Study of the first-excited K π=0+ and 2+ bands in 228Th in the 226Ra(α,2n) reaction

Excited bands of ²²⁸Th were studied in the ²²⁶Ra(α,2n) reaction by gamma-ray and conversion-electron spectroscopy. The first-excited K ^π=0⁺ and 2⁺ bands were identified up to I ^π= 12⁺ and 10⁺, respectively. The spin dependence of the moments of inertia is discussed. The experimental data indicate a structural change of these bands from ²²⁸Th to ²³⁰Th and ²³²Th. Received: 11 August 1997 / Revised version: 19 September 1997     

Self-stabilizing additive-pulse mode-locking due to thermo-optical non-linearity in an optical fiber

16 , 1671 (1991)] described a Nd:YLF APM laser which somehow automatically adjusted the relative resonator phase. We reproduce this behavior and analyse its origin. Thermal effects due to the light power guided in the fiber affect the effective fiber length, which in turn influences the phase and thus the power level; hence a closed servo loop results. We demonstrate this explanation to be correct in quantitative terms. Consequences arise for other systems involving fiber-optic loops or interferometers. Received: 7 April 1997/Revised version: 15 July 1997     

一类不可微泛函拟极小问题的C1,α正则性

考虑一类不可微泛函I(u,G) =∫GF(x,u, u)dx的拟极小问题,证明了解的局部C1,α正则性,推广和发展了Anzellotti[6]的一些成果,而且与Anzellotti的方法不同.     

Microscopic study of yrast bands and backbending anomaly in 78-82Kr isotopes

The yrast spectra of ^78-82Kr are studied by using the projected shell model (PSM) approach. The energy states are obtained by taking oblate as well as prolate quadrupole deformations for ^78-82Kr. The structure of yrast states and backbending phenomena are investigated. The theoretical results predict low-lying states in ^{78, 82}Kr to be oblate and coexistence of oblate-prolate shapes for ⁸⁰Kr. The B(E2) transition probabilities and g-factors are obtained and compared with the available experimental data.     

Variable-coefficient higher-order nonlinear Schrödinger model in optical fibers: Variable-coefficient bilinear form,Bäcklund transformation,brightons and symbolic computation

Symbolically investigated in this Letter is a variable-coefficient higher-order nonlinear Schrödinger (vcHNLS) model for ultrafast signal-routing, fiber laser systems and optical communication systems with distributed dispersion and nonlinearity management. Of physical and optical interests, with bilinear method extend, the vcHNLS model is transformed into a variable-coefficient bilinear form, and then an auto-Bäcklund transformation is constructed. Constraints on coefficient functions are analyzed. Potentially observable with future optical-fiber experiments, variable-coefficient brightons are illustrated. Relevant properties and features are discussed as well. Bäcklund transformation and other results of this Letter will be of certain value to the studies on inhomogeneous fiber media, core of dispersion-managed brightons, fiber amplifiers, laser systems and optical communication links with distributed dispersion and nonlinearity management.     

嵌入原子法研究Ni3Al中点缺陷以及Re择优占位和集团化

基于纯金属元素Ni,Al和Re的基本物理性质,建立了一个Ni-Al-Re三元体系的分析型嵌入原子多体势.结合分子动力学计算了Ni3Al的平衡晶格常数、弹性模量、结合能、空位形成能以及反位置缺陷形成能,并分析了Ni3Al中点缺陷的存在形式.计算结果表明, 当成分偏离理想化学配比时出现反位置缺陷.同时研究了Re在Ni3Al中的择优占位以及Re在Ni3Al和Ni中的集团化行为.计算结果表明,Re在Ni3Al中优先置换Al的位置,且发现当Re原子团的尺寸接近于11。A时,Re原子团的长大趋势变弱.计算结果与实验以及其他的理论计算结果相符合.     

Stable collective triaxial rotation in <Superscript>77</Superscript>Kr

Based on the γ -spectroscopic analysis of G.N. Sylvan et al., configuration-dependent cranked Nilsson-Strutinsky calculations have been performed. They describe the nucleus ⁷⁷Kr globally in good agreement with the experimental findings and the expectations derived from single-particle orbitals in a deformed potential. Within these calculations, the unambiguous assignment of a configuration with three protons and five neutrons in the g _9/2 shell to the high-spin Yrast states of negative parity indicates that the nucleus ⁷⁷Kr has stable triaxial deformation and rotates about the intermediate axis. This not only disproves the recent interpretation of an occupation of the d _5/2 orbital being responsible for the strong deformation in this band, but also represents one of the first examples in this mass region for such a rotation.     

Harmonic Mode-Locked Ytterbium-Doped Fibre Ring Laser

We demonstrate a harmonic mode-locked ytterbium-doped fibre ring laser, which consists of a polarization-sensitive isolator, two polarization controllers, two 976nm laser diodes as the pump source and a two-segment ytterbium-doped fibre. Utilizing an additive pulse mode-locked technique based on nonlinear polarization evolution, the ytterbium-doped fibre laser can operate in mode-locked state by adjusting the position of polarization controllers. The cavity fundamental repetition rate is 23.78 MHz. We also observe the second- and third-harmonic mode locking in the normal dispersion region, and their repetition rates are 47.66 MHz and 71.56 MHz, respectively. Over-driving of the saturable absorber in the harmonic mode-locking pulse is analysed and discussed in detail.     

Controlling of Slope of Carrier-Envelope Phase of Few-Cycle Laser Pulses on Propagation Distance near the Focus

The effect of focusing geometry on slope of carrier-envelope （CE） phase ФCE versus propagation distance from the focus in few-cycle laser pulses is investigated. The slope could be adjusted by changing the distance L between the waist of the incident beam and the lens. At the focus, 偏dФCE/O（Z/ZR） = 0 when L = 0, and 偏dФCE/偏d（z/zR） = -2 when L = ∞. The longer the distance L, the steeper the curve of the CE phase at the focus.     

Coherent Phase Control of Ultrafast Polarization Beats in Reverse V-Type Three-Level System

We investigate the third-order nonlinear absorption and dispersion of femto- and atto-second polarization beats between the one-photon degenerate four-wave mixing process and the two-photon nondegenerate four-wave mixing process in the pure homogeneously-broadened reverse V-three-level using twin noisy fields. The third-order nonlinear response can be controlled and modified by the colour-locked correlation of twin noisy fields. Most importantly, the coherent phase control in optical heterodyne detection for studying the phase dispersion of the third-order susceptibility is demonstrated. The radiation-matter detuning oscillation is also considered in the freauencv domain.