1,326 research outputs found

    Exact Equilibrium Solutions of the Magnetohydrodynamic Plasma Model

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    The use of plasma descriptions in areas such as space sciences and thermonuclear fusion devices are of great importance. Of these descriptions, the most widely used are the fluid descriptions which view plasma as a continuum medium and out of these fluid descriptions, the idealized isotropic magnetohydrodynamics (MHD) system of equations is the most used and arguably the most important. Due to the complex nonlinear structure of this system of equations, very few exact solutions are known, and of the know ones, even fewer have physically relevant behaviour. In most cases, solutions are sought for simpler forms of the MHD equations such as the time independent and static equilibrium simplifications. In this work, new exact solutions are derived for the incompressible axially and helically symmetric static and dynamic equilibrium MHD equations. The static equilibrium MHD equations with axial or helical symmetry reduce to a single partial differential equation (PDE). In the case of axial symmetry this is known as the Grad-Shafranov equation and in the case of helical symmetry this is the JFKO equation. New families of separated solutions are found for both of these PDEs and in both cases, the two separate families of solutions arise depending on the type of pressure profile. As most literature focuses on a pressure profile which is lower in the centre of the plasma and goes to a higher ambient pressure at the boundary (that is, the plasma configuration is supported by external pressure), such as those found in [11, 12] emphasis in this work is directed towards the other type of pressure profile where the pressure is higher inside the plasma domain and lower or vanishing outside. Such solutions are relevant to modelling plasma in a vacuum. Using a transformation described in [13, 14], the new static solutions are transformed into dynamic solutions which satisfy the incompressible equilibrium MHD equations. In the last chapter, a modern derivation of Hill’s spherical vortex [31] is presented that employs the Galilean invariance and the axially symmetry reduction to the Grad-Shafranov equation. Along with this, a similar and more general MHD spherical vortex-type solution is derived. Stability analysis of the localized vortex-type solutions is considered

    Neuroprotective role of lactate in a human in vitro model of the ischemic penumbra

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    In patients suffering from cerebral ischemic stroke, there is an urgent need for treatments to protect stressed yet viable brain cells. Recently, treatment strategies that induce neuronal activity have been shown to be neuroprotective. Here, we hypothesized that neuronal activation might maintain or trigger the astrocyte-to-neuron lactate shuttle (ANLS), whereby lactate is released from astrocytes to support the energy requirements of ATP-starved hypoxic neurons, and this leads to the observed neuroprotection. We tested this by using a human cell based in vitro model of the ischemic penumbra and investigating whether lactate might be neuroprotective in this setting. We found that lactate transporters are involved in the neuroprotective effect mediated by neuronal activation. Furthermore, we showed that lactate exogenously administered before hypoxia correlated with neuroprotection in our cellular model. In addition, stimulation of astrocyte with consequent endogenous production of lactate resulted in neuroprotection. To conclude, here we presented evidence that lactate transport into neurons contributes to neuroprotection during hypoxia providing a potential basis for therapeutic approaches in ischemic stroke.</p

    Nutrient Control of Microbial Carbon Cycling Along an Ombrotrophicminerotrophic Peatland Gradient

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    Future climate change and other anthropogenic activities are likely to increase nutrient availability in many peatlands, and it is important to understand how these additional nutrients will influence peatland carbon cycling. We investigated the effects of nitrogen and phosphorus on aerobic CH4 oxidation, anaerobic carbon mineralization (as CO2 and CH4 production), and anaerobic nutrient mineralization in a bog, an intermediate fen, and a rich fen in the Upper Peninsula of Michigan. We utilized a 5-week laboratory nutrient amendment experiment in conjunction with a 6-year field nutrient fertilization experiment to consider how the relative response to nitrogen and phosphorus differed among these wetlands over the short and long term. Field fertilizations generally increased nutrient availability in the upper 15 cm of peat and resulted in shifts in the vegetation community in each peatland. High nitrogen concentrations inhibited CH4 oxidation in bog peat during short-term incubations; however, long-term fertilization with lower concentrations of nitrogen stimulated rates of CH4 oxidation in bog peat. In contrast, no nitrogen effects on CH4 oxidation were observed in the intermediate or rich fen peat. Anaerobic carbon mineralization in bog peat was consistently inhibited by increased phosphorus availability, but similar phosphorus additions had few effects in the intermediate fen and stimulated CH4 production and nutrient mineralization in the rich fen. Our results demonstrate that nitrogen and phosphorus are important controls of peatland microbial carbon cycling; however, the role of these nutrients can differ over the short and long term and is strongly mediated by peatland type

    The Preparation Temperature Influences the Physicochemical Nature and Activity of Nanoceria

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    Cerium oxide nanoparticles, so-called nanoceria, are engineered nanomaterials prepared by many methods that result in products with varying physicochemical properties and applications. Those used industrially are often calcined, an example is NM-212. Other nanoceria have beneficial pharmaceutical properties and are often prepared by solvothermal synthesis. Solvothermally synthesized nanoceria dissolve in acidic environments, accelerated by carboxylic acids. NM-212 dissolution has been reported to be minimal. To gain insight into the role of high-temperature exposure on nanoceria dissolution, product susceptibility to carboxylic acid-accelerated dissolution, and its effect on biological and catalytic properties of nanoceria, the dissolution of NM-212, a solvothermally synthesized nanoceria material, and a calcined form of the solvothermally synthesized nanoceria material (ca. 40, 4, and 40 nm diameter, respectively) was investigated. Two dissolution methods were employed. Dissolution of NM-212 and the calcined nanoceria was much slower than that of the non-calcined form. The decreased solubility was attributed to an increased amount of surface Ce4+ species induced by the high temperature. Carboxylic acids doubled the very low dissolution rate of NM-212. Nanoceria dissolution releases Ce3+ ions, which, with phosphate, form insoluble cerium phosphate in vivo. The addition of immobilized phosphates did not accelerate nanoceria dissolution, suggesting that the Ce3+ ion release during nanoceria dissolution was phosphate-independent. Smaller particles resulting from partial nanoceria dissolution led to less cellular protein carbonyl formation, attributed to an increased amount of surface Ce3+ species. Surface reactivity was greater for the solvothermally synthesized nanoceria, which had more Ce3+ species at the surface. The results show that temperature treatment of nanoceria can produce significant differences in solubility and surface cerium valence, which affect the biological and catalytic properties of nanoceria
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