The shoulder complex in the human body consists of the scapula, clavicle, humerus, and thorax and bears the load imposed by arm movements while at the same time realizing a wide range of motions. To mimic and exploit its role, several musculoskeletal robot arms with shoulder complex mechanisms have been developed. However, although many research groups have tried to design the structures using links and joints that faithfully correspond to the bones and joints in the human shoulder complex, its function has not been successfully reproduced because biologically plausible designs seriously compromise engineering plausibility. In this paper, we propose a linkage mechanism that can reproduce complex three-dimensional scapulo movements and considers the trade-off between biological and engineering plausibilities. Subsequently, the design was validated by driving the mechanism using pneumatic artificial muscles (PAMs) placed similarly to muscles in humans. Further, we present experiments in which the robot was controlled by surface electromyographic signals from a human. We show that the proposed design, due to its kinematic similarity with human musculoskeletal systems, eases the conversion between the surface electromyogram signals and the PAMs control inputs.
Each vertebrate species, as a general rule, has either the XX/XY or ZZ/ZW chromosomes by which sex is determined. However, the Japanese Rana (R.) rugosa frog is an exception, possessing both sex-determining combinations within one species, varying with region of origin. We collected R. rugosa frogs from 104 sites around Japan and South Korea and determined the nucleotide sequences of the mitochondrial 12S ribosomal RNA gene. Based on the sequences, R. rugosa frogs were divided into four groups from Japan and one from South Korea. The ZZ/ZW type is reportedly derived from the XX/XY type, although recently a new ZZ/ZW type of R. rugosa was reported. However, it still remains unclear from where the sex chromosomes in the five groups of this species were derived. In this study, we successfully isolated a sex-linked DNA maker and used it to classify R. rugosa frogs into several groupings. From the DNA marker as well as from nucleotide analysis of the promoter region of the androgen receptor (AR) gene, we identified another female heterogametic group, designated, West-Central. The sex chromosomes in the West-Central originated from the West and Central groups. The results indicate that a sex-linked DNA marker is a verifiable tool to determine the origin of the sex chromosomes in R. rugosa frogs in which the sex-determining system has changed, during two independent events, from the male to female heterogamety.
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