Semiparametric estimate of the efficiency of imperfect maintenance actions for a gamma deteriorating system

International audienceA system is considered, which is deteriorating over time according to a non homogeneous gamma process with unknown parameters. The system is subject to periodic and instantaneous imperfect maintenance actions (repairs). Each imperfect repair removes a proportion ρ of the accumulated degradation since the previous repair. The parameter ρ hence appears as a measure for the maintenance efficiency. This model is called arithmetic reduction of degradation of order 1. The system is inspected right before each maintenance action, thus providing some multivariate measurement of the successively observed deterioration levels. Based on these data, a semiparametric estimator of ρ is proposed, considering the parameters of the underlying gamma process as nuisance parameters. This estimator is mainly based on the range of admissible ρ's, which depends on the data. Under technical assumptions, consistency results are obtained, with surprisingly high convergence rates (up to exponential). The case where several i.i.d. systems are observed is next envisioned. Consistency results are obtained for the efficiency estimator, as the number of systems tends to infinity, with a convergence rate that can be higher or lower than the classical square root rate. Finally, the performances of the estimators are illustrated on a few numerical examples

Evaluating enhanced hydrological representations in Noah LSM over transition zones : an ensemble-based approach to model diagnostics

textThis work introduces diagnostic methods for land surface model (LSM) evaluation that enable developers to identify structural shortcomings in model parameterizations by evaluating model 'signatures' (characteristic temporal and spatial patterns of behavior) in feature, cost-function, and parameter spaces. The ensemble-based methods allow researchers to draw conclusions about hypotheses and model realism that are independent of parameter choice. I compare the performance and physical realism of three versions of Noah LSM (a benchmark standard version [STD], a dynamic-vegetation enhanced version [DV], and a groundwater-enabled one [GW]) in simulating high-frequency near-surface states and land-to-atmosphere fluxes in-situ and over a catchment at high-resolution in the U.S. Southern Great Plains, a transition zone between humid and arid climates. Only at more humid sites do the more conceptually realistic, hydrologically enhanced LSMs (DV and GW) ameliorate biases in the estimation of root-zone moisture change and evaporative fraction. Although the improved simulations support the hypothesis that groundwater and vegetation processes shape fluxes in transition zones, further assessment of the timing and partitioning of the energy and water cycles indicates improvements to the movement of water within the soil column are needed. Distributed STD and GW underestimate the contribution of baseflow and simulate too-flashy streamflow. This work challenges common practices and assumptions in LSM development and offers researchers more stringent model evaluation methods. I show that, because of equifinality, ad-hoc evaluation using single parameter sets provides insufficient information for choosing among competing parameterizations, for addressing hypotheses under uncertainty, or for guiding model development. Posterior distributions of physically meaningful parameters differ between models and sites, and relationships between parameters themselves change. 'Plug and play' of modules and partial calibration likely introduce error and should be re-examined. Even though LSMs are 'physically based,' model parameters are effective and scale-, site- and model-dependent. Parameters are not functions of soil or vegetation type alone: they likely depend in part on climate and cannot be assumed to be transferable between sites with similar physical characteristics. By helping bridge the gap between the model identification and model development, this research contributes to the continued improvement of our understanding and modeling of environmental processes.Geological Science

Regulating the automobile

Division of Policy Research and Analysis. National Science Foundatio

Improving the measurement of live weight and body condition score in sheep : a thesis presented in fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science, Massey University, Turitea, Palmerston North, New Zealand

Liveweight (LW) and body condition score (BCS) are important performance indicators in sheep management, providing a basis for decision making. Therefore, accurate measurement of these traits is imperative. The overall aims of this thesis were to 1) Determine the factors affecting the rate of LW loss of fasting sheep, 2) derive equations to predict LW and LW change over a short time period (1 to 8 hours), 3) evaluate the factors affecting the relationship between ewe LW and BCS, and 4) derive equations for predicting ewe BCS. In the LW studies, lambs were offered three herbage availability levels (Low, Medium and High) in autumn or winter. Similarly, mixed-aged ewes at different physiological states were offered two herbage levels (Low or High). These studies were conducted in two stages: A) calibration stage and B) validation stage. Equations to predict without delay LW were developed at the calibration stage and validated on data collected from independent ewes from different farms. The rate of ewe LW loss was influenced by herbage type and availability, and season. Further, in pregnant ewes, liveweight loss was influenced by the stage of pregnancy, but not pregnancy-rank. Applying correction equations improved the prediction accuracy of without delay LW estimates up to 55% and 69% in ewe lambs and mixed aged ewes compared with using the delayed weights, respectively. For the BCS studies, LW and BCS data of ewes were collected at regular times of the annual production cycle until they were six years of age. Using a ewe’s LW and BCS records to predict their current BCS using a linear model gave moderately accurate estimates. A different dataset, which included foetal- and fleece weight-adjusted LW and height at withers was then used. It was found that equations combining LW, LW change and previous BCS explained more variability in current BCS and were more accurate than LW-alone based models but the addition of adjusted LW and height at withers gave no further benefit to the BCS prediction models. Applying machine learning classification algorithms such as extreme gradient boosted trees and Random forest on a 3-point BCS scale achieved very good BCS prediction accuracies (> 85%). These combined findings provide useful prediction equations that could be incorporated into weighing systems, which along with EID would improve sheep production by aiding management decision making

Facing the development challenge in Mozambique: an economywide perspective

"Following Mozambique's economic collapse in 1986, the country began a wide-ranging process of reform, with the support of the international community. The diagnosis was of an economy that failed to maintain monetary control, consumed beyond its means, focused production excessively on nontraded goods, and relied on inefficient and inflexible microeconomic structures. Nevertheless, Mozambique was also at war. The pace of stabilization and structural adjustment quickened after 1992, when, concurrent with the demise of apartheid, civil strife finally came to an end. After more than 10 years of adjustment, the reform program has now been essentially implemented. Yet, this does not imply, as shown in this study, that sufficient conditions for sustained economic development are in place. Mozambique remains very poor, and even under highly optimistic assumptions about the future, the development process is set to last for decades. This report attempts to respond to some of the basic development challenges facing Mozambique and to provide both qualitative and quantitative insights for policymaking in the years to come. Throughout, the issues addressed are approached from an economywide perspective ....Finally, this study aims to demonstrate that sophisticated analytical tools can be of significant value, even in “data-poor” situations. The need for a clear perspective and in-depth understanding of the socioeconomic complexities of the country in question stands out. However, while the analyses in this report are Mozambique specific, the basic analytical approach is replicable and could be brought to bear on other countries both within and outside Africa." From Authors' Introduction.Structural adjustment (Economic policy) Mozambique., Mozambique Economic conditions 1975- ., Mozambique Social conditions., Agriculture Economic aspects Africa., Poverty.,

Modelling, thermoeconomic analysis and optimization of hybrid solar-biomass organic Rankine cycle power plants

The need for modern energy systems to embrace the requirements of energy security, sustainability and affordability in their designs has placed emphatic importance on exploitation of renewable resources, such as solar and wind energy, etc. However, these resources often lead to reduced reliability and dispatchability of energy systems; less-efficient conversion processes; high cost of power production; etc. One promising way to ameliorate these challenges is through hybridization of renewable energy resources, and by using organic Rankine cycle (ORC) for power generation. Thus, this PhD research project is aimed at conceptual design and techno-economic optimization of hybrid solar-biomass ORC power plants. The methodologies adopted are in four distinct phases: - First, novel hybrid concentrated solar power (CSP)-biomass scheme was conceived that could function as retrofit to existing CSP-ORC plants as well as in new hybrid plant designs. Thermodynamic models were developed for each plant sub-unit, and yearly techno-economic performance was assessed for the entire system. Specifically, the ORC was modelled based on characteristics of an existing CSP-ORC plant, which currently operates at Ottana, Italy. Off-design models of ORC components were integrated, and their performance was validated using experimental data obtained from the aforementioned real plant. - Second, detailed exergy and exergoeconomic analyses were performed on the proposed hybrid plant, in order to examine the system components with remarkable optimization potentials. The evaluation on optimization potentials considered intrinsic irreversibilities in the respective components, which are imposed by assumptions of systemic and economic constraints. This has been termed enhanced exergy and enhanced exergoeconomic analyses here. - Third, the techno-economic implications of using siloxane mixtures as ORC working fluid were investigated, with the aim of improving heat transfer processes in the ORC plant. The studied fluid pairs were actively selected to satisfy classical thermodynamic requirements, based on established criteria. - Fourth, the biomass retrofit system was optimized multi-objectively, to minimize biomass consumption rate (maximize exergetic efficiency) and to minimize exergy cost rate. Non-dominated Sorting Genetic Algorithm (NSGA-II) was adopted for multi-objective optimization. The conceptual scheme involves parallel hybridization of CSP and biomass systems, such that each is capable of feeding the ORC directly. Results showed that the proposed biomass hybridization concept would increase both thermodynamic efficiency and economic performance of CSP-ORC plants, thereby improving their market competitiveness. Total exergy destroyed and exergy efficiency were quantified for each component, and for the whole system. Overall system exergetic efficiency of about 7 % was obtained. Similarly, exergoeconomic factor was obtained for each system component, and their implications were analysed to identify system components with high potentials for optimization. Furthermore, it was observed that thermodynamic performance of the hybrid plant would be optimized by using siloxane mixtures as ORC working fluid. However, this would result in larger heat exchange surface area, with its attendant cost implications. Lastly, biomass combustion and furnace parameters were obtained, which would simultaneously optimize exergetic efficiency and exergy cost rate for the hybrid plant. In sum, a novel scheme has been developed for hybridizing solar and biomass energy for ORC plants, with huge potentials to improve techno-economic competitiveness of solar-ORC systems

Quantifying genotypic and environmental factors affecting potato canopy growth

There is a high degree of variation in potato yield which may contribute to the current UK yield plateau. There is a strong correlation between light intercepted, total biomass produced and biomass partitioned to the tubers as yield. Variation in potato canopy growth can be analysed using non-destructive measurements and the size of the canopy determines radiation interception. Proportion of soil covered by green leaves (percentage of ground covered, GC) is a simple proxy for light intercepted. Two empirical models were compared for ability to summarize GC throughout the growing season. Both models showed a similar ability to describe GC, but differed in output and ease of interpretation, so the simpler, more descriptive model was selected for use in further canopy quantification. The effects of planting date, nitrogen rate, cultivar and stem density were examined in two multi-year experiments. Planting date had a strong effect on early growth, though subsequent growth was less sensitive to temperature. Leaf production and canopy duration varied with cultivar determinacy. Cultivar and nitrogen fertilizer rate determined the potential for branch and branch leaf production (and therefore canopy longevity), altering distribution of leaf area index (LAI) within the canopy, but duration of growth was determined by planting date, which when delayed, shortened the season. The effects of stem density were most noticeable early in the season when higher stem density resulted in faster canopy expansion and earlier canopy closure. Branch production was reduced at high stem densities, but total LAI varied little. Canopy quantification was also used to analyse historical data and across 20 cultivars, decreasing duration of early canopy expansion was the only universal response to increasing stem density. By quantifying the growth and maintenance of experimental and commercial crop canopies, causes of variation in light interception and subsequent yield can be identified. ‘Best agronomic practice’ can then be identified, enabling targeted changes to reduce the variability in yields and improve resource use efficiency. Additionally, this greater understanding of canopy development will refine existing potato yield models, enabling more specific and more accurate predictions. Future yield models should include stem density to better predict early season canopy growth and cultivar determinacy to predict interactions between canopy production and season length.This PhD was funded by the Cambridge University Potato Growers Association (CUPGRA)

Aerobic Exercise for the Promotion of Healthy Aging: Changes in Brain Structure Assessed with New Methods

As the proportion of older individuals in the population increases, so does the scientific concern surrounding age-related deterioration of brain tissue and related cognitive decline. One modifiable lifestyle factor of interest in the pursuit to slow or even reverse age-related brain atrophy is aerobic exercise. A number of studies have already demonstrated that aerobic exercise in older age can induce maintenance (i.e., reduction of loss) of both gray and white matter volume, particularly in the frontal regions of the brain, which are vulnerable to shrinkage in older age. Other magnetic resonance imaging (MRI)-based techniques, such as quantitative MRI and diffusion-weighted MRI, have been used to measure age-related deterioration of gray and white matter integrity in both voxel-wise analyses as well as on the latent level, but whether these negative changes can be ameliorated through exercise has yet to be shown. The current dissertation includes three papers which used a number of both established and novel MRI-based metrics to quantify changes in brain tissue integrity resulting from aging, as well as to investigate whether these changes can be ameliorated through aerobic exercise. In Paper I (Wenger et al., 2022), we tested the reliability of quantitative MRI measures, namely longitudinal relaxation rate, effective transverse relaxation rate, proton density, and magnetization transfer saturation, by measuring them in a two-day, four-session design with repositioning in the scanner. Using the intra-class effect decomposition model, we found that magnetization transfer saturation could reliably detect individual differences, validating its use to investigate changes in brain structure longitudinally, as well as correlations with other variables of interest, such as change in cardiovascular fitness. In Paper II (Polk et al., 2022), we tested the effects of aerobic exercise on a latent factor of gray-matter structural integrity, comprising observed measures of gray-matter volume, magnetization transfer saturation, and mean diffusivity, in regions of interest that have previously shown volumetric effects of aerobic exercise. We found that gray-matter structural integrity was maintained in frontal and midline regions, and that change in gray-matter structural integrity in the right anterior cingulate cortex was positively correlated with change in cardiovascular fitness within exercising participants. These results suggest a causal relationship between aerobic exercise, cardiovascular fitness, and gray-matter structural integrity in this region. In Paper III (Polk et al., 2022), we tested the effects of aerobic exercise on white matter integrity, measured with both established and recently developed metrics. We were able to replicate findings from a previous study on the effects of aerobic exercise on white matter volume, and we also found change-change correlations between white matter volume and cardiovascular fitness as well as between white matter volume and performance on a test of perceptual speed. We also found unexpected exercise-induced changes in the diffusion weighted imaging-derived metrics of fractional anisotropy, mean diffusivity, fiber density, and fiber density and cross-section. Specifically, we found increases (or decreases in the case of mean diffusivity) within control participants and decreases (or increases in mean diffusivity) in exercisers. Furthermore, we found that percent change in fiber density and fiber density and cross-section correlated negatively with percent change in both cardiovascular fitness and cognitive performance. This casts doubt on the functional interpretation of these measures and suggests that the “more is better” principle may not be universally applicable when investigating age-related and exercise-induced changes in white matter integrity. In sum, this dissertation showed that regular at-home aerobic exercise, which may be more accessible for older individuals than supervised exercise, can be an effective tool to ameliorate age-related decreases in a latent measure of gray-matter structural integrity as well as white matter volume. It also illuminated potential limitations of other measures of white matter integrity in the context of aging and aerobic exercise, and calls for further research into these novel measures, especially when considering functional outcomes such as cognitive performance

Analysis of the Effects of Formative Assessment in Promoting Transfer of Learning in an Undergraduate General Microbiology Laboratory Course

The undergraduate microbiology lab serves an important role in establishing a foundation of best practices in aseptic technique and infection control for pre-medical, pre-nursing, pre-pharmacy, or pre-allied health students. The high incidence of hospital-acquired infections (HAIs) in the US and evidence in the literature of less effective implementation of proper aseptic technique among apprentice doctors and nursing students suggests that more effective transfer of learning could improve implementation of these procedures in the clinical setting. The research described in this study aimed to assess learning transfer as it applied to aseptic techniques and infection control skills learned in the undergraduate microbiology lab from pre- and post-lab formative assessments to midterm and lab practical summative assessments. Assisting students in building connections between the aseptic techniques learned in general microbiology and their application in the clinical setting through pre-lab formative assessments and reflective practices may lead to improvements in use of aseptic techniques and infection control measures as they progress into clinical careers and may ultimately reduce infection rates and mortality rates due to HAIs. The first major aim of this study was to explore the experiences of students with respect to learning transfer through qualitative analysis of student responses to post-lab free-response questions regarding difficulties faced in the lab and the relevance of microbiology to students\u27 future careers. The second major aim of this study was to determine if the implementation of an in-class pre-lab formative assessment facilitates learning transfer as evidenced by significant improvements on summative lab midterm and final lab practical exam scores. Qualitative analysis of student responses to open-ended reflection questions indicated evidence of predominantly low-road transfer with respect to transfer of automaticity. Additionally, qualitative analysis of student responses indicated evidence of lateral transfer regarding transfer of complexity. Finally, there was evidence of an evolution from near to far transfer of context indicating that students were able to perceive the application of the knowledge gained in the microbiology lab in contexts similar to the lab as well as contexts outside of the lab. Evidence from student responses suggested that primarily students intending to pursue careers in healthcare fields were able to perceive specific applications of the microbiology lab to their future careers. Further, evidence from student responses suggested that students predominantly had difficulties with procedures, interpretation of results, manual dexterity with microbiological equipment and materials, and expressed the need to practice these procedures and techniques. Statistical analyses provided quantifiable evidence that the implementation of pre-lab quizzes had both a statistically significantly positive impact and a practically positive impact on lab practical final scores in both of the semesters studied as compared to historical control groups with a large effect size. The statistically and practically significant impact of the pre-lab quizzes on lab practical final exams is an important finding and will add to the current literature on the importance of formative assessment in undergraduate microbiology education