National Repository of Grey Literature 24 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Dynamika živých organismů
Vondrák, Marek ; Pelikán, Josef (advisor) ; Kavan, Ladislav (referee)
The computer animation of articulated figures is one of the most interesting and the most developing areas of the modern computer graphics. The goal of this thesis is to get the reader acquainted with the theory of constrained rigid body simulation, which is subsequently used to construct a generic rigid body simulator with constraints and friction and the figure library suitable for the animation of articulated human-like figures. Articulated figures are represented by sets of rigid bodies (segments) connected by joints and their motion is determined by the dynamics of the corresponding segments. Additional constraints, specifying e.g. desired angles at joints or the positions of selected sites on the surface of the figure segments, allow to control the figure motion. A rich set of interactive demonstration examples presents the features of the actual simulator and the capabilities of the figure library to process motion capture data (replay motion capture data, adapt the data to external influences, map the "raw" motion capture data to the motion of figure segments, etc).
ELECTROCHEMICAL STUDY OF CuSCN INORGANIC HOLE-TRANSPORT MATERIAL FOR SOLAR CELLS PREPARED BY ELECTRODEPOSITION FROM AQUEOUS SOLUTION
Vlčková Živcová, Zuzana ; Mansfeldová, Věra ; Bouša, Milan ; Kavan, Ladislav
A comparative study is reported for electrodeposited copper(I) thiocyanate layers (ca. 500 nm) on two types of conductive/semiconductive substrates: i) carbon (boron-doped diamond_BDD, glass-like carbon_GC), and ii) carbon-free F-doped SnO2 conducting glass (FTO). SEM and Raman evidence that electrodeposition from aqueous solution results in homogenous CuSCN layers with dominant thiocyanate ion bounded to copper through its S-end (Cu−SCN bonding), as in spin-coated CuSCN layers. Electrochemical impedance spectroscopy (EIS) confirms the p-type semiconductivity of layers with a flatband potential from 0.1 to 0.18 V vs. Ag/AgCl depending on the substrate type, and the acceptor concentration (NA) of 5 x 1020cm-3 in all cases. The flatband potentials determined from Mott-Schottky plots (EIS) are in good agreement with the Kelvin probe measurements. The blocking quality of CuSCN layers was tested using Ru(NH3)63+/2+ redox probe. CuSCN deposited on BDD substrate exhibits better blocking properties compared to CuSCN deposited on FTO.
Electrochemical, photoelectrochemical and spectroelectrochemical characterization of nanomaterials
Pitňa Lásková, Barbora ; Kavan, Ladislav (advisor) ; Šubrt, Jan (referee) ; Krýsa, Josef (referee)
Titanium dioxide (TiO2) and spinel Li4Ti5O12 belong to widely studied semiconducting metal oxides. Nanocrystalline TiO2 and Li4Ti5O12 are attractive materials for applications in Li-ion batteries and the former also for photoelectrochemical solar cells. Moreover, spinel Li4Ti5O12 could be a promising material for Na-ion batteries too, because of possible accommodation of larger Na+ ions (compared to Li+ ). The nanocrystalline TiO2 anatase with a predominant {001} facet was studied electrochemically by cyclic voltammetry of Li+ insertion and by chronoamperometry and compared with anatase materials with dominating {101} facet. Both voltammetric and chronoamperometric diffusion coefficients and activation energies proved higher activity of anatase {001} nanosheets toward Li+ insertion than that of the usual anatase nanoparticles exposing the {101} facet. Subsequently, the flatband potential and electron kinetics of TiO2 anatase nanocrystals with mostly exposed facet {101} or {001} were compared. The anatase {001} nanoplatelets exhibited more negative flatband potential, higher chemical capacitance and longer electron lifetime than anatase {101} nanoparticles. The Li+ insertion into TiO2 anatase nanoparticles was studied by Raman spectroscopy and by in situ Raman spectroelectrochemistry. Four...
Preparation and characterization of nanomaterials for electrochemical energy storage
Bouša, Milan ; Kavan, Ladislav (advisor) ; Fejfar, Antonín (referee) ; Velický, Matěj (referee)
Graphene research is nowadays one of the worldwide most prominent fields of interest in material science due to many extraordinary properties of graphene and related materials. However, the different techniques of synthesis and subsequent handling and/or treatment have a substantial impact on the properties of the graphene and thus a lot of efforts have been focused on developing of the advanced methods for graphene preparation and characterization. Graphene can be easily produced by oxidation and consequent exfoliation of the bulk graphite; however, resulting graphene oxide needs to be reduced back to graphene-like structure due to partial restoration of sp2 network. Herein, a detailed study of the structural evolution of the graphene oxide during electrochemical treatment has been performed using X-ray photoelectron, Raman and infrared spectroscopies and the results were compared with non-oxidized graphene nano-platelets. Additionally, graphene oxide in composite with LiFePO4 olivine material, which is electrochemically almost inactive in a freshly made state, has been tested by repeated electrochemical cycling. Using various electrochemical methods, the progressive electrochemical activity enhancement has been observed and spontaneous graphene reduction was identified as responsible for this...
Analysis of very low pollutant concentrations in air and their photocatalytic oxidation
Vaněčková, Eva ; Rathouský, Jiří (advisor) ; Kavan, Ladislav (referee)
For preparation of the mesoporous thin layers of TiO2 of define structure was used a sol-gel method in combination with structure directing surface-active agents. Various properties of the layers, such as size of surface area, thickness, porosity, light absorption ability and their relationschip to photocatalytic activity during NO oxidation, were investigated. A significant influence of these properties to activity of the photocatalyst was proved.
Study of Properties of Titanium Dioxide Nanoparticles
Procházka, Jan ; Kavan, Ladislav (advisor) ; Mička, Zdeněk (referee) ; Šubrt, Jan (referee)
Charles University in Prague Faculty of Science Department of Inorganic Chemistry STUDY OF PROPERTIES OF TITANIUM DIOXIDE NANOPARTICLES. PhD Thesis Abstract Jan Procházka Prague 2009 8. This PhD thesis is based on publications and patent applications (1-9) to which the author contributed considerably. The list of the publications is attached at the end of this text. Systematic research of the properties of TiO2 nanoparticles brought new pieces of knowledge into syntheses of titanium dioxide nanoparticles organized in the templated structures. When the structures were used in the solar cells, their solar efficiency significantly surpassed the performance of the conventional TiO2 films. The study was focused on the engineering and optimization of parameters of the nanostructures used as anodes in the dye sensitized solar cells (DSC). Several new technical solutions have been delivered during the work on variety of TiO2 structures. First, the factors with an impact on the proper function of the TiO2 multilayer film were determined 9. and then, the layer by layer deposition technique was perfected. Introduction of phosphorus into the templated mesoporous film synthesis protocol represented significant progress. The presence of phosphorus stabilized the TiO2 surface area at a high temperature and allowed a...
Dynamika živých organismů
Vondrák, Marek ; Pelikán, Josef (advisor) ; Kavan, Ladislav (referee)
The computer animation of articulated figures is one of the most interesting and the most developing areas of the modern computer graphics. The goal of this thesis is to get the reader acquainted with the theory of constrained rigid body simulation, which is subsequently used to construct a generic rigid body simulator with constraints and friction and the figure library suitable for the animation of articulated human-like figures. Articulated figures are represented by sets of rigid bodies (segments) connected by joints and their motion is determined by the dynamics of the corresponding segments. Additional constraints, specifying e.g. desired angles at joints or the positions of selected sites on the surface of the figure segments, allow to control the figure motion. A rich set of interactive demonstration examples presents the features of the actual simulator and the capabilities of the figure library to process motion capture data (replay motion capture data, adapt the data to external influences, map the "raw" motion capture data to the motion of figure segments, etc).
Experimental and Theoretical Comparative Study of Monolayer and Bulk MoS2 under Compression
del Corro, Elena ; Morales-García, A. ; Peňa-Alvarez, M. ; Kavan, Ladislav ; Kalbáč, Martin ; Frank, Otakar
Recently, a new family of 2D materials with exceptional optoelectronic properties has stormed into the scene of nanotechnology, the transition metal dichalcogenides (e.g., MoS2). In contrast with graphene, which is a zero band gap semiconductor, many of the single layered materials from this family show a direct band-gap in the visible range. This band-gap can be tuned by several factors, including the thickness of the sample; the transition from a direct to indirect semiconductor state takes place in MoS2 when increasing the number of layers from 1 towards the bulk. Applying strain/stress has been revealed as another tool for promoting changes in the electronic structure of these materials; however, only a few experimental works exist for MoS2. In this work we present a comparative study of single layered and bulk MoS2 subjected to direct out-of-plane compression, using high pressure anvil cells and monitoring with non-resonant Raman spectroscopy; accompanying the results with theoretical DFT studies. In the case of monolayer MoS2 we observe transitions from direct to indirect band-gap semiconductor and to semimetal, analogous to the transitions observed under hydrostatic pressure, but promoted at more accessible pressure ranges (similar to 25 times lower pressure). For bulk MoS2, both regimes, hydrostatic and uniaxial, lead to the semimetallization at similar pressure values, around 30 GPa. Our calculations reveal different driving forces for the metallization in bulk and monolayer samples.
EXPERIMENTAL STUDY OF PIB-BASED CVD GRAPHENE TRANSFER EFFICIENCY
Bouša, Milan ; Kalbáč, Martin ; Jirka, Ivan ; Kavan, Ladislav ; Frank, Otakar
The transfer of graphene prepared by Chemical Vapor Deposition (CVD) from metal catalyst to target substrate is an important step in preparing desirable nanoscale structures in various fields of science, and thus searching for fast, cheap and clean method attracts great interest. Investigation of mechanical properties of graphene, which are crucial for applications in flexible electronics, performed on bendable synthetic materials, requires a transfer technique using polymers soluble in aliphatic solvents harmless for target polymer substrates. In this study we explore a dry technique using polydimethylsiloxane (PDMS) as stamping polymer and polyisobutylene (PIB) layer as graphene-support polymer. After the transfer PDMS is peeled off and PIB is dissolved in hexane, hence this method fulfils the above mentioned prerequisite. The effectiveness of this transfer was examined by scanning electron microscopy, optical microscopy and Raman microspectroscopy including micro-mapping, and finally by X-ray photoelectron spectroscopy. With all methods carried out, it was found that this sort of stamp-technique is suitable for a high precision transfer of small grains of CVD graphene onto polymer substrates with large yields and similar purity compared to poly(methylmethacrylate) (PMMA)based transfer methods. However, it introduces substantial quantity of surface discontinuities, and therefore this is not a proper method for large scale applications.
STRAIN ENGINEERING OF THE ELECTRONIC STRUCTURE OF 2D MATERIALS
del Corro, Elena ; Peňa-Alvarez, M. ; Morales-García, A. ; Bouša, Milan ; Řáhová, Jaroslava ; Kavan, Ladislav ; Kalbáč, Martin ; Frank, Otakar
The research on graphene has attracted much attention since its first successful preparation in 2004. It possesses many unique properties, such as an extreme stiffness and strength, high electron mobility, ballistic transport even at room temperature, superior thermal conductivity and many others. The affection for graphene was followed swiftly by a keen interest in other two dimensional materials like transition metal dichalcogenides. As has been predicted and in part proven experimentally, the electronic properties of these materials can be modified by various means. The most common ones include covalent or non-covalent chemistry, electrochemical, gate or atomic doping, or quantum confinement. None of these methods has proven universal enough in terms of the devices' characteristics or scalability. However, another approach is known mechanical strain/stress, but experiments in that direction are scarce, in spite of their high promises.\nThe primary challenge consists in the understanding of the mechanical properties of 2D materials and in the ability to quantify the lattice deformation. Several techniques can be then used to apply strain to the specimens and thus to induce changes in their electronic structure. We will review their basic concepts and some of the examples so far documented experimentally and/or theoretically.

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