Effects of Surface Recombination on Heat Transfer to Bodies in a High Enthalpy Stream of Partially Dissociated Nitrogen

Heat-transfer rates to two surfaces having widely different catalytic effectiveness are compared at a Mach number of 6 in a low-density stream of partially dissociated nitrogen. The heat-transfer rate to a polished copper cylinder is twice as great as the heat-transfer rate to a silicon-monoxide-coated cylinder when the stream total energy content is 9000 Btu/lb. Various methods for determining the stream energy content, the stream velocity, and the stream Mach number have been developed and compared. It is shown that methods for estimating the stream energy content by means of purely aerodynamic concepts may neglect the sizable fraction of the stream energy contained in molecular dissociation

Concordance between a neuroradiologist, a consultant radiologist and trained reporting radiographers interpreting MRI head examinations: An empirical study

Introduction: This study assessed agreement between MRI reporting radiographers and a consultant radiologist compared with an index neuroradiologist when reporting MRI head (brain/internal auditory meati [IAMs]) examinations. The effect on patient management of any discordant reports was also examined. Methods: Two trained MRI reporting radiographers (RRs), a consultant radiologist (CR) and an index neuroradiologist (INR) reported on a random sample of 210 MRI examinations. The radiographers reported during clinical practice and the radiologists in clinical practice conditions. Two independent consultant physicians (neuro-rehabilitation and neuropsychiatry) compared these reports with the index neuroradiologist report for agreement and the clinical importance of discrepant reports. Results: Overall observer agreement between the RRs and CR was comparable in relation to agreement with the INR: RR; 93/210 (44.3%); and the CR; 83/210 (39.4%) for all head MRI examinations (p = 0.32). For brain examinations the difference was similar: RR; 64/180 (35.6%); and CR; 54/190 (30.0%), p = 0.26. Agreement rates for the IAMs examinations were identical, 29/30 (97.7%). For all head MRI examinations (n = 210) there was a very small observed difference of <0.5% in mean agreement between the reporting radiographers and the consultant radiologist (p = 0.92) for examinations where a major disagreement would have been likely to have led to a change in patient management. Conclusion: MRI reporting radiographers reported during clinical practice on MRI head examinations to a level of agreement comparable with a consultant radiologist. Implications for practice: This is an area in which radiographers could provide additional reporting roles to the reporting service to increase capacity. Wider potential benefits include cost-effectiveness and role development/retention of radiographers

Wind-Tunnel Investigation of the Low-Speed Static Longitudinal Characteristics of the Republic RF-84F Airplane

Tests in the Ames 40- by 80-foot wind tunnel of the static longitudinal characteristics of the Republic RF-84F were made to determine both the origin and a suitable remedy for a pitch up tendency of the airplane encountered at moderate lift coefficients. The results indicated that the pitch-up at moderate lift coefficients was caused by an abrupt change in downwash at the tail which in turn was traceable presumably to flow conditions associated with the inlet-to-wing leading-edge discontinuity.. Attempts to eliminate this pitch-up characteristic with various fairings and stall-control devices. were not wholly successful. The investigation revealed, however, that significant gains in the performance of the airplane could be achieved in the upper lift range.. Three different configurations consisting of a partial-span modified leading edge combined with one or with two-fenees or a leading-edge extension each delayed the onset of separation to higher lift coefficients and provided large improvements in the stability of the airplane in the upper lift range

What determines the density structure of molecular clouds? A case study of Orion B with <i>Herschel</i>

A key parameter to the description of all star formation processes is the density structure of the gas. In this Letter, we make use of probability distribution functions (PDFs) of Herschel column density maps of Orion B, Aquila, and Polaris, obtained with the Herschel Gould Belt survey (HGBS). We aim to understand which physical processes influence the PDF shape, and with which signatures. The PDFs of Orion B (Aquila) show a lognormal distribution for low column densities until AV ~ 3 (6), and a power-law tail for high column densities, consistent with a ρα r-2 profile for the equivalent spherical density distribution. The PDF of Orion B is broadened by external compression due to the nearby OB stellar aggregates. The PDF of a quiescent subregion of the non-star-forming Polaris cloud is nearly lognormal, indicating that supersonic turbulence governs the density distribution. But we also observe a deviation from the lognormal shape at AV > 1 for a subregion in Polaris that includes a prominent filament. We conclude that (1) the point where the PDF deviates from the lognormal form does not trace a universal AV -threshold for star formation, (2) statistical density fluctuations, intermittency, and magnetic fields can cause excess from the lognormal PDF at an early cloud formation stage, (3) core formation and/or global collapse of filaments and a non-isothermal gas distribution lead to a power-law tail, and (4) external compression broadens the column density PDF, consistent with numerical simulations

A multi-scale, multi-wavelength source extraction method: getsources

We present a multi-scale, multi-wavelength source extraction algorithm called getsources. Although it has been designed primarily for use in the far-infrared surveys of Galactic star-forming regions with Herschel, the method can be applied to many other astronomical images. Instead of the traditional approach of extracting sources in the observed images, the new method analyzes fine spatial decompositions of original images across a wide range of scales and across all wavebands. It cleans those single-scale images of noise and background, and constructs wavelength-independent single-scale detection images that preserve information in both spatial and wavelength dimensions. Sources are detected in the combined detection images by following the evolution of their segmentation masks across all spatial scales. Measurements of the source properties are done in the original background-subtracted images at each wavelength; the background is estimated by interpolation under the source footprints and overlapping sources are deblended in an iterative procedure. In addition to the main catalog of sources, various catalogs and images are produced that aid scientific exploitation of the extraction results. We illustrate the performance of getsources on Herschel images by extracting sources in sub-fields of the Aquila and Rosette star-forming regions. The source extraction code and validation images with a reference extraction catalog are freely available.Comment: 31 pages, 27 figures, to be published in Astronomy & Astrophysic

Far-infrared observations of a massive cluster forming in the Monoceros R2 filament hub

We present far-infrared observations of Monoceros R2 (a giant molecular cloud at approximately 830 pc distance, containing several sites of active star formation), as observed at 70 μm, 160 μm, 250 μm, 350 μm, and 500 μm by the Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging Receiver (SPIRE) instruments on the Herschel Space Observatory as part of the Herschel imaging survey of OB young stellar objects (HOBYS) Key programme. The Herschel data are complemented by SCUBA-2 data in the submillimetre range, and WISE and Spitzer data in the mid-infrared. In addition, C18O data from the IRAM 30-m Telescope are presented, and used for kinematic information. Sources were extracted from the maps with getsources, and from the fluxes measured, spectral energy distributions were constructed, allowing measurements of source mass and dust temperature. Of 177 Herschel sources robustly detected in the region (a detection with high signal-to-noise and low axis ratio at multiple wavelengths), including protostars and starless cores, 29 are found in a filamentary hub at the centre of the region (a little over 1% of the observed area). These objects are on average smaller, more massive, and more luminous than those in the surrounding regions (which together suggest that they are at a later stage of evolution), a result that cannot be explained entirely by selection effects. These results suggest a picture in which the hub may have begun star formation at a point significantly earlier than the outer regions, possibly forming as a result of feedback from earlier star formation. Furthermore, the hub may be sustaining its star formation by accreting material from the surrounding filaments

A census of dense cores in the Taurus L1495 cloud from the Herschel Gould Belt Survey

We present a catalogue of dense cores in a ∼4° × 2° field of the Taurus star-forming region, inclusive of the L1495 cloud, derived from HerschelSPIRE and PACS observations in the 70 μm, 160 μm, 250 μm, 350 μm, and 500 μm continuum bands. Estimates of mean dust temperature and total mass are derived using modified blackbody fits to the spectral energy distributions. We detect 528 starless cores of which ∼10–20% are gravitationally bound and therefore presumably prestellar. Our census of unbound objects is ∼85% complete for M > 0.015 M⊙ in low density regions (AV∼M > 0.1 M⊙ overall. The prestellar CMF is consistent with lognormal form, resembling the stellar system initial mass function, as has been reported previously. All of the inferred prestellar cores lie on filamentary structures whose column densities exceed the expected threshold for filamentary collapse, in agreement with previous reports. Unlike the prestellar CMF, the unbound starless CMF is not lognormal, but instead is consistent with a power-law form below 0.3 M⊙ and shows no evidence for a low-mass turnover. It resembles previously reported mass distributions for CO clumps at low masses (M∼<0.3M⊙M∼<0.3M⊙). The volume density PDF, however, is accurately lognormal except at high densities. It is consistent with the effects of self-gravity on magnetized supersonic turbulence. The only significant deviation from lognormality is a high-density tail which can be attributed unambiguously to prestellar cores