ORCID Profile
0000-0001-5996-2413
Current Organisation
University of Oxford
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Publisher: Elsevier BV
Date: 09-2023
Publisher: IOP Publishing
Date: 30-07-2019
Publisher: International Union of Crystallography (IUCr)
Date: 06-09-2022
DOI: 10.1107/S1600576722007646
Abstract: Bragg coherent X-ray diffraction imaging (BCDI) allows the 3D measurement of lattice strain along the scattering vector for specific microcrystals. If at least three linearly independent reflections are measured, the 3D variation of the full lattice strain tensor within the microcrystal can be recovered. However, this requires knowledge of the crystal orientation, which is typically attained via estimates based on crystal geometry or synchrotron microbeam Laue diffraction measurements. Presented here is an alternative method to determine the crystal orientation for BCDI measurements using electron backscatter diffraction (EBSD) to align Fe–Ni and Co–Fe alloy microcrystals on three different substrates. The orientation matrix is calculated from EBSD Euler angles and compared with the orientation determined using microbeam Laue diffraction. The average angular mismatch between the orientation matrices is less than ∼6°, which is reasonable for the search for Bragg reflections. The use of an orientation matrix derived from EBSD is demonstrated to align and measure five reflections for a single Fe–Ni microcrystal via multi-reflection BCDI. Using this data set, a refined strain field computation based on the gradient of the complex exponential of the phase is developed. This approach is shown to increase accuracy, especially in the presence of dislocations. The results demonstrate the feasibility of using EBSD to pre-align BCDI s les and the application of more efficient approaches to determine the full lattice strain tensor with greater accuracy.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 25-05-2011
DOI: 10.1002/HEP.24315
Abstract: Clinical studies of bone marrow (BM) cell therapy for liver cirrhosis are under way but the mechanisms of benefit remain undefined. Cells of the monocyte-macrophage lineage have key roles in the development and resolution of liver fibrosis. Therefore, we tested the therapeutic effects of these cells on murine liver fibrosis. Advanced liver fibrosis was induced in female mice by chronic administration of carbon tetrachloride. Unmanipulated, syngeneic macrophages, their specific BM precursors, or unfractionated BM cells were delivered during liver injury. Mediators of inflammation, fibrosis, and regeneration were measured. Donor cells were tracked by sex-mismatch and green fluorescent protein expression. BM-derived macrophage (BMM) delivery resulted in early chemokine up-regulation with hepatic recruitment of endogenous macrophages and neutrophils. These cells delivered matrix metalloproteinases-13 and -9, respectively, into the hepatic scar. The effector cell infiltrate was accompanied by increased levels of the antiinflammatory cytokine interleukin 10. A reduction in hepatic myofibroblasts was followed by reduced fibrosis detected 4 weeks after macrophage infusion. Serum albumin levels were elevated at this time. Up- regulation of the liver progenitor cell mitogen tumor necrosis factor-like weak inducer of apoptosis (TWEAK) preceded expansion of the progenitor cell compartment. Increased expression of colony stimulating factor-1, insulin-like growth factor-1, and vascular endothelial growth factor also followed BMM delivery. In contrast to the effects of differentiated macrophages, liver fibrosis was not significantly altered by the application of macrophage precursors and was exacerbated by whole BM. Macrophage cell therapy improves clinically relevant parameters in experimental chronic liver injury. Paracrine signaling to endogenous cells lifies the effect. The benefits from this single, defined cell type suggest clinical potential.
Publisher: Elsevier BV
Date: 12-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D1CE01586A
Abstract: Morphology, 3D lattice strain, and dissolution of a Co–Fe microcrystal was monitored using in situ Bragg coherent X-ray diffraction imaging.
Publisher: Springer Science and Business Media LLC
Date: 21-06-2022
DOI: 10.1557/S43578-022-00613-2
Abstract: Understanding the mechanisms of plasticity in structural steels is essential for the operation of next-generation fusion reactors. This work on the deformation behaviour of FeCr, focusses on distinguishing the nucleation of dislocations to initiate plasticity, from their propagation through the material. Fe3Cr, Fe5Cr, and Fe10Cr were irradiated with 20 MeV Fe 3+ ions at room temperature to doses of 0.008 dpa and 0.08 dpa. Nanoindentation was then carried out with Berkovich and spherical indenter tips. Our results show that the nucleation of dislocations is mainly from pre-existing sources, which are not significantly affected by the presence of irradiation defects or Cr%. Yield strength, an indicator of dislocation mobility, increases with irradiation damage and Cr content, while work hardening capacity decreases mainly due to irradiation defects. The synergistic effects of Cr and irradiation damage in FeCr appear to be more important for the propagation of dislocations than for their nucleation.
Publisher: Springer Science and Business Media LLC
Date: 23-03-2021
DOI: 10.1557/S43578-021-00153-1
Abstract: Traditional fibre push-outs for the evaluation of interfacial properties in long fibre ceramic matrix composites present their limitations—solutions for which are addressed in this work by introducing the novel trench push-out test. The trench push-out makes use of a FIB milling system and an SEM in-situ nanoindenter to probe a fibre pushed into a trench underneath, allowing in-situ observations to be directly correlated with micromechanical events. SiC f /BN/SiC composites—candidate material for turbine engines—were used as model materials in this work. Different fibre types (Hi-Nicalon and Tyranno type SA3) were coated with BN interphases, presenting mean interfacial shear stresses of 14 ± 7 MPa and 20 ± 2 MPa, respectively, during fibre sliding. The micromechanical technique enabled visualisation of how defects in the interphase (voids, inclusions & milled notches) or in the fibre (surface asperities, non-uniform coatings) affected the variability of interfacial property measurement. Graphic abstract
Publisher: International Union of Crystallography (IUCr)
Date: 19-02-2021
DOI: 10.1107/S1600577520016264
Abstract: Focused ion beam (FIB) techniques are commonly used to machine, analyse and image materials at the micro- and nanoscale. However, FIB modifies the integrity of the s le by creating defects that cause lattice distortions. Methods have been developed to reduce FIB-induced strain however, these protocols need to be evaluated for their effectiveness. Here, non-destructive Bragg coherent X-ray diffraction imaging is used to study the in situ annealing of FIB-milled gold microcrystals. Two non-collinear reflections are simultaneously measured for two different crystals during a single annealing cycle, demonstrating the ability to reliably track the location of multiple Bragg peaks during thermal annealing. The thermal lattice expansion of each crystal is used to calculate the local temperature. This is compared with thermocouple readings, which are shown to be substantially affected by thermal resistance. To evaluate the annealing process, each reflection is analysed by considering facet area evolution, cross-correlation maps of the displacement field and binarized morphology, and average strain plots. The crystal's strain and morphology evolve with increasing temperature, which is likely to be caused by the diffusion of gallium in gold below ∼280°C and the self-diffusion of gold above ∼280°C. The majority of FIB-induced strains are removed by 380–410°C, depending on which reflection is being considered. These observations highlight the importance of measuring multiple reflections to unambiguously interpret material behaviour.
Publisher: Elsevier BV
Date: 02-2022
Publisher: IOP Publishing
Date: 28-01-2018
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 25-09-2020
Abstract: The innate immune system is central to injury and repair in the kidney, but the heterogeneity of myeloid cell subsets behind these processes is unknown. Complementary technologies—including bulk tissue transcriptomics, integrated droplet– and plate-based single-cell RNA sequencing, and paired blood exchange—resolved myeloid cell heterogeneity in a murine model of reversible unilateral ureteric obstruction, creating a single-cell atlas. The identified novel myeloid subsets could be targeted to ameliorate injury or enhance repair, including an Arg1+ monocyte subset present during injury and Mmp12+ macrophages present during repair. Standard flow cytometry to detect cell surface markers would have missed these subsets. Complementary techniques capture the complexity and dynamics of monocyte, dendritic cell, and macrophage phenotypes in the injured and repairing kidney. Little is known about the roles of myeloid cell subsets in kidney injury and in the limited ability of the organ to repair itself. Characterizing these cells based only on surface markers using flow cytometry might not provide a full phenotypic picture. Defining these cells at the single-cell, transcriptomic level could reveal myeloid heterogeneity in the progression and regression of kidney disease. Integrated droplet– and plate-based single-cell RNA sequencing were used in the murine, reversible, unilateral ureteric obstruction model to dissect the transcriptomic landscape at the single-cell level during renal injury and the resolution of fibrosis. Paired blood exchange tracked the fate of monocytes recruited to the injured kidney. A single-cell atlas of the kidney generated using transcriptomics revealed marked changes in the proportion and gene expression of renal cell types during injury and repair. Conventional flow cytometry markers would not have identified the 12 myeloid cell subsets. Monocytes recruited to the kidney early after injury rapidly adopt a proinflammatory, profibrotic phenotype that expresses Arg1 , before transitioning to become Ccr2 + macrophages that accumulate in late injury. Conversely, a novel Mmp12 + macrophage subset acts during repair. Complementary technologies identified novel myeloid subtypes, based on transcriptomics in single cells, that represent therapeutic targets to inhibit progression or promote regression of kidney disease.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Prakash Ramachandran.