Number Flow Research Articles

Choriocapillaris Assessment In Patients Under Mek-Inhibitor Therapy For Cutaneous Melanoma: An Optical Coherence Tomography Angiography Study

ABSTRACT Purpose: The present study investigates by optical coherence tomography angiography (OCTA) the retinal capillary plexus and choriocapillaris flow voids and their possible correlation with MEKAR. Methods: 34 eyes of 17 patients (61.5 years [30.4–77.4]) with stage IV cutaneous melanoma were included prospectively. All patients showed disease progression under treatment with Nivolumab/Ipilimumab and were subsequently treated with the MEK-inhibitor Trametinib 2 mg once daily. At the start and every 6 weeks during follow-up of 4 months, patients underwent a complete ophthalmologic exam, OCTA and when needed fluorescein angiography. Results: Statistical analysis was performed on 17 eyes of 9 patients. Eight patients were excluded due to missing OCTA images or due to drop-out because of decease or change of treatment. Comparing vessel area density (P = .625 and 0.681, respectively), vessel skeleton density (P = .996 and 0.766, respectively) of the superficial and deep capillary plexus, flow void number and total flow void area (mm2 and %) (P = .495; 0.197 and 0.298, respectively) of choriocapillaris slab, before and after treatment, revealed no significant difference. The evolution of choriocapillaris flow void parameter did not significantly differ in patients, who developed MEKAR compared to patients who did not. Conclusion: In patients receiving MEK-inhibitor with and without MEKAR, no significant different characteristics of the retinal capillary plexus and choriocapillaris were found. These data suggest that the development of MEKAR, has no correlation with vascular alteration.

Evaluating the influence of humidity on asphalt mixture performance by the flow number test

Moisture damage greatly influences the performance of asphalt pavements. However, existing studies evaluating the moisture sensitivity of asphalt mixtures either ignore the influence of water vapor or use inappropriate testing methods. This study examined the moisture sensitivity of asphalt mixtures by using the flow number (FN) test. Four levels of the humidity condition (2%, 50%, 80% and 100% RH) were first designed to condition specimens, after which the FN test was employed to assess the moisture susceptibility of mixtures. The results show that it took 50 days for specimens to reach humidity equilibrium at Humidity Level 1, while approximately 4300 h (180 days) were required for specimens to achieve the respective Humidity Levels 2, 3, and 4. The evaluation indicators—in other words, FN, the onset of the secondary stage N4, their corresponding permanent strains (PS2 and PS3), and the slope of secondary stage S2—were then determined by applying a two-step secant method. It was observed that N4 and FN exhibit a gradually decreasing tendency, while PS2 and PS3 tend to increase with the rise in humidity level, but this phenomenon seems indiscernible in some groups. A newly modified exponential function model was proposed to characterize the interaction between humidity levels and S2. It was also demonstrated that the slope of the secondary stage is positively correlated with humidity conditions, which indicates that more deformation will occur with a faster deformation rate during higher humidity levels. The combined use of FN and S2 is a recommended way to assess the trend of permanent deformation of asphalt mixtures under different humidity conditions.

Turbulent flow and heat transfer in a partially filled ventilated cavity using the local thermal non-equilibrium method

In this study, a thermal energy storage system is modeled as an axisymmetric ventilated cavity partially filled with a porous medium that is subject to turbulent flow. Local thermal non-equilibrium is considered to analyze the heat transport and the turbulent k−ε model is used to account for the high inlet flow velocities. Finite volume method is employed for discretization of the equations that are relaxed with the SIMPLE method. The investigation is concerned with the turbulence field, heat fluxes and pressure drop in the system relative to variations in Reynolds number (from 8.3 × 103 to 5 × 104), porosity (ϕ from 0.6 to 0.8) and Da number (from 4x10−5 to 4x10−7). Results indicate that porosity effects slight changes in the turbulence field while the temperatures increase significantly faster for higher porosity cases. Turbulence in higher porosity cases was lower, accompanying the increase in thermal efficiencies. Variations in Da number with fixed porosity showed that, for lower Da number, recirculation in the clear region increased while for higher Da number porous region turbulence increased. Also, higher Da decreased heat exchange between fluid and solid phases. Finally, an increase in thermal efficiency for lower Da number flows was followed by increased average turbulent kinetic energy and relative pressure drop.

Experimental research on the influence of aviation fuel temperature on swirl nozzle velocity

The purpose of this research was to explore the effects of various fuel temperatures on the injection velocity of swirl nozzles. A phase Doppler particle analyzer (PDPA) and particle image velocimetry (PIV) were used to measure the velocity of fuel sprayed by an injector into the normal atmosphere. The flow characteristics and velocities of the droplet were studied at low to high temperatures (−40 °C to 80 °C). The results showed that: 1) the flow number (FN) and mass flow of the swirl nozzle decreased with the increase of the fuel temperature under the same supply pressure; 2) the existence of “pressure critical point” and “temperature critical point” makes the nozzle flow pattern and spray pattern change, thereby changing the distribution of droplet velocity and particle size in space; 3) the PDPA measurement results showed that under the same supply pressure, a larger droplet velocity on the fuel mist cone and a smaller Sauter Mean Diamter (SMD) were measured at high temperature of fuel.

Observations of salinity, flushing time and dispersion in the Waitemata Estuary

ABSTRACT The physical behaviour of estuaries controls the transport of substances from freshwater to the ocean. We conducted the first investigation of salinity distribution and its response to spring-neap tides and freshwater flow rates in the Waitemata Estuary, and estimated several estuarine parameters. Four surveys were conducted: two surveys were conducted in summer during spring-tide, low flow and neap-tide, high flow conditions and two in June during spring-tide, high flow and neap-tide, low flow conditions. The vertical and longitudinal salinity variations were measured with shipboard surveys and river flow data were provided from gauged stations. We found the Waitemata Estuary can be classified as a well-mixed estuary due to the combination of strong tidal currents and weak river flow. Highwater slack stratification can reach 0.5 psu over 10 m during times of weak tidal mixing (neap tides) and with increased freshwater flows after a storm. The estimated freshwater flushing time varied from a week to a month. Dispersion coefficients varied from 50 to 150 m2 s−1 on average, depending on river flows and the location along the channel. Using the Simpson number and historical river flows, we expect stronger stratification could develop in the upper estuary during high flows, temporarily creating a partially-mixed estuary.

The effect of different loading patterns on the resistance to shear flow of hot mix asphalt

The aim of this study was to evaluate the performance of hot mix asphalt against shear deformations. Loading axles (single, tandem and tridem) as well as vehicle speed were considered as research variables. The combination of research variables creates different loading scenarios with different loading pulse times. Using theoretical principles, loading scenarios similar to the field mode were simulated. Then, using the repeated load uniaxial test (RLUT), a quantitative analysis was performed on the mentioned variables. Flow number (FN) and tertiary flow (TF) were used as quantitative output parameters to analyze the test results. In addition, the regression coefficients of the power-law model represent the effect of initial densification and shear flow. It was observed that at higher speeds and in the mode of multiple axles, the initial densification had more effect on the permanent strain compared to the effects of the shear flow. On the other hand, in the single axle, the shear flow was the dominant factor at all speeds. At the middle speed (60 km⁄h), the shear flow (the slope) was the dominant parameter for the tridem axle. Low pulse times, high speeds and proximity of the load impact peaks can cause higher initial densifications in multiple axles. It was also indicated that by increasing the number of axles, values of the FN and the TF, and the value of the interval between these two parameters reduced. This reduction became more tangible by increasing the number of axles from single to other axle modes. In all axle modes, by increasing the speed, the FN and the TF increased. The rate of these increases was higher when transitioning from low speed (20 km⁄h) to middle speed (60 km⁄h) was more intense. Therefore, low speeds had more destructive effects. Thus, higher speeds reduced the destruction effects of multiple axles loads and increased the service life of the mixtures, and improved their performance against shear deformations.

Experimental investigation on the rutting resistance of permeable friction courses

This paper presents an experimental investigation on the rutting resistance of permeable friction courses (PFC). In practice, PFC are prone to permanent deformation due to heavy traffic loads and a weak mineral skeleton caused by their high air void contents. Consequently, the draining capacity of the PFC is diminished making the roads unsafe in wet conditions. Hence, the rutting mechanism of PFC is evaluated through three laboratory tests: dynamic modulus (DM), flow number (FN), and Hamburg wheel tracking test (HWTT). The samples were prepared and compacted considering four air voids (AV) contents: 18%, 20%, 22% and 25%. From the HWTT, a comparative analysis was conducted using X-ray computer tomography (X-ray CT) images obtained before and after the tests in order to investigate AV distribution due to rutting. The results show that the dynamic modulus, the flow number and the rutting response are severely affected by increasing the AV content in the PFC mixes. After increasing the AV content, the dynamic modulus and the flow number decreases significantly, while the rutting depth increases. From the analysis of the X-ray CT images, a larger AV densification was observed in the upper part of the samples beneath the developed rut, whereas in the bottom part the AV content increased further weakening the mineral skeleton.

Hydrodynamics of an inertial active droplet

Abstract

Performance characteristics of asphalt mixtures with industrial waste/by-product materials as mineral fillers under static and cyclic loading

The mineral filler is an integral constituent of asphalt mixture, which affects its performance. This research investigates the effect of using four local industrial waste/by-product materials (marble, granite, steel slag and hydrated lime powder) as mineral fillers on asphalt mixtures characteristics. The detailed performance of these materials as well as asphalt binder and asphalt mixture characteristics are presented. In Egypt, limestone powder is a typical mineral filler in asphalt mixture composition. A control asphalt mixture with limestone mineral filler is designed using Marshall method. Other four asphalt mixtures are prepared using similar constituents and volumetrics except replacing the limestone filler with other types of industrial waste/by-product materials, while maintaining the same percentage of mineral filler as in the control mix. Marshall stability and moisture-induced damage of the investigated asphalt mixtures are determined and compared to the control asphalt mixture results. In addition, the performance characteristics of the investigated mixtures are evaluated by conducting cyclic performance tests including the dynamic modulus (E*) and flow number (FN). Testing results show that the asphalt mixture containing marble as a filler yields the highest stability; while, the hydrated lime filler noticeably enhances the performance of the asphalt mixture in terms of moisture damage resistance, E*, and FN. Unexpectedly, steel slag filler does not improve the asphalt mixture performance. Finally, the stiffness of the investigated mixtures is evaluated using three well-known E*-predictive models (NCHRP 1-37A, Hirsh, and NCHRP 1-40D); while, the resistance of the investigated mixtures to permanent deformation is evaluated using a calibrated version of Apeagyei-literary model based on the investigated mixtures to predict FN at 54.4°C and 1 Hz frequency.

Refinement and estimation of asphalt flow number using partial load history

Abstract The effect of tertiary flow length on asphalt concrete (AC) flow number (FN) has been studied in this paper. The standard FN test (AASHTO T378) designated by American Association of State Highway and Transportation Officials (AASHTO) is currently among the widely adopted test for assessing the rutting performance of AC mixtures. The standard adopts the Fracken model (FM) for fitting the permanent deformation curve (PDC), prior to FN estimation. The FN was observed to vary as tertiary flow progresses. The FM, along with other PDC models (MFM-1 and MFM-2) obtained by modifying the FM, was utilized to analyze and minimized this variation. Variation of FN resulted because of mathematization of the PDC data. Instead of representing the actual initiating point of permanent shear deformation of the strain data, estimated values of FN were observed to indicate the inflection points of the fitted parent curve. As per standard FN range suggested by AASHTO T378, the observed variation in FN leads to the situation, where a single asphalt mix specimen can be regarded as appropriate for two different traffic levels, depending on the tertiary flow point at which the test is terminated. Supplementary steps in the FN estimation methods were proposed for refinement of FN values. For the refinement and further standardization of FN value and FN test respectively, FN:T (flow number to test duration ratio) has been recognized as the key and most simple solution. Two potential options for employing FN:T in the estimation of FN have also been highlighted. Several important correlations have been reported herein as well. Comparatively, MFM-1 was found to be more robust in FN:T curve utilization than MFM-2 and FM.

Effect of particle orientation on the drag force in random arrays of oblate ellipsoids in low‐Reynolds‐number flows

AbstractThrough particle‐resolved direct numerical simulations of flows past random arrays of oblate ellipsoids at low Reynolds numbers, this work demonstrates how the drag force on oblate ellipsoids depends on the Hermans orientation factor S, the mean crosswise sphericity φ⊥, the aspect ratio AR, and the solid volume fraction c. Wide ranges of S, AR, and c are considered and they are in the intervals (−0.5, 1), (0.2, 0.8), and (0.1, 0.4), respectively. This study extends the work on prolate ellipsoids by Li et al (AIChE Journal, 2019, 65, e16621). Based on the simulation results, two models are respectively developed using S and φ⊥as the independent orientation factor. The model based on S could give accurate prediction of the drag force and the lateral force exerted on arrays of particles. The model based on φ⊥ is able to use one generalized drag correlation for both oblate and prolate ellipsoids.

Temperature Wave Fatigue Damage and Dissipated Energy Approach to Flow Number Estimation of Asphalt Concrete

Abstract The effect of sinusoidal temperature on the fatigue life of asphalt concrete (AC) under continuous loading was investigated. The traditional failure criteria of 50 % loss in stiffness, stiffness ratio, and dissipated energy ratio were employed to analyze the AC fatigue test results. Dissipated energy approach and dissipated energy ratio were also extended to estimate the flow number (FN) of AC. The varying temperature induces a continuously changing temperature gradient across the AC beam. This, in turn, triggers the formation of continuously alternating weaker and harder outer layer relative to the beam core, thus creating a stiffness undulation. The combined effect of the load and temperature cycles resulted in a stiffness diminishing trend similar to that of damped harmonic vibration energy. The bottom of the beam is subjected to additional tensile strain/stress for a negative temperature gradient, while the top of the AC beam is subjected to additional compressive strain/stress for a positive temperature gradient. The temperature amplitude and period have a significant influence on the diminishing trend of the stiffness. Results from all the fatigue life estimation and prediction methods employed showed that the fatigue life of AC under variable temperature is shorter than that under constant temperature. However, the effect of the variable temperature is felt much more at lower strain loading. Nonrecovered strain energy method was successfully employed to estimate the AC FN.

Modeling and simulation of a supercritical CO2-liquid sodium compact heat exchanger for sodium-cooled fast reactors

The study focuses on modeling and simulations of sodium-sCO2 intermediary compact heat exchangers for sodium-cooled fast reactors (SFR). A simplified 1-D analytical model was developed in companion with a 3-D CFD model. Using classic heat transfer correlations for Nusselt number, some simulation results using the 1-D model have achieved reasonable match with the CFD simulation results for longer channels (i.e., 40 cm and 80 cm). However, for short channel (10 cm) when axial conduction within the sodium fluid is significant, the 1-D model significantly over-predicted the heat transfer effectiveness. By incorporating the temperature-jump model, the 1-D model can extend its predictive capability for low-Prandtl number fluid/Peclet number flows. The results can help improve the understanding of heat transfer for sodium and low-Prandtl number fluids in general and improve designs of sodium-sCO2 compact heat exchangers. The results also confirmed that the sCO2 side dominates the overall heat transfer for Na-sCO2 heat exchangers. A preliminary attempt of optimizing the channel geometry shows mixing results – while heat transfer effectiveness was significantly increased for the wavy channel, much greater pressure drop was also predicted by the simulations.

Orographic effects on the propagation and rainfall modification associated with the 2007–08 Madden–Julian oscillation (MJO) past the New Guinea Highlands

Based on the tropical rainfall measuring mission (TRMM)-measured rainfall and estimated outgoing longwave radiation (OLR) fields, it is found that 2007–08 Madden–Julian Oscillation (MJO07-08) went through blocking, splitting, and merging stages when it passed over the New Guinea Highlands (NGH). The TRMM-estimated OLR fields fail to capture detailed TRMM rainfall field and thus is not suitable to serve as proxy for rainfall, as also found in previous studies. The mechanism of orographic blocking is explained by strong orographic blocking on the incoming, low-Froude number, and moist flow, which belonged to the flow-around regime. This is evidenced by estimating the Froude number by upstream soundings. The strong blocking forced the flow to go around the mountains on NGH, leading to the splitting of flow and MJO precipitating system and the merging at the southeast tip of New Guinea. Orographic, MJO, and cyclone clouds were shown in both observed and model-simulated results. The major differences of the model-simulated and TRMM-measured precipitation are as follows: (a) the model-simulated rainfall area is much larger than that covered by the observed rainfall and (b) even though they both show comparable maximum rainfall rate, the rainfall estimated by TRMM reveals more localized rainfall spots, which is unexpected since the WRF simulation uses a relatively fine resolution (5 km). In summary, during the blocking stage, the mountains have slowed down the MJO propagation and increased the rainfall amount upstream of the local mountains, while during the splitting and merging stages, the mountains have made significant impacts on the MJO rainfall distribution.

Accuracy Verification of a 2D Adaptive Mesh Refinement Method Using Backward-Facing Step Flow of Low Reynolds Numbers

Identifying centers of vortices of fluid flow accurately is one of the accuracy measures for computational methods. After verifying the accuracy of the 2D adaptive mesh refinement (AMR) method in the benchmarks of 2D lid-driven cavity flow, this paper shows the accuracy verification by the benchmarks of 2D backward-facing step flow. The AMR method refines a mesh using the numerical solution of the Navier–Stokes equations computed on the mesh by an open source software Navier2D which implemented a vertex centered finite volume method (FVM) using the median dual mesh to form control volumes about each vertex. The accuracy is shown by the comparison between vortex center locations calculated from the linearly interpolated numerical solutions and those obtained in the benchmark. The AMR method is proposed based on the qualitative theory of differential equations, and it can be applied to refine a mesh as many times as required and used to seek accurate numerical solutions of the mathematical models including the continuity equation for incompressible fluid or steady-state compressible flow with low computational cost.

Performance and blending evaluation of asphalt mixtures containing reclaimed asphalt pavement

This study aims to (1) determine an optimum amount of Reclaimed Asphalt Pavement (RAP) such that its addition does not adversely impact the fracture resistance of asphalt mixtures, and (2) determine the amount of RAP binder that is active in the total mix. For this purpose, the asphalt mixtures containing three RAP contents (15, 25 and 35%) and their recovered binders were characterized. The binders were subjected to the performance grading, frequency sweep, multiple stress creep and recovery (MSCR) and linear amplitude sweep (LAS) tests. The mixtures were evaluated using dynamic modulus, Hamburg Wheel Tracking (HWT), Flow Number (FN), Semi Circular Bend (SCB), and Ideal Cracking Tolerance (Ideal-CT). The blending efficiency of the RAP binder was determined using the Hirsch model. Based on the performance results and the relatively low binder content of asphalt mixtures in Qatar, it is recommended to use up to 20% RAP in asphalt mixtures.

Effect of aggregate shape properties and binder’s adhesiveness to aggregate on results of compression and tension/compression tests on hot mix asphalt

The mechanical behavior of hot mix asphalt is affected by their constituent properties, i.e., aggregate and asphalt binder properties. The loading path used in laboratory testing is also a factor that may influence results. The objective of this work was to investigate the effect of aggregate particle shape properties and texture, as well as of the aggregate-binder adhesion, on different tests used to evaluate mixture resistance: indirect tensile strength in axial compression (ITS); moisture-induced damage—modified Lottman; uniaxial repeated load permanent deformation—Flow number (FN); dynamic modulus, both at compression and at tension/compression; and tension/compression fatigue life. The Aggregate Image Measurement System was used for analyzing aggregate particle shape properties. Asphalt Bond Strength test results were used as an indicator of aggregate-binder adhesion. The results indicate that the binder is relatively more important for tension/compression tests, while aggregate properties are relatively more important for compression tests. For the latter, the higher the load applied in the test, the greater the importance of the aggregate to the mixture result, which is expected since this favors interlocking. ITS and FN results appear to be strongly affected by aggregate sphericity and texture. Dynamic modulus at compression depends more on aggregate shape properties, while fatigue life is more influenced by aggregate-binder adhesion.

A lattice Boltzmann study of 2D steady and unsteady flows around a confined cylinder

In this work, the lattice Boltzmann (LB) method was applied to simulate incompressible steady and unsteady low Reynolds number (Re) flows around a confined cylinder. In the LB method, different collision models (Bhatnagar–Gross–Krook model, two-relaxation-time model, multi-relaxation-time model, and entropic lattice Boltzmann model) and a regularization model were used, and the results were compared. Numerical results pertaining to a two-dimensional flow around a cylinder are reported and compared with numerical and experimental data available in the literature. The results agree with the predictions made from the literature. A correlation for Strouhal number (St) for 55 le Re le 300 is suggested.

Prediction of Drag Reduction Rate in Turbulent Channel Flow Based on BP Neural Network

The technology of turbulent drag reduction by viscoelastic additives cannot be widely applied in practical engineering due to the difficulty in judging the effect of drag reduction. To solve this problem, the experiment of drag-reducing channel flow of polymer solution was carried out based on the comprehensive analysis of the factors affecting the drag reduction rate. Abundant drag reduction rate data were obtained. A three-layer BP neural network prediction model was established with polymer solution concentration, Reynolds number and injection flow rate as input parameters. Based on the test results, the prediction accuracy on drag reduction rate of the model was analysed. The prediction and model validation of drag reduction rate are carried out further according to the historical data in literature. The results show that the predicted drag reduction rate of BP neural network is close to the real drag reduction rate in the drag-reducing flow of polymer solution. The prediction is with high accuracy and with good generalization ability. It is expected to be applied to practical projects and to promote the development of turbulent drag reduction technology by additives.

Vibration Performance of a Flow Energy Converter behind Two Side-by-Side Cylinders

Flow-induced vibrations of a flexible cantilever plate, placed in various positions behind two side-by-side cylinders, were computationally investigated to determine optimal location for wake-excited energy harvesters. In the present study, the cylinders of equal diameter D were fixed at center-to-center gap ratio of T / D = 1 . 7 and immersed in sub-critical flow of Reynold number R e D = 10 , 000 . A three-dimensional Navier–Stokes flow solver in an Arbitrary Lagrangian–Eulerian (ALE) description was closely coupled to a non-linear finite element structural solver that was used to model the dynamics of a composite piezoelectric plate. The cantilever plate was fixed at several positions between 0 . 5 < x / D < 1 . 5 and - 0 . 85 < y / D < 0 . 85 measured from the center gap between cylinders, and their flow-induced oscillations were compiled and analyzed. The results indicate that flexible plates located at the centerline between the cylinder pairs experience the lowest mean amplitude of oscillation. Maximum overall amplitude in oscillation is predicted when flexible plates are located in the intermediate off-center region downstream of both cylinders. Present findings indicate potential to further maximize wake-induced energy harvesting plates by exploiting their favorable positioning in the wake region behind two side-by-side cylinders.