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Diffusion

About: Diffusion is a research topic. Over the lifetime, 28368 publications have been published within this topic receiving 643228 citations.


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TL;DR: In this article, a derivation of the effect of a time-dependent magnetic field gradient on the spin-echo experiment, particularly in the presence of spin diffusion, is given.
Abstract: A derivation is given of the effect of a time‐dependent magnetic field gradient on the spin‐echo experiment, particularly in the presence of spin diffusion. There are several reasons for preferring certain kinds of time‐dependent magnetic field gradients to the more usual steady gradient. If the gradient is reduced during the rf pulses, H1 need not be particularly large; if the gradient is small at the time of the echo, the echo will be broad and its amplitude easy to measure. Both of these relaxations of restrictions on the measurement of diffusion coefficients by the spin‐echo technique serve to extend its range of applicability. Furthermore, a pulsed gradient can be recommended when it is critical to define the precise time period over which diffusion is being measured.The theoretical expression derived has been verified experimentally for several choices of time dependent magnetic field gradient. An apparatus is described suitable for the production of pulsed gradients with amplitudes as large as 100 ...

7,781 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that the rate of adsorption of persistent organic compounds on granular carbon is quite low and the rate is partially a function of the pore size distribution of the adsorbent, of the molecular size and configuration of the solute, and of the relative electrokinetic properties of adsorbate and adsorbents.
Abstract: Laboratory investigations show that rates of adsorption of persistent organic compounds on granular carbon are quite low. Intraparticle diffusion of solute appears to control the rate of uptake, thus the rate is partially a function of the pore size distribution of the adsorbent, of the molecular size and configuration of the solute, and of the relative electrokinetic properties of adsorbate and adsorbent. Systemic factors such as temperature and pH will influence the rates of adsorption; rates increase with increasing temperature and decrease with increasing pH. The effect of initial concentration of solute is of considerable significance, the rate of uptake being a linear function of the square-root of concentration within the range of experimentation. Relative reaction rates also vary reciprocally with the square of the diameter of individual carbon particle for a given weight of carbon. Based on the findings of the research, fluidized-bed operation is suggested as an efficient means of using adsorption for treatment of waters and waste waters.

7,115 citations

Journal ArticleDOI
TL;DR: It is found that as the surface charge of the lipid lamellae is increased, the amount of cation per μmle of lipid increases, and the phospholipid liquid crystalline structures appear to “bind” or “capture” cations.

4,341 citations

Journal ArticleDOI
TL;DR: The theory of reaction rates yields an equation for absolute viscosity applicable to cases involving activation energies where the usual theory of energy transfer does not apply as mentioned in this paper, which provides an explanation of the law of rectilinear diameters of Cailletet and Mathias.
Abstract: Since to form a hole the size of a molecule in a liquid requires almost the same increase in free energy as to vaporize a molecule, the concentration of vapor above the liquid is a measure of such ``molecular'' holes in the liquid. This provides an explanation of the law of rectilinear diameters of Cailletet and Mathias. The theory of reaction rates yields an equation for absolute viscosity applicable to cases involving activation energies where the usual theory of energy transfer does not apply. This equation reduces to a number of the successful empirical equations under the appropriate limiting conditions. The increase of viscosity with shearing stress is explained. The same theory yields an equation for the diffusion coefficient which when combined with the viscosity and applied to the results of Orr and Butler for the diffusion of heavy into light water gives a satisfactory and suggestive interpretation. The usual theories for diffusion coefficients and absolute electrical conductance should be replaced by those developed here when ion and solvent molecule are of about the same size.

2,656 citations

Journal ArticleDOI
TL;DR: In this paper, the stimulated echo attenuation due to self-diffusion was derived for the general case of a time-dependent field gradient, and the result was found experimentally to be correct for the special case of field gradient applied in two equal, square pulses.
Abstract: The stimulated echo in a three‐rf‐pulse experiment is shown to be useful in extending the range of measurement of diffusion coefficients to more viscous substances or the measurement of barrier separations to wider spacings in systems where the diffusing substance has T1 > T2. The spin‐echo attenuation due to self‐diffusion is derived for the general case of a time‐dependent field gradient, and the result is found experimentally to be correct for the special case of a field gradient applied in two equal, square pulses.

1,549 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20242
20234,592
20228,627
2021916
2020689
2019704