两种不同焊丝对7A05铝合金焊接性的影响

选择两种焊丝,对Al Zn Mg系合金7A05 T6进行焊接性研究。焊接裂纹试验结果表明,采用两种焊丝焊接7A05合金时,接头均具有较好的抗热裂纹敏感性。两种焊丝焊接接头的拉伸强度均为母材强度的75%以上,经过时效处理的焊接接头力学性能有了明显的提高。分析认为微观组织中沉淀物质点越小,均匀分散到晶界上越多,接头的拉伸强度越高。     

基于iButton(R)的智能门禁安全管理系统

利用DS1961 GUID和用户密码作为密匙,实现智能开门和记录用户进出门信息的门禁安全管理系统.系统主要由上位机和门禁子系统组成:上位机负责管理本地数据库和获取门禁子系统的登录信息等工作;子系统负责受控门开启和用户信息的无线通信传送.用户使用iButton和输入密码后,由nRF905将STM32处理后信息传至上位机,由上位机查询和匹配本地数据库并将核对信息发送给控制端,从而决定门道是否开启.系统很好地满足了智能门禁的要求,在智能安防系统中有很高的推广应用前景.     

大功率超快半导体光电导开关的触发瞬态特性

报道了用ns和fs超快脉冲激光器触发GaAs光电导开关的实验结果.用μJ量级的ns光脉冲触发3mm间隙的GaAs光电导开关,观察到线性和非线性工作模式,峰值电流达560A.当用重复率为76MHz的fs激光脉冲串触发同一器件时,电流脉冲上升时间小于200ps.     

Periodic autoregressive conditional duration

We propose an autoregressive conditional duration (ACD) model with periodic time-varying parameters and multiplicative error form. We name this model periodic autoregressive conditional duration (PACD). First, we study the stability properties and the moment structures of it. Second, we estimate the model parameters, using (profile and two-stage) Gamma quasi-maximum likelihood estimates (QMLEs), the asymptotic properties of which are examined under general regularity conditions. Our estimation method encompasses the exponential QMLE, as a particular case. The proposed methodology is illustrated with simulated data and two empirical applications on forecasting Bitcoin trading volume and realized volatility. We found that the PACD produces better in-sample and out-of-sample forecasts than the standard ACD.     

ASME规范第Ⅱ卷A篇A05增补情况

ASME锅炉和压力容器规范已成为一部国际规范。ASME规范2004版A05增补、修订了一批钢板、钢管、铸钢件的标准。认真分析并掌握ASME规范的变动和其中的新技术、新规则,是正确使用ASME规范的基础。     

Ca,Sr掺杂BNT-BT压电陶瓷结构与性能研究

采用传统的电子陶瓷制备工艺制备了一系列0.93Bi05Na05Tio3-0.07(Ba1-xAx)TiO3(简写为BNBAT100x;其中A=Ca,sr,x:0.02,0.04,0.06,0.08,0.10)陶瓷,研究了陶瓷的结构、介电、压电性能变化特征.XBD分析表明,陶瓷样品均形成了单一的钙钛矿结构固溶体.陶瓷的介电、压电性能受Ca,Sr含量的影响显著.所有陶瓷样品表现出弥散相变特征.当x<0.08时,BNBCT陶瓷的介电常数大干BNBST陶瓷,同时,BNBCT陶瓷室温介电常数在x=0.04时达到最大.而BNBST陶瓷此时具有最小的室温介电常数.陶瓷的压电性能受Ca,Sr含量的显著影响,当Ca含量为6mol%时,压电常数(d33)和平面机电耦合(kp)达到最大,分别为1 40.5 pc/N和1 9.7%.而当Sr含量为4mol%时,BNBST陶瓷的压电常数(d13)达到最大为1 39.8pC/N.此时平面机电耦合(kp)为1 8.9%.     

基于FCMISVM的自适应软测量建模算法及其在PX吸附分离过程中的应用

To overcome the problem that soft sensor models cannot be updated with the process changes, a soft sensor modeling algorithm based on hybrid fuzzy c-means (FCM) algorithm and incremental support vector machines (ISVM) is proposed. This hybrid algorithm FCMISVM includes three parts: samples clustering based on FCM algorithm, learning algorithm based on ISVM, and heuristic sample displacement method. In the training process, the training samples are first clustered by the FCM algorithm, and then by training each clustering with the SVM algorithm, a sub-model is built to each clustering. In the predicting process, when an incremental sample that represents new operation information is introduced in the model, the fuzzy membership function of the sample to each clustering is first computed by the FCM algorithm. Then, a corresponding SVM sub-model of the clustering with the largest fuzzy membership function is used to predict and perform incremental learning so the model can be updated on-line. An old sample chosen by heuristic sample displacement method is then discarded from the sub-model to control the size of the working set. The proposed method is applied to predict the p-xylene (PX) purity in the adsorption separation process. Simulation results indicate that the proposed method actually increases the model’s adaptive abilities to various operation conditions and improves its generalization capability.     

Turbulent natural convection in an enclosure with localized heating from below

This study reports the results of a numerical investigation of turbulent natural convection in a square enclosure with localized heating from below and symmetrical cooling from the vertical side walls. The present study simulates the case of an accidental heat generation due to fire in a typical isolated building of a nuclear reactor or electronic components cabin. The source of fire is considered to be centrally located at the bottom wall with different heated widths, which is assumed to be either isothermal or with isoflux. For the purpose of the analysis, the source length is varied from 20 to 80% of the total width of the bottom wall. The top wall and the unheated portion of the bottom wall are considered to be adiabatic, whereas sidewalls are isothermal. Steady as well as transient forms of two-dimensional Reynolds–Averaged-Navier–Stokes equations and conservation equations of mass and energy, coupled with the Boussinesq approximation, are solved by the control volume based discretisation method employing the SIMPLE algorithm for pressure–velocity coupling. Turbulence is modeled using the standard k–ε model. Rayleigh number, Ra, based on the enclosure height is varied from 10⁸ to 10¹². Stream lines and isotherms are presented for various combinations of Ra and the heated width. A double cell flow pattern is observed with marginal loss in symmetry as Ra increases. The results are reported in the form of local and average Nusselt number on the heated floor. Correlations are developed to predict the heat transfer rates from the enclosure as a function of dimensionless heated width of the bottom wall and Ra, by least square linear regression analysis.     

Potential method in the theory of thermoviscoelastic mixtures

In this article, the linear theory of binary thermoviscoelastic mixtures is considered and the basic boundary value problems (BVPs) of steady vibrations are investigated. Namely, the fundamental solution of the system of equations of steady vibrations is constructed explicitly and its basic properties are established. Green’s second and third identities are obtained and the uniqueness theorems for classical solutions of the internal and external basic BVPs of steady vibrations are proved. The surface and volume potentials are constructed and their basic properties are given. The determinants of symbolic matrices are calculated explicitly. The BVPs are reduced to the always solvable singular integral equations for which Fredholm’s theorems are valid. Finally, the existence theorems for classical solutions of the internal and external BVPs of steady vibrations are proved by the potential method and the theory of singular integral equations.