Elastic Waves in a Hybrid Multilayered Piezoelectric Plate

An analytical-numerical method is presented for analyzing dispersion and characteristic surface of waves in a hybrid multilayered piezoelectric plate. In this method, the multilayered piezoelectric plate is divided into a number of layered elements with three-nodal-lines in the wall thickness, the coupling between the elastic field and the electric field is considered in each element. The associated frequency dispersion equation is developed and the phase velocity and slowness, as well as the group velocity and slowness are established in terms of the Rayleigh quotient. Six characteristic wave surfaces are introduced to visualize the effects of anisotropy and piezoelectricity on wave propagation. Examples provide a full understanding for the complex phenomena of elastic waves in hybrid multilayered piezoelectric media.

Strain Gradient Effects on Deformation Strengthening Behavior of Particle Reinforced Metal Matrix Composites

Dislocation models with considering the mismatch of elastic modulus between matrix and reinforcing particles are used to determine the effective strain gradient \ita for particle reinforced metal matrix composites (MMCp) in the present research. Based on Taylor relation and the kinetics of dislocation multiplication, glide and annihilation, a strain gradient dependent constitutive equation is developed. By using this strain gradient-dependent constitutive equation, size-dependent deformation strengthening behavior is characterized. The results demonstrate that the smaller the particle size, the more excellent in the reinforcing effect. Some comparisons with the available experimental results demonstrate that the present approach is satisfactory.

Copper homeostasis in Salmonella is atypical and copper-CueP is a major periplasmic metal complex.

Salmonella enterica sv. typhimurium (S. enterica sv. Typhimurium) has two metal-transporting P(1)-type ATPases whose actions largely overlap with respect to growth in elevated copper. Mutants lacking both ATPases over-accumulate copper relative to wild-type or either single mutant. Such duplication of ATPases is unusual in bacterial copper tolerance. Both ATPases are under the control of MerR family metal-responsive transcriptional activators. Analyses of periplasmic copper complexes identified copper-CueP as one of the predominant metal pools. Expression of cueP was recently shown to be controlled by the same metal-responsive activator as one of the P(1)-type ATPase genes (copA), and copper-CueP is a further atypical feature of copper homeostasis in S. enterica sv. Typhimurium. Elevated copper is detected by a reporter construct driven by the promoter of copA in wild-type S. enterica sv. Typhimurium during infection of macrophages. Double mutants missing both ATPases also show reduced survival inside cultured macrophages. It is hypothesized that elevated copper within macrophages may have selected for specialized copper-resistance systems in pathogenic microorganism such as S. enterica sv. Typhimurium.

Coherent Structures in Transition of a Flat-Plate Boundary Layer at Ma=0.7

Direct numerical simulation (DNS) of a spatially evolving flat-plate boundary layer transition process at free stream Mach number 0.7 is performed. Tollmien-Schlichting (T-S) waves are added on the inlet boundary as the disturbances before transition. Typical coherent structures in the transition process are investigated based on the second invariant of velocity gradient tensor. The instantaneous shear stress and the mean velocity profile in the transition region are studied. In our view, the fact that the peak value of shear stress in the stress concentration area increases and exceeds a threshold value during the later stage of the transition process plays an important role in the laminar breakdown process.