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In this study, we investigate mullite containing ceramics prepared from alumina (α-Al 2 O 3 ) and silica xerogel converted from sago waste ash. The silica xerogel was ground and then mixed with a varying content of α-Al 2 O 3 . The measurements were performed on cylindrical samples sintered at temperatures ranging from 900 °C to 1700 °C. In order to understand the mullitization process and structure formation a series of analyses were carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, thermo-gravimetric analysis (TGA) and a differential scanning calorimetry (DSC). The results show that the mullite phase can be formed at a temperature as low as 1100 °C. It was found that a complete mullitization takes place for the composition of 40 mol% α-Al 2 O 3 sintered at 1600 °C. [ABSTRACT FROM AUTHOR]

Abstract: A gyrotron with an axis-encircling electron beam is useful for high frequency operation, because the high beam efficiency is kept even at high harmonic of electron–cyclotron resonance. We have designed and constructed such a gyrotron with a permanent magnet. The gyrotron has already succeeded in operation at the third harmonic and the fourth harmonic resonances. The operation frequencies are 89.3 and 112.7GHz, respectively. Operation cavity modes are TE311 and TE411. The permanent magnet system consists of many magnet elements made of NbFeB and additional coils for controlling the field intensities in cavity and electron gun regions. The magnetic field at the cavity region can be varied from 0.97 to 1.18T. At the optimum condition of the magnetic field intensity, the output power at the third harmonic operation is 2.5kW. The operation is pulsed, the pulse length is 1 ms and the repetition frequency is 1Hz. The beam energy and current are 40kV and 1.2 or 1.3A. Starting current, beam efficiency and emission pattern also have been measured. In this paper, the operation results of the gyrotron and comparison with the computer simulation results are described. [Copyright &y& Elsevier]

Abstract: We have investigated photoluminescence (PL) of Mg2SnO4:Mn phosphors synthesized by the irradiation with millimeter-wave of 24 GHz. The PL spectrum at room temperature is dominated by a green band peaking at 500 nm, suggesting the existence of tetrahedral Mn2+ sites. When the phosphors are grown by the millimeter-wave heating, the 500 nm band is so much intense compared to those by the electric furnace heating. To clarify the origin of the PL enhancement, we have carried out the measurements of scanning electron microscope (SEM) and electron spin resonance (ESR). The SEM image exhibits the growth of small round particles with an average size of 1.6 μm. Such well-grown micron-sized particles were not observed under the electric furnace heating. The ESR spectra exhibit six prominent lines, the intensity of which becomes greater for the phosphors obtained by the millimeter-wave heating. From this observation, it is supposed that the PL enhancement is mainly due to the increase in the number of tetrahedral Mn2+ sites. Therefore, the millimeter-wave heating has an important advantage over the electric furnace heating in the synthesis of Mg2SnO4:Mn phosphors. [Copyright &y& Elsevier]

Abstract: Modelling and simulation of gyrotrons have two interconnected aspects, namely beam formation in the electron-optical system (EOS) and beam-field interaction in the resonant cavity. In this paper we address both problems and outline the physical models and numerical techniques implemented in our problem-oriented package of computer codes. In order to illustrate our approach we present some results of numerical experiments carried out at the FIR FU centre and directed towards analysis and optimization of the existing devices of the Gyrotron FU Series as well as applied to the development of simulation-based design (SBD) of a novel high harmonic gyrotron with the electron beam encircling the axis and a permanent magnet system. [Copyright &y& Elsevier]

The magnetic susceptibility, high-field magnetization and specific heat of Cu3(CO3)2(OH)2, an actual material for the frustrating diamond chain spin model, have been measured using single crystals. Two broad peaks were observed at around 22 and 5 K both in the magnetic susceptibility and the specific heat. The magnetization curve had a definite plateau at one-third of the saturation magnetization. [Copyright &y& Elsevier]