China’s tourism industry has witnessed rapid progress in recent years, and is now an important part of global tourism in dealing with climate change. Within a framework of Pressure-State-Response (PSR), this paper focuses on the emission reduction pressure, carbon emission status, and responses of stakeholders in China’s tourism industry. Findings include: 1) The central government’s strategy and rapid growth of the industry scale exert rising pressure on China’s tourism to reduce carbon emissions. 2) Carbon emissions of China's tourism account for 13%-14.6% of global tourism, and about 3% of China’s emissions overall. Chinese tourists’ per capita carbon emission is lower than half of the global level. 3) The Chinese government attaches great importance to energy-saving and carbon emission reduction. In the tourism industry, documents, standards and other regulative measures have been issued to ensure that business practitioners set up green operational and managerial systems. In the field of tourism transportation, China's high-speed rail, new energy vehicles, and urban shared bicycles, have developed very rapidly in recent years, and they have effectively reduced the carbon emissions in traveling. Furthermore, this paper finds that Chinese tourists already have awareness and willingness for low-carbon tourism.
Based on the interactive development of new industrialization, rapid urbanization and agricultural modernization (IUAM), and from the viewpoint of interactive responses and supply-demand relationships between regional water resources carrying capacity and economic-social development, this paper puts forward the concepts and characterization methods of water resources relative intensity (WRI), water resources carrying rate (WCR) and sustainable index of water resources system (WSI). Considering the catastrophic trait of water resources carrying capacity and its contradictory relationship with WRI, a modified Catastrophe Model, which combines Catastrophe Theory and Fuzzy Mathematic Theory, was introduced to perform a multi-objective and multi-criterion comprehensive assessment of the sustainability of water resources carrying capacity (WSCC) based on benchmarking. According to these concepts and models, land WSCC for the China mainland was set as an example for empirical analysis. The results showed that at the scale of first-grade water regions, Liaohe River, Yangtze River and Pearl River regions had high WRI of domestic water, while Northwestern Rivers, Southeastern Rivers regions and Yangtze River region in some years had high WRI of eco-environment water. However, they were all in a downtrend, while the other four northern regions had low WRI in an uptrend. The agricultural WRI in Songhua River, Yellow River and Northwestern Rivers regions were relatively high and industrial WRI in Songhua River, Yangtze River and Pearl River regions were also relatively high. At the provincial scale, WSCC of urban domestic water was relatively stable, WSCC of eco-environment was obviously fluctuating, and WSCC of agriculture and industry were constantly rising. Overall, WRI in the China mainland generally decreased. The convergence of provinces with high consumption intensity of water resources and spatial spillover of WUE in high WCR provinces promotes water resources development and utilization, progressing toward doubly sustainable development. In the future, China should try to find new ideas and methods of dynamic management of regional water resources and unified management of basin water resources, building on the foundation of traditional water resources planning. Meanwhile, water resources should be considered in regional PRED (population, resources, ecology and development) systems for integrated dispatching and optimizing configuration so that the improvements of WSCC and harmonious development of water resources and regional populations, eco-environment, economy and society can be achieved.
The storage of inorganic carbon in estuarine wetlands is of great significance for mitigating global warming. The Dagu River estuary and Yanghe River estuary of Jiaozhou Bay were selected as sampling areas, and data analysis was carried out by Duncan method to explore the distribution characteristics and influencing factors of soil inorganic carbon (SIC) reserves. The results showed that increasing distance from the estuary led to higher reserves in the mudflat along the coastal zone. The scouring action of seawater bodies was the main factor driving this distribution. In the vertical section, the SIC reserves in 40-60 cm depth were relatively high, accounting for 34.11% of the 0-60 cm soil depth, and resulting from the transport of water and salt in seawater. In the river flat along the vertical coastal zone, the SIC reserves first decreased and then increased with increasing distance from the sea, and the SIC reserves in 0-20 cm depth were relatively high in the vertical section, accounting for 38.18% of the 0-60 cm soil depth. These reserves were affected by synergetic factors such as oceanic factors and anthropogenic activities. The invasion of Spartina alterniflora decreased the SIC reserves of wetlands, mainly due to its root transformation and the differences of growth characteristics and years being the main reasons for the observed decreases. Aquaculture activities changed the physical and chemical properties of the soil in aquaculture ponds, and consequently changed the distribution of SIC reserves.
Analysis of the nexus between vegetation dynamics and climatic parameters like surface temperature is essential in environmental and ecological studies and for monitoring of the natural resources. This study explored the spatio-temporal distribution of land surface temperature (LST) and Normalized Difference Vegetation Index (NDVI) and the relationship between them in the Andassa watershed from 1986 to 2016 periods using Landsat data. Monthly average air temperature data of three meteorological sites were used for validating the results. The findings of the study showed that the LST of the Andassa watershed has increased during the study periods. Overall, average LST has been rising with an increasing rate of 0.081°C per year. Other results of this study also showed that there has been a dynamic change in vegetation cover of the watershed in all seasons. There was also a negative correlation between LST and NDVI in all the studied years. From this study we can understand that there has been degradation of vegetation and intensification of LST from 1986 to 2016.
Soil microbes play important roles in terrestrial ecosystem carbon and nitrogen cycling. Climatic warming and elevated CO2 are two aspects of climatic change. In this study, we used a meta-analysis approach to synthesise observations related to the effects of warming and elevated CO2 on soil microbial biomass and community structure. Ecosystem types were mainly grouped into forests and grasslands. Warming methods included open top chambers and infrared radiators. Experimental settings included all-day warming, daytime warming and nighttime warming. Warming increased soil actinomycetes and saprotrophic fungi, while elevated CO2 decreased soil gram-positive bacteria (G+). Mean annual temperature and mean annual precipitation were negatively correlated with warming effects on gram-negative bacteria (G-) and total phospholipid fatty acid (PLFA), respectively. Elevation was positively correlated with the warming effect on total PLFA, bacteria, G+ and G-. Grassland exhibited a positive response of total PLFA and actinomycetes to warming, while forest exhibited a positive response in the ratio of soil fungi to bacteria (F/B ratio) to warming. The open top chamber method increased G-, while the infrared radiator method decreased the F/B ratio. Daytime warming rather than all-day warming increased G-. Our findings indicated that the effects of warming on soil microbes differed with ecosystem types, warming methods, warming times, elevation and local climate conditions.
Payments for ecosystem services (PES) are one kind of important tool for environmental protection, and have been widely studied by international scholars and conservationists. Based various definitions of PES from recent articles, we have outlined four principles for PES: parity, measurability, additionality and conditionality, and then have used these principles to develop a formula to calculate a standard for PES. Finding a way to use PES to achieve a win-win relationship between economic growth and environmental protection in the Beijing-Tianjin-Hebei Region (BTHR) is a key task for Chinese government. Synergetic development of BTHR has become a national strategy, like The Belt and Road Initiative. This article employed the formula we developed to calculate the net horizontal PES amounts that each provincial government within BTHR should pay. Our findings show that Beijing should have paid 10.44×109 Yuan (0.4% of Beijing’s GRP) and Tianjin 16.56×109 Yuan (0.93% of Tianjin’s GRP) to Hebei in 2016.
Can deserts be transformed into resources, into assets, and further into cash? It is necessary to scientifically assess desert ecological assets and incorporate them into the national economic accounting system and the current evaluation system for socio-economic development. This study will provide a scientific basis and robust data for establishing a target system that is compatible with both ecological civilization and an associated reward and punishment mechanism, as well as for designing and implementing effective compensation policies for desert ecosystems. This paper first defines desert ecological assets, and then develops a framework for assessing them based on the evaluation of desert ecological resources and desert ecosystem services. This framework paves the foundation for quantitatively assessing desert ecological assets and preparing balance sheets of desert ecological assets. Finally, this paper analyzes current policies relating to desert ecological compensation, discusses how to design compensation policies based on assessment of desert ecological assets, and puts forward suggestions for improving current policies.
Beijing, Tianjin and Hebei each contributed to the comprehensive governance of bulk coal to treat bulk coal pollution in a mutually beneficial way in 2017. The cooperative game theory is used in this paper to study the environmental benefits and cost effectiveness brought about by this comprehensive governance strategy, primarily focusing on the issue of how to maximize the environmental benefits by choosing an appropriate strategy since the benefits to Beijing, Tianjin and Hebei are closely related. Therefore, the linear optimization, game theory and Shapley value method in the cooperative game model are used to find the ways to minimize the total governance cost of bulk coal in the three areas. In addition, the issues of how to carry out rational distribution and transfer of governance capital among the three places are explored according to the actual amounts of consumption of bulk coal, the influence of the coal burning on the PM2.5 and the actual cost of coal governance in Beijing, Tianjin and Hebei in 2017. The results show that the governance task in Hebei Province is the most onerous, and requires more investment than the other two cities. Thus, it requires the support from other two cities, with the amount of increased capital required of about 600 million Yuan. At the same time, the cost saved after optimization in Tianjin is calculated to be the largest, which thus can be adjusted appropriately and allocated to Hebei for the governance of bulk coal. The model constructed in this paper can not only be used to solve the issues related to bulk coal consumption in Beijing, Tianjin and Hebei, but also to carry out the effective distribution of capital, by which a win-win scenario among the three places can be achieved.
Liaoning Province is in a critical period of economic transformation. The rational utilization of ecological resources and the balance of the relationship between the resource environment and economic growth have become the key factors affecting its sustainable economic development. This paper uses data from the Human Development Index and an ecological footprint to construct the ecological well-being performance of Liaoning Province from 2006 to 2016. It then examines the relationship of ecological well-being performance with economic growth, considers the factors influencing the well-being level effect, and analyzes the trends for sustainable economic development from the perspective of ecological well-being. There is a horizontal comparison of the current situation of ecological well-being performance in Liaoning Province and with other coastal provinces in China and clarification of the stage and development gap. The conclusions show that: 1) The trend of ecological well-being performance in Liaoning Province during this period first decreased and then rose, with this movement mainly affected by changes in the ecological footprint; 2) There is a U-shaped relationship between ecological well-being performance and economic growth, and resource consumption contributes less to promote well-being; 3) There are three stages to the sustainable development trend: inferior, medium and advanced. When compared with others coastal provinces, Liaoning Province belongs to the high consumption and low well-being type.
Transportation as a means to support industrial development can impact the economic development of important agricultural heritage sites. Because the central towns in mountainous areas have weak economic interactions with each other, an appropriate method is needed to evaluate their transportation accessibility. This paper takes the Honghe Hani Rice Terraced System (HHRTS) as a study area and develops a model to determine shortest time-distances from central towns in the study area to the nearest high-grade city as a way to evaluate transportation accessibility (TA). We then analyze the relationship between the accessibility of these towns and their economies. The study finds that the TA of the central towns in HHRTS is not good as a whole. More than 70% of the towns are more than 1 hour away from their nearest high-grade city. Of the four counties in the study area, Yuanyang County has the best traffic conditions, while Lvchun County has the worst traffic conditions. The central towns in the northern and middle regions have better TA than those in the west, southwest and east margin regions. The small-scale rural economy has little dependence on the transportation network, while secondary industries are obviously impacted by the transportation network. In the future, to support the integrated development of industries in HHRTS, traffic conditions in each town should be improved appropriately according to the industrial orientation of the town, but excessive investments to construct roads irrespective of eco-environmental impacts and economic benefits should be avoided. Especially in the case of ecologically vulnerable towns, the building high-grade roads should be banned.
The overexploitation of water resources has a substantial influence on their sustainable utilization and the ecological environment in a river basin. Quantification of the development and utilization of water resources plays an important role in guiding the rational utilization of water resources. Based on this, this paper develops the concept of water resource utilization polarization (WRUP) in order to qualitatively analyze whether water resources are being overexploited in the process of utilization. An index model of WRUP was built to quantify the degree of water resources overexploitation. In addition, taking seven secondary basins of the Yellow River as examples, the available quantity, overdraft and polarization indexes of surface water and groundwater resources were calculated. The results show that there are 34.49×108 m3 of surface water available, which accounts for 56.21% of the total surface water volume. A total of 5.84×108 m3 of groundwater is available, which is 58.74% of the total groundwater resources. We also found that the water resources are heavily overexploited and that there is extensive polarization in the middle and lower reaches of the Yellow River. The highest polarization of water resources occurs from Lanzhou to Toudaoguai where the polarization index is 19.88 and from Longmen to Sanmenxia where it is 11.81. There is no polarization above Longyangxia or from Toudaoguai to Longmen. Overall, the polarization of water resources is 7.95 over the entire Yellow River area. These results provide a reference for the availability of water resources that can be used to determine the degree of overexploitation of the water resources in the Yellow River.
Benefit sharing on transboundary rivers is an approach to address equitable and reasonable development and utilization of transboundary water resources (TWR). Through analyzing a few typical benefit sharing cases, this paper provides a systematic discussion of the theory of TWR benefits sharing. TWR features a kind of common pool resources (CPRs). Its benefit sharing subjects are the riparian countries. The shared benefits usually include flood prevention, power generation, navigation, irrigation, contributions to society and culture, etc. The benefit sharing modes mainly include shared benefits and responsibilities, reciprocal rights and obligations, equal benefit distribution, cost proportion-based benefit sharing, and demand-based benefit sharing. The first step in the realization process of benefit sharing is the sharing of data and information. Second is the benefit identification and evaluation. Third is the establishment of a mechanism to guarantee the benefit sharing. The conditions for realizing benefit sharing depends on, first, if the riparian countries are willing to cooperate with each other; second, whether the cooperation can bring incremental benefit or cost reduction in comparison with unilateral operation; and third, if the benefit distribution is equitable and reasonable and can stand the test of time.
The mining industry has made outstanding contributions to China’s economic and social development, but a series of environmental problems remain. As Green Mines and ecological civilization concepts are put forward, the relationship between people and nature is receiving more attention, and especially mining ethics. Present construction standards encompass legal mining, management standardization, comprehensive utilization, technological advancement, energy saving and waste reduction, environmental protection, land reclamation, harmonious community and enterprise culture. As at 2014 the Chinese Ministry of Land and Resources had published 661 Green Mines. Here, we analyze the present situation and prospects of Green Mines in China by the distribution from regional and mine type perspectives. Green Mines are nearly spread over every province and mine type, but Eastern China participated earlier than other areas. We discuss constructing Chinese mining ethics on the basis of traditional ethics and Western ecological ethics as theoretical foundations and practices. We consider that the significance of building Chinese mining ethics in Green Mine construction includes promoting social responsibility, improving environmental protection awareness and accelerating society development. Under the guidance of Chinese mining ethics we propose mining enterprise development models for the future, such as comprehensive utilization, circular economy and community harmony.
Being a developing country, the evaluation of Chinese circular economy should have its particular criterion that suits for specific national conditions. With the growth of economy, Chinese environmental loads should be permitted to increase at an appropriate speed. Based on this concept, this paper divides the process of evaluation into two parts which include evaluation of development level and evaluation of development performance. Firstly, this paper sets up a reference system which includes Zaozhuang City of Shandong Province, Jiaozuo City of Henan province, Shizuishan City of Ningxia Hui Autonomous Region and China that is regarded as a region respectively, analyzes the development level of circular economy of coal resource cities based on the evaluation indicator of ecological efficiency, and puts forward the future direction of circular economy of coal resource cities. Secondly, based on C Model of Circular Economy, this paper constructs the measurement model of development performance in which study regions are analyzed in a particular period that is from 2000 to 2020, and evaluates the development performance of circular economy for study regions according to the relationship of growth multiples between economic scale and environmental loads. We can draw several main conclusions: firstly, the development pathways of all four study regions belong to type Ⅱ which resource efficiency is preferred. Secondly, the comprehensive energy consumption efficiencies of coal resource cities were left far behind by China’s average level. Thirdly, the circular economies of all study regions have achieved remarkable progress. Fourthly, the development level of circular economy can be evaluated from two dimensions which consist of horizontal comparison method and vertical comparison method. Fifthly, C model is an appropriate development model that suits for Chinese national conditions and could be selected as an important method to evaluate regional development performance of circular economy.
Water footprint of production can be used to identify pressure on national or regional water resources generated by production activities. Water stress is defined as the ratio of water use (the difference between a regional water footprint of production and a green water footprint) to renewable water resources available in a country or region. Water stress can be used to identify pressure on national or regional water resources generated by production activities. This paper estimates the water footprint of production and the water stress in China during the years 1985-2009. The result shows that China’s water footprint of production increased from 781.58 × 109 m3 in 1985 to 1109.76 × 109 m3 in 2009. Mega-cities and regions with less agriculture production due to local climatic conditions (Tibet and Qinghai) had lower water footprint of production, while the provinces (Henan, Shandong) with higher agriculture production had higher footprint. Provinces with severe water stress increased from 6 in 1985 to 9 in 2009. High to severe water stress exists mainly in mega-cities and agricultural areas located in the downstream areas of the Yellow River and the Yangtze River in North and Central China. The outlook for water resources pressure in China is not optimistic, with areas of stress expanding from northern to southern of China.
The Silk Road Economic Belt (SREB) opens new development opportunities for Russia in general, and its Eastern regions in particular, via larger-scale and multi-level international cooperation. The eastern regions of Russia, rich in natural resources, have traditionally focused on resource extraction. In the context of the SREB, the issues of environmental security in Eastern Russia come to the fore. Here, we propose tools for ‘diagnosis’ if a chosen path of regional economic development proceeds according to the concept of a green economy. We use different indicators based on eco-intensity. We determine ecological-economic development trends in the Eastern border regions of Russia at the initial stage of the Silk Road Economic Belt formation to serve as a starting point and guideline for development processes within the SREB. If cooperation is directed to implementing the best Chinese production chains, significant improvements in the quality of economic growth in Russia will be achieved.
In recent years, large areas of farmland in the North China Plain have been converted into short-rotation poplar plantations. To analyze the impacts of poplar plantations on soil, 22 soil samples were collected and assayed from the soil profiles of a corn field and a poplar plantation. The results showed that the average soil moisture content of the soil profile in the poplar field was 2.6 percent lower than that of the arable land. The maximum difference in soil moisture content was found in the upper 0-10 cm of topsoil. Soil organic matter and nitrogen, phosphorus and potassium in the cornfield were significantly higher than in the poplar field. Higher nutrient content in the corn field may result from higher fertilizer inputs and the practice of returning straw to the cropped field. The analysis also showed no significant increase in soil organic matter content in deeper soil layers of the poplar field, which means that the conditions are not favorable for the formation of soil organic matter, or that soil organic matter needs a longer time to develop. Elements such as magnesium, iron, manganese and copper in both the corn field and the poplar field had a tendency to accumulate with increasing soil depth. Magnesium, iron, manganese and copper in the 0-80 cm soil layer of the poplar field were higher than those of the cornfield, but the situation was reversed at depths greater than 80 cm. It is concluded that poplar trees consume a large amount of soil moisture and soil nutrients. Local governments should prevent the development of new plantations of fast-growing trees in farmland and help farmers to recover their farmland from forestry plantations.
Nowadays, increased attention is being paid to the causal relationship between electricity consumption and economic growth. This paper attempts to examine the causal relationship between electricity consumption and economic growth for China’s Beijing-Tianjin-Hebei agglomeration, using annual data covering the period 1982- 2008. In this study, unit root tests, the Johansen co-integration test, and the Granger causality test are applied. The empirical results indicate that the two series (electricity consumption and economic growth) of the three locales (Beijing, Tianjin, and Hebei) are non-stationary. But first differences of the two series are stationary. The results of the Johansen co-integration test indicate that electricity consumption and economic growth are co-integrated in Hebei and Tianjin while this is not the case in Beijing. The Granger causality test implies that there is causality running from electricity consumption to economic growth in all of the three locales. Causality running from economic growth to electricity consumption is found in Hebei and Beijing while this is not the case in Tianjin. This means that an increase in electricity consumption directly affects economic growth and that economic growth also stimulates further electricity consumption in Hebei and Beijing. But in Tianjin, an increase in electricity consumption directly affects economic growth while economic growth cannot affect electricity consumption. These findings can provide useful information for local governments of the three locales to formulate sustainable energy and economic policies. The study is of great significance for circular economy and building a resource-conserving society.
With global warming, rainstorms and other extreme weather events are occurring frequently, leading to urban waterlogging disasters. A study on spatiotemporal variation characteristics of rainstorms in urban areas can provide scientific support for the design of urban drainage facilities to mitigate the damage of urban flooding disasters. Drawing on daily rainfall data from 20 meteorological stations during 1960-2010, this study analyzed change trends for annual rainstorms in Beijing, using the Mann-Kendall approach and cumulative departure curve as methodology. The results show that annual days of rainstorms in Beijing decreased non-significantly, but the precipitation of rainstorms and annual maximum daily precipitation declined significantly. The frequency of rainstorms generally decreased from southeast to northwest, with the greatest decrease occurring in the southeast plain areas. The results of this study contribute to the understanding of rainstorm risk in Beijing.
Due to the impact of climate change and human activities, the upper and middle reaches of the Tao’er River have become an ecologically sensitive area in Northeast China. It is important to evaluate the contributions of climate change and human activities to water suitability in the Tao’er River area. From the perspective of water and heat balance, the water suitability index (cr) was used to analyze the water suitability of the upper and middle reaches of the river. The nonparametric Mann-Kendall, moving t-test and cumulative anomaly methods were used to detect abrupt changes in Taonan station runoff from 1961 to 2012. Three inflexion years were detected. Thus, the entire time period was divided into four periods: 1961-1974, 1975-1983, 1984-1998, and 1999-2012. In order to estimate the impacts of climate change and human activities on runoff, the slope change ratio of cumulative quantity (SCRCQ) was adopted. Finally, the contribution of climate change and human activity to cr was transformed from the contribution of climate change and human activity to runoff by the sensitivity coefficient method and SCRCQ method. The results showed that the water suitability index (cr) had a decreasing trend 1961-2012. Factors influencing cr, such as net radiation and runoff, also exhibited a decreasing trend, while precipitation exhibited an increasing trend over the past 52 years. The trends of cr, net radiation and runoff were obvious, which passed the Mann-kendall test of significance at α=0.05. Human activities were the main factors that affected runoff, although the degree of impact was different at different times. During the past 52 years, the biggest contributor to the change in cr was precipitation.
In a world of climate change and socio-economic development, oil is the strategic resource that is closely intertwined and interdependent. Tracing the evolution of petroleum resources flow is fundamental to understanding petroleum supply and demand, and can also serve as the basis for assessing CO2 emissions from petroleum products. This paper aims to provide a petroleum products flow accounting framework that divides petroleum flow into four phases, three flows, three libraries, and two processes, and summarizes the approach to measure and analyze petroleum resources flows. It takes China as an example for empirical research, and finds that: ① China’s petroleum production, consumption and import have significantly increased over the past two decades, and the combination of increasing demand and limited supply have created an urgent need for China to diversify its petroleum sources globally to ensure its oil security. ② Final consumption accounts for the use of most petroleum products and special attention should be paid to the losses in the petroleum refining process. ③ With the exception of crude oil, petroleum product flows among various sectors has changed greatly. Particularly, the flow of petroleum products into transport and residential consumption has trended upward significantly, whereas the flow to industry is trending downward. ④ CO2 emission data shows that CO2 emission amounts increased rapidly from 456Mt in 1993 to 1517Mt in 2013. Previously, the top three CO2 emitters were the industrial sector, the transport sector including the transport, storage and post segments, and the thermal power sector. Currently, the largest emitters are the transport sector, the industrial sector and the residential consumption sector. Finally, poorly demarcated system boundaries and incomplete databases and models constrain research on industry flows of petroleum resources for non-energy use.
In order to investigate the feasibility of reintroducing the South China tiger (Panthera tigris amoyensis) in the Jiangxi Matoushan National Nature Reserve, field surveys were conducted to assess prey distribution in the reserve. Twelve permanent transects were set in three distinct functional zones from February to April 2012 and May to July 2013. A total of 112 ungulate signs were recorded on these transects. In addition, 20 camera traps were used to survey ungulates and predators in 2012, while the following year we extended the survey site by using 30 cameras. Overall, 6641 capture events on 2930 camera days were obtained, presenting a variety of ungulate species: muntjak (Muntiacus muntjak), tufted deer (Elaphodus cephalophus), serow (Capricornis sumatraensis) and wild boar (Sus scrofa). Population structure and composition of ungulates was compared in different functional zones using a single factor of variance analysis in SPSS software. Significant differences in the distribution of ungulates were recognized between the core zone and experimental zone, but not in other zones due to differences in habitat types and management practices of the nature reserve. Using ArcGIS analysis and Salford Predictive Modeler software, we ran several predictive models to understand which areas are most suitable for ungulates. We conclude that muntjac and wild boar are mainly distributed in the experimental zone, serow are more common in the core zone, while tufted deer are located evenly in the three functional zones. Finally, suggestions for effective and feasible management strategies and techniques for Matoushan National Nature Reserve were recommended based on the results and analysis in this study.