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Bioactive and antibacterial Ti6Al4V for bone contact applications
No full textSilver is a well-known antibacterial agent with broad spectrum activity and low resistance development . An increasing interest is registered for silver nanoparticles because of their large surface area and multiple mode of action (damage of the cell membrane, induction of ROS and release of silver ions). Despite of a wide research on surface enrichment of titanium surfaces with silver, the identification of an affective technology is a still an open issue. The aim of the present research is the surface modification of Ti6Al4V alloy in order to induce bioactive and antibacterial behaviou
An optimized magnetostatic field solver on GPU using open computing language
No full textRecent graphic processing units (GPUs) have remarkable raw computing power, which can be used for very computationally challenging problems. Like in micromagnetic simulations, where the magnetostatic field computation to analyze the magnetic behavior at very small time and space scale demands a huge computation time. This paper presents a multidimensional FFT-based parallel implementation of a magnetostatic field computation on GPUs. We have developed a specialized 3D FFT library for magnetostatic field calculation on GPUs. This made it possible to fully exploit the symmetries inherent in the field calculation and other optimizations specific to the GPUs architecture. We have compared our results with the widely used CPU-based parallel OOMMF program and with an equivalent serial implementation on CPU. The results have shown a speedup of up to 95x and 8.7x for single and 66x and 4.6x for double precision floating point accuracy against equivalent serial implementation and OOMMF, respectively
Process investigations on second generation lignin as a source of high-value molecules
No full textThere is an increasing demand of renewable biomass-derived fuels, generally known as biofuels, in order to overcome the need of fossil ones, and ultimately, deal with the environmental regulations imposed by the recent international agreements, which will hopefully lead to a limitation of global warming below 2 °C. The human being has used biomasses to solve its energetic and non-energetic needs for millennia before the Industrial Era, but in the 21st century there is the need to go a little bit further, for this reason, it is born the concept of biorefinery, or biofactory, in contrast with the oil-based refinery. In a fully integrated biorefinery, biomasses with variable origin are transformed through chemical and biochemical processes in a plethora of chemicals, fuels like ethanol and FAMEs, but also polymer monomers, drug precursors and food additives. The biorefinery will provide the scale dimensions and production flexibility to compete with the oil industry and, ultimately, will cause a global change in the geography of the energy and chemical industry. However, the development of efficient models of biorefinery based on non-edible second generation biomasses is still economically tricky, and there the need to couple fuels production with high-value chemical building blocks. Particular attention should be addressed to lignin fraction which is the most underutilized component of lignocellulosic biomass. Despite lignin is an incredible source of aromatic compounds, it is commonly intended to landfill or, in the best case, used as solid combustible. In this sense, this work has dealt with the development of processes for the transformation of industrial lignin streams into chemicals of interest for the industry, as alternative to pyrolysis or mere combustion. On one hand, we investigated the reductive route which involves the use of H2 firstly, to carry out the hydrogenolysis of lignin to give a phenols-rich bio-oil, and secondly, to transform this phenols mixture to other products through a hydrodeoxygenation reaction. On the other hand, we explored the oxidative route which involves the use of an oxidant to break down lignin matrix to functionalized phenols and carboxylic acids. Both pathways offer the opportunity to produce significant quantities of renewable building blocks, which will ultimately support the economic sustainability of the integrated biorefinery. The following paragraphs resume the content of the main chapters of this dissertation. The hydrodeoxygenation (HDO) of guaiacol has been chosen as a model process for the upgrading of lignin-derived bio-oils. Tests were carried out in a batch reactor at 350 °C, 40 bar of H2, in the presence of several Mo-based catalysts prepared by impregnation of ammonium molybdate on SiO2, Al2O3, NaY zeolite, MgO, activated carbon and graphite. These materials have been characterized by means of: N2 physisorption, XRD, FESEM/EDS, XPS, TPR-H2, TPD-NH3, with the aim of correlating the physical and chemical properties of the prepared samples with the resulting features in the HDO reaction. Mo on activated carbon showed the best performances towards guaiacol demethoxylation, exhibiting complete conversion, 72 % of selectivity to phenol and 19 % to p- and o-cresol. The high surface area and low acidity of activated carbon allow good dispersion of MoOx which exhibits characteristic fragments with lamellar shape, capable to provide large active surface with localized acidity. A phenolic bio-oil, derived from an industrial hydrogenolysis facility treating 2nd generation lignin, was used as starting material for the recovery of phenolic monomers by means of an ad hoc vacuum distillation apparatus. The initial 20 %wt content of monomers was efficiently separated with the 90 % of yield, showing guaiacol, phenol and ethylphenol as main components. Afterwards, the distillate was upgraded through an HDO reaction in order to narrow the compounds distribution and to improve the stability of the mix. The process was carried out under similar conditions as the ones adopted in Chapter 3, allowing achieving the complete demethoxylation of the mix with high selectivity. Notably, the presence of the Mo-base catalyst over activated carbon significantly enhanced the performances of the reaction. Wet air oxidation (WAO) of lignocellulosic biomasses is a promising route for the production of renewable and valuable compounds, involving air as primary oxidant and mild reaction temperatures. In this work, an industrial residue of bioethanol production, steam exploded lignin derived from wheat straw, undergoes a WAO process with the aim to achieve more insights on the process performances in terms of potential yields of aromatic compounds and carboxylic acids (CAs). The experiments were carried out in a pressurized 50 ml batch reactor loaded with water or other aqueous solutions as solvent, the standard conditions were 150 °C of temperature, 20 bar of initial air pressure and 2 h. Afterwards, several solvothermal pretreatments were applied in order to depolymerize and solubilize lignin under inert atmosphere; the residues-free solutions obtained in this way were used as substrate for the WAO reaction. The choice of the pretreatment temperature, solvent alkalinity and presence of perovskite catalysts were evaluated with regard to the mass yields of resulting aromatic compounds and CAs, their carbon content and the products distribution. Best performance exhibits a lignin dissolution ratio of 53 % with 1.3 % of yield towards aromatic compounds where vanillin is the principal product (59.1 %) but also the 32 % of yield in CAs with glycolic acid as major product (40.9 %). Acetovanillone (AV) was selected as lignin model molecule in order to investigate its behavior under the WAO reaction conditions. The experiments were carried out in a pressurized 50 ml batch reactor loaded with NaOH 2 M as solvent, the reaction takes 1 h with temperatures ranging from 130 to 190 °C and air pressures between 5 and 30 bar. A heterogeneous catalyst, the perovskite-type mixed oxide LaFeO3 was synthetized and used as catalyst in order to improve the activation of molecular oxygen. Vanillin yield resulted to benefit from high reaction temperature showing a maximum carbon yield of 22 %, instead the formation of carboxylic acids from the oxidative degradation of AV largely benefits from high pressure of air, exhibiting an overall carbon yield of 35 %. The produced compounds include oxalic, glycolic, lactic, malonic and levulinic acid
Modeling, design, testing and analysis of biogas-fed SOFC power plants
No full textThe present work is related to the complete analysis of biogas-fed SOFC system. The first part of the work has been related to a review on the concept of polygeneration system and on the analysis of the current status of SOFC installations, especially when fed with biogas. The use of a renewable fuel, coupled with carbon capture, can lead to negative emissions plants, defined as key technologies for reaching the goals set in the Paris Agreement. Furthermore, biogas and SOFC show many affinities which have been discussed in the works: from the high efficiency at low sizes to the availability of already existing subsidy schemes for electricity production. An analysis of the potential biogas production in EU is proposed, with focus on wastewater treatment plants. In this particular area, the work tries to point out the numbers of potential installed power by using SOFCs. The experimental and modeling activities are then proposed. The PhD activity is linked to two European projects, SOFCOM and DEMOSOFC. The first project is related to the analysis of biogas fed SOFC system with carbon capture and re-use. In this context, a demonstration plant has been developed and tested in the SMAT Castiglione wastewater treatment plant. Results show an easy process for the CO2 capture from the SOFC exhaust, thus pointing SOFC as a key technology in the framework of negative carbon emissions plants. More criticalities have been found in the choice of CO2 utilization for production of algae in a photobioreactor: the unstable quality of the inlet wastewater coming from the plant, the fluctuating algae productivity as function of the weather conditions, and the algae attachment to the pipe, pointed out a need for improvements and research on this technology. The experimental activity has been coupled with a modeling activity on the same concept of biogas fed SOFC, with the possibility of a downstream carbon capture and use/ sequestration. Different plant layout and different system sizes have been analyzed from a technical and economical point of view. Finally, the analysis of a real industrial size SOFC system is proposed. This activity has been developed in the framework of the DEMOSOFC EU project, where the first industrial size biogas fed SOFC system will be installed. Being the first installation of its kind, many issued and improvements have been detected. The analysis is related to the system design and description, for what concerning plant integration (electrical and thermal), system operation, and biogas processing. Biogas processing has been especially pointed out as a key component in a biogas-fed SOFC system. Because of the low admissible contaminants levels for fuel cell, a new and dedicated cleaning unit is required, which is not currently available on the market. The processing unit design is proposed and ongoing experimental activity on the adsorption with activated carbons are proposed. The main harmful contaminants found in wastewater biogas are sulphur (in the form of H2S) and siloxanes (mainly D4 and D5)
Design and Development of Multi-Emitter High Power Laser Diode Modules
No full textThe growing demand for high-power laser diode modules for laser-based material processing machines has stimulated the development of a number of architectures that, taking advantage of multiple beam combination techniques, have allowed the realization of multi-emitter devices with unprecedented performance. However, these designs typically rely on roughly approximated relations, which have reached their limit of applications. Therefore, to further scale the output power and increase the brightness, new and more accurate models are necessary. From the market point-of-view, the deployment of high-power multi-emitter modules is limited by the cost per emitted watt, which is proportional to the number of required optical elements and package assembly time. Cost reduction, therefore, requires, again, accurate models to properly optimize the package layout, but also new assembly strategies and tools. The thesis analyzes in detail these two aspects - accurate models and assembly strategies and tools - and presents for both innovative solutions to help to push the technology beyond the current state-of-the-art. In particular, for what concerns the multi-emitter model, a new relation to predict the beam quality at the pigtail fiber input by taking into account the impact of lenses and the distance between two adjacent chips in spatial beam multiplexing has introduced. The model is based on the propagation and transformation of paraxial Gaussian beams and analyzes, not only the impact of the choices on the focal length of each collimating or focusing lens but also of the truncation caused by their finite aperture. Then, as the model requires the knowledge of the individual laser chip beam characteristics, specific benches for the measurement of the near and far field emissions have been developed. The proposed model has been validated in different working conditions and found to lead to an error lower than 6%. As for the multi-emitter assembly, an industrial grade procedure has been devised and a completely new approach based on back-propagation artificial neural network to automatically determine the optimal positioning of each optical element has been developed. The neural network is trained using ray tracing of Gaussian beams, starting from the emission characteristics of the laser chips. The new tool has been tested in practical cases with the most critical of all the components, the positioning of the fast axis collimator, obtaining a reduction of the assembly time of more than 50% with respect to current automatic assembly machines. Finally, the design model and the assembly procedure have been applied to the development of a prototype of a multi-emitter module that, by exploiting spatial, wavelength, and polarization multiplexing of a plurality of chips emitting about 10W each, delivers over 300W in a 105/0.15 fiber pigtail, figures that represent a remarkable improvement over the current state-of-the-art. This result has been very challenging because it required the combination of theoretical, experimental, and technological aspects, not limited to photonics, but including also measurement theory, precision mechanics and thermal management
Human exploration of complex knowledge spaces
No full textDriven by need or curiosity, as humans we constantly act as information seekers. Whenever we work, study, play, we naturally look for information in spaces where pieces of our knowledge and culture are linked through semantic and logic relations. Nowadays, far from being just an abstraction, these information spaces are complex structures widespread and easily accessible via techno-systems: from the whole World Wide Web to the paramount example of Wikipedia. They are all information networks. How we move on these networks and how our learning experience could be made more efficient while exploring them are the key questions investigated in the present thesis. To this end concepts, tools and models from graph theory and complex systems analysis are borrowed to combine empirical observations of real behaviours of users in knowledge spaces with some theoretical findings of cognitive science research. It is investigated how the knowledge space structure can affect its own exploration in learning-type tasks, and how users do typically explore the information networks, when looking for information or following some learning paths. The research approach followed is exploratory and moves along three main lines of research. Enlarging a previous work in algorithmic education, the first contribution focuses on the topological properties of the information network and how they affect the \emph{efficiency} of a simulated learning exploration. To this end a general class of algorithms is introduced that, standing on well-established findings on educational scheduling, captures some of the behaviours of an individual moving in a knowledge space while learning. In exploring this space, learners move along connections, periodically revisiting some concepts, and sometimes jumping on very distant ones. To investigate the effect of networked information structures on the dynamics, both synthetic and real-world graphs are considered, such as subsections of Wikipedia and word-association graphs. The existence is revealed of optimal topological structures for the defined learning dynamics. They feature small-world and scale-free properties with a balance between the number of hubs and of the least connected items. Surprisingly the real-world networks analysed turn out to be close to optimality. To uncover the role of semantic content of the bit of information to be learned in a information-seeking tasks, empirical data on user traffic logs in the Wikipedia system are then considered. From these, and by means of first-order Markov chain models, some users paths over the encyclopaedia can be simulated and treated as proxies for the real paths. They are then analysed in an abstract semantic level, by mapping the individual pages into points of a semantic reduced space. Recurrent patterns along the walks emerge, even more evident when contrasted with paths originated in information-seeking goal oriented games, thus providing some hints about the unconstrained navigation of users while seeking for information. Still, different systems need to be considered to evaluate longer and more constrained and structured learning dynamics. This is the focus of the third line of investigation, in which learning paths are extracted from advances scientific textbooks and treated as they were walks suggested by their authors throughout an underlying knowledge space. Strategies to extract the paths from the textbooks are proposed, and some preliminary results are discussed on their statistical properties. Moreover, by taking advantages of the Wikipedia information network, the Kauffman theory of adjacent possible is formalized in a learning context, thus introducing the adjacent learnable to refer to the part of the knowledge space explorable by the reader as she learns new concepts by following the suggested learning path. Along this perspective, the paths are analysed as particular realizations of the knowledge space explorations, thus allowing to quantitatively contrast different approaches to education
Thermal Conductivity Evaluation of Fractional-Slot Concentrated-Winding Machines
No full textThe use of fractional-slot concentrated windings (FSCW) in electrical machines allows more compact, efficient, and reliable design with respect to machines equipped with distributed windings. However, an electromagnetic design linked to a thermal analysis of the electrical machine is mandatory to achieve the desired performance, and to fulfill the requirements of efficiency and reliability. One of the most critical issues in thermal design of electrical machines is to assign fair values for the input parameters of the thermal simulation models, particularly those related to the stator winding insulation system. This paper deals with the assessment of the equivalent thermal conductivity of the insulation system of FSCW machines. For this purpose, three FSCW electrical machines for different applications were evaluated via an experimental method based on a dc thermal transient test. Whereas the investigated machines present different characteristics among themselves, different approaches were required to properly estimate the thermal conductivity
Groundwater-level risk assessment by using statistical and geographic information system (GIS) techniques: a case study in the Aosta Valley region, Italy
No full textIn the present study, groundwater-level monitoring has been carried out on 26 observation dug wells in the Aosta Valley region, Italy, during the dry season (June 2013) and wet season (November 2013) in order to assess the water-level fluctuation (WLF). The depth to water level varied from 3.04 to 28.70 metres below ground level (mbgl) in the dry season and from 2.92 to 25.62 mbgl in the wet season. The WLF of the study area varied from 0.01 to 6.80 mbgl, and the western and north-western regions of the study area showed higher WFL. The WLF map was validated with a statistical analysis and elevation value of the area in a geographic information system environment, and this indicated that validation can be accepted for the WLF in the Aosta Valley. The results of the study demonstrated that the eastern region could be considered as a safe and good recharge zone for the groundwater in the Aosta Valley region. The WLF map generated in this study could also be used for the management of future groundwater resources and environmental planning of the area
Evaluation of hydrogeochemical processes and groundwater quality for suitability of drinking and irrigation purposes: a case study in the Aosta Valley region, Italy
No full textThe present study aims to discuss the hydrogeochemical processes in the Aosta Valley region and assess the quality of its groundwater for suitability of drinking and irrigation purposes. One hundred twenty-two samples were collected from the Aosta Valley region in the years 2007 and 2008 (61 per year), and analysed for pH, electrical conductivity, total dissolved solids (TDS), total hardness, major cations and anions. The pH of the samples in both years indicated a near-neutral to alkaline nature of the groundwater. The cation and anion chemistry showed the general ionic abundance as: Ca2+ > Mg2+ > Na+ > K+ and HCO3− >SO4 2− >Cl− >NO3− >F− in both years. Ca2+, Mg2+, HCO3− and Ca2+ , Mg2+ ,Cl− , SO4 2− were the dominant hydrogeochemical facies. The computed saturation indices demonstrated that the groundwater was supersaturated with respect to dolomite and calcite in both years. The groundwater chemistry of the study area was mainly controlled by the dissolution of carbonate, sulphate and silicate minerals, as well as ion exchange processes. A comparison of the groundwater quality in relation to drinking water standards showed that most of the water samples were suitable for drinking and domestic uses. The computed water quality index (WQI) values of the study area groundwater ranged from 24 to 84 in the year 2007 and from 22 to 82 in the year 2008, and all the location fell under the Excellent to Good category
Lavoro o disoccupazione con i robot?
No full textVengono esaminate le implicazioni industriali e sociali dell'uso esteso dei robot