初始啁啾对光纤中传播的飞秒光孤子的影响

采用分步傅里叶变换作为数值模拟的方法，以二阶飞秒光孤子和基态飞秒光孤子为例，讨论了初始啁啾对光纤中传播的飞秒光孤子的时域特征和频谱结构的影响，概括出如下的结论：初始啁啾通过影响飞秒光孤子谱线的红移，而对飞秒光孤子由拉曼效应引发的脉冲延迟产生较大影响，正的初始啁啾使脉冲延迟加剧，负的初始啁啾使脉冲延迟减小。

Asymptotic soliton train solutions of the defocusing nonlinear Schrodinger equation

Asymptotic behavior of initially large and smooth pulses is investigated at two typical stages of their evolution governed by the defocusing nonlinear Schrodinger equation. At first, wave breaking phenomenon is studied in the limit of small dispersion. A solution of the Whitham modulational equations is found for the case of dissipationless shock wave arising after the wave breaking point. Then, asymptotic soliton trains arising eventually from a large and smooth initial pulse are studied by means of a semiclassical method. The parameter varying along the soliton train is calculated from the generalized Bohr-Sommerfeld quantization rule, so that the distribution of eigenvalues depends on two functions-intensity rho(0)(x) of the initial pulse and its initial chirp v(0)(x). The influence of the initial chirp on the asymptotic state is investigated. Excellent agreement of the numerical solution of the defocusing NLS equation with predictions of the asymptotic theory is found.

Stability of trapped Bose-Einstein condensates

In three-dimensional trapped Bose-Einstein condensate (BEC), described by the time-dependent Gross-Pitaevskii-Ginzburg equation, we study the effect of initial conditions on stability using a Gaussian variational approach and exact numerical simulations. We also discuss the validity of the criterion for stability suggested by Vakhitov and Kolokolov. The maximum initial chirp (initial focusing defocusing of cloud) that can lead a stable condensate to collapse even before the number of atoms reaches its critical limit is obtained for several specific cases. When we consider two- and three-body nonlinear terms, with negative cubic and positive quintic terms, we have the conditions for the existence of two phases in the condensate. In this case, the magnitude of the oscillations between the two phases are studied considering sufficient large initial chirps. The occurrence of collapse in a BEC with repulsive two-body interaction is also shown to be possible.

Generation of triangular pulses in normally dispersive fibre

In this scheme, nonlinearity and dispersion in the NDF lead to various reshaping processes of an initial, conventional pulse according to the chirping value and power level at the input of the fibre. In particular, we have observed that triangular-shaped pulses can be generated for sufficiently high energies and a positive initial chirp parameter. In our experiments, 2.8 ps-FWHM, transform-limited pulses generated from a mode-locked fibre laser source at a repetition rate of 1.25 GHz were pre-chirped by propagating the pulses through different lengths of standard mono-mode fibre. The chirped pulses were then amplified to different power levels before being launched into a 2.3 km section of True Wave fibre (TWF). The corresponding numerically calculated pulse temporal intensity profile and numerical and experimental second-harmonic generation frequency-resolved optical gating (SHG FROG) spectrograms were also derived. In conclusion, we have presented numerical modelling results which show the system design parameters required for the generation of triangular-shaped pulses in a nonlinear NDF, and experimentally demonstrated triangular pulse shaping in conventional NDF.

Optimization of single attosecond x-ray pulses by genetic algorithm control of the chirp and initial phase of 5 fs laser pulses

We show that the peak intensity of single attosecond x-ray pulses is enhanced by 1 or 2 orders of magnitude, the pulse duration is greatly compressed, and the optimal propagation distance is shortened by genetic algorithm optimization of the chirp and initial phase of 5 fs laser pulses. However, as the laser intensity increases, more efficient nonadiabatic self-phase matching can lead to a dramatically enhanced harmonic yield, and the efficiency of optimization decreases in the enhancement and compression of the generated attosecond pulses. (c) 2006 Optical Society of America.

Optimization of high-order harmonic by genetic algorithm for the chirp and phase of few-cycle pulses

The brightness of a particular harmonic order is optimized for the chirp and initial phase of the laser pulse by genetic algorithm. The influences of the chirp and initial phase of the excitation pulse on the harmonic spectra are discussed in terms of the semi-classical model including the propagation effects. The results indicate that the harmonic intensity and cutoff have strong dependence on the chirp of the laser pulse, but slightly on its initial phase. The high-order harmonics can be enhanced by the optimal laser pulse and its cutoff can be tuned by optimization of the chirp and initial phase of the laser pulse.

Initial CFD investigation of an MR fluid in a bicycle ergometer

A bicycle ergometer is a scientific device used by exercise physiologists which attempts to mimic on-road cycling characteristics such as foot technique, EMG activity, VO2, VCO2 and rider cardiology in a laboratory environment. Presently there are no known useful scientific ergometers that mimic these characteristics and are able to provide a satisfactory controlled resistance that is independent of speed. Previous research has suggested the use of a Magneto-Rheological (MR) Fluid as part of the ergometer design, as when used in a rotary brake application it is able to be controlled electronically to increase resistance instantly and independent of speed. In the target application, MR fluids are subject to immense tribological wear and temperature during viscous shearing, and will eventually show some degree of deterioration which is usually manifested as an increase in off-state viscosity. It is not known exactly how the fluid fails, however the amount of deterioration is related to the shear rate, temperature and duration and directly related to the power dissipation. Currently, there is very little literature that investigates the flow and thermal characteristics of MR fluid tribology using CFD. In this paper, we present initial work that aims to improve understanding of MR fluid wear via CFD modelling using Fluent, and results from the model are compared with those obtained from a experimental test rig of an MR fluid-based bicycle ergometer.

Initial steps in optimal planning of a distribution system

This paper reports the initial steps of research on planning of rural networks for MV and LV. In this paper, two different cases are studied. In the first case, 100 loads are distributed uniformly on a 100 km transmission line in a distribution network and in the second case, the load structure become closer to the rural situation. In case 2, 21 loads are located in a distribution system so that their distance is increasing, distance between load 1 and 2 is 3 km, between 2 and 3 is 6 km, etc). These two models to some extent represent the distribution system in urban and rural areas, respectively. The objective function for the design of the optimal system consists of three main parts: cost of transformers, and MV and LV conductors. The bus voltage is expressed as a constraint and should be maintained within a standard level, rising or falling by no more than 5%.

Women's participation in the Australian Digital Content Industry : initial case study findings

An exploratory case study which seeks to understand better the problem of low participation rates of women in Information Communication Technology (ICT) is currently being conducted in Queensland, Australia. Contextualised within the Digital Content Industry (DCI) multimedia and games production sectors, the emphasis is on women employed as interactive content creators rather than as users of the technologies. Initial findings provide rich descriptive insights into the perceptions and experiences of female DCI professionals. Influences on participation such as: existing gender ratios, gender and occupational stereotypes, access into the industry and future parental responsibilities have emerged from the data. Bandura’s (1999) Social Cognitive Theory (SCT) is used as a “scaffold” (Walsham, 1995:76) to guide data analysis and assist analytic generalisation of the case study findings. We propose that the lens of human agency and theories such as SCT assist in explaining how influences are manifested and affect women’s agency and ultimately participation in the DCI. The Sphere of Influence conceptual model (Geneve et al, 2008), which emerges from the data and underpinning theory, is proposed as a heuristic framework to further explore influences on women’s participation in the DCI industry context.