Exploring behavioural patterns during complex problem-solving

In this explorative study, we investigate how sequences of behaviour are related to success or failure in complex problem-solving (CPS). To this end, we analysed log data from two different tasks of the problem-solving assessment of the Programme for International Student Assessment 2012 study (n = 30,098 students). We first coded every interaction of students as (initial or repeated) exploration, (initial or repeated) goal-directed behaviour, or resetting the task. We then split the data according to task successes and failures. We used full-path sequence analysis to identify groups of students with similar behavioural patterns in the respective tasks. Double-checking and minimalistic behaviour was associated with success in CPS, while guessing and exploring task-irrelevant content was associated with failure. Our findings held for both tasks investigated, from two different CPS measurement frameworks. We thus gained detailed insight into the behavioural processes that are related to success and failure in CPS.     

Organic pollutant removal versus toxicity reduction in industrial wastewater treatment: the example of wastewater from fluorescent whitening agent production

Industrial wastewater treatment in the chemical industry aims at eliminating organic contaminants, as these pollutants may be persistent and ecotoxic. In a case study performed in collaboration with the chemical industry, we investigated the removal of a fluorescent whitening agent and its side products in the wastewater-treatment system. Adsorption to activated carbon and biological treatment were simulated in laboratory tests. Algae toxicity tests were performed to quantify the toxicity of the wastewater mixture and of single components. The contaminants identified accounted for up to 82% of the wastewater's total organic carbon (TOC). Adsorption to activated carbon eliminated the TOC and the single contaminants only slightly. Nevertheless, the toxicity of the wastewater decreased by 40%. In contrast, biological treatment reduced the TOC by up to 80%, and the whole effluent toxicity increased. These results indicate that new ecotoxic metabolites were formed during the biological treatment. They also illustrate that mere reduction of the TOC in the wastewater-treatment system is not sufficient for ensuring a reduction of environmental impact. Therefore, simultaneously conducting TOC measurements and toxicity tests, as demonstrated in the current work, is recommended.     

Shape alteration of large string instruments due to changing climate conditions

Large string instruments, such as cellos and double basses, are manufactured, bought and played all over the world. Thereby they are exposed to different climate conditions. This paper describes shape alterations using the example of a double bass stored at different climatic conditions. By means of an optical measurement these shape alterations were recorded and represented. The results clearly show spots with strong and without deformations. Thus, weak points of the construction are localised and improvements can be established for the construction of string instruments.     

Kinetic and stoichiometric characterisation of streptavidin-binding aptamers

Aptamers are oligonucleotide ligands that are selected for high-affinity binding to molecular targets. Only limited knowledge relating to relations between structural and kinetic properties that define aptamer-target interactions is available. To this end, streptavidin-binding aptamers were isolated and characterised by distinct analytical techniques. Binding kinetics of five broadly similar aptamers were determined by surface plasmon resonance (SPR); affinities ranged from 35-375 nM with large differences in association and dissociation rates. Native mass spectrometry showed that streptavidin can accommodate up to two aptamer units. In a 3D model of one aptamer, conserved regions are exposed, strongly suggesting that they directly interact with the biotin-binding pockets of streptavidin. Mutational studies confirmed both conserved regions to be crucial for binding. An important result is the observation that the most abundant aptamer in our selections is not the tightest binder, emphasising the importance of having insight into the kinetics of complex formation. To find the tightest binder it might be better to perform fewer selection rounds and to focus on post-selection characterisation, through the use of complementary approaches as described in this study.     

The influence of vacuum impregnation on the fortification of apple parenchyma with quercetin derivatives in combination with pore structures X-ray analysis

The study aim was to investigate the vacuum impregnation (VI) technique for apple enrichment with quercetin glycosides from apple peel. Beside the determination of the quercetin content, structural effects on the apple parenchyma were analyzed by computerized microtomography (μCT). VI was an efficient method to enrich apples with quercetin derivatives which was affected by the apple cultivar, the vacuum pressure, the soluble solid concentration (SSC) and the viscosity of VI solution. After VI of 13 apple cultivars the quercetin content varied between 368 and 604 μg/g dry mass and correlated with the firmness of the native apple and the increased apple weight. The use of low SSC solution resulted in increased quercetin enrichment in contrast to apple pectin solutions with elevated viscosity. The μCT analyses demonstrate that VI was more effective in the inner apple sections than in the outer parts. The study indicates that differences of pore size and microstructure within the apple cortex substantially affected the enrichment process.     

Mixture toxicity of reactive chemicals by using two bacterial growth assays as indicators of protein and DNA damage

The mixture toxicity of reactive chemicals was investigated with a set of bioanalytical tests that quantify not only the toxic effects but also allow the identification of the preferred target of reactive chemicals in bacterial cells. Softer electrophiles such as acrylates react preferentially with thiol groups in proteins and peptides, and harder electrophiles such as epoxides preferentially attack DNA. In addition, some compounds, e.g., benzyl chloride, have no preference for a biological target and damage both DNA and proteins. A thiophenol was used as a model compound representing nucleophiles. We explored if the paradigms of mixture toxicity also hold true for reactive chemicals. Compounds with the same targets and the same modes of action should act concentration additive in mixtures, and compounds with different modes of action should act according to the concept of independent action. In addition, we investigated the potential for interaction of compounds of mixtures of electrophiles or electrophiles plus nucleophiles, which might lead to synergistic or antagonistic effects. The toxicity of mixtures of electrophiles with a single preferred target was consistent with the prediction for concentration addition. Unfortunately, the predictions for independent action did not differ much from those for concentration addition; therefore it was not possible to differentiate between these two models. Mixtures of two groups with different preferred target sites clearly showed concentration addition. In contrast, mixtures of compounds with multiple targets, i.e., compounds that show nonspecific reactivity toward any biological nucleophile, exhibited effects that lay distinctly between the predictions for concentration addition and independent action. We observed neither synergism (higher toxicity than predicted by concentration addition) nor antagonism (lower toxicity than predicted by independent action) for mixtures of electrophiles. Binary combinations of different electrophiles with the nucleophile 4-chlorothiophenol yielded smaller effects than those expected from the prediction for independent action. The degree of antagonism was correlated with the reaction rate constant of the electrophile with the thiol group of glutathione, which indicates that the interaction between the mixture components occur in the toxicokinetic phase and is purely a result of chemical reactivity between the mixture components. Overall, we conclude that the concepts of mixture toxicity apply not only for baseline toxicity and receptor-mediated mechanisms, as has been shown in a large number of studies, but also for reactive mechanisms of toxicity, provided that one has checked beforehand that no chemical reactions occur between the mixture components.