AMS-14C样品制备系统的研制及其性能研究

为了开展加速器质谱仪（accelerator mass spectrometry, AMS）在¹⁴C测量方面的研究,研制了可采用锌法、氢法、氢化钛法制备¹⁴C样品的装置,该制样系统以石英玻璃为主要结构材料,分为以下三个单元：系统真空维护单元、CO₂纯化单元和CO₂还原单元。为验证此装置的可靠性,进行了系列 ¹⁴C样品的制备实验,得到的石墨产率基本达到80%,同时对商业碳粉、树木的含碳量与实验过程中测量区域对应的CO₂量进行了线性拟合,结果呈现明显的线性关系。对一批标准样品和本底样品进行AMS测试,结果显示每个样品¹²C^-的引出束流均大于20 μA,系列空白样品的测量结果表明,¹⁴C/¹²C丰度比平均值为1.061×10^-15,样品制备系统稳定且在制样过程中引入的碳污染较小,符合制样要求,现代木头样品的AMS绝对测量值为（9.13±0.05)×10^-13,与预期值~9.0×10^-13相符合。上述结果表明,该系统结构紧凑,能避免相互污染,高效且便于操作,满足AMS对¹⁴C样品的测试要求。     

Zero-Sequence Voltage-based Method for Determination and Classification of Unloaded Overhead Line Operating Conditions at the Moment of Energization

Overhead line energization can be performed under normal or faulty conditions. The latter indicates an occurrence of a fault along the line that exists at the moment of energization. This can lead to significant over-voltages that could endanger proper line operation. The issue gets more complex to protective devices when it comes to high-resistance faults, which impair the ability of relays to react promptly and accurately. Consequently, installation of additional detection devices becomes necessary. This paper proposes a novel method that properly detects and classifies line operating conditions at the moment of energization. The method is designed to be useful for utilities and it can be considered as a low-cost, fast, and accurate detection and classification approach, suitable for dealing with both low-resistance and high-resistance faults. Through comprehensive mathematical modeling it was found that both normal and faulty conditions during line energization are accompanied by the zero-sequence voltages of specific characteristics. The differences between zero voltage sequences are reflected in harmonic content, magnitudes of dominant frequencies, and their phase angles in regard to supply voltage. These findings are taken as the method's detection and classification criteria. The validity of the proposed model is verified by simulations and by field measurements.     

Preparation and photoluminescence of Tb3+ doped SrAl2O4 phosphor by composite combustion method

High-efficient Tb3 activated SrAl2O4 phosphor was synthesized by a combined combustion-solid-state reaction method. The precursor of SrAl2O4:Th3 phosphr was prepared via a combustion process, and then the as-prepared powder was heated in a reductive am-bient of activated carbon at 1250 ℃ for 1 h. The results of X-ray diffraction, scanning electron microscopy, and photoluminescence spectra revealed the influence of the dosage of urea and heated process on the crystallinity, morphology, and photoluminescence of the phosphor.Comparing with tradidonal solid-sate reaction, the crystallinity and emission intensity of the SrAl2O4:Th3 phosphor were improved by this two-step process.     

半桥级联型三相多电平逆变器及其控制

把传统级联型三相多电平逆变器的H全桥单元,改为半桥单元,可减少一半的功率器件数和两个主电源。分别分析了倍压、等压电源供电情况下的SPWM调制控制方法,以及调制结果。利用等能量和等电量方法,解出电源功率分配比和倒灌功率比。倍压电源供电逆变的倒灌功率,可通过增大电源电容量和PWM软件算法,使倒灌功率的影响减至很小。等压电源供电逆变,利用循环脉冲控制,可使除公用电源外的级联电源功率达到均衡。     

Different Narrow-Band Light Ranges Alter Plant Secondary Metabolism and Plant Defense Response to Aphids

Light of different wavelengths affects various physiological processes in plants. Short-wavelength radiation (like UV) can activate defense pathways in plants and enhance the biosynthesis of secondary metabolites (such as flavonoids and glucosinolates) responsible for resistance against certain herbivorous insects. The intensity of light-induced, metabolite-based resistance is plant- and insect species-specific and depends on herbivore feeding guild and specialization. In this study, broccoli (Brassica oleracea var. italica) plants were grown for 4 weeks in a climate chamber under conventional fluorescent tubes and were additionally treated with UV-B (310 nm), UV-A (365 or 385 nm), or violet (420 nm) light generated with UV-B tubes or light-emitting diodes (LEDs). The objective was to determine the influence of narrow bandwidths of light (from UV-B to violet) on plant secondary metabolism and on the performance of the cabbage aphid Brevicoryne brassicae (a specialist) and the green peach aphid Myzus persicae (a generalist). Among flavonol glycosides, specific quercetin and kaempferol glycosides increased markedly under UV-B, while among glucosinolates only 4-methoxy-3-indolylmethyl showed a 2-fold increase in plants exposed to UV-B and UV-A. The concentration of 3-indolylmethyl glucosinolate in broccoli plants increased with UV-B treatment. Brevicoryne brassicae adult weights and fecundity were lower on UV-B treated plants compared to UV-A or violet light-treated plants. Adult weights and fecundity of M. persicae were increased under UV-B and UV-A treatments. When specific light wavelengths are used to induce metabolic changes in plants, the specificity of the induced effects on herbivores should be considered.     

酶法动态动力学拆分制备R-(-)-乙酰基邻氯扁桃酸

采用假单胞菌脂肪酶Pseudomonas sp. ECU1011催化乙酰基邻氯扁桃酸进行不对称水解,利用突变后的扁桃酸消旋酶(V29I)对拆分后的产物S-(-)-邻氯扁桃酸进行消旋,消旋后的邻氯扁桃酸经过酰化重新被利用到水解反应中,实现了酶法动态动力学拆分制备R-(-)-乙酰基邻氯扁桃酸。通过对拆分反应、拆分混合物的分离回收以及消旋反应的工艺优化,最终获得光学纯度ee>99.9%的R-(-)-乙酰基邻氯扁桃酸,其收率达80%。本研究建立的R-(-)-乙酰基邻氯扁桃酸的动态动力学拆分工艺,对其工业化应用具有重要的指导意义。     

Status and research programs of the multinuclide accelerator mass spectrometry system at the University of Tsukuba

We present the current status and research programs of a multinuclide accelerator mass spectrometry (AMS) system on the 12UD Pelletron tandem accelerator at the University of Tsukuba (Tsukuba AMS system), Japan. A maximum terminal voltage of 12 MV is available for the AMS system. The Tsukuba AMS system can measure environmental levels of long-lived radioisotopes of ¹⁴C, ²⁶Al, ³⁶Cl and ¹²⁹I by employing a molecular pilot beam. Recently, enhancements in AMS techniques and equipment, including sample preparation, the ion source and the data acquisition system, have improved the performance of ³⁶Cl-AMS. The standard deviation of fluctuations is typically ±2%, and the machine background level for the ³⁶Cl/Cl ratio is lower than 1 × 10^?15 with a halite sample. We have measured over 500 samples in 1 year, including samples for earth and environmental sciences and nuclear safety research.     

露天矿精细化开采信息采集与处理系统设计

基于精细生产的基本原理,提出了露天矿精细化开采技术体系。利用虚拟仪器技术、数据库技术,建立一个集安全生产工艺信息、隐患信号监测数据及预警决策指挥模块于一体的露天矿精细化开采信息采集与处理系统。该系统由传感器、信号硬件调理设备、数据采集卡与计算机等组成,软件平台的设计采用LabVIEW虚拟仪器软件。本系统采集项目可扩充,能够对露天开采信息进行实时采集与传输,进而实现露天矿开采工艺环节的实时监控、数据共享和安全状况的实时监测。研究成果有望改变传统露天矿山粗放式的开采模式,进一步丰富露天矿精细化开采技术体系。     

增强现实辅助维修技术研究进展

增强现实技术应用于复杂装备维修,可增加维修保障工作信息量与对复杂维修任 务及维修过程的理解能力,提高维修保障效率。在分析当前典型增强现实原型系统基础上,研 究了增强现实技术在复杂装备维修保障中应用的可行性,提出了增强现实装备维修中关键技术 的解决途径,并对增强现实技术的发展趋势进行了展望。     

碳基三维集流体在锂金属电池中的应用研究

锂金属负极具有较高的理论比容量(3860 mAh/g)和较低的还原电势(-3.04 V vs.标准氢电势),被誉为最具发展潜力的负极材料,但是锂金属负极中的枝晶、死锂等问题阻碍了锂金属电池的商业化发展.针对锂金属负极中出现的问题,研究人员提出了大量的解决方案,其中,三维集流体不仅可以降低电流密度,缓解枝晶生长,还可以容...