Nitrogen-oxygen Mixtures Research Articles

Risk factors and treatment outcome in scuba divers with spinal cord decompression sickness

Purpose This study was designed to determine the recompression strategy and the potential risk factors associated with the development of severe diving-related spinal cord decompression sickness (DCS). Material and Methods Sixty-three injured recreational divers (52 men and 11 women; 46 ± 12 years) presenting with symptoms of spinal involvement were retrospectively included. Diving information, symptom latency after dive completion, and time interval between symptom onset and hyperbaric treatment were studied. The severity of spinal cord DCS was rated numerically for both the acute event and 1-month later. Initial recompression treatment at 2.8 atmosphere absolute (ATA) with 100% oxygen breathing or deeper recompression at 4 atmosphere absolute with nitrogen-oxygen or helium-oxygen breathing mixture was also noted. Results Twenty-one divers (33%) had incomplete resolution after 1 month. The clinical severity at presentation was the only independent predictor of poor outcome (odd ratio, 2.68; P < .033). Time to treatment did not influence the recovery with a similar median delay (3 hours) between the divers with or without long-term sequelae. Choice of recompression procedure was not also a determinant factor for treatment outcome. Conclusion The initial clinical course before treatment is a major prognostic factor of spinal cord DCS. Delay to recompression less than 3 hours and use of deep treatment tables did not improve outcome in DCS divers.

Methane ignition catalyzed by in situ generated palladium nanoparticles

Catalytic ignition of methane over the surfaces of freely-suspended and in situ generated palladium nanoparticles was investigated experimentally and numerically. The experiments were conducted in a laminar flow reactor. The palladium precursor was a compound (Pd(THD) 2, THD: 2,2,6,6-tetramethyl-3,5-heptanedione) dissolved in toluene and injected into the flow reactor as a fine aerosol, along with a methane–oxygen–nitrogen mixture. For experimental conditions chosen in this study, non-catalytic, homogeneous ignition was observed at a furnace temperature of ∼1123 K, whereas ignition of the same mixture with the precursor was found to be ∼973 K. In situ production of Pd/PdO nanoparticles was confirmed by scanning mobility, transmission electron microscopy and X-ray photoelectron spectroscopy analyses of particles collected at the reactor exit. The catalyst particle size distribution was log-normal. Depending on the precursor loading, the median diameter ranged from 10 to 30 nm. The mechanism behind catalytic ignition was examined using a combined gas-phase and gas-surface reaction model. Simulation results match the experiments closely and suggest that palladium nanocatalyst significantly shortens the ignition delay times of methane–air mixtures over a wide range of conditions.

Evolution of the structures and sorption properties of dehydrochlorinated chloropolymers during their thermal conversions

A microporous carbon material can be obtained by dehydrochlorination of the polymeric formulation poly(vinyl chloride)-poly(vinylidene chloride) in the presence of KOH followed by thermal treatment at a relatively low temperature (350°C in a nitrogen-oxygen gas mixture (10: 1 w/w)). This is because the chemical dehydrochlorination gives highly reactive chloro-containing polyconjugate systems. The conversion of chloropolyene systems into carbon structures is confirmed by Raman spectroscopy and TGA with MS analysis of volatile pyrolysis products. The resulting carbon material has a system of pores including ultramicropores 6.5 ± 0.5 A), micropores (16 ± 1 A), and mesopores (average pore size 150 ± 7 A).

Compensatory and adaptive rearrangement in the human respiratory system under acute hypoxic conditions

Relationships between the parameters of external respiration (minute volume and respiration rate) and those of internal, tissue respiration (oxygen consumption, arteriovenous oxygen difference and efficiency of oxygen uptake) were studied during a period of acute hypoxia and upon its completion. The subjects were exposed to hypoxia for 25 min using oxygen-nitrogen hypoxic gas mixtures (HGMs) differing in oxygen content (8 and 12%, HGM-8 and HGM-12, respectively). From the third to the fifth minutes of exposure to HGM-8, the respiration minute volume (RMV) was found to increase by 51 ± 33% as compared to the background value; however, the body’s oxygen consumption (OC) was 35 ± 22% reduced. Afterwards, OC grew to reach, from the 20th to the 25th min of hypoxia, 108 ± 21% of the background value and 181% of the value determined from the third to the fifth minutes of hypoxia. OC growth was accompanied by an insignificant RMV increase (by 12%) as compared to the level determined from the third to the fifth minutes of hypoxia, whereas the efficiency of oxygen uptake from the arterial blood increased by 75% for the same period. RMV growth from the third to the fifth minutes of hypoxia occurred as expense result of a higher breathing depth; at the same time, the respiration rate decreased as compared to the background value. By the period from the 20th to the 25th min of exposure to HGM-8, the respiration rate increased by 21% as compared to the period from the third to the fifth minutes of hypoxia. The efficiency of oxygen uptake from the arterial blood remained higher than the background value for at least 5 min after completion of the exposure to HGM-8. During the same period, the ventilation equivalent, an indicator of the efficiency of external respiration, i.e., of oxygen supply to the body, was significantly lower than the background value. During the exposure to HGM-12, RMV increased to a lesser extent than on exposure to HGM-8, however, the efficiency of oxygen uptake was higher during exposure to HGM-12; therefore, OC was also higher in the latter case. Therefore, the assumption that, during hypoxia, intensified external respiration (ventilatory response) itself compensates oxygen deficiency in inhaled air is revised. Ventilatory response is only a portion of the entire functional system of respiration (both external and tissue respiration). The role of ventilatory response is important for conditioning the tissue respiration rearrangement to eliminate deficiency of oxygen consumption during hypoxia. The retained higher oxygen uptake from the arterial blood during the period after completion of hypoxic treatment testifies to the adaptive implication of changes in tissue respiration; the same is confirmed by a reduced ventilation equivalent after hypoxia, which is indicative of the growing efficiency of external respiration, i.e., of an improved oxygen supply to the body.

N–O mix optimisation in low energy dense DC glow surface Ti conditioning

Samples of pure titanium have been treated by means a plasma immersed ion implantation (PIII) process in a DC glow discharge in pure oxygen and in different nitrogen-oxygen mixtures. In contrast with conventional voltage supply based glow PIII, the present study has been conducted with a novel specifically designed high current supply which allows a high electron density to be kept constant, regardless of gas pressure variations, within the operational ranks. Thus, the acquired sample characteristics can be more clearly ascribed to the chemical composition of the mixture. One stratified TiO2 (rutile) and TiN0.26 layer was identified from XRD and Raman spectroscopy, both of these compounds reputedly being highly biocompatible. The superficial hardness of the samples was improved up to more than five times that of the untreated reference sample, namely, ∼1600 Vickers microhardness (10 g load) thanks to a 2–6 μm deep implanted layer. These optimal results have been obtained from an 80% nitrogen 20% oxygen mixture at 1×10-2 torr. Furthermore, with this gas proportion, the best roughness finishing of the sample set was accomplished, which can be relevant for biocompatible applications.

Gas heating in fast pulsed discharges in N2–O2mixtures

The dynamics of gas heating in fast pulsed discharges in nitrogen-oxygen mixtures was analyzed using a state-specific plasmachemical model and an energy conservation equation. It was shown that the heating rate changes over time according to the changes of the species involved in the heating processes. An increasing dependence on time was shown. The results show that higher electron density, electric field or partial pressure of oxygen leads to a faster gas heating. However, the heating rate associated with excitation of vibrational and electronic degrees of freedom is almost independent of the value of the applied field in the studied range of fields.

Free iron, total F2‐isoprostanes and total F4‐neuroprostanes in a model of neonatal hypoxic–ischemic encephalopathy: neuroprotective effect of melatonin

Oxidative stress due to free radical formation and initiation of abnormal oxidative reactions is involved in several diseases of newborns, such as hypoxic-ischemic encephalopathy. Melatonin, an endogenously produced indoleamine primarily formed in the pineal gland, is a potent free radical scavenger as well as an indirect antioxidant. The present study was conducted to evaluate the formation of oxidative damage mediators and the possible effect of melatonin treatment in a model of hypoxic-ischemic encephalopathy in 7-day-old rats. Pups were subjected to permanent ligation of the right common carotid artery and exposed for 2.5 hr to a nitrogen-oxygen mixture (92% and 8%, respectively) (hypoxia-ischemia, HI). Melatonin was injected intraperitoneally to a group of rats at the dose of 15 mg/kg 30 min before starting the ischemic procedure (HI-Melatonin). After 24 hr of treatment, in homogenized cerebral cortex, desferoxamine (DFO)-chelatable free iron, total F(2)-isoprostanes and total F(4)-neuroprostanes, originating from the free radical-catalyzed peroxidation of arachidonic and docosahexaenoic acids, respectively, were determined. HI induced a significant increase in DFO-chelatable iron, total F(2)-isoprostanes and F(4)-neuroprostanes in both right and left side of the cerebral cortex. In HI-Melatonin-treated animals the levels of free iron, F(2)-isoprostanes, and F(4)-neuroprostanes were significantly lower than that in HI rats and the values were similar to controls. These data show the important neuroprotective role of melatonin in reducing oxidative damage resulting from HI. Melatonin could represent a potential safe approach to perinatal brain damage in humans.

Fine temporal control of the medium gas content and acidity and on-chip generation of series of oxygen concentrations for cell cultures

We describe the design, operation, and applications of two microfluidic devices that generate series of concentrations of oxygen, [O(2)], by on-chip gas mixing. Both devices are made of polydimethylsiloxane (PDMS) and have two layers of channels, the flow layer and the gas layer. By using in-situ measurements of [O(2)] with an oxygen-sensitive fluorescent dye, we show that gas diffusion through PDMS leads to equilibration of [O(2)] in an aqueous solution in the flow layer with [O(2)] in a gas injected into the gas layer on a time scale of approximately 1 sec. Injection of carbon dioxide into the gas layer causes the pH in the flow layer to drop within approximately 0.5 sec. Gas-mixing channel networks of both devices generate series of 9 gas mixtures with different [O(2)] from two gases fed to the inlets, thus creating regions with 9 different [O(2)] in the flow layer. The first device generates nitrogen-oxygen mixtures with [O(2)] varying linearly between 0 and 100%. The second device generates nitrogen-air mixtures with [O(2)] varying exponentially between 0 and 20.9%. The flow layers of the devices are designed for culturing bacteria in semi-permeable microchambers, and the second device is used to measure growth curves of E. coli colonies at 9 different [O(2)] in a single experiment. The cell division rates at [O(2)] of 0, 0.2, and 0.5% are found to be significantly different, further validating the capacity of the device to set [O(2)] in the flow layer with high precision and resolution. The degree of control of [O(2)] achieved in the devices and the robustness with respect to oxygen consumption due to respiration would be difficult to match in a traditional large-scale culture. The proposed devices and technology can be used in research on bacteria and yeast under microaerobic conditions and on mammalian cells under hypoxia.

Chemical speciation of premixed ethylbenzene flames at the soot onset limit at various ( [formula omitted]) pairs

This work investigates the similarities/differences of one-dimensional, laminar, atmospheric pressure premixed ethylbenzene flames at their soot onset threshold ( ϕ critical ). The goals of this investigation are to contrast the entire temperature profiles of the flames at various critical equivalence ratios, ϕ critical , and to report on hydrocarbon specie profiles. Liquid ethylbenzene was pre-vaporized in nitrogen, blended with an oxygen–nitrogen mixture and, upon ignition, premixed flat flames were stabilized over a burner at atmospheric pressure. The C/O ratio was regulated and simultaneously the temperature profile was adjusted by varying the heat lost from the flame to the burner, to obtain visually similar flames, all at their apparent soot onset limit. Temperature profiles of five such flames were determined with thermocouples. The results indicate that as the axial temperature profiles in the flames rose, ϕ critical ((C/O) critical) also increased. Sampling was performed at various heights along the axes of three of these flames ( ϕ c 1 = 1.68 , ϕ c 2 = 1.74 and ϕ c 3 = 1.83 ) to monitor changes in chemical speciation. The mole fractions of CO increased in the order of increasing equivalence ratio and hence increasing flame temperature. The CO 2 mole fractions of the three flames were similar. However, the mole fractions of light hydrocarbons and polycyclic aromatic hydrocarbons (PAH), which are suspected soot precursors, decreased in the order of increasing equivalence ratio and hence increasing flame temperature. Whereas direct measurements of particulate matter in the flame were not made in this work, these observations on soot precursors along with theoretical flame emissivity considerations suggest that particulate loadings at the sooting limit also decreased in the order of increasing equivalence ratio and hence increasing flame temperature.

Experimental and modeling study of laminar flame speed and non-premixed counterflow ignition of n-heptane

Laminar flame speeds were determined for n-heptane–oxygen–nitrogen mixtures over the pressure range of 0.5–2atm and equivalence ratio range of 0.7–1.4, using the counterflow twin-flame technique. For pressure at or below 1.5atm, the laminar flame speeds were collected for n-heptane–air mixtures, whereas the data at 2atm are reported for diluted air of 18% O2–82% N2. These experimental data, together with those acquired previously on the non-premixed counterflow ignition temperature of n-heptane determined over the same range of pressure, were simulated with a high-temperature, detailed kinetic model of n-heptane oxidation. After demonstrating satisfactory comparison between the model and experiment, the influence of pressure-induced kinetic effects on the laminar mass flux was analyzed through a computational determination of the overall reaction order. The non-premixed ignition temperature responses were in addition analyzed by numerical sensitivity analysis on reaction kinetics and fuel diffusion rate. The influence of uncertainties in the molecular transport on the model prediction of diffusive ignition is discussed.

Detonation Initiation in a Tube via Imploding Toroidal Shock Waves

The effectiveness of imploding waves at detonation initiation of stoichiometric ethylene- and propane–oxygen– nitrogen mixtures in a tube was investigated. Implosions were driven by twice-shocked gas located at the end of a shock tube, and wave strength was varied to determine the critical conditions necessary for initiation as a function of diluent concentration for each fuel. Hydrocarbon–air mixtures were not detonated due to facility limitations, however, detonations were achieved with nitrogen dilutions as large as 60 and 40% in ethylene and propane mixtures, respectively. The critical-energy input required for detonation of each dilution was then estimated using the unsteady energy equation. Blast-wave initiation theory was reviewed and the effect of tube wall proximity to the blast-wave source was considered. Estimated critical energies were found to scale better with the planar initiation energy than the spherical initiation energy, suggesting that detonation initiation was influenced by wave reflection from the tube walls.

Comparison of Nitrogen Narcosis and Helium Pressure Effects on Striatal Amino Acids: A Microdialysis Study in Rats

Exposure to nitrogen-oxygen mixture at high pressure induces narcosis, which can be considered as a first step toward general anaesthesia. Narcotic potencies of inert gases are attributed to their lipid solubility. Nitrogen narcosis induces cognitive and motor disturbances that occur from 0.3 MPa in man and from 1 MPa in rats. Neurochemical studies performed in rats up to 3 MPa have shown that nitrogen pressure decreases striatal dopamine release like argon, another inert gas, or nitrous oxide, an anaesthetic gas. Striatal dopamine release is under glutamatergic and other amino acid neurotransmission regulations. The aim of this work was to study the effects of nitrogen at 3 MPa on striatal amino acid levels and to compare to those of 3 MPa of helium which is not narcotic at this pressure, by using a new technique of microdialysis samples extraction under hyperbaric conditions, in freely moving rats. Amino acids were analysed by HPLC coupled to fluorimetric detection in order to appreciate glutamate, aspartate, glutamine and asparagine levels. Nitrogen-oxygen mixture exposure at 3 MPa decreased glutamate, glutamine and asparagine concentrations. In contrast, with helium-oxygen mixture, glutamate and aspartate levels were increased during the compression phase but not during the stay at maximal pressure. Comparison between nitrogen and helium highlighted the narcotic effects of nitrogen at pressure. As a matter of fact, nitrogen induces a reduction in glutamate and in other amino acids that could partly explain the decrease in striatal dopamine level as well as the motor and cognitive disturbances reported in nitrogen narcosis.

Interaction of Streamer Discharges in Air and Other Oxygen-Nitrogen Mixtures

The interaction of streamers in nitrogen-oxygen mixtures such as air is studied. First, an efficient method for fully three-dimensional streamer simulations in multiprocessor machines is introduced. With its help, we find two competing mechanisms how two adjacent streamers can interact: through electrostatic repulsion and through attraction due to nonlocal photoionization. The nonintuitive effects of pressure and of the nitrogen-oxygen ratio are discussed. As photoionization is experimentally difficult to access, we finally suggest to measure it indirectly through streamer interactions.

Positive Streamers in Ambient Air and a $\hbox{N}_{2}\!:\!\hbox{O}_{2}$ Mixture (99.8 : 0.2)

Photographs show distinct differences between positive streamers in air or in a nitrogen-oxygen mixture (0.2% O2). The streamers in the mixture branch more frequently, but the branches also extinguish more easily. Probably related to that, the streamers in the mixture propagate more in a zigzag manner, whereas they are straighter in air. Furthermore, streamers in the mixture can become longer; they are thinner and more intense.

Photoinduced field-assisted electron emission from dielectric-coated electrodes into gases

A photoinduced non-self-sustained discharge in a point–plane gap at near-atmospheric pressures in nitrogen and nitrogen–oxygen mixture was studied. Molybdenum and platinum points were coated with thin layers of MgO and TiO2 of different thicknesses. Static current–voltage characteristics were recorded at different intensities of triggering light, layer thickness and gas pressure. The common regularities of current–voltage characteristics were independent of the electrode/coating combinations used. The studies showed that the field-assisted two-step model of emission describes the experimental findings. The electron emission is controlled by Schottky and Fowler–Nordheim mechanisms at the metal–dielectric interface and by a recombination of positive ions with ‘hot’ and free electrons near the dielectric–gas interface.

The effect of temperature on the soot onset chemistry in one-dimensional, atmospheric-pressure, premixed ethylbenzene flames

This work was conducted to investigate the effects of temperature on soot formation/oxidation chemistry in the vicinity of the soot onset threshold ( ϕ critical) in one-dimensional, laminar, atmospheric-pressure premixed ethylbenzene flames. The effects of temperature on the evolution of soot precursors were observed just prior and subsequent to soot onset. Liquid ethylbenzene was prevaporized in nitrogen and blended with an oxygen–nitrogen mixture and, upon ignition, premixed flat flames were stabilized over a burner at atmospheric pressure. Three flames at the same fuel-to-air equivalence ratio ( ϕ = 1.74 ) but with different temperature profiles were obtained by regulating the total heat loss from the flame to the burner, as a result of altering the cold gas velocity of the reacting gases through the burner. A 100-K spread was detected among the three flame temperature profiles. The coolest flame was slightly sooting, the intermediate temperature flame was at the visible onset of sooting, and the hottest flame was not sooting. Combustion products were sampled at various heights in these flames. CO and CO 2 mole fractions were found to increase with temperature, supporting the hypothesis that with increasing temperature the rate of oxidation reactions increases faster than the rate of soot formation reactions. Again supporting the same hypothesis, the mole fractions of at least some of the suspected soot precursor hydrocarbons decreased with increasing temperature. Similarly, both the number and the concentrations of detected polycyclic aromatic hydrocarbons (PAH) and oxygenated aromatic hydrocarbons were highest in the slightly sooting, i.e., the coolest flame. This flame also had the highest condensed phase/gaseous phase PAH ratio among the three flames. However, whereas in all three flames the mole fractions of PAH were disparate in the broad neighborhood of the flame zone, they converged to similar values in the postflame zone at 7 mm height from the surface of the burner. Experimentally obtained mole fractions of effluent species were compared with predictions from a detailed kinetic model.

Spectral resolved measurement of the nitrogen fluorescence emissions in air induced by electrons

For the calorimetric determination of the primary energy of extensive air showers, measured by fluorescence telescopes, a precise knowledge of the conversion factor (fluorescence yield) between the deposited energy in the atmosphere and the number of emitted fluorescence photons is essential. The fluorescence yield depends on the pressure and the temperature of the air as well as on the water vapor concentration. Within the scope of this work the fluorescence yield for the eight strongest nitrogen emission bands between 300 nm and 400 nm has been measured using electrons from a 90Sr-source with energies between 250 keV and 2000 keV. Measurements have been performed in dry air, pure nitrogen, and a nitrogen–oxygen mixture at pressures ranging from 2 hPa to 990 hPa. Furthermore the influence of water vapor has been studied. A new approach for the parametrization of the fluorescence yield was used to analyze the data, leading to a consistent description of the fluorescence yield with a minimal set of parameters. The resulting absolute accuracies for the single nitrogen bands are in the order of 15%. In the investigated energy range, the fluorescence yield proved to be independent of the energy of the ionizing electrons.

Decomposition Characteristics of Acetone in a DC Corona Discharge at Atmospheric Pressure

Decomposition characteristics of acetone in a DC corona discharge generated between a multi-needle and a plane electrodes in nitrogen-oxygen mixtures at atmospheric pressure are investigated mainly by infrared absorption spectroscopy in this work. It is found that CO2, CO, CH4, HCHO, HCOOH and HCN are the by-products of acetone in the corona discharge, and that CO, CH4, HCHO, HCOOH and HCN are intermediate products, which tend to be decomposed in the corona discharge. CO2 is found to be the major and end-product. It is also found that acetone is chiefly inverted to CO2 via CO at high oxygen concentration (20%) and via CO and CH4 at relatively low oxygen concentration (0.2%), in addition to the direct conversion from acetone to CO2. As the oxygen concentration increases, the percentages of carbon atoms contained in deposit on the plane electrode and the wall of the discharge chamber increases. Further, the decomposition process of acetone is deduced from the examination of rate constants for the reactions in the gaseous phase.

Low-Temperature Processing of Sol-Gel Derived Metal Oxide Thin Films using Supercritical Carbon Dioxide Fluid

ABSTRACTWe demonstrate a novel technique using supercritical carbon dioxide (scCO2) fluid for lowering processing temperature of sol-gel-derived metal oxide thin films. The film processing was performed in a hot-wall closed vessel filled with scCO2 fluid. The effects of fluid temperature and additives on the sol-gel synthesis reaction under scCO2 fluid were also investigated. Precursor films of titanium dioxide (TiO2) prepared on silicon wafer and silica glass by sol-gel coating using Ti-alkoxide were converted to crystalline TiO2 (anatase) films successfully by treatment in scCO2 without additive agent at a fluid pressure of 15 MPa and at a substrate temperature of above 250°C, which is significantly lower than the processing temperature of conventional sol-gel deposition. Furthermore, additive agents such as water (H2O) and nitrogen-oxygen mixture (N2-O2) promoted the decomposition and crystallization of precursor films in scCO2 fluid to form the crystalline TiO2 (anatase) films at a substrate temperature at as low as 200°C although it also produced surface absorbates consisted of hydroxides on the film surface. The experimental results suggested that the hydrolysis and polymerization reactions of Ti-alkoxide in the precursor films were proceeded by the scCO2 processing to form titanium-oxygen (Ti-O) networks and that byproducts such as alcohols were removed from the resulting films.

Decomposition of benzene in a corona discharge at atmospheric pressure

We investigated the decomposition characteristics of benzene in a positive DC corona discharge between multineedle and plane electrodes with a background gas of nitrogen–oxygen mixture at atmospheric pressure. We obtained C 2H 2, HCN, HCOOH, CO and CO 2 as benzene fragments and by-products, and C 2H 2 and HCN as minor intermediate products. Benzene was primarily converted into CO 2 via CO at low oxygen concentrations (0.2%) and via CO and HCOOH at the atmospheric oxygen concentration (20%). Further, 57% and 24% of carbon atoms were deposited on the plane electrode and the discharge chamber at oxygen concentrations of 0.2% and 20%, respectively.