Search

Drylands cover about 40% of the terrestrial surface and are sensitive to climate change, but their relative contributions to global vegetation greening and productivity increase in recent decades are still poorly known. Here, by integrating satellite data and biosphere modeling, we showed that drylands contributed more to global gross primary productivity (GPP) increase (65% ± 16%) than to Earth greening (33% ± 15%) observed during 1982–2015. The enhanced productivity per unit leaf area, i.e., light-use efficiency (LUE), was the mechanism behind this pattern. We also found that LUE was more sensitive to soil moisture than to atmospheric vapor pressure deficit (VPD) in drylands, while the opposite was observed (i.e., LUE was more sensitive to VPD) in humid areas. Our findings suggest the importance of using different moisture stress metrics in projecting the vegetation productivity changes of dry versus humid regions and highlight the prominent role of drylands as key controllers of the global carbon cycle. This work was supported by the National Natural Science Foundation of China (41991230), the European Research Council (ERC grant agreement 647038 (BIODESERT)) and Generalitat Valenciana (CIDEGENT/2018/041). We especially thanks Hanqin Tian from Auburn University for support with the Trendy v7 GPP data.

The impact of human carbon emissions on climate has generated widespread global concern. We selected 24 countries as research objects and analysed the changes in carbon emissions in different countries between the establishment of emission reduction actions in 1990 and 2014. Then, we selected 19 factors representing four categories (economy, population, technology and energy) to explore the key factors that led to changes in carbon dioxide (CO2) emissions in different countries. Emission reduction actions since 1990 did not lead to marked improvements, and only five countries (Russia, Germany, the United Kingdom, Italy and France) achieved reductions in carbon emissions. The factors that influenced CO2 emissions varied among countries. In most developing countries, reductions in CO2 emissions were caused by reductions in poverty and inherent natural conditions. Moreover, the extent of influence of a given factor on CO2 emissions differed among countries. The global economic crisis may cause similar fluctuations in CO2 emissions in many countries. Adjustments to energy and industrial structures are the main reason for the reduction in carbon emissions, whereas economic growth and urbanization are the two major contributors to the growth of carbon emissions. According to historical carbon emissions data, a green energy revolution must be implemented to address global climate change and ensure the sustainable development of human societies.

Under the navigational process of simultaneous beacon-calibrating and target-positioning, the real-time positioning and calibrating accuracy in indoor scenarios is significantly limited. To solve it, a novel Simultaneous Calibration and Localization (SCAL) algorithm framework for indoor scenarios is proposed. The proposed framework is mainly divided into the Target Localization and Beacon Calibration (TLBC) and the Global Optimization (GO) section: in the TLBC section, under the typical distributed beacon layout, a processing mechanism for synchronously locating the target and calibrating beacons is proposed; in GO section, parallel to TLBC section, a global optimization method based on Geometric Dilution of Precision based on Error-propagation (EGDOP) model is further proposed, and it can utilize the geometric trajectory of target and positioning error of target and beacons to efficiently and simultaneously optimize the positioning of target trajectory and beacons from TLBC section. The numerical simulation results show that the improvement of the GO section on the positioning performance is verified. Compared with the SCAL algorithm based on backward processing with inverse trajectory, the proposed framework has improved the accuracy of target and beacon positioning by 39.06% and 58.01%, respectively, and accuracy of positioning reaches 0.2557m and 0.2437m, respectively, in an actual indoor positioning scene.

Oriented towards the requirements for reliable positioning and navigation of aircraft under the condition of rejection of navigation satellite, we proposed cross-domain guide positioning methods based on multi-layer network coverage, and designed the relative positioning network construction methods between ground nodes, aircrafts and ground nodes, aircrafts and target nodes. Combined with the relative positioning network characteristics of each layer, at the same time, considered the computational complexity and location accuracy, the self-established multi-point coordinate system method and the robust location method are proposed.

Physical geography is the cornerstone of geography. In this article, the starting points of disciplines in physical geography in recent years in China are discussed. With the coupling of systems set as the research object, and sustainable development as the ultimate goal, the upgrade of physical geography can be deconstructed into three steps: deepen physical geography from the perspective of pattern-process coupling, improve the focus of physical geography from ecosystem processes to ecosystem services, and increase the understanding of the physical geography ‘pattern, process, service, sustainability’ research cascade. The incorporation of human activities into physical geographic processes is essential to conduct integrated analysis on physical and human factors at different scales. The development of ecosystem service models that couple supply-demand and sustainable development are of great importance to bridge the role of ecosystem services between the natural environment and human well-being. Moreover, human-land systems and sustainable development have become the core areas and frontiers of integrated physical geography and even geography in general. China faces the great strategic demand of constructing an ecological civilization in a new era, and the development of the disciplines of physical geography should give full access to the advantages of intersecting and comprehensive disciplines, focus on the human-land system patterns, processes, and services in key research areas, and provide disciplinary support for regional, national, and global sustainable development.

The multi-source fusion positioning, which utilize kinds of signals in 2.4 G ISM band, requires a variety of special sensors to identify the signal type. This leads to low utilization rate of equipment resources, high equipment cost and the difficulty of optimizing the location signal source. In this paper, an ISM band multi-source signal sensing method is proposed, we use Short-time Fourier transform (STFT) to transform signal data into time-frequency images dimensional. Based on the SVM image classification method, the time-frequency image features of each signal are extracted, then the classifier is designed to recognize the unknown positioning signals within 100 MHz bandwidth. The method has been tested by Simulink simulation in a Gaussian noise environment. The results show that compared to traditional single time/frequency domain signal detection, this approach maintains recognition performance no need to equip sensors for each type of signal.

随着遥感技术的不断发展，中高分辨率影像逐渐在植被监测中发挥着重要的作用。为了明确高分辨率传感器在不同生态系统植被提取中的必要性，以内蒙古鄂伦春自治旗为研究对象，设置城市区域和森林区域两个应用靶区，以GF1-WFV和Landsat8-OLI两种传感器同期影像为对比数据集，探究不同分辨率下遥感植被信息提取差异。结果表明：① Landsat 8对比GF-1在城市区域和森林区域的植被指数高估、低估状态相反，城市区域GF-1的NDVI（Normalized Difference Vegetation Index，NDVI）和SAVI（Soil-Adjusted Vegetation Index，SAVI）均值比Landsat 8低5.69%和1.41%，在森林区域则高出0.77%和5.86%；②高分辨率影像避免了城市中绿化植被（GF-1植被占比71.30%和71.31%，Landsat 8为58.28%和58.30%）和森林中裸地、道路（GF-1植被占比94.97%和94.92%，Landsat 8为95.00%和94.99%）被漏提。③在分级面积上，Landsat 8相比GF-1数据在城市区域存在低覆盖度等级的6.67%和6.77%低估，在森林区域出现高覆盖度等级的12.11%和12.47%高估。研究结果反映了低绿化建成区和高密度林区更加需要使用高分影像作为植被监测工具。

In the current paper, the synthesis of RE 2 AlTaO 7 (RE = Gd and Yb) oxides was performed through a high-temperature sintering method using Gd 2 O 3 , Yb 2 O 3 , Al 2 O 3 and Ta 2 O 5 as raw chemicals. The phase-structure, micro-morphology and thermal-physical properties of RE 2 AlTaO 7 (RE = Gd and Yb) oxides were analyzed. The RE 2 AlTaO 7 (RE = Gd and Yb) oxides exhibit single pyrochlore-type crystal-structure. Compared to Yb 2 AlTaO 7 , the Gd 2 AlTaO 7 has greater thermal conductivity owning to relatively weaker phonon scattering. Because of higher electro-negativity of Yb, the Yb 2 AlTaO 7 has lower coefficient of thermal expansion than Gd 2 AlTaO 7 . The RE 2 AlTaO 7 (RE = Gd and Yb) oxides also exhibit no phase-transition between ambient and 1473 K.

The temporal and spatial characteristics of landscape pattern change can reflect the spatial impact of urbanization on the ecological environment. Studying the relationship between urbanization and landscape patterns can provide supports for urban ecological management. Previous studies have examined the quantitative relationship between the social economy and landscape patterns of an entire region, but have not considered the spatial non-stability of this relationship. In this study, we characterized the landscape patterns in Beijing City, China during 2000 and 2010 using four landscape metrics, i.e. patch density (PD), edge density (ED), Shannon’s diversity index (SHDI) and the aggregation index (AI). Geographically weighted regression (GWR) was employed to identify the spatial heterogeneity and evolution characteristics of the relationship between the urbanization of population density (POP), gross domestic production (GDP) and nighttime lighting (NTL), and landscape patterns. The evolution of urban landscape patterns indicated a decentralized, aggregated, and fragmented change from the downtown to the suburb and outer suburb. During the 10-year period, the average PD in the downtown increased by 100.6%, and the increase of AI in the suburb was the largest. The PD, ED and SHDI increased by different degrees in the outer suburb. The influences of different urbanization modes on landscape patterns were also different. Infilling mode made the landscape patterns more regular and integrated. The landscape was more broken and complicated under the edge-expanding mode, and the leapfrog mode made PD and SHDI increase slightly. In the relationship interpretation, GWR effectively identified the spatial heterogeneity, and improved the explanatory ability compared to ordinary least squares (OLS). The most intense response to urbanization was the forest landscape and the forest-cultivated land ecotone in the northwest of Beijing City, indicating that this region was ecologically fragile. The population density in the urbanization index had a direct effect on landscape patterns, while the PD affected by urbanization was greater than the shape, aggregation and diversity index. Affected by development policy, urban planning and other factors, the explanation degree of social economy to landscape patterns decreased in 2010. GWR is an effective method for quantifying the spatial differentiation characteristics of urbanization impacts on landscape patterns, which can provide more spatial information and decision criteria for the green development of a compact city.

The La 3 TaO 7 and La 2 AlTaO 7 oxides were prepared by solid state reaction method. The phase composition, microstructure and thermal properties were examined. Results show that pure La 3 TaO 7 and La 2 AlTaO 7 oxides are prepared successfully. From 20 °C to 1200 °C, the average thermal conductivities of La 3 TaO 7 and La 2 AlTaO 7 ceramics are 1.12 W/m K and 1.71 W/m K, respectively, which are much lower than that of YSZ. Compared to La 2 AlTaO 7 , La 3 TaO 7 has lower thermal conductivity due to its higher atom-mass difference between the substituting and the substituted atoms. The thermal expansion coefficient of La 3 TaO 7 is higher than that of YSZ, and the thermal expansion coefficient of La 2 AlTaO 7 is close to that of YSZ. As compared with La 2 AlTaO 7 , the higher thermal expansion coefficient of La 3 TaO 7 can be ascribed to its lower electro-negativity difference between ions at sites A and B. The La 3 TaO 7 and La 2 AlTaO 7 oxides can be explored as potential ceramic materials for thermal barrier coatings.

Human activities directly or indirectly affect the changes in ecosystem services as well as the relationships among ecosystem services. However, the linear or non-linear relationships between human activities and ecosystem services are still unclear when considering large geographical differences. In this study, four ecosystem services (ESs), including habitat quality (HQ), soil retention (SR), water yield (WY), carbon sequestration (CS) and total ESs, were measured in the Belt and Road region in 2015. We mapped the tradeoffs among the ESs and the partitioned responses of the total ESs and ES tradeoffs in response to human activities (i.e., population density, GDP density, and nighttime light) using piecewise linear regressions at different scales. Then, the GeoDetector method was used to detect the major driving factors based on q value. The four findings were as follows. 1) The regions with low values for the 4 ESs were consistently distributed in arid areas, and the distribution of the areas with high values of the 4 ESs was clearly heterogeneous. 2) The responses of the total ESs to the GDP and nighttime light each had a threshold. However, there was a positive linear relationship between the population density and the total ESs throughout the region. At the national scale, the responses of the total ESs to human activities were more obvious in China than in Russia and India. 3) The thresholds of the impact of the GDP on the tradeoffs among the ESs were obvious. 4) Population density was a major driver of the ESs and the tradeoffs with q values greater than 0.4. The findings of this study contribute to the exploration of the influence of human activities on the total ESs and the tradeoff between ESs, thereby providing spatial indications for promoting the construction of a green Belt and Road region to support sustainable development goals.

Two kinds of novel Ln 2 LaTaO 7 (Ln=Er and Yb) ceramics were prepared via high-temperature solid reaction method. The phase composition, micro-morphology and thermophysical properties were investigated. Results indicate that pure Ln 2 LaTaO 7 ceramics with single fluorite-type structure are synthesized successfully. The thermal conductivities of Er 2 LaTaO 7 and Yb 2 LaTaO 7 are in the range of 1.22–1.43 W/m K and 1.17–1.51 W/m K, respectively, which are much lower than that of YSZ. The lower thermal conductivity can be attributed to the phonon scattering caused by oxygen vacancies and the substituting atoms. The average thermal expansion coefficients of Yb 2 LaTaO 7 and Er 2 LaTaO 7 are 9.94×10 −6 /K and 9.63×10 −6 /K, respectively. As compared with Yb 2 LaTaO 7 , the higher thermal expansion coefficient of Er 2 LaTaO 7 can be ascribed to its lower ionic-bond strength between cations at sites A and B.

The change of impervious surface area (ISA) can effectively reveal the gradual process of urbanization and act as a key index for monitoring urban expansion. Experiencing rapid growth of the built environment in the 2000s, urban expansion of Beijing has not been fully characterized through ISA. In this study, Landsat TM images of Beijing in 2001 and 2009 were obtained, and the eight-year urban expansion process in Beijing was analyzed using the ISA extracted by means of the vegetation-imperious surface-soil (V-I-S) model. From the spatial variation in ISA, the ring structure of urban expansion in Beijing was significant during the study period, with decreasing urban density from the city center to the periphery. In the ring road analysis, the most dramatic changes of ISA were found between the fifth ring and the sixth ring. This area has experienced the most new residential development, and is currently the main source of urban expansion. The typical profile lines revealed the directional characteristics of urban expansion. The east-west profile was the most urbanized axes in Beijing, while ISA change in the east-north profile was more significant than in the other five profiles. Moreover, the transition matrix of ISA levels revealed an increase in urban density in the low density built areas; the Moran′s I index showed a clear expansion of the central urban area, which spread contiguously; and the standard deviational ellipse indicated the northeast was the dominant direction of urban expansion. These findings can provide important spatial control guidelines in the next round of national economic and social development planning, overall urban and rural planning, and land use planning.

An ecologically constrained and scenario oriented urban growth simulation provides an effective means to address and mitigate ecological impacts resulting from urban expansion. However, current urban growth simulations usually set ecological indicators as explanatory variables in the model, while ignoring the trade-off relationship between the requirement for additional urban space and the prevention of ecological loss. In this study, ecological loss was set as a constraint parallel to the urban growth simulation indicator system. The Minimum losses of key ecosystem functions were set as constraints in order to realize optimized urban growth pattern. Taking Beijing's urban growth from 2000 to 2010 as a case, we proposed an optimized coupling model with ecological loss as a constraint in urban growth simulation. The results showed a 22.96% reduction in the total amount of ecological loss under the ecological constraint. According to the urban growth simulation, the "constant growth scenario" had the least ecological loss. Moreover, a combination of multiple ecosystem functions is required for describing the ecological constraint. We suggest that ecological constraint in an urban growth simulation model could be an effective policy tool to plan urban expansion and provide more accurate support for the formulation of spatial planning.

In this work, the Sm2AlTaO7 was synthesized by solid reaction method, and its phase composition, microstructure, and thermophysical properties were investigated. XRD results show that pure Sm2AlTaO7 with single pyrochlore-type structure is prepared successfully. The thermal conductivity of Sm2AlTaO7 at 1,273 K is about 1.13 W m−1 K−1, which is much lower than that of YSZ. The low thermal conductivity can be attributed to the phonon scattering caused by substituting atoms. Its thermal expansion coefficient is lower than that of Sm2Ce2O7, but close to that of YSZ. There is no phase transformation occurred between 293 and 1,673 K. The excellent thermophysical property means that the Sm2AlTaO7 has potential to be used as candidate ceramic material for thermal barrier coatings.

This paper takes the South Yellow Sea as an example to show a new method for comprehensive geological-geophysical research such as residual basin and tectonolayering using airborne gravity and magnetic data in China. Based on airborne gravity and magnetic data, by measuring and analyzing stratigraphic density and susceptibility, the depths to the pre-Sinian magnetic basement top, the pre-Jurassic top and the Cenozoic bottom, are obtained by forward and inverse methods constrained by seismic and drilling data; and furthermore, the residual thicknesses of the Sinian–Triassic, the Jurassic–Cretaceous and the Cenozoic are calculated. Based on airborne gravity and magnetic anomalies, the faults in the pre-Sinian magnetic basement, the Jurassic-Cretaceous and the Cenozoic are respectively interpreted by the qualitative and quantitative methods. On the basis of the above study, and combining regional important tectonic events, four tectonolayers are divided in the vertical succession in South Yellow Sea, namely the pre-Sinian magnetic basement, the Sinian-Triassic, the Jurassic-Cretaceous and the Cenozoic. The result shows that there are thick Cenozoic and Jurassic-Cretaceous strata and thin residual Sinian-Triassic strata in the Suzhong-Huangnan depression area, but there are thin or only sporadic Mesozoic-Cenozoic terrestrial strata and thick Sinian-Triassic marine strata reserved in Subei-Huangzhong uplift area and Sunan-Wunansha uplift area. The four tectonolayers are very different in structures as well as distributions in plane.

Potential evapotranspiration(ET0),as an estimate of the evaporative demand of the atmosphere,it has been widely applied in irrigation management and predictions in ungauged basins.Analysis of ET0 spatial and temporal variation is the basic research on the impact of climate change on water resources,and is also important to the optimal allocation of agricultural water resources.In recent years,change trends in ET0 and its dominant factors across the different regions of the world have been studied by many researchers.Despite global warming,decreasing trends in ET0 have been detected in several countries including United States,Russia,India,China,Australia and New Zealand.Decreasing sunshine duration,declining wind speed and increasing relative humidity have been considered to be the main causes for the decreasing ET0.Northern and southern regions of the Qinling Mountains is far away from oceans,water shortage is a serious problem for agriculture in this area.So far,detailed investigation on the change trend in ET0 over this area has been lacking.In this study,based on the daily data from 47 meteorological stations in northern and southern regions of the Qinling Mountains between 1960 and 2011,ET0 was calculated by using FAO Penman-Monteith formula.We analyzed the change trend of ET0 and air temperature as well as the main factors affecting the decrease of ET0.It also discussed the existence of the "evaporation paradox",the results are as following.(1)Air temperature of the whole region experienced two periods which increased initially and then decreased,1993 was abrupt change point.The decreasing rate between 1960 and 1993 as well as increasing rate between 1994 and 2011 both presented an pattern that declined from south to north,while increasing rate between 1960 and 2011 decreased from north to south.(2)1979 and 1993 were the change point of ET0,which divided ET0 into two periods,ET0 increased from 1960 to 1979 and then decreased from 1993 to 2011.Between 1960 and 1979,"Evaporation paradox" only existed in Han River Basin(HRB) and Bawu Valley(BWV),the periods of 1980—1993,1994—2011 and 1960—2011 all had "Evaporation paradox" phenomenon.Both the last 18 years and the whole 52 years in autumn as well as the initial 34 years and the whole 52 years in winter had "Evaporation paradox" phenomenon,which was more obvious in winter.(3)Precipitation decreased insignificantly in the past 52 years,and the precipitation and ET0 exhibited a contrary trend,which accounted 53% in the whole year and 79% in summer,respectively.The contrary trend between precipitation and ET0 was more obvious in summer than year scale.(4)According to the effect of meteorological elements change on ET0 change,the order was sunshine hours,wind speed,maximum temperature,relative humidity,mean temperature,mean air pressure and minimum temperature.On the year scale,the significant decrease of solar radiation(sunshine hours) was the dominating factor leading to the decrease of ET0.While on the seasonal scale,the dominating factor of spring′s ET0 was wind speed,the other three seasons were all solar radiation(sunshine hours).

The flow of rural labor to urban is a significant phenomenon in China during the last 20 years. In spite of many researches focus on the driving force of economy, terrain is an important index in the rural development. There is a question that whether the flow of rural labor has some relationships with terrain. The study used the relief degree of land surface (RDLS) as terrain index, and the cost distance model and the center of gravity model to analyze the relationship between terrain and labor flows. The results indicated: (1) In the last 20 years, the rural labor force was not simply flowing to the low terrain region in Shaanxi province. And the RDLS was constantly strengthening the influence on the movement. (2) The RDLS was low in Guanzhong region, and the translation of rural labors relatively was not significant. Since North Shaanxi act as the energy industry base, the number of rural labors there increased faster than in South Shaanxi. (3) The movements of economical centers took an impor...

The airborne gravimetry was an important leap and innovation in the world's history of geophysical exploration. China's first test of the airborne gravity geological survey in the onshore-offshore transitional area of the western and southern part of the Bohai Sea was successful and effective in geology. Based on the airborne gravity data, and combining previous ground gravity, seismic and drilling data etc., we carried out the geological interpretation by forward and inverse methods. The result shows that the airborne Bouguer gravity anomaly was clear, the fracture interpretation was reliable, and the inversion depth of the main geological interfaces was relatively accurate. This airborne gravity geological survey not only filled the exploring gaps in the onshore-offshore transitional area, and realized the geological and tectonic junction between the sea and the land, but also discovered four local gravity anomalies, 11 fractures and three sags or subsags, and so on. The good geological effect of airborne gravimetry not restricted by terrain condition shows that it can be served as a new geophysical method in the exploration of complex terrain physiognomy area such as mountain, jungle, desert, marsh, onshore-offshore transitional area and so on, and has an extensive application prospect in China in the future.

This dissertation addresses issues pertinent to the control of an invasive species, issues that pertain both to a species��� introduction at a country���s international border and its spread within the country���s border. In the first essay, tariffs and inspections are examined as a joint border control mechanism. In a deterministic setting, where the invasive species level is functionally related to a foreign (i.e., exporting) country���s shipment size, a traditional tariff can be optimal for the home (i.e., importing) country in the short run, but distorts the entry condition for foreign firms and results in a suboptimal industry size in the foreign country in the long run. When the foreign country���s abatement effort determines the invasive species level, an additional home-country tariff on the invasive-species level (which I call an ���invasive-species tariff���) is necessary to motivate the foreign firms to abate the invasive species at socially optimal level. In the second essay I consider the case where the invasive species contamination level is jointly determined by the foreign countries��� abating efforts and random environmental factors. The home country may use standard contracts to mitigate imperfect observability caused by the random factors. However, I show that the home country must provide risk-averse foreign countries with higher subsidy rates than the first-best rates with perfect information as compensation for partially bearing the risk. When risk-averse foreign countries face both individualistic and common random environmental factors, a standard tournament scheme is capable of attaining the home country���s first-best invasive-species solution. The third essay addresses the control of an established invasive species outbreak in the home country with multiple spatially-connected individuals. The optimal response to invasion (eradicating, stopping, or ignoring invasion) is determined by the incremental damage of invasion and the marginal control cost. Different spatial scales lead to a divergence between the control incentives of society and individuals, and result in a deficiency of individualistic control, which in turn results in a larger steady-state invasion area. Numerical analysis also demonstrates that the number, size, and spatial configuration of small and large individual land parcels influence the severity of the externality and the insufficiency of privately supplied control. I introduce a dynamic multiple-source-subsidy scheme to internalize the externalities, which prompts individuals to coordinate and follow the social optimal control path without a budget burden on the government.