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Snow cover influences the thermal regime of active layer in Urumqi River Source,Tianshan Mountains,China

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Journal of Mountain Science 2018年第12期15卷 2622-2636页

作者： ZHAO Jing-yi CHEN Ji wu qing-bai HOU Xin State Key Laboratory of Frozen Soil Engineering Northwest Institute of Eco-environment and ResourcesChinese Academy of SciencesLanzhou 730000China University of Chinese Academy of Sciences Beijing 100049China Beiluhe Observation and Research Station on Frozen soil Engineering and Environment in qinghai-Tibet Plateau Northwest Institute of Eco-environment and ResourcesChinese Academy of SciencesLanzhou 730000China

Snow cover is characterized by the high albedo, low thermal conductivity, and notable heat transition during phase changes. Thus, snow cover significantly affects the ground thermal regime. A comparison of the snow cover in high latitudes or high-altitude snowy mountain regions indicates that the eastern Tianshan Mountains(China) show a characteristically thin snow cover(snow depth below 15 cm) with remarkable temporal variability. Based on snow depth, heat flux, and ground temperature from 2014 to 2015 in the Urumqi River source, the spatialtemporal characteristics of snow cover and snow cover influences on the thermal conditions of active layer in the permafrost area were analyzed. During the autumn(Sept.-Oct.), thin and discontinuous snow cover can noticeably accelerate the exothermic process of the ground, producing a cooling effect on the shallow soil. During the winter(Nov.-Mar.), it is inferred that the effective thermal insulation starts with snow depth exceeding 10 cm during early winter.However, the snow depth in this area is generally below 15 cm, and the resulting snow-induced thermal insulation during the winter is very limited. Due to common heavy snowfalls in the spring(Apr. to May), the monthly mean snow thickness in April reached to 15 cm and remained until mid-May. Snow cover during the spring significantly retarded the ground warming. Broadly, snow cover in the study area exerts a cooling effect on the active layer and plays a positive role in the development and preservation of permafrost.

关键词： Snow cover Permafrost Ground temperature Tianshan Mountains Heat flux

Degrading permafrost and its impacts

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Advances in Climate Change Research 2021年第1期12卷 1-5页

作者： JIN Hui-Jun wu qing-bai Vladimir E.ROMANOVSKY Northeast-China Observatory and Research Station of Permafrost Geological Environment(Ministry of Education) School of Civil EngineeringInstitute of Cold Region Scienceand TechnologyNortheast Forestry UniversityHarbin150040China State Key Laboratory of Frozen Soils Engineering Northwest Institute of Eco-Environment and ResourcesChinese Academy of SciencesLanzhou730000China Geophysical Institute University of Alaska FairbanksFairbanks99775USA

1.Introduction Permafrost is present extensively in polar,high-plateau,alpine,and mountainous regions,with a model-estimated total extent of permafrost regions at 22.79 million km^(2)(Gruber,2012).However,among ever increasing modeling results,these estimates are based on applications of different permafrost models of various validity,but with a large range of uncertainty.Permafrost affects terrestrial ecosystems and ground hydrothermal dynamics,biogeochemical cycles,engineered infrastructures,and socioeconomic development to varied extents.Under a warming climate,permafrost has been degrading extensively.Permafrost studies have been flourishing due to increasing concerns on the climatic feedbacks of permafrost carbon,ecological impacts from degrading permafrost,sustainable water supplies,and engineering ramifications.

关键词： terrestrial mountainous plateau

Permafrost change in Northeast China in the 1950s-2010s

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Advances in Climate Change Research 2021年第1期12卷 18-28页

作者： ZHANG Zhong-Qiong wu qing-bai HOU Mei-Ting TAI Bo-Wen AN Yu-Ke State Key Laboratory of Frozen Soils Engineering Northwest Institute of Eco-Environment and ResourcesChinese Academy of ScienceLanzhou730000China China Meteorological Administration Training Centre Beijing100081China Gansu Province Transportation Planning Survey&Design Institute Limited Liability CompanyLanzhou730000China

Permafrost in Northeast China is highly sensitive to climate warming.Permafrost degradation significantly affects forest and vegetation ecosystems,as well as the safety of engineering projects and other man-made infrastructures.However,the permafrost change in the region is still unclear.This study uses metrological data from 258 weather stations,alongside reanalysis data,and other environmental data to investigate permafrost degradation and its related environmental impacts in Northeast China from the 1950s to 2010s.Results show that the total permafrost area decreased from 4.8×10^(5)to 3.1×10^(5)km^(2)from the 1950s to the 2010s.The southern limit of permafrost moved 0.1-1.1°northward,and its average elevation rose 160.5 m.During the study period,the degradation of predominantly continuous permafrost,and discontinuous and island permafrost was more pronounced than that of sparsely island permafrost.The south boundary of those three permafrost zones northward by 0-3.4°,0-5.5°and 0.4-1.1°,the average altitude raised by 339.2 m,208.3 m,67.1 m.The permafrost degradation shows the elevation and latitude zonality.Permafrost degradation is mainly caused by the rising of surface temperatures and the impacts of other environmental factors.The snowfall warming the ground of 1.1-10.2℃in cold seasons and rainfall cooling on surface conditions in warm seasons,those may result in temporal and spatial differences in permafrost degradation.However,there are lack of researches in the impact of environment factors on soil temperatures,moisture and permafrost degradation.

关键词： Northeast China Climate warming Permafrost degradation Impact of environmental factors

Seasonal variations of organic carbon and nitrogen in the upper basins of Yangtze and Yellow Rivers

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Journal of Mountain Science 2017年第8期14卷 1577-1590页

作者： LI Xiang-ying DING Yong-jian HAN Tian-ding XU Jian-zhong KANG Shi-chang wu qing-bai Mika Sillanp?? YU Zhong-bo YU Cong-rong College of Hydrology and Water Resources/State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hohai University State Key Laboratory of Cryospheric Sciences Northwest Institute of Eco-Environment and ResourcesChinese Academy of Sciences University of Chinese Academy of Sciences State Key Laboratory of Frozen Soil Engineering Northwest Institute of Eco-Environment and ResourcesChinese Academy of Sciences Laboratory of Green Chemistry School of Engineering ScienceLappeenranta University of Technology Department of Civil and Environmental Engineering Florida International University

The profound impacts exerted by climate warming on the Tibetan Plateau have been documented extensively, but the biogeochemical responses remain poorly understood. This study was aimed at seasonal variations of total organic carbon(TOC) and total organic nitrogen(TON) in stream water at two gauging sections(TTH, ZMD) in the upper basin of Yangtze River(UBYA) and at fourgauging sections(HHY, JM, JG, TNH) in the upper basin of Yellow River(UBYE) in 2013. Results showed that concentrations of TON exhibit higher values in spring and winter and lower values in summer. TOC exhibits higher concentrations in spring or early summer and lower concentrations in autumn or winter. Seasonal variations of TOC and TON fluxes are dominated by water flux. In total, the UBYE and UBYA delivers 55,435 tons C of organic carbon and 9,872 tons N of organic nitrogen to downstream ecosystems in 2013. Although the combined flux ofTOC from UBYA and UBYE is far lower than those from large rivers, their combined yields is higher than, or comparable with, those from some large rivers(e.g. Nile, Orange, Columbia), implying that organic carbon from the Tibetan Plateau may exert a potentially influence on regional and/or global carbon cycles in future warming climate.

关键词：山地科学

Thermal stability of permafrost under U-shaped crushed rock embankment of the qinghai-Tibet Railway

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Advances in Climate Change Research 2024年第1期15卷 158-169页

作者： Kun-Ming XU Guan-Li JIANG Ji CHEN qing-bai wu State Key Laboratory of Frozen Soil Engineering Northwest Institute of Eco-Environment and ResourcesChinese Academy of SciencesLanzhou 730000China University of Chinese Academy of Sciences Beijing 100049China Beiluhe Observation Station of Frozen Soil Environment and Engineering Northwest Institute of Eco-Environment and ResourcesChinese Academy of SciencesLanzhou730000China

The U-shaped crushed rock embankment(UCRE),of which widely utilized in the permafrost regions along the qinghai-Tibet Railway,has the capability to rapidly reduce the ground temperature of the underlying permafrost.However,there remains uncertainty regarding the adaptation of UCRE to climate change and its long-term cooling trend.This study focuses on nine UCRE monitoring sites along the qinghai-Tibet Railway to analyze the dynamic variations of the ground temperature underlying permafrost from 2006 to 2020.The efficiency of UCRE in stabilizing permafrost temperature in different permafrost zones is evaluated by considering the permafrost table,ground temperature,and MAGT,as well as the temperature difference between the top and bottom of the crushed rock layer and the ground temperature variation index(GTVI).The results show that UCRE is suitable for application in extremely unstable warm permafrost regions where the MAGT is higher than-0.5℃.Moreover,UCRE effectively diminishes the disparity in permafrost thermal stability between the sunny and shaded shoulders of the embankment.The short-term and long-term effect of cooling permafrost is experiencing a change related with permafrost stability.Notably,in stable cold permafrost regions with MAGT lower than-1.5℃,the long-term cooling effect of UCRE on permafrost seems to gradually di-minishes,but UCRE continues to fulfill the role of stabilizing the underlying permafrost thermal state over the long-term.These results show that UCRE can quickly restore and stabilize the thermal state of permafrost in the early stages of construction,and adapt to the influence of future climate change.The findings provide important guidance for understanding the variations of permafrost thermal stability beneath the embankment in permafrost regions,as well as for improving the embankment stability and operational safety of the qinghai-Tibet Railway.

关键词： qinghai-Tibet Railway U-shaped crushed rock embankment Climate change Permafrost zone Ground temperature variation index Long-term coolingrole

Effect of stress-relief annealing on thermal fatigue cracks for die-casting die steels

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Journal of Iron and Steel Research(International) 2024年第5期31卷 1164-1176页

作者： Zhi-xiong bai Xiao-chun wu School of Materials Science and Engineering Shanghai UniversityShanghai200444China

The effect of stress-relief annealing at different stages of thermal fatigue tests on crack growth was investigated using a self-built thermal cycle setup.The results showed that annealing could limit crack expansion effectively.It reduced dislocation density and released the accumulation of residual stress.In addition,the strain accumulation in carbides was reduced by this process.It was also found that double annealing was even more effective at inhibiting crack expansion compared to single stress-relief annealing.After 1000 cycles,the maximum crack length was reduced by 31.1%and 45.2%for the samples after using the optimal single and double annealing processes,respectively.For single stress-relief annealing,earlier annealing provides more benefit in delaying crack expansion.However,effective double stress-relief annealing requires a suitable time interval between the annealing steps.Besides,after 800 cycles,surface hardness decreased significantly accompanied by an increase in the size and number of carbides,and cracks expanded predominantly along grain boundaries.

关键词： Thermal fatigue Steel Carbide Stress-relief annealing Dislocation Residual stress

Palladium-catalyzed multi components oxy-aminofluorination and aminofluorination of gem-difluoroalkenes

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Chinese Chemical Letters 2024年第2期35卷 420-425页

作者： Fen wu Xin Li Junbiao Chang Dachang bai State Key Laboratory of Antiviral Drugs NMPA Key Laboratory for Research and Evaluation of Innovative DrugKey Laboratory of Green Chemical Media and ReactionsMinistry of EducationSchool of Chemistry and Chemical EngineeringPingyuan LaboratoryHenan Normal UniversityXinxiang 453007China State Key Laboratory of Organometallic Chemistry Shanghai Institute of Organic ChemistryChinese Academy of SciencesShanghai 200032China

Organofluorine compounds are widely used in the realm of drug discovery and material science.Herein,we developed palladium catalyzed intermolecular aminofluorination and oxy-aminofluorination of gem‑difluoroalkenes with N-fluorobenzenesulfonimide(NFSI),in which NFSI was used as the nitrogen source and oxidant.The reaction provides an efficient and straightforward synthesis route of a series ofα-trifluoromethyl benzylic amines.Notably,three/four components oxy-aminofluorination processes were realized to giveα-trifluoromethyl benzylic ether with a terminal amino group,which proceed through C(sp^(3))-O bond cleavage of easily available ether and simultaneous introduced a fluorine,an amino and an oxy substituent in one pot with excellent regioselectivity.The divergent reactivity not only included the incorporation of one ether molecular,but also much more challenged two ether insertion with excellent selectivity through succession C(sp^(3))-O bonds cleavage.This protocol allows for concise synthesis of high value amines with fluoroalkyl-substituents and selectively transformation of easily available ethers by high-valent palladium catalysis.

关键词： Palladium Multi components Aminofluorination Oxy-aminofluorination C(sp^(3))-O bond cleavage

Numerical Study on Local Flow and Heat Transfer Characteristics of Supercritical CO_(2) in PCHE with Sinusoidal Channels

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Journal of Thermal Science 2024年第1期33卷 41-55页

作者： WENZhexi LV Yigao LI qing wu Jinglin School of Energy Science and Engineering Central South UniversityChangsha 410083China

Local heat transfer and flow characteristics,which is crucial to the overall performance of supercritical CO_(2) recuperators,is rarely examined in details in reported studies.In this paper,the local heat transfer and flow characteristics of supercritical CO_(2) in sinusoidal channel printed circuit heat exchangers are numerically investigated under the working conditions of recuperators.Based on the simplified physical model constituted by10 pitches,the variations of Re,heat flux,Nu,secondary flow and other relevant parameters along the flow direction are analyzed firstly.Comparison is further made between the high and low temperature recuperators(HTR and LTR).It's observed that the local heat transfer and flow characteristics vary greatly from the inlet to the outlet,especially in the LTR.Differences of 127.5% and 61.7% can be observed on the cold side of the LTR for Re and heat transfer coefficient h, respectively.Results indicate that the temperature difference and heat transfer coefficient h should not be regarded as constant and the distribution of h should be carefully considered in the design of the LTR.The complicated interactions among the varying thermophysical properties,buoyancy and the periodically changed centrifugal force are believed to be the key that shapes the flow fields.Furthermore,the changes of the wavy angle θ are found to have greater influence than the changes of mass flow rate in reshaping the flow field when θ>25°.Though gravity direction strongly affects the local heat transfer and flow characteristics,it's also found that the effects on the overall thermal-hydraulic performance are relatively minor.Yet the installation direction that yields a_y=g should better be avoided for the sinusoidal channel printed circuit heat exchanger.

关键词： printed circuit heat exchanger supercritical CO_(2) sinusoidal channel heat transfer recuperator

Decouple charge transfer reactions in the Li-ion battery

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Journal of Energy Chemistry 2024年第5期92卷 759-798页

作者： Yuxuan bai Qiu-An Huang Kai wu Jiujun Zhang Institute for Sustainable Energy/College of Sciences Shanghai UniversityShanghai 200444China Ningde Contemporary Innovation Laboratory Contemporary Amperex Technology Co.LimitedNingde 352100FujianChina

In the development of Li-ion batteries(LIBs)with high energy/power density,long cycle-life,fast charging,and high safety,an insight into charge transfer reactions is required.Although electrochemical impedance spectroscopy(EIS)is regarded as a powerful diagnosis tool,it is not a direct but an indirect measurement.With respect to this,some critical questions need to be answered:(i)why EIS can reflect the kinetics of charge transfer reactions;(ii)what the inherent logical relationship between impedance models under different physical scenes is;(iii)how charge transfer reactions compete with each other at multiple scales.This work aims at answering these questions via developing a theory framework so as to mitigate the blindness and uncertainty in unveiling charge transfer reactions in LIBs.To systematically answer the above questions,this article is organized into a three-in-one(review,tutorial,and research)type and the following contributions are made:(i)a brief review is given for impedance model development of the LIBs over the past half century;(ii)an open source code toolbox is developed based on the unified impedance model;(iii)the competive mechanisms of charge transfer reactions are unveiled based on the developed EIS-Toolbox@LIB.This work not only clarifies theoretical fundamentals,but also provides an easy-to-use open source code for EIS-Toolbox@LIB to optimize fast charge/discharge,mitigate cycle aging,and improve energy/power density.

关键词： Electrochemical impedance spectroscopy Unified impedance model Charge transfer reactions Solid/electrolyte diffusion Porous electrode EIS-Toolbox@LIB