Mechanics and dynamics of the strain-induced M1-M2 structural phase transition in individual VO2 nanowires.

The elastic properties and structural phase transitions of individual VO(2) nanowires were studied using an in situ push-to-pull microelectromechanical device to realize quantitative tensile analysis in a transmission electron microscope and a synchrotron X-ray microdiffraction beamline. A plateau was detected in the stress-strain curve, signifying superelasticity of the nanowire arising from the M1-M2 structural phase transition. The transition was induced and controlled by uniaxial tension. The transition dynamics were characterized by a one-dimensionally aligned domain structure with pinning and depinning of the domain walls along the nanowire. From the stress-strain dependence the Young's moduli of the VO(2) M1 and M2 phases were estimated to be 128 ± 10 and 156 ± 10 GPa, respectively. Single pinning and depinning events of M1-M2 domain wall were observed in the superelastic regime, allowing for evaluation of the domain wall pinning potential energy. This study demonstrates a new way to investigate nanoscale mechanics and dynamics of structural phase transitions in general.

Ultrahigh stress and strain in hierarchically structured hollow nanoparticles.

Nanocrystalline materials offer very high strength but are typically limited in their strain to failure, and efforts to improve deformability in these materials are usually found to be at the expense of strength. Using a combination of quantitative in situ compression in a transmission electron microscope and finite-element analysis, we show that the mechanical properties of nanoparticles can be directly measured and interpreted on an individual basis. We find that nanocrystalline CdS synthesized into a spherical shell geometry is capable of withstanding extreme stresses (approaching the ideal shear strength of CdS). This unusual strength enables the spherical shells to exhibit considerable deformation to failure (up to 20% of the sphere's diameter). By taking into account the structural hierarchy intrinsic to novel nanocrystalline materials such as this, we show it is possible to achieve and characterize the ultrahigh stresses and strains that exist within a single nanoparticle during deformation.

Mechanical annealing and source-limited deformation in submicrometre-diameter Ni crystals.

The fundamental processes that govern plasticity and determine strength in crystalline materials at small length scales have been studied for over fifty years. Recent studies of single-crystal metallic pillars with diameters of a few tens of micrometres or less have clearly demonstrated that the strengths of these pillars increase as their diameters decrease, leading to attempts to augment existing ideas about pronounced size effects with new models and simulations. Through in situ nanocompression experiments inside a transmission electron microscope we can directly observe the deformation of these pillar structures and correlate the measured stress values with discrete plastic events. Our experiments show that submicrometre nickel crystals microfabricated into pillar structures contain a high density of initial defects after processing but can be made dislocation free by applying purely mechanical stress. This phenomenon, termed 'mechanical annealing', leads to clear evidence of source-limited deformation where atypical hardening occurs through the progressive activation and exhaustion of dislocation sources.

Dislocation dynamics in nanocrystalline nickel.

It is believed that the dynamics of dislocation processes during the deformation of nanocrystalline materials can only be visualized by computational simulations. Here we demonstrate that observations of dislocation processes during the deformation of nanocrystalline Ni with grain sizes as small as 10 nm can be achieved by using a combination of in situ tensile straining and high-resolution transmission electron microscopy. Trapped unit lattice dislocations are observed in strained grains as small as 5 nm, but subsequent relaxation leads to dislocation recombination.

[Clinical study on effect of hewei capsule on promoting gastric dynamics].

OBJECTIVE: To investigate the effect of Hewei capsule (HWC) on gastric dynamics. METHODS: Sixty-two patients with dysmotility-like functional dyspepsia (DFD) were included in the study. The principal symptoms, electrogastrogram (EGG), plasma motilin (MTL), serum gastrin (Gas) and nitric oxide (NO) of the patients were the chief parameters observed before and after treatment. RESULTS: There were arrhythmia of EGG, deficiency of MTL, Gas and NO in the patients with DFD, and these abnormal changes could be improved significantly by treating with HWC. CONCLUSION: The abnormal gastric dynamics of the patients with DFD could be improved by HWC through multiple pathways.

[Clinical study on Helicobacter pylori infected chronic gastritis treated with supplementing qi and promoting blood circulation drugs].

The syndrome of Qi Deficiency and Blood Stasis of chronic gastritis infected by Helicobacter Pylori (HP) was treated with the principle of supplementing Qi and promoting blood circulation. The clinical symptoms, inhibiting and killing of HP and pathohistological study have been observed. It was proved that the treatment could improve the clinical symptoms, reduce the infiltration of inflammatory cells and ameliorate the hyperemia and edema of gastric mucosa. Its inhibition and killing of HP was similar to the gentamycin sulfate (P > 0.05). Toxic and side effects have not been observed by taking this remedy.