Oxygen-nitrogen Gas Mixtures Research Articles

Effectiveness of ultra-/very-high-frequency oscillations combined with helium–oxygen gas mixture in a rabbit model

High-frequency oscillatory ventilation (HFOV) at frequencies of approximately 15 Hz is associated with optimal CO2 excretion. Higher frequencies using a nitrogen–oxygen gas mixture worsen CO2 excretion. An in vitro experiment using HFOV and a helium–oxygen gas mixture showed a significant increase in CO2 transport, which increased with increases in ventilation frequency. We hypothesised that in HFOV, the change in the arterial partial pressure of CO2 (PaCO2) would be greater at frequencies above 15 Hz when combined with helium–oxygen gas mixture administration. We tested this hypothesis in a hypoventilated healthy rabbit model by administering a helium–oxygen gas mixture at 15, 25, 35, and 45 Hz frequencies. One-way repeated measures ANOVA showed a significant decrease in PaCO2 among the four ventilation frequency groups. Post-hoc analysis showed significant differences between 15 and 35 Hz frequencies and between 15 and 45 Hz frequencies. The mean (standard error) decrease of PaCO2 was 10.8 (2.2), 14.1 (2.3), 21.3 (3.3), and 23.1 (2.5) mmHg at 15, 25, 35, and 45 Hz, respectively. Combination therapy of helium–oxygen gas mixture and high-frequency oscillation using ultra/very high frequencies (35–45 Hz) was associated with a greater PaCO2 decrease than that using the standard frequency (15 Hz).

Administration of Drugs/Gene Products to the Respiratory System: A Historical Perspective of the Use of Inert Liquids.

The present review is a historical perspective of methodology and applications using inert liquids for respiratory support and as a vehicle to deliver biological agents to the respiratory system. As such, the background of using oxygenated inert liquids (considered a drug when used in the lungs) opposed to an oxygen-nitrogen gas mixture for respiratory support is presented. The properties of these inert liquids and the mechanisms of gas exchange and lung function alterations using this technology are described. In addition, published preclinical and clinical trial results are discussed with respect to treatment modalities for respiratory diseases. Finally, this forward-looking review provides a comprehensive overview of potential methods for administration of drugs/gene products to the respiratory system and potential biomedical applications.

Solid-electrolyte amperometric sensor for measuring NO in air, nitrogen, and nitrogen-oxygen gas mixtures

In the present research, the possibility of using the electrochemical amperometric sensor with a diffusion barrier, based on yttria-stabilized zirconia electrolyte and two Pt electrodes, for measuring small NO concentration (below 1 vol.%) in nitrogen, air, and О2 + N2 gas mixtures, was discussed. The sensor testing at 450–600°С demonstrated high stability and reproducibility of results and good dynamic characteristics. It was shown that the sensor exhibits specific values of the limiting current for different contents of nitric oxide in the considered gas mixtures that allows precise determining of small NO concentrations. The presence of NO in the gas mixtures containing free oxygen was found to significantly increase the sensor limiting current. The catalytic role of NO molecules in oxygen exchange at the triple phase boundary between the solid electrolyte, electrode, and gas was discussed. Effect of NO2, CO2, and H2O impurities on the sensor performance was studied.

Discharge propagation on a dielectric surface in a single-filament arrangement

Discharge development and streamer propagation on a dielectric surface were investigated in nitrogen-oxygen gas mixtures at atmospheric pressure. A coaxial pin-to-pin arrangement was used to generate single surface discharges driven by positive unipolar square wave high voltages of between 7 and 9 kV at 4.3 kHz. The development of surface discharges was recorded by ICCD and streak cameras. The discharges developed on the surface using pin electrodes attached directly to the dielectric plate. The accumulation over several discharge events showed a propagation front evolving from the electrode tip, while images of single discharges showed a non-uniform and branched structure of discharge channels. The electrode polarity influenced the discharge expansion and propagation velocity. Positive polarity of the metallic electrode (rising slope of HV pulses) led to a cathode-directed streamer with higher propagation velocities (5 × 105 m/s) than for negative polarity (relative to surface charges; falling slope). The increase in the O2 content in N2 from 0.1 to 20 vol% resulted in a decrease in discharge duration and an increase in streamer velocities.

Habitable Underwater Hyperbaric Facilities: Respiratory Balance in the Human Organism During Adapting to Saturation Nitrogen-Oxygen Hyperbaria

Abstract There were evaluated responses of the respiratory system to changes in the variables of the external environment under increased pressure. To the model of professional underwater human activity underwater served the conditions of full saturation in compressed air or nitrogen-oxygen gas mixtures. Technical devices were presented by a number of underwater laboratories, mounted at the bottom (Ikhtiander-66, 67 and 68), hyperbaric chambers, submersible drilling rigs (Bur-1 and 2), and an autonomous diving Ikhtiander-2 for a long stay in the water. Studies of respiratory gases mass transport conditions in man showed than within the pressure range of 0.25-1.1 MPa at density of moderate hyperoxic and nitrogen-helio-oxygen environment up to 14 kg/m3 oxygen and carbon dioxide regimes of the organism come to a new functional level which provides the adaptation to the extremal conditions. It is determined that an increase of physiological dead breathing space, a decrease of the rate of the O2 diffusion through the alveole-capillary barrier, intensification of unevenness of ventilator-perfusional relations in lungs and an increase of blood shunting in lungs are the main respiratory mechanisms which regulate mass transfer of O2 and CO2 in man under hyperbaria. The leading hemodynamic mechanism is the retention of volume blood circulation and cardiac output. It is studied how the compression rate, high partial pressures of oxygen and nitrogen, microclimate parameters in inhabited hypebaric chambers influence changes of functional breathing system. Absence of hypoxic state is proved in man (full saturation of man with nitrogen) under normoxia in nitrogen-oxygen environment with the density 6.34 kg/m3. These are also the data about accelerated rehabilitation of divers using the method of active adaptation o high altitudes. Basic directions in physiological studies of functional breathing system under increased pressure of gas and water environment are described.

Early detection of diving-related cognitive impairment of different nitrogen-oxygen gas mixtures using critical flicker fusion frequency.

Cognitive impairment related to inert gas narcosis (IGN) is a threat to diving safety and operations at depth that might be reduced by using enriched air nitrox (EANx) mixtures. Using critical flicker fusion frequency (CFFF), a possible early detection of cognitive abilities/cerebral arousal impairment when breathing different oxygen (O2) fractions was investigated. Eight male volunteers performed, in random order, two dry chamber dives breathing either air or EANx40 (40% O₂-60% nitrogen) for 20 minutes (min) at 0.4 MPa. Cognition and arousal were assessed before the dive; upon arrival at 0.4 MPa; after 15 min exposure at 0.4 MPa; on surfacing and 30 min post-dive using behavioural computer-based testing psychology experiment building language (PEBL) and by CFFF while continuously recording brain oxygenation with near-infrared spectroscopy. In both breathing conditions, CFFF and PEBL demonstrated a significant inverse correlation (Pearson r of -0.90, P < 0.0001), improved cognitive abilities/cerebral arousal occurred upon arrival at 0.4 MPa followed by a progressive deterioration. Initial brain activation was associated with a significant increase in oxyhaemoglobin (HbO2) and a simultaneous decrease of deoxyhaemoglobin (HHb). The magnitude of the changes was significantly greater under EANx (P = 0.038). Since changes were not related to haemodynamic variables, HbO₂ and HHb values indicate a significant, O₂-dependent activation in the prefrontal cortex. Owing to the correlation with some tests from the PEBL, CFFF could be a convenient measure of cognitive performance/ability in extreme environments, likely under the direct influence of oxygen partial pressure, a potent modulator of IGN symptoms.

Branching characteristics of positive streamers in nitrogen-oxygen gas mixtures

One of the most important feature of streamers is that they frequently branch during the development process. In this paper, the branching characteristics of positive streamers are experimentally investigated in nitrogen-oxygen gas mixtures. Pulsed voltages with the amplitude of 10–20 kV are applied to a point-plane gap. The gas pressure is 100 mbar and the concentrations of the oxygen are 0.01 and 20%. The branch angle, the cross-sectional area of streamer channels before and after branching, as well as the ratio between streamer branching length and width are obtained. It is found that the streamer branching angle for 0.01% oxygen is less than that for 20% oxygen. The average ratio of the streamer cross-section area after branching to that before branching is 0.711 and changes slightly for different oxygen concentrations. The branching ratio decreases significantly from 12.6±2.6 to 6.7±1.5 when lowering the oxygen content from 20% to 0.01%, which indicates that the streamers branch more frequently at a certain distance. Since the nitrogen-oxygen ratio directly decides the electron production rate by photoionization ahead of streamers, the results imply that the possibility of streamer branching may correlate with the photoionization rate in the streamer tip.

The Benefits of Small Quantities of Nitrogen in the Oxygen Feed to Ozone Generators

ABSTRACTThis paper reports the ozone generation in pulsed multichannel dielectric barrier discharge. The influence of nitrogen addition (0.1%–10%) on ozone concentration and ozone generation efficiency in nitrogen–oxygen gas mixtures is studied. Results show that adding 0.1% N2 would not seriously increase the ozone production. Meanwhile, 1% N2 content exhibits the highest ozone production efficiency in low SIE (J/L, defined as the ratio of power to gas flow rate) region (0–200 J/L) while adding 0.3% N2 would lead to the highest ozone generation efficiency in high SIE region (300–800 J/L). The increase of ozone production induced by N2 addition is more significant in low SIE region compared with that in high SIE region. At 100 J/L, ozone production efficiency increases 26.9% to 201.6 g/kWh with 1% N2 addition when compared with that in oxygen. At 18 J/L, the observed maximum ozone generation efficiency reaches 252 g/kWh at 1.3 g/Nm3 with 1% N2 addition. An increase of ozone production can be obtained with 0.3%–2% N2 addition in all explored SIE ranges.

PP and PT Intervals and TP Segment in Human Electrocardiogram under Experimental Acute Normobaric Hypoxia

Seven male volunteers aged 22–27 years took part in the laboratory experiment for the determination of body response to acute normobaric hypoxia where they inhaled an oxygen–nitrogen gas mixture (9% of О2) for 25 min. At least 100 cardiac cycles at each of six experimental time points have been recorded by using an electrocardiogram (ECG) recording technique in standard lead II. Mean heart rate (±SD) before hypoxia was 64 ± 2 bpm; the duration of the PP interval was 0.94 ± 0.07 s, that of the PT interval was 0.51 ± 0.02 s, and that of the TP segment was 0.41 ± 0.07 s. Five minutes after hypoxia, it has been found that heart rate (HR) increased by 19%; the duration of the PP and PT intervals and TP segment decreased by 16%, 6%, and 30%, respectively. Twenty minutes after hypoxia, all the parameters reached their initial values. Five and fifteen minutes after hypoxia, HR reached 59 ± 3 bpm; PP interval and TP segment increased by 9% and 14%, respectively, compared to the initial values; PT interval was the same as the initial value at the baseline. The correlation coefficient rp (PP/PT) was 0.10–0.54; rp (PP/TP) was 0.94–0.99. The intervals PP and TP were found to be identical.

About the development of single microdischarges in dielectric barrier discharges in CO2 and CO2/N2 gas mixtures

The conversion of carbon dioxide as one of the main greenhouse gases into carbon monoxide as a chemical feedstock is considered as so-called carbon capture usage technology. Recently it was shown, that the dissociation of carbon dioxide to carbon monoxide in Dielectric Barrier Discharges can be enhanced by the addition of nitrogen gas. Here, the development of microdischarges in CO2 and CO2/N2 gas mixtures is studied. Therefore, a single filament DBD arrangement operated under sinusoidal high-voltage is investigated by means of spectroscopic and electrical diagnostics with high spatial and temporal resolution and sensitivity. The filament development is similar as in air or other nitrogen-oxygen gas mixtures, but the gas composition influences the duration and other parameters. The higher the CO2 content the weaker the filaments and the faster the quenching of excited molecular states. The optimum power dissipation into single discharge is obtained for a CO2 content between 20 and 30 vol.%.

Oxidation-Induced Surface Roughening of Aluminum Nanoparticles Formed in an Ablation Plume.

Nanoparticles formed within an ablation plume produced by the impact of a nanosecond laser pulse on the surface of an aluminum target have been directly measured using small-angle x-ray scattering. The target was immersed in an oxygen-nitrogen gas mixture at atmospheric pressure with the O_{2}/N_{2} ratio being precisely controlled. The results for an increasing oxygen content reveal remarkable effects on the morphology of the generated particles, which include a decrease in the particle volume but a marked increase in its surface ruggedness. Molecular dynamics simulations using a reactive potential and performed under similar conditions as the experiment reproduce the experimental trends and show in detail how the shape and surface structure of the nanoparticles evolve with increasing oxygen content. This good agreement between insitu observations in the plume and atomistic simulations emphasizes the key role of chemical reactivity together with thermodynamic conditions on the morphology of the particles thus produced.

High flow nasal cannula (HFNC) with Heliox decreases diaphragmatic injury in a newborn porcine lung injury model

High flow nasal cannula (HFNC) improves ventilation by washing out nasopharyngeal dead space while delivering oxygen. Heliox (helium-oxygen gas mixture), a low-density gas mixture, decreases resistance to airflow, reduces the work of breathing, and facilitates distribution of inspired gas. Excessive lung work and potential injury increases the workload on the immature diaphragm predisposing the muscle to fatigue, and can lead to inflammatory and oxidative stress, thereby contributing to impaired diaphragmatic function. We tested the hypothesis that HFNC with Heliox will decrease the work of breathing thereby unloading the neonatal diaphragm, and potentially reducing diaphragmatic injury. Spontaneously breathing neonatal pigs were randomized to Nitrox (nitrogen-oxygen gas mixture) or Heliox, and studied over 4 hr following oleic acid injury. Gas exchange, pulmonary mechanics indices, and systemic markers of inflammation were measured serially. Diaphragm inflammation biomarkers and histology for muscle injury were assessed at termination. Heliox breathing animals demonstrated decreased respiratory load and work of breathing with lower pressure-rate product, lower labored breathing index, and lower levels of diaphragmatic inflammatory markers, and muscle injury score as compared to Nitrox. These results suggest that HFNC with Heliox is a useful adjunct to attenuate diaphragmatic fatigue in the presence of lung injury by unloading the diaphragm, resulting in a more efficient breathing pattern, and decreased diaphragm injury.

Revised model coefficients for vibrational relaxation in a nitrogen–oxygen gas mixture

A numerical investigation of thermal non-equilibrium flows requires species specific relaxation rates, which are often calculated using the Landau–Teller model. This model requires the determination of collision specific relaxation times, which can be computed using Millikan and White’s empirical formula. The coefficients used in this formula for each specific collision pair form a set of coefficients, which are assessed here. The focus of the investigation lies on their performance in hypersonic low-temperature (300–2,500 K) flows that occur at shock-tunnel nozzle exits or in supersonic combustion ramjets (scramjets) before combustion. Two experimental validation cases are chosen; a shock-tunnel nozzle and a sharp cone in hypersonic cross-flow experiment. A comparison of the experimentally measured vibrational temperatures at the nozzle exit against numerical data shows large discrepancies for two commonly used coefficient sets. A revised set of coefficients is proposed that greatly improves the agreement between the numerical and experimental results. Furthermore, the numerically generated shock shape over the sharp cone using the revised set of coefficients correlates well with the experimental measurements.

Experimental determination of dielectric barrier discharge capacitance

The determination of electrical parameters (such as instantaneous power, transferred charge, and gas gap voltage) in dielectric barrier discharge (DBD) reactors relies on estimates of key capacitance values. In the classic large-scale sinusoidal-voltage driven DBD, also known as silent or ozonizer discharge, capacitance values can be determined from charge-voltage (Q-V) plot, also called Lissajous figure. For miniature laboratory reactors driven by fast pulsed voltage waveforms with sub-microsecond rise time, the capacitance of the dielectric barriers cannot be evaluated from a single Q-V plot because of the limited applicability of the classical theory. Theoretical determination can be problematic due to electrode edge effects, especially in the case of asymmetrical electrodes. The lack of reliable capacitance estimates leads to a "capacitance bottleneck" that obstructs the determination of other DBD electrical parameters in fast-pulsed reactors. It is suggested to obtain capacitance of dielectric barriers from a plot of the maximal charge versus maximal voltage amplitude (Q(max) - V(max) plot) in a manner analogous to the classical approach. The method is examined using measurements of current and voltage waveforms of a coaxial DBD reactor in argon at 100 mbar driven by square voltage pulses with a rise time of 20 ns and with different voltage amplitudes up to 10 kV. Additionally, the applicability of the method has been shown for the data reported in literature measured at 1 bar of nitrogen-oxygen gas mixtures and xenon.

Effects of extracellular-signal regulated kinase signaling pathway activation on hypoxic-ischemic brain damage of neonatal rats

Objective To investigate the effects of extracellular-signal regulated kinase (ERK) on hypoxic-ischemic brain damage of neonatal rats.Methods The hypoxic-ischemic brain damage model of neonatal Wistar rats was established as following:first the right common carotid artery of the rats was ligated;2 h after operation,the rats began to inhale 8%-oxygen oxygen-nitrogen gas mixture lasting for 2 h.Rats were randomly divided into three groups:sham-group,hypoxic-ischemic group and ERK inhibitor PD98059 group (the rats were injected PD98059 2 mg/kg 10 min before the ligation).Six hours after the models were done,hippocampi and cortex of the ligation side of rats in the three groups were collected,and the levels of malondialdehyde (MDA) and superoxide dismutase (SOD) were measured.Apoptosis of neuron was assessed by TUNEL staining.The expression of ERK1,ERK 2,Bcl-2 and Bax were examined by Western blot.The differences among the groups were analyzed with ANOVA and q test.Results Compared with the sham-group,the MDA level [(342.9± 10.8) μmol/L vs (181.5± 17.0) μmol/L,q= 6.35,P＜0.01) and the apoptosis rate of neuron [(18.80±1.37)% vs (3.53±0.34)%,q=6.06,P＜0.01) of hypoxic-ischemic group was higher,and SOD level was lower [(34.8±4.3) U/ml vs (63.4±4.3) U/ml,q=4.99,P＜0.01].While the apoptosis rate of neuron [(15.53±0.64) %] and MDA level [(252.0± 17.1) μmol/L] of PD98059 group were lower than those of hypoxic-ischemic group(q=3.87 and 5.28,P＜0.01respectively),the SOD level [(51.5 ± 3.8) U/ml] was higher than that of hypoxic-ischemic group (q=4.17,P＜0.01).There were no differences of ERK1 and ERK2 expressions among the three groups.The phosphorylated ERK1 and ERK2 levels of hypoxic-ischemic group were higher than those of sham-group (q=3.82 and 4.08,P＜0.01) and PD98059 group (q=4.79 and 5.12,P＜0.01).The expression of Bcl-2 and Bax of hypoxic-ischemic group were higher than those of sham-group (q=3.55 and 3.42,P＜0.01).Compared with hypoxic-ischemic group,Bcl-2 expression (q=3.71,P＜0.01) of PD98059 group was higher,and Bax expression (q=5.86,P ＜ 0.01) was lower.Conclusions ERK is involved in hypoxic-ischemic brain damage of neonatal rats through regulating the expression of apoptosis protein. Key words: Hypoxia-ischemia,brain; Extracellular-signal regulated MAP kinases; Animals,newborn; Rats; Apoptosis

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.

Differences in the strategies and potentials of human adaptation to hypoxia

The general patterns and individual specific features of human adaptation to acute hypoxic hypoxia caused by breathing a hypoxic oxygen-nitrogen gas mixture containing 8.0% oxygen have been studied. It was found that, at the initial stage of hypoxia, all examined subjects demonstrated a reduced oxygen consumption as compared to normoxia; then, this parameter increased and, beginning from a certain moment (after 5–15 min of exposure), exceeded the baseline level by 10–40%. Hypotheses explaining the mechanisms of this growth in oxygen consumption during hypoxia are considered. It has been found that the roles of the cardiovascular system and mechanisms of the tissue and cellular utilization of oxygen in the growth of the rate of oxygen consumption caused by hypoxia vary in different subjects. The hypothesis is put forward that the relatively low potential for rearrangement of the biological oxidation system at the cellular level, aimed at increasing the rate of oxygen consumption, predetermines a need to increase the rate of oxygen supply by the blood and, therefore, a greater strain of the cardiovascular system. In many cases, this strain can cause failure of adaptation to hypoxia. Other parameters that can serve as characteristics of a subject’s resistance to hypoxia, such as the intensity of EEG slow waves and the level of blood oxygenation, are also considered.

Interaction between changes in local and temporospatial spectral EEG characteristics during exposure of humans to hypoxia

The temporospatial and local characteristics of the EEG were studied in healthy subjects during the respiration of a hypoxic oxygen-nitrogen gas mixture containing 8% oxygen. Analysis of the spectral power density, coherence, phase shift, similarity of dominant frequencies in the EEG in different leads was performed separately for epochs containing and not containing visually apparent patterns of EEG spatial synchronization. In addition, assessment of spectral measures took account of the fact of the dominance of the frequency being analyzed in the EEG spectrum of the corresponding lead. The results of these studies showed that overall, hypoxia was accompanied by a decrease in EEG coherence in the alpha range and, for connections in the left mid-temporal lead, the delta range. The beta range showed an increase in the values of this measure, while the theta range showed different changes in coherence: increases in epochs containing spatial synchronization patterns and decreases from control levels in other epochs. Hypoxia was also associated with increases in the EEG phase shift in the frontal and temporal leads (in relation to the EEG recordings in the other leads) in the delta and theta ranges. In the beta range, conversely, there was a decrease in the mean phase shift. Consideration of the fact of dominance of one or another frequency in the spectra of local EEG traces is needed for correct interpretation of analyses of temporospatial measures. A mathematical model of the interaction between processes at different frequencies is presented to explain some of the observations in the current work.

Highly accurate measurement of oxygen using a paramagnetic gas sensor

The amount fraction of oxygen in oxygen–nitrogen gas mixtures has been measured with a relative uncertainty of ±0.02% within the range 100–1000 mmol mol−1. The method employed uses an auto-null ‘dumbbell’ type paramagnetic oxygen sensor, which has high resolution (10 µmol mol−1) and excellent linearity. The sensor is used to compare the sample gas mixture with pure oxygen and nitrogen gases, which compensates for drift and pressure change, and avoids the uncertainty from using bottled calibration gas mixtures. The method was verified by measuring primary standard gas mixtures at the National Physical Laboratory. To the authors knowledge the uncertainty achieved is better than any other analytical instrument, within the specified range.