Pressure Difference Research Articles

Enhanced Speed Control of Pipeline Pigs with Adjustable Bypass Using Quantitative Feedback Theory and Cascade PID Algorithm

During pipeline pigging operations, precise control of the pig's running speed is crucial. However, external speed disturbances often occur during these operations. In response to this challenge, adjustments are made to the flow rate through the pig body, thereby modifying the pressure difference and achieving a targeted speed range of 1 m/s to 3 m/s. Since a pig with an adjustable bypass port operates in a dynamically changing state, conventional control algorithms face difficulties in providing effective control. Moreover, there is limited research on speed control algorithms for pigs with adjustable bypass ports. To address these challenges, this paper introduces a control system based on Quantitative Feedback Theory (QFT), coupled with cascaded Proportional-Integral-Derivative (PID) tuning, for the precise speed control of a bypass pig. The state equation is derived from the pig's operational state, and the QFT Toolbox is employed to design a pre-filter and controller. This integration of QFT with cascaded PID not only facilitates both speed control and disturbance rejection but also demonstrates significantly improved control stability under variable operational conditions. The model, implemented using the Simulink Toolbox, shows that this approach can quickly stabilize the pig's speed, effectively managing continuous variations and enhancing the efficiency and safety of pipeline pigging.

Characteristics of altered biventricular hemodynamics after arterial switch operation for patients with d-transposition of the great arteries with preserved ejection fraction: a four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) study.

The long-term monitoring of biventricular function is essential to identify potential functional decline in patients following the arterial switch operation (ASO). The underlying pathophysiological mechanisms responsible for altered biventricular hemodynamics in ASO patients are not yet well understood. This study sought to: (I) compare the biventricular kinetic energy (KE) and vorticity of ASO patients and age- and sex-matched controls; (II) investigate the associations of four-dimensional (4D) flow biventricular hemodynamics parameters and neo-aortic root dilation, supravalvular pulmonary stenosis, and pulmonary artery transvalvular pressure difference. A total of 34 patients with dextro-transposition of the great arteries (D-TGA) who underwent ASO, and 17 age- and gender-matched healthy controls were prospectively recruited for this study. All the subjects underwent cine and 4D flow and late gadolinium enhancement scans, and all the patients underwent echocardiography within two weeks of cardiovascular magnetic resonance (CMR) imaging. The following four flow components were analyzed: direct flow, retained inflow, delayed ejection flow, and residual volume. In addition, the following six phasic blood flow KE parameters, normalized to the end-diastolic volume (EDV) and vorticity, were analyzed for both the left ventricle (LV) and right ventricle (RV): peak systolic phase, average systolic phase, peak diastolic phase, average diastolic phase, peak E-wave phase, and peak A-wave phase. The independent sample Student's t-test, Mann-Whitney U-test, univariable and multivariable stepwise regression analyses, intra and inter-observer variability analyses were used to compare patients and controls. In relation to the LV, the D-TGA patients had significantly decreased average vorticity, peak systolic vorticity, systolic vorticity, diastolic vorticity, and peak A-wave vorticity compared to the controls (all P<0.01). In relation to the RV, the pulmonary stenosis group had significantly increased peak E- and A-wave kinetic energy normalized to the end-diastolic volume (KEiEDV), and peak and average vorticity compared to the non-pulmonary stenosis group (all P<0.05). in the multivariable logistic regression model analysis, diastolic KEiEDV, peak E-wave KEiEDV peak A-wave KEiEDV, and average vorticity were associated a with transvalvular pressure difference (β=13.54, P<0.001 for diastolic KEiEDV; β=105.26, P<0.001 for peak E-wave KEiEDV; β=-49.36, P=0.027 for peak A-wave KEiEDV; and β=-56.37, P<0.001 for average vorticity). We found that 4D flow biventricular hemodynamics were more sensitive markers than the ejection fraction in the postoperative D-TGA patients. The RV diastolic KEiEDV parameters and average vorticity were risk factors for pulmonary artery obstruction in the multivariable model.

Warming triggers stomatal opening by enhancement ofphotosynthesis and ensuing guard cell CO2 sensing,whereashigher temperatures induce a photosynthesis-uncoupled response.

Plants integrate environmental stimuli to optimize photosynthesis vs water loss by controlling stomatal apertures. However, stomatal responses to temperature elevation and the underlying molecular genetic mechanisms remain less studied. We developed an approach for clamping leaf-to-air vapor pressure difference (VPDleaf) to fixed values, and recorded robust reversible warming-induced stomatal opening in intact plants. We analyzed stomatal temperature responses of mutants impaired in guard cell signaling pathways for blue light, abscisic acid (ABA), CO2, and the temperature-sensitive proteins, Phytochrome B (phyB) and EARLY-FLOWERING-3 (ELF3). We confirmed that phot1-5/phot2-1 leaves lacking blue-light photoreceptors showed partially reduced warming-induced stomatal opening. Furthermore, ABA-biosynthesis, phyB, and ELF3 were not essential for the stomatal warming response. Strikingly, Arabidopsis (dicot) and Brachypodium distachyon (monocot) mutants lacking guard cell CO2 sensors and signaling mechanisms, including ht1, mpk12/mpk4-gc, and cbc1/cbc2 abolished the stomatal warming response, suggesting a conserved mechanism across diverse plant lineages. Moreover, warming rapidly stimulated photosynthesis, resulting in a reduction in intercellular (CO2). Interestingly, further enhancing heat stress caused stomatal opening uncoupled from photosynthesis. We provide genetic and physiological evidence that the stomatal warming response is triggered by increased CO2 assimilation and stomatal CO2 sensing. Additionally, increasing heat stress functions via a distinct photosynthesis-uncoupled stomatal openingpathway.

Aeolian dust dynamics in southern Central Asia revealed by the multi-timescale loess records in southern Tajikistan

Dust activities in Central Asia (CA) hold significant scientific interest due to their broad social and environmental impacts. Loess deposits in CA serve as crucial natural archives, recording regional atmospheric characteristics and dust dynamics. The oldest loess in CA has been discovered in southern Tajikistan. However, debates persist regarding the wind dynamics of the Tajikistan loess deposition, which motivates our current study. By analyzing grain sizes of the last glacial loess and previous loess records since 800 ka, we determined that the Tajikistan loess consisted of post-storm floating dust and fine-grained dust transported by the westerlies. The reduced grain sizes may indicate less frequent dust storms. Our results provided evidence for the influence of global ice volume changes on the dust dynamics in southern Tajikistan, primarily by modulating sea-level pressure differences between the Caspian Sea and Hindu Kush/Pamirs. These ice volume changes also intensified rapid atmospheric fluctuations in CA, suggesting a sensitive response of the latter to glacial boundary conditions. Moreover, although precipitation variations may influence dust activities, their impact appears to be minimal. Collectively, our findings offer vital insights into the formation of loess strata and the development of extensive modern loess landforms in southern CA.

Interarm systolic blood pressure difference is associated with left ventricular concentricity and concentric remodeling.

Interarm systolic blood pressure difference (IASD) values >15 mmHg (IASD > 15) are associated with increased cardiovascular risk, yet the underlying mechanisms remain unclear. This report evaluated whether IASD >15, assessed by different protocols [sequential or simultaneous; based on one or several blood pressure (BP) readings], was associated with adverse left ventricular (LV) remodeling. This cross-sectional study evaluated 605 individuals who underwent clinical and echocardiography evaluation and three pairs of simultaneous arm BP readings. IASD was estimated by seven distinct protocols (three simultaneous and four sequential BP measurements criteria). The cohort had a mean age of 53.5 ± 15.4 years, with 51% being women, 23% with LV hypertrophy, 14% with LV concentricity, 69% with normal geometry, 8% with concentric remodeling, 17% with eccentric hypertrophy and 6% with concentric hypertrophy. Multivariable logistic regression revealed that IASD >15 defined by simultaneous measures of the last two pairs of BP readings (IASDsim2) and sequential arm BP readings (right-left-right arm sequence; IASDseq3) were related to LV concentricity (odds ratio [95% CI] = 3.24 [1.02-10.28], P = 0.046 and 2.56 [1.09-6.00], P = 0.030, respectively) and LV concentric remodeling (odds ratio [95% CI] = 4.12 [1.08-15.78], P = 0.039 and 4.16 [1.61-10.76], P = 0.003, respectively). Conversely, IASD >15 defined by any criteria showed no association with LV hypertrophy. Individuals with IASD >15 defined by IASDsim2 and IASDseq3 are associated with adverse LV remodeling, namely LV concentricity and LV concentric remodeling. These findings suggest that both criteria might be potentially used to preferentially assess abnormal IASD in the setting of clinical practice.

Experimental study on current density distribution characteristics in a novel oxygen recirculation system of dead-ended proton exchange membrane fuel cell

ABSTRACT Dead-ended proton exchange membrane fuel cells (PEMFCs) using pure hydrogen and oxygen can improve fuel efficiency and cell performance, making them widely applicable in enclosed spaces. However, dead-ended PEMFCs are prone to flooding, which reduces cell performance and service life. To address this issue, an oxygen recirculation system utilizing oscillating flow generated by pressure differences is designed in this study. This system not only achieves close to 100% fuel utilization but also optimizes water management and enhances current density uniformity. The optimal oxygen cycling conditions were selected based on current density uniformity and cell performance enhancement. The results show that a larger pressure difference amplitude improves water removal from the cell; however, excessively large pressure differences can lead to unstable cell operation. The oscillating flow generated by pressure differences significantly improved current density uniformity, particularly at higher output load currents. Current density uniformity improved by 16.29% at a current of 75 A. The experiment demonstrates that the best current density uniformity is achieved when managing water using a pressure difference at 4-minute intervals, as longer or shorter oscillation intervals are unsuitable for dead-ended performance.

Myogenic response of the cerebral vessel: a mathematical model

The myogenic response is most typical for small arterial vessels and consists in constriction of the vessel with an increase in transmural pressure, the pressure difference between the inner and outer surfaces of the vascular wall. There are many models describing this response. In models of last decades, in addition to macrostretchings and macrostrains, their microanalogues are introduced into consideration, that significantly complicates the description. In the presented work a simple model of the wall of the small cerebral artery is described, which includes the main parameters that control the myogenic response and corresponds to physiological processes underlining this response. It is believed that active stresses depend on stretching and the concentration of free calcium ions in the cytoplasm of the smooth muscle cell. In turn, the calcium content depends on the membrane potential, determined by the pressure. An axisymmetric stationary problem is considered; the wall material in the non-activated state is assumed to be pseudoelastic. Calculations showed a qualitative difference in the dependence of active stress on stretching and its distribution in the radial direction before and after the development of the vascular response. The calculated diameter values before and after exposure to substances affecting the polarization of the smooth muscle cell membrane are within the range of experimental values. These results indicate that the introduction of the dependence of calcium concentration on membrane potential expands the area of applicability of simple models of this kind for evaluating the value of vascular diameter.

Experimental comparison of the effects of the two designed probes for exfoliation of graphene by sonication.

In the present research, comparative simulation and experimental investigation were carried out for two different probes to improve the efficiency and quality of few-layer graphene utilizing liquid-phase exfoliation. Two differently designed shaped probes are fabricated for this study, i.e., a simple probe and a stepped probe. The acoustic pressure distribution in the vessel is simulated for both probes at different output powers. In the experiment, both probes exfoliate graphite powder in a mixture of deionized water and ethanol. Different sonication times and output power were studied for different pulse modes. The graphene layers were characterized using Ultraviolet-visible spectroscopy (UV‒Vis), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Raman Microscope. The simulation shows that the total displacement on the tip of the stepped probe is 5.7% greater than that of the simple probe. Also, the pressure difference produced by the stepped probe is 9.15 × 106 pa compared to the pressure difference of the simple probe which is 8.23 × 106 pa. Consequently, the stepped probe was more effective in exfoliating graphene. The experimental results show that the absorbance peak in the stepped probe is approximately 32% greater than the absorbance peak in the simple probe with the same output power. Also, the graphene with better quality is produced with the stepped probe compared to the simple probe, which verifies the simulation findings. Additionally, the optimum output power, pulse duration, and sonication time to produce graphene with less time and energy consumption are obtained. The best graphene flakes were obtained via sonication with a pulse duration of 0.7 s, an output power of 282 W, and a sonication time of 45 min using a stepped probe. UV-Vis., SEM and TEM analysis show increases in quantity and quality of the exfoliated flakes. These results are approved by the peak ratio of I2D/IG around 1 in Raman spectra revealed the production of the few-layer graphene by the simple probe and the bilayer graphene by the stepped probe. So, this method is suitable for the production of graphene flakes from graphite in suitable quantity and quality.

Modeling Arterial Blood Flow under Stenosis: A Comparative Study of Newtonian and Carreau-Yasuda Non-Newtonian Approaches

This study investigates the simulation of blood flow within arteries experiencing stenosis using both Newtonian and non-Newtonian models. The Newtonian model employs standard fluid dynamics assumptions, while the non-Newtonian Carreau-Yasuda model accounts for the unique viscoelastic properties of blood, providing a more accurate representation of its flow behavior under various shear rates. By utilizing COMSOL Multiphysics, the simulations are conducted with parameters including blood velocity, viscosity, and pressure in normal and narrowed artery conditions. Results reveal that while the Newtonian model predicts general flow patterns, it lacks the precision needed to reflect the complexities of blood behavior in stenosed regions. Conversely, the Carreau-Yasuda model demonstrates enhanced accuracy by capturing viscosity variations and pressure differentials, particularly in the narrowed artery sections, showing the significance of non-Newtonian characteristics in modeling blood flow. These findings underscore the potential of non-Newtonian models in improving diagnostic and therapeutic approaches for vascular conditions.

Structural simulation and performance evaluation of self-priming electrostatic diesel vehicle emission particle sensor

Here is reported a self-priming electrostatic particulate matter (PM) sensor for real-time monitoring of diesel exhaust under different operating conditions. Initially, a multi-physics coupling model for the sensor was established. By varying the exhaust flow and temperature, the emissions of diesel vehicles were simulated to evaluate the sensor. The results showed that within the typical velocities (5 to 60 m/s) and temperature ranges (100 to 500 °C) of diesel exhaust, the sensor outlet pressure was consistently below the inlet pressure, with a maximum differential pressure of 259 Pa, indicating the capability for self-priming sampling of exhaust under different operating conditions. Additionally, the calibration platform was constructed using a miniature inverted soot generator which produced a series of samples to calibrate the relationship between current and mass concentration with a correlation coefficient of 0.99. From 0 to 100 mg/m3, the PM sensor exhibited a relative error between −6.00% and 6.00% with good stability and consistency for samples of different sizes and concentrations, with correlation coefficients exceeding 0.98. The results between the self-developed sensor and a commercial instrument revealed that the former provided high-precision real-time measurement of diesel exhaust.

Development of operable modular louvers Sited in a single-sided ventilated room through 3D parametric optimization

The current design practices of buildings to respond to environmental inputs have led to operable envelopes with external louver blinds systems. The key aspect of any openable louver flap design is to optimize inlets that might induce ventilation for occupants with low indoor airflow. Computational Fluid Dynamics (CFD) in 3D parametric modeling investigated the influence of openable louver inlet geometries (right trapezoid) and positions in a ventilated room. A single-sided ventilated room designed with two mirrored split blocks of inlets attached to that wall perpendicular to the wind was employed for this study. Twenty-eight different inlet shape geometries with their cross-sectional changes were investigated. In addition, the inlets' rotation, orientation, and elevation differences were also studied. Wind tunnel experiments were conducted to measure airflows inside the model room to validate the CFD simulations. A discernible impact was observed when the inclined side of the right trapezoid was oriented upward or downward, where inlet flaps open to the sides of the window. The mean air velocity in the ventilated room becomes more than double when inlet flaps open to the sides of the window, where the elevation difference in the inlet blocks introduces the pressure difference compared to no elevation difference in inlets. This study guides into refining an operable modular louver design to enhance air circulation and natural ventilation in dwelling spaces.

Maximal heat transfer density from cross‐flow heat exchanger with tapered fins using constructal design method

AbstractTapered fins are widely used in heat sinks cooled by forced convection. In this study, maximal forced convective heat transfer from a set of tapered fins in cross‐flow is investigated based on the constructal design method. The tapering of the fins is done for a three‐fin base‐to‐tip ratio (taper ratio). The first taper ratio is TR = 0.5 (fin base &lt; fin tip), the second taper ratio is TR = 1 (fin base = fin tip, straight fin), and the third taper ratio is TR = 2 (fin base &gt; fin tip). In all these cases, the fin length is constant. The fins are heated at constant surface temperature and they are cooled by cross‐flow. A constant pressure difference pushes the cross‐flow toward the fins. The Bejan number ranges from 105 to 107. The forced convective heat transfer density is maximized from the fins for the three taper ratios, and a comparison between them is carried out. The maximization is conducted by numerical and scale analysis. In the numerical analysis, the pressure‐driven flow equations (continuity, momentum, and energy) are solved by means of the finite volume method. In the scale analysis, two extremes are considered. The first extreme is for TR &lt; 1, and the second extreme is for TR &gt; 1. These two extremes are intersected to find the maximal forced convective heat transfer density. The results obtained from numerical and scale analysis confirmed that the maximal forced convective heat transfer density occurs for straight fins (TR = 1) in the whole range of the Bejan number. The heat transfer density from straight fins (TR = 1) is higher than that of tapered fins (TR = 2) by 45.2%, and it is higher than that of tapered fins (TR = 0.5) by 52.7% at Be = 107.

Mathematical modelling and performance analysis of an AEM electrolyzer

In this study, an analytical model including electrochemical reactions and mass transfer in an anion-exchange membrane electrolyzer (AEMEL) has been developed by considering water sorption/desorption in electrodes. The model developed was used to investigate the performance of the AEMEL in terms of efficiency, transport phenomena and operating parameters. The numerical results revealed that the voltage losses in the AEMEL are mainly due to activation losses. The effects of important parameters such as membrane thickness, operating pressure on cell performance, and species transport were also investigated. The results also revealed that the AEMEL performance improves with decreasing membrane thickness, but the membrane thickness should be considered together with hydrogen permeability and differential operating pressure to operate the electrolyzer safely.

Modeling The Hydrogen Crossover Through Membrane With And Without Catalyst Layers

The hydrogen crossover flux is expressed as a function of the difference in the partial pressure of hydrogen and total pressure difference between the supply and permeate sides of a membrane. The hydrogen crossover rate was measured under several operating conditions by micro gas chromatography. The permeation flux was not influenced by the total pressure difference up to 50 kPa. A bare Nafion membrane and the membrane with catalyst layers were modeled as a stack of bulk and skin layers. Hydrogen permeability of both samples showed identical bulk layer expressed by a power-law equation of the moisture content and an Arrhenius equation of temperature with an activation energy of 22.8 kJ mol–1. The measurement of skin layer resistance wasn’t successful since the skin layer resistance was too low to be measured. A skin layer of Nafion with a catalyst layer wasn’t observed due to formation of fused layer.

Microtopography and vegetation generate uneven predation pressure on forest insects

Predation plays an important role in the coexistence of multiple species within forest ecosystems. It is spatially heterogeneous and influenced by the surrounding environment at different spatial scales. Studies focusing on multiple environmental factors in systems with high spatial complexity are lacking, but elucidating the effects of local environmental factors within a forest could assist in understanding the effects of local differences in predation pressures on multispecies coexistence. Here, we examined the effects of microtopography and vegetation on predation pressure using the model caterpillar method. We hypothesized that differences in microtopography and vegetation types would result in different predation pressures on invertebrates within a forest. Insect attacks were dominant throughout the study period. The attack rates on the model caterpillars were also lower on hill tops and evergreen deciduous trees. Predation pressure within the forest was heterogeneous and independently influenced by topography and vegetation type. Our results suggest that environmental heterogeneity within forests may lead to highly variable predation pressures and affect multispecies coexistence. This study suggests that microtopography and vegetation types within forests should be considered for biological control.

Qualitative somatosensory evaluation of recipient and donor sites of subepithelial connective tissue grafts: a preliminary study.

The subepithelial connective tissue graft (SCTG) plus coronal advanced flap is commonly evaluated by clinical parameters, but potential sensory changes (patients' perception of painful or painless sensations) need to be further explored. This preliminary study aimed to qualitatively evaluate the somatosensory profile of recipient and palatal donor sites of SCTG. Sensory tests were applied at SCTG recipient and donor sites at baseline, after 3 and 6 months. A single calibrated examiner applied Douleur Neuropathique 4 questionnaire (DN4), qualitative sensory test (QualST), discriminating the areas as hypersensitive, hyposensitive or normosensitive, and two-point acuity test. Descriptive statistics, non-parametric Kruskal Wallis test for QualST evaluation and ANOVA for Two-point test (p < 0.05) were used. QualST revealed that recipient areas presented no significant differences in tactile, pressure and thermal tests. Brush test revealed hyposensitivity after 3 months (p = 0.03). In donor areas, only thermal evaluation showed a significant difference (p = 0.01), being hypersensitive after 3 months and hyposensitive after 6 months. At baseline, all evaluations in recipient and donor areas were normosensitive. According to DN4, no patient reported pain in recipient and donor sites. Non-painful sensory perception was reported as numbness in recipient (3.14% of patients) and donor (18.4%) areas. No significant differences were found for two-point acuity test values. Somatosensory variations were observed in donor and recipient areas using qualitative tests, with no detection of painful sensations, only non-painful sensations of numbness and electric shock. This preliminary study demonstrated that alterations of hypo- and hypersensitivity may occur in donor and recipient areas of gingival grafts. However, when present, these alterations were non-painful and did not impact oral functions. ReBEC #RBR-7zz3b6p.

Modeling The Hydrogen Crossover Through Membrane With And Without Catalyst Layers

The hydrogen crossover flux is expressed as a function of the difference in the partial pressure of hydrogen and total pressure difference between the supply and permeate sides of a membrane. The hydrogen crossover rate was measured under several operating conditions by micro gas chromatography. The permeation flux was not influenced by the total pressure difference up to 50 kPa. A bare Nafion membrane and the membrane with catalyst layers were modeled as a stack of bulk and skin layers. Hydrogen permeability of both samples showed identical bulk layer expressed by a power-law equation of the moisture content and an Arrhenius equation of temperature with an activation energy of 22.8 kJ mol–1. The measurement of skin layer resistance wasn’t successful since the skin layer resistance was too low to be measured. A skin layer of Nafion with a catalyst layer wasn’t observed due to formation of fused layer.

Effect of wearing N95 masks for 10 hours on ambulatory blood pressure in healthy adults.

The impact of wearing a face mask for an extended duration is unknown. This study aimed to determine if wearing a face mask for 10 h impacts blood pressure (BP) and arterial stiffness. Subjects received an ambulatory blood pressure cuff and were asked to wear it for 10 h while readings were taken every 15 min. During the face mask trial, subjects wore an N95 mask for 10 h. During the control, subjects did not wear a mask. Subjects were randomized to start their trial. An accelerometer was given to ensure no physical activity differences. Linear mixed models were used to determine group differences, and McNemar test was used to assess frequency differences when determining BP load. Twelve college-aged (20.5 ± 1.5 years) male (n = 5) and female (n = 7) individuals with normal BP participated in this study. There were no differences in time spent in any physical activity domain (all P > 0.05). There was no difference in brachial SBP (P = 0.688), brachial DBP (P = 0.063), central SBP (P = 0.875), central DBP (P = 0.246), heart rate (P = 0.125), and augmentation pressure (P = 0.158) between conditions. During mask condition, augmentation pressure was reduced by 5.2 ± 3.1% compared to control (P < 0.001). There were no frequency differences in the number of BP readings above 140 mmHg for SBP (P = 0.479) and >90 mmHg for DBP (P = 0.212). The current study found that wearing an N95 mask for 10 h did not affect brachial or central BP but significantly decreased augmentation pressure.

Concentric circular flow field to improve mass transport in large-scale proton exchange membrane water electrolysis cells

Uniform reactant supply is challenging for high-performance proton exchange membrane water electrolysis (PEMWE) in renewable energy storage. The anode flow-field pattern, anode flow-field orientation, and stoichiometric ratio influence mass transport. In this study, the performances of two flow-field patterns were compared for a single PEMWE cell with an active area of 100 cm2. Straight serpentine was used as the reference model and a concentric circle with an arc shape was designed. In addition, the optimal anode flow field orientation and stoichiometric ratio were determined. The results indicate that the optimal anode flow-field pattern differs depending on the stoichiometric ratio. At low flow rates, mass transfer via diffusion was dominant; therefore, a straight serpentine flow was preferred. In contrast, a concentric circle, which induces a significant differential pressure between adjacent channels, is preferable at a high flow rate. This is because convection is dominant in mass transfer. Maintaining a stoichiometric ratio of 10 or more is recommended during the operation. At a ratio of less than 10, the reactant was depleted at a high current density, and the mass transfer resistance increased. In addition, water is better distributed by gravity and buoyancy when the electrolyte membrane is parallel to the ground, and the anode flow path is above the porous medium. This leads to high PEMWE cell performance.

Red blood cell passage through deformable interendothelial slits in the spleen: Insights into splenic filtration and hemodynamics

The spleen constantly clears altered red blood cells (RBCs) from the circulation, tuning the balance between RBC formation (erythropoiesis) and removal. The retention and elimination of RBCs occur predominantly in the open circulation of the spleen, where RBCs must cross submicron-wide inter-endothelial slits (IES). Several experimental and computational studies have illustrated the role of IES in filtrating the biomechanically and morphologically altered RBCs based on a rigid wall assumption. However, these studies also reported that when the size of IES is close to the lower end of clinically observed sizes (less than 0.5 μm), an unphysiologically large pressure difference across the IES is required to drive the passage of normal RBCs, sparking debates on the feasibility of the rigid wall assumption. In this work, We propose two deformable IES models, namely the passive model and the active model, aiming to explore the impact of the deformability of IES on the filtration function of the spleen. In the passive model, we implement the worm-like string model to depict the IES’s deformation as it interacts with blood plasma and allows RBC to traverse. In contrast, the active model involved regulating the IES deformation based on the local pressure surrounding the slit. To demonstrate the validity of the deformable model, we simulate the filtration of RBCs with varied size and stiffness by IES under three scenarios: (1) a single RBC traversing a single slit; (2) a suspension of RBCs traversing an array of slits, mimicking in vitro spleen-on-a-chip experiments; (3) RBC suspension passing through the 3D spleen filtration unit known as’the splenon’. Our simulation results of RBC passing through a single slit show that the deformable IES model offers more accurate predictions of the critical cell surface area to volume ratio that dictate the removal of aged RBCs from circulation compared to prior rigid-wall models. Our biophysical models of the spleen-on-a-chip indicate a hierarchy of filtration function stringency: rigid model > passive model > active model, providing a possible explanation of the filtration function of IES. We also illustrate that the biophysical model of ‘the splenon’ enables us to replicate the ex vivo experiments involving spleen filtration of malaria-infected RBCs. Taken together, our simulation findings indicate that the deformable IES model could serve as a mesoscopic representation of spleen filtration function closer to physiological reality, addressing questions beyond the scope of current experimental and computational models and enhancing our understanding of the fundamental flow dynamics and mechanical clearance processes within in the human spleen.