Tracer Gas Research Articles

Effect of rearing conditions on fatty acid allocation during flight in nectivorous lepidopteran Mythimna unipuncta

Insect species that are nectivorous as adults acquire essential fatty acids almost exclusively from host plants during larval development. Thus, as essential fatty acids are important for a number of different biological processes, adult allocation of this limited resource may result in important trade-offs. Most lepidopteran species that migrate do so as sexually immature adults, so essential fatty acids used for migratory flight would not be available for subsequent reproduction. Using the true armyworm, Mythimna unipuncta, as a model system we analyzed fat body samples to test the hypothesis that environmental cues would influence the use of essential fatty acids during migratory flight. We used diets manipulated isotopically to trace origins and use of stored lipids and used chromatographic analyses to determine fatty acid composition. In the first experiments, 5-day old moths that had been reared in summer or fall (migratory) conditions and were force flown for different lengths of time (0–6 h) after which samples of the fat body were analyzed. Rearing conditions did not affect fatty acid loading however patterns of use during flight differed with essential fatty acids being conserved under fall but not summer conditions. As migratory flight can take several days, we repeated the experiment when 5-day old moths were flown for 8 h each day for up to 5 days. Some moths were provided access to sugar water after each flight while others were only given water or only given sugar water once. When sugar water was readily or sporadically available, moths reared under fall conditions conserved their essential fatty acids indicating that the environmental cues responsible for the onset of migratory flight result in physiological changes that modify lipid use. However, when moths had only water, the essential fatty acids were not conserved, highlighting the importance of nectar availability at stopovers for the conservation essential fatty acids during migration. Isotopic analysis of the moth fat body indicated a large contribution of adult-derived diet to lipids used as fuel. The implications of using isotopic approaches to other flight studies and future research on differential resource allocation in winged monomorphic migratory insects are discussed. Summary statement: Isotopic tracing methods and gas chromatography were used to demonstrate that environmental cues can impact patterns of fatty acid use in true armyworm moths. In particular, essential fatty acids are conserved during migratory flight. However, availability of adult food sources will determine the degree to which essential fatty acids are conserved.

Beef Steers and Enteric Methane: Reducing Emissions by Managing Forage Diet Fiber Content.

Understanding the methane (CH4) emissions that are produced by enteric fermentation is one of the main problems to be solved for livestock, due to their GHG effects. These emissions are affected by the quantity and quality of their diets, thus, it is key to accurately define the intake and fiber content (NDF) of these forage diets. On the other hand, different emission prediction equations have been developed; however, there are scarce and uncertain results regarding their evaluation of the emissions that have been observed in forage diets. Therefore, the objectives of this study were to evaluate the effect of the NDF content of a forage diet on CH4 enteric emissions, and to evaluate the ability of models to predict the emissions from the animals that are consuming these forage diets. In total, thirty-six Angus steers (x¯ = 437 kg live weight) aged 18 months, blocked by live weight and placed in three automated feeding pens, were used to measure the enteric CH4. The animals were randomly assigned to two forage diets (n = 18), with moderate (<50%, MF) and high (>50%, HF) NDF contents. Their dry matter intake was recorded individually, and the CH4 emissions were measured using the SF6 tracer gas technique. For the model evaluation, six prediction equations were compared with 29 studies (n = 97 observations), analyzing the accuracy and precision of their estimates. The emission intensities per unit of DMI, per ADG, and per gross energy intake were significantly lower (p < 0.05) in the animals consuming the MF diet than in the animals consuming the HF diet (21.7 vs. 23.7 g CH4/kg DMI, 342 vs. 660 g CH4/kg ADG, and 6.7% vs. 7.5%, respectively), but there were no differences in the absolute emissions (p > 0.05). The best performing model was the IPCC 2006 model (r2 = 0.7, RMSE = 74.04). These results show that reducing the NDF content of a forage diet by at least 10% (52 g/kg DM) reduces the intensity of the g CH4/kg DMI by up to 8%, and that of the g CH4/kg ADG by almost half. The use of the IPCC 2006 model is suitable for estimating the CH4 emissions from animals consuming forage-based diets.

Post-LOCA control room dose analysis for Maanshan NPP using the AST methodology

Abstract To address the issue identified in USNRC’s Generic Letter (GL) 2003-01 that the unfiltered air in-leakage rate through plant’s control room envelope during design basis accident may exceed that assumed in the licensing analysis and thus threat the control room habitability, the control room envelope unfiltered in-leakage Tracer Gas Test (TGT) for Maanshan nuclear power plant (NPP) has been performed in 2020. For future applications, an improved control room dose analysis approach using Alternative Source Terms (AST) has been developed in present study to check whether the TGT results meet regulatory limits and have sufficient safety margins. The AST method follows Regulatory Guide 1.183 (RG 1.183) and the TGT results must be fulfilled the total effective dose criteria set forth in 10 CFR 50.67. Based on the AST approach and the TGT results, the control room personnel dose for Maanshan NPP during Loss of Coolant Accident (LOCA) is 14.35 mSv, and the safety margin is 71.3%. It is sufficient to cover the effects of structural ageing and changes in meteorological data during the control room habitability reassessment and the analysis uncertainty.

Analysis of single-sided ventilation flows of a generic isolated building using particle tracking method in LES simulation

The main objective of this study is to investigate the airflow patterns in single-sided ventilation of isolated buildings in which the ventilation rate can not be easily predicted by the conventional Orifice equation. The research focuses on buildings with two openings located either at the front or back external wall, with building aspect ratios of 1:1 and 1:2.The study utilizes Large Eddy Simulation (LES) with the particle tracking technique validated by velocity data obtained from a wind tunnel experiment. Ventilation performance is evaluated by Airflow Rate (AFR) and Purging Flow Rate (PFR). AFR was obtained based on the instantaneous velocity over the openings, and PFR was determined by the tracer gas method. The results show that the influence of pulsation flow and eddy penetration both exist in single-sided ventilation. The comparison of AFR and PFR indicates part of the airflow through the opening does not contribute to effectively removing the indoor contaminants, which is quantitively evaluated by ventilation efficiency (εv) defined as the ratio of PFR and AFR. In order to explicitly observe and depict the airflow, the massless particles were emitted at the opening, and the trajectories were analysed. The Probability Density Function (PDF) of indoor residence and indoor travel distance was calculated. The high probability of short indoor travel distance and the residence time, which is mainly caused by the eddy at the openings and time-variant pulsation flow, can explain the difference between AFR and PFR.

Deep learning models of the discrete component of the Galactic interstellar γ -ray emission

A significant point-like component from the small scale (or discrete) structure in the H2 interstellar gas might be present in the Fermi-LAT data, but modeling this emission relies on observations of rare gas tracers only available in limited regions of the sky. Identifying this contribution is important to discriminate gamma-ray point sources from interstellar gas, and to better characterize extended gamma-ray sources. We design and train convolutional neural networks to predict this emission where observations of these rare tracers do not exist and discuss the impact of this component on the analysis of the Fermi-LAT data. In particular, we evaluate prospects to exploit this methodology in the characterization of the Fermi-LAT Galactic center excess through accurate modeling of point-like structures in the data to help distinguish between a point-like or smooth nature for the excess. We show that deep learning may be effectively employed to model the gamma-ray emission traced by these rare H2 proxies within statistical significance in data-rich regions, supporting prospects to employ these methods in yet unobserved regions.

The role of near-façade flow in wind-dominant single-sided natural ventilation for an isolated three-storey building: An LES study

Wind-driven single-sided ventilation is present in many existing buildings globally, and its performance can be unreliable and challenging to improve. To address these performance challenges, a better understanding of the interconnected relationship between the external and internal flows is required. Therefore, a detailed assessment of this type of natural ventilation is vital. A detailed CFD analysis of wind-dominant single-sided natural ventilation is presented by adopting the Large Eddy Simulation method, validated using previous wind tunnel studies. An isolated cube, representing a three-storey building, was used to investigate four case studies with different opening positions on the building façade. The presence of parallel flow near the building façade and the effect this has, both on the structure of the flow at the opening and the internal secondary flow, is investigated. Results demonstrate that a mixing layer jet of air is the main structure of the flow at the opening. The flow characteristics of this jet are a function of how the external near-façade flow interacts with the building. It can be deflected or attenuated by the near-façade fluctuating pressure and vortex structures close to the opening. Tracer gas decay results show that only 3/5 of the flow at the opening contributes to effective ventilation in this type of natural ventilation. Comparisons between the ventilation rates for openings at different positions on the building façade demonstrate the importance of the pressure role at the opening in single-sided natural ventilation.

Retention of noble and rare isotope gases in plasma-facing components – Experience from the JET tokamak with the ITER-like wall

Plasma edge cooling, ion cyclotron wall conditioning and disruption mitigation techniques involve massive gas injection (by puffs or pellets) to the torus. A certain fraction remains in plasma-facing components (PFC) due to co-deposition and implantation. An uncontrolled release/desorption of such retained species affects the stability of plasma operation. The aim of this work was to determine the lateral and depth distribution of noble (3He, 4He, Ne, Ar), seeded (N2, Ne, Ar) and tracer gases (15N, 18O) in PFC retrieved from the JET tokamak with the ITER-Like Wall (JET-ILW) after three experimental campaigns (ILW-1, ILW-2, ILW-3). Results regarding the retention of those gases are shown as well as a comparison to the deuterium retention in the studied areas. Heavy ion elastic recoil detection analysis was used, being the only technique capable of detection and quantitative assessment of all elements, especially low-Z isotopes. Helium was found on the divertor Tile 5, locally up to 44·1015 3He cm−2 and 12·1015 4He cm−2, and on the limiters as well. Neon was found in two positions on the limiters, with up to 10·1015 Ne cm−2 and the 15N tracer on Be limiters exposed to ILW-3. A correlation of N retention with the N seeding rates for each campaign has also been found.

Mitigation of breathing contaminants: Exhaust location optimization for indoor space with impinging jet ventilation supply

Densely occupied spaces (e.g., classrooms) are generally over-crowded and pose a high risk of cross-infection during the pandemic of COVID-19. Among various ventilation systems, impinging jet ventilation (IJV) system might be promising for such spaces. However, the exhaust location of the IJV system used for densely occupied classrooms is unclear. This study aims to investigate the effects of exhaust location on the removal of exhaled contaminants in a classroom (15 × 7 × 5 m3) occupied by 50 students. Exhaled contaminants are modeled by a tracer gas released at the top of each manikin. The reference case has three exhausts evenly distributed in the ceiling. The results indicate that: a) a recirculation airflow entraining exhaled contaminants exists above the occupied zone; b) this recirculation air flow entrains contaminants and accumulates them at the upper part of the room near the diffuser; c) locating merely one exhaust on the same side of the supply diffuser leads to the best indoor air quality, i.e., it reduces the mean age of air from 278 s to 243 s, the mass fraction of CO2 from 753 ppm to 726 ppm, and the concentration of tracer gas from 305 ppm to 266 ppm; d) this layout still performs the best when the supply velocity drops to 0.5 m/s. It is worth noting that the proposed layout has fewer exhausts than the reference case but performs better. These results conclude that the exhaust for large spaces is not evenly distributed but depends on the indoor airflow pattern: the key is locating the exhaust near the region with high contaminant concentration. Factors determining the recirculation airflow are suggested to be further studied.

The JCMT nearby galaxies legacy survey: SCUBA-2 observations of nearby galaxies

ABSTRACT We present 850 $\mu$m observations of a sample of 8 nearby spiral galaxies, made using the SCUBA-2 camera on the James Clerk Maxwell Telescope (JCMT) as part of the JCMT Nearby Galaxies Legacy Survey (NGLS). We corrected our data for the presence of the 12CO J = 3 → 2 line in the SCUBA-2 850 $\mu$m bandwidth using NGLS HARP data, finding a typical 12CO contribution of ∼20 per cent. We measured dust column densities, temperatures, and opacity indices by fitting spectral energy distributions constructed from SCUBA-2 and archival Herschel observations, and used archival GALEX and Spitzer data to make maps of surface density of star formation ($\Sigma _{\small {\rm SFR}}$). Typically, comparing SCUBA-2-derived H2 surface densities ($\Sigma _{\rm H_2}$) to $\Sigma _{\small {\rm SFR}}$ gives shallow star formation law indices within galaxies, with SCUBA-2-derived values typically being sublinear and Herschel-derived values typically being broadly linear. This difference is likely due to the effects of atmospheric filtering on the SCUBA-2 data. Comparing the mean values of $\Sigma _{\rm H_2}$ and $\Sigma _{\small {\rm SFR}}$ of the galaxies in our sample returns a steeper star formation law index, broadly consistent with both the Kennicutt–Schmidt value of 1.4 and linearity. Our results show that a SCUBA-2 detection is a good predictor of star formation. We suggest that Herschel emission traces gas in regions which will form stars on time-scales ∼5 − 100 Myr, comparable to the star formation time-scale traced by GALEX and Spitzer data, while SCUBA-2 preferentially traces the densest gas within these regions, which likely forms stars on shorter time-scales.

Examining the decline in the C iv content of the Universe over 4.3 ≲ z ≲ 6.3 using the E-XQR-30 sample

ABSTRACT Intervening C iv absorbers are key tracers of metal-enriched gas in galaxy haloes over cosmic time. Previous studies suggest that the C iv cosmic mass density ($\Omega _{\rm C \, \small {IV}}$) decreases slowly over 1.5 $\lesssim \, z\lesssim$ 5 before declining rapidly at z ≳ 5, but the cause of this downturn is poorly understood. We characterize the $\Omega _{\rm C \, \small {IV}}$ evolution over 4.3 ≲ z ≲ 6.3 using 260 absorbers found in 42 XSHOOTER spectra of z ∼ 6 quasars, of which 30 come from the ESO Large Program XQR-30. The large sample enables us to robustly constrain the rate and timing of the downturn. We find that $\Omega _{\rm C \, \small {IV}}$ decreases by a factor of 4.8 ± 2.0 over the ∼300 Myr interval between z ∼ 4.7 and ∼5.8. The slope of the column density (log N) distribution function does not change, suggesting that C iv absorption is suppressed approximately uniformly across 13.2 ≤ log N/cm−2 &amp;lt; 15.0. Assuming that the carbon content of galaxy haloes evolves as the integral of the cosmic star formation rate density (with some delay due to stellar lifetimes and outflow travel times), we show that chemical evolution alone could plausibly explain the fast decline in $\Omega _{\rm C \, \small {IV}}$ over 4.3 ≲ z ≲ 6.3. However, the C iv/C ii ratio decreases at the highest redshifts, so the accelerated decline in $\Omega _{\rm C \, \small {IV}}$ at z ≳ 5 may be more naturally explained by rapid changes in the gas ionization state driven by evolution of the UV background towards the end of hydrogen reionization.

Numerical simulation study on the influence of air leakage on oxygen concentration in goafs of fully mechanized caving mining with shallow buried and large mining height

In order to reveal the influence of air leakage on oxygen concentration in goafs of fully mechanized caving mining with a shallow buried and high mining height, the air leakage of No.122108 working face in Caojiatan coal mine in different seasons was tested by the SF6 tracer gas test method. Based on the result of the air leakage test, the “three zones” of spontaneous combustion in the goaf were simulated using Ansys Fluent fluid dynamics software, and the simulated result was compared with that of the field test. The result shows that the vertical air leakage of the working face is serious, the wind speed is high, and the air leakage rate is up to 86.96%. The air leakage rate is higher in winter and lower in summer. The air leakage intensity decreases from the air inlet side to the air return side through the middle of the goaf. The range of the oxidation heating zone of the goaf is 98–245 m on the air inlet side and 33–96 m on the air return side. The numerical simulation result is well consistent with the field test data. The research conclusion can guide fire prevention and the extinguishing of No.122108 working face and lay a foundation for the prevention and control of spontaneous fire in goafs of fully mechanized caving mining with a shallow buried and high mining height.

Does the HCN/CO Ratio Trace the Star-forming Fraction of Gas? I. A Comparison with Analytical Models of Star Formation

We use archival ALMA observations of the HCN and CO J = 1–0 transitions, in addition to the radio continuum at 93 GHz, to assess the relation between dense gas, star formation, and gas dynamics in 10 nearby (ultra)luminous IR galaxies (U)LIRGs and late-type galaxy centers. We frame our results in the context of turbulent and gravoturbulent models of star formation to assess whether the HCN/CO ratio tracks the gravitationally bound star-forming gas in molecular clouds (f grav) at subkiloparsec scales in nearby galaxies. We confirm that the HCN/CO ratio is a tracer of gas above n SF ≈ 104.5 cm−3, but the subkiloparsec variations in HCN/CO do not universally track f grav. We find strong evidence for the use of varying star formation density-threshold models, which are able to reproduce trends observed in t dep and ϵ ff that fixed-threshold models do not reproduce. Composite lognormal and power-law models outperform pure lognormal models in reproducing the observed trends, even when a fixed power-law slope is used. The ability of the composite models to better reproduce the star formation properties of the gas provides additional indirect evidence that the star formation efficiency per freefall time is proportional to the fraction of gravitationally bound gas.

Central molecular zones in galaxies: Multitransition survey of dense gas tracers HCN, HNC, and HCO+

New measurements of 46 nearby galaxy centers in up to three transitions of HCN, HNC, and HCO+ combined with literature surveys establish a database of 130 galaxies measured in both HCN and HCO+, and 94 galaxies in HNC as well, allowing a systematic exploration of the relations between normalized luminosities and line ratios. The almost linear relations between luminosities are predominantly caused by distance effects and do not reflect galaxy physical properties. Individual galaxies show significant dispersion in both their luminosity and line ratio, which will be analyzed in more detail in a later paper. Very few line ratios correlate either with luminosities or with other line ratios. Only the normalized transition ladders of HCN and HCO+ and the J = 1 − 0 12CO/13CO isotopologue ratio are positively correlated with CO and far infrared (FIR) luminosity. On average, HCN and HCO+ have very similar intensities and trace the same gas. In galaxies dominated by an active nucleus, HCO+ intensities appear to be depressed relative to HCN intensities. Only a small fraction of CO emission is associated with gas emitting in HCN and HCO+, yet a significant fraction of even that gas appears to be translucent molecular gas. In the observed galaxy centers, the HCN/CO line intensity ratio is not a proxy for the dense gas fraction, and the FIR/HCN and FIR/CO ratios are not proxies for the star formation efficiency. A proper understandig of star formation requires a more appropriate determination of gas mass than provided by the intensities of individual HCN or CO transitions. The observed molecular line emission is fully consistent with UV-photon heating boosted by significant mechanical heating. The molecular gas sampled by HCN and HCO+ has low kinetic temperatures Tkin = 10 − 50 K, low densities nH = 104 − 105 cm−3, and low optical depths in the ground-state lines. Most of the gas sampled by CO has densities lower by one to two orders of magnitude. For a mechanical heating fraction of 0.5, a modest energy input of only G = 300 G0 is required.

A nearly constant CN/HCN line ratio in nearby galaxies: CN as a new tracer of dense gas

ABSTRACT We investigate the relationship between CN N = 1 − 0 and HCN J = 1 − 0 emission on scales from 30 to 400 pc using ALMA archival data, for which CN is often observed simultaneously with the CO J = 1 − 0 line. In a sample of nine nearby galaxies ranging from ultra-luminous infrared galaxies to normal spiral galaxies, we measure a remarkably constant CN/HCN line intensity ratio of 0.86 ± 0.07 (standard deviation of 0.20). This relatively constant CN/HCN line ratio is rather unexpected, as models of photon dominated regions have suggested that HCN emission traces shielded regions with high column densities while CN should trace dense gas exposed to high ultraviolet radiation fields. We find that the CN/HCN line ratio shows no significant correlation with molecular gas surface density but shows a mild trend (increase of ∼1.3 per dex) with both star formation rate surface density and star formation efficiency (the inverse of the molecular gas depletion time). Some starburst and active galactic nuclei show small enhancements in their CN/HCN ratio, while other nuclei show no significant difference from their surrounding discs. The nearly constant CN/HCN line ratio implies that CN, like HCN, can be used as a tracer of dense gas mass and dense gas fraction in nearby galaxies.

Implementation of thermo-responsive polymer coatings for an early warning against critical temperature states of thermo-sensitive electronic devices with metal oxide (MOx) gas sensors

Thermo-sensitive electronic devices such as Li-ion battery systems have reached a tremendous importance over the past years, in particular due to the increased pace of technology developments in the sector of e-mobility. In the present study, thermo-responsive functional coatings which release volatile cleavage products at well-defined temperatures were developed towards their use for indirect detection of critical temperatures by metal oxide (MOx) sensors. 1,1′-Azobis(cyclohexanecarbonitrile) (ABCN) and 2,2′-azodi(isobutyronitrile) (AIBN) were implemented as additives with a concentration of 4.7 wt% in polyurethane coating formulations. The thermolysis of the blowing agents and release of tracer gases were studied by differential scanning calorimetry, thermogravimetric analysis and evolved gas analysis coupled with mass spectrometry, showing comparable peak temperatures of gas release and no significant impact of the polyurethane matrix on gas release. In addition, the released gases could be successfully monitored by implementing MOx gas sensors in combination with effective algorithms to compute a warning signal in real-time with high robustness against false positives. This work therefore paves the way towards functional coatings, which have the ability to trace critical temperatures and hot spots of sensitive electronic-based systems on large and non-conformal surfaces by indirect measurements through low-cost MOx gas sensors.

A Case Study of Empirical Validation of EnergyPlus Infiltration Models Based on Different Wind Data

Building retrofitting is an efficient means of reducing greenhouse gas emissions. Its first focus is on building façade, as transmission and air leakage are the main sources of energy loss in buildings. Nowadays, building modellers cannot easily implement envelope air leakage and assume constant values, which results in erroneous energy estimates. Additionally, in energy simulations, a weather file is usually inserted with measurements provided by a weather station. In this study, we revealed the use of wind data from the weather file (herein as global wind) to calculate the infiltration of a test case in Spain, using the three algebraic equations of EnergyPlus. Furthermore, four other wind data were applied: eastbound and westbound winds from the weather file and two from in situ measurements (on the southeast and on the northwest façades). The fifteen combinations of the three infiltration models and the five wind data were empirically evaluated, using the tracer gas results performed during three different periods. The combinations were validated according to the American Society for Testing Materials D5157 standard criteria, and the best and the only ones that complied with the standard were those using the wind data from the southeast in situ sensor and the west wind from the weather station. The global wind was not able to generate accurate infiltration models, which raises doubts about its use in the highly-time calibration of energy models. However, its disaggregation was a cost-effective strategy to estimate the infiltration of this case study.

Air Leakage Law and Prevention Technology of Coal Spontaneous Combustion in the Goaf of “Isolated Island” Fully Mechanized Caving Face

ABSTRACT The coal pillar along the goaf of the completely mechanized caving face of “Isolated Island” is severely damaged, with complex air leakage and a high risk of coal spontaneous combustion. In order to research the law of goaf air leakage in “Isolated Island” working face and effectively control the hidden threat of coal spontaneous combustion in goaf, it is necessary to investigate the goaf air leakage law. In this work, the 3302 “Isolated Island” entirely mechanized caving face of Jining No. 2 Coal Mine in Shandong province, China, served as an example. SF6 tracer gas air leakage measurement was utilized to identify the air leaking route in the goaf. In conjunction with the numerical modeling, the air leakage route surrounding the goaf was evaluated to establish the coal spontaneous combustion risk region, and the targeted prevention and controlled ways of coal spontaneous combustion were proposed. The results indicated that the primary source of air leakage was the seepage of air flow through the working face to the rear goaf and the diffusion to the adjacent goaf through the broken coal pillar. The risk area for coal spontaneous combustion was 40–80 m behind the rear goaf and 50 m within the coal pillar of the adjacent goaf. Regarding this region, the comprehensive prevention and control strategies of plugging and oxygen reduction, inerting and cooling, monitoring and forecasting were proposed. In addition, the fire prevention and extinguishing system combining slurry spraying, sodium silicate, and liquid CO2 injection was designed at both ends of the 3302 track and haulage roads. Using field measurements during the working face mining process, the corresponding methods for reducing the CO volume fraction in 3302 return air roadway and air return corner effectively prevented and controlled the hidden danger of coal spontaneous combustion in the goaf and ensured the safety of working face mining. This research developed a new technology for the prevention and management of coal spontaneous combustion in the goaf of the “Isolated Island” working face.

Research on the Tracing and Fire Prevention Performance of New Mining Composite Gel

ABSTRACT A WG/C/XG (water glass/sodium carboxymethyl cellulose/xanthan gum) gel was created in this study by incorporating a tracer indicator into the fire protection material. The gel is both a tracer and flame retardant. First, scanning electron microscopy, UV spectrophotometer, and chromatography-mass spectrometer was used to characterize the samples. The microstructure of the WG/C/XG gel was investigated, as well as its impact on high-temperature response. The average rate of tracer gas release varies significantly before and after 55°C. Moreover, the release patterns of the two tracer gases are similar, indicating that the WG/C/XG gel is suitable for the solid loading of tracer gases. A thermal analyzer and programmed warming oxidation experiment analysis were used to investigate the inhibitory effect of WG/C/XG gel on the oxidation of spontaneous coal combustion. The experimental results demonstrated that the WG/C/XG gel improved the thermal stability of coal samples and inhibited spontaneous coal combustion. In mined areas, WG/C/XG gel is an excellent tracer material.

The ALMOND survey: molecular cloud properties and gas density tracers across 25 nearby spiral galaxies with ALMA

ABSTRACT We use new HCN(1–0) data from the ACA Large-sample Mapping Of Nearby galaxies in Dense gas (ALMOND) survey to trace the kpc-scale molecular gas density structure and CO(2–1) data from the Physics at High Angular resolution in Nearby GalaxieS–Atacama Large Millimeter/submillimeter Array (PHANGS–ALMA) to trace the bulk molecular gas across 25 nearby star-forming galaxies. At 2.1 kpc scale, we measure the density-sensitive HCN/CO line ratio and the star formation rate (SFR)/HCN ratio to trace the star formation efficiency in the denser molecular medium. At 150 pc scale, we measure structural and dynamical properties of the molecular gas via CO(2–1) line emission, which is linked to the lower resolution data using an intensity-weighted averaging method. We find positive correlations (negative) of HCN/CO (SFR/HCN) with the surface density, the velocity dispersion, and the internal turbulent pressure of the molecular gas. These observed correlations agree with expected trends from turbulent models of star formation, which consider a single free-fall time gravitational collapse. Our results show that the kpc-scale HCN/CO line ratio is a powerful tool to trace the 150 pc scale average density distribution of the molecular clouds. Lastly, we find systematic variations of the SFR/HCN ratio with cloud-scale molecular gas properties, which are incompatible with a universal star formation efficiency. Overall, these findings show that mean molecular gas density, molecular cloud properties, and star formation are closely linked in a coherent way, and observations of density-sensitive molecular gas tracers are a useful tool to analyse these variations, linking molecular gas physics to stellar output across galaxy discs.

Investigation of Air Change Rate in a Single Room Using Multiple Carbon Dioxide Breathing Models in China: Verification by Field Measurement

It is difficult to accurately measure the air exchange rate (AER) in residential and office buildings during occupation via on-site field measurement. The tracer gas method was widely applied to estimate the AER in these buildings, and human metabolic carbon dioxide (CO2) was often used as a tracer gas in different models. This study introduced three models (the ASHRAE model, the ASHRAE China-specific modified model, and the BMR model), which were proposed to estimate the AER based on exhaled CO2. We verified these models by comparing the exhaled CO2-based AER with AER from field measurements using sulfur hexafluoride (SF6) as a tracer gas. We also analyzed the potential factors that could affect the uniformity of the indoor tracer gas distribution. Our results indicate that the ASHRAE China-specific modified model has the best performance with an average deviation of −6.67% and a maximum deviation of −14.6% with multiple measurement points, a stable personnel activity, and proper Parameter settings in a single room in China.