Untersuchungen und Modellierung von hydraulischen und hydrochemischen Prozessen

In the densely populated semiarid territory in and around Delhi (India), the water demand is rising continuously, while the surface- and groundwater resources are threatened by contamination and overexploitation. This is a typical scenario in many newly industrialising and developing countries, where new approaches for a responsible water management have to be found. River bank filtration (RBF) holds great potential, thus being a reliable and low tech method, benefiting from the storage and contaminant attenuation capacity of the aquifer. For this study, three field sites have been constructed to investigate hydraulic, hydrochemical and microbiological processes during river bank filtration in different environments in the mega city of Delhi. The frequent (monthly) and long term (1.5 years) monitoring of the hydraulic behaviour of RBF and the wide range of investigated water quality parameters (e.g. major ions, pH, electrical conductivity, temperature), pathogens and its indicators (e.g. adeno-, norovirus, bacteriophages) and organic compounds (e.g. pesticides, pharmaceuticals) provided new insights to the function of RBF under the given environmental conditions. In order to characterize the environmental conditions of the study area the origin and dynamics of groundwater salinity was investigated on both regional and local scale in detail. Density stratification and local up coning of saline waters was identified by multi level monitoring and temperature logging. Stable isotope ratios ( 18O, 2H) were used to identify evaporation rates and for a better understanding of recharge processes and mixing dynamics in the study area. The results lead to the conclusion, that surface and groundwater influx into the poorly drained semiarid, geomorphological basin naturally results in the accumulation of salts in soil, sediments and groundwater. Man made changes of hydrological conditions, especially the implementation of traditional canal and modern groundwater irrigation have augmented evapotranspiration and led to water logging in large areas. In addition, water level fluctuations and perturbation of the natural hydraulic equilibrium favour the mobilization of salts from salt stores in the unsaturated zone and deeper aquifer sections. Another part of this thesis was focusing on a RBF system in northern Delhi which was sampled monthly for hydrochemical/-physical parameters over one and a half years. Environmental tracers (chloride, P18PO and temperature) were used to estimate travel time of the bank filtrate from the river to the abstraction well. Selected physico-chemical parameters were used to investigate purification and attenuation capacity of the RBF system. The study revealed that the combination of environmental tracers, with different transport behaviour, allow to characterise travel times during RBF reliably. The winter peak in the Yamuna River was found in the RBF well around 2.5 months later, while the summer or monsoon peak is observed in the bankfiltrate after 2 months of travel time. In terms of purification and attenuation capacity a good equilibration of temperature, electrical conductivity (EC) and 58 % attenuation of dissolved organic carbon (DOC) was observed after RBF passage. At the central Delhi field site the impact of highly contaminated surface water infiltration on the urban aquifer systems was investigated. At this field site, RBF takes place because of dominant loosing river conditions due to large groundwater abstraction. Fluctuations of the hydraulic head in combination with a conservative tracer (chloride) and a retarded tracer (heat) were measured, evaluated and modelled to determine (i) infiltration rates and (ii) groundwater travel times, (iii) to perform a sensitivity analysis and (iv) to calculate a water budget for the flood plain aquifer. This study leads to the conclusion, that groundwater recharge by bank filtration is the most important recharge mechanisms. This calibrated numerical model was then used to describe the transport and deposition of indigenous bacteriophages during RBF. Removal of bacteriophages was calculated by non-equilibrium (rate- limited) sorption approach. The measurement of bacteriophages at this high contaminated field site offered the opportunity to test removal models based on the Colloid Filtration Theory (CFT). Somatic, indigenous bacteriophages underwent attenuation of almost 5 log after only 8 days of travel time during RBF. Additional, a series of organic trace compounds were considerably attenuated and human pathogenic viruses, two of them present in the Yamuna at 10P5P genomes/100 ml, were undetectable after RBF passage. Considering all three field sites and depending on site-specific conditions, distinct hydrogeological conditions were observed and both positive and negative effects on RBF performance were identified during this study. Most concerning issues are the impact of anthropogenic ammonium, the mixing with ambient brackish groundwater and the mobilisation of arsenic during the reductive dissolution of manganese- and iron-(hydr)oxides. Positive aspects are the dilution of contaminants during the mixing of waters from different sources, the sorption of arsenic, denitrification, the high attenuation capacity of pathogens and the precipitation of fluoride under favourable conditions. On a generic level, this thesis also aims at identifying climate sensitive factors affecting bank filtration performance and assesses their relevance based on hypothetical ‘drought’ and ‘flood’ climate scenarios. The climate sensitive factors influencing water quantity and quality also have influence on substance removal parameters such as redox conditions and travel time. Droughts are found to promote anaerobic conditions during bank filtration passage, while flood events can drastically shorten travel time and cause breakthrough of pathogens, suspended solids, DOC and organic micropollutants. The study revealed that only RBF systems comprising an oxic to anoxic redox sequence ensure maximum removal efficiency. The storage capacity of the banks and availability of two source waters renders BF for drinking water supply less vulnerable than surface water or groundwater abstraction alone. Considering all parts, this thesis provides new insights on the function and relevance of RBF both on the site-specific and generic level. It also contains knowledge and solutions for science and practioners of RBF.In dem dicht besiedelten, semiariden Territorium in und um Delhi (Indien) steigt der Wasserbedarf kontinuierlich, während das Oberflächen- und Grundwasser von Verschmutzung und Überbeanspruchung belastet ist. Dies ist ein typisches Szenario für viele Schwellen- und Entwicklungsländer, für die neue Ansätze für ein verantwortungsvolles Wasser Management gefunden werden müssen. Die Uferfiltration (UF) besitzt ein großes Potenzial, da es eine nur mit geringem technischem Aufwand verbundene und bewährte Methode ist, die von der Speicher- und Reinigungskapazität des Grundwasserleiters profitiert. In dieser Studie wurden drei Feldstandorte entwickelt um hydraulische, hydrochemische und mikrobielle Transport- und Abbauprozesse bei der Uferfiltration unter unterschiedlichen Umweltbedingungen in der Megastadt Delhi zu untersuchen. Durch das häufige (monatlich) und langzeitliche (eineinhalb Jahre) Monitoring des hydraulischen Verhaltens der Uferfiltrations-Standorte und die große Bandbreite der beobachteten Wasserqualitätsparameter (z.B. Hauptinhaltsstoffe, pH, elektrische Leitfähigkeit, Temperatur), Pathogene und Pathogenindikatoren (z.B. Adeno- und Noroviren, Bakteriophagen) und organische Spurenstoffe (z.B. Pestizide, Medikamentenrückstände) wurden neue Einsichten in die Funktionsweise der UF unter den gegebenen Umweltbedingungen erlangt. Um die Umweltbedingungen im Untersuchungsgebiet besser charakterisieren zu können, wurde die Herkunft und Dynamik der Grundwasserversalzung auf regionaler sowie lokaler Ebene näher untersucht. Dichteschichtungen und lokales Upconing von Salzwasser wurden mithilfe tiefenorientierter Beprobung und durch Temperatur Messungen festgestellt. (…) Die Ergebnisse führen zu den Schlussfolgerungen, dass der Zufluss von Oberflächen- und Grundwasser in ein semiarides, geomorphologisches Becken mit geringem Abfluss, zur Akkumulation von Salz im Boden und Grundwasser führt. Anthropogene Änderungen der hydraulischen Bedingungen, insbesondere der Bau von Bewässerungskanälen führen zu vermehrter Evapotranspiration und Staunässe in Teilen des Untersuchungsgebietes. (…) Ein weiterer Teil dieser Arbeit widmet sich einem einzelnen UF System im nördlichen Teil von Delhi. (…) Die Studie zeigt, dass eine Kombination von Markern mit unterschiedlichem Transport Verhalten eine zuverlässige Charakterisierung von Fließzeiten erlaubt. Dabei wurde festgestellt, dass die Aufenthaltszeiten des Uferfiltrats im Jahresverlauf sehr variabel sind und zwischen ca. 2,5 Monaten im Winter und ca. 2 Monaten im Sommer schwanken. Hinsichtlich der Reinigungsleistung wurde eine Abschwächung des Temperatursignals und der elektrischen Leitfähigkeit und eine Verminderung des gelösten organischen Kohlenstoffs (DOC) um 58% nach der UF Passage beobachtet. An einem weiteren Feldstandort, im zentralen Bereich Delhis, wurde der Einfluss der Infiltration von stark kontaminiertem Oberflächenwasser auf den städtischen Grundwasserleiter untersucht. (…) Ein Numerisches 2D Modell wurde entwickelt um (i) Infiltrationsraten des Flusses und (ii) Fließzeiten des Uferfiltrats zu bestimmen und um (iii) eine Sensitivitätsanalyse durchzuführen und (iv) ein Wasserbudget für den Grundwasserleiter der Überflutungsebene zu berechnen. (…) Dabei wurde festgestellt, dass die Infiltration von kontaminiertem Oberflächenwasser in den städtischen Grundwasserleiter die dominierende Art der Grundwasserneubildung ist. Das kalibrierte numerische Modell wurde dann benutzt, um das Transport- und Sorptionsverhalten von Bakteriophagen bei der Uferfiltration zu beschreiben. Die Entfernung von Bakteriophagen wurde mithilfe eines Nicht-Gleichgewichts Sorptions Ansatzes berechnet. (…). Die somatischen, indigenen Phagen wurden um 5 log Stufen nach nur acht Tagen Aufenthaltszeit im Grundwasserleiter verringert. Dabei wurde auf den ersten Infiltrationsmeter die höchste Entfernungsrate festgestellt. Zusätzlich waren eine ganze Reihe von organischen Spurenstoffen, die im Fluss gemessen wurden, nach der UF Passage erheblich verringert oder nicht mehr nachweisbar. Humanpathogene Viren, welche im Fluss in Konzentrationen von bis zu 105 Genome/100 mL vorhanden waren, waren nach der UF Passage nicht mehr nachweisbar. (…). Insgesamt betrachtet bietet diese Arbeit neue Einsichten in die Funktionsweise und Relevanz der Uferfiltration auf standortspezifischer und übergeordneter Ebene. Diese Arbeit beinhaltet Wissen und Lösungen für Wissenschaftler und Praktiker von Uferfiltration

SoK: Delegation and Revocation, the Missing Links in the Web's Chain of Trust

The ability to quickly revoke a compromised key is critical to the security of any public-key infrastructure. Regrettably, most traditional certificate revocation schemes suffer from latency, availability, or privacy problems. These problems are exacerbated by the lack of a native delegation mechanism in TLS, which increasingly leads domain owners to engage in dangerous practices such as sharing their private keys with third parties. We analyze solutions that address the long-standing delegation and revocation shortcomings of the web PKI, with a focus on approaches that directly affect the chain of trust (i.e., the X.509 certification path). For this purpose, we propose a 19-criteria framework for characterizing revocation and delegation schemes. We also show that combining short-lived delegated credentials or proxy certificates with an appropriate revocation system would solve several pressing problems.Comment: IEEE European Symposium on Security and Privacy (EuroS&P) 202

Simulation Logic, Applets and Compositional Verification

We present a compositional verification method for control flow based safety properties of smart card applets. Our method rests on a close correspondence between transition system models ordered by simulation and Hennessy-Milner logic extended with simultaneous greatest fixed points. We show that simulation can be characterised logically and, vice versa, logical satisfaction can be represented behaviourally by a maximal model for a given formula. Based on these results and earlier ideas by Grumberg and Long we develop a compositional verification technique, where maximal models replace logical assumptions to reduce compositional verification to standard model checking. However, in the context of applets, equipped with interfaces, this technique needs to be refined. Since for a given behavioural formula and interface a maximal applet does not always exist, we propose a two-level approach, where local assumptions restrict the control flow \emph{structure} of applets, while the global property restricts the control flow \emph{behaviour} of the system. By separating the tasks of verifying global and local properties of applets, our method supports secure post-issuance loading of new applets onto a smart card

Wave curves: Simulating Lagrangian water waves on dynamically deforming surfaces

We propose a method to enhance the visual detail of a water surface simulation. Our method works as a post-processing step which takes a simulation as input and increases its apparent resolution by simulating many detailed Lagrangian water waves on top of it. We extend linear water wave theory to work in non-planar domains which deform over time, and we discretize the theory using Lagrangian wave packets attached to spline curves. The method is numerically stable and trivially parallelizable, and it produces high frequency ripples with dispersive wave-like behaviors customized to the underlying fluid simulation

Smart framework for real-time monitoring and control of subsurface processes in managed aquifer recharge applications: project outlook

International audienc

Altered resting-state functional connectivity in patients with chronic bilateral vestibular failure

AbstractPatients with bilateral vestibular failure (BVF) suffer from gait unsteadiness, oscillopsia and impaired spatial orientation. Brain imaging studies applying caloric irrigation to patients with BVF have shown altered neural activity of cortical visual–vestibular interaction: decreased bilateral neural activity in the posterior insula and parietal operculum and decreased deactivations in the visual cortex. It is unknown how this affects functional connectivity in the resting brain and how changes in connectivity are related to vestibular impairment.We applied a novel data driven approach based on graph theory to investigate altered whole-brain resting-state functional connectivity in BVF patients (n= 22) compared to age- and gender-matched healthy controls (n= 25) using resting-state fMRI. Changes in functional connectivity were related to subjective (vestibular scores) and objective functional parameters of vestibular impairment, specifically, the adaptive changes during active (self-guided) and passive (investigator driven) head impulse test (HIT) which reflects the integrity of the vestibulo-ocular reflex (VOR).BVF patients showed lower bilateral connectivity in the posterior insula and parietal operculum but higher connectivity in the posterior cerebellum compared to controls. Seed-based analysis revealed stronger connectivity from the right posterior insula to the precuneus, anterior insula, anterior cingulate cortex and the middle frontal gyrus. Excitingly, functional connectivity in the supramarginal gyrus (SMG) of the inferior parietal lobe and posterior cerebellum correlated with the increase of VOR gain during active as compared to passive HIT, i.e., the larger the adaptive VOR changes the larger was the increase in regional functional connectivity.Using whole brain resting-state connectivity analysis in BVF patients we show that enduring bilateral deficient or missing vestibular input leads to changes in resting-state connectivity of the brain. These changes in the resting brain are robust and task-independent as they were found in the absence of sensory stimulation and without a region-related a priori hypothesis. Therefore they may indicate a fundamental disease-related change in the resting brain. They may account for the patients' persistent deficits in visuo-spatial attention, spatial orientation and unsteadiness. The relation of increasing connectivity in the inferior parietal lobe, specifically SMG, to improvement of VOR during active head movements reflects cortical plasticity in BVF and may play a clinical role in vestibular rehabilitation

Evaluation of a new approach for semi-automatic segmentation of the cerebellum in patients with multiple sclerosis

Cerebellar dysfunction is an important contributor to disability in patients with multiple sclerosis (MS), however, few in vivo studies focused on cerebellar volume loss so far. This relates to technical challenges regarding the segmentation of the cerebellum. In this study, we evaluated the semi-automatic ECCET software for performing cerebellar volumetry using high-resolution 3D T1-MR scans in patients with MS and healthy volunteers. We performed test-retest as well as inter-observer reliability testing of cerebellar segmentation and compared the ECCET results with a fully automatic cerebellar segmentation using the FreeSurfer software pipeline in 15 MS patients. In a pilot matched-pair analysis with another data set from 15 relapsing-remitting MS patients and 15 age- and sex-matched healthy controls (HC), we assessed the feasibility of the ECCET approach to detect MS-related cerebellar volume differences. For total normalized cerebellar volume as well as grey and white matter volumes, intrarater (intraclass correlation coefficient (ICC)=0.99, 95% CI=0.98-0.99) and interobserver agreement (ICC=0.98, 95% CI=0.74-0.99) were strong. Comparison between ECCET and FreeSurfer results likewise yielded a good intraclass correlation (ICC=0.86, 95% CI=0.58-0.95). Compared to HC, MS patients had significantly reduced normalized total brain, total cerebellar, and grey matter volumes (p≤0.05). ECCET is a suitable tool for cerebellar segmentation showing excellent test-retest and inter-observer reliability. Our matched-pair analysis between MS patients and healthy volunteers suggests that the method is sensitive and reliable in detecting cerebellar atrophy in M