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A study on compressive shock wave propagation in metallic foams

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Science china(Physics,{1. & Astronomy) 2010年第2期53卷 279-287页

作者： wang ZhiHua1,2.zhang YiFen2.REN HuiLan1 & ZHAO LongMao2.1 State Key Laboratory of Explosion Science and Technology,{2. institute of Technology,{2. 100081,china 2.institute of Applied mechanics and Biomedical Engineering,Taiyuan University of Technology,Taiyuan 03002.,china 1. State Key Laboratory of Explosion Science and Technology Beijing Institute of Technology Beijing 100081 China2. Institute of Applied Mechanics and Biomedical Engineering Taiyuan University of Technology Taiyuan 030024 China

Metallic foam can dissipate a large amount of energy due to its relatively long stress plateau,which makes it widely applicable in the design of structural crashworthiness. However,in some experimental studies,stress enhancement has been observed when the specimens are subjected to intense impact loads,leading to severe damage to the objects being protected. This paper studies this phenomenon on a 2. mass-spring-bar model. With the model,a constitutive relationship of metal foam and corresponding loading and unloading criteria are presented; a nonlinear kinematics equilibrium equation is derived,where an explicit integra-tion algorithm is used to calculate the characteristic of the compressive shock wave propagation within the metallic foam; the effect of heterogeneous distribution of foam microstructures on the shock wave features is also included. The results reveal that under low impact pulses,considerable energy is dissipated during the progressive collapse of foam cells,which then reduces the crush of objects. When the pulse is sufficiently high,on the other hand,stress enhancement may take place,especially in the heterogeneous foams,where high peak stresses usually occur. The characteristics of compressive shock wave propagation in the foam and the magnitude and location of the peak stress produced are strongly dependent on the mechanical properties of the foam material,amplitude and period of the pulse,as well as the homogeneity of the microstructures. This research provides valuable insight into the reliability of the metallic foams used as a protective structure.

关键词： aluminum foam heterogeneous intensive pulse loading stress enhancement

Co/N co-doped flower-like carbon-based phase change materials toward solar energy harvesting

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Aggregate 2024年第1期5卷 321-330页

作者： Xiao Chen lei {1. Yan Gao Yang Li Xiaowei {2. Yu Jiang Ge {1. institute of Advanced Materials Beijing Normal UniversityBeijingChina beijing Advanced Innovation Center for Materials Genome Engineering Beijing Key Laboratory of Function Materials for Molecule and Structure ConstructionSchool of Materials Science and EngineeringUniversity of Science and Technology BeijingBeijingChina

The photothermal conversion capacity of pristine organic phase change materials(PCMs)is inherently insufficient in solar energy *** upgrade their photothermal conversion capacity,we developed bimetallic zeolitic imidazolate framework(ZIF)derived Co/N co-doped flower-like carbon(Co/N-FLC)-based composite PCMs toward solar energy harvesting.3D interconnected carbon framework with low interfacial thermal resistance,abundant carbon defects and high content of nitrogen doping,excellent localized surface plasmon resonance(LSPR)effect of Co nanoparticles,and light absorber Co_(3)ZnC in Co/N-FLC synergistically upgrade the photothermal capacity of(polyethylene glycol)PEG@Co/N-FLC composite PCMs with an ultrahigh photothermal conversion efficiency of 94.8%under 0.1. W/cm^(2..Uniformly anchored Co and Co_(3)ZnC nanoparticles in carbon framework guarantee excellent photon capture *** carbon nanotubes(CNTs)in 2. carbon nanosheets further accelerate the rapid transport of phonons by constructing cross-connected heat transfer ***,PEG@Co/N-FLC exhibits a thermal energy storage density of 1.0.69 J/g and excellent thermal stability and durable ***,PEG@Co/N-FLC composite PCMs are promising candidates to accelerate the efficient utilization of solar energy.

关键词： bimetallic ZIF Co/N co-doped carbon phase change materials photothermal conversion thermal energy storage

Spectroscopic evidence for triplet excitation energy transfer among carotenoids in the LH2.complex from photosynthetic bacterium Rhodopseudomonas palustris

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Science china Chemistry 2004年第1期47卷 80-90页

作者： FENG Juan, wang Qian, zhang Xujia, HUANG Youguo, Al Xicheng, zhang Xingkang & zhang JianpingState Key Laboratory for Structural Chemistry of Unstable and Stable Species, institute of Chemistry, chinese academy of sciences, beijing 100080, china National Laboratory of Biomacromolecules, institute of Biophysics, chinese academy of sciences, beijing 100101, china 1. State Key Laboratory for Structural Chemistry of Unstable and Stable Species institute of Chemistry Chinese Academy of Sciences 100080 Beijing China 2. National Laboratory of Biomacromolecules {1. of Biophysics Chinese Academy of Sciences 100101 Beijing China

The LH2.complex from Rhodopsudomonas (Rps.) palustris is unique in the heterogeneous carotenoid compositions. The dynamics of triplet excited state Carotenoids (3Car* has been investigated by means of sub-microsecond time-resolved absorption spectroscopy both at physiological temperature (2.5 K) and at cryogenic temperature (77K). Broad and asymmetric T n ←T 1.transient absorption was observed at room temperature following the photo-excitation of Car at 532.nm, which suggests the contribution from various carotenoid compositions having different numbers of conjugated C=C double bonds (Nc=c). The triplet absorption bands of different carotenoids, which superimposed at room temperature, could be clearly distinguished upon decreasing the temperature down to 77 K. At room temperature the shorter-wavelength side of the main Tn04T1.absorption band decayed rapidly to reach a spectral equilibration with a characteristic time constant of ∽1.μs, the same spectral dynamics, however, was not observed at 77 K. The aforementioned spectral dynamics can be explained in terms of the triplet-excitation transfer among heterogeneous carotenoid compositions. Global spectral analysis was applied to the time-resolved spectra at room temperature, which revealed two spectral components peaked at 545 and 565 nm, and assignable to the Tn04 T1.absorption of Cars with Nc=c=1. and Nc=c=1., respectively. Surprisingly, the decay time constant of a shorter-conjugated Car, i.e. 0.72.?s (aerobic) and 1.36 ?s (anaerobic), is smaller than that of a longer-conjugated Car, i.e. 2.1.0}us (aerobic) and 3.75 ?s (anaerobic), which is contradictory to the general rule of carotenoids and relative polyenes. The results are explained in terms of triplet-excitation transfer among different types of Cars. It is postulated that two Cars with different conjugation lengths coexist in an α, β-subunit in the LH2.complex.

关键词： purple photosynthetic bacteria, carotenoid, excited-state, time-resolved spectroscopy.

The Suitability of Using Leaf Area Index to Quantify Soil Loss under Vegetation Cover

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Journal of Mountain Science 2011年第4期8卷 564-570页

作者： zhang Wentai YU Dongsheng SHI Xuezheng {1. Hongjie GU Zhujun zhang Xiangyan TAN Manzhi State Key Laboratory of Soil and Sustainable Agriculture Institute of Soil Science Chinese Academy of SciencesNanjing 21o0o8 China Graduate University of the chinese academy of sciences Beijing 100039 China School of Bio-Chemical and Environmental Engineering Nanjing Xiaozhuang University Nanjing 211171 China

Soil erosion by water under forest cover is a serious problem in southern china.A comparative study was carried out on the use of leaf area index(LAI) and vegetation fractional coverage(VFC) in quantifying soil loss under vegetation *** types of vegetation with varied LAI and VFC under field conditions were exposed to two rainfall rates(40 mm h-1.and 54 mm h-1. using a portable rainfall *** rate,sediment concentration and soil loss rate were measured at relatively runoff stable *** negative exponential relationship(p 1.= 0.83) and linear relationship(p 1.= 0.84) were obtained between LAI and sediment concentration,while no significant relationship existed between VFC and sediment *** mechanism by which vegetation canopy prevents soil loss was by reducing rainfall kinetic energy and sediment *** could better quantify such a role than ***,neither LAI nor VFC could explain runoff rate or soil loss *** must be taken when using LAI to quantify the role of certain vegetation in soil and water conservation.

关键词： Leaf area index(LAI) Runoff steady state Sediment concentration Simulated rainfall

Paleozoic Multi-Stage Magmatic Events Related to Proto-Tethys and Paleo-Tethys Evolution:Insights from Intrusive Rocks in the Eastern Altyn Orogen,NW china

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Journal of Earth Science 2024年第4期35卷 1130-1148页

作者： Jiyong Li Yanqing Xia Xilong zhang Haoyuan Jiang Tianzhu {1. Yongchao {2. Yanhong Liu Shanpin Liu Xiaobao zhang Northwest institute of Eco-Environment and Resources Chinese Academy of SciencesLanzhou730000China Key Laboratory of Petroleum Resources Gansu ProvinceLanzhou730000China University of chinese academy of sciences Beijing100049China

Abundant mafic-felsic intrusions distributed in the Altyn Orogen record orogenic histories related to Proto-Tethys and Paleo-Tethys *** U-Pb dating of the intrusive rocks in the eastern Altyn Orogen identifies at least three major tectono-magmatic episodes,yielding ages of∼42.,∼376–373 and∼2.9–2.4 *** first two emplacement episodes correspond to the post-collisional magmatism in the Altyn ***∼42. Ma granitoids possess adakitic characteristics coupled with enriched isotopes,suggesting that they originated from partial melting of thickened lower continental crust induced by upwelling asthenospheric mantle after slab break-off of the South Altyn Ocean ***,the∼376–373 Ma mafic-intermediate rocks and coeval granitoids represent a large thermal event that involved mantle melting with induced new juvenile lower continental crust melting in a post-collisional extensional ***,the∼2.4 Ma diabase dykes intruded into the∼2.9 Ma granitoids,which were related to the widespread Late Paleozoic magmatism resulting from Paleo-Tethys Ocean ***-collisional magmatism in the Altyn Orogen significantly enhances understanding of the tectono-magmatic evolution in the northern Tibetan *** penetrative influence of Paleo-Tethys Ocean subduction was more extensive than previously thought.

关键词： Proto-Tethys Paleo-Tethys Altyn Orogen multi-stage magmatic events magnetic cores

Single-atom-mediated electron islands boost photocatalytic CO_(2.chemical fixation

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Science china Chemistry 2024年第7期67卷 2292-2299页

作者： Shu Shang lei Li Xin He Hui {1. Lirong Zheng Wei Shao Xiaodong {2. Yi Xie Hefei National Research Center for Physical sciences at the Microscale University of Science and Technology of ChinaHefei 230026China institute of Energy Hefei Comprehensive National Science CenterHefei 230031China beijing Synchrotron Radiation Facility Institute of High Energy PhysicsChinese Academy of SciencesBeijing 100049China School of Chemistry and Chemical Engineering Hefei Normal UniversityHefei 230031China

Photocatalytic cycloadditions of CO_(2.with epoxides are emerging as a significant platform for the green synthesis of valuable carbonates,where efficient catalytic systems with spatially separated charge carriers are ***,a single p-block metal atom is proposed to be a candidate for photogenerated electron localization on a metal oxide *** taking the Bi single-atom supported on ZnO nanosheet(Bi1.ZnO)as an example,we show that the Bi atom plays the role of an electron island in the sea of delocalized holes within ***,the as-formed electron island could readily promote the rate-determining ring-opening process of cycloaddition *** from the unique spatially separated electrons and holes,the Bi1.ZnO achieves a high yield of cyclic carbonates with almost 1.0%*** study provides a pioneering strategy for enhancing the performances of photocatalytic CO_(2.chemical fixation.

关键词： electron islands CO_(2.photofixation photogenerated charge carriers

Risk Factors for Norovirus Outbreaks in Schools and Kindergartens—beijing Municipality,{1.,July 2.1.–June 2.2.

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china CDC weekly 2024年第33期6卷 841-845页

作者： Baiwei Liu Yu wang Mengdi Tan Boran E Dongxue {1. Hanqiu Yan Quanyi wang Daitao {1. lei Jia Zhiyong Gao institute for Infectious Disease and Endemic Disease Control Beijing Center for Disease Prevention and ControlBeijingChina School of Public Health China Medical UniversityShenyang CityLiaoning ProvinceChina School of Public Health Capital Medical UniversityBeijingChina Department of Endocrinology Beijing Shijitan HospitalCapital Medical UniversityBeijingChina

What is already known on this topic?Norovirus is the leading cause of global acute gastroenteritis *** outbreaks mainly occur in schools and kindergartens in china,always causing public health *** is added by this report?Conditional logistic regression method was used to analyze the risk factors for norovirus outbreaks in schools and kindergartens,and found that students vomiting at school or kindergarten,case activity in public areas,and the first case’s classroom less than 5 meters from toilets were risk *** are the implications for public health practice?Effective measures to address these factors can help reduce the risk of norovirus outbreaks in schools and kindergartens.

关键词： let garten schools

The comparison study of diagnostics of light filaments in air

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Science china(Physics,{1. & Astronomy) 2006年第2期49卷 228-235页

作者： HAO Zuoqiang1, zhang Jie1, YU Jin2. ZHENG Zhiyuan1, YUAN Xiaohui1,3, zhang Zhe1, LI Yutong1, {2. Zhaohua1, LING Weijun1 & WEI Zhiyi11. Laboratory of Optical Physics, institute of Physics, chinese academy of sciences, beijing 100080, china 2. Laboratoire de Spectrométrie Ionique et Moléculaire,UMR CNRS 5579,Université Claude Bernard-Lyon 1,43, Bd. du 11 Novembre 1918, F-6962. Villeurbanne Cedex, France 3. State Key Laboratory of Transient Optics Technology, Xi’an institute of Optics and Precision mechanics, chinese academy of sciences, Xi’an 710068, china Laboratory of Optical Physics Institute of Physics Chinese Academy of Sciences Beijing 100080 China Laboratoire de Spectrométrie Ionique et Moléculaire UMR CNRS 5579 Université Claude Bernard-Lyon 143 Bd. du 11 Novembre 1918 F-69622 Villeurbanne Cedex France State Key Laboratory of Transient Optics Technology Xi’an Institute of Optics Precision mechanics Chinese Academy of Sciences Xi’an 710068 China

Long plasma channels in air induced by femtosecond laser pulses are inves-tigated using three different methods, including the cross-section imaging, resistivity measuring and acoustic diagnostics. These methods are based on different properties of the light filaments. A comparison of the three diagnostics shows that the imaging method is the most precise one in studying the filaments distribution and evolution, that the sono-graphic method is the most convenient approach to detecting long plasma channels by detecting the acoustic wave generation, and that the resistivity measurement can only be applied for giving a rough estimate. The diagnostics of filaments allow us to choose ap-propriate detecting methods and provide further insight into the dynamic evolution of the light filaments in air.

关键词： plasma channels filaments cross-section imaging resistivity measurement acoustic diagnostics.

Blackening failure of poly-α-olefin impregnated porous polymide due to the splitting of lubrication oil catalyzed by iron

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Friction 2024年第9期12卷 1969-1979页

作者： Pengfei SHI Yang YIN Shaohua zhang Diankai zhang Yuanyuan JIANG Yang {2. Ningning ZHOU Tao QING Jintao WU Linmao QIAN Jiyang zhang lei CHEN Tribology Research institute State Key Laboratory of Rail Transit Vehicle SystemSchool of Mechanical EngineeringSouthwest Jiaotong UniversityChengdu 610031China beijing Key Laboratory of Long-life Technology of Precise Rotation and Transmission Mechanisms Beijing Institute of Control EngineeringBeijing 100094China Technology and Equipment of Rail Transit Operation and Maintenance Key Laboratory of Sichuan Province School of Mechanical EngineeringSouthwest Jiaotong UniversityChengdu 610031China

Lubrication failure accompanying with blackening phenomenon significantly reduces the long-running operational reliability of porous polymide(PPI)lubricated with poly-α-olefin(PAO)***,the effects of lubrication condition and counter-surface chemistry on the blackening failure of PAO impregnated PPI were studied through the comparison of the tribological tests against GCr1. steel ball and Al_(2.O_(3)ceramic ball with and without PAO oil *** products were found to be formed on the PAO impregnated PPI surface slid against steel ball or Al_(2.O_(3)ball added with iron nano-particles,but be absent under the conditions without iron or PAO *** analysis indicated that the iron-catalyzed splitting of PAO oil into small molecule alkanes and following the formation of black organic matter should be mainly responsible for the blackening *** dynamic(MD)simulations demonstrated that the iron facilitated the separation of hydrogen atom and the following broken of C–C bonds in PAO molecules,final resulting in the splitting of PAO oil.

关键词： porous polyimide poly-α-olefin oil friction-induced blackening phenomenon tribological performance ReaxFF MD simulation