Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session V30: Biologically Inspired Physics |
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Sponsoring Units: DFD Chair: Marilyn Gunner, City College of New York Room: Colorado Convention Center 304 |
Thursday, March 8, 2007 11:15AM - 11:27AM |
V30.00001: Investigating gecko setae adhesion using a dual-axis MEMS force sensor Ginel Hill, Daniel Soto, Anne Peattie, Robert Full, Thomas Kenny A dual-axis piezoresistive MEMS force sensor was used to investigate the role of orientation angle on the adhesion of gecko hairs, called setae. Made of keratin with nanoscale features, gecko setae are a spectacular, robust dry adhesive with anisotropic adhesion properties. A wealth of recent research has been devoted to synthetic mimicry of the gecko seta. However, most synthetics do not yet display anisotropic adhesion, which is critical for controllable attachment and release. Previous research using a wire gauge tested the role of the pitch angle between the stalk of natural setae and the substrate and found a dramatic cutoff angle of 30$^{\circ}$, above which setae detach from the substrate [1]. The present work details the effect of the ``roll'' angle on natural setae adhesion. [1] K. Autumn, et al. Nature, 405: 681 (2000). [Preview Abstract] |
Thursday, March 8, 2007 11:27AM - 11:39AM |
V30.00002: The venation network in leaves as anticracks? Pedro Reis, Denis Vallet, Benoit Roman Thus far, existing models of venation in leaves are entirely biochemical, involving hormonal diffusive processes. These are, however, unable to capture some crucial structural features of the vascular bundles' network such as the existence of reconnection loops. Couder et. al. [1] have recently highlighted the striking similarities between leaf venation and fracture patterns in drying gels, suggesting that a tensorial mechanism may be at play. It is known that, in the initial stages of the formation of vascular bundles, the promesophyll (leave's \emph{bulk}) is under compression since it grows at a faster rate than the protoderm (leave's \emph{skin}). Hence, to take this analogy further, we introduce the concept of an \emph{anticrack}: a localization of deformation under compressive stresses. We have developed an experimental system to develop and explore this concept as when a solid foam is compressed, either uniaxially or biaxially. We analyze the resulting anticrack networks and relate them to the fracture and venation counterparts. For this purpose we use a high resolution image correlation technique to measure the statistics of the localization zones, structural hierarchy and reconnection loops. [1] Y. Couder, L. Pauchard, C. Allain, M. Adda-Bedia and S. Douady, \emph{Eur. Phys. J. B} \textbf{28} 135 (2002). [Preview Abstract] |
Thursday, March 8, 2007 11:39AM - 11:51AM |
V30.00003: Dynamics of macromolecules in confined environments Armin Rahmanisisan, Claudio Castelnovo, Jeremy Schmit, Claudio Chamon The dynamics of a ring macro-molecule confined to a two dimensional cell is studied. A connectivity-preserving kinetically constrained lattice gas model is introduced and used to study the effects of the shrinking of the box on dynamical correlations using Monte-Carlo simulations. It is found that the monomers comprising the macro-molecule manage to diffuse around the box with a mean squared displacement of the order of the square of the box dimensions, even at densities close to the frozen fully-packed configuration where the overall geometry remains almost unchanged over long times. Reptation and fingering events are observed and appropriate correlation functions are introduced to analyze the monomer motion and polymer reshaping at different densities. [Preview Abstract] |
Thursday, March 8, 2007 11:51AM - 12:03PM |
V30.00004: Piezoelectricity as possible mechanism for mechano-, and magneto-receptions Antal Jakli, John Harden, Cody Notz, Chris Bailey We have studied the piezoelectric responses of 2 dry phospholipids (L-a-Phosphatidylcholine) purchased from Avanti Inc.model membranes. The material was sandwiched between two parallel plates separated by 5$\mu $m-60$\mu $m distances and aligned with smectic layers mainly parallel to the substrates. The material has a SmA* phase which is similar to the bilayers of cell membranes. Due to its symmetry it should be piezoelectric and may produce electric current normal to the shear plane when one of the substrates is moved with respect to the other one. We have experimentally verified this statement and found the generation of electric polarization up to 300nC/cm$^{2}$ when the shear induced a director tilt of about 5 degrees. We have also measured generation of electric current in phospholipids doped with 1{\%} of ferrofluid of Fe$_{2}$O$_{3}$ nanoparticles when 100G magnetic field was applied periodically on the material. Details of the observations and the relevance of these effects in mechano-, and magneto-receptions will de discussed. [Preview Abstract] |
Thursday, March 8, 2007 12:03PM - 12:15PM |
V30.00005: Planar Model of Orbital Paramagnetism in B-DNA and A-DNA at Low Temperatures. Michael J. Harrison We develop a planar model of B-DNA which exhibits orbital paramagnetic properties at low temperatures arising from a small number of conducting pi electrons that move in a parabolic potential attracting them towards the central axis of the model molecule. The paramagnetism is nonlinear in applied field and can have a maximum several times the magnitude of diamagnetism per particle in an extended 2DES. The model is consistent with recent experimental observations [1] provided that only a small number of itinerant pi band electrons of higher energy are assumed to participate, amounting to only 1{\%} of the total number of pi stack electrons from base pairs which are thought to constitute a hybridized core within the actual double helix. The model indicates that the encladding water molecules attached to wet B-DNA provide dielectric screening of the attractive parabolic potential, and can explain the presence of orbital paramagnetism, which is experimentally absent in dry A-DNA [1]. S. Nakamae, et al, PRL 94, 248102, (2005). [Preview Abstract] |
Thursday, March 8, 2007 12:15PM - 12:27PM |
V30.00006: Electromechanics: An analytic solution for graded biological cell. Kin Lok Chan, K. W. Yu Electromechanics of graded material has been established recently to study the effective response of inhomogeneous graded spherical particles under an external ac electric field.[1, 2]Such particles having a complex dielectric profile varies along the radius of the particles. The gradation in the colloidal particles is modeled by assuming both the dielectric and conductivity vary along the radius. More precisely, both the dielectric and conductivity function are assumed to be a isotopic linear function dependence on the radius variable $r$, namely, $\varepsilon (r)=\varepsilon (0)+A_1 r$, $\sigma (r)=\sigma (0)+A_2 r$.In this talk, we will present the exact analytical solutions of the dipole moment of such particle in terms of the hypergeometric functions, and the effective electric response in dilute limit. Moreover, we applied the dielectric dispersion spectral representation (DDSR) to study the Debye Behavior of the cell. Our exact results may be applied to graded biological cell suspensions, as their interior must be inhomogeneous in nature. [1] En-Bo Wei, L. Dong, K. W. Yu, Journal of Applied Physics 99, 054101(2006) [2] L. Dong, Mikko Karttunen, K. W. Yu, Phys. Rev. E, Vol. 72, art. no. 016613 (2005) [Preview Abstract] |
Thursday, March 8, 2007 12:27PM - 12:39PM |
V30.00007: TASEP with extended particles and local inhomogeneities Jiajia Dong, Beate Schmittmann, Royce K.P. Zia Though much is known about the totally asymmetric simple exclusion process (TASEP), there are still non-trivial characteristics worthy of further exploration. In particular, in TASEPs with extended particles that ``cover'' $\ell >1$ lattice sites, non-trivial correlations between the particles exist, even for a case with a trivial distribution for the microscopic configurations. Further, $\xi $, the characteristic length of these correlations can be extremely long, e.g., $O\left( 10^{2}\right) $. They set up interesting structures in the density profile behind ``bottlenecks'' (localized inhomogeneities, with hopping rates $q$ smaller than those in the rest of the lattice: $q<1$) in the system. For TASEPs with open boundaries, we study how one or more such bottlenecks affect both the profiles and the overall current. Using simulations, we present results for a range of $% q,\ell ,$ and the {\em locations }of the inhomogeneities: $x_{i}$. For example, the current is somewhat enhanced if a single bottleneck is located close to either system boundary. But it is reduced significantly if two bottlenecks are present and closely spaced, i.e., provided $\left| x_{1}-x_{2}\right| $$\leq$ $\xi .$ We also discuss the possible impact of these findings on ribosome queueing and codon optimization in protein production. [Preview Abstract] |
Thursday, March 8, 2007 12:39PM - 12:51PM |
V30.00008: The Real-Time Dose Measurement Scintillating Fiber Array for Brachytherapy Procedures Lawrence Tynes Brachytherapy is a treatment modality that uses tiny radioactive sources (few mm in length) by delivering enough doses to kill cancer tumors or plaque build-up. The type of sources used in hospitals include both gamma and beta emitters. Presently, the technique suffers from not having a single detector with the capability of providing accurate dose distribution information within sub-mm accuracy. The current standard is based primarily on well chambers and film dosimetry. The Center for Advanced Medical Instrumentation (CAMI) at Hampton University is developing a Scintillating Fiber Based Beta Detector prototype in collaboration with the National Institute for Standards and Technology (NIST) to address this problem. The device is composed of an array of 1x1 \textbf{mm}$^{2}$ scintillating fibers optically coupled to photo-multiplier tubes for photon-to-current conversion. A CAMAC LabView based data acquisition system is used for real time data collection and histogramming, data analysis. A set of data were collected at the nearby Bon Secours DePaul Medical Center using a GammaMed 12i HDR after-loader housing a 6.62 mCi Ir-192 source. Preliminary comparison between our device and film dosimetry will be discussed. [Preview Abstract] |
Thursday, March 8, 2007 12:51PM - 1:03PM |
V30.00009: Modeling Blood Filtration in the Treatment of Septic Shock Glenn Foster, Alfred Hubler Sepsis, the overreaction of the inflammation and coagulation responses to infection, is the leading cause of death in non-coronary intensive care unit patients in the US. Anti-mediator drugs have been generally ineffective, but by considering the network of cytokine interactions, we illustrate how filtering the cytokines in the blood leads to a reduced response. We further illustrate by applying an appropriate filter to existing immune response models as well as discuss both practical and optimal filter parameters. [Preview Abstract] |
Thursday, March 8, 2007 1:03PM - 1:15PM |
V30.00010: A novel flow cytometry configuration for the detection of magnetic microparticles. John Martin, Christopher Carr, Andrei Matlachov, Henrik Sandin, Michelle Espy, Robert Kraus We have developed a technique for detecting magnetic microparticles in a novel laser-based flow cytometry configuration that incorporates a giant magnetoresistive (GMR) sensor. To achieve the highest possible sensitivity, it is advantageous to minimize the distance from the GMR sensor to the microparticle. Initially, we passed ferromagnetic microparticles (diameter $<$100 microns) through polymer capillary tubing that passed directly on top of the GMR. While the capillary tubing provides a controlled flow path, it imposes a standoff between the sensor and the microparticle that is never less than 200 microns (due to the tube wall thickness). This standoff limits the range of magnetic microparticles we can detect. Another proposed technique to achieve minimum standoff is to fabricate microfluidic flow channels on top of the GMR itself. We have developed a new approach for minimum standoff, which does not require microfluidics. We will describe this technique, discuss the performance of the commercial GMR sensor and finally report on the detection of magnetic microparticles in this new flow configuration. [Preview Abstract] |
Thursday, March 8, 2007 1:15PM - 1:27PM |
V30.00011: Computational Phlebology: The Simulation of a Vein Valve Gavin Buxton, Nigel Clarke We present a three-dimensional computer simulation of the dynamics of a vein valve. In particular, we couple the solid mechanics of the vein wall and valve leaflets with the fluid dynamics of the blood flow in the valve. Our model captures the unidirectional nature of blood flow in vein valves; blood is allowed to flow proximally back to the heart, while retrograde blood flow is prohibited through the occlusion of the vein by the valve cusps. Furthermore, we investigate the dynamics of the valve opening area and the blood flow rate through the valve, gaining interesting insights into the physics of vein valve operation. It is anticipated that through computer simulations we can help raise our understanding of venous hemodynamics and various forms of venous dysfunction. [Preview Abstract] |
Thursday, March 8, 2007 1:27PM - 1:39PM |
V30.00012: ABSTRACT WITHDRAWN |
Thursday, March 8, 2007 1:39PM - 1:51PM |
V30.00013: Evolution of DNA Compaction in X-Ray Compatible Microflow Foil Devices Sarah Koester, Heather M. Evans, Rolf Dootz, Bernd Struth, Thomas Pfohl Spatially resolved X-ray microdiffraction in hydrodynamic focusing microdevices provides new opportunities to study time-resolved reactions of complex fluids. A demonstration of this technique as applied to the liquid crystal 8CB was recently reported [1]. Here, we discuss the dynamics of the compaction of DNA by polyimine dendrimers, as studied using microfluidic devices. Due to the laminar flow inside the channels a highly defined, diffusion controlled compaction of DNA occurs. Different snapshots in the time of the reaction are accessible at varying spatial positions along the interaction jet. We use newly developed X-ray compatible microflow foils made from PDMS and Kapton and having dimensions ranging from 30 to 150 micrometers. The real-time evolution of a DNA-dendrimer columnar mesophase with an in-plane square symmetry is reported. These studies are also extended to include a larger library of dendrimers whose size and charge approach those of the biological histone proteins. [1] Dootz, Evans, Koester, Pfohl, accepted to Small. [Preview Abstract] |
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