Shock-tube measurements of carbon to oxygen atom ratios for incipient soot formation with C2H2, C2H4 and C2H6 fuels

The critical atomic carbon to oxygen ratios, Phi sub C, for incipient soot formation in shock heated acetylene, ethylene, ethane/oxygen/ argon mixtures was measured over the temperature range 2000 K to 2500 K for reactant partial pressures between 0.1 and 0.4 atoms. Absorption of light from a He-Ne laser at 6328A was was used to detect soot. It was observed that the values of Phi sub C for all three fuels increased uniformly with temperature such that at the highest temperatures Phi sub C was considerably greater than unity, i.e. greater than the value of about unity at which solid carbon should have been precipitated on a thermochemical equilibrium basis. Observations were made over periods extending up to about one millisecond, which was well in excess of the time required for the major heat release of the combustion reactions. The relevance of these experimental findings to the problem of soot formation in gas turbine combustion chambers is discussed

The design and fabrication of microstrip omnidirectional array antennas for aerospace applications

A microstrip antenna design concept was developed that will provide quasi-omnidirectional radiation pattern characteristics about cylindrical and conical aerospace structures. L-band and S-band antenna arrays were designed, fabricated, and, in some cases, flight tested for rocket, satellite, and aircraft drone applications. Each type of array design is discussed along with a thermal cover design that was required for the sounding rocket applications

Soot oxidation rates in gas turbine engines

A basis is proposed for extrapolating soot oxidation rate measurements obtained in laboratory flames to the more extreme operating conditions of gas turbine combustion chambers. The proposal is based on the observation that, within probable experimental uncertainty, the limited soot oxidation measurements correlate with the more extensive measurements of the surface oxidation rates of macroscopic samples of pyrographite. The soot oxidation rates thus determined for the conditions of a typical gas turbine combustion chamber are considerably lower than estimates which were based on simple extrapolations of the flame data

Enhanced dust heating in the bulges of early-type spiral galaxies

Stellar density and bar strength should affect the temperatures of the cool (T ~ 20–30 K) dust component in the inner regions of galaxies, which implies that the ratio of temperatures in the circumnuclear regions to the disk should depend on Hubble type. We investigate the differences between cool dust temperatures in the central 3 kpc and disk of 13 nearby galaxies by fitting models to measurements between 70 and 500 μm. We attempt to quantify temperature trends in nearby disk galaxies, with archival data from Spitzer/MIPS and new observations with Herschel/SPIRE, which were acquired during the first phases of the Herschel observations for the KINGFISH (Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel) sample. We fit single-temperature modified blackbodies to far-infrared and submillimeter measurements of the central and disk regions of galaxies to determine the temperature of the component(s) emitting at those wavelengths. We present the ratio of central-region-to-disk-temperatures of the cool dust component of 13 nearby galaxies as a function of morphological type. We find a significant temperature gradient in the cool dust component in all galaxies, with a mean center-to-disk temperature ratio of 1.15 ± 0.03. The cool dust temperatures in the central ~3 kpc of nearby galaxies are 23 (±3)% hotter for morphological types earlier than Sc, and only 9 (±3)% hotter for later types. The temperature ratio is also correlated with bar strength, with only strongly barred galaxies having a ratio over 1.2. The strong radiation field in the high stellar density of a galactic bulge tends to heat the cool dust component to higher temperatures, at least in early-type spirals with relatively large bulges, especially when paired with a strong bar

Embedded Voxel Colouring

The reconstruction of a complex scene from multiple images is a fundamental problem in the field of computer vision. Volumetric methods have proven to be a strong alternative to traditional correspondence-based methods due to their flexible visibility models. In this paper we analyse existing methods for volumetric reconstruction and identify three key properties of voxel colouring algorithms: a water-tight surface model, a monotonic carving order, and causality. We present a new Voxel Colouring algorithm which embeds all reconstructions of a scene into a single output. While modelling exact visibility for arbitrary camera locations, Embedded Voxel Colouring removes the need for a priori threshold selection present in previous work. An efficient implementation is given along with results demonstrating the advantages of posteriori threshold selection

Plasma and Warm Dust in the Collisional Ring Galaxy VIIZw466 from VLA and ISO Observations

We present the first mid-infrared (Mid-IR) ($\lambda5-15\mu$m) and radio continuum ($\lambda\lambda$20,~6 and 3.6 cm) observations of the star-forming collisional ring galaxy VII Zw 466 and its host group made with the Infrared Space Observatory and the NRAO Very Large Array. A search was also made for CO line emission in two of the galaxies with the Onsala 20m radio telescope and upper limits were placed on the mass of molecular gas in those galaxies. The ring galaxy is believed to owe its morphology to a slightly off-center collision between an `intruder' galaxy and a disk. An off-center collision is predicted to generate a radially expanding density wave in the disk which should show large azimuthal variations in overdensity, and have observational consequences. The radio continuum emission shows the largest asymmetry, exhibiting a crescent-shaped distribution consistent with either the trapping of cosmic-ray particles in the target disk, or an enhanced supernova rate in the compressed region. On the other hand, the ISO observations (especially those made at $\lambda9.6\mu$m) show a more scattered distribution, with emission centers associated with powerful star formation sites distributed more uniformly around the ring. Low-signal to noise observations at $\lambda15.0\mu$m show possible emission inside the ring, with little emission directly associated with the \ion{H}{2} regions. The observations emphasize the complex relationship between the generation of radio emission and the development of star formation even in relatively simple and well understood collisional scenarios.Comment: Accepted for publication in The Astrophysical Journal, 23 pages + 6 PS figure

IRAC Observations of M81

IRAC images of M81 show three distinct morphological constituents: a smooth distribution of evolved stars with bulge, disk, and spiral arm components; a clumpy distribution of dust emission tracing the spiral arms; and a pointlike nuclear source. The bulge stellar colors are consistent with M-type giants, and the disk colors are consistent with a slightly younger population. The dust emission generally follows the blue and ultraviolet emission, but there are large areas that have dust emission without ultraviolet and smaller areas with ultraviolet but little dust emission. The former are presumably caused by extinction, and the latter may be due to cavities in the gas and dust created by supernova explosions. The nucleus appears fainter at 8 um than expected from ground-based 10 um observations made four years ago.Comment: ApJS in press (Spitzer special issue); 15 pages, 3 figures. Changes: unused references removed, numbers and labels in Table 1 change

Why is timing of bird migration advancing when individuals are not?

Recent advances in spring arrival dates have been reported in many migratory species but the mechanism driving these advances is unknown. As population declines are most widely reported in species that are not advancing migration, there is an urgent need to identify the mechanisms facilitating and constraining these advances. Individual plasticity in timing of migration in response to changing climatic conditions is commonly proposed to drive these advances but plasticity in individual migratory timings is rarely observed. For a shorebird population that has significantly advanced migration in recent decades, we show that individual arrival dates are highly consistent between years, but that the arrival dates of new recruits to the population are significantly earlier now than in previous years. Several mechanisms could drive advances in recruit arrival, none of which require individual plasticity or rapid evolution of migration timings. In particular, advances in nest-laying dates could result in advanced recruit arrival, if benefits of early hatching facilitate early subsequent spring migration. This mechanism could also explain why arrival dates of short-distance migrants, which generally return to breeding sites earlier and have greater scope for advance laying, are advancing more rapidly than long-distance migrants