用一种新式的串珠分子模型来介绍分子的点群

利用生活中常见的串珠编制分子模型,得到了一系列属于不同点群的C84同分异构体的串珠分子模型。这些模型可作为可视化教具,帮助学生理解抽象的分子点群的相关知识,也可以作为科普产品向大家介绍与对称性相关的知识。     

Instability in a Vlasov–Fokker–Planck binary mixture

This paper is concerned with a kinetic model of a Vlasov–Fokker–Planck system used to describe the evolution of two species of particles interacting through a potential and a thermal reservoir at given temperature. We prove that at low temperature, the homogeneous equilibrium is dynamically unstable under certain perturbations. Our work is motivated by a problem arising in [4].     

WGS84椭球下的UTM坐标与Clarke80椭球下的兰勃特坐标转换方法研究

介绍了两种椭球下的两种投影之间的坐标转换方法.在进行坐标转换时,WGS84椭球下的UTM坐标首先被转换成地理坐标,然后被转换成笛卡尔坐标;采用7参数法,可得到Clarke80椭球下的笛卡尔坐标,通过相应的坐标变换模型便可计算出该椭球下的大地坐标以及相应的兰勃特坐标.在给定了坐标系之间的7个转换参数以及单标准线的兰勃特投影(1SP)参数时,采用本方法WGS84椭球下的UTM和大地坐标可以很容易地被转换成Clarke80椭球下的大地坐标和兰勃特坐标,其转换精度优于0.1 m,适用于很多应用领域.     

Pressure Response of the Higher Fullerene C 84 Studied by Raman and X-ray Scattering

The pressure behavior of the intramolecular phonon modes of the fullerene C 84 and its structural stability have been studied for the first time by means of Raman spectroscopy and synchrotron X-ray diffraction at high pressure up to ～10 GPa. The volume of the cubic unit cell has been measured as a function of pressure. The experimental data fitted by the Murnaghan equation-of-state (EOS) gave K_{0}=19.5\pm 0.9\,\hbox{GPa} and K_{0}^{\prime}=16.4\pm 0.6 . The pressure coefficients and Grüneisen parameters of the intramolecular phonon modes of C 84 have been determined and compared with those of other fullerenes. The data obtained do not show any phase transition and the pressure behavior of the material is entirely reversible in the pressure region investigated.     

Spectral property and its shape transition on 72—84Kr isotopes in microscopic core plus two—quasiparticle approach

By using a microscopic sdIBM-2+2q.p. approach, the levels of the ground-band, γ-band and partial two-quasi-particle bands for {}^{72-84}Kr isotopes are calculated. The data obtained are in good agreement with the recent experimental results, and successfully reproduce the nuclear shape phase transition of {}^{72-84}Kr isotopes at zero temperature. The ground-state band is described successfully up to J^π=18^+ and E_x=10.0MeV. Based on this model, the aligned requisite minimum energy has been deduced. The theoretical calculations indicate that no distinct change of nuclear states is caused by the abruptly broken pair of a boson, and predict that the first backbending of Kr isotopes may be the result of aligning of two quasi-neutrons in orbit g_{9/2}, which gains the new experimental support of the measurements of g factors in the {}^{78-86}Kr isotopes.     

Boundary feedback stabilization of the undamped Timoshenko beam with both ends free

In this paper, we study a boundary feedback system of a class of nonuniform undamped Timoshenko beam with both ends free. We give some sufficient conditions and some necessary conditions for the system to have exponential stability. Our method is based on the operator semigroup technique, the multiplier technique, and the contradiction argument of the frequency domain method.     

Interrelation between electronic structure and interatomic distances for compounds

The heat capacity was studied for LaMn₂Si₂, La_0.75Y_0.25Mn₂Si₂, La_0.7Y_0.3Mn₂Si₂, YMn₂Si₂ and LaFe₂Si₂ isostructural intermetallic compounds in the temperature range 1.8–360 K. The electronic, magnetic and lattice contributions to the heat capacity of the compounds were determined and analyzed. The interrelation was found between values of the electronic contribution to the heat capacity (density of states at the Fermi level) and crystal lattice parameters of R(Mn,Fe,Ni)₂Si₂ compounds. The electronic contribution and the density of states at Fermi level increase with increasing lattice parameters of the compounds. The change of interlayer Mn–Mn exchange interactions with change of Y concentration in La_1-xY_xMn₂Si₂ compounds is not accompanied by considerable changes in the electronic contribution to the heat capacity and density of states at the Fermi level. The performed analysis of the magnetic contribution shows that no essential differences exist between the behavior of the heat capacity of the compounds with d_Mn–Mnd_c and with d_Mn–Mn<d_c upon various types of the magnetic phase transitions.     

Magnetic properties of the spinel-type

The spinel sulphide CuCr₂S₄ is a metallic ferromagnet with a Curie temperature , while CuHf₂S₄ has no magnetic anomaly. Magnetic properties of the quaternary spinel-type Cu(Cr_1-xHf_x)₂S₄ system have been studied. With increasing x the ferromagnetic properties are weakened gradually from a predominant ferromagnetic, a spin-glass, finally to a simple paramagnetic behavior. For the composition of x0.50, a re-entrant spin-glass phase could emerge, even though the Curie temperature is ill-defined as a ferromagnetic phase boundary. Specimens with x≥0.90 remain paramagnetic down to 4.2 K. A spin crossover phenomenon is found around 160 K in the specimens of x=0.50–0.70. A step-like anomaly is manifestly detected in the magnetization, which corresponds with the change of the spin state. This crossover indicates that the spin state converts from high temperature S=2 into low temperature states. In the ordered states in , the magnetic moment originates from only Cr³⁺ ions.     

On semi-R-boundedness and its applications

R-Boundedness is a randomized boundedness condition for sets of operators which in recent years has found many applications in the maximal regularity theory of evolution equations, stochastic evolution equations, spectral theory and vector-valued harmonic analysis. However, in some situations additional geometric properties such as Pisier's property (α) are required to guaranty the R-boundedness of a relevant set of operators. In this paper we show that a weaker property called semi-R-boundedness can be used to avoid these geometric assumptions in the context of Schauder decompositions and the H^∞-calculus. Furthermore, we give weaker conditions for stochastic integrability of certain convolutions.