Disk Surface Research Articles

Evaluation on frictional performance of three different oil-lubricated impregnated graphite seal rings for aircraft integrated drive generators

Abstract The frictional performance of the shaft-end graphite seal rings plays a critical role in determining the maintenance-free duration of aircraft integrated drive generators, and significantly depends on the types of graphite materials used. In this study, three types of graphite materials, including epoxy resin, metal antimony and furan resin impregnated ones, were selected for evaluation using a rotating-type tribometer. The frictional test configuration involved an actual graphite seal ring sliding against the surface of a 12Cr2Ni4A disc under the lubrication of 4050 high-temperature synthetic aerospace lubricating oil, which was highly consistent with the practical operational conditions. The frictional performance of the three different impregnated graphite seal rings, including coefficient of friction, two-dimensional (2D)/three-dimensional (3D) morphologies of wear marks and wear rate of ring mass, were quantitatively analyzed and compared. The experimental results indicated that the metal antimony-impregnated graphite seal ring behaved with the smallest coefficient of friction among the three seal rings. 2D and 3D surface roughness parameters of the metal antimony impregnated graphite seal are the smallest. The wear rate of the seal ring’s mass is only approximately 22% of that of furan resin impregnated seal ring. The corresponding investigations demonstrated that the currently employed epoxy resin-impregnated graphite seal rings could be replaced by new candidates with better frictional performance to improve the service life.

JWST Detects Neon Line Variability in a Protoplanetary Disk

We report the first detection of variability in the mid-infrared neon line emission of a protoplanetary disk by comparing a JWST Mid-InfraRed Instrument Medium Resolution Spectrometer spectrum of SZ Cha taken in 2023 with a Spitzer Infrared Spectrograph Short-High spectrum of this object from 2008. We measure the [Ne iii]-to-[Ne ii] line flux ratio, which is a diagnostic of the high-energy radiation field, to distinguish between the dominance of EUV- or X-ray-driven disk photoevaporation. We find that the [Ne iii]-to-[Ne ii] line flux ratio changes significantly from ∼1.4 in 2008 to ∼0.2 in 2023. This points to a switch from EUV-dominated to X-ray-dominated photoevaporation of the disk. We present contemporaneous ground-based optical spectra of the Hα emission line that show the presence of a strong wind in 2023. We propose that this strong wind prevents EUV radiation from reaching the disk surface while the X-rays permeate the wind and irradiate the disk. We speculate that at the time of the Spitzer observations, the wind was suppressed and EUV radiation reached the disk. These observations confirm that the MIR neon emission lines are sensitive to changes in high-energy radiation reaching the disk surface. This highlights the [Ne iii]-to-[Ne ii] line flux ratio as a tool to gauge the efficiency of disk photoevaporation in order to provide constraints on the planet formation timescale. However, multiwavelength observations are crucial to interpret the observations and properly consider the star–disk connection.

MINDS

Context. The Mid-InfraRed Instrument (MIRI) Medium Resolution Spectrometer (MRS) on board the James Webb Space Telescope (JWST) allows us to probe the inner regions of protoplanetary disks, where the elevated temperatures result in an active chemistry and where the gas composition may dictate the composition of planets forming in this region. The disk around the classical T Tauri star Sz 98, which has an unusually large dust disk in the millimetre with a compact core, was observed with the MRS, and we examine its spectrum here. Aims. We aim to explain the observations and put the disk of Sz 98 in context with other disks, with a focus on the H2O emission through both its ro-vibrational and pure rotational emission. Furthermore, we compare our chemical findings with those obtained for the outer disk from Atacama Large Millimeter/submillimeter Array (ALMA) observations. Methods. In order to model the molecular features in the spectrum, the continuum was subtracted and local thermodynamic equilibrium (LTE) slab models were fitted. The spectrum was divided into different wavelength regions corresponding to H2O lines of different excitation conditions, and the slab model fits were performed individually per region. Results. We confidently detect CO, H2O, OH, CO2, and HCN in the emitting layers. Despite the plethora of H2O lines, the isotopo-logue H218O is not detected. Additionally, no other organics, including C2H2, are detected. This indicates that the C/O ratio could be substantially below unity, in contrast with the outer disk. The H2O emission traces a large radial disk surface region, as evidenced by the gradually changing excitation temperatures and emitting radii. Additionally, the OH and CO2 emission is relatively weak. It is likely that H2O is not significantly photodissociated, either due to self-shielding against the stellar irradiation, or UV shielding from small dust particles. While H2O is prominent and OH is relatively weak, the line fluxes in the inner disk of Sz 98 are not outliers compared to other disks. Conclusions. The relative emitting strength of the different identified molecular features points towards UV shielding of H2O in the inner disk of Sz 98, with a thin layer of OH on top. The majority of the organic molecules are either hidden below the dust continuum, or not present. In general, the inferred composition points to a sub-solar C/O ratio (<0.5) in the inner disk, in contrast with the larger than unity C/O ratio in the gas in the outer disk found with ALMA.

Evolution of microscopic characteristics of rolling contact fatigue coexisting with wear of U75V rail

During the damage and defects related to rolling contact fatigue (RCF), together with wear occurring at the rail surface, the microscopic characteristics of the rail material change with the accumulation of wheel cycles. To find the relationship between rail material characteristics and RCF damage under wheel-rail contact situations, a series of twin-disc rolling-sliding tests, based on real wheel-rail contact situations at a radius of 80 mm rail profile, was established for a heavy-haul railway in China. The microscale characteristics of the rail disc contact surface was researched, including crack, wear, roughness, and hardness of the U75V rail with different load cycles. The results show that the damage mechanism of RCF and wear alternately dominates the rail disc surface at the microscale, taking a certain cycle as a boundary which makes the RCF crack number and wear rate have opposite evolutionary trends. The above factors also affect the wear at the surface rail discs, alternating between fatigue and adhesion. Meanwhile, increasing the surface micro-hardness leads to a decrease in the relative wear rate and an increase in the roughness, length and number of RCF cracks. The plastic deformation layers, including the severely deformed layer (SDL) and the transition layer (TL), almost maintain the same thickness and the dynamic equilibrium increases during the cycles. Two kinds of cracks are initiated and propagated at the rail disc surface, one at the SDL and the other at the junction of SDL and TL. The number of each kind of crack depends on the SDL thickness.

Thermal transport of magnetized hybrid nanofluid swirling over a disk surface with Hall current and thermal radiation effects

The current research focuses on the impact of Hall current on the flow of hybrid nanofluids over an unsteady, radially stretching, and rotating slippery disk surface. Additionally, the noteworthy characteristics of the Lorentz force resulting from the collaboration of the magnetic field with the motion of hybrid nanofluids are investigated. The convective condition, heat source/sink, and thermal radiation are used to study the heat transfer process. In the present physical model, which is made up of aluminium oxide (Al2O3) and copper oxide (CuO) with water, a novel class of nanofluids known as the hybrid nanofluid is being used. The system of partial differential equations from the current model is converted into ordinary differential equations using similarity transformations and then solved using the bvp4c scheme in MATLAB. The statistics show that a hybrid nanofluid transfers heat at a rate that is significantly higher than a nanofluid. Furthermore, it is noted that the Hall current effect increases radial and azimuthal flows while lowering the fluid temperature. By changing the radiation and Eckert numbers, energy transport is improved.

Pulp cell response to the application of silver diamine fluoride and potassium iodide on caries-like demineralized dentin.

To investigate the response of pulp cells to the application of silver diamine fluoride (SDF) and potassium iodide (KI) on demineralized dentin. The occlusal surfaces of human dentin discs (0.4mm thick) with similar permeability were subjected to an artificial caries protocol, and then the discs were adapted into artificial pulp chambers. MDPC-23 cells were seeded on the healthy pulp dentin surface, while the demineralized surface was treated with SDF, KI, SDF + KI, or hydrogen peroxide (positive control-PC) (n = 8). The negative control (NC) received ultrapure water. After 24h, cell viability (alamarBlue) and morphology (SEM) were evaluated. The extracts were then applied to new MDPC-23 cells seeded in culture plates to assess their viability and the formation of mineralized nodules (MN; Alizarin Red) after seven days. The data were analyzed using one-way analysis of variance/Tukey or Games-Howell tests (α = 5%). SDF and PC significantly reduced the viability of cells seeded on discs (45.6% and 71.0%, respectively). Only cells treated with SDF or PC detached from the dentin substrate, while the remaining cells showed altered morphology. Cells in contact with extracts showed less reduction in viability, but it was still more toxic compared to NC. Only PC reduced MN deposition. SDF + KI or KI alone did not affect the cell response. SDF applied alone showed a mild to moderate transdentinal cytotoxic effect on pulp cells. However, the combination of SDF + KI reduced the cytotoxic effects. Both materials used alone or in combination did not affect the mineralization ability of pulp cells. Besides improving esthetic results, associating potassium iodide with silver diamine fluoride may reduce the transdentinal cytotoxic effects of this cariostatic agent on pulp cells.

High‐Efficiency Single‐Droplet Energy Harvester for Self‐Sustainable Environmental Intelligent Networks

AbstractOur community is still far away from achieving self‐sustainable ambient intelligence, since it calls for rational energy layouts to satisfy the ubiquitous power demands from diverse terminal products. Harnessing energy directly from the surroundings thus provides ideal solutions. The majority of existing environmental harvesters rely on sophisticated procedures and expensive or toxic materials; while others attempt to streamline the complexity at the cost of compromising performance. This entails transducers that exhibit superb outputs and also employ cost‐effective, even recycled materials and straightforward protocols to render ubiquitous deployments. Here, a high‐efficiency droplet energy nanogenerator (DENG) is devised to satisfy all the requirements. The DENG is fabricated by directly coating a composite layer on a recycled digital video disk surface. It achieves superb electricity generation from one droplet, with an output voltage of >190 V at an instantaneous power density of 65 W m−2, and an energy conversion efficiency of 3.60%. Diverse demonstrations confirm the applicability of the DENG in environmental networks, encompassing self‐sustainable “on plants” sensing systems, smart building windows, and remote environmental monitoring platforms. In light of these superiorities, it is believed that the DENG may open up new alternative routes for future energy strategies.

Surface assessment of CNC laser treated commercially pure Titanium and Ti 13 Zr 13 Nb alloy

This study aimed to evaluate the surface changes of commercial pure Titanium disks (CP Ti) and the Ti 13Nb 13 Zr (Alloy) with a zigzag pattern of laser surface treatment. In vitro, experimental study of CNC Laser treatment on the CP Ti and Alloy disks. Texturing the surfaces of CP Ti and Alloy disks via CNC laser, the sample disks were analyzed using surface roughness, wettability and FESEM. The FESEM revealed a proper increase in the surface texturing and roughness on macro and micro measures without crack formation or dramatic change of the core substance of the CP Ti and Alloy disks. The CNC laser is an effective and suitable method for surface texturing CP Ti and Alloy for dental implantology. Keywords: Commercial pure Titanium; Ti 13 Zr 13 Nb alloy; CNC Laser; Laser surface texturing; Dental implant and surface roughness

Advanced lithium disilicate: A comparative evaluation of translucency and fatigue failure load to other ceramics for monolithic restorations

The aim of this in vitro study was to evaluate the surface roughness, translucency, fatigue failure load (FFL), and number of cycles for fatigue failure (CFF) of a recently released lithia-based material called advanced lithium disilicate and three other ceramics indicated for monolithic restorations. First, ALD (advanced lithium disilicate, CEREC Tessera, Dentsply Sirona), LD (lithium disilicate, IPS e. max CAD, Ivoclar), LS (lithium silicate-disilicate, Suprinity, Vita Zahnfabrik), and 4Y-PSZ (Yttria-stabilized zirconia, IPS e.max ZirCAD MT, Ivoclar) discs (n = 15, Ø = 10 mm and thickness = 1.0 mm) were fabricated from CAD/CAM blocks/discs, A2 shade. The discs were sintered/crystallized and subsequently analyzed by a rugosimeter (Mitutoyo SJ-410) to determine Ra and Rz surface roughness parameters. Next, they were evaluated to determine the translucency parameter (TP) using a bench-top spectrophotometer (SP60, EX-Rite). The discs were subsequently cemented to glass fiber epoxy resin discs, and the specimens were tested under cyclic loading (Step-test), immersed in distilled water at a frequency of 20 Hz, with an initial cyclic load of 200 N for 5,000 cycles and increments of 50 N every 10,000 cycles until failure. Fatigue failure load (FFL) and number of cycles for fatigue failure (CFF) were recorded for subsequent Kaplan Meier analysis, with post-hoc Mantel-Cox and Weibull analysis (α = 0.05). Complementary fractographic, topographic and energy dispersive spectroscopy analyses (EDS) were performed. 4Y-PSZ showed higher survival (p < 0.05), with higher FFL and CFF (1077 N; 180,333 cycles), followed by LD (980 N; 161,000 cycles), LS (937 N; 152,333 cycles) and ALD (910 N; 147,000 cycles). No differences were observed between the tested groups regarding Weibull modulus. ALD presented TP (28.14) equal to DL (28.27) and higher than LS (25.51). All lithia-based materials had higher translucency than 4Y-PSZ (TP = 8.62) (p < 0.05). ALD appears to have a similar elemental composition to LD and LSD for oxygen and silicon. ALD and LSD have a similar zirconium content. Fractures originated on the cemented surface of the ceramic discs. Lithia-based ceramics showed lower surface roughness, with ALD (Ra = 0.04 μm; Rz = 0.66 μm) showing the lowest values (p < 0.05). Despite showing lower FFL when compared to LD and 4Y-PSZ, ALD has compatible translucency and mechanical fatigue performance with its indication for fabricating monolithic, anterior and posterior adhesively cemented single-unit restorations. However, further studies are needed to substantiate its clinical performance.

The Impact of Mechanical Debridement Techniques on Titanium Implant Surfaces: A Comparison of Sandblasted, Acid-Etched, and Femtosecond Laser-Treated Surfaces.

This study evaluated the effects of various mechanical debridement methods on the surface roughness (Ra) of dental implants, comparing femtosecond laser-treated surfaces with conventionally machined and sandblasted with large-grit sand and acid-etched (SLA) implant surfaces. The fabrication of grade 4 titanium (Ti) disks (10 mm in diameter and 1 mm thick) and the SLA process were carried out by a dental implant manufacturer (DENTIS; Daegu, Republic of Korea). Subsequently, disk surfaces were treated with various methods: machined, SLA, and femtosecond laser. Disks of each surface-treated group were post-treated with mechanical debridement methods: Ti curettes, ultrasonic scaler, and Ti brushes. Scanning electron microscopy, Ra, and wettability were evaluated. Statistical analysis was performed using the Kruskal-Wallis H test, with post-hoc analyses conducted using the Bonferroni correction (α = 0.05). In the control group, no significant difference in Ra was observed between the machined and SLA groups. However, femtosecond laser-treated surfaces exhibited higher Ra than SLA surfaces (p < 0.05). The application of Ti curette or brushing further accentuated the roughness of the femtosecond laser-treated surfaces, whereas scaling reduced the Ra in SLA surfaces. Femtosecond laser-treated implant surfaces, with their unique roughness and compositional attributes, are promising alternatives in dental implant surface treatments.

Allelopathic effects of three lichen secondary metabolites on cultures of aposymbiotically grown lichen photobionts and free-living alga Scenedesmus quadricauda

In the present work, we studied the influence of lichen secondary metabolites (evernic acid, orcinol, usnic acid) on selected species of algae: Trebouxia erici, photobiont of lichen Cladonia cristatella producing typical lichen secondary metabolites, Coccomyxa solorinae-saccatae, photobiont of lichen Solorina saccata which does not produce typical secondary metabolites of lichens, and free-living alga Scenedesmus quadricauda.For the determination of the cytotoxic effects of these compounds, algae were cultivated on the surface of disks composed of glass microfibers, in quantities of 0.1 mg/disk for each metabolite. After 14-days prolonged cultivation, we analysed selected physiological parameters: growth of algae, chlorophyll a fluorescence, the content of ascorbic acid, content of reduced and oxidized glutathione and contents of selected organic acids. The presence of secondary compounds typically inhibited the growth of tested algae and chlorophyll a fluorescence. In the presence of evernic acid and usnic acid, we observed a decrease of ascorbic acid, glutathione, and significant changes in the composition of organic acids.Lichen metabolites, except for their other biological and ecological roles, may act as phytotoxic substances, causing oxidative stress in photobiont cells. These metabolites may play an important role in the “controlled parasitism” of fungal partner on algal/cyanobacterial partner of symbiosis. Differences in the sensitivity of algal cells from different habitats to lichen compounds are, however, not understood sufficiently.

Wettability and Frictional Studies of PEEK Composites against Co-Cr Alloys with Surface Textures.

With the aim of promoting the qualities for total hip joint replacement, the wettability and tribological behaviors of PEEK composites pins with two sets of different fillers (PEEK/CF or PEEK/CF/PTFE/graphite) against Co-Cr alloy discs with five categories of surface textures (polished, orthogonal, spiral, r-θ, and orthogonal combined with spiral) were explored. It is revealed that the existence of CF in PEEK matrix increases the hydrophilicity in addition to the strength of PEEK, while the addition of PTFE increases the hydrophobicity of PEEK. The Co-Cr alloy discs with hydrophilic properties can be adjusted as hydrophobic, with the depth of textured grooves exceeding the critical sag height determined by the contact angle and the groove width. It can be concluded that PEEK/CF/PTFE/graphite composite has a lower wear rate than PEEK only reinforced with CF against Co-Cr alloy, both without surface texture and with shallow or deep grooves. The existence of shallow grooves on the disc surface could help the PEEK blends to achieve a steady friction against Co-Cr alloy in addition to collecting the worn debris. PEEK blend pins with 10 vol% CF, 10 vol% PTFE and 10 vol% graphite can achieve a lower friction coefficient of no more than 0.2 against Co-Cr alloy discs with shallow grooves around 3.5 μm in orthogonal or spiral textures.

A resolved rotating disk wind from a young T Tauri star in the Bok globule CB 26

Context. The disk-outflow connection plays a key role in extracting excess angular momentum from a forming protostar. Although indications of jet rotation have been reported for a few objects, observational constraints of outflow rotation are still very scarce. We have previously reported the discovery of a small collimated molecular outflow from the edge-on T Tauri star-disk system in the Bok globule CB 26 that shows a peculiar velocity pattern, reminiscent of an outflow that corotates with the Keplerian disk. However, we could not ultimately exclude possible alternative explanations for the origin of the observed velocity field. Aims. We report new, high angular resolution millimeter-interferometric observations of CB 26 with the aim of revealing the morphology and kinematics of the outflow at the disk-outflow interface to unambiguously discriminate between the possible alternative explanations for the observed peculiar velocity pattern. Methods. The IRAM PdBI array and the 30 m telescope were used to observe HCO+(1–0) and H13CO+(1–0) at 3.3 mm and 12CO(2–1) at 1.3 mm in three configurations plus zerospacing, resulting in spectral line maps with angular resolutions of 3.″5 and 0.″5, respectively. The SMA was used to observe the HCO+(3–2) line at 1.1 mm with an angular resolution of 1.″35. Additional earlier observations of 13CO(1-0) at 2.7mm with an angular resolution of 1.″0, obtained with OVRO, are also used for the analysis. Using a physical model of the disk, which was derived from the dust continuum emission, we employed chemo-dynamical modeling combined with line radiative transfer calculations to constrain kinematic parameters of the system and to construct a model of the CO emission from the disk that allowed us to separate the emission of the disk from that of the outflow. Results. Our observations confirm the disk-wind nature of the rotating molecular outflow from CB 26 - YSO 1. The new high-resolution data reveal an X-shaped morphology of the CO emission close to the disk, and vertical streaks extending from the disk surface with a small half-opening angle of ≈7°, which can be traced out to vertical heights of ≈500 au. We interpret this emission as the combination of the disk atmosphere and a well-collimated disk wind, of which we mainly see the outer walls of the outflow cone. The decomposition of this emission into a contribution from the disk atmosphere and the disk wind allowed us to trace the disk wind down to vertical heights of ≈40 au, where it is launched from the surface of the flared disk at radii of RL ≈ 20–45 au. The disk wind is rotating with the same orientation and speed as the Keplerian disk and the velocity structure of the cone walls along the flow is consistent with angular momentum conservation. The observed CO outflow has a total gas mass of ≈ 10−3 M⊙, a dynamical age of τdyn ≈ 740 yr, and a total momentum flux of ṖCO ≈ 1.0 × 10−5 M⊙ km s−1 yr−1, which is nearly three orders of magnitude larger than the maximum thrust that can be provided by the luminosity of the central star. Conclusions. We conclude that photoevaporation cannot be the main driving mechanism for this outflow, but it must be predominantly a magnetohydrodynamic disk wind. It is thus far the best-resolved rotating disk wind observed to be launched from a circumstellar disk in Keplerian rotation around a low-mass young stellar object (YSO), albeit also the one with the largest launch radius. It confirms the observed trend that disk winds from Class I YSOs with transitional disks have much larger launch radii than jets ejected from Class 0 protostars.

Thick accretion disk configurations around a compact object in the brane-world scenario

We have studied the equipotential surfaces of a thick accretion disk around a Casadio–Fabbri–Mazzacurati compact object in the brane-world scenario, which possesses a mass parameter together with a parameterized post-Newtonian (PPN) parameter. With the increase in the PPN parameter, the size of the thick accretion disk decreases, but the corresponding Roche lobe size increases. Thus, the larger PPN parameter yields the larger region of existing bound disk structures, where the fluid is not accreted into the central wormhole. Moreover, with the increase in the PPN parameter, the position of the Roche lobe gradually moves away from the central compact object, and the thickness of the region enclosed by the Roche lobe decreases near the compact object but increases in the region far from the compact object. Our results also show that the pressure gradient in the disk decreases with the PPN parameter. These effects of the PPN parameter on the thick accretion disk could help one to further understand compact objects in the brane-world scenario.

A theoretical investigation of the MHD water-based hybrid nanofluid flow over a convectively heated rotating disk surface with velocity slips and zero mass flux conditions

A theoretical investigation of the MHD water-based hybrid nanofluid flow over a convectively heated rotating disk surface with velocity slips and zero mass flux conditions

Modeling of the High-velocity Jet Powered by the Massive Star MWC 349A

MWC 349A is a massive star with a well-known circumstellar disk rotating following a Keplerian law, and an ionized wind launched from the disk surface. Recent observations with the Atacama Large Millimeter/submillimeter Array (ALMA) carried out toward this system, however, have revealed an additional high-velocity component in the strong, maser emission of hydrogen radio recombination lines (RRLs), suggesting the presence of a high-velocity ionized jet. In this work, we present 3D non-LTE radiative transfer modeling of the emission of the H30α and H26α maser lines, and of their associated radio continuum emission, toward MWC 349A. By using the MORELI code, we reproduce the spatial distribution and kinematics of the high-velocity emission of the H30α and H26α maser lines with a high-velocity ionized jet expanding at a velocity of ∼250 km s−1, surrounded by MWC 349A’s wide-angle ionized wind. The bipolar jet, which is launched from MWC 349A’s disk, is poorly collimated and slightly misaligned with respect to the disk rotation axis. Thanks to the unprecedented sensitivity and spatial accuracy provided by ALMA, we also find that the already known, wide-angle ionized wind decelerates as it expands radially from the ionized disk. We briefly discuss the implications of our findings for understanding the formation and evolution of massive stars. Our results show the huge potential of RRL masers as powerful probes of the innermost ionized regions around massive stars and of their high-velocity jets.

A Novel Apparatus to Standardize the Polishing Protocol to Achieve Different Roughness of Titanium and Zirconia Disc Surfaces.

To propose and evaluate standardized polishing protocols for in vitro experiments using a custommade apparatus under controlled force to create consistent surface roughness on titanium and zirconia discs. A total of 160 discs were manufactured with a diameter of 10 mm, 80 titanium (Ti) and 80 zirconium oxide (Zr). Specimens were categorized into two groups: controlled force (CF) and without controlled force (WCF). Specimens in the CF group were polished with a custom apparatus incorporating a tension gauge on the Ti and Zr disc surfaces to achieve consistent roughness. The WCF group was polished without the use of a tension gauge. Each group had four subgroups (n &#61; 10): control/machined with no polishing (C), rough (R), smooth (S), and very smooth (VS). The subgroups were processed using a sequence of diamond-impregnated polishing burs and polishing paste. The CF group showed consistent surface roughness and a gradual decrease in surface roughness. Control in Ti (Ra &#61; 6.5 ± 0.03 μm) and in Zr (Ra &#61; 5.4 ± 0.04 μm); R in Ti (Ra &#61; 3.5 ± 0.06 μm) and in Zr (Ra &#61; 3.2 ± 0.07 μm); S in Ti (Ra &#61; 1.5 ± 0.04 μm) and in Zr (Ra &#61; 1.1 ± 0.06 μm); and VS in Ti (Ra &#61; 0.05 ± 0.002 μm) and in Zr (Ra &#61; 0.02 ± 0.005 μm). There were significant differences for R, S, and SV under CF and WCF in Ti and Zr surfaces. The specimens polished under control force produced significantly more uniform surface roughness than those polished without controlled force and were produced with a higher degree of consistency.

Simulation of adsorption at rotating disk

Abstract Diffusion-controlled adsorption at the rotating disk is calculated for Frumkin isotherm. The near equilibrium isotherms are simulated and their time components are analysed. The purpose of the work is to investigate the physical meanings of S-shaped isotherms that appear for strong attractions in the adsorbed layer. It is demonstrated that the surface coverage that is created gradually, by the diffusion process, consumes the concentration gradient of the dissolved surfactant in the diffusion layer. Once the equilibrium with the bulk of the solution is established, the driving force of diffusion-controlled adsorption vanishes and no additional adsorption is possible. The diffusion layer thickness on the rotating disk tends to the constant value and the flux depends only on the concentration of dissolved adsorbent at the disk surface. Hence, the equilibrium with the bulk of solution is established faster than at the stationary disk. This equilibrium takes an infinite amount of time to reach, but the system can approach close to the equilibrium within a definite period of time. The near equilibration time depends on the bulk concentration of surfactant. These relationships exhibit sharp maxima under the influence of attractions in the adsorbed layer.

Evaluation of UV photofunctionalization effect on ultrastructural properties of SLA titanium disks: An in vitro study.

The success rate of dental implants diminishes over time; the lack of osseointegration and infection are the major causes of most implant failures. One of the effective methods to improve the surface properties is to irradiate ultraviolet (UV) light. This study investigated the effect of UV photofunctionalization on the ultrasuperficial properties of sandblasted, large-grit, acid-etched (SLA) titanium discs. In this in vitro study, 24 sandblasted and acid-etched titanium discs, with a lifespan of more than four weeks, were categorized into three groups (n=8): control, ultraviolet C (UVC), and ultraviolet B (UVB). Then, they were exposed to a UV light source for 48 hours at a 1-cm distance. In addition to measuring the contact angle between the liquid and the disc surface in each of the three groups, the atomic concentrations of carbon, oxygen, and nitrogen atoms were measured at three different sites on each disc. One-way ANOVA and post hoc Tukey tests were used to analyze data. The mean concentration of carbon atoms significantly differed in the control, UVC, and UVB groups (P<0.001). The mean concentrations of nitrogen atoms differed significantly between the three groups (P<0.001). However, the mean concentrations of oxygen atoms were not significantly different between the three groups. In examining the contact angle, wettability was higher in the UVC group than in the UVB group and higher in the UBV group than in the control group. Photofunctionalization with UV light significantly decreased carbon and nitrogen concentrations on the surface of titanium implants, indicating that the implant's superficial hydrocarbons were eliminated. It was observed that UVC photofunctionalization was more effective than UVB photofunctionalization in reducing superficial contamination and improving wettability.

Investigation of friction and scuffing during loss of lubrication on a high velocity twin-disc test rig

Increasing demands on gear components such as high-pressure and high speeds are aggravated by weight saving strategies eliminating an optional secondary lubrication system during negative g operations or windmilling, which result in loss of lubrication conditions (LOL) and scuffing. In order to understand gear design options able to withstand LOL at high velocities, systematic, fundamental studies on model test-rigs, e.g. twin-disc rigs, are required. For this purpose, a twin-disc rig was designed which is able to perform test at high entrainment velocities of up to 80 m/s and high lubricant injection temperatures. Systematic studies have been carried out in continuous lubrication and LOL condition and evaluated in terms of friction and time-of failure (TOF). A mixed EHL model complemented the experimental matrix for wider range of temperatures and additionally compared the influence of the grinding direction on the lubricant gap.Entrainment velocity showed to have the most prominent influence on friction in continuous mode, mostly for the increase from 8 m/s to 23 m/s, followed by minor changes upon further increase to 30 m/s. The influence of injection temperature was mostly prominent at high entrainment velocities. Contact pressure had the strongest influence on TOF. Comparisons with superfinished disc surfaces exhibited a high increase in TOF and significantly less scuffing damage fractures on the runway.