Bulk Gas Research Articles

Assessment of hydrocarbon generation potential and thermal maturity of the deep offshore Lamu Basin, Kenya

In this study, the secondary well data for Cretaceous to Miocene cutting samples in four deep offshore exploration wells, i.e., Pomboo-1 in the north, Kubwa-1 in the central, Simba-1 and Kiboko-1 in the south of the deep offshore Lamu Basin were assessed for identifying source rock presence and examining thermal maturity of the source rocks. The 2D basin modelling was used to analyse the bulk gas transformation in the basin. Total organic carbon (TOC) content values for the wells range from 0.09 wt % to 2.23 wt % with an average of 0.78 wt %. The average organic richness is higher in the Upper Cretaceous (0.83 wt %) than in the Palaeogene (0.65 wt %), Lower Cretaceous (0.28 wt %) and Upper Jurassic (0.30 wt %). The S1 averages for the Upper Cretaceous are 3.76 mg HC/g rock in Pomboo-1 and 0.31mg HC/g rock in Kubwa-1. The S2 averages for the Upper Cretaceous are 5.00 mg HC/g rock in Pomboo-1 and 0.72 mg HC/g rock in Kubwa-1. Hydrogen index (HI) values vary between 4 and 512 mg HC/g TOC with an average of 157.09 mg HC/g TOC. Organic matters were identified as mixed types of II-III (oil and gas prone) and III-IV (gas prone) kerogen in the potential source rocks. The HI and S2 yield values are exceptionally high for the observed TOC values in Pomboo-1. The vitrinite reflectance and Tmax values of deep offshore Lamu Basin are in the ranges of 0.38%–0.72% and 360–441 °C, respectively. It suggests the existence of both immature and mature source rocks. Vitrinite reflectance maturity favours near coastal region in the Upper Cretaceous. These results explain why Pomboo-1, Kubwa-1, Simba-1 and Kiboko-1 wells were dry. The temperatures are still cool for hydrocarbon generation in deep offshore. The critical risk for deep offshore Lamu Basin is charge, primarily source presence, and a lack of definitive evidence of a deep-water marine source rock being present. The four wells penetrate good quality reservoir and seal rocks, but source rock presence and maturity remain the critical play risk in the deep offshore Lamu Basin.

Fire and Explosion Consequence Analysis of Occupied Buildings in an LPG Storage Facility in Southern Nigeria

The purpose of this work was to carry out an evaluation of occupied buildings from the devastating impact of an explosion in a Liquefied Petroleum Gas (LPG) bulk storage facility with the intention to provide information on blast requirements of the buildings and make layout modification as needed using the consequence-based approach. The simulation was done using DNV’s Process Hazard Analysis Software Tool (PHAST) and the process data were obtained from a process plant located in the Niger-Delta region of Nigeria. Three major scenarios; catastrophic rupture, full bore rupture was considered for a 6-inch pipe and fixed duration release of the stored LPG and propane gas using the TNO multi-energy method to determine the Maximum Credible Event on the occupied buildings within the facility From the study, the catastrophic rupture of LPG vessel #18 at 2/F weather category gave the worst impact with an overpressure effect of 0.7barg at a hazard distance of 166.959m. The thermal radiation intensity of 37.5KW/m2 due to Jet fire from the fixed duration release of Propane vessel #22 at 2/F weather category was found to produce the greatest consequence/impact at a hazard distance of 180.72m. The results from this work show that most of the occupied buildings within the location are in the vicinity of the effect zone of both explosion overpressure and Jet fire thermal radiation.

Gas permeation through nanoporous single-walled carbon nanotubes: the confinement effect

The gas permeation through nanoscale membranes like graphene has been extensively studied by experiments and empirical models. In contrast to planar membranes, the single-walled carbon nanotube has a natural confined hollow structure, which shall affect the gas permeation process. We perform molecular dynamics simulations to investigate the effect of the nanotube diameter on the gas permeation process. It is found that the permeance constant increases with the increase of the nanotube diameter, which can not be explained by existing empirical models. We generalize the three-state model to describe the diameter dependence for the permeance constant, which discloses a distinctive confinement-induced adsorption phenomenon for the gas molecule on the nanotube’s inner surface. This adsorption phenomenon effectively reduces the pressure of the bulk gas, leading to the decrease of the permeance constant. These results illustrate the importance of the adsorption within the confined space on the gas permeation process.

Disentangling catalysis and mass transport: Using diffusion measurements by pulsed field gradient NMR to reveal the microkinetics of CO oxidation over nanoporous gold

Since the first studies reporting on its surprising catalytic properties, nanoporous gold (npAu) has emerged as a novel and ever since intensively investigated type of Au based catalyst. To judge its genuine catalytic potential and to be able to optimize its use in applications, it is mandatory, however, to quantify the influence of mass transport in the porous structure on the observed catalytic rates, i.e., to study the interplay between diffusion and reaction. To this end, we used pulsed field gradient (PFG) NMR for the first time to directly determine the diffusivities of reaction gases in a nanoporous metal – in this case for CO and CO2 as species involved in low temperature CO oxidation efficiently catalyzed by npAu. By comparing the diffusion coefficients within the 20 nm pores of the material with the values in the bulk gas phase, the tortuosity of npAu’s pore system was assessable as the central geometrical parameter describing the extent to which diffusive transport in the pore system is slowed down. This knowledge allowed us in the following to disentangle the contributions of mass transport and the kinetics of the surface reaction (microkinetics). In particular, we were able to determine the rate constant and turnover frequency for low-temperature CO oxidation without previous ambiguities arising from potential transport limitations and to compare the results with other reported values. Based on the results, it was furthermore possible to predict optimized dimensions of the catalyst, resulting in minimized or even suppressed diffusion limitations. These predictions could be successfully verified, using np-Au platelets with lateral dimensions in the range of a few hundred microns. In this way, the catalytic conversion could be ramped up by 50 % and an activity level advanced which reflected the microkinetic potential of np-Au.

Methane at the gas/water interface: Molecular simulations of surface adsorption and second surface virial coefficients

Liquid surface tensions are moderated by the adsorption of species like surfactants and gases at interfaces. In order to disentangle the competing polar and nonpolar interactions that oppose/favor adsorption at a gas/water interface and gain molecular insights into the role of inter-solute interactions on moderating the surface tension, we report here molecular simulations of purely nonpolar methane adsorption onto aqueous surfaces over a broad range of temperatures (0–50 °C) and bulk gas pressures (up to ~750 bar). As expected, positive methane adsorption at the interface significantly lowers the surface tension with increasing pressure, although this effect is not without bound as plateaus/minima in the surface tension are observed near 500 bar. The excess surface adsorption of methane directly observed from simulation agrees quantitatively with those determined from the surface tension following Gibbs adsorption isotherm, giving confidence in the thermodynamic consistency of the simulation results and Gibbs’ interpretation of the effect of solute adsorption. From the simulation results we were able to evaluate surface adsorption coefficients and second surface virial coefficients for methane’s sitting at the interface. The second virial coefficients determined from simulation were found to be slightly more attractive than those predicted from statistical thermodynamic integrals for two-dimensional gases, suggesting water could help drive methane interactions in the interface. Generalizing the statistical thermodynamic integral for the second surface virial coefficient to that for a gas confined to a pseudo-two-dimensional slit, however, near quantitative agreement with the simulation results is observed, indicating water plays effectively no role. Comparisons of the simulation results with experiment are generally favorable, although the simulations appear to under predict net adsorption likely as a result of the neglect of methane polarization interactions.

Formula omitted] and [formula omitted] signatures of methane aerobically oxidized by Methylosinus trichosporium with implications for deciphering the provenance of methane gases

Aerobic oxidation of methane (MOx) is an important biologically mediated process that consumes methane in a wide range of environments. Here we report results of culture experiments with the aerobic methane-oxidizing bacterium Methylosinus trichosporium (OB3b) that are used to characterize the mass-18 isotopologue (Δ13CH3D and Δ12CH2D2) signatures of MOx in residual methane gases. MOx activity was confirmed by simultaneous decrease of methane and oxygen in the bulk gas headspace. Bulk carbon (13C/12C) and hydrogen (D/H) isotope ratios of the methane gas increased while both Δ13CH3D and Δ12CH2D2 decreased as the oxidation proceeded. The corresponding fractionation factors (α) calculated from our experimental results are 0.98485 ± 0.00006 for 13C/12C, 0.7265 ± 0.0010 for D/H, 0.7141 ± 0.0011 for 13CH3D/12CH4, and 0.4757 ± 0.0023 for 12CH2D2/12CH4. Deviations of the mass-18 fractionation factors from the Rule of the Geometric Mean (RGM) expressed as γ values are 0.9981 ± 0.0017 for 13CH3D/12CH4 and 0.9013 ± 0.0045 for 12CH2D2/12CH4. Our α and γ values suggest that while MOx fractionates 13CH3D within error of the RGM, the Δ13CH3D and Δ12CH2D2 trajectories are very sensitive to even small deviations in 13CH3D/12CH4 from the RGM. Fractionation of 12CH2D2 deviates considerably from RGM, and this causes dramatic and robust effects on the trajectories of residual methane in Δ13CH3D vs. Δ12CH2D2 space. Our models suggest that Δ13CH3D and Δ12CH2D2 could potentially mimic microbial methanogenesis signatures in an environment that exhibits a strong Rayleigh Distillation process with little to no replenishment of methane during oxidation. However, in closed or open systems where oxidation is attended by simultaneous methane production, we find that modest increases in Δ13CH3D and dramatic increases in Δ12CH2D2 are to be expected, thus resulting in isotopologue signatures distinct from microbial methanogenesis. The overall trend in these conditions suggest that methane altered by MOx is distinguishable from other methane sources in Δ13CH3D and Δ12CH2D2 space.

The Si + SO2 collision and an extended network of neutral–neutral reactions between silicon and sulphur bearing species

ABSTRACT The Si + SO2 reaction is investigated to verify its impact on the abundances of molecules with astrochemical interest, such as SiS, SiO, SO, and others. According to our results Si(3P) and SO2 react barrierlessly yielding only the monoxides SO and SiO as products. No favourable pathway has been found leading to other products, and this reaction should not contribute to SiS abundance. Furthermore, it is predicted that SiS is stable in collisions with O2, and that S(3P) + SiO2 and O(3P)+OSiS will also produce SO + SiO. Using these results and gathering further experimental and computational data from the literature, we provide an extended network of neutral–neutral reactions involving Si- and S-bearing molecules. The effects of these reactions were examined in a protostellar shock model, using the nautilus gas–grain code. This consisted in simulating the physicochemical conditions of a shocked gas evolving from (i) primeval cold core, (ii) the shock region itself, (iii) and finally the gas bulk conditions after the passage of the shock. Emphasizing on the cloud ages and including systematically these chemical reactions, we found that [SiS/H2] can be of the order of ∼10−8 in shocks that evolves from clouds of t = 1 × 106 yr, whose values are mostly affected by the SiS + O $\longrightarrow$SiO + S reaction. Perspectives on further models along with observations are discussed in the context of sources harbouring molecular outflows.

Pore-scale systematic study on the disconnection of bulk gas phase during water imbibition using visualized micromodels

When water imbibes into tight rocks, the disconnection of bulk gas phase will significantly impact the performance of gas recovery. In this work, we have conducted a systematic micromodel study on the disconnection of gas phase during water imbibition. Seven types of micromodels were designed that can geometrically mimic basic pore structures of a tight sandstone. Then, we conducted capillary-dominant imbibition experiments and analyzed the effects of pore geometry and pore-throat ratio on the transient evolutions of gas–water interfaces. Our pore-scale results reveal that snap-off and bypassing flows are the two main mechanisms that determine disconnection and entrapment of the gas phase. Moreover, we qualitatively linked the pore-scale two-phase displacements to the core-scale “permeability jail” phenomenon (i.e., nearly immobile of non-wetting and wetting phases across a wide range of saturation values). Our study will enrich the knowledge of entrapment behaviors of the gas phase during water imbibition into tight formations.

Property evolution of gas diffusion layer and performance shrink of fuel cell during operation

The last decade has seen a renewed emphasis on proton exchange membrane fuel cells. As an essential component in proton exchange membrane fuel cells, gas diffusion layer assumes significant responsibility on water management, as well as on the performance and durability of proton exchange membrane fuel cells. However, researchers have not determined what is the relationship between gas diffusion layer characteristic evolution and the mass transport shrink in proton exchange membrane fuel cells during operation. The objective of this study is to investigate how the property of the gas diffusion layer evolves during cell operation and its relationship with the mass transport of the stack. The results showed that the hydrophilicity of the gas diffusion layer surface and bulk phase increased obviously after the endurance test. The loss of hydrophobic agents and the exposure of hydrophilic surfaces are mainly responsible for this phenomenon. In addition, the structural collapse severely damages the mechanical strength of the gas diffusion layer and thus hinders the electrical conductivity and mass transfer capability of the gas diffusion layer. Loss of hydrophobicity and mechanical strength cause a serious decline in the performance of proton exchange membrane fuel cells.

Exceeding Equilibrium CO2 Conversion by Plasma-Assisted Chemical Looping

We propose and demonstrate an integrated electrified plasma-assisted chemical looping (PACL) process that yields supra-equilibrium CO2 conversions unattainable with conventional catalysis at temperatures ≪3000 K. CO2 is first dissociated inside plasma into CO/O at supra-equilibrium conversions (up to 60%) at a bulk gas temperature of 773 K and a 403 kJ/mol energy cost. Supra-equilibrium CO2 conversions (29% on average) are achieved at the reactor outlet by placing a nanostructured CeO2/Fe2O3 oxygen scavenger, prereduced by H2 plasma, downstream of the plasma zone, to capture produced oxygen species and suppress CO/O recombination. Without plasma-material synergy, such an average CO2 conversion can only be attained at temperatures ≥ 2775 K, according to chemical equilibrium calculations. This concept of plasma-assisted chemical looping allows reaching 3-fold higher conversions than state-of-the-art plasma technologies.

The 3D Direct Simulation Monte Carlo Study of Europa’s Gas Plume

Europa has been spotted as having water outgassing activities by space- and ground-based telescopes as well as reanalysis of the Galileo data. We adopt a 3D Direct Simulation Monte Carlo (DSMC) model to investigate the observed plume characteristics of Europa assuming that supersonic expansion originated from the subsurface vent. With a parametric study of the total gas production rate and initial gas bulk velocity, the gas number density, temperature and velocity information of the outgassing plumes from various case studies were derived. Our results show that the plume gases experience acceleration through mutual collisions and adiabatic cooling when exiting from the surface. The central part of the plume with relatively large gas production rates (1029 and 1030 H2O s−1) was found to sustain thermal equilibrium and near continuum condition. Column density maps integrated along two different viewing angles are presented to demonstrate the importance of the projection effect on remote sensing diagnostics. Finally, the density profiles at different altitudes are provided to prepare for observations of Europa’s plumes including upcoming spacecraft missions such as JUICE and Europa Clipper.

Kinematic Decomposition of the H i Gaseous Component in the Large Magellanic Cloud

Abstract We perform a profile analysis of the combined H i data cube of the Large Magellanic Cloud (LMC) from observations with the Australia Telescope Compact Array and the Parkes radio telescope. For the profile analysis, we use a newly developed algorithm that decomposes individual line profiles into an optimal number of Gaussian components based on a Bayesian nested sampling. The decomposed Gaussian components are then classified into kinematically cold, warm, and hot gas components based on their velocity dispersion. The estimated masses of the kinematically cold, warm, and hot gas components are ∼12.2%, ∼58.3%, and ∼29.5% of the total H i mass of the LMC, respectively. Our analysis reveals the highly complex H i structure and kinematics of the LMC that are seen in previous studies but in a more quantitative manner. We also extract the undisturbed H i gas bulk motions and derive new H i gas bulk rotation curves of the LMC by applying a 2D tilted-ring analysis. In contrast to previously derived H i rotation curves, the newly derived bulk rotation curves are much more consistent with the carbon star kinematics, with rotation velocity linearly increasing in the inner part and reaching a maximum of ∼60 km s−1 at the outermost measured radius. By comparing the lower bulk rotation curves with previous studies, we conclude that there is a lower dynamical contribution of dark matter in the central part of the LMC.

An Experimental Study of In-Cylinder Heat Transfer from a Pressurized Motored Engine with Varying Peak Bulk Gas Temperatures

<div class="section abstract"><div class="htmlview paragraph">The variation of in-cylinder heat transfer with parameters such as engine speed, air-to-fuel ratio, coolant temperature and compression ratio were frequently studied in classical research. These experimentally-obtained relationships are important for improving in-cylinder heat transfer models, essential in developing CO<sub>2</sub> reducing strategies. In this publication, a 2.0 liter compression ignition engine was tested in the pressurized motored configuration. This developed experimental setup allowed testing of the engine at speeds ranging between 1400 rpm and 3000 rpm, with peak in-cylinder gas pressures from 40 bar to 100 bar. The engine was motored using different gas compositions chosen specifically to have ratios of specific heats of 1.40, 1.50, 1.60 and 1.67 at room temperature. This enabled motored testing with peak in-cylinder bulk gas temperatures ranging from 700 K to 1500 K. This wide variation of peak bulk gas temperature was achievable even at constant peak in-cylinder gas pressure, which gave the possibility of varying the thermal load of the engine independently from the gas pressure load. This experimental setup offered the repeatability and robustness of motored testing, with the benefit of a fired-representative gas pressure and thermal load. Throughout the test matrix, the engine was instrumented with eroding surface thermocouples at two locations in the cylinder head; at the cylinder central axis, and at the periphery in the squish region. The steady-state and transient components of heat flux were investigated separately, along with the average surface temperature and its swing. The transient component of heat flux was computed using the Impulse Response method, coupled with a two-dimensional finite element model of the eroding thermocouples, as presented in SAE 2021-24-0018. This method takes into account the two-dimensional nature of heat flux through the thermocouples and hence presents a more robust analysis than the more common one-dimensional treatment using the Fast-Fourier Transform method.</div></div>

A 2–3 mm high-resolution molecular line survey towards the centre of the nearby spiral galaxy NGC 6946

The complex physical, kinematic, and chemical properties of galaxy centres make them interesting environments to examine with molecular line emission. We present new 2 − 4″ (∼75 − 150 pc at 7.7 Mpc) observations at 2 and 3 mm covering the central 50″ (∼1.9 kpc) of the nearby double-barred spiral galaxy NGC 6946 obtained with the IRAM Plateau de Bure Interferometer. We detect spectral lines from ten molecules: CO, HCN, HCO+, HNC, CS, HC3N, N2H+, C2H, CH3OH, and H2CO. We complemented these with published 1 mm CO observations and 33 GHz continuum observations to explore the star formation rate surface density ΣSFRon 150 pc scales. In this paper, we analyse regions associated with the inner bar of NGC 6946 – the nuclear region (NUC), the northern (NBE), and southern inner bar end (SBE) and we focus on short-spacing corrected bulk (CO) and dense gas tracers (HCN, HCO+, and HNC). We find that HCO+correlates best with ΣSFR, but the dense gas fraction (fdense) and star formation efficiency of the dense gas (SFEdense) fits show different behaviours than expected from large-scale disc observations. The SBE has a higher ΣSFR,fdense, and shocked gas fraction than the NBE. We examine line ratio diagnostics and find a higher CO(2−1)/CO(1−0) ratio towards NBE than for the NUC. Moreover, comparison with existing extragalactic datasets suggests that using the HCN/HNC ratio to probe kinetic temperatures is not suitable on kiloparsec and sub-kiloparsec scales in extragalactic regions. Lastly, our study shows that the HCO+/HCN ratio might not be a unique indicator to diagnose AGN activity in galaxies.

Sensitivity study of coupled chemical-CFD simulations for analyzing aluminum-clad spent nuclear fuel storage in sealed canisters

The United States Department of Energy (DOE) manages over 50 Metric Tons Heavy Metal (MTHM) of aluminum-clad spent nuclear fuel. One main source for DOE’s Aluminum-clad spent nuclear fuel (ASNF) inventory is the advanced test reactor (ATR) at the INL site, which makes this fuel of particular interest for storage scenarios. Road-ready and final disposition packaging configurations for the ATR fuel dictates storage within helium-backfilled, sealed DOE standard canisters. The conditions within these sealed canisters for extended (greater than50 year dry) storage is of interest. To further this goal, a three-dimensional (3D) multi-physics computational fluid dynamics (CFD) model is developed of the sealed DOE standard canisters. This 3D CFD model is one-way coupled with bulk gas radiolysis reactions considering sealed canisters with inert gas and possible trace amounts of air and water vapor. This study looks at the evolution of the thermal history of the canisters over a 50 year time period with a coupling to the chemical reactions occurring from radiolytic breakdown of residual water. A sensitivity study is then carried out over the parameters of the model including the fuel decay heat, residual water content, sealed pressure, canister external temperature, and canister emissivity. In pure helium, hydrogen generation rates are low, under 10 ppm, but hydrogen generation rates are affected greatly by the presence of even 1% residual air, increasing by 50-plus-fold, and nitric acid generation with residual air also occurs ranging from 500 to 4000 ppm after 50 years. The fuel decay heat and the residual water content show the most importance in the generation of hydrogen gas in pure air, and for nitric acid with a residual air condition. External temperature, canister emissivity and sealed pressure all show minor sensitivity effects to the generation of potentially harmful species.

The evolution of temperature and density structures of OB cluster-forming molecular clumps

Context. OB star clusters originate from parsec-scale massive molecular clumps, while individual stars may form in ≲0.1 pc scale dense cores. The thermal properties of the clump gas are key factors governing the fragmentation process, and are closely affected by gas dynamics and feedback of forming stars. Aims. We aim to understand the evolution of temperature and density structures on the intermediate-scale (≲0.1–1 pc) extended gas of massive clumps. This gas mass reservoir is critical for the formation of OB clusters, due to their extended inflow activities and intense thermal feedback during and after formation. Methods. We performed ~0.1 pc resolution observations of multiple molecular line tracers (e.g., CH3CCH, H2CS, CH3CN, CH3OH) that cover a wide range of excitation conditions, toward a sample of eight massive clumps. The sample covers different stages of evolution, and includes infrared-weak clumps and sources that are already hosting an HII region, spanning a wide luminosity-to-mass ratio (L∕M) range from ~1 to ~100 (L⊙/M⊙). Based on various radiative transfer models, we constrain the gas temperature and density structures and establish an evolutionary picture, aided by a spatially dependent virial analysis and abundance ratios of multiple species. Results. We determine temperature profiles varying in the range 30–200 K over a continuous scale, from the center of the clumps out to 0.3–0.4 pc radii. The clumps’ radial gas density profiles, described by radial power laws with slopes between −0.6 and ~−1.5, are steeper for more evolved sources, as suggested by results based on dust continuum, representing the bulk of the gas (~104 cm−3), and on CH3OH lines probing the dense gas (≳106–108 cm−3) regime. The density contrast between the dense gas and the bulk gas increases with evolution, and may be indicative of spatially and temporally varying star formation efficiencies. The radial profiles of the virial parameter show a global variation toward a sub-virial state as the clump evolves. The linewidths probed by multiple tracers decline with increasing radius around the central core region and increase in the outer envelope, with a slope shallower than the case of the supersonic turbulence (σv ∝ r0.5) and the subsonic Kolmogorov scaling (σv ∝ r0.33). In the context of evolutionary indicators for massive clumps, we also find that the abundance ratios of [CCH]/[CH3OH] and [CH3CN]/[CH3OH] show correlations with clump L∕M.

The carrier mobility of monolayer and bulk GaS: from first-principles calculations.

Metal chalcogenides have become popular materials for next-generation electronic devices due to their wide band gap and excellent transport properties. Specifically, two-dimensional metal chalcogenides also have outstanding physical properties. For electronic devices, the carrier mobility is a key parameter because it affects the material conductivity and the response time. As a member of metal chalcogenides, GaS has attracted the attention of scholars. In this work, by using first principles calculations and the Wannier function interpolation, the electronic and phonon properties, the electron-phonon interaction, the scattering rate, and the carrier mobility of monolayer and bulk GaS are systematically studied. The results show that GaS is a semiconductor and both monolayer and bulk GaS are dynamically stable. The LO phonon modes at long wavelengths strongly affect the carrier migration in GaS. We give the carrier mobility of monolayer and bulk GaS as a function of temperature (100 < K < 500). In addition, we compare the carrier mobility of GaS with several other metal chalcogenides (monolayer and bulk InSe, monolayer GeS, and monolayer GeSe) at 300 K. The results show that an increase in temperature leads to a decrease in the carrier mobility and the electron (hole) mobility of monolayer and bulk GaS is 10.85 cm2 V-1 s-1 (0.22 cm2 V-1 s-1) and 1229.79 cm2 V-1 s-1 (9.28 cm2 V-1 s-1), respectively. By comparing with the carrier mobility of other chalcogenides, we can find that the electron mobility of bulk GaS is the highest, which indicates that bulk GaS has high application potential.

Dynamically regulated star formation in the strongly interacting Taffy galaxies

The Taffy system stands out as one of the strongest gas-rich galaxy mergers with little star formation (SF) activity. We study the causes of this SF inefficiency by observing with the IRAM 30m telescope the line emission of several species in 6 positions. We report clear detections of tracers of bulk (12CO and 13CO) and dense (HCN and HCO+) molecular gas in all regions, as well as evidence for shocks (SiO J=2–1) over the intergalactic bridge. Our observations not only confirm the SF inefficiency of the bulk gas, but they also show that the SF efficiency of the dense gas phase is abnormally low too (∼1 dex below ULIRGs). The dense gas fraction (∝ HCN/CO) only shows small variations across the entire system, with a typical value of 4%. Although this fraction is somewhat low compared to other interacting/merging systems, it is similar to the values measured in the disk of nearby, normal star-forming galaxies. Finally, we use the outstanding properties of the Taffy system to place constraints on some of the turbulence-regulated SF models from the literature.

Characterizing the bulk and turbulent gas motions in galaxy clusters

The most massive halos of matter in the Universe grow via accretion and merger events throughout cosmic times. These violent processes generate shocks at many scales and induce large-scale bulk and turbulent motions. These processes inject kinetic energy at large scales, which is transported to the viscous dissipation scales, contributing to the overall heating and virialisation of the halo, and acting as a source of non-thermal pressure in the intra-cluster medium. Characterizing the physical properties of these gas motions will help us to better understand the assembly of massive halos, hence the formation and the evolution of these large-scale structures. We base this characterization on the study of the X-ray and Sunyaev-Zel’dovich effect brightness fluctuations. Our work relies on three complementary samples covering a wide range of red-shifts, masses and dynamical states of clusters. We present the results of our X-ray analysis for the low redshift sample, X-COP, and a subsample of higher redshift clusters. We investigate the derived properties according to the dynamical state of our clusters, and the possibility of a self-similar behaviour based on the reconstructed gas motions power-spectra and the correlation with various morphological indicators.

Nanoscale gas accumulation at solid-liquid interfaces: a molecular dynamics study.

The development of the interfacial gas enrichment layer at the solid-liquid interface is coupled with the stability of surface nanobubbles. Depending upon the concentration of gas molecules, solid-liquid-gas interaction strengths, and other thermodynamic parameters, gas molecules can take several different forms such as dense gas layer, bulk and surface nanobubble, and other gaseous domains. Using molecular dynamics simulations we study the characteristics of gas accumulation into a dense gas layer, surface nanobubble and local gas aggregation at the graphene-water interface with no pinning sites. We find that gas molecules can migrate over the solid surface and can collect together to take the morphological form of a surface nanobubble. The developed nanobubble is mobile and can move over the homogeneous hydrophobic solid surface without losing its shape. We find that the gas adsorption on surfaces in the presence of a solvent is strongly affected by the wetting characteristics of the solid. In the absence of a solvent, gas adsorption is found to be universal for all surface types. Individual gas adsorption is found to be prominent and occurs in a short period, and is essential for the stability of the formed gaseous domains. Simulation results show gas adsorption density on surfaces to have a strong dependence on the solid-liquid interaction parameter than on solid-gas interaction strength.