Potential and costs of carbon dioxide removal by enhanced weathering of rocks

The chemical weathering of rocks currently absorbs about 1.1 Gt CO2 a−1 being mainly stored as bicarbonate in the ocean. An enhancement of this slow natural process could remove substantial amounts of CO2 from the atmosphere, aiming to offset some unavoidable anthropogenic emissions in order to comply with the Paris Agreement, while at the same time it may decrease ocean acidification. We provide the first comprehensive assessment of economic costs, energy requirements, technical parameterization, and global and regional carbon removal potential. The crucial parameters defining this potential are the grain size and weathering rates. The main uncertainties about the potential relate to weathering rates and rock mass that can be integrated into the soil. The discussed results do not specifically address the enhancement of weathering through microbial processes, feedback of geogenic nutrient release, and bioturbation. We do not only assess dunite rock, predominantly bearing olivine (in the form of forsterite) as the mineral that has been previously proposed to be best suited for carbon removal, but focus also on basaltic rock to minimize potential negative side effects. Our results show that enhanced weathering is an option for carbon dioxide removal that could be competitive already at 60 US $t−1 CO2 removed for dunite, but only at 200 US$ t−1 CO2 removed for basalt. The potential carbon removal on cropland areas could be as large as 95 Gt CO2 a−1 for dunite and 4.9 Gt CO2 a−1 for basalt. The best suited locations are warm and humid areas, particularly in India, Brazil, South-East Asia and China, where almost 75% of the global potential can be realized. This work presents a techno-economic assessment framework, which also allows for the incorporation of further processes

Quantum Policy Gradient Algorithm with Optimized Action Decoding

Quantum machine learning implemented by variational quantum circuits (VQCs) is considered a promising concept for the noisy intermediate-scale quantum computing era. Focusing on applications in quantum reinforcement learning, we propose a specific action decoding procedure for a quantum policy gradient approach. We introduce a novel quality measure that enables us to optimize the classical post-processing required for action selection, inspired by local and global quantum measurements. The resulting algorithm demonstrates a significant performance improvement in several benchmark environments. With this technique, we successfully execute a full training routine on a 5-qubit hardware device. Our method introduces only negligible classical overhead and has the potential to improve VQC-based algorithms beyond the field of quantum reinforcement learning.Comment: Accepted to the 40th International Conference on Machine Learning (ICML 2023), Honolulu, Hawaii, USA. 22 pages, 10 figures, 3 table

Quantum Natural Policy Gradients: Towards Sample-Efficient Reinforcement Learning

Reinforcement learning is a growing field in AI with a lot of potential. Intelligent behavior is learned automatically through trial and error in interaction with the environment. However, this learning process is often costly. Using variational quantum circuits as function approximators can reduce this cost. In order to implement this, we propose the quantum natural policy gradient (QNPG) algorithm -- a second-order gradient-based routine that takes advantage of an efficient approximation of the quantum Fisher information matrix. We experimentally demonstrate that QNPG outperforms first-order based training on Contextual Bandits environments regarding convergence speed and stability and thereby reduces the sample complexity. Furthermore, we provide evidence for the practical feasibility of our approach by training on a 12-qubit hardware device.Comment: This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessible. 7 pages, 5 figures, 1 tabl

Dynamics of water fluxes and storages in an Alpine karst catchment under current and potential future climate conditions

Karst aquifers are difficult to manage due to their unique hydrogeological characteristics. Future climate projections suggest a strong change in temperature and precipitation regimes in European karst regions over the next decades. Alpine karst systems can be especially vulnerable under changing hydro-meteorological conditions since snowmelt in mountainous environments is an important controlling process for aquifer recharge and is highly sensitive to varying climatic conditions. Our paper presents the first study to investigate potential impacts of climate change on mountainous karst systems by using a combined lumped and distributed modeling approach with consideration of subsurface karst drainage structures. The study site is characterized by high-permeability (karstified) limestone formations and low-permeability (non-karst) sedimentary Flysch. The model simulation under current conditions demonstrates that a large proportion of precipitation infiltrates into the karst aquifer as autogenic recharge. Moreover, the result shows that surface snow storage is dominant from November to April, while subsurface water storage in the karst aquifer dominates from May to October. The climate scenario runs demonstrate that varied climate conditions significantly affect the spatiotemporal distribution of water fluxes and storages: (1) the total catchment discharge decreases under all evaluated future climate conditions. (2) The spatiotemporal discharge pattern is strongly controlled by temperature variations, which can shift the seasonal snowmelt pattern, with snow storage in the cold season (December to April) decreasing significantly under all change scenarios. (3) Increased karst aquifer recharge in winter and spring, and decreased recharge in summer and autumn, partly offset each other. (4) Impacts on the karst springs are distinct; the lowest permanent spring presents a “robust” discharge behavior, while the highest overflow outlet is highly sensitive to changing climate. This analysis effectively demonstrates that the impacts on subsurface flow dynamics are regulated by the characteristic dual flow and spatially heterogeneous distributed drainage structure of the karst aquifer. Overall, our study highlights the fast groundwater dynamics in mountainous karst catchments, which make them highly vulnerable to future changing climate conditions. Additionally, this work presents a novel holistic modeling approach, which can be transferred to similar karst systems for studying the impact of climate change on local karst water resources with consideration of their individual hydrogeological complexity and hydraulic heterogeneity

RECENT TEST EXPERIENCES WITH APPLYING MULTIPLE UNSHROUDED IMPELLERS IN A SINGLE-SHAFT COMPRESSOR

LectureThe use of unshrouded impellers to increase the pressure ratio and volume reduction achieved in low mole weight, single-shaft compressor applications is discussed. The aerodynamic and mechanical implications of using multiple unshrouded impellers in series is also addressed. Test results will show that with proper management of impeller tip gaps good aerodynamic performance can be achieved with three unshrouded impellers in a single process section. The development effort also leveraged a knowledge-based impeller design system to provide new impeller designs that were optimized as a function of Mach number to provide a 30% axially shorter section without compromising aerodynamic performance. The shorter axial stages in the first section pushed the rotor natural frequency 20% higher, enabling faster rotor tip speeds. Test results from a single-stage test rig and from a full-size prototype testing are provided and generally show good agreement

Post Hoc Analysis of a Randomized Controlled Trial on Fasting and Plant-Based Diet in Rheumatoid Arthritis (NutriFast): Nutritional Supply and Impact on Dietary Behavior

This study aimed at comparing the nutrient supply and dietary behaviors during a plant-based diet (PBD) combined with time-restricted eating (TRE) to standard dietary recommendations in rheumatoid arthritis patients. In this open-label, randomized, controlled clinical trial, patients were assigned to either a 7-day fast followed by an 11-week PBD including TRE (A) or a 12-week anti-inflammatory diet following official German guidelines (German Nutrition Society, DGE) (B). Dietary habits were assessed by 3-day food records at weeks -1, 4 and 9 and food frequency questionnaires. 41 out of 53 participants were included in a post-hoc per protocol analysis. Both groups had similar energy, carbohydrate, sugar, fiber and protein intake at week 4. Group A consumed significantly less total saturated fat than group B (15.9 +/- 7.7 vs. 23.2 +/- 10.3 g/day; p = 0.02). Regarding micronutrients, group B consumed more vitamin A, B-12, D, riboflavin and calcium (each p <= 0.02). Zinc and calcium were below recommended intakes in both groups. Cluster analysis did not show clear group allocation after three months. Hence, dietary counselling for a PBD combined with TRE compared to a standard anti-inflammatory diet does not seem to lead to two different dietary clusters, i.e., actual different dietary behaviors as expected. Larger confirmatory studies are warranted to further define dietary recommendations for RA

Global distribution of carbonate rocks and karst water resources

Karstregionen beinhalten eine Vielzahl natürlicher Ressourcen, wie Süßwasser und Biodiversität, sowie zahlreiche kulturelle und historische Ressourcen. Die Welt-Karstaquifer-Karte (WOKAM) ist die erste detaillierte und vollständige globale Datenbasis über die Verbreitung von verkarstungsfähigen Gesteinen (Carbonate und Evaporite), welche potentielle Karstaquifere darstellen. Diese Studie präsentiert eine statistische Auswertung von WOKAM, mit dem Fokus auf Karst in Carbonatgesteinen, und adressiert vier wesentliche Aspekte: (i) globales Vorkommen und geografische Verteilung von Karst; (ii) Karst in verschiedenen topografischen Settings und in Küstengebieten; (iii) Karst in verschiedenen Klimazonen; und (iv) Bevölkerung in Karstgebieten. Die Analyse ergibt, dass 15,2 % der globalen, eisfreien Kontinentalfläche durch Carbonatgesteine charakterisiert sind. Der höchste prozentuale Anteil tritt in Europa auf (21,8 %); die größte absolute Fläche in Asien (8,35 Mio. km²). Weltweit treten 31,1 % aller anstehenden Carbonatgesteine in Ebenen auf, 28,1 % im Hügelland und 40,8 % in Gebirgen; 151,400 km oder 15,7 % der globalen marinen Küstenlinie wird von Carbonatgesteinen geprägt. Etwa 34,2 % aller Carbonatgesteine kommen im ariden Klima vor, gefolgt von 28,2 % in kalten und 15,9 % in gemäßigten Klimaten, während nur 13,1 % bzw. 8,6 % im tropischen bzw. polaren Klima anzutreffen sind. Global leben etwa 1,18 Milliarden Menschen (16,5 % der Weltbevölkerung) in Karstgebieten. Die höchste absolute Anzahl wurde in Asien ermittelt (661,7 Mio.), während die höchsten prozentualen Anteile in Europa (25,3 %) und Nordamerika (23,5 %) auftreten. Diese Ergebnisse zeigen die globale Bedeutung von Karst und dienen als Basis für weitere Forschung und internationale Wassermanagement-Strategien

Global distribution of carbonate rocks and karst water resources

Karstregionen beinhalten eine Vielzahl natürlicher Ressourcen, wie Süßwasser und Biodiversität, sowie zahlreiche kulturelle und historische Ressourcen. Die Welt-Karstaquifer-Karte (WOKAM) ist die erste detaillierte und vollständige globale Datenbasis über die Verbreitung von verkarstungsfähigen Gesteinen (Carbonate und Evaporite), welche potentielle Karstaquifere darstellen. Diese Studie präsentiert eine statistische Auswertung von WOKAM, mit dem Fokus auf Karst in Carbonatgesteinen, und adressiert vier wesentliche Aspekte: (i) globales Vorkommen und geografische Verteilung von Karst; (ii) Karst in verschiedenen topografischen Settings und in Küstengebieten; (iii) Karst in verschiedenen Klimazonen; und (iv) Bevölkerung in Karstgebieten. Die Analyse ergibt, dass 15,2 % der globalen, eisfreien Kontinentalfläche durch Carbonatgesteine charakterisiert sind. Der höchste prozentuale Anteil tritt in Europa auf (21,8 %); die größte absolute Fläche in Asien (8,35 Mio. km²). Weltweit treten 31,1 % aller anstehenden Carbonatgesteine in Ebenen auf, 28,1 % im Hügelland und 40,8 % in Gebirgen; 151,400 km oder 15,7 % der globalen marinen Küstenlinie wird von Carbonatgesteinen geprägt. Etwa 34,2 % aller Carbonatgesteine kommen im ariden Klima vor, gefolgt von 28,2 % in kalten und 15,9 % in gemäßigten Klimaten, während nur 13,1 % bzw. 8,6 % im tropischen bzw. polaren Klima anzutreffen sind. Global leben etwa 1,18 Milliarden Menschen (16,5 % der Weltbevölkerung) in Karstgebieten. Die höchste absolute Anzahl wurde in Asien ermittelt (661,7 Mio.), während die höchsten prozentualen Anteile in Europa (25,3 %) und Nordamerika (23,5 %) auftreten. Diese Ergebnisse zeigen die globale Bedeutung von Karst und dienen als Basis für weitere Forschung und internationale Wassermanagement-Strategien

Monophyletic group of unclassified γ-Proteobacteria dominates in mixed culture biofilm of high-performing oxygen reducing biocathode

International audienceSeveral mixed microbial communities have been reported to show robust bioelectrocatalysis of oxygen reduction over time at applicable operation conditions. However, clarification of electron transfer mechanism(s) and identification of essential micro-organisms have not been realised. Therefore, the objective of this study was to shape oxygen reducing biocathodes with different microbial communities by means of surface modification using the electrochemical reduction of two different diazonium salts in order to discuss the relation of microbial composition and performance. The resulting oxygen reducing mixed culture biocathodes had complex bacterial biofilms variable in size and shape as observed by confocal and electron microscopy. Sequence analysis of ribosomal 16S rDNA revealed a putative correlation between the abundance of certain microbiota and biocathode performance. The best performing biocathode developed on the unmodified graphite electrode and reached a high current density for oxygen reducing biocathodes at neutral pH (0.9A/m(2)). This correlated with the highest domination (60.7%) of a monophyletic group of unclassified γ-Proteobacteria. These results corroborate earlier reports by other groups, however, higher current densities and higher presence of these unclassified bacteria were observed in this work. Therefore, members of this group are likely key-players for highly performing oxygen reducing biocathodes.[on SciFinder (R)