Steady-state Saturation Research Articles

Ungated, plug-and-play preclinical cardiac CEST-MRI using radial FLASH with segmented saturation.

Electrocardiography (ECG) and respiratory-gated preclinical cardiac CEST-MRI acquisitions are difficult because of variable saturation recovery with T1, RF interference in the ECG signal, and offset-to-offset variation in Z-magnetization and cardiac phase introduced by changes in cardiac frequency and trigger delays. The proposed method consists of segmented saturation modules with radial FLASH readouts and golden angle progression. The segmented saturation blocks drive the system to steady-state, and because center k-space is sampled repeatedly, steady-state saturation dominates contrast during gridding and reconstruction. Ten complete Z-spectra were acquired in healthy mice using both ECG and respiratory-gated and ungated methods. Z-spectra were also acquired at multiple saturation B1 values to optimize for amide and Cr contrasts. There was no significant difference between CEST contrasts (amide, Cr, magnetization transfer) calculated from images acquired using ECG and respiratory-gated and ungated methods (p = 0.27, 0.11, 0.47). A saturation power of 1.8μT provides optimal contrast amplitudes for both amide and total Cr contrast without significantly complicating CEST contrast quantification because of water direct saturation, magnetization transfer, and RF spillover between amide and Cr pools. Further, variability in CEST contrast measurements was significantly reduced using the ungated radial FLASH acquisition (p = 0.002, 0.006 for amide and Cr, respectively). This method enables CEST mapping in the murine myocardium without the need for cardiac or respiratory gating. Quantitative CEST contrasts are consistent with those obtained using gated sequences, and per-contrast variance is significantly reduced. This approach makes preclinical cardiac CEST-MRI easily accessible, even for investigators without prior experience in cardiac imaging.

Size-dependent steady state saturation limit in biomolecular transport through nuclear membranes.

The nucleus preserves the genomic DNA of eukaryotic organisms and maintains the integrity of the cell by regulating the transport of molecules across the nuclear membrane. It is hitherto assumed that small molecules having a size below the passive permeability limit are allowed to diffuse freely to the nucleus while the transport of larger molecules is regulated via an active mechanism involving energy. Here we report on the kinetics of nuclear import and export of dextran molecules having a size below the passive permeability limit. The studies carried out using time-lapse confocal fluorescence microscopy show a clear deviation from the passive diffusion model. In particular, it is observed that the steady-state concentration of dextran molecules inside the nucleus is consistently less than the concentration outside, in contradiction to the predictions of the passive diffusion model. Detailed analysis and modeling of the transport show that the nuclear export rates significantly differ from the import rates, and the difference in rates is dependent on the size of the molecules. The nuclear export rates are further confirmed by an independent experimental study where we observe the diffusion of dextran molecules from the nucleus directly. Our experiments and transport model would suggest that the nucleus actively rejects exogenous macromolecules even below the passive permeability limit. This result can have a significant impact on biomedical research, especially in areas related to targeted drug delivery and gene therapy.

Response of ZrC to swift heavy ion irradiation

Zirconium carbide (ZrC) is commonly used for energy sector research, as well as a surrogate for the proposed advanced nuclear fuel candidate uranium carbide. This study investigates structural modifications to nanocrystalline and microcrystalline ZrC resulting from dense electronic excitations induced by swift heavy ion exposure. Samples were irradiated with 946 MeV Au ions to various fluences up to 6 × 1013 ions cm−2 and characterized using synchrotron-based x-ray diffraction. The evolution of the unit-cell parameter and heterogeneous microstrain were evaluated as a function of fluence and compared with those of nanocrystalline and microcrystalline CeO2 (a surrogate for UO2 fuel) irradiated under identical conditions. Distinct differences were observed in the radiation responses of the carbide and oxide across both grain sizes. Most notably, microcrystalline ZrC exhibits swelling characterized by two distinct regimes, which does not result in saturation at the ion fluences achieved. This contrasts with CeO2, which exhibits the well-documented direct-impact defect accumulation mechanism, reaching a steady-state saturation of swelling at higher fluences. Nanocrystalline CeO2 undergoes more pronounced swelling compared with microcrystalline CeO2, in contrast to nanocrystalline ZrC, which exhibits only minimal unit-cell changes. These results demonstrate that swift heavy ion-induced structural changes can be quite different in carbides and oxides, which must be considered when extrapolating fission-fragment type damage in current fuels to advanced fuels.

Mechanistic insights on the catalytic ozonation of trimethoprim in aqueous phase using geopolymer catalysts produced from mining waste

The catalytic properties of low-cost ceramic aluminosilicate polymers (geopolymers) containing metakaolin and different amounts of magnetic mining waste, up to 75% w/w, were investigated for the degradation of the antibiotic drug trimethoprim (TMP) in water in the presence of ozone. In the presence of the geopolymers, the removal of TMP increased by up to 11% to reach 71% conversion, while its mineralization increased by 4% to reach 40%. Moreover, the catalyst also decreased the steady-state ozone saturation level of the solution. Reactive species (ROS) trapping experiments demonstrated that superoxide (O2•–) had the most significant impact on the removal rate (55% decrease), followed by singlet oxygen (1O2) (30% decrease). The 20 intermediate reaction products identified by mass spectroscopy was consistent with a four-branch reaction mechanism by superoxide attack on the TMP molecule including i) the methylene bridge rupture, ii) the oxidation of the diaminopyrimidine amine with further hydroxylation and carbonylation, iii) the hydroxylation of diaminopyrimidine amines and iv) 1,2,3-trimethoxybenzene demethylation. XRF, FTIR, ss-NMR and XPS analyses of the geopolymers before and after the reaction also demonstrated the robustness of the geopolymers catalysts during the ozonation reaction. Overall, this study demonstrates that inexpensive geopolymers produced from mining waste could be used in catalytic ozonation reactions for water decontamination.

Intercept Method for Accurately Estimating Residual Fluid Saturation and Approximate Transient Solutions with Production Time Scales in Centrifuge Core Plug Experiments

Summary The centrifuge experiment is used to measure capillary pressure in core plugs by forced displacement (imbibition or drainage): Strong gravitational forces (imposed by rotation) displace fluid held in place by capillary forces. This setup is also used to measure and establish residual saturation, the saturation where a fluid loses connectivity and can no longer flow. Obtaining this saturation is challenging as the capillary end effect causing outlet fluid accumulation theoretically only vanishes at infinite rotation speed. First, we derive a novel “intercept method” to estimate residual saturation with a centrifuge: Plotting steady-state average saturation data against inverse squared rotation speed gives a straight line at high speeds where the intercept equals the residual saturation. The linear behavior starts once the core saturation profile contains the residual saturation. The result is theoretically valid for all input parameters and functions, derived assuming uniform gravity along the core at a given speed. Then the saturation profile near the outlet is invariant and compresses at a higher speed. The method was, however, demonstrated numerically to be highly accurate even for extremely nonuniform gravity: The saturation data are linear and the correct residual saturation value is estimated. This is because when the residual saturation enters, most of the end effect profile is located in a narrow part of the core and thus uniformly compressed. Several experimental and numerical data sets validated the method. Second, an analytical solution (using all relevant input) is derived for transient production toward equilibrium after the rotation speed is increased starting from an arbitrary initial state. For this result, we assume the outlet (or initial) profile compresses also transiently. The displacing and displaced regions have fixed mobilities but occupy different lengths with time. Time as a function of production has a linear term and logarithmic term (dominating late time behavior). Production rate can thus be constant most of the time or gradually reducing, resulting in very distinct profiles. The correlation could fit experimental data well and confirmed the possible profile shapes. A time scale was derived analytically that scales all production curves to end (99.5% production) at same scaled time. The solution predicted similar time scales and trends in time scale with rotation speed and viscosity as numerical simulations. Numerical simulations indicated that the saturations near the residual saturation traveled slowly, which caused production to tail and span 5 log units of time (the analytical solution predicted 2–3). The correlation better matched low-speed data where the residual saturation had not entered.

Gas Fluxes and Steady State Saturation Anomalies at Very High Wind Speeds

AbstractGas exchange at high wind speeds is not well understood—few studies have been conducted at wind speeds above 20 ms−1 and significant disagreement exists between gas exchange models at high wind speeds. In this study, noble gases (He, Ne, Ar, Kr, and Xe) were measured in 35 experiments in the SUSTAIN wind‐wave tank where the wind speeds ranged from 20 to 50 m s−1 and mechanical waves were generated as monochromatic or with a short‐crested JONSWAP frequency spectrum. Bubble size spectra were determined using shadowgraph imagery and wave statistics were measured using a wave wire array. The steady state saturation anomalies and gas fluxes initially increased as wind speeds increased but then leveled off, similar to prior studies of heat and momentum flux coefficients. Noble gas fluxes and steady state saturation anomalies are correlated most strongly with bubble volumes for the less soluble noble gases and with wind speed and wave Reynolds number for the more soluble noble gases. In the JONSWAP experiments, significant wave height was the most important predictor for gas steady state saturation anomalies with correlation coefficients of greater than 0.92 for He, Ne, and Ar (P < 0.05). Furthermore, invasion fluxes were larger than evasion fluxes when other conditions were similar. Taken together, these lab‐based experiments suggest more attention should be paid to parameterizations based on wave characteristics and bubbles and that current wind‐speed based gas exchange parameterizations should not be applied to conditions with very high wind speeds.

Comparison of Intercept Methods for Correction of Steady-State Relative Permeability Experiments for Capillary End Effects

Summary Steady-state relative permeability experiments are performed by coinjection of two fluids through core plug samples. The relative permeabilities can be calculated using Darcy’s law from the stabilized pressure drop and saturation of the core if capillary end effects and transient effects are negligible. In most cases, such conditions are difficult to obtain. Recent works have presented ways to extrapolate steady-state pressure drop and average saturation measurements affected by capillary end effects collected at different rates to obtain correct relative permeabilities at correct saturations. Both the considered methods are based on linear extrapolations to determine intercepts. Gupta and Maloney (2016) derived their method intuitively and validated it with numerical and experimental data. Andersen (2021a) derived a method from fundamental assumptions and presented an intercept method in a different form where the saturation and relative permeabilities are found directly and uniquely from straightline intercepts. All system parameters, including saturation functions and injection conditions, appear in the model. In this work, the two methods are compared. It is proven theoretically that Gupta and Maloney’s method is correct in that it produces the correct saturation and pressure drops corrected for capillary end effects. Especially, a constant pressure drop was assumed and here proved to exist, as a result of capillary end effects in addition to the Darcy law pressure drop with no end effects. Their method assumes a well-defined end effect region with length xCEE, but this length can be defined almost arbitrarily. This choice has little impact on average saturation and pressure drop, however. They also assumed that for a defined end effect region, the average saturation was constant and equal to the slope in their saturation plot. It is shown that if the region is defined, the average saturation is indeed constant, but not given by the slope. The correct slope is predicted by the Andersen model. We also comment on theoretical misinterpretations of the Gupta and Maloney method. A few works have correctly calculated that the pressure drop over the end effect region is independent of rate, but not accounted for that its length is rate dependent. We show that the combined pressure drop is equal to a constant plus the Darcy pressure drop over the full core. Examples are presented to illustrate the model behaviors. Literature datasets are investigated showing that (a) apparently rate-dependent CO2-brine relative permeability endpoints can be explained by capillary end effects and (b) the intercept methods can be applied to correct shale relative permeabilities.

Dynamic pore network model to predict residual saturation and pressure drop in mist oleo-phobic filters

A dynamic pore network modelling (DPNM) framework is used to evaluate pressure drop and residual saturation in oleo-phobic nonwoven media in mist filters. The advanced fully-resolved VOF simulations along with μ-CT measurements are also carried out to substantiate the validity of the DPNM simulations. The results of the study show that PNM could be a beneficial and reliable tool for predicting oil saturation and pressure drop during early-stage design of oleo-phobic filters with nonwoven media. Given the considerably higher efficiency of PNM models compared to CFD-based techniques, some parametric studies were also conducted. Our findings suggest that, for a given set of operating conditions, efficiency/performance can be improved by appropriate choice of filters with optimized properties (fibre diameter, packing density, contact angle, etc.) for which the overall oil saturation and pressure drop in the filter attain minimum, may offer a self-cleaning mist filter. Finally, a correlation was developed for evaluating the performance of oleo-phobic media using the filter specifications and the data of steady state saturation and pressure drop found in open literature. The obtained correlation shows a good conformity with the experimental measurements with an average of 12.1% error for about 93% of data out of 68 data sets collected with a correlation coefficient of (R2) of 0.934.

Active Middle Ear Implant Evoked Auditory Brainstem Response Intensity-Latency Characteristics.

ObjectiveTo analyze intensity-latency functions of intraoperative auditory evoked brainstem responses (ABRs) to stimulation by the Vibrant Soundbridge (VSB) active middle ear implant with respect to coupling efficiency, VSB evoked ABR thresholds, and coupling modality [oval window (OW) placement vs. Incus placement and vs. round window (RW) placement].Study DesignExploratory study.SettingBi-centric study at tertiary referral centers.PatientsTwenty-four patients (10 female, 14 male, mean age: 58 years) who received a VSB.Outcome MeasuresWave-V intensity-latency functions of intraoperative VSB evoked ABRs using a modified audio processor programmed to preoperative bone conduction thresholds for stimulation. Threshold level correction to coupling efficiency and ABR thresholds. Individual plots and exponential function fits.ResultsAfter ABR threshold level correction, the latency functions could be aligned. A large variance of latencies was observed at individual threshold level. Wave-V latency was longest in the Incus placement subgroup (9.73 ms, SD: 1.04) as compared to OW placement subgroup (9.47 ms, SD: 1.05), with the shortest latency in the RW placement subgroup (8.99 ms, SD: 0.68). For increasing stimulation levels, the variance decreased with intensity-latency function slopes converging toward a steady-state (saturation) latency caused by saturation of audio processor (stimulation) gain. Latency saturation was reached at a stimulation level of 50 dB nHL for the OW placement subgroup, 35 dB nHL for the Incus placement subgroup, and 30 dB nHL for the RW placement subgroup. The latency and saturation results indicated decreased dynamic range for RW placement, i.e., reverse stimulation.ConclusionsVSB evoked ABR wave-V intensity-latency function slopes were similar to acoustic stimulation at high stimulation levels with a shift toward longer latencies caused by audio processor signal delay. Saturation of latencies occurred for higher stimulation levels due to saturation of audio processor gain. Thus, the analysis of VSB evoked intensity-latency functions appears to allow for the objective assessment of a patient's individual dynamic range. This can further improve diagnostics as well as intraoperative and postoperative quality control.

Structure Refinement and Fragmentation of Precipitates under Severe Plastic Deformation: A Review.

During severe plastic deformation (SPD), the processes of lattice defect formation as well as their relaxation (annihilation) compete with each other. As a result, a dynamic equilibrium is established, and a steady state is reached after a certain strain value. Simultaneously, other kinetic processes act in opposite directions and also compete with each other during SPD, such as grain refinement/growth, mechanical strengthening/softening, formation/decomposition of solid solution, etc. These competing processes also lead to dynamic equilibrium and result in a steady state (saturation), albeit after different strains. Among these steady-state phenomena, particle fragmentation during the second phase of SPD has received little attention. Available data indicate that precipitate fragmentation slows down with increasing strain, though saturation is achieved at higher strains than in the case of hardness or grain size. Moreover, one can consider the SPD-driven nanocrystallization in the amorphous phase as a process that is opposite to the fragmentation of precipitates. The size of these crystalline nanoprecipitates also saturates after a certain strain. The fragmentation of precipitates during SPD is the topic of this review.

Whole-brain amide CEST imaging at 3T with a steady-state radial MRI acquisition.

To develop a steady-state saturation with radial readout chemical exchange saturation transfer (starCEST) for acquiring CEST images at 3 Tesla (T). The polynomial Lorentzian line-shape fitting approach was further developed for extracting amideCEST intensities at this field. StarCEST MRI using periodically rotated overlapping parallel lines with enhanced reconstruction-based spatial sampling was implemented to acquire Z-spectra that are robust to brain motion. Multi-linear singular value decomposition postprocessing was applied to enhance the CEST SNR. The egg white phantom studies were performed at 3T to reveal the contributions to the 3.5 ppm CEST signal. Based on the phantom validation, the amideCEST peak was quantified using the polynomial Lorentzian line-shape fitting, which exploits the inverse relationship between Z-spectral intensity and the longitudinal relaxation rate in the rotating frame. The 3D turbo spin echo CEST was also performed to compare with the starCEST method. The amideCEST peak showed a negligible peak B1 dependence between 1.2 µT and 2.4 µT. The amideCEST images acquired with starCEST showed much improved image quality, SNR, and motion robustness compared to the conventional 3D turbo spin echo CEST method with the same scan time. The amideCEST contrast extracted by the polynomial Lorentzian line-shape fitting method trended toward a stronger gray matter signal (1.32% ± 0.30%) than white matter (0.92% ± 0.08%; P = .02, n = 5). When calculating the magnetization transfer contrast and T1 -corrected rotating frame relaxation rate maps, amideCEST again was not significantly different for white matter and gray matter. Rapid multi-slice amideCEST mapping can be achieved by the starCEST method (< 5 min) at 3T by combing with the polynomial Lorentzian line-shape fitting method.

Effect of wettability heterogeneity and compression on liquid water transport in gas diffusion layer coated with microporous layer of PEMFC

This study applied the pseudo-potential Lattice Boltzmann method (LBM) for investigating liquid water transport in the microporous layer (MPL) and gas diffusion layer (GDL) of polymer electrolyte fuel cell. The MPL and GDL reconstruction is performed by using a stochastic method. Unlike previous studies that examined the GDL as two distinct layers of hydrophilic and hydrophobic, this study considered the wettability heterogeneity. In the present study, some of the carbon fibers in the GDL are randomly considered hydrophilic. Moreover, liquid water transport in the compressed and uncompressed GDL with different hydrophilic fibers percentage are compared. The effect of hydrophilic fibers percentage and the compression ratio of the GDL on the liquid water saturation level, the steady-state time, and the formation and growth of droplets in the gas channel (GC) are investigated. The results indicated that more than 10% of hydrophilicity of the fibers lead to the formation of discontinuous water clusters. This phenomenon increased the steady-state time and water saturation level significantly. The simulation showed that compression increased the number of discontinuous water clusters in the GDL. The obtained results demonstrated that the hydrophilic fibers may have positive or negative effects on water transport in the GDL due to their location. In addition, this study indicated that for 10% of hydrophilic fibers with 10% compression, water saturation level and time required to reach steady-state decreased by 5.2% and 22% respectively compared to purely hydrophobic GDL.

Realizable Reference Antiwindup Implementation for Parallel Controller Structures

Parallel controller structures are often used for the control of harmonic components in those power converters, including harmonic-compensation functions. The controlled signal can be distorted during the voltage saturation of the power converter output. This article proposes an implementation of the realizable reference antiwindup technique suitable for parallel controllers in multiple reference frames. The proposed implementation is simple and does not require a particular type of controllers nor special controller arrangements. The proposed implementation can be used for any kind of linear controller structure regardless of the variables being controlled. In the context of harmonic current controllers, the antiwindup implementation allows separating the harmonic controller outputs for canceling or decreasing them during steady-state saturation to improve the waveform quality. Different saturation options are analyzed for the inner loop current controller of grid-forming converter applications.

Towards Relative Permeability Measurements in Tight Gas Formations

Relative permeability is a concept used to convey the reduction in flow capability due to the presence of multiple fluids. Relative permeability governs the multiphase flow, therefore it has a significant importance in understanding the reservoir behavior. These parameters are routinely measured on conventional rocks, however their measurement becomes quite challenging for low permeability rocks such as tight gas formations. This study demonstrates a methodology for relative permeability measurements on tight gas samples. The gas permeability has been measured by the Step Decay method and two different techniques have been used to vary the saturations: steady state flooding and vapor desorption. Series of steady-state gas/water simultaneous injection have been performed on a tight gas sample. After stabilization at each injection ratio, NMR T2, NMR Saturation profile and low pressure Step Decay gas permeability have been measured. In parallel, progressive desaturation by vapor desorption technique has been performed on twin plugs. After stabilization at each relative humidity level the NMR T2 and Step Decay gas permeability have been measured in order to compare and validate the two approaches. The techniques were used to gain insight into the tight gas two phase relative permeability of extremely low petrophysical properties (K&lt;100 nD, phi &lt; 5 pu) of tight gas samples of Pyrophyllite outcrop. The two methods show quite good agreement. Both methods demonstrate significant permeability degradation at water saturation higher than irreducible. NMR T2 measurements for both methods indicates bimodal T2-distributions, and desaturation first occurs on low T2 signal (small pores). Comparison of humidity drying and steady-state desaturation technique has shown a 12-18 su difference between critical water saturation (Swc) measured in gas/water steady-state injection and irreducible saturation (Swirr) measured by vapor desorption.

Remarkable nuances of crystallization: From ordinary crystal nucleation to rival mechanisms of crystallite coalescence

Crystal growth and crystal coalescence processes in supercooled systems strongly depend on the concentration of crystallization centers. We perform atomistic dynamics simulations of the crystallization process in the ultrathin metallic film at different supercooling levels corresponding to supercooled liquid and amorphous solid states. Scaled relations are applied to identify the characteristic regimes in the time-dependent crystalline nuclei concentration: steady-state nucleation regime, saturation regime and coalescence regime. We show that the crystal growth at the saturation regime appears due to mixing nucleation and coalescence processes. We find that the crystallite coalescence realizes mainly through the mechanism of restructurization/absorption of crystal nuclei, whereas the mechanism of oriented attachment is manifested only at low levels of supercooling.

High-resolution creatine mapping of mouse brain at 11.7 T using non-steady-state chemical exchange saturation transfer.

The current study aims to optimize the acquisition scheme for the creatine chemical exchange saturation transfer weighted (CrCESTw) signal on mouse brain at 11.7T, in which a strong magnetization transfer contrast (MTC) is present, and to further develop the polynomial and Lorentzian line-shape fitting (PLOF) method for quantifying CrCESTw signal with a non-steady-state (NSS) acquisition scheme. Studies on a Cr phantom with cross-linked bovine serum albumin (BSA) as well as on mouse brain demonstrated that the maximum CrCESTw signal was reached with a short saturation time determined by the rotating frame relaxation time of the MTC pool instead of the steady-state saturation. The saturation power for the maximal signal was around 1-1.5 μT for Cr with 20% cross-linked BSA and in vivo applications, but 2 μT was found to be most practical for signal stability. For the CrCEST acquisition with strong MTC interference, the optimal saturation power and length are completely different from those on Cr solution alone. This observation could be explained well using R1ρ theory by incorporating the strong MTC pool. Finally, a high-resolution Cr map was obtained on mouse brain using the PLOF method with the NSS CEST acquisition and a cryogenic coil. The Cr map obtained by CEST showed homogenous intensity across the mouse brain except for regions with cerebrospinal fluid.

Fast bound pool fraction mapping via steady-state magnetization transfer saturation using single-shot EPI.

To enable clinical applications of quantitative magnetization transfer (qMT) imaging by developing a fast method to map one of its fundamental model parameters, the bound pool fraction (BPF), in the human brain. The theory of steady-state MT in the fast-exchange approximation is used to provide measurements of BPF, and bound pool transverse relaxation time ( ). A sequence that allows sampling of the signal during steady-state MT saturation is used to perform BPF mapping with a 10-min-long fully echo planar imaging-based MRI protocol, including inversion recovery T1 mapping and B1 error mapping. The approach is applied in 6 healthy subjects and 1 multiple sclerosis patient, and validated against a single-slice full qMT reference acquisition. BPF measurements are in agreement with literature values using off-resonance MT, with average BPF of 0.114(0.100-0.128) in white matter and 0.068(0.054-0.085) in gray matter. Median voxel-wise percentage error compared with standard single slice qMT is 4.6%. Slope and intercept of linear regression between new and reference BPF are 0.83(0.81-0.85) and 0.013(0.11-0.16). Bland-Altman plot mean bias is 0.005. In the multiple sclerosis case, the BPF is sensitive to pathological changes in lesions. The method developed provides accurate BPF estimates and enables shorter scan time compared with currently available approaches, demonstrating the potential of bringing myelin sensitive measurement closer to the clinic.

Dynamic measurements of drainage capillary pressure curves in carbonate rocks

The heterogeneity of rocks represents a challenge for interpreting and using outcomes from multiphase-flow experiments carried out on laboratory samples. While the capillary pressure–saturation function, pc(S), is known to vary spatially and cause local saturation development during immiscible displacements, its variation remains difficult to measure. This is particularly challenging for rocks with complex fabrics, such as carbonates. Here, we present a workflow for the dynamic measurement of core- and subcore-scale drainage pc(S) curves in heterogeneous porous media. Multi-rate, two-phase core-flooding tests are conducted on three carbonate rocks with direct observations of local saturation data. The interpretation of the experiments is done by fitting the parameters of the pc(S) curve, while describing both steady-state saturation and pressure profiles with a detailed one-dimensional model that accounts for the variation of subcore-scale properties in the direction of displacement. Workflow validation is achieved by means of synthetic data, thereby demonstrating the uniqueness of the solution of the resulting multi-objective optimisation problem. The model reproduces accurately experimental data on the three rocks and enables computing the effective core-scale pc(S) curve in the limit of zero velocity, as it would be expected during a porous-plate experiment. The output of the proposed technique is however much richer and includes the relativepc(S) curve that is universal and independent of the specific pattern of heterogeneity, in addition to a set of scaling factors. The latter describe the distribution of the pc(S) curves at the subcore-scale due to heterogeneity and form the statistical basis needed for upscaling studies.

Increasing the performance of gas diffusion layer by insertion of small hydrophilic layer in proton-exchange membrane fuel cells

The present study applied Lattice Boltzmann method (LBM) for examining the transport of liquid water in a GDL carbonic paper of polymer electrolyte membrane (PEM) fuel cells. The stochastic method is used for GDL carbonic paper reconstruction. In order to study the behavior of liquid water, different simulations are carried out on the reconstructed GDL. While removing from the GDL of a PEM fuel cell, the dynamics of liquid water is simulated by LBM in this study. The effects that the wettability of GDL imposes on the removal process and liquid water distribution are investigated. In addition, the dynamic behaviors and the saturation process of the liquid water in GDL in a steady state and a transient mode are also explored. The effects of surface wettability on the effective clusters in GDL, merging of different clusters and the loops developed by the fingers are investigated. Moreover, the effects of mixed wettability on the liquid water dynamic behavior and liquid water saturation within the GDL are studied in detail. The results show that the best location for insertion of the hydrophilic layer inside the GDL is near the GDL-GC interface. In this case, the time required for liquid water to reach the GDL/GC interface is reduced about 17% than purely hydrophobic GDL. A decrease of 18.7% in the steady-state saturation level is also observed by insertion of hydrophilic layer; therefore, use of hydrophilic layer near GDL-GC interface is more effective than increasing the contact angle of GDL-fibers. Different validation studies are also reported to show the accuracy of the model.

Effects of carrier concentrations on the charge transport properties in monolayer silicene

Using analytical band Monte Carlo approach, we have carried out a systematic study on the effects of carrier concentrations on the steady-state and transient electron transports that occur within a monolayer silicene. In particular, we have observed the following: First at steady-state, the electron mobility reduces with higher carrier concentrations. Secondly, in the transient regime we found that the drift velocity overshoot can be controlled by varying the carrier concentrations. We uncover that at carrier concentration of 1 × 1013 cm−2, the drift velocity overshoot can reach up to 3.8 × 107 cm s−1 which is close to the steady-state drift velocity saturation of graphene. Thirdly, the distance of the velocity over shoot can be further extended with higher carrier concentrations. Our findings could be useful and can be used as benchmark for future development of nanoscale silicene based devices.