Unsteady MHD heat and mass transfer of a non-Newtonian nanofluid flow of a two-phase model over a permeable stretching wall with heat generation/absorption

The combined effects of magnetic field and heat generation or absorption on unsteady boundary-layer convective heat and mass transfer of a non-Newtonian nanofluid over a permeable stretching wall have been addressed. A power-law model includes Brownian motion and thermophoresis influences are utilized for non-Newtonian nanofluids with a convective boundary condition. The non-linear governing equations are reduced into ODEs by similarity transformations and solved numerically by using Runge-Kutta-Fehlberg 4th–5th order numerical method (RKF45) with shooting technique. The different physical parameters effects such as the magnetic parameter $(M)$, the heat source/sink parameters $(\lambda )$, the unsteadiness parameter $(A)$, the generalized Prandtl and Lewis numbers on the dimensionless velocity, temperature and nanoparticles volume fraction, in addition to the skin friction, local Nusselt and Sherwood numbers are analyzed. It is reached that the thermal and concentration boundary-layer thickness has higher values with the increasing of magnetic field and heat generation in the case of a pseudo-plastic nanofluid than others.     

Noise-induced transitions for random versions of Verhulst model

According to the Verhulst model the rate of increase/decrease of a biological population with size x(t) at time t is equal to the sum of $\rho x\left(t\right)$ and $-x{(t)}^2$, where $\rho \in \mathbb{R}$ is a constant. The constant ρ is positive and negative for favorable and hostile environments, respectively. The limitation of resources is quantified by the term $-x{(t)}^2$. We examine random versions of the Verhulst model obtained by replacing ρ with $(\rho +\mathrm{white}\mathrm{noise})$. Gaussian (GWN) and Poisson (PWN) white noise processes are considered. The state X(t) of the random Verhulst model satisfies stochastic differential equations driven by Gaussian and Poisson white noises. Our objective is to identify noise-induced transitions, that is, noise levels at which the stationary density of X(t) exhibits qualitative changes. It is shown that noise levels causing transitions under Poisson white noise approach those under Gaussian white noise as the frequency of Poisson jumps increases indefinitely while their size approaches zero.     

Microstructure,texture evolution and mechanical properties of cold rolled Ti-32.5Nb-6.8Zr-2.7Sn biomedical beta titanium alloy

Ti-32.5 Nb-6.8 Zr-2.7 Sn(TNZS,wt%) alloy was produced by using vacuum arc melting method,followed by solution treatment and cold rolling with the area reductions of 50% and 90%.The effects of cold rolling on the microstructure,texture evolution and mechanical properties of the experimental alloy were investigated by optical microscopy,X-ray diffraction,transmission electron microscopy and universal material testing machine.The results showed that the grains of the alloy were elongated along rolling direction and stress-induced α' martensite was not detected in the deformed samples.The plastic deformation mechanisms of the alloy were related to {112} 111 type deformation twinning and dislocation slipping.Meanwhile,the transition from γ-fiber texture to α-fiber texture took place during cold rolling and a dominant {001} 110_(α-fiber) texture was obtained after 90% cold deformation.With the increase of cold deformation degree,the strength increased owing to the increase of microstrain,dislocation density and grain refinement,and the elastic modulus decreased owing to the increase of dislocation density as well as an enhanced intensity of {001} 110_(α-fiber)texture and a weakened intensity of {111} 112_(γ-fiber)texture.The 90% cold rolled alloy exhibited a great potential to become a new candidate for biomedical applications,since it possesses low elastic modulus(47.1 GPa),moderate strength(883 MPa) and high elastic admissible strain(1.87%),which are superior than those of Ti-6 Al-4 V alloy.