Hexagonal High-Entropy Alloys

We report on the discovery of a high-entropy alloy with a hexagonal crystal structure. Equiatomic samples in the alloy system Ho-Dy-Y-Gd-Tb were found to solidify as homogeneous single-phase high-entropy alloys. The results of our electron diffraction investigations and high-resolution scanning transmission electron microscopy are consistent with a Mg-type hexagonal structure. The possibility of hexagonal high-entropy alloys in other alloy systems is discussed.Comment: Changes upon replacement: inserted submission date of manuscript to journal. No other changes were mad

A single-phase bcc high-entropy alloy in the refractory Zr-Nb-Ti-V-Hf system

We report on the production and characterization of a high-entropy alloy in the refractory Zr-Nb-Ti-V-Hf system. Equiatomic ingots were produced by arc and levitation melting, and were subsequently homogenized by high-temperature annealing. We obtained a coarse-grained, single-phase high-entropy alloy, with a homogeneous distribution of the constituting elements. The phase is a chemically disordered solid solution, based on a bcc lattice with a lattice parameter of 0.336(5) nm.Comment: 6 pages, 4 figure

Tiling models for metadislocations in AlPdMn approximants

The AlPdMn quasicrystal approximants xi, xi', and xi'_n of the 1.6 nm decagonal phase and R, T, and T_n of the 1.2 nm decagonal phase can be viewed as arrangements of cluster columns on two-dimensional tilings. We substitute the tiles by Penrose rhombs and show, that alternative tilings can be constructed by a simple cut and projection formalism in three dimensional hyperspace. It follows that in the approximants there is a phasonic degree of freedom, whose excitation results in the reshuffling of the clusters. We apply the tiling model for metadislocations, which are special textures of partial dislocations.Comment: 7 pages, 2 figures, Proceedings of International Conference on Quasicrystals

Economy-wide Modelling of Seasonal Labour and Natural Resource Policies

Die vorliegende Dissertation widmet sich methodischen und empirischen Forschungsfragen mit Bezug auf saisonale Arbeitsmärkte und Politiken zur nachhaltigen Nutzung natürlicher Ressourcen. Hierfür wird ein gesamtwirtschaftlicher Modellierungsansatz angewendet, für den das im südöstlichen Himalaya gelegene Königreich Bhutan als empirische Fallstudie dient. Das methodische Forschungsziel der Arbeit ist, die Relevanz der Darstellung von saisonalen Arbeitsmärkten innerhalb von allgemeinen Gleichgewichtsmodellen (sog. CGE Modelle) zu ergründen. Dies stellt eine Neuheit in der Literatur dar. Die Arbeit zeigt auf, dass Modelle ohne saisonale Arbeitsmärkte systematisch Ergebnisse, wie Angebotsreaktionen und Wohlstandseffekte, verzerren. Die Saisonalität von Arbeit hat eine hohe Relevanz für gesamtwirtschaftliche Analysen im Kontext landwirtschaftlich geprägter Volkswirtschaften, insbesondere für Untersuchungen des Strukturwandels und agrarpolitischer Interventionen. Empirisch wird die wechselseitige Abhängigkeit von Politiken zum nachhaltigen Management natürlicher Ressourcen mit Zielen des Umweltschutzes und der ländlichen Entwicklung untersucht. Basierend auf unterschiedlichen Modellierungsansätzen, konzentrieren sich drei Studien auf agrar- und forstpolitische Szenarien in Bhutan. Es wird gezeigt, dass Bhutans Ziel, seinen landwirtschaftlichen Sektor auf 100% ökologische Landwirtschaft umzustellen, zu substantiellen Wohlfahrtsverlusten und negativen Folgen für die Ernährungssicherung führen würde. Die Analyse verschiedener forstpolitischer Szenarien demonstriert, dass eine höhere Forstnutzung in Bhutan im Sinne der gesamtwirtschaftlichen und ländlichen Entwicklung nachhaltig möglich ist. Die Arbeit weist auf verschiedene zukünftige Forschungsfelder hin, wie zum Beispiel die Integration von Ökosystemdienstleistungen, was als eine der wesentlichen Einschränkungen bei der modellgestützten Analyse von Politiken zur Nutzung natürlicher Ressourcen identifiziert wurde.Using an economy-wide modelling approach, this dissertation investigates methodological and empirical research questions related to seasonal labour markets and natural resource policies. The Kingdom of Bhutan, located in the south-eastern Himalayas, serves as a case study. The methodological research objective of this thesis is to gain an understanding of the relevance of seasonal labour markets in the context of economy-wide modelling. The depiction of seasonal labour markets at national scale using a seasonal social accounting matrix (SAM) and computable general equilibrium (CGE) model presents a novel development within the literature. It is demonstrated, that the absence of seasonal labour markets leads to systematic bias of model results. The consequences are distorted supply responses and biased welfare effects, underlining the pivotal implications of seasonality for economy-wide analysis in the context of agrarian economies, particularly for scenario analysis involving structural changes and agricultural policy interventions. The empirical research objective addresses the interdependence of natural resource policies with objectives of environmental conservation and rural development. Employing modelling techniques, three studies focus on specific agricultural and forest policy scenarios in Bhutan. Simulating Bhutan’s ambitious policy objective to convert to 100% organic agriculture demonstrates substantial welfare losses and adverse impacts on food security, causing trade-offs with objectives of rural development and food self-sufficiency. Analysing forest policy reforms shows that increased forest utilization contributes to economic development, particularly in rural areas, without jeopardizing the country’s forest conservation agenda. The dissertation points at numerous areas of future research, as for example the incorporation of ecosystem services, which is identified as one key limitation of economy-wide analysis of natural resource policies

Perturbative Check of the Action and Energy Lattice Sum Rules

Lattice sum rules are checked using lattice perturbation theory. The action sum rule gives a relation between the quark-antiquark potential, its logarithmic derivative with respect to distance and the expectation value of the action; the energy sum rule expresses the potential as the sum of the energy in the gluon fields and of an anomalous term. Two different independent calculations of the quark-antiquark potential are presented, and the transversality of the gluonic vacuum polarization on the lattice is proven. The crucial part of the action sum rule is an identity whose explicit check using perturbation theory provides methods and results which are useful for checking the energy sum rule. Additionally, the gauge invariance of the expectation value of the Wilson loop up to next-to-leading order is proven. The possibility of restricting the expectation value of the action to one fixed time slice is discussed. The energy sum rule is checked perturbatively up to next-to-leading order and shown to be satisfied with good numerical accuracy. The various contributions to the quark-antiquark potential are analyzed, and the restriction of the expectation value of the sum over all spatial plaquettes (the energy in the magnetic fields) to one fixed time slice is examined.Comment: PhD Thesis, 126 pages, 20 figure

Cleaved surface of i-AlPdMn quasicrystals: Influence of the local temperature elevation at the crack tip on the fracture surface roughness

Roughness of i-AlPdMn cleaved surfaces are presently analysed. From the atomic scale to 2-3 nm, they are shown to exhibit scaling properties hiding the cluster (0.45 nm) aperiodic structure. These properties are quantitatively similar to those observed on various disordered materials, albeit on other ranges of length scales. These properties are interpreted as the signature of damage mechanisms occurring within a 2-3 nm wide zone at the crack tip. The size of this process zone finds its origin in the local temperature elevation at the crack tip. For the very first time, this effect is reported to be responsible for a transition from a perfectly brittle behavior to a nanoductile one.Comment: 8 page

Labour‐saving technologies in smallholder agriculture: An economy‐wide model with field operations

Labour-saving technologies are relevant for agricultural development. Yet, as this study shows, they are poorly integrated into agricultural production functions of economy-wide models. We report a computable general equilibrium (CGE) model, which explicitly incorporating field operations (e.g. land preparation, weeding or harvesting) in the context of smallholder agriculture. The field operations approach allows to model technological trade-offs in organic and conventional production systems at various stages of the agricultural production process. Simulating a structural change scenario, we compare the performance of the field operations approach with published benchmark production structures by assessing how they replicate empirically observed changes in land and agrochemical use. This benchmark analysis shows that incorporating field operations replicates the observed empirical changes most accurately and allows for more realistic modelling of labour-saving technologies. We use the field operations model to investigate three policy options to mitigate labour shortages in the agricultural sector of Bhutan. Permitting the employment of Indian workers in agriculture has the highest short-term potential in this respect. We find that subsidising agricultural machinery hiring services and removing import tariffs on agrochemical inputs are found to be less effective. Further options for model developments, such as combining field operations and labour market seasonality, are highlighted.Stiftung fiat panis, Ulm, Germany http://dx.doi.org/10.13039/501100011087Humboldt‐Universität zu Berlin http://dx.doi.org/10.13039/501100006211Peer Reviewe