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Operando QEXAFS Study of Pt–Fe Ammonia Slip Catalysts During Realistic Driving Cycles
Get PDFBifunctional Fe–Pt ammonia slip catalysts were studied by operando quick-scanning extended X-ray absorption fine structure spectroscopy (QEXAFS) under conditions mimicking rapid temperature variations that occur in an automotive exhaust gas aftertreatment system during real driving. Two catalysts, Pt/Al₂O₃ and Fe-ZSM-5, were tested individually, as mixtures and in dual bed arrangements. Applying QEXAFS allowed to track changes of active metal state with high time resolution. It uncovered a strong dependence of the active metal state on reaction conditions and catalyst bed layout. For example, proximity to platinum stabilized iron species in their more active oxidized state and led to higher Fe-ZSM-5 activity. On the contrary, isolated iron species were more susceptible to overreduction by ammonia which led to deactivation and low selectivity. The use of transient conditions uncovered the influence of non-equilibrium phenomena on catalytic performance under industrially relevant conditions. Specifically, the effect of ammonia storage on the increase of activity was shown. This was also accompanied by elevated N₂O production not observed during tests with gradual heating. Additionally, unusually high NOₓ selectivity was detected for Fe-ZSM-5 under these conditions. Lastly, tracking catalyst state under dynamic reaction conditions disclosed that Fe-ZSM-5 activity did not grow directly with temperature increase but rather depended on the oxidation state of Fe and surface concentration of ammonia
When nature inspires technology : Henry Dicks. The biomimicry revolution: learning from nature how to inhabit the earth. New York: Columbia University Press, 2023, 320 pp, $35.00 HB
No full textOne of the central themes of Western philosophical reflection has always been the relationship between technology, culture, and nature: Should technology imitate the forms of nature? Is technology a cultural praxis capable of improving the natural world? What validity and autonomy does the creativity of the technician have if nature is the starting point for engineering practices? In other words, is there a gap between nature and technology
The scientists' responsibility in communicating the sustainability crisis
No full textHumankind and, in general, all life on earth, face a fundamental sustainability crisis. We have realized many decades ago that both our sources and our sinks on our planet are limited. International treaties have been adopted, panels have been formed and assessments have been published. Yet, almost all nations regularly fail to comply with their goals. Many potential barriers to swift actions exist, and sustainability in its many facets reveals complex interdependencies and rebounds. Humankind relies on an infrastructure in terms of energy supply, housing, and others, which take decades to change. At the same time, we face tipping points, which describe an irreversible acceleration of degradation of our fundamental life’s resources. This concerns not only the climate crisis, which is visible in so many nations with floods and heat waves and a surge of new temperature extremes and costs due to mitigation and adaptation. No, the problem also lies in a set of planetary limits, including a terrifying loss of agricultural soil, an increasing level of acidity in the oceans, enhanced nitridation, and loss of biodiversity and natural habitats. In this situation, it appears obvious, that scientists, meaning all scientists beyond our representatives in international panels, need to respond. We need to inform ourselves across the disciplines and disseminate available information into society. We need to spell out that a transformation of society is required combining technological advances and a change in lifestyle with a reduction in demand for our planet’s sources and sinks
Breaking and Fixing Garbled Circuits When a Gate has Duplicate Input Wires
Get PDFGarbled circuits are a fundamental cryptographic primitive that allows two or more parties to securely evaluate an arbitrary Boolean circuit without revealing any information beyond the output using a constant number of communication rounds. Garbled circuits have been introduced by Yao (FOCS’86) and generalized to the multi-party setting by Beaver, Micali and Rogaway (STOC’90). Since then, several works have improved their efficiency by providing different garbling schemes and several implementations exist. Starting with the seminal Fairplay compiler (USENIX Security’04), several implementation frameworks decoupled the task of compiling the function to be evaluated into a Boolean circuit from the engine that securely evaluates that circuit, e.g., using a secure two-party computation protocol based on garbled circuits. In this paper, we show that this decoupling of circuit generation and evaluation allows a subtle attack on several prominent garbling schemes. It occurs when violating the implicit assumption on the circuit that gates have different input wires which is most often not explicitly specified in the respective papers. The affected garbling schemes use separate calls to a deterministic encryption function for the left and right input wire of a gate to derive pseudo-random encryption pads that are XORed together. When a circuit contains a gate where the left and right input wire are the same, these two per-wire encryption pads cancel out and we demonstrate that this can result in a complete break of privacy. We show how the vulnerable garbling schemes can be fixed easily
Standardized Schoeller diagrams — A Matlab plotting tool
Get PDFA complete water analysis typically contains at least 65 chemical and physical parameters. This variety of parameters complicates temporal or spatial comparisons of different water samples. Hence, special hydrogeological diagrams, such as the Schoeller diagram, were developed to facilitate the evaluation and interpretation of analytical results of multiple samples. In conventional Schoeller diagrams, the concentrations of calcium, magnesium, sodium, chloride, sulfate, and bicarbonate/carbonate are plotted as points on logarithmic scales. Points of one analysis are connected to form characteristic signatures of each sample. Occasionally, resulting parallel signatures indicate a similar water genesis. Here, we present standardized Schoeller diagrams and introduce a practical Matlab tool for this purpose. Standardization means that the different logarithmic axes are shifted towards each other so that the signature of a selected sample becomes a horizontal line. This procedure greatly facilitates comparisons of water samples to the chosen standard and increases the informative value of the diagrams. However, manual implementations of standardizations are arduous and time-consuming, as a single calculation of the relocation of each axis is necessary. In addition, the calculations must be repeated if another sample is chosen as the standard. We developed a Matlab tool that allows the fast generation of standardized Schoeller diagrams with many options and implements user-specific preferences with just one command. Probably the most useful feature is that users can choose which parameters are displayed, opening up new areas of application for Schoeller diagrams
Mapping Buried Fault Zones in a Granitic Pluton Using Aeromagnetic Data
No full textGlobally, the largest geothermal resources are linked to the crystalline basement, which could be exploited using Enhanced Geothermal Systems (EGS). The planned underground laboratory GeoLaB aims to facilitate the large-scale application of EGS technologies by performing in-situ high-flowrate experiments on fault zones. The Tromm Granite at the northwestern margin of the Upper Rhine Graben was preselected as one of two potential sites for GeoLaB. To improve the understanding of the natural fault network in the target area, a drone-based aeromagnetic survey was conducted in March 2022, covering an area of about 13.3 km2 in the center of the pluton. A selection of eight filters to enhance the signal was tested against each other using a synthetic model. Based on this comparison, the tilt derivative appears to be the most reliable method for mapping and characterizing natural fault zones. The filtered aeromagnetic dataset reveals a network of linear anomalies interpreted as altered fault zones. The relative abundance of magnetic lineaments correlates broadly with slip tendency in the current stress field. Thus, the aeromagnetic may provide insights into the reactivation potential and deformation history of fault zones, which significantly influence the hydraulic properties. However, additional geophysical surveys or exploration wells are needed to validate the results
Label modification and bootstrapping for zero-shot cross-lingual hate speech detection
Get PDFThe goal of hate speech detection is to filter negative online content aiming at certain groups of people. Due to the easy accessibility and multilinguality of social media platforms, it is crucial to protect everyone which requires building hate speech detection systems for a wide range of languages. However, the available labeled hate speech datasets are limited, making it difficult to build systems for many languages. In this paper we focus on cross-lingual transfer learning to support hate speech detection in low-resource languages, while highlighting label issues across application scenarios, such as inconsistent label sets of corpora or differing hate speech definitions, which hinder the application of such methods. We leverage cross-lingual word embeddings to train our neural network systems on the source language and apply them to the target language, which lacks labeled examples, and show that good performance can be achieved. We then incorporate unlabeled target language data for further model improvements by bootstrapping labels using an ensemble of different model architectures. Furthermore, we investigate the issue of label imbalance in hate speech datasets, since the high ratio of non-hate examples compared to hate examples often leads to low model performance. We test simple data undersampling and oversampling techniques and show their effectiveness
Fusion of SAR and Multi-spectral Time Series for Determination of Water Table Depth and Lake Area in Peatlands
No full textPeatlands as natural carbon sinks have a major impact on the climate balance and should therefore be monitored and protected. The hydrology of the peatland serves as an indicator of the carbon storage capacity. Hence, we investigate the question how suitable different remote sensing data are for monitoring the size of open water surface and the water table depth (WTD) of a peatland ecosystem. Furthermore, we examine the potential of combining remote sensing data for this purpose. We use C-band synthetic aperture radar (SAR) data from Sentinel-1 and multi-spectral data from Sentinel-2. The radar backscatter σ0, the normalized difference water index (NDWI) and the modified normalized difference water index (MNDWI) are calculated and used for consideration of the WTD and the lake size. For the measurement of the lake size, we implement and investigate the methods: random forest, adaptive thresholding and an analysis according to the Dempster–Shafer theory. Correlations between WTD and the remote sensing data σ⁰ as well as NDWI are investigated. When looking at the individual data sets the results of our case study show that the VH polarized σ⁰ data produces the clearest delineation of the peatland lake. However the adaptive thresholding of the weighted fusion image of σ⁰-VH, σ⁰-VV and MNDWI, and the random forest algorithm with all three data sets as input proves to be the most suitable for determining the lake area. The correlation coefficients between σ⁰/NDWI and WTD vary greatly and lie in ranges of low to moderate correlation
Contribution of wedge and bulk viscous forces in droplets moving on inclined surfaces: Contribution of wedge and bulk viscous forces
Get PDFEmploying direct numerical simulations, we investigate water and water-glycerol (85 wt%) droplets (∼25 µL) moving on smooth surfaces, with contact angles of around 90°, at varying inclinations. Our focus is on elucidating the relative contribution of local viscous forces in the wedge and bulk regions in droplets to the total viscous force. We observe that, for fast-moving droplets, both regions contribute comparably, while the contribution of the wedge region dominates in slow-moving cases. Comparisons with existing estimates reveal the inadequacy of previous predictions in capturing the contributions of wedge and bulk viscous forces in fast-moving droplets. Furthermore, we demonstrate that droplets with identical velocities can exhibit disparate viscous forces due to variations in internal fluid dynamics
Effective Rates for Iterations Involving Bregman Strongly Nonexpansive Operators
Get PDFWe develop the theory of Bregman strongly nonexpansive maps for uniformly Fréchet differentiable Bregman functions from a quantitative perspective. In that vein, we provide moduli witnessing quantitative versions of the central assumptions commonly used in this field on the underlying Bregman function and the Bregman strongly nonexpansive maps. In terms of these moduli, we then compute explicit and effective rates for the asymptotic regularity of Picard iterations of Bregman strongly nonexpansive maps and of the method of cyclic Bregman projections. Further, we also provide similar rates for the asymptotic regularity and metastability of a strongly convergent Halpern-type iteration of a family of such mappings and we use these new results to derive rates for various special instantiations like a Halpern-type proximal point algorithm for monotone operators in Banach spaces as well as Halpern-Mann- and Tikhonov-Mann-type methods