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71.
Cristina Medina Guillermo M. Álamo Juan J. Aznárez Luis A. Padrón Orlando Maeso 《地震工程与结构动力学》2019,48(7):772-791
Although the seismic actions generally consist of a combination of waves, which propagates with an angle of incidence not necessarily vertical, the common practice when analyzing the dynamic behavior of pile groups is based on the assumption of vertically incident wave fields. The aim of this paper is to analyze how the angle of incidence of SV waves affects the dynamic response of pile foundations and piled structures. A three-dimensional boundary element-finite element coupling formulation is used to compute impedances and kinematic interaction factors corresponding to several configurations of vertical pile groups embedded in an isotropic homogeneous linear viscoelastic half-space. These results, which are provided in ready-to-use dimensionless graphs, are used to determine the effective dynamic properties of an equivalent single-degree-of-freedom oscillator that reproduces, within the range where the peak response occurs, the response of slender and nonslender superstructures through a procedure based on a substructuring model. Results are expressed in terms of effective flexible-base period and damping as well as maximum shear force at the base of the structure. The relevance and main trends observed in the influence of the wavefront angle of incidence on the dynamic behavior of the superstructure are inferred from the presented results. It is found that effective damping is significantly affected by the variations of the wave angle of incidence. Furthermore, it comes out that the vertical incidence is not always the worst-case scenario. 相似文献
72.
Carlos Neira Jennifer Cossaboon Guillermo Mendoza Eunha Hoh Lisa A. Levin 《Marine pollution bulletin》2017,114(1):466-479
Polycyclic aromatic hydrocarbons (PAHs) have garnered much attention due to their bioaccumulation, carcinogenic properties, and persistence in the environment. Investigation of the spatial distribution, composition, and sources of PAHs in sediments of three recreational marinas in San Diego Bay, California revealed significant differences among marinas, with concentrations in one site exceeding 16,000 ng g? 1. ‘Hotspots’ of PAH concentration suggest an association with stormwater outfalls draining into the basins. High-molecular weight PAHs (4–6 rings) were dominant (> 86%); the average percentage of potentially carcinogenic PAHs was high in all sites (61.4–70%) but ecotoxicological risks varied among marinas. Highly toxic benzo(a)pyrene (BaP) was the main contributor (> 90%) to the total toxic equivalent quantity (TEQ) in marinas. PAHs in San Diego Bay marina sediments appear to be derived largely from pyrogenic sources, potentially from combustion products that reach the basins by aerial deposition and stormwater drainage from nearby streets and parking lots. 相似文献
73.
José Franco Stan E. Kurtz José A. GarcÍa-Barreto Guillermo GarcÍa-Segura Eduardo de la Fuente Peter Hofner Alejandro Esquivel 《Astrophysics and Space Science》2001,277(1):71-74
Here we discuss the effects of large ambient pressures and decreasing density gradients on the observed properties of dusty UC hii regions. Dust absorption can effectively reduce the size of the photo ionized region, and density gradients can modify the spectral index of the emission. The effects of the density gradients seem to be present in both galactic and extragalactic HII regions. 相似文献
74.
75.
Miquel Grau Guillermo González-Casado 《Celestial Mechanics and Dynamical Astronomy》1998,72(3):169-186
A comparative study of the evolution of the Sun–Jupiter–Asteroid system near the 4:1 and 7:2 resonances is performed by means
of two techniques that proceed differently from the Hamiltonian corresponding to the planar restricted elliptic three-body
problem. One technique is based on the classical Schubart averaging while the other is based on a mapping method in which
the perturbing part of the Hamiltonian is expanded and the resulting terms are ordered according to a weight function that
depends on the powers of eccentricities and the coefficients of the terms. For the mapping method the effect of Saturn on
the asteroidal evolution is introduced and the degree of chaos is estimated by means of the Lyapunov time. Both methods are
shown to lead to similar results and can be considered a suitable tool for describing the evolution of asteroids in the Kirkwood
gap and the group corresponding to the 4:1 and 7:2 Jovian resonances, respectively.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
76.
José J. Rodes Guillermo Bernabeu Juan Fabregat 《Astrophysics and Space Science》1998,263(1-4):259-262
We present measured radial velocities of two peculiar early B type stars, to check their membership to the open cluster NGC
663. The radial velocities have been obtained with the cross correlation technique, using as a template stars from the list
of Liu et al. (1989).
We have obtained accuracies around 3-4 km/s in our radial velocity measurements. From our results we conclude that both stars
are probably non members of the cluster.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
77.
Sergey A. Silich & Guillermo Tenorio-Tagle 《Monthly notices of the Royal Astronomical Society》1998,299(1):249-266
Two-dimensional calculations of the evolution of remnants generated by the strong mechanical energy deposited by stellar clusters in dwarf galaxies ( M ∼ 109 –1010 M⊙) are presented. The evolution is followed for times longer than both the blowout time and the presumed span of energy injection generated by a coeval massive stellar cluster. The remnants are shown to end up wrapping around the central region of the host galaxy, while growing to kiloparsec-scale dimensions. Properties of the remnants such as luminosity, size, swept-up mass and expansion speed are given as functions of time for all calculated cases. The final fate of the swept-up galactic gas and of the matter processed by the central starburst is shown to be highly dependent on the properties of the low-density galactic halo. Superbubbles powered by star clusters, with properties similar to those inferred from the observations, slow down in the presence of an extended halo to expansion speeds smaller than the host galaxy escape velocity. Values of the critical luminosity required for the superbubbles to reach the edge of the galaxies with a speed comparable to the escape speed are derived analytically and numerically. The critical luminosities are larger than those in the detected sources, and thus the superbubbles in amorphous dwarf galaxies must have already undergone blowout and are presently evolving into an extended low-density halo. This will inhibit the loss of the swept-up and processed matter from the galaxy. 相似文献
78.
The structure and function of many Korean ecosystems have been rapidly modified since the 1960s when industrialization of the nation began. Ulsan City was the first in Korea to develop into a major industrial complex. To assess anthropogenic impacts on ecosystems surrounding Ulsan, sediment cores were collected from Mujechi-neup (bog) and Sanggae reservoir of Ulsan, and these cores were 210Pb dated using the CRS model. Physical and chemical characteristics and pollen were analyzed, and the rates of sediment accumulation were calculated. Unsupported 210Pb inventories in Mujechi-neup and the Sanggae reservoir were 18.04 and 16.53 pCi cm–2, and the corresponding 210Pb fluxes were 0.56 and 0.52 pCi cm–2 yr–1, respectively. The overall accumulation rate of dry matter was 0.26 kg m–2 yr–1 since 1852 (14 cm in depth) in Mujechi-neup. In the Sanggae reservoir, the accumulation rates of dry matter were increased from 2.1 in 1965 to 6.0 kg m–2 yr–1 in 1999. Pollen analysis revealed that three pollen zones existed in Mujechi-neup; a Pinus pollen-dominated zone from 0 to 5 cm in depth (1974 year), an Alnus pollen-dominated zone from 5 to 15 cm in depth (1827 year), and a Quercus pollen-dominated zone below 15 cm in depth. The shift from an Alnus dominated zone to a Pinus dominated zone was related to the Korean War between 1951 and 1953 and reforestation activities in the 1970s. In the Sanggae reservoir, there was an increase of Humulus pollen since 1996, an increase of Ambrosia pollen since the 1960s and the decrease of Graminae pollen since 1993 with the expansion of the industrial area. Similar to Mujechi-neup, the Sanggae reservoir also consists of three pollen zones: a Pinus and Typha pollen-dominated zone from 0 to 10 cm in depth (since 1993), a Graminae pollen-dominated zone from 10 to 22 cm in depth (between 1947 and 1993), and a Pinus pollen-dominated zone below 22 cm in depth (before 1947). The increase of Typha and Humulus in the 1990s indicates an increase in the inflow of nutrients into the wetlands. Also, pollen analysis revealed that Ambrosia was introduced in the 1960s during industrialization of the area. The sediment was composed of humic peat in Mujechi-neup and was composed of clay in the Sanggae reservoir. High LOI, P, and low C/N ratio between the depths of 5 to 7 cm in the Sanggae reservoir indicates an increased input of P and N. As a result, the growth of Typha was at its maximum. The total Pb content in Mujechi-neup has been increasing since the 1870s, and its accumulation in the Sanggae reservoir has been increasing since the 1960s. Thus, the history of local-scale disturbances and human activities in the watershed was reconstructed through paleoecological studies in Ulsan. 相似文献
79.
80.
Christie A. Robinson Joan M. Bernhard Lisa A. Levin Guillermo F. Mendoza & Jessica K. Blanks 《Marine Ecology》2004,25(4):313-336
Abstract. Infauna, including foraminifera and metazoans, were enumerated and identified from five types of seep habitats and two adjacent non-seep habitats. Collections were made with the deep submergence research vessel 'Alvin' from three areas of active seepage in the Gulf of Mexico (Alaminos Canyon [2220 m], Atwater Canyon [1930 m], and Green Canyon lease block 272 [700 m]) and on the Blake Ridge Diapir [2250 m], which is located off the southeastern coast of the United States. The seep habitats sampled included four types of microbial mats ( Beggiatoa , Thioploca , thin and thick Arcobacter ) and the periphery of a large mussel bed. Sediments under large rhizopod protists, xenophyophores, were sampled adjacent to the mussel bed periphery. A non-seep site, which was >1 km away from active seeps, was also sampled for comparison. Densities of most taxa were higher in the Gulf of Mexico seeps than in Blake Ridge samples, largely because densities in the thick microbial mats of Blake Ridge were significantly lower. Diversity was higher in the Thioploca mats compared to other microbial-mat types. Within an ocean basin ( i.e. , Atlantic, Gulf of Mexico) we did not observe significant differences in meiofaunal or macrofaunal composition in Beggiatoa versus Thioploca mats or thin versus thick Arcobacter mats. Foraminifera represented up to 16% of the seep community, a proportion that is comparable to their contribution at adjacent non-seep communities. In general, the observed densities and taxonomic composition of seep sites at the genus level was consistent with previous observations from seeps ( e.g. , the foraminifers Bolivina and Fursenkoina , the dorvilleid polychaete Ophryotrocha ). 相似文献