210 research outputs found
Readout of relaxation rates by nonadiabatic pumping spectroscopy
We put forward nonadiabatic charge pumping as a method for accessing the
different charge relaxation rates as well as the relaxation rates of excited
orbital states in double-quantum-dot setups, based on extremely size-limited
quantum dots and dopant systems. The rates are obtained in a well-separated
manner from plateaus, occurring when comparing the steady-state current for
reversed driving cycles. This yields a reliable readout independent of any
fitting parameters. Importantly, the nonadiabatic pumping spectroscopy
essentially exploits the same driving scheme as the operation of these devices
generally employs. We provide a detailed analysis of the working principle of
the readout scheme as well as of possible errors, thereby demonstrating its
broad applicability. The precise knowledge of relaxation rates is highly
relevant for the implementation of time-dependently operated devices, such as
electron pumps for metrology or qubits in quantum information.Comment: 14 pages, 5 figure
Morphogenesis through elastic phase separation in a pneumatic surface
We report a phenomenon of phase separation that relates in many aspects to
Yves Couder's work: an inflatable architectured elastomer plate, expected to
expand homogeneously in its plane, buckles instead widely out-of-plane into
very complex shape when internal pressure is applied. We show that this
morphogenetic pattern formation is due to a two-dimensional elastic phase
separation, which induces incompatible patchy non-Euclidean reference metric
A variational model of fracture for tearing brittle thin sheets
Tearing of brittle thin elastic sheets, possibly adhered to a substrate, involves a rich interplay between nonlinear elasticity, geometry, adhesion, and fracture mechanics. In addition to its intrinsic and practical interest, tearing of thin sheets has helped elucidate fundamental aspects of fracture mechanics including the mechanism of crack path selection. A wealth of experimental observations in different experimental setups is available, which has been often rationalized with insightful yet simplified theoretical models based on energetic considerations. In contrast, no computational method has addressed tearing in brittle thin elastic sheets. Here, motivated by the variational nature of simplified models that successfully explain crack paths in tearing sheets, we present a variational phase-field model of fracture coupled to a nonlinear Koiter thin shell model including stretching and bending. We show that this general yet straightforward approach is able to reproduce the observed phenomenology, including spiral or power-law crack paths in free standing films, or converging/diverging cracks in thin films adhered to negatively/positively curved surfaces, a scenario not amenable to simple models. Turning to more quantitative experiments on thin sheets adhered to planar surfaces, our simulations allow us to examine the boundaries of existing theories and suggest that homogeneous damage induced by moving folds is responsible for a systematic discrepancy between theory and experiments. Thus, our computational approach to tearing provides a new tool to understand these complex processes involving fracture, geometric nonlinearity and delamination, complementing experiments and simplified theories.Fil: Li, Bin. Universidad Politécnica de Catalunya; España. Sorbonne Université; Francia. Centre National de la Recherche Scientifique; FranciaFil: Millán, Raúl Daniel. Universidad Nacional de Cuyo. Facultad de Ciencias Aplicadas a la Industria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; Argentina. Universidad Politécnica de Catalunya; EspañaFil: Torres Sánchez, Alejandro. Universidad Politécnica de Catalunya; EspañaFil: Roman, Benoît. Centre National de la Recherche Scientifique; Francia. Sorbonne Université; FranciaFil: Arroyo Balaguer, Marino. Universidad Politécnica de Catalunya; Españ
Spiral rupture of thin sheet with a blunt object.
Thin layers are commonly used in a wide kind
of industrial products (from everyday packaging to airplanes) and are also frequently
found in biological systems. The mechanics of thin sheets is rich and complex, with
strong geometrical non-linearities leading for example to the intricate folds and
singularities that we can observe in a crumpled sheet of paper. But here, we show that
fracture in thin sheets can follow remarkably regular geometrical path. We have observed
crack path that evolved from an initial notch a few millimeter wide into a logarithmic
spiral that reached a meter in diameter. We present a model that explains the impressive
regularity of this crack propagation
Wrapping an adhesive sphere with a sheet
We study the adhesion of an elastic sheet on a rigid spherical substrate.
Gauss'Theorema Egregium shows that this operation necessarily generates metric
distortions (i.e. stretching) as well as bending. As a result, a large variety
of contact patterns ranging from simple disks to complex branched shapes are
observed as a function of both geometrical and material properties. We describe
these different morphologies as a function of two non-dimensional parameters
comparing respectively bending and stretching energies to adhesion. A complete
configuration diagram is finally proposed
A new failure mechanism in thin film by collaborative fracture and delamination: Interacting duos of cracks
International audienceWhen a thin film moderately adherent to a substrate is subjected to residual stress, the cooperation between fracture and delamination leads to unusual fracture patterns such as spirals, alleys of crescents and various types of strips, all characterized by a robust characteristic length scale. We focus on the propagation of a duo of cracks : two fractures in the film connected by a delamination front and progressively detaching a strip. We show experimentally that the system selects an equilibrium width on the order of 25 times the thickness of the coating and independent of both fracture and adhesion energies. We investigate numerically the selection of the width and the condition for propagation by considering Griffith's criterion and the principle of local symmetry. In addition, we propose a simplified model based on the criterion of maximum of energy release rate, which provides insights of the physical mechanisms leading to these regular patterns, and predicts the effect of material properties on the selected with of the detaching strip
Programming stiff inflatable shells from planar patterned fabrics
Lack of stiffness often limits thin shape-shifting structures to small
scales. The large in-plane transformations required to distort the metrics are
indeed commonly achieved by using soft hydrogels or elastomers. We introduce
here a versatile single-step method to shapeprogram stiff inflated structures,
opening the door for numerous large scale applications, ranging from space
deployable structures to emergency shelters. This technique relies on channel
patterns obtained by heat-sealing superimposed flat quasi-inextensible fabric
sheets. Inflating channels induces an anisotropic in-plane contraction and thus
a possible change of Gaussian curvature. Seam lines, which act as a director
field for the in-plane deformation, encode the shape of the deployed structure.
We present three patterning methods to quantitatively and analytically program
shells with non-Euclidean metrics. In addition to shapes, we describe with
scaling laws the mechanical properties of the inflated structures. Large
deployed structures can resist their weight, substantially broadening the
palette of applications.Comment: 6 pages, 4 figures and Supplementary Information (14 pages, 3
figures
Capillary origami: spontaneous wrapping of a droplet with an elastic sheet
The interaction between elasticity and capillarity is used to produce three
dimensional structures, through the wrapping of a liquid droplet by a planar
sheet. The final encapsulated 3D shape is controlled by tayloring the initial
geometry of the flat membrane. A 2D model shows the evolution of open sheets to
closed structures and predicts a critical length scale below which
encapsulation cannot occur, which is verified experimentally. This {\it
elastocapillary length} is found to depend on the thickness as , a
scaling favorable to miniaturization which suggests a new way of mass
production of 3D micro- or nano-scale objects.Comment: 5 pages, 5 figure
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