Dynamics of RC helicopter and control

It is hard to fly an RC helicopter desirably because of its dynamical instability and the fast responce of motion, so that some stabilizing control system has to be developed. The first step of design is the derivation of the mathematical model. Dynamics of a helicopter is much complicated due to the rotating blades and its validity is difficult to be evaluated. In this paper, the mathematical model of a hovering RC helicopter is derived and its validity is confirmed experimentally by designing the stabilizing control system of the gimbal equipment which has three degrees of freedom, rolling, pitching and yawing. At the same time, two kinds of small sensors are investigated and used to control the above equipment.     

Preparation and Optical Properties of Transparent Glass-Ceramics Containing Cobalt(ll) Ions

Transparent glass-ceramics containing ZnAl₂O₄:Co²⁺ and LiGa₅O₈:Co²⁺ crystallites have been prepared by heat treatment of glasses in the zinc aluminosilicate and lithium gallate silicate systems, respectively. Crystalline LiGa₅O₈ was already precipitated in an as-prepared specimen, while ZnAl₂O₄:Co²⁺ precipitated from the glass upon heat treatment. The crystallite size varies from about 5 to 20 nm with increasing heat treatment temperature for both systems, and glass-ceramics containing crystallites of less than about 10 nm are transparent. The low-temperature optical absorption and emission spectra are compared with those of single crystals, indicating that almost all of the Co²⁺ ions replace Zn²⁺ ions in the ZnAl₂O₄ system, while some of the Co²⁺ ions are incorporated into the LiGa₃O₈ system, although the amount of Co²⁺ which remains in the glass matrix is rather large in the latter system.     

Transmission electron microscopic X-ray quantitative analysis of human dentin at 200 kV accelerating voltage

Qualitative and quantitative x-ray energy dispersive spectroscopy is now used successfully to analyze many features and processes in inorganic samples. When applied to inorganic samples, however, the results are often less satisfactory due to problems of preparation of organic samples, difficulty of measuring x-rays from organic samples, damage of the sample by the electron beam, and other practical problems. In the present study we used a high voltage transmission electron microscope equipped with an energy dispersive x-ray spectrometer to examine accurate quantitative standardless analysis of thin sections of an organic sample, human dentin. Based on our experiments we found the important parameters for quantitative analysis were sample thickness and appropriate choice of model sample. Further, we show that the method of Cliff and Lorimer can be used with biological samples at 200 kV, and we show that quantitative analysis of human dentin can be carried out at 200 kV. Finally, we show that areas of human dentin can be differentiated by their morphological characteristics and x-ray analyses obtained in the transmission electron microscope.     

Coking reaction in hydrogenation

Asphaltene prepared from a Japanese coal (Akabira, 81.2 wt% C) and coal tar pitch were heat treated under nitrogen or hydrogen. Under nitrogen the initial thermal decomposition produced radicals which abstracted hydrogen from other molecules to stabilize and to produce smaller molecules and gas. The molecules from which hydrogen was abstracted as well as other radicals polycondensed to produce heavier solvent-insoluble fractions. Under hydrogen the radicals were stabilized by hydrogen gas to produce smaller molecules avoiding the production of a heavier fraction. The higher the hydrogen pressure, the smaller was the yield of heavier fraction and the larger the yield of lighter fraction. Higher temperature accelerated the production of the heavier fraction. Donor solvents could reduce the production of the heavier fraction.     

Pressure and temperature effects on the hydrogenation of coal-derived asphaltene

Pressure and temperature effects on hydrogenation reactions were examined using coal-derived asphaltene at 390,420 and 450 °C, under 3 and 10 MPa of hydrogen partial pressure. Higher conversion was obtained at higher reaction temperatures. Benzene-insoluble material (Bl) was formed at higher temperatures especially at low hydrogen pressure, this Bl being one-third of the reaction product at 450 °C. From structural analysis of unreacted asphaltenes and product oils, at 390 °C, it was concluded that smaller molecular components convert to oil initially and the larger molecules remain as unreacted asphaltene. Under higher hydrogen pressure for all temperatures carbon aromaticity (f_a) and number of aromatic ring per structural unit (R_aus) in unreacted asphaltenes were lower than those under lower hydrogen pressure suggesting that hydrogenation of the aromatic nucleus was promoted by higher pressure. At lower hydrogen pressure, R_aus for asphaltenes at higher temperature is larger than that at lower temperature. This suggests that at lower hydrogen pressure, dehydrogenation or condensation reactions occur more easily. A large effect at higher hydrogen pressure was a reduction in the extent of condensation reactions. Higher reaction temperatures contribute to splitting of bridged linkages so reducing molecular size and degree of aromatization.     

Three dimensional measurement of nanostructures by single event TOF-RBS with nuclear nano probe

Single, double and triple-layer test structures were measured by time of flight (TOF) Rutherford backscattering spectrometry (RBS) for checking the sensitivity and resolution. A single-layer nanostructure with Au stripes on a Si substrate was resolved by TOF-RBS measurement within a short time of 256 s. The spatial resolution, measured by the edge of the Au stripes, was 42 nm. Another single-layer nanostructure with Pt stripes fabricated by electron beam (EB) induced deposition on a Si substrate was resolved by TOF-RBS measurement even at a thickness of Pt stripes less than one mono-layer. Ga embedded layers implanted by a focused ion beam under the Pt stripes fabricated by EB induced deposition on a Si substrate could be detected for a double-layer nanostructure. Furthermore, a triple-layer nanostructure with two Pt stripe layers isolated by a SiO₂ layer fabricated by EB induced deposition on a Si substrate could be resolved and cross-sections shown.     

Study on time resolution of single event TOF-RBS measurement

Flight paths and times of secondary electrons, induced by a focused ion beam, from a sample to a secondary electron detector (SED), were simulated with various shield shapes of a SED for improving the time resolution of time-of-flight Rutherford backscattering spectrometry (TOF-RBS) using the secondary electron signal as a start signal, the results of which were compared with experimental time resolutions of the TOF-RBS measurement. The fluctuation in the flight path and, hence, flight time of the secondary electron deteriorates the time resolution of TOF-RBS. The simulated flight time differences for SEDs with or without a shield were 4.4–41 ns with a shield and 1.0 ns without a shield, respectively, indicating that the SED without the shield would improve the time resolution of the single event TOF-RBS. The time resolutions of TOF-RBS using 150 keV Be⁺ for Au/Si sample with SEDs with and without a shield were 5.6–9.2 and 4.4 ns, respectively. The improved time resolution for SEDs without the shield was confirmed experimentally.     

Sliding mode control of a discrete system

Conventional sliding mode control designed on the basis of a continuous system is known to be robust to the plant uncertainties. A realized digital system, however, not only yields chattering, but also may become unstable by a long sampling interval. This paper presents a stable discrete sliding mode control insensitive to the choice of sampling interval and not yielding chattering. The control system is designed on the basis of a discrete Lyapunov function and a sufficient condition of the control gain to make the system stable is given. Contrary to the continuous case, the derived switching plane of the control law is different from the sliding mode, and in its neighborhood, the control law is given by the linear state feedback. Simulations show the effectiveness of the proposed method.     

Modeling for flexible manufacturing systems with an FMS blocking mechanism and a BDSM job routing

We consider a Flexible Manufacturing System (FMS) which is composed of a set of workstations, a common buffer and a Material Handling System (MHS). Each workstation includes a limited input buffer, several machines and a limited output buffer. The MHS consists of several carts moving jobs among the workstations according to the process paths required by the jobs. The carts treat blocked jobs in accordance with a new blocking mechanism, called the 'FMS blocking mechanism'. The function of the common buffer is to temporarily store blocked jobs. Such an FMS is formulated as an open queueing network, in which the MHS is modeled as a central station routing jobs to the workstations. In the model, the machines process jobs with an exponentially distributed processing time, and the carts route jobs to the workstations following a 'Blocking Depended Static Markov (BDSM) job routing' with an exponentially distributed routing time and treat blocked jobs in accordance with the FMS blocking mechanism. It is shown that the equilibrium state distribution of the model has a product-form solution. The blocking probabilities are obtained by computing a fixed point problem whose solution is revealed by an iterative algorithm. Moreover, it is shown that the throughputs of the workstations are independent of the spaces on the local buffers at the workstations. Several numerical examples are presented.     

Relation between breakdown voltage and prebreakdown current in vacuum gap

Two different surface treatments (mechanical polishing, thin film deposition) were performed on cathode surfaces, and the field emission currents from the cathodes were measured with a microchannel plate. In order to discuss the relationship between the breakdown voltage and prebreakdown current in the vacuum gap, the breakdown voltage was measured after field emission measurement. The V–I characteristics of the field emission and breakdown voltage were influenced by surface treatment, and the breakdown voltages of mechanical polished cathodes were lower than those of the thin film deposited cathodes. It was found that the probability of breakdown increased when the field emission current reached 10^–11 A. Atomic force microscope (AFM) measurements showed numerous protrusions on the cathode surface in the case of thin film deposition treatment, but we estimated by the finite element method that these protrusions make the field enhancement effect low. It was inferred that the breakdown voltage in vacuum gaps could be increased by the thin film deposition method. © 2000 Scripta Technica, Electr Eng Jpn, 131(4): 11–18, 2000