Characterisation of the Dynamics of Leachate Contamination Plumes in the Surrounding of the Hulene - B Waste Dump, Maputo, Mozambique

The contamination of areas around solid urban waste dumps is a global challenge for the maintenance of environmental quality in large urban centres in developing countries. This study applied geophysical methods (electrical resistivity) to identify leachate contamina-tion plumes in the subsoil and groundwater, as well as to describe their temporal (2020 and 2021) dynamics in the lithology and groundwater around the Hulene - B waste dump, Maputo, Mozambique. Geophysical methods (electrical resistivity) were applied to identify possible groundwater contamination plumes, their dynamics, mechanisms of their enrichment and dispersion. Eight 400 m electrical resistivity profiles were performed, four profiles in January 2020 and four profiles in May 2021, overlapped, and the data were inverted with RES2D software. The electrical resistivity models indicate an E - W move-ment of large contamination plumes that dilute superficially into the natural surface wa-ter receiving basin and groundwater, creating zones of resistive anomalies. The thickness of the plumes in the subsurface environment was shown to be extensive in summer for profiles 1a and 2b and we associate it with the higher leachate production and migration mechanisms, which are intense in the hot and rainy season. Profile 4b showed the prop-agation of anomalous surface and subsurface areas, which was associated with higher leachate production and migration process in the new deposition zone (west). The spatial distribution of contamination plumes at both stations reduced significantly as we moved further away from the waste deposit, revealing the attenuating effect of groundwater and lithological substrate (Profile 3 a, b, and fig.7).

Supersonic Laser Deposition of Self-Lubricating Coatings

Supersonic Laser Deposition (SLD) is a coating and fabrication process combining cold spray (CS) with laser heating of the deposition zone. Laser heating increases deformation on impact, improving bonding for a given particle velocity, eliminating the need to use helium while retaining the advantages of CS; solid-state deposition, low oxidation and high build rate (≤ 10 kg/hr). Although solid lubricants offer advantages over liquid lubrication, remaining effective over a wide range of operating temperatures and loads, while simplifying sealing, their use is limited by current application methods. SLD enables the deposition of metallic coatings which incorporate solid lubricants into metallic coatings, onto a range of substrates. This paper details the powders and conditions used to deposit nickel/graphite using SLD, and the structure and tribological properties of the coatings produced. Co-efficients of friction below 0.14 were demonstrated for nickel/graphite coatings on aluminium substrates.

Microstructure, Mechanical Properties, and Galvanic Corrosion of 10CrNi3MoV Fabricated by Wire Arc Additive Manufacturing

Wire arc additive manufacturing (WAAM) technology is widely used in the fields of aerospace, shipbuilding, and automobile industry due to the advantages of fast forming speed, high material utilization and low production cost. WAAM is extremely sensitive to parameters, and different processes and materials produce different deposition effects and properties. Therefore, it is of great significance to study the WAAM formability of various materials. Herein, the microstructure, mechanical properties, and galvanic corrosion behavior of the low-carbon high-strength steel (10CrNi3MoV) fabricated by cold metal transfer (CMT) WAAM technology were investigated. The single-channel multilayer deposition parts were prepared by reciprocating deposition, and the forming parts were divided into six zones by observing the different positions of the structure: matrix, heat-affected zone, remelting zone, initial deposition zone, interlayer zone, and interlayer bonding zone. Electron backscattered diffraction (EBSD) analysis showed that the amount of recrystallization and substructure in the deposition layer had no obvious change, and the texture phenomenon was the most obvious in the initial deposition zone of the pole map reaction. The texture phenomenon gradually weakened with the increase of the deposition layers. The microhardness from the matrix to the deposition stable zone was tested. The hardness of the matrix changed smoothly, that of the heat-affected zone was the largest, and that of the deposition layer was 221–282 HV0.2. The tensile properties were tested in different directions and angles, and the yield strength and tensile strength of the deposited layer were more than 550 MPa and 760 MPa, respectively. The galvanic corrosion behavior between the deposited layer and the matrix was investigated, and the polarization curve showed that the corrosion potential of the deposited layer was lower than that of the matrix, and the corrosion current density of the deposited layer was higher than that of the matrix.

The Debris Distribution Model for Removal Planning of an Urbanized Estuarine Complex

We checked the spatial pattern of debris stranding at Praia de Santos (Brazil) in the first hour after the peak of high and low tide in summer and winter. We recorded and counted 20 types of debris (natural and anthropogenic) in 6 transects arranged in 3 zones along the beach (deposition, transport, and erosion). Canonical Correspondence Analysis (CCA) showed that buoyancy was an essential property in distinguishing debris stranding behaviours. The erosion zone, closer to the estuary showed that many mollusk shells, ropes and rocks, while plastics, styrofoam and fiber nylon were in the deposition zone. Throughout the estuary, we inspected the beach, identifying sections of origin and accumulation associated with the circulation system and currents. We propose the removal and recycling of debris from accumulation sites near highways and urban systems.

Municipal waste landfill as a source of polychlorinated biphenyls releases to the environment

This study aimed to investigate the impact of municipal waste landfill on polychlorinated biphenyls (PCBs) release to the environment concerning groundwater flow directions. The contents of polychlorinated biphenyls in soils, plants and water were analysed at various distances from the landfill. Thanks to low solubility PCBs in water groundwater flow direction, under the landfill, have an influence on PCBs concentration in groundwater. Strong PCBs’ sorption to organic matter caused that no affect groundwater flow directions on PCB content in soils and plants’ tissues was observed. The largest PCBs deposition zone was located 50 m from the contamination source (landfill). Tri-CB and tetra-CB homologues were capable of migration deep into the soil profile, which could be related to the geological material from which the soils under study were developed, as well as to the properties of the PCB homologues.

Implication of Long-Term Terracing Watershed Development on Soil Macronutrients and Crop Production in Maybar Subwatershed, South Wello Zone, Ethiopia

Long-term watershed management in Ethiopia was evaluated in various agro-ecologies starting in the 1980s. Our research was carried out to investigate the effects of long-term watershed management on soil macronutrient status and crop production in the Maybar subwatershed terrace positioning system, which has a long-term data set on various aspects, such as hydroclimatology, agriculture, and social studies. Crop yield data were collected from 40 fixed plots of that data set, and soil samples were collected by topo-sequencing of the catchment from the cultivation field based on different terrace position plot arrangements. The results showed higher crop yield and production of biomass in the upper section or deposition zone of soil and water conservation structure than below the structure or loss zone, but did not vary significantly from the annual production potential. The annual production of cereals was marginally decreased, but not pulse crops, reducing the wheat harvest production from the middle to the loss zone (23.8%) rather than the deposition zone to middle portion of the terrace (8.0%). In comparison, to increase the slope position of the terrace, the redaction percentage of pulse crops (field pea and lentil) is greater, because in the first terrace location (upper to middle) and in the second terrace, the output capacity of field pea was reduced by 22.4%. The condition of soil fertility between the 2 consecutive systems for soil and water protection differed from the upper to the lower land positions. Improvement in soil chemical and physical properties relatively increased toward the upper land position. Soil organic matter, available phosphorus, bulk density, and soil moisture content were significantly affected by soil and water conservation structures ( P ⩽ .05). Long-term terrace growth typically has a positive effect on improvements in onsite soil resources and the capacity for crop production. It therefore has a beneficial impact on onsite natural resources, such as enhancing soil macronutrients and increasing productivity in crop yields.

DESINGN OF GAS SENSOR BASED ON TIN OXIDE NANOWHISKERS

Методом осаждения из паровой фазы были выращены нитевидные нанокристаллы диоксида олова. Исследовано влияние технологических параметров синтеза на морфологию выращенных наноструктур. Показано, что увеличение парциального давления кислорода в диапазоне от 0,06 мбар до 9,3 мбар и температуры зоны осаждения в диапазоне от 940 °С до 995 °С приводит к увеличению диаметра формируемых нитевидных нанокристаллов. В экспериментах установлено, что средний диаметр нитевидных нанокристаллов варьировался от 80 нм до 250 нм. На основе полученных нанокристаллов был сформирован активный слой газового сенсора, чувствительный к парам ацетона в воздухе. Величина газочувствительности и характерные времена отклика полученного сенсора достаточны для практического применения в газоанализаторах и системах распознавания газовых смесей и запахов. Tin dioxide nanowhiskers were grown by the vapor deposition. The effect of technological parameters on the morphology of the grown nanostructures was investigated. It is shown that an increase in the partial pressure of oxygen in the range from 0,06 mbar to 9,3 mbar and the temperature of the deposition zone in the range from 940 °C to 995 °C leads to an increase in the diameter of the formed nanocrystals. Experimentally it was shown that the average diameter of nanowhiskers varied from 80 nm to 250 nm. A gas sensor was formed with an active layer, based on the nanocrystals, sensitive to acetone vapor. The value of the gas sensitivity and the characteristic times of the sensor are sufficient for practical use in gas analyzers and systems for recognizing gas mixtures and odors.

The mechanical origin of snow avalanche dynamics and flow regime transitions

Snow avalanches cause fatalities and economic damages. Key to their mitigation entails the understanding of snow avalanche dynamics. This study investigates the dynamic behaviors of snow avalanches, using the Material Point Method (MPM) and an elastoplastic constitutive law for porous cohesive materials. By virtue of the hybrid Eulerian-Lagrangian nature of MPM, we can handle processes involving large deformations, collisions and fractures. Meanwhile, the elastoplastic model enables us to capture the mixed-mode failure of snow, including tensile, shear and compressive failure. Using the proposed numerical approach, distinct behaviors of snow avalanches, from fluid-like to solid-like, are examined with varied snow mechanical properties. In particular, four flow regimes reported from real observations are identified, namely, cold dense, warm shear, warm plug and sliding slab regimes. Moreover, notable surges and roll-waves are observed peculiarly for flows in transition from cold dense to warm shear regimes. Each of the flow regimes shows unique flow characteristics in terms of the evolution of the avalanche front, the free surface shape, and the vertical velocity profile. We further explore the influence of slope geometry on the behaviors of snow avalanches, including the effect of slope angle and path length on the maximum flow velocity, the $\\alpha$ angle and the deposit height. Unified trends are obtained between the normalized maximum flow velocity and the scaled $\\alpha$ angle as well as the scaled deposit height, reflecting analogous rules with different geometry conditions of the slope. It is found the maximum flow velocity is mainly controlled by the friction between the bed and the flow, the geometry of the slope, and the snow properties. In addition to the flow behavior before reaching the deposition zone, which has long been regarded as the key factor governing the $\\alpha$ angle, we reveal the crucial effect of the stopping behavior in the deposition zone. Furthermore, our MPM model is benchmarked with simulations of real snow avalanches. The evolution of the avalanche front position and velocity from the MPM modeling shows reasonable agreement with the measurement data from literature. The MPM approach serves as a novel and promising tool to offer systematic and quantitative analysis for mitigation of gravitational hazards like snow avalanches.

The 1513 Monte Crenone Rock Avalanche. Numerical model and geomorphological analysis

<p>The Monte Crenone rock avalanche of 30 September 1513 is one of the most catastrophic natural events in Switzerland and throughout the Alps. The enormous mass of rock that broke away from the western slope of Pizzo Magn or Monte Crenone, estimated at 50-90 million cubic metres, caused the complete damming of the course of the Brenno river, leading to the formation of a basin that extended from Biasca to the Castello di Serravalle in Semione (De Antoni et al. 2016). On 20 May 1515 the basin formed behind the dam overflowed, giving rise to a wave of more than 10 meters high that led to devastation in the territories downstream to reach Lake Maggiore (Scapozza et al. 2015).</p><p>In this project, we analyze the dynamics of the 1513 rock avalanche, trying to reconstruct the event through a numerical model, calculated with the software RAMMS::Debrisflow (RApid Mass Movement Simulation) provided by the Federal Institute for the Study of Snow and Avalanches (SLF/WSL).</p><p>The realization of the numerical model was preceded by the reconstruction of the topography before the landslide. This first phase of work, included a geological survey of the landslide body, the analysis of digital data (orthophotos, digital topographic maps, shaded model derived from swissALTI3D) and the collection of previous historical data.</p><p>The observation of the stratigraphic data obtained from the 701.27, 701.30 and 701.31 boreholes (part of the geotechnical studies for the Chiasso-San Gottardo highway) of the GESPOS database (GEstione Sondaggi, POzzi e Sorgenti) of the Institute of Earth Sciences SUPSI was essential to understand the landslide body thickness and volume in the deposition zone.</p><p>From the first phase of data collection and interpretation, we then moved on to the actual reconstruction of the digital model of the terrain before the landslide. This operation was carried out using ESRI's ArcGIS software, which made it possible recreating multiple models of the pre-event topography and thus finding the most realistic solution applicable to the subsequent RAMMS model.</p>