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Mesoporous organosilica materials with amine functions : surface characteristics and chirality
(2005)
In this work mesoporous organisilica materials are synthesized through the silica sol-gel process. For this a new class of precursors which are also surfactant are synthesized and self-assembled. This leads to a high surface area functionality which is analysized with copper (II) and water adsorption.
During this PhD project three technical platforms were either improved or newly established in order to identify interesting genes involved in SNF, validate their expression and functionally characterise them. An existing 5.6K cDNA array (Colebatch et al., 2004) was extended to produce the 9.6K LjNEST array, while a second array, the 11.6K LjKDRI array, was also produced. Furthermore, the protocol for array hybridisation was substantially improved (Ott et al., in press). After functional classification of all clones according to the MIPS database and annotation of their corresponding tentative consensus sequence (TIGR) these cDNA arrays were used by several international collaborators and by our group (Krusell et al., 2005; in press). To confirm results obtained from the cDNA array analysis different sets of cDNA pools were generated that facilitate rapid qRT-PCR analysis of candidate gene expression. As stable transformation of Lotus japonicus takes several months, an Agrobacterium rhizogenes transformation system was established in the lab and growth conditions for screening transformants for symbiotic phenotypes were improved. These platforms enable us to identify genes, validate their expression and functionally characterise them in the minimum of time. The resources that I helped to establish, were used in collaboration with other people to characterise several genes like the potassium transporter LjKup and the sulphate transporter LjSst1, that were transcriptionally induced in nodules compared to uninfected roots, in more detail (Desbrosses et al., 2004; Krusell et al., 2005). Another gene that was studied in detail was LjAox1. This gene was identified during cDNA array experiments and detailed expression analysis revealed a strong and early induction of the gene during nodulation with high expression in young nodules which declines with the age of the nodule. Therefore, LjAox1 is an early nodulin. Promoter:gus fusions revealed an LjAox1 expression around the nodule endodermis. The physiological role of LjAox1 is currently being persued via RNAi. Using RNA interference, the synthesis of all symbiotic leghemoglobins was silenced simultaneously in Lotus japonicus. As a result, growth of LbRNAi lines was severely inhibited compared to wild-type plants when plants were grown under symbiotic conditions in the absence of mineral nitrogen. The nodules of these plants were arrested in growth 14 post inoculation and lacked the characteristic pinkish colour. Growing these transgenic plants in conditions where reduced nitrogen is available for the plant led to normal plant growth and development. This demonstrates that leghemoglobins are not required for plant development per se, and proves for the first time that leghemoglobins are indispensable for symbiotic nitrogen fixation. Absence of leghemoglobins in LbRNAi nodules led to significant increases in free-oxygen concentrations throughout the nodules, a decrease in energy status as reflected by the ATP/ADP ratio, and an absence of the bacterial nitrogenase protein. The bacterial population within nodules of LbRNAi plants was slightly reduced. Alterations of plant nitrogen and carbon metabolism in LbRNAi nodules was reflected in changes in amino acid composition and starch deposition (Ott et al., 2005). These data provide strong evidence that nodule leghemoglobins function as oxygen transporters that facilitate high flux rates of oxygen to the sites of respiration at low free oxygen concentrations within the infected cells.
Wetting and phase transitions play a very important role our daily life. Molecularly thin films of long-chain alkanes at solid/vapour interfaces (e.g. C30H62 on silicon wafers) are very good model systems for studying the relation between wetting behaviour and (bulk) phase transitions. Immediately above the bulk melting temperature the alkanes wet partially the surface (drops). In this temperature range the substrate surface is covered with a molecularly thin ordered, solid-like alkane film ("surface freezing"). Thus, the alkane melt wets its own solid only partially which is a quite rare phenomenon in nature. The thesis treats about how the alkane melt wets its own solid surface above and below the bulk melting temperature and about the corresponding melting and solidification processes. Liquid alkane drops can be undercooled to few degrees below the bulk melting temperature without immediate solidification. This undercooling behaviour is quite frequent and theoretical quite well understood. In some cases, slightly undercooled drops start to build two-dimensional solid terraces without bulk solidification. The terraces grow radially from the liquid drops on the substrate surface. They consist of few molecular layers with the thickness multiple of all-trans length of the molecule. By analyzing the terrace growth process one can find that, both below and above the melting point, the entire substrate surface is covered with a thin film of mobile alkane molecules. The presence of this film explains how the solid terrace growth is feeded: the alkane molecules flow through it from the undercooled drops to the periphery of the terrace. The study shows for the first time the coexistence of a molecularly thin film ("precursor") with partially wetting bulk phase. The formation and growth of the terraces is observed only in a small temperature interval in which the 2D nucleation of terraces is more likely than the bulk solidification. The nucleation mechanisms for 2D solidification are also analyzed in this work. More surprising is the terrace behaviour above bulk the melting temperature. The terraces can be slightly overheated before they melt. The melting does not occur all over the surface as a single event; instead small drops form at the terrace edge. Subsequently these drops move on the surface "eating" the solid terraces on their way. By this they grow in size leaving behind paths from were the material was collected. Both overheating and droplet movement can be explained by the fact that the alkane melt wets only partially its own solid. For the first time, these results explicitly confirm the supposed connection between the absence of overheating in solid and "surface melting": the solids usually start to melt without an energetic barrier from the surface at temperatures below the bulk melting point. Accordingly, the surface freezing of alkanes give rise of an energetic barrier which leads to overheating.
In an experimental study the attempt was made to examine the effects of the Reciprocal Teaching method on measures of metacognition and try to identify the effective features of this method that are necessary for the learning gains to occur. Reciprocal Teaching, originally developed by Palincsar and Brown (1984), is a very successful training program which was designed to improve student's reading comprehension skills by teaching them reading strategies. In the present study the tasks and responsibilities assumed by 5thgrade elementary students (N = 55) participating in a 16-session reading strategy training were varied systematically. Not only the students who participated in the training program in one of the three experimental conditions were compared with respect to knowledge and performance measures, but there was also a comparison to their control classmates who did not participate in strategy training (N = 86). Detailed analyses of video-taped sessions provided additional information. The strategy training was most beneficial for measures of knowledge and performance more closely related to the content of the training program, namely knowledge about specific reading strategies taught in training and application of those strategies. No significant effects were observed for more distal measures (general strategy knowledge, reading comprehension). As for the features of the program, it could be shown that students of the two experimental conditions where the students were responsible for giving each other feedback on performance (with respect to both content and strategy application) and guiding the correction of the answer outperformed both the experimental condition in which the trainer was responsible for those tasks and the control group. It is concluded that it is not merely the application of strategies, but the combination of strategy application with concurrent teaching and learning of metacognitive acquisition procedures (analysis, monitoring, evaluation, and regulation) in an inter-individual way as the precedent of these processes occurring intra-individually that seems to be an efficient way of acquiring metacognitive knowledge and skills. It was also shown that strategy training does not necessarily have to include the precise kind of interaction that characterizes the Reciprocal Teaching method. Instead, the tasks of monitoring, evaluating, and regulating other children's learning processes - i.e., tasks associated with the "teacher role" - are the ones that promote the acquisition of metacognitive knowledge and skills. Generally, any strategy training program that not only provides children with plentiful opportunities for practice, but also prompts them to engage in these kinds of metacognitive processes, may help children to acquire metacognitive knowledge and skills.
At present, carbon sequestration in terrestrial ecosystems slows the growth rate of atmospheric CO2 concentrations, and thereby reduces the impact of anthropogenic fossil fuel emissions on the climate system. Changes in climate and land use affect terrestrial biosphere structure and functioning at present, and will likely impact on the terrestrial carbon balance during the coming decades - potentially providing a positive feedback to the climate system due to soil carbon releases under a warmer climate. Quantifying changes, and the associated uncertainties, in regional terrestrial carbon budgets resulting from these effects is relevant for the scientific understanding of the Earth system and for long-term climate mitigation strategies. A model describing the relevant processes that govern the terrestrial carbon cycle is a necessary tool to project regional carbon budgets into the future. This study (1) provides an extensive evaluation of the parameter-based uncertainty in model results of a leading terrestrial biosphere model, the Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ-DGVM), against a range of observations and under climate change, thereby complementing existing studies on other aspects of model uncertainty; (2) evaluates different hypotheses to explain the age-related decline in forest growth, both from theoretical and experimental evidence, and introduces the most promising hypothesis into the model; (3) demonstrates how forest statistics can be successfully integrated with process-based modelling to provide long-term constraints on regional-scale forest carbon budget estimates for a European forest case-study; and (4) elucidates the combined effects of land-use and climate changes on the present-day and future terrestrial carbon balance over Europe for four illustrative scenarios - implemented by four general circulation models - using a comprehensive description of different land-use types within the framework of LPJ-DGVM. This study presents a way to assess and reduce uncertainty in process-based terrestrial carbon estimates on a regional scale. The results of this study demonstrate that simulated present-day land-atmosphere carbon fluxes are relatively well constrained, despite considerable uncertainty in modelled net primary production. Process-based terrestrial modelling and forest statistics are successfully combined to improve model-based estimates of vegetation carbon stocks and their change over time. Application of the advanced model for 77 European provinces shows that model-based estimates of biomass development with stand age compare favourably with forest inventory-based estimates for different tree species. Driven by historic changes in climate, atmospheric CO2 concentration, forest area and wood demand between 1948 and 2000, the model predicts European-scale, present-day age structure of forests, ratio of biomass removals to increment, and vegetation carbon sequestration rates that are consistent with inventory-based estimates. Alternative scenarios of climate and land-use change in the 21<sup>st century suggest carbon sequestration in the European terrestrial biosphere during the coming decades will likely be on magnitudes relevant to climate mitigation strategies. However, the uptake rates are small in comparison to the European emissions from fossil fuel combustion, and will likely decline towards the end of the century. Uncertainty in climate change projections is a key driver for uncertainty in simulated land-atmosphere carbon fluxes and needs to be accounted for in mitigation studies of the terrestrial biosphere.
Vitamin E : elucidation of the mechanism of side chain degradation and gene regulatory functions
(2005)
For more than 80 years vitamin E has been in the focus of scientific research. Most of the progress concerning non-antioxidant functions, nevertheless, has only arisen from publications during the last decade. Most recently, the metabolic pathway of vitamin E has been almost completely elucidated. Vitamin E is metabolized by truncation of its side chain. The initial step of an omega-hydroxylation is carried out by cytochromes P450 (CYPs). This was evidenced by the inhibition of the metabolism of alpha-tocopherol by ketoconozole, an inhibitor of CYP3A expression, whereas rifampicin, an inducer of CYP3A expression increased the metabolism of alpha-tocopherol. Although the degradation pathway is identical for all tocopherols and tocotrienols, there is a marked difference in the amount of the release of metabolites from the individual vitamin E forms in cell culture as well as in experimental animals and in humans. Recent findings not only proposed an CYP3A4-mediated degradation of vitamin E but also suggested an induction of the metabolizing enzymes by vitamin E itself. In order to investigate how vitamin E is able to influence the expression of metabolizing enzymes like CYP3A4, a pregnane X receptor (PXR)-based reporter gene assay was chosen. PXR is a nuclear receptor which regulates the transcription of genes, e.g., CYP3A4, by binding to specific DNA response elements. And indeed, as shown here, vitamin E is able to influence the expression of CYP3A via PXR in an in vitro reporter gene assay. Tocotrienols showed the highest activity followed by delta- and alpha-tocopherol. An up-regulation of Cyp3a11 mRNA, the murine homolog of the human CYP3A4, could also be confirmed in an animal experiment. The PXR-mediated change in gene expression displayed the first evidence of a direct transcriptional activity of vitamin E. PXR regulates the expression of genes involved in xenobiotic detoxification, including oxidation, conjugation, and transport. CYP3A, e.g., is involved in the oxidative metabolism of numerous currently used drugs. This opens a discussion of possible side effects of vitamin E, but the extent to which supranutritional doses of vitamin E modulate these pathways in humans has yet to be determined. Additionally, as there is arising evidence that vitamin E's essentiality is more likely to be based on gene regulation than on antioxidant functions, it appeared necessary to further investigate the ability of vitamin E to influence gene expression. Mice were divided in three groups with diets (i) deficient in alpha-tocopherol, (ii) adequate in alpha-tocopherol supply and (iii) with a supranutritional dosage of alpha-tocopherol. After three months, half of each group was supplemented via a gastric tube with a supranutritional dosage of gamma-tocotrienol per day for 7 days. Livers were analyzed for vitamin E content and liver RNA was prepared for hybridization using cDNA array and oligonucleotide array technology. A significant change in gene expression was observed by alpha-tocopherol but not by gamma-tocotrienol and only using the oligonucleotide array but not using the cDNA array. The latter effect is most probably due to the limited number of genes represented on a cDNA array, the lacking gamma-tocotrienol effect is obviously caused by a rapid degradation, which might prevent bioefficacy of gamma-tocotrienol. Alpha-tocopherol changed the expression of various genes. The most striking observation was an up-regulation of genes, which code for proteins involved in synaptic transmitter release and calcium signal transduction. Synapsin, synaptotagmin, synaptophysin, synaptobrevin, RAB3A, complexin 1, Snap25, ionotropic glutamate receptors (alpha 2 and zeta 1) were shown to be up-regulated in the supranutritional group compared to the deficient group. The up-regulation of synaptic genes shown in this work are not only supported by the strong concentration of genes which all are involved in the process of vesicular transport of neurotransmitters, but were also confirmed by a recent publication. However, a confirmation by real time PCR in neuronal tissue like brain is now required to explain the effect of vitamin E on neurological functionality. The change in expression of genes coding for synaptic proteins by vitamin E is of principal interest thus far, since the only human disease directly originating from an inadequate vitamin E status is ataxia with isolated vitamin E deficiency. Therefore, with the results of this work, an explanation for the observed neurological symptoms associated with vitamin E deficiency can be presented for the first time.
Interpretation of and reasoning with conditionals : probabilities, mental models, and causality
(2003)
In everyday conversation "if" is one of the most frequently used conjunctions. This dissertation investigates what meaning an everyday conditional transmits and what inferences it licenses. It is suggested that the nature of the relation between the two propositions in a conditional might play a major role for both questions. Thus, in the experiments reported here conditional statements that describe a causal relationship (e.g., "If you touch that wire, you will receive an electric shock") were compared to arbitrary conditional statements in which there is no meaningful relation between the antecedent and the consequent proposition (e.g., "If Napoleon is dead, then Bristol is in England"). Initially, central assumptions from several approaches to the meaning and the reasoning from causal conditionals will be integrated into a common model. In the model the availability of exceptional situations that have the power to generate exceptions to the rule described in the conditional (e.g., the electricity is turned off), reduces the subjective conditional probability of the consequent, given the antecedent (e.g., the probability of receiving an electric shock when touching the wire). This conditional probability determines people's degree of belief in the conditional, which in turn affects their willingness to accept valid inferences (e.g., "Peter touches the wire, therefore he receives an electric shock") in a reasoning task. Additionally to this indirect pathway, the model contains a direct pathway: Cognitive availability of exceptional situations directly reduces the readiness to accept valid conclusions. The first experimental series tested the integrated model for conditional statements embedded in pseudo-natural cover stories that either established a causal relation between the antecedent and the consequent event (causal conditionals) or did not connect the propositions in a meaningful way (arbitrary conditionals). The model was supported for the causal, but not for the arbitrary conditional statements. Furthermore, participants assigned lower degrees of belief to arbitrary than to causal conditionals. Is this effect due to the presence versus absence of a semantic link between antecedent and consequent in the conditionals? This question was one of the starting points for the second experimental series. Here, the credibility of the conditionals was manipulated by adding explicit frequency information about possible combinations of presence or absence of antecedent and consequent events to the problems (i.e., frequencies of cases of 1. true antecedent with true consequent, 2. true antecedent with false consequent, 3. false antecedent with true consequent, 4. false antecedent with false consequent). This paradigm allows testing different approaches to the meaning of conditionals (Experiment 4) as well as theories of conditional reasoning against each other (Experiment 5). The results of Experiment 4 supported mainly the conditional probability approach to the meaning of conditionals (Edgington, 1995) according to which the degree of belief a listener has in a conditional statement equals the conditional probability that the consequent is true given the antecedent (e.g., the probability of receiving an electric shock when touching the wire). Participants again assigned lower degrees of belief to the arbitrary than the causal conditionals, although the conditional probability of the consequent given the antecedent was held constant within every condition of explicit frequency information. This supports the hypothesis that the mere presence of a causal link enhances the believability of a conditional statement. In Experiment 5 participants solved conditional reasoning tasks from problems that contained explicit frequency information about possible relevant cases. The data favored the probabilistic approach to conditional reasoning advanced by Oaksford, Chater, and Larkin (2000). The two experimental series reported in this dissertation provide strong support for recent probabilistic theories: for the conditional probability approach to the meaning of conditionals by Edgington (1995) and the probabilistic approach to conditional reasoning by Oaksford et al. (2000). In the domain of conditional reasoning, there was additionally support for the modified mental model approaches by Markovits and Barrouillet (2002) and Schroyens and Schaeken (2003). Probabilistic and mental model approaches could be reconciled within a dual-process-model as suggested by Verschueren, Schaeken, and d'Ydewalle (2003).
Subject of this work is the study of applications of the Galactic Microlensing effect, where the light of a distant star (source) is bend according to Einstein's theory of gravity by the gravitational field of intervening compact mass objects (lenses), creating multiple (however not resolvable) images of the source. Relative motion of source, observer and lens leads to a variation of deflection/magnification and thus to a time dependant observable brightness change (lightcurve), a so-called microlensing event, lasting weeks to months. The focus lies on the modeling of binary-lens events, which provide a unique tool to fully characterize the lens-source system and to detect extra-solar planets around the lens star. Making use of the ability of genetic algorithms to efficiently explore large and intricate parameter spaces in the quest for the global best solution, a modeling software (Tango) for binary lenses is developed, presented and applied to data sets from the PLANET microlensing campaign. For the event OGLE-2002-BLG-069 the 2nd ever lens mass measurement has been achieved, leading to a scenario, where a G5III Bulge giant at 9.4 kpc is lensed by an M-dwarf binary with total mass of M=0.51 solar masses at distance 2.9 kpc. Furthermore a method is presented to use the absence of planetary lightcurve signatures to constrain the abundance of extra-solar planets.
Even though the structure of the plant cell wall is by and large quite well characterized, its synthesis and regulation remains largely obscure. However, it is accepted that the building blocks of the polysaccharidic part of the plant cell wall are nucleotide sugars. Thus to gain more insight into the cell wall biosynthesis, in the first part of this thesis, plant genes possibly involved in the nucleotide sugar interconversion pathway were identified using a bioinformatics approach and characterized in plants, mainly in Arabidopsis. For the computational identification profile hidden markov models were extracted from the Pfam and TIGR databases. Mainly with these, plant genes were identified facilitating the “hmmer” program. Several gene families were identified and three were further characterized, the UDP-rhamnose synthase (RHM), UDP-glucuronic acid epimerase (GAE) and the myo-inositol oxygenase (MIOX) families. For the three-membered RHM family relative ubiquitous expression was shown using variuos methods. For one of these genes, RHM2, T-DNA lines could be obtained. Moreover, the transcription of the whole family was downregulated facilitating an RNAi approach. In both cases a alteration of cell wall typic polysaccharides and developmental changes could be shown. In the case of the rhm2 mutant these were restricted to the seed or the seed mucilage, whereas the RNAi plants showed profound changes in the whole plant. In the case of the six-membered GAE family, the gene expressed to the highest level (GAE6) was cloned, expressed heterologously and its function was characterized. Thus, it could be shown that GAE6 encodes for an enzyme responsible for the conversion of UDP-glucuronic acid to UDP-galacturonic acid. However, a change in transcript level of variuos GAE family members achieved by T-DNA insertions (gae2, gae5, gae6), overexpression (GAE6) or an RNAi approach, targeting the whole family, did not reveal any robust changes in the cell wall. Contrary to the other two families the MIOX gene family had to be identified using a BLAST based approach due to the lack of enough suitable candidate genes for building a hidden markov model. An initial bioinformatic characterization was performed which will lead to further insights into this pathway. In total it was possible to identify the two gene families which are involved in the synthesis of the two pectin backbone sugars galacturonic acid and rhamnose. Moreover with the identification of the MIOX genes a genefamily, important for the supply of nucleotide sugar precursors was identified. In a second part of this thesis publicly available microarray datasets were analyzed with respect to co-responsive behavior of transcripts on a global basis using nearly 10,000 genes. The data has been made available to the community in form of a database providing additional statistical and visualization tools (http://csbdb.mpimp-golm.mpg.de). Using the framework of the database to identify nucleotide sugar converting genes indicated that co-response might be used for identification of novel genes involved in cell wall synthesis based on already known genes.
This article examines the multiple governments of independent Estonia since 1992 referring to their stability. Confronted with the immense problems of democratic transition, the multi-party governments of Estonia change comparatively often. Following the elections of March 2003 the ninth government since 1992 was formed. A detailed examination of government stability and the example of Estonia is accordingly warranted, given that the country is seen as the most successful Central Eastern European transition country in spite of its frequent changes of government. Furthermore, this article questions whether or not internal government stability can exist within a situation where the government changes frequently. What does stability of government mean and what are the varying multi-faceted depths of the term? Before analysing the term, it has to be clarified and defined. It is presumed that government stability is composed of multiple variables influencing one another. Data about the average tenure of a government is not very conclusive. Rather, the deeper political causes for governmental change need to be examined. Therefore, this article discusses the conceptual and theoretical basics of governmental stability first. Secondly, it discusses the Estonian situation in detail up to the elections of 2003, including a short review of the 9th government since independence. In the conclusion, the author explains whether or not the governments of Estonia are stable. In the appendix, the reader finds all election results and also a list of all previous ministers of Estonian governments (all data are as of July 2002).