Nitrogen-oxygen Mixtures Research Articles

Rearrangement of total electrical activity of the cerebral cortex and subcortical structures in experimental hypoxia

Rearrangements of the parameters of the electric activity of the cortical and subcortical regions were studied at different stages of experimental hypoxia (exposure to oxygen–nitrogen mixtures with an oxygen content of 7.5–8.0%) in chronic experiments of rabbits with the use of electrodes implanted into the brain. Acute hypoxia was shown to cause characteristic changes in electrical activity in the cortex, reticular formation, caudate nuclei, and hippocampus. The sequence of these changes may be divided into the following stages: (1) a short-term activation of all cerebral structures during the first 15–30 s and a shift of the frequency spectrum towards higher frequencies (β and α waves), (2) a decrease in β and α waves and an increase in θ activity during the next 2–4 min, and (3) a gradual shift towards slow waves (the Δ rhythm) and paroxysmal episodes in some animals. These shifts first appear in the frontal cortical regions and the reticular formation and then in the caudate nuclei and hippocampus. The degree of the changes in electric activity is correlated with the decrease in oxygen tension in the arterial blood.

Direct Experimental Impulse Measurements for Detonations and Deflagrations

Direct impulse measurements were carried out by using a ballistic pendulum arrangement for detonations and deflagrations in a tube closed at one end. Three tubes of different lengths and inner diameters were tested with stoichiometric propane– and ethylene–oxygen–nitrogen mixtures. Results were obtained as a function of initial pressure and percent diluent. The experimental results were compared to predictions from an analytical model and generally agreed to within 15% (Wintenberger, E., Austin, J., Cooper, M., Jackson, S., and Shepherd, J. E., “Analytical Model for the Impulse of a Single-Cycle Pulse Detonation Engine, AIAA Paper 2001–3811, July 2001). The effect of internal obstacles on the transition from deflagration to detonation was studied. Three different extensions were tested to investigate the effect of exit conditions on the ballistic impulse for stoichiometric ethylene–oxygen–nitrogen mixtures as a function of initial pressure and percent diluent.

Nitrogen oxide conversion in nitrogen-oxygen mixtures excited by a microsecond electron beam

The removal of nitrogen oxides from gas mixtures under the action of an ionizing microsecond pulsed electron beam is studied experimentally. Experiments were carried out with gas mixtures simulating flue gases of thermal power plants. The current density and pulse duration of the electron beam, as well as the concentrations of oxygen and the impurity to be removed, are shown to affect the cleaning characteristics. It is found that the nitrogen oxide conversion initiated by a pulsed electron beam cannot be described by models developed for steady-state electron beams.

Relationships between cerebral blood flow dynamics and bioelectric activity of the human brain in experimental acute hypoxia

The relationships between the parameters of oxygen content in the body (hemoglobin saturation with oxygen and trancutaneous oxygen tension), central hemodynamics (cardiac output), and cerebral hemodynamics (cerebral blood flow rate) were studied during a hypoxic test (inhalation of an oxygen–nitrogen mixture containing 8% oxygen for 15 min). Special attention was paid to the relationships between the dynamics of cerebral blood flow and cerebral bioelectric activity measured by EEG parameters. It was demonstrated that the trancutaneous oxygen tension decreased to a greater extent than the hemoglobin saturation with oxygen and the cerebral blood flow increased to a greater extent than the cardiac output. The increase in cerebral blood flow and the increase in the indices and power of θ and Δ EEG waves in the course of hypoxia were strongly positively correlated with each other in most subjects. However, if these parameters were considered in the series of subjects, the degree of the increase in the indices and power of θ and Δ waves in different subjects was negatively correlated with the increase in the cerebral blood flow. The results are explained in terms of redistribution of blood flow in the body to provide a better oxygen supply to the brain and optimization of the ratios between the cerebral oxygen consumption and the functional load on the system of oxygen supply.

Influence of Temperature on SO2 Removal Enhanced by Water Vapor Using a Corona-Discharge Reactor

A reactor using d.c. corona discharge of negative polarity was applied to remove sulfur dioxide from an oxygen-nitrogen mixture in the presence or absence of water vapor for temperatures ranging from room temperature to 350 °C. It was observed that increasing the reactor temperature caused a decrease in the removal efficiency. Mixing water vapor with the process gas resulted in an increase of the removal efficiency. The effect of the presence of water vapor on improving the removal efficiency was significant under low temperature conditions, while it was relatively moderate under high temperature conditions. In addition, the solid deposit formed inside the reactor at two temperatures, room temperature and 200 °C, was analyzed with both a differential scattering calorimeter and an X ray diffractometer. The analysis indicated that SO2 was ultimately converted to solid sulfur in both the presence and absence of water vapor in the gas flow.

Investigation of the mechanism for rapid heating of nitrogen and air in gas discharges

A rapid heating of nitrogen-oxygen mixtures excited by gas discharges is investigated numerically with allowance for the following main processes: the reactions of predissociation of highly excited electronic states of oxygen molecules (which are populated via electron impact or via the quenching of the excited states of N2 molecules), the reactions of quenching of the excited atoms O(1 D) by nitrogen molecules, the VT relaxation reactions, etc. The calculated results adequately describe available experimental data on the dynamics of air heating in gas-discharge plasmas. It is shown that, over a broad range of values of the reduced electric field E/N, gas heating is maintained by a fixed fraction of the discharge power that is expended on the excitation of the electronic degrees of freedom of molecules (for discharges in air, ηE⋍28%). The lower the oxygen content of the mixture, the smaller the quantity ηE. The question of a rapid heating of nitrogen with a small admixture of oxygen is discussed.

Control and characterization of the nucleation process during co-expansion of ternary mixtures

In this paper, we show how the use of a third non-condensable species gives both new insight and control on the binary nucleation process during supersonic expansion of gas mixtures. We present the case of an oxygen-nitrogen mixture diluted in various proportions of helium. Using beam diagnostics, we determine the mean cluster composition and size as well as the percentage of uncondensed matter present in the beam. The presence of helium permits us to understand the cooling and clustering role played by each species during the expansion process. We discuss, in particular, its influence on the dramatic composition change observed at the nucleation onset.

Recreational scuba diving, patent foramen ovale and their associated risks.

Scuba diving has become a popular leisure time activity with distinct risks to health owing to its physical characteristics. Knowledge of the behaviour of any mixture of breathable gases under increased ambient pressure is crucial for safe diving and gives clues as to the pathophysiology of compression or decompression related disorders. Immersion in cold water augments cardiac pre- and afterload due to an increase of intrathoracic blood volume and peripheral vasoconstriction. In very rare cases, the vasoconstrictor response can lead to pulmonary oedema. Immersion of the face in cold water is associated with bradycardia mediated by increased vagal tone. In icy water, the bradycardia can be so pronounced, that syncope results. For recreational dives, compressed air (i.e., 4 parts nitrogen and 1 part oxygen) is the preferred breathing gas. Its use is limited for diving to 40 to 50 m, otherwise nitrogen narcosis ("rapture of the deep") reduces a diver's cognitive function and increases the risk of inadequate reactions. At depths of 60 to 70 m oxygen toxicity impairs respiration and at higher partial pressures also functioning of the central nervous system. The use of special nitrogen-oxygen mixtures ("nitrox", 60% nitrogen and 40% oxygen as the typical example) decreases the probability of nitrogen narcosis and probably bubble formation, at the cost of increased risk of oxygen toxicity. Most of the health hazards during dives are consequences of changes in gas volume and formation of gas bubbles due to reduction of ambient pressure during a diver's ascent. The term barotrauma encompasses disorders related to over expansion of gas filled body cavities (mainly the lung and the inner ear). Decompression sickness results from the growth of gas nuclei in predominantly fatty tissue. Arterial gas embolism describes the penetration of such gas bubbles into the systemic circulation, either due to pulmonary barotrauma, transpulmonary passage after massive bubble formation ("chokes") or cardiac shunting. In recreational divers, neurological decompression events comprise 80% of reported cases of major decompression problems, most of the time due to pathological effects of intravascular bubbles. In divers with a history of major neurological decompression symptoms without evident cause, transoesophageal echocardiography must be performed to exclude a patent foramen ovale. If a cardiac right-to-left shunt is present, we advise divers with a history of severe decompression illness to stop diving. If they refuse to do so, it is crucial that they change their diving habits, minimising the amount of nitrogen load on the tissue. There is ongoing debate about the long term risk of scuba diving. Neuro-imaging studies revealed an increased frequency of ischaemic brain lesions in divers, which do not correlate well with subtle functional neurological deficits in experienced divers. In the light of the high prevalence of venous gas bubbles even after dives in shallow water and the presence of a cardiac right-to-left shunt in a quarter of the population (i.e., patent foramen ovale), arterialisation of gas bubbles might be more frequent than usually presumed.

Recreational scuba diving, patent foramen ovale and their associated risks.

Scuba diving has become a popular leisure time activity with distinct risks to health owing to its physical characteristics. Knowledge of the behaviour of any mixture of breathable gases under increased ambient pressure is crucial for safe diving and gives clues as to the pathophysiology of compression or decompression related disorders. Immersion in cold water augments cardiac pre- and afterload due to an increase of intrathoracic blood volume and peripheral vasoconstriction. In very rare cases, the vasoconstrictor response can lead to pulmonary oedema. Immersion of the face in cold water is associated with bradycardia mediated by increased vagal tone. In icy water, the bradycardia can be so pronounced, that syncope results. For recreational dives, compressed air (i.e., 4 parts nitrogen and 1 part oxygen) is the preferred breathing gas. Its use is limited for diving to 40 to 50 m, otherwise nitrogen narcosis ("rapture of the deep") reduces a diver's cognitive function and increases the risk of inadequate reactions. At depths of 60 to 70 m oxygen toxicity impairs respiration and at higher partial pressures also functioning of the central nervous system. The use of special nitrogen-oxygen mixtures ("nitrox", 60% nitrogen and 40% oxygen as the typical example) decreases the probability of nitrogen narcosis and probably bubble formation, at the cost of increased risk of oxygen toxicity. Most of the health hazards during dives are consequences of changes in gas volume and formation of gas bubbles due to reduction of ambient pressure during a diver's ascent. The term barotrauma encompasses disorders related to over expansion of gas filled body cavities (mainly the lung and the inner ear). Decompression sickness results from the growth of gas nuclei in predominantly fatty tissue. Arterial gas embolism describes the penetration of such gas bubbles into the systemic circulation, either due to pulmonary barotrauma, transpulmonary passage after massive bubble formation ("chokes") or cardiac shunting. In recreational divers, neurological decompression events comprise 80% of reported cases of major decompression problems, most of the time due to pathological effects of intravascular bubbles. In divers with a history of major neurological decompression symptoms without evident cause, transoesophageal echocardiography must be performed to exclude a patent foramen ovale. If a cardiac right-to-left shunt is present, we advise divers with a history of severe decompression illness to stop diving. If they refuse to do so, it is crucial that they change their diving habits, minimising the amount of nitrogen load on the tissue. There is ongoing debate about the long term risk of scuba diving. Neuro-imaging studies revealed an increased frequency of ischaemic brain lesions in divers, which do not correlate well with subtle functional neurological deficits in experienced divers. In the light of the high prevalence of venous gas bubbles even after dives in shallow water and the presence of a cardiac right-to-left shunt in a quarter of the population (i.e., patent foramen ovale), arterialisation of gas bubbles might be more frequent than usually presumed.

Removal of Trimethylamine in Gas by Corona-Discharge Reactor.

Trimethylamine, one component of malodorous gases from crematory emission, was removed by a corona-discharge reactor to apply the reactor to purification of crematory emission gas. The effects of discharge current and coexisting oxygen or water vapor on the removal efficiency of trimethylamine were investigated. Although trimethylamine was not effectively removed from nitrogen by corona discharge, the removal efficiency was improved greatly by mixing oxygen or water vapor. The amounts of reaction by-products generated were extremely large at high discharge current in the removal from a nitrogen-oxygen mixture. On the other hand, the by-products were greatly suppressed by mixing water vapor. The deposit on the anode of the reactor was analyzed by a thermogravimetry. As a result, trimethylamine was found on the anode surface as the deposit of carbon compounds which have high boiling point.

Flammability limits, ignition energy, and flame speeds in H 2–CH 4–NH 3–N 2O–O 2–N 2 mixtures

Experiments on flammability limits, ignition energies, and flame speeds were carried out in a 11.25- and a 400-liter combustion vessel at initial pressures and temperatures of 100 kPa and 295 K, respectively. Flammability maps of hydrogen–nitrous oxide–nitrogen, methane–nitrous oxide–nitrogen, ammonia–nitrous oxide–nitrogen, and ammonia–nitrous oxide–air, as well as lean flammability limits of various hydrogen–methane–ammonia–nitrous oxide–oxygen–nitrogen mixtures were determined. Ignition energy bounds of methane–nitrous oxide, ammonia–nitrous oxide, and ammonia–nitrous oxide–nitrogen mixtures have been determined and the influence of small amounts of oxygen on the flammability of methane–nitrous oxide–nitrogen mixtures has been investigated. Flame speeds have been measured and laminar burning velocities have been determined for ammonia–air–nitrous oxide and various hydrogen–methane–ammonia–nitrous oxide–oxygen–nitrogen mixtures. Lower and upper flammability limits (mixing fan on, turbulent conditions) for ignition energies of 8 J are: H 2–N 2O: 4.5 ∼ 5.0% H 2(LFL), 76 ∼ 80% H 2(UFL); CH 4–N 2O: 2.5 ∼ 3.0% CH 4(LFL), 43 ∼ 50% CH 4(UFL); NH 3–N 2O: 5.0 ∼ 5.2% NH 3(LFL), 67.5 ∼ 68% NH 3(UFL). Inerting concentrations are: H 2–N 2O–N 2: 76% N 2; CH 4–N 2O–N 2: 70.5% N 2; NH 3–N 2O–N 2: 61% N 2; NH 3–N 2O–air: 85% air. Flammability limits of methane–nitrous oxide–nitrogen mixtures show no pronounced dependence on small amounts of oxygen (<5%). Generally speaking, flammable gases with large initial amounts of nitrous oxide or ammonia show a strong dependence of flammability limits on ignition energy.

Heliox improves ventilation during high-frequency oscillatory ventilation in pediatric patients.

OBJECTIVE: To describe improved ventilation during high-frequency oscillatory ventilation when a nitrogen-oxygen gas mixture is replaced by a helium-oxygen gas mixture. DESIGN: Case series. SETTING: A tertiary pediatric intensive care unit. PATIENTS: Five patients with hypoxemic respiratory failure who developed persistent respiratory acidosis during treatment with high-frequency oscillatory ventilation. INTERVENTIONS: Introduction of helium-oxygen into a conventional high-frequency oscillatory ventilation circuit. MEASUREMENTS AND MAIN RESULTS: Blood gas values (pH, Pco2, and Po2) were compared in these patients during treatment with high-frequency oscillatory ventilation with nitrogen-oxygen gas flow and then for several hours after a change in treatment to helium-oxygen gas flow. An initial 24% decrease in Pco2 was documented, and an ultimate 43% decrease in Pco2 was observed. The mechanism for this improved ventilation may be related to improved gas flow properties as well as increased CO2 diffusion resulting from helium's low-mass density. Oxygenation was not adversely affected in any way. CONCLUSION: In patients with hypoxemic respiratory failure and in whom respiratory acidosis develops during high-frequency oscillatory ventilation, the use of helium-oxygen rather than nitrogen-oxygen may improve ventilation and decrease ventilator-related trauma. Further investigation is needed to validate these findings and to elucidate the mechanisms of improved ventilation.

Streamer corona removes styrene vapor from air flow

Decomposition of the styrene vapor in air induced by a 60-ns pulsed streamer corona discharge was studied. Empirical relationships were obtained that allow the necessary energy consumption to be evaluated depending on the required degree of purification, the initial styrene content in air, and the nitrogen-oxygen mixture composition. On this basis, a general equation is derived that provides systematization of the experience in air purification.

Oxygenation in status asthmaticus improves during ventilation with helium-oxygen.

To determine the effect of breathing helium-oxygen (HELIOX) mixtures on pulmonary gas exchange during severe asthma. A retrospective case-match control design was used to compare the changes in alveolar to arterial gradient [(A-a)gradient] in the first 2 hrs of mechanical ventilation (MV) for status asthmaticus (SA) in patients who received HELIOX with those who did not. Patients were matched for diagnosis of asthma, ventilatory failure, ventilator mode and settings, and equivalent pharmacologic therapy. The adult and pediatric intensive care units of a tertiary-care hospital. Adult and pediatric patients undergoing MV for SA. Use of HELIOX or standard nitrogen-oxygen mixtures during MV. A total of 11 patients receiving HELIOX in the first 2 hrs of MV for SA were compared with 11 case-matched controls who did not. At baseline, the HELIOX and control groups had similar (A-a)gradients (216+/-92 torr and 226+/-82 torr, respectively). The (A-a)gradient decreased significantly to 85+/-44 torr after initiation of ventilation with HELIOX (p < .0003), whereas it did not change significantly in the control group in a similar time frame and during identical treatment without HELIOX. The reduction in (A-a)gradient in the HELIOX group facilitated a reduction in F(IO)2 from 0.8+/-0.2 initially to 0.4+/-0.1 at the time of the second blood gas determination, thus permitting greater concentrations of helium to be administered. MV with HELIOX improves (A-a)gradient in patients with SA. Although this improvement adds little to routine therapy with supplemental oxygen, it does permit reduction in concentration of inspired oxygen to levels that maximize helium concentration and thus permit full benefits of HELIOX on lung mechanics to be realized in even the most severely ill asthmatics.

An asymptotic and numerical investigation of homogeneous ignition in catalytically stabilized channel flow combustion

The gas-phase ignition of a fuel-lean premixed combustible gas is investigated in a forced convection two-dimensional laminar channel flow configuration established by two catalytically-active parallel plates placed at a distance 2 b apart. The gaseous mixture has uniform inlet properties and both plate temperatures are constant and equal. First-order matched activation energy asymptotics are used to describe the reactive gaseous flow in conjunction with the boundary layer approximation, a one-step large activation energy gaseous reaction, and an infinitely fast (mass-transport-limited) catalytic reaction. A closed form ignition criterion is obtained for the gas-phase ignition distance in terms of nondimensional groups that are relevant to confined flows. The characteristic chemical and transverse diffusion time scales are included explicitly in the ignition criterion clearly demonstrating the competition between gaseous and catalytic fuel conversion while the effect of flow confinement ( b) is included implicitly. The ignition criterion is valid over the range 0.002 < x/( bRePr) < 0.16, with x the streamwise distance, Re the flow Reynolds number based on the channel halfwidth b and the uniform inlet properties, and Pr the Prandtl number. The temperature and transport parameter ranges of applicability are 1.5 < T W / T IN < 3 (with T W / T IN the ratio of the catalytic wall to the inlet temperature) and 0.9 < Le < 2.0 (with Le the Lewis number) respectively, rendering the ignition criterion of particular interest to hydrocarbon catalytically stabilized combustion (CST) applications. Numerical simulations are performed for channel flow catalytic combustion of a fuel-lean (equivalence ratio 0.32) propane–oxygen–nitrogen mixture using the same underlying chemistry assumptions as in the analytical asymptotic approach. The analytically calculated ignition distances are in good agreement with those numerically predicted. The effect of flow confinement (finite b) on gaseous ignition is examined by comparing ignition distances with the corresponding ones of the unconfined (flat plate) case. Flow confinement (decreasing b) increases the ignition distances due to the resulting increase in the channel surface-to-volume ratio. Moreover, the effect of flow confinement is important already from x/( bRePr) = 0.002.

Equilibrium adsorption of an oxygen-nitrogen mixture on zeolite NaX

Dependences of the Helmholtz energy, entropy, and internal energy in single micropores on the total number of guest molecules and the oxygen to nitrogen ratio were found by analysis of experimental data on adsorption of the binary oxygen-nitrogen mixture on zeolite NaX using the statistical model. A substantially non-ideal character of the adsorption phase, which exhibits negative deviations from Raout's law, can result from heterogeneity of the adsorption field inside single cavities.

Reaction Kinetics of Paddy Husk Thermal Decomposition

The physical characteristics, proximate analysis, elemental analysis and chemical analysis of paddy husk, an important renewable source of energy, are reported in this paper. The kinetic parameters for the thermal degradation of paddy husk at heating rates of 10 and 100°C min−1 and under atmospheres of air and oxygennitrogen mixture (5:95) have been evaluated from experimentally obtained TGA data. The limitations of the existing TGA models are discussed, and a modified model has been used for correlation of the data.

Heliox improves pulmonary mechanics in a pediatric porcine model of induced severe bronchospasm and independent lung mechanical ventilation.

BACKGROUND: A helium-oxygen gas mixture (heliox) has low gas density and low turbulence and resistance through narrowed airways. The effects of heliox on pulmonary mechanics following severe methacholine-induced bronchospasm were investigated and compared to those of a nitrogen-oxygen gas mixture (nitrox) in an innovative pediatric porcine, independent lung, mechanical ventilation model. RESULTS: All of the lungs showed evidence of severe bronchospasm after methacholine challenge. Prospective definition of 'heliox response' was a 15% or greater improvement in lung function in the lung receiving heliox compared with the matched lung receiving nitrox. Seven out of 10 pigs responded to heliox therapy with respect to resistance and eight out of 10 pigs responded to heliox therapy with respect to compliance and tidal volume (P < 0.03). After crossover from nitrox to heliox, eight out of eight lungs significantly improved with respect to tidal volume, resistance and compliance (P < 0.001). After crossover from heliox to nitrox all eight lungs showed a significant increase in resistance and a significant decrease in tidal volume (P < 0.001). CONCLUSIONS: In a pediatric porcine model of acute, severe methacholine-induced bronchospasm and independent lung mechanical ventilation, administration of heliox improves pulmonary mechanics, gas flow, and ventilation. Administration of heliox should be considered for support of pediatric patients with acute, severe bronchospasm requiring mechanical ventilation through small artificial airways.

The effect of precursor in flame synthesis of SiO 2

The effect of silicon precursor source concentration and oxidant composition on the specific surface area of flame made nanostructured silica particles was investigated in a diffusion flame reactor. Hexamethyl-disiloxane (HMDS) and octamethylcyclotetrasiloxane (OMCTS) were used as the organometallic Si sources along with SiCl 4. As oxidant various oxygen–nitrogen mixtures and as fuel methane were used. Particles generated by oxidation of organometallic compounds tend to have a smaller specific surface area than the ones made by employing SiCl 4 as precursor. This is attributed primarily to the increase of the flame temperature by the additional fuel coming from the organometallic compound. This effect is further pronounced with increasing precursor concentration as it was shown with experiments in a premixed flame reactor.

Occult nitric oxide inhalation improves oxygenation in mechanically ventilated children.

Auto-inhalation of nitric oxide (NO) produced in the upper airways may have physiologic effects on lung function. For intubated patients, the upper airway source of NO is eliminated, but the hospital compressed air source from the environment is contaminated with varying levels of NO, creating an "occult" form of NO therapy. We examined the physiologic significance of occult inhaled NO in ventilator-dependent pediatric patients. We hypothesized that very low levels of NO contamination in inspired gas improve PaO2 in ventilator-dependent children. Inspired NO levels at the mouth were measured by chemiluminescence in 4 pediatric subjects with normal lungs and 3 with parenchymal lung disease. Subjects were sequentially ventilated with first standard hospital gas (H1), switched to pure nitrogen-oxygen at a similar FIO2 but with no NO contamination (A2), hospital gas again (H2), the nitrogen-oxygen (A2) to control for time and sequence, and finally the nitrogen-oxygen mixture with supplemental NO in an amount equal to the NO previously measured in hospital gas (A2 + NO). Inhaled NO levels and PaO2 were recorded 15 minutes into each of the 5 steps. Two patients were studied a second time, remote from their first examination. NO levels in inhaled hospital gas mixtures ranged from 13 to 79 ppb (mean H1 = 53.3 +/- 23.7 ppb, mean H2 = 53.2 +/- 20.7 ppb, mean A2 + NO = 45 +/- 15.3 ppb; P < .0001). Removing NO from ventilator gas decreased PaO2 in all subjects, whereas replacing NO in artificial gas restored PaO2 to baseline values (P < .0001). Concentrations of NO in hospital compressed air are variable and have physiologic effects. The long-term implications of these findings remain to be defined.