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121.
Florian Gallien Aberra Mogessie Ernesto Bjerg Sergio Delpino Brigida Castro de Machuca 《Mineralogy and Petrology》2009,95(1-2):135-157
High-temperature, intermediate-pressure calc-silicate marbles occur in the granulite-facies terrain of the La Huerta Range in the Province of San Juan, NW-Argentina, in three bulk-compositional varieties: Type (1) dolomite-absent scapolite-wollastonite-grandite-clinopyroxene-quartz—calcite marbles; Type (2) diopside-forsterite-spinel-corundum—calcite marbles with dolomite exolution lamellae in calcite; Type (3) serpentinized forsterite-spinel-dolomite marbles. An isobaric cooling path from peak-metamorphic conditions of 860°C to 750°C at 6.5 kbar is inferred from scapolite-wollastonite-grandite reaction textures in Type (1) and is consistent with cooling after an advective heat input from related gabbroic and tonalitic intrusive bodies. Stable carbon and oxygen isotope geochemistry was used to decipher the fluid/rock evolution of the three marble types. An interpreted four-stage temperature-time-fluid flow path comprises: (1) infiltration of pre-peak-metamorphic fluids, depleted in δ18O, that caused a shift of primary sedimentary δ18O ratios to lower values (19.6–20.0); (2) syn-metamorphic fluid liberation from Type (1) marbles with evidence for processes close to batch devolatilization that caused a weak coupled 13C and 18O depletion during prograde metamorphism. A different devolatilization behaviour, close to Rayleigh fractionation, texturally associated with fold settings indicates that granulite-facies fluid flow was focused rather than pervasive; (3) H2O-absent conditions were dominant when coronal grandite formed during incipient high-temperature isobaric cooling at the expense of scapolite and wollastonite in the Type (1) marbles; (4) intense post-peak- hydration of Type (2) and Type (3) marbles is the last recognizable metasomatic event. In combination, the three marble types record fluid infiltration both before and after the metamorphic peak. 相似文献
122.
Carmen Sánchez de Cos Jose M. Sánchez-Laulhé Carlos Jiménez-Alonso Juan M. Sancho-Avila Ernesto Rodriguez-Camino 《Climate Dynamics》2013,40(7-8):1969-1984
A novel approach is proposed for evaluating regional climate models based on the comparison of empirical relationships among model outcome variables. The approach is actually a quantitative adaptation of the method for evaluating global climate models proposed by Betts (Bull Am Meteorol Soc 85:1673–1688, 2004). Three selected relationships among different magnitudes involved in water and energy land surface budgets are firstly established using daily re-analysis data. The selected relationships are obtained for an area encompassing two river basins in the southern Iberian Peninsula corresponding to 2 months, representative of dry and wet seasons. The same corresponding relations are also computed for each of the thirteen regional simulations of the ENSEMBLES project over the same area. The usage of a metric based on the Hellinger coefficient allows a quantitative estimation of how well models are performing in simulating the relations among surface magnitudes. Finally, a series of six rankings of the thirteen regional climate models participating in the ENSEMBLES project is obtained based on their ability to simulate such surface processes. 相似文献
123.
In this paper we present an extension of the ensemble Kalman filter (EnKF) specifically designed for multimodal systems. EnKF
data assimilation scheme is less accurate when it is used to approximate systems with multimodal distribution such as reservoir
facies models. The algorithm is based on the assumption that both prior and posterior distribution can be approximated by
Gaussian mixture and it is validated by the introduction of the concept of finite ensemble representation. The effectiveness
of the approach is shown with two applications. The first example is based on Lorenz model. In the second example, the proposed
methodology combined with a localization technique is used to update a 2D reservoir facies models. Both applications give
evidence of an improved performance of the proposed method respect to the EnKF. 相似文献
124.
A theoretical investigation of the dynamic response of earth dams to the travelling seismic waves is presented. The earth dam is simplified as a truncated two-dimensional elastic wedge. The dam body consists of an isotropical linear viscoelastic material with homogeneous elastic modulus and density. The seismic waves travel along the longitudinal direction of the earth dam. The numerical calculations show the following. (i) For the longitudinal mode of vibration, the greater the ratio (H/L) of the height to the lenght of the complete wedge, the more the natural transverse period of vibrational of the two-dimensional wedge is less than that of the one-dimensional wedge. Especially for the first two natural transverse period, this influence is large. The decrease of the ratio of the natural transverse period for a two-dimensional wedge to that for a one-dimensional wedge with the ratio H/L is rapid for the higher than for the lower longitudinal modes. (ii) Comparing with the one-dimensional wedge, the natural transverse periods for the two-dimensional case in the complete wedge are lower, and they will increase as the coefficient of truncation, h/H increases. (iii) When the frequency of forced vibration is less than the natural transverse frequency for one-dimensional wedge, the amplification is less for a two-dimensional wedge than for a one-dimensional wedge. (iv) When the phase difference of ground motion at both ends of the dam equals π, the amplification for a two-dimensional wedge is less than that for a one-dimensional wedge, but when the phase difference equals nπ, (n > 1), the situation is reversed. (v) As the coefficient of truncation, h/H, increases, the displacement model partecipations decrease monotically. (vi) In general, the displacement caused by an earthquake is greater for a one-dimensional wedge than for a two-dimensional wedge when considering the seismic waves travelling, but the acceleration response of a two-dimensional wedge with long length of dam to travelling seismic waves with long dominant period is greater than that of a one-dimensional wedge. When the length of the dam is short enough, the response of a two-dimensional wedge without considering the influence of travelling seismic waves always gives the greatest value. 相似文献
125.
V. Ernesto Méndez Christopher M. Bacon Meryl Olson Katlyn S. Morris Annie Shattuck 《The Professional geographer》2013,65(3):357-376
We used households as the primary unit of analysis to synthesize agrobiodiversity research in small-scale coffee farms and cooperatives of Nicaragua and El Salvador. Surveys, focus groups, and plant inventories were used to analyze agrobiodiversity and its contribution to livelihoods. Households managed high levels of agrobiodiversity, including 100 shade tree and epiphyte species, food crops, and medicinals. Small farms contained higher levels of agrobiodiversity than larger, collectively managed cooperatives. Households benefited from agrobiodiversity through consumption and sales. To better support agrobiodiversity conservation, our analysis calls for a hybrid approach integrating bottom-up initiatives with the resources from top-down projects. 相似文献
126.
127.
Company Julio Ruiz-Omeñaca José Ignacio Pereda Suberbiola Xabier 《Geologie en Mijnbouw》1999,78(3-4):319-333
Fragmentary remains, including cervical vertebrae and limb bones, of a large pterosaur from the Upper Cretaceous of Tous, province of Valencia (Spain), are described. The material was recovered from lacustrine beds in the upper part of the Calizas y Margas de Sierra Perenchiza Formation, which is probably Maastrichtian in age. Six fragments of vertebrae allow a reconstruction of the anatomy of the mid-series cervicals of the animal. The general morphology of the cervical vertebrae is closely similar to that of the long-necked Azhdarchidae. Compared to other azhdarchids, the Valencia pterosaur shows minor differences from the genera Azhdarcho and Quetzalcoatlus, and is here provisionally referred to as Azhdarchidae indet. A wingspan of about 5.5 m is calculated by comparison with other known azhdarchids. This is the second azhdarchid pterosaur described from the Iberian peninsula. It confirms the wide distribution of this group of large pterosaurs at the end of the Cretaceous. 相似文献
128.
Summary. Palaeomagnetic results for a sequence of Permocarboniferous rhythmites presented in the previous paper have been submitted to maximum entropy spectral analysis to test whether these palaeomagnetic data could supply information on geomagnetic variations. There is a good correlation between the thickness of the rhythmites and sunspot spectra, suggesting that these sediments are really seasonal. The palaeomagnetic spectra are compared with those of observatory records. Periods of approximately 24.4, 12.4, 8.6, 6.7 and 5.5 found for palaeomagnetic data have corresponding values in the geomagnetic spectrum. Most of these periods, however, are the same as those found in the thickness data, implying that magnetization can be influenced by the sedimentation process as suggested by other investigators. On the other hand, both geomagnetic and climatic (thickness) variations seem to be related to solar activity. Therefore, at least indirectly, palaeomagnetic data may reflect geomagnetic variations. 相似文献
129.
130.
Blanca Mendoza Virginia García-Acosta Victor Velasco Ernesto Jáuregui Rosa Díaz-Sandoval 《Climatic change》2007,83(1-2):151-168
Using unprecedented catalogues of past severe drought data for the Yucatan Peninsula between 1502 and 1900 coming from historical
written documentation, we identified five conspicuous time lapses with no droughts between 1577–1647, 1662–1724, 1728–1764,
1774–1799 and 1855–1880, as well as time epochs with most frequent droughts between 1800 and 1850. Moreover, the most prominent
periodicity of the historical drought time series was that of ∼40 years. Using the Palmer Drought Severity Index for the Yucatan
Peninsula for the period 1921–1987 we found prominent negative phases between ∼1942–1946 and 1949–1952, 1923–1924, 1928–1929,
1935–1936, 1962–1963, 1971–1972 and 1986–1987. Two prominent periodicities clearly appear at ∼5 and 10 years. Most modern
and historical severe droughts lasted 1 year, and share a quasi-decadal frequency. Also, in the first 66 years of the twentieth
century the frequency of occurrence of severe drought has been lower compared with the nineteenth century. Some of the major
effects and impacts of the most severe droughts in the Yucatan region are examined. We also studied the relation between historical
and modern droughts and several large scale climate phenomena represented by the Atlantic Multidecadal Oscillation (AMO) and
the Southern Oscillation Index (SOI). Our results indicate that historical droughts and the cold phase of the AMO coincide,
while the influence of the SOI is less clear. The strongest coherence between historical droughts and AMO occurred at periodicities
of ∼40 years. For modern droughts the coherence of a drought indicator (the Palmer Drought Severity Index) is similar with
AMO and SOI, although it seems more sustained with the AMO. They are strongest at ∼10 years and very clearly with the AMO
cold phase. Concerning the solar activity proxies and historical droughts, the coherence with a record of beryllium isotope
Be10, which is a good proxy of cosmic rays, is higher than with Total Solar Irradiance. We notice that the strongest coherence
between historical droughts and Be10 occurs at periods ∼60–64 years. When studying modern droughts and solar activity, frequencies of ∼8 years appear, and the
coherences are similar for both sunspots and cosmic rays. Comparing natural terrestrial and solar phenomena, we found that
the most sustained and strongest modulation of historical drought occurrence is at ∼60–64 years and is between the historical
drought series and the solar proxy Be10. For modern droughts we notice that the coherence is similar among AMO, SOI and the solar indices. We can conclude that the
sea surface temperatures (AMO) and solar activity leave their signal in terms of severe droughts in the Maya lands, however
in the long term, the influence of the SOI on this type of phenomenon is less clear. 相似文献