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As two necessary steps in phase-field simulation, parameters calculation and results storage play an important role to ensure the accuracy of simulation results. A strategy of parameters calculation and results storage was presented for phase-field simulation in α-Mg dendrite growth of Mg-5wt%Zn alloy under isothermal solidification. Based on the phase diagram and empirical formulas, key parameters of the phase-field model (equilibrium partition coefficient k, liquidus slope m, solutal diffusion coefficient in liquid Dl , solutal diffusion coefficient in solid Ds , etc.) can be obtained. Both structured grid and structured point storage methods can be used to store simulation results, but using the latter method will reduce about 60% storage space and 37.5% storage time compared to the former. Finally, convergent simulation results of α-Mg dendrite growth were obtained and in good agreement with the optical micrograph of experimental results, which verify the accuracy of parameters and stability of storage methods.

Simultaneous observation of Tamm plasmon (TP) and surface plasmon (SP) resonances has attracted much attention to improve the sensing performance and broaden the application field of plasmonic biosensors. Currently, enormous effort is devoted to simultaneously excite both SP and TP modes by exploiting total internal reflection. However, this method requires bulky and complicated prism or microscopy setup to fulfill the phase-matching condition, limiting the miniaturization and integration of sensors. Herein, we propose and theoretically demonstrate a nanograting-coupled plasmonic-photonic multilayer structure potentially integrated on the optical fiber tip, comprising a multilayer of photonic crystal inserted between a flat gold film and a gold nanograting. The proposed plasmonic-photonic multilayer structure enables the simultaneous excitation of TP and SP modes at the normal incidence by using zeroth and first-order diffraction light of nanograting, respectively. The resonant positions of both SP and TP modes can be independently adjusted by changing the nanograting period and the center wavelength of photonic crystal bandgap. Due to the insensitivity of TP mode to ambient surroundings, the proposed structure can be served as a self-reference SP resonance sensor for robust measurement where the sensitivity of the SP resonance sensor is determined by the wavelength shift of SP mode relative to TP mode. Moreover, the spectral overlapping of both TP and SP modes resulting in the abrupt change of reflection intensity, enables a rapid judgment to the refractive index of ambient surroundings by observing the red or blue shifts of SP resonant position relative to the case of TP. The simultaneous excitation of both TP and SP modes in the proposed structure opens a new path for improving detection accuracy and broadening application scenarios of fiber-optic SP resonance sensors.

Resistively shunted Nb/Al–AlOx/Nb Josephson junctions have been widely used in large-scale superconducting electronics such as the single-flux quantum circuit. The critical current determines substantially the working margin of the circuit. The distribution of vortices in the niobium film around superconducting devices is also commonly suspected to degrade the performance of devices. Unfortunately, most studies on Nb/Al–AlOx/Nb Josephson junctions only present electric transport measurements. Using a magnetic force microscope, we observed the static distribution of the vortices around the junction after sweeping the current–voltage curves of the junction in-situ. The measurements showed that the distribution density of vortices affected the critical current of the junction. Furthermore, we observed an aggregation of vortices arising from the Joule heat generated by the shunt resistor. It caused an irreversible decrease in the junction’s critical current.

For high-voltage direct current (HVDC) power grid transmission with higher voltages, the energy-consuming branch of the DC circuit breaker is required to dissipate huge energies of more than megajoules in a short time in the case of a fault and short circuit. The requirements for huge volume and weight are difficult to meet with energy-consuming equipment based on ZnO. In this paper, a new energy consumption method is proposed based on gallium indium tin (GaInSn) liquid metal in the arcing process, and a test platform with adjustable short-circuit current is built. The mechanism triggering GaInSn liquid metal arcing energy consumption is studied. It is found that short-circuit current and channel aperture are the key parameters affecting the energy consumption of liquid metal arcing. The characteristics of GaInSn liquid metal energy consumption are investigated, and four stages of liquid metal energy consumption are found: oscillatory shrinkage, arc breakdown, arc burning phase change and arc extinction. The influence of short-circuit current and channel aperture on the energy consumption characteristics of GaInSn liquid metal is investigated. To further explore the physical mechanism of the above phenomena, a magneto-hydrodynamic model of energy consumption in the GaInSn liquid metal arcing process is established. The influence of short-circuit current and channel aperture on the temperature distribution of the liquid metal arc is analyzed. The mechanism of the effect of short-circuit current and channel aperture on peak arc temperature and the temperature diffusion rate is clarified. The research results provide theoretical support for this new liquid metal energy consumption mode DC circuit breaker.

PVC-TiO2-DBD nanocomposites were synthesized via combined approaches of electrospinning, H2 plasma treatment and hydrothermal reaction. The spinning solution composition and the amount of PVC were investigated and optimized in order to obtain membranes with uniform structure and high chemical activity. It was found that TiO2 NPs were distributed homogeneously on the surface of the PVC fibers. Chemical bonds such as Ti-Cl and C-O-Ti bonds were formed to tightly immobilize the TiO2 NPs on the PVC surface. The effect of H2 plasma treatment on the surface of the PVC membranes was studied. Meanwhile, using ABS and PS as substrates, the influence of various groups, including chlorine bonds, C=C double bonds, cyano and phenyl groups on the possible promotion mechanism of different chemical bonds for the TiO2 deposition was also studied. Possible mechanisms for the enhancement of the deposition of TiO2 were given.

Vortex dynamics is crucial for practical applications and to understand the nature of the mixed state for high-T c superconductors. Mechanically exfoliated ultra-thin single crystals provide a unique platform for exploring vortex physics in the two-dimensional (2D) limit. Here, we systematically investigated the current–voltage (I–V) characteristics as functions of the temperature and magnetic field in a single-crystalline Bi2223 sub-microbridge of 2.5 unit cells thickness. The nonlinear I–V characteristics are excellently described by the scaling theory for a quasi-2D vortex glass (VG) phase transition, and a phase diagram revealing the VG and vortex liquid phase is drawn. The scaling parameter v is consistent with previous reports, while the critical exponent z is far smaller than that in most investigations. Moreover, the VG transition temperature T g of the present sample is higher than that in the reported Bi2223 epitaxial thin films and tapes. In addition, the pinning force density of our sample is calculated, which is stronger than that reported in Bi2223 epitaxial thin films and tapes. Our results indicate that a high pinning force density may suppress the dynamical critical exponent z and enhance the VG phase transition temperature, providing new insight into the flux dynamics in cuprates.

In this work, we present a detailed study of the electrical properties of stacked NbN/(TaN/NbN) N Josephson junctions. Cross-sectional scanning transmission electron microscopy analysis of the 5-stacked junction shows that the multilayer interface is very flat, each barrier has the same thickness, and the sidewalls of the junctions are nearly perpendicular to the substrate. Stacked junctions of different sizes and stacking numbers all have only one transition in their current–voltage curves. This indicates that the critical currents of the junctions in the stacked junctions are almost the same, showing the stability and repeatability of the multilayer fabrication and etching process. At 4.2 K, the 4-stacked junction shows excellent Josephson properties with characteristic voltage V c of 3.54 mV, which is about four times the 0.88 mV of the single junction. The temperature dependence of critical current density J c and V c of the stacked junction with N = 1, 2, 4 were measured, all of which can be fitted with dirty-limit theory. Stacked junctions with larger V c or more stacked layers can be achieved by optimizing electrode and barrier thickness, barrier resistivity, and thermal relaxation rate, etc.

The Janus monolayer transition metal dichalcogenides (TMDs) MXY (M = Mo, W, etc. and X, Y = S, Se, etc.) have been successfully synthesized in recent years. The Rashba spin splitting in these compounds arises due to the breaking of out-of-plane mirror symmetry. Here we study the pairing symmetry of superconducting Janus monolayer TMDs within the weak-coupling framework near critical temperature T c, of which the Fermi surface (FS) sheets centered around both Γ and K (K′) points. We find that the strong Rashba splitting produces two kinds of topological superconducting states which differ from that in its parent compounds. More specifically, at relatively high chemical potentials, we obtain a time-reversal invariant s + f + p-wave mixed superconducting state, which is fully gapped and topologically nontrivial, i.e., a ℤ2 topological state. On the other hand, a time-reversal symmetry breaking d + p + f-wave superconducting state appears at lower chemical potentials. This state possess a large Chern number |C| = 6 at appropriate pairing strength, demonstrating its nontrivial band topology. Our results suggest the Janus monolayer TMDs to be a promising candidate for the intrinsic helical and chiral topological superconductors.

We present a class of two-dimensional memristive maps with a cosine memristor. The memristive maps do not have any fixed points, so they belong to the category of nonlinear maps with hidden attractors. The rich dynamical behaviors of these maps are studied and investigated using different numerical tools, including phase portrait, basins of attraction, bifurcation diagram, and Lyapunov exponents. The two-parameter bifurcation analysis of the memristive map is carried out to reveal the bifurcation mechanism of its dynamical behaviors. Based on our extensive simulation studies, the proposed memristive maps can produce hidden periodic, chaotic, and hyper-chaotic attractors, exhibiting extremely hidden multi-stability, namely the coexistence of infinite hidden attractors, which was rarely observed in memristive maps. Potentially, this work can be used for some real applications in secure communication, such as data and image encryptions.

Storage of a single magnetic flux quantum in a superconducting loop containing a Josephson junction represents a promising unit cell configuration for construction of a cryogenic memory of superconducting digital circuits. However, application of a DC bias current is required for operation of such a memory cell to maintain trapping of the flux quantum in the storage loop. In this work, we present a superconducting memory cell that uses a superconducting-magnetic π junction. The cell characteristics show flux quantum hysteresis centering at the zero-bias current. We develop a fabrication process that combines superconductor–ferromagnet–superconductor (SFS) junctions with superconductor–normal metal–superconductor (SNS) junctions. The critical current density of the SFS junctions shows a 0–π oscillation as a function of the ferromagnetic layer thickness. The formation of the π junction is confirmed further by the flux modulation curves of a superconducting quantum interference device made from SNS junctions with an additional SFS junction.

This study investigates the evolution of superconducting properties as a function of disorder in epitaxial and polycrystalline niobium nitride (NbN) thin films grown on MgO and SiO2/Si substrates, respectively. By reducing the film thickness from 100 to 4 nm, the effective disorder in these two sets of films encompasses a large range, with the Ioffe–Regel parameter in the range of 5.7–9.3 and 1.5–3.0, respectively. Moreover, the density of states at the Fermi level [N(0)] of epitaxial NbN films decreases from 1.91 × 1028 to 1.46 × 1028 states eV−1m−3 with the superconducting transition temperature (Tc ) ranging from 16.0 to 11.8 K. In contrast, the N(0) of polycrystalline NbN films decreases from 2.18 × 1028 to 1.80 × 1028 states eV−1m−3 with Tc ranging from 14.9 to 2.56 K. The experimental results reveal that the Tc of NbN films with different thicknesses is mainly controlled by N(0), and the greater Coulomb pseudopotential (μ*) in the polycrystalline films leads to lower Tc and larger resistivity. The changes in N(0) and μ* should collectively account for the reduction of Tc with disorder in NbN thin films.

To address the limitations of current classification prediction models, an algorithm DPC-ASMOTE-IRF for Clustering by fast search and find of density peaks (DPC) with adaptive SMOTE (ASMOTE) coupled with improved random forest (IRF) is proposed. The algorithm first introduces in the data processing stage DPC clustering algorithm to cluster the samples, and proposes ASMOTE oversampling technique to process a minority class of samples to get relatively balanced samples. In the algorithm stage, the model’s overall classification performance for unbalanced data is improved by assigning weights to each decision tree in the random forest through the classification accuracy. The experimental results show that the classification performance indexes of the proposed method are all improved compared with similar classification experimental models.

Superconducting circuits based on Josephson junctions have the potential to achieve high speed and ultra-low power consumption, but their integration is limited by the low controllability of Nb-based tunnel junction and the existence of shunt resistors. In this work, we report the fabrication of superconductor/normal metal/superconductor (SNS) Josephson junctions with high reproducibility on oxidized Si substrates. The junctions based on NbN/TaN/NbN trilayers measured at 4.2 K show excellent Josephson properties with a wide range of critical current (I c) from 227 to 2000 μA. The variations of critical current density (J c) and characteristic voltage (V c) are respectively less than 7.1% and 7.5% in the 2 inch region. The standard deviation of I c is calculated to be less than 1.7% for Josephson arrays with the number of junctions up to 10 000 occupying an area of 0.34 mm2. The results provide a guarantee for the applications of NbN-SNS Josephson junctions in superconducting large-scale integrated circuits.

High quality superconducting thin films are the basis for the application of superconducting devices. Here, we report on the film growth and superconducting properties of Ta films. The films were grown by the pulsed laser deposition technique on the α-Al2O3 substrates. It is found that, with the increase of the film thickness from 20 nm to 61 nm, both the superconducting transition temperature T c and residual resistance ratio (RRR) display an upward trend, while the upper critical field decreases monotonously in a wide temperature region. A clear anisotropic behavior is revealed by comparing the upper critical fields with two different orientations ( H ⊥ film and H ∥ film ). The anisotropy parameter Γ is found to be as high as 20 for the sample with the thickness of 20 nm. The systematical evolution from two- to three-dimensional features for the superconductivity with increasing the film thickness is observed in the temperature dependent upper critical field data. Moreover, the vortex liquid region tends to expand with the increase in the film thickness.

A cold preamplifier based on superconducting quantum interference devices (SQUIDs) is currently the preferred readout technology for the low-noise transition edge sensor (TES). In this work, we have designed and fabricated a series SQUID array (SSA) amplifier for the TES detector readout circuit. In this SSA amplifier, each SQUID cell is composed of a first-order gradiometer formed using two equally large square washers, and an on-chip low pass filter (LPF) as a radio-frequency (RF) choke has been developed to reduce the Josephson oscillation interference between individual SQUID cells. In addition, a highly symmetric layout has been designed carefully to provide a fully consistent embedded electromagnetic environment and achieve coherent flux operation. The measured results show smooth V–Φ characteristics and a swing voltage that increases linearly with increasing SQUID cell number N. A white flux noise level as low as 0.28 μ Φ 0/Hz1/2 is achieved at 0.1 K, corresponding to a low current noise level of 7 pA/Hz1/2. We analyze the measured noise contribution at mK-scale temperatures and find that the dominant noise derives from a combination of the SSA intrinsic noise and the equivalent current noise of the room temperature electronics.

In this paper, a 450 km simulation circle method is used to extract all meteorological records from 1949 to 2018, and to obtain random samples. The Yanmeng typhoon wind field model is compiled by MATLAB, the optimal typhoon wind profile index α is calculated. The harmonic superposition method is used to simulate the typhoon wind field at the construction site. Stress time-history of cables under buffeting is analyzed using ANSYS and MATLAB. Palmgren-miner linear cumulative fatigue damage method is used for fatigue damage analysis, combined with rain flow counting method and S-N curve. It is shown that the damage value of cable increases with the growth of wind speed. The damage of cable has a similar trend with the variance of axial stress. The cable of middle span, about an eighth of the way to bridge tower, is extremely sensitive to the wind. The low stress region is the main circulating region of the cable. The region of low stress expands with the increase of wind speed. The amplitude of cable stress mainly circulates from low amplitude to high amplitude with the increase of wind speed.

Lithium niobate (LN) exhibits outstanding properties in various application of photonics, electronics, and optoelectronics, showing potentials in integration. Due to the directional dependence of LN tensor properties, optical elements made up by LN favor the type of LN substrate. To introduce high-performance superconducting nanowire single-photon detectors (SNSPDs) to LN-integrated photonics chips, superconducting NbN thin films with thicknesses from 3 to 50 nm were deposited on X-cut, Y-cut, and Z-cut LN substrates using magnetron sputtering at room temperature. The different thickness dependencies of T c, δT c, and residual resistance ratios are observed in NbN thin films on different LN substrates. NbN thin films on X-cut and Y-cut LN substrates are polycrystalline with a transition temperature (T c) of ∼6 K for a 6 nm thick film. While NbN thin films are epitaxially textured on Z-cut LN substrates with T c of 11.5 K for a 6 nm thick film. NbN-SNSPD on X-cut LN substrates shows a weak saturation trend of its system detection efficiency; however, the performance of NbN-SNSPD on Z-cut LN substrates is limited. We evaluated the selection of cuts and concluded that X-cut and Y-cut LN are more suitable to be a platform of integrated LN photonic chips from the aspect of NbN-SNSPD. This study helps fabricate high-performance SNSPDs on fully integrated photonics chips on LN substrates.

In this work, we report the electrical properties of NbN internally shunted Josephson junctions with NbN x barriers. Cross-sectional scanning transmission electron microscopy analysis shows that all layers have the same cubic structure; NbN/NbN x /NbN trilayers were epitaxially grown on MgO substrates. The resistivity of the NbN x films could be varied in the range of 1–104 mΩ cm by controlling both the N2 partial pressure and the deposition time during reactive sputtering. The temperature dependence of the critical current density (J c) and characteristic voltage (I c R n) of the junctions with different barrier resistivities were measured for various barrier thicknesses. For the 10 nm-thick NbN x layer with resistivities of 73.44, 385.72, and 711 mΩ cm, the coherence length of the barrier was determined to be 5.55 ± 0.07, 4.88 ± 0.06, and 1.40 ± 0.13 nm, respectively, corresponding to carrier diffusion rates of 2.741 ± 0.004, 1.211 ± 0.002, and 0.008 ± 0.001 cm2 s−1, respectively. Thus, the reduction in barrier resistivity leads to a larger coherence length and a faster diffusion rate, which will further increase the J c and I c R n of the junction. By adjusting the barrier resistivity and thickness, the J c of the junction can be easily tuned over more than four orders of magnitude, and an I c R n value of 0.97 ± 0.07 mV was obtained at 10 K. The results indicate that the all-NbN self-shunt junction is a promising candidate in high-speed and high-temperature applications.

Objective. Non-invasive brain stimulation has been promoted to facilitate neuromodulation in treating neurological diseases. Recently, high-definition (HD) transcranial electrical stimulation and a novel electrical waveform combining a direct current (DC) and theta burst stimulation (TBS)-like protocol were proposed and demonstrated high potential to enhance neuroplastic effects in a more-efficient manner. In this study, we designed a novel HD transcranial burst electrostimulation device and to preliminarily examined its therapeutic potential in neurorehabilitation. Approach. A prototype of the transcranial burst electrostimulation device was developed, which can flexibly output a waveform that combined a DC and TBS-like protocol and can equally distribute the current into 4 × 1 HD electrical stimulation by automatic impedance adjustments. The safety and accuracy of the device were then validated in a series of in vitro experiments. Finally, a pilot clinical trial was conducted to assess its clinical safety and therapeutic potential on upper-extremity rehabilitation in six patients with chronic stroke, where patients received either active or sham HD transcranial burst electrostimulation combined with occupational therapy three times per week for four weeks. Main results. The prototype was tested, and it was found to comply with all safety requirements. The output parameters were accurate and met the clinical study needs. The pilot clinical study demonstrated that the active HD transcranial burst electrostimulation group had greater improvement in voluntary motor function and coordination of the upper extremity than the sham control group. Additionally, no severe adverse events were noted, but slight skin redness under the stimulus electrode immediately after stimulation was seen. Conclusions. The results demonstrated the feasibility of incorporating the HD electrical DC and TBS-like protocol in our device; and the novel neuromodulatory device produced positive neurorehabilitation outcomes in a safe fashion, which could be the basis for the future clinical implementation for treating neurological diseases. Trial registration: ClinicalTrials.gov Identifier: NCT04278105. Registered on 20 February 2020.