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561.
In recent years, through the availability of remotely sensed data and other national datasets, it has become possible to conduct national-scale flood risk assessment in England and Wales. The results of this type of risk analysis can be used to inform policy-making and prioritisation of resources for flood management. It can form the starting point for more detailed strategic and local-scale flood risk assessments. The national-scale risk assessment methodology outlined in this paper makes use of information on the location, standard of protection and condition of flood defences in England and Wales, together with datasets of floodplain extent, topography, occupancy and asset values. The flood risk assessment was applied to all of England and Wales in 2002 at which point the expected annual damage from flooding was estimated to be approximately £1 billion. This figure is comparable with records of recent flood damage. The methodology has subsequently been applied to examine the effects of climate and socio-economic change 50 and 80 years in the future. The analysis predicts increasing flood risk unless current flood management policies, practices and investment levels are changed – up to 20-fold increase in real terms economic risk by the 2080s in the scenario with highest economic growth. The increase is attributable primarily to a combination of climate change (in particular sea level rise and increasing precipitation in parts of the UK) and increasing economic vulnerability. 相似文献
562.
Re-evaluation of the petrogenesis of the Proterozoic Jabiluka unconformity-related uranium deposit, Northern Territory, Australia 总被引:1,自引:0,他引:1
Paul A. Polito T. Kurt Kyser David Thomas Jim Marlatt Garth Drever 《Mineralium Deposita》2005,40(3):257-288
The world class Jabiluka unconformity-related uranium deposit in the Alligator Rivers Uranium Field, Australia, contains >163,000 tons
of contained U3O8. Mineralization is hosted by shallow-to-steeply dipping basement rocks comprising graphitic units of chlorite–biotite–muscovite
schist. These rocks are overlain by flat-lying coarse-grained sandstones belonging to the Kombolgie Subgroup. The deposit
was discovered in 1971, but has never been mined. The construction of an 1,150 m decline into the upper eastern sector of
the Jabiluka II deposit combined with closely spaced underground drilling in 1998 and 1999 allowed mapping and sampling from
underground for the first time. Structural mapping, drill core logging and petrographic studies on polished thin sections
established a detailed paragenesis that provided the framework for subsequent electron microprobe and X-ray diffraction, fluid
inclusion, and O–H, U–Pb and 40Ar/39Ar isotope analysis. Uranium mineralization is structurally controlled within semi-brittle shears that are sub-conformable
to the basement stratigraphy, and breccias that are developed within the hinge zone of fault-related folds adjacent to the
shears. Uraninite is intimately associated with chlorite, sericite, hematite ± quartz. Electron microprobe and X-ray diffraction
analysis of syn-ore illite and chlorite indicates a mineralization temperature of 200°C. Pre- and syn-ore minerals extracted
from the Kombolgie Subgroup overlying the deposit and syn-ore alteration minerals in the Cahill Formation have δ18Ofluid and δD
fluid values of 4.0±3.7 and −27±17‰, respectively. These values are indistinguishable from illite separates extracted from diagenetic
aquifers in the Kombolgie Subgroup up to 70 km to the south and east of the deposit and believed to be the source of the uraniferous
fluid. New fluid inclusion microthermometry data reveal that the mineralising brine was saline, but not saturated. U–Pb and
207Pb/206Pb ratios of uraninite by laser-ablation ICP-MS suggest that massive uraninite first precipitated at ca. 1,680 Ma, which is
coincident with the timing of brine migration out from the Kombolgie Subgroup as indicated by 40Ar/39Ar ages of 1,683±11 Ma from sandstone-hosted illite. Unmineralized breccias cemeted by chlorite, quartz and sericite cross-cut
the mineralized breccias and are in turn cut by straight-sided, high-angle veins of drusy quartz, sulphide and dolomite. U–Pb
and 207Pb/206Pb ratios combined with fluid inclusion and stable isotope data indicate that these post-ore minerals formed when mixing between
two fluids occurred sometime between ca. 1,450 and 550 Ma. Distinct 207Pb/206Pb age populations occur at ca. 1,302±37, 1,191±27 and 802±57 Ma, which respectively correlate with the intrusion of the Maningkorrirr/Mudginberri
phonolitic dykes and the Derim Derim Dolerite between 1,370 and 1,316 Ma, the amalgamation of Australia and Laurentia during
the Grenville Orogen at ca. 1,140 Ma, and the break-up of Rodinia between 1,000 and 750 Ma. 相似文献
563.
564.
Combinations of station coordinates and velocities from independent space-geodetic techniques have long been the standard
method to realize robust global terrestrial reference frames (TRFs). In principle, the particular strengths of one observing
method can compensate for weaknesses in others if the combination is properly constructed, suitable weights are found, and
accurate co-location ties are available. More recently, the methodology has been extended to combine time-series of results
at the normal equation level. This allows Earth orientation parameters (EOPs) to be included and aligned in a fully consistent
way with the TRF. While the utility of such multi-technique combinations is generally recognized for the reference frame,
the benefits for the EOPs are yet to be quantitatively assessed. In this contribution, which is a sequel to a recent paper
on co-location ties (Ray and Altamimi in J Geod 79(4–5): 189–195, 2005), we have studied test combinations of very long baseline
interferometry (VLBI) and Global Positioning System (GPS) time-series solutions to evaluate the effects on combined EOP measurements
compared with geophysical excitations. One expects any effect to be small, considering that GPS dominates the polar motion
estimates due to its relatively dense and uniform global network coverage, high precision, continuous daily sampling, and
homogeneity, while VLBI alone observes UT1-UTC. Presently, although clearly desirable, we see no practical method to rigorously
include the GPS estimates of length-of-day variations due to significant time-varying biases. Nevertheless, our results, which
are the first of this type, indicate that more accurate polar motion from GPS contributes to improved UT1-UTC results from
VLBI. The situation with combined polar motion is more complex. The VLBI data contribute directly only very slightly, if at
all, with an impact that is probably affected by the weakness of the current VLBI networks (small size and sparseness) and
the quality of local ties relating the VLBI and GPS frames. Instead, the VLBI polar motion information is used primarily in
rotationally aligning the VLBI and GPS frames, thereby reducing the dependence on co-location tie information. Further research
is needed to determine an optimal VLBI-GPS combination strategy that yields the highest quality EOP estimates. Improved local
ties (including internal systematic effects within the techniques) will be critically important in such an effort. 相似文献
565.
566.
Diana Hannikainen Duncan Campbell-Wilson Richard Hunstead Vince McIntyre Jim Lovell John Reynolds Tasso Tzioumis Kinwah Wu 《Astrophysics and Space Science》2001,276(1):45-48
In 1998 September, the X-ray transient XTE J1550–564 underwent amajor outburst in soft and hard X-rays, followed by a radio flare. Australian Long Baseline Array imagesobtained shortly after the peak in the radio flare showed evolving structure.The components observed have an apparent separation velocity of >2c. 相似文献
567.
H. Aguilera S. Castaño L. Moreno M. E. Jiménez-Hernández A. de la Losa 《Hydrogeology Journal》2013,21(3):623-641
Las Tablas de Daimiel National Park (TDNP) in Spain is one of the most important semiarid wetlands of the Mediterranean area. The inversion of the regional groundwater flow, primarily due to overexploitation and inadequate aquifer management, has led to degradation. The system has turned from a groundwater discharge zone into a recharge zone, and has remained mostly dry since the 1980s. High heterogeneity and complexity, enhanced by anthropogenic management action, hampers prediction of the surface–groundwater system response to flooding events. This study analyses these interactions and provides empirical evidence to define a conceptual model of flooding-infiltration-groundwater dynamics through the application of a few simple analysis tools to basic hydrological data. Relevant surface water–groundwater interactions are mainly localized in the left (west) margin of TDNP, as confirmed by the fast responses to flooding observed in the hydrochemic, hydrodynamic and isotopic data. During drying periods, small artificial and/or low-flow natural floods are followed by infiltration of evaporated poor-quality ponding water into saline low-permeability layers. The results allow an improved understanding of the hydrological behaviour essential to support efficient management practices. The relative simplicity of the methodology allows for its application in other similar complex groundwater-linked wetlands where detailed knowledge of local geology is still absent. 相似文献
568.
Philippe Lamy Pierre Vernazza Joel Poncy Vincent Martinot Emmanuel Hinglais Elisabet Canalias Jim Bell Dale Cruikshank Olivier Groussin Joern Helbert Francesco Marzari Alessandro Morbidelli Pascal Rosenblatt Holger Sierks 《Experimental Astronomy》2012,33(2-3):685-721
In our present understanding of the Solar System, small bodies (asteroids, Jupiter Trojans, comets and TNOs) are the most direct remnants of the original building blocks that formed the planets. Jupiter Trojan and Hilda asteroids are small primitive bodies located beyond the ‘snow line’, around respectively the L4 and L5 Lagrange points of Jupiter at ~5.2?AU (Trojans) and in the 2:3 mean-motion resonance with Jupiter near 3.9?AU (Hildas). They are at the crux of several outstanding and still conflicting issues regarding the formation and evolution of the Solar System. They hold the potential to unlock the answers to fundamental questions about planetary migration, the late heavy bombardment, the formation of the Jovian system, the origin and evolution of trans-neptunian objects, and the delivery of water and organics to the inner planets. The proposed Trojans’ Odyssey mission is envisioned as a reconnaissance, multiple flyby mission aimed at visiting several objects, typically five Trojans and one Hilda. It will attempt exploring both large and small objects and sampling those with any known differences in photometric properties. The orbital strategy consists in a direct trajectory to one of the Trojan swarms. By carefully choosing the aphelion of the orbit (typically 5.3?AU), the trajectory will offer a long arc in the swarm thus maximizing the number of flybys. Initial gravity assists from Venus and Earth will help reducing the cruise time as well as the ΔV needed for injection thus offering enough capacity to navigate among Trojans. This solution further opens the unique possibility to flyby a Hilda asteroid when leaving the Trojan swarm. During the cruise phase, a Main Belt Asteroid could be targeted if requiring a modest ΔV. The specific science objectives of the mission will be best achieved with a payload that will perform high-resolution panchromatic and multispectral imaging, thermal-infrared imaging/ radiometry, near- and mid-infrared spectroscopy, and radio science/mass determination. The total mass of the payload amounts to 50?kg (including margins). The spacecraft is in the class of Mars-Express or a down-scaled version of Jupiter Ganymede Orbiter. It will have a dry mass of 1200?kg, a total mass at launch of 3070?kg and a ΔV capability of 700?m/s (after having reached the first Trojan) and can be launched by a Soyuz rocket. The mission operations concept (ground segment) and science operations are typical of a planetary mission as successfully implemented by ESA during, for instance, the recent flybys of Main Belt asteroids Steins and Lutetia. 相似文献
569.
Jing-Sen Cai Tian-Chyi Jim Yeh E-Chuan Yan Rui-Xuan Tang Jet-Chau Wen Shao-Yang Huang 《Landslides》2018,15(6):1193-1204
An adaptive sampling approach is proposed, which can sample spatially varying shear strength parameters efficiently to reduce uncertainty in the slope stability analysis. This approach employs a limit equilibrium model and stochastic conditional methodology to determine the likely sampling locations. Karhunen-Loève expansion is used to conduct the conditional Monte Carlo simulation. A first-order analysis is also proposed to ease the computational burden associated with Monte Carlo simulation. These approaches are then tested using borehole data from a field site. Results indicate that the proposed adaptive sampling approach is an effective and efficient sampling scheme for reducing uncertainty in slope stability analysis. 相似文献
570.
Entrainment fluxes in a shear-free convective boundary layer have been measured with a saline water tank set-up. The experiments were targeted towards measuring the entrainment behaviour for medium to high Richardson numbers and use a two-layer design, i.e. two stacked non-stratified (neutral) layers with different densities. With laser induced fluorescence (LIF), the entrainment flux of a fluorescent dye is measured for bulk Richardson numbers in the range 30–260. It is proposed that a carefully chosen combination of top-down and bottom-up processes improves the accuracy of LIF-based entrainment observations. The observed entrainment fluxes are about an order of magnitude lower than reported for thermal water tanks: the derived buoyancy entrainment ratio, $A$ , is found to be $A \approx 0.02$ , which is to be compared with $A\approx 0.25$ for a thermal convection tank (Deardorff et al., J Fluid Mech 100:41–64, 1980). An extensive discussion is devoted to the influence of the Reynolds and Prandtl numbers in laboratory experiments on entrainment. 相似文献