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nuclear Science and Techniques 2019年第8期30卷 100-113页

作者： Lenka Frybortova UJV Rez a.s. Faculty of Nuclear Sciences and Physical Engineering Czech Technical University in Prague

There is an obvious effort to increase the burn up of used fuel assemblies in order to improve fuel utilization.A more effective operation can be realized by extending the fuel cycles or by increasing the number of reloadings.This change is nevertheless connected with increasing the uranium enrichment even above 5% of 235U. Burnable absorbers are widely used to compensate for the positive reactivity of fresh fuel. With proper optimization, burnable absorbers decrease the reactivity excess at the beginning of the cycle, and they can help with stabilization of power distribution. This paper describes properties of several materials that can be used as burnable absorbers. The change in concentration or position of the pin with a burnable absorber in a fuel assembly was analyzed by the HELIOS transport lattice code. The multiplication factor and power peaking factor dependence on fuel burn up were used to evaluate the neutronic properties of burnable absorbers. The following four different materials are discussed in this paper: Gd2O3, IFBA, Er2O3,and Dy2O3.Gadolinium had the greatest influence on fuel characteristics. The number of pins with a burnable absorber was limited in the VVER-440 fuel assembly to six. In the VVER-1000 fuel assembly, 36 pins with a burnable absorber can be used as the assembly is larger. The erbium depletion rate was comparable with uranium burn up.Dysprosium had the largest parasitic absorption after depletion.

关键词： Burnable absorber Gadolinium IFBA Erbium Dysprosium Power peaking VVER fuel HELIOS code

Weyl Group Orbit Functions in Image Processing

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Applied Mathematics 2014年第3期5卷 501-511页

作者： Goce Chadzitaskos Lenka Háková Ondrej Kajínek Faculty of Nuclear Sciences and Physical Engineering Czech Technical University in PraguePragueCzech Republic

We deal with the Fourier-like analysis of functions on discrete grids in two-dimensional simplexes using C- and E-Weyl group orbit functions. For these cases, we present the convolution theorem. We provide an example of application of image processing using the C-functions and the convolutions for spatial filtering of the treated image.

关键词： Orbit Functions Convolution Image Processing

Nonabelian Dualization of Plane Wave Backgrounds

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Journal of Modern Physics 2012年第9期3卷 1088-1095页

作者： Ladislav Hlavaty Miroslav Turek Faculty of Nuclear Sciences and Physical Engineering Czech Technical University in PraguePragueCzech Republic

We investigate plane-parallel wave metrics from the point of view of their (Poisson-Lie) T-dualizability. For that purpose we reconstruct the metrics as backgrounds of nonlinear sigma models on Lie groups. For construction of dual backgrounds we use Drinfel’d doubles obtained from the isometry groups of the metrics. We find dilaton fields that enable to satisfy the vanishing beta equations for the duals of the homogenous plane-parallel wave metric. Torsion potentials or B-fields, invariant w.r.t. the isometry group of Lobachevski plane waves are obtained by the Drinfel’d double construction. We show that a certain kind of plurality, different from the (atomic) Poisson-Lie T-plurality, may exist in case that metrics admit several isometry subgroups having the dimension of the Riemannian manifold. An example of that are two different backgrounds dual to the homogenous plane-parallel wave metric.

关键词： Sigma Model String Duality pp-Wave Background

Periodic surface functional group density on graphene via laserinduced substrate patterning at Si/SiO2 interface

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Nano Research 2020年第9期13卷 2332-2339页

作者： Karolina A.Drogowska-Horna Inam Mirza Alvaro Rodriguez Petr Kovaricek Juraj Sladek Thibault J.-Y.Derrien Mindaugas Gedvilas Gediminas Raciukaitis Otakar Frank Nadezhda M.Bulgakova Martin Kalbac J.Heyrovsky Institute of physical Chemistry of the Czech Academy of sciences Dolejskova 2155/318223 PragueCzech Republic HiLASE Centre Institute of Physics of the Czech Academy of SciencesZa Radnict 82825241 Dolni BrezanyCzech Republic Faculty of Nuclear Sciences and Physical Engineering Czech Technical University in PragueBrehova 78/711519Czech Republic Center for physical sciences and Technology Savanoriu Ave.231LT-023000VilniusLithuania

Controlling the spatial distribution of functional groups on two-dimensional(2D)materials on a micrometer scale and below represents a fascinating opportunity to achieve anisotropic(opto)electronic properties of these materials.Periodic patterns of covalent functionalization can lead to pericxJic potentials in the monolayer;however,creating such superstructures is very challenging.Here,we describe an original approach to the periodic functionalization of graphene induced by substrate patterning using a pulsed laser.Laser-induced periodic surface structures(LIPSS)are produced on silicon wafers with thermally-grown oxide layers.The irradiation conditions for the formation of UPSS confined at the SiO2/Si interface have been unravelled.LIPSS imprint their periodicity to the reactivity of the monolayer graphene placed on the substrate via modulation of its local doping level.This method is clean,straightforward and scalable with high spatial resolution.

关键词： two-dimensional(2D)materials graphene functionalization laser-induced periodic surface structures(LIPSS) periodic patterns Raman spectroscopy atomic force microscopy(AFM)

Computational Studies of Bacterial Colony Model

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American Journal of Computational Mathematics 2013年第2期3卷 147-157页

作者： Ondrej Partl Department of Mathematics Faculty of Nuclear Sciences and Physical Engineering Czech Technical University in Prague Prague Czech Republic

Microbiological experiments show that the colonies of the bacterium bacillus subtilis placed on a dish filled with an agar medium and nutrient form varied spatial patterns while the individual cells grow, reproduce and migrate on the dish in clumps. In this paper, we discuss a system of reaction-diffusion equations that can be used with a view to modelling this phenomenon and we solve it numerically by means of the method of lines. For the spatial discretization, we use the finite difference method and Galerkin finite element method. We present how the spatial patterns obtained depend on the spatial discretization employed and we measure the experimental order of convergence of the numerical schemes used. Further, we present the numerical results obtained by solving the model in a cubic domain.

关键词： Bacterial Colony Model Reaction-Diffusion Equations Method of Lines Galerkin Finite Element Method

Computational Studies of Reaction-Diffusion Systems by Nonlinear Galerkin Method

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American Journal of Computational Mathematics 2013年第2期3卷 137-146页

作者： Miroslav Kolar Department of Mathematics Faculty of Nuclear Sciences and Physical Engineering Czech Technical University in Prague Prague Czech Republic

This article deals with the computational study of the nonlinear Galerkin method, which is the extension of commonly known Faedo-Galerkin method. The weak formulation of the method is derived and applied to the particular Scott-Wang-Showalter reaction-diffusion model concerning the problem of combustion of hydrocarbon gases. The proof of convergence of the method based on the method of compactness is introduced. Presented results of numerical simulations are composed of the computational study, where the nonlinear Galerkin method and Faedo-Galerkin method are compared for the problem with analytical solution and the numerical results of the Scott-Wang-Showalter model in 1D.

关键词： Nonlinear Galerkin Method Scott-Wang-Showalter Model Compactness Method

Application of the Level-Set Model with Constraints in Image Segmentation

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Numerical Mathematics(Theory,Methods and Applications) 2016年第1期9卷 147-168页

作者： Vladimiır Klement Tomas Oberhuber Daniel Sevcovic Department of Mathematics Faculty of Nuclear Sciences and Physical EngineeringCzech Technical University in PragueTrojanova 13Praha 212000Czech Republic Department of Applied Mathematics and Statistics Comenius University84248 BratislavaSlovakia

We proposeand analyze a constrained level-set method forsemi-automatic image segmentation.Our level-set model with constraints on the level-set function enables us to specify which parts of the image lie inside respectively outside the segmented objects.Such a-priori information can be expressed in terms of upper and lower constraints prescribed for the level-set function.Constraints have the same conceptual meaning as initial seeds of the popular graph-cuts based meth-ods for image segmentation.A numerical approximation scheme is based on the complementary-finite volumes method combined with the Projected successive over-relaxation method adopted for solving constrained linear complementarity prob-lems.The advantage of the constrained level-set method is demonstrated on several artificial images as well as on cardiac MRI data.

关键词： linear complementarity image processing segmentation level-set method projected successive over-relaxation method

Faraday effect measurements of holmium oxide(Ho2O3) ceramics-based magneto-optical materials

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High Power Laser Science and engineering 2018年第1期6卷 7-12页

作者： David Vojna Ryo Yasuhara Hiroaki Furuse Ondrej Slezak Simon Hutchinson Antonio Lucianetti Tomas Mocek Miroslav Cech Hi LASE Centre Institute of Physics Czech Academy of Sciences Za Radnici 828 Dolni Brezany 252 41 Czech Republic National Institute for Fusion Science National Institutes of Natural Sciences 322-6 Oroshi-cho Toki Gifu 509-5292 Japan Kitami Institute of Technology 165 Koen-cho Kitami Hokkaido Japan Department of physical Electronics Faculty of Nuclear Sciences and Physical Engineering Czech Technical University in PragueBrehova 7 Prague 115 19 Czech Republic

Faraday effect measurements of holmium oxide(Ho_2O_3) ceramics-based magneto-optical materials, highly potential material candidates for high-energy laser Faraday isolators, are presented in this paper. Temperature dependence of the Verdet constant of nondoped Ho_2O_3 ceramics was measured for temperatures 15–305 K at 1.064 μm wavelength.The Verdet constant dispersion for wavelengths 0.5–1 μm and 1.064 μm was measured for both nondoped Ho_2O_3 ceramics and Ho_2O_3 ceramics doped with terbium Tb3+(0.2 at. %) and cerium Ce3+(0.1 at. %) ions. The results suggest that the relatively low level of doping of Ho_2O_3 with these ions has no significant boosting impact on the Faraday effect. Therefore, other compositions of Ho_2O_3 ceramics-based magneto-optical materials, as well as various doping concentrations, should be further examined.

关键词： Faraday effect magneto-optics optical materials

Development of a radiographic method for measuring the discrete spectrum of the electron beam from a plasma focus device

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Plasma Science and Technology 2017年第7期19卷 26-33页

作者： Neda SHAMSIAN Babak SHIRANI BIDABADI Hosein PIRJAMADI Department of nuclear engineering Faculty of Advanced Sciences and Technologies University of Isfahan

An indirect method is proposed for measuring the relative energy spectrum of the pulsed electron beam of a plasma focus device. The Bremsstrahlung x-ray, generated by the collision of electrons against the anode surface, was measured behind lead filters with various thicknesses using a radiographic film system. A matrix equation was considered in order to explain the relation between the x-ray dose and the spectral amplitudes of the electron beam. The electron spectrum of the device was measured at 0.6 mbar argon and 22 kV charging voltage, in four discrete energy intervals extending up to 500 keV. The results of the experiments show that most of the electrons are emitted in the 125-375 keV energy range and the spectral amplitude becomes negligible beyond 375 keV.

关键词： magnetized plasma plasma focus plasma diagnostics electron beam energyspectrum x-ray dosimetry