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21.
In many coastal catchments of south eastern New South Wales, Australia, changes in river morphology are a response to human impact superimposed on spatial and temporal patterns of variability in precipitation and discharge. Understanding, and preferably quantifying, spatial and temporal patterns of hydrologic variability are essential to understanding natural changes, and to separate these from artificial changes in river systems. Prediction and management of water resources are also dependent upon this understanding. We assess the variability in precipitation and discharge using the wavelet transform which projects the time series of data into a three dimensional surface of frequency, amplitude and time. The analysis reveals that changes across time often reflect changes in individual seasons and may be linked to changes in particular seasonal atmospheric circulation systems. Strong perturbations in the analysis of one catchment are consistent with documented, geomorphically‐effective, flooding sequences. The characteristics of the series in the transformed data reveal interesting differences at certain times and scales which may be a reflection of changes in larger scale atmospheric processes.  相似文献   
22.
福建籍遗民史家郑郊前半生在明朝、后半生在清朝。初成于崇祯末年、终定于康熙初期的《史统》是一部以阐明中国历史之统为主旨的通史著作。《史统》提供了一种哲理化的中国历史解释模式,洵可称为晚明理学化史学代表作。惜因未刊,近代以来、所知甚鲜。  相似文献   
23.
Recent research refines previous interpretations about the role of climatic factors in the development of Mapungubwe. First, the Medieval Warm Epoch started at about AD 1000, rather than 900. At about AD 900, Zhizo people moved into the Shashe-Limpopo Basin, most likely to hunt elephants for the East Coast trade. Secondly, a dry period at about AD 1200–1250 affected farming societies over a wide area. In the Basin, multiple rainmaking episodes occurred at this time. A similar situation took place around Makapansgat and at Great Zimbabwe. Thirdly, Mapungubwe was probably abandoned in AD 1300 because of cooler and drier conditions. At this time, it would have been impossible to maintain floodplain agriculture at the intensity necessary to support the large population. Agricultural failures probably undermined political authority, contributing to Mapungubwe's abandonment and shift in power to Great Zimbabwe. This detailed sequence challenges the re-calibrated climatic series from Makapansgat.  相似文献   
24.
本文运用黄土地层学、气候地层学、生物地层学的方法尝试建立中国北方旧石器时代中期文化发展序列,认为大荔遗址、丁村遗址、周口店15地点、许家窑遗址、陕西长武窑头沟、辽宁喀左鸽子洞的年代分别相当于深海氧同位素的阶段7-8、6-4、6、4、4、3。并认为中更新世哺乳动物群在北方的最终消失大约在阶段6,如以中更新世哺乳动物群的消失作为中晚更新世界限,则和黄土地层学的研究结果比较吻合。  相似文献   
25.
钧瓷系与禹州钧窑   总被引:1,自引:0,他引:1  
瓷器研究中,“瓷系”的概念比“窑系”在某些时候显得更为合理.钧瓷系产生于北宋末年,并一直延续至清代,而禹州钧台、刘家门等钧瓷系窑址很可能就是北宋的汴京官窑所在.  相似文献   
26.
The origin of large‐scale ancient dolomite is one of the most hotly debated topics in sedimentology. The Loushanguan group of the upper 3rd‐Furongian Cambrian series on the south‐eastern margin of the Sichuan Basin consists of numerous dolomites, and the origins of these dolomites have never been reported previously although they are probably good hydrocarbon reservoirs. Based on a systematic analysis of petrology, fluid inclusions, carbon and oxygen isotopes, trace elements and rare earth elements (REEs), this study provides some unique insights into the origins of the dolomites. Four dolomite types have been identified in the study area: dolomicrite, fabric‐retentive oolitic dolomite, fabric‐obliterative dolomite and saddle dolomite cement. In the dolomicrite and fabric‐retentive oolitic dolomite, high Sr contents (with respect to the fabric‐obliterative dolomite) and the lack of two‐phase aqueous inclusions suggest that they formed at shallow‐to‐intermediate burial depths at low temperatures (<50–60°C). Carbon and oxygen isotopes and seawater‐like REE+Y characteristics of the dolomicrite and fabric‐retentive oolitic dolomite indicate that the dolomitizing fluids were evaporated seawater or slightly modified seawater. The obliteration of the original sedimentary fabric and relatively low δ18O and Sr values compared to the fabric‐retentive dolomite indicate that fabric‐obliterative dolomite formed at intermediate‐to‐deep burial diagenesis. The chemical composition approaches pure dolomite and the REE+Y characteristics are similar to those of the fabric‐retentive dolomite, indicating that the fabric‐obliterative dolomite was formed due to the recrystallization of the previously formed fabric‐retentive dolomite at elevated burial depths and temperatures. High fluid inclusion homogenization temperatures (115–150°C), low δ18O values, nonplanar‐a crystals and seawater‐like REE+Y characteristics suggest that saddle dolomite cement formed by reprecipitation of dolomite that related to seawater‐driven and deep burial fluid. In the study area, dolomicrite and fabric‐retentive oolitic dolomite may have been formed by penecontemporaneous or seepage‐reflux dolomitization during early‐stage diagenesis. Subsequently, during progressive burial, most of the fabric‐retentive dolomite was converted into fabric‐obliterative dolomite by recrystallization. This study confirms that fabric‐obliterative dolomite was the main dolomite type, and although deeply buried, these Cambrian dolomites most likely have preserved coeval seawater geochemical signals.  相似文献   
27.
Iceland's centuries-long history of epidemics with its unusually complete disease records has attracted study from several disciplines. But detailed spatial data of particular interest to historical geographers date only from 1895 and were consistently maintained for about a century thereafter. Within this period, this paper concentrates on morbidity records of reported cases of infectious diseases for an 87-year window which was open between 1902 and 1988. In this time slice, spatially detailed data for seven demographically important infectious diseases allow the geography of 131 discrete epidemic waves with a recorded total of 529,000 cases to be tracked. Changes in the behaviour of the seven diseases over the period are analyzed and related to both epidemiological theory and to the changing historical geography of the island. The paper complements earlier Icelandic work by the authors on the historical geography of single diseases (measles, influenza and poliomyelitis) by extending the range of diseases, and by considering their common spatial behaviour and their interrelationships.  相似文献   
28.
Due to the global increases in urbanisation rates, urban sprawl has become a worldwide issue. In China, the development of rural areas has been affected by urban expansion and adjustments of metropolitan areas by administrative divisions that have led to losses in agricultural lands and ecosystem services. There is the ‘paradoxical’ desire for governments to promote rural development and protect land resources. Urban fringe sprawl is a prominent issue in the process of rural development. Identifying and measuring sprawl at the urban fringe could assist policymakers to either encourage or discourage this phenomenon. This paper demonstrates use of multidimensional indicators to effectively measure urban fringe sprawl by remote sensing, in addition to demographic and socio‐economic data. Using integrated indicators observed in the recent Chinese development context, urban fringe sprawl was measured comprehensively for Jiangning, a district in the city of Nanjing, China. This study indicates that Jiangning is sprawling rapidly. The results also show that the multidimensional indicator approach could provide decision support to create effective long‐term land‐use planning policies for controlling urban sprawl patterns.  相似文献   
29.
The normalised difference vegetation index (NDVI) has evolved as a primary tool for monitoring continental‐scale vegetation changes and interpreting the impact of short to long‐term climatic events on the biosphere. The objective of this research was to assess the nature of relationships between precipitation and vegetation condition, as measured by the satellite‐derived NDVI within South Australia. The correlation, timing and magnitude of the NDVI response to precipitation were examined for different vegetation formations within the State (forest, scrubland, shrubland, woodland and grassland). Results from this study indicate that there are strong relationships between precipitation and NDVI both spatially and temporally within South Australia. Differences in the timing of the NDVI response to precipitation were evident among the five vegetation formations. The most significant relationship between rainfall and NDVI was within the forest formation. Negative correlations between NDVI and precipitation events indicated that vegetation green‐up is a result of seasonal patterns in precipitation. Spatial patterns in the average NDVI over the study period closely resembled the boundaries of the five classified vegetation formations within South Australia. Spatial variability within the NDVI data set over the study period differed greatly between and within the vegetation formations examined depending on the location within the state. ACRONYMS AVHRR Advanced Very High Resolution Radiometer ENVSAEnvironments of South Australia EOS Terra‐Earth Observing System EVIEnhanced Vegetation Index MODIS Moderate Resolution Imaging Spectro‐radiometer MVC Maximum Value Composite NDVINormalised Difference Vegetation Index NIRNear Infra‐Red NOAANational Oceanic and Atmospheric Administration SPOT Systeme Pour l’Observation de la Terre  相似文献   
30.
The U and Th concentrations of 16 miliolite samples from the Hiran Valley in Saurashtra ranged from 0·3 to 2·14ppm and 0·12 to 0·82ppm respectively. The 234U/238U activity ratio ranged from 1·09 to 1·16, with a mean of 1·12±0·02. It agrees well with the seawater value of 1·14±0·02 within the quoted errors. Nine of the samples were datable by the 230Th/234U method and the ages ranged from 56·8 to 190 Kyr. The problem of chronology of Palaeolithic artifacts is interlinked with the miliolite and other coastal formations. The present investigations permit the development of a chronological framework for the Palaeolithic cultures in the Hiran Valley in particular, and generally in Saurashtra Peninsula. On the basis of radiometric dates and relative chronology, the Lower Palaeolithic cultures fall in a time-bracket of 190-69 Kyr bp. The Middle Palaeolithic industry is much older than 56·8 Kyr bp. The dates obtained for the Lower Palaeolithic cultures are perhaps the oldest reported to date.  相似文献   
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