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161.
162.
Marisol Monterrubio-Velasco F. R. Zúñiga Victor Hugo Márquez-Ramírez Angel Figueroa-Soto 《Journal of Seismology》2017,21(6):1623-1639
The rupture processes of any heterogeneous material constitute a complex physical problem. Earthquake aftershocks show temporal and spatial behaviors which are consequence of the heterogeneous stress distribution and multiple rupturing following the main shock. This process is difficult to model deterministically due to the number of parameters and physical conditions, which are largely unknown. In order to shed light on the minimum requirements for the generation of aftershock clusters, in this study, we perform a simulation of the main features of such a complex process by means of a fiber bundle (FB) type model. The FB model has been widely used to analyze the fracture process in heterogeneous materials. It is a simple but powerful tool that allows modeling the main characteristics of a medium such as the brittle shallow crust of the earth. In this work, we incorporate spatial properties, such as the Coulomb stress change pattern, which help simulate observed characteristics of aftershock sequences. In particular, we introduce a parameter (P) that controls the probability of spatial distribution of initial loads. Also, we use a “conservation” parameter (π), which accounts for the load dissipation of the system, and demonstrate its influence on the simulated spatio-temporal patterns. Based on numerical results, we find that P has to be in the range 0.06 < P < 0.30, whilst π needs to be limited by a very narrow range (0.60 < π < 0.66) in order to reproduce aftershocks pattern characteristics which resemble those of observed sequences. This means that the system requires a small difference in the spatial distribution of initial stress, and a very particular fraction of load transfer in order to generate realistic aftershocks. 相似文献
163.
A genetic and evolutionary model is established for saline depressions in continental areas. These depressions are located in arid or subarid areas, and are developed on low permeability geological mediums (K<10 mm/day) with a lack of streams reaching the small lakes. The phenomenon of evaporation is fundamental, since it is the basic requirement for the presence or absence of a free water surface in the lake, and also for depression of the phreatic surface, which causes inflow of groundwater towards the lake. With these conditions, the proposed model includes the following stages: (i) initiation of the close depression; (ii) deepening of the depression; (iii) formation of the lake basin and the end of the deepening; and (iv) levelling and lateral extension of the lake basin. The combined effects of groundwater flows and aeolian action offer a coherent explanation for the origin and evolution both of the closed depressions found in the Ebro Valley, and of the salt lakes that subsequently form. The processes described form morphologies of oval shape with the main axis parallel to the direction of the wind, flat floors and evaporitic sedimentation, although they act on geological materials with different lithologies. © 1998 John Wiley & Sons, Ltd. 相似文献
164.
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166.
Seoane S Garmendia M Revilla M Borja A Franco J Orive E Valencia V 《Marine pollution bulletin》2011,62(7):1484-1497
Inverted microscopy is widespread employed for the analysis of phytoplankton composition within water quality monitoring networks. However, the analysis at the lowest taxonomical level is not always required for ecological status assessment. In addition, inverted microscopy can underestimate the small phytoplankton, and not always distinguish photoautotrophic from heterotrophic cells. In this study, as alternative tools, epifluorescence microscopy and High Performance Liquid Chromatography (HPLC) were employed to characterize phytoplankton communities within waters of different trophic condition. Epifluorescence microscopy confirmed its effectiveness to count the small phytoplankton. Furthermore, significant correlations between nutrients of anthropogenic origin and nanoplankton abundances were found. However, this technique resulted very time-consuming. HPLC together with the CHEMTAX program was more appropriate than inverted microscopy, in terms of cost-effectiveness. Also, the main variability patterns observed in the phytoplankton community structure by HPLC coincided with previous findings in the study area. Nevertheless, a rapid screening at the inverted microscope is recommended. 相似文献
167.
In the past several decades, the techniques used to discern the different sedimentary fractions of P have been refined. This
has allowed for a better understanding of P burial of the different P fractions and diagenetic reactions and, ultimately,
the constraining of P residence time in the oceans. P sequential extraction was performed on eight sediment cores (between
16 and 24 cm deep) collected along a salinity gradient from the Ojo de Liebre Lagoon and the salt evaporation saltern of Guerrero
Negro, Baja California Sur, Mexico in order to determine, under purely diagenetic conditions (in the absence of anthropogenic
activities and biogenic sediment reworking), the fractionation and flux of P to the sediments. The majority of P was found
in the authigenic fraction (37 ± 5.4% to 53 ± 8.9%), with P associated to organic matter comprising the overall smallest percentage
(0.25 ± 0.43% to 21 ± 6.0%) relative to total P. The average flux of total P to the sediments for all the sites was found
to be (451 ± 127) × 10−4 mol m−2 year−1, up to several orders of magnitude greater than those found in other studies. It is concluded that P is most likely transformed
from P associated to organic matter to the authigenic mineral phase and that P was retained in the sediments in its mineral
form rather than in reactive forms. This particular study area has the ability to retain large quantities of P in the sediments. 相似文献
168.
A. B. Woodland K. Schollenbruch M. Koch T. Boffa Ballaran R. J. Angel D. J. Frost 《Contributions to Mineralogy and Petrology》2013,166(6):1677-1686
Experiments at high pressures and temperatures reveal the stability of a Fe4O5-type structured phase in several simple chemical systems. On the one hand, the Fe4O5 end-member is stable in the presence of SiO2-rich phases, including stishovite, but contains ≤0.01 Si cations per formula unit. This indicates that Si is essentially excluded from this phase. On the other hand, the Fe4O5 phase can form solid solutions with Mg and Cr and can coexist with silicate phases at the high P–T conditions expected in the transition zone of the mantle (i.e. >~9 GPa). It can coexist with both wadsleyite and Mg-rich ringwoodite and can contain at least 25 mol% Mg2Fe2O5 component. The Fe4O5 phase always contains the least amount of Mg in any given mineral assemblage. Cr-bearing Fe4O5 has been synthesised with up to 46 mol% Fe2Cr2O5 component and can coexist with spinel and/or hematite-eskolatite solid solutions. Substitution of Mg and Cr for Fe2+ and Fe3+, respectively, leads to variations in Fe3+/∑Fe from the ideal value of 0.5 for the Fe4O5 end-member composition, which can influence its redox stability. These cations also have contrasting effects on the unit-cell parameters, which indicate that they substitute into different sites. This initial study suggests that Fe4O5-type structured phases may be stable over a range of P–T–fO2 conditions and bulk compositions, and can be important in understanding the post-spinel phase relations in a number of chemical systems relevant to the Earth’s transition zone. Thus, the presence of even small amounts of Fe3+ could alter the expected phase relations in peridotitic bulk compositions by stabilising this additional phase. 相似文献
169.
DALLA VECCHIA Fabio M. RIERA Violet OMS Josep Oriol DINARèS-TURELL Jaume GAETE Rodrigo GALOBART Angel 《《地质学报》英文版》2013,87(5):1198-1127
Pterosaur bones are for the first time reported from the Tremp Syncline(Spain) and the southern Pyrenees.They come from the Torrebilles-2 site(Isona,Lleida Province) in the upper Maastrichtian part of the Tremp Formation,which falls within the C29r magnetochron.Fragmentary long bones are referred to the Pterosauria based on their cortical thinness,micro-architecture,and histological features.They belong to very large to possibly giant individuals.The most complete specimen is possibly a partial right femur.The review of the Maastrichtian pterosaur record shows that only a few specimens can be referred to the C29r(which contains the K/Pg boundary).The identification of fragmentary remains could improve our knowledge about the abundance and distribution of these flying sauropsids just before the end-Cretaceous mass extinction. 相似文献
170.
Nancy Elizabeth Dávila‐Guzmán Felipe de Jesús Cerino‐Córdova Eduardo Soto‐Regalado Jose Rene Rangel‐Mendez Paola Elizabeth Díaz‐Flores Maria Teresa Garza‐Gonzalez José Angel Loredo‐Medrano 《洁净——土壤、空气、水》2013,41(6):557-564
The potential use of spent coffee ground (SCG) for the removal of copper has been investigated as a low‐cost adsorbent for the biosorption of heavy metals. Adsorption batch experiments were conducted to determine isotherms and kinetics. The biosorption equilibrium data were found to fit well the Freundlich model and an experimental maximum biosorption capacity of copper ions 0.214 mmol/g was achieved. The biosorption kinetics of SCG was studied at different adsorbate concentrations (0.1–1.0 mM) and stirring speeds (100–400/min). The results showed an increase in the copper ion uptake with raising the initial metal concentration and the kinetic data followed the pseudo‐second order rate expression. The effect of stirring speed was a significant factor for the external mass transfer resistance at 100/min and coefficients were estimated by the Mathews and Weber model. Biosorption of copper ions onto SCG was observed to be related mainly with the release of calcium and hydrogen ions suggesting that biosorption performance by SCG can be attributed to ion‐exchange mechanism with calcium and hydrogen ions neutralizing the carboxyl and hydroxyl groups of the biomass. 相似文献