Roughness Patterns Research Articles

Study of Surface Roughness Effect on the Performance of Multilobe Hybrid Journal Bearing

In this paper, influence of surface roughness on the performance of two lobe and three lobe symmetric non-recessed hybrid journal bearing system has been presented. A modified form of Reynolds' equation using flow factors on the similar line of Patir and Cheng model and flow restrictor equation have been solved by finite element method. In this study, the consequence of roughness orientations on the bearing surfaces on the performance of a 2- lobe and 3-lobe symmetric hole entry hybrid journal bearing are presented for different bearing geometries defined by offset factor (δ=0.9, 1.0 and 1.1). The results of the study indicate that the surface orientation have noteworthy effect on the bearing performance characteristics. An enhanced threshold speed margin has been observed for longitudinal roughness pattern. Further, results of the study indicate that a proper choice of bearing configuration and bearing surface roughness orientation is essential to obtain better performance characteristics of capillary restrictor hybrid journal bearing system.

Numerical Simulation of Rough Thrust Pad Bearing Under Thin-Film Lubrication Using Variable Mesh Density

A numerical simulation of rough slider bearing under thin-film lubrication using variable mesh density has been carried out. The current investigation deals with the effect of deterministic surface roughness patterns, such as triangular, sawtooth, square and sinusoidal roughness patterns and temperature on pressure and film thickness distribution. The nature and shape of roughness and temperature play a significant role in pressure generation, which in turn influences load capacity and frictional coefficient. It has been observed that variable mesh density takes around 25% less number of iterations compared to fixed mesh density. Among all roughness patterns, square roughness dominates the generated pressure. Elastic deformation of greater than 50 nm in bounding surfaces has been found to influence the film formation. Small pressure generated under piezoviscous elastic and thermo-piezoviscous elastic conditions was deficient in causing squeezing effect on lubricant, which suggests that bearing is operating under isoviscous elastic and thermo-viscous elastic conditions instead of piezoviscous elastic and thermo-piezoviscous elastic. Insensitivity in load capacity was observed for a smaller value of film thickness.

Evaluation of reversible shape memory effect in porous SHS TiNi-based compounds fabricated at various ignition temperature

The present study focuses on the relationship between the structural features and reversible shape memory effect (SME) including the related martensitic transformation (MT) in porous TiNi-based compounds fabricated by self-propagating high-temperature synthesis (SHS) at various ignition temperatures. Exploring the as-synthesized samples (S-1 and S-2) ignited at T1 = 400 and T2 = 600 °C, respectively, using a set of research instruments has revealed a key feature that modulates the resultant porous structure and SME parameters. Evidently, the one-step B2 ↔ B19′ MT in both samples is considered to be diffuse within a broad temperature gap, where the hysteresis loop width excels 70 degrees. The fine-porous S-1 indicated the well-developed macrostructure having a rough surface pattern of pore walls, whereas the high-porous S-2 did a dissimilar macrostructure having an even pore surface topology. From a phase-chemical point of view, the metal matrix of S-2 was found to be more homogeneous as compared to that of S-1, that in turn has led to the distinctive SME performance in terms of ε-T upon thermocycling. The extremely heterogeneous S-1 featured by more uniform pore shape and distribution has demonstrated the feasible strain behavior despite the fewer TiNi volume fraction and depressed MT was observed. Conversely, the SME performance for S-2 was shown to be impaired because of the discrepancy in the deformation behavior of small and large pore walls, even though the redundant TiNi volume fraction facilitated the MT.

Turbulent structures in a statistically three-dimensional boundary layer

We investigate the behaviour of large-scale coherent structures in a spanwise-heterogeneous turbulent boundary layer, using particle image velocimetry on multiple orthogonal planes. The statistical three-dimensionality is imposed by a herringbone riblet surface, although the key results presented here will be common to many cases of wall turbulence with embedded secondary flows in the form of mean streamwise vortices. Instantaneous velocity fields in the logarithmic layer reveal elongated low-momentum streaks located over the upwash-flow region, where their spanwise spacing is forced by the$2\unicode[STIX]{x1D6FF}$periodicity of the herringbone pattern. These streaks largely resemble the turbulence structures that occur naturally (and randomly located) in spanwise-homogeneous smooth-/rough-wall boundary layers, although here they are directly formed by the roughness pattern. In the far outer region, the large spanwise spacing permits the streaks to aggressively meander. The mean secondary flows are the time-averaged artefact of the unsteady and spanwise asymmetric large-scale roll modes that accompany these meandering streaks. Interestingly, this meandering, or instability, gives rise to a pronounced streamwise periodicity (i.e. an alternating coherent pattern) in the spatial statistics, at wavelengths of approximately 4.5$\unicode[STIX]{x1D6FF}$. Overall, the observed behaviours largely resemble the streak-instability model that has been proposed for the buffer region, only here at a much larger scale and at a forced spanwise spacing. This observation further confirms recent observations that such features may occur at an entire hierarchy of scales throughout the turbulent boundary layer.

Correlation between anti-thyroid peroxidase antibody levels and diffuse thyroid uptake of 18F-fluorodeoxyglucose in Hashimoto\u2019s thyroiditis: a retrospective study

BackgroundOn 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET), diffuse uptake in the thyroid gland is often observed in patients with Hashimoto’s thyroiditis. In this study, we evaluated the factors associated with diffuse uptake by comparing Hashimoto’s thyroiditis patients with or without diffuse uptake in the thyroid.MethodsA retrospective study was conducted of 18 patients with Hashimoto’s thyroiditis who underwent blood tests, thyroid ultrasonography, and FDG-PET during the period from 2014 to 2015. The patients were divided into two groups: one with diffuse thyroid uptake (group 1, n = 13) and one without diffuse thyroid uptake (group 2, n = 5). Clinical and laboratory parameters, including maximum standardized uptake in the thyroid (SUVmax), which was defined as the higher value obtained in either the right or left thyroid lobe, were compared in the two groups.ResultsThe frequency of abnormal findings, such as a rough or heterogeneous pattern, was significantly higher in group 1 (p < 0.01), as were anti-thyroid peroxidase (TPO) antibody titers, anti-thyroglobulin (Tg) antibody titers, and SUVmax (p < 0.01). The frequency of hypothyroidism did not differ significantly in the two groups. Anti-TPO and anti-Tg titers were positively correlated with SUVmax (r = 0.856, p < 0.01 and r = 0.821, p < 0.01, respectively); in univariate analysis, anti-TPO titer was predictive of SUVmax (p < 0.01).ConclusionsThe results of the current study suggest that Hashimoto’s thyroiditis patients with high titers of anti-thyroid antibodies are likely to exhibit intense diffuse FDG uptake in the thyroid, and that thyroid function may be clearly impaired, even in the presence of mild FDG uptake in the thyroid.

Introduction of lithography-compatible conducting polymer as flexible electrode for oxide-based charge-trap memory transistors on plastic poly(ethylene naphthalate) substrates

To realize highly-functional flexible nonvolatile memories, the organic/inorganic hybrid structures were introduced as suitable approaches to exploit both advantages of flexibility of organic materials and the electrical performance of inorganic materials. Electrically conductive poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) thin film was transferred on plastic poly(ethylene naphthalate) (PEN) substrates and then patterned by conventional photo-lithography process through the optimization of the surface properties in terms of the enhanced interaction between the PEDOT:PSS and the PEN substrate. The gate-stack structure of the charge-trap memory thin-film transistors was designed to be Al2O3 blocking/ZnO charge-trap/Al2O3 tunneling/In-Ga-Zn-O active/PEDOT:PSS source-drain layers. The fabricated device showed the nonvolatile memory operations including charge-trap-assisted memory window. However, the long-tapered rough patterns of PEDOT:PSS and damaged back-channel on organic barrier were demonstrated to be feasible origins for some drawbacks including the high contact resistance of the fabricated prototype device. Appropriate ideas for further improvements memory device characteristics was also suggested.

Ferrofluid-based annular squeeze film bearing with the effects of roughness and micromodel patterns of porous structures

ABSTRACTBased on the ferrohydrodynamic theory by R.E. Rosensweig and roughness effects by Christensen’s stochastic theory, a mathematical model of ferrofluid lubricated flat (parallel) annular disks (plates or surfaces) squeeze film bearing, is developed with the effects of porosity at the upper disk, circumferential or radial roughness at the lower disk and radially variable magnetic field. The validity of the Darcy’s law is assumed for the porous matrix. The resultant modified Reynolds-Darcy equation is solved in terms of Bessel function. Expressions for dimensionless load-carrying capacity are obtained and computed. The results for circumferential roughness pattern show that dimensionless load-carrying capacity increases when thickness & permeability of the porous matrix decreases, and effect of surface roughness & width of the annular part increases. The effects of micromodel patterns of two different porous structures are also discussed. Slightly better performances of the bearing are observed for globular sphere permeability model. A comparative study is also made when lower disk is circumferentially rough or radially rough or smooth for globular sphere model.

Low relative-submergence effects in a rough-bed open-channel flow

ABSTRACTMulti-plane stereoscopic PIV measurements were performed in an open-channel flume fitted with cubes to investigate very low submergence ratios, , where h is the water depth and k the roughness height. The spatial standard deviation of the mean flow components reveals that the extent of the roughness sublayer increases drastically with the decrease in h/k to span the entire water column for the lowest h/k investigated. Despite this, the logarithmic law is still observed on the double-averaged velocity profiles for all h/k, first with a fixed von Kármán constant κ and, second, via the indicator function where κ is a free parameter. Also, the longitudinal and vertical normal stresses indicate a universal boundary layer behaviour independent of h/k. The results suggest that the logarithmic and wake-defect laws can still be applied at such low h/k. However, the lateral normal stress depends on h/k in the range investigated as well as on the geometry of the roughness pattern.

A Study of Hydromagnetic Longitudinal Rough Circular Step Bearing

This article discusses the effect of longitudinal roughness on the performance of hydromagnetic squeeze film in circular step bearing. To characterize the random roughness of the bearing surfaces the stochastic model of Christensen and Tonder has been employed. The stochastically averaged Reynolds’ type equation is solved using suitable boundary conditions to obtain the pressure distribution and then the load bearing capacity is computed. The results are presented in graphical form. The graphical results presented here establish that the hydromagnetic lubrication offers significant help to the longitudinal roughness pattern to enhance the performance of the bearing system. Of course, conductivities of the plates, standard deviation, and the supply pressure contribute towards reducing the negative effect induced by variance (+ve) and skewness (+ve).

Direct replication of micro-nanostructures in the fabrication of superhydrophobic silicone rubber surfaces by compression molding

We describe a simple method for fabricating superhydrophobic high temperature vulcanized (HTV) silicone rubber surfaces by direct replication using a compression molding system. The resulting rubber samples possessed micro-nanostructures on the surface. This micro- and nano-scale roughness produced a water contact angle of >160° and a contact angle hysteresis of <3°. The roughness patterns on chemically etched aluminum surfaces, which served as templates, were successfully replicated on the rubber surfaces. An antistiction coating applied to the template surface ensured that the rubber was completely removed during demolding and that the replicated micro-nanostructures on the silicone surface were preserved. Surface roughness of the aluminum templates was optimized at HCl concentrations of 15 wt.%, with a lower roughness value observed at acid concentrations above and below this value. The developed HTV silicone rubber surfaces also demonstrated a freezing delay and a self-cleaning capacity.

Effects of hole shape on impingement jet array heat transfer with small-scale, target surface triangle roughness

Considered is the addition of special surface roughness patterns to impingement target surfaces to improve the effectiveness and surface heat transfer augmentation levels of impingement cooling. Three different impingement hole shapes are employed within a jet array: circle, racetrack, and triangle. These are designed so that all three hole shapes have the same hydraulic diameter. Different sizes, different shapes, and different distributions of surface roughness elements are utilized, including arrays of small triangle roughness, with different roughness heights, employed with and without the addition of large pin roughness elements. Data are presented for impingement jet Reynolds numbers of 900, 1500, 5000, and 11,000. Overall, the racetrack hole configuration generally provides approximately the same heat transfer augmentation as the circle hole configuration, with slightly better performance, under some conditions. The triangle hole configuration provides lower heat transfer augmentation, compared to both the circle hole and racetrack hole configurations. The addition of small triangle roughness to the target plates shows an increase in heat transfer augmentation, compared to the baseline target plate, for both the circle and racetrack hole configurations. For the triangle hole configuration, the addition of small triangle roughness generally shows negligible or negative improvement, compared to the baseline target plate. Also illustrated is significantly different Reynolds number dependence for impingement cooling, as hole shape changes from circle to racetrack, and triangle.

Hydraulic resistance in open-channel flows over self-affine rough beds

ABSTRACTKnowledge of hydraulic resistance of single-valued self-affine fractal surfaces remains very limited. To advance this area, a set of experiments have been conducted in two separate open-channel flumes to investigate the effects of the spectral structure of bed roughness on the drag at the bed. Three self-affine fractal roughness patterns, based on a simple but realistic three-range spectral model, have been investigated with spectral scaling exponents of −1, −5/3 and −3, respectively. The different widths of the flumes and a range of flow depths also afforded an opportunity to consider effects of the flow aspect ratio and relative submergence. The results show that with all else equal the friction factor increases as the spectral exponent decreases. In addition, the relationship between the spectral exponent and effective slope of the roughness is demonstrated, for the first time. Aspect ratio effects on the friction factor within the studied range were found to be negligible.

Mechanistic Study of HafSOx Extreme Ultraviolet Inorganic Resists

Inorganic resists are promising for nanomanufacturing because of their potential for high-resolution and low line-edge roughness patterning and exceptional sensitivity to extreme ultraviolet (EUV) radiation. Hafnium oxide peroxide hydroxide sulfate (HafSOx) is a model EUV inorganic photoresist, wherein the EUV absorption coefficients for hafnium and O are much higher than for conventional polymer resists. Absorption of EUV radiation leads to electron emission that results in the HafSOx solubility change. We used desorption-based techniques to elucidate thermal- and radiation-induced processes that contribute to the HafSOx solubility switch. We found that low kinetic energy electrons render HafSOx insoluble and result in the desorption of molecular O2. Electron-stimulated desorption and postexposure Raman spectroscopy indicate similar kinetics for peroxide loss in HafSOx. Temperature-programmed desorption studies found that peroxide ligand desorption is best characterized as first order, with a broad distr...

The effects of surface roughness on the transient characteristics of hydrodynamic cylindrical bearings during startup

Abstract The effect of surface roughness on the transient characteristics of the hydrodynamic cylindrical bearing during startup is studied. A mixed lubrication model considering both asperity contact and hydrodynamic fluid flow is solved. The asperity contact pressure is obtained by the Greenwood-Williamson (GW) contact model. The hydrodynamic pressure is calculated by modified average Reynolds equation with finite element method (FEM). The transient movement of the journal center, the transient average film thickness, the hydrodynamic pressure and the contact pressure are presented for different surface roughnesses. The contact time and contact zone in different types of surface roughness are obtained. The influences of the standard deviation of asperity height (σ) and rough surface patterns on these parameters are analyzed. The results show that the surface roughness has an important influence on the transient characteristics of the bearing during the initial period of startup.

Statistical significance of spatial correlation patterns in armoured gravel beds

ABSTRACTStructure function analyses are increasingly used to investigate spatial correlation patterns of river bed roughness. However, traditional structure function analyses remain mostly qualitative as the statistical significance of correlation patterns has not been explicitly addressed. This paper proposes a methodology for the analysis of 2D second-order structure functions based on statistical significance testing. Using data from flume experiments with gravel beds, a method to create surrogate rough beds is proposed. The surrogate beds are subsequently used to carry out Monte-Carlo simulations which in turn are used to evaluate statistical significance of the structure functions values. The method is applied to two datasets of gravel surfaces and the results are used to investigate the physical meaning of the obtained significance patterns. The results confirm previous studies that the orientation of large grains can be described by 2D second-order structure functions through a central ellipse reflecting areas of high spatial correlation. The main axes of the ellipses can hence be interpreted to define characteristic roughness length scales. The novelty of the present paper is that the proposed significance testing allows for a more rigorous definition of the spatial extent of the central ellipse.

Activated partial thromboplastin time derivative curves: helpful diagnostic tool in mixing test interpretation.

: The mixing test is used to evaluate whether prolonged activated partial thromboplastin time (APTT) is due to an inhibitor or a factor deficiency. The coagulation reaction is demonstrated with APTT derivative curves on the ACL TOP series. We aimed to determine the utility of APTT derivative curves in the mixing test process. The plasma of a patient was mixed with normal plasma in a 1 : 1 ratio and APTT assay was performed with SynthASil reagent. We observed roughness, biphasic and shoulder patterns in derivative curves during the mixing test. An extended laboratory investigation revealed a positive lupus anticoagulant, low factors XI and IX activities. Along with mixing test cut-off limits, we recommend analysing changes in APTT derivative curves to minimize erroneous interpretations of the mixing test. Derivative curves display either a normalizing pattern in factor deficiencies or an atypical pattern in the presence of lupus anticoagulant.

Molecular Glass Photoresists with High Resolution, Low LER, and High Sensitivity for EUV Lithography

AbstractNovel molecular glasses (MGs) containing bisphenol A backbone (BPA‐6 and BPA‐10) are synthesized and characterized. BPA‐6 and BAP‐10 are excellent amorphous materials for extreme ultraviolet (EUV) patterning applications with good thermal stability (Td more than 160 °C). The MGs can be used as positive‐tone photoresists combined with triphenylsulfonium perfluoro‐1‐butanesulfonate and trioctylamine dissolved in propylene glycol monomethyl ether acetate. High‐resolution feature sizes as small as 23.1 nm with extremely low line edge roughness (less than 2 nm), high sensitivity (less than 20 mJ cm−2), and good high aspect ratio patterns are obtained by using EUV lithography.

Combined effect of surface roughness and pressure-dependent viscosity over couple-stress squeeze film lubrication between circular stepped plates

In this paper, the effect of surface roughness and pressure-dependent viscosity over couple-stresses squeeze film lubrication between circular stepped plates is studied. The modified average Reynolds equation is derived for the one-dimensional roughness structures, namely the radial roughness pattern and azimuthal roughness pattern. Modified equations for the nondimensional pressure, load-carrying capacity, and nondimensional squeeze film time are obtained. Also, the obtained results of our study for some special cases are compared with the previously published smooth surface case, and the results are found to be in very good agreement. It is observed that, one-dimensional azimuthal (radial) roughness pattern on the rough circular stepped plate increases (decreases) the load-carrying capacity and the squeeze film time as compared to the smooth case.

The Effect of Surface Roughness on Diffusion and Chemical Reaction Controlled Limiting Currents on a Rotating Cylinder Electrode in Deaerated Solutions with and Without CO2

The influence of surface roughness on mass transfer on a rotating cylinder electrode apparatus is investigated experimentally for a roughness pattern consisting of grooves parallel to the direction of fluid flow. Mass transfer from four different samples, with roughness values of 0.5 μm, 6 μm, 20 μm, and 34 μm, is measured using the limiting current technique for a range of rotational speeds in NaCl solutions saturated with N2 at pH = 3 and 4. Comparison with available correlations for the Sherwood number in literature (which are independent of surface roughness and are either for specific or arbitrary roughness patterns) shows that H+ mass transfer only correlates well for particular levels of roughness and that their accuracy can be increased if a correlation is utilized which is a function of surface roughening. A new correlation for Sherwood number as a function of the Reynolds number, Schmidt number, and surface roughness is proposed which agrees well with the mass transfer observed from all of the rough surface cases considered for this particular roughness pattern. Complementary experiments in CO2 environments were used to assess the combined limiting current associated with H+ and H2CO3 reduction (with the latter occurring via the buffering effect and being associated with the slow CO2 hydration step). Although the increase in sample roughness clearly leads to an increase in the rate of H+ mass transfer, in the CO2 environments considered, surface roughness is found to have no significant influence on the limiting current contribution from H2CO3, which can therefore be determined from Vetter’s equation across this range of operating conditions.

SAR Mode Altimetry Observations of Internal Solitary Waves in the Tropical Ocean Part 1: Case Studies

It is well known that internal waves (IWs) of tidal frequency (i.e., internal tides) are successfully detected in sea surface height (SSH) by satellite altimetry. Shorter period internal solitary waves (ISWs), whose periods (and spatial scales) are an order of magnitude smaller than tidal internal waves, have been generally assumed too small to be detected with conventional altimeters. This is because conventional (pulse-limited) radar altimeter footprints are somewhat larger than or of similar size, at best, as the typical wavelengths of the ISWs. Here we demonstrate that the synthetic aperture radar altimeter (SRAL) on board the Sentinel-3A can detect short-period ISWs. A variety of signatures owing to the surface manifestations of the ISWs are apparent in the SRAL Level-2 products over the ocean. These signatures are identified in several geophysical parameters, such as radar backscatter (sigma0), sea level anomaly (SLA), and significant wave height (SWH). Radar backscatter is the primary parameter in which ISWs can be identified owing to the measurable sea surface roughness perturbations in the along-track sharpened SRAL footprint. The SRAL footprint is sufficiently small to capture radar power fluctuations over successive wave crests and troughs, which produce rough and slick surface patterns arrayed in parallel bands with scales of a few kilometers. The ISW signatures are unambiguously identified in the SRAL because of the exact synergy with OLCI (Ocean Land Colour Imager) images, which in cloud-free conditions allow clear identification of the ISWs in the sunglint OLCI images. We show that both sigma0 and SLA yield realistic estimates for routine observation of ISWs with the SRAL, which is a significant improvement from previous observations recently reported for conventional pulse-limited altimeters (Jason-2). Several case studies of ISW signatures are interpreted in light of our knowledge of radar backscatter in the internal wave field. An analysis is presented for the tropical Atlantic Ocean off the Amazon shelf to infer the frequency of the phenomena, being consistent with previous satellite observations in the study region.