246 research outputs found
Dyck Paths Enumerated by the Q-bonacci Numbers
No full textWe consider Dyck paths having height at most two with some constraints on the number of consecutive valleys at height one which must be followed by a suitable number of valleys at height zero. We prove that they are enumerated by so-called Q-bonacci numbers (recently introduced by Kirgizov) which generalize the classical q-bonacci numbers in the case where q is a positive rational.In Proceedings GASCom 2024, arXiv:2406.1458
Automatizzazione di un'accurata descrizione delle funzioni di risposta nei sistemi a bassa dimensionalità tramite teoria delle perturbazioni dei sistemi a molti corpi
No full textNella scienza dei materiali, la combinazione di simulazioni teoriche con tecniche High-throughput(HT) sta guadagnando maggiore attenzione, in quanto può accelerare la ricerca e la scoperta di nuovi materiali con le proprietà desiderate. Nell'ultimo decennio, i metodi HT sono stati applicati principalmente alla density functional theory (DFT) con grande successo. Tuttavia, la DFT manca di accuratezza quando si tratta di eccitazioni e spettroscopie, come ad esempio nella previsione delle proprietà delle quasiparticelle (esperimenti ARPES) o degli spettri di assorbimento ed electron energy loss(EELS), dove è necessaria una descrizione accurata degli effetti eccitonici.
In questa tesi vogliamo combinare la potenza dello screening HT con l'accuratezza della many-body-perturbation-theory (MBPT) per studiare le proprietà elettroniche e ottiche di sistemi a bassa dimensionalità. In particolare, adottiamo l'approssimazione GW per studiare la struttura elettronica delle bande, e l'equazione di Bethe-Salpeter per calcolare gli spettri ottici.
La prima parte del lavoro è stata dedicata allo sviluppo di una serie di workflow per eseguire studi di convergenza automatizzati dei principali parametri computazionali che entrano nei calcoli MBPT. Essendo i test di convergenza in MBPT di fondamentale importanza per ottenere risultati significativi, rappresentando anche la parte che richiede più tempo umano nei calcoli GW/BSE, questo passaggio è stato essenziale nello sforzo di unire MBPT con gli schemi HT. I workflow sopra menzionati sono stati prima validati su sistemi ben noti come hBN o TiO2, e poi applicati per studiare gli effetti eccitonici in C3N, un sistema 2D recentemente realizzato.
Il C3N è un semiconduttore a gap indiretto 2D emergente con interessanti proprietà meccaniche, termiche ed elettroniche. In questa tesi abbiamo eseguito una descrizione completa delle proprietà elettroniche e dielettriche di C3N, concentrandoci sulla struttura a bande eccitonica. Come per altri materiali 2D, troviamo una dispersione eccitonica lineare non analitica prossima a q=0, che però mostra una convessità verso il basso legata alla natura indiretta del band gap.
Successivamente, questi workflow sono stati utilizzati per studiare l'accuratezza della Godby-Needs plasmon-pole approximation (GN-PPA) implementata nel codice Yambo sul set GW100, un set di 100 molecole utilizzate per confrontare i principali codici MBPT mediante G0W0. Per tutte le molecole abbiamo calcolato il potenziale di ionizzazione (IP) e l'affinità elettronica (EA) e confrontato i risultati con gli altri codici MBPT con i dati GW100 disponibili. I risultati di questo studio ci hanno permesso di concludere che lo schema GN-PPA supera altre approssimazioni comunemente usate, come il modello Hybertsen-Louie, e fornisce risultati in un accordo ragionevole con implementazione più sofisticate del GW come full-frequency e contour-deformation. Recentemente, il gruppo EPFL-THEOS (Lausanne, CH), guidato dal Prof. Nicola Marzari, ha eseguito una HT computational exfoliation di composti 3D sperimentalmente conosciuti, scoprendo più di 1800 materiali 2D esfoliabili.
La parte finale di questa tesi è dedicata allo studio delle proprietà elettroniche e ottiche di un sottoinsieme di questi sistemi, al fine di identificare possibilmente materiali candidati che possano realizzare la tanto ricercata fase di isolante eccitonico (EI). La fase EI è una fase correlata della materia, proposta più di 50 anni fa da L. Keldysh, W. Kohn, in cui lo stato fondamentale di un sistema, al di sotto di una temperatura critica, è formato da un condensato di eccitoni di Bose. Per fare previsioni sulle possibili instabilità eccitoniche nello stato fondamentale, sono indispensabili una stima molto accurata del band gap elettronico e delle energie di legame eccitoniche, e workflow per automatizzare calcoli MBPT costituiscono uno strumento estremamente efficace per questa ricerca.In materials science, the combination of theoretical simulations with high-throughput (HT) techniques is gaining larger attention, as it can speed up the search and discovery of novel materials expressing desired properties. In the last decade, HT methods have been mostly applied to density functional theory (DFT) demonstrating great success. Nevertheless, DFT lacks of predictive accuracy when dealing with excitations and spectroscopies, as for instance in the prediction of quasiparticle properties (ARPES experiments), or absorption and electron energy loss spectra (EELS) where an accurate description of the excitonic effects is needed.
In this Thesis we want to combine the power of HT screening with the accuracy of many-body perturbation theory (MBPT) to study the electronic and optical properties of low-dimensional systems. In particular, we adopt the GW approximation to study the electronic band structure and the Bethe-Salpeter equation to compute optical spectra.
The first part of the work has been devoted to developing a set of workflows to perform automated convergence studies of the main computational parameters entering in MBPT calculations. Being convergence tests in MBPT of paramount importance to obtain meaningful results, also representing the most human time-consuming part of a GW/BSE calculation, this step has been essential in the effort of joining MBPT with HT schemes. The above mentioned workflow was first validated on well-known systems like hBN or TiO2, and then applied to study excitonic effects in C3N, a recently synthesized 2D system.
Monolayer C3N is an emerging 2D indirect gap semiconductor with interesting mechanical, thermal, and electronic properties. In this thesis we have performed a complete description of C3N electronic and dielectric properties, focusing on the momentum-resolved excitonic band structure. As for other 2D materials, we find a linear non-analytic excitonic dispersion close to q=0, which however shows a downward convexity related to the indirect nature of the band gap.
Next, these workflows were used to study the accuracy of the Godby-Needs plasmon-pole approximation (GN-PPA) implemented in the Yambo code on the GW100 set, a set of 100 molecules used to benchmark the main MBPT codes by means of G0W0 approximation. For all the molecules we computed converged ionization potential (IP) and electron affinity (EA), and compared the results with the other MBPT codes with available GW100 data. The results of this study allowed us to conclude that the GN-PPA scheme outperforms other commonly used approximations such as the Hybertsen-Louie plasmon pole model, and provides results in a reasonable agreement with more sophisticated implementation of GW as the full-frequency and contour deformation methods.
Recently, the EPFL-THEOS (Lausanne, CH) group, led by Prof. Nicola Marzari, performed a HT computational exfoliation of experimentally known 3D compounds, discovering more than 1800 exfoliable layered materials.
The final part of this Thesis is dedicated to the investigation of the electronic and optical properties of a subset of these recently discovered 2D systems, in order to possibly identify candidate materials that can realize the long sought excitonic insulator (EI) phase.The EI phase is a correlated phase of matter, proposed more than 50 years ago by L. Keldysh, W. Kohn, in which the ground state of a system, below a critical temperature, is formed by a Bose condensate of excitons. To make prediction on the possibile excitonic instabilities in the ground state, very accurate estimation of the electronic band gap and excitonic binding energies are indispensable and workflows capable of making automatic calculations based on MBPT constitute an extremely effective tool for this research
Spaghetti Enriched with Inulin: Effect of Polymerization Degree on Quality Traits and α-Amylase Inhibition
No full textInulin is considered a dietary fiber and represents a noteworthy ingredient for food biofortification due to its health effects and its neutral taste. The aim of the work was the evaluation of the quality of pasta produced using whole-meal flours of two ancient Sicilian landraces (Senatore Cappelli-CAP and Timilia—TIM) fortified with two types of inulin (long-chain topinambur inulin IT and low-chain chicory inulin IC), at two different levels of substitution (2 and 4%) to evaluate its possible effect on α-amylase inhibition. The color indices L* and a* were mainly influenced by cultivars, while IT improved the sensory attributes, mainly the elasticity sensation, and influenced less the other sensory attributes: adhesiveness, color, odor, taste, and Over Quality Score for both landraces. The cooking quality was linked mainly to the landrace used, due to the very different gluten matrix of CAP and TIM. IC and IT showed promising α-Amy inhibitory activity with comparable IC50 values of 0.45 ± 0.04 and 0.50 ± 0.06 mg/mL. The enrichment of spaghetti with inulin with an inhibitory effect on α-amylase determined the hypoglycemic properties of pasta, thus lowering the corresponding IC50 value
Hemp Flour Particle Size Affects the Quality and Nutritional Profile of the Enriched Functional Pasta
No full textThe rheological and chemical quality of pasta samples, which were obtained using the durum wheat semolina fortified with the hemp seed solid residue, after oil extraction, sieved at 530 mu m (Hemp 1) or 236 mu m (Hemp 2) at different percentages of substitution (5%, 7.5%, and 10%, were evaluated. The total polyphenolic content in hemp flour was quantified in the range of 6.38-6.35 mg GAE/g, and free radical scavenging was included in the range from 3.94-3.75 mmol TEAC/100 g in Hemp 1 and Hemp 2, respectively. The phenolic profiles determined by UHPLC-ESI/QTOF-MS showed that cannabisin C, hydroxycinnamic and protocatechuic acids were the most abundant phenolic compounds in both hemp flours. Among the amino acids, isoleucine, glutamine, tyrosine, proline, and lysine were the most abundant in raw materials and pasta samples. Although the hemp seeds were previously subjected to oil extraction, hemp flours retain about 8% of oil, and the fatty acids present in the largest amount were linoleic acid and alpha-linolenic acid. Characterization of the minerals showed that the concentration of macro and trace elements increased according to fortification percentage. Sensory evaluation and cooking quality indicated that the best performance in terms of process production and consumer acceptance was obtained using Hemp 2 at 7.5%. Hemp supplementation could be a potential option for producing high-quality, nutritionally rich, low-cost pasta with good color and functionality
Rheological and nutritional profile of spaghetti and bread fortified with hemp flours
No full textIn recent years, the demands of food consumers have changed considerably. Food today is not only intended to satisfy hunger and provide the necessary nutrients, but also to prevent food-related diseases and improve the physical and mental well-being of consumers.
Functional foods are formulated to contain healthy components, which when consumed daily as part of the diet, can have beneficial health effects.
Cereal-based products, especially pasta and bread, are well suited for adding nutrients. Both bread and pasta, traditionally produced using durum wheat flour, can be prepared also using "non-wheat flours" in variable percentages or by incorporating food by-products, capable of increasing their nutritional value [1].
Unfortunately, fortification often affects the quality of cereal-based products, in terms of texture, color, cooking quality and sensory properties. Therefore, one of the main challenges of the food industry is to increase the healthiness of foods without sacrificing sensory attributes.
In this study the rheological and chemical qualities of spaghetti and bread samples were evaluated, obtained by using a durum wheat cultivar, called "Ciclope", fortified with different percentages of hemp flour, called "Futura 75". The hemp flours, obtained after grinding the seeds and the subsequent separation of the oil, were sieved at 0.530 mm (Hemp -1) and 0.236 mm (Hemp -2)
Functional End-Use of Hemp Seed Waste: Technological, Qualitative, Nutritional, and Sensorial Characterization of Fortified Bread
No full textDue to its multipurpose usability, short production cycle, and low capital requirement in cultivation, hemp represents an excellent material applicable to the Sustainable Development Goals (SDGs) defined by the United Nations Organization as a strategy “to achieve a future better and more sustainable for all”. Hemp seeds represent the only edible part of Cannabis sativa and have a distinctly different nutritional composition from other representative foods such as rice and wheat (high protein content, low carbohydrate content, polyunsaturated fatty acids, dietary fiber, and gluten-free). Hemp seeds are mainly used for the production of oil; the waste obtained after extraction, reduced to a fine powder and rich in bioactive components, is added to durum wheat flour and used for the preparation of fortified bread. The aim of this study was to use varying percentages of hemp seed flour for bread production and determine the impact of fortification on texture, organoleptic characteristics, crumb color, changes in crumb texture, total polyphenols, the scavenging activity of free radicals, and amino acid content. The solid residue remaining after oil extraction from hemp seeds (generally discarded as waste or added to feed) was triturated and sieved to 0.530 mm (Hemp 1) or 0.236 mm (Hemp 2). Samples of fortified bread were obtained by replacing variable percentages of durum wheat semolina with the two hemp flours (5%, 7.5%, and 10%). The total phenolic content of the fortified bread was between 0.73 and 1.73 mg GAE/g, and the antiradical activity was between 1.17 and 3.18 mmol TEAC/100 g on the basis of the growing fortification. A comparison of Ciclope semolina bread with hemp flour-enriched bread showed a large increase in amino acid content in the fortified samples. In particular, bread enriched with 10% hemp flour 2 showed a higher content of glutamic acid, tyrosine, proline, and essential amino acids such as leucine and isoleucine compared to other samples with the same percentage of substitution. The amount of hemp seed flour influenced the color of the crumb by increasing the yellow index from 18.24 (100% Ciclope) to 21.33 (bread with 5% hemp flour 2). The results of the sensory analysis were very good, demonstrating the high acceptability of fortified breads at higher percentages
Seasonal screening of AChE, GSH and gonad histology in European sea bass Dicentrarchus labrax (L.) reared in three different fish farms
No full textThe aim of this work was to do a preliminary seasonal screening of ecotoxicological
biomarkers in European sea bass Dicentrarchus labrax in three different
fish farms, to know if the different location and typology can discriminate them.
A set of selected biomarkers of xenobiotic exposure, such as acetylcholinesterase
(AChE) activity, Glutathione (GSH) and gonad morphology were investigated
seasonally in male European sea bass D. labrax (L.) reared in three different
intensive farms: a land-based farm of cement tanks (T), an in-shore sea cages farm
(C1) and an off-shore sea cages farm (C2). The results showed that both location
and typology can discriminate AChE activity, GSH content and gonad
morphology. Further investigation is needed to propose these biomarkers in
the protocol of fish farm quality control
A biochemical study of the effects of tributyltin on unfertilized eggs, embryos and larvae of the sea squirt Ciona intestinalis
No full textWe have used unfertilized eggs, embryos and larvae of the sea squirt Ciona intestinalis (Ascidiacea, Urochordata) to study the effects of tributyltin (TBT) on acetylcholine esterase (AChE) activity. Our results showed an increase of AChE enzyme activity levels after TBT exposure in both unfertilized eggs and embryos. The effects of TBT were more pronounced during the gastrula stage, while no differences between exposed larvae and controls were observed. A mechanism of TBT action on enzyme activity during ascidian embryonic development and the possibility of employing AChE in C. intestinalis as a biomarker of TBT exposure are suggested and discussed
Screening of ecotoxicological, qualitative and reproductive variables in male European sea bass Dicentrarchus labrax (L.) reared in three different fish farms: Facility location and typology
No full textThe aim of this work was to do a preliminary seasonal screening of ecotoxicological biomarkers in European sea bass Dicentrarchus labrax in three different fish farms, to know if the different location and typology can discriminate them. A set of selected biomarkers of xenobiotic exposure, such as acetylcholinesterase (AChE) activity, Glutathione (GSH) and gonad morphology were investigated seasonally in male European sea bass D. labrax (L.) reared in three different intensive farms: a land-based farm of cement tanks (T), an in-shore sea cages farm (C1) and an off-shore sea cages farm (C2). The results showed that both location and typology can discriminate AChE activity, GSH content and gonad morphology. Further investigation is needed to propose these biomarkers in the protocol of fish farm quality control
Esterase activities in the bivalve molluscs Adamussium colbecki as biomarkers for pollution monitoring in the Antarctic marine environment: a preliminary field study
No full textMarine environments are continuously being threatened by a large number of xenobiotics from anthropogenic sources. Even in sparsely populated and relatively pristine areas, such as Antarctica, hazardous chemicals can pose a serious environmental problem. The main aims of the present study were to (1) validate and optimize an analytical technique utilizing a microtitre-plate photometer to ascertain background levels of esterase activities in the Antarctic bivalve Adamussium colbecki, (2) carry out in situ monitoring of esterase activities to assess any potential environmental impacts of the Italian Scientific Antarctic Base "Terra Nova Bay" on the surrounding marine area. Results showed the presence of organophosphorous-sensitive cholinesterase (ChE) and carboxylesterase (CbE) activities in the gills of A. colbecki and optimal assay conditions were comparable with those found for bivalve species from temperate areas. A higher sensitivity of ChE versus acetylthiocholine activity in A. colbecki to chlorpyrifos compared to species from temperate areas may also be inferred. The in situ study indicated no differences in the environmental quality of the three study sites located around the Italian Base. © 2004 Elsevier Ltd. All rights reserved
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