RESUMO
The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, is composed of primitive objects preserving information about Solar System formation. In January 2019, the New Horizons spacecraft flew past one of these objects, the 36-kilometer-long contact binary (486958) Arrokoth (provisional designation 2014 MU69). Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters in diameter) within a radius of 8000 kilometers. Arrokoth has a lightly cratered, smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism.
RESUMO
The Kuiper Belt is a distant region of the outer Solar System. On 1 January 2019, the New Horizons spacecraft flew close to (486958) 2014 MU69, a cold classical Kuiper Belt object approximately 30 kilometers in diameter. Such objects have never been substantially heated by the Sun and are therefore well preserved since their formation. We describe initial results from these encounter observations. MU69 is a bilobed contact binary with a flattened shape, discrete geological units, and noticeable albedo heterogeneity. However, there is little surface color or compositional heterogeneity. No evidence for satellites, rings or other dust structures, a gas coma, or solar wind interactions was detected. MU69's origin appears consistent with pebble cloud collapse followed by a low-velocity merger of its two lobes.
RESUMO
We used a two-angle scattering technique to investigate the soot distribution in an ethylene diffusion flame in conjunction with extinction measurements. In the framework of a fractal description, we introduced a modified structure factor to interpret the scattering intensity from polydisperse aggregates. The connection between a mean value of a structural radius of gyration, R(gm1), and the quantities experimentally measured was then established. Soot parameters (volume fraction, particle size, and number densities) were determined along three radial sections of a 8-cm high-diffusion flame. The stability of the results with respect to the parameters of the distribution function was studied.
RESUMO
The time-delayed detection of soot incandescence is demonstrated to discriminate against other laser-induced signals that have shorter decay times. This technique exhibits high sensitivity and no need for any verification of the spectral content of the signal; it is promising for two-dimensional imaging applications in hostile environments, such as in practical flame and combustion chambers, in which it permits an easy visualization of sooty regions.
RESUMO
Laser-induced fluorescence measurements were performed in several regions of an ethylene-air diffusion flame. With the use of a 290-nm excitation wavelength, the fluorescence emissions from OH molecules and polycyclic aromatic hydrocarbons (PAH's) could be detected. Linear (one-dimensional) visualizations of OH, PAH's, and soot scattering were performed by utilizing an intensified photodiode array detector. Measurements taken at different heights above the burner permitted a two-dimensional reconstruction of the flame structure. Finally the simultaneous visualization of the three species for a rapid determination of the relative distributions was demonstrated.
RESUMO
A cross-beam saturated absorption spectroscopy technique, utilizing a single pulsed dye laser, has been developed for local concentration measurements in flames. With a differential detection of the probe and the reference laser beam intensities, a significant improvement of the technique has been achieved. In this work the basic theory of the method is discussed. Its use in combustion studies is demonstrated by presenting OH concentration profiles in two premixed laminar methane-air flames.
