Multimodal reliability analysis of 3D slopes with a genetic algorithm

Acta Geotechnica - This paper presents a genetic algorithm (GA) to solve the multimodal optimisation problem resulting from 3D slopes prone to multiple regions of failure. A probabilistic approach...     

Determination of Moho dip using PS reflections

Summary. A clear PS reflection was recorded in the northern section of the LISPB line (shot-point N1, profile ALPHA). Travel times of PS and PP phases reflected at the same part of the Moho were used to model the lower crustal structure. The observed high apparent velocity of the PS phase (8.4 km/s) is interpreted as due to a localized Moho dip of 7 per cent (4°) towards the north. This is supported by observations of Pn refractions from other shots. It is shown that PS reflections could be very useful for determination of Moho dips.     

Mixing at the front of gravity currents

Observations made with the help of a movable-bed tank designed and operated to freeze the motion of gravity current fronts indicate that both the scale of the apparatus and the magnitude of the current Reynolds number have a strong influence on mixing rates. Low mixing rates are associated with fronts in relatively shallow fresh water depths and low Reynolds numbers. Mixing rates increase more rapidly as the ratio of current thickness to fresh water depth increases. For the deepest fresh water flow conditions, when scale effects can be expected to be negligible, the dimensionless mixing rate is approximately equal to three times the relative current thickness and has an upper limit of about 0.3. Lower mixing rates are observed as the current Reynolds number decreases, suggesting that viscous effects can still exist even for deep fresh water conditions. Application of the experimental results to estimate some parameters of a hypothetical gravity current on the continental shelf yield reasonable values. However, it is clear that, owing to the scale and Reynolds number effects that might be present in laboratory experiments, particular care should be exercised when trying to extrapolate results to gravity currents in nature.     

Waveshapes of continuing currents and properties of M-components in natural negative cloud-to-ground lightning from high-speed video observations

Continuing current is a continuous mode of charge transfer to ground in a lightning flash. The extent to which the continuing current contributes to the total negative charge lowered to earth is large. In order to study the waveshape of the continuing currents of natural flashes, we developed a computational algorithm that analyzes the pixels of the images obtained by a high-speed camera and plots luminosity-versus-time. Tower measurements have shown that during the continuing current phase of the flash the luminosity of the channel is directly proportional to the current that flows through it. Using this information it was possible to infer the continuing current waveshape for 63 natural discharges and classify them into six different types. Statistics on some characteristics of 345 M-components (that occurred during the same 63 events) are also presented. As far as we know, this is the first study on waveshapes of continuing currents for natural lightning.     

Wien effect of Cd/Zn on soil clay fraction and their interaction

Background

The coexistence of Cd²⁺ and Zn²⁺ ions in nature has a significant influence on their environmental behaviors in soils and bioavailability for plants. While many studies have been done on the mutual toxicity of Cd²⁺ and Zn²⁺, few studies can be found in the literature focused on the interaction of Cd²⁺ and Zn²⁺ on soil clay fractions especially in terms of energy relationship.

Results

The binding energies of Cd²⁺ on boggy soil (Histosols) particles and Zn²⁺ on yellow brown soil (Haplic Luvisols) particles were the highest, while those of Cd²⁺ and Zn²⁺ on paddy soil (Inceptisols) particles were the lowest. These results indicated that Cd²⁺ and Zn²⁺ have a strong capacity to adsorb in the solid phase at the soil–water interface of boggy soil and yellow brown soil, respectively. However, both Cd²⁺ and Zn²⁺ adsorbed on paddy soil particles easily release into the solution of the soil suspension. Unlike the binding energy, the higher adsorption energies of ions in boggy and yellow brown soils showed a weak binding force of ions in boggy soil and yellow brown soil. A 1:1 ratio of Cd²⁺ to Zn²⁺ promotes the mutual inhibition of their retentions. Cd²⁺ and Zn²⁺ have high mobility and bioavailability in paddy soil and yellow drab soil (Ustalfs), whereas they have high potential mobility and bioavailability in boggy soil and yellow brown soil.

Conclusion

In the combined system, Zn²⁺ had preferential adsorption than Cd²⁺ on soil clay fractions. Boggy soil and yellow brown soil have a low environmental risk with lower mobility and bioavailability of Cd²⁺ and Zn²⁺ while paddy soil and yellow drab soil present a substantial environmental risk. In the combined system, Cd²⁺ and Zn²⁺ restrain each other, resulting in the weaker binding force between ions and soil particles at a 1:1 ratio of Cd²⁺–Zn²⁺.

     

BRAMS model performance for significant event involving Brazilian platform ship

Natural Hazards - After a storm displaced the P-70 platform ship located in Guanabara Bay to the coast on January 30, 2020, a numerical investigation was carried out with the BRAMS (Brazilian...     

Damaging flood severity assessment in Northern Portugal over more than 150 years (1865–2016)

Floods are a major natural hazard, with vast implications over a wide range of socio-economic activities. A harmonized post-flood classification is critical for a better understanding of this hazard, by providing homogeneous flood catalogues for future research on triggering mechanisms. We apply a flood severity index (FSI) to damaging floods in Northern Portugal over a 152-year period (1865–2016) and identify the most critical areas to flood occurrences. The index is a damage-based post-event assessment tool, which includes five categories ranging from minor flooding (1) to catastrophic flooding (5). FSI is applied to a historical damaging flood database with 2318 occurrences. In Northern Portugal, serious floods (3) are the most frequent typology, while catastrophic floods are typically river floods occurring in the Douro basin. Overall, damaging flood occurrences are favoured by the positive phase of the East Atlantic pattern and by the negative phase of the North Atlantic Oscillation. Furthermore, the north-western areas reveal higher concentrations of damaging flood occurrences, mainly due to higher population density, higher precipitation values and more flood plain areas. In particular, 48% of all occurrences are concentrated in the Porto Metropolitan Area, mainly the Porto city centre and nearby riverside areas of the Douro River. High-population density and heavily urbanized areas lead to greater exposure to flood risk, whereas the most peripheral municipalities, with large agricultural/forested areas, show much lower numbers of damaging floods. FSI is tool to communicate the magnitude of the flood risk and is, therefore, of foremost relevance to civil protection and risk management.     

The bubble bursts for cavitation in natural rivers: laboratory experiments reveal minor role in bedrock erosion

The erosion of rock‐bedded channels generally is considered a slow process caused mainly by abrasion due to bedload or suspended sediments, but the mechanisms of rapid erosion remain unclear. Cavitation is a clear‐fluid erosive process, well known for its effect on engineering structures, when water vapour bubbles collapse and the resultant pressure shocks erode the boundary. However, although the occurrence of cavitation erosion in natural watercourses has long been a matter of debate, as yet there are no incontrovertible examples of cavitation damage to natural river beds. Using flume experiments, we show for the first time that only weakly‐cavitating clear‐water flows can occur for the range of flow velocities observed in rivers, and these do not erode medium‐hardness rocks after 68 hours. During this time period, only a very soft rock featured erosional marks due to dissolution. Thus, our results cast significant doubt on the likelihood of identifying cavitation damage in most rivers, and provide pointers to those river systems that might be investigated further to identify cavitation erosion. Copyright © 2016 John Wiley & Sons, Ltd.     

Spatial distribution of morphometric parameters of glacial cirques in the Central Pyrenees(Aran and Boí valleys)

Glacial cirques are typical landscape features of mid-latitude mountain environments like the Central Pyrenees. Their morphology as well as their spatial distribution provides insights about past glaciers and climates. In this study, we examine the distribution, morphometrical and topographical characteristics of glacial cirques in two U-shaped glacial valleys located in the Central Pyrenees – the Aran and the Boí valleys. They are located in different aspects of this mountain range(north vs south) under different climatic influences that promoted distinct glaciation patterns during the late Pleistocene. The spatial mapping of these landforms was carried out using high-resolution imagery and field observations. We analysed the data of the morphometrical and topographical variables of the glacial cirques by using different statistical and geospatial methods in order tounveil the factors controlling their formation and development. A total of 186 glacial cirques were mapped in the study area, including 119 in the Aran and 67 in the Boí valleys. The local topography and microclimate conditions lead to substantial differences in both areas in terms of the morphology and dimensions of the cirques. Glacial cirques in Boí are distributed at slightly higher elevations than in Aran and they are also larger, though their dimensions decrease with elevation in both valleys. Aran cirques are mostly oriented NE, while Boí landforms do not show any prevailing aspect. Even though lithology does not control the distribution of the glacial cirques, some specific lithological settings may favour the development of larger cirques. In general, glacial cirques in the Aran and the Boí valleys show morphometrical properties similar to those reported in other mid-latitude mountain ranges.