Packing 16, 17 of 18 circles in an equilateral triangle

We present new, efficient packings for 16, 17 and 18 congruent circles in an equilateral triangle. The results have been found by the use of simulated annealing and a quasi-Newton optimization technique, supplemented with some human intelligence

Fast movement strategies for a step-and-scan wafer stepper

We describe algorithms for the determination of fast movement strategies for a step-and-scan wafer stepper, a device that is used for the photolithographic processing of integrated circuits. The proposed solution strategy consists of two parts. First, we determine the maximum number of congruent rectangular chips that can be packed on a wafer, subject to the restriction that the chips are placed in a rectangular grid. Second, we find fast movement strategies for scanning all chips of a given packing, given the mechanical restrictions of the wafer stepper. The corresponding combinatorial optimization problem is formulated as a generalized asymmetric traveling salesman problem. We show how feasible scan strategies are determined, and how these strategies are improved by local search techniques, such as iterative improvement based on 2- and 3-exchanges, and simulated annealing based on 2-exchanges.\ud \u

Improved coverings of a square with six and eight equal circles

In a recent article, Tarnai and Gáspár used computer simulations to find thin coverings of a square with up to ten equal circles. We will give improved coverings with six and eight circles and a new, thin covering with eleven circles, found by the use of simulated annealing. Furthermore, we present a combinatorial method for constructing lower bounds for the optimal covering radius

Rebel diplomacy and digital communication: public diplomacy in the Sahel

Most research on social media as a tool for public diplomacy focuses on its use by recognized international actors to advance their national interest and reputation, deliver foreign policy objectives or promote their global interests. This article highlights the need for paying more attention to non-state diplomacy in conflict situations outside the western world. We examine how rebel groups use new media to enhance their communications, and what the motivations behind this are. Our public diplomacy perspective helps convey the scope of rebel communications with external actors and provides insights for policy-makers seeking to ascertain the nature, intentions and capacities of myriad rebel groups. Our focus is on the Sahel region, where numerous such groups vying for international attention and support make use of multiple social media channels. We analyse two groups in Mali: the MNLA, a Tuareg secessionist group; and Ansar Dine, a Salafist insurgency with ties to Al-Qaeda in the Islamic Maghreb. Our qualitative analysis of Ansar Dine and MNLA communications on several digital platforms helps identify these African rebel groups' international and local framing activities. Rebel groups use public diplomacy nimbly and pragmatically. The digital age has fundamentally changed which stakeholders such groups can reach, and we suggest that social media increase the power they are able to carve out for themselves on the international stage

Critical issues in sustainability - Part III

This booklet is the third of its kind and, as such, the sequel to ‘Critical Issues in Sustainability – Part I’ and ‘Critical Issues in Sustainability – Part II’. It contains several of our reflections as they have appeared in writing throughout 2020, notably but not exclusively through opinion articles. Just as much as we hope this booklet will challenge your ideas and actions and will provide you with the inspiration to change our world for the better, we hope it will be the ancestor of our and others’ future work. In any case, we invite you to let us know what you think about it and how we might join force

Addressing sustainability in hotel management education: designing a curriculum based on input from key stakeholders

This paper reports on combining generic reference points that can be distilled from literature with the analysis of 18 face-to-face interviews with relevant stakeholders as input for designing a sustainability course within a (higher education) hotel management curriculum. The train of thought presented here shows that by using this input as design parameters for a curriculum, education could serve as a crucial catalyst and change agent for a societal transition towards sustainable development. It shows that this is also true and relevant, maybe even especially, for the hospitality industry. Subsequently, it is explained that for the specific hotel management education addressed in this paper to fulfil this role, the sustainability course incorporated in its curriculum needs to combine various components and approaches. It needs to provide students with an ethical framework that helps them develop a reflective attitude towards their own and others’ actions and decisions. This framework needs to focus on generic values and norms, but also on envisioning practical social, ecological and economic consequences. Therefore, it also needs to help students acquire the knowledge and develop the skills required to envision and discuss these consequences, also with involved stakeholders, and (jointly) devise context-dependent solutions.Keywords: hospitality industry, sustainable development, education for sustainability (EfS

Towards a simplified description of thermoelectric materials: Accuracy of approximate density functional theory for phonon dispersions

We calculate the phonon-dispersion relations of several two-dimensional materials and diamond using the density-functional based tight-binding approach (DFTB). Our goal is to verify if this numerically efficient method provides sufficiently accurate phonon frequencies and group velocities to compute reliable thermoelectric properties. To this end, the results are compared to available DFT results and experimental data. To quantify the accuracy for a given band, a descriptor is introduced that summarizes contributions to the lattice conductivity that are available already in the harmonic approximation. We find that the DFTB predictions depend strongly on the employed repulsive pair-potentials, which are an important prerequisite of this method. For carbon-based materials, accurate pair-potentials are identified and lead to errors of the descriptor that are of the same order as differences between different local and semi-local DFT approaches