Controlling the motion of solitons in BEC by a weakly periodic potential

By developing multiple-scale method combined with Wentzel--Kramer--Brillouin expansion, this paper analytically studies the modulating effect of weakly periodic potential on the dynamical properties of the Bose--Einstein condensates (BEC) trapped in harmonic magnetic traps. A black--grey soliton transition is observed in the BEC trapped in harmonic magnetic potential, due to the weakly periodic potential modulating effect. Meanwhile, it finds that with the slight increase of the weakly periodic potential strength, the velocity of the soliton decreases, while its width firstly decreases then increases, a minimum exists there. These results show that the amplitude, velocity, and width of matter solitons can be effectively managed by means of a weakly periodic potential.     

Unique geometric and electronic structure of CO adsorbed on Ge(100): A DFT study

CO adsorption on the Ge(100) surface has been investigated using a slab model with density functional theory implemented in SIESTA. CO was found to be exclusively adsorbed on the asymmetric dimer with C attaching on the lower Ge dimer atom. The adsorption process is barrierless. The calculated adsorption energy and vibration frequencies are comparable to previous experimental results. The crystal orbital Hamilton analysis showed that the bonding between Ge and CO is mainly attributable to the Ge 4p_z orbital overlapping with C 2 s, or with CO molecular orbitals 3σ and 4σ. The repulsive energy between adsorbed CO molecules is less than 1 kcal/mol. The diffusion barrier of CO on the Ge(100) surface is about 14 kcal/mol.     

A class of hybrid DG/FV methods for conservation laws I: Basic formulation and one-dimensional systems

By comparing the discontinuous Galerkin (DG) and the finite volume (FV) methods, a concept of ‘static reconstruction’ and ‘dynamic reconstruction’ is introduced for high-order numerical methods. Based on the new concept, a class of hybrid DG/FV schemes is presented for one-dimensional conservation law using a ‘hybrid reconstruction’ approach. In the hybrid DG/FV schemes, the lower-order derivatives of a piecewise polynomial solution are computed locally in a cell by the DG method based on Taylor basis functions (called as ‘dynamic reconstruction’), while the higher-order derivatives are re-constructed by the ‘static reconstruction’ of the FV method, using the known lower-order derivatives in the cell itself and its adjacent neighboring cells. The hybrid DG/FV methods can greatly reduce CPU time and memory required by the traditional DG methods with the same order of accuracy on the same mesh, and they can be extended directly to unstructured and hybrid grids in two and three dimensions similar to the DG and/or FV methods. The hybrid DG/FV methods are applied to one-dimensional conservation law, including linear and non-linear scalar equation and Euler equations. In order to capture the strong shock waves without spurious oscillations, a simple shock detection approach is developed to mark ‘trouble cells’, and a moment limiter is adopted for higher-order schemes. The numerical results demonstrate the accuracy, and the super-convergence property is shown for the third-order hybrid DG/FV schemes. In addition, by analyzing the eigenvalues of the semi-discretized system in one dimension, we discuss the spectral properties of the hybrid DG/FV schemes to explain the super-convergence phenomenon.     

Infrared broadband emission of bismuth–thulium co-doped lanthanum–aluminum–silica glasses

The Bi–Tm co-doped SiO₂–Al₂O₃–La₂O₃ (SAL) glasses, which exhibited a broadband near-infrared (NIR) emission was investigated by the optical absorption and photoluminescence spectra. The super broadband near-infrared emission from 1000 to 2100 nm, which covered the whole O, E, S, C and L bands, was observed in the Bi–Tm co-doped samples, as a result of the overlap of the Bi-related emission band (centered at 1270 nm) and the emission from Tm^{3+ 3}H₄→³F₄ transition (1440 nm) as well as Tm^{3+ 3}F₄→³H₆ transition (1800 nm). Relative luminescence intensity at 1270, 1440 and 1800 nm wavelength varied depending on the mixing ratio of Bi and Tm and the full-width at half-maximum (FWHM) extending from 1000 to 1600 nm could be 400 nm. These results indicated that Bi–Tm co-doped SiO₂–Al₂O₃–La₂O₃ glasses could provide potential applications in tunable lasers as well as the broadband optical amplifiers in WDM system.     

Investigation of Brillouin effects in small-core holey optical fiber: lasing and scattering

We demonstrate for what is believed to be the first time a Brillouin laser based on a holey fiber (HF). Using a simple Fabry-Perot resonator scheme containing a 73.5-m-long highly nonlinear HF with an effective area of 2.85 microm(2) , we obtain a threshold of 125 mW and a slope efficiency of ~70% . Stimulated and spontaneous Brillouin scattering effects are investigated in the HF, and we show that the high lasing threshold is due mainly to reduction of the effective gain coefficient caused by structural nonuniformity along the fiber length.     

Cholesterol-oleate-doped polymer-dispersed liquid-crystal voltage-controlled ring projector

We report a cholesterol-oleate-doped polymer-dispersed liquid-crystal (PDLC) device that, under laser illumination, exhibits a ring diffraction pattern, the radius of which is controlled by an externally applied voltage. This effect is accurately explained by modeling of the random distribution of spiral cells shown in the microstructure with a voltage-dependent shape variation.     

A scanning superconducting quantum interference device microscope for room temperature samples

We have constructed a scanning low-T_c superconducting quantum interference device (SQUID) microscope, in which the SQUID is mounted on the lower end of a copper rod and cooled to liquid helium temperature. There is a 65μm thick sapphire window under the SQUID. The sample at room temperature underneath the window can be scanned to produce magnetic images. The microscope has a spatial resolution of 100－150μm and a magnetic field sensitivity of 3－60pT/$\sqrt{Hz}$ in a magnetically unshielded environment. We have used this scanning SQUID microscope to measure various room temperature samples.     

Modulational instability of ion—acoustic waves in a warm plasma

Using the standard reductive perturbation technique,a nonlinear Schroedinger equation is derived to study the modulational instability of finite-amplitude ion-acoustic waves in a non-magnetized warm plasma.It is found that the inclusion of ion temperature in the equation modifies the nature of the ion-acoustic wave stability and the soliton stuctures.The effects of ion plasma temperature on the modulational stability and ion-acoustic wave properties are inestigated in detail.     

广义H non映射的滑模变结构控制同步

基于可线性化的非线性离散变结构跟踪控制方法实现了广义H non映射混沌系统的同步 .广义H non映射的混沌吸引子比H non映射的混沌吸引子要复杂得多 ,对于保密通信来说 ,这种复杂性正是所期望的 .提出的同步方法允许参数有适当的失配程度 ,这对工程实现是非常有利的 ,理论分析和仿真结果证实了该方法的有效性