scholarly journals On the Validity of the Relationship 1/T = 1/TB+1/TS+1/TD in NMR Techniques With Regards to Permeability Estimation of Natural Porous Media

2021 ◽  
Vol 9 ◽  
Author(s):  
Jesús Díaz-Curiel ◽  
Bárbara Biosca ◽  
Lucía Arévalo-Lomas ◽  
María Jesús Miguel ◽  
Raúl Loayza-Muro
Keyword(s):  
Porous Media ◽  
Decay Time ◽  
Decay Rates ◽  
Surface Relaxation ◽  
Free Fluid ◽  
Resonance Signal ◽  
Decay Times ◽  
Small Pore ◽  
Geophysical Techniques ◽  
The Relationship

One of the most relevant feature of geophysical techniques based on nuclear magnetic resonance is their ability to estimate the permeability of natural porous media, since other geophysical techniques, as the use of the formation factor and neutron well-logs, allow to quantify the volume of water in the media. Permeability is conventionally obtained from decay time of the total resonance signal. However, the fluid in the pores of a medium normally has different mobility degree that can be differentiated by the NMR results. Therefore, a detailed estimation of permeability requires decomposing the total resonance signal as a function of the decay times corresponding to the three mechanisms that contribute to the signal: the intergranular free fluid, the surface layer, and the diffusion relaxation mechanism. The relationship currently used to make this decomposition states that the exponential decay rate attributed to the total resonance signal is the sum of the three existing decay rates. We demonstrate that this relationship is not generally applicable in porous media, showing the contradiction with the much more widely accepted relationships as well as computation examples from three typical decay rates in a single pore and from sandstone with bulk and surface relaxation mechanisms. Consequently, we conclude that the assertion whereby the permeability of any porous medium does not depend on the decay time of the free fluid is an overstatement, since it only applies to very small pore sizes.

Properties of spontaneous inhibitory synaptic currents in cultured rat spinal cord and medullary neurons

1996 ◽  
Vol 76 (1) ◽  
pp. 448-460 ◽  
Author(s):  
C. A. Lewis ◽  
D. S. Faber
Keyword(s):  
Spinal Cord ◽  
Time Constant ◽  
Decay Time ◽  
Cultured Cells ◽  
Decay Time Constant ◽  
Inhibitory Synapses ◽  
Gamma Aminobutyric Acid ◽  
Postsynaptic Receptor ◽  
Decay Times ◽  
Medullary Neurons

1. To identify the type(s) and properties of inhibitory postsynaptic receptor(s) involved in synaptic transmission in cultured rat embryonic spinal cord and medullary neurons, we have used whole cell patch-clamp techniques to record miniature inhibitory postsynaptic currents (mIPSCs) in the presence of tetrodotoxin, DL-2-amino-5-phosphonovaleric acid, and 6-cyano-7-nitroquinoxaline-2,3-dione. 2. The mIPSCs recorded from both spinal cord and medullary neurons had skewed amplitude distributions. 3. The glycinergic antagonist strychnine and the GABAergic antagonist bicuculline each decreased both the frequency and mean peak amplitudes of mIPSCs. We conclude that both glycine and gamma-aminobutyric acid (GABA) are neurotransmitters at inhibitory synapses in our cultured cells. 4. Most (approximately 96-97%) mIPSCs decay with single-exponential time constants, and decay time distributions were consistently best fitted by the sum of four Gaussians with decay constants as follows: D1 = 5.8 +/- 0.1 (SE) ms (n = 63), D2 = 12.2 +/- 0.2 ms (n = 61), D3 = 23.2 +/- 0.4 ms (n = 54), and D4 = 44.7 +/- 1.0 ms (n = 57). We conclude that the four classes of decay times represent kinetically different inhibitory postsynaptic receptor populations. 5. Strychnine and bicuculline usually had one of two different effects on the mIPSC decay time constant distributions; either selective decreases in the frequency of mIPSCs with decay times in certain classes (i.e., the D1 class was reduced by bicuculline, the D2 class by strychnine, and the D3 and D4 classes by both antagonists) or a nonselective depression in the frequency of mIPSCs with decay times in all four classes. The particular effect observed in a given neuron was correlated with the presence or absence of ATP and guanosine 5'-triphosphate (GTP) in the patch pipette. Namely, in 71% of the antagonist applications where the pipette contained ATP and GTP, the result was a nonselective decrease in mIPSCs in all decay time constant classes. Conversely, in 54% of the antagonist applications in their absence, the result was a selective decrease in the frequency of mIPSCs in specific decay time constant classes. 6. In some experiments, mIPSCs reappeared in antagonist solution after an essentially complete block. Recovery from block in the continued presence of antagonist was never observed in the absence of ATP and GTP (8 neurons), and, at the same time, 5 of 9 neurons patched with ATP and GTP in the pipette did show recovery (56%).

scholarly journals The Yamada Model for a Self-Pulsing Laser: Bifurcation Structure for Nonidentical Decay Times of Gain and Absorber

2020 ◽  
Vol 30 (14) ◽  
pp. 2030039
Author(s):  
Robert Otupiri ◽  
Bernd Krauskopf ◽  
Neil G. R. Broderick
Keyword(s):  
Three Dimensional ◽  
Equation Model ◽  
Decay Rates ◽  
Phase Portraits ◽  
Stable Phase ◽  
Bifurcation Structure ◽  
Decay Times ◽  
Comprehensive Picture ◽  
Two Parameter ◽  
Parameter Bifurcation

We consider self-pulsing in lasers with a gain section and an absorber section via a mechanism known as [Formula: see text]-switching, as described mathematically by the Yamada ordinary differential equation model for the gain, the absorber and the laser intensity. More specifically, we are interested in the case that gain and absorber decay on different time-scales. We present an overall bifurcation structure by showing how the two-parameter bifurcation diagram in the plane of pump strength versus decay rate of the gain changes with the ratio between the two decay rates. In total, there are ten cases BI to BX of qualitatively different two-parameter bifurcation diagrams, which we present with an explanation of the transitions between them. Moroever, we show for each of the associated eleven cases of structurally stable phase portraits (in open regions of the parameter space) a three-dimensional representation of the organization of phase space by the two-dimensional manifolds of saddle equilibria and saddle periodic orbits. The overall bifurcation structure provides a comprehensive picture of the observable dynamics, including multistability and excitability, which we expect to be of relevance for experimental work on [Formula: see text]-switching lasers with different kinds of saturable absorbers.

scholarly journals On the validity of the ambipolar diffusion assumption in the polar mesopause region

2008 ◽  
Vol 26 (11) ◽  
pp. 3439-3443 ◽  
Author(s):  
A. P. Ballinger ◽  
P. B. Chilson ◽  
R. D. Palmer ◽  
N. J. Mitchell
Keyword(s):  
Ambient Temperature ◽  
Decay Time ◽  
Ambipolar Diffusion ◽  
Northern Sweden ◽  
Mesopause Region ◽  
Decay Times ◽  
Meteor Trail ◽  
Temperature And Pressure ◽  
Ion Recombination ◽  
Meteor Trails

Abstract. The decay of underdense meteor trails in the polar mesopause region is thought to be predominantly due to ambipolar diffusion, a process governed by the ambient temperature and pressure. Hence, observations of meteor decay times have been used to indirectly measure the temperature of the mesopause region. Using meteor observations from a SKiYMET radar in northern Sweden during 2005, this study found that weaker meteor trails have shorter decay times (on average) than relatively stronger trails. This suggests that processes other than ambipolar diffusion can play a significant role in trail diffusion. One particular mechanism, namely electron-ion recombination, is explored. This process is dependent on the initial electron density within the meteor trail, and can lead to a disproportionate reduction in decay time, depending on the strength of the meteor.

A Visual Study of Phase Change Heat Transfer in Horizontal Bottom Heating Beads Packed Porous Structures

2008 ◽  
Author(s):  
C. H. Li
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Bubble Dynamics ◽  
Heating Surface ◽  
Bubble Generation ◽  
Wide Range ◽  
Bottom Heating ◽  
Phase Change Heat Transfer ◽  
The Relationship ◽  
Horizontal Bottom

An experimental investigation was conducted to study the influence of the sphere material and size on the bubble generation, growth, and detachment on nucleate pool boiling heat transfer in two different sphere-packed porous media, copper sphere and glass sphere at the same size of 3 mm diameter, respectively. By measuring the heating surface temperatures and visualizing the bubble dynamics over a wide range of heat flux, an effort was made to find the relationship between the normalized bubble dynamics process and the factors of sphere material and size. By comparing the experimental results of two different sphere material porous media, the interfacial heat and mass transport will be analyzed to provide the information how the bubble generation, growth, detachment and the liquid replenished process were influence by the liquid/copper and liquid/glass interfaces in different size porous media.

Magnetorheological Energy Absorbers Employing a Valve Filled With Porous Media

2008 ◽  
Author(s):  
Ryan Robinson ◽  
Wei Hu ◽  
Norman M. Wereley
Keyword(s):  
Porous Media ◽  
Flow Analysis ◽  
Mr Damper ◽  
Area Ratio ◽  
Experimental Results ◽  
Equivalent Damping ◽  
Piston Valve ◽  
Energy Absorbers ◽  
The Relationship ◽  
Valve Area

The effects of porous media selection on the performance of a porous-valve-based magnetorheological (MR) damper are evaluated. Important media parameters affecting the damper performance, i.e. porosity and morphology (shape), are identified using flow analysis. The relationship between the controllable force of the damper and the porous valve characteristics is studied for three types of porous media. Equivalent damping is determined, and damping performance is compared. Effects of piston-valve area ratio on damper performance are also evaluated. A nonlinear hysteretic biviscous model is applied to the damper and the experimental results are compared with predicted results.

scholarly journals Coupling of two-phase flow in fractured-vuggy reservoir with filling medium

Open Physics ◽  
2017 ◽  
Vol 15 (1) ◽  
pp. 12-17 ◽  
Author(s):  
Haojun Xie ◽  
Aifen Li ◽  
Zhaoqin Huang ◽  
Bo Gao ◽  
Ruigang Peng
Keyword(s):  
Porous Media ◽  
Oil Recovery ◽  
Two Phase Flow ◽  
Water Injection ◽  
Free Flow ◽  
Flow In Porous Media ◽  
Free Fluid ◽  
Phase Flow ◽  
Fluid Exchange ◽  
Two Phase

AbstractCaves in fractured-vuggy reservoir usually contain lots of filling medium, so the two-phase flow in formations is the coupling of free flow and porous flow, and that usually leads to low oil recovery. Considering geological interpretation results, the physical filled cave models with different filling mediums are designed. Through physical experiment, the displacement mechanism between un-filled areas and the filling medium was studied. Based on the experiment model, we built a mathematical model of laminar two-phase coupling flow considering wettability of the porous media. The free fluid region was modeled using the Navier-Stokes and Cahn-Hilliard equations, and the two-phase flow in porous media used Darcy's theory. Extended BJS conditions were also applied at the coupling interface. The numerical simulation matched the experiment very well, so this numerical model can be used for two-phase flow in fracture-vuggy reservoir. In the simulations, fluid flow between inlet and outlet is free flow, so the pressure difference was relatively low compared with capillary pressure. In the process of water injection, the capillary resistance on the surface of oil-wet filling medium may hinder the oil-water gravity differentiation, leading to no fluid exchange on coupling interface and remaining oil in the filling medium. But for the water-wet filling medium, capillary force on the surface will coordinate with gravity. So it will lead to water imbibition and fluid exchange on the interface, high oil recovery will finally be reached at last.

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