Incident energy dependence of the scattering dynamics of water molecules on silicon and graphite surfaces: the effect on tangential momentum accommodation

The scattering dynamics of water molecules on solid surfaces was investigated using the molecular beam technique. In contrast to the experiments previously reported in the literature, the range of incident energy was chosen to cover the typical kinetic energies of gas molecules in equilibrium at room temperature (35–130 meV). Even in such a narrow energy range, the angular distribution of scattered molecules is heavily affected by the incident energy, exhibiting both a nearly cosine distribution and a lobular distribution, which has a clear peak close to the specular direction. Interestingly, the tangential momentum accommodation coefficients (TMACs) estimated from the scattering experiments show opposite energy dependences on graphite (0001) and silicon (100) surfaces. As the incident energy increases, the TMAC decreases on the graphite surface, whereas it increases on the silicon surface. These trends can be attributed to the relatively large adsorption energy of water molecules on these surfaces and the atomic-scale surface corrugation, although a rigorous understanding requires further analysis by molecular dynamics simulations. Our findings suggest the need for an elaborate slip-flow model that takes account of the incident energy effect to accurately analyze water vapor flow in micro/nanostructures, which is ubiquitous in nature and engineering applications.     

High-speed stability of a rigid rotor supported by aerostatic journal bearings with compound restrictors

Demands for higher rotational speed and accuracy for effective manufacture of small holes on printed circuit boards and very small precise parts have been increasing remarkably. Aerostatic journal bearings with compound restrictors have greater stiffness than those with conventional inherently compensated restrictors and are one of the most effective candidates to satisfy these demands. In this work, the instability of a rigid rotor supported by aerostatic journal bearings with compound restrictors was investigated numerically and experimentally. It was found that this type of aerostatic bearings showed a much higher threshold speed for instability compared with bearings with inherently compensated restrictors.     

Nonlinear analysis on dynamic behavior of buoyancy-induced flame oscillation under swirling flow

From the viewpoint of nonlinear dynamics, the dynamic behavior of buoyancy-induced flame oscillation has been experimentally investigated under a swirling flow produced by rotating a cylindrical burner tube. As the rotational Reynolds number increases, the dynamic behavior undergoes a significant transition from periodic oscillation to low-dimensional deterministic chaos, through quasi-periodic oscillation. This is clearly demonstrated by nonlinear time series analysis based on chaos theory. The motion of the vortical structure around the burner tube due to the centrifugal instability associated with a rotating Taylor–Couette flow plays an important role in the onset of low-dimensional deterministic chaos.     

Effect of reaction temperature on Fe–Al analcime formation

The effects of reaction period, temperature, and iron species on the zeolite framework type were studied in this work. Gismondine (GIS) is usually synthesized by hydrothermal method at 80°C from sodium metasilicate and aluminum nitrate as starting materials preferentially independent of the presence/absence of iron source. However, the present work revealed that pure analcime (ANA) could be formed at temperatures more than 120°C. A large polyhedral ANA crystal with a diameter of 180 μm was obtained even at a comparatively low temperature such as 150°C at a short reaction period of 1 week. The presence of iron source promoted the formation of pure ANA. Infrared spectroscopy, X-ray diffraction, and ICP-OES analysis suggested that the iron component added as a reactant was incorporated into the ANA framework through the isomorphous substitution for Al.     

Baggage Transportation and Navigation by a Wheeled Inverted Pendulum Mobile Robot

Our goal is to configure an automatic baggage-transportation system by an inverted pendulum robot and realize a navigation function in a real environment. The system consists of two cooperative subsystems: a balancing-and-traveling control subsystem and a navigation subsystem. Position errors of the inverted pendulum robot are often caused by a drift error in the gyro sensor and a change in the center of gravity by a loaded baggage when applying the linear state feedback control method for balancing and traveling. We have reduced the position errors for navigation by resetting the balance position occasionally while traveling with simple methods without an external observer or alternative sensors. In this paper, we state the method and show the experimental results of navigation in a real environment by the implemented robot system.     

Epidemic models and a self-repairing network with a simple lattice

We have proposed a self-repairing network where nodes are capable of repairing neighboring nodes by mutually copying. A critical point where faulty nodes can be eliminated has been investigated. This paper further studies the dynamics of eradicating faulty nodes by comparing the self-repairing network with mathematical epidemic models such as SIS models. It is shown that the self-repairing network, which is a probabilistic cellular automaton, can be regarded as an epidemic model in some restricted situations. This work was presented in part at the 12th International Symposium on Artificial Life and Robotics. Oita, Japan, January 25–27, 2007     

Effects of laser peening on the fatigue strength and defect tolerance of aluminum alloy

The effects of laser peening (LP) on the bending fatigue strength of the 7075‐T651 aluminum alloy were investigated. Accordingly, the defect tolerance of the aluminum alloy subjected to LP is discussed on the basis of fracture mechanics. The results indicate that a deeper compressive residual stress was induced by LP compared with the case of shot peening (SP). The fatigue strengths increased when both peening types were used. Semicircular slits with depths less than 0.4 and 0.1 mm were rendered harmless on the basis of the applications of LP and SP, respectively. The apparent threshold stress intensity factor range ΔK_th,ap increased by approximately five and two times owing to LP and SP, respectively. The increase of the ΔK_th,ap was caused by the compressive residual stress induced by the peening. The Kitagawa‐Takahashi diagram of the laser‐peened specimens shows that the defect tolerance of the aluminum alloy was improved by LP.     

Fabrication of SnO2 Particle-Layers using the Electrospray Method and Gas Sensing Properties for H2

The particle layers of SnO₂ were prepared using the electrospray pyrolysis method from SnCl₂ ethanol solution on the glass substrates heated at 773 K. Pyrex and quartz glass were used for the substrates. The effects of the concentration and the conductivity of the precursor solutions on the morphology and gas sensitivity of the SnO₂ layers were investigated. The sensitivity measurements were carried out for 0.5% H₂ in synthetic air at the operating temperature of 573 K and that was defined by the resistance ratio of the specimen under synthesized dry-air (R_air) and 0.5% H₂ (R_gas), R_air/R_gas. Among the examined concentrations of 1× 10^–4, 1× 10^–3 and 1× 10^–2 mol dm^–3, the layer prepared at 1× 10^–3 mol dm^–3 exhibited the maximum sensitivity of 20. The particle sizes were 110(30), 160(40), and 150(35) nm in diameter at 1× 10^–4, 1× 10^–3, and 1× 10^–2 mol dm^–3, respectively. The values in the parentheses indicate the standard deviation of the measured data. On the other hand, the conductivity of the solution exerted no significant influence on the sensitivity, which was adjusted by the addition of dilute hydrochloric acid. The particle size decreased with the conductivity and became 134(30), 105(20) and 87(20) nm in diameter at 7.8, 27.0 and 86.6 S cm^–1, respectively. Under all the conditions the layers had the dendrite-like structure, indicating the in-flight particle formation. The crystallite size was evaluated to be 6 nm from XRD using the Scherrers equation. These particles of 87–160 nm was thought to consist of smaller primary particles (crystallites). The Pd doping by 1 wt% to SnO₂ enhanced the gas sensitivity by a factor of 4.