检索结果-南通市图书馆

Numerical Simulation of the Rapid Intensification of Hurricane Katrina(2005):Sensitivity to Boundary Layer Parameterization Schemes

在线全文

学校读者我要写书评

暂无评论

Advances in Atmospheric Sciences 2017年第4期34卷 482-496页

作者： Jianjun liu Feimin ZHANG Zhaoxia pu Nanjing University of Information and Technology NanjingJiangsu 210044China Department of Atmospheric Sciences University of UtahSalt Lake CityUtah 84112USA College of Atmospheric Sciences Lanzhou UniversityLanzhouGansu 73000China Ningxia Meteorological Bureau YinchuanNingxia 750002China

Accurate forecasting of the intensity changes of hurricanes is an important yet challenging problem in numerical weather prediction. The rapid intensification of Hurricane Katrina（2005） before its landfall in the southern US is studied with the Advanced Research version of the WRF（Weather Research and Forecasting） model. The sensitivity of numerical simulations to two popular planetary boundary layer（PBL） schemes, the Mellor–Yamada–Janjic（MYJ） and the Yonsei University（YSU） schemes, is investigated. It is found that, compared with the YSU simulation, the simulation with the MYJ scheme produces better track and intensity evolution, better vortex structure, and more accurate landfall time and location. Large discrepancies（e.g.,over 10 hPa in simulated minimum sea level pressure） are found between the two simulations during the rapid intensification period. Further diagnosis indicates that stronger surface fluxes and vertical mixing in the PBL from the simulation with the MYJ scheme lead to enhanced air–sea interaction, which helps generate more realistic simulations of the rapid intensification process. Overall, the results from this study suggest that improved representation of surface fluxes and vertical mixing in the PBL is essential for accurate prediction of hurricane intensity changes.

关键词： hurricane PBL numerical simulation hurricane intensity change

Spatial patterns nitrogen transfer models of ectomycorrhizal networks in a Mongolian scotch pine plantation

在线全文

学校读者我要写书评

暂无评论

Journal of Forestry Research 2018年第2期29卷 337-344页

作者： Yanbin liu Hongmei Chen pu Mou College of Life Science Beijing Normal UniversityBeijing 100875People’s Republic of China Institute of Forestry Science Heilongjiang Academy of ForestryHarbin 150081People’s Republic of China Institute of Biology University of LeipzigJohannisallee 2104103 LeipzigGermany State Key Laboratory of Earth Surface Processes and Resource Ecology Beijing 100875People’s Republic of China

Ectomycorrhizal(EM)networks provide a variety of services to plants and ecosystems include nutrient uptake and transfer,seedling survival,internal cycling of nutrients,plant competition,and so *** deeply their structure and function in ecosystems,we investigated the spatial patterns and nitrogen(N)transfer of EM networks usingN labelling technique in a Mongolian scotch pine(Pinus sylvestris *** Litv.)plantation in Northeastern *** August 2011,four plots(20 × 20 m)were set up in the plantation.125 ml 5 at.%0.15 mol/LNHNOsolution was injected into soil at the center of each *** and 2,6,30 and 215 days after theN application,needles(current year)of each pine were sampled along four 12 m sampling *** total N andN concentrations were *** observed needle N andN concentrations increased significantly over time afterN application,up to 31 and0.42%,*** was no correlation between needle N concentration andN/N ratio(R2=0.40,n=5,P=0.156),while excess needle N concentration and excess needleN/N ratio were positively correlated across different time intervals(R~2=0.89,n=4,P\0.05),but deceased with time interval ***/N ratio increased with time,but it was not correlated with ***/N ratio was negative with distance before and 6th day and 30th day,positive with distance at 2nd day,but the trend was considerably weaker,their slop were close to *** results demonstrated that EM networks were ubiquitous and uniformly distributed in the Mongolian scotch pine plantation and a random *** found N transfer efficiency was very high,absorbed N by EM network was transferred as wide as possible,we observed N uptake of plant had strong bias forN andN,namely N *** the structure and function of EM networks in ecosystems may lead to a deeper understanding of ecological stability and evolution,and thus provide new theoretical approaches to improve conservation practices for the ma

关键词： Ectomycorrhizal networks Spatial patterns Nitrogen transfer Mongolian scotch pine plantation Stable isotope 15N labelling

Effects of fluid recirculation on mass transfer from the arterial surface to flowing blood

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2012年第3期28卷 904-910页

作者： Zhi-Guo Zhang xi-Wen Zhang Ying-xi liu Department of Engineering Mechanics Faculty of Vehicle Engineering and MechanicsState Key Laboratory of Structural Analysisfor Industrial EquipmentDalian University of Technology116024 DalianChina School of Aerospace Tsinghua University100084 BeijingChina

The effect of disturbed flow on the mass trans- fer from arterial surface to flowing blood was studied nu- merically, and the results were compared with that of our previous work. The arterial wall was assumed to be vis- coelastic and the blood was assumed to be incompressible and non-Newtonian fluid, which is more close to human arte- rial system. Numerical results indicated that the mass trans- fer from the arterial surface to flowing blood in regions of disturbed flow is positively related with the wall shear rates and it is significantly enhanced in regions of disturbed flow with a local minimum around the reattachment point which is higher than the average value of the downstream. There- fore, it may be implied that the accumulation of cholesterol or lipids within atheromatous plaques is not caused by the reduced efflux of cholesterol or lipids, but by the infiltration of the LDL （low-density lipoprotein） from the flowing blood to the arterial wall.

关键词： Disturbed flow Arterial wall Mass transfer Atherosclerosis Wall shear rates

Multi-objective optimization of equipment capacity and heating network design for a centralized solar district heating system

在线全文

学校读者我要写书评

暂无评论

Building Simulation 2023年第1期16卷 51-67页

作者： Yanfeng liu Ting Mu xi Luo School of Building Services Science and Engineering Xi'an University of Architecture and TechnologyXi'an 710055China State Key Laboratory of Green Building in Western China Xi'an 710055China

Northwest China has abundant solar energy resources and a large demand for winter *** solar energy for centralized heating is a clean and effective way to solve local heating *** present studies usually decoupled solar heating stations and the heating network in the optimization design of centralized solar heating systems,this study developed a joint multi-objective optimization model for the equipment capacity and the diameters of the heating network pipes of a centralized solar district heating system,using minimum total life cycle cost and CO_(2)emission of the system as the optimization *** typical cities in northwest China with different solar resource conditions(Lhasa,xining,and xi'an)were selected as cases for *** to the results,the solar heating system designed using the method proposed in this study presents lower economic cost and higher environmental protection in comparison to separately optimizing the design of the solar heating station and the heating ***,the solar fraction of the optimal systems are 90%,70%,and 31%for Lhasa,xining,and xi'an,and the minimum water supply temperatures are 55℃,50℃,and 65℃for an optimal economy and 55℃,45℃,and 45℃for optimal environmental protection,*** was also established that the solar collector price has a greater impact on the equipment capacity of the solar heating station than the gas boiler price.

关键词： solar energy solar energy system district heating optimization design genetic algorithm

μ-Synthesis control with reference model for aeropropulsion system test facility under dynamic coupling and uncertainty

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2023年第10期36卷 246-261页

作者： Jiashuai liu xi WANG xi liu Meiyin ZHU xitong PEI Song ZHANG Zhihong DAN School of Energy and Power Engineering Beihang UniversityBeijing 100191China Zhongfa Aviation Institute Beihang UniversityHangzhou 311115China Research Institute of Aero-Engine Beihang UniversityBeijing 100191China Science and Technology on Altitude Simulation Laboratory AECC(Aero Engine Corporation of China)Sichuan Gas Turbine EstablishmentMianyang 621703China

Due to the dynamic coupling and multi-source uncertainties,it is difficult to accurately control the pressure and temperature of the Aeropropulsion System Test Facility(ASTF)in the presence of rapid command and large *** paper presents the design ofμ-synthesis control to solve the *** incorporating the pressure ratio into the linear equation of the control valve,the modeling error of ASTF in the low frequency range is effectively ***,an uncertain model is established by considering various factors,including parameter variations,modeling error in the low frequency range,unmodeled dynamics,and changes in the working *** address the dynamic coupling,a diagonal reference model with desired performance is incorporated intoμ-***,all weighting functions are designed according to the performance ***,theμ-controller is obtained by using the standardμ-synthesis *** results indicate that theμ-controller decouples the pressure and temperature dynamics of *** with the multivariable PI controller,integral-μcontroller,and double integral-μcontroller,the proposedμ-controller can achieve higher transient accuracy and better disturbance ***,the robustness of theμ-controller is demonstrated by Monte Carlo simulations.

关键词： Aeropropulsion System Test Facility(ASTF) Decoupling Robustness μ-Synthesis Uncertainty

Anomalous Hall effect,magneto-optical properties,and nonlinear optical properties of twisted graphene systems

在线全文

学校读者我要写书评

暂无评论

npj Computational Materials 2020年第1期6卷 1172-1181页

作者： Jianpeng liu xi Dai Department of Physics Hong Kong University of Science and TechnologyKowloonHong KongChina

We study the anomalous Hall effect,magneto-optical properties,and nonlinear optical properties of twisted bilayer graphene aligned with hexagonal boron nitride substrate,as well as twisted double bilayer graphene *** show that non-vanishing valley polarizations in twisted graphene systems would give rise to the anomalous Hall effect,which can be tuned by in-plane magnetic *** valley polarized states are also associated with giant Faraday and Kerr rotations in the terahertz frequency ***,we propose that the twisted graphene systems exhibit colossal nonlinear optical responses by virtue of the inversion-symmetry breaking,the small bandwidth,and the small excitation gaps of the *** twisted double bilayer graphene,we find that certain components of the nonlinear photo-conductivity tensor are directly proportional to the orbital magnetization of the system,which would exhibit remarkable hysteresis behavior in response to perpendicular magnetic fields.

关键词： twisted nonlinear hexagonal

Organocopper(Ⅲ)Compounds with Well-defined Structures Undergo Reductive Elimination to Form C-C or C-Heteroatom Bonds

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Journal of Chemistry 2018年第12期36卷 1213-1221页

作者： Liang liu Zhenfeng xi Beijing National Laboratory for Molecular Sciences (BNLMS) Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education/College of ChemistryPeking UniversityBeijing 100871China

Reductive elimination around Cu(III) atom arises an increasing attention, since this organometallic pathway has been often proposed in a range of Cu‐based reactions. However, due to limited organocopper(III) compounds with well‐defined structures, this elementary reaction still remains an extremely challenging issue. In this review, structurally well‐defined organocopper(III) compounds are mainly divided into three classes based on their ligands: perfluoromethyl Cu(III) compounds, macrocyclic ligand‐based aryl‐Cu(III) compounds, and spiro organocopper(III) compounds chelated by bidentate ligands. The majority of organocopper(III) compounds display the typical square planar geometry. There also exist a few penta‐coordinated organocopper(III) complexes, which share a weak apical Cu‐L bond. In order to form a cis Cu(III)-C and Cu(III)-Nu bonding geometry required for reductive elimination, the re‐arrangement of coordination modes around tetra‐coordinated Cu(III) atoms is necessary. For the aryl‐Cu(III) cationic complexes with one Cu(III)-C bond, the re‐arrangement is triggered by the coordination of the fifth ligand (solvent or nucleophiles), while for the tetra‐carbon‐coordinated organocuprate(III) compounds, the process might be realized via the cleavage of one Cu(III)-C bond by attack of electrophiles. Stoichiometric and catalytic reactions involving well‐defined organocopper(III) compounds to form C—C or C-heteroatom bonds are discussed to support their intermediacy.

关键词： structure elucidation copper reactive intermediate organocopper(III) organocuprate(III) reductive elimination

ELASTIC-PLASTIC DYNAMIC RESPONSE OF A CANTILEVER BEAM SUBJECTED TO OBLIQUE IMPACT AT ITS TIP

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Mechanica Solida Sinica 2005年第4期18卷 316-325页

作者： xi Feng liu Feng Shandong Institute of Architecture and Engineering Jinan 250101 China

By employing large deformation governing equations expressed in the form of finite difference, the dynamic responses of an elastic, perfectly plastic cantilever subjected to an oblique impact at its tip was numerically studied. Through analyzing the instantaneous distribution of the yield function （φ = ｜M/Mo｜＋（N/No）^2）, bending moment and axial force during the early stage of the response, the elastic-plastic deformation mechanism and the influence of axial component of an oblique impact on the dynamic response of a cantilever beam were discussed. The present analysis shows that the deformation mechanism of an elastic-plastic cantilever subjected to an oblique impact consists of four phases, i.e. ‘the expanding compressed plastic region＇ mode; the ‘generalized traveling plastic hinge＇ and ‘shrinking plastic region＇ mixed mode; the ‘stationary plastic hinge＇ mode and ‘elastic vibration＇ mode. Compared with the two-phase deformation mode obtained by using the rigid, perfectly plastic approach, the mode of shrinking plastic region that occurred instantly after the oblique impact and the mode of stationary hinge were both confirmed. The primary features of the deformation mechanism are captured by both analysis methods. It has also been found that the beam＇s deformation is mainly controlled by the axial component of the oblique impact in the early phase of the dynamic response, the deformation mechanism is obviously different from the case of a transverse impact. With further development of the response, the axial component attenuates rapidly and gives negligible contribution to the yielding of the beam cross-section. At the same time, the bending moments along the cantilever develop gradually and dominate the beam＇s deformation. The numerical results indicate that the mass, impact speed and oblique angle are the important factors that influence the elastic-plastic dynamic response of a cantilever beam.

关键词： oblique impact elastoplasticity large deformation dynamic response cantilever

A Brief Overview of the Development and Significance of Modern Scientific Medicine in China:Take Chinese Academy of Medical Science and Peking Union Medical College as an Example

在线全文

学校读者我要写书评

暂无评论

Chinese Medical Sciences Journal 2024年第2期39卷 140-143页

作者： pu-An Cui Zhe-xi Gong Zhong He School of Humanities and Social Sciences Chinese Academy of Medical Science&Peking Union Medical CollegeBeijing 100730China

Since the early 20th century,China has gradually established a clinical,educational,and research system centered around modern scientific medicine,which has now become the dominant force in China's medical and health system and services,with the construction and development of the Chinese Academy of Medical Sciences and Peking Union Medical College as the most prominent *** scientific medicine in the new era requires close cooperation across multiple disciplines and fields to build a high-quality and efficient medical and health service *** also involves combining the excellent traditional Chinese culture with Western medicine to explore a unique path of modern scientific medicine with Chinese characteristics.

关键词： modern scientific medicine cultural confidence multiple view