Pressure Gradient Ratio Research Articles

Reduced-Order Modeling of Steady and Unsteady Flows with Deep Neural Networks

Large-eddy and direct numerical simulations generate vast data sets that are challenging to interpret, even for simple geometries at low Reynolds numbers. This has increased the importance of automatic methods for extracting significant features to understand physical phenomena. Traditional techniques like the proper orthogonal decomposition (POD) have been widely used for this purpose. However, recent advancements in computational power have allowed for the development of data-driven modal reduction approaches. This paper discusses four applications of deep neural networks for aerodynamic applications, including a convolutional neural network autoencoder, to analyze unsteady flow fields around a circular cylinder at Re = 100 and a supersonic boundary layer with Tollmien–Schlichting waves. The autoencoder results are comparable to those obtained with POD and spectral POD. Additionally, it is demonstrated that the autoencoder can compress steady hypersonic boundary-layer profiles into a low-dimensional vector space that is spanned by the pressure gradient and wall-temperature ratio. This paper also proposes a convolutional neural network model to estimate velocity and temperature profiles across different hypersonic flow conditions.

Magnetohydrodynamic Flow of Immiscible Jeffrey Fluids Through a Horizontal Porous Cylinder

This paper investigates the steady and fully developed magnetohydrodynamic (MHD) flow of two nonmiscible Jeffrey fluids in a horizontal cylinder filled with a homogenous porous medium. A constant pressure gradient drives the flow in both regions, and a uniform magnetic field is applied transversely to the flow direction. Instead of the usual no‐slip condition, the linear Navier slip is used as a boundary condition on the cylinder’s surface, whereas the usual continuity conditions of velocity and shear stress are presumed at the fluid–fluid interface. The equations describing the problem under consideration are mathematically formulated and transformed into nondimensional forms with the proper choice of nondimensional variables. Analytical solutions have been obtained by solving the transformed equations of motion. The effects of different nondimensional parameters involved in the flow problem, including the magnetic number, Jeffrey parameter, Darcy number, ratio of viscosities, Reynolds number, slip parameter, and pressure gradient, on the velocity in each region are studied, and the results are exhibited graphically. In addition, numerical values for stress at the wall and volume flow rates are calculated for various fluid parameters and shown in tables. It is noticed that an increase in the values of the magnetic number and viscosity ratio reduces the velocity of the fluid, whereas increasing the Jeffrey parameters, Darcy number, Reynolds number, slip parameter, and pressure gradient enhances fluid velocity. Furthermore, the most favorable agreement was observed between the results of this study and the results of the previous studies.

Estimation of pulmonary vascular resistance for Glenn physiology.

Children with single ventricle heart disease typically require a series of three operations, (1) Norwood, (2) Glenn, and (3) Fontan, which ultimately results in complete separation of the pulmonary and systemic circuits to improve pulmonary/systemic circulation. In the last stage, the Fontan operation, the inferior vena cava (IVC) is connected to the pulmonary arteries (PAs), allowing the remainder of deoxygenated blood to passively flow to the pulmonary circuit. It is hypothesized that optimizing the Fontan anatomy would lead to decreased power loss and more balanced hepatic flow distribution. One approach to optimizing the geometry is to create a patient-specific digital twin to simulate various configurations of the Fontan conduit, which requires a computational model of the proximal PA anatomy and resistance, as well as the distal Pulmonary Vascular Resistance (PVR), at the Glenn stage. To that end, an optimization pipeline was developed using 3D computational fluid dynamics (CFD) and 0D lumped parameter (LP) simulations to iteratively refine the PVR of each lung by minimizing the simulated flow and pressure error relative to patients' cardiac magnetic resonance (CMR) and catheterization (CATH) data. While the PVR can also be estimated directly by computing the ratio of pressure gradients and flow from CATH and CMR data, the computational approach can separately identify the different components of PVR along the Glenn pathway, allowing for a more detailed depiction of the Glenn vasculature. Results indicate good correlation between the optimized PVR of the CFD and LP models (n = 16), with an intraclass correlation coefficient (ICC) of 0.998 (p = 0.976) and 0.991 (p = 0.943) for the left and right lung, respectively. Furthermore, compared to CMR flow and CATH pressure data, the optimized PVR estimates result in mean outlet flow and pressure errors of less than 5%. The optimized PVR estimates also agree well with the computed PVR estimates from CATH pressure and CMR flow for both lungs, yielding a mean difference of less than 4%.

Overload of the Right Ventricle in Patients with Pulmonary Embolism: Analysis of New Evaluation Criteria

INTRODUCTION: The increasing incidence of pulmonary embolism (PE) and high mortality from it necessitates development of new echocardiographic (EchoCG) criteria for assessing the severity of pressure and volume overload of the right ventricle (RV) in patients with PE.
 AIM: To perform critical analysis of the developed EchoCG criteria of overload of the right heart chambers in PE with the aim to determine severity of the course and outcomes of the disease.
 MATERIALS AND METHODS: The study included 428 patients with PE divided to 4 groups: group 1 42 patients with recorded death, group 2 51 patients with hemodynamically significant disease, group 3 193 hemodynamically stable patients with EchoCG signs of the overload of the right ventricle, group 4 142 patients with no identified symptoms. Comparison of the developed EchoCG criteria was conducted: the volume of tricuspid regurgitation, its ratio to the volume of the right atrium and the stroke volume of the heart, and also the pressure in the pulmonary trunk, the pressure gradient on the pulmonic valve and its ratio to the pressure gradient on the tricuspid valve in the studied groups with the determination of threshold values having diagnostic and prognostic significance.
 RESULTS: It was found that the level of the estimated pressure gradient on the pulmonic valve has statistically significant correlation with the hemodynamic significance of the course of the disease (r = 0.91, р 0.01) and fatal outcome (r = 0.99, р 0.01) and possesses high sensitivity (more than 92.7%) and specificity (more than 97.8%). This parameter is proved to be the most important prognostic EchCG criterion. To determine the expression of the RV dysfunction and the priority flow of blood from its cavity, the following parameters equivalent to EhcoCG, such as the ratio of pressure gradient on the pulmonic artery to the pressure gradient on the tricuspid valve and the ratio of the tricuspid regurgitation volume to the stroke volume, are also significant.
 CONCLUSION: Calculation of the pressure gradient on the pulmonic valve and its correlation with the pressure gradient on the tricuspid valve, just as the ratio of the volume of tricuspid regurgitation to the stroke volume can be reliable criteria for assessment of the hemodynamic significance of PE and predictors of its outcome.

Effective Relative Permeabilities Based on Momentum Equations with Brinkman Terms and Viscous Coupling

Summary The relative permeability expresses the mobility reduction factor when a fluid flows through a porous medium in the presence of another fluid and appears in Darcy’s law for multiphase flow. In this work, we replace Darcy’s law with more general momentum equations accounting for fluid-rock interaction (flow resistance), fluid-fluid interaction (drag), and Brinkman terms responding to gradients in fluid interstitial velocities. By coupling the momentum equations with phase transport equations, we study two important flow processes—forced imbibition (coreflooding) and countercurrent spontaneous imbibition. In the former, a constant water injection rate is applied and capillary forces are neglected, while in the latter, capillary forces drive the process and the total flux is zero. Our aim is to understand what relative permeabilities result from these systems and flow configurations. From previous work, when using momentum equations without Brinkman terms, unique saturation-dependent relative permeabilities are obtained for the two flow modes that depend on the flow mode. Now, with Brinkman terms included, the relative permeabilities depend on local spatial derivatives of interstitial velocity and pressure. Local relative permeabilities are calculated for both phases utilizing the ratio of phase Darcy velocity and phase pressure gradient. In addition, we use the Johnson-Bossler-Naumann (JBN) method for forced imbibition (with data simulated under the assumption of negligible capillary end effects) to calculate interpreted relative permeabilities from pressure drop and average saturation. Both flow setups are parameterized with literature data, and sensitivity analysis is performed. During coreflooding, Brinkman terms give a flatter saturation profile and higher front saturation. The saturation profile shape changes with time. Local water relative permeabilities are reduced, while they are slightly raised for oil. The saturation range where relative permeabilities can be evaluated locally is raised and made narrower with increased Brinkman terms. JBN relative permeabilities deviate from the local values: The trends in curves and saturation range are the same but more pronounced as they incorporate average measurements, including the strong impact at the inlet. Brinkman effects vanish after sufficient distance traveled, resulting in the unique saturation functions as a limit. Unsteady state (USS) relative permeabilities (based on transient data from single-phase injection) differ from steady-state (SS) relative permeabilities (based on SS data from coinjection of two fluids) because the Brinkman terms are zero at SS. During spontaneous imbibition, the higher effect from the Brinkman terms caused oil relative permeabilities to decrease at low water saturations and slightly increase at high saturations, while water relative permeability was only slightly reduced. The net effect was a delay in the imbibition profile. Local relative permeabilities approached the unique saturation functions without Brinkman terms deeper in the system because phase velocities (involved in the Brinkman terms) decreased with distance. In both systems, scaling and simulations demonstrate that the relative change in relative permeabilities due to Brinkman terms increases with the Brinkman coefficient, permeability, and inverse squared distance from the inlet.

ANALYSIS OF THE INFLUENCE OF THE GEOMETRY OF THE BLADE MIXER ON THE TURBULENCE AND INTENSITY OF LIQUID MIXING

Turbulent fluid mixing is an important aspect of many industrial and technological processes where efficient mixing of various components is of paramount importance to achieve the desired results. Optimal mixing can improve product quality, ensure the unity of complex reactions, and reduce process lead times. In this regard, the study and understanding of the influence of the geometry of the mixer on the characteristics of the turbulent flow becomes an urgent task of scientific research. The relevance of the study is explained by the wide application of mixers in industrial and technological processes, where the efficiency of mixing is crucial for achieving optimal results. The work used methods of experimental and numerical modeling of turbulent flow in various geometric configurations of blade mixers. Indicators such as turbulence intensity, pressure gradient, and fluid mixing ratio were used to quantify the turbulent characteristics. The obtained results demonstrate that the geometric configuration of the blade mixer has a significant effect on the formation of the turbulent flow. Some geometric parameters of the mixer can contribute to increasing the intensity of liquid mixing, while others can reduce its efficiency. Scientific results can be useful for designing optimal paddle mixers for specific industrial tasks that require intensive liquid mixing. The use of optimized mixers can help increase process productivity, save energy resources, and improve product quality.

Unsteady MHD hybrid nanofluid flow over a convectively heated linear stretching cylinder with velocity slip: A comparative study

This paper provides a comparative numerical analysis of unsteady hybrid nanofluid ([Formula: see text]/H2O) and nanofluid (TiO2/H2O) flows through a permeable linear stretching cylinder placed in a porous medium has been presented in the presence of oblique Lorentz force. The flow regulating boundary layer equations has been governed due to the sway of the suction, viscous-Ohmic dissipation, heat source, thermal radiation and first-order velocity slip with imposing convective boundary conditions on the surface. The self-similar transformation has been employed to convert the governing coupled nonlinear PDEs into a set of ODEs and finally solved them numerically by fifth-order Runge–Kutta method with shooting technique. Finally, a comparative study has been made on the thickness of the momentum and thermal boundary layers due to the effect of governing parameters for simple and hybrid nanofluids. Further, a numerical observation on local skin friction and thermal-transport coefficients is presented with the help of tables. The result indicates that the progressiveness of the velocity profile reduces for the unsteadiness parameter, Hartree pressure gradient, velocity slip parameter, inclination parameter, porous medium parameter, magnetic parameter and suction parameter while improving for velocity ratio parameter and temperature profiles increases with Biot number, Eckert number, heat generation parameter and thermal radiation parameter, but decreases for Hartree pressure gradient and velocity ratio parameter. This work has found various applications in high-temperature and cooling processes, paints, conductive coatings, medicines, space technology, biosensors, conductive coatings and so on.

Functional assessment of serial coronary lesions and diffuse coronary disease

Functional assessment performed during diagnostic coronary angiography has gained an increasing role during the last few decades. Traditional coronary angiography using only anatomical data cannot provide information whether intermediate lesions cause ischaemia or not, and frequently there is no evidence from non-invasive functional tests with appropriate sensitivity and specificity to guide us regarding the localization and severity of ischaemia. Several studies proved the clinical benefit of the use of invasive functional tests. The functional severity of unrevascularized coronary artery disease is correlated with prognosis. It is important to precisely define the lesions causing ischaemia when we plan to improve the blood supply to the heart. The functional assessment of diffuse or serial lesions is not well established. New investigations and methods have been developed such as pullback pressure gradient or instantaneous wave-free ratio intensity besides the well-established and studied functional tests. This could help us find and revascularize the lesions within a coronary vessel primarily responsible for ischaemia and symptoms or, in the case of diffuse disease and no obvious target, to optimize medical therapy. Orv Hetil. 2022; 163(48): 1902-1908.

Computational 2D parameter study of suction and oscillatory blowing actuator with experimental validation

Fluidic oscillators and ejectors were combined to create an effective flow control device, proved effective but have not been optimized yet. In the current study, mostly steady RANS simulations were used to optimize 11 geometric parameters of a generic-simplified suction and oscillatory blowing actuator (SaOB). Selected unsteady simulations and experiments validated the numerical optimization procedure findings. In the parameter optimization process, multiple input and output parameters are chosen to identify the strongest correlations between them. Non- or weakly- correlated parameters are eliminated from further study and others are combined to obtain a reduced set of correlated parameters. It was found that the Throat ratio (ejector to oscillator) parameter predicts the Entrainment ratio, while the cross-flow pressure gradient ratio can predict the ability of the SaOB actuator to produce effective oscillation. The optimized device performs significantly better than the starting point device.While the approach is appealing, open questions remain concerning the comparison of 2D simulations and the actual 3D geometry and compressibility effects.

Nonlinear Seepage Behaviors of Pore-Fracture Sandstone under Hydro-Mechanical Coupling

This work focused on the nonlinear seepage behaviors of flow in pore-fracture media. Natural sandstones were selected to prefabricate single-fracture specimens with different inclinations (0–90°). Seepage tests of combined media were performed under different confining pressures (8–10 MPa) and different water pressures (3–7 MPa) in a triaxial pressure chamber. The fitting analysis of experimental data showed that Forchheimer’s law described the nonlinear characteristics of flow in the pore-fracture media. Linear term coefficient a and nonlinear term coefficient b of the sandstone samples with different inclinations changed more obviously with the increased inclination. When the fracture inclination was greater than 30°, a and b values had a sudden jump. The nonlinear inertial-parameter equation of fluid flow in pore-fracture media was proposed based on non-Darcy flow coefficient β and inherent permeability k. The applicability of the following methods to evaluate Darcy’s law was discussed, including normalized hydraulic conductivity, pressure gradient ratio, and discharge ratio. The three methods were able to determine critical parameters and distinguish linear and nonlinear flow. Furthermore, it was specified for the first time that when β was negative, critical nonlinear effect E was −0.1, and Forchheimer’s coefficient F0 was −0.091. In the −∇P-Q relationship, the fitting curve was convex to the −∇P axis, and the increase of Q was higher than the linear increase, presenting the nonlinearity of overflow. On the one hand, the fractures and pores were compressed under the confining pressure due to the prefabricated fractures of different shapes and different inclinations. A higher seepage water pressure was needed to stabilize the seepage system with the excessive flow rate. On the other hand, the barrier effect of the fluid inside the rock was completely lost because the fluid expanded the seepage channel. Its permeability was changed, leading to seepage instability.

Prognostic value of pulmonary artery pulsatility index in chronic heart failure patients with reduced ejection fraction

Background The co-existence of right ventricular dysfunction (RVD) in heart failure patient with reduced ejection fraction (HFrEF) is an independent maker of poor prognosis. A novel right ventricular hemodynamic composite measure is the pulmonary artery pulsatility index (PAPi), which is the pulmonary artery pressure gradient ratio. It is a strong predictor of RVD in patients with acute inferior myocardial infarction and patients undergoing left ventricular assist device (LVAD) implantation. However, little is known about its prognostic value in patients with HFrEF. Methods Between September 2010 and July 2013, 172 patients with HFrEF admitted to the tertiary hospital were included in this analysis. We carried out a cardiac catheterisation for each patient, at baseline. Subsequently, we evaluated both PAPi and the other hemodynamic parameters with longitudinal follow-up of adverse outcomes such as cardiac mortality, LVAD, and heart transplantation (HTx). Results During a median follow-up period of 52 months we observed 50 cardiac deaths, 12 LVAD implantations and 10 HTx. A threshold for PAPi value of 2.82 was ascertained (Area: 0.76, p < 0.001, CI: 0.67–0.85, sensitivity 67%, specificity 69%). After dividing the study population into two groups, PAPi ≤2.82 and PAPi >2.82, no significant difference was demonstrated with respect to the aetiology of heart failure (ischaemic HFrEF p = 0.29 and non-ischaemic HFrEF p = 0.29). In Cox regression survival analysis, PAPi was an independent predictor of cardiac death (hazard ratio 0.73 [95% confidence interval 0.53–0.99], p = 0.045). Conclusion In patients with HFrEF, a low PAPi value (<2.82) was associated with increased cardiac mortality risk.

Predicting the co-extrusion flow of non-Newtonian fluids through rectangular ducts – A hybrid modeling approach

Co-extrusion has become the state-of-the-art process technology in nearly all application areas of polymer processing. By combining different types of polymeric materials within multilayer structures, products with a broad range of property profiles can be obtained for advanced applications. Design of co-extrusion dies and feedblock systems requires extensive knowledge of process and material behavior. To accurately describe the shear-thinning behavior of polymer melts in co-extrusion processes and to predict characteristic process quantities, numerical methods are essential. We present a hybrid approach to modeling stratified co-extrusion flows of two power-law fluids through rectangular ducts. By applying the theory of similarity and transforming the problem into dimensionless representation, we identified four independent influencing parameters that fully describe the flow situation: (i) the power-law index of the first fluid, (ii) the power-law index of the second fluid, (iii) the dimensionless position of the interface, and (iv) the ratio of dimensionless pressure gradients. We varied these input parameters within ranges that cover almost all combinations of industrial relevance, creating in the process a set of more than 44,000 design points. By means of the shooting method, numerical solutions were obtained for (i) pressure-throughput behavior, (ii) interfacial shear stress, (iii) interfacial velocity, and (iv) individual volume flow rates. Finally, we used symbolic regression based on genetic programming to model these target quantities as functions of their influencing parameters and obtain algebraic relationships between them. Our mathematical models thus enable accurate prediction of several characteristic process quantities in two-layer co-extrusion flows of shear-thinning fluids through rectangular ducts. The models are not restricted to the field of polymer processing, but can be used in all industrial applications that involve such co-extrusion flows.

Low Relative Valve Load is Associated With Paradoxical Low-Flow Aortic Stenosis Despite Preserved Left Ventricular Ejection Fraction and Adverse Clinical Outcomes

Paradoxical low-flow (LF) severe aortic stenosis (AS) despite preserved left ventricular (LV) ejection fraction (LVEF) has been shown to be distinct from normal-flow (NF) AS, with a poorer prognosis. Relative valve load (RVL) is a novel echocardiographic haemodynamic index based on the ratio of transaortic mean pressure gradient to the global valvulo-arterial impedance (Zva) in order to estimate the contribution of the valvular afterload to the global LV load. We aimed to determine the usefulness of RVL in LF AS versus NF AS. A total of 450 consecutive patients with medically managed severe AS (aortic valve area <1.0 cm2) with preserved LVEF (>50%) were studied. Patients were divided into LF (stroke volume index <35 mL/m2) or NF, and high RVL or low RVL. Baseline clinical and echocardiographic profiles, as well as clinical outcomes, were compared. There were 149 (33.1%) patients with LF. Despite higher global impedance in LF (Zva 6.3±2.4 vs 3.9±0.9 mmHg/mL/m2; p<0.001) compared with NF, the RVL in LF AS was significantly lower (5.4±2.7 vs 9.8±5.1 mL/m2; p<0.001). On multivariable analysis, low RVL (≤7.51) remained independently associated with poor clinical outcomes on Cox regression (hazard ratio, 1.31; 95% confidence interval, 1.03-1.68), with 53.2% sensitivity and 70.3% specificity. This was comparable to other prognostic indices in AS. Kaplan-Meier curves demonstrated that low RVL was associated with increased mortality. Increased systemic arterial afterload may be important in the pathophysiology of LF AS. Low RVL was an independent predictor of poor clinical outcomes in medically managed severe AS. There may be a greater role in the attenuation of systemic arterial afterload in AS to improve outcomes.

Core annular flow theory as applied to the adiabatic section of heat pipes

Core annular flow theory is used to model the parallel flow of fluids of different phases and has been used to describe drag reduction in the context of internal flows bounded by superhydrophobic surfaces. The work presented here is an extension of core annular flow theory to the study of the adiabatic section of heat pipes. Our aim is to develop a first-principles estimate of the conditions necessary to maximize the (counter) flow of liquid and vapor and, by extension, the axial flow of heat. The planar and axisymmetric geometries are examined as are heat pipes containing vs being devoid of a wick. In the wick vs no-wick cases, the peripheral return flow of liquid is, respectively, driven by capillarity and by gravity. Our model is used to predict velocity profiles and the flux-maximizing pressure gradient ratio (vapor-to-liquid). We further obtain estimates for the optimum thickness of the liquid layer. Note finally that when the liquid flow occurs via capillary pumping, there is a minimum surface tension below which the wick cannot supply a sufficient flow of liquid. We characterize this critical point in terms of the properties of the working fluid and of the wick.

Changes in the Interventricular Septal Curvature in Healthy Full-term Neonates During the First 14 Days of Life.

Interventricular septal geometry and motion reflect the interaction between the ventricles, and an abnormal shape and abnormal motion are always regarded as signs of increased right ventricular or pulmonary artery pressure. During the neonatal period, there are profound changes in the cardiac circulation. The aims of this study were to quantitatively analyze neonatal septal deformations under normal physiologic conditions and evaluate the changes in association with the hemodynamic changes occurring during the transitional period. This was a retrospective study of 114 healthy full-term neonates from birth to 14 days of age. Normalized septal curvatures were measured on left ventricular parasternal short-axis views during end diastole and end systole. The interventricular pressure gradient, ratio of ventricular volumes, septal strain, thickness, and some clinical characteristics were assessed, along with the association of these parameters with septal curvature. All 4 normalized septal curvatures were found to have a significant correlation with the trans-septal pressure gradient (TSPG) and the end-diastolic volume ratio of the left and right ventricles (P < .0001). The TSPG had the highest impact on septal curvature, and among the 4 curvatures, the middle end-systolic normalized septal curvature had the highest correlation with the TSPG (r2 = 0.948; P < .0001). There were significant correlations between septal curvature and the interventricular pressure gradient and ventricular volume ratio in healthy full-term neonates. The normalized septal curvatures gradually increased with increasing age and could be good indicators of the hemodynamic changes occurring during the transitional period.

Core Annular Flow Theory as Applied to the Adiabatic Section of Heat Pipes

Core annular flow theory is used to model the parallel flow of fluids of different phases and has been used to describe drag reduction in the context of internal flows bounded by superhydrophobic surfaces. The work presented here is an extension of core annular flow theory to the study of the adiabatic section of heat pipes. Our aim is to develop a first-principles estimate of the conditions necessary to maximize the (counter) flow of liquid and vapor and, by extension, the axial flow of heat. The planar and axisymmetric geometries are examined as are heat pipes containing vs being devoid of a wick. In the wick vs no-wick cases, the peripheral return flow of liquid is, respectively, driven by capillarity and by gravity. Our model is used to predict velocity profiles and the flux-maximizing pressure gradient ratio (vapor-to-liquid). We further obtain estimates for the optimum thickness of the liquid layer. Note finally that when the liquid flow occurs via capillary pumping, there is a minimum surface tension below which the wick cannot supply a sufficient flow of liquid. We characterize this critical point in terms of the properties of the working fluid and of the wick.

Risk classification of pulmonary arterial hypertension by echocardiographic combined assessment of pulmonary vascular resistance and right ventricular function.

Which combination of clinical parameters improves the prediction of prognosis in patients with pulmonary arterial hypertension (PAH) remains unclear. We examined whether combined assessment of pulmonary vascular resistance and right ventricular function by echocardiography is useful for classifying risks in PAH. In 41 consecutive patients with PAH (mean age of 48.9 ± 17.3years, 31 females), a 6-min walk test, pulmonary function test, and echocardiography were performed at baseline and during PAH-specific therapies. The study endpoint was defined as a composite of cardiovascular death and hospitalization for PAH and/or right ventricular failure. During a follow-up period of 9.2 ± 8.7months, 18 patients reached the endpoint. Multivariate regression analysis showed that the ratio of tricuspid regurgitation pressure gradient to the time-velocity integral of the right ventricular outflow tract (TRPG/TVI) and tricuspid annular plane systolic excursion (TAPSE) during PAH-specific treatment were independent prognostic predictors of the endpoint. Using cutoff values indicated by receiver operating characteristic analysis, the patients were divided into four subsets. Multivariate analyses by Cox's proportional hazards model adjusted for age, sex and body mass index indicated that subset 4 (TRPG/TVI ≥ 3.89 and TAPSE ≤ 18.9mm) had a significantly higher event risk than did subset 1 (TRPG/TVI < 3.89 and TAPSE > 18.9mm): HR = 25.49, 95% CI 4.70-476.97, p < 0.0001. Combined assessment of TRPG/TVI and TAPSE during adequate PAH-specific therapies enables classification of risks for death and/or progressive right heart failure in PAH.

Risk factors for residual mitral regurgitation after aortic valve replacement in patients with severe aortic valve stenosis and moderate mitral regurgitation.

While it was reported that patients with residual moderate mitral regurgitation (MR) after surgical aortic valve replacement (SAVR) had a poorer prognosis than those without it, the risk factors for residual MR have not been fully elucidated. The aim of the study was to evaluate risk factors for residual MR after SAVR. Of the 222 patients who underwent isolated SAVR from 2001 to 2018, 33 (11 men; age: 74 ± 7years) had functional moderate MR before surgery. The risk factors for residual MR were evaluated by comparing patients with residual moderate MR (n = 11, 33%) with those who exhibited improved post-surgery MR (n = 22, 67%). The left atrial diameter was significantly larger in the residual MR group (51 ± 7mm) than in the improved MR group (46 ± 5mm; P = 0.049). The mean pressure gradient at the aortic valve was significantly smaller in the residual MR group (52 ± 18mmHg) than in the improved MR group (69 ± 22mmHg; P = 0.043). A ratio of left atrial diameter (mm) and mean aortic valve pressure gradient (mmHg) greater than 0.9 predicted residual MR with a sensitivity of 70% and a specificity of 74% (area under the ROC curve: 0.779; P = 0.015). In patients with severe aortic valve stenosis and moderate MR, a high ratio of preoperative left atrial diameter and mean aortic valve pressure gradient would be a parameter predicting residual moderate MR post-SAVR.

A study of relative permeability for transient two-phase flow in a low permeability fractal porous medium

In this paper, a relative permeability prediction method considering the effects of capillary pressure and threshold pressure gradient in a low permeability fractal porous medium is established and analyzed based on the fractal approximation model that porous medium consist of a bundle of tortuous capillaries. With this method, every parameter has clear physical meaning without empirical constants, and the model's predictions have a good agreement with experimental data. In addition to this, it makes some discussions that how the characteristic parameters (such as tortuosity fractal dimension, pore fractal dimension, ratio of minimum-maximum capillaries diameters and threshold pressure gradient) influence the relative permeability. This study may be conducible to a better understanding of the mechanism for transient two-phase flow in the low permeability fractal porous medium.

Numerical analysis of heat and mass transfer along a stretching wedge surface

In this work, the effects of dimensionless parameters on the velocity field, thermal field and nanoparticle concentration have been analyzed. In this respect, the magnetohydrodynamic (MHD) boundary layer nanofluid flow along a moving wedge is considered. Therefore, a similarity solution has been derived like Falkner – Skan solution and identified the point of inflexion. So the governing partial differential equations transform into ordinary differential equations by using the similarity transformation. These ordinary differential equations are numerically solved using fourth order Runge–Kutta method along with shooting technique. The present results have been shown graphically and in tabular form. From the graph, the results indicate that the velocity increases with increasing values of pressure gradient, magnetic induction and velocity ratio. The temperature decreases for velocity ratio, Brownian motion and Prandtl number but opposite result arises for increasing values of thermophoresis. The nanoparticle concentration decreases with an increase in pressure gradient, Brownian motion and Lewis number, but increases for thermophoresis. Besides, the solution of nanoparticle concentration exists in the case of Brownian motion is less than 0.2, thermophoresis is less than 0.14 and lewis number is greater than 1.0. Finally, for validity and accuracy the present results have been compared with previous work and found to be in good agreement.