Conditions Of Partial Saturation Research Articles

Influence of oil saturation upon spectral induced polarization of oil-bearing sands

SUMMARY The induced polarization model developed recently by Revil and Florsch to understand the complex conductivity of fully saturated granular materials has been extended to partial saturation conditions. It is an improvement over previous models like the Vinegar and Waxman model, which do not account explicitly for the effect of frequency. The Vinegar and Waxman model can be considered as a limiting case of the Revil and Florsch model in the limit where the distribution of relaxation times is very broad. The extended model is applied to the case of unconsolidated sands partially saturated with oil and water. Laboratory experiments were performed to investigate the influence of oil saturation, frequency, grain size, and conductivity of the pore water upon the complex resistivity response of oil-bearing sands. The low-frequency polarization (below 100 Hz) is dominated by the polarization of the Stern layer (the inner part of the electrical double layer coating the surface of the grains in contact with water). The phase exhibits a well-defined relaxation peak with a peak frequency that is dependent on the mean grain diameter as predicted by the model. Both the resistivity and the magnitude of the phase increase with the relative saturation of the oil. The imaginary (quadrature) component of the complex conductivity is observed to decrease with the oil saturation. All these observations are reproduced by the new model.

Relative hydraulic conductivity and effective saturation from Earth’s field nuclear magnetic resonance – a method for assessing the vadose zone

ABSTRACTBeside the water content, petrophysical nuclear magnetic resonance (NMR) techniques in the lab and in boreholes as well as in the field, provide estimates of the hydraulic conductivity of water saturated sediments and rocks. In the vadose zone, the hydraulic conductivity is a function of the water saturation. Regarding the characterization of the vadose zone, the magnetic resonance sounding (MRS) method is expected to have great potential. However, so far, the petrophysical relationship of the hydraulic properties under partial saturation conditions and the NMR parameters in the Earth’s magnetic field is not fully understood. In this study, laboratory NMR experiments in the Earth’s field (EFNMR) are performed in comparison to conventional high field NMR (HFNMR). Sand‐filled columns were used to generate partially saturated conditions by simulating capillary fringes (grain sizes from fine to coarse). We investigate the ability of both NMR techniques to determine the residual water content and the dependency of the NMR relaxation times on the water saturation degree. We note that EFNMR measurements tend to underestimate the residual water content due to long measurement dead times. Furthermore, it shows that the HFNMR relaxation time , as a function of the saturation, behaves according to the Brooks‐Corey model that describes the water retention function and thus allows for the prediction of the relative hydraulic conductivity ,. The EFNMR relaxation time as a function of the saturation degree differs from the Brooks‐Corey expectation due to the influence of the dephasing relaxation rate that is, in general, responsible for the difference of and . We assume that the dephasing relaxation rate itself, when induced by internal magnetic field gradients, depends on the water saturation. We introduce a model that accounts for this dependency with a weighting factor for the dephasing relaxation rate, given as a power law of the saturation degree. The model enables the description of as a function of the water saturation and thus provides the estimation of from . We compare the NMR based predictions with the functions estimated from gravity induced outflow experiments at the columns. The results are in agreement within half a decade for every sand sample of the study. In principle, the suggested approach can be applied for estimating in situ by MRS measurements in the vadose zone. We discuss the potential and limitations of this approach for MRS.

Concerted Nitric Oxide Formation and Release from the Simultaneous Reactions of Nitrite with Deoxy- and Oxyhemoglobin

Recent studies reveal a novel role for hemoglobin as an allosterically regulated nitrite reductase that may mediate nitric oxide (NO)-dependent signaling along the physiological oxygen gradient. Nitrite reacts with deoxyhemoglobin in an allosteric reaction that generates NO and oxidizes deoxyhemoglobin to methemoglobin. NO then reacts at a nearly diffusion-limited rate with deoxyhemoglobin to form iron-nitrosyl-hemoglobin, which to date has been considered a highly stable adduct and, thus, not a source of bioavailable NO. However, under physiological conditions of partial oxygen saturation, nitrite will also react with oxyhemoglobin, and although this complex autocatalytic reaction has been studied for a century, the interaction of the oxy- and deoxy-reactions and the effects on NO disposition have never been explored. We have now characterized the kinetics of hemoglobin oxidation and NO generation at a range of oxygen partial pressures and found that the deoxy-reaction runs in parallel with and partially inhibits the oxy-reaction. In fact, intermediates in the oxy-reaction oxidize the heme iron of iron-nitrosyl-hemoglobin, a product of the deoxy-reaction, which releases NO from the iron-nitrosyl. This oxidative denitrosylation is particularly striking during cycles of hemoglobin deoxygenation and oxygenation in the presence of nitrite. These chemistries may contribute to the oxygen-dependent disposition of nitrite in red cells by limiting oxidative inactivation of nitrite by oxyhemoglobin, promoting nitrite reduction to NO by deoxyhemoglobin, and releasing free NO from iron-nitrosyl-hemoglobin.

Reappraisal of vertical motion effects on soil liquefaction

INTRODUCTION Ground motion induced by an earthquake is in general characterised by a vector with its components along the vertical and two horizontal directions. In current practice and research, the effect of vertical ground motion is often disregarded while attention is focused mainly on the horizontal ground motion. Two primary reasons have been accepted for neglect of the vertical seismic motion. First, engineering structures are considered to have adequate resistance to dynamic forces induced by the vertical ground motion, which is generally much smaller than its horizontal counterparts. If the effect of vertical motion is explicitly included in design, it is typically assumed that the ratio of vertical to horizontal (V/H) response spectra will not exceed two-thirds (International Code Council, 1996). Second, the vertical ground motion is considered to have negligible influence on soil liquefaction because it induces almost purely compressive stresses, which cannot cause changes in the effective stress in the subsoil (Ishihara, 1996). However, there are repeated observations from recent earthquakes, such as those in Northridge, California, in 1994 and Kobe, Japan, in 1995 (Bardet et al., 1997; NCEER, 1997), that the rule-of-thumb ratio of two-thirds is a poor descriptor of vertical ground motions. The (V/H) spectral ratios may substantially exceed two-thirds in the near field of moderate and large earthquakes and at short periods. A typical case comes from the three-dimensional borehole array recordings obtained at Port Island, Kobe, during the 1995 Kobe earthquake (Yang & Sato, 2000), which indicated that the peak vertical acceleration was twice as high as the peak horizontal acceleration at the ground surface (Fig. 1). An integrated study of this case history (Yang & Sato, 2000; Yang et al., 2000) has revealed that both the horizontal and the vertical ground motions were closely related to the liquefied soil layers and, particularly, the condition of partial saturation in the near-surface soils played a crucial role in the amplification of vertical motion. Partial saturation conditions may occur in certain situations as a result of fluctuating groundwater tables associated with natural or man-made processes. They may also exist in offshore sites or marine sediments. Thus considerable interest arises in reappraising the effect of vertical ground motion on soil liquefaction and, especially, in clarifying whether or not this effect is dependent on the saturation condition. Aimed at this goal, analyses have been conducted by means of a verified, fully coupled numerical procedure for a model deposit subjected to a variety of combinations of loading and saturation conditions. A significant finding of the analyses is that the current understanding that the effect of vertical motion on liquefaction is negligible may not always hold true; rather, the effect is dependent on the saturation condition. This paper presents the main results and the related mechanisms. Implications of the results for dynamic model testing in the geotechnical laboratory are also addressed briefly.

Streaming potential of a sand column in partial saturation conditions

The understanding of the streaming potential in partial water saturation conditions in porous media is of great interest for the interpretation of spontaneous polarization observations. We built a device which allows us to quantify the streaming potential at various saturation conditions using a sand column of 1‐m height and 8‐cm diameter. This is the first time that such a quantification has been performed. Different gases such as argon, nitrogen, and carbon dioxide are injected into the sand to decrease its water saturation, and to make the fluid flow within the sand. The measured electrokinetic coupling coefficient in partial saturation is either constant or decreases by a factor ∼3 with decreasing water saturation from 100 to 40%, whereas the sand electrical resistivity is enhanced by a factor of ∼5.

Magnetization Evolution in Network Models of Porous Rock under Conditions of Drainage and Imbibition

Surface-enhanced relaxation of nuclear magnetization in fully and partially saturated water-wet porous media is studied using a pore network simulator. The simulator is based on a description of the pore space in terms of a regular cubic lattice of pores and throats following respective size distributions. The latter are obtained from geometric characterization of 3D stochastic replicas of real porous rock samples. Concepts of percolation theory are used to simulate the pore-scale distribution of a strongly wetting phase under conditions of quasistatic drainage by or imbibition against a nonwetting phase. The results of these simulations compare favorably with experimental mercury intrusion/retraction curves. The equations governing magnetization evolution in a connected pore system are then solved by matrix diagonalization for different values of wetting-phase saturation along the primary drainage and secondary imbibition paths. Analysis of the corresponding spectra of decay rates provides new insights regarding the influence of pore structure (pore and throat size distributions, spatial correlation), surface relaxation strength, and fluid distribution on diffusive coupling between pores. For pore and throat size distributions and surface relaxation strength representative of sandstones, diffusive coupling is quite important, especially under conditions of partial saturation. Remarkably, simulations show that correlated heterogeneity is the main reason pores appear poorly coupled with respect to NMR relaxation—an assumption underlying the correspondence between pore size and relaxation time distributions. Finally, for a given value of wetting-phase saturation, the history of saturation change (drainage or imbibition) is shown to have a profound effect on the spectrum of decay rates.

The performance of volume selection sequences for in vivo NMR spectroscopy: implications for quantitative MRS

Previous work has demonstrated that deficiencies in volume selection sequences used in magnetic resonance spectroscopy may compromise the quality of the spectra obtained. In this paper, further studies on the ISIS and PRESS sequences are presented. Under conditions of partial saturation, ISIS can exhibit serious contamination with extraneous signal, particularly when a small volume of interest (VOI) is selected. ISIS protocols should therefore use VOIs that are large relative to the target volume, and repetition times that are as long as practicable. In PRESS, contamination is found to be minimised by using a VOI that is small relative to the target volume, and to be independent of repetition time. PRESS performance is also independent of echo time, except when very short echo times are used. These results are consistent with previously published work on ISIS and PRESS, and it is now possible to establish generic features of these sequences and to understand the implications for quantitative spectroscopy. T 1-weighting of contamination in ISIS can compromise both relative and absolute quantification techniques in several respects. Contamination in PRESS is largely independent of relaxation times and would be easier to model and correct for in the context of quantitative spectroscopy.

Spin Relaxation Measurements Using First-Harmonic Out-of-Phase Absorption EPR Signals

The dependence on spin–lattice (T1) relaxation of the first-harmonic absorption EPR signal (V′1) detected in phase quadrature with the Zeeman modulation has been investigated both theoretically and experimentally for nitroxide spin labels. Spectral simulations were performed by iterative solution of the Bloch equations that contained explicitly both the modulation and microwave magnetic fields (T. Páli, V. A. Livshits, and D. Marsh, 1996,J. Magn. Reson. B113, 151–159). It was found that, of the various non-linear EPR displays, the first-harmonic out-of-phaseV′1-signal, recorded under conditions of partial saturation of the microwave absorption, is particularly favorable for determining spin–lattice relaxation enhancements because of its superior signal intensity and relative insensitivity to spin–spin (T2) relaxation. By varying the Zeeman modulation frequency it is also possible to tune the optimum sensitivity of theV′1-signal to different ranges of theT1-relaxation time. A Zeeman modulation frequency of 25 kHz appears to be particularly suited to spin label applications. Calibrations are given for the dependence onT1-relaxation time of both the amplitude and the second integral of theV′1-signal recorded under standard conditions. Experiments on different spin labels in solution and in membranes demonstrate the practical usable sensitivity of theV′1-signal, even at modulation frequencies of 25 kHz, and these are used to investigate the dependence on microwave field intensity, in comparison with theoretical predictions. The practicable sensitivity to spin–lattice relaxation enhancements is demonstrated experimentally for a spin-labeled membrane system in the presence of paramagnetic ions. The first-harmonic out-of-phaseV′1-signal appears to be the non-linear CW EPR method of choice for determiningT1-relaxation enhancements in spin-labeled systems.

Comments on "Operation of ground sensor relays under conditions of partial CT saturation" [with reply

The author argues that the original paper Operation of Ground Sensor Relays Under Conditions of Partial CT Saturation by B. Bridger et al. (see ibid., vol. 33, p. 1111-16, 1997) would have had added value if the conclusions summarized at the end of it had included a statement that the fact that core balance-type ground sensors normally operate with the current transformers' (CT's) being saturated should be factored into the ground fault protection relay coordination curves. The original authors' reply to these comments are also presented.

Closure to Comments on "Operation of Ground Sensor Relays Under Conditions of Partial CT Saturation"

Closure to Comments on "Operation of Ground Sensor Relays Under Conditions of Partial CT Saturation"

Optical saturation thermal lens spectrometry in non-polar solvents

A model for thermal lens spectrometry (TLS) in partial optical saturation conditions which was previously applied to polar solutes in aqueous media is now checked with non-polar organic dyes and metal dithizonates in carbon tetrachloride. Some literature data are also examined. Most data can be consistently explained on the basis of the molecular structures, the sensitivity increasing with the capability of the solute to rapidly communicate the absorbed energy to the solvent molecules.

Operation of ground sensor relays under conditions of partial CT saturation

Operation of ground sensor relays under conditions of partial CT saturation

Non-linear, continuous-wave EPR spectroscopy and spin–lattice relaxation: spin-label EPR methods for structure and dynamics †

The sensitivity of continuous-wave, non-linear EPR signals to spin–lattice (T1) relaxation has been investigated. The aim was to identify those spectral displays that are most appropriate to obtain structural and dynamic information from spin-label EPR experiments that involve detection of T1-relaxation enhancements. This has been achieved by solving the Bloch equations for the various harmonics of the absorption and dispersion components of the spin magnetisation. Of interest are the magnetisation components that are out-of-phase with respect to the static magnetic field modulation, under conditions of partial saturation of the microwave absorption. It is found that both the first- and second-harmonic out-of-phase absorption EPR signals are particularly sensitive to T1-relaxation. The first-harmonic absorption quadrature-phase signal is favoured for determining T1-relaxation enhancements because of its superior intensity and relative insensitivity to transverse (T2) relaxation. The second-harmonic absorption quadrature-phase EPR signal has lower relative intensity and is more sensitive to T2-relaxation, but has a unique sensitivity to rotational diffusion that is exploited in saturation transfer EPR spectroscopy. The non-linear dispersion signals are less appropriate because of their principal sensitivity to T2-relaxation and because they saturate less readily. These novel non-linear EPR spectroscopies can be contrasted with the conventional progressive saturation behaviour of the in-phase absorption signals that are determined by the T1T2 relaxation time product.

Albedo of dirty snow during conditions of melt

The evolution of spectrally averaged albedo (wavelengths between 0.28 μm and 2.8 μm) of snow surfaces treated with known initial concentrations of particles of submicron‐sized soot and air fall volcanic ash was investigated during conditions of natural melt. Depending on the particle type and concentration, the initial applications reduced the surface albedo to values ranging from 0.18 to 0.41 which were substantially lower than the albedo of the untreated natural snow (about 0.61). Many of the soot particles flushed through the snowpack with the meltwater, and surface concentrations of soot greater than about 5 × 10−7 kg/kg did not persist for more than a few days. The migration of particles to depth caused the snow to brighten after the initial application, thus limiting the amount of albedo reduction and the consequent effects on melting. Nevertheless, the soot remaining near the surface had a substantial, long‐term effect. The residual concentration of 5 × 10−7 kg/kg persisted for several weeks and, compared to the untreated surface, reduced the albedo by about 30% and increased melting by 50%. Particles of volcanic ash with diameters larger than about 5 μm remained at or near the snow surface. Although many of the smaller particles flushed through the snow with the meltwater, the surface albedo was not changed significantly by their removal. The different behaviors of the ash and soot are probably related to the difference in their particle size distributions in relation to the thickness of water films that form the transport paths under conditions of partial saturation that are characteristic of melting snow.

Optical saturation, diffusion and convection effects in thermal lens spectrometry

In thermal lens spectrometry (TLS) the intense pump radiation can lead the chromophore to partial optical saturation conditions in which the ground state is depleted and the population of an intermediate excited state increases. A model in which the excitation process competes with both the decay processes and diffusion and convection of the species in the excited and ground states is developed. The model is used to explain the variations of the TLS/spectrophotometry sensitivity ratios found for a series of phthalein and azo dyes in aqueous media.

A model for optical saturation thermal lens spectrometry

A model for thermal lens spectrometry (TLS) in partial optical saturation conditions is developed. The model predicts that optical saturation is approached to a significant degree in many TLS experiments, and that it can be reached to a high degree with the currently available laser and optical technologies. When optical saturation is approached, the sensitivity decreases and the signal depends on the rate constant of the slowest step of the decay process. Important consequences for the future development of photothermal spectrometric techniques can be derived.

Actomyosin interactions in the presence of ATP and the N-terminal segment of actin.

The binding of myosin subfragment 1 (S-1) to actin in the presence of ATP and the acto-S-1 ATPase activities of acto-S-1 complexes were determined at 5 degrees C under conditions of partial saturation of actin, up to 90%, by antibodies against the first seven N-terminal residues on actin. The antibodies [Fab(1-7)] inhibited strongly the acto-S-1 ATPase and the binding of S-1 to actin in the presence of ATP at low concentrations of S-1, up to 25 microM. Further increases in S-1 concentration resulted in a partial and cooperative recovery of both the binding of S-1 to actin and the acto-S-1 ATPase while causing only limited displacement of Fab(1-7) from actin. The extent to which the binding and the ATPase activity were recovered depended on the saturation of actin by Fab(1-7). The combined amounts of S-1 and Fab binding to actin suggested that the activation of the myosin ATPase activity was due to actin free of Fab. Examination of the acto-S-1 ATPase activities as a function of S-1 bound to actin at different levels of actin saturation by Fab(1-7) revealed that the antibodies inhibited the activation of the bound myosin. Thus, the binding of antibodies to the N-terminal segment of actin can act to inhibit both the binding of S-1 to actin in the presence of ATP and a catalytic step in ATP hydrolysis by actomyosin. The implications of these results to the regulation of actomyosin interaction are discussed.

Nucleotide-induced changes in the interaction of myosin subfragment 1 with actin: detection by antibodies against the N-terminal segment of actin

The binding of myosin subfragment 1 (S-1) to actin in the presence and absence of nucleotides was determined under conditions of partial saturation of actin, up to 80%, by Fab(1-7), the antibodies against the first seven N-terminal residues on actin. In the absence of nucleotides, the binding constant of S-1 to actin (2 x 10(7) M-1) was decreased by 1 order of magnitude by Fab(1-7). The binding of S-1 to actin caused only limited displacement of Fab, and between 30 and 50% of actin appeared to bind both proteins. In the presence of MgAMP.PNP, MgADP, and MgPPi and at low S-1 concentrations, the same antibodies caused a large decrease in the binding of S-1 to actin. However, the binding of S-1.nucleotide to actin in the presence of Fab(1-7) increased cooperatively with the increase in S-1 concentration. Also, in contrast to rigor conditions, there was no indication for the binding of Fab(1-7) and S-1.nucleotide to the same actin molecules. These results show a nucleotide-induced transition in the actomyosin interface, most likely related to the different roles of the N-terminal segment of actin in the binding of S-1 and S-1.nucleotide. The possible implications of these findings to the regulation of actomyosin interactions are discussed.

Steady fluid flow and travel times in partially saturated fractures using a discrete air‐water interface

Fracture flow under conditions of partial fluid saturation is studied where a portion of the fracture is filled with water and the remaining portion is filled with air. A discrete air‐water interface is used to separate the saturated from the drained regions within the fracture. A laboratory flow experiment is presented which demonstrates the interface concept. The steady state air‐water interface position is observed by maintaining a circular water source at constant positive pressure head between two vertical glass plates. An analytic solution to the flow problem is compared to the observed interface position and to simulated results which assume that a constant capillary pressure head can be assigned along the interface. Simulations performed for a hypothetical vertical fracture indicate zones of positive and negative pressure head in the saturated zone as well as an air‐filled zone. For the hypothetical fracture examined, fluid travel times are not substantially changed as fracture saturation decreases. This result may not hold generally for all fractures.

Non-Darcy Gas Flow Through Propped Fractures: Effects of Partial Saturation, Gel Damage, and Stress

Summary The objective of this work was to identify and quantify important parameters affecting gas production through propped fractures under a non-Darcy gas flow regime. The gas flow capacity of a simulated propped fracture was studied systematically to determine the effects of partial saturation, gel damage, and stress conditions. The flow-capacity response of the 20/40-mesh sand tested throughout this project was affected significantly by variations in the effective gas porosity of the proppant pack. Permeability and non-Darcy flow characteristics were correlated to effective gas porosity. Partial saturation was found to be a key parameter influencing the permeability and non-Darcy gas flow behavior of a proppant pack. Partially saturated fractures may result from incomplete removal of fracturing fluid, mobility of formation waters, or production of condensates. The partial saturation of the proppant pack, in effect, changes the open porosity available for gas flow, which adversely affects gas permeability and non-Darcy flow parameters. The results from this investigation demonstrate that non-Darcy gas flow behavior through propped fractures in which a saturation phase is present cannot be estimated from results using dry-proppant-pack tests.