Stability of Ferromagnetism in Fe, Co, and Ni Metals under High Pressure with GGA and GGA+U

The stability of the ferromagnetic state in Fe, Co, and Ni metals under high pressure is investigated using generalized gradient approximation (GGA) and GGA+U within the density functional theory (DFT). It is found that the ferromagnetic state under pressure is very different for Fe, Co, and Ni metals, and is closely associated with the crystal structure. In the case of Fe, a ferromagnetic bcc ground state is obtained at ambient pressure and a nonmagnetic hcp ground state is found at pressure around 12 and 115 GPa for GGA and GGA+U, respectively. For Co, the phase transition from a ferromagnetic hcp to a nonmagnetic fcc is found around 107 GPa for GGA. In contrast to Fe and Co, a ferromagnetic fcc state in Ni is maintained even at 200 GPa. The calculated results suggest that the suppression of ferromagnetism in Fe, Co, and Ni is due to pressure-induced decrease of the density of state at the Fermi level.     

First-order non-homogeneous q-difference equation for Stieltjes function characterizing q-orthogonal polynomials

In this paper, we give a characterization of some classical q-orthogonal polynomials in terms of a difference property of the associated Stieltjes function, i.e. this function solves a first-order non-homogeneous q-difference equation. The solutions of the aforementioned q-difference equation (given in terms of hypergeometric series) for some canonical cases, namely, q-Charlier, q-Kravchuk, q-Meixner and q-Hahn, are worked out.     

Oscillatory persistent currents in quantum rings: Semiconductors versus superconductors

Persistent currents are a hallmark of superconductivity in metals. To observe those dissipationless currents in a non-superconducting ring, the circumference of the ring must be short enough so that the phase coherence of the electronic wave functions is preserved around the loop. Recent progress in the fabrication of self-assembled semiconductor quantum rings (SAQRs), which can be filled with only a few (1–2) electrons, has offered the unique possibility to study the magnetic-field-induced oscillations in the persistent current carried by a single electron. In this paper, we discuss similarities and distinctions between the behavior of persistent currents in semiconductor and superconductor samples and give an overview of the recent results for oscillatory persistent currents in SAQRs. Although the real SAQR shape differs strongly from an idealized circular-symmetric open ring structure, the Aharonov–Bohm oscillations of the magnetization survive, as observed in low temperature magnetization measurements on In_xGa_1−xAs/GaAs SAQRs.     

Hessians of the Calabi Functional and the Norm Function

We first present a new proof of a result of Calabi, nonnegativeness of the Hessian of the Calabi functional at an extremal Kähler metric. Then we extend the result to the general context of a reductive group action on a Kähler manifold admitting a moment map. Precisely, we show nonnegativeness of the Hessian of the norm function along a complex orbit at a critical point. Mathematics Subject Classification (1991): Primary 53C55; Secondary 53D20, 58E11     

两参数指数分布产品全样本场合下步进应力加速寿命试验损伤失效率模型下的统计分析

本文给出了两参数指数分布产品全样本场合下步进应力加速寿命试验损伤失效率模型下参数的极大似然估计和拟矩估计,并通过Monte-Carlo模拟说明本文方法的可行性.     

The dipole moment of HOCl in vOH=4

Pulsed laser excitation and photofragment detection methods are used to observe the 17_0,17←16_1,16 pure rotational transition within the v_OH=4 vibrational state of HO³⁵Cl. Microwave frequency and Stark effect measurements give ν₀=27484.33(10) MHz and μ_b=1.562(9) D. The dependence of μ_b, which is approximately parallel to the OH bond, on the level of OH stretch excitation appears linear and is consistent with that of H₂O over the same 0-14 000 cm⁻¹ energy range.     

稀土核区三轴超形变全同带

系统地考察了稀土核区三轴超形变带的跃迁能量、角动量增量顺排和动力学转动惯量.研究表明这些三轴超形变带为全同带.     

An upper bound on the expectation of simplicial functions of multivariate random variables

We introduce an upper bound on the expectation of a special class of sublinear functions of multivariate random variables defined over the entire Euclidean space without an independence assumption. The bound can be evaluated easily requiring only the solution of systems of linear equations thus permitting implementations in high-dimensional space. Only knowledge on the underlying distribution means and second moments is necessary. We discuss pertinent techniques on dominating general sublinear functions by using simpler sublinear and polyhedral functions and second order quadratic functions.     

指数分布串—并联混合系统产品的统计分析

给出单元寿命服从同一指数分布的串-并联混合系统产品参数的矩估计和极大似然估计,并通过大量Monte-Carlo模拟比较了估计的精度,得到在样本容量小于35时矩估计优于极大似然估计,而样本容量不小于35时极大似然估计优于矩估计.另外,还给出了参数的精确区间估计与近似区间估计,并通过大量Monte-Carlo模拟考察了区间估计的精度.