443 research outputs found
Reversible magnetomechanical collapse: virtual touching and detachment of rigid inclusions in a soft elastic matrix
Soft elastic composite materials containing particulate rigid inclusions in a
soft elastic matrix are candidates for developing soft actuators or tunable
damping devices. The possibility to reversibly drive the rigid inclusions
within such a composite together to a close-to-touching state by an external
stimulus would offer important benefits. Then, a significant tuning of the
mechanical properties could be achieved due to the resulting mechanical
hardening. For a long time, it has been argued whether a virtual touching of
the embedded magnetic particles with subsequent detachment can actually be
observed in real materials, and if so, whether the process is reversible. Here,
we present experimental results that demonstrate this phenomenon in reality.
Our system consists of two paramagnetic nickel particles embedded at finite
initial distance in a soft elastic polymeric gel matrix. Magnetization in an
external magnetic field tunes the magnetic attraction between the particles and
drives the process. We quantify the scenario by different theoretical tools,
i.e., explicit analytical calculations in the framework of linear elasticity
theory, a projection onto simplified dipole-spring models, as well as detailed
finite-element simulations. From these different approaches, we conclude that
in our case the cycle of virtual touching and detachment shows hysteretic
behavior due to the mutual magnetization between the paramagnetic particles.
Our results are important for the design and construction of reversibly tunable
mechanical damping devices. Moreover, our projection on dipole-spring models
allows the formal connection of our description to various related systems,
e.g., magnetosome filaments in magnetotactic bacteria.Comment: 14 pages, 7 figure
Microbial turnover of PAH: analysis of degradation and dissolution kinetics and simulation of remediation options
Atomic structure of Ge quantum dots on the Si(001) surface
In situ morphological investigation of the {105} faceted Ge islands on the
Si(001) surface (hut clusters) have been carried out using an ultra high vacuum
instrument integrating a high resolution scanning tunnelling microscope and a
molecular beam epitaxy vessel. Both species of hut clusters--pyramids and
wedges--were found to have the same structure of the {105} facets which was
visualized. Structures of vertexes of the pyramidal clusters and ridges of the
wedge-shaped clusters were revealed as well and found to be different. This
allowed us to propose a crystallographic model of the {105} facets as well as
models of the atomic structure of both species of the hut clusters. An
inference is made that transitions between the cluster shapes are impossible.Comment: 6 pages, 6 figures. Accepted to JETP Letters (publication date
2010-03-25
New approaches for low-invasive contaminated site characterization, monitoring and modelling
Cross‐scale seismic anisotropy analysis in metamorphic rocks from the COSC‐1 borehole in the Scandinavian Caledonides
Metamorphic and deformed rocks in thrust zones show particularly high seismic anisotropy causing challenges for seismic imaging and interpretation. A good example is the Seve Nappe Complex in central Sweden, an old exhumed orogenic thrust zone that is characterized by a strong but incoherent seismic reflectivity and considerable seismic anisotropy. However, only little is known about their origin in relation to composition and structural influences on measurements at different seismic scales. Here, we present a new integrative study of cross‐scale seismic anisotropy analyses combining mineralogical composition, microstructural analyses and seismic laboratory experiments from the COSC‐1 borehole, which sampled a 2.5 km‐deep section of metamorphic rocks deformed in an orogenic root now preserved in the Lower Seve Nappe. While there is strong crystallographic preferred orientation in most samples in general, variations in anisotropy depend mostly on bulk mineral composition and dominant core lithology as shown by a strong correlation between these. This relationship enables to identify three distinct seismic anisotropy facies providing a continuous anisotropy profile along the borehole. Moreover, comparison of laboratory seismic measurements and electron‐backscatter diffraction data reveals a strong scale‐dependence, which is more pronounced in the highly deformed, heterogeneous samples. This highlights the need for comprehensive cross‐validation of microscale anisotropy analyses with additional lithological data when integrating seismic anisotropy over seismic scales
Classification and modelling of non-extractable residue (NER) formation from pesticides in soil
Entscheidungsunterstützung bei der Gestaltung von Agrarumweltprogrammen
In dem Beitrag wird dargelegt, wie in Zusammenarbeit von Wissenschaft, Politik und Verwaltung konkrete Entscheidungsunterstützung für die Politikgestaltung in komplexen Systemen geleistet werden kann. Zur Anwendung kommt ein interaktiver PC-gestützter Programmierungsansatz, dessen Möglichkeiten für die Verbesserung von Agrarumweltprogrammen in Sachsen-Anhalt genutzt werden. Gemeinsam mit den betroffenen Akteuren wird auf der Grundlage interaktiv durchgeführter Simulationsrechungen unter Einbeziehung verschiedener Einflussfaktoren (Zielgewichtung, Kofinanzierungssätze und Budgetumfang) eine Strategie zur Verbesserung des Agrarumweltprogramms entwickelt.Peer Reviewe
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