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Diesel engines are widely used in automotive sector due to their high fuel efficiency, distinguished durability and great reliability. However, NOx and particulate matters (PM) are main concerns of the Diesel engines due to their lean burn conditions. To reduce these emissions, Diesel engines are usually coupled with state-of-the-art Diesel aftertreatment systems including a Diesel Oxidation Catalyst (DOC), a Diesel Particulate Filter (DPF), and a Selective Catalytic Reduction system (SCR). With increasingly stringent regulations, the estimation and control strategies of Diesel after-treatment systems for NOx and PM reduction are becoming more and more critical and challenging, especially under transient conditions with unknown system dynamics including disturbances and model uncertainties. To address these problems, this thesis focuses on advanced strategies based on disturbance estimation and compensation for improving the performance of Diesel after-treatment systems. Urea injection and ammonia storage ratio are critical for the SCR system to achieve high NOx reduction efficiency and low NH3 slip. Nevertheless, unknown system dynamics including input (urea injection) disturbances and model uncertainties of SCR system make it challenging to achieve high NOx reduction efficiency and low NH3 slip. To deal with these obstacles, Paper 1, Paper 2 and Paper 3 (Chapter 2, 3, and 4 respectively) proposed active disturbance estimation and compensation methods for enhancing the SCR performance. Paper 1 (Chapter 2) introduces two different methods to accurately detect urea injection and correct for urea dosing control. Paper 2 (Chapter 3) depicts a robust Nonlinear Disturbance Observer (robust NDO) to effectively estimate the ammonia storage ratio in a cost-effective way. Paper 3 (Chapter 4) presents a compound control strategies based on active disturbance rejection control (ADRC) to precisely keep NH3 slip low and achieve high NOx reduction efficiency. DOC thermal management is critical to effectively burn the soot during DPF regeneration (PM reduction). But unknown system dynamics including DOC inlet emissions and model uncertainties make it difficult for DOC mean temperature estimation and DOC outlet temperature control during DPF regeneration. To deal with these challenges, Paper 4 and Paper 5 (Chapter 5 and 6 respectively) developed active disturbance estimation and compensation strategies for improving DOC thermal management during DPF regeneration. Paper 4 (Chapter 5) introduces a robust filter based on Smooth Variable Structure Filter (SVSF) with augmented disturbance states to estimate the mean temperature of DOC. Paper 5 (Chapter 6) presents a composite controller combining a feedforward controller and an modified Active Disturbance Rejection Controller (mADRC) with time delay compensation for the DOC outlet temperature control. The proposed methods in the 5 papers are either validated by the calibrated GT-power model or experiments with Diesel after-treatment systems. / Thesis / Doctor of Philosophy (PhD)

This research investigates the harmonic and narrowband disturbance rejection problem for linear time-periodic (LTP) systems. The consequence of disturbances on LTP systems is similar to their linear time-invariant (LTI) counterparts, but is complicated by the interaction of the disturbance and plant acting at different frequencies, which manifests itself in the modulation of the disturbance signal. The result, for an m-periodic plant and disturbance containing a single tone, is that the output contains m tones. Using various disturbance rejection architectures, harmonic and narrowband disturbance rejection is investigated for linear time-periodic plants. Included are classical and multivariable feedback controllers, fixed-gain feedforward designs using finite impulse response (FIR) filters and H-infinity synthesis tools, and adaptive feedforward controllers. The objective of time-periodic, narrowband, disturbance rejection seeks to place a zero in the controlled system's disturbance path and align the zero direction, defined by the null space of the controlled system at the disturbance frequency, with the disturbance. In this research, constraints on controlled system infinity-norms specify nominal performance and robust stability objectives. Periodic controllers are found using existing LTI H-infinity control theory, and causality is satisfied using two techniques which can be added easily to H-infinity solvers: loop-shifting and Q-parameterization. The resulting controllers are high-gain, narrowband-pass, periodic filters; the closed-loop sensitivity has a zero at the disturbance frequency, and the disturbance is in the sensitivity's null space. It is also shown that classical designs do not achieve the same performance levels as periodic controllers. Similar developments are made using the feedforward disturbance rejection architecture. Objectives are given which minimize the weighted infinity-norm of the controlled system. Such feedforward controllers achieve perfect disturbance rejection. A multivariable equivalent of the tapped-delay line is used in the description of periodic FIR filters. In addition, periodic FIR filters are made adaptive using an algorithm similar to filtered-X least mean square (LMS) but modified for periodic systems. / Ph. D.

Streams are ecosystems organized by disturbance. One of the most frequent disturbances within a stream is elevated flow. Elevated flow can both stimulate ecosystem processes and impede them. Consequently, flow plays a critical role in shifting the dominant stream function between biological transformation and physical transportation of materials. To garner further insight into the complex interactions of stream function and flow, I assessed the influence of elevated flow and flow disturbances on stream metabolism. To do so, I analyzed five years of dissolved oxygen data from an urban- and agriculturallyinfluenced stream to estimate metabolism. Stream metabolism is estimated from the production (gross primary production; GPP) and consumption (ecosystem respiration; ER) of dissolved oxygen. With these data, I evaluated how low and elevated flows differentially impact water quality (e.g., turbidity, conductivity) and metabolism using segmented metabolism- and concentration- discharge analyses. I found that GPP declined at varying rates across discharge, and ER decreased at lower flows but became constant at higher flows. Net ecosystem production (NEP; = GPP - ER) reflected the divergence of GPP and ER and was unchanging at lower flows, but declined at higher discharge. These C-Q patterns can consequently influence or be influenced by changes in metabolism. I coupled metabolism-Q and C-Q trends to examine linked flow-induced changes to physicochemical parameters and metabolism. Parameters related to metabolism (e.g., turbidity and GPP, pH and NEP) frequently followed coupled trends. To investigate metabolic recovery dynamics (i.e., resistance and resilience) following flow disturbances, I analyzed metabolic responses to 15 isolated flow events and identified the antecedent conditions or disturbance characteristics that most contributed to recovery dynamics. ER was both more resistant and resilient than GPP. GPP took longer to recover (1 to >9 days, mean = 2.5) than ER (1 to 2 days, mean = 1.1). ER resistance was strongly correlated with the intensity of the flow event, whereas GPP was not, suggesting that GPP responds similarly to flow disturbances, regardless of the magnitude of flow event. Flow may be the most frequent disturbance experienced by streams. However, streams are exposed to a multitude of other disturbances; here I also highlight how anthropogenic alterations to streams – namely, burying a stream underground – can change biogeochemical function. This thesis proposes novel frameworks to explore the nexus of flow, anthropogenic disturbances, and stream function, and thereby to further our understanding of the complex relationship between streams and disturbances. / Master of Science / A stream is defined by its flowing water. Flow brings the nutrients, organic matter, and other materials necessary to the algae and bacteria within the stream as well as the invertebrates and fishes they sustain, and is consequently integral to in-stream biology and ecology. However, elevated flow is also one of the most frequent disturbances experienced by streams. Elevated flow dilutes or enriches concentrations of water quality parameters, moves the water faster, reduces the amount of time essential nutrients are available to organisms within streams, and scours the algae and bacteria on stream bottoms. Here, I analyzed five years of data from an urban- and agriculturally-influenced stream and estimated stream metabolism to explore the influence of flow on stream biology, chemistry, and ecology. Stream metabolism is a process that reflects the respiration and photosynthesis of bacteria and algae, estimated from the production and consumption of dissolved oxygen. The primary research objective of my thesis was to investigate how changing flow impacts metabolism, by: (1) examining how low and high flows impact metabolism differently, and (2) studying the response and recovery of metabolism following multiple flow disturbances. Flow not only influences in-stream biology and processes, such as stream metabolism, but also changes the water quality of the stream (e.g., conductivity, pH, turbidity). To examine the interconnection between flow-induced changes to water quality parameters and metabolism, I measured how low and high flows impacted water quality and then compared water quality-flow relationships with metabolism at low and high flows. I found that metabolic processes and related water quality parameters were frequently coupled. Next, to test how water quality might also influence the response and recovery of metabolism after a flow disturbance, I examined whether prior environmental conditions (e.g., temperature, light) or the magnitude of the flow disturbance influenced metabolic response and recovery. I found that the size of the flow disturbance did change a critical piece of stream metabolism. Flow is not the only prevalent disturbance streams face: increasingly, streams are being altered by ongoing urban and suburbanization. Therefore, to highlight the full suite of disturbances to streams caused by human modification, I wrote a public science communication piece documenting the biological, chemical, and ecological ramifications of burying streams underground. Ultimately, this thesis proposes new frameworks to more adequately explore the complex relationships between water quality, stream ecology, and disturbances.

The southern pine beetle (SPB) (Dendroctonus frontalis Zimm.) is one of the most destructive forest insect pests in the southeastern United States and has historically had a large impact on the forests of North Carolina. Many characteristics of a forest can contribute to SPB susceptibility including stand density, growth rate, age, soil type, and position on the landscape. This work was undertaken in an effort to assist and improve on the current federal SPB hazard modeling being conducted for North Carolina by the USDA Forest Service – Forest Health Protection's Forest Health Technology Enterprise Team (FHTET). In our study, predictive SPB susceptibility models were developed for each physiographic region in North Carolina using two variables not currently included in the FHTET modeling, mean stand age and the in-stand percentage of sawtimber-sized pines. These variables were obtained from USDA Forest Service – Forest Inventory and Analysis (FIA) data and North Carolina Forest Service historical SPB records creating a dataset of both infested and non-infested stands and the models were developed using the CART® classification tree approach. Two model-derived age classes (older than and younger than 22 years) were identified on the landscape using current Landsat 5 Thematic Mapper (TM) imagery chronosequences of disturbance index (DI) â transformed scenes to identify stand-replacing disturbances, resulting in a kappa statistic of 0.6364 for the younger than 22 year age class and 0.7778 for the older than 22 years age class. A kappa value of 1 is ideal. The CART® modeling effort produced valid models in all three physiographic regions of North Carolina, though the complexity of the piedmont model makes it impractical for use in the field. The dependent variable in the classification tree was presence or absence of SPB outbreak and the test sample error percentages were similar across regions, with errors ranging between 23.76 - 34.95 percent. Overall prediction success, based on the software's internal cross-validation procedure, was likewise comparable across the regions with 72.28 - 89.56 percent correctly predicted. Based on our modeling, stand age and percent sawtimber should be included in future FHTET SPB hazard modeling efforts for the coastal plain and mountains, respectively. Age classes can be reasonably estimated using Landsat or other multispectral imagery. / Master of Science

Exurbanization is occurring where large tracts of land are being sold to developers. Typically these are ranches that are then divided into 40-acre parcels and sold by developers, avoiding subdivision regulations requiring paved streets, utilities and other amenities. The result is an unplanned subdivision with no infrastructure, and tax revenues that cannot offset the cost of providing it. Interviews with professional planners suggested there may be independent variables capable of predicting the amount of human disturbance in an exurban area: parcel size, full cash value, tenure, distance to paved roads, site-built housing, mobile homes, and presence of biological or riparian areas. A total of 7,465 acres (3,022 ha) of parcel disturbance were digitized in exurban Arivaca, acreage values were converted to a binary dependent variable and used in logistic regression analysis to test independent variables' predictive value. Four were statistically significant: parcel size, full cash value, mobile homes and site-built housing. Landscape fragmentation was also tested using the presence of the variable scoring highest in probability - site-built housing. Zones of influence with a negative ecological influence surrounded the homes - up to 5,055 acres (2,046 ha) were impacted. Interviews with an exemplary sample of residents regarding their land use ethic found all had very strong opinions on how their properties should be treated as well as undesirable land uses such as overgrazing, over-use of groundwater for short-term economic gain and use of off-road vehicles. An explanation of the small sample size of both planners and residents is warranted. Planners were limited to those working in Pima County government who had professional experience with the study area of Arivaca and were familiar with its particular situation. The number of Arivaca residents interviewed was intended to discern an exemplary group's opinions based on how large a parcel they owned, the various sizes being a typical cross-section of acreage in the study area. What these findings illustrate is (1) the difficulty of predicting human-induced disturbance, (2) land fragmentation is more than the actual areas of physical disturbance and (3) some residents are aware of impacts related to their activities, mitigating damage wherever possible.

Dendroecological methods play a critical role in developing our understanding of forest processes by contributing historical evidence of climate variability and the temporal characteristics of disturbance. We seek to contribute to these methods by developing a research protocol for decoupling radial-growth signatures related to climate, fire, and insect outbreaks in central Oregon. Our methods are based on three independent, crossdated tree-ring data sets: 1) a 545-year tree-ring climate reconstruction, 2) a 550-year fire history, and 3) a 250-year pandora moth outbreak history derived from host (Pinus ponderosa) and non-host (Abies grandis-Abies concolor) tree-ring chronologies. Based on these data, we use visual criteria (marker and signature rings), statistical comparisons, and Superposed Epoch Analysis (SEA) to identify the timing of growth anomalies and establish the temporal relationships between drought, climate variation (ENSO and PDO), fire events, and pandora moth (Coloradia pandora) outbreaks. Our results show pandora moth outbreaks generally coincide with periods of below-average moisture, whereas fire in central Oregon often follows a period of wetter than average conditions. Fire events in central Oregon appear to be related to shifts in hemispheric climate variability but the relationship between fire and pandora moth outbreaks remains unclear.

Hurricanes can temporarily disrupt seasonal patterns of fish assemblage change or result in permanent changes in fish assemblages. I studied the effects of two hurricanes on fish assemblages at the Chandeleur Islands and the possible influence that storm-generated tidal channels may have on the composition of local fish assemblages. I also compared recently collected data to historic ichthyofaunal survey data collected over thirty years ago at the Chandeleur Islands. Near shore fish assemblages changed the most after hurricanes but changes in species composition were primarily due to increases in abundance and diversity. During July 2007 there was no significant difference between fish assemblages in channel and seagrass habitats, although significant differences among wash-over channels existed. Loss of habitat and the increased intensity and frequency of recent storms may explain why current fish assemblages at the Chandeleur Islands are less diverse (as measured by taxonomic distinctness) than assemblages collected during 1969-1971.

Nowadays global companies view the world as a single entity, sourcing materials fromanywhere and performing operations to create the optimal supply chain for their products.This leads to an increasing complexity which is driving supply management to becomea core capability of businesses. As supply chains are inherently vulnerable to disturbances,supply management will have to play a key role in the field of risk analysisand risk management. An increased awareness of sources of disturbances is essential tocreate significant improvements in the handling and prevention of disturbances.The purpose of this thesis is to identify and classify sources of disturbance which canhave a negative influence on a company’s supply management. This is achieved by theinvestigation of theories available in literature, as well as identifying and analyzing thedisturbances in the supply management of an international manufacturing company.Additionally, the theories on disturbance management are reviewed to create a foundationfor managerial implications.The company studied is Husqvarna, which currently is in a situation with several disturbancesin its supply management. The performed case study aims at both, describingthese phenomena, as well as testing of the theories. The chosen qualitative approachmakes it possible to gain in-depth knowledge and investigate different aspects ofsources of disturbances in this case study. The interviews performed are standardizedopen ended questionnaires in order to get in-depth knowledge of the situation.The empirical findings are then analyzed in regard to the purpose of the thesis. The goalof this analysis is to compare the sources of disturbances of the classification schemecreated in the literature review to the respondents’ answers from the interviews. Moreover,inputs and opinions from the respondents on how to manage disturbances are connectedwith the theories provided in the literature review within this field.Various sources of disturbance with a negative influence on the supply management ofcompanies are identified. It was also possible to compare the classification schemewhich was created based on the theoretical findings with the finding of the case study ofHusqvarna. Consequently a holistic overview of potential and actual sources of disturbancein supply management has been created. Furthermore, it is possible to contribute tothe body of knowledge on how to manage disturbances in supply management. Theprovided insights highlight implications that can help companies to successfully managedisturbances and hence improve their performance.