Simulation of optical fibre communication systems influenced by stimulated brillouin scattering

Boyd's SBS model which includes distributed thermal acoustic noise (DTAN) has been enhanced to enable the Stokes-spontaneous density depletion noise (SSDDN) component of the transmitted optical field to be simulated, probably for the first time, as well as the full transmitted field. SSDDN would not be generated from previous SBS models in which a Stokes seed replaces DTAN. SSDDN becomes the dominant form of transmitted SBS noise as model fibre length (MFL) is increased but its optical power spectrum remains independent of MFL. Simulations of the full transmitted field and SSDDN for different MFLs allow prediction of the optical power spectrum, or system performance parameters which depend on this, for typical communication link lengths which are too long for direct simulation. The SBS model has also been innovatively improved by allowing the Brillouin Shift Frequency (BS) to vary over the model fibre length, for the nonuniform fibre model (NFM) mode, or to remain constant, for the uniform fibre model (UFM) mode. The assumption of a Gaussian probability density function (pdf) for the BSF in the NFM has been confirmed by means of an analysis of reported Brillouin amplified power spectral measurements for the simple case of a nominally step-index single-mode pure silica core fibre. The BSF pdf could be modified to match the Brillouin gain spectra of other fibre types if required. For both models, simulated backscattered and output powers as functions of input power agree well with those from a reported experiment for fitting Brillouin gain coefficients close to theoretical. The NFM and UFM Brillouin gain spectra are then very similar from half to full maximum but diverge at lower values. Consequently, NFM and UFM transmitted SBS noise powers inferred for long MFLs differ by 1-2 dB over the input power range of 0.15 dBm. This difference could be significant for AM-VSB CATV links at some channel frequencies. The modelled characteristic of Carrier-to-Noise Ratio (CNR) as a function of input power for a single intensity modulated subcarrier is in good agreement with the characteristic reported for an experiment when either the UFM or NFM is used. The difference between the two modelled characteristics would have been more noticeable for a higher fibre length or a lower subcarrier frequency.

PSD modifications of FHRV due to interpolation and CTG storage rate

Cardiotocographic data provide physicians information about foetal development and permit to assess conditions such as foetal distress. An incorrect evaluation of the foetal status can be of course very dangerous. To improve interpretation of cardiotocographic recordings, great interest has been dedicated to foetal heart rate variability spectral analysis. It is worth reminding, however, that foetal heart rate is intrinsically an uneven series, so in order to produce an evenly sampled series a zero-order, linear or cubic spline interpolation can be employed. This is not suitable for frequency analyses because interpolation introduces alterations in the foetal heart rate power spectrum. In particular, interpolation process can produce alterations of the power spectral density that, for example, affects the estimation of the sympatho-vagal balance (computed as low-frequency/high-frequency ratio), which represents an important clinical parameter. In order to estimate the frequency spectrum alterations of the foetal heart rate variability signal due to interpolation and cardiotocographic storage rates, in this work, we simulated uneven foetal heart rate series with set characteristics, their evenly spaced versions (with different orders of interpolation and storage rates) and computed the sympatho-vagal balance values by power spectral density. For power spectral density estimation, we chose the Lomb method, as suggested by other authors to study the uneven heart rate series in adults. Summarising, the obtained results show that the evaluation of SVB values on the evenly spaced FHR series provides its overestimation due to the interpolation process and to the storage rate. However, cubic spline interpolation produces more robust and accurate results. © 2010 Elsevier Ltd. All rights reserved.

PSD modifications of FHRV due to CTG storage rate

Cardiotocographic data provide physicians information about foetal development and, through assessment of specific parameters (like accelerations, uterine contractions, ...), permit to assess conditions such as foetal distress. An incorrect evaluation of foetal status can be of course very dangerous. In the last decades, to improve interpretation of cardiotocographic recordings, great interest has been dedicated to FHRV spectral analysis. It is worth reminding that FHR is intrinsically an uneven series and that to obtain evenly sampled series, many commercial cardiotocographs use a zero-order interpolation (storage rate of CTG data equal to 4 Hz). This is not suitable for frequency analyses because interpolation introduces alterations in the FHR power spectrum. In particular, this interpolation process can produce artifacts and an attenuation of the high-frequency components of the PSD that, for example, affects the estimation of the sympatho-vagal balance (SVB - computed as low-frequency/high-frequency ratio), which represents an important clinical parameter. In order to estimate the frequency spectrum alterations due to zero-order interpolation and other CTG storage rates, in this work, we simulated uneven FHR series with set characteristics, their evenly spaced versions (with different storage rates) and computed SVB values by PSD. For PSD estimation, we chose the Lomb method, as suggested by other authors in application to uneven HR series. ©2009 IEEE.

Numerical modelling of devices and advanced transmission schemes embracing Raman effect

This thesis presents a theoretical investigation on applications of Raman effect in optical fibre communication as well as the design and optimisation of various Raman based devices and transmission schemes. The techniques used are mainly based on numerical modelling. The results presented in this thesis are divided into three main parts. First, novel designs of Raman fibre lasers (RFLs) based on Phosphosilicate core fibre are analysed and optimised for efficiency by using a discrete power balance model. The designs include a two stage RFL based on Phosphosilicate core fibre for telecommunication applications, a composite RFL for the 1.6 μm spectral window, and a multiple output wavelength RFL aimed to be used as a compact pump source for fiat gain Raman amplifiers. The use of Phosphosilicate core fibre is proven to effectively reduce the design complexity and hence leads to a better efficiency, stability and potentially lower cost. Second, the generalised Raman amplified gain model approach based on the power balance analysis and direct numerical simulation is developed. The approach can be used to effectively simulate optical transmission systems with distributed Raman amplification. Last, the potential employment of a hybrid amplification scheme, which is a combination between a distributed Raman amplifier and Erbium doped amplifier, is investigated by using the generalised Raman amplified gain model. The analysis focuses on the use of the scheme to upgrade a standard fibre network to 40 Gb/s system.

The deformation behaviour of the collapsing and destructured soils of the Sana'a area and their response to field treatment

Previous work has indicated the presence of collapsing and structured soils in the surface layers underlying Sana's, the capital of Yemen Republic. This study set out initially to define and, ultimately, to alleviate the problem by investigating the deformation behaviour of these soils through both field and laboratory programmes. The field programme was carried out in Sana'a while the laboratory work consisted of two parts, an initial phase at Sana's University carried out in parallel with the field programme on natural and treated soils and the major phase at Aston University carried out on natural, destructured and selected treated soils. The initial phase of the laboratory programme included classification, permeability, and single (collapsing) and double oedometer tests while the major phase, at Aston, was extended to also include extensive single and double oedometer tests, Scanning Electron Microscopy and Energy Dispersive Spectrum analysis. The mechanical tests were carried out on natural and destructed samples at both the in situ and soaked moisture conditions. The engineering characteristics of the natural intact, field-treated and laboratory destructured soils are reported, including their collapsing potentials which show them to be weakly bonded with nil to severe collapsing susceptibility. Flooding had no beneficial effect, with limited to moderate improvement being achieved by preloading and roller compaction, while major benefits were achieved from deep compaction. From these results a comparison between the soil response to the different treatments and general field remarks were presented. Laboratory destructuring reduced the stiffness of the soils while their compressibility was increasing. Their collapsing and destructuring mechanisms have been examined by studying the changes in structure accompanying these phenomena. Based on the test results for the intact and the laboratory destructured soils, a simplified framework has been developed to represent the collapsing and deformation behaviour at both the partially saturated and soaked states, and comments are given on its general applicability and limitations. It has been used to evaluate all the locations subjected to field treatment. It provided satisfactory results for the deformation behaviour of the soils destructed by field treatment. Finally attention is drawn to the design considerations together with the recommendations for the selection of potential improvement techniques to be used for foundation construction on the particular soils of the Sana's region.

Analysis of power jitter induced by interchannel interactions in dispersion-managed optical soliton transmission systems

Collision-induced power jitter is theoretically and numerically examined in dispersion-managed wavelength-division-multiplexed optical soliton transmission systems. The variational method is mainly used to develop a time efficient jitter calculation approach. The power jitter causes a serious problem for a singly periodic dispersion managed line having almost zero average dispersion, which can be reduced by applying doubly periodic dispersion management.

Cost and performance analysis of new wood-fuelled power plant concepts

The objective of the thesis was to analyse several process configurations for the production of electricity from biomass. Process simulation models using AspenPlus aimed at calculating the industrial performance of power plant concepts were built, tested, and used for analysis. The criteria used in analysis were performance and cost. All of the advanced systems appear to have higher efficiencies than the commercial reference, the Rankine cycle. However, advanced systems typically have a higher cost of electricity (COE) than the Rankine power plant. High efficiencies do not reduce fuel costs enough to compensate for the high capital costs of advanced concepts. The successful reduction of capital costs would appear to be the key to the introduction of the new systems. Capital costs account for a considerable, often dominant, part of the cost of electricity in these concepts. All of the systems have higher specific investment costs than the conventional industrial alternative, i.e. the Rankine power plant; Combined beat and power production (CUP) is currently the only industrial area of application in which bio-power costs can be considerably reduced to make them competitive. Based on the results of this work, AsperiPlus is an appropriate simulation platform. How-ever, the usefulness of the models could be improved if a number of unit operations were modelled in greater detail. The dryer, gasifier, fast pyrolysis, gas engine and gas turbine models could be improved.

The dynamics of organizational change : an analysis of power, professions and new managerialism in the case of CoastElectric

It is widely accepted that the Thatcher years and their immediate aftermath were associated with substantive social and organizational change. The privatisation programme, 'the rolling back of the State', prosecuted by the successive Conservative Governments from 1979-1997 was a central pillar of Governmental policy. This thesis seeks to engage with privatization through the of CoastElectric, a newly privatised Regional Electricity Company. This thesis contributes to the extant understanding of the dynamics of organizational change in four major ways. Firstly, the study into CoastElectric addresses the senior management decision making within the organization: in particular, it will attempt to make sense of 'why' particular decisions were made. The theoretical backdrop to this concern will draw on the concepts of normalization, cultural capital and corporate fashion. The argument presented in this thesis is that the decision-making broadly corresponded with that which could be considered to be at the vanguard of mangerialist thought. However, a detailed analysis suggested that at different junctures in CoastElectric's history there were differences in the approach to decision making that warranted further analysis. The most notable finding was that the relative levels of new managerialist cultural capital possessed by the decision-making elite had an important bearing upon whether the decision was formulated either endogenously or exogenously, with the assistance of cultural intermediaries such as management consultants. The thesis demonstrates the importance of the broader discourse of new managerialism in terms of shaping what is considered to be a 'commonsensical, rational' strategy. The second concern of this thesis is that of the process of organizational change. The study of CoastElectric attempts to provide a rich account of the dynamics of organizational change. This is realized through, first, examining the pre-existing context of the organization; second, through analyzing the power politics of change interventions. The master concepts utilised in this endeavour are that of: dividing practices, the establishment of violent hierarchies between competing discourses; symbolic violence; critical turning points; recursiveness; creative destruction; legitimation strategies and the reconstitution of subjects in the workplace.

A barrier and techno-economic analysis of small-scale bCHP (biomass combined heat and power) schemes in the UK

bCHP (Biomass combined heat and power) systems are highly efficient at smaller-scales when a significant proportion of the heat produced can be effectively utilised for hot water, space heating or industrial heating purposes. However, there are many barriers to project development and this has greatly inhibited deployment in the UK. Project viability is highly subjective to changes in policy, regulation, the finance market and the low cost fossil fuel incumbent. The paper reviews the barriers to small-scale bCHP project development in the UK along with a case study of a failed 1.5MWel bCHP scheme. The paper offers possible explanations for the project's failure and suggests adaptations to improve the project resilience. Analysis of the project's: capital structuring contract length and bankability; feedstock type and price uncertainty, and plant oversizing highlight the negative impact of the existing project barriers on project development. The research paper concludes with a discussion on the effects of these barriers on the case study project and this industry more generally. A greater understanding of the techno-economic effects of some barriers for small-scale bCHP schemes is demonstrated within this paper, along with some methods for improving the attractiveness and resilience of projects of this kind. © 2014 Elsevier Ltd.

Modeling of the spectrum in a random distributed feedback fiber laser within the power balance modes

The simplest model for a description of the random distributed feedback (RDFB) Raman fiber laser is a power balance model describing the evolution of the intensities of the waves over the fiber length. The model predicts well the power performances of the RDFB fiber laser including the generation threshold, the output power and pump and generation wave intensity distributions along the fiber. In the present work, we extend the power balance model and modify equations in such a way that they describe now frequency dependent spectral power density instead of integral over the spectrum intensities. We calculate the generation spectrum by using the depleted pump wave longitudinal distribution derived from the conventional power balance model. We found the spectral balance model to be sufficient to account for the spectral narrowing in the RDFB laser above the threshold of the generation. © 2014 SPIE.

Analysis and design of power management scheme for an on-board solar energy storage system

This paper investigates the power management issues in a mobile solar energy storage system. A multi-converter based energy storage system is proposed, in which solar power is the primary source while the grid or the diesel generator is selected as the secondary source. The existence of the secondary source facilitates the battery state of charge detection by providing a constant battery charging current. Converter modeling, multi-converter control system design, digital implementation and experimental verification are introduced and discussed in details. The prototype experiment indicates that the converter system can provide a constant charging current during solar converter maximum power tracking operation, especially during large solar power output variation, which proves the feasibility of the proposed design. © 2014 IEEE.

Simulation of surface EMG for the analysis of muscle activity during whole body vibratory stimulation

This study aims to reproduce the effect of motor-unit synchronization on surface EMG recordings during vibratory stimulation to highlight vibration evoked muscle activity. The authors intended to evaluate, through numerical simulations, the changes in surface EMG spectrum in muscles undergoing whole body vibration stimulation. In some specific bands, in fact, vibration induced motion artifacts are also typically present. In addition, authors meant to compare the simulated EMGs with respect to real recordings in order to discriminate the effect of synchronization of motor units discharges with vibration frequencies from motion artifacts. Computations were performed using a model derived from previous studies and modified to consider the effect of vibratory stimulus, the motor unit synchronization and the endplates-electrodes relative position on the EMG signal. Results revealed that, in particular conditions, synchronization of MUs' discharge generates visible peaks at stimulation frequency and its harmonics. However, only a part of the total power of surface EMGs might be enclosed within artifacts related bands (±1. Hz centered at the stimulation frequency and its superior harmonics) even in case of strong synchronization of motor units discharges with the vibratory stimulus. © 2013 Elsevier Ireland Ltd.