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Micromagnetic modelling with a Monte Carlo method was performed to obtain 2-D micromagnetic structures of pseudo-single-domain (PSD) magnetite (0.2–2.5 μm). Cubic model grains were subdivided into a 2-D array with a maximum of 100×100 cells. In order to find an appropriate cell size, the variation of the self-consistency parameter ( S ) with cell size was examined. We regard solutions with S >0.95, which corresponds to cell sizes ≤0.03 μm, as representing realistic micromagnetic structures. For saturation remanence states, we found vortex structures for small PSD grains (≤0.25 μm) and closure domain structures for larger PSD grains (0.6–2.5 μm). Between 0.25 and 0.6 μm, structures remained chaotic even after a very large number of Monte Carlo steps. In grains with a closure domain structure, domain walls were usually subdivided into several segments with opposite polarities of magnetization rotation. 相似文献
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This article addresses representations of Saigon/Ho Chi Minh City in four films made since đ i m i , the opening up of Vietnam to western influences, initiated in 1986. The Lover/L'Amant (1992) is a Franco-British heritage film which reconstructs the city from a Eurocentric neocolonial perspective, while Cyclo/Xích lô (1995), a French-funded film made by a France-based Vietnamese filmmaker, is a contemporary poetic thriller which treats the city expressively as the site of present-day corruption and violence. The nostalgia evident in these two 'outsider' films is contrasted with the more complex views of the city in two state-funded low-budget 'insider' films by local Vietnamese filmmakers, Collective Flat/Chung c (1999) and Bargirls/Gái nh y (2003); the first, an intellectual fable set in the decade or so following reunification/Independence in 1975 which recalls an attempt at collective living, the second, a hugely popular treatment of contemporary urban realities, both corrupt and progressive. Examining how the mise-en-scène and narratives of the city differ from film to film, the essay takes the representation of the city through changing historical, political, social and economic times, from colonial-orientalist Saigon to corrupt, capitalist Ho Chi Minh City via the slow degeneration of the postwar socialist/collectivist experiment. In so doing, it confirms the importance of the films' moments and contexts of production in the construction of Saigon/Ho Chi Minh City as a cinematic 'city-text'. 相似文献
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Novaya Zemlya was covered by the eastern part of the Barents–Kara ice sheet during the glacial maximum of marine isotope stage 2 (MIS 2). We obtained 14 C ages on 37 samples of mollusc shells from various sites on the islands. Most samples yielded ages in the range of 48–26 14 C Ky. Such old samples are sensitive to contamination by young 14 C, and therefore their reliability was assessed using replicate analyses and amino acid geochronology. The extent of aspartic acid racemization (Asp D/L) indicates that many of the 14 C ages are correct, whereas some are minimum ages only. The results indicate that a substantial part of Novaya Zemlya was ice-free about 35–27 14 C Kya, and probably even earlier. Corresponding shorelines up to >140 m a.s.l. indicate a large Barents–Kara ice sheet during early MIS 3. These results are consistent with findings from Svalbard and northern Russia: in both places a large MIS 4/3 Barents–Kara ice sheet is postulated to have retreated about 50 Kya, followed by an ice-free interstadial that lasted until up to ca. 25 Kya. The duration of the MIS 2 glaciation in Novaya Zemlya was calculated by applying the D/L values to a kinetic equation for Asp racemization. This indicates that the islands were ice covered for less than 3000 years if the basal temperature was 0o C, and for less than 10 000 years if it was −5o C. 相似文献
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Tropicality,the unruly Atlantic and social utopias: the French explorer Henri Coudreau (1859 − 1899) 
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下载免费PDF全文 Federico Ferretti 《Singapore journal of tropical geography》2017,38(3):332-349
This paper addresses the works of Henri Coudreau, a little‐known French explorer of Guiana and Amazonia who was later forgotten by the ‘heroic’ histories of exploration because of his unruliness and nonconformist attitudes. Drawing on the literature of postcolonialism and tropicality as well as on recent studies of anti‐colonialist geographies, I address for the first time Coudreau's geography from the perspective of anarchist and critical thinking. My main argument is that Coudreau's work is a further example of the complexity and heterogeneity of the European intellectual field during the imperial age. Despite having come of age intellectually among all the European racist and ethnocentric prejudices of his day, Coudreau developed a different outlook thanks to two factors, viz., his personal experience in living for years with the indigenous communities of Amazonia, and his exposure to anarchist anti‐colonialist ideas through his collaboration with Elisée Reclus. Coudreau's tropical utopia of an independent Amazonia, and his endorsement of the stateless nature of local communities, ran counter to French imperial politics, occasioning Coudreau's dismissal from the French administration and his professional exile in Brazil at the time of the Franco‐Brazilian border dispute (1897?1900). 相似文献
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Observation of Coriolis coupled modes below 1 mHz 总被引：3，自引：0，他引：3
W. Zürn G. Laske R. WidmerSchnidrig F. Gilbert 《Geophysical Journal International》2000,143(1):113-118
We present observations of spectral energy at toroidal mode frequencies in vertical seismic recordings of the 1998 Balleny Islands earthquake. Since toroidal modes on a spherically symmetric, nonrotating Earth have horizontally polarized particle motion these observations call for an explanation. We first rule out local and instrumental effects as being responsible for the verticalcomponent signal of the toroidal modes 0 T 3 (0.59 mHz) and 0 T 4 (0.77 mHz). The global effects that we consider are general heterogeneous mantle structure, ellipticity of figure and rotation. We find that rotation through Coriolis coupling of loworder spheroidal and toroidal oscillations is the dominant mechanism. 相似文献
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南京古都景观核心和生态文化研究 总被引：3，自引：0，他引：3
探讨建立以地理景观为视角的古都风貌研究思路新框架.目前中国的古都风貌保护规划往往是从建筑学角度出发,而缺少从地理格局角度的古都景观研究.南京地理格局使其历史古都发展具有独特深厚的景观传统,主要结构是:3条山脉、2条河流和3个湖泊.南京从其诞生到后来城市几次大的变化都是依据这个自然地理系统而构思规划.现代南京城市发展支离破碎地分解了历史上的连绵山峦整体,河流水系网络已经断断续续.本文研究思路是顺延山峦与河流脉络调查分析古都遗址,探寻现状山脉河流系统之中,古都文化景观格局在时空变化和演替规律.进而认定和寻求景观系统之中的历史城市发展的地理关键内核,以地理景观分析并规划南京古都景观保护:以连绵丘岗山系、河流城濠为骨干,保持山体轮廓的连续性,河流水网的完整性;以自然山水地形为纽带贯通各自相对独立的历史遗迹:以明朝城垣、历史街区为网络,以及分散在各地的重点建筑保护范围,构成完整的古都风貌保护的格局.把风景的概念扩大到整个城市区域内,使得自然资源保护、土地利用与景观规划结合为一体. 相似文献
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Richard W. Ferdinand 《Geophysical Journal International》1998,134(3):818-830
The investigation of L g attenuation characteristics in the region bounding the western branch of the East African rift system using digital recordings from a seismic network located along the rift between Lake Rukwa and Lake Malawi is reported. A set of 24 recordings of L g waves from 12 regional earthquakes has been used for the determination of anelastic attenuation, Q Lg , and regional body-wave magnitude, m b Lg , scale. The events used have body-wave magnitudes, m b , between 4.6 and 5.5, which have been determined teleseismically and listed in ISC bulletins. The data were time-domain displacement amplitudes measured at 10 different frequencies (0.7–5.0 Hz). Q Lg and its frequency dependence, η , in the region can be represented in the form Q Lg = (186.2 ± 6.5) f (0.78±0.05) . This model is in agreement with models established in other active tectonic regions. The L g -wave-based magnitude formula for the region is given by m b Lg = log A + (3.76 ± 0.38) log D − (5.72 ± 1.06), where A is a half-peak-to-peak maximum amplitude of the 1 s L g wave amplitude in microns and D is the epicentral distance in kilometres. Magnitude results for the 12 regional earthquakes tested are in good agreement with the ISC body-wave magnitude scale. 相似文献
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《Basin Research》2018,30(3):564-585
Studies in both modern and ancient Cordilleran‐type orogenic systems suggest that processes associated with flat‐slab subduction control the geological and thermal history of the upper plate; however, these effects prove difficult to deconvolve from processes associated with normal subduction in an active orogenic system. We present new geochronological and thermochronological data from four depositional areas in the western Sierras Pampeanas above the Central Andean flat‐slab subduction zone between 27° S and 30° S evaluating the spatial and temporal thermal conditions of the Miocene–Pliocene foreland basin. Our results show that a relatively high late Miocene–early Pliocene geothermal gradient of 25–35 °C km−1 was typical of this region. The absence of along‐strike geothermal heterogeneities, as would be expected in the case of migrating flat‐slab subduction, suggests that either the response of the upper plate to refrigeration may be delayed by several millions of years or that subduction occurred normally throughout this region through the late Miocene. Exhumation of the foreland basin occurred nearly synchronously along strike from 27 to 30° S between ca. 7 Ma and 4 Ma. We propose that coincident flat‐slab subduction facilitated this wide‐spread exhumation event. Flexural modelling coupled with geohistory analysis show that dynamic subsidence and/or uplift associated with flat‐slab subduction is not required to explain the unique deep and narrow geometry of the foreland basin in the region implying that dynamic processes were a minor component in the creation of accommodation space during Miocene–Pliocene deposition. 相似文献
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We report on the palaeomagnetism of the gabbroic Cape St Mary's sills of the Avalon Peninsula of Newfoundland, which have previously yielded a 441±2 Ma U–Pb baddeleyite age (latest Ordovician or earliest Silurian). At 12 of 19 sites, stepwise alternating-field or thermal demagnetization isolated a stable characteristic remanence carried by magnetite. This remanence is shown to pre-date Early Devonian folding of the sills. Although a baked-contact test was inconclusive, the positive fold test and the low grade of metamorphism of the sills (prehnite–pumpellyite facies) make it likely that the characteristic remanence is primary. The tilt-corrected site-mean characteristic remanence has a declination of 343° and an inclination of −51° ( k =25, α 95 =9°), yielding a ∼440 Ma palaeopole at 10°N, 140°E ( dm =12°, dp =8°) for West (North American) Avalonia. The corresponding ∼440 Ma palaeolatitude for the Avalon Peninsula is 32°S±8°. The only other West Avalonian palaeolatitude determination from rocks that could be of similar age is from the Dunn Point volcanics of Nova Scotia; their more southerly palaeolatitude of 41°S±5° suggests that they are significantly older than 440 Ma, a possibility that we recommend testing with U–Pb dating. Although no ∼440 Ma palaeolatitude determinations are available for East Avalonia (parts of southern Britain and Ireland), interpolating between mid-Ordovician and mid-Silurian determinations gives an estimate of ∼25°S. This is consistent with our Cape St Mary's result and, if the Iapetus Ocean closed orthogonally, with a narrow (∼1000 km) Iapetus Ocean of approximately east–west orientation between Avalonia and Laurentia by 440 Ma. 相似文献
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