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Investigating the Interaction between Ilmenite and Zinc for Chemical Looping
Full text linkThe iron and titanium oxide ilmenite is a benchmark oxygen carrier for chemical looping combustion (CLC) and oxygen carrier-aided combustion (OCAC). Both of them are combustion technologies for biomass and waste fuels with lower emissions and low costs for carbon capture. Here, the interaction between the ash component zinc and oxygen carrier ilmenite is studied in a two-staged vertical tube reactor. Three types of ilmenites─Norwegian rock ilmenite, synthesized ilmenite, and ilmenite extracted after 200 h of OCAC in a full-scale fluidized bed unit─were exposed to gas-phase Zn and ZnCl2. Following the exposure, samples were analyzed concerning morphology, chemical distribution, composition, and crystalline phases. The observations were complemented with thermodynamic equilibrium calculations. It is observed that the iron-rich layer formed on the external surface of rock ilmenite after activation promotes the reaction with both gaseous zinc compounds, with zinc ferrite formed in the external Fe-rich layer. In contrast, ilmenite with no segregation of Fe and Ti showed to interact less with zinc species. Metallic Zn penetrated the particles, while the interaction depth was shallow with ZnCl2\ua0for all investigated ilmenite oxygen carriers. The gaseous conditions, particle ash layer composition, and iron availability are shown to play an important role in the interaction between zinc compounds and ilmenite particles. Based on these results, interaction mechanisms for Zn and ZnCl2\ua0are proposed. This interaction could have environmental implications for the toxicity of ash streams from waste combustion in addition to possibilities for Zn recycling
Site Communication in Direct Formation of H2O2 over Single-Atom Pd@Au Nanoparticles
Full text linkSingle atom alloy catalysts offer possibilities to obtain turnover frequencies and selectivities unattainable by their monometallic counterparts. One example is direct formation of H2O2 from O2 and H2 over Pd embedded in Au hosts. Here, a first-principles-based kinetic Monte Carlo approach is developed to investigate the catalytic performance of Pd embedded in Au nanoparticles in an aqueous solution. The simulations reveal an efficient site separation where Pd monomers act as active centers for H2 dissociation, whereas H2O2 is formed over undercoordinated Au sites. After dissociation, atomic H may undergo an exothermic redox reaction, forming a hydronium ion in the solution and a negative charge on the surface. H2O2 is preferably formed from reactions between dissolved H+ and oxygen species on the Au surface. The simulations show that tuning the nanoparticle composition and reaction conditions can enhance the selectivity toward H2O2. The outlined approach is general and applicable for a range of different hydrogenation reactions over single atom alloy nanoparticles
Inference of the Life Cycle of Environmental Phages from Genomic Signature Distances to Their Hosts
Full text linkThe environmental impact of uncultured phages is shaped by their preferred life cycle (lytic or lysogenic). However, our ability to predict it is very limited. We aimed to discriminate between lytic and lysogenic phages by comparing the similarity of their genomic signatures to those of their hosts, reflecting their co-evolution. We tested two approaches: (1) similarities of tetramer relative frequencies, (2) alignment-free comparisons based on exact k = 14 oligonucleotide matches. First, we explored 5126 reference bacterial host strains and 284 associated phages and found an approximate threshold for distinguishing lysogenic and lytic phages using both oligonucleotide-based methods. The analysis of 6482 plasmids revealed the potential for horizontal gene transfer between different host genera and, in some cases, distant bacterial taxa. Subsequently, we experimentally analyzed combinations of 138 Klebsiella pneumoniae strains and their 41 phages and found that the phages with the largest number of interactions with these strains in the laboratory had the shortest genomic distances to K. pneumoniae. We then applied our methods to 24 single-cells from a hot spring biofilm containing 41 uncultured phage-host pairs, and the results were compatible with the lysogenic life cycle of phages detected in this environment. In conclusion, oligonucleotide-based genome analysis methods can be used for predictions of (1) life cycles of environmental phages, (2) phages with the broadest host range in culture collections, and (3) potential horizontal gene transfer by plasmids
Similarity-based Web Element Localization for Robust Test Automation
Full text linkNon-robust (fragile) test execution is a commonly reported challenge in GUI-based test automation, despite much research and several proposed solutions. A test script needs to be resilient to (minor) changes in the tested application but, at the same time, fail when detecting potential issues that require investigation. Test script fragility is a multi-faceted problem. However, one crucial challenge is how to reliably identify and locate the correct target web elements when the website evolves between releases or otherwise fail and report an issue. This article proposes and evaluates a novel approach called similarity-based web element localization (Similo), which leverages information from multiple web element locator parameters to identify a target element using a weighted similarity score. This experimental study compares Similo to a baseline approach for web element localization. To get an extensive empirical basis, we target 48 of the most popular websites on the Internet in our evaluation. Robustness is considered by counting the number of web elements found in a recent website version compared to how many of these existed in an older version. Results of the experiment show that Similo outperforms the baseline; it failed to locate the correct target web element in 91 out of 801 considered cases (i.e., 11%) compared to 214 failed cases (i.e., 27%) for the baseline approach. The time efficiency of Similo was also considered, where the average time to locate a web element was determined to be 4 milliseconds. However, since the cost of web interactions (e.g., a click) is typically on the order of hundreds of milliseconds, the additional computational demands of Similo can be considered negligible. This study presents evidence that quantifying the similarity between multiple attributes of web elements when trying to locate them, as in our proposed Similo approach, is beneficial. With acceptable efficiency, Similo gives significantly higher effectiveness (i.e., robustness) than the baseline web element localization approach
Cost–benefit analysis of a trans-arctic alternative route to the Suez canal: a method based on high-fidelity ship performance, weather, and ice forecast models
Full text linkClimate change in recent years has produced viable shipping routes in the Arctic. However,\ua0critical uncertainties related to maritime operations in the Arctic make it difficult to predict ship\ua0speeds in ice and, thus, the voyage time and fuel costs. Cost–benefit analysis of alternative Arctic\ua0routes based on accurate environmental condition modeling is required. In this context, this paper\ua0presents a holistic approach that considers the major voyage-related costs of a trans-Arctic route as\ua0an alternative to the conventional routes via the Suez Canal Route (SCR) for existing merchant ships.\ua0This tool is based on high-fidelity models of ship performance, metocean forecasting, and a voyage\ua0optimization algorithm. Case studies are performed based on a general cargo vessel in operation\ua0to quantify realistic expenses inclusive of all the major operational, fuel, and voyage costs of the\ua0specific voyages. A comparison is made between the total costs of the trans-Arctic route and SCR for\ua0different seasons, which proves the economic feasibility of the trans-Arctic route. Overall, this work\ua0can provide valuable insights to help policymakers as well as shipbuilders, owners, and operators\ua0to assess the potential cost-effectiveness and sustainability of future Arctic shipping, thereby better\ua0developing future strategies
Cakes That Bake Cakes: Dynamic Computation in CakeML
Full text linkWe have extended the verified CakeML compiler with a new language primitive, Eval, which permits evaluation of new CakeML syntax at runtime. This new implementation supports an ambitious form of compilation at runtime and dynamic execution, where the original and dynamically added code can share (higher-order) values and recursively call each other. This is, to our knowledge, the first verified run-Time environment capable of supporting a standard LCF-style theorem prover design. Modifying the modern CakeML compiler pipeline and proofs to support a dynamic computation semantics was an extensive project. We review the design decisions, proof techniques, and proof engineering lessons from the project, and highlight some unexpected complications
Spectacular: Finding Laws from 25 Trillion Terms
No full textWe present Spectacular, a new tool for automatically discovering candidate laws for use in property-based testing. By using the recently-developed technique of ECTAs (Equality-Constrained Tree Automata), Spectacular improves upon previous approaches such as QuickSpec: it can explore vastly larger program spaces and start generating candidate laws within 20 seconds from a benchmark where QuickSpec runs for 45 minutes and then crashes (due to memory limits, even on a 256 GB machine). Thanks to the ability of ECTAs to efficiently search constrained program spaces, Spectacular is fast enough to find candidate laws in more generally typed settings than the monomorphized one, even for signatures with dozens of functions
The operating cycle representation of road transport missions
No full textThe difficulties that conventionally road vehicles are facing in meeting regulation standards require ad-hoc solutions. Moreover, the impellent shift of paradigm towards full electrification and partial automation is posing great challenges to the automotive industry, which has set a zero-emissions target to be reached within a short time horizon. In this context, the energy performance of commercial vehicles may be dramatically improved if the characteristics of the transport application, that is, the intended usage, are known prior to prototype development and design selection. To tailor the vehicle\u27s specifications, however, a representative description of the mission and the surroundings is needed.Where many conventional approaches fail, the operating cycle format (OC) has revealed great potential in describing road operations in a way that is, to a large extent, independent of both vehicle and driver. More specifically, the framework consists of three levels of representation. The first, called the bird\u27s-eye view, serves mainly as a classification tool and makes use of metrics and labels to completely characterise the overall application of a vehicle during its lifetime. The second description, the stochastic operating cycle (sOC), condenses the main properties of a road operation using elementary statistics. It is conceived as an intermediate representation with a higher resolution. Finally, the deterministic operating cycle (dOC) is the most detailed description of a transport mission and collects deterministic models to be used in simulations.In previous studies, the OC format was demonstrated to work in theory, but some margins for improvement could still be identified. Furthermore, the benefits deriving from the use of the OC were explored only partially.The first objective of this thesis consists in extending the OC representation to include stochastic models for weather, traffic, and mission properties, which were missing in the original formulation. The new models are built to be parsimonious and to facilitate parametrisation and implementation starting from real data. This enables reproducing and simulating realistic environments where a transport mission may take place, with a substantial gain in accuracy.The second purpose of this work is to showcase how the OC concept can be used in practical applications concerning the design and sale phases. To this end, the relationships existing between the three levels of representation included in the format are formalised mathematically by exploiting the stochastic nature of the sOC, which acts as a bridge between the bird’s-eye view and the dOC. It is argued that the three descriptions can work synergically to support manufacturers in their internal processes of classification, optimal development and selection, and virtual testing of energy-efficient vehicles
Replenishing the pipeline: A quantitative approach to optimising the sourcing of new projects
Full text linkLarge pharmaceutical companies maintain a portfolio of assets, some of which are projects under development while others are on the market and generating revenue. The budget allocated to R&D may not always be sufficient to fund all the available projects for development. Much attention has been paid to the selection of optimal subsets of available projects to fit within the available budget. In this paper, we argue the need for a forward-looking approach to portfolio decision-making. We develop a quantitative model that allows the portfolio management to evaluate the need for future inflow of new projects to achieve revenue at desired levels, often aspiring to a certain annual revenue growth. Optimisation methods are developed for the presented model, allowing an optimal choice of number, timing and type of projects to be added to the portfolio. The proposed methodology allows for a proactive approach to portfolio management, prioritisation, and optimisation. It provides a quantitatively based support for strategic decisions regarding the efforts needed to secure the future development pipeline and revenue stream of the company
A novel vented tunnel hood with decreasing open ratio to mitigate micro-pressure wave emitted at high-speed maglev tunnel exit
No full textThe significant increase in train speed contributes to stronger vehicle/tunnel coupling aerodynamic effect, especially on the intensity of the micro-pressure wave (MPW) emitted at high-speed maglev tunnel exit. Hence when the train speed reaches 600 km/h and more, how to effectively mitigate the MPW becomes a challenge for aerodynamic researchers. In this study, a novel vented tunnel hood with the decreasing open ratio along the enlarged cross-section wall was proposed, while one consistent and two inconsistent layouts of the hoods applied at the tunnel portals were attempted to obtain a better hood combination for the mitigation of MPW. In addition, the sliding mesh technique was used to simulate the train passing through the single-track high-speed maglev tunnel. The validation of the methodology has been carried out to compare with the previous moving model test results. The peak variations of pressure wave and MPW were analysed in combination with the grid-independence study and numerical validation. The new hoods installed consistently at the tunnel portals (entrance and exit), can reduce the maximums of MPWs at required locations, i.e., 20m and 50m from the tunnel exit, by 66.9% and 40.9% respectively, when compared to the existing unvented tunnel hood; however, when the new hood at the tunnel exit is replaced by the existing tunnel hood without vents, the maximums of MPWs at the corresponding 20m and 50m are significantly increased by 79.1% and 71.0%. After changing the set-up of the inconsistent hoods, i.e., the tunnel entrance hood is unvented and this novel hood is installed at the tunnel exit, the corresponding MPW peaks can be reduced by 84.0% and 71.1%. Therefore, the hoods at both of tunnel entrance and exit can affect the variations of MPWs, and a reasonable arrangement of the hood openings at tunnel portals can effectively mitigate the MPW emitted at the high-speed maglev tunnel exit