THE KAUST Repository is an initiative of the University Library to expand the impact of conference papers, technical reports, peer-reviewed articles, preprints, theses, images, data sets, and other research-related works of King Abdullah University of Science and Technology (KAUST).
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Center pivot field delineation and mapping: A satellite-driven object-based image analysis approach for national scale accounting(ISPRS Journal of Photogrammetry and Remote Sensing, Elsevier BV, 2021-03-06) [Article]Center pivot irrigation systems are used to enhance crop production in many countries around the world. Establishing the location and extent of such fields provides information that assists in describing a range of agricultural metrics, including crop identification, yield forecasts, monitoring of irrigation requirements and crop water use, as well as supporting national and regional auditing, licensing and compliance efforts. However, detailed information on the number, extent and changing dynamics of agricultural fields is often lacking in many countries: nowhere more so than in developing regions. To address this lack, we performed a national scale accounting of center pivot fields in Saudi Arabia, using a three year multi-temporal analysis of Landsat-8 satellite data. A geographic object-based image analysis approach was developed based on five 50 × 50 km sub-areas extracted from Landsat data for the year 2015, and applied to delineate individual center pivot fields at a national scale for 2013, 2014 and 2015. The extent of fields was determined via a map of the annual maximum Normalized Difference Vegetation Index (NDVI), while a 15 m spatial resolution map of annual panchromatic band minimums was used to produce an edge detection layer to delineate individual adjoining fields. Amongst a range of classification parameters that were included in the object-based mapping approach, shape information, such as the center pivot field length, length:width ratio, and elliptic fit, were identified as critical parameters. Applying the rule-set that was developed from the five 50 × 50 km sub-regions to the national scale resulted in the identification of 36,052 (11,103 km2), 38,114 (11,902 km2), and 37,254 (11,555 km2) individual fields in 2013, 2014, and 2015, respectively. Approximately 94% of these fields were correctly detected, while their individually measured area was mapped with >95% combined accuracy for fields >0.225 km2 when evaluated against manually delineated fields. Smaller center pivot fields, and specifically those adjoining neighbouring fields, had lower area mapping accuracies (>91% in 75% of cases). The object-based approach allowed a national scale and multi-temporal assessment of center pivot field delineation and mapping, affording new insights into agricultural practice and providing a methodological basis for examining the impact of water management and related policy initiatives, amongst many other potential applications. Apart from filling a clear knowledge gap in Saudi Arabia, the approach has the potential to be expanded elsewhere: particularly to similar locations within the Middle East and North Africa.
High Thermal Effusivity Nanocarbon Materials for Resonant Thermal Energy Harvesting(Small, Wiley, 2021-03-06) [Article]Carbon nanomaterials have extraordinary thermal properties, such as high conductivity and stability. Nanocarbon combined with phase change materials (PCMs) can yield exceptionally high thermal effusivity composites optimal for thermal energy harvesting. The progress in synthesis and processing of high effusivity materials, and their application in resonant energy harvesting from temperature variations is reviewed.
Strategies for Integrated Capture and Conversion of CO 2 from Dilute Flue Gases and the Atmosphere(ChemSusChem, Wiley, 2021-03-05) [Article]The integrated capture and conversion of CO<sub>2</sub> has the potential to make valorization of the greenhouse gas more economically competitive, by eliminating energy-intensive regeneration processes. However, integration is hindered by the extremely low concentrations of CO<sub>2</sub> present in the atmosphere (0.04 vol.%), and the presence of acidic gas contaminants, such as SO<sub>x</sub> and NO<sub>x</sub> , in flue gas streams. This Review summarizes the latest technological progress in the integrated capture and conversion of CO<sub>2</sub> from dilute flue gases and atmospheric air. In particular, the Review analyzes the correlation between material properties and their capture and conversion efficiency through hydrogenation, cycloaddition, and solar thermal-mediated electrochemical processes, with a focus on the types and quantities of product generated, in addition to their energy requirements. Prospects for commercialization are also highlighted and suggestions are made for future research.
Highly Selective and Stable Production of Aromatics via High-Pressure Methanol Conversion(ACS Catalysis, American Chemical Society (ACS), 2021-03-05) [Article]In the current petrochemical market, the global demand for aromatics, especially benzene, toluene, and xylenes (BTXs), has increased sharply. The methanol-to-aromatic conversion (MTA) over ZSM-5 is among the most promising routes to satisfy this ever-growing demand. In this work, we show that highpressure operation during MTA leads to a large increase in aromatic selectivity while enhancing stability on-stream. Stable operation along with a very high selectivity to aromatics (up to 50%, with 20% BTXs) can be achieved on a commercial high-silica ZSM-5 (SiO2/Al2O3 = 280) at 400 °C, 30 bar total pressure, and WHSV = 8 h−1. The high partial pressure of primary olefins and the promoted methanol-induced hydrogen-transfer pathway result in an exponential increase in aromatization, while the high partial pressure of steam generated via dehydration of methanol leads to in situ coke removal and, therefore, to a much slower deactivation of the zeolite
Recent Progress on Flexible Capacitive Pressure Sensors: From Design and Materials to Applications(Advanced Materials Technologies, Wiley, 2021-03-05) [Article]For decades, the revolution in design and fabrication methodology of flexible capacitive pressure sensors using various inorganic/organic materials has significantly enhanced the field of flexible and wearable electronics with a wide range of applications in aerospace, automobiles, marine environment, robotics, healthcare, and consumer/portable electronics. Mathematical modelling, finite element simulations, and unique fabrication strategies are utilized to fabricate diverse shapes of diaphragms, shells, and cantilevers which function in normal, touch, or double touch modes, operation principles inspired from microelectromechanical systems (MEMS) based capacitive pressure sensing techniques. The capacitive pressure sensing technique detects changes in capacitance due to the deformation/deflection of a pressure sensitive mechanical element that alters the separation gap of the capacitor. Due to advancement in state-of-the-art fabrication technologies, the performance and properties of capacitive pressure sensors are enhanced. In this review paper, recent progress in flexible capacitive pressure sensing techniques in terms of design, materials, and fabrication strategies is reported. The mechanics and fabrication steps of paper-based low-cost MEMS/flexible devices are also broadly reported. Lastly, the applications of flexible capacitive pressure sensors, challenges, and future perspectives are discussed.