Hipparcos and the age of the Galactic disc     

Raul Jimenez  Chris Flynn  & Eira Kotoneva 《Monthly notices of the Royal Astronomical Society》1998,299(2):515-519

We use the Hipparcos colour–magnitude diagram of field stars with Tycho colours to make a new minimum age estimate for the Galactic disc. The method is based on fits to the red envelope of subgiants in the Hipparcos colour–magnitude diagram with synthetic isochrones covering the range of disc metal abundance. The colours and luminosities of the isochrones as a function of abundance are checked using new techniques involving 'red-clump' stars in the giant branch region and on the main sequence using G and K dwarfs. We derive a minimum disc age of 8 Gyr, in good agreement with other methods.  相似文献   

Response of the mixed-function oxidase system to toxicant dose, food and acclimation temperature in the bluegill sunfish     

Braulio D Jimenez  Lisa S Burtis 《Marine environmental research》1988,24(1-4)

The degree of induction of hepatic mixed function oxidase (MFO) enzymes in fish is modulated by environmental conditions. This study was designed to investigate the influence of water temperature, presence or absence of food, and exposure to benzo(a]pyrene (BaP) on the inductive response of bluegill sunfish (Lepomis macrochirus). The results show an increase in 7-ethoxyresorufin O-deethylase (EROD) activity with an increase in acclimation temperature and dose. This activity appears to be associated with a very small fraction of the total cytochrome P-450 induced. Major changes were observed in the 53- and 57-kilodaltons (kDa) electrophoretic bands.  相似文献   

A review of the impacts of salmonid farming on marine coastal ecosystems in the southeast Pacific   总被引：2，自引：0，他引：2  

Buschmann  Alejandro H.; Riquelme  Veronica A.; Hernandez-Gonzalez  Maria C.; Varela  Daniel; Jimenez  Jaime E.; Henriquez  Luis A.; Vergara  Pedro A.; Guinez  Ricardo; Filun  Luis 《ICES Journal of Marine Science》2006,63(7):1338-1345

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Fuzzy spectral clustering for identification of rock discontinuity sets   总被引：1，自引：1，他引：0  

R. Jimenez 《Rock Mechanics and Rock Engineering》2008,41(6):929-939

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Response of three krill species to hypoxia and warming: an experimental approach to oxygen minimum zones expansion in coastal ecosystems          下载免费PDF全文

Nelly Tremblay  Doris Abele 《Marine Ecology》2016,37(1):179-199

To understand the adaptation of euphausiid (krill) species to oxygen minimum zones (OMZs), respiratory response and stress experiments combining hypoxia‐reoxygenation exposure with warming were conducted. Experimental krill species were obtained from the Antarctic (South Georgia area), the Humboldt Current System (HCS, Chilean coast) and the Northern California Current System (NCCS, Oregon). Euphausia mucronata from the HCS showed oxyconforming pO₂‐dependent respiration below 80% air saturation (18 kPa). Normoxic subsurface oxygenation in winter posed a ‘high oxygen stress’ for this species. The NCCS krill, Euphausia pacifica, and the Antarctic krill, Euphausia superba, maintained respiration rates constant down to low critical pO₂ values of 6 kPa (30% air saturation) and 11 kPa (55% air saturation), respectively. Antarctic krill had low antioxidant enzyme activities, but high concentrations of the molecular antioxidant glutathione (GSH) and was not lethally affected by 6 h exposure to moderate hypoxia. The temperate krill species (E. pacifica) had higher superoxide dismutase (SOD) values in winter than in summer, which relates to a higher winter metabolic rate. In all species, antioxidant enzyme activities remained constant during hypoxic exposure at the typical temperature for their habitat. Warming by 7 °C above habitat temperature in summer increased SOD activities and GSH levels in E. mucronata (HCS), but no oxidative damage occurred. In winter, when the NCCS is well mixed and the OMZ is deeper, +4 °C of warming combined with hypoxia represents a lethal condition for E. pacifica. In summer, when the OMZ expands upwards (100 m subsurface), antioxidant defences counteracted hypoxia and reoxygenation effects in E. pacifica, but only at mildly elevated temperature (+2 °C). In this season, experimental warming by +4 °C reduced antioxidant activities and the combination of warming with hypoxia again caused mortality of exposed specimens. We conclude that a climate change scenario combining warming and hypoxia represents a serious threat to E. pacifica and, as a consequence, NCCS food webs.  相似文献   

Thermal history of the westernmost Eastern Alps (Penninic Rhenodanubian Flysch nappes,Helvetic nappes,and Subalpine Molasse thrust sheets)     

Michael Zerlauth  Audrey Bertrand  Gerd Rantitsch  Doris Groß  Hugo Ortner  Hannah Pomella  Bernhard Fügenschuh 《International Journal of Earth Sciences》2016,105(5):1525-1547

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A Simple Genetic Algorithm for Calibration of Stochastic Rock Discontinuity Networks     

R. Jimenez  R. Jurado-Pi?a 《Rock Mechanics and Rock Engineering》2012,45(4):461-473

We present a novel approach for calibration of stochastic discontinuity network parameters based on genetic algorithms (GAs). To validate the approach, examples of application of the method to cases with known parameters of the original Poisson discontinuity network are presented. Parameters of the model are encoded as chromosomes using a binary representation, and such chromosomes evolve as successive generations of a randomly generated initial population, subjected to GA operations of selection, crossover and mutation. Such back-calculated parameters are employed to make assessments about the inference capabilities of the model using different objective functions with different probabilities of crossover and mutation. Results show that the predictive capabilities of GAs significantly depend on the type of objective function considered; and they also show that the calibration capabilities of the genetic algorithm can be acceptable for practical engineering applications, since in most cases they can be expected to provide parameter estimates with relatively small errors for those parameters of the network (such as intensity and mean size of discontinuities) that have the strongest influence on many engineering applications.  相似文献   

A Simplified Failure Criterion for Intact Rocks Based on Rock Type and Uniaxial Compressive Strength   总被引：2，自引：1，他引：1  

Jiayi Shen  Rafael Jimenez  Murat Karakus  Chaoshui Xu 《Rock Mechanics and Rock Engineering》2014,47(2):357-369

The uniaxial compressive strength (UCS) of intact rock, which can be estimated using relatively straightforward and cost-effective techniques, is one of the most practical rock properties used in rock engineering. Thus, constitutive laws to represent the strength and behavior of (intact) rock frequently use it, along with additional intrinsic rock properties. Although triaxial tests can be employed to obtain best-fit failure criterion parameters that provide best strength predictions, they are more expensive and require time-consuming procedures; as a consequence, they are often not readily available at early stages of a project. Based on the analysis of an extensive triaxial test database for intact rocks, we propose a simplified empirical failure criterion in which rock strength at failure is expressed in terms of confining stress and UCS, with a new parameter which can be directly estimated from the UCS for a specified rock type in the absence of triaxial test data. Performance of the proposed failure criterion is then tested for validation against experimental data for eight rock types. The results show that strengths of intact rock estimated by the proposed failure criterion are in good agreement with experimental test data, with small discrepancies between estimated and measurements strengths. Therefore, the proposed criterion can be useful for preliminary (triaxial) strength estimation of intact rocks when triaxial tests data are not available.  相似文献   

Chemical pollution--has it been tackled sufficiently? Visions of a healthier Baltic Sea     

Lehtonen KK  Schiedek D 《Marine pollution bulletin》2006,53(8-9):375-376

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Benthic biodiversity indices versus salinity gradient in the southern Baltic Sea   总被引：2，自引：0，他引：2  

Zettler ML  Schiedek D  Bobertz B 《Marine pollution bulletin》2007,55(1-6):258-270

The need to assess the environmental status of marine and coastal waters according to the EU Water Framework Directive (WFD) encouraged the design of specific biotic indices to evaluate the response of benthic communities to human-induced changes in water quality. In the present study three of these indices, the traditional Shannon Wiener Index (H') and the more recently published AMBI (AZTI' Marine Biotic Index) and BQI (Benthic Quality Index), were tested along a salinity gradient in the southern Baltic Sea. The comparison of the three indices demonstrates that in the southern Baltic Sea the ecological quality (EcoQ) classification based on macrozoobenthic communities as indicator greatly depends on the biotic index chosen. We found a significant positive relation between species number, H', BQI and salinity resulting in EcoQ status of "Bad", "Poor" or "Moderate" in areas with a salinity value below 10 psu. The AMBI was less dependent on salinity but appear to partly overestimate the EcoQ status. Presently none of these biotic indices appear to be adjusted for application in a gradient system as given in the southern Baltic Sea. A potential approach describing how to overcome this limitation is discussed.  相似文献