The world of mathematics is often considered abstract, with its symbols, concepts, and topics appearing unrelated to physical objects. However, it is important to recognize that the development of mathematics is fundamentally influenced by a basic fact: mathematicians and computers are physical objects subject to the laws of physics. Through an analysis of the Turing machine, it becomes evident that Turing and his contemporaries overlooked a physical possibility: information carriers can be quantum systems. As a result, computing models like the Turing machine can only process classical information, limiting their computing power. Gödel's incompleteness theorem highlights the basic fact that mathematicians and computers are made up of finite numbers of atoms and molecules. They can only start with a finite number of axioms, use a finite number of symbols and deduction rules, and arrive at theorems with a finite number of steps. While the number of proofs may be infinite after including all future mathematicians and computers, they must still be enumerable. In contrast, the number of mathematical statements is uncountable, meaning that there will always be mathematical statements that cannot be proved true or false. Just as Landauer claimed that information is physical, mathematics is also physical, limited or empowered by the physical entities that carries it out or embodies it.
In this paper,an optimization design method for high field superconducting magnet with ferromagnetic shield is discussed.Firstly,the analytical formula for calculating the magnetic field at any space point is derived based on the equivalent magnetic charge model.Then the validity and accuracy of the formula are discussed by comparing the results with that of the finite element method(FEM)for the same model.Finally,a joint optimization of MRI magnet system with ferromagnetic shielding is carried out in order to improve the homogeneity of magnetic field in the DSV(diameter of spherical volum)region and enhance the field intensity in the center.
钙钛矿结构LaNiO3因其高电导的金属性输运行为,有望作为电极材料在今后的氧化物器件工艺中发挥重要作用.为了细致认识氧缺位对其金属输运的影响,本文采用溶胶凝胶法在氧气、空气和真空等气氛下烧结获得具有不同缺氧量的LaNiO3-δ薄膜,并利用Mn3+的还原性进一步调整其缺氧量δ.对这些样品的电阻率温度关系测量结果表明,缺氧量δ＞0.1后薄膜的高温电阻率开始超过Mott-Ioffe-Regel极限,变成"坏金属";增大δ至0.2,薄膜的低温剩余电阻率大幅度上升,说明氧空位分布无序性导致的载流子局域化有明显作用.以上样品的金属输运都呈非费米液体行为.继续增加氧缺位浓度,样品电阻率在低温～30 K以下呈绝缘体温度关系,同时高温金属态转变为费米液体行为,说明钙钛矿结构镍酸盐的金属-绝缘体转变与费米液体输运之间或存在关联性.
AuCu3型超导体兼具非平庸的拓扑能带,是近期受到关注的拓扑超导体候选材料之一.理论预言SrPb3具有非平庸的拓扑能带,然而,实验上尚未得到证实.本工作观察到德哈斯-范阿尔芬振荡,验证了 SrPb3中电子能带的非平庸拓扑性质.通过分析提取出两个振荡频率Fα=3.54 T和Fβ=7.43 T.进一步利用Lifshitz-Kosevich公式以及朗道量子化理论,得到两个对应费米面的载流子有效质量分别为m*α=0.006m.和m*β=0.008mo,同时它们的贝里相位分别为φαβ=(1.32±0.25)π和χβB=(1.10±0.25)π.这些结果表明SrPb3中存在有效质量接近于零的相对论费米子和非平庸拓扑能带.SrPb3中超导电性与非平庸拓扑能带的共存,为研究超导与拓扑的关联以及探索拓扑超导体提供新的研究体系.
以YBCO(YBa2Cu3O7-δ)为代表的二代高温超导带材因具有高临界转变温度、高临界磁场和强载流能力,受到了国际学界高度关注,在各个领域具有广泛的应用前景.二代高温超导带材在绕制、冷却和运行过程中会受到不同来源的外力作用,且超导带材的韧性、延展性较差,因此其机械性能是影响安全性与设备运行可靠性的关键.本文基于二代超导带材各向异性的特点,对超导带材轴向、横向、弯曲三个方向的静态机械性能及疲劳性能进行了介绍.同时,也对超导带材各方向机械性能的测试方法、影响因素及机理进行了总结.
静止无功发生器(Static Var Generator,SVG)具有提高系统功率因数、动态改善电能质量、稳定电网以及节能降耗、降低运行成本等优点.针对其优点,作为水冷磁体电源的使用需求,考虑将高压链式SVG技术作为磁体电源无功补偿的方案,以实现无功动态补偿.本文主要介绍了链式串联SVG的工作原理,对其参数进行设计并利用PSCAD进行仿真实验,实验验证了方案的可行性,为强光磁关键技术预研项目14 MW水冷磁体电源无功补偿装置提供了理论支持.
超导量子干涉仪、超导光子探测器等深空探测器需要液氦温区制冷技术提供极低温温度,固体界面接触热阻的存在会增大耦合界面温度差,进而增加制冷机系统冷损.为定量探究4～20 K深低温区固体接触热阻,采用GM作为冷源,设计了一台可同时调节压力和低温温度的固体界面接触热阻测试实验台.利用感压纸进行接触界面压力校核,并对温度重复性进行验证.实验测试了不同导热介质填充情况下,温度和压力变化时固体接触热阻的变化规律.基于最小二乘法对实验数据进行半经验公式拟合,获得4～20 K温区不同压力加载条件下的接触热阻的定量参考.
Recently, topological materials have stimulated unprecedented research interest in condensed matter physics.In the presence of a perpendicular magnetic field and a longitudinal thermal gradient, the diffusion of carriers can produce a longitudinal electric field and a transverse electric field, which are defined as thermoelectric effects. In principle, thermoelectric effects are sensitive and promising probes to novel quantum states and exotic physical effects for those topological materials. However, the studies of thermoelectric properties in ultra-high magnetic fields are rare. In this work, aiming at the problems of fast field-sweeping rate and large mechanical vibration, we have designed and constructed a high-precision measurement device for detecting the thermoelectric effect in water-cooled magnet up to 32 T. Meanwhile, the reliability of our measurement system is further confirmed by measuring the thermoelectric effects for several topological materials.
In this paper, GO/Cu-Nb multi-core（19~2-cores） composite wires reinforced with Graphene oxide and Cu-Nb multi-core（19~2-cores） composite wires undoped with Graphene oxide were successfully prepared by powder in tube method. The filament microstructure, interface topography and the characteristics peaks of the two composite wires under different sizes were analyzed by metallography, SEM and Raman spectroscopy, respectively. The results showed that the deformation of the core wires and the matrix was coordinated owing to the good self-lubricating property of graphene oxide. The dispersed distribution of graphene oxide effectively blocked the agglomeration of Nb particles and the generation of large-sized grains, consequently the deformation of the core wires was more uniform and the shape was more regular. The mechanical and electrical properties of the Cu-Nb composite wires are significantly improved by graphene oxide doping. The analysis indicates that the size, dispersion uniformity of graphene oxide and heat treatment temperature of wires are the main reasons for improving the comprehensive performance of the wires.
Superconducting quantum circuits have become one of the mainstream technical routes to realize quantum computers, where quarter-wavelength superconducting resonators are mainly used to readout the information of qubit state and are the key devices for realizing superconducting quantum circuits. In this work, a quarter-wavelength superconducting resonator is designed. Two electromagnetic simulation algorithms（finite element method and moment method） are used to model and simulate the transmission characteristics of the superconducting resonator. The designed superconducting resonator sample was prepared and its transmission characteristics were measured at a low temperature of 20±5 mK. By comparing the simulation results with the design values and measured values, it is found that the sonnet software based on the method of moments is superior to the HFSS software based on the finite element method in terms of simulation accuracy, simulation speed and resource consumption. At the same time, the influence of crosstalk between resonators on simulation accuracy is studied. When the number of resonators is small, the influence of crosstalk between resonators can be almost ignored.
Toroidal Field（TF） coils are an important part of the comprehensive research facility for fusion technology（CRAFT）, which is wound by CICC conductors and insulated by Vacuum Pressure Impregnation（VPI）. Immerse the insulation layer of the coil in the resin, and then conduct high temperature curing for a long time to completely cure the resin of the entire insulation layer. During impregnation and curing, VPI mould not only bears the load of the coil itself, but also bears atmospheric pressure, internal pressure, thermal deformation, etc. In order to ensure the insulation quality of the coil, CATIA software is used for 3D modeling of VPI mould, and Ansys Workbench finite element software is used for analysis and verification of VPI mould. The analysis shows that the VPI mould design is reasonable, which provides a theoretical and practical basis for engineering design.
In the superconducting microwave cavity-qubit hybrid device, the kinetic inductance of the superconducting material can be tuned with the DC current, so that the frequency of the cavity can be adjusted and thus it can be better matched with the frequency of qubit. In order to suppress the leakage of microwave signals while introducing DC-bias electrode, it is an effective solution to add filters on the tunable cavity. This research takes the filter as the starting point and uses computer simulation to develop a new working mode of the original Double-"E"-shaped filter. On this basis, a tunable superconducting microwave cavity was fabricated. The experimental results show that the quality factor of the cavity is ～7800 with the impedance ～1700 ohm. The frequency of the resonator can be tuned with the DC-bias current, and the maximum change value is ～26 MHz.
Optical lattice atomic clocks with clock transition frequencies in the optical frequency have achieved E-19 level of frequency stability and E-18 level of frequency uncertainty, which have important applications in quantum frequency standard, quantum simulation and precision measurement. In this paper, the development history, operation principle, performance evaluation, application and prospect of optical lattice atomic clocks are reviewed.
With the decrease of temperature, the HTS bulk exhibits different superconducting characteristics. This article aims to use a method of taking vacuum decompression to realize the super-cooling condition and research the Levitation Characteristics between the HTS bulk array and Halbach permanent magnetic guideway（PMG） at different pressure conditions. Due to the limitations of the experimental measurement, the study can only be completed under partial working conditions by relying on the experiment. To study the levitation characteristics of superconductors systematically and comprehensively under the super-cooling state, a superconductor simulation model was established. The simulation parameters are determined by comparing them with the experimental results. The results show that the simulation results calculated by the proposed model agree with the experimental data well. The simulation model provides simulation tools for levitation force optimization.
Ruddlesden-Popper iridates, the 5d electron counterpart of cuprate high temperature superconductors, have attracted much interest due to the cooperation between spin-orbit coupling and Coulomb repulsion. A central issue is to understand the metal insulator transition as a function of doping, which would provide important insights on doped Mott insulators and high temperature superconductivity in cuprates. In this review, we focus on the hole doped iridates, which parallel the electron doped cuprates, due to the sign difference in the next-nearest hopping term（t’） of the one band Hubbard model. The materials are classified by different elements of the chemical substitution. In each category, the electronic structure probed by angle-resolved photoemission spectroscopy（ARPES） are summarized and the possible origins for the metal insulator transition are discussed. Finally, we mention the future research directions in this field.
Ferroelectric materials possess spontaneous electrical polarization, which have reversible and nonvolatile effects on the electronic structure of the heterojunction. In this work, Pb nanoislands are successfully fabricated on a two-dimensional ferroelectric α-In 2 Se 3 substrate by molecular beam epitaxy to construct a Pb/α-In 2 Se 3 superconductor-ferroelectric heterojunction, and its atomic structure and electronic structure are characterized by scanning tunneling microscopy. Further scanning tunneling spectroscopy measurements show that the quantum well states of the Pb nanoislands disappear, and we do not observe superconducting energy gap at the temperature of as low as 4.5 K, indicating that the ferroelectric substrate affects the electronic structure and even the superconductivity of the Pb nanoislands. These findings not only provide a reference for understanding the effect of ferroelectricity on superconductivity, but also offer a new platform to tune the electronic structure and superconductivity in low-dimensional quantum systems.
Electronic expansion valve is the main regulating component of electric vehicle air conditioning system. It is of great significance to explore its regulating characteristics for formulating system control strategy. In this work, an experimental bench for electric vehicle air conditioning system with R134a as refrigerant was built, and the dynamic variation of refrigerant flow rate and pressure in the air conditioning system during the electronic expansion valve regulation was studied. The effects of valve opening on system cooling capacity, air outlet temperature of air conditioning box, compressor power consumption and COP were analyzed under different compressor speed. The results show that the phase state of refrigerant in front of valve is an important factor affecting the system pressure variation during electronic expansion valve adjustment. When the refrigerant in front of the valve is supercooled liquid, regulating the valve opening has a greater impact on the system pressure, and when the refrigerant in front of the valve has a large undercooling degree（greater than 10 ℃）, reducing the valve opening will lead to a short time of over-throttling, resulting in large fluctuation of system pressure. The refrigerant circulating flow rate in the system changes linearly with the valve opening, and is not affected by the phase state of the refrigerant before the valve. Under the experimental condition, the refrigerant circulating flow corresponding to 100% valve opening is 97.2～115.5 kg/h. When the valve opening is reduced by 10%, the circulating refrigerant flow decreases by 6%～9%.
Powder filter is a low-pass filter that can be applied to low-temperature experimental systems such as superconducting quantum computing. As the frequency increases, the filter will effectively attenuate the high-frequency signal. The parameters such as the filling material of the powder filter, the length of the center wire, the thickness of the center wire, and the structure of the center wire will affect its frequency response characteristics. In this work, the CST microwave studio is used for the first time to conduct a 3D simulation study on the frequency response characteristics of powder filters with different central structures based on the filling method of micron particles. The qualitative consistency between the simulation results and the measured results shows the feasibility and accuracy of the simulation method. The proposed simulation method can effectively speed up the iteration speed of the filter structure, thereby reducing the development cycle and cost. This work facilitates the development of a new generation of powder filters that can be applied to superconducting quantum computing.
The steady-state strong magnetic field experimental device water cold storage system is one of the representative large flow and large temperature difference water cold storage systems at home and abroad. The system includes two 3000 m~3 water storage tanks, both of which use naturally stratified technology to increase the cold storage capacity. Due to the characteristics of this technology, in the later stage of chilled water storage, the inlet water temperature of the centrifugal chiller will be lower, which causes the new added 12 °C large temperature difference chiller to have low-load surge failures during the trial operation stage, which affects the stability of the refrigeration operation. This article first describes the surge mechanism of the centrifugal chiller; then the anti-surge optimization measures for the chiller before the transformation are analyzed. Through the hot vapor bypass modification combined with the reasonable setting of related parameters, the surge risk of the unit is solved; through the optimization of DDC control, the load reduction capacity of the unit is optimized, and low-load vibration and noise are avoided. This transformation provides a guarantee for the safe and stable operation of the system.
In order to investigate the microscopic mechanism of flash spray cooling, a droplet-suspended vacuum flash evaporation experimental setup was designed and built to investigate the flash characteristics and bubble growth mechanism during the flash evaporation of Tween20 droplets using a visualization window. The droplet morphology undergoes four stages of rapid pressure drop, namely bubble nucleation, bubble growth, accompanying bubble growth and bursting, and the process is repeatedly cycled until the droplet evaporates stably. For droplet temperature changes, the final state pressure of the flash chamber plays a decisive role and its final state temperature rises significantly with increasing pressure. The morphological analysis of the droplet flashing process also shows that the temperature of the droplet drops significantly during the violent explosion phase; during the stable evaporation phase, the temperature will also start to stabilize. Therefore, it can be seen that the violent explosion of the droplet will take away a large amount of its own heat. The effect of Tween20 concentration on the temperature of the droplet is minimal, but it causes a significant lag in the initial nucleation time of the bubbles within the droplet and inhibits the rupture of the bubbles within the droplet.
