ABSTRACT
We present Atacama Compact Array and Atacama Pathfinder Experiment observations of the N ii 205 μm fine-structure line in 40 sub-millimetre galaxies lying at redshifts z = 3–6, drawn from ...the 2500 deg2 South Pole Telescope survey. This represents the largest uniformly selected sample of high-redshift N ii 205 μm measurements to date. 29 sources also have C ii 158 μm line observations allowing a characterization of the distribution of the C ii to N ii luminosity ratio for the first time at high redshift. The sample exhibits a median L$_{{\rm{C\,{\small II}}}}$/L$_{{\rm{N\,{\small II}}}}$ ≈ 11.0 and interquartile range of 5.0 –24.7. These ratios are similar to those observed in local (Ultra)luminous infrared galaxies (LIRGs), possibly indicating similarities in their interstellar medium. At the extremes, we find individual sub-millimetre galaxies with L$_{{\rm{C\,{\small II}}}}$/L$_{{\rm{N\,{\small II}}}}$ low enough to suggest a smaller contribution from neutral gas than ionized gas to the C ii flux and high enough to suggest strongly photon or X-ray region dominated flux. These results highlight a large range in this line luminosity ratio for sub-millimetre galaxies, which may be caused by variations in gas density, the relative abundances of carbon and nitrogen, ionization parameter, metallicity, and a variation in the fractional abundance of ionized and neutral interstellar medium.
Additives such as ozone have been shown both experimentally and numerically to enhance detonation properties, but the effects of ozone on one of the most common fuels used in detonation engines, ...ethylene, have not been sufficiently investigated. In the present study, the impact of ozonolysis reactions between ethylene and ozone on detonations is numerically examined in detail. Specifically, a combined flow reactor and detonation simulation is performed with residence times within the flow reactor corresponding to timescales relevant to detonation engines. The simulations are carried out over a range of equivalence ratios, ethylene–methane fuel blends, temperatures, and pressures. The results show that ozone addition to ethylene–methane–air mixtures leads to the formation of multiple peaks in thermicity. In some cases, particularly for lean mixtures or high ozone concentrations, the first peak in thermicity caused by the consumption of ozone can surpass the second peak caused by high-temperature fuel oxidation. It is also found that the maximum pressure of ozonolysis-assisted detonations decreases and the induction length increases for higher residence times. Comparisons are made between ozonolysis reactions and parasitic combustion due to the tendency of each to raise the pre-shock temperature but decrease the post-shock pressure.
By combining in situ and ex situ transmission electron microscopy measurements, we examine the factors that control the morphology of “hybrid” nanowires that include group III–V and group IV ...materials. We focus on one materials pair, GaP/Si, for which we use a wide range of growth parameters. We show through video imaging that nanowire morphology depends on growth conditions, but that a general pattern emerges where either single kinks or inclined defects form some distance after the heterointerface. We show that pure Si nanowires can be made to exhibit the same kinks and defects by changing their droplet volume. From this we derive a model where droplet geometry drives growth morphology and discuss optimization strategies. We finally discuss morphology control for material pairs where the second material kinks immediately at the heterointerface and show that an interlayer between segments can enable the growth of unkinked hybrid nanowires.
Device integration on flexible or low-cost substrates has driven interest in the low-temperature growth of semiconductor nanostructures. Using in situ electron microscopy, we examine the Au-catalyzed ...growth of crystalline Ge at temperatures as low as 150 °C. For this materials system, the model for low temperature growth of nanowires, we find three distinct reaction pathways. The lowest temperature reactions are distinguished by the absence of any purely liquid state. From measurements of reaction rates and parameters such as supersaturation, we explain the sequence of pathways as arising from a kinetic competition between the imposed time scale for Ge addition and the inherent time scale for Ge nucleation. This enables an understanding of the conditions under which catalytic Ge growth can occur at very low temperatures, with implications for nanostructure formation on temperature-sensitive substrates.
The flyby of Pluto and Charon by the New Horizons spacecraft provided high-resolution images of cratered surfaces embedded in the Kuiper belt, an extensive region of bodies orbiting beyond Neptune. ...Impact craters on Pluto and Charon were formed by collisions with other Kuiper belt objects (KBOs) with diameters from ~40 kilometers to ~300 meters, smaller than most KBOs observed directly by telescopes. We find a relative paucity of small craters ≲13 kilometers in diameter, which cannot be explained solely by geological resurfacing. This implies a deficit of small KBOs (≲1 to 2 kilometers in diameter). Some surfaces on Pluto and Charon are likely ≳4 billion years old, thus their crater records provide information on the size-frequency distribution of KBOs in the early Solar System.
The Thermal Infrared Sensor (TIRS) on Landsat 8 is the latest thermal sensor in that series of missions. Unlike the previous single-channel sensors, TIRS uses two channels to cover the 10-12.5 micron ...band. It is also a pushbroom imager; a departure from the previous whiskbroom approach. Nevertheless, the instrument requirements are defined such that data continuity is maintained. This paper describes the design of the TIRS instrument, the results of pre-launch calibration measurements and shows an example of initial on-orbit science performance compared to Landsat 7.
We examine individual Si nanowires grown by the vapor-liquid-solid mechanism, using real-time in situ ultra high vacuum transmission electron microscopy. By directly observing Au-catalyzed growth of ...Si wires from disilane, we show that the growth rate is independent of wire diameter, contrary to the expected behavior. Our measurements show that the unique rate-limiting step here is the irreversible, kinetically limited, dissociative adsorption of disilane directly on the catalyst surface. We also identify a novel dependence of growth rate on wire taper.
We present an extensive investigation of the epitaxial growth of Au-assisted axial heterostructure nanowires composed of group IV and III−V materials and derive a model to explain the overall ...morphology of such wires. By analogy with 2D epitaxial growth, this model relates the wire morphology (i.e., whether it is kinked or straight) to the relationship of the interface energies between the two materials and the particle. This model suggests that, for any pair of materials, it should be easier to form a straight wire with one interface direction than the other, and we demonstrate this for the material combinations presented here. However, such factors as kinetics and the use of surfactants may permit the growth of straight double heterostructure nanowires. Finally, we demonstrate that branched nanowire heterostructures, also known as nanotrees, can be successfully explained by the same model.
In the United States, nonreligious people face stigma, prejudice, and discrimination because they are viewed as immoral and distrustful. This is partly because of othering, by which nonreligious ...people are subjugated to a minority status. Othering also occurs in academic research and writing. Applying feminist principles can improve research about nonreligious populations. Grounded in results of a US-based online study, we recommend two feminist principles to facilitate the study of nonreligion: (1) rejecting othering of minority groups, and (2) intersectionality. As a result of applying these principles, the nuanced differences between nonreligious groups can be better understood and the complex identities of nonreligious people can be more accurately represented. Researchers benefit from increased accuracy and understanding of nonreligion via better informed theoretical and methodological decisions and nonreligious people benefit from their more accurate representation in academic research. Keywords: Nonreligion, feminist methods, intersectionality, epistemology, mixed methods
![The [C ii]/[N ii] ratio in ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0035-8711/small "The [C ii]/[N ii] ratio in 3 < z < 6 sub-millimetre galaxies from the South Pole Telescope survey")
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