Simulating Rayleigh-Taylor induced magnetohydrodynamic turbulence in prominences

Solar prominences represent large-scale condensations suspended against gravity within the solar atmosphere. The Rayleigh-Taylor (RT) instability is proposed to be one of the important fundamental processes leading to the generation of dynamics at many spatial and temporal scales within these long-lived, cool, and dense structures amongst the solar corona. We run 2.5D ideal magnetohydrodynamic (MHD) simulations with the open-source MPI-AMRVAC code far into the nonlinear evolution of an RT instability perturbed at the prominence-corona interface. Our simulation achieves a resolution down to $\sim 23$ km on a 2D $(x,y)$ domain of size 30 Mm $\times$ 30 Mm. We follow the instability transitioning from a multi-mode linear perturbation to its nonlinear, fully turbulent state. Over the succeeding $\sim 25$ minute period, we perform a statistical analysis of the prominence at a cadence of $\sim 0.858$ s. We find the dominant guiding $B_z$ component induces coherent structure formation predominantly in the vertical velocity $V_y$ component, consistent with observations, demonstrating an anisotropic turbulence state within our prominence. We find power-law scalings in the inertial range for the velocity, magnetic, and temperature fields. The presence of intermittency is evident from the probability density functions of the field fluctuations, which depart from Gaussianity as we consider smaller and smaller scales. In exact agreement, the higher-order structure functions quantify the multifractality, in addition to different scale characteristics and behavior between the longitudinal and transverse directions. Thus, the statistics remain consistent with the conclusions from previous observational studies, enabling us to directly relate the RT instability to the turbulent characteristics found within quiescent prominence.Comment: 21 pages, 17 figures, Accepted for publication in Astronomy and Astrophysic

An Approach to Enhance the Efficiency of the Solar PV Panel in Partial Shading Condition: a Review

Hot spot heating causes permanent destruction of the solar cell structure. Areas with high impurity contaminants and high concentration of transition metals have the most number of hot spot heating. When the operating current of the overall series string approaches the short circuit current of a bad cell then the overall current becomes limited by the bad cell. The good cell becomes forward bias, which reverse biases the bad cell. This leads to large dissipation of power in the bad cell. Enormous power is dissipated in the bad cell or hot spot that results in destructive effects like glass cracking, melting of solder or degradation of a solar cell. The solar panel works best when there is no shade on them. If there is a partial shadow in any one of the arrays, the efficiency of the solar panel drops to a great extent. The shaded cell becomes reverse biased so maximum power will be dissipated on the shaded cell. The heat developed due to the reverse biased of the shaded region adds to the dissipated power

Al2O3 nanoparticles synthesized using various oxidizing agents: Defluoridation performance

This study concerns the removal of fluoride using aluminium oxide nanoparticles synthesized in the presence of oxidizing agents H2SO4, KMnO4 and K2Cr2O7. The obtained nanoparticles were characterized using TGA, FESEM, EDX and XRD. The almost constant weight loss was observed from the TGA data for the temperature range from 400 to 650 °C. XRD analysis with and without oxidizing agents indicated the crystalline behaviour which increased with increasing the temperature. Prepared Al2O3 nanoparticles exhibited a considerable potential for fluoride adsorption from an aqueous medium in the concentration range of 2–8 mg/l. In this case, around 92% fluoride was adsorbed at pH = 4.7. The equilibrium data were well fitted with Freundlich adsorption isotherm, whereas the adsorption kinetic data followed the pseudo second order model

BxC: a swift generator for 3D magnetohydrodynamic turbulence

Magnetohydrodynamic turbulence is central to laboratory and astrophysical plasmas, and is invoked for interpreting many observed scalings. Verifying predicted scaling law behaviour requires extreme-resolution direct numerical simulations (DNS), with needed computing resources excluding systematic parameter surveys. We here present an analytic generator of realistically looking turbulent magnetic fields, that computes 3D ${\cal{O}}(1000^3)$ solenoidal vector fields in minutes to hours on desktops. Our model is inspired by recent developments in 3D incompressible fluid turbulence theory, where a Gaussian white noise vector subjected to a non-linear transformation results in an intermittent, multifractal random field. Our $B\times C$ model has only few parameters that have clear geometric interpretations. We directly compare a (costly) DNS with a swiftly $B\times C$-generated realization, in terms of its (i) characteristic sheet-like structures of current density, (ii) volume-filling aspects across current intensity, (iii) power-spectral behaviour, (iv) probability distribution functions of increments for magnetic field and current density, structure functions, spectra of exponents, and (v) partial variance of increments. The model even allows to mimic time-evolving magnetic and current density distributions and can be used for synthetic observations on 3D turbulent data cubes.Comment: 18 pages, 14 figures, Accepted for publication in Physical Review

A magnetically separable acid-functionalized nanocatalyst for biodiesel production

A robust, magnetically recoverable Fe3O4@SiO2-SO3H core@shell nanoparticulate acid catalyst was successfully synthesized by a stepwise co-precipitation, coating, and functionalization. It was utilized as a heterogeneous catalyst for the transesterification and esterification of triglycerides and free fatty acids in Jatropha curcas oil (JCO) to a fatty acid methyl ester (FAME) mixture. This product conformed to ASTM standards for biodiesel. The as-prepared catalyst had a magnetic saturation of 30.94 emu g-1, surface area of 32.88 m2g-1, acidity of 0.76 mmol g-1, and pore diameter of 3.48 nm. The catalyst showed 98±1% conversion using the optimized reaction conditions of methanol:oil molar ratio of 9:1, 8 wt.% catalyst loading, 80 °C, and 3.5 h. The transesterification of JCO to FAME using the present catalyst benefitted from a very low activation energy of 37.0 kJ mol-1. The solid acid catalyst exhibited excellent chemical and thermal stability, and also reusability based on easy separation from the reaction mixture due to its inherently magnetic nature. Modest deterioration in oil conversion after multiple uses was offset by one-pot, quantitative regeneration of catalyst active sites. This enabled identical performance in JCO methyl transesterification and esterification in the 1st and 10th catalytic cycles

Contrasting maternal and paternal genetic variation of hunter-gatherer groups in Thailand

The Maniq and Mlabri are the only recorded nomadic hunter-gatherer groups in Thailand. Here, we sequenced complete mitochondrial (mt) DNA genomes and ~2.364 Mbp of non-recombining Y chromosome (NRY) to learn more about the origins of these two enigmatic populations. Both groups exhibited low genetic diversity compared to other Thai populations, and contrasting patterns of mtDNA and NRY diversity: there was greater mtDNA diversity in the Maniq than in the Mlabri, while the converse was true for the NRY. We found basal uniparental lineages in the Maniq, namely mtDNA haplogroups M21a, R21 and M17a, and NRY haplogroup K. Overall, the Maniq are genetically similar to other negrito groups in Southeast Asia. By contrast, the Mlabri haplogroups (B5a1b1 for mtDNA and O1b1a1a1b and O1b1a1a1b1a1 for the NRY) are common lineages in Southeast Asian non-negrito groups, and overall the Mlabri are genetically similar to their linguistic relatives (Htin and Khmu) and other groups from northeastern Thailand. In agreement with previous studies of the Mlabri, our results indicate that the Malbri do not directly descend from the indigenous negritos. Instead, they likely have a recent origin (within the past 1,000 years) by an extreme founder event (involving just one maternal and two paternal lineages) from an agricultural group, most likely the Htin or a closely-related group