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991.
Louise K. Harra Nancy U. Crooker Cristina H. Mandrini Lidia van Driel-Gesztelyi Sergio Dasso Jingxiu Wang Heather Elliott Gemma Attrill Bernard V. Jackson Mario M. Bisi 《Solar physics》2007,244(1-2):95-114
We describe the interplanetary coronal mass ejections (ICMEs) that occurred as a result of a series of solar flares and eruptions
from 4 to 8 November 2004. Two ICMEs/magnetic clouds occurring from these events had opposite magnetic orientations. This
was despite the fact that the major flares related to these events occurred within the same active region that maintained
the same magnetic configuration. The solar events include a wide array of activities: flares, trans-equatorial coronal loop
disappearance and reformation, trans-equatorial filament eruption, and coronal hole interaction. The first major ICME/magnetic
cloud was predominantly related to the active region 10696 eruption. The second major ICME/magnetic cloud was found to be
consistent with the magnetic orientation of an erupting trans-equatorial filament or else a rotation of 160° of a flux rope
in the active region. We discuss these possibilities and emphasize the importance of understanding the magnetic evolution
of the solar source region before we can begin to predict geoeffective events with any accuracy. 相似文献
992.
K.E. Westaway M.J. Morwood T. Sutikna M.W. Moore A.D. Rokus G.D. van den Bergh R.G. Roberts E.W. Saptomo 《Quaternary Science Reviews》2009,28(25-26):2897-2912
Evidence from Liang Bua, a limestone cave on the island of Flores in East Indonesia, provides a unique opportunity to explore the long term relationship between hominins and their environment. Occupation deposits at the site span ~95 ka and contain abundant stone artefacts, well preserved faunal remains and evidence for an endemic species of hominin: Homo floresiensis. Work at the site included detailed geomorphological and environmental analysis, which has enabled comparisons to be drawn between changes in the occupational intensity in the cave, using stone tool and faunal counts, and changes in the environmental conditions, using the characteristics of the sedimentary layers in the cave and speleothem records. These comparisons demonstrate that H. floresiensis endured rapidly fluctuating environmental conditions over the last ~100 ka, which influenced the geomorphological processes in the cave and their occupational conditions. The intensity of occupation in the cave changed significantly between 95 and 17 ka, with peaks in occupation occurring at 100–95, 74–61 and 18–17 ka. These correlate with episodes of channel formation and erosion in the cave, which in turn correspond with high rainfall, thick soils and high bio-productivity outside. In contrast, periods of low occupational intensity correlate with reduced channel activity and pooling associated with drier periods from 94 to 75 and 36 to 19 ka. This apparent link between intensity of hominin use of the cave and the general conditions outside relates to the expansion and contraction of the rainforest and the ability of H. floresiensis to adapt to habitat changes. This interpretation implies that these diminutive hominins were able to survive abrupt and prolonged environmental changes by changing their favoured occupation sites. These data provide the basis for a model of human–environment interactions on the island of Flores. With the addition of extra data from other sites on Flores, this model will provide a greater understanding of H. floresiensis as a unique human species. 相似文献
993.
In the past decade, the European Commission has developed the Marine Strategy Directive and the Maritime Policy. Both policies aim at governing the marine environment; yet the two policies have a differing signature in policy formulation and implementation. From a fisher's perspective these policies present a change in institutional setting; major policy measures no longer descend from the EU Common Fisheries Policy alone, but increasingly are derived from general environmental policy developments. In this paper, the policy arrangement approach is used to analyse the differences between the two maritime policies, and the way in which they can affect fisheries management. 相似文献
994.
Joeri van Leeuwen Robert D. Ferdman Sol Meyer Ingrid Stairs 《Monthly notices of the Royal Astronomical Society》2007,374(4):1437-1440
Low-mass white dwarfs can be produced either in low-mass X-ray binaries by stable mass transfer to a neutron star, or in a common envelope phase with a heavier white dwarf companion. We have searched eight low-mass white dwarf candidates recently identified in the Sloan Digital Sky Survey for radio pulsations from pulsar companions, using the Green Bank Telescope at 340 MHz. We have found no pulsations down to flux densities of 0.6–0.8 mJy kpc−2 and conclude that a given low-mass helium-core white dwarf has a probability of <0.18 ± 0.05 of being in a binary with a radio pulsar. 相似文献
995.
Maureen D. Long Bradford H. Hager Maarten V. de Hoop Rob D. van der Hilst 《Geophysical Journal International》2007,170(2):839-856
We present a series of 2-D numerical models of viscous flow in the mantle wedge induced by a subducting lithospheric plate. We use a kinematically defined slab geometry approximating the subduction of the Philippine Sea plate beneath Eurasia. Through finite element modelling we explore the effects of different rheological and thermal constraints (e.g. a low-viscosity region in the wedge corner, power law versus Newtonian rheology, the inclusion of thermal buoyancy forces and a temperature-dependent viscosity law) on the velocity and finite strain field in the mantle wedge. From the numerical flow models we construct models of anisotropy in the wedge by calculating the evolution of the finite strain ellipse and combining its geometry with appropriate elastic constants for effective transversely isotropic mantle material. We then predict shear wave splitting for stations located above the model domain using expressions derived from anisotropic perturbation theory, and compare the predictions to ∼500 previously published shear wave splitting measurements from seventeen stations of the broad-band F-net array located in southwestern Japan. Although the use of different model parameters can have a substantial effect on the character of the finite strain field, the effect on the average predicted splitting parameters is small. However, the variations with backazimuth and ray parameter of individual splitting intensity measurements at a given station for different models are often different, and rigorous analysis of details in the splitting patterns allows us to discriminate among different rheological models for flow in the mantle wedge. The splitting observed in southwestern Japan agrees well with the predictions of trench-perpendicular flow in the mantle wedge along with B-type olivine fabric dominating in a region from the wedge corner to about 125 km from the trench. 相似文献
996.
As a complement to our efforts to update and revise the thermodynamic basis for predicting garnet-melt trace element partitioning
using lattice-strain theory (van Westrenen and Draper in Contrib Mineral Petrol, this issue), we have performed detailed statistical
evaluations of possible correlations between intensive and extensive variables and experimentally determined garnet-melt partitioning
values for trivalent cations (rare earth elements, Y, and Sc) entering the dodecahedral garnet X-site. We applied these evaluations
to a database containing over 300 partition coefficient determinations, compiled both from literature values and from our
own work designed in part to expand that database. Available data include partitioning measurements in ultramafic to basaltic
to intermediate bulk compositions, and recent studies in Fe-rich systems relevant to extraterrestrial petrogenesis, at pressures
sufficiently high such that a significant component of majorite, the high-pressure form of garnet, is present. Through the
application of lattice-strain theory, we obtained best-fit values for the ideal ionic radius of the dodecahedral garnet X-site,
r
0(3+), its apparent Young’s modulus E(3+), and the strain-free partition coefficient D
0(3+) for a fictive REE element J of ionic radius r
0(3+). Resulting values of E, D
0, and r
0 were used in multiple linear regressions involving sixteen variables that reflect the possible influence of garnet composition
and stoichiometry, melt composition and structure, major-element partitioning, pressure, and temperature. We find no statistically
significant correlations between fitted r
0 and E values and any combination of variables. However, a highly robust correlation between fitted D
0 and garnet-melt Fe–Mg exchange and D
Mg is identified. The identification of more explicit melt-compositional influence is a first for this type of predictive modeling.
We combine this statistically-derived expression for predicting D
0 with the new expressions for predicting E and r
0 outlined in the first of our pair of companion papers into an updated set of formulae that use easy-to-measure quantities
(e.g. garnet composition, pressure, temperature) to predict variations in E, r
0, and D
0. These values are used in turn to calculate D values for those garnets. The updated model substantially improves upon a previous model (van Westrenen et al. in Contrib
Mineral Petrol 142:219–234, 2001), and accounts well for trivalent cation partitioning in nominally anhydrous systems up to at least 15 GPa, including for
eclogitic bulk compositions and for Fe-rich systems appropriate to magmagenesis on the Moon and Mars. The new model is slightly
less successful in predicting partitioning with strongly majoritic garnets, although the mismatch is much less than with the
original 2001 model. Although it also improves upon the 2001 model in predicting partitioning in hydrous systems, the mismatch
between model and observation is still unacceptably large. The same statistical tools were applied in an attempt to predict
tetravalent partitioning as well, because lattice-strain based techniques are not applicable to such partitioning. However,
no statistically significant predictive relationships emerged from that effort. Our analyses show that future efforts should
focus on filling the gap in partitioning data between ∼10 and 25 GPa to evaluate more closely the gradual transition of garnet
to majorite, and on systematically expanding the hydrous partitioning database to allow extension of our model to water-bearing
systems. 相似文献
997.
998.
An unresolved issue in the study of pressure solution in rock materials is the dependence of grain boundary structure and
diffusive properties on the mutual orientation of neighbouring grain lattices. We report electrical measurements yielding
the diffusivity of differently oriented halite–glass and halite–halite contacts loaded in the presence of brine. The halite–glass
contact experiments show pressure solution of the halite and an effect of halite lattice orientation on grain boundary transport.
Post-mortem observations show an orientation-dependent grain boundary texture controlled by the periodic bond chains in the
halite structure. It is inferred that this texture determines the internal grain boundary structure and properties during
pressure solution. In the halite–halite experiments neck-growth occurred, its rate depending on twist-misorientation. The
results imply that deformation by pressure solution may lead to lattice-preferred orientation development, and that polymineralic
rocks may deform faster at lower stresses than monomineralic rocks. 相似文献
999.
Vassilis Karakitsios Harilaos Tsikos Yvonne van Breugel Lyda Koletti Jaap S. Sinninghe Damsté Hugh C. Jenkyns 《International Journal of Earth Sciences》2007,96(2):343-352
Integrated biostratigraphic (planktonic foraminifera, calcareous nannofossils), chemostratigraphic (bulk C and O isotopes)
and compound-specific organic geochemical studies of a mid-Cretaceous pelagic carbonate—black shale succession of the Ionian
Zone (western Greece), provide the first evidence for the Cenomanian–Turonian oceanic anoxic event (OAE2, ‘Bonarelli’ event)
in mainland Greece. The event is manifested by the occurrence of a relatively thin (35 cm), yet exceptionally organic carbon-rich
(44.5 wt% TOC), carbonate-free black shale, near the Cenomanian–Turonian boundary within the Vigla limestone formation (Berriasian–Turonian).
Compared to the ‘Bonarelli’ black-shale interval from the type locality of OAE2 in Marche–Umbria, Italy, this black shale
exhibits greatly reduced stratigraphic thickness, coupled with a considerable relative enrichment in TOC. Isotopically, enriched
δ13C values for both bulk organic matter (−22.2‰) and specific organic compounds are up to 5‰ higher than those of underlying
organic-rich strata of the Aptian-lower Albian Vigla Shale member, and thus compare very well with similar values of Cenomanian–Turonian
black shale occurrences elsewhere. The relative predominance of bacterial hopanoids in the saturated, apolar lipid fraction
of the OAE2 black shale of the Ionian Zone supports recent findings suggesting the abundance of N2-fixing cyanobacteria in Cretaceous oceans during the Cenomanian–Turonian and early Aptian oceanic anoxic events. 相似文献
1000.
Problems in predicting the mobility of slow-moving landslides 总被引:4,自引:0,他引:4
This paper discusses problems in predicting the mobility of slow-moving landslides. Three case studies are presented here where research has been carried out by the Utrecht University: The La Valette landslide complex in the French Alps, the La Mure landslide in the French pre-Alps near Grenoble and the Hau landslide in Switzerland.To predict field velocities of these slow-moving landslides the viscosity parameters of the material of these landslides were determined by strain-controlled tests in a ring shear apparatus based on Bishop's design at Utrecht University. The viscosity parameters from the laboratory proved to be 10 to 1000 times lower than viscosities obtained from back analyses on the observed velocities in the field. This discrepancy may be explained by the development of negative pore pressures when the plastic material slides over a rigid, wavy slip surface and/or by convergent flow effects. The associated gain in strength results in a higher apparent viscosity.A more detailed analysis is made for the movements of the La Valette landslide. Observed velocities at the La Valette landslide are difficult to describe by one parameter set as the response to a change in groundwater level is not the same during a rise or fall in the piezometric level. This deviation may be explained by rapid changes in total stresses and consequently changes in pore pressure under (partly) undrained conditions. The emerging hysteresis with local and temporal variations in pore pressure makes it difficult to predict in detail the moving pattern of landslides. 相似文献