Medium wave DRM field trials in Brazil – Some daytime and nighttime results in urban environment

The Digital Radio Mondiale (DRM) system broadcasts audio in the frequency band below 174 MHz  and . In this experiment in urban areas in Brazil, a hybrid signal composed of an analog AM signal and a digital DRM30 signal, with the same content, were broadcasted in diurnal and nocturnal transmissions. This paper describes the experimental setup, which employs the spectral shaping technique in simulcast transmission [14], and presents some results of medium wave propagation measurements campaigns that are being carried out in Brazil. The experiment is part of a series of field trials that are being conducted by the Brazilian Government which includes campaigns at MW, HF and VHF frequency bands.     

浇注温度和压射速度对Al-30Si压铸组织和力学性能的影响

研究液态压铸过程中浇注温度和压射速度对Al-30Si压铸组织和力学性能的影响.结果表明,随着浇注温度的升高,Al-30Si压铸组织中的初生硅尺寸在不断减小.温度从780℃升高到820℃时,初生硅的尺寸出现了大幅度的减小,温度再升高则变化不明显;同时,抗拉强度随温度的变化也表现出同样的趋势.而压射速度对Al-30Si液态压铸组织的影响要比浇注温度的影响小得多.初生硅的尺寸随压射速度的增加有减小的趋势,但减小的幅度不大.当压射速度为8m/s时,压铸组织出现了明显的气孔、缩孔等缺陷.随着压射速度的增加,其抗拉强度呈现出了先增大后减小的趋势,最大值217N/mm2出现在压射速度为4m/s时.     

Microstructure and mechanical properties of NZ30K alloy by semicontinuous direct chill and sand mould casting processes

The Mg-3.0Nd-0.2Zn-0.4Zr (NZ30K) alloys were prepared by direct-chill casting (DCC) and sand mould casting (SMC) processes,respectively and their microstructures and mechanical properties were investigated.The results indicate that casting method plays a remarkable influence on the microstructure and mechanical properties of as-cast NZ30K alloy.The grain size increases from 35-40μm in the billets made by the DCC to about 100-120μm in the billets by the SMC.The aggregation of Mg12Nd usually found at the trip...     

Effect of tunneling barrier as spacer on exchange coupling of CoFeB/AlOx/Co trilayer structures

Magnetic tunneling junctions (MTJs) have a sandwiched structure, which comprises a top ferromagnetic (FM1) layer, an insulating tunneling layer (spacer), and a bottom ferromagnetic (FM2) layer. Exchange coupling in MTJs has been extensively widely examined because the effect of spacer thickness on the ferromagnetic spin-coupling can be exploited in read-head sensors, spin-valve structures, and magntoresistance random access memories (MRAMs). In this investigation, MTJs were deposited in the sequence, glass/CoFeB(50 Å)/AlO_x(d)/Co(100 Å), where the thickness of the AlO_x layer d = 12, 17, 22, 26 or 30 Å. Saturation magnetization (M_s) results demonstrate that the exchange coupling strength and coercivity (H_c) can be varied considerably by varying the tunneling barrier AlO_x spacer. The X-ray diffraction patterns (XRD) include a main peak from hexagonal close-packed (HCP) Co with a highly (0 0 2) textured structure at 2θ = 44.7°, and AlO_x and CoFeB are amorphous phases. The full width at half maximum (FWHM) of the Co (0 0 2) peak declines as the AlO_x thickness increases, revealing that the Co layer becomes more crystalline. The magnetic results reveal that the magnetic characteristics are related to the Co crystallinity. The exchange coupling strength increases with AlO_x thickness. The coercivity (H_c) also increases, because the Co crystallinity is eliminated.     

基于T.38网关的实时IP传真技术设计与实现

讨论了IP传真技术和IP传真标准,并给出了实时IP传真的实现方案。由于IP网固有的特点决定了IP传真必须解决时延与抖动,丢包与纠错等技术难点。T.38传真网关将从传真机接收到的传真信号解调成T.30控制消息和传真图像数据,对这些消息和数据重新封装成IFP包,通过IP网络将IFP包发送到T.38接收网关,接收网关对T.30控制消息和图形数据再调制,然后发给接收传真机,可获得与PSTN网相媲美的传真质量。     

BFe30-1-1铜合金的化学抛光工艺研究

研究以含硝酸的化学抛光液对BFe30-1-1铜合金进行化学抛光的方法,考察光亮剂的种类、缓蚀剂的种类、化学抛光液各组分的含量、抛光温度以及抛光时间对铜合金抛光效果的影响。结果表明,在实验范围内优化工艺条件为:350～450 mL/L H2SO4,3～5 mL/L HCl,30～40 mL/L HNO3,2～4 mL/L辛基酚聚氧乙烯醚(OP-10),3 g/L苯骈三氮唑(BTA),水余量,抛光温度30℃左右,抛光时间3～5 min。在此工艺条件下对BFe30-1-1铜合金进行化学抛光,可以获得较好的抛光效果。     

30%毒氟磷可湿性粉剂对环境生物的毒性与安全性评价

[目的]为顺利实现30%毒氟磷可湿性粉剂在今后农业生产中的广泛推广,参照《化学农药环境安全评价试验准则》的规定,进行了30%毒氟磷可湿性粉剂对环境有益生物鱼、蜂、鸟、蚕的急性毒性测定,并对其进行环境安全性评价。[结果]30%毒氟磷可湿性粉剂对鱼96 h的LC50值为12.4 mg/L,对蜂48 h的LC50>5 000 mg/L,对鸟7 d的LD50>450 mg/kg体质量,对2龄家蚕胃杀毒性LC50>5 000 mg/kg桑叶。[结论]30%毒氟磷可湿性粉剂对鱼类、蜂类、鸟类、家蚕均为低毒,实际风险为零。     

基于DSC的无刷直流风机控制系统

为提高厂矿及汽车空调用调速风机的运行效率和调速性能,研究了以Microchip公司的数字信号控制器(DSC) dsPIC30F4012芯片为核心的无刷直流风机控制系统.首先结合风机的使用环境,采用了高可靠性的硬件系统,并对硬件各个部分进行了阐述;然后介绍了系统所使用的控制算法和软件;最后通过实验对整个系统进行了评估并得...     

LB-30隔热防水涂料在轻型金属屋面上的应用

介绍了LB-30隔热防水涂料隔热防水原理及各项性能指标,并以在广州本田汽车装配车间金属屋面的成功应用为例,介绍了其施工要点,指出该涂料一方面能有效隔热,减少屋面的变形和开裂几率,一方面能用于屋面防水,是一种新型绿色多功能涂料.     

30Cr3Si2Mn2NiNb钢中未溶相的热力学计算及分析

采用Thermo-Calc热力学软件模拟了30Cr3Si2Mn2NiNb钢奥氏体化时平衡相的演化规律以及非平衡态相的演化规律,研究了合金元素C,Mo,Nb和V对实验钢中未溶相的影响.通过SEM,XRD对30Cr3Si2Mn2NiNb钢淬火态组织进行实验观察及分析.结果表明:常规奥氏体化处理后,钢中未溶相主要有富Nb的M...