In situ transformation of toluene and xylene to benzylsuccinic acid analogs in contaminated groundwater

The rate of removal of benzene, toluene, ethylbenzene and the xylene isomers (BTEX) from contaminated groundwater is needed to design remediation processes. Benzylsuccinic acid (BSA) and methyl-benzylsuccinic acid (methyl BSA) are unambiguous metabolites of anaerobic BTEX biodegradation. An analytical method for quantitative determination of BSA in groundwater samples was developed. Samples containing BSA and methyl BSA were extracted onto 0.5 g of styrene-divinylbenzene, eluted with ethyl acetate, and methylated with diazomethane. Gas chromatography coupled to mass spectrometry with electron impact ionization was used for separation and detection. The recovery from spiked 1 L groundwater samples was 88 to 100 %. The precision of the method, indicated by the relative standard error was ± 4% with a method detection limit of 0.2 μg/L. The method was then used to analyze samples from single-well push-pull tests conducted by injecting deuterated toluene and xylene into BTEX-contaminated wells in order to demonstrate in-situ biodegradation. Unambiguous evidence for deuterated toluene and xylene biodegradation was obtained with the observation of deuterated BSA and methyl BSA coupled with the utilization of nitrate presumably due to denitrification as terminal-electron-accepting process. Minimum first-order degradation rates for deuterated toluene estimated from formation of BSA were 0.0004 to 0.001 day⁻¹. Rates of methyl BSA formation were not calculated because methyl BSA, although detected, was not above the quantitation limit. Removal rates of deuterated toluene and o-xylene were not directly measurable because the rates were too low to measure significant changes in parent compound concentrations. Wells for which the formation of deuterated BSA and methyl BSA were observed had lower relative concentrations of toluene and xylenes relative to total BTEX than wells for which no deuterated BSA and methyl BSA were observed. Retardation factors for injected deuterated toluene and background toluene of 2 and 14, respectively, were obtained from push-pull tests conducted to determine toluene transport properties. Differences in retardation factors for injected and background toluene indicate differences between injected and background solute transport and is a topic that requires further study

Implementation of technology-supported personalized learning—its impact on instructional quality

Digital technology especially raised hopes to open up new possibilities to personalize learning. Although various schools have implemented approaches of technology-supported personalized learning, the impact on instructional quality remains unclear. As a common definition of the multilayered construct personalized learning is lacking, our study focuses on two theoretical dimensions of technology-supported personalized learning to investigate the impact on instructional quality. For this purpose, our study has analyzed data from a survey of N = 860 students (8th grade) from 31 Swiss schools with personalized learning concepts. Results show that student-centered teaching methods in the context of technology-supported personalized learning stimulate the cognitive activation of the students, and the supportive climate increases slightly with a higher degree of students’ voice and choice on the computer

Web technologies for environmental big data

Recent evolutions in computing science and web technology provide the environmental community with continuously expanding resources for data collection and analysis that pose unprecedented challenges to the design of analysis methods, workflows, and interaction with data sets. In the light of the recent UK Research Council funded Environmental Virtual Observatory pilot project, this paper gives an overview of currently available implementations related to web-based technologies for processing large and heterogeneous datasets and discuss their relevance within the context of environmental data processing, simulation and prediction. We found that, the processing of the simple datasets used in the pilot proved to be relatively straightforward using a combination of R, RPy2, PyWPS and PostgreSQL. However, the use of NoSQL databases and more versatile frameworks such as OGC standard based implementations may provide a wider and more flexible set of features that particularly facilitate working with larger volumes and more heterogeneous data sources

The size distribution, scaling properties and spatial organization of urban clusters: a global and regional percolation perspective

Human development has far-reaching impacts on the surface of the globe. The transformation of natural land cover occurs in different forms, and urban growth is one of the most eminent transformative processes. We analyze global land cover data and extract cities as defined by maximally connected urban clusters. The analysis of the city size distribution for all cities on the globe confirms Zipf’s law. Moreover, by investigating the percolation properties of the clustering of urban areas we assess the closeness to criticality for various countries. At the critical thresholds, the urban land cover of the countries undergoes a transition from separated clusters to a gigantic component on the country scale. We study the Zipf-exponents as a function of the closeness to percolation and find a systematic dependence, which could be the reason for deviating exponents reported in the literature. Moreover, we investigate the average size of the clusters as a function of the proximity to percolation and find country specific behavior. By relating the standard deviation and the average of cluster sizes—analogous to Taylor’s law—we suggest an alternative way to identify the percolation transition. We calculate spatial correlations of the urban land cover and find long-range correlations. Finally, by relating the areas of cities with population figures we address the global aspect of the allometry of cities, finding an exponent δ ≈ 0.85, i.e., large cities have lower densities

The size distribution, scaling properties and spatial organization of urban clusters: A global and regional percolation perspective

Human development has far-reaching impacts on the surface of the globe. The transformation of natural land cover occurs in different forms, and urban growth is one of the most eminent transformative processes. We analyze global land cover data and extract cities as defined by maximally connected urban clusters. The analysis of the city size distribution for all cities on the globe confirms Zipf’s law. Moreover, by investigating the percolation properties of the clustering of urban areas we assess the closeness to criticality for various countries. At the critical thresholds, the urban land cover of the countries undergoes a transition from separated clusters to a gigantic component on the country scale. We study the Zipf-exponents as a function of the closeness to percolation and find a systematic dependence, which could be the reason for deviating exponents reported in the literature. Moreover, we investigate the average size of the clusters as a function of the proximity to percolation and find country specific behavior. By relating the standard deviation and the average of cluster sizes—analogous to Taylor’s law—we suggest an alternative way to identify the percolation transition. We calculate spatial correlations of the urban land cover and find long-range correlations. Finally, by relating the areas of cities with population figures we address the global aspect of the allometry of cities, finding an exponent δ ≈ 0.85, i.e., large cities have lower densities

Ergebnisse und Herausforderungen der Arbeit in Theorie-Praxis-Netzwerken

In diesem Kapitel ziehen wir eine Zwischenbilanz nach fünf Jahren Arbeit in Theorie-Praxis-Netzwerken im Rahmen des Projekts „Zukunftszentrum Lehrkräftebildung-Netzwerk“ (ZZL-Netzwerk) der „Qualitätsoffensive Lehrerbildung“ (2016 bis 2021). Wir bilanzieren, welche Arbeitsweisen und Formen der Kooperation sich in dem Projekt bewährt haben (Abschnitt 1), welche Ergebnisse und Produkte entstanden sind (Abschnitt 2) und welche theoretischen und praktischen Erkenntnisse gewonnen werden konnten (Abschnitt 3). Die besonderen Herausforderungen, die sich für die weitere Arbeit in dem Projekt stellen, werden in Abschnitt 4 beschrieben. Das Kapitel schließt mit einem kurzen Fazit (Abschnitt 5)