Highly thermo-conductive aqueous medium is a crucial premise to demonstrate high-performance thermal-related applications.Graphene has the diamond comparable thermal conductivity,while the intrinsic two-dimensional re...Highly thermo-conductive aqueous medium is a crucial premise to demonstrate high-performance thermal-related applications.Graphene has the diamond comparable thermal conductivity,while the intrinsic two-dimensional reality will result in strong anisotropic thermal conductivity and wrinkles or even crumples that significantly sacrifices its inherent properties in practical applications.One strategy to overcome this is to use three-dimensional(3D)architecture of graphene.Herein,3D graphene structure with covalent-bonding nanofins(3D-GS-CBF)is proposed,which is then used as the filler to demonstrate effective aqueous medium.The thermal conductivity and thermal conductivity enhancement efficiency of 3D-GS-CBF(0.26 vol%)aqueous medium can be as high as 2.61 W m-1 K-1 and 1300%,respectively,around six times larger than highest value of the existed aqueous mediums.Meanwhile,3D-GS-CBF can be stable in the solution even after 6 months,addressing the instability issues of conventional graphene networks.A multiscale modeling including non-equilibrium molecular dynamics simulations and heat conduction model is applied to interpret experimental results.3D-GS-CBF aqueous medium can largely improve the solar vapor evaporation rate(by 1.5 times)that are even comparable to the interfacial heating system;meanwhile,its cooling performance is also superior to commercial coolant in thermal management applications.展开更多
Recently, the Tertiary red clay sequence underlying Pleistocene loess has attracted much attention. The remarkable progress is the recognition that the Tertiary red clay sequence is also wind-blown in origin, thus pro...Recently, the Tertiary red clay sequence underlying Pleistocene loess has attracted much attention. The remarkable progress is the recognition that the Tertiary red clay sequence is also wind-blown in origin, thus providing a good opportunity to reconstruct long-term monsoon changes. In contrast to the loess deposits, the magnetic susceptibility and the pedogenic characteristics are almost independent of each other in the red clay, thus challenging the validity of the readily measurable magnetic susceptibility in describing the monsoon history recorded by the red clay. With the objective to address the long-term East Asia summer monsoon evolution, the free to total Fe2O3 ratios were calculated in a continuous eolian red clay-loess sequence at Lingtai, the Chinese Loess Plateau, which has a thickness of 305 m and a basal age of 7.0 Ma. The seven million-year Fe2O3 ratio record from the red clay-loess sequence indicates that (i) variations of the free to total Fe2O3 ratios of the loess can correlate展开更多
lsotopic analyses for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai (35°N), the Loess Plateau. Stable carbon isotopic ...lsotopic analyses for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai (35°N), the Loess Plateau. Stable carbon isotopic composition indicates that ( ⅰ ) C<sub>4</sub> plants might be present at least by7.0 Ma; ( ⅱ ) C<sub>4</sub> plants expanded gradually between ~4.0 and ~3.2 Ma, and their biomass fraction was up to 50%; and ( ⅲ ) the biomass of C<sub>4</sub> vegetation since ~2.0 Ma seems to have been decreased to the level (about 20%) before 4.0 Ma. C<sub>4</sub> plant expansion at Lingtai cannot be fully understood with the 'global C<sub>4</sub> expansion' model because it occurred much later up to 3.0 Ma than in Pakistan, which indicates that some changes in the regional climatic system may also contribute to C<sub>3</sub>/C<sub>4</sub> shift except changes in atmospheric CO<sub>2</sub> concentrations and temperature. The latitudinal zone for C<sub>3</sub>/C<sub>4</sub> transition seems to move southwards slightly in East Asia, compared with the case in North America where 37°N is the ideal展开更多
The impact of global warming on the climate of northern China has been investigated intensively, and the behavior of the East Asian monsoon during previous intervals of climatic warming may provide insight into future...The impact of global warming on the climate of northern China has been investigated intensively, and the behavior of the East Asian monsoon during previous intervals of climatic warming may provide insight into future changes. In this study, we use paleovegetation records from loess and lake sediments in the marginal zone of the East Asian summer monsoon(EASM) to reconstruct the EASM during the interval of warming from the Last Glacial Maximum(LGM) to the Holocene. The results show that during the LGM, desert steppe or dry steppe dominated much of northern China;in addition, the southeastern margin of the deserts east of the Helan Mountains had a distribution similar to that of the present-day, or was located slightly further south, due to the cold and dry climate caused by a strengthened East Asian winter monsoon(EAWM) and weakened EASM. During the last deglaciation, with the strengthening of the EASM and concomitant weakening of the EAWM, northern China gradually became humid. However, this trend was interrupted by abrupt cooling during the Heinrich 1(H1) and Younger Dryas(YD) events. The EASM intensified substantially during the Holocene, and the monsoon rain belt migrated at least 300 km northwestwards, which led to the substantial shrinking of the desert area in the central and eastern part of northern China, and to the large expansion of plants favored by warm and humid conditions. Paleoclimatic records from the marginal zone of the EASM all show that the EASM reached its peak in the mid-Holocene, and past global climatic warming significantly strengthened the EASM, thereby greatly improving the ecological environment in northern China. Thus, northern China is expected to become wetter as global warming continues. Finally, high resolution Holocene vegetation records are sparse compared with the numerous records on the orbital timescale, and there is a need for more studies of Holocene climatic variability on the centennial-to-decadal scale.展开更多
基金the financial support from National Natural Science Foundation of China(No.51906211)the China Postdoctoral Science Foundation(No.2019M662048)+1 种基金the Key R&D Program of Zhejiang Province(No.2019C01044)the Zhejiang Provincial Natural Science Foundation of China(No.LR17E060002)。
文摘Highly thermo-conductive aqueous medium is a crucial premise to demonstrate high-performance thermal-related applications.Graphene has the diamond comparable thermal conductivity,while the intrinsic two-dimensional reality will result in strong anisotropic thermal conductivity and wrinkles or even crumples that significantly sacrifices its inherent properties in practical applications.One strategy to overcome this is to use three-dimensional(3D)architecture of graphene.Herein,3D graphene structure with covalent-bonding nanofins(3D-GS-CBF)is proposed,which is then used as the filler to demonstrate effective aqueous medium.The thermal conductivity and thermal conductivity enhancement efficiency of 3D-GS-CBF(0.26 vol%)aqueous medium can be as high as 2.61 W m-1 K-1 and 1300%,respectively,around six times larger than highest value of the existed aqueous mediums.Meanwhile,3D-GS-CBF can be stable in the solution even after 6 months,addressing the instability issues of conventional graphene networks.A multiscale modeling including non-equilibrium molecular dynamics simulations and heat conduction model is applied to interpret experimental results.3D-GS-CBF aqueous medium can largely improve the solar vapor evaporation rate(by 1.5 times)that are even comparable to the interfacial heating system;meanwhile,its cooling performance is also superior to commercial coolant in thermal management applications.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA19050104 and XDB26020401)the National Key Research and Development Program of China(2017YFA0603404)+1 种基金the National Natural Science Foundation of China(42007282 and 42077409)the Key Research Program of the Institute of Geology&Geophysics,Chinese Academy of Sciences(IGGCAS-201905)。
基金supported by the National Natural Science Foundation of China(41725010 and 42107472)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB26000000 and XDB31000000)the Key Research Program of the Institute of Geology&Geophysics,Chinese Academy of Sciences(IGGCAS-201905)。
文摘上新世(5.33~2.58 Ma)是距今最近的大气CO_(2)浓度超过400 ppmv的暖期,是理解未来气候变化的地质历史相似型.地质记录显示,上新世气候主要响应地球倾角和岁差变化,比如深海氧同位素和高纬陆相记录表现出强的倾角周期(41 ka),低纬和地中海地区的粉尘和花粉记录以岁差周期(21 ka)为主.然而,这些气候周期空间差异的机制尚不清楚.我们使用全球海气耦合模式HadCM3,开展了轨道参数极值实验.结果表明:(1)倾角变化主要对高纬温度影响显著(>5℃),很好地解释了高纬记录和受高纬冰量调节的深海氧同位素记录的41 ka周期;(2)岁差变化主要影响低纬降水(>2 mm d-1),很好地解释了低纬和地中海地区与季风活动相关的21 ka气候周期.
基金the National Natural Science Foundation of China (Grant No. 49525203).
文摘Recently, the Tertiary red clay sequence underlying Pleistocene loess has attracted much attention. The remarkable progress is the recognition that the Tertiary red clay sequence is also wind-blown in origin, thus providing a good opportunity to reconstruct long-term monsoon changes. In contrast to the loess deposits, the magnetic susceptibility and the pedogenic characteristics are almost independent of each other in the red clay, thus challenging the validity of the readily measurable magnetic susceptibility in describing the monsoon history recorded by the red clay. With the objective to address the long-term East Asia summer monsoon evolution, the free to total Fe2O3 ratios were calculated in a continuous eolian red clay-loess sequence at Lingtai, the Chinese Loess Plateau, which has a thickness of 305 m and a basal age of 7.0 Ma. The seven million-year Fe2O3 ratio record from the red clay-loess sequence indicates that (i) variations of the free to total Fe2O3 ratios of the loess can correlate
文摘lsotopic analyses for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai (35°N), the Loess Plateau. Stable carbon isotopic composition indicates that ( ⅰ ) C<sub>4</sub> plants might be present at least by7.0 Ma; ( ⅱ ) C<sub>4</sub> plants expanded gradually between ~4.0 and ~3.2 Ma, and their biomass fraction was up to 50%; and ( ⅲ ) the biomass of C<sub>4</sub> vegetation since ~2.0 Ma seems to have been decreased to the level (about 20%) before 4.0 Ma. C<sub>4</sub> plant expansion at Lingtai cannot be fully understood with the 'global C<sub>4</sub> expansion' model because it occurred much later up to 3.0 Ma than in Pakistan, which indicates that some changes in the regional climatic system may also contribute to C<sub>3</sub>/C<sub>4</sub> shift except changes in atmospheric CO<sub>2</sub> concentrations and temperature. The latitudinal zone for C<sub>3</sub>/C<sub>4</sub> transition seems to move southwards slightly in East Asia, compared with the case in North America where 37°N is the ideal
基金supported by the National Key Research and Development Program of China (Grant No. 2017YFA0603403)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos. XDB26000000 & XDA05120204)the National Natural Science Foundation of China (Grant Nos. 41672175 & 41725010)
文摘The impact of global warming on the climate of northern China has been investigated intensively, and the behavior of the East Asian monsoon during previous intervals of climatic warming may provide insight into future changes. In this study, we use paleovegetation records from loess and lake sediments in the marginal zone of the East Asian summer monsoon(EASM) to reconstruct the EASM during the interval of warming from the Last Glacial Maximum(LGM) to the Holocene. The results show that during the LGM, desert steppe or dry steppe dominated much of northern China;in addition, the southeastern margin of the deserts east of the Helan Mountains had a distribution similar to that of the present-day, or was located slightly further south, due to the cold and dry climate caused by a strengthened East Asian winter monsoon(EAWM) and weakened EASM. During the last deglaciation, with the strengthening of the EASM and concomitant weakening of the EAWM, northern China gradually became humid. However, this trend was interrupted by abrupt cooling during the Heinrich 1(H1) and Younger Dryas(YD) events. The EASM intensified substantially during the Holocene, and the monsoon rain belt migrated at least 300 km northwestwards, which led to the substantial shrinking of the desert area in the central and eastern part of northern China, and to the large expansion of plants favored by warm and humid conditions. Paleoclimatic records from the marginal zone of the EASM all show that the EASM reached its peak in the mid-Holocene, and past global climatic warming significantly strengthened the EASM, thereby greatly improving the ecological environment in northern China. Thus, northern China is expected to become wetter as global warming continues. Finally, high resolution Holocene vegetation records are sparse compared with the numerous records on the orbital timescale, and there is a need for more studies of Holocene climatic variability on the centennial-to-decadal scale.