Bulk Gas Research Articles

Radiative transfer of Lyman-α photons at cosmic dawn with realistic gas physics

Abstract Lyman-α photons enable the cosmic dawn 21-cm signal through a process called the Wouthuysen-Field effect. An accurate model of the signal in this epoch hinges on the accuracy of the computation of the Lyα coupling, which requires one to calculate the specific intensity of Lyα photons emitted from the first stars. Most traditional calculations of the Lyα coupling assume a delta-function scattering cross-section, as the resonant nature of the Lyα scattering makes an accurate radiative transfer (RT) solution computationally expensive. Attempts to improve upon this traditional approach using numerical RT have recently emerged. However, some of these treatments suffer from assumptions such as a uniform gas distribution, coherent scattering in the gas frame and isotropic scattering. While others which do not account for these only do so through certain schemes along with core-skipping algorithms. We present results from a self-consistent Monte Carlo RT simulations devoid of any of the assumptions in the previous work for the first time. We find that gas bulk motion is the most important effect to account for in RT resulting in an RMS difference of 37% in the 21-cm signal and anisotropic scattering being the least important effect contributing to less than 3% RMS difference in 21-cm signal. We also evaluate the 21-cm power spectrum and compare that with the traditional results at cosmic dawn. This work points the way towards higher-accuracy models to enable better inferences from future measurements.

Abatement of Volatile Organic Compounds (VOCs) and Fluorine gases by a Microwave Plasma Torch (MPT)

The use of microwave plasma torch (MPT) in the abatement of potent greenhouse and fluorinated (F-gases) gases is crucial due to their high global warming potential. The purpose of this study was the abatement of volatile organic compounds (VOCs) and carbon tetrafluoride (CF4) using specifically designed reverse vortex flow reactor (RVR) and pillar of fire reactor (POF). The RVR has properties that are crucial for their synergistic effects with the MPT, and the POF configurations showed high-efficiency combustion due to plasma radicals and a large contact area with the MPT. The study used Aspen Plus and COMSOL software to analyse the mass balance involved in the thermal decomposition of isopropyl alcohol (C₃H₈O) and CF4 and to design the RVR and POF reactors. Using MPT without hydrocarbon fuel, low-concentration C₃H₈O and CF4 were successfully destroyed in high-flow streams. The experiment on C₃H₈O showed that using a plasma power of 2kW and 1 cubic meter per minute (CMM) of bulk gas, a destruction removal efficiency (DRE) of 95% was achieved for a polluted C₃H₈O of 410 ppm. In a second experiment, a DRE of 94% was achieved for a polluted C₃H₈O of 370 ppm. The first CF4 experiment achieved a DRE of 93.3% with a 7kW plasma power and 1 CMM bulk gas polluted at 285 ppm. In the second experiment, the presence of highly reactive hydroxyl radicals (OH⁎) in steam plasma improved the DRE to 99.8% at 7kW plasma power and 100 LPM bulk polluted at 180 ppm.

Non-Idealities in adsorption thermodynamics for CO2 capture from humid natural gas using CALF-20

The focus of this article is on CO2 capture from natural gas under humid conditions using CALF-20. Configurational-Bias Monte Carlo (CBMC) simulations are used to investigate adsorption of CO2/CH4/H2O mixtures in CALF-20 with varying relative humidities in the bulk gas phase. The CBMC simulations reveal that the mixture adsorption equilibrium shows strong deviations from the estimations of the Ideal Adsorbed Solution Theory (IAST). CBMC simulations for mixture adsorption of the constituent binary pairs, CH4/H2O, and CO2/H2O, reveal that the origin of thermodynamic non-idealities stem from segregated nature of the adsorbed phase and inhomogeneous distribution of guest adsorbates within the pore landscape of CALF-20. The extent and nature of the segregation depends strongly on the % relative humidity of the bulk gas mixture.The important message that emerges from this investigation is the need to incorporate the Real Adsorbed Solution Theory (RAST) for quantitative modelling of fixed-bed adsorbers in natural gas purification with CALF-20.

Structural, electronic, and phonon properties of Gallium Sulfide (GaS)

In this study, we explore the geometric characteristics, electronic, and phonon properties, and specific heat capacity of the monolayer and bulk GaS systems. The approach relies on the density functional theory (DFT), which involves diverse atom vibrations and examines several key aspects: the energy band structures, the weighted band structure corresponding to van Hove singularities in the density of states, the phonon energy band structure where atoms dominate across different frequency ranges, and the analysis of the projected phonon density of states. On the other hand, the thermal properties at extremely low temperatures will be elucidated using in-plane and out-of-plane vibrations, phonon dispersion, and polarizations as key components of the analysis. This work holds significant importance, not only in the realm of fundamental physics but also in practical technical applications. Many of the anticipated outcomes presented in this research necessitate meticulous high-resolution experimental scrutiny for validation.

Solid-liquid interfacial nanobubble nucleation dynamics influenced by surface hydrophobicity and gas oversaturation

Over the past two decades, extensive research efforts have been devoted to exploring the existence, stability, and applications of interfacial nanobubbles (INBs). However, investigations into the microscopic nucleation process of INBs have been relatively limited. In this study, we utilized molecular dynamics simulations to elucidate the nucleation dynamics of INBs, with a particular focus on examining the influence of surface hydrophobicity and gas oversaturation. Our findings revealed a distinct preference for INBs to form on hydrophobic surfaces compared to hydrophilic ones, which agrees well with the experimental results. Temporal evolution analysis of the interfacial density of gas and liquid near the solid–liquid interface indicated a gradual enrichment of gas molecules at the hydrophobic surface, accompanied by a gradual disruption of the hydration layer, phenomena not observed on hydrophilic surfaces. The affinity of gas molecules towards the hydrophobic surface was further confirmed by potential of mean force (PMF) analysis, which demonstrated a decrease in the energy barrier and an increase in the potential well with increasing surface hydrophobicity. Moreover, increasing bulk gas supersaturation and surface hydrophobicity both contribute to shortening the INB nucleation time, primarily due to the enhanced gas enrichment rate. Further studies indicated that the gas enrichment rate had a directly proportional linear relationship with the bulk gas concentration. However, as the surface hydrophobicity increased, the gas enrichment rate initially rose rapidly and then entered a plateau phase. This may be because, when surface hydrophobicity is strong, the gas enrichment rate becomes limited by the diffusion of gas molecules in the liquid. These findings offer valuable insights into the nucleation mechanism of INBs on hydrophobic surfaces under gas oversaturation, contributing to a deeper understanding of their behavior and potential applications.

A Unified Multiscale Framework for Simulating Electrochemical Gas Evolving Reactions

The presence of gas bubbles in electrochemical systems, such as water-splitting, significantly increases overpotential and diminishes energy efficiency. High-fidelity simulation holds significant promise to gain mechanistic understanding of bubble dynamics and guide high-performance electrolytic cell design. However, the extreme length scales involved into electrochemical gas evolving systems, from sub-nanometer dictated by the electrical double layer (EDL) to a few centimeters featured by the electrolytic cell, have posed a huge challenge to enable sufficient numerical accuracy and superior computational efficiency. As a result, state-of-the-art numerical approaches either can only simulate a nanoscale computational domain or neglect the electrochemical kinetics within the EDL, impeding an in-depth understanding of how bubbles could intervene with the electrochemical process.In this work, we demonstrate a full-field simulation approach of electrochemical gas evolving reactions that can capture the electrochemical kinetics of the EDL in a centimeter-scale electrolytical cell with the presence of micro-to-millimeter scale bubbles. To resolve all characteristic length scales, the EDL is geometrically decoupled from the electrolytical cell but physically coupled with the bulk electrolyte and gas bubble through a quasi-1D treatment. As a result, the Nernst-Planck-Poisson-Boltzmann model can be rigorously solved in both the EDL and the rest of the electrolytical cell with highly affordable computational cost. Taking hydrogen evolution reaction as an example, we validated our approach by comparing with a variety of existing numerical and experimental results. For the first time, the impact of bubbles on the increase of overpotential observed in experiments can be quantitatively confirmed through numerical simulation. More notably, compared to state-of-the-art high-fidelity simulations, our approach exhibits a remarkable computational efficiency, which reduced the computational time by a factor of 100,000. This work provides a viable solution to simulate electrochemical gas evolving reactions with highly desirable numerical accuracy and unprecedented computational efficiency, which can serve as an effective tool to understand bubble dynamics and guide the design of next-generation electrolytical cells.

Influence of rice husk dosage on PM emissions during the co-firing of coal with refuse derived fuel

A self-designed drop tube furnace (DTF) was constructed to investigate the particulate matter (PM) emissions generated from blending 0–30 wt% refuse derived fuel (RDF) and 0–20 wt% rice husks (RH) with bituminous coal during co-firing. The physiochemical characteristics of PM were determined using XRD, XRF, and SEM-EDS, and the creation of the liquid components at varying temperatures was investigated using theoretical thermodynamic calculations based on fuel composition and combustion atmospheres. The results demonstrated that blending 0–30 wt% RDF with coal did not result in significant PM emissions. PM0.5 and PM2.5 yields declined by 31.5% and 39.5%, respectively, with the addition of 20 wt% RH. By solely adding RDF, more Ca-Al-Si and K/Ca-Si formed viscous surfaces or particle bodies that could capture Ca/K vapor released from the volatiles of RDF in the gas bulk. Si-rich and Al-Si species from coal were consumed and transformed into Na/K-Ca-Al-Si to enhance the production of the liquid phase by the abundant Si in the volatiles of RH. Two possible paths of mineral transformations during co-firing were discussed to prove that alkali metals and alkaline earth metals preferentially condensed on Si-rich and Al-Si species to form liquid substances and capture the vapor and grains in the gas bulk, rather than combining with nonmetallic elements to generate precursors for PM generation via the evaporation–condensation mechanism. This study contributes to the search for an efficient pathway to realize simultaneous waste utilization and greenhouse gas reduction.

Energetics of the OH radical H-abstraction reactions from simple aldehydes and their geminal diol forms.

Carbonyl compounds, especially aldehydes, emitted to the atmosphere, may suffer hydration in aerosols or water droplets in clouds. At the same time, they can react with hydroxyl radicals which may add or abstract hydrogen atoms from these species. The interplay between hydration and hydrogen abstraction is studied using density functional and quantum composite theoretical methods, both in the gas phase and in simulated bulk water. The H-abstraction from the aldehydic and geminal diol forms of formaldehyde, acetaldehyde, glycolaldehyde, glyoxal, methylglyoxal, and acrolein is studied to determine whether the substituent has any noticeable effect in the preference for the abstraction of one form or another. It is found that abstraction of the H-atom adjacent to the carbonyl group gives a more stable radical than same abstraction from the geminal diol in the case of formaldehyde, acetaldehyde, and glycolaldehyde. The presence of a delocalizing group in the Cα (a carbonyl group in glyoxal and methylglyoxal, and a vinyl group in acrolein), reverts this trend, and now the abstraction of the H-atom from the geminal diol gives more stable radicals. A further study was conducted abstracting hydrogen atoms from the other different positions in the species considered, both in the aldehydic and geminal diol forms. Only in the case of glycolaldehyde, the radical formed by H-abstraction from the -CH2OH group is more stable than any of the other radical species. Abstraction of the hydrogen atom in one of the hydroxyl groups in the geminal diol is equivalent to the addition of the •OH radical to the aldehyde. It leads, in some cases, to decomposition into a smaller radical and a neutral molecule. In these cases, some interesting theoretical differences are observed between the results in gas phase and (simulated) bulk solvent, as well as with respect to the method of calculation chosen. DFT (M06-2X, B2PLYP, PW6B95), CCSD(T), and composite (CBS-QB3, jun-ChS, SCVECV-f12) methods using Dunning basis sets and extrapolation to the CBS limit were used to study the energetics of closed shell aldehydes in their keto and geminal-diol forms, as well as the radical derived from them by hydrogen abstraction. Both gas phase and simulated bulk solvent calculations were performed, in the last case using the Polarizable Continuum Model.

Research on temperature distribution in container ship with Type-B LNG fuel tank based on CFD and analytical method

The liquefied natural gas (LNG) fuel tank in a large container ship is loaded with liquid LNG at an ultra-low temperature (-163°C), there is a significant temperature difference in the cargo hold area where the entire fuel tank is located, which will have an important impact on the steel grade design and structural safety of the cargo tank in container ship. This paper develops two heat transfer models using Computational Fluid Dynamics method (CFD method) and an analytical method to analyze the temperature distribution in a large container ship equipped with Type-B LNG fuel tank. These models incorporate the arrangement and heat transfer characteristics of LNG fuel tanks. The temperature field analysis is conducted under typical the environmental conditions specified in the Code for the Construction and Equipment of Ships Transporting Liquefied Gas in Bulk (IGC Code) and the United States Coast Guard Code (USCG Code), based on the CFD method and the analytical method, and the results of temperature field distribution are compared. Additionally, a parametric analysis of the hull temperature field is further carried out, the results show that the thermal conductivity of the insulation layer in LNG storage tanks and the types of the loaded liquid cargo have a limited impact on the final temperature field distribution in hull structure. However, the selection of steel grade in the local structure of the cargo hold, especially in the inner hull part, may lead to significant changes.

Eulerian-Eulerian-VOF multifluid modelling of liquid–gas reacting flow for hydrogen generation in an alkaline water electrolyser

Alkaline water electrolysis is a promising technology for hydrogen production. However, its efficiency drops considerably at high current densities due to the mass transfer limitation and the increase in electrical resistivity arising from the complexity of the liquid–gas reacting flow behaviour within the electrolyser cell. In this work, a computational fluid dynamics (CFD) model is developed to describe the liquid–gas reactive flow behaviour. The model integrates the Eulerian-Eulerian two-fluid model and the multifluid Volume of Fluid (VOF) model, allowing the mathematical model to capture the electrochemical reaction effect on hydrogen gas formation and bulk flow bubble behaviour. The model is validated against prior experimental results. The simulation results suggest that, at higher current densities, the electrical performances and the mass transfer rates are highly influenced by the formation of gas bubbles, which may block the active sites for the electrochemical reaction to occur. Quantitatively, at 4000 A/m2, the mass transfer rate is reduced by 50% at regions above the cathode compared to electrode region, while electrical conductivity near the flow channel wall, drops by 17% compared to the bulk liquid electrical conductivity. The predicted electrical conductivity is comparable to the Bruggemann correlation with an average relative error of less than 2%, confirming the model’s validity in predicting the reacting flow behaviour and performance of the electrolyser. The numerical model offers a cost-effective tool for insightful understanding and refining the design and operation of hydrogen generation systems.

Tidal forces in Kerr-AdS and Grey galaxies

In a recent paper (Kim et al 2023 arXiv:2305.08922 [hep-th]), it has been proposed that the endpoint of the Kerr-AdS superradiant instability is a Grey Galaxy. The conjectured solutions are supposed to be made up of a black hole with critical angular velocity in the centre of AdS, surrounded by a large flat disk of thermal bulk gas that revolves around the black hole. In the analysis of the proposed solutions so far, gravitational effects due to the black hole on the thermal gas have been neglected. A way to estimate these effects is via computing tidal forces. With this motivation, we study tidal forces on objects moving in the Kerr-AdS spacetime. To do so, we construct a parallel-transported orthonormal frame along an arbitrary timelike or null geodesic. We then specialise to the class of fast rotating geodesics lying in the equatorial plane, and estimate tidal forces on the gas in the Grey galaxies, modelling it as a collection of particles moving on timelike geodesics. We show that the tidal forces are small (and remain small even in the large mass limit), thereby providing additional support to the idea that the gas is weakly interacting with the black hole.

High Density Loading and Collisional Loss of Laser-Cooled Molecules in an Optical Trap.

We report optical trapping of laser-cooled molecules at sufficient density to observe molecule-molecule collisions for the first time in a bulk gas. SrF molecules from a red-detuned magneto-optical trap (MOT) are compressed and cooled in a blue-detuned MOT. Roughly 30% of these molecules are loaded into an optical dipole trap with peak number density n_{0}≈3×10^{10} cm^{-3} and temperature T≈40 μK. We observe two-body loss with rate coefficient β=2.7_{-0.8}^{+1.2}×10^{-10} cm^{3} s^{-1}. Achieving this density and temperature opens a path to evaporative cooling towards quantum degeneracy of laser-cooled molecules.

Mapping the intracluster medium in the era of high-resolution X-ray spectroscopy

ABSTRACT High-resolution spectroscopy in soft X-rays will open a new window to map multiphase gas in galaxy clusters and probe physics of the intracluster medium (ICM), including chemical enrichment histories, circulation of matter and energy during large-scale structure evolution, stellar and black hole feedback, halo virialization, and gas mixing processes. An eV-level spectral resolution, large field of view, and effective area are essential to separate cluster emissions from the Galactic foreground and efficiently map the cluster outskirts. Several mission concepts that meet these criteria have been proposed recently, e.g. LEM, HUBS, and Super DIOS. This theoretical study explores what information on ICM physics could be recovered with such missions and the associated challenges. We emphasize the need for a comprehensive comparison between simulations and observations to interpret the high-resolution spectroscopic observations correctly. Using Line Emission Mapper (LEM) characteristics as an example, we demonstrate that it enables the use of soft X-ray emission lines (e.g. O vii/viii and Fe-L complex) from the cluster outskirts to measure the thermodynamic, chemical, and kinematic properties of the gas up to r200 and beyond. By generating mock observations with full backgrounds, analysing their images/spectra with observational approaches, and comparing the recovered characteristics with true ones from simulations, we develop six key science drivers for future missions, including the exploration of multiphase gas in galaxy clusters (e.g. temperature fluctuations, phase-space distributions), metallicity, ICM gas bulk motions and turbulence power spectra, ICM-cosmic filament interactions, and advances for cluster cosmology.

Study on heat transport analysis and improvement method in a single CaCO3 pellet for thermochemical energy storage

CaCO3/CaO thermochemical energy storage (TCES) pellets have significant advantages in bulk energy storage density, transport, and utilization. However, severe heat transport limitations within the milli-sized CaCO3 significantly affect the TCES efficiency and economy. Currently, investigations on the effect of initial porosity, bulk gas flow velocity, and reaction rate on heat transport and methods of enhancing the heat transport inside the pellet are lacking. In this paper, we developed a mathematical model coupling calcination reaction, mass transfer, and heat transfer to reveal the effects of pellet parameters and operating conditions on heat transport and reaction conversion rate within a CaCO3 pellet. The results show that the size of the CaCO3 pellet, bulk gas temperature, and reaction rate generate the most pronounced impacts on heat transport in a single CaCO3 particle during the TCES process. Furthermore, the heat transport inside the CaCO3 pellet can be improved by appropriately increasing the bulk gas flow velocity. Finally, this paper first numerically investigates the addition of SiC as a thermal conductivity enhancer to improve the heat transport performance inside a CaCO3 pellet. This study can guide the design of high-performance CaCO3 composite pellets and inform the selection of operating conditions for subsequent reactor applications.

A 3D FRACTAL MODEL COUPLED WITH TRANSPORT AND ACTION MECHANISMS TO PREDICT THE APPARENT PERMEABILITY OF SHALE MATRIX

The permeability of shale controls gas transport in shale gas reservoirs. The shale has a complex pore structure at the nanoscale and its permeability is affected by multiple transport and action mechanisms. In this study, a 3D fractal model for predicting the apparent gas permeability of shale matrix is presented, accounting for the effects of the transport mechanisms (bulk gas transport and adsorption gas diffusion) and action mechanisms (gas adsorption, real gas properties, water film, stress dependence, and total organic carbon (TOC) content). The proposed model is validated with the published experimental data. A series of sensitivity analyses are performed to investigate the influence of fractal characteristics and action mechanisms on the apparent permeability caused by each transport mechanism. The results show that the real gas properties, water film, and stress dependence cause different effects on the total apparent permeability of shale under different fractal characteristics. The maximum pore diameter is inversely proportional to the effects of these action mechanisms, and the porosity is positively proportional to the effects of real gas properties and water film but inversely proportional to the effects of stress dependence. An increase in TOC content can cause an improvement in the total apparent permeability. Furthermore, the effects of action mechanisms on the apparent permeability caused by different transport mechanisms are differently affected by the fractal characteristics. Changes in fractal characteristics mainly affect the apparent permeability caused by slip flow in the real gas effect, slip flow and Knudsen diffusion in the water film effect, and all transport mechanisms in the stress dependence effect.

Understanding the Development and Properties of SEI in Concentrated Aqueous Electrolytes Via Scanning Electrochemical Microscopy

Solid-electrolyte interphases (SEI) are essential to the stability of high voltage lithium-ion batteries (LIBs) where they act as a protective barrier that prevents electrolyte decomposition during charge-discharge and during storage of the energy. Within emerging water-in-salt electrolytes (WISE), the SEI are thought to play a similar role in preventing electrolyte decomposition and expanding the potential window.(1, 2) The SEI reported in WISE are derived from the electrolyte ions, producing inorganic SEI (e.g. LiF) of similar thickness to non-aqueous batteries.(1) Others suggest the superconcentrated regimes promote anion reduction and shift its reduction potential at similar or more positive potentials to hydrogen evolution. However, our knowledge on the SEI found in concentrated aqueous electrolytes and their properties remains quite limited. Furthermore, WISE full cells can access >1000 cycles at high rates, but their capacities and retention are still heavily lacking compared with commercial LIBs.(2) Improving our understanding of the WISE-based SEI formation process, its stabilization, and prevention of gas evolution are key to achieving higher performing aqueous batteries.Herein, we explore the use of advanced scanning electrochemical microscopy (SECM) methods(3) to characterize an SEI within a highly concentrated K(FSA)0.6(OTf)0.4 electrolyte. Focusing on a 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) composite electrode, we use both ex situ, approach curves as well as in situ single spot measurements to analyze SEI formation (Figure 1a). The approach curves were collected before and after galvanostatic cycling by using a three-electrode cell that could easily be converted between closed (cycling) and open-cell (SECM) measurements. After cycling, we observed passivating SEI structures with electron transfer rates comparable to those found in LIBs (Figure 1b). At the same time, our results indicated the SEI deposition was discontinuous with some regions showing reactivity comparable to an uncycled electrode. We noted an increase in roughness with cycling, which could produce some of the more reactive regions exposed at the electrode surface. Thereafter, we conducted in situ measurements at a constant distance from the PTCDI surface.(4) During the first cycle, we observed a reversible/transient decrease in the feedback current at ~ -0.7 V vs. Ag/AgCl, far positive to H2 evolution (Figure 1c,d). In addition, more stable passivation was observed when the PTCDI electrode reached more negative potentials accessing the second redox process of PTCDI (Figure 1c,e). As the electrode reached potentials more negative to -1.3 V, we observed significant hydrogen evolution. Our results were further confirmed with operando electrochemical mass spectrometry (OEMS). OEMS showed similar potentials for evolving hydrogen as well as the evolution of other gases indicative of SEI formation. In all, our interfacial SECM analyses combined with traditional battery measurements and OEMS provides direct quantification of the passivating properties of the SEI as well as identification of local and bulk gas evolution that can be expanded for other emerging aqueous systems.References1 L. Suo, et al., Science, 2015, 350, 938-943.2 L. Droguet, et al., Adv. Energy Mater., 2020, 10, 2002440.3 Gossage, Z.T., et al., "Application to Batteries and Fuel Cells." Scanning Electrochemical Microscopy. CRC Press, 2022. 481-512.4 G. Zampardi, et al., RSC Advances, 2015, 5, 31166-31171. Figure 1

Exploring the Influence of the Phosphorus-Heteroatom Substitution in Nicotine on Its Electronic and Vibrational Spectroscopic Properties.

The influence of phosphorus substitution of nitrogen in heterocyclic compounds on the vibrational spectroscopy as well as frontier molecular orbitals are analyzed. Nicotine with two nitrogen atoms in its structure is taken as the sample system to be studied computationally. By replacing the nitrogen atom in one or both rings of this molecule with phosphorus, three nicotine derivatives are created. The vibrational circular dichroism and infrared spectra of these four molecules in their monomer state, as well as the assemblies up to trimers are determined. The aforementioned spectra are calculated using static quantum chemical calculations employing a cluster-weighted approach. The calculated gas phase spectra of nicotine are compared to their respective experimental spectra. It is observed that the nicotine derivatives with phosphorus in the methylpyrrolidine ring have considerably different gas phase and bulk phase vibrational circular dichroism spectra when compared to nicotine. The phosphorus substitution reduces the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital as well as altering the polarizability and reactivity of the investigated molecules.

C ii] Spectral Mapping of the Galactic Wind and Starbursting Disk of M82 with SOFIA

M82 is an archetypal starburst galaxy in the local Universe. The central burst of star formation, thought to be triggered by M82's interaction with other members in the M81 group, is driving a multiphase galaxy-scale wind away from the plane of the disk that has been studied across the electromagnetic spectrum. Here, we present new velocity-resolved observations of the [C ii] 158 μm line in the central disk and the southern outflow of M82 using the upGREAT instrument on board SOFIA. We also report the first detections of velocity-resolved (ΔV = 10 km s−1) [C ii] emission in the outflow of M82 at projected distances of ≈1–2 kpc south of the galaxy center. We compare the [C ii] line profiles to observations of CO and H i and find that likely the majority (>55%) of the [C ii] emission in the outflow is associated with the neutral atomic medium. We find that the fraction of [C ii] actually outflowing from M82 is small compared to the bulk gas outside the midplane (which may be in a halo or tidal streamers), which has important implications for observations of [C ii] outflows at higher redshift. Finally, by comparing the observed ratio of the [C ii] and CO intensities to models of photodissociation regions, we estimate that the far-ultraviolet (FUV) radiation field in the disk is ∼103.5 G 0, in agreement with previous estimates. In the outflow, however, the FUV radiation field is 2–3 orders of magnitudes lower, which may explain the high fraction of [C ii] arising from the neutral medium in the wind.

Grey Galaxies’ as an endpoint of the Kerr-AdS superradiant instability

Kerr-AdSd+1 black holes for d ≥ 3 suffer from classical superradiant instabilities over a range of masses above extremality. We conjecture that these instabilities settle down into Grey Galaxies (GGs) — a new class of coarse-grained solutions to Einstein’s equations which we construct in d = 3. Grey Galaxies are made up of a black hole with critical angular velocity ω = 1 in the ‘centre’ of AdS, surrounded by a large flat disk of thermal bulk gas that revolves around the centre of AdS at the speed of light. The gas carries a finite fraction of the total energy, as its parametrically low energy density and large radius are inversely related. GGs exist at masses that extend all the way down to the unitarity bound. Their thermodynamics is that of a weakly interacting mix of Kerr-AdS black holes and the bulk gas. Their boundary stress tensor is the sum of a smooth ‘black hole’ contribution and a peaked gas contribution that is delta function localized around the equator of the boundary sphere in the large N limit. We also construct another class of solutions with the same charges; ‘Revolving Black Holes (RBHs)’. RBHs are macroscopically charged SO(d, 2) descendants of AdS-Kerr solutions, and consist of ω = 1 black holes revolving around the centre of AdS at a fixed radial location but in a quantum wave function in the angular directions. RBH solutions are marginally entropically subdominant to GG solutions and do not constitute the endpoint of the superradiant instability. Nonetheless, we argue that supersymmetric versions of these solutions have interesting implications for the spectrum of supersymmetric states in, e.g. N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{N} $$\\end{document} = 4 Yang-Mills theory.

Discharge Randomness and Attraction Process of Epoxy Surface on Discharge Channel in SF6 Gas Under Uniform Electric Field

It is generally believed that due to the electric field distortion effect and the photoemission process of the solid surface, the discharge channel near the solid surface trends to develop along the surface than that in bulk gas. One way to improve insulation performance is to avoid the solid surface from participating in the gas discharge process. However, the mechanism of the solid surface’s effect on the gas discharge process is still unclear. In this paper, we recorded high-speed framing pictures of the discharge process in SF6 gas near the epoxy surface under lightning impulse voltage in the uniform electric field. The arc pictures show that the attraction effect of the solid surface to the discharge channel is related to the surface shape, gas gap height, and distance from the discharge channel to the solid surface. Besides, discharge randomness also plays a role, which is more obvious in the cylinder insulator than in the conical insulator, for the surface with conical shape could easily attract and arrest the discharge channel to its surface. According to the pictures of discharge process near the cylinder surface, we found that the photoemission process occurs in the streamer stage but has little effect on the attraction effect. The leader initiates after the streamer bridges the gas gap, and its random stepped walk could induce the attraction effect from the solid surface: only when the random stepped leader deflects close to the solid surface, the discharge channel could be further attracted to the solid surface by the electrostatic force, especially its normal component. The result indicates that there are three points to prevent the solid surface from participating in the gas discharge process and further improve insulation performance: choose a cylinder shape (avoid a conical shape), keep the surface away from the high electric field area where discharge may start, and reduce the normal component of the surface electric field.