金属离子与腺嘌呤异构体复合物的稳定性

在B3LYP/6-311++G**//6-31+G*基组水平上结合PCM模型系统的优化了气相和液相环境中14种腺嘌呤异构体与四种金属离子(Na+,K+,Mg2+,Ca2+)形成的132个稳定复合物。通过能量对比,得到了所有复合物异构体在气液两相中的稳定性顺序及不同金属离子与同一异构体形成的复合物的能量排序,首次给出了液相中这些不同金属离子复合物的最稳定结构。结果发现溶剂效应导致了液相中的复合物稳定性顺序与气相中的相比发生了很大变化;同一异构体与不同金属离子形成的复合物其稳定性在排序中也变化很大。对于这些变化,本文分别从金属离子与腺嘌呤的复合物在气相中的结合能(EBE)及在液相中的溶质溶剂相互作用能(Epol)能等方面进行了系统的阐述     

Effect of Mn substitution on superconductivity in iron selenide(Li,Fe)OHFeSe single crystals

We synthesize a series of Mn substituted(Li, Fe)OHFeSe superconductor single crystals via a modified ion-exchange method, with the Mn concentration z(the atomic ratio of Mn:Se) ranging from 0 to 0.07. The distribution homogeneity of the Mn element incorporated into the lattice of(Li, Fe)OHFeSe is checked by combined measurements of high-angleannular-dark-field(HAADF) imaging and electron energy-loss spectroscopy(EELS). Interestingly, we find that the superconducting transition temperature T_c and unit cell parameter c of the Mn-doped(Li, Fe)OHFeSe samples display similar V-shaped evolutions with the increasing dopant concentration z. We propose that, with increasing doping level, the Mn dopant first occupies the tetrahedral sites in the(Li, Fe)OH layers before starting to substitute the Fe element in the superconducting Fe Se layers, which accounts for the V-shaped change in cell parameter c. The observed positive correlation between the T_c and lattice parameter c, regardless of the Mn doping level z, indicates that a larger interlayer separation, or a weaker interlayer coupling, is essential for the high-T_c superconductivity in(Li, Fe)OHFeSe. This agrees with our previous observations on powder, single crystal, and film samples of(Li, Fe)OHFeSe superconductors.     

残余应力分析方法比较:X射线衍射法与应力释放法

残余应力分析方法主要有衍射法、应力释放法和声、光、磁等方法。其中,X射线衍射法与应力释放中的钻孔技术与理论最为成熟,应用最广。在应力均匀且数值较小时,两者可以给出相互接近的结果。然而当样品微小且微观结构复杂时,两者给出的结果会有明显的差异。本文利用上述两种方法对同一纯铜样品表面的残余应力进行分析,对比分析结果并讨论了相关的影响因素。我们对X射线衍射法与环芯法的适用性进行了讨论:前者适用于晶体材料的无损检测,而后者更能反映当前应力水平。此外,对方法的选用需要考虑应力测试的目的。     

Controllable synthesis of high aspect ratio Mg_2B_2O_5 nanowires and their applications in reinforced polyhydroxyalkanoate composites

Highly pure magnesium borate （Mg2B2O5） nanowires with an average diameter of - 30 nm, an average length of 15 μm, and a high aspect ratio of - 500 have been synthesized on a large scale via a two-step method. MgBO2（OH） nanowires with high aspect ratios were first prepared via a PVP-assisted hydrothermal technique. Using these nanowires as precursors, single crystalline Mg2B205 nanowires were synthesized by post-annealing treatment at a relatively low temperature of 700 ℃. The important effect of the MgBO2（OH）-Mg2B2O5 conversion process on the morphology of the Mg2B2O5 nanowires was investigated and it was indicated that the recrystallization process plays an important role in the protection of the one-dimensional （1D） nanostructure. Moreover, the rigidity and the toughness of the Mg2B2O5 nanowire- reinforced PHA composites were tremendously improved compared to those of the pure PHA. Our results demonstrate the effectiveness of Mg2B2O5 nanowires for reinforcement applications in polymer composites.     

Effects of interface roughness on photoluminescence full width at half maximum in GaN/AlGaN quantum wells

Low temperature photoluminescence(PL) measurements have been performed for a set of GaN/AlxGa1-xN quantum wells(QWs). The experimental results show that the optical full width at half maximum(FWHM) increases relatively rapidly with increasing Al composition in the AlxGa1-xN barrier, and increases only slightly with increasing GaN well width. A model considering the interface roughness is used to interpret the experimental results. In the model, the FWHM’s broadening caused by the interface roughness is calculated based on the triangle potential well approximation. We find that the calculated results accord with the experimental results well.     

AlGaN合金中局域态和极化电场的竞争机制

通过MOVPE方法生长了不同Al组分的3块Al_xGa_1-xN样品,利用稳态光谱和时间分辨光谱对其样品的光学特性进行了分析。鉴于影响氮化物发光性质的极化电场或局域态的单一机制不能充分解释我们的实验现象,提出了局域态-内部极化电场竞争的机制。通过对实验数据的分析,得出如下重要结论：样品PL峰位蓝移的温度起点基本对应于局域态和极化电场起作用的交替点,PL峰位发生蓝移的温度起点与光强-温度曲线的斜率出现明显变化的温度点一致;随着温度的升高,若AlGaN合金样品中PL峰位存在二次蓝移,则说明样品中电场分布不均匀。     

炸药水中爆炸冲击因子的新型计算方法

针对水中爆炸冲击因子在近场范围内的一些不足,利用水中爆炸冲击波的最大峰值压力与正相冲量的乘积推导了冲击因子的表达式。通过水中爆炸实验,得到了几种典型炸药的冲击波参数及其相似方程。利用该公式计算了水中爆炸冲击因子及其装药指数,并与基于平面波的水下爆炸冲击因子进行了对比。结果表明:冲击因子中的装药指数n＝0.5不仅适合所有以TNT为基本组分的炸药,也适合于RDX、HMX基的炸药。在修正冲击波形状的基础上,由峰值压力与冲量的乘积推导的冲击因子计算公式,从冲击波的毁伤作用的角度表述了水中爆炸冲击因子的物理意义,在计算近场冲击因子时具有更高的准确性。     

2-位碲桥联环糊精的制备、表征及其谷胱甘肽过氧化物酶活性的研究

该文以三种母体环糊精(CD),即α-、β-和γ-CD为修饰模板,将功能性基团有机碲引入到环糊精次面的2位羟基上,制备得到了三种具有谷胱甘肽过氧化物酶(GPX)活性的GPX模拟物。采用元素分析、红外光谱、核磁共振等手段对三种环糊精衍生物的结构进行了表征。运用GPX经典双酶体系法测定了三种环糊精衍生物的GPX活性,实验结果表明三者均具有很高的催化活性,其中2-位碲桥联γ-环糊精(2-Te-γ-CD)具有最高的GPX活性,其催化谷胱甘肽(GSH)还原过氧化氢(H2O2),叔丁基过氧化氢(t-BuOOH)和枯烯过氧化氢(CuOOH)的活力分别是传统"小分子硒酶"Ebselen的80.5,333.3和118.3倍。     

Electronic Phase Separation in Iron Selenide(Li,Fe)OHFeSe Superconductor System

The phenomenon of phase separation into antiferromagnetic(AFM) and superconducting(SC) or normal-state regions has great implication for the origin of high-temperature(high-T_c) superconductivity. However, the occurrence of an intrinsic antiferromagnetism above the T_c of(Li,Fe)OHFe Se superconductor is questioned. Here we report a systematic study on a series of(Li,Fe)OHFe Se single crystal samples with T_c up to ～41 K. We observe an evident drop in the static magnetization at T_(afm) ～ 125 K, in some of the SC(T_c 38 K, cell parameter c■9.27 ?) and non-SC samples. We verify that this AFM signal is intrinsic to(Li,Fe)OHFe Se. Thus, our observations indicate mesoscopic-to-macroscopic coexistence of an AFM state with the normal(below T_(afm)) or SC(below T_c) state in(Li,Fe)OHFe Se. We explain such coexistence by electronic phase separation, similar to that in high-T_c cuprates and iron arsenides. However, such an AFM signal can be absent in some other samples of(Li,Fe)OHFe Se, particularly it is never observed in the SC samples of T_c 38 K, owing to a spatial scale of the phase separation too small for the macroscopic magnetic probe. For this case, we propose a microscopic electronic phase separation. The occurrence of two-dimensional AFM spin fluctuations below nearly the same temperature as T_(afm), reported previously for a(Li,Fe)OHFe Se(T_c ～ 42 K) single crystal, suggests that the microscopic static phase separation reaches vanishing point in high T_c(Li,Fe)OHFe Se. A complete phase diagram is thus established. Our study provides key information of the underlying physics for high-T_c superconductivity.     

济南地区表层土壤及沉积物中饱和烃分布特征及源解析

研究了济南地区不同功能区的表层土壤及沉积物中饱和烃的组成和分布特征,在此基础上初步分析了其来源.结果表明,饱和烃主要有正构烷烃、类异戊二烯、环烷烃等组成,正构烷烃碳数分布范围为n-C10-n-C34,类异戊二烯类主要是姥姣烷、植烷及甲基C13-C17烷等,同时还检出烷基环己烷,甾烷、三萜烷及藿烷等环烷烃.饱和烃总体含量分布为北高南低,北部化工区、高速入口处等饱和烃主要来源于原油或成品油等化石燃料及其燃烧产物;南部山区、水库沉积物及农田土壤等饱和烃主要来源于化石燃料的燃烧及高等植物.