The problem of hydrodynamic loads arising from the interaction of gravity currents with an obstacle on the channel bottom was studied experimentally. The gravity-current structure was visualized at the stage of formation and at the stage of interaction with the obstacle. The dependence of the propagation velocity of the gravity-current front on the nondimensional current depth and the Archimedes number was studied. In the region of self-similarity in the Archimedes number, the behavior of hydrodynamicload coefficients was studied as a function of the nondimensional gravity current depth.Introduction. The problems of estimating the propagation velocity of gravity currents and the hydrodynamic loads induced by these currents on various obstacles are of great practical importance. In particular, much attention has been given to the dynamics of snow avalanches (see a review [1]). In oceans, an analog of such currents are gravity turbidity currents that propagate down seamounts covered with bottom sediments (see a review [2]). Such currents are a great hazard to underwater vehicles and service lines. In the present work, we studied experimentally the model problem of the action of internal gravity current due to intrusion of a denser fluid into fresh water on an obstacle on the channel bottom. The subrange of the problem parameters is determined in which the fluid viscosity effects are self-similar (in particular, the propagation velocity of the current front does not depend on the particular value of the Archimedes number), because of which the main modeling criterion is the Froude number. For this subrange of the parameters, the characteristic values of the hydrodynamic loads generated by gravity currents at submerged obstacles are determined as functions of the ratio of the vertical dimension of the current core to the total fluid depth.Experimental Technique. A diagram of the experimental setup is shown in Fig. 1. The experiments were performed in a 320 × 20 × 12 cm hydrodynamic tank separated by a partition 1 into two equal parts. The left half of the tank was filled with pure water of density ρ 1 and depth H, and the right half with an aqueous solution of sugar of density ρ 2 and depth h 2 , above which there was a pure water layer of density ρ 1 and depth h 1 ; h 1 + h 2 = H. In the experiments, the depth ratio h 2 /H was varied in the range 0.1 < h 2 /H < 0.84. To analyze the role of the scale effect, we performed experimental measurements of the gravity current characteristics at H = 6 cm and H = 10 cm. When the partition was removed, an internal gravity current 2 propagated to the left over the tank bottom and a depression wave 3 (the dashed curves in Fig. 1) propagated in the right part of the tank.The instantaneous hydrodynamic loads resulting from the interaction of gravity currents with an obstacle in the shape of a rectangular cylinder 4 of height b = 2 cm and width 1 cm were measured using a two-component hydrodynamic balance 5 [3]. The gap between the lower surface of the rectangular-cylinder cross se...

By studying Fe-doped ZnO pellets and thin films with various x-ray spectroscopic techniques, and complementing this with density functional theory calculations, we find that Fedoping in bulk ZnO induces isovalent (and isostructural) cation substitution (Fe 2+ → Zn 2+ ).In contrast to this, Fe-doping near the surface produces both isovalent and heterovalent substitution (Fe 3+ → Zn 2+ ). The calculations performed herein suggest that the most likely defect structure is the single or double substitution of Zn with Fe, although, if additional oxygen is available, then Fe substitution with interstitial oxygen is even more energetically favourable.Furthermore, it is found that ferromagnetic states are energetically unfavourable, and ferromagnetic ordering is likely to be realized only through the formation of a secondary phase (i.e.ZnFe 2 O 4 ), or codoping with Cu.

Bulk and thin-film ZnO and TiO 2 samples were doped with Sn by pulsed ion implantation and studied by means of X-ray photoelectron core-level and valence-band spectroscopy as well as density functional theory calculations for a comprehensive study of the incorporation of Sn. XPS spectral analysis showed that isovalent Sn cation substitution occurs in both zinc oxide (Sn 2þ !Zn 2þ ) and titanium dioxide (Sn 4þ !Ti 4þ ) for bulk and film morphologies. For TiO 2 films, the implantation also led to occupation of interstitials by dopant ions, which induced the clustering of substituted and embedded Sn atoms; this did not occur in ZnO:Sn film samples. Density functional theory (DFT) formation energies were calculated of various incorporation processes, explaining the prevalence of substitutional defects in both matrices. Possible mechanisms and reasons for the observed trends in Sn incorporation into the ZnO and TiO 2 matrices are discussed.

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Cobalt and manganese ions are implanted into SiO 2 over a wide range of concentrations. For low concentrations, the Co atoms occupy interstitial locations, coordinated with oxygen, while metallic Co clusters form at higher implantation concentrations. For all concentrations studied here, Mn ions remain in interstitial locations and do not cluster. Using resonant x-ray emission spectroscopy and Anderson impurity model calculations, we determine the strength of the covalent interaction between the interstitial ions and the SiO 2 valence band, finding it comparable to Mn and Co monoxides. Further, we find an increasing reduction in the SiO 2 electronic band gap for increasing implantation concentration, due primarily to the introduction of Mn-and Co-derived conduction band states. We also observe a strong increase in a band of x-ray stimulated luminescence at 2.75 eV after implantation, attributed to oxygen deficient centers formed during implantation.