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The initial stage of fatigue failure has not been thoroughly clarified for carbon fiber reinforced plastics (CFRPs). Although the initiation of fatigue cracks has been regarded to be interfacial debonding between the carbon fiber and polymer matrix, their detection among numerous carbon fibers, whose diameter is only 7 µm, is extremely difficult. In this study, a single carbon fiber was transversely embedded in a dumbbell-shaped epoxy sample to focus on the interfacial debonding and was observed using synchrotron radiation (SR) X-ray computed tomography (CT). A tabletop fatigue testing machine driven by a piezoelectric actuator was developed to apply static and cyclic loads along the beamline. SR X-ray multiscale CT imaging was conducted by switching between an absorption-contrast projection method (micro-CT) and a phase-contrast imaging-type X-ray microscopic CT (nano-CT). The carbon fiber was entirely captured by micro-CT and then magnified at both ends on the free surfaces. Nano-CT clearly visualized the interfacial debonding under 30 MPa static tensile load and the implication of the coalescence of nano-voids along the interface under 50 MPa. Under cyclic loads, the interfacial debonding gradually progressed under a 8–40 MPa sinusoidal stress after 10,000 cycles, whereas it did not propagate under a stress below 30 MPa.

The melting temperature of Earth's mantle provides key constraints on the thermal structures of both the mantle and the core. Through high-pressure experiments and three-dimensional x-ray microtomographic imaging, we showed that the solidus temperature of a primitive (pyrolitic) mantle is as low as 3570 ± 200 kelvin at pressures expected near the boundary between the mantle and the outer core. Because the lowermost mantle is not globally molten, this provides an upper bound of the temperature at the core-mantle boundary (TCMB). Such remarkably low TCMB implies that the post-perovskite phase is present in wide areas of the lowermost mantle. The low TCMB also requires that the melting temperature of the outer core is depressed largely by impurities such as hydrogen.

Brain blood vessels constitute a micrometer-scale vascular network responsible for supply of oxygen and nutrition. In this study, we analyzed cerebral tissues of the anterior cingulate cortex and superior temporal gyrus of schizophrenia cases and age/gender-matched controls by using synchrotron radiation microtomography or micro-CT in order to examine the three-dimensional structure of cerebral vessels. Over 1 m of cerebral blood vessels was traced to build Cartesian-coordinate models, which were then used for calculating structural parameters including the diameter and curvature of the vessels. The distribution of vessel outer diameters showed a peak at 7–9 μm, corresponding to the diameter of the capillaries. Mean curvatures of the capillary vessels showed a significant correlation to the mean curvatures of neurites, while the mean capillary diameter was almost constant, independent of the cases. Our previous studies indicated that the neurites of schizophrenia cases are thin and tortuous compared to controls. The curved capillaries with a constant diameter should occupy a nearly constant volume, while neurons suffering from neurite thinning should have reduced volumes, resulting in a volumetric imbalance between the neurons and the vessels. We suggest that the observed structural correlation between neurons and blood vessels is related to neurovascular abnormalities in schizophrenia.

Palaeohistological analysis has numerous applications in understanding the palaeobiology of extinct dinosaurs. Recent developments of synchrotron‐radiation‐based X‐ray micro‐tomography (SXMT) have allowed the non‐destructive assessment of palaeohistological features in fossil skeletons. Yet, the application of the technique has been limited to specimens on the millimetre to micrometre scale because its high‐resolution capacity has been obtained at the expense of a small field of view and low X‐ray energy. Here, SXMT analyses of dinosaur bones with widths measuring ∼3 cm under a voxel size of ∼4 µm at beamline BL28B2 at SPring‐8 (Hyogo, Japan) are reported, and the advantages of virtual‐palaeohistological analyses with large field of view and high X‐ray energy are explored. The analyses provide virtual thin‐sections visualizing palaeohistological features comparable with those obtained by traditional palaeohistology. Namely, vascular canals, secondary osteons and lines of arrested growth are visible in the tomography images, while osteocyte lacunae are unobservable due to their micrometre‐scale diameter. Virtual palaeohistology at BL28B2 is advantageous in being non‐destructive, allowing multiple sampling within and across skeletal elements to exhaustively test the skeletal maturity of an animal. Continued SXMT experiments at SPring‐8 should facilitate the development of SXMT experimental procedures and aid in understanding the paleobiology of extinct dinosaurs. Synchrotron‐radiation‐based X‐ray micro‐tomography at beamline BL28B2 at SPring‐8 (Hyogo, Japan) enables the non‐destructive assessment of palaeohistological features in dense, fossilized bones of an allosauroid dinosaur, Fukuiraptor kitadaniensis, demonstrating its effectiveness in virtual palaeohistology.

Dendrite arm fragmentation is considered in solidification structure tailoring. Time-resolved and in situ imaging using synchrotron radiation X-rays allows the observation of dendrite arm fragmentation in Fe–C alloys. Here we report a dendrite arm fragmentation mechanism. A massive-like transformation from ferrite to austenite rather than the peritectic reaction occurs during or after ferrite solidification. The transformation produces refined austenite grains and ferrite–austenite boundaries in dendrite arms. The austenite grains are fragmented by the liquid phase that is produced at the grain boundary. In unidirectional solidification, a slight increase in temperature moves the ferrite–austenite interface backwards and promotes detachment of the primary and secondary arms at the δ–γ interface via a reverse peritectic reaction. The results show a massive-like transformation inducing the dendrite arm fragmentation has a role in formation of the solidification structure and the austenite grain structures in the Fe–C alloys. Transitioning from columnar to equiaxed grains is paramount for desired microstructures during steel casting. Here, the authors report a new fragmentation mechanism based on a phase transition at grain boundaries that can contribute to equiaxed grains.

High‐energy X‐ray micro‐laminography has been developed to observe inner‐ and near‐surface structures in dense planar objects that are not suitable for observation by X‐ray micro‐tomography. A multilayer‐monochromator‐based high‐intensity X‐ray beam with energy of 110 keV was used for high‐energy and high‐resolution laminographic observations. As a demonstration of high‐energy X‐ray micro‐laminography for observing dense planar objects, a compressed fossil cockroach on a planar matrix surface was analyzed with effective pixel sizes of 12.4 µm and 4.22 µm for wide field of view and high‐resolution observations, respectively. In this analysis, the near‐surface structure was clearly observed without undesired X‐ray refraction‐based artifacts from outside of the region of interest, a problem typical in tomographic observations. Another demonstration visualized fossil inclusions in a planar matrix. Micro‐scale features of a gastropod shell and micro‐fossil inclusions in the surrounding matrix were clearly visualized. When observing local structures in the dense planar object with X‐ray micro‐laminography, the penetrating path length in the surrounding matrix can be shortened. This is a significant advantage of X‐ray micro‐laminography where desired signals generated at the region of interest including optimal X‐ray refraction effectively contribute to image formation without being disturbed by undesired interactions in the thick and dense surrounding matrix. Therefore, X‐ray micro‐laminography allows recognition of the local fine structures and slight difference in the image contrast of planar objects undetectable in a tomographic observation. The development of synchrotron‐radiation‐based high‐energy X‐ray micro‐laminography to visualize microstructures in dense planar objects such as planar fossils is described.

In situ observation of solidification cracking at the weld bead during tungsten inert gas (TIG) welding for type 310S and 316L austenitic stainless steels without the application of an external force was carried out using synchrotron X-ray radiography. The temperature distribution at the weld bead was simultaneously measured using a high-speed camera to directly determine the temperature, in which the propagation of solidification cracking occurred. The solidification cracking was clearly identified and it continuously propagated in the welding direction. The interface of the solidification cracking showed an irregular and zigzag morphology. It was found that the tip velocity of the solidification cracking periodically changed by translating between the high solid fraction (~ 90%) and the relatively lower solid fraction (~ 70%) regions at the centerline of the weld bead for both the type 310S and 316L stainless steels. The solidification cracking propagated at the lower temperature than the solidus temperature due to the segregation of low melting-point components. The tensile strain and strain rate were highly localized in the propagated area every 0.1 s which was the almost same as the time period, in which the tip velocity of the solidification cracking remarkably increased. The periodicity of the solidification cracking velocity at the weld bead can be explained by the dendrite morphology at each solid fraction and strain rate.

Ferromanganese minerals are widely distributed in subseafloor sediments and on the seafloor in oceanic abyssal plains. Assessing their input, formation and preservation is important for understanding the global marine manganese cycle and associated trace elements. However, the extent of ferromanganese minerals buried in subseafloor sediments remains unclear. Here we show that abundant (10 8 –10 9 particles cm −3 ) micrometer-scale ferromanganese mineral particles (Mn-microparticles) are found in the oxic pelagic clays of the South Pacific Gyre (SPG) from the seafloor to the ~100 million-year-old sediments above the basement. Three-dimensional micro-texture, and major and trace element compositional analyses revealed that these Mn-microparticles consist of poorly crystalline ferromanganese oxides precipitating from bottom water. Based on our findings, we extrapolate that 1.5–8.8 × 10 28 Mn-microparticles, accounting for 1.28–7.62 Tt of manganese, are globally present in oxic subseafloor sediments. This estimate is at least two orders of magnitude larger than the manganese budget for nodules and crusts on the seafloor. Subseafloor Mn-microparticles thus contribute significantly to the global manganese budget. Ferromanganese minerals are abundant in marine environments but the extent of these minerals in subseafloor sediments remains unknown. Here the authors find abundant ferromanganese microparticles in oxic pelagic clays, accounting for 14–16% of the new estimate of the global manganese budget (9.2–47.4 Tt).

A crucial evolutionary change in vertebrate history was the Palaeozoic (Devonian 419–359 million years ago) water-to-land transition, allowed by key morphological and physiological modifications including the acquisition of lungs. Nonetheless, the origin and early evolution of vertebrate lungs remain highly controversial, particularly whether the ancestral state was paired or unpaired. Due to the rarity of fossil soft tissue preservation, lung evolution can only be traced based on the extant phylogenetic bracket. Here we investigate, for the first time, lung morphology in extensive developmental series of key living lunged osteichthyans using synchrotron x-ray microtomography and histology. Our results shed light on the primitive state of vertebrate lungs as unpaired, evolving to be truly paired in the lineage towards the tetrapods. The water-to-land transition confronted profound physiological challenges and paired lungs were decisive for increasing the surface area and the pulmonary compliance and volume, especially during the air-breathing on land. All life on Earth started out under water. However, around 400 million years ago some vertebrates, such as fish, started developing limbs and other characteristics that allowed them to explore life on land. One of the most pivotal features to evolve was the lungs, which gave vertebrates the ability to breathe above water. Most land-living vertebrates, including humans, have two lungs which sit on either side of their chest. The lungs extract oxygen from the atmosphere and transfer it to the bloodstream in exchange for carbon dioxide which then gets exhaled out in to the atmosphere. How this important organ first evolved is a hotly debated topic. This is largely because lung tissue does not preserve well in fossils, making it difficult to trace how the lungs of vertebrates changed over the course of evolution. To overcome this barrier, Cupello et al. compared the lungs of living species which are crucial to understand the early stages of the water-to-land transition . This included four species of lunged bony fish which breathe air at the water surface, and a four-legged salamander that lives on land. Cupello et al. used a range of techniques to examine how the lungs of the bony fish and salamander changed shape during development. The results suggested that the lungs of vertebrates started out as a single organ, which became truly paired later in evolution once vertebrates started developing limbs. This anatomical shift increased the surface area available for exchanging oxygen and carbon dioxide so that vertebrates could breathe more easily on land. These findings provide new insights in to how the lung evolved into the paired structure found in most vertebrates alive today. It likely that this transition allowed vertebrates to fully adapt to breathing above water, which may explain why this event only happened once over the course of evolution.

Palaeospondylus gunni , from the Middle Devonian period, is one of the most enigmatic fossil vertebrates, and its phylogenetic position has remained unclear since its discovery in Scotland in 1890 (ref.  1 ). The fossil’s strange set of morphological features has made comparisons with known vertebrate morphotype diversity difficult. Here we use synchrotron radiation X-ray micro-computed tomography to show that Palaeospondylus was a sarcopterygian, and most probably a stem-tetrapod. The skeleton of Palaeospondylus consisted solely of endoskeletal elements in which hypertrophied chondrocyte cell lacunae, osteoids and a small fraction of perichondral bones developed. Despite the complete lack of teeth and dermal bones, the neurocranium of Palaeospondylus resembles those of stem-tetrapod Eusthenopteron 2 and Panderichthys 3 , and phylogenetic analyses place Palaeospondylus in between them. Because the unique features of Palaeospondylus , such as the cartilaginous skeleton and the absence of paired appendages, are present in the larva of crown tetrapods, our study highlights an unanticipated heterochronic evolution at the root of tetrapods. Detailed structural analysis of Palaeospondylus gunni from the Middle Devonian period shows strong resemblance to Eusthenopteron and Panderichthys , indicating that it was a sarcopterygian and most probably a stem-tetrapod.