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231.
A detailed photometric analysis has been made of a narrow elongated coronal streamer observed at the 1973 total eclipse. After deriving real intensity distributions, the electron density has been deduced under the assumption that the distribution is axially symmetric and that the decrease in density from the central axis follows the gaussian law. The results show that the gradient of the electron density is much steeper at the lower part, nearest to the solar limb, than those reported previously for larger scale streamers.On leave from the Observatorio de Huancayo, Instituto Geoflsico del Peru as a trainee of the Japan International Cooperation Agency. 相似文献
232.
Landslide risk management in Switzerland 总被引:1,自引:2,他引:1
233.
Ben De Mol Max Kozachenko Andy Wheeler Hugo Alvares Jean-Pierre Henriet Karine Olu-Le Roy 《International Journal of Earth Sciences》2007,96(1):103-120
High-resolution seismic profiles, swath bathymetry, side-scan sonar data and video imageries are analysed in this detailed
study of five carbonate mounds from the Belgica mound province with special emphasis on the well-surveyed Thérèse Mound. The
selected mounds are located in the deepest part of the Belgica mound province at water depths of 950 m. Seismic data illustrate
that the underlying geology is characterised by drift sedimentation in a general northerly flowing current regime. Sigmoidal
sediment bodies create local slope breaks on the most recent local erosional surface, which act as the mound base. No preferential
mound substratum is observed, neither is there any indication for deep geological controls on coral bank development. Seismic
evidence suggests that the start-up of the coral bank development was shortly after a major erosional event of Late Pliocene–Quaternary
age. The coral bank geometry has been clearly affected by the local topography of this erosional base and the prevailing current
regime. The summits of the coral banks are relatively flat and the flanks are steepest on their upper slopes. Deposition of
the encased drift sequence has been influenced by the coral bank topography. Sediment waves are formed besides the coral banks
and are the most pronounced bedforms. These seabed structures are probably induced by bottom current up to 1 m/s. Large sediment
waves are colonised by living corals and might represent the initial phase of coral bank development. The biological facies
distribution of the coral banks illustrate a living coral cap on the summit and upper slope and a decline of living coral
populations toward the lower flanks. The data suggest that the development of the coral banks in this area is clearly an interaction
between biological growth processes and drift deposition both influenced by the local topography and current regime. 相似文献
234.
A new interpretation of the Inntal–Tauern sector of the TRANSALP seismic section is presented. One of the most prominent contrasts in reflectivity in the TRANSALP seismic section is the contact between the Bajuvaric unit in the footwall and the overlying Tirolic unit and its basement across a moderately south-dipping interface. We trace this contact from the surface at the southern margin of the Inn valley to a depth of 5 km. There, the contact is deformed or cut by the Tauern Window northern margin. We define the contact between Bajuvaric and Tirolic units as Brixlegg thrust, which is older than Miocene Tauern window exhumation and has a Paleogene age. The sub-Tauern ramp connects with the Inntal fault system at the surface and roots below the Tauern window. Oblique thrust movements across this fault system in the Miocene caused exhumation of the hanging wall, where the fault has a ramp geometry, which is in the area of the TRANSALP cross section and west of it. East of the TRANSALP cross section, the fault system merges with Alpine basal thrust, which is a flat. No Miocene exhumation occurred above the flat. 相似文献
235.
Hugo de Boorder Maarten J. Zeylmans van Emmichoven Vitaliy A. Privalov 《Ore Geology Reviews》2006,29(3-4):242-259
The East European Platform is underlain by Archaean and Proterozoic complexes of the East European Craton. In the southwest these are locally exposed in the Ukrainian Shield and the Voronezh Massif on either side of the ca. 2000 km long ESE-striking late Palaeozoic Pripyat–Dniepr–Donets rift. Evaluation with Landsat imagery of 1 : 1,000,000 scale published maps of the Precambrian complexes [Zaritsky, A.I., Galetsky, L.S. (Eds.), 1992. Geology and Metallogeny of the Southwest of the East-European Platform Map Series, 1 : 1,000,000, Ukrainian State Committee on Geology and Utilization of Mineral Resources, Kiev.] is largely obstructed by a cover of post-Palaeozoic sediments and soils of variable thickness. This obstruction is aggravated by an almost continuous patchwork of farmlands. However, analysis of the current drainage patterns in the Dniepr River basin and surrounding regions reveals a spatial coincidence of numerous stream courses and watersheds with previously inferred steep, transcrustal discontinuities of most probably Precambrian age.Transcrustal dislocations constituted important pathways for heat and fluids as is indicated by the distribution of a large proportion of assumed Early Proterozoic hydrothermal iron and gold deposits along them. This distribution is underpinned by the spatial coincidence of mineralization and elongate areas of highly irregular magnetization attributed to uneven distribution of hydrothermal magnetite in banded iron formation. In view of the extent of these dislocations, both vertically and laterally, the generation of hydrothermal fluid flow, emplacement of mantle-sourced magma and associated mineral potential away from banded iron formation complexes is likely. A second group of gold deposits, of Archaean age, is known to occur in association with still recognizable volcanic edifices in greenstone complexes. It is not known if and to what extent such Archaean gold deposits are related to these major transcrustal discontinuities. The kinematics and dynamics of these dislocations and pathways appear largely unknown and deserve high-priority investigation. The geological longevity of the transcrustal dislocation framework till the present day inferred from the current drainage systems is corroborated, however, by repeated regional topographical levelling surveys. 相似文献
236.
Graeme Hugo 《The Australian geographer》2006,37(2):211-231
Australia's labour market is most influenced by international migration among OECD nations, but Australian research on this issue focuses almost exclusively on permanent settlement migration. The present paper, however, demonstrates that non-permanent migration has an important impact on the Australian labour market, although such migrants are not included in standard data collections and research on migrants and the labour market. A number of data sources are utilised to estimate the labour-market impact of Working Holiday Makers, Temporary Business Entrants, Overseas Students, and New Zealand temporary migrants. It is shown that their impact is equivalent to more than 400?000 full-time jobs. However, the effect is magnified because it is concentrated in particular sectors of the economy and in particular communities within Australia. A number of issues relating to temporary migration are discussed, including the nature of its relationship with permanent migration, the effects on job training, and the implications for regional development. 相似文献
237.
Hugo A. Loáiciga 《Mathematical Geosciences》2008,40(2):199-211
The equation of groundwater flow in marine island aquifers in which there is time-independent, spatially-variable recharge
and pumping is solved in closed form for rectangular, circular, and elliptical island geometries. The solution of the groundwater
flow equation is expressed in terms of the elevation of the phreatic surface within the flow domain. The depth of the seawater-freshwater
interface below mean sea level follows from the Dupuit–Ghyben–Herzberg relation. The method of solution presented in this
work relies on expanding the hydraulic head and forcing function (recharge and groundwater extraction) as Fourier series that
transforms the two-dimensional Poisson-type flow equations into second-order ordinary differential equations solvable using
classical theory. The important case of constant recharge (without groundwater extraction) leads to solutions in which the
hydraulic head is expressible as the product of a flow factor equal to the squared root of the ratio of recharge over hydraulic
conductivity times a geometric factor involving island shape parameters and flow boundary conditions. Estimability conditions
for the hydraulic conductivity are derived for the cases of constant recharge and spatially variable recharge with pumping. 相似文献
238.
We diagnose climate feedback parameters and CO2 forcing including rapid adjustment in twelve atmosphere/mixed-layer-ocean (“slab”) climate models from the CMIP3/CFMIP-1 project (the AR4 ensemble) and fifteen parameter-perturbed versions of the HadSM3 slab model (the PPE). In both ensembles, differences in climate feedbacks can account for approximately twice as much of the range in climate sensitivity as differences in CO2 forcing. In the AR4 ensemble, cloud effects can explain the full range of climate sensitivities, and cloud feedback components contribute four times as much as cloud components of CO2 forcing to the range. Non-cloud feedbacks are required to fully account for the high sensitivities of some models however. The largest contribution to the high sensitivity of HadGEM1 is from a high latitude clear-sky shortwave feedback, and clear-sky longwave feedbacks contribute substantially to the highest sensitivity members of the PPE. Differences in low latitude ocean regions (30°N/S) contribute more to the range than those in mid-latitude oceans (30–55°N/S), low/mid latitude land (55°N/S) or high latitude ocean/land (55–90°N/S), but contributions from these other regions are required to account fully for the higher model sensitivities, for example from land areas in IPSL CM4. Net cloud feedback components over the low latitude oceans sorted into percentile ranges of lower tropospheric stability (LTS) show largest differences among models in stable regions, mainly due to their shortwave components, most of which are positive in spite of increasing LTS. Differences in the mid-stability range are smaller, but cover a larger area, contributing a comparable amount to the range in climate sensitivity. These are strongly anti-correlated with changes in subsidence. Cloud components of CO2 forcing also show the largest differences in stable regions, and are strongly anticorrelated with changes in estimated inversion strength (EIS). This is qualitatively consistent with what would be expected from observed relationships between EIS and low-level cloud fraction. We identify a number of cases where individual models show unusually strong forcings and feedbacks compared to other members of the ensemble. We encourage modelling groups to investigate unusual model behaviours further with sensitivity experiments. Most of the models fail to correctly reproduce the observed relationships between stability and cloud radiative effect in the subtropics, indicating that there remains considerable room for model improvements in the future. 相似文献
239.
Topological redundancy and ‘small‐world’ patterns in a food web in a subtropical ecosystem of Brazil
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Hugo Bornatowski Rodrigo Barreto Andrés F. Navia Alberto Ferreira de Amorim 《Marine Ecology》2017,38(2)
According to graph theory, the frequency distribution of trophic interactions within a food web has deep structural implications, as it can highlight the presence of patterns associated with the web and indicate whether the properties of the web are independent of its size. A hypothesis is that ‘small‐world’ food webs are sensitive to the loss of species with the highest values. Therefore, the present work aimed to evaluate the degree to which a subtropical food web in Southern Brazil displays small‐world patterns and their resistance. As part of the assessment, we evaluated the topological redundancy values of species in the food web and then we simulated the exclusion of these species (such as sharks and sea birds), and also the exclusion of high centrality species (such as squids Loligo sp., portunid swimming crabs and the cutlassfish Trichiurus lepturus). The food web showed a ‘broad‐scale’ distribution of connections by node, and a small‐world pattern. As expected, a simplification of the network was observed after elimination of some species with high centrality. However, the food web was resistant to the loss of species with low topological redundancy, probably because these species occupy a high trophic level and do not participate in lots of routes within the food web. We highlight however, the importance of the application of multiple analyses to evaluate the importance of components in food webs, and fisheries management plans should consider both species of high centrality values and species with low topological redundancy. 相似文献
240.
Rick Verberne Hugo W. van Schrojenstein Lantman Steven M. Reddy Matteo Alvaro David Wallis Denis Fougerouse Antonio Langone David W. Saxey William D. A. Rickard 《Journal of Metamorphic Geology》2023,41(1):3-24
The trace-element composition of rutile is commonly used to constrain P–T–t conditions for a wide range of metamorphic systems. However, recent studies have demonstrated the redistribution of trace elements in rutile via high-diffusivity pathways and dislocation-impurity associations related to the formation and evolution of microstructures. Here, we investigate trace-element migration in low-angle boundaries formed by dislocation creep in rutile within an omphacite vein of the Lago di Cignana unit (Western Alps, Italy). Zr-in-rutile thermometry and inclusions of quartz in rutile and of coesite in omphacite constrain the conditions of rutile deformation to around the prograde boundary from high pressure to ultra-high pressure (~2.7 GPa) at temperatures of 500–565°C. Crystal-plastic deformation of a large rutile grain results in low-angle boundaries that generate a total misorientation of ~25°. Dislocations constituting one of these low-angle boundaries are enriched in common and uncommon trace elements, including Fe and Ca, providing evidence for the diffusion and trapping of trace elements along the dislocation cores. The role of dislocation microstructures as fast-diffusion pathways must be evaluated when applying high-resolution analytical procedures as compositional disturbances might lead to erroneous interpretations for Ca and Fe. In contrast, our results indicate a trapping mechanism for Zr. 相似文献