Simulation studies of permeation through two-dimensional ideal polymer networks

We study the diffusion process through an ideal polymer network, using numerical methods. Polymers are modeled by random walks on the bonds of a two-dimensional square lattice. Molecules occupy the lattice cells and may jump to the nearest-neighbor cells, with probability determined by the occupation of the bond separating the two cells. Subjected to a concentration gradient across the system, a constant average current flows in the steady state. Its behavior appears to be a non-trivial function of polymer length, mass density and temperature, for which we offer qualitative explanations.Comment: 8 pages, 4 figure

Gas permeation through a polymer network

We study the diffusion of gas molecules through a two-dimensional network of polymers with the help of Monte Carlo simulations. The polymers are modeled as non-interacting random walks on the bonds of a two-dimensional square lattice, while the gas particles occupy the lattice cells. When a particle attempts to jump to a nearest-neighbor empty cell, it has to overcome an energy barrier which is determined by the number of polymer segments on the bond separating the two cells. We investigate the gas current $J$ as a function of the mean segment density $\rho$, the polymer length $\ell$ and the probability $q^{m}$ for hopping across $m$ segments. Whereas $J$ decreases monotonically with $\rho$ for fixed $\ell$, its behavior for fixed $\rho$ and increasing $\ell$ depends strongly on $q$. For small, non-zero $q$, $J$ appears to increase slowly with $\ell$. In contrast, for $q=0$, it is dominated by the underlying percolation problem and can be non-monotonic. We provide heuristic arguments to put these interesting phenomena into context.Comment: Dedicated to Lothar Schaefer on the occasion of his 60th birthday. 11 pages, 3 figure

Poetry Curriculum

The purpose of this project is to aid the classroom teacher in exposing children to poetry through a curriculum guide with enabling activities which will encourage children to develop an appreciation and understanding of poetry

Identifizierung und Charakterisierung von Silencing Suppressoren in Arabidopsis

Post-transcriptional gene silencing (PTGS) often limits the expression of transgenes. Transgene mRNAs are recognized by RNA-DEPENDENT RNA POLYMERASE 6 (RDR6) which produces double-stranded RNA (dsRNA) and thus contributes to the production of small interfering RNAs (siRNAs). These mediate the sequence specific endonucleolytic cleavage of target mRNA, which prevents its accumulation. Quantitative and qualitative factors trigger the initiation of transgene silencing. Mutations in genes of mRNA metabolism may disturb the balance between synthesis and turnover of mRNA which can cause transgene silencing. Upon altered mRNA metabolism so called aberrant mRNA may accumulate which can be recognized by RDR6 to initiate the silencing cascade. New insights into the initiation of transgene silencing should be gained in the course of this thesis. The focus was the identification and characterization of genes important to prevent transgene silencing. Previously transgenic Arabidopsis were EMS-mutagenized and screened for mutants that showed increased transgene silencing. Suitable candidate mutants were characterized by a loss of MP17:GFP mRNA accumulation. One suppressor mutant (tss4e, transgene silencing suppressor) that showed a clear genetically reproducible inheritance could be isolated. By means of Map-based cloning a mutation in the AtDCP2 gene could be identified. The gene identity was confirmed by complementation of the mutant phenotype and through analysis of another dcp2 allele which could not complement the mutant phenotype. Based on protein modeling, it was proposed that the DCP2 catalytic function may be alleviated due to the R138C mutation which disturbs mRNA metabolism. This is supported by in vivo measurements that showed reduced amounts of uncapped mRNA. By crossing the mutant to a RDR6-deficient genetic background it could be confirmed that transgene silencing in the mutant is initiated in a RDR6-dependent manner and caused by the accumulation of aberrant mRNA. Thus there is an accumulation of capped but deadenylated mRNA in the tss4e mutant. Another characteristic of the mutant is the accumulation of anthocyanins in source leaves. Based on transcriptome data it was speculated that this effect may be linked to an altered biogenesis of TAS4 ta-siRNA. This causes an induction of PAP1/2 transcription factors and the induction of corresponding anthocyanin related genes. Thus, the analysis of the tss4e mutant provided an experimental indication for the proposed regulation of anthocyanin biosynthesis by TAS4. The macroscopic phenotype of the tss4e mutant was more pronounced in the dcp2-1/tss4e mutant, which shows that tss4e is a new hypomorphic dcp2 allele. In contrast to post-embryo lethal null mutants of dcp2 the tss4e mutant provides the opportunity to analyze the DCP2 function and its relevance for Arabidopsis development.Post-transkriptionelles gene silencing (PTGS) kann ein limitierender Faktor für die Expression von Transgenen sein. Transgene mRNAs können von der RNA-DEPENDENT RNA POLYMERASE 6 (RDR6) erkannt werden, was die Synthese doppelsträngiger RNA (dsRNA) initiiert und die Akkumulation von small interfering RNAs (siRNAs) zur Folge hat. Diese vermitteln die sequenzspezifische endonukleolytische Spaltung einer Ziel-mRNA und verhindern somit deren Akkumulation. Für die Initiierung des Transgen Silencing spielen quantitative aber auch vor allem qualitative Faktoren eine Rolle. Mutationen im mRNA Metabolismus können die Balance zwischen Synthese und Degradation von mRNAs stören und folglich das Transgen Silencing verursachen. Aufgrund eines gestörten mRNA Metabolismus können sogenannte aberrante mRNAs akkumulieren, die durch RDR6 erkannt werden und die Silencing Kaskade in Gang bringen. Im Zuge dieser Doktorarbeit sollten neue Erkenntnisse zur Initiierung des Transgen Silencing gewonnen werden. Hierbei stand die Identifizierung und Charakterisierung von Genen, deren Mutation zu verstärktem Transgen Silencing führt, im Vordergrund. Im Vorfeld wurde eine transgene Arabidopsis-Linie EMS-mutagenisiert und nach Mutanten mit verstärkten Transgen Silencing durchmustert. Geeignete Mutanten zeichneten sich durch einen Verlust der MP17:GFP mRNA Akkumulation aus. Es konnte die MP17:GFP Suppressormutante tss4e (transgene silencing suppressor) mit einer eindeutig genetisch nachvollziehbaren Vererbung isoliert werden. In dieser akkumulieren Transgen-spezifische siRNAs, was durch Infektion mit dem Potyvirus TuMV überkommen werden konnte. Daher wurde angenommen, dass es in der tss4e Mutante zum PTGS der Transgene gekommen war. Durch die Marker-gestützte Kartierung konnte eine Mutation im AtDCP2 Gen identifiziert werden. Die Genidentität wurde durch Komplementation des Mutanten Phänotyps und der Analyse eines weiteren dcp2 Allels, das nicht in der Lage war die Mutante zu komplementieren, bestätigt. Anhand einer Protein-Modellierung wurde postuliert, dass die tss4e spezifische R138C Mutation vermutlich die katalytische Funktion des DCP2 Proteins in den Mutanten beeinträchtigt, was zu einer Veränderung des mRNA Metabolismus führt. Durch in vivo Analysen konnte bestätigt werden, dass die Menge ungecappter mRNA in den Mutanten reduziert war, was diese Vermutung bekräftigte. Durch Kreuzung in einen RDR6-defizienten Hintergrund konnte bestätigt werden, dass das Transgen Silencing in den tss4e Mutanten RDR6-abhängig initiiert wird und vermutlich auf die Akkumulation aberranter mRNA zurückzuführen ist. Daher kommt es in der tss4e Mutante vermutlich zur Akkumulation gecappter mRNA ohne Poly-(A) Schwanz. Ein weiteres charakteristisches Merkmal der tss4e Mutante ist die Akkumulation von Anthocyanen in Source-Blättern. Durch Transkriptom-Analysen konnte beobachtet werden, dass dies möglicherweise auf eine Veränderung der TAS4 ta-siRNA Biogenese zurückzuführen ist. Diese bedingt eine Induktion der PAP1/2 Transkriptionsfaktoren und Anthocyan-Synthese-assoziierter Genen. Somit konnte durch die Analyse der tss4e Mutante ein experimenteller Hinweis auf die postulierte Assoziation von TAS4 und seiner Regulation der Anthocyan-Biosynthese erbracht werden. Der äußerliche Phänotyp der tss4e Mutante ließ sich verstärkt in der dcp2-1/tss4e Mutante beobachten, was demonstriert, dass mit tss4e erstmals ein hypomorphes dcp2 Allel isoliert werden konnte. Im Gegensatz zu post-embryoletalen dcp Nullmutanten kann mit tss4e im Folgenden die Relevanz der DCP2 Funktion für die Entwicklung von Arabidopsis untersucht werden

A non-canonical RNA silencing pathway promotes mRNA degradation in basal fungi

The increasing knowledge on the functional relevance of endogenous small RNAs (esRNAs) as riboregulators has stimulated the identification and characterization of these molecules in numerous eukaryotes. In the basal fungus Mucor circinelloides, an emerging opportunistic human pathogen, esRNAs that regulate the expression of many protein coding genes have been described. These esRNAs share common machinery for their biogenesis consisting of an RNase III endonuclease Dicer, a single Argonaute protein and two RNA-dependent RNA polymerases. We show in this study that, besides participating in this canonical dicer-dependent RNA interference (RNAi) pathway, the rdrp genes are involved in a novel dicer-independent degradation process of endogenous mRNAs. The analysis of esRNAs accumulated in wild type and silencing mutants demonstrates that this new rdrp-dependent dicer-independent regulatory pathway, which does not produce sRNA molecules of discrete sizes, controls the expression of target genes promoting the specific degradation of mRNAs by a previously unknown RNase. This pathway mainly regulates conserved genes involved in metabolism and cellular processes and signaling, such as those required for heme biosynthesis, and controls responses to specific environmental signals. Searching the Mucor genome for candidate RNases to participate in this pathway, and functional analysis of the corresponding knockout mutants, identified a new protein, R3B2. This RNase III-like protein presents unique domain architecture, it is specifically found in basal fungi and, besides its relevant role in the rdrp-dependent dicer-independent pathway, it is also involved in the canonical dicer-dependent RNAi pathway, highlighting its crucial role in the biogenesis and function of regulatory esRNAs. The involvement of RdRPs in RNA degradation could represent the first evolutionary step towards the development of an RNAi mechanism and constitutes a genetic link between mRNA degradation and post-transcriptional gene silencing

Embedded-grid silver transparent electrodes fabricated by selective metal condensation

We report a new materials system for the fabrication of embedded silver grid electrodes with micron-sized linewidth >10 times narrower than can be achieved using the conventional printing techniques of screen, inject and flexographic printing. Using micro-contact printed thin films of the highly fluorinated polymer poly(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate) together with low temperature heating of the substrate during metal deposition by thermal evaporation, we have fabricated embedded silver transparent grid electrodes on flexible plastic substrates without the need for a metal etching step or a separate grid-embedding step. This simplified approach to grid electrode fabrication is made possible by the very low condensation coefficient of Ag on areas of the substrate covered with the printed organofluorine layer, removing the need for harmful chemical etchants and slow chemical intensive electrochemical deposition steps

Schwerpunkt: Rechtsextremismus und Soziale Arbeit

Das SI:SO-Heft widmet sich den folgenden Fragen: - Unter welchen Gesichtspunkten lassen sich Rechtspopulismus und Rechtsextremismus differenziert diskutieren? - Wie werden Rechtsextreme bestimmt und Rechtsextremismus identifiziert? - Inwiefern ist Soziale Arbeit von Rechtsextremismus und Rechtspopulismus betroffen? - Welche Kritiken gelten als zulässig, welche nicht und welche Auseinandersetzungen werden in der Sozialen Arbeit gemieden? - Welche politischen und zivilgesellschaftlichen Beiträge leistet Soziale Arbeit im Phänomenbereich Rechtsextremismus und Rechtspopulismus? - Welche Folgen ergeben sich für Hochschulen und Studium im Umgang mit Rechtsextremismus und Rechtspopulismus