Ring Of Functions Research Articles

Characteristics of secondary droplets produced by the impact of drops onto a smooth surface

This work investigates the splashing behaviors of droplets impacting on solid surfaces and mainly focuses on the characteristics of secondary droplets. According to the experimental results, two different splashing patterns, corona splash and levitating-lamella breakup, are observed. A new breakup mode, named rim-segmenting, is found during the levitating-lamella breakup. In particular, the detailed information of the splashing secondary droplets, including the size, velocity, angle, and total volume of the splashing secondary droplets is obtained from the experimental data. The size distribution of the splashing secondary droplets obeys the gamma distribution function. The average diameter and splashing angle of the secondary droplets are mainly related to the Reynolds number Re, and can be expressed as functions of Re. High impact velocity and liquid viscosity will result in a wider size distribution range of splashing secondary droplets. We also put forward an empirical model to predict the total splashing volume, which is consistent with the experimental data both in this work and previous studies. This work is believed to provide insights on the prediction of the characteristics of splashing secondary droplets.

Numerical Investigation of Laminar Impinging Jet Cooling of a Protruded Heat Source

Abstract Thermofluid dynamics of an unconfined steady two-dimensional laminar jet impinging on an isothermal protruded heater is numerically studied for low jet inlet Reynolds number (Re) between 50 and 250. Results are shown for a range of impingement distances (h/W) between 1 and 10 for Prandtl numbers (Pr) 0.71 and 7.56. The volumetric entrainment increases with increasing h/w and decreasing Re. The reattachment distance of the wall jet appears to increase with Re and shows discernible deviation from the backward-facing step flow prediction for Re>150. Correlations are presented for average heater surface and sidewall Nusselt numbers as functions of Re and h/w for Pr=0.71 and Pr=7.56. In an overall convection dominant heat transfer, a relatively warmer and diffusion-dominated recirculation zone is identified adjacent to the sidewall with a low Nusselt number, which enhances significantly at Pr=7.56 when Re is increased above 100. At a low impingement distance, integrated kinetic energy flux shows greater magnitude in the impingement region but with a higher rate of decay. The integrated heat flux is greatly influenced by Re, and the effect is more pronounced at Pr=0.71. Self-similar behavior is observed for the velocity and heat flux profiles throughout the length in the developed region and for the temperature distribution over the heater surface. Both high Re and high h/w seem to adversely affect the self-similar behavior owing to a slower wall jet development.

Bone-forming perivascular cells: Cellular heterogeneity and use for tissue repair.

Mesenchymal progenitor cells are broadly distributed across perivascular niches-an observation conserved between species. One common histologic zone with a high frequency of mesenchymal progenitor cells within mammalian tissues is the tunica adventitia, the outer layer of blood vessel walls populated by cells with a fibroblastic morphology. The diversity and functions of (re)generative cells present in this outermost perivascular niche are under intense investigation; we have reviewed herein our current knowledge of adventitial cell potential with a somewhat narrow focus on bone formation. Antigens of interest to functionally segregate adventicytes are discussed, including CD10, CD107a, aldehyde dehydrogenase isoforms, and CD140a, among others. Purified adventicytes (such as CD10+ , CD107alow , and CD140a+ cells) have stronger osteogenic potential and promote bone formation in vivo. Recent bone tissue engineering applications of adventitial cells are also presented. A better understanding of perivascular progenitor cell subsets may represent a beneficial advance for future efforts in tissue repair and bioengineering.

Pore-scale convection-conduction heat transfer and fluid flow in open-cell metal foams: A three-dimensional multiple-relaxation time lattice Boltzmann (MRT-LBM) solution

Flow and heat transfer in porous foams are usually simulated based on averaged properties that are far from the actual values and can lead to substantial inaccuracies in the results. The pore-scale simulation could provide accurate and realistic models for such properties. Accordingly, a multiple-relaxation time lattice Boltzmann (MRT-LBM) code is extended for pore-scale direct numerical simulation (DNS) of fluid flow and conductive-convective heat transfer in open-cell metal foams (OCMFs) using the Palabos code, an open-source parallel LB solver. Three foam models with different numbers of pores per inch (PPI) are generated, and through simulations, the permeability, the non-Darcy coefficient β, the onset of non-Darcy flow, and Nusselt number (Nud) are determined. The results show that by increasing the PPI of the samples from 20 to 40, the flow becomes more complex, and velocity and permeability are reduced by up to 70%. On the other hand, the heat transfer coefficient increases significantly so that in the same Reynolds number (Re), the overall heat transfer coefficient of sample 3 (40 PPI) is on average 110% higher than that of sample 1 (20 PPI). Finally, the global Nusselt number (Nud) is determined as a function of Re, and the related correlations are presented.

Numerical modeling of pulsatile blood flow through a mini-oxygenator in artificial lungs

While previous in vitro studies showed divergent results concerning the influence of pulsatile blood flow on oxygen advection in oxygenators, no study was done to investigate the uncertainty affected by blood flow dynamics. The aim of this study is to utilize a computational fluid dynamics model to clarify the debate concerning the influence of pulsatile blood flow on the oxygen transport. The computer model is based on a validated 2D finite volume approach that predicts oxygen transfer in pulsatile blood flow passing through a 300-micron hollow-fiber membrane bundle with a length of 254 mm, a building block for an artificial lung device. In this study, the flow parameters include the steady Reynolds number (Re = 2, 5, 10 and 20), Womersley parameter (Wo = 0.29, 0.38 and 0.53) and sinusoidal amplitude (A = 0.25, 0.5 and 0.75). Specifically, the computer model is extended to verify, for the first time, the previously measured O2 transport that was observed to be hindered by pulsating flow in the Biolung, developed by Michigan Critical Care Consultants. A comprehensive analysis is carried out on computed profiles and fields of oxygen partial pressure (PO2) and oxygen saturation (SO2) as a function of Re, Wo and A. Based on the present results, we observe the positive and negative effects of pulsatile flow on PO2 at different blood flow rates. Besides, the SO2 variation is not much influenced by the pulsatile flow conditions investigated. While being consistent with a recent experimental study, the computed O2 volume flow rate is found to be increased at high blood flow rates operated with low frequency and high amplitude. Furthermore, the present study qualitatively explains that divergent outcomes reported in previous in vitro experimental studies could be owing to the different blood flow rates adopted. Finally, the contour analysis reveals how the spatial distributions of PO2 and SO2 vary over time.

Hyporheic Exchange Driven by Submerged Rigid Vegetation: A Modeling Study

AbstractFlow‐vegetation interaction affects fluid flow hydraulics and associated material transport in river corridors. Concomitant changes in pressure within the flow field due to the presence of vegetation may act as a driver for the formation of hyporheic flow across the sediment‐water interface. This potentially important process, however, has yet to be studied. In order to investigate vegetation‐induced hyporheic exchange, a series of numerical models of interlinked surface‐subsurface flow modified by plant stems was conducted. Periodically staggered plant stem arrays on a flat sediment bed were considered within a coupled multiphysics computational fluid dynamics approach. Plants were idealized as rigid cylinders and arranged in different streamwise and spanwise spacing distances. Each vegetation array was then subjected to a broad range of flow Reynolds Numbers (Re). The results showed that hyporheic flow occurs in all conditions with the presence of vegetation. The vegetation‐induced hyporheic flux is found to be a function of Re via a power law. The flux increases with interstem space until the space reaches the distance that rigid stems no longer affect the flow structures in the vicinity of each other. Larger intervegetation distances lead to a larger hyporheic zone. A direct comparison with bedform‐induced hyporheic flow showed that vegetation can induce higher hyporheic flux through relatively shallower exchange zones. The results of all the simulations were synthesized into predictive models for hyporheic flux, bulk residence time and exchange depth based on drag coefficient, vegetation density, and Reynolds Number.

Analytical Formula for the Mean Velocity Profile in a Pipe Derived on the Basis of a Spatial Polynomial Vorticity Distribution

The derivation of the mean velocity profile for a given vorticity distribution over the pipe cross-section is presented in this paper1. The velocity profile and the vorticity distribution are axisymmetric, which means that the radius is the only variable. The importance of the vortex field for the flow analysis is discussed in the paper. The polynomial function with four free parameters is chosen for the vorticity distribution. Free parameters of this function are determined using boundary conditions. There are also two free exponents in the polynomial. These exponents are determined based on the comparison of this analytical formula with experimental data. Experimental data are taken from the Princeton superpipe data which consist of 26 velocity profiles for a wide range of Reynolds numbers (Re). This analytical formula for the mean velocity profile is more precise than the previous one and it is possible to use it for the wide range of Reynolds number <31,577; 35,259,000>. This formula is easy to use, to integrate, or to derivate. The empirical formulas for the profile parameters as a function of Re are also included in this paper. All information for the mean velocity profile prediction in the mentioned Re range are in the paper. It means that it is necessary to know the average velocity v(av), the pipe radius R, and Re to be able to predict the turbulent mean velocity profile in a pipe.

Grid resolution requirement for resolving rare and high intensity wall-shear stress events in direct numerical simulations

Wall-shear stress becomes more intermittent as the Reynolds number (Re) of a flow increases. To properly resolve wall shear stress events in direct numerical simulations thus requires finer grids at higher Re. In this work we examine the grid resolution required to resolve a given percentage of wall shear stress events as a function of Re. We find that the standard grid resolution does not capture a fraction of high intensity events which increases with Re and quantify the grid resolution needed to do so.

Flow and Heat Transfer Property of Oldroyd-B-Fluid-Based Nanofluids Containing Cylindrical Particles in a Pipe

Flow and heat transfer property of Oldroyd-B-fluid-based nanofluids containing cylindrical particles are studied in a pipe with circular cross-section in the range of Reynolds number (Re) from 100 to 2000, Weissenberg number (We) from 0.1 to 2, particle aspect ratio (β) from 2 to 16 and particle volume concentration (Φ) from 0.1% to 2.5%. The motion equation of Oldroyd-B fluid with particles, the equation for probability density function of particle orientation and convection-diffusion equation for particles are solved numerically. The numerical method used in the simulation is validated by comparing with the available results. The effects of Re, We, β and Φ on the friction factor (f), Nusselt number (Nu) and ratio of energy performance evaluation criterion (PECt/PECf) for Oldroyd-B-fluid-based nanofluids to that for Oldroyd-B fluids are discussed. The results showed that the values of f and Nu of Oldroyd-B-fluid-based nanofluids are larger than that of water-based nanofluids and that of pure Oldroyd-B fluids. The values of f increase with increasing Re, We and Φ, but with decreasing β. The values of Nu and PECt/PECf are enhanced with increasing Re, We, β and Φ. The increase of f is larger than that of Nu at lower Re, but is less than that of Nu at higher Re. It is more effective to use Oldroyd-B-fluid-based nanofluids with cylindrical nanoparticles to improve the heat transfer at the conditions of higher Re, We, β and Φ. Finally, the correlation formula of PECt/PECf as a function of Re, We, β and Φ is derived.

Thermal performance enhancement of a double-tube heat exchanger with novel twisted annulus formed by counter-twisted oval tubes

A novel twisted annulus between two counter-twisted oval tubes is proposed for a double-tube heat exchanger. The oval tubes of the annuli have same twist pitch, but twist with opposite twisting directions. The thermohydraulic performance of the annuli with different aspect ratios and twist ratios is numerically presented. The results indicate that strong secondary flow is generated in the twisted annulus, which can significantly promote the heat transfer. The maximum Nu and f of the twisted annuli are separately 157% and 118% larger than those of the corresponding straight annuli. The largest value of the thermal performance factor is 1.98 in the studied range of geometrical parameters. Correlations of Nu and f as a function of Re, twist ratio and aspect ratio are proposed with the deviations within ±10% and ±8%, respectively.

Synthesis and Light-Harvesting Functions of Ring-Shaped Re(I) Trinuclear Complexes Connected with an Emissive Ru(II) Complex

Ring-shaped Re(I) multinuclear complexes (Re(I) rings) in which Re(I)-diimine-biscarbonyl complexes are connected to each other through bisphosphine bridging ligands exhibit very suitable photophysical and electrochemical properties as redox photosensitizers. We developed two approaches for synthesizing Re(I) rings connected with a Ru(II) complex: cyclization of a linear Re(I) trinuclear complex connected with a Ru(II) complex and Mizoroki–Heck coupling of a ring-shaped Re(I) trinuclear complex and a Ru(II) complex. Photophysical measurements of these heteromultinuclear complexes and comparisons with their model complexes indicated that they exhibit efficient light-harvesting abilities, where energy transfer from the excited ring-shaped Re(I) trinuclear complex unit to the Ru(II) complex unit proceeds efficiently.

Settling of inertial nonspherical particles in wavy flow

Motivated by the problem of microplastics in the ocean, we experimentally investigate settling of plastic rods, disks, and spheres in wavy flows. We find that particle average vertical velocity can both increase and decrease in waves, relative to particle settling velocity in quiescent flow. This variation is a function of flow inertia at the particle length scale, characterized by particle Reynolds number Re${}_{p}$, and also of particle shape. We find that even though the relative vertical velocities between particles and flow remain constant with Re${}_{p}$, the particles nonuniformly sample the flow as a function of particle shape and Re${}_{p}$.

Molecular characterization of a RING E3 ligase SbHCI1 in sorghum under heat and abscisic acid stress.

Molecular function ofRING E3 ligase SbHCI1is involved in ABA-mediated basal heat stress tolerancein sorghum. Global warming generally reduces plant survival, owing to the negative effects of high temperatures on plant development. However, little is known about the role of Really Interesting New Gene (RING) E3 ligase in the heat stress responses of plants. As such, the aim of the present study was to characterize the molecular functions of the Sorghum bicolor ortholog of the Oryza sativa gene for Heat- and Cold-Induced RING finger protein 1 (SbHCI1). Subcellular localization revealed that SbHCI1 was mainly associated with the cytosol and that it moved to the Golgi apparatus under heat stress conditions. The fluorescent signals of SbHCI1 substrate proteins were observed to migrate to the cytoplasm under heat stress conditions. Bimolecular fluorescence complementation (BiFC) and yeast two-hybrid (Y2H) assays revealed that SbHCI1 physically interacted with OsHCI1 ortholog partner proteins in the cytoplasm. Moreover, an in vitro ubiquitination assay revealed that SbHCI1 polyubiquitinated each of the three interacting proteins. The ectopic overexpression of SbHCI1 in Arabidopsis revealed that the protein was capable of inducing abscisic acid (ABA)-hypersensitivity and basal heat stress tolerance. Therefore, SbHCI1 possesses E3 ligase activity and may function as a positive regulator of heat stress responses through the modulation of interacting proteins.

The A-fibered Burnside Ring as A-Fibered Biset Functor in Characteristic Zero

Let A be an abelian group such that torn(A) is finite for every n ≥ 1 and let ${\mathbb{K}}$ be a field of characteristic zero containing roots of unity of all orders equal to finite element orders in A. In this paper we prove fundamental properties of the A-fibered Burnside ring functor $B_{\mathbb{K}}^{A}$ as an A-fibered biset functor over K. This includes a description of the composition factors of $B^{A}_{\mathbb{K}}$ and the lattice of subfunctors of $B_{\mathbb{K}}^{A}$ in terms of what we call BA-pairs and a poset structure on their isomorphism classes. Unfortunately, we are not able to classify BA-pairs. The results of the paper extend results of Coskun and Yilmaz for the A-fibered Burnside ring functor restricted to p-groups and results of Bouc in the case that A is trivial, i.e., the case of the Burnside ring functor as a biset functor over fields of characteristic zero. In the latter case, BA-pairs become Bouc’s B-groups which are also not known in general.

Identification of flow states around three staggered square cylinders at two symmetrical arrangements by a numerical investigation

The fluid flow over three staggered square cylinders at two symmetrical arrangements has been numerically investigated in this study. The numerical calculations are carried out for several values of the Reynolds number (Re) ranging from 1 to 180. The results are presented in the form of vorticity contours and temporal histories of drag and lift coefficients. Furthermore, the physical parameters, namely, the average drag and lift coefficients and Strouhal number are presented as a function of Re. Two different states of flow are found in this work by systematically varying Re: steady and unsteady states. The transition to unsteady state regime is exhibited via Hopf bifurcation first in the second configuration followed consequently by the first one with critical Reynolds number of Re[Formula: see text] and Re[Formula: see text], respectively. It is observed that the bifurcation point of the steady regime to the unsteady one is very much influenced by the change in the geometry of the obstacle. The unsteady periodic wake is characterized by the Strouhal number, which varies with the Reynolds number and the obstacle geometry. Hence, the values of vortex shedding frequencies are estimated for both the considered configurations. Computations obtained also reveal that the spacing in the wake leads to reducing the pressure and enhancing the fluid flow velocity for both arrangements by monotonically strengthening the Reynolds number value. Furthermore, the drag and lift coefficients are determined, which allowed determining; the best configuration in terms of both lift and drag. It is observed that the drag force is dependent on the obstacle geometry and strengthens while lowering the Reynolds number. On the other hand, an opposite trend of the lift drag evolutions is observed for both configurations and considerably affected by the arrangements shape.

Extracting reaction systems from function behavior

Reaction systems, introduced by Ehrenfeucht and Rozenberg, are a theoretical model of computation based on the two main features of biochemical reactions: facilitation and inhibition, which are captured by the individual reactions of the system. All reactions, acting together, determine the global behavior or the result function, res, of the system. In this paper, we study decomposing of a given result function to find a functionally equivalent set of reactions. We propose several approaches, based on identifying reaction systems with Boolean functions, Boolean formulas, and logic circuits. We show how to minimize the number of reactions and their resources for each single output individually, as a group, and when only a subset of the states are considered. These approaches work both when the reactions of the given res function are known and not known. We characterize the minimal number of reactions through the minimal number of logical terms of the Boolean formula representation of the reaction system. Finally, we make applications recommendations for our findings.

Solitary waves on falling liquid films in the low Reynolds number regime

We study the problem of a thin liquid film falling down an inclined slope. We use a simplified model to study the evolution and morphology of the solitary waves on a thin film with a periodic forcing at the inlet. In recent work by Denner et al (2016 Phys. Rev. E 93, 033121), the regime for high Re was studied and results obtained on the geometry and dispersion of the waves. We wish to establish whether similar results are observed in a regime of smaller Re and examine quantities which can be compared with experiment, such as the maximum and minimum film height as a function of a rescaled Reynolds number which accounts for the inclination of the substrate. Our results show some evidence that h min collapses onto a single curve when plotted as a function of Re*, and approaches the absolute value of h min/h N = 0.375 in agreement with results obtained at higher Re. We also obtain a curve for d/λ which can be compared with the results reported in (Denner et al 2016 Phys. Rev. E 93, 033121).

Eliminating Boundary Layer Separation on a Cylinder with Nonuniform Suction

Boundary layer separation negatively influences the performance of aerospace vehicles, for example, by triggering static stall or reducing combustion engine efficiency. Developing effective flow control to delay or eliminate separation is therefore of real use to the field. In this paper, numerical studies were carried out to optimise distributed suction profiles for preventing boundary layer separation on a circular cylinder in the fully laminar regime (Re<188), with the least control effort. Relationships were found between the Reynolds number, the separation angle of the uncontrolled case, and the uniform suction needed to eliminate separation. It was found that for Re>20, the uniform suction required to eliminate separation followed a quadratic profile, as a function of Re. Maximum uniform suction effort was needed at Re=20, requiring a suction coefficient of CQ=49.14 (as a percentage of the free-stream velocity) to eliminate separation. To resolve the best nonuniform suction profile at Re=180, a variety of optimisation studies were performed using the coordinate search method. It was determined that the use of six control segments on each half of the cylinder provided the best control and efficient convergence to the optimal solution. 6-segment nonuniform suction eliminated separation at Re=180 with net suction effort of CQ=13.26 compared to CQ=31.25 for the uniform case. These optimal suction profiles were compared using time-dependent simulations to confirm that both methods eliminate separation when introduced to an already unsteady case. Nonuniform suction eliminated separation faster, though uniform suction was more stable.

Excited states of holographic superconductors

In this paper we re-investigate the model of the anti-de Sitter gravity coupled to Maxwell and charged scalar fields, which has been studied as the gravitational dual to a superconductor for a long time since the famous work [Phys. Rev. Lett.101 (2008) 031601]. By numerical method, we present a novel family of solutions of holographical superconductor with excited states, and find there exists a lower critical temperature in the corresponding excited state. Moreover, we study the condensate and conductivity in the excited states. It is very interesting that the conductivity σ of each excited state has an additional pole in Im[σ] and a delta function in Re[σ] arising at the low temperature inside the gap, which is just the evidence of the existence of excited states.

Development of drag correlation for suspensions of ellipsoidal particles

To model drag the current state-of-the-art is to use isolated non-spherical particle drag correlations modified by a solid fraction correlation that is based on experimental or simulation results of spherical particle suspensions. It is shown that this practice can lead to substantial inaccuracies when the particle geometry deviates significantly from a spherical geometry. In this paper particle resolved simulations (PRS) are conducted for ellipsoids of aspect ratio 5 (AR5) and 10 (AR10) in random suspensions with no preferential orientation. Simulations are performed for a Reynolds number Re = 10 to 200, and solid fraction φ = 0.1 to 0.3 and 0.1 to 0.2 for AR5 and AR10 suspensions, respectively. Combined with PRS data from past studies for spherical particle suspensions and ellipsoids with AR2.5, a drag correlation is developed for the mean drag force in suspension as a function of Re, φ , aspect ratio, and inclination angle θ.