Newly discovered pelvic and reproductive structures within placoderms, representing some of the most crownward members of the gnathostome stem group and the most basal jawed vertebrates, challenge established ideas on the origin of the pelvic girdle and reproductive complexity. Here we critically review previous descriptions of the pelvic structures in placoderms and reinterpret the morphology of the pelvic region within the arthrodires and ptyctodonts, in particular the position of the pelvic fin and the relationship of the male clasper to the pelvic girdle. Absence of clear articular surfaces on the clasper and girdle in the Arthrodira, along with evidence from the Ptyctodontida, suggest that these are separate structures along the body. We describe similarities between the pectoral and pelvic girdles and claspers, for example, all these have both dermal and perichondral (cartilaginous) components. Claspers in placoderms and chondrichthyans develop in very different ways; in sharks, claspers develop from the pelvic fin while the claspers in placoderms develop separately, suggesting that their independent development involved a posterior extension of the 'competent stripes' for fin development previously limited to the region between the paired pectoral and pelvic fins. Within this expanded zone, we suggest that clasper position relative to the pelvic fins was determined by genes responsible for limb position. Information on early gnathostome reproductive processes is preserved in both the Ptyctodontida and Arthrodira, including the presence of multiple embryos in pregnant females, embryos of differing sizes and of different sexes (e.g. male claspers preserved in some embyros). By comparison with chondrichthyans, these observations suggest more complex reproductive strategies in placoderms than previously appreciated.
X-ray dark-field and bright-field imaging in the Laue geometry has been successfully demonstrated. Using a Bragg-case asymmetric monochromator that produces an X-ray beam with a 0.3 mrad divergence incident onto an object and a Laue geometry analyzer that can simultaneously provide dark-field imaging (DFI) and bright-field imaging (BFI). The DFI has only an X-ray refraction component on the object without illumination, while the BFI has reasonable illumination. This was achieved by a 1.075 mm thick silicon analyzer with 4, 4, 0 diffraction at 35 keV X-ray photon energy. An image of an insect embedded in polymethylmethacrylate, which can not be visualized by absorption, has been obtained.
The Multi-modal Australian ScienceS Imaging and Visualization Environment (MASSIVE) is a national imaging and visualization facility established by Monash University, the Australian Synchrotron, the Commonwealth Scientific Industrial Research Organization (CSIRO), and the Victorian Partnership for Advanced Computing (VPAC), with funding from the National Computational Infrastructure and the Victorian Government. The MASSIVE facility provides hardware, software, and expertise to drive research in the biomedical sciences, particularly advanced brain imaging research using synchrotron x-ray and infrared imaging, functional and structural magnetic resonance imaging (MRI), x-ray computer tomography (CT), electron microscopy and optical microscopy. The development of MASSIVE has been based on best practice in system integration methodologies, frameworks, and architectures. The facility has: (i) integrated multiple different neuroimaging analysis software components, (ii) enabled cross-platform and cross-modality integration of neuroinformatics tools, and (iii) brought together neuroimaging databases and analysis workflows. MASSIVE is now operational as a nationally distributed and integrated facility for neuroinfomatics and brain imaging research.
Computed tomographic (CT) reconstruction technique is widely used in many fields of research. Commonly the CT-reconstruction is based on the x-ray absorption contrast. However, recently, methods for generating other x-ray contrasts have been developed. One of them is the refraction contrast which provides information on the deflection of the x-ray beam when penetrating through the object. This contrast has certain advantages and allows us to observe details invisible in the absorption images. Thus, CT based on the refraction contrast must have the same advantages. However, it requires a new mathematical algorithm and software. This letter is dedicated to the solution of the problem including theoretical consideration on the mathematical model which is the basis for the computer modeling and experimental realization of the technique. Actual experimental results together with the reconstructed images are presented and described.
Purpose: To investigate how an intrinsic speckle-tracking approach to speckle-based X-ray imaging can be used to extract an object's effective dark-field signal, which is capable of providing object information in three dimensions. Approach:The effective dark-field signal was extracted using a Fokker-Planck type formalism, which models the deformations of illuminating reference-beam speckles due to both coherent and diffusive scatter from the sample. We here assumed that (a) small-angle scattering fans at the exit surface of the sample are rotationally symmetric, and (b) the object has both attenuating and refractive properties. The associated inverse problem, of extracting the effective dark-field signal, was numerically stabilised using a "weighted determinants" approach.Results: Effective dark-field projection images are presented, as well as the dark-field tomographic reconstructions of the wood sample. Dark-field tomography was performed using a filtered-back projection reconstruction algorithm. The dark-field tomographic reconstructions of the wood sample provided complementary, and otherwise inaccessible, information to augment the phase-contrast reconstructions, which were also computed.Conclusions: An intrinsic speckle-tracking approach to speckle-based imaging can tomographically reconstruct an object's dark-field signal at a low sample exposure and with a simple experimental set-up. The obtained dark-field reconstructions have image quality comparable to alternative X-ray dark-field techniques.
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