658 research outputs found
Mechanics and force transmission in soft composites of rods in elastic gels
We report detailed theoretical investigations of the micro-mechanics and bulk
elastic properties of composites consisting of randomly distributed stiff
fibers embedded in an elastic matrix in two and three dimensions. Recent
experiments published in Physical Review Letters [102, 188303 (2009)] have
suggested that the inclusion of stiff microtubules in a softer, nearly
incompressible biopolymer matrix can lead to emergent compressibility. This can
be understood in terms of the enhancement of the compressibility of the
composite relative to its shear compliance as a result of the addition of stiff
rod-like inclusions. We show that the Poisson's ratio of such a composite
evolves with increasing rod density towards a particular value, or {\em fixed
point}, independent of the material properties of the matrix, so long as it has
a finite initial compressibility. This fixed point is in three
dimensions and in two dimensions. Our results suggest an important
role for stiff filaments such as microtubules and stress fibers in cell
mechanics. At the same time, our work has a wider elasticity context, with
potential applications to composite elastic media with a wide separation of
scales in stiffness of its constituents such as carbon nanotube-polymer
composites, which have been shown to have highly tunable mechanics.Comment: 10 pages, 8 figure
Integrated Solution Support System for Water Management
Solving water management problems involves technical, social, economic, political and legal challenges and thus requires an integrated approach involving people from different backgrounds and roles. The integrated approach has been given a prominent role within the European Union¿s Water Framework Directive (WFD). The WFD requires an integrated approach in water management to achieve good ecological status of all water bodies. It consists amongst others of the following main planning stages: describing objectives, assessing present state, identifying gaps between objectives and present state, developing management plan, implementing measures and evaluating their impacts. The directive prescribes broad participation and consultation to achieve its objectives. Besides the obvious desktop software, such an integrated approach can benefit from using a variety of support tools. In addition to tools for specific tasks such as numerical models and questionnaires, knowledge bases on options and process support tools may be utilized. Water stress, defined as the lack of water of appropriate quality is one issue related to, but not specifically addressed by the WFD. However, like in the WFD, a participatory approach could be used to mitigate water stress. Similarly various tools can or need to be used in such a complex process. In the AquaStress Integrated project the Integrated Solution Support System (I3S ¿ I-triple-S) is developed. One of the cornerstones of the approach taken in AquaStress is that organizing available knowledge provides sufficient information to improve the possibility to make a water stress mitigation process truly end-user driven, meaning that dedicated local information is only collected after specific need is expressed by the stakeholders in the process. The novelty of the I3S lies in the combination of such knowledge stored in knowledge-bases, with adaptable workflow management facilities and with specific task-oriented tools ¿ all originating from different sources. This paper describes the I3S
A PIONIER View on Mass-Transferring Red Giants
Symbiotic stars display absorption lines of a cool red giant together with
emission lines of a nebula ionized by a hotter star, indicative of an active
binary star system in which mass transfer is occurring. PIONIER at the VLT has
been used to combine the light of four telescopes at a time to study in
unprecedented detail how mass is transferred in symbiotic stars. The results of
a mini-survey of symbiotic stars with PIONIER are summarised and some tentative
general results about the role of Roche lobe overflow are presented.Comment: Report for the ESO Messenger June issu
Roche-lobe filling factor of mass-transferring red giants - the PIONIER view
Using the PIONIER visitor instrument that combines the light of the four
Auxiliary Telescopes of ESO's Very Large Telescope Interferometer, we measure
precisely the diameters of several symbiotic and related stars: HD 352, HD
190658, V1261 Ori, ER Del, FG Ser, and AG Peg. These diameters - in the range
of 0.6 to 2.3 milli-arcseconds - are used to assess the filling factor of the
Roche lobe of the mass-losing giants and provide indications on the nature of
the ongoing mass transfer. We also provide the first spectroscopic orbit of ER
Del, based on CORAVEL and HERMES/Mercator observations. The system is found to
have an eccentric orbit with a period of 5.7 years. In the case of the
symbiotic star FG Ser, we find that the diameter is changing by 13% over the
course of 41 days, while the observations of HD 352 are indicative of an
elongation. Both these stars are found to have a Roche filling factor close to
1, as is most likely the case for HD 190658 as well, while the three other
stars have factors below 0.5-0.6. Our observations reveal the power of
interferometry for the study of interacting binary stars - the main limitation
in our conclusions being the poorly known distances of the objects.Comment: A&A, in pres
Remarks on the classification of quasitoric manifolds up to equivariant homeomorphism
We give three sufficient criteria for two quasitoric manifolds (M,M') to be
(weakly) equivariantly homeomorphic.
We apply these criteria to count the weakly equivariant homeomorphism types
of quasitoric manifolds with a given cohomology ring.Comment: 11 page
Reconstructing a Simple Polytope from its Graph
Blind and Mani (1987) proved that the entire combinatorial structure (the
vertex-facet incidences) of a simple convex polytope is determined by its
abstract graph. Their proof is not constructive. Kalai (1988) found a short,
elegant, and algorithmic proof of that result. However, his algorithm has
always exponential running time. We show that the problem to reconstruct the
vertex-facet incidences of a simple polytope P from its graph can be formulated
as a combinatorial optimization problem that is strongly dual to the problem of
finding an abstract objective function on P (i.e., a shelling order of the
facets of the dual polytope of P). Thereby, we derive polynomial certificates
for both the vertex-facet incidences as well as for the abstract objective
functions in terms of the graph of P. The paper is a variation on joint work
with Michael Joswig and Friederike Koerner (2001).Comment: 14 page
OpenMI: the essential concepts and their implications for legacy software
International audienceInformation & Communication Technology (ICT) tools such as computational models are very helpful in designing river basin management plans (rbmp-s). However, in the scientific world there is consensus that a single integrated modelling system to support e.g. the implementation of the Water Framework Directive cannot be developed and that integrated systems need to be very much tailored to the local situation. As a consequence there is an urgent need to increase the flexibility of modelling systems, such that dedicated model systems can be developed from available building blocks. The HarmonIT project aims at precisely that. Its objective is to develop and implement a standard interface for modelling components and other relevant tools: The Open Modelling Interface (OpenMI) standard. The OpenMI standard has been completed and documented. It relies entirely on the "pull" principle, where data are pulled by one model from the previous model in the chain. This paper gives an overview of the OpenMI standard, explains the foremost concepts and the rational behind it
Current Results of the EC-sponsored Catchment Modelling (CatchMod) Cluster
To support the Water Framework Directive implementation, much research has been commissioned at both national and European levels. CatchMod is a cluster of these projects, which is focusing on the development of computational catchment models and related tools. This paper presents an overview of the results of the CatchMod cluster to dat
Teelt op water van bladgewassen 2012
Vanaf 2007 doet Proeftuin Zwaagdijk in diverse gewassen onderzoek naar de mogelijkheden van alternatieve teeltsystemen. Uit het onderzoek van 2008 t/m 2011 bleek dat het drijvend teeltsysteem de meeste potentie heeft om in te spelen op de ontwikkelingen in de sector. Dit teeltsysteem vormt dan ook de basis van het onderzoek in 2012. Er zijn verschillende drijvers, zaaimethoden en kiemomstandigheden getest voor de teelt van zaaigewassen op het drijvende teeltsysteem. Goede kiempercentages zijn mogelijk en de opbrengst lijkt toe te nemen met verhoging van de zaaidichtheid
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