Interstellar Clouds Research Articles

Численное моделирование процессов естественного проветривания карьера при вариации его глубины в условиях инверсионного состояния атмосферы

The research objective is to assess the influence of the background stratification parameter and the depth of an open pit mine on the time of natural ventilation of the mine and the level of atmospheric pollution at the upper side of the pit downwind of blasting operations in conditions of the North. An aerothermodynamic model of the atmosphere was used, in which the equations of dynamics in the approximation of incompressible fluid were supplemented with the heat transfer equation, and the buoyancy and background stratification mechanisms were taken into account. The model was created in a general-purpose COMSOL software package and makes it possible to study aerothermogasodynamics of the atmosphere in its various states. A two-dimensional CFD-model of the open pit atmosphere was tested using the recirculation ventilation process. The background stratification parameter (from 0.0 to +0.025 °С/m with the increment of 0.005 °С/m) and the quarry depth from 300 to 700 m were variated. The wind velocity of 1 m/s at the upper side of the pit, the initial location of the dust and gas cloud (in the center of the pit near its floor) and the slope angle of the pit wall of 45° were recorded. A significant increase in the time of natural ventilation of the open pit is demonstrated at intensifying inversion of the atmosphere. Two formation types of the maximum pollution area with the increasing pit depth are predicted: (1) displacement from the center to the lee side of the pit at neutral stratification; and (2) position in the center of the pit near its floor at positive background stratification. It is shown that increasing of both the pit depth and the background stratification parameter leads to a noticeable increase in the time to reach the maximum concentration at the upper side of the pit and a decrease in the value of this maximum. For the recirculation ventilation scheme, intensification of inversion in the atmosphere increases the time of natural ventilation, but reduces the level of atmospheric contamination at the upper side of the pit downstream.

A strontium-rich ultra-metal-poor star in the Atari disc component

ABSTRACT We report on the discovery of the first ultra-metal-poor (UMP) star 2MASS J20500194−6613298 (J2050−6613; [Fe/H] = −4.05) selected from the Gaia BP/RP spectral catalogue that belongs to the ancient Atari disc component. We obtained a high-resolution spectrum for the star with the MIKE spectrograph on the Magellan-Clay telescope. J2050−6613 displays a typical chemical abundance pattern for UMP stars, including carbon and zinc enhancements. In contrast, J2050−6613 shows extremely high [Sr/Fe] and [Sr/Ba] ratios compared to other stars in the [Fe/H] < −4.0 regime. J2050−6613 is most likely an early Population II star that formed from a gas cloud that was chemically enriched by a massive Population III hypernova (E > 1052 erg). Such a Population III core-collapse hypernova could simultaneously explain the origin of the abundance pattern of light and heavy elements of 2MASS J2050−6613 if a large amount of Sr of ∼10−5 M⊙ was produced, possibly by neutrino-driven (wind) ejecta. Therefore, the abundance pattern of 2MASS J2050−6613 places important constraints on Sr-producing nucleosynthesis sources operating in the Atari progenitor at the earliest times.

Application of machine learning methods for process safety assessments

AbstractThe accurate prediction of gas dispersion and the potential consequences of gas explosions hold a pivotal role in the assessment of explosion design loads for oil and gas processing facilities. This often involves the use of computational fluid dynamics (CFD) simulations, a widely adopted practice in the field. The extent of CFD simulations required depends on the specific characteristics and size of the facility. In many cases, a substantial number of simulations, often in the thousands, are needed to comprehensively assess the potential outcomes in the event of a hydrocarbon loss of containment. These simulations account for the complex three‐dimensional nature of the facility, the surrounding environmental conditions, and the properties of the leaking hydrocarbon fluids. Although unquestionably invaluable, CFD simulations impose significant temporal constraints upon their execution and necessitate the allocation of substantial efforts and Central Processing Unit (CPU) time. In this paper we develop a neural model tailored specifically for the analysis of CFD gas dispersion and gas explosion scenarios. This model leverages the capabilities of machine learning algorithms to expedite the execution of these complex studies. The proposed neural network model has the advantage of being able to handle a wide range of scenarios in a fraction of time it takes to perform the CFD simulations, making it particularly useful for large‐scale processes facilities. The accuracy of the predictions is remarkably high, providing a high level of confidence in the predictions of the flammable gas clouds sizes across various scenarios, as well as the resulting explosion overpressures.

Ground and excited electronic structures of electride and alkalide units: The cases of Metal-Tren, -Azacryptand, and -TriPip222 complexes.

A systematic electronic structure analysis was conducted for M(L)n molecular electrides and their corresponding alkalide units M(L)n @M' (M/M' = Na, K; L = Tren, Azacryptand, TriPip222; n = 1, 2). All complexes belong to the "superalkali" category due to their low ionization potentials. The saturated molecular electrides display M+ (L)n - form with a greatly diffuse quasispherical electron cloud. They were identified as "superatoms" considering the contours of populating atomic-type molecular orbitals. The observed superatomic Aufbau order of M(Tren)2 is 1S, 1P, 1D, 1F, 2S, 2P, and 1G and it is consistent with those of M(Azacryptand) and M(TriPip222) up to the analyzed 1F level. Their excitation energies decrease gradually moving from M(Tren)2 to M(Azacryptand) and to M(TriPip222). The studied alkalide complexes carry [M(L)n ]+ @M'- ionic structure and their dissociation energies vary in the sequence of K(L)n @Na > Na(L)n @Na > K(L)n @K > Na(L)n @K. Similar to molecular electrides, the anions of alkalide units occupy electrons in diffuse Rydberg-like orbitals. In this work, excited states of [M(L)n @M']0/+/- and their trends are also analyzed.

Fueling Processes on (Sub-)kpc Scales

Since the 1970s, astronomers have struggled with the issue of how matter can be accreted to promote black-hole growth. While low-angular-momentum stars may be devoured by a black hole, they are not a sustainable source of fuel. Gas, which could potentially provide an abundant fuel source, presents another challenge due to its enormous angular momentum. While viscous torques are not significant, gas is subject to gravity torques from non-axisymmetric potentials such as bars and spirals. Primary bars can exchange angular momentum with the gas within corotation, causing it to spiral inwards until reaching the inner Lindblad resonance. An embedded nuclear bar can then take over. As the gas reaches the black hole’s sphere of influence, the torque becomes negative, fueling the center. Dynamical friction also accelerates the infall of gas clouds closer to the nucleus. However, because of the Eddington limit, growing a black hole from a stellar-mass seed is a slow process. The existence of very massive black holes in the early universe remains a puzzle that could potentially be solved through direct collapse of massive clouds into black holes or super-Eddington accretion.

Relativistic Exploration of Dark Matter Effectsin Rotating Galaxy, Studied Fluid-Dynamically

Galactic space is filled with interstellar clouds of neutral gases. Motion of the space-clouds is viewed as a flow of continuous fluid in curved space with gravity. Dynamical motions of the space-fluid of rotating galaxies are investigated by extending Fluid Dynamics to that in the frame of general relativity. Fluid flow field to be extended to that of a relativistic theory is reinforced by the fluid gauge theory equipped with a background (dark) gauge field conditioning the fluid continuity. The Gravity-space Fluid Dynamics thus developed captures main feature of the dark-matter effect as the action of the gauge field on the motion of space fluids. In the present formulation, the stress-energy tensor in the general relativity is revised in order to take account of general nature of stress field by extending the isotropic pressure to an-isotropic stress field.

Observations of Multiphase, High-velocity, Shocked Gas in the Vela Supernova Remnant* *Based on observations made with the NASA/ESA Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer, obtained from the MAST data archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Based in part on

We present an analysis of high-resolution far-UV archival spectra obtained with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope of the star HD 75309, which probes high-velocity shocked gas in the Vela supernova remnant (SNR). We examine high-velocity features from intrinsically strong absorption lines of O i, Si ii, Si ii*, C ii, C ii*, and Si iii. We also detect high-velocity components in the N v doublet and compare these features to observations of high-velocity O vi absorption, available from archival Far Ultraviolet Spectroscopic Explorer data. Kinetic temperatures are derived from the observed fractional abundances of the various ions, while gas densities and thermal pressures are obtained from the relative populations in excited fine-structure levels of C ii and Si ii. Our results indicate that the highly ionized species at high velocity probe gas in a region immediately behind a shock driven into an interstellar cloud, while the lower-ionization species trace material further downstream in the cooling region of the postshock flow. Low-velocity N v and O vi absorption may trace gas in a conductive boundary layer between the unshocked portion of the cloud and the hot X-ray-emitting intercloud medium. Temporal variations in high-velocity Ca ii absorption features observed toward HD 75309 further confirm the highly inhomogeneous nature of the interstellar medium interacting with the Vela SNR.

SPLUS J142445.34–254247.1: An r-process–enhanced, Actinide-boost, Extremely Metal-poor Star Observed with GHOST

We report on a chemo-dynamical analysis of SPLUS J142445.34−254247.1 (SPLUS J1424−2542), an extremely metal-poor halo star enhanced in elements formed by the rapid neutron-capture process (r-process). This star was first selected as a metal-poor candidate from its narrowband S-PLUS photometry and followed up spectroscopically in medium resolution with Gemini-South/GMOS, which confirmed its low-metallicity status. High-resolution spectroscopy was gathered with GHOST at Gemini-South, allowing for the determination of the chemical abundances for 36 elements, from carbon to thorium. At [Fe/H] = −3.39, SPLUS J1424−2542 is one of the lowest-metallicity stars with measured Th and has the highest observed to date, making it part of the “actinide-boost” category of r-process–enhanced stars. The analysis presented here suggests that the gas cloud from which SPLUS J1424−2542 formed must have been enriched by at least two progenitor populations. The light-element (Z ≤ 30) abundance pattern is consistent with the yields from a supernova explosion of metal-free stars with 11.3–13.4 M ⊙, and the heavy-element (Z ≥ 38) abundance pattern can be reproduced by the yields from a neutron star merger (1.66 M ⊙ and 1.27 M ⊙) event. A kinematical analysis also reveals that SPLUS J1424−2542 is a low-mass, old halo star with a likely in situ origin, not associated with any known early merger events in the Milky Way.

Two-photon Production in Low-velocity Shocks

The Galactic interstellar medium abounds in shocks with low velocities v s ≲ 70 km s−1. Some are descendants of higher velocity shocks, while others start off at low velocity (e.g., stellar bow shocks, intermediate velocity clouds, spiral density waves). Low-velocity shocks cool primarily via Lyα and two-photon continuum, augmented by optical recombination lines (e.g., Hα), forbidden lines of metals and free-bound emission, free–free emission. The dark far-ultraviolet (FUV) sky, aided by the fact that the two-photon continuum peaks at 1400 Å, makes the FUV band an ideal tracer of low-velocity shocks. GALEX FUV images reaffirm this expectation, discovering faint and large interstellar structure in old supernova remnants and thin arcs stretching across the sky. Interstellar bow shocks are expected from fast stars from the Galactic disk passing through the numerous gas clouds in the local interstellar medium within 15 pc of the Sun. Using the bests atomic data available to date, we present convenient fitting formulae for yields of Lyα, two-photon continuum, and Hα for pure hydrogen plasma in the temperature range of 104–105 K. The formulae presented here can be readily incorporated into time-dependent cooling models as well as collisional ionization equilibrium models.

Hazardous Area Classification in Simultaneous Production and Drilling at Oil and Gas Platform

Hazardous area, three-dimensional space, in which a flammable/explosive atmosphere is or may be expected to be present in quantity, requiring ignition source controls to manage safety risks, such as fires and explosions. Fire and explosion can result in catastrophic consequences for people and property, causing loss of life or severe injury and possible loss of business. Hazardous Area Classification is a method of analyzing and classifying the environment where explosive gas atmospheres may occur. The primary purpose of this classification is to facilitate the proper selection and installation of the apparatus to be used safely in that environment, considering the properties of the flammable materials that will be present. The method used is the point source approach, where equipment with variabilities of temperature, pressure, equipment, and the degree and type of ventilation that would take place on release may vary significantly, making individual assessment necessary. This study discusses the extent of the hazardous area due to an explosive atmosphere in Simultaneous Production and Drilling mode. It classifies the identified hazardous area based on frequency and likelihood of flammable release or ignitable cloud expected to be present. Using this information, ignition of flammable release or explosive gas cloud suspension in the air, which inevitably occurs in a Simultaneous Production and Drilling area handling flammable components, can be avoided.

Evolution of the Shape of a Gas Cloud during Pulsed Laser Evaporation into Vacuum: Direct Simulation Monte Carlo and the Solution of a Model Equation

Evolution of the Shape of a Gas Cloud during Pulsed Laser Evaporation into Vacuum: Direct Simulation Monte Carlo and the Solution of a Model Equation

Evolution of the Shape of a Gas Cloud during Pulsed Laser Evaporation into Vacuum: Direct Simulation Monte Carlo and the Solution of a Model Equation

The dynamics of gas expansion during nanosecond laser evaporation into vacuum is studied. The problem is considered in an axisymmetric formulation for a wide range of parameters: the number of evaporated monolayers and the size of the evaporation spot. To obtain a reliable numerical solution, two different kinetic approaches are used—the direct simulation Monte Carlo method and solution of the BGK model kinetic equation. The change in the shape of the cloud of evaporated substance during the expansion process is analyzed. The strong influence of the degree of rarefaction on the shape of the forming cloud is shown. When a large number of monolayers evaporate, good agreement with the continuum solution is observed.

Deuteration of molecular clumps induced by cosmic rays

The D/H ratio in astrophysical environments has instigated the scientists for at least 50 years. The wide range of values in the interstellar medium (ISM) from 10e to 7 to 10e-1 have usually been claimed to be due to small zero-point energy differences between reactants and products involving D and H (mainly at low temperatures). Here, we present a new source of deuteration processes in the ISM clouds as a result of cosmic ray irradiation. As a study object, we consider a typical molecular clump under the presence of incoming cosmic rays simulated computationally. The calculations were performed employing the Monte Carlo toolkit GEANT4 code (considering hadronic physics) and considering mainly the proton and alpha component of the incoming cosmic rays from the ISM (the dominant ones for the production of secondary protons and deuterons). The results suggest an increasing D/H ratio as function of time in the central part of molecular clumps (<200 AU) with the largest deuteration in the central region of the cloud, and a bump in the D/H ratio around 2–10 AU (which becomes more pronounced for clouds with larger timescales; > 10 Myrs). The results also show that for timescales between 10 and 100 Myrs the central part of the cloud has D/H around 6-16e-3, a value compatible with the observed D/H in some interstellar clouds. This work adds a new piece to the D/H puzzle of the ISM and might also help to explain the D/H ratio measured in different objects inside the Solar system.

Enhancing flammable gas dispersion and explosion prediction: A novel hybrid analytical-numerical approach with exploCFD

The analysis of explosion consequences involves two primary approaches: analytical methods and Computational Fluid Dynamics (CFD). Analytical methods offer a simplified one-dimensional model of overpressure, while CFD provides a more detailed numerical analysis capturing asymmetric and inhomogeneous overpressure distribution. However, CFD simulations can be computationally demanding and require additional sub-grid models to enable calculations to be carried out in realistic timeframes. Both approaches have large irreducible uncertainty. The hybrid analytical-numerical approach aims to simplify and speed up the calculation process, yet producing results that remain within this irreducible uncertainty. This study describes the theoretical basis and demonstrates the successful implementation of the hybrid methodology in exploCFD for predicting flammable gas dispersion and explosions with special focus on hydrogen. The methodology combines analytical source terms with numerical simulations, capturing the inhomogeneity of explosion overpressure distribution in realistic explosion cases, and gas release dispersion cases, which can only be achieved by taking obstacles and obstructions into account. We then compare the predictions of exploCFD with dispersion and explosion experiments with experimental results, with a special focus on Hydrogen. The focus on hydrogen utilization in recent years necessitates the development of predictive capabilities to assess the consequences of hydrogen-fuelled accidents in industrial facilities due to its unique properties. The methodology exhibits good agreement with experiment, for maximum and transient overpressure readings as well as dispersion concentrations. The study demonstrates that exploCFD's hybrid methodology is well-suited for modeling flammable gas releases, particularly hydrogen, and simulating explosion events resulting from the ignition of premixed gas clouds. This approach offers a superior alternative to more time-consuming and costly purely numerical methods, as well as crude analytical methods still in use today.

Spectroscopic characterization and photochemistry of HC3N− and CH3C3N−: implications for ion chemistry in Titan's atmosphere

ABSTRACT Molecular ions are key intermediates in the build-up of chemical complexity in interstellar clouds. Among the more than 300 interstellar molecules, only eight negative ions, i.e. C2n+1N− (n = 0–3) and HC2n− (n = 2–5), have been astronomically observed. Understanding the formation mechanism of these ions under the interstellar conditions is essential for astrochemical modelling and establishing the astrochemical networks. Cyanopolyynes including the parent molecule HC3N are carbon-chain molecules that have been observed in a variety of astronomical objects such as the Titan's atmosphere. Herein, two cyanoacetylene anions HC3N‒ and CH3C3N‒ were generated in solid Ne matrix at 3 K and characterized with matrix-isolation infrared spectroscopy, as aided by isotopic substitutions and the ab initio calculations at the UCCSD(T)-F12a/cc-pVTZ-F12 level using second-order vibrational perturbation theory. Upon red-light irradiation at 625 nm, both ions undergo electron detachment by reformation of the neutral species. Importantly, the concomitant dehydrogenation of HC3N‒ has also been observed in the matrix, providing new insight into the intriguing mechanism for the formation of C3N‒ in the upper atmosphere of Titan.

UV-photoprocessing of acetic acid (CH3COOH)-bearing interstellar ice analogues

ABSTRACT Acetic acid (CH3COOH) was detected in the gas towards interstellar clouds, hot cores, protostars, and comets. Its formation in ice mantles was proposed, and acetic acid awaits detection in the infrared spectra of the ice as most of the other complex organic molecules except methanol. The thermal annealing and UV-irradiation of acetic acid in the ice was simulated experimentally in this work under astrophysically relevant conditions. The experiments were performed under ultrahigh vacuum conditions. An ice layer was formed by vapour deposition onto a cold substrate, and was warmed up or exposed to ultraviolet (UV) photons. The ice was monitored by infrared spectroscopy, while the molecules desorbing to the gas phase were measured using a quadrupole mass spectrometer. The transformation of the CH3COOH monomers to cyclic dimers occurs at 120 K, and the crystal form composed of chain polymers was observed above 160 K during warm-up of the ice. Ice sublimation proceeds at 189 K in our experiments. Upon UV-irradiation, simpler species and radicals are formed, which leads to a residue made of complex molecules after warm-up to the room temperature. The possible formation of oxalic acid needs to be confirmed. The photodestruction of acetic acid molecules is reduced when mixed with water in the ice. This work may serve to search for the acetic acid photoproducts in lines of sight where this species is detected. A comparison of the reported laboratory infrared spectra with current JWST observations allows to detect or set upper limits on the CH3COOH abundances in interstellar and circumstellar ice mantles.

α-enhanced astrochemistry: the carbon cycle in extreme galactic conditions

ABSTRACT Astrochemistry has been widely developed as a power tool to probe the physical properties of the interstellar medium (ISM) in various conditions of the Milky Way (MW) Galaxy, and in near and distant galaxies. Most current studies conventionally apply linear scaling to all elemental abundances based on the gas-phase metallicity. However, these elements, including carbon and oxygen, are enriched differentially by stellar nucleosynthesis and the overall galactic chemical evolution, evident from α-enhancement in multiple galactic observations such as starbursts, high-redshift star-forming galaxies, and low-metallicity dwarfs. We perform astrochemical modelling to simulate the impact of an α-enhanced ISM gas cloud on the abundances of the three phases of carbon (C+, C, CO) dubbed as ‘the carbon cycle’. The ISM environmental parameters considered include two cosmic-ray ionization rates (ζCR = 10−17 and $10^{-15}\, {\rm s}^{-1}$), two isotropic FUV radiation field strengths (χ/χ0 = 1 and 102), and (sub-)linear dust-to-gas relations against metallicity, mimicking the ISM conditions of different galaxy types. In galaxies with [C/O] &amp;lt; 0, CO, C, and C+, all decrease in both abundances and emission, though with differential biases. The low-J CO emission is found to be the most stable tracer for the molecular gas, while C and C+ trace H2 gas only under limited conditions, in line with recent discoveries of [C i]-dark galaxies. We call for caution when using [C ii] $158\, \mu$m and [C i](1–0) as alternative H2-gas tracers for both diffuse and dense gas with non-zero [C/O] ratios.

Correction to: An accurate set of H3O+ − H2 collisional rate coefficients for non-LTE modelling of warm interstellar clouds

Correction to: An accurate set of H3O+ − H2 collisional rate coefficients for non-LTE modelling of warm interstellar clouds

Enhancing the integrity of a buried gas pipelines: Investigating ruptures, explosions, and strengthening solutions

The present paper presents findings from a case study of a buried gas pipeline that ruptured, causing a gas cloud explosion and subsequent fire. The study aimed to identify the incident's cause and improve the pipeline's strength under specific conditions. The study measured the pipe's actual wall thickness and conducted stress analysis using analytical and finite element methods to assess its integrity under corrosion. It evaluated if the 20-inch pipeline near road crossings could withstand external forces.In conclusion, the research underscores the importance of accurately assessing the structural integrity of buried pipelines, especially under conditions of corrosion. It highlights the utility of finite element analysis in providing a more precise understanding of stress distribution and can aid in designing pipelines that are better equipped to withstand various external pressures.The investigation illustrates the importance of increasing the strength of buried natural gas pipelines, in the crossing road area and, for this purpose, it was proposed (in terms of novelty associated with the study) a solution consisting in introduction of the pipeline in protective sleeves fitted with spacer rings.

A Robust Localization Approach Based on Point Cloud Descriptor and SLAM in Urban Environment

The importance of autonomous driving localization to autonomous driving systems cannot be overstated, reliable and high-precision localization is the focus of research in autonomous driving. Many studies at this stage use multiple sensors to generate high-definition maps for matching and localization. The labor and economic costs required to maintain such maps are often high. This paper proposes a fusion localization framework for simultaneous localization and mapping (SLAM) and matching localization. It could afford high-precision localization results of autonomous vehicles using only light detection and ranging (LiDAR) sensors. Concretely, a novel global point cloud descriptor, named binary scan context (BSC) is proposed, for matching localization. It encodes the structural features in the z-height direction in the point cloud space in a binary way. An efficient two-stage matching strategy is proposed to improve the efficiency of matching. Experiments on public datasets and vehicles have demonstrated the validation and precision of the method.