环式M(SO2)(M=Zn, Cd)分子及其阴离子的基质隔离红外光谱和密度泛函理论计算

激光溅射锌和镉原子与SO₂分子反应的低温基质隔离红外光谱实验表明,在氩和氖的惰性基质中,形成了环式M(SO₂)分子及其阴离子M(SO₂)^- (M=Zn, Cd)．相关同位素(³⁴SO₂和S¹⁸O₂)替代实验及密度泛函理论计算均证实了这一结果．此外,自然电荷布居分析表明电子从金属锌和镉的s轨道转移到了SO₂配体上形成了M⁺(SO₂)^-“离子对”复合物,且该分子中的Zn-O键以及Cd-O键均表现出强的极化共价性．而Hg原子在与SO₂反应中所表现出来的惰性可由其较强的相对论效应所致的6s价电子层收缩与高电离电位得以解     

Shifting the Superparamagnetic Limit of Nanosized Copper Iron Spinel

In this paper we analyze trend of EFG values measured at Cd impurity in a group of semiconducting delafossites with chemical formula CuBO₂ (B = Al, Fe, Cr, Nd). We conclude that this trend reveals one of the most subtle details in electronic spectrum of the compounds: if impurity states are formed within or out of the band gap. In CuAlO₂ and CuFeO₂ the Cd EFG exhibits larger value than in CuCrO₂ and CuNdO₂, when Cd substitutes the Cu atom. This occurs because in the first two compounds the Cd forms shallow band within the gap, and in the second two compounds does not. When Cd occupies the B position it exhibits almost the same EFG in all delafossites. In this case, Cd does not form its states within the gap in none of the compounds. To arrive to these conclusions we analyzed and calculated various systems (Cd-doped CuAlO₂ and CuCrO₂ compounds, fictitious molecules), using the FP-LAPW method.     

基于权重比的民航飞行员安全行为指标权重算法

确定飞行员安全行为指标的权重,对发现民航飞行员飞行安全风险的短板,提高民航飞行安全性具有重要意义.基于指标权重比,提出了一种飞行员安全行为指标权重算法.并以此算法分析了职业安全意识、飞行情景意识、特情应变能力以及机组资源管理能力等指标对飞行员安全行为的影响程度,研究可为飞行员安全行为风险管理提供依据,对安全飞行具有积极的指导意义.     

Inherent Conformational Preferences of Ac‐Gln‐Gln‐NHBn: Sidechain Hydrogen Bonding Supports a β‐Turn in the Gas Phase

Gas‐phase single‐conformation spectroscopy is used to study Ac‐Gln‐Gln‐NHBn in order to probe the interplay between sidechain hydrogen bonding and backbone conformational preferences. This small, amide‐rich peptide offers many possibilities for backbone–backbone, sidechain–backbone, and sidechain–sidechain interactions. The major conformer observed experimentally features a type‐I β‐turn with a canonical 10‐membered ring C=O—H?N hydrogen bond between backbone amide groups. In addition, the C=O group of each Gln sidechain participates in a seven‐membered ring hydrogen bond with the backbone NH of the same residue. Thus, sidechain hydrogen‐bonding potential is satisfied in a manner that is consistent with and stabilizes the β‐turn secondary structure. This turn‐forming propensity may be relevant to pathogenic amyloid formation by polyglutamine segments in human proteins.     

The boundedness and asymptotic behavior of solutions of differential system of second-order with variable coefficients

In this paper, the differential system of second-order withvariable coefficients is studied. and some criteria of theboundedness and asymptotic behavior for solutions are given.Consider a system of differential equationsdx_1/dt=p_(11)(t)x_1 p_(12)(t)x_2dx_2/dt=p_(21)(t)x_1 p_(22)(t)x_2Now we studg the boundedness and asymptotic behavior of its so-lutions. In the case of Pij(t)being periodic functions. it wasinvestigated by Burdina; in the case of Pij(t) being arbitraryfunctions. it has not been investigated yet. Besides. the me-thod used by Burdina is only oppropriate for the former but notfor the latter case. In this paper we shall give a method whichis appropriate for both cases.     

Pressure controllable phase transition in MoTe2 by the interlayer band occupancy

High pressure can effectively control the phase transition of MoTe₂ in experiment, but the mechanism is still unclear. In this work, we show by first-principles calculations that the phase transition is suppressed and $1T^{\prime }$ phase becomes more stable under high pressure, which originates from the pressure-induced change of the interlayer band occupancies near the Fermi energy. Specifically, the interlayer states of $1T^{\prime }$ phase tend to be fully occupied under high pressure, while they keep partially occupied for the $T_d$ phase. The increase of the band occupancies makes the $1T^{\prime }$ phase more favorable in energy and prevents the structure changing from $1T^{\prime }$ to $T_d$ phase. Moreover, we also analyze the superconductivity under high pressure based on BCS theory by calculating the density of states and phonon spectra. Our results may shed some light on understanding the relationship between the interlayer band occupancy and crystal stability of MoTe₂ under high pressures.     

Effects of temperature and pressure on thermodynamic properties of Cd0.25Zn0.75 alloy

Thermodynamic properties of Cd_0.25Zn_0.75Se alloy are studied using quasi harmonic model for pressure range of 0 GPa-10 GPa and temperature range 0 K-1000 K. The structural optimization is obtained by self-consistent field calculations and full-potential linearized muffin-tin orbital method with GGA+U as an exchange correlation functional where U=2.3427 eV is Hubbard potential. The effects of temperature and pressure on bulk modulus, Helmholtz free energy, internal energy, entropy, Debye temperature, Grüneisen parameter, thermal expansion coefficient, and heat capacities of the material are observed and discussed. The bulk modulus, Helmholtz free energy, and Debye temperature are found to be decreased on increasing temperature while there is an increasing behavior with rise of the pressure. Whereas the internal energy has increasing trend with the rise in temperature and it almost remains insensitive to pressure. The entropy of the system increases (decreases) with rise of pressure (temperature).     

Making Use of Incomplete Observations for Regression in Bivariate Normal Model

Two estimates of the regression coefficient in bivariate normal distribution are considered: the usual one based on a sample and a new one making use of additional observations of one of the variables. They are compared with respect to variance. The same is done for two regression lines. The conclusion is that the additional observations are worth using only when the sample is very small.     

颗粒内传质参数作为工具用于催化剂颗粒的设计(英文)

A chromatographic method and a dynamic Wicke-Kallenbach method (DMWK) were used to determine the diffusion characteristics of two industrial copper containing catalysts. The first catalyst was used in nitrobenzene hydrogenation to aniline and the second was used in a low temperature water-gas shift reaction. Experimental results show that application of these two methods leads to similar results. Experimental data obtained allow for monitoring changes in the texture of the catalyst grains and intraparticle diffusivity of gaseous reagents at different states of the catalyst activity and use, which can be used as criteria for designing optimal industrial catalyst pellets.     

一个具最佳常数的复合核积分不等式

引入Γ-函数等特殊函数,利用权函数方法和实分析技巧,建立一个具最佳常数的复合核积分不等式.考虑了它的等价式,证明了它们的常数因子是最佳的,并通过取特殊的参数值,得到一些有意义的结果.