Band-pass filtered velocity statistics in decaying turbulent box

For homogeneous isotropic turbulence study, the acquisition of band-pass filtered velocity increments (FVI) in a non-forced turbulent box is still a challenge both experimentally and numerically. Turbulence and associated physical processes, at a given instant, are permanently contaminated by a forcing process which can seldom be universal. The situation tends to be the origin of intermittency and the non-Gaussian probability density distribution for acceleration and velocity gradients. To reveal implied mechanism, grid turbulence is adapted to observe non-perturbed homogeneous isotropic turbulence. The velocity increments (VI) can be obtained following Comte-Bellot and Corrsin (GCBC) by means of two point-two time shifted velocity measurements. It is difficult to obtain decaying turbulence (DT) at large turbulent Reynolds number without pollution coming from walls. Nevertheless it is also significant to investigate DT in low Reynolds number regimes to determine non-polluted tendencies. The similarity of DT between particle image velocimetry (PIV) and hot wire anemometry measurements by GCBC are presented. Here we focus our tendency on VI and FVI probability density function (PDF) shapes in this letter. In conclusion, the tendency to Gaussian shape in inertial zone wavenumbers, demonstrates that there will be no intermittency if turbulent cascade is not perturbed.     

Reactive Nanoparticles Derived from Polysaccharide Phenyl Carbonates

Polysaccharide (PS) based nanoparticles (NP) are of great interest for biomedical applications. A key challenge in this regard is the functionalization of these nanomaterials. The aim of the present work was the development of reactive PS-NP that can be coupled with an amino group containing compounds under mild aqueous conditions. A series of cellulose phenyl carbonates (CPC) and xylan phenyl carbonates (XPC) with variable degrees of substitution (DS) was obtained by homogeneous synthesis. The preparation of PS-NP by self-assembling of these hydrophobic derivatives was studied comprehensively. While CPC mostly formed macroscopic aggregates, XPC formed well-defined spherical NP with diameters around 100 to 200 nm that showed a pronounced long-term stability in water against both particle aggregation as well as cleavage of phenyl carbonate moieties. Using an amino group functionalized dye it was demonstrated that the novel XPC-NP are reactive towards amines. A simple coupling procedure was established that enables direct functionalization of the reactive NP in an aqueous dispersion. Finally, it was demonstrated that dye functionalized XPC-NP are non-cytotoxic and can be employed in advanced biomedical applications.     

Surface characteristics of Zinc–TiO2 coatings prepared via micro-arc oxidation

Titanium (Ti) and its alloys are widely used as metallic biomaterials for fabrication of dental and orthopedic implants due to their favorable biocompatibility and corrosion resistance in a body environment. However, the thin oxide layer (TiO₂) on Ti substrate formed naturally in air or in many aqueous environments is bioinert and surrounded by fibrous tissues without producing any chemical or biological bond to bone when implanted. In the present work, Zinc-incorporated porous TiO₂ coatings (Zn–TiO₂) were prepared on Ti substrate by micro-arc oxidation (MAO) technique in the zinc gluconate-containing electrolyte. The surface morphology, cross-sectional morphology, composition, and phase of the coatings were analyzed using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry, respectively. Surface topography and roughness of the coatings were investigated by atomic force microscopy operated in tapping mode. The results showed that Zn was successfully incorporated into the porous TiO₂ coatings, which did not alter apparently its surface topography and phase composition. In conclusion, the formation of porous Zn–TiO₂ coatings endow Ti with potential bioactivity and antibacterial activity, and we believe that the porous Zn–TiO₂ coatings on Ti by MAO technique might be promising candidates for orthopedic and dental implants