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Biomedical subjects

En Ma

Publications and source records attributed to En Ma.

4 recordsLinked to original sources
PubMed2003

Deformation twinning in nanocrystalline aluminum.

We report transmission electron microscope observations that provide evidence of deformation twinning in plastically deformed nanocrystalline aluminum. The presence of these twins is directly related to the nanocrystalline structure, because they are not observed in coarse-grained pure aluminum. We propose a dislocation-based model to explain the preference for deformation twins and stacking faults in nanocrystalline materials. These results underscore a transition from deformation mechanisms controlled by normal slip to those controlled by partial dislocation activity when grain size decreases to tens of nanometers, and they have implications for interpreting the unusual mechanical behavior of nanocrystalline materials.

Journal Article↗
PubMed2002

High tensile ductility in a nanostructured metal.

Nanocrystalline metals--with grain sizes of less than 100 nm--have strengths exceeding those of coarse-grained and even alloyed metals, and are thus expected to have many applications. For example, pure nanocrystalline Cu (refs 1-7) has a yield strength in excess of 400 MPa, which is six times higher than that of coarse-grained Cu. But nanocrystalline materials often exhibit low tensile ductility at room temperature, which limits their practical utility. The elongation to failure is typically less than a few per cent; the regime of uniform deformation is even smaller. Here we describe a thermomechanical treatment of Cu that results in a bimodal grain size distribution, with micrometre-sized grains embedded inside a matrix of nanocrystalline and ultrafine (<300 nm) grains. The matrix grains impart high strength, as expected from an extrapolation of the Hall-Petch relationship. Meanwhile, the inhomogeneous microstructure induces strain hardening mechanisms that stabilize the tensile deformation, leading to a high tensile ductility--65% elongation to failure, and 30% uniform elongation. We expect that these results will have implications in the development of tough nanostructured metals for forming operations and high-performance structural applications including microelectromechanical and biomedical systems.

Journal Article↗
PubMed2002

Trisomy 15 in a case of pediatric hemangiopericytoma and review of the literature.

This study reports on a pediatric case of hemangiopericytoma (HPC) showing trisomy 15 as a sole anomaly. Trisomy 15 was observed in a total of 11 cells harvested at a very early passage from two different in-situ cultures. Trisomy 15, as a sole anomaly, has been described in hematologic disorders such as myelodysplastic syndromes but, to our knowledge, has never been documented in solid tumors. This is the first report of HPC with trisomy 15.

Chromosomes, Human, Pair 15↗