fluid dynamics and statistical physics.