Bulletin of the American Physical Society
74th Annual Meeting of the Southeastern Section
Volume 52, Number 13
Thursday–Saturday, November 8–10, 2007; Nashville, Tennessee
Session BB: Fluids and Biophysics |
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Chair: Lloyd M. Davis, University of Tennessee Space Institute Room: Scarritt-Bennett Center Laskey C |
Thursday, November 8, 2007 8:30AM - 8:42AM |
BB.00001: Measurement of swimming force generation during flagella regeneration in \textit{Chlamydomonas reinhardtii} John N. Yukich, Mona Shaban, Catherine Clodfelter, Karen Bernd The green alga \textit{Chlamydomonas reinhardtii }has been at the forefront of many studies investigating the establishment and function of flagella in facilitating cellular motility. Previously we reported an intriguing pattern during flagella regeneration in which increases in force do not always correspond with increase in flagella length. That work made direct measurement of maximum flagellar swimming force by measuring the cell's ability to escape from an optical trap (\textit{optical} \textit{tweezers}). Here, we report on optimization and automation of the force measurement using power spectral density calibration of the trap and distance of periodic displacement from the trap center. This process yields an average value for the swimming force. The intriguing pattern described for maximum swimming force is also evident in the average swimming force data, suggesting that the phenomenon reflects a change in flagella functionality during regeneration. [Preview Abstract] |
Thursday, November 8, 2007 8:42AM - 8:54AM |
BB.00002: Numerical modeling of single-molecule detection and trapping in a nanochannel William Robinson, Zbigniew Sikorski, Lloyd M. Davis Confocal fluorescence microscopy with single-photon counting enables detection of individual fluorescent molecules as they randomly diffuse through a tightly focused laser beam. However, for many biophysical studies, there is a need to observe the same molecule for an extended duration, without immobilizing it to a surface. The problem of trapping a single fluorescent molecule in solution is examined here via numerical simulation. Optical trapping provides insufficient force for trapping small biomolecules. Instead, a means for sensing the molecule's position and applying real-time feedback of motion to compensate diffusional displacement is used for trapping. The use of a nanochannel to confine the molecule reduces the problem to one dimension. The position of the molecule along the nanochannel is measured from its fluorescence induced by a pulse-interleaved two-beam laser-irradiance pattern. The time-gated photons are analyzed via maximum-likelihood methods and an electrophoretic motion provides the trapping mechanism. Flexible parameters allow a multi-variable analysis of the trapping efficiency and effectiveness. The reaction of the flow is set to the time-delayed response of a realistic field-programmable gate array (FPGA) controller. Trapping algorithms developed in the simulation are to be experimentally implemented in the FPGA. [Preview Abstract] |
Thursday, November 8, 2007 8:54AM - 9:06AM |
BB.00003: Quantification of the Motion of Non-Adherent Cells in a Microfluidic Device Eric Kim, Kevin Seale, John Wikswo Cellular motion involves a large number of intracellular processes impacted by environmental factors or toxins. Non-adherent cells such as Jurkats constantly move non-translationally when trapped in microfluidic devices. The degree to which they move may be indicative of many environmental influences and intracellular conditions. We have devised a technique wherein we assay intracellular conditions by utilizing the quantification of overall cellular motion irrespective of center of mass. Differential image stacks are formed from bright field image stacks by subtracting from spatial pixels their next temporal counterparts. Image pixels in each frame are summed to develop a quantitative plot of overall cellular kinetics over time in the field of view. To demonstrate intracellular correlation, we used paraformaldehyde to fix cells and halt cell movement. Our results indicate an average percent drop of 6.6{\%} in processed pixel intensity with fixation relative to baseline (n=6 and p $<$0.05). Within each plot we find p$<$0.05 between baseline and fixation points. This simple, image-processing assay shows promise for characterization of intracellular conditions in response to environmental influences in microfluidics. [Preview Abstract] |
Thursday, November 8, 2007 9:06AM - 9:18AM |
BB.00004: Molecular Dynamics simulation of Buttiker-Landauer ratchet Ronald Benjamin, Ryoichi Kawai A position dependent temperature profile in presence of a periodic potential leads to directed current of Brownian particles, commonly known as Buttiker-Landauer ratchet. Onsager symmetry tells us that inhomogeneous temperature profile can be generated by reversing the Buttiker-Landauer ratchet. When Brownian particles driven by a constant external force cross over the potential barrier, they carry heat from one side to the other. Hence, starting with uniform temperature the flow of Brownian particles induces inhomogeneous temperature profile. We investigate this phenomenon using first principles molecular dynamics simulations as well as the phenomenologial Langevin equation. [Preview Abstract] |
Thursday, November 8, 2007 9:18AM - 9:30AM |
BB.00005: Fast and slow ultrasonic group velocities in aqueous suspensions of polymer microspheres Robert Heithaus, Joel Mobley Suspensions of narrowly sized polymer microspheres can exert surprisingly large dispersive effects on through-transmitted ultrasonic wavepackets. In a recent set of experiments, the transmission of arbitrarily large and negative group velocities were observed in an aqueous suspension of 160 $\mu $m diameter spheres at a volume fraction of 3{\%}. In this talk, we report on both broadband and narrowband measurements of the phase and group velocity spectra in these media, including the observation of superluminal, negative and abnormally slow group speeds. [Preview Abstract] |
Thursday, November 8, 2007 9:30AM - 9:42AM |
BB.00006: Multiple non-ergodic transitions in supercooled liquids Rachel Aga, James Morris, Valentin Levashov, Takeshi Egami We present simulation results for a simple model supercooled liquid showing changes in behavior of properties resulting to the observed onset of ergodicity loss within the timescale of the simulation, the breakdown of hydrodynamic flow in the liquid, and the double-peak formation in g(r). We find that these changes all occur at the same temperature. The identification of a common crossover temperature suggests the existence of significant changes in dynamics at that temperature. The crossover temperature identified is different from the critical temperature defined in mode coupling theory (MCT) as it occurs at a much higher temperature. Thus, in this work, we demonstrate that prior to glass transition are two distinct changes in behavior: a lower temperature transition associated with MCT and a higher temperature transition associated with the onset of ergodic to nonergodic behavior. [Preview Abstract] |
Thursday, November 8, 2007 9:42AM - 9:54AM |
BB.00007: Characterization of High Q Spherical Resonator Kenneth Bader, Jason Raymond, Joel Mobley, Felipe Gaitan, Ross Tessien, Robert Hiller This paper describes the vibrational dynamics of a spherical acoustical resonator system used in the study of acoustic cavitation phenomena in liquids as part of an effort to scale up the energy density of collapse of transient cavitation. The system consists of a stainless steel shell (10" OD and 0.5" thick) filled with degassed water that exhibits several high Q ($>$10 000) modes in the 20-40 kHz range, and which is driven by an external horn-type transducer. This paper will focus on the characterization of the vibrational spectrum of the resonator as well as the radial variations of the pressure fields in the liquid internal to the shell. The vibrations of the shell surface are monitored using an attached ultrasonic transducer as well as a laser Doppler vibrometer. The internal pressure fields of the sphere are mapped using needle type hydrophones. The vibrational spectrum will be compared with theoretical predictions for moderately thick shell resonators developed by Mehl (JASA 78(2), 1985, pp. 782-788). [Preview Abstract] |
Thursday, November 8, 2007 9:54AM - 10:06AM |
BB.00008: Unusual Particle Drift in a Rotating Flow. Antonino Carnevali, Rebecca Scott An unexpected, asymmetry-induced steady particle drift in viscous liquids filling a horizontal cylinder rotating around its axis was first reported by Bluemink \textit{et al}. [Physics of Fluids \textbf{17}, 2005]. We have explored the motion further, particularly its dependence on the aspect ratio (L/r) of the cylinder. Experiments at smaller aspect ratio show that the drift is not steady, rather it is formed of repeated leaps, which are associated with the changing axial tilt of the particle or air bubble. We investigate the forces acting on the particle and the possible sources of this particular motion. [Preview Abstract] |
Thursday, November 8, 2007 10:06AM - 10:18AM |
BB.00009: Kinetics, Stretching and Cross-Stream Migration of Polymer Solutions in Nanoscale pores under Poiseuille Flow Jaime Millan, Mohamed Laradji Polymer solutions in nanoscale slit pores and under Poiseuille flow are systematically investigated via dissipative particle dynamics simulations. We consider the effects of molecular weight, volume fraction, pressure gradient, and Schmidt number on the velocity profiles, polymer density and conformational profiles. We found that the mean fluid velocity decreases with increasing chain length and/or polymer volume fraction. The deviation of the velocity profile from the quadratic profile is more pronounced as the polymer molecular weight or concentration is increased. The polymer chains are least stretched along the direction of the flow in the midsection of the slit. In the direction perpendicular to the flow, the polymers are more stretched in the midsection of the slit. In the case of polymer solutions with a low Schmidt number, the polymer density profile is found to be non-uniform, and migration is observed either toward the walls or toward the midsection. However, in the case of polymer solutions with high Schmidt number, a migration toward the midsection of the slit is observed. [Preview Abstract] |
Thursday, November 8, 2007 10:18AM - 10:30AM |
BB.00010: Application of Vorticity Confinement to Turbulence Nicholas Lynn, John Steinhoff The Vorticity Confinement (VC) technique will be described that can accurately and efficiently compute high Reynolds number turbulence. Physically these flows are dominated by thin vortices that can be convected long distances without significant dissipation; VC treats these features as modeled solitary waves directly represented on the computational grid. Another feature of VC is that it contains an immersed boundary model, which allows the simple treatment of complex bodies. The VC method then models the boundary layer, which may separate, over 2-3 grid cells near the surface. VC will be contrasted with conventional Eulerian computational methods. It will be explained how VC, particularly for flows containing treating thin, convecting vortices, eliminates the deficiencies of the conventional methods. Following the description of the model, a sequence of turbulent VC results is presented. First presented is turbulent flow over a cylinder. The cylinder is immersed in a uniform Cartesian grid. Results will be compared against experiments showing the ability of VC to compute the resulting wake despite utilizing a coarse grid. Also present will be a study on the Taylor-Green vortex. [Preview Abstract] |
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