Analysis of structure characteristics in laminated graphene oxide nanocomposites using molecular dynamics simulation

The characteristics of laminated graphene oxide (LGO) nanocomposite, which are expected to be used for highly functional composites, are known to be related to its microstructure. In this study, we investigate the influences of hydrogen-bonding and cross-linked network structures on the initial stiffness and yield stress, using molecular dynamics simulations. Our results show that each structure increases the mechanical properties, and the combination of these structures strengthens the properties. Moreover, we found that the physical origin of the enhancement is cross-linked networks that generate stretched polymers connecting graphene sheets. Our study concludes by suggesting an appropriate selection of materials for high-performance LGO nanocomposites.     

High-Temperature Compressive Properties of TiC-Added Mo-Si-B Alloys

High-temperature compressive properties of two TiC-added Mo-Si-B alloys with nominal compositions of Mo-5Si-10B-7.5TiC (70Mo alloy) and Mo-6.7Si-13.3B-7.5TiC (65Mo alloy) (at.%) were investigated. The alloys were composed of four constituent phases: Mo solid solution (Mo_ss), Mo₅SiB₂, (Mo,Ti)C, and (Mo,Ti)₂C. The primary phases of the 70Mo and 65Mo alloys were Mo_ss and T₂, respectively. The compressive deformability of the 65Mo alloy was significantly limited even at 1600°C because of the elongated, coarse primary T₂ phase, whereas the 70Mo alloy had good compressive deformability and a high strength in the test-temperature range of 1000–1600°C; the peak stresses were 1800 MPa at 1000°C, 1230 MPa at 1200°C, and 350 MPa at 1600°C. At and above 1200°C, the peak stress values were more than double those of Mo-6.7Si-7.9B, Ti-Zr-Mo, and Mo-Hf-C alloys. The plastic strain in the 70Mo alloy at temperatures lower than the ductile–brittle transition temperature of T₂ was generated by plastic deformation of not only Mo_ss but also of (Mo,Ti)C and (Mo,Ti)₂C. This work indicates that (Mo,Ti)C and (Mo,Ti)₂C play an important role in determining the high-temperature strength and deformation properties of TiC-added Mo-Si-B alloys.     

Development of a Digital Signal Processing System for the X-Ray Microcalorimeter Onboard ASTRO-H (II)

The Pulse Shape Processor is a digital signal processing electronics for the microcalorimeter instrument onboard ASTRO-H. Receiving digitized waveform (14?bit, 12.5?kHz sample) from 2×18 channels, two identical units of PSP-A and -B trigger X-ray events, assign five kinds of event grade, and perform optimal filtering to measure energy deposit on the 6×6 microcalorimeter pixels. One unit of PSP is composed of one FPGA board and two CPU boards. This paper describes the event processing algorithm to fulfill requirements for the signal processing, and task sharing between FPGA and CPU.     

Integrated fuzzy logic generator controller for stabilityenhancement

An integrated fuzzy logic controller is proposed in this paper for the generator excitation and speed governing control. The proposed controller has three control loops: the first one is the voltage control loop which has the function of automatic voltage regulator (AVR), the second one is the damping control loop which has the function of power system stabilizer (PSS), and the last one is the speed governing control loop which has the function of governor (GOV). A simple fuzzy logic control scheme is applied to all these three loops. The control scheme is simple enough so as not to require heavy computation for the controller, therefore, its real time application is feasible. The effectiveness is demonstrated through nonlinear simulations using a one machine infinite bus system. Comparison studies are also performed to show the advantages of the proposed controller with conventional excitation and speed governing control systems     

Clinical usefulness of fat suppression technique for MR cholangiopancreatography (MRCP)

In order to obtain high quality of MRCP image, it is important to reduce the background signal intensity and increase the contrast of the pancreatobiliary ducts relative to surrounding fat tissue. The combination of long effective-TE and fat suppression technique including the short-TI inversion recovery and chemical-selective fat suppression enables to suppress the background signal intensity enough to obtain high quality MR cholangiopancreatogram. However, susceptibility artifacts from the metal, gastroduodenal gas, and vascular pulsation can be augmented by using the chemical-selective fat suppression technique, which may result in signal loss of the pancreatobiliary ducts. This potential diagnostic pitfalls can be avoided by interpreting the coronal source images obtained with long effective-TE and without fat suppression technique.     

Acquisition of ground penetrating radar data to detect lava tubes: preliminary results on the Komoriana cave at Fuji volcano in Japan

Ground penetrating radar (GPR) has been successfully used to detect a lava tube in a basaltic lava flow from the Fuji volcano, Japan. The target lava tube, Komoriana cave, is in the northern part of the Aokigahara lava flow which was emplaced over 1,000 years ago. The lava tube was detected by simply dragging the GPR antenna along a prefecture road, demonstrating the advantages of this method compared with detailed mapping and geological investigations. As a massive basaltic lava flow allows deep penetration of the radar pulse, the reflection radar profile obtained showed two very clear structures which were interpreted from the waveforms to be the roof and the bottom of the lava tube from the waveforms alone. This was subsequently confirmed by careful survey measurements of the Komoriana cave lava tube. The feasibility study clearly demonstrated that GPR is a very effective and convenient tool for discovering unknown lava tubes hidden deeply inside lava flows.     

Simulation Studies of the Transients of Squirrel-Cage Induction Motors

A new simulation approach is proposed in consideration of a saturation and a deep bar effect for the study of transients of three-phase squirrel-cage type induction motors. The mathematical model of an induction motor is expressed by the six differential equations of three-phase instantaneous voltage and current. The torque of an electric equation is related to the motion equations of motor and driven machine in the mathematical model. The values of reactance of stator and rotor are changed by the saturation of core caused by starting current. Also both the values of reactance and resistance of rotor bar are varied by the deep bar effect in the rotor core during starting. The calculation method of circuit constant that adds the influence of saturation and deep bar effect is proposed in this paper. The circuit constant of simulation model in consideration of saturation and the deep bar effect are decided by these computation methods in accordance with the conditions of rotation speed and current. If the large current flows, the leakage reactance of the stator and the rotor decreases by saturation. Moreover, the resistance of the rotor gradually decreases when the rotational speed rises from stop to synchronous speed, and the leakage reactance increases gradually. The calculated values were compared with the observed values of the examination machine of 1100 kW4P and an excellent agreement was obtained demonstrating the accuracy of the proposed simulation. Consequently, it is shown that the saturation and the deep bar effect are the essential factors to perform the accurate simulations of the induction motor. After checking the validity of the proposed approach, the simulation of the grounding faults was performed. In this study, all the simulation programs have been developed in the Matlab/Simulink environment.