Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session P11: Focus Session: Extreme Mechanics III |
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Sponsoring Units: GSNP Chair: A. Kudrolli, Clark University Room: A107-A109 |
Wednesday, March 17, 2010 8:00AM - 8:12AM |
P11.00001: ABSTRACT WITHDRAWN |
Wednesday, March 17, 2010 8:12AM - 8:24AM |
P11.00002: Geometrical Frustration and Lattice Defects in Twisted, Two-Dimensionally Ordered Filament Bundles Gregory Grason We study a continuum-elastic description of filament assemblies, bundles or fibrils, that are two-dimensionally organized in cross-section while simultaneously adopting a globally twisted structure. In this model, twisting may occur in response to external forces or as a consequence of the intrinsic interfilament torques acting between {\it chiral} macromolecules, like F-actin and collagen, ubiquitous in biological systems. We show that the geometrical, non-linear couplings between tilt and in-plane strain required by the elastic description of ordered filament arrays frustrate the lattice packing of filaments in precisely the same way that out-of-plane deflection frustrates the formation of two-dimensional crystals on curve surfaces. Hence, the elastic cost of forming a twisted bundle corresponds directly the with stretching cost of arranging crystal on a sphere of an appropriate radius. Based on this mapping we demonstrate that above a critical size, a twisted bundle is unstable to the incorporation of a finite number of line {\it disclinations}, that partially screen the twisted-induced stresses. We present results on the complex spectrum of groundstate bundle packings that result from the consideration of stress-locallizing, lattice defects and discuss the implications of the defect-riddled groundstates for the mechanics and thermodynamics of self-assembled molecular filaments. [Preview Abstract] |
Wednesday, March 17, 2010 8:24AM - 8:36AM |
P11.00003: On the mechanics of entangled random fiber networks with friction Gopinath Subramanian, Catalin Picu The mechanics of random fiber networks which are not bonded or cross-linked but are subjected to topological constrains imposed by the excluded volume of the fibers is studied by means of a computational model. The fibers do not cross, have linear constitutive behavior in the axial and bending deformation modes and interact with each other frictionally. The response to hydrostatic (compaction) and shear loading is studied with focus on the emergence of hysteretic behavior and texture. The role of friction and of fiber aspect ratio in defining the onset of stiffness percolation, the response to large deformations and the overall dissipation is analyzed. [Preview Abstract] |
Wednesday, March 17, 2010 8:36AM - 8:48AM |
P11.00004: Statistical properties of a folded elastic rod Elsa Bayart, St\'ephanie Deboeuf, Laurent Bou\'e, Francis Corson, Arezki Boudaoud, Mokhtar Adda-Bedia A large variety of elastic structures naturally seem to be confined into environments too small to accommodate them; the geometry of folded structures span a wide range of length-scales. The elastic properties of these confined systems are further constrained by self-avoidance as well as by the dimensionality of both structures and container. To mimic crumpled paper, we devised an experimental setup to study the packing of a dimensional elastic object in 2D geometries: an elastic rod is folded at the center of a circular Hele-Shaw cell by a centripetal force. The initial configuration of the rod and the acceleration of the rotating disk allow to span different final folded configurations while the final rotation speed controls the packing intensity. Using image analysis we measure geometrical and mechanical properties of the folded configurations, focusing on length, curvature and energy distributions. [Preview Abstract] |
Wednesday, March 17, 2010 8:48AM - 9:00AM |
P11.00005: Flexural wave properties of nanotubes conveying fluid Pin Lu Carbon nanotubes (CNTs) with diameters in the range of nanometers have shown various potential applications in nanofluidics. In this work, the flexural wave properties of carbon nanotubes conveying fluid are studied by considering van der Waals (vdW) interactions between the nanotube surface and the fluid. Based on the modified model, the expressions of dispersion relations are derived, and the vdW effect dependent cut-off frequency is obtained. It is found that the wave properties by considering the vdW interactions are significantly different from those obtained based on the conventional models. The propagating flexural waves in the CNTs are shown to occur above the vdW effect dependent cut-off frequency. In addition, in the four branches of the dispersion relations obtained, two of them are found relating to the non-propagating fields, and the other two branches represent propagating flexural waves. These properties may provide a better understanding on the relationships between the flexural waves and the flow velocities of the fluid-conveying components at small length scale level and help to design stable nanotube-based nanofluidic channels. [Preview Abstract] |
Wednesday, March 17, 2010 9:00AM - 9:12AM |
P11.00006: Smooth contact and buckling in asymmetric bubble break-up Wendy Zhang, Lipeng Lai When an underwater bubble breaks up, the final dynamics is dominated by shape vibrations excited by initial asymmetries. As a result, the break-up is qualitatively different from that observed for a typical liquid drop. The dynamics does not evolve towards a universal singularity, one independent of initial and boundary conditions. Instead, the shape vibrations create a variety of final dynamics. We use theory and simulation to enumerate the different possible break-up modes for a simple class of initial distortions. For some initial conditions, the break-up is severely asymmetric. An initially nearly cylindrically-symmetric bubble neck implodes into a thin air sheet. The thin air sheet subsequently fails in two distinct modes. The opposite sides of the interface can contact smoothly and break the air sheet up into several pieces, reminiscent of coalescence. More surprisingly, the thin edge of the sheet can also ``buckle'' inwards, as if it were a solid shell. [Preview Abstract] |
Wednesday, March 17, 2010 9:12AM - 9:24AM |
P11.00007: Capillary Origami Controlled by Electrowetting Miguel Pineirua, Jose Bico, Benoit Roman What happens if a water droplet is deposited over an elastic sheet? The sheet spontaneously wraps around droplet? This is possible if the capillary forces due to the liquid/air interface overcome the bending stiffness of the elastic sheet [1]. This technique called ``capillary origami'' could be used not only to encapsulate micro droplets but also to produce 3-D objects out from planar patterns. Once the microstructure has closed, could it be possible to reopen it at will? The wetting properties of liquids can be modified by the action of an electric field [2]. This phenomenon known as electrowetting can be seen as the electric energy minimization of a capacitor. In order to be capable of reopening the capillary origami, we propose to apply an electric field between the droplet and the substrate, with the flexible sheet as an isolating layer between them. The sheet will stay wrapping the droplet while the circuit is open and will eventually unwrap it if a sufficiently intense electric field is applied. We attempt to describe the original interaction between the electric field, capillarity and elasticity.\\[4pt] [1] C. Py, P. Reverdy, L. Doppler, J. Bico, B. Roman, C.N.Baroud, Capillary origami : spontaneous wrapping of a droplet with an elastic sheet, Phys. Rev. Lett., 98, 156103 (2007).\\[0pt] [2] F. Mugele, J.-C. Baret, Electrowetting : from basics to applications, J. Phys. Cond. Mat., 17, R705 (2005). [Preview Abstract] |
Wednesday, March 17, 2010 9:24AM - 9:36AM |
P11.00008: Plant Root Growth In Granular Media Dawn Wendell, Peko Hosoi Roots grow in a variety of granular substrates. However, the substrates are often treated in ways which minimize or neglect the inhomogeneities arising from the influence of inter-particle forces. Experiments are often run using gels or average stress measurements. This presentation discusses the effect of the local structure of the particulate environment on the root's direction. Using photoelastic particles and particles with a variety of Young's Moduli, we investigate the influence of inter-particle forces and particle stiffness on a pinto bean root's ability to grow through a fully-saturated granular medium. The level of particle contact force through which the roots successfully grow is determined and the influence of particle stiffness on root direction is investigated. [Preview Abstract] |
Wednesday, March 17, 2010 9:36AM - 9:48AM |
P11.00009: Universal branch statistics of branched flows Jakob Metzger, Ragnar Fleischmann, Theo Geisel Branched flow is a universal phenomenon of particle and wave flows which are subjected to weak, correlated disorder. It has been observed on length scales ranging from a few micrometres, affecting the transport properties of semiconductor devices [1], up to several thousand kilometres, influencing sound propagation through the ocean [2]. It is also responsible for the appearance of large and hazardous freak waves and tsunamis [3]. Here, we address the question of how many branches can be observed on average as a function of distance from an ordered source. We derive a universal curve for this quantity which applies to a wide range of parameters and correlation functions of the underlying disorder [4]. \\[4pt] [1] e.g. M. A. Topinka et al., Nature \textbf{410}, 183 (2001), M. P. Jura et al., Nature Physics \textbf{3}, 841 (2007) \\[0pt] [2] M. Wolfson \& S. J. Tomsovich, Acous. Soc. Am., \textbf{109}, 2693 (2001) \\[0pt] [3] M. V. Berry , New J. Phys. \textbf{7}, 129 (2005); M. V. Berry, Proc. R. Soc. A \textbf{463}, 3055 (2007); E. J. Heller, L. Kaplan \& A. Dahlen, J. Geophys. Res., \textbf{113}, C09023 (2008) \\[0pt] [4] J. J. Metzger, R. Fleischmann and T. Geisel, in preparation [Preview Abstract] |
Wednesday, March 17, 2010 9:48AM - 10:00AM |
P11.00010: Flucutations in power dissipation in a gravity driven system Zrinka Greguric, Miguel Cervoni, John Cressman We have studied the three dimensional motion of a disk falling through a column of water. The disk's position and orientation are measured with a high speed video camera enabling an analysis of the fluid forces acting on the disk. On average the fluid exerts a dissipative drag on the falling body. However, these forces are dynamic and lead to fluctuations in the kinetic energy of the disk. The resulting power fluctuations are of the same magnitude as the mean power dissipated by the fluid and can be large enough to cause the disk to move upward against the force of gravity. We have analyzed these fluctuations and compared their statistics to those predicted by non-equilibrium statistical theory. [Preview Abstract] |
Wednesday, March 17, 2010 10:00AM - 10:12AM |
P11.00011: A new effect in the propulsion of chiral particles Eleftherios Kirkinis, Anton Andreev, Boris Spivak We study motion of small chiral ferromagnetic particles diluted in a classical liquid in the presence of d.c. magnetic field $\bf{H}$ and a.c. electric field $\bf{E}$. The time averaged drift velocity of the particle $\bf{V}$ has the following chiral contribution, \begin{equation} \mathbf{V}=\alpha \mathbf{H} E^{2} +\beta \mathbf{E} (\mathbf{H}\cdot\mathbf{E}), \end{equation} where the coefficients $\alpha$ and $\beta$ have opposite signs for particles of opposite chirality. Thus particles of opposite chirality move in opposite directions. We assume that the magnetic moment is frozen into the particle by the magnetic anisotropy. The chiral component of the drift velocity is caused by the spin torques exerted on the particle by the magnetized electrons. It vanishes in the approximation where the orbital moment of the magnetized electrons, $\mathbf{L}_e=-g \frac{e\hbar}{mc}\, \mathbf{M}$, with $\mathbf{M}$ being the magnetic moment of the particle, is neglected. Therefore $\alpha,\beta\propto \mathbf{L}_e$. [Preview Abstract] |
Wednesday, March 17, 2010 10:12AM - 10:24AM |
P11.00012: Formation of 3D microstructures through swelling of photo-crosslinked hydrogel films Jungwook Kim, Marcelo Dias, Christian Santangelo, Ryan Hayward Thin sheets of hydrogels with spatially-varying propensities to swell or shrink provide a powerful means to controllably fold 2D elastic sheets into 3D structures. We have developed a material system based on photo-crosslinkable temperature-responsive polymers wherein films of several micrometers in thicknesses can be spatially patterned with locally varying equilibrium degrees of swelling. At ambient temperature where the gel is highly hydrated, the mutually constrained swelling of different regions leads to development of stresses within the microstructure and therefore out-of-plane deformation into well-defined 3D structures. By increasing temperature, the gel shrinks to a state with nearly uniform swelling, regenerating the original 2D shape. We theoretically model the buckling of the polymer film due to local swelling to explore the resulting three-dimensional shapes. This strategy for preparing patterned 2D soft elastic films that reversibly fold into 3D structures is anticipated to provide a tool for studying fundamental questions concerning the elasticity of thin sheets as well as stimuli-responsive smart micro-structures. [Preview Abstract] |
Wednesday, March 17, 2010 10:24AM - 10:36AM |
P11.00013: Thermally Induced Local Failures in Quasi-One-Dimensional Systems: Collapse in Carbon Nanotubes, Necking in Nanowires and Opening of Bubbles in DNA Cristiano Nisoli, Douglas Abraham, Turab Lookman, Avadh Saxena We present a general framework to explore thermally activated failures in quasi one dimensional systems. We apply it to the collapse of carbon nanotubes, the formation of bottlenecks in nanowires, both of which limit conductance, and the opening of local regions or ``bubbles'' of base pairs in strands of DNA that are relevant for transcription and danaturation. We predict an exponential behavior for the probability of the opening of bubbles in DNA, the average distance between flattened regions of a nanotube or necking in a nanowire as a monotonically decreasing function of temperature, and compute a temperature below which these events become extremely rare. These findings are difficult to obtain numerically, however, they could be accessible experimentally. [Preview Abstract] |
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