Interstellar Clouds Research Articles

Two Heads Are Better than One: Image-Point Cloud Network for Depth-Based 3D Hand Pose Estimation

Depth images and point clouds are the two most commonly used data representations for depth-based 3D hand pose estimation. Benefiting from the structuring of image data and the inherent inductive biases of the 2D Convolutional Neural Network (CNN), image-based methods are highly efficient and effective. However, treating the depth data as a 2D image inevitably ignores the 3D nature of depth data. Point cloud-based methods can better mine the 3D geometric structure of depth data. However, these methods suffer from the disorder and non-structure of point cloud data, which is computationally inefficient. In this paper, we propose an Image-Point cloud Network (IPNet) for accurate and robust 3D hand pose estimation. IPNet utilizes 2D CNN to extract visual representations in 2D image space and performs iterative correction in 3D point cloud space to exploit the 3D geometry information of depth data. In particular, we propose a sparse anchor-based "aggregation-interaction-propagation'' paradigm to enhance point cloud features and refine the hand pose, which reduces irregular data access. Furthermore, we introduce a 3D hand model to the iterative correction process, which significantly improves the robustness of IPNet to occlusion and depth holes. Experiments show that IPNet outperforms state-of-the-art methods on three challenging hand datasets.

Direct observations of the atomic-molecular phase transition in the Milky Way’s nuclear wind

ABSTRACT Hundreds of high-velocity atomic gas clouds exist above and below the Galactic Centre, with some containing a molecular component. However, the origin of these clouds in the Milky Way’s wind is unclear. This paper presents new high-resolution MeerKAT observations of three atomic gas clouds and studies the relationship between the atomic and molecular phases at ∼1 pc scales. The clouds’ atomic hydrogen column densities, NH i, are less than a few × 1020 cm−2, but the two clouds closest to the Galactic Centre none the less have detectable CO emission. This implies the presence of H2 at levels of NH i at least a factor of ten lower than in the typical Galactic interstellar medium. For the cloud closest to the Galactic Centre, detectable CO coexists across the entire range of H i column densities. In contrast, for the intermediate cloud, detectable CO is heavily biased towards the highest values of NH i. The cloud most distant from the Galactic Centre has no detectable CO at similar NH i values. Moreover, we find that the two clouds with detectable CO are too molecule-rich to be in chemical equilibrium, given the depths of their atomic shielding layers, which suggests a scenario whereby these clouds consist of pre-existing molecular gas from the disc that the Galactic wind has swept up, and that is dissociating into atomic hydrogen as it flows away from the Galaxy. We estimate that entrained molecular material of this type has a ∼few − 10 Myr lifetime before photodissociating.

Cooling-driven coagulation

ABSTRACT Astrophysical gases such as the interstellar-, circumgalactic-, or intracluster-medium are commonly multiphase, which poses the question of the structure of these systems. While there are many known processes leading to fragmentation of cold gas embedded in a (turbulent) hot medium, in this work, we focus on the reverse process: coagulation. This is often seen in wind-tunnel and shearing layer simulations, where cold gas fragments spontaneously coalesce. Using 2D and 3D hydrodynamical simulations, we find that sufficiently large (≫cstcool), perturbed cold gas clouds develop pulsations which ensure cold gas mass growth over an extended period of time (≫r/cs). This mass growth efficiently accelerates hot gas which in turn can entrain cold droplets, leading to coagulation. The attractive inverse square force between cold gas droplets has interesting parallels with gravity; the ‘monopole’ is surface area rather than mass. We develop a simple analytic model which reproduces our numerical findings.

Determining Body Condition of Dairy Cows for Early Diagnosis of Physiological Diseases

The paper points out the problem with automated diagnostics of body condition in dairy cattle, including ketosis. The conducted research is aimed at determining the possibility for non-contact automated diagnostics of the cattle physiological state on a daily basis. (Research purpose) To develop an algorithm for complex operational diagnostics of the physiological state of dairy cows by their live weight and body condition. (Materials and methods) Field data were collected in 2021-2022 on the FSUE Grigoryevskoye (Yaroslavl Region), Istra Cheese Factory and Lenin Dairy State Farm (Moscow Region). A commercial 3D ToF (Time-of-Flight) camera O3D303 was used. The 3D camera is capable of calculating and displaying the Point Cloud space as a multidimensional array. The program received 144 images, 136 images passed the filtering stage, 6 images did not detect the areas of interest, because of the high level of image noise, and the sacrum was not detected. 62 cows were subject to research. (Results and discussion) The sample and the dependence are proved to be representative as the Pearson correlation coefficient equals R=0.849, which shows a strong linear relationship between the body condition score and live weight. It was determined that in 24 percent of cases the body condition score is less than the least normal one. An algorithm was developed to help veterinarians to detect the animals that need additional examination. (Conclusions) It was found that the developed algorithm helps to quickly detect ketosis in dairy cows and automatically diagnose physiological diseases at an early stage, without additional labor and monetary costs.

PO+−He collision: ab initio potential energy surface and inelastic rotational rate coefficients

ABSTRACT Computations involving quantum dynamics are performed to attain cross-sections corresponding to rotational de-excitation and excitation rates of the PO+ species including four rotational lines recently detected in the interstellar molecular clouds. New ab initio potential energy surface (PES) for PO+−He collision is constructed by using CCSD(T) method and basis set extrapolated to complete basis set limit (CBS) considering a rigid rotor approximation. The PES is then trained to create neural network (NN) model to construct an augmented surface with angular coordinates at 1° intervals. The PES has a global minimum located at $\theta =110{}^{\circ }$ and R = 3.1 Å. An analytical fitting is performed on the NN surface to obtain the first 41 radial coefficients needed to solve the equations of the coupled-channel method. The essentially precise close coupling approach is used to compute the rotational (de-)excitation cross-sections till 1400 cm−1 with rotational states converged up to 26. Further, these cross-sections are thermally averaged to get the rate coefficients for various rotational transitions till 200 K. The propensity rule favours the odd transitions (Δj = 1) for the current study. The rate for the transition 5 → 4 is found to be higher than transition 1→ 0 by a factor of 3.1 at T = 20 K that decreases to 2.1 at T = 100 K.

Computational analysis of the hydrogen dispersion in semi-confined spaces

Although green hydrogen is an appropriate clean energy alternative, hydrogen leakage and dispersion are the challenges to establishing safe and reliable hydrogen infrastructure. Released hydrogen in confined or semi-confined space may build up flammable gas clouds, which can have severe consequences for the safety of human life and property. Proper ventilation systems will help in reducing hydrogen gas accumulation. This study presents a comprehensive study to analyse hydrogen dispersion behaviour and the influence of ventilation variations on hydrogen volumetric concentration and stratification. A computational model is developed for the leakage diffusion of hydrogen in an enclosed cuboid space with roof and door ventilation. A detailed analysis is conducted to shed light on the impact of door and roof ventilation positions on forming the flammable cloud. It is observed that the displacement flow and multi-layer stratification are established in the absence of wind or imperceptible air circulation. Single-vent configurations were ineffective, when installed at the top of the leakage point, but multiple-vent arrangements incorporating door and roof vents were found to be more efficient in extracting hydrogen. However, it should be noted that not all multiple-vent arrangements may meet safety requirements. The result indicated that the optimal arrangement for minimizing the size of a flammable cloud involves placing the door vent close to the ceiling while situating the roof vent near the source of leakage. These findings will aid in devising strategies for minimizing the occurrence of flammable cloud formation and preventing hydrogen fire and explosion incidents within partially enclosed facilities.

Investigating the OH-H2 relation in diffuse Galactic clouds

Abstract We investigate the correlation between OH and H2 column densities in diffuse Galactic clouds, in order to identify potential molecular tracers of interstellar H2. For this, we analyse near-UV spectra extracted from the ESO/VLT archives towards seventeen sightlines (five of them new) with known N(H2), along with nine sightlines with no H2 information. N(OH) shows only marginal correlation with N(H2) (1020 to 2 × 1021 cm−2), at the 95 per cent confidence level. We use orthogonal distance regression analysis to obtain N(OH) /N(H2) = (1.32±0.15) × 10−7, which is ∼ 33 per cent higher than the previous estimates based on near-UV data. We also obtain N(CH) /N(H2) = (3.83±0.23) × 10−8 and a significant correlation between N(OH) and N(CH), with N(OH) = (2.61±0.19) × N(CH), both of which are consistent with previous results. Comparison with predictions of numerical models indicate that OH absorption arises from diffuse gas (nH ∼ 50 cm−3) illuminated by radiation fields ∼ 0.5–5 G0, while CH is associated with higher density of 500 cm−3. We posit that the apparent dichotomy in the properties of the diffuse clouds giving rise to OH and CH absorption could be due to either (a) the presence of multiple spectroscopically unresolved clouds along the line-of-sight, or, (b) density gradients along the line-of-sight within a single cloud.

Numerical study on the effects of bund on liquid pool spreading and vapor dispersion after a catastrophic LNG tank failure

Liquefied natural gas (LNG) storage tanks are usually equipped with bunds to provide an additional layer of protection. However, the catastrophic failure of an LNG storage tank usually results in a bund overtopping. The overtopped LNG will evaporate rapidly at ground surface to form the flammable gas cloud. Previous studies have developed computational fluid dynamics (CFD) models to investigate the ability of bunds to retain liquids; However, the models were developed based on ambient liquid, ignoring the evaporation phenomena and vapor dispersion of LNG. In this work, a multiphase CFD model which integrated with the evaporation model was proposed to simulate the complete overtopping process (including LNG overtopping, LNG spread, LNG evaporation and vapor dispersion). The data from two field experiments were used to validate the model. In addition, this paper studied a case of catastrophic failure that derived from an industrial LNG Tank. The effect of the bund configurations on the wind flow field, the overtopping fraction, the spread of LNG and the dispersion of LNG vapor cloud was analyzed. The present work can help relevant personnel to better assess the engineering risks associated with catastrophic failure of storage tanks for decision making in the process safety framework.

Supermassive black hole seeds from sub-keV dark matter

Quasars observed at redshifts z ∼ 6–7.5 are powered by supermassive black holes which are too large to have grown from early stellar remnants without efficient super-Eddington accretion. A proposal for alleviating this tension is for dust and metal-free gas clouds to have undergone a process of direct collapse, producing black hole seeds of mass M seed ∼ 105 M ⊙ around redshift z ∼ 17. For direct collapse to occur, a large flux of UV photons must exist to photodissociate molecular hydrogen, allowing the gas to cool slowly and avoid fragmentation. We investigate the possibility of sub-keV mass dark matter decaying or annihilating to produce the UV flux needed to cause direct collapse. To do so, we calculate the produced UV flux from dark matter annihilations and decays within the gas cloud's halo and compare these to the requirements of the UV spectrum found by previous hydrodynamical simulations. We find that annihilating dark matter with a mass in the range of 13.6 eV ≤ mdm ≤ 20 eV can produce the required flux while avoiding existing constraints. A non-thermally produced dark matter particle which comprises the entire dark matter abundance requires a thermally averaged cross section of 〈σv〉 ∼ 10-35 cm3/s. Alternatively, the flux could originate from a thermal relic which comprises only a fraction ∼ 10-9 of the total dark matter density. Decaying dark matter models which are unconstrained by independent astrophysical observations are unable to sufficiently suppress molecular hydrogen, except in gas clouds embedded in dark matter halos which are larger, cuspier, or more concentrated than current simulations predict. Lastly, we explore how our results could change with the inclusion of full three-dimensional effects. Notably, we demonstrate that if the H2 self-shielding is less than the conservative estimate used in this work, the range of both annihilating and decaying dark matter models which can cause direct collapse is significantly increased.

Traveling waves in an evolving interstellar gas cloud

This paper considers the possible emergence of traveling waves within an evolving interstellar gas cloud. To model this evolution, we use Euler–Poisson equations with the additional assumptions that the gas is incompressible, stratified, and self-gravitating. Within this framework, we establish that when the cloud has low density, the speed of these traveling waves is low. We suggest that the self-gravitational coalescence of embedded solid matter in the gas to form larger aggregates, such as cometary nuclei, may occur in the vicinity of wave crests where the mass density is highest. This idea is consistent with the widely agreed mechanism for planetary formation in proto-planetary disks, namely, that the accumulation of solids to form larger planetoids is initiated at the location of pressure maxima in the gas disk.

Spectroscopic survey of faint planetary-nebula nuclei – II. The subdwarf O central star of Fr 2-30

ABSTRACT Fr 2-30 = PN? G126.8−15.5 is a faint emission nebula, hosting a 14th-mag central star that we identify here for the first time. Deep Hα and [O iii] images reveal a roughly elliptical nebula with dimensions of at least 22 arcmin × 14 arcmin, fading into a surrounding network of even fainter emission. Optical spectrograms of the central star show it to have a subdwarf O spectral type, with a Gaia parallax distance of 890 pc. A model-atmosphere analysis gives parameters of $T_{\rm eff}=60\, 000$ K, log g = 6.0, and a low helium content of nHe/nH = 0.0017. The location of the central star in the log g–Teff plane is inconsistent with a post-asymptotic-giant-branch evolutionary status. Two alternatives are that it is a helium-burning post-extreme-horizontal-branch object, or a hydrogen-burning post-red-giant-branch star. In either case, the evolutionary ages are so long that a detectable planetary nebula (PN) should not be present. We find evidence for a variable radial velocity (RV), suggesting that the star is a close binary. However, there are no photometric variations, and the spectral-energy distribution rules out a companion earlier than M2 V. The RVs of the star and surrounding nebula are discordant, and the nebula lacks typical PN morphology. We suggest that Fr 2-30 is a ‘PN mimic’ – the result of a chance encounter between the hot sdO star and an interstellar cloud. However, we note the puzzling fact that there are several nuclei of genuine PNe that are known to be in evolutionary states similar to that of the Fr 2-30 central star.

Ultrafast formation dynamics of D3+ from the light-driven bimolecular reaction of the D2-D2 dimer.

The light-driven formation of trihydrogen cation has been attracting considerable attention because of its important role as an initiator of chemical reactions in interstellar clouds. To understand the formation dynamics, most previous studies focused on creating H3+ or D3+ from unimolecular reactions of various organic molecules. Here we observe and characterize the ultrafast formation dynamics of D3+ from a bimolecular reaction, using pump-probe experiments that employ ultrashort laser pulses to probe its formation from a D2-D2 dimer. Our molecular dynamics simulations provide an intuitive representation of the reaction dynamics, which agree well with the experimental observation. We also show that the emission direction of D3+ can be controlled using a tailored two-colour femtosecond laser field. The underlying control mechanism is in line with what is known from the light control of electron localization in the bond breaking of single molecules.

Code Comparison in Galaxy-scale Simulations with Resolved Supernova Feedback: Lagrangian versus Eulerian Methods

We present a suite of high-resolution simulations of an isolated dwarf galaxy using four different hydrodynamical codes: Gizmo, Arepo, Gadget, and Ramses. All codes adopt the same physical model, which includes radiative cooling, photoelectric heating, star formation, and supernova (SN) feedback. Individual SN explosions are directly resolved without resorting to subgrid models, eliminating one of the major uncertainties in cosmological simulations. We find reasonable agreement on the time-averaged star formation rates as well as the joint density–temperature distributions between all codes. However, the Lagrangian codes show significantly burstier star formation, larger SN-driven bubbles, and stronger galactic outflows compared to the Eulerian code. This is caused by the behavior in the dense, collapsing gas clouds when the Jeans length becomes unresolved: Gas in Lagrangian codes collapses to much higher densities than that in Eulerian codes, as the latter is stabilized by the minimal cell size. Therefore, more of the gas cloud is converted to stars and SNe are much more clustered in the Lagrangian models, amplifying their dynamical impact. The differences between Lagrangian and Eulerian codes can be reduced by adopting a higher star formation efficiency in Eulerian codes, which significantly enhances SN clustering in the latter. Adopting a zero SN delay time reduces burstiness in all codes, resulting in vanishing outflows as SN clustering is suppressed.

Study on CO migration characteristics and hazard potential function under ventilation after roof cutting blasting

Multiple toxic gases, such as carbon monoxide (CO), are generated by roof-cutting blasting (RCB) in the automatically formed roadway without coal pillars (AFRCP). To eliminate potential hazards in time, a ventilation model was established based on field data from Dianping Coal Mine. The spatial and temporal evolution characteristics of CO under different conditions after roof-cutting by shaped-charge blasting (SCB) and shaped-charge hydraulic blasting (SCHB), respectively, were investigated by using the Computational Fluid Dynamics (CFD) method. The results demonstrate that the CO gas cloud presents the coupling effect of movement and dilution under ventilation. The charge mainly affects the peak value of CO concentration (PVC). The air velocity affects the PVC and the CO gas cloud's over-limit time (OLT) and migration velocity. Roadway cross-sectional area and corner structure affect the PVC by influencing local air velocity. The CO hazard potential functions of the roadway after RCB were established, indicating a Gaussian-like distribution. The maximum hazard potential of SCHB was found to be 60% lower than that of SCB, and the re-entry time for personnel reduced by 36%. This study can serve as a guide for optimizing the ventilation design of roadways after RCB and contribute to the promotion of AFRCP.

What Can We Learn about Compton-thin AGN Tori from Their X-Ray Spectra?<sup>1</sup>

We have developed a Monte Carlo code for simulation of X-ray spectra of active galactic nuclei (AGN) based on a model of a clumpy obscuring torus. Using this code, we investigate the diagnostic power of X-ray spectroscopy of obscured AGN with respect to the physical properties and orientation of the torus, namely: the average column density, \(\langle N_{\textrm{H}}\rangle\), the line-of-sight column density, \(N_{\textrm{H}}\), the abundance of iron, \(A_{\textrm{Fe}}\), the clumpiness (i.e. the average number of gas clouds along the line of sight), \(\langle N\rangle\), and the viewing angle, \(\alpha\). In this first paper of a series, we consider the Compton-thin case, where both \(\langle N_{\textrm{H}}\rangle\) and \(N_{\textrm{H}}\) do not exceed \(10^{24}\) cm\({}^{-2}\). To enable quantitative comparison of the simulated spectra, we introduce five measurable spectral characteristics: the low-energy hardness ratio (ratio of the continuum fluxes in the 7–11 keV and 2–7 keV energy bands), the high-energy hardness ratio (ratio of the continuum fluxes in the 10–100 keV and 2–10 keV energy bands), the depth of the iron K absorption edge, the equivalent width of the Fe K\(\alpha\) line, and the fraction of the Fe K\(\alpha\) flux contained in the Compton shoulder. We demonstrate that by means of X-ray spectroscopy it is possible to tightly constrain \(\langle N_{\textrm{H}}\rangle\), \(N_{\textrm{H}}\) and \(A_{\textrm{Fe}}\) in the Compton-thin regime, while there is degeneracy between clumpiness and viewing direction.

Study on Overpressure Explosion of Oil and Gas Pipelines and Risk Prevention & Control Measures

In view of the flammable and explosive characteristics of oil and gas pipeline transportation medium, once it leaks, production safety accidents are easy to occur. This study uses explosions with severe consequences caused by natural gas pipeline leakage as an example. The risk factors and accident modes of oil and gas storage and transportation pipelines are analyzed; the explosion load is calculated by a scaling explosion prediction model with the TNO multi-energy method; the relationship between overpressure load and combustible gas cloud radius is studied. The methane-air explosion volume fraction of 9.5% is taken as another example, with which the overpressure attenuation law of explosion wave is obtained. Based on the above research, safety risk prevention and control measures are proposed. The research results can provide technical support for daily management and risk prevention and control of oil and gas storage and transportation pipelines.

Absorption-line Observations of and CO in Sight Lines Toward the Vela and W28 Supernova Remnants

Supernova remnants act as particle accelerators, providing the cosmic-ray protons that permeate the interstellar medium and initiate the ion–molecule reactions that drive interstellar chemistry. Enhanced fluxes of cosmic-ray protons in close proximity to supernova remnants have been inferred from observations tracing particle interactions with nearby molecular gas. Here I present observations of and CO absorption, molecules that serve as tracers of the cosmic-ray ionization rate and gas density, respectively, in sight lines toward the W28 and Vela supernova remnants. Cosmic-ray ionization rates inferred from these observations range from about 2 to 10 times the average value in Galactic diffuse clouds (∼3 × 10−16 s−1), suggesting that the gas being probed is experiencing an elevated particle flux. While it is difficult to constrain the line-of-sight locations of the absorbing gas with respect to the supernova remnants, these results are consistent with a scenario where cosmic rays are diffusing away from the acceleration site and producing enhanced ionization rates in the surrounding medium.

Experimental investigation on the effect of a barrier wall on unconfined hydrogen explosion

27 m3 unconfined hydrogen explosion experiments are conducted to investigate the effect of barrier wall on explosion characteristics. The results show that the flame propagation velocity is highly related with the development of the flame instability, not only dependent on the laminar burning velocity. In front of the wall, due to the wave reflection, the overpressure peak Pmax and positive overpressure impulse IP increase while the positive overpressure duration time tdur decreases. In the rear of the wall, due to the wave diffraction, Pmax and IP decrease while tdur increases. The time reaching overpressure peak tpeak increases on both sides of the wall. Pmax is about twice the incident overpressure on the wall surface because of the pressure reflection. The enhancement or mitigation effect of the barrier wall only works in a certain range. The mitigation effect is highly related with the relative height between gas cloud and barrier wall.

Observation of Helium in Mercury's Exosphere by PHEBUS on Bepi‐Colombo

AbstractOn 1 October 2021, Bepi‐Colombo performed its first flyby of Mercury. During the maneuver, the short wavelength channel (55–155 nm) of “Probing the Hermean Exosphere by UV Spectroscopy” (PHEBUS) was activated for a total duration of 1 hr. The helium resonance line at 58.4 nm was clearly observed during the whole sequence. At large distance from the planet, the emission was due to helium atoms in the interplanetary medium (interplanetary UV glow). Just after crossing the terminator of the planet and entering the dawn side of the exosphere, PHEBUS observed a clear additional emission due to scattering of solar photons by helium atoms in the exosphere of Mercury. The first detection of the 58.4 nm line in the exosphere of Mercury was reported by Broadfoot et al. (1976, https://doi.org/10.1029/gl003i010p00577) following the Mariner 10 flybys in 1974. The PHEBUS observation of exospheric helium emissions is the first for this element since the UVS measurements. In this paper, we present the results of our analysis of the PHEBUS data at 58.4 nm. Calibration of both instruments are compared with observations of the interplanetary glow, showing that the measurements of both instruments are accurate. However, we find that the exospheric density of helium atoms deduced from the PHEBUS data is 4.5–7.5 times lower than the previous estimate from UVS on Mariner 10. Possible explanations are considered. We show that some of the helium atoms present in the exosphere of Mercury could originate from the local interstellar cloud.

Time-conserving deduplicated data retrieval framework for the cloud computing environment

Cloud computing technology is quite inevitable in today’s smart world. The excessive utilization of data mandates updated storage space, which is highly expensive and cloud storage is the best solution to it. As charges are levied for the utilized space, data redundancy must be avoided for the effective exploitation of cloud space. Data deduplication is a technique, which removes redundant data and conserves storage, bandwidth and charges. However, data retrieval upon deduplicated data is not well explored in the existing literature. This work attempts to present an effective retrieval framework for deduplicated data in a cloud environment by presenting two protocols namely Data Outsourcing Protocol (DOP) and Data Retrieval Protocol (DRP). The retrieval performance of the proposed approach is tested and compared with the existing approaches in terms of standard performance measures. The work performance of the proposed Deduplicated Data Retrieval (DDR) framework performs better in terms of retrieval precision, recall and time conservation rates. The average precision and recall rates attained by the proposed work are 97.9% and 95.75% respectively.