An application of Trotter's algorithm to DMRG simulation

La seguente tesi presenta l'implementazione in codice C++ di un algoritmo per l'evoluzione temporale del DMRG, basato sull'approssimazione di Trotter per primi vicini. Il corretto funzionamento del codice è stato controllato calcolando un ristema risolubile esattamente, la catena di fermioni liberi senza spin (con condizioni al contorno aperte); in seguito il nuovo algoritmo è stato comparato con l'evoluzione temporale del DMRG basata sul metodo di Runge-Kutta. L'analisi degli errori ha mostrato come, per brevi periodi di tempo, il metodo di Runge-Kutta sia il più adatto fra i due, mentre per periodi di media durata il metodo di Trotter offra prestazioni migliori. Le evoluzioni temporali per tempi elevati sono attualmente al di là della portata di entrambi gli algoritmi

Additive manufacturing of porous ceramic structures

This doctoral thesis describes the additive manufacturing of porous structures starting from preceramic mixtures. Preceramic polymers are a class of inorganic polymers which can be converted to a ceramic with high yield. The use of a preceramic polymer has been explored in this work with the double aim of providing the desired ceramic phases and of facilitating the shaping processes. The work is divided in three parts. In a first project, the powder-based three-dimensional printing technology has been applied to a preceramic polymer powder. Complex porous structures with Kagome and octahedral geometries have been replicated. The preceramic polymer was successively converted to a unique SiOC phase upon heat treatment in inert atmosphere. This approach, in contrast to the use of a ceramic powder, allows an easier shaping and the achievement of relatively higher green densities, due to the dissolution and re-solidification of the polymer in the process. The shaping of fine porous structures is particularly suited to this material because problems related to gas release during the polymer-to-ceramic transformation are limited. In a second project, the same powder-based technology was applied to mixtures of a preceramic polymer and ceramic fillers. In this case, the preceramic polymer acts as a binder for the fillers during the printing process. Upon heat treatment in air, the polymer is converted to silica, which then can be reacted with the fillers in the mixture in order to form silicate ceramic phases. This approach is very versatile and has been used to form apatite-wollastonite bioceramic composites, which have been shaped into porous scaffolds with designed porosity and cylindrical or cubic geometries. Finally, a different technology, which is an extrusion-based printing, has been applied. In this technique, as opposite to powder-based technologies, the part is not supported during its buildup, therefore a careful tailoring of the ink rheology is necessary in order to create spanning features. In this context, mixtures of a preceramic polymer and fillers were formulated which had a suitable shear-thinning behaviour, with the help of suitable additives. A hardystonite ceramic, which is a bio-silicate phase, was formed upon heat treatment in air. Hardystonite scaffolds with orthogonal pores were successfully shaped by the deposition of fine (< 0.5 mm) filaments

Additive Manufacturing of Porous Ceramic Structures from Preceramic Polymers

This doctoral thesis describes the additive manufacturing of porous structures starting from preceramic mixtures. Preceramic polymers are a class of inorganic polymers which can be converted to a ceramic with high yield. The use of a preceramic polymer has been explored in this work with the double aim of providing the desired ceramic phases and of facilitating the shaping processes. The work is divided in three parts. In a first project, the powder-based three-dimensional printing technology has been applied to a preceramic polymer powder. Complex porous structures with Kagome and octahedral geometries have been replicated. The preceramic polymer was successively converted to a unique SiOC phase upon heat treatment in inert atmosphere. This approach, in contrast to the use of a ceramic powder, allows an easier shaping and the achievement of relatively higher green densities, due to the dissolution and re-solidification of the polymer in the process. The shaping of fine porous structures is particularly suited to this material because problems related to gas release during the polymer-to-ceramic transformation are limited. In a second project, the same powder-based technology was applied to mixtures of a preceramic polymer and ceramic fillers. In this case, the preceramic polymer acts as a binder for the fillers during the printing process. Upon heat treatment in air, the polymer is converted to silica, which then can be reacted with the fillers in the mixture in order to form silicate ceramic phases. This approach is very versatile and has been used to form apatite-wollastonite bioceramic composites, which have been shaped into porous scaffolds with designed porosity and cylindrical or cubic geometries. Finally, a different technology, which is an extrusion-based printing, has been applied. In this technique, as opposite to powder-based technologies, the part is not supported during its build-up, therefore a careful tailoring of the ink rheology is necessary in order to create spanning features. In this context, mixtures of a preceramic polymer and fillers were formulated which had a suitable shear-thinning behaviour, with the help of additives. A hardystonite ceramic, which is a bio-silicate phase, was formed upon heat treatment in air. Hardystonite scaffolds with orthogonal pores were successfully shaped by the deposition of fine (< 0.5 mm) filaments

Produzione e funzionamento di un dispositivo spin valve

Il fenomeno della magnetoresistenza gigante (GMR) consiste nella marcata variazione della resistenza elettrica di una struttura in forma di film sottile, composta da un’alternanza di strati metallici ferromagnetici (FM) e non magnetici (NM), per effetto di un campo magnetico esterno. Esso è alla base di un gran numero di sensori e dispositivi magnetoelettronici (come ad esempio magnetiche ad accesso casuale, MRAM, ad alta densità) ed ulteriori innovazioni tecnologiche sono in via di elaborazione. Particolarmente rilevanti sono diventate le Spin Valve, dispositivi composti da due strati FM separati da uno spaziatore NM, metallico. Uno dei due film FM (free layer) è magneticamente più soffice rispetto all’altro (reference layer), la cui magnetizzazione è fissata mediante accoppiamento di scambio all’interfaccia con uno strato antiferromagnetico (AFM) adiacente. Tale accoppiamento causa l’insorgenza di una anisotropia magnetica unidirezionale (anisotropia di scambio) per lo strato FM, che si manifesta in uno shift orizzontale del ciclo di isteresi ad esso associato (effetto di exchange bias), solitamente accompagnato anche da un aumento del campo coercitivo. Questo lavoro di tesi riporta la deposizione e la caratterizzazione magnetica e magnetoresistiva di due valvole spin, una a struttura top (SVT) composta da strati di Si/Cu[5 nm]/Py[5 nm]/Cu[5 nm]/Py[5 nm]/IrMn[10 nm], ed una a struttura bottom (SVB), di composizione Si/Cu[5 nm]/IrMn[10 nm]/Py[5 nm]/Cu[5 nm]/Py[5 nm], allo scopo di verificare il comportamento magnetoresistivo gigante del dispositivo per questa particolare scelta dei materiali. I campioni sono stati depositati mediante DC Magnetron sputtering, e caratterizzati magneticamente mediante magnetometro SQUID; la caratterizzazione resistiva è stata eseguita tramite metodo di van der Pawn. Vengono infine presentati i risultati sperimentali, in cui si osserva una variazione di magnetoresistenza nei campioni nell’ordine del punto percentuale

Economic assessment of managing processionary moth in pine forests: a case study in Portugal

This paper assesses the private and social profitability of current strategies for managing processionary moth (Thaumetopoea pityocampa) in Portuguese pine forests, looking at economic and environmental costs and benefits. Costs include the expenses for forest treatment and the social costs of threats to human health (dermatitis amongst others); benefits are assessed in terms of both revenue and social benefits such as carbon fixation and recreation. The evaluation was done using Cost Benefit Analysis (CBA) as an analytical framework. While this tool is currently applied to forest and environmental assessment and specific applications to pest management strategies are to be found in agricultural economics, rather few attempts have been made in the field of forest pest management. In order to assess and comparewithewithout options, a case-study was analysed for the Setu´bal Peninsula, south of Lisbon, an area where extensive stands of maritime pine (Pinus pinaster) grow. The exercise has shown that CBA can be a valuable tool for assessing the economic and social profitability of pest management. The results demonstrate that the loss of revenues in the no-management option is not sufficient to make pest management profitable for private forest owners in the shortterm. Conversely, a social profit is gained as pest management minimizes health risks for humans and avoids possible recreational losses

Preliminary characterization of an expanding flow of siloxane vapor MDM

The early experimental results on the characterization of expanding flows of siloxane vapor MDM (C8H24O2Si3, octamethyltrisiloxane) are presented. The measurements were performed on the Test Rig for Organic VApors (TROVA) at the CREA Laboratory of Politecnico di Milano. The TROVA test-rig was built in order to investigate the non-ideal compressible-fluid behavior of typical expanding flows occurring within organic Rankine cycles (ORC) turbine passages. The test rig implements a batch Rankine cycle where a planar converging-diverging nozzle replaces the turbine and represents a test section. Investigations related to both fields of non-ideal compressible-fluid dynamics fundamentals and turbomachinery are allowed. The nozzle can be operated with different working fluids and operating conditions aiming at measuring independently the pressure, the temperature and the velocity field and thus providing data to verify the thermo-fluid dynamic models adopted to predict the behavior of these flows. The limiting values of pressure and temperature are 50 bar and 400 °C respectively. The early measurements are performed along the nozzle axis, where an isentropic process is expected to occur. In particular, the results reported here refer to the nozzle operated in adapted conditions using the siloxane vapor MDM as working fluid in thermodynamic regions where mild to medium non-ideal compressible-fluid effects are present. Both total temperature and total pressure of the nozzle are measured upstream of the test section, while static pressure are measured along the nozzle axis. Schlieren visualizations are also carried out in order to complement the pressure measurement with information about the 2D density gradient field. The Laser Doppler Velocimetry technique is planned to be used in the future for velocity measurements. The measured flow field has also been interpreted by resorting to the quasi-one-dimensional theory and two dimensional CFD viscous calculation. In both cases state-of-the-art thermodynamic models were applied

Searching for biological feedstock material: 3D printing of wood particles from house borer and drywood termite frass

Frass (fine powdery refuse or fragile perforated wood produced by the activity of boring insects) of larvae of the European house borer (EHB) and of drywood termites was tested as a natural and novel feedstock for 3D-printing of wood-based materials. Small particles produced by the drywood termite Incisitermes marginipennis and the EHB Hylotrupes bajulus during feeding in construction timber, were used. Frass is a powdery material of particularly consistent quality that is essentially biologically processed wood mixed with debris of wood and faeces. The filigree-like particles flow easily permitting the build-up of wood-based structures in a layer wise fashion using the Binder Jetting printing process. The quality of powders produced by different insect species was compared along with the processing steps and properties of the printed parts. Drywood termite frass with a Hausner Ratio HR = 1.1 with ρBulk = 0.67 g/cm3 and ρTap = 0.74 g/cm3 was perfectly suited to deposition of uniformly packed layers in 3D printing. We suggest that a variety of naturally available feedstocks could be used in environmentally responsible approaches to scientific material sciences/additive manufacturing

Sintering of ceramics for clay in situ resource utilization on Mars

The sintering of wet processed Mars global simulant green bodies is explored. Green bodies shaped using slip casting, throwing on a potter’s wheel and additive manufacturing, including material extrusion (robocasting) and layerwise slurry deposition (LSD) are sintered in terrestrial and simulated Mars atmosphere. A sintering schedule is developed using hot stage microscopy, water absorption, sintering shrinkage and sintering mass loss. Sintered parts are characterized in respect to their density, porosity, phase composition, microstructure and mechanical properties. Densification behavior for different green bodies was generally similar, enabling the fabrication of larger green bodies (tiles, cups, bowls) and parts with fines details (test cubes and cuneiform tables) with low water absorption. Sintered LSD discs had a bending strength between terracotta and typical porcelains with 57.5/53.3 ​MPa in terrestrial/simulated Mars atmosphere. Clay ISRU for sintered ceramics can be considered an eminently favorable construction technology for soft and hard ISRU on Mars.DFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berli

Experimental evidence of non-ideal compressible effects in expanding flow of a high molecular complexity vapor

Supersonic expansions of a molecularly complex vapor occurring within the non-ideal thermodynamic region in the close proximity of liquid-vapor saturation curve were characterized experimentally for the first time. Results for two planar converging–diverging nozzles in the adapted regime and at different inlet conditions, from highly non-ideal to dilute gas state, are reported. Measurements of upstream total pressure and temperature are performed in the plenum ahead of the nozzle, while static pressure and supersonic Mach number measurements are carried out along the nozzle centerline. The investigated expansions are of interest for both fundamental research on non-ideal compressible flows and industrial applications, especially in the energy field. Siloxane MDM (octamethyltrisiloxane, C8H24O2Si3), a high molecular complexity organic compound, is used. Local pressure ratio P/ PTand Mach number M measurements display a dependence on the inlet total state, a typical non-ideal feature different from dilute gas conditions

Clay in situ resource utilization with Mars global simulant slurries for additive manufacturing and traditional shaping of unfired green bodies

The wet processing of regolith simulant for clay in situ resource utilization (ISRU) on Mars is presented. The two raw materials from the Mars global simulant family, one without clay (MGS-1) and one with clay - sodium montmorillonite smectite - (MGS-1C) were milled and mixed to produce a simulant with small particle size and reduced clay content (MGS-1C/8). All three simulants and the pure clay raw material were extensively characterized using XRF, synchrotron XRD, gas adsorption and gas pycnometry methods. In a straightforward processing approach, MGS-1C/8 was mixed with water and different dispersant approaches were investigated, all of which gave stable slurries. Particle size distribution, rheology, ion concentration, pH and electrical conductivity of these slurries were characterized. The slurry systems can easily be adapted to fit all typical ceramic shaping routes and here parts of varying complexity from slip casting, throwing on a potter's wheel and additive manufacturing, including material extrusion (robocasting) and binder jetting (powder bed 3D printing) were produced. The unique properties of the sodium montmorillonite clay, which is readily accessible in conjunction with magnesium sulfate on the Martian surface, acted as a natural nanosized binder and produced high strength green bodies (unfired ceramic body) with compressive strength from 3.3 to 7.5 MPa. The most elaborate additive manufacturing technique layerwise slurry deposition (LSD) produced water-resistant green bodies with a compressive strength of 30.8 ± 2.5 MPa by employing a polymeric binder, which is similar or higher than the strength of standard concrete. The unfired green bodies show sufficient strength to be used for remote habitat building on Mars using additive manufacturing without humans being present