Artículos de revistas: "Distribution of relaxation time"

1

Stephanovich, V. A., M. D. Glinchuk y B. Hilczer. "Relaxation time distribution function". Ferroelectrics 240, n.º 1 (enero de 2000): 1495–505. http://dx.doi.org/10.1080/00150190008227975.

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2

Sudo, Seiichi, Naoki Shinyashiki, Yusuke Kitsuki y Shin Yagihara. "Dielectric Relaxation Time and Relaxation Time Distribution of Alcohol−Water Mixtures". Journal of Physical Chemistry A 106, n.º 3 (enero de 2002): 458–64. http://dx.doi.org/10.1021/jp013117y.

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3

Al-Refaie, S. N. y H. S. B. Elayyan. "The relaxation time distribution in dielectrics". Journal of Materials Science Letters 11, n.º 14 (1992): 988–90. http://dx.doi.org/10.1007/bf00729902.

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4

Tarasov, Andrey y Konstantin Titov. "Relaxation time distribution from time domain induced polarization measurements". Geophysical Journal International 170, n.º 1 (julio de 2007): 31–43. http://dx.doi.org/10.1111/j.1365-246x.2007.03376.x.

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5

Kim, Bog-gi, Jong-Jean Kim, Do-Hyun Kim y Hyun M. Jang. "Relaxation time distribution of deuterated dipole glass". Ferroelectrics 240, n.º 1 (enero de 2000): 1515–22. http://dx.doi.org/10.1080/00150190008227977.

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6

Friedrich, Christian, Richard J. Loy y Robert S. Anderssen. "Relaxation time spectrum molecular weight distribution relationships". Rheologica Acta 48, n.º 2 (30 de octubre de 2008): 151–62. http://dx.doi.org/10.1007/s00397-008-0314-z.

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7

Magyari, Miklós y János Liszi. "Determination of Relaxation Time Distribution in Dielectrics". Zeitschrift für Physikalische Chemie 187, Part_1 (enero de 1994): 85–92. http://dx.doi.org/10.1524/zpch.1994.187.part_1.085.

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8

Floudas, G., G. Fytas y I. Alig. "Brillouin scattering from bulk polybutadiene: distribution of relaxation times versus single relaxation time approach". Polymer 32, n.º 13 (enero de 1991): 2307–11. http://dx.doi.org/10.1016/0032-3861(91)90065-q.

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9

Nicolai, Taco, Jean Christophe Gimel y Robert Johnsen. "Analysis of Relaxation Functions Characterized by a Broad Monomodal Relaxation Time Distribution". Journal de Physique II 6, n.º 5 (mayo de 1996): 697–711. http://dx.doi.org/10.1051/jp2:1996206.

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10

Vasquez, Alexis, Oscar Sotolongo y Francois Brouers. "Cluster Size Distribution and Relaxation Long Time Tails". Journal of the Physical Society of Japan 66, n.º 8 (15 de agosto de 1997): 2324–27. http://dx.doi.org/10.1143/jpsj.66.2324.

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11

Tong, Maosong, Li Li, Weinan Wang y Yizhong Jiang. "Determining capillary-pressure curve, pore-size distribution, and permeability from induced polarization of shaley sand". GEOPHYSICS 71, n.º 3 (mayo de 2006): N33—N40. http://dx.doi.org/10.1190/1.2195989.

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An appropriate form of induced polarization (IP) acts as a bridge between the structure of a water-saturated core plug and its transport properties. The induced-polarization decay curves of natural rocks can be modeled as a weighted superposition of exponential relaxations. A singular-value decomposition method makes it possible to transform the induced-polarization decay data of the shaley sands into relaxation-time spectrum, defined as plot of weight versus the relaxation-time constant. We measured the induced-polarization decay curves of core samples from a formation of Daqing oil field using a four-electrode method. The decay curves were transformed to relaxation-time spectra that were used to estimate the capillary-pressure curves, the pore-size distribution, and the permeability of the shaley sands. The results show that salinity ranges from [Formula: see text] have little effect on the IP relaxation-time spectra. A pseudocapillary pressure curve can be derived from the IP relaxation-time spectrum by matching the pseudocapillary curve with that from HgAir. The best-matching coefficients of the studied cores change slightly for the samples. Defined as the value of pressure at which the injected mercury saturation is 5%, entry pressures of the cores can be estimated well from IP-derived capillary-pressure curves. Pore-size distributions generated from induced polarization and mercury capillary-pressure curves are comparable. Permeability can be predicted from IP measurements in the form of [Formula: see text], where [Formula: see text] is the estimated permeability from IP relaxation spectrum in millidarcies (md), [Formula: see text] is the porosity in percentage, and [Formula: see text] is average time constant of IP relaxation-time spectra in millis (ms). The constants and exponents from various rock formations are slightly different.

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12

Shan, Xiaowen, Xuhui Li y Yangyang Shi. "A multiple-relaxation-time collision model by Hermite expansion". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 379, n.º 2208 (30 de agosto de 2021): 20200406. http://dx.doi.org/10.1098/rsta.2020.0406.

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The Bhatnagar–Gross–Krook (BGK) single-relaxation-time collision model for the Boltzmann equation serves as the foundation of the lattice BGK (LBGK) method developed in recent years. The description of the collision as a uniform relaxation process of the distribution function towards its equilibrium is, in many scenarios, simplistic. Based on a previous series of papers, we present a collision model formulated as independent relaxations of the irreducible components of the Hermite coefficients in the reference frame moving with the fluid. These components, corresponding to the irreducible representation of the rotation group, are the minimum tensor components that can be separately relaxed without violating rotation symmetry. For the 2nd, 3rd and 4th moments, respectively, two, two and three independent relaxation rates can exist, giving rise to the shear and bulk viscosity, thermal diffusivity and some high-order relaxation process not explicitly manifested in the Navier–Stokes-Fourier equations. Using the binomial transform, the Hermite coefficients are evaluated in the absolute frame to avoid the numerical dissipation introduced by interpolation. Extensive numerical verification is also provided. This article is part of the theme issue ‘Progress in mesoscale methods for fluid dynamics simulation’.

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13

Grunewald, Elliot y Rosemary Knight. "A laboratory study of NMR relaxation times and pore coupling in heterogeneous media". GEOPHYSICS 74, n.º 6 (noviembre de 2009): E215—E221. http://dx.doi.org/10.1190/1.3223712.

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Nuclear magnetic resonance (NMR) relaxation times of geologic materials are closely related to pore geometry. In heterogeneous media, however, the details of this relationship are poorly understood because of a phenomenon known as pore coupling, which arises when diffusing protons sample multiple pores before relaxing. Laboratory experiments allow us to explore whether surface geochemistry can influence pore coupling and how this process affects the observed relaxation-time distribution. Measurements of the NMR response for microporous silica gel packs, treated with varying amounts of surface-coating iron, demonstrate that samples with less iron exhibit stronger pore coupling than those with abundant iron. When pore coupling is strong, the relaxation-time distribution grossly misrepresents the underlying bimodal pore-size distribution of micropores and macropores. Specifically, the bimodal relaxation-time distribution becomes merged and the relative amplitude of the peaks fails to reflect the true macropore and micropore volume. A reduction in pore coupling, observed with increasing iron content, is attributed to a decrease in the distance protons are able to diffuse before relaxing. Basic parameters describing the shape of the relaxation-time distributions for this range of samples are well-predicted by a 1D analytical model. Experimental results conclusively demonstrate that surface geochemistry is an important factor determining the degree to which pore coupling occurs and illustrate how this phenomenon can affect the interpretation of NMR relaxation measurements in heterogeneous porous media.

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14

Aslani, F. y L. Sjögren. "Relaxation rate distribution from frequency or time dependent data". Chemical Physics 325, n.º 2-3 (junio de 2006): 299–312. http://dx.doi.org/10.1016/j.chemphys.2006.01.004.

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15

Medvedev, Dmitry. "Distribution of relaxation time analysis for solid state electrochemistry". Electrochimica Acta 360 (noviembre de 2020): 137034. http://dx.doi.org/10.1016/j.electacta.2020.137034.

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16

Yang, Bowen, Dafang Wang, Shiqin Chen, Xu Sun y Beike Yu. "Electrochemical impedance preprocessing with distribution of relaxation time transform". Journal of Power Sources 571 (julio de 2023): 233062. http://dx.doi.org/10.1016/j.jpowsour.2023.233062.

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17

Anh, Chu Thuy, Do Hong Lien y Nguyen Ai Viet. "Simple Model for Market Returns Distribution". Communications in Physics 23, n.º 2 (8 de mayo de 2013): 185. http://dx.doi.org/10.15625/0868-3166/23/2/2382.

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It has been observed that at the large time scales the distributionof stock market returns is convergent from Boltzmann distribution to Gaussianasymptotic one. To explain this universal phenomenon, we propose a new andsimple dynamic model to describe this convergence by the time parameter inassociation with the introducing the concept of relaxation time for nancialmarkets. The analysis of stock market data packages in dierent time intervalsshowed that our model ts well the nancial market data. The meaning ofso{called relaxation time has been qualitatively made clear, as a measure toestimate the stability of the market.

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18

TSAO, YUAN-YING y BANU ONARAL. "FRACTAL RELAXATION SYSTEMS. Part II: Distribution of Relaxation Times". International Journal of General Systems 19, n.º 2 (septiembre de 1991): 133–53. http://dx.doi.org/10.1080/03081079108935168.

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19

Ni, Qingwen, Anahi Tinajero y Daniel P. Nicolella. "Characterization of Baboon Cortical Bone Microstructural Changes by Low Field NMR and Correlation of Bone Mechanical Properties". International Journal of Emerging Technology and Advanced Engineering 10, n.º 11 (30 de noviembre de 2020): 89–95. http://dx.doi.org/10.46338/ijetae1120_10.

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A NMR spin-spin (T2) relaxation technique has been described for determining the porosity, mobile and the bound water distribution in baboon cortical bone and correlate to their mechanical properties. The technique of low-field proton NMR involves spin-spin relaxation and free induction decay (FID) measurements, and the computational inversion methods for decay data analysis. The advantages of using NMR T2 relaxation techniques for bone water distribution are illustrated. The CPMG T2 relaxation data can be inverted to T2 relaxation distribution and this distribution then can be transformed to a pore size distribution with the longer relaxation times corresponding to larger pores. The FID T2 relaxation data can be inverted to T2 relaxation distribution and this distribution then can be transformed to bound and mobile water distribution with the longest relaxation time corresponding to mobile water and the middle relaxation time corresponding to bound water. The technique is applied to quantify apparent changes in porosity, bound and mobile water in cortical bone. Overall bone porosity is determined using the calibrated NMR fluid volume from the proton relaxation data divided by overall bone volume. The NMR porosity, bound and mobile water components are determined from cortical bone specimens obtained from baboon donors of different ages, and the results are correlated to bone mechanical properties.

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20

Grombacher, Denys, Emily Fay, Matias Nordin y Rosemary Knight. "The impact of pore-scale magnetic field inhomogeneity on the shape of the nuclear magnetic resonance relaxation time distribution". GEOPHYSICS 81, n.º 5 (septiembre de 2016): EN43—EN55. http://dx.doi.org/10.1190/geo2015-0466.1.

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Measurements of the nuclear magnetic resonance (NMR) signal’s behavior with time provide powerful noninvasive insight into the pore-scale environment. The time dependence of the NMR signal, which is a function of parameters called relaxation times, is intimately linked to the geometry of the pore space and has been used successfully to estimate pore size and permeability. The basis for the pore size and permeability estimates is that interactions occurring at the grain surface often function as the primary mechanism controlling the time dependence of the NMR signal. In this limit, called the fast diffusion limit, and when each pore can be considered to be isolated, the measured relaxation times are often interpreted as representative of pore sizes. In heterogeneous media, where the NMR signal is described by a distribution of relaxation times, the measured relaxation time distribution is often interpreted as representative of the underlying pore-size distribution. We have explored a scenario in which an additional relaxation mechanism, which arises due to magnetic field inhomogeneity across the pore space, violates the assumption that interactions occurring at the grain surface are the dominant relaxation mechanism. Using both synthetic and laboratory studies, we demonstrate that magnetic field inhomogeneity can lead to a complex relationship between the measured relaxation time distribution and the underlying pore-size distribution. Magnetic field inhomogeneity is observed to lead to a spatially heterogeneous magnetization density across the pore space requiring multiple eigenmodes to describe the evolution of the magnetization within a single pore during the NMR experiment. This results in a breakdown of the validity of the interpretation of the relaxation time distribution as representative of the underlying pore-size distribution for sediments with high magnetic susceptibility.

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21

Shao, Wei, Songhua Chen, Gabor Hursan y Shouxiang Ma. "Temperature Dependence of Nuclear Magnetic Resonance Relaxation Time in Carbonate Reservoirs". SPE Reservoir Evaluation & Engineering 25, n.º 01 (1 de diciembre de 2021): 36–51. http://dx.doi.org/10.2118/206184-pa.

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Summary Nuclear magnetic resonance (NMR)-based interpretation models are commonly calibrated using laboratory ambient core NMR measurements. For applying the core calibrated models to downhole NMR logging interpretation, the difference between the NMR responses measured at ambient and reservoir temperature needs to be evaluated. The temperature dependence of NMR relaxation time in high-quality (HQ) carbonate reservoirs has been studied, and NMR temperature dependence models were established using data analytic methods. In this paper, we extend our early studies on temperature dependence of NMR relaxation time to low-quality (LQ) carbonate formations. For more than 95% of the LQ samples investigated, NMR relaxation time shows a positive correlation with temperature. The correlation is similar to that observed in HQ carbonate rocks but slightly less significant. Temperature-dependent correlations for predicting the geometric mean of NMR transverse relaxation time (T2,GM) from a measured temperature to any other temperature were derived from HQ to LQ carbonate rocks independently first, then a unified T2,GM correlation was derived including both the HQ and LQ carbonate reservoirs. Predicting NMR transverse relaxation time T2 distribution from one temperature to other temperatures was achieved using a dimension reduction approach involving the principal component analysis (PCA) technique. It was found that the T2 distributions at any given temperature for both HQ and LQ carbonate reservoirs can be predicted robustly from the T2 distributions at the ambient temperature by representing the T2 distributions with principal components (PCs) at the ambient temperature and then using these PCs to predict the PCs at a different temperature. The optimal number of PC components depends on the multimodality of the T2 distribution. This work extends the validity range of the data analytic methods, in particular parameter and dimension reduction methods, that quantify the temperature dependence of carbonate NMR properties. The new NMR temperature model enables the integration of NMR laboratory studies and downhole measurements for advanced petrophysical analyses in a wide range of carbonate reservoirs.

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22

LI JIAN, ZHANG LI-DE y WANG JING. "CALCULATION OF RELAXATION TIME DISTRIBUTION OF α-PEAK IN PVC WITH GAUSSIAN DISTRIBUTION". Acta Physica Sinica 41, n.º 5 (1992): 814. http://dx.doi.org/10.7498/aps.41.814.

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23

Vallianatos, Filippos y Vassilis Sakkas. "Multiscale Post-Seismic Deformation Based on cGNSS Time Series Following the 2015 Lefkas (W. Greece) Mw6.5 Earthquake". Applied Sciences 11, n.º 11 (24 de mayo de 2021): 4817. http://dx.doi.org/10.3390/app11114817.

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In the present work, a multiscale post-seismic relaxation mechanism, based on the existence of a distribution in relaxation time, is presented. Assuming an Arrhenius dependence of the relaxation time with uniform distributed activation energy in a mesoscopic scale, a generic logarithmic-type relaxation in a macroscopic scale results. The model was applied in the case of the strong 2015 Lefkas Mw6.5 (W. Greece) earthquake, where continuous GNSS (cGNSS) time series were recorded in a station located in the near vicinity of the epicentral area. The application of the present approach to the Lefkas event fits the observed displacements implied by a distribution of relaxation times in the range τmin ≈ 3.5 days to τmax ≈ 350 days.

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24

Li, Shaobo, Jianhu Zhao, Hongmei Zhang y Siheng Qu. "Sub-Bottom Sediment Classification Using Reliable Instantaneous Frequency Calculation and Relaxation Time Estimation". Remote Sensing 13, n.º 23 (27 de noviembre de 2021): 4809. http://dx.doi.org/10.3390/rs13234809.

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The shift in IF (instantaneous frequency) series and the corresponding relaxation time have the potential to characterize sediment properties. However, these attributes derived from SBP (sub-bottom profiler) data are seldom used for offshore site investigations because of the unsoundness in attribute calculation. To overcome this problem, a new reliable method combining VMD (variational mode decomposition) and WVD (Wigner–Ville distribution), as well as relaxation time, is presented. Since the number of modes in classical VMD should be provided in advance, a modified VMD algorithm, MVMD (modified variational mode decomposition), is proposed here, where the distribution of the frequency domain of modes is taken into account to automatically determine the number of modes. Through the relaxation time model, the IF data of a series of pings calculated through MVMD-WVD are transformed into a relaxation time map. A robust estimation algorithm is applied to the relaxation time map to reduce the effects of interferences and obtain robust relaxation times. The final relaxation time data are used to determine the sediment types. Real data from SBP experiments, as well as borehole sampling and geotechnical analysis results, verified the good performance of the proposed method.

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25

SHAN, XIAOWEN y HUDONG CHEN. "A GENERAL MULTIPLE-RELAXATION-TIME BOLTZMANN COLLISION MODEL". International Journal of Modern Physics C 18, n.º 04 (abril de 2007): 635–43. http://dx.doi.org/10.1142/s0129183107010887.

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We formulate a simple extension to the Bhatnagar-Gross-Krook collision model by expanding the distribution function in Hermite polynomials and assigning a relaxation time to each hydrodynamic moment. By discretizing the velocity space, multiple-relaxation-time lattice Boltzmann models can be constructed. The transport coefficients are analytically calculated and numerically verified. At the lowest order, allowing different relaxation rates for the second and third Hermite components results in a variable Prandtl number. Comparing with the previously proposed multiple-relaxation-time lattice Boltzmann models, the present formulation is general in the sense that it is independent of the underlying lattice structure and does not require a procedure for transformation of base vectors.

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26

Cho, Kwang Soo, Kyung Hyun Ahn y Seung Jong Lee. "An Iterative Nonlinear Mapping Method for the Relaxation Time Distribution". Nihon Reoroji Gakkaishi 32, n.º 3 (2004): 139–44. http://dx.doi.org/10.1678/rheology.32.139.

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27

KOBAYASHI, Kiyoshi y Tohru S. SUZUKI. "Extended Distribution of Relaxation Time Analysis for Electrochemical Impedance Spectroscopy". Electrochemistry 90, n.º 1 (15 de enero de 2022): 017004. http://dx.doi.org/10.5796/electrochemistry.21-00111.

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28

Ktitorov, S. A. "Determination of the relaxation time distribution function from dielectric losses". Technical Physics Letters 29, n.º 11 (noviembre de 2003): 956–58. http://dx.doi.org/10.1134/1.1631377.

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29

Zhang, Yanxiang, Yu Chen, Mufu Yan y Fanglin Chen. "Reconstruction of relaxation time distribution from linear electrochemical impedance spectroscopy". Journal of Power Sources 283 (junio de 2015): 464–77. http://dx.doi.org/10.1016/j.jpowsour.2015.02.107.

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30

Roura, P. "The general relaxation time distribution of a logarithmic capacitance transient". Journal of Applied Physics 67, n.º 7 (abril de 1990): 3529–30. http://dx.doi.org/10.1063/1.345348.

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31

Tomizawa, Morio, Keisuke Nagato, Kohei Nagai y Masayuki Nakao. "Distribution of Relaxation Time Analysis of Cathode Micro-Patterned PEFC". ECS Meeting Abstracts MA2020-02, n.º 33 (23 de noviembre de 2020): 2158. http://dx.doi.org/10.1149/ma2020-02332158mtgabs.

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32

Tomizawa, Morio, Keisuke Nagato, Kohei Nagai y Masayuki Nakao. "Distribution of Relaxation Time Analysis of Cathode Micro-Patterned PEFC". ECS Transactions 98, n.º 9 (23 de septiembre de 2020): 81–86. http://dx.doi.org/10.1149/09809.0081ecst.

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33

Jin, Dan, Wu Yao y Hong Zhi Wang. "Studying Blended Cement Paste with Nuclear Magnetic Resonance Relaxation Time". Key Engineering Materials 492 (septiembre de 2011): 433–36. http://dx.doi.org/10.4028/www.scientific.net/kem.492.433.

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The pore structure of cement paste has a relationship with its strength and durability. An appropriate method of measurement is a prerequisite to study the pore structure of cement paste. Among many test methods, Nuclear Magnetic Resonance (NMR) relaxation time is a novel testing methods to study pore structure of cement paste. Different from previous research object is limited to white cement, the test sample in this paper is the blended cement paste containing mineral admixture and has been widely used in practical engineering applications. The factors of pore structure are water to cementitious material ratio, kind of mineral admixture, and mineral admixture content. Measure the same sample at four different ages to obtain the relaxation time distribution to reflect the pore structure. The test results show that, in most cases, the distribution curves of the same kind of paste are in good agreement, and the change of relaxation time distribution of the blended cement paste with different ages can be interpreted as the characteristic of the mineral admixtures in cement paste. So the NMR relaxation time is suitable for study on the blended cement paste. However due to side effects caused by iron content and unsaturated water in gel pore, this method needs further improvement.

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34

Petrov, Oleg V. y Siegfried Stapf. "Parameterization of NMR relaxation curves in terms of logarithmic moments of the relaxation time distribution". Journal of Magnetic Resonance 279 (junio de 2017): 29–38. http://dx.doi.org/10.1016/j.jmr.2017.04.009.

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35

Ustra, Andrea, Carlos Alberto Mendonça, Dimitrios Ntarlagiannis y Lee D. Slater. "Relaxation time distribution obtained from a Debye decomposition of spectral induced polarization data". GEOPHYSICS 81, n.º 2 (1 de marzo de 2016): E129—E138. http://dx.doi.org/10.1190/geo2015-0095.1.

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We have developed an alternative formulation for Debye decomposition of complex electric conductivity spectra, by recasting it into a new set of parameters with a close relationship to the continuous formulation for the complex conductivity method. The procedure determines a relaxation time distribution (RTD) and two frequency-independent parameters that modulate the complex conductivity spectra. These two parameters represent (1) the direct current contribution and (2) the conductivity range spanned by the low- and high-frequency limits. The distribution of relaxation times quantifies the contribution of each distinct relaxation process. Assuming that characteristic times with insignificant contributions can be ignored, a minimum set of characteristic relaxation times is determined. Each contribution can then be associated with specific polarization processes that can be interpreted in terms of electrochemical or interfacial parameters of mechanistic models derived from inverted parameters obtained from the proposed approach. Synthetic tests show that the procedure can fit spectral induced polarization (SIP) data and successfully retrieve the RTD. We have applied the procedure to laboratory SIP data from experiments with sand and oil mixtures undergoing microbial degradation of hydrocarbons. The RTD reveals evidence of a length scale at which a new polarization process takes place as a result of the biodegradation process.

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Mikonis, A., J. Banys, R. Grigalaitis, S. Lapinskas, A. Matulis y G. Völkel. "Two Dimensional Distribution of Relaxation Times". Ferroelectrics 353, n.º 1 (18 de mayo de 2007): 154–63. http://dx.doi.org/10.1080/00150190701368117.

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37

GOSWAMI, PARTHA S. y V. KUMARAN. "Particle dynamics in a turbulent particle–gas suspension at high Stokes number. Part 2. The fluctuating-force model". Journal of Fluid Mechanics 646 (8 de marzo de 2010): 91–125. http://dx.doi.org/10.1017/s0022112009992813.

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A fluctuating-force model is developed for representing the effect of the turbulent fluid velocity fluctuations on the particle phase in a turbulent gas–solid suspension in the limit of high Stokes number, where the particle relaxation time is large compared with the correlation time for the fluid velocity fluctuations. In the model, a fluctuating force is incorporated in the equation of motion for the particles, and the force distribution is assumed to be an anisotropic Gaussian white noise. It is shown that this is equivalent to incorporating a diffusion term in the Boltzmann equation for the particle velocity distribution functions. The variance of the force distribution, or equivalently the diffusion coefficient in the Boltzmann equation, is related to the time correlation functions for the fluid velocity fluctuations. The fluctuating-force model is applied to the specific case of a Couette flow of a turbulent particle–gas suspension, for which both the fluid and particle velocity distributions were evaluated using direct numerical simulations by Goswami & Kumaran (2010). It is found that the fluctuating-force simulation is able to quantitatively predict the concentration, mean velocity profiles and the mean square velocities, both at relatively low volume fractions, where the viscous relaxation time is small compared with the time between collisions, and at higher volume fractions, where the time between collisions is small compared with the viscous relaxation time. The simulations are also able to predict the velocity distributions in the centre of the Couette, even in cases in which the velocity distribution is very different from a Gaussian distribution.

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38

Kumar, Indresh, Bommakanti V. L. Kumar, Ramesh V. Babu, Jugal K. Dash y Anand K. Chaturvedi. "Relaxation time distribution approach of mineral discrimination from time domain-induced polarisation data". Exploration Geophysics 50, n.º 4 (30 de mayo de 2019): 337–50. http://dx.doi.org/10.1080/08123985.2019.1606198.

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39

Ogasa, Mayumi Y., Kenichi Yazaki, Yasuhiro Utsumi, Naoko H. Miki y Kenji Fukuda. "Short-time xylem tension relaxation prevents vessel refilling and alleviates cryo-fixation artifacts in diffuse-porous Carpinus tschonoskii and Cercidiphyllum japonicum". Tree Physiology 39, n.º 10 (21 de junio de 2019): 1685–95. http://dx.doi.org/10.1093/treephys/tpz072.

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Abstract Xylem tension relaxation is an important procedure that closely resembles the in vivo xylem water distribution when measuring conductivity or observing water distribution of plant tissue samples by cryo-scanning electron microscopy (cryo-SEM). Recent studies have shown that partial xylem embolism occurs when samples under tension are cut under water and that gas-filled vessels are refilled during tension relaxation. Furthermore, the frequency of gas-filled vessels has been reported to increase in samples without tension relaxation before cryo-fixation by liquid nitrogen, particularly in samples with significant tension. Here, we examined the effect of tension relaxation on these artifacts in Carpinus tschonoskii and Cercidiphyllum japonicum using magnetic resonance imaging. We observed that xylem embolism rarely occurs in bench-dried samples cut under water. In both species, a small portion of the xylem was refilled within ~1 h after tension relaxation. Cryo-SEM observations revealed that short-time (<1 h) xylem tension relaxation decreases the frequency of gas-filled vessels in samples frozen after xylem tension relaxation regardless of the water potential compared with that in samples frozen without rehydration in both species. Therefore, short-time tension relaxation is necessary to retain xylem water distribution during sample preparation against artifacts.

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40

Kumaran, V. y Donald L. Koch. "Properties of a bidisperse particle–gas suspension Part 1. Collision time small compared with viscous relaxation time". Journal of Fluid Mechanics 247 (febrero de 1993): 623–41. http://dx.doi.org/10.1017/s002211209300059x.

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The properties of a dilute bidisperse particle–gas suspension under low Reynolds number, high Stokes number conditions are studied in the limit τcτv using a perturbation analysis in the small parameter v, which is proportional to the ratio of timescales τc/τv. Here, τc is the time between successive collisions of a particle, and tv is the viscous relaxation time. The leading-order distribution functions for the two species are isotropic Gaussian distributions, and are identical to the molecular velocity distributions in a two-component gas at equilibrium. Balance equations are written for the mean and mean-square velocities, using a distribution function that is a small perturbation from the isotropic Gaussian. The collisional terms are calculated by performing an ensemble average over the relative configurations of the colliding particles, and the mean velocity and velocity variances are calculated correct to O(v2) by solving the balance equations. The difference in the mean velocities of the two species is O(v) smaller than the mean velocity of the suspension, and the fluctuating velocity is O(v½) smaller than the mean velocity.

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41

Bamdad, Mehrdad, Saman Alavi, Bijan Najafi y Ezat Keshavarzi. "Investigation of the density dependence of the shear relaxation time of dense fluids". Canadian Journal of Chemistry 83, n.º 3 (1 de marzo de 2005): 236–43. http://dx.doi.org/10.1139/v05-047.

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The shear relaxation time, a key quantity in the theory of viscosity, is calculated for the LennardJones fluid and fluid krypton. The shear relaxation time is initially calculated by the ZwanzigMountain method, which defines this quantity as the ratio of the shear viscosity coefficient to the infinite shear modulus. The shear modulus is calculated from highly accurate radial distribution functions obtained from molecular dynamics simulations of the LennardJones potential and a realistic potential for krypton. This calculation shows that the density dependence of the shear relaxation time isotherms of the LennardJones fluid and Kr pass through a minimum. The minimum in the shear relaxation times is also obtained from calculations using the different approach originally proposed by van der Gulik. In this approach, the relaxation time is determined as the ratio of shear viscosity coefficient to the thermal pressure. The density of the minimum of the shear relaxation time is about twice the critical density and is equal to the common density, which was previously reported for supercritical gases where the viscosity of the gas becomes independent of temperature. It is shown that this common point occurs in both gas and liquid phases. At densities lower than this common density, even in the liquid state, the viscosity increases with increasing temperature.Key words: dense fluids, radial distribution function, shear modulus, shear relaxation time, shear viscosity.

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42

Kumaran, V. y Donald L. Koch. "Properties of a bidisperse particle–gas suspension Part 2. Viscous relaxation time small compared with collision time". Journal of Fluid Mechanics 247 (febrero de 1993): 643–60. http://dx.doi.org/10.1017/s0022112093000606.

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The properties of a dilute bidisperse particle–gas suspension under low Reynolds number, high Stokes number conditions are studied in the limit τv [Lt ] τc, where τc is the time between successive collisions of a particle, and τv is the viscous relaxation time. In this limit, the particles relax close to their terminal velocity between successive collisions, and we use a perturbation analysis in the small parameter ε, which is proportional to τv/τc, about a base state in which all the particles settle at their terminal velocities. The mean velocities of the two species are O(ε) different from their terminal velocities, and the mean-square velocities are O(ε) smaller than the square of the terminal velocity. The distribution functions for the two species, which incorporate the first effects of collisions between particles settling at their terminal velocities, are derived. The velocity distribution is highly anisotropic in this limit, and the mean-square velocity in the vertical direction is twice that in the horizontal plane. The distribution function for each species is singular at its terminal velocity, and the distributions are non-zero in a finite region in velocity space between the two terminal velocities.

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43

Malý, Pavel, J. Michael Gruber, Richard J. Cogdell, Tomáš Mančal y Rienk van Grondelle. "Ultrafast energy relaxation in single light-harvesting complexes". Proceedings of the National Academy of Sciences 113, n.º 11 (22 de febrero de 2016): 2934–39. http://dx.doi.org/10.1073/pnas.1522265113.

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Energy relaxation in light-harvesting complexes has been extensively studied by various ultrafast spectroscopic techniques, the fastest processes being in the sub–100-fs range. At the same time, much slower dynamics have been observed in individual complexes by single-molecule fluorescence spectroscopy (SMS). In this work, we use a pump–probe-type SMS technique to observe the ultrafast energy relaxation in single light-harvesting complexes LH2 of purple bacteria. After excitation at 800 nm, the measured relaxation time distribution of multiple complexes has a peak at 95 fs and is asymmetric, with a tail at slower relaxation times. When tuning the excitation wavelength, the distribution changes in both its shape and position. The observed behavior agrees with what is to be expected from the LH2 excited states structure. As we show by a Redfield theory calculation of the relaxation times, the distribution shape corresponds to the expected effect of Gaussian disorder of the pigment transition energies. By repeatedly measuring few individual complexes for minutes, we find that complexes sample the relaxation time distribution on a timescale of seconds. Furthermore, by comparing the distribution from a single long-lived complex with the whole ensemble, we demonstrate that, regarding the relaxation times, the ensemble can be considered ergodic. Our findings thus agree with the commonly used notion of an ensemble of identical LH2 complexes experiencing slow random fluctuations.

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44

Zorn, Reiner. "Logarithmic moments of relaxation time distributions". Journal of Chemical Physics 116, n.º 8 (22 de febrero de 2002): 3204–9. http://dx.doi.org/10.1063/1.1446035.

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45

Mohnke, O., C. Nordlund, R. Jorand y N. Klitzsch. "Understanding NMR relaxometry of partially water-saturated rocks". Hydrology and Earth System Sciences Discussions 11, n.º 11 (17 de noviembre de 2014): 12697–729. http://dx.doi.org/10.5194/hessd-11-12697-2014.

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Abstract. Nuclear Magnetic Resonance (NMR) relaxometry measurements are commonly used to characterize the storage and transport properties of water-saturated rocks. These assessments are based on the proportionality of NMR signal amplitude and relaxation time to porosity (water content) and pore size, respectively. The relationship between pore size and NMR relaxation time depends on pore shape, which is usually assumed to be spherical or cylindrical. However, the NMR response at partial water saturation for natural sediments and rocks differs strongly from the response calculated for spherical or cylindrical pores, because these pore shapes cannot account for water menisci remaining in the corners of de-saturated angular pores. Therefore, we consider a bundle of pores with triangular cross-sections. We introduce analytical solutions of the NMR equations at partial saturation of these pores, which account for water menisci of de-saturated pores. After developing equations that describe the water distribution inside the pores, we calculate the NMR response at partial saturation for imbibition and drainage based on the deduced water distributions. For this pore model, NMR amplitude and NMR relaxation time at partial water saturation strongly depend on pore shape even so the NMR relaxation time at full saturation only depends on the surface to volume ratio of the pore. The pore-shape-dependence at partial saturation arises from the pore shape and capillary pressure dependent water distribution in pores with triangular cross-sections. Moreover, we show the qualitative agreement of the saturation dependent relaxation time distributions of our model with those observed for rocks and soils.

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46

Keating, Kristina y Samuel Falzone. "Relating nuclear magnetic resonance relaxation time distributions to void-size distributions for unconsolidated sand packs". GEOPHYSICS 78, n.º 6 (1 de noviembre de 2013): D461—D472. http://dx.doi.org/10.1190/geo2012-0461.1.

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Nuclear magnetic resonance (NMR) is used in near-surface geophysics to understand the pore-scale properties of geologic material. The interpretation of NMR data in geologic material assumes that the NMR relaxation time distribution ([Formula: see text]-distribution) is a linear transformation of the void-size distribution (VSD). This interpretation assumes fast diffusion and can be violated for materials with high surface relaxivity and/or large pores. We compared [Formula: see text]-distributions to VSDs using grain-size distributions (GSDs) as a proxy for VSDs. Measurements were collected on water-saturated sand packs with a range of grain sizes and surface relaxivities, such that some samples were expected to violate the fast diffusion assumption. Samples were prepared from silica sand with three different average grain sizes and were coated with the iron-oxide mineral hematite to vary the surface relaxivity. We found analytically that outside the fast diffusion regime, the [Formula: see text]-distributions are broader than in the fast diffusion regime, which could lead to misinterpretation of NMR data. The experimental results showed that the [Formula: see text]-distributions were not linear transformations of the GSDs. The GSDs were a single peak independent of the hematite coating. The [Formula: see text]-distributions were broader than the measured GSDs, and the center of the distribution depended on the coating. Using an equation that does not assume fast diffusion to transform the [Formula: see text]-distributions to NMR-estimated VSDs resulted in distributions that were centered on a single radius. However, our attempts to recover the VSDs, as estimated from laser particle size analysis, were unsuccessful; the NMR-estimated VSDs were broader and yielded average pore radii that were much smaller than expected. We found that our approach was useful for determining relative VSDs from [Formula: see text]-distributions; however, future research is needed to develop a method for calibrating the NMR-estimated VSDs for unconsolidated sands.

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47

Hetman, P., B. Szabat, K. Weron y D. Wodziński. "On the Rajagopal relaxation-time distribution and its relationship to the Kohlrausch–Williams–Watts relaxation function". Journal of Non-Crystalline Solids 330, n.º 1-3 (noviembre de 2003): 66–74. http://dx.doi.org/10.1016/j.jnoncrysol.2003.08.060.

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48

Sartor, Günter, Erwin Mayer y G. P. Johari. "Thermal history and enthalpy relaxation of an interpenetrating network polymer with exceptionally broad relaxation time distribution". Journal of Polymer Science Part B: Polymer Physics 32, n.º 4 (marzo de 1994): 683–89. http://dx.doi.org/10.1002/polb.1994.090320410.

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49

KOBAYASHI, Kiyoshi. "Basic Theory of Distribution of Relaxation Time Analysis and Its Expansion". Denki Kagaku 90, n.º 3 (5 de septiembre de 2022): 265–78. http://dx.doi.org/10.5796/denkikagaku.22-te0004.

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50

Bzenic, S., Z. M. Raspopovic, S. Sakadzic y Z. Lj Petrovic. "Relaxation of electron swarm energy distribution functions in time-varying fields". IEEE Transactions on Plasma Science 27, n.º 1 (1999): 78–79. http://dx.doi.org/10.1109/27.763048.

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