A Look-Ahead Method for Forecasting the Concrete Price

Price movement of building materials increases the uncertainty of architectural planning. As a basic building material, commercial concrete is an important part of various construction costs. It is of great significance to predict its price change trend in advance. In this paper, a univariate autoregressive series is constructed based on the daily average price of concrete in major cities in China;then it uses a combined model of Convolutional Neural Network (CNN) and Long Short-Term Memory Network (LSTM) to extract the spatial and temporal rules of time series, to achieve accurate prediction of the trend of concrete price changes 10 days ago. The prediction accuracy rate of the model is 97.13%, and the precision, recall rate, and F1 score are: 97.15%, 97.27%, and 97.20%, respectively. The prediction result is of great significance to various architectural planning.

中国高技术产品出口中东欧主要市场比较优势的动态变化

本文基于2010—2019年十类高技术产品HS六位码的进出口数据,利用NRCA指数结合核密度估计和条件概率密度估计两种非参数估计方法,深入剖析了中国十类高技术产品对中东欧三大主要市场捷克、匈牙利和波兰出口比较优势的动态演进现状,并对比分析其差异性。研究表明:从产品类别和区域差异看,信息与通信类产品对三大市场出口的比较优势均显著,但显著水平波动较大,其中,对捷克的出口比较优势相对于匈牙利和波兰更高;生物技术类、生命科学类、电子器件类、弹性制造类、先进材料类、航空航天类、武器类和核技术类产品对中东欧主要市场出口的比较优势均不明显,从而导致中国高技术产品出口结构较为单一。因此,中国在《中欧全面投资协定》全面达成和“一带一路”合作框架积极推进的背景下,应结合高技术产品类别特征和出口国具体情况制定有效的扶持政策,采取差异化合作策略,释放中国和中东欧国家间的贸易潜力,共享协同发展红利。

锂金属电池电解液的理论计算模拟研究

锂金属电池电解液的调控对锂枝晶生长抑制具有重要意义。传统的电解液设计思路主要依赖经验直觉与实验试错,较少借助计算模拟方法以高通量筛选电解液配方。理论计算模拟手段能够建立电解液微观特征与宏观性质之间的联系,从原子尺度上指导电解液设计、预测电解液性能,在电解液研究领域发挥了重要作用。本文综述了锂金属电池电解液在理论计算模拟方面的相关进展。首先,介绍了电解液研究中量子化学计算和分子动力学模拟的基本原理与计算方法;其次,总结了这两种计算模拟手段在电解液组分静态化学性质、电解液体相和电极-电解液界面的微观结构与性质研究中的应用,如配位络合物中的结合能,电解液组分的氧化还原稳定性、静电势,体相电解液的溶剂化结构、离子电导率、介电常数,电极-电解液界面的微观结构、性质与化学反应;最后,讨论了理论计算模拟面临的挑战及未来的发展方向,为锂金属电池电解液的计算模拟提供了新的研究思路。

Structure and electrical properties of La_(2)O_(3)-doped(K,Na,Li)(Nb,Ta)O_(3)-(Bi,Na)TiO_(3) ceramics

In this paper,Lead-free based on 0.97(K_(0.48)Na_(0.48)Li_(0.04))(Nb_(0.8)Ta0.2)O_(3)-0.03Bi_(0.5)Na_(0.5)TiO_(3) with additives La_(2)O_(3)(1,2,3,4 wt.%)was prepared by the solid reaction method,and the effect of La dopant on the structural and electrical properties is investigated.The result indicates La dopant considerably decreases the optical band gap compared to the undoped composition.On the other hand,La doping leads to the higher dielectric property in a wider temperature,providing possibilities and directions for the sub­sequent development of ferroelectric photovoltaic materials with electrical properties and low optical band gap in a dramatical manner.

A generic high-throughput microstructure classification and quantification method for regular SEM images of complex steel microstructures combining EBSD labeling and deep learning

We present an electron backscattered diffraction(EBSD)-trained deep learning(DL)method integrating traditional material characterization informatics and artificial intelligence for a more accurate classification and quantification of complex microstructures using only regular scanning electron microscope(SEM)images.In this method,EBSD analysis is applied to produce accurate ground truth data for guiding the DL model training.An U-Net architecture is used to establish the correlation between SEM input images and EBSD ground truth data using only small experimental datasets.The proposed method is successfully applied to two engineering steels with complex microstructures,i.e.,a dual-phase(DP)steel and a quenching and partitioning(Q&P)steel,to segment different phases and quantify phase content and grain size.Alternatively,once properly trained the method can also produce quasi-EBSD maps by inputting regular SEM images.The good generality of the trained models is demonstrated by using DP and Q&P steels not associated with the model training.Finally,the method is applied to SEM images with various states,i.e.,different imaging modes,image qualities and magnifications,demonstrating its good robustness and strong application ability.Furthermore,the visualization of feature maps during the segmenting process is utilised to explain the mechanism of this method’s good performance.

EBSD investigation of the crystallographic features of deformation-induced martensite in stainless steel

Variant selection during the martensitic transformation in steels may play an important role in determining the transformation kinetics and the resulting mechanical properties.In this study,the variant selection and crystallographic features of deformation-induced martensite were investigated by quasi in situ electron backscatter diffraction(EBSD) in grade SUS321 during tensile deformation.Significant differences in variant selection between austenite(γ)→hcp-martensite(ε)→bcc-martensite(α’) and γ→α’transformation routes were observed and reported in detail,which demonstrated that s-martensite plays an important role in the variant selection of α’.Variant selection at diffe rent deformation stages was also analysed and revealed that α’ variants with the highest priority and variant pairs were preferred at the initial and last deformation stages in the γ→ε→α’sequence,respectively.Meanwhile,the single α’ variant nucleated at the thin slip band keeps its crystallography feature upon further deformation in the γ→α’sequence.In addition,the strain work of the martensitic transformation for applied loads was quantitatively estimated to explain the variant selection and associated mechanism.When these calculations are compared to the experimental results it is found that they are not able to predict which α’ variant is forming pre ferentially during either during the γ→α’ or the ε→α’ sequences,while only accurate predictions are obtained for the γ→ε-transformation which indicates that the γ→α’ variant selection is more complex.

Dual band metamaterial absorber:Combination of plasmon and Mie resonances

A dual band metamaterial absorber composed of dielectric and metallic atoms with high symmetry was numerically designed and experimentally verified.Due to simultaneously generated electric and magnetic resonances of both plasmon and Mie resonators,two absorption peaks with near unity absorptivity were obtained at 9.45 and 9.80 GHz.The loss of the electromagnetic wave at the first resonance frequency was mainly caused by ohmic loss based on plasmon resonance.For the second absorption peak resonance frequency,the incident wave was trapped inside the dielectric cube and the main loss of the electromagnetic wave was caused by dielectric loss based on Mie resonance.Most of the proposed dual band metamaterial absorbers were sensitive to the polarization direction hindering its potential applications in scientific and technological areas.Combing both plasmon and Mie resonances provides a new and simple way to build dual band isotropic metamaterial perfect absorbers eliminating polarization effect.