Material,energy and spatial fields for metallogenic prediction:Theory and practice An example:Limu Sn polymetallic crisis mines

The Limu tin deposits located in the Nanling tin and tungsten-polymetallic ore belt are now facing resource depletion after decades of exploitation.Peripheral mineral exploration therefore has become an urgent task.Using mineral exploration around the Limu crisis mines as an example,we introduce a breakthrough method of how the three-field theory,i.e.,the material,energy and spatial fields,is applied to intensively studies areas,a history of years of mineral exploitation and complex ore-forming systems.Taking a cue from Limu regional metallogeny,we based our investigation on the metallogenic information from geology,geophysics,geochemistry and remote sensing.We conducted our study of the three-field integrated information system,associated with metallogenic prognoses from deposits,with assignments and calculations which correct and allocate synthetic metallogenic prognosis by relying on GIS.We submitted a synthetic metallogenic prognosis map of tin in Limu where we delineated three ore target areas.A breakthrough was achieved by finding about 4785 t of tin metal outside the Shiziling deposit,which has been confirmed by drilling.The successful application in Limu shows that this three-field theory is of scientific and practical importance and deserves to be extended to utilization.

State-of-the-Art and Perspectives in the Field of Particulate Nanostructured Materials

A great attention has been paid to the research and development of nanostructured materials.The main preparation methods of ultrafine particles and nanostructured materials have been summarized. The applications of zone typical nanostructured materials have also been reviewed.The peculiar characteristics and properties. such as density, grain size, hardness, superplasticity,magnetic and catalytic properties have been discussed

Thermodynamic and rate variational formulation of models for inhomogeneous gradient materials with microstructure and application to phase field modeling

In this work,thermodynamic models for the energetics and kinetics of inhomogeneous gradient materials with microstructure are formulated in the context of continuum thermodynamics and material theory.For simplicity,attention is restricted to isothermal conditions.The materials of interest here are characterized by（1） first- and secondorder gradients of the deformation field and（2） a kinematic microstructure field and its gradient（e.g.,in the sense of director,micromorphic or Cosserat microstructure）.Material inhomogeneity takes the form of multiple phases and chemical constituents,modeled here with the help of corresponding phase fields.Invariance requirements together with the dissipation principle result in the reduced model field and constitutive relations.Special cases of these include the wellknown Cahn-Hilliard and Ginzburg-Landau relations.In the last part of the work,initial boundary value problems for this class of materials are formulated with the help of rate variational methods.

Synergistic Promotion of Electrical, Mechanical and Thermal Properties for Silicone Rubber-based Field Grading Material via Compound Modification

Use of nonlinearconductive SiC/silicone rubber(SR)field grading material(FGM)can improve the local field concentration of composite insulators.Adding large volume fraction and large-size SiC particles(SiCp)into SR can obtain a good field grading effect,but it is accompanied by the deterioration of mechanical properties.Compounding SiC with different shapes can solve this contradiction.By incorporating one-dimensional SiC whiskers(SiCw)to synergize with granular SiCp,SiC/SR FGM with better field-dependent conductivity,mechanical properties and thermal conductivity than large-size SiCp and large volume fraction filling case can be obtained by using smaller size SiCp and lower filling contents.The simulations of 500 kv line insulators show that the modified SiC/SR FGM can reduce the maximum field strength along the insulator surface and at sheath-core rod interfaces by 55%and 71.4%,respectively.The combined application of FGM and grading ring can achieve a complementary effect.Using FGM to partially replace the role of the grading rings,the field strength indicators can still meet the operational requirements after the tube radius and shielding depth of the grading rings at both ends are reduced by 36.2%and 40%separately,which is a benefit to alleviating the problems of high weight and large volume faced by traditional field grading methods.

Simulation of facet dendrite growth with strong interfacial energy anisotropy by phase field method

Numerical simulations based on a new regularized phase-field model were presented, to simulate the solidification of hexagonal close-packed materials with strong interfacial energy anisotropies. Results show that the crystal grows into facet dendrites,displaying six-fold symmetry. The size of initial crystals has an effect on the branching-off of the principal branch tip along the<100> direction, which is eliminated by setting the b/a(a and b are the semi-major and semi-minor sizes in the initial elliptical crystals, respectively) value to be less than or equal to 1. With an increase in the undercooling value, the equilibrium morphology of the crystal changes from a star-like shape to facet dendrites without side branches. The steady-state tip velocity increases exponentially when the dimensionless undercooling is below the critical value. With a further increase in the undercooling value, the equilibrium morphology of the crystal grows into a developed side-branch structure, and the steady-state tip velocity of the facet dendrites increases linearly. The facet dendrite growth has controlled diffusion and kinetics.

Influence of the gassing materials on the dielectric properties of air

Influence of the gassing materials, such as PA6, PMMA, and POM on the dielectric properties of air are investigated. In this work, the fundamental electron collision cross section data were carefully selected and validated. Then the species compositions of the air–organic vapor mixtures were calculated based on the Gibbs free energy minimization. Finally, the Townsend ionization coefficient, the Townsend electron attachment coefficient and the critical reduced electric field strength were derived from the calculated electron energy distribution function by solving the Boltzmann transport equation. The calculation results indicated that H;O with large attachment cross sections has a great impact on the critical reduced electric field strength of the air–organic vapor mixtures. On the other hand, the vaporization of gassing materials can help to increase the dielectric properties of air circuit breakers to some degree.

A MATLAB code for the material-field series-expansion topology optimization method

This paper presents a MATLAB implementation of the material-field series-expansion(MFSE)topology optimization method.The MFSE method uses a bounded material field with specified spatial correlation to represent the structural topology.With the series-expansion method for bounded fields,this material field is described with the characteristic base functions and the corresponding coefficients.Compared with the conventional density-based method,the MFSE method decouples the topological description and the finite element discretization,and greatly reduces the number of design variables after dimensionality reduction.Other features of this method include inherent control on structural topological complexity,crisp structural boundary description,mesh independence,and being free from the checkerboard pattern.With the focus on the implementation of the MFSE method,the present MATLAB code uses the maximum stiffness optimization problems solved with a gradientbased optimizer as examples.The MATLAB code consists of three parts,namely,the main program and two subroutines(one for aggregating the optimization constraints and the other about the method of moving asymptotes optimizer).The implementation of the code and its extensions to topology optimization problems with multiple load cases and passive elements are discussed in detail.The code is intended for researchers who are interested in this method and want to get started with it quickly.It can also be used as a basis for handling complex engineering optimization problems by combining the MFSE topology optimization method with non-gradient optimization algorithms without sensitivity information because only a few design variables are required to describe relatively complex structural topology and smooth structural boundaries using the MFSE method.

Thermomagnetic viscoelastic responses in a functionally graded hollow structure

This paper presents an analytical solution for the interaction of electric potentials, electric displacements, elastic deformations, and thermoelasticity, and describes electromagnetoelastic responses and perturbation of the magnetic field vector in hollow structures （cylinder or sphere）, subjected to mechanical load and electric potential. The material properties, thermal expansion coefficient and magnetic permeability of the structure are assumed to be graded in the radial direction by a power law distribution. In the present model we consider the solution for the case of a hollow structure made of viscoelastic isotropic material, reinforced by elastic isotropic fibers, this material is considered as structurally anisotropic material. The exact solutions for stresses and perturbations of the magnetic field vector in FGM hollow structures are determined using the infinitesimal theory of magnetothermoelasticity, and then the hollow structure model with viscoelastic material is solved using the correspondence principle and Illyushin＇s approximation method. Finally, numerical results are carried out and discussed.

The Precursor Phase of an X-class Flare: Magnetic Reconnection, Powering and Non-thermal Electrons

In this paper,we report three interesting phenomena that occurred during the precursor phase of the X1.6 class flare on 2014 September 10.(1) The magnetic reconnection initiating the flare occurs between one of the two J-shaped magnetic flux ropes that constitute a sigmoidal structure and the overlying sheared magnetic arcade that runs across the sigmoid over its middle part.The reconnection formed an erupting structure that ultimately leads to flare onset.Another J-shaped magnetic flux rope remains unaffected during the whole eruption.The phenomenon is revealed by the observation made by the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory(SDO)at 94 and 131 A.(2) Being simultaneously with starting time of the precursor,photospheric vertical electric current(VEC) around the footpoint region of the overlying magnetic arcade underwent an obvious increase,as observed by the Helioseismic and Magnetic Imager(HMI) on board SDO.By only taking into account the VEC with current density over 3σ value(1σ:10 mA m^(-2)),we are able to pick out precursor-associated VEC increase starting from nearly the level of zero.We regard it as a kind of powering process for the magnetic reconnection between the two magnetic loops.(3) With high-resolution narrow-band Helium 10830 A images taken by Goode Solar Telescope at Big Bear Solar Observatory(BBSO),we observe a narrow absorption(dark) front that runs along the erupting magnetic structure(or the erupting hot channel) and moves in the direction of the eruption during the precursor phase.Assuming the excitation mechanism of Helium atoms along the absorption front by non-thermal electrons,the phenomenon shows that the interaction between the erupted hot channel and the overlying(or surrounding)magnetic field has yielded electron acceleration.

Filler Size Effect on Tuning Electrical,Mechanical,and Thermal Properties of Field Grading Composites

field-grading composite with a low switching field,stable nonlinear conductivity performance,and excellent mechanical and thermal properties was prepared by using hybrid ZnO micro-spherical varistors of different particle sizes as the fillers and silicone rubber as the matrix.The hybrid effects of particle size on the electrical,mechanical,and thermal properties of ZnO micro-spherical varistors composites are investigated.An increase in the ZnO micro-spherical varistor size in the composites will lower the switching field but lead to degradation of the mechanical properties and stability of the nonlinear conductivity properties.The silicone rubber is incorporated with a mixture of hybrid ZnO micro-spherical varistors of different sizes at an optimal mass ratio range exhibited low switching field,stable nonlinear conductivity performance,and excellent mechanical and thermal properties.Our findings are helpful to comprehensively regulate performance of advanced field-grading materials and increase stability and durability of electronic and electrical devices.

Magnetic-field enhanced high-thermoelectric performance in topological Dirac semimetal Cd3As2 crystal

Thermoelectric materials can be used to convert heat to electric power through the Seebeck effect. We study magneto-thermoelectric figure of merit （ZT） in three-dimensional Dirac semimetal Cd3A 5 2 crystal. It is found that enhancement of power factor and reduction of thermal conductivity can be realized at the same time through magnetic field although magnetoresistivity is greatly increased. ZT can be highly enhanced from 0.17 to 1.1 by more than six times around 350 K under a perpendicular magnetic field of 7 T. The huge enhancement of ZT by magnetic field arises from the linear Dirac band with large Fermi velocity and the large electric thermal conductivity in CdsA 5 2. Our work paves a new way to greatly enhance the thermoelectric performance in the quantum topological materials.

An unconventional phase field modeling of domains formation and evolution in tetragonal ferroelectrics

Based on characteristic functions of variants, we developed an unconventional phase field modeling for investigating domains formation and evolution in tetragonal ferroelectrics. In order to develop this computational approach, we constructed the anisotropy energy of tetragonal variants, which is used instead of Landau-Devonshire potential in the conventional phase field method, resulting in that much fewer parameters are needed for simulations. This approach is advantageous in simulations of emerging ferroelectric materials. We employ it to study the formation and evolution of domains in tetragonal barium titanate single crystal, as well as the nonlinear behaviors under cyclical stress and electric field loading. A multi-rank laminated ferroelectric domain pattern, 90° domain switching accompanied by polarization rotation, and 180° domain switching accompanied by move of domain wall are predicted. It is found that the speed of 90° domain switching is slower than that of 180° domain switching, due to both polarization and transformation strain changed in 90° domain switching. It also suggests that large strain actuation can be generated in single crystal ferroelectrics via combined electromechanical loading inducing 90° domain switching. The good agreement between simulation results and experimental measurements is observed.

Manganese and chromium doping in atomically thin MoS2

Recently,two-dimensional materials have been attracting increasing attention because of their novel properties and promising applications.However,the impurity doping remains a significant challenge owing to the lack of the doping strategy in the atomically thin layers.Here we report on the chromium（Cr） and manganese（Mn）doping in atomically-thin MoS_2 crystals grown by chemical vapor deposition.The Cr/Mn doped MoS_2 samples are characterized by a peak at 1.76 and 1.79 eV in photoluminescence spectra,respectively,compared with the undoped one at 1.85 eV.The field-effect transistor（FET） devices based on the Mn doping show a higher threshold voltage than that of the pure MoS_2 while the Cr doping exhibits the opposite behavior.Importantly,the carrier concentration in these samples displays a remarkable difference arising from the doping effect,consistent with the evolution of the FET performance.The temperature-dependent conductivity measurements further demonstrate a large variation in activation energy.The successful incorporation of the Mn and Cr impurities into the monolayer MoS_2 paves the way towards the high Curie temperature two-dimensional dilute magnetic semiconductors.