scholarly journals Calculations of the potential and effective diffusion constant in a polyelectrolyte solution

1963 ◽  
Author(s):  
Sam R Coriell
Keyword(s):  
Effective Diffusion ◽  
Diffusion Constant ◽  
Polyelectrolyte Solution

Effective Diffusion Constant in a Polyelectrolyte Solution

1963 ◽  
Vol 38 (4) ◽  
pp. 959-968 ◽  
Author(s):  
Julius L. Jackson ◽  
Sam R. Coriell
Keyword(s):  
Effective Diffusion ◽  
Diffusion Constant ◽  
Polyelectrolyte Solution

scholarly journals Airborne infection in a fully air-conditioned hospital: III. Transport of gaseous and airborne particulate material along ventilated passageways

1975 ◽  
Vol 75 (1) ◽  
pp. 45-56 ◽  
Author(s):  
O. M. Lidwell
Keyword(s):  
Mathematical Model ◽  
Flow Velocity ◽  
Effective Diffusion ◽  
Diffusion Constant ◽  
Particulate Material ◽  
Airborne Particulate ◽  
Airborne Infection ◽  
Directional Flow ◽  
A Value

SUMMARYA mathematical model is described for the transport of gaseous or airborne particulate material between rooms along ventilated passageways.Experimental observations in three hospitals lead to a value of about 0.06m.2/sec. for the effective diffusion constant in air without any systematic directional flow. The ‘constant’ appears to increase if there is any directional flow along the passage, reaching about 0.12 m.2/sec. at a flow velocity of 0.04 m./sec.Together with previously published methods the present formulae make it possible to calculate the expected average amounts of gaseous or particulate material that will be transported from room to room in ventilated buildings in which the ventilation and exchange airflows can be calculated.The actual amounts transported in occupied buildings, however, vary greatly from time to time.

scholarly journals Perturbation theory for the effective diffusion constant in a medium of random scatterers

2004 ◽  
Vol 37 (44) ◽  
pp. 10459-10477 ◽  
Author(s):  
D S Dean ◽  
I T Drummond ◽  
R R Horgan ◽  
A Lefèvre
Keyword(s):  
Perturbation Theory ◽  
Effective Diffusion ◽  
Diffusion Constant

WALKING ON RATCHETS WITH TWO BROWNIAN MOTORS

2004 ◽  
Vol 04 (01) ◽  
pp. L161-L170 ◽  
Author(s):  
JOSE L. MATEOS
Keyword(s):  
Effective Diffusion ◽  
Diffusion Constant ◽  
Brownian Motors ◽  
Coherent Transport ◽  
Dimensionless Ratio ◽  
Bistable Potential ◽  
External Time ◽  
Stable Points ◽  
White Noises ◽  
Ratchet Potential

We analyze a model for a walker moving on an asymmetric periodic ratchet potential. This model is motivated by the properties of transport of the motor protein kinesin. The walker consists of two feet represented as two particles coupled nonlinearly through a double-well bistable potential. In contrast to linear coupling, the bistable potential admits a richer dynamics where the ordering of the particles can alternate during the walking. The transitions between the two stable points on the bistable potential, correspond to a walking with alternating particles. In our model, each particle is acted upon by independent white noises, modeling thermal noise, and additionally we have an external time-dependent force that drives the system out of equilibrium, allowing directed transport. In the equilibrium case, where only white noise is present, we perform a bifurcation analysis which reveals different walking patterns. In particular, we distinguish between two main walking styles: alternating and no alternating. These two ways of walking resemble the hand-over-hand and the inchworm walking in kinesin, respectively. Numerical simulations showed the existence of current reversals and significant changes in the effective diffusion constant. We obtained an optimal coherent transport, characterized by a maximum dimensionless ratio of the current and the effective diffusion (Péclet number), when the periodicity of the ratchet potential coincides with the equilibrium distance between the two particles.

Brownian Simulation of Matrix Diffusion

2000 ◽  
Vol 663 ◽  
Author(s):  
Sofie Andersson ◽  
Allan T. Emrén
Keyword(s):  
Effective Diffusion ◽  
Diffusion Constant ◽  
Boltzmann Distribution ◽  
Matrix Diffusion ◽  
Rock Matrix ◽  
Dissolved Species ◽  
Apparent Diffusion ◽  
Wide Variability ◽  
Far From Equilibrium ◽  
Solid Piece

ABSTRACTThe commonly used approach in dealing with matrix diffusion is to assign an effective diffusion constant for the radionuclide in the rock matrix. The idea behind this approach is that, on a scale much larger than the pore size, the irregularities tend to cancel out. Although it might look plausible at first sight, this approach has been questioned both for theoretical and experimental reasons.Here, Brownian simulation has been used to investigate the transport of dissolved material in a rock matrix modeled as a system of pores with a wide variability in size and shape. The Boltzmann distribution is used locally, although the system globally is far from equilibrium.The simulation consists of two main parts. First, the model rock is formed by precipitation of irregular mineral grains from a liquid phase. As the grains grow, they tend to form a mostly solid piece of rock.In the second part of the simulation, a dissolved species is introduced at one side of the rock and allowed to diffuse through its pore system. It is found that no apparent diffusion constant, D, can explain the properties of the system. Rather, D is found to be a function of both distance and time.

scholarly journals The accidental ally: Nucleosomal barriers can accelerate cohesin mediated loop formation in chromatin

2019 ◽  
Author(s):  
Ajoy Maji ◽  
Ranjith Padinhateeri ◽  
Mithun K. Mitra
Keyword(s):  
Effective Diffusion ◽  
Diffusion Constant ◽  
Loop Formation ◽  
Base Pairs ◽  
Diffusion Constants ◽  
Dna Backbone ◽  
The Mean ◽  
The Times ◽  
Lower Loop ◽  
Kinetics Of

AbstractAn important question in the context of the 3D organization of chromosomes is the mechanism of formation of large loops between distant base pairs. Recent experiments suggest that the formation of loops might be mediated by Loop Extrusion Factor proteins like cohesin. Experiments on cohesin have shown that cohesins walk diffusively on the DNA, and that nucleosomes act as obstacles to the diffusion, lowering the permeability and hence reducing the effective diffusion constant. An estimation of the times required to form the loops of typical sizes seen in Hi-C experiments using these low effective diffusion constants leads to times that are unphysically large. The puzzle then is the following, how does a cohesin molecule diffusing on the DNA backbone achieve speeds necessary to form the large loops seen in experiments? We propose a simple answer to this puzzle, and show that while at low densities, nucleosomes act as barriers to cohesin diffusion, beyond a certain concentration, they can reduce loop formation times due to a subtle interplay between the nucleosome size and the mean linker length. This effect is further enhanced on considering stochastic binding kinetics of nucleosomes on the DNA backbone, and leads to predictions of lower loop formation times than might be expected from a naive obstacle picture of nucleosomes.

scholarly journals Chemotaxis and topotaxis add vectorially for amoeboid cell migration

2019 ◽  
Author(s):  
Joeri A. J. Wondergem ◽  
Maria Mytiliniou ◽  
Falko C. H. de Wit ◽  
Thom G. A. Reuvers ◽  
David Holcman ◽  
...  
Keyword(s):  
Cell Migration ◽  
Chemical Cues ◽  
Effective Diffusion ◽  
Diffusion Constant ◽  
Emergent Property ◽  
Coarse Grained ◽  
Chemical Gradients ◽  
Amoeboid Cell ◽  
Physical And Chemical ◽  
Chemotactic Gradient

AbstractCells encounter a wide variety of physical and chemical cues when navigating their native environments. However, their response to multiple simultaneous cues is not yet clear. In particular, the influence of topography, in the presence of a chemotactic gradient, on their migratory behavior is understudied. Here, we investigate the effects of topographical guidance on highly motile amoeboid cell migration (topotaxis) generated by asymmetrically placed micropillars. The micropillar field allows for an additional, natural chemotactic gradient in two different directions, thereby revealing the relevance of topotaxis in the presence of cell migration directed by chemical gradients (chemotaxis). Interestingly, we found that the topotactic drift generated by the pillar field is conserved during chemotaxis. We show that the drifts generated by both these cues add up linearly. A coarse-grained analysis as a function of pillar spacing subsequently revealed that the strength and direction of the topotactic drift is determined by (i) the pore size, (ii) space between pores, and (iii) the effective diffusion constant of the cells. Finally, we argue that topotaxis must be conserved during chemotaxis, as it is an emergent property of both the asymmetric properties of the pillar field and the inherent stochasticity of (biased) amoeboid migration.

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