Design of aircraft turbine fan drive gear transmission system

The following basic types of gear reduction concepts were studied as being feasible power train systems for a low-bypass-ratio, single-spool, geared turbofan engine for general aircraft use: (1) single-stage external-internal reduction, (2) gears (offset shafting), (3) multiple compound idler gear system (concentric shafting), and (4) star gear planetary system with internal ring gear final output member (concentric shafting-counterrotation). In addition, studies were made of taking the accessories drive power off both the high-speed and low-speed shafting, using either face gears or spiral bevel gears. Both antifriction and sleeve-type bearings were considered for the external-internal and star-planet reduction concepts

Submillimetre dust polarisation and opacity in the HD163296 protoplanetary ring system

We present ALMA images of the sub-mm continuum polarisation and spectral index of the protoplanetary ringed disk HD163296. The polarisation fraction at 870{\mu}m is measured to be ~0.9% in the central core and generally increases with radius along the disk major axis. It peaks in the gaps between the dust rings, and the largest value (~4%) is found between rings 1 and 2. The polarisation vectors are aligned with the disk minor axis in the central core, but become more azimuthal in the gaps, twisting by up to +/-9degrees in the gap between rings 1 and 2. These general characteristics are consistent with a model of self-scattered radiation in the ringed structure, without requiring an additional dust alignment mechanism. The 870/1300{\mu}m dust spectral index exhibits minima in the centre and the inner rings, suggesting these regions have high optical depths. However, further refinement of the dust or the disk model at higher resolution is needed to reproduce simultaneously the observed degree of polarisation and the low spectral index.Comment: 5 pages +2 pages supplemental data. v2 - revised figures and final values; conclusions unchange

Gravitational Stirring in Planetary Debris Disks

We describe gravitational stirring models of planetary debris disks using a new multi-annulus planetesimal evolution code. The current code includes gravitational stirring and dynamical friction; future studies will include coagulation, fragmentation, Poynting-Robertson drag, and other physical processes. We use the results of our calculations to investigate the physical conditions required for small bodies in a planetesimal disk to reach the shattering velocity and begin a collisional cascade. Our results demonstrate that disks composed primarily of bodies with a single size will not undergo a collisional cascade which produces small dust grains at 30-150 AU on timescales of 1 Gyr or smaller. Disks with a size distribution of bodies reach conditions necessary for a collisional cascade in 10 Myr to 1 Gyr if the disk is at least as massive as a minimum mass solar nebula and if the disk contains objects with radii of 500 km or larger. The estimated 500 Myr survival time for these disks is close to the median age of roughly 400 Myr derived for nearby stars with dusty disks.Comment: 23 pages of text + 16 Figures; to appear in the Astronomical Journal, January 200

A Mid-Infrared Imaging Survey of Embedded Young Stellar Objects in the Rho Ophiuchi Cloud Core

Results of a comprehensive, new, ground-based mid-infrared imaging survey of the young stellar population of the Rho Ophiuchi cloud are presented. Data were acquired at the Palomar 5-m and at the Keck 10-m telescopes with the MIRLIN and LWS instruments, at 0.25 arcsec and 0.25 arcsec resolutions, respectively. Of 172 survey objects, 85 were detected. Among the 22 multiple systems observed, 15 were resolved and their individual component fluxes determined. A plot of the frequency distribution of the detected objects with SED spectral slope shows that YSOs spend ~400,000 yr in the Flat Spectrum phase, clearing out their remnant infall envelopes. Mid-infrared variability is found among a significant fraction of the surveyed objects, and is found to occur for all SED classes with optically thick disks. Large-amplitude near-infrared variability, also found for all SED classes with optically thick disks, seems to occur with somewhat higher frequency at the earlier evolutionary stages. Although a general trend of mid-infrared excess and NIR veiling exists proceeding through SED classes, with Class I objects generally exhibiting K-veilings > 1, Flat Spectrum objects with K-veilings > 0.58, and Class III objects with K-veilings =0, Class II objects exhibit the widest range of K-band veiling values, 0-4.5. However, the highly variable value of veiling that a single source can exhibit in any of the SED classes in which active disk accretion can take place is striking, and is direct observational evidence for highly time-variable accretion activity in disks. Finally, by comparing mid-infrared vs. near-infrared excesses in a subsample with well-determined effective temperatures and extinction values, disk clearing mechanisms are explored. The results are consistent with disk clearing proceeding from the inside-out.Comment: 18 pages + 5 tables + 7 figure

Slow roll inflation in the presence of a dark energy coupling

In models of coupled dark energy, in which a dark energy scalar field couples to other matter components, it is natural to expect a coupling to the inflaton as well. We explore the consequences of such a coupling in the context of single-field slow-roll inflation. Assuming an exponential potential for the quintessence field we show that the coupling to the inflaton causes the quintessence field to be attracted toward the minimum of the effective potential. If the coupling is large enough, the field is heavy and is located at the minimum. We show how this affects the expansion rate and the slow-roll of the inflaton field, and therefore the primordial perturbations generated during inflation. We further show that the coupling has an important impact on the processes of reheating and preheating

The JCMT 12CO(3-2) Survey of the Cygnus X Region: I. A Pathfinder

Cygnus X is one of the most complex areas in the sky. This complicates interpretation, but also creates the opportunity to investigate accretion into molecular clouds and many subsequent stages of star formation, all within one small field of view. Understanding large complexes like Cygnus X is the key to understanding the dominant role that massive star complexes play in galaxies across the Universe. The main goal of this study is to establish feasibility of a high-resolution CO survey of the entire Cygnus X region by observing part of it as a Pathfinder, and to evaluate the survey as a tool for investigating the star-formation process. A 2x4 degree area of the Cygnus X region has been mapped in the 12CO(3-2) line at an angular resolution of 15" and a velocity resolution of ~0.4km/s using HARP-B and ACSIS on the James Clerk Maxwell Telescope. The star formation process is heavily connected to the life-cycle of the molecular material in the interstellar medium. The high critical density of the 12CO(3-2) transition reveals clouds in key stages of molecule formation, and shows processes that turn a molecular cloud into a star. We observed ~15% of Cygnus X, and demonstrated that a full survey would be feasible and rewarding. We detected three distinct layers of 12CO(3-2) emission, related to the Cygnus Rift (500-800 pc), to W75N (1-1.8 kpc), and to DR21 (1.5-2.5 kpc). Within the Cygnus Rift, HI self-absorption features are tightly correlated with faint diffuse CO emission, while HISA features in the DR21 layer are mostly unrelated to any CO emission. 47 molecular outflows were detected in the Pathfinder, 27 of them previously unknown. Sequentially triggered star formation is a widespread phenomenon.Comment: 18 pages, 13 figures, accepted for publication in Astronomy & Astrophysic

Cosmological perturbations in f(T) gravity

We investigate the cosmological perturbations in f(T) gravity. Examining the pure gravitational perturbations in the scalar sector using a diagonal vierbien, we extract the corresponding dispersion relation, which provides a constraint on the f(T) ansatzes that lead to a theory free of instabilities. Additionally, upon inclusion of the matter perturbations, we derive the fully perturbed equations of motion, and we study the growth of matter overdensities. We show that f(T) gravity with f(T) constant coincides with General Relativity, both at the background as well as at the first-order perturbation level. Applying our formalism to the power-law model we find that on large subhorizon scales (O(100 Mpc) or larger), the evolution of matter overdensity will differ from LCDM cosmology. Finally, examining the linear perturbations of the vector and tensor sectors, we find that (for the standard choice of vierbein) f(T) gravity is free of massive gravitons.Comment: 11 pages, 4 figures. Analysis of the vector and tensor sectors adde

Combined assessment (aspiration cytology and mammography) of clinically suspicious breast masses

We examined the safety and utility of the combined assessment of aspiration cytology and mammography in 705 women who had clinically suspicious or malignant palpable breast masses. Histological assessment confirmed 176 benign and 529 malignant lesions. There were no incorrect (false positive) diagnoses made in the 176 benign masses when combined assessment was used (specificity 1,0; predictive value 0,86); in isolation, however, there was a false positive cytological diagnosis («papillary carcinoma») and 3 false positive mammographic diagnoses. Benign disease (false negative) was incorrectly diagnosed by combined assessment in 4 of the 529 malignant masses (sensitivity 0,99; predictive value 0,98): cytological diagnoses were of fat necrosis (2) and benign cells on cytospin (1) and aspiration biopsy (1); mammographic diagnoses were of benign disease (2) and normality (2). Indeterminate («atypical», «suspicious») diagnoses were problematic and frequent (overall 223 (31,6%), malignant masses 137 (25,9%), benign masses 86 (48,9%); cytology 117 (16,6%), mammography 141 (20%). Thus, with the combined assessment of mammography and cytology in clinically suspicious breast masses, a decisive diagnosis was made in about two-thirds of cases allowing the safe commencement of therapy; the balance of patients required cone or excision biopsy