Persistence of lutetium disilicate     

María D. Alba  Pablo Chaín 《Applied Geochemistry》2007

RE₂Si₂O₇ is one of the final products of the chemical interaction of radioactive cation simulators and the silicates used in the engineered barrier of deep geological repositories. The aim of this paper is to study the chemical and structural behaviour of Lu₂Si₂O₇ (Lu as actinide tripositive state simulator) in several different chemical systems. The conditions expected at the repositories are simulated in the laboratory with solutions of different compositions and pH. Both the solid products and remnant solutions were analyzed using techniques that give information on the short- and long-range structural order. The results show good stability of Lu₂Si₂O₇, under the studied conditions, and, therefore, encapsulation of the radioactive actinide cations as a disilicate phase could be considered a viable method to ensure the long-term safety of the repositories.  相似文献   

The impact of water resources development projects on water vapor pressure trends in a semi-arid region, Turkey     

Tahsin Tonkaz  Mahmut Çetin  Kâzım Tülücü 《Climatic change》2007,82(1-2):195-209

The aim of this study was to investigate long-term seasonal trends and decadal change patterns of monthly mean water vapor pressure (WVP) observation series at 16 meteorological stations scattered point-wisely over the Southeastern Anatolian Project (GAP) area in Turkey, where large-scale soil and water development projects have been put into practice since the 1970s. The record length of WVP observation series of each station varied between 31- and 41-years between 1962 and 2002. The monthly mean WVP observation series of each station was rearranged on seasonal basis. Sequential Mann–Kendall trend test, Sen’s slope estimator, and Spearman’s rank–order correlation tests were employed for detection of likely trends, and Kruskall–Wallis test was used to detect decadal variations in WVP series of each observation station. A possible area of representation for each meteorological station was determined by using the Thiessen polygons technique in a geographical information systems media. It was found that 15 seasonal WVP series have a positive trend covering 97% of the GAP area in the summer season; although one WVP series has a negative trend direction. However, in the spring season, 33% of the area had a positive trend, and a negative trend did not appear in any stations. WVP records in the winter season showed an increasing trend over 19% of the GAP area, whereas a decreasing trend prevailed in 9% of the area. The study results led us to conclude that the substantial increase of WVP observations in summer season could be attributed to both the shift from rain-fed agriculture to irrigated agriculture being made increasingly spacious year by year and building large water reservoirs in the GAP located in a semi-arid region. The results also indirectly suggested that the historical trends in the WVP parameters might be related to global climate change phenomenon.  相似文献   

Earthquake ground motion in Mexico City: An analysis of data recorded at Roma array     

Martín Crdenas-Soto  Francisco J. Chvez-García 《Soil Dynamics and Earthquake Engineering》2007,27(5):475-486

We analysed in detail three earthquakes recorded in a small-aperture accelerometric array in Mexico City, using the correlation of the records as a function of time along the accelerogram and frequency. Ground response is strongly conditioned by the fundamental period of the soft soils at the site of the array (T₀). Energy at periods longer than 2T₀ is guided by the crustal structure (with a thickness of 45 km). The wave field at periods between T₀ and 2T₀ also consists of surface waves but guided by the upper 2–3 km of volcanic sediments in central Mexico. For periods smaller than T₀, ground motion is uncorrelated among the stations. Our results indicate that seismic response of Mexico City, including its very long duration, results from deeply guided surface waves (between 2 and 45 km depth) interacting with the very local response of the soft surficial clay layer.  相似文献   

Community structure and phenology of chironomids (Insecta: Chironomidae) in a Patagonian Andean stream     

Patricia Elizabeth García  Diego Alejandro An Surez 《Limnologica》2007,37(1):109-117

In this paper, we studied the assemblage of Chironomidae from headwaters of Ñireco stream by recording drifting pupal exuviae caught in the debris close to the shore. Samples were collected in three stations along 18 km of the stream every 2 weeks during spring–summer months and monthly during autumn–winter over a year. A total of 15949 exuviae were collected and 55 taxa were identified. The most abundant taxa were Cricotopus spp. with highest numbers of exuviae recorded in each station over the study period. Subfamily Orthocladiinae was the most abundant taxa, followed by Chironominae and Podonominae. The emergence period in the stream occurred between December 1998 and March 1999. Most of the dominant and frequent species were univoltine. The emergence peaks at each sampling station occurred at the highest temperature of the water recorded.  相似文献   

Modelling Subsurface Heterogeneity by Coupled Markov Chains: Directional Dependency,Walther’s Law and Entropy     

A.?M.?M.?ElfekiEmail author  F.?M.?Dekking 《Geotechnical and Geological Engineering》2005,23(6):721-756

This paper is an extension of the two-dimensional coupled Markov chain model developed by Elfeki and Dekking (2001) supplemented with extensive simulations. We focus on the development of various coupled Markov chains models: the so-called fully forward Markov chain, fully backward Markov chain and forward–backward Markov chain models. We addressed many issues such as: sensitivity analysis of optimal sampling intervals in horizontal and lateral directions, directional dependency, use of Walther’s law to describe lateral variability, effect of conditioning on number of boreholes on the model performance, stability of the Monte Carlo realizations, various implementation strategies, use of cross validation techniques to evaluate model performance and image division for statistically non-homogeneous deposits are addressed. The applications are made on three sites; two sites are located in the Netherlands, and the third is in the USA. The purpose of these applications is to show under which conditions the Markov models can be used, and to provide some guidelines for the practice. Entropy maps are good tools to indicate places where high uncertainty is present, so can be used for designing sampling networks to reduce uncertainty at these locations. Symmetric and diagonally dominant horizontal transition probabilities with proper sampling interval show plausible results (fits with geologists prediction) in terms of delineation of subsurface heterogeneous structures. Walther’s law can be utilised with a proper sampling interval to account for the lateral variability.  相似文献   

Cyanobacterial blooms in estuarine ecosystems: characteristics and effects on Laeonereis acuta (Polychaeta, Nereididae)     

da Rosa CE  de Souza MS  Yunes JS  Proença LA  Nery LE  Monserrat JM 《Marine pollution bulletin》2005,50(9):956-964

In January of 2003, a cyanobacterial bloom in the Patos' Lagoon (Southern Brazil) (32 degrees 05'S-52 degrees 12'W) was observed. Water samples were taken to identify the composition and abundance of the bloom, as well as the occurrence of toxins. The effects of this occurrence on the estuarine worm Laeonereis acuta (Polychaeta, Nereididae) was also evaluated. Predominance of cyanobacteria, particularly Anabaena trichomes ( approximately 2.5.10(6) individuals per liter) was observed, and low concentrations of microcystins and anticholinesterasic toxins were detected. Augmented levels of lipid hydroperoxides (LPO) and glutathione-S-transferase activity, and lowering of total protein content were also observed in organisms collected during the bloom event. Although non-toxic, the cyanobacterial bloom could augment the cycle of hyper-oxygenation and hypoxia in the water. During hyperoxia, L. acuta, an oxyconformer, should consume more oxygen, thus augmenting the rate of reactive oxygen species generation. A repeated cycle of hyper-oxygenation and hypoxia would finally induce oxidative stress, as evidenced by the high levels of LPO and glutathione-S-transferase activity.  相似文献   

Effects of artificial and natural recharge on chemical equilibrium in the Cerro Prieto reservoirs, Baja California, México     

Enrique Portugal  Rosa María Barragn  Jesús de Len 《Journal of Geochemical Exploration》2006,89(1-3):339

Chemical equilibrium modeling studies of two aquifers in the western part of the Cerro Prieto (CP-I) geothermal field were performed to obtain the activities of the main ions and complexes by using the EQQYAC program. The results provided a pH of 6.44 for the deep aquifer, which is slightly higher than the value of 5.5 found for the shallower reservoir. In the northern part of the field, the reservoir pH has decreased up to 1.5 units compared to that modeled for 1990. Variations of pH with respect to time were also found to occur in the southern part of the field. In spite of the large changes in hydrodynamic conditions occurring in the reservoir due to exploitation, the equilibrium between both K- and Na-feldspars and between K-feldspar and K-mica seems to control the chemical composition of the fluids, in both reservoirs.  相似文献   

Hydrothermal alteration and fluid inclusion study of the Lower Cretaceous porphyry Cu–Au deposit of Tiámaro, Michoacán, Mexico     

Carlos Garza-Gonzlez  Antoni Camprubí  Eduardo Gonzlez-Partida  Germn Arriaga-García  Fernando Rosique-Naranjo 《Journal of Geochemical Exploration》2006,89(1-3):124

The Tiámaro deposit in Michoacán state has been dated as Lower Cretaceous (Valanginian), though most of the porphyry deposits in central Mexico were dated or have an attributed Eocene–Oligocene age. The host rocks belong to a volcanoplutonic complex overlain by red conglomerates. These rocks were intruded by pre-Valanginian plutonic and hypabissal rocks. Propylitic, phyllic, and argillic alteration assemblages developed, and their superimposition draws the evolution of the deposit. Stage I is represented by propylitic assemblages, stage II contains the main ore forming stockworks and both phyllic and argillic assemblages, and stage III contains late carbonatization assemblages. The obtained temperatures and salinities from inclusion fluids are low for a porphyry-type deposit, but we interpret that the known part of the deposit represents the shallow portion of a bigger deposit. The evolution of mineralizing fluids draws a dilution trend of brines from “porphyry-like” to “epithermal-like” stages. The richest ore zone is roughly located between the 300 and 350 °C isotherms, though unnoticed resources may occur at depth.  相似文献   

Light curve variations in ER vulpeculae     

C. İbanoĝlu  S. Evren  Z. Tunca 《Astrophysics and Space Science》1987,136(2):225-229

Photoelectric observations of the peculiar eclipsing variable ER Vul were obtained in blue and yellow light, in the 1981 and 1982 observing seasons. The light curves suffer to change in short time-intervals. The wave-like distortion superimposed on the light curves is clearly seen, but sometimes there is no indication about its existence. The migration period has been estimated roughtly about eight months. Moreover, small-amplitude light fluctuations in the light curves are noticeable. These variations seem to be occur randomly. When the IUE and optical observations are taken into consideration together it is strongly suggested that both of the components in the system ER Vul are too active.  相似文献   

Compact Groups of Galaxies: Evolution of the Stellar Population     

I. García De La Rosa  R. Coziol  R.R. De Carvalho  S. Zepf 《Astrophysics and Space Science》2001,276(2-4):717-723

We present a study focusing on the nature of compact groups (CGs) through the study of their elliptical (E) galaxies. Parameters describing the internal dynamics and the stellar populations of the galaxies are compared with their counterparts in other environments. Our sample has24 bright E galaxies located in the core of Hickson CGs and 11 bright ‘bona fide’ Es, located in the field or very loose groups. Their spectra were obtained with the 2.1 m Telescope at KPNO and have a 4.1 Å resolution over the wavelength range 3500–7000 Å. We have found that, from the dynamical point of view, E galaxies in CGs are essentially similar to those in dense clusters. Moreover, the stellar populations of Es in CGs seem to be older and less metal rich than those in the field, behaviour which has also been observed by Rose et al. (1994).  相似文献