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The main objective of this work is to contribute to the understanding of the grafting of nitrogen and amino surface functional groups on polymers by means of plasmas containing nitrogen and hydrogen. For this purpose, many aspects of plasma surface modification were studied. In the frame of this work, a new, UHV-sealed plasma reactor system was put into operation. The system is special for its clean reaction environment and the possibility to perform quasi in situ XPS measurements. A comparison of the UHV system to a fine vacuum reactor showed that a clean reaction environment is mandatory for reproducible plasma processing and efficient nitrogen and amino functionalisation. A key motivation for the present work was the observation that the non-coating plasma processes reported in literature fail to graft primary amino groups on polymer surfaces with densities that significantly exceed 3 - 4% NH2/C. In order to investigate this phenomenon in detail, this work followed two experimental tracks: On the one hand, a broad systematic study of plasma processing parameters was performed. On the other, the surface diagnostics methods used for the quantification of amino groups were critically reviewed. For this, a numerical algorithm was developed to reconstruct the element depth profile from angle-resolved XPS data. In the scope of the process parameter study, cw and pulsed microwave (MW) plasma excitation was compared to radio-frequency (RF) excitation. The home-built MW source was studied and optimised with respect to ignition behaviour and power efficiency. The performance of the MW and RF plasmas in polymer surface modifications was studied in various gas mixtures containing NH3 and H,, or N2 and H,. Also the differences of glow and afterglow processing of polymers were investigated. Large variations of the nitrogen and primary amino grafting efficiencies were obtained. They triggered a number of new ideas for the underlying reaction mechanisms. Special attendance was devoted to the selectivity of the functionalisation processes for primary amino groups. Nitrogen-containing discharges that were rich in hydrogen achieved selectivities up to 100%. The upper limit of 3 - 4% amino groups on the surface, however, was not passed. Angle-resolved XPS measurements revealed a systematic problem for the definition of a surface density, which is capable of explaining the upper limit for amino groups. It is either due to a limited labelling depth of amino groups by the applied TFBA derivatisation reaction, or to a limited functionalisation depth of the plasma process. One very efficient nitrogen-grafting plasma process that was developed on polystyrene was applied to seven other unfluorinated polymers. The similarity of the resulting functionalisation demonstrated a good transfer-ability of plasma surface functionalisation processes. Plasma treatments of polymer surfaces, especially in hydrogen-containing gases, are known to be generally followed by uncontrollable oxidation phenomena. The properties of plasma-functionalised polymer surfaces were therefore studied in conjunction with ageing effects. Quasi in situ XPS analysis allowed to distinguish the influence of oxygen contamination during the plasma process from post-process oxidation due to contact of plasma-treated samples to atmospheric oxygen. The surface modification experiments were accompanied by several gas phase diagnostic techniques. In the scope of this work, the UHV reactor system was equipped with optical emission spectroscopy (OES), two-photon absorption laser-induced fluorescence (TALIF), and tunable diode laser absorption spectroscopy (TDLAS). A separate plasma source was setup to perform an absolute quantification of the vacuum-ultra-violet (VUV) emission intensity of hydrogen-containing MW-excited plasmas. The techniques were evaluated with respect to their contribution to an understanding of the plasma processing of polymers. The rich experimental data allowed to suggest new reaction mechanisms for the grafting of nitrogen- and amino functional groups. Surface passivation experiments in H, plasmas of nitrogen-functionalised surfaces initiated a re-evaluation and an extension of the mechanism of selective etching [1]. Together with two other new reaction mechanisms, a hypothetical reaction scheme was suggested. It was studied by the help of two numerical models for heterogenous reactions of radicals with the surface. In order to avoid the complexity of the fragmentation process of NH,, the models were restricted to discharges in N, and H9. Despite the sparse information on the composition of the gas phase, the data of two experimental series showed a very particular phenomenology that allowed a first test of the model. The test supports the newly-suggested reaction mechanisms. Especially the role of NH2 attachment to open reaction sites for the grafting of amino groups was emphasised. A more stringent test of the model is left to future experiments with extended gas phase diagnostic means.
We improved our previous model of tracheal tube preparation and examined the effects of oral treatment of rats with carbocisteine (CCS) and its interaction with bronchial epithelium. The model permitted isometric or isotonic measurements of smooth muscle contraction or relaxation in cannulated or tracheal ring preparations, with or without epithelium. We found that oral treatment with carbocisteine and not preincubation of preparations in vitro, diminished sensitivity of preparations without epithelium to carbachol (EC50, -log(M) values: IN -luminary perfusion, -EP, controls vs. CCS: 5.8±0.06 vs. 5.5±0.09, p<0.005; OUT - serosal perfusion, -EP, controls vs. CCS: 5.9±0.06 vs. 5.6±0.05, p<0.005), while the sensitivity to aminophylline, degree of shortening, and the velocity of contraction of rat tracheal rings stimulated by 10-6M carbachol was not affected. Normal sensitivity to carbachol stimulation was re-established if preparations were preincubated with capsaicin. We conclude that carbocisteine has small inhibitory effects on the sensitivity to carbachol of the rat tracheal smooth muscle denuded of epithelium. Described model is valuable for examining the effects of bronchial epithelium on bronchial smooth muscle contraction.
In the thesis the reason for the low breeding success of white rhinos in captivity was investigated and solutions suggested. It was also investigated how to improve management of free ranging populations. It was establish whether female white rhinoceros choose their mates and, if so, which factors influence their choice. The study also seeks to establish whether there is any relationship between androgens, environmental factors and mating activity. The study was carried between March 1997 and May 1999 on a private game farm in South Africa. The study animals enjoyed conditions similar to those enjoyed by free-ranging populations. A non-invasive endocrine monitoring technique was developed to assess the androgen concentrations in faeces of male white rhinos. The body and horn size of adult males was measured, the concentration of testosterone in their faeces determined, and the characteristics of their territories investigated. All of these factors were then set in relation to their reproductive success. The reproductive success was established by genetic analysis of fatherhood using AFLP methods. The quality of male territories was described by vegetation structure, tree and grass species composition, the availability of frequently foraged or selected grass species as well as the nutritional composition of the forage. In addition, the influence of seasonal rainfall, presence of receptive females and territorial activity on androgen metabolite concentrations was established.
The present experimental work investigates plasma turbulence in the edge region of magnetized high-temperature plasmas. A main topic is the turbulent dynamics parallel to the magnetic field, where hitherto only a small data basis existed, especially for very long scale lengths in the order of ten of meters. A second point of special interest is the coupling of the dynamics parallel and perpendicular to the magnetic field. This anisotropic turbulent dynamics is investigated by two different approaches. Firstly, spatially and temporally high-resolution measurements of fluctuating plasma parameters are investigated by means of two-point correlation analysis. Secondly, the propagation of signals externally imposed into the turbulent plasma background is studied. For both approaches, Langmuir probe arrays were utilized for diagnostic purposes. The main findings can be summarized as follows: Greatly elongated fluctuation structures exist in plasma edge turbulence. The structures are aligned along the confining magnetic field (k|| = 0). The correlation degree of fluctuations for a short connection length of 0.75m is greater than 80%. For much longer connection lengths of 23m and 66m, the correlation degree is reduced to approximately 40%. A conceptual interpretation of these observations is the coexistence of two different fluctuation components. One component has a correlation length parallel to the magnetic field below 20m and the other component a correlation length greater than 70m. Sine signals in the frequency range 1-100 kHz were injected into the turbulent plasma background. The propagation parallel and perpendicular to the magnetic field of the signals was studied. In poloidal direction, an asymmetry is observed, that can be explained by a copropagation of the signal with the background E × B-rotation of the plasma. The signal propagation parallel to the magnetic field shows no such asymmetry. As an advanced approach, spatio-temporal wave patters were injected into the edge plasma. The waves launched that way can be seen as test waves' in a turbulent background. The coupling strength of the imposed wave patterns to the background turbulence relies on the match of the imposed waves to the dynamics of turbulent structures. If the propagation direction of the imposed waves is parallel to the propagation direction of the background plasma, improved coupling is observed. This finding underlines the importance of the background plasma rotation for future attempts of controlling the plasma edge turbulence. Further optimization of frequency and wave vector of the imposed waves is probably a promising approach for achieving a significant and systematic influence of turbulence. Taking into account the present experimental state-of-the-art, for a deeper insight into the mechanism of the plasma edge turbulence of magnetized high-temperature plasmas a joint effort of numerical modeling and experimental results is a valuable approach. Such a cooperation should cover the explanation of the correlation observations as well as the experiments on signal injection into background turbulence. A quantitative comparison between the results presented in this work and a dedicated numerical drift wave simulation would be a significant step forward to a better understanding of plasma edge turbulence.
Until today most social, historical and cultural studies of the American postwar era have contributed to the myth of a relatively homogeneous society and culture. Even though they understood these years as a turning point for modern American society, they failed to encompass the polyvalence and heterogeneity of American society. Focussing mostly on white and middle class males, these studies formed a onedimensional picture of sociocultural conformity, a picture in which issues of gender, race and class were largely absent. Crossing the boundaries of feminist, cultural and historical studies this dissertation starts from identifying the gaps and problems in current academic research. Those sociopolitical structures that affected non-white women are then juxtaposed with the dominant postwar discourse of womanhood. The literary texts by women of color show them grappling with the conflicting demands of socioecnomic realities and pervasive role definitions. On the surface these literary interventions seemed to submit to dominant ideologies while opposing them at the same time. Thus they are both anticipatory and antagonistic. The dissent and criticism in writings by women of color seem to have become a catalyst for the deep social transformations in the following decades.
Studies of stroke in experimental animals have demonstrated the neuroprotective efficacy of a variety of interventions; however, most such strategies have failed to show clinical benefits in aged humans. One possible explanation for this discrepancy between animal and clinical studies may be the role that age plays in the recovery of the brain following insult. For example, the poor functional recovery of aged rats after stroke may be caused by a decline in brain plasticity. Although the incidence of ischemic stroke increases dramatically with advancing age, relatively few studies have been conducted on aged animals, which would mimic most closely the context in which stroke occurs in humans. We have shown that, at one week following stroke, there was vigorous expression of MAP1B and its mRNA, as well as MAP2 protein, in the border zone adjacent to the infarct of 3 month- and 20 month-old male Sprague Dawley rats. Hypothesis: The decline in brain plasticity is caused by an age-related decline in the upregulation of factors promoting brain plasticity (MAP1B, ßAPP) and an age-related increase in astroglial scaring and in the expression of neurotoxins such as beta amyloid. Methods: Focal cerebral ischemia was produced by reversible occlusion of the right middle cerebral artery in 3- and 20-month-old male Sprague Dawley rats. The functional outcome was assessed in neurobehavioral tests at 3, 7, 14, and 28 days post-stroke. At these time points, brains were removed and analyzed for markers of (i) brain plasticity (microtubule-associated protein 1B, MAP1B, secreted forms of fi-amyloid precursor protein); (ii) neurogenesis (BrdU-positive cells, doublecortin, nestin); (iii) neurotoxicity (B-amyloid aggregates); (iv) inflammation (microglia, astrocytes, oligodendrocytes, endothelial cells). Results: (1) There was a non-significant tendency for blood pressure to be higher in old than in young rats. By post-stroke day 3 the infarct volume covered about 15% of the cortical neurons in young and 28% in aged rats. By day 7, infarct volumes were roughly equal in the two age groups. (2) Cell counting showed increases in the number of BrdU-positive cells in the infarcted area of old rats at day 3 post-stroke. This increase became even more dramatic at day 7 post-stroke in aged rats. There was no significant contribution of apoptosis to cell death. (3) Behaviorally, young rats recovered gradually and reached a maximum of 90% of baseline performance at day 14, post-stroke while the aged rats recovered only to a maximum of 70% of pre-surgery performance by week 2 post-stroke, and remained at that level. (4) The temporal pattern of recovery correlated well with the expression of growth-associated phenotype of ßAPP as well as with MAP1B accumulation in varicosities along axons (an indicator of growth) in cortical areas affected by stroke and was at maximum between days 14 to 28 in young rats. In contrast, aged rats showed delayed (day 28) and reduced axonal remodelling as well as a delayed (day 28) expression of growth-associated ßAPP. Instead, the neurotoxic carboxy-terminal form of ßAPP steadily accumulated over time and reached a maximum at day 14 in aged rats as compared to 28d for the young rats. Nestin, a marker for immature neurons, overlapped with BrdU-labelled cells at day 7 post-stroke in corpus callosum and at the infarct border in both young and aged rats, suggesting increased stroke-induced neurogenesis. (5) In young rats there was a gradual activation of both microglia and astrocytes that peaked by days 14 to 28 with the formation of a glial scar. In contrast, aged rats showed an accelerated astrocytic and microglial reaction that peaked in week 1 post-stroke. We also noted a strong activation of oligodendrocytes at early stages of infarct development in all rats that persisted in aged rats. Evolution of astrocytic and microglial reactivity closely paralled the time course of scar formation in both young and aged rats and coincided with the stagnation in the recovery rate of aged rats. Conclusions: The time course of functional recovery in young rats correlated well with the expression of plasticity proteins such as MAP1B and ßAPP while an early and persistent expression of the neuro toxic fragment AB in conjunction with a delayed expression of MAP1B and ßAPP may impede functional recovery in aged rats. The results also suggest that a temporally anomalous glial reaction to cerebral ischemia in aged rats leads to the premature formation of scar tissue that impedes functional recovery to stroke.
Serbian Tertiary ultrapotassic province is part of widespread but not voluminous basaltic magmatism in Serbia. Two principal groups of ultrapotassic rocks are recognized; the lamproite affinity group (LAG) and the kamafugite affinity group (KAG). My results demonstrate three dominant low-pressure evolutional processes: magma mixing and fractional crystallization, analcimization and heteromorphism. The two suites of ultrapotassic rocks show large ranges of Sr and Nd isotopic values but a restricted variation of Pb isotopes. LAG is characterized by wide ranges of Sr and Nd isotopes (87Sr/86Sri 0.70735- 0.71299, 143Nd/144Ndi 0.51251-0.51216). KAG is isotopically homogeneous with a limited range of Sr-Nd isotopes (87Sr/86Sri 0.70599-0.70674, 143Nd/144Ndi 0.51263-0.51256). The Pb isotope compositions of both groups are similar (206Pb/204Pb 18.581-18.832, 207Pb/204Pb 15.624-15.696 and 208Pb/204Pb 38.744-38.987), and fall within the pelagic sediment field resembling Mesozoic flysch sediments from the Vardar ophiolitic composite suture zone. Highly variable Sr and Nd isotopic signatures of primitive-LAG rocks correlate with REE fractionation and enrichment of the HFSE. I explain this correlation using vein+wall-rock melting model, invoking the presence of different metasomatic domains (veins with phlogopite, Cpx and F-apatite) that are out of isotopic equilibrium with the peridotite wall rock. Relatively uniform Sr and Nd isotopic data of KAG rocks, similar trace element patterns and small but regular variations of HFSE ratios, indicate different degrees of melting of a relatively homogeneously metasomatized mantle source. Geochemical modelling implies the role of phlogopite, apatite and Ti-oxide in their mantle source.
Challenge of immunized mice with H. pylori induces protective gastric inflammation that is histologically indistinguishable from chronic H. pylori-associated gastritis in non-immune mice. To identify mechanisms of protective immunity gene expression in the gastric tissue from infected mice and mice vaccinated prior to challenge was compared by DNA array analysis. Message RNA was used to screen over 10,000 murine genes. Major Histocompatibility Complex antigens and IFN-γ dependent GTP binding proteins were strongly upregulated in both infected and immunized/challenged mice compared to naive controls. Differences in gene expression were also observed in novel T cell genes, which were exclusively upregulated in immunized/challenged mice. Both IFN I and II associated genes like the IFN-a/ßreceptor or IFN dependent transcription factors mIRF-1 and ISGF3 were also predominantly expressed in this group. These results were confirmed for several candidate genes by semi-quantitative RT-PCR. Additionally, H. pylori-stimulation of CD4+ T cells from immune mice induced significantly more IFN-γ production than stimulation of cells from infected mice. The present study provides evidence that the inflammatory infiltrate that arises in the gastric mucosa when immunized mice are challenged with H. pylori is associated with specific T cells sets and protein families that are distinct from those present in Helicobacter-associated chronic inflammation. Gene array profiles and in vitro assays indicate that immunized mice are more readily poised than infected mice to promote IFN-γ production and IFN related events and thus promote a strong proinflammatory THi response. This study supports recent findings that an immune response dominated by THi cytokines is essential for protection from H. pylori infection. This insight could facilitate the choice of the appropriate adjuvants for the development of vaccines against H. pylori, which are efficient and safe for use in humans. The mechanisms by which THi cells induce protective immunity or reduce Helicobacter colonization remain poorly understood and will be subject of future research.
Within the scope of this work, a versatile large linear magnetised plasma experiment was designed, constructed, and subsequently put into operation. The magnetised plasma was used to investigate the dispersion of whistler waves (circular polarised electromagnetic waves) with regard to the influence of the plasma boundaries. After a brief review over electromagnetic plasma waves and the three discharge modes of a helicon source, the experimental device and the diagnostic tools are explained in detail. Great attention is devoted to the identification of a reliable, calibrated magnetic fluctuation probe design. To the understanding of dynamical phenomena in ionospheric plasmas, whistler wave measurements in laboratory experiments may contribute significantly because of the ability to vary plasma parameters and to do measurements with high spatial and temporal resolution. However, the boundaries of laboratory experiments change the dispersion behaviour of whistler waves significantly if compared to the unbounded ionospheric situation. The influence of the plasma boundary is studied in the present work on three different levels of increasing complexity. First, a high density, small wavelength regime is established to make the effect of the boundary negligible. Measurements are in full agreement with whistler wave theory for unbounded plasma geometry. Measurements below the ion cyclotron frequency reveal the strong influence of the ion dynamics on whistler wave propagation, but are not straightforward to interpret in terms of dispersion theory. Second, the other limit case is examined: bounded plasma helicon modes. These waves are, mathematically speaking, eigenfunctions of the plasma-boundary system and are of great practical importance for high density plasma discharges, the helicon source. Careful measurements of the equilibrium plasma parameters as well as the magnetic fluctuation profiles of the helicon source are done in all three modes of operation, the capacitive, inductive, and helicon wave sustained mode. The first two modes are fairly well understood and the measurements are consistent with existing models. The high density helicon mode, however, is still a scientific case. The measurements partially confirm existing assumptions. It is demonstrated that the plasma production is detached from the antenna edge region. Moreover, it is shown that the plasma parameters are self-consistently determined by the antenna geometry and the discharge parameters according to basic helicon wave theory. Finally, it is ruled out that the plasma density is the control parameter determining the transition point into the high density helicon mode. The measurements rather suggest that the rf power density is the important value. As a third aspect, whistler waves in an intermediate wavelength regime are studied and the transition from unbounded to bounded plasma wave dispersion is systematically investigated. It is shown both experimentally and numerically that the wave dispersion in a plasma filled metal waveguide cannot be determined solely from wave vector measurements parallel to the magnetic field. For a correct description, the perpendicular mode profile has to be correctly taken into account. In contrast to simple helicon wave theory, it is demonstrated that the perpendicular mode profile is not only determined by the conducting vessel boundaries alone but the entire plasma-boundary system has to be considered as a unity. To summarise, this work has contributed to a better understanding of the physics of the propagation of whistler waves, where the particular role of metal boundaries acting as wave guides was highlighted. This basic science approach to the waves' dynamics is believed to be of significance in the course of the scientific debate on the physics principles of helicon discharges.
Two main aspects concerning drift wave dynamics in linear, magnetized plasma devices are addressed in the work: In part I of the thesis, drift waves are studied in a helicon plasma. The plasma parameter regime is characterized by comparably high collision frequencies and comparably high plasma-p exceeding the electron-ion mass ratio. Single Langmuir probes and a poloidal probe array are used for spatiotemporal studies of drift waves as well as for characterization of background plasma parameters. The main goals are the identification of a low-frequency instability and its major destabilization mechanisms. All experimentally observed features of the instability were found to be consistent with drift waves. A new code, based on a non-local cylindrical linear model for the drift wave dispersion, was used to gain more insight into the dominating destabilzation mechanisms, and also into dependencies of mode frequencies and growth rates on different parameters. In the experiment and in the numerical model, poloidal mode structures were found to be sheared. Part II of the thesis reports about mode-selective spatiotemporal synchronization of drift wave dynamics in a low-P plasma. Active control of the fluctuations is achieved by driving a preselected drift mode to the expense of other modes and broadband turbulence. It is demonstrated that only if a resonance between the driver signal and the drift waves in both space and time is reached, the driver has a strong influence on the drift wave dynamics. The synchronization effect is qualitatively well reproduced in a numerical simulation based on a Hasegawa-Wakatani model.