Simulation test results for lift/cruise fan research and technology aircraft

A flight simulation program was conducted on the flight simulator for advanced aircraft (FSAA). The flight simulation was a part of a contracted effort to provide a lift/cruise fan V/STOL aircraft mathematical model for flight simulation. The simulated aircraft is a configuration of the Lift/Cruise Fan V/STOL research technology aircraft (RTA). The aircraft was powered by three gas generators driving three fans. One lift fan was installed in the nose of the aircraft, and two lift/cruise fans at the wing root. The thrust of these fans was modulated to provide pitch and roll control, and vectored to provide yaw, side force control, and longitudinal translation. Two versions of the RTA were defined. One was powered by the GE J97/LF460 propulsion system which was gas-coupled for power transfer between fans for control. The other version was powered by DDA XT701 gas generators driving 62 inch variable pitch fans. The flight control system in both versions of the RTA was the same

Mathematical model for lift/cruise fan V/STOL aircraft simulator programming data

Simulation data are reported for the purpose of programming the flight simulator for advanced aircraft for tests of the lift/cruise fan V/STOL Research Technology Aircraft. These simulation tests are to provide insight into problem areas which are encountered in operational use of the aircraft. A mathematical model is defined in sufficient detail to represent all the necessary pertinent aircraft and system characteristics. The model includes the capability to simulate two basic versions of an aircraft propulsion system: (1) the gas coupled configuration which uses insulated air ducts to transmit power between gas generators and fans in the form of high energy engine exhaust and (2) the mechanically coupled power system which uses shafts, clutches, and gearboxes for power transmittal. Both configurations are modeled such that the simulation can include vertical as well as rolling takeoff and landing, hover, powered lift flight, aerodynamic flight, and the transition between powered lift and aerodynamic flight

A Tunable Echelle Imager

We describe and evaluate a new instrument design called a Tunable Echelle Imager (TEI). In this instrument, the output from an imaging Fabry-Perot interferometer is cross-dispersed by a grism in one direction and dispersed by an echelle grating in the perpendicular direction. This forms a mosaic of different narrow-band images of the same field on a detector. It offers a distinct wavelength multiplex advantage over a traditional imaging Fabry-Perot device. Potential applications of the TEI include spectrophotometric imaging and OH-suppressed imaging by rejection.Comment: 11 pages, 12 figures, accepted by PAS

Correlated modal mineralogy, aqueous alteration and oxygen isotope composition of CM Chondrites

In this study we move beyond defining alteration sequences in CM chondrites towards understanding the relationship between modal mineralogy, the extent of aqueous alteration and O-isotope compositions

NGC 300: an extremely faint, outer stellar disk observed to 10 scale lengths

We have used the Gemini Multi-object Spectrograph (GMOS) on the Gemini South 8m telescope in exceptional conditions (0.6" FWHM seeing) to observe the outer stellar disk of the Sculptor group galaxy NGC 300 at two locations. At our point source detection threshold of r' = 27.0 (3-sigma) mag, we trace the stellar disk out to a radius of 24', or 2.2 R_25 where R_25 is the 25 mag/arcsec**2 isophotal radius. This corresponds to about 10 scale lengths in this low-luminosity spiral (M_B = -18.6), or about 14.4 kpc at a cepheid distance of 2.0 +/- 0.07 Mpc. The background galaxy counts are derived in the outermost field, and these are within 10% of the mean survey counts from both Hubble Deep Fields. The luminosity profile is well described by a nucleus plus a simple exponential profile out to 10 optical scale lengths. We reach an effective surface brightness of 30.5 mag/arcsec**2 (2-sigma) at 55% completeness which doubles the known radial extent of the optical disk. These levels are exceedingly faint in the sense that the equivalent surface brightness in B or V is about 32 mag/arcsec**2. We find no evidence for truncation of the stellar disk. Only star counts can be used to reliably trace the disk to such faint levels, since surface photometry is ultimately limited by nonstellar sources of radiation. In the Appendix, we derive the expected surface brightness of one such source: dust scattering of starlight in the outer disk.Comment: ApJ accepted -- 30 pages, 13 figures -- see ftp://www.aao.gov.au/pub/local/jbh/astro-ph/N300 for full resolution figures and preprin

Photonic ring resonator filters for astronomical OH suppression

Ring resonators provide a means of filtering specific wavelengths from a waveguide, and optionally dropping the filtered wavelengths into a second waveguide. Both of these features are potentially useful for astronomical instruments. In this paper we focus on their use as notch filters to remove the signal from atmospheric OH emission lines from astronomical spectra, however we also briefly discuss their use as frequency combs for wavelength calibration and as drop filters for Doppler planet searches. We derive the design requirements for ring resonators for OH suppression from theory and finite difference time domain simulations. We find that rings with small radii (<10 microns) are required to provide an adequate free spectral range, leading to high index contrast materials such as Si and Si$_{3}$N$_{4}$. Critically coupled rings with high self-coupling coefficients should provide the necessary Q factors, suppression depth, and throughput for efficient OH suppression. We report on our progress in fabricating both Si and Si$_{3}$N$_{4}$ rings for OH suppression, and give results from preliminary laboratory tests. Our early devices show good control over the free spectral range and wavelength separation of multi-ring devices. The self-coupling coefficients are high (>0.9), but further optimisation is required to achieve higher Q and deeper notches, with current devices having $Q \approx 4000$ and $\approx 10$ dB suppression. The overall prospects for the use of ring resonators in astronomical instruments is promising, provided efficient fibre-chip coupling can be achieved.Comment: Submitted to Optics Express feature issue on Recent Advances in Astrophotonics (27 pages, 20 figs

The Taurus Tunable Filter Field Galaxy Survey: Sample Selection and Narrowband Number-Counts

Recent evidence suggests a falling volume-averaged star-formation rate (SFR) over z ~ 1. It is not clear, however, the extent to which the selection of such samples influences the measurement of this quantity. Using the Taurus Tunable Filter (TTF) we have obtained an emission-line sample of faint star-forming galaxies over comparable lookback times: the TTF Field Galaxy Survey. By selecting through emission-lines, we are screening galaxies through a quantity that scales directly with star-formation activity for a given choice of initial mass function. The scanning narrowband technique furnishes a galaxy sample that differs from traditional broadband-selected surveys in both its volume-limited nature and selection of galaxies through emission-line flux. Three discrete wavelength intervals are covered, centered at H-alpha redshifts z = 0.08, 0.24 and 0.39. Galaxy characteristics are presented and comparisons made with existing surveys of both broadband and emission-line selection. When the number-counts of emission-line objects are compared with those expected on the basis of existing H-alpha surveys, we find an excess of ~ 3 times at the faintest limits. While these detections are yet to be independently confirmed, inspection of the stronger subsample of galaxies detected in both the line and continuum (line-on-continuum subsample; 13 %) is sufficient to support an excess population. This increase in the emission-line field population implies higher star-formation densities over z ~ 0.4. However, further study in the form of multi-object spectroscopic follow-up is necessary to quantify this and confirm the faintest detections in the sample.Comment: 48 pages, 12 figures. To appear in the Astrophysical Journal. An abridged version of the Abstract is shown her

Bayes and health care research.

Bayes’ rule shows how one might rationally change one’s beliefs in the light of evidence. It is the foundation of a statistical method called Bayesianism. In health care research, Bayesianism has its advocates but the dominant statistical method is frequentism. There are at least two important philosophical differences between these methods. First, Bayesianism takes a subjectivist view of probability (i.e. that probability scores are statements of subjective belief, not objective fact) whilst frequentism takes an objectivist view. Second, Bayesianism is explicitly inductive (i.e. it shows how we may induce views about the world based on partial data from it) whereas frequentism is at least compatible with non-inductive views of scientific method, particularly the critical realism of Popper. Popper and others detail significant problems with induction. Frequentism’s apparent ability to avoid these, plus its ability to give a seemingly more scientific and objective take on probability, lies behind its philosophical appeal to health care researchers. However, there are also significant problems with frequentism, particularly its inability to assign probability scores to single events. Popper thus proposed an alternative objectivist view of probability, called propensity theory, which he allies to a theory of corroboration; but this too has significant problems, in particular, it may not successfully avoid induction. If this is so then Bayesianism might be philosophically the strongest of the statistical approaches. The article sets out a number of its philosophical and methodological attractions. Finally, it outlines a way in which critical realism and Bayesianism might work together. </p

The Metal-Enriched Outer Disk of NGC 2915

We present optical emission-line spectra for outlying HII regions in the extended neutral gas disk surrounding the blue compact dwarf galaxy NGC 2915. Using a combination of strong-line R23 and direct oxygen abundance measurements, we report a flat, possibly increasing, metallicity gradient out to 1.2 times the Holmberg radius. We find the outer-disk of NGC 2915 to be enriched to a metallicity of 0.4 Z_solar. An analysis of the metal yields shows that the outer disk of NGC 2915 is overabundant for its gas fraction, while the central star-foming core is similarly under-abundant for its gas fraction. Star formation rates derived from very deep ~14 ks GALEX FUV exposures indicate that the low-level of star formation observed at large radii is not sufficient to have produced the measured oxygen abundances at these galactocentric distances. We consider 3 plausible mechanisms that may explain the metal-enriched outer gaseous disk of NGC 2915: radial redistribution of centrally generated metals, strong galactic winds with subsequent fallback, and galaxy accretion. Our results have implications for the physical origin of the mass-metallicity relation for gas-rich dwarf galaxies.Comment: 11 pages, 4 figures, accepted to ApJ April 8th, 201

Weighing the local dark matter with RAVE red clump stars

We determine the Galactic potential in the solar neigbourhood from RAVE observations. We select red clump stars for which accurate distances, radial velocities, and metallicities have been measured. Combined with data from the 2MASS and UCAC catalogues, we build a sample of 4600 red clump stars within a cylinder of 500 pc radius oriented in the direction of the South Galactic Pole, in the range of 200 pc to 2000 pc distances. We deduce the vertical force and the total mass density distribution up to 2 kpc away from the Galactic plane by fitting a distribution function depending explicitly on three isolating integrals of the motion in a separable potential locally representing the Galactic one with four free parameters. Because of the deep extension of our sample, we can determine nearly independently the dark matter mass density and the baryonic disc surface mass density. We find (i) at 1kpc Kz/(2piG) = 68.5 pm 1.0 Msun/pc2, and (ii) at 2 kpc Kz/(2piG) = 96.9 pm 2.2 Msun/pc2. Assuming the solar Galactic radius at R0 = 8.5 kpc, we deduce the local dark matter density rhoDM (z=0) = 0.0143 pm 0.0011Msun pc3 = 0.542 pm 0.042 Gev/cm3 and the baryonic surface mass density Sigma = 44.4 pm 4.1 Msun/pc2 . Our results are in agreement with previously published Kz determinations up to 1 kpc, while the extension to 2 kpc shows some evidence for an unexpectedly large amount of dark matter. A flattening of the dark halo of order 0.8 can produce such a high local density in combination with a circular velocity of 240 km/s . Another explanation, allowing for a lower circular velocity, could be the presence of a secondary dark component, a very thick disc resulting either from the deposit of dark matter from the accretion of multiple small dwarf galaxies, or from the presence of an effective phantom thick disc in the context of effective galactic-scale modifications of gravity.Comment: 14 pages, 13 figures, accepted to Astronomy and Astrophysic