A continuum model of multi-phase reactive transport in igneous systems

Multi-phase reactive transport processes are ubiquitous in igneous systems. A challenging aspect of modelling igneous phenomena is that they range from solid-dominated porous to liquid-dominated suspension flows and therefore entail a wide spectrum of rheological conditions, flow speeds, and length scales. Most previous models have been restricted to the two-phase limits of porous melt transport in deforming, partially molten rock and crystal settling in convecting magma bodies. The goal of this paper is to develop a framework that can capture igneous system from source to surface at all phase proportions including not only rock and melt but also an exsolved volatile phase. Here, we derive an n-phase reactive transport model building on the concepts of Mixture Theory, along with principles of Rational Thermodynamics and procedures of Non-equilibrium Thermodynamics. Our model operates at the macroscopic system scale and requires constitutive relations for fluxes within and transfers between phases, which are the processes that together give rise to reactive transport phenomena. We introduce a phase- and process-wise symmetrical formulation for fluxes and transfers of entropy, mass, momentum, and volume, and propose phenomenological coefficient closures that determine how fluxes and transfers respond to mechanical and thermodynamic forces. Finally, we demonstrate that the known limits of two-phase porous and suspension flow emerge as special cases of our general model and discuss some ramifications for modelling pertinent two- and three-phase flow problems in igneous systems.Comment: Revised preprint submitted for peer-reviewed publication: main text with 8 figures, 1 table; appendix with 3 figures and 2 table

Volatiles beneath mid-ocean ridges: deep melting, channelised transport, focusing, and metasomatism

Deep-Earth volatile cycles couple the mantle with near-surface reservoirs. Volatiles are emitted by volcanism and, in particular, from mid-ocean ridges, which are the most prolific source of basaltic volcanism. Estimates of volatile extraction from the asthenosphere beneath ridges typically rely on measurements of undegassed lavas combined with simple petrogenetic models of the mean degree of melting. Estimated volatile fluxes have large uncertainties; this is partly due to a poor understanding of how volatiles are transported by magma in the asthenosphere. Here, we assess the fate of mantle volatiles through numerical simulations of melting and melt transport at mid-ocean ridges. Our simulations are based on two-phase, magma/mantle dynamics theory coupled to idealised thermodynamic model of mantle melting in the presence of water and carbon dioxide. We combine simulation results with catalogued observations of all ridge segments to estimate a range of likely volatile output from the global mid-ocean ridge system. We thus predict global MOR crust production of 66-73 Gt/yr (22-24 km3/yr) and global volatile output of 52-110 Mt/yr, corresponding to mantle volatile contents of 100--200~ppm. We find that volatile extraction is limited: up to half of deep, volatile-rich melt is not focused to the axis but is rather deposited along the LAB. As these distal melts crystallise and fractionate, they metasomatise the base of the lithosphere, creating rheological heterogeneity that could contribute to the seismic signature of the LAB.Comment: 42 pages; 8 figures; 2 appendices (incl 1 table); 7 suppl. figures; 1 suppl. tabl

Metal oxides in fluidized bed conversion systems

Several fluidized bed conversion concepts utilizing metal oxide particles have been proposed in the last decade. The use of metal oxide particles in fluidized bed conversion systems stems largely from the research around chemical-looping combustion (CLC). Here, a metal oxide is used as an oxygen carrier for transport of oxygen from combustion air to the fuel. Although the concept was proposed already in the 1950’s, most of the research has been carried out after the turn of the century. The research was sparked by the need for viable technologies for carbon capture, and CLC is here a breakthrough technology with low costs for capture and a high carbon capture efficiency. Today a large number of oxygen carrier particles have been developed and tested and around 30 continuous units up to 3 MW have been operated around the world. The research around CLC and oxygen carriers has sparked the development of several other fluidized bed processes where oxygen carriers or metal oxide particles can be used to enhance performance. These include fluidized bed processes for gas, solid and liquid fuels for heat, power and syngas production. Chalmers has been active within CLC research for over 15 years and also has activities within these related processes. In addition to CLC, this paper will provide an overview of these technologies: i) Oxygen carrier aided combustion, ii) Dual-bed fluidized bed gasification (DFBG), iii) Chemical-looping reforming (CLR) and iv) gasification gas conditioning (CLTR). Some important criteria for metal oxides will be discussed in relation to the application

On the lifetime of bioinformatics web services

Web services are used through all disciplines in life sciences and the online landscape is growing by hundreds of novel servers annually. However, availability varies, and maintenance practices are largely inconsistent. We screened the availability of 2396 web tools published during the past 10 years. All servers were accessed over 133 days and 318 668 index files were stored in a local database. The number of accessible tools almost linearly increases in time with highest availability for 2019 and 2020 (∼90%) and lowest for tools published in 2010 (∼50%). In a 133-day test frame, 31% of tools were always working, 48.4% occasionally and 20.6% never. Consecutive downtimes were typically below 5 days with a median of 1 day, and unevenly distributed over the weekdays. A rescue experiment on 47 tools that were published from 2019 onwards but never accessible showed that 51.1% of the tools could be restored in due time. We found a positive association between the number of citations and the probability of a web server being reachable. We then determined common challenges and formulated categorical recommendations for researchers planning to develop web-based resources. As implication of our study, we propose to develop a repository for automatic API testing and sustainability indexing

Immersive Storytelling for Information Security Awareness Training in Virtual Reality

Due to the central role of the human factor in information security, the need for information security awareness (ISA) is constantly increasing. In order to maintain a high level of ISA, trainings have to be carried out frequently to ensure sustainability. Since education via VR has led to a sustainable learning effect in other fields, we evaluated the use of VR for ISA trainings. Moreover, we combined our VR training with immersive storytelling. For the evaluation we used two sets of participants. The first used a traditional e-Learning method to answer the questionnaire. The second used our VR training. After one week we repeated the questionnaires. The results showed that the VR group could achieve higher scores than the noVR group. Moreover, the VR group achieved even higher scores after one week which might be due to the sustained learning effect from the VR training

Periodic outgassing as a result of unsteady convection in Ray Lava Lake, Mount Erebus, Antarctica

Persistently active lava lakes show continuous outgassing and open convection over years to decades. Ray Lake, the lava lake at Mount Erebus, Ross Island, Antarctica, maintains long-term, near steady-state behavior in temperature, heat flux, gas flux, lake level, and composition. This activity is superposed by periodic small pulses of gas and hot magma every 5-18 minutes and disrupted by sporadic Strombolian eruptions. The periodic pulses have been attributed to a variety of potential processes including unstable bidirectional flow in the conduit feeding the lake. In contrast to hypotheses invoking a conduit source for the observed periodicity, we test the hypothesis that the behavior could be the result of dynamics within the lake itself, independent of periodic influx from the conduit. We perform numerical simulations of convection in Ray Lake driven by both constant and periodic inflow of gas-rich magma from the conduit to identify whether the two cases have different observational signatures at the surface. Our simulations show dripping diapirs or pulsing plumes leading to observable surface behavior with periodicities in the range of 5-20 minutes. We conclude that a convective speed faster than the inflow speed can result in periodic behavior without requiring periodicity in conduit dynamics. This finding suggests that the surface behavior of lava lakes might be less indicative of volcanic conduit processes in persistently outgassing volcanoes than previously thought, and that dynamics within the lava lake itself may modify or overprint patterns emerging from the conduit

DYST (Did You See That?): An Amplified Covert Channel That Points To Previously Seen Data

Covert channels are unforeseen and stealthy communication channels that enable manifold adversary scenarios. However, they can also allow the exchange of confidential information by journalists. All covert channels described until now therefore need to craft seemingly legitimate information flows for their information exchange, mimicking unsuspicious behavior. In this paper, we present DYST, which represents a new class of covert channels we call history covert channels jointly with the new paradigm of covert channel amplification. History covert channels can communicate almost exclusively by pointing to unaltered legitimate traffic created by regular network nodes. Only a negligible fraction of the covert communication process requires the transfer of actual covert channel information by the covert channel's sender. This allows, for the first time, an amplification of the covert channel's message size, i.e., minimizing the fraction of actually transferred secret data by a covert channel's sender in relation to the overall secret data being exchanged. We extend the current taxonomy for covert channels to show how history channels can be categorized. We describe multiple scenarios in which history covert channels can be realized, theoretically analyze the characteristics of these channels and show how their configuration can be optimized for different implementations. We further evaluate the robustness and detectability of history covert channels.Comment: 18 pages, rev