2,699 research outputs found
Stochastic model of dispersive multi-step polarization switching in ferroelectrics due to spatial electric field distribution
A stochastic model for polarization switching in tetragonal ferroelectric
ceramics is introduced, which includes sequential 90{\deg}- and parallel
180{\deg}-switching processes and accounts for the dispersion of characteristic
switching times due to a nonuniform spatial distribution of the applied field.
It presents merging of the recent multistep stochastic mechanism (MSM) with the
earlier nucleation limited switching (NLS) and inhomogeneous field mechanism
(IFM) models. The new model provides a much better description of simultaneous
polarization and strain responses over a wide time window and a deeper insight
into the microscopic switching mechanisms, as is exemplarily shown by
comparison with measurements on lead zirconate titanate.Comment: 11 pages, 3 figure
Architectural Information Modelling in Construction History
The past few years show a significant increase in the usage of three-dimensional modelling and semantic description techniques for architectural research purposes. Where this increase has already shaped today’s design and construction industry, research in architectural and construction history can still improve its work methods and results through these techniques. Therefore, we propose a new conceptual approach for Architectural Information Modelling (AIM), which aims at describing historical information in construction and architecture directly related to design information and design practice. This paper will give an introduction into existing 3D modelling techniques and semantic description techniques, continuing with how these techniques are applied in the AIM approach. This investigation of 3D modelling and semantic technology shows promising results. However, in order to integrate these techniques into an AIM framework, more work is needed. Future work in this research project will therefore explore in further detail the semantic description scheme proposed below and the implementation of a proof-of-concept
Countably determined ends and graphs
The directions of an infinite graph are a tangle-like description of its
ends: they are choice functions that choose compatibly for all finite vertex
sets a component of . Although every direction is
induced by a ray, there exist directions of graphs that are not uniquely
determined by any countable subset of their choices. We characterise these
directions and their countably determined counterparts in terms of star-like
substructures or rays of the graph. Curiously, there exist graphs whose
directions are all countably determined but which cannot be distinguished all
at once by countably many choices. We structurally characterise the graphs
whose directions can be distinguished all at once by countably many choices,
and we structurally characterise the graphs which admit no such countably many
choices. Our characterisations are phrased in terms of normal trees and
tree-decompositions. Our four (sub)structural characterisations imply
combinatorial characterisations of the four classes of infinite graphs that are
defined by the first and second axiom of countability applied to their end
spaces: the two classes of graphs whose end spaces are first countable or
second countable, respectively, and the complements of these two classes.Comment: 17 pages, 2 figure
Development and characterization of composites consisting of woven fabrics with integrated prismatic shaped cavities
Composites are extensively used in automotive, construction, airplanes, wind turbines etc. because of their good mechanical properties such as high specific stiffness, high specific strength and resistance against fatigue. The main issues with composites are delamination and the manual labour in the production process. If hollow structures like stiffeners need to be manufactured, these problems become even more apparent. As a result, there is a lot of interest in woven fabrics with integrated prismatic shaped cavities for composites as they reduce the manual labour, have a higher resistance against delamination and can lead to special properties and applications. In this work several of these woven fabrics with integrated prismatic shaped cavities are designed and produced in high-tenacity polyester yarns. Then, the possibility to use these fabrics in composites is explored: reproducibility of the production process is assessed and static testing is performed. A reproducible production process is developed and static testing shows promising results
Prevention or Control: Optimal Government Policies for Invasive Species Management
We present a conceptual, but empirically applicable, model for determining the optimal allocation of resources between exclusion and control activities for managing an invasive species with an uncertain discovery time. This model is used to investigate how to allocate limited resources between activities before and after the first discovery of an invasive species and the effects of the characteristics of an invasive species on limited resource allocation. The optimality conditions show that it is economically efficient to spend a larger share of outlays for exclusion activities before, rather than after, a species is first discovered, up to a threshold point. We also find that, after discovery, more exclusionary measures and fewer control measures are optimal, when the pest population is less than a threshold. As the pest population increases beyond this threshold, the exclusionary measures are no longer optimal. Finally, a comparative dynamic analysis indicates that the efficient level of total expenditures on preventive and control measures decreases with the level of the invasive species stock and increases with the intrinsic population growth rate, the rate of additional discoveries avoided, and the maximum possible pest population.invasive species, exclusion, control, eradication, public expenditures, Environmental Economics and Policy, Resource /Energy Economics and Policy,
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