These results demonstrate that exposure of healthy humans to three 2-hour hypoglycemic episodes over 30 hours leads to significant blunting in counterregulatory and symptom response to subsequent hypoglycemia on day 5.

The metamaterial structure composed of cubic high dielectric resonators periodically arrayed in a low dielectric substrate is analysed and a flat metamaterial lens is used to improve the gain of a rectangular patch antenna. A dielectric slab is also discussed and compared with the metamaterial lens. Experimental results show that the proposed metamaterial flat lens can improve the gain of a patch antenna remarkably at both the first and the third resonant mode.Introduction: Metamaterials or negative index materials may be realised with purely dielectric resonators as proposed by [1][2][3][4]. Holloway et al.[1] have a periodic magnetic spherical-particle array to obtain negative index effects, whereas [2] uses a periodic structure composed of two sets of resonating dielectric spheres with different radii resulting in negative real parts of both permittivity and permeability. Peng et al. [3] show electric and magnetic resonance simultaneously at the second resonant mode in a cylindrical high dielectric resonator, while [4] proposes an array of cubic high dielectric resonators producing a magnetic resonant dipole at the lowest-order resonant mode aided by the photonic bandgap effect. In this Letter, the calculated and measured metamaterial structure is composed of cubic high dielectric resonators (CHDRs) (1 r ¼ 30) periodically arrayed in a low dielectric substrate (1 r ¼ 2.08), and a flat metamaterial lens using CHDRs has been implemented to improve the gain of a rectangular patch antenna. A dielectric slab having an average permittivity of CHDRs (1 r ¼ 10.35) is also analysed to compare with the proposed metamaterial lens. Both numerical simulations and measurements with a rectangular patch antenna at its negative index regions are discussed and results at third resonance are emphasised. There are no previous reports to the best of our knowledge, of analysis of the high dielectric resonator cubic structure at the third resonant mode. The numerical simulation and experimental results confirm that a dielectric metamaterial flat lens improves the gain of a rectangular patch antenna owing to a magnetic dipole at 5.7 GHz (first resonance) and coexisting electric and magnetic dipoles at 9 GHz (third resonance).

The effects of streamwise convex curvature, recovery, and free-stream turbulence intensity on the turbulent transport of heat and momentum in a mature turbulent boundary layer are investigated. A special three-wire hot-wire probe developed for this purpose is described. Two cases with free-stream turbulence levels of 0.68 and 2.0 percent, taken in the same facility with moderate strength of curvature, δ/R = 0.03, are compared. Profiles of u′v′, t′, u′t′, and v′t′ are dramatically reduced within the curve, with asymptotic profiles being achieved quickly for the low TI case. Recovery occurs rapidly, with the profiles often overshooting flat-wall upstream values. Increased free-stream turbulence has the effect of increasing the profiles throughout the boundary layer on the flat developing wall. Profiles agreeing with the asymptotic profiles of the low TI case are observed by the end of the curve, however, illustrating the dominance of curvature over free-stream turbulence intensity. For the higher TI case, a reversal in the sign of u′v′ in the outer half of the boundary layer is observed, leading to negative values of the turbulent Prandtl number in this region. This indicates a breakdown in Reynolds analogy.

No abstract

Free-stream turbulence intensity effects on a convex-curved turbulent boundary layer are investigated. An attached fully turbulent boundary layer is grown on a flat plate and is then introduced to a downstream section where the test wall is convexly curved, having a constant radius of curvature. Two cases, with free-stream turbulence intensities of 1.85 and 0.65 percent, are discussed. They were taken in the same facility and with the same strength of curvature, δ/R = 0.03−0.045. The two cases have similar flow conditions upon entry to the curve, thus separating the free-stream turbulence effects under study from other effects. The higher turbulence case displayed stronger curvature effects on the skin friction coefficient Cf, and on streamwise-normal and shear stress profiles, than observed in the lower turbulence case. Observations of this are: (1) As expected, the higher turbulence case has a higher Cf value ( ∼ 5 percent) upstream of the curve than does the lower turbulence case, but this difference diminishes by the end of the curve. (2) Streamwise turbulence intensity profiles, differing upstream of the curve for the two cases, are found to be similar near the end of the curve, thus indicating that the effect of curvature is dominating over the effect of free-stream turbulence intensity. Many effects of curvature observed in the lower turbulence intensity case, and reported previously, e.g., a dramatic response to the introduction of curvature and the rapid assumption of an asymptotic shape within the curve, are also seen in the higher turbulence case.