How geographic distance and depth drive ecological variability and isolation of demersal fish communities in an archipelago system (Cape Verde, Eastern Atlantic Ocean)     

Anibal Medina  Jean-Claude Brêthes  Jean-Marie Sévigny  & Bruno Zakardjian 《Marine Ecology》2007,28(3):404-417

  相似文献   

A review of the analyses of ocean wave groups     

J.R. Medina  R.T. Hudspeth 《Coastal Engineering》1990,14(6)

The most common parameters and functions used to characterize wave groups in linear seas are reviewed and interrelated in a unified manner. A three-axes representation of run lengths is used to characterize wave groups using exponential and Markov chain approximations. A relationship between four parameters (Q_p, Q_e, κ², and ρ²) and the correlation coefficient between consecutive wave heights [r_HH(1)] is demonstrated. The wave-height function method is reviewed in some detail in order to relate the run length theory with envelope theories. The theoretical estimates used to demonstrate the relationships between the various parameters must be considered as only first-order trends to parameter estimates computed from real wave data due to the statistical variability in these estimates when computed from real wave data.  相似文献   

The new accelerograph network for Santa Fe De Bogota, Colombia and implications for microzonation     

Anibal Ojeda  Samuel Martinez  Maria Bermudez  Kuvvet Atakan 《Soil Dynamics and Earthquake Engineering》2002,22(9-12):791-797

The new accelerographic network of Santa Fe de Bogotá is composed of 29 three-component stations with sensors at the surface and three additional six-component borehole stations with three sensors at the surface and three at depth (115, 126 and 184 m). In total, 32 stations have been operative in the metropolitan area of Bogotá since 1999. During this period of time, a significant number of weak motion are recorded and used for a preliminary analysis of local site effects. Using the SH-wave response spectra we verify the behavior of the different seismic zones proposed by the previous microzonation study of the city. A comparison between normalized SH-wave response spectra and the normalized design spectra for each zone clearly depicts that parts of the design spectra should be revised, as well as the boundaries between different zones may require some changes. The spectral amplification levels reach up to a factor of 5. The predominant periods obtained by the amplification spectra in different stations in the city, show variability from 0.3 to 3.0 s. A comparison is also made between the predominant periods obtained using H/V spectral ratios of microtremors and those using weak motion. In general, microtremors tend to predict slightly lower values of dominant periods than those calculated by the weak motion spectra. However, there is a general correlation between the two data sets. Using the data recorded by one of the borehole station, an equivalent linear seismic response analysis was conducted. The modeled and recorded response spectra show similarities in period peaks, however, the modeled soil amplification is underestimated for periods less than 0.8 s. Since the available record is weak motion which represents mostly the linear response of the soils, further analysis is required.  相似文献   

Mixed extreme wave climate model for reanalysis databases   总被引：1，自引：0，他引：1  

R. Mínguez  A. Tomás  F. J. Méndez  R. Medina 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(4):757-768

Hindcast or wave reanalysis databases (WRDB) constitute a powerful source with respect to instrumental records in the design of offshore and coastal structures, since they offer important advantages for the statistical characterization of wave climate variables, such as continuous long time records of significant wave heights, mean and peak periods, etc. However, reanalysis data is less accurate than instrumental records, making extreme data analysis derived from WRDB prone to under predict design return period values. This paper proposes a mixed extreme value model to deal with maxima, which takes full advantage of both (i) hindcast or wave reanalysis and (ii) instrumental records, reducing the uncertainty in its predictions. The resulting mixed model consistently merges the information given by both kinds of data sets, and it can be applied to any extreme value analysis distribution, such as generalized extreme value, peaks over threshold or Pareto–Poisson. The methodology is illustrated using both synthetically generated and real data, the latter taken from a given location on the northern Spanish coast.  相似文献   

Characterizing and Predicting Traffic Accidents in Extreme Weather Environments     

Richard M. Medina  Guido Cervone  Nigel M. Waters 《The Professional geographer》2017,69(1):126-137

Motorists are vulnerable to extreme weather events, which are likely to be exacerbated by climate change throughout the world. Traffic accidents are conceptualized in this article as the result of a systemic failure that includes human, vehicular, and environmental factors. The snowstorm and concurrent accidents that occurred in the Northeastern United States on 26 January 2011 are used as a case study. Traffic accident data for Fairfax County, Virginia, are supplemented with Doppler radar and additional weather data to characterize the spatiotemporal patterns of the accidents resulting from this major snowstorm event. A kernel density smoothing method is implemented to identify and predict patterns of accident locations within this urban area over time. The predictive capability of this model increases over time with increasing accidents. Models such as these can be used by emergency responders to identify, plan for, and mitigate areas that are more susceptible to increased risk resulting from extreme weather events.  相似文献   

Long-term tidal level distribution using a wave-by-wave approach     

Sonia Castanedo  Fernando J. Mendez  Raul Medina  Ana J. Abascal 《Advances in water resources》2007

  相似文献   

Decision support for conceptual performance‐based design     

Helmut Krawinkler  Farzin Zareian  Ricardo A. Medina  Luis F. Ibarra 《地震工程与结构动力学》2006,35(1):115-133

Performance assessment implies that the structural, non‐structural, and content systems are given and that decision variables, DVs, (e.g. expected annual loss, mean annual frequency of collapse) are computed and compared to specified performance targets. Performance‐based design (PBD) is different by virtue of the fact that the building and its components and systems first have to be created. Good designs are based on concepts that incorporate performance targets up front in the conceptual design process, so that subsequent performance assessment becomes more of a verification process of an efficient design rather than a design improvement process that may require radical changes of the initial design concept. In short, the design approach could consist of (a) specifying performance targets (e.g. tolerable probability of collapse, acceptable dollar losses) and associated seismic hazards, and (b) deriving engineering parameters for system selection, or perhaps better, using the relatively simple design decision support tools discussed in this paper. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

The effects of agriculture on the volcanic aquifers of the canary islands     

E. Custodio  J. A. Guerra  J. Jiménez  J. A. Medina  C. Soler 《Environmental Geology》1983,5(4):225-231

Agriculture is a basic economic activity in the Canary Islands, a Spanish region in the Atlantic Ocean, facing the Sahara. The main crops are bananas, tomatoes, and other special ones suitable for exportation. Fertilizers are applied in high quantities on the scarce land available. The relatively good vertical permeability of the soils favors the deep infiltration of irrigation return flows. Water is obtained by an extraordinary net of shaft wells and water galleries, supplemented when possible by surface reservoirs in the deep gullies. Water is distributed by an extensive network of pipes and canals, allowing the transportation of water to virtually any point from any water source. Water quality is widely variable, from almost rain water to brackish, with a high frequency of sodium bicarbonate types. Return flows, especially when water is applied with good irrigation techniques and the original quality is poor, are saline and contain chemicals leached from the fertilizers. On Tenerife Island, most of the return flows go to coastal aquifers, while most of the water comes from high-altitude water galleries. Agricultural pollution is not generally appraised, but it exists. It can be masked by the frequent, high natural nitrate content in groundwater. On Gran Canaria Island, since water comes mainly from deep shaft wells near the irrigated areas, the nitrate pollution is much more clear. On La Palma Island, besides the nitrate pollution, a potassium pollution of agricultural origin has been mentioned. Other situations on the remaining islands are also discussed. It can be concluded that agriculture is a big concern for the water quality in many areas and impairs its suitability for other uses. Because of the great depth of the water table, the nitrate pollution may not become obvious for many years, especially for the deep-water galleries. Presented at the 16th Congress of the International Association of Hydrogeologists, “Impact of Agricultural Activity on Ground Water Quality and Quantity,” September 1982, Prague, Czechoslovakia.  相似文献   

Cost-Effective Monitoring Strategies to Estimate Mean Water Table Depth   总被引：1，自引：0，他引：1  

H.E. Mew Jr.    M.A. Medina Jr  R.C. Heath  K.H. Reckhow  T.L. Jacobs 《Ground water》1997,35(6):1089-1096

  相似文献   

Environmental and pollution condition of the huizache-caimanero lagoon, in the north-west of Mexico     

R.JoséGuillermo Galindo  J.María Alejandra Medina  L.Cecilio Villagrana  C.Leonardo Ibarra 《Marine pollution bulletin》1997,34(12):1072-1077

The fish and shrimp production of the Huizache-Caimanero Lagoon, located on the Mexican Pacific, has been decreasing in recent years, which may be due to environmental and pollution conditions. Therefore, water and sediment samples were analysed to quantify nutrients, pesticides, and coliform bacteria. The results indicated that the system is polluted considerably during the rainy season due to continental runoff carrying municipal and agricultural wastes, thereby increasing coliform pollution and nitrate concentrations. This is less apparent for phosphates and pesticides. We conclude that pollution and environmental changes are important causes decreasing production; recent studies have reported biochemical and physiological alteration in aquatic organisms exposed to similar levels of pesticides as reported here. During the rainy season, coliform levels are above permissible levels established by sanitary regulations, and are thus pose a risk to public health.  相似文献