Abundant shallow underground brackish water resources could help in alleviating the shortage of fresh water resources and the crisis concerning agricultural water resources in the North China Plain. ...Improper brackish water irrigation will increase soil salinity and decrease the final yield due to salt stress affecting the crops. Therefore, it is urgent to develop a practical and low-cost method to monitor the soil salinity of brackish irrigation systems. Remotely sensed spectral vegetation indices (SVIs) of crops are promising proxies for indicating the salinity of the surface soil layer. However, there is still a challenge concerning quantitatively correlating SVIs with the salinity of deeper soil layers, in which crop roots are mainly distributed. In this study, a field experiment was conducted to investigate the relationship between SVIs and salinity measurements at four soil depths within six winter wheat plots irrigated using three salinity levels at the Yucheng Comprehensive Experimental Station of the Chinese Academy of Sciences during 2017–2019. The hyperspectral reflectance was measured during the grain-filling stage of winter wheat, since it is more sensitive to soil salinity during this period. The SVIs derived from the observed hyperspectral data of winter wheat were compared with the salinity at four soil depths. The results showed that the optimized SVIs, involving soil salt-sensitive blue, red-edge, and near-infrared wavebands, performed better when retrieving the soil salinity (R2 ≥ 0.58, root mean square error (RMSE) ≤ 0.62 g/L), especially at the 30-cm depth (R2 = 0.81, RMSE = 0.36 g/L). For practical applications, linear or quadratic models based on the screened SVIs in the form of normalized differential vegetation indices (NDVIs) could be used to retrieve soil salinity (R2 ≥ 0.63, RMSE ≤ 0.62 g/L) at all soil depths and then diagnose salt stress in winter wheat. This could provide a practical technique for evaluating regional brackish water irrigation systems.
Comprehensive Mission Spectrum (CMS) of an aero-engine can reflect the usage characteristics of the engine. It can provide load input for engine life prediction and accelerated mission test. In this ...paper, a novel compilation method of CMS of aero-engine maneuvering load based on mission segment is proposed. Firstly, the use-related Typical Mission Segment (TMS) of maneuvering load is divided and identified according to spectral characteristics. Secondly, the mathematical model of different kinds of TMS are established based on stochastic process theory. Finally, the CMS of maneuvering load is compiled based on TMS. The proposed method can accurately quantify the compilation of CMS. The compiled CMS shows good agreement with the original load spectrum. According to damage consistency inspection, the compiled CMS is consistent with the damage caused by the original load spectrum in terms of low cycle fatigue.
The efficiency of the numerical propagators for solving the time-dependent Schrödinger equation in the wave packet approach to reactive scattering is of vital importance. In this Perspective, we ...first briefly review the propagators used in quantum reactive scattering calculations and their applications to triatomic reactions. Then we present a detailed comparison of about thirty higher-order split operator propagators for solving the Schrödinger equation with their applications to the wave packet evolution within a one-dimensional Morse potential, and the total reaction probability calculations for the H + HD, H + NH, H + O(2), and F + HD reactions. These four triatomic reactions have quite different dynamic characteristics and thus provide a comprehensive picture of the relative advantages of these higher-order propagation methods for describing reactive scattering dynamics. Our calculations reveal that the most often used second-order split operator method is typically more efficient for a direct reaction, particularly for those involving flat potential energy surfaces. However, the optimal higher-order split operator methods are more suitable for a reaction with resonances and intermediate complexes or a reaction experiencing potential energy surface with fluctuations of considerable amplitude. Three 4th-order and one 6th-order split operator methods, which are most efficient for solving reactive scattering in various conditions among the tested ones, are recommended for general applications. In addition, a brief discussion on the relative performance between the Chebyshev real wave packet method and the split operator method is given. The results in this Perspective are expected to stimulate more applications of (high-order) split operators to the quantum reactive scattering calculation and other related problems.
Quantum dynamical theories have progressed to the stage in which state-to-state differential cross sections can now be routinely computed with high accuracy for three-atom systems since the first ...such calculation was carried out more than 30 years ago for the H + H(2) system. For reactions beyond three atoms, however, highly accurate quantum dynamical calculations of differential cross sections have not been feasible. We have recently developed a quantum wave packet method to compute full-dimensional differential cross sections for four-atom reactions. Here, we report benchmark calculations carried out for the prototypical HD + OH → H(2)O + D reaction on an accurate potential energy surface that yield differential cross sections in excellent agreement with those from a high-resolution, crossed-molecular beam experiment.
We present a simple and effective nonequilibrium heat-treatment approach that allows for the facile fabrication of maghemite (γ-Fe2O3) fiber-in-tube and tube-in-tube nanostructures by heat-treating ...electrospun precursor fibers composed of polyvinylpyrrolidone (PVP) and iron citrate with a carefully devised heating rate (R). In this nonequilibrium heat-treatment procedure, R can be easily utilized to tune the temperature gradient established in the inner portion of the fibers and the difference between the cohesive force and the adhesive force at the interface layer between the inner gel and the dense rigid shell generated in situ by a high R. Therefore, the contraction direction of the precursor nanofibers and the final morphology of the resultant γ-Fe2O3 fibers ranging from a simple tube to a fiber in tube to a tube in tube are realized for control. The nonequilibrium heat-treatment approach reported here can be readily extended to the fabrication of other materials with controllable interior structures by fast heating their corresponding gel precursors, which may be fabricated on the basis of electrospinning techniques and others. The resultant γ-Fe2O3 fiber-in-tube and tube-in-tube nanostructures may have important applications in a number of areas, such as magnetic separable catalysts or catalyst supporting materials, sensors, absorbents, microreactors, and so forth, because of their structural characteristics and good magnetic properties.
Achieving food and feed self‐sufficiency is important for both China and the world. While China's food self‐sufficiency has been examined at the national and provincial levels, few studies consider ...lower administrative levels or different food and feed items. This study quantifies self‐sufficiency in the eastern regions of China and examines correlations with agronomic (arable area, yield, fertilizer input, and machinery power) and socioeconomic (population density, gross domestic product GDP) variables at the local level, which are related to the interactions of the Sustainable Development Goals. We calculated food and feed balances, and checked correlations across and within regions grouped by population density levels between production, balance indices, and other agronomic and socioeconomic variables. The results showed that most regions can achieve self‐sufficiency in cereals, vegetables, and meat. Regarding eggs and maize, there was self‐sufficiency in the north but deficiency in the south. Nearly all regions demonstrated extreme shortages of milk and soybeans. The results also showed a positive correlation between the production of some food commodities and the population in eastern regions of China, demonstrating that the aim of achieving food self‐sufficiency at the local level is pursued. For cereals, vegetables, and maize, the yield and arable land per capita were positive factors for self‐sufficiency, while GDP per capita was a negative factor for cereals, meat, and maize. Various factors have different impacts on the food and feed self‐sufficiency of regions based on population density. Protecting arable land by rural revitalization and mitigating urban sprawl can retain food and feed self‐sufficiency in large cities. This study outlines important implications for policymakers seeking to achieve food and feed self‐sufficiency in China.
Food and feed self‐sufficiency was quantified at the local level in the eastern regions of China. For cereals, vegetables, and maize, the yield and arable land per capita were positive factors for self‐sufficiency, while GDP per capita was a negative factor for cereals, meat, and maize. Food and feed self‐sufficiency are driven by different factors in different population density regions.
•A UAV-based grain yield estimation was developed to monitor the spatial variability of wheat yield at ripening stage.•Three wheat ear phenotypic features (ear count, ear size, and ear anomaly index) ...extracted by Mask R-CNN was used to estimate wheat yield.•Random forest regression was the most accurate in phenotypic feature-based wheat yield estimation.•The method is a promising supplement to traditional field sampling.
A non-destructive, convenient, and low-cost yield estimation at the field scale is vital for precision farming. Significant progress has been made in using UAV-based canopy features to predict crop yield during the mid-growth stages. However, there has been limited effort to explore yield estimation specifically after crop maturity. Researching the effectiveness of artificial intelligence for estimating wheat yield utilizing phenotypic features extracted from UAV images, this study applied a deep learning algorithm (Mask R-CNN) to extract three wheat ear phenotypic features at ripening stage, including ear count, ear size, and ear anomaly index. Subsequently, machine learning algorithms (i.e., multiple linear regression, support vector regression, and random forest regression) driven by ear features were intercompared to obtain the optimal grain yield estimation. Based on the findings, (1) field observed ear count which was linearly associated with grain yield (R2 = 0.93), can be largely detected by UAV images (81 %); (2) Mask R-CNN demonstrated satisfactory performance in ear segmentation, achieving an F1 score of 0.87; (3) random forest regression resulted in the most accurate yield estimation (R2 = 0.86 and rRMSE = 17.53 %), when all three ear phenotypic features were combined. Overall, this study demonstrates that utilizing ear phenotypic features is an alternative approach for estimating wheat grain yield at ripening stage, showing potential as a viable substitute to tedious field sampling methods.
This paper describes an enhanced optimal-torque-control strategy for fault-tolerant permanent-magnet (PM) machines under flux-weakening operations. By adjusting the degree of flux weakening according ...to estimated instantaneous-torque-control errors, the torque-control performance of the machine can be improved when operating above its base speed under either open- or short-circuit fault condition. Extensive simulations under both healthy and fault conditions have been undertaken in order to validate the effectiveness of the proposed control strategy. Experimental results have also been given based on the testing of a prototype five-phase fault-tolerant PM machine.
Four iron smelting related sites were discovered in Zouma Town, western Chongqing, China. Among these sites, two (Luduizi and Tieshazitu) were dated to the end of the Ming Dynasty in the sixteenth to ...seventeenth centuries a.d. and the other two (Gaoluchang and Nianmigou) were dated to the Late Qing Dynasty in the nineteenth century. Large amounts of smelting-related materials were excavated from these sites. Ten metallographic samples collected from excavated slags, a furnace wall, and iron ore were prepared and analyzed. This article reports the first scientific analysis of smelting-related materials in the area. The results provide a preliminary understanding of iron production technology in Chongqing in the sixteenth and seventeenth centuries.
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