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A one-step method was developed to create a highly biocompatible micropatterned surface on a diamond-like carbon (DLC) through irradiation with a nitrogen ion beam and thus enhance the biocompatibility of osseointegrated surfaces and biotribological performance of articular surfaces. The biocompatibility and biotribological mechanisms were analyzed in terms of the structure and morphology of DLC. It was demonstrated that a layer enriched in sp3 C−N bonds was formed on the surface of the DLC after nitrogen ion beam irradiation. Moreover, with an increase in the radiation dose, the content of sp3 C−N on the DLC surface increased significantly, and the biocompatibility was positively correlated with it. The adhesion of the MC3T3 osteoblasts increased significantly from 32% to 86% under an irradiation dose of 8 × 1015 ions/cm2. In contrast, the micropattern had a significant negative effect on the adhesion of the osteoblasts as it physically hindered cell expansion and extension. The micropattern with a depth of 37 nm exhibited good friction properties, and the coefficient of friction was reduced by 21% at relatively high speeds.

Graphene is considered as a promising material for reducing friction and wear, owing to its structural features. The tribological properties of graphene depend on several factors, including thickness, fabrication process and substrate properties. However, the effect of substrate on the tribological behaviors of graphene films are not well known. Previous reports describe the nanoscale friction and wear behaviors of graphene films on different substrates, but the substrate effect-dependent macroscale tribological behaviors have not been demonstrated yet. In this work, the macroscale tribological performance of graphene films on different types of molybdenum (Mo)-based substrate coatings was investigated. It was found that the substrate coating hardness significantly influenced the tribological performance of graphene films as well as the formation of an effective lubricating transfer film. At a critical hardness value of the Mo-based substrate coating, the graphene film showed a low friction coefficient of ∼0.16 for 10,000 sliding cycles and a significant (∼16 × ) reduction in wear rate compared to that of the Mo single-layer coating without the graphene film. These findings aid in understanding the substrate-related tribological behaviors of graphene and thus widen its application in various industries.

PurposeThe current study aims to explain the influence of technological interactivity and media sociability on sport consumer value co-creation behavior via collective efficacy and collective intelligence.Design/methodology/approachSubjects were individuals who have a mobile smart device and experience of accessing sport-related community websites (n = 513). A face-to-face self-administered survey was employed based on the convenience sampling method. A structural equation modeling test was conducted to examine the relationships between the variables.FindingsTechnological interactivity and media sociability based on mobile smart devices improve sport consumers' collective efficacy, and media sociability positively affects collective intelligence. Also, perceived collective efficacy and collective intelligence in virtual communities induce consumers to engage in the value co-creation process more actively (i.e. consumer participation behavior and citizenship behavior). One of the key findings includes the significant role of media sociability in the process of value co-creation between consumers and sport organizations. Media sociability is more likely to contribute to improving sport consumers' collective efficacy and the development of intelligence than the properties of technological interactivity.Originality/valueResearch findings contribute to extending the body of knowledge in interactivity studies related to sport consumers' value co-creation behaviors in the virtual environment context.

Reduced graphene oxide (rGO) has received significant attention as a potential solid lubricant material owing to its superior mechanical and tribological properties. It is considered to be a self-lubricating derivative of graphite because of its low interlayer shear stress. To further understand rGO as a lubricant material, it is necessary to clarify its evolution on the wear track during the sliding process. In this work, a dual in-situ analysis was performed via a tribo-tester instrumented with three-dimensional (3D) laser microscopy and micro-Raman spectrometer. This novel method was employed to investigate the evolutions of tribological, topographical and microstructural characteristics of the rGO coating during the sliding process. The evolution process on the wear track was demonstrated in real time via Raman spectroscopy and 3D confocal profiler. The tribological properties of the rGO coating were affected by the morphology and microstructure of the rGO on the wear track. In addition, the failure mechanism of the rGO coating was attributed to the processes of formation, removal and re-deposition of rGO-based tribofilm. Furthermore, it was determined that variation of morphology and chemical structure of wear track were synchronous in certain sliding stages.

Epoxy is a polymeric material that is widely used in various fields as an adhesive, coating, and bulk material due to its outstanding properties. Many research studies on reinforced polymers have been conducted by adding micro/nanoparticles or fibers to attain better tribological properties. However, the tribological properties of patterning on the epoxy surface are relatively obscure. In this study, friction and wear properties of flat and V-groove patterned epoxy specimens were analyzed in dry and water lubricated sliding conditions to assess the effectiveness of the surface pattern in reducing friction and wear. It was found that under low applied force conditions in which the V grooves remained almost intact, the surface pattern contributed to decreasing the friction coefficient as much as 0.12 and increasing the stability of frictional behavior in dry sliding condition. This outcome was attributed to the ability of the grooves to trap wear debris inside the cavities. However, under water lubrication with polytetrafluoroethylene (PTFE) particles used as additives, the V-groove specimens were less effective in reducing friction due to the relatively small contact area. As the contact area increased, the effect of water lubrication with PTFE particles in reducing friction could be enhanced. These results are expected to serve as a fundamental basis for designing and fabricating the surface of polymeric components for tribological applications in dry and lubricated conditions.

Polymer gears are used extensively in various applications. However, durability issues have been emerging because of friction at gear tooth contact areas. To extend the lifetime of polymer gears, a low-frictional coating has been considered as a possible strategy. In this study, a finite element simulation method was performed to investigate the contact stress between a pair of coated polymer gears. The simulation included various friction coefficients (COFs) for studying the effects of friction during the operation. Numerical results revealed that the friction causes the contact stress to shift over the roll angle, which is attributed to the direction of the sliding friction based on a free-body diagram. We also investigated the effects of coating and found that a thin coating has little effect on the bulk deformation behavior of the gear. Moreover, the stress distribution in the coating at the pitch point was investigated as the COF increased. Under zero friction, three notable stress regions were observed: 1) the center of the surface, 2) the end of the contact, and 3) the overall contact area. As COF was increased in the micro-slip region of the contact interface, both tensile and compressive stresses in the coating increased. This study provides significant aid to engineers for understanding the stress response of the coating applied to polymer gears to achieve an optimal design.

Although high dynamic range (HDR) display has become popular recently, the legacy content such as standard dynamic range (SDR) video is still in service and needs to be properly converted on HDR display devices. Therefore, it is desirable for HDR TV sets to have the capability of automatically converting input SDR video into HDR video, which is called reverse tone mapping (RTM). In this paper, we propose a novel learning-based low-complexity RTM scheme that not only expands the suppressed dynamic ranges (DR) of the SDR videos (or images), but also effectively restores lost detail in the SDR videos. Most existing conventional RTM schemes have focused on how to expand the DR of global contrast, resulting in limitations in recovering lost detail of SDR videos. On the other hand, the recent convolutional neural network-based approaches show promising results, but they are too complex to be applied on the users’ devices in practice. In this paper, our learning-based RTM scheme is computationally simple but effective in recovering lost detail. To learn the SDR-to-HDR relation, training “SDR-HDR” images are first separated into their base layer components and detail layer components by applying a guided filter. The detail layer components of the “SDR-HDR” pairs are used to train the SDR-to-HDR mapping. The mapping matrices are computed based on kernel ridge regression. In the meantime, the global contrast of the base layers is expanded by a nonlinear function that suppresses darker regions and amplifies brighter regions to fit the full DR of a target HDR display. To verify the effectiveness of our learning-based RTM scheme, we performed subjective quality assessment for images and videos. The experimental results show that our RTM scheme outperforms the existing RTM scheme with the successful restoration of lost detail in SDR images.

In swarm robotic systems, task allocation is a challenging problem aiming to decompose complex tasks into a series of subtasks. We propose a self-organizing method to allocate a swarm of robots to perform a foraging task consisting of sequentially dependent subtasks. The method regulates the proportion of robots to meet the task demands for given tasks. Our proposed method is based on the response threshold model, mapping the intensity of task demands to the probability of responding to candidate tasks depending on the response threshold. Each robot is suitable for all tasks but some robots have higher probability of taking certain tasks and lower probability of taking others. In our task allocation method, each robot updates its response threshold depending on the associated task demand as well as the number of neighbouring robots performing the task. It relies neither on a centralized mechanism nor on information exchange amongst robots. Repetitive and continuous task allocations lead to the desired task distribution at a swarm level. We also analyzed the mathematical convergence of the task distribution among a swarm of robots. We demonstrate that the method is effective and robust for a foraging task under various conditions on the number of robots, the number of tasks and the size of the arena. Our simulation results may support the hypothesis that social insects use a task allocation method to handle the foraging task required for a colony’s survival.

C60 fullerene has been utilized in various applications, including low friction and wear coatings, due to its unique molecular structure. In this work, molecular dynamics simulations were conducted to assess the nano-mechanical behaviour of a single C60 fullerene and its crystallized structure. A single C60 model and a model of a face-centred cubic structured C60 crystal with a one-unit-cell thickness were prepared for compression and unloading simulations based on the adaptive intermolecular reactive empirical bond-order potential for carbon. Force–displacement curves and molecule-averaged virial stresses were obtained during the simulation. The models applied during the compression and unloading processes were visualized to confirm the deformation behaviour. Both the single and crystal C60 models showed a perfectly reversible deformation before the point of force decrease that occurred during compression. In particular, the face-centred cubic structure of the crystal C60 model was severely altered during compression before the individual C60 molecules experienced permanent deformation. The maximum values of the normal virial stress in the compression direction before the permanent deformation of the molecules were almost same for both the single and crystallized models.

Poly(methyl methacrylate) (PMMA)-based denture base resins easily develop oral bacterial and fungal biofilms, which may constitute a significant health risk. Conventional bacterial-resistant additives and coatings often cause undesirable changes in the resin. Reduced bacterial resistance over time in the harsh oral environment is a major challenge in resin development. Poly(2-methoxyethyl acrylate) (PMEA) has anti-fouling properties; however, due to the oily/rubbery state of this polymer, and its surface aggregation tendency in a resin mixture, its direct use as a resin additive is limited. This study aimed to optimize the use of PMEA in dental resins. Acrylic resins containing a series of PMEA polymers with various molecular weights (MWs) at different concentrations were prepared, and the mechanical properties, surface gloss, direct transmittance, and cytotoxicity were evaluated, along with the distribution of PMEA in the resin. Resins with low-MW PMEA (2000 g mol

Description, By engineering the interfaces, a coating with superior properties compared to conventional nanolayered coatings was designed., Notwithstanding the success of nanolayered coatings in the reduction of wear at nano-/microscales, the improvement of the wear resistance at the macroscale remains an issue. Moreover, the effects of nanointerfaces in nanolayered coatings on their macrotribological properties are not understood well. This paper reports on the engineering of nanointerfaces in diamond-like C/Cr nanolayered coatings to tailor their characteristics including the degree of intermixing, defects, and Cr growth mode. The result was the fabrication of a coating with subnanometer-thick periodic albeit discrete Cr interlayers. This was achieved using our patented deposition technique. This coating contained less interfacial defects compared to classic nanolayered coatings with continuous nanolayers and presented record-breaking wear rates at the macroscale. Finite Element analysis was performed and micropatterning strategy was used to reduce the wear rate further. Last, we report on discovery of a dimensionless parameter that can be used to predict the wear resistance of carbon-based nanolayered coatings.

Thermochromic microcapsules with two kinds of phase change materials that can change color with gradient under 70 °C were prepared. To induce gradient color change in the thermochromic microcapsule...

Purpose The aim of this study is to find how the pyruvate intake and aerobic exercise effect on the body composition, exercise performance ability, blood factor and obesity related hormone, and to verify the effect of pyruvate intake and aerobic exercise as an effective substance for obesity improvement. Methods This study selected 20 obese men in their twenties who has more BMI than 25kg/m2, and are applicable in 25% of the body fat, and randomly sampled group of 10 people for pyruvate intake and aerobic exercise (PYA), and 10 people for placebo intake and aerobic exercise (PLA). Intake of pyruvate and placebo was implemented for 10 weeks, 6 g a day, and aerobic exercise, treadmill exercise in the intensity of 50 ~ 60%’s target heart rate, was conducted for 10 weeks, 3 times a week, 60 minutes a day. To demonstrate the effect of pyruvate intake and aerobic exercise, all of the body composition, exercise performance ability, Lactate, and blood factor and hormone related to obesity were measured before and after the test in the same manner. Results The main results from this study are as follow; 1) In the case of body composition, in PYA, weight(p < .01), BMI(p < .05), body fat percentage(p < .01), and body weight without fat(p < .001) are reduced meaningfully. 2) In the exercise performance ability increased significantly in both PYA(p < .01) and PLA(p < .001) for VO2max, Also, in the case of distance during the exercise, PYA(p < .01) and PLA(p < .05) increased significantly in 15 minutes and PYA(p < .01) and PLA​(p < .05) 30 minutes, but only in PYA from 45 minutes(p < .01) to 60 minutes(p < .05) 3) In case of Lactate, the significant decrease in PYA during stabilization and the significant increase in PYA after 30 minutes of exercise was not seen after 45 minutes 4) In the case of blood factor, HDL-C showed a meaningful decrease in PLA(p < .05) and Leptin showed a meaningful decrease in PYA(p < .001). Conclusions To sum up these results, it was more effective for the group of PYA which ingested pyruvate in improving obesity, even when the same aerobic exercise is conducted.

Titanium-diamond-like carbon (Ti-DLC) composite coatings were deposited on 304 SUS substrates by periodic sputtering of Ti in between DLC deposition with different Ti target powers using a magnetron sputtering system. Microstructure as well as the mechanical and tribological properties of the Ti-DLC composite coatings were highly dependent on the Ti target power which was varied from 75 to 150 W. Transmission electron microscopy (TEM) confirmed that the Ti atoms in DLC coatings were in an amorphous state which was beneficial for deterring crack nucleation within the coating. Furthermore, premature delamination of a pure DLC coating with a thickness of ∼330 nm could be prevented by inclusion of Ti in DLC. All the Ti-DLC composite coatings were capable of drastically enhancing the friction and wear properties of bare 304 SUS. The coating deposited with a target power of 85 W showed the highest wear resistance with a wear rate of ∼3.13 × 10−11 mm3/N mm, which was extremely low for a dry sliding condition. This outcome was attributed to ultra-fine distribution of amorphous Ti in DLC which led to low internal stress and high ID/IG ratio of the coating.

Electrical contacts are widely utilized in numerous engineering applications that require high reliability. However, fretting wear due to repeated contact may lead to increased electrical contact resistance that can cause failure of the electrical system. Herein, an Ag-based coating was prepared by an electroless co-deposition technique in order to improve the electroconductive properties under fretting conditions. By carefully controlling the deposition time, a relatively smooth and continuous Ag coating could be obtained. The structure of the coating was analyzed using X-ray diffraction, 3D confocal microscopy, and scanning electron microscopy techniques. The electroconductive tribological properties of the coating were assessed using a custom-built fretting tester. The Ag coating possessed good crystallinity and exhibited improved electroconductive properties compared with the Ni interlayer deposited on a steel substrate. The high temperature of the contact zone generated by friction contributed to the reduced electric resistance. Furthermore, incorporation of graphene as a dopant could improve the coating wear resistance, resulting in more reliable electroconductive properties in the fretting condition. The wear mechanism of the coating was also investigated through wear track analysis. The experimental results are expected to aid in understanding the electroconductive tribological properties of Ag coatings used in electrical contact applications.

Sputtered carbon material has been receiving much attention as a solid lubricant coating owing to its high hardness and low coefficient of friction. However, its relatively low wear resistance performance when applied on a ductile substrate has limited its use in certain applications. In this work, a porous WS2 sublayer was introduced to the sputtered carbon-based nanoscale multilayer coating to improve its tribological properties. The microstructural, mechanical and tribological properties of the nanoscale C/WS2 multilayer coating were systematically investigated using various analytical techniques. Through structural optimization, a durable coating with excellent wear resistance and low frictional performances could be attained for a ductile steel substrate. The excellent toughness allowed the coating to deform with the ductile substrate without fracturing during contact sliding process. Furthermore, the first self-destruction and then recombination behaviors of dense/porous-coupled nanoscale multilayer coating as well as the selective release of carbon component to the contact interface driven by the frictional interaction aided in maintaining low friction. As a result, the nanoscale multilayer coating showed approximately 100-fold greater wear resistance than that of pure hard carbon coating on a ductile steel substrate.

Ion-beam irradiation of diamond-like carbon (DLC) by He ions was studied. Molecular dynamics simulation was performed to understand the effects of irradiation on the nano-topography and chemical state of the coatings and determine the optimal irradiation conditions. Then, the experiment was conducted to validate the results of the simulation and correlate surface modifications to biomedical properties. It was demonstrated that the irradiation led to the formation of a low-density and low-sp3 content surface layer. The structural and chemical properties of the final surface were nearly independent of the initial sp3 content and irradiation energy. The biocompatibility of DLC-based nanocomposite coatings was significantly improved by ion-beam irradiation. Nanocomposite coatings were irradiated by 1 keV He ions. Irradiation with a dose of 4.2 × 1015 ion/cm2 increased the adhesion of MG63 cells dramatically from 10 to ∼100%.

In this study, SiN x/BN periodical nanolayered coatings (PNCs) are developed. PNCs were deposited at the room temperature on plastic and glass substrates. They demonstrate the excellent mechanical durability of inorganic materials and optical transparency and flexibility of organic ones. The 150 nm thick PNC shows optical transparency, sapphire-like hardness, high wear protection, and flexibility. Such a coating with a superior combination of optical and mechanical properties has not been reported previously.

The task allocation problem has been a challenging issue in swarm robotic systems. In this paper, we handle dynamic task allocation in the object foraging task, where multiple robots are supposed to collect various objects in parallel during a given time span. We propose a decentralized strategy of the response threshold model without any communication among robots. Here, we introduce a task selection probability function for each robot to balance the task demands with robots working on tasks. The method can produce varying tendencies to tasks by changing the response thresholds given in the task selection probability function. With this property, each robot can select its own task among all available tasks, by regulating the response threshold values. This ultimately promotes a desired task distribution in a group level and reduces the number of task changes. Our approach suggests that the response threshold of robot is updated based on what objects have been observed recently and what tasks have been done by its neighboring robots observed in the local surrounding area. We provide a convergence analysis that the system can stochastically converge to the equilibrium of the desired task distribution. The method is effective even when only local information about the environment is given to individual robots. The suggested method is tested with a simulation of multiple robots taking the foraging task, and a dynamic task allocation process is demonstrated.