The nature and role of defects is of primary importance to understand the physical properties of C and BN single walled nanotubes. Transmission electron microscopy (TEM) is a well known powerful tool to study the structure of defects in materials. However, in the case of SWNTs, the electron irradiation of the TEM may knock out atoms. This effect may alter the native structure of the tube, and has also been proposed as a potential tool for nanoengineering of nanotubular structures. Here we develop a theoretical description of the irradiation mechanism. First, the anisotropy of the emission energy threshold is obtained via density functional based calculations. Then, we numerically derive the total Mott cross section for different emission sites of carbon and boron nitride nanotubes with different chiralities. Using a dedicated STEM microscope with experimental conditions optimised on the basis of derived cross-sections, we are able to control the generation of defects in nanotubular systems. Either point or line defects can be obtained with a spatial resolution of a few nanometers. The structure, energetics and electronics of point and line defects in BN systems have been investigated. Stability of mono- and di- vacancy defects in hexagonal boron nitride layers is investigated, and their activation energies and reaction paths for diffusion have been derived using the nudged elastic band method (NEB) combined with density functional based techniques. We demonstrate that the appearance of extended linear defects under electron irradiation is more favorable than a random distribution of point defects and this is due to the existence of preferential sites for atom emission in the presence of pre-existing defects, rather than thermal vacancy nucleation and migration.

Neurogenesis is the process of generation of neurons during embryonic development and adulthood. The focus of this doctoral work is the study of the cell biological aspects of neurogenesis and the mechanisms regulating the switch of neural stem cells from proliferation to differentiation. During embryonic development neurogenic divisions occur at the apical or basal side of the pseudostratified epithelium that forms the wall of the neural tube, the neuroepithelium. Apical asymmetric neurogenic divisions (AP) give rise to a neuron and a progenitor cell, while basal symmetric neurogenic divisions (BP) give rise to two neurons. The first part of this thesis is focused on the study of some cell biological aspects of BPs. We first validated the use of the Tis21-GFP knock in mouse line, previously generated in our laboratory. We found that the totality of neurogenic progenitors is marked by the expression of a nuclear GFP. We calculated the abundance of BPs overtime since the onset of neurogenesis showing that BPs overcome APs over development. We studied the loss of apical contact of the basal dividing cells. We found that both neurogenic and non-neurogenic basally dividing progenitors miss the apical contact; which is lost prior mitosis. We generated and characterized a second mouse line, the Tubb3-GFP line expressing a plasma membrane-localized GFP in neurons. These two lines were crossed to obtain a new line (TisTubb-GFP) allowing detection of neurogenic divisions and tracking daughter cells. Using this model: (i) we imaged symmetric neurogenic divisions of BPs, identifying daughter cells as neurons, during imaging; (ii) we compared the kinetics of betaIII-tubulin-GFP appearance after apical or basal mitosis, showing that daughters of BPs express betaIII-tubulin-GFP faster than daughters coming from apical divisions; (iii) we imaged neuronal migration and localization of the Golgi apparatus. Neurogenesis in the adult is confined to two specific regions in the telencephalon: the sub ependymal zone, lining the ventricle, and dentate gyrus of the hippocampus. The second part of this thesis focuses on the adult neurogenic progenitors lineage. Tis21-GFP expression was found and characterized in the two adult neurogenic regions from early postnatal to adulthood. Using a panel of markers for the adult neurogenic cell lineage and confocal imaging, we characterized Tis21-GFP expression, in the dentate gyrus. Tis21-GFP is first expressed in the neurogenic subpopulation of doublecortin positive cells. Tis21-GFP is inherited by the neurons and eventually degraded. Moreover, our data suggest that mitotic Tis21-GFP cells are an indicator of the levels of neurogenesis more accurate than doublecortin positive cells, in the early postnatal mouse. (Anlage Quick time movies 77,88 MB)

The modification of the radiation pattern and radiative lifetime of dye molecules in three-dimensional colloidal photonic crystals is studied, using high-resolution optical microscopy and spectroscopy. The experimental observations are compared to corresponding calculations of the local optical density of states. It can be concluded, that the fluorescence of the molecules is redistributed spectrally and spatially within the photonic crystal. / Mit Hilfe hochauflösender optischer Mikroskopie und Spektroskopie werden Änderungen der Abstrahlcharakteristik und strahlenden Lebensdauer von Farbstoffmolekülen in dreidimensionalen kolloidalen photonischen Kristallen untersucht. Die experimentellen Beobachtungen werden mit entsprechenden Berechnungen der lokalen optischen Zustandsdichte verglichen. Hieraus kann auf eine spektrale und räumliche Umverteilung der Fluoreszenz der Moleküle im photonischen Kristall geschlossen werden.

Gegenstand der Dissertation sind Untersuchungen zur Photolumineszenz von Silizium-Nanokristallen. Den Schwerpunkt bilden dabei die Messungen an isolierten Partikeln mittels konfokaler Mikroskopie und optischer Spektroskopie. Von einzelnen Silizium-Partikeln konnten relativ schmale, strukturierte Photolumineszenzbanden detektiert werden, die die Aussagen des Quantum-Confinement-Modells bestätigen. Ein weiteres Merkmal der Photolumineszenz von einzelnen Halbleiter-Nanopartikeln ist das so genannte Blinken. Die Erstellung von Blinkstatistiken unter verschiedenen Anregungsbedingungen ermöglichte es, die zum Blinken führenden photophysikalischen Prozesse genauer zu charakterisieren. Es wird unter anderem gezeigt, dass das reversible Bleichen der Lumineszenz von Silizium-Nanokristall-Ensemblen und porösem Silizium auf ein instationäres Blinkverhalten zurückzuführen ist. Abschließend werden Bezüge zu den astrophysikalischen Beobachtungen von der Extended Red Emission hergestellt und verschiedene Tunnel- und Random-Walk-Modelle zur Beschreibung der photophysikalischen Prozesse diskutiert.

Gegenstand dieser Diplomarbeit ist die Untersuchung der Dynamik in dünnen Polymerfilmen anhand von einzelnen Molekülen. Zu diesem Zweck wurden dünne Filme (kleiner 100nm) hergestellt und mittels Einzelmoleküldetektion und zeitaufgelöster Einzelphotonenzählung analysiert, was eine orts- und zeitaufgelöste Untersuchung einzelner Farbstoffmoleküle ermöglicht. Ziel war es, festzustellen ob, und auf welchem Weg, die Dynamik der Umgebung in Fluktuationen der Fluoreszenzlebensdauer einzelner Moleküle sichtbar wird. Neben der Evaluierung der Untersuchungsmethoden wurden in dieser Arbeit zwei Arten von Sensormolekülen - DiD und Malachit Grün - näher untersucht. / The subject of this diploma thesis is the analysis of dynamics in thin polymer films using single molecules. Thin polymer films (less than 100nm) were produced and analysed by Single Molecule Detection (SMD) and Time Correlated Single Photon Counting (TCSPC). This allows a spatial and time resolved investigation of the single dye molecule. The aim was to ascertain if, and in which way, the dynamics of the environment are reflected by fluctuations of the fluorescence lifetime of the single molecule. In addition to evaluating the investigation methods two kinds of molecules - DiD and Malachite Green - were also analysed.

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This diploma thesis deals with evaluation of the conditions for laboratory testing of composite profiles with fiber-reinforced polymer (FRP). Theoretical part describes the main material properties of FRP profiles and method of manufacturing by pultrusion. Experimental part evaluates imposition of the test samples in alkaline environment and their subsequent changes in physical properties. Next part contains evaluation of cuts FRP profiles by electron microscopy in combination with element analysis. The outcome of this work is the method of evaluation of accelerated durability FRP profiles.

The alkali-silica reaction is one of the most damaging chemical reactions taking place in concrete, which can cause fatal damage. ASR originates under following conditions: high moisture (> 80 %), sufficient amount of alkaline ions (Ca2+ , Na+ , K+ ) and use of reactive aggregates (low crystaline or deformed quartz, amorphous SiO2). Reactive aggretates react with high alkaline pore solution and produce hydrofile gels. These gels absorb water and swell. Dilatometric test methods are commonly used to evaluate the reactivity of aggregates. The principle of dilatometric test methods is simple. Mortar or concrete prisms are created in a laboratory, then they are stored in the special environment, which accelerates the inception of ASR. The creation and expansion of alkali-silica gels cause prism's length changes. The major goal of this diploma thesis was to evaluate the alkali-silica reactivity potential of quartz-rich rocks using microscopic (polarizing microscopy, scanning electron microscopy combined with SEM/BSE image analysis) and dilatometric (ASTM C1260, RILEM AAR-4.1) methods. Rocks were assessed as reactive, potentially reactive and non-reactive by the ASTM C1260 method. The reactivity of aggregates was connected with the amount of cryptocrystaline matrix, grain size, shape of grain boundaries,...

Title: Deconvolution fluorescence microscopy of yeast cells Author: Tomáš Štec Department: Institute of Physics of Charles University Supervisor: prof. RNDr. Jarmoír Plášek, CSc., Institute of Physics of Charles Uni- versity Abstract: Fluorescence microscopy presents an fast and cheap alternative to more advanced imaging methods like confocal and electron microscopy, even though it is subject to heavy image distortion. It is possible to recover most of the original distortion-free image using deconvolution in computer image processing. This al- lows reconstruction of 3D structure of studied objects. Deconvolution procedure of NIS Elements AR program undergoes an thorough inspection in this diploma the- sis. It is then applied on restoration of 3D structure of calcofluor stained cell wall of budding yeast Saccharomyces cerevisiae. Changes of the structure of the cell wall during cell ageing are being examined. Cell wall of aged cells shows increased surface roughness and even ruptures at the end of cell life. Keywords: fluorescence, microscopy, deconvolution, NIS Elements AR, calcofluor, yeast, cell wall, ageing