The phenomenon of changing coiling-chirality in carbon nanocoils obtained by catalytic pyrolysis of acetylene with various catalysts

Carbon nanocoils were prepared by the chemical vapor deposition process of the catalytic pyrolysis of acetylene at 700-800 degrees C with various catalysts. Twisting or coiling-formed carbon nanocoils with changing coiling-chirality and zigzag-formed carbon nanofibers were obtained with SUS 304, WS2, Pt-Pd, TiN, and Ni as the catalysts. Their morphologies and microstructures were examined in detail, and then the changing mechanism of the coiling-chirality was discussed. No apparent difference in the microstructure between the part of a nanocoil with changing coiling-chirality and the part of a zigzag nanofiber with changing zigzag-chirality, or between a bulk right-clockwise coil and a bulk left-clockwise coil was observed. It was supposed that changing coiling-chirality was mainly caused by the gradual or successive change in chemical composition on the thin layers present on the surface of catalyst grains during the chemical vapor deposition process.     

Preparation of Si3N4 whiskers by reaction of wheat husks with NH3

-Si₃N₄ whiskers that are 1–10 mm long and 0.5–1.1 m thick were obtained by the reaction of wheat husks with NH₃ at 1250–1450 °C. A maximum whisker yield of about 30% was obtained at 1450 °C with the addition of an iron impurity. Whiskers with 1.3–2.2 m thickness (average 1.6 m) were obtained by the addition of an H₂S impurity. Thin whiskers with periodic thick and thin diameters were also obtained.     

Electron holographic observation of micro-magnetic fields current-generated from single carbon coil

A carbon coil was evaluated for use as a micro-solenoid in a small magnetic device. A single carbon coil was lifted out of the aggregate using a tungsten fine probe in a focused ion beam (FIB) system and was wired to two small electrodes in the specimen holder of a transmission electron microscope (TEM). A direct current was supplied to the single carbon coil. A micro/nano-magnetic field generated from the coil was directly observed by electron holography. A computer simulation of electron holography was also done to quantitatively analyze the magnetic field. Details on the FIB technique, the electron holographic observation and the simulation are described.     

Preparation of carbon micro-coils with the application of outer and inner electromagnetic fields and bias voltage

The carbon micro-coils were prepared by the catalytic pyrolysis of acetylene at 770-775 °C using Ni, Nb, Ta and their oxides with the superimposed application of an electromagnetic field (AC, DC) from both the outer and inner sides of the reaction tube as well as with application of a bias voltage to the substrate. The effect of the electromagnetic field on the coil yield and morphology were examined. The coil yield increased by 1.1-1.2 times with the superimposed application of the AC or DC electromagnetic field. It was found that the superimposed application of the outer and inner electric magnetic fields resulted in the strong influence on the morphology of the grown carbon coils. The effect of the non-inductive zero magnetic field obtained with a counter magnetic field on the growth of the carbon coils was also examined. The maximum coil yield of 30-32.5 mg/cm²-substrate was obtained with the application of both the outer and inner DC-EM fields or non-inductive EM field.     

Chemical vapour growth of HfP whiskers and their properties

Whiskers and ribbon-like single crystals of -HfP (hexagonal) have been prepared from HfCl₄+PCl₃+H₂+Ar gas mixtures at 1100–1200 °C using a metal impurity-activated chemical vapour deposition process. The growth conditions, morphology and chemical properties were examined. The 3.5–6.5 mm (average 4 mm) long HfP whiskers were obtained at 1200 °C using Si+Pt or Si+Pd mixed impurities. The HfP whiskers were very stable against oxidation up to 3 h exposure at 1000 °C and for 80 min immersion in concentrated HCl solution at 50 °C.     

Analysis for hydrogen particle balance of plasma-wall system in the large helical device

The hydrogen particle balance of the plasma-wall system in the large helical device (LHD) is analyzed, using a zero dimensional model for plasma particles, neutrals in vessel and hydrogen inventory in wall. Based on the measurement of neutral gas pressure, plasma density and the pumping speed of the cryo-pumping system, it is found that the hydrogen retained in the wall desorbes with short and long time constant. The short term desorption is of order of 10²¹ atoms with a time constant of a few minutes, which is much smaller than the wall pumping for one shot, 10²² atoms. In a long time scale of about one experimental day, the wall absorbs significantly large amounts of hydrogen, up to 10²⁴ atoms. One of the possible reasons for the large wall pumping is a carbon deposition layer on the first wall surface. The effect of hydrogen retention on density control is also discussed.     

Dynamic motion learning for multi-DOF flexible-joint robots using active–passive motor babbling through deep learning

This paper proposes a learning strategy for robots with flexible joints having multi-degrees of freedom in order to achieve dynamic motion tasks. In spite of there being several potential benefits of flexible-joint robots such as exploitation of intrinsic dynamics and passive adaptation to environmental changes with mechanical compliance, controlling such robots is challenging because of increased complexity of their dynamics. To achieve dynamic movements, we introduce a two-phase learning framework of the body dynamics of the robot using a recurrent neural network motivated by a deep learning strategy. The proposed methodology comprises a pre-training phase with motor babbling and a fine-tuning phase with additional learning of the target tasks. In the pre-training phase, we consider active and passive exploratory motions for efficient acquisition of body dynamics. In the fine-tuning phase, the learned body dynamics are adjusted for specific tasks. We demonstrate the effectiveness of the proposed methodology in achieving dynamic tasks involving constrained movement requiring interactions with the environment on a simulated robot model and an actual PR2 robot both of which have a compliantly actuated seven degree-of-freedom arm. The results illustrate a reduction in the required number of training iterations for task learning and generalization capabilities for untrained situations.     

Motion of a “drift island” in a toroidal magnetic confinement device with Coulomb scattering of the particles

A resonant drift trajectory of a charged-particle in a magnetic field (a “drift island”) can be used to remove high-energy impurities from a thermonuclear plasma and to introduce (inject) high-energy particles into the plasma. As a rule, these effects are studied neglecting the Coulomb scattering, i.e., in the collisionless approximation. In the present letter, the effect of Coulomb scattering of a particle with a resonant trajectory by plasma particles is studied. The conditions under which the drift resonance is maintained are found, i.e., the plasma densities and plasma density profiles for which the “drift island” can still move over the transverse section of the plasma are determined. Pis’ma Zh. Tekh. Fiz. 25, 19–27 (September 26, 1999)     

10 years of engineering and physics achievements by the Large Helical Device project

This article reviews 10 years of engineering and physics achievements by the Large Helical Device (LHD) project with emphasis on the latest results. The LHD is the largest magnetic confinement device among diversified helical systems and employs the world's largest superconducting coils. The cryogenic system has been operated for 50,000 h in total without any serious trouble and routinely provides a confining magnetic field up to 2.96 T in steady state. The heating capability to date is 23 MW of NBI, 2.9 MW of ICRF and 2.1 MW of ECH. Negative-ion-based ion sources with the accelerating voltage of 180 keV are used for a tangential NBI with the power of 16 MW. The ICRF system has full steady-state operational capability with 1.6 MW. In these 10 years, operational experience as well as a physics database have been accumulated and the advantages of stable and steady-state features have been demonstrated by the combination of advanced engineering and the intrinsic physical advantage of helical systems in LHD. Highlighted physical achievements are high beta (5% at the magnetic field of 0.425 T), high density (1.1 × 10²¹ m^?3 at the central temperature of 0.4 keV), high ion temperature (T_i of 5.2 keV at 1.5 × 10¹⁹ m^?3), and steady-state operation (3200 s with 490 kW). These physical parameters have elucidated the potential of net-current free helical plasmas for an attractive fusion reactor. It also should be pointed out that a major part of these engineering and physics achievements is complementary to the tokamak approach and even contributes directly to ITER.     

A combination of hard and soft templating for the fabrication of silica hollow microcoils with nanostructured walls

Hollow silica microcoils have been prepared by using functionalized carbon microcoils as hard templates and surfactant or amphiphilic dye aggregates as soft templates. The obtained materials have been characterized by electron and optical microscopy, nitrogen sorption and small angle X-ray scattering. The obtained hollow microcoils resemble the original hard templates in shape and size. Moreover, they have mesoporous walls (pore size ≈ 3 nm) with some domains where pores are ordered in a hexagonal array, originated from surfactant micelles. The obtained silica microcoils also show preferential adsorption of cationic fluorescent dyes. A mechanism for the formation of silica microcoils is proposed.