检索结果-南通市图书馆

Triangle-free Graphs with Three Positive Eigenvalues

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Algebra Colloquium 2024年第3期31卷 525-540页

作者： Fang duan School of Mathematical Sciences Xinjiang Normal UniversityUrumqi 830017China

A graph G is called triangle-free if G does not contain any triangle as its induced *** G_(n)be the set of triangle-free graphs of order n each of which has three positive *** this paper,we find 20 specific graphs in G_(n),each of which has nullity.no more than 2,and we show that in terms of three graph transformations all the other graphs of G_(n)can be constructed from these 20 specific ***,we completely characterize the triangle-free graphs with exactly three positive eigenvalues.

关键词： positive(negative)inertia index nullity triangle-free graph

Measuring Financial Systemic Risk:net Liability Clearing Mechanism and Contagion Effect

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Systems Science & Complexity 2024年第3期37卷 1114-1146页

作者： MA Jiali ZHU Shushang LI duan College of Big Data Statistics Guizhou University of Finance and EconomicsGuiyang 550025China School of Business Sun Yat-Sen UniversityGuangzhou 510275China School of Data Science City University of Hong KongHong Kong 999077China

Following the framework of E-n model(Eisenberg and noe,2001),the authors consider a new clearing mechanism based on net liabilities among financial institutions since the liabilities between the counterparties should be deducted accordingly when clearing in *** the basis for systemic risk measurement,similar to the original E-n model,the authors first establish some good properties for the clearing payment vector according to a more general ***,the authors investigate how risk spreads among institutions through the liability.network forming the risk contagion ***,the authors illustrate with a specific example that the original E-n clearing mechanism may misidentify the systemic important institutions,and theoretically show that it may also overestimate the risk compared with the netting clearing mechanism.

关键词： Clearing mechanism contagion net liability.network systemic risk

Accurate Distinction of Weak and Strong AC Grids for Emerging Hierarchical-Infeed LCC-UHVDC Systems

在线全文

学校读者我要写书评

暂无评论

CSEE Journal of Power and Energy Systems 2024年第2期10卷 772-777页

作者： Hao Xiao Xianzhong duan yi Zhang Department of Electrical and Computer Engineering University of ManitobaWinnipeg R3T 2N2ManitobaCanada State Key Laboratory of Advanced Electromagnetic Engineering and Technology Hubei Electric Power Security and High Efficiency Key LaboratorySchool of Electrical and Electronic EngineeringHuazhong University of Science and TechnologyWuhan 430074HubeiChina RTDS Technologies Inc. Winnipeg R3T 2E1ManitobaCanada

Distinction of weak and strong AC grids for emerging hierarchical-infeed LCC-UHVDC systems is important for planning and operation departments. However, accuracy of earlier distinction methods is limited as they were developed by empirical reasoning without rigorous theoretical analysis. Hence in this letter, hierarchical-infeed interactive effective short-circuit ratio (HIESCR) index is first used for strength evaluation of HIDC systems with complex inter-inverter interactions considered. Boundary HIESCR (BHIESCR) is also introduced in the proposed distinction method of weak and strong AC grids. That is, weak (or strong) AC grids are, respectively, identified when HIESCR is less (or greater) than BHIESCR. Second, it is shown BHIESCR remains almost unchanged as 3.0 versus various system parameters and rated operation variables based on rigorous theoretical analysis. This salient feature makes the proposed method more accurate than earlier methods. Finally, the proposed method is validated by simulations based on the PSCAD/EMTDC program.

关键词： Hierarchical-Infeedinteractive effective short-circuit ratio hierarchical-infeed LCC-UHVDC systems inter-inverter interactions strong AC grids weak AC grids

High-throughput screening of single-atom catalysts confined in monolayer black phosphorus for efficient nitrogen reduction reaction

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

nano Research 2024年第4期17卷 2360-2367页

作者： Xiao-y.n Li Manyi duan Pengfei Ou Department of Electrical and Computer Engineering University of TorontoTorontoOntario M5S 1A4Canada School of Physics and Electronic Engineering Sichuan Normal UniversityChengdu 610101China Department of Chemistry Northwestern UniversityEvanstonIL 60208USA

The discovery of metal-nitrogen centers as the active sites for electrolysis has aroused significant interest in utilizing single-atom catalysts for nitrogen reduction reaction(nRR).Properly designed nanostructured catalysts that strongly interact with nitrogen molecules(n_(2))can promote adsorption and activation,thereby resulting in efficient catalysts with high stability,activity,and *** this study,using density functional theory calculations,we selected monolayer black phosphorus(BP)as the substrate and screened a series of single-atom transition metals confined in tri-coordinated and tetra-coordinated active centers(without and with n dopants)to electro-catalyze *** a result,we have identified two promising candidates(Hf_(1)-n_(1)P_(2)-1 and Tc_(1)-n_(4)),which exhibit not only low overpotentials of 0.56 and 0.49 V but also high thermodynamic and electrochemical stability,as well as good selectivity towards nRR over the competing hydrogen evolution *** also demonstrate the ability of Hf_(1)-n_(1)P_(2)-1 and Tc_(1)-n_(4) to activate and hydrogenate n_(2) by donating electrons and regulating charge *** study.not only predicts new BP-based promising catalysts but also provides guidance for the rational design of high-performance nRR electrocatalysts under ambient conditions.

关键词： n_(2) electroreduction reaction single-atom catalysts black phosphorus density functional theory high-throughput calculations

Efficient Direct Decomposition of nO over La_(0.8)A_(0.2)niO_(3)(A=K, Ba, y) Catalysts under Microwave Irradiation

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Wuhan University of Technology(Materials Science) 2024年第1期39卷 17-23页

作者：王浩 ZHAO Zijian duan Xinghui ZHOU Shijia School of Materials Science and Engineering Wuhan University of TechnologyWuhan 430070China

La_(0.8)A_(0.2)niO_(3) (A=K,Ba,y) catalysts supported on the microwave-absorbing ceramic heating carrier were prepared by the sol-gel *** crystalline phase and the catalytic activity of the La_(0.8)A_(0.2)niO_(3)catalysts were characterized by XRD and H_(2) temperature-programmed reduction (TPR).The effects of reaction temperature,oxygen concentration,and gas flow rate on the direct decomposition of nitric oxide over the synthesized catalysts were studied under microwave irradiation (2.45 GHz).The XRD results indicated that the La_(0.8)A_(0.2)niO_(3) catalysts formed an ABO_(3) perovskite structure,and the H_(2)-TPR results revealed that the relative reducibility of the catalysts increased in the order of La_(0.8)K_(0.2)niO_(3)>La_(0.8)Ba_(0.2)niO_(3)>La_(0.8)y_(0.2)ni O_(3).Under microwave irradiation,the highest nO conversion amounted to 98.9%,which was obtained with the La_(0.8)K_(0.2)niO_(3) catalyst at 400℃.The oxygen concentration did not inhibit the nO decomposition on the La_(0.8)A_(0.2)niO_(3) catalysts,thus the n_(2) selectivity exceeded 99.8%under excess oxygen at 550℃.The nOconversion of the La_(0.8)A_(0.2)niO_(3) catalysts decreased linearly with the increase in the gas flow rate.

关键词： microwave catalysis direct decomposition of nO microwave-absorbing heating ceramics perovskite catalyst

P-symmetric Subharmonic Solutions for nonlinear Hamiltonian Systems

在线全文

学校读者我要写书评

暂无评论

Acta Mathematica Sinica,English Series 2024年第6期40卷 1388-1408页

作者： duan Zhi ZHAnG Zhi Hao ZHAO School of Mathematical Sciences Nankai UniversityTianjin 300071P.R.China

In this paper,we prove that for each positive k≡1 mod m there exists a P-symmetric kmτ-periodic solution xk for asymptotically linear mτ-periodic Hamiltonian systems,which are nonautonomous and endowed with a *** the P-symmetric Hamiltonian function is semi-positive,one can prove,under a new iteration inequality of the Maslov-type P-index,that xk_(1) and xk_(2) are geometrically distinct for k_(1)/k_(2)≥(2n+1)m+1;and xk_(1),xk_(2) are geometrically distinct for k_(1)/k_(2)≥m+1 provided xk_(1) is non-degenerate.

关键词： P-symmetric subharmonic Hamiltonian systems Maslov-type index theory iteration inequality asymptotically linear

Two-Dimensional Graphitic Carbon-nitride(g-C_(3)n_(4))-Coated Lini_(0.8)Co_(0.1)Mn_(0.1)O_(2)Cathodes for High-Energy-Density and Long-Life Lithium Batteries

在线全文

学校读者我要写书评

暂无评论

Energy & Environmental Materials 2024年第6期7卷 140-149页

作者： Zhenliang duan Pengbo Zhai ning Zhao Xiangxin Guo College of Physics Qingdao UniversityQingdao 266071China College of Materials Science and Engineering Qingdao UniversityQingdao 266071China Tianmushan Laboratory Xixi Octagon CityHangzhou 310023China

High-capacity.nickel-rich layered oxides are promising cathode materials for high-energy-density lithium ***,the poor structural stability and severe side reactions at the electrode/electrolyte interface result in unsatisfactory cycle ***,the thin layer of two-dimensional(2D)graphitic carbon-nitride(g-C_(3)n_(4))is uniformly coated on the Lini_(0.8)Co_(0.1)Mn_(0.1)O_(2)(denoted as nCM811@Cn)using a facile chemical vaporization-assisted synthesis *** an ideal protective layer,the g-C_(3)n_(4)layer effectively avoids direct contact between the nCM811 cathode and the electrolyte,preventing harmful side reactions and inhibiting secondary crystal ***,the unique nanopore structure and abundant nitrogen vacancy edges in g-C_(3)n_(4)facilitate the adsorption and diffusion of lithium ions,which enhances the lithium deintercalation/intercalation kinetics of the nCM811 *** a result,the nCM811@Cn-3wt%cathode exhibits 161.3 mAh g^(−1)and capacity retention of 84.6%at 0.5 C and 55°C after 400 cycles and 95.7 mAh g^(−1)at 10 C,which is greatly superior to the uncoated nCM811(i.e.129.3 mAh g^(−1)and capacity retention of 67.4%at 0.5 C and 55°C after 220 cycles and 28.8 mAh g^(−1)at 10 C).The improved cycle performance of the nCM811@Cn-3wt%cathode is also applicable to solid–liquid-hybrid cells composed of PVDF:LLZTO electrolyte membranes,which show 163.8 mAh g^(−1)and the capacity retention of 88.1%at 0.1 C and 30°C after 200 cycles and 95.3 mAh g^(−1)at 1 C.

关键词： cathode materials g-C_(3)n_(4)coating Lini_(0.8)Co_(0.1)Mn_(0.1)O_(2) lithium batteries PVDF:LLZTO electrolyte membranes

Recent advances in the synthesis and application of n-heterocyclic carbene-based molecular cages

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Science China Chemistry 2024年第5期67卷 1510-1523页

作者： Qiongjie Chai Lixin duan y.nzhe Ma Tianheng Hou Tao Tu Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials Department of ChemistryFudan UniversityShanghai 200438China State Key Laboratory of Organometallic Chemistry Shanghai Institute of Organic ChemistryChinese Academy of SciencesShanghai 200032China

n-Heterocyclic carbene(nHC)-based cages have emerged as a prominent and dynamic research area within the research field of chemistry. Leveraging the distinctive electronic and steric properties of nHC ligands, the design, synthesis, and application of these corresponding cages have garnered substantial scholarly interest. In recent years, we have witnessed the successful fabrication of diverse nHC-based cages through a range of synthetic methodologies, which hold significant potential for applications in molecular recognition and catalysis. In this review, we delve into the foundational synthetic strategies that underlie the creation of nHC-based cages, employ.ng approaches encompassing metal–nHC chelation, coordination assembly,and covalent bonding. Additionally, we compile the diverse applications of these cages within catalytic processes and molecular recognition. Lastly, we shed light on the current limitations of synthesis and outline future trends in the development of nHCbased cages.

关键词： n-heterocyclic carbene molecular cages supramolecular chemistry synthetic strategies applications

Crystalline-amorphous M@Mn_x(M=Co,Fe,ni)encapsulated in nitrogen-doped carbon for enhanced efficient and durable hydrogen evolution reaction

在线全文

学校读者我要写书评

暂无评论

Rare Metals 2024年第4期43卷 1547-1556页

作者： y.ng y.ng Xiao-Chuan duan Shao-Hui Guo Xian-Ming Zhang College of Materials Science and Engineering College of ChemistryKey Laboratory of Interface Science and Engineering in Advanced MaterialsTaiyuan University of TechnologyYuci030600China

Developing earth-abundant electrocatalysts for hydrogen evolution reaction(HER)is important for the sustainable energy ***,efficient and stable heterocatalysts consisting of crystalline-amorphous M@Mn_(x)(M=Co,Fe,ni)encapsulated in n-doped carbon layers supported with n-doped graphene sheets(denoted as M@Mn_(x)@nC-nG)are synthesized by facile hydrothermal reaction and nitridation *** the nitriding process,metal ions in M(tzbc)_2(H_(2)O)_4(tzbc=4-(1H-1,2,4-triazol-1-yl)benzoic acid)complexes are reduced to crystalline M cores,accompanied by the formation of amorphous Mn_(x)shells;the tzbc ligands are insitu carbonized to form outermost n-doped carbon(nC)layers that connect with inner Mn_(x)via M-n-C motifs inherited from the complex precursors and inhibit the transition of Mn_(x)from amorphous to crystalline *** Co@Con_(x)@nC-nG catalyst exhibits excellent HER activity with small overpotentials of 45 and 64 mV at a cathode current density of 10 mA·cm^(-2)and low Tafel slopes of 40 and 85 mV·dec^(-1)in 0.5 mol·L^(-1)H_(2)SO_4 and1.0 mol·L^(-1)KOH electrolytes,*** Co@Con_(x)@nC-nG retains 97%of the initial overpotential after 100,000 s in both acidic and alkaline *** outstanding HER performance originates from the crystalline-amorphous Co@Con_(x)that redistributes electrons around the heterointerfaces,facilitating the conversion process of H^(+)/H_(2)O to hydrogen and thereby promoting HER *** outermost nC layers serve as the armor of Co@Con_(x),and graphene nanosheets act as carriers of egg-like Co@Con_(x)@nC and conduction paths for electron shuttles,ensuring stable and continuous electrocatalytic hydrogen production.

关键词： Hydrogen evolution reaction Electrocatalysts Iron group metals Heterojunction Crystalline-amorphous structure