Senior Flute Recital: Catherine F. Cornman, Flute; Carol Giagnoni, Piano; May 16, 1971

Centennial East Recital HallMay 16, 19713:00 p.m

STUDIES ON THE OCCURRENCE OF THIOL RELATED AROMAS IN WINE

Gli aromi a funzione tiolica svolgono una funzione importante nella determinazione delle caratteristiche sensoriali di alcuni vini. In particolare, il 3-mercaptoesanolo, l\u2019acetato di 3-mercaptoesile ed il 4-mercapto-4-metilpentan-2-one, identificati inizialmente in vini derivanti da uve Sauvignon blanc, sono stati riscontrati anche in altre variet\ue0 suggerendo che essi possano contribuire all\u2019aroma di diversi vini. L\u2019elevato impatto olfattivo di tali molecole ne spiega l\u2019importanza nonostante esse siano presenti nei vini a concentrazioni estremamente basse (ng/L). Quest\u2019ultima caratteristica rappresenta la difficolt\ue0 maggiore alla loro identificazione e quantificazione. I tioli varietali sono presenti in mosti e uve come precursori non volatili. In particolare, coniugati del glutatione e della cisteina sono stati identificati come precursori. Nel corso del processo di vinificazione, l\u2019attivit\ue0 del lievito \ue8 alla base della liberazione di questi aromi. Le pratiche enologiche possono influenzare il contenuto in tali precursori nei mosti anche se non \ue8 stata identificata una diretta correlazione tra contenuto in precursori nei mosti e tioli liberi nei vini, suggerendo che vie sintetiche alternative ed interazioni pi\uf9 complesse siano responsabili della presenza di tali aromi nei vini. Gli scopi della ricerca sono stati la valutazione di nuovi approcci analitici volti ad evidenziare la presenza di aromi a funzione tiolica nei vini, indagini riguardanti possibili vie biosintetiche alternative e l\u2019effetto del ceppo di lievito sul contenuto in molecole responsabili della stabilit\ue0 degli aromi tiolici nei vini. L\u2019impiego di composti mercurati \ue8 il metodo pi\uf9 efficace ad oggi in uso per l\u2019analisi dei tioli volatili. L\u2019utilizzo di tali molecole rappresenta tuttavia un rischio per la salute e la sicurezza, inoltre le metodiche proposte sono estremamente complesse. Nuovi approcci analitici sono quindi stati valutati al fine di individuare una metodica pi\uf9 semplice e sicura. Nel corso di approcci gas cromatografici la reattivit\ue0 del gruppo tiolico verso addizioni nucleofile \ue8 stata utilizzata per la formazione di derivatizzati. Alcuni autori hanno proposto la derivatizzazione mediante pentafluorobenzil bromuro, solitamente correlata ad acquisizioni spettrometriche con ionizzazione chimica e selezione di ioni negativi. Si ottiene pertanto sensibilit\ue0 favrita da una minor frammentazione delle molecole ed una maggior selettivit\ue0 per elettrofili, qual \ue8 il fluoro. Tuttavia queste tecniche sono poco diffuse. Si \ue8 pertanto testata la possibilit\ue0 di utilizzare la ionizzazione ad impatto elettronico e selezione degli ioni positivi (pi\uf9 diffusa nei laboratori di ricerca enologica). La tecnica messa a punto ha permesso di individuare ioni caratteristici, nonostante una maggior frammentazione. La reazione di derivatizzazione \ue8 stata possibile in diversi solventi organici. La formazione dei prodotti di derivatizzazione \ue8 possibile in ambiente acquoso dal quale possono esser estratti selettivamente utilizzando diverse fasi stazionarie, grazie alle loro caratteristiche di idrofobicit\ue0, anche se l\u2019ambiente fortemente basico determina l\u2019idrolisi di gruppi esteri. L\u2019estrazione di tioli aromatici da soluzioni acquose mediante fasi solide \ue8 possibile. Ciononostante, la derivatizzazione applicata a molecole tioliche trattenute in fase solida od eluite mediante solvente organico non ha permesso l\u2019identificazione di aromi a funzione tiolica ad un livello sufficiente di sensibilit\ue0. Si \ue8 pertanto studiato l\u2019impiego di un estere alchinico come derivatizzante capace di addizione ai gruppi tiolici. Il prodotto di addizione tra etil propiolato e tioli volatili pu\uf2 essere identificato mediante tecniche di spettrometria di massa. La reazione, che avviene in ambiente acquoso, \ue8 favorita da condizioni basiche non cos\uec drastiche da condurre all\u2019drolisi di gruppi esteri. Il prodotto ottenuto da tale addizione nucleofila pu\uf2 esser selettivamente estratto da soluzioni acquose. Una metodica analitica innovativa basata su tale reazione ha dunque permesso l\u2019identificazione di tioli aromatici in vino a concentrazioni prossime alla loro soglia di percezione. La quantificazione di aromi tiolici in vino anche mediante metodiche di cromatografia liquida \ue8 possibile grazie all\u2019impiego di derivatizzanti con caratteristiche fluorescenti. L\u2019individuazione delle condizioni ottimali di derivatizzazione e di composti responsabili della perdita di tioli volatili hanno giocato un ruolo chiave nel successo di tale approccio analitico. L\u2019interazione tra ione bisolfito ed esenale \ue8 stata indagata nel corso della valutazione di vie biosintetiche alternative responsabili della presenza di 3-mercaptoesan-1-olo (3-MH) nei vini. La formazione di sulfonati stabili \ue8 strettamente correlata a specie la cui struttura \ue8 simile al 3-MH. Tali reazioni avvengono in ambiente acido, suggerendo un simile meccanismo anche nei mosti. La prima addizione dello ione bisolfito \ue8 al gruppo carbonilico dell\u2019aldeide insatura. Ciononostante il prodotto pi\uf9 stabile \ue8 rappresentato da un disulfonato che si \ue8 rivelato non essere un precursore dell\u2019aroma tiolico. La formazione di tale sulfonato \ue8 correlata ad un monosulfonato di struttura simile al 3-mercaptoesan-1-olo. La sintesi della specie pura permetter\ue0 di valutare se possa esserne considerato un precursore. L\u2019addizione nucleofila di tioli a chinoni \ue8 la maggior responsabile della perdita di tali aromi nei vini. La presenza di composti che riducano tali chinoni \ue8 strettamente correlata alla stabilit\ue0 degli aromi tiolici. Il glutatione, naturalmente presente nelle uve e nei vini, \ue8 in grado di svolgere tale funzione. Il contenuto di GSH nei vini \ue8 influenzato dalle operazioni di vinificazione. In particolare, sono stati testati diversi ceppi di lievito nel corso della fermentazione alcolica e si \ue8 verificato che la scelta del ceppo di lievito pu\uf2 influenzare il contenuto in tale tripeptide. Inoltre nel corso della fase sur lies non \ue8 stato riscontrata una variazione del contenuto totale di glutatione, ascrivendo il rilascio del tripeptide alle fasi di attivit\ue0 metabolica.Thiol related aromas play a key role in sensory profile of certain wines. In particular, 3-mercaptohexan-1-ol, 3-mercaptohexyl acetate and 4-mercapto-4-methypentan-2-one were firstly identified in Sauvignon blanc wines. Same molecules were then evaluated to contribute to several wine made from different grape varieties. The strong smelling properties of volatile thiols explain their importance, even if such molecules are present at extremely low concentration in wine (ng/L). This characteristic represents the main issue in their identification and quantification in wine. Aromatic thiols are present in grape and juice as non-volatile compounds. In particular, glutathione and cysteine conjugates were identified to be precursors of such smelling molecules. During vinification process, yeast activity is responsible for their release from the cysteinilated precursors. The amount of thiol precursor in juice is influenced by oenological practices. Despite this, no direct correlation between the level of precursors in juice and concentration of thiol in wine has been observed, thus suggesting that alternative biogenetic pathway and/or more complex interaction are responsible for occurrence of aromatic thiol in wine. The aims of this PhD were to evaluate new analytical approaches aimed to evaluate the occurrence of volatile thiols in wine, to study alternative biogenetic pathway leading to thiol realted aroma and to assess yeast strain effect on the amount in molecules responsible for thiol stability in wine. The employmet of organo-mercury compounds represents the most effective method for thiol quantification in wine. The use of mercury constitutes hazard for health and environmental safety. Furthermore, such methods are extremely time-consuming. New analytical approaches were evaluated with the aim to develop an easy-to-apply method. In gas chromatographic approaches, thiol group reactivity towards nucleophilic addition was used to make derivatised product. Pentafluorobenzyl bromide has been reported by several authors. This derivatising agent has been employed by means of negative ions chemical ionization mass spectrometry. Chemical ionization is responsible for low fragmentation and shares with the electron capture detection a selective and sensitive response to electrophilic atoms (halogens), as fluorine is. Despite this, such techniques are not widespread. In this study electron impact ionization in positive mode mass spectrometry was then evaluated. The developed method allowed to identify characteristic fragments even if high amount of fragmentation was present. Derivatisation reaction was possible in different organic solvents. Derivatisation of aromatic thiol can be carried out in aqueous media too. Thanks to their hydrophobicity, reaction products can be extracted by means of different sorbents. Despite this, the presence of alkali is required, thus leading to the hydrolysis of esters. Solid phase extraction of volatile thiol from aqueous media is possible. Despite this, in-sorbent derivatization process, as well as derivatisation of volatile thiol in organic solvent, did not allow to quantify thiol related aroma at concentration close to their perception threshold. The employment of an unsaturated alkene as derivatising agent was then studied. The key feature of ethyl propiolate employment in volatile thiols derivatization, is the thiol nucleophilic addition to ynonates. The derivatised product can be identified by MS technique. The reaction take place in aqueous media. Neutral or mild basic conditions are required to carry out the derivatization procedure, where no ester hydrolysis was showed. The employment of this new derivatising agent allowed the assessment of volatile thiols in wine at concentration close to their perception threshold. Thanks to the employment of fluorescent derivatising agent, quantification of volatile thiol in wine was demonstrated to be possible by means of liquid chromatographic approaches too. The key feature in this analytical approach was the optimization of derivatisation reaction and the individuation of chemical compounds responsible for volatile thiol loss. Interaction between trans-2-hexenal and bisulfte was studied in order to evaluate alternative biogenetic pathways leading to 3-mercaptohexan-1-ol (3-MH) in wine. Biogeneic pathway of stable sulfonates is stricktly related to species whose structure is similar to 3-MH. The addition occours in aqueous acidic media, thus suggesting similar pathway in grape juice. The initial addition of bisulfite to the unsaturated aldehyde is at the aldehydic function. Despite this, the most stable product is a disulfonate which was demonstrated it is not a putative precursor of volatile thiol in wine. The formation of such stable product is correlated to a mono-sulfonate whose structure is similar to 3-mercaptohexan-1-ol. Pure species synthesis will allow to evaluate if this compound can be regarded as a precursor of the volatile thiol in wine. Thiol nucleophilic addition to quinones is the major responsible for thiol related aroma loss in wine. The presence of compounds able to reduce such quinone is strictly correlated to thiol stability in wine. The tripeptide glutathione, naturally occurring in grape and wine, is responsible for this protective effect. Wine making technique can affect GSH content in wine. In particular, several yeast strains were tested during laboratory-scale alcoholic fermentation. As a result, yeast strain was evaluated to influence GSH content. Moreover, during aging on lees total glutathione content did not vary, thus production and liberation of this tripeptide is related to living cells

Numerical Investigation on mixture formation and combustion process of innovative piston bowl geometries in a swirl-supported light-duty diesel engine

In recent years, several innovative diesel combustion systems were developed and optimized in order to enhance the air and injected fuel mixing for engine e-ciency improvements and to mitigate the formation of fuel-rich regions for soot emissions reduction. With these aims, a three-dimensional computational fl uid dynamics (3D-CFD) numerical study was carried out in order to evaluate the impact of three di erent piston bowl geometries on a passenger car four-cylinder diesel engine, 1.6 liters. Once the numerical model was validated considering the baseline re-entrant bowl, two inno vative bowl geometries were defi ned: one based on the stepped-lip bowl; the other including a number of radial bumps equal to the nozzle holes number. Firstly, the rated power engine operating condition was investigated under nonreacting conditions to evaluate the piston bowl e ects on the in-cylinder mixing. Results highlight for both the innovative piston bowls better air utilization with respect to the re-entrant bowl: The stepped-lip bowl creates a dual toroidal vortex leading to a higher air/fuel mixing, while the radial-bumps bowl signifi cantly a ects the jet-To-jet interaction and promotes the recirculation of the fuel jet downstream to the bump, where the available oxygen enhances the mixing rate. After that, the combustion analysis was carried out for both rated power and partial-load engine operating conditions. Results confi rmed that thanks to the better air-fuel mixing, the combustion process can be improved thanks to the innovative bowl designs, both increasing the engine e-ciency at full-load condition and minimizing the engine-out soot emissions at partial-load operating point

Supraseasonal drought in an Alpine river: Effects on benthic primary production and diatom community

Over the last decades, the ongoing global climate change, combined with consequent increasing water demand for human needs, is causing recurrent droughts in previously perennial streams. These phenomena have been dramatically increasing their extent, with significant repercussions on the entire food web. Consequences of water scarcity are particularly remarkable in mountain streams, where the frequency of droughts is increasing at a rate that does not allow species to adapt. In the present research, we monitored benthic diatom communities within an intermittent Alpine river (Pellice River; North-Western Italy) during the three key phases of its hydrological cycle: i) stable flow ii) lentification iii) rewetting of the riverbed after a supraseasonal drought lasting five months. We tested the response of diatom communities in terms of compositional, structural and functional metrics (primary production, species composition, ecological guilds, life forms and eco-morphological groups) hypothesising both taxonomic and functional changes during the different steps of this hydrological cycle. Significant changes in benthic chlorophyll a occurred in the three hydrological phases. In particular, the relative proportion of the chlorophyll a of the three main autotrophic groups inhabiting the periphyton (namely diatoms, cyanobacteria and green algae) resulted as a reliable metric for the evaluation of the hydrological disturbance. Diatom chlorophyll a significantly decreased during both lentification and drought. The three phases were significantly characterized by different species and functional groups. During the stable flow the low profile (i.e., species of short stature, adapted to high current velocities and low nutrients concentrations) was the most representative guild and Achnanthidium pyrenaicum was the most abundant species; this phase was also characterized by the presence of stalked taxa. We observed a significant decrease of high profile species (i.e., species of tall stature, adapted to high nutrients concentrations and low current velocities) during the lentification phase, which was characterized by taxa belonging to the genera Navicula, Nitzschia and Ulnaria. During the rewetting, small and medium sized high profile diatoms as well as motile ones (i.e., fast moving species) characterized the assemblages. Our results showed that the complete recovery of diatom communities took at least 70 days after water return. The rapid and widespread extension of droughts in the Alpine area will have severe consequences on the river biota, also favouring the spread of invasive taxa. For this reason, outlining patterns of diatom response to droughts and detecting reliable metrics for the evaluation of this specific impact is very urgent and important

Numerical Assessment on the Influence of Engine Calibration Parameters on Innovative Piston Bowls Designed for Light-Duty Diesel Engines

The optimization of the piston bowl design has been shown to have a great potential for air–fuel mixing improvement, leading to significant fuel consumption and pollutant emissions reductions for diesel engines. With this aim, a conventional re-entrant bowl for a 1.6 L light-duty diesel engine was compared with two innovative piston designs: a stepped-lip bowl and a radial-bumps bowl. The potential benefits of these innovative bowls were assessed through 3D-CFD simulations, featuring a calibrated spray model and detailed chemistry. To analyse the impact of these innovative designs, two different engine operating conditions were scrutinized, corresponding to the rated power and a partial load, respectively. Under the rated power engine operating condition, a start of injection sensitivity was then carried out to assess the optimal spray–wall interaction. Results highlighted that, thanks to optimal injection phasing, faster mixing-controlled combustion could be reached with both the innovative designs. Moreover, the requirements in terms of swirl were also investigated, and a higher swirl ratio was found to be necessary to improve the mixing process, especially for the radial-bumps design. Finally, at part-load operating conditions, different exhaust gas recirculation (EGR) rates were analysed for two injection pressure levels. The stepped-lip and radial-bumps bowls highlighted reduced indicated specific fuel consumption (ISFC) and soot emissions values over different rail pressure levels, guaranteeing NOx control thanks to the higher EGR tolerance compared with the re-entrant bowl. The results suggested the great potential of the investigated innovative bowls for improving efficiency and reducing emissions, thus paving the way for further possible optimization through the combination of these designs

Numerical Assessment of Additive Manufacturing-Enabled Innovative Piston Bowl Design for a Light-Duty Diesel Engine Achieving Ultra-Low Engine-Out Soot Emissions

The design of diesel engine piston bowls plays a fundamental role in the optimization of the combustion process, to achieve ultra-low soot emissions. With this aim, an innovative piston bowl design for a 1.6-liter light-duty diesel engine was developed through a steel-based additive manufacturing (AM) technique, featuring both a sharp step and radial bumps in the inner bowl rim. The potential benefits of the proposed hybrid bowl were assessed through a validated three-dimensional computational fluid dynamics (3D-CFD) model, including a calibrated spray model and detailed chemistry. Firstly, the optimal spray targeting was identified for the novel hybrid bowl over different injector protrusions and two swirl ratio (SR) levels. Considering the optimal spray targeting, an analysis of the combustion process was carried out over different engine working points, both in terms of flame-wall interaction and soot formation. At rated power engine operating conditions, the hybrid bowl highlighted faster mixing-controlled combustion due to the reduced flame-to-flame interaction and the higher air entrainment into the flame front. At partial-load operating points, the hybrid bowl showed a remarkable soot reduction in comparison with the re-entrant bowl due to a more intense soot oxidation rate in the late combustion phase. Moreover, for the hybrid bowl, a robust Exhaust Gas Recirculation (EGR) tolerance was highlighted, leading to a flat soot-brake-specific oxides of nitrogen (BSNOx) trade-off. At constant BSNOx, a 70% soot reduction was achieved without any detrimental effect on fuel consumption, suggesting the high potential of the proposed innovative bowl for soot attenuation

Exploiting the potential of large eddy simulations (LES) for ducted fuel injection investigation in non-reacting conditions

The diesel combustion research is increasingly focused on ducted fuel injection (DFI), a promising concept to abate engine-out soot emissions in compression-ignition engines. A large set of experiments carried out in constant volume vessel and numerical simulations, at medium-low computational cost, showed that the duct adoption in front of the injector nozzle activates several soot mitigation mechanisms, leading to quasi-zero soot formation in several engine-like operating conditions. However, although the simplified CFD modelling so far played a crucial role for the preliminary understanding of DFI technology, a more accurate turbulence description approach, combined with a large set of numerical experiments for statistical purposes, is of paramount importance for a robust knowledge of the DFI physical behaviour. In this context, the present work exploits the potential of large eddy simulations (LES) to analyse the non-reacting spray of DFI configuration compared with the unconstrained spray. For this purpose, a previously developed spray model, calibrated and validated in the RANS framework against an extensive amount of experimental data related to both free spray and DFI, has been employed. The tests have been carried out considering a single-hole injector in an optical accessible constant volume vessel, properly replicated in the simulation environment. This high-fidelity simulation model has been adapted for LES, firstly selecting the best grid settings, and then carrying out several numerical experiments for both spray configurations until achieving a satisfying statistical convergence. With this aim, the number of independent samples for the averaging procedure has been increased exploiting the axial symmetry characteristics of the present case study. Thanks to this approach, a detailed description of the main DFI-enabled soot mitigation mechanisms has been achieved, shrinking the knowledge gap in the physical understanding of the impact of spray-duct interaction

The Second AGILE MCAL Gamma-Ray Burst Catalog: 13 yr of Observations

We present the results of a systematic search and analysis of GRBs detected by the Astrorivelatore Gamma ad Immagini LEggero (AGILE) MiniCALorimeter (MCAL; 0.4–100 MeV) over a time frame of 13 yr, from 2007 to 2020 November. The MCAL GRB sample consists of 503 bursts triggered by MCAL, 394 of which were fully detected onboard with high time resolution. The sample consists of about 44% short GRBs and 56% long GRBs. In addition, 109 bursts triggered partial MCAL onboard data acquisitions, providing further detections that can be used for joint analyses or triangulations. More than 90% of these GRBs were also detected by the AGILE Scientific RateMeters (RMs), providing simultaneous observations between 20 keV and 100 MeV. We performed spectral analysis of these events in the 0.4–50 MeV energy range. We could fit the time-integrated spectrum of 258 GRBs with a single power-law model, resulting in a mean photon index 〈β〉of−2.3. Among them, 43 bursts could also be fitted with a Band model, with peak energy above 400 keV, resulting in a mean low-energy photon index 〈α〉 = −0.6, a mean high-energy photon index 〈β〉 = −2.5, and a mean peak energy 〈Ep〉 = 640 keV. The AGILE MCAL GRB sample mostly consists of hard-spectrum GRBs, with a large fraction of short-duration events. We discuss properties and features of the MCAL bursts, whose detections can be used to perform joint broad-band analysis with other missions, and to provide insights on the high-energy component of the prompt emission in the tens of mega electron volt energy range.publishedVersio