| 1. |
- Dalla Barba, Federico, et al.
(author)
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An interface capturing method for liquid-gas flows at low-Mach number
- 2021
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In: Computers & Fluids. - : Elsevier Ltd. - 0045-7930 .- 1879-0747. ; 216
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Journal article (peer-reviewed)abstract
- Multiphase, compressible and viscous flows are of crucial importance in a wide range of scientific and engineering problems. Despite the large effort paid in the last decades to develop accurate and efficient numerical techniques to address this kind of problems, current models need to be further improved to address realistic applications. In this context, we propose a numerical approach to the simulation of multiphase, viscous flows where a compressible and an incompressible phase interact in the low-Mach number regime. In this frame, acoustics are neglected but large density variations of the compressible phase can be accounted for as well as heat transfer, convection and diffusion processes. The problem is addressed in a fully Eulerian framework exploiting a low-Mach number asymptotic expansion of the Navier-Stokes equations. A Volume of Fluid approach (VOF) is used to capture the liquid-gas interface, built on top of a massive parallel solver, second order accurate both in time and space. The second-order-pressure term is treated implicitly and the resulting pressure equation is solved with the eigenexpansion method employing a robust and novel formulation. We provide a detailed and complete description of the theoretical approach together with information about the numerical technique and implementation details. Results of benchmarking tests are provided for five different test cases.
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| 2. |
- Poojary, Mahesha M., et al.
(author)
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Influence of Innovative Processing on γ-Aminobutyric Acid (GABA) Contents in Plant Food Materials
- 2017
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In: Comprehensive Reviews in Food Science and Food Safety. - : Wiley. - 1541-4337. ; 16:5, s. 895-905
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Journal article (peer-reviewed)abstract
- Over the last several decades, γ-aminobutyric acid (GABA) has attracted much attention due to its diverse physiological implications in plants, animals, and microorganisms. GABA naturally occurs in plant materials and its concentrations may vary considerably, from traces up to μmol/g (dry basis) depending on plant matrix, germination stage, and processing conditions, among other factors. However, due to its important biological activities, considerable interest has been shown by both food and pharmaceutical industries to improve its concentration in plants. Natural and conventional treatments such as mechanical and cold stimulation, anoxia, germination, enzyme treatment, adding exogenous glutamic acid (Glu) or gibberellins, and bacterial fermentation have been shown effective to increase the GABA concentration in several plant materials. However, some of these treatments can modify the nutritional, organoleptic, and/or functional properties of plants. Recent consumer demand for food products which are "healthy," safe and, having added benefits (nutraceuticals/functional components) has led to explore new ways to improve the content of bioactive compounds while maintaining desirable organoleptic and physicochemical properties. Along this line, nonthermal processing technologies (such as high-pressure processing, pulsed electric fields, and ultrasound, among others) have been shown as means to induce the biosynthesis and accumulation of GABA in plant foods; and the main findings so far reported are presented in this review. Moreover, the most novel tools for the identification of metabolic response in plant materials based on GABA analysis will be also described.
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| 3. |
- Scapin, Nicolo, et al.
(author)
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Finite-size evaporating droplets in weakly compressible homogeneous shear turbulence
- 2022
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In: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 934
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Journal article (peer-reviewed)abstract
- We perform interface-resolved simulations of finite-size evaporating droplets in wealdy compressible homogeneous shear turbulence. The study is conducted by varying three dimensionless physical parameters: the initial gas temperature over the critical temperature T-g,T-0/T-c, the initial droplet diameter over the Kolmogorov scale d(0)/eta and the surface tension, i.e. the shear-based Weber number, We(S). For the smallest We(S), we first discuss the impact on the evaporation rate of the three thermodynamic models employed to evaluate the gas thermophysical properties: a constant property model and two variable-properties approaches where either the gas density or all the gas properties are allowed to vary. Taking this last approach as reference, the model assuming constant gas properties and evaluated with the '1/3' rule is shown to predict the evaporation rate better than the model where the only variable property is the gas density. Moreover, we observe that the well-known Frossling/Ranz-Marshall correlation underpredicts the Sherwood number at low temperatures, T-g,T-0/T-c = 0.75. Next, we show that the ratio between the actual evaporation rate in turbulence and the one computed in stagnant conditions is always much higher than one for wealdy deformable droplets: it decreases with T-g,T-0/T-c without approaching unity at the highest T-g,T-0/T-c considered. This suggests an evaporation enhancement due to turbulence also in conditions typical of combustion applications. Finally, we examine the overall evaporation rate and the local interfacial mass flux at higher Wes, showing a positive correlation between evaporation rate and interfacial curvature, especially at the lowest T-g,T-0/T-c.
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| 4. |
- Wang, Jietuo, et al.
(author)
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Modelling the direct virus exposure risk associated with respiratory events
- 2022
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In: Journal of the Royal Society Interface. - : The Royal Society. - 1742-5689 .- 1742-5662. ; 19:186, s. 20210819-20210819
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Journal article (peer-reviewed)abstract
- The outbreak of the COVID-19 pandemic highlighted the importance of accurately modelling the pathogen transmission via droplets and aerosols emitted while speaking, coughing and sneezing. In this work, we present an effective model for assessing the direct contagion risk associated with these pathogen-laden droplets. In particular, using the most recent studies on multi-phase flow physics, we develop an effective yet simple framework capable of predicting the infection risk associated with different respiratory activities in different ambient conditions. We start by describing the math- ematical framework and benchmarking the model predictions against well-assessed literature results. Then, we provide a systematic assessment of the effects of physical distancing and face coverings on the direct infection risk. The present results indicate that the risk of infection is vastly impacted by the ambient conditions and the type of respiratory activity, suggesting the non-existence of a universal safe distance. Meanwhile, wearing face masks provides excellent protection, effectively limiting the transmission of pathogens even at short physical distances, i.e. 1 m.
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