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31.
Javier Palarea-Albaladejo Josep A. Martín-Fernández Juan Gómez-García 《Mathematical Geology》2007,39(7):625-645
In this work, a parametric approach for replacing data below the detection limit, also known as rounded zeros, in compositional
data sets is proposed. Compositional rounded zeros correspond to small proportions of some whole that cannot be reliably detected
by the analytical instruments under given operating conditions. This kind of zeros appear frequently in the data collection
process in geosciences. They must be treated in an adequate way before some multivariate analysis can be applied. Our procedure
results from a modification of the Expectation-Maximization (EM) algorithm and is based on the additive log-ratio transformation.
Its coherence with the nature of compositional data and with basic operations in the simplex sample space is checked. Using
real data sets, we find that this approach improves other parametric and non-parametric techniques for compositional rounded
zeros. 相似文献
32.
Ground-based visible differential absorption spectrometry during twilight has been used for NO2 total column observations at the Antarctica Peninsula, Marambio Base (64S, 56W), during the austral spring of 1989 (9 September to 25 November).Results show moderate NO2 vertical column levels of 1.5 to 2.5×1015 molec cm-2 in the morning and 2 to 3×1015 molec cm-2 in the evening until middle October, highly modulated by planetary wave activity. From that date until the end of the period, a steady increase occurs which is associated with the rising of lower stratosphere temperature as the vortex weakens, reaching values of 5×1015 molec cm-2 in late November, with small a.m.-p.m. differences. NO2 is found to be positively correlated to both total ozone and 50 hPa temperature during the entire spring. However, when analyzing the departures from linear trends, a highly negative correlation has been observed from day 301 onwards. 相似文献
33.
ABSTRACTWater indicators and indices are useful tools to assess river basin performance, that is, to measure whether the basin operates satisfactorily under a wide range of possible future demands and hydrological conditions. Spanish regulations assess the performance of water demands by using reliability indicators (RIs), established by law in 2008. This article raises the possibility of updating RIs by comparing them with sustainability indicators (SIs). SIs are widely used for the assessment of river basin performance and several policy scenarios. We applied a water allocation model to the Guadiana River basin in Spain to compare indicators under three scenarios. The study was framed within the science of socio-hydrology, combining the physical environment of a water system with its influence on social aspects. SIs gave better results than RIs when comparing future scenarios. We also propose the introduction of a vulnerability indicator into Spanish regulations. 相似文献
34.
35.
Dabrio Cristino J. Zazo Cari Lario Javier Goy José Luis Sierro Francisco J. Borja Francisco González José Ángel Flores José Abel 《Geologie en Mijnbouw》1998,77(3-4):263-281
This first sedimentary interpretation of two incised-valley fills in the Gulf of Cádiz (southern Spain), which accumulated during the last fourth-order eustatic cycle in response to fluvial incision, changes of sea level, and correlative deposition, relates the filling of the estuarine basins and their barriers with four regional progradation phases, H1 to H4. The cases studied are the wave-dominated Guadalete, and the mixed, tide and wave-dominated Odiel-Tinto estuaries. The sequence boundary is a type-1 surface produced during the lowstand of the Last Glacial period ca. 18 000 14C yr BP. No fluvial lowstand deposits were found in the area. Due to rapid transgression the valley fills consist of transgressive and highstand sediments. The maximum landward advance of the estuarine barriers occurred ca. 6500–6000 14C yr BP during the maximum of the Flandrian transgression, but there is no evidence of sea level rising appreciably above the present. A large part of the estuaries was filled during H1 (ca. 6500–4400 14C yr BP) but ravinement by shifting tidal inlets destroyed most of the coeval barriers. During the H2 phase (ca. 4200–2550 14C yr BP) sedimentation was favoured by arid conditions and concentrated in the axial estuarine zones and the barriers. Between H2 and H3 prevailing winds changed from W to WSW, increasing spit growth to the east and south-east. Progradation of bay-head deltas and flood-plains during H3 (ca. 2300–800 14C yr BP) and H4 (500 yr ago to the present) further reduced the accommodation space in the largely-filled valleys, and sediment by-passed the estuaries and accumulated in the estuarine barriers as fast-growing spits. Arid conditions and increasing human activity have caused rapid coastal modifications. 相似文献
36.
Javier Rico 《Astrophysics and Space Science》2007,309(1-4):285-291
During its Cycle I (2005/2006), the MAGIC telescope targeted about 250 hours several galactic γ-ray sources detected previously by other experiments or expected to emit in the same energy domain. This paper reviews some results of such MAGIC observations. We cover, among others, supernova remnants, the Galactic Center and microquasars. We will concentrate on the recent discovery of very high energy γ-rays from the microquasar LS I +61 303. 相似文献
37.
Ronaldo?S.?S.?VieiraEmail author Javier?Ramos-Caro 《Celestial Mechanics and Dynamical Astronomy》2016,126(4):483-500
We consider the three-dimensional bounded motion of a test particle around razor-thin disk configurations, by focusing on the adiabatic invariance of the vertical action associated with disk-crossing orbits. We find that it leads to an approximate third integral of motion predicting envelopes of the form \(Z(R)\propto [\varSigma (R)]^{-1/3}\), where R is the radial galactocentric coordinate, Z is the z-amplitude (vertical amplitude) of the orbit and \(\varSigma \) represents the surface mass density of the thin disk. This third integral, which was previously formulated for the case of flattened 3D configurations, is tested for a variety of trajectories in different thin-disk models. 相似文献
38.
39.
Arias-Molinares Daniela García-Palomares Juan Carlos Romanillos Gustavo Gutiérrez Javier 《Journal of Geographical Systems》2023,25(3):403-427
Journal of Geographical Systems - In the past ten years, cities have experienced a burst of micromobility services as they offer a flexible transport option that allows users to cover short trips... 相似文献
40.
Ricardo León Luis Somoza Teresa Medialdea Francisco Javier González Carmen Julia Gimenez-Moreno Raúl Pérez-López 《Geo-Marine Letters》2014,34(2-3):131-151
Integrating novel and published swath bathymetry (3,980 km2), as well as chirp and high-resolution 2D seismic reflection profiles (2,190 km), this study presents the mapping of 436 pockmarks at water depths varying widely between 370 and 1,020 m on either side of the Strait of Gibraltar. On the Atlantic side in the south-eastern Gulf of Cádiz near the Camarinal Sill, 198 newly discovered pockmarks occur in three well localized and separated fields: on the upper slope (n=14), in the main channel of the Mediterranean outflow water (MOW, n=160), and on the huge contourite levee of the MOW main channel (n=24) near the well-known TASYO field. These pockmarks vary in diameter from 60 to 919 m, and are sub-circular to irregularly elongated or lobate in shape. Their slope angles on average range from 3° to 25°. On the Mediterranean side of the strait on the Ceuta Drift of the western Alborán Basin, where pockmarks were already known to occur, 238 pockmarks were identified and grouped into three interconnected fields, i.e. a northern (n=34), a central (n=61) and a southern field (n=143). In the latter two fields the pockmarks are mainly sub-circular, ranging from 130 to 400 m in diameter with slope angles averaging 1.5° to 15°. In the northern sector, by contrast, they are elongated up to 1,430 m, probably reflecting MOW activity. Based on seismo-stratigraphic interpretation, it is inferred that most pockmarks formed during and shortly after the last glacial sea-level lowstand, as they are related to the final erosional discontinuity sealed by Holocene transgressive deposits. Combining these findings with other existing knowledge, it is proposed that pockmark formation on either side of the Strait of Gibraltar resulted from gas and/or sediment pore-water venting from overpressured shallow gas reservoirs entrapped in coarse-grained contourites of levee deposits and Pleistocene palaeochannel infillings. Venting was either triggered or promoted by hydraulic pumping associated with topographically forced internal waves. This mechanism is analogous to the long-known effect of tidal pumping on the dynamics of unit pockmarks observed along the Norwegian continental margin. 相似文献