Showing papers on "Atmospheric pressure published in 1981"

Array measurements of atmospheric pressure fluctuations above surface gravity waves

Abstract: A joint experiment to study microscale fluctuations of atmospheric pressure above surface gravity waves was conducted in the Bight of Abaco, Bahamas, during November and December 1974. Field hardware included a three-dimensional array of six wave sensors and seven air-pressure sensors, one of which was mounted on a wave follower. The primary objectives of the study were to resolve differences in previous field measurements by Dobson (1971), Elliott (1972b) and Snyder (1974), and to estimate the vertical profile of wave-induced pressure and the corresponding input of energy and momentum to the wave field.Analysis of a pre-experiment intercalibration of instruments and of 30 h of field data partially removes the discrepancy between the previous measurements of the wave-induced component of the pressure and gives a consistent picture of the profile of this pressure over a limited range of dimensionless height and wind speed. Over this range the pressure decays approximately exponentially without change of phase; the decay is slightly less steep than predicted by potential theory. The corresponding momentum transfer is positive for wind speeds exceeding the phase speed. Extrapolation of present results to higher frequencies suggests that the total transfer is a significant fraction of the wind stress (0·1 to 1·0, depending on dimensionless fetch).Analysis of the turbulent component of the atmospheric pressure shows that the ‘intrinsic’ downwind coherence scale is typically an order-of-magnitude greater than the crosswind scale, consistent with a ‘frozen’ turbulence hypothesis. These and earlier data of Priestley (1965) and Elliott (1972c) suggest a horizontally isotropic ‘intrinsic’ turbulent pressure spectrum which decays as k−ν where k is the (horizontal) wave-number and ν is typically −2 to −3; estimates of this spectrum are computed for the present data. The implications of these findings for Phillips’ (1957) theory of wave growth are examined.

Microwave-excited atmospheric pressure helium plasma emission detection characteristics in fused silica capillary gas chromatography

Abstract: Interfacing of fused silica gas chromatographic capillary columns to a microwave-excited atmospheric pressure helium plasma (MED) is investigated. The system for glass and fused silica capillary operation incorporates an interface where excess solvent can be vented by a chemically deactivated fluidic-logic gas switching system. A TM/sub 010/ resonant cavity allows axial viewing of plasma emission. A quartz refractor plate background corrector improves selectivity ratios for elements whose emission occurs in the high-carbon (cyanogen) background region. Background emission characteristics of the helium plasma under various conditions are established from 200 to 500 nm. Calibration curves, selectivity ratios, and detection limits are established for the elements vanadium, niobium, chromium, molybdenum, tungsten, manganese, iron, ruthenium, osmium, cobalt, nickel, mercury, boron, aluminum, carbon, silicon, germanium, tin, lead, phosphorus, arsenic, sulfur, selenium, fluorine, chlorine, bromine, iodine, hydrogen, and deuterium.

Telemetric differential pressure sensing system and method therefore

Abstract: A differential pressure sensing device is fully implanted in the body of a patient to monitor internal pressure such as intracranial pressure. A movable element in the sensor communicates with the internal pressure of the body to be measured on one side and the atmospheric pressure on the other, the latter communicated through the intact skin and a nearly coplanar membrane. The movable element's differential pressure dependent displacement changes a physical characteristic of the sensor, such as the resonant frequency of a tuned L-C circuit, and the change is detected external to the body by a radiating detector system, such as a frequency swept radio frequency oscillator, by which the internal pressure is read out.

Seasonal variations in global sea level pressure and the total mass of the atmosphere

Abstract: The annual cycles of sea level and surface pressures and the atmospheric pressure owing to water vapor have been analyzed in detail. Global sea level pressures undergo an annual cycle of 0.5 mbar range with a maximum in the northern winter. Global surface pressures, which represent the total mass of the atmosphere, also undergo an annual cycle of 0.5 mbar range but with the maximum in the southern winter. The changes in water vapor concentrations are responsible for the latter—water vapor has a maximum in the southern winter. The constancy of the mass of dry air is used as a check on the accuracy of computations. The total mass of the atmosphere is 513.7 × 1016 kg with a standard error of 0.02 × 1016 kg and an annual cycle of amplitude 0.1 × 1016 kg. The corresponding global mean surface pressure of the atmosphere is 984.68 mbar. The mean total mass of water vapor is 1.3 × 1016 kg which corresponds to 2.53 cm of precipitable water or 12906 km3 of water at 0°C. The distribution of pressure and mass as a function of latitude are also presented. A substantial annual exchange of mass occurs between the hemispheres amounting to 0.7 × 1016 kg of dry air (2.7 mbar range in hemispheric averaged pressure). Maximum pressures occur in winter, and the summer loss of mass is partially compensated for by increased water vapor amounts. The maximum net meridional flow occurs across 5°N in the transition seasons. In the northern hemisphere, water vapor undergoes an annual cycle with a range of 1.5 mbar (area averaged) and a summer maximum, and the sea level pressure owing to dry air undergoes an annual cycle of range 5 mbar and a winter maximum. Of this, 54% is due to exchanges with the southern hemisphere and 46% is due to changes in the artificial atmospheric mass used to correct from the surface to sea level.

The oxygen content of air-saturated fresh waters over - ranges of temperature and atmospheric pressure of - limnological interest

Abstract: SIL Mitteilung No. 6 (MORTIMER 1956) and its aids for calculation of per cent oxygen saturation, widely distributed and still in use, were later shown to be based on erroneous experimental data. Fo...

Design and construction of an atmospheric or environmental SEM (part 1)

Abstract: Progress in designing and constructing an atmospheric or environmental scanning electron microscope (SEM) is reported. The introduction of vacuum pumping between the objective and pressure limiting aperture has allowed the use of relatively large pressure limiting apertures, i.e., up to 57 μm for operation at atmospheric pressure or up to 400 μm for operation at saturation water vapour pressure and room temperature. The imaging obtained has been considerably improved by these developments. The first part of experimentation and analysis on the vacuum characteristics of the new system together with different detection configurations is also presented.

Rate constants for ozone–alkene reactions under atmospheric conditions

Abstract: By measuring the rates of decay of ozone in a large excess of reactant, second-order rate constants have been obtained for the reactions of ozone with ethene, propene, but-1-ene, trans-but-2-ene, isobutene, hex-1-ene, cyclopentene, cyclohexene, isoprene, vinyl fluoride, 1,1-difluoroethene, cis-1,2-difluoroethene, trans-1,2-difluoroethene, trifluoroethene, tetrafluoroethene, and 2,5dihydrofuran. The reactions have been studied in synthetic air at atmospheric pressure and at temperatures of 294 and 260 K. The rate constants and Arrhenius parameters are discussed in relation to existing kinetic data on ozone–alkene reactions.

The structure of X-ray illuminated stellar atmospheres

Abstract: The theory of X-ray illuminated stellar atmospheres in binary X-ray systems is described. Particular attention is directed to the location of the transition zone between the photosphere and the corona, which largely determines the mass flux in the evaporative wind caused by X-ray heating. A controversy in previous work concerning the effect of emission line cooling on this location is resolved. The lines are found to be optically thick, and they do not greatly affect the location of the transition region. Detailed NLTE stellar atmosphere models are constructed, including continuum radiation only. The pressure at the transition zone is proportional to the local X-ray heating rate, and the spectrum emitted by the atmosphere is nearly stellar, but with reduced continuum jumps. The mass loss in the wind may be enough to power the X-ray emission in the HZ Her--Her X-1 system if a large fraction is captured by the neutron star.

Tank contents gauge

Abstract: A tank contents gauge comprises pressure sensors 11 for sensing the pressure at two positions in the tank at known vertical separation, a port 24 for sensing the ambient pressure in the tank, which may be atmospheric pressure, and a transducer 19 to which three pressure readings are transmitted one at a time via a switching mechanism 21,22. Where the transducer is a differential transducer the second side thereof is connected to the port 24 so that the pressure readings are compared in each case with the ambient pressure reading, and the transducer offset can be determined and catered for in calculations made from the readings. A data processing system 25 with a memory 26 is provided for analysing the readings and making the required calculations of liquid depth and, by using internal look-up calibration tables, those of volume and weight. The data processing system may also serve to control the switching mechanism 21,22. The specific gravity of the contents can be calculated from the pressure readings and the known vertical separation and stored for use when the contents approaches, or falls below, the upper sensor 11.

The influence of pressure on the self-assembly of the thick filament from the myosin of vertebrate skeletal muscle.

Abstract: The thick-filament-monomeric-myosin equilibrium was prepared from pure myosin at pH 8.1. The application of hydrostatic pressure to the self-assembly equilibrium resulted in a biphasic dissociation curve in which a linear decrease in turbidity (a measure of weight added to or lost from the filament) was followed by a transition to a second pressure-insensitive phase. The first phase represents the effect of hydrostatic pressure on the growth or propagation phase of filament assembly. Here is was shown that hydrostatic pressure served to shorten the filaments in concert towards the bare zone whilst maintaining the narrow length distribution seen at atmospheric pressure; the filament concentration remained constant during the experiment. A more precise definition of the delta-v for the assembly of monomer into filament was obtained than had hitherto been possible. The positioning of the bare zone at the centre of the filament seems to be one of the more obvious functions of the length-regulation mechanism. It also appears that all the basic structural elements of the native thick filament are potentially present in the pH 8.1 homopolymer; its length can be increased by physiological concentrations of MgCl2 and decreased by pressure. The monodisperse native filament could then be formed by a fine tuning of the basic length-regulation mechanism of the homopolymer by the co-polymerization of the other thick-filament proteins.

Gauge pressure sensor

Abstract: An atmospheric differential pressure sensor is disclosed comprising a pressure transducer, having a diaphram, mounted within a two piece protective transducer housing. An ambient atmospheric pressure receiving cavity is formed by the housing and coupled to the transducer diaphragm by a pressure transmitting tube that has a isolating oil drop within the tube to keep atmospheric contaminants away from the diaphram. The atmospheric pressure receiving cavity has external openings extending peripherally over more than 180° of rotation about a central axis of said housing, and the ambient cavity provides a non-linear directional path between the end of the tube connected to the cavity and the exterior of the housing.

The pressure dependence of elastic constants and bond bending in HgTe

Abstract: The elastic stiffness constants of HgTe have been obtained from ultrasonic wave velocities measured as a function of hydrostatic pressure up to 15·5 × 108 Pa, which is just below the pressure pt at which the structural transition from zinc blende to cinnabar takes place. The shear constants 1/2(C11 – C12) and C44, which are small even at atmospheric pressure, decrease linearly with pressure up to p t, but do not reach zero; all the shear acoustic mode Gruneisen gammas are negative in the long-wavelength limit. It is concluded that the densification phase transition is associated with collapse under a macroscopic shear which takes place when a modified Born stability criterion that 1/2C11−-C12)/B is 0·17 is reached. At pt the ratio βt/αt, of the bond-bending βt to stretching αt force constants is 0·075. The ionicity is found to increase under pressure towards the Phillips critical value of 0·785; as this happens, the bond-bending force constant β reduces until the crystal can no longer withstand s...

Air pressure shock absorber

Abstract: An air pressure shock absorber for smoothly stopping a moving object reciprocated by a rod in an air pressure cylinder. The shock absorber absorbs and reduces the internal pressure of a chamber in the cylinder to smoothly stop the moving object by the communication of air compressed in the chamber to the atmosphere through a bypass passage formed in a cylinder wall. The air pressure is released to the atmosphere after the piston has moved through a predetermined stroke.

Reentrant nematic and columnar phases in disc-like liquid crystals at atmospheric pressure

Abstract: 2014 We describe the first example of reentrant ND nematic and Dr columnar mesophases at atmospheric pressure in a pure disc-like compound. J. Physique LETTRES 42 (1981 ) L-417 L-419 15 SEPTEMBRE 1981, Classification Physics Abstracts 61.30 64.70E

The action of high hydrostatic pressure on the membrane currents of Helix neurones.

Abstract: 1. The actions of high hydrostatic pressure (10.4, 20.8 MPa) on the membrane currents of Helix neurones were examined under voltage clamp. 2. High hydrostatic pressure (20.8 MPa) reduced the maximum inward current to 0.78 and the delayed outward current, measured at the inward current reversal potential, to 0.75 of their value at atmospheric pressure. 3. High hydrostatic pressure shifted the curve relating the inward current conductance to membrane potential to more positive values but the maximum conductance was altered. 4. The rates of activation of the inward and delayed outward currents were slowed by pressure. 5. The steady-state level and time course of inactivation of the inward current was unaffected by high pressure over the investigated range. 6. The effects of high hydrostatic pressure on the fast outward current identified in gastropod neurones by Connor & Stevens (1971) were also examined. 20.8 MPa reduced the current measured at -30 mV to 0.71 of its control value. 7. The rate of activation of the fast outward current was slowed by high pressure but the time constant of inactivation was unchanged. 8. The majority of the effects of high hydrostatic pressure were completely reversible upon decompression. 9. These results are discussed with reference to the known effects of high hydrostatic pressure on the action potential and discharge frequency of gastropod neurones. Possible sites and mechanisms of pressure action on the excitable cell are briefly discussed.

Low Pressure Vapor Phase Epitaxy of GaAs in a Halogen Transport System

Abstract: Deposition of from the system at 1023 K and pressures from 1 down to 0.01 bar leads to controlled growth rates ranging from 40 to 1 μm/hr. Due to the surface kinetic limitation of the process, very uniform films are obtained at reduced pressures. The background impurity level is low; 77 K electron mobilities of 73,000 cm2 V−1 sec−1 were obtained for not purposely doped samples with electron concentrations in the upper 1014 cm−3region. Using as a dopant, the electron concentration increases linearly with the pressure. The sulfur‐doped films show the same values for the mobility and the saturation concentration of electrons as layers obtained at atmospheric pressure.

Shock tube studies of the acetylene and ethylene pyrolysis by UV absorption.

Abstract: Absorption measurements at 216 and 230 nm of shock heated C2H2, C2H2+H2, and C2H4 diluted in Ar were made over the temperature range 1800 K to 2600 K at half of atmospheric pressure. Absorptivities were evaluated for C4H2, which is the main product of C2H2 pyrolysis, as well as for C2H2 and C2H4. The relative value of C4H2 absorption was confirmed to decrease with the presence of H2 in accordance with a computer modeling result using a 25-reaction mechanism. The time profile of C4H2 absorption could be modeled well with k=1012.4 cm3 mol−1 s−1 for the reaction H2+C2H=C2H2+H.

Bottom Pressure and Sea Level Measurements in the Gulf of Lions

Abstract: Bottom and atmospheric pressure, sea level, wind, current and temperature measurements have been obtained during summer in the coastal zone of the Gulf of Lions. Relations between these parameters are estimated mainly with coherence analysis. First, it is shown that the atmospheric pressure forcing is small and that the sea level and bottom pressure spectra are very similar. Then the characteristics of tides are computed with a least-squares method. Removing the tidal signal from the original time series allows us to study in a clearer way the inertial frequency band: arguments for the possible occurrence of sea surface oscillations at this frequency are discussed. At lower frequencies, large sea level variations are due to the wind. At frequencies higher than the tidal ones, very energetic signals are connected with natural oscillations of the Gulf of Lions induced by atmospheric pressure perturbations of a relatively small scale. This paper is concerned with regional oceanograhy, but the result...

Composition for use in an absorption refrigeration system

Abstract: A composition for use in an absorption refrigeration system which comprises at least one refrigerant of a fluorinated alcohol having 2 to 10 carbon atoms, being a liquid at ordinary room temperature, and being vaporizable under normal atmospheric or reduced pressure when heated, and at least one absorbent having a higher boiling point at normal atmospheric pressure than the refrigerant and being capable of absorbing the refrigerant, and an absorption refrigeration system wherein said composition is used.