Effects of Moisture Content on Selected Physical and Mechanical Properties of Alfalfa Seeds

Alfalfa is one of the most widely planted forage legume in the world and that because of its tolerance, adaptation, high yield and nutritious value. Physico-mechanical properties of alfalfa seed are very crucial in the machine designing and processing operations. In this study, some of the physical and mechanical properties of alfalfa seed cultivar were investigated under laboratory condition, as desired for the design of a metering device.  Seven moisture contents were introduced to the initial content of 7.98%, d.b. The geometric and gravimetric characteristics were determined. Correlation equation models were developed based on the function of moisture contents. The means average parameter values of the length, width, thickness, aspect ratio, seed mass, arithmetic, geometric mean diameter, true and bulk density, porosity seed volume, and surface area ranged between 2.356 to 2.718mm, 1.390 to 1.473mm, 1.071 to 1.345mm, 0.68 to 0.776%, 1.7968 to 2.295g, 1.466 to 1.589mm, 1.141 to 1.517mm and 1.466 to 1.589g/cm31.199 to 0.830g/cm3, 0.10 to 0.44%, 0.7383 to 0.79426, and 6.305 to 7.2438mm2, respectively. While, the plywood surface had the highest value of the coefficient of friction as the roughest, followed by polished steel and rubber, glass the least surface roughness. However, the germination rate (%) increased as seed damages decreased, as the coefficient of internal friction decreases from 0.127 to 0.095, while the cohesion increasing from 2.11 to 5.95. The angle of repose resulted in a non-linear increase from 27.05o to 28.68o, 28.86o to 29.86o, 31.49o to 32.35o, and 32.47o to 33.21o as moisture content increased from7.98 to 22.12% d.b. Keywords: alfalfa seed, moisture content, mechanical property, physical propert

Resolving the puzzle of single-atom silver dispersion on nanosized γ-Al2O3 surface for high catalytic performance

Ag/γ-Al2O3 is widely used for catalyzing various reactions, and its performance depends on the valence state, morphology and dispersion of Ag species. However, detailed anchoring mechanism of Ag species on γ-Al2O3 remains largely unknown. Herein, we reveal that the terminal hydroxyls on γ-Al2O3 are responsible for anchoring Ag species. The abundant terminal hydroxyls existed on nanosized γ-Al2O3 can lead to single-atom silver dispersion, thereby resulting in markedly enhanced performance than the Ag cluster on microsized γ-Al2O3. Density-functional-theory calculations confirm that Ag atom is mainly anchored by the terminal hydroxyls on (100) surface, forming a staple-like local structure with each Ag atom bonded with two or three terminal hydroxyls. Our finding resolves the puzzle on why the single-atom silver dispersion can be spontaneously achieved only on nanosized γ-Al2O3, but not on microsized γ-Al2O3. The obtained insight into the Ag species dispersion will benefit future design of more efficient supported Ag catalysts. https://doi.org/10.1038/s41467-019-13937-1 OPEN

Theoretical study of flow ripple for an aviation axial-piston pump with damping holes in the valve plate

Based on the structure of a certain type of aviation axial-piston pump’s valve plate which adopts a pre-pressurization fluid path (consisting a damping hole, a buffer chamber, and an orifice) to reduce flow ripple, a single-piston model of the aviation axial-piston pump is presented. This single-piston model comprehensively considers fluid compressibility, orifice restriction effect, fluid resistance in the capillary tube, and the leakage flow. Besides, the instantaneous discharge areas used in the single-piston model have been calculated in detail. Based on the single-piston model, a multi-piston pump model has been established according to the simple hydraulic circuit. The single- and multi-piston pump models have been realized by the S-function in Matlab/Simulink. The developed multi-piston pump model has been validated by being compared with the numerical result by computational fluid dynamic (CFD). The effects of the pre-pressurization fluid path on the flow ripple and the instantaneous pressure in the piston chamber have been studied and optimized design recommendations for the aviation axial-piston pump have been given out

Resolving the puzzle of single-atom silver dispersion on nanosized γ-Al\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e surface for high catalytic performance

Ag/γ-Al2O3 is widely used for catalyzing various reactions, and its performance depends on the valence state, morphology and dispersion of Ag species. However, detailed anchoring mechanism of Ag species on γ-Al2O3 remains largely unknown. Herein, we reveal that the terminal hydroxyls on γ-Al2O3 are responsible for anchoring Ag species. The abundant terminal hydroxyls existed on nanosized γ-Al2O3 can lead to single-atom silver dispersion, thereby resulting in markedly enhanced performance than the Ag cluster on microsized γ-Al2O3. Density-functional-theory calculations confirm that Ag atom is mainly anchored by the terminal hydroxyls on (100) surface, forming a staple-like local structure with each Ag atom bonded with two or three terminal hydroxyls. Our finding resolves the puzzle on why the single-atom silver dispersion can be spontaneously achieved only on nanosized γ-Al2O3, but not on microsized γ-Al2O3. The obtained insight into the Ag species dispersion will benefit future design of more efficient supported Ag catalysts

Research on the neutralization control of the RF ion micropropulsion system for the ‘Taiji-1’ satellite mission

Abstract To achieve the neutralization control requirements of the radio-frequency (RF) ion microthruster (μRIT) in the ‘Taiji-1’ satellite mission, we proposed an active neutralization control solution that is based on the carbon nanotube field emission technology. The carbon nanotube field emission neutralizer (CNTN) has the characteristics of light weight, small size, and propellantless, which is especially suitable for the neutralization control tasks of ion microthrusters. The Institute of Mechanics, Chinese Academy of Sciences, in collaboration with Tsinghua University, has successfully developed a CNTN to meet mission requirements. On the ground, the feasibility of cooperation working between μRIT and CNTN was fully verified, as well as the simulation and experimental study of neutralization control strategy, which finally passed the engineering assessment test. Since the launch of ‘Taiji-1’ satellite on 31 August, 2019, the RF ion micropropulsion system has successfully completed nearly one hundred test missions in space. The test results indicate that CNTN does not have performance degradation, and the neutralization control strategy is effective