Axis switching of pulsating jet issued from rectangular nozzle at low Reynolds number

Axis switching of a jet ejected from a rectangular nozzle affects flow mixing characteristics. To elucidate such a mixing mechanism, the axis switching and vortex structure deformation should be investigated in detail. This study performed a numerical analysis of the axis switching of a pulsating jet ejected from a rectangular nozzle at a low Reynolds number. At all aspect ratios, a rectangular vortex ring similar to the shape of the nozzle cross-section is periodically shed downstream, and the side of the vortex ring deforms into a hairpin shape downstream. A vortex pair is generated inside the vortex ring downstream of the nozzle corner. When the aspect ratio is AR=1.0, the vortex pair consists of symmetrical vortices, while as AR increases, the asymmetry of the vortex pair enlarges. At AR=1.0, regeneration of a vortex ring occurs downstream. For AR=2.0, alternately on the long and short sides of the nozzle, an upstream vortex ring overtakes a downstream vortex ring. Regardless of AR, downstream near the nozzle, as the vortex pair existing inside the vortex ring distorts the vortex ring, the positions of the side and corner of the vortex ring exchange, resulting in a 45-degree axis switching. For AR>1.0, further downstream, the hairpin part of the vortex ring on the long side develops away from the jet center compared to the short side, causing a 90-degree axis switching. As a result, high turbulence occurs over a wide area, strengthening the mixing action. As AR increases, intensive interference between the vortex rings on the upstream and downstream sides diffuses the vortices downstream. Then, as turbulence by the diffused vortices widely occurs, the mixing effect is further strengthened.Comment: 26 pages, 31 figure

Contribution of executive functions to learning sequential actions in young children

This study examined whether executive functions impact how flexibly children represent task context in performing repeated sequential actions. Japanese children in Experiments 1 (N = 52; 3–6 years) and 2 (N = 50, 4–6 years) performed sequential actions repeatedly; one group received reminders. Experiment 1 indicated that reminders promote flexible changes in contextual representations. Experiment 2 observed such effects in younger children and showed executive functions were associated with the flexible representation of task context. Reminders did not perfectly compensate for the role of executive functions but wiped out individual differences in executive functions that contribute to children’s acquisition of routines. Therefore, setting goals before context-dependent actions is necessary, but not sufficient, to modulate contextual representations in routines

Cognitive and neural underpinnings of goal maintenance in young children

Active maintenance of goal representations is an integral part of our mental regulatory processes. Previous developmental studies have highlighted goal neglect, which is the phenomenon caused by a failure to maintain goal representations, and demonstrated developmental changes of the ability to maintain goal representations among preschoolers. Yet, few studies have explored the cognitive mechanisms underlying preschoolers' development of goal maintenance. The first aim of this study was to test whether working memory capacity and inhibitory control contribute to goal maintenance using a paradigm for measuring goal neglect. Moreover, although recent studies have shown that preschoolers recruit lateral prefrontal regions in performing executive functions tasks, they could not specify the neural underpinnings of goal maintenance. Thus, the second aim was to examine whether lateral prefrontal regions played a key role in maintaining goal representations using functional near-infrared spectroscopy. Our results showed that developmental differences in inhibitory control predicted the degree of goal neglect. It was also demonstrated that activation in the right prefrontal region was associated with children's successful avoidance of goal neglect. These findings offer important insights into the cognitive and neural underpinnings of goal maintenance in preschoolers

Response of a stretched cylindrical diffusion flame to a sinusoidal velocity oscillation of air stream

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Repeated sequential action by young children: Developmental changes in representational flexibility of task context

A wealth of developmental research suggests that preschoolers are capable of reporting, imitating, and performing sequential actions they engage in routinely. However, few studies have explored the developmental and cognitive mechanisms required for learning how to perform such routines. A previous computational model of routines argued that a representation of task contexts underlying routines could change flexibly. This position was supported by the empirical evidence that if adults are interrupted in the course of a routine, they make fewer errors if they are interrupted just before the selection of context-dependent action than if they are interrupted earlier. Another computational model examined how efficiently adults learned to perform routines and suggested the relationship of learning efficacy with executive functions. The present study aimed to examine whether the above-mentioned models and evidence from adults can be extended to preschoolers by using an experimental task, in which children were required to play the role of a baker and repeatedly make toast for either a cat or mouse, with momentary distractions. Experiment 1 showed that earlier interruption tended to cause older children to produce more branch point errors than interruption immediately before the branch points, whereas younger children tended to be vulnerable to both interruptions. Further, across 2 experiments, this study showed that the developmental differences in how young children represent task contexts were associated with their executive functions. These findings indicate that the representational flexibility of task contexts underlies children’s performance of repeated sequential actions and its association with executive functions

Evidence for positive and negative transfer of abstract task knowledge in adults and school-aged children

Engaging cognitive control is essential to flexibly adapt to constantly changing environments. However, relatively little is known about how prior task experience impacts on the engagement of cognitive control in novel task environments. We aimed to clarify how individuals learn and transfer the engagement of cognitive control with a focus on the hierarchical and temporal aspects of task knowledge. Highlighting two distinct cognitive control processes, the engagement of cognitive control in advance (proactive control) and in response to conflicts (reactive control), we conducted six preregistered online experiments with both adults (Experiment 1, 3, and 5: N = 71, N = 108, and N = 70) and 9- to 10-year-olds (Experiment 2, 4, 6: N = 69, N = 108, and N = 70). Using two different experimental paradigms, we demonstrated that prior task experience of engaging reactive control makes adults and 9-to 10-year-olds respond in a reactive way in a subsequent similar-structured condition with different stimuli in which proactive control could have been engaged. This indicates that individuals do learn knowledge about the temporal structure of task goal activation and, on occasion, negatively transfer this knowledge. Furthermore, individuals exhibited these negative transfer effects in a similar-structured condition with different task goals and stimuli, indicating that they learn hierarchically-structured task knowledge. The collective findings suggest a new way of understanding how hierarchical and temporal task knowledge influences the engagement of cognitive control and highlight potential mechanisms underlying the near transfer effects observed in cognitive control training

When stimulus variability accelerates the learning of task knowledge in adults and school-aged children

Experience with instances that vary in their surface features helps individuals to form abstract task knowledge, leading to transfer of that knowledge to novel contexts. The current study sought to examine the role of this variability effect in how adults and school-aged children learn to engage cognitive control. We focused on the engagement of cognitive control in advance (proactive control) and in response to conflicts (reactive control) in a cued task-switching paradigm, and conducted four preregistered online experiments with adults (Experiment 1A:N = 100, Experiment 1B: N = 105) and 9- to 10-year-olds (Experiment 2A: N = 98, Experiment 2B: N = 97). It was shown that prior task experience of engaging reactive control makes both adults and 9- to 10-year-olds respond more slowly in a subsequent similar-structured condition with different stimuli in which proactive control could have been engaged. 9- to 10-year-olds (Experiment 2B) exhibited more negative transfer of a reactive control mode when uninformative cue and pre-target stimuli, which do not convey task-relevant information, were fixed, compared to when they were changed in each block. Furthermore, adults showed suggestive evidence of the variability effect both when cue and target stimuli were varied (Experiment 1A) and when uninformative cue and pre-target stimuli were varied (Experiment 1B). The collective findings of these experiments provide important insights into the contribution of stimulus variability to the engagement of cognitive control

末梢血サブセットのトランスクリプトーム解析を用いたANCA関連血管炎の病態解明

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 佐藤 伸一, 東京大学教授 岡崎 仁, 東京大学准教授 清水 潤, 東京大学特任准教授 瀧本 英樹, 東京大学特任准教授 岩部 真人University of Tokyo(東京大学