Sat, 26 Jul 2008 08:32:06 BST CiteULike: dchen tracer http://www.citeulike.org/user/dchen/tag/tracer CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/dchen/article/2874167 <i>Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 77, No. 4. (2008)</i><br /><br />We calculated tracer diffusion in a sheared suspension of non-Brownian rigid spheres and propose a numerical method based on a boundary element method and Stokesian dynamics method. We present details of the numerical method and examine the accuracy of the method. The limitation of semidiluteness is due to the accuracy of the tracer velocity calculation. The results show that the diffusivity of fluid tracers is greater than that of suspended spheres in the semidilute regime. The diffusivity of the velocity gradient direction is about threefold greater than that in the vorticity direction. Simple scaling demonstrates that the diffusivity of fluid tracers increases with the square of the volume fraction of spheres in the semidilute regime, which is confirmed numerically. Shear-induced fluid-tracer diffusion in a semidilute suspension of spheres Takuji Ishikawa Takami Yamaguchi doi:10.1103/PhysRevE.77.041402 Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 77, No. 4. (2008) 2008-06-08T23:08:06-00:00 2008 Physical Review E (Statistical, Nonlinear, and Soft Matter Physics) 77 4 APS 2008 diffusion pre shear simulation tracer http://www.citeulike.org/user/dchen/article/2801926 <i>Fungal Genetics and Biology, Vol. 44, No. 1. (January 2007), pp. 1-13.</i><br /><br />Optical tweezers have been little used in experimental studies on filamentous fungi. We have built a simple, compact, easy-to-use, safe and robust optical tweezer system that can be used with brightfield, phase contrast, differential interference contrast and fluorescence optics on a standard research grade light microscope. We have used this optical tweezer system in a range of cell biology applications to trap and micromanipulate whole fungal cells, organelles within cells, and beads. We have demonstrated how optical tweezers can be used to: unambiguously determine whether hyphae are actively homing towards each other; move the Spitzenkörper and change the pattern of hyphal morphogenesis; make piconewton force measurements; mechanically stimulate hyphal tips; and deliver chemicals to localized regions of hyphae. Significant novel experimental findings from our study were that germ tubes generated significantly smaller growth forces than leading hyphae, and that both hyphal types exhibited growth responses to mechanical stimulation with optically trapped polystyrene beads. Germinated spores that had been optically trapped for 25 min exhibited no deleterious effects with regard to conidial anastomosis tube growth, homing or fusion. Optical tweezer micromanipulation of filamentous fungi Graham Wright Jochen Arlt Wilson Poon Nick Read doi:10.1016/j.fgb.2006.07.002 Fungal Genetics and Biology, Vol. 44, No. 1. (January 2007), pp. 1-13. 2008-05-15T14:58:07-00:00 2007 Fungal Genetics and Biology 44 1 1 13 2006 biology opticaltweezer poon tracer http://www.citeulike.org/user/dchen/article/2763281 <i>Physical Review Letters, Vol. 100, No. 12. (2008)</i><br /><br />Applications of probe diffusion in polymer matrices typically envision that for particles sizes (R) larger than the correlation length of the polymer solution (), the probe (at long times) diffuses as in a continuum polymer solution. We present simulation results for probe diffusion in rod solutions which challenge this conventional wisdom and indicate a new mechanism of a probe diffusion operative for R>. Our simulation results are rationalized by scaling arguments invoking a novel mechanism of the constraint release motion of the rods, and suggest that the dynamical characteristics of the polymer matrix also proves important in developing a complete description of the probe motion. Dynamics of Probe Diffusion in Rod Solutions Victor Pryamitsyn Venkat Ganesan doi:10.1103/PhysRevLett.100.128302 Physical Review Letters, Vol. 100, No. 12. (2008) 2008-05-07T00:55:39-00:00 2008 Physical Review Letters 100 12 APS diffusion dynamics rod tracer http://www.citeulike.org/user/dchen/article/1505138 <i>Journal of Magnetism and Magnetic Materials, Vol. 293, No. 1. (May 2005), pp. 663-670.</i><br /><br />Metal-capping of one hemisphere of a nano or microparticle breaks the particle's optical symmetry, allowing its orientation to be tracked using fluorescence and reflection. Tracking orientation and rotation allows the torques acting on the particles be inferred. In addition to serving as rotational nanoviscometers these probes report on local Brownian, magnetic and biomechanical torques. Microrheology with modulated optical nanoprobes (MOONs) Caleb Behrend Jeffrey Anker Brandon Mcnaughton Raoul Kopelman doi:10.1016/j.jmmm.2005.02.072 Journal of Magnetism and Magnetic Materials, Vol. 293, No. 1. (May 2005), pp. 663-670. 2007-07-26T18:15:07-00:00 2005 Journal of Magnetism and Magnetic Materials 293 1 663 670 nano tracer http://www.citeulike.org/user/dchen/article/2730833 <i>Europhys. Lett., 67 (3), p. 477 (2004)</i><br /><br />We use confocal microscopy to study the motion of a magnetic bead in a dense colloidal suspension, near the colloidal glass transition volume fraction $φ_ g$. For dense liquid-like samples near $φ_ g$, below a threshold force the magnetic bead exhibits only localized caged motion. Above this force, the bead is pulled with a fluctuating velocity. The relationship between force and velocity becomes increasingly nonlinear as $φ_ g$ is approached. The threshold force and nonlinear drag force vary strongly with the volume fraction, while the velocity fluctuations do not change near the transition. Forced motion of a probe particle near the colloidal glass transition Habdas Europhys. Lett., 67 (3), p. 477 (2004) 2008-04-28T19:13:52-00:00 Europhys. Lett., 67 (3), p. 477 (2004) colloids glass tracer weeks