Smooth Disk Research Articles

Derivation of Non-Newtonian Magnetic Fluid Lubricated Rough Centrosymmetric Squeeze Film Reynolds Equation and its Application

AbstractBased upon the Shliomis ferromagnetic fluid model and the Stokes microcontinuum theory incorporating with the Christensen stochastic model, a modified Reynolds equation of centrosymmetric squeeze films has been derived in this paper. The Reynolds equation includes the combined effects of non-Newtonian rheology, magnetic fluids with applied magnetic fields, rotational inertia forces, and surface roughness. To guide the use of the derived equation, the squeeze film of rotational rough-surface circular disks lubricated with non-Newtonian magnetic fluids is illustrated. According to the results obtained, the effects of rotation inertia decrease the load capacity and the squeeze film time of smooth circular disks. By the use of non-Newtonian magnetic fluids with applied magnetic fields, the rotational circular disks predict better squeeze film performances. When the influences of circumferential roughness patterns are considered, the non-Newtonian magnetic-fluid lubricated rotational rough disks with applied magnetic fields provide further higher values of the load capacity and the squeeze film time as compared to those of the smooth case.

Effect of cathode porosity on the Lithium-air cell oxygen reduction reaction – A rotating ring-disk electrode investigation

The kinetics of the oxygen reduction reaction (ORR) on the practical air cathode in a Lithium-air cell, which is conventionally composed of porous carbon with or without catalysts supported on it, was investigated. The mechanism and kinetics of the oxygen reduction reaction (ORR) was studied on a porous carbon electrode in an oxygen saturated solution of 0.1M Lithium bis-trifluoromethanesulfonimide (LiTFSI) in Dimethoxyethane (DME) using cyclic voltammetery (CV) and the rotating ring-disk electrode (RRDE) technique. The oxygen reduction and evolution reactions were found to occur at similar potentials to those observed on a smooth, planar glassy carbon (GC) electrode. The effect of porosity and the resultant increase in surface area were readily observed in the increase in the transient time required for the intermediates to reach the ring and the much larger disk currents (compared to smooth, planar GC) recorded respectively. The RRDE data was analyzed using a kinetic model previously developed by us and the rate constants for the elementary reactions were calculated. The rates constant for the electrochemical reactions were found to be similar in magnitude to the rate constants calculated for smooth GC disks. The porosity of the electrode was found to decrease the rate of desorption of the intermediate and the product and delay their diffusion by shifting it from a Fickian regime in the electrolyte bulk to the Knudsen regime in the film pores. Thus, it is shown that the effect of the electrode porosity on the kinetics of the ORR is physical rather than electrochemical.

GASP. II. A MUSE View of Extreme Ram-Pressure Stripping along the Line of Sight: Kinematics of the Jellyfish Galaxy JO201

Abstract This paper presents a spatially resolved kinematic study of the jellyfish galaxy JO201, one of the most spectacular cases of ram-pressure stripping (RPS) in the GAs Stripping Phenomena in galaxies with MUSE (GASP) survey. By studying the environment of JO201, we find that it is moving through the dense intracluster medium of Abell 85 at supersonic speeds along our line of sight, and that it is likely accompanied by a small group of galaxies. Given the density of the intracluster medium and the galaxy’s mass, projected position, and velocity within the cluster, we estimate that JO201 must so far have lost ∼50% of its gas during infall via RPS. The MUSE data indeed reveal a smooth stellar disk accompanied by large projected tails of ionized ( ) gas, composed of kinematically cold (velocity dispersion <40 km s−1) star-forming knots and very warm (>100 km s−1) diffuse emission, that extend out to at least from the galaxy center. The ionized -emitting gas in the disk rotates with the stars out to ∼6 kpc; but, in the disk outskirts, it becomes increasingly redshifted with respect to the (undisturbed) stellar disk. The observed disturbances are consistent with the presence of gas trailing behind the stellar component resulting from intense face-on RPS along the line of sight. Our kinematic analysis is consistent with the estimated fraction of lost gas and reveals that stripping of the disk happens outside-in, causing shock heating and gas compression in the stripped tails.

CFD Simulation of the Distribution of Pressure and Shear Rate on the Surface of Rotating Membrane Equipped with Vanes for the Ultrafiltration of Dairy Effluent

This paper reports computational fluid dynamics (CFD) studies on the performance of flow inside a rotating disk filtration module. This module consists of a disk rotating at speeds between 1000 and 3000 rpm inside a cylindrical housing equipped with a stationary circular flat membrane. In order to investigate the influence of surface geometry, a smooth disk and a disk equipped with vanes were used. Commercial CFD software was utilized for the characterization of the flow inside the membrane module. The predicted results were compared at different values of rotating and inlet velocities with previous works and also with experimental ones obtained in the filtration of dairy effluent in the same conditions. The influence of the geometry of the disk was also evaluated. The obtained results show that an increase in rotating velocity leads to an increase in the pressure and shear stress at the membrane surface. The highest pressures were obtained when using disks equipped with vanes, this was due to the turbulent area created between the vanes visualized in animated views. It was also found that the presence of vanes on the surface of disk has a great effect on the shear stress; it contributes to the reduction in fouling and improvement in filtration flux.

Evaluation and modeling of a spinning disc photoreactor for degradation of phenol: Impact of geometry modification

Abstract A new spinning disc photoreactor with two different designs employing baffles in its structure for degradation of phenol was studied and compared with conventional ones. TiO2 was successfully immobilized on stainless steel disc and Teflon baffles. X-ray diffraction, scanning electron microscopy, field emission scanning electron microscopy and transmission electron microscopy analysis were performed in order to give information on the crystal phase and structure of both TiO2 coatings and size of particles. The wettability of the photocatalyst film on the disc surface was evaluated by contact angle test. The results have demonstrated that complete phenol removal was achieved using baffles after 180 and 150 min of reaction time, which was 60 and 90 min faster than the reactor with smooth disc under optimum condition of the reactor (rotational speed = 290 rpm, flow rate = 2000 mL/min, disc diameter = 22 cm). Influence of rotational speed for smooth and baffled discs was studied. Results indicated that there was no considerable mass transfer limitation for new designs above approximately 150 rpm. For description of flow regime in the reactor residence time distribution (RTD) measurements was performed experimentally. According to RTD data, reactor was accurately modeled using tanks-in-series model. The estimated equivalent number of tanks-in-series in baffled discs were 8 and 10 compared to 4 for smooth disc. The Langmuir-Hinshelwood (L-H) kinetic model was combined with hydrodynamic model for prediction of degradation of phenol and rate coefficients. Predicted results were in agreement with experimental data.

Planetesimal formation near the snowline: in or out?

The formation of planetesimals in protoplanetary disks is not well-understood. Streaming instability is a promising mechanism to directly form planetesimals from pebble-sized particles, provided a high enough solids-to-gas ratio. However, local enhancements of the solids-to-gas ratio are difficult to realize in a smooth disk, which motivates the consideration of special disk locations such as the snowline. In this article we investigate the viability of planetesimal formation by streaming instability near the snowline due to water diffusion and condensation. We adopt a viscous disk model, and numerically solve the transport equations for vapor and solids on a cylindrical, 1D grid. We take into account radial drift of solids, gas accretion on to the central star, and turbulent diffusion. We study the importance of the back-reaction of solids on the gas and of the radial variation of the mean molecular weight of the gas. We find that water diffusion and condensation can locally enhance the ice surface density by a factor 3--5 outside the snowline. Assuming that icy pebbles contain many micron-sized silicate grains that are released during evaporation, the enhancement is increased by another factor $\sim$$2$. In this `many-seeds' model, the solids-to-gas ratio interior to the snowline is enhanced as well, but not as much as just outside the snowline. In the context of a viscous disk, the diffusion-condensation mechanism is most effective for high values of the turbulence parameter $\alpha$ ($10^{-3}$--$10^{-2}$). Therefore, assuming young disks are more vigorously turbulent than older disks, planetesimals near the snowline can form in an early stage of the disk. In highly turbulent disks, tens of Earth masses can be stored in an annulus outside the snowline, which can be identified with recent ALMA observations.

Influence of Humidity on Grip and Release Adhesion Mechanisms for Gecko-Inspired Microfibrillar Surfaces.

Geckos have developed foot pads that allow them to maintain their unique climbing ability despite vast differences of surfaces and environments, from dry desert to humid rainforest. Likewise, successful gecko-inspired mimics should exhibit adhesive and frictional performance across a similarly diverse range of climates. In this work, we focus on the effect of relative humidity (RH) on the "frictional-adhesion" behavior of gecko-inspired adhesive pads. A surface forces apparatus was used to quantitatively measure adhesion and friction forces of a microfibrillar cross-linked polydimethylsiloxane surface against a smooth hemispherical glass disk at varying relative humidity, from 0 to 100% (including fully submerged under water). Geometrically anisotropic tilted half-cylinder microfibers yield a "grip state" (high adhesion and friction forces after shearing along the tilt of the fibers, Fad+ and F∥+) and a "release state" (low adhesion and friction after shearing against the tilt of the fibers, Fad- and F∥-). By appropriate control of the loading path, this allows for transition between strong attachment and easy detachment. Changing the preload and shear direction gives rise to differences in the effective contact area at each fiber and the microscale and nanoscale structure of the contact while changing the relative humidity results in differences in the relative contributions of van der Waals and capillary forces. In combination, both effects lead to interesting trends in the adhesion and friction forces. At up to 75% RH, the grip state adhesion force remains constant and the ratio of grip to release adhesion force does not drop below 4.0. In addition, the friction forces F∥+ and F∥- and the release state adhesion force Fad- exhibit a maximum at intermediate relative humidity between 40% and 75%.

Characterization of interface stresses and lubrication of rough elastic surfaces under ball-on-disc rolling

This paper presents a statistical method for characterizing the interface stresses between an elastic rough ball and a smooth rigid disc under lubrication by considering the percolation effect of lubricant flow. The statistical analysis was carried out to integrate the random, microscopic asperity deformation with the asperity–lubricant interaction. An efficient solution process with the aid of the fast Fourier transform was developed for the multi-scale analysis. To avoid numerical instability, the Poiseuille term of the average Reynolds equation was turned off when the average lubricant film thickness was below the percolation threshold and the average hydrodynamic pressure was solved by using the Couette term. This successfully overcomes the limitation in the conventional statistical treatment of mixed lubrication. Moreover, it enables a smooth transition from mixed to boundary lubrication and allows a large range of dimensionless rolling speed, which cannot be achieved by conventional approaches. Also, an empirical formula was developed to evaluate the average central and minimum film thicknesses between lubricated rough surfaces in contact. It was found that the method developed can precisely predict the effect of surface roughness on contact stresses, can effectively estimate the contribution of the direct asperity–disc contacts, and can be used to describe the lubricant performance at a rolling–sliding contact interface.

Mass, Density, and Formation Constraints in the Compact, Sub-Earth Kepler-444 System including Two Mars-mass Planets

Abstract Kepler-444 is a five-planet system around a host star approximately 11 billion years old. The five transiting planets all have sub-Earth radii and are in a compact configuration with orbital periods between 3 and 10 days. Here, we present a transit-timing analysis of the system using the full Kepler data set in order to determine the masses of the planets. Two planets, Kepler-444 d ( ) and Kepler-444 e ( ), have confidently detected masses due to their proximity to resonance that creates transit-timing variations. The mass ratio of these planets combined with the magnitude of possible star–planet tidal effects suggests that smooth disk migration over a significant distance is unlikely to have brought the system to its currently observed orbital architecture without significant post-formation perturbations.

The role of surface roughness and slide-roll ratio on the decomposition of MoDTC in tribological contacts

In this study, the role of surface roughness and slide-roll ratio in the decomposition and friction performance of molybdenum dialkyldithiocarbamate (MoDTC) has been investigated. Tribotests were carried out in a minitraction machine (MTM) using steel discs of varying roughness rubbing against smooth steel balls in a sliding/rolling contact. Tests were conducted at slide-roll ratio (SRR) values of SRR = 100% and 200%. Raman spectroscopy was used to perform chemical characterisation on the resulting wear scars. The friction performance of rough discs was not affected by the SRR. On the other hand, increasing the SRR from 100% to 200% in tests with smooth discs resulted in higher friction with large instabilities. Raman analysis showed significant differences in chemical composition of the wear scars generated after tests with smooth and rough discs. Wear scars generated using rough discs were mainly composed of MoS2 indicating complete MoDTC decomposition while those generated using smooth discs were composed of a mixture of MoS2, MoSx (x > 2) and FeMoO4 indicating partial MoDTC decomposition. Numerical simulation of the contact revealed that under similar loading conditions rough surfaces have higher local pressures than smoother surfaces. It is proposed that higher local pressures in rough surfaces promoted complete MoDTC decomposition. The novel finding from results presented in this study is that at similar temperature and MoDTC concentration, the degradation of MoDTC within tribocontacts is highly dependent on the roughness of the tribopair. This is because surface roughness determines the local pressure at the asperity–asperity contact.

The Effect of Passive-Active Interaction Method on Drag Reduction Performance in Rotating Disk Apparatus

Objectives:Turbulent Drag Reduction (DR) efficacy of diesel fuelin a Rotating Disk Apparatus (RDA) using anionic surfactant of Sodium Lauryl Ether Sulfate (SLES) was investigated with smooth andSV-groove disks(riblets height of 900 and 3100 μm). Methods: The DR efficacy indicates how the torque is being reduced with a tiny amount of additives under a turbulent flow at a Reynolds number (Re) range of 302227 to 453341. The effects of different variables such as rotary disk type (smooth or structured), surfactant concentration, and Reynolds number were also studied. Findings: SLES shows a good ability to reduce the frictional drag forces with smooth and SV-groove of height 3100μm. In contract, there is no drag reduction can be observed by using this surfactant with SV-groove of height 900 μm. Application/Improvements: The passive-active interaction method can be used to improve petroleum liquid flow in pipelines.

A transversely isotropic medium containing a penny-shaped crack subjected to a non-uniform axisymmetric loading via an anchored smooth rigid disk

A smooth rigid circular anchor disk encapsulated by a penny-shaped crack is embedded in and unbounded transversely isotropic medium. The lamellar rigid disk exerts a nonuniform axisymmetric loading to the upper face of the crack. With the aid of an appropriate stress function and Hankel transform, the governing equations are converted to a set of triple integral equations which in turn are reduced to a Fredholm integral equation of the second kind. For some transversely isotropic materials the normalized stiffness of the system falls well outside of the envelope pertinent to isotropic media. It is shown that mode I stress intensity factor is independent of the material properties and solely depends on the ratio of the radius of the rigid disk to that of the crack; moreover, for the cases where this ratio is less than about 0.9 a simple explicit approximate expression for the mode I stress intensity factor is derived. In contrast, the normalized mode II stress intensity factor is independent of the mentioned geometrical parameters but depends on the elastic properties of the material; depending on the material properties, the normalized mode II stress intensity factor can vary between 0 to ∞ for transversely isotropic materials and between 0 to π/4 for isotropic materials.

Investigation of film formation mechanism of oil-in-water (O/W) emulsions at high speeds

The film forming mechanism of oil-in-water (O/W) emulsions has been investigated at high speeds in the present paper. The lubricant reservoir formed in nano-confined space between a smooth plate disc and a highly polished ball could be observed via the microscope and the film thickness was calculated by the technique of relative optical interference intensity (ROII). The film formation mechanism and influencing factors including the oil percentage, the high speed and the width of nano-gap were discussed.

A new ultrasonic fatigue testing device for biaxial bending in the gigacycle regime

A new fatigue testing device has been developed to test specimens under biaxial loading at 20kHz. The specimen is a flat smooth disc. It is placed on a torus frame and cyclically loaded in compression at the center of its upper face. Consequently disc bending generates a biaxial proportional stress state at the center of the specimen lower face. Any positive loading ratio can be applied. This device has been tested and is well functioning on specimens made of a cast aluminum alloy used to produce cylinder heads. Preliminary results in VHCF regime are compared with literature results obtained under similar stress state but in HCF regime and at 20Hz only.

KILOPARSEC-SCALE DUST DISKS IN HIGH-REDSHIFT LUMINOUS SUBMILLIMETER GALAXIES

ABSTRACT We present high-resolution (0.″16) 870 μm Atacama Large Millimeter/submillimeter Array (ALMA) imaging of 16 luminous ( ) submillimeter galaxies (SMGs) from the ALESS survey of the Extended Chandra Deep Field South. This dust imaging traces the dust-obscured star formation in these galaxies on ∼1.3 kpc scales. The emission has a median effective radius of R e = 0.″24 ± 0.″02, corresponding to a typical physical size of 1.8 ± 0.2 kpc. We derive a median Sérsic index of n = 0.9 ± 0.2, implying that the dust emission is remarkably disk-like at the current resolution and sensitivity. We use different weighting schemes with the visibilities to search for clumps on 0.″12 (∼1.0 kpc) scales, but we find no significant evidence for clumping in the majority of cases. Indeed, we demonstrate using simulations that the observed morphologies are generally consistent with smooth exponential disks, suggesting that caution should be exercised when identifying candidate clumps in even moderate signal-to-noise ratio interferometric data. We compare our maps to comparable-resolution Hubble Space Telescope -band images, finding that the stellar morphologies appear significantly more extended and disturbed, and suggesting that major mergers may be responsible for driving the formation of the compact dust disks we observe. The stark contrast between the obscured and unobscured morphologies may also have implications for SED fitting routines that assume the dust is co-located with the optical/near-IR continuum emission. Finally, we discuss the potential of the current bursts of star formation to transform the observed galaxy sizes and light profiles, showing that the descendants of these SMGs are expected to have stellar masses, effective radii, and gas surface densities consistent with the most compact massive ( 1–2 × 1011 ) early-type galaxies observed locally.

Effect of structure height on the drag reduction performance using rotating disk apparatus

The drag reduction characteristics in a rotating disk apparatus were investigated by using structured disks with different riblet types and dimensions. Two disk types were fabricated with right angle triangular (RAT) grooves and space v-shape (SV) grooves, with six dimensions for each type. A high-accuracy rotating disk apparatus was fabricated and then used to investigate the turbulent drag reduction characterization of the disk in diesel fuel. In this work, the effects of several parameters are investigated; riblet types, riblet dimensions, and rotational disk speed (rpm) on the drag reduction performance. It was found that the surface structure of the disk reduced the drag, this was clearly seen from the comparison of torque values of smooth and structured disks. Drag reduction for structured disks was higher than that for smooth disks, and SV-grooves showed better drag reduction performance than RAT-grooves. In addition, it was observed that the drag reduction performance increased with decreasing groove height for both groove types. The maximum drag reduction achieved in this study was 37.368% for SV-groove at 1000 rpm, compared with 30% for RAT-groove, at the same rotational speed.

Biconcave shape of human red-blood-cell ghosts relies on density differences between the rim and dimple of the ghost's plasma membrane

The shape of the human red blood cell is known to be a biconcave disk. It is evident from a variety of theoretical work that known physical properties of the membrane, such as its bending energy and elasticity, can explain the red-blood-cell biconcave shape as well as other shapes that red blood cells assume. But these analyses do not provide information on the underlying molecular causes. This paper describes experiments that attempt to identify some of the underlying determinates of cell shape. To this end, red-blood-cell ghosts were made by hypotonic hemolysis and then reconstituted such that they were smooth spheres in hypo-osmotic solutions and smooth biconcave discs in iso-osmotic solutions. The spherical ghosts were centrifuged onto a coated coverslip upon which they adhered. When the attached spheres were changed to biconcave discs by flushing with an iso-osmotic solution, the ghosts were observed to be mainly oriented in a flat alignment on the coverslip. This was interpreted to mean that, during centrifugation, the spherical ghosts were oriented by a dense band in its equatorial plane, parallel to the centrifugal field. This appears to be evidence that the difference in the densities between the rim and the dimple regions of red blood cells and their ghosts may be responsible for their biconcave shape.

The Effect of UV Treatment on the Osteoconductive Capacity of Zirconia-Based Materials.

Objective: Improvements in the bioactivity of zirconia implants for accelerated healing and reduced morbidity have been of continuing interest in the fields of dentistry and orthopedic surgery. The aim of the present study was to examine whether UV treatment increases the osteoconductivity of zirconia-based materials. Materials and Methods: Smooth and rough zirconia-based disks and cylindrical implants were treated with UV light for 15 min and subsequently placed in rat femurs. Surface characterization was performed using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle measurements. Results: In vivo histomorphometry revealed that the percentage of bone-implant contact and the amount of bone volume, formed around UV-treated implants, increased by 3–7-fold for smooth surfaces and by 1.4–1.7-fold for rough surfaces compared to non-treated specimens at Weeks 2 and 4 of healing, respectively. A biomechanical test showed that UV treatment accelerated the establishment of bone-zirconia integration and enhanced the strength of the bone-implant interface by two-fold. Additionally, surface characterization of the zirconia disks revealed that UV treatment decreased the amount of surface carbon and converted the hydrophilic status from hydrophobic to superhydrophilic. Conclusions: This study indicates that UV light pretreatment enhances the osteoconductive capacity of zirconia-based materials.

Liquid–solid mass transfer to a rotating mesh electrode in a rotor–stator spinning disc configuration

Here we present the mass transfer coefficient for liquid–solid mass transfer to a rotating mesh electrode and a smooth flat disc electrode in a rotor–stator spinning disc reactor. The mass transfer coefficients are measured with the limiting current density technique. Additionally, the torque is measured and the energy dissipation rate in the system is calculated. The volumetric mass transfer coefficient of the mesh electrode increases a factor 5 compared to that of the flat disc electrode at virtually equal energy dissipation rates. Due to the characteristics of the mesh, the mesh electrode offers 2.77 times higher electrode area than the flat disc. The mass transfer coefficients measured for the rotating mesh electrode are a factor 1.74 higher compared to the flat disc. Average Sherwood numbers are reported and a correlation is presented that predicts mass transfer rates of rotating meshes in rotor–stator spinning disc reactor configurations.

Elastomeric PDMS Planoconvex Lenses Fabricated by a Confined Sessile Drop Technique.

The ubiquity of high quality smartphones at affordable prices not only accelerated the social penetration in the global population but also promoted nontraditional usage of smartphones as point-of-care medical diagnostic devices, sensors, and portable digital microscopes. This paper reveals a simple, rapid, cost-effective, and template-free technique for mass-scale production of an elastomeric PDMS (ePDMS) planoconvex lens capable of converting a smartphone into a portable digital microscope. By taking advantage of the resistance to spreading of liquid by a sharp edge, highly stable spherical cap of viscous liquid PDMS (lPDMS) on a smooth PMMA circular disk was fabricated. The axisymmetric spreading of lPDMS under the gravitational force and interfacial tension force enable the formation of spherical cap with a certain radius of curvature. A thermal treatment at 80 °C for 30 min cured the spherical cap lPDMS into a bubble-free ePDMS planoconvex lens. Lenses with focal lengths of 55.2-3.4 mm could be reproducibly fabricated by adjusting the volume of dispensed lPDMSs and diameter of PMMA disks. High-resolution panoramic microscope images without a distortion of small cylindrical object could be constructed on-the-fly using the imbedded smartphone app. Applications of the smartphone digital microscope equipped with an ePDMS planoconvex lens for imaging of micro printings, gun shot residues, cylindrical objects, and bullet toolmarks were explored.