Komplexchemie - Diagnose und Prävention von Fehlvorstellungen (German Edition)

Among the proteins studied in detail were i D. Filopodia are bundles of actin filaments projecting from the cell surface. They are found on a variety of cell types and are needed among others, for cell adhesion, sensory and exploratory functions. Filopodia are frequently found associated with sheet-like arrays of actin filaments called lamellipodia and membrane ruffles.

The in vitro nucleating activity of DdVASP is salt dependent and its nucleating activity is completely abolished at mM salt. However, the F-actin bundling activity as determined by the low speed sedimentation assay was not disturbed. The ability of DdVASP to influence the binding of capping protein to the growing ends of the actin filaments was tested through elongation of capped F-actin seeds and by depolymerization of capped filaments upon dilution below the critical concentration of the barbed ends.

Results from both sets of experiments showed that DdVASP cannot remove capping protein from the barbed ends. In vitro biochemical data led to the conclusion that the bundling activity of DdVASP is the essential in vivo function to stabilise actin filaments in emerging filopodia. As expected the mutant failed to produce any filopodia. The results indicated that VASPs are functionally well conserved throughout evolution.

During this study, a third profilin isoform, profilin III, was further characterised. Profilin III shares a limited homology at the amino acid level with the other two and well studied profilins. This suggests a distinct role for profilin III, because a low protein concentration argues against an actin sequestering function.

Immunolocalisation studies showed profilin III in filopodia and enriched at their tips. Cells lacking the profilin III protein show defects in cell motility during chemotaxis. The second part of the project dealt with the characterisation of two D. The regulatory region harbours the putative inhibitory domain aa and a possible multimerization SARAH domain aa de. Notch-Signale spielen bei der Entwicklung von Lymphozyten eine wichtige Rolle.

Die Expression von Zielgenen wurde anhand einer Microarray- Analyse untersucht. Notch2IC konnte Gene induzieren und Gene reprimieren. Die Auswertung der Zielgene in der Clusteranalyse ergab, dass viele Gene reguliert wurden, die mit dem Zellzyklus und der Immunmodulation assoziiert sind. Myelin antigen s specific T cells, B cells, and antibodies are thought to play a role in the pathogenesis of MS.

The original aim of the present study was to create a new mouse model with which to investigate the interaction of myelin autoantigen specific B and T cells and their role in MS pathogenesis. The study was further expanded to analyze the nature and triggers of spontaneous disease and similarity of the mouse lesion pattern to that in human disease. In contrast, all single transgenic littermates were free of clinical disease. Histological analysis of the CNS of affected mice revealed restricted localization of lesions in the spinal cord and optic nerves as well as severe demyelination and axonal damage that spared brain and cerebellum.

It is not well understood what triggers the initiation of spontaneous EAE. The microbial environment does not significantly affect the clinical disease. Stimulation of the innate immune system with toll-like receptor TLR ligands or depletion of putative regulatory cells did not significantly affect EAE development. The re- activation of lymphocytes in sick Devic mice mainly occurs in the CNS without evidence of priming in the peripheral lymphoid organs.

MOG-specific B and T cells cooperate by means of several mechanisms. This resulted in the enhanced proliferation of T and B cells as well as rapid activation. In addition, MOG-stimulated T and B cells expressed a set of co-stimulatory molecules, which further help to modulate the proliferation and activation. Surprisingly, the doubletransgenic Devic mice, but not their single transgenic littermates, had high titers of MOG-specific IgG1 antibodies in the serum, which indicates a previous encounter with antigen in vivo.

In summary, Devic mice show several salient features that are important for study of the pathogenic mechanisms of CNS autoimmunity. As a model of spontaneous autoimmunity, they may allow us to study the triggering factors of autoimmunity as well as the factors that determine restricted infiltration of immune cells into the CNS. In addition, the model may be useful for validating novel th.

Clean Mechanism of chromatin reassembly at the yeast PHO5 promoter upon repression. The goal of this study has been to elucidate the mechanisms responsible for rebuilding nucleosomes at the PHO5 promoter upon rerepression. In this work, I could unambiguously show that histones are incorporated at the PHO5 promoter upon repression.

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Regarding the source of these histones, I provide evidence that a significant fraction of the deposited histones originate from a soluble histone pool, i. Promoter closure occurs with strikingly rapid kinetics and is independent of replication. In agreement with the finding that PHO5 repression does not require cell division, I found that histone chaperones which are associated with replication-independent nucleosome assembly are important for rapid PHO5 promoter closure.

Strains deleted for histone chaperones involved in replication-dependent nucleosome assembly did not exhibit any defect in promoter closure. Other factors contributing to rapid PHO5 repression turned out to be nucleosome remodelers, whose characteristic mode of action is chromatin assembly in trans. Nucleosome remodeling mutants typically catalyzing nucleosome movements in cis are not implicated in PHO5 promoter reassembly. The phenomenon of trans-deposition of histones upon repression is not restricted to the PHO5 promoter but is also found at two other phosphate regulated promoters, PHO8 and PHO By its rapid mode of action, this mechanism contributes to efficiently shutting off transcription.

This might also hold true for other yeast genes. In the second part of this work I present results that indicate a role for the histone chaperone Asf1p in the activation of the PHO5 gene. Interestingly, the induction of PHO5 in an asf1 mutant is dependent on the phosphate concentration of the growth medium. Full induction occurs only when the medium is completely free of phosphate.

The abundance of even trace amounts of phosphate precludes PHO5 activation altogether.

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Clean Models of adaptation and speciation. Chapter 1 There are two ways in which a population can adapt to a rapid environmental change or habitat expansion. It may either adapt through new beneficial mutations that subsequently sweep through the population or by using alleles from the standing genetic variation. We use diffusion theory to calculate the probabilities for selective adaptations and find a large increase in the fixation probability for weak substitutions, if alleles originate from the standing genetic variation.

We then determine the parameter regions where each scenario — standing variation vs. Adaptations from the standing genetic variation are favored if either the selective advantage is weak or the selection coefficient and the mutation rate are both high. Chapter 2 In the classical model of molecular adaptation, a favored allele derives from a single mutational origin. This ignores that beneficial alleles can enter a population recurrently, either by mutation or migration, during the selective phase. In this case, descendents of several of these independent origins may contribute to the fixation.

As a consequence, all ancestral haplotypes that are linked to any of these copies will be retained in the population, affecting the pattern of a selective sweep on linked neutral variation. In this study, we use analytical calculations based on coalescent theory and computer simulations to analyze molecular adaptation from recurrent mutation or migration.

Under the assumption of complete linkage, we derive a robust analytical approximation for the number of ancestral haplotypes and their distribution in a sample from the population. Chapter 3 Polymorphism data can be used to identify loci at which a beneficial allele has recently gone to fixation, given that an accurate description of the signature of selection is available. In the classical model that is used, a favored allele derives from a single mutational origin. This ignores the fact that beneficial alleles can enter a population recurrently by mutation during the selective phase.

In this study, we present a combination of analytical and simulation results to demonstrate the effect of adaptation from recurrent mutation on summary statistics for polymorphism data from a inked neutral locus. We also analyze the power of standard neutrality tests based on the frequency spectrum or on linkage disequilibrium LD under this scenario.

For recurrent beneficial mutation at biologically realistic rates we find substantial deviations from the classical pattern of a selective sweep from a single new mutation. Deviations from neutrality in the level of polymorphism and in the frequency spectrum are much less pronounced than in the classical sweep pattern. In contrast, for levels of LD the signature is even stronger if recurrent beneficial mutation plays a role. We suggest a variant of existing LD tests that increases their power to detect this signature.

Chapter 4 Models of competitive sympatric speciation have created much excitement, but they are also highly controversial. We present a thorough and largely analytical analysis of the evolution of assortative mating in a Roughgarden model, in which the ecological trait is determined by a single diallelic locus. The genetic architecture is then given by a single parameter: Vor und zu Beginn der Blastodermdifferenzierung wird die dpp-Expression stark durch anteroposteriore Faktoren bestimmt. Die anteroventrale dpp-Expression des Blastoderms hat eine Funktion bei der Determination der anterioren Amnionanlage, die sich zwischen Serosa und Embryo differenziert.

Die posterioren Amnionanlagen entstehen aus pnr- und dpp-exprimierenden dorsalen Schicksalen. Anteriore und posteriore Amnionanlage werden durch die Anatrepsis-Bewegung zum geschlossenen, dpp- und gbb-exprimierenden Amnionepithel. Clean Molecular evolution of sex-biased genes in Drosophila. Clean Protein Import into Chloroplasts.

Import of a hybrid construct consisting of the transit sequence of SSU, the N-proximal part of mature Tic and the mature SSU into chloroplasts led to the appearance of a soluble stromal import intermediate and the proposal that Tic might use a re-export pathway from the stroma to the inner envelope membrane. For full length Tic no soluble intermediate has been observed yet. One of the goals of this work was to investigate the import pathway of Tic in more detail.

In this research the soluble stromal intermediate of Tic was observed, its re-export to the membrane was followed, and finally, the intermediate was isolated and co-immunoprecipitated with the stromal chaperones Hsp93, Hsp70 and to a lesser extent Cpn The obtained results indicate that Tic, as proposed, uses a re-export pathway conservative sorting during its import into the chloroplast inner envelope membrane.

Tic also requires stromal chaperones for achieving its native conformation, prior to the insertion into the inner envelope membrane. The pathway for targeting to the intermembrane space of chloroplasts had not been intensively studied yet. For this reason, the analysis of two intermembrane space localized proteins was conducted: Both proteins are nuclear-encoded and synthesized on cytosolic ribosomes with a cleavable N?

Forschung in der Fakultät für Chemie

Tic22 was found to be associated with the outer face of the inner envelope membrane, as well as with the inner face of the outer envelope membrane, even though at a lower level. MGD1 was proposed to be associated with one of the envelopes by weak electrostatic interactions. Results presented in this thesis show that import of MGD1 is dependent on, and that of Tic22 is enhanced by, but not dependent on, addition of external ATP. Both preproteins need thermolysin sensitive components on the chloroplast surface for successful import.

Chemical crosslinking and immunoprecipitation have demonstrated that Tic22 and MGD1 interact with the components of the Toc translocon of the chloroplast outer envelope during their translocation. Import competition experiments showed that both proteins use the Toc machinery of the general import pathway. Therefore, proteins targeted to the intermembrane space seem to use the same translocation mode across the outer envelope as stromal proteins.

The first step of preprotein translocation across the membranes of chloroplasts is facilitated by the Toc translocon. Aim of this work was to elucidate the dynamics and the mechanism of action of this molecular machine. The central, stably associated part of the Toc translocon, the Toc core complex, consists of the pore forming Toc75 and two receptors with GTPase activity, Toc34 and Toc The question of Toc localization was addressed since controversal results on this topic were reported.

In this study, membrane localization of Toc was confirmed, which has further implications on the mode of its action. To understand the necessity of multiple isoforms of Toc components as found in Arabidopsis thaliana, expression analysis and tissue-specific localization were conducted.

Gathered data suggested the existence of several types of the complex, assembled from different types of subunits. These complexes have different preprotein specificities. Expression analysis provided further arguments for dynamic association of the intermembrane space complex with the Toc core complex. Comparison of gene expression and protein presence of translocon subunits contradicts the function of Tic20 as a general pore for stromal targeted proteins, but not as a protein conducting channel per se. For further analysis of the Toc translocon structure and function, its purification and reconstitution into proteoliposomes was reinvestigated.

To this end, a technique for liposome size determination in a single spectrophotometric measurement was developed. Die Proteinkinasen At4g und At4g wurden durch einen Abgleich mit dem Proteom von Arabidopsis thaliana identifiziert. Mitochondrielle Vorstufenproteine werden von den drei Proteinkinasen nicht phosphoryliert. Die Proteinkinasen At2g und At4g weisen vergleichbare Transkriptmengen in allen Pflanzengeweben auf. The Retinoblastoma protein pRb was the first tumor suppressor protein to be identified.

It is the founding member of the so called pRb or pocket protein family, comprising two additional members p and p in mammalian cells, and its best characterized function is the regulation of the E2F family of transcription factors. Today, the pRb-E2F network represents one of the best understood pathways implicated in cell cycle regulation and differentiation.

Pocket proteins negatively regulate the transactivation properties of E2F proteins by two mechanisms: First, binding of pocket proteins to E2F masks the E2F transactivation domain and thereby impairs transcriptional activation. Second, pocket proteins interact with several chromatin modifying and chromatin binding proteins and recruit these proteins to E2F target genes, where they help to establish a repressive chromatin conformation. In this work, advantage was taken of the relative simplicity of the Drosophila melanogaster pRb-E2F network to purify and functionally characterize native pRb repressor complexes.

Two related multisubunit complexes that only differ in their pocket protein subunit RBF1 or RBF2 have been purified from Drosophila embryo nuclear extract. These complexes contain several novel pocket protein-associated polypeptides and localize to transcriptionally silent regions on Drosophila polytene chromosomes. Moreover, they specifically associate with deacetylated histone tails, which are a hallmark of transcriptionally silent chromatin. In cycling Drosophila S2 cells, the purified complexes redundantly repress the expression of a certain class of E2F target genes implicated in differentiation and development, whereas they do not control the expression of cell cycle-regulated E2F targets.

Interestingly, the isolated complexes seem to be highly conserved between different organisms. Genes encoding the Caenorhabditis elegans homologs of the complex subunits act within the same genetic pathway involved in vulval cell fate determination and they functionally cooperate in different developmental processes.



Furthermore, a complex with striking homology to the Drosophila complexes also exists in human cells. In the light of the specific repression of developmentally regulated E2F target genes in cycling Drosophila cells, it is conceivable that the complexes prevent the uncontrolled expression of genes important during differentiation. Genomic integrity largely depends on the accurate replication and faithful transmission of the genetic information to the progeny each time a cell divides. To ensure the fidelity of these fundamental processes, highly sophisticated protein networks have evolved.

This study investigated how the diverse mechanisms for maintaining genomic integrity are integrated and coordinated at the replication fork. In the first part, the roles of post-translational modifications with ubiquitin and SUMO in regulating replication through DNA lesions were investigated. Previous work in S. Moreover, being devoid of enzymatic activity, PCNA is perfectly suited to act as a platform for recruitment of factors to the replication fork, including DNA repair enzymes, chromatin remodelers and replication regulators.

PCNA modifications by ubiquitin govern two distinct modes of lesion bypass, either channeling the repair processes into error-prone translesion synthesis by recruiting specialized polymerases, or promoting an error-free mechanism involving a template switch to the sister chromatid. In this study, the importance and universality of PCNA-modifications could be demonstrated by showing that PCNA ubiquitylation in human and chicken cells is well conserved.

Interestingly, SUMO modification appeared less preserved, indicating that the pathways controlled by PCNA modifications are used to different degrees throughout species. A further finding of this thesis was the identification of DNA polymerase. Jedoch anders als bei E. Zeaxanthin wirkt sich positiv auf die NPQ aus. Clean Nuclear positioning and functional regulation of endogenous genes and transgenes in the fruit fly Drosophila melanogaster and in mammalian cells. The goal of the work was to address the role of higher order nuclear architecture in the functional regulation of endogenous genes and transgenes in different species.

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In the first part of the work, 3D distance measurements were performed to analyze in WT flies and in different transgenic lines of Drosophila melanogaster Cavalli and Paro, ; Zink and Paro, the nuclear localization of endogenous genes and transgenic constructs containing the Polycomb Response Element PRE Fab-7 relative to the nuclear periphery and heterochromatin. Transgenic constructs containing the Fab-7 element and three endogenous genes, Abd-B, sd, and Ubx, were first analyzed at their inactive state.

The results showed that they were preferentially associated with the nuclear periphery and did not display specific associations with heterochromatin. The localization of the transgenic Fab-7 element was further analyzed at different states of activity. The percentages of such associations were tissue- and fl y line-dependent. Further investigations of the boundary of heterochromatin showed that this region has a complex organization, where euchromatic sites enriched in the active form of RNA pol II and trimH3K4, sites enriched in dimH3K4 and Pc-binding sites, as well as pericentromeric satellite DNA are exposed and juxtaposed towards each other.



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The concentration and specific architecture of such sites at the boundary of heterochromatin might help to maintain the equilibrium between activation and repression at this boundary. This specific environment might be favourable for maintaining PREs in the active state.

I also investigated in three transgenic lines whether endogenous and transgenic copies of the Fab-7 element interact physically, using 3D distance measurements. In five tissues analyzed, no pairing between endogenous and transgenic copies of the Fab-7 element was observed. Also enhancement of Pc-mediated silencing did not induce pairing. Additionally, the general organization of Pc-binding sites was addressed in six larval tissues. We used different methods of microscopy and image analyses to count the numbers of Pc foci in nuclei from these tissues.

However, corresponding analyses are not without problems at the current stage of methodology and results must be interpreted carefully. Together with the results of previously published studies, which investigated pairing between PREs Bantignies et al. Activity-related positioning of transgenes was also addressed in transgenic porcine cell lines Hofmann et al.

Results of 2D erosion analyses showed that the LV-PGK transgene was associated with the nuclear periphery in its inactive state, while it occupied more interior positions in its active state. This corresponds to my results obtained with transgenic Drosophila lines. My data also suggested that the active LV-PGK construct might be associated with heterochromatin in one case.

However, further experiments would be necessary to confirm such associations. The results obtained with Drosophila and porcine cells suggested conserved mechanisms for tethering inactive loci to the nuclear periphery. These were further addressed using the human CFTR locus as a model, which is closely associated with the nuclear periphery in its inactive state Zink et al. The question was addressed whether Tpr, a protein associated with the nuclear basket, plays a role in the perinuclear localization of the inactive CFTR locus.

Clean Characterisation of mechanisms and components of protein phosphorylation in photosynthetic membranes of Synechocystis sp. Clean Biogenesis and function of mitochondrial outer membrane proteins. The mitochondrial outer membrane harbors different sub-classes of proteins that mediate numerous interactions between the mitochondrial metabolic and genetic system and the rest of the eukaryotic cell.

Two classes of these proteins were investigated in this thesis. The first class, tail-anchored proteins, exposes a large domain to the cytosol and is anchored to the membrane by a single hydrophobic segment close to the C-terminus. This segment is usually flanked by positively—charged amino acids residues. In the first part of my study I could identify that the tail anchor domain fulfills four distinct functions: First, the tail anchor domain mediates the targeting to mitochondria in a process that probably requires the positive charges down stream the transmembrane segment.

Second, the domain facilitates the insertion into the outer membrane. Third, the tail anchor domain is required for assembly of the proteins into the relevant complexes. Finally, it can stabilize such complexes. These membrane proteins are unique for the outer membrane of mitochondria, chloroplast and gram-negative bacteria.

At the beginning of this work, the TOB complex was known to consist of the peripheral associated membrane protein Mas37 and the essential membrane embedded component Tob Initially, we could identify Tob38 as a new component of the TOB complex. Tob38 is encoded by an essential gene and the protein associates with the TOB complex at the cytosolic side of mitochondria.

It interacts with Mas37 and Tob55 and is associated with Tob55 even in the absence of Mas Notably, such an effect was not observed for other precursors of the outer membrane proteins and precursors distained to the various sub-mitochondrial compartments. Next, the import and the assembly pathways of Mas37 and Tob55 were analyzed in detail. Reduced insertion of the Tob55 precursor in the absence of Tom20 and Tom70 argues for initial recognition of the precursor of Tob55 by the import receptors.

It is then transferred through the import channel formed by Tom Variants of the latter protein influenced the insertion of Tob Assembly of newly synthesized Tob55 into pre-existing TOB complexes, as analyzed by blue native gel electrophoresis, depended on pre-existing Tob55 and Tob38 but to a less extent on Mas In contrast, both the association of Mas37 precursor with mitochondria and its assembly into the TOB complex were not affected by mutation in the TOM complex. My results suggest that Mas37 assembled directly with the TOB core complex.

Hence, the biogenesis of Mas37 represents a novel import pathway of mitochondrial proteins. Finally, the structure function relationships of Tob55 were investigated by combination of biochemical and genetic approaches. Deletion of various lengths at the N-terminal domain did not affect the targeting of Tob55 precursor to mitochondria and its insertion into the outer membrane.

Replacement of wild type Tob55 by these deletion variants resulted in reduced growth of cells. Clean Selection and Population Structure in Drosophila melanogaster. In this thesis I scrutinized a specific region of the X chromosome of Drosophila melanogaster for evidence of positive directional selection. In the first chapter, I analyzed a region that showed no polymorphism in a previous scan of the X chromosome in a European D. This region, which I named the wapl region, is located on the distal part of the X chromosome, in cytological division 2C10 - 2E1.

I observed a Loci flanking this region show a skewed frequency spectrum at segregating sites, strong haplotype structure, and high levels of linkage disequilibrium. Neutrality tests revealed that these patterns of variation are unlikely under the neutral equilibrium model or simple bottleneck scenarios. In contrast, newly developed likelihood ratio tests suggest that strong positive selection has acted recently on the region under investigation, resulting in a selective sweep.

Evidence is presented that this sweep may have originated in an ancestral population in Africa. In the second chapter, I revisited the center of the wapl region analyzed in chapter 1. I concentrated on the African D. This valley is located between the genes ph-d and Pgd. I therefore termed this part the ph-d - Pgd region. The new results confirm previous conclusions about selection having shaped nucleotide variability in this part of the D. Moreover, by sequencing the center of the selective sweep I was able to establish the haplotype structure in that region and to infer the historical context of the sweep.

Most likely a positively selected substitution occurred at ph-p and was fixed before the out-of-Africa expansion of D. This substitution might be associated with the specialization of ph-p in gene regulation. In addition, the results obtained from the European sample indicate that sequence variation was not affected by demography alone. In fact, it was found that selection affected nucleotide diversity in the ph-d - Pgd region of the European sample as well. Since heterozygosity across the whole wapl region is substantially reduced, I propose that an additional selective sweep occurred at a different site in the European population.

This is supported by an analysis regarding the time since the fixation of the first beneficial mutation at ph-p, which points toward a substitution in D. In chapter 3, I obtained sequence data from six SE Asian samples for ten putatively neutrally evolving X-linked loci. Population genetic parameters were estimated and compared to those previously obtained from the European and the African sample. I observe substantially lower levels of nucleotide diversity in SE Asia than in either Africa or Europe.

In particular, samples taken from more peripheral populations e. Manila and Cebu, located on the Philippines show a paucity of haplotypes. Common summary statistics indicate that genetic drift had a significant impact on these populations, which also led to considerable population substructure. Kuala Lumpur, however, shows rather high levels of heterozygosity among all SE Asian samples and is on average least differentiated from these. This indicates that the Kuala Lumpur population is ancestral to the other SE Asian populations, which is supported by a hi.

Proliferation erfordert die Koordination des Zellwachstums mit der Zellzyklusmaschinerie. Die Koordinatorfunktion des Komplexes scheint von der Hefe bis zum Menschen konserviert zu sein. Die p53 Antwort konnte damit als Ursache des Zellzyklusarrests ausgemacht werden. Clean Molekulare Charakterisierung neuer centrosomaler und centrosomassoziierter Proteine in Dictyostelium discoideum. In einem Proteomics-Ansatz mit verschiedenen Auftrennungsmethoden wurde das Dictyostelium-Centrosom systematisch untersucht. Hier konnte in durch gezielte Mutationen gezeigt werden, dass DdLIS1 eine Rolle bei der Entwicklung spielt, auch wenn es selbst nicht entwicklungsreguliert ist.

Clean Ressourcennutzung und Paarungssystem der nektarivoren Flughundart Macroglossus minimus Pteropodidae: Sequenzhomologien zwischen Rpl25p und seinem Homolog Rl23p aus E. Clean The rabies virus phosphoprotein P: Interferons are the key cytokines of innate immunity and represent the first line of defense against invading viruses. By activating immediate antiviral mechanisms and stimulating the adaptive immune response, interferon signaling is decisive for the outcome of disease and virus clearance.

The work presented in this thesis reveals a central role of the phosphoprotein P of rabies virus Rhabdoviridae family , known as a polymerase cofactor, as an inhibitor of the host interferon system. Counter-mechanism to escape form recognition by the immune system were previously unknown for the neurotropic rabies virus, which is characterized by the highest case-fatality ratio.

The factor responsible is the viral phosphoprotein P. Unphosphorylated IRFs are unable to dimerize and fail to enter the nucleus. The inhibitory activities of RV P on IFN induction and signaling are independent functions, as shown by site-directed mutagenesis of P and identification of different short amino acid stretches required for either function. Importantly, the inhibitory activities of P were demonstrated in the context of recombinant viruses.

The described work contributes to the understanding of host responses to virus infections in general and of rabies virus pathogenicity in particular. In addition, viruses with modified IFN antagonists provide interesting opportunities for development of attenuated vaccines and vectors. In der vorliegenden Arbeit wurde gezeigt, dass der Proteinimport in Chloroplasten in das Calcium-Netzwerk der Pflanzenzelle integriert ist.

Sowohl heterolog exprimiertes als auch natives Tic32 binden an Calmodullin nur in Anwesenheit von Calcium. Clean Untersuchungen zur Rolle des endogenen Cannabinoidsystems bei der Anpassung an aversive Situationen. Ziel der vorliegenden Arbeit war es zu untersuchen, auf welche Art und Weise das endogene Cannabinoidsystem die Extinktion konditionierter Furcht vermittelt. Dabei gliedert sich diese Arbeit in vier Teile. In diesem Zusammenhang wurde in der vorliegenden Arbeit erstmalig nachgewiesen, dass die bei der Furchtkonditionierung auftretende unabdingbare, stark aversive Situation neben der klassischen Konditionierung auch eine Stress-Sensitivierung hervorrufen kann.

Medieneinsatz im mathematisch-naturwissenschaftlichen Unterricht: Joachim Herz Stiftung Verlag, - Naturwissenschaften. Zakeri, Banafshe; Niebling, S. Molecular recognition of carboxylates in the protein leucine zipper by a multivalent supramolecular ligand: Residue-specific, sensitive and label-free probing by UV resonance Raman spectroscopy,. Norbornane-based cationic antimicrobial peptidomimetics targeting the bacterial membrane,. On the influence of substitution patterns in thioether-based luminophores with aggregation-induced emission properties,. On the potential of using dual-function hydrogels for brackish water desalination,.

Origin of Xylitol in Chewing Gum: Journal of Agricultural and Food Chemistry, Vol. Ortho-Fluorination of azophenols increases the mesophase stability of photoresponsive hydrogen-bonded liquid crystals,. Knoop, Oliver; Hohrenk, Lotta L. Ozonation of Tamoxifen and Toremifene: Reaction Kinetics and Transformation Products,.

Environmental Science and Technology, Vol. Patterned functionalization of textiles using uv-based techniques for surface modification - patterned wetting behavior,. Polyarylsulfone-based blend ultrafiltration membranes with combined size and charge selectivity for protein separation,. Poly ethylene oxide -block-poly methyl methacrylate diblock copolymers as functional additive for poly vinylidene fluoride ultrafiltration membranes with tailored separation performance,.

Journal of the American Chemical Society, Vol. Potassium-sensitive poly N-isopropylacrylamide -based hydrogels for sensor applications,. Precipitation with polyethylene glycol followed by washing and pelleting by ultracentrifugation enriches extracellular vesicles from tissue culture supernatants in small and large scales,. Primary particle diameter differentiation and bimodality identification by five analytical methods using gold nanoparticle size distributions synthesized by pulsed laser ablation in liquids,.

Prolonged release of bone morphogenetic protein-2 in vivo by gene transfection with DNA-functionalized calcium phosphate nanoparticle-loaded collagen scaffolds,. Recent advances in anaerobic biological processes for textile printing and dyeing wastewater treatment: Recent trends in water analysis triggering future monitoring of organic micropollutants,. Reciprocal peer assessment as a learning tool for secondary school students in modeling-based learning,.

European Journal of Psychology of Education, Vol. Silver nanoparticles in complex media: An easy procedure to discriminate between metallic silver nanoparticles, reprecipitated silver chloride, and dissolved silver species,. Spontaneous shape alteration and size separation of surfactant-free silver particles synthesized by laser ablation in acetone during long-period storage,.

Stability of organochlorine pesticides during storage in water and loaded SPE disks containing sediment,. Stable isotope informed genome-resolved metagenomics reveals that Saccharibacteria utilize microbially-processed plant-derived carbon. Stereoselective Sensing of l- and d-Amino Acids: Streptavidin-coated surfaces suppress bacterial colonization by inhibiting non-specific protein adsorption,. Journal of biomedical materials research: Strontium carbonate precipitation as a sample preparation technique for isotope ratio analysis of Sr in mineral water and wine by quadrupole-based inductively coupled plasma mass spectrometry,.

Rapid Communications in Mass Spectrometry: Structural and thermoelectrical characterization of epitaxial Sb2Te3 high quality thin films grown by thermal evaporation,. Structuring of electrode surfaces with ligand-free nanoparticles via electrophoretic deposition: Sulfolobus acidocaldarius transports pentoses via a carbohydrate uptake transporter 2 CUT2 -type ABC transporter and metabolizes them through the aldolase-independent Weimberg pathway,.

Surface-enhanced Raman spectroscopic detection of molecular chemo- and plasmo-catalysis on noble metal nanoparticles,. Surface enhanced spectroscopies of a molecular monolayer in an all-dielectric nanoantenna,. Synthesis and biological characterization of alloyed silver—platinum nanoparticles: Synthesis and x-ray crystal structures of homotrimetallic zinc bisureate complexes,. Synthesis of well-defined cross-linkable zwitterionic macromolecular building blocks for hydrogels,. Transforming Assessment - Cham: The furan microsolvation blind challenge for quantum chemical methods: The influence of internal and external electric fields on the transport of energetic electrons in nanostructures,.

The monogenean Paradiplozoon ichthyoxanthon behaves like a micropredator on two of its hosts, as indicated by stable isotopes,. The role of composition of uniform and highly dispersed cobalt vanadium iron spinel nanocrystals for oxygen electrocatalysis,. Two mechanisms of nanoparticle generation in picosecond laser ablation in liquids: The origin of the bimodal size distribution,. Using molecular tweezers to remodel abnormal protein self-assembly and inhibit the toxicity of amyloidogenic proteins,. Validation of a constrained 2D slab model for water adsorption simulation on 1D periodic TiO,.

Komplexchemie Teil 3 - Nomenklatur

Wahl- und Abwahlprofile im Fach Chemie: From Nanostructure to Biological Properties,. Joachim Herz-Stiftung Verlag, - Naturwissenschaften , pp. X-ray spectroscopic and stroboscopic analysis of pulsed-laser ablation of Zn and its oxidation,. Materials Science and Processing, Vol. Francisco, Issotta; Covarrubias, Paulo C. Angewandte Chemie - International Edition, Vol. Activity-based protein profiling as a robust method for enzyme identification and screening in extremophilic Archaea,. Adhesion properties of a three-layer system based on RF-magnetron sputter deposited calcium-phosphate coating and silver nanoparticles,.

June , , Novosibirsk, Russia - Piscataway: Institute of Electrical and Electronics Engineers Inc. Adjusting the catalytic properties of cobalt ferrite nanoparticles by pulsed laser fragmentation in water with defined energy dose,. Advanced SERS sensor based on capillarity-assisted preconcentration through gold nanoparticle-decorated porous nanorods,. A four dimensional separation method based on continuous heart-cutting gas chromatography with ion mobility and high resolution mass spectrometry,.

A highly selective protein adsorber via two-step surface-initiated molecular imprinting utilizing a multi-functional polymeric scaffold on a macroporous cellulose membrane,. Albumin-derived perfluorocarbon-based artificial oxygen carriers: A physico-chemical characterization and first in vivo evaluation of biocompatibility,. European Journal of Pharmaceutics and Biopharmaceutics, Vol.

A metal-free fluorescence turn-on molecular probe for detection of nucleoside triphosphates,. Synthesis, Characterization and Cell Uptake Studies,. Ammonia decomposition and synthesis over multinary magnesioferrites: Richter, Franziska; Subramaniam, Sudhakar R. Implementation fachdidaktischer Innovation im Spiegel von Forschung und Praxis: Analysis of the time-resolved magneto-optical Kerr effect for ultrafast magnetization dynamics in ferromagnetic thin films,.

A new chemometric approach for automatic identification of microplastics from environmental compartments based on FT-IR spectroscopy,. An inverted supramolecular amphiphile and its step-wise self-assembly into vesicular networks,. A quarter-century of nanoparticle generation by lasers in liquids: Where are we now, and what's next?

Aromatic thioethers as novel luminophores with aggregation-induced fluorescence and phosphorescence,. A systematic structure—activity study of a new type of small peptidic transfection vector reveals the importance of a special oxo-anion-binding motif for gene delivery,. Au I -Catalyzed dimerization of two alkyne units - interplay between butadienyl and cyclopropenylmethyl cation: Avidin-conjugated calcium phosphate nanoparticles as a modular targeting system for the attachment of biotinylated molecules in vitro and in vivo,.

Bacterial and archaeal community distribution and stabilization of anaerobic sludge in a strengthen circulation anaerobic SCA reactor for municipal wastewater treatment,. Bioleaching of pyrite by iron-oxidizing acidophiles under the influence of reactive oxygen species,. Biological application of laser-generated nanoparticle in nanocomposites, surface coatings and nanobioconjugates,.

Capillary electrophoresis method with UV-detection for analysis of free amino acids concentrations in food,. Characterization of methane oxidation in a simulated landfill cover system by comparing molecular and stable isotope mass balances,. Characterization of peak capacity of microbore liquid chromatography columns using gradient kinetic plots,.

Cluster formation of NaCl in bulk solutions: Colloids created by light: Laser-generated nanoparticles for applications in biology and medicine,. Comparative evaluation of the sand blasting, acid etching and electron beam surface treatments of titanium for medical application,.

Composition control of pure MnO nanoparticles for photocatalytic water oxidation by pulsed laser fragmentation of MnO micro powder,. Constructing accurate interaction potentials to describe the microsolvation of protonated methane by helium atoms,. Weyrauch, Philip; Zaytsev, Andrey V. Conversion of ciscarboxycyclohexylacetyl-CoA in the downstream pathway of anaerobic naphthalene degradation,. Degradation of sulfamethoxazole using ozone and chlorine dioxide: Compound-specific stable isotope analysis, transformation product analysis and mechanistic aspects,.

Delivery of the TLR ligand poly I: C to liver cells in vitro and in vivo by calcium phosphate nanoparticles leads to a pronounced immunostimulation,. Determination of mineral oil aromatic hydrocarbons in edible oils and fats by online liquid chromatography—gas chromatography—flame ionization detection: Evaluation of automated removal strategies for biogenic olefins,. Determination of pore size distributions of virus filtration membranes using gold nanoparticles and their correlation with virus retention,.

Development of a novel immobilization method by using microgels to keep enzyme in hydrated microenvironment in porous hydrophobic membranes,. Diagnose — Intervention — Implementation im Spannungsfeld zwischen fachdidaktischer Forschung und unterrichtlicher Praxis,. Dilute suspensions in annular shear flow under gravity: Industrial and Engineering Chemistry Research, Vol.

Do we need retarded delivery of bone growth factors in facial bone repair? An experimental study in rats,. Electron-rich two-, three- and four-center bonds between chalcogens: New prospects for old molecules,. Empirische Beschreibung der schwierigkeitserzeugenden Elemente von Fachsprache im Chemieunterricht,. Enzymatic hydrolysis of poly ethyleneterephthalate used for and analysed by pore modification of track-etched membranes,. Experimental variation of the level and the ratio of angiogenic and osteogenic signaling affects the spatiotemporal expression of bone-specific markers and organization of bone formation in ectopic sites,.

Fabrication of modified polyethersulfone membranes for wastewater treatment by submerged membrane bioreactor,. Journal of materials chemistry: C, materials for optical and electronic devices, Vol. Functionality of albumin-derived perfluorocarbon-based artificial oxygen carriers in the Langendorff-heart,. Artificial Cells, Nanomedicine and Biotechnology, Vol. Marzun, Galina; Haxhiaj, I. Functionality of ligand-free alloy nanoparticles for heterogeneous catalysis made by scalable laser synthesis,.

Functionality of ligand-free alloy nanoparticles for heterogeneous catalysis made by scaleable laser synthesis,. Functional Mechanically Interlocked Molecules: Gradual modification of ITO particle's crystal structure and optical properties by pulsed UV laser irradiation in a free liquid jet,. Hierarchical self-assembly of a small monomer with two orthogonal binding sites: High productive and continuous nanoparticle fabrication by laser ablation of a wire-target in a liquid jet,. Host—Guest complexes of cyclodextrins and nanodiamonds as a strong non-covalent binding motif for self-assembled nanomaterials,.

How composition and cellular uptake of silver and gold-silver alloy nanoparticles may affect their antimicrobial mode of action,. How do polyethylene glycol and poly sulfobetaine hydrogel layers on ultrafiltration membranes minimize fouling and stay stable in cleaning chemicals? How persistent microbubbles shield nanoparticle productivity in laser synthesis of colloids - Quantification of their volume, dwell dynamics, and gas composition,. How Size Determines the Value of Gold: How to design a proper membrane for a membrane contactor-based air conditioning system,. Hybrid biocomposites based on titania nanotubes and a hydroxyapatite coating deposited by RF-magnetron sputtering: Hydrophilic polyethersulfone-based microfiltration membranes by electrospinning of polymer blends,.

Imidazolium Based Ionic Liquids: Improvement of virus removal using ultrafiltration membranes modified with grafted zwitterionic polymer hydrogels,. Improving the zT value of thermoelectrics by nanostructuring: Tuning the nanoparticle morphology of Sb2Te3 by ionic liquids,. Incorporation of arginine mimetic residue into peptides for recognition of double stranded nucleic acid structure: Incorporation of silver nanoparticles into magnetron-sputtered calcium phosphate layers on titanium as an antibacterial coating,. Elsevier Science, , pp. Intestinal helminth infection drives carcinogenesis in colitis-associated colon cancer,.

Intramolecularly-stabilized Group 14 Alkoxides: Osorio Barajas, Xochitli L. Investigation of carbon-based nanomaterials as sorbents for headspace in-tube extraction of polycyclic aromatic hydrocarbons,. Investigation of the iron-peroxo complex in the fenton reaction: Schulmagazin 5 - Laser-induced growth of YVO: Factors Limiting the Scale-Up Process,. Laser micromachining of metals with ultra-short pulses: Laser synthesis, structure and chemical properties of colloidal nickel-molybdenum nanoparticles for the substitution of noble metals in heterogeneous catalysis,.

Ligand-free metal nanoparticle colloids: Ligand-free nanoparticles made by scalable laser synthesis for catalysis applications,. Waste material or potential resource; Investigation of metal recovery and utilization options,. Live-cell imaging to compare the transfection and gene silencing efficiency of calcium phosphate nanoparticles and a liposomal transfection agent,.

Local delivery of siRNA-loaded calcium phosphate nanoparticles abates pulmonary inflammation,. Nanotechnology, Biology, and Medicine, Vol. Mechanical and chemical studies on EPS from Sulfobacillus thermosulfidooxidans: Seifarth, Volker; Grosse, Joachim O. Mechanical induction of bi-directional orientation of primary porcine bladder smooth muscle cells in tubular fibrin-poly vinylidene fluoride scaffolds for ureteral and urethral repair using cyclic and focal balloon catheter stimulation,. Merging empirical valence bond theory with quantum chemistry to model proton transfer processes in water,.

Mineral in skeletal elements of the terrestrial crustacean Porcellio scaber: Molecular dynamics study of stability and disintegration of long rod-like micelles: Dodecyltrimethylammonium chloride in solutions of hydroxybenzoates,. Multi-spectroscopic and theoretical analyses on the diphenyl ether—tert-butyl alcohol complex in the electronic ground and electronically excited state,. Nanoparticle-based B-cell targeting vaccines: Tailoring of humoral immune responses by functionalization with different TLR-ligands,.

Nanotechnology, Biology and Medicine, Vol. Therapeutic Approaches and Supramolecular Chemistry. Nanoparticulate versus ionic silver: Behavior in the tank water, bioaccumulation, elimination and subcellular distribution in exposure studies with the freshwater mussel Dreissena polymorpha,. Nanoscale interface confinement of ultrafast spin transfer torque driving non-uniform spin dynamics. Nano-sized metal organic framework to improve the structural properties and desalination performance of thin film composite forward osmosis membrane,.

New and emerging technologies: Nucleobase-Guanidiniocarbonyl-Pyrrole conjugates as novel fluorimetric sensors for single stranded RNA,. Order and melting stability of calcium arachidate Langmuir-Blodgett monolayers prepared at different pH,. Organic compounds in fluid inclusions of Archean quartz - Analogues of prebiotic chemistry on early Earth,. Oxidative Stickland reactions in an obligate aerobic organism — amino acid catabolism in the Crenarchaeon Sulfolobus solfataricus,.

Particle image velocimetry compared to CFD simulation of stirred vessels with helical coils,. Journal of materials science: Kouril, Theresa; Eicher, Johann J. Pilot-scale synthesis of catalysis-relevant nanoparticles by high-power ultrafast laser ablation in liquids,. Planarized and twisted intramolecular charge transfer: Polymer Brushes on Cellulose Nanofibers: Polyvinylamine-coated polyester fibers as a carrier matrix for the immobilization of peroxidases,.

Preparation, catalytical activity and crystal structure of a heptanuclear zinc acetate cluster,. Chemical Engineering and Technology, Vol. Particle and Powder Technology: Process-stable, highly pure nanomaterials by pilot-scale, continuous high-power laser production,. Springer VS, , pp.

Pulsed laser ablation in liquids: Impact of the bubble dynamics on particle formation,. Pulsed laser ablation of wire-shaped target in a thin water jet: Effects of plasma features and bubble dynamics on the PLAL process,. Reconstructing metabolic pathways of a member of the genus Pelotomaculum suggesting its potential to oxidize benzene to carbon dioxide with direct reduction of sulfate,. Removal of humic acid and chloroform from drinking water by using commercial nanofiltration and reverse osmosis membranes,.

Reply to delmont and eren: An international journal to further the chemical science, Vol. Response and recovery of a pristine groundwater ecosystem impacted by toluene contamination: RF magnetron sputtering of a hydroxyapatite target: Rigidly tethered Bis-phosphoric acids: Sand-blasting treatment as a way to improve the adhesion strength of hydroxyapatite coating on titanium implant,.

Ein wichtiges Merkmal effektiven Chemieunterrichts,. Self-Assembly of a tripodal triszwitterion forms a pH-switchable hydrogel that can reversibly encapsulate hydrophobic guests in water,. Sorbent material characterization using in-tube extraction needles as inverse gas chromatography column,. Study the influence of licorice and pomegranate drinks on nicotine metabolism in human urine by LC-orbitrap MS,.

Journal of Pharmaceutical and Biomedical Analysis, Vol. Surface-Enhanced raman spectroscopy and density functional theory calculations of a rationally designed rhodamine with thiol groups at the xanthene ring,. Journal of physical chemistry: C, nanomaterials and interfaces, Vol. Surface micro-patterning as a promising platform towards novel polyamide thin-film composite membranes of superior performance,. Survival of 'Deinococcus Geothermalis' in biofilms under desiccation and simulated space and martian conditions,.

Suspect screening of micropollutants and their transformation products in advanced wastewater treatment,. Reactions in Ionic Liquids, pp. Dedicated to Professor Dietrich Gudat on the occasion of his 60th birthday , pp. Synthesis, structure and dispersion interactions in bis 1,8-naphthalendiyl distibine,. Systems biology of the modified branched Entner-Doudoroff pathway in Sulfolobus solfataricus. Tailored protein encapsulation into a DNA host using geometrically organized supramolecular interactions,. Teaching the growth, ripening, and agglomeration of nanostructures in computer experiments,.

Journal of chemical education: JCE; print, software, online, books, Vol. The benefits of coupling miniaturized comprehensive 2D LC with hybrid high-resolution mass spectrometry,. The formation mechanism and internal phase structure of AU-FE alloy nanoparticlesgenerated via pulsed laser ablation in liquids,. The peculiar glycolytic pathway in hyperthermophylic archaea: Understanding its whims by experimentation in silico,. Triplex-hybridizing bioconjugated gold nanoparticles for specific Y-chromosome sequence targeting of bull spermatozoa,.

Chemistry - A European Journal, Vol. Ultrasmall yttrium iron garnet nanoparticles with high coercivity at low temperature synthesized by laser ablation and fragmentation of pressed powders,. Colloids with Lasers, pp. Understanding trophic interactions in host-parasite associations using stable isotopes of carbon and nitrogen,. Effect of the Stabilizing Environment,. Recent Developments and Future Trends - Hoboken: Wiley Blackwell, - Adhesion and adhesives: Validation of weak biological effects by round robin experiments: Water-based, surfactant-free cytocompatible nanoparticle-microgel-composite biomaterials-rational design by laser synthesis, processing into fiber pads and impact on cell proliferation,.

Water-free synthesis of ZnO quantum dots for application as an electron injection layer in light-emitting electrochemical cells,. Journal of Materials Chemistry C: Materials for optical and electronic devices, Vol. Zwischen Neu-Entdecken und Nach-Entdecken: Experimentieren als naturwissenschaftliche Arbeitsweise im Unterricht,.

Ab initio calculations of doped TiO2 anatase nanotubes for photocatalytical water splitting applications,. Journal of Photopolymer Science and Technology, Vol. A fast and reliable approach to benchmark low pressure hollow fibre filtration membranes for water purification,. A FRET-enabled molecular peptide beacon with a significant red shift for the ratiometric detection of nucleic acids,. Agglutination of bacteria using polyvalent nanoparticles of aggregation-induced emissive thiophthalonitrile dyes,. September , Berlin - Regensburg: European journal of inorganic chemistry: EurJIC , Is.

A modular approach towards functional supramolecular aggregates: Meckenstock, Rainer; Himmelberg, A. Journal of molecular microbiology and biotechnology, Vol. Anaerobic Microbial Degradation of Hydrocarbons: From Enzymatic Reactions to the Environment,. A new method for the determination of peak distribution across a two-dimensional separation space for the identification of optimal column combinations,.

Rapid communications in mass spectrometry, Vol. Isolation of Highly Concentrated Iodide,. Assessing biofouling resistance of a polyamide reverse osmosis membrane surface-modified with a zwitterionic polymer,. A systems biology approach reveals major metabolic changes in the thermoacidophilic archaeon Sulfolobus solfataricus in response to the carbon source L-fucose versus D-glucose,. Barium sulfate micro- and nanoparticles as bioinert reference material in particle toxicology,.

Barrierless growth of precursor-free, ultrafast laser-fragmented noble metal nanoparticles by colloidal atom clusters: Biocompatible gold submicrometer spheres with controlled surface textures fabricated by Pulsed Laser Melting in Liquids,. Biofilm formation and interspecies interactions in mixed cultures of thermo-acidophilic archaea Acidianus spp. Biological application of laser-generated nanoparticle conjugates in femtogram precision and kilogram scale,.

Bound rubber morphology and loss tangent properties of carbon-black-filled rubber compounds,. Bridging the Time Gap: Capillary pore membranes with grafted diblock copolymers showing reversibly changing ultrafiltration properties with independent response to ions and temperature,. Journal of Membrane Science: Catalysis and biomedical applications of naked nanoparticle building blocks made by high-power lasers in liquid,.

Characterization of the efficiency of microbore liquid chromatography columns by van Deemter and kinetic plot analysis,. Chemical energy dissipation at surfaces under UHV and higher pressure conditions studied using metal- insulator-metal and similar devices,. Helsingin yliopisto, , pp. Comparison of different methods to study effects of silver nanoparticles on the pro- and antioxidant status of human keratinocytes and fibroblasts,.

Lenzen, Claudia; Winterfeld, Gottfried A. Composites of fluoroapatite and methylmethacrylate-based polymers PMMA for biomimetic tooth replacement,. Conjugation of thiol-terminated molecules to ultrasmall 2 nm-gold nanoparticles leads to remarkably complex 1H-NMR spectra,. Journal of materials chemistry B: Continuous multigram nanoparticle synthesis by high-power, high-repetition-rate ultrafast laser ablation in liquids,. Controlling the shape of Janus nanostructures through supramolecular modification of ABC terpolymer bulk morphologies,.

Cu,Zn-based catalysts for methanol synthesis: On the effect of calcination conditions and the part of residual carbonates,. Cyclic volatile methylsiloxanes in human blood as markers for ruptured silicone gel-filled breast implants,. Debris-free rear-side picosecond laser ablation of thin germaniumwafers in water with ethanol,. Degradation of polymeric brominated flame retardants: Dependence of transformation product formation on pH during photolytic and photocatalytic degradation of ciprofloxacin,.

Inclusion of Exchange Effects,. Journal of Chemical Theory and Computation, Vol. Kandemir, Timur; Friedrich, Matthias; F. Different routes to methanol: Different types of prompts and their impact on cognitive load while learning chemistry,. Do different types of feedback in formative assessment enhance inquiry skills differently? University of Helsinki, , pp. Effect of annealing temperature on pore formation in preparation of advanced polyethylene battery separator membranes,. Effect of pH on the spontaneous synthesis of palladium nanoparticles on reduced graphene oxide,.

Effect of various dispersing agents on the stability of silver microparticle dispersion and the formulation of uniform silver film by laser melting,. Efficient nucleic acid delivery to murine regulatory T cells by gold nanoparticle conjugates,. Electrochemistry at single bimetallic nanoparticles: Enhancement of biofilm formation on pyrite by Sulfobacillus thermosulfidooxidans,. Chemieunterricht im Zeichen der Erkenntnisgewinnung: Applications and biochemical relevance,.

Fabrication and physico-mechanical properties of thin magnetron sputter deposited silver-containing hydroxyapatite films,. Materials Science and Engineering, Vol. Formative assessment in inquiry-based science education — an extensive systematic literature review,. Fully automated determination of the sterol composition and total content in edible oils and fats by online liquid chromatography—gas chromatography—flame ionization detection,. Funktionalisierung lasergenerierter Metallnanopartikel gegen pathologische Proteinaggreation,. Gene transfection of human mesenchymal stem cells with a nano-hydroxyapatite-collagen scaffold containing DNA-functionalised calcium phosphate nanoparticles,.

Guanidiniocarbonyl-pyrrole-aryl conjugates as inhibitors of human dipeptidyl peptidase III: Combined experimental and computational study,. The importance of DNA condensation,. Human iPS-derived cardiac myocyte-fibroblast 3D co-cultures: Journal of Pharmacological and Toxicological Methods, Vol. Focused Issue on Safety Pharmacology, pp.

Improving the in vitro and in vivo properties of neural electrodes by coating with platinum nanoparticles,. Annual Conference of the German Society for Biomaterials Li, Mao; Ehlers, Martin; Mosel geb. Angewandte Chemie - International edition, Vol. Influence of the drying step within disk-based solid-phase extraction both on the recovery and the limit of quantification of organochlorine pesticides in surface waters including suspended particulate matter,. Insertion stability of poly ethylene glycol -cholesteryl-based lipid anchors in liposome membranes,.

European journal of pharmaceutics and biopharmaceutics, Vol. Interaction of C60 fullerene complexed to cisplatin with model bilipid membranes and its uptake by HeLa cells,. Materialwissenschaft und Werkstofftechnik, Vol. Prylutskyy, Yu; Bychko, A. Interaction of C60 fullerene complexed to doxorubicin with model bilipid membranes and its uptake by HeLa cells,.

Introduction of a tailor made anion receptor into the side chain of small peptides allows fine-tuning the thermodynamic signature of peptide-DNA binding,. Investigating dry reforming of methane with spatial reactor profiles and particle-resolved CFD simulations,. Rehbock, Christoph; Koenen, S. In vivo applications of neural electrodes structured with laser-generated platinum nanoparticles,. Strain x1 and Its Unusual Multidomain Glycosidase,. Je mehr, desto besser? Kinetics of chemotaxis, cytokine, and chemokine release of NR macrophages after exposure to inflammatory and inert granular insoluble particles,.

Electrostatics In a brief introduction to electrostatics, students learn that conductors, such as metals, can be negatively or positively charged and that two oppositely-charged objects attract each other while two objects with the like charge repel each other. Furthermore, they learn that the reason why objects are electrically charged is a lack or an excess of electrons, which can almost move freely in metals like copper while the atomic core remains stationary. Pressure differences cause air flows Based on the students everyday experiences e.

By blowing air through a scarf or a towel, students then learn that the thicker a piece of cloth is, the more it obstructs the air flow in order to prepare students for the concept of electrical resistance. A thin piece of cloth is impeding the air flow. A thick piece of cloth is strongly impeding the air flow. Pressure differences are the causal reason for air flow while a piece of cloth impedes air flow. Based on the idea that electrons can move just as freely in the wire as air particles can move in a tube, it is postulated that a battery causes a high electric pressure in the wires attached to the negative terminal and a low electric pressure in the wires attached to the positive terminal.

This electric pressure is initially visualised using the same dot-density representation used to illustrate air pressure, but is then swapped for the colour representation since colour coding has proven to be far more practical in real lessons and draws the students attention to the electric pressure instead of the electric current. At the example of various open electric circuits, it is then emphasised that pressure and pressure difference are two different concepts and that the electric pressure in conductors is determined solely by the battery terminals and is not dependent on the length or size of the conductor.

Similarly to weather maps, the potential is visualised using different colours: Dot-density representation left and colour coding right of the electric pressure potential. The electric current and resistance After the concept of electric pressure has been established at the example of open circuits, electric pressure differences in analogy to air pressure differences are now introduced as the causal reason for electric currents in closed circuits.

For this purpose, it is argued at the example of a simple electric circuit consisting of a battery and a light bulb that the electric pressure difference across the light bulb drives the electrons through the bulb, which subsequently lights up. For each electron flowing through the light bulb from high electric pressure to low electric pressure, the battery moves an electron from its positive to its negative terminal. As a result, the battery maintains the same electric pressure difference in the attached wires and hence also the across light bulb. Similarly to the dense fabric cushion impeding the air flow, electrical resistance is initially introduced by simply stating that the higher the resistance, the more difficult it is for the electrons to move through the light bulb.

A more in-depth explanation of electrical resistance referring to the collision of electrons with atomic nuclei is given at a later point. The effect of voltage and resistance on current is then discussed in order to work out the semiquantitatively relationships the higher the electric pressure difference across the bulb, the higher the electric current and the higher the resistance, the lower the electric current.

The objective here is to give the students a semi-quantitatively understanding of the cause-effect relationships in electric circuits. Semi-quantitative relationship between resistance and current The higher the resistance, the harder it is for electrons to pass through the light bulb and the smaller is hence the current.

Semi-quantitative relationship between current, voltage and resistance. Parallel circuits Parallel circuits can be easily understood using the electron gas model. Furthermore, they provide an excellent learning opportunity for students to help them distinguish clearly between the electric pressure concept and the electric current. As a first step, students have to learn that an ideal battery maintains the same electric pressure in the wires attached to its terminals at all times.

In order to then analyse the electric current in a parallel circuit, students simply have to look at the electric pressure differences at the light bulbs and their resistance. As shown in Figure 9, the electric current through the two light bulbs with a low resistance on the left is 2 A while it is 1 A through the light bulb on the right, which has a higher resistance.

The individual branch currents, which are a result of the electric pressure differences across the light bulbs, then sum up at each node of the parallel circuit. In other words, the total current which the battery needs to supply, is directly determined by the branch currents, which are in turn determined by the pressure differences at and resistance of the light bulbs.

Another advantage of colour coding lies in the fact that it makes it extremely easy for students to identify blubs in parallel: If two bulbs have the same adjacent colours, they are connected in parallel. Parallel circuit with three light bulbs. The right bulb has a higher resistance than the other two.

Capacitors By analysing capacitor charging and discharging, students are introduced to the concept of transient states and dynamic model thinking in order to prepare them for the analysis of series circuits.

Fakultät für Biologie - Digitale Hochschulschriften der LMU - Teil 02/06

The idea behind transient states is that it takes some time for the electric pressure to reach a steady state in the whole circuit and that the steady state is only achieved gradually over so-called transient states. At the example of Figure 10, this can easily be explained. Transient state during capacitor charging.

Initially, we have a high electric pressure in section A and a low electric pressure in section C while we still have a normal electric pressure in section B and D. The reason is that no electron has flown through the light bulbs yet they have only just started moving, which is why the bulbs are lit. During the transient state, electrons now flow from section A to section B high electric pressure to normal electric pressure and as a consequence the electric pressure in section B increases.

At the same time, electrons flow from section D to section C normal electric pressure to low electric pressure and as a consequence the electric pressure in section D decreases. After the transient state of capacitor charging, the capacitor reaches the steady state, where the electric pressures on each side of the light bulbs have become aligned. Discussing capacitor charging and discharging can also help students overcome a number of common misconception, e.

Initially, when the battery is not yet connected, we have a normal electric pressure in all parts of the wire yellow. Once the battery is connected, we have a high electric pressure in the top wire red and a low electric pressure in the bottom wire blue. In the middle wire, we still have a normal electric pressure yellow since no electrons have flown through the light bulbs yet transient state.

As a result, the electric pressure in the middle wire decreases so that the electric pressure difference increases at the top bulb and decreases at the bottom bulb. This makes the electron flow rates through the top and bottom bulbs more and more equal until they are identical.

This state is called the steady state since both the electric pressure in the wires and the electric current in the circuit do not change any further. Initial state Transient state Steady state Figure Step by step analysis of a series circuit with two different light bulbs. Ohm s Law and quantitative measurements After a qualitative understanding of the basic concepts voltage, current and resistance has been established, students then learn about the quantitative relationship between these physical quantities using the definition of resistance R: For this purpose, the voltmeter and ammeter are introduced as measuring instruments and visualised as illustrated in Figure In order to determine the pressure difference, the voltmeter is equipped with two sensor cables, which measure the electric pressure before and after a resistor.

By not colouring in these sensor cables, it is clearly visualised that they are part of an external measuring instrument and at least at this stage not part of the actual electric circuit. As can also be seen in Figure 12, the wide electron tubes that have so far been used to illustrate wires, are now dropped for conventional circuit diagrams. Illustration of voltmeters and ammeters in a simple circuit. In the teaching concept, Ohm s law is treated as an exception rather than the rule since most resistors do not have a fixed resistance value. Since the students are already familiar with the qualitative relationship between the physical quantities voltage, current and resistance, the known qualitative relationship is transformed into a quantitative relationship as a last step of the teaching concept.

Transition from a qualitative to a quantitative relationship of the physical quantities current, voltage and resistance. The conducted teaching interviews show that students generally accept and understand all basic concepts and ideas behind the teaching concept and develop a solid understanding of voltage as an electric pressure difference that makes the electrons flow through light bulbs. This is a particularly promising result given the relatively short time frame for the teaching interviews and that many students fail to develop an adequate concept of voltage in traditional teaching concepts.

Based on the findings of the teaching interviews, a teaching concept including various resources for teachers and students was developed and is currently being evaluated in the classroom. Using a pre- and post-test design, it is planned to compare the learning progress of traditionally taught classes with physics classes that were taught using the new teaching concept.

The learning progress is measured using Urban-Woldron s valid and reliable electricity test cf. Furthermore, it is planned to conduct a survey with some of the 25 teachers around Frankfurt who have agreed to participate in our study in order to get some qualitative feedback on their experiences with the new teaching concept. Das Elektronengasmodell in der Sekundarstufe I. A Learning-Aloud Case Study. Kann man sie beheben? Der Physikunterricht, 18 2 , DiSessa, A.

Toward an Epistemology of Physics. Cognition and Instruction, 10, Gleixner, C. Das elektrische Potential im Unterricht der Sekundarstufe I. MNU, 37 8 , Kircher, E. Neue Wege im Elektrikunterricht: Naturwissenschaften im Unterricht Physik, 34 13 , Schumacher, M. Fields that accompany currents. Aspects of Understanding Electricity: Proceedings of an International Workshop,. In this contribution we discuss the application of a quantitative, non-hierarchical clustering method to make sense of the answers that engineering undergraduates students at the University of Palermo, Italy, gave to four open-ended questions on the meaning of the modeling processes in Science.

We will show that the use of non-hierarchical analysis allows us to easily separate students into groups that can be recognized and characterized by common traits in students answers without any prior knowledge on the part of the researcher of what form those groups would take unbiased classification. Some of these studies examined the consistency of students answers in a variety of situations. Others looked at problems where the underlying physical systems are similar from the point of view of an expert.

In recent years, some papers have tried to develop more detailed models of the consistency of students reasoning, or to subdivide a sample of students into intellectually similar subgroups. Bao and Redish introduced model analysis as a framework for exploring the structure of the consistency of the application of student knowledge, by separating a group of students into intellectually similar subgroups.

The problem of taking a set of data and separating it into subgroups where the elements of each subgroup are more similar to each other than they are to elements not in the subgroup has been extensively studied through the statistical method of Cluster Analysis ClA. ClA can separate students into groups that can be recognized and characterized by common traits in their answers, without any prior knowledge of what form those groups would take unbiased classification.

Tyron in , has been the subject of research since the beginning of the s, with its first systematic use by Sokal e Sneath in The application of techniques related to ClA is common in many fields, including Information Technology, Biology, Medicine, Archeology, Econophysics and Market Research. For example, in market research it is important to classify the key elements of the decision-making processes of business strategies as the characteristics, needs and behavior of buyers.

These techniques allow the researcher to locate subsets or clusters within a set of objects of any nature. These have a strong tendency to be homogeneous in some sense. The results of the analysis should reveal a high homogeneity within the group intracluster , and high heterogeneity between groups inter-clusters , in line with the criteria chosen. In the literature concerning research in education, some studies using ClA methods are found. A recent paper Stewart et al. This paper shows that ClA methods are an effective way to examine the structure of student understanding and can produce significant subgroups of a data sample.

The authors conclude that the ClA method is an effective mechanism for extracting the underlying subgroups in student data and that additional insight may be gained from a careful, qualitative analysis of clustering results. In fact, each cluster is characterized by means of a careful reading of the typical trends in the answers of the individuals that are part of the cluster.

It is well known that there are inherent difficulties in the classification of student responses in the studies mainly involving open-ended questionnaires. In fact, the problem of quantifying qualitative data has been widely discussed in the literature for many years Green, , and it has been pointed out that, very often, a small or even unconscious researcher bias means that the categories picked out tend to find those groups of students that the researcher is already looking for.

Another paper Chi, discussed the need to describe the process of developing a coding scheme, by outlining that in the process of quantifying qualitative data, data means the qualitative records supplied by students and not the result of the coding scheme. It is important for this to be taken into account in the interpretation of the results of the subsequent quantitative analysis.

In this paper we start from a description of the data coding needed in ClA, in order to discuss the meanings and the limits of the interpretation of quantitative results. Then a method commonly used in ClA is described and the variables and parameters involved are outlined and criticized. The application of this method to the analysis of data from an open-ended questionnaire administered to a sample of university students and the related quantitative results is presented.

In the last section we discuss the meaning of our results for the physics education researcher and outline some points of strength and limits. METHODS Data setting Research in education that uses open-ended questions and is aimed at quantifying qualitative data usually involves the development of coding procedures. This requires an accurate reading of student answers in order to reveal and then examine patterns and trends, and to find common themes emerging from them.

These themes are then developed in a number of categories, which can be considered the typical answering strategies put into action by the N students tackling the questionnaire items. Therefore, it is possible to summarize the whole set of answers given to the questionnaire into a limited number, M, of answering strategies, making the subsequent analysis easier. Through coding and categorization we produce a set of M data the answering strategies for each of the sample subjects the N students doing the questionnaire.

Then, a M x N binary matrix the matrix of answers modeled on the one shown in Table 1, is built. The columns in it show the N student arrays, a i, and the rows represent the M components of each array, i. Therefore, S 1 column in Table 1 will contain the binary digit 1 in the three cells corresponding to these strategies, while all the other cells will be filled with 0. The matrix depicted in Table 1 contains all the information to describe the sample behavior with respect to the questionnaire items.

However, it needs some elaboration in order to make this information understandable. ClA classifies subset behaviors in different groups the clusters. These groups can be analyzed in order to deduce their distinctive characteristics and point out similarities and differences among them.

ClA requires the definition of new quantities that are used to build the grouping, like the similarity or distance indexes. These indexes are defined by starting from the M x N binary matrix discussed above. The distance index can be defined by starting from the Pearson s correlation coefficient. It allows the researcher to study the correlation between elementsi and j if the related variables describing them are numerical. If these variables are non-numerical variables as in our case, where we are dealing with the arrays a i and a j containing the binary coding of the answers of elementsi and j, respectively , we propose a modified form of the Pearson s correlation coefficient, R mod, similar to that defined by Tumminello et al.

All these correlation coefficients can be placed in a N x N matrix that contains the information we need to discuss the mutual relationships between our students. The similarity between subjects i and j can be defined by choosing a type of metric to calculate the distance d ij. Such a choice is often complex and depends on many factors. If we want two subjects, represented by arrays a i and a j and negatively correlated, to be more dissimilar than two positively correlated subjects as is often advisable in research in education , a possible definition of the distance between a i and a j, making use of the modified correlation coefficient, R mod a i, a j , is: Moreover, D is symmetrical with respect to the main diagonal.

Clustering technique In this paper we use a technique known as Non-Hierarchical Clustering NH-ClA , that basically allows us to partition the data space into a structure known as a Voronoi diagram a number of regions including subsets of similar data. In this method, the final result is a bi-dimensional Cartesian plane containing points that represent the students of the sample placed in the graph according to their mutual distances. As said before, for each student, i, we know N distances. It is, then, necessary to define a procedure to find two Cartesian coordinates for each student, starting from these N distances.

The starting point is the choice of the number of clusters one wants to populate and of an equal number of seed points, randomly selected in the bi-dimensional Cartesian plane representing the data. The subjects are then grouped on the basis of the minimum distance between them and the seed points. Starting from an initial classification, subjects are transferred from one cluster to another or swapped with subjects from other clusters, until no further improvement can be made. The subjects belonging to a given cluster are used to find a new point, representing the average position of their spatial distribution.

This is done for each cluster and the resulting points are called the cluster centroids. This process is repeated and ends when the new centroids coincide with the old ones. The spatial distribution of the set elements is represented in a two-dimensional Euclidean space, creating what is known as the k-means graph see Figure 2. NH-ClA has some points of weakness and here we will describe how it is possible to overcome them. The first involves the a-priori choice of the initial positions of the centroids. This can usually be resolved by repeating the clustering procedure for several values of the initial conditions and selecting those that lead to the minimum values of the distances between each centroid and the cluster elements.

Furthermore, at the beginning of the procedure, it is necessary to arbitrarily define the number of clusters. A method widely used to decide if the number of clusters, q, initially used to perform the calculations is the one that best fits the sample element distribution is the calculation of the so-called Silhouette Function, S.

Several values of the function S are calculated once a value of the number of clusters, q, is fixed: It gives a measure of how similar student iis to the other students in its own cluster Cl k, when compared to students in other clusters. If most students have a high silhouette value, then the clustering solution is appropriate. If many students have a low or negative silhouette value, then the clustering solution could have either too many or too few clusters i.

It gives the average value of S k,i q , calculated on all the students belonging to cluster Cl k and it is a measure It gives the average value of S k,i q , calculated on all the students belonging to the sample. In particular, for each centroid, C k, we find an array b k with the same number M of components of the array, a i, that identifies a generic real student i, i. By considering the meaning of cluster Cl k centroid, we could use the answering strategies contained in array b k to make sense of the features of the clusterreal students.

A remarkable feature of array b k, that can validate our idea to use the centroid to characterize the features of the cluster Cl k real students, is that it contains 1 values exactly in correspondence to the answering strategies most frequently given by students belonging to Cl k. In fact, since a centroid is defined as the geometric point that minimizes the sum of the distances between it and all the cluster elements, by minimizing this sum the correlation coefficients between the cluster elements and the centroid are maximized and this happens when each centroid has the largest number of common strategies with all the students that are part of its cluster.

It is worth noting that if some answering strategies are only slightly more frequent than the other ones all those with similar frequencies should be also considered. In order to analyze how well each centroid characterizes its own cluster Cl k, we propose a coefficient, r k, defined as the centroid reliability, that relates the cluster density to its dimension. It is calculated as follows: High values of r k indicate that the centroid characterizes well the cluster, as this happens for dense clusters or for clusters with a low number of students.

In fact, considering two equally dense clusters, the one with a lower number of students involves smaller cluster dimensions, i. Example of quantitative study In this section we analyze the answer strategies to an open-ended questionnaire supplied by a sample of university students, using the techniques discussed above. The questionnaire and the sample The questionnaire is made up of four-items that focus on an understanding of the modeling concept see Appendix.

They are part of a more complex questionnaire, which has already been used, in previous research Fazio et al. The selected four items refer to: I the definition of a physics model, II the subjects beliefs about the representational modes of k The students were given the questionnaire during the first lesson of general physics, before any discussion on the model concept had started.

Categorization of student answers After the questionnaire had been submitted to our student sample, three researchers independently read the students answers in order to identify the main characteristics of the different student records the raw data. Then, they agreed to construct a coding scheme through the identification of keywords that were relevant for an understanding of these records.

During the first meeting, the selected keywords were compared and contrasted, and then grouped into categories based on epistemological and linguistic similarities for example, students that defined models as simple phenomena or experiments or reproductions of an object on a small scale have been put on the same category since the three definitions have been intended as giving a ontological reality to models.

These categories were also reanalyzed through the researchers interactions with the data, and taking into account the existing literature about models and modeling Grosslight et al. As a third step, the researchers read the student records again and applied the new coding scheme, by assigning each student to a given category for each question. Given the inevitable subjectivity of the researchers interpretations, the three lists were compared and contrasted in order to get to single agreed list.

Monodispersed Particles (Studies in Surface Science and by Tadao Sugimoto

The inter-rater reliability of the analysis was good. Discordances between researcher lists were usually a consequence of the different personal decisions of the researchers to divide the student answers into a more or less restricted number of typologies. In some cases, discordances were due to different researcher interpretations of student statements.

This happened 14 times when comparing tables of researchers 1 and 2, 9 times for researchers 2 and 3, and 12 times for researchers 1 and 3. When a consensus was not obtained, the student answer was classified in the category statement not understandable. It is worth noting that very often the researchers discussions while assigning each student to a given category produced a more refined definition of these categories. The complete list of 20 categories shared by researchers with respect to the four questions can be seen in Appendix A. This matrix of data represents a set of properties the categories to which student answers have been assigned for each subject the student being analyzed.

Average Silhouette values for different cluster partitions of our sample. Figure 2 shows the representation of this partition in a 2-dimensional graph. The four clusters show a partition of our sample into groups made up of different numbers of students see Table 2 Figure 2. Each point in this Cartesian plane represents a student. Points labeled C 1, C 2, C 3, C 4 are the centroids.

They are the four points in the graph whose arrays, b k, contain the answering strategies most frequently applied by students in the related clusters see Table 2. The codesused refer to the answering strategies for the questionnaire items described in Appendix A. Furthermore, the values of r norm k show that centroid C 3 best represents its cluster, whereas centroid C 1 is the least representative and characterizes less well the cluster.

I the definition of a physics model, II the subjects beliefs about ways of representing physics models, III the main characteristics of models and IV the subjects' beliefs about the modeling process. We have classified student answers into categories, also called answering strategies, that explain student reasoning strategies.

Looking at our results, the four clusters identified are characterized by the related centroids and each centroid is represented by one array b k, which describes the different answering strategies categorized for each question. These strategies are defined as follows: We have already pointed out that the array describing the cluster centroid describes to the answers most frequently given by the students in the cluster, and in this sense we can identify at what frequency each answering strategy is shared by the cluster students.

In particular, cluster Cl 4 is mainly composed of students that use higher level answering strategies to deal with the concepts in the questionnaire. In fact, these students recognize that a model is a mental representation of a real object or phenomenon,which takes into account the characteristics that are significant for the modeler 1C. The modeling process is seen as a construction where the model can still contain errors or uncertainty connected with the possibility or ability to carefully reproduce the characteristicswe are interested in 4B.

Such low percentages are also found in the literature Grosslight et al. Students in cluster Cl 2 show the weakest understanding of the model concept. For these students every natural phenomenon can be simplified in order to be referred to a given model 4A. Cl 2 students can be reported to the level II modelers based on the classification scheme developed by Grosslight et al.

Level II modelers see models as representations of realworld objects or events and not as representations of ideas about real-world objects or events. They also see the use of different models as that of capturing different spatio-temporal views of the object rather than different theoretical views. Similar results have been obtained in other studies, as for example paper Treagust et al. To sum up, we can say that the students in cluster Cl 4 seem to share many conceptions connected with an epistemological constructivist view Treagust et al.

Students in clusters Cl 1 and Cl 3 do not show a full coherence in their answers, although in different ways. Cl 3 students seem to share with Cl 2 students the ideas concerning the definition of physics models and the modeling process, but they also share their beliefs about the function as well as the characteristics of physics models with the students from cluster Cl 4. In fact, they state that physics defines models as a simple phenomenon or the exemplification of a phenomenon through an experiment or a reduced scale reproduction of an object 1B.

However, they also say that they are creations of human thought and their creation comes from continuous interaction with the real external world and from its simplification 2C. Such conception of physics model can be reported to literature findings Fazio et al. In particular, Bao and Redish developed a way to deal with these composite mental models and define students model states that can change with specific contextual features in different equivalent questions.

Our data point out that such inconsistency is deployed in the elicitation of model constituents as well as of functions and characteristic of the modeling process. Students in cluster Cl 1 share the idea that a model is a mental representation aimed at describing a real object or a phenomenon, which takes into account the characteristics that are significant for the modeler 1C.

These ideas are not completely consistent with the characteristics assigned to the model or with the students ideas about the modeling process. Their focus on the process of simplification is also made explicit in the examples they report in order the explain their sentences. For example, for many of such students the motion without friction is a model as well as the perfect gas not the motion with friction or real gases". On the other hand, it must be taken into account that the value of the reliability, r k norm, of the C 1 centroid is the lowest, showing that array b 1 is not very significant in representing the answering strategies of thecluster students.

Also, looking in detail at b 1 array, the answering strategies are not easily understandable from the point of view of consistency and although they represent the answers most commonly given by Cl 1 students, these do not have very high frequencies. Other answers were also given by a large number of students; for example answering strategy 1B A physics model is a simple phenomenon or the exemplification of a phenomenon through an In our opinion, this may show that a substructure is present in cluster Cl 1, and this should be analyzed through different analysis methods, like, for example Hierarchical Cluster Analysis Everit et al.

In conclusion, in this paper, we discussed the problem of quantifying qualitative data in order to analyze how to identify groups with common behavior, ideas, beliefs and conceptual understanding in a sample of students. We presented a method of cluster analysis and analyzed definitions, variables and algorithms in detail, in order to understand the possibilities offered by such a method and its limits. We gave an example of their application in order to demonstrate the necessary approximations and the different ways of interpreting results. The example is an analysis of the answers to a questionnaire given to a sample of university students.

It is worth remembering that data that are quantitatively analyzed are the results of a categorization of raw data the individual student answers and this reduction of the initial data can be subject to errors, which obviously influences the final evaluation and the inference about the reasoning strategies supporting students answers. Such errors can only be reduced through a clear process of coding and subsequent categorization and not eliminated, and this must be taken into account when we try to infer typical students reasoning strategies.

Our analysis gives details of student conceptions about the function of a physics model and its properties, by identifying features of intermediate conceptions as well as groups of students sharing such conceptions, in a continuum of this type. Furthermore, the results of this study provide important hints and insights for teaching methods that may improve students modelbased reasoning, and provide teachers with information about their students level of understanding, with which they can make instructional decisions.

Representing and assessing the dynamics of student learning, Phys. Quantifying Qualitative Analyses of Verbal Data: Approaches to data analysis of multiple-choice questions, Phys. Prospective elementary teachers perceptions of the processes of modeling: A case study, Phys. Investigating the quality of mental models deployed by undergraduate engineering students in creating explanations: Field Methods 13 1 , Grosslight, L. Understanding models and their use in science: Confusing Claims for Data: Eliciting and Representing Hybrid Mental Models.

Science teachers knowledge about and attitudes towards the use of models and modelling in learning science. The development of science teachers knowledge on modelsand modelling: Promoting, characterizing, and understanding the process. Some methods for classification and analysis of multivariate observations.