Terms Of High Mobility Research Articles

Self-propulsion of a sticky sphere partially covered with a surface slip velocity

Microorganisms follow various strategies to swim in a viscous medium. In an attempt to understand the swimming of ciliated microorganisms, we study low Reynolds number locomotion of a rigid slip-stick swimmer where the propulsive slip velocity is concentrated around an annular patch, which imitates the distinctive surface activity of the microorganisms. In addition, we assume the Navier slip condition at the rigid-fluid interface, which contributes to the hydrodynamic slip or stickiness across the surface. We solve for the locomotion speed and the corresponding flow fields of the swimmer in an axisymmetric unbounded medium. Our analysis reveals insights into how the choice of active slip influences the swimming velocity and the other relevant swimming characteristics. Interestingly, we find that for an optimal active slip in the annular range [π/4, 3π/4], the locomotion speed of the partially covered swimmer is enhanced by a factor of 2 compared to the standard fully covered squirmer. In addition, the corresponding swimming efficiency is enhanced by ∼2.4 times. We independently treat the influence of stickiness of the swimmer on the swimming characteristics. We find that the stickiness reduces the hydrodynamic resistance for the partially covered swimmer and further enhances the swimming speed and efficiency. These findings will be helpful to design efficient artificial swimmers in terms of higher mobility and lower power dissipation.

Extreme magnetoresistance and Shubnikov-de Haas oscillations in ferromagnetic DySb

The electronic structures of a representative rare earth monopnictide (i.e., DySb) under high magnetic field (i.e., in the ferromagnetic state) are studied from both experimental and theoretical aspects. A non-saturated extremely large positive magnetoresistance (XMR) is observed (as large as 3.7 × 104% at 1.8 K and 38.7 T), along with the Shubnikov-de Haas oscillations that are well reproduced by our first principles calculations. Three possible origins of XMR are examined. Although a band inversion is found theoretically, suggesting that DySb might be topologically nontrivial, it is deeply underneath the Fermi level, which rules out a topological nature of the XMR. The total densities of electron-like and hole-like carriers are not fully compensated, showing that compensation is unlikely to account for the XMR. The XMR is eventually understood in terms of high mobility that is associated with the steep linear bands. This discovery is important to the intensive studies on the XMR of rare earth monopnictides.

A gait transition algorithm based on hybrid walking gait for a quadruped walking robot

This paper presents a quasi-dynamic gait, called Hybrid Walking Gait, and a new gait transition algorithm for a quadruped walking robot. The Hybrid Walking gait reduces the steps of a generic walking gait with primitive foot trajectory generation using some of parameters easily defined. It shows great improvements over existing ones in terms of higher mobility, less complexity to define the motion, and smooth body movements that affect to the stability of the robot. The Gait Transition pattern generated with the Hybrid Walking Gait guarantees stability as good as that of a traditional walking gait and high mobility such as the dynamic trot gait. We perform experiments with a quadruped robot called "Artificial Digitigrade for Natural Environments Version III", and validate the effectiveness of our proposed gait patterns over several types of terrains.

Effect of Grain Growth Control by Atmospheric Micro-Thermal- Plasma-Jet Crystallization of Amorphous Silicon Strips on TFT Characteristics

INTRODUCTION.For large area electronics on glass substrate, improvement of thin film transistor (TFT) performance is a key technological issue because higher resolution and functionality, such as 500 pixels per inch (ppi) displays, are required. Low temperature poly-silicon (LTPS) technology is quite promising in terms of high mobility (μFE ), high reliability and CMOS capability. However, present LTPS technology, based excimer laser annealing (ELA) technique, must solve the cost and variability issues. We have proposed micro-thermal-plasma-jet (µ-TPJ) technique for crystallization of amorphous silicon (a-Si) films [1]. Because of its simple structure and atmospheric pressure process, µ-TPJ enables low cost fabrication compared with ELA technique. We have demonstrated zone-melting recrystallization (ZMR) of a-Si by µ-TPJ irradiation [2]. However, ZMR forms random grain boundaries (GBs), which cause characteristic variability in TFTs. To solve these issues, we have attempted to control the grain growth by µ-TPJ crystallization of a-Si strip pattern and demonstrated CMOS circuit operation with high integrity and high frequency for peripheral circuit of displays [3]. In this work, we investigated in detail characteristics of TFTs with conventional and strip pattern. EXPERIMENTAL.A 200-nm-thick a-Si films were formed on quartz substrate and were patterned to form source, drain and channel. Then, 3×1012/cm2 phosphorus ions and boron ions were implanted in PMOS and NMOS respectively, because non-doped channel behaved as intrinsic P-type nature by this fabrication process [3]. After dehydrogenation at 450 °C, a-Si patterns were crystallized by µ-TPJ irradiation. In this condition, ~200 μm wide molten zone is formed and rapid re-crystallization to lateral direction is induced by the fast movement of molten Si. Here, we formed conventional and 1μm wide strip channel patterns before crystallization. After fabrication process [3], we compared electrical property and channel crystallinity. Crystallographic orientations and GBs were investigated by electron backscattering diffraction (EBSD) method. And TFT characteristics with respect to channel width (W) of both patterns were investigated. RESULTS AND DISCUSSION. In conventional pattern TFT, reduced field effect mobility (μFE ) and threshold voltage (Vth ) shift with respect to W were observed (Fig.1 (a)). On the other hand, strip pattern showed stable characteristics in all W (Fig.1 (b)). As shown in Fig.2, random GB were formed in W>3µm, but were clearly suppressed in narrow strips. In addition, strip pattern suppressed off leak current and showed high on current compared to conventional pattern. While μFE and Vth varied by increasing of W in conventional pattern, stable characteristics of μFE > 350 cm2/Vs, Vth = 3.6 ± 0.1V and outputs were obtained in strip pattern. In consideration of drawback of area loss by strip pattern, high μFE , low Vth and stable outputs are sufficient to compensate it as understood by the output characteristics (Fig.3). In addition, although the kink effect increased by degradation of Vth in conventional pattern (Fig.3 (a)), they were significantly suppressed in strip pattern by its uniformity of Vth (Fig.3 (b)). Thus, strip pattern is quite promising for layout and operation of CMOS circuit with high reliability. CONCLUSIONS.The µ-TPJ irradiation to a-Si strip pattern is quite effective for grain growth control. TFTs with proposed pattern showed high performance and low characteristics variability. This enabled us to operate CMOS circuit on insulating substrate under low supply voltage and high frequency. ACKNOWLEDGEMENTS. A part of this work was supported by Research Institute for Nanodevice and Bio Systems (RNBS), Hiroshima University and Funding Program for Next Generation World-Leading Researchers (NEXT Program) from the Japan Society for the Promotion of Science (JSPS). REFERENCES. [1] S. Hayashi, et al., Appl. Phys. Express 3(2010) 061401.[2] Y. Fujita, et al., Jpn. J. Appl. Phys. 51(2012) 02BH05.[3] S. Morisaki, et al., 10th Int. Thin-Film Transistor Conf. (2014) 15.