载体MCM-41对Tb(aspirin)3phen发光性能的影响

在室温下,乙二胺环境中合成了高度有序的介孔材料MCM-41,并将经热处理的发光客体Tb(aspi-rin)3phen组装进其孔道,通过激发发射光谱对其光致发光性能进行了研究。结果表明,Tb(aspirin)3phen240～375 nm区间的宽激发峰归属于配体aspirin羰基n→π*跃迁、苯环π→π*跃迁,和phen的杂菲基团吸收,Tb3 的特征发射是由于Antenna效应引起的。相对于纯Tb(aspirin)3phen,Tb(aspirin)3phen-MCM-41B和Tb(aspirin)3phen/MCM-41A的激发谱带出现了明显的分裂,而Tb(aspirin)3phen-MCM-41A只在353nm处剩下了相对较窄的单峰。Tb(aspirin)3phen-MCM-41B,Tb(aspirin)3phen/MCM-41A和Tb(aspirin)3phen-MCM-41A的短波段激发峰依次减弱消失,长波段激发峰逐渐增强,而405 nm发射峰强度IL和544 nm发射峰强度ILn的比值I(I=IL/ILn)依次减小。MCM-41骨架与Tb(aspirin)3phen成键后,不同程度降低了配体aspirin和phen单重态S1和三重态T1能级,且对phen的影响大于aspirin。不同的MCM-41表面晶格场对配体能级的影响顺序为:MCM-41B外表面>MCM-41A外表面>MCM-41A内表面。I值可定性表示MCM-41表面晶格场对配体能级影响程度和MCM-41表面Tb(aspirin)3phen的含量。     

稳态平板法测量导热系数的若干影响因素分析

研究发现,热源温度和环境温度等因素通过试样的侧面散热影响平板稳态法测量导热系数的精度,散热铜板的上下表面散热功率不一致也将影响导热系数测量的准确性.用大空间自然对流理论对实验数据处理公式修正后,可有效减小侧面散热对测量的影响.在设计实验时应首先获得散热铜板的散热功率曲线,选择合适的散热铜板温度,而后通过综合考虑试样厚度和热源温度以控制传热温差,使测量时散热铜板温度处于最佳温度附近.     

Electrical characteristics of AlInN/GaN HEMTs under cryogenic operation

Electrical properties of an AlInN/GaN high-electron mobility transistor (HEMT) on a sapphire substrate are investi-gated in a cryogenic temperature range from 295 K down to 50 K. It is shown that drain saturation current and conductance increase as transistor operation temperature decreases. A self-heating effect is observed over the entire range of temperature under high power consumption. The dependence of channel electron mobility on electron density is investigated in detail. It is found that aside from Coulomb scattering, electrons that have been pushed away from the AlInN/GaN interface into the bulk GaN substrate at a large reverse gate voltage are also responsible for the electron mobility drop with the decrease of electron density.     

基于多维时空的NPCA-PSR-IGM(1,1)组合模型的短时交通流预测

针对城市短时交通流序列非线性和混沌性的特点,为提高短时交通流的预测精度,该文提出一种基于多维时空的非线性主成分分析(NPCA)和相空间重构(PSR)的改进灰色(IGM(1,1))组合预测模型。首先,使用数据相关性的非线性主成分分析算法对多维交通流量序列进行时空降维,同时保留影响预测点的主要交通流量数据,从而提高建模的精确度;其次,利用多维时空交通流量序列相空间重构放大交通流量内部的细微特征,以使其内在规律得以充分展现,进一步提升预测精度;最后,结合背景值改进的灰色模型适应于线性、非线性以及所需数据少的特点,进行短时交通流预测。实验结果表明,NPCA-PSR-IGM(1,1)组合预测模型的平均相对误差相比NPCA-PSR-GM(1,1)组合预测模型减小3.12%,其标准偏差相对PCA-PSR-IGM(1,1)组合预测模型从15.7091下降到2.0589。同时与最新的预测模型相比,该组合预测模型也提高了预测精度,达到了较好的预测效果。     

超声和钼靶X线检查对更年期女性乳腺微小肿块的诊断比较

本研究的目的是探讨超声和钼靶X线检查在更年期女性乳腺微小肿块诊断中的价值。选取乳腺微小肿块更年期女性患者115例,其中良性与恶性病变分别为79例和36例。患者均进行超声和钼靶X线检查,分析两种方法的图像特征及诊断价值。恶性病变超声图像边缘不光滑、有微钙化、纵横比>0.8比例、钼靶微小钙化比例明显高于良性病变(P<0.05);超声诊断恶性病变的灵敏性、准确性和阴性预测值明显高于钼靶X线检查(P<0.05)。直径1～2 cm恶性病灶钼靶诊断准确性明显高于直径<1 cm恶性病灶(P<0.05);直径<1 cm恶性病灶时,超声诊断准确性明显高于钼靶X线检查(P<0.05)。超声在更年期女性乳腺微小肿块诊断中的价值优于钼靶X线检查,尤其在直径<1 cm病灶中。     

DNA依赖的蛋白激酶抑制剂STL127705的合成工艺研究

DNA依赖的蛋白激酶（DNA-PK）是肿瘤治疗的一个潜在靶点,其抑制剂具有增强放化疗敏感性的作用。STL127705是一种有效的DNA-PK抑制剂,本文采用逆合成分析,以2-甲硫醚-4-氯嘧啶-5-基甲酸乙酯为起始原料,先后经过氨化、水解、酰胺缩合、合环、氧化、取代等6步反应制备得到目标化合物,总收率为36.8%,纯度达到95.5%,产物结构通过1H-NMR、13C-NMR、MS等表征。     

ADENYLATE CYCLASE-MODULATING MEDIATORS OF INSULIN

Plasma membranes prepared from pig liver incubated with insulin (50—300 μU/ml) resulted in the release of at least two insulin chemical mediators. They appeared to modulate the activity of adenylate cyclase in liver plasma membrances of pig. One of them was fraction 1 of insulin mediator (M. W. about 3700—4000 dalton) which markedly stimulated the activity of the enzyme, the other was fraction 2 of insulin mediator (M. W. about 1000 dalton) which inhibited the enzyme activity. The results showed that the inhibitor of fraction 2 generated was significantly higher than that of fraction 1 when the membranes were incubated with insulin of low concentration (50—100 μU/ml). On the other hand, the generation of stimulator of fraction 1 from plasma membranes incubated with insulin of high concentration (200 μU/ml) was higher than that of fraction 2. So the ratio of yield between two mediators produced from the membranes was dependent on the concentration of insulin added. The results also showed that the     

2000年全国高中学生化学竞赛（初赛）试题及答案的讨论

化学教育2001年第1期刊登的“2000年全国高中学生化学竞赛（初赛）试题”命题形式新颖,特别是紧密结合了当代化学发展的前沿,给人以耳目一新的感觉。在考察学生运用所学知识解决实际问题能力的同时,又对学生进行了化学新领域、新信息的传授,对培养学生创造性思维、提高对化学的兴趣起了非常好的作用。