Probe Gas Research Articles

Flow field and emission characterization of a novel enclosed jet-in-hot-coflow canonical burner

The jet-in-hot-coflow is a canonical combustion setup, which has been used in several studies to study Flameless/MILD combustion and auto-ignition of fuels. However, the NOx and CO emission measurements from these combustion setups were not possible due to the entrainment of laboratory air and a lack of a well-defined physical system limit. These limitations have been overcome by a new enclosed jet-in-hot-coflow setup. The combustor was operated by injecting a mixture of CH4-Air in the central jet, and the coflow comprised of hot products from CH4-Air combustion in burners upstream. The coflow composition was further controlled by adding diluents such as N2 and CO2. Measurements were done using stereoscopic particle image velocimetry, suction probe gas analysis, thermocouples, and chemiluminescence imaging. Increasing central jet velocity and equivalence ratio led to lower NOx and a reaction zone that enlarged and shifted downstream. The reduction in NOx emission was attributed to the returning mechanism. Adding CO2 and N2 as diluents in the coflow resulted in a longer combustion zone and reduced temperatures in the combustion chamber, leading to decreased NOx production and increased reburning. These experiments provide relevant flowfield and emissions data for modelers and help characterize combustion regimes such as Flameless/MILD.

Convective assembly of silica colloidal particles inside photonic integrated chip-based microfluidic systems for gas sensing applications.

Optofluidics is a new field of modern science that stands at the interface of microfluidics and photonics and has good prospects for application in gas sensors. Microfluidics offers a promising platform for tuning and assembling monolayer structures that are used as sensitive layers for gas detection. Herein, we evaluate the concept of monolayer formation on a silicon nitride substrate enabling a surface coverage up to 59% through a microfluidic convective assembly and couple it with a photonic integrated chip to probe gas sensing performance.

A Sensor Probe with Active and Passive Humidity Management for In Situ Soil CO2 Monitoring.

Soil CO2 concentration and flux measurements are important in diverse fields, including geoscience, climate science, soil ecology, and agriculture. However, practitioners in these fields face difficulties with existing soil CO2 gas probes, which have had problems with high costs and frequent failures when deployed. Confronted with a recent research project's need for long-term in-soil CO2 monitoring at a large number of sites in harsh environmental conditions, we developed our own CO2 logging system to reduce expense and avoid the expected failures of commercial instruments. Our newly developed soil probes overcome the central challenge of soil gas probes-surviving continuous exposure to soil moisture while remaining open to soil gases-via three approaches: a 3D printed housing (economical for small-scale production) following design principles that correct the usual water permeability flaw of 3D printed materials; passive moisture protection via a hydrophobic, CO2-permeable PTFE membrane; and active moisture protection via a low-power micro-dehumidifier. Our CO2 instrumentation performed well and yielded a high-quality dataset that includes signals related to a prescribed fire as well as seasonal and diel cycles. We expect our technology to support underground CO2 monitoring in fields where it is already practiced and stimulate its expansion into diverse new fields.

Investigation on radon levels in soil and water associated with Mount Tampomas geothermal activity in Indonesia

ObjectiveTo investigate radon emanation in geothermal manifestations around Mount Tampomas, West Java, Indonesia, and assess radon concentrations in soil and water samples. MethodsRadon measurements were conducted using the Durridge Rad7 instrument, supplemented with a soil gas probe for in-situ soil radon measurements at a depth of 80 ​cm. In-situ water radon measurements were performed using the Rad Aqua instrument, while radon measurements for hot water samples were conducted separately. Radon measurements for hot water samples were corrected for decay using a radon decay correction factor. ResultsThe analysis of radon measurements revealed a wide range of concentrations in soil and water samples. Soil radon concentrations ranged from 15 Bq/m³ to 4,660 Bq/m³, with localized hotspots exhibiting exceptionally high concentrations. Water radon measurements showed elevated levels, ranging from 0.2 Bq/L to 13.4 Bq/L in-situ, particularly in hot springs. In collected water samples, radon concentrations ranged from 1 Bq/L to 6 Bq/L. These combined results highlight significant variability in radon levels across different water sources influenced by geothermal activity. ConclusionsThese findings indicate active emanation processes influenced by geological factors and underscore the role of subsurface geology and aquifer characteristics in radon transport mechanisms. The presence of localized radon hotspots suggests the need for comprehensive monitoring and proactive management strategies to mitigate environmental and public health risks associated with radon exposure.

On the Interpretation of Mid-infrared Absorption Lines of Gas-phase H2O as Observed by JWST/MIRI

Rovibrational absorption lines of H2O in the 5–8 μm wavelength range selectively probe gas against the mid-infrared continuum-emitting background of the inner regions of young stellar objects and active galactic nuclei and deliver important information about these warm, dust-obscured environments. JWST/Mid-Infrared Instrument (MIRI) detects these lines in many lines of sight at a moderate spectral resolving power of R ∼ 3500 (full width at half-maximum of 85 km s−1). Based on our analysis of high-resolution SOFIA/EXES observations, we find that the interpretation of JWST/MIRI absorption spectra can be severely hampered by the blending of individual transitions and the lost information on the intrinsic line width or the partial coverage of the background continuum source. In this paper, we point out problems such as degeneracy that arise in deriving physical properties from an insufficiently resolved spectrum. This can lead to differences in the column density by 2 orders of magnitude. We emphasize the importance of weighting optically thin and weak lines in spectral analyses and provide recipes for breaking down the coupled parameters. We also provide an online tool to generate the H2O absorption line spectra that can be compared to observations.

Analysis of the Effect of Sampling Probe Geometry on Measurement Accuracy in Supersonic Gas Flow

The accuracy of sampling of gas components has a significant impact on the measurement of various performance parameters in the combustion chamber of an aero-engine. In order to investigate the effect of the probe geometry of a six-point gas sampling probe on sampling accuracy in supersonic gas flow, a three-dimensional probe gas flow characteristic solution model is established through numerical simulation methods of components of transport and fluid–solid coupling. Probes with three angles of 28°, 30°, and 32° and an optimized conical probe are constructed. The sampling accuracy of the probes with different geometries is compared and evaluated by the deviation of the component volume fraction before and after sampling and the resulting combustion efficiency error. This paper presents a set of calculation methods for solving the relative deviation of volume fraction by an iterative method based on the ideal gas law and the Redlich–Kwong equation (R-K equation). The method is designed to solve the exact component volume fraction problem in the simulation calculation. The study results demonstrate that the 28° and optimized conical probes improve sampling accuracy more effectively than the original 30° structure. The deviation of the volume fractions of the two structures is less than 1.7%, and the combustion efficiency error is less than 0.09%. The developed iterative calculation method can significantly reduce the theoretical calculation error to less than 0.06%. The experimental data of the test bench are in good agreement with the simulation results, thereby demonstrating the reliability and accuracy of the sampling probe following structural optimization.

Natural and simulated weathering of polystyrene: A molecular view of the polymeric interface

This work presents the changing abundance of surface functional groups (SFGs) on polystyrene (PS) upon weathering within one or a few molecular monolayers from a molecular point of view. PS particles were aged by exposing it to a gas flow of typically (5 %) O3 in O2 (PSO3), UV radiation using a solar simulator under controlled conditions in the laboratory (PSSS) and to the water/air interface immerged in a freshwater lake for 2 months (PSL). The chemical composition of the interface of weathered, compared to pristine (virgin or PSV) material was established using a titration technique that probed the chemical composition of the molecular interface of the polymer. The main conclusions of this exploratory study are: (a) The interface of PS changes significantly compared to ATR-FTIR spectra that do not show additional absorptions in the mid-IR spectrum over a penetration depth of more than hundred monolayers at 10 μm; (b) The average surface functionalization of the gas-solid interface, corresponding to the sum of all examined types of SFG, increases from 20 % of a monolayer for PSV to 40, 50 and 84 % for PSL, PSO3 and PSSS, respectively; (c) in all cases the most important SFG was surface -OH ranging from 11.2 to 64 % for PSV and PSSS, respectively; (d) each PS sample shows a characteristic SFG pattern or fingerprint using several probe gases; (e) O3 interaction led to interface acidification; (f) UV treatment leads to the highest degree of surface -OH functionalization compared to PSO3 and PSL. The accumulation of SFG's renders the interface more reactive towards adsorption of probe gases.

Integrated Stopped-Flow Device for the Study of Porous Materials Using Hyperpolarized 129Xe NMR.

A simple, low-cost, and efficient device is proposed for the study of porous materials via NMR using small gas probes. Mainly built through additive manufacturing and being equipped with a radiofrequency solenoid microcoil, it only requires tiny quantities of sample and/or gas and is particularly suited for hyperpolarized xenon. The performances of this device have been accessed on a commercial sample of MCM-41 exhibiting multiporosity. Both the delivery mode of hyperpolarized xenon and the stopped-flow system are judged as efficient according to 2D 129Xe self-diffusion and EXSY experiments.

Chemical Potential Analysis as an Alternative to the van't Hoff Method: Hypothetical Limits of Solar Thermochemical Hydrogen.

The van't Hoff method is a standard approach for determining reaction enthalpies and entropies, e.g., in the thermochemical reduction of oxides, which is an important process for solar thermochemical fuels and numerous other applications. However, by analyzing the oxygen partial pressure pO2, e.g., as measured by thermogravimetric analysis (TGA), this method convolutes the properties of the probe gas with the solid-state properties of the examined oxides, which define their suitability for specific applications. The "chemical potential method" is here proposed as an alternative. Using the oxygen chemical potential ΔμO instead of pO2 for the analysis, this method does not only decouple gas-phase and solid-state contributions but also affords a simple and transparent approach to extracting the temperature dependence of the reduction enthalpy and entropy, which carries important information about the defect mechanism. For demonstration of the approach, this work considers three model systems; (1) a generic oxide with noninteracting, charge-neutral oxygen vacancy defects, (2) Sr0.86Ce0.14MnO3(1-δ) alloys with interacting vacancies, and (3) a model for charged vacancy formation in CeO2, which reproduces the extensive experimental TGA data available in the literature. The reduction behavior of these model systems obtained from the chemical potential method is correlated with simulated results for the thermochemical water splitting cycle, highlighting the exceptional behavior of CeO2, which originates from defect ionization. The theoretical performance limits for solar thermochemical hydrogen within the charged defect mechanism are assessed by considering hypothetical materials described by a variation of the CeO2 model parameters within a plausible range.

Deep Synoptic Array Science: First FRB and Host Galaxy Catalog

Fast radio bursts (FRBs) are a powerful and mysterious new class of transients that are luminous enough to be detected at cosmological distances. By associating FRBs to host galaxies, we can measure intrinsic and environmental properties that test FRB origin models, in addition to using them as precise probes of distant cosmic gas. The Deep Synoptic Array (DSA-110) is a radio interferometer built to maximize the rate at which it can simultaneously detect and localize FRBs. Here, we present the first sample of FRBs and host galaxies discovered by the DSA-110. This sample of 11 FRBs is the largest, most uniform sample of localized FRBs to date, as it is selected based on association with host galaxies identified in optical imaging by Pan-STARRS1. These FRBs have not been observed to repeat, and their radio properties (dispersion, temporal scattering, energy) are similar to that of the known nonrepeating FRB population. Most host galaxies have ongoing star formation, as has been identified before for FRB hosts. Two hosts of the new sample are massive, quiescent galaxies. The distribution of star formation history across this host-galaxy sample shows that the delay time distribution is wide, with a power-law model that spans from ∼100 Myr to ≳2 Gyr. This requires the existence of one or more progenitor formation channels associated with old stellar populations, such as the binary evolution of compact objects.

Characterization of SOL profiles and turbulence in ICRF-heated plasmas in EAST

Scrape-off layer (SOL) profiles and turbulence in ion cyclotron range of frequency (ICRF)-heated plasmas are investigated by the reciprocating probe diagnostic system (FRPs) and gas puff imaging (GPI) diagnostic in EAST. A radio-frequency (RF) sheath potential reaching up to 100 V is identified proximate to the ICRF antennas. Notably, the amplitude of this RF sheath potential escalates in response to rising ICRF power and inversely with plasma density. When a RF sheath is present in the far SOL, a pronounced density ‘shoulder’ forms in front of the ICRF antennas, while the ‘shoulder’ fade away as the antenna and associated RF sheath shift outwards. A strong E r shear is revealed by measurements from both FRPs and GPI. Analysis of the poloidal wave number-frequency spectrum reveals suppression of high-frequency turbulence in the far SOL due to the RF sheath. This effect is manifested in the reduced autocorrelation time τ c and reduced average blob size δ blob of the SOL plasma. Intriguingly, the poloidal propagation direction of the low-frequency turbulence reverses from the electron to the ion diamagnetic drift direction at the RF sheath location. A surge of tungsten impurity is potentially attributed to the heightened interaction between the SOL plasmas and the wall material. Shifting the ICRF antennas outward, to alleviate heat spots, results in the relocation of the RF sheath to the shaded region of the main limiter. This shift amplifies the radial velocity of blobs in the far SOL and concurrently diminishes the SOL density when compared to conditions without ICRF injection. The properties of ion saturation current fluctuations are consistent with the stochastic model predictions.

Development of a Thermal Separation Probe Gas Chromatography–Mass Spectrometry Method for Evaluating Wax–Resin Removal by Evolon® CR

Historically, many canvas paintings were infused with wax–resin mixtures that have discolored over time, distorting the aesthetics of the work, limiting treatment options, and introducing unstable materials into the object. Removal of the wax–resin is often desirable, but before works of art can be treated, a protocol to evaluate the efficacy of the treatment must be established. A mock-up painting was infused with a known amount of a wax–resin mixture made from beeswax and dammar; this material was then extracted through six intervals of exposure to solvent-loaded and dry sheets of Evolon® CR, a non-woven textile with a high sorbent capacity. Samples from the Evolon® CR sheets from each extraction round were analyzed using thermal separation probe gas chromatography–mass spectrometry (TSP-GC/MS). Normalization of peak areas related to beeswax and dammar to those of Evolon® CR revealed the relative amount of wax and resin removed throughout the extraction. The data show that, under these test conditions, the beeswax and dammar appear to be extracted with the same relative efficiency, information that cannot be provided through UV-induced visible fluorescence imaging of the Evolon® CR sheets or weight data alone, but which is critical to capture as it has implications for treatment success and the long-term stability of an artwork.

Novel 2-Aminobenzothiazole Derivatives: Docking, Synthesis, and Biological Evaluation as Anticancer Agents.

Sixteen novel 2-aminobenzothiazole compounds with different amines or substituted piperazine moieties were designed, synthesized, and tested using various methods. Potential interactions were assessed by docking new compounds in the adenosine triphosphate (ATP) binding domain of the PI3Kγ enzyme (PDB code: 7JWE) by nucleophilic substitution or solvent-free/neat fusion for docked compound synthesis. Final 2-aminobenzothiazole compounds were characterized by direct probe gas chromatography-mass spectrometry (GC-MS), proton (1H-NMR), carbon-13 (13C-NMR), and attenuated total reflectance-infrared Fourier transform infrared (ATR FT-IR). The synthesized compounds were investigated for anticancer activities on lung cancer (A549) and breast cancer (MCF-7) cell lines. The compounds' PI3Kγ inhibition was evaluated at a 100 μM concentration. 4-Nitroaniline and piperazine-4-nitroaniline combination in OMS5 and OMS14 reduced lung and breast cancer cell line growth. IC50 values for OMS5 and OMS14, the strongest compounds, ranged from 22.13 to 61.03 μM. OMS1 and OMS2 inhibited PI3Kγ at the highest rates (47 and 48%, respectively) at a 100 μM concentration. Results show that the PI3Kγ enzyme suppression is not the main mechanism behind these OMS5 and OMS14 anticancer effects. CDK2, Akt, mTOR, and p42/44 MAPK are affected. EGF receptor suppression matters. AKT1, AKT3, CDK1/cyclin B, PDK1 direct, PIK3CA E542 K/PIK3R1 (p110 α/p85 α), PIK3CD/PIK3R1 (p110 δ/p85 α), and PKN inhibition were measured to evaluate the possible mechanism of compound OMS14. PIK3CD/PIK3R1 (p110 δ/p85 α) is the most, with 65% inhibition, suggesting a possible mechanism of anticancer properties. Furthermore, the NCI 60-cell line inhibition demonstrates promising broad anticancer inhibition against numerous cancer cell lines of OMS5 and OMS14, which could be good lead compounds for future development.

Competitive adsorption-diffusion coupling process of helium-nitrogen mixture in shale kerogen nano-slit

Helium, as a probe gas with low adsorption capacity, is widely used for measuring porosity, permeability, and specific surface area in reservoir rocks of unconventional gas such as shale and coal. The pretreatment duration of these rock samples determines the amount of residual nitrogen in their pores, and the competitive adsorption and diffusion of residual nitrogen with the probe gas has a significant impact on the measurement results of their physical properties. This work aims to reveal the mechanisms involved in the competitive adsorption-diffusion coupling process of nitrogen-helium mixtures. Brief experiments were conducted to demonstrate the competitive adsorption between nitrogen and helium in shale. Subsequently, molecular dynamics simulation was employed to investigate this process and provide necessary details. Meanwhile, a theoretical model was developed to describe the diffusion of gas molecules in this process. Our results indicate that helium rapidly permeates shale samples and reaches an equilibrium distribution. However, the competitive adsorption between nitrogen and helium can slow down the helium permeation process, which can be attributed to the main adsorption sites occupied by nitrogen. The agreement between FEM computations and MD simulations validates our model for various mechanisms. Furthermore, our model can be applied to a wider range of porous materials and gas mixtures in related fields.

Resolved ALMA observations of water in the inner astronomical units of the HL Tau disk

The water molecule is a key ingredient in the formation of planetary systems, with the water snowline being a favourable location for the growth of massive planetary cores. Here we present Atacama Large Millimeter/submillimeter Array data of the ringed protoplanetary disk orbiting the young star HL Tauri that show centrally peaked, bright emission arising from three distinct transitions of the main water isotopologue (H216O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathrm{H}}_{2}^{16}{\\mathrm{O}}$$\\end{document}). The spatially and spectrally resolved water content probes gas in a thermal range down to the water sublimation temperature. Our analysis implies a stringent lower limit of 3.7 Earth oceans of water vapour available within the inner 17 astronomical units of the system. We show that our observations are limited to probing the water content in the atmosphere of the disk, due to the high dust column density and absorption, and indicate that the main water isotopologue is the best tracer to spatially resolve water vapour in protoplanetary disks.

A multi-method investigation of the permeability structure of brittle fault zones with ductile precursors in crystalline rock

Brittle faults and fault zones are among the most hydraulically active elements in predominantly impermeable crystalline host rock. They pose a significant challenge to underground infrastructure like nuclear waste repositories. Brittle fault zones frequently occur along pre-existing ductile shear zones as they introduce weakness planes in the rock.Four brittle fault zones of ductile origin were analyzed in the Rotondo Granite at the “BedrettoLab” in the Swiss Central Alps. Scanline mapping, rock sampling and permeability measurements using three different methods provide detailed insights into the heterogeneous fault zone architecture and hydrogeology. Average intact rock permeability is in the range of 10−19 to 10−17 m2. Fluid flow is channeled into single open or partially mineralized fractures of, at point-scale, up to 10−14 m2, demonstrated by selective gas probe permeameter measurements and borehole hydraulic testing. Reduced permeabilities have been measured in close proximity to these permeable features, indicating alteration of and around the fracture walls.

Formaldehyde observations of the Perseus Molecular Cloud

ABSTRACT Large-scale observations of the Perseus Molecular Cloud (MC) with Nanshan 26-m telescope are presented using the 6 cm ortho-H2CO (110–111) transition. As a probe of dense gas at low temperatures, the H2CO absorption extends over the main parts of the Perseus MC. A comparison of the H2CO absorption line with the 12CO and 13CO (J = 1–0) emissions shows that the H2CO and CO are similarly distributed over the Perseus but that H2CO correlates better with 13CO. Comparison with the Herschel-derived H2 column density shows that both the 13CO and H2CO column densities vary linearly with the H2 column density. The main parameters of H2CO absorption line data show a log-normal distribution, which suggests that the strong non-thermal line-broadening results from large-scale supersonic turbulence related to the star formation. Formaldehyde absorption serves well as a tracer of star formation activity and also the H2CO-to-13CO and H2CO-to-H2 abundances systematically trace the star formation activity in the six subregions of Perseus MC. The H2CO abundances anticorrelate with the number of prestellar and protostellar cores and the IRIS 12 μm flux in the six subregions and reveal the star formation history in the Perseus MC.

Evaluation and optimization of the performance characteristics of fast response fiber optic oxygen gas probes

Even though many different designs for currently available, fluorescence-based fiber optic sensors for measuring oxygen concentration (O2) are well known (and indeed some are commercially available), they often are limited by their response time and long-term stability. This will cause problems in the important industrial applications of fiber optic sensors of this type that are developing, with limitations that are evident, for example, in physiology and other fields where rapid sensor responses are required. Research by a number of groups has discussed various new designs of fiber optical sensors, which have been developed in recent years where the key features of such probes to achieve the performance required are, for example, optimization of design features such as tip shape and coating layer thickness. The research reported in this paper represents an evaluation of such key factors to allow the design of better fiber optic-based sensors for oxygen measurement, where the optimized performance of a new, specially tapered tip O2 sensor designed has been compared with the output of conventional and commercially available probe designs. The performance of a group of such sensors has been analyzed and cross-compared, examining the key features of such a probe including sensor accuracy, response time and overall long-term stability, as well as cross-sensitivity to any temperature changes which may occur in ‘real’ measurement situations.

Resolved Velocity Profiles of Galactic Winds at Cosmic Noon

We study the kinematics of the interstellar medium (ISM) viewed “down the barrel” in 20 gravitationally lensed galaxies during cosmic noon (z = 1.5–3.5). We use moderate-resolution spectra (R ∼ 4000) from Keck’s Echellette Spectrograph and Imager and Magellan/MagE to spectrally resolve the ISM absorption in these galaxies into ∼10 independent elements and use double Gaussian fits to quantify the velocity structure of the gas. We find that the bulk motion of gas in this galaxy sample is outflowing, with average velocity centroid km s−1 (±111 km s−1 scatter) measured with respect to the systemic redshift. A total of 16 out of the 20 galaxies exhibit a clear positive skewness, with a blueshifted tail extending to ∼ −500 km s−1. We examine scaling relations in outflow velocities with galaxy stellar mass and star formation rate, finding correlations consistent with a momentum-driven wind scenario. Our measured outflow velocities are also comparable to those reported for FIRE-2 and TNG50 cosmological simulations at similar redshift and galaxy properties. We also consider implications for interpreting results from lower-resolution spectra. We demonstrate that while velocity centroids are accurately recovered, the skewness, velocity width, and probes of high-velocity gas (e.g., v 95) are subject to large scatter and biases at lower resolution. We find that R ≳ 1700 is required for accurate results for the gas kinematics of our sample. This work represents the largest available sample of well-resolved outflow velocity structure at z > 2 and highlights the need for good spectral resolution to recover accurate properties.

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

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