A single colloidal sphere circulating around a periodically modulated optical vortex trap can enter a dynamical state in which it intermittently alternates between freely running around the ringlike optical vortex and becoming trapped in local potential energy minima. Velocity fluctuations in this randomly switching state still are characterized by a linear Einstein-like diffusion law, but with...

The Fick diffusion equation is combined with the Langmuir adsorption isotherm and the relevant equations from the Gouy-Chapman theory of the electrical diffuse double layer to demonstrate that the effective diffusion coefficient of calcium ions, both in the cytoplasm of the rod outer segment and within the aqueous space bounded by the disk membrane, should be reduced by a factor of 10-100 becau...

What is a “diffusion coefficient” or “diffusion tensor” in living tissue, anyway? While the measurement of the self-diffusivity in an NMR tube represents a "gold standard", in complex media particularly in living tissue, water “diffusivity” ceases to have a clear meaning or definition. The apparent diffusion coefficient (ADC) and apparent diffusion tensor (ADT) concepts were introduced to answe...

The transient diffusion of fluorescent tracers into biofilm cell clusters of Staphylococcus epidermidis was visualized by time lapse confocal scanning laser microscopy. Rhodamine B diffused into the center of cell clusters that were 200 to 600 microm in diameter within a few minutes. The apparent effective diffusion coefficient calculated from these data averaged 3.7 x 10(-7) cm(2) s(-1) or 11%...

Based on an independent forward model in fluorescent tomography, a parallel reconstructed scheme for inhomogeneous mediums with unknown absorption property is proposed in this paper. The method considers the two diffusion equations as separately describing the propagation of excited light in tissues with and without fluorescent probes inside. Then the concentration of fluorophores is obtained d...

Self-diffusion of a sphere in a network of rods is analyzed theoretically. Hydrodynamic interactions are taken into account according to the model of Dhont et al. [J. Chem. Phys. 122, 044905 (2005); ibid.124, 044907 (2006); ibid.126, 214501 (2007)] based on the Debye-Bueche-Brinkman equation. The hydrodynamic screening length of the effective medium is assumed to be much larger than the sphere ...

Biological cluster of cells may be seen as porous media, where the cells are the “solid grains” and the extracellular space (ECS) the “pores”. It is often the case in dense clusters of cells that the flow rate of liquid inside the extracellular space is negligible in front of the molecular diffusion. In the particular case of tumoral cells, the extra-cellular path is the tumor interstitial matr...

Objectives: The purpose the study was to evaluate role of diffusion weighted magnetic resonance imaging (DW-MRI) in diagnosis benign and malignant breast lesions, calculate a cut-off apparent coefficient (ADC) value explore use relative ADC (r ADC) for improving sensitivity specificity MRI cancer. Methods: This retrospective based on cohort patients who underwent dynamic contrast enhanced (DCE)...