甘氨酸-苯丙氨酸-甘氨酸-甘氨酸四肽气相稳定构型的系统寻找

利用PM3、HF和BHandHLYP方法的结合,系统寻找了甘氨酸-苯丙氨酸-甘氨酸-甘氨酸(GFGG)四肽在气相中的稳定构型．对该构型寻找方法进行了详细的描述,并给出了一些重要构型的基本参数,如电子能、零点振动能、偶极矩、转动常数、垂直电离能和不同温度的构型分布等．通过对重要构型结构特征的分析,发现熵的效应是决定构型稳定性的重要因素,并讨论指出了对构型偶极矩和特征振动模的测量是验证理论预言的有效途径．对GFGG构型与蛋白质二级结构的联系的分析表明,GFGG低能构型出现了类似于α-螺旋的局域结构,以及数量可观的蛋白质β转角和γ转角的局域结构.     

氢化石墨烯作为不含金属的催化剂用于催化类Fenton反应

采用室温辐照还原与氢化的方法制备氢化石墨烯. 透射电子显微镜、元素分析、X射线光电子能谱和紫外可见光谱等测试证实了获得的产物为氢化石墨烯. 以该氢化石墨烯为不含金属的催化剂进行了类Fenton反应,发现其有高的催化活性,可以用于水中有机物的氧化降解.     

糠醇辅助的聚合凝胶法制备纳米Li4Ti5O12负极材料

以硝酸锂、钛酸正丁酯和糠醇为反应物,采用糠醇聚合凝胶法制备了纳米Li₄Ti₅O₁₂粉体．利用XRD、SEM和BET比表面测试对产物进行了表征,并研究了纳米Li₄Ti₅O₁₂粉体作为锂离子电池负极材料的电化学性能．在700℃或更高温度烧结时产物为纯相的尖晶石型．通过柠檬酸、聚乙烯吡咯烷酮、十六烷基三甲基溴化铵(CTAB)表面活性剂的加入能够减少产物颗粒的团聚程度,增大粉体的比表面积,提高其电化学性能．加入0.5 g CTAB、700℃烧结12 h的Li₄Ti₅O₁₂粉体展示出最高的比容量和最佳的循环性能,10 C下充电比容量高达156.7 mAh/g．     

SiN掺杂提高BaMgAl10O17:Eu2+荧光粉光学性能的第一性原理研究

使用基于密度泛函理论的CASTEP软件计算了BAM:Eu²⁺(BaMgAl₁₀O₁₇:Eu²⁺)荧光粉在SiN掺杂前后的能带、态密度、吸收光谱和Mulliken布居．Eu²⁺处于BR位置光吸收更强;SiN掺杂使处于BR位置的Eu²⁺的数量上升,而处于mO位置的Eu²⁺的数量下降,抵消了SiN掺杂降低Eu的态密度对光谱的影响．所以适量掺杂的SiN提高了BAM:Eu²⁺荧光粉的吸收发射光谱强度．Si-N键和Eu-N键的Mulliken布居数分别高于Al-O键和Eu-O键, 说明Si-N键和Eu-N键的共价性分别强于Al-O键和Eu-O键．发光中心Eu²⁺局域结构共价性的增强降低了BAM:Eu²⁺镜面层的活性,这是SiN掺杂提高BAM:Eu²⁺+荧光粉光学稳定性的主要原因．     

Charge ordering modulations in a Bi_0.4Ca_0.6MnO₃ film with a thickness of 110 nm

The low temperature sample stage in a transmission electron microscope is used to investigate the charge ordering behaviours in a Bi 0.4 Ca 0.6 MnO 3 film with a thickness of 110 nm at 103 K.Six different types of superlattice structures are observed using the selected-area electron diffraction(SAED) technique,while three of them match well with the modulation stripes in high-resolution transmission electron microscopy(HRTEM) images.It is found that the modulation periodicity and direction are completely different in the region close to the Bi 0.4 Ca 0.6 MnO 3 /SrTiO 3 interface from those in the region a little further from the Bi 0.4 Ca 0.6 MnO 3 /SrTiO 3 interface,and the possible reasons for this are discussed.Based on the experimental results,structural models are proposed for these localized modulated structures.     

Effect of C doping on the structural and electronic properties of LiFePO₄:A first-principles investigation

Using first-principles calculations within the generalized gradient approximation (GGA) +U framework, we investigate the effect of C doping on the structural and electronic properties of LiFePO 4 . The calculated formation energies indicate that C doped at O sites is energetically favoured, and that C dopants prefer to occupy O 3 sites. The band gap of the C doped material is much narrow than that of the undoped one, indicating better electro- conductive properties. To maintain charge balance, the valence of the Fe nearest to C appears as Fe 3+ , and it will be helpful to the hopping of electrons.     

Effective electromagnetic and chiral parameters of chiral composite material

The effective parameters of chiral composite are studied using a simple model, that is, randomly oriented non-interacting wire helices embedded in a nonchiral host medium. It is found that both the effective permittivity and permeability are independent on the handedness of the chiral objects while the effective chirality admittance is dependent. It is also found that when the ratio of the radius of the chiral helix to its pitch is about 0.23, maximum chirality admittance is achieved. The effective parameters of equichiral sample are also discussed.     

High-efficiency continuous-wave diode-pumped Tm:Ho:LuAG laser at 2.1 μm

Continuous Wave (CW) laser action has been observed from a Ho:Tm:LuAG rod at 2.1 m pumped by a diode laser at 785 nm in the temperature range of 77–200 K. The maximum power observed was 1.38 W at an incident power of 4 W at a crystal temperature of 77 K. The optical-to-optical conversion efficiency was observed to be 35.6% at a threshold power of 0.2 W with a 95% output coupling mirror.     

198Bi的高自旋态结构研究

利用能量为85—105MeV的¹⁶O束流,通过¹⁸⁷Re(¹⁶O,5n)反应研究了¹⁹⁸Bi的高自旋态能级结构.用6台BGO(AC)HPGe探测器和一台用于探测低能γ跃迁的平面探测器进行了γ射线的激发函数、γ-γ—t符合及γ射线的角分布测量.基于这些测量,首次建立了包括26条γ跃迁的¹⁹⁸Bi的高自旋能级纲图,确定了一个半寿命为(8.0±3.6)ns,自旋和宇称为15+的同质异能态.基于较重的双奇铋核^200—206Bi能级结构的系统性,定性地对¹⁹⁸Bi的能级结构进行了解释.     

Zn Belavin模型的反射矩阵

本文得到了Zⁿ Belavin模型反射矩阵的矩阵元表达式,在退化到三角极限后,得到了非对角的三角统计模型的反射矩阵.