944 research outputs found
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
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