On the integration of diverging material flows into resource‐constrained project scheduling

This study deals with an extension of the resource-constrained project scheduling problem (RCPSP) by constraints on material flows released during the execution of project activities. These constraints arise from limited processing capacities for materials and maximum inventories of intermediate storage facilities. Production scheduling problems with converging material flows have been studied extensively. However, this is the first project scheduling problem integrating diverging material flows typically observed in dismantling projects, e.g., building deconstruction, power plant decommissioning, or battery/car decommissioning. Diverging material flows do not directly impact the project planning but only impose delays in the case of congestion. We model material flows by using operations that represent the processing of materials, and cumulative resources that represent storage facilities. As a method for efficiently generating starting solutions, we propose a schedule generation scheme tailored to the particular precedence structure of such problems. Furthermore, we extensively study the schedule generation scheme’s performance on generated test instances and compare it to the constraint programming solver IBM ILOG CP Optimizer. It turns out that the solution quality strongly depends on the employed model and that neither of the two solution methods is generally superior

Instance dataset for resource-constrained project scheduling with diverging material flows

This data article describes an instance dataset motivated by the problem of scheduling a project with diverging material flows. Such material flows are released during the execution of the project and are subject to limited processing and storage capacities. Typical examples are nuclear dismantling or other deconstruction/demolition projects, where large amounts of material must be classified, scanned for hazardousness, and processed accordingly. The problem setting is mathematically described as a resource-constrained project scheduling problem with cumulative resources (RCPSP/c). The RCPSP/c deals with finding a project schedule with minimal makespan that satisfies temporal, renewable resource, and cumulative resource constraints. In total, the dataset comprises 192 artificially generated instances that are suitable for testing models and solution methods. In addition, we provide our best found solution for each instance and different modeling variants (e.g., for two types of objective functions). These solutions were computed by heuristic solution methods. The dataset serves as a benchmark for researchers evaluating the performance of solution methods for the RCPSP/c or the more general problem class with resources that can be produced and consumed

Quantum key distribution for data center security -- a feasibility study

Data centers are nowadays referred to as the digital world's cornerstone. Quantum key distribution (QKD) is a method that solves the problem of distributing cryptographic keys between two entities, with the security rooted in the laws of quantum physics. This document provides an assessment of the need and opportunity for ushering QKD in data centers. Together with technical examples and inputs on how QKD has and could be integrated into data-center like environments, the document also discusses the creation of value through future-proof data security as well as the market potential that QKD brings on the table through e.g., crypto-agility. While primarily addressed to data center owners/operators, the document also offers a knowledge base to QKD vendors planning to diversify to the data center market segment.Comment: 23 pages, 7 figures, study initiated and supported by Copenhagen Fintech (see https://www.copenhagenfintech.dk/projects/using-qkd-for-data-center-security

A Primer on the Differential Calculus of 3D Orientations

The proper handling of 3D orientations is a central element in many optimization problems in engineering. Unfortunately many researchers and engineers struggle with the formulation of such problems and often fall back to suboptimal solutions. The existence of many different conventions further complicates this issue, especially when interfacing multiple differing implementations. This document discusses an alternative approach which makes use of a more abstract notion of 3D orientations. The relative orientation between two coordinate systems is primarily identified by the coordinate mapping it induces. This is combined with the standard exponential map in order to introduce representation-independent and minimal differentials, which are very convenient in optimization based methods

Shallow landslide disposition in burnt European beech (Fagus sylvatica L.) forests

Tree roots contribute significantly to soil strength on hillslopes. In the case of wildfires, this effect may abruptly vanish and be lacking for a considerable period of time depending on the resistance and resilience of the forest. Despite its importance, quantitative data on the impact and dynamics of wildfires on slope stabilization is still lacking. We use the study case of the Fagus sylvatica L. to quantify the medium-term evolution of root reinforcement and its effect on slope stability in fire-injured forests. In the study, we upscale root reinforcement using field data for the calibration of the Root Bundle Model and detailed information on forest structure in 244 plots, and calculate the spatio-temporal dynamics of forest protective capacity using a three-dimensional probabilistic slope stability model (slideforNET) for different site types. In unburnt and low-burn forests, the protective capacity was found to remain constant over time. Forests hit by moderate burns continue to provide adequate protection for shallow (depth < 0.5 m) and cohesive soils only, whereas in the case of high severity fires, the protective capacity vanishes for 15 years and an increased shallow landslide probability remains for at least 40 years. These conditions call for appropriate sylvicultural post-fire measures

Quadrupedal Robots with Stiff and Compliant Actuation

In the broader context of quadrupedal locomotion, this overview article introduces and compares two platforms that are similar in structure, size, and morphology, yet differ greatly in their concept of actuation. The first, ALoF, is a classically stiff actuated robot that is controlled kinematically, while the second, StarlETH, uses a soft actuation scheme based on Changedhighly compliant series elastic actuators. We show how this conceptual difference influences design and control of the robots, compare the hardware of the two systems, and show exemplary their advantages in different application