Abstract:The quantum anomalous Hall effect (QAHE) is a quantized Hall effect without external magnetic field, which has chiral edge states and can be used for developing low consumption electronic devices and constructing other novel quantum states. At the end of 2012, the QAHE was first observed by Chinese scientists in Cr-doped (Bi,Sb)₂Te₃ topological insulator thin films. In the past seven years, the observation temperature has been raised from 30 mK to about 2 K. Further raising observation temperature is essential for the applications of many quantum effects, which is one of the major research directions in the field of topological quantum physics and materials. In this review, we summarize the experimental progresses in the study of QAHE in magnetic topological insulators, especially in the aspect of QAHE observation temperature. The article consists of four parts: in the first two parts, the QAHE in doping and proximity-effect induced magnetic topological insulators is introduced. In the third part, the newly discovered intrinsic magnetic topological insulator system is presented. The last part gives some perspectives about possible principle and roadmap of how to design and build QAH systems at high temperatures.

Abstract:Light beams carrying orbital angular momentum (OAM) are called vortex beams. Due to the novel phase distribution and the physical properties, such beams are widely used in optical micro-manipulation, super-resolution imaging, high-capacity communication, and quantum information technologies. As different applications require light sources with different wavelengths, nonlinear frequency conversions in optical superlattice through quasi-phase-matching provide a promising way to extend the wavelength of vortex beams. For the interaction between vortex lights and nonlinear medium, the conservation of energy, linear momentum as well as OAM should be concerned. Herein, recent progress on nonlinear generation and manipulation of optical vortices in optical superlattice is reviewed. Through nonlinear frequency conversion including second and third harmonic generation, sum frequency generation, and frequency down conversion processes, the working wavelength of the vortex beam can be efficiently extended from blue-violet to mid-infrared band. The transfer of OAM in the frequency conversion process can be flexibly controlled by precisely designing the optical superlattice. Designing nonlinear photonic crystals exploiting nonlinear holography, one can modulate the wavefront, phase, and amplitude of the light field during the frequency conversion process, thus the nonlinear generation and manipulation of vortex beam can be realized. With the development of the superlattice fabrication technology, the manipulating dimension of light field has been expanded from two-dimension to three-dimension. Investigations on the generation and manipulation of vortex beams in optical superlattice can deepen the understanding of OAM as well as promote the progress of the related applied research.

Abstract:To understand the deformation and failure mechanism of fractured rock masses under hydromechanical coupling and correctly evaluate the safety and stability of rock mass engineering, the research progress and results of the studies of deformation and failure of intact and fractured rock masses under hydromechanical coupling were systematically reviewed by collecting and collating literatures at home and abroad. The mechanical characteristics of intact and fractured rock masses under hydromechanical coupling were briefly described. The seepage laws of single fractured rock masses under hydromechanical coupling were summarized, including the mathematical formulas of the relations between flow and gap width index n, permeability (water conductivity) coefficient and normal stress, and permeability characteristics and shear stress. The latest research progress of deformation and failure mechanism under hydromechanical coupling was mainly analyzed, and the applications of advanced auxiliary test technologies such as acoustic emission (AE), ultrasonic testing (UT), polarizing microscope (PM), scanning electron microscope (SEM), and computed tomography (CT) scanning system in deformation and failure analysis were introduced. The advantages and disadvantages of the coupled seepage-stress model of fractured rock mass, the numerical analysis method, and the applicable conditions were summarized. Finally, limitations in the current studies of fractured rock masses under hydromechanical coupling were pointed out, and suggestions were put forward. The future development trend was discussed from several aspects, that is, the mechanism research changes from macro and meso to micro, the numerical simulation changes from rough to fine, and the engineering application changes from hydromechanical coupling to multi-field coupling.

Abstract:With the advantages of respective component materials, metal laminates can achieve comprehensive performance that cannot be satisfied by a single metal, which are one of the most important metal structural materials in recent years and have been widely used in the fields of aerospace, defense and military industry, transportation, and equipment manufacturing. Rolling method is one of the main preparation methods of metal laminates, and has the advantages of stable and continuous production. In this paper, the research progress of metal laminates roll bonding process at home and abroad is reviewed, and the currently recognized metal laminates roll bonding hypotheses including mechanical meshing theory and metal bonding theory are discussed. The advantages, disadvantages, and application scope of hot rolling, cold rolling, differential temperature rolling, accumulative rolling, asymmetrical rolling, and other bonding processes are classified and summarized. The characteristics of metal laminates roll bonding technologies are analyzed by theoretical analysis of slab method, stream function method, and upper bound method. Aiming at the connection problem of the interface to be bonded in numerical simulation, the interface processing models such as bonding model and common node model are briefly described. The bonding criteria of the fixed value or functional relationship of stress field, strain field, and velocity field are summarized. Based on the shortcomings of the current roll bonding process, the internationally pioneered corrugated-flat rolling (CFR) process proposed by the research team is introduced, which has low residual stress, good shape, and high bonding strength. Besides, the prospect of the future research emphases of roll bonding process is put forward.

Abstract:To investigate the development trends and challenges of long-endurance unmanned aerial vehicle (UAV), the research status of key technologies were analyzed and summarized. Long-endurance UAV has extensive application prospects because of its characteristics of high flight height, long operation time, and wide operation coverage. First, the representative long-endurance UAVs in the world were classified based on conventional power and new energy power, and the development history of long-endurance UAV was reviewed. Based on the demand of high lift, high lift-drag ratio, and moderate stall aerodynamic characteristics of long-endurance UAV, the large flexibility of high-aspect-ratio composite wing, and the complex mission environment of long-endurance UAV, the key technologies were analyzed, including high efficiency aerodynamic integrated design technology, aeroelastic analysis of high-aspect-ratio wing and active control technology, aeroelastic tailoring technology, flexible flight dynamics modeling and control technology, and autonomous navigation technology, etc. Finally, combined with the development situations of foreign long-endurance UAV, suggestions for the development of long-endurance UAV in China were put forward. Research shows that the conventional power long-endurance UAV has been widely used, while the new energy power long-endurance UAV is still in the prototype development stage. Technologies applied on the ultra-long-endurance UAV which has a duration of more than a week have become the focus of attention. The intelligence, collaboration, and network security of long-endurance UAV systems will be the main development directions in the future.

Abstract:Major water conservancy projects are important national infrastructures, whose damages caused by underwater explosions are noteworthy. Hence, centrifuge model tests and finite element simulations were used to study the effect of water storage level changes on the responses of dam. First, the similarity between the scaled model and the prototype in the hyper-gravity field was verified by numerical simulation. Next, based on the centrifuge model test at 50g, the effectiveness of the numerical simulation was verified. Then, a numerical simulation system was adopted to analyze the effects of underwater explosion on vibration and deformation of dam under different water storage levels. Results show that under the condition that the explosive equivalent and position remained unchanged, increasing the height of the water storage level caused the increase of the responses of the dam velocity and displacement. When the water depth exceeded 25 m, the peak velocity of multiple parts of the dam body exceeded the norm, and the dam might be damaged. Changes of the water storage level caused the impact energy of the dam to change, which affected the kinetic energy and strain energy of the dam. The energy change could be described by the spherical wave shock factor in this experiment.

Abstract:To explore the removal route of ammonia nitrogen, a biological purification process operation test for high concentration of iron and manganese associated ammonia nitrogen [Fe(Ⅱ) 9.2-15.1 mg/L, Mn(Ⅱ) 0.6-1.4 mg/L, NH+₄-N 0.9-2.0 mg/L] was carried out at low temperature (5-6 ℃) in a groundwater plant for iron, manganese, and ammonia nitrogen removal. Results show that the filter column had good removal effect of ammonia nitrogen at the initial stage of start-up. The analysis along the process and the adsorption test of mature filter material and backwash sludge show that when the influent ammonia nitrogen was about 1.1 mg/L, the ammonia nitrogen was mainly removed by the iron and manganese oxides in the upper part of the filter layer, and the removal rate by biological action was very small. In order to further explore the biological and adsorption effects of filter column on ammonia nitrogen, gradient was used to adjust the concentration of ammonia nitrogen in influent. With the increase of the influent ammonia nitrogen concentration, the ammonia nitrogen removal by biological action increased. Under the condition of influent iron and manganese concentration, the ammonia nitrogen removal by iron and manganese oxides adsorption was about 1 mg/L in the upper 20 cm range of the filter.

Abstract:Direct predictive speed control (DPSC) is an appropriate solution to achieve high-performance cascade-free control structure of permanent magnet motors, which has the technical limitations of large amount of online calculation and limited control degree of freedom. Based on the two-level inverter-fed permanent magnet synchronous motors (PMSMs) drive system, this paper proposes an improved DPSC strategy with incremental predictive model for improving the speed dynamic control performance of the system. First, in order to reduce the amount of online calculation of the algorithm, a low-complexity incremental speed prediction model was constructed, which can realize long-horizon multi-step speed prediction and ensure the stability of the algorithm. Then, the control-set was expanded with virtual vectors to increase the control degree of freedom, and its corresponding vector synthesis method and two-stage exhaustive optimization were designed to screen the optimal output vector efficiently. Combined with the established speed prediction model and control-set, the stable speed control performance could be obtained with relatively low computational burden. Experimental results show that compared with classical speed control strategies, the proposed strategy had better speed dynamic regulation ability, and the speed reached its reference value rapidly and directly without shooting. Besides, the proposed strategy could operate normally under the condition of parameter mismatch.

Abstract:Based on the problems of decentralized water supply and conventional ultrafiltration process, a gravity-driven membrane (GDM) filtration process was developed, which combined the dual rejections between bio-cake layer and ultrafiltration membrane and had the advantages of no cleaning, no chemical supply, simple operation, low energy consumption, and low maintenance. Results showed that flux stabilizations of GDM were observed during the long-term treatments of river water, reservoir water, and synthesized water, indicating the practical universality of GDM process in treating different types of water resources. The operating conditions, including raw water quality, operating pressure, membrane configuration type, membrane material, membrane pore size, temperature, intermittent filtration, and pre-treatment, affected the structures and compositions of bio-cake layer formed on the membrane surface, and consequently exerted impacts on the stable flux of GDM and its membrane fouling characteristics. Flux stabilization of GDM process was mainly determined by the structures and compositions of bio-cake layer regulated by the biological activities. The bio-cake layer with rougher structures, more abundant pores, and less extracellular polymeric substance (EPS) excretions, could contribute to a higher stable flux in long-term GDM filtration. Compared with conventional ultrafiltration process, the bio-cake layer formed on the surface of GDM could efficiently enhance the removal performance for turbidity, assimilable organic carbon (AOC), and ammonia. In addition, pre-treatment of slow filter could effectively modify the structural characteristics of bio-cake layer, improve the stable flux of GDM, and enhance the removal performance. The findings of this paper are expected to promote the extensive applications of ultrafiltration technology in decentralized drinking water supply.

Abstract:To improve the ability of overcoming the spatial disturbance, and reduce the joint torque fluctuations and energy consumption during operation, a learning strategy from demonstration based on dynamics constraints for space manipulators is proposed. This strategy is divided into two phases. Phase 1 is Gaussian process-based learning from demonstration, in which the motion model of the task is obtained by utilizing Gaussian process based on the kinesthetic demonstrations. Then, the desired trajectory distribution of the current task is reproduced using the model according to the environment. Phase 2 is the design of dynamics-constraint-based controller. The input of this controller is the trajectory distribution from phase 1, and the outputs are the joint desired torques. This controller is used to generate smoother joint control torques, while ensuring that the trajectory of manipulator can meet the task requirements. Finally, the strategy is verified by the on-orbit locating bolts task with Tiangong-2 space manipulator. Compared with the strategy of traditional learning from demonstration combined with computed torque controller, the joint torques peak-peak value of the large load joint is reduced by 45%, the number of peaks is reduced by 40%, and the energy consumption is reduced by 31%. Besides, the joint torques, accelerations and velocities are much smoother.

Abstract:To deal with the bio-refractory substances of penicillin in antibiotic wastewater, boron-doped diamond (BDD) electrodes prepared by direct current plasma chemical vapor deposition system were used to investigate the degradation rule and pathway of penicillin wastewater with penicillin G sodium as target pollutant. Results show that penicillin G sodium with different concentrations could be completely degraded at BDD electrodes by electrochemical combustion reaction. The degradation of penicillin G sodium and chemical oxygen demand (COD) accorded with the pseudo-first-order rate kinetics. When the current density was increased from 10 mA/cm² to 20 mA/cm², the apparent reaction rate constant of penicillin G sodium and COD increased by 51.3% and 29.1%, respectively. The degradation of penicillin G sodium at BDD electrodes was controlled by mass transfer in liquid phase. The concentration of penicillin G sodium and current density greatly influenced the current efficient (E_C). Major intermediate products of the degradation pathway of penicillin G sodium at BDD electrodes were penillic acid, isopenillic acid, penicillenic acid, and penicilloic acid.

Abstract:Due to the periodic nonlinear error, heterodyne laser interferometer cannot meet the requirements of the sub-nanometer and even picometer measurement accuracy of the next generation of ultra-precision equipment manufacturing and major scientific engineering. Aiming at the problem, this paper analyzes two types of periodic nonlinear errors in heterodyne laser interferometer and investigates their compensation methods. Results show that the first type of periodic nonlinear error is caused by optical mixing due to the incomplete separation of dual-frequency lasers, whose amplitude ranges from several nanometers to tens of nanometers. The second type of periodic nonlinear error is induced by multi-order Doppler frequency shift (DFS) ghost beam generated by the ghost reflection of measurement beam at the optical interface, whose amplitude ranges from several picometers to several nanometers. For the first type of periodic nonlinear errors, the current nonlinear error compensation methods, such as ellipse fitting method, can suppress them to 0.1 nm level. In particular, the spatially separated heterodyne laser interferometers proposed in recent years can completely eliminate the first type of nonlinear error in principle. As for the second type of error, by reducing ghost reflectivity and spatial filter, the error can be reduced to tens of picometers or hundreds of picometers, while the residual error is still too large to meet the accuracy requirements of picometer measurement. Thus, it is urgent to develop new error suppression or compensation technologies.

Abstract:To promote the development of iron oxide-based photocatalysts and its application in the field of water environment remediation, the key is to tackle the issues of insufficient thermodynamic reaction capacity of electrons and poor surface catalytic sites for O₂ catalytic activation due to the positive conduction band bottom position of iron oxide. In this regard, modulating the photo-generated electrons via modification on the controlled nano-sized iron oxide is an effective method for improving the photocatalytic activity of iron oxide. In this work, small sized pure α-Fe₂O₃ nanoparticles were synthesized by a urea modulate phase separation hydrolysis-solvothermal method. Based on this, the α-Fe₂O₃ nanoparticles were controllably modified by copper phthalocyanine (CuPc) through a simple wet chemical method. Results show that the as-prepared optimized sample (mass fraction of CuPc and α-Fe₂O₃ is 1%) exhibited nearly 2.5 times enhancement for photocatalytic 2,4-DCP degradation compared with the pure α-Fe₂O₃ sample. Through DRS, Raman, and FT-IR, it was revealed that CuPc and α-Fe₂O₃ had an effective interface connection by hydrogen bonding. Based on the analysis of hydroxyl radicals test and electrochemical test, the enhanced photocatalytic degradation activities could be attributed to the significantly improved photo-generated charge separation and the promoted O₂ activation. In addition, the characteristic absorption of CuPc in longer wavelengths could further extend the range of visible-light response of the nanocomposites. Significantly, this efficient strategy can also be applied to other metal phthalocyanine materials for the modification of α-Fe₂O₃.

Abstract:To study the static stability of suspension bridges under different simplified models and comprehensively analyze the entire instability process and failure modes, based on the mechanical characteristic that the instability of main tower results in the instability of the entire bridge, a full-bridge multiscale model and a single-tower solid model were established by ABAQUS, taking Nanjing Xianxin Road Yangtze River Bridge under construction as the project background. Linear stability coefficients, double nonlinear load coefficients, linear buckling modes, and failure modes were analyzed and compared. Results show that the double nonlinear stability safety coefficients were greatly reduced compared with the linear stability coefficients, and nonlinear stability calculation should be necessary for long-span earth-anchored suspension bridges. The linear stability coefficients of the full-bridge multiscale model were slightly larger than those of the single-tower solid model, while it was opposite for the nonlinear load coefficients. The stability results of the simplified single-tower model could not fully represent the real situation. The concrete principal compressive stress and reinforcement stress near the bottom of the tower both reached standard strength values when the main tower experienced nonlinear instability, indicating that the material yield led to the structural instability. The tower leg on the leeward side failed in the typical compression-flexural failure mode, while that on the windward side failed in the compressive-flexural-torsional failure mode. With the development of the thin-walled structure, more attention should be paid to stability when the strength requirements are met. The research can provide reference for the design and model simplification of long-span earth-anchored suspension bridges.

Abstract:Based on the mega-columns in the projects of China Zun and Tianjin 117 Tower, 4 multi-cell concrete-filled steel tube mega-column specimens were designed, and experimental study was conducted under one-way repeated eccentric compression load. The specimens include one 1/13 scaled octagonal 13-cell model of China Zun, one 1/13 scaled octagonal 13-cell model of China Zun with circular steel tube at corners, and two 1/12 scaled hexagonal 6-cell models of Tianjin 117 Tower. The damage evolution, bearing capacity, deformation restoration capacity, stiffness, and degeneration of the specimens with different section shapes and constructions were theoretically analyzed. Results show that all the specimens had good behaviors under eccentric compression. The setting of octagonal 13-cell mega-column with circular steel tube at corners could effectively reduce the damage evolution and significantly improve the bearing capacity and deformation capacity. Higher bearing capacity could be obtained when the eccentricity of the hexagonal 6-cell mega-column specimen was small, and the restoration capacity of the specimen was relatively good when the eccentricity was large. Various codes and the fiber based method were used to estimate the N-M interaction curves and F-Δ curves of the specimens, and the calculation results were more conservative compared with experimental results. Hence, referring to the features of multi-cell concrete-filled steel tube columns, a modified simplified calculation method for compressive strength of multi-cell concrete-filled steel tube (f_sc) was proposed on the basis of the calculation method in code GB 50936 and the constitutive relation of concrete proposed by Han. The calculated N-M interaction curves and bearing capacity were in good agreement with measured results, which suggests that the simplified method can be used as a reference for the calculation of multi-cell concrete-filled steel tube columns under eccentric compression.

Abstract:Nearspace hypersonic flight vehicles have become a new threat to national defense due to their characteristics of high speed, large maneuverability, and global arrival. The vehicle has non-inertial trajectory and complex strategic maneuvers, which brings new challenges to its trajectory estimation. In order to deal with vehicle maneuvers and improve the trajectory estimation performance, a trajectory estimating method was proposed based on the learnable extended Kalman filter (L-EKF) by combining the recurrent neural networks (RNNs) and the extended Kalman filter (EKF). First, a parametric characteristic model was established to describe the vehicle maneuvers. Then, the L-EKF was proposed, in which two RNNs were designed and embedded into EKF. By training with available trajectory data of the vehicle, the two embedded RNNs could find the hidden laws of the vehicle maneuvers and dynamically compensate for the parametric and model uncertainties online. Finally, the proposed L-EKF method was compared with EKF and adaptive EKF methods in several typical estimation scenarios of a hypersonic vehicle. Simulation results show that the proposed L-EKF had a higher estimation accuracy and better dynamic performance than EKF and adaptive EKF, especially when the flight vehicle performs unknown complex maneuvers.

Abstract:To meet the micro-newton adjustable thrust requirements of gravitational wave detection tasks, the design concept of micro-newton hall thrusters is analyzed based on the working principle of this electric propulsion technology. After a series of research of thruster size optimization, a micro-newton Hall electric thruster with outlet diameter being 4 mm and the length of 30 mm is designed. The experimental results of the thruster show that the thruster can achieve the continuous adjustable thrust output 0.2~112.7 μN, which meets the requirements of the gravitational wave detection missions. To further improve the dynamic performance of the thruster, the design and simulation of thruster control system are carried out, and the drag-free satellite simulation system is established based on the principle of drag-free control. Simulation results show that the closed-loop control of the thruster can not only effectively reduce the thrust noise and improve the response speed and accuracy of thrust output, but also improve the compensation accuracy of non-conservative forces, so that the displacement errors between spacecraft and test mass could satisfy the drag-free control accuracy indexes of gravitational wave detection tasks. Therefore, this kind of Hall thruster can meet the propulsion requirements of gravitational wave detection tasks and has the possibility to be applied to such space science missions.

Abstract:As a typical vertebrate model animal, zebrafish has been widely studied in the biomedical field because of its high similarity with human genes and transparent body for convenient observation. It is vital to recognize and monitor the heart of zebrafish larvae to study the pathogenesis of cardiovascular diseases and drug effects. A high-throughput heart recognition and monitoring method based on micro-vision was proposed to solve the problems of micromanipulation in the manipulation and observation of anisotropic zebrafish larvae. First, the Gaussian mixture model was used to determine the positions and directions of larvae. After one of the larvae was moved to the center of the POV of the microscope, a convolutional neural network was built to identify the roll angle of the larvae, and the larvae in abnormal postures were adjusted to make their hearts easy to monitor. After increasing magnification, a heart monitoring algorithm based on pixel intensity was proposed to realize heartbeat monitor. Experimental results show that the proposed system could realize accurate recognition and provide graphs of heartbeats and beat-rates of zebrafish larvae, which provides a novelty, stable, and efficient experimental observation method for the biomedical research of zebrafish.

Abstract:To explore the influence of pore diameter and constraint degree on cracking time and crushing effect in static crushing process, static crushing tests of 13 plain concrete specimens were carried out. The ratio of concrete area in inscribed circle of test specimen to crushing agent area was defined as constraint ratio, which was used to express the constraint degree of concrete to crushing agent. Volume expansion rate of crushing agent was utilized to indicate the crushing effect of specimens. Results show that: 3 or 4 cracks appeared after the broken of the concrete blocks under a single hole, and 3 cracks were the commonest, when the cracks became stable, the distribution forms were in the shapes of “Y”, “T”, and “cross”; The time-history curve of the volume expansion rate of crushing agent after cracking was in the form of quadratic parabola, which developed rapidly in early stage, slowly in later stage, and gradually became stable; Both pore diameter and constraint degree had obvious effects on volume expansion rate of crushing agent, the larger the pore diameter was, the larger the volume expansion rate of crushing agent became, and the better the crushing effect was, as constraint ratio increased, volume expansion rate of crushing agent decreased, and crushing effect was weakened; When constraint ratio was small, pore diameter had major effects on cracking time, where the larger the pore diameter was, the shorter the cracking time became, when constraint ratio was large, constraint ratio had major effects on cracking time, where the larger the constraint ratio was, the longer the cracking time became.

Abstract:In order to break through the bottleneck of narrowness of the local resonance band-gap (LRBG) and obtain wide band-gaps in low frequencies, we apply the local resonator based on magnetorheological elastomer (MRE) to the design of the new metamaterial beam. In this paper, the spectral element method is used for modeling and calculation. Based on the discrete Fourier transform theory and the variational method, the spectral beam element is constructed. According to the force-displacement relationship method, the spectral element of the local resonator is established. The correctness of the results in this paper is validated by the convergence of the finite element method results. The influences of the applied magnetic field, the mass of the local resonator and the material combination of the beam in a cell on the band-gap property are discussed and analyzed. It is found that the metamaterial beam designed by the local resonator based on MRE can effectively increase the bandwidth of LRBG, which is comparable to that of the Bragg band-gap (BBG), and can improve the vibration isolation performance. With the increase of the local resonator mass, the lower bound frequency of the BBG decreases while the bandwidth increases. Increasing the unit-cell number of the MRE metamaterial beam is an effective means to improve the attenuation properties of the BBG and LRBG. The larger the difference of the material combination is, the more the band-gaps in low frequency are, the larger the total bandwidth of band-gaps and the stronger the attenuation capability become.

Abstract:To solve the problems that fabric/paper has many surface defects and poor bonding with conductive ink, a more universal method, i.e., PVA modification and PVC modification, as well as conductive silver ink was adopted to prepare fabric/paper-based flexible electronic films with a sheet resistance of less than 10 Ω. The scanning electron microscope was applied to characterize the original morphology of the substrate, the modified layer in the middle, and the sintered layer of silver particles on the surface. The four-probe tester was used to characterize changes of sheet resistance with increasing bending times, tearing times, and immersion time. The flexible electronic film still showed excellent electrical conductivity after being bent for 100 000 times, immersed for 120 hours, and torn for more than 20 times. Effects of screen printing process parameters on printing accuracy were explored, and common printing defects of screen printing were summarized. The application value of flexible electronic thin films was preliminarily discussed. LED array circuit was designed and printed. Temperature and strain distributions of the printed circuit board surface mount resistor during operation were modeled and simulated. Screen-printed electrode for glucose detection was designed and prepared. Printed electrode has excellent electron transfer performance and better detection performance for glucose detection.

Abstract:Variable-flux machine (VFM) is designed to solve the problems of energy crisis and environmental pollution for traditional automotive industry, which satisfies the requirements of high-efficiency operation of new energy vehicle driving machines in a wide speed range. The development of VFM system and its key technologies were reviewed. First, the application background and operating principle of VFMs were introduced. Then, the topologies, advantages, and disadvantages of various VFMs (including VFMs using AC flux-adjustment coils, DC flux-adjustment coils, and mechanical structures) were analyzed, and the structure characteristics and design methods of different VFMs were summarized. Finally, in view of the special working principle of VFMs and the requirements of on-line parameter identification, flux-adjusting current control, and torque ripple suppression during load and on-line flux-adjustment operations, the control strategies specific to VFMs (including flux observer, current and torque control strategies, flux-adjustment, and speed regulation strategies) were summarized. The theoretical method, implementation approach, system structure, advantages, and disadvantages of various control strategies of VFMs were analyzed. Results show that the air-gap magnetic field of VFMs could be adjusted to expand the speed range and improve the efficiency of machines in high-speed range. By adopting advanced control methods, the on-line flux-adjustment and speed regulation could be realized, and the system could operate efficiently and steadily with torque ripple and flux-adjusting loss reduced. Thus, with the development of VFM topologies and related technologies, VFMs have great application prospects in the fields of electric vehicles and numerically controlled machines, and will become one of the key technologies in the future development of new energy fields.

Abstract:The superfluid gyroscope, atomic gyroscope and micro-hemispherical gyroscope have the possibility of high precision and miniaturization which make them the promising gyroscopes. The preparation quality of the key component of these three gyroscopes will directly affect their working performance, so it is necessary to perform in-depth research on the status of the key component preparation processes. Firstly, the structural characteristics, quality and technical indicators and their effect, and preparation technical requirements of these key components are briefly described. On this basis, the research progress on the fabrication technology of high-precision micro gyroscope key components is described, and the manufacturing processes such as the commonly used MEMS processing technology and micro-nano processing technology are reviewed in detail. By comparatively analyzing the preparation process of each key component, the advantages and limitations of each related process are emphasized. For micro-resonators, the process characteristics of mold processing technology in each preparation process and their influence on the quality of the micro-resonator are analyzed. Through analyzing the research progress of the preparation methods of each key component, the existing problems and challenges are discussed to provide a reference for the subsequent combination of micro-nano manufacturing technology and gyroscope technology, and further to promote the practical engineering application of related preparation technologies.

Abstract:Shape memory polymer is a kind of intelligent material which can change shapes under the stimulation of external environment. The advent of 4D printing technology promotes the development of smart materials and brings new opportunities for further research in the fields of minimally invasive medical, intelligent robots, flexible electronics and other high-tech industries. In this paper, the emerging and development as well as five new polymer printing technologies of 4D printing technology are introduced firstly. Then, the research progress of shape memory polymers and their composites are demonstrated in the perspectives of thermal, electrical, magnetic and optical driving. Next, we summarize the preparation and properties of shape memory polymers and their composites, as well as the potential applications of the printed structures in biomedical, aerospace, intelligent devices and biomimetic fields. Finally, the problems of 4D printing are pointed out in four aspects of technology, material, driving mode and application verification and the future research directions are discussed.