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1.
In the present paper, we propose a new method for the estimation of the variogram, which combines robustness with efficiency under intrinsic stationary geostatistical processes. The method starts by using a robust estimator to obtain discrete estimates of the variogram and control atypical observations that may exist. When the number of points used in the fit of a model is the same as the number of parameters, ordinary least squares and generalized least squares are asymptotically equivalent. Therefore, the next step is to fit the variogram by ordinary least squares, using just a few discrete estimates. The procedure is then repeated several times with different subsets of points and this produces a sequence of variogram estimates. The final estimate is the median of the multiple estimates of the variogram parameters. The suggested estimator will be called multiple variograms estimator. This procedure assures a global robust estimator, which is more efficient than other robust proposals. Under the assumed dependence structure, we prove that the multiple variograms estimator is consistent and asymptotically normally distributed. A simulation study confirms that the new method has several advantages when compared with other current methods. 相似文献
2.
V. G. Kuznetsov 《Lithology and Mineral Resources》2008,43(2):180-186
Analysis of the growth pattern of stromatolites and relationships of their thick carbonate bodies with host rocks are used to substantiate the lack of reefs sensu stricto, i.e., buildups notably towering above the sea bottom, in the Proterozoic. 相似文献
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4.
Robert W. Thompson Andrew G. Dickson Samuel E. Kahng Christopher D. Winn 《Aquatic Geochemistry》2014,20(5):467-481
Inorganic carbon measurements made in the late 1980s suggest that alkalinity in the waters surrounding the Hawaiian Archipelago is elevated relative to the oligotrophic waters of the North Pacific. These observations have been interpreted as evidence for a “halo” of elevated carbonate saturation state produced by the dissolution of highly soluble magnesium calcites and aragonite on the island platform or in the water column surrounding the islands. If present, this “halo” has implications for air–sea carbon dioxide exchange in Hawaiian waters and may impact the response of coral reef communities to the acidification of the surface waters of the global ocean. The purpose of this study was to assess the magnitude and extent of the elevated calcium carbonate saturation state observed on previous expeditions to this region. Transects were conducted near several atolls in the Northwestern Hawaiian Islands from shallow water adjacent to the forereef to the open ocean 15 km from the island. Hydrographic profiles were collected at each station, and discrete water samples were collected for the measurement of carbon system parameters necessary to compute calcium carbonate saturation state. Our data were compared with observations made at the Hawaii Ocean Time-series site at Station ALOHA and with hydrographic data collected on the WOCE lines in the North Pacific around the archipelago. We did not detect a carbonate dissolution halo around the islands. We conclude that the previously observed halo was probably an analytical artifact, or possibly a result of extreme variability in carbon chemistry surrounding the islands. 相似文献
5.
Is geographical proximity necessary in the innovation networks in the era of global economy? 总被引：7，自引：0，他引：7
In the analysis of geographical spillovers, a commonly accepted hypothesis is that the different actors of innovation need to be physically closed to one another because the transfer of tacit knowledge implies frequent face-to-face relations. This hypothesis is put under closer examination in this paper. The first section analyses the need for economic agents to be closely located to develop research and innovative activities, starting with the analysis of their need for co-ordination and using some case studies. Based on the example of three French regions, the second section examines the importance given by the local development policies to geographical proximity in order to support the rapid development of local networks favouring innovation. In both sections, nonlocal relations appear as a key factor to develop innovation. As a conclusion, nonlocal relations should be encouraged by local development policies in the same way as local relations. 相似文献
6.
<正>supported by the Science and Technology Project of China(grant no.WFSD-00003),focuses on the in-situ stress measurements in the WFSD-1 borehole Stress is defined as the natural stress existing between 相似文献
7.
《地学前缘(英文版)》2016,7(6)
Life was limited for most of Earth's history, remaining at a primitive stage and mostly marine until about 0.55 Ga. In the Paleozoic, life eventually exploded and colonized the continental realm. Why had there been such a long period of delayed evolution of life? Early life was dominated by Archaea and Bacteria,which can survive ionizing radiation better than other organisms. The magnetic field preserves the atmosphere, which is the main shield of UV radiation. We explore the hypothesis that the Cambrian explosion of life could have been enabled by the increase of the magnetic field dipole intensity due to the solidification of the inner core, caused by the cooling of the Earth, and the concomitant decrease with time of the high-energy solar flux since the birth of the solar system. Therefore, the two phenomena could be responsible for the growth and thickening of the atmosphere and the development of land surface life. 相似文献
8.
Georg Miehe Sabine Miehe Kerstin Bach Jürgen Kluge Karsten Wesche Yang Yongping Liu Jianquan 《Quaternary Research》2011,76(2):243-252
Arid and Alpine ecosystems are known for extreme environmental changes during the Late Quaternary. We hypothesize that the world's largest Alpine arid ecosystem however, the Alpine Steppes of the Tibetan highlands, remained ecologically stable during the LGM and the mid-Holocene. This hypothesis is tested by distributional range of plant species, plant life forms and rate of endemism. The set of character species has a precipitation gradient between 50 and 350 mm/a, testifying for resilience to precipitation changes. 83% of the species have a wider vertical range than 1000 m used as a proxy for resilience to temperature changes. 30% of the species are endemic with 10 endemic genera, including plate-shaped cushions as a unique plant life form. These findings are in line with palaeo-ecological proxies (δ18O, pollen) allowing the assumption that Alpine Steppes persisted during the LGM with 3 to 4 K lower summer temperatures.During the mid-Holocene, forests could have replaced Alpine Steppes in the upper catchments of the Huang He, Yangtze, Mekong, Salween and Yarlung Zhangbo, but not in the interior basins of the north-western highlands, because the basins were then flooded, suppressing forests and supporting the environmental stability of this arid Alpine grassland biome. 相似文献
9.
YAN Zhen FU Changlei Jonathan C. AITCHISON ZHOU Renjie Solomon BUCKMAN CHEN Lei 《《地质学报》英文版》2020,94(4):901-913
The South Qilian belt mainly comprises an early Paleozoic arc-ophiolite complex, accretionary prism, microcontinental block, and foreland basin. These elements represent accretion-collision during Cambrian to Silurian time in response to closure of the Proto-Tethyan Ocean in the NE of the present-day Tibet Plateau. Closure of the Proto-Tethyan Ocean between the Central Qilian block and the Oulongbuluke block and the associated collision took place from NE to SW in a zipper-like style. Sediment would have been dispersed longitudinally SW-ward with a progressive facies migration from marginal alluvial sediments toward slope deep-water and deep-sea turbidites. This migration path indicates an ocean basin that shrank toward the SW. The Balonggongga'er Formation in the western South Qilian belt represents the fill of a latest Ordovician-Silurian remnant ocean basin that separated the Oulongbuluke block from the Central Qilian block, and records Silurian closure of the Proto-Tethyan Ocean and subduction beneath the Central Qilian block. However, alluvial deposits in the Lajishan area were accumulated in a retro-foreland basin, indicating that continent-continent collision in the eastern South Qilian belt occurred at c. 450–440 Ma. These results demonstrate that the Proto-Tethyan Ocean closed diachronously during early Paleozoic time. 相似文献
10.
Harm E. Rondell 《Journal of African Earth Sciences》1999,28(4):867-871
A large number of changes affect the professional environment of the earth scientist. These changes are quite rapid when seen within the human life span. They are brought about by improved communication networks, continuously developing instrumentation, the increasingly interdisciplinary nature of the sciences and the changing demands of society. If taken seriously, then these changes must lead to a revision of the earth science curriculum, in which the fundamentals of the earth sciences should be studied in an integrated manner and in which skills, rather than just knowledge, are valued. Practical suggestions on how to revise the curriculum are made. 相似文献
11.
《Geoforum》2017
Cities worldwide are becoming tourism destinations and tourism is at the centre of urban economic production built around networks and connections. Attractions within the city are driving regional economies. However, there is little information about the practices of the city by tourists and residents and how they change the understanding of the place as city and destination. Research still focus on reasons for tourists to be attracted to a city and their impacts. Yet, how this infusion is conceptualized in the touristified city remains unanswered. The objective of this paper is to conceptualize specific tourism trends in the urban context, where boundaries are becoming less visible and where network hospitality is an enabler of urban infusion. This concept paper is structured to correspond with the research propositions, an investigation of the infusion in the global city. 相似文献
12.
Following on paleomagnetic studies in the sixties showing ~ 35° counterclockwise rotation of Iberia during the Mesozoic, two classes of scenarios have been proposed for the motion history of Iberia which are currently competing. One class infers convergence in the Pyrenees in response to a scissor-type opening of the Bay of Biscay, described by a pole of rotation for Iberia with respect to Europe located within the Bay. The other class of scenarios assumes extensional or transtensional motions in the Pyrenees, compatible with opening of the Bay of Biscay described by a pole of rotation located in northern France. Although plate-kinematic studies over the last decade increasingly support the scissor-type model, geological studies in the Pyrenees have accumulated arguments in favour of an extensional or transtensional regime in the Pyrenean realm.We perform a detailed plate-kinematic analysis of the Late Jurassic and Cretaceous motion history of Iberia and surrounding plates with respect to Europe. A total of six sea-floor reconstructions in combination with paleomagnetic studies onland allow to recognize four distinct stages. (1) Early rifting and ultraslow spreading since the Kimmeridgean led to the development of an oceanic Neotethys domain north of Iberia. (2) This was followed by ~ 35° CCW rotation of Iberia during the Aptian, kinematically linked to progressive opening of the Bay of Biscay. (3) Motions in the Bay became stagnant during the Albian till Santonian, followed by the latest stages of spreading in the Bay, and (4) onset of largely Tertiary continental collision between Iberia and Europe eventually leading to the present day structure of the belt.Our analysis confirms the results of previous studies indicating that extensional or transtensional motions in the Pyrenean realm during opening of the Bay of Biscay and concurrent rotation of Iberia are incompatible with plate-kinematic reconstructions based on sea-floor anomalies. This invites a reappraisal of the geological data. Convergence in the Pyrenean realm during opening of the Bay and rotation of Iberia was accommodated by up to 300 km of subduction of mantle-dominated ocean floor exhumed during the late Jurassic and early Cretaceous. The stagnant stage in the progressive opening of the Bay indicates that convergence in the Pyrenean realm virtually came to a halt during the Albian. We hypothesize that the lithosphere previously subducted during Aptian convergence became gravitationally unstable, leading to asthenospheric upwelling and consequent magmatism and high temperature metamorphism in the overlying European margin now exposed in the North Pyrenean Zone. Aside from these magmatic and thermal effects, an enhanced gravitational potential energy of the remaining lithosphere column underlain by shallow asthenosphere may have led to a stress state allowing belt-parallel extensional deformation. Such a detachment scenario, inspired by plate-kinematic results, may provide an alternative to explain many of the geological data commonly quoted to infer a transtensional or extensional tectonic regime in the Pyrenees during the rotation of Iberia. 相似文献
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14.
Crowdsourced knowledge websites such as Wikipedia and OpenStreetMap are increasingly attracting a critical literature which has highlighted the fact that the contributor bases of these sites are often geodemographically biased: drawn from more affluent and better educated segments of the population. However, while bias in contributors is well known, we know less about whether this also results in a bias in outcomes on these websites: or whether the partial portion of the population which does make contributions also works to “fill in the blanks”, by adding knowledge about other less well-off neighbouring areas which have not attracted a contributor base. This article addresses the question of whether such “neighbourhood effects” exist in practice. It makes use of a novel dataset of alcohol license data in the UK to assess variation in the completeness of the volunteer geographic information site OpenStreetMap. The results support existing literature in showing that completeness is related to demographics: areas with higher levels of wealth and education typically exhibit higher levels of completeness. The article then makes a novel contribution by showing evidence of the existence of neighbourhood effects: poorer regions with more affluent neighbours typically having higher levels of completeness than poorer regions which are also surrounded by poorer neighbours. The results suggest that crowdsourced knowledge websites can aspire to a kind of completeness even whilst user bases remain partial and biased. 相似文献
15.
In the United States, there is a growing awareness of the implications of our globalized food system, a system that incorporates all manner of agriculture, food distribution, food processing and transformation, and consumption. The ever increasing distance between where our food is produced and where it is consumed has helped spur a movement to develop a system of place based foods. Right now multiple models are in play, including farmers markets, community supported agriculture, and the localvore movement. This article will do a close examination of another model from France, the French system of appellation d’origine contrôlée (AOC); nationally regulated by the French Ministry of Agriculture it supports and protects foods and drinks with unique links to particular territories. The AOC system is based on geographically distinct and historically specific food and drink found throughout France. By closely examining one AOC product—Comté cheese produced in the rural agricultural region in Jura—the authors consider the possibilities for an AOC-style system in the United States. 相似文献
16.
In this study uranium and thorium contents and depositional characteristics of ay rhan bituminous shales（ BS）, west of Ankara（central Anatolia）, are investigated. Samples used were collected from boreholes opened by Park Holding Ltd. A total of 25 samples were taken from bituminous shale levels in boreholes drilled at 6 different locations in the study area. The H rka formation which hosts bituminous shale deposits is a volcanosedimentary sequence and all lithofacies indicate that a lacustrine environment where the water level was continuously changed. In addition to hydrocarbon generation potential, bituminous shales also accumulate significant amount of radioactive elements such as uranium and thorium. The average uranium and thorium concentrations of BS（1.83/2.62 ppm） are much lower than averages of UC, NASK and PAAS（uranium： 2.70/2.66/3.10 ppm; thorium： 8.50/12.30/14.60 ppm）. Low uranium contents in comparison to those of similar lacustrine environments might be attributed to that waters of depositional environment of BS contain low concentration of dissolved uranium and redox conditions were of oxic and dioxic character. Correlation data indicate that U and Th have a similar source and are associated predominantly with clays and phosphates and dominantly with organic material. Radioactive elements in the basin might be derived from Paleozoic granites and metamorphites（e.g. gneiss, schist） which comprise the basement and volcanism which was active in the region throughout the Miocene period. These elements are probably associated with uraniferous phosphate minerals（e.g. autunite, torbernite） which occur in granite, gneiss and schist. BS with average TOC content of 10.96 % shows very good/perfect source rock potential. Positive correlations between Gamma-Ray values and U, Th and K concentrations imply that radioactivity might be originated from these three elements. 相似文献
17.
We present new fault data for the region of the Manaus, Central Amazonia, Brazil. Field measurements concentrate on the Miocene–Holocene sedimentary deposits exposed on the Amazonas River Basin, in order to investigate the development of this region in this time-interval. Two faulting events are distinguished since the Miocene. The oldest one is related to NW–SE extension during Miocene times and associated with paleoseismicity, while the younger is associated with NE–SW extension direction and seems to persist today. These two deformational events may be thereby considered Neotectonic. Moreover, the second extensional pulse with NE–SW orientation can be explained by the surface hydrological loading, which induces the Central Amazonia flexural subsidence and may promote extensional stresses in the upper crust. 相似文献
18.
《Gondwana Research》2015,27(3-4):803-815
The early Proterozoic Era between 2.45 and 2.2 Ga is well known for a distinct minima in juvenile magmatism and detrital zircon abundance, an intriguing observation given its coincidence with many fundamental changes in Earth processes. A recent hypothesis seeks to explain this Siderian ‘Quiet Interval’ as the result of a plate tectonic shutdown in which extended tectonic quiescence is due to widespread lithospheric stagnation in an episodic mantle overturn regime. The model suggests that this period characterizes a ‘pre-modern’ geodynamic style and has profound implications for many geodynamic processes.We use spatially-linked chronostratigraphic and paleomagnetic databases to assess the major predictions of the model and find six of its key predictions are not supported by current data. The quiet interval includes a greater extent of contractional orogenesis and a broader range of paleopressures than previously known and is not characterized by LP–HT metamorphism proposed to have been related to higher upper mantle temperatures from decreased upper mantle cooling. Glacial conditions do not appear to have been triggered by the coincidence of the onset of magmatic shutdown with the end of mass-independent sulphur isotope fractionation and oxygenation of the atmosphere, as the initial glacial episodes predate this time. The glacial record, moreover, requires four episodes of climatic amelioration during the proposed shutdown, for which a mechanism appears lacking. A purported gap in Large-Igneous-Province formation, related to decreased mantle vigour, is not apparent. Quiet interval magmatism includes juvenile, arc-type and TTG magmatism, supporting significant crustal additions on a number of cratons. The prediction of negligible plate velocities during shutdown is not borne out by the well-constrained Superior Province paleomagnetic record. We suggest that plate tectonics did not shut down but that the Siderian Quiet Interval represents overall diminished tectonic activity during peripheral orogenesis, as is known for other relatively quiet periods following supercontinent or supercraton amalgamation. 相似文献
19.
刘庆生 《中国地质大学学报(英文版)》2011,(1)
I found high Q values (Q-ratio=Jn/Ji, Jn, Ji are remanent magnetization and induced magnetization) in the Sulu ultrahigh pressure (UHP) metamorphic rocks, eastern China which is the world's largest UHP 相似文献
20.
Plasma with a temperature close to the chromospheric one is ejected in solar eruptions. Such plasma can occult some part of
emission of compact sources in active regions as well as quiet solar areas. Absorption phenomena can be observed in the microwave
range as the so-called “negative bursts” and also in the He II 304 ? line. The paper considers three eruptive events associated
with rather powerful flares. Parameters of absorbing material of an eruption are estimated from multi-frequency records of
a “negative burst” in one event. “Destruction” of an eruptive filament and its dispersion like a cloud over a huge area observed
as a giant depression of the 304 ? line emission has been revealed in a few events. One of the three currently known events
is considered in this paper. One more of the events considered here is a possible candidate for such events. 相似文献