Forced Flow Research Articles

Prediction of spirometry outcome in Croatian patients with chronic obstructive pulmonary disease

The current study offers an extensive examination of the influence of 29 diverse parameters on spirometry measurement variables in a cohort of 534 patients with chronic obstructive pulmonary disease (COPD) from five different centers in Croatia. The study elucidates both the magnitude and direction of the effect exerted by the 29 predictors on forced vital capacity (FVC), forced expiratory volume in one second (FEV1), the ratio FEV1/FVC, and predicted forced expiratory flow at 50% of FVC. Additionally, the development of prediction models for these parameters has been undertaken using several statistical methods. The study identifies fat-free mass index, 6-minute walk distance, predicted diffusing capacity of the lung for carbon monoxide, arterial partial pressure of oxygen, and both arterial and tissue hemoglobin oxygen saturation percentage as robust positive predictors for all four spirometry parameters. Body mass index is recognized as a weak positive predictor for FEV1 and FEV1/FVC, commonly observed in COPD patients. As expected, smoking years is identified as a strong negative predictor for all four spirometry parameters, while age and illness duration exhibit strong predictive negative associations. Furthermore, modified medical research council, arterial partial pressure carbon dioxide, St George's respiratory questionnaire, COPD assessment test, depression anxiety stress scales, and nutritional risk screening are identified as weak negative predictors. Charlson comorbidity index, phase angle, and number of comorbidities do not exhibit a significant impact on spirometry variables. Ultimately, the performed factorial analysis categorized the 29 parameters into five groups, which were identified as relating to lung function, health status, nutritional status, age, and smoking. Multiple regression analysis, including four newly derived parameters based on the results of factorial analysis, identified nutritional status as a positive predictor for spirometry readings, while smoking, poor health status, and age were identified as negative predictors in successive order.

Development and Validation of a Flow-Dependent Endothelialized 3D Model of Intracranial Atherosclerotic Disease.

Intracranial atherosclerotic disease (ICAD) is a major cause of stroke globally, with mechanisms presumed to be shared with atherosclerosis in other vascular regions. Due to the scarcity of relevant animal models, testing biological hypotheses specific to ICAD is challenging. We developed a workflow to create patient-specific models of the middle cerebral artery (MCA) from neuroimaging studies, such as CT angiography. These models, which can be endothelialized with human endothelial cells and subjected to flow forces, provide a reproducible ICAD model. Using imaging from the SAMMPRIS clinical trial, we validated this novel model. Computational fluid dynamics flow velocities correlated strongly with particle-derived flow, regardless of stenosis degree. Post-stenotic flow disruption varied with stenosis severity. Single-cell RNA-seq identified flow-dependent endothelial gene expression and specific endothelial subclusters in diseased MCA segments, including upregulated genes linked to atherosclerosis. Confocal microscopy revealed flow-dependent changes in endothelial cell proliferation and morphology in vessel segments related to stenosis. This platform, rooted in the specific anatomy of cerebral circulation, enables detailed modeling of ICAD lesions and pathways. Given the high stroke risk associated with ICAD and the lack of effective treatments, these experimental models are crucial for developing new ICAD-related stroke therapies.

Small but mighty: Platelets as multifunctional architects of tumor metastasis and immune regulation

AbstractPlatelets play an irreplaceable role in hemostasis and wound healing. However, beyond these classical roles, as the smallest anucleate cells in the blood stream, they are crucial for immune response which have inflammatory functions through specialized receptors and different signaling pathways, influencing both innate and adaptive immune response. Furthermore, many research have proved that platelets significantly contribute to tumor metastasis and are associated with poor prognoses in cancer patients through its coagulability and supporting an immunosuppressive tumor microenvironment. When tumor cells detach from the primary tumor mass and enter the bloodstream, they rapidly initiate the direct activation and adhesion of platelets, forming a protective microenvironment. This environment shields circulating tumor cells (CTCs) from the mechanical shear forces of blood flow and immune surveillance. Here we delve into the interaction between platelets and immunomodulation and explore the multifaceted roles and underlying mechanisms by which platelets influence tumor cell metastasis and tumor growth. Furthermore, we also discussed the diagnostic role of platelets in cancer occurrence and progression, as well as the feasibility and prospects of targeting platelets for antitumor immunotherapy. This review provides a multidimensional perspective and reference for platelet‐related cancer treatment strategies and diagnosis.

Abstract 4124084: Nitric Oxide Releasing Bionanomatrix Gel For Dialysis Arteriovenous Fistula Maturation

Introduction: About 600,000 patients in the US suffer from end-stage renal disease (ESRD); more than 75% of ESRD patients undergo dialysis. Vascular access dysfunction is a major cause of morbidity and hospitalization in dialysis patients. Arteriovenous fistulas (AVFs) are considered the gold standard of vascular access for dialysis. However, about 60% of AVFs fail to mature because of early venous neointimal development and poor vasodilation and vascular wall remodeling. Therefore, to promote AVF maturation, we propose the application of a nitric oxide (NO) releasing nanomatrix gel, or ‘NO gel’, on the created AVF. The NO gel is composed of peptide amphiphiles (PA), which contain a polylysine (KKKKK) group to form NO-donating residues. In this study, we test our hypothesis that the NO gel applied at AVF can promote AVF maturation by decreasing venous intimal hyperplasia, enhancing vasodilation and vascular outward remodeling in porcine model. Materials and Methods: PA containing with KKKKK was synthesized and charged with NO to produce NO gel. For in vivo studies, AVFs in porcine were created by connecting the jugular vein and carotid artery. The NO gel was applied perivascularly over the AVF anastomosis. And the pigs were sacrifice after 35 days. AVF hemodynamics were evaluated using MRI-based computed fluid dynamics analysis. Results: We found significant decrease in neointimal hyperplasia in porcine AVFs treated with NO gel compared to the control groups. Additionally, the percentage of open lumens was significantly higher in the NO gel-treated group. It is indicated that veins in NO treated group showed less fibrosis as an less type I collagen I produced in the NO treated group than control. Also, the NO gel significantly improved hemodynamics and vascular remodeling of porcine AVFs compared to the control. Conclusion: These results suggest that the NO gel plays a crucial role in AVF maturation by reducing intimal hyperplasia and stenosis following AVF creation in a pig model. When intimal hyperplasia is reduced and the vessel is dilated, less tensile force of blood flow is applied on the arterialized vein, directing the AVF to appropriate maturation.

Stacked hydrogel-based brain-on-chips utilizing capillary force flow pinning

Cellular processes in brain tissue such as migration, proliferation, morphology, and differentiation are influenced by mechanical cues, demonstrating the interplay between the structure and function. Given the complexity, it remains a substantial challenge to establish a reliable in vitro model mimicking structural properties as brain tissue. To address this challenge, we propose an innovative approach to create vertical hydrogel stacks based on microfluidic technology. 3D-printed microfluidic features in the sidewall profile of our chip designs allowed us to faithfully replicate these capillary force flow pinning structures in polydimethylsiloxane. After the successful application of hydrogel of a defined height, thanks to the pinning process and plating of stem-cell-derived neurons, the results demonstrated the potential of our BoC platform, providing a valuable tool for neuroscience research.

Submicrometre spatiotemporal characterization of the Toxoplasma adhesion strategy for gliding motility.

Toxoplasma gondii is a protozoan apicomplexan parasite that uses an adhesion-dependent mode of motility termed gliding to access host cells and disseminate into tissues. Previous studies on Apicomplexa motile morphotypes, including the T. gondii tachyzoite, have identified a cortical actin-myosin motor system that drives the rearward translocation of transmembrane adhesins, thus powering forward movement. However, this model is currently questioned. Here, combining micropatterning and tunable surface chemistry (to edit parasite surface ligands) with flow force and live or super-resolution imaging, we show that tachyzoites build only one apical anchoring contact with the substrate, over which it slides. Furthermore, we show that glycosaminoglycan-parasite interactions are sufficient to promote such force-productive contact and find that the apicobasal flow is set up independent of adhesin release and surface interactions. These findings should enable further characterization of the molecular functions at the T. gondii-substrate mechanosensitive interface and their comparison across apicomplexans.

Analysis of the influence of bottom flow holes in control rod guide tubes on flow field and control rod displacement

During the operation of pressurized water reactors, flow-induced vibration issues are commonly encountered, where control rod components vibrate due to the impact of coolant flow, leading to wear, thereby posing a threat to the safe operation of the reactor. This paper conducts a detailed numerical simulation of the flow field and force distribution inside a full-scale lower control rod guide tube based on the CFD method. The fluid–structure interaction analysis is performed to reveal the influence of cross-flow under various operating conditions on the vibration and displacement of control rods. The research subject consists of 24 control rods, one continuous guide section, and six control rod guide cards. The lower part of the guide tube has two flow holes on each surface, with one assumed to be a cross-flow inlet and the others as outlets. The results indicate that when considering the cross-flow effect at the flow holes, 90 % of the coolant flows out from other flow holes at the bottom of the guide tube, resulting in increased transverse velocity at the bottom and the presence of numerous vortices. The magnitude and location of the force exerted on the control rod by coolant impact are correlated. The control rod closest to the inlet of the flow hole experiences the greatest force, approximately 5.35 times the average at other positions. At a cross-flow velocity of 0.4 m/s and a low frequency of 10 Hz, the maximum displacement of the control rod is 0.3355 mm.

Measurement of intelligent computing via Levenberg Marquardt algorithm (LMA) for accurate prediction of fluid forces in a transient non-Newtonian thermal flow

Predicting precise results for the quantities of interest in time-dependent Computational Fluid Dynamics (CFD) simulations requires a significant investment of computational resources and time. To get around these issues, CFD simulations have been joined with Artificial Neural Networks (ANN). An optimally configured artificial neural network (ANN) is given the training and validation data sets produced by computational fluid dynamics (CFD). The flow around a cylinder, which is a well-known benchmark problem for incompressible flows, has been taken into consideration by the hybrid-CFD system. The mathematical model is based on the non-stationary Navier-Stokes and energy equations with viscosity. The basic architecture of the ANN model consists of 10 hidden layers, three output levels, and five input layers. Fast second-order LMA, a top-tier approach, was used to train the network. Both the Mean Square Error (MSE) and the coefficient of determination (R) provide statistical evidence that the ANN projected values for the drag and lift coefficients and average Nusselt number obtained from the finite element analysis are accurate. This analysis suggests that ANNs have the potential to significantly cut down on the amount of time and energy needed to run time-dependent simulations.

Investigation of aerodynamic characteristics of concept wing design inspired by the sooty shearwater

Biomimetics, the practice of drawing inspiration from nature to solve engineering challenges, has gained significant traction in aerospace design, particularly in the development of more efficient wing structures. This study investigated the aerodynamic potential of concept wing designs inspired by the Sooty Shearwater (Ardenna Grisea), a seabird renowned for its long-distance migratory capabilities and energy-efficient flight patterns. By leveraging the unique wing morphology of the Sooty Shearwater, three biomimetic wing models were developed using the Goettingen 173 airfoil. These designs were tested in a wind tunnel, where force measurements and flow visualization techniques were employed to evaluate their performance. Force measurement results show that a two-stage stall occurs for both models 1 and 2, with lift coefficient (CL) reaching an intermediate value when the first step occurs. Based on flow visualization results, model 1 demonstrates enhanced aerodynamic performance relative to the other models by dividing the laminar separation bubble into two sections in the spanwise direction as a result of the large stall cell formation. The findings reveal how specific aspects of the shearwater's wing structure can be translated into unmanned aerial vehicle designs, potentially enhancing aerodynamic efficiency in low-speed, low-Reynolds-number flight regimes.

Analysis of forces on nodules during Coandă-effect-based hydraulic collection

The nodule pickup device is a crucial component of a deep-sea mining system. It is widely perceived that leveraging water flow for the separation and retrieval of nodules is a promising approach. A series of experiments and numerical simulations were conducted to examine the impact of non-dimensional parameters on the force characteristics and flow field of the particle in Coandă-effect-based hydraulic collection. The results showed that the lift coefficient of the particle initially increased before subsequently diminishing from the jet nozzle to the rear. Notably, the lift coefficient α reached its maximum at the convex curved surface between x/d = −0.17 and 0.33. Furthermore, a distinct linear correlation was established between the maximum lift coefficient αmax and Froude number Fr across varying h/d, and an empirical formula for predicting the lift coefficient was developed through data fitting. Upon experimental validation, the prediction exhibited a maximum error of less than 20%. Additionally, numerical simulations revealed that the particle significantly influenced the flow dynamics within the collection area, and the flow field characteristics and the particle forces can be corroborated with each other. The findings not only provided a reliable quantitative tool for assessing the particle force but also facilitated precise predictions of collection performance, aiding in the selection of optimal operational parameters in deep-sea hydraulic collection.

Extending the horizon in cardiovascular risk prediction: A synergy of conventional predictors and spirometry data

Aim. To assess a correlation between conventional cardiovascular risk factors and unprovoked pulmonary volumes and flows.Material and methods. The subjects (n = 153, median age 43 [32; 51] years) were divided into two groups depending on age. Questionnaires, anthropometry, biochemical blood analysis, spirometry without bronchodilation test, calculation of the lower limit of normal (LLN – low limit of normal) were carried out. Using the Mann – Whitney U-test, the two groups were compared quantitatively. When analyzing four-field conjugacy tables, a comparison was performed using the Pearson criterion χ2. The direction and closeness of the correlation were estimated using Spearman’s rank correlation coefficient. A predictive model was developed using the linear regression method. The differences were considered statistically significant at p < 0.05.Results. In group I (median age 29 [26; 33] years), reliable connections were established between the volume of forced expiratory volume in one second and high-sensitivity C-reactive protein (hsCRP); modified Tiffno index (m-TI) and total cholesterol, lowdensity lipoproteins, glucose. When analyzing the LLN data, reliable associations between m-IT and glucose (p = 0.004), hsCRP (p = 0.011) were obtained. In persons over 40 years of age with a smoking index of more than 10 packs/year, a relationship was found between a decrease in LLN m-TI and LLN of forced expiratory flow between 25 and 75% of forced vital capacity and an increase in creatinine (p < 0.001) and lipoprotein (a) (p = 0.03), respectively. Conclusion. There are differences in the relationship between the function of external respiration and laboratory indicators of cardiovascular risk in people before and after 40 years of age, which makes it possible to individualize the prediction of chronic non-communicable diseases.

Stem cell seeding of decellularised porcine right ventricular outflow tracts to advance repair of congenital heart defects

Abstract Background Replacement of the right ventricular outflow tract (RVOT) is necessary in many critical congenital heart disease subtypes, often when the child is less than one year old. Poor availability of small-diameter cardiac homografts necessitates the use of xenografts in paediatric surgical reconstruction. Currently used xenografts are limited by immunoincompatibility and lack of growth, requiring repeat surgery to replace the defective graft. One approach to tackle acute immune rejection of animal tissue is aldehyde fixation of grafts prior to xenotransplantation. Though masking antigenicity, fixation is associated with multiple issues, including toxicity of fixative remnants and calcification. Decellularisation of biological grafts to remove foreign material is a promising alternative to reduce immunogenicity and dampen the risk of rejection. To combat lack of growth, in vitro cellularisation with stem cells is a promising solution. Purpose Current RVOT substitutes have not proven to be a lifelong solution for paediatric cardiac repair. This research has optimised a novel decellularisation technique for porcine RVOTs to produce a durable and cell-free scaffold with translational capability. Current work is looking to seed mesenchymal stem cells (MSCs) onto the acellular RVOT in vitro to enhance immune tolerance and endow the graft with growth capacity upon implant. Methods First, this decellularisation technique produces acellular RVOT scaffolds by simultaneously utilising three methods: enzymatic, chemical, and mechanical decellularisation. Novel to this method, the latter is realised using a 3D printed flow chamber to utilise the shear forces of continuous fluid flow for cell removal from the external and internal RVOTs structure. Coating the acellular graft with poly-lysine has then enabled recellularisation with MSCs isolated from the umbilical cord. Results Nuclei quantification demonstrates decellularisation of all structures of the RVOT, and elimination of residual nucleic acids is evidenced. Immunohistochemical analysis confirms the xenoantigen Galα1-3Galβ1-4GlcNAc-R is absent from the decellularised tissue. In parallel with removal of typical immunogens associated with the rejection response, the elastin and collagen fibres of the extracellular matrix are maintained, supported by histology and electron microscopy. Importantly, the tensile properties of the decellularised grafts are preserved. Finally, MSCs adhered onto the external pulmonary artery surface in vitro, achieving a uniform monolayer of cells. Conclusion RVOTs have been successfully decellularised and proven to possess seeding potential. Future work aims to characterise the seeded MSCs to assess parameters including proliferative capacity and expression of typical MSC markers. Overall, this work has the potential to produce a non-immunogenic graft possessing growth potential as a surgical alternative for paediatric RVOT replacement.

Non-invasive assessment of left ventricular hemodynamic forces in hypertrophic cardiomyopathy

Abstract Background Hemodynamic force (HDF) analysis allows non-invasive measurement of intraventricular pressure gradients, portraying cyclic spatial-temporal interaction between blood and tissues. Impaired HDFs have been implicated in early detecting of adverse cardiac remodelling and treatment response in various cardiovascular disorders, providing insights into cardiac physiology not offered by traditional cardiovascular imaging (1). Mainly explored in heart failure, HDF analysis has not been previously applied to hypertrophic cardiomyopathy (HCM). Purpose To investigate differences in systo-diastolic function in HCM patients compared to healthy controls using HDF analysis. Methods Forty patients with HCM diagnosis (20 obstructive and 20 non-obstructive) were retrospectively evaluated in comparison with 22 healthy controls. Left ventricular (LV) HDFs were derived from routine transthoracic apical 4-, 2- and 3-chamber views using a dedicated software. Apical-basal HDF curves were generated, where positive deflections represent forces directed from the LV apex to the base, whilst negative ones are directed toward the apex. Amplitude and timing parameters were derived, the latter indexed to total cardiac cycle duration. Results Table 1 shows the demographic, clinical and echocardiographic characteristics of HCM compared to controls. Patients with HCM were older, had a slower heart rate due to treatment with beta-blockers, and showed hypercontractility, as expressed by higher LV ejection fraction. Compared to controls, HCM patients showed reduced LV longitudinal force, i.e. the force during the whole cardiac cycle (4.17% [2.36-5.52] vs. 6.01% [4.73-7.78], p=0.002), shorter time interval to systolic peak (0.15 [0.12-0.16] vs. 0.19 [0.17-0.20], p <0.001), and shorter duration of LV impulse (0.29 [0.27-0.32] vs. 0.34 [0.32-0.37], p <0.001) (Figure 1). However, no differences in terms of systolic force peak (p=0.283) or LV impulse intensity (p=0.689) were detected. During the transition between systole and diastole, LV suction (i.e. the interval including late systolic deceleration and early diastolic suction) was significantly longer (0.26 [0.22-0.29] vs. 0.23 [0.21-0.25], p=0.023) but less pronounced (6.30% [4.56-8.44] vs. 8.72% [6.71-12.59], p=0.005), likely reflecting a relaxation impairment from the very beginning of diastole. Such impairment was maintained during early diastolic filling, where the amplitude of the positive deceleration flow force was severely reduced in HCM compared to controls (2.98% [1.98-4.58] vs. 7.11% [4.55-8.72], p <0.001). Conclusions HDF analysis in HCM patients revealed unique systolic and diastolic changes reflecting faster LV contraction during systole and slower and weaker LV forces during diastole. This analysis deepens our understanding of HCM mechanic abnormalities and may help assess response to innovative treatment options.

Fluid Force Reduction and Flow Structure at a Coastal Building with Different Outer Frame Openings Following Primary Defensive Alternatives: An Experiment-Based Review

A well-constructed tsunami evacuation facility can be crucial in a disaster. Understanding a tsunami’s force and the flow structure variation across various building configurations are essential to engineering designs. Hence, this study assessed the steady-state flow structure at building models (BM) incorporating outer frame openings, including piloti-type designs with a different width-to-spacing ratio of piloti-type columns following an embankment model (EM) with a vegetation model (VM). The experiments also demonstrated the outer frame opening percentage’s impact and orientation toward the overtopping tsunami flow at the BM. The results show that the arrangement of an opening on the outer frame and the piloti-type columns are critical in reducing the tsunami force concerning the experimental setup. Moreover, allowing a free surface flow beneath the BM implies that the correct piloti-pillar arrangement is crucial for resilient structure design. In addition, the three-dimensional numerical simulation was utilized to explain the turbulence intensity of the overtopping flow around the critical BM type. The derived resistance coefficient (CR) defined the drag and the hydrostatic characteristics at the BM due to the overtopping tsunami flow. Furthermore, for the impervious BM, the value CR was consistent with the previous studies, while the CR value for the BMs with an outer frame opening was directly coincident with the percentage of porosity.

Research on the distribution of debris flow impact on the upstream surface of the check dam

The impact force of debris flow is not only an important indicator of the risk assessment of debris flow and the strength impact resistance of buildings against debris flow, but also an important parameter in the design of various debris flow prevention projects (such as the check dam and the drainage channel, etc.). The pressure sensors are arranged at different positions (monitoring points) on the upstream face of the check dam. By changing the slope of the drainage channel, the bulk density of debris flow and the slope gradient of the upstream face of the check dam, the time history curves of the impact force at the monitoring points under different experiment conditions are obtained. The characteristic value of the impact force of debris flow acting on the surface of the sand retaining dam is analyzed, and the evolution law of mean value and maximum value of impact force of debris flow at the same detection location with the above conditions is obtained. The mean value and maximum value of debris flow impact force at different detection locations under the same working condition are analyzed to obtain the evolution law of debris flow impact force at different locations, and then the distribution trend of debris flow impact force on the upstream face of the check dam is obtained. The research results provide scientific and reasonable theoretical basis and technical support for the stability analysis of the check dam, so as to better serve the disaster prevention and reduction of debris flow, which will improve the technical level of the debris flow prevention project to a certain extent.

Exploring the correlation between body mass index and lung function test parameters: a cross-sectional analytical study

PurposeThe correlation between body weight and health is a significant public health concern. While the adverse effects of obesity on pulmonary function are well-known, the impact of being underweight remains debated due to limited research. This study aimed to investigate the correlation between Body Mass Index (BMI) categories and lung function parameters.ResultsA study of 3077 participants found significant differences in gender, age, height, and weight across various Body Mass Index (BMI) categories. The study found non-significant variations in forced expiratory flow (FVC) across BMI categories, with underweight individuals showing lower FVC compared to normal and overweight individuals. BMI significantly impacted mean forced expiratory flow during the middle half of FVC. A significant negative correlation was observed between age and FVC, FEV1, FEV1/FVC ratio, and FEF25-75. A significant positive correlation was observed between weight, height, and lung function parameters. Multiple regression analysis revealed a decrease in lung function with advancing age, while height showed significant positive associations. The study concluded that age, sex, smoking, height, and weight collectively explained 41.0% of the variance in FVC, FEV, and FEF25-75.

Transport behavior of Polymeric Methyl Methacrylate nanoplastics in saturated and unsaturated porous media: Combined influence of electrolyte and organic acids

The migration behavior of Polymeric Methyl Methacrylate (PMMA) nanoplastics in saturated porous media and unsaturated porous media is investigated under conditions of electrolytes in combination with organic acids. In the saturated porous media, the mass recovery rate of PMMA decreases with ionic strength. The inhibition effect of Ca2+ on PMMA transport is stronger than that of Na+. Under the conditions of the coexistence of electrolytes with humic acid (HA), increasing the concentration of HA does not consistently enhance PMMA migration in porous media. However, citric acid (CA) exerts solely an inhibitory effect on PMMA transport. The orthogonal analysis suggests that Ca2+ concentration is the major factor affecting PMMA transport. Extended Darjaguin-Landau-Verwe-Overbeek (XDLVO) interaction energy considering the heterogeneity of HA adsorption on PMMA is calculated to quantify the interactions of PMMA-PMMA and PMMA-quartz sand under different physiochemical conditions. In unsaturated porous media, gravity leads to the creation of dominant channels, and the shear force of water flow in porous media leads to the rapid passage of PMMA through the dominant channels. However, as the water content decreases, the recovery rate of PMMA decreases from 0.99 to 0.71. Significantly, the capillary energy of a colloid retained in a thin film or at the air-water-solid (AWS) interface is several orders of magnitude larger than the XDLVO interaction energy. Findings obtained by this study may improve the current understanding of the environmental fate of nanoplastics in subsurface environments and can provide scientific methods to assess the associated risk of nanoplastics.

Numerical Simulation of the Diffusion of Electroactive Molecule in Biosimilar Hydrogel Media

Based on experimental data of cyclic voltammetry, the values of the diffusion coefficients for toluidine blue in alginate hydrogel, gelatine hydrogel and alginate-gelatine hydrogels were obtained. Using the experimental values of the coefficients in a numerical model, the values of the recovery of flows have been calculated showing them consistent with what was the experimental. It is proposed to use the period in time during which the value of the flow force reaches the value of steady state flow force as an indicator of the diffusion properties of the hydrogel medium. The findings of this study can be used for the development of methods for the evaluation of the diffusion properties of hydrogel media: bioinks and tissue-engineered structures.

Turbulent flow and wall forces in staggered square cylinder porous media: An LES Analysis

Abstract The Wall-Modeled-Large Eddy Simulation (WMLES) technique was used to analyze turbulent flow in a porous medium composed of a staggered arrangement of square cylinders. The study focused on a porosity range of 0.3 to 0.8 at a pore Reynolds number of 10×103. The research provides novel information on pressure and shear force distributions around the cylinders and time-averaged values of particle drag and fluctuating lift coefficients. Results indicate that the flow physics are mainly driven by an expansion region in front of the central particle and another in the rear, where the flow is contracted and strongly accelerated. In the first region, velocities, turbulence kinetic energy (k), and its dissipation rate (e) are attenuated by a sudden pressure increase, while in the contraction region, the effect is the opposite. As porosity decreases, flow gradients and the overall levels of k, e, and Reynolds stresses become more significant. Turbulent anisotropy increases as porosity decreases below 0.6. Hydrodynamic stresses in the last interval present relatively uniform levels, which is a unique feature that may be considered in designing dedicated engineering devices with controlled stresses.

Shear-driven magnetic buoyancy in the solar tachocline: Dependence of the mean electromotive force on diffusivity and latitude

Abstract The details of the dynamo process that is responsible for driving the solar magnetic activity cycle are still not fully understood. In particular, whilst differential rotation provides a plausible mechanism for the regeneration of the toroidal (azimuthal) component of the large-scale magnetic field, there is ongoing debate regarding the process that is responsible for regenerating the Sun’s large-scale poloidal field. Our aim is to demonstrate that magnetic buoyancy, in the presence of rotation, is capable of producing the necessary regenerative effect. Building upon our previous work, we carry out numerical simulations of a local Cartesian model of the tachocline, consisting of a rotating, fully compressible, electrically conducting fluid with a forced shear flow. An initially weak, vertical magnetic field is sheared into a strong, horizontal magnetic layer that becomes subject to magnetic buoyancy instability. By increasing the Prandtl number we lessen the back reaction of the Lorentz force onto the shear flow, maintaining stronger shear and a more intense magnetic layer. This in turn leads to a more vigorous instability and a much stronger mean electromotive force, which has the potential to significantly influence the evolution of the mean magnetic field. These results are only weakly dependent upon the inclination of the rotation vector, i.e. the latitude of the local Cartesian model. Although further work is needed to confirm this, these results suggest that magnetic buoyancy in the tachocline is a viable poloidal field regeneration mechanism for the solar dynamo.