Showing papers on "Atmospheric pressure published in 1992"

Effects of Atmospheric Pressures on Gas Transport in the Vadose Zone

Abstract: Temporal variations in barometric pressure due to weather patterns may induce air intrusion into the subsurface. This air intrusion can affect monitoring activities aimed at characterizing the composition and movement of gases in the vadose zone. Expressions are presented to estimate gas fluxes due to the combined effects of Knudsen diffusion, multicomponent molecular diffusion, and viscous flow. These expressions are used to evaluate the validity of the single-component advection-dispersion equation for simulating gas transport in the presence of atmospheric pressure variations. The single-component equation provides reasonable results when used to simulate transport in media with relatively high gas permeability. Computer simulations of vertical transport at sites with homogeneous soils indicate that “fresh” air can migrate several meters into the subsurface during a typical barometric pressure cycle. Horizontal pressure gradients can develop at sites with near-surface heterogeneities. These gradients may cause fresh air to intrude meters or tens of meters into the vadose zone during a storm event.

Superheating effects associated with microwave dielectric heating

Abstract: Fluoroptic temperature measurements have established that organic solvents in a microwave cavity superheat by 13–26 °C above their conventional boiling points at atmospheric pressure; this behaviour is interpreted using a model of nucleate boiling that emphasises the importance of the wetting properties of the solvents.

Application of compressed carbon dioxide in the incorporation of additives into polymers

Abstract: It has been found that carbon dioxide remarkably accelerates the absorption of many low molecular weight additives into a number of glassy polymers. This effect is due to the high diffusivity, solubility, and plasticizing action of compressed CO2 in polymers. The transport of CO2 and the effects of CO2 pressure on the transport of other low molecular weight compounds in polymers have been studied by a simple gravimetric method: Polymer film samples were contacted in a pressure vessel with compressed CO2, or with CO2 plus various organic liquids or solids, and the sample weight was followed with a fast-response electronic balance during subsequent desorption at atmospheric pressure. Upon release of the pressure, absorbed CO2 rapidly diffuses from the polymer, while the other compounds desorb much more slowly. The amount of additive absorbed can be determined from the plateau weight of the sample after most of the CO2 has escaped. Extensive kinetic and equilibrium data are reported for the model system poly(vinyl chloride)/dimethyl phthalate/CO2, and a number of other examples of CO2-assisted additive absorption are given. This “infusion” process, in effect, amounts to the partitioning of the additive between the CO2- and polymer-rich phases; consequently, the relative solubility of the additive in CO2 and in the polymer is a major factor governing the amount of additive absorbed. Data reported here illustrate the generality and potentially broad applicability of CO2-assisted polymer impregnation.

Atmospheric pressure and gravity

Abstract: SUMMARY Gravity Green's functions for a column load of a model atmosphere on a spherical, elastic Earth are presented and they are used to evaluate the contribution of global atmospheric pressure variations to local gravity. The Green's functions are found to be relatively insensitive to the details of the model atmosphere, but they are dependent on the temperature at the base of the column, and on the relative height difference between the base of the column and the gravity station. The total signal that global pressure systems contribute to gravity is about 30 μgal, of which about 90 per cent is produced by the atmosphere within 50 km of the gravity station. A zone between 50 and 1000km from the gravity station contributes a couple of μgal, as does the remainder of the globe. This pattern, the coherence scale of pressure fluctuations, the time and spatial scales appropriate to the hydrostatic approximation, and the distance of the gravity station from the oceans, suggest a division of the globe into local, regional, and global zones. Data requirements, processing details, and the reliability of the computed signal are different in each zone. The local zone is within about 50 km of the gravity station. Within this zone pressure changes rapidly in time, but is spatially coherent, so that hourly observations of pressure and temperature at the gravity site alone are sufficient to compute an accurate correction, except when a front is passing through. The regional zone extends from the edge of the local zone to between several hundred and a thousand kilometres. The signal from this zone is small and is only weakly coherent with the signal from the central zone, so that a rather sparse array of hourly samples of pressure and temperature are required. The gravity signal from the global zone can reach about a μgal. It varies on a time-scale of days, and is influenced by the response of the oceans to pressure variations. Previously reported observations that the admittance between local pressure and gravity residuals depends on epoch, frequency, or site, are most probably due to incorrect modelling. A proper local, regional, temperature, and global correction can adequately account for the gravity signal from the atmosphere to within a few tens of ngal in the diurnal band, and about 100 ngal in the days to seasonal band, except during extreme weather conditions. The application of the local correction lowers the power spectral density of the gravity residuals in every band from seasonal to hourly. The regional, global, and temperature corrections lower the residual noise in the seasonal and synoptic bands, but are not consistently effective at periods less than about half a day.

Surface science at atmospheric pressure: Reconstructions on (001) GaAs in organometallic chemical vapor deposition

Abstract: We report the first observation of reconstructions on semiconductor surfaces in atmospheric pressure (AP) environments. Using reflectance-difference spectroscopy we show that the primary reconstructions that occur on (001) GaAs in ultrahigh vacuum (UHV) also occur under AP H 2 , He, and N 2 . These results demonstrate that dimer formation is not restricted to surfaces in UHV and justify the use of UHV studies to determine (001) GaAs chemistry during AP organometallic chemical vapor deposition (OMCVD)

Densities and viscosities of the ethanolamines

Abstract: This paper reports the densities and viscosities of a series of ethnolamines consisting of monoethanolamine, diethanolamine, triethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, N-methyldiethanolamine, and N-ethyldiethanolamine. The densities and viscosities of these ethanolamines were measured up to the normal boiling point of the liquids at atmospheric pressure. The data were correlated using simple expressions and using a modified rough hard sphere model for the viscosity

Two-dimensional modelling of the dielectric barrier discharge in air

Abstract: A self-consistent two-dimensional modelling of microdischarges in devices in which one of the electrodes is covered with a dielectric is presented. The discharge development can be divided into four phases, a Townsend, an ionization wave or streamer, a cathode layer formation, and a decay phase. While during the Townsend phase the initial field strength distribution is hardly distorted, an ionization wave propagates towards the cathode during the following phase. On the wave reaching the cathode, a cathode layer develops. Its radical extension is determined by the increase of the current. During the decay phase the distributions of, for example, field strength and charge carriers are nearly frozen. The discharge fades because of the slow decrease of the field strength within its column. Energy and temperature distributions of microdischarge channels in air at atmospheric pressure are given.

An experimental and modeling study of ethanol oxidation kinetics in an atmospheric pressure flow reactor

Abstract: Experimental profiles of stable species concentrations and temperature are reported for the flow reactor oxidation of ethanol at atmospheric pressure, initial temperatures near 1100 K and equivalence ratios of 0.61–1.24. Acetaldehyde, ethene, and methane appear in roughly equal concentrations as major intermediate species under these conditions. A detailed chemical mechanism is validated by comparison with the experimental species profiles. The importance of including all three isomeric forms of the C2H5O radical in such a mechanism is demonstrated. The primary source of ethene in ethanol oxidation is verified to be the decomposition of the C2H4OH radical. The agreement between the model and experiment at 1100 K is optimized when the branching ratio of the reactions of C2H5OH with OH and H is defined by (30% C2H4OH + 50% CH3CHOH + 20% CH3CH2O) + XH. As in methanol oxidation, HO2 chemistry is very important, while the H + O2 chain branching reaction plays only a minor role until late in fuel decay, even at temperatures above 1100 K.

Kinetic study of n‐heptane oxidation

Abstract: The oxidation of n-heptane has been studied in a jet-stirred flow reactor in the temperature range 950–1200 K at atmospheric pressure for a wide range of fuel-oxygen equivalence ratios (0.2 to 2.0). A chemical kinetic reaction mechanism developed from previous studies on smaller hydrocarbons and extended to C6 and C7 species was used to reproduce the experimental data. Good agreement between computed and measured concentrations of major chemical species was obtained for the entire range of experimental conditions. Sensitivity analyses were carried out to identify the reactions having the greatest influence on the modeling results. The major reaction paths for n-heptane consumption and for the formation of the main products have been identified. In addition n-heptane ignition delays behind a reflected shock wave measured by other investigators were used to validate the present reaction mechanism at higher temperature and pressure.

Hydraulic Conductivity Recovery versus Water Pressure in Xylem of Acer saccharum

Abstract: Experiments were conducted to determine the influence of stem diameter, xylem pressure potential, and temperature on the rate of recovery of hydraulic conductivity in embolized stems of Acer saccharum Marsh Recovery of conductivity was accompanied by an increase in stem water content as water replaced air bubbles and bubbles dissolved from vessels into the surrounding water The time required for stems to go from less than 3 to 100% hydraulic conductivity increased approximately with the square of the stem diameter and increased with decreasing xylem pressure potential Recovery was halted when xylem pressure potential decreased below -6 kPa Increasing xylem pressure from 13 to 150 kPa reduced the time for recovery by a factor of 4 Temperature had little influence on the rate of recovery of hydraulic conductivity All of these results are in accord with a theory of bubble dissolution in which it is assumed that: (a) the rate of bubble dissolution is rate limited by diffusion of air from the bubbles to the outer surface of the stems, (b) the equilibrium concentration of gases in liquid in stems is determined by Henry's law at all air-water interfaces, (c) the equilibrium solubility concentration is determined only by the partial pressure of the gas in the gas phase and not directly by the liquid-phase pressure, and (d) the gas pressure of an entrapped air bubble in the lumen of a cell can never be less than atmospheric pressure at equilibrium

Pressure measurement device with selective pressure threshold crossings accumulator

Abstract: A pressure measurement device (10) with a selective altitude threshold crossings accumulator and method therefor provides for selective accumulation of relative pressure thresholds. A pressure sensor (12) measures atmospheric pressure and provides analog pressure signals (30) representing measured atmospheric pressures. A digital-to-analog converter (14) converts the analog pressure signals (30) to digital pressure signals (32) for a computer (16) which then computes altitudes corresponding to the measured atmospheric pressures. The computer (16) assigns a threshold flag value which corresponds to the relative direction (e.g. 'up' or 'down') from a first (e.g. lower) altitude to a second (e.g. higher) altitude when the magnitude of the first-to-second altitude differential exceeds a first threshold. The computer (16) then generates a unit count (34) when both the relative direction from the second altitude to a third (e.g. lower) altitude opposes the first-to-second altitude direction and the magnitude of the second-to-third altitude differential exceeds a second threshold. An accumulator (18) accumulates the unit counts (34), and the accumulated count (36) is displayed on a display device (20, 22).

Thermodynamic and transport properties of Ar-H2 and Ar-He plasma gases used for spraying at atmospheric pressure. I: Properties of the mixtures

Abstract: The transport properties of argon/ helium and argon/hydrogen mixtures used (or] plasma spraying were calculated according to the Chapman-Enskog theory with the following approximations: third for electrical conductivity and for electron translational thermal conductivity, second for heavy species translational thermal conductivity and internal thermal conductivity, and first for reactional thermal conductivity and viscosity. The results are as follows: The simplified mixing rule of Wilke must be used very cautiously especially for Ar-He where it predicts higher values for the mixture. The addition of hydrogen or helium to argon increases its thermal conductivity drastically. When considering the mean integrated thermal conductivity, the addition of hydrogen results in a step variation when dissociation occurs, while the increase is more regular when adding He.

Ozone generation in an oxygen-fed wire-to-cylinder ozonizer at atmospheric pressure

Abstract: A numerical simulation, including transport phenomena, is presented in this paper for the calculation of ozone generation in an oxygen-fed wire-to-cylinder ozonizer. The ozone density dependence on the first excited states of atomic and molecular oxygen and ozone is analysed, introducing three kinetic models. The influence of excited states on ozone production is shown as well as the correlation between the first excited state of atomic oxygen O(1D) and the second excited state of molecular oxygen O2(1 Sigma +g). Furthermore, these results confirm the validity of the plug-flow reactor hypothesis in the case of an oxygen-fed ozonizer.

Atmospheric pressure afterglow ionization system and method of use, for mass spectrometer sample analysis systems

Abstract: An system and method for use for analyzing samples in mass spectrometers using afterglow metastable species at atmospheric pressure to controllably dissociate, fragment and ionize sample is disclosed. Metastable species are created at atmospheric pressure by application of adjustable intensity and/or frequency electrical energy in one portion of a modular electric discharge chamber, then are caused to interact with sample in a distally located portion of the electric discharge chamber, termed the "afterglow" portion, to produce ionized sample molecules and ionized sample fragments etc. The system and method can be used with any source of sample but a preferred embodiment utilizes an ultrasonic nebulizer to nebulize sample solutions, such as conventional liquid chromatography system effluents, into sample solution droplets, followed by desolvation thereof to provide nebulized sample particles, prior to sample entry to the "afterglow" portion of an electric discharge chamber. Ionization of sample occures as a result of interaction with energy released by relaxing metastable species. Operation at atmospheric pressure reduces operational, contamination and maintenance problems and allows easy introduction of sample in a liquid form.

Atmospheric pressure calibration systems and methods

Abstract: Systems are provided to derive a value of barometric pressure at a defined location in the atmosphere at a computed geometric height. By using the geometric height in a look-up table of pressure/height values representing a standard atmospheric profile, atmospheric deviation data indicative of the difference between measured and reference pressures at that atmospheric location (C) is derived. Ground-based interrogators (10,20) located at spaced positions are used to initiate response signals from airborne transponders commonly installed in transient aircraft (C). Using resulting range data based on round-trip timing differences in signals sent to (12,16) and received from (16,14) the airborne transponder (C), geometric analysis and computation is used (18) to determine the geometric height of the transponder representing a specific atmospheric location. The height, together with barometric pressure data transmitted by the airborne transponder, are used (28) for the look-up of reference pressure data and derivation of atmospheric deviation data for that atmospheric location. Systems and methods provide such data for inflight altimeter calibration, height determination, atmospheric pressure profile development, weather forecasting, transponder calibration and other purposes.

Double tank pinch trigger pump water gun

Abstract: The present invention is directed toward a toy water gun which is operated by selectively releasing water from a water reservoir pressurized with air. The present invention has a manually operated pump incorporated into the design. As the pump is cycled, water and air is drawn from a water storage tank. Once drawn, the water and air are forced into a pressure reservoir. As the amount of water and air forced into the pressure reservoir increases, the pressure on the water within the pressure reservoir increases. The pressure of the water and air within the pressure reservoir increases with each cycle of the pump, until the pump can no longer overcome the pressure of the water and air within the pressure tank. The pressurized water and air within the pressure tank has an avenue of release that is regulated by the trigger mechanism of the invention. When no force is applied to the trigger, the pressurized water and air are held at bay with no means of release. When force is applied to the trigger, the water is first released from the pressurized container and is channeled through a narrow nozzle. The escape of the water, under pressure, through the narrow nozzle creates a stream of propelled water that lasts as long as the trigger is engaged or until the air pressure propelling the water equals the ambient pressure.

On-line measurement of benzene and toluene in dilute vehicle exhaust by mass spectrometry

Abstract: Tandem mass spectrometry (MS/MS), using either an atmospheric pressure ionization (API) or a low-pressure chemical ionization (LPCI) source, has the potential for measuring concentrations of individual hydrocarbon species in real time. In this study, a triple quadrupole mass spectrometer is used to monitor two environmentally important exhaust hydrocarbons species, benzene and toluene. Real-time data for concentrations ranging from 5 ppb to 30 ppm can be measured, with a time resolution of as little as 100 ms/data point.

Arsenic dimers and multilayers on (001)GaAs surfaces in atmospheric pressure organometallic chemical vapor deposition

Abstract: Arsenic dimers and multilayers are shown to exist on (001)GaAs surfaces under atmospheric pressure (AP) organometallic chemical vapor deposition (OMCVD) conditions. We obtained reflectance‐difference spectra from surfaces in AP H2 that are equivalent to those obtained from the (2×4) and disordered‐c(4×4) reconstructions prepared in ultrahigh vacuum by molecular beam epitaxy. Implications for models of OMCVD growth.

Novel method for C60 synthesis: A thermal plasma at atmospheric pressure

Abstract: We report here that fullerenes (C60,C70,C84, etc.) can be fabricated in a 7% yield by carbon particle evaporation in a hybrid plasma which is characterized by the superposition of a rf plasma and a dc arc jet operated at atmospheric pressure. We found that increasing the pressure in the plasma gas increases the yield of fullerenes. We also investigated the effect of introducing the gas for quenching the plasma gas on the yield of fullerenes. Furthermore, this method has also been used to produce metal fulleride.

Calibration of ion spray mass spectra using cluster ions

Abstract: Mass calibration for ion spray mass spectrometry can be achieved by using cluster ions formed by flow injection of solutions of alkali metal salts in aqueous acetonitrile into the liquid flowing to the ion spray needle. Source contamination is thereby reduced to a minimum. For quadrupole mass analyzers, sodium iodide provides an ideal compromise between undesirable spectral complexity and spacings between calibrant mass peaks sufficiently close that interpolation errors are negligible. When much closer spacings are required, protonated water clusters provide an excellent calibration up to about m/z 1000. If higher mass ranges are required with a large number of calibrant peaks, a solution of mixed alkali metal iodides does provide the expected spectra but intensities are poor at higher m/z values. For liquid chromatography with on-line mass spectrometry (LC/MS) the mass calibration may be checked without changing the mobile phase by post-column flow injection of a cesium carbonate solution, since the carbonate anion is wholly displaced by the anion of the mobile phase acid modifier, resulting in no mixed clusters. The metal salt calibrants have the additional advantage of being useful over a wide range of tuning parameters in the atmospheric pressure ionization source, covering those appropriate to both relative molecular mass determinations of large proteins and to LC/MS of small analyte species.

The effects of fluctuations in atmospheric pressure on landfill gas migration and composition

Abstract: Measurements of landfill gas emissions from a single site frequently show large variations in chemical composition and magnitude, often on the same time scale as the monitoring interval. These changes are generally ascribed to faulty instrumentation or mysterious alterations in the internal biological processes. This paper demonstrates a simple deterministic physical mechanism able to explain many of these changes, and discusses the implications this has for monitoring strategies. The main conclusions are that the total rate of gas venting depends linearly on the rate of change of the atmospheric pressure, with the stoichiometric variations depending additionally on the physical characteristics and moisture distribution within the site.

Liquid sample injection using an atmospheric pressure direct current glow discharge ionization source.

Abstract: An atmospheric pressure DC glow discharge in helium has been used as an ionization source for organic samples introduced by liquid injection into atmospheric pressure ionization mass spectrometry (API/MS). The glow source operates typically in the range up to 1 mA of current at less than 1 kV, although the source can be operated up to a discharge current of 10 mA. Even at the high current used in this work, the protonated molecule, MH+, is observed with little or no fragmentation for many of the samples studied. The detection limits achieved for API glow discharge detection are typically in the low femtomole region for small organic molecules including small biological neurotransmitters, drugs, pesticides, phenylthiohydantoin-substituted amino acids, and explosives. A detection limit of approximately 2 pg has been achieved for tyramine with linear quantitation over at least 3 orders of magnitude. The sensitivity in these experiments has been further improved by optimization of the skimmer-interface system and the liquid injection/nebulization design.

Experimental Generation Of A Steady-state Glow Discharge At Atmospheric Pressure

Abstract: In industrial plasma engineering, a steady-state atmospheric glow discharge would allow many surface modification and other plasma processing operations to be carried out under atmospheric conditions, rather than in expensive vacuum systems which enforce batch processing. In this paper, we report some encouraging results of an experimental program conceived independently of the work reported by Kanda, et al. (Ref 1). Our experiments were conducted on an experimental apparatus shown schematically in Figure 1. A Parallel Plate plasma reactor with square electrodes 25 cm on a side, covered with an insulating surface (rubber or glass), and with variable spacing, was set up in an enclosed box which made it possible to control the type of working gas used. This reactor was energized by a very specialized RF power supply capable of supplying up to 5 kilowatts of RF power at rms voltages up to 5 kilovolts, and over a frequency range from 1kHz to 100 kHz.

Ventilation method and means for the same

Abstract: The invention relates to a method of establishing and maintaining in sealed tents or the like mobile units, an environment which is independent of the surroundings with regard to temperature and contamination. The invention is characterized by taking air from the surroundings, extracting contaminated particles and gas from the air by filtration, and causing the air to pass into the mobile unit so as to establish a predetermined air pressure which is higher than the air pressure of the surroundings. The filtered air is mixed with air recycled from within the mobile unit when the aforesaid predetermined air pressure has been reached and mixing of the filtered air with recycled air is continued for as long as the internal air pressure is equal to or greater than the predetermined air pressure. The air mixture is heated or cooled to a predetermined temperature and is then distributed essentially uniformly in the mobile unit and filtered, in conjunction therewith, so as to extract any remaining particles and gas. The invention also relates to an arrangement for carrying out the method.

Advanced technique to improve the bonding arrangement on silicon surfaces to promote uniform nitridation

Abstract: The present invention teaches a method for fabricating an ultrathin uniform dielectric layer over a silicon or polysilicon semiconductor substrate. The method entails first providing a substrate having a conductive area into a chamber. Subsequently, the first conductive material is destabilized by introducing it to reactive gas and radiant energy in situ. The reactive gas can be Ar-H2, H2, GeH4 or NF3 gas. The radiant energy source can be ultraviolet ("UV") or Tungsten Halogen lamps preferably having an approximate range of 0.2 to 1.6 μm to provide heat of approximately 850° to 1150° C. for approximately 10 to 60 seconds at a vacuum pressure range of 10-10 Torr to atmospheric pressure. This process removes the native oxide and breaks the molecular clusters present on the silicon or polysilicon surface. Thereafter, a first dielectric layer having a substantially uniform thickness forms directly above the substrate by the in situ introduction of NH3 with the radiant energy generating heat of approximately 850° to 1150° C. for approximately 10 to 60 seconds at a vacuum pressure range of 10-10 Torr to atmospheric pressure. Finally, a second silicon nitride layer is deposited by low pressure chemical vapor deposition or plasma nitridation to create a combined thickness of both dielectric layers of 40 to 100 Å.