Interaction between coherent structures and surface temperature and its effect on ground heat flux in an unstably stratified boundary layer

Surface layer plumes, thermals, downdrafts and roll vortices are the most prominent coherent structures in an unstably stratified boundary layer. They contribute most of the temperature and vertical velocity variance, and their time scales increase with height. The effects of these multi-scale structures (surface layer plumes scale with surface layer depth, thermals scale with boundary layer height and the resulting roll vortices scale with convective time scale) on the surface temperature and ground heat flux were studied using turbulence measurements throughout the atmospheric boundary layer and the surface temperature measurements from an infrared camera. Plumes and thermals imprint on the surface temperature as warm structures and downdrafts imprint as cold structures. The air temperature trace shows a ramp-like pattern, with small ramps overlaid on a large ramp very close to the surface; on the other hand, surface temperature gradually increases and decreases. Turbulent heat flux and ground heat flux show similar patterns, with the former lagging the latter. The maximum values of turbulent heat flux and ground heat flux are 4 and 1.2 times the respective mean values during the ejection event. Surface temperature fluctuations follow a similar power-law exponent relationship with stability as suggested by surface layer similarity theory. © 2013 Copyright Taylor and Francis Group, LLC

Portable heatable container

A container is provided which can be designed to heat its outer surface to sterilize it, or to heat its inner surface and any contents therewithin. In a container that self sterilizes its outer surface, the container includes a combustible layer of thermite-type pyrotechnic material which can be ignited to generate considerable heat, and a thin casing around the combustible layer which is of highly thermally conductive materials such as aluminum which can be heated to a high temperature by the ignited combustible layer. A buffer layer which may be of metal, lies within the combustible layer, and a layer of insulation such as Teflon lies within the buffer layer to insulate the contents of the container from the heat

Ion-implantation induced anomalous surface amorphization in silicon

Spectroscopic ellipsometry (SE), high-depth-resolution Rutherford backscattering (RBS) and channeling have been used to examine the surface damage formed by room temperature N and B implantation into silicon. For the analysis of the SE data we used the conventional method of assuming appropriate optical models and fitting the model parameters (layer thicknesses and volume fraction of the amorphous silicon component in the layers) by linear regression. The dependence of the thickness of the surface-damaged silicon layer (beneath the native oxide layer) on the implantation parameters was determined: the higher the dose, the thicker the disordered layer at the surface. The mechanism of the surface amorphization process is explained in relation to the ion beam induced layer-by-layer amorphization. The results demonstrate the applicability of Spectroscopic ellipsometry with a proper optical model. RBS, as an independent cross-checking method supported the constructed optical model

On the validity of the “thin” and “thick” double-layer assumptions when calculating streaming currents in porous media

We find that the thin double layer assumption, in which the thickness of the electrical diffuse layer is assumed small compared to the radius of curvature of a pore or throat, is valid in a capillary tubes model so long as the capillary radius is >200 times the double layer thickness, while the thick double layer assumption, in which the diffuse layer is assumed to extend across the entire pore or throat, is valid so long as the capillary radius is >6 times smaller than the double layer thickness. At low surface charge density (0.5 M) the validity criteria are less stringent. Our results suggest that the thin double layer assumption is valid in sandstones at low specific surface charge (<10 mC· m -2), but may not be valid in sandstones of moderate- to small pore-throat size at higher surface charge if the brine concentration is low (<0.001 M). The thick double layer assumption is likely to be valid in mudstones at low brine concentration (<0.1 M) and surface charge (<10 mC· m -2), but at higher surface charge, it is likely to be valid only at low brine concentration (<0.003 M). Consequently, neither assumption may be valid in mudstones saturated with natural brines. Copyright © 2012 Matthew D. Jackson and Eli Leinov

Effect of surface hydrogen on the anomalous surface segregation behavior of Cr in Fe-rich Fe-Cr alloys

The segregation behavior of Cr in dilute Fe-Cr alloys is known to be anomalous since the main barrier for surface segregation of Cr in these alloys arises not from the topmost surface layer but from the subsurface layer where the solution energy of Cr is much more endothermic as compared to the topmost surface layer. The Fe-Cr alloys are candidate structural materials for the new generation of nuclear reactors. The surfaces of these alloys will be exposed to hydrogen or its isotopes in these reactors, and although hydrogen is soluble neither in Fe nor in Fe-Cr alloys, it is known that the adsorption energy of hydrogen on the surface of iron is not only exothermic but relatively large. This clearly raises the question of the effect of the hydrogen adsorbed on the surface of iron on the segregation behavior of chromium towards the surface of iron. In this paper we show, on the basis of our ab initio density functional theory calculations, that the presence of hydrogen on the surface of iron leads to a considerably reduced barrier for Cr segregation to both the topmost surface layer and the subsurface layer, but the subsurface layer still controls the barrier for surface segregation. This reduction in the barrier for surface segregation is due to the nature of the Cr-H couple that acts in a complex and synergistic manner. The presence of Cr enhances the exothermic nature of hydrogen adsorption that in turn leads to a reduced barrier for surface segregation. These results should be included in the multiscale modeling of Fe-Cr alloys

Corrosion behaviour of mechanically polished AA7075-T6 aluminium alloy

In the present study, the effects of mechanical polishing on the microstructure and corrosion behaviour of AA7075 aluminium alloy are investigated. It was found that a nano-grained, near-surface deformed layer, up to 400 nm thickness, is developed due to significant surface shear stress during mechanically polishing. Within the near-surface deformed layer, the alloying elements have been redistributed and the microstructure of the alloy is modified; in particular, the normal MgZn2 particles for T6 are absent. However, segregation bands, approximately 10-nm thick, containing mainly zinc, are found at the grain boundaries within the near-surface deformed layer. The presence of such segregation bands promoted localised corrosion along the grain boundaries within the near-surface deformed layer due to microgalvanic action. During anodic polarisation of mechanically polished alloy in sodium chloride solution, two breakdown potentials were observed at −750 mV and −700 mV, respectively. The first breakdown potential is associated with an increased electrochemical activity of the near-surface deformed layer, and the second breakdown potential is associated with typical pitting of the bulk alloy

Structure of the electrospheres of bare strange stars

We consider a thin ($\sim 10^2-10^3$ fm) layer of electrons (the electrosphere) at the quark surface of a bare strange star, taking into account the surface effects at the boundary with the vacuum. The quark surface holds the electron layer by an extremely strong electric field, generated in the electrosphere to prevent the electrons from escaping to infinity by counterbalancing the degeneracy and thermal pressure. Because of the surface tension and depletion of $s$ quarks a very thin (a few fm) charged layer of quarks forms at the surface of the star. The formation of this layer modifies the structure of the electrosphere, by significantly changing the electric field and the density of the electrons, in comparison with the case when the surface effects are ignored. Some consequences of the modification of the electrosphere structure on the properties of strange stars are briefly discussed.Comment: 23 pages, 6 figures, to appear in Ap