1,721,019 research outputs found
Ex-post assessment of climate and hydrological projections: reliability of CMPI6 outputs in Northern Italy
No full textThis paper presents a validation of outputs from some GCMs of the CMIP6 project when used to assess climate projection and hydrological flows at a catchment scale for the case study area of the Lombardy region (Northern Italy). The modeling chain consists of (i) a choice of climatic scenarios from 10 GCMs of the CMIP6, (ii) the application of a stochastic downscaling procedure to make projections usable at the local scale, and (iii) the use of a semi-distributed physically based hydrological model Poli-Hydro for the generation of hydrological scenarios. Data on observed precipitation and temperature were collected from automatic weather stations, and the hydrological budget of four target catchments within the study area was assessed using Poli-Hydro. An ex-post (back-casting) analysis was performed upon the control data series from the GCMs by comparing statistics of relevant climate variables and model-simulated discharges against observed counterparts during the historical period 2002-2014. Then, during 2015-2021, the goodness of projections was assessed using confidence intervals. Our results show that the accuracy of GCMs in representing regional climate is not always reflected in a credible evaluation of local hydrology. The validation of climate patterns provides somewhat poor results; thus, the interaction among climate and hydrology needs to be explored carefully to warrant the credibility of hydrological scenarios. Overall, the spatial and temporal consistency of GCM projections, as explored here climatically and hydrologically, provides a clue about their dependability for basin scale management
Functional feasibility in optimal evaluation of water distribution network performances
Full text linkThe traditional approach for the optimization of water distribution networks (WDNs) does
not always lead to consistent solutions from an operational point of view. The latest optimization
algorithms identify solutions that are “the best solutions” in mathematical terms but that can be
less than robust against changes in operating conditions, resulting in the worst case in hydraulically
infeasible configurations. Thus, this paper aims to provide a methodology that can synthesize the
network performance capabilities under the change in operating conditions with two convergent
strategies. The first consists of the implementation of new performance indices (PIs), the demand
deficit and the pressure range, and the evaluation of their ability to criticality highlight in operating
conditions. The second is the introduction of a new approach to weight the infeasible solutions in the
final result, which are those inconsistent with the real hydraulic network performances. The analysis
shows that the use of these new indices makes it easier to understand the behavior of the network
and to identify any weaknesses. This is true if these indices consider the hydraulically inconsistent
solutions that may arise from the simulations of different operation conditions; otherwise, results that
poorly represent the real behavior of the network would be obtained
Influence of ns laser texturing of AISI 316L surfaces for reducing bacterial adhesion
Full text linkNanosecond pulsed laser texturing has been performed on stainless steel with the objective of developing surface treatments to reduce bacterial adhesion on mechanical components in food handling machinery. The adhesion of Escherichia coli (E. coli) on four distinct textures has been investigated with standardised protocols for measurement of antibacterial performance. Surface morphology has been studied in detail for each texture to ascertain the presence of hierarchical structures and determine the role of topography in reducing bacterial adhesion. Despite the absence of sub-micrometric features comparable with bacterial size, this work highlights the crucial role that nanosecond pulsed laser irradiation plays in promoting a thin layer of iron oxide that reduces E. coli adhesion through local repulsive electrostatic interactions
Molecular dynamics model for the antibactericity of textured surfaces
No full textAn original model has been developed for the initial stage of bacterial adhesion on textured surfaces. Based on molecular dynamics, the model describes contact between individual bacterial cells in a planktonic state and a surface, accounting for both the mechanical properties of the cells and the physico-chemical mechanisms governing interaction with the substrate. Feasibility of the model is assessed via comparison with experimental results of bacterial growth on stainless steel substrates textured with ultrashort laser pulses. Simulations are performed for two different bacterial species, Staphylococcus aureus and Escherichia coli, on two distinct surface types characterised by elongated ripples and isolated nanopillars, respectively. Calculated results are in agreement with experiment outcomes and highlight the role of mechanical stresses within the cell wall due to deformation upon interaction with the substrate, creating unfavourable conditions for bacteria during the initial phases of adhesion. Furthermore, the flexibility of the model provides insight into the intricate interplay between topography and the physico-chemical properties of the substrate, pointing to a unified picture of the mechanisms underlying bacterial affinity to a textured surface
Nanostructure patterns on stainless-steel upon ultrafast laser ablation with circular polarization
Full text linkRipple-like nanostructure patterns are known to occur in ultrafast laser ablation with linearly polarized radiation. The observation of similar features at the bottom of grooves produced during laser ablation of stainless-steel with circular polarization is reported here. A comprehensive morphological analysis of the machined surfaces, carried out by electron and scanning probe microscopes, reveals a marked dependence of feature shape on process parameters, in particular on the scanning velocity of the laser spot. Such a dependence is interpreted based on the occurrence of an inclined surface during the ablation and on the consequent differential absorption of s- and p-polarized components of the laser radiation by stainless-steel. The resulting anisotropy of the absorbed energy mimics irradiation with elliptical polarization that can drive formation of ripple-like, elongated nanostructures
Molecular dynamics model for the antibactericity of textured surfaces
Full text linkAn original model has been developed for the initial stage of bacterial adhesion on textured surfaces. Based on molecular dynamics, the model describes contact between individual bacterial cells in a planktonic state and a surface, accounting for both the mechanical properties of the cells and the physico-chemical mechanisms governing interaction with the substrate. Feasibility of the model is assessed via comparison with experimental results of bacterial growth on stainless steel substrates textured with ultrashort laser pulses. Simulations are performed for two different bacterial species, Staphylococcus aureus and Escherichia coli, on two distinct surface types characterised by elongated ripples and isolated nanopillars, respectively. Calculated results are in agreement with experiment outcomes and highlight the role of mechanical stresses within the cell wall due to deformation upon interaction with the substrate, creating unfavourable conditions for bacteria during the initial phases of adhesion. Furthermore, the flexibility of the model provides insight into the intricate interplay between topography and the physico-chemical properties of the substrate, pointing to a unified picture of the mechanisms underlying bacterial affinity to a textured surface
Future hydrology of the cryospheric driven lake como catchment in Italy under climate change scenarios
Full text linkWe present an assessment of climate change impact on the hydrology of the Lago di Como lake catchment of Italy. On one side, the lake provides water for irrigation of the Po valley during summer, and on the other side its regulation is crucial to prevent flood risk, especially in fall and winter. The dynamics of lake Como are linked to the complex cryospheric hydrology of its Alpine contributing catchment, which is in turn expected to change radically under prospective global warming. The Poli-Hydro model is used here to simulate the cryospheric processes affecting the hydrology of this high-altitude catchment. We demonstrated the model’s accuracy against historical hydrological observations, available during 2002-2018. We then used four Representative Concentration Pathways scenarios, provided by three Global Circulation Models under the AR6 of IPCC, to project potential climate change until 2100. We thereby derived daily series of rainfall and temperature, to be used as inputs for hydrological simulations. The climate projections here highlight a substantial increase in temperature at the end of the century, between +0.61° and +5.96°, which would lead to a decrease in the total ice volume in the catchment, by -50% to -77%. Moreover, there would be a decrease in the contribution of snow melt to the annual lake inflow, and an increase in ice melt under the worst-case scenarios. Overall, the annual Lake inflows would increase during autumn and winter and would decrease in summer. Our study may provide a tool to help policy makers to henceforth evaluate adaptation strategies in the area
Modelling the interaction between bacterial cells and laser-textured surfaces
Full text linkThe influence of surface topography resulting from ultrashort pulsed laser texturing on bacterial cell adhesion is studied as a method for preventing contamination on stainless steel components. The initial adhesion of a single spherical cell on a rough surface prior to the onset of any chemical or biological effect is simulated with a numerical approach including non-covalent interactions between the cell and textured substrate. The study demonstrates that when asperities are large enough to allow the cell to occupy valleys between two adjacent protrusions, the cell is protected from hydrodynamic turbulence and is therefore more prone to adhere to the substrate. Results pave the way to validating, in quantitative terms, hypotheses relating to the influence of surface topography on bacterial growth. Two different levels of anisotropy are taken into account to contrast the high adaptability of spherical cells, demonstrating that laser texturing can invoke a specific biological response
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