Artemisia ordosica Krasch. is a dominant shrub occurring mainly on stable sand dunes in the Gobi Desert of China, in the Mongolian phytogeographic region. Achenes of A. ordosica germinate in light but poorly in ...Artemisia ordosica Krasch. is a dominant shrub occurring mainly on stable sand dunes in the Gobi Desert of China, in the Mongolian phytogeographic region. Achenes of A. ordosica germinate in light but poorly in dark and light is the limiting factor regulating the achene germination in sand depth. Achenes germinate in spring or autumn with an optimal temperature of 20 ℃. Achene mucilage can absorb large amounts of water and has important ecological function. Salt concentrations and sand moisture may regulate achene germination in sand. A. ordosica, A. sphaerocephala Krasch. and A. monosperma Delile. from different climates have similar responses to light, the underground location of achene, and sand moisture. Percentage of seedling emergence from different levels of sand depth is depends on the specific, temperature and intensity of light penetrating through the sand depths, as well as on sand moisture. The desert sand habitat seems to have had a dominant influence on the evolution of the germination strategies of these 3 Artemisia species.展开更多
Permafrost on the Qinghai-Tibet Plateau (QTP) is widespread, thin, and thermally unstable. Under a warming climate during the past few decades, it has been degrading extensively with generally rising ground temperatur...Permafrost on the Qinghai-Tibet Plateau (QTP) is widespread, thin, and thermally unstable. Under a warming climate during the past few decades, it has been degrading extensively with generally rising ground temperatures, the deepening of the maximum summer thaw, and with lessening of the winter frost penetration. The permafrost has degraded downward, upward and laterally. Permafrost has thinned or, in some areas, has totally disappeared. The modes of permafrost degradation have great significance in geocryology, in cold regions engineering and in cold regions environmental management. Permafrost in the interior of the QTP is well represented along the Qing-hai-Tibet Highway (QTH), which crosses the Plateau through north to south and traverses 560 km of permafrost-impacted ground. Horizontally, the degradation of permafrost occurs more visibly in the sporadic permafrost zone in the vicinity of the lower limit of permafrost (LLP), along the margins of taliks, and around permafrost islands. Downward degradation develops when the maximum depth of seasonal thaw exceeds the maximum depth of seasonal frost, and it generally results in the formation of a layered talik disconnecting the permafrost from the seasonal frost layer. The downward degrada- tion is divided into four stages: 1) initial degradation, 2) accelerated degradation, 3) layered talik and 4) finally the conversion of permafrost to seasonally frozen ground (SFG). The upward degradation occurs when the geothermal gradient in permafrost drops to less than the geothermal gradients in the underlying thawed soil layers. Three types of permafrost temperature curves (stable, degrading, and phase-changing transitory permafrost) illustrate these modes. Although strong differentiations in local conditions and permafrost types exist, the various combinations of the three degradation modes will ultimately transform permafrost into SFG. Along the QTH, the downward degradation has been proceeding at annual rates of 6 to 25 cm, upward degradation at 12 to 30 cm, and later展开更多
The increased prevalence of high temperatures （HTs） around the world is a major global concern, as they dramatically affect agronomic productivity. Upon HT exposure, plants sense the temperature change and initiate ...The increased prevalence of high temperatures （HTs） around the world is a major global concern, as they dramatically affect agronomic productivity. Upon HT exposure, plants sense the temperature change and initiate cellular and metabolic responses that enable them to adapt to their new environmental conditions.Decoding the mechanisms by which plants cope with HT will facilitate the development of molecular markers to enable the production of plants with improved thermotolerance. In recent decades, genetic, physiological, molecular, and biochemical studies have revealed a number of vital cellular components and processes involved in thermoresponsive growth and the acquisition of thermo- tolerance in plants. This review summarizes the major mechanisms involved in plant HT responses, with a special focus on recent discoveries related to plant thermosensing, heat stress signaling, and HT-regulated gene expression networks that promote plant adaptation to elevated environmental temperatures.展开更多
Based on data from six meteorological stations in the permafrost regions, 60 boreholes for long-term monitoring of permafrost temperatures, and 710 hand-dug pits and shallow boreholes on the Qinghai-Tibet Plateau （QT...Based on data from six meteorological stations in the permafrost regions, 60 boreholes for long-term monitoring of permafrost temperatures, and 710 hand-dug pits and shallow boreholes on the Qinghai-Tibet Plateau （QTP）, the spatiotemporal variability of permafrost degradation was closely examined in relation to the rates of changes in air, surface, and ground temperatures. The de- cadal averages and increases in the mean annual air temperatures （MAATs） from 1961-2010 were the largest and most persistent during the last century. MAATs rose by 1.3 ℃, with an average increase rate of 0.03 ℃/yr. The average of mean annual ground surface temperatures （MAGSTs） increased by 1.3 ℃ at an average rate of 0.03 ℃/yr. The rates of changes in ground temperatures were -0.01 to 0.07 ℃/yr. The rates of changes in the depths of the permafrost table were -1 to ＋10 cm/yr. The areal extent of permafrost on the QTP shrank from about 1.50× 10^6 km^2 in 1975 to about 1.26× 10^6 km^2 in 2006. About 60% of the shrinkage in area of permafrost occurred during the period from 1996 to 2006. Due to increasing air temperature since the late 1980s, warm （〉-1 ℃） permafrost has started to degrade, and the degradation has gradually expanded to the zones of transitory （-1 to -2 ℃） and cold （〈-2 ℃） permafrost. Permafrost on the southern and southeastem plateau degrades more markedly. It is projected that the degradation of permafrost is likely to accelerate, and substantial changes in the distributive features and thermal regimes of permafrost should be anticipated. However, regarding the relationships between degrading permafrost and the degradation of rangelands, it is still too early to draw reliable conclusions due to inadequate scientific criteria and evidence.展开更多
Carbon dioxide（CO2） capture using magnesium oxide（MgO）-based adsorbents at intermediate temperatures has been regarded as a very prospective technology for their relatively high adsorption capacity,low cost, and w...Carbon dioxide（CO2） capture using magnesium oxide（MgO）-based adsorbents at intermediate temperatures has been regarded as a very prospective technology for their relatively high adsorption capacity,low cost, and wide availability. During the past few years, great effort has been devoted to the fabrication of molten salts-modified MgO-based adsorbents. The extraordinary progress achieved by coating with molten salts greatly promotes the COcapture capacity of MgO-based adsorbents. Therefore, we feel it necessary to deliver a timely review on this type of COcapturing materials, which will benefit the researchers working in both academic and industrial areas. In this work, we classified the molten saltsmodified MgO adsorbents into four categories:（1） homogenous molten salt-modified MgO adsorbents,（2） molten salt-modified double salts-based MgO adsorbents,（3） mixed molten salts-modified MgO adsorbents, and（4） molten salts-modified MgO-based mixed oxides adsorbents. This contribution critically reviews the recent developments in the synthetic method, adsorption capacity, reaction kinetics, promotion mechanism, operational conditions and regenerability of the molten salts-modified MgO COadsorbents. The challenges and prospects in this promising field of molten salts-modified MgO COadsorbents in real applications are also briefly mentioned.展开更多
Outstanding mechanical properties of graphene nanoplatelets(GNPs)make them ideal reinforcement for mass production of composites.In this research,the composites were fabricated by stir-casting method.GNPs were added i...Outstanding mechanical properties of graphene nanoplatelets(GNPs)make them ideal reinforcement for mass production of composites.In this research,the composites were fabricated by stir-casting method.GNPs were added in 1.5 and 3.0 wt.%into Mg–3wt.%Al–1wt.%Zn(AZ31)magnesium alloy.As cast ingots were preheated for one hour and extruded at 350℃ with extrusion ratio of 5.2:1.As extruded AZ31-GNPs composites were micro-structurally characterized with X-ray diffraction,optical microscopy and scanning electron microscopy.Vickers microhardness of synthesized materials was investigated both in parallel and perpendicular to extrusion directions.Room temperature mechanical testing revealed that with increasing GNP’s content,tensile fracture strain was remarkably increased without significant compromise in tensile strength.Furthermore,as extruded AZ31-3GNPs composites were subjected to tensile testing at temperatures ranging from 75℃ to 300℃ with initial strain rate of 2×10^(−3)s^(−1) to evaluate high temperature formability of composite.It was found that like CNTs,GNPs also have the potential to sustain tensile strength at high temperatures.展开更多
文摘Artemisia ordosica Krasch. is a dominant shrub occurring mainly on stable sand dunes in the Gobi Desert of China, in the Mongolian phytogeographic region. Achenes of A. ordosica germinate in light but poorly in dark and light is the limiting factor regulating the achene germination in sand depth. Achenes germinate in spring or autumn with an optimal temperature of 20 ℃. Achene mucilage can absorb large amounts of water and has important ecological function. Salt concentrations and sand moisture may regulate achene germination in sand. A. ordosica, A. sphaerocephala Krasch. and A. monosperma Delile. from different climates have similar responses to light, the underground location of achene, and sand moisture. Percentage of seedling emergence from different levels of sand depth is depends on the specific, temperature and intensity of light penetrating through the sand depths, as well as on sand moisture. The desert sand habitat seems to have had a dominant influence on the evolution of the germination strategies of these 3 Artemisia species.
基金This work was supprted by CAS Hundred Talents Progam"Stability of linear engineering foundations in warm permafrost regions under a changing cimte"(2004)CAS Knowledge Inovation Key Programs(Grant Nos.KZCX1-SW-04,KZCX3-SW-345 and KZCX3-SW-339-3).
文摘Permafrost on the Qinghai-Tibet Plateau (QTP) is widespread, thin, and thermally unstable. Under a warming climate during the past few decades, it has been degrading extensively with generally rising ground temperatures, the deepening of the maximum summer thaw, and with lessening of the winter frost penetration. The permafrost has degraded downward, upward and laterally. Permafrost has thinned or, in some areas, has totally disappeared. The modes of permafrost degradation have great significance in geocryology, in cold regions engineering and in cold regions environmental management. Permafrost in the interior of the QTP is well represented along the Qing-hai-Tibet Highway (QTH), which crosses the Plateau through north to south and traverses 560 km of permafrost-impacted ground. Horizontally, the degradation of permafrost occurs more visibly in the sporadic permafrost zone in the vicinity of the lower limit of permafrost (LLP), along the margins of taliks, and around permafrost islands. Downward degradation develops when the maximum depth of seasonal thaw exceeds the maximum depth of seasonal frost, and it generally results in the formation of a layered talik disconnecting the permafrost from the seasonal frost layer. The downward degrada- tion is divided into four stages: 1) initial degradation, 2) accelerated degradation, 3) layered talik and 4) finally the conversion of permafrost to seasonally frozen ground (SFG). The upward degradation occurs when the geothermal gradient in permafrost drops to less than the geothermal gradients in the underlying thawed soil layers. Three types of permafrost temperature curves (stable, degrading, and phase-changing transitory permafrost) illustrate these modes. Although strong differentiations in local conditions and permafrost types exist, the various combinations of the three degradation modes will ultimately transform permafrost into SFG. Along the QTH, the downward degradation has been proceeding at annual rates of 6 to 25 cm, upward degradation at 12 to 30 cm, and later
基金supported,in part,by grants from the National Natural Science Foundation of China(31670265)the Science and Technology Department of Hebei Province(15966306D)
文摘The increased prevalence of high temperatures （HTs） around the world is a major global concern, as they dramatically affect agronomic productivity. Upon HT exposure, plants sense the temperature change and initiate cellular and metabolic responses that enable them to adapt to their new environmental conditions.Decoding the mechanisms by which plants cope with HT will facilitate the development of molecular markers to enable the production of plants with improved thermotolerance. In recent decades, genetic, physiological, molecular, and biochemical studies have revealed a number of vital cellular components and processes involved in thermoresponsive growth and the acquisition of thermo- tolerance in plants. This review summarizes the major mechanisms involved in plant HT responses, with a special focus on recent discoveries related to plant thermosensing, heat stress signaling, and HT-regulated gene expression networks that promote plant adaptation to elevated environmental temperatures.
基金supported by the China Key Research Project for Global Change (No.2010CB951404) the China National Science Foundation (No.40821001)
文摘Based on data from six meteorological stations in the permafrost regions, 60 boreholes for long-term monitoring of permafrost temperatures, and 710 hand-dug pits and shallow boreholes on the Qinghai-Tibet Plateau （QTP）, the spatiotemporal variability of permafrost degradation was closely examined in relation to the rates of changes in air, surface, and ground temperatures. The de- cadal averages and increases in the mean annual air temperatures （MAATs） from 1961-2010 were the largest and most persistent during the last century. MAATs rose by 1.3 ℃, with an average increase rate of 0.03 ℃/yr. The average of mean annual ground surface temperatures （MAGSTs） increased by 1.3 ℃ at an average rate of 0.03 ℃/yr. The rates of changes in ground temperatures were -0.01 to 0.07 ℃/yr. The rates of changes in the depths of the permafrost table were -1 to ＋10 cm/yr. The areal extent of permafrost on the QTP shrank from about 1.50× 10^6 km^2 in 1975 to about 1.26× 10^6 km^2 in 2006. About 60% of the shrinkage in area of permafrost occurred during the period from 1996 to 2006. Due to increasing air temperature since the late 1980s, warm （〉-1 ℃） permafrost has started to degrade, and the degradation has gradually expanded to the zones of transitory （-1 to -2 ℃） and cold （〈-2 ℃） permafrost. Permafrost on the southern and southeastem plateau degrades more markedly. It is projected that the degradation of permafrost is likely to accelerate, and substantial changes in the distributive features and thermal regimes of permafrost should be anticipated. However, regarding the relationships between degrading permafrost and the degradation of rangelands, it is still too early to draw reliable conclusions due to inadequate scientific criteria and evidence.
基金the Fundamental Research Funds for the Central Universities (2016ZCQ03)Beijing Excellent Young Scholar (2015000026833ZK11)+1 种基金the National Natural Science Foundation of China (51622801, 51572029, and 51308045)the Xu Guangqi grant
文摘Carbon dioxide（CO2） capture using magnesium oxide（MgO）-based adsorbents at intermediate temperatures has been regarded as a very prospective technology for their relatively high adsorption capacity,low cost, and wide availability. During the past few years, great effort has been devoted to the fabrication of molten salts-modified MgO-based adsorbents. The extraordinary progress achieved by coating with molten salts greatly promotes the COcapture capacity of MgO-based adsorbents. Therefore, we feel it necessary to deliver a timely review on this type of COcapturing materials, which will benefit the researchers working in both academic and industrial areas. In this work, we classified the molten saltsmodified MgO adsorbents into four categories:（1） homogenous molten salt-modified MgO adsorbents,（2） molten salt-modified double salts-based MgO adsorbents,（3） mixed molten salts-modified MgO adsorbents, and（4） molten salts-modified MgO-based mixed oxides adsorbents. This contribution critically reviews the recent developments in the synthetic method, adsorption capacity, reaction kinetics, promotion mechanism, operational conditions and regenerability of the molten salts-modified MgO COadsorbents. The challenges and prospects in this promising field of molten salts-modified MgO COadsorbents in real applications are also briefly mentioned.
基金the National Natural Science Foundation of China(Projects 51531002,51474043,51571043)Fundamental Research Funds for the Central Universities(Grant 106112015CDJZR135515)Chongqing Municipal Government(CSTC2013JCYJC60001,CEC project,Two River Scholar Project andThe Chief Scientist Studio Project).
文摘Outstanding mechanical properties of graphene nanoplatelets(GNPs)make them ideal reinforcement for mass production of composites.In this research,the composites were fabricated by stir-casting method.GNPs were added in 1.5 and 3.0 wt.%into Mg–3wt.%Al–1wt.%Zn(AZ31)magnesium alloy.As cast ingots were preheated for one hour and extruded at 350℃ with extrusion ratio of 5.2:1.As extruded AZ31-GNPs composites were micro-structurally characterized with X-ray diffraction,optical microscopy and scanning electron microscopy.Vickers microhardness of synthesized materials was investigated both in parallel and perpendicular to extrusion directions.Room temperature mechanical testing revealed that with increasing GNP’s content,tensile fracture strain was remarkably increased without significant compromise in tensile strength.Furthermore,as extruded AZ31-3GNPs composites were subjected to tensile testing at temperatures ranging from 75℃ to 300℃ with initial strain rate of 2×10^(−3)s^(−1) to evaluate high temperature formability of composite.It was found that like CNTs,GNPs also have the potential to sustain tensile strength at high temperatures.
