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Extended kinetic theory applied to pressure-controlled shear flows of frictionless spheres between rigid, bumpy planes.
Soft Matter
November 2024
Politecnico di Milano, 20133 Milano, Italy.
We numerically investigate, through discrete element simulations, the steady flow of identical, frictionless spheres sheared between two parallel, bumpy planes in the absence of gravity and under a fixed normal load. We measure the spatial distributions of solid volume fraction, mean velocity, intensity of agitation and stresses, and confirm previous results on the validity of the equation of state and the viscosity predicted by the kinetic theory of inelastic granular gases. We also directly measure the spatial distributions of the diffusivity and the rate of collisional dissipation of the fluctuation kinetic energy, and successfully test the associated constitutive relations of the extended kinetic theory, , a kinetic theory which includes the role of velocity correlations.
View Article and Find Full Text PDFHarnessing collisional nonlinearity for enhanced harmonic generation by ultraviolet plasmonic nanoparticles.
J Chem Phys
August 2024
Department of Physical and Chemical Sciences, University of L'Aquila, Via Vetoio, 67100 L'Aquila, Italy.
We investigate the contribution of inelastic electron collisions to nonlinear (NL) dynamics in ultraviolet plasmonic nanoparticles, exploring their potential for harmonic generation. Employing the Landau weak coupling formalism to model radiation-driven electron dynamics in sodium and aluminum, we account for both electron-electron and electron-phonon scattering processes by a set of hydrodynamic equations, which we solve perturbatively to obtain third-order NL susceptibilities. Furthermore, we model high harmonic generation enhanced by localized surface plasmons in nanospheres composed of such poor metals, demonstrating their efficient operation for extreme ultraviolet generation.
View Article and Find Full Text PDFInverse bremsstrahlung absorption rate for super-Gaussian electron distribution functions including plasma screening.
Phys Rev E
May 2024
Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
We provide analytic expressions for the effective Coulomb logarithm for inverse bremsstrahlung absorption which predict significant corrections to the Langdon effect and overall absorption rate compared to previous estimates. The calculation of the collisional absorption rate of laser energy in a plasma by the inverse bremsstrahlung mechanism usually makes the approximation of a constant Coulomb logarithm. We dispense with this approximation and instead take into account the velocity dependence of the Coulomb logarithm, leading to a more accurate expression for the absorption rate valid in both classical and quantum conditions.
View Article and Find Full Text PDFMagnetoacoustic cutoff effect in numerical simulations of the partially ionized solar atmosphere.
Philos Trans A Math Phys Eng Sci
June 2024
Shenzhen Key Laboratory of Numerical Prediction for Space Storm, Harbin Institute of Technology, Shenzhen 51805, People's Republic of China.
The cutoff effect is a significant determinant of solar magnetohydrodynamic wave propagation and hence pivotal in energy transfer studies, such as solar plasma heating and seismological diagnostics. Despite continuous efforts, no good agreement between observed waveperiods and theory or numerical simulations was found. Our objective is to investigate the magnetoacoustic cutoff effect in the partially ionized solar atmosphere, factoring in the two-fluid effects.
View Article and Find Full Text PDFStructures of strong shocks in low-density helium and neon gases.
Phys Rev E
September 2023
Center for Energy Research and Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, California 92093, USA.
Article Synopsis
- Strong shocks are critical in high-energy-density environments, like inertial confinement fusion, but spatial measurements of these shocks are limited.
- This study utilized an imaging spectrometer to examine soft x-ray emissions from shock fronts in helium-neon mixtures and pure neon, finding that the shock width in the helium mixture is approximately double that in pure neon.
- The research indicates distinct precursor layers in both gases, with higher electron temperatures in the helium mixture, and simulations reveal that thermal conduction and ion kinetics significantly influence precursor formation and shock characteristics.
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