JUSTC

Study on the effect of laser cladding Ni35A + TiC composite cladding morphology and forming efficiency

LIAN Guofu, ZHANG Hao, CHEN Changrong, HUANG Xu, JIANG Jibin

2020, 50(6): 715-725. doi: 10.3969/j.issn.0253-2778.2020.06.001

Abstract:
In order to investigate the influence of laser cladding process parameters and TiC powder ratio on the cladding morphology and forming efficiency of composite materials ，improve the cladding morphology in terms of surface quality and substrate melting depth, and improve the forming efficiency of composite materials, the central composite design module of the response surface methodology(RSM) was adopted to analyze the effects of laser power, scanning speed, gas flow and TiC powder ratio on the morphology of composite claddings. A mathematical model was established between process parameters and TiC powder ratio, and composite cladding efficiency and substrate melting depth. The accuracy of the model was verified by variance analysis. Results show that, the effect of gas flow on the morphology of composite claddings is not significant. The cladding morphology is remarkably improved by increasing laser power, decreasing scanning speed and reducing TiC powder ratio. The scanning speed and TiC powder ratio have the most remarkable effects on the cladding efficiency. Therefore, reducing the TiC powder ratio and increasing the scanning speed appropriately could improve the cladding efficiency. Laser power has the most significant influence on the melting depth of the substrate and shows a secondary positive correlation, and the remaining parameters show a negative linear correlation. The analysis reveals that different materials’ requirement for cladding energy is the most important cause of the difference in the cladding efficiency and the morphology of composite materials with different compositions. With the maximum cladding efficiency and the minimum melting depth of the substrate as the goal of optimization, a comparison was made between the predicted and test values and found that the error rate of the cladding efficiency and that of the melting depth of the substrate were 3.450% and 5.386% respectively. This research provides a theoretical guidance for composite materials in improving the cladding morphology, and for predicting and controlling the cladding efficiency.

A multi-target tracking algorithm based on feature point trajectories

LI Yongjun, CAO Weihua, LING Qiang

2020, 50(6): 726-732. doi: 10.3969/j.issn.0253-2778.2020.06.002

Article Views:144 Full article PDF

Abstract:
In a continuous video stream, the multi-target tracking task is to determine the positions of the concerned targets in each frame. However, the tracking algorithm suffer from many challenging issues, such as appearance variation, lighting change, occlusion and cluttered background. Especially, occlusion has the most negative impact on tracking performance. Therefore, a tracking algorithm is proposed based on feature point trajectory to solve the tracking problem where multiple targets may occlude each other. The main idea of the proposed tracking algorithm is to introduce the delay during tracking, and acquire future N frame images in advance when processing the current frame; extract feature points from the obtained frame images and connect them to form feature trajectories, and estimate the positions of targets after N frames according to the obtained trajectories. After predicting the future positions of the targets, the motion of targets can be analyzed so as to precisely determine their locations at the current frame. Experiments show the this algorithm can effectively deal with occlusion. Moreover, the complexity of the proposed algorithm is lower than that of many traditional algorithms, which guarantees real-time tracking on the low-end processor in actual applications.

Pulsed laser deposition derived Sb2S3 thin film for solar cell applications

ZHENG Haotian, ZHANG Lijian, CHEN Chao, JIANG Guoshun, CHEN Tao, ZHU Changfei

2020, 50(6): 733-737. doi: 10.3969/j.issn.0253-2778.2020.06.003

Article Views:103 Full article PDF

Abstract:
High quality Sb2S3 thin films were prepared by pulsed laser deposition (PLD) method. The thickness of the Sb2S3 thin film was adjusted by changing the deposition duration to investigate the thickness dependent power conversion efficiency in complete solar devices. It was found that the Sb2S3 solar cell achieved power conversion efficiency of 3.98% when the deposition time was 5 min. Based on external quantum efficiency and electrochemical impedance spectroscopy analysis, it was observed that the change of thickness affects both the light harvesting capacity of the Sb2S3 layer and non-radiative recombination of photo generated carriers, thus affecting the efficiency of the solar cell.

The optimal decisions of remanufactured products and profit allocation under competitions of service and price

CUI Huiming, JI Lei

2020, 50(6): 738-743. doi: 10.3969/j.issn.0253-2778.2020.06.004

Article Views:84 Full article PDF

Abstract:
This paper studies the decisions of price and service level of remanufactured products in three-stage supply chain including retail traders, new product manufacturers and remanufactured product manufacturers. The optimal decisions of the supply chain members under financial “guiding principal” decentralized circumstance, manufacturers-alliance circumstance and centralized circumstance are analyzed. The result shows that when the intensity of price competition of the new products and remanufactured products is pretty violent, the higher the wholesale price of one kind of product, the lower the retail price and service level of the other kind of product; when both of the manufacturer costs and service cost factors are equal, the higher the market base, the higher the wholesale price and service level. In the part of numerical experiments, the profit is distributed by using weighted Shapley value, the results show that the supply chain cannot always be coordinated.

Change-points estimation and model selection for piecewise stationary autoregressive processes based on modified adaptive LASSO method

LIU Jie, CHEN Xiaoyuan, WU Zun

2020, 50(6): 744-751. doi: 10.3969/j.issn.0253-2778.2020.06.005

Article Views:102 Full article PDF

Abstract:
Considering the problems of change-points estimation and model selection for nonstationary time series such as piecewise stationary autoregressive (PSAR) processes, a method which can simultaneously conduct change-point estimation and model selection with a two-stage LASSO (TS-LASSO) algorithm based on the existing method to transform the problem of change-points estimation into the problem of variable selection was proposed. Specifically, in the first stage, the preliminary estimation of change-points and the selection of the models can be derived by LASSO algorithm. Then, in the second stage, a modified adaptive LASSO algorithm was used to screen the overestimated results, so the consistent estimation could be obtained and the accurate model could be selected. The large sample properties of the results for the variable-point estimation. In addition, the TS-LASSO algorithm can also achieve the estimation and recognition for the mean change-points sequences and no change-points sequences in special cases effectively. Finally, combined with the test of different type of simulative sequences and the case study of a seismic wave data, it was shown that TS-LASSO algorithm is effective and has certain practicability.

Scalable confidence intervals of precision matrices in high dimensions

ZHOU Huiting, ZHOU Jia, ZHENG Zemin

2020, 50(6): 752-757. doi: 10.3969/j.issn.0253-2778.2020.06.006

Article Views:78 Full article PDF

Abstract:
In order to solve the problem of the computational inefficiency in confidence intervals of high-dimensional precision matrices, the De-SCIO was proposed. Compared with other methods, the computational efficiency of the confidence intervals based on De-SCIO statistic are greatly improved, and their average coverage is closer to the true level. The construction of the De-SCIO statistic is simple and avoids complicated theoretical derivation. Under reasonable assumptions, the asymptotic normality of the De-SCIO statistic was proved. The advantages of this method in average coverage and computational efficiency were demonstrated by the numerical studies and real data example.

Dielectric responses enhanced by nanofiller-polymer interfaces in PVDF-based terpolymer nanocomposites

CHE Yaping, CHU Baojin, TAN Qi

2020, 50(6): 758-768. doi: 10.3969/j.issn.0253-2778.2020.06.007

Article Views:148 Full article PDF

Abstract:
The interfaces between nanofillers and the polymer matrix in nanocomposites are known to be increasingly important when nanofillers become smaller. A P(VDF-TrFE-CFE) terpolymer is used as the template polymer matrix and low-K（dielectric constant） SiO2 and high-K BaTiO3 nanoparticles as fillers to determine the enhancement effect of the interfaces. For both kinds of fillers, anomalous increases in the dielectric constant and polarization response are observed at nanoparticle loading less than 1%( volume fraction). These increases are not related to the intrinsic dielectric properties of the nanofillers and the change of crystallinity of the terpolymer. The crystalline phase is slightly changed from a non-polar structure towards a more polar one, improving the dielectric response in the interfacial regions. An interfacial model is proposed and the non-uniform dielectric response of the interfacial regions is responsible for the observed dielectric phenomena. The overlapping of the interfacial regions leads to the maximum dielectric response of the nanocomposites with certain particle loading.

Pricing of conspicuous products in the presence of high-similarity counterfeits

XU Chuanyong, ZHAN Jiajuan

2020, 50(6): 769-776. doi: 10.3969/j.issn.0253-2778.2020.06.008

Article Views:99 Full article PDF

Abstract:
The conspicuous goods not only meet the functional needs of consumers, but also meet the needs of consumers’ social status. Some consumers, who cannot afford genuine products, seek to satisfy their needs by using counterfeits which is very similar to genuine ones but at a much lower price. Considering the existence of high-similarity counterfeits, the pricing of conspicuous goods was studied. The social utility of conspicuous goods was incorporated into the consumer utility model, and the quality level of counterfeit goods was considered, a pricing game model for genuine and counterfeit manufacturers was constructed to obtain an equilibrium. It was found that in equilibrium, as the degree of conspicuousness increases, the price and demand of genuine and counterfeit goods both increase, but the price gap between counterfeit and genuine goods gradually narrows. It is shown that when the degree of conspicuousness is higher, the counterfeit product poses a greater threat to the authentic product. With the improvement in the quality of counterfeit goods, the price and demand of genuine and counterfeit products are not monotonous. In particular, as the level of imitation quality rises, there is a case where the demand for genuine products rises and the demand for counterfeit goods decreases. This shows that under certain circumstances, the market demand for genuine products increases as the level of imitation quality rises. In addition, the impact of the entry of counterfeit products on genuine products was analyzed by comparing with the case where counterfeit products do not exist. The entry of counterfeit products into the market leads to a decline in the price and profit of genuine products, but the market demand for genuine products may actually increase under certain circumstances. When the degree of conspicuousness is higher and the quality of imitation is higher (the imitation cost efficiency is higher than a certain value), the profit loss of the genuine product is the largest.

Experimental study on differences of meteorological elements and surface fluxes in urban and suburban Hefei

GUI Yu, YUAN Renmin, WU Xiaoqing, TAO Xiaoping, CUI Yanxuan, LIU Hao

2020, 50(6): 777-783. doi: 10.3969/j.issn.0253-2778.2020.06.009

Article Views:106 Full article PDF

Abstract:
Based on the data collected by the automatic weather station and the eddy correlation system from the urban and suburban areas in Hefei from 5 May to 10 October, 2013, differences in the urban and suburban areas are quantitatively analyzed from three aspects: meteorological factors, urban heat island(UHI) intensity, and surface energy balance. The result shows: ① UHI in the evening is stronger than that in the daytime, but not obvious in the daytime. The order of intensity of UHI in four seasons at night is winter> autumn> spring> summer. The average value of UHI intensity at night reached the maximum of 1.97℃ on clear winter nights, and the minimum of 0.76℃ was reached on clear summer nights. ② The sensible heat flux played a major role in urban energy budget, while the latent heat flux played a major role in suburban energy budgets. The daily average time of unstable stratification in urban sites is 2.3 h longer than that in suburban areas. The Bowen ratio of the four seasons in the urban area fluctuated greatly, reaching the maximum of 8.66 on sunny days in winter, and the minimum of 0.95 on sunny days in autumn. The order of the Bowen ratio of four seasons in the urban area is winter > spring> summer> autumn. The Bowen ratio in the suburban area had less fluctuations in four seasons with the maximum being 1.65 on sunny days in winter and the minimum being 0.49 on sunny days in autumn.

Optimal threshold of pairs trading

YU Xiaoyu, BI Xiuchun, ZHANG Shuguang

2020, 50(6): 784-792. doi: 10.3969/j.issn.0253-2778.2020.06.010

Article Views:144 Full article PDF

Abstract:
Considering the volatility and uncertainty of the market, how to effectively control the risk on the basis of maintaining stable return is an urgent problem to be solved. Here genetic algorithm was used to solve the optimal threshold of pairs trading with stop loss condition. Empirical test was carried out in the matching stocks of CSI 300 and CSI 500 Indices industries under the condition of cointegration and partial cointegration. Results show that the presented method controls risk and loss more effectively on high return than 10% stop loss and no stop loss.

Limit theorems for contact processes with cooperative mechanisms on homogeneous trees and complete graphs

ZHANG Yanhao, SHI Weihua

2020, 50(6): 793-800. doi: 10.3969/j.issn.0253-2778.2020.06.011

Article Views:46 Full article PDF

Abstract:
Several limit theorems for contact processes with cooperation mechanisms were given from the case where the base maps are homogeneous trees and complete graphs. First, the solution of the limit equation of the contact process with the cooperation mechanism was obtained under the homogeneous tree at a given point and a given time. Next, by means of the idea of the fixed point of the differential equation, the critical value of the cooperation mechanism parameter β was obtained. Then, changing the base map to the complete map, the contact process with the cooperation mechanism was studied, and the density of diseased points at a given moment was obtained when the dimensionality tended to infinity. Finally, as a special case of the contact process of the mechanism, the contact process under the classic mechanism (that is β=0) was reviewed, and the limit function of the number of diseased points was derived.

High frequency algorithm and its back-testing results based on GAN

MENG Xuran, BI Xiuchun, ZHANG Shuguang

2020, 50(6): 801-810. doi: 10.3969/j.issn.0253-2778.2020.06.012

Article Views:165 Full article PDF

Abstract:
In the financial classification mission, due to the big noise and low information-ratio in financial data, traditional supervised-learning regime may extend the noise influence because of the over dependent on the data label. GAN(generative adversarial network) can learn the data characters and reduce the influence of noise. When it is used to analyze the financial data, it has great results. We apply GAN to the high frequency trading: set the data labeled or unlabeled based on its volatility, then use the adversarial training between generative network G and discriminative network D to learn the intrinsic characters of the data, finally use the well trained D to get the up and down classification model and the quantization strategy. The sample is based on the future data, and the final results show that the LSTM model training by GAN is better than the deep learning models such as LSTM with supervised training and the Logistic regression model.

A Hamiltonian matrix based algorithm for simulating evolution of electronic wave functions

WANG Tao, ZHANG Guozhen, YANG Li, JIANG Jun

2020, 50(6): 811-818. doi: 10.3969/j.issn.0253-2778.2020.06.013

Article Views:32 Full article PDF

Abstract:
Accurate simulation and analysis of electronic motion and evolution are the key to developing efficient electron modulation methods for practical applications.Some traditional methods, such as TDHF(time-dependent Hartree-Fock) and TDDFT (time-dependent density functional theory), work well when dealing with small scale systems. However, they are not suitable enough for large scale systems, in terms of computational complexity and costs.Considering that in some large systems the relative position of atoms are quite stable, and perturbations have limited effect on inner interaction Hamiltonian, a simple yet effective method is proposed capable of quickly simulating the evolution of electronic wave function based on Hamiltonian matrix. The method is applied in four different systems and the results demonstrate the applicability of this algorithm to treat the charge evolution behavior in large systems, providing a new perspective for the development of electron modulation.

Effect of magnetic nanoparticle concentration and other conditions on ice crystal growth of VS55 solution during devitrification

XIANG Xingxue, XU Yi, LIU Zhifeng

2020, 50(6): 819-824. doi: 10.3969/j.issn.0253-2778.2020.06.014

Article Views:44 Full article PDF

Abstract:
The effects of the concentration of magnetic nanoparticles, isothermal temperature and the rate of cooling/rewarming on the crystallization behavior of VS55 during the devitrification process under isothermal scanning and continuous scanning methods were studied using a cryomicroscope system. The results show that: With the increase of nanoparticle concentration and isothermal temperature, the growth rate, initial size and crystal density of ice crystals increase generally, promoting the growth of ice crystals. Continuous scanning of VS55 with different magnetic nanoparticle concentration groups was performed, and the results were consistent with the isothermal scanning conclusions. The crystal devitrification growth of the magnetic nanoparticle-added solution was obvious. When the cooling rate is increased to 5 ℃ / min, the initial size of ice crystals and their number increase significantly and the growth rate also increases slightly. A cooling rate above 5 ℃ / min has little effect on the growth of ice crystals. As the heating rate increases, the ice crystal size, growth rate, and number of ice crystals decrease.

A read/write balanced high-performance key-value store

WU Jiayu, LI Yongkun, XU Yinlong

2020, 50(6): 825-831. doi: 10.3969/j.issn.0253-2778.2020.06.015

Article Views:87 Full article PDF

Abstract:
Log-structured merge tree (LSM-tree) is widely used as the core data structure of modern key-value stores due to its ability to utilize sequential access performance of external storage. However, it suffers from expensive merge operations to maintain the layered and ordered data organization, which induces significant write amplification. Recent researches have proposed various optimizations to mitigate write amplification, but at the cost of query performance and space utilization. A new architecture for LSM-tree based key-value store is proposed. The key idea is to leverage the key-value separation design to mitigate merge overhead, while maintaining a certain degree of order for values by using a new tree structure called vTree to improve the range query performance. In the meantime, corresponding data merge and space reclaim algorithms were developed for the vTree. The experimental results show that the key-value store developed with this architecture has well balanced performance on write, point lookup, and range query, with low space cost.

Two-dimensional temperature field measurement by laser interference based on fringes Fourier transformation

CHEN Yu, ZHANG Haifeng, LU Rongde, CHEN Yue, HE Liqun

2020, 50(6): 832-838. doi: 10.3969/j.issn.0253-2778.2020.06.016

Article Views:59 Full article PDF

Abstract:
A temperature measurement method using laser interference fringe Fourier transformation was presented. Based on the Mach-Zehnder interferometer, the candle axisymmetric flame temperature field was used to verify the presented method. Using interferogram undisturbed by temperature field in the process of recovering phase shift, the linear deviation caused by image digitization in the phase was corrected. By comparing the results of various filters, it is shown that features of the filter have a significant impact on the result, and the cosine-shaped edge filter with appropriate parameters can effectively extract the spectrum information. Experimental results of candle flame indicate that the presented method can be used to measure two-dimensional temperature distributions quickly and conveniently.

Modulation of graphene carrier density by a mixed doping route

TANG Jing, FAN Xiaodong, ZENG Changgan

2020, 50(6): 839-843. doi: 10.3969/j.issn.0253-2778.2020.06.017

Article Views:48 Full article PDF

Abstract:
Graphene has a significant advantage that its carrier density can be easily tuned. Various methods for controlling carrier density have been proposed, of which gate tuning is the most widely used. However, in practical applications, gate tuning also has some limitations. For example, some designed circuits and test instruments cannot stand high voltages over hundreds or even tens of volts. Recently, a method of doping with electron beam irradiation has appeared, which can change graphene carrier density locally and continuously, but the tuning range is small. Here a new mixed doping route combining HNO3 doping and electron beam irradiation was presented, which shows greater ability to tune carrier density continuously in a larger range. By analyzing the results of the scanning near-field optical microscope and electrical transport, it was found that the mixed doping route adjusts the graphene carrier density from 2.15×103 cm-2 to -1.49×102 cm-2,which is equivalent in tuning effect to 320 V for gate tuning of the 300 nm silicon dioxide.In addition, graphene can be written into pre-designed electric patterns via electron beam irradiation, which is potentially widely applicable.

AI-based descriptor for predicting alloy formation energy

LI Jiancong, WANG Tairan, SHU Wu, HU Sulei, OUYANG Runhai, LI Weixue

2020, 50(6): 844-851. doi: 10.3969/j.issn.0253-2778.2020.06.018

Article Views:139 Full article PDF

Abstract:
Because of their rich geometric structure and electronic properties, metal alloys have been widely used in catalysis and materials science. Among them, alloys formation energy has an important influence on the formation and catalytic activity of metal alloys. With the development of artificial intelligence and databases in recent years, machine learning has been used to rationally design new materials. Based on the multi-task compressed sensing algotithm in artificial intelligence, the alloy formation energy descriptor of the AB2 alloy formation energy database was investigated. A universal descriptor of the corresponding alloy formation energy was established, and the sensitivity analysis of features revealed the importance of electronic and geometrical properties of metal alloys. The results show that this descriptor has a prediction error lower than 8.10kJ·mol-1 and a better physical interpretation. Finally, the formation energy of a large number of unknown metal alloys was predicted.

Inverse degree and properties of graphs

CAI Gaixiang, MEI Peilin, YU Guidong

2020, 50(6): 852-859. doi: 10.3969/j.issn.0253-2778.2020.06.019

Article Views:64 Full article PDF

Abstract:
Let G=(V(G), E(G)) be a simple graph

Cryptocurrency risk measurement based on MIDAS-Expectile regression model

ZHANG Zhiyuan, YE Wuyi

2020, 50(6): 860-872. doi: 10.3969/j.issn.0253-2778.2020.06.020

Article Views:49 Full article PDF

Abstract:
As an alternative to the quantile-based QVaR, the risk measure EVaR based on the Expectile model is simpler to calculate and can more accurately reflect the effects of extreme values. In order to make full use of the information contained in mixed frequency data, a MIDAS-Expectile regression model was constructed, and the estimation of the parameters and conditional EVaR were obtained based on the nonlinear asymmetric least squares method. The asymptotic normality of the estimates and coverage test for conditional Expectile were also given. In addition, the likelihood function and information criterion of the Expectile regression model were given from the perspective of maximum likelihood estimation, which could compare and test different models. In order to study the financial risks of cryptocurrencies, in the empirical part, the MIDAS-Expectile regression model was applied to the measurement of cryptocurrency returns risk, and the risk contagion of other tradition financial markets to this emerging financial asset was discussed. The empirical results of the risk of cryptocurrency monthly data indicate that signals from other financial markets will have a significant or positive or negative impact on the risks of the cryptocurrency market, and that the cryptocurrency market is not isolated from traditional financial markets.

2020 Vol. 50, No. 6

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