Zeitschriftenaufsätze

The weakly entangled ultrahigh molecular weight polyethylene (UHMWPE) was synthesized by a Ziegler-Natta catalyst, where the titanium tetrachloride was anchored on the polystyrene (PS)-modified silica. The PS chains were successfully incorporated into silica hierarchical pores even with the size less than 10 nm through the in situ free-radical polymerization of styrene. The self-diffusion coefficient and crystallization of probing molecules inside the pores were investigated by the pulsed field gradient NMR and thermoporosimetry to address the swollen behavior of incorporated PS blocks. This PS blocks compartmentalized the polyethylene chains, where the less entangled UHMWPE was synthesized with an exceptional activity at 70˚C. The ubiquitous PS isolators effectively hindered the formation of chains overlaps during the polymerization, showing a long-term efficiency to reduce the entanglements of nascent UHMWPE even at 4 h of polymerization The toughness/stiffness/strength balance of weakly entangled UHMWPE was significantly improved.

An optimal waste collection is a very complicated task in different countries. However, this task is more intricate, when there is not an organized procedure between people, government and technology. In this research it was studied and proposed strategies, to optimize the waste collection by technical suggestions, that were based on mathematical analysis and new technologies applications of sensors based on nanostructures due to this kind of sensors have good performance to measure physical variables in not simple places and conditions, such as around waste. Hence the reason, this work is prepared to contribute in the development of sensors based on nanostructures according to detect the physical variables: temperature, humidity, infrared reflection, moreover carbon dioxide (CO2) and methane (CH4) gases, which help to monitor the consequences of a not correct waste collection.As dependence on central and local government rules of waste management, it could be possible to find solution about organized waste collection, in which every family and walkers in streets would have the task to select the organic and inorganic garbage before the government trucks take the contents of the garbage trash cans to the landfill garbage dumps. However, many times the trash cans are not taken on time by the government trucks and garbage from them are producing gases and decomposition that causes contamination that damages health. Therefore, in this work there are proposed designed intelligent sensors, which are fixed in the trash cans due to measure physical parameters to give alarm for administrators controllers of boxes and to enhance the garbage selections from homes and streets to the main garbage landfills of the city. In other side, there will not be right solution in the waste collection, no matter the high advantage technologies, while humans could not be sensitive under this problematic. There are cleaned areas in cities, as for example touristic places, nevertheless, there are plenty places, where are not cared and people in streets through residual solids around, hence the technical solution will be useful only whether humans can get the environment caring condition compromise.

Spatial displacements of spins between radio frequency pulses in a Double-Quantum (DQ) nuclear magnetic resonance pulse sequence generate additional terms in the effective DQ Hamiltonian. We derive a simple expression that allows the estimation and control of these contributions to the initial rise of the DQ build up function by variation of experimental parameters in systems performing anomalous diffusion. The application of polymers is discussed.

Passively mode-locked semiconductor disk lasers have received tremendous attention from both science and industry. Their relatively inexpensive production combined with excellent pulse performance and great emission-wavelength flexibility make them suitable laser candidates for applications ranging from frequency-comb tomography to spectroscopy. However, due to the interaction of the active medium dynamics and the device geometry, emission instabilities occur at high pump powers and thereby limit their performance potential. Hence, understanding those instabilities becomes critical for an optimal laser design. Using a delay-differential equation model, we are able to detect, understand, and classify three distinct instabilities that limit the maximum achievable pump power for the fundamental mode-locking state and link them to characteristic positive-net-gain windows. We furthermore derive a simple analytic approximation in order to quantitatively describe the stability boundary. Our results enable us to predict the optimal laser-cavity configuration with respect to positive-net-gain instabilities and therefore may be of great relevance for the future development of passively mode-locking semiconductor disk lasers.

We study the origin and formation of antiphase domains (APDs) and related defects in 7 nm thin, lattice-matched GaP buffer layers deposited by metal-organic chemical vapor deposition (MOCVD) on well-defined, nearly single-domain, double-layer stepped, low-miscut Si(100) substrates obtained by specific treatment with arsenic. Using dark-field imaging modes in low-energy electron microscopy (LEEM), the minority reconstruction domains of Si(100):As and the APDs of the deposited GaP epilayer are identified, quantified, and compared. We show that residual (2x1)-reconstructed terraces of the minority domain on the Si substrate cause the formation of APDs and that the fraction of the minority domain of the substrate (≅0.07) entails a comparable fraction of APDs in thin GaP epilayers. The topographies of APDs are revealed by atomic force microscopy (AFM) and by scanning tunneling microscopy (STM). We observe two very different APD-related defects in the GaP epilayer, both pinned to residual monolayer steps of the substrate. GaP growth on minority domain terraces with widths in the range of 40-100 nm gives rise to APDs of comparable lateral dimensions. Minority domain terraces of the substrate with widths <20 nm cause the formation of 7-20 nm wide trenches in the GaP layer with rampart-like mounds along their rims. Using nanoscale Auger electron spectroscopy (AES), we provide evidence that these trenches extend through the GaP layer down to the exposed, uncovered Si substrate. We conclude that nucleation of GaP on small minority domain terraces is largely inhibited as most Ga and P atoms deposited on these terraces diffuse across the domain boundary and side walls of emerging trenches to adjacent majority domain terraces where they form the observed mounds. Nucleation of GaP does take place on minority domain terraces with widths ≥40 nm and leads to the growth of APDs.