方策最適化による機会制約付き確率モデル予測制御の高速アルゴリズム

京都大学新制・課程博士博士(情報学)甲第24743号情博第831号新制||情||139(附属図書館)京都大学大学院情報学研究科システム科学専攻(主査)教授 大塚 敏之, 教授 加納 学, 教授 東 俊一学位規則第4条第1項該当Doctor of InformaticsKyoto UniversityDFA

Stochastic Model Predictive Control Using Simplified Affine Disturbance Feedback for Chance-Constrained Systems

This letter covers the model predictive control of linear discrete-time systems subject to stochastic additive disturbances and chance constraints on their state and control input. We propose a simplified control parameterization under the framework of affine disturbance feedback, and we show that our method is equivalent to parameterization over the family of state feedback policies. Using our method, associated finite-horizon optimization can be computed efficiently, with a slight increase in conservativeness compared with conventional affine disturbance feedback parameterization

Chinese Students’ Ambivalent Perceptions of Grammar Correction in L2 Writing

The efficacy of Grammar Correction (GC) in second language (L2) writing classes has been the subject of much controversy and the field seems to take Ferris’ (1999) generalization that students believe in GC and want to receive it for granted. To test Ferris’ generalization, this study examines Chinese students’ perceptions of GC in their English writing. The results of a questionnaire administered to six groups of three proficiency levels of university students majoring in or not in English show ambivalent perceptions towards GC. On the one hand, all learners believe GC has obvious effects and can improve their accuracy in L2 writing. On the other hand, they all agree that GC is not enough for improving learners’ writing ability and that the time spent on GC should be allocated on training other writing abilities. All groups of participants gave a negative to uncertain answer to GC, though different perception patterns figure in whether or not majoring in English: English-major groups’ mean expectation scores of GC increase while those of non-English-major groups decrease in keeping with their English levels. These results provide strong evidence for Truscott’s (1996) view that GC should be abandoned. We believe that the different perceptions of GC shown by English and non-English major students stem from the fact that the former receives a more systematic grammar instruction than the latter. The ambivalent perceptions of GC originate in the fact that grammar accuracy occupies an important proportion in various writing evaluation systems

Long-term degradation, damage and fracture in deep rock tunnels: A review on the effect of excavation methods

Rocks are frequently host materials for underground structures, particularly for deep Tunnels. Their behavior plays a fundamental role in the overall stability of these structures. In fact, the erection of deep tunnels imposes rocks excavations around the defined routes. These excavations are generally carried out by various methods of which the most used are Drill-and-Blast (DB) and Tunnel Boring Machine (TBM).  However, regardless of the tunnelling method used, the impacts such as the perturbation of the initial stress field in rocks and the release of the stored energy are always significant. The impacts produce damage, fractures and deformations which are generally time-dependent and influence the long-term stability of deep tunnels built in rocks. Thus, by considering the aforementioned excavation methods, this paper identifies, reviews and describes the relevant factors generated during and after rock excavations. Interestingly, such factors directly or indirectly influence the long-term stability and therefore the structural integrity of deep rock tunnels. In addition, some recommendations and proposals for future works are presented. This paper can provide useful references in understanding the degradations, damage and fractures generated by tunnelling methods and facilitate suitable actions to ensure long-term stability of deep underground structures