Effect of metallic walls on dynamos generated by laminar boundary-driven flow in a spherical domain

We present a numerical study of dynamo action in a conducting fluid encased in a metallic spherical shell. Motions in the fluid are driven by differential rotation of the outer metallic shell, which we refer to as "the wall". The two hemispheres of the wall are held in counter-rotation, producing a steady, axisymmetric interior flow consisting of differential rotation and a two-cell meridional circulation with radial inflow in the equatorial plane. From previous studies, this type of flow is known to maintain a stationary equatorial dipole by dynamo action if the magnetic Reynolds number is larger than about 300 and if the outer boundary is electrically insulating. We vary independently the thickness, electrical conductivity, and magnetic permeability of the wall to determine their effect on the dynamo action. The main results are: (a) Increasing the conductivity of the wall hinders the dynamo by allowing eddy currents within the wall, which are induced by the relative motion of the equatorial dipole field and the wall. This processes can be viewed as a skin effect or, equivalently, as the tearing apart of the dipole by the differential rotation of the wall, to which the field lines are anchored by high conductivity. (b) Increasing the magnetic permeability of the wall favors dynamo action by constraining the magnetic field lines in the fluid to be normal to the wall, thereby decoupling the fluid from any induction in the wall. (c) Decreasing the wall thickness limits the amplitude of the eddy currents, and is therefore favorable for dynamo action, provided that the wall is thinner than the skin depth. We explicitly demonstrate these effects of the wall properties on the dynamo field by deriving an effective boundary condition in the limit of vanishing wall thickness.Comment: accepted for publication in Physical Review

Experimental research of a new generation of support systems for the transport of mineral raw materials

Within the transportation of materials in mining using the belt conveyor systems, a conveyor belt is particularly the component with the highest wear rate. The development trends in the field of conveyor belt wear, in terms of disruption damage, are mostly focused on the innovation of damping components of buffer beds with impact rubber bars. Impact bars are an essential component of innovative buffer beds suitable for several types of belt conveyors. In mining, these bars are also used in buffer beds of bucket wheel excavator used for the extraction of overlying soils. The most important attribute of this support system is the impact resistance. Therefore, the output of the present paper is the determination of the limit impact dynamic loading based on the quantification of the force effect. The buffer bed eliminates the shortcomings of classic constructions, above all a point contact, and it allows better sealing-off of the whole place of an impact if required. Construction of the buffer bed should provide sufficient stiffness, flexibility, ability to direct conveyor belts at the direction of conveying, absorb the kinetic energy of the transported material, and ensure a surface contact between the material and the conveyor belt by increasing the surface friction drag. This paper deals with the experimental measurement of three kinds of impact rubber bars with different frameworks. Impact characteristics of the bars are significantly affected by the material and the type of metallic framework. The examined impact bars were exposed to the effects of the dynamic impact loading that is of great importance and facilitates the simulation of the belt conveyor system operation. The entire loading process was documented and impact load curves in time were analysed. The depth of penetration and the values of impact load were determined.Web of Science22438537

TAO Conceptual Design Report: A Precision Measurement of the Reactor Antineutrino Spectrum with Sub-percent Energy Resolution

The Taishan Antineutrino Observatory (TAO, also known as JUNO-TAO) is a satellite experiment of the Jiangmen Underground Neutrino Observatory (JUNO). A ton-level liquid scintillator detector will be placed at about 30 m from a core of the Taishan Nuclear Power Plant. The reactor antineutrino spectrum will be measured with sub-percent energy resolution, to provide a reference spectrum for future reactor neutrino experiments, and to provide a benchmark measurement to test nuclear databases. A spherical acrylic vessel containing 2.8 ton gadolinium-doped liquid scintillator will be viewed by 10 m^2 Silicon Photomultipliers (SiPMs) of >50% photon detection efficiency with almost full coverage. The photoelectron yield is about 4500 per MeV, an order higher than any existing large-scale liquid scintillator detectors. The detector operates at -50 degree C to lower the dark noise of SiPMs to an acceptable level. The detector will measure about 2000 reactor antineutrinos per day, and is designed to be well shielded from cosmogenic backgrounds and ambient radioactivities to have about 10% background-to-signal ratio. The experiment is expected to start operation in 2022

A New Code for Nonlinear Force-Free Field Extrapolation of the Global Corona

Reliable measurements of the solar magnetic field are still restricted to the photosphere, and our present knowledge of the three-dimensional coronal magnetic field is largely based on extrapolation from photospheric magnetogram using physical models, e.g., the nonlinear force-free field (NLFFF) model as usually adopted. Most of the currently available NLFFF codes have been developed with computational volume like Cartesian box or spherical wedge while a global full-sphere extrapolation is still under developing. A high-performance global extrapolation code is in particular urgently needed considering that Solar Dynamics Observatory (SDO) can provide full-disk magnetogram with resolution up to $4096\times 4096$. In this work, we present a new parallelized code for global NLFFF extrapolation with the photosphere magnetogram as input. The method is based on magnetohydrodynamics relaxation approach, the CESE-MHD numerical scheme and a Yin-Yang spherical grid that is used to overcome the polar problems of the standard spherical grid. The code is validated by two full-sphere force-free solutions from Low & Lou's semi-analytic force-free field model. The code shows high accuracy and fast convergence, and can be ready for future practical application if combined with an adaptive mesh refinement technique.Comment: Accepted by ApJ, 26 pages, 10 figure

Genera Esfera: Interacting with a trackball mapped onto a sphere to explore generative visual worlds

Genera Esfera is an interactive installation that allows the audience to interact and easily become a VJ (visual DJ) in a world of generative visuals. It is an animated and generative graphic environment with a music playlist, a visual spherical world related with and suggested by the music, which reacts and evolves. The installation has been presented at MIRA Live Visual Arts Festival 2015, in Barcelona. Genera Esfera was envisioned, developed and programmed on the basis of two initial ideas: first, to generate our spherical planets we need to work with spherical geometry and program 3D graphics; second, the interaction should be easy to understand, proposing a direct mapping between the visuals and the interface. Our main goal is that participants can focus on exploring the graphic worlds rather than concentrate on understanding the interface. For that purpose we use a trackball to map its position onto sphere rotations. In this paper, we present the interactive installation Genera Esfera, the design guidelines, the mathematics behind the generative visuals and its results.Postprint (published version