859 research outputs found
Shear modulus and Dilatancy Softening in Granular Packings above Jamming
We investigate experimentally the mechanical response of a monolayer of
bi-disperse frictional grains to an inhomogeneous shear perturbation across the
jamming transition. We inflate an intruder inside the packing and use
photo-elasticity and tracking techniques to measure the induced shear strain
and stresses at the grain scale. We quantify experimentally the constitutive
relations for strain amplitudes as low as 0.001 and for a range of packing
fractions within 2% variation around the jamming transition. At the transition
strong nonlinear effects set in : both the shear modulus and the dilatancy
shear-soften at small strain until a critical strain is reached where effective
linearity is recovered. The dependencies of the critical strain and the
associated critical stresses on the distance from jamming are extracted via
scaling analysis. We check that the constitutive laws, when applied to the
equations governing mechanical equilibrium, lead to the observed stress and
strain profiles. These profiles exhibit a spatial crossover between an
effective linear regime close to the inflater and the truly nonlinear regime
away from it. The crossover length diverges at the jamming transition.Comment: 5 pages, 5 figure
Multi-step self-guided pathways for shape-changing metamaterials
Multi-step pathways, constituted of a sequence of reconfigurations, are
central to a wide variety of natural and man-made systems. Such pathways
autonomously execute in self-guided processes such as protein folding and
self-assembly, but require external control in macroscopic mechanical systems,
provided by, e.g., actuators in robotics or manual folding in origami. Here we
introduce shape-changing mechanical metamaterials, that exhibit self-guided
multi-step pathways in response to global uniform compression. Their design
combines strongly nonlinear mechanical elements with a multimodal architecture
that allows for a sequence of topological reconfigurations, i.e., modifications
of the topology caused by the formation of internal self-contacts. We realized
such metamaterials by digital manufacturing, and show that the pathway and
final configuration can be controlled by rational design of the nonlinear
mechanical elements. We furthermore demonstrate that self-contacts suppress
pathway errors. Finally, we demonstrate how hierarchical architectures allow to
extend the number of distinct reconfiguration steps. Our work establishes
general principles for designing mechanical pathways, opening new avenues for
self-folding media, pluripotent materials, and pliable devices in, e.g.,
stretchable electronics and soft robotics.Comment: 16 pages, 3 main figures, 10 extended data figures. See
https://youtu.be/8m1QfkMFL0I for an explanatory vide
Synthesis, metal complexation and biological evaluation of a novel semi-rigid bifunctional chelating agent for 99mTc labelling
A novel bifunctional chelating agent bearing an aromatic ring has been synthesised and characterised. This ligand formed well-defined oxorhenium complexes. The analogous 99mTcO-complex was obtained in an excellent yield with high radiochemical purity (>95%). The biodistribution of the 99mTo-complex after intravenous injection studied in normal rats showed that the activity was excreted mainly via renal-urinary pathway indicating its use for labelling peptides with 99mTc
A characteristic length scale causes anomalous size effects and boundary programmability in mechanical metamaterials
Article / Letter to editorLeids Instituut Onderzoek Natuurkund
A characteristic length scale causes anomalous size effects and boundary programmability in mechanical metamaterials
Article / Letter to editorLeids Instituut Onderzoek Natuurkund
A characteristic length scale causes anomalous size effects and boundary programmability in mechanical metamaterials
Article / Letter to editorLeids Instituut Onderzoek Natuurkund
A characteristic length scale causes anomalous size effects and boundary programmability in mechanical metamaterials
Article / Letter to editorLeids Instituut Onderzoek Natuurkund
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