Current status of turbulent dynamo theory: From large-scale to small-scale dynamos

Several recent advances in turbulent dynamo theory are reviewed. High resolution simulations of small-scale and large-scale dynamo action in periodic domains are compared with each other and contrasted with similar results at low magnetic Prandtl numbers. It is argued that all the different cases show similarities at intermediate length scales. On the other hand, in the presence of helicity of the turbulence, power develops on large scales, which is not present in non-helical small-scale turbulent dynamos. At small length scales, differences occur in connection with the dissipation cutoff scales associated with the respective value of the magnetic Prandtl number. These differences are found to be independent of whether or not there is large-scale dynamo action. However, large-scale dynamos in homogeneous systems are shown to suffer from resistive slow-down even at intermediate length scales. The results from simulations are connected to mean field theory and its applications. Recent work on helicity fluxes to alleviate large-scale dynamo quenching, shear dynamos, nonlocal effects and magnetic structures from strong density stratification are highlighted. Several insights which arise from analytic considerations of small-scale dynamos are discussed.Comment: 36 pages, 11 figures, Spa. Sci. Rev., submitted to the special issue "Magnetism in the Universe" (ed. A. Balogh

Applications of lignin in the agri-food industry

Of late, valorization of agri-food industrial by-products and their sustainable utilization is gaining much contemplation world-over. Globally, 'Zero Waste Concept' is promoted with main emphasis laid towards generation of minimal wastes and maximal utilization of plantbased agri-food raw materials. One of the wastes/by-products in the agri-food industry are the lignin, which occurs as lignocellulosic biomass. This biomass is deliberated to be an environmental pollutant as they offer resistance to natural biodegradation. Safe disposal of this biomass is often considered a major challenge, especially in low-income countries. Hence, the application of modern technologies to effectively reduce these types of wastes and maximize their potential use/applications is vital in the present day scenario. Nevertheless, in some of the high-income countries, attempts have been made to efficiently utilize lignin as a source of fuel, as a raw material in the paper industry, as a filler material in biopolymer based packaging and for producing bioethanol. However, as of today, agri-food industrial applications remains significantly underexplored. Chemically, lignin is heterogeneous, bio-polymeric, polyphenolic compound, which is present naturally in plants, providing mechanical strength and rigidity. Reports are available wherein purified lignin is established to possess therapeutic values; and are rich in antioxidant, anti-microbial, anti-carcinogenic, antidiabetic properties, etc. This chapter is divided into four sub-categories focusing on various technological aspects related to isolation and characterization of lignin; established uses of lignin; proved bioactivities and therapeutic potentials of lignin, and finally on identifying the existing research gaps followed by future recommendations for potential use from agri-food industrial wastes.Theme of this chapter is based on our ongoing project- Valortech, which has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 810630