房地产估价方法若干问题的思考

对目前房地产估价中常用的市场法、成本法、收益法中存在的问题进行了探讨,并提出了一些改进措施,以期完善现有的估价方法,使其更好的为房地产业健康发展提供服务。     

Al2O3/TiB2/Al复合材料的微观结构和高温力学性能

以细雾化铝粉和TiB₂颗粒为原料,通过粉末冶金和热轧制制备微米TiB₂和纳米Al₂O₃颗粒增强铝基复合材料。室温时,由于TiB₂和Al₂O₃的综合强化作用,Al₂O₃/TiB₂/Al复合材料的屈服强度和抗拉强度分别为258.7 MPa和279.3 MPa,测试温度升至350℃时,TiB₂颗粒的增强效果显著减弱,原位纳米Al₂O₃颗粒与位错的交互作用使得复合材料的屈服强度和抗拉强度达到98.2MPa和122.5 MPa。经350℃退火1000 h后,由于纳米Al₂O₃对晶界的钉扎作用抑制晶粒长大,强度和硬度未发生显著的降低。     

Photonic envelope detection and fiber transmission of 24 GHz IR-UWB signal based on phase modulation

A novel scheme for photonic envelope detection and fiber transmission of 24 GHz impulse radio ultra-wideband(IRUWB) signal is proposed based on phase modulator(PM). In the system, an optics assisted envelope detection unit(OAEDU) is used for filtering one of the first sidebands at the output of PM, then this narrow band optical signal transfers over single-mode fiber(SMF), and the envelope of 24 GHz IR-UWB signal is obtained after photodetection(PD) and low pass filter(LPF). The numerical simulation results show that the combination of PM and OAEDU can alleviate the fiber chromatic dispersion(CD) effectively. The proposed system may provide a simple and cost-effective solution for IR-UWB receiver.     

一种基于串行通信接口的采样速率测试方法

串行接口在工业控制领域得到广泛的应用,而且对串口的功能进行验证具有较为完善的测试设备和方法。另一方面,如何简化并快速进行串口模块的功能验证具有重要的意义。基于此观点,在研究了模块自身的功能特性的基础上,提出一种具有一定通用性的设计思想,即利用通信速率和采样速率之间的关系,将串口收/发送器速率与串口接收器采样速率配置成一定配比关系,从而实现用于测试串口接收器的任意帧结构数据。     

一种带改进开关和使用新型按比例缩小策略的10位120兆的流水线模数转换器

这篇文章介绍了一种精度为10比特,采样率为120兆的双通道流水线模数转换器(ADC)。这个模数转换器利用了体效应来改善开关的导通性能。在版图绘制中应用了一种新型的按比例缩小的策略。基于0.18μm的CMOS工艺,ADC的整个版图面积为2.05x1.83 mm2。在采样频率为120兆,输入信号频率为4.9兆的情况下,无杂散动态范围达到了74.32dB,信号噪音失真比为55.34dB,3伏供电电压下每通道的功耗为220毫瓦。     

PIλ 电流内环控制器实现的链式APF在外超导磁体中的应用

稳态强磁场超导磁体电源采用双反星型可控硅整流技术方案,是一种典型的非线性负载,运行时会带来较大的无功冲击及谐波污染。针对科学装置的链式高压有源电力滤波方案规划,结合有源滤波系统的非线性特性,提出一种采用分数阶PI控制器代替普通PI控制器实现的电流内环解耦方法,基于改进的Oustaloup算法,实现分数阶微积分的求解。通过仿真与实验对比分析了分数阶PI与常规PI控制器的运行效果。经仿真与实验表明,采用的分数阶PI电流内环控制器是正确的,且具有一定的参考价值。     

SINAMICS S120基本定位的监视功能与应用

SINAMJCSS120是西门子新一代伺服驱动器,其主要用于现场设备的转速与位置控制。通过参数配置,可以实现S120的位置监控功能,对驱动器各伺服轴的位置状态进行检测,优化驱动轴的状态。本文主要对监视功能的工作原理和可配置的参数进行介绍。     

高频电磁涡流检测系统及实验研究

针对碳纤维复合材料电磁涡流检测的特点,自主设计研制了一套高频电磁涡流检测系统,其最高检测频率可以达到10 MHz以上。该系统下位机以高速ARM微控制器STM32F407VGT6芯片为控制核心,上位机以虚拟仪器软件LabVIEW设计用户界面。系统集成了信号发生模块、功率放大模块、可调增益放大模块、锁相放大模块、USB模块以及数据采集模块,集成度高、体积小、使用简单方便。利用制作的高频电磁涡流检测系统对碳纤维复合材料的常见损伤形式进行了检测,包括冲击以及分层等,证明了系统的可行性以及实用性。     

Study on poly(butylene adipate‐co‐terephthalate)/starch composites with polymeric methylenediphenyl diisocyanate

To lower the cost of poly(butylene adipate‐co‐terephthalate) or PBAT, starch was used as a filler in this study. To increase tensile strength of PBAT/starch composites, polymeric methylenediphenyl diisocyanate (pMDI) was used as a compatibilizer. PBAT was melt‐mixed with starch in a kneader, and then the mixtures were compression‐molded. The effects of starch and pMDI content on the tensile strength and elongation at break of PBAT/starch composites were examined. The morphology and biodegradability of the composites in soil were also studied. The tensile strength of PBAT and PBAT/starch composites increases with increasing content of pMDI. The increase of weight average molecular weight of PBAT and improved interaction between PBAT and starch were observed with increasing content of pMDI. The weight average molecular weights of buried PBAT and the composites in soil significantly decrease. Especially, the reduction of the weight average molecular weight of PBAT/starch (70/30) composite is the most significant. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41884.     

Effects of Gd Substitution on Sintering and Optical Properties of Highly Transparent (Y0.95−xGdxEu0.05)2O3 Ceramics

Highly transparent (Y_0.95?xGd_xEu_0.05)₂O₃ (x = 0.15–0.55) ceramics have been fabricated by vacuum sintering at the relatively low temperature of 1700°C for 4 h with the in‐line transmittances of 73.6%–79.5% at the Eu³⁺ emission wavelength of 613 nm (~91.9%–99.3% of the theoretical transmittance of Y_1.34Gd_0.6Eu_0.06O₃ single crystal), whereas the x = 0.65 ceramic undergoes a phase transformation at 1650°C and has a transparency of 53.4% at the lower sintering temperature of 1625°C. The effects of Gd³⁺ substitution for Y³⁺ on the particle characteristics, sintering kinetics, and optical performances of the materials were systematically studied. The results show that (1) calcining the layered rare‐earth hydroxide precursors of the ternary Y–Gd–Eu system yielded rounded oxide particles with greatly reduced hard agglomeration and the particle/crystallite size slightly decreases along with increasing Gd³⁺ incorporation; (2) in the temperature range 1100°C–1480°C, the sintering kinetics of (Y_0.95?xGd_xEu_0.05)₂O₃ is mainly controlled by grain‐boundary diffusion with similar activation energies of ~230 kJ/mol; (3) Gd³⁺ addition promotes grain growth and densification in the temperature range 1100°C–1400°C; (4) the bandgap energies of the (Y_0.95?xGd_xEu_0.05)₂O₃ ceramics generally decrease with increasing x; however, they are much lower than those of the oxide powders; (5) both the oxide powders and the transparent ceramics exhibit the typical red emission of Eu³⁺ at ~613 nm (the ⁵D₀→⁷F₂ transition) under charge transfer (CT) excitation. Gd³⁺ incorporation enhances the photoluminescence and shortens the fluorescence lifetime of Eu³⁺.