三峡库区水体溶解有机质的荧光光谱特性

利用荧光发射和三维荧光光谱(EEM)研究了三峡库区(TGRA)长江干流及嘉陵江、乌江两支流水体溶解有机质(DOM)的荧光特性.结合采样段面溶解有机碳(DOC)、氧化还原电位(ORP)、pH等参数,考察了干流、两支流及其汇合后各水体DOM的荧光指数f450/500和类腐殖酸与类富里酸强度比值rC/D变化,分析了类腐殖酸、类富里酸及类蛋白质在库区支流与干流、上游与下游水体的来源、组成、分布及环境行为.实验表明: 干流水体中DOM以类富里酸、类蛋白质荧光有机质为主;嘉陵江水体DOM以类蛋白质为主,富里酸次之; 在朝天门与长江汇合后,类蛋白峰强减弱而类腐殖酸有一定增加;乌江以类富里酸为主,汇合干流后,富里酸和类蛋白质峰增强;库区上游水体DOM主要受嘉陵江影响;干流DOM受陆源性影响.初步揭示了水体DOM的EEM特性与库区水质参数的相关性,为水体监测与分析提供参考.     

应用超高效液相色谱-四极杆-飞行时间质谱法建立谷物中18种真菌毒素非靶向筛查数据库及确证方法

建立了基于超高效液相色谱-四极杆-飞行时间质谱(UPLC-Q-TOF/MS)的18种真菌毒素非靶向筛查方法。真菌毒素标准物质用HSS T3色谱柱进行色谱分离后在UPLC-Q-TOF/MS MS^E模式下分别用正、负离子模式采集,获取MS和MS/MS的信息,记录对应保留时间、加合物离子、碎片离子精确质量数等信息,设置保留时间偏移为0.3 min,加合物离子和碎片离子的精确质量匹配容差为5×10^-6,在UNIFI中建立18种真菌毒素的数据库。在稻谷、小麦基质中,以筛查检出限(SDL)作为主要参数对筛查方法进行了验证。18种真菌毒素分为有最大限量和无最大限量两种类型,结果有最大限量的真菌毒素均能在其限量水平被准确筛查,无最大限量的真菌毒素其SDL的范围为2～800μg/kg。基质效应考察表明,稻谷中有14种真菌毒素有中等基质效应,小麦中有11种真菌毒素有中等基质效应。样品经乙腈提取后用QuEChERS萃取盐包和HLB净化柱净化,用建立的方法对25批稻谷、小麦进行筛查,结果2批稻谷中检出4种真菌毒素,2批小麦中检出2种真菌毒素。该方法能准确筛查SDL水...     

Analysis and simulation of a 4H-SiC semi-superjunction Schottky barrier diode for softer reverse-recovery

In this paper,a 4H-SiC semi-superjunction (SJ) Schottky barrier diode is analysed and simulated.The semi-SJ structure has an optimized design and a specific on-resistance lower than that of conventional SJ structures,which can be achieved without increasing the process difficulty.The simulation results show that the specific on-resistance and the softness factor depend on the aspect and thickness ratios,and that by using the semi-SJ structure,specific on-resistance can be reduced without decreasing the softness factor.It is observed that a trade-off exists between the specific on-resistance and the softness of the diode.     

Study and optimal simulation of 4H-SiC floating junction Schottky barrier diodes’ structures and electric properties

This paper stuides the structures of 4H-SiC floating junction Schottky barrier diodes. Some structure parameters of devices are optimized with commercial simulator based on forward and reverse electrical characteristics. Compared with conventional power Schottky barrier diodes, the devices are featured by highly doped drift region and embedded floating junction layers, which can ensure high breakdown voltage while keeping lower specific on-state resistance, and solve the contradiction between forward voltage drop and breakdown voltage. The simulation results show that with optimized structure parameter, the breakdown voltage can reach 4.36 kV and the specific on-resistance is 5.8 mΩ·cm2 when the Baliga figure of merit value of 13.1 GW/cm2 is achieved.     

Simulation of near-infrared photodiode detectors based on β-FeSi2/4H-SiC heterojunction

In this paper, we propose the near-infrared p-type β-FeSi₂/n-type 4H-SiC heterojunction photodetector with semiconducting silicide (β-FeSi₂) as the active region for the first time. Optoelectronic characteristics of the photodetector are simulated using a commercial simulator at room temperature. The results show that the photodetector has a good rectifying character and a good response to the near-infrared light. Interface states should be minimized to obtain a lower reverse leakage current. The response spectrum of the β-FeSi₂/4H-SiC detector, which consists of a p-type β-FeSi₂ absorption layer with a doping concentration of 1×10¹⁵ cm^-3 and a thickness of 2.5 μm, has a peak of 755 mA/W at 1.42 μm. The illumination of the SiC side obtains a higher responsivity than that of the β-FeSi₂ side. The results illustrate that the β-FeSi₂/4H-SiC heterojunction can be used as a near-infrared photodetector compatible with near-infrared optically-activated SiC-based power switching devices.     

Analysis and simulation of a 4H-SiC semi-superjunction Schottky barrier diode for softer reverse-recovery

In this paper, a 4H-SiC semi-superjunction (SJ) Schottky barrier diode is analysed and simulated. The semi-SJ structure has an optimized design and a specific on-resistance lower than that of conventional SJ structures, which can be achieved without increasing the process difficulty. The simulation results show that the specific on-resistance and the softness factor depend on the aspect and thickness ratios, and that by using the semi-SJ structure, specific on-resistance can be reduced without decreasing the softness factor. It is observed that a trade-off exists between the specific on-resistance and the softness of the diode.     

重庆主城区两江溶解有机质的荧光光谱特征

应用荧光发射、三维荧光光谱(EEM)技术研究了重庆主城区长江、嘉陵江水体中溶解有机质(DOM)的荧光光谱特征在2008年4～8月的变化规律,以"5·12"汶川地震及唐家山堰塞湖事件与7和8月丰水期为出发点,结合两江各采样段面的pH,DO,DOC,TOC与EEM指纹特征、荧光指数(f_(450/500))等参数,探讨了两江DOM的组成、分布及其变化规律,着重阐述了EEM中类腐殖酸、类富里酸和类蛋白质3类荧光峰的环境生态行为特征及其影响。实验结果显示两江水体中DOM以类富里酸和类腐殖酸为主,嘉陵江类蛋白质较强,两江水体汇合后,各荧光峰都有所减弱;5月、6月和丰水期两江DOM的类蛋白显著增强,多为陆源所致,丰水期两江各荧光峰在汇合后明显降低。     

羟基甘氨酸溶液性质研究

采用核磁共振等仪器分析与官能团鉴定相配合的方法，对乙醛酸与铵盐反应形 成的羟基甘氨酸进行了研究。确认了羟基甘氨酸的结构，探讨了羟基甘氨酸的水溶 液中的主要存在形式，得出了与普遍接受的羟基甘氨酸在水溶液中不稳定的观点相 悖的结论。并对羟基甘氨酸的溶液稳定性，氨解，水解进行了研究。本结果为乙醛 酸以及羟基甘氨酸在有机合成上的应用提供了依据。     

基于均值向量检验法的模板比较算法

模板比较算法是核弹头及其核部件模板识别技术的一项关键技术.文中介绍了一种基于均值向量检验法的高分辨γ能谱指纹模板比较算法,并用放射源对其进行了有效性检验.检验结果表明,该算法是有效的,能够准确识别不同强度、不同组成的辐射源.研究还就模板构型的设计提出了两条建议. 关键词： 模板比较算法 模板识别技术 能谱指纹 均值向量检验法     

离子色谱法测定蚀刻槽废氢氟酸中的六氟硅酸

建立了一种新的检测蚀刻槽废氢氟酸中六氟硅酸的离子色谱方法。色谱柱为Metrosep A Supp 7阴离子交换柱,流动相为3.2 mmol/L碳酸钠-1.0 mmol/L碳酸氢钠,流速为0.7 mL/min。六氟硅酸经过抑制型电导检测器后进行衍生化反应,在360 nm波长下用紫外检测器检测。六氟硅酸的线性范围为2.4~120 mg/L,相关系数r²大于0.999,定量限为0.24 mg/L,平均加标回收率为97.2%。本方法还可以同时利用电导检测器检测废氢氟酸中的氢氟酸、醋酸、盐酸、硝酸、磷酸和硫酸的含量。该方法快速、准确,适用于蚀刻槽液中六氟硅酸的检测。