Search results for "Stability"
showing 10 items of 3085 documents
Physically-based and distributed approach to analyze rainfall-triggered landslides at watershed scale
2011
Abstract Landslides are a serious threat to life and property throughout the world. The causes of landslides are various since multiple dynamic processes are involved in driving slope failures. One of these causes is prolonged rainfall, which affects slope stability in different ways. Water infiltrating in a hillslope may cause a rise of the piezometric surface, which, in turn, involves an increase of the pore water pressure and a decrease of the soil shear resistance. For this reason, knowledge of spatio-temporal dynamics of soil water content, infiltration processes and groundwater dynamics, is of considerable importance in the understanding and prediction of landslides dynamics. In this …
The influence of slope angle on sediment, water and seed losses on badland landscapes
1997
Abstract By means of simulated rainfall the influence of the slope angle on the soil, water and seed erosion has been studied on badland surfaces. Slope angle has a clear positive effect controlling soil erodibility and erosion rates, but it does not have any influence on the volume of runoff after 40 minutes of rain at an intensity of 55 mm h−1. In contrast, slope angle has a clear influence on runoff initiation, with cracks and crusts as the main factors controlling the time to ponding and time to runoff. Both ponding and runoff initiation start earlier on pediments than on slopes, where more cracks exist. Steady-state infiltration rates and seed losses have an inverse relationships with …
The influence of geomorphological position and vegetation cover on the erosional and hydrological processes on a Mediterranean hillslope
1998
Soil erosion and runoff rates are assumed to be highly dependent on slope position. However, little knowledge exists about the hydrogeomorphological processes at the pedon scale that support this idea. In order to assess the hydrological and erosional behaviour of soils at different slope positions, simulated rainfall experiments (55 mm was applied during one hour) were carried out on a south-facing slope with underlying limestone in south-east Spain. In the mean terms, the erosion rates (9 g m2 hr−1) and the runoff coefficients (12%) were very low at the scale of measurement (0·25 m2). The slope position does not affect erosion rates when the measurements are carried out under extreme dry …
Hydrogeological hazards and weather events: Triggering and evolution of shallow landslides
2014
Abstract Landslides are the most intense and serious manifestations of the degradation of slopes and they are the main causes of geological hazard when they, directly or indirectly, involving towns and infrastructures. They are a global environment problem; there are several examples that have produced untold damages and loss of human lives in many parts of the world. In 1920 the landslides mobilization, as a result of a strong earthquake in China, in the province of Kansu, killed 200,000 people; in 1938 fast debris flow, triggered by heavy rainfalls in Japan, caused the death of 600 people; in 1963 in Italy the Vajont disaster caused the death of 1,899 people, as a result of a landslide lo…
Comparison of aggregate stability indices for soil classification and assessment of soil management practices
1989
Summary In view of soil structure analysis and land-use and management history evaluation, several mechanical indices of soil structure were tested on 13 Italian soils. From the wet and dry sieving aggregate distributions, a pseudo-textural aggregation index (Ipta) and a mechanical aggregation index (Ima)) were determined and compared with other soil structure stability indices based on single-sieve analysis. The single-sieve indices S and WSI were good correlated with Ipta and Ima, showing the possibility of substituting the time-consuming aggregate-size distribution determinations. All the soil structure indices were correlated with selected semi-permanent soil characteristics. Soil struc…
Soil aggregate stability in three Mediterranean environments
1996
Abstract This paper considers the effect of vegetation on soil aggregate stability in three different Mediterranean landscapes in Southeast Spain. Soils on limestone, marls and clays, with two levels of vegetation cover at each north-facing slopes of the study areas, were investigated. Three aggregate stability tests (CND, TDI and UD) based on the drop impact and ultrasonic dispersion methods and the Emerson dispersion test were performed. The results of the experiments show the positive influence of vegetation on aggregate stability. However, vegetation is less important than lithology in influencing soil aggregate stability. Soil depth and moisture also affect aggregation, but the relatio…
Mono- and polynuclear hydroxo complexes of monophenylthallium(III)
1974
Summary The hydrolysis of PhTl(OH)ClO4 has been studied in a medium 0.3 M in NaClO4 by a potentiometric technique. The complexes formed by the hydrolysis reactions together with their formation constants have been determined by the general minimizing computer programme LETAGROP. The hydrolysis species observed in the pH range 3–5 are the mononuclear [(PhTlOH)(OH)], the dinuclear [(PhTlOH)2(OH)]+ and the dimer [(PhTlOH)2(OH)2]. The formation constants are log *β11=−4.92±0.2, log *β21=−1.52±0.03 and log *β22=−6.11±0.05. Stepwise reactions are then postulated whose formation constants are respectively log (*β21/*β11)=3.40±0.25, log (*β22/*β21)=−4.59±0.08 and log (*β22/*β112)=3.73±0.09.
Electrochemical Monitoring of Compartmentalization Effects in the Stability of Meisenheimer Anions Supported in Hydrotalcite and X and Y Zeolites
2005
Meisenheimer anions (MS - ) derived from 2,4-dinitroaniline are stabilized into Li + - and Na + -exchanged zeolites X and Y forming alkali ion-MS ion pairs. Upon attachment of the zeolites to polymer film electrodes immersedinto Et 4 N + /MeCN and Li + /MeCN electrolytes, boundary-associated MS - ions display two oxidation processes at +0.40 and +0.65 V vs. AgCl/Ag. This response sharply contrasts with that recorded for MS - in solution and incorporated within hydrotalcite, for which a unique oxidation peak at +0.35 V is recorded. The electrochemistry of zeolite-associated MS - can be described in terms of an unusual electron-transfer/ chemical reaction/electron-transfer/comproportionation …
Eckhaus instability of stationary patterns in hyperbolic reaction–diffusion models on large finite domains
2022
AbstractWe have theoretically investigated the phenomenon of Eckhaus instability of stationary patterns arising in hyperbolic reaction–diffusion models on large finite domains, in both supercritical and subcritical regime. Adopting multiple-scale weakly-nonlinear analysis, we have deduced the cubic and cubic–quintic real Ginzburg–Landau equations ruling the evolution of pattern amplitude close to criticality. Starting from these envelope equations, we have provided the explicit expressions of the most relevant dynamical features characterizing primary and secondary quantized branches of any order: stationary amplitude, existence and stability thresholds and linear growth rate. Particular em…
Online Hyperparameter Search Interleaved with Proximal Parameter Updates
2021
There is a clear need for efficient hyperparameter optimization (HO) algorithms for statistical learning, since commonly applied search methods (such as grid search with N-fold cross-validation) are inefficient and/or approximate. Previously existing gradient-based HO algorithms that rely on the smoothness of the cost function cannot be applied in problems such as Lasso regression. In this contribution, we develop a HO method that relies on the structure of proximal gradient methods and does not require a smooth cost function. Such a method is applied to Leave-one-out (LOO)-validated Lasso and Group Lasso, and an online variant is proposed. Numerical experiments corroborate the convergence …