1,721,205 research outputs found
Modello dell’autotrasformatore per lo studio dei transitori elettromagnetici
Full text linkQuesta tesi si concentra sullo sviluppo di un modello black box per un autotrasformatore trifase da 250 MVA, con specifiche di tensione 400/155±10 kV, impiegato nella rete di trasmissione elettrica italiana. L’obiettivo principale è ottenere un modello in grado di replicare con precisione il comportamento transitorio dell’autotrasformatore in risposta a diverse sollecitazioni elettriche, come sovratensioni, cortocircuiti o commutazioni. Questo modello black box non richiede la conoscenza dei parametri fisici o geometrici dell’autotrasformatore, ma si basa unicamente sulla misura della sua risposta in frequenza. Per acquisire le informazioni necessarie, è stata eseguita una misura della risposta in frequenza dell’autotrasformatore nel campo di frequenza compreso tra 20 Hz e 2 MHz, utilizzando la tecnica della Frequency Response Analysis (FRA). La curva misurata è stata approssimata utilizzando una funzione razionale tramite il metodo del Vector Fitting (VF), un algoritmo iterativo che minimizza l’errore quadratico medio tra i dati misurati e la funzione approssimante. È stata poi verificata la passività della funzione razionale per garantire la stabilità e la causalità del modello. Infine, la funzione razionale è stata trasformata nel dominio del tempo mediante la trasformata inversa di Laplace, ottenendo un modello black box sotto forma di equazioni differenziali lineari. Il modello è stato validato attraverso simulazioni nel dominio del tempo, dimostrando una buona corrispondenza con i risultati. Implementato in un software di analisi dei transitori elettromagnetici (EMTP), il modello è stato applicato allo studio di una rete a 380 kV con un generatore sincrono, mostrando una buona aderenza sia per le condizioni stazionarie che per quelle transitorie. Il modello black box proposto offre numerosi vantaggi rispetto ai modelli tradizionali, tra cui facilità di acquisizione, flessibilità, accuratezza e universalità. Può essere utilizzato per lo studio delle sovratensioni causate da fulmini, manovre o risonanze nella rete elettrica, e per il monitoraggio e la diagnostica dell’autotrasformatore
RESTING CYSTS FROM COASTAL MARINE PLANKTON
Full text linkCoastal plankton show fluctuations in abundance and species composition. Resting stage (cyst) production is a common strategy adopted by hundreds of plankton species to ensure reproduction and to avoid adverse conditions. During the resting period, these species are normally absent from the water column, and cysts produced in the plankton accumulate in the sediment where they wait for the return of suitable conditions. A portion of the cyst bank does not hatch, instead undergoing a dormancy that may extend for decades. Confined coastal areas accumulate cysts in sediment due to one or more possibilities, including reduced water movement/hydrodynamics, high population density, abundance of cyst-producing species, and the absence or scarcity of possible cyst consumers in the benthos. The pelagic-benthic nexus, which affects both the sediment and the water column (and possibly sea ice) is still poorly understood. In fact, the presence of cysts in the life cycle of organisms is likely to have considerable consequences for the ecology of coastal plankton, as well as the evolution and biogeography of species. This review aims to depict the presence (and even abundance) of resting stages in marine environments and their impact on ecosystem functioning. The review starts with a description of encysted resting stages in all marine planktonic taxa, listing a total of 501 species with known cysts, and methods and tools for their collection and study. The physiology and timing of the rest period is then described for various taxa, followed by a discussion of the evolutionary implications of resting. The presence of encysted stages in different realms and phyla of plankton suggests an ancient origin and a successive diversification of morphologies that, today, roughly characterise each taxa. Ecological and biogeographical implications stem from this general framework and support the hypothesis of seasonal occurrences of planktonic life in ecosystems where productivity is suspended for a long time (e.g. in polar seas). The potential to suspend or resume life has implications for human activities, such as the risk of translocations through ship ballast water and contamination of water and seafood with toxins but also the benefit of cysts for the production of aquaculture feed. The review concludes with perspectives on present knowledge and outstanding questions to address in future studies
RegExpBlasting (REB), a Regular Expression Blasting algorithm based on multiply aligned sequences
No full textBackground: One of the most frequent uses of bioinformatics tools
concerns functional characterization of a newly produced nucleotide
sequence (a query sequence) by applying Blast or FASTA against a set of
sequences (the subject sequences).
However, in some specific contexts, it is useful to compare the query
sequence against a cluster such as a MultiAlignment (MA). We present
here the RegExpBlasting (REB) algorithm, which compares an unclassified
sequence with a dataset of patterns defined by application of Regular
Expression rules to a given-as-input MA datasets.
The REB algorithm workflow consists in
i. the definition of a dataset of multialignments
ii. the association of each MA to a pattern, defined by application of
regular expression rules;
iii. automatic characterization of a submitted biosequence according to
the function of the sequences described by the pattern best matching the
query sequence.
Results: An application of this algorithm is used in the "characterize
your sequence" tool available in the PPNEMA resource. PPNEMA is a
resource of Ribosomal Cistron sequences from various species, grouped
according to nematode genera. It allows the retrieval of plant nematode
multialigned sequences or the classification of new nematode rDNA
sequences by applying REB. The same algorithm also supports automatic
updating of the PPNEMA database. The present paper gives examples of the
use of REB within PPNEMA.
Conclusion: The use of REB in PPNEMA updating, the PPNEMA "characterize
your sequence" option clearly demonstrates the power of the method.
Using REB can also rapidly solve any other bioinformatics problem, where
the addition of a new sequence to a pre-existing cluster is required.
The statistical tests carried out here show the powerful flexibility of
the method
A perspective review on the bonding mechanisms in cold gas dynamic spray
No full textThe Cold Gas Dynamic Spray technology, generally referred as Cold Spray, is a relatively new additive manufacturing technique able to produce fully dense coatings through the deposition of particles on a substrate. Fine powders are accelerated to high velocity and projected onto a substrate, upon impact with the target surface, conversion of kinetic energy to plastic deformation occurs and the solid particles deform and bond together. During the cold spray deposition process, the particles remain in a solid state during the deposition, resulting in high-quality coatings with low residual stresses and oxide inclusions. The relative lower process temperatures allow the cold spray to manufacture coatings on high temperature-sensitive materials. It could also be a valid method for deposition of a wide variety of materials, from metallic alloys up to ceramics and composites. Depending on the materials employed as substrate and coating, different bonding mechanisms can occur during the deposition. The present review aims to summarise the main bonding theories proposed up to now for the cold spray, focusing on both the particle deformation behaviour during the contact with the surface and the interfacial bonding mechanisms. The available theories for different substrate/coating configurations will be discussed and compared. The effects of deposition parameters, the substrate’s surface and microstructure of feedstock powders on the bonding mechanism will also be discussed
Finite element modeling of superplastic forming of friction stir processed AZ31B mg alloy
No full textSuperplastic forming (SPF) is considered to be a near net shape manufacturing technique, mainly adopted to realize aircraft and automotive parts, which requires relatively high tooling and assembly costs. Furthermore the tuning of the process is a non trivial operation since very limited reliable models have been developed to predict the complex geometries obtained through SPF. In such context several researches, based on finite element method (FEM,) have been conducted on the numerical optimization of conventional SPF processes. Friction Stir Processing (FSP) can be used combined with conventional SPF to enhance the superplastic material behavior by means of grain refinement treatment locally performed. From this point of view very few models have been developed to simulate the different superplastic behavior distinguishing the materials after the application of FSP. In this work free bulge forming tests of AZ31B Mg alloy was experimentally performed by means of blow forming laboratory-scale equipment as well as FEM analysis were conducted to simulate the SPF in two different cases: unprocessed and friction stir processed (FSProcessed) condition. The most relevant parameters of the constitutive numerical model were optimized by numerical-experimental comparison. More specifically material strength factor (K) and strain rate sensitivity index (m) were considered during the parametric optimization. Strain and thickness distributions were compared to the experimental measurements in order to individuate the optimized constitutive equations governing the superplastic behavior in both case studies
Museums on-chain? A designerly contribution in the development of blockchain-based digital strategies in cultural institutions
Full text linkBlockchain technologies have been referred to as potential drivers for paradigm shifts in the arts and cultural sector. Their multiple applications in the cultural and creative industries have recently started to be discussed by scholars, mainly coming from social and computer science disciplines. From crypto collectibles for archiving and documentation, to rights management and digital protection, fundraising and decentralization purposes: the potential use cases of blockchain technologies are varied, so as are varied the actors in the cultural and creative ecosystems that have started experimenting with these disruptive technologies. Nevertheless, despite the turmoil experienced from the practitioners’ side, cultural institutions remain largely sceptical about the expected benefit. Museums refrain from engaging with decentralized technologies like blockchain due to their perception of the numerous risks involved, as well as to the inevasible barriers to entry. The present paper relies on the hypothesis that design knowledge, methods, and tools may foster the envisioning of valuable applications of blockchain technologies within cultural institutions, and museums. It includes a systematic review of blockchain technologies use cases in cultural institutions, and the preliminary results from a set of semi-structured interviews to practitioners active in the implementation of blockchain in cultural institutions. To discuss the results, the work aims to reckon on design knowledge to stimulate reflection on alternative, and future-oriented ways of experiencing culture and cultural assets, providing museums and their stakeholders with a fulfilling cultural experience and with novel revenue sources through blockchain
The effect of manufacturing defects on the high-cycle fatigue of electron-beam-welded Ti-6Al-4V titanium alloy: experimental and numerical analysis
No full textPurpose
Electron-beam welding has been widely used in industry to join different titanium alloys (Ti-6Al-4V) components. During welding production defects, such as porosity, lack of penetration or thinning are often observed. High-cycle fatigue (HCF) tests have been performed on welded specimens to understand the effect of weld defects on fatigue capabilities. The fatigue life of different types of “defective” welds has been compared against a non-welded reference specimen.
Design/methodology/approach
The results of the experimental campaign have been correlated with finite elements models.
Findings
It is concluded the geometry produced by the weld process, e.g. toe radius and under-bead shape, and the related stress raisers play a relevant role on fatigue capabilities of welds. This conclusion is valid only for a Ti-6Al-4V T-joint weld and only for flaw initiation. Knock down in materials properties has not been considered.
Originality/value
There is a lack of HCF fatigue data for welds of this geometry and material in the open literature. The paper is of relevance for industrial application and practical interest, although a lot more validation tests are required to draw a final conclusion
resting vs active stages in plankton dynamics
No full textare reported the first results of a interdisciplinary and integrated study to understand the plankton dynamics in a confined basin (mar piccolo of Taranto). Cyst production rate, Cyst accumulation, Cyst germination rate, Plankton abundance and composition, and Cyst abundance and composition, have been alltogether considere
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