Yasushi TAUCHI

3D SLAM (Simultaneous Localization and Mapping) is a technique for creating circumstance maps which are usable for measuring the environments and providing navigation information. One of the problems in 3D SLAM is computational efficiency of inserting new points into the circumstance map, since the efficiency is essential for keeping the quality and quantity of the obtained circumstance map and keeping the stability of the mapping procedure. This study focuses on how to improve the computational efficiency of 3D SLAM as a UGV (unmanned ground vehicle) application. We employ a sophisticated and well-organized 3D SLAM package, ETHZASL-ICP-Mapper, as a fundamental implementation. After analyzing the reason why the efficiency becomes decreased through the mapping procedure, we point out main two problems. Then we propose two approaches for overcoming these problems. The first approach is to divide the circumstance maps into sub-grid maps. The second approach is to alternate the k-d tree data structure in the point density control with a voxel grid data structure. The improvements are discussed based on the comparative experimental results.

本論文では，山口大学メディア基盤センターにおいて行っているサーバ室の空調に対する省エネルギーの取り組みについての紹介を行う．具体的には，既存の空調施設を利用した外気取り込みの効果の検証，サーバ室内の温度分布計測および気流制御の方策に関する検討を行う This paper introduces an action of energy saving for air conditioner of server room tried in media and information technology center of Yamaguchi University. Verification of effectiveness of the open air utilization for an existing facilities, measurement results of a temperature distribution in a server room and discussions of air-flow control scheme are presented.

Using a grid bias method for plasma parameter control, volume production of hydrogen negative ions H^- is studied in pure hydrogen rf plasmas. Relationship between the extracted H^? ion currents and plasma parameters is discussed. It is confirmed that both high and low electron temperature T_e plasmas are produced in the separated regions when the grid is negatively biased. In addition, with changing grid potential V_g, values of n_e increase while T_e decrease in their values. The negative ion production depends strongly on the grid potential and related plasma conditions.

Isotope effect on H^-/D^- volume production is studied by measuring both VUV emission and negative ion density in the source. In a double plasma type source, under some discharge conditions, extracted D^- currents are nearly the same as H^- currents, although VUV emission intensity (corresponding to production of vibrationally excited molecules) in D_2 plasmas is slightly lower than that in H_2 plasmas. Considering the factor √<2> due to mass difference, D^- ion density in the extraction region of the source is higher than H^- ion density. In another experiment with a rectangular arc chamber, axial distributions of H^-/D^- ion densities in the source are measured directly using a laser photodetachment method. Relationship between H^-/D^- production and plasma parameter control with using a magnetic filter (MF) is discussed. Furthermore, relative intensities of extracted negative ion currents are discussed compared with the negative ion densities in the source. Production and control of D_2 plasmas are well realized with the MF including good combination between the filament position and field intensity of the MF. Extracted H^- and D^- currents depend directly on negative ion densities in the source.

An asymmetric plasma divided by a magnetic filter is numerically simulated by the one-dimensional particle-in-cell code VSIM1D [Koga et al., J. Phys. Soc. Jpn. 68, 1578 (1999)]. Depending on the asymmetry, the system behavior is static or dynamic. In the static state, the potentials of the main plasma and the subplasma are given by the sheath potentials, φM≒3TMe/e and φS≒3TSe/e, respectively, with e being an electron charge and TMe and TSe being electron temperatures (TMe>TSe). In the dynamic state, while φM≒3TMe/e, φS oscillates periodically between φS,min≒3TSe/e and φS,max≒3TMe/e. The ions accelerated by the time varying potential gap get into the subplasma and excite the laminar shock waves. The period of the limit cycle is determined by the transit time of the shock wave structure.

Plasma parameters (CH_4/H_2+Ar plasmas) are spatially well controlled using a movable magnetic filter. At any filter position, plasma parameters change dramatically across the magnetic filter. The plasma is divided into two parts, the source plasma region (high density plasmas with energetic electrons) and the diffused plasma region (low electron-temperature plasmas without energetic electrons). Carbon thin films are prepared well in the diffused plasma region. The effects of bias potential of the substrate and control of neutral radicals on formation of thin films are discussed briefly.