Civil tiltrotor missions and applications. Phase 2: The commercial passenger market

The commercial passenger market for the civil tiltrotor was examined in phase 2. A market responsive commercial tiltrotor was found to be technically feasible, and a significant worldwide market potential was found to exist for such an aircraft, especially for relieving congestion in urban area-to-urban area service and for providing cost effective hub airport feeder service. Potential technical obstacles of community noise, vertiport area navigation, surveillance, and control, and the pilot/aircraft interface were determined to be surmountable. Nontechnical obstacles relating to national commitment and leadership and development of ground and air infrastructure were determined to be more difficult to resolve; an innovative public/private partnership is suggested to allow coordinated development of an initial commercial tiltrotor network to relieve congestion in the crowded US Northeast corridor by the year 2000

Laser cooling in the Penning trap: an analytical model for cooling rates in the presence of an axializing field

Ions stored in Penning traps may have useful applications in the field of quantum information processing. There are, however, difficulties associated with the laser cooling of one of the radial motions of ions in these traps, namely the magnetron motion. The application of a small radio-frequency quadrupolar electric potential resonant with the sum of the two radial motional frequencies has been shown to couple these motions and to lead to more efficient laser cooling. We present an analytical model that enables us to determine laser cooling rates in the presence of such an 'axializing' field. It is found that this field leads to an averaging of the laser cooling rates for the two motions and hence improves the overall laser cooling efficiency. The model also predicts shifts in the motional frequencies due to the axializing field that are in qualitative agreement with those measured in recent experiments. It is possible to determine laser cooling rates experimentally by studying the phase response of the cooled ions to a near resonant excitation field. Using the model developed in this paper, we study the expected phase response when an axializing field is present.Comment: 22 pages, 7 figure

Constraints on z~10 Galaxies from the Deepest HST NICMOS Fields

We use all available fields with deep NICMOS imaging to search for J dropouts (H<28) at z~10. Our primary data set for this search were the two J+H NICMOS parallel fields taken with the ACS HUDF. The 5 sigma limiting mags were 28.6 in J and 28.5 in H. Several shallower fields were also used: J+H NICMOS frames available over the HDF North, the HDF South NICMOS parallel, and the ACS HUDF. The primary selection criterion was (J-H)>1.8. 11 such sources were found in all search fields using this criterion. 8 of these were clearly ruled out as credible z~10 sources, either as a result of detections (>2 sigma) blueward of J or their colors redward of the break (H-K~1.5). The nature of the 3 remaining sources could not be determined from the data. The number appears consistent with the expected contamination from low-z interlopers. Analysis of the stacked images for the 3 candidates also suggests contamination. Regardless of their true redshifts, the actual number of z~10 sources must be <=3. To assess the significance of these results, two lower redshift samples (a z~3.8 B-dropout and z~6 i-dropout sample) were projected to z~8-12 using a (1+z)^{-1} size scaling. They were added to the image frames, and the selection repeated, giving 15.6 and 4.8 J-dropouts, respectively. This suggests that to the limit of this probe (0.3 L*) there has been evolution from z~3.8 and possibly from z~6. This is consistent with the strong evolution already noted at z~6 and z~7.5 relative to z~3-4. Even assuming that 3 sources from this probe are at z~10, the rest-frame continuum UV (~1500 A) luminosity density at z~10 (integrated down to 0.3 L*) is just 0.19_{-0.09}^{+0.13}x that at z~3.8 (or 0.19_{-0.10}^{+0.15}x including cosmic variance). However, if none of our sources is at z~10, this ratio has a 1 sigma upper limit of 0.07. (abridged)Comment: 13 pages, 3 figures, 2 tables, accepted for publication in the Astrophysical Journal Letter

In-flight calibration of the fine pointing Sun sensor on the solar maximum mission

The attitude control objectives of solar maximum mission are to point the boresight of the payload fine pointing sun sensor (FPSS) to any point within 30 arc-minutes of the Sun's center with an accuracy of 5 arc-seconds (3 sigma, pitch and yaw) and a jitter of less than 3 arc-seconds (3 sigma). To meet these stringent accuracy requirements, a procedure was developed for in-flight calibration of the FPSS. The spacecraft was maneuvered using FPSS offset commands to position the Sun at different points within the FPSS field of view. The coefficients of the FPSS digital to analog nonlinear transfer function were determined by minimizing the residuals between the pitch and yaw angles computed from the FPSS measurements and the corresponding reference angles obtained from inertial reference unit measurements. The actual in-flight calibration and the calibration algorithm are discussed

A non-LTE abundance analysis of the post-AGB star ROA 5701

An analysis of high-resolution Anglo-Australian Telescope (AAT)/ University College London Echelle Spectrograph (UCLES) optical spectra for the ultraviolet (UV)-bright star ROA 5701 in the globular cluster omega Cen (NGC 5139) is performed, using non-local thermodynamic equilibrium (non-LTE) model atmospheres to estimate stellar atmospheric parameters and chemical composition. Abundances are derived for C, N, O, Mg, Si and S, and compared with those found previously by Moehler et al. We find a general metal underabundance relative to young B-type stars, consistent with the average metallicity of the cluster. Our results indicate that ROA 5701 has not undergone a gas-dust separation scenario as previously suggested. However, its abundance pattern does imply that ROA 5701 has evolved off the AGB prior to the onset of the third dredge-up.Comment: 9 pages, 2 figures. Accepted for publication in MNRAS (Online Early

A Decision Support Framework for Automated Screening of Diabetic Retinopathy

The early signs of diabetic retinopathy (DR) are depicted by microaneurysms among other signs. A prompt diagnosis when the disease is at the early stage can help prevent irreversible damages to the diabetic eye. In this paper, we propose a decision support system (DSS) for automated screening of early signs of diabetic retinopathy. Classification schemes for deducing the presence or absence of DR are developed and tested. The detection rule is based on binary-hypothesis testing problem which simplifies the problem to yes/no decisions. An analysis of the performance of the Bayes optimality criteria applied to DR is also presented. The proposed DSS is evaluated on the real-world data. The results suggest that by biasing the classifier towards DR detection, it is possible to make the classifier achieve good sensitivity

Physical Mechanisms for the Variable Spin-down of SGR 1900+14

We consider the physical implications of the rapid spindown of Soft Gamma Repeater 1900+14, and of the apparent "braking glitch", \Delta P/P = l x 10^-4, that was concurrent with the Aug. 27th giant flare. A radiation-hydrodynamical outflow associated with the flare could impart the required torque, but only if the dipole magnetic field is stronger than ~ 10^14 G and the outflow lasts longer and/or is more energetic than the observed X-ray flare. A positive period increment is also a natural consequence of a gradual, plastic deformation of the neutron star crust by an intense magnetic field, which forces the neutron superfluid to rotate more slowly than the crust. Sudden unpinning of the neutron vortex lines during the August 27th event would then induce a glitch opposite in sign to those observed in young pulsars, but of a much larger magnitude as a result of the slower rotation. The change in the persistent X-ray lightcurve following the August 27 event is ascribed to continued particle heating in the active region of that outburst. The enhanced X-ray output can be powered by a steady current flowing through the magnetosphere, induced by the twisting motion of the crust. The long term rate of spindown appears to be accelerated with respect to a simple magnetic dipole torque. Accelerated spindown of a seismically-active magnetar will occur when its persistent output of Alfven waves and particles exceeds its spindown luminosity. We suggest that SGRs experience some episodes of relative inactivity, with diminished spindown rates, and that such inactive magnetars are observed as Anomalous X-ray Pulsars (AXPs). The rapid reappearence of persistent X-ray emission following August 27 flare gives evidence against accretion-powered models.Comment: 24 pages, no figure