Viriato: a Fourier-Hermite spectral code for strongly magnetised fluid-kinetic plasma dynamics

We report on the algorithms and numerical methods used in Viriato, a novel fluid-kinetic code that solves two distinct sets of equations: (i) the Kinetic Reduced Electron Heating Model (KREHM) equations [Zocco & Schekochihin, Phys. Plasmas 18, 102309 (2011)] (which reduce to the standard Reduced-MHD equations in the appropriate limit) and (ii) the kinetic reduced MHD (KRMHD) equations [Schekochihin et al., Astrophys. J. Suppl. 182:310 (2009)]. Two main applications of these equations are magnetised (Alfvenic) plasma turbulence and magnetic reconnection. Viriato uses operator splitting (Strang or Godunov) to separate the dynamics parallel and perpendicular to the ambient magnetic field (assumed strong). Along the magnetic field, Viriato allows for either a second-order accurate MacCormack method or, for higher accuracy, a spectral-like scheme composed of the combination of a total variation diminishing (TVD) third order Runge-Kutta method for the time derivative with a 7th order upwind scheme for the fluxes. Perpendicular to the field Viriato is pseudo-spectral, and the time integration is performed by means of an iterative predictor-corrector scheme. In addition, a distinctive feature of Viriato is its spectral representation of the parallel velocity-space dependence, achieved by means of a Hermite representation of the perturbed distribution function. A series of linear and nonlinear benchmarks and tests are presented, including a detailed analysis of 2D and 3D Orszag-Tang-type decaying turbulence, both in fluid and kinetic regimes.Comment: 42 pages, 15 figures, submitted to J. Comp. Phy

The influence of the HAZ softening on the mechanical behaviour of welded joints containing cracks in the weld metal

The mechanical behaviour of welds containing cracks was analysed through the numerical simulation of the three-point bending tests of welded specimens. This paper presents the mechanical model and the methodology used for the numerical simulation of the tests. The variation in crack driving force of cracked welds is studied as a function of the strength mismatch in the heat affected zone and of the crack position relative to the weld metal/heat affected zone interface. This analysis was performed with recourse to the numerical calculation of the J integral.http://www.sciencedirect.com/science/article/B6V2R-4B0X38N-6/1/7027467d6e068a7f5c062427de733a1

Numerical study of the plastic behaviour in tension of welds in high strength steels

The influence of the mismatch between material properties and constraint on the plastic deformation behaviour of the heat affected zone of welds in high strength steels is investigated in this study, using finite element simulations. An elastoplastic implicit three-dimensional finite element code (EPIM3D) was used in the analysis. The paper presents the mechanical model of the code and the methodology used for the numerical simulation of the tensile test of welded joints. Numerical results of the tensile test of welded samples with different hypothetical widths for the Heat Affected Zone and various material mismatch levels are shown. The analysis concerns the overall strength and ductility of the joint and in relation to the plastic behaviour of the heat affected zone. The influence of the yield stress, tensile strength and constraint on the stress and plastic strain distribution in the soft heat affected zone is also discussed.http://www.sciencedirect.com/science/article/B6TWX-47G3PVT-2/1/f1caf121d3e6678da6f3259e6d795cd

Magnetic-field generation and amplification in an expanding plasma

WOS:000335816700013Particle-cell simulations are used to investigate the formation of magnetic fields B in plasmas with perpendicular electron density and temperature gradients. For system sizes L comparable to the ion skin depth d(i), it is shown that B similar to i/L, consistent with the Biermann battery effect. However, for large L/d(i), it is found that the Weibel instability (due to electron temperature anisotropy) supersedes the Biermann battery as the main producer of B. The Weibel-produced fields saturate at a finite amplitude (plasma beta approximate to 100), independent of L. The magnetic energy spectra below the electron Larmor radius scale are well fitted by the power law with slope -16/3, as predicted by Schekochihin et al

The generation of magnetic fields by the Biermann battery and the interplay with the Weibel instability

An investigation of magnetic fields generated in an expanding bubble of plasma with misaligned temperature and density gradients (driving the Biermann battery mechanism) is performed. With gradient scales L, large-scale magnetic fields are generated by the Biermann battery mechanism with plasma 1, as long as L is comparable to the ion inertial length di. For larger system sizes, L/de 100 (where deis the electron inertial length), the Weibel instability generates magnetic fields of similar magnitude but with wavenumber kde0.2. In both cases, the growth and saturation of these fields have a weak dependence on mass ratio mi/me, indicating electron mediated physics. A scan in system size is performed at mi/me= 2000, showing agreement with previous results with mi/me= 25. In addition, the instability found at large system sizes is quantitatively demonstrated to be the Weibel instability. Furthermore, magnetic and electric energy spectra at scales below the electron Larmor radius are found to exhibit power law behavior with spectral indices -16/3 and -4/3, respectively

Extreme Plasma Astrophysics

This is a science white paper submitted to the Astro-2020 and Plasma-2020 Decadal Surveys. The paper describes the present status and emerging opportunities in Extreme Plasma Astrophysics -- a study of astrophysically-relevant plasma processes taking place under extreme conditions that necessitate taking into account relativistic, radiation, and QED effects.Comment: A science white paper submitted to the Astro-2020 and Plasma-2020 Decadal Surveys. 7 pages including cover page and references. Paper updated in late March 2019 to include a several additional co-authors and references, and a few small change

Electrophoretic analysis of the polypeptide composition during berry development

Research Note

An examination of the influence of emotional solidarity on value cocreation with international muslim travelers

Given the rising Muslim travel market and the scarcity of research on Muslim inbound market, it is important to elucidate how international Muslim travelers are perceived through the lens of residents in non-Islamic countries. This study provided an insight into how value cocreation is created through emotional solidarity and attitudes in the context of the Muslim travel market. Results of the structural model for American residents were comparatively similar to those of their Korean counterparts, which is indicative of both countries’ acceptance and tolerance of international Muslim travelers. In particular, residents’ openness to experience and the perceived benefit of international Muslim travelers for development of the tourist destination were significant predictors of emotional solidarity. Residents’ emotional solidarity subsequently explained their attitude toward international Muslim travelers. Attitude toward international Muslim travelers would lead to a positive attitude toward Muslim tourism, which in turn, triggered value cocreation behavior with international Muslim travelers.info:eu-repo/semantics/acceptedVersio