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Threshold of climate extremes that impact vegetation productivity over the Tibetan Plateau

Science China Earth Sciences 2024年第6期67卷 1967-1977页

作者： Zhenggang PIAO Xiangyi LI Hao XU kai WANG Shuchang TANG Fei kan Songbai HONG College of Urban and Environmental Sciences Peking UniversityBeijing 100871China

Vegetation growth is adversely impacted by multiple climate extremes related to the water and thermal stress over the Tibetan Plateau(TP).However,it remains unknown at which stress level these climate extremes can trigger the abrupt shifts of vegetation response to climate extremes and result in the maximum vegetation response across *** fill this knowledge gap,we combined the hydrometeorological data and the satellite-derived vegetation index to detect two critical thresholds that determine the response of vegetation productivity to droughts,high-temperature extremes,and low-temperature extremes,respectively,during *** results show that the response of vegetation productivity to droughts rapidly increases once crossing -1.41±0.6 standard deviation(σ)below the normal conditions of soil *** crossing-2.98σ±0.9σ,vegetation productivity is maximum damaged by ***-temperature extremes,which have the two thresholds of 1.34σ±0.4σand 2.31σ±0.4σover TP,are suggested to trigger the strong response of vegetation productivity at a milder stress level than low-temperature extremes(two thresholds:-1.44σ±0.5σand-2.53σ±0.8σ).Moreover,we found the compounded effects of soil moisture deficit in reducing the threshold values of both high-and low-temperature *** on the derived thresholds of climate extremes that impact vegetation productivity,Earth System Models project that southwestern TP and part of the northeastern TP will become the hotspots with a high exposure risk to climate extremes by *** study deciphers the high-impact extreme climates using two important thresholds across TP,which advances the understanding of the vegetation response to different climate extremes and provides a paradigm for assessing the impacts of climate extremes on regional ecosystems.

关键词： Tibetan Plateau Climate extremes Thresholds Vegetation productivity

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Plastic Deformation of Nanocrystalline Zinc Investigated by Positron Annihilation Lifetime Spectroscopy

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Chinese Physics Letters 2013年第5期30卷 165-168页

作者： ZHOU kai LI Hui WANG zhu School of Physics and Optoelectronic Engineering Nanjing University of Information Science&TechnologyNanjing 210044 College of Physics and Optoelectronics Taiyuan University of TechnologyTaiyuan 030024 School of Physics and Technology Wuhan UniversityWuhan 430072

The plastic deformation of nanocrystalline Zn is investigated by positron annihilation lifetime spectroscopy. The deformation is carried out by exerting a pressure on the surface of the samples, which causes a thickness reduction of the samples. The different behavior of the relative thickness reduction with the increasing pressure between the nanocrystalline sample and the conventional bulk sample indicates that a distinct plastic deformation mechanism is operating in the nanocrystalline sample. The positron lifetime results confirm indirectly that the mechanism is grain boundary based, such as grain boundary sliding. Once the nanocrystalline sample is annealed at high temperature, the changes in the thickness reduction and the positron lifetime results become similar to those of the conventional bulk sample. Furthermore, vacancy clusters inside the nanocrystalline sample are found to be an impediment to the plastic deformation process.

关键词： deformation grain lifetime

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Temporal Stability of Apparent Soil Electrical Conductivity Measured by Electromagnetic Induction Techniques

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Journal of Mountain Science 2014年第1期11卷 98-109页

作者： LIAO kai-hua zhu Qing James DOOLITTLE State Key Laboratory of Lake Science and Environment Nanjing Institute of Geography and LimnologyChinese Academy of Sciences USDA-NRCS National Soil Survey Center

Assessing and managing the spatial variability of hydropedological properties are important in environmental,agricultural,and geological *** spatial variability of soil apparent electrical conductivity(ECa) measured by electromagnetic induction(EMI) techniques has been widely used to infer the spatial variability of hydrological and pedological *** this study,temporal stability analysis was conducted for measuring repeatedly soil ECa in an agricultural landscape in *** temporal stability was statistically compared with the soil moisture,terrain indices(slope,topographic wetness index(TWI),and profile curvature),and soil properties(particle size distribution,depth to bedrock,Mn mottle content,and soil type).Locations with great and temporally unstable soil ECa were also associated with great and unstable soil moisture,*** ECa were greater and more unstable in the areas with great TWI(TWI > 8),gentle and concave slope(slope 0.2).Soil ECa exponentially increased with depth to bedrock,and soil profile silt and Mn mottle contents(R2= 0.57),quadratically(R2 = 0.47),and linearly(R 2 = 0.47),*** ECa was greater and more unstable in Gleysol and Nitosol soils,which were distributed in areas with low elevation( 3 m),and fluctuated water table(shallow in winter and spring but deep in summer and fall).In contrast,Acrisol,Luvisol,and Cambisol soils,which are distributed in the upper slope areas,had lower and more stable soil *** these observations,we concluded that the temporal stability of soil ECa can be used to interpret the spatial and temporal variability of these hydropedological properties.

关键词： Geophysics Pedology Soil hydrology Soil water content

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Observational constraints on the new generalized Chaplygin gas model

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Research in Astronomy and Astrophysics 2013年第2期13卷 159-169页

作者： kai Liao Yu Pan Zong-Hong zhu Department of Astronomy Beijing Normal University

We use the latest data to investigate observational constraints on the new generalized Chaplygin gas （NGCG） model. Using the Markov Chain Monte Carlo method, we constrain the NGCG model with type Ia supernovae from the Union2 set （557 data）, the usual baryonic acoustic oscillation （BAO） observation from the spectroscopic Sloan Digital Sky Survey data release 7 galaxy sample, the cosmic mi- crowave background observation from the 7-year Wilkinson Microwave Anisotropy Probe results, newly revised data on H（z）, as well as a value of θBAO （Z = 0.55） = （3.90° ±0.38°） for the angular BAO scale. The constraint results for the NGCG model are ωX=-1.0510＋0.1563-0.1685（1σ）＋0.2226-0.2398（2σ）,η=1.0117＋0.0469-0.0502（1σ）＋0.0693-0.0716（2σ）and ΩX=0.7297＋0.0229-0.0276（1σ）＋0.0329-0.0402（2σ）, which give a rather stringent constraint. From the results, we can see that a phantom model is slightly favored and the proba- bility that energy transfers from dark matter to dark energy is a little larger than the inverse.

关键词： new generalized Chaplygin gas -- angular BAO scale -- cosmologicalobservations

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Construction of polycyclic spirooxindoles through[3+2]annulations of Morita–Baylis–Hillman carbonates and 3-nitro-7-azaindoles

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Chinese Chemical Letters 2017年第3期28卷 512-516页

作者： kai-kai Wang Wei Du Jin zhu Ying-Chun Chen Chengdu Institute of Organic Chemistry Chinese Academy of Sciences Chengdu 610041 China Key Laboratory of Drug-Targeting and Drug Delivery System of the Ministry of Education West China School of Pharmacy Sichuan University Chengdu 610041 China University of Chinese Academy of Sciences Beijing 100049 China

A mild and efficient dearomatic [3＋2] annulation reaction of 3-nitro-7-azaindoles and Morita Baylis Hillman carbonates from isatins was developed catalyzed by DMAP, affording the corresponding polycyclic spirooxindoles containing fused azaindoline architectures and vicinal quaternary centers in excellent yields（up to 96%） with high regio- and diastereoselectivity（dr 〉 19：1）. Moderate enantioselectivity（79% ee） was obtained by employing a chiral DMAP-type Lewis base catalyst.

关键词： Morita–Baylis–Hillman carbonates [3+2] annulation Spirooxindoles Regioselectivity Dearomatization

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Analysis of Equilibrium and Kinetics of Chromium-Fluoride Complexation from Spectroscopic Data via Chemometrics Methods

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Chemical Research in Chinese Universities 2006年第4期22卷 435-438页

作者： CHEN kai zhu Zhong-liang ZHANG De-jun Department of Chemistry Tongfi University Shanghai 200092 P. R. China

The complexation of Cr^3＋ with F^- undergoes a muhistep reversible process. An approach to research the involved equilibria and kinetics using suitable chemometrics methods to the online measured UV-Vis spectra is proposed. By investigating the equilibrium spectra of the complexes at different molar ratios of M to L（ metal to ligand） and 50 ℃, the result of Principal Component Analysis（PCA） shows that three complexes, ML, ML2 and ML3, can be formed under the research conditions. The spectrum of each complex was then analyzed and the accumulated equilibrium constants were calculated by applying Target Testing Factor Analysis（TITA）. Meanwhile, a reactive intermediate was observed before the formation of MLx during the specific kinetic study at 15℃. The equilibrium constant and spectrum of the intermediate as well as the rate constants were all resolved by using TTFA.

关键词： Metal complexation Kinetics Equilibrium Reactive intermediate

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Simulation of three-phase flow and lance height effect on the cavity shape

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International Journal of Minerals,Metallurgy and Materials 2014年第6期21卷 523-530页

作者： kai Dong Rong zhu Wei Gao Fu-hai Liu School of Mechanical Engineering University of Science and Technology Beijing School of Metallurgical and Ecological Engineering University of Science and Technology Beijing Beijing Shougang Design Institute

A three-dimensional computational fluid dynamics （CFD） model was developed to simulate a 150-t top-blown converter. The ef-fect of different lance heights on the cavity shape was investigated using the volume of fluid （VOF） method. Numerical simulation results can reflect the actual molten bath surface waves impinged by the supersonic oxygen jets. With increasing lance height, the cavity depth de-creases, and the cavity area, varying like a parabola, increases and then decreases. The cavity area maximizes at the lance height of 1.3 m. Under the three different lance heights simulated in this study, all of the largest impact velocities at the molten bath surface are between 50 m/s and 100 m/s.

关键词： metallurgical furnaces basic oxygen converters lance height cavity shape computational fluid dynamics computer simulation

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Effect of temperature compensation on properties and interfacial structure evolution of Al/CFRTP ultrasonic welded joints

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Journal of Iron and Steel Research International 2024年第10期31卷 2505-2519页

作者： kai-hang zhu Yong-zhen Liang Liu-kai Li Ting-ting Zhang Wen-xian Wang College of Mechanical and Vehicle Engineering Taiyuan University of TechnologyTaiyuan030024ShanxiChina Engineering Research Center of Advanced Metal Composites Forming Technology and Equipment of Ministry of Education Taiyuan University of TechnologyTaiyuan030024ShanxiChina College of Materials Science and Engineering Taiyuan University of TechnologyTaiyuan030024ShanxiChina

5052 Al and carbon fiber-reinforced polyamide 6 composite(CF-PA6)were jointed via ultrasonic welding with the assistance of temperature compensation *** effects of the ultrasonic welding time and temperature compensation on the microstructure and mechanical properties of the joints were *** analysis of the wettability and fluidity of the molten carbon fiber-reinforced thermoplastic composites(CFRTP),the bonding mechanism and failure path of Al/CFRTP were *** results show that under the conditions of temperature compensation of 220°C and welding time of 1500 ms,the joint strength of the two components reaches 2480.4 N,which is 813.6%higher than that of Al/CFRTP components obtained at room ***,temperature compensation prolonged the wetting time of molten CFRTP on the aluminum alloy *** the fluidity and wettability were coordinated with each other,a high-quality joint was *** addition,the ultrasonic welding process of Al/CFRTP mainly relies on“physical adsorption,”“diffusion effect,”and“mechanical locking effect”to achieve sufficient bonding,and the effect of hydrogen bonding is weak.

关键词： Carbon fiber-reinforced polyamide 6 composite Ultrasonic welding Temperature compensation Mechanical property Bonding mechanism

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Study on Sound-Speed Dispersion in A Sandy Sediment at Frequency Ranges of 0.5–3 kHz and 90–170 kHz

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China Ocean Engineering 2017年第1期31卷 103-113页

作者： YU Sheng-qi LIU Bao-hua YU kai-ben kan Guang-ming YANG Zhi-guo National Deep Sea Center State Oceanic Administration Qingdao 266237 China Key Laboratory of Marine Sedimentology and Environmental Geology First Institute of Oceanography Qingdao 266061 China Laboratory for Marine Geology Qingdao National Laboratory for Marine Science and Technology Qingdao 266237 China

In order to study the properties of sound-speed dispersion in a sandy sediment, the sound speed was measured both at high frequency （90-170 kHz） and low frequency （0.5-3 kHz） in laboratory environments. At high frequency, a sampling measurement was conducted with boiled and uncooked sand samples collected from the bottom of a large water tank. The sound speed was directly obtained through transmission measurement using single source and single hydrophone. At low frequency, an in situ measurement was conducted in the water tank, where the sandy sediment had been homogeneously paved at the bottom for a long time. The sound speed was indirectly inverted according to the traveling time of signals received by three buried hydrophones in the sandy sediment and the geometry in experiment. The results show that the mean sound speed is approximate 1710-1713 m/s with a weak positive gradient in the sand sample after being boiled （as a method to eliminate bubbles as much as possible） at high frequency, which agrees well with the predictions of Biot theory, the effective density fluid model （EDFM） and Buckingham＇s theory. However, the sound speed in the uncooked sandy sediment obviously decreases （about 80%） both at high frequency and low frequency due to plenty of bubbles in existence. And the sound-speed dispersion performs a weak negative gradient at high frequency. Finally, a water-unsaturated Biot model is presented for trying to explain the decrease of sound speed in the sandy sediment with plenty of bubbles.

关键词： acoustic properties of sediment sound-speed dispersion sandy sediment bubbles

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Strongly Lensed Transient Sources:A Review

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Chinese Physics Letters 2022年第11期39卷 72-91页

作者： kai Liao Marek Biesiada Zong-Hong zhu School of Physics and Technology Wuhan UniversityWuhan 430072China National Centre for Nuclear Research Pasteura 702-093 WarsawPoland Department of Astronomy Beijing Normal UniversityBeijing 100875China

The past decades have witnessed a lot of progress in gravitational lensing with two main targets:stars and galaxies(with active galactic nuclei).The success is partially attributed to the continuous luminescence of these sources making the detection and monitoring relatively *** the running of ongoing and upcoming large facilities/surveys in various electromagnetic and gravitational-wave bands,the era of time-domain surveys would guarantee constant detection of strongly lensed explosive transient events,for example,supernovae in all types,gamma ray bursts with afterglows in all bands,fast radio bursts,and even gravitational *** transients have many advantages over the traditional targets in studying the Universe,and magnification effect helps to understand the transients themselves at high *** this review article,on base of the recent achievements in literature,we summarize the methods of searching for different kinds of lensed transient signals,the latest results on detection and their applications in fundamental physics,astrophysics,and *** the same time,we give supplementary comments as well as prospects of this emerging research direction that may help readers who are interested in entering this field.

关键词： gravitational galaxies stars

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