Maximum Flow Research Articles

Effect of High-Intensity Focused Electromagnetic Technology in the Treatment of Female Stress Urinary Incontinence

Background: The aim of the study was to assess the effect of high-intensity focused electromagnetic (HIFEM) technology in the treatment of female stress urinary incontinence (SUI). Materials and Methods: 20 women with SUI were delivered a treatment course with HIFEM technology. Patients attended 6 therapies scheduled twice a week. Validated questionnaires were assessed, including the overactive bladder symptoms score (OABSS), urogenital distress inventory-6 (UDI-6), incontinence impact questionnaire-7 (IIQ-7), international consultation on incontinence questionnaire (ICIQ), and valued living questionnaire (VLQ). Some urodynamic parameters, such as maximum flow rate (Qmax), residual urine (RU), and bladder volume at first sensation to void (Vfst). Bladder neck mobility in ultrasound topography was also collected pre- and post-treatment at 1- and 6-month follow-up visits. Results: HIFEM treatment significantly improved SUI symptoms on pad tests from 4.2 ± 5.5 to 0.6 ± 1.3 and patients’ self-assessment in the 6-month follow-up. Additionally, the data from urinary-related questionnaires, including OABSS (5.3 ± 3.9 to 3.9 ± 3.6), UDI-6 (35.7 ± 22.3 to 15.2 ± 10.6), IIQ-7 (33.1 ± 28.7 to 14.3 ± 17.2), and ICIQ (9.4 ± 5.0 to 5.4 ± 3.6), all showed a significant reduction. Then, the analysis of the urodynamic study revealed that only maximum urethral closure pressure (MUCP) (46.4 ± 25.2 to 58.1 ± 21.2) and urethral closure angle (UCA) (705.3 ± 302.3 to 990.0 ± 439.6) significantly increased after the six sessions of HIFEM treatment. The urethral and vaginal topography were performed and found that HIFEM mainly worked on pelvic floor muscles (PFM) and enhanced their function and integrity. Conclusions: The results suggest that HIFEM technology is an efficacious therapy for the treatment of SUI.

Adaptive high flow oxygen therapy: New concept

Background High-flow oxygen therapy (HFOT) is increasingly utilized in clinical settings due to its potential to improve oxygenation, patient comfort and possibly outcomes in different respiratory failure states. The potential benefits of HFOT include matching the patients’ flow to reduce the work of breathing, creating airway pressure, humidification, and reducing dead space. However, it has some shortcomings including the difficulty of setting the flow to match patients’ efforts, the continuous flow does not represent normal physiologic spontaneous breathing, and the lack of traditional airway pressure monitoring. We are testing a new adaptive high-flow oxygen delivery technique “Auto Positive Airway Pressure” (Auto-PAP) where the flow delivered from the ventilator adapts to patients’ efforts taking into consideration the patients’ dead space Methods A bench study using ASL 5000 simulator, we created a single-compartment active model of a male with IBW 70 kg, with compliance of 40 ml/cmH20 and resistance of 10 cmH2o/L/s. The respiratory rate was set at 20 bpm, with inspiratory time of 1 second. Muscle pressure (Pmus) was gradually increased by increments of 5 cmH2O from 5 to 50. Adaptive high flow mode (Auto PAP) using a Bellavista 1000e ventilator (Zoll MA, USA) using a large bore nasal cannula to an adult-sized mannequin nose that was connected to the lung simulator. Pearson correlation coefficient was used in correlating the Pmus to the maximum, mean flow and pressure, and the simulator to the ventilator flow. Results There was significant strong correlation between the Pmus and the maximum flow R: 0.949, CI (0.794, 0.988) P < 0.001, and mean flow R: 0.955, P < 0.001, CI (0.816, 0.989). There was a significant strong correlation with Pmus and the maximum pressure R: 0.972, P < 0.001, CI (0.883, 0.993) and mean pressure R: 0.942, P < 0.001, CI (0.768, 0.986). There was significant strong correlation between the simulator and the ventilator flow R: 0.961, P < 0.001. There was significant strong correlation between the simulator and the ventilator mean pressure R: 0.951, P < 0.001, CI (0.799, 0.988). There was significant strong correlation between the mean flow from the ventilator to the mean airway pressure measured at the simulator R: 0.936, P < 0.001 CI (0.747, 0.985). Conclusion Results suggest a significant correlation between the flow and pressure from adaptive HFOT and the patient muscle effort, indicating that the flow and pressure increase in response to the patients’ effort. This may reduce respiratory muscle workload compared to traditional high flow oxygen therapies and reduce the need for multiple manual adjustment of the flow. These findings underscore the potential of this technology to enhance respiratory support while minimizing patient effort. Further research is warranted to validate these findings in real patient cohorts in diverse clinical scenarios. Keywords: High flow oxygen therapy, mean flow, mean pressure

How to measure peak expiratory flow rate.

Peak expiratory flow rate (PEFR) is an important test in the diagnosis and monitoring of respiratory conditions, especially asthma. PEFR measures the speed at which air is forcefully exhaled from full inspiration, expressed in litres per minute (L/min). It involves using a peak flow meter - a simple, affordable, portable and widely available device that can be used in clinic or home settings. Nurses obtaining a patient's PEFR must have the knowledge and skills required to do so safely and effectively and must work within their level of competence. • PEFR is a simple-to-obtain measure that records the maximal flow rate of air that can be achieved in one forceful expiration following a full inspiration. • Where possible, it is advisable that patients and/or carers learn how to perform the test themselves, so that they can self-manage and monitor conditions such as asthma and chronic obstructive pulmonary disease. • The procedure is simple to teach, but it is necessary to use the correct technique to achieve accurate results. REFLECTIVE ACTIVITY: 'How to' articles can help to update your practice and ensure it remains evidence-based. Apply this article to your practice. Reflect on and write a short account of: • How this article might improve your practice when obtaining a patient's PEFR. • How you could use this information to educate nursing students or colleagues about the technique for obtaining an accurate PEFR.

Some Aspects of the Use of Carbon Dioxide as a Carrier and Makeup Gas in GC–FID Analysis

The paper presents the possibility of using carbon dioxide as a carrier gas in capillary gas chromatography (with a stationary liquid phase) to analyze semi-volatile compounds (boiling points of up to 400 °C). Based on the experiments carried out for compounds from the group of organochlorine pesticides (OCPs), organophosphate pesticides (OPPs), polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), the maximum volumetric flow rate (2.4 mL/min for CO2) was determined, enabling the correct separation of the tested standard mixtures (except for two compounds from the OCP group: 4,4′-DDD and Endrin aldehyde and two other pairs of compounds with Rs slightly less than 1.5). Compared to using helium as a carrier gas (and makeup), carbon dioxide produces wider (about 1.6 times) and lower (about 1.8 times) peaks of analytes; these values can vary depending on the separation efficiency of the column. Carbon dioxide can also be effectively used as a makeup gas for the FID detector. The signal increase is comparable to that obtained with helium used as makeup (on average 40–50% depending on the carrier gas). When high sensitivity and high resolution are not required, CO2 can be an alternative carrier and makeup gas to helium under the same flow conditions. The paper also describes practical aspects related to the implementation of CO2 as a carrier and makeup gas in GC.

Effects of NUSS surgery on degree of flat thoracic cage, cardiopulmonary function, and bone metabolism in pectus excavatum patients of different ages.

This study was to explore the degree of flat thoracic cage (FTC), cardiopulmonary function, and bone metabolism of pectus excavatum (PE) children of different ages after NUSS surgery. A retrospective analysis was conducted on 90 children with PE who underwent minimally invasive pectus excavatum correction surgery (NUSS), divided into three age groups: group I (1-3years), group II (3-6years), and group III (6-12years), with 30 patients in each group. The study compared differences in thoracic flattening index, surgical-related metrics, pulmonary function, peripheral blood levels of alkaline phosphatase (ALP), calcium, magnesium, zinc, and phosphorus, and complication rates among the groups. Preoperative ALP level increased with aging of the children (P < 0.05). After surgery, the FTC index and ALP level of all the three groups greatly decreased, but increased with aging (P < 0.05). The operating time, intraoperative blood loss, and postoperative duration of analgesia also showed a trend of group III > group II > group I (P < 0.05). Postoperative levels of pulmonary function, including vital capacity (VC), forced vital capacity (FVC), forced expiratory volume in 1s (FEV1), peak expiratory flow (PEF), maximum expiratory flow at 75% of vital capacity (MEF75), maximum expiratory flow at 50% of vital capacity (MEF50), maximum expiratory flow at 25% of vital capacity (MEF25), and maximal mid-expiratory flow (MMEF), were significantly higher than preoperative levels in group I (P < 0.05); but without significant changes in groups II and III (P > 0.05). Neglectable differences were found in peripheral blood Ca, Mg, Zn, and P levels before and after surgery and postoperative complications in three groups (P > 0.05). The degree of FTC worsened with aging; the younger the children receiving NUSS surgery are, the more obvious the improvement of postoperative PF.

Comparisons between chest trunk mobilization with sustained maximum inspiration and flow incentive spirometry on chest expansion, respiratory muscle strength, and functional exercise capacity in patients undergoing video-assisted thoracoscopic surgery

IntroductionChest trunk mobilization with sustained maximum inspiration (SMI) and flow incentive spirometry (flow IS) are breathing techniques that mostly apply to patients undergoing video-assisted thoracoscopic surgery (VATS). The purpose of this study was to determine the effects of chest trunk mobilization with SMI and flow IS on chest expansion, respiratory muscle strength, and functional exercise capacity in patients undergoing VATS.MethodsSixty VATS patients were randomly allocated into chest trunk mobilization with SMI (&lt;i&gt;n&lt;/i&gt; = 30) and flow IS (&lt;i&gt;n&lt;/i&gt; = 30) groups. Each group performed a physical therapy program preoperatively and 4 days post-operatively. Chest expansion at upper, middle, and lower levels, inspiratory and expiratory muscle strengths, and functional exercise capacity were determined at pre- and post-VATS.ResultsIn both groups, chest expansion at all levels, expiratory muscle strength, and distance of the 6MWT significantly increased (&lt;i&gt;p&lt;/i&gt; &lt; 0.05) post-operatively compared to pre-operative assessments, although there was no significant difference between groups. In addition, inspiratory muscle strength significantly improved from baseline in both groups (&lt;i&gt;p&lt;/i&gt; &lt; 0.05), but the flow IS group showed a greater increase than the chest trunk mobilization with the SMI group (78.17 ± 24.16 and 65.57 ± 20.39 cmH2O, respectively, &lt;i&gt;p&lt;/i&gt; &lt; 0.05).ConclusionsChest trunk mobilization with SMI and flow IS can improve chest expansion at all levels, as well as respiratory muscle strength and the distance of the 6MWT. However, flow IS enhances inspiratory muscle strength to a greater extent than chest trunk mobilization with SMI. Ultimately, both techniques can be applied effectively in patients undergoing VATS.

Dual-weight decay mechanism and Nelder-Mead simplex boosted RIME algorithm for optimal power flow

The increasing demand for electricity presents substantial challenges in power system planning, particularly optimizing the Optimal Power Flow (OPF) problem. The OPF problem entails establishing the best settings for control variables in a power system to reduce objectives such as generating cost and transmission losses while meeting operational restrictions. This research introduces an upgraded RIME optimization algorithm (WDNMRIME) to address these challenges. WDNMRIME integrates a dual-weight decay mechanism and the Nelder-Mead simplex (NMs), enhancing population diversity and mitigating the risk of local optima. Additionally, NMs expedites convergence by refining the population's optimal solution set. Experimental validation on the IEEE 30-bus test system demonstrates that WDNMRIME achieves a generation cost of $806.00298 per hour and reduces total power loss from 1.43 MW to 1.39 MW. These results surpass the performance of the original RIME algorithm, showcasing a 15% improvement in convergence speed. The algorithm effectively optimizes multiple concurrent Flexible Alternating Current Transmission Systems (FACTS) devices, even under the uncertain nature of wind energy resources modeled using the Weibull probability density function. These findings highlight WDNMRIME's significant contribution to improving OPF optimization in dynamic power systems.

Information-theory-based System-level Babcock–Leighton Flux Transport Model–Data Comparisons

Abstract System-level Babcock–Leighton flux transport model–data comparisons are performed using information theory. The model is run with a maximum meridional flow speed of 16.5 m s−1 with the flow speed systematically varied by 20% (BLFT20) and 50% (BLFT50). Overall, the comparisons show that the models qualitatively capture much of the information flow among the toroidal field (sunspot number), polar field, and meridional flow. BLFT20 generally compares better than BLFT50, suggesting that meridional flow variation of 20% may be more realistic than 50%. However, the information flow from the meridional flow to the polar field is captured better in BLFT50. There is more information flow from the sunspot number to the polar field than the other way around in BLFT20 and observations. The information flow from the polar field to the sunspot number peaks at lag times (τ) of ∼2 yr and 7–9 yr. The results can shed light on the nature of the Sun’s magnetic memory and the diffusive/dissipative processes and advection in the turbulent flux transport at the Sun.

The influence of yoga exercises with voluntary pulmonary ventilation changes on intracranial arterial blood flow

Introduction. Yoga breathing exercises that involve voluntary changes in pulmonary ventilation parameters can potentially influence cerebral circulation due to changes in CO2 content in arterial blood. Objective. To assess the effect of yoga breathing exercises with changes in pulmonary ventilation levels on blood flow parameters in the middle cerebral artery (MCA). Methods. The study included 21 participants, with an average age of 39.5±8.7 years, who were capable of performing yoga exercises at respiratory rates (RR) of 3–3.5/min and 1–1.5/min. For 5 minutes, participants underwent three stages: free breathing (stage 1), breathing with RR=3–3.5/min (stage 2), and breathing with RR=1–1.5/min (stage 3). During stages 2 and 3, the «full breathing» technique, which involves maximum deep inhalation and exhalation, was employed. Respiratory rate (RR), tidal volume (TI), minute ventilation (MV), end-tidal CO2 partial pressure (PetCO2), and oxygen fraction in exhaled air (FeO2) were recorded using spiro-gas analysis. Transcranial duplex scanning was used to measure peak systolic blood flow velocity (Vps), end-diastolic blood flow velocity (Vd), time-averaged maximum blood flow velocity (TAMAX), and resistance index (RI) in the right MCA. The velocity variation index (VVI) was calculated for each stage. Results. Compared to stage 1 (free breathing), stage 2 (RR = 3–3.5/min) showed an increase in MV and FeO2, a decrease in PetCO2, and reductions in Vps, Vd, and TAMAX, with an increase in RI. VVI decreased statistically insignificantly. In stage 3 (RR = 1–1.5/min), compared to stage 1, there was an increase in PetCO2, a decrease in MV and FeO2, and increases in Vps, Vd, and TAMAX, with a decrease in RI. VVI increased significantly. Conclusions. Yoga breathing exercises at respiratory rates of 3–3.5/min and 1–1.5/min result in multidirectional shifts in ventilation and gas exchange parameters, leading to changes in arterial cerebral blood flow (a decrease and increase in blood flow velocity with an increase and decrease in MV, respectively). VVI, reflecting fluctuations in blood flow velocity, increases significantly with reduced MV, likely due to the vasodilatory effect of CO2.

Lower Urinary Tract Dysfunction Among Patients Undergoing Surgery for Deep Infiltrating Endometriosis: A Prospective Cohort Study

Background/Objectives: Postsurgical lower urinary tract dysfunction (LUTD) is a common problem following deep infiltrating endometriosis (DIE) resection. The condition may be caused either by surgically induced damage to the bladder innervation or by pre-existing endometriosis-associated nerve damage. The aim of this study is to evaluate the efficacy of preoperative and postoperative multichannel urodynamic testing (UD) in identifying pre-existing or surgically induced LUTD among patients with DIE. Methods: Women with suspected DIE and planned surgical resection of DIE at the Department of Obstetrics and Gynecology at the University Hospital of Bern from September 2015 to October 2022 were invited to participate in this prospective cohort study. UD was performed before and 6 weeks after surgery. The primary outcome was the maximum flow rate (uroflow), an indicator of LUTD. Secondary outcomes were further urodynamic observations of cystometry and pressure flow studies, lower urinary tract symptoms (LUTS) as assessed by the International Prostate Symptom Score (IPSS), and pain as assessed by the visual analog scale (VAS). Results: A total of 51 patients requiring surgery for DIE were enrolled in this study. All patients underwent surgical excision of the DIE. The cohort demonstrated a uroflow of 22.1 mL/s prior to surgery, which decreased postoperatively to 21.5 mL/s (p = 0.56, 95%CI −1.5–2.71). The mean bladder contractility index (BCI) exhibited a notable decline from 130.4 preoperatively to 116.6 postoperatively (p = 0.046, 95%CI 0.23–27.27). Significant improvements were observed in the prevalence of dysmenorrhea, abdominal pain, dyspareunia, and dyschezia following surgical intervention (p = &lt;0.001). The IPSS score was within the lower moderate range both pre- and postoperatively (mean 8.37 vs. 8.51, p = 0.893, 95%CI −2.35–2.05). Subgroup analysis identified previous endometriosis surgery as a significant preoperative risk factor for elevated post-void residual (43.6 mL, p = 0.026, 95%CI 13.89–73.37). The postoperative post-void residual increased among participants with DIE on the rectum to 54.39 mL (p = 0.078, 95%CI 24.06–84.71). Participants who underwent hysterectomy exhibited a significantly decreased uroflow (16.4 mL/s, p = 0.014, 95%CI 12–20) and BCI (75.1, p = 0.036, 95%CI 34.9–115.38). Conclusions: Nerve-respecting laparoscopy for DIE may alter bladder function. UD is not advisable before surgery, but the measurement may detect patients with LUTD.

An Experimental Study for Radial-Gated Ogee Spillway Discharge and Comparison with Other Model Studies

The book "Design of Small Dams" is a renowned reference publication used for the design of dams in America and it is commonly used in Turkey as well. Flood spillways of many dams are ogee profile radial-gated weirs, and accurate calculation of discharges passing over a partially open radial-gated ogee spillway is important in flood routing computations. Because each spillway and its appurtenant structures have geometrical and hydraulic properties peculiar to their own, a generalizable method for calculating the discharge over a partially open radial-gated spillway should not be realistic. Therefore, many laboratory experimental studies are done both in America and in Turkey for more accurate calculation of spillway discharge of dams individually. With the objective of comparing the results of these studies and the method given in that book another experimental study is performed as summarized in this paper. For this purpose, experiments for the partially open radial gate in a laboratory setup having a 95 mm high, 10 cm wide ogee spillway model with an adjustable radial gate of proportionate dimensions both placed in a 5 meter long, 10 cm wide and 30 cm high channel are done with many combinations of flow rates and gate openings as allowed by the physical dimensions of the open channel setup available in our laboratory and the maximum flow rate its pump can generate. Taking a scale ratio of 1/100, the relative differences of the discharge coefficients given in the above-mentioned book from the experimental discharge coefficients measured in this study for the same configurations are found to be between +3% and +34%. Although the discharge coefficients determined by this experimental study are not too deviant from those obtained from 15 laboratory model studies done by the United States Bureau of Reclamation and the United States Army Corps of Engineers in America and seven such studies done by the State Water Works in Turkey, it is concluded that the discharge – head relationship of a radial-gated spillway of a dam should be determined by a laboratory experiment on a model of not too small a scale, and a generalized method cannot be applicable to all spillways in the world as a whole.

Elastoinertial stability analysis and structure formation in viscoelastic subdiffusive pipe flow

The modal temporal stability analysis of viscoelastic, subdiffusive, pressure driven, axisymmetric pipe flow, representing thick polymer solutions, exhibits the presence of temporally stable regions at high fluid inertia. The stress constitutive equation, previously derived for channel flows [Chauhan et al., Phys. Fluids 35(12), 123121 (2023)] is the fractional variant of the upper convected Maxwell equation. The parameters governing the stability are the Reynolds number, Re=ρU0R0η0, the elasticity number, El=λαη0ρR02, and the ratio of the solvent to the polymer solution viscosity, ν=ηsη0, where R0,U0,ρ,λ,α are the pipe radius, the maximum mean flow velocity, density, the polymer relaxation time, and the fractional order of the time derivative, respectively. The neutral curves indicate, in the limit of small elasticity numbers or in the limit when the viscosity ratio approaches unity, El(1−ν)≪1, that the critical Reynold number, Rec diverges as Rec∼[(1−ν)El]−3α/2, while the critical wavenumber, kc increases as kc∼[(1−ν)El]−α/2. Using a novel fractional variant of the pressure correction method as well as a metric in the Riemannian manifold of symmetric positive definite conformation tensors, the direct numerical simulations quantify the formation of spatiotemporally stable macrostructures (or the non-homogeneous regions of high viscosity) at moderate inertia, thereby corroborating the qualitative features of the experimentally observed flow-instability transition of subdiffusive axisymmetric pipe flows.

An improved body force model based on a data-driven region-segmentation combinational loss model for a transonic fan rotor under uniform and non-uniform inflow

Boundary layer ingestion (BLI) fans are required to continuously operate under distorted inflow conditions, which severely reduces the fan's efficiency. Therefore, it is necessary to focus efforts on designing a high-performance distortion-tolerant fan. During the preliminary design stage of the fan, it is inevitable to repeatedly evaluate the aerodynamic performances of different design cases through low-fidelity computational approaches. However, the predictive accuracy of these low-fidelity computational methods generally depends on the precision of the loss models integrated into them. These loss models are built using simplified physics or human experience, making it difficult to depict the complex non-linear mapping relationships between losses and their influencing factors under BLI inflow distortion. In this work, a high-accuracy data-driven based region-segmentation combinational loss model is used for the first time to attempt to improve the overall prediction accuracy of the body force model. As a low-fidelity computational approach, the body force model has the ability to predict the spatial distribution of three-dimensional, non-uniform flow under inflow distortion conditions. Various operating conditions, including different rotational speeds, radial inflow, and BLI-distorted inflow, are selected to test the predictive accuracy of this improved body force model based on a region-segmentation combinational loss model. The results show that, compared with the one based on traditional loss prediction approach, the improved body force model in this work has shown higher prediction accuracy for the fan adiabatic efficiency characteristic curve. In addition, further evaluations of the flow loss spatial distributions under BLI inflow distortion conditions indicate that the body force model based on region-segmentation combinational loss model can more accurately capture the radial loss distributions at different circumferential locations. Specifically, for the loss distribution in the tip area, it can capture the sharp increase in variation trend near the end wall, and the average prediction errors can be reduced by more than 10% at different annulus locations under various BLI inflow distortions. Meanwhile, this improved body force model also enhances the accuracy of predicting the loss distribution in the circumferential direction at different span positions, including more accurately capturing the circumferential positions corresponding to the maximum and minimum flow losses.

Angiographic reconstructions of CT perfusion for occlusion detection in ischemic stroke

BackgroundBoth CT angiography and CT perfusion involve the administration and tracking of a contrast medium bolus for different purposes. In this study, we aim to compare the diagnostic accuracy and subjective image quality of CTP-angiographic reconstructions with conventional CTA for occlusion detection in ischemic stroke patients. MethodsIn this retrospective study, patients with a final diagnosis of ischemic stroke and who underwent both CTA and CTP from September 2020 up to and including September 2021 were included. CTP-AR was reconstructed from the 1 mm CTP series at the time of maximum arterial inflow. Three readers with different levels of experience assessed both CTA and CTP for occlusion detection, expressed certainty, and rated subjective image quality. The reference standard was set at the consensus meeting. Pooled sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated. Differences in subjective and objective image quality and certainty were assessed using Kendall’s tau correlation and paired samples t-tests. ResultsIn total, 107/210 included patients had an occlusion based on our reference standard. Pooled sensitivity and specificity for occlusion detection were 90 % (95 %CI 85–93 %) and 94 % (95 %CI 90–97 %) for CTA, and 89 % (95 %CI 84–93 %) and 93 % (95 %CI 89–96) for CTP-AR, respectively. The pooled certainty did not significantly differ between CTA and CTP-AR (P=.43). The pooled subjective image quality scores significantly differed between CTA and CTP-AR (τ = 0.3, P < 0.001), where one reader rated subjective image quality higher in CTA and two readers in CTP-AR. ConclusionCTP-AR has comparable diagnostic accuracy to conventional CTA imaging for occlusion detection in ischemic stroke patients. Thus, using CTP-AR instead of CTA plus CTP may conserve contrast medium.

Flow simulation in curved compound channels: Effect of changing the sinuosity of the main channel and width of floodplain

In this research, the effect of different sinuosity (s) and width of floodplain on the flow structures in curved compound channels was investigated numerically. Six different sinuosities of main channel (s = 1, 1.026, 1.096, 1.209, 1.381, and 1.641) and three different relative depths (Dr = 0.26, 0.35, and 0.45) have been used. The findings revealed that with the increase in sinuosity from 1 to 1.641 (64% increase), the maximum flow velocity in the apex section (CS1) and the middle crossover section (CS4) decreases by 23% and 62%, respectively. In the relative depth (Dr) of 0.26, 0.35, and 0.45 with the increase in sinuosity from 1 to 1.641 (with the corresponding decrease in width of floodplain), the ratio of main channel discharge to total discharge (Qmc/Q) is reduced by 40%, 45%, and 45%, respectively. Also, with the increase in relative depth (Dr), the main channel discharge is reduced, and the majority of the flows discharge through floodplain, so that with the increase in the relative depth from 0.26 to 0.45, the amount of Qmc/Q in the channel with maximum sinuosity (s = 1.641) and straight channel (s = 1) decreases by 30% and 14%, respectively. With the increase in sinuosity, the changes of v/u and the angle of flow deviation are more noticeable in the middle sections and above the bankfull level, so that in the most critical state, with an increase in the sinuosity from 1 to 1.641, the relative intensity of secondary flow (v/u) increases from 0 to 3.6, and along a meander, the size of the secondary flow cell in each section becomes larger with increasing sinuosity.

Mechanical Responses and Deformation Mechanisms of Low-Cost High-Entropy Alloy AlCrFe2Ni2 with Heterogeneous Structure Subjected to High-Strain Rate Deformation

Introducing heterogeneous structures into metallic materials through composition design is a promising strategy for simultaneously improving the strength and ductility of the materials. In this work, a novel dual-phase low-cost AlCrFe2Ni2 high-entropy alloy (HEA) was designed and prepared. Its phase constitution, microstructure, dynamic mechanical responses at strain rates ranging from 1100[Formula: see text]s[Formula: see text] to 4800[Formula: see text]s[Formula: see text] as well as deformation mechanisms were investigated. It was found that the HEA consists of FCC, B2 and BCC phases and has a heterogeneous microstructure containing dual-phase alternate lamellar and high-density precipitates. The HEA displays the optimal mechanical properties at the strain rate of 4800[Formula: see text]s[Formula: see text], of which the yield strength, maximum flow stress and strain are 1222.9[Formula: see text]MPa, 2340.8[Formula: see text]MPa and 30.5[Formula: see text]%, respectively, better than that of most single-phase FCC or BCC HEAs, dual-phase HEAs and traditional alloys. The deformation mechanism of the HEA at the strain rate of 4800[Formula: see text]s[Formula: see text] involves both dislocation slip and deformation twinning, with the former dominating. This work could provide guidance and insights for designing metallic materials with excellent mechanical properties at high strain rates.

Flow analysis of steady state forward flow of aortic valve prostheses using Particle Image Velocimetry

Abstract Transcatheter aortic valve replacement (TAVR) has become the standard therapy for aortic valve stenosis in patients with high surgical risk. Understanding the flow dynamics in TAVR is crucial for its evaluation and optimization. Experimental flow measurement by means of Particle Image Velocimetry (PIV) is increasingly applied alongside numerical analyses. This study introduces a novel test rig concept enabling the determination of velocity fields using Stereo-PIV under steady forward flow conditions through a TAVR during the peak systole matching the ISO 5840-1:2021 requirements. The experimental setup utilized an impeller pump to generate steady forward flow through a silicone aortic root model with implanted TAVR. A Stereo-PIV setup captured velocity fields in both ventricular inflow and aortic outflow regions. Test conditions were based on physiological flow rates determined from pulsatile measurements. Illumination of the added particles in the test fluid was achieved using an Nd:YAG laser. Fluorescent polystyrol particles (size: 50 μm) were used for flow visualization. Results showed characteristic flow patterns: a central jet flow entering the TAVR in the ventricular flow field. A jet flow directed towards the sinus side and a recirculation zone forming on the opposite side of the sinus could be detected in the aortic outflow. The width of the recirculation zone increases with distance from the TAVR. Maximum flow velocities were detected at 0.78 m/s for the ventricular flow field and 0.94 m/s for the aortic flow field. This study provides a comprehensive approach for fluid dynamic analysis of TAVR under steady flow conditions, offering insights into flow mechanics performance crucial for device optimization. Further investigations could enhance the PIV - measurement procedure by increasing both the spatial resolution and the tracer particle density within the acquired images for a comprehensive characterization of TAVR flow dynamics.

Comparative analysis of two static var compensator models in voltage control of transmission network

The static var compensator (SVC) is a member of the family of flexible alternating current transmission systems controllers used in power system engineering to manage specific transmission network characteristics to enhance the performance of the transmission networks and thus increase the networks’ reliability. Power system engineers typically find it difficult to choose which SVC model to implement for simulations. This research aims to address this issue by conducting a comparative examination of two key SVC models on a transmission network. The two models of SVC variable shunt susceptance and firing angle were mathematically modeled and methodically included into the Newton-Raphson power flow algorithm for the network power flow solution. The IEEE 30-bus network was adopted as the test case, and the method was implemented in the MATLAB/Simulink environment. The network performance metric utilized was the voltage profile of the network. The two SVC models were successful in enhancing the network's performance; however, the variable shunt susceptance model was computationally faster than the firing angle model, as revealed by the simulation results. Therefore, among the two SVC models, the variable shunt susceptance model may be taken into account for simulation to enhance the performance of the transmission networks.

Formation of Hybrid Membranes for Water Desalination by the Method of Membrane Distillation

A method has been developed for the formation of hybrid membranes consisting of a hydrophilic microporous substrate and a hydrophobic nanofiber polymer layer deposited by electroforming. A track-etched membrane made of polyethylene terephthalate was used as a hydrophilic microporous substrate, on the surface of which a thin layer of titanium was applied by magnetron sputtering to ensure adhesion of the nanofiber layer. Simultaneously, the titanium coating was used to make a conductive track-etched membrane that served as a collector electrode. It is been shown that the application of this method for the formation of polymer coatings when used as a starting material for the formation of polyvinylidene fluoride nanofibers makes it possible to obtain a layer with highly hydrophobic properties, the water contact angle of the surface of which, depending on the deposition density, averages 143.3 ± 1.3°. A study of the morphology of the nanofiber coating shows that it has a microstructure typical of non-woven materials. The nanofibers forming the porous system of this layer have a wide range in size. The study of the molecular structure of the nanofiber layer by IR-Fourier spectroscopy and X-ray diffraction analysis showed that its structure is dominated by the β-phase, which is characterized by a maximum dipole moment. It is been shown that the hybrid membranes of the developed sample provide high separation selectivity when desalting an aqueous solution of sodium chloride with a concentration of 26.5 g/l by membrane distillation. The salt rejection coefficient for membranes with a nanofiber layer density from 20.7 ± 0.2 to 27.6 ± 0.2 g/m2 in the studied mode of the membrane distillation process is 99.97−99.98%. It has been established that the use of a highly hydrophobic nanofiber layer with a developed pore structure in combination with a hydrophilic microporous base makes it possible to increase the productivity of the membrane distillation process. The value of the maximum condensate flow through the membranes is on average 7.0 kg m2/h and its depends on the density of the deposited nanofiber layer.

Documenting weld pool behavior differences in variable-gap laser self-melting and wire-filling welding of titanium alloys

In large-scale welding processes involving complex geometries, variations in gap dimensions and the transition of filler wire form distinctive molten pool flow behaviors, significantly affecting weld formation and quality. This paper investigates the differences in the laser self-melting and wire-filling welding pool behavior of titanium alloy with variable gaps through both simulation and experimentation. An innovative three-dimensional transient heat-flow coupling model is developed to simulate laser welding with variable gap structures, incorporating the dynamics of the welding wire-filling process. The different laser welding modes and the filling process under the variable gap structure were numerically simulated. The results indicate that the maximum flow rate of the laser self-melting pool remains stable in proximity to the keyhole, reaching a maximum of approximately 2.491 m/s, with molten metal entering through the area surrounding the keyhole. As the gap size gradually increases to 0.2 mm during the laser self-fusion welding stage, keyhole instability becomes more pronounced. In transitioning from laser self-fusion to wire-filling welding, the welding wire behavior can be divided into three stages. The molten metal at the end of the welding wire is transferred to the liquid melt pool through a liquid metal bridge. The flow rate of this bridge initially rises before gradually decreasing, reaching a maximum flow rate of 1.606 m/s. Notably, the welding wire lags approximately 0.6 mm behind the laser's focal point, with the narrowest width of the liquid bridge measuring about 0.89 mm. Based on the simulation results and considering the melting transition time of the welding wire, the initiation time for the welding wire has been further adjusted to the first 10 ms when the gap threshold reaches 0.2 mm. Experimental verification confirms the successful laser welding of a 2 mm variable gap structure thin plate. This study elucidates the melt pool flow, keyhole fluctuations, and metal transition behaviors during the laser welding process, contributing to a deeper understanding of the complex heat and mass transfer dynamics inherent in variable gap structure laser self-melting and wire-filling welding. Ultimately, these insights aim to enhance the application of laser welding in adaptive welding for large structural components.