υ-representability of one-body density matrices

We consider low-dimensional model systems with a fixed two-body interaction and a variable (nonlocal) one-body potential. It is shown explicitly that an extended domain of allowed (N-representable) one-body density matrices cannot be generated in this way, the excluded domain depending on the two-body interaction under consideration. This stands in contrast to the behavior of the diagonal part of the density matrix

Circular economy indicators : what do they measure?

Circular Economy (CE) is a growing topic, especially in the European Union, that promotes the responsible and cyclical use of resources possibly contributing to sustainable development. CE is an umbrella concept incorporating different meanings. Despite the unclear concept, CE is turned into defined action plans supported by specific indicators. To understand what indicators used in CE measure specifically, we propose a classification framework to categorise indicators according to reasoning on what (CE strategies) and how (measurement scope), Despite different types, CE strategies can be grouped according to their attempt to preserve functions, products, components, materials, or embodied energy; additionally, indicators can measure the linear economy as a reference scenario. The measurement scope shows how indicators account for technological cycles with or without a Life Cycle Thinking (LCT) approach; or their effects on environmental, social, or economic dimensions. To illustrate the classification framework, we selected quantitative micro scale indicators from literature and macro scale indicators from the European Union 'CE monitoring framework'. The framework illustration shows that most of the indicators focus on the preservation of materials, with strategies such as recycling. However, micro scale indicators can also focus on other CE strategies considering LCT approach, while the European indicators mostly account for materials often without taking LCT into account. Furthermore, none of the available indicators can assess the preservation of functions instead of products, with strategies such as sharing platforms, schemes for product redundancy, or multifunctionality. Finally, the framework illustration suggests that a set of indicators should be used to assess CE instead of a single indicator

Unit Process Impact Assessment for Discrete Part Manufacturing: A State of the Art

Manufacturing processes, as used for discrete part manufacturing, are responsible for a substantial part of the environmental impact of products, but are still poorly documented in terms of their environmental footprint. The lack of thorough analysis of manufacturing processes has as consequence that optimization opportunities are often not recognized and that improved machine tool design in terms of ecological footprint has only been targeted for a few common processes. To address these shortcomings, a worldwide consortium of universities and research institutes launched the CO2PE! – Initiative (Cooperative Effort on Process Emissions in Manufacturing) [1]. This paper starts with an overview of the current shortcomings in terms of the coverage of production steps during LCA studies with existing tools. Further on, the CO2PE! - methodology used to analyze manufacturing unit processes is summarized and some initial case studies conducted at the K.U.Leuven, which allowed to identify significant improvement potential, are presented.status: publishe

Machine tool oriented ecodesign perspectives based on systematic manufacturing process impact assessment

To address the lack of thorough environmental analysis of manufacturing processes, a worldwide consortium of universities and research institutes recently launched the CO2PE! (Cooperative Effort on Process Emissions in Manufacturing) initiative. In addition to life cycle analysis, in depth process analysis also provides insight in achievable emission reducing measures towards machine builders and eco-design recommendations for product developers. Influences of choices, made during the manufacturing stage, on the environmental impact of a product could be indicated. In this paper, first an overview is offered of the methodology used to analyze manufacturing unit processes. In a second part, the focus is on promising ecodesign perspectives for both, production machines and products. Some initial case studies conducted at the K.U.Leuven, illustrating the effectiveness of the developed methodology, are presented.This paper received the Best Paper Award on the 6th International Symposium on Environmentally Conscious Design and Inverse Manufacturing (EcoDesign 2009), 7-9 December 2009, Sapporo, Japanstatus: publishe

Environmental data collection and analysis of discrete part manufacturing processes: results of some case studies

status: publishe

Environmental Analysis of the Air Bending Process

This paper presents the results of a data collection effort, allowing to assess the overall environmental impact of the air bending process using the CO2PE!-Methodology. First the different modes of the air bending process are investigated, including both productive and non-productive modes. In particular consumption of electric power is recorded for the different modes. Subsequently, time studies allow determining the importance of productive and non-productive modes of the involved process. The study demonstrates that the influence of standby losses can be substantial. In addition to life cycle analysis, in depth process analysis also provides insight in achievable environmental impact reducing measures towards machine tool builders and eco-design recommendations for product developers. The energy consumption of three different machine tool architectures are analysed and compared within this paper.status: publishe

THE CO2PE!-INITIATIVE (COOPERATIVE EFFORT ON PROCESS EMISSIONS IN MANUFACTURING): International Framework for Sustainable Production

Manufacturing processes are responsible for a substantial part of the environmental impact of products but are still poorly documented in terms of their environmental footprint. The lack of thorough analysis of manufacturing processes has as consequence that optimization opportunities are often not recognized and that improved machine tool design in terms of ecological footprint has only been targeted for a few common processes. At the same time, a trend can be observed towards more energy intensive, unconventional processing techniques. In order to address these shortcomings, a worldwide consortium of universities and research institutes launched the CO2PE!–Initiative. This initiative has as objective to coordinate international efforts aiming to document and analyze the overall environmental impact for a wide range of available and emerging manufacturing processes with respect to direct and indirect emissions, and to provide guidelines to improve these processes. In addition to life cycle analysis, in depth process analysis also provides insight in achievable environmental impact reducing measures towards machine builders and eco-design recommendations for product developers. In this paper, the CO2PE!-Initiative is described along with an overview of case studies to illustrate how the CO2PE! methodology works.status: publishe

Energy efficient trajectories for an industrial ABB robot

This paper presents a systematic methodology for on-site identification and energy-optimal path planning of an industrial robot. The identification experiments are carried out on-site, in a quick, non-invasive way using a CA8335 Qualistar three-phase electrical networks analyser. Next, the collected data is compared with a parametrised dynamic robot model in an optimisation routine. This routine results in the specification of a parametric dynamic robot model. The model is used as a dynamic constraint for a model predictive control problem, where other physical constraints are added i.e. the limited workspace and the constraints on the joint velocities and accelerations. A sequential quadratic programming solver is used to minimise a mechanical energy based cost function. The resulting energy-optimal path is translated into custom robot commands executable on an industrial robot. The systematic methodology is validated on an IRB1600 industrial ABB robot performing a custom pick-and- place operation. The obtained dynamic robot model is given and compared to the collected measurements. To demonstrate the possibility of energy saving by ‘intelligently’ programming a robot trajectory the energy and time-optimal paths are generated taking all physical constraints into account. Simulation results show a significant time and energy improvement (up to 5%) compared to most trajectories generated by the ABB software. The most remarkable result is that the fastest energy-optimal trajectory turns out to be 4% more energy efficient and 3% faster then the commercially available fastest trajectory. Additional stand-still experiments show that activation of the brakes is favored over an actuated stand-still from an energy point of view, assuming that the start-up time when releasing the brakes is limited.status: publishe

Energy Efficiency of Sheet Metal Working Processes - Where do we stand today?

Due to increasing energy and resource costs at the one hand and upcoming regulations on energy and resource efficiency at the other, a growing interest of machine tool builders to the environmental performance of their machine tools can be observed today. The last decade, academic as well as industrial research groups started to assess the energy demand of discrete part manufacturing processes and indicated a significant potential for improvement. In contrast to conventional machining processes (e.g. milling, turning…), (sheet) metal forming processes are still less well documented in terms of their energy demand. In consequence, potential energy efficiency improvement measures for these processes are often not yet recognized. This contribution provides a short discussion on energy assessment methods followed by a structured overview of available studies on the energy demand of (sheet) metal forming processes. A range of identified energy efficiency improvement measures, suitable for these processes, is presented and quantified.status: publishe

Exergy Efficiency Definitions for Manufacturing Processes

The original application of thermodynamic metrics for manufacturing processes has been under development throughout the last decade. The metrics are based on the second law of thermodynamics. Therefore, the exergy value of both input and output streams is used to quantify them. Different definitions of exergy efficiency metric have been employed in previous studies. This difference may hamper its application outside the academic setting. This paper presents comparisons between different definitions for a variety of manufacturing processes. The objectives are to determine the applicability of each definition for specific processes and to demonstrate why more robust definitions still require development.status: publishe