Structural Signature of ß-Relaxation in La-Based Metallic Glasses.

The secondary ß-relaxation is an intrinsic feature in glassy materials. However, its structural origin is still not well understood. Here we report that the ß-relaxations in La50Al15Ni35 and La50Al15Cu35 metallic glasses (MGs) mainly depend on the vibration of small Ni and Cu atoms in local cages. By using advanced synchrotron X-ray techniques and theoretical calculations, we elucidate that the tricapped-trigonal-prism-like polyhedra with more large La atoms in shells favor the local vibration of center Ni atoms, leading to the pronounced ß-relaxation event. In contrast, the in-cage vibration of Cu atoms is somehow suppressed by the appearance of more shell Cu atoms. Nevertheless, they could easily diffuse out of the cages compared with Ni, thus triggering the onset of α-relaxation. This work provides a pathway to understand the different structural relaxation behaviors in MGs and other disordered materials from their local atomic packing and dynamics points of view.

Structural evolution and atomic dynamics in Ni-Nb metallic glasses: A molecular dynamics study.

The composition and temperature dependence of static and dynamic structures in NixNb1-x (x = 50-70 at. %) were systematically studied using molecular dynamics with a new-released semi-empirical embedded atom method potential by Mendelev. The calculated pair correlation functions and the structure factor match well with the experimental data, demonstrating the reliability of the potential within relatively wide composition and temperature ranges. The local atomic structures were then characterized by bond angle distributions and Voronoi tessellation methods, demonstrating that the icosahedral ⟨0,0,12,0⟩ is only a small fraction in the liquid state but increases significantly during cooling and becomes dominant at 300 K. The most abundant clusters are identified as ⟨0,0,12,0⟩ and distorted icosahedron ⟨0,2,8,2⟩. The large fraction of these two clusters hints that the relatively good glass forming ability is near the eutectic point. Unlike Cu-Zr alloys, both the self-diffusion coefficient and shear viscosity are insensitive to compositions upon cooling in Ni-Nb alloys. The breakdown of the Stokes-Einstein relation happens at around 1.6Tg (Tg: glass transition temperature). In the amorphous state, the solid and liquid-like atoms can be distinguished based on the Debye-Waller factor ⟨u2⟩. The insensitivity of the dynamic properties of Ni-Nb alloys to compositions may result from the relatively simple solidification process in the phase diagram, in which only one eutectic point exists in the studied composition range.

Elevated tumor necrosis factor alpha of blood mononuclear cells in patients with congestive heart failure.

To study the changes of tumor necrosis factor-alpha (TNF-alpha) produced by peripheral blood mononuclear cells (PBMC) of patients with congestive heart failure (CHF), we determined the TNF-alpha concentrations of plasma and culture supernatant of PBMCs in 113 patients with various heart diseases. The results showed that plasma levels of TNF-alpha were significantly higher in CHF patients (n=50, 13.36+/-6.09 pg/ml) and in cachetic CHF patients (n=26, 19.20+/-10.42 pg/ml) than in the controls (n=37, 6.73+/-3.91 ng/ml). The supernatant levels of TNF-alpha in cultured PBMC (PBMC-TNF-alpha) were also significantly elevated in CHF patients (5.77+/-2.11 ng/ml), and even higher in cachetic CHF patients (7.01+/-5.11 ng/ml), as compared with the controls (2.27+/-2.24 ng/ml). There was a significant correlation between levels of PBMC-TNF-alpha and severity of heart failure (r=0.48, P<0.01). But no correlation between PBMC-TNF-alpha and plasma TNF-alpha was observed. These results demonstrate that the expression of TNF-alpha in PBMC is increased in patients with CHF, especially in patients with CHF accompanied by cachexia, suggesting that PBMC-TNF-alpha may be a potential biochemical indicator to evaluate the patients with CHF.