DLC films have many excellent properties, such as high wear resistance and a low friction coefficient, and are used in an increasing range of application fields. However, their low transmission of visible light prevents DLC films from being used for transparent materials. Nano-segment structured DLC (S-DLC) film with a segmented pitch equal to or less than the wavelength of visible light is supposed to not only solve this problem but also improve its mechanical properties. In this study as preliminary stage of nano S-DLC film, we fabricated DLC films consisting of 1-μm-size segments which have not only high wear resistance but also unique optical characteristics. This structure on DLC film was fabricated by electron beam lithography followed by liftoff method, which is suitable for nanoscale micromachining. The micro segment structured DLC films with groove width of 1 μm and pitch of 20 μm had rounded edges because the resist mask acted as an electrode. Micro S-DLC film exhibited structural colors because of the reflection-type diffraction grating and its transmittance was lower than that of continuous DLC films. From ball on disk test, it was found that the wear resistance of the micro S-DLC film with a groove of 1 μm was superior to that of a normal continuous DLC film and the small edge curvature could improve wear resistance furthermore.
Metal nanoparticles such as platinum (Pt) and gold (Au) decorated CNTs have been thoroughly investigated as electrode of fuel cells and chemical and biological sensors. In these applications, the size and the density of nanoparticles are very important, because the catalyst activation depends on the particle size and the deposition amount. We focused on a dry processing without solutions and attempted to fabricate metal nanoparticles on CNTs by sputtering. In this study, the effect of the crystallinity of CNTs surface on the morphology of Pt film deposited by sputtering process was investigated. To control the crystallinity of CNTs surface, the Ar plasma irradiation was applied to CNTs and the crystallinity of CNTs surface was analyzed by Raman spectroscopy. As results, the ID/IG ratio of CNTs surface increased with the Ar plasma irradiation time. This suggested that the crystallinity of CNTs was changed to amorphous carbon with increasing the plasma time. Furthermore, the morphology of Pt on as-received CNTs and plasma-treated CNTs was changed to island shape by annealing at 750°C. As a result, the particle size on plasma-treated CNTs was smaller with increasing the plasma treatment time. This indicated that morphology of Pt on CNTs related to crystallinity of CNTs surface.
This paper describes the characterization of a metal-core piezoelectric ceramics fiber/aluminum composite as a metal-based piezoelectric composite. Piezoelectric materials, especially piezoelectric ceramics are generally used as excellent transducer materials. However, there are serious disadvantages, as they are very brittle and need a complicated electrode system with an adhesion layer to generate piezoelectricity. Therefore, the application of piezoelectric ceramics is limited. In order to solve these problems, a metal-core piezoelectric ceramics fiber/aluminum composite was developed. The metal-core piezoelectric fiber is not as brittle as bulk ceramics, but it is still too brittle to be embedded in an aluminum matrix using a conventional process. Therefore, the interphase forming/bonding method was applied to embed it in an aluminum matrix without fracture. Using this successful approach, a simple electrode system was formed between the metal core of the embedded fiber and the matrix. As this material system is expected to be used as a robust sensor and energy harvester, its output voltage and power characteristics were evaluated with vibration test equipment and compression vibration equipment. According to the results, the output voltage generated from the specimen is proportional to its strain, and dependent on its direction. It was also found that the output power generated from the specimen increases with the square of its strain, and in proportion to its frequency, and the calculated maximum output power reaches approximately 3.4 mW when the specimen undergoes 0.2 % strain and 600 Hz frequency by vibration. As this output power is generated from the single embedded fiber, it is suggested that the energy for driving a wireless module can be secured by embedding multiple fibers. Consequently, a composite embedded with multiple fibers will be able to be used as a wireless strain sensor owing to its strain measurement and energy-harvesting capabilities.
This paper describes the development of a metal-core piezoelectric ceramics fiber/aluminum composite using a low cost hollow fiber. To develop this composite, this study applied a new fabrication process to fill the Al-Cu liquid phase alloy produced during the interphase forming/bonding (IF/B) method in the hollows. The IF/B method is a sophisticated transient liquid phase (TLP) bonding method developed to enable embedding fragile functional fibers at low temperature and low pressure in a short time period by using the eutectic reaction of inserting material and matrix. To increase the filling rate as well as removing the voids and the excessive Al-Cu alloy that remained in the matrix, the effects of the hot pressing temperature, the pressure, and the period were optimized in experiments. Under a hot pressing temperature of 873 K, a pressure of 2.2 MPa, and a period for 3.0 ks, the filling rate attained 99% without harmful chemical reactions between the fiber and the matrix, and the voids were successfully removed. In addition, it was clarified that the Al-Cu alloy core and the aluminum matrix worked as electrodes and that the embedded fiber could generate a relatively high output voltage, as well as the conventional metal-core piezoelectric ceramics fiber.
We reveal the fundamental and dominant flow structures of thermal convection in a cubic cavity under forced oscillation heated differentially by analysing the flow field with the proper orthogonal decomposition (referred to as POD). The database is made of consequtive series of three-dimensional results obtained by the direct numerical simulation based on the Boussinesq approximation for a forcedly-oscillating cube under the zero-gravity environment, at vibrational Rayleigh number (the Rayleigh number based on the cavity's acceleration amplitude instead of the gravitational acceleration) Raη = 5.0×104 - 1.1×105, Plandtl number Pr = 7.1 (water) and non-dimensional forced-oscillating frequency ω = 1.0×100 - 2.0×102. The direction of the forced sinusoidal oscillation is parallel to the temperature gradient. It appears that the most energetic POD modes, or the first POD eigenfunctions with large eigenvalues, account for the transient process on flow structures during one forcing cycle. The first eigenfunctions correspond to the steady and laminar flow structures which appear inside a non-oscillating cube in the terrestrial environments. The POD expansion coefficient is found to be useful for predicting a consecutive series of the dominant flow structures.
We have investigated the feasibility of the hybrid-type method of lattice Boltzmann and Brownian dynamics as a simulation technique for a magnetic particle suspension. To do so, we have addressed aggregation phenomena in thermodynamic equilibrium and have compared the present results with those of Monte Carlo method and the previous lattice Boltzmann method based on fluctuation hydrodynamics (FH). The viscosity-modifying technique has been employed for sophisticating the activation level of the translational and rotational Brownian motion of magnetic particles. From the results regarding the snapshots and pair correlation functions, the present hybrid-type simulation method is seen to show good agreement with the results of Monte Carlo and FH-based lattice Boltzmann method both quantitatively and qualitatively. For example, the characteristics of the magnetization are in good agreement with Monte Carlo and FH-based lattice Boltzmann results. This clearly shows that the rotational Brownian motion of magnetic particles is activated at a physically reasonable level.
To date, no study has been conducted on analytical methods to solve the fluid dynamics governing equations system for the fluid-elastic vibration of tube arrays in a straightforward manner. In this paper, a semi-analytical method for this vibration problem is investigated by considering the system as a collection of regular polygon cells and expressing unknowns on each side of the cells by base expansion. Based on this expression, the solutions in the cell are expressed in terms of polar coordinates, allowing for circumferential variation in the radial coordinate interval. Via this means, a reduced-order model is developed for the tube array-fluid system and the proposed method is verified by comparing with earlier experimental results.
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