124 research outputs found

    Fractional diffusion in Gaussian noisy environment

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    We study the fractional diffusion in a Gaussian noisy environment as described by the fractional order stochastic partial equations of the following form: Dtαu(t,x)=Bu+uWHD_t^\alpha u(t, x)=\textit{B}u+u\cdot W^H, where DtαD_t^\alpha is the fractional derivative of order α\alpha with respect to the time variable tt, B\textit{B} is a second order elliptic operator with respect to the space variable xRdx\in\mathbb{R}^d, and WHW^H a fractional Gaussian noise of Hurst parameter H=(H1,,Hd)H=(H_1, \cdots, H_d). We obtain conditions satisfied by α\alpha and HH so that the square integrable solution uu exists uniquely

    Fractional Diffusion in Gaussian Noisy Environment

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    We study the fractional diffusion in a Gaussian noisy environment as described by the fractional order stochastic heat equations of the following form: D(α)tu(t,x)=Bu+u⋅W˙H, where D(α)t is the Caputo fractional derivative of order α∈(0,1) with respect to the time variable t, B is a second order elliptic operator with respect to the space variable x∈Rd and W˙H a time homogeneous fractional Gaussian noise of Hurst parameter H=(H1,⋯,Hd). We obtain conditions satisfied by α and H, so that the square integrable solution u exists uniquely

    Development of a methanol to hydrocarbons process over zeolite coatings in a microstructured reactor

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    In this work, the hydrothermal synthesis of ZSM-5 and its coating with controllable crystal size and Si/Al ratio has been performed. The obtained catalysts have been studied in the methanol to hydrocarbon (MTH) reaction. This reaction is the last step in an integrated fuel processor for the conversion of bio resources to liquid fuels. The development of ZSM-5 coatings has been supported by advanced characterization and testing of catalysts for the determination of property/performance relationships. An optimal synthesis time of 72 h was found to provide the highest crystallinity of ZSM-5 coatings. The larger crystal size of ZSM-5 coatings leads to a higher selectivity towards gasoline (C8-11) hydrocarbons. The selectivity towards the gasoline fraction over ZSM-5 coatings with a thickness of 14 μm was similar to that of an industrial ZSM-5 catalyst, however the yield of the undesirable aromatics by-products was reduced by half due to shorter diffusion pathways in thin catalyst layers. In an attempt to improve the yield of the C8-11 hydrocarbons, two post-synthesis modifications have been performed: Ca ion-exchange and desilication by alkaline treatment. The maximum gasoline selectivity over Ca-H-ZSM-5 was observed at a Ca/H ratio of 0.1 while the longest lifetime in the reaction was observed at the ratio of 0.2. Mesoporosity has been introduced into microporous ZSM-5 catalysts. The obtained meso-microporous ZSM-5 coating show 3 times lifetime and 2.7 times selectivity towards C8-11 hydrocarbon fraction than microporous coating in the MTH reaction. Lumped kinetics of MTH reaction over H-ZSM-5 were used to design a microstructured reactor/heat-exchanger (MRHE) with reaction channels coated with the ZSM-5 catalyst. 2D and 3D convection and conduction heat transfer models coupled with the MTH reaction kinetics were employed to investigate temperature distribution in the MRHE. The effect of the dimension of the microreactor/ heat-exchanger and flow condition on the temperature field has been studied. The 2D model under-predicts the magnitude of temperature gradient. The optimised reactor configuration shows a temperature gradient of 21 K in the reaction channels

    Evaluation of daily precipitation extremes in reanalysis and gridded observation‐based datasets over Germany

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    Accurate and reliable gridded datasets are important for analyzing extreme weather and climate events. Specifically, these datasets should produce extreme value statistics that are close to reality. Here we use various statistical methods to evaluate the quality of four gridded data products in representing daily precipitation extremes. The data products are the COSMO-REA6 regional reanalysis, the ERA5 global reanalysis, and the E-OBS and HYRAS gridded observation-based datasets. The statistical methods we use offer a thorough insight into the quality of the different datasets by providing temporal and spatial extreme value statistics of daily precipitation. Our results show that all datasets except HYRAS underestimate the magnitude of daily precipitation extremes when compared with weather station data. Moreover, the reanalysis datasets give generally worse extreme value statistics of daily precipitation than the gridded observation-based datasets. In particular, the reanalysis datasets often fail in reproducing the accurate timing of observed daily precipitation extremes

    Fractional Diffusion in Gaussian Noisy Environment

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    Three types of stochastic partial differential equations are studied in this dissertation. We prove the existence and uniqueness of the solutions and obtain some properties of the solutions. Chapter 3 studies the linear stochastic partial differential equation of fractional orders both in time and space variables. We prove the existence and uniqueness of the solution and calculate the moment bounds of the solution when the noise has Reisz kernel as space covariance. Along the way, we obtain some new properties of the fundamental solutions. Chapter 4 studies the time-fractional diffusion with fractional Gaussian noise. We obtain conditions so that the square integrable solution exists uniquely. Chapter 5 studies the time-fractional diffusion where the Gaussian noise is general in time with space covariance given by fractional, Riesz and Bessel kernel
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