Predicting Shear Transformation Events in Metallic Glasses.

Shear transformation is the elementary process for plastic deformation of metallic glasses, the prediction of the occurrence of the shear transformation events is therefore of vital importance to understand the mechanical behavior of metallic glasses. In this Letter, from the view of the potential energy landscape, we find that the protocol-dependent behavior of shear transformation is governed by the stress gradient along its minimum energy path and we propose a framework as well as an atomistic approach to predict the triggering strains, locations, and structural transformations of the shear transformation events under different shear protocols in metallic glasses. Verification with a model Cu_{64}Zr_{36} metallic glass reveals that the prediction agrees well with athermal quasistatic shear simulations. The proposed framework is believed to provide an important tool for developing a quantitative understanding of the deformation processes that control mechanical behavior of metallic glasses.

Inhibiting p21-activated kinase (PAK7) enhances radiosensitivity in hepatocellular carcinoma.

OBJECTIVE: In light of the upregulation of p21-activated kinase (PAK7) in a variety of cancers, including hepatocellular carcinoma (HCC), we aimed to investigate the effect of PAK7 on the sensitivity of HCC cells to radiotherapy. METHODS: PAK7 expression was determined in normal adult liver epithelial THLE-2 and human HCC cell lines. The effect of ionizing radiation (IR) on the HCC cell viability was evaluated by Sulforhodamine B (SRB) assay. HCC cell lines Mahlavu and Huh7 were chosen to assess the effect of PAK7 shRNAs on the viability, clone formation, apoptosis, cycle distribution and γ-H2AX expression after exposure to IR. RESULTS: As compared to THLE-2 cells, PAK7 was upregulated in poorly differentiated Mahlavu and SK-Hep-1 cells, but moderately or lowly expressed in well-differentiated Huh7 and HepG2 cells. HCC cells with moderate or low expression of PAK7 presented a decreased viability at 2 Gy IR, which had no significant effect on PAK7high HCC cells. Mahlavu and Huh7 cells transfected with PAK7 shRNAs showed increased inhibitory effect of IR on viability. In addition, PAK7 shRNAs reduced clone formation, facilitated the cell apoptosis, arrested cells at G2/M phase, and increased γ-H2AX expression. Moreover, changes above were more evident in the HCC cells co-treated with IR and PAK7 shRNAs. CONCLUSION: PAK7 downregulation could inhibit the viability, promote the apoptosis, arrest cells in G2/M phase, and induce the DNA damage in HCC cells, thereby enhancing the radiosensitivity in HCC.

First-principles calculations of the structural stability and magnetic property of the metastable phases in the equilibrium immiscible Co-Au system.

To reveal the energetic sequence of the alloy phases in the Co-Au system, the lattice constants, cohesive energies, and bulk modulus of the fcc Au, hcp Co, the B1, B2, and L1(0) structured CoAu phases, and the D0(3), L1(2), and D0(19) structured Co(3)Au and CoAu(3) phases, respectively, are acquired by first-principles calculations within the generalized-gradient approximation (GGA) as well as within the local density approximation (LDA). In addition, the magnetic moment of the Co atom in the studied phases are also calculated. To further examine the structural stability, the elastic constants of the studied phases are calculated and the results suggest that the fcc-type structures could be elastically stable at Co/Au = 1:3, 1:1, and 3:1, whereas the hcp-type structures could be stable at Co/Au = 1:3 and 3:1. Moreover, the spatial valence charge density (SVCD) and spin density of the studied phases are also calculated to clarify the physical origin of the structural stability. It turns out that, in the relatively stable phases, the high SVCDs mostly distribute between the similar atoms, thus forming the attractive covalent bonding to stabilize the respective structures, and that the spin density may also play an important role in influencing the stability of the ferromagnetic metastable phases.