Modified analogue forecasting in the hidden Markov frameworkfor meteorological droughts

An analogue method(AM) is a nonparametric approach that has been applied to predict the future states of a dynamic system by following the evolution of the analogues in the historical archive. In this study, we proposed a hidden Markov model(HMM)framework for a modified analogue forecasting(MAF) approach for meteorological droughts in Korea. The unobservable(hidden) state process in the framework aims to model the underlying drought state, while the observation process was formed from the time series of the standardized precipitation index(SPI) as a drought index. Within the framework, the likelihood estimator was used as the measure of similarity between past SPI analogues and current data. The MAF approach was conducted on the selected analogues to make forecasts at lead times of one and three months. The proposed model was applied to five selected stations in Korea using the SPI data from 1973 to 2016. The forecasting performance of the proposed model was tested during the validation period(2003–2016) using several statistical criteria and it was compared to a persistence-based benchmark model. The results showed significant improvement in the forecasting capacity, and satisfactory performance for numerical SPI forecasting and categorical drought forecasting. The results also suggested that the proposed model was able to provide useful information for determining future drought categories for early drought warning with a lead time of up to three months.     

1 100 kV GIS用断路器的设计

介绍了所研制的1 100 kV、50 kA GIS用断路器的技术规范、基本结构及合闸电阻的合理布置;利用商用Maxwell2D,3D软件及专用的程序,对断路器灭弧室的电场分布情况进行了分析,对合闸电阻的热容量进行了计算,并做了相关的试验验证,证明该型断路器的开断性能良好,其所配用的合闸电阻的热容量满足使用要求。     

基于子结构的内力约束连续体拓扑优化

通过拓扑优化可以得到传力路径,不同传力路径对应不同内力载荷。如果将内力载荷作为目标或约束进行拓扑优化,可以得到满足不同需求的传力路径,为拓扑优化的发展提供新思路和新方法。为了得到不同内力载荷需求的传力路径,基于子结构法将结构分开使内力暴露出来。以结构质量最小为目标,以内力为约束建立拓扑优化模型,基于独立、连续、映射( independent, continuous, mapping, ICM)方法和单位载荷法将内力显式化,通过累加获得需要控制的传力路径上的内力,通过迭代调整2个路径上的内力使其比值达到一个稳定的值,从而获得满足内力约束的传力路径。算例表明：不同的内力约束可以得到不同的传力路径。     

Structure Electrical Conducting and Thermal Expansion Properties of Ln0.6Sr0.4Co0.8Fe0.2O3 (Ln=La,Pr,Nd,Sm)Ceramics

Ln0.6Sr0.4Co0.8Fe0.2O3 (Ln=La, Pr, Nd, Sm) perovskite-type complex oxides were synthesized using a glycine-nitrate process, and the structure, electrical conducting and thermal expansion properties of the resulting ceramics were examined with regard to the nature of the lanthanide cations. The results indicated that the La, Pr and Nd specimens had a rhombohedral symmetry, while an orthorhombic structure was determined for the Sm specimen. The pseudo-cubic lattice constant decreased with smaller lanthanide cations. It was found that the electrical conducting properties declined with decreasing lanthanide cation size. Fortunately, all the compositions remained rather high electrical conductivities exceeding 650Ω1.cm-1 in the intermediate temperature range (600-800℃). An appreciable thermal expansion increase at high temperatures was detected for all the compositions. Decreasing the size of the lanthanide cations resulted in an increase of thermal expansion. With respect to the high electrical conductivities, the Ln0.6Sr0.4Co0.8Fe0.2O3 oxides are considered to be acceptable as mixed conducting component in composite cathode designs together with doped ceria electrolytes.     

热挤压对AZ31-0.25%Sb合金组织与性能的影响

通过不同温度热挤压处理、力学性能测试和组织形貌观察,研究了热挤压处理对AZ31-0.25%Sb镁合金组织与性能的影响.结果表明：热挤压处理可有效提高合金的力学性能,经220 ℃热挤压处理,合金的室温抗拉强度由263 MPa提高到297.6 MPa,屈服强度由96 MPa提高到222.1 MPa,提高幅度达131.4%;热挤压处理提高AZ31-0.5Sb%合金强度的原因是：挤压期间产生了形变强化和发生的动态再结晶,形变产生的高密度位错可提高合金的抗拉强度,而发生动态再结晶形成的细小晶粒可有效提高合金的屈服强度.     

Calculation of optimal current density of double side permanent magnet linear synchronous motor

The use of design method considering a coil temperature to maximize the thrust density of a double side coreless permanent magnet linear synchronous motor (PMLSM) was presented. The optimal current density where the coil temperature reaches an allowable temperature with heat analysis was applied to a magnetic circuit design. Changing optimal current density is verified whenever the design parameters of the motor are altered. The design parameters of the motor were applied to thrust calculation. In this way, the optimal model, which is a reversal of the existing design method, is deduced. The results were compared with the experimental data to verify their validity. When the convection heat transfer coefficient is applied to other models, the results of the analysis and test values show good concordance. The method proposed has some limitations.     

Effects of foundation damage and water-level change on vibration modal parameters of gravity-type caisson structure

In this paper,the effects of foundation damage and water-level change on vibration characteristics of gravity-type caisson structure are examined by analyzing modal parameters extracted from output-only information.To achieve the objective,the following approaches are implemented.Firstly,vibration response analysis methods are selected to estimate power spectral density and modal parameters such as natural frequency,damping ratio and mode shape of a lab-scale caisson structural system.Secondly,vibration tests on the lab-scale caisson system are performed under a series of test scenarios which include three water-level changes and three damage levels.Thirdly,experimental modal parameters corresponding to the damaging cases as well as the water level cases are extracted by frequency domain decomposition method and stochastic subspace identification method.Finally,the effects of the water-level variation and foundation damage on the extracted modal parameters are examined to assess the feasibility of the vibration-based damage detection in gravity-type caisson structures under water-level uncertainty.     

Enhancement of Ferroelectric Properties of Pb(Zr,Ti)O3 Films Grown by Metal-Organic Chemical Vapor Deposition on Noble-Alloy Bottom Electrodes

Pb(Zr,Ti)O₃ (PZT) films grown on Ir electrodes by a metal-organic chemical vapor deposition (MOCVD) have suffered from high leakage and rough surface. We sputtered Pt and Ir simultaneously onto Ti/SiO₂/Si substrates and formed Ir-Pt alloy bottom electrodes with various compositions. With an optimal composition of Ir and Pt, PZT films grown by MOCVD on this substrate showed smoother surface and suppressed leakage via the bottom interface. At the specific composition of Ir and Pt, two different phases seemed to be acquired. They constituted the electrodes and affected the PZT grain nucleation independently so that the grains with different origins grew and restrained the vicinal grains, and finally soothed the faceted-grain-formation. No fatigue was observed even in PZT on Ir-Pt alloy with much Pt content.     

STRESS CONTROLLED FERROELECTRIC (BA0.5Sr0.5)TiO3 THIN FILMS PREPARED ON GD2O3/SRTiO3(001) BY A PULSED LASER DEPOSITION

ABSTRACT

Stress controlled epitaxial ferroelectric Ba_0.5Sr_0.5TiO₃ (BST) films have been deposited on Gd₂O₃/SrTiO₃ by pulsed laser deposition with oxygen background pressure of 200 mTorr at the deposition temperature of 750°C. In order to control the stress in BST films, oxygen pressures for Gd₂O₃ buffer layers have been varied from 0.1 to 100 mTorr, while that of BST films have been fixed at 200 mTorr. It has been found that the lattice parameters of the BST films deposited on Gd₂O₃ were changed. Furthermore, microwave properties of co-planar waveguide (CPW) fabricated on BST films were investigated by a HP 8510C vector network analyzer from 1–20 GHz. Large dielectric tunabilities were observed from the CPW's fabricated on BST films deposited on Gd₂O₃ layers deposited at low and high oxygen pressures, 0.1 and 100 mTorr, respectively.     

FABRICATION AND ELECTRICAL PROPERTIES OF PZT-PVDF 0–3 TYPE COMPOSITE FILM

ABSTRACT

A film speaker was fabricated with 0–3 type piezoelectric composite. The 0–3 type composite was developed to incorporate the advantages of both ceramic and polymer. The pastes of PZT-PVDF composite were made with various mixing ratio. The paste was printed by conventional screen-printing method on ITO (Indium Tin Oxide) bottom electrode which was deposited on PET (polyethylene terephthalate) polymer film. The prepared composite film was about 80 μm in thickness. After printing the top-electrode of silver-paste, 4 kV/mm of DC field was applied at 120°C for an hour to align the electric dipole in the 0–3 composite film. The piezoelectric charge constant of d₃₃ was increased with increasing the PZT weight percent. The maximum value was 24 pC/N at 70 wt% of PZT. But the piezoelectric voltage constant of g₃₃ had the maximum value about 32 mV · m/N at 65 wt% of PZT. The SPL (Sound Pressure Level) of the speaker fabricated with the 65:35 composite film was tested at various driving voltages of 1 ～ 100V_rms. The SPL was saturated at the driving voltage of 70V_rms and the value was about 68 dB at 1 kHz.