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291.
Ercilla G Córdoba D Gallart J Gràcia E Muñoz JA Somoza L Vázquez JT Vilas F;Prestige Group 《Marine pollution bulletin》2006,53(5-7):208-219
The tanker Prestige sank off NW Iberia on the 19th November 2002. The stern and bow of the Prestige wreck are located on the southwestern edge of the Galicia Bank, at 3565 m and 3830 m water depths, respectively. This bank is a structural high controlled by major faults with predominant N-S, NNE-SSW, and NNW-SEE trends. It is characterized by moderate to low seismic activity. The faults have controlled the local depositional architecture, deforming, fracturing, relocating and distributing sediments since the Valangian (early Cretaceous). The Prestige sinking area corresponds to an asymmetric half-graben structure with a N-S trend, which conditions the present-day morphology. The faulted flank outcrops and its activity and erosion have favoured the occurrence of mass-movements (slumps, slump debris, mass-flows and turbidity currents), building valleys and depositional lobes. Nearsurface sediments comprise mostly terrigenous and biogenous turbiditic muds and sands with a minor presence of hemipelagic muds, except on the fault scarp where pelagites predominate. Potential geological hazards resulting from tectonic and sedimentary processes affect almost the entire Prestige sinking area. 相似文献
292.
293.
Joshua F. Snape Katherine H. Joy Ian A. Crawford Louise Alexander 《Meteoritics & planetary science》2014,49(5):842-871
A detailed petrologic survey has been made of 17 basaltic chips (sized between 1 and 10 mm) from the 12003 soil sample as part of an ongoing study of basaltic diversity at the Apollo 12 landing site. An attempt has been made to classify these samples according to the well‐established grouping of olivine, pigeonite, ilmenite, and feldspathic basalts. Particular attention has been paid to variations in major, minor, and trace element mineral chemistry (determined by electron microprobe analysis and laser ablation ICP‐MS), which may be indicative of particular basaltic suites and less susceptible to sampling bias than bulk sample characteristics. Examples of all three main (olivine, pigeonite, and ilmenite) basaltic suites have been identified within the 12003 soil. One sample is identified as a possible new addition to the feldspathic suite, which currently consists of only one other confirmed sample. Identification of additional feldspathic basalts strengthens the argument that they represent a poorly sampled basaltic flow local to the Apollo 12 site, rather than exotic material introduced to the site by impact mixing processes. Three samples are identified as representing members of one or two previously unrecognized basaltic suites. 相似文献
294.
Predrag Vuli? Ton?i Bali?-?uni? Louise Josefine Belmonte Volker Kahlenberg 《Mineralogy and Petrology》2011,101(3-4):185-194
Ten nepheline single crystals from five different localities representing rocks from nepheline-syenite pegmatites to urtite, ijolite and cancrinite-ijolite were investigated chemically and structurally. The chemical compositions were determined by electron microprobe, whereas the crystal structures were refined against X-ray diffraction data to R values of 0.022?C0.031. In all cases the crystal structures conformed to space group P63, but at the same time all crystals produced some satellite reflections testifying to the modulation effects in their structure. This work confirms the presence of satellite reflections as a universal property of nepheline and resolves some controversy about this issue present in older works. The samples show a range of compositions with variable excess of Si over Al combined with vacancies in the alkaline sites. Vacancies are present exclusively in the symmetric ditrigonal channels occupied preferentially by K atoms in natural nepheline. The influence of the variable amounts of K, Na and vacancies to the increase of volume at this site is shown to be in the order ??>K>Na. It has been confirmed that natural nepheline can partly depart from Loewenstein??s rule and show some degree of disorder in the Si/Al distribution. Most of the samples revealed a practically full Si-Al-ordering, but the crystals from one of the nepheline-syenite pegmatites in Langesundsfjord, Norway and from the type locality of ijolite, Iivaara, Finland, showed a disorder of 10?C20% suggesting a different cooling history for these rocks. 相似文献
295.
Michael Hilbe Flavio S. Anselmetti Raymond S. Eilertsen Louise Hansen Walter Wildi 《Swiss Journal of Geoscience》2011,104(3):425-443
Bathymetric data available for Swiss lakes have typically only low to moderate resolution and variable quality, making them
insufficient for detailed underwater geomorphological studies. This article presents results of a new bathymetric survey in
perialpine Lake Lucerne using modern hydrographic equipment. A digital terrain model (DTM) of the lake floor (raster dataset
with 1 m cell size) covering the Chrüztrichter and Vitznau basins documents signatures of major Holocene mass movements and
relics from the glacial history of the lake. Combining the bathymetry data with reflection seismic profiles and an existing
event chronology allows investigating the morphology in its geological context. Subaqueous sediment slide scars with sharp
headwalls cover large areas on moderately inclined slopes. The particularly large Weggis slide complex, correlated with an
historical earthquake (ad 1601), features a ~9 km long and 4–7 m high headwall and covers an area of several square kilometers. Large debris cones
of prehistoric rockfalls and the deposits of recent rockfall events imaged on the almost flat basin plain document mass-movement
activity on steep slopes above the lake. Six transverse moraines, visible as subaqueous ridges, as lake-floor lineaments,
or only imaged on reflection seismic profiles, indicate a complex glacial-inherited morphology. As many of the documented
features result from potentially catastrophic events, high-resolution bathymetry can significantly improve natural hazard
assessment for lakeshore communities by extending classical hazard maps to the subaqueous domain. 相似文献
296.
An Improved Parallel Multiple-point Algorithm Using a List Approach 总被引:15,自引:8,他引:7
Julien Straubhaar Philippe Renard Gr��goire Mariethoz Roland Froidevaux Olivier Besson 《Mathematical Geosciences》2011,43(3):305-328
Among the techniques used to simulate categorical variables, multiple-point statistics is becoming very popular because it allows the user to provide an explicit conceptual model via a training image. In classic implementations, the multiple-point statistics are inferred from the training image by storing all the observed patterns of a certain size in a tree structure. This type of algorithm has the advantage of being fast to apply, but it presents some critical limitations. In particular, a tree is extremely RAM demanding. For three-dimensional problems with numerous facies, large templates cannot be used. Complex structures are then difficult to simulate. In this paper, we propose to replace the tree by a list. This structure requires much less RAM. It has three main advantages. First, it allows for the use of larger templates. Second, the list structure being parsimonious, it can be extended to include additional information. Here, we show how this can be used to develop a new approach for dealing with non-stationary training images. Finally, an interesting aspect of the list is that it allows one to parallelize the part of the algorithm in which the conditional probability density function is computed. This is especially important for large problems that can be solved on clusters of PCs with distributed memory or on multicore machines with shared memory. 相似文献
297.
Gerald Patrick Roberts Ian A. Crawford David Peacock Joyce Vetterlein Elisabeth Parfitt Louise Bishop 《Earth, Moon, and Planets》2007,100(1-2):1-16
High quality CCD images obtained at two different observatories in North Italy allowed the identification of four morphological
structures near the nuclear region of the comet Ikeya-Zhang (I-Z): haloes, jets, shells and spirals. The interpretation of
the nature of these structures has been attempted by means of a comparison of different up-to-date image processing techniques,
which led to a single common estimate of the rotation period (p=1.48±0.20 days). 相似文献
298.
Leads and polynyas have a great impact on the energy budget of the polar ocean and atmosphere. Since atmospheric general
circulation models are not able to resolve the spatial scales of these inhomogeneities, it is necessary to include the effect
of fractional sub-grid scale sea-ice inhomogeneities on climate by a suitable parametrization. In order to do this we have
divided each model grid-cell into an ice-covered and an ice-free part. Nevertheless, a numerical model requires effective
transports representative for the whole grid-box. A simple procedure would be to use grid averages of the surface parameters
for the calculation of the surface fluxes. However, as the surface fluxes are non-linearly dependent on the surface properties,
the fluxes over ice and open water should be calculated separately according to the individual surface-layer structure of
each surface type. Then these local fluxes should be averaged to obtain representative fluxes. Sensitivity experiments with
the Hamburg atmospheric general circulation model ECHAM3 clearly show that a subgrid scale distribution of sea ice is a dominant
factor controlling the exchange processes between ocean and atmosphere in the Arctic. The heat and water vapour transports
are strongly enhanced leading to a significant warming and moistening of the polar troposphere. This affects the atmospheric
circulation in high- and mid-latitudes; e.g. the stationary lows are modified and the transient cyclonic activity over the
subpolar oceans is reduced. A pronounced impact of sub-grid scale sea-ice distribution on the model climate can only be obtained
when the non-linear behaviour of the surface exchange processes is considered by a proper, physically based, averaging of
the surface fluxes. A simple linear averaging of surface parameters is not sufficient.
Received: 13 September 1994 / Accepted: 25 July 1995 相似文献
299.
Louise O. V. Edwards Michael J. Hudson Michael L. Balogh Russell J. Smith 《Monthly notices of the Royal Astronomical Society》2007,379(1):100-110
We examine the optical emission-line properties of brightest cluster galaxies (BCGs) selected from two large, homogeneous data sets. The first is the X-ray selected National Optical Astronomy Observatory Fundamental Plane Survey (NFPS), and the second is the C4 catalogue of optically selected clusters built from the Sloan Digital Sky Survey Data Release 3 (SDSS DR3). Our goal is to better understand the optical line emission in BCGs with respect to properties of the galaxy and the host cluster. Throughout the analysis we compare the line emission of the BCGs to that of a control sample made of the other bright galaxies near the cluster centre. Overall, both the NFPS and SDSS show a modest fraction of BCGs with emission lines (∼15 per cent). No trend in the fraction of emitting BCGs as a function of galaxy mass or cluster velocity dispersion is found. However, we find that, for those BCGs found in cooling flow clusters, 71+9 −14 have optical emission. Furthermore, if we consider only BCGs within 50 kpc of the X-ray centre of a cooling flow cluster, the emission-line fraction rises further to 100+0 −15 per cent. Excluding the cooling flow clusters, only ∼10 per cent of BCGs are line emitting, comparable to the control sample of galaxies. We show that the physical origin of the emission-line activity varies: in some cases it has LINER-like line ratios, whereas in others it is a composite of star-formation and LINER-like activity. We conclude that the presence of emission lines in BCGs is directly related to the cooling of X-ray gas at the cluster centre. 相似文献
300.
Anisotropy and heterogeneity of hydraulic conductivity (K) are suspected of greatly affecting rates and patterns of ground‐water seepage in peats. A new laboratory method, termed here the modified cube method, was used to measure horizontal and vertical hydraulic conductivity (Kh and Kv) of 400 samples of bog peat. The new method avoids many of the problems associated with existing field and laboratory methods, and is shown to give relatively precise measurements of K. In the majority of samples tested, Kh was much greater than Kv, indicating that the bog peat was strongly anisotropic. Log10Kh, log10Kv, and log10 (Kh/Kv) were found to vary significantly with depth, although none of the relationships was simple. We comment on the scale dependency of our measurements. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献