Inert Gas Concentration Research Articles

Counterflow diffusion flames of quasi-monodisperse electrostatic sprays

The structure of counterflow diffusion flames of quasi-monodisperse electrostatic sprays of heptane has been studied by measuring droplet size, velocity and gas-phase temperature in two flames characterized by the same overall equivalence ratio. The first flame was found to behave much like a purely gaseous diffusion flame, since droplets evaporate completely before directly interacting with the flame. In the second spray flame, whose strain rate, initial mean droplet size and relative velocity were respectively 43%, 30% and 200% larger than in the first one, droplets have sufficient momentum to penetrate the flame and continue to burn in an oxygen rich environment. The flame appearance is also dramatically different the two cases. The flow strain rate flame appears as a thin blue sheet, whereas the other flame exhibits an additional thick orange region on the oxidizer side, whose luminosity is presumably due to the presence of small soot particles. A comparison between temperature profiles shows that the flame with the higher strain rate has a substantially broader temperature profile, in contrast with the typical behavior of purely gaseous diffusion flames. Furthermore, even though the two flames have identical overall equivalence ratios and nearly equal adiabatic flame temperatures, the high strain rate flame has a peak temperature 240 K higher than the other. This finding can be explained in terms of N 2 dilution effects: droplets cross the blue flame and continue to burn stoichiometrically in an oxygen rich environment while the inert gas concentration progressively decreases. In the course of droplet evaporation, the size distribution, initially monodisperse, broadens because of size-dependent evaporation rate and residence time.

Hard diamond-like carbon films prepared by various physical vapour deposition techniques

Amorphous diamond-like carbon (DLC) films were prepared both by dual-ion-beam sputtering (DIBS) and by ion-beam-assisted d.c. magnetron sputtering (IBAM) of a graphite target under an argon atmosphere. The growing film was bombarded with 50–300 eV inert gas ions. Homogeneous, adherent films up to 0.8 μm thick were deposited on glass, steel and silicon substrates at a highest deposition rate of 5 nm min −1 observed with IBAM. This technique, as compared with DIBS, allowed the ion energy per deposited carbon atom to vary in a larger range and achieved a reduced stress level. The film properties were carefully examined and related to the process parameters in order to determine the growth conditions favouring DLC films with respect to poor quality carbon ones. The hardness reached 40 000 MPa and the morphology was very compact. The inert gas concentration rose from 1 to 2.5 at.% with film bombardment. The low hydrogen content (0.5–1 at.%) measured for DIBS films was increased to 10 at.% with IBAM. The density was strongly dependent on the ion bombardment parameters (ion energy, nature and flux). It ranged from 1.6 to 2.7 g cm −3 for the DIBS films and from 1.4 to 2.3 g cm −3 for the IBAM layers. Ball-on-disc tests performed in a laboratory environment pointed out a low friction coefficient varying from 0.08 to 0.1. Furthermore, the ion bombardment raised the optical indices.

Effects Of Fire Retardant Additin On The Combustion Properties Of A Charring Fuel

Results are presented which show the effect of fire retardant addition on the fuel related properties used in diffusion flame calculations. Samples of cellulose retarded with up to 3 wt. percent of sodium hydroxide were subjected to a radiant heat flux of 40 kWm2 in a special apparatus designed for this purpose. The volatile products of pyrolysis were analyzed using a gas chromatograph to determine the concentration of inert gases (carbon dioxide and water). Retardant addition was found to increase both the char yield and the production of inert gases. This results in a decrease in the fuel fraction in the pyrolysate from 69 wt. percent for pure cellulose to 35 wt. percent for retarded cellulose. The corresponding change in the stoichiometric oxygen/fuel ratio is from 1.6 for pure cellulose to a maximum of 2.3 for retarded cellulose. Retardant addition also causes a decrease in the heat of gasification (defined as the energy input to generate a unit mass of volatiles) and an increase in the heat of combustion of the combustible gases in the pyrolysate.

Effects of two inotropic drugs, dopamine and dobutamine, on pulmonary gas exchange in artificially ventilated patients

The inotropic agents, dopamine (DP) and dobutamine (DB), both decrease PaO2, probably by a redistribution of the VA/Q ratio. The aim of this study was to assess the effect of both drugs on the VA/Q ratio, using the multiple inert gas elimination method. Ten artificially ventilated patients (eight males), aged 45-74 years were investigated. Blood gases, cardiac output and concentrations of inert gases were measured before and 30 min after infusion of DB or DP. DP and DB were administered alternatively at a rate of 5 micrograms.k-1 min-1. The decrease in PaO2 was significantly greater with DP (12 +/- 9 torr) than with DB (7 +/- 9 torr) (P less than 0.01). Both drugs similarly increased cardiac output: +2.61.min-1 +/- 1.4 for DP and 2.21.min-1 +/- 1.5 for DB. Both DP and DB significantly (P less than 0.01) increased the perfusion of alveoli with VA/Q = 0 (+4 +/- 7% for DP and +3 +/- 7% for DB) and 0 less than VA/Q less than 0.1 (+11 +/- 8.5% for DP and +5.5 +/- 10.5% for DB) (no significant difference between the drugs). When shunt and "shunt-like" effect are considered together, there was a significantly greater increase in the amount of blood going to alveoli with a low VA/Q ratio with DP compared to DB. Both drugs decreased the perfusion of alveoli with 0.1 less than VA/Q less than 10, but the decrease was significantly less for DB than for DP (-15 +/- 6.5% for DP and -8.5 +/- 7% for DB, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Precipitation of Ar, Kr and Xe in Ni at Room Temperaturey

ABSTRACTTransmission electron microscopy (TEM) has been used to study the precipitation of inert gases (Ar, Kr and Xe) injected into Ni at room temperature. The nucleation and size distribution of precipitates were found to be insensitive to the type of inert gas atom but dependent on gas concentration (ion fluence). The precipitate density decreases and the sizes increases with increasing gas concentration. In all cases, the inert gases precipitate as solid fcc crystals with their axes aligned with those of the host Ni lattice. For the same inert gas concentration, the lattice parameter is larger for the higher atomic mass in accord with bulk results. The lattice parameter of each type of inert gas precipitate increases with increasing gas concentration owing to the pressure relaxation that accompanies precipitate growth. This results in melting of large precipitates in accord with the behavior of bulk quantities of the gases at low temperatures.

On the characterization of CO2 laser photosensitized reactions

The study of the effect of some variable parameters of the cw CO2 laser photosensitized reactions as concentration of inert gas and sensitizer, and laser output upon the temperature distribution inside the reactor is presented together with the application of two kinetic approaches to the laser photosensitized (SF6) dehydrochlorination of 1,1,1-trichloroethane.

Enhancement of hypoxic pulmonary vasoconstriction by almitrine in the dog.

In order to test the hypothesis of enhancement of hypoxic pulmonary vasoconstriction by Almitrine, 12 anesthetized and paralyzed dogs with normal lungs were studied under controlled ventilation. They were ventilated in random sequence with air, 12% O2, and 100% O2, and almitrine (0.1 mg/kg body weight) was infused over 30 min during each O2 mixture. The multiple inert gas elimination technique was used to detect alterations in ventilation-perfusion (VA/Q) mismatching before and during the interventions and to measure cardiac output (QT). Arterial, mixed venous and expired gases, inert gas concentrations, and hemodynamic measurements were made while the dogs were breathing the different O2 mixtures before infusing the drug, near the end of 30 min of infusion and 30 min after infusion had ended. There were no significant changes in pH, PaO2, PaCO2, QT, oxygen uptake, oxygen delivery index, systemic vascular resistance, mean systemic arterial pressure, heart rate, stroke volume index, or VA/Q distribution during the experiment. Significant increases in: (a) pulmonary artery pressure (PA), (b) the pressure difference between PA and pulmonary capillary wedge pressure (PCw), and (c) pulmonary vascular resistance (PVR) occurred when the drug was infused during 12% O2 and air, but not during 100% O2. The PVR increased 59.7% with almitrine infusion during 12% O2 and 38.4% during air breathing (p less than or equal to 0.01), but there was no significant change during 100% O2. Vascular responses were not dependent on the order in which the different O2 mixtures were administered. These data strongly suggest that almitrine enhances hypoxic vasoconstriction in the lung, and this effect may explain reported improvement in PaO2 in hypoxic patients given the drug.

Influence of composition and substrate bias on structure and inert gas content of sputter-deposited Ni–La alloys

High concentrations of inert gases can be incorporated into the structure of certain bias-sputtered rare earth/transition metal alloys, and these materials are useful as stable reservoirs of inert gas. Ni–La alloys containing a composition gradient ranging from about 0.3 to 30 at.% La have been deposited at several bias voltages, in a dc triode system, with cylindrical target–substrate geometry, using an asymmetric composite target, and a Kr discharge. The dependence of Kr content and alloy structure on composition (La/Ni atom ratio) and substrate bias has been determined systematically. Deposit structure was examined by x-ray diffraction, and Kr content was measured by energy dispersive x-ray spectroscopy and by vacuum fusion. At constant bias, Kr content initially increases rapidly with La/Ni, then saturates. As La/Ni ratio increases, alloy structure changes from fully crystalline to fully amorphous. Bias has a pronounced effect on preferred orientation and on relative fraction of crystalline phase. The work is discussed in terms of previous studies of sputter-deposited RE/TM alloys and amorphous metals.

Uneven gas mixing during rebreathing assessed by simultaneously measuring dead space.

To evaluate the rate of gas mixing in human lungs during rebreathing maneuvers used to measure pulmonary tissue volume (Vt) and pulmonary capillary blood flow (Qc), we devised a method to determine the dead space during rebreathing (VRD). Required measurements are initial concentration of a foreign inert insoluble gas in the rebreathing bag, first mixed expired concentration, equilibrated concentration, volume inspired, and volume of the first expired breath. In subjects breathing rapidly at 30 breaths/min with inspired volumes in excess of 2 liters, VRD had values three or more times greater than the predicted anatomical dead space (VD). Breath holding after the first inspiration progressively diminished VRD so that after 10-15 s, it approximately equaled predicted VD. VRD measured with helium was smaller than VRD measured with sulfur hexafluoride. The reported degree of uneven ventilation from gravitational forces in normal humans can account for only about one-third of the difference between VRD and VD. These findings support the concept that mixing by diffusion between peripheral parallel airways is incomplete at normal breathing rates in humans and can result in errors as high as 25% in Vt and Qc.

Ventilation-perfusion ratio distributions by mass spectrometry with membrane catheters.

We previously developed a quadrupole mass spectrometer system for measuring gas phase concentrations of multiple inert gases at trace levels. A new inlet with two silicone rubber membrane catheters now allows quantitative analysis of the inert gas concentrations in both blood and gas phase samples. We have determined the sensitivity, linearity, and reproducibility of this system by measuring blood-to-gas phase calibration curves for the following inert gases: sulfur hexafluoride, krypton, Freon 12, enflurane, diethyl ether, and acetone. We have used our mass spectrometer system to obtain multiple inert gas elimination data from three anesthetized, spontaneously breathing dogs. We conclude that our dual-membrane mass spectrometer system provides useful measurements of trace multiple inert gas concentrations in both blood and gas phase samples. Furthermore, the inert gases in blood can be measured directly without having to extract them into a gas phase, and the multiple inert gas elimination data acquired with our system can be used to provide estimates of ventilation-perfusion ratio distributions. Our mass spectrometer technique provides an alternative to the gas chromatographic approach for these measurements.

Development of a double mass spectrometer for the determination of metabolism and inert gas concentrations in blood at two parts of the body (author's transl)

Development of a double mass spectrometer for the determination of metabolism and inert gas concentrations in blood at two parts of the body (author's transl)

Cellular flame structure and turbulent combustion

Knowledge of flame interaction with perturbation of the surrounding medium is insufficient. This study investigates various parameters and methods for clarifying the combustion mechanism. The conditions for the appearance of a cellular structure were formed by analysis of diffusion phenomenon. Because such a spontaneous transition is characteristic of laminar regimes, photographs of laminar flames of hydrogen 2H2 plus (alpha) 2 plus nN2 are shown. The mixture becomes leaner as the flame surface breaks into pieces. It is determined that the more strongly the laminar flame is broken up, the steeper is the slope K /SUB p/ on the initial segment of the curve of turbulent burnup velocity as a function of pulsation velocity. Other examples are also given. The change in laminar flame surface with fixed excess oxidizer coefficient as inert gas concentration varies is studied. In conclusion, an approximate expression is derived which corresponds to burnup velocities which can be predicted for various operational regimes by this function.

A method for calculating regional cerebral blood flow from emission computed tomography of inert gas concentrations.

Emission tomography of positron or gamma emitting inert gases allows calculation of regional cerebral blood flow (rCBF) in cross-sectional slices of human brain. An algorithm is presented for rCBF calculations from a sequence of time averaged tomograms using inhaled 133Xe. The approach is designed to avoid loss of information in brain areas with low flow rates. It is based on linearizing and scaling the early isotope distribution picture (recorded from 0 to 2 min) in rCBF units of ml/100 g/min. This is done by calculating the time constant ki for pixels with high count rate using the entire sequence of four 1 min pictures and using a fixed value for the brain:blood partition coefficient, lambda. The method is essentially based on the bolus distribution principle, and it allows the estimation of blood flow in ischemic areas. Application to positron emission tomography is discussed.

Exchanges of oxygen and carbon dioxide alter inert gas pattern in single-breath tests.

Concentration of inert gas in the lung is lowered when CO2 entrance exceeds O2 exit and is raised when O2 exit predominates. In air-breathing subjects who expire to residual volume, this "metabolic gas effect" often causes a rising N2 concentration when in fact there should be a terminal fall because of low N2 in apical regions. In single-breath tests, we compared the dilution of resident N2 with dilution of an inspired gas, Ne, to find the "ideal" inert gas concentration (due only to mixing of resident gas with inspired gas). The displacement from the ideal concentration vs. volume pattern depends on the timing of the breath, because early CO2 entrance gives way later to O2 exit. Sometimes observed patterns are above or below but parallel to the ideal, and sometimes the observed slope of phase III is steeper than ideal for N2 and flatter than ideal for Ne. In addition to phase III distortions, the metabolic gas effect sometimes also distorts phase IV height and the intersection between phases III and IV. The distortions depend strongly on absolute concentration of the indicator gas in the lung, so they are very small when "closing volume" maneuvers are done in the conventional manner. However, distortions can be large and misleading when single-breath maneuvers are done in unconventional ways.

Compressive stress and inert gas in Mo films sputtered from a cylindrical-post magnetron with Ne, Ar, Kr, and Xe

Previous work by the present authors on metal films sputtered from cylindrical-post magnetron sources has established the existence of an abrupt transition in internal stress and other properties that occurs as the working pressure is lowered. High compressive stress, maximum reflectance, minimum resistivity, entrapped inert gas, and dense, Zone-T microstructure were found in a wide variety of pure metals and alloys when sputtered in argon at sufficiently low pressures. The present study reports this same phenomenon for a single metal (Mo) sputtered in a variety of gases (Ne, Ar, Kr, Xe). In this case the transition pressure varies inversely with the mass of the sputtering gas, from less than 0.3 Pa for xenon to over 0.9 Pa for neon. The concentration of inert gas in the films also varies inversely with the mass, increasing by two orders of magnitude from krypton to neon. Deposition through a narrow slit-aperature established that the entrapped gas comes from the sputtering cathode (backscattered, neutralized ions) by line-of-sight trajectories. Moreover, right-angle scattering of gas from the sides of the cylindrical-post magnetron, as viewed by a given substrate, becomes increasingly prominent for the heavier gasses, and is shown to be a principal factor in causing compressive stresses. The evidence indicates that compressive stress and the presence of entrapped inert gas in the films are both by-products of inert gas bombardment of the condensing material during deposition. A significant correlation is found between the variation in transition pressure and the decreased scattering cross sections reported in the literature for energetic inert gas particles, such as those scattered from sputtering targets of greater mass.

Two Methods for Calculating Regional Cerebral Blood Flow from Emission Computed Tomography of Inert Gas Concentrations

Two methods are described for calculation of regional cerebral blood flow from completed tomographic data of radioactive inert gas distribution in a slice of brain tissue. It is assumed that the tomographic picture gives the average inert gas concentration in each pixel over data collection periods of 30 to 60 sec. In the early picture method a single picture taken during maximum inert gas concentration (by intaarterial injection or by inhalation) is analyzed. In the sequence of pictures method the alterations in local inert gas concentration are followed over time. The proposed methods are implemented using synthetic data of xenon-133 emission computed tomography and some of the difficulties likely to be encountered in practice are stressed.

Effect of intrapulmonary hematocrit maldistribution on O2, CO2, and inert gas exchange

The potential effect of intrapulmonary variations in hematocrit on gas exchange has been studied in theoretical models of the lung containing maldistribution of both hematocrit (Hct) and ventilation-perfusion (VA/Q) ratio. Hematocrit inequality enhanced gas exchange when units of low VA/Q were given a low Hct, arterial PO2 rising by as much as 14 Torr and PCO2 falling by up to 2 Torr depending on the particular distributions of Hct and VA/Q, whereas gas exchange was depressed when units of low VA/Q had a high Hct. After measuring inert gas solubilities in both dog and human blood of different Hct, the effect of Hct inequality on inert gas exchange was similarly assessed. Solubility was found to increase with HCT for less soluble gases. Because of this, conditions for enhancement of inert and O2 exchange by HCt inequality coincided, and it was found that in general the effects on O2 and inert gas transfer were quantitatively internally consistent. Even when Hct inequality was extreme, the resulting perturbation of inert gas concentrations was sufficiently small that the main features of the recovered VA/Q distributions were unaltered.

Calculations on the recombination of halogen atoms in the presence of various inert gas atoms and molecules

The recombination reactions of two halogen atoms (chlorine and iodine) have been simulated using a molecular dynamics technique. The rate of recombination has been calculated in the presence of helium (chlorine and iodine) and two simple polyatomics (iodine only), over a range of inert gas concentrations. The polyatomics have been treated as rigid rotors. Most of the calculated rate constants agree quite well with the experimental results. However, the absence of information on polyatomic interaction potentials makes it difficult to assess the suitability of rigid-rotor techniques for studying reactions involving complex polyatomics.

Computer study of the hydrogen atom recombination reaction under high pressure conditions

AbstractThe hydrogen‐atom recombination reaction has been simulated using a molecular dynamics technique recently formulated by the authors [1]. The rate of recombination has been calculated over a range of temperatures and inert gas concentrations (He and Ar) and agrees well with available experimental data. The calculations reproduce the negative activation energy characteristic of an atom recombination process. Over the range of conditions studied recombination was found to proceed via the energy transfer mechanism only, no evidence of bound HAr or HHe species was observed. Recombination was found to occur through an intermediate metastable diatomic molecule which is in equilibrium with its environment and from which there is a bottleneck to the formation of a stable molecule. The initial formation of a metastable species is sensitive to the hydrogen‐inert gas potential, but relaxation of the total energy is primary determined by the mass of the third‐body and the collision frequency.

A Shock-Tube Study on the Combustion Process of Hydrocarbon Fuels : 2nd Report; Systematic Measurements of Ignition Delays and Presentation of a Reaction Scheme

Measurements were made, with shock-tubes, on the ignition delays of three kinds of representative saturated higher-hydrocarbon fuels over the temperature range of 900-1700K, varying systematically the equivalence ratio, the inert gas concentration and the overall pressure of the mixture. A simplified model of the reaction mechanism for the ignition of general higher-hydrocarbon fuels was proposed, on which the ignition delays under various conditions were calculated with use of available rate constant data. The experimental results, with their dependence on various parameters, were found to be well correlated with the calculations above a boundary temperature where a sharp change in the apparent activation energy takes place.