共查询到20条相似文献,搜索用时 15 毫秒
1.
Serrano Martinez JM 《Acta geographica》1989,(79):20-37
This is an analysis of regional differences in population trends in Spain during the twentieth century. Data are from a variety of official sources, including the censuses of 1900, 1960, 1970, and 1981. The author notes that up until 1975, interregional migration flows had acccentuated regional economic differences. However, the economic problems that have occurred since 1975, coupled with the political changes associated with greater regional autonomy, have resulted in new trends in internal migration that could have significant effects on the future distribution of the country's population. 相似文献
2.
Currently, the historical archive images of Landsat family sensors are probably the most effective data products for tracking global longitudinal changes since the 1970s. However, the issue of the degree and extent of cloud coverage is always a challenge and varies distinctively worldwide. So far, acquisition probability (AP) analyses of cloud cover (CC) of Landsat observations have been conducted with different sensors at regional scale. To our knowledge, CC probability analysis for the newly-launched Landsat-8 Operational Land Imager (OLI) across China is not reported. In this paper, monthly, seasonal, and annual APs for Landsat OLI (44,228 in total) images over China acquired from April 2013 to October 2016 with various CC thresholds were analyzed. The results showed that: first, the cumulative average APs of all OLI data over China at the CC thresholds ≤30% was about 49.6% which illustrated the availability of OLI imagery across China. Second, the spatial patterns of 10%, 20%, and 30% CC thresholds of OLI observations, coincided well with the precipitation distributions separated by the respective 200 mm, 400 mm, and 800 mm isohyetal lines. Third, the APs of images with the 30% CC threshold are the highest in autumn and winter especially in October of 58.7%, while the corresponding lowest probability occurred in June of 41.0%. Finally, the spatial differences in APs of targeted images with ≤30% CC thresholds were quite significant. At regional scales, the arid and semi-arid areas, Inland River and Songliao River basins, and northwestern side of the Hu Huanyong population line had the larger probabilities of obtaining high-quality images. Our study suggested that OLI imagery satisfy the data requirements needed for land surface monitoring, although there existed obvious spatio-temporal differences in APs over China at the 30% CC threshold. 相似文献
3.
The formal opportunity to learn geography in the United States is unevenly distributed across space, creating possible geography deserts. Data on the number of exams taken in Advanced Placement Human Geography (APHG) and bachelor’s degrees earned in geography are mapped at the state and regional scales. Normalized rates are ranked and grouped into quintiles. For APHG exams, states in the southeastern region of the United States are in the uppermost quintiles while states in the northeastern region are in the lowermost quintiles. The pattern for bachelor’s degrees in geography is somewhat the spatial inverse of that for APHG. 相似文献
4.
Andrea Pollio 《Urban geography》2016,37(4):514-534
In the heyday of the late 2000s financial crisis, austerity urbanism became a dominant practice of state financial restructuring—an intensification in the encroachment of the neoliberal project into the agendas of local governments. In the specific case of Italy, which faced political and economic distress between 2011 and 2013, “smart city” policies became one of the foundational political technologies for the implementation of austerity measures. In this paper, I analyse how the smart city provided a lexicon for urban austerity through a series of different sites and vehicles of policymaking, from practitioners to companies and other institutions. I argue that smart city discourses and practices functioned as a political technology that was effective in justifying cost containment measures and supporting the shift to pro-innovation public expenditures. Yet, at the same time, the smart city techno-utopian vocabulary created spaces where other meanings and, potentially, alternative political outcomes were made possible by diverse alignments of knowledge and expertise. 相似文献
5.
Soil texture greatly influences soil water movement, thus may affect the water balance and vegetation growth in the desert–Loess Plateau transition zone. This study is to determine if the water balance differs in homogeneous and layered soils with Caragana korshinkii stands in semiarid region. Soil water measurements up to 500-cm depth were taken in 2006 and 2007 on homogeneous sandy soil, homogeneous silt loam soil, and layered soil with sand overlying silt loam. HYDRUS-1D was used to simulate the soil water balance. The results indicated the annual water balance components were greatly affected by soil layering. The ratio of average actual evapotranspiration (ETa) to precipitation (P) during the two years in the layered soil was slightly lower than that in homogeneous soils. The ratios of annual actual transpiration (Tr) to evapotranspiration were 50.9%, 41.2% and 30.6% in layered soil, homogeneous sandy soil, and homogeneous silt loam soil, respectively. C. korshinkii grown in layered soil had deeper soil water recharge and higher Tr/ETa ratio, thus had more available water for transpiration than that in homogeneous soils. This study suggested the layered soil with sand overlying silt loam is more favorable to C. korshinkii growth in terms of water use than homogeneous soils in the desert–Loess Plateau transition zone. 相似文献
6.
Research has shown persistent inequalities in access to health care between and within sociodemographic groups and geographic areas. Yet much of what we know about geographical disparities in access comes from studies of regional and urban/rural contrasts, or from studies of intra-urban, neighborhood-level variations. We know relatively little about variations in access to primary health care across different urban areas, and whether such variations translate into differences among residents’ health. This study examines how health status and access to primary care vary across five of Canada’s largest cities, paying particular attention to populations that may be particularly vulnerable based on age and income. Across all outcomes, there was a consistently strong relationship with individual socioeconomic status. We show that city of residence is important for access to health care but not for health status. Results are discussed in terms of their relevance for urban health-care policy and delivery, and impacts on health and access to care. 相似文献
7.
Seasonal stratospheric ozone depletion in the Arctic has raised the question of whether the associated increases in ultraviolet-B (290-320 nm) constitute a significant health risk in Arctic populations. Increases in skin cancer in Europe and the USA from excess UV-B resulting from ozone depletion have been predicted. Skin cancer is, however, rare in Inuit populations.
UV-B also causes a selective down regulation of the immune system which may be a natural regulatory mechanism evolved to prevent autoimmune attack on sunlight-altered skin. The action spectrum for UV-B immunosuppression implicated a unique skin photoreceptor molecule, urocanic acid (UCA), which isomerizes from the trans to the cis isomer on exposure to UV-B, the cis isomer being immunosuppressive. This form of immunosuppression is important in skin cancer and possibly in infectious diseases.
The epidemiology of non-Hodgkin's lymphoma shows a relationship with UV exposure, postulated to be via the immunosuppressive effects of UV-B. Cancers which show an excess in Inuit populations include nasopharyngeal and salivary gland cancer. Genetic factors appear to be involved, but these are thought to be virally related cancers possibly associated with the high viral load in these populations. In several studies on non-Arctic populations, salivary gland cancer has been linked to ultraviolet exposure. A potential role for UV-B exposure in these cancers in the Arctic needs to be explored.
In view of the high levels of POPS in some Arctic regions, potential interactions between the immunosuppression caused by some of these pollutants and the effects of UV-B need to be investigated. 相似文献
UV-B also causes a selective down regulation of the immune system which may be a natural regulatory mechanism evolved to prevent autoimmune attack on sunlight-altered skin. The action spectrum for UV-B immunosuppression implicated a unique skin photoreceptor molecule, urocanic acid (UCA), which isomerizes from the trans to the cis isomer on exposure to UV-B, the cis isomer being immunosuppressive. This form of immunosuppression is important in skin cancer and possibly in infectious diseases.
The epidemiology of non-Hodgkin's lymphoma shows a relationship with UV exposure, postulated to be via the immunosuppressive effects of UV-B. Cancers which show an excess in Inuit populations include nasopharyngeal and salivary gland cancer. Genetic factors appear to be involved, but these are thought to be virally related cancers possibly associated with the high viral load in these populations. In several studies on non-Arctic populations, salivary gland cancer has been linked to ultraviolet exposure. A potential role for UV-B exposure in these cancers in the Arctic needs to be explored.
In view of the high levels of POPS in some Arctic regions, potential interactions between the immunosuppression caused by some of these pollutants and the effects of UV-B need to be investigated. 相似文献
8.
Dorothy Ives Dewey 《The Professional geographer》2013,65(1):149-151
Haiti and other developing countries have increasingly turned to emigrant remittances as a potential source of development capital. There is a vigorous debate in the development community about the impacts of remittances, however, with concerns about dependence challenging the optimism about a potential new development engine. Based on interviews with forty-two remittance recipients in Haiti and forty-five corresponding senders in New York State, we find that the remittance economy in Haiti is indeed productive and has the potential to generate employment and other important development benefits. That said, there are important limitations created by broader political–economic conditions and deeply entrenched inequalities. 相似文献
9.
JI Zhengxin LIU Chao XU Yueqing SUN Minxuan WEI Hejie SUN Danfeng LI Yaoyao ZHANG Ping SUN Qiangqiang 《地理学报(英文版)》2023,33(4):779-800
Developed here is an integrated framework for identifying production–living–ecological space(PLES) quantitatively at grid scale from the perspective of multifunction land use, and 25 compound space types are classified to highlight the multiple functions of PLES. As a typical mountainous city in northern Hebei province, Zhangjiakou is used as a case study, and the results show that more than 80% of the land space in Zhangjiakou has remarkable triple functionality. The living-dominated space and ... 相似文献
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11.
LIU Chengwu LI Xiubin 《地理学报(英文版)》2006,16(3):286-292
Based on the cost-benefit data (1980-2002) of farm products and China Agriculture Yearbooks, this paper studies the regional disparity in the changes of the agricultural land use in China during the period 1980-2002 from three aspects such as the degree of intensity, the sown area and the abandoned farmland. The results show that: (1) The degree of intensity of land use in the westena region during 1980-2000 has a strong uptrend, but in the eastern and central regions the degree of intensity descends obviously and has shown a continuous downtrend since 1997. (2) The total sown area shrinks notably in the eastern region, while it enlarges constantly in the western region. (3) The sown area in the eastern, central and western regions has gone through a similar cyclic process: down (1980-1985)-up (1985-1991)-down (1991-1994)-up (1994-1999)-down (1999-2002). However, there are obvious differences in amplitude variation and tendency among them. The sown area has shrunk in the eastern region and expanded in the central and western regions especially before 1999. (4) The most cases of abandoned farmland are reported in the central region, the second in the eastern region and the least in the western region. The abandonment phenomena chiefly occurred during 1992-1995 in the eastern region, and during 1998-2002 in the central region. 相似文献
12.
Using land reclamation information from gazetteers and corresponding historical records as further evidence, we extracted information about land reclamation in the early years of reclamation (at the “beginning date”) and during the climax period (the maximum extent). We analyzed land reclamation processes in the farming–grazing transitional zone in northeast China during the Qing Dynasty (1644–1911). Among thirty-seven counties for which the beginning date of land reclamation was recorded, 32 percent began reclamation early, primarily between the Shunzhi (1644–1661) and the Kangxi reigns (1662–1722), 19 percent were exploited during the Yongzheng reign (1723–1735), and 19 percent were exploited during the Guangxu reign (1875–1908). Among forty-six counties for which the maximum extent of land reclamation was recorded, the counties of Fengning, Longhua, and Longjiang were extensively exploited before 1800. From 1800 to 1860, four counties were extensively exploited, including Changtu County, Horqin Left Wing and Behind Banner, Horqin Left Wing and Middle Banner, and Shangyi County. Most counties were extensively exploited after 1860. Land reclamation was usually carried out by Han farmers, who were either recruited by Mongol landowners or were fleeing famine. Extensive land reclamation in the majority of counties was conducted during the Guangxu reign (1875–1908) in the late Qing Dynasty, when the Qing government implemented the policy of promoting Han migration to strengthen its hold on the frontier by distributing land. 相似文献
13.
This study aims to test the effectiveness of the changes detection techniques to determine the evolution of the various geomorphological units identified in Ebro River mouth, in order to establish their evolutionary trends and to explain the changes between 1957 and 2013 years. To evaluate the most significant changes in the Ebro River mouth, the different geomorphological units present in the area were obtained by interpretation of aerial imagery. It has been noted that the period 1957–1984 was more dynamic and intense than the period 1984–2013, indicating a loss of capacity of the processes causing changes, and the shoreline is evolving toward a more stable morphology. It was determined that the most important processes that took place were mainly marine erosion processes and anthropogenic expansion. On the characterization in the entire period studied, it was determined that growth or decrease processes (net change) are as relevant in the region as processes which include location changes (swap). The change analysis methodology allows analyzing the evolution of coastal geomorphology, since it allows the determination and characterization of the principal transitions amongst the identified geomorphological units, and, therefore, to obtain the main processes that dominate the area, which is particularly relevant on highly vulnerable environments, such as coastal deltaic areas. 相似文献
14.
《The Professional geographer》2013,65(4):451-464
In our study, 48 U.S. departments that grant geography PhDs are compared along four measures of academic productivity. Using 1980–1994 as the base period, research productivity of faculty was assessed by counting book titles, as well as authorships in 77 journals. Teaching productivity was determined by placement of PhDs in graduate programs of geography in North America, and by a weighted index of teaching outcomes. Data were summed for departments, but are reported primarily as productivity per person (per FTE count). The results point to a wide variety of departmental profiles, from those departments that appear to emphasize teaching outcomes to those that are more productive in book publishing and journal authorship, with several exhibiting a balance between teaching and research. 相似文献
15.
Richard Wright Mark Ellis Steven R. Holloway Sandy Wong 《The Professional geographer》2013,65(2):173-182
The growing ethnic and racial diversity of the United States is evident at all spatial scales. One of the striking features of this new mixture of peoples, however, is that this new diversity often occurs in tandem with racial concentration. This article surveys these new geographies from four points of view: the nation as a whole, states, large metropolitan areas, and neighborhoods. The analysis at each scale relies on a new taxonomy of racial composition that simultaneously appraises both diversity and the lack thereof (Holloway, Wright, and Ellis 2012). Urban analysis often posits neighborhood racial segregation and diversity as either endpoints on a continuum of racial dominance or mirror images of one another. We disturb that perspective and stress that segregation and diversity must be jointly understood—they are necessarily related, although not as inevitable binary opposites. Using census data from 1990, 2000, and 2010, the research points to how patterns of racial diversity and dominance interact across varying spatial scales. This investigation helps answer some basic questions about the changing geographies of racialized groups, setting the stage for the following articles that explore the relationship between geography and the participation of underrepresented groups in higher education. 相似文献
16.
Daniel M. Deocampo 《Journal of Paleolimnology》2004,31(1):1-9
Ultrafine clays (<0.1 m) from six East African basins show wide chemical variability that can be conveniently described as the octahedral cation index (OCI), calculated as octahedral element ratio Mg/(Al+Fe). Values range from dioctahedral clays with OCI < 0.1 (upland soils/detrital sources) to trioctahedral clays with OCI > 4 (saline, alkaline lake deposits). The association of Mg-rich clays with saline, alkaline conditions provides a paleochemical proxy in sedimentary contexts. The octahedral chemistry of central-basin clays from paleolake Olduvai (1.79 Ma) records two lake expansions, with an intervening lake contraction, over 18,000 years. The initial lake expansion correlates well with the marine record of increased African humidity, but the subsequent drying episode does not, suggesting that some high-frequency environmental oscillations in East Africa may occur independent of obliquity and precession control. The clay record correlates well with the fossiliferous and archaeologically rich stratigraphy of the lake margin, and suggests that fossils and artifacts accumulated on the exposed lake margin over <4000 years. The chemistry of clays is a potentially powerful tool to add to multi-proxy studies in basins with alkaline waters, particularly in stratigraphic intervals that lack pollen, calcareous, or siliceous microfossils. 相似文献
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18.
Wind tunnel simulation of the effects of freeze–thaw cycles on soil erosion in the Qinghai–Tibet Plateau 总被引:1,自引:1,他引:0
Intense freezing and thawing actions occur in the Qinghai–Tibet Plateau because of its high elevation and cold temperature. The plateau's unique environment makes it easy to generate wind erosion under dry, windy weather conditions, resulting in the emergence of desertification. As a major form of freeze–thaw erosion, freeze–thaw and wind erosion is displayed prominently on the Qinghai–Tibet Plateau. Therefore, in this study, soil samples were collected from the surface of the plateau to undergo freeze–thaw and wind erosion simulation experiments. Results show that wind erosion strength increases with an increasing number of freeze–thaw cycles, water content in the freezing–thawing process, and the difference in freeze–thaw temperatures. Therefore, in the conditions of water participation, the main reason for the freeze–thaw and wind erosion in the Qinghai–Tibet Plateau is the damage to the soil structure by repeated, fierce freeze–thaw actions, and the sand-bearing wind is the main driving force for this process. The research results have theoretical significance for exploring the formation mechanism of freeze–thaw and wind erosion in the Qinghai–Tibet Plateau, and provide a scientific basis for freeze–thaw desertification control in the plateau. 相似文献
19.
The Tonle Sap is an invaluable resource for the people of Cambodia, and is a globally significant ecological site. Much of the literature published on the environmental health and management of the lake suggests that its sustainability is threatened by accelerated rates of infilling related to unfettered land-use in the catchment. However, the evidence for supposedly increased sedimentation rates is confused and contradictory, and there have been very few studies that have attempted to actually measure the rate at which sediment is accumulating on the bed of the lake. This research measures long-term sedimentation rates in the Tonle Sap in an attempt to provide an empirically derived baseline against which more recent and allegedly accelerated sedimentation rates can be compared. Radiometric dating techniques (14C, 210Pb, 137Cs) reveal that sediment has been accumulating in the lake at an average long-term rate of less than 1 mm per year. There is a clear and consistent decline in the rate of sediment accumulation in the lake basin over time, with the highest rates recorded in the middle to early Holocene epoch. It is recommended that research be directed toward measuring changes in the morphology of the lake margin over time, rather than focus on changes in the bathymetry of the lake basins themselves, which are here shown to be effectively stable in terms of sediment accumulation. 相似文献
20.
Urban regeneration has intermittently been identified within Commonwealth policy circles as central to the functioning of Australian cities since the 1940s. This paper adds to existing knowledge by exploring the role of the Commonwealth Department of Urban and Regional Development (DURD) in the 1970s in facilitating a series of urban regeneration projects in Sydney. Drawing upon ministerial correspondence and minutes recently out of confidential embargo, the genesis of a holistic urban regeneration agenda is explored. The paper traces the approaches to Commonwealth intervention at a time marked by disillusionment with the comprehensive redevelopment paradigm. It explores the relationships and tensions apparent between and within different levels of government in establishing a Commonwealth presence, focusing on three inner city neighbourhoods: Waterloo, Glebe and Woolloomooloo. The significance of the interventions is considered to lie primarily in the pioneering of an all-of-government approach to urban governance. 相似文献