Application for system reliability evaluation using fault tree analysis (FTA)

Tato bakalářská práce řeší spolehlivostní metodou FTA (analýza stromu poruchových stavů). Cílem práce v teoretické části je zpracování informací o metodě pro praktickou část práce. V praktické části je hlavním cílem udělat rešerši existujících softwarů a vytvořit uživatelsky přívětivý software pro metodu FTA, který umožní výpočet analýzy systému ze vstupních dat. Pro tvorbu aplikace je zvolen programovací jazyk JavaScript s technologií Node.js a webovým frameworkem Express.js. Dalším bodem v praktické části je ověření výpočtů vytvořené aplikace.This bachelor thesis is about reliability method FTA (Fault Tree Analysis). The goal of the thesis in a theoretical part is to process information about the method for practical part of the thesis. The main goal in the practical part is to research existing softwares and create an user-friendly software for FTA method that can calculates a system analysis from data inputs. Programming language JavaScript is chosen for app creation with Node.js technology and web framework Express.js. The next goal in the practical part is verification of calculations by created application

Increasing Agricultural Competitiveness of Sub-Saharan Countries

Tato diplomová práce se soustředí na rozvoj a konkurenceschopnost zemědělství v subsaharské Africe (SSA), jednom z nejchudších regionů na světě. Autor práce se odkazuje na řadu studií o rozvoji zemědělství v chudých regionech a poukazuje na pozitivní vliv agrárního sektoru při boji s chudobou. Úkolem této práce je analyzovat překážky bránící v rozvoji zemědělství a navrhnout cesty pro jejich odstranění. Práce se v první části zabývá vnitřními problémy, mezi které patří zejména degradace půdy způsobená nedostatečným hnojením a zavlažováním, používání nekvalitního osiva, nízká míra investic, zaostalé technologie, špatné zdraví obyvatelstva a komunální vlastnictvím půdy. Hlavním doporučením pro tuto část je užší spolupráce mezi farmáři, která v konečném důsledku může odstranit všechny výše uvedené problémy. V druhé části se autor zaměřuje vnější problémy, zejména na mezinárodní obchodní politiku. Popisuje vývoj africké obchodní politiky a komentuje současný stav. V této části autor doporučuje hlubší regionální integraci a zároveň větší ochranu před levným dovozem z rozvinutých zemí, což zahrnuje i větší protekcionistická opatření.This master degree thesis focuses on development and competitiveness of agriculture in Sub-Saharan Africa, one of the world's poorest regions. The author of the thesis refers to various studies written on agricultural development in the poorest regions worldwide and points out its positive influence on poverty reduction. This paper analyzes constraints of agricultural development and suggests ways of eliminating them. The first part of the thesis focuses on internal issues including soil degradation caused by low fertilization and irrigation, poor quality seeds, low level of investment, obsolete technology, bad health of citizens and communal property rights. In this part, the author recommends closer cooperation between farmers which he believes can solve the aforementioned issues. In the second part, the author writes on external issues concerning mainly international trade policy. He describes development of African policy and comments on its current state. In this part, the author recommends deeper regional integration and stronger protection from cheap imports from developed countries, which includes higher protectionist measures

Stochastic models of dense or hollow nanoparticles and their scattering properties

peer reviewedA family of stochastic models of disordered particles is proposed, obtained by clipping a Gaussian random field with a function that is space dependent. Depending on the shape of the clipping function, dense or hollow particles can be modelled. General expressions are derived for the form factor of the particles, for their average volume and surface area, and for their density and surface-area distributions against the distance to the particle centre. A general approximation for the form factor is also introduced, based on the density and surface-area distributions, which coincides with the Guinier and Porod expressions in the limits of low and high scattering vector magnitude q. The models are illustrated with the fitting of small-angle X-ray scattering (SAXS) data measured on Pt/Ni hollow nanoparticles. The SAXS analysis and modelling notably capture the collapse of the particles' porosity after being used as oxygen-reduction catalysts

Probing Exfoliated Graphene Layers and Their Lithiation with Microfocused X-rays

X-ray diffraction is measured on individual bilayer and multilayer graphene single-crystals and combined with electrochemically induced lithium intercalation. In-plane Bragg peaks are observed by grazing incidence diffraction. Focusing the incident beam down to an area of about 10 μm × 10 μm, individual flakes are probed by specular X-ray reflectivity. By deploying a recursive Parratt algorithm to model the experimental data, we gain access to characteristic crystallographic parameters of the samples. Notably, it is possible to directly extract the bi/multilayer graphene c-axis lattice parameter. The latter is found to increase upon lithiation, which we control using an on-chip peripheral electrochemical cell layout. These experiments demonstrate the feasibility of in situ X-ray diffraction on individual, micron-sized single crystallites of few- and bilayer two-dimensional materials

Electronic and structural reconstructions of the polar (111) SrTiO3 surface

Polar surfaces are known to be unstable due to the divergence of the surface electrostatic energy. Here we report on the experimental determination, by grazing incidence x-ray diffraction, of the surface structure of polar Ti-terminated (111) SrTiO3 single crystals. We find that the polar instability of the 1 x 1 surface is solved by a pure electronic reconstruction mechanism, which induces out-of-plane ionic displacements typical of the polar response of SrTiO3 layers to an electron confining potential. On the other hand, the surface instability can be also eliminated by a structural reconstruction driven by a change in the surface stoichiometry, which induces a variety of 3 x 3 (111) SrTiO3 surfaces consisting in an incomplete Ti (surface)-O-2 (subsurface) layer covering the 1 x 1 Ti-terminated (111) SrTiO3 truncated crystal. In both cases, the TiO6 octahedra are characterized by trigonal distortions affecting the structural and the electronic symmetry of several unit cells from the surface. These findings show that the stabilization of the polar (111) SrTiO3 surface can lead to the formation of quasi two-dimensional electron systems characterized by radically different ground states which depend on the surface reconstructions

Insights from Operando and Identical Location (IL) Techniques on the Activation of Electrocatalysts for the Conversion of CO2: A Mini-Review

In this mini-review we compare two prototypical metal foam electrocatalysts applied to the transformation of CO2 into value-added products (e.g. alcohols on Cu foams, formate on Bi foams). A substantial improvement in the catalyst performance is typically achieved through thermal annealing in air of the as-deposited foam materials, followed by the electro-reduction of the pre-formed oxidic precursors prior or during the actual CO2 electrolysis. Utilizing highly insightful and sensitive complementary operando analytical techniques (XAS, XRD, and Raman spectroscopy) we demonstrate that this catalyst pre-activation process is entirely accomplished in case of the oxidized Cu foams prior to the formation of hydrocarbons and alcohols from the CO2. The actually active catalyst is therefore the metallic Cu derived from the precursor by means of its oxide electroreduction. Conversely, in their oxidic form, the Cu-based foam catalysts are completely inactive towards the CO2 reduction reaction (denoted ec-CO2RR). Oxidized Bi foams can be regarded as an excellent counter example to the above-mentioned Cu case as both metallic and the thermally derived oxidic Bi foams are highly active towards ec-CO2RR (formate production). Indeed, operando Raman spectroscopy reveals that CO2 electrolysis occurs upon its embedment into the oxidic Bi2O3 foam precursor, which itself undergoes partial transformation into an active sub-carbonate phase. The potential-dependent transition of sub-carbonate/oxides into the corresponding metallic Bi foam dictates the characteristic changes of the ec-CO2RR pathway. Identical location (IL) microscopic inspection of the catalyst materials, e.g. by means of scanning electron microscopy, demonstrates substantial morphological alterations on the nm length scale on the material surface as consequence of the sub-carbonate formation and the potential-driven oxide reduction into the metallic Bi foam. The foam morphology on a mesoscopic length scale (macroporosity) remains, by contrast, fully unaffected by these phase transitions

Departure from solid solution behavior in double perovskites

Mixed ionic electronic conducting oxides (MIEC) serve a plethora of electrochemical applications such as cathodes for solid oxide electrochemical cells and oxygen evolution reaction catalysts for water splitting. These applications rely to a large extent on the MIEC’s ability for electron and/or ion transfer across the solid/gas or solid/liquid interface. The efficacy of these reactions being governed by the surface defect chemistry and electronic structure, rational design of the (surface) chemistry presents itself as an auspicious path to tune these properties towards optimal device performance. Please click Additional Files below to see the full abstract

Anodic and Cathodic Platinum Dissolution Processes Involve Different Oxide Species

The degradation of Pt-containing oxygen reduction catalysts for fuel cell applications is strongly linked to the electrochemical surface oxidation and reduction of Pt. Here, we study the surface restructuring and Pt dissolution mechanisms during oxidation/reduction for the case of Pt(100) in 0.1 M HClO4 by combining operando high-energy surface X-ray diffraction, online mass spectrometry, and density functional theory. Our atomic-scale structural studies reveal that anodic dissolution, detected during oxidation, and cathodic dissolution, observed during the subsequent reduction, are linked to two different oxide phases. Anodic dissolution occurs predominantly during nucleation and growth of the first, stripe-like oxide. Cathodic dissolution is linked to a second, amorphous Pt oxide phase that resembles bulk PtO2 and starts to grow when the coverage of the stripe-like oxide saturates. In addition, we find the amount of surface restructuring after an oxidation/reduction cycle to be potential-independent after the stripe-like oxide has reached its saturation coverage.Funding is acknowledged from Deutsche Forschungsgemeinschaft for OMM and SC (project number 418603497), for OMM by the German Federal Ministry of Education and Research (BMBF) via project 05K19FK3, and for DAH by the NSERC (grant RGPIN-2017-04045). FCV acknowledges that the grants PID2021-127957NB-I00 and TED2021-132550B-C21 were funded by MCIN/AEI/ 10.13039/501100011033 and by the European Union. The use of supercomputing facilities at SURFsara was sponsored by NWO Physical Sciences, with financial support by NWO. Open Access funding enabled and organized by Projekt DEAL