Yin-Chen Wang  Takeshi Emura  Tsai-Hung Fan  Simon M.S. Lo  Ralf Andreas Wilke 《Quality and Reliability Engineering International》2020,36(5):1622-1638

A competing risks phenomenon arises in industrial life tests, where multiple types of failure determine the working duration of a unit. To model dependence among marginal failure times, copula models and frailty models have been developed for competing risks failure time data. In this paper, we propose a frailty-copula model, which is a hybrid model including both a frailty term (for heterogeneity among units) and a copula function (for dependence between failure times). We focus on models that are useful to investigate the reliability of marginal failure times that are Weibull distributed. Furthermore, we develop likelihood-based inference methods based on competing risks data, including accelerated failure time models. We also develop a model-diagnostic procedure to assess the adequacy of the proposed model to a given dataset. Simulations are conducted to demonstrate the operational performance of the proposed methods, and a real dataset is analyzed for illustration. We make an R package “gammaGumbel” such that users can apply the suggested statistical methods to their data.  相似文献   

    

Takeshi Fujimori  Satoru Fujii  Michito Shoji 《JAPAN ARCHITECTURAL REVIEW》2023,6(1):e12319

The elastic wave caused by the input at the wallhead spreads throughout the plane of the wall, and thus, inspecting the soundness of underground walls using a pile integrity test (PIT) is a challenging task. This paper presents a feasible method for evaluating the soundness of underground walls via a PIT. In particular, by applying a low-pass filter to the reflected wave recorded at the wall head, the wave components reflected from the wall ends and cracks are effectively separated from the components reflected from the wall sides. Hence, through the proposed strategy, the wave can be clearly identified for soundness evaluation.  相似文献   

    

Shuji Fujisawa  Kazuho Daicho  Ayhan Yurtsever  Takeshi Fukuma  Tsuguyuki Saito 《Small (Weinheim an der Bergstrasse, Germany)》2023,19(30):2302276

Nanocellulose is attracting attention in the field of materials science as a sustainable building block. Nanocellulose-based materials, such as films, membranes, and foams, are fabricated by drying colloidal dispersions. However, little is known about how the structure of a single nanocellulose changes during the complex drying process. Here, all-atom molecular dynamics simulations and atomic force microscopy is used to investigate the structural dynamics of single nanocellulose during drying. It is found that the twist morphology of the nanocellulose became localized along the fibril axis during the final stage of the drying process. Moreover, it is shown that conformational changes at C6 hydroxymethyl groups and glycoside bond is accompanied by the twist localization, indicating that the increase in the crystallinity occurred in the process. It is expected that the results will provide molecular insights into nanocellulose structures in material processing, which is helpful for the design of materials with advanced functionalities.  相似文献   

    

Junya Nakamura  Sayaka Kamei  Yukiko Yamauchi 《Concurrency and Computation》2023,35(14):e6628

A metamorphic robotic system (MRS) is composed of anonymous, memoryless, and autonomous modules that execute an identical distributed algorithm to move while keeping the connectivity of the modules. For an MRS, the number of modules required to solve a given task is an important complexity measure. Here, we consider evacuation from a finite two-dimensional square grid field by an MRS. This study aims to establish the minimum number of modules required to solve the evacuation problem under several conditions. We consider a rectangular field surrounded by walls with at least one exit. Our results show that two modules are necessary and sufficient for evacuation from any rectangular field if equipped with a global compass, which provides the modules with a common sense of direction. After that, we focus on the case of modules without a global compass and show that four (resp. seven) modules are necessary and sufficient for restricted (resp. any) initial shapes of an MRS. We also show that two modules are sufficient when an MRS is touching a wall in an initial configuration. Then, we clarify the condition to stop an MRS after evacuation of a rectangular field. Finally, we extend these results to mazes and convex fields.  相似文献   

    

Barthélemy  Jeanne  Kubo  Takatomi  Itoh  Takeshi D.  Ikeda  Kiyoka  Ikeda  Kazushi 《Artificial Life and Robotics》2023,28(2):295-306

Artificial Life and Robotics - Gaze behavior of human coders could allow to improve programmer-aiding tools relying on program comprehension algorithms, as gaze reveals which subsets of source code...  相似文献   

    

Yotam Ashkenazi  Shlomi Dolev  Sayaka Kamei  Fukuhito Ooshita  Koichi Wada 《Concurrency and Computation》2023,35(11):e6123

In this article, we consider the case in which a swarm of robots collaborates in a mission, where a few of the robots behave maliciously. These malicious Byzantine robots may be temporally or constantly controlled by an adversary. The scope is synchronized full information robot operations, where a robot that does not follow the program/policy of the swarm is immediately identified and can be remembered as Byzantine. As robots may be suspected of being Byzantine due to benign temporal malfunctions, it is imperative to forgive and forget, otherwise, a robot cannot assume collaborative actions with any other robot in the swarm. Still, remembering for a while may facilitate a policy of surrounding, isolating and freezing the movement of the misbehaving robots, by several robots, allowing the rest to perform the swarm task with no intervention. We demonstrate the need to periodically forgive and forget to realize swarm several tasks including patrolling/cleaning in the presence of possible Byzantine robots. The policy for achieving the task consists of blocking the movement of the Byzantine robot(s) by some of the robots, while the rest patrol/clean the plane.  相似文献   

    

Fumitaka Nakajima  Yoshiyuki Furumatsu  Takatomi Yurugi  Yoshifumi Amari  Takeshi Iida  Takayuki Fukui  Takanori Kuramoto 《Hemodialysis international. International Symposium on Home Hemodialysis》2019,23(1):77-80

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Takeshi Saito  Eva A. Mørtsell  Sigurd Wenner  Calin D. Marioara  Sigmund J. Andersen  Jesper Friis  Kenji Matsuda  Randi Holmestad 《Advanced Engineering Materials》2018,20(7)

In Al–Mg–Si alloys, additions of only a few weight percent of Mg and Si enable formation of hardening precipitates during heat treatment. The precipitation is complex and is influenced by chemical compositions and thermo‐mechanical treatment. Structural analysis at the atomic scale has played an important role for understanding the Al–Mg–Si system. This review paper gives a summary of the influence of elements on the precipitate structures of Al–Mg–Si alloys at the atomic scale. The structures are modified by small additions of different elements, but all the encountered precipitates are structurally connected with the Si network, except for the main hardening phase which exhibit a partially discontinuous Si network. The influence of the selected elements (Li, Cu, Zn, Ge, Ag, Ni, Co, and Au) is discussed in detail.

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Toshinori Matsushima  Chuanjiang Qin  Kenichi Goushi  Fatima Bencheikh  Takeshi Komino  Matthew Leyden  Atula S. D. Sandanayaka  Chihaya Adachi 《Advanced materials (Deerfield Beach, Fla.)》2018,30(38)

The development of host materials with high performance is essential for fabrication of efficient and stable organic light‐emitting diodes (OLEDs). Although host materials used in OLEDs are typically organics, in this study, it is shown that the organic–inorganic perovskite CH₃NH₃PbCl₃ (MAPbCl₃) can be used as a host layer for OLEDs. Vacuum‐evaporated MAPbCl₃ films have a wide band gap of about 3 eV and very high and relatively balanced hole and electron mobilities, which are suitable for the host material. Photoluminescence and electroluminescence take place through energy transfer from MAPbCl₃ to an organic emitter in films. Incorporation of an MAPbCl₃ host layer into OLEDs leads to a reduction of driving voltage and enhancement of external quantum efficiency as compared to devices with a conventional organic host layer. Additionally, OLEDs with an MAPbCl₃ host layer demonstrate very good operational stability under continuous current operation. These results can be extensively applied to organic‐ and perovskite‐based optoelectronics.  相似文献   

    

Shuyuan Lin  Yujia Zhong  Xuanliang Zhao  Toshiki Sawada  Xinming Li  Wenhai Lei  Moran Wang  Takeshi Serizawa  Hongwei Zhu 《Advanced materials (Deerfield Beach, Fla.)》2018,30(34)

Since graphene is a type of 2D carbon material with excellent mechanical, electrical, thermal, and optical properties, the efficient preparation of graphene macroscopic assemblies is significant in the potentially large‐scale application of graphene sheets. Conventional preparation methods of graphene macroscopic assemblies need strict conditions, and, once formed, the assemblies cannot be edited, reshaped, or recycled. Herein, inspired by the biomineralization process, a feasible approach of shapeable, multimanipulatable, and recyclable gel‐like composite consisting of graphene oxide/poly(acrylic acid)/amorphous calcium carbonate (GO‐PAA‐ACC) is designed. This GO‐PAA‐ACC material can be facilely synthesized at room temperature with a cross‐linking network structure formed during the preparation process. Remarkably, it is stretchable, malleable, self‐healable, and easy to process in the wet state, but tough and rigid in the dried state. In addition, these two states can be readily switched by adjusting the water content, which shows recyclability and can be used for 3D printing to form varied architectures. Furthermore, GO‐PAA‐ACC can be functionalized or processed to meet a variety of specific application requirements (e.g., energy‐storage, actuators). The preparation method of GO‐PAA‐ACC composite in this work also provides a novel strategy for the versatile macroscopic assembly of other materials, which is low‐cost, efficient, and convenient for broad application.  相似文献