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981.
Carlos Sainz Ismael Fuente Luis Quindós Jose Luis Gutierrez Jose Luis Arteche Luis Santiago Quindós 《Acta Geophysica》2010,58(5):957-962
People working with ionising radiation are receiving radiation coming from artificial and natural sources. In Spain, as in
many other countries, there is a serious control by the national authorities, Spanish Nuclear Safety Council, of the dose
the workers receive from artificial sources. However, until the publication of the European Basic Safety Standards Directive,
96/29/EURATOM, the old criteria referring to the “above natural background” were widely used. This directive was incorporated
to the Spanish legislation in July 2001 (BOE 178); in its Title VII it recommends to evaluate the dose coming from natural
sources and take it into account for establishing the safety criteria. It is noteworthy to assess the natural doses received
at homes and the dose received by workers of radioactive installations subject to regulations, and to compare the two results.
The social and economical implications of the results derived can be important in the practical application of the recommendations
included in the above-mentioned BOE 178 Directive. 相似文献
982.
The Pearl River Estuary (PRE) in South China's Guangdong Province is a subtropical estuary with highly irregular topography
and dynamically complicated circulations. A nested-grid coastal circulation modelling system is used in this study to examine
dynamic responses of the PRE to tides, meteorological forcing and buoyancy forcing. The nested-grid modelling system is based
on the Princeton Ocean Model and consists of three downscaling subcomponents: including an outer-most model with a coarse
horizontal resolution of ~7 km for simulating tidally forced and wind-driven surface elevations and depth-mean currents over
the China Seas from Bohai Sea to the northern South China Sea and an innermost model with a fine resolution of ~1.2 km for
simulating the 3D coastal circulation and hydrography over the PRE and adjacent coastal waters. Model results during the winter
northeast monsoon surge in January and super typhoon Koryn in June of 1993 are used to demonstrate that the 3D coastal circulation
and hydrographic distributions in the PRE are affected by tides, winds and buoyancy forcing associated with river discharge
from the Pearl River with significant seasonal and synoptic variabilities. 相似文献
983.
Nathalie Vigouroux A. E. Williams-Jones Paul Wallace Thomas Staudacher 《Bulletin of Volcanology》2009,71(9):1077-1089
The November 2002 eruption of Piton de la Fournaise in the Indian Ocean was typical of the activity of the volcano from 1999
to 2006 in terms of duration and volume of magma ejected. The first magma erupted was a basaltic liquid with a small proportion
of olivine phenocrysts (Fo81) that contain small numbers of melt inclusions. In subsequent flows, olivine crystals were more abundant and richer in Mg
(Fo83–84). These crystals contain numerous melt and fluid inclusions, healed fractures, and dislocation features such as kink bands.
The major element composition of melt inclusions in this later olivine (Fo83–84) is out of equilibrium with that of its host as a result of extensive post-entrapment crystallization and Fe2+ loss by diffusion during cooling. Melt inclusions in Fo81 olivine are also chemically out of equilibrium with their hosts but to a lesser degree. Using olivine–melt geothermometry,
we determined that melt inclusions in Fo81 olivine were trapped at lower temperature (1,182 ± 1°C) than inclusions in Fo83–84 olivine (1,199–1,227°C). This methodology was also used to estimate eruption temperatures. The November 2002 melt inclusion
compositions suggest that they were at temperatures between 1,070°C and 1,133°C immediately before eruption and quenching.
This relatively wide temperature range may reflect the fact that most of the melt inclusions were from olivine in lava samples
and therefore likely underwent minor but variable amounts of post-eruptive crystallization and Fe2+ loss by diffusion due to their relatively slow cooling on the surface. In contrast, melt inclusions in tephra samples from
past major eruptions yielded a narrower range of higher eruption temperatures (1,163–1,181°C). The melt inclusion data presented
here and in earlier publications are consistent with a model of magma recharge from depth during major eruptions, followed
by storage, cooling, and crystallization at shallow levels prior to expulsion during events similar in magnitude to the relatively
small November 2002 eruption. 相似文献
984.
Giuseppe D. Chirico Massimiliano Favalli Paolo Papale Enzo Boschi Maria Teresa Pareschi Arthur Mamou-Mani 《Bulletin of Volcanology》2009,71(4):375-387
Mt. Nyiragongo is one of the most dangerous volcanoes in the world for the risk associated with the propagation of lava flows.
In 2002 several vents opened along a huge system of fractures, pouring out lava which reached and destroyed a considerable
part of Goma, a town of about 500,000 inhabitants on the shore of Lake Kivu. In a companion paper (Favalli et al. in Bull
Volcanol, this issue, 2008) we employed numerical simulations of probable lava flow paths to evaluate the lava flow hazard on the flanks of the volcano,
including the neighbouring towns of Goma (DRC) and Gisenyi (Rwanda). In this paper we use numerical simulations to investigate
the possibility of significantly reducing the lava flow hazard in the city through the construction of protective barriers.
These barriers are added to the DEM of the area as additional morphological elements, and their effect is evaluated by repeating
numerical simulations with and without the presence of barriers. A parametric study on barrier location, size, shape and orientation
led to the identification of barriers which maximize protection while minimizing their impact. This study shows that the highest
hazard area corresponding to eastern Goma, which was largely destroyed by lava flows in 2002, cannot be effectively protected
from future lava flows towards Lake Kivu and should be abandoned. On the contrary, the rest of the town can be sheltered from
lava flows by means of two barriers that deviate or contain the lava within the East Goma sector. A proposal for the future
development of the town is formulated, whereby “new” Goma is completely safe from the arrival of lava flows originating from
vents outside its boundaries. The proposal minimizes the risk of further destruction in town due to future lava flows. 相似文献
985.
Seismic refraction survey and DC resistivity measurements were made across the margin of the Lake Ngami. The structure and
stratigraphy at the lake were determined. High resolution aeromagnetic data showed a prominent anomaly coinciding with the
Kunyere Fault. Estimated depths to magnetic sources are increasing towards the lake. Two velocity layers were mapped. The
top layer (500 m/s) is thin outside the lake and thicker inside the lake. The underlying layer (3125 m/s) has undeterminable
thickness. Resistivity sounding results inside the lake showed that the low velocity layer has four sub-units: dry hard clays;
diatomaceous earth; soft clays interlayered with silts; and wet whitish clays interlayered with silts. Normal faults were
mapped along the profile with a total displacement up to 50 m. The results of the study indicate that the formation of the
Lake Ngami basin was structurally controlled and probably initiated by the tectonics of the Okavango Rift Zone. 相似文献
986.
Based on a large set of arrival times of the Pg phase reported by local and regional stations, we estimate azimuthal anisotropy of the Pg-wave velocity in focal volumes of the upper crust in NW Croatia. The method is based on analyses of the azimuthal dependence
of ratios of cumulative differences of arrival times and travel paths between foci of earthquake pairs, computed for rays
propagating within narrow azimuthal windows. The results clearly indicate the presence of anisotropy of 3.3% with the direction
of fast velocity (approximately NNE-SSW) coinciding with the direction of the maximum tectonic pressure as revealed by 23
available focal mechanisms and previous geological investigations. Although a large part of observed anisotropy can be explained
assuming that focal volumes are pervaded by a system of vertical extensive-dilatancy anisotropy (EDA) cracks aligned under
the influence of local tectonic stress field, there is indication that — to a smaller extent — some role was also played by
alignment of structural features in the region. 相似文献
987.
We present a new development in the asymmetric continuum theory with the shear oscillations (twist motions) and independent
spin; these motions (displacement velocities and spin) can be shifted in phase to describe the independent rebound processes.
Our approach provides an extension of the asymmetric continuum theory by including the microfragmentation processes with a
double transport which may appear in an advanced fracture process under very high load. The related nonlinear equations, leading
to soliton solutions, are derived. 相似文献
988.
The seasonal nature of Australia’s tropical rivers means that connected groundwater aquifers are an important source of both
consumptive and non-consumptive water, particularly during the dry season. The management of these common pool groundwater
resources is one of the predominant water issues facing northern Australia. A national program of water reform stipulates
the expansion of water trading as a key instrument for water allocation. The effectiveness of new institutional arrangements
such as water markets will be determined mostly by how well they coordinate with local environmental requirements, local institutions
and local norms. This paper describes a novel application of combined field work, institutional analysis, experimental economics
and agent-based modeling to the analysis of a potential water market in the Katherine region of the Northern Territory, Australia.
The effectiveness of different versions of the policy instrument is assessed in light of local conditions. Instruments that
enable personal relationships and local institutions and norms to play a role in water management are found to be more effective
in terms of both farming income and environmental impact. 相似文献
989.
The relationship between aquifer hydraulic conductivity and aquifer resistivity, either measured on the ground surface by
vertical electrical sounding (VES) or from resistivity logs, or measured in core samples have been published for different
types of aquifers in different locations. Generally, these relationships are empirical and semi-empirical, and confined in
few locations. This relation has a positive correlation in some studies and negative in others. So far, there is no potentially
physical law controlling this relation, which is not completely understood. Electric current follows the path of least resistance,
as does water. Within and around pores, the model of conduction of electricity is ionic and thus the resistivity of the medium
is controlled more by porosity and water conductivity than by the resistivity of the rock matrix. Thus, at the pore level,
the electrical path is similar to the hydraulic path and the resistivity should reflect hydraulic conductivity. We tried in
this paper to study the effect of degree of groundwater saturation in the relation between hydraulic conductivity and bulk
resistivity via a simple numerical analysis of Archie’s second law and a simplified Kozeny-Carmen equation. The study reached
three characteristic non-linear relations between hydraulic conductivity and resistivity depending on the degree of saturation.
These relations are: (1) An inverse power relation in fully saturated aquifers and when porosity equals water saturation,
(2) An inverse polynomial relation in unsaturated aquifers, when water saturation is higher than 50%, higher than porosity,
and (3) A direct polynomial relation in poorly saturated aquifers, when water saturation is lower than 50%, lower than porosity.
These results are supported by some field scale relationships. 相似文献
990.
Three finite element codes, namely TELEMAC, ADCIRC and QUODDY, are used to compute the spatial distributions of the M2, M4 and M6 components of the tide in the sea region off the west coast of Britain. This region is chosen because there is an accurate
topographic dataset in the area and detailed open boundary M2 tidal forcing for driving the model. In addition, accurate solutions (based upon comparisons with extensive observations)
using uniform grid finite difference models forced with these open boundary data exist for comparison purposes. By using boundary
forcing, bottom topography and bottom drag coefficients identical to those used in an earlier finite difference model, there
is no danger of comparing finite element solutions for “untuned unoptimised solutions” with those from a “tuned optimised
solution”. In addition, by placing the open boundary in all finite element calculations at the same location as that used
in a previous finite difference model and using the same M2 tidal boundary forcing and water depths, a like with like comparison of solutions derived with the various finite element
models was possible. In addition, this open boundary was well removed from the shallow water region, namely the eastern Irish
Sea where the higher harmonics were generated. Since these are not included in the open boundary, forcing their generation
was determined by physical processes within the models. Consequently, an inter-comparison of these higher harmonics generated
by the various finite element codes gives some indication of the degree of variability in the solution particularly in coastal
regions from one finite element model to another. Initial calculations using high-resolution near-shore topography in the
eastern Irish Sea and including “wetting and drying” showed that M2 tidal amplitudes and phases in the region computed with TELEMAC were in good agreement with observations. The ADCIRC code
gave amplitudes about 30 cm lower and phases about 8° higher. For the M4 tide, in the eastern Irish Sea amplitudes computed with TELEMAC were about 4 cm higher than ADCIRC on average, with phase
differences of order 5°. For the M6 component, amplitudes and phases showed significant small-scale variability in the eastern Irish Sea, and no clear bias between
the models could be found. Although setting a minimum water depth of 5 m in the near-shore region, hence removing wetting
and drying, reduced the small-scale variability in the models, the differences in M2 and M4 tide between models remained. For M6, a significant reduction in variability occurred in the eastern Irish Sea when a minimum 5-m water depth was specified. In
this case, TELEMAC gave amplitudes that were 1 cm higher and phases 30° lower than ADCIRC on average. For QUODDY in the eastern
Irish Sea, average M2 tidal amplitudes were about 10 cm higher and phase 8° higher than those computed with TELEMAC. For M4, amplitudes were approximately 2 cm higher with phases of order 15° higher in the northern part of the region and 15° lower
in the southern part. For M6 in the north of the region, amplitudes were 2 cm higher and about 2 cm lower in the south. Very rapid M6 tidal-phase changes occurred in the near-shore regions. The lessons learned from this model inter-comparison study are summarised
in the final section of the paper. In addition, the problems of performing a detailed model–model inter-comparison are discussed,
as are the enormous difficulties of conducting a true model skill assessment that would require detailed measurements of tidal
boundary forcing, near-shore topography and precise knowledge of bed types and bed forms. Such data are at present not available. 相似文献