On the 2S1/2–1S1/2 photon-plasmon transition in hydrogenous atoms

The probabilities of the two-quantum induced (according to the number of plasmons) photon-plasmon transitions 2S_1/2–1S_1/2 are calculated for hydrogenous atoms. In a turbulent plasma medium this process may be more effective than conventional two-photon radiation and collisions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 2, pp. 305–307, February, 1972.The authors thank L. A. Vainshtein and Yu. P. Nikitin for discussing the work and for their valuable comments.     

A Quantum Monte Carlo Study on Mixed-Spin Chains of 1/2-1/2-1-1 and 3/2-3/2 -1-1

The ground-state and thermodynamic properties of quantum mixed-spin chains of1/2-1/2-1-1and 3/2-3/2-1-1are investigated by a quantum Monte Carlo simulation with the loop-cluster algorithm. For 1/2-1/2-1-1 chain, we find it has two phases separated by an energy-gap vanishing point in the ground-state. For 3/2-3/2-1-1 chain, the numerical results show two energy-gap vanishing points isolated by different phases in its ground-state. Our calculations indicate that all these ground state phases can be understood by means of valence-bond-solid picture, and the thermodynamic behavior at finite temperatures is continuous as a function of parameterα=J2/J1.     

A Quantum Monte Carlo Study on Mixed-Spin Chains of 1／2-1／2-1-1 and 3／2-3／2-1-1

The ground-state and thermodynamic properties of quantum mixed-spin chains of 1/2-1/2-1-1 and 3/2-3/2-1-1 are investigated by a quantum Monte Carlo simulation with the loop-cluster algorithm. For 1/2-1/2-1-1 chain, we find it hastwo phases separated by an energy-gap vanishing point in the ground-state. For 3/2-3/2-1-1 chain,the numerical results show two energy-gap vanishing points isolated by different phases in its ground-state. Our calculations indicate that all these ground state phases can be understood by means of valence-bond-solid picture, and the thermodynamic behavior at finite temperatures is continuous as a function of parameter α=J2/J1.     

1+3/2与1+1/2对转涡轮对比分析

为理清1 1/2对转涡轮及1 3/2对转涡轮使用范围和效能,从而帮助设计决策,本文采用Stewart方法,从速度三角形基本分析入手,以速功比为主要变量,考察、对比1 3/2和1 1/2对转涡轮性能特点.研究表明:各转速比下,1 3/2对转涡轮高效率范围都比1 1/2对转涡轮窄,但其高效区发生在更小的总速功比区域;随转速比绝对值增加,两种涡轮高效率区都增加,高效率区位置都偏向大的总速功比区域;相比于1 1/2对转涡轮,1 3/2对转涡轮具有较低出功比,且偏向于低速功比区域;随转速比绝对值增加,两种对转涡轮出功比范围均拓展.这些结果为未来先进航空发动机涡轮选型提供了重要借鉴.     

(1/2+1/2+1)腔型热阴极微波电子枪

 介绍了一种新型的轴耦合热阴极微波电子枪的设计，该枪采用了缩短首腔以及在首腔与主加速腔间插入耦合半腔的设计思想，在不破坏粒子束性能的基础上尽量减小反轰功率，给出了用Superfish 及Pamela软件进行物理设计以及粒子动力学计算的结果，在脉冲宽度为6μs, 重复频率为25Hz时，阴极上平均反轰功率为3.6W,达到设计要求。     

1，1－二氯双硅烷热分解的理论研究

用ＭＮＤＯ方法研究了１，１－二氯双硅烷的热分解反应，得到了两条反应途径及其过渡态，证明了１，１－二氯双硅烷的热分解是通过１，２－氢迁移和２，１－氢迁移实现的。     

Two-photon E1M1 and E1E2 transitions between 2p and 1s levels in hydrogen

Two-photon transitions in the hydrogen atom are analytically evaluated within the nonrelativistic limit utilizing the Coulomb Green function method. The two-photon emission probability for the transition process 2s→2γ(E1)+1s serves as a test for the other calculations and was compared with the results of previous analytical and numerical calculations. The two-photon emission probabilities for the processes 2p→ γ(E1)+γ(M1)+1s and 2p→γ(E1)+γ(E2)+1s are also evaluated and compared with previous numerical calculations. Different nonrelativistic “forms" for the decay probabilities in combination with different gauge choices are considered.     

The physics of 2≠1+1

One of the most surprising consequences of quantum mechanics is the entanglement of two or more distant particles. In an entangled EPR two-particle system, the value of the momentum (position) for neither single subsystem is determined. However, if one of the subsystems is measured to have a certain momentum (position), the other subsystem is determined to have a unique corresponding value, despite the distance between them. This peculiar behavior of an entangled quantum system has surprisingly been observed experimentally in two-photon temporal and spatial correlation measurements, such as “ghost” interference and “ghost” imaging. This article addresses the fundamental concerns behind these experimental observations and to explore the nonclassical nature of two-photon superposition by emphasizing the physics of 2 ≠ 1 + 1.      

Distinct electronic and transport properties between 1T-HfSe2 and 1T-PtSe2

In this study, we employed the first-principles calculation to investigate the structural, electronic and transport properties of 1T-HfSe₂ and 1T-PtSe₂ transition metal dichalcogenides, and further explain why they share the same 1T (octahedral) layered structure but exhibit very different electronic and transport properties. There are two underlying concepts: the degree of interlayer bond ionicity and the number of 5d valence electrons of transition metal. The high degree of Hf-Se bond ionicity not only gives rise to the indirect energy gap of HfSe₂ bulk and thin films, but also results in the weak Se-Se vdW interlayer coupling to further restrict the electron transport only within a HfSe₂ layer. On the other hand, the modulation of metallic/semiconducting property of PtSe₂ bulk and thin films can be understood by the significant vdW interlayer coupling, which induces charge redistribution of Se atom and allows electrons to transport within a PtSe₂ layer as well as cross neighboring layers. Finally, our transport calculation for 1T-HfSe₂/1T-PtSe₂ bulks and monolayers suggests the great electron transport within Hf-Se/Pt-Se layer but suppresses/allows electron from neighboring layers. The robust two-dimensional characteristic of 1T-HfSe₂ and the metal-to-semiconductor transition of 1T-PtSe₂ may provide more knowledge for future application in nanoelectronic and optoelectronic devices.     

Luminescence properties of K1/2Bi1/2TiO3:Pr3+ and Na1/2Bi1/2TiO3:Pr3+

The luminescence properties of K(1/2)Bi(1/2)TiO(3):Pr(3+) and Na(1/2)Bi(1/2)TiO(3):Pr(3+) powders are investigated in the temperature range 10-600 K. The experimental data are interpreted on the basis of metal-to-metal charge transfer processes and by considering Bi(3+)-to-Pr(3+) sensitization effects.     

Magnetoelectricity in the PbFe1/2Nb1/2O3 Ceramics

The magnetodielectric effect (the influence of a magnetic field H on the dielectric constant ?) and the magnetoelectric effect (the influence of an electric field E on the magnetoelectric constant ??) of the PbFe_1/2Nb_1/2O₃ ceramics have been investigated at temperatures T in the range from 50 to 200°C, including the Curie point T _C ? 98°C. It has been demonstrated that there is a correlation of these effects with the shift of the ferroelectric-paraelectric phase transition temperature in a magnetic field.     

Twists in Hopf algebras andRT 1 T 2=T 2 T 1 relations

LetR be a matrix unitary quasi-classical solution of the Yang-Baxter equation. Considering an associative algebra defined by the relationRT ₁ T ₂=T ₂ T ₁ we find a universal twistF such thatR is the image ofR=F ₂₁ F ⁻¹ in the vector representation. Presented at the 11th Colloquium “Quantum Groups and Integrable Systems”, Prague, 20–22 June 2002.     

Theoretical study of the Renner-Teller A 2A1 − X 2B1 system of NH2

(Molec. Phys., 1994, 81, 1445–1461)     

Crystal structures and phonon modes of Ba(Ca1/2W1/2)O3, Ba(Ca1/2Mo1/2)O3 and Ba(Sr1/2W1/2)O3 complex perovskites investigated by Raman scattering

This work investigates the crystal structures and phonon modes of Ba(Ca_1/2W_1/2)O₃, Ba(Ca_1/2Mo_1/2)O₃ and Ba(Sr_1/2W_1/2)O₃ perovskites by Raman spectroscopy. The samples were produced by conventional solid‐state processing at 1200 °C. X‐ray diffraction showed that single‐phase homogeneous materials were produced, which are cubic or pseudo‐cubic in symmetry. The existing controversies in the literature for these complex perovskites were investigated by comparing experimental Raman data with group‐theory analysis. Ceramics with Ca and W or Mo were found to be cubic, space group Fm3 m. For these materials, four Raman‐active bands were observed and the fitting parameters showed that the Ba(Ca_1/2Mo_1/2)O₃ ceramic presents bands at lower wavenumbers if compared with the Ba(Ca_1/2W_1/2)O₃ sample. For the Ba(Sr_1/2W_1/2)O₃ material, two hypotheses were investigated for monoclinic or triclinic structures. The experimental results showed 12 Raman‐active modes for this ceramic, which is in perfect agreement with the theoretical predictions for a monoclinic (I2/m) structure. Copyright © 2009 John Wiley & Sons, Ltd.