scholarly journals Effects of salinity and pH on the spectral induced polarization signals of graphite particles

2020 ◽  
Vol 221 (3) ◽  
pp. 1532-1541
Author(s):  
Yuxin Wu ◽  
Luca Peruzzo
Keyword(s):  
Relaxation Time ◽  
Time Constant ◽  
Negative Impact ◽  
Positive Impact ◽  
Electronic Conductivity ◽  
Induced Polarization ◽  
Graphite Inclusion ◽  
Relaxation Time Constant ◽  
Graphite Particles ◽  
Spectral Induced Polarization

SUMMARY The electrical property of micrometre-sized graphite particles was investigated under different particle concentration, particle size, fluid conductivity and pH conditions. Due to its large internal electronic conductivity and ability to polarize under external potential field, significant enhancement of its spectral induced polarization (SIP) responses is observed when graphite is included in sand mixtures. While a small amount of graphite inclusion significantly increases the SIP response of its mixtures with sand, further concentration increase does not necessarily lead to a proportional increase of the SIP response. This is shown to be related to the formation of graphite aggregates at higher concentrations. Changes of fluid salinity have a significant effect on graphite's SIP behaviour. This includes a positive impact on normalized chargeability and imaginary conductivity, but a negative impact on chargeability and relaxation time constant. The effect of pH on the SIP response of graphite is small but shows consistent trend, where pH increase leads to a decrease of both the chargeability and relaxation time constant. The underlying cause of this effect is not clear.

scholarly journals The Application of Spectral Induced Polarization to Determination of Hydraulic Conductivity

2021 ◽  
Author(s):  
◽  
Sheen Joseph
Keyword(s):  
Grain Size ◽  
Relaxation Time ◽  
New Zealand ◽  
Hydraulic Conductivity ◽  
Time Constant ◽  
Coastal Aquifers ◽  
Induced Polarization ◽  
Pore Fluid ◽  
Relaxation Time Constant ◽  
Spectral Induced Polarization

<p>Spectral Induced Polarization (SIP) is a geophysical technique that measures the frequency dependence of the electrical conductivity of a material. This thesis is an attempt to investigate the potential of using SIP as a proxy to predict the hydraulic conductivity of New Zealand shallow coastal aquifers. SIP measurements were made on sand samples that are typical of New Zealand coastal aquifers with a custom built impedance spectrometer and sample holder allowing the measurement of a phase difference as small a milliradian.  Even though the relaxation time shows a small dependence on pore fluid conductivity, especially at lower pore fluid conductivities, this variation is not serious enough to affect the hydraulic conductivity estimation at the field scale, but could be significant in the investigation of mechanisms that cause polarization in porous media.  Measurements on sieved fractions of sand established that there is an excellent correlation between the Cole-Cole relaxation time constant and grain size. The Cole-Cole relaxation time constant is very sensitive to the grain size distribution. Hydraulic conductivity predictions were attempted using various existing models. While the results are encouraging, it looks like there may not be a single universal model to predict hydraulic conductivity using SIP response.  When a correction term in the form of a multiplication constant is used, all the tested models seem to make very good predictions. But the constants calculated by fitting to the measured data could be applicable only to the type of materials studied. The dependence of the existing models on quantities like counterion diffusion coefficient, electrical formation factor and porosity makes hydraulic conductivity prediction challenging as these quantities are difficult to measure accurately in a field setting. Nevertheless it is concluded that SIP can be successfully applied to study hydraulic conductivity of New Zealand shallow coastal aquifers.</p>

scholarly journals The Application of Spectral Induced Polarization to Determination of Hydraulic Conductivity

2021 ◽  
Author(s):  
◽  
Sheen Joseph
Keyword(s):  
Grain Size ◽  
Relaxation Time ◽  
New Zealand ◽  
Hydraulic Conductivity ◽  
Time Constant ◽  
Coastal Aquifers ◽  
Induced Polarization ◽  
Pore Fluid ◽  
Relaxation Time Constant ◽  
Spectral Induced Polarization

<p>Spectral Induced Polarization (SIP) is a geophysical technique that measures the frequency dependence of the electrical conductivity of a material. This thesis is an attempt to investigate the potential of using SIP as a proxy to predict the hydraulic conductivity of New Zealand shallow coastal aquifers. SIP measurements were made on sand samples that are typical of New Zealand coastal aquifers with a custom built impedance spectrometer and sample holder allowing the measurement of a phase difference as small a milliradian.  Even though the relaxation time shows a small dependence on pore fluid conductivity, especially at lower pore fluid conductivities, this variation is not serious enough to affect the hydraulic conductivity estimation at the field scale, but could be significant in the investigation of mechanisms that cause polarization in porous media.  Measurements on sieved fractions of sand established that there is an excellent correlation between the Cole-Cole relaxation time constant and grain size. The Cole-Cole relaxation time constant is very sensitive to the grain size distribution. Hydraulic conductivity predictions were attempted using various existing models. While the results are encouraging, it looks like there may not be a single universal model to predict hydraulic conductivity using SIP response.  When a correction term in the form of a multiplication constant is used, all the tested models seem to make very good predictions. But the constants calculated by fitting to the measured data could be applicable only to the type of materials studied. The dependence of the existing models on quantities like counterion diffusion coefficient, electrical formation factor and porosity makes hydraulic conductivity prediction challenging as these quantities are difficult to measure accurately in a field setting. Nevertheless it is concluded that SIP can be successfully applied to study hydraulic conductivity of New Zealand shallow coastal aquifers.</p>

Regarding the Néel relaxation time constant in magnetorelaxometry

2014 ◽  
Vol 116 (16) ◽  
pp. 163914 ◽  
Author(s):  
J. Leliaert ◽  
A. Coene ◽  
G. Crevecoeur ◽  
A. Vansteenkiste ◽  
D. Eberbeck ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Time Constant ◽  
Relaxation Time Constant ◽  
Néel Relaxation

scholarly journals Calculation of Left Ventricular Relaxation Time Constant-Tau in Patients With Aortic Regurgitation by Continuous-Wave Doppler

2008 ◽  
Vol 2 (1) ◽  
pp. 28-30 ◽  
Author(s):  
Bai Xufang
Keyword(s):  
Relaxation Time ◽  
Aortic Regurgitation ◽  
Time Constant ◽  
Continuous Wave ◽  
Left Ventricular ◽  
Simple Method ◽  
Relaxation Time Constant ◽  
Left Ventricular Relaxation ◽  
Ventricular Relaxation ◽  
Continuous Wave Doppler

Left ventricular relaxation time constant, Tau, is the best index to evaluate left ventricular diastolic function. The measurement is only available traditionally in catheter lab. In Echo lab, several methods of non-invasive measurement of Tau have been tried since 1992, however almost all the methods are still utilizing the same formula to calculate Tau as in catheter lab, which makes them inconvenient, time-consuming and sometimes not very accurate. A simple method to calculate Tau in patients with mitral regurgitation has been developed just based on Weiss’ formula and simplified Bernoulli’s equation. Similarly, formulas are developed here by pure mathematical derivative to calculate Tau by continuous-wave Doppler in patients with aortic regurgitation.

scholarly journals Calculation of Left Ventricular Relaxation Time Constant-Tau in Humans by Continuous-Wave Doppler

2008 ◽  
Vol 2 (1) ◽  
pp. 9-11 ◽  
Author(s):  
Xufang Bai
Keyword(s):  
Relaxation Time ◽  
Time Constant ◽  
Continuous Wave ◽  
Left Ventricular Diastolic Function ◽  
Left Ventricular ◽  
Simple Method ◽  
Relaxation Time Constant ◽  
Left Ventricular Relaxation ◽  
Ventricular Relaxation ◽  
Continuous Wave Doppler

Left ventricular relaxation time constant, Tau, is the best index to evaluate left ventricular diastolic function, but the measurement is only available traditionally in catheter lab. In Echo lab, several methods of non-invasive measurement of Tau have been tried since 1992, however almost all the methods are still utilizing the same formula to calculate Tau as in catheter lab, which makes them inconvenient, time-consuming and sometimes not very accurate. Based on Weiss’ formula and simplified Bernoulli’s equation, a simple method is developed by pure mathematical derivative to calculate Tau by continuous-wave Doppler in patients with mitral regurgitation.

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