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Blockchain – a distributed and public database of transactions – has become a platform for decentralized applications. Despite its increasing popularity, blockchain technology faces a scalability problem: the throughput does not scale with the increasing network size. Thus, in this paper, we propose a scalable blockchain protocol to solve the scalability problem. The proposed method was designed based on a proof of stake (PoS) consensus protocol and a sharding protocol. Instead of transactions being processed by the whole network, the sharding protocol is employed to divide unconfirmed transactions into transaction shards and to divide the network into network shards. The network shards process the transaction shards in parallel to produce middle blocks. Middle blocks are then combined into a final BLOCK in a timestamp recorded on the blockchain. Experiments were performed in a simulation network consisting of 100 Amazon EC2 instances. The latency of the proposed method was approximately 27 s and the maximum throughput achieved was 36 transactions per second for a network containing 100 nodes. The results of the experiments indicate that the throughput of the proposed protocol increases with the network size. This confirms the scalability of the proposed protocol.

In this study, numerical investigations of the tip clearance flow characteristics of a pumpjet propulsor based on Computational Fluid Dynamics (CFD) method have been presented. The Zwart-Gerber-Belamri (Z-G-B) cavitation model based on Reynolds Averaged Navier–Stokes (RANS) method is employed. The structured gird is applied. The formation and development of the tip clearance flows has been investigated and presented. The structure of the tip leakage vortex has been shown. The radial distributions of different velocity components with different Span along the axial direction have been carried out to present the influence of the tip clearance flow on the main flow. In addition, the influences of the tip clearance size on the pumpjet propulsor performance, including the impact on the velocity flow fields and the cavitation characteristic, have been presented. Keywords: Pumpjet propulsor, Numerical investigation, Tip clearance characteristic, Tip leakage vortex, Tip clearance size

Based on the working principle of the artillery impact loading test rig, in order to make the impact load on the tested artillery in the simulation test more in line with the load requirements, a buffer is designed and installed between the impulse generator and the tested artillery. Through the buffer, the shock load between the two structures is avoided, and the load transferred to the recoil part is closer to the resultant force produced by propellant gas. According to the requirement of dynamic recoil simulation test of gun, a permanent magnet eddy current buffer structure with Halbach array is proposed in this paper. For resistance calculating of the permanent magnet eddy current recoil mechanism, a mathematical model is then formulated by using the finite element analysis method for two-dimensional axisymmetric transient electromagnetic. By comparing the simulation results with the actual firing test data, it is concluded that the recoil motion of the gun tested in the shock loading test is consistent with the real firing recoil motion trend and the error meets the design requirements.

2018, 【要旨】

Construction of the quality and safety evaluation model for dairy products is significant to ensure food safety for people. In the case that there is a big error in the BP neural network quality and safety evaluation model for dairy products, this paper put forward the optimization method based on the PSO algorithm to reduce the output error of the BP neural network evaluation model through optimizing the weights and thresholds of BP neural network. By simulation of optimizing the BP evaluation model through specific data, experiments showed that compared with the standard BP evaluation model and standard BP evaluation, the optimized BP evaluation model is greatly improved in output error.

ZnO nanowires deposited on Si substrates were prepared by thermal evaporation of a mixture of ZnO and carbon powder. Ag ions with an energy of 63 keV and a dose of 5 × 1015 ions/cm2 were implanted into the as-prepared ZnO nanowires. After ion implantation, the Ag-implanted ZnO nanowires were annealed in air at different temperatures from 600°C to 1000°C. Effects of ion implantation and thermal annealing on the structural and photoluminescent (PL) properties of the ZnO nanowires were investigated by transmission electron microscopy (TEM), selected area energy dispersive X-ray spectroscopy (SAEDX), X-ray diffraction (XRD), and fluorescence spectrophotometry. TEM, HR-TEM, and SAEDX analyses demonstrated that efficient doping of Ag was achieved by ion implantation and the subsequent annealing process. XRD patterns revealed that the hexagonal wurtzite structure of ZnO nanowires was maintained after ion implantation. Photoluminescent emissions of ZnO nanowires were decreased significantly by Ag implantation but could be recovered by thermal annealing. The mechanism of the influence of ion implantation and annealing on the PL intensity was assessed.