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Conductive edge-warping graphite mesas for robust structural superlubricity

Science China(Technological Sciences) 2024年第7期67卷 2040-2049页

作者： FENG WeiJia LIU Ying MA Ming peng deli NIE JinHui State Key Laboratory of Tribology in Advanced Equipment&Department of Mechanical Engineering Tsinghua UniversityBeijing 100084China Center for Nano and Micro Mechanics Tsinghua UniversityBeijing 100084China Institute of Superlubricity Technology Research Institute of Tsinghua University in ShenzhenShenzhen 518057China

Structural superlubricity(SSL) refers to a state of ultralow friction and zero wear when two solid surfaces slide against each other. Recent investigations have identified amorphous carbon at the edge of the graphite mesa as the primary source of friction in such SSL systems. Here, the tensile stress of metal thin film is exploited to engineer vertically conductive edge-warping graphite mesas(EWGM). Through this approach, robust SSL performance is realized, demonstrated by sliding an 8 μm side length square EWGM on an atomically smooth Au substrate for 10000 cycles at a constant voltage of 1 m V. In this SSL system,differential friction coefficients lower than 1.5 × 10^(-4) are achieved, with static contact resistance between EWGM and Au substrate as low as 28Ω and sliding contact resistance as low as 32Ω. Moreover, the EWGM exhibits SSL behavior on polished Si wafer substrates. Furthermore, because of the no-edge contact with the substrate during sliding, friction is independent of the sliding speed of the EWGM. This study presents the first successful fabrication of conductive EWGM. Remarkably, in both EWGM-Au and EWGM-Si SSL systems, the measured frictions are more than one order of magnitude lower than those of ordinary self-retracting graphite mesas with no-edge warping, and no wear is observed during extended current-carrying ***, these findings establish a solid groundwork for the future realization of macroscale conductive SSL systems.

关键词： structural superlubricity graphite mesa contact resistance tensile stress edge warping

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Patterns and drivers of plant sexual systems in the dry-hot valley region of southwestern China

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Plant Diversity 2024年第2期46卷 158-168页

作者： Rong Ma Qi Xu Yongqian Gao deli peng Hang Sun Bo Song State Key Laboratory of Plant Diversity and Specialty Crops/Yunnan Key Laboratory for Integrative Conservation of Plant Species with Extremely Small Populations Kunming Institute of BotanyChinese Academy of SciencesKunming 650201China College of Life Sciences Shaanxi Normal UniversityXi'an 710119China Yunnan Forestry Technological College Kunming 650224China School of Life Science/Key Laboratory of Yunnan for Biomass Energy and Biotechnology of Environment Yunnan Normal UniversityKunming 650500YunnanChina

Sexual systems play important roles in angiosperm evolution and exhibit substantial variations among different floras. Thus, studying their evolution in a whole flora is crucial for understanding the formation and maintenance of plant biodiversity and predicting its responses to environmental change. In this study, we determined the patterns of plant sexual systems and their associations with geographic elements and various life-history traits in dry-hot valley region of southwestern China, an extremely vulnerable ecosystem. Of the 3166 angiosperm species recorded in this area, 74.5% were hermaphroditic,13.5% were monoecious and 12% were dioecious, showing a high incidence of diclinous species. Diclinous species were strongly associated with tropical elements, whereas hermaphroditic species were strongly associated with temperate and cosmopolitan elements. We also found that hermaphroditism was strongly associated with showy floral displays, specialist entomophily, dry fruits and herbaceous *** was strongly associated with inconspicuous, pale-colored flowers, generalist entomophily, fleshy fruits, and woody plants, whereas monoecy was strongly associated with inconspicuous, pale-colored flowers, anemophily, dry fruits, and herbaceous plants. In addition, hermaphroditic species with generalist entomophily tended to flower in the dry season, whereas diclinous species with specialist entomophily tended to flower in the rainy season. However, independent of sexual systems, plants that produce dry fruits tended to flower in the rainy season and set fruits in the dry season, but the opposite pattern was found for fleshy fruit-producing plants. Our results suggest that in the dry-hot valleys, plant sexual systems are associated with geographic elements as well as various life-history traits that are sensitive to environmental change.

关键词： Floral traits Fruit type Growth form Pollination system Reproductive phenology

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不同采集年份大花红景天种子萌发对温度的响应

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草业科学 2024年第8期41卷 1924-1933页

作者：耿博阳覃滢卜杨丽娥彭德力云南师范大学生命科学学院云南昆明650500 云南师范大学地理学部云南昆明650500 云南省生物质能与环境生物技术重点实验室云南昆明650500

为确定温度变化对大花红景天(Rhodiola crenulata)种子萌发的影响,本研究以云南省香格里拉市大雪山居群的种子为材料,探究不同采集年份(2014、2015、2016、2019、2020、2021年)种子的萌发对温度(恒温:1、5、10、15、20、25、30、35℃;变... 详细信息

为确定温度变化对大花红景天(Rhodiola crenulata)种子萌发的影响,本研究以云南省香格里拉市大雪山居群的种子为材料,探究不同采集年份(2014、2015、2016、2019、2020、2021年)种子的萌发对温度(恒温:1、5、10、15、20、25、30、35℃;变温:15℃/5℃、25℃/15℃)的响应机制。结果表明:大花红景天种子萌发温度阈值较宽,1~35℃均可萌发,具有较宽的萌发温度生态位幅度(0.831~0.891),15~25℃萌发效果最佳;变温与相应恒温相比不能显著增加最终萌发率。通过积温模型模拟,种子萌发最低温度(Tb)为−0.49~0.82℃,萌发最适温度(To)为19.38~20.88℃,萌发最高温度(Tc)为34.21~38.76℃,亚适温条件下的种子萌发积温值为40.7~67.11℃·d。综上,大花红景天种子具有“机会主义”萌发行为,萌发最低温度较低且具有较宽的萌发温度窗口,使其可以在早春大量萌发,以保证幼苗拥有较长的生长季。研究结果为保护与利用野生大花红景天资源提供了一些参考。

关键词：濒危植物大花红景天采集年份温度种子萌发积温模型萌发生态位

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Function of male and hermaphroditic flowers and size-dependent gender diphasy of Lloydia oxycarpa (Liliaceae) from Hengduan Mountains

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Plant Diversity 2017年第4期39卷 187-193页

作者： Yang Niu Qiangbang Gong deli peng Hang Sun Zhimin Li School of Life Sciences Yunnan Normal University 650500 Kunming Yunnan China Key Laboratory for Plant Diversity and Biogeography of East Asia Kunming Institute of Botany Chinese Academy of Sciences 132 Lanhei Road 650201 Kunming Yunnan China

Although hermaphroditism is common in flowering plants, unisexual flowers occur in many plant taxa,forming various sexual systems. However, the sexual system of some plants is difficult to determine morphologically, given that their sex expression may be influenced by both genetic and environmental factors. Specifically, androdioecy(the coexistence of both male and hermaphroditic individuals in the same population) has often been confused with the gender diphasy, a gender strategy in which plants change their sex expression between seasons. We studied the reproductive function of male and hermaphroditic flowers of Lloydia oxycarpa(Liliaceae), in order to investigate its sexual system and determine whether it is a gender-diphasic species. We found that although male flowers occur in a considerable number of plants, relative to hermaphrodites, they did not exhibit any significant reproductive advantage in terms of flower size, pollen quantity, attractiveness to visitors or siring success. In addition, this plant has spontaneous self-pollination and showed no inbreeding depression. These results render the maintenance of male individuals almost impossible. Furthermore, a considerable number of individuals changed their sex in successive years. The sex expression was found to be related to bulb size and dry weight, with larger individuals producing hermaphroditic flowers and smaller individuals producing male flowers. These results suggest that L. oxycarpa is not an androdioecious plant but represents a rare case of size-dependent gender diphasy.

关键词： Gender diphasy Lloydia Reproductive ecology Sexual system Size-dependent sex allocation

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Seed dormancy and germination characteristics of two Rheum species in the Himalaya-Hengduan Mountains

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植物多样性：英文版 2017年第4期39卷 180-186页

作者： deli peng Zhe Chen Xiaojian Hu Zhimin Li Bo Song Hang Sun Key Laboratory for Plant Diversity and Biogeography of East Asia Kunming Institute of Botany Chinese Academy of Sciences Kunming 650201 Yunnan China School of Life Science Yunnan Normal University Kunming 650500 Yunnan China Germplasm Bank of Wild Species in Southwest China Kunming Institute of Botany Chinese Academy of Sciences Kunming 650201 Yunnan China University of Chinese Academy of Sciences Belting 100049 China

Seed dormancy and germination characteristics are important factors determining plant reproductive success, and may be expected to have a major influence on plant distribution. In this study, we aimed to explore the characteristics of seed dormancy and germination in two endemic Rheum species(Rheum nobile and Rheum alexandrae) in the Himalaya-Hengduan Mountains. To determine the type of dormancy,fresh seeds of the two species(one population each) were incubated in light at 25/15 and 15/5℃, and then dry after-ripening(DAR) seeds were incubated on water agar substrate with or without GA_3. To determine the effect of temperature and light on germination, DAR seeds of the two species(two populations each) were incubated both in the light and in the dark at several temperatures, including constant and alternating temperatures. Base temperature(T_b) and thermal times for 50% germination(θ_(50)) were calculated. DAR released physiological dormancy(PD), increasing final germination at 15/5℃ and widening the range of germination temperatures from higher to lower, indicative of type 2 non-deep PD for the two Rheum species. Light had no significant effect on germination of seeds from the two species(two populations each). Seeds of the two species germinated significantly better(>80%) at medium temperatures(10-25℃) than at extreme low(5℃) or high(35℃) temperatures. Alternating temperatures(25/15 and 15/5℃) did not significantly increase the final germination of the two species either in the light and in the dark, but it promoted seed germination more quickly than corresponding constant temperatures in the light in both Rh. alexandrae populations, especially at 15/5℃. Germination in response to temperature was well described by the thermal-time model at suboptimal temperatures. The estimated Tbvalues were 1 and 0.9℃, respectively, in two Rh. nobile populations; 4 and 4.1℃,respectively, in two Rh. alexandrae populations; θ_(50)(thermal time) were 100 and 125℃d, respectively in tw

关键词： Germination Light Rheum alexandrae Rheum nobile Dormancy Temperature

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Investigation on the Formation Mechanism of Double-Layer Vertically Aligned Carbon Nanotube Arrays via Single-Step Chemical Vapour Deposition

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Nano-Micro Letters 2017年第1期9卷 137-143页

作者： Shoumo Zhang deli peng Huanhuan Xie Quanshui Zheng Yingying Zhang Center for Nano and Micro Mechanics School of Aerospace EngineeringTsinghua UniversityBeijing 100084People’s Republic of China Department of Chemistry Tsinghua UniversityBeijing 100084People’s Republic of China State Key Laboratory of Tribology and Applied Mechanics Laboratory Tsinghua UniversityBeijing 100084People’s Republic of China

The mechanism for the formation of double-layer vertically aligned carbon nanotube arrays(VACNTs) through single-step CVD growth is investigated. The evolution of the structures and defect concentration of the VACNTs are tracked by scanning electron microscopy(SEM) and Raman spectroscopy. During the growth, the catalyst particles are stayed constantly on the substrate. The precipitation of the second CNT layer happens at around 30 min as proved by *** the growth of the first layer, catalyst nanoparticles are deactivated with the accumulation of amorphous carbon coatings on their surfaces, which leads to the termination of the growth of the first layer CNTs. Then, the catalyst particles are reactivated by the hydrogen in the gas flow, leading to the precipitation of the second CNT layer. The growth of the second CNT layer lifts the amorphous carbon coatings on catalyst particles and substrates. The release of mechanical energy by CNTs provides big enough energy to lift up amorphous carbon flakes on catalyst particles and substrates which finally stay at the interfaces of the two layers simulated by finite element analysis. This study sheds light on the termination mechanism of CNTs during CVD process.

关键词： Synthesis Vertically aligned carbon nanotube arrays CVD Double-layer

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100 km wear-free sliding achieved by microscale superlubric graphite/DLC heterojunctions under ambient conditions

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National Science Review 2022年第1期9卷 17-24页

作者： deli peng Jin Wang Haiyang Jiang Shuji Zhao Zhanghui Wu Kaiwen Tian Ming Ma Quanshui Zheng Department of Engineering Mechanics Tsinghua University Center for Nano and Micro Mechanics Tsinghua University Institute of Superlubricity Technology Research Institute of Tsinghua University in Shenzhen State Key Laboratory of Tribology Tsinghua University Department of Mechanical Engineering Tsinghua University

Wear-free sliding between two contacted solid surfaces is the ultimate goal in the effort to extend the lifetime of mechanical devices,especially when it comes to inventing new types of micro-ele ctromechanical systems where wear is often a major *** we report experimental observations of wear-free sliding for a micrometer-sized graphite flake on a diamond-like-carbon(DLC) surface under ambient conditions with speeds up to 2.5 m/s,and over a distance of 100 *** coefficient of friction(COF) between the microscale graphite flake,a van der Waals(vdW) layered material and DLC,a non-vdW-layered material,is measured to be of the order of 10-3,which belongs to the superlubric *** ultra-low COFs are also demonstrated for a microscale graphite flake sliding on six other kinds of non-vdW-layered materials with sub-nanometer *** a synergistic analysis approach,we reve al the underlying mechanism to be the combination of interfacial vdW interaction,atomic-smooth interfaces and the low normal stiffness of the graphite *** features guarantee a persistent full contact of the interface with weak interaction,which contributes to the ultra-low *** with the extremely high in-plane strength of graphene,wear-free sliding is achieve *** results broaden the scope of superlubricity and promote its wider application in the future.

关键词： structural superlubricity wear-free microscale graphite DLC

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寨子路大桥拱肋垂直提升施工关键技术

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世界桥梁 2023年第6期51卷 48-52页

作者：彭德力重庆两江新区龙兴工业园建设投资有限公司重庆401135

重庆两江新区龙兴新城寨子路大桥主桥为(131+205)m的提篮式连拱钢结构体系桥,其中大拱理论矢高为116 m,矢跨比为1/1.77,拱肋与铅垂面夹角为11.31°。针对该桥主拱拱高且较陡等特点,结合桥址处地质条件以及设备储备情况,采用支架法和垂... 详细信息

重庆两江新区龙兴新城寨子路大桥主桥为(131+205)m的提篮式连拱钢结构体系桥,其中大拱理论矢高为116 m,矢跨比为1/1.77,拱肋与铅垂面夹角为11.31°。针对该桥主拱拱高且较陡等特点,结合桥址处地质条件以及设备储备情况,采用支架法和垂直提升法进行大拱拱肋施工。大拱拱肋分为29个节段,主拱肋分单元节段在工厂制造并预拼装,将拱肋单元节段运至岸边拼装场内,搭设大拱满堂施工栈桥形成工作平台,其中大拱两岸拱脚底部的6个拱肋节段采用支架法安装;对于中间拱轴线纵向水平投影段113 m内的15个拱肋节段,利用设计拱肋轴线投影下方栈桥上的弧形支架组拼成整体提升段,再利用两侧提升塔架将整体提升段垂直提升至设计位置;最后在整体提升段的两端吊装嵌补段焊接合龙成拱。垂直提升施工中,通过计算确定了使整体提升段在提升过程中变形最小的提升塔架纵向净间距,以及预留嵌补段合龙的方式,最大合龙误差22.7 mm,合龙精度满足设计要求。

关键词：拱桥钢箱拱肋提升塔架弧形支架节段拼装垂直提升施工栈桥桥梁施工

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Time-Periodic Solutions to Quasilinear Hyperbolic Systems on General Networks

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Chinese Annals of Mathematics,Series B 2024年第1期45卷 41-72页

作者： peng QU School of Mathematical Sciences Fudan UniversityShanghai 200433China

For quasilinear hyperbolic systems on general networks with time-periodic boundary-interface conditions with a dissipative structure,the existence and stability of the time-periodic classical solutions are discussed.

关键词： Time-periodic solution Quasilinear hyperbolic system General net-work Classical solution Asymptotic stability

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Thermal and mechanical behavior of casting copper alloy wheel during wheel and belt continuous casting process

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China Foundry 2024年第1期21卷 82-90页

作者： Kun Gao Yan peng School of Mechanical Engineering Yanshan UniversityQinhuangdao 066004HebeiChina

To investigate the thermal and mechanical behavior of casting wheel,a two-dimensional thermoelastic-plastic finite element model was used to predict the temperature,stress and distortion distribution of the casting wheel during the wheel and belt continuous casting *** effects of grinding thickness and casting speed on the thermal and mechanical behaviors of the center of the hot face of the casting wheel were discussed in *** each rotation,the casting wheel passes through four different spray *** results show that the temperature distribution of the casting wheel in different spray zones is similar,the temperature of the hot face is the highest and the temperature reaches the peak in the spray zoneⅢ.The stress and distortion depend on the temperature distribution,and the maximum stress and distortion of the hot face are 358.2 MPa and 1.82 mm,*** temperature at the center of the hot face decreases with increasing grinding thickness and increases with increasing casting speed.

关键词： casting wheel finite element model grinding thickness casting speed hot face spray zones

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