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In fish, the pectoral appendage is adjacent to the head, but during vertebrate evolution a long neck region emerged via caudal relocation of the pectoral appendage. The pectoral appendage is comprised of endochondral portions, such as the humerus and the scapula, and a dermal portion, such as the clavicle, that contributes to the shoulder girdle. In the search for clues to the mechanism of the caudal relocation of the pectoral appendage, the cell lineage of the rostral lateral plate mesoderm was analyzed in chickens. It was found that, despite the long neck region in chickens, the origin of the clavicle attached to the head mesoderm ranged between 1 and 14 somite levels. Because the pectoral limb bud and the endochondral pectoral appendage developed on 15-20 and 15-24 somite levels, respectively, the clavicle-forming region corresponds to the embryonic neck, which suggests that the relocation would have been executed by the expansion of the source of the clavicle. The rostral portion of the clavicle-forming region overlaps the source of the cucullaris muscle, embraces the pharyngeal arches caudally, and can be experimentally replaced with the head mesoderm to form the cucullaris muscle, which implies that the mesodermal portion could have been the head mesodermand that the clavicle would have developed at the head/trunk boundary. The link between the head mesoderm and the presumptive clavicle appears to have been the developmental constraint needed to create the evolutionarily conserved musculoskeletal connectivities characterizing the gnathostome neck. In this sense, the dermal girdle of the ganathostomes would represent the wall of the branchial chamber into which the endochondral pectoral appendage appears to have attached since its appearance in evolution.

DOI： 10.1111/joa.12502

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The shoulder girdle in turtles is encapsulated in the shell and has a triradiate morphology. Due to its unique configuration among amniotes, many theories have been proposed about the skeletal identities of the projections for the past two centuries. Although the dorsal ramus represents the scapular blade, the ventral two rami remain uncertain. In particular, the ventrorostral process has been compared to a clavicle, an acromion, and a procoracoid based on its morphology, its connectivity to the rest of the skeleton and to muscles, as well as with its ossification center, cell lineage, and gene expression. In making these comparisons, the shoulder girdle skeleton of anurans has often been used as a reference. This review traces the history of the debate on the homology of the shoulder girdle in turtles. And based on the integrative aspects of developmental biology, comparative morphology, and paleontology, we suggest acromion and procoracoid identities for the two ventral processes.

DOI： 10.1002/jez.b.22584

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Language：English   Publisher：WILEY-BLACKWELL  

The shoulder girdle in turtles is encapsulated in the shell and has a triradiate morphology. Due to its unique configuration among amniotes, many theories have been proposed about the skeletal identities of the projections for the past two centuries. Although the dorsal ramus represents the scapular blade, the ventral two rami remain uncertain. In particular, the ventrorostral process has been compared to a clavicle, an acromion, and a procoracoid based on its morphology, its connectivity to the rest of the skeleton and to muscles, as well as with its ossification center, cell lineage, and gene expression. In making these comparisons, the shoulder girdle skeleton of anurans has often been used as a reference. This review traces the history of the debate on the homology of the shoulder girdle in turtles. And based on the integrative aspects of developmental biology, comparative morphology, and paleontology, we suggest acromion and procoracoid identities for the two ventral processes. J. Exp. Zool. (Mol. Dev. Evol.) 324B: 244-254, 2015. (c) 2014 Wiley Periodicals, Inc.

DOI： 10.1002/jez.b.22584

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

The turtle shell provides a fascinating model for the investigation of the evolutionary modifications of developmental mechanisms. Different conclusions have been put forth for its development, and it is suggested that one of the causes of the disagreement could be the differences in the species of the turtles used - the differences between hard-shelled turtles and soft-shelled turtles. To elucidate the cause of the difference, we compared the turtle shell development in the two groups of turtle. In the dorsal shell development, these two turtle groups shared the gene expression profile that is required for formation, and shared similar spatial organization of the anatomical elements during development. Thus, both turtles formed the dorsal shell through a folding of the lateral body wall, and the Wnt signaling pathway appears to have been involved in the development. The ventral portion of the shell, on the other hand, contains massive dermal bones. Although expression of HNK-1 epitope has suggested that the trunk neural crest contributed to the dermal bones in the hard-shelled turtles, it was not expressed in the initial anlage of the skeletons in either of the types of turtle. Hence, no evidence was found that would support a neural crest origin.

DOI： 10.1111/joa.12189

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

The shoulder girdle of turtles has a triradiate morphology. Although its dorsal process represents the scapular blade, the skeletal identities of the two ventral processes remain uncertain. To elucidate the question, developmental patterns of the girdles were compared between Chinese soft-shelled turtles, chickens, and mice. Despite the morphological diversity of adults, the initial primordia of the shoulder girdles showed similar morphological patterns. The ventral two processes developed from the anlagen comparable to those of the acromion and the coracoid in other amniotes. The developmental pattern of the acromion is very similar among embryos, whereas that of the coracoid in mammals differs from that in non-mammals, implying that coracoids are not homologous between non-mammals and mammals. Therefore, amniotes have retained the ancestral pattern of the girdle anlage, and the shoulder girdle of turtles has been achieved through a transformation of the pattern in the late ontogenic period.

DOI： 10.1111/joa.12116

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Language：English   Publishing type：Part of collection (book)   Publisher：Springer Japan  

Because of their unique morphology, turtles have raised profound questions as to their evolutionary origin. In striking contrast to the body plan of other tetrapods, the shoulder girdle of turtles sits inside the rib cage, which comprises the dorsal shell, or carapace. By this topological change of the skeletal elements, the carapace has been regarded as an example of evolutionary novelty that violates the ancestral body plan of tetrapods. In this chapter, we first overview the phylogenetic positioning of turtles, and then review how turtles evolved their unique body plan. In brief, three points have been clarified by recent studies. (1) Turtles have birds/crocodilians (or archosaurians) affinity of evolutionary origin. (2) During embryogenesis, the turtle also establishes the vertebrate basic body plan, as in other vertebrates, followed by the late developmental stages of generating turtle-specific structures, such as folding of the lateral body wall to make the apparent inside-out topology of shoulder girdle against ribs. (3) One of the causal factors of folding appears to be the concentric growth of carapacial margin, which involves an ancestral gene expression cascade in a new location. These reports allow us to hypothesize the stepwise, not necessarily saltatory, evolution of turtles, consistent with the recent finding of a transitional fossil animal, Odontochelys, that did not have the carapace but already possessed the plastron.

DOI： 10.1007/978-4-431-54634-4_23

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

The turtle body plan, with its solid shell, deviates radically from those of other tetrapods. The dorsal part of the turtle shell, or the carapace, consists mainly of costal and neural bony plates, which are continuous with the underlying thoracic ribs and vertebrae, respectively. Because of their superficial position, the evolutionary origins of these costo-neural elements have long remained elusive. Here we show, through comparative morphological and embryological analyses, that the major part of the carapace is derived purely from endoskeletal ribs. We examine turtle embryos and find that the costal and neural plates develop not within the dermis, but within deeper connective tissue where the rib and intercostal muscle anlagen develop. We also examine the fossils of an outgroup of turtles to confirm that the structure equivalent to the turtle carapace developed independently of the true osteoderm. Our results highlight the hitherto unravelled evolutionary course of the turtle shell.

DOI： 10.1038/ncomms3107

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Language：English   Publishing type：Part of collection (book)   Publisher：Springer  

The turtle shell is comprised of a dorsal carapace and a ventral plastron, and is an autapomorphy of this group. The carapace consists of the vertebral column and ribs as well as a specialized dermis. The formation of the shell is accompanied by a change in the spatial relationship of the ribs and the pectoral girdle. Because of this rearrangement, the turtle shell has been regarded as an example of an evolutionary novelty. Understanding the changes behind this developmental repatterning will help us elucidate the evolutionary history of turtles. The change has been attributed to a deflected pattern of development of the ribs, which in normal tetrapods grow ventrally into the lateral body wall. In turtles, they grow laterally toward the primordium of the carapacial margin, called the carapacial ridge (CR), while remaining in the axial part of the embryonic body. Based on a similarity in histological configuration, the CR has been thought to possess inductive activity for rib growth, as seen in the apical ectodermal ridge of the amniote limb bud. The CR does not function as a guidance cue for rib progenitor cells but rather functions in the marginal growth of the carapacial primordium, resulting in fanned-out growth of the ribs. This peripheral and concentric expansion of the axial domain makes the lateral body wall fold inward, while the ribs cover the pectoral girdle. The turtle ribs develop along the muscle plate as in other amniotes, and do not take a different trajectory from that in other amniotes, unlike the scenario hypothesized previously. This folding enables turtles to change the apparent spatial relationships between the ribs and the pectoral girdle without altering their topological alignment and body plan as amniotes. This developmental sequence of the modern turtles aligns with a stepwise evolutionary process in the group, which is supported by the anatomy of a recently discovered fossil species, Odontochelys.

DOI： 10.1007/978-94-007-4309-0_4

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The evolution of the turtle shell has long been one of the central debates in comparative anatomy. The turtle shell consists of dorsal and ventral parts: the carapace and plastron, respectively. The basic structure of the carapace comprises vertebrae and ribs. The pectoral girdle of turtles sits inside the carapace or the rib cage, in striking contrast to the body plan of other tetrapods. Due to this topological change in the arrangement of skeletal elements, the carapace has been regarded as an example of evolutionary novelty that violates the ancestral body plan of tetrapods. Comparing the spatial relationships of anatomical structures in the embryos of turtles and other amniotes, we have shown that the topology of the musculoskeletal system is largely conserved even in turtles. The positional changes seen in the ribs and pectoral girdle can be ascribed to turtle-specific folding of the lateral body wall in the late developmental stages. Whereas the ribs of other amniotes grow from the axial domain to the lateral body wall, turtle ribs remain arrested axially. Marginal growth of the axial domain in turtle embryos brings the morphologically short ribs in to cover the scapula dorsocaudally. This concentric growth appears to be induced by the margin of the carapace, which involves an ancestral gene expression cascade in a new location. These comparative developmental data allow us to hypothesize the gradual evolution of turtles, which is consistent with the recent finding of a transitional fossil animal, Odontochelys, which did not have the carapace but already possessed the plastron.

DOI： 10.1007/s12565-011-0121-y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

P>Turtles are characterized by their shell, composed of a dorsal carapace and a ventral plastron. The carapace first appears as the turtle-specific carapacial ridge (CR) on the lateral aspect of the embryonic flank. Accompanying the acquisition of the shell, unlike in other amniotes, hypaxial muscles in turtle embryos appear as thin threads of fibrous tissue. To understand carapacial evolution from the perspective of muscle development, we compared the development of the muscle plate, the anlage of hypaxial muscles, between the Chinese soft-shelled turtle, Pelodiscus sinensis, and chicken embryos. We found that the ventrolateral lip (VLL) of the thoracic dermomyotome of P. sinensis delaminates early and produces sparse muscle plate in the lateral body wall. Expression patterns of the regulatory genes for myotome differentiation, such as Myf5, myogenin, Pax3, and Pax7 have been conserved among amniotes, including turtles. However, in P. sinensis embryos, the gene hepatocyte growth factor (HGF), encoding a regulatory factor for delamination of the dermomyotomal VLL, was uniquely expressed in sclerotome and the lateral body wall at the interlimb level. Implantation of COS-7 cells expressing a HGF antagonist into the turtle embryo inhibited CR formation. We conclude that the de novo expression of HGF in the turtle mesoderm would have played an innovative role resulting in the acquisition of the turtle-specific body plan.

DOI： 10.1111/j.1525-142X.2011.00474.x

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DOI： 10.1111/j.1525-142X.2010.00451.x

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We investigated the development of the whole skeleton of the soft-shelled turtle Pelodiscus sinensis, with particular emphasis on the pattern and sequence of ossification. Ossification starts at late Tokita-Kuratani stage (TK) 18 with the maxilla, followed by the dentary and prefrontal. The quadrate is the first endoskeletal ossification and appears at TK stage 22. All adult skull elements have started ossification by TK stage 25. Plastral bones are the first postcranial bones to ossify, whereas the nuchal is the first carapacial bone to ossify, appearing as two unstained anlagen. Extensive examination of ossification sequences among autopodial elements reveals much intraspecific variation. Patterns of ossification of cranial dermal elements are more variable than those of endochondral elements, and dermal elements ossify before endochondral ones. Differences in ossification sequences with Apalone spinifera include: in Pelodiscus sinensis the jugal develops relatively early and before the frontal, whereas it appears later in A. spinifera; the frontal appears shortly before the parietal in A. spinifera whereas in R sinensis the parietal appears several stages before the frontal. Chelydrids exhibit an early development of the postorbital bone and the palatal elements as compared to trionychids. Integration of the onset of ossification data into an analysis of the sequence of skeletal ossification in cryptodirans using the event-pairing and Parsimov methods reveals heterochronies, some of which reflect the hypothesized phylogeny considered taxa. A functional interpretation of heterochronies is speculative. In the chondrocranium there is no contact between the nasal capsules and planum supraseptale via the sphenethmoid commissurae. The pattern of chondrification of forelimb and hind limb elements is consistent with a primary axis and digital arch. There is no evidence of anterior condensations distal to the radius and tibia. A pattern of quasi- simultaneity is seen in the chondrogenesis of the forelimb and the hind limb. J. Morphol. 270:1381-1399, 2009. (C) 2009 Wiley-Liss, Inc.

DOI： 10.1002/jmor.10766

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER ASSOC ADVANCEMENT SCIENCE  

The turtle shell offers a fascinating case study of vertebrate evolution, based on the modification of a common body plan. The carapace is formed from ribs, which encapsulate the scapula; this stands in contrast to the typical amniote body plan and serves as a key to understanding turtle evolution. Comparative analyses of musculoskeletal development between the Chinese soft-shelled turtle and other amniotes revealed that initial turtle development conforms to the amniote pattern; however, during embryogenesis, lateral rib growth results in a shift of elements. In addition, some limb muscles establish new turtle-specific attachments associated with carapace formation. We propose that the evolutionary origin of the turtle body plan results from heterotopy based on folding and novel connectivities.

DOI： 10.1126/science.1173826

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Language：English   Publishing type：Part of collection (book)   Publisher：Cambridge University Press  

Introduction Turtles are characterized by the possession of shells. For acquisition of this structure, this animal group appears to have undergone various types of anatomical changes in their body plan, not only in their skeletal system, but also in the muscular, nervous and respiratory systems (Bojanus 1819
Thomson 1932). These features often lead to confusion in determining homology, especially of amniote ribs, as well as in establishing the phylogenetic position of this animal group (Goodrich 1930
Remane 1936). To understand the origins of the morphology of turtles, a number of embryologists and morphologists have studied their embryonic developmental patterns (e.g. Rathke 1848
Agassiz 1857
Mitsukuri and Ishikawa 1887
Mitsukuri 1894, 1896
Ogushi 1911, 1913
Ruckes 1929
Walker 1947
Burke 1989, 1991
Gilbert et al. 2001, 2008
Nagashima et al. 2005, 2007
2009
Sánchez-Villagra et al. 2009
Werneburg et al. 2009
reviewed by Gilbert et al. 2008
Kuratani et al. 2011). The phylogenetic position of turtles remains controversial, but considerable progress has been made. Although recent molecular phylogenetics and genomic analyses have placed this taxon close to or even within the archosaurians, including birds and crocodiles (Caspers et al. 1996
Zardoya and Meyer 1998, 2001
Hedges and Poling 1999
Kumazawa and Nishida 1999
Mannen and Li 1999
Mindell et al. 1999
Cao et al. 2000
Iwabe et al. 2005
Matsuda et al. 2005
Kuraku et al. 2006
Hugall et al. 2007
Chapus and Edwards 2009), morphological analyses do not always agree with this conclusion (reviewed by Kuratani et al. 2011). However, some early embryologists supported an affinity to archosaurians (Haeckel 1891
de Beer 1937
see also Figure 1.1 in Asher and Müller, this volume).

DOI： 10.1017/CBO9780511760174.011

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The chelonian carapace is composed of dorsolaterally expanded ribs; an evolutionary change in the rib-patterning program is assumed to be related to this novelty. Turtle embryos exhibit a longitudinal ridge called the carapacial ridge (CR) on the flank, and its histological resemblance to the apical ectodermal ridge of the limb bud implies its inductive activity in the unique patterning of the ribs. We studied the Chinese soft-shelled turtle, Pelodiscus sinensis, and confirmed by labeling with a lipophilic dye, DiI, that the CR contains the somite-derived dermis and that it is a unique structure among amniotes. Using electroporation of a dominant-negative form of LEF-1, the CR-specific gene, we showed that CR-specific genes function in the growth and maintenance of the CR. Microcauterization or implantation of the CR did not change the dorsoventral pattern of the ribs, and only their fan-shaped pattern was arrested by CR removal. We conclude that the CR is a true embryonic novelty among amniotes and, because of the specific expression of regulatory genes, it functions in the marginal growth of the carapacial primordium, thereby inducing the fan-shaped arrangement of the ribs.

DOI： 10.1242/dev.002618

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ZOOLOGICAL SOC JAPAN  

The manus and pes were studied using whole-mount and histological preparations of ontogenetic series of Chelonia mydas and Caretta caretta. Patterns of connectivity and sequences of chondrification events are similar to those reported for other turtle species, with respect to both the primary axis and the digital arch. There is no evidence of anterior condensations in the region distal to the radius and the tibia, supporting the hypothesis that the radiale and tibiale are absent in turtles. The three middle metacarpals are the first elements to start ossification in the manus of C. mydas, while ossification has not started in the pes. In the hatchling of C. mydas, most carpals have started ossification, whereas tarsals are mostly still cartilaginous. In C. caretta, the first carpals to ossify are the ulnare and intermedium, followed by the pisiform. Among metatarsals, the fifth hooked metatarsal is the last one to start ossification. The fibulare and intermedium fuse early in chondrogenesis, later becoming the astragalocalcaneum. Ossification in the carpals of C. caretta starts while tarsals are still cartilaginous. The derived autopodial proportions in each autopodium of adults are laid out at the condensation stage, and features that were present in basal turtles are absent at all stages examined (developmental penetrance). In contrast to this, conservatism is expressed in the presence of similar patterns of connectivity during early chondrogenesis, and in the development of overall proportions of the manus versus pes. As in adult anatomy, the development of the autopodium of marine turtles is a mosaic of derived and plesiomorphic features.

DOI： 10.2108/zsj.24.257

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DOI： 10.1111/j.1525-142X.2006.00115.x

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Turtles have a body plan unique among vertebrates in that their ribs have shifted topographically to a superficial layer of the body and the trunk muscles are greatly reduced. Identifying the developmental factors that cause this pattern would further our understanding of the evolutionary origin of the turtles. As the first step in addressing this question, we replaced newly developed epithelial somites of the chicken at the thoracic level with those of the Chinese soft-shelled turtle Pelodiscus sinensis (P. sinensis somites into a chicken host) and observed the developmental patterning of the grafted somites in the chimera. The P. sinensis somites differentiated normally in the chicken embryonic environment into sclerotomes and dermomyotomes, and the myotomes differentiated further into the epaxial and hypaxial muscles with histological morphology similar to that of normal P. sinensis embryos and not to that of the chicken. Epaxial dermis also arose from the graft. Skeletal components, however, did not differentiate from the P. sinensis sclerotome, except for small fragments of cartilage associated with the host centrum and neural arches. We conclude that chicken and P. sinensis share the developmental programs necessary for the early differentiation of somites and that turtle-specific traits in muscle patterning arise mainly through a cell-autonomous developmental process in the somites per se. However, the mechanism for turtle-specific cartilage patterning, including that of the ribs, is not supported by the chicken embryonic environment.

DOI： 10.1002/dvdy.20235

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Environmental contamination by polyaromatic hydrocarbons (PAHs) and dioxin-like compounds was evaluated by chemical analysis and biological tests. Though soils and road dust samples revealed more potent biological activities than incinerator ashes, the contribution of PAHs were low.

DOI： 10.1246/cl.2002.1070

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Material Cycles and Waste Management  

To develop a more applicable means to screen for toxicity, we have selected a battery of three biotests for a six-month monitoring period of the risk in leachate from a landfill site. To validate this battery, we measured genotoxicty, proliferation activity of MCF-7 and cytotoxicity of leachate, its treated effluent and receiving river waters once a week. A new measure, named Negative Dilution Factor (NDF) become apparent from <I>umu</I>-test. In the experiments genotoxicity was detected in leachates, and reduced through the treatment process. Leachate showed same seasonal changes in proliferation activity of MCF-7 cells in river samples. Since the average proliferation activity of MCF-7 cells in leachate was low, there may be little effect of leachates on the river. Cytotoxicity of leachate and treated effluent were stronger than river water but almost all of these toxicities were less than 50% inhibitiing. Cytotoxicity was observed in concentrated samples from a landfill site, but it derived from osmotic pressure by salinity. As the maximum cytotoxicity of treated effluent was 9 times that of upstream samples, it may be necessary to dilute treated effluent about 10 times for the management of impact on the environment.

DOI： 10.3985/jswme.13.289

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society on Water Environment  

To evaluate the toxicity existing in effluent water, three different bioassays, <i>in vitro</i> cytotoxicity tests using three human cell lines, bioluminescene inhibition test using luminescent bacteria and daphnia acute immobilization test, were applied to effluent water samples collected from solid-waste incineration plants. Results obtained from bioassays were compared with the results from chemical and physical analysis.<br>Toxicity observed with bioassays were not necessarily correlated with individual indices from chemical analysis, such as AOX (adsorbable organic halides), dioxins, heavy metal contents and pH. However, the toxicity to human cell lines and daphnia were well correlated with the osmolarity of the samples. Moreover the dose-response curves coincided well with those of standard osmolarity solutions made of sodium chloride or glucose, suggesting that the osmolarity plays a significant role in the toxic effects of these effluent water samples.<br>Therefore, for the application of bioassays to effluent water samples, especially in case of <i>in vitro</i> cytotoxicity tests and daphnia test, consideration of the osmolarity of the samples is essential for accurate assessment of their toxicity.

DOI： 10.2965/jswe.24.110

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DOI： 10.2965/jswe.24.58

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