Kineto-elastodynamic analysis of high-speed four-bar mechanism

This thesis addresses the kineto-elastodynamic analysis of a four-bar mechanism running at high-speed where all links are assumed to be flexible. First, the mechanism, at static configurations, is considered as structure. Two methods are used to model the system, namely the finite element method (FEM) and the dynamic stiffness method. The natural frequencies and mode shapes at different positions from both methods are calculated and compared. The FEM is used to model the mechanism running at high-speed. The governing equations of motion are derived using Hamilton's principle. The equations obtained are a set of stiff ordinary differential equations with periodic coefficients. A model is developed whereby the FEM and the dynamic stiffness method are used conjointly to provide high-precision results with only one element per link. The principal concern of the mechanism designer is the behaviour of the mechanism at steady-state. Few algorithms have been developed to deliver the steady-state solution without resorting to costly time marching simulation. In this study two algorithms are developed to overcome the limitations of the existing algorithms. The superiority of the new algorithms is demonstrated. The notion of critical speeds is clarified and a distinction is drawn between "critical speeds", where stresses are at a local maximum, and "unstable bands" where the mechanism deflections will grow boundlessly. Floquet theory is used to assess the stability of the system. A simple method to locate the critical speeds is derived. It is shown that the critical speeds of the mechanism coincide with the local maxima of the eigenvalues of the transition matrix with respect to the rotational speed of the mechanism.

Comparative analysis of BER estimation methods in numerical simulation of 40-Gb/s RZ-DPSK transmission with in-line SOAs

Applying direct error counting, we compare the accuracy and evaluate the validity of different available numerical approaches to the estimation of the bit-error rate (BER) in 40-Gb/s return-to-zero differential phase-shift-keying transmission. As a particular example, we consider a system with in-line semiconductor optical amplifiers. We demonstrate that none of the existing models has an absolute superiority over the others. We also reveal the impact of the duty cycle on the accuracy of the BER estimates through the differently introduced Q-factors.

Investigation of EDFA power transients in circuit-switched and packet-switched optical networks

Erbium-doped fibre amplifiers (EDFA’s) are a key technology for the design of all optical communication systems and networks. The superiority of EDFAs lies in their negligible intermodulation distortion across high speed multichannel signals, low intrinsic losses, slow gain dynamics, and gain in a wide range of optical wavelengths. Due to long lifetime in excited states, EDFAs do not oppose the effect of cross-gain saturation. The time characteristics of the gain saturation and recovery effects are between a few hundred microseconds and 10 milliseconds. However, in wavelength division multiplexed (WDM) optical networks with EDFAs, the number of channels traversing an EDFA can change due to the faulty link of the network or the system reconfiguration. It has been found that, due to the variation in channel number in the EDFAs chain, the output system powers of surviving channels can change in a very short time. Thus, the power transient is one of the problems deteriorating system performance. In this thesis, the transient phenomenon in wavelength routed WDM optical networks with EDFA chains was investigated. The task was performed using different input signal powers for circuit switched networks. A simulator for the EDFA gain dynamicmodel was developed to compute the magnitude and speed of the power transients in the non-self-saturated EDFA both single and chained. The dynamic model of the self-saturated EDFAs chain and its simulator were also developed to compute the magnitude and speed of the power transients and the Optical signal-to-noise ratio (OSNR). We found that the OSNR transient magnitude and speed are a function of both the output power transient and the number of EDFAs in the chain. The OSNR value predicts the level of the quality of service in the related network. It was found that the power transients for both self-saturated and non-self-saturated EDFAs are close in magnitude in the case of gain saturated EDFAs networks. Moreover, the cross-gain saturation also degrades the performance of the packet switching networks due to varying traffic characteristics. The magnitude and the speed of output power transients increase along the EDFAs chain. An investigation was done on the asynchronous transfer mode (ATM) or the WDM Internet protocol (WDM-IP) traffic networks using different traffic patterns based on the Pareto and Poisson distribution. The simulator is used to examine the amount and speed of the power transients in Pareto and Poisson distributed traffic at different bit rates, with specific focus on 2.5 Gb/s. It was found from numerical and statistical analysis that the power swing increases if the time interval of theburst-ON/burst-OFF is long in the packet bursts. This is because the gain dynamics is fast during strong signal pulse or with long duration pulses, which is due to the stimulatedemission avalanche depletion of the excited ions. Thus, an increase in output power levelcould lead to error burst which affects the system performance.

Brady et al.'s (2005) service evaluation models: A replication and extension in China

The research described in this study replicates and extends the Brady et al., [Brady, M. K., Knight, G. A., Cronin Jr. J. Toma, G., Hult, M. and Keillor, B. D. (2005), emoving the Contextual Lens: A Multinational, Mult-setting Comparison of Service Evaluation Models, Journal of Retailing, 81(3), pp. 215-230] study suggestion that future research in service evaluations should focus on emerging service economies such as China. The intent of the research was to examine the suitability of the models suggested by Brady and colleagues in the Chinese market. The replication somewhat successfully duplicated their finding as to the superiority of the comprehensive service evaluation model. Additionally, we also sought to examine as to whether the service evaluation model is gender invariant. Our findings indicate that there are significant differences between gender. These findings are discussed relative to the limitations associated with the study.

Comparative analysis of BER estimation methods in numerical simulation of 40-Gb/s RZ-DPSK transmission with in-line SOAs

Applying direct error counting, we compare the accuracy and evaluate the validity of different available numerical approaches to the estimation of the bit-error rate (BER) in 40-Gb/s return-to-zero differential phase-shift-keying transmission. As a particular example, we consider a system with in-line semiconductor optical amplifiers. We demonstrate that none of the existing models has an absolute superiority over the others. We also reveal the impact of the duty cycle on the accuracy of the BER estimates through the differently introduced Q-factors. © 2007 IEEE.

Retinal vessel analysis:flicker reproducibility, methodological standardisations and practical limitations

The Retinal Vessel Analyser (RVA) is a commercially available ophthalmoscopic instrument capable of acquiring vessel diameter fluctuations in real time and in high temporal resolution. Visual stimulation by means of flickering light is a unique exploration tool of neurovascular coupling in the human retina. Vessel reactivity as mediated by local vascular endothelial vasodilators and vasoconstrictors can be assessed non-invasively, in vivo. In brief, the work in this thesis • deals with interobserver and intraobserver reproducibility of the flicker responses in healthy volunteers • explains the superiority of individually analysed reactivity parameters over vendorgenerated output • links in static retinal measures with dynamic ones • highlights practical limitations in the use of the RVA that may undermine its clinical usefulness • provides recommendations for standardising measurements in terms of vessel location and vessel segment length and • presents three case reports of essential hypertensives in a -year follow-up. Strict standardisation of measurement procedures is a necessity when utilising the RVA system. Agreement between research groups on implemented protocols needs to be met, before it could be considered a clinically useful tool in detecting or predicting microvascular dysfunction.

Influential DMUs and outlier detection in data envelopment analysis with an application to health care

This paper explains some drawbacks on previous approaches for detecting influential observations in deterministic nonparametric data envelopment analysis models as developed by Yang et al. (Annals of Operations Research 173:89-103, 2010). For example efficiency scores and relative entropies obtained in this model are unimportant to outlier detection and the empirical distribution of all estimated relative entropies is not a Monte-Carlo approximation. In this paper we developed a new method to detect whether a specific DMU is truly influential and a statistical test has been applied to determine the significance level. An application for measuring efficiency of hospitals is used to show the superiority of this method that leads to significant advancements in outlier detection. © 2014 Springer Science+Business Media New York.

Forecasting the term structure when short-term rates are near zero

This paper compares the experience of forecasting the UK government bond yield curve before and after the dramatic lowering of short-term interest rates from October 2008. Out-of-sample forecasts for 1, 6 and 12 months are generated from each of a dynamic Nelson-Siegel model, autoregressive models for both yields and the principal components extracted from those yields, a slope regression and a random walk model. At short forecasting horizons, there is little difference in the performance of the models both prior to and after 2008. However, for medium- to longer-term horizons, the slope regression provided the best forecasts prior to 2008, while the recent experience of near-zero short interest rates coincides with a period of forecasting superiority for the autoregressive and dynamic Nelson-Siegel models. © 2014 John Wiley & Sons, Ltd.

Optimisation of optical regeneration at 40 Gbit/s in dispersion-managed transmission lines with modified synchronous modulators

Numerical optimisation of a 40 Gbit/s dispersion-managed soliton transmission system with in-line synchronous intensity modulation is performed. Using a time-saving numerical approach, superiority of the modified synchronous modulation over conventional synchronous modulation is demonstrated and an optimal operational regime is found.

Pharmaceutical process optimisation of bulk lyophilisates:implications of powder handling

Lyophilisation or freeze drying is the preferred dehydrating method for pharmaceuticals liable to thermal degradation. Most biologics are unstable in aqueous solution and may use freeze drying to prolong their shelf life. Lyophilisation is however expensive and has seen lots of work aimed at reducing cost. This thesis is motivated by the potential cost savings foreseen with the adoption of a cost efficient bulk drying approach for large and small molecules. Initial studies identified ideal formulations that adapted well to bulk drying and further powder handling requirements downstream in production. Low cost techniques were used to disrupt large dried cakes into powder while the effects of carrier agent concentration were investigated for powder flowability using standard pharmacopoeia methods. This revealed superiority of crystalline mannitol over amorphous sucrose matrices and established that the cohesive and very poor flow nature of freeze dried powders were potential barriers to success. Studies from powder characterisation showed increased powder densification was mainly responsible for significant improvements in flow behaviour and an initial bulking agent concentration of 10-15 %w/v was recommended. Further optimisation studies evaluated the effects of freezing rates and thermal treatment on powder flow behaviour. Slow cooling (0.2 °C/min) with a -25°C annealing hold (2hrs) provided adequate mechanical strength and densification at 0.5-1 M mannitol concentrations. Stable bulk powders require powder transfer into either final vials or intermediate storage closures. The targeted dosing of powder formulations using volumetric and gravimetric powder dispensing systems where evaluated using Immunoglobulin G (IgG), Lactate Dehydrogenase (LDH) and Beta Galactosidase models. Final protein content uniformity in dosed vials was assessed using activity and protein recovery assays to draw conclusions from deviations and pharmacopeia acceptance values. A correlation between very poor flowability (p<0.05), solute concentration, dosing time and accuracy was revealed. LDH and IgG lyophilised in 0.5 M and 1 M mannitol passed Pharmacopeia acceptance values criteria with 0.1-4 while formulations with micro collapse showed the best dose accuracy (0.32-0.4% deviation). Bulk mannitol content above 0.5 M provided no additional benefits to dosing accuracy or content uniformity of dosed units. This study identified considerations which included the type of protein, annealing, cake disruption process, physical form of the phases present, humidity control and recommended gravimetric transfer as optimal for dispensing powder. Dosing lyophilised powders from bulk was demonstrated as practical, time efficient, economical and met regulatory requirements in cases. Finally the use of a new non-destructive technique, X-ray microcomputer tomography (MCT), was explored for cake and particle characterisation. Studies demonstrated good correlation with traditional gas porosimetry (R2 = 0.93) and morphology studies using microscopy. Flow characterisation from sample sizes of less than 1 mL was demonstrated using three dimensional X-ray quantitative image analyses. A platinum-mannitol dispersion model used revealed a relationship between freezing rate, ice nucleation sites and variations in homogeneity within the top to bottom segments of a formulation.

Ensuring QoE in contemporary mobile networks for video content distribution

A framework that aims to best utilize the mobile network resources for video applications is presented in this paper. The main contribution of the work proposed is the QoE-driven optimization method that can maintain a desired trade-off between fairness and efficiency in allocating resources in terms of data rates to video streaming users in LTE networks. This method is concerned with the control of the user satisfaction level from the service continuity's point of view and applies appropriate QoE metrics (Pause Intensity and variations) to determine the scheduling strategies in combination with the mechanisms used for adaptive video streaming such as 3GP/MPEG-DASH. The superiority of the proposed algorithms are demonstrated, showing how the resources of a mobile network can be optimally utilized by using quantifiable QoE measurements. This approach can also find the best match between demand and supply in the process of network resource distribution.

A semantic paradigm for intelligent data access

An implementation of Sem-ODB—a database management system based on the Semantic Binary Model is presented. A metaschema of Sem-ODB database as well as the top-level architecture of the database engine is defined. A new benchmarking technique is proposed which allows databases built on different database models to compete fairly. This technique is applied to show that Sem-ODB has excellent efficiency comparing to a relational database on a certain class of database applications. A new semantic benchmark is designed which allows evaluation of the performance of the features characteristic of semantic database applications. An application used in the benchmark represents a class of problems requiring databases with sparse data, complex inheritances and many-to-many relations. Such databases can be naturally accommodated by semantic model. A fixed predefined implementation is not enforced allowing the database designer to choose the most efficient structures available in the DBMS tested. The results of the benchmark are analyzed. ^ A new high-level querying model for semantic databases is defined. It is proven adequate to serve as an efficient native semantic database interface, and has several advantages over the existing interfaces. It is optimizable and parallelizable, supports the definition of semantic userviews and the interoperability of semantic databases with other data sources such as World Wide Web, relational, and object-oriented databases. The query is structured as a semantic database schema graph with interlinking conditionals. The query result is a mini-database, accessible in the same way as the original database. The paradigm supports and utilizes the rich semantics and inherent ergonomics of semantic databases. ^ The analysis and high-level design of a system that exploits the superiority of the Semantic Database Model to other data models in expressive power and ease of use to allow uniform access to heterogeneous data sources such as semantic databases, relational databases, web sites, ASCII files, and others via a common query interface is presented. The Sem-ODB engine is used to control all the data sources combined under a unified semantic schema. A particular application of the system to provide an ODBC interface to the WWW as a data source is discussed. ^

Boundary maintenance in Qatar: Interpretation of domination, segregation and subordination

This study explores the interaction of expatriates in Qatar and their perception of their subordination. The study design included participant observation in an all female University and University housing as well as interviews with Qatari government agencies and ministries, expatriate embassies and expatriates. Semi-structured interviews were conducted across seven expatriate groups: domestic workers, unskilled laborers, semiskilled, professionals, housewives, second-generation expatriates with host country other than Qatar, second-generation expatriates with host country Qatar, and Gulf Cooperation Council citizens. Forty-two subjects completed the interview schedule while 87 interviews were incomplete. ^ Physical control of expatriates occurs through the Gulf practice of sponsorship (The Kafeel System), and local cultural and Islamic related controls intertwined with the Arab Code of honor. Interviews and observations revealed rankings of Arabs and foreigners which emphasize Qatari superiority such as tribal identity, moral ranking of female groups by dress, legal protection and power, sexual consideration and desexualization and salaries and job opportunities based on nationality and ethnicity. Individuals who desire to transcend boundaries into the Qatari realm through citizenship or marriage view Qataris as possessing the “image of the unlimited good” and have acquired Qatari social and cultural capital. Members from all expatriate groups engaged in various forms of resistance to labor and gender domination which ranged from forms of “exit,” expressing a hidden transcript in the privacy of their own group, disguised resistance in public, and occasionally, direct confrontation with the Qatari. Although the legal arena created the appearance that worker's needs were being addressed, laborers engaged in forms of “exit” to escape their oppression. Omani students in the hostel disguised their resistance by spreading gossip, nick-naming homosexual Qatari students at the University, acting out a skit depicting their exclusion from Qatari privilege, spreading rumors of impending freedom, and singing songs of despair in the courtyard. Other sites of resistance were expatriate embassies, the road, the newspaper and technology. This study emphasizes that blaming oppression of the expatriate worker on globalization is a simplistic view of oppression in the Gulf, and ignores complex issues within Qatari society and other Gulf States. Sponsorship, servitude, and gender segregation intersect in Qatar to create a system of segregation and domination of expatriates. ^

Essays on international macroeconomics and conflict analysis

This dissertation addressed two broad problems in international macroeconomics and conflict analysis. The first problem in the first chapter looked at the behavior of exchange rate and its interaction with industry-level tradable goods prices for three countries, USA, UK and Japan. This question has important monetary policy implications. Here, I computed to what extent changes in exchange rate affected prices of consumer, producer, and export goods. I also studied the timing of these changes in these prices. My results, based on thirty-four industrial prices for USA, UK and Japan, supported the view that changes in exchange rates significantly affect prices of industrial and consumer goods. It also provided an insight to the underlying economic process that led to changes in relative prices. ^ In the second chapter, I explored the predictability of future inflation by incorporating shocks to exchange rates and clearly specified the transmission mechanisms that link exchange rates to industry-level consumer and producer prices. Employing a variety of linear and state-of-the-art nonlinear models, I also predicted growth rates of future prices. Comparing levels of inflation obtained from the above approaches showed superiority of the structural model incorporating the exchange rate pass-through effect. ^ The second broad issue addressed in the third chapter of the dissertation investigated the economic motives for conflict, manifested by rebellion and civil war for seventeen Latin American countries. Based on the analytical framework of Garfinkel, Skaperdas and Syropoulos (2004), I employed ordinal regressions and Markov switching for a panel of seventeen countries to identify trade and openness factors responsible for conflict occurrence and intensity. The results suggested that increased trade openness reduced high intensity domestic conflicts but overdependence on agricultural exports, along with a lack of income earning opportunities lead to more conflicts. Thereafter, using the Cox Proportional Hazard model I studied “conflict duration” and found that over-reliance on agricultural exports explained a major part of the length of conflicts in addition to various socio-political factors. ^

An exergy based engineering and economic analysis of sustainable building

To achieve the goal of sustainable development, the building energy system was evaluated from both the first and second law of thermodynamics point of view. The relationship between exergy destruction and sustainable development were discussed at first, followed by the description of the resource abundance model, the life cycle analysis model and the economic investment effectiveness model. By combining the forgoing models, a new sustainable index was proposed. Several green building case studies in U.S. and China were presented. The influences of building function, geographic location, climate pattern, the regional energy structure, and the technology improvement potential of renewable energy in the future were discussed. The building’s envelope, HVAC system, on-site renewable energy system life cycle analysis from energy, exergy, environmental and economic perspective were compared. It was found that climate pattern had a dramatic influence on the life cycle investment effectiveness of the building envelope. The building HVAC system energy performance was much better than its exergy performance. To further increase the exergy efficiency, renewable energy rather than fossil fuel should be used as the primary energy. A building life cycle cost and exergy consumption regression model was set up. The optimal building insulation level could be affected by either cost minimization or exergy consumption minimization approach. The exergy approach would cause better insulation than cost approach. The influence of energy price on the system selection strategy was discussed. Two photovoltaics (PV) systems—stand alone and grid tied system were compared by the life cycle assessment method. The superiority of the latter one was quite obvious. The analysis also showed that during its life span PV technology was less attractive economically because the electricity price in U.S. and China did not fully reflect the environmental burden associated with it. However if future energy price surges and PV system cost reductions were considered, the technology could be very promising for sustainable buildings in the future.