Translational and rotational dynamical heterogeneities in granular systems

We use X-ray tomography to investigate the translational and rotational dynamical heterogeneities of a three dimensional hard ellipsoids granular packing driven by oscillatory shear. We find that particles which translate quickly form clusters with a size distribution given by a power-law with an exponent that is independent of the strain amplitude. Identical behavior is found for particles that are translating slowly, rotating quickly, or rotating slowly. The geometrical properties of these four different types of clusters are the same as those of random clusters. Different cluster types are considerably correlated/anticorrelated, indicating a significant coupling between translational and rotational degrees of freedom. Surprisingly these clusters are formed already at time scales that are much shorter than the $\alpha-$relaxation time, in stark contrast to the behavior found in glass-forming systems.Comment: 9 page

Structural and Topological Nature of Plasticity in Sheared Granular Materials

Upon mechanical loading, granular materials yield and undergo plastic deformation. The nature of plastic deformation is essential for the development of the macroscopic constitutive models and the understanding of shear band formation. However, we still do not fully understand the microscopic nature of plastic deformation in disordered granular materials. Here we used synchrotron X-ray tomography technique to track the structural evolutions of three-dimensional granular materials under shear. We establish that highly distorted coplanar tetrahedra are the structural defects responsible for microscopic plasticity in disordered granular packings. The elementary plastic events occur through flip events which correspond to a neighbor switching process among these coplanar tetrahedra (or equivalently as the rotation motion of 4-ring disclinations). These events are discrete in space and possess specific orientations with the principal stress direction.Comment: 26 pages, 11 figures, 2 tables, to be published in Nature Communication

Grating-based phase-contrast imaging of tumor angiogenesis in lung metastases.

PurposeTo assess the feasibility of the grating-based phase-contrast imaging (GPI) technique for studying tumor angiogenesis in nude BALB/c mice, without contrast agents.MethodsWe established lung metastatic models of human gastric cancer by injecting the moderately differentiated SGC-7901 gastric cancer cell line into the tail vein of nude mice. Samples were embedded in a 10% formalin suspension and dried before imaging. Grating-based X-ray phase-contrast images were obtained at the BL13W beamline of the Shanghai Synchrotron Radiation Facility (SSRF) and compared with histological sections.ResultsWithout contrast agents, grating-based X-ray phase-contrast imaging still differentiated angiogenesis within metastatic tumors with high spatial resolution. Vessels, down to tens of microns, showed gray values that were distinctive from those of the surrounding tumors, which made them easily identifiable. The vessels depicted in the imaging study were similar to those identified on histopathology, both in size and shape.ConclusionsOur preliminary study demonstrates that grating-based X-ray phase-contrast imaging has the potential to depict angiogenesis in lung metastases

Reconstructed tomogram of lung metastasis sample (sample one) from HE pathology, GPI-CT, MIP and gray value graphs.

<p>(a) Reconstructed tomogram in GPI-CT, yellow arrows: tumor lesion. (b) Histological section: yellow arrows: two lung metastatic tumors; green arrows: microvascular structures in the tumor. (c) MIP. (d) Enlarged view of the red box in (c), which reveals the presence of two blood vessels with blood cells inside. Three ROIs were selected, including 1) tumor (red square), 2) vessel (yellow square) and 3) the background region (blue square). The gray values along the red dashed lines across the blood vessels in (d) are plotted in (e). (a-c scale bar: 600 μm; d scale bar: 300 μm).</p

Reconstructed tomogram of lung metastasis sample (sample two) from HE pathology, GPI-CT and gray value graphs.

<p>(a) Reconstructed tomogram in GPI-CT. (c, e) Enlarged view of the red box in (a), which indicates the presence of branch-like blood vessels with blood cells inside within the tumor. Three ROIs were selected, including 1) tumor (red square), 2) vessel (yellow square) and 3) the background region (blue square). (b) Histological section. (d) Enlarged view of the red box in (b); yellow arrow: blood vessel. The gray values along the red dashed lines across the blood vessel in (e) are plotted in (f). (Scale bar in (a) and (b): 2 mm; Scale bar in (c), (d) and (e): 500 μm).</p

Schematic of the grating interferometer set-up at the BL13W beamline of SSRF.

<p>Schematic of the grating interferometer set-up at the BL13W beamline of SSRF.</p

Relevant imaging conditions of two samples.

<p>Relevant imaging conditions of two samples.</p