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121.
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
122.
Gabriela Ferracutti Ernesto Bjerg Aberra Mogessie 《International Journal of Earth Sciences》2013,102(3):701-720
The layered mafic–ultramafic rocks in the Sierras de San Luis, Argentina (Las Águilas, Las Higueras and Virorco), constitute a 3–5-km-wide belt that extends over 100 km from NE to SW. They carry a sulphide mineralization consisting of pyrrhotite, pentlandite and chalcopyrite, in veins and as disseminated to massive ore. Disseminated spinels are frequently associated with the sulphide minerals as well as platinum group minerals. A strong correlation between S, Ni, Co, Cu, Cr, Pt and Pd indicates the presence of one to three levels of mineralization within the ultramafic units. The maximum concentration of these elements coincides with the units containing platinum group minerals (PGM) and spinel group minerals. This clear relationship constitutes a good prospecting guide in the search for layers with high-grade ore, probably associated with deeper stratigraphic levels where ultramafic rocks are dominant. The bulk rock chemistry and concentrations of metals and platinum group elements as well as textural evidence suggest that the parental magma was mafic with tholeiitic affinities and MgO rich. The Las Águilas layered mafic–ultramafic body and the remaining bodies in the area bear similar characteristics to well-known stratified complexes developed in extensional tectonic regimes, as it is the case of Jinchuan (China), Kabanga (Tanzania) and Fiambala (Argentina). 相似文献
123.
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
124.
125.
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
126.
Chlorine atom-initiated photooxidations of CH2FCF3 (HFC-134a) in O2-N2 diluent were carried out to identify the products formed from the \(CF_3 CHF\dot O\) radical reactions and to determine the product yields as a function of temperature, pressure and O2 concentration. CF3C(O)F and HC(O)F were the major ‘first-generation’ products observed, along with smaller yields of C(O)F2 and, as yet, undetermined yields of CF3OOOCF3 and CF3OOC(O)F. The relative importance of the two major \(CF_3 CHF\dot O\) reaction pathways, is expressed by the rate constant ratio $$k_{O_2 } /k_d = 3.2 \times 10^{ - 25} e^{(3510 \pm 470)/T} cm^3 molecule^{ - 1}$$ The decomposition reaction leading to HC(O)F and ?F3 radical products is predicted to be the dominant pathway at the Earth's surface while mainly CF3C(O)F formation will occur at the tropopause. 相似文献
127.
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
128.
Ernesto Martínez Alfonso Aranda Yolanda Díaz-De-Mera Ana Rodríguez Diana Rodríguez Alberto Notario 《Journal of Atmospheric Chemistry》2004,48(3):283-299
The reaction of Cl with cyclohexanone (1) was investigated, for the first time, as a function of temperature (273–333 K) and at a low total pressure (1 Torr) with helium as a carrier gas using a discharge flow-mass spectrometry technique (DF-MS). The resulting Arrhenius expression is proposed, k
1= (7.7 ± 4.1) × 10–10 exp[–(540 ± 169)/T]. We also report a mechanistic study with the quantitative determination of the products of the reaction of Cl with cyclohexanone. The absolute rate constant derived from this study at 1 Torr of total pressure and room temperature is (1.3 ± 0.2) × 10–10 cm3 molecule–1 s–1. A yield of 0.94 ± 0.10 was found for the H-abstraction channel giving HCl. In relative studies, using a newly constructed relative rate system, the decay of cyclohexanone was followed by gas chromatography coupled with flame-ionisation detection. These relative measurements were performed at atmospheric pressure with synthetic air and room temperature. Rate constant measured using the relative method for reaction (1) is: (1.7 ± 0.3) × 10–10 cm3 molecule–1 s–1. Finally, results and atmospheric implications are discussed and compared with the reactivity with OH radicals. 相似文献
129.
The effects of horizontal components of ground motion on the linear response of torsionally stiff and torsionally flexible systems, on soft and firm soil conditions, are examined. A one‐story, two‐way asymmetric structural system is used, subjected to uncorrelated ground motion components along their principal directions. Spectral densities for ground accelerations in firm and soft soils are modeled based on recorded data from large intensity Mexican earthquakes. It is shown that for firm soils, in general, these effects are important in the case of torsionally flexible systems that are stiff under translation, or for torsionally stiff systems that are flexible in translation. The percentage combination rules usually specified in seismic design codes are assessed against the dynamic response. Such combination rules can result in overly conservative design forces or underestimated design forces, particularly for torsionally flexible structures. Given the relative magnitude of the response to each ground motion component, it was found that using different percentage values in the combination rules has no significant effect on improving the estimation of the total response. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
130.
This article describes a methodology to monitor dynamic vertical sub-centimeter displacement, of a GPS antenna. The dynamic
movement of an antenna is determined by choosing the appropriate reference satellite for measurement differencing and by applying
a FFT filter on the double-difference phase residuals. The validity of the method depends on the time variations of the GPS
residuals and errors, such as, receiver noise, atmospheric contribution, multipath effects, and the antenna movement. This
research is under development and results for simulated motion are presented here. ? 2002 Wiley Periodicals, Inc. 相似文献