Changes In Gas Density Research Articles

Laser heterodyne measurement of electron densities in a hollow cathode discharge

A laser heterodyne system has been developed to measure electron densities in a hollow-cathode discharge as used in metal vapour lasers. The beat frequency between two helium-neon lasers, one of which contains the discharge under investigation within its cavity, is monitored in real time as the discharge is rapidly switched off. The beat frequency changes because of refractive index changes in the plasma. By comparing the beat frequency changes at two wavelengths (0.6328 and 1.15 mu m), electron density and gas density changes have been determined. Electron densities have been measured in a cylindrical hollow cathode discharge (6 mm diameter, 10 cm long) in helium gas over a range of filling pressures (1-15 Torr) and discharge currents (10-150 mA). Electron density is found to behave linearly with discharge current, and to follow the cathode fall potential with pressure.

Changes in the single-breath nitrogen washout curve on exposure to 17,600 ft

Seventeen volunteers were exposed to 17,600 ft after an acclimatization period, at 9,800 ft. Single-breath nitrogen washout curves were done at base camp (2,600 ft), on days 2 and 4 at 9,800 ft, and on days 1, 2,3 4, and 7 at 17,600 ft. There was a significant 39% increase in the slope of phase III on day 2 at 9,800 ft, accompanied by a 125 ml mean increase in anatomic dead space (Vd) and a marked decrease in cardiac oscillations. By day 4 at 9,800 ft phase III slopes were reduced and were not significantly different from base-line controls, while cardiac oscillations were increased and Vd decreased from day 2. Subsequent exposure to 17,600 ft produced another significant increase in phase III slope to 87% above control, which by day 7 had decreased significantly to 63% above control. Cardiac oscillations were again diminished and Vd increased. These changes cannot be accounted for by changes in gas density, nor by the decrease in PIOO2 per se, since this alone would decrease the range of PaNN2. They suggest a pathophysiologic lung lesion which impairs gas mixing and increases asynchronous emptying during early altitude exposure. high-altitude pulmonary edema; gas-mixing impairment at altitude Submitted on November 7, 1974

Interferometric measurements of the gas density distribution in the dark space of an abnormal glow discharge in xenon

Measurements of the spatial dependence of the gas density distribution near the cathode of an abnormal glow discharge on the current density are described. The technique uses a pulsed discharge in xenon with a mercury cathode, placed in one arm of a Michelson interferometer so that the changing density influences the optical path length. The sensitivity of the system is equivalent to approximately 0.04 Torr at 300K. Considerable changes in gas density are observed in the dark space, particularly at high current densities. The proposed theoretical model for this non-uniform gas density agrees well with the experimental results.

A spark gap switching system for gasdynamic facilities

A spark gap switching system has been developed to coordinate the discharge of a 300 kJ capacitor bank with the high speed flow of helium in a shock tube driver. The trigger system includes a flow transducer, a pulse forming circuit, a high voltage spark generator, and four heavy duty spark gaps that can carry total peak currents greater than 1.5×106 A. A glow gauge flow transducer sensitive to small gas density changes was used whose input power and signal output can withstand high voltage fluctuations. This switching system is of use with gasdynamic discharge devices requiring a minimum number of switches.

Gas Heating Effects in the Constriction of a High-Pressure Glow Discharge Column

Numerical calculations have been made to examine effects of rapid gas heating and subsequent gas density changes on the current density distribution in a high-pressure positive column. Radial profiles of gas temperature, radial expansion velocity, density, and pressure and of electron current density are calculated as functions of time for a simplified model of a glow discharge column. Initially, the glow is diffuse and the background gas is uniform. Considered specifically is a hydrogen discharge with an initial pressure of 500 Torr, an initial current of 6.0 A, a constant axial electric field of 10 kV/cm, and a radius of ∼0.75 mm. The gas dynamics are described by conservation equations for mass, momentum, and energy in a viscous, thermally conductive, compressible fluid and by the equation of state for a perfect gas. The dependence of the ionization rate on the electric field to gas density ratio makes the electron current density a sensitive function of the gas density. At 60 nsec the gas temperature near the axis is sufficiently high for the onset of rapid thermal dissociation in an axial core, and effects of gas transport are significant. The axial gas density is decreased ∼10%; the axial current density is twice its initial value; and the column is partially constricted. Calculated results are consistent with properties of a similar discharge studied experimentally by Cavenor and Meyer, particularly at the time of the formation of a filamentary channel, observed experimentally after the first stage of the glow-to-arc transition.

A discussion on D and E region winds over Europe - Results of an experimental investigation of correlations between D-region neutral gas winds, density changes and short-wave radio-wave absorption

Between December 1969 and March 1970 a total of 26 Skua II rockets were successfully launched close to local noon at Arenosillo, Spain. Using an ultralight chaff the winds and chaff fall rates have been determined at heights between 75 and 95 km. At the same time A 3 -absorption measurements were carried out on 2.83 MHz between Aranjuez (Madrid) and Arenosillo. From the wind and fall-rate measurements a quantity which is roughly proportional to the air mass flow has been derived for each km height range. These flow vectors were obtained on different days at different height levels and correlated with the noon absorption values L ~ N v d h which were taken from the short-wave propagation path between Arenosillo and Aranjuez. A significant but not very high correlation was found between the mass flow at 90 to 93 km and the absorption L , with L increasing with increased flow from the north-northeast, and at 85 km with L increasing with increased flow from the south-southwest. For the other heights between 75 and 95 km a significant correlation could not be found although there is some indication at 77 km.

Proposed ultrastable CO2oscillator

Stabilized gas laser systems have failed to achieve the ideal stability, determined by fundamental noise, by as much as five orders of magnitude. Regardless of techniques used, long term stability has been limited by changes in discharge parameters affecting the center frequency of the spectral line used as the reference. The most serious causes of instability are the changes in gas density, composition, temperature, and electron density which are difficult to avoid in a gas discharge.

Physiologic Mechanisms of Maintaining Thermal Balance in High-Pressure Environments

This review of body-temperature control aims to define the optimal environment for deep submergence habitats, at pressures of 15-20 atm. Environmental factors demand major attention since they will largely dictate the physiologic adjustments which will be required. Inherent changes in gas composition and density indicate major increases in surface heat transfer, depending upon atmospheric temperature and movement. Habitat insulation and ocean temperature suggest that body-surf ace heat transfer will also be increased by radiation, but this may be modified by heating techniques, special insulation methods, or by treatment of cold habitat surfaces. Humidity may be an important determinant of comfort and skin hygiene. Psychrometric methods for hyperbaric atmospheres are discussed. Experimental data on body heat transfer in helium-rich environments are presented from simulation studies, showing a major increase in convective heat transfer from the skin, in helium at increased pressures. The implications of these findings upon physiologic and environmental aspects of deep submergence programs are discussed.

Measurement of gas density in a hydrogen-filled thyratron in modulator duty

A probe technique is described which can be used to measure transient changes in neutral gas density in a low-pressure gas discharge.The technique has been used to study changes in neutral gas density in the discharge space of a hydrogen thyratron on recurrent pulse load. The study reveals that the local density immediately prior to a current pulse depends on the gas filling pressure and the average value of the electrical load. During the current pulse the local density falls by an amount which depends on the pulse-current amplitude and duration, but recovers to its original value after the end of the current pulse in a few tens of microseconds.Since the arc-voltage drop, and therefore the power dissipated within the thyratron, varies with gas density and has a minimum value near the middle of the working density range, the observed changes in density result in the complex relation which exists between the energy losses in the thyratron and the electrical load to which it is subjected.

Gaseous Detonations. VI. The Rarefaction Wave

The density profile of the rarefaction wave which follows a detonation has been determined using the technique of x-ray absorption measurements to follow rapid gas density changes. The observed density-time dependence was found to agree, within experimental errors, with the predictions of the hydrodynamic theory developed by Taylor, Doering, and others. As the theory predicts, the density in the rarefaction wave decreases for approximately one-half of the distance traveled by the detonation wave; behind this is the region of quiescent gas at constant density.

A Simplified Method for Computing Oil Recovery by Gas or Water Drive

Abstract The approximate methods which are now in use for calculating oil displacement from reservoirs by gas-cycling or gravity-drainage at constant gas pressure, or by water flooding, make use of fundamental relationships derived by Leverett and Buckley and Leverett. The mathematical equations needed are derived by applying Darcy's law to the flowing phases, and by material balance considerations. In general, any treatment of this type gives, for any particular exploitation time considered, a plot of oil saturation against distance in the reservoir. The oil recovery must then be obtained by integrating in some manner the area under the plot. A useful analytical method has been derived for computing the average saturation, and hence the oil recovery. Use of this method simplifies the calculations because it makes unnecessary any numerical integrations, and even the saturation distribution plots are not needed. A further advantage of the method is that knowledge of the relative permeabilities is required only for a limited and intermediate saturation range. In both the Buckley and Leverett method and the method discussed here, a linear sand section is assumed, and in the case of gas drive the gas pressure is assumed sufficiently constant both with respect to reservoir position and time so that changes in gas density, solubility, or reservoir volume factor are negligible. Thus, the exploitation contemplates oil displacement as by an immiscible phase. Examples are given to illustrate how the new method can be used. Introduction and Theoretical Background This paper treats a simplified method for computing oil recovery when the oil is displaced from the reservoir sand by a fluid which, within the limits of accuracy desired, can be assumed to be incompressible and immiscible with the oil. The method makes use of two basic relations originally developed for the case of water displacing oil. However, the case of gas displacing oil saturated with gas at a constant (or nearly constant) pressure may also be considered a displacement by an immiscible fluid. This is possible for the reason that the concentration of the gas in the oil never changes if the pressure is fixed. Consequently, any additional free gas must remain undissolved in the oil, and so must act essentially as an immiscible phase. For convenience, the case of gas drive will be considered first.