The modelling of physical processes gives rise to mathematical systems of increasing complexity. Good mathematical models have to reproduce the physical process as precisely as possible while the computing time and the storage resources needed to simulate the mathematical model are limited. As a consequence, there must be a tradeoff between accuracy and computational constraints. At the present time, one is often faced with systems that have an unacceptably high level of complexity. It is then desirable to approximate such systems by systems of lower complexity. This is the Model Reduction Problem. This thesis focuses on the study of new model reduction techniques for linear systems. Our objective is twofold. First, there is a need for a better understanding of Krylov techniques. With such techniques, one can construct a reduced order transfer function that satisfies a set of interpolation conditions with respect to the original transfer function. A study of the generality of such techniques and their extension for MIMO systems via the concept of tangential interpolation constitutes the first part of this thesis. This also led us to study the generality of the projection technique for model reduction. Most large scale systems have a particular structure. They can be modelled as a set of subsystems that interconnect to each other. It then makes sense to develop model reduction techniques that preserve the structure of the original system. Both interpolation-based and gramian-based structure preserving model reduction techniques are developed in a unified way. Second order systems that appear in many branches of engineering deserve a special attention. This constitutes the second part of this thesis.

In this paper we describe an approach for generating geometrically-parameterized integrated-circuit interconnect models that are efficient enough for use in interconnect synthesis. The model generation approach presented is automatic, and is based on a multi-parameter model-reduction algorithm. The effectiveness of the technique is tested using a multi-line bus example, where both wire spacing and wire width are considered as geometric parameters. Experimental results demonstrate that the generated models accurately predict both delay and cross-talk effects over a wide range of spacing and width variation. / Singapore-MIT Alliance (SMA)

Attenuating random and coherent noise is an important part of seismic data processing. Successful removal results in an enhanced image of the subsurface geology, which facilitate economical decisions in hydrocarbon exploration. This motivates the search for new and more efficient techniques for noise removal. The main goal of this thesis is to present an overview of the Singular Spectrum Analysis (SSA) technique, studying its potential application to seismic data processing. An overview of the application of SSA for time series analysis is presented. Subsequently, its applications for random and coherent noise attenuation, expansion to multiple dimensions, and for the recovery of unrecorded seismograms are described. To improve the performance of SSA, a faster implementation via a randomized singular value decomposition is proposed. Results obtained in this work show that SSA is a versatile method for both random and coherent noise attenuation, as well as for the recovery of missing traces. / Geophysics

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Bottom water hypoxia and its influence on the environment have been topics of increasing concern for many coastal regions. This research addresses both spatial and temporal variability in sediment biogeochemistry at the southeastern region of Corpus Christi Bay, TX, where seasonal (summer) hypoxia occurs. Traditional techniques for determination of a variety of dissolved and solid components, benthic oxygen demand, and sulfate reduction rates were augmented by measurements using solid state microelectrodes to simultaneously determine concentrations of dissolved O2, Mn2+, Fe2+, and [sigma]H2S in multiple small - interval (1 mm) depth profiles of sediment microcosms. Oxygen concentrations in the overlying water were manipulated in the sediment microcosms and electrode depth profile measurements were made over ~ 500 hours of experimentation. Laboratory and field microelectrode results were in good agreement for both norm - oxic and anoxic time periods. Results indicated that iron (Fe2+) and sulfide ([sigma]H2S) were the redox reactive species in these sediments. During hypoxic conditions an upward migration of dissolved Fe2+and [sigma]H2S through the sediment column and, at times, into the overlying water was observed as the dissolved oxygen concentrations decreased. A corresponding decline in the vertical extent of these redox species occurred when the overlying water was re-oxidized. When both dissolved iron and sulfide coexisted, FeS minerals were formed in the sediment, preventing sulfide diffusion into the overlying water. However, after a long duration of hypoxia (> 200 hours) this buffering capacity was exceeded and both iron and sulfide penetrated into the overlying waters. Results indicated that iron may have a greater influence on hypoxia than sulfide because its concentration in the overlying waters during induced hypoxia was an order of magnitude greater than those of sulfide. Moreover, in the southeastern region of the Bay, where mixing was minimal and the water column was shallow, the sediments alone may have caused the onset of the hypoxic event in a relatively short time period (< 5.5 days). These results demonstrated that in shallow marine environments where seasonal hypoxia occurs, such as Corpus Christi Bay, the associated major changes that take place in the sediment biogeochemistry must be included in benthic - pelagic models for overlying water hypoxia.

This thesis presents a methodology for data aggregation for capacity management. It is assumed that there are a very large number of products manufactured in a company and that every product is stored in the database with its standard unit per hour and attributes that uniquely specify each product. The methodology aggregates products into families based on the standard units-per-hour and finds a subset of attributes that unambiguously identifies each family. Data reduction and classification are achieved using well-known multivariate statistical techniques such as cluster analysis, variable selection and discriminant analysis. The experimental results suggest that the efficacy of the proposed methodology is good in terms of data reduction.

Dendrimer-encapsulated nanoparticles (DENs) were prepared, characterized, and immobilized on solid surfaces. The resulting films were applied as electrocatalysts for the oxygen reduction reaction (ORR). First, the synthesis, physical and chemical properties, and stability of Pd DENs prepared within poly(amidoamine) (PAMAM) dendrimers were studied in aqueous solution. In this part of the study, the following new findings were reported: (1) the maximum Pd ion loading in the dendrimer was correlated to the number of interior amines available for complexation; (2) Pd DENs could be synthesized within amine-terminated Pd DENs by controlling the solution pH; (3) the oxidative stability of Pd DENs was significantly improved by removing solution-phase impurities; (4) exposure to hydrogen gas reversibly converts partially oxidized Pd DENs back to the zerovalent state. Second, Pt and Pd DENs were prepared using amine-terminated PAMAM dendrimers, and then the free amine groups on the periphery were used to immobilize Pt and Pd DENs onto Au surfaces via an intermediate self-assembled monolayer. The resulting DEN films were more robust and had higher coverages of DENs compared to the DEN films prepared via physisorption. Third, Pt DENs were prepared and immobilized on glassy carbon electrodes using an electrochemical coupling method. The resulting films were electrochemically active for the ORR. These electrocatalytic monolayers were also robust, surviving up to 50 consecutive electrochemical scans for ORR and sonication in acid solution with no significant change in activity. Finally, PtPd bimetallic nanoparticles containing an average of 180 atoms (~1.8 nm in diameter) and composed of seven different Pt:Pd ratios were prepared within sixth-generation, hydroxyl-terminated PAMAM dendrimers. Transmission electron microscopy and single-particle energy dispersive spectroscopy confirmed the sizes and compositions of the particles. These DENs were immobilized on glassy carbon electrodes, and their electrocatalytic properties were evaluated as a function of composition using cyclic voltammetry and rotating disk voltammetry. The results showed that the maximum rate for the ORR occurs at a Pt:Pd ratio of 5:1, which corresponds to a relative mass activity enhancement of 2.5 compared to otherwise identical monometallic Pt nanoparticles.

No description available.

Drag reduction is a well-observed phenomenon, it was first observed by the British chemist Toms in 1946, yet its mechanism is still unknown to this day. Polymer Drag reduction has found application in reducing pumping costs for oil pipelines (its use in the Trans Alaska Pipeline has resulted in an increase from 1.44 million bbl./day to 2.1356 million bbl./day), increasing the flow rate in firefighting equipment , and in supporting irrigation and drainage systems. Surfactant drag reducers are used industrially in district heating and cooling systems. Though the fields of Surfactant Drag Reduction and Polymer Drag Reduction are each independently well-developed the effect of their interaction on drag reduction is a less explored phenomenon. Through a well chosen pairing of surfactant and polymer, drag reduction can be maximized while minimizing surfactant and polymer concentrations cutting down on cost and environmental impact. The focus of this work was to determine if there was any positive interaction between the polymers Polyethylene Oxide (PEO) and Anionic PolyAcrylAmide (PAM) and the surfactant Amphosol CG (Cocamidopropyl Betaine) as well as any interaction between the polymers themselves. Both polymers are popular drag reducers while Amphosol is a practically nontoxic (LD50=5g/kg) zwitterionic surfactant and is readily biodegradable. In order to determine if any interaction was present and at what concentration was this most notable 4 techniques were used: Surface tension, Conductivity, Relative Viscosity and Shear Viscosity measurement. From this analysis the polymer Saturation point (PSP), Critical aggregation concentration (CAC) and Critical micelle concentration (CMC) were found as well as the concentrations that optimized the viscosity for the pilot plant runs. The bench scale results were used to pick the optimum concentrations for the polymer surfactant solutions. Pressure readings and flowrate measurements were used to plot the Fanning Friction Factor against the Generalized Reynolds Number for the surfactant polymer mixtures and compared to their pure polymer and surfactant counterparts. The Blasius line was found to hold for water measurements taken and is the base to determine percentage drag reduction. The effect of the presence of amphosol on degradation and overall drag reduction were noted. Other factors considered were pipe diameter and the effect of ionic impurities in the solvent.

Syftet med studien var att undersöka hur personer med ett injektionsmissbruk, som medverkade i sprututbytesverksamhet i Sverige, upplevde att deras livskvalitet blivit annorlunda. Vidare undersöktes också vilka insatser de blivit erbjudna och om de upplevde att de hade ett minskat riskbeteende. Frågeställningarna som användes i studien för att undersöka detta var:  Vilka insatser inom sprututbytesverksamheten erbjuds personer med injektionsmissbruk att ta del av?  Hur använder sig personer som medverkar i sprututbytesverksamhet av den kunskap de erhåller om hur de ska minska sitt riskbeteende?  Hur upplever personerna som deltar i sprututbytesverksamheten att deras livskvalitet blivit annorlunda? För att kunna svara på frågeställningarna användes en enkät som skickades till sprututbytesverksamheter i Sverige. De centrala begrepp som går att återfinna i studien är harm reduction och livskvalitet och dessa begrepp är väsentliga när det gäller konstruktionen av enkäten i relation till syfte och frågeställningar. Slutligen inkom 15 stycken enkäter av de 60 stycken som hade skickats ut, vilket gjorde att resultatet som kom fram inte gick att generalisera. Enkäterna behandlades i datorprogrammet SPSS för att kunna ge en tydlig bild av hur respondenterna svarat. Det som framkom i resultatet var att respondenterna främst använde sig av insatser som byte av sprutor, vaccinationer och att testa sig för sjukdomar. Smittskydd och smittspridning var de områden där respondenterna uppgav att de erbjöds mest information, vilket också var de områden de ansåg sig ha bäst kunskap om. Det framkom även att respondenterna ansåg att deras livskvalitet hade blivit bättre sedan de började i sprututbytesverksamheten. Insatser som syftade till att personerna som deltog skulle avsluta sitt narkotikamissbruk var inte något som det angavs att det erbjöds speciellt mycket av. Slutsatsen som drogs av studien var att de insatser som erbjöds på sprututbytesverksamheten i första hand syftade till att minska riskbeteende och smittspridning av HIV