scholarly journals A rapid method for determining diffusion constants in solution

1948 ◽  
Vol 192 (1030) ◽  
pp. 382-402 ◽  
Keyword(s):  
Monochromatic Light ◽  
Diffusion Constant ◽  
Initial Boundary ◽  
Optic Axis ◽  
Theory And Practice ◽  
Dilute Solution ◽  
Sharp Boundary ◽  
Diffusion Constants ◽  
A Cell ◽  
Molecular Substances

A method has been rediscovered, and developed in theory and practice, for optical observation of the earliest stages of diffusion across an initially sharp boundary between a dilute solution and a solvent. It enables the diffusion constant of a monodisperse solute to be measured about fifty times as quickly as by other methods, at lower concentration and possibly with greater accuracy; it should therefore be particularly valuable for the study of high molecular substances. The method is based on the interference pattern which is formed when monochromatic light from a horizontal slit is focused after passing through a cell where diffusion is occurring. The pattern, a set of horizontal bands, contracts towards the optic axis as diffusion proceeds, at a rate from which the diffusion constant can be calculated. By counting the bands in the pattern the refractive increment of the solute can be determined. The sharp initial boundary is obtained by flowing the solution and solvent out through a common narrow horizontal slit. The construction, calibration, and use of the apparatus are described.

The dynamics of auxin transport

1980 ◽  
Vol 209 (1177) ◽  
pp. 489-511 ◽  
Keyword(s):  
Plant Hormone ◽  
Auxin Transport ◽  
Unit Area ◽  
Aqueous Media ◽  
Diffusion Constant ◽  
Directed Motion ◽  
Concentration Gradients ◽  
Forward Movement ◽  
A Cell ◽  
Polar Mechanism

The plant hormone auxin is transported with a well defined velocity through many tissues. To explain this, one type of theory proposes that a polar mechanism operates at the interface between two cells. I show that, if auxin diffuses freely through the interior of cells, then there is an upper limit to the velocity that can be achieved by such a mechanism. This is compatible with the observed velocities provided that the diffusion constant for auxin within a cell is not much less than that measured for auxin in aqueous media. Cytoplasmic streaming, unless specially organized, would not assist the movement of auxin. This is because rapid diffusion between streams will cancel out any directed motion. I also show that the permeability that characterizes the forward movement between cells must exceed a certain limit. If auxin moves mainly through the cytoplasm, which occupies only a small part of the volume of a cell, then the permeability per unit area of membrane needed to achieve a given velocity is much reduced. Transport would be channelled through the cytoplasm if the membrane bounding the vacuole were relatively impermeable to auxin. The theory that I develop leads to predictions about, for example, the route of auxin and its concentration gradients within cells, and the dependence of velocity on cell length.

DIFFUSION OF Tl+ IONS THROUGH THE INTERFACE OF SOLID NaCl, KCl OR RbCl AND LIQUID TlCl

2002 ◽  
Vol 16 (01n02) ◽  
pp. 108-113
Author(s):  
W. YU ◽  
A. FUJII
Keyword(s):  
Sodium Chloride ◽  
Single Crystals ◽  
Optical Method ◽  
Diffusion Constant ◽  
Liquid Interface ◽  
Diffusion Constants ◽  
Diffusion Phenomena ◽  
Diffusion Source ◽  
Solid Liquid Interface ◽  
Solid Liquid

The diffusion phenomena of thallous ions ( Tl + ions) through solid-liquid interface of liquid Tl + ions diffusion source and sodium chloride (NaCl) , potassium chloride (KCl) or rubidium chloride (RbCl) single crystals are studied by optical method. The characterisic absorption peaks of Tl + center in NaCl, KCl or RbCl single crystals were used as the tracer for measurements and the diffusion constants are evaluated at various temperatures. The results show that the diffusion constant of solid-liquid interface is about 103 times larger than that of solid-solid interface of KCl and TlCl .

Electrochemical Lithium Intercalation into Nb2O5Cathode for 2 V Class-Secondary Lithium Batteries

1999 ◽  
Vol 575 ◽  
Author(s):  
Naoaki Kumagai ◽  
Shinichi Komaba ◽  
Nobuko Kumagai
Keyword(s):  
Lithium Battery ◽  
Lithium Intercalation ◽  
Free Energies ◽  
Discharge Performance ◽  
Self Diffusion ◽  
Diffusion Constants ◽  
Secondary Lithium Batteries ◽  
A Cell ◽  
Kinetics Of ◽  
Crystal Lattice Parameters

ABSTRACTNb2O5powder was prepared by heating niobium hydroxide in the temperature range from 600 to 1000°C. The crystal system of Nb2O5compounds depended on the heating temperatures,i.e., hexagonal, orthorhombic and monoclinic Nb2O5compounds were obtained at 600, 800 and 1000°C, respectively. Electrochemical lithium intercalation into the three Nb2O compounds was investigated in a cell with an LiClO4-propylene carbonate electrolytic solution for the application as lithium battery cathodes. As a result, they displayed good charge-discharge performance as the cathode of 2 V class-lithium battery, which will play important role in power supply for IC memory backup developed recently. The thermodynamics and kinetics of the lithium intercalation into the Nb2O5cathode have been investigated. The thermodynamic parameters, such as standard free energies, lithium partial molar entropy, interaction energies between ions, the crystal lattice parameters, and the kinetic parameters, such as chemical and self diffusion constants, have been obtained as a function ofx-value in LiNb2O5.

DIFFUSION CONSTANT MEASUREMENT IN THEORY AND PRACTICE

1945 ◽  
Vol 46 (5 The Diffusion) ◽  
pp. 309-327 ◽  
Author(s):  
Edward M. Bevilacqua ◽  
Ellen B. Bevilacqua ◽  
Margaret M. Bender ◽  
J. W. Williams
Keyword(s):  
Diffusion Constant ◽  
Theory And Practice ◽  
Constant Measurement

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.

An experiment showing an increase with dilution in a physical parameter

1981 ◽  
Vol 70 (03) ◽  
pp. 129-135 ◽  
Author(s):  
S.J. Hadley
Keyword(s):  
Phase Shift ◽  
Physical Parameter ◽  
High Frequency ◽  
Alternating Current ◽  
Dilute Solution ◽  
Simple Apparatus ◽  
A Cell

SummaryA simple apparatus is described with which it is possible to measure the phase shift induced in a high frequency alternating current by a cell containing a dilute solution of an electrolyte.This phase shift is seen to INCREASE WITH DILUTION up to a limit determined by the electrolyte chosen (but usually within the range 10−4 to 10−6) and then to decrease with further dilution to zero.Solutions of salts and sugar in water and dilute alcohol are investigated.The findings are discussed.

Choosing the right fictions of scientific law

1980 ◽  
Vol 239 (5) ◽  
pp. R365-R371
Author(s):  
D. O. Walter
Keyword(s):  
Cell Culture ◽  
Quantum Mechanics ◽  
Quantum Theory ◽  
Civil Law ◽  
Theory And Practice ◽  
A Cell ◽  
The Right ◽  
Biological Simulation ◽  
The Brain ◽  
Surprising Fact

Fictions are well established in the theory and practice of civil law; similar importance is here claimed for fictions in the theory and application of scientific law. A puzzle from quantum mechanics, previously referred to in this Journal [Am. J. Physiol. 238 (Regulatory Integrative Comp. Physiol. 7(: R277-R290, 1980], is reinterpreted by suggesting quantum logic as a source of relevant fictions, which indicate a solution to that puzzle. Another physiological application of quantum theory suggests that the concept of "the state of the brain" may, in its usual classical sense, not be useful for an individual brain--but may well be suggestively modeled by a quantum state. The notion of "myths," usually only pejoratively applied in positivistic writings, is suggested for rehabilitation, in view of their helpful function (often unnoticed) even in positivistic thinking. Finally, an example of a biological simulation (of a tumor by a cell culture) is presented, to show that its multilayered fictionalizations illustrate the surprising fact that a simulation that is insulated from the system being simulated can be logically more powerful than any uninsulated simulation.

Protection of Archival Record From Pollutants the Diffusion of SO2 Through Archival Boxboard

1992 ◽  
Vol 267 ◽  
Author(s):  
Charles M. Guttman ◽  
Kenneth L. Jewett
Keyword(s):  
Sulfur Dioxide ◽  
Diffusion Constant ◽  
Gas Concentration ◽  
Diffusion Constants ◽  
National Archives ◽  
Archival Storage ◽  
Archival Documents ◽  
Archival Record

ABSTRACTThe diffusion constants of sulfur dioxide in boxboards, commonly used to store archival documents, have been measured. For the most common boxes used by National Archives and Record Administration a diffusion constant of about 0.001 cm2 / sec was determined independent of gas concentration. These results are discussed in terms of a model of the microenvironment provided by these boxboards as used in archival storage.

scholarly journals A Markov chain identity and monotonicity of the diffusion constants for a random walk in a heterogeneous environment

1990 ◽  
Vol 108 (1) ◽  
pp. 111-126 ◽  
Author(s):  
J. B. T. M. Roerdink
Keyword(s):  
Random Walk ◽  
Transition Probabilities ◽  
Monotonicity Property ◽  
Square Lattice ◽  
Electric Networks ◽  
Monotonic Functions ◽  
Diffusion Constants ◽  
A Cell ◽  
Finite Markov Chains ◽  
The Individual

AbstractWe consider a 2-dimensional square lattice which is partitioned into a periodic array of rectangular cells, on which a nearest neighbour random walk with symmetric increments is defined whose transition probabilities only depend on the relative position within a cell. On the basis of a determinantal identity proved in this paper, we obtain a result for finite Markov chains which shows that the diffusion constants for the random walk are monotonic functions of the individual transition probabilities. We point out the similarity of this monotonicity property to Rayleigh's Monotonicity Law for electric networks or, equivalently, reversible random walks.

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