Decrease In Pressure Gradient Research Articles

Deformation and Heating of an Elastoviscoplastic Cylindrical Layer Moving Owing to a Varying Pressure Drop

Within the framework of the theory of large elastoplastic deformations generalized to the case of viscous and thermophysical properties of materials, we give a solution of a sequence of coupled problems on the onset and development of a flow in a material layer filling the gap between two rigid coaxial cylindrical surfaces under increasing pressure drop and on the subsequent flow deceleration under decreasing pressure gradient. Here the thermophysical and deformation processes are coupled, and the yield stress depends on temperature. Heat production due to the layer material friction against the rough cylindrical boundary surfaces is taken for an additional heat source.

Эндоваскулярное лечение больных с критическим аортальным стенозом: сoвременное состояние проблемы и перспективы

The article contains the review of current understanding of the etiology and pathogenesis of degenerative aortic stenosis, approaches to surgical treatment depending on various factors, e. g. severity of defect and comorbidity, description of endovascular techniques (balloon valvuloplasty and transcatheter aortic valve implantation), and features of the selection of patients for these procedures. The authors also present assessment of results of operations performed from 2011 to 2016 in the city hospital № 2 in Saint-Petersburg. They analyze data from 72 high-risk aortic stenosis patients aged 81±6 years treated with transcatheter aortic valve implantation. In 68 out of 72 patients (94.4 %) clinical improvement was achieved with reduction of dilation of left ventricular cavity, decrease of functional class of heart failure, and decrease of mean pressure gradient across the aortic valve. A conclusion is made that these results confirm advantages and perspectives of the use of endovascular methods of treatment in this complicated group of patients.

The Effect of ENSO on the Variability of Chlorophyll-a and Sea Surface Temperature in the Maluku Sea

The Maluku Sea features strong Chlorophyll-a (Chl-a) bloom and sea surface temperature (SST) cooling during the Southeast Monsoon season. Using high-resolution Chl-a and SST satellite observations over a long time window, this study aims to investigate the effect of El Nino Southern Oscillation (ENSO) on the seasonal variability of Chl-a and SST in the Maluku Sea. During the El Nino and La Nina, the maximum Chl-a concentration (greater than 0.5 mg/m3) and minimum SST (less than 27.5 °C) are observed in August. This finding is in line with prior investigation. Moreover, we reveal that the ENSO does not alter the seasonal variability of Chl-a and SST in the region, but the magnitudes of summertime Chl-a bloom and SST cooling are enhanced (reduced) by about 0.1 mg/m3 and 0.5 °C during the El Nino (La Nina). This is caused by an increase (decrease) in the sea level pressure gradients, which possibly enhanced (reduced) wind-driven mixing in the Maluku Sea.

Foam and thin films of hydrophilic silica particles modified by β-casein

HypothesisFoaming properties of particle dispersions can be modified by addition of amphiphiles. The molar ratio between particles and amphiphiles will influence the wetting properties of the particles as well as the bulk concentration of the amphiphiles. This will have an effect on air/water interfacial composition as well as on the thin film and foam stability of the mixed system. ExperimentsIn this research foams and thin films of hydrophilic silica particles in presence of β-casein (β-CN) were investigated with different particle sizes and varying β-CN/silica weight ratios (between 1:10 and 1:100). Samples were characterized for particles size, morphology as well as contact angle and related to their foaming, interfacial, and thin film properties. FindingsA threshold weight ratio of β-CN/silica was found to be 1:50 for foam stabilization with mixtures containing silica particles no larger than 1 μm and 1:30 for film stabilization with mixtures containing larger particles. At the interface, the modified silica particles were rather diluted without much interaction for surface compressions up to 30%. Large silica particles (0.0015% β-CN, Csilica ≤ 0.15%) were dragged to the periphery of the thin liquid films but no decrease of the inner film draining rate by a decrease of capilary pressure gradient across the film was observed. The depletion of β-casein in the bulk by particles played a major role in foam destabilization.

On the ability of RCMs to capture the circulation pattern of Etesians

The Etesians are among the most persistent regional scale wind systems in the lower troposphere that prevail over the eastern Mediterranean during the extended summer season. The performance of five high-resolution EURO-CORDEX regional climate models (RCMs) in simulating the Etesian climatology as well as the associated large-scale atmospheric circulation is investigated. The model outputs are validated against reanalysis datasets (ERA-Interim, 20CR-v2c and ERA20-C) and daily station observations covering the period May to September 1989–2004. Results show that most RCMs coherently reproduce the number of observed Etesian days, the duration of their episodes and the wind field over the Aegean Sea. The majority of RCMs better reproduce in situ wind speed than the driving model, especially over the central and southwestern Aegean Sea. All models represent very well the mean state of the large-scale atmospheric circulation associated with Etesians both at the surface and at mid to upper troposphere, compared to reanalyses. Statistically significant differences vary depending on the subperiod, generally with a better performance for September. The performance of the models improves significantly with decreasing pressure gradient over the Aegean. Finally, results highlight the ability of EURO-CORDEX RCMs in simulating the Etesians over the Aegean, especially the DMI, SMHI and IPSL, which makes them efficient tools for wind energy applications.

Analysis of electroosmotic flow and Joule heating effect in a hydrophobic channel

In this paper, a mathematical model has been developed to analyze the fluid flow and heat transfer effect in a hydrophobic microchannel filled with a power law fluid. The effects of Joule heating, thermal radiation and velocity slip boundary conditions are analyzed by considering different slip parameters, EDL thickness, pressure gradient and flow behavior indices. The analytical expression for fluid flow and heat transfer have been derived in terms of the flow governing parameters based on the Debye-Huckel linearizing principle. Depending on the experimental existing flow behavior index, the analytical solutions are obtained in closed form where as numerical results are presented for general parametric values. The impact of slip velocity parameters in terms of a flow enhancement factor (Efb), is studied to obtain the average flow velocity variation in a hydrophobic microchannel compared to a plane microchannel. The pressure assisted flow for pseudo-plastic (shear thinning) fluids achieve maximum velocity as compared to dilatant (shear thickening) fluids. The study finds that increase in thermal radiation minimizes heat transfer rate close to the hydrophobic wall, plays a vital role for the therapeutic treatment of hyperthermia (to understand the effect of heat transfer due to electric potential). It is also observed that Joule heating parameters enhance the heat transfer rate for classical Newtonian/non-Newtonian fluids for decrease in power indices and pressure gradient.

Impact of prosthesis-patient mismatch after mitral valve replacement in rheumatic population: Does mitral position prosthesis-patient mismatch really exist?

BackgroundProsthesis-patient mismatch (PPM) is characterised by the effects of inadequate prosthesis size relative to body surface area (BSA).The purpose of this study was to determine the impact of PPM on late clinical outcomes after mitral valve replacement (MVR) in rheumatic population.MethodsFrom 2000 to 2013, a total of 445 patients (mean age 54.2 ± 11.7 years) underwent isolated MVR (±tricuspid annuloplasty) for rheumatic disease were investigated. Effective orifice area (EOA) was determined by the continuity equation and PPM was defined as indexed EOA (EOA/BSA) ≤ 1.2 cm2/m2. Clinical and echocardiographic follow-up (mean follow up 8.7 ± 4.0 years) results were compared.Results37% of patients (n = 165) had PPM. There were no significant differences in baseline and operative characteristics between patients with and without PPM except age and IEOA. A significant decrease in mean trans-valvular pressure gradient (MPG) over time following MVR, however the change of MPG showed no differences between groups (No PPM vs. PPM: 8.9 ± 4.7 mmHg → 3.6 ± 1.2 mmHg vs. 8.7 ± 4.5 mmHg → 3.8 ± 1.4 mmHg, p-value = 0.28). In all patients, there was a reduction of left atrium dimension (58.6 ± 12.0 mm → 53.2 ± 12.0 mm vs. 57.9 ± 8.9 mm → 52.2 ± 8.9 mm, p-value = 0.68) and left ventricular end diastolic diameter (49.9 ± 5.7 mm → 48.9 ± 5.7 mm vs. 49.7 ± 6.0 mm → 48.3 ± 5.0 mm, p = 0.24) without statistical significance. Freedom from TR progression rates at 3 and 5 years (99% vs.98%, 99% vs. 98%, p-value = 0.1), and overall survival rates at 3 and 5 years (97% vs. 96%, 94% vs. 94%, p-value = 0.7) were similar.ConclusionThis study shows that mitral PPM is not associated with atrial /ventricular remodeling and might not influence late clinical outcome including late TR progression, survival in rheumatic population.

Intraoperative measurement of pressure gradient in median arcuate ligament syndrome as a rationale for radical surgical approach

Background: Median arcuate ligament syndrome (MALS) describes clinical symptoms in patients with stenosis of the celiac artery due to external compression by the ligament. There is an ongoing debate, whether sole release of the median arcuate ligament warrants long-term relief of the symptoms.Materials and methods: Eight patients diagnosed with MALS underwent open surgical treatment beginning with the release of the ligament. Systemic pressure and pressure in the left gastric artery were measured before and after division of the median arcuate ligament and release of the celiac artery. In patients with persistent gradient above 15 mm Hg after the release a PTFE bypass was performed.Results: After the release, the pressure gradient decreased from 66 ± 19 to 48 ± 14 mm Hg (p = .001) and therefore in all patients either an aorto-celiac bypass (n = 6) or aorto-hepatic bypass (n = 2) was created. Consequently, the gradient decreased to 7 ± 2 mm Hg (p = .0001). One month postoperatively, three patients were free of symptoms and the rest reported relief of symptoms.Conclusions: Release of the celiac artery resulted in insufficient decrease of pressure gradient, which was achieved by bypassing the segment with favorable mid-term outcome. We believe that the effect of the release should always be assessed to decide on subsequent treatment.

Transjugular Intrahepatic Portosystemic Shunt for Portal Hypertension in Hepatocellular Carcinoma with Portal Vein Tumor Thrombus.

In patients with hepatocellular carcinoma (HCC), limited therapeutic options are available for portal hypertension resulted from portal vein tumor thrombus (PVTT). We aimed to determine safety and efficacy of TIPS for treatment of symptomatic portal hypertension in HCC with PVTT. We evaluated clinical characteristics of 95 patients with HCC and PVTT out of 992 patients who underwent TIPS. The primary endpoints included success rate, procedural mortality, serious complications, decrease in portosystemic pressure gradient, and symptom relief. The secondary endpoints included recurrence of portal hypertension, overall survival, adverse events related to treatments for HCC, and quality of life measured by Karnofsky Performance Status Scale (KPS). Success rate of TIPS was 95.8% (91/95), with procedural mortality of 1.1%. Serious complications related to TIPS procedure occurred in 2.1% (2/95) of patients. The symptoms of portal hypertension were well relieved. Variceal bleeding was successfully controlled and terminated in 100% of patients, with a recurrence rate of 39.2% in 12months. Refractory ascites/hydrothorax was controlled partially or completely in 92.9% of patients during 1month after TIPS, with a recurrence rate of 17.9% in 12months. Survival rate at 6, 12, 24, and 36months was 75.8, 52.7, 26.4, and 3.3%, respectively. No unexpected adverse event related to treatments for HCC was observed. The KPS score was 49±4.5 and 63±4.7 before and 1month after TIPS, respectively (p<0.001). TIPS is a safe and efficacious treatment for symptomatic portal hypertension in HCC with PVTT.

Molecular dynamics simulation of single pulse discharge process: clarifying the function of pressure generated inside the melting area in EDM

Due to the unique and superior properties of using thermal energy to machine electrically conductive material regardless of its hardness, electrical discharge machining has been widely used and has become indispensable in the manufacturing industry. However, the incompleteness and imperfection of the fundamental theory behind it seriously hinders its further application and development. In this work, a single pulse discharge in deionised water was simulated to study the material removal motivity and mechanisms with molecular dynamics simulations. The results show that during the discharge process, there exists a decreasing pressure gradient along the depth direction towards the surface of the melting area. When the pressure gradient overcomes the atomic bonding forces, the melting material can be ablated from the electrode. Thus, it is not the case that the melting material cannot be removed during the discharge process; material removal occurs throughout the whole discharge process. In addition, it was found that the bulge is formed for two reasons: the main reason is the shearing flow of the melting material caused by the pressure gradient along the radial direction in the melting area, and the other is the accumulation of the spattering material from the opposite electrode.

Shear banding of semidilute polymer solutions in pressure-driven channel flow

Shear banding is observed in many soft materials. We recently developed a two-fluid model for semidilute entangled polymer solutions by using the generalized bracket approach of nonequilibrium thermodynamics. This model assumes that Fickian diffusion and stress-induced migration generate a nontrivial velocity difference between the polymers and the solution, thereby resulting in shear band formation. A straightforward implementation of the slip boundary conditions is possible because the differential velocity is treated as a state variable. Numerical calculations showed obvious shear banding in the polymer concentration profile. Increasing the pressure gradient reduces the inhomogeneity of the concentration profile and moves the transition region toward the center of the channel. Moreover, the velocity deviates from the typical parabolic form and shows a plug-like profile with a low shear band near the center and a high one near the walls. The lack of hysteresis in the profiles of the volumetric flow rate calculated with the increasing and decreasing pressure gradient demonstrates the uniqueness of the solution. In addition, the flow rate exhibits a spurt at a critical pressure gradient, as experimentally observed for shear banding materials. The simplicity of the new model encourages us to analyze it in more complicated flows.

Impact of transjugular intrahepatic portosystemic shunt implantation on liver perfusion measured by volume perfusion CT.

Background Implantation of a transjugular intrahepatic portosystemic shunt (TIPS) induces changes of liver perfusion. Purpose To determine the changes in arterial, portal venous, and total perfusion of the liver parenchyma induced by TIPS using the technique of volume perfusion computed tomography (VPCT) and compare results with invasively measured hepatic intravascular pressure values. Material and Methods VPCT quantification of liver perfusion was performed in 23 patients (mean age, 62.5 ± 8.8 years) with portal hypertension in the pre-TIPS and post-TIPS setting, respectively. A commercially available software package was used for post-processing, enabling separate calculation of the dual (arterial [ALP] and portal venous [PVP]) blood supply and additionally of the hepatic perfusion index (HPI) (HPI = ALP/(ALP + PVP)*100%). Invasive pressure measurements were performed during the intervention, before and after TIPS placement. Liver function tests performed before and after the procedure were compared. Results Mean decrease of pressure gradient through TIPS was 13.3 mmHg. Mean normal values for ALP, PVP, and total perfusion (ALP + PVP) before TIPS were 15.9, 37.7, and 53.5 mL/100 mL/min, respectively, mean HPI was 35.4%. After TIPS, ALP increased to a mean value of 37.7 mL/100 mL/min, PVP decreased (15.7 mL/100 mL/min, P < 0.05), whereas total perfusion remained unchanged (53.4 mL/100 mL/min, P = 0.97). HPI increased (71.9%; P < 0.05). No correlation between invasive pressure measurement and VPCT parameters was observed. After TIPS, liver function tests were found to worsen with a significant increase of bilirubin ( P < 0.05). Conclusion Following TIPS placement, ALP and HPI increased in all patients, whereas PVP markedly decreased. Interestingly, the magnitude of decrease in portosystemic pressure gradients was not found to correlate with VPCT parameters.

ALCOHOL-BASED SEPTAL ABLATION OF INTERVENTRICULAR SEPTUM WITH CONTRAST ECHOCARDIOGRAPHIC CONTROL

Alcohol septal ablation was introduced in 1994 as an alternative for surgical septal myectomy in patients with obstructive hypertrophic cardiomyopathy refractory to drug treatment. The procedure decreases symptoms of the disease creating targeted localized infarction focus of the upper part of interventricular spetum leading to increase of outgoing tract diameter, decrease of pressure gradient at the level of outgoing left ventricle tract and hypertrophy regression caused by overload. Such clinical improvement can be achieved in most cases. Main complication of the alcohol-based ablation — complete atrioventricular block with necessity, in some patients, of permanent cardiostimulator. Contrast echocradiography during alcohol septal ablation makes it to localize infarction, to use less amount of alcohol and, therefore, to decrease complications rate.

Outcomes in Percutaneous Balloon Mitral Valvuloplasty: A Single Centre Experience

Objective: Rheumatic mitral stenosis continues to be prevalent in Australia particularly in Indigenous populations. This study is aimed to evaluate the safety and efficacy of mitral balloon valvuloplasty in a single teaching hospital in Australia. Methods: A retrospective cohort study was performed on data involving mitral stenosis patients who underwent percutaneous mitral balloon valvuloplasty. The Prince Charles Hospital database was analysed for various measurements before and after the procedure. All patients received echocardiograms before and on the first day following the procedure. Echocardiogram measurements performed before and after the procedure were analysed. Results: A total of 67 percutaneous mitral balloon valvuloplasties for mitral stenosis performed from 2004 to 2016 at this single centre. All cases of mitral stenosis were secondary to rheumatic heart disease. Average age was 54 +/- 16 years. 80% of the patients were female. Average decrease in mean transmitral pressure gradient (MPG) was 3.6 mmHg (10 to 6 +/-2, p < 0.01). There was one post-procedure mitral regurgitation that required emergency surgical repair. There were otherwise no immediate post procedure complications including death, stroke, MI, or major vascular complications requiring blood transfusion. There was a total of 2 unsuccessful balloon valvuloplasties. Average time until mitral valve replacement was performed was 29.5 months which was indicated in 16 patients. Conclusion: Percutaneous balloon mitral valvuloplasty provides good immediate and midterm results as previously shown. It is a safe and well tolerated procedure.

Separation of Hydrogen from Carbon Dioxide through Porous Ceramics.

The gas permeability of α-alumina, yttria-stabilized zirconia (YSZ), and silicon carbide porous ceramics toward H2, CO2, and H2–CO2 mixtures were investigated at room temperature. The permeation of H2 and CO2 single gases occurred above a critical pressure gradient, which was smaller for H2 gas than for CO2 gas. When the Knudsen number (λ/r ratio, λ: molecular mean free path, r: pore radius) of a single gas was larger than unity, Knudsen flow became the dominant gas transportation process. The H2 fraction for the mixed gas of (20%–80%) H2–(80%–20%) CO2 through porous Al2O3, YSZ, and SiC approached unity with decreasing pressure gradient. The high fraction of H2 gas was closely related to the difference in the critical pressure gradient values of H2 and CO2 single gas, the inlet mixed gas composition, and the gas flow mechanism of the mixed gas. Moisture in the atmosphere adsorbed easily on the porous ceramics and affected the critical pressure gradient, leading to the increased selectivity of H2 gas.

Experimental investigation of non-boiling gas-liquid two phase flow in upward inclined pipes

In comparison to horizontal and vertical two phase flow, very little information is available on the two phase flow phenomenon in upward inclined pipes. To explore and contribute to the current state of knowledge, the main objective of this work is to experimentally investigate the effect of upward pipe inclinations (horizontal to vertical upward) on gas-liquid two phase flow phenomenon. To accomplish this objective, experiments focused on flow visualization, void fraction, pressure drop and heat transfer measurements in non-boiling gas-liquid two phase flow are carried out in 12.7mm I.D. polycarbonate and 12.5mm I.D. stainless steel pipes using air-water as fluid combination. Different flow patterns are generated by varying the gas and liquid phase mass flow rates in a range of 0.001–0.2kg/min and 1–10kg/min, respectively. Experimental data for void fraction, pressure drop and heat transfer coefficient is analyzed for its dependency on phase flow rates and pipe inclination. Two distinct trends of the relation between these two phase flow variables and the phase flow rates or alternatively the flow patterns are observed. The experimental results show that increase in pipe inclination from horizontal significantly affects the void fraction, total pressure drop and heat transfer coefficient at low values of gas and liquid flow rates. With increase in the gas and liquid flow rates, effect of pipe inclination on two phase flow variables is observed to diminish. The issue of decreasing pressure gradient minimum in upward pipe inclinations is analyzed using non-dimensional form of gas and liquid flow rates. Finally, based on the heat transfer measurements, the circumferential variation of two phase heat transfer coefficient and its relation to the flow symmetry is discussed.

Classification of Pressure Gradient of Human Common Carotid Artery and Ascending Aorta on the Basis of Age and Gender

The current work is done to see which artery has more chance of having cardiovascular diseases by measuring value of pressure gradient in the common carotid artery (CCA) and ascending aorta according to age and gender. Pressure gradient is determined in the CCA and ascending aorta of presumed healthy volunteers, having age between 10 and 60 years. A real 2D model of both aorta and common carotid artery is constructed for different age groups using computational fluid dynamics (CFD). Pressure gradient of both the arteries are calculated and compared for different age groups and gender. It is found that with increase in diameter of common carotid artery and ascending aorta with advancing age pressure gradient decreases. The value of pressure gradient of aorta is found less than common carotid artery in both cases of age and gender.

Pressure profiles of sport compression stockings.

While sport compression stockings (SCS) have become increasingly popular, there is no regulatory norm as exists for medical compression stockings (MCS). The objective of this pilot study was to compare five SCS with respect to their pressure profiles ex vivo and in vivo, and in relation to German standards for MCS (RAL norm). In vivo (10 competitive athletes; standardized procedure using the Kikuhime pressure monitor) and ex vivo (tested at the Hohenstein Institute) pressure profiles were tested for the following products: CEP Running Progressive Socks, Falke Running Energizing, Sigvaris Performance, X-Socks Speed Metal Energizer, and 2XU Compression Race Socks. Ex vivo ankle pressures of CEP (25.6mmHg) and 2XU (23.2mmHg) corresponded to class 2 MCS; that of Sigvaris (20.8mmHg), to class 1 MCS. The remaining SCS achieved lower pressure values. The pressure gradients showed marked differences, and did not meet MCS standards. Average in vivo pressures were higher for 2XU, CEP, and Sigvaris than for Falke and X-Socks. However, in vivo values for all SCS were below those of class 1 MCS. None of the SCS showed the decreasing pressure gradient (from distal to proximal) required for MCS. In vivo and ex vivo pressure profiles of all SCS examined showed marked heterogeneity, and did not meet MCS standards. Consequently, the clinical and practical effects of SCS cannot be compared, either. It would therefore be desirable to establish a classification that allows for the categorization and comparison of various SCS as well as their selection based on individual preferences and needs (high vs. low pressure, progressive vs. degressive profile).

Dependence of pedestal structure on collisionality at fixed beta in JT-60U

The dependence of pedestal structure on collisionality at fixed beta has been investigated in JT-60U. In the ITER-relevant low collisionality regime, the pedestal width does not change with edge collisionality. In the high collisionality regime, the pedestal width broadens with increased edge collisionality. The pedestal pressure gradient and width are not significantly changed when the pedestal is close to an intermediate n peeling-ballooning mode boundary at low collisionality. The experimental result indicates that conventional pedestal models where the pedestal width is independent of collisionality and is determined by at the pedestal is not a bad assumption in the ITER-relevant low collisionality regime. On the other hand, the pressure gradient decreases and the pedestal width increases at high collisionality. The pedestal broadening becomes significant when the pedestal is marginal to be unstable at the high n ballooning mode in the high collisionality regime.

Risk Factors for Hepatic Encephalopathy after Transjugular Intrahepatic Portosystemic Shunt in Patients with Hepatocellular Carcinoma and Portal Hypertension.

This study aimed at assessing the risk factors for hepatic encephalopathy (HE) after transjugular intrahepatic portosystemic shunt (TIPS) in patients with hepatocellular carcinoma (HCC) and portal hypertension. Consecutive patients (n=279) with primary HCC who underwent TIPS between January 1997 and March 2012 at a single institution were retrospectively reviewed. Patients were followed up for 2 years. Pre-TIPS, peri-TIPS and post-TIPS clinical variables were reviewed using univariate and multivariate analyses to identify risk factors for HE after TIPS. The overall incidence of HE was 41% (114/279). Multivariate analysis showed an increased odds for HE in patients with: &gt;3 treatments with transcatheter arterial chemoembolization (TACE) and/or trans-arterial embolization (TAE) (odds ratio [OR], 4.078; 95% confidence interval [95%CI], 1.748-9.515); hepatopetal portal flow (OR, 2.362; 95%CI, 1.032-5.404); high portosystemic pressure gradient (OR, 1.198; 95%CI, 1.073-1.336) and high pre-TIPS MELD score (OR, 1.693; 95%CI, 1.390-2.062). Odds for HE were increased 1.693 fold for each 1-point increase in the MELD score, and 1.198 fold for each 1-mmHg decrease in the post-TIPS portosystemic pressure gradient. The identification of clinical variables associated with increased odds of HE may be useful for the selection of appropriate candidates for TIPS. Results suggest that an inappropriate decrease in the portosystemic pressure gradient might be associated with HE after TIPS. In addition, >3 treatments with TACE/TAE, hepatopetal portal flow, and high MELD score were also associated with increased odds of HE after TIPS.