Intake Ground Vortex Prediction Methods

For an aircraft turbofan engine in ground operations or during the take-off run a ground vortex can occur which is ingested and could potentially adversely affect the engine performance and operation. The vortex characteristics depend on the ground clearance, intake flow capture ratio and the relative wind vector. It is a complex flow for which there is currently very little appropriate quantitative preliminary design information. These aspects are addressed in this work where a range of models are developed to provide a method for estimating the key metrics such as the formation boundary and the ground vortex size and strength. Three techniques are presented which utilize empirical, analytical and semi-empirical approaches. The empirical methods are primarily based on a large dataset of model-scale experiments which quantitatively measured the ground vortex characteristics for a wide range of configurations. These include the effects of intake ground clearance, approaching boundary layer thickness, intake Mach number and capture velocity ratio. Overall the models are able to predict some of the key measured behaviours such as the velocity ratio for maximum vortex strength. With increasing empiricism for key sub-elements of the model construction, an increasing level of agreement is found with the experimental results. Overall the three techniques provide a relatively quick and easy method in establishing the important vortex characteristics for a given headwind configuration which is of significant use from a practical engineering perspective

Intake ground vortex characteristics

The development of ground vortices when an intake operates in close proximity to the ground has been studied computationally for several configurations including front and rear quarter approaching flows as well as tailwind arrangements. The investigations have been conducted at model scale using a generic intake geometry. Reynolds Averaged Navier–Stokes calculations have been used and an initial validation of the computational model has been carried out against experimental data. The computational method has subsequently been applied to configurations that are difficult to test experimentally by including tailwind and rear quarter flows. The results, along with those from a previous compatible study of headwind and pure cross-wind configurations, have been used to assess the ground vortex behaviour under a broad range of velocity ratios and approaching wind angles. The characteristics provide insights on the influence of the size and strength of ground vortices on the overall quality of the flow ingested by the intake

Poincaré inequalities and Sobolev spaces

Our understsanding of the interplay between Poincaré inequalities, Sobolev inequalities and the geometry of the underlying space has changed considerably in recent years. These changes have simultaneously provided new insights into the classical theory and allowed much of that theory to be extended to a wide variety of different settings. This paper reviews some of these new results and techniques and concludes with an example on the preservation of Sobolev spaces by the maximal function

Raising Bi-O bands above the Fermi energy level of hole-doped Bi2_2Sr2_2CaCu2_2O8+δ_{8+\delta} and other cuprate superconductors

The Fermi surface (FS) of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212) predicted by band theory displays Bi-related pockets around the $(\pi,0)$ point, which have never been observed experimentally. We show that when the effects of hole doping either by substituting Pb for Bi or by adding excess O in Bi2212 are included, the Bi-O bands are lifted above the Fermi energy ($E_F$) and the resulting first-principles FS is in remarkable accord with measurements. With decreasing hole-doping the Bi-O bands drop below $E_F$ and the system self-dopes below a critical hole concentration. Computations on other Bi- as well as Tl- and Hg-based compounds indicate that lifting of the cation-derived band with hole doping is a general property of the electronic structures of the cuprates.Comment: 4 pages, 4 figures; PRL (2006, in press

Angular dependent vortex pinning mechanisms in YBCO coated conductors and thin films

We present a comparative study of the angular dependent critical current density in YBa2Cu3O7 films deposited on IBAD MgO and on single crystal MgO and SrTiO3 substrates. We identify three angular regimes where pinning is dominated by different types of correlated and uncorrelated defects. We show that those regimes are present in all cases, indicating that the pinning mechanisms are the same, but their extension and characteristics are sample dependent, reflecting the quantitative differences in texture and defect density. In particular, the more defective nature of the films on IBAD turns into an advantage as it results in stronger vortex pinning, demonstrating that the critical current density of the films on single crystals is not an upper limit for the performance of the IBAD coated conductors.Comment: 14 pages, 3 figures. Submitted to AP

Normal state properties of high angle grain boundaries in (Y,Ca)Ba2Cu3O7-delta

By lithographically fabricating an optimised Wheatstone bridge geometry, we have been able to make accurate measurements of the resistance of grain boundaries in Y1-xCaxBa2Cu3O7-d between the superconducting transition temperature, Tc, and room temperature. Below Tc the normal state properties were assessed by applying sufficiently high currents. The behaviour of the grain boundary resistance versus temperature and of the conductance versus voltage are discussed in the framework charge transport through a tunnel barrier. The influence of misorientation angle, oxygen content, and calcium doping on the normal state properties is related to changes of the height and shape of the grain boundary potential barrier.Comment: 17 pages, 1 table, 5 figures, submitted to PR

Fatalities due to intestinal obstruction following the ingestion of foreign bodies

Two fatalities due to an occlusive ileus following the ingestion of foreign bodies in patients with psychiatric disorders are described. A severely mentally handicapped young man developed a temperature and died 1 h after admission to a surgical ward. At autopsy, not, vert, similar 2000 cm3 of foreign material, including broken glass and porcelain, branches, buttons, parts of clothing and other material were found in the gastrointestinal tract, leading to a complete obstruction of the distal intestine and colon with resulting faecal vomiting. The other case was even more unusual as a hair fetishist had swallowed a thick strand of his own hair, 50 cm long, also resulting in mechanical obstruction of the distal intestine

Induced magnetization in La0.7_{0.7}Sr0.3_{0.3}MnO3_3/BiFeO3_3 superlattices

Using polarized neutron reflectometry (PNR), we observe an induced magnetization of 75$\pm$ 25 kA/m at 10 K in a La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO)/BiFeO$_3$ superlattice extending from the interface through several atomic layers of the BiFeO$_3$ (BFO). The induced magnetization in BFO is explained by density functional theory, where the size of bandgap of BFO plays an important role. Considering a classical exchange field between the LSMO and BFO layers, we further show that magnetization is expected to extend throughout the BFO, which provides a theoretical explanation for the results of the neutron scattering experiment.Comment: 5 pages, 4 figures, with Supplemental Materials. To appear in Physical Review Letter