Modelling shadow in agroforestry systems based on 3D data

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Surface-Enhanced Spectroelectrochemistry using Synchrotron Infrared Radiation

Electrochemical reactions are inherently heterogeneous, occurring at the interface between a solid electrode and an electrolyte solution. Therefore, detailed mechanistic understanding requires the electrode/solution interface (ESI) to be interrogated. Doing so with spectroelectrochemical techniques generally encounters several analytical challenges. Sampling the ESI requires a surface-sensitive spectroscopy capable of addressing a buried interface, placing strong limitations on photon energy and spectroelectrochemical cell design. Furthermore, dynamic measurements are fundamentally limited by the finite rise time of the electrode. For many important processes with characteristic timescales in the milli- to microsecond regime, achieving a suitably low rise time requires the use of an electrode with critical dimensions in the hundreds of micrometers, i.e. a microelectrode. In this thesis, I develop the spectroscopic platform necessary to perform surface-sensitive, time-resolved infrared measurements in the milli- to microsecond regime. I will make the case that an infrared spectroelectrochemical technique, namely attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), is applicable because it is intrinsically surface-sensitive, yields detailed information on molecular structure, and is compatible with a range of electrocatalytic metals. I will show that the small size of the microelectrode requires an unconventional infrared source, namely highly focused synchrotron radiation. This thesis will present the characterization of a new internal reflection element which is fully compatible with ATR-SEIRAS and easily amenable to microfabrication. A custom horizontal microscope endstation will be developed at the mid-IR beamline at the Canadian Light Source. Its general utility beyond the primary goal of this thesis will be demonstrated with imaging experiments of a simple interfacial reaction in a microfluidic device. Finally, a 500 micrometer wide linear microelectrode compatible with ATR-SEIRAS will be fabricated and preliminary kinetic measurements of a model electrochemical process, namely the potential-induced desorption of 4-methoxypyridine, will be discussed

Alley coppice—a new system with ancient roots

International audience& Context Current production from natural forests will not satisfy future world demand for timber and fuel wood, and new land management options are required. & Aims We explore an innovative production system that combines the production of short rotation coppice in wide alleys with the production of high-value trees on narrow strips of land; it is an alternative form of alley cropping which we propose to call 'alley coppice'. The aim is to describe this alley coppice system and to illustrate its potential for produc-ing two diverse products, namely high-value timber and ener-gy wood on the same land unit. & Methods Based on a comprehensive literature review, we compare the advantages and disadvantages of the alley cop-pice system and contrast the features with well-known existing or past systems of biomass and wood production. & Results We describe and discuss the basic aspects of alley coppice, its design and dynamics, the processes of competi-tion and facilitation, issues of ecology, and areas that are open for future research. & Conclusion Based on existing knowledge, a solid founda-tion for the implementation of alley coppice on suitable land is presented, and the high potential of this system could be shown

High resolution time of arrival estimation for a cooperative sensor system

Distance resolution of cooperative sensors is limited by the signal bandwidth. For the transmission mainly lower frequency bands are used which are more narrowband than classical radar frequencies. To compensate this resolution problem the combination of a pseudo-noise coded pulse compression system with superresolution time of arrival estimation is proposed. Coded pulsecompression allows secure and fast distance measurement in multi-user scenarios which can easily be adapted for data transmission purposes (Morhart and Biebl, 2009). Due to the lack of available signal bandwidth the measurement accuracy degrades especially in multipath scenarios. Superresolution time of arrival algorithms can improve this behaviour by estimating the channel impulse response out of a band-limited channel view. For the given test system the implementation of a MUSIC algorithm permitted a two times better distance resolution as the standard pulse compression

Evaluation of Low-Grade Geothermal Energy Recovery From a Cold Climate Municipal Solid Waste Landfill

With an increased focus on climate change and environmental footprint in recent years, methods to mitigate the use of non-renewable energy resources have received increased attention. Over the last two decades, research has been performed exploring the processes associated with gas and heat generation within municipal solid waste (MSW) landfills. Discussions have since commenced about the potential to utilize landfills as a low-grade geothermal energy source. Field tests investigating this topic have taken place globally, but they have not taken place in a colder and semi-arid climate where the initial waste temperatures are known to be lower. In addition, the analysis of the previous field tests (including the MSW thermal properties, radius of influence, and heat extraction rate) have either not been possible due to the testing methods, and/or have been simplified to one-dimensional analytical solutions. The research presented investigates the feasibility of low-grade geothermal heat extraction from medium-sized MSW landfills in cold and semi-arid climates, while also exploring different methods of analysis. The Northern Landfill, operated by Loraas Disposal Ltd., is a medium-sized landfill located 10 km north of Saskatoon, Saskatchewan. As of 2018, approximately 2.5 megatonnes of MSW over three million cubic metres have been placed. A vertical borehole heat exchanger (BHE) and surrounding temperature-measuring thermistors were installed into the landfill using sonic drilling methods. A thermostatic system was also constructed to provide a constant fluid temperature as it entered the BHE. Two active thermal response tests (TRTs) with recovery periods (one heat injection test and one heat extraction test) were performed with the temperature of the circulating fluid and the surrounding MSW being measured along the landfill depth. The results from the tests were compared to each other, as well as to passive thermal responses previously measured at the Northern Landfill, and to previous active TRTs in MSW performed globally. In addition, the tests were analyzed with one-dimensional analytical models and a two-dimensional finite element model (with and without the backfilled materials), to determine the thermal properties of the MSW with depth. The heat transfer rate was also estimated with a two-dimensional model. The maximum thermal response of the waste from the heat extraction test was similar to a previous test performed in a warmer California climate (Yeşiller et al., 2016) in terms of normalized depth location and radial trend. The radius of influence for the heat extraction test was found to be between 1.8 m and 5.1 m using the observational method and 4.0 m when evaluated with the two-dimensional finite element model. It was determined that the analytical infinite line source (ILS) method was suitable for providing initial MSW thermal properties with depth for a more complex two-dimensional finite element model. For the heat injection and heat extraction test, the two methods estimated the MSW thermal diffusivity to range from 1.9 x 10-7 m2/s to 3.9 x 10-7 m2/s for the sections of MSW known to not be dependent on atmospheric temperatures. The analytical Cooper Jacob distance-drawdown method was determined to be an unsuitable method for estimating initial MSW thermal properties with depth, overestimating the MSW thermal diffusivity by an order of magnitude with a thermal diffusivity of 4.0 x 10-6 m2/s. However, it did verify that at a constant depth, the MSW could be treated as a homogenous material within the spatial testing limits. It was determined that the MSW thermal diffusivity was greatest at the central depths. This finding did not follow the theory of MSW thermal diffusivity increasing with depth. It did follow the trend of the measured volumetric water content of in-situ MSW cores from a borehole that was retrieved without additional drilling fluid and within proximity of the test. The results and analysis of the field testing found that low-grade geothermal heat extraction is not a practical in-situ energy recovery method for medium-sized landfills in cold and semi-arid regions. Twenty-six vertical BHEs would be required to extract 11.5 kW of power, the capacity of an average closed loop ground heat available for Canadian residents (Government of Canada, 2021). While also not practical, the number of required vertical BHEs can be reduced to 14 if the circulation fluid temperature is reduced to -4.0°C. In terms of in-situ energy recovery at MSW landfills in cold and semi-arid regions, it is recommended to evaluate the feasibility of optimizing the quantity of methane generated in a mesophilic bacteria landfill with heat exchangers and extract the methane as a source of energy. Future active TRTs performed in MSW landfills are recommended to account for the mechanical, hydraulic, and pneumatic processes inside landfills that are known to influence heat transport, as well as additional external factors such as radiation, wind, and snow to predict the shallower waste depth more accurately

Factors affecting branch wound occlusion and associated decay following pruning – a case study with wild cherry (Prunus avium L.)

Pruning wild cherry (Prunus avium L.) is a common silvicultural practice carried out to produce valuable timber at a veneer wood quality. Sub-optimal pruning treatments can permit un-occluded pruning wounds to develop devaluing decay. The aim of this study is to determine relevant branch, tree and pruning characteristics affecting the occlusion process of pruning wounds. Important factors influencing occlusion time for an optimised pruning treatment for valuable timber production utilising wild cherry are derived. 85 artificially pruned branches originating from ten wild cherry trees were retrospectively analysed. Branch stub length, branch diameter and radial stem increment during occlusion were found to be significant predictors for occlusion time. From the results it could be concluded that for the long term success of artificial pruning of wild cherry it is crucial to (i) keep branch stubs short (while avoiding damage to the branch collar), (ii) to enable the tree to maintain significant radial growth after pruning, (iii) to avoid large pruning wounds (>2.5 cm) by removing steeply angled and fast growing branches at an early stage

A comparative analysis of federated and centralized learning for SpO2 prediction in five critical care databases

This study explores the potential of federated learning (FL) to develop a predictive model of hypoxemia in intensive care unit (ICU) patients. Centralized learning (CL) and local learning (LL) approaches have been limited by the localized nature of data, which restricts CL approaches to the available data due to data privacy regulations. A CL approach that combines data from different institutions, could offer superior performance compared to a single-institution approach. However, the use of this method raises ethical and regulatory concerns. In this context, FL presents a promising middle ground, enabling collaborative model training on geographically dispersed ICU data without compromising patient confidentiality. This study is the first to use all five public ICU databases combined. The findings demonstrate that FL achieved comparable or even slightly improved performance compared to local or centralized learning approaches

A federated learning model for the prediction of blood transfusion in intensive care units

Accurate prediction of blood transfusion requirements is crucial for patient outcomes and resource management in clinical settings. We developed a machine learning model using XGBoost to predict the need for a blood transfusion 2 hours in advance based on up to 7 hours of prior data from two large databases, MIMIC-IV and eICU-CRD. Our federated model showed promising results, with F1 scores of 0.72 and 0.66, respectively

Federated learning for predictive analytics in weaning from mechanical ventilation

Mechanical ventilation is crucial for critically ill patients in ICUs, requiring accurate weaning and extubations timing for optimal outcomes. Current prediction models struggle with generalizability across datasets like MIMIC-IV and eICU-CRD. We propose a federated learning approach using XGBoost with bagging aggregation to improve weaning predictions while ensuring patient data privacy, compliant with GDPR and HIPAA. Using the OMOP Common Data Model, our method integrates machine learning techniques across three ICU databases, encompassing over 33,000 patients. Our model achieved robust performance with 77% AUC and 73% AUPRC. Planned pilot studies in Germany will further refine and validate our approach. This study demonstrates the potential of federated learning to enhance critical care by providing personalized, data-driven insights for ventilation management