Archivio Istituzionale della Ricerca- Università del Salento
Not a member yet
80217 research outputs found
Sort by
Solving the Master Equation on river networks: A computer algebra approach
No full textWe describe the algorithms and the software that have been used in a new computational method based on the use of Master Equations. Our computer algebra procedures simulate the diffusion of a pollutant in river networks. The representation of river networks as trees makes the derivation of governing equations for pollutant transport an easy task. This includes mass balance equations that account for the sources, sinks, and transport of pollutants in the river network. In two previous papers we described the model and some simulations obtained from our software. In this paper we describe two software libraries, respectively for the Reduce and the Mathematica computer algebra systems, that have been developed on the basis of our model. The libraries can be found in our GitHub repository
Evaluating the direct radiative forcing of a giant Saharan dust storm
No full textThe radiative effects caused by a massive desert dust outbreak that took place in the Western Sahara Desert, in the proximity of the Atlantic Ocean, in June 2020 are studied. This outbreak featured two significant dust plumes, the second of which is the focus of the present study.
For the identification of the dust plume, we adopted a multi-platform set of remote sensing data, including satellite retrievals from the sensors VIIRS, MODIS and SEVIRI onboard the NOAA-20, Aqua and MSG spacecrafts, respectively. The analysis of aerosol-radiation effects is based on a regional simulation with the WRF-Chem model, implementing the coupling between the aerosols of the GOCART speciation and the radiative modules defined in WRF-Chem model by the “New Goddard Shortwave and Longwave Schemes”. In this context, two sets of simulations are proposed: the first one (CTL) without any feedback, and the second (CPL) adopting the fully-coupling strategy.
From the comparison between the simulated and the observed (SEVIRI) incoming SW/LW radiation it follows that: (i) the presence of dust in the domain causes a reduction of the incoming SW radiation in the CPL runs; (ii) this reduction is fully in agreement with experimental data; (iii) conversely, the LW component appears to be insensitive to model coupling. Hence, the Goddard radiative coupling is effective in reducing the incoming SW radiation: the difference in terms of average daily values between model and SEVIRI is 123.7 vs 37.0 W m−2 for CTL and CPL runs, respectively. The incoming longwave radiation seems to be less correlated with the coupling strategy, being the difference of 31.15 vs 15.8 W m−2 for CTL and CPL runs, respectively.
The dust radiative forcing (DRF), that characterises the aerosol–radiation interactions, results in an average surface cooling of −16.9 W m−2 between the CPL and the CTL runs that could be attributed to a reduction of SW radiation absorbed and scattered by dust particles in the coupled run. At the top of the atmosphere (TOA), a warming, caused by the decrease in atmospheric transparency to the terrestrial thermal radiation, results in an average DRF of +1.5 W m−2.
Finally, the space- and time-averaged surface energy balance results in a difference (E(CPL) - E(CTL)) of about −7.5 W m−2. Similarly, the dynamic response of the dust forcing within the Planetary Boundary Layer is characterised by a mean temperature difference (CPL-CTL) of about −0.7 K near the surface. Our findings strongly encourage the use of fully-coupled modelling strategy, between aerosols and meteorology, for regional-scale studies and in climate risk assessments
Cork-derived magnetic composites: a preliminary study
No full textMaterials based on graphitic carbon are used for environmental remediation, due to their high surface area and their capacity to adsorb pollutants in liquid environments. Carbonaceous materials derived from residues are particularly interesting, as their synthesis has a smaller impact on the environment. In the present work, we report a preliminary study on the preparation of graphitic carbon made from cork waste powder modified with magnetic nanoparticles (MNPs). This is the first time such composites were prepared using pyrolysed/carbonised cork, from a powder residue of cork stopper production. This makes the process sustainable and in line with the circular economy. The composites were prepared by vacuum infiltration of the MNPs on pyrolysed cork powder, with a successive thermal treatment, resulting in a carbon material that retained the porous microstructure of the original cork, ideal for the absorption of pollutants or separation of oils and water, while also being magnetically separable afterwards. It was seen that post-infiltration heating was better in air than under nitrogen, with the nitrogen atmosphere and presence of highly porous carbon possibly partially reducing magnetite to FeO, with a reduction in magnetic properties. MNPs with different chemical compositions were tested - zinc ferrite (ZnFe2O4) and magnetite (Fe3O4) - with the magnetite composites showing the highest magnetisation. Moreover, magnetite particles of different dimensions were considered: 6, 9 and 15 nm; results indicated that the 9 nm magnetite NPs were the most easily infiltrated; the magnetisation, however, was higher for the composites with the 15 nm magnetite NPs (about 9 emu g−1), despite the oxide component comprising only around 12 wt% of the composite, due to their greater initial magnetisation. This value is higher than those of similar composites prepared using carbon from other natural sources. SEM analysis showed the presence of MNPs on the surface of the material, with the particles being on the nanometric scale and showing no aggregation on the micron scale. Composites prepared with these 15 nm MNPs also showed greater stability in both water and an organic solvent (chloroform) and were demonstrated to be magnetically separable from suspensions, making them the most suitable for environmental remediation applications
Fabrication and Characterization of Low-Size and Compact AlN PMUT Arrays for Advanced Ultrasonic Applications
No full textThe piezoelectric micromachined ultrasonic transducers (PMUT) are based on the flexural movement of thin membranes coupled with thin piezoelectric film. These devices can find applications in several fields, like ultrasound imaging techniques for medical diagnostics and non-destructive and real-time structural monitoring. This work proposes the manufacturing, the computational study by Finite Element Method (FEM) and the characterization of Aluminum Nitride (AlN)-based PMUT arrays, suitable as ultrasound transmitters and receivers. In detail, two PMUT arrays, shaped as annular and square matrix, respectively, were developed by an optimized manufacturing process. It exploits a controlled Bosch process, used to release the membranes without using any stop layer to control the residual Si membrane thickness, resulting in great flexibility in tuning the PMUT operating frequency. The PMUT arrays were designed to operate at 2.5-3 MHz frequency. An annular configuration was deployed, featured by a common ground contact connecting all membranes’ bottom electrodes and separate contacts to drive the top electrodes of each ring. The modular structure allows easy customization depending on the application and operating scenario. AIN-based PMUT arrays were fully characterized as transmitters and receivers; in detail, time- and frequency-domain responses of a 33 square matrix and a 3-ring and 5-ring annular PMUT arrays were analyzed and discussed as a function of the number of membranes composing the probe’s rings and the amplitudes of driving pulse. Finally, fundamental mode bandwidth analysis is reported in relation of the driving voltage amplitude. Experimental tests have demonstrated that the designed annular PMUT arrays operate at a 3 MHz central frequency with a 1 MHz bandwidth
Individual and collective memories as narratives of identities
No full textThe chapter analyses the role of narratives in the construction of both individual and collective memorie
Gaussian Poincare Inequalities on the Half-Space with Singular Weights
No full textWe prove Rellich–Kondrachov-type theorems and weighted Poincaré inequalities on the half-space R+N+1={z=(x,y):x∈RN,y>0} endowed with the weighted Gaussian measure μ:=yce-a|z|2dz where c+1>0 and a>0. We prove that for some positive constant C>0, one has (Formula presented.) where u ̄=1μ(R+N+1)∫R+N+1udμ(z). Besides this, we also consider the local case of bounded domains of R+N+1 where the measure μ is ycdz