Flow Curves Research Articles

Resting time effects on flow properties of cementitious materials: a study on self-compacting concrete equivalent mortar made with recycled aggregates

The concrete equivalent mortar (CEM) method, mainly used in the laboratory, offers a course that facilitates and accelerates experimental test programs with relatively small amounts of materials. To this end, two CEM mixes, with natural and recycled aggregates, at different superplasticizer (SP) concentrations, were tested. The key objective was to investigate how CEM flow property changed at 0, 30, and 60 min of resting time, emphasizing the material’s structuring and destructuring effects. This study describes the flow behaviour of CEMs applying specific tools. Also, a vane-geometry rheometer was used to obtain rheological flow curves. Whatever the SP content in the structuring state, the results indicated reduced flow properties over time. However, an SP content of 1.3% retard the structural build-up property that was not evident at 60 min-rest time. Spread diameters ranging between 300 and 400 mm are measured with the mini cone immediately after mixing. After 60 min of resting time, these diameters were reduced between 260 and 300 mm. Remixing after prolonged rest periods reduces the flow stress values, which decrease from 10 to 18 Pa to 6 to 14 Pa. After a structural build-up at a rest time, the structural break-down effect by remixing re-fluidifies the mixtures. The fluidity has recovered its initial state, reflecting a thixotropic property.

Screening transparent model fluids to emulate the rheological properties of high solid anaerobic digestate of food waste

Due to the opacity of high solid anaerobic digestate, optical visualization techniques (e.g., particle image velocimetry) cannot be used directly for measuring the flow field inside high solid anaerobic digestion (HSAD) systems. This study mainly focused on selecting suitable surrogate fluids for optical visualization techniques by comparing the flow curves, thixotropic properties, viscoelastic behavior and creep recovery properties of HSAD digestate with a total solid from 10 % to 15 % (w/w) and transparent model fluids. Results indicated that the Bingham model outperformed the power-law model and Herschel-Bulkley model in describing the flow curves of HSAD digestate, xanthan gum and laponite. The digestate and xanthan gum had a similar thixotropic kinetic coefficient of 0.003 and 0.004, respectively. Besides, the digestate and xanthan gum had a similar modulus transformation trend with a power function whose power exponents were 0.17 and 0.19, respectively. In general, xanthan gum can be a suitable substitute for HSAD digestate with a total solid from 10 % to 15 %. The results can guide the implementation of optical visualization techniques to understand the flow pattern within HSAD systems, and improve the mass and heat transfer efficiency during food waste disposal processes.

Global Existence of a Mean Curvature Flow in a Cone

Global Existence of a Mean Curvature Flow in a Cone

Mean curvature flow solitons in warped products: nonexistence, rigidity and stability

Mean curvature flow solitons in warped products: nonexistence, rigidity and stability

Rotationally invariant translators of the mean curvature flow in Einstein's static universe

In this paper, we deal with non-degenerate translators of the mean curvature flow in the well-known Einstein's static universe. We focus on the rotationally invariant translators, that is, those invariant by a natural isometric action of the special orthogonal group on the ambient space. In the classification list, there are three space-like cases and five time-like cases. All of them, except a totally geodesic example, have one or two conic singularities. Also, we show a uniqueness result based on the behaviour of the translator on its boundary. As an application, we extend an isometry of the sphere to the whole translator under simple conditions. This leads to a characterization of a bowl-like example.

Microstructure Prediction of 80MnSi8-6 Steel After Hot Deformation Based on Dynamic Recrystallization Kinetics and FEM Simulation

The microstructure evolution during hot deformation of 80MnSi8-6 nanobainitic steel was investigated through hot compression tests at deformation temperatures of 900–1250°C and strain rates of 0.1–20 s−1. The flow curves revealed strain-hardening behavior at the beginning of deformation followed by softening effects caused by microstructure evolution. A Johnson–Mehl–Avrami–Kolmogorov (JMAK) model for grain growth and dynamic recrystallization was developed, and the kinetics were determined. Critical and peak strains were identified, and coefficients for the microstructure evolution models were determined using linear regression. The analysis of S-curves revealed that decreasing the temperature delays the onset of recrystallization and that the strain rate significantly effects the recrystallization rate at lower temperatures. Constitutive modeling and determination of the Zener–Hollomon parameter allowed the determination of the influence of hot processing conditions on material behavior during deformation. Microstructure analysis showed that, at higher deformation temperatures, grain growth occurs simultaneously with grain refinement. Coefficients for the JMAK model were implemented in QForm software. Simulation results were compared with experimental measurements exhibited good arrangement, which confirms the accuracy of the JMAK model in predicting the microstructure evolution. This study demonstrated how microstructure evolution modeling and FEM simulations combined can be used to predict the grain size of 80MnSi8-6 steel after hot deformation.

Development of a simple calculation method for the conductance of rarefied gas flow in cylindrical pipe applicable to divertor exhaust investigation of nuclear fusion reactor

ABSTRACT A gas pressure distribution calculation method for viscous laminar and intermediate flows is developed. By introducing the pseudo-conductance for viscous laminar flow, linearized equations describing pressure distribution are obtained. In intermediate flow, the pressure distribution is iteratively obtained. The validity of the method is confirmed by demonstrating a pressure in a long-tube flow path with various flow rates. The result smoothly connects theoretical curves of molecular flow and viscous laminar flow between two regions. Then, the calculation method is applied to an actual device and is compared to the measurement. The comparison between the calculation and measurement shows the qualitative agreement and reveals the requirement for a more detailed implementation of the actual conditions.

The Parabolic U(1)-Higgs Equations and Codimension-Two Mean Curvature Flows

The Parabolic U(1)-Higgs Equations and Codimension-Two Mean Curvature Flows

Time-global existence of generalized BV flow via the Allen–Cahn equation

We show that a mean curvature flow obtained as the limit of the Allen–Cahn equation is not only a Brakke flow but also a generalized BV flow proposed by Stuvard and Tonegawa (2024).

Research on the formation of the structure of dairy desserts with a combined composition of raw materials under the influence of technological factors

Subject of study. Dairy products are complex in chemical composition and have a complex of various properties that affect the quality of the fnished product, in particular, its structure. Consumer demands for food quality are constantly growing, which leads to the improvement of technological processes. Therefore, the study of the influence of technological factors in the production of dairy products for dessert purposes on the formation of their structure is an urgent issue. The study aimed to investigate the influence of technological factors, in particular, different temperature regimes of packaging on the structure of the fnished product. The results. The article presents the results of studies on the formation of the structure of pudding and cream packaged at different temperatures. It has been shown that the flow curves of dairy desserts, characteristic of thixotropic systems, change their structure under the influence of mechanical loads. It was found that samples of dairy desserts packaged immediately after thermomechanical processing had a lower thixotropy coefcient compared to samples packaged after cooling. It was found that the viscosity of the retentate-based milk dessert was 10-20 % lower than that of a similar product based on butter. In addition, the viscosity values for retentate-based pudding were 20- 30 % higher than for cream. Conclusions. It has been proved that the temperature of the packaging of dairy desserts, as one of the decisive technological factors, has an impact on the formation of the structure, and, as a result, on the quality of the fnished product. For example, to produce dairy desserts with a consistency typical of pudding or cream, it is necessary to pack at a temperature of at least 65°C. At the same time, the viscosity and ultimate shear stress for cream should be in the range of 55...75 Pa-s and 70...100 Pa, respectively, for pudding - 117...124 Pa-s and 90...110 Pa, respectively. Key words: dairy desserts, creams, puddings, combined composition of raw materials, temperature conditions, packaging, structure, rheological indicators, quality.

Rheological Behavior Features of Feedstocks with a Two-Component Wax–Polyolefin Binder Compared to Analogs Based on Polyoxymethylene

Despite the large number of studies devoted to different compositions of polymer binders for PIM technology, the actual task is still a comparative analysis of the properties of different types of binders to determine their advantages and disadvantages and optimize the compositions used. In this regard, this study aims at the identification and comparative analysis of the rheological properties of the most demanded feedstocks with binders based on polyoxymethylene and a wax–polyolefin mixture under the condition of using identical steel powder filler. The rate of change in the volume fraction of the liquid phase of the binder in the compared feedstocks with temperature change was determined by the calculation–experimental method. As shown, the temperature dependence of the viscosity of feedstocks with a binder based on a polymer blend depends on factors with variable power, i.e., the viscosity change with temperature occurs by different mechanisms with their relaxation spectra. Thus, the principle of temperature–time superposition for feedstocks with multicomponent binders is not applicable, and the study of the viscosity of such materials should involve a wide range of shear rates and temperatures using experimental methods. Capillary rheometry was used to measure the flow curves of feedstocks based on polyoxymethylene and wax–polyolefin binders. The analysis of flow curves of feedstocks showed that feedstocks with a binder of solution–thermal type of debinding have significantly lower viscosity, which is an advantage for molding thin-walled products. However, their difference of 1.5 times sensitivity to the shear rate gradient leads to their lower resistance to “jets” and liquation of components because of shear rate gradients when molding products with elements of different cross-sectional areas.

Directionally‐split volume‐of‐fluid technique for front propagation under curvature flow

AbstractA directionally‐split volume‐of‐fluid (VOF) methodology for evolving interfaces under curvature‐dependent speed is devised. The interface is reconstructed geometrically and the volume fraction is advected with a technique to incorporate a topological volume conservation constraint. The proposed approach uses the idea that the role of curvature in a speed function is analogous to the role of viscosity in the corresponding hyperbolic conservation law to propagate complex interfaces where singularities may exist. The approach has the advantage of simple implementation and straightforward extension to more complex multiphase systems by formulating the interface evolution problem using energy functionals to derive an expression for the interface‐advecting velocity. The numerical details of the volume‐of‐fluid based formulation are discussed with emphasis on the importance of curvature estimation. Finally, canonical curves and surfaces traditionally investigated by the level set (LS) method are tested with the devised approach and the results are compared with existing work in LS.

#2115 Phase-contrast magnetic resonance imaging (PC-MRI) for quantification of volumetric flow in renal transplant arteries: an observational cohort study

Abstract Background and Aims Impaired renal transplant blood flow, a manifestation of severe transplant renal artery stenosis (TRAS), can negatively impact transplant function and survival. Phase-contrast magnetic resonance imaging (PC-MRI) is a non-invasive method of quantifying blood flow volume. Recent work has demonstrated the utility of this technique in measuring native renal blood flow, whilst validating the use of flow measurements taken on the aorta above and below the origin of the renal arteries to calculate flow in the renal arteries [1]. As part of a quality improvement study incorporating PC-MRI into renal transplant assessment, this study set out to (a) establish the normal range for transplant renal blood flow volume and (b) assess whether PC-MRI improved screening for TRAS. Method Between January 2019 and February 2021, PC-MRI sequences were included in the protocols for all magnetic resonance angiograms (MRA) performed as part of clinically-indicated renal transplant assessment. As part of the MRA study, using a coronal localizer MR image, planes were prescribed on the external iliac artery (EIA) both proximal and distal to the transplant artery anastomosis site in a perpendicular orientation (Fig. 1A). Using CV142 software [2], arterial cross-sections were highlighted manually at the pre-determined planes (Fig. 1B) to generate flow curves that coincided with the cardiac cycle (Fig. 1C). Studies were excluded if: the EIA flow waveform was incongruous with the cardiac cycle, contemporaneous heart rate data was not recorded, or the calculated flow volume was a negative value. Results During the study period 392 transplant MRAs were performed, of which 218 were included in this analysis. Potential TRAS was identified in 49 (22.5%) studies, with 19 (8.7%) having this diagnosis confirmed by intra-arterial digital subtraction angiography (IADSA). In the 169 (77.5%) studies without evidence of TRAS, the mean flow in the proximal EIA was 0.90 L/min (95% CI 0.85-0.94 L/min) and in the distal EIA 0.47 L/min (95% CI 0.44-0.50 L/min). The difference between the two measurement points, that is the flow in the transplant renal artery, was 0.42 L/min (95% CI 0.39-0.45 L/min) (Fig. 2A). In the 19 studies with TRAS confirmed by IADSA, mean flow at the time of the initial MRA was 0.34 L/min (95% CI 0.25-0.43 L/min); there was no difference when compared with the group without evidence of TRAS on MRA (p = 0.09) (Fig. 2B). Of the patients who had potential TRAS identified on MRA, 30 patients proceeded to IADSA; there was no difference in PC-MRI flow volume in the 11 who had a diagnosis of TRAS refuted on IADSA and the 19 who had diagnosis of TRAS confirmed (p = 0.97). ROC curve analysis of PC-MRI arterial flow measurement as a diagnostic test for TRAS, whereby the positive group of 19 had IADSA confirmed TRAS, the negative group of 176 had either normal MRA artery appearances or normal IADSA, and the disease prevalence is 13.7% [3], shows AUC 0.62 (95% CI 0.55-0.69) P = 0.09, sensitivity 57.9 specificity 67.1 (Fig. 2C). Conclusion This is the largest study to incorporate functional PC-MRI sequences into MRA protocols for the assessment of people with any form of kidney disease. The results suggest that the blood flow volume in healthy transplant renal arteries lies between 0.39–0.45 L/min. In comparative analysis between patients with healthy transplant arteries and those with IADSA-confirmed TRAS, there was no difference in arterial flow volume, though the study was limited by the small population in the group with IADSA-confirmed TRAS. PC-MRI does not appear to improve the screening accuracy of MRA in identifying TRAS. However, there may be a future role for PC-MRI as part of multi-parametric MR protocols for comprehensive assessment of patients with kidney transplants.

Hot deformation behavior of NiTiHf alloy under compression: Effect of deformation heating on flow softening

High-temperature shape memory alloys are suitable materials for substituting hydraulic elements in the aerospace industry due to light weight and high reactive stresses developing during thermoelastic martensitic transformation and acceptable recoverable strain. These properties may be improved by plastic deformation; however, the plastic deformation of NiTiHf alloys along with structure investigation has yet to be studied systematically. Here, the hot deformation behavior of a NiTiHf alloy with hafnium content >20 at.% has been investigated, and the processing map has been elaborated according to the dynamic material model (DMM) based on the Prasad instability criterion. The deformation heating effect has been shown to affect the flow curves and accounts for profound softening during deformation due to quasi-adiabatic deformation mode at high strain rates. NiTiHf alloys have a much higher activation energy of plastic flow, and the instability region of plastic flow is much larger compared to binary NiTi alloys. Microstructural observations have revealed that in the instability regions, oxide bands and crack nucleation occur, whereas outside this region, such defects are not observed. Electron backscatter diffraction has demonstrated that at high temperatures and slow strain rates, discontinuous dynamic recrystallization occurs resulting in the necklace-type structure, while at high strain rates, this phenomenon has not been observed. Based on the obtained results, the preferable deformation conditions are established to be 850–1000 °C and 0.003–0.05 s−1.

On the rheological and sensory properties of a novel natural salivary substitute

The prevalence of xerostomia, the sensation of dry mouth, is estimated at 20 % in the general population and up to 50 % in older adults. Saliva plays different roles during bolus formation: lubrication, mixing, coating, hydration, dissolution, and comminution of food particles. This study proposes and tests artificial saliva formulations mimicking human saliva rheological and sensory perceptions. Shear and extensional rheology were assessed to select the type of formulation closest to saliva rheological characteristics. After evaluating three alternative sources, an extract simulating saliva rheology was produced from flax seeds. Friction coefficient and rheological properties, such as flow curves, relaxation times, and Trouton ratios, were compared favorably with human saliva. The sensory evaluation demonstrated that flaxseed extracts induce perceived mouth hydration, slipperiness, and adhesion exceeding that of human saliva. The flaxseed extract proposed in this can i) be used to study in vitro food oral processing and ii) pave the way to novel natural salivary substitutes to alleviate the symptoms of xerostomia.

On complete embedded translating solitons of the mean curvature flow that are of finite genus

On complete embedded translating solitons of the mean curvature flow that are of finite genus

Dam–calf contact rearing in Switzerland: Aspects of management and milking

Cow-calf contact (CCC) rearing is becoming an increasingly popular alternative to the common practice of early separation of cow and calf in dairy management. Milkability can be impaired in nursing cows, which contributes to the loss of machine milk yield caused by calf intake, especially in pure dam-calf contact (DCC) systems. The aims of this study were (1) to describe the current status quo of DCC rearing regarding management and milking and (2) to evaluate the effects of DCC (suckling and milking vs. milking alone) and the effects of different types of DCC on milkability parameters, teat condition, and behavior during milking on Swiss DCC farms. By means of 17 telephone interviews with DCC farmers, we collected data on DCC management, housing, separation and weaning processes, milking procedures and techniques, and perceived milkability problems. Subsequently, we collected data on 10 of the interviewed DCC farms (183 cows): 4 DCC farms with a whole-day contact (WDC) system, 3 farms with DCC before milking (CBM), and 3 farms with DCC after milking (CAM). Five farms on which calves had no contact with dams were chosen as reference farms (178 cows). Using a milk flow meter, the occurrence of ejection disorders, bimodality of the milk flow curve, machine milk yield, duration of the decline phase, and duration of prestimulation were measured. The average mouthpiece chamber vacuum during the main milking phase and hind leg activity during milking were measured using a pressure sensor and an accelerometer, respectively. After cluster removal, the teat condition was evaluated, and a stripping milk sample was taken for fat content analysis. The interview results revealed that 8 of the 17 farms surveyed had a WDC system, and 2 farms operated a daytime DCC system. Contact before milking was applied by 3 farms, and 3 farms allowed CAM. On one farm, calves had access to dams 3 times a day. A great diversity in cow-calf management was found. In the on-farm data collection, 20 milkings of a total of 701 milkings examined met the criteria for a clear ejection disorder, with 17 of these observations occurring on WDC farms and none on reference farms. The stripping milk fat content was lower in nursing cows, indicating a lower degree of udder emptying. Machine milk yield was higher in nursing CAM cows than in nursing WDC and CBM cows. Farm types did not differ regarding teat condition, hind leg activity, or the occurrence of bimodal milk flow curves. In conclusion, the large variation in individual management approaches to DCC rearing even within DCC types, such as calf housing or cow breeds, implies caution when interpreting results. Contact after milking may be the system most beneficial for some productivity parameters, but adequate calf supply must be ensured. Higher amounts of milk remaining in the udder after cluster removal indicate that nursing can affect milkability, but future research should consider the effects of udder filling before milking to better interpret the fat content of stripping milk.

Diffuse-interface approximation and weak–strong uniqueness of anisotropic mean curvature flow

Abstract The purpose of this paper is to derive anisotropic mean curvature flow as the limit of the anisotropic Allen–Cahn equation. We rely on distributional solution concepts for both the diffuse and sharp interface models and prove convergence using relative entropy methods, which have recently proven to be a powerful tool in interface evolution problems. With the same relative entropy, we prove a weak–strong uniqueness result, which relies on the construction of gradient flow calibrations for our anisotropic energy functionals.

Mean curvature flow with generic low-entropy initial data

Mean curvature flow with generic low-entropy initial data

Volume preserving mean curvature flow of L2-almost umbilical hypersurfaces in hyperbolic space

In this paper, we study the stability of the volume preserving mean curvature flow of closed hypersurfaces in the hyperbolic space. We prove that an [Formula: see text]-almost umbilical hypersurface will be deformed to a totally umbilical hypersurface along the flow. Our result removes the assumption on the mean curvature in the theorems of Huang-Lin-Zhang [Peking J. Math. (2023)] and Leng-Xu-Zhao [Int. J. Math. (2014)].