Mechanical properties and microstructural evolution of rheocast A356 semi-solid slurry prepared by annular electromagnetic stirring

Nowadays,having an effective technique in preparing semi-solid slurries for rheocasting process seems to be an essential requirement.In this study,semi-solid slurry of A356 aluminum alloy was prepared by three-phase annular electromagnetic stirring(A-EMS)technique under different conditions.The effects of stirring current,pouring temperature and stirring time on microstructural evolution,mean particle size,shape factor and solid fraction were investigated.The rheocasting process was carried out by using a drop weight setup and to inject the prepared semi-solid slurry in optimal conditions into the step-die cavity.The filling behavior and mechanical properties of parts were studied.Microstructural evolution showed that the best semi-solid slurry which had fine spherical particles with the average size of~27μm and a shape factor of~0.8 was achieved at the stirring current of 70 A,melt pouring temperature of 670℃,and stirring time of 30 s.Under these conditions,the step-die cavity was completely filled at die preheating temperature of 470℃.The hardness increases by decreasing step thickness as well as die preheating temperature.Moreover,the tensile properties are improved at lower die preheating temperatures.The fracture surface,which consists of a complex topography,indicates a typical ductile fracture.

DEVELOPMENT OF THE CONTROL METHODOLOGY OF THE GIANT MAGNETOSTRICTIVE ACTUATOR BASED ON MAGNETIC FLUX DENSITY

According to the principle of the magnetostriction generating mechanism, thecontrol model of giant magnetostriction material based on magnetic field and the control method withmagnetic flux density are developed. Furthermore, this control method is used to develop a giantmagnetostrictive micro-displacement actuator (GMA) and its driving system. Two control methods whosecontrol variables are current intensity and magnetic flux density are compared with each other byexperimental studies. Finally, effective methods on improving the linearity and control precision ofmicro-displacement actuator and reducing the hysteresis based on the controlling magnetic fluxdensity are obtained.

Distribution of Magnetic Flux Density in Soft-Contact EMCC Rectangular Mold

The distribution of the magnetic flux density in a soft-contact electromagnetic continuous casting （EMCC） rectangular mold was investigated. The experimental results show that with an increase in electric power, the magnetic flux density increases. The position where the maximum magnetic flux density appears will shift up when the coil moves to the top of the mold. At the same time, the maximum magnetic flux density will increase and the effective acting range of electromagnetic pressure will widen. As a result, in practice, the coil should be placed near the top part of the mold. The meniscus should be controlled near the top part of the coil, as this not only remarkably improves the billet surface quality but also saves energy. With the same electric power input, the higher the frequency, the lower the magnetic flux density.

Effect of Distribution of Magnetic Flux Density on Purifying Liquid Metal by Travelling Magnetic Field

The distribution of the magnetic flux density in the magnetic field generator which provided travelling magnetic field was determined. The experiments using liquid gallium and aluminum silicon alloy to observe the turbulent flow or remove inclusions were performed to obtain the basic principles how the distribution of the magnetic flux density took effect on removing inclusions from molten metal by electromagnetic field. The suitable area in the field for purifying metal was suggested.

Simulation research on effect of magnetic nanoparticles on physical process of magneto–acoustic tomography with magnetic induction

Magneto–acoustic tomography with magnetic induction（MAT-MI） is a multiphysics coupled imaging technique that is combined with electrical impedance tomography and ultrasound imaging. In order to study the influence of adding magnetic nanoparticles as a contrast agent for MAT-MI on its physical process, firstly, we analyze and compare the electromagnetic and acoustical properties of MAT-MI theoretically before and after adding magnetic nanoparticles, and then construct a two-dimensional（2 D） planar model. Under the guidance of space-time separation theory, we determine the reasonable simulation conditions and solve the electromagnetic field and sound field physical processes in the two modes by using the finite element method. The magnetic flux density, sound pressure distribution, and related one-dimensional（1 D）, 2 D, and three-dimensional（3 D） images are obtained. Finally, we make a qualitative and quantitative analysis based on the theoretical and simulation results. The research results show that the peak time of the time item separated from the sound source has a corresponding relationship with the peak time of the sound pressure signal. At this moment, MAMPTMI produces larger sound pressure signals, and the sound pressure distribution of the MAMPT-MI is more uniform, which facilitates the detection and completion of sound source reconstruction. The research results may lay the foundation for the MAT-MI of magnetically responsive nanoparticle in subsequent experiments and even clinical applications.

Propagation effects of low frequency electromagnetic waves in production well

The frequency domain electromagnetic method has already been widely used for tomographic imaging or electromagnetic well logging. However, different from open hole logging, the metal casing existing in production well logging has a strong shielding effect on the electromagnetic waves, thus bringing some difficulties to the application of the frequency domain electromagnetic method in production well logging. According to the relation of the field source geometry to the ring around the mandrel, the general expressions of frequency domain electromagnetic responses in axially symmetrical layered conductive medium are deduced. The propagation effects caused by the low-frequency electromagnetic waves in cased hole are also analyzed. The distribution curves of eddy current density and magnetic flux density along the radial direction in the mandrel indicate that the eddy loss within the mandrel is proportional to the transmission signal frequency and the mandrel conductivity. The secondary field responses of different casing materials show that the transmission frequency has an important effect on the ability of electromagnetic waves penetrating the metal casing. The transmission frequency should be ultra-low in order to enable the electromagnetic signal to penetrate the casing easily. The numerical results of frequency responses for different casing physical parameters show that the casing thickness has a significant impact on the choice of the transmission frequency. It is also found that the effect of the casing radius on the transmission frequency can be neglected.

Effect of power parameter and induction coil on magnetic field in cold crucible during continuous melting and directional solidification

Bottomless electromagnetic cold crucible is a new apparatus for continuous melting and directional solidification;however,improving its power efficiency and optimizing the configuration are important for experiment and production.In this study,a 3-D finite element (FE) method based on experimental verification was applied to calculate the magnetic flux density (Bz).The effects of the power parameters and the induction coil on the magnetic field distribution in the cold crucible were investigated.The results show that higher current intensity and lower frequency are beneficial to the increase of Bz at both the segment midpoint and the slit location.The induction coil with racetrack section can induce greater Bz,and a larger gap between the induction coil and the shield ring increases Bz.The mechanism for this effect is also discussed.

A brief introduction to recent applications of several sediment-analysis techniques in palaeolimnological studies-dry bulk density and water content, mineral magnetism, carbonate content, and content of total organic carbon,nitrogen content and carbon/ni

Determination of dry bulk density and water content measurement of magnetic susceptibility (x) and saturation isothermal remanent magnetization (SIRM), determination of carbonate content, and determination of total organic carbon (TOC) content nitrogen content (N%) and carbon/nitrogen (C/N) ratio are some of the techniques which have been widely applied to lacustrine-sediment analyses. The techniques,complemented by others, are usually useful for revealing characteristics of lacustrine-sediments and thus for postulating hydrological regimes in the lake and environmental conditions and human activity around it in palaeolimnological studies. A very brief review is presented on recent applications of these techniques in palaeolimnological work with English literatures published mainly since 1985 and focus given on interpretations of results of these analyses related to palaeoenvironmental reconstructions. Low dry bulk density and high water content often imply relatively warm and wet conditions. High X and SIRM are usually resulted from reduced dilutions in the lake and intensified erosions on its catchment. both of which can be in turn attributed to environmental changes. While variations in patterns of X and SIRM may give further insight on mineral magnetism and thus implications on environmental conditions. Increased carbonate content seems likely to associate to warm and dry conditions.Increased TOC content is virtually used as one of indicators of warm and wet conditions and variations in C/N ratio may hint variations in relative contributions of different sources, aquatic and terrestrial, to the total organic matter in lake sediments and hence to lake-level fluctuations and climate changes.

Structure and magnetic properties of Osn （n=11～22） clusters

The structure and magnetic properties of Osn （n=11～22） clusters are systematically studied by using density functional theory （DFT）. For each size, the average binding energy per atom, the second-order differences of total energies and the highest occupied molecular orbital （HOMO）–the lowest unoccupied molecular orbital （LUMO） gaps are calculated to analyze the stability of the cluster. The structures of Os14 and Os18 clusters are based on a close-packed hexagonal structure, and they have maximum stabilities, so n=14, 18 are the magic numbers. The 5d electrons play a dominant role in the chemical reaction of Osn clusters. The magnetic moments of Osn clusters are quenched around n=12, and when n=18～22 the value approximates to zero, due to the difference of electron transfer.

Tunable Electronic and Magnetic Properties from Structure Phase Transition of Layered Vanadium Diselenide

The atomic geometry, structure stability, electronic and magnetic properties of VSe2 were systematically investigated based on the density functional theory（DFT）. Varying from 3D to 2D four VSe2 structures, bulk 2H-VSe2 and 1T-VSe2, monolayer H-VSe2 and T-VSe2 are all demonstrated as thermodynamically stable by lattice dynamic calculations. More interestingly, the phase transition temperature is dramatically different due to the lattice size. Finally, owing to different crystal structures, H-VSe2 is semimetallic whereas T-VSe2 is totally metallic and also they have different magnetic moments. Our main argument is that being exfoliated from bulk to monolayer, 2H-VSe2 transforms to T-VSe2, accompanied by both semimetallic-metallic transition and dramatic magnetic moment variation. Our calculations provide a novel structure phase transition and an efficient way to modulate the electronic structure and magnetic moment of layered VSe2, which suggests potential applications as high-performance functional nanomaterial.

Development of a Miniature Permanent Magnetic Circuit for Nuclear Magnetic Resonance Chip

The existing researches of miniature magnetic circuits focus on the single-sided permanent magnetic circuits and the Halbach permanent magnetic circuits. In the single-sided permanent magnetic circuits, the magnetic flux density is always very low in the work region. In the Halbach permanent magnetic circuits, there are always great difficulties in the manufacturing and assembly process. The static magnetic flux density required for nuclear magnetic resonance(NMR) chip is analyzed based on the signal noise ratio(SNR) calculation model, and then a miniature C-shaped permanent magnetic circuit is designed as the required magnetic flux density. Based on Kirchhoff’s law and magnetic flux refraction principle, the concept of a single shimming ring is proposed to improve the performance of the designed magnetic circuit. Using the finite element method, a comparative calculation is conducted. The calculation results demonstrate that the magnetic circuit improved with a single shimming has higher magnetic flux density and better magnetic field homogeneity than the one improved with no shimming ring or double shimming rings. The proposed magnetic circuit is manufactured and its experimental test platform is also built. The magnetic flux density measured in the work region is 0.7 T, which is well coincided with the theoretical design. The spatial variation of the magnetic field is within the range of the instrument error. At last, the temperature dependence of the magnetic flux density produced by the proposed magnetic circuit is investigated through both theoretical analysis and experimental study, and a linear functional model is obtained. The proposed research is crucial for solving the problem in the application of NMR-chip under different environmental temperatures.

A Novel High Performance Magnetic Gear with Auxiliary Silicon Steel Sheet

Magnetic gear is a transmission device with novel structure.It uses the principle of magnetic field modulation to transmit torque.In view of the magnetic leakage of the magnetic gear in the process of rotation and cannot be eliminated,a magnetic gear model with auxiliary silicon steel sheet is proposed.Based on the conventional magnetic gear structure,the silicon steel sheet is placed outside the permanent magnet of the outer rotor.The magnetization mode of the outer rotor permanent magnet is tangential magnetization,and the spoke structure is adopted,and the inner rotor PMs is surface mounted and magnetized in the radial magnetization.The improved model is simulated by finite element method under three-dimensional conditions,and the electromagnetic performances of the model are optimized.Compared with the conventional magnetic gear model,the improved model has good performance,which improves the transmission capacity of output torque and reduces torque ripple.It is a great significance to improve the performance of magnetic gear.

Study of magnetic and optical properties of Zn1-xTMxTe(TM = Mn,Fe,Co,Ni) diluted magnetic semiconductors：First principle approach

We present structural,magnetic and optical characteristics of Zn_（1-x）TM_xTe（TM = Mn,Fe,Co,Ni and x = 6.25%）,calculated through Wien2 k code,by using full potential linearized augmented plane wave（FP-LAPW） technique.The optimization of the crystal structures have been done to compare the ferromagnetic（FM） and antiferromagnetic（AFM） ground state energies,to elucidate the ferromagnetic phase stability,which further has been verified through the formation and cohesive energies.Moreover,the estimated Curie temperatures T_c have demonstrated above room temperature ferromagnetism（RTFM） in Zn_（1-x）TM_xTe（TM =Mn,Fe,Co,Ni and x= 6.25%）.The calculated electronic properties have depicted that Mn- and Co-doped ZnTe behave as ferromagnetic semiconductors,while half-metallic ferromagnetic behaviors are observed in Fe- and Ni-doped ZnTe.The presence of ferromagnetism is also demonstrated to be due to both the p-d and s-d hybridizations between the host lattice cations and TM impurities.The calculated band gaps and static real dielectric constants have been observed to vary according to Penn＇s model.The evaluated band gaps lie in near visible and ultraviolet regions,which make these materials suitable for various important device applications in optoelectronic and spintronic.

The Nonzero External Magnetic Field of Long Solenoids

A widespread assertion has existed for a long time, believing the external field of an infinitely long solenoid should be zero, but it is proofed to be wrong in this work. The components of magnetic flux density of current-carrying, closely wound cylindrical solenoids are calculated. At a distant field point, the external field definitely has a nonzero component, being equal to that of a straight wire of equal length. Since this equivalence is length-independent, it still holds true for ideal solenoids having infinite length. Hence the incorrect and still spreading inference about long solenoids should be rectified. Furthermore, theoretical and experimental discussions involving solenoids should be reviewed again carefully.

An Inquiry into Two Intriguing Values of the Critical Current Density of Bi-2212

The empirically reported values of the critical current density (jc) of Bi-2212 as 2.4 × 105 (jc1;Sample 1) and 1.0 × 106 A/cm2 (jc2;Sample 2) are intriguing because both of them correspond to the same values of the temperature T = 4.2 K and the applied magnetic field H = 12 × 104 G. This difference is conventionally attributed to such factors—not all of which are quantifiable—as the geometry, dimensions and the nature of dopants and the manners of preparation of the samples which cause their granular structures, grain boundaries, alignment of the grains and so on to differ. Based on the premise that the chemical potential μ subsumes most of these features, given herein is a novel explanation of the said results in terms of the values of μ of the two samples. This paper revisits the problem that was originally addressed in [Malik G.P., Varma V.S. (2020) WJCMP, 10, 53-70] in the more accurate framework of a subsequent paper [Malik G.P., Varma V.S. (2021) JSNM, 34, 1551-1561]. Besides, it distinguishes between the contributions of the electro-electron (e-e) and the hole-hole (h-h) pairs to jc—a feature to which no heed was paid earlier. The essence of our findings is that the jcs of the two samples differ because they are characterized by different values of the primary variables μi and , where is the effective mass of a charge-carrier and me is the free-electron mass and i = 1 and 2 denote Sample 1 and Sample 2, respectively. In the scenario of the charge-carriers being predominantly h-h pairs, the values of these parameters are estimated to be: μ1 ≈ 12.3 meV, η1 ≈ 0.58;μ2 ≈ 22.7 meV, η2 ≈ 0.94. Following from these and similar estimates when the charge-carriers are e-e pairs, given below for each sample are the detailed results for the values of the secondary variables viz. the number density of the charge-carriers and their critical velocity, the number of occupied Landau levels and the magnetic interaction parameter.

Direct synthesis of Fe-Si-B-C-Cu nanocrystalline alloys with superior soft magnetic properties and ductile by melt-spinning

Structure,magnetic properties and ductile of melt-spun Fe_(83-x)Si_(4)B_(13-y)C_(y)Cu_(x)(x=0-1.7;y=0-8)alloys were investigated.The addition of 1.7 at.%Cu in a Fe_(83)Si_(4)B_(13) amorphous alloy generates abundantα-Fe crystals by providing nucleation sites,and further C doping promotes the growth of the crystals by suitable turning amorphous-forming ability,hence they increase saturation magnetic flux density(B_(s))and slightly worse magnetic softness of the as-spun alloys.The as-spun Fe_(81.3)Si_(4)B_(7)C_(6)Cu_(1.7) alloy possesses a combined structure of a fully amorphous layer in wheel side surface and predominating nanocrystalline structure with gradually enlargedα-Fe crystal,whose average size and volume fraction are determined as about 12 nm and 32%,respectively,therefore superior soft magnetic properties and ductile with a high B_(s)of 1.74 T,coercivity(H_(c))of 32.7 A/m,effective permeability(μ_(e),at 1 kHz)of 3200 and high relatively strain at fracture(ε_(f))of 3.61%can be achieved directly in this alloy by only using melt-spinning.The annealing at 578 K releases internal stress,promotes the growth of theα-Fe crystals and remains the amorphous layer of the Fe_(81.3)Si_(4)B_(7)C_(6)Cu_(1.7) alloy,then improves the soft magnetic properties and maintains the superior ductile with increasing the B_(s)andμ_(e)to 1.80 T and 14,100,respectively,lowering the H_(c)to9.4 A/m and slightly reducing theε_(f)to 2.39%.The combination of superior soft magnetic properties and ductile and simplified synthesis process entitles the Fe-Si-B-C-Cu nanocrystalline alloys great potentials in high performance electromagnetic applications.

Magnetic field distribution simulation and performance experiment of a magnetic seed-metering device based on the combined magnetic system

The magnetic seed-metering method is one of the universal approaches for plug tray seeding.Conventional electromagnetic and permanent-magnetic seed-metering devices either cannot supply a desirable magnitude of magnetic force or need a seed-clearing mechanism.Thus the objective of this research was to develop a combined magnetic system(CMS)seed-metering device for generating higher magnetic forces than the electromagnetic ones without using any auxiliary seed-clearing mechanisms.Firstly,the CMS component was designed and its magnetic field distributions in both attractive and clearing states were obtained by finite element method simulations.Secondly,based on the CMS components,a magnetic seed-metering device was developed and validated by a prototype experiment.The simulation results displayed that along the axial direction of the magnetic head,the maximum magnetic flux density in the clearing state was 21.03%of that in the attractive state.In addition,along the radial direction,the proportion was 24.16%.Concerning the spatial magnetic flux density distribution,the magnetic flux density on the seeding planes of CMS components(approximately 60 mT)was higher than that of transitional space between two CMS components(nearly 0 mT).As for the seeding performance experiment,when the rotational speed of the roller was 21 r/min and the exciting current was 0.15 A,the highest single rate was acquired(90.20%).In the same condition,the reseeding rate was 5.88%and the miss-seeding rate was 3.92%.The results suggest that the magnetic field distribution and seeding performance of the developed magnetic seed-metering device are acceptable.Therefore,the developed magnetic seed-metering device can be used in practical plug tray seeding processes.

Compute extremely low-frequency electromagnetic field exposure by 3-D impendance method

A 3-D impedance method has been introduced to compute the electric currents induced in a human body exposed to extremely low-frequency electromagnetic field. The 3-D impedance method has been deduced from Maxwell equations and is put into the computation and simulation effectively to the visible human body model, which has 196×114×626 cells and more than 40 types of tissues. As the result, two representative cases are investigated. One is exposure of the human body to 100 μT （1 000 mG）, the limit recommended by the International Commission on Non-Ionizing Radiation Protection for the public and the other one is the exposure of human body to 0.4 laT （4 mG）, the level at which a statistical link appears with a doubled risk of development of childhood leukaemia. The distribution of induced current density can be obtained and the maximum of induced current are found to be 16 mA/m^2 and 0.07 mA/m^2.

Discrepancies between Nonalcoholic and Metabolic-associated Fatty Liver Disease by Multiple Steatosis Assessment

Background and Aims:The redefinition of metabolic-as-sociated fatty liver disease(MAFLD)from nonalcoholic fat-ty liver disease(NAFLD)has caused a revolution in clinical practice,and the characteristics of patients with steatosis but not MAFLD remain unclear.The aims were to compare the diagnosis rate of MAFLD in NAFLD using different steato-sis methods and explore the features of non-MAFLD-NAFLD and MAFLD-non-NAFLD.Methods:A cross-sectional study enrolling consecutive individuals was conducted at three medical centers in southern China from January 2015 to September 2020.Steatosis was evaluated by liver biopsy or magnetic resonance imaging-based proton density fat frac-tion(MRI-PDFF),ultrasound,controlled attenuation param-eter(CAP),and fatty liver index(FLI).Fibrosis was assessed by the NAFLD fibrosis score,transient elastography,or shear wave elastography.Results:The study enrolled 14,985 Chi-nese adults.The agreement of MAFLD and NAFLD diagnoses were 83%for FLI,95%for ultrasound,94%for both CAP and MRI-PDFF,and 95%for liver biopsy.The body mass index,blood pressure and lipid levels among non-MAFLD-NAFLD pa-tients were similar metabolic parameters(p>0.05 for all),but not the alanine aminotransferase and the proportion of pa-tients with insulin resistance,which were significantly higher in non-MAFLD-NAFLD with significant fibrosis.Conclusions:The new MAFLD definition ruled out 5-17%of NAFLD cases.NAFLD and MAFLD-NAFLD involved more severe metabolic abnormalities than MAFLD and MAFLD-non-NAFLD.Non-MAFLD-NAFLD patients with significant fibrosis had more se-vere liver injury and increased glycemic dysregulation within the normal range.Attention should be paid to its progression.