Because of the recent advances in drones or Unmanned Aerial Vehicle (UAV) platforms, sensors and software, UAVs have gained popularity among precision agriculture researchers and stakeholders for ...estimating traits such as crop yield and diseases. Early detection of crop disease is essential to prevent possible losses on crop yield and ultimately increasing the benefits. However, accurate estimation of crop disease requires modern data analysis techniques such as machine learning and deep learning. This work aims to review the actual progress in crop disease detection, with an emphasis on machine learning and deep learning techniques using UAV-based remote sensing. First, we present the importance of different sensors and image-processing techniques for improving crop disease estimation with UAV imagery. Second, we propose a taxonomy to accumulate and categorize the existing works on crop disease detection with UAV imagery. Third, we analyze and summarize the performance of various machine learning and deep learning methods for crop disease detection. Finally, we underscore the challenges, opportunities and research directions of UAV-based remote sensing for crop disease detection.
Abstract
Catalytic reductive coupling of two electrophiles and one unsaturated bond represents an economic and efficient way to construct complex skeletons, which is dominated by transition-metal ...catalysis via two electron transfer. Herein, we report a strategy of visible-light photoredox-catalyzed successive single electron transfer, realizing dearomative arylcarboxylation of indoles with CO
2
. This strategy avoids common side reactions in transition-metal catalysis, including ipso-carboxylation of aryl halides and β-hydride elimination. This visible-light photoredox catalysis shows high chemoselectivity, low loading of photocatalyst, mild reaction conditions (room temperature, 1 atm) and good functional group tolerance, providing great potential for the synthesis of valuable but difficultly accessible indoline-3-carboxylic acids. Mechanistic studies indicate that the benzylic radicals and anions might be generated as the key intermediates, thus providing a direction for reductive couplings with other electrophiles, including D
2
O and aldehyde.
The interaction between biochar and soil changes nitrogen (N) dynamics in different ecosystems. Although multiple studies have reported influences of biochar on soil inorganic N (SIN) including ...ammonium (NH4+-N) and nitrate (NO3−-N), the influences reported are contradictory. We undertook a meta-analysis to investigate how biochar properties and the interaction among biochar, soil and fertilisation affect SIN. This quantitative analysis used 56 studies with 1080 experimental cases from manuscripts published between 2010 and 2015. Overall, we found that biochar reduced SIN regardless of experimental conditions (approximately −11±2% of NH4+-N and −10±1.6% of NO3−-N); however, 95% of cases were observed within one year after biochar application. SIN was best explained by residence time of biochar in soil, pyrolysis temperature, application rate, fertiliser type, and soil pH. The effects of biochar were complex due to the interaction of biochar with environmental factors. Most biochar trials used wood as a feedstock, but woody biochar did not decrease SIN as much as other plant-derived biochars. When biochar was used with NH4-based fertilisers, SIN decreased compared to biochar with no fertiliser. In contrast, adding organic fertiliser with biochar increased SIN compared to biochar alone. SIN was clearly reduced after one month of biochar application, suggesting that biochar should be applied at least one month prior to planting so plants are not affected by decreased N. Our results revealed that the interactions between biochar and environmental factors, pyrolysis temperature of biochar and biochar surface properties are the main driving factors affecting SIN. There were limited long-term studies of >1year, thus the long-term effects of biochar on SIN still remain unclear.
•Overall reduction is 10% of soil inorganic nitrogen after biochar addition.•Interactions between biochar and environmental factors best explained SIN changes.•Woody biochar did not decrease soil inorganic nitrogen as much as other biochars.•Effect of biochar on soil inorganic nitrogen is strongly affected by fertilisation.
Abiotic stresses rewire plant central metabolism to maintain metabolic and energy homeostasis. Metabolites involved in the plant central metabolic network serve as a hub for regulating carbon and ...energy metabolism under various stress conditions. In this review, we introduce recent metabolomics techniques used to investigate the dynamics of metabolic responses to abiotic stresses and analyze the trend of publications in this field. We provide an updated overview of the changing patterns in central metabolic pathways related to the metabolic responses to common stresses, including flooding, drought, cold, heat, and salinity. We extensively review the common and unique metabolic changes in central metabolism in response to major abiotic stresses. Finally, we discuss the challenges and some emerging insights in the future application of metabolomics to study plant responses to abiotic stresses.
The College of Family Physicians of Canada (CFPC) recently recommended extending family medicine residency programs in Canada from 2 to 3 years. This recommendation aims to better equip graduates to ...meet societal needs, manage complexity, and address medical comorbidity through comprehensive primary care practice. However, there are important concerns to consider during this transition period. These include the potential impact on medical student interest in family medicine, as well as the effect on the number of candidates pursuing a focused area of practice. It is crucial for administrators at the CFPC and postgraduate training programs to be creative in program design to reinvigorate interest in family medicine as a career choice. While curricular renewal is important, it is not sufficient to strengthen primary care in Canada. Attention must also be given to system, organizational, and personal factors to support the provision of comprehensive and continuous primary care. Innovative thinking in educational delivery, along with addressing these factors, will attract talented physicians to the practice of family medicine.
Internal initiation and propagation of micro cracks in rock materials might result in macroscopic fragmentation and energy dissipation under dynamic strain rate. Understanding the internal mechanism ...of rock failure and energy consumption is significant in assessing the stability of engineering rock mass under dynamic disturbance. This study experimentally investigated the energy dissipation and fragment distribution of rock specimens containing symmetrical and asymmetrical cross fissures under static and dynamic loadings. Our results reveal that the dynamic strength of rock specimens evidently increases with increasing strain rate, while the dynamic elastic modulus does not depend on the loading rate. For a given dynamic strain rate, the rock specimens containing asymmetrical cross fissures (one of the fissures had a relatively large dip angle) had higher dynamic strengths than those containing symmetrical cross fissures. During loading process, tensile cracks and shear cracks significantly affect the failure patterns of cross-fissured rock specimens under static and dynamic loadings, respectively. All the cross-fissured specimens show similar “X” shaped shear failure mode regardless of fissure configuration subjected to dynamic strain rate. The cross-fissured rock specimens with higher strain rates feature smaller location parameter and scale parameter of the fragment size distribution by GEV fitting. The fractal dimension of cross-fissured specimens show an evident loading rate dependence, and the size distribution of the fragments in asymmetrically cross-fissured specimens under dynamic loading is most homogeneous. The dissipated energy density of all the rock specimens obviously increase as the dynamic strain rate increases, while the energy utilization efficiency is less affected by the strain rate.
Mo‐ and Fe‐containing enzymes catalyze the reduction of nitrate and nitrite ions in nature. Inspired by this activity, we study here the nitrate reduction reaction (NO3RR) catalyzed by an ...Fe‐substituted two‐dimensional molybdenum carbide of the MXene family, viz., Mo2CTx : Fe (Tx are oxo, hydroxy and fluoro surface termination groups). Mo2CTx : Fe contains isolated Fe sites in Mo positions of the host MXene (Mo2CTx) and features a Faradaic efficiency (FE) and an NH3 yield rate of 41 % and 3.2 μmol h−1 mg−1, respectively, for the reduction of NO3− to NH4+ in acidic media and 70 % and 12.9 μmol h−1 mg−1 in neutral media. Regardless of the media, Mo2CTx : Fe outperforms monometallic Mo2CTx owing to a more facile reductive defunctionalization of Tx groups, as evidenced by in situ X‐ray absorption spectroscopy (Mo K‐edge). After surface reduction, a Tx vacancy site binds a nitrate ion that subsequently fills the vacancy site with O* via oxygen transfer. Density function theory calculations provide further evidence that Fe sites promote the formation of surface O vacancies, which are identified as active sites and that function in NO3RR in close analogy to the prevailing mechanism of the natural Mo‐based nitrate reductase enzymes.
Inspired by the active sites of the nitrate reductase enzymes, Fe‐substituted two‐dimensional molybdenum carbide, Mo2CTx : Fe, is studied here and found to display unique performances in the electrochemical reduction of nitrate to ammonia, outperforming its monometallic counterpart Mo2CTx. In situ XAS and DFT calculations reveal that this difference in reactivity results from the vacancy‐formation‐promoting effect of Fe sites in Mo2CTx : Fe.
A novel and facile CH bond fluorination proceeds under remarkably mild conditions (close to room temperature in most cases). Both aromatic and olefinic C(sp2)H bonds with a wide range of electronic ...properties are selectively fluorinated in the presence of a catalytic amount of simple, cheap, and nontoxic nitrate as the promoter. A PdII/PdIV catalytic cycle that is initiated by an in situ generated cationic Pd(NO3)+ species was proposed based on preliminary mechanistic studies.
Nitrate makes it possible: A novel and facile method for CH bond fluorination entails remarkably mild reaction conditions (close to room temperature in most cases). Both aromatic and olefinic C(sp2)H bonds were selectively fluorinated in the presence of a catalytic amount of inexpensive and nontoxic nitrate as the promoter.
China has deployed the world’s largest fleet of sulfur dioxide (SO2) scrubbers (flue gas desulfurization systems), and most of them now appear to be operating properly. Although many plant managers ...avoided using their SO2 scrubbers in the past, recent evidence, based on a series of field interviews conducted by the author, suggests that managers of coal power plants now have incentives to operate their scrubbers properly. China’s new policy incentives since 2007 appear well designed to overcome the hurdle of high operation and maintenance costs of SO2 scrubbers. Furthermore, it is now far more likely that offenders will be caught and punished. Continuous emission monitoring systems have played a key role in this change of attitudes. Plant inspections have become much more common, facilitated by a significant increase in the number of inspectors and the fact that the 461,000-megawatt SO2 scrubbers at the end of 2009 were located in only 503 coal power plants, making frequent inspections little constrained by the shortage of inspectors. Because SO2 is the precursor of sulfate particles believed to cause significant cooling effects on climate, China’s SO2 mitigation may make it more urgent to control the world’s greenhouse gas emissions.
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