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Asimilace časoprostorového rozložení radionuklidů v časné fázi radiační nehody
Hofman, Radek ; Šmídl, Václav
Exploitation of the data assimilation methodology in the early phase of radiation accident is studied. When radioactive pollutants are released into the atmosphere, a radioactive plume is passing over the terrain. The released radioactive material causes pathway-specific irradiation which has detrimental effects on population health. In order to ensure efficiency of introduced countermeasures, it is necessary to predict spatial and temporal distribution of the aerial pollution and material already deposited on the ground. The predictions are made by the means of a numerical dispersion model with many inputs. Output of such a model is a prediction of radiation situation given in terms of radiological quantities. Exact values of the inputs are uncertain due to the stochastic nature of the dispersion, lack of accurate information, etc. Their subjective choice can introduce significant errors into the predictions and thus decrease the positive impact of the countermeasures.
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Aplikace opomíjeného praktického filtru pro lineárně Gausovské problémy s neznámým modelem chyb kovariantních struktur
Hofman, Radek
The paper presents a scheme for estimation of spatio-temporal evolution of a quantity with unknown model error. Model error is estimated on basis of measured-minus-observed residuals evaluated upon measured and modeled values. Methods of Bayesian filtering are applied to the problem. The main contribution of this paper is application of general marginalized particle filter algorithm to the linear-Gaussian problem with unknown model error covariance structure. Methodology is demonstrated on the problem of modeling of spatio-temporal evolution of groundshine-dose from radionuclides deposited on terrain in long-time horizon.
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Aplikace pokročilých statistických metod v odhadu pozdních fázý nukleárních nehod
Hofman, Radek
The paper presents a new methodology for improving of estimates of radiological situation on terrain in the late phase of a nuclear accident. Methods of Bayesian filtering are applied to the problem. The estimates are based on combination of modeled and measured data provided by responsible authorities. Exploiting information on uncertainty of both the data sources, we are able to produce improved estimate of the true situation on terrain. We also attempt to account for model error, which is unknown and plays crucial role in accuracy of the estimates. The main contribution of this paper is application of an approach based on advanced statistical methods, which allows for estimating of model error covariance structure upon measurements. Model error is estimated on basis of measured-minus-observed residuals evaluated upon measured and modeled values. The methodology is demonstrated on a sample scenario with simulated measurements.
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Interakce vodíkového plazmatu s ferity
Hofman, R. ; Vacík, M. ; Brožek, Vlastimil ; Eliáš, M. ; Janča, J.
Ferrites are a well-known ferroelectric materials based on metal oxides with different oxidation levels. They found thanks its advisable properties a broad field of exercise, especially in electronics. In our work we made an effort to amplify this field of exercise. An intention of our work was explaining how the ferrites behave in strongly reducing atmosphere realized in hydrogen plasma. The emphasis was laid on readiness and selectivity of reduction. And further we are interested in morphology and granulometry of obtained products and last but not least in mechanical properties, especially of obtained ceramics composite with metal matrix ( MMC
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Impregnace keramických membrán anatasem
Vacík, M. ; Hofman, R. ; Mastný, L. ; Šrank, Z. ; Brožek, Vlastimil
Catalytic properties of anatase have been known for a certain time but its practical usage has been hindered by technological limits of preparation of either compact massive intermediate products of various shapes which are necessary as a component of catalytic reactors or nanosized anatase powder. Our aim was to prepare ceramic membrane which would contain catalytic form of titanium oxide - i.e. anatase in its entire volume or on its surface only. Ceramic membranes of any shape (mostly tabular or piped) may be prepared by hot spattering technology. If plasma torch is used we call this process plasma spraying. The advantage of plasma spraying is in chance to provide semi-finished membranes with high dimension accuracy with defined radius of voids and/or as functionally graded materials, i.e. with changing concentration of some ceramic, metallic or combined components. The pores developed in membranes can be readily filled up with substances that allow modification of its properties. In this area, the possibility to impregnate membrane ceramic intermediates with other functional components, e.g. photocatalytic forms of titanium oxide, arises as well.
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