Technical optimization of a long span beam made of glulam elements

LAUREA MAGISTRALELe costruzioni in legno stanno diventando sempre più comuni in questi anni, principalmente per l’agevole prefabbricazione e il materiale sostenibile e poco costoso. Gli studi di ottimizzazione sviluppati in passato stanno ora iniziando ad essere applicati anche a questo nuovo ambito. Moelven, un’azienda svedese leader nella produzione di strutture in lamellare, è interessata a migliorare la prestazione di una trave su grande luce usata per coperture industriali. L’obiettivo principale è la minimizzazione del volume di legname necessario a sostenere i carichi assegnati; gli altri vincoli del problema sono chiaramente altrettanto definiti. La configurazione ottimale degli elementi è stata ricercata attraverso analisi teoriche di reticolari che seguono le direzioni principali di sforzo. Gli aspetti positivi accademici emersi hanno fornito le linee guida per sviluppare nuove soluzioni tecniche, dove l’efficienza meccanica interagisce con le reali difficoltà realizzative. Le peculiarità del materiale e del sistema produttivo svedese sono state considerate. I confronti finali con la proposta originaria concludono il lavoro, suggerendo i miglioramenti ottenibili.Timber constructions are becoming more and more common in these years, mostly due to the easy prefabrication and the cheap, sustainable material. The optimization studies developed formerly are now starting to be applied also to this new field. Moelven, a swedish company leader in the production of glulam structures, is interested in improving the performance of a long spam beam used for industrial ceilings. The main goal is the minimization of the volume of wood required to carry the assigned loads; the other boundaries of the problem are of course also defined. The optimal arrangement of the elements has been searched through theoretical analyses of trusses which follow the principal directions of stress. The positive academical aspects arised have provided the guidelines to develop new technical solutions, where the mechanical efficiency interacts with the real manufacturing issues. The peculiarities of the material and of the swedish productive system have been dealt. Final comparisons with the original proposal conclude the work, suggesting the improvements achievable

An adaptive high-order isogeometric discontinuous Galerkin method for the Reynolds-averaged Navier-Stokes equations with general equations of state

Questa tesi presenta una discretizzazione Galerkin discontinua per le equazioni di Navier-Stokes mediate alla Reynolds (RANS), basata sull'analisi isogeometrica con NURBS, applicata sia a regimi di gas ideale che reale. L'uso delle NURBS consente di risolvere le equazioni direttamente sulla geometria esatta, come definita in un ambiente di progettazione assistita al computer (CAD), senza essere influenzati dall'accuratezza della discretizzazione geometrica, ovvero dal numero di elementi della mesh. Questo approccio è integrato con un algoritmo di adattazione anisotropa in h, che permette di raffinare una mesh inizialmente grossolana in base all'accuratezza del campo di soluzione, valutata secondo diversi criteri di raffinamento. Grazie alle proprietà delle NURBS, la suddivisione della mesh può essere implementata direttamente, senza necessità di ulteriori manipolazioni, poiché la geometria è sempre esattamente preservata. Le equazioni RANS sono accoppiate con un modello di turbolenza Spalart-Allmaras modificato, e le capacità predittive del solutore sono migliorate grazie all'implementazione di equazioni di stato cubiche e multiparametriche, per considerare le caratteristiche dei flussi non ideali. Il solutore è stato validato con successo su una serie di casi test di riferimento che includono regimi non viscosi e turbolenti, subsonici e supersonici. L'algoritmo di adattazione in h viene descritto in dettaglio, confrontando diversi criteri di raffinamento e analizzando l'impatto della raffinazione anisotropa sull'efficienza complessiva. Questo lavoro esplora inoltre il potenziale dell'analisi isogeometrica nell'ottimizzazione di forma per flussi turbolenti, grazie alla possibilità di modificare direttamente la geometria agendo sulla definizione NURBS anziché sui nodi della mesh. Un approccio di programmazione quadratica sequenziale è utilizzato per risolvere problemi di ottimizzazione con vincoli di uguaglianza. Viene eseguita un'ottimizzazione basata sul gradiente, mostrando risultati promettenti che evidenziano i vantaggi di formulare il problema di ottimizzazione rispetto alla posizione dei punti di controllo NURBS.This thesis presents a high-order discontinuous Galerkin discretization for the Reynolds-averaged Navier-Stokes (RANS) equations within a NURBS-based isogeometric analysis framework for both the ideal and real gas regime. The use of NURBS allows to solve the equations on the exact geometry, as defined in a computer-aided design environment, which is not influenced by the accuracy of the geometry discretization, i.e., by the number of mesh elements. This approach is coupled with an anisotropic h-refinement algorithm, which allows to refine an initial coarse mesh according to the accuracy of the solution field, evaluated with different refinement criteria. NURBS properties enable a straightforward implementation of the mesh subdivision without the need of further manipulations since the geometry is always exactly preserved. The RANS equations are coupled with a modified Spalart-Allmaras turbulence model, and the prediction capabilities of the solver are enhanced by implementing a cubic and multiparameter equations of state to account for nonideal flow characteristics. The solver is successfully validated over a series of benchmark test cases ranging from inviscid to turbulent, from subsonic to supersonic regimes. The implemented h-refinement procedure is detailed, comparing different refinement criteria, and investigating the impact of the anisotropic refinement on the overall efficiency. This work also investigates the potential of isogeometric analysis in shape optimization for turbulent flows, since a direct morphing of the geometry is allowed by acting directly on the NURBS definition rather than on the mesh nodes. A sequential quadratic programming approach is used to solve the equality-constrained optimization problem. A gradient-based optimization is performed, showing promising results that put in evidence the advantages of solving an optimization problem with respect to the position of NURBS control points

Characterization of the capping layer of selenium nanoparticles synthesized by environmental bacterial strains and new hypothesis on selenium nanoparticles transport in Bacillus mycoides SeITE01

Selenium nanoparticles (SeNPs) are 10 to 400nm spheres composed of zero-valent selenium. SeNPs can be synthesized either chemically or biologically by microorganisms, plant extracts or enzymes. Biogenic SeNPs display a capping layer of organic molecules, which confer unique characteristics to such SeNPs, e.g. a major stability over time and a more efficient antimicrobial activity. Composition and role of the capping layer are mostly unknown and currently under investigation. In this study, environmental strains Bacillus mycoides SeITE01, Stenotrophomonas maltophilia SeITE02, Achromobacter sp. R2A, Ensifer sp. R2D and Lysinibacillus sp. R1E are considered, which are able to biosynthesize SeNPs. In the first section, SeNPs from the five bacteria are analyzed: microplate colorimetric assays are performed in order to quantify total carbohydrates, protein and lipids contents of such SeNPs capping layers. Moreover, SeNPs are treated with different protocols to remove part of the organic layer. Effect of such treatments on capping composition and SeNPs stability are studied and compared for all the five strains. In the second section, SeNPs produced by B. mycoides SeITE01 are analyzed from a proteomic point of view: biogenic SeNPs capping layer proteins are identified. Chemical SeNPs exposed to a SeITE01 cell free extract are analyzed as well. Identified proteins are compared in order to establish which proteins bind specifically biogenic SeNPs and are more probably involved in SeNPs formation. Finally, a model for SeNPs transport through SeITE01 cell wall is formulated, based on proteomic evidence. Native proteins activity assay and microscopy analysis are performed, in order to confirm the new model. In conclusion, studying the organic capping layer of biogenic SeNPs from different strains is of paramount importance to understand the effect of such molecules on SeNPs characteristics and formulate hypotheses on biosynthesis mechanism. SeITE01, SeITE02, R2A, R2D and R1E biosynthesized SeNPs show a different ratio of carbohydrates, proteins and lipids components of the capping layer and differently respond to treatments. Particularly, Gram-negative strains (SeITE02, R2A, R2D) show similar composition and respond to treatments in a similar fashion, while Gram-positive strains (SeITE01, R1E) show more variability. For SeITE01, proteomic and microscopy analyses led to a new model formulation for SeNPs transport outside the cell. Together with previous studies, this new hypothesis can contribute to a more complete vision of SeNPs synthesis in this aerobic strain

Predatory ability of generalist predators on eggs, young nymphs and adults of the invasive Halyomorpha halys in southern Europe

Halyomorpha halys (Stål, 1855) is an invasive pest causing serious damage to agricultural crops in Europe and the USA. Very little is known about H. halys predators in Europe. This survey evaluated the potential of generalist predators/omnivorous species by means of predation bioassays in tri-dimensional arenas, where the predator had to locate H. halys prey items on the leaves of a bean plant. Eleven species of different taxa were tested and the prey items consisted in fresh eggmasses, 1st and 2nd instar nymphs. One species was also tested against adults. Some predators were species commercially available as biocontrol agents against plant pests, other predators were wild, captured in habitats shared with H. halys. All tested specimens were starved 24 h before starting the experiment. The survivorship of control prey items in predator-excluding cages was compared to that of predator treatment groups to determine the effect of predator presence. According to the results, the generalist species showed a quite low acceptance of H. halys prey items, since only two species caused 80% mortality on at least one item (Eupholidoptera chabrieri and Rhynocoris iracundus) and mortality due the other species never exceed 60%. Among commercially available species only Adalia bipunctata adults and Chrysoperla carnea larvae were effective, predating the eggs and 1st instar nymphs, respectively. Among the field collected specimens, the orthopteran E. chabrieri and the predatory hemipterans R. iracundus, Nagusta goedelii and Himacerus mirmicoides showed efficacy against 1st instar nymphs, E. chabrieri and R. iracundus showed efficacy against 2nd instar nymphs, whereas only E. chabrieri and N. goedelii predated the eggs. R. iracundus was also tested on the adults and successfully predated them. By identifying some of the species that can exploit H. halys as a suitable prey in southern Europe, the present investigation provides an important contribution for conservation biological control of this pest

Biomolecular composition of capping layer and stability of biogenic selenium nanoparticles synthesized by five bacterial species

Biogenic metal/metalloid nanoparticles of microbial origin retain a functional biomolecular capping layer that confers structural stability. Little is known about the composition of such capping material. In this study, selenium nanoparticles (SeNPs) synthesized by five different bacterial strains underwent comparative analysis with newly proposed protocols for quantifying the concentration of carbohydrates, proteins and lipids present in capping layers. SeNPs were therefore treated with two different detergents to remove portions of the surrounding caps in order to assess the resulting effects. Capping material quantification was carried out along with the measure of parameters such as hydrodynamic diameter, polydispersity and surface charge. SeNPs from the five strains showed differences in their distinct biomolecule ratios. On the other hand, structural changes in the nanoparticles induced by detergents did not correlate with the amounts of capping matrix removed. Thus, the present investigation suggests a hypothesis to describe capping layer composition of the bacterial SeNPs: some biomolecules are bound more strongly than others to the core metalloid matrix, so that the diverse capping layer components differentially contribute to the overall structural characteristics of the nanoparticles. Furthermore, the application of the approach here in combining quantification of cap-associated biomolecules with the measurement of structural integrity-related parameters can give the biogenic nanomaterial field useful information to construct a data bank on biogenically synthesized nanostructures

Avalanche amplification of a single exciton in a semiconductor nanowire

Interfacing single photons and electrons is a crucial ingredient for sharing quantum information between remote solid-state qubits. Semiconductor nanowires offer the unique possibility to combine optical quantum dots with avalanche photodiodes, thus enabling the conversion of an incoming single photon into a macroscopic current for efficient electrical detection. Currently, millions of excitation events are required to perform electrical read-out of an exciton qubit state. Here we demonstrate multiplication of carriers from only a single exciton generated in a quantum dot after tunneling into a nanowire avalanche photodiode. Due to the large amplification of both electrons and holes (> 10^4), we reduce by four orders of magnitude the number of excitation events required to electrically detect a single exciton generated in a quantum dot. This work represents a significant step towards single-shot electrical read-out and offers a new functionality for on-chip quantum information circuits