Observation of Spin Polarized Clock Transition in 87Sr Optical Lattice Clock

Atomic clocks operating at optical frequencies, with much better accuracy compared with microwave atomic clocks, have been assumed to be the next- generation time and frequency standards, Many applications will benefit from this lower frequency un- certainty of optical clocks, such as the re-definition of ＇the second＇, i.e. one of the seven base units of the international system of units （SI）, test of the time variation of fundamental physical constants and rel- ativity geodesy. Recently, the neutral atom lattice clock has achieved a lower frequency uncertainty com- pared with the optical ion clock, mainly due to the im- provement of the clock laser frequency stability refer- enced to a long high-finesse ULE cavity and the more accurate evaluation of black-body radiation shift. Strontium is an excellent candidate for the neutral atom optical clock. For the fermionic isotope of stron- tium, it has intrinsically less collision shift and the first order Zeeman shift can be removed by an inter- leaved probing approach.Recently, through the pre-cise measurement of the polarizability of strontium, the black body radiation （BBR） shift of the stron- tium lattice clock, which remains to be the limitation factor of its total frequency uncertainty, is reduced to a lower 10^-18 value.The instability of the strontium lattice clock has reached 3.1 × 10-16/√T, showing the significant advantage over the single ion optical clock. The total systematic uncertainty has reached 6.4 × 10^-18 in fractional frequency, which is the best among all optical clocks until now.     

基于氨基偶氮苯的光和pH响应聚[（三甲基丙烯酸乙酯胺）8-（4-氨基-4’-甲基丙烯酰胺基偶氮苯）1]（T8A1）的合成与表征

以对硝基苯胺为原料,经过偶联、还原和酰化反应,合成了4-氨基-4’-甲基丙烯酰胺基偶氮苯(AMAB);将三乙醇胺和甲基丙烯酰氯反应制得水溶性的十字交联剂三甲基丙烯酸乙酯胺(TMAEA);将AMAB和TMAEA进行自由基沉淀聚合反应,制得基于氨基偶氮苯的新型纳米级聚合物——聚[(三甲基丙烯酸乙酯胺)8-(4-氨基-4’-甲基丙烯酰胺基偶氮苯)1](T8A1),并用紫外-可见光谱(UV-Vis)、红外光谱(IR)、热失重(TG)和扫描电子显微镜(SEM)对T8A1进行了表征.结果表明,T8A1在水中具有光和pH双重响应性能,弥补了传统的偶氮苯类材料仅能在有机溶剂中具有响应的缺陷,具有广阔的仿生应用前景.     

1-甲氧基-3,5-二-O-苄基-β-D-呋喃型核糖苷-2-酮糖的合成

1-甲氧基-3,5-二-O-苄基-β-D-呋喃型核糖苷-2-酮糖是重要的医药中间体.以廉价D-木糖为起始原料,经过9步反应,合成了1-甲氧基-3,5-二-O-苄基-β-D-呋喃型核糖苷-2-酮糖;中间产物不需柱层析分离提纯,可以直接用于下一步反应;各步产物的结构均经核磁共振氢谱和质谱分析确认.     

基于时间反转MUSIC的奥氏体不锈钢超声成像分析

奥氏体不锈钢管道广泛应用于核电及某些化工领域等,但奥氏体不锈钢焊缝缺陷的检测仍然比较困难。在时间反转的基础上,采用DORT算法和MUSIC算法对较低信噪比(-5 dB和-10 dB)的缺陷定位进行仿真分析,在定制的奥氏体不锈钢对接焊缝试块上(300 mm×90 mm×30 mm),采用16阵元超声相控阵探头对缺陷进行检测,引入TR-MUSIC算法对缺陷回波信号进行频域分析。结果表明,低信噪比时,TR-MUSIC算法较TR-DORT算法能更好的抑制旁瓣,使信号能量能更好的聚焦于缺陷;在奥氏体不锈钢焊缝相距25 mm的Φ2mm缺陷(深度为50 mm)检测实验数据基础上,TR-MUSIC算法能够更准确定位缺陷。     

低阻抗大面积二极管的研制

采用高纯石墨环状阴极和有机玻璃绝缘子,研制了一套低阻抗大面积二极管系统。使用理论计算和数值模拟方法对二极管进行优化设计,在保证绝缘要求的同时,尽量优化二极管轴向长度和内外筒距离以减小二极管的回路电感。实验结果表明,优化后的二极管能在200 kV左右的电压上稳定工作,绝缘结构未发生击穿现象;实验中最高输出电压为213 kV,电流为221 kA,特性阻抗约为1 ,电流密度为8 kA/cm2,脉宽(FWHM)为50 ns。     

单扫描示波极谱法测定食品中禁用色素苏丹红Ⅰ

在pH 10硼砂缓冲介质中,苏丹红Ⅰ产生一个峰电位在-0.95 V(vs.SCE)的灵敏的吸附还原极谱波.其峰电流的一阶导数值(I'p)与苏丹红Ⅰ的质量浓度在0.1～2.0 mg·L-1范围内呈线性关系,检出限为0.01 mg·L-1.应用此方法分析了辣椒酱及腐乳等试样,均未测出苏丹红Ⅰ,以此试样为基体加入苏丹红Ⅰ标准溶液做回收试验,测得回收率在95.3%～103.0%之间.     

网络型聚醚酯弹性体聚柠檬酸二甘醇酯的合成与性能

用一缩二乙二醇(二甘醇)和柠檬酸通过熔融缩聚的方法,合成了一种新型的网络型聚醚酯弹性体—po-ly(diethylene glycol citrate)(PDGC).用FTIR初步表征了预聚物的结构;通过ATR-FTIR、DSC、XRD等表征了PDGC的结构;测试了材料的静态水接触角、力学性能以及体外降解性能,考察了单体的摩尔比以及后期交联时间对材料上述性能的影响.     

Slow-rise and fast-drop current feature of ultraviolet response spectra for ZnO-nanowire film modulated by water molecules

This study describes the fabrication of ZnO-nanowire films by electro-chemical anodization of Zn foil. The ZnO films are characterized by field emission scanning electron microscopy, X-ray diffraction patterns, and transmission electron microscopy, respectively. The ultraviolet (UV) photo-response properties of the surface-contacted ZnO film are studied through the current evolution processes under different relative humidities. Unlike the usually observed current spectra of the ZnO films, the drop time is shorter than the rise time. The photo-conductivity gain G and the response time τ are both increased with the increase of the applied bias. The photo-conductivity gain G is lowered with the increase of the environmental humidity, while the response time τ is increased. These results can be explained by considering three different surface processes: 1) the electron-hole (e-p) pair generation by the UV light illumination, 2) the following surface O₂^- species desorption, and 3) the photo-catalytic hydrolysis of water molecules adsorbed on the ZnO surface. The slow-rise and fast-drop current feature is suggested to originate from the sponge-like structure of the ZnO nanowires.     

Performance of La₂O₃/InAlN/GaN metal-oxide-semiconductor high electron mobility transistors

We report on the performance of La2O3/InAlN/GaN metal-oxide-semiconductor high electron mobility transistors(MOSHEMTs) and InAlN/GaN high electron mobility transistors(HEMTs).The MOSHEMT presents a maximum drain current of 961 mA/mm at Vgs = 4 V and a maximum transconductance of 130 mS/mm compared with 710 mA/mm at Vgs = 1 V and 131 mS/mm for the HEMT device,while the gate leakage current in the reverse direction could be reduced by four orders of magnitude.Compared with the HEMT device of a similar geometry,MOSHEMT presents a large gate voltage swing and negligible current collapse.     

A study of GaN MOSFETs with atomic-layer-deposited A1203 as the gate dielectric

Accumulation-type GaN metal-oxide-semiconductor field-effect transistors （MOSFETs） with atomic-layerdeposited Al₂O₃ gate dielectrics are fabricated.The device,with atomic-layer-deposited Al₂O₃ as the gate dielectric,presents a drain current of 260 mA/mm and a broad maximum transconductance of 34 mS/mm,which are better than those reported previously with Al₂O₃ as the gate dielectric.Furthermore,the device shows negligible current collapse in a wide range of bias voltages,owing to the effective passivation of the GaN surface by the Al₂O₃ film.The gate drain breakdown voltage is found to be about 59.5 V,and in addition the channel mobility of the n-GaN layer is about 380 cm2 /Vs,which is consistent with the Hall result,and it is not degraded by atomic-layer-deposition Al₂O₃ growth and device fabrication.