Generating Instructions at Different Levels of Abstraction

When generating technical instructions, it is often convenient to describe complex objects in the world at different levels of abstraction. A novice user might need an object explained piece by piece, while for an expert, talking about the complex object (e.g. a wall or railing) directly may be more succinct and efficient. We show how to generate building instructions at different levels of abstraction in Minecraft. We introduce the use of hierarchical planning to this end, a method from AI planning which can capture the structure of complex objects neatly. A crowdsourcing evaluation shows that the choice of abstraction level matters to users, and that an abstraction strategy which balances low-level and high-level object descriptions compares favorably to ones which don't.Comment: Accepted COLING 2020 long pape

Effect of Process Parameters and High-Temperature Preheating on Residual Stress and Relative Density of Ti6Al4V Processed by Selective Laser Melting

The aim of this study is to observe the effect of process parameters on residual stresses and relative density of Ti6Al4V samples produced by Selective Laser Melting. The investigated parameters were hatch laser power, hatch laser velocity, border laser velocity, high-temperature preheating and time delay. Residual stresses were evaluated by the bridge curvature method and relative density by the optical method. The effect of the observed process parameters was estimated by the design of experiment and surface response methods. It was found that for an effective residual stress reduction, the high preheating temperature was the most significant parameter. High preheating temperature also increased the relative density but caused changes in the chemical composition of Ti6Al4V unmelted powder. Chemical analysis proved that after one build job with high preheating temperature, oxygen and hydrogen content exceeded the ASTM B348 limits for Grade 5 titanium

Prospects of carbon capture and storage (CCS) in India's power sector : an integrated assessment

Objective: The aim of the present article is to conduct an integrated assessment in order to explore whether CCS could be a viable technological option for significantly reducing future CO2 emissions in India. Methods: In this paper, an integrated approach covering five assessment dimensions is chosen. However, each dimension is investigated using specific methods (graphical abstract). Results: The most crucial precondition that must be met is a reliable storage capacity assessment based on site-specific geological data since only rough figures concerning the theoretical capacity exist at present. Our projection of different trends of coal-based power plant capacities up to 2050 ranges between 13 and 111 Gt of CO2 that may be captured from coal-fired power plants to be built by 2050. If very optimistic assumptions about the country's CO2 storage potential are applied, 75 Gt of CO2 could theoretically be stored as a result of matching these sources with suitable sinks. If a cautious approach is taken by considering the country's effective storage potential, only a fraction may potentially be sequestered. In practice, this potential will decrease further with the impact of technical, legal, economic and social acceptance factors. Further constraints may be the delayed commercial availability of CCS in India, a significant barrier to achieving the economic viability of CCS, an expected net maximum reduction rate of the power plant’s greenhouse gas emissions of 71-74%, an increase of most other environmental and social impacts, and a lack of governmental, industrial or societal CCS advocates. Conclusion and practice implications: Several preconditions need to be fulfilled if CCS is to play a future role in reducing CO2 emissions in India, the most crucial one being to determine reliable storage capacity figures. In order to overcome these barriers, the industrialised world would need to make a stronger commitment in terms of CCS technology demonstration, cooperation and transfer to emerging economies like India. The integrated assessment might also be extended by a comparison with other low-carbon technology options to draw fully valid conclusions on the most suitable solution for a sustainable future energy supply in India

Integrated assessment of carbon capture and storage (CCS) in South Africa's power sector

This article presents an integrated assessment conducted in order to explore whether carbon capture and storage (CCS) could be a viable technological option for significantly reducing future CO2 emissions in South Africa. The methodological approach covers a commercial availability analysis, an analysis of the long-term usable CO2 storage potential (based on storage capacity assessment, energy scenario analysis and source-sink matching), an economic and ecological assessment and a stakeholder analysis. The findings show, that a reliable storage capacity assessment is needed, since only rough figures concerning the effective capacity currently exist. Further constraints on the fast deployment of CCS may be the delayed commercial availability of CCS, significant barriers to increasing the economic viability of CCS, an expected net maximum reduction rate of the power plant's greenhouse gas emissions of 67%-72%, an increase in other environmental and social impacts, and low public awareness of CCS. One precondition for opting for CCS would be to find robust solutions to these constraints, taking into account that CCS could potentially conflict with other important policy objectives, such as affordable electricity rates to give the whole population access to electricity

Da kocht was hoch : wozu brauchen wir die CCS-Technologie?

Bis vor wenigen Jahren diskutierten vor allem Energieversorger und Umweltverbände über die Abscheidung und Lagerung von CO2. Mittlerweile ist die öffentliche Wahrnehmung von CCS gestiegen. Dabei dürfte die umstrittene Technologie für Deutschlands Kraftwerke weit weniger bedeutsam sein als für energiehungrige Schwellenländer

Integrated assessment of carbon capture and storage (CCS) in the German power sector and comparison with the deployment of renewable energies

If the current energy policy priorities are retained, there may be no need to focus additionally on carbon capture and storage (CCS) in the power plant sector of Germany. This applies even in the case of ambitious climate protection targets, according to the results of the presented integrated assessment study. These cover a variety of aspects: Firstly, the technology is not expected to become available on a large scale in Germany before 2025. Secondly, if renewable energies and combined heat and power are expanded further and energy productivity is enhanced, there is likely to be only a limited demand for CCS power plants, as a scenario analysis of CCS deployment in Germany shows. Thirdly, cost analysis using the learning curve approach shows that the electricity generation costs of renewable electricity approach those of CCS power plants. This leads to the consequence that, from 2020, several renewable technologies may well be in a position to offer electricity at a cheaper rate than CCS power plants. In addition, a review of new life cycle assessments for CO2 separation in the power plant sector indicates that the greenhouse gas emissions from 1 kW h of electricity generated by first-generation CCS power plants could only be reduced by 68 % to 87 % (95 % in individual cases). Finally, a cautious, conservative estimate of the effective German CO2 storage capacity of approximately 5 billion tonnes of CO2 is calculated, including a fluctuation range yielding values between 4 and 15 billion tonnes of CO2. Therefore, the total CO2 emissions caused by large point sources in Germany could be stored for 12 years (basic value) or for 8 or 33 years (sensitivity values)