Leaf area index (LAI) is an important indicator of crop growth. In this paper, a hybrid inversion method was developed to estimate the LAI values of crops. Based on PROSAIL simulation datasets, 43 ...hyperspectral vegetation indices (VIs), including the optimized soil-adjusted vegetation index (OSVAI) and modified triangular vegetation index (MTVI2), were analyzed to identify optimal VIs for estimating LAI values. Hybrid inversion models were then built to determine the relationships between optimal simulated VIs and the LAI values (generated by the PROSAIL model) using modeling methods, including curve fitting, artificial neural network (ANN) and random forest regression (RFR) algorithms. Finally, remote sensing mapping of a Compact High Resolution Imaging Spectrometer (CHRIS) image was completed using the inversion model to verify the LAI estimation accuracy. The remote sensing mapping of the CHRIS image yielded an accuracy of R2=0.928 and RMSE=0.485 for OSAVI and R2=0.910 and RMSE=0.554 for MTVI2, demonstrating the feasibility of high-accuracy estimation of crop LAI using hyperspectral VIs and a hybrid inversion method. The estimation results of various VIs suggested that the identification of the appropriate VIs is critical to improve the inversion accuracy. In addition, to obtain the appropriate VIs, the factors must be evaluated with respect to two aspects, i.e., the sensitivity to target parameters and the insensitivity to interference. In this study, OSVAI and MTVI2 were sensitive to LAI and relatively insensitive to the effects of interference factors, such as chlorophyll, soil background, sky scattered light and observed geometry. Therefore, these indices could be primarily used as VIs for an LAI estimation. The inversion results of different datasets demonstrated that prior information is critical for improving the inversion accuracy and identifying the optimal VIs. Additionally, based on the comparison of the curve fitting, ANN, and RFR algorithms, RFR was an optimal method for modeling in this study, as indicated by the higher R2 and lower RMSE values for different datasets and various VIs.
•A hybrid inversion method was developed to estimate crop LAI accurately.•RFR yielded more accurate predictions than ANN or parametric curve-fitting.•Sensitivity and interference immunity are both important to evaluate a VI.•VI selection and prior knowledge are critical to improve retrieval accuracy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Intensive studies have been conducted globally in the past decades to understand the evolution of several large deltas. However, despite being one of the largest tropical deltas, the Irrawaddy ...(Ayeyarwady) Delta has received relatively little attention from the research community. To reduce this knowledge gap, this study aims to provide a comprehensive assessment of the delta's evolution and identify its influencing factors using remote sensing images from 1974 to 2018, published literature and available datasets on the river, and human impacts in its drainage basin. Our results show that 1) Based on the topographic and geomorphological features, the funnel-shaped Irrawaddy Delta can be divided into two parts: the upper fluvial plain and the lower low-lying coastal plain; 2) The past 44-year shoreline changes show that overall accretion of the delta shoreline was at a rate of 10.4 m/year, and approximately 42% of the shoreline was subjected to erosion from 1974 to 2018. In the western coast, 60% of shoreline was under erosion with an average shoreline change rate of 0.1 m/year. In the east part, 81% of the shoreline was accreted with an average accretion rate of 24 m/year; 3) River channel geomorphological analysis indicates that three distributaries of the Irrawaddy, Bogale, and Toe have developed most active sandbars, which coincides with the amount of water they discharged (>50%). This implies that these three distributaries might be the currently most active channels in the delta; 4) The Irrawaddy mainstream in the Central Dry Zone (the original high sediment yield area) has become less braided and some tributaries have become increasingly straightened, which are highly likely related to reductions in sediment supply and peak flow induced by dam construction; 5) The large geomorphological adjustments at the two bifurcation points means that the diversions and fractions of water and sediment into the distributaries have likely already changed due to anthropogenic impacts.
Our comprehensive analysis suggests that increasing human activities have caused reductions in coarse sediment supply entering the coastal delta plain, further inducing the erosion of the major channels in the lowermost delta and the western delta coast, and the adjustments of fluvial and coastal geomorphology; meanwhile, deforestation and terrestrial mining have provided extra fine sediment, which is mainly transported by the monsoon-driven current to the eastern coast to in part maintain its rapid accretion. Given the situation of rapidly increasing population and climate change, the current natural equilibrium state of the delta setting will most likely be disturbed in the near future. Therefore, our work calls for more intensive monitoring- and modeling-based study in order to better understand the controlling factors influencing the delta evolution in the future.
•Approximately 42% of the shoreline has undergone erosion in the Irrawaddy Delta.•The western coast was eroded and the eastern part was accreted during 1974 to 2018.•Channel and coastal geomorphology have undergone evident adjustments.•Human activities have had substantial adverse impacts on the geomorphology.•The delta is in sedimentary equilibrium state that may be disturbed in near future.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Shoreline change rates vary spatiotemporally.•Accretion rate is continuing but decreasing.•A close relationship exists between shoreline change and sediment discharge.•Contrasting temporal patterns ...of shoreline change exist between the eastern and northern segments.•Different shoreline segments respond differently to decreasing sediment supply.
Chongming Dongtan, located in the center of the Yangtze estuary, is a Ramsar Wetland of International Importance and National Nature Reserve. The dramatic decrease in river sediment load has attracted considerable scientific interest to this area, but few studies have paid attention to the shoreline dynamics. This study uses Landsat images spanning from 1987 to 2010 and an orthogonal transect method, which was previously developed by the authors, to model the spatial and temporal characteristics of shoreline change and explore its relationship to reduced river sediment load by use of regression analysis on three different spatial scales. Results show a general decrease in the average rates of shoreline change throughout the entire study period. The maximum average shoreline change rate of +115.5m/year occurred in the 1987–1990 interval and the minimum rate of +20.4m/year occurred from 2006 to 2008. Based on average rates of shoreline change, the coast of Dongtan was divided into three segments: the erosion segment, eastern accretion segment, and northern accretion segment. The temporal pattern of the northern accretion segment is almost completely opposite to that of the eastern accretion segment. The strongest-correlation transects are located on the northern side of the eastern tip of Dongtan and the next strongest transects are located on the south side. Other transects have a very low correlation. Transect 19 near the easternmost tip of Dongtan has a near zero correlation (r2=0.0045) but has the fastest accretion rate, and in general an increase in the shoreline change rate. The average rate of shoreline change and the net accretion area in Dongtan as a whole are significantly associated with sediment discharge at Datong Station (r2=0.69 and 0.75, respectively). This implies that shoreline accretion in Dongtan will probably slow down gradually, if the river sediment load continues to decrease in the future. The shoreline change rates achieved using our approach are consistent with previous studies, but the relationship with the river sediment load is different from results in a previous study on intertidal wetland based on bathymetric maps. The results and methods may be helpful in coastal management and understanding the evolution of the entire delta from the perspective of shoreline change.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
As the last barrier to preventing nuclear leakage, it is crucial to enhance the load-bearing capacity and cracking resistance of nuclear containment under internal pressure accidents. Currently, ...fiber-reinforced polymers are widely used in prestressing concrete structures because of their superior performance, but little research has been conducted on fiber-reinforced polymers in the field of nuclear power plants. In this paper, carbon fiber-reinforced polymer (CFRP) is used as a prestressing tendon material instead of traditional steel strands to study the damage mode of the new type of containment under internal pressure and the feasibility of using CFRP as prestressing tendons. In this study, a three-dimensional refinement model is established, employing ABAQUS 2020 software to analyze and quantify the pressure-bearing performance of nuclear containment with CFRP tendons and finally determine the reasonable range of CFRP tendons that can be used as a replacement. The research shows that the containment with CFRP tendons has an obvious strengthening effect in delaying the generation of cracks, restraining the speed of crack development, reducing the plastic damage of the steel liner, and improving the ultimate bearing capacity of the containment.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Current investigations of performance improvement in prestressed concrete containment vessels (PCCVs) with fiber reinforcement are scarce, and the type of fiber to select for PCCVs is not explicitly ...stated. The failure mechanism of PCCVs with fiber reinforcement under internal pressure is investigated in this paper. The effects of different fiber types, including rigid fiber, flexible fiber, and hybrid fiber, are considered for the creation of fiber-reinforced PCCVs. The mechanical behavior between conventional and fiber-reinforced PCCVs is scientifically compared and identified. The results demonstrate that to achieve the aim of inhibiting early cracking of the concrete, any type of fiber can be taken into account. The performance of the ultimate pressure capacity and yielding of the liner can be promoted, respectively, by introducing steel, steel-PP, and steel-PVA fiber-reinforced concrete. Additionally, the failure regions can be controlled to a certain extent under ultimate internal pressure via the appropriate use of FRC.
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A concise method for the preparation of tryptanthrins from indoles via the copper-catalyzed aerobic oxidation is described. The reactions can be carried out under mild reaction conditions with ...varying functional group tolerance.
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Nowadays, the fast expansion of the economy and industry results in a considerable volume of wastewater being released, severely affecting water quality and the environment. It has a significant ...influence on the biological environment, both terrestrial and aquatic plant and animal life, and human health. Therefore, wastewater treatment is a global issue of great concern. Nanocellulose's hydrophilicity, easy surface modification, rich functional groups, and biocompatibility make it a candidate material for the preparation of aerogels. The third generation of aerogel is a nanocellulose-based aerogel. It has unique advantages such as a high specific surface area, a three-dimensional structure, is biodegradable, has a low density, has high porosity, and is renewable. It has the opportunity to replace traditional adsorbents (activated carbon, activated zeolite, etc.). This paper reviews the fabrication of nanocellulose-based aerogels. The preparation process is divided into four main steps: the preparation of nanocellulose, gelation of nanocellulose, solvent replacement of nanocellulose wet gel, and drying of nanocellulose wet aerogel. Furthermore, the research progress of the application of nanocellulose-based aerogels in the adsorption of dyes, heavy metal ions, antibiotics, organic solvents, and oil-water separation is reviewed. Finally, the development prospects and future challenges of nanocellulose-based aerogels are discussed.
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The copper-mediated cyanation of indoles with DMF as a single surrogate has been realized. This approach could be applied for the cyanation of some electron-rich arenes and aryl aldehydes as well. ...Aryl aldehydes were demonstrated to be the key intermediates in the cascade process of cyanation of indoles and electron-rich arenes.
Biomass-based adhesives have attracted extensive research interest in recent years as an effective alternative to formaldehyde-based adhesives which are non-renewable and harmful to human health. In ...this paper, citric acid-based hyperbranched polyester (HBPCA) resins were synthesized by green and simple strategy using natural citric acid (CA) and succinic anhydride (SA) as raw materials. Hyperbranched polyol (HBP) was prepared by nucleophilic addition reaction of SA with diethanolamine and later condensed with CA to produce HBPCA resins. The chemical structure of HBPCA resins was characterized using Fourier transform infrared spectroscopy (FTIR), 13C nuclear magnetic resonance (13C NMR), X-ray photoelectron spectroscopy (XPS), liquid chromatography−mass spectrometry (LC-MS), and gel permeation chromatography (GPC). The introduction of HBP enabled the resins to form a hyperbranched network cross-linked structure, which increased the cross-link density and thus prevented the intrusion of moisture. The results showed that HBPCA resin plywood has excellent adhesive strength and water resistance. The shear strength was 1.49 MPa and 1.47 MPa after immersion in hot water at 63 °C and boiling water at 93 °C for 3 h. The green and simple synthesis of HBPCA resins and their excellent properties provide a novel strategy for preparing biomass-based adhesives.
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•Strategy for a novel citric acid-based hyperbranched polyester wood adhesives with excellent mechanical strength.•Without potential hazard of formaldehyde release.•Boiling water resistant super performance adhesives.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Timely and accurate information on rural settlements is essential for rural development planning. Remote sensing has become an important means for accurately mapping large scale rural settlements. ...Nevertheless, numerous difficulties remain in accurate and efficient rural settlement extraction. In this study, by combining multi-dimensional features derived from Sentinel-1/2 images, Visible Infrared Imaging Radiometer Suite supporting a Day-Night Band (VIIRS-DNB) dataset, and Digital Elevation Model (DEM) data using the Google Earth Engine (GEE) platform, we proposed an efficient framework with good transferability for mapping rural settlements in the Yangtze River Delta. To avoid the time-consuming selection of a large number of training samples in the whole study area, we employed four random forest models obtained from the training samples in respective training municipal districts in four different regions to classify other municipal districts in their corresponding region. We found that different features play diverse vital roles in the extraction of rural settlements in various regions. Compared to results only using optical data, accuracies obtained by the proposed method were significantly improved. The average user’s accuracy, producer’s accuracy, overall accuracy, and Kappa coefficient increased by 16.75%, 17.75%, 11.50%, and 14.50% in the four training municipal administrative areas, respectively. The overall accuracy and Kappa coefficient were 96% and 0.84, respectively. By contrast, our classification results are superior to other public datasets. The final mapping results provided a detailed spatial distribution of the rural settlements in the Yangtze River Delta and revealed that the total area of rural settlements is approximately 32,121.1 km2, accounting for 17.41% of the total area. The high-density rural settlements are mainly distributed in the Northern Plain and East Coast, while the low-density rural settlements are located in the Central Hills and Southern Mountain.
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