The Change of Total Anthocyanins in Blueberries and Their Antioxidant Effect After Drying and Freezing

This study examined the effects of freezing, storage, and cabinet drying on the anthocyanin content and antioxidant activity of blueberries (Vaccinium corymbosum L). Fresh samples were stored for two weeks at 5(°)C while frozen samples were kept for up to three months at −20(°)C. There were two drying treatments, one including osmotic pretreatment followed by cabinet drying and the other involving only cabinet drying. Total anthocyanins found in fresh blueberries were 7.2 ± 0.5 mg/g dry matter, expressed as cyanidin 3-rutinoside equivalents. In comparison with fresh samples, total anthocyanins in untreated and pretreated dried blueberries were significantly reduced to 4.3 ± 0.1 mg/g solid content, 41% loss, and 3.7 ± 0.2 mg/g solid content, 49% loss, respectively. Osmotic treatment followed by a thermal treatment had a greater effect on anthocyanin loss than the thermal treatment alone. In contrast, the frozen samples did not show any significant decrease in anthocyanin level during three months of storage. Measurement of the antioxidant activity of anthocyanin extracts from blueberries showed there was no significant difference between fresh, dried, and frozen blueberries

A study of the ion exchange behaviour of plutonium in aqueous nitric acid solutions

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Stochastic models of ventilation driven by opposing wind and buoyancy

Stochastic versions of a classical model for natural ventilation are proposed and investigated to demonstrate the effect of random fluctuations on stability and predictability. In a stochastic context, the well-known deterministic result that ventilation driven by the competing effects of buoyancy and wind admits multiple steady states can be misleading, due to two distinct phenomena. First, with unbounded fluctuations in the buoyancy exchanged with an external environment, such systems eventually reside in the vicinity of global minima of their potential, rather than local minima associated with meta-stable equilibria. In the particular context of one heated space with a leeward low-level and windward high-level opening, sustained buoyancy-driven flow opposing the wind direction is unlikely for wind strengths that exceed a statistically critical value, which is slightly larger than the critical value of the wind strength at which bifurcation in the deterministic system occurs. Second, fluctuations in the applied wind modify the topology of the system's potential due to the nonlinear role that wind strength has in the equation for buoyancy conservation. Sufficiently large fluctuations in the wind rule out the possibility of ventilation opposing the wind direction at large base wind strengths. Although the phenomena described above might be perceived as making prediction easier, the results also highlight that certainty in the eventual state of the system goes hand in hand with uncertainty associated with longer transient effects. The work addresses growing interest in applying stochastic analysis to problems relating to building ventilation and urban fluid mechanics by describing a mathematically accessible example of the `stochasticisation' of a canonical deterministic model, while highlighting the subtleties and challenges of developing stochastic models for ventilation in the future.Comment: 28 pages, 12 figure

Relating quanta conservation and compartmental epidemiological models of airborne disease outbreaks in buildings

We investigate the underlying assumptions and limits of applicability of several documented models for outbreaks of airborne disease inside buildings by showing how they may each be regarded as special cases of a system of equations which combines quanta conservation and compartmental epidemiological modelling. We investigate the behaviour of this system analytically, gaining insight to its behaviour at large time. We then investigate the characteristic timescales of an indoor outbreak, showing how the dilution rate of the space, and the quanta generation rate, incubation rate and removal rate associated with the illness may be used to predict the evolution of an outbreak over time, and may also be used to predict the relative performances of other indoor airborne outbreak models. The model is compared to a more commonly used model, in which it is assumed the environmental concentration of infectious aerosols adheres to a quasi-steady-state, so that the the dimensionless quanta concentration is equal to the the infectious fraction. The model presented here is shown to approach this limit exponentially to within an interval defined by the incubation and removal rates. This may be used to predict the maximum extent to which a case will deviate from the quasi steady state condition

Unsteady turbulent jets and plumes

This thesis investigates the physics of statistically unsteady axisymmetric turbulent jets and plumes using theory and direct numerical simulation. The focus is on understanding and modelling the physics that govern the behaviour of radially integrated quantities, such as the integral scalar flux, momentum flux and buoyancy flux. To this end, a framework is developed that generalises previous approaches, making no assumption about the longitudinal velocity profile, turbulence transport or pressure. The framework is used to develop well-posed integral models that exhibit a good agreement with simulation data. In the case of passive scalar transport, shear-flow dispersion is observed to be dominant in comparison with longitudinal turbulent mixing. A dispersion closure for free-shear flows based on the classical work of Taylor (Proc. R. Soc. Lond. A, vol. 219 1954b, pp. 186-203) is therefore developed. In the analysis of jets whose source momentum flux undergoes an instantaneous step change, it is demonstrated that a momentum–energy framework, of the kind used by Priestley & Ball (Q. J. R. Meteorol. Soc., vol. 81 1955, pp. 144-157), is the natural choice for unsteady free-shear flows. The framework is used to demonstrate why existing top-hat models of unsteady jets and plumes are ill-posed and that jets and plumes with Gaussian velocity profiles remain approximately straight-sided and are insensitive to source perturbations. Contrary to the view that the unsteady jet and plume equations are parabolic, it is shown that the generalised system of equations is hyperbolic. In unsteady plumes, the relative orientation of three independent families of characteristic curves determines whether propagating waves are lazy, forced or pure. To relate findings that are based on the momentum–energy framework to the classical mass–momentum framework, an unsteady entrainment coefficient is defined that generalises the decomposition proposed by Kaminski et al. (2005, J. Fluid Mech., vol. 526, pp. 361-376).Open Acces

Etude du phénomène d'entraînement dans des jets turbulents dits Non-Boussinesq

Nous présentons une étude numérique de la dynamique de jets turbulents de fluides léger ou lourd dans un environnement non stratifié. La densité du jet est choisie bien inférieure ou bien supérieure à la densité du fluide environnant afin d'explorer les effets dits ""non-Boussinesq"" sur la dynamique de l'écoulement. Une question centrale est de savoir comment l'entraînement du fluide ambiant par le jet est modifiée lorsque l'écart entre les densités du jet et de l'environnement est fortement augmenté. L'entraînement est mesurée traditionnellement par un coefficient ? qui représente le rapport entre la vitesse d'entraînement horizontale du fluide ambiant et la vitesse verticale du jet. L'étude expérimentale de Ricou et Spalding (1961) a été interprétée de la façon suivante: le coefficient ? évoluerait comme la racine carrée du rapport de densité entre les deux fluides. Ainsi, pour un jet très léger, ? serait plus petit que pour un jet traditionnel dit ""Boussinesq"" tandis que pour un jet très lourd ? augmenterait comme la racine carrée du rapport de densité. Cependant l'origine physique de cette dépendance du coefficient d'entraînement avec le rapport de densité est sujette à caution. Afin de déterminer la dépendance du coefficient d'entraînement avec la densité du jet, des simulations numériques de jets légers et lourds ont été menées et les résultats ont été interprétés en suivant l'analyse proposée par Craske et Van Reeuwijk (2015) et Ezzamel et al. (2015). Cet approche permet de sonder les effets du rapport de densité des deux fluides sur la production d'énergie cinétique turbulente ainsi que ses relations avec le coefficient d'entraînement