Variance of Local Concentration Fluctuations

1967 ◽  
Vol 10 (9) ◽  
pp. S76 ◽  
Author(s):  
G. T. Csanady
Keyword(s):  
Concentration Fluctuations ◽  
Local Concentration

Reactive transport in porous media with local mixing limitation: A Lagrangian modeling approach

2020 ◽  
Author(s):  
Guillem Sole-Mari ◽  
Daniel Fernàndez-Garcia ◽  
Xavier Sanchez-Vila ◽  
Diogo Bolster
Keyword(s):  
Porous Media ◽  
Reactive Transport ◽  
Mathematical Formulation ◽  
Random Motion ◽  
Concentration Fluctuations ◽  
Local Concentration ◽  
Flow And Transport ◽  
Transport In Porous Media ◽  
Lagrangian Modeling ◽  
Rate Interaction

<p>Hydrological models are unable to fully resolve subsurface flow and transport down to the microscale. Instead, modelers usually work with upscaled flow and transport properties that represent the behavior of the system at a given coarse scale. While this approach is justified from a practical standpoint, it disregards the local heterogeneity of porous media flows, which tend to produce mixing-limited reactive transport behaviors that cannot be captured by classical modeling approaches. While some innovative methods have been suggested in the past in order to address this problem, none of them has proposed a mathematical formulation which can potentially reproduce the generation, transport and decay of local concentration fluctuations and their impact on chemical reactions, for general initial and boundary conditions. Here, we propose a Lagrangian approach based on the random motion of fluid particles that locally mix following a Multi-Rate Interaction by Exchange with the Mean (MRIEM) formulation. Concentration fluctuations in the proposed model display the typical behavior associated to transport in porous media with mixing-limited conditions. Experimental results of reactive transport are successfully reproduced by the model.</p>

scholarly journals Influence of Concentration Fluctuations on Relaxation Processes in Spin Glasses

2018 ◽  
Vol 2 (4) ◽  
pp. 26 ◽  
Author(s):  
Julia Wagner ◽  
Wolfgang Häußler ◽  
Olaf Holderer ◽  
Andreas Bauer ◽  
Stephen Shapiro ◽  
...  
Keyword(s):  
Phase Transition ◽  
Spin Glass ◽  
Spin Glasses ◽  
Glass Phase ◽  
Concentration Fluctuations ◽  
Neutron Resonance ◽  
Relaxation Processes ◽  
Local Concentration ◽  
Spin Glass Phase ◽  
Resonance Spin

Using the unique combination of atomically resolved atom probe tomography (APT) and volume averaged neutron (resonance) spin echo (NRSE and NSE) experiments, the influence of nano-scaled clusters on the spin relaxation in spin glasses was studied. For this purpose, the phase transition from the paramagnetic phase to the spin glass phase in an Fe-Cr spin glass with a composition of Fe 17 . 8 Cr 82 . 2 was studied in detail by means of NRSE. The microstructure was characterised by APT measurements, which show local concentration fluctuations of Fe and Cr on a length scale of 2 to 5 nm, which lead (i) to the coexistence of ferro- and anti-ferromagnetic clusters and (ii) a change of the magnetic properties of the whole sample, even in the spin glass phase, where spins are supposed to be randomly frozen. We show that a generalized spin glass relaxation function, which was successfully used to describe the phase transition in diluted spin glasses, can also be used for fitting the spin dynamics in spin glasses with significant concentration fluctuations.

scholarly journals Iron Catalyst Local Concentration Fluctuations Found in Dissipative Reactions by X-Ray Microanalysis

1981 ◽  
Vol 54 (1) ◽  
pp. 321-322 ◽  
Author(s):  
Csaba P. Keszthelyi ◽  
József Soós ◽  
András G. S. Janossy ◽  
Kristóf Vovács
Keyword(s):  
Iron Catalyst ◽  
Concentration Fluctuations ◽  
Local Concentration ◽  
X Ray

scholarly journals Simulation of V(CN) Precipitation in Steels Allowing for Local Concentration Fluctuations

2006 ◽  
Vol 47 (11) ◽  
pp. 2732-2736 ◽  
Author(s):  
Javier Aldazabal ◽  
Carlos Garcia-Mateo ◽  
Carlos Capdevila
Keyword(s):  
Concentration Fluctuations ◽  
Local Concentration

scholarly journals Influence of Concentration Fluctuations on Relaxation Processes in Spin Glasses

2018 ◽  
Author(s):  
Julia Wagner ◽  
Wolfgang Häussler ◽  
Olaf Holderer ◽  
Andreas Bauer ◽  
Stephen Shapiro ◽  
...  
Keyword(s):  
Phase Transition ◽  
Spin Glass ◽  
Spin Glasses ◽  
Glass Phase ◽  
Concentration Fluctuations ◽  
Neutron Resonance ◽  
Relaxation Processes ◽  
Local Concentration ◽  
Spin Glass Phase ◽  
Resonance Spin

Using the unique combination of atomically resolved atom probe tomography (APT) and volume averaged neutron (resonance) spin echo (NRSE and NSE) experiments, the influence of nano-scaled clusters on the spin relaxation in spin glasses was studied. For this purpose, the phase transition from the paramagnetic phase to the spin glass phase in a Fe-Cr spin glass with a composition of Fe17.8Cr82.2 was studied in detail by means of NRSE. The microstructure was characterised by APT measurements, which show local concentration fluctuations of Fe and Cr on a length scale of 2 to 5 nm, which lead i) to the coexistence of ferro- and anti-ferromagnetic clusters and ii) a change of the magnetic properties of the whole sample, even in the spin glass phase, where spins are supposed to be randomly frozen. We show that a generalized spin glass relaxation function, which was successfully used to describe the phase transition in diluted spin glasses, can also be used for fitting the spin dynamics in spin glasses with significant concentration fluctuations.

Grain boundary segregation in metals

1992 ◽  
Vol 50 (2) ◽  
pp. 1204-1205
Author(s):  
C.L. Briant
Keyword(s):  
Fracture Surface ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Material Properties ◽  
Electron Spectroscopy ◽  
High Vacuum ◽  
Boundary Segregation ◽  
Grain Boundary Segregation ◽  
Local Concentration ◽  
The One

Grain boundary segregation is the process by which solute elements in a material diffuse to the grain boundaries, become trapped there, and increase their local concentration at the boundary over that in the bulk. As a result of this process this local concentration of the segregant at the grain boundary can be many orders of magnitude greater than the bulk concentration of the segregant. The importance of this problem lies in the fact that grain boundary segregation can affect many material properties such as fracture, corrosion, and grain growth.One of the best ways to study grain boundary segregation is with Auger electron spectroscopy. This spectroscopy is an extremely surface sensitive technique. When it is used to study grain boundary segregation the sample must first be fractured intergranularly in the high vacuum spectrometer. This fracture surface is then the one that is analyzed. The development of scanning Auger spectrometers have allowed researchers to first image the fracture surface that is created and then to perform analyses on individual grain boundaries.

Concentration determination of chromatin in unstained resin-embedded sections by means of Z-contrast in STEM

1990 ◽  
Vol 48 (2) ◽  
pp. 186-187
Author(s):  
M. Haider ◽  
B. Bohrmann
Keyword(s):  
Energy Loss ◽  
Freeze Substitution ◽  
Biological Macromolecules ◽  
Local Concentration ◽  
E Coli ◽  
Concentration Determination ◽  
Phosphorous Content ◽  
Z Contrast ◽  
Electron Energy Loss

The technique of Z-contrast in STEM offers the possibility to determine the local concentration of macromolecules like lipids, proteins or DNA. Contrast formation depends on the atomic composition of the particular structure. In the case of DNA, its phosphorous content discriminates it from other biological macromolecules. In our studies, sections of E. coli, the dinoflagellate Amphidinium carterae and Euglena spec. cells were used which were obtained by cryofixation followed by freeze-substitution into acetone with 3% glutaraldehyde. The samples were then embedded either in Lowicryl HM20 at low temperature or in Epon at high temperature. Sections were coated on both sides with 30Å carbon.The DF- and the inelastic image have been recorded simultaneously with a Cryo-STEM. This Cryo-STEM is equipped with a highly dispersive Electron Energy Loss Spectrometer. With this instrument pure Z-contrast can be achieved either with a Filtered DF-image divided by the inelastic image or, as is used in this paper, by dividing the conventional DF-image by an inelastic image which has been recorded with an inelastic detector whose response is dependent on the total energy loss of the inelastically scattered electrons.

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