Multi-Agent Coverage Control with Energy Depletion and Repletion

We develop a hybrid system model to describe the behavior of multiple agents cooperatively solving an optimal coverage problem under energy depletion and repletion constraints. The model captures the controlled switching of agents between coverage (when energy is depleted) and battery charging (when energy is replenished) modes. It guarantees the feasibility of the coverage problem by defining a guard function on each agent's battery level to prevent it from dying on its way to a charging station. The charging station plays the role of a centralized scheduler to solve the contention problem of agents competing for the only charging resource in the mission space. The optimal coverage problem is transformed into a parametric optimization problem to determine an optimal recharging policy. This problem is solved through the use of Infinitesimal Perturbation Analysis (IPA), with simulation results showing that a full recharging policy is optimal

Some considerations on coastal processes relevant to sea level rise

The effects of potential sea level rise on the shoreline and shore environment have been briefly examined by considering the interactions between sea level rise and relevant coastal processes. These interactions have been reviewed beginning with a discussion of the need to reanalyze previous estimates of eustatic sea level rise and compaction effects in water level measurement. This is followed by considerations on sea level effects on coastal and estuarine tidal ranges, storm surge and water level response, and interaction with natural and constructed shoreline features. The desirability to reevaluate the well known Bruun Rule for estimating shoreline recession has been noted. The mechanics of ground and surface water intrusion with reference to sea level rise are then reviewed. This is followed by sedimentary processes in the estuaries including wetland response. Finally comments are included on some probable effects of sea level rise on coastal ecosystems. These interactions are complex and lead to shoreline evolution (under a sea level rise) which is highly site-specific. Models which determine shoreline change on the basis of inundation of terrestrial topography without considering relevant coastal processes are likely to lead to erroneous shoreline scenarios, particularly where the shoreline is composed of erodible sedimentary material. With some exceptions, present day knowledge of shoreline response to hydrodynamic forcing is inadequate for long-term quantitative predictions. A series of interrelated basic and applied research issues must be addressed in the coming decades to determine shoreline response to sea level change with an acceptable degree of confidence. (PDF contains 189 pages.

Use of Proteomics to Probe Dynamic Changes in Cyanobacteria

Cyanobacteria are unicellular photosynthetic microorganisms that capture and convert light energy to chemical energy, which is the precursor for feed, fuel, and food. These oxygenic phototrophs appear blue-green in color due to the blue bilin pigments in their phycobilisomes and green chlorophyll pigments in their photosystems. They also have diverse morphologies, and thrive in terrestrial, marine water, fresh water, as well as extreme environments. Cyanobacteria have developed a number of protective mechanisms and adaptive responses that allow the photosynthetic process to operate optimally under diverse and extreme conditions. Prolonged deprivation of essential nutrients, such as nitrogen and sulfur, commonly found in the natural environments cyanobacteria grow in, can disrupt crucial metabolic activities and promote the production of lethal reactive oxygen species. The dynamic remodeling of protein complexes and structures facilitates adaptation to environmental stresses, however, specific protein modifications are poorly understood. Synthetic and systems biology approaches have been used to study how photosynthetic microorganisms optimize their cellular metabolism in response to adverse environmental conditions. To gain insights on how cyanobacteria cope with environmental changes, we created a global proteomics map of redox-sensitive amino acid residues and examined the degradation of light harvesting apparatus in cyanobacteria. These studies offered significant insights into the broad redox regulation and protein degradation, advancing knowledge of how photosynthetic microbial cells dynamically rely on protective mechanisms to survive changing environmental conditions

Double volumetric navigators for real-time simultaneous shim and motion measurement and correction in Glycogen Chemical Exchange Saturation Transfer (GlycoCEST) MRI

Glycogen is the primary glucose storage mechanism in in living systems and plays a central role in systemic glucose homeostasis. The study of muscle glycogen concentrations in vivo still largely relies on tissue sampling methods via needle biopsy. However, muscle biopsies are invasive and limit the frequency of measurements and the number of sites that can be assessed. Non-invasive methods for quantifying glycogen in vivo are therefore desirable in order to understand the pathophysiology of common diseases with dysregulated glycogen metabolism such as obesity, insulin resistance, and diabetes, as well as glycogen metabolism in sports physiology. Chemical Exchange Saturation Transfer (CEST) MRI has emerged as a non-invasive contrast enhancement technique that enables detection of molecules, like glycogen, whose concentrations are too low to impact the contrast of standard MR imaging. CEST imaging is performed by selectively saturating hydrogen nuclei of the metabolites that are in chemical exchange with those of water molecules and detecting a reduction in MRI signal in the water pool resulting from continuous chemical exchange. However, CEST signal can easily be compromised by artifacts. Since CEST is based on chemical shift, it is very sensitive to field inhomogeneity which may arise from poor initial shimming, subject respiration, heating of shim iron, mechanical vibrations or subject motion. This is a particular problem for molecules that resonate close to water, such as - OH protons in glycogen, where small variations in chemical shift cause misinterpretation of CEST data. The purpose of this thesis was to optimize the CEST MRI sequence for glycogen detection and implement a real-time simultaneous motion and shim correction and measurement method. First, analytical solution of the Bloch-McConnell equations was used to find optimal continuous wave RF pulse parameters for glycogen detection, and results were validated on a phantom with varying glycogen concentrations and in vivo on human calf muscle. Next, the CEST sequence was modified with double volumetric navigators (DvNavs) to measure pose changes and update field of view and zero- and first-order shim parameters. Finally, the impact of B0 field fluctuations on the scan-rescan reproducibility of CEST was evaluated in vivo in 9 volunteers across 10 different scans. Simulation results showed an optimal RF saturation power of 1.5µT and duration of 1s for glycoCEST. These parameters were validated experimentally in vivo and the ability to detect varying glycogen concentrations was demonstrated in a phantom. Phantom data showed that the DvNav-CEST sequence accurately estimates system frequency and linear shim gradient changes due to motion and corrects resulting image distortions. In addition, DvNav-CEST was shown to yield improved CEST quantification in vivo in the presence of motion and motion-induced field inhomogeneity. B0 field fluctuations were found to lower the reproducibility of CEST measures: the mean coefficient of variation (CoV) for repeated scans was 83.70 ± 70.79 % without shim correction. However, the DvNav-CEST sequence was able to measure and correct B0 variations, reducing the CoV to 2.6 ± 1.37 %. The study confirms the possibility of detecting glycogen using CEST MRI at 3 T and shows the potential of the real-time shim and motion navigated CEST sequence for producing repeatable results in vivo by reducing the effect of B0 field fluctuations

Transcriptomic investigation of the adaptation of Streptococcus pneumoniae

Streptococcus pneumoniae colonises the human nasopharynx as a commensal but can translocate to the lungs, meninges, and blood to cause potentially fatal infections. These host niches exhibit diverse physiological environments. Differences in adaptation to these conditions may explain differences between serotypes and genotypes in their ability to colonise the human host, be transmitted, and to cause disease. RNA sequencing (RNA-Seq) was used to investigate adaptation of clinical S. pneumoniae strains to different stress environments. In Chapter 3, to establish the optimal experimental conditions, the effects of carbohydrate source, temperature, and iron concentrations on bacterial growth dynamics were evaluated. S. pneumoniae strains selected on the basis of their ability to be carried and cause disease, showed differential growth phenotypes. In Chapter 4, to facilitate robust transcriptomic analysis, high-quality genome assemblies of S. pneumoniae serotype 1 (highly invasive, rarely found in carriage) and serotype 6B (rarely invasive, highly carried) strains were generated and characterised. A pneumococcal transcriptomic analysis pipeline was developed in Chapter 5 by investigating the transcriptomic response of two single gene knockouts of S. pneumoniae serotype 6B lacking the biosynthesis genes fhs or proABC. These mutants have been shown to be attenuated in vivo and the aim was to identify the transcriptomic basis for this. Adaptation by fhs S. pneumoniae included upregulation of pathways involved in secondary metabolites biosynthesis and quorum sensing while the proABC S. pneumoniae was upregulated for carbohydrate metabolism pathways. In Chapters 6 and 7, the transcriptomic adaptations of S. pneumoniae serotype 1 and serotype 6B strains to altered iron and temperature levels were delineated respectively, indicating strain specific gene expression with the majority of differential regulation occurring in core pneumococcal genes. In Chapter 8, to pave the way for investigating the S. pneumoniae transcriptome in human samples, a challenge in pneumococcal research, an approach to directly isolate high-quality pneumococcal RNA from human carriers was developed. The work in this thesis provides new insights in the gene regulation of clinical S. pneumoniae strains under various environmental exposures

Identification and functional characterization of cell cycle genes in the pennate diatom Phaeodactylum tricornutum

Accounting for almost one fifth of the primary production on Earth, diatoms play a key ecological and biogeochemical role in our contemporary oceans. Furthermore, as producers of various lipids and pigments, and characterized by their finely ornamented silica cell wall, diatoms gained an emerging interest of different industrial fields, including biofuel production, nanotechnology and pharmaceutics. However, despite their major ecological importance and their high commercial value, little is known about the mechanisms that control their life cycle. Their ability to live and dominate in highly unstable and sometimes harsh environments, suggests that diatoms have evolved specific strategies to adapt to and survive in such conditions. Unraveling the regulatory mechanisms that underlie their unique life cycle strategies will therefore be of crucial importance to understand diatom ecology and evolution and to further exploit their industrial potential. In this thesis I aimed to gain insights in the genetic mechanisms and environmental factors that control the diatom cell cycle. Using a variety of molecular analyses, it is demonstrated that diatoms use a common eukaryotic base of cell cycle regulatory components to control their cell division, complemented with some novel diatom-specific features, including an expanded set of diatom-specific cyclins, which most probably are part of a complex integrative network allowing them to pace the cell cycle with the surrounding conditions

Materials for high energy Li-ion and post Li-ion batteries

L'abstract è presente nell'allegato / the abstract is in the attachmen

Water Resources Management and Modeling

Hydrology is the science that deals with the processes governing the depletion and replenishment of water resources of the earth's land areas. The purpose of this book is to put together recent developments on hydrology and water resources engineering. First section covers surface water modeling and second section deals with groundwater modeling. The aim of this book is to focus attention on the management of surface water and groundwater resources. Meeting the challenges and the impact of climate change on water resources is also discussed in the book. Most chapters give insights into the interpretation of field information, development of models, the use of computational models based on analytical and numerical techniques, assessment of model performance and the use of these models for predictive purposes. It is written for the practicing professionals and students, mathematical modelers, hydrogeologists and water resources specialists