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An axion insulator is a three-dimensional (3D) topological insulator (TI), in which the bulk maintains the time-reversal symmetry or inversion symmetry but the surface states are gapped by surface magnetization. The axion insulator state has been observed in molecular beam epitaxy (MBE)-grown magnetically doped TI sandwiches and exfoliated intrinsic magnetic TI MnBi2Te4 flakes with an even number layer. All these samples have a thickness of ~10 nm, near the 2D-to-3D boundary. The coupling between the top and bottom surface states in thin samples may hinder the observation of quantized topological magnetoelectric response. Here, we employ MBE to synthesize magnetic TI sandwich heterostructures and find that the axion insulator state persists in a 3D sample with a thickness of ~106 nm. Our transport results show that the axion insulator state starts to emerge when the thickness of the middle undoped TI layer is greater than ~3 nm. The 3D hundred-nanometer-thick axion insulator provides a promising platform for the exploration of the topological magnetoelectric effect and other emergent magnetic topological states, such as the high-order TI phase., Comment: 24 pages, 5 figures. Comments are very much welcome

Additional file 2. Full images of the western blotting results (Fig. S14-S15).

Heterostructures between topological insulators (TI) and magnetic insulators represent a pathway to realize the quantum anomalous Hall effect (QAHE). Using density functional theory based systematic screening and investigation of thermodynamic, magnetic and topological properties of heterostructures, we demonstrate that forming a type-I heterostructure between a wide gap antiferromagnetic insulator Cr$_2$O$_3$ and a TI-film, such as Sb$_2$Te$_3$, can lead to pinning of the Fermi-level at the center of the gap, even when magnetically doped. Cr-doping in the heterostructure increases the gap to $\sim$ 64.5 meV, with a large Zeeman energy from the interfacial Cr dopants, thus overcoming potential metallicity due to band bending effects. By fitting the band-structure around the Fermi-level to a 4-band k.p model Hamiltonian, we show that Cr doped Sb$_2$Te$_3$/Cr$_2$O$_3$ is a Chern insulator with a Chern number C = -1. Transport calculations further show chiral edge-modes localized at the top/bottom of the TI-film to be the dominant current carriers in the material. Our predictions of a large interfacial magnetism due to Cr-dopants, that coupled antiferromagnetically to the AFM substrate is confirmed by our polarised neutron reflectometry measurements on MBE grown Cr doped Sb$_2$Te$_3$/Cr$_2$O$_3$ heterostructures, and is consistent with a positive exchange bias measured in such systems recently. Consequently, Cr doped Sb$_2$Te$_3$/Cr$_2$O$_3$ heterostructure represents a promising platform for the development of functional topological magnetic devices, with high tunability.

Additional file 1. Supplementary methods, figures (Figures S1-S13) and tables (Tables S1-S9).

In order to provide the AES/EBU digital audio interface for the input and output interface sub-boards of the digital audio matrix equipment and improve the system integration and flexibility, a method of using FPGA to realize the multi-channel AES/EBU digital audio transmission and reception interface is designed. The sending unit receives the audio data signal in TDM format, and then converts it to AES/EBU audio format for output after demultiplexing; the receiving unit receives the AES/EBU digital audio signal, decodes it, and converts it into TDM format signal for output. The system design has passed logic function simulation and hardware testing, and the output signals of the sender and receiver are in compliance with the standard.

The emergence of energy internet has changed people’s understanding of energy production, transmission, storage, conversion and consumption. However, how to promote the development of energy Internet, how to integrate it with various existing energy entities, and really play a role, still need more in-depth research and practice. To solve the problem of optimal management and control of energy and power system, a multi-level peer-to-peer collaborative optimization method for smart energy system based on big data analysis is proposed. In the constructed optimization scheduling model, combined with the demand response characteristics of different energy loads, and based on the time-sharing price of energy such as electricity and natural gas, the user IDR response is described in detail from the aspects of load reduction, transferable load and replaceable load, so that it can effectively cooperate with MES equipment in IEGS, thus minimizing the system operation cost. Multi-source energy storage mode is helpful to improve the economic efficiency of smart energy system, reduce the influence of uncertainty on the actual operation of the system, and reduce the power fluctuation burden of power grid.

The quantum anomalous Hall effect (QAHE) in a magnetic topological insulator system without the need of an external magnetic field becomes of great interest because of its dissipationless spin currents. The proximity effect via a magnetic adlayer is a promising strategy to bring magnetism into a topological insulator (TI) due to its boosted Curie temperature for a realistic application. In this work, a proximity-induced magnetism above 90 K in a TI, (Bi 0.25 Sb 0.75 ) 2 Te 3 , on a ferrimagnetic adlayer with perpendicular magnetic anisotropy, thulium-iron-garnet (TIG), was evidenced directly by using magnetic circular dichroism. A competition between exchange couplings with different sublattice-sites was further revealed element-specifically in a temperature-driven spin-reorientation of TI, bringing an issue on magnetic inhomogeneity at the interface, which might cause difficulties in obtaining QAHE in such a TI/TIG bilayer system. Our results prove directly the robust magnetism of TI above liquid nitrogen temperatures and also give a deep insight into the mechanism of interfacial coupling in the proximity effect for the bilayer of TI and magnetic oxide, which could be essential for the design of a system with QAHE.

A quantum anomalous Hall (QAH) insulator coupled to an s-wave superconductor is predicted to harbor a topological superconducting phase, the elementary excitations of which (i.e. Majorana fermions) can form topological qubits upon non-Abelian braiding operations. A recent transport experiment interprets the half-quantized two-terminal conductance plateau as the presence of chiral Majorana fermions in a millimeter-size QAH-Nb hybrid structure. However, there are concerns about this interpretation because non-Majorana mechanisms can also generate similar signatures, especially in a disordered QAH system. Here, we fabricated QAH-Nb hybrid structures and studied the QAH-Nb contact transparency and its effect on the corresponding two-terminal conductance. When the QAH film is tuned to the metallic regime by electric gating, we observed a sharp zero-bias enhancement in the differential conductance, up to 80% at zero magnetic field. This large enhancement suggests high probability of Andreev reflection and transparent interface between the magnetic topological insulator (TI) and Nb layers. When the magnetic TI film is in the QAH state with well-aligned magnetization, we found that the two-terminal conductance is always half-quantized. Our experiment provides a comprehensive understanding of the superconducting proximity effect observed in QAH-superconductor hybrid structures and shows that the half-quantized conductance plateau is unlikely to be induced by chiral Majorana fermions., Comment: 17 pages, 4 figures. Comments are welcome. Supplementary materials will be provided upon request

By using pulsed laser induced detachment technique assisted with a Langmuir probe, the electronegative characteristics of the capacitively coupled Ar plasma doped with 5% O2 are studied in this paper. We first focus on the electrical signal of the probe after laser pulse has induced negative ion detachment, and then analyze characteristics of the probe signal with the probe bias below or above the plasma space potential. When the bias is set to be lower than the plasma potential, the probe signal usually shows a downward surge signal. As the bias is higher than the plasma potential, the main characteristics of the signal takes on an upward wide wave packet. The evolution behavior of the probe signal with bias from the downward surge valley to the upward wide wave packet might be due to the potential difference between the plasma space potential and the probe bias voltage. Furthermore, it shows that the position of the upward peak appears later than that of the downward surge valley, which may be related to the changing of the rate of the electron diffusion flux and the electric field drift flux. According to the dependence of probe collection signal on bias, the electronegativity describing the Ar+O2 plasma electronegative property is defined as saturation ratio of electron current after pulsed laser radiation to that of collection probe at a potential above plasma spatial potential. Plasma electronegativity is diagnosed with discharge pressure, radio-frequency (RF) input power and axial position. The experimental results show that the electronegativity of plasma decreases with input RF power increasing. As the gas pressure is kept at 12.0 Pa, the plasma electronegativity decreases from 5.05 to 0.98 with RF input power increasing from 50 to 300 W. It also shows an increasing trend of electronegativity with plasma discharge pressure increasing. Due to asymmetrical distribution of electrodes, the plasma electronegativity also takes on asymmetric one with respect to the axial position. In our experiments, the electronegativity near the power electrode shows about 1-4 times higher than that near the ground electrode, the lowest point of the plasma electronegativity seems to be located in the center of the plasma discharge. This may be related to the dynamics of the secondary electrons emitted from electrode and the competition processes between negative ion production in collisional dissociation of oxygen molecules and the losses of high energy electron and negative ion in collisional detachment of negative ion with oxygen molecule.

Th is paper presents a new random mu ltiple access control protocol - 1-persistent CSMA control protocol based on improved binary tree conflict resolution algorithm. First, the paper gives an outline of 1-persistent CSMA and the binary tree conflict-resolving algorith m by build ing a mathematical model and using the average cycle method, and then respectively obtains the throughput and the number of time -slots of the protocol and the algorith m. The simulation results are g iven, and agree well with theoretical values. But, in a shared channel, each user independently sends information packets randomly, and it is prone to conflict and resulting in the failure. Especially to the 1-persistent CSMA control protocol, when the load is larger, it has a lower throughput and greatly increasing the probability of channel conflict. Therefore, bringing in the binary tree conflict-resolving algorith m is a good method to imp rove the throughput, especially the improved binary tree conflict resolution algorith m. So at last, the paper introduces the random mu ltip le access protocol comb ined improved binary tree conflict resolution algorith m and 1-persistent CSMA protocol, obtains the throughput and gives the simulations of the joint protocol. Theoretical calculations and experimental results show that 1-persistent CSMA protocol with conflict-resolving has a better performance.

This paper puts forward a joint control protocol based on binary tree conflict-resolving algorithm combined probability detection and 1-persistent CSMA. Under the protocol, all terminals use the joint control protocol of p-detection and 1-persistent to access the channel before sending information packets, and transmit packets immediately when the channel is idle, but when there are any collisions on the channel, the system will use isolated binary tree conflict-resolving technology to decompose the impacted packets. Meanwhile, the paper analyzes the protocol and gets the computational formula of the throughput for the protocol by building a mathematical model and using the average cycle method and compared with the joint control protocol of p-detection and 1-persistent. And finally, the paper gives the MATLAB simulation results. The results not only show that the correctness of the theoretical analysis and illustrates the validity of the protocol, but also gives some meaningful conclusions. Therefore, it is very necessary and important to integrate the binary tree conflict-resolving technology into the joint control protocol of p-detection and 1-persistent under high load, which can the successful probability and channel utilization.

This paper proposed a new type of discrete random contention system based on the literature (1), researched it using the average cycle method, then get the formu la of the systemic throughput for the new random access protocol by building mathematical modeling; but the uncertainty of random mult iple access on frequency and time resulting in the conflict probability increases as the higher loading, therefore, introducing binary tree conflict resolution algorithm is very important to improve the channel utilizat ion. The paper analyzed the isolated binary tree conflict resolution algorithm and then got the average length of t imeslot of the algorithm; on the basis, the paper puts forward a new type of discrete random contention system based on binary tree conflict resolution algorith m. Analytic formulate for throughput of the new d iscrete random contention system and the system based on the conflict resolution algorith m are derived by build ing mathematical model and using the average cycle method. Finally, the computer simu lation experiments show that the correctness of the theoretical, at the same t ime, show that the new discrete random contention system protocol based on binary tree conflict resolution algorithm is effective to further improve the system performance.

Some life tests result in few or no failures. In such cases, we can, and should, consider using degradation measurements to assess reliability. In real world, product degradation is a stochastic process. Since such degradation is often seen as a monotonous process, literature widely uses Gamma Process to describe and quantify degradation. However, in these publications, scale parameter is considered constant over time and results under this assumption may have big deviation from the actual measurements under nonlinear condition. The purpose of this paper is to improve Gamma Process method to fit a broader class of degradation models. Firstly, we use MLE to estimate the parameters under the timely constant-scale-parameter assumption and analyze why the model does not fit data well. Then we propose an improved model to improve the method and use Monte Carlo simulation to verify the validity of the improved method.

The technology of strengthening RC structures with grouting material is a new type of reinforcement techniques in the field of construction reinforcement in recent years. Considering the reduction of the strength and stiffness of flexural members in RC structures due to steel corrosion, this paper simulated steel corrosion artificially and then reinforced with grouting material to study the grouting material reinforcement effect of corroded RC flexural members. Based on the test of 3 beams and 2 slabs, failure characteristics and their effects on the ultimate bearing capacity and stiffness of corroded RC flexural members strengthened with grouting material were researched and analyzed. The result shows that grouting material reinforcement can observably improve RC bending members' flexural behavior and supporting capacity, meanwhile enlarge structural stiffness to put off the appearance of cracks and inhibit the expansion and extension of cracks. The research results are of great value in the practical design.

A solution is urgently expected to meet the higher-quality web service requirements of multimedia applications on the limited bandwidth of internet. Based on the ideas of priority-based service and dynamic load adaptation, this paper presents a new scheduling algorithm for multimedia support in web cluster servers , making possible the service of the two-class priority station polling system under the mixed policy of exhaustive and gated services, optimizing the services of the system in time of load change input via adjustment of the times of the access gated services, and strengthening the flexibility and fairness of multimedia transmissions in web service system. The theoretical model of this algorithm is established with Markov chain and probability generating function. Mathematical analysis is made on the mean queue length and the mean inquiry cyclic time of the common queue and the key station. It turns out that the findings from theoretical analysis correspond well with those from simulated experiments.

In the Internet of Things, the remote monitoring, network status tracking, fault alarm, automatic measurement and control functions of the random access system require the system has the function of the receiver to send client feedback monitoring information. For the network status monitoring requirements in the Internet of Things, this article proposes a monitoring function for random access system, and we get to the throughput, idle rate and information packet collision rate of the system with the average cycle analysis method, through computer simulations to verify the correctness of the analysis.

A solution is urgently expected to meet the higher-quality web service requirements of various applications on the limited bandwidth of internet. This paper presents a new scheme of load balance of web cluster servers, making possible the service of the two-class priority station polling system under the mixed policy of exhaustive and gated services, optimizing the services of the system in time of load change input via adjustment of the times of the access gated services, and strengthening the flexibility and fairness of multimedia transmissions in web cluster system. The theoretical model of this scheme is established with Markov chain and probability generating function. Mathematical analysis is made on the mean queue length and the mean inquiry cyclic time of the common queue and the key station. It turns out that the findings from theoretical analysis correspond well with those from simulated experiments.

With the development of wireless network, a solution is urgently expected to meet the higher-quality QoS demands of multimedia traffics especially when the network is heavily loaded. This paper presents a new scheme of MAC protocol of wireless network, optimizing the services of the system in time of load change input via adjustment of the times of the access gated services. The scheme does not modify the current protocol infrastructure or add any overheads. The theoretical model is established with Markov chain and probability generating function. Mathematical analysis is made on the mean queue length and the mean cyclic time of the common queue and the key station. It turns out that the findings from theoretical analysis correspond well with those from simulated experiments and strengthen the flexibility and fairness of multimedia transmissions in wireless system.

This paper proposed a novel analytical model of the polling MAC protocol using M-gated services in continuous time. By the imbedded Markov chain theory, the generating functions of queue length at server arrival epoch is obtained. Also, the Laplace-Stieltjes transform (LST) of packet delay distribution function is derived. Then computational equations are explicitl determined for the mean queue length and the mean packet delay. Through analysis of the mechanism of the polling model, its control values of the M-gated service and the related properties have been obtained. Meanwhile, the basic polling systems using gated service and exhaustive service have been improved. The polling MAC control protocol in the application is more effective.

In this paper we consider the polling system with multiple vacations using exhaustive service. By the imbedded Markov chain theory, the generating functions of queue length at the station is obtained. Then computational equations are explicitly determined for the mean queue length and the mean waiting time of information packet. Especially we obtain some corresponding results under some especial cases. The results are verified through extensive simulations.

Many wireless sensor networks (WSN) application systems are composed of multiple sensor nodes serial processing system. This paper sets up the model for the serial processing system using gated service in wireless sensor networks, and studies it by the Markov chain theory and the probability generating function method, the calculating equation of the mean waiting time of message packet is obtained by every sensor node in the serial processing system. We obtain corresponding results under some especial cases. Finally, the simulation results are given.

To discover firing case in time, the technique of wireless sensor networks is applied to fire early system. This paper establishes the early warning system applied to fire prevention model of serial transmission mode with vacation using exhaustive service for wireless sensor networks. We derive the calculating equation of information packet delay for each sensor node in the system by the Markov chain theory and the probability generating function method. Finally, the theoretical analysis results are confirmed through using simulation.