A model of friendship networks based on social network analysis

It is important for teachers to understand the characteristics of forming and changing of friendship networks to manage their classes effectively. Many studies have analyzed friendship networks using agent-based models. Most of the models used were designed for capturing basic phenomena in a micro-viewpoint. The purpose of our study is to simulate actual friendship networks. In this paper, we present an agent-based friendship-network model based on our analysis of friendship networks among university students. We focused on Hiramatsu’s model based on a cost-benefit analysis and modified the model with the aim of closing to the actual friendship. With our modified model, the benefit function was based on their cluster structure. The results with the modified model better matched the actual friendship networks. The clique size in the modified model approached that in the actual friendship networks, and the values of several network properties approached those of the actual friendship networks.     

Obstacle arrangement detection using multichannel ultrasonic sonar for indoor mobile robots

In the last few years, mobile robot systems that perform complicated tasks have been studied. To work in complicated environments, the robot has to avoid collisions with obstacles. Therefore the robot needs to detect the arrangement of any surrounding obstacles. We considered a simple distance estimation algorithm using ultrasonic sonar. Since the algorithm was able to estimate distance accurately, we also attempted stereo reception using two ultrasonic microphones. The stereo reception sonar was able to detect the direction of obstacles. In order to make precise measurements, we attempted to use the signal coherence of ultrasonic waves. In order to install a small system into mobile robots and to detect any surrounding obstacles, we designed a multichannel sonar signal processing system using a high-performance embedded microcontroller. This article describes our ideas for the distance estimation algorithm for ultrasonic sonar, and a design for a signal processing system using a high-performance microcontroller.     

Three-dimensional ionic wind and electrohydrodynamics of tuft/point corona electrostatic precipitator

The two-dimensional flow interaction between the primary flow and the secondary flow (often called an electric wind or ionic wind) in the wire-duct electrostatic precipitator (ESP) has been investigated theoretically and experimentally in the past. However, the analysis was limited to the two-dimensional, which is acceptable only for the positive polarity and small tuft spacing. The negative corona, commonly used for the industrial ESPs, generates tufts along the corona wire and the point coronas on the discharge wire and requires three-dimensional analysis. Three-dimensional electric field and space-charge density distributions, and the flow interaction between the primary flow and secondary flow, i.e., electrohydrodynamics were investigated. The computational results show that the secondary flow distribution consists of a donut-shaped ring from each tuft or corona point, which was predicted by the first author 16 years ago. When the primary flow exists, a pair of spiral rings, like Goertler vortices, is formed in the direction of the primary flow. The flow interaction was described using dimensionless number N/sub EHD/, which is the ratio of the ionic wind velocity to the primary flow velocity. The effects of particle motion in the electrohydrodynamic field in the tuft/point corona ESPs are discussed.     

SH-SAW Sensor for Superfluid 3He

No Heading We have developed a new technique to study the transverse acoustic properties of superfluid ³He, employing a shear horizontal surface acoustic wave (SH-SAW) sensor. The transverse acoustic impedance can be obtained from the velocity and damping of SH-SAW which acoustically couples with liquid ³He all the interface. Since ultrasonic measurements provide the information about superfluid order-parameter through the excitation of collective modes, the SH-SAW sensor is expected to be a useful tool to study the boundary effect of superfluid ³He. Preliminary measurements were carried out at pressures of 17 and 23 bar, by the pulse transmission method at a frequency of 70 MHz. At 17 bar, imaginary squashing mode was observed as the sharp drop of the imaginary part of acoustic impedance. At 23 bar, the supercooled A-B phase transition was observed, as a jump of the real part of acoustic impedance, which was not observed in the warming process.PACS numbers: 67.57.Jj, 43.58.+z     

Hydrodynamic properties on superfluid3He in high magnetic fields up to 12 tesla

Using a torsional oscillator, superfluid fraction and viscosity of superfluid³He were measured in the A₁ and the a₂ phase up to 12 Tesla below 1 mK in the pressure of 29 bar. This is the first measurement in the high magnetic field region in a well defined geometry and in a controlled texture. The a₁ and the a₂ transition were seen clearly in the torsional oscillator frequency and amplitude. Two GL parameters, ₂₄₅ and ₂₄, are independent of field up to 12 Tesla. ₂₄₅ is 1.18 from the A₂ phase measurements, which agree with those from heat capacity measurement. While ₂₄ is 3.08 from the a₁ phase, which is smaller than that from recent spin entropy wave measurement.     

Optimization of the process parameters of an electrochemical cell in the IS process

One of the key reactions for efficient hydrogen production using the water-splitting iodine–sulfur (IS or S–I) process is the Bunsen reaction (SO₂+I₂+2H₂O=H₂SO₄+2HI). The Bunsen reaction was examined using an electrochemical cell with a cation exchange membrane as the separator. The optimal molalities of anolyte and catholyte were evaluated by total thermal efficiency using the heat/mass balance of the IS process. The I₂/HI ratio had little effect on the required total voltage; the I₂/HI ratio can be reduced to 0.5 without decreasing the total thermal efficiency. On the other hand, HI and H₂SO₄ molality greatly affected the total thermal efficiency. The total thermal efficiency increased with increasing HI molality up to and the maximum thermal efficiency was found at of H₂SO₄. Membrane resistances are very important parameters affecting the efficiency. The total thermal efficiency increased by 3.0% at a current density of the electrochemical cell of by increasing the operating temperature from 313 to 363 K.     

Dispersion of Ceramic Particles in Aqueous Media with Surface-Grafted Dispersant

One important goal to be achieved in the colloidal processing of ceramics is to fully disperse a solid substance into finely divided particles in a liquid medium to avoid the generation of agglomerates. A novel preparation method of aqueous ceramic slurries is described in this paper. The process can be characterized by creating a chemically grafted dispersant molecule layer on particles' surfaces which is very soluble in water. The tuned configuration of dispersant molecules causes neither bridging nor depletion flocculation but induces steric repulsion effectively. The obtained aqueous slurry was quite stable and yielded green bodies with high relative density.     

Design Method of a Hanger System for Long-Span Suspension Bridge

A parallel wire strand (PWS) rope instead of a strand rope of the center fit rope core type was used as the hanger rope in the world's longest suspension bridge, the Akashi Kaikyo Bridge, one of the Honshu-Shikoku Bridges in Japan. The strand ropes of the center fit rope core type are inconvenient and uneconomical to maintain as 100–200 m-long hanger ropes. This paper presents the design method for the PWS hanger system in long-span suspension bridges. The structural characteristics, structural analysis, stress calculation, and the examination of fatigue against random wind load of the PWS hanger system were also investigated.     

Data-parallel computation of EBE finite element method for air/water/soil coupled system

The authors developed a method to adequately compute the fluid-structure interactions to analyze a coupled phenomena for gas, liquid and solid. With the implementation of VOF method, the new methodology may handle the moving boundaries as well. The present technique is based on the predecessing approach for analyzing the incompressible viscous fluid for large scale problems [3]. The characteristic of this method is that by implementing the matrix-storage free formulation [1], which is based on the one-point quadrature scheme, the amount of necessary storage and the number of operations for calculating the integration are considerably. Moreover, the data-parallel coding is implemented taking advantage of the element-by-element structure of the program. We selected two problems in order to examine the effectiveness of this newly developed program:flow inside a subway station and water scour around a bridge pier.     

Surface relief of α″ martensite in a Ti-Mo alloy

The surface relief of α″ martensite plates in a polycrystalline Ti-4.74 at. pct Mo alloy was studied by atomic force microscopy (AFM). The orientation of matrix grains was measured by electron backscatter diffraction (EBSD), and measured surface tilt angles were compared with calculation by the crystallographic theory of martensite transformation. The observed maximum tilt angle was close to the predicted value of 7.57 deg. The overall agreement between measured and calculated tilt angles was improved significantly by taking into account not only the inclination of habit plane to the specimen surface, but also the shear direction predicted from the theory. The tilt angle may vary with the moving direction of the interface unless the habit plane is perpendicular to the specimen surface. However, this effect was small in this transformation.