共查询到20条相似文献,搜索用时 0 毫秒
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《Journal of Atmospheric and Terrestrial Physics》1987,49(5):439-441
The average daily variation profiles of the H component at Huancayo on the west coast and Eusébio, Fortaleza, on the east coast in the dip equator region and La Quiaca near the west coast and Vassouras near the east coast in the southern low latitude region of the South American continent indicate that the profiles are broader for the east coast. Thus, distortions in the overhead current systems while passing from one coast to the other are indicated. 相似文献
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Andrew Phillips 《Australian Journal of International Affairs》2013,67(2):125-140
This article considers the regional order-building challenges that Australia presently confronts in the Indian Ocean region (IOR). The author argues that while regional stability within the IOR constitutes an increasingly important Australian security interest, policy makers will struggle to translate the order-building strategies they have previously pursued in East Asia into an Indian Ocean context. In East Asia, Australia has historically pursued a ‘dual track’ order-building strategy centred on its participation in a US-dominated ‘hub and spokes’ alliance system alongside multilateral regional engagement. The absence of an equivalent alliance system or an established tradition of multilateral security diplomacy conversely precludes an extension of this strategy into the IOR. Growing tensions between the USA and China and between China and India, meanwhile, further complicate IOR security dynamics, while underscoring the urgent need for a more coherent approach to regional order-building. With these challenges in mind, the author concludes by proposing a range of bilateral, minilateral and multilateral initiatives that Australia should pursue to stimulate the emergence of a more cooperative IOR security environment. 相似文献
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《Journal of Atmospheric and Terrestrial Physics》1988,50(10-11):983-1000
A theoretical study is presented bearing on the thermospheric circulation and composition at polar latitudes. The observed motions and density perturbations in N2, O and He have signatures which may be understood in terms of two different source mechanisms. We consider electric field momentum coupling and Joule heating as well as interactions between both processes. A spectral model in terms of vector spherical harmonics (with magnetic coordinates) is used, delineating the diurnal and mean (time independent) components. The important non-linearities are evaluated in configuration space. The electric field model of Volland and the global average density and temperature variations of Hedin (MSIS) are adopted as input. Our analysis leads to the following conclusions. (1) The vortex type double cell polar circulation (zonal wave number m = 1) is primarily driven by collisional momentum transfer from electric field induced ion convection. (2) Because of the thermospheric low pass filter, a large time independent component (zonal wave number m = 0) is produced by Joule heating; the heavier species (N2) being concentrated where the lighter ones (O, He) are depleted, and vice versa due to wind induced diffusion (3) The electric field driven vortex circulation redistributes the mass and energy in the time independent density and temperature variations (from Joule heating), producing primarily diurnal variations (m = 1) in the temperature and composition near the pole and at auroral latitudes, again the heavier and lighter species varying out of phase. The above results are in substantial agreement with observations. It is worth noting that momentum rectification associated with the diurnally varying electric field and conductivity induces a weak zonally symmetric (single cell) prograde polar vortex. However, this motion is partially compensated by a retrograde vortex from geostrophic balance due to Joule heating, which dominates near the pole. These motions are small compared with the diurnally varying component in the polar circulation. 相似文献
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none 《Journal of Field Archaeology》2013,38(2):244-255
AbstractField archaeology is normally associated with outdoor excavation and exposure to the natural environment. Archaeological excavations have adapted to a wide spectrum of these conditions, but the recent prominence of archaeological sites as tourist attractions and educational facilities has occasionally led to dramatically different environments for the archaeological recovery, interpretation, and preservation of evidence, including facilities that permit indoor excavation. This article explores 15 years of experience at the Mitchell Prehistoric Indian Village in South Dakota. An “Archeodome” covering part of the site represents a non-traditional excavation and preservation environment that presents considerable benefits and challenges for archaeologists. The structure provides the basis for evaluating the nature of indoor excavation within its archaeological and educational context and provides a cautionary note for archaeologists, heritage groups, tourist boards, and others interested in the preservation of archaeological sites. Though this article focuses on the Mitchell site, the information reported has broad implications for sites where structures cover archaeological deposits. 相似文献
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《Journal of Atmospheric and Terrestrial Physics》1986,48(4):399-414
Existing evidence for the ionospheric dynamo being the source of quiet time electric fields in the plasmasphere is reviewed. Part of a 24 h set of whistler data recorded continuously at Sanae, Antarctica (L = 4), during quiet magnetic (average Kp = 1) is analysed to obtain westward electric fields in the equatorial plane. These electric fields are examined as a function of L-value in order to infer their source. It is found that for periods of outward flow of plasma during the noon-midnight local time period, the electric fields are consistent with the dominant source being the ionospheric dynamo. There is some evidence that during the evening period of inward flow the electric fields are magnetospheric in origin, although this could also be consistent with a refined dynamo model. The observed whistler duct convection patterns do not fit either of two theoretical models, which invoke a magnetospheric field but not a dynamo field. 相似文献
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Indo-Iranian Journal - 相似文献
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《Political Geography》2007,26(7):757-774
Although the concept of diaspora is sometimes regarded as oppositional to the interests of existing political regimes, we argue that it can become a site where the negotiation of new terms of membership embraces the transnational and de-territorialized networks of overseas populations. Drawing on work on transnational governance, we explore the uneven geographies that accompany India's recent discussions of its dual citizenship provisions. Constructions of diaspora membership are revealed by mapping the discourses contained within the Dual Citizenship legislation of 2003, the 2003 Pravasi Bharatiya Divas (Overseas India Day) campaign, and the 2001 report of the Diaspora Committee onto the case of South Africa. The results suggest that the construction of diaspora membership focuses on professional success, ecumenical Hinduism, and multicultural incorporation. We also trace how diaspora membership betrays a continuing anxiety over the terms of Indianness. The results remind us that diasporic times and spaces mediate transnational governance. 相似文献
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《Journal of Atmospheric and Terrestrial Physics》1995,57(12):1513-1523
The present work is a systematic review cum report on theoretical and experimental investigations of the Solar Terminator (ST) as a physical, permanent, and global source of waves in near-Earth space (NES). From the founding work by Beer (1973) Nature242, 34–35 and Somsikov and Troitskii (1975) Geomagn. and Aeron., 15, 856–860, up to the present, twenty years of theoretical and experimental investigations on the effectiveness of wave generation in various geophysical situations have been considered. Linear mechanisms of atmospheric inhomogeneity formation are considered for the case of a moving discontinuity in some of the atmospheric parameters, whereas nonlinear mechanisms are characterized by various instabilities caused by the gradient in solar radiation absorption. Numerical simulations of an ST model and the pressure wave field generated by it are discussed. 相似文献
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Bidisha Biswas 《Nations & Nationalism》2023,29(3):1112-1124
This paper explores the motivations and actions of Indian Americans who actively oppose Hindutva, that is, a Hindu nationalist vision for India. Diaspora activists who advocate in favour of progressive values for India tend to be underreported in the media and underanalysed in scholarship. The following study addresses this gap. Based on public records, interviews with activist leaders, and participant-observation, the paper demonstrates how anti-Hindutva diaspora actors identify and leverage political opportunities in order to engage in moral signalling in local, national and global spaces. By shining a light on ongoing counternarratives to Hindutva, this study highlights contestations within Indian-origin communities and challenges monolithic portrayals of diaspora politics. 相似文献
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Here we present geoarchaeological results from Tromelin, a small 1-km2 atoll in the Indian Ocean, looking to elucidate human–environment interactions following the wrecking of the l'Utile in 1761. Abandoned by their French crew, around 60 Madagascans were enforced to form a micro-society on this remote island for a 15-year period. Little, however, is known about the cultural and environmental adaptations the population made during their stay. This study focuses on sediment archives from Site 5, where GRAN/INRAP archaeological work in 2008 brought to light three rooms attributed to the survivor's living quarters. Particular emphasis is placed on the impacts of cyclonic storm surges, natural hazards that presented serious environmental risks to the long-term survival of the slaves. The small size of Tromelin renders it a particularly discrete unit of analysis for such a study. We have identified four chronostratigraphic units at the site. (1) Unit 4 constitutes coarse white sand incorporating rounded gravels and reworked head and branch corals. No anthropogenic material is attested. We attribute this unit to a storm layer preceding the 1761 occupation of Tromelin. (2) Unit 3 yielded a multiplicity of archaeological material and corresponds to the 18th century cultural layer. The unit varies in thickness from 10 to 40 cm. (3) Unit 2 constitutes a 20 to 40 cm sand sheet across much of Site 5 that we attribute to a powerful cyclone event. It forms an unconformable contact above unit 3 and can be divided into two distinct sub-units, 2a and 2b. Sub-unit 2a is characterised by an inverse grading of the sediments, constituting coarse sands at the base grading into rounded biogenic gravels in the upper part. This sedimentology is typical of increasing flow velocity and is diagnostic of a storm setup flow. The transition to sub-unit 2b marks the onset of the waning flow, characterised by a sharp fall in relative flow velocities. These overwash deposits buried much of the archaeological remains and have been critical to the preservation of the vestiges through to present-day. (4) Unit 1 corresponds to a layer of infill incorporating blocks of coral and cultural objects dating from the 19th to 20th centuries. 相似文献
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Although research on the history of the eugenics movement in the United States is legion, its impact on state policies that identified and defined American Indians has yet to be fully addressed. The exhibit, Our Lives: Comtemporary Life and Identities (ongoing until September 21, 2014) at the National Museum of the American Indian provides a provocative vehicle for examining how eugenics-informed public policy during the first quarter of the twentieth century served to "remove" from official records Native peoples throughout the Southeast. One century after Indian Removal of the antebellum era, Native peoples in the American Southeast provide an important but often overlooked example of how racial policies, this time rooted in eugenics, effected a documentary erasure of Native peoples and communities. 相似文献