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排序方式: 共有257条查询结果,搜索用时 31 毫秒
71.
Helene E. Unland Altaf M. Arain Chawn Harlow Paul R. Houser Jaime Garatuza-Payan Paul Scott Omer L. Sen W. James Shuttleworth 《水文研究》1998,12(4):527-542
Measurements of micrometeorological variables were made for a complete annual cycle using an automatic weather station and two energy budget–Bowen ratio systems at a field site adjacent to the Santa Cruz River in southern Arizona. These data were used to provide the basis of an estimate of the evaporation from a one-mile long losing reach of a riparian corridor in this semi-arid environment. A remotely sensed map of vegetation cover was used to stratify the corridor into five categories of surface cover. The total evaporation was calculated as the area-weighted average of the measured evaporation for sampled areas of the two most common covers, and appropriate estimates of evaporation for the less common covers. Measurements showed a substantial, seasonally dependent evaporation from the taller, deep-rooted riparian cover in the study reach, while the short, sparse vegetation provided little evaporation. In terms of the volume of water evaporated from the study reach, the evaporation from irrigated agriculture accounts for almost half of the total loss, while the majority of the remaining evaporation is from the taller riparian vegetation covers, with about one-quarter of the total loss estimated as coming from obligatory phreatophytes, primarily cottonwood. © 1998 John Wiley & Sons, Ltd. 相似文献
72.
Jaime E. Forero-Romero Jérémy Blaizot Julien Devriendt Ludovic Van Waerbeke Bruno Guiderdoni 《Monthly notices of the Royal Astronomical Society》2007,379(4):1507-1518
We present the Lensed Mock Map Facility ( lemomaf ), a tool designed to perform mock weak-lensing measurements on numerically simulated chunks of the Universe. Coupling N -body simulations to a semi-analytical model of galaxy formation, lemomaf can create realistic lensed images and mock catalogues of galaxies, at wavelengths ranging from the ultraviolet to the submillimetre. To demonstrate the power of such a tool, we compute predictions of the source–lens clustering (SLC) effect on the convergence statistics, and quantify the impact of weak lensing on galaxy counts in two different filters. We find that the SLC effect skews the probability density function of the convergence towards low values, with an intensity which strongly depends on the redshift distribution of galaxies. On the other hand, the degree of enhancement or depletion in galaxy counts due to weak lensing is independent of the SLC effect. We discuss the impact on the two-point shear statistics to be measured by future missions like SNAP and LSST . The SLC effect would bias the estimation of σ8 from two-point statistics up to 5 per cent for a narrow redshift distribution of mean z ∼ 0.5 , and up to 2 per cent in small angular scales for a redshift distribution of mean z ∼ 1.5 . We conclude that accurate photometric redshifts for individual galaxies are necessary in order to quantify and isolate the SLC effect. 相似文献
73.
74.
Lázaro Valentin Zuquette Jaime Quintas dos Santos Collares Osni José Pejon 《Environmental Geology》2007,52(5):899-922
Preventive, controlling, rehabilitative and corrective measures to improve the environmental quality of the hydrographic basins
of the Fortaleza metropolitan region in the state of Ceará (Brazil) are presented based on geological and geotechnical data,
land degradation rates and sources, and other geoindicators. The region is affected by coastal and stream erosion, gravitational
mass movement, dunes, silting, and water pollution, sanitary landfills in inappropriate sites, decommissioned and abandoned
aggregate mining, and swamp areas. Geoindicators were used to classify each of the 12 hydrographic basins as possessing low
(4), intermediate (3), or high (5) degradation levels. A group of 59 environmental management measures related to ecological,
bioengineering, mechanical, policy and administrative, agricultural and clean-up methods was selected. From this general group
a set of 31 measures was chosen considering goals, efficacy for specific environmental problems, suitability for large or
small areas, behavior under different annual climatic conditions, environmental problems of the region, geological and geotechnical
limitations and degradation level of the basins. A set of the more suitable geoindicators was selected for monitoring efficiency
of the measures for each basin. 相似文献
75.
Juan Morales Avto Goguitchaichvili Luis M. Alva-Valdivia Jaime Urrutia-Fucugauchi 《Comptes Rendus Geoscience》2006,338(8):507-513
Twenty years after Tanaka and Kono's pioneering contribution (Tanaka and Kono, 1984), we give some new details on the effect of applied field strength during Thellier paleointensity experiments. Special attention is paid to the relation of magnitude of laboratory field and Coe's quality factors (Coe et al., 1978). Full thermoremanent magnetizations were imparted on natural samples containing low-Ti titanomagnetites of pseudo-single domain structure in a 40-μT magnetic field from 600?°C to room temperature. The samples were subjected to the routine Thellier procedure using a wide range of applied laboratory fields. Results indicate that values of laboratory fields may be accurately reproduced within 2% of standard error. The quality factors, however, decrease when the magnitude of ‘ancient’ field does not match to applied laboratory fields. To cite this article: J. Morales et al., C. R. Geoscience 338 (2006). 相似文献
76.
Hermann D. Bermúdez Jenny García Wolfgang Stinnesbeck Gerta Keller José Vicente Rodríguez Michael Hanel Jens Hopp Winfried H. Schwarz Mario Trieloff Liliana Bolívar Francisco J. Vega 《地学学报》2016,28(1):83-90
The discovery of a new Cretaceous/Palaeogene (K/Pg) bathyal marine sequence on Gorgonilla Island, SW Colombia, extends the presence of Chicxulub impact spherule deposits to the Pacific region of northern South America and to the Eastern Pacific Ocean. The Gorgonilla spherule layer is approximately 20 mm thick and consists of extraordinarily well‐preserved glass spherules up to 1.1 mm in diameter. About 70–90% of the spherules are vitrified, and their chemical composition is consistent with Haiti (Beloc) impact glass spherules. Normal size‐grading, delicate spherule textures, welded melt components and an absence of bioturbation or traction transport suggest that the Gorgonilla spherule layer represents an almost undisturbed settling deposit. 相似文献
77.
Jaime A. Santos Pedro Chitas Isabel Lopes Carlos Sousa Oliveira Isabel Moitinho de Almeida João Carlos Nunes 《Soil Dynamics and Earthquake Engineering》2011
The Azores archipelago is located at the North America, Eurasia and Africa triple junction and shows seismicity and volcanism typical of an active plate boundary. Terceira Island has been affected by several damaging earthquakes being the 1980 January 1st event (M=7.2) the strongest in Azores during the last century. 相似文献
78.
An approach to handling non-Gaussianity of parameters and state variables in ensemble Kalman filtering 总被引:4,自引:0,他引:4
The ensemble Kalman filter (EnKF) is a commonly used real-time data assimilation algorithm in various disciplines. Here, the EnKF is applied, in a hydrogeological context, to condition log-conductivity realizations on log-conductivity and transient piezometric head data. In this case, the state vector is made up of log-conductivities and piezometric heads over a discretized aquifer domain, the forecast model is a groundwater flow numerical model, and the transient piezometric head data are sequentially assimilated to update the state vector. It is well known that all Kalman filters perform optimally for linear forecast models and a multiGaussian-distributed state vector. Of the different Kalman filters, the EnKF provides a robust solution to address non-linearities; however, it does not handle well non-Gaussian state-vector distributions. In the standard EnKF, as time passes and more state observations are assimilated, the distributions become closer to Gaussian, even if the initial ones are clearly non-Gaussian. A new method is proposed that transforms the original state vector into a new vector that is univariate Gaussian at all times. Back transforming the vector after the filtering ensures that the initial non-Gaussian univariate distributions of the state-vector components are preserved throughout. The proposed method is based in normal-score transforming each variable for all locations and all time steps. This new method, termed the normal-score ensemble Kalman filter (NS-EnKF), is demonstrated in a synthetic bimodal aquifer resembling a fluvial deposit, and it is compared to the standard EnKF. The proposed method performs better than the standard EnKF in all aspects analyzed (log-conductivity characterization and flow and transport predictions). 相似文献
79.
80.
We present a systematic study of chain-length distributions and D/H ratios of n-alkyl lipids (both n-alkanes and n-alkanoic acids) in a wide range of terrestrial and aquatic plants around and in Blood Pond, Massachusetts, USA. The primary goal is to establish a model to quantitatively assess the aquatic plant inputs of the mid-chain length n-alkyl lipids to lake sediments and to determine the average hydrogen isotopic ratios of these lipids in different plants. Our results show that middle-chain n-alkyl lipids (C21-C23n-alkanes and C20-C24n-alkanoic acids) are exceptionally abundant in floating and submerged aquatic plants, in contrast to the dominance of long-chain n-alkyl lipids (C27-C31n-alkanes and C26-C32n-alkanoic acids) in other plant types, which are consistent with previously published data from Mountain Kenya and the Tibetan Plateau. Combining available data in different environmental settings allows us to establish statistically robust model distributions of n-alkyl lipids in floating/submerged macrophytes relative to other plant types. Based on the model distributions, we established a multi-source mixing model using a linear algebra approach, in order to quantify the aquatic inputs of mid-chain n-alkyl lipids in lake sediments. The results show that ∼97% of the mid-chain n-alkyl lipids (C23n-alkane and C22n-acid (behenic acid)) in Blood Pond sediments are derived from floating and submerged macrophytes. In addition, D/H ratios of C22n-acid and C23n-alkane in the floating and submerged plants from Blood Pond display relatively narrow ranges of variation (−161 ± 16‰ and −183 ± 18‰, respectively). Our study demonstrates that mid-chain n-alkyl lipids such as C23n-alkane and C22n-acid could be excellent recorders of past lake water isotopic ratios in lakes with abundant floating and submerged macrophyte inputs. 相似文献