紫外-可见光谱法快速测定丁酮过氧化氢反应体系中的乙酸乙酯

提出了一种基于紫外-可见光谱法快速测定乙酸乙酯的方法。研究表明,在经盐酸羟胺乙醇及三氯化铁进行显色反应后,乙酸乙酯在530 nm处具有最大吸收峰。因此,通过双波长法,乙酸乙酯可以被定量检测。此方法简单、快速,且具有较合理的测定精密度和准确性,适合用于化工合成转化领域中乙酸乙酯制备的研究。     

First-principles analysis of the structural,electronic, and elastic properties of cubic organic-inorganic perovskite HC(NH_2)_2PbI_3

The structural, electronic, and elastic properties of cubic HC(NH_2)_2PbI_3 perovskite are investigated by density functional theory using the Tkatchenko–Scheffler pairwise dispersion scheme. Our relaxed lattice parameters are in agreement with experimental data. The hydrogen bonding between NH_2 and I ions is found to have a crucial role in FAPbI_3 stability. The first calculated band structure shows that HC(NH_2)_2PbI_3 has a direct bandgap(1.02 eV) at R-point, lower than the bandgap(1.53 eV) of CH_3NH_3PbI_3. The calculated density of states reveals that the strong hybridization of s(Pb)–p(I) orbital in valence band maximum plays an important role in the structural stability. The photo-generated effective electron mass and hole mass at R-point along the R–Γ and R–M directions are estimated to be smaller: m_e~*= 0.06 m0 and m_h~*= 0.08 m0 respectively, which are consistent with the values experimentally observed from long range photocarrier transport. The elastic properties are also investigated for the first time, which shows that HC(NH_2)_2PbI_3 is mechanically stable and ductile and has weaker strength of the average chemical bond. This work sheds light on the understanding of applications of HC(NH_2)_2PbI_3 as the perovskite in a planar-heterojunction solar cell light absorber fabricated on flexible polymer substrates.     

Structural,elastic, electronic,and thermodynamic properties of MgAgSb investigated by density functional theory

The structural, elastic, electronic, and thermodynamic properties of thermoelectric material Mg Ag Sb in γ, β, α phases are studied with first-principles calculations based on density functional theory. The optimized lattice constants accord well with the experimental data. According to the calculated total energy of the three phases, the phase transition order is determined from α to γ phase with cooling, which is in agreement with the experimental result. The physical properties such as elastic constants, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and anisotropy factor are also discussed and analyzed, which indicates that the three structures are mechanically stable and each has a ductile feature. The Debye temperature is deduced from the elastic properties. The total density of states(TDOS) and partial density of states(PDOS) of the three phases are investigated. The TDOS results show that the γ phase is most stable with a pseudogap near the Fermi level, and the PDOS analysis indicates that the conduction band of the three phases is composed mostly of Mg-3s,Ag-4d, and Sb-5p. In addition, the changes of the free energy, entropy, specific heat, thermal expansion of γ-MgAgSb with temperature are obtained successfully. The obtained results above are important parameters for further experimental and theoretical tuning of doped MgAgSb as a thermoelectric material at high temperature.     

额外维紧致球空间的变形与K-K粒子质量的修正计算

本文根据高维时空中的Einstein宇宙学场方程研究了额外维空间的变形和K-K粒子质量的修正.在模型中假定内部空间中存在高阶U(1)规范场和真空能密度的作用,然后分别计算了紧致单球和紧致双球的半径和对应的K-K粒子质量.另外,通过内部球度规的单参量变形和双单参量变形计算了半径和K-K粒子质量的修正值,还分析和讨论了额外维数目和变形效应对内部球半径和K-K粒子质量的影响.本文还研究了单球和双球紧致化中涨落解的变化规律,即假定围绕标度因子的静态解产生随时间变化的微小涨落,仔细分析了Einstein场方程对应的线性涨落方程解的增长性质.结果发现单球和双球紧致化中涨落解都可以达到稳定状态,这一结论和标量场势能的稳定性结果完全一致,因此时空上度规涨落可以导致K-K粒子质量的产生.     

一种改进的认知无线电信道选择方法

认知无线电可以通过动态频谱接入技术来有效的提高频谱的利用率,而在动态频谱接入中信道选择策略的优劣直接影响着系统的性能.提出了一种新的基于预测信道空闲概率的信道选择方法.仿真实验表明,该方法能有效减小主次用户之间的碰撞率,从而减小了认知用户对主用户的干扰以及降低了进行信道切换的可能.     

收音机改装的射线探测器

在讲解物质的放射性这一题目时,有一具射綫探側仪将是很方便的。但是射线探测仪是比较贵重的仪器,一般中学里是沒有的。为了解决这一问题,我們可以利用收音机略加改装,使它成为一具简单的射线探测仪。收音机的改装工作很簡单。