检索结果-南通市图书馆

Impact of the COVID-19 pandemic on agricultural exports

在线全文

学校读者我要写书评

暂无评论

Journal of Integrative Agriculture 2020年第12期19卷 2937-2945页

作者： LIN Ben-xi Yu Yvette zhang School of Economics Fujian Agriculture and Forestry UniversityFuzhou 350002P.R.China Department of Agricultural Economics Texas A&M UniversityCollege StationTX 77843USA

The COVID-19 outbreak has shocked the world’s economies in the year of *** this pandemic spreads around the globe,many experts feared that the global food supplies might start running short,especially if supply chains were ***-19 also added to the uncertainty of the business ***,it is critical to understand how COVID-19 pandemic affected global food supply and *** this study,we investigate the impact of COVID-19 on agricultural export companies in China using a unique firm-level survey *** found that although on average agricultural businesses experienced declines in the exports,exports of some agricultural products especially grain and oil held strong and even increased,implying the essential demand for staple food during the *** surprisingly,exports of medicinal herb also increased significantly during the ***,exports of goods such as edible fungus and horticultural products sharply *** results also showed that in general,impact of COVID-19 on smaller firms was more severe than that on larger *** results of this study can provide useful guidance and implications for agricultural businesses and policy makers on their COVID-19 mitigation efforts to navigate this global pandemic.

关键词： COVID-19 pandemic agricultural exports business survey international trade China

A note on the generalization of the Kodaira embedding theorem

在线全文

学校读者我要写书评

暂无评论

Science China Mathematics 2021年第7期64卷 1563-1572页

作者： Chao Li xi zhang Qizhi Zhao School of Mathematical Sciences University of Science and Technology of ChinaHefei 230026China

In this paper,we generalize the famous Kodaira embedding theorem.

关键词： Kodaira embedding theorem holomorphic fibration ampleness

Dynamical analysis for hybrid virus infection system in switching environment

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2020年第9期29卷 186-193页

作者： Dong-xi Li Ni zhang College of Data Science Taiyuan University of TechnologyTaiyuan 030024China College of Mathematics Taiyuan University of TechnologyTaiyuan 030024China

We investigate the dynamical behavior of hybrid virus infection systems with nonlytic immune response in switching environment, which is modeled as a stochastic process of telegraph noise and represented as a multi-state Markov chains. Firstly, The existence of unique positive solution and boundedness of the new hybrid system is proved. Furthermore, the sufficient conditions for extinction and persistence of virus are established. Finally, stochastic simulations are performed to test and demonstrate the conclusions. As a consequence, our work suggests that stochastic switching environment plays a crucial role in the process of virus prevention and treatment.

关键词： dynamical behavior hybrid virus infection system switching environment extinction

Resilience Enhancement of Urban Energy Systems via Coordinated Vehicle-to-grid Control Strategies

在线全文

学校读者我要写书评

暂无评论

CSEE Journal of Power and Energy Systems 2023年第2期9卷 433-443页

作者： Lascelle Mauricette Zihang Dong Linan zhang xi zhang Ning zhang Goran Strbac Department of Electrical and Electronic Engineering Imperial College LondonLondon SW72AZUnited Kingdom Department of Grid Digitalization Technology State Grid Smart Grid Research Institute Co.LtdBeijing 102209China State Key Lab of Power Systems Department of Electrical EngineeringTsinghua UniversityBeijing 100084China

Coordinated vehicle-to-grid(V2G)control strategies can sustain essential loads of an energy system during islanding,thereby increasing *** this context,this paper investigates the resilience enhancement benefits of smart V2G control,the value of electric vehicle(EV)owner cooperation on system resilience,as well as the complementary effects of PV and EV interaction in an urban multi-energy microgrid(MEMG).By using a rolling horizon approach to optimize day-ahead operation of the MEMG and subsequently dispatching EVs,uncertainties in outage start time,EV arrival/departure times,and initial state of charge(SOC)are *** show that smart V2G control can provide a substantial essential load curtailment reduction compared to a non-EV scenario,meanwhile,non-coordinated grid-to-vehicle(G2V)operation was shown to slightly burden the system with a slight increase in non-essential load *** into the influence of EV cooperation on resilience showed that a high percentage of system-prioritized(SP)EVs could help greatly further reduce essential load curtailment compared to individual-prioritized(IP)***,the complementary benefits of smart V2G control and PV were demonstrated,showing a reduction in both PV and essential load curtailments with increasing numbers of ***,the application of smart V2G control,especially with cooperation of EV owners,can drive significant resilience enhancement during islanding,while further benefits can be obtained through having a sufficient number of EVs to utilize high PV penetration.

关键词： Multi-energy system renewable energy sources resilience rolling horizon optimization vehicle-to-grid

RATE OF INTRA-MOLECULAR CONTACT FORMATION IN SHORT TWO-DIMENSIONAL COMPACT POLYMERS CHAINS

维普期刊数据库评论

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 Polymer Science 2006年第1期24卷 13-19页

作者： Jin Chen Lin-xi zhang A-gen xia Department of Physics Zhejiang University Hangzhou 310027 China Department of Physics Wenzhou Normal College Wenzhou 325027 China

It is important to know the rate of intra-molecular contact formation in proteins in order to understand how proteins fold clearly. Here we investigate the rate of intra-molecular contact formation in short two-dimensional compact polymer chains by calculating the probability distribution p（r） of end-to-end distance r using the enumeration calculation method and HP model on two-dimensional square lattice. The probability distribution of end-to-end distance p（r） of short two-dimensional compact polymers chains may consist of two parts, i.e. p（r） = p1（r）＋ p2（r）, where p1（r） and p2（r） are different for small r. The rate of contact formation decreases monotonically with the number of bonds N, and the rate approximately conforms to the scaling relation of k（N）∝ N^-α. Here the value of α increases with the contact radius a and it also depends on the percentage of H （hydrophobic） residues in the sequences of compact chains and the energy parameters of ^εНН、 ^εНН and ^εpp. Some comparisons of theoretical predictions with experimental results are also made. This investigation may help us to understand the protein folding.

关键词： Two-dimensional compact polymer HP model Rate of contact formation.

A Novel Design of Efficient Multi-channel UART Controller Based on FPGA

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2007年第1期20卷 66-74页

作者： HU Zhe zhang Jun LUO xi-ling Department of Electronic Information Engineering BeO＇ing University of Aeronautics and Astronautics Beijing 100083 China

In traditional universal asynchronous receiver transmitter （UART） controller, the data transmission is inefficient and the data bus utilization ratio is low. A novel design is provided to solve these problems. The architecture of the system is introduced, the flow charts of data processing as well as the implementation state machine are also presented in detail. This paper is concluded by comparing the performance of this design, which is realized on field programmable gate army （FPGA） using Verilog hardware description language （HDL）, with other traditional UART controllers.

关键词： serial communication UART multi-channel FPGA

Properties of (Fe-B)-doped Sn-1.0Ag-0.5Cu solders prepared by mechanical alloying

在线全文

学校读者我要写书评

暂无评论

Rare Metals 2019年第7期38卷 665-674页

作者： ruo-Da Wang Qiang Hu Shao-Ming zhang Fu-Wen zhang Cai-Tao Lu Zhi-Gang Wang General Research Institute for Nonferrous Metals Beijing 100088 China Beijing COMPO Advanced Technology Co. Ltd. Beijing 101407 China

To introduce boron (B) into the Sn-1.0Ag-0.5Cu (SAC 105) solder, based on the thermodynamic calculations, iron (Fe) is a competent carrier component for bonding B and Sn. The Sn-Fe-B master alloys were prepared by mechanical alloying initially;then, the SAC 105- 0.05(Fe-B) and SAC 105-0.1 (Fe-B) solder alloys were prepared using 72-h-milling Sn-Fe-B master alloys. The preparation process and the properties of solders were studied in this work. For the Sn-Fe-B master alloys, the results show that with the increase in the ball-milling time, the powder changes illustrate a cold welding-crushingcold welding cyclic process. Moreover, the supersaturated solid solubility of (Fe-B) increases gradually in the alloys, matrix and the lattice distortion increases to 0.167% after 72-h milling. Meanwhile, the alloying degree is increasingly apparent, and after 72-h milling, the content of B in the Sn matrix reaches 2.38 wt%. For the solder alloys, with the (Fe-B) content in creasing, the melting point decreases and a significant grain refinement occurs in the matrix. Compared to the benchmark SAC105, the hardness of SAC105-0.05(Fe-B) and SAC 105-0.1 (Fe-B) solder alloys prepared by this method is improved by 20.65% and 34.79%, respectively. The present research provides a novel approach for introducing the immiscible component into the lead-free solder alloys.

关键词： Sn-1.0Ag-0.5Cu Sn-Fe-B Mechanical alloying Supersaturated solid solution

Modified adaptive controller for synchronization of incommensurate fractional-order chaotic systems

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2012年第3期21卷 126-130页

作者： zhang ruo-Xun (张若洵) College of Elementary Education, xingtai University, xingtai 054001, China College of Physics Science and Information Engineering Hebei Normal University Shijiazhuang 050016 China College of Elementary Education Xingtai University Xingtai 054001 China

We investigate the synchronization of a class of incommensurate fractional-order chaotic systems, and propose a modified adaptive controller for fractional-order chaos synchronization based on the Lyapunov stability theory, the fractional order differential inequality, and the adaptive strategy. This synchronization approach is simple, universal, and theoretically rigorous. It enables the synchronization of O fractional-order chaotic systems to be achieved in a systematic way. The simulation results for the fractional-order Qi chaotic system and the four-wing hyperchaotic system are provided to illustrate the effectiveness of the proposed scheme.

关键词： synchronization modified adaptive controller incommensurate fractional-order chaotic system

Mine laneway 3D reconstruction based on photogrammetry

在线全文

学校读者我要写书评

暂无评论

中国有色金属学会会刊：英文版 2011年第S3期21卷 686-691页

作者： zhang Chun-sen College of Geomatics, xi’an University of Science and Technology, xi’an 710054, China College of Geomatics Xi'an University of Science and Technology Xi'an 710054 China

Aiming at the problem of 3D reconstruction for mine laneway, the technique route and step were given based on digital close range photogrammetry and traverse surveying. 3D coordinates of laneway traverse point, photogrammetric station, control strip points were obtained by electronic total station based on mine coordinate system. The feature points were extracted from the scene images. The camera was calibrated by direct linear transformation (DLT). 3D relative coordinates of the arbitrary feature points in mine laneway were calculated after feature points being matched, in which the origin of coordinate system is photogrammetric station. The 3D absolute coordinates of the feature points in mine laneway can be obtained by the combined adjustment of photogrammetry and non-photogrammetric observations and coordinate conversion. The measurable 3D model of the underground laneway terrain surface was constructed with the 3D coordinates of feature points on the image pairs obtained. The measurable 3D model of a corridor was reconstructed by the mentioned method and the experiment precision with an average standard deviation of 0.013 6 m between the 3D model and practical measure was obtained by electronic total station. The experimental resulted show the validity of the proposed approach.

关键词： digital mine mine laneway photogrammetry 3D reconstruction direct linear transformation (DLT)