Spatio-temporal intensity dynamics of passively mode-locked fiber laser

We present recent results on measurements of intensity spatio-temporal dynamics in passively mode-locked fibre laser. We experimentally uncover distinct, dynamic and stable spatio-temporal generation regimes of various stochasticity and periodicity properties in though-to-be unstable laser. We present a method to distinguish various types of generated coherent structures, including rogue and shock waves, within the radiation by means of introducing of intensity ACF evolution map. We also discuss how the spectral dynamics could be measured in fiber lasers generating irregular train of pulses of quasi-CW generation via combination of heterodyning and intensity spatio-temporal measurement concept.

The performance of stabilized and unstabilized minestone in an aqueous environment with emphasis on its erosion resistance

Britain's sea and flood defences are becoming increasingly aged and as a consequence, more fragile and vulnerable. As the government's philosophy on resources shifts against the use of prime quarried and dredged geo-materials, the need to find alternative bulk materials to bolster Britain's prone defences becomes more pressing. One conceivable source for such a material is colliery waste or minestone. Although a plethora of erosion-abrasion studies have been carried out on soils and soil-cements, very little research has been undertaken to determine the resistance of minestone and its cement stabilized form to the effects of water erosion. The thesis reviews the current extent to which soil-cements, minestone and cement stabilized minestone (CSM) have been employed for hydraulic construction projects. A synopsis is also given on the effects of immersion on shales, mudstones and minestone, especially with regard to the phenomena of slaking. A laboratory study was undertaken featuring a selection of minestones from several British coalfields. The stability of minestone and CSM in sea water and distilled water was assessed using slaking tests and immersion monitoring and the bearing on the use of these materials for hydraulic construction is discussed. Following a review of current erosion apparatus, the erosion/abrasion test and rotating cylinder device were chosen and employed to assess the erosion resistance of minestone and CSM. Comparison was made with a sand mix designed to represent a dredged sand, the more traditional, bulk hydraulic construction material. The results of the erosion study suggest that both minestone and CSM were more resistant to erosion and abrasion than equivalently treated sand mixes. The greater resistance of minestone to the agents of erosion and abrasion is attributed to several factors including the size of the particles, a greater degree of cement bonding and the ability of the minestone aggregate to absorb, rather than transmit shock waves produced by impacting abrasive particles. Although minestone is shown to be highly unstable when subjected to cyclic changes in its moisture content, the study suggests that even in an intertidal regime where cyclic immersion does takes place, minestone will retain sufficient moisture within its fabric to prevent slaking from taking place. The slaking study reveals a close relationship between slaking susceptibility and total pore surface area as revealed by porosimetry. The immersion study shows that although the fabric of CSM is rapidly attacked in sea water, a high degree of the disruption is associated with the edges and corners of samples (ie. free surface) while the integrity of the internal fabric remains relatively intact. CSM samples were shown to be resilient when subjected to immersion in distilled water. An overall assessment of minestone and CSM would suggest that with the implementation of judicious selection and appropriate quality control they could be used as alternative materials for flood and sea defences. It is believed, that even in the harsh regime of a marine environment, CSM could be employed for temporary and sacrificial schemes.

How SME owners’ characteristics influences external advice and access to finance

This paper aims to investigate the linkage between the use of external advice and access to finance for small and medium-sized enterprises (SMEs) in the UK, with particular consideration of differences in personal characteristics: gender, ethnicity and education. The approach adopted for the research is a telephone survey conducted by the Barclays small business research team in late 2005 on behalf of the authors. These data are quantitative in nature and involve a large sample of 400 SMEs with specific questions analysed by gender, ethnicity and education level. The approach adopted is robust and empirically sound and is a long established research methodology. We find that there appears to be a correlation between the provision of external advice and the ability to raise bank finance. Furthermore, there are clear gender, ethnic and educational differentials in the use of particular sources of advice, for example: Gender • men and women are equally likely to use accountants as sources of advice. • men are more likely to use family and friends and solicitors. • women, however, are around twice as likely to access external advice from Business Link and Enterprise Agencies. Ethnicity • family and friends is predominant amongst Asians or black respondents and the other ethnic group, which is also slightly true of accountants and solicitors. • ethnic minority respondents were considerably less likely to use Business Link/ Enterprise Agencies. Education • graduates are most likely to use solicitors and accountants, whilst they are very low users of advice from family and friends and Business Links/Enterprise Agencies. • O level and A level educated respondents predominate in family and friends and Business Link/ Enterprise Agencies.

Non-English-speaking defendants in the magistrates court:a comparative study of face-to-face and prison video link interpreter-mediated hearings in England

This study compares interpreter-mediated face-to-face Magistrates Court hearings with those conducted through prison video link in which interpreters are located in court and non- English-speaking defendants in prison. It seeks to examine the impact that the presence of video link has on court actors in terms of interaction and behaviour. The data comprises 11 audio-recordings of face-to-face hearings, 10 recordings of prison video link hearings, semistructured interviews with 27 court actors, and ethnographic observation of hearings as viewed by defendants in Wormwood Scrubs prison in London. The over-arching theme is the pervasive influence of the ecology of the courtroom upon all court actors in interpretermediated hearings and thus on the communication process. Close analysis of the court transcripts shows that their relative proximity to one another can be a determinant of status, interpreting role, mode and volume. The very few legal protocols which apply to interpretermediated cases (acknowledging and ratifying the interpreter, for example), are often forgotten or dispensed with. Court interpreters lack proper training in the specific challenges of court interpreting, whether they are co-present with the defendant or not. Other court actors often misunderstand the interpreter’s role. This has probably come about because courts have adjusted their perceptions of what they think interpreters are supposed to do based on their own experiences of working with them, and have gradually come to accept poor practice (the inability to perform simultaneous interpreting, for example) as the norm. In video link courts, mismatches of sound and image due to court clerks’ failure to adequately track current speakers, poor image and sound quality and the fact that non-English-speaking defendants in pre-and post-court consultations can see and hear interpreters but not their defence advocates are just some of the additional layers of disadvantage and confusion already suffered by non- English-speaking defendants. These factors make it less likely that justice will be done.

Weak Langmuir optical turbulence in a fiber cavity

We study theoretically and numerically the dynamics of a passive optical fiber ring cavity pumped by a highly incoherent wave: an incoherently injected fiber laser. The theoretical analysis reveals that the turbulent dynamics of the cavity is dominated by the Raman effect. The forced-dissipative nature of the fiber cavity is responsible for a large diversity of turbulent behaviors: Aside from nonequilibrium statistical stationary states, we report the formation of a periodic pattern of spectral incoherent solitons, or the formation of different types of spectral singularities, e.g., dispersive shock waves and incoherent spectral collapse behaviors. We derive a mean-field kinetic equation that describes in detail the different turbulent regimes of the cavity and whose structure is formally analogous to the weak Langmuir turbulence kinetic equation in the presence of forcing and damping. A quantitative agreement is obtained between the simulations of the nonlinear Schrödinger equation with cavity boundary conditions and those of the mean-field kinetic equation and the corresponding singular integrodifferential reduction, without using adjustable parameters. We discuss the possible realization of a fiber cavity experimental setup in which the theoretical predictions can be observed and studied.

Failure analysis of cold-formed steel sections

The purlin-sheeting system has been the subject of numerous theoretical and experimental investigations over the past 30 years, but the complexity of the problem has led to great difficulty in developing a sound and general model. The primary aim of the thesis is to investigate the failure behaviours of cold-formed zed and channel sections for use in purlin-sheeting systems. Both the energy method and finite strip method are used to develop an approach to investigate cold-formed zed and channel section beams with partial-lateral restraint from the metal sheeting when subjected to a uniformly distributed transverse load. The stress analysis of cold-formed zed and channel section beams with partially-lateral restraint from the metal sheeting when subjected to a uniformly distributed transverse load is investigated firstly by using the analytical model based on the energy method in which the restraint actions of the sheeting are modelled by using two springs representing the translational and rotational restraints. The numerical results have showed that the two springs have significantly different influences on the stresses of the beams. The influence of the two springs has also been found to depend on the anti-sag bar and the position of the loading line. A novel method is presented for analysing the elastic local buckling behaviour of cold-formed zed and channel section beams with partial-lateral restraint from metal sheeting when subjected to a uniformly distributed transverse load, which is carried out by inputting the cross sectional stresses with the largest compressive stress into the finite strip analysis. By using the presented novel method, individual influences of warning stress, partially lateral restraints from the sheeting and the dimensions of the cross section and position of the loading line on the buckling behaviour are investigated.

Efficiency enhancement of components based on talbot effect

Two ways to improve efficiency of components based on Talbot effect are considered in the present paper. One way is based on optimization of waveguide wall impedance, another one consists in modification of waveguide cross-section shape. Both methods allow correction of waveguide modes spectrum and lead to efficiency enhancement. For the important application of Talbot effect-remote steering antenna of a wavebeam in plasma-the steering band is expanded by 40-50%. © 2007 Springer Science+Business Media, LLC.

Accurate modelling of pulse transformation by adjustable-in-time medium parameters

A possibility of a strong change of an electromagnetic signal by a short sequence of time cycles of pulses that modulate the medium parameters is shown. The backward wave is demonstrated to be an inevitable result of the medium time change. Dependence of the relation between backward and forward waves on the parameters of the medium modulation is investigated. The finite statistical complexity of the electromagnetic signal transformed by a finite sequence of modulating cycles is calculated. Increase of the complexity with the number of cycles is shown.

Effect of microstructure upon elastic behaviour of human tooth enamel

Tooth enamel is the stiffest tissue in the human body with a well-organized microstructure. Developmental diseases, such as enamel hypomineralisation, have been reported to cause marked reduction in the elastic modulus of enamel and consequently impair dental function. We produce evidence, using site-specific transmission electron microscopy (TEM), of difference in microstructure between sound and hypomineralised enamel. Built upon that, we develop a mechanical model to explore the relationship of the elastic modulus of the mineral-protein composite structure of enamel with the thickness of protein layers and the direction of mechanical loading. We conclude that when subject to complex mechanical loading conditions, sound enamel exhibits consistently high stiffness, which is essential for dental function. A marked decrease in stiffness of hypomineralised enamel is caused primarily by an increase in the thickness of protein layers between apatite crystals and to a lesser extent by an increase in the effective crystal orientation angle. © 2009 Elsevier Ltd. All rights reserved.

NLSE-based model of a random distributed feedback fiber laser

In this work we propose a NLSE-based model of power and spectral properties of the random distributed feedback (DFB) fiber laser. The model is based on coupled set of non-linear Schrödinger equations for pump and Stokes waves with the distributed feedback due to Rayleigh scattering. The model considers random backscattering via its average strength, i.e. we assume that the feedback is incoherent. In addition, this allows us to speed up simulations sufficiently (up to several orders of magnitude). We found that the model of the incoherent feedback predicts the smooth and narrow (comparing with the gain spectral profile) generation spectrum in the random DFB fiber laser. The model allows one to optimize the random laser generation spectrum width varying the dispersion and nonlinearity values: we found, that the high dispersion and low nonlinearity results in narrower spectrum that could be interpreted as four-wave mixing between different spectral components in the quasi-mode-less spectrum of the random laser under study could play an important role in the spectrum formation. Note that the physical mechanism of the random DFB fiber laser formation and broadening is not identified yet. We investigate temporal and statistical properties of the random DFB fiber laser dynamics. Interestingly, we found that the intensity statistics is not Gaussian. The intensity auto-correlation function also reveals that correlations do exist. The possibility to optimize the system parameters to enhance the observed intrinsic spectral correlations to further potentially achieved pulsed (mode-locked) operation of the mode-less random distributed feedback fiber laser is discussed.

Reflection of a spatial-temporal airy pulse from a layer

The interaction of an Airy pulse with a dielectric layer is investigated theoretically. Approximate analytical expressions for reflected and transmitted waves are derived in the form of Taylor series. These series consist of shifted Airy pulses which are decelerated in time and space and deceleration becomes stronger with a number of a term of series. © 2012 IEEE.

Statistical properties of partially coherent CW fiber lasers

A detailed quantitative numerical analysis of partially coherent quasi-CW fiber laser is performed on the example of high-Q cavity Raman fiber laser. The key role of precise spectral performances of fiber Bragg gratings forming the laser cavity is clarified. It is shown that cross phase modulation between the pump and Stokes waves does not affect the generation. Amplitudes of different longitudinal modes strongly fluctuate obeying the Gaussian distribution. As intensity statistics is noticeably non-exponential, longitudinal modes should be correlated. © 2011 SPIE.