This study presents an example of creating and optimizing a task sequence required in an automated remote dismantling system using a digital manufacturing system. An automated remote dismantling system using a robotic arm has recently been widely studied to improve the efficiency and safety of the dismantling operations. The task sequence must be verified in advance through discrete eventbased process simulation in a digital manufacturing system to avoid problems in actual remote cutting operations as the main input of the automated remote dismantling system. The laser cutting method can precisely cut complicated target structures such as reactor internals with versatility, but a robot and a pre-prepared program are required to deploy sophisticated motion of the laser cutting head on the target structure. For safe and efficient dismantling operations, the robot’s program must be verified in advance in a virtual environment that can represent the actual dismantling site. This study presents creating and optimizing the task sequence of a robotic underwater laser cutting as part of the project of developing an automated remote dismantling system. A task sequence is created to implement the desired cutting path for the target structure using the automated remote dismantling system in the virtual environment. The task sequence is optimized for the posture of the laser cutting head and the robot to avoid collisions during the operation through discrete event-based process simulation since the target structure is complicated and the volume occupied by the laser cutting head and the robot arm is considerably large. The task sequence verified in the digital manufacturing system is demonstrated by experiments cutting the target structure along the desired cutting path without any problems. The various simulation cases presented in this study are expected to contribute not only to the development of the automated remote dismantling system, but also to the establishment of a safe and efficient dismantling process in the nuclear facility decommissioning.

This study examines the effects of the sequence of increasing task complexity in different modalities on the learning of the English past tense of Korean secondary learners. Robinson’s (2007) Cognition Hypothesis argued that learners pay more attention to grammatical forms in complex tasks than in less complex tasks. He suggested that tasks should be sequenced in such a way that resource-dispersing dimensions are first increased in complexity followed by an increase in the complexity of resource-directing dimensions. However, little empirical research has been done on how tasks are sequenced according to their cognitive complexity and how task modality affects second language development in the sequence. Fifty-four learners were divided into an integrated (writing with oral interaction) task group (EG 1), an oral-only task group (EG 2) and a comparison group (CG). After the sequence of six tasks was completed, one-way ANOVA revealed the EGs outperformed the CG significantly on the posttest. The mean score of EG 1 was the highest, while the improvement rate of EG 2 was the highest among the three groups. It is hoped that this result will contribute to building a solid basis on which practitioners can make decisions about sequencing tasks and implementing task modality.