Zugl.: Frankfurt (Main), Universiẗat, Diss., 1986.

Zugl.: Frankfurt am Main, Univ., Diss., 2005. / Literaturverz. S. 126 - 144.

Bayreuth, Universiẗat, Diss., 2003.

No description available.

This dissertation presents the synthesis and characterization of a variety of neutral and cationic complexes featuring Group 13-15 element centres stabilized by N-, P-, and O-based donors. Unique aluminum and gallium cationic complexes are obtained from equimolar reactions of the metal halide with the chelating alkyl phosphine dmpe. However, using the analogous amine donor tmeda, neutral adducts are preferred for aluminum as well as for GaCl3, while cations are obtained for GaBr3 and GaI3. New cations of Ge(II) and Sn(II) were also discovered, featuring the coordination of either bipyridine ligands or dmpe. Utilizing bipyridine led to the expected mono and dicationic chelate complexes, however, using dmpe led to the formation of unprecedented tetracationic molecules. The reactivities of the bipyridine complexes were investigated with a variety of substrates which showcased their Lewis acidity as well as their ability to be oxidized. Finally, a new series of high oxidation-state main group cations have been synthesized using a variety of ligands. The ligand choice was found to be an important role in compound isolation as ligand degradation occurred for some of the compounds due to their high electrophilicity. Additionally, the Lewis acidity of some of the complexes leads to interesting reaction chemistry including sp3 C-H activation. Overall, the results presented herein represent new coordination chemistry for the main group elements and opens the door towards new reactivity pathways including small molecule activation and catalysis. / Graduate

The Main Zone is dominated by medium – grained, homogeneous gabbronorite, and anorthosites. The plagioclase compositions of the core is ((Na(0.227 – 0.353), K (0.012 – 0.046), Ca (0.651 – 0.777)) Al (1.630 – 1.752) Si (2.183 – 2.345) O8) and at the rim is ((Na (0.189 – 0.371), K (0.005 – 0.108), Ca (0.651 – 0.777)) Al (1.630 – 1.752) Si (2.183 – 2.345) O8). The composition of orthopyroxene is ((Mg (0.660 – 0.808), Fe (0.206 – 0.309), Ca (0.007 – 0.081)) Si (0.960 – 1.037) O3) and the compositions of clinopyroxene is ((Mg (0.229 – 0.678), Fe (0.092 – 0.427), Ca (0.012 – 0.475) Si (0.776 – 1.012) O3. The Mg# and An# varies with depth, where plagioclase increase in concentration the An# increases and the Mg# decreases. The variations in magma compositions are attributed to interlayering of different lithologies which are the result of fractional crystallisation in the magma chamber. This is supported by linear trends of the major and trace element bivariant plots. The magmatic event forming the Main Zone resulted in lateral expansion of the sheet – like magma chamber. The Main Zone formed through two magmas; first magma forming the lower Main Zone and the second magma, intruded the Main Zone at the level of the Pyroxenite Marker, forming the upper Main Zone. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Geology / unrestricted

The aim of this work is to develop a preliminary design of a six-seat helicopter with a turboshaft engine. The preliminary design of the helicopter consists of processing statistical data on similar helicopters, which are then, based on the specified requirements, used to estimate the basic weight parameters of the helicopter, the main geometric parameters and to determine the type and power of the propulsion unit. It consists of calculations of basic geometric parameters of the aircraft and engine selection. Part of another solution is the aerodynamic calculation of the supporting rotor, from which both the performance of the helicopter in suspension and in forward flight flow. In a special part of the project, the attention is paid to the system of balancing the reaction torque, in this case fenestrone and the solution is supplemented by some specific means installed on the tail beam, which help to balance the reaction torque and improve the directional control parameters of the helicopter.

La stimulation associative-pairée (PAS) est utilisée pour induire de manière non invasive des changements plastiques dans le cortex moteur primaire (M1). Les paradigmes de PAS classiques impliquent la combinaison d'une stimulation électrique sur un nerf périphérique et d'une stimulation magnétique transcrânienne (TMS) du M1. La PAS permet d'augmenter ou de réduire l'excitabilité de M1 selon l'intervalle de temps entre les deux stimuli et présente un intérêt pour la neuroréhabilitation. Toutefois, la stimulation électrique périphérique peut être inconfortable pour certaines personnes. Ainsi, nous proposons un nouveau paradigme de PAS excitateur non invasif et indolore qui consiste en la répétition à basse fréquence d'une stimulation magnétique périphérique simple sur le nerf médian suivie 25 ms plus tard d'une TMS du M1 controlatéral. Ce projet visait à tester et comparer, chez des sujets sains, l'influence de ce nouveau paradigme de PAS (PAS25-magnétique) à un paradigme de PAS classique (PAS25) sur M1 et l'excitabilité corticospinale, l'excitabilité des motoneurones spinaux, ainsi que la fonction manuelle. Nos résultats ont révélé une augmentation significative de l'excitabilité corticospinale en temps réel durant la PAS25-magnétique et la PAS25. De plus, nous avons observé une augmentation plus forte et soutenue de l'excitabilité corticospinale ainsi qu'une diminution importante de l'inhibition GABAergique dans M1 chez les répondants à la PAS25-magnétique par rapport aux répondants à la PAS25. Dans tous les cas, aucun changement de la fonction manuelle n'a été détecté, possiblement en raison d'un effet plafond chez les participants sains. Il s'agit de la première étude à tester et à démontrer l'efficacité de ce nouveau paradigme pour moduler l'excitabilité de M1. Par ailleurs, les participants ont perçu la PAS25-magnétique comme plus confortable par rapport au PAS25. Toutefois, des études à plus large échelle seront nécessaires afin d'évaluer plus précisément les effets de la PAS25-magnétique et ses mécanismes sous-jacents. / Paired associative stimulation (PAS) is used to non-invasively induce plastic changes in the primary motor cortex (M1). Conventional PAS paradigms involve the combination of an electrical peripheral nerve stimulation and transcranial magnetic stimulation (TMS) delivered over the primary motor cortex (M1). PAS can either enhance or reduce M1 excitability depending on the paired stimuli timing and is of interest in neurorehabilitation. However, the use of electrical peripheral nerve stimulation may be unpleasant to some people. Thus, in this project, we proposed a new noninvasive and painless excitatory PAS paradigm which consists of delivering low-frequency repetitive pairing of a single peripheral magnetic stimulus over the median nerve 25 ms before a TMS pulse to the contralateral M1. This thesis aimed to assess and compare, in healthy individuals, the influence of this new PAS paradigm (magnetic-PAS25) to the conventional PAS (PAS25) on M1 and corticospinal excitability, spinal motoneuron excitability, as well as hand motor function. Our findings revealed a significant real-time increase of corticospinal excitability during both magnetic-PAS25 and PAS25. Moreover, we observed a stronger and sustained increase of corticospinal excitability along with a prominent decrease of M1 GABAergic inhibition in the responders to magnetic-PAS25 as compared to responders to PAS25. Hand motor function remained unchanged in all cases likely due to a ceiling effect in healthy participants. This is the first study to test and provide evidence that magnetic-PAS25 has the capacity to promote changes in M1 excitability. Importantly, participants reported that magnetic-PAS25 was comfortable and not with the unpleasantness experienced during PAS25. These findings encourage future larger-sampled studies to further evaluate the effects of magnetic-PAS25 and its underlying mechanisms.

No description available.

No description available.