A New View of Convective-Diffusive Transport Processes in the Arterial Intima

1991 ◽  
Vol 113 (3) ◽  
pp. 314-329 ◽  
Author(s):  
F. Yuan ◽  
S. Chien ◽  
S. Weinbaum
Keyword(s):  
Early Time ◽  
Transport Processes ◽  
Special Role ◽  
Diffusive Transport ◽  
Internal Elastic Lamina ◽  
Time Model ◽  
Feeding Experiments ◽  
Endothelial Surface ◽  
Extracellular Lipid ◽  
Order Of Magnitude

In this paper a new theoretical framework is presented for analyzing the filtration and macromolecular convective-diffusive transport processes in the intimal region of an artery wall with widely dispersed macromolecular cellular leakage sites, as proposed in the leaky junction-cell turnover hypothesis of Weinbaum et al. [11]. In contrast to existing convection-diffusive models, which assume that the transport is either 1-D, or convection is primarily in a direction normal to the endothelial surface, the present model considers for the first time the nonuniform subendothelial pressure field that arises from the different hydraulic resistances of normal and leaky endothelial clefts and the special role of the internal elastic lamina (IEL) in modulating the horizontal transport of macromolecules after they have passed through the leaky clefts of cells that are either in mitosis or demonstrate IgG labeling. The new theory is able to quantitatively explain the growing body of recent experiments in which an unexpectedly rapid early-time growth of the leakage spot has been observed and the longer time asymptotic behavior in which the leakage spot appears to approach an equilibrium diameter. The new theory also predicts the observed doubling in macromolecular permeability between EBA labeled blue and white areas when the frequency of leakage sites is doubled. This frequency for doubling of permeability, however, is an order of magnitude smaller than predicted by the author’s previous model, Tzeghai et al. [10], in which only convection normal to the endothelial surface was considered and the pressure was uniform in the intima. The longer time model predictions are used to explain the time scale for the formation of liposomes [4] in subendothelial tissue matrix in animal feeding experiments where it has been observed that the extracellular lipid concentration rises sharply prior to the entry of monocytes into the intima [45].

Effect of non-uniform passive advection on A+B->C radial reaction-diffusion fronts 

2021 ◽  
Author(s):  
Alessandro Comolli ◽  
Anne De Wit ◽  
Fabian Brau
Keyword(s):  
Molecular Diffusion ◽  
Early Time ◽  
Reaction Diffusion ◽  
Transport Processes ◽  
Calcium Carbonate Precipitation ◽  
Atmospheric Reactions ◽  
Passive Advection ◽  
Reaction Fronts ◽  
Time Regime ◽  
Long Time

<p>The interplay between chemical and transport processes can give rise to complex reaction fronts dynamics, whose understanding is crucial in a wide variety of environmental, hydrological and biological processes, among others. An important class of reactions is A+B->C processes, where A and B are two initially segregated miscible reactants that produce C upon contact. Depending on the nature of the reactants and on the transport processes that they undergo, this class of reaction describes a broad set of phenomena, including combustion, atmospheric reactions, calcium carbonate precipitation and more. Due to the complexity of the coupled chemical-hydrodynamic systems, theoretical studies generally deal with the particular case of reactants undergoing passive advection and molecular diffusion. A restricted number of different geometries have been studied, including uniform rectilinear [1], 2D radial [2] and 3D spherical [3] fronts. By symmetry considerations, these systems are effectively 1D.</p><p>Here, we consider a 3D axis-symmetric confined system in which a reactant A is injected radially into a sea of B and both species are transported by diffusion and passive non-uniform advection. The advective field <em>v<sub>r</sub>(r,z)</em> describes a radial Poiseuille flow. We find that the front dynamics is defined by three distinct temporal regimes, which we characterize analytically and numerically. These are i) an early-time regime where the amount of mixing is small and the dynamics is transport-dominated, ii) a strongly non-linear transient regime and iii) a long-time regime that exhibits Taylor-like dispersion, for which the system dynamics is similar to the 2D radial case.</p><p>                                  <img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.ff5ab530bdff57321640161/sdaolpUECMynit/12UGE&app=m&a=0&c=360a1556c809484116c55812c8c06624&ct=x&pn=gnp.elif&d=1" alt="" width="299" height="299">                                                     <img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.671a6980bdff51231640161/sdaolpUECMynit/12UGE&app=m&a=0&c=c5a857c3fab835057e3af84001a91d15&ct=x&pn=gnp.elif&d=1" alt="" width="302" height="302"></p><p>                                                   Fig. 1: Concentration profile of the product C in the transient (left) and asymptotic (right) regimes.</p><p> </p><p>References:</p><p>[1] L. Gálfi, Z. Rácz, Phys. Rev. A 38, 3151 (1988);</p><p>[2] F. Brau, G. Schuszter, A. De Wit, Phys. Rev. Lett. 118, 134101 (2017);</p><p>[3] A. Comolli, A. De Wit, F. Brau, Phys. Rev. E, 100 (5), 052213 (2019).</p>

scholarly journals Real time model-based diagnosis enabled by hybrid modeling

2020 ◽  
Vol 12 (1) ◽  
pp. 10
Author(s):  
Ion Matei ◽  
Alexander Feldman ◽  
Johan De Kleer ◽  
Alexandre Perez
Keyword(s):  
Automatic Differentiation ◽  
Complex Model ◽  
Hybrid Modeling ◽  
High Fidelity ◽  
Time Model ◽  
Order Of Magnitude ◽  
Switch System ◽  
Using Data ◽  
Model Components ◽  
Fidelity Model

In this paper we propose a hybrid modeling approach for generating reduced models of a high fidelity model of a physical system. We propose machine learning inspired representations for complex model components. These representations preserve in part the physical interpretation of the original components. Training platforms featuring automatic differentiation are used to learn the parameters of the new representations using data generated by the high-fidelity model. We showcase our approach in the context of fault diagnosis for a rail switch system. We generate three new model abstractions whose complexities are two order of magnitude smaller than the complexity of the high fidelity model, both in the number of equations and simulation time. Faster simulations ensure faster diagnosis solutions and enable the use of diagnosis algorithms relying heavily on large numbers of model simulations.

Response of 31P-nuclear magnetic resonance spectra of frog skin to variations in PCO2 and hypoxia

1983 ◽  
Vol 245 (6) ◽  
pp. F792-F800
Author(s):  
R. L. Nunnally ◽  
J. S. Stoddard ◽  
S. I. Helman ◽  
J. P. Kokko
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Epithelial Transport ◽  
Transport Processes ◽  
Nmr Studies ◽  
Nernst Potential ◽  
31P Nuclear Magnetic Resonance ◽  
Order Of Magnitude ◽  
Epithelial Sheets ◽  
Nuclear Magnetic

31P-nuclear magnetic resonance (NMR) studies were conducted on split epithelial sheets of frog skins to examine the effects of hypoxia and respiratory pH variations on various phosphate-containing intracellular substrates. Frog skins were split into epithelial sheets from which the supporting tissue was removed. Epithelial sheets in either phosphate-free Cl--Ringer or phosphate-free SO2-4-Ringer were bubbled at room temperature with 100% N2, 100% O2, 2% CO2-98% O2, 5% CO2-95% O2, and 15% CO2-85% O2. The results show that the intracellular pH (pHi) with Cl- -Ringer was 7.19 and with SO2-4-Ringer was 7.42 with extracellular pH of 7.52 when bubbled with 100% O2. These pHiS indicate that H+ concentration is at least an order of magnitude less than predicted from the previously measured Nernst potential. With exposure to increasing extracellular PCO2, there is a polynomial decrease in pHi. The pHi tended to be more alkaline in SO2-4 -Ringer, suggesting the presence of a HCO-3/Cl- exchange mechanism. The ATP concentration is critically and reversibly dependent on PO2. ADP concentrations were consistently low in well-oxygenated conditions. Variable but small quantities of phosphocreatine were detected. These studies demonstrate further the potential importance in utilizing NMR spectroscopy to examine coupling of biochemical substrates to epithelial transport processes.

scholarly journals A Cellular Automaton Model as a First Model-Based Assessment of Interacting Mechanisms for Insulin Granule Transport in Beta Cells

Cells ◽  
2020 ◽  
Vol 9 (6) ◽  
pp. 1487
Author(s):  
Michael Müller ◽  
Mathias Glombek ◽  
Jeldrick Powitz ◽  
Dennis Brüning ◽  
Ingo Rustenbeck
Keyword(s):  
Cellular Automaton ◽  
Beta Cells ◽  
Transport Processes ◽  
Cellular Automaton Model ◽  
Special Role ◽  
Actin Network ◽  
Cell Interior ◽  
Actin Networks ◽  
Insulin Granules ◽  
Secretion Rates

In this paper a first model is derived and applied which describes the transport of insulin granules through the cell interior and at the membrane of a beta cell. A special role is assigned to the actin network, which significantly influences the transport. For this purpose, microscopically measured actin networks are characterized and then further ones are artificially generated. In a Cellular Automaton model, phenomenological laws for granule movement are formulated and implemented. Simulation results are compared with experiments, primarily using TIRF images and secretion rates. In this respect, good similarities are already apparent. The model is a first useful approach to describe complex granule transport processes in beta cells, and offers great potential for future extensions. Furthermore, the model can be used as a tool to validate hypotheses and associated mechanisms regarding their effect on exocytosis or other processes. For this purpose, the source code for the model is provided online.

scholarly journals No gastric mill in sauropod dinosaurs: new evidence from analysis of gastrolith mass and function in ostriches

2006 ◽  
Vol 274 (1610) ◽  
pp. 635-640 ◽  
Author(s):  
Oliver Wings ◽  
P. Martin Sander
Keyword(s):  
Body Mass ◽  
Digestive System ◽  
Gastric Mill ◽  
Theropod Dinosaurs ◽  
Feeding Experiments ◽  
Stem Lineage ◽  
Order Of Magnitude ◽  
Food Retention ◽  
And Function ◽  
New Evidence

Polished pebbles occasionally found within skeletons of giant herbivorous sauropod dinosaurs are very likely to be gastroliths (stomach stones). Here, we show that based on feeding experiments with ostriches and comparative data for relative gastrolith mass in birds, sauropod gastroliths do not represent the remains of an avian-style gastric mill. Feeding experiments with farm ostriches showed that bird gastroliths experience fast abrasion in the gizzard and do not develop a polish. Relative gastrolith mass in sauropods (gastrolith mass much less than 0.1% of body mass) is at least an order of magnitude less than that in ostriches and other herbivorous birds (gastrolith mass approximates 1% of body mass), also arguing against the presence of a gastric mill in sauropods. Sauropod dinosaurs possibly compensated for their limited oral processing and gastric trituration capabilities by greatly increasing food retention time in the digestive system. Gastrolith clusters of some derived theropod dinosaurs (oviraptorosaurs and ornithomimosaurs) compare well with those of birds, suggesting that the gastric mill evolved in the avian stem lineage.

Early-Time Model of Laser Plasma Expansion

1971 ◽  
Vol 14 (9) ◽  
pp. 1905 ◽  
Author(s):  
Thomas P. Wright
Keyword(s):  
Laser Plasma ◽  
Early Time ◽  
Plasma Expansion ◽  
Time Model

scholarly journals THEMIS observations of plasma transport via eddy diffusion

2012 ◽  
Vol 30 (12) ◽  
pp. 1703-1707
Author(s):  
T. Izutsu ◽  
M. Fujimoto
Keyword(s):  
Boundary Layer ◽  
Eddy Diffusion ◽  
Quantitative Agreement ◽  
Transport Processes ◽  
Plasma Transport ◽  
Navier Stokes ◽  
Diffusive Transport ◽  
Low Latitude ◽  
Stokes Fluid ◽  
Low Latitude Boundary Layer

Abstract. We provide an event study of THEMIS observations of the low-latitude boundary layer in the dayside magnetosphere. Simultaneous multipoint observations obtained on 5 December 2008 show that the magnetosheath-like plasma in the low-latitude boundary layer is transferred earthward from the magnetopause. This earthward transport is accompanied by decrease in the density and fluctuating bulk flow. We calculate the eddy diffusion coefficients, which can be estimated from the observed velocity data, and found that the numbers are in good quantitative agreement with the spatial and time scales of the observed earthward transport signatures. It is shown that other possible plasma transport processes such as convection or diffusion induced by plasma wave turbulence are inconsistent with the observations. Our study strongly suggests that the observed transport is due to diffusive transport via turbulent eddy motions as is the case of an ordinary (Navier–Stokes) fluid.

Aortic transmural serum protein transport: effect of concentration, time, and location

1981 ◽  
Vol 240 (1) ◽  
pp. H54-H61 ◽  
Author(s):  
D. L. Fry ◽  
R. W. Mahley ◽  
S. Y. Oh ◽  
C. R. Swyt
Keyword(s):  
Protein Transport ◽  
Serum Proteins ◽  
Density Lipoprotein ◽  
Transport Processes ◽  
Diffusive Transport ◽  
Fixed Tissue ◽  
Human High Density Lipoprotein ◽  
Tissue Specimens ◽  
Plasma Partition Coefficient ◽  
Short Times

The diffusive transport of certain 125I-labeled purified serum proteins, canine (C), human (H), and porcine (P) serum albumin (A), as well as human high-density lipoprotein (HDL), into the isolated deendothelialized intimal-medial thoracic aortic preparation was measured as a function of protein concentration (c0), intimal surface exposure time (T), and location (z) along the vessel at 21 degrees C. Selected proteins were studied in each of 11 canine preparations and 1 porcine preparation. The resulting uptake (M, nmol/cm2) was measured by direct gamma counting of specially excised fixed tissue specimens, and the transmural concentration distributions [c(xi), nmol/cm3] were calculated from electron probe X-ray microanalysis of the silver distributions across specially prepared microautoradiographs. The results showed 1) that the processes associated with the diffusive transport of CA, HA, PA, and HDL into the intimal-medial system are independent of c0, i.e., uptake is proportional to c0, 2) that the uptake of CA for short times appeared to be linear with T 1/2, 3) that the apparent wall-plasma partition coefficient for albumin rangers between 0.1 and 0.2, 4) that the apparent tissue albumin diffusion coefficient is approximately 2.7 X 10(-8) cm2/s, 5) that the transport processes for HA and CA are indistinguishable, 6) that the processes for the transport of HDL are two times slower than those for HA or CA, and 7) that the transport rate for albumin tends to decrease with z.

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