Behavior of chemical contaminants under controlled Redox conditions in an artificial sequential soil column system and in batch cultures

A leachate pollution plume was simulated in a sequential soil columnsystem (SSCS), defined by a longitudinal redox cascade from methanogenic,sulfate-, nitrate-reducing to aerobic conditions. A mixture of contaminants,including compounds such as perchloroethene (PER), 1,1-dichloroethene(DCE), 1,4-dichlorobenzene (DCB), 2-nitrophenol (NP), and benzene (BEN)was supplied to the methanogenic column; their conversion was followed during passage through the SSCS. After establishment of a steady state, parameters were changed to simulate changes in the environment and to follow the reactions of the system. Acetate, initially introduced as an anaerobically easy degradable carbon source, was first omitted and later added again to the system. Furthermore, the medium flow rate and by that the load of the test compounds was increased 4 fold. Changes transiently increased the residual concentrations of most of the xenobiotics. Within seven months after acetate omission, turnover ofcontaminants had almost returned to the original steady state. Flow andload increase resulted in increased transformation of compounds such asPER, NP, and BEN. After readdition of acetate, the turnover of most ofthe xenobiotics increased within the next five weeks.Microbial populations for the anaerobic batch cultures, obtained from thespecific columns, were used to investigate metabolites formed and conversion kinetics of the xenobiotics. Almost the sameconversion pattern was found in batches and columns, except no transformation of DCE and DCB was detected in the SSCS, though both compounds were converted in batch culture

Influence of the meso-structure in numerical simulation of dynamic tensile fracture of concrete

International audienceThe macroscopic modeling of the tensile response of concrete in dynamic has considerably evolved and the current constitutive laws are able to represent more and more complex phenomena. Nevertheless, in these approaches the different scales present in the structure of the material are not represented despite their strong influence on the macroscopic behaviour. In this work the influence of the heterogeneous meso-structure of concrete on the dynamic tensile response is analyzed. For this purpose a 2D geometrical model of concrete consisting of aggregates, interfacial transition zones and a matrix is modeled. We use a finite element framework with cohesive elements to explicitly represent the crack nucleation and growth. The debonding process in the cohesive elements is controlled by a traction separation law based on the popular linear extrinsic irreversible law proposed by Camacho and Ortiz [1]. This numerical approach has proved its efficiency on brittle material like ceramics [2] without an explicit meso-structure representation. We validate our model by simulating a direct dynamic tension test of a concrete specimen. The role of the meso-structure and the influence of the loading rate are then analyzed. We especially focus on the evolution of the stress peak and the energy dissipated. We can observe that with a traction separation law independent of the strain rate we are not able to reproduce the macroscopic rate effect experimentally observed while the global dissipated energy is correctly simulated. We will also show the respective influences of the meso-structure and the loading rate on the variability of the stress peak in tension

Aforismos

Aforismos del arquitecto suizo Luigi Snozzi (1932).Facultad de Arquitectura y Urbanism

Determination of the dynamic tensile response and dissipated fracture energy of concrete with a cohesive element model

International audienc

Aforismos

Aforismos del arquitecto suizo Luigi Snozzi (1932).Facultad de Arquitectura y Urbanism

A meso-scale computational approach to dynamic failure in concrete

The aim of the present thesis is to provide a numerical tool for the mechanical modeling of dynamic failure in concrete. This widely used construction material is characterized by a non-linear failure behavior, which is consequently difficult to describe with macroscopic quantities. In order to grasp the mechanical damage response of this heterogeneous brittle material, our approach is based on a meso-mechanical point of view. The whole research work is, therefore, mainly focused on the understanding of the mechanisms that are linked with the material’s heterogeneous composition. The advantage of this level of observation is that it allows to represent the most important concrete constituents (e.g. aggregates and cement paste), thus facilitating the physical identification of the material parameters of the model and of the mechanisms (interaction between matrix and inclusions) that characterize its constitutive behavior. For this purpose we exploit the capabilities of a two-dimensional finite-element model. The onset of fracture is explicitly modeled using the well-known cohesive approach. We first investigate the dynamic tensile response of concrete specimens. Different simulations are carried out to assess the influence of aggregates properties on peak strength and dissipated fracture energy at different strain rates. The model aims to explain the strain-rate strengthening through structural effects. However, to capture the full extent observed experimentally, our results suggest that is not possible to discard the combination of inertial with material rate hardening mechanisms. Next, in order to account for crack-interactions as well as path dependent behavior, the model is enriched with the introduction of an explicit contact algorithm and a mode-dependent fracture energy. To demonstrate the capability of the proposed approach to provide accurate results, the model is first applied to two benchmark tests in masonry engineering. Afterwards, the developed framework is applied to reproduce dynamic compressive failure of meso-scale concrete samples. Simulations involving different strain rates and levels of lateral confinement are conducted. An energetic analysis shows that dissipation of energy through fracture and friction is an increasing function of the applied confinement and strain rate. Our results underline thus the importance of capturing frictional mechanisms, which appear to dissipate a raising amount of frictional energy with increasing strain and applied pressure. Finally, a multi-scale computational framework is developed to up scale the obtained fine scale response to the coarse scale. The selected approach considers concrete macroscopically as being homogeneous and to behave linear elastically aside from the propagating cracks. The cohesive macroscopic tractions are however extracted from the response of meso-scale representative volume elements, which are activated on the fly when a macroscopic discontinuity propagates. Parallel simulation shows the capability of the model to predict the structural response of a tested unit including the physical mechanisms occurring at the fine scale

Quantification of bacterial mRNA involved in degradation of 1,2,4-trichlorobenzene by Pseudomonas sp. strain P51 from liquid culture and from river sediment by reverse transcriptase PCR (RT/PCR)

Competitive reverse transcriptase polymerase chain reaction (RT/PCR) was used to quantify the mRNA of the tcbC gene of Pseudomonas sp. strain P51. The tcbC gene encodes the enzyme chlorocatechol-1,2-dioxygenase involved in 1,2,4-trichlorobenzene (TCB) degradation. The mRNA content per cell was monitored in a batch culture growing on 1,2,4-TCB. No mRNA could be detected in the first 2 days of the lag phase. mRNA production became maximal with 20 molecules per cell in the early exponential growth phase but then decreased to less than 10 molecules per cell. When TCB was depleted and the cells entered the stationary phase, the mRNA content decreased slowly below the detection limit within 4 days. In order to compare detection of tcbC mRNA in pure culture and in river sediment, cells of strain P51 pregrown on TCB were added to sediment and RNAs extracted. In sediment samples containing 5×108 cells per gram the tcbC mRNA was quantifiable by RT/PCR. The mRNA recovery was about 3% as compared to the inoculum. The detection limit of the RT/PCR method was about 107 mRNA molecules per gram sediment or 106 copies per ml culture medium which corresponded in our case to 105 molecules per reaction via

Effects of Oxytocin and Prosocial Behavior on Brain Responses to Direct and Vicariously Experienced Pain

In this study, we tested the validity of 2 popular assumptions about empathy: (a) empathy can be enhanced by oxytocin, a neuropeptide known to be crucial in affiliative behavior, and (b) individual differences in prosocial behavior are positively associated with empathic brain responses. To do so, we measured brain activity in a double-blind placebo-controlled study of 20 male participants either receiving painful stimulation to their own hand (self condition) or observing their female partner receiving painful stimulation to her hand (other condition). Prosocial behavior was measured using a monetary economic interaction game with which participants classified as prosocial (N = 12) or selfish (N = 6), depending on whether they cooperated with another player. Empathy-relevant brain activation (anterior insula) was neither enhanced by oxytocin nor positively associated with prosocial behavior. However, oxytocin reduced amygdala activation when participants received painful stimulation themselves (in the nonsocial condition). Surprisingly, this effect was driven by “selfish” participants. The results suggest that selfish individuals may not be as rational and unemotional as usually suggested, their actions being determined by their feeling anxious rather than by reason

adreizehn 2014/2015

Korrigierte Fassung der im Universitätsverlag der TU Berlin gedruckt erschienenen Auflage, ISBN 978-3-7983-2810-5, ISSN 2198-6703Das Jahrbuch 'adreizehn 2014/2015' umfasst Studentenarbeiten des 3. und 4. Semesters im Bachelorstudiengang Architektur. Gegenstand der gezeigten Hochbauentwürfe sind exemplarische Vorschläge zur urbanen Nachverdichtung im Zentrum Berlins. Programme verschiedener Nutzungen werden zu Stadtimplantaten verdichtet, die privaten und öffentlichen Raum in hybriden Strukturen neu und beispielgebend verbinden können. Eine Auswahl der besten Arbeiten des Jahrgangs 2014 / 2015 wird mittels Plänen, Schnitten, Ansichten, Modellfotos und Visualisierungen dokumentiert. Ergänzt wird die Publikation durch Texte und Beiträge von Prof. Ute Frank, Sabine Böhl, Prof. Thomas Hasler, Prof. Alban Janson, Prof. Luigi Snozzi und Thomas Torkler.Yearbook 2014/2015 of department adreizehn for building construction and building design, Faculty VI, Institute for Architecture, Technische Universität Berlin With students' works of the 1st and 2nd year and texts by Prof. Ute Frank, Sabine Böhl, Prof. Thomas Hasler, Prof. Alban Janson, Prof. Luigi Snozzi und Thomas Torkler