Residual closeness in networks

A new characteristic (residual closeness) which can measure the network resistance is presented. It evaluates closeness after removal of vertices or links, hence two types are considered—vertices and links residual closeness. This characteristic is more sensitive than the well-known measures of vulnerability—it captures the result of actions even if they are small enough not to disconnect the graph. A definition for closeness is modified so it still can be used for unconnected graphs but the calculations are easier.     

亚纯函数的导函数分担集合的唯一性

研究了两个亚纯函数的导函数分担两个值集的唯一性问题. 证明了对于集合$S$和$T$, 如果$\overline{E}_{f^{(k)}}(S)=\overline{E}_{g^{(k)}}(T)$, 则存在非零常数$A$, 使得$f^{(k)}=Ag^{{(k)}}$. 特别地, 当$k=0$时, 有$f=Ag$.     

求解广义绝对值方程的交替牛顿矩阵多分裂方法

本文针对广义绝对值方程,提出了基于牛顿法的矩阵多分裂方法.并在该方法的基础上进一步改进,得到了基于牛顿法的交替矩阵多分裂方法.给出两种算法在一定条件下的全局收敛性,并分析当分裂为H分裂时,基于牛顿法的矩阵多分裂方法的收敛条件.通过数值实验验证了所提出的算法的可行性和有效性.     

大气降雨俘获空气中短寿命氡子体实验研究

为了研究降雨对空气中短寿命氡子体的清洗机制,设计了分别模拟大气降雨的水汽凝结过程和雨粒下降过程的两个实验装置,并进行了多次实验,实验水样采用低本底 能谱仪进行测量。实验结果表明:凝结水的短寿命放射性计数与本底相近,说明水汽凝结不能俘获短寿命氡子体。某一次自来水冲刷空气后获得了高出本底30.9% 的初始 计数,其半衰期为35.7 min,纯净水冲刷空气后获得了高出本底19.6%的初始计数,这些计数主要是由氡子体214Pb 和214Bi 引起的。可见,无论是自来水还是纯净水,它们冲刷空气后都能俘获短寿命氡子体,且半衰期和放射性核素种类均与雨水相似。这一实验结果充分说明:大气降雨的短寿命放射性不是在水汽凝结阶段而是在降落阶段对空气的冲刷获得的,是在降落过程中俘获了空气中的短寿命氡子体214Pb 和214Bi 而引起的。本次实验结果为降雨对空气中短寿命氡子体的冲刷清洗机制提供了最有力的证据。To investigate the underpinning mechanism of rainfall-scavenging of the atmospheric short-lived radon daughters, two experiments simulating water vapor condensing procedure and raindrop falling procedure were conducted. The radioactivity of the tested water was measured by low-background   γ spectrometry. The obtained results showed that the γ-ray counts of condensed water was on the same level as the background,which proved that water vapor condensation cannot trap short-lived radon daughters. In contrast, the initial γ-ray count of washout water (35.7 min half-life) was increased by 30.9% after washing the atmosphere with tap water. Similarly, the initial  -ray count of washout water was increased by 19.6% after washing the atmosphere with puri ed water. These counts originated mainly from radon daughters 214Pb and 214Bi. Obviously, both tap water and puri ed water can trap short-lived radon daughters when washing the atmosphere. Furthermore, the half-life and the kinds of radioactive nuclides in the washout water are similar to that in the rainfall water.These experimental results are able to ascertain that short-lived radon daughters in precipitation come mainly from scavenging (washout) and not from water vapor condensation within the cloud. It is in the process of falling that raindrops trapped short-lived radon daughters 214Pb and 214Bi. The obtained results as demonstrated here provide a powerful evidence for understanding the washout mechanism of short-lived radon daughters from theatmosphere by rainfall.     

Upconversion luminescence in Tm3+/Yb3+co-doped lead tungstate tellurite glasses

This work reports the upconversion luminescence properties of Tm³⁺/Yb³⁺ ions in lead tungstate tellurite (LTT) glasses. Judd–Oflet intensity parameters have been obtained from the absorption band intensities of Tm³⁺ singly-doped and Tm³⁺/Yb³⁺ co-doped LTT glasses. The spontaneous emission probabilities, radiative lifetimes and branching ratios for ¹G₄ and ³H₄ emission levels of Tm³⁺ have been determined. Upconversion luminescence has been observed by exciting the samples at 980 nm (Yb³⁺:²F_7/2→²F_5/2) at room temperature. Four upconversion emission bands corresponding to the ¹G₄→³H₆ (477 nm), ¹G₄→³F₄ (651 nm), ¹G₄→³H₅ (702 nm) and ³H₄→³H₆ (810 nm) transitions have been identified. The relative variation in the intensities of upconversion bands, the different channels responsible for upconversion spectra and the effect of Yb³⁺ ions concentration on the upconversion luminescence of Tm³⁺ ions have also been discussed.     

Time-Like Conformal Homogeneous Hypersurfaces with Three Distinct Principal Curvatures

A hypersurface x(M) in Lorentzian space R_1~4 is called conformal homogeneous,if for any two points p, q on M, there exists σ, a conformal transformation of R_1~4, such thatσ(x(M)) = x(M), σ(x(p)) = x(q). In this paper, the authors give a complete classification for regular time-like conformal homogeneous hypersurfaces in R_1~4 with three distinct principal curvatures.     

Cr二维单层薄片中Jahn-Teller效应的第一性原理研究

采用基于密度泛函理论的第一性原理计算,本文对Cr单层薄片的一系列二维结构（长方、正方、六角、斜方和中心长方晶格）进行了结构稳定性和电子性质研究.结果表明,在Cr的二维体系中,对称性较低的斜方晶格和中心长方晶格是稳定的,对称性较高的正方和六角晶格是不稳定的,而长方晶格的形成能很小.Cr二维原子薄片的两种稳定结构都是六角结构畸变的结果,六角晶格的键角减小时会形变成斜方晶格,键角增大时会形变成中心长方晶格,这是由于Jahn-Teller效应使简并能级自发破缺,继而结构产生降低对称性的形变,最终使得体系变得稳定.     

Extremely fast ambipolar diffusion in n-i-p-i doping superlattices investigated by an all-optical pump-and-probe technique

We report on investigations of the ambipolar diffusion process in n-i-p diodes and n-i-p-i doping superlattices performed by a new all-optical pump-and-probe technique. This new technique allows not only the determination of the ambipolar diffusion coefficient but also the spatially resolved investigation of the stationary distribution of the optically-induced excess carriers. The n-i-p-i doping superlattice exhibited an extremely large ambipolar diffusion coefficient in the range of 10⁴cm²s⁻¹. The ambipolar diffusion coefficient of the n-i-p and n-i-p-i structure was demonstrated not to be a constant but a function of the charge carrier density. This strongly affects the spatial distribution of the excess carriers especially in the large signal regime (density of photo-generated carriers much larger than dark carrier concentration). The spatial distribution of the carriers in the small as well as in the large signal case can be understood theoretically if the real dependence of the ambipolar diffusion coefficient on the carrier density is taken into account.