Tensile Strength of Liquids: Equivalence of Temporal and Spatial Scales in Cavitation

It is well known that strain rate and size effects are both important in material failure, but the relationships between them are poorly understood. To establish this connection, we carry out molecular dynamics (MD) simulations of cavitation in Lennard-Jones and Cu liquids over a very broad range of size and strain rate. These studies confirm that temporal and spatial scales play equivalent roles in the tensile strengths of these two liquids. Predictions based on smallest-scale MD simulations of Cu for larger temporal and spatial scales are consistent with independent simulations, and comparable to experiments on liquid metals. We analyze these results in terms of classical nucleation theory and show that the equivalence arises from the role of both size and strain rate in the nucleation of a daughter phase. Such equivalence is expected to hold for a wide range of materials and processes and to be useful as a predictive bridging tool in multiscale studies.

Opening the band gap of graphene through silicon doping for the improved performance of graphene/GaAs heterojunction solar cells

Graphene has attracted increasing interest due to its remarkable properties. However, the zero band gap of monolayered graphene limits it's further electronic and optoelectronic applications. Herein, we have synthesized monolayered silicon-doped graphene (SiG) with large surface area using a chemical vapor deposition method. Raman and X-ray photoelectron spectroscopy measurements demonstrate that the silicon atoms are doped into graphene lattice at a doping level of 2.7-4.5 at%. Electrical measurements based on a field effect transistor indicate that the band gap of graphene has been opened via silicon doping without a clear degradation in carrier mobility, and the work function of SiG, deduced from ultraviolet photoelectron spectroscopy, was 0.13-0.25 eV larger than that of graphene. Moreover, when compared with the graphene/GaAs heterostructure, SiG/GaAs exhibits an enhanced performance. The performance of 3.4% silicon doped SiG/GaAs solar cell has been improved by 33.7% on average, which was attributed to the increased barrier height and improved interface quality. Our results suggest that silicon doping can effectively engineer the band gap of monolayered graphene and SiG has great potential in optoelectronic device applications.

Cavitation in a metallic liquid: homogeneous nucleation and growth of nanovoids

Large-scale molecular dynamics (MD) simulations are performed to investigate homogeneous nucleation and growth of nanovoids during cavitation in liquid Cu. We characterize in detail the atomistic cavitation processes by following the temporal evolution of cavities or voids, analyze the nucleation behavior with the mean first-passage time (MFPT) and survival probability (SP) methods, and discuss the results against classical nucleation theory (CNT), the Tolman equation for surface energy, independent calculation of surface tension via integrating the stress profiles, the Johnson-Mehl-Avrami (JMA) growth law, and the power law for nucleus size distributions. Cavitation in this representative metallic liquid is a high energy barrier Poisson processes, and the steady-state nucleation rates obtained from statistical runs with the MFPT and SP methods are in agreement. The MFPT method also yields the critical nucleus size and the Zeldovich factor. Fitting with the Tolman's equation to the MD simulations yields the surface energy of a planar interface (~0.9 J m⁻²) and the Tolman length (0.4-0.5 Å), and those values are in accord with those from integrating the stress profiles of a planar interface. Independent CNT predictions of the nucleation rate (10(33 - 34) s(-1) m(-3)) and critical size (3-4 Å in radius) are in agreement with the MFPT and SP results. The JMA law can reasonably describe the nucleation and growth process. The size distribution of subcritical nuclei appears to follow a power law with an exponent decreasing with increasing tension owing to coupled nucleation and growth, and that of the supercritical nuclei becomes flattened during further stress relaxation due to void coalescence.

Loss of IKKbeta activity increases p53 stability and p21 expression leading to cell cycle arrest and apoptosis

Elevated levels of NF-kappaB are frequently detected in many inflammatory diseases and cancers. Blocking the IKK-NF-kappaB pathway has been seen as a promising approach for new therapies. By employing the dominant-negative mutant of IKKbeta, our data revealed that loss of IKKbeta activity reduces not only the proliferation and invasion of lung adenocarcinoma A549 cells in vitro but also the tumour formation, metastasis and angiogenesis in mouse xenograft model. Treatment of IKKbeta inhibitors (CYL-19s and CYL-26z) leads to the arrest of cell cycle progression at G1 and G2/M, followed by apoptosis. IKKbeta inhibitors can increase the protein stability, nuclear accumulation and promoter-binding activity of p53, leading to the p21 gene transcription. Furthermore, knockdown of IKKbeta by siRNA increased the stability and expression of p53 and p21 promoter activity. In addition, IKKbeta inhibitor-induced p53 and p21 expressions were augmented in the presence of IKKbeta siRNA. Correlation between p53 acetylation and its protein stabilization was also seen after treatment with IKKbeta inhibitors. These results suggest that loss of IKKbeta activation is important for the enhancement of p53 stability, leading to p21 expression and cell cycle arrest and apoptosis of tumour cells.

[Determination of catechol-O-methyltransferase activity in human erythrocytes by high performance liquid chromatography]

A rapid assay method for catechol-O-methyltransferase (COMT) activity in human erythrocyts by high performance liquid chromatography (HPLC) with UV detection was established. Enzyme activity was determined from erythrocyte lysates using S-adenosyl-L-methionine (SAM) as methyl donor and 3, 4-dihydroxybenzoic acid (DBA) as substrate. The 3-O-methylated reaction products were measured by HPLC with UV detection. The linear range of COMT was from 1 U/mL to 60 U/mL with an average RSD < 10%, and the detection limit was 0.5 U/mL(S/N > or = 5).