Development of Growth Theory for Vapor–Liquid–Solid Nanowires: Wetting Scenario, Front Curvature, Growth Angle, Linear Tension, and Radial Instability

In this paper, we report that under wetting conditions (or modes) of nanowire (NW) growth, when a nonplanar crystallization front emerges under a catalyst droplet, a shift in the three-phase line (TPL) of the vapor–liquid–crystal interface occurs under thermodynamically stable conditions when the angle with respect to the droplet surface, termed the growth angle, is fixed. The growth angle of the NWs is determined not from a geometrical perspective but on the basis of the physical aspects of the processes occurring around the TPL, revealing a size dependence caused by the influence of linear tension of the three-phase contact of a vapor–liquid crystal. The observed radial periodic instability of the NWs is described according to the size dependence of the thermodynamic growth angle, which induces negative feedback in the system. Under the influence of linear tension and positive feedback, the tips or needles of NWs can be formed.

Surface Preparation of (2024-T4) Aluminum Alloy by Electroless Plating

This study dealt with the process of coating (immersion) and the factors affecting this process stability of the solution and change the time and temperature of immersion. In this study, aluminum alloy (2024-T4) was applied with a solution consisting of zinc oxide and sodium hydroxide (81 g/l NaOH+81 g/l ZnO). Thus, zinc sulphate formed by immersing the sample with nitric acid solution (50 % HNO3+50%water). Then immersed in distilled water. The immersion process was carried out at a different temperature between (25, 55 and 65) °C and different time periods. The results showed an increase in the growth of the deposition layer with increasing duration of the sample and the electrical resistance of the samples and for the same periods. A correlation was drawn between time change and oxide layer growth. Curvature growth was shown with increasing time period for sample exposure to air. The correlation between electrical resistance and time period change was also determined. Simulation between the experimental results and theoretical calculated by using ANSYS version 15. Finally, to confirm the formation and growth of the oxide layer draw by using MATLAB version 15A, Topographic test was examined and XRD.

Shape Coherence and Finite-Time Curvature Evolution

We introduce a definition of finite-time curvature evolution along with our recent study on shape coherence in nonautonomous dynamical systems. Comparing to slow evolving curvature preserving the shape, large curvature growth points reveal the dramatic change on shape such as the folding behaviors in a system. Closed trough curves of low finite-time curvature (FTC) evolution field indicate the existence of shape coherent sets, and troughs in the field indicate the most significant shape coherence. Here, we will demonstrate these properties of the FTC, as well as contrast to the popular Finite-Time Lyapunov Exponent (FTLE) computation, often used to indicate hyperbolic material curves as Lagrangian Coherent Structures (LCS). We show that often the FTC troughs are in close proximity to the FTLE ridges, but in other scenarios, the FTC indicates entirely different regions.

Compressible vortex reconnection

Reconnection of two antiparallel vortex tubes is studied as a prototypical coherent structure interaction to quantify compressibility effects in vorticity dynamics. Direct numerical simulations of the Navier-Stokes equations for a perfect gas are carried out with initially polytropically related pressure and density fields. For an initial Reynolds number (Re = Γ /v, circulation divided by the kinematic viscosity) of 1000, the pointwise initial maximum Mach number (M) is varied from 0.5 to 1.45. At M=0.5, not surprisingly, the dynamics are essentially incompressible. As M increases, the transfer of Γ starts earlier. For the highest M, we find that shocklet formation between the two vortex tubes enhances early Γ transfer due to viscous cross-diffusion as well as baroclinic vorticity generation. The reconnection at later times occurs primarily due to viscous cross-diffusion for all M. However, with increasing M, the higher early Γ transfer reduces the vortices’ curvature growth and hence the Γ transfer rate; i.e. for the Re case studied, the reconnection timescale increases with M. With increasing M, reduced vortex stretching by weaker ‘bridges’ decreases the peak vorticity at late times. Compressibility effects are significant in countering the stretching of the bridges even at late times. Our observations suggest significantly altered coherent structure dynamics in turbulent flows, when compressible.

A DESEEDED AVENA TEST METHOD FOR SMALL AMOUNTS OF AUXIN AND AUXIN PRECURSORS

The main results presented in this article may be summarized as follows: 1. A test method with deseeded Avena seedlings for small concentrations of auxin and precursors of auxin has been described. 2. This method makes possible quantitative determinations of about ten times as low concentrations of hormone as can be obtained with the standard method, (a) Through an increase in the time of the test, so that nearly all the hormone applied can be utilized. (b) Through an increase in sensitivity of deseeded plants to unilaterally applied small concentrations of hormone. 3. The effect of deseeding in relation to curvature growth is primarily the prevention of auxin regeneration through the removal of the material for auxin synthesis, and in addition the prevention of physiological aging. 4. The mechanism of auxin synthesis in the tip of the coleoptile and the mechanism of auxin regeneration in the new physiological tip have been shown to be identical. 5. The application of the deseeded method is illustrated by determinations of auxin in primary leaves and coleoptile sections of Avena seedlings. 6. The deseeded method has been used as a test method for precursors of auxin obtainable from the coleoptile and from other sources. The method further makes possible a distinction between auxins and these substances which may become activated by the plant. 7. Evidence for the existence of a precursor of auxin in the plant is given (a) indirectly by determinations of the decrease in auxin synthesis in deseeded plants. (b) Directly by its isolation from the plant. 8. Precursors of hetero-auxin are demonstrated; their chemical nature and activation are briefly considered.