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An integrative mathematical model of microwave ion thruster for mHz-frequency thrust noise analysis

American Journal of Plant Sciences（美国植物学期刊） 2024年第3期 180页

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Chinese Journal of Aeronautics 2024年第4期37卷 121-136页

作者： Xiang NIU Hui LIU daren YU Plasma Propulsion Laboratory Harbin Institute of TechnologyHarbin 150001China

Many high-precision space missions need thrusters to produce thrust with low noise to compensate for disturbances and ensure satellite platform stability. Microwave ion thruster is characterized with a wide thrust range and potential for these missions. A cost-effective and accurate mathematical model is crucial for mHz-frequency thrust noise analysis and feedback controller design. The Particle-In-Cell(PIC) and global models are two common simulation tools. The PIC model is characterized with high accuracy but huge computation cost, which is difficult to analyze long-time performance characteristics. Now, the global model is only used for the discharge chamber with low accuracy and cannot reflect ion extraction properties. In this paper, an integrative mathematical model is built for a 1-cm microwave ion thruster and can reflect ion beamlet divergence and impingement on the Accelerator Grid(AG). Simulation results show good agreement with experiments at 0.06 sccm. However, the model demonstrates worse consistency with experiments when the flux increases to 0.1 sccm, which may be because the influence of neutral gas on the Electron Cyclotron Resonance(ECR) is not considered in the model. A long-time(1000 s) simulation is conducted with this model under 35 μN. It takes 3 hrs, and the thrust noise reaches 1 μN/Hz^(0.5) at 1 mHz.

关键词： Electric propulsion Microwave ion thruster Integrative model Sheath property Ion beamlet divergence Thrust noise Plasma

Microphysical Characteristics of Rainfall Based on Long-Term Observations with a 2dVd in Yangbajain,Tibet

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Advances in Atmospheric Sciences 2024年第9期41卷 1721-1734页

作者： Ming LI Yongheng BI Yonghai SHEN Yinan WANG Ciren Nima Tianlu CHEN daren LYU Key Laboratory for Cosmic Rays of the Ministry of Education Tibet UniversityLhasa 850000China Key Laboratory of Middle Atmosphere and Global Environment Observation(LAGEO) Institute of Atmospheric PhysicsChinese Academy of ScienceBeijing 100029China University of Chinese Academy of Sciences Beijing 100049China

Raindrop size distribution(dSd)plays a crucial role in enhancing the accuracy of radar quantitative precipitation estimates in the Tibetan Plateau(TP).However,there is a notable scarcity of long-term,high-resolution observations in this *** address this issue,long-term observations from a two-dimensional video disdrometer(2dVd)were leveraged to refine the radar and satellite-based algorithms for quantifying precipitation in the hinterland of the *** was observed that weak precipitation(Rdrops(ddrop ***,the average spectral width of the dSd increases with increasing rain *** dSd characteristics of convective and stratiform precipitation were discussed across five different rain rates,revealing that convective precipitation in Yangbajain(YBJ)exhibits characteristics similar to maritime-like *** constrained relationships between the slopeΛand shapeμ,d_(m)and N_(w)of gamma dSds were ***,we established a correlation between the equivalent diameter and drop axis ratio and found that raindrops on the TP attain a nearly spherical ***,the application of the rainfall retrieval algorithms of the dual-frequency precipitation radar in the TP is improved based on the statistical results of the dSd.

关键词： Tibetan Plateau raindrop size distribution 2dVd dual frequency radar microphysical features

Adding Value to Crop Production Systems by Integrating Forage Cover Crop Grazing

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American Journal of Plant Sciences 2024年第3期15卷 180-192页

作者： Robert B. Mitchell daren d. redfearn Kenneth P. Vogel Terry J. Klopfenstein Galen Erickson P. Stephen Baenziger Bruce E. Anderson Mary E. drewnoski Jay Parsons Steven d. Masterson Marty R. Schmer Virginia L. Jin USdA-ARS Wheat Sorghum and Forage Research Unit University of Nebraska-Lincoln Lincoln NE USA department of Agronomy and Horticulture University of Nebraska-Lincoln Lincoln NE USA department of Animal Science University of Nebraska-Lincoln Lincoln NE USA department of Agricultural Economics University of Nebraska-Lincoln Lincoln NE USA USdA-ARS Agroecosystem Management Research Unit University of Nebraska-Lincoln Lincoln NE USA

In addition to their value as cereal grains, wheat (Triticum aestivum L.) and triticale (× Triticosecale Wittmack) are important cool-season annual forages and cover crops. Yearling steer (Bos taurus) performance was compared in the spring following autumn establishment as for age cover crops after soybean [Glycine max (L.) Merr.] grain harvest. Replicated pastures (0.4 ha) were no-till seeded in three consecutive years into soybean stubble in autumn, fertilized, and grazed the following spring near Ithaca, NE, USA. Each pasture (n = 3) was continuously stocked in spring with four yearling steers (380 ± 38 kg) for 17, 32, and 28 d in 2005, 2006, and 2007, respectively. In 2005, average daily gain (AdG) for steers grazing triticale exceeded the AdG for wheat by 0.31 kghd-1d-1. In 2006, wheat AdG exceeded that for triticale by 0.12 kghd-1d-1. In 2007, steers grazing wheat lost weight, while steers grazing triticale gained 0.20 kghd-1d-1. Based on the 3-year average animal gains valued at $1.32 kg-1, mean net return ($ ha-1 yr-1) was $62.15 for triticale and $22.55 for wheat. Since these grazed cover crops provide ecosystem services in addition to forage, grazing could be viewed as a mechanism for recovering costs and adds additional value to the system. Based on this 3-year grazing trial, triticale was superior to wheat and likely will provide the most stable beef yearling performance across years with variable weather for the western Cornbelt USA.

关键词： Cover crops Soybean Triticale Wheat

Observations of Spring Hard Freeze Injury to C<sub>4</sub>Perennial Grasses Native to the Great Plains, USA

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American Journal of Plant Sciences 2019年第5期10卷 723-729页

作者： Rob Mitchell daren redfearn Wheat Sorghum and Forage Research Unit USDA-ARS Lincoln Nebraska USA department of Agronomy and Horticulture University of Nebraska Lincoln Nebraska USA

The native prairies of the Great Plains USA are dominated by perennial C4 grasses like switchgrass (Panicum virgatum) and big bluestem (Andropogon gerardii). Spring hard freeze injury to C4 perennial grasses is rare but information is lacking in the literature. Our objective was to document effects of spring hard freeze damage to C4 perennial grasses native to the Great Plains USA. On 2 May at 24:00 pm, air temperature near Mead, Nebraska was below freezing and remained below freezing until 8:00 am on 3 May, with a minimum air temperature of -2.8°C. Based on 50-year of weather data for this site, a minimum threshold temperature of 0°C on or after 3 May occurred 16 times, but a minimum threshold temperature of -2.8°C on or after 3 May occurred only twice. Grass tillers were visually evaluated to determine extent of freeze damage. The terminal 3- to 5-cm of the leaf lamina was blackened 4-d after freezing and had complete browning, rolling, and desiccation 14-d after freezing. Tiller survival was not negatively affected by the freezing temperatures in May 2004. As the growing season progressed, all agronomic and livestock responses were within normal ranges for these C4 grasses. This is the first field report of multiple C4 prairie grass species responses to a spring hard freeze following significant spring growth. Plant recovery to this late-spring hard freeze demonstrates the ecological resilience of these C4 prairie grasses. These rare spring hard freezes had short-term impacts on C4 grasses but did not negatively impact agronomic performance for forage or bioenergy later in the growing season.

关键词： C4 Perennial Grasses Spring Hard Freeze

Improved Known-Key distinguisher on Round-Reduced 3d Block Cipher

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Chinese Journal of Electronics 2015年第1期24卷 199-204页

作者： ZHA daren WU Shuang WANG Qiongxiao University of Chinese Academy of Sciences data Assurance and Communication Security Research Center of Chinese Academy of Sciences

The 3d block cipher is a three-dimensional version of AES(Advanced encryption standard), which use a three-dimensional state and similar round functions. In this paper, we will use the known-key attack model proposed by Knudsen and Rijmen, and propose an improved distinguisher on 15 rounds of 3d, which has 22 rounds in total. The distinguisher is constructed using rebound techniques. In the previous distinguisher, only three inbound phases are merged. Here we propose a method to merge four inbound phases using gradual matching *** improved complexity of this distinguisher is 2128 computations and 264 memory. The computational complexity is significantly reduced from 2200 in the previous attack.

关键词： 3d block cipher Known-key distinguisher Rebound attack Gradual matching.

A New Cluster Updating for 2-d SU(2)×SU(2) Chiral Model

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Chinese Physics Letters 1993年第9期10卷 554-557页

作者： ZHANG Jianbo JI daren Zhejiang Institute of Modern Physics Zhejiang UniversityHangzhou 310027

We propose a variant version of Wolffs cluster algorithm,which may be extended to SU(N)×SU(N)dural model,and test it in 2-diniensiontil SU(2)×SU(2)chiral *** results show that the new method can efficiently reduce t... 详细信息

关键词： SU(2) model. chiral

The Impact of Surface Properties on downward Surface Shortwave Radiation over the Tibetan Plateau

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Advances in Atmospheric Sciences 2015年第6期32卷 759-771页

作者： WANG Leidi L daren HE Qing Key Laboratory of Middle Atmosphere and Global Environmental Observation Institute of Atmospheric PhysicsChinese Academy of Sciences University of Chinese Academy of Sciences

The complexity of inhomogeneous surface-atmosphere radiation transfer is one of the foremost problems in the field of atmospheric physics and atmospheric radiation. To date, the influence of surface properties on shortwave radiation has not been well studied. The daily downward surface shortwave radiation of the latest FLASHFlux/CERES （Fast Longwave And Shortwave Fluxes_Time Interpolated and Spatially Averaged/Clouds and the Earth＇s Radiant Energy System） satellite data was evaluated against in situ data. The comparison indicated that the differences between the two data sets are unstable and large over rugged terrain compared with relatively flat terrain, and the mean absolute error of the satellite products reaches 31.4 W m-2 （12.3%） over rugged terrain. Based on the SSF （single satellite footprint）/CERES product, the influence of surface properties on the distribution of downward surface shortwave radiation （dSSR） was analyzed. The influence of surface properties on dSSR over the Tibetan Plateau is about twice as large as that in two other regions located at the same latitude （eastern China-western Pacific and subtropical North Pacific）. A simulation was carried out with the help of the I3RC （International Intercomparision of Three-dimensional Radiation Code） Monte Carlo 3d radiative transfer community model. The results showed that dSSR increases as surface albedo increases. Moreover, the impact of surface albedo on dSSR is larger if the spatial distribution of clouds is more non-uniform. It is hoped that these results will contribute to the development of 3d radiative transfer models and the improvement of satellite inversion algorithms.

关键词： shortwave radiation surface properties Tibetan Plateau satellite remote sensing

Magnet stage optimization of 5 kW multi-cusped field thruster

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Plasma Science and Technology 2020年第9期22卷 128-138页

作者： Peng HU daren YU Yan SHEN Beijing Institute of Control Engineering Beijing 100094People's Republic of China Lab of Advanced Space Propulsion Beijing 100094People’s Republic of China Beijing Engineering Research Center of Efficient and Green Aerospace Propulsion Technology Beijing 100094People’s Republic of China Plasma Propulsion Laboratory of Harbin Institute of Technology Harbin 150001People's Republic of China School of Aeronautics and Astronautics Sun Yat-sen UniversityGuangzhou 510006People's Republic of China

The multi-cusped field thruster is a unique electric thruster device,which has many advantages such as long lifetime,large-range thrust throttling ability,high thrust density,and low *** thruster employs several alternating polarity permanent magnets to create a periodic magnetic field with several *** studies have indicated that the basic ionization and acceleration processes are directly related to the electron motion behavior,which mainly depends on the magnetic field *** magnet number and magnet stage length are two key magnetic field parameters that have important effects on the thruster *** this paper,both the magnet number and magnet stage length parameters are studied for the optimization of a 5 k W multi-cusped field *** results indicate that the three-stage thruster has a better electron confinement than the two-stage *** has lower ion energy loss at the wall,and shows a higher ionization ***,the three-stage magnetic field is a superior magnetic field ***,the three-stage magnetic field simulation results indicate that an optimal accelerating electric field distribution and ionization region distribution could be obtained when the magnet length ratio is 78:25:20.

关键词： multi-cusped field magnet number magnet length performance optimization

dNA methylation in inflammatory bowel disease and beyond

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World Journal of Gastroenterology 2013年第32期19卷 5238-5249页

作者： daren Low Atsushi Mizoguchi Emiko Mizoguchi Gastrointestinal Unit Department of MedicineMassachusetts General HospitalHarvard Medical School Molecular Pathology Unit Department of PathologyMassachusetts General HospitalHarvard Medical School Center for the Study of Inflammatory Bowel disease Massachusetts General HospitalHarvard Medical School

Inflammatory bowel disease(IBd)is a consequence of the complex,dysregulated interplay between genetic predisposition,environmental factors,and microbial composition in the *** a great advancement in identifying host-susceptibility genes using genome-wide association studies(GWAS),the majority of IBd cases are still *** immediate challenge in post-GWAS era is to identify other causative genetic factors of *** methylation has received increasing attention for its mechanistical role in IBd *** stable,yet dynamic dNA modification,can directly affect gene expression that have important implications in IBd *** alterations in dNA methylation associated with IBd are likely to outset as early as embryogenesis all the way until *** this review,we will discuss the recent advancement in understanding how dNA methylation alterations can contribute to the development of IBd.

关键词： Intestinal inflammation Crohn’s disease Colitis dNA methyltransferase Epi-therapy