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Finite element analysis of dynamic stability of bearingless rotor

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航空动力学报 2014年第5期29卷 1112-1121页

作者： WEI li-jun li shu li Xue-chang School of Aeronautic Science and Engineering Beijing University of Aeronautics and Astronautics

Dynamic stability equations of bearingless rotor blades were investigated using a simplified *** aerodynamic loads of blades were evaluated using two-dimensional airfoil *** equations were obtained by linearization of the perturbation.A normal-mode approach was used to transform the equations expressed by nodal degrees of freedom into equations expressed by modal degrees of freedom,which can reduce the dimension of the *** stability results of rotor blades were presented using eigenvalue *** shape function matrix was obtained using spline interpolation,which simplified the analysis and made assembly of the inertial matrix,damping matrix,and stiffness matrix a simple mathematical *** results indicate that the method is efficient and greatly simplifies the analysis.

关键词：无轴承转子动态稳定性有限元法样条插值特征值分析

Direct gas-phase epoxidation of propylene to propylene oxide using air as oxidant on supported gold catalyst

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Journal of Natural Gas Chemistry 2008年第2期17卷 184-190页

作者： Zhanghuai suo Mingshan Jin Jiqing Lu Zhaobin Wei Can li Institute of Applied Catalysis Yantai University Yantai 264005 Shandong China State Key Laboratory of Catalysis Dalian Institute of Chemical Physics Chinese Academy of Sciences Dalian 116023 Liaoning China

Gold catalysts supported on SiO2, TiO2, TiO2-SiO2, and ZrO2-SiO2 supports were prepared by impregnating each support with a basic solution of tetrachloroauric acid. X-ray diffraction （XRD）, transmission electron microscopy （TEM）, and X-ray photoelectron spectroscopy （XPS） techniques were used to characterize their structure and surface composition. The results indicated that the size of gold particles could be controlled to below 10 nm by this method of preparation. Washing gold catalysts with water could markedly enhance the dispersion of metallic gold particles on the surface, but it could not completely remove the chloride ions left on the surface. The catalytic performance of direct vapor-phase epoxidation of propylene using air as an oxidant over these catalysts was evaluated at atmospheric pressure. The selectivity to propylene oxide （PO） was found to vary with reaction time on the stream. At the reaction conditions of atmosphere pressure, temperature 325 ℃, feed gas ratio V（C3H6）/V（O2）= 1/2, and GHSV =6000h^-1, 17.9% PO selectivity with 0.9% propylene conversion were obtained at initial 10 min for Au/SiO2 catalyst. After reacting 60 min only 8.9% PO selectivity were detected, but the propylene conversion rises to 1.4% and the main product is transferred to acrolein （72% selectivity）. Washing Au/TiO2-SiO2 and Aa/ZrO2-SiO2 samples with magnesium citrate solution could markedly enhance the activity and PO selectivity because smaller gold particles were obtained.

关键词： gold catalyst support modified impregnation method epoxidation of propylene molecular oxygen

Contribution of Root Proliferation in Nutrient-Rich Soil Patches to Nutrient Uptake and Growth of Maize

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Pedosphere 2012年第6期22卷 776-784页

作者： li Hong-Bo ZHANG Fu-suo SHEN Jian-Bo Department of Plant Nutrition China Agricultural UniversityKey Laboratory of Plant-Soil InteractionsMinistry of EducationBeijing 100193(China)

Root proliferation can be stimulated in a heterogeneous nutrient patch; however, the functions of the root proliferation in the nutrient-rich soil patches are not fully understood. In the present study, a two-year field experiment was conducted to examine the comparative effects of localized application of ammonium and phosphorus (P) at early or late stages on root growth, nutrient uptake, and biomass of maize (Zea mays L.) on a calcareous soil in an intensive farming system. Localized supply of ammonium and P had a more evident effect on shoot and root growth, and especially stimulated fine root development at the early seedling stage, with most of the maize roots being allocated to the nutrient-rich patch in the topsoil. Although localized ammonium and P supply at the late stage also enhanced the fine root growth, the plant roots in the patch accounted for a low proportion of the whole maize roots in the topsoil at the flowering stage. Compared with the early stage, fine root length in the short-lived nutrient patch decreased by 44%-62% and the shoot dry weight was not different between heterogeneous and homogeneous nutrient supply at the late growth stage. Localized supply of ammonium and P significantly increased N and P accumulation by maize at 35 and 47 days after sowing (DAS); however, no significant difference was found among the treatments at 82 DAS and the later growth stages. The increased nutrient uptake and plant growth was related to the higher proportion of root length in the localized nutrient-enriched patch. The results indicated that root proliferation in nutrient patches contributed more to maize growth and nutrient uptake at the early than late stages.

关键词： biomass growth stage intensive farming system localized nutrient supply root length

Yet More Elementary Proof of Matrix-Tree Theorem for Signed Graphs

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Algebra Colloquium 2023年第3期30卷 493-502页

作者： shu li Jianfeng Wang School of Mathematics and Statistics Shandong University of TechnologyZiboShandong 255049China

A signed graph G˙=(G,σ)is a graph G=(V(G),E(G))with vertex set V(G)and edge set E(G),together with a functionσ:E→{+1,−1}assigning a positive or negative sign to each *** this paper,we present a more elementary proof for the matrix-tree theorem of signed graphs,which is based on the relations between the incidence matrices and the Laplcians of signed *** an application,we also obtain the results of Monfared and Mallik about the matrix-tree theorem of graphs for signless Laplacians.

关键词： signed graph matrix-tree theorem Laplacian signless Laplacian incidence matrix

Non-probabilistic reliability method and reliability-based optimal LQR design for vibration control of structures with uncertain-but-bounded parameters

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Acta Mechanica Sinica 2013年第6期29卷 864-874页

作者： shu-Xiang Guo Ying li Faculty of Mechanics College of ScienceAir Force Engineering University

Uncertainty is inherent and unavoidable in almost all engineering systems. It is of essential significance to deal with uncertainties by means of reliability approach and to achieve a reasonable balance between reliability against uncertainties and system performance in the control design of uncertain systems. Nevertheless, reliability methods which can be used directly for analysis and synthesis of active control of structures in the presence of uncertainties remain to be developed, especially in non-probabilistic uncertainty situations. In the present paper, the issue of vibration con- trol of uncertain structures using linear quadratic regulator （LQR） approach is studied from the viewpoint of reliabil- ity. An efficient non-probabilistic robust reliability method for LQR-based static output feedback robust control of un- certain structures is presented by treating bounded uncertain parameters as interval variables. The optimal vibration con- troller design for uncertain structures is carried out by solv- ing a robust reliability-based optimization problem with the objective to minimize the quadratic performance index. The controller obtained may possess optimum performance un- der the condition that the controlled structure is robustly re- liable with respect to admissible uncertainties. The proposed method provides an essential basis for achieving a balance between robustness and performance in controller design ot uncertain structures. The presented formulations are in the framework of linear matrix inequality and can be carried out conveniently. Two numerical examples are provided to illustrate the effectiveness and feasibility of the present method.

关键词： Structural control Vibration control Robust control linear quadratic regulator (LQR) Robust reliabil- ity Structural reliability

Impacts of Climate Change on Agriculture and Adaptive Strategies in China

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Journal of Integrative Agriculture 2013年第8期12卷 1402-1408页

作者： li Rui-li shu Geng School of Environment and Energy Shenzhen Graduate SchoolPeking University Department of Plant Sciences University of California

China is the world＇s most populous country and a major emitter of greenhouse gases. Consequently, China＇s role in climate change has received a great deal of attention, whereas the impact of climate change on China has been largely ignored. Studies on the impacts of climate change on agriculture and adaptation strategies are increasingly becoming major areas of scientific concern. However, the clear warming that has been sounded in China in recent decades has not been matched with a clear assessment of the impact of climate change on China＇s water resources and agriculture. In the present study, we review observations on climate change, hydrology, and agriculture in China and relate these observations to likely future changes. We also analyse the adaptive strategies in China＇s agriculture.

关键词： agriculture China climate change hydrology temperature

Shoot Apex Demand Determines Assimilate and Nutrients Partitioning and Nutrient-uptake Rate in Tobacco Plants

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Journal of Integrative Plant Biology 2007年第11期49卷 1654-1661页

作者： Huai-Yu Yang Chun-Jian li Fu-suo Zhang The Key Laboratory of Plant Nutrition Ministry of Agriculture Key Laboratory of Plant-Soil Interactions Ministry of Education Department of Plant Nutrition China Agricultural University Beijing 100094 China

Our previous experiment revealed that apex-removed plants have larger root systems but a lower K＋-uptake rates than intact tobacco plants. Since the apex is not only a center of growth and metabolism, but also an important place of auxin synthesis and export, the aims of this study were to distinguish whether the apex demand or auxin synthesized in the apex regulates assimilate and nutrients partitioning within plant, and to explain the reason for the lower K＋-uptake rate of the apex-removed plant. In comparison with the control plant, covering the shoot apex with a black transparent plastic bag reduced net increases in dry matter and nutrients; however, the distribution of the dry matter and nutrients between shoot and roots and nutrient-uptake rates were not changed. Removal of the shoot apex shifted the dry mass and nutrients distributions to roots, and reduced the rate of nutrient uptake. Application of 1-naphthylacetic acid （NAA） could partly replace the role of the removed apex, stimulated assimilate and nutrient deposition into the treated tissue, and enhanced the reduced plasma membrane ATPase activity of roots to the control level. However, treatment of the apex-removed plants with NAA could not rescue the reduced nutrient uptake rate and the shifted assimilates and nutrients partitioning caused by excision of the apex. Higher nutrient uptake rate of the intact plants could not be explained by root growth parameters, such as total root surface area and number of root tips. The results from the present study indicate that strong apex demand determined assimilates and nutrients partitioning and nutrient-uptake rate in tobacco （Nicotiana tabacum） plants.

关键词： assimilate and nutrient partitioning auxin nutrient uptake removal of the shoot apex shoot apex demand tobacco (Nicotiana tabacum).

Binding Capacity for Aflatoxin B_1 by Different Adsorbents

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Agricultural Sciences in China 2010年第3期9卷 449-456页

作者： li Juan-juan suo De-cheng SU Xiao-ou Institute of Quality Standard and Testing Technology for Agro-Product Chinese Academy of Agricultural Sciences Beijing 100081 P.R.China

In this article, in vitro adsorption of aflatoxin B1 （AFB1） onto different adsorbents was characterized and the result was verified by comparing the growth performance and serum protein levels of broilers exposed to aflatoxin-contamination feed. Main components of adsorbents selected were yeast cell extracts （Product A）, HSCAS （Product B）, and a mixture of yeast product and HSCAS （Product C）, respectively. A total of 240 broilers were assigned to eight treatments, and the effects of three types of adsorbents on growth performance and serum protein levels were evaluated. Results indicated that Product B had the highest in vitro affinity for AFB1, followed by Product C and Product A. Product B bound 97.69% of the AFB1 in solution in 10 min, and it remained over 96.03% in 60 min at pH 8.0. The B-AFB1 complex was much stronger than the other two complexes in vitro condition （P 〈 0.05）. Feed intake （FI） and average daily gain （ADG） decreased （P 〈 0.05） and feed gain ratio increased （P 〈0.05） in the treatment fed aflatoxin-contaminated feed versus treatment on the basal feed. Serum total protein （TP）, albumin （ALB）, and globulin （GLOB） levels were significantly decreased （P〈0.05）. Product B （0.15%） increased growth performance and improved serum protein levels, Product A and Product C were not as effective as Product B. Three adsorbents tested here had sufficient potential to AFBt in some extents and Product B could bind AFB1 more effectively than Product A and Product C. These results indicated that Product B could alleviate some of the AFBt toxic effect in broilers.

关键词： adsorbent AFB 1 absorption efficacy

Projecting Spring Consecutive Rainfall Events in the Three Gorges Reservoir Based on Triple-Nested Dynamical Downscaling

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Advances in Atmospheric Sciences 2024年第8期41卷 1539-1558页

作者： Yanxin ZHENG shuanglin li Noel KEENLYSIDE Shengping HE lingling suo Department of Atmospheric Science CMA-CUG Joint Centre for Severe Weather and Climate and Hydro-geological HazardsChina University of GeosciencesWuhan 430074China Institute of Atmospheric Physics and Climate Change Research Center Chinese Academy of SciencesBeijing 100029China Three Gorges National Climatological Observatory Yichang 443099China Geophysical Institute University of Bergen and Bjerknes Centre for Climate ResearchBergen 5007Norway Nansen Environmental and Remote Sensing Center and Bjerknes Centre for Climate Research Bergen 5007Norway Nansen-Zhu International Research Centre Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China

Spring consecutive rainfall events(CREs) are key triggers of geological hazards in the Three Gorges Reservoir area(TGR), China. However, previous projections of CREs based on the direct outputs of global climate models(GCMs) are subject to considerable uncertainties, largely caused by their coarse resolution. This study applies a triple-nested WRF(Weather Research and Forecasting) model dynamical downscaling, driven by a GCM, MIROC6(Model for Interdisciplinary Research on Climate, version 6), to improve the historical simulation and reduce the uncertainties in the future projection of CREs in the TGR. Results indicate that WRF has better performances in reproducing the observed rainfall in terms of the daily probability distribution, monthly evolution and duration of rainfall events, demonstrating the ability of WRF in simulating CREs. Thus, the triple-nested WRF is applied to project the future changes of CREs under the middle-of-the-road and fossil-fueled development scenarios. It is indicated that light and moderate rainfall and the duration of continuous rainfall spells will decrease in the TGR, leading to a decrease in the frequency of CREs. Meanwhile, the duration, rainfall amount, and intensity of CREs is projected to regional increase in the central-west TGR. These results are inconsistent with the raw projection of MIROC6. Observational diagnosis implies that CREs are mainly contributed by the vertical moisture advection. Such a synoptic contribution is captured well by WRF, which is not the case in MIROC6,indicating larger uncertainties in the CREs projected by MIROC6.

关键词： triple-nested downscaling Three Gorges Reservoir area consecutive rainfall events geological hazards projection