The asymmetry (skewness) of marine magnetic anomaly 32 (72.1–73.3 Ma) on the Pacific plate has been analysed in order to estimate a new palaeomagnetic pole. Apparent effective remanent inclinations of the seafloor magnetization were calculated from skewness estimates of 108 crossings of anomaly 32 distributed over the entire Pacific plate and spanning a great-circle distance of ~12 000 km. The data were inverted to obtain a palaeomagnetic pole at 72.1°N, 26.8°E with a 95 per cent confidence ellipse having a 4.0° major semi-axis oriented 98° clockwise of north and a 1.8° minor semi-axis; the anomalous skewness is 14.2° ± 3.7°. The possible dependence of anomalous skewness on spreading rate was investigated with two empirical models and found to have a negligible effect on our palaeopole analysis over the range of relevant spreading half-rates, ~25 to ~90 mm yr−1 . The new pole is consistent with the northward motion for the Pacific plate indicated by coeval palaeocolatitude and palaeoequatorial data, but differs significantly from, and lies to the northeast of, coeval seamount poles. We attribute the difference to unmodelled errors in the seamount poles, mainly in the declinations. Comparison with the northward motion inferred from dated volcanoes along the Hawaiian–Emperor seamount chain indicates 13° of southward motion of the Hawaiian hotspot since 73 Ma. When the pole is reconstructed with the Pacific plate relative to the Pacific hotspots, it differs by 14°–18° from the position of the pole relative to the Indo–Atlantic hotspots. This has several possible explanations including bias in one or more of the palaeomagnetic poles, motion between the Pacific and Indo–Atlantic hotspots, and errors in plate reconstructions relative to the hotspots. 相似文献
This study presents a geographic information systems-based multi-criteria site selection of non-hazardous regional landfill in Polog Region, Macedonia. The multi-criteria decision framework integrates legal requirements and physical constraints that relate to environmental and economic concerns and builds a hierarchy model for landfill suitability. The methodology is used for preliminary assessment of the most suitable landfill sites by combining fuzzy set theory and analytic hierarchy process (AHP). The fuzzy set theory is used to standardize criteria using different fuzzy membership functions while the AHP is used to establish the relative importance of the criteria. The AHP makes pairwise comparisons of relative importance between hierarchy elements grouped by environmental and economic decision criteria. The landfill suitability is achieved by applying weighted linear combination that uses a comparison matrix to aggregate different importance scenarios associated with environmental and economic objectives. The results from the study suggested that a least suitable landfill area of 1.0% from the total is generated when environmental and economic objectives are valued equally while a most suitable landfill area of 1.8% area is generated when the economic objective is valued higher. Such results are aimed for enhancement of regional landfill site selection in the country that is compliant with modern EU standards. 相似文献
The center of the 35.3 Ma Chesapeake Bay impact structure (85 km diameter) was drilled during 2005/2006 in an ICDP–USGS drilling project. The Eyreville drill cores include polymict impact breccias and associated rocks (1397–1551 m depth). Tens of melt particles from these impactites were studied by optical and electron microscopy, electron microprobe, and microRaman spectroscopy, and classified into six groups: m1—clear or brownish melt, m2—brownish melt altered to phyllosilicates, m3—colorless silica melt, m4—melt with pyroxene and plagioclase crystallites, m5—dark brown melt, and m6—melt with globular texture. These melt types have partly overlapping major element abundances, and large compositional variations due to the presence of schlieren, poorly mixed melt phases, partly digested clasts, and variable crystallization and alteration. The different melt types also vary in their abundance with depth in the drill core. Based on the chemical data, mixing calculations were performed to determine possible precursors of these melt particles. The calculations suggest that most melt types formed mainly from the thick sedimentary section of the target sequence (mainly the Potomac Formation), but an additional crystalline basement (schist/gneiss) precursor is likely for the most abundant melt types m2 and m5. Sedimentary rocks with compositions similar to those of the melt particles are present among the Eyreville core samples. Therefore, sedimentary target rocks were the main precursor of the Eyreville melt particles. However, the composition of the melt particles is not only the result of the precursor composition but also the result of changes during melting and solidification, as well as postimpact alteration, which must also be considered. The variability of the melt particle compositions reflects the variety of target rocks and indicates that there was no uniform melt source. Original heterogeneities, resulting from melting of different target rocks, may be preserved in impactites of some large impact structures that formed in volatile‐rich targets, because no large melt body exists, in which homogenization would have taken place. 相似文献
Efficiency in modern shipping must not come at the expense of undertaking avoidable risks. The complexity of most activities in shipping requires a cooperative effort made by specialists to comprehend the uncertainties of risk and to seek measures for its reduction. Such an effort, however, must not hinder operations but aim at promoting productivity by addressing those factors that have a negative effect on it. This imperative need to deal with the problems of risk led to the development of a series of risk-related disciplines. Identifying the factors that create hazards and finding an effective way of minimizing them, whenever possible, leads to smoother operations, better time frames and, eventually, lower costs. One of the factors that can generate risks and reduce productivity in maritime-related operations is weather. Like any other factor that bears uncertainties and risks, weather hampers actual port operations (such as the loading/unloading of goods and passengers), but it also leads to problems for a whole chain of upstream and downstream industries. In this study, an attempt is made to identify and register hazardous weather trends in the Port of Limassol (used as a case study for Mediterranean ports). An up-to-date picture of the prevailing weather conditions in the area is presented with the aim to provide vital information for risk assessment purposes, both in the short and in the long term. 相似文献
The occurrence of disasters such as extreme flooding in urban environments has severe consequences, not only on the human population but also on critical infrastructures such as the road networks, which are of vital importance for everyday living and particularly for emergency response. In this article, our main goal is to present-conceptually and in praxis-a model that could be used from the emergency responders for timely and efficient emergency management and response in an urban complex environment. For the city of Cologne in Germany, we aim to indicate possible ways to decrease the emergency response time during an extreme flood scenario through the development of an accessibility indicator, which consists of different components. Therefore, we will investigate the opportunities that occur, in a flood risk scenario, from the use of geographic information in different forms such as Volunteered Geographic Information (VGI) and open-source data in an ArcGIS environment, to increase urban resilience through the decreasing emergency response time. We will focus on network analysis for the fire brigades (first acting emergency responders) during a flood scenario to calculate their emergency response ranges and emergency response routes through flooded road networks, for the assistance of the possibly affected hospitals, refugee homes and fire brigades, which can be flooded. At the end of the paper, we suggest that the vulnerable community of the refugees could be taken into consideration as a new source of VGI, as an additional component that would lead to the decrease in the emergency response time. The geo-located information that could be provided by the refugee community can be very useful in emergency situations, such as those examined in this article where timely information can be forwarded to the proper authorities for a more focused and timely emergency response, increasing the resilience of the urban population and their community.
The impact of climate warming on the seasonal variability of the Humboldt Current system ocean dynamics is investigated. The IPSL-CM4 large scale ocean circulation resulting from two contrasted climate scenarios, the so-called Preindustrial and quadrupling CO2, are downscaled using an eddy-resolving regional ocean circulation model. The intense surface heating by the atmosphere in the quadrupling CO2 scenario leads to a strong increase of the surface density stratification, a thinner coastal jet, an enhanced Peru–Chile undercurrent, and an intensification of nearshore turbulence. Upwelling rates respond quasi-linearly to the change in wind stress associated with anthropogenic forcing, and show a moderate decrease in summer off Peru and a strong increase off Chile. Results from sensitivity experiments show that a 50% wind stress increase does not compensate for the surface warming resulting from heat flux forcing and that the associated mesoscale turbulence increase is a robust feature. 相似文献
Statistical methods are widely applied in visibility forecasting. In this article, further improvements are explored by extending
the standard probabilistic neural network approach. The first approach is to use several models to obtain an averaged output,
instead of just selecting the overall best one, while the second approach is to use deterministic neural networks to make
input variables for the probabilistic neural network. These approaches are extensively tested at two sites and seen to improve
upon the standard approach, although the improvements for one of the sites were not found to be of statistical significance. 相似文献
The scientific community that includes meteorologists, physical scientists, engineers, medical doctors, biologists, and environmentalists
has shown interest in a better understanding of fog for years because of its effects on, directly or indirectly, the daily
life of human beings. The total economic losses associated with the impact of the presence of fog on aviation, marine and
land transportation can be comparable to those of tornadoes or, in some cases, winter storms and hurricanes. The number of
articles including the word ``fog' in Journals of American Meteorological Society alone was found to be about 4700, indicating
that there is substantial interest in this subject. In spite of this extensive body of work, our ability to accurately forecast/nowcast
fog remains limited due to our incomplete understanding of the fog processes over various time and space scales. Fog processes
involve droplet microphysics, aerosol chemistry, radiation, turbulence, large/small-scale dynamics, and surface conditions
(e.g., partaining to the presence of ice, snow, liquid, plants, and various types of soil). This review paper summarizes past
achievements related to the understanding of fog formation, development and decay, and in this respect, the analysis of observations
and the development of forecasting models and remote sensing methods are discussed in detail. Finally, future perspectives
for fog-related research are highlighted. 相似文献