Abstract. Precision planting has been proven to be an effective method for seeding row crops with uniform seed spacing, which favors crop yields. However, most precision planters were developed for low field operating speeds. In this study, a mechanical seed-metering device was developed with double-setting seed pickers, which allows high-quality planting at high field operating speeds. A discrete element model (DEM) was used to examine the effects of the design parameters on the metering performance, as indicated by the quality index (Iq), miss index (Imiss), and multiples index (Imult). Based on the model results, a seed-metering device was fabricated with the optimal design parameters and tested in laboratory conditions for model validation. Results showed that the critical parameters for the seed picker design were the lengths of the first and second setting plates (L1 and L2, respectively) and the seed cell and seed holder angles (a and ß, respectively). The Iq was generally high and the Imiss and Imult were generally low over the ranges of L1 from 15.5 to 17.5 mm, L2 from 4.6 to 5.5 mm, a from 57.5° to 65.0°, and ß from 50.0° to 70.0°. The most influential factors were ß and L2 and their interactions. The best performance, represented by the highest Iq, occurred at L2 = 5.18 mm and ß = 61.9°, where the Iq was 99.59%. The model results agreed well with the test results, as demonstrated by the low relative error (2.5%). Keywords: DEM, Modeling, Precision metering, Quality index, Seed, Travel speed.
The Lancang-Mekong Cooperation (LMC) is a new type of regional cooperation mechanism in the Greater Mekong Subregion (GMS). It was officially co-founded by six Lancang-Mekong countries in 2016. Water resources cooperation is the flagship field of the LMC. The goal of this article is to introduce comprehensively the LMC and to illustrate why it can be regarded as a new choice for regional water resources cooperation in the GMS. This paper first reviews the background to LMC's foundation, and then introduces the structural framework, operating mechanism and recent advances of the LMC. It will then analyze the deficiencies of the present water resources cooperation mechanisms in the GMS and the comparative advantages of water resources cooperation under LMC. Finally, some suggestions were given to improve and reinforce water resources cooperation under the LMC. This research concludes that the LMC is more suitable for the actual needs and objective reality of Lancang-Mekong countries owing to its high-level and all-round regional cooperation mechanism. It was established jointly by all riparian states, with a shared vision to enhance the well-being of six countries' people, and works to narrow the development gap among regional countries.
The purpose of this study is to outline global performance, and to quantitatively evaluate the current research field hot spots, and the future trends about the Lancang‐Mekong River (LMR). Bibliometric methods are used to analyze 3,924 records retrieved from the collection of the Web of Science Core (WoS). The performance of publications, categories, countries, institutes, research hot spots and trends is analyzed in this study by applying CiteSpace and VOSviewer tools. The results revealed that publications about the LMR field have been increasing rapidly since the beginning of the 21st century. The research pertaining to LMR is mainly in the fields of environmental sciences & ecology, water resources, geology, engineering and agriculture. Vietnam, The People's Republic of China, The United States of America, Japan and Thailand get higher rankings in paper output, and Can Tho University, the Chinese Academy of Sciences, Beijing Normal University and the University of Tokyo achieve a high ranking on LMR research. In addition, further studies in research frontiers have revealed that health, security, climate change and international waters will become the new and popular directions and trends in the LMR research.
HighlightsThe instability of the seed release point in a seed-metering device is proved theoretically.A double-curved guiding groove at the seed-release point improves the seed-metering uniformity.A discrete element model was used to examine effects of the design parameters on the metering performance.The critical parameters for the double-curved guiding groove design were determined.Abstract. The instability of the seed release point in a seed-metering device is one of the main causes of the non-uniformity of seed spacing. To improve the seed spacing uniformity, a double-curved guiding groove (DGG) was designed based on the prerelease adaptive principle. The DGG was used at the seed release point of an existing high-speed precision soybean seed-metering device with a double-setting plate. The results showed that the prerelease curved surface of the DGG was capable of guiding seeds to be released at the same seed release point at all times, and the adaptive curved surface of the DGG prevented any changes in seed velocity caused by friction or collisions between seeds and the meter, thereby improving the seed spacing uniformity significantly. A discrete element model was developed and validated with laboratory tests. Through simulations using the model, the primary and secondary factors of the DGG impacting the qualified rate of seed metering (QRM) and the coefficient of variation of the seed spacing uniformity (CVU) were identified and were, in descending order, the spacing of prerelease (SPR), the starting position of prerelease (SPP), the inclination angle of the seed outlet (ASO), and the inclination angle of the receiving cup (ABR). Regression equations of the QRM and CVU with the two main impacting factors were then established. For a planter travel speed of 10 km h-1, the optimal SPR was 10 mm, and the optimal SPP was 40°, where the QRM was 100% and the CVU was 16.61%. When compared to seed metering without the DGG, the CVU was reduced by 2.55%, showing that the DGG significantly improved the uniformity of seed spacing. Keywords: Double-curved guiding groove, Discrete element method, Seed-metering device, Travel speed, Uniformity.
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