ATOMS : ALMA Three-millimeter Observations of Massive Star-forming regions - I. Survey description and a first look at G9.62+0.19

The ATOMS, standing for ALMA Three-millimeter Observations of Massive Star-forming regions, survey has observed 146 active star-forming regions with ALMA band 3, aiming to systematically investigate the spatial distribution of various dense gas tracers in a large sample of Galactic massive clumps, to study the roles of stellar feedback in star formation, and to characterize filamentary structures inside massive clumps. In this work, the observations, data analysis, and example science of the ATOMS survey are presented, using a case study for the G9.62+0.19 complex. Toward this source, some transitions, commonly assumed to trace dense gas, including CS J = 2-1, HCO+ J = 1-0, and HCN J = 1-0, are found to show extended gas emission in low-density regions within the clump; less than 25 per cent of their emission is from dense cores. SO, CH3OH, (HCN)-C-13, and HC3N show similar morphologies in their spatial distributions and reveal well the dense cores. Widespread narrow SiO emission is present (over similar to 1 pc), which may be caused by slow shocks from large-scale colliding flows or HII regions. Stellar feedback from an expanding HII region has greatly reshaped the natal clump, significantly changed the spatial distribution of gas, and may also account for the sequential high-mass star formation in the G9.62+0.19 complex. The ATOMS survey data can be jointly analysed with other survey data, e.g. MALT90, Orion B, EMPIRE, ALMA IMF, and ALMAGAL, to deepen our understandings of 'dense gas' star formation scaling relations and massive protocluster formation.Peer reviewe

ATOMS : ALMA three-millimeter observations of massive star-forming regions - II. Compact objects in ACA observations and star formation scaling relations

We report studies of the relationships between the total bolometric luminosity (L-bol or L-TIR) and the molecular line luminosities of J = 1 - 0 transitions of (HCN)-C-13, (HCO+)-C-13, HCN, and HCO+ with data obtained from ACA observations in the 'ATOMS' survey of 146 active Galactic star-forming regions. The correlations between L-bol and molecular line luminosities L-mol' of the four transitions all appear to be approximately linear. Line emission of isotopologues shows as large scatters in L-bol-L-mol' relations as their main line emission. The log(L-bol/L-mol') for different molecular line tracers have similar distributions. The L-bol-to-L-mol' ratios do not change with galactocentric distances (R-GC) and clump masses (M-clump). The molecular line luminosity ratios (HCN-to-HCO+, (HCN)-C-13-to-(HCO+)-C-13, HCN-to-(HCN)-C-13, and HCO+-to-(HCO+)-C-13) all appear constant against L-bol, dust temperature (T-d), M-clump, and R-GC. Our studies suggest that both the main lines and isotopologue lines are good tracers of the total masses of dense gas in Galactic molecular clumps. The large optical depths of main lines do not affect the interpretation of the slopes in star formation relations. We find that the mean star formation efficiency (SFE) of massive Galactic clumps in the 'ATOMS' survey is reasonably consistent with other measures of the SFE for dense gas, even those using very different tracers or examining very different spatial scales.Peer reviewe

ATOMS : ALMA three-millimeter observations of massive star-forming regions - III. Catalogues of candidate hot molecular cores and hyper/ultra compact H II regions

A correction has been published: Monthly Notices of the Royal Astronomical Society, Volume 511, Issue 1, March 2022, Pages 501–505, https://doi.org/10.1093/mnras/stac039We have identified 453 compact dense cores in 3mm continuum emission maps in the ALMA Three-millimetre Observations of Massive Star-forming regions survey, and compiled three catalogues of high-mass star-forming cores. One catalogue, referred to as hyper/ultra compact (H/UC)-HII catalogue, includes 89 cores that enshroud H/UC HII regions as characterized by associated compact H40 alpha emission. A second catalogue, referred to as pure s-cHMC, includes 32 candidate hot molecular cores (HMCs) showing rich spectra (N >= 20 lines) of complex organic molecules (COMs) and not associated with H/UC-HII regions. The third catalogue, referred to as pure w-cHMC, includes 58 candidate HMCs with relatively low levels of COM richness and not associated with H/UC-Hii regions. These three catalogues of dense cores provide an important foundation for future studies of the early stages of high-mass star formation across the Milky Way. We also find that nearly half of H/UC-HII cores are candidate HMCs. From the number counts of COM-containing and H/UC-HII cores, we suggest that the duration of high-mass protostellar cores showing chemically rich features is at least comparable to the lifetime of H/UC-HII regions. For cores in the H/UC-HII catalogue, the width of the H40 alpha line increases as the core size decreases, suggesting that the non-thermal dynamical and/or pressure line-broadening mechanisms dominate on the smaller scales of the H/UC-HII cores.Peer reviewe

The Divide-and-Swap Cube: A New Hypercube Variant with Small Network Cost

The hypercube is one of the most popular interconnection networks. Its network cost is �(�2) . In this paper, we propose a new hypercube variant, the divide-and-swap cube DSC(�)(�=2�,�≥1) , which reduces the network cost to �(�log�) while maintaining the same number of nodes and the same asymptotic performances for fundamental algorithms such as the broadcasting. The new network has nice hierarchical properties. We first show that the diameter of DSC(�) is lower than or equal to 5�4−1 . However, unlike the hypercube of dimension n whose degree is n, the node degree of the network is log�+1 , resulting in a network cost of �(�log�) . We then examine the one-to-all and all-to-all broadcasting times of DSC(�) , based on the single-link-available and multiple-link-available models. We also present an upper bound on the bisection width of the DSC(�) and show that DSC(�) is Hamiltonian. Finally, we introduce the folded divide-and-swap cube, FDSC(�) , a variant of the DSC(�) and study its many properties including its hierarchical structure, routing algorithm, broadcasting algorithms, bisection width, and its Hamiltonicity. All the broadcasting algorithms presented in this paper are asymptotically optimal

On the expansive cracking of a cement matrix containing atomized basic oxygen furnace slag with a metallic iron

A series of experiments was conducted to investigate the crack-expansion of a cement matrix containing atomized basic oxygen furnace slag with a metallic iron. The BOF slag particles were dispersed in supersaturated Ca(OH)2 solution mimicking the pore solution in a cement matrix and the changes in these particles were visually observed. X-ray diffraction, thermogravimetry, and X-ray photoelectron spectroscopy were conducted on different slag powders and cement paste in the slag. Our major observations indicated that 1) cracks in the BOF slag-containing cement matrix were initiated from the slag particles, 2) the BOF slag contained metallic Fe and free MgO, and 3) Fe oxides, portlandite, and brucite were formed at slag crack points. Therefore, corrosion of metallic Fe is proposed as the main reason for the cracking of a cement matrix with atomized BOF slag; further, hydration of free MgO helps in crack growth and propagation. ?? 2020 Elsevier Lt