N2 Concentration Research Articles

The peculiar physiological responses of Rhizoctonia solani under the antagonistic interaction coupled by a novel antifungalmycin N2 from Streptomyces sp. N2.

A novel antifungalmycin N2 (3-methyl-3,5-amino-4-vinyl-2-pyrone, C6H7O2N) was previously discovered from Streptomyces sp. N2, which exerted a broad-spectrum antagonistic activity against phytopathogenic fungi. To provide comprehensive insights into the antagonistic mechanisms and biocontrol efficacy of antifungalmycin N2, the present work investigated the physiological responses of Rhizoctonia solani under interaction with antifungalmycin N2. First, the mycelial growth of R. solani was significantly inhibited by antifungalmycin N2 during liquid shake-flask culture. Morphological observations showed that the morphogenesis of R. solani was influenced by antifungalmycin N2, in which the hyphae became severely shriveled and flattened, irregularly folded and branched. Additionally, an obvious accumulation of reactive oxygen species (ROS) was detected in R. solani hyphae, indicating oxidative stress induced by antifungalmycin N2. Further results showed that chitinase activity and its hydrolytic N-acetylglucosamine were significantly accelerated by antifungalmycin N2, demonstrating the cell wall of R. solani was damaged. Interestingly, the enzymatic antioxidant activities of R. solani were significantly induced in response to a relatively low concentration of antifungalmycin N2 (1.44-5.77µg/mL). However, all antioxidant enzymes became highly inactive when the antifungalmycin N2 was increased to 11.53µg/mL, suggesting that the enzymatic antioxidant system in R. solani was probably collapsed by the oxidative stress beyond its acceptance scope. In conclusion, antifungalmycin N2 exerted its antagonistic activity by inducing both cell wall degradation and oxidative stress in R. solani, thus leading to fungal morphogenesis and autolysis. Meanwhile, R. solani could induce and activate its antioxidant enzymes as a defence response to the oxidative stress caused by antifungalmycin N2.

Development of a Method and Means for Transporting High-Purity Liquid Hydrogen

Preservation of the purity of liquid hydrogen (H2 ), which is used to fuel electrochemical generators of spacecraft power supply systems, during storage and transportation in model ZhVTs-100M railroad tank cars is studied. The quality of liquid H2 at various technological stages of transportation from the railroad tank-car filling plant to the consumer is analyzed. Experimental results are compared with the calculated stepwise increase of impurity N2 and O2 concentrations in the liquid H2. The methodology for calculating the purity of liquid H2 during transportation is clarified based on the assessment. Tanks with improved thermal insulation are proposed for maintaining its quality.

Using noble gases to trace groundwater evolution and assess helium accumulation in Weihe Basin, central China

Abstract The severe shortage of helium resources is an impending global problem. However, the helium accumulation processes and conditions favorable for helium enrichment in reservoirs remain poorly understood, which makes helium exploration challenging. Noble gases are good tracers of subsurface fluids provenance, migration and storage, as well as indicators of the nature and quantity of associated phases. In this study the variation of major gases and noble gases data in Weihe Basin provide us with an excellent opportunity to understand the groundwater evolution and helium accumulation processes. Twelve gas samples collected from wellheads of geothermal wells can be classified into three groups, in which Group A has high concentrations of N2 (58.57–91.66%) and He (0.32–2.94%); Group B has high contents of CH4 (52.94% and 69.50%) and low concentrations of He (0.057% and 0.062%); Group C has a high content of CH4 (71.70%) and He (2.11%). Helium isotopic ratios are predominantly radiogenic in origin and therefore crustally derived. Measured elemental ratios of noble gases are compared with multiple fractionation models for Group A and B samples, implying that open system heavy oil-water fractionation with excess heavy noble gases has occurred in the basin with Voil/Vwater ratios of 0.06–0.18. The amount of helium in Group A and B samples requires the release of all 4He produced in the crust since 0.30–1.98 Ma into the groundwater. The Group C sample requires an additional He flux from adjacent granitic bodies. The accumulation of helium and hydrocarbon in the Weihe Basin can be explained by a 4-stage process. Accumulation of commercially viable helium requires high He flux from source rocks, the existence of a free gas phase of major gas components (CH4 in most cases, N2 or CO2) and minimal major gas addition after formation of the free gas phase.

Influence of Reaction Conditions and Promoting Role of Ammonia Produced at Higher Temperature Conditions in Its Synthesis Process over Cs‐Ru/MgO Catalyst

AbstractCs promoted Ru/MgO catalyst was prepared by an impregnation method using Ru(NO3)3 and Cs(NO3)2 as precursor compounds. The activity measurements for ammonia (NH3) synthesis were carried out in a fixed‐bed flow reactor. A reactant stream of H2 and N2 was used for NH3 synthesis. The influences of reaction temperature, pressure and H2/N2 ratio on the performance of the catalyst were investigated in detail. The relative concentration of H2 and N2 in the reactant stream highly influenced the catalytic activity. The remarkably higher rate of NH3 synthesis was observed for the higher H2/N2 ratio at 400 °C and lower H2 concentration in the reactant stream improved the catalytic activity at lower temperature conditions. A sharp increase in the catalytic activity of Cs−Ru/MgO with an increase in pressure was observed at 400 °C for a reactant stream with higher H2 concentration. Relatively less interaction of H2 with the surface of the catalyst is suggested in the presence of NH3 produced during the reaction conducted at elevated temperature conditions. This less susceptibility for H2 adsorption on the active sites of the catalyst is a plausible reason for a higher rate of NH3 synthesis at higher temperature conditions. We modified the Temkin equation model by considering the adsorbed species on the surface of the catalyst affecting NH3 synthesis.

Mechanisms of element precipitation in carbonatite-related rare-earth element deposits: Evidence from fluid inclusions in the Maoniuping deposit, Sichuan Province, southwestern China

Carbonatite-related rare-earth element (REE) deposits (CARDs) are the major global source of REEs. The ore-forming fluids of CARDs usually comprise multiple components and record complicated evolutions. The Maoniuping REE deposit, located in the eastern Tibetan Plateau, is the second-largest CARD in China and contains total reserves of 3.17 Mt of light rare-earth oxides (REOs). Geochronological and geological data show that the deposit was formed at ∼25 Ma and was only moderately affected by tectonic and hydrothermal activities, thereby allowing us to study the evolution of ore fluids as well as the mechanisms of REE mineralization. The Maoniuping REE deposit is spatially associated with a carbonatite–syenite complex and includes two sections: Guangtoushan and Dagudao. The Dagudao section is the main focus of exploration and hosts well-developed vein systems. In the uppermost vein system, minerals are zoned from the syenite wall-rock contact to the vein centers in the order of biotite, aegirine-augite, arfvedsonite, calcite, quartz, barite, fluorite, and bastnäsite-(Ce). Based on geological observations and the petrography of fluid inclusions, the mineralization processes are classified into magmatic, pegmatitic, hydrothermal I, hydrothermal II, and REE stages. The inclusions in these stages include melt (M), melt–fluid (M–L), pure CO2 (C), aqueous–CO2 (L–C), aqueous–CO2 with crystals (L − C + S), liquid–vapor aqueous with crystals (L − V + S), and liquid–vapor (L–V) type inclusions. The magmatic stage is marked by a carbonatite–syenite complex with minor bastnäsite-(Ce), whereas the pegmatitic stage consists of coarse-grained calcite, barite, fluorite, and quartz that contain M, M–L, and L–C type inclusions with a fluid system of NaCl–Na2SO4–H2O–CO2 at high temperature (>600 °C) and high salinity (>45 wt% NaCl equiv.). The hydrothermal I stage is characterized by fenitization and is marked by aegirine-augite and arfvedsonite containing abundant L–V and few L–C type inclusions. This stage is characterized by high temperatures (∼480 °C) and moderate salinity (10.2–17.9 wt% NaCl equiv.), with a fluid system of NaCl–Na2SO4–H2O and minor CO2 and CH4 + C2H6. The hydrothermal II stage is dominated by L–C, L − C + S, L − V + S, and L–V type inclusions that are hosted in barite, calcite, fluorite, and quartz, and formed at moderate to high temperatures (260–350 °C), with a wide range of salinity (9.4–47.8 wt% NaCl equiv.), a fluid system of NaCl–Na2SO4–CO2–H2O, and abundant CH4 + C2H6. During the REE stage, pervasive bastnäsite-(Ce) containing abundant L–V type and few L–C type inclusions crystallized under low temperatures (160–240 °C) and low salinities (8.8–13.1 wt% NaCl equiv.) with a fluid system of NaCl–H2O and minor CO2 and CH4 + C2H6.The results of ion-chromatographic analysis show that the ore fluids are rich in Na+, K+, Cl−, F−, and (SO4)2−, and have low Cl−/(SO4)2− ratios (0.78–2.00), showing a marked contrast with the fluids of granite-related REE deposits (Cl−/(SO4)2− > 50) and a similarity to subcontinental lithospheric mantle (SCLM). The δD and δ18Ofluid values and the high N2/Ar ratios indicate that the ore fluids originated from carbonatitic magma and were dominated by magmatic water during the hydrothermal I stage, whereas magmatic and meteoric water co-existed during the hydrothermal II and REE stages. Moreover, the higher ratios of CO2/N2 (9–64) and CO2/CH4 (17–472) and the higher concentrations of CO2, CH4, C2H6, and N2 in the hydrothermal II stage compared with the hydrothermal I stage are attributed to intense immiscibility that resulted from decompression and is constrained to temperatures of 310–350 °C and pressures of 2.0–2.4 kbar. In contrast, microthermometric data and low CH4, C2H6, and N2 contents for the REE stage show that fluid cooling and mixing with meteoric water played an important role during the intensive mineralization of this stage, which occurred under shallow open-system conditions at temperatures of ∼200 °C and pressures of <0.5 kbar. The mineral assemblages, together with experimental petrology results, suggest that the REE transport capability of the hydrothermal fluids was due to the high contents of (SO4)2−, Cl−, and F− complexes. In addition, CO2 that separates during immiscibility is known to act as a buffer that constrains the pH of ore fluids. Thus, immiscibility during the hydrothermal II stage could have provided favorable conditions for the migration of REEs. The subsequent cooling of fluids, the involvement of meteoric water, and increased fluid pH, favored the precipitation of REEs in the Maoniuping deposit.

One-year evolution and variability in multiple-breath washout indices in children and young adults with primary ciliary dyskinesia

ABSTRACTBackground and objective: Cross-sectional and longer-term studies have demonstrated abnormal yet stable multiple-breath inert gas washout (MBW) indices in patients with primary ciliary dyskinesia (PCD). This study aimed to assess the intermediate term evolution and the between-occasion variability of MBW indices in PCD over 1 year.Methods: Children and young adults with a confirmed diagnosis of PCD were included in this single-centre, prospective, observational, longitudinal study. Over 1 year, nitrogen (N2) MBW and spirometry were performed at three occasions during ordinary scheduled outpatient visits. Trends and variability in lung clearance index (LCI), moment ratios, normalized N2 concentration at six lung volume turnovers, and regional ventilation inhomogeneity indices of the conducting and intra-acinar airways (Scond*VT and Sacin*VT) were analysed using linear mixed models.Results: Forty-two patients, aged 6–29 years (median: 15.4), performed 116 N2 MBW test occasions and 96.6% were technically acceptable. A minimal, although significant, increase in LCI over 1 year (mean: 0.51 units, 95% CI: 0.12–0.91, p = 0.01) was found; while, all other N2 MBW indices and FEV1 remained unchanged. A moderate correlation was observed between LCI and FEV1 (r = −0.47, p = 0.0001). The limits of agreement between tests 1 year apart were for LCI: −1.96 to 2.98; Scond*VT: ± 0.039; Sacin*VT: −0.108 to 0.128.Conclusions: Children and young adults with PCD managed at a specialist centre showed slightly, but significant, increasing LCI and otherwise unchanged ventilation inhomogeneity indices and dynamic volumes over the intermediate term of 1 year. Estimates of the variability of N2 MBW indices may inform sample size calculations of future randomized controlled trials.

Effects of nitrogen and carbon monoxide on the detonation of hydrogen-air gaseous mixtures

Nitrogen inhibition is considered as a mitigation measure against chemically sensitive mixtures in industry and carbon monoxide is possibly generated during molten corium concrete interaction in a severe accident of nuclear power plants. To study the effects of the N2 and CO on the detonation of H2-air mixtures, a detonation facility of 78 mm inner diameter and 10 m length is set up. Key measured parameters includes detonation cell size, flame velocity, lean and rich detonation limits. All the measured detonation parameters are theoretically predicted by CJ theory or one-dimensional ZND model. Detailed chemical kinetics mechanism for H2-air and H2-CO-air mixtures is coupled with reactive Euler equations. Experiments and theoretically analysis has been performed mostly at 0.101 MPa and 293 K. Results shows that N2 increases the detonation cell size and narrows down the detonable range significantly. Especially when N2 concentration is more than 43%, all mixtures are unable to detonate. Moreover, when the added N2 concentration is larger than 20%, detonation velocity does not increase with hydrogen concentration for rich mixtures. The above effects of N2 is explained by the replacement of O2 with N2 and by the weak chemical reaction of N2. CO significantly decreases the cell size of lean H2-air mixtures and increased the cell size for rich H2-air mixtures. For lean H2-air mixtures, the added CO linearly decreases the lean detonation limit, thus increasing the possibility of detonation to occur in the severe accidents. Therefore, the contribution of CO must be carefully considered in the safety assessment. Results also shows that pure CO is difficult to detonate in the air, while small quantity of hydrogen can significantly enhance the rate of CO oxidation reactions.

CO2/N2 mixture sequestration in depleted natural gas hydrate reservoirs

Carbon dioxide (CO2) emission is one of the primary causes of global warming, while CO2 storage is an effective way to solve this problem. Moreover, CO2 storage as CO2 hydrate is regarded as a viable and promising way. The development of natural gas hydrate mining technologies has provided a safe and appropriate method to store CO2 in depleted gas hydrate reservoirs. In addition, different concentrations of N2 are contained in the captured CO2 from flue gas. Therefore, CO2 storage with different N2 concentrations in depleted natural gas hydrate reservoirs with excess water was investigated in this study. Three types of gas (pure CO2, 90 mol%CO2 + 10 mol%N2 and 80 mol%CO2 + 20 mol%N2) and three pressures (3.0 MPa, 3.2 MPa and 3.5 MPa) in the constant pressure process were investigated. Magnetic Resonance Imaging (MRI) was employed to monitor the entire experimental process. The experimental results showed that the hydrate was nucleated and generated in different areas independently during the storage process. N2 was beneficial for quick hydrate formation; however, pure CO2 was most efficient for hydrate formation from a long-term perspective. In addition, CO2 was primarily stored as hydrate; a portion of CO2 was stored in the form of gas; and a small amount of CO2 was dissolved in the pore water. Moreover, the CO2 storage density (226.56 kg/m3) was the highest at the conditions of 275.15 K and 3.5 MPa using 90 mol%CO2 + 10 mol%N2 in the experiments. The highest CO2 storage density (229.99 kg/m3) calculated through water conversion occurred at the conditions of 275.15 K and 3.5 MPa using pure CO2.

Experimental and computational investigations of electron dynamics in micro atmospheric pressure radio-frequency plasma jets operated in He/N2 mixtures

The electron power absorption dynamics in radio frequency driven micro atmospheric pressure capacitive plasma jets are studied based on experimental phase resolved optical emission spectroscopy and the computational particle in cell simulations with Monte Carlo treatment of collisions. The jet is operated at 13.56 MHz in He with different admixture concentrations of N2 and at several driving voltage amplitudes. We find the spatio-temporal dynamics of the light emission of the plasma at various wavelengths to be markedly different. This is understood by revealing the population dynamics of the upper levels of selected emission lines/bands based on comparisons between experimental and simulation results. The populations of these excited states are sensitive to different parts of the electron energy distribution function and to contributions from other excited states. Mode transitions of the electron power absorption dynamics from the Ω- to the Penning-mode are found to be induced by changing the N2 admixture concentration and the driving voltage amplitude. Our numerical simulations reveal details of this mode transition and provide novel insights into the operation details of the Penning-mode. The characteristic excitation/emission maximum at the time of maximum sheath voltage at each electrode is found to be based on two mechanisms: (i) a direct channel, i.e. excitation/emission caused by electrons generated by Penning ionization inside the sheaths and (ii) an indirect channel, i.e. secondary electrons emitted from the electrode due to the impact of positive ions generated by Penning ionization at the electrodes.

An Empirical Model for Dinitrogen Gas Emission from Inland Waters

The motivation to calculate this empirical model resulted from often observing—at the time disconcerting—excess dinitrogen gas (N2 concentration > background concentration) in bubble-gas emission samples, collected primarily for the purpose of carbon budget research, from Brazilian rivers and reservoirs sampled during roughly 100 field surveys lasting 4 days each on average and executed between years 2000 and 2012. We model the (serendipitously) measured dinitrogen gas above environmental concentration (N2aec) escaping in bubbles from Brazilian rivers as a function of dissolved nitrogen (N) in water. To this model, we mathematically add a pre-existing model of diffusively emitted denitrified dinitrogen (also as a function of dissolved N) from streams in the United States of America (USA). The resulting model predicts denitrified dinitrogen water-air emission from inland waters in the USA, China and Germany.

Differences in desorption rate and composition of desorbed gases between undeformed and mylonitic coals in the Zhina Coalfield, Southwest China

Desorption is routinely employed for assessing the recoverability of coalbed gas resources. However, desorption behavior is strongly affected by coal structure. Canister desorption experiments on undeformed and mylonitic coals collected from drill holes in the Zhina Coalfield (Southwest China) were conducted to study temporal desorption rates and gas compositional shifts. Low-pressure N2 and CO2 adsorption tests revealed that the micropores, mesopores, and macropores in mylonitic coal have larger pore volumes and greater specific surface areas compared to those of undeformed coal. The “ink-bottle-shaped” pore is the main type of pore structure in mylonitic coal, whereas undeformed coal shows well-developed slit-shaped pores with good interconnectivity. The detailed desorption experiments in this study lasted 61 d and 110 h for undeformed and mylonitic coal, respectively. For undeformed coal, CH4 and C2H6 concentrations steadily increased with desorption time, whereas N2 and CO2 concentrations progressively decreased. The gas compositional shift of mylonitic coal during the entire desorption process could be divided into two stages: an initial stage, when CH4 and C2H6 concentrations in the desorbed gas increased (within the first 12 h), and a later stage, when they decreased rapidly; N2 and CO2 concentrations exhibited the opposite trend. The two-stage gas compositional shifts in mylonitic coal are likely linked to its pore structure. Gases in the “parallel-plate-shaped” pores of undeformed coal are mobile, whereas those in ink-bottle-shaped pores of mylonitic coal have restricted mobility. This is because CO2 and N2 can enter the narrow throats (with diameters of 3.3–3.8 Å) of ink-bottle-shaped pores, which are inaccessible to CH4 and C2H6 because of their larger diameter, causing the late-desorbed gas of mylonitic coal to be relatively enriched in CO2 and N2. The initial desorption rate of mylonitic coal is much greater than that of undeformed coal, which is closely related to developed microfractures in mylonitic coal. The desorption rate of undeformed coal is a power function of time, whereas that of mylonitic coal can be divided into two stages in which the relationship between desorption rate and time is a power function. The results suggest that the two-stage desorption rate is attributable to the molecular sieve effect due to the presence of massive ink-bottle-shaped pores in mylonitic coal.

NbO2 Electrocatalyst Toward 32% Faradaic Efficiency for N2 Fixation

AbstractThe electrocatalytic N2 reduction reaction (NRR) to produce ammonia is an attractive but highly challenging approach, due to the extreme inertness of N2 molecules and significantly lower N2 concentration compared to the surrounding water molecules. Herein, NbO2 nanoparticles are demonstrated as an efficient NRR electrocatalyst with significantly improved electrochemical performances. Compared to Nb2O5 with a similar crystal structure unit but different linkage, the Nb4+ cation not only provides empty d‐orbitals for strong N2 adsorption, but also a single d‐electron to further enable back donation to activate the NN triple bond. As a result, the NbO2 nanoparticles present an outstanding ammonia production rate of 11.6 µg h−1 mgcat.−1 at −0.65 V versus reversible hydrogen electrode (RHE) and an excellent electrochemical stability, significantly higher than those of the Nb2O5 nanorods under similar conditions. More importantly, a peak faradaic efficiency of ammonia production of 32% is obtained for NbO2 at −0.60 V versus RHE, which is one of the highest reported NRR faradaic efficiencies to date.

Onset of convection controlled by N2 impurity during CO2 storage in saline aquifers

This paper presents experimental and theoretical studies of the onset of natural convection induced by the dissolution of carbon dioxide- nitrogen (CO2-N2) mixtures into brine. Using a high- pressure Hele-Shaw cell, we conducted four sets of experiments under high-pressure conditions (with initial pressure range of 3375 to 3691 kPa) where 0%, 10%, 20% and 100% (molar base) N2 at different brine salinities and permeability (Rayleigh number of 3120 to 4840) were conducted to obtain quantitative and qualitative data from pressure decay and image analysis respectively. Furthermore, we performed Linear Stability Analysis (LSA) based on the quasi-steady-state approximation and Direct Numerical Simulation (DNS) to theoretically examine the effect of N2 on the onset of convection. We calculated effective diffusion coefficients from experimental data, and then used them in the LSA and DNS analyses. The experimental results confirmed by theoretical analysis revealed that the onset of convection occurred earlier in 10% N2 - 90% CO2 cases than in the pure CO2 cases. On the other hand, the onset of convection for an impure CO2 mixture with 20% N2 was close to that of the pure CO2 system. These findings suggest that, depending on the mole fraction of N2, the presence of N2 as an impurity may impede or promote the onset of natural convection. Since both the solubility and diffusion of CO2 in brine are nonlinear functions of N2 concentration, increasing N2 concentration reduces the solubility and diffusion coefficient, which have opposing impacts on the stability of the diffusive boundary layer.

Molecular dynamics simulation to estimate minimum miscibility pressure for oil with pure and impure CO2

CO2 enhanced oil recovery (CO2-EOR) has gained great attention worldwide for increasing oil production and reducing greenhouse emissions. In CO2-EOR project, the minimum miscibility pressure (MMP) is the key factor to determine the possibility of CO2 miscible-phase displacement. In this study, we used molecular dynamics (MD) simulation to estimate the MMP of pure and impure CO2 with oil by obtaining interfacial tensions (IFTs) based on the vanishing interfacial tension technique. To get accurate IFTs, modified Lorentz-Berthelot rules were developed for all simulations. Then, we performed MD simulations for CO2 + n-hexane binary system, CO2 + n-hexane + n-decane ternary system and complex CO2 + crude oil system to calculate the MMPs. Firstly, MMPs predicted by MD simulation show good agreement with previous experimental data. Secondly, the effects of injected gas components, oil components and reservoir temperature on the MMP are investigated. The results demonstrate that methane and N2 will increase the MMP of CO2-oil system significantly; the effects of a certain oil component on the MMP depend on the properties of crude oil, generally speaking, heavy oil components will increase the MMP while light oil components decrease it; temperature will increase the MMP of CO2-oil system, while it will decrease the MMP of N2-oil system, which is due to their different solubility in oil. Thirdly, sensitivity analysis is conducted to evaluate the effects of those influence parameters on the MMP of CO2-oil system, finding that N2 concentration in CO2 and reservoir temperature have more significant impacts on the MMP.

Backbone‐Based LCST‐Type Hyperbranched Poly(oligo(ethylene glycol)) with CO2‐Reversible Iminoboronate Linkers

AbstractDue to the very weak acidity of CO2 in water, the trigger of CO2 is always used to tune the physico‐chemical properties of polymeric materials through the protonation of organic bases rather than the hydrolysis of acid‐labile moieties contained in polymeric structures. Herein, a novel strategy of gas‐switchable lower critical solution temperature (LCST)‐type hyperbranched polymer of iminoboronate‐linked hyperbranched poly(oligo‐(ethylene glycol)) (IB‐hPOEG), by employing CO2‐acidolyzable iminoboronates as linkers and protonable tertiary amines as branch points, is presented. Upon alternative CO2 and N2, iminoboronates are partially reversibly hydrolyzed and tertiary amines are repeatedly protonated. This leads to a tunable thermo‐responsive behavior of IB‐hPOEG aqueous solution with a broad range of T cp at 28–78 °C intervals by varying the molar ratio of boronic acid, polymer concentration, or bubbling of CO2 and N2. This gas‐controllable LCST‐type hyperbranched polymer with CO2‐hydrolyzable iminoboronates is believed to have a promising potential for advanced biomedical and material applications such as drug delivery, gene transfection, functional coatings, etc.

Nitrous oxide quartz-enhanced photoacoustic detection employing a broadband distributed-feedback quantum cascade laser array

We present a gas sensing system based on quartz-enhanced photoacoustic spectroscopy (QEPAS) employing a monolithic distributed-feedback quantum cascade laser (QCL) array operated in a pulsed mode as a light source. The array consists of 32 quantum cascade lasers emitting in a spectral range from 1190 cm−1 to 1340 cm−1. The optoacoustic detection module was composed of a custom quartz tuning fork with a prong spacing of 1 mm, coupled with two micro-resonator tubes to enhance the signal-to-noise ratio. The QEPAS sensor was validated by detecting the absorption of the P- and R-branches of nitrous oxide. The measurements were performed by switching the array QCLs in sequence while tuning their operating temperature to retrieve the fine structure of the two N2O branches. A sensor calibration was performed, demonstrating a linear responsivity for N2O:N2 concentrations from 1000 down to 200 parts-per-million. With a 10 s lock-in integration time, a detection sensitivity of less than 60 parts-per-billion was achieved permitting the monitoring of nitrous oxide at global atmospheric levels.

Uranium nitride-silicide advanced nuclear fuel: higher efficiency and greater safety

ABSTRACTAs part of Accident Tolerant Fuel initiative for light water reactors, uranium silicide and silicide-nitride are being considered as fuels that can be combined with a more robust cladding such as a ferritic (FeCrAl) alloy. Although these materials have been studied in the past, uncertainties remain concerning the fundamental behaviour of these systems. In this study, four compositions between U3Si5 and USi2 were fabricated by arc-melting. Additionally, in an effort to understand the UN–U3Si2 fuel system, an unidentified U–Si–N ternary was observed in samples fabricated by arc-melting U3Si2 in the presence of varied concentrations of N2 in Ar. The analyses of compositions prepared to investigate these systems include structural characterisation using X-ray diffraction and compositional analysis employing scanning electron microscopy with energy dispersive spectrometry. Initial values of the Gibbs energy parameters via the CALPHAD (CALculation of PHAse Diagrams) method have been developed for the ternary phases observed upon U3Si2–FeCrAl interactions.

Effects of vibrationally excited N2 molecules on dielectric breakdown properties of SF6-N2 mixtures

This paper aims at studying the effects of the vibrationally excited N2 molecules on the dielectric breakdown properties of the SF6-N2 mixtures. The population of the vibrationally excited N2 molecules is determined from the Boltzmann distribution. For the cold SF6-N2 mixtures, the critical reduced electric field strength (E/N)cr decreases with the increasing vibrational temperature. For the hot SF6-N2 mixtures, the equilibrium compositions are calculated by the minimizing the Gibbs free energy before determining the vibrational distribution function by assuming the vibrational temperature equals to the gas temperature. The calculation results show that when the influence of the vibrationally excited N2 molecules is considered, the critical reduced electric field (E/N)cr of the SF6-N2 mixtures is reduced, and the deviation may be enhanced with a further increase in gas pressure and N2 concentration.

Influence of Process Parameters and Formation of Highly c-Axis Oriented AlN Thin Films on Mo by Reactive Sputtering

It is challenging to grow aluminum nitride (AlN) in c-axis orientation on a metal electrode, primarily due to lattice mismatch and the difference between the coefficients of thermal expansion. In this work, we investigate and optimize the effects of several process parameters such as plasma power, N2 flow concentration, quality of the bottom electrode, and oxygen content. The optimized deposition parameters are necessary for the growth of highly c-axis textured AlN thin film having a thickness of 300 nm on a Mo/SiO2/Si substrate. To this end, c-axis oriented AlN thin films were sputtered on a molybdenum (Mo) electrode at the low substrate temperature (300°C). The quality of the Mo electrode was optimized in terms of the surface roughness, interfacial energy, and full width at half maximum (FWHM) of x-ray diffraction (XRD) peak for facilitating the c-axis growth of the AIN film. Results indicate that the growth of AlN film in (002) orientation on the Mo electrode strongly depends on plasma power, the optimum value of which is found to be 300 W. Also, an extremely low FWHM of AlN (002) peak 0.62° is achieved at ∼ 38% N2 concentration. The oxygen content is also found to be an influential parameter, with a threshold value of 28% by atomic weight, beyond which amorphous growth of the AIN film is observed. The fabricated Mo-AlN-Mo structure has a dielectric constant of 8.89 and a capacitance value of 42 pF measured across the top electrode area of 400 × 400 μm2. The grown c-axis oriented AlN film can be used in applications such as the piezoelectric energy harvester (PEH) and the thin-film bulk acoustic resonator (FBAR).

Diagnostics of Ar/N2 mixture plasma with detailed electron-impact argon fine-structure excitation cross sections

A collisional-radiative model is developed for the Ar/N2 mixture plasma using reliable fully relativistic electron impact excitation cross sections of argon. We consider several fine structure transitions of argon and their corresponding cross sections used in the model have been obtained using fully relativistic distorted wave (RDW) theory. Processes, which account for the coupling of argon with nitrogen molecules, have been further added in the model. The applicability of the model with the RDW cross sections is tested by coupling it to the recent available spectroscopic measurements for a low pressure electron beam generated Ar/N2 plasma. The plasma parameters viz. electron density (ne) and electron temperature (Te) are evaluated by optimizing the model simulated intensities with the eight emission lines (out of 3p54p (2pi) → 3p54s (1si) transitions) observed through the measurements. We find from our study that as the concentration of N2 increases in the Ar/N2 mixture from 0 to 10%, our extracted electron density varies from 2.3 × 1011 to 2.8 × 1011 cm−3 and the electron temperature decreases from 1.0 to 0.43 eV which are in good agreement with the available probe measurement. Using present collisional radiative model, the individual contributions from the ground and 1si states to the radiating states are also evaluated as a function of N2 concentrations.