An application of a homogenization method to the estimation of effective thermal conductivity of a hydrogen storage alloy bed considering variation of contact conditions between alloy particles

A homogenization method is applied to the estimation of effective thermal conductivity of a hydrogen storage alloy bed. By including the contact conditions between the alloy particles, the effect of contact conditions on the thermal conductivity is investigated.     

Structure and magnetic properties of mono- and bi-layer graphene films on ultraprecision figured 4H-SiC(0001) surfaces

Monolayer and bilayer graphene films with a few hundred nm domain size were grown on ultraprecision figured 4H-SiC(0001) on-axis and 8 degrees -off surfaces by annealing in ultra-high vacuum. Using X-ray photoelectron spectroscopy (XPS), atomic force microscopy, reflection high-energy electron diffraction, low-energy electron diffraction (LEED), Raman spectroscopy, and scanning tunneling microscopy, we investigated the structure, number of graphene layers, and chemical bonding of the graphene surfaces. Moreover, the magnetic property of the monolayer graphene was studied using in-situ surface magneto-optic Kerr effect at 40 K. LEED spots intensity distribution and XPS spectra for monolayer and bilayer graphene films could become an obvious and accurate fingerprint for the determination of graphene film thickness on SiC surface.     

Motion control of industrial robots by considering serial two-link robot arm model with joint nonlinearities

This paper presents a model based motion control approach for industrial robots by considering a serial two-link robot arm model with joint nonlinearities. In order to achieve the desired performance using the model based control approaches, it is important to obtain relevant models of both kinematics and dynamics including nonlinear characteristics. Main nonlinear components that lead to trajectory tracking errors of typical multi-axis industrial robot are joint nonlinearities in each axis and dynamic coupling effects between different axes. In this paper, a parametric modeling approach is introduced to reproduce behaviors of a serial two-link robot arm with joint nonlinearities. Nonlinear stiffness, angular transmission errors, and friction in these two links are directly identified as joint nonlinearities. This approach is applied for the serial two-link arm of a typical multi-axis industrial robot, which has low frequency vibration modes and significantly affects to the trajectory performance. Effectiveness of the modeling is verified by comparative studies with numerical simulations and experiments. Finally, a 2-DOF control scheme with the identified two-link dynamic model and a feedback loop-shaping with a variable notch filter are applied to improve the performance of trajectory tracking and residual vibration suppression.     

Structural aspects of the LCST phase behavior of poly(benzyl methacrylate) in room-temperature ionic liquid

The structure and lower critical solution temperature (LCST) phase behavior of well-defined poly(benzyl methacrylate) (PBnMA) solution using 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, [C₂mim][NTf₂] ionic liquid (IL) as a solvent have been studied by dynamic light scattering (DLS) and small-angle neutron scattering (SANS) at various temperatures. The SANS profiles observed for fully deuterated IL ([C₂mim]-d₁₁[NTf₂]) containing PBnMA were kept practically unchanged in the temperature range between 298 and 363 K, while they suddenly changed at 363 K. This indicates that the LCST behavior of PBnMA-IL solution is a first-order phase transition, which is consistent with the DLS results. The SANS profiles below 363 K were well represented by the theoretical Debye scattering function with inter-molecular interaction and the radius of gyration, R_g was estimated to be almost constant, i.e., ∼45 Å. The SANS result obtained here was compared with those in aqueous PNIPAm solutions as a typical LCST system, and some differences between IL and aqueous solution systems are pointed out. It is found that thermodynamic quantities (ΔH_demix, ΔS_demix and ΔG_demix) from the homogeneous solution to the phase separation states strongly depend on the solvation of the PBnMA polymer by the IL ([C₂mim] cation and [NTf₂] anion). We propose an LCST phase separation mechanism in the polymer-IL solution.     

Initial stage of carbon nanotube formation process by surface decomposition of SiC: STM and NEXAFS study

Formation process of carbon nanocaps, which are formed at the beginning of carbon nanotube (CNT) growth by surface decomposition of SiC, was investigated by scanning tunneling microscopy (STM) and in situ near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. As Si atoms were desorbed, carbon nanoparticles 1-2 nm in diameter were accumulated on SiC(000-1) surfaces. At around 1200 °C, these were coalesced and crystallized to carbon nanocaps. In addition, just before the crystallization, majority of C-C bonds were directed nearly parallel to the surface. Based on these experimental results, we proposed a model for carbon nanocap formation, which plays an important role to determine the CNTs.     

Superplastic deformation of hydroxyapatite ceramics with B2O3 or Na2O addition fabricated by pulse current pressure sintering

High-density and fine-grained transparent hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂: HAp) ceramics with B₂O₃ and Na₂O addition were fabricated using pressureless sintering and pulse-current pressure sintering between 1000 and 1100 °C; the superplastic deformation of these HAp specimens was evaluated. The relative density of pure HAp compacts pulse-current pressure sintered at 1000 °C for 10 min under a pressure of 50 MPa attained 99.9% and exhibited translucency. The tensile elongation of the pure HAp specimen, which was measured at 1000 °C under a strain rate of 1.48 × 10⁻⁴ s⁻¹, was as high as 364%. The relative density of HAp compacts with 3.0 mol.% B₂O₃ addition pulse-current pressure sintered under the same conditions as those of pure HAp compacts was 98.9%, whereas the grain size was as low as 0.24 μm. The elongation of HAp specimens, measured at a test temperature of 1000 °C under a strain rate of 1.48 × 10⁻⁴ s⁻¹, was as high as 578%.     

Novel unidirectional porous hydroxyapatite used as a bone substitute for open wedge high tibial osteotomy

Purpose: The purpose of this study was to clinically and radiologically evaluate the availability, osteoconductivity, and resorption of a novel unidirectional porous hydroxyapatite (UDPHAp) used as an artificial substitute for open wedge high tibial osteotomy (OWHTO). Our hypothesis was that UDPHAp is a safe and useful bone substitute for OWHTO. Materials and methods: Seven patients (2 men and 5 women aged 34-72years) who underwent OWHTO and were followed up for more than 12months were retrospectively studied. After the osteotomy, the gap created was filled with UDPHAp(REGENOS® Kuraray Co.Ltd). Radiography and computed tomography(CT) were performed, and gap healing was assessed postoperatively. The Japanese Orthopaedic Association (JOA) knee score was determined pre- and post-operatively for clinical evaluation. Results: Neither gross displacement nor collapse of the UDPHAp block graft was observed within 12 months after surgery. Both radiographs and CT showed attenuation of lucency and increasing sclerosis over time. JOA score improved from 71.2 (65?80) to 95.8 (85?100). Conclusions: Short term results for OWHTO using UDPHAp was satisfactory. Clinical improvement of JOA scores were seen, besides osteogenesis was progressing in and around the artificial bone grafts.     

On the damping analysis of FRP laminated composite plates

This paper presents the damping analysis of fiber reinforced plastics laminated composite plates. For this purpose, the maximum strain and kinetic energies of a cross-ply laminated plate are evaluated analytically based on the three-dimensional theory of elasticity. The displacements of the simply supported rectangular plates are expanded into the polynomial forms with respect to a thickness coordinate, and then governing equations are formulated by using the Ritz's method. In the numerical calculations, natural frequencies and modal damping ratios are calculated for the plates with different stacking sequence and thickness ratios. The validity of the assumption of deformations and the applicability of the other plate theories (e.g. classical lamination theory (CLT), first-order shear deformation theory (FSDT) and higher-order shear deformation theory) to the laminated thick plates are discussed by comparing the numerical results obtained by the present method with the CLT and the FSDT solutions.     

Quantum size effect in TiO2 nanoparticles prepared by finely controlled metal assembly on dendrimer templates

The use of dendrimer templates to make metal-based nanoparticles of controlled size has attracted much interest. These highly branched macromolecules have well-defined structures that enable them to bind metal ions to generate precursors that can be converted into nanoparticles. We describe the sub-nanometre size control of both anatase and rutile forms of TiO2 particles with phenylazomethine dendrimers, leading to samples with very narrow size distributions. Such fine tuning is possible because both the number and location of metal ions can be precisely controlled in these templates. Quantum size effects are observed in the particles, and the energy gap between the conduction and valence bands exhibits a blueshift with decreasing particle size and is dependent on the crystal form of the material. The dependency of the bandgap energy on these factors is explained using a semi-empirical effective mass approximation.