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11.
Boška J. Šauli P. Altadill D. German Solé J. Alberca L.F. 《Studia Geophysica et Geodaetica》2003,47(3):579-586
We investigate the short-term fluctuations in the period range from 15 to 180 minutes in the electron density variations of the F region ionosphere. Electron density profiles obtained at the ionospheric stations of Pruhonice (49.9° N, 14.5° E) and Ebro (40.8° N, 0.5° E) at five minute time sampling have been used for this analysis. The diurnal changes of the activity of the acoustic gravity wave fluctuations (AGW) show a clear enhancement during and several hours after sunrise. The periods of such AGW's are about 60 to 75 minutes and these waves propagates vertically through the ionosphere from a source located at an altitude of 180-220 km. The most likely source for these events seems to be passage of the Solar terminator. 相似文献
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Factors influencing the distribution of coastal lichens Hydropunctaria maura and Wahlenbergiella mucosa
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Responses to abiotic and biotic stresses that potentially drive the vertical zonation of the intertidal lichens Hydropunctaria maura, an upper littoral lichen, and Wahlenbergiella mucosa, a lower littoral lichen, were investigated in field and laboratory experiments. When transplanted, both lichens exhibited an inability to survive outside their normal vertical distribution range. W. mucosa appeared to be unable to tolerate prolonged periods of desiccation following translocation from lower to upper littoral regions, whereas H. maura was unable to survive in lower littoral zones possibly owing to increased grazing pressure. The effect of desiccation in both lichens was compared using pulse amplitude modulated chlorophyll fluorescence and infra‐red gas analysis; results indicated a more hydration‐dependent nature of W. mucosa. Photosynthetic (algal) pigments and phenolic compounds were determined in both lichen thalli, and a range of additional coastal lichens occupying a natural gradient from upper to lower shore levels. Pigment composition and concentration in both lichen thalli were similar whereas levels of phenolic compounds were up to three times higher in W. mucosa than H. maura. Pigment and phenolic concentration and composition exhibited some seasonality across 13 different lichens originating from different shore levels. Phenolic concentration increased towards the lower shore, suggesting a potential anti‐herbivory function. This marks the first study of pigments and phenolics in coastal lichen communities, and prompts further investigations on the particular physiological features of marine and maritime lichens that enable them to thrive in this extreme environment. 相似文献
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Modelling shallow landslide susceptibility: a new approach in logistic regression by using favourability assessment 总被引:2,自引:0,他引:2
María José Domínguez-Cuesta Montserrat Jiménez-Sánchez Ana Colubi Gil González-Rodríguez 《International Journal of Earth Sciences》2010,99(3):661-674
A new method for estimating shallow landslide susceptibility by combining Geographical Information System (GIS), nonparametric
kernel density estimation and logistic regression is described. Specifically, a logistic regression is applied to predict
the spatial distribution by estimating the probability of occurrence of a landslide in a 16 km2 area. For this purpose, a GIS is employed to gather the relevant sample information connected with the landslides. The advantages
of pre-processing the explanatory variables by nonparametric density estimation (for continuous variables) and a reclassification
(for categorical/discrete ones) are discussed. The pre-processing leads to new explanatory variables, namely, some functions
which measure the favourability of occurrence of a landslide. The resulting model correctly classifies 98.55% of the inventaried
landslides and 89.80% of the landscape surface without instabilities. New data about recent shallow landslides were collected
in order to validate the model, and 92.20% of them are also correctly classified. The results support the methodology and
the extrapolation of the model to the whole study area (278 km2) in order to obtain susceptibility maps. 相似文献
16.
Romero Jorge E. Vergara-Pinto Francisca Aguilar Germn Garcs Alex Montserrat Santiago 《Landslides》2022,19(4):865-883
Landslides - An extreme precipitation event produced catastrophic debris flows in central Chile during 29–31 January 2021 (austral summer). Our study focuses on the triggering factors and... 相似文献
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Active galactic nuclei and galaxy interactions 总被引:1,自引:0,他引:1
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Hypsometry of drainage basins (area–elevation analysis) has generally been used to infer the stage of geomorphic development and to study the influence of varying forcing factors (i.e. tectonics, climate, lithology) on topography. However, the scale dependence of hypsometry has generally been neglected. In order to assess the scale dependence of hypsometry, this study focuses on the sensitivity of hypsometry to different Digital Elevation Model (DEM) resolutions and on the influence of drainage area. Hypsometry inferred from different DEMs is shown to be robust against variations of their resolution. However, hypsometry appears to be dependent on drainage area. We propose that this scale dependence may reflect the varying importance of river and hillslope processes with basin area. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
19.
Anastasiia Kurgaeva Sergey Sedov Sol Moreno-Roso Hermenegildo Barceinas Cruz Beatriz Ortega Guerrero Elizabeth Solleiro-Rebolledo Andrei Sinitsyn 《Geoarchaeology》2024,39(2):143-167
In geoarchaeological studies, there is an issue with distinguishing between natural and anthropogenic signals in pedological paleoarchives. With the pedostratigraphy of the Upper Paleolithic site of Kostenki 14, this issue is reflected by problems with the determination of features of pedogenic and pyrogenic processes. This issue was addressed by means of a thorough analysis of the magnetic properties of paleosols accompanied by micromorphological observations. Most of the humic samples were shown to be a result of pedogenesis, but two samples (a Paleolithic hearth sample and a sample from paleosol IIc) had features of intensely burnt material. The difference in the typical intensity of large-scale (natural or human-induced) and local-scale anthropogenic fire allowed for suggesting that the magnetic properties of the burnt sample were the result of an anthropogenically controlled fire event, that is, a hearth. This study shows that the magnetic properties of paleosols can be used to differentiate anthropogenic activity, in particular—burning, from pedogenic processes. This indicator is especially helpful in finding disturbed combustion features when the hearth structure is lost. This methodology used to demonstrate the local human-induced pyrogenic effect at the Upper Paleolithic site can contribute to the discussion of the niche construction effect of human activities in the Pleistocene. 相似文献
20.
Palynological analyses were completed for the A and B horizons of a forested Mollic Hapludalf to determine type, amount, and distribution of pollen and spores within the soil solum. Hypotheses regarding the origin of pollen and the mechanisms of its movement within soil bodies are also advanced. Pollen downwash within the mineral soil seems to be very slow and confined to the uppermost porous and most homogenized part of the solum. The predominance of non-arboreal pollen at depth was believed to be a result of deposition with the loess parent material. High arboreal pollen frequencies in the upper horizons coupled with increases in non-arboreal types at depth indicate gradual ongoing mixing from the present vegetation into the soil. 相似文献