1,355,003 research outputs found
INDAGINI SUGLI EFFETTI DEL TRATTAMENTO CON ULTRASUONI SUI PRECURSORI TIOLICI DELLE UVE
No full textLa tecnologia ad ultrasuoni, pur a fronte di diverse applicazioni nel settore alimentare e delle bevande, in enologia non è stata ancora introdotta in modo significativo, sebbene siano molteplici gli studi di laboratorio relativi agli effetti durante alcune fasi del processo di vinificazione. Sono riportate interessanti applicazioni nell’ottimizzazione delle fasi fermentativa e post-fermentativa quali l’effetto sulla lisi del lievito (Cacciola et al., 2013, Del Fresno et al., 2018 e 2019), sull’invecchiamento accelerato (Garcia Martin e Sun, 2013; Ferraretto e Celotti, 2016) o sull’estrazione di composti presenti nelle bucce delle uve a bacca rossa (Celotti e Ferraretto 2016; El Darra et al., 2013, Ferraretto et al., 2013; Morata et al., 2017). Recenti lavori sembrano anche evidenziare l'effetto positivo della sonicazione sulle reazioni di polimerizzazione dei tannini nei vini rossi, probabilmente per azioni radicaliche attivate dal trattamento (Ferraretto e Celotti, 2016). Tutte queste evidenze hanno portato recentemente all’inserimento da parte dell’OIV della tecnologia ad ultrasuoni tra le pratiche ammesse nel trattamento dell’uva pigiata per l'estrazione di composti dalle bucce (Risoluzione OIV-OENO 616-2019).
A seguito dei positivi risultati sull’estrazione dei composti dal pigiato delle uve rosse e di esperienze preliminari su uve bianche (Celotti e Ferraretto, 2016), si è voluto verificare la possibilità di sostituire la macerazione prefermentativa di uve bianche aromatiche con un breve trattamento con ultrasuoni. Questa tecnica permetterebbe da una parte di minimizzare i potenziali rischi associati alla macerazione, quali lo sviluppo di microorganismi dannosi per la qualità del vino, e, dall'altra, di ottimizzare le risorse in termini di frigorie e di volume a disposizione durante la vendemmia (in vasca o in pressa). Le ricerche di seguito presentate sono il risultato di un approccio empirico iniziato con un prototipo industriale utilizzato per il trattamento dell’uva. I positivi risultati sensoriali ottenuti hanno spinto ad approfondire in scala di laboratorio la capacità estrattiva e l’effetto degli ultrasuoni sulle molecole precursori dei tioli varietali
A fireworks model for gamma-ray bursts
No full textThe energetics of the long duration GRB phenomenon is compared with models of a rotating Black Hole (BH) in a strong magnetic field generated by an accreting torus. A rough estimate of the energy extracted from a rotating BH with the Blandford-Znajek mechanism is obtained with a very simple assumption: an inelastic collision between the rotating BH and the torus. The GRB energy emission is attributed to an high magnetic field that breaks down the vacuum around the BH and gives origin to a e+- fireball. Its subsequent evolution is hypothesized, in analogy with the in-flight decay of an elementary particle, to evolve in two distinct phases. The first one occurs close to the engine and is responsible of energizing and collimating the shells. The second one consists of a radiation dominated expansion, which correspondingly accelerates the relativistic photon--particle fluid and ends at the transparency time. This mechanism simply predicts that the observed Lorentz factor is determined by the product of the Lorentz factor of the shell close to the engine and the Lorentz factor derived by the expansion. An anisotropy in the fireball propagation is thus naturally produced, whose degree depends on the bulk Lorentz factor at the end of the collimation phase
Dietary calcium and mineral/vitamin supplementation: a controversial problem
No full textThere is a consensus that adequate calcium intake during bone development, and possibly in adulthood and senescence, helps to prevent bone resorption and osteoporosis. The uptake of dietary calcium should be sufficient to maintain both normal serum calcium concentrations and parathyroid hormone levels in the low normal range throughout the day, otherwise, increased bone resorption occurs. Calcium intake varies with race and with environmental and dietary conditions. Estimating the appropriate amount of calcium to be added to dietary sources for an optimal supplementation regimen is therefore difficult. Few intervention studies have evaluated the dose-effect relationship for calcium supplementation conclusively. The mechanisms regulating fractional calcium absorption as a function of intake suggest that very high daily doses are probably useless. They may be unsafe in the long term because of the risks of hypercalciuria and kidney stones, and of an imbalance in the ratio of calcium to magnesium. Concomitant supplementation with limited amounts of magnesium may reduce this risk and improve mineralization. Dietary intake is 500-600 mg/day in most studies, making 400 mg/day an appropriate supplementary dose for most premenopausal women (RDA 1000 mg/day). After the menopause and during lactation (RDA 1200-1500 mg/day), 800 mg/day is probably appropriate, particularly if low doses of vitamin D are taken concomitantly
A model for the spectral variability of BL Lac objects at high frequencies
No full textThe average amplitude of variability of BL Lac objects is larger at higher frequencies, and the spectra in the X-ray range show a hardening with increasing intensity. This is shown to be a natural consequence of the relativistic jet model proposed by Ghisellini et al. (1985), where higher frequencies are produced nearer to the jet core. Time-dependent properties are computed assuming that a perturbation travels at fixed speed down the jet, producing enhancements of constant amplitude of the relativistic particle density and of the magnetic field, in a slab of self-similar cone geometry. The time-dependent spectral intensities due to synchrotron radiation and first-order Compton scattering are computed numerically, and approximate analytic formulae are given. The evolution of the spectral shape with time and the light curves at fixed frequencies are presented and discussed in detail
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