Preparation of barium hexaferrite nanopowders by the sol-gel method, using goethite

A series of barium hexaferrite nanoparticles (BaO·nFe₂O₃) with different n values were prepared by the sol-gel method, using goethite and Ba carbonate as raw materials. Phase identification of the samples was investigated by X-ray diffraction (XRD). XRD investigations show that the samples with n=5 and calcined at temperatures higher than 875 °C are single-phase Ba ferrite. An average crystallite size of 22 nm was obtained for the single-phase sample with minimum calcining temperature of 875 °C, using the Scherrer's formula. The morphology of the samples was checked by transmission electron microscope (TEM) and magnetic properties were measured by a sensitive permeameter. The results show that the samples have nonzero coercivities, which shows the particle size are not less than the critical size of Ba ferrite and then are not superparamagnet.     

Corrosion behavior of Nd9.4Pr0.6Febal.Co6B6Ga0.5TixCx (x=0, 1.5, 3, 6) nanocomposites annealed melt-spun ribbons

The effect of Ti and C additions on the corrosion behavior of Nd_9.4Pr_0.6Fe_bal.Co₆B₆Ga_0.5Ti_xC_x (x=0, 1.5, 3, 6) isotropic nanocomposite melt-spun ribbons in 3.5 wt% sodium chloride solution was studied. The melt-spun ribbons were annealed at 750 °C for 10 min in argon-filled quartz capsules. The microstructure of multiphase nanocrystalline samples and corrosion products was characterized using the X-ray diffraction and electron microscopy techniques. The electrochemical behavior was assessed using potentiodynamic polarization and electrochemical impedance spectroscopy. The results show that the addition of Ti and C increases the corrosion resistance of NdFeB ribbons; the best corrosion resistance was obtained for 1.5 wt% Ti and C content.     

基于手机APP实现驻波法对声速的测量

介绍了一种利用普通智能手机和一根两端开口奶茶管基于声驻波现象来测量声速的方法。这种实验方法所用的实验仪器随手可得,无需学生再到学校的实验室进行实验,激发了学生的学习兴趣,增强了学生的动手能力。     

多光束激光外差高精度测量玻璃厚度的方法

利用基于激光外差测量技术和激光多普勒技术的非接触式多光束激光外差测量方法,得到了光电探测器输出电流的谐波表达式.讨论了该测量方法用于玻璃厚度超精密测量的可行性及理论依据,并利用Matlab软件对不同情况进行了仿真实验.结果表明：该方法在不同入射角时测量平板玻璃厚度最大的误差为0.3%,明显比其他测量方法精度高. 关键词： 外差探测 多光束激光外差 激光多普勒技术 非接触式测量     

椰胡声功率级的半消声室测试

椰胡是具有地方特色的拉弦乐器之一,多用于演奏广东音乐和广东戏曲、曲艺的伴奏。但对其发声强度一直未进行过科学的测试。本文介绍在华南理工大学半消声室内参照ISO(GB)标准对椰胡声功率级的测量工作。由两位资深乐师分别用两把椰胡在pp,mp,f和ff力度下演奏单音、音阶和乐曲,对每一把椰胡的每一测试内容,由十通道测试设备同步测试中心频率为100～10000 Hz的1/3倍频带声压级谱,通过计算获得每把椰胡在演奏每项内容时的声功率级和动态范围。通过对两把椰胡的测试结果进行平均,获得该乐器在演奏上述内容时的典型声功率级数值及频谱。文中并将半消声室内的测试结果与混响室内的测试结果相对比,探讨测试环境对测试结果的影响。民族乐器发声强度及其频谱特性的获得是开展民族音乐厅堂音质研究的基础。     

Hysteresis of ruby fluorescent line by pressure and annealing effect

Abstract

Accuracy of hydrostatic pressure measurement in a diamond-anvil cell (DAC) depends on the reproducibility of ruby RI fluorescent measurement. The larger scatter in R, fluorescent wavelength shift than the reproducibility of spectroscopic measurement was observed among appropriately mirror-finished ruby plates before setting up in DAC. The characteristics of the scatter changed after loading DAC up to pressure over hydrostatic limit. They vanished by annealing the ruby plates. These phenomena are presumably due to the appearance and disappearance of the residual stress in the ruby crystal. Such hysteresis of ruby fluorescent wavelength shift by pressure and its annealing effect are discussed.     

Analysis of polycyclic aromatic hydrocarbons extracted from air particulate matter using a temperature programmable injector coupled to GC–C–IRMS†

Compound specific isotopic analysis (CSIA) can provide information about the origin of analysed compounds – in this case, polycyclic aromatic hydrocarbons (PAHs). In the study, PAHs were extracted from three dust samples: winter and summer filter dust and tunnel dust. The measurement was performed using the method validated in our laboratory using pure, solid compounds and EPA 610 reference assortment.

CSIA required an appropriate clean-up method to avoid an unresolved complex in the gas chromatographic analysis usually found in the chromatography of PAHs. Extensive sample clean-up for this particular matrix was found to be necessary to obtain good gas chromatography–combustion–isotope ratio mass spectrometry analysis results. The sample purification method included two steps in which the sample is cleaned up and the aliphatic and aromatic hydrocarbons are separated.

The concentration of PAHs in the measured samples was low; so a large volume injection technique (100 μl) was applied. The δ_VPDB ¹³C was measured with a final uncertainty smaller than 1 ‰. Comparison of the δ_VPDB ¹³C signatures of PAHs extracted from different dust samples was feasible with this method and, doing so, significant differences were observed.     

Eine Apparatur zur Messung natürlicher 4C-Aktivitäten

Aufbau, Arbeitsweise und Eigenschaften einer Apparatur, mit der naturliche ^l4C-Aktiviäten in Grund- und Oberflächenwässern gemessen werden können, werden beschrieben.

Die Messung erfordert 3 Arbeitsschritte: Probenahme, Synthese von Benzol, welches dann den Probenkohlenstoff enthält, und Messung der ¹⁴C-Aktivität in einem Flüssigkeitsszintillationszähler.

Die Apparatur kann zur Datierung von Wasserproben im Altersbereich zwischen 200 und 37000 a verwendet werden.     

Z箍缩软X射线辐射能量薄膜量热计改进技术

薄膜量热计是进行Z箍缩辐射总能量测量的主要手段之一,准确可信的总能量参数对Z箍缩研究具有重要意义。对薄膜量热计装置进行技术改进,采用脉冲恒流源代替脉冲恒压源驱动镍薄膜量热计,撤除了回路中的串接电阻,可直接测量薄膜探测器的电阻变化,从而有效提高了辐射总能量测量的精度,拓宽了该设备的适用范围,使其可对目前强光一号加速器Z箍缩实验中所有典型负载进行测量。改进后平面型铝丝阵负载实验中总能量测量的相对不确定度由49.0%降低为19.6%。与闪烁探测系统功率测量结果积分值进行了对比,二者比值在0.87~1.04之间。