Analytical and experimental investigation of circulation control by means of a turbulent Coanda jet

An analytical and experimental investigation of circulation control on a circular cylinder by means of tangential blowing (Coanda effect) is presented. The analytical method developed has also been used to estimate the blowing coefficients required for achieving potential flow on airfoils with flaps. The analysis is presented for conditions for which the flow in the boundary layer ahead of the jet exit is turbulent. The turbulent boundary layer and the jet layer on the upper surface, and the turbulent boundary layer on the lower surface are computed by a multi-strip integral method. The region of integration is between the correponding transition and separation points on each surface. Longitudinal curvature effects, which give rise to a radial pressure gradient across the jet layer and to an additional adverse tangential pressure gradient just upstream of the separation point, are included in the jet layer analysis in an approximate manner. The longitudinal curvature effect is found to have a pronounced influence on the separation of the jet layer

MHD boundary layers with non-equilibrium ionization and finite rates Quarterly report, 1 Jun. - 1 Sep. 1969

Ionization and recombination rates in boundary layer of magnetohydrodynamic channel electrod

Light Transmission Through Metallic-Mean Quasiperiodic Stacks with Oblique Incidence

The propagation of s- and p-polarized light through quasiperiodic multilayers, consisting of layers with different refractive indices, is studied by the transfer matrix method. In particular, we focus on the transmission coefficient of the systems in dependency on the incidence angle and on the ratio of the refractive indices. We obtain additional bands with almost complete transmission in the quasiperiodic systems at frequencies in the range of the photonic band gap of a system with a periodic alignment of the two materials for both types of light polarization. With increasing incidence angle these bands bend towards higher frequencies, where the curvature of the transmission bands in the quasiperiodic stack depends on the metallic mean of the construction rule. Additionally, in the quasiperiodic systems for p-polarized light the bands show almost complete transmission near the Brewster's angle in contrast to the results for s-polarized light. Further, we present results for the influence of the refractive indices at the midgap frequency of the periodic stack, where the quasiperiodicity was found to be most effective.Comment: 10 pages, 7 figure

Backward Tamm states in left-handed metamaterials

We study the electromagnetic surface waves localized at an interface separating a one-dimensional photonic crystal and left-handed metamaterial, the so-called surface Tamm states. We demonstrate that the metamaterial allows for a flexible control of the dispersion properties of surface states, and can support the Tamm states with a backward energy flow and a vortex-like structure.Comment: 3 pages, 5 figure

Average and worst-case specifications of precipitating auroral electron environment

The precipitation electrons in the auroral environment are highly variable in their energy and intensity in both space and time. As such they are a source of potential hazard to the operation of the Space Shuttle and other large spacecraft operating in polar orbit. In order to assess these hazards both the average and extreme states of the precipitating electrons must be determined. Work aimed at such a specification is presented. First results of a global study of the average characteristics are presented. In this study the high latitude region was divided into spatial elements in magnetic local time and corrected geomagnetic latitude. The average electron spectrum was then determined in each spatial element for seven different levels of activity as measured by K sub p using an extremely large data set of auroral observations. Second a case study of an extreme auroral electron environment is presented, in which the electrons are accelerated through field aligned potential as high as 30,000 volts and in which the spacecraft is seen to charge negatively to a potential approaching .5 kilovolts

Fluorous Mixture Synthesis (FMS) of Four Isomers of 4,8,12,-Trimethylnonadecanol and the Development of an NMR-based Method for Determining the Configurations of Polyisoprenoid Structures

The chiral polyisoprenoid motif has been identified in various natural products such as vitamin E, chlorophyll-d, and beta-mannosyl phosphomycoketide. This motif features stereocenters bearing branched methyl groups at every fourth carbon of a long alkyl chain. Due to the lack of function group, assigning the configurations of these structures is difficult. Herein, we describe the fluorous mixture synthesis (FMS) of the 4S,8S,12S-, 4S,8R,12S-, 4R,8S,12S-, and 4R,8R,12S-trimethylnonadecanol isomers. The FMS features a new family of ultra-light fluorous O-phenyl thionocarbonate tags and employees the most efficient fluorous tagging strategy to date. The analyses of these four isomers were found to exhibit small but reliable differences in 1H and 13C NMR spectra. Furthermore, these chemical shifts of the branched methyl groups were diagnostic of relative configurations. By deducing the relative relationship between configuration and chemical shift, we developed predictions of 4,8,12,16-tetramethyltricoanol, and 4,8,12,16,20-pentamethyl-heptacosanol

The complexes of palladium (II) and nickel (II) with cycloalkanecarboxylic acid

Although some organic hydroxy acid complexes of palladium(II) and nickel(II) have been described (1-9), crystalline palladium(II) and mickel(II) dicycloalkanecarboxylates have not been reported. The interaction of a palladium salt such as NA2PdCl4 or a nickel salt such as NiCl2·6H2 with cycloalkane carboxylic acids which contain 3, 4, 5, 6, and 7 carbons produces deep green carboxylates with palladium(II) and yellowish green carboxylates with nickel(II)

Efficient input and output fiber coupling to a photonic crystal waveguide

The efficiency of evanescent coupling between a silica optical fiber taper and a silicon photonic crystal waveguide is studied. A high reflectivity mirror on the end of the photonic crystal waveguide is used to recollect, in the backwards propagating fiber mode, the optical power that is initially coupled into the photonic crystal waveguide. An outcoupled power in the backward propagating fiber mode of 88% of the input power is measured, corresponding to a lower bound on the coupler efficiency of 94%