Photopolymerizations offer many advantages (such as temporal and spatial control of initiation, cost efficiency, and solvent-free systems) over traditional thermopolymerization. While they are now well-established as the preferred option for a variety of films and coating applications, they are limited from many applications due to problems such as oxygen inhibition, light attenuation, additive interference, or the creation of shadow regions and oxygen pockets due to complex shapes. These problems can be solved by using an underutilized form of photopolymerization--cationic photopolymerization. Cationic photopolymerizations have unique active centers which are essentially non-terminating causing extremely long active center lifetimes. In this contribution, the unique characteristics of cationic active centers are explored for their ability to be used in many new applications where previous photopolymerization techniques failed. It was found that the long lifetimes of the active centers permitted them to be very mobile, allowing them to migrate into and polymerize regions that were never illuminated in a process termed shadow cure. The mobility of cationic active centers provides a very efficient means of photopolymerizing of thick and pigmented systems. The long lifetimes of the cationic active centers can be used in the creation of a sequential stage curable polymer system and in the development of novel methods to cure complex shapes, two applications previously unattainable by photopolymerization. The termination of the cationic active centers was found to be reversible and can be used as a technique for external temporal control of the photopolymerization after the illumination has ceased. These abilities have great potential and will allow cationic photopolymerization to be used in many new applications where previous photopolymerization techniques failed, expanding their influence and benefits.

Understanding changes in materials properties as a function of size is crucial for both fundamental science development and technological applications. Size restriction results in quantum confinement effects that modify both energy level structures and electron dynamics of solid materials. This study investigates individual quantum states in a single nanocrystal. Single electron charging effects in gold and semiconductor nanocrystals are observed. Charging effects are found to be dominant in samples, where the nanocrystals are weakly coupled to the substrate. For nanocrystals strongly coupled to the substrate, nanocrystal-substrate tunneling rate is larger than tip-nanocrystal tunneling rate. Therefore, the resulting peaks in the dI/dV spectrum are attributed to tunneling through the energy levels of the nanocrystal. A newly developed nanocrystals BEES technique is used successfully to further explore quantized energy levels and electron dynamics in single gold nanocrystals. BEES samples were grown successfully by depositing $unit[10]{nm}$ thick gold on silicon substrates. Nanocrystals are chemically attached to the gold substrate using a self assembled monolayer (SAM) of xyelendithiol molecules. Immobile and single isolated nanocrystals were imaged at low temperature. A BEES turn-on voltage of $unit[0.84]{V}$ was found on nanocrystal-free region of the substrate. The BEES spectrum acquired on a single gold nanocrystal is found to be attenuated by a factor of 10 when compared with BEES acquired on the substrate. The attenuation is attributed to electron relaxation to lower energy states before tunneling out of the nanocrystal. The measured hot electron lifetimes from experimental data were found to be on the order of $unit[16]{picoseconds}$, which is a long time compared to lifetimes in bulk metals or large nanocrystals. The long measured lifetimes result from the molecular-like energy level structures of these small nanocrystals.

This dissertation presents a novel modeling framework for understanding the dynamics of peer-to-peer (P2P) networks under churn (i.e., random user arrival/departure) and designing systems more resilient against node failure. The proposed models are applicable to general distributed systems under a variety of conditions on graph construction and user lifetimes. The foundation of this work is a new churn model that describes user arrival and departure as a superposition of many periodic (renewal) processes. It not only allows general (non-exponential) user lifetime distributions, but also captures heterogeneous behavior of peers. We utilize this model to analyze link dynamics and the ability of the system to stay connected under churn. Our results offers exact computation of user-isolation and graph-partitioning probabilities for any monotone lifetime distribution, including heavy-tailed cases found in real systems. We also propose an age-proportional random-walk algorithm for creating links in unstructured P2P networks that achieves zero isolation probability as system size becomes infinite. We additionally obtain many insightful results on the transient distribution of in-degree, edge arrival process, system size, and lifetimes of live users as simple functions of the aggregate lifetime distribution. The second half of this work studies churn in structured P2P networks that are usually built upon distributed hash tables (DHTs). Users in DHTs maintain two types of neighbor sets: routing tables and successor/leaf sets. The former tables determine link lifetimes and routing performance of the system, while the latter are built for ensuring DHT consistency and connectivity. Our first result in this area proves that robustness of DHTs is mainly determined by zone size of selected neighbors, which leads us to propose a min-zone algorithm that significantly reduces link churn in DHTs. Our second result uses the Chen-Stein method to understand concurrent failures among strongly dependent successor sets of many DHTs and finds an optimal stabilization strategy for keeping Chord connected under churn.

>Magister Scientiae - MSc / Measurements of nuclear level lifetimes are an important aspect of experimental nuclear physics. Such measurements determine transition matrix elements for nuclear structure research and also provide the widths of relevant excited states in nuclei that are of astrophysical interest. In the latter, the measured widths are used to obtain reaction rates in main sequence stars such as the Sun and in binary-star systems where the accretion of material from one star to another provides an opportunity to study extreme stellar environments such as novae and x-ray bursts. This thesis work describes the design and simulation of a new experimental set up at iThemba LABS that will allow for highprecision femtosecond-level lifetime measurements of nuclear states using the Doppler Shift Attenuation Method (DSAM). We use the Solid Edge computer-aided design (CAD) software to design a new scattering chamber with a cooled target ladder specifically for such measurements using inverse-kinematic transfer reactions with ion implanted targets. The light charged ejectiles from the reaction will be detected with a ΔE - E silicon telescope, while Doppler shifted rays will be registered using a high-purity and 100% efficient germanium (HPGe) detector. We also describe preliminary Monte Carlo simulation codes that are being developed in a relativistically invariant framework to optimize the experimental set up and to obtain predicted lineshapes of γ rays from several astrophysically relevant states in nuclei using this experimental set up. / National Research Foundation (NRF)

The aim of this diploma thesis will be to create a plan for maintenance and repairs of the building on the street of the brothers Čapků in Brno. The first part will describe the individual concepts dealing with the life of individual structural elements, maintenance and repair and revisions of dedicated technical equipment. The second part will be focused on practice. A plan for maintenance and repairs of the building structures and a plan for revisions and inspections on the dedicated technical equipment will be prepared for the given building. The proposed plan will be designed to spread the funds over the whole period considered.

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This dissertation consists of three major studies. The first study, described in Chapter 3, focuses on the experimental work we carried out; experimental study of the electronic transition dipole moment matrix elements (TDMM) for the and electronic transitions of the sodium dimer molecule. Here we obtained the electronic transition dipole moments through Autler-Townes and resolved fluorescence spectroscopy and compared them to the theory. The second study, described in Chapter 4, is on sodium dimer ion-pair states. In this work, we calculated the radiative lifetimes and electronic transition dipole moments between Na2 ion-pair states ( , , , ) and state. This study was published in 2015. The last study, described in Chapter 5, is the total lifetime (bound-bound plus bound-free) and transition dipole moment calculations of the ion-pair electronic states, , of the lithium dimer molecule. / Physics