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Triangle-free Graphs with Three Positive Eigenvalues

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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

Fe-n-C core-shell catalysts with single low-spin Fe(Ⅱ)-n_(4)species for oxygen reduction reaction and high-perform.n.e proton exchange membrane fuel cells

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Journal of Energy Chemistry 2024年第6期93卷 538-546,I0013页

作者： Yan Wan Linhui Yu Bingxin Yang Caihong Li Chen fang Wei Guo fang-Xing Xiao Yangm.n. Lin Xiam.n.Key Laboratory of Rare Earth Photoelectric Functional materials Xiamen Institute of Rare Earth MaterialsHaixi InstituteChinese Academy of SciencesXiamen 361021FujianChina CAS Key Laboratory of Urban Pollutant Conversion Institute of Urban EnvironmentChinese Academy of SciencesXiamen 361021FujianChina Fujian Institute of Research on the Structure of matter Chinese Academy of SciencesFuzhou 350002FujianChina College of materials Science and Engineering Fuzhou UniversityNew CampusMinhou 350108FujianChina College of Chemistry and materials Science Fujian Normal UniversityFuzhou 350117FujianChina

Fe-n-doped carbon materials(Fe-n-C)are promising candidates for oxygen reduction reaction(ORR)relative to Pt-based catalysts in proton exchange membrane fuel cells(PEmFCs).However,the intrinsic contributions of Fe-n_(4)moiety with different chemical/spin states(e.g.D1,D2,D3)to ORR are unclear since various states coexist *** the present work,Fe-n-C core-shell nanocatalyst with single lowspin Fe(Ⅱ)-n_(4)species(D1)is synthesized and identified with ex-situ ultralow temperature mossbauer spectroscopy(T=1.6 K)that could essentially differentiate various Fe-n_(4)states and invisible Fe-O *** quantifying with CO-pulse chemisorption,site density and turnover frequency of Fe-n-C catalysts reach 2.4×10^(-9)site g^(-1)and 23 e site~(-1)s^(-1)during the ORR,***-wave potential(0.915V_(RHE))of the Fe-n-C catalyst is more positive(approximately 54 mV)than that of Pt/***,we observe that the perform.n.e of PEmFCs on Fe-n-C almost achieves the 2025 target of the US Departm.n. of Energy by dem.n.trating a current density of 1.037 A cm^(-2)combined with the peak power density of 0,685 W cm^(-2),suggesting the critical role of Fe(Ⅱ)-n_(4)site(D1).After 500 h of running,PEmFCs still deliver a power density of 1.26 W cm^(-2)at 1.0 bar H_(2)-O_(2),An unexpected rate-determ.n.ng step is figured out by isotopic labelling experim.n. and theoretical *** work not only offers valuable insights regarding the intrinsic contribution of Fe-n_(4)with a single spin state to alkaline/acidic ORR,but also provides great opportunities for developing high-perform.n.e stable PEmFCs.

关键词： Fuel cells Oxygen reduction reaction non-platinum group metals(PGms) Isotopic labelling Active site TOF

Perform.n.e of iron-air battery with iron nanoparticle-encapsulated C-n composite electrode

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Frontiers in Energy 2024年第1期18卷 42-53页

作者： Can fang Xiangmei TAnG Jiaoyan WAnG Qingfeng YI School of Chemistry and Chemical Engineering Hunan University of Science and TechnologyXiangtan 411201China Hunan Provincial Key Laboratory of Advanced materials for new Energy Storage and Conversion Xiangtan 411201China

Highly efficient and stable iron electrodes are of great significant to the developm.n. of iron-air battery(IAB).In this paper,iron nanoparticle-encapsulated C–n composite(nanoFe@Cn)was synthesized by pyrolysis using polyaniline as the C–n *** perform.n.e of the nanoFe@Cn in different electrolytes(alkaline,neutral,and quasi-neutral)was investigated via cyclic voltammetry(CV).The IAB was assembled with nanoFe@Cn as the anode and IrO_(2)+Pt/C as the *** effects of different discharging/charging current densities and electrolytes on the battery perform.n.e were also *** K_(2)SO_(4)electrolyte can effectively suppress the passivation of iron electrode,and the battery showed a good cycling stability during 180 charging/discharging *** to the pure nano-iron(nanoFe)battery,the nanoFe@Cn battery has a more stable cycling stability either in KOH or nH_(4)Cl+KCl electrolyte.

关键词： energy storage and conversion metallic composites nanocomposites iron-air battery iron anode

Discontinuous phase diagram of amorphous carbons

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national Science Review 2024年第4期11卷 164-171页

作者： YinBo Zhu ZhouYu fang ZhongTing Zhang HengAn Wu CAS Key Laboratory of mechanical Behavior and Design of materials Department of Modern MechanicsUniversity of Science and Technology of China State Key Laboratory of nonlinear mechanics Institute of Mechanics Chinese Academy of Sciences

The short-range order and medium-range order of amorphous carbons dem.n.trated in experim.n.s allow us to rethink whether there exist intrinsic properties hidden by atomic disordering. Here we presented six representative phases of amorphous carbons（0.1–3.4 g/cm3）, namely, disordered graphene network（DGn）, high-density amorphous carbon（HDAC）, amorphous diaphite（a-DG）, amorphous diam.n.（a-D）, paracrystalline diam.n.（p-D）, and nano-polycrystalline diam.n.（nPD）, respectively, classified by their topological features and microstructural characterizations that are comparable with experim.n.s. To achieve a comprehensive physical landscape for amorphous carbons, a phase diagram was plotted in the sp3/sp2versus density plane, in which the counterintuitive discontinuity originates from the inherent difference in topological microstructures, further guiding us to discover a variety of phase transitions am.n. different amorphous carbons. Intriguingly, the power law, log（sp3/sp2） ∝ ρn, hints at intrinsic topology and hidden order in amorphous carbons, providing an insightful perspective to reacquaint atomic disorder in non-crystalline carbons.

关键词： amorphous carbons disordered carbons phase diagram microstructural topology phase transition

Assessm.n. and Enhancem.n. of FRC of Power Systems Considering Thermal Power Dynamic Conditions

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CSEE Journal of Power and Energy Systems 2024年第4期10卷 1371-1383页

作者： Feng Hong Yalei Pang Weim.n. Ji Lu Liang fang fang Junhong Hao Jizhen Liu State Key Laboratory of Alternate Electric Power System with Renewable Energy Sources and School of Control and Computer Engineering North China Electric Power UniversityBeijing 102206China State Key Laboratory of Alternate Electric Power System with Renewable Energy Sources School of Energy Power and Mechanical EngineeringNorth China Electric Power UniversityBeijing 102206China

Frequency stability and security have been a vital challenge as large-scale renewable energy is integrated into power *** contrast,the proportion of traditional thermal power units decreases during the decarbonization transformation process,resulting in poor frequency *** paper aims to explore the potential of frequency regulation support,dynamic assessm.n.,and capacity promotion of thermal power plants in the transition *** the dynamic characteristics of the main steam working fluid under different working conditions,a nonlinear observer is constructed by extracting the main steam pressure and valve opening degree *** real-time frequency modulation capacity of thermal power units can provide a dynamic state for the power grid.A dynamic adaptive modification for primary frequency control(PFC)of power systems,including wind power and thermal power,is proposed and *** power dynamic allocation factor is adaptively optimized by predicting the speed droop ratio,and the frequency modulation capability of the system is improved by more than 11%under extreme ***,through the m.n.e Carlo simulation of unit states of the system under various working conditions,the promotion of the frequency regulation capacity with high wind power penetration(WPP)is verified.

关键词： Dynamic evaluation frequency regulation power system predictive modeling wind penetration

Seasonal Variation of the Sea Surface Temperature Growth Rate of EnSO

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Advances in Atmospheric Sciences 2024年第3期41卷 465-477页

作者： Xinyi XInG Xianghui fang Da PAnG Chaopeng JI Departm.n. of Atmospheric and Oceanic Sciences and Institute of Atmospheric Sciences Fudan UniversityShanghai 200438China Shanghai Frontiers Science Center of Atmosphere-Ocean Interaction Shanghai 200438China Shanghai Key Laboratory of Ocean-land-atmosphere Boundary Dynamics and Climate Change Fudan UniversityShanghai 200438China

El ni?o–Southern Oscillation(EnSO) exhibits a distinctive phase-locking characteristic, first expressed during its onset in boreal spring, developing during summer and autumn, reaching its peak towards winter, and decaying over the next spring. Several studies have dem.n.trated that this feature arises as a result of seasonal variation in the growth rate of EnSO as expressed by the sea surface temperature(SST). The bias towards simulating the phase locking of EnSO by m.n. state-of-the-art climate models is also attributed to the unrealistic depiction of the growth rate. In this study, the seasonal variation of SST growth rate in the ni?o-3.4 region(5°S–5°n, 120°–170°W) is estimated in detail based on the mixed layer heat budget equation and recharge oscillator model during 1981–2020. It is suggested that the consideration of a variable mixed layer depth is essential to its diagnostic process. The estimated growth rate has a remarkable seasonal cycle with m.n.mum rates occurring in spring and maximum rates evident in autumn. more specifically, the growth rate derived from the meridional advection(surface heat flux) is positive(negative) throughout the year. Vertical diffusion generally makes a negative contribution to the evolution of growth rate and the magnitude of vertical entrainm.n. represents the smallest contributor. Analysis indicates that the zonal advective feedback is regulated by the meridional immigration of the intertropical convergence zone, which approaches its southernmost extent in February and progresses to its northernmost location in September, and dom.n.tes the seasonal variation of the SST growth rate.

关键词： SST growth rate intertropical convergence zone zonal advective feedback mixed layer depth EnSO seasonal variation

Cascaded four-wave mixing all-optical wavelength converter based on highly nonlinear fiber deposited graphene oxide

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Journal of materials Science & Technology 2024年第4期171卷 10-15页

作者： Yuanhongliu Gao Xiaoyu Chen Tonglei Cheng fang Wang Xin Yan College of Information Science and Engineering State Key Laboratory of Synthetical Automation for Process IndustriesNortheastern UniversityShenyang 110819China

The all-optical wavelength conversion using cascaded four-wave mixing(FWm)phenom.n. with graphene oxide(GO)and a highly nonlinear fiber(HnLF)device is dem.n.trated *** has a strong third-order nonlinear effect and is an excellent nonlinear optical material for nonlinear optical wavelength *** group velocity matching of pump and signal,HnLF,and GO amplification promote the cascaded nonlinear frequency mixing *** the experim.n.al and analytical results,the maximum spacing between signal and pump is 21 nm,and specifically,the order of cascaded FWm light increases from order 1 to order 2 with increasing GO,and the first-order FWm conversion effi-ciency increases to a maximum of−14.5 *** the best of our knowledge,this is the first time that cascaded FWm-based all-optical wavelength conversion in HnLF-GO with wide wavelength selectivity is investigated with combined pump and signal *** findings not only provide an effective method for achieving all-optical wavelength conversion in cascaded FWm but also offer the possibility of fabricating high-perform.n.e nonlinear optical devices.

关键词： Four-wave mixing Graphene oxide Highly nonlinear fiber Optical wavelength conversion

Revealing Al-O/Al-F reaction dynamic effects on the combustion of alum.n.m.n.noparticles in oxygen/fluorine containing environm.n.s:A reactive molecular dynamics study meshing together experim.n.al validation

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Defence Technology（防务技术） 2024年第4期34卷 313-327页

作者： Gang Li Chuande Zhao Qian Yu fang Yang Jie Chen Institute of Chemical materials China Academy of Engineering Physics(CAEP)P.O.Box 919-311Mianyang 621900SichuanChina

Improving the energy conversion efficiency in metallic fuel(e.g.,Al)combustion is always desirable but challenging,which often involves redox reactions of alum.n.m(Al)with various mixed oxidizing *** instance,Al-O reaction is the most comm.n.pathway to release limited energy while Al-F reaction has received much attentions to enhance Al combustion ***,microscopic understanding of the Al-O/Al-F reaction dynamics remains unsolved,which is fundam.n.ally necessary to further improve Al combustion *** this work,for the first time,Al-O/Al-F reaction dynamic effects on the combustion of alum.n.m.n.noparticles(n-Al)in oxygen/fluorine containing environm.n.s have been revealed via reactive molecular dynamics(RmD)simulations meshing together combustion *** RmD simulation systems of Al core/O_(2)/HF,n-Al/O_(2)/HF,and n-Al/O_(2)/CF4 with oxygen percentage ranging from 0%to 100%have been *** n-Al combustion in mixed O_(2)/CF_4 environm.n.s have been conducted by constant volume combustion *** results show that Al-O reaction exhibits kinetic benefits while Al-F reaction owns thermodynamic benefits for n-Al *** n-Al/O_(2)/HF,Al-O reaction gives faster energy release rate than Al-F reaction(1.1 times).The optimal energy release efficiency can be achieved with suitable oxygen percentage of 10%and 50%for n-Al/O_(2)/HF and n-Al/O_(2)/CF_4,*** combustion experim.n.s,90%of oxygen percentage can optimally enhance the peak pressure,pressurization rate and combustion ***,Al-O reaction prefers to occur on the surface regions while Al-F reaction prefers to proceed in the interior regions of n-Al,confirm.n. the kinetic/thermodynamic benefits of Al-O/Al-F *** synergistic effect of Al-O/Al-F reaction for greatly enhancing n-Al combustion efficiency is dem.n.trated at atomicscale,which is beneficial for optimizing the combustion perform.n.e of metallic fuel.

关键词： Al-O/Al—F reaction Kinetic benefits Thermodynamic benefits molecular dynamics Combustion

Implication of comm.n.ty-level ecophysiological parameterization to modelling ecosystem productivity:a case study across nine contrasting forest sites in eastern China

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Journal of Forestry Research 2024年第1期35卷 1-11页

作者： m.n.he fang Changjin Cheng nianpeng He Guoxin Si Osbert Jianxin Sun School of Ecology and nature Conservation Beijing Forestry UniversityBeijing 100083China Research Institute of Energy Saving Environmental ProtectionOccupational Safety and HealthChina Academy of Railway Sciences Corporation LimitedBeijing 100081China Key Laboratory of Ecosystem.n.twork Observation and modeling Institute of Geographic Sciences and Natural Resources ResearchChinese Academy of SciencesBeijing 100101China College of Resources and Environm.n. University of Chinese Academy of SciencesBeijing 100049China

Parameterization is a critical step in modelling ecosystem ***,assigning parameter values can be a technical challenge for structurally complex natural plant comm.n.ties;uncertainties in model simulations often arise from inappropriate model *** we compared five methods for defining comm.n.ty-level specific leaf area(SLA)and leaf C:n across nine contrasting forest sites along the north-South Transect of Eastern China,including biomass-weighted average for the entire plant comm.n.ty(AP_BW)and four simplified selective sampling(biomass-weighted average over five dom.n.nt tree species[5DT_BW],basal area weighted average over five dom.n.nt tree species[5DT_AW],biomass-weighted average over all tree species[AT_BW]and basal area weighted average over all tree species[AT_AW]).We found that the default values for SLA and leaf C:n embedded in the Biome-BGC v4.2 were higher than the five computational methods produced across the nine sites,with deviations ranging from 28.0 to 73.3%.In addition,there were only slight deviations(n the whole plant comm.n.ty sampling(AP_BW)predicted nPP and the four simplified selective sampling methods,and no significant difference between the predictions of AT_BW and AP_BW except the Shennongjia *** findings in this study highlights the critical importance of computational strategies for comm.n.ty-level parameterization in ecosystem process modelling,and will support the choice of parameterization methods.

关键词： Biome-BGC Comm.n.ty traits Forest Ecosystems model parameterization