Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session M17: Fracture and Other Problems in Statistical Physics |
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Sponsoring Units: GSNP Room: 402 |
Wednesday, March 5, 2014 11:15AM - 11:27AM |
M17.00001: Fracture on Curved Surfaces Noah Mitchell, Vinzenz Koning, Vincenzo Vitelli, William T.M. Irvine When an elastic film conforms to a surface with Gaussian curvature, stresses arise in the film. As a result, cracks---typically studied in flat materials---interact with curvature when propagating through the system. Using silicone elastomer sheets that conform to the surface of a Gaussian bump, we find experimental evidence for the deflection of a crack propagating through the material. We interpret our experiments with reference to analytical modeling and simulations of a simplified model system. [Preview Abstract] |
Wednesday, March 5, 2014 11:27AM - 11:39AM |
M17.00002: Fracture of Thin Anisotropic Sheets: selection of the fracture path Jose Bico, Atsushi Takei, Benoit Roman, Eugenio Hamm, Francisco Melo It is often postulated that quasistatic cracks propagate along the direction allowing fracture for the lowest load. Nevertheless, this statement is debated, in particular for anisotropic materials. We performed tearing experiments in anisotropic brittle thin sheets that validate this principle in the case of weak anisotropy. We also predict the existence of forbidden directions and facets in strongly anisotropic materials, through an analogy with the description of equilibrium shapes in crystals. However, we observe cracks that do not necessarily follow the easiest direction but can select a harder direction, which is only locally more advantageous than neighboring paths. These results challenge the traditional description of fracture propagation, and we suggest a modified, less restrictive criterion compatible with our experimental observations. [Preview Abstract] |
Wednesday, March 5, 2014 11:39AM - 11:51AM |
M17.00003: Fracture of a solid with vanishing shear modulus Maxime Lefranc, Olivier Dauchot, Elisabeth Bouchaud The dissipative processes -damage, secondary crack openings- taking place ahead of a propagating crack tip in an amorphous solid are not yet completely characterized, despite the ubiquity of these materials in industrial applications. Questions regarding the extent of the process zone and the nature of the plastic events were addressed with models and numerical simulations but have never been confronted with experiments. In order to tackle this problem, we have designed a novel on-chip experiment that enables altogether to check the physical chemistry of the tested soft materials, to grow controlled cracks at a prescribed velocity, and to visualize the crack tip and its surroundings from a macroscopic to a microscopic scale. Although this experiment is aimed at studying crack propagation in model amorphous materials like colloidal glasses or gels, we have first studied fracture of polymeric gels. From the analysis of crack morphology and crack-induced deformation fields, we have disclosed the relevant time and length scales and investigated their evolution in the vicinity of the sol-gel transition, where the shear modulus vanishes. [Preview Abstract] |
Wednesday, March 5, 2014 11:51AM - 12:03PM |
M17.00004: Fracture and material geometry Michelle Driscoll, Sidney Nagel, Bryan Chen, Vincenzo Vitelli Linear elastic fracture mechanics provides a firm foundation for understanding crack propagation in a continuum material-- how are these predictions modified when a material elastic constant becomes vanishingly small? We study fracture in fragile lattices in experiments by fabricating materials containing voids, thus modifying the ratio of shear to bulk modulus, G/B, such that G/B$\rightarrow$0. We compare these results to simulations on a braced square lattice where rigidity is controlled by varying coordination number [1]. In the quasi-static limit for both experiment and simulation, we observe a crossover as the material becomes more fragile: propagating cracks are progressively superseded by isolated bond-breaking events. This crossover is signaled by the crack width increasing as G/B$\rightarrow$0, until it saturates at the system size, consistent with the random breaking of bonds. We also study dynamic fracture in a material containing a 1D array of voids. We measure the crack velocity, and again find two distinct regimes of behavior governed by material rigidity.\\ $[1]$ B. G. Chen, S. Ulrich, N. Upadhyaya, L. Mahadevan, V.Vitelli, in preparation [Preview Abstract] |
Wednesday, March 5, 2014 12:03PM - 12:15PM |
M17.00005: Highly stretchable and transparent electrodes of Au nanomeshes Chuanfei Guo Metallic nano-networks or nanomeshes may serve as the flexible transparent electrodes (FTEs) for bendable and foldable electronics. Here we present Au nanomeshes made by grain boundary lithography, showing good electrical conductance and transparency comparable to ITO film, but exceptionally high stretchability. The sheet resistance increases only $\sim$ 3 times when stretched to an ultra-large strain of 160{\%}. The Au nanomeshes also exhibit excellent performance under cyclic strain, and work well after exposing to high temperature of up to 500 $^{\circ}$C. In addition, the low surface roughness enables good compatibility with device integration. The ultra-large stretchability of the Au nanomesh FTEs lies in a subtle balance between two roles played by the underlying elastomeric substrate. The vast difference in the elastic moduli of Au and the substrate allows the stretched Au mesh to deflect and twist out of the plane, while the elastomeric substrate stabilizes distributed rupture of Au ligaments. The Au nanomesh may be used as a FTE for bendable and foldable electronics. [Preview Abstract] |
Wednesday, March 5, 2014 12:15PM - 12:27PM |
M17.00006: Nanoscale Tribological Properties of Nanodiamond Luke Lutkus, Vasudeva Rao Aravind, Benjamin Legum Due to their rich surface chemistry, excellent mechanical properties, and non-toxic nature, nanodiamond particles have found applications in a wide variety of fields such as filler materials in nanocomposites, biomedicine, tribology and lubrication, targeted drug delivery systems, and surgical implants. This study is focused on nanodiamond particles synthesized using detonation synthesis. We used peak force tapping atomic force microscopy to study adhesion and agglomeration in nanodiamond particles. We find that adhesion force between nanodiamond particles and sharp atomic force microscope tips can range from 0.1 to 2.0 nN depending on purity of particles, size of the probe, and environmental conditions. We observed that these particles can form agglomerates consisting of about 4 to 6 particles, due to interparticle forces. [Preview Abstract] |
Wednesday, March 5, 2014 12:27PM - 12:39PM |
M17.00007: Parametrically driven field emission in strongly nonlinear coupled electron-shuttles Chulki Kim, Marta Prada, Gloria Platero, Minah Seo, Taikjin Lee, Jae Hun Kim, Seok Lee, Robert Blick The transition of coupled electron shuttles from a stable to a strongly nonlinear response is demonstrated at room temperature. The electron transport is Coulomb-controlled at low voltages but changes to the conventional field emission in this transition. This reversible process forms a well-defined band within a broad frequency range in the parameter space. Both the experimental data and numerical calculations indicate that the source of the nonlinearity is provided by the electromechanical coupling. The increased current in the nonlinear regime has the potential to form the basis for energy harvesting via nanomechanical shuttles. [Preview Abstract] |
Wednesday, March 5, 2014 12:39PM - 12:51PM |
M17.00008: Computational and experimental studies of charged particles in a scalable 1D spatial and temporal periodic potential created with twin periodic electrode curtains Owen Myers, Junru Wu, Jeffrey Marshall A Twin Electric Curtains (TEC) used in our study consists of two parallel planar arrays of linear electrodes. The electrodes are driven by an oscillating two-phase electric potential. The electric potentials applied to two electrodes of the TEC are in phase when the two electrodes are in the same vertical plane whereas the potentials of the neighboring electrodes in each planar array are $180^{\circ}$ out of phase. A linear quadrupole trap is also used to constrain charged particles' motion to a straight line perpendicular and equidistant to the electrodes of the two electric curtain arrays where the component of the electric field generated by the TEC perpendicular to the axis of the quadrupole is zero. Dynamic motion of charged particles under excitation of electric field in the form $f(t)h(x)$ are studied, where $f(t)$ is periodic in time and $h(x)$ is periodic in space. The presentation will be on interesting single and multiple particle dynamic behavior including stable oscillations as well as propagating and chaotic characteristics. They may be considered as simple models related to current research in areas of molecular motors, Hamiltonian and artificial thermal ratchets, and the variety of particle transport phenomena that occur in self excited systems. [Preview Abstract] |
Wednesday, March 5, 2014 12:51PM - 1:03PM |
M17.00009: The Plasmoelectric Effect: Optical Control of the Electrochemical State of Plasmonic Absorbers Matthew Sheldon, Ana Brown, Harry Atwater The plasmonic properties of metallic nanostructures depend strongly on charge carrier density. While researchers have reported shifts of the resonant absorption frequency of plasmonic nanostructures due to electrostatically induced changes of charge density, the converse ---the dependence of charge density and electrostatic potential on optical absorption---has been largely overlooked. Here, we report a theoretical framework and provide experimental evidence for a `plasmoelectric effect', an optically induced electrochemical potential in plasmonic nanostructures. Our thermodynamic model shows that, unlike the more familiar thermoelectric or photovoltaic effects, the magnitude and sign of the plasmoelectric potential depends on the frequency difference between the plasmon resonance and incident radiation. Radiation at higher frequencies induces an increase of electron density in the nanostructure that blue-shifts the plasmon resonance. This response is favored due to increased entropy from increased absorption. Similarly, radiation at lower frequencies decreases electron density. Systematic electrical and optical studies of plasmonic Au nanostructures display clear evidence for the structure-dependent and wavelength-dependent trends consistent with our theoretical framework. [Preview Abstract] |
Wednesday, March 5, 2014 1:03PM - 1:15PM |
M17.00010: Bound states and perfect transmission scattering states in $\mathcal{PT}$-symmetric open quantum systems Savannah Garmon, Mariagiovanna Gianfreda, Naomichi Hatano We study the point spectrum and transmission scattering spectrum in $\mathcal{PT}$-symmetric open quantum systems containing balanced regions of energy amplification and attenuation, using tight-binding chains with matching sink and source sites as prototype models. For a given system geometry, we write the boundary conditions that permit scattering state and bound state solutions with wave functions that likewise satisfy $\mathcal{PT}$ symmetry; we further demonstrate the $\mathcal{PT}$-symmetric scattering states give rise to perfect transmission through the scattering region. We also discuss bound states in continuum and other spectral effects that may be discovered in $\mathcal{PT}$-symmetric open quantum systems. Finally we discuss the potential for experimental realization of our models in systems containing whispering gallery mode resonators with balanced loss and gain. [Preview Abstract] |
Wednesday, March 5, 2014 1:15PM - 1:27PM |
M17.00011: The Asymmetric Top Molecule In An Electric Field Suzanne Pittman, Jose Almaguer, Eric Heller The quantum and classical behavior of the asymmetric top has been studied in a variety of different contexts, and is known for its dynamical complexity due to have greater than 2 DOF. In this presentation the focus will be on the classical dynamics of an asymmetric top molecule with a dipole moment in an electric field (a non-integrable system), and how the underlying classical phase space structures, such as resonances, can impact the behavior of its quantum analog. Specifically, we will be presenting results from a classical simulation, which highlights both chaotic and regular regions for small electric fields depending on initial conditions. [Preview Abstract] |
Wednesday, March 5, 2014 1:27PM - 1:39PM |
M17.00012: Wigner-function approach to study the radiation of complex electromagnetic sources Gabriele Gradoni, Stephen Creagh, Gregor Tanner In this work, we develop a mathematical framework to predict the radiation of complex electromagnetic sources in free-space. We show how to propagate field-field correlation functions from near- to far-field using the formalism of Wigner-Weyl quantum mechanics. In so doing, the key point is to make a connection between the field-field correlation function in configuration space and a corresponding Wigner function in phase space. We make an analogy between the evolution of waves and the evolution in phase space of the underlying classical trajectories, for which we derive and generalize a Frobenius-Perron Equation. In the context of electromagnetic problems, the Wigner-function approach has been championed by Marcuvitz using the ``quasiparticle'' picture of wave evolution. In the proposed approach, we approximate the propagation of field-field correlation functions by propagating phase-space densities of ray families, which is effectively a lower-dimensional calculation and therefore easier to compute. In particular, we discuss how the Wigner-function approach can be extended to boundary-value problems by using the results of semiclassics and the random matrix theory. [Preview Abstract] |
Wednesday, March 5, 2014 1:39PM - 1:51PM |
M17.00013: Steering most probable escape paths by varying relative noise intensities Stephen Teitsworth, Paul Dannenberg, John Neu We demonstrate the possibility to systematically steer the most probable escape paths (MPEPs) by adjusting the relative noise intensities in non-gradient dynamical systems that exhibit escape from a metastable point via a saddle point in the limit of small noise. Based on a geometric formulation of this escape process, an asymptotic theory is developed which is broadly applicable to fast-slow systems of two or more dimensions. In simple systems, our theory permits analytical expressions for the MPEPs and their associated minimum action values as a function of the relative noise intensities. These analytical predictions are in excellent agreement with computed MPEPs obtained using a geometric minimum action method (gMAM) [1], and both of these results are consistent with prehistory probability distributions obtained by direct simulation of the underlying stochastic differential equations. [1] M. Heymann and E. Vanden-Eijnden, Phys. Rev. Lett. $\mathbf{100}$, 140601 (2008). [Preview Abstract] |
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