Analysis of Urbanization Based on Center-of-gravity Movement and Characteristics in Songhua River Basin of China and its Southern Source Sub-basin between 1990 and 2010

Urbanization in modern times led to a series of development strategies that brought new opportunities in China. Rapid urbanization caused severe stress to the ecosystems and the environment. Using the center-of-gravity(COG) method and parameters such as population, economy, and land, we studied the urbanization pattern in Songhua River Basin and its southern source sub-basin from 1990 to 2010. Urbanization was analyzed based on the COG position, eccentric distance, movement direction of COG, and distance of COG movement. Various characteristics of urbanization in the southern source sub-basin of the Songhua River were explained in relation to the whole Songhua River Basin. Urbanization in the southern source sub-basin of the Songhua River is balanced, relatively advanced, and stable compared to the whole Songhua River Basin. The average eccentric distance between the urbanization COGs in the Songhua River′s south source basin indicated rapid expansion of land urbanization during the span of this study. A basic pattern of urbanization COG in the whole Songhua Basin was observed, but there existed differences among the three aspects of urbanization process. Land urbanization is still in its active stage, so future studies should focus on analysis of such urbanization trends.

Spatiotemporal variation and influencing factors of desertification sensitivity on the Qinghai-Xizang Plateau,China

Due to irrational human activities and extreme climate,the Qinghai-Xizang Plateau,China,faces a serious threat of desertification.Desertification has a detrimental effect on the ecological environment and socioeconomic development.In this study,the desertification sensitivity index(DSI)model was established by integrating the spatial distance model and environmentally sensitive area index evaluation method,and then the model was used to quantitatively analyze the spatial and temporal characteristics of desertification sensitivity of the Qinghai-Xizang Plateau from 1990 to 2020.The results revealed that:(1)a general increasing tendency from southeast to northwest was identified in the spatial distribution of desertification sensitivity.The low-sensitivity areas were mostly concentrated in the Hengduan and Nyaingqêntanglha mountains and surrounding forest and meadow areas.The high-sensitivity areas were located mainly in the Kunlun and Altun mountains and surrounding decertified areas.The center of gravity of all types of desertification-sensitive areas moved to the northwest,and the desertification sensitivity showed a decreasing trend as a whole;(2)the area of highly sensitive desertification areas decreased by 8.37%,with extreme sensitivity being the largest change among the sensitivity types.The desertification sensitivity transfer was characterized by a greater shift to lower sensitivity levels(24.56%)than to higher levels(2.03%),which demonstrated a declining trend;(3)since 1990,the change in desertification sensitivity has been dominated by the stabilizing type Ⅰ(29.30%),with the area of continuously increasing desertification sensitivity accounting for only 1.10%,indicating that the management of desertification has achieved positive results in recent years;and(4)natural factors have had a more significant impact on desertification sensitivity on the Xizang Plateau,whereas socioeconomic factors affected only localized areas.The main factors influencing desertification sensitivity were vegetation drought tolerance and aridity index.Studying spatiotemporal variations in desertification sensitivity and its influencing factors can provide a scientific foundation for developing strategies to control desertification on the Qinghai-Xizang Plateau.Dividing different desertification-sensitive areas on the basis of these patterns of change can facilitate the formulation of more targeted management and protection measures,contributing to ecological construction and sustainable economic development in the area.

Optimization of Center of Gravity Position and Anti-Wave Plate Angle of Amphibious Unmanned Vehicle Based on Orthogonal Experimental Method

When the amphibious vehicle navigates in water,the angle of the anti-wave plate and the position of the center of gravity greatly influence the navigation characteristics.In the relevant research on reducing the navigation resistance of amphibious vehicles by adjusting the angle of the anti-wave plate,there is a lack of scientific selection of parameters and reasonable research of simulation results by using mathematical methods,and the influence of the center of gravity position on navigation characteristics is not considered at the same time.To study the influence of the combinations of the angle of the anti-wave plate and the position of the center of gravity on the resistance reduction characteristics,a numerical calculation model of the amphibious unmanned vehicle was established by using the theory of computational fluid dynamics,and the experimental data verified the correctness of the numerical model.Based on this numerical model,the navigation characteristics of the amphibious unmanned vehicle were studied when the center of gravity was located at different positions,and the orthogonal experimental design method was used to optimize the parameters of the angle of the anti-wave plate and the position of the center of gravity.The results show that through the parameter optimization analysis based on the orthogonal experimental method,the combination of the optimal angle of the anti-wave plate and the position of the center of gravity is obtained.And the numerical simulation result of resistance is consistent with the predicted optimal solution.Compared with the maximum navigational resistance,the parameter optimization reduces the navigational resistance of the amphibious unmanned vehicle by 24%.

Evolvement Characteristics of Population and Economic Gravity Centers in Tarim River Basin,Uygur Autonomous Region of Xinjiang,China

Using the data at the county levcl and the regional gravity center model, we calculated six key socio-economic gravity centers, namely population, GDP, output values of primary, secondary and tertiary industries, and arable land area in the Tarim River Basin for each year from 1980 to 2009. We inspected the spatial dynamics of these centers and found that the gravity centers of population and economy evolved simultaneously. The disproportional growth between the population and the economy is also analyzed. The results show that： 1） The gravity centers of the GDR the output values of the main three industries and arable land area show migration trending from southwest to northeast, while the population gravity center shows an excessive growth in the southwest during the same time period. The migration amplitude of the GDP and output values of primary industry, secondary industry, tertiary industry are measurably higher than that of the population. 2） The population gravity center has a negative correlation with the gravity centers of secondary and tertiary industries output values in both longitudinal and latitudinal directions, and a positive correlation with that of primary industry output value in the longitudinal direction. Based on the analysis of correlation coefficient and offset distance, the imbalance between the population and the economy has increased since the 1980s, with regional economic differences now exceeding the international cordon.

Uncertainty analysis of ship model vertical center of gravity and transverse moment of inertia test

The usability of test results of ship model vertical center of gravity and transverse moment of inertia is generally depends on its uncertainty. Referring to the guidelines for uncertainty analysis in examination of liquid dynamic recommended by International Towing Tank Conference （ ITTC）, the results were analyzed, bias limits and precision limits were calculated and total uncertainty was estimated. The total uncertainty of six tests on ship model vertical center of gravity is is 0. 16% of the mean value, and the total uncertainty of six tests on ship model transverse moment of inertia is 5.66% of the mean value. The test results show that the total uncertainty of both the multiple tests and the single test is from the precision limits of ship model vertical center of gravity and transverse moment of inertia tests. Thus, the improved measurement system stability can enormously decrease the total uncertainty of multiple tests and the single test.

Analysis and Study on Spatial Gravity Center of PM_(2.5) and Population Scale

With the rapid development of urbanization construction in China,population and industries are rapidly gathering in cities,bringing about economic development and also causing a large number of environmental problems,among which PM_(2.5) is the most concerned.In this paper,a spatial gravity center model was used to systematically analyze the spatiotemporal distribution characteristics of PM_(2.5) and population scale in China from 1999 to 2016.Conclusions were as below:(1)there were significant regional differences in PM_(2.5) pollution from 1999 to 2016,characterized by a spatial distribution of"high in the north and low in the south,and high in the inland and low in the coastal areas".(2)Nationwide,there was a significant spatial mismatch between the gravity center of PM_(2.5) pollution and the gravity center of population scale,with the two centers showing a trend of reverse dislocation development.

Centered simple waves for the two-dimensional pseudo-steady isothermal ?ow around a convex corner

The two-dimensional(2D) pseudo-steady isothermal flow, which is isentropic and irrotational, around a convex corner is studied. The self-similar solutions for the supersonic flow around the convex corner are constructed, where the properties of the centered simple wave are used for the 2D isentropic irrotational pseudo-steady Euler equations. The geometric procedures of the center simple waves are given. It is proven that the supersonic flow turns the convex corner by an incomplete centered expansion wave or an incomplete centered compression wave, depending on the conditions of the downstream state.

Classification of densities and characteristics of curve of population centers in China by GIS

In this paper, with the spatial analysis functions in ArcGIS and the county-level census data of 2000 in China, the population density map was divided and shown by classes, meanwhile, the map system of population distribution and a curve of population centers were formed; in accordance with the geographical proximity principle, the classes of population densities were reclassified and a population density map was obtained which had the spatial clustering characteristic. The multi-layer superposition based on the population density classification shows that the population densities become denser from the Northwest to the Southeast; the multi-layer clustering phenomenon of the Chinese population distribution is obvious, the populations have a water-based characteristic gathering towards the rivers and coastlines. The curve of population centers shows the population densities transit from the high density region to the low one on the whole, while in low-density areas there are relatively dense areas, and in high-density areas there are relatively sparse areas. The reclassification research on the population density map based on the curve of population centers shows that the Chinese population densities can be divided into 9 classes, hereby, the geographical distribution of Chinese population can be divided into 9 type regions： the concentration core zone, high concentration zone, moderate concentration zone, low concentration zone, general transitional zone, relatively sparse area, absolute sparse area, extreme sparse area, and basic no-man＇s land. More than 3/4 of the population of China is concentrated in less than 1/5 of the land area, and more than half of the land area is inhabited by less than 2% of the population, the result reveals a better space law of China＇s population distribution.

Algorithm for 2D irregular-shaped nesting problem based on the NFP algorithm and lowest-gravity-center principle

The nesting problem involves arranging pieces on a plate to maximize use of material. A new scheme for 2D ir- regular-shaped nesting problem is proposed. The new scheme is based on the NFP (No Fit Polygon) algorithm and a new placement principle for pieces. The novel placement principle is to place a piece to the position with lowest gravity center based on NFP. In addition, genetic algorithm (GA) is adopted to find an efficient nesting sequence. The proposed scheme can deal with pieces with arbitrary rotation and containing region with holes, and achieves competitive results in experiment on benchmark datasets.

Spatial-temporal characteristics of the coupling coordination of social security and economic development in China during 2002–2018

Clarifying the relationship between social security and economic development is helpful to realize the sustainable social security system and the stable function of sustainable economic development.In this paper,the entropy method,coupling coordination degree,standard deviation ellipse model,and spatial autocorrelation were used to study the spatial-temporal characteristics of coupling coordination of social security and economic development in China from 2002 to 2018.The results indicate that the relationship between social security and economic development in China has been gradually strengthened in the process of mutual adaptation and common development.The benign interaction between the two was unstable,though the coupling coordination degree gradually transitioned to the primary coupling coordination type.Besides,from a spatial perspective,first,the coupling coordination degree of social security and economic development in China contracted in the east-west and north-south directions,and the coupling coordination clustered in the central region in this period;second,the coupling coordination degree generally presented a positive spatial autocorrelation,and regions with similar coupling coordination degrees were in a state of agglomeration;finally,the hot spots clumped together to form a continuous area in the eastern coastal area while the cold spots expanded toward the northwest and northeast.Furthermore,the random distribution areas exhibited a trend of contraction.

Study on Location of Wuhan Steel Logistics Distribution Center

This paper studies the location of Wuhan steel logistics distribution center. First of all, according to Wuhan Iron and Steel Plant sales in Hunan Province and the relative position of the city, the transport costs are calculated from Wuhan Iron and Steel Plant to the demand point. We further analyze the necessity of establishing steel logistics distribution center, using the precise center of gravity to determine the actual location of the distribution center. After the establishment of distribution center, the total freight is reduced by 15.46 million yuan from Wuhan Iron and Steel Plant to each city in Hunan province via distribution center each year. The results of this paper can provide theoretical basis for the logistics node planning of related enterprises.

Prospects for an Eastward Shift of the Global Economic Center

The rapid growth of Asian economies and their rising share of the global economy give rise to a prevailing view that the global economic center is moving eastward. At least over the next decade, however, Asia is unlikely to become the global economic center. There are multiple reasons .for this. First, insufficient demands from end consumers will make it difficult to reduce Asian economies＇ reliance on other markets for exports. Second, Asian economies＇ continued growth will be constrained both by insufficient innovation and by future global climate change regulations. Because of international labor division, moreover, it will be increasingly difficult to achieve leapfrog development. Third, there are several obstacles to building an integrated Asian market： these will prevent Asian economies .from shaping a common ground regarding international affairs. If Asian countries are unable to make breakthroughs in these three areas, the global economic system may exhibit asymmetrical ＂dual centers＂, i.e, a global manufacturing center in Asia and a global financial center in Europe and America.

Spatial and temporal change patterns of net primary productivity and its response to climate change in the Qinghai–Tibet Plateau of China from 2000 to 2015

The vegetation ecosystem of the Qinghai–Tibet Plateau in China,considered to be the′′natural laboratory′′of climate change in the world,has undergone profound changes under the stress of global change.Herein,we analyzed and discussed the spatial-temporal change patterns and the driving mechanisms of net primary productivity(NPP)in the Qinghai–Tibet Plateau from 2000 to 2015 based on the gravity center and correlation coefficient models.Subsequently,we quantitatively distinguished the relative effects of climate change(such as precipitation,temperature and evapotranspiration)and human activities(such as grazing and ecological construction)on the NPP changes using scenario analysis and Miami model based on the MOD17A3 and meteorological data.The average annual NPP in the Qinghai–Tibet Plateau showed a decreasing trend from the southeast to the northwest during 2000–2015.With respect to the inter-annual changes,the average annual NPP exhibited a fluctuating upward trend from 2000 to 2015,with a steep increase observed in 2005 and a high fluctuation observed from 2005 to 2015.In the Qinghai–Tibet Plateau,the regions with the increase in NPP(change rate higher than 10%)were mainly concentrated in the Three-River Source Region,the northern Hengduan Mountains,the middle and lower reaches of the Yarlung Zangbo River,and the eastern parts of the North Tibet Plateau,whereas the regions with the decrease in NPP(change rate lower than–10%)were mainly concentrated in the upper reaches of the Yarlung Zangbo River and the Ali Plateau.The gravity center of NPP in the Qinghai–Tibet Plateau has moved southwestward during 2000–2015,indicating that the increment and growth rate of NPP in the southwestern part is greater than those of NPP in the northeastern part.Further,a significant correlation was observed between NPP and climate factors in the Qinghai–Tibet Plateau.The regions exhibiting a significant correlation between NPP and precipitation were mainly located in the central and eastern Qinghai–Tibet Plateau,and the regions exhibiting a significant correlation between NPP and temperature were mainly located in the southern and eastern Qinghai–Tibet Plateau.Furthermore,the relative effects of climate change and human activities on the NPP changes in the Qinghai–Tibet Plateau exhibited significant spatial differences in three types of zones,i.e.,the climate change-dominant zone,the human activity-dominant zone,and the climate change and human activity interaction zone.These research results can provide theoretical and methodological supports to reveal the driving mechanisms of the regional ecosystems to the global change in the Qinghai–Tibet Plateau.

The Relationship between Normalized Difference Vegetation Index(NDVI) and Climate Factors in the Semiarid Region:A Case Study in Yalu Tsangpo River Basin of Qinghai-Tibet Plateau

The Yalu Tsangpo River basin is a typical semi-arid and cold region in the Qinghai-Tibet Plateau, where significant climate change has been detected in the past decades. The objective of this paper is to demonstrate how the regional vegetation, especially the typical plant types, responds to the climate changes. In this study, the model of gravity center has been firstly introduced to analyze the spatial-temporal relationship between NDVI and climate factors considering the time-lag effect. The results show that the vegetation grown has been positively influenced by the rainfall and precipitation both in moving tracks of gravity center and time-lag effect especially for the growing season during the past thirteen years. The herbs and shrubs are inclined to be influenced by the change of rainfall and temperature, which is indicated by larger positive correlation coefficients at the 0.05 confidence level and shorter lagging time. For the soil moisture, the significantly negative relationship of NDV-PDI indicates that the growth and productivity of the vegetation are closely related to the short-term soil water, with the correlation coefficients reaching the maximum value of o.81 at Lag 0-1. Among the typicalvegetation types of plateau, the shrubs of low mountain, steppe and meadow are more sensitive to the change of soil moisture with coefficients of -0.95, -0.93, -0.92, respectively. These findings reveal that the spatial and temporal heterogeneity between NDVI and climatic factors are of great ecological significance and practical value for the protection of eco-environment in Qinghai-Tibet Plateau.

Research on Comprehensive Performance Assessment for WSN Based on ANP with Equilibrium Variable Weight and Cloud Gravity Center

The index system of comprehensive performance assessment for WSN is established firstly according to the requirement of Smart Grid application, and ANP is adopted to determine the constant weight of index. Then the equilibrium variable weight is used to adjust the constant weight under extreme case. Moreover, the section division of comment grade for qualitative index is treated by the numerical characteristics of cloud model. Finally the cloud gravity center is used to calculate the weight deviation degree presenting the final evaluation result. The method proposed fully considers the interaction among indices and guarantees randomness and fuzziness in evaluation process. The reliability and efficiency of the method is demonstrated by the assessment of actual WSN examples.

Kinematics analysis for obstacle-surmounting capability of a joint double-tracked robot

A double-tracked robot is designed from mechanical and control perspectives,which consists of two segments connected with a swing joint. As the angle between the two segments of the robot platform can be changed,the robot can move like a four-tracked robot on many terrains. The center of gravity（ CG） kinematics model is established,which plays an important role in the process of traveling over obstacles and climbing up stairs. Using this model,the CG change situation and the maximal height of the climbable obstacle are obtained. Then the relationship between the robot pitch angle and the height of the obstacle is established. Finally,a reasonable system structure for the robot is designed and its kinematics analysis for obstacle-surmounting capability is conducted through experiments.

Dynamics of vehicles with high gravity centre

The vehicles with high gravity centre are more prone to roll over. The paper deals with a method of dynamics analysis of fire engines which is an example of these types of vehicle. Algorithms for generating the equations of motion have been formulated by homogenous transformations and Lagrange＇s equation. The model presented in this article consists of a system of rigid bodies connected one with another forming an open kinematic chain. Road maneuvers such as a lane change and negotiating a circular track have been presented as the main simulations when a car loses its stability. The method has been verified by comparing numerical results with results obtained by experimental measurements performed during road tests.

Stable Transition of Quadruped Rhythmic Motion Using the Tracking Differentiator

Since the quadruped robot possesses predominant environmental adaptability,it is expected to be employed in nature environments. In some situations,such as ice surface and tight space,the quadruped robot is required to lower the height of center of gravity( COG) to enhance the stability and maneuverability. To properly handle these situations,a quadruped controller based on the central pattern generator( CPG) model,the discrete tracking differentiator( TD) and proportional-derivative( PD) sub-controllers is presented. The CPG is used to generate basic rhythmic motion for the quadruped robot. The discrete TD is not only creatively employed to implement the transition between two different rhythmic medium values of the CPG which results in the adjustment of the height of COG of the quadruped robot,but also modified to control the transition duration which enables the quadruped robot to achieve the stable transition. Additionally,two specific PD sub-controllers are constructed to adjust the oscillation amplitude of the CPG,so as to avoid the severe deviation in the transverse direction during transition locomotion. Finally,the controller is validated on a quadruped model. A tunnel with variable height is built for the quadruped model to travel through. The simulation demonstrates the severe deviation without the PD sub-controllers,and the reduced deviation with the PD sub-controllers.

Effects of land use/cover change(LUCC) on the spatiotemporal variability of precipitation and temperature in the Songnen Plain,China

Understanding the effects of land use/cover change(LUCC) on regional climate is critical for achieving land use system sustainability and global climate change mitigation. However, the quantitative analysis of the contribution of LUCC to the changes of climatic factors, such as precipitation & temperature(P&T), is lacking. In this study, we combined statistical methods and the gravity center model simulation to quantify the effects of long-term LUCC on P&T in the Songnen Plain(SNP) of Northeast China from 1980–2018. The results showed the spatiotemporal variability of LUCC. For example, paddy field had the largest increase(15 166.43 km2) in the SNP, followed by dry land, while wetland had the largest decrease(19 977.13 km;) due to the excessive agricultural utilization and development. Annual average precipitation decreased at a rate of –9.89 mm per decade, and the warming trends were statistically significant with an increasing rate of 0.256°C per decade in this region since 1980. The model simulation revealed that paddy field, forestland, and wetland had positive effects on precipitation, which caused their gravity centers to migrate towards the same direction accompanied by the center of precipitation gravity, while different responses were seen for building land, dry land and unused land. These results indicated that forestland had the largest influence on the increase of precipitation compared with the other land use types.The responses in promoting the temperature increase differed significantly, being the highest in building land, and the lowest in forestland. In general, the analysis of regional-scale LUCC showed a significant reduction of wetland, and the increases in building land and cropland contributed to a continuous drying and rapid warming in the SNP.