Showing papers on "Atmospheric pressure published in 1999"

Kinetic spray coatings

Abstract: Coatings have been produced by entraining metal powders in an air flow which is accelerated by a de Laval type of nozzle. The particles are not melted or thermally softened prior to impingement onto the substrate. The coating process depends primarily on the kinetic energy of the incident powders. The coatings have low oxide content and low thermal stress, and can exhibit relatively low porosity and high adhesion. The mechanism by which the coatings are formed is not well understood, and it is the goal of this work to provide some insights into this mechanism. We have produced a new high-velocity spray apparatus which allows the spray parameters to be controlled and monitored for the first time. This, together with our simulations of air and particle velocities and temperatures, has provided new information on the coating process. Al, Cu, and Fe powders were sprayed onto Al, brass, Cu, and steel substrates. A threshold behavior was observed for coating deposition as a function of nozzle inlet air temperature, with a roughly linear behavior above the threshold. Results are obtained as a function of nozzle inlet air pressure and temperature, powder feed rate, and nozzle–substrate stand-off distance. The effect of the choice of substrate metal was relatively weak in our experiments. Results seem consistent with necessary inelastic processes such as plastic deformation and/or partial melting of the powder particles upon collision with the substrate. More research is needed to define the relative importance of these phenomena or of other possible mechanisms.

Direct current glow discharges in atmospheric air

Abstract: Direct current glow discharges have been operated in atmospheric air by using 100 μm microhollow cathode discharges as plasma cathodes. The glow discharges were operated at currents of up to 22 mA, corresponding to current densities of 3.8 A/cm2 and at average electric fields of 1.2 kV/cm. Electron densities in the glow are in the range from 1012 to 1013 cm−3. Varying the current of the microhollow cathode discharge allows us to control the current in the atmospheric pressure glow discharge. Large volume atmospheric pressure air plasmas can be generated by operating microhollow cathode discharges in parallel.

Process for Polycrystalline film silicon growth

Abstract: A process for depositing polycrystalline silicon on substrates, including foreign substrates, occurs in a chamber at about atmospheric pressure, wherein a temperature gradient is formed, and both the atmospheric pressure and the temperature gradient are maintained throughout the process Formation of a vapor barrier within the chamber that precludes exit of the constituent chemicals, which include silicon, iodine, silicon diiodide, and silicon tetraiodide The deposition occurs beneath the vapor barrier One embodiment of the process also includes the use of a blanketing gas that precludes the entrance of oxygen or other impurities The process is capable of repetition without the need to reset the deposition zone conditions

Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) data processing and atmospheric temperature and trace gas retrieval

Abstract: The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment aboard the Shuttle Pallet Satellite (SPAS) was successfully flown in early November 1994 (STS 66) and in August 1997 (STS 85). This paper focuses on the first flight of the instrument, which was part of the Atmospheric Laboratory for Application and Science 3 (ATLAS 3) mission of NASA. During a free flying period of 7 days, limb scan measurements of atmospheric infrared emissions were performed in the 4 to 71 μm wavelength region. For improved horizontal resolution, three telescopes (viewing directions) were used that sensed the atmosphere simultaneously. Atmospheric pressures, temperatures, and volume mixing ratios of various trace gases were retrieved from the radiance data by using a fast onion-peeling retrieval technique. This paper gives an overview of the data system including the raw data processing and the temperature and trace gas profile retrieval. Examples of version 1 limb radiance data (level 1 product) and version 1 mixing ratios (level 2 product) of ozone, ClONO 2 , and CFC-11 are given. A number of important atmospheric transport processes can already be identified in the level 1 limb radiance data. Radiance data of the lower stratosphere (18 km) indicate strong upwelling in some equatorial regions, centered around the Amazon, Congo, and Indonesia. Respective data at the date line are consistent with convection patterns associated with El Nino. Very low CFC-11 mixing ratios occur inside the South Polar vortex and cause low radiance values in a spectral region sensitive to CFC-11 emissions. These low values are a result of considerable downward transport of CFC-11 poor air that occurred during the winter months. Limb radiance profiles and retrieved mixing ratio profiles of CFC-11 indicate downward transport over ∼5 km. The accuracy of the retrieved version 1 mixing ratios is rather different for the various trace gases. In the middle atmosphere the estimated systematic error of ozone is ∼14%. Ozone data of correlative satellite measurements are well within this error bar. CRISTA agrees, for example, with Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) sunset measurements typically within 5%. The random error of version 1 ozone mixing ratios is 4%. Similar values apply to other trace gases. These low random errors allow the identification of small and medium scale horizontal and vertical structures in the measured trace gas distributions. Examples of structures in mixing ratio fields of ozone, ClONO 2 , and CFC-11 are given.

Improvements in Quantitative Analysis of Steel Composition by Laser-Induced Breakdown Spectroscopy at Atmospheric Pressure Using an Infrared Nd:YAG Laser

Abstract: The experimental conditions and procedure for quantitative analysis of steel by laser-induced breakdown spectroscopy in argon at atmospheric pressure using an infrared Nd:YAG laser have been studied. Satisfactory analytical results have been obtained for the determination of C, Si, Cr, and Ni contents in low-alloyed steels. The lens-to-sample distance is shown to be a relevant parameter, which can be selected at each pulse energy to enhance the line intensities and the repeatability of measurements. A higher precision has been obtained for line-intensity ratios (0.9-2.5% relative standard deviation for concentrations higher than 0.1%) than for absolute intensity measurements. The calibration curves for all the elements have correlation coefficients above 0.999. Detection limits are in the range 6-80 ppm.

A comparison of the temperatures and electron densities of laser-produced plasmas obtained in air, argon, and helium at atmospheric pressure

Abstract: Time-resolved measurements of temperatures and electron densities of laser-produced plasmas generated in air, argon, and helium at atmospheric pressure are presented. The plasmas are obtained by the focusing of a Nd:YAG laser on a low-alloyed steel sample. The relative experimental error for temperatures is in the range 0.6–3% and for electron densities, it is 4.5%. The higher temperatures and electron densities are obtained in argon, and the lower ones are found in helium. The temporal evolution of temperature and electron density in the three gases is compared, showing that a faster decay of both magnitudes takes place in helium.

Atmospheric correction over land for MERIS

Abstract: A three-stage atmospheric correction is proposed for the Medium Resolution Imaging Spectrometer (MERIS) from a validated formulation of the signal. We correct first for the gaseous transmittance. Assuming the ozone correction is well defined, we illustrate the need to include a correction for water vapour continuum which covers most of the MERIS bands. The water vapour transmittance can be computed from the water vapour content obtained from a twoband ratio at 900nm and 890nm. We demonstrate that a direct association between the transmittance in a given band and the two band ratio is more accurate due to the removal of the coupling between absorption and scattering. Secondly, the Rayleigh correction depends on the barometric pressure determined here from a two band ratio method with the oxygen A band. Good accuracy is obtained for the pressure when accounting for the coupling between scattering and gas absorption, which mostly depends on the surface reflectance. The Rayleigh reflectance is computed from a...

Carbon emissions following 1.064 μm laser ablation of graphite and organic samples in ambient air

Abstract: Laser ablation of graphite and organic samples is studied in the context of chemical analysis by laser-induced plasma spectroscopy. Ablation is performed using an Nd:YAG laser at 1.064 μm in ambient air at atmospheric pressure. Following ablation of graphite, we find results consistent with C2 (as well as C) being released directly from the target, and CN being formed later on by the interaction of C2 with atmospheric nitrogen (N2). In the case of organic compounds, we find a clear relationship between C2 emission from the plasma and the presence of aromatic rings (containing carbon–carbon double bonds) in the compounds.

Dependence of the fundamental band gap of AlxGa1−xN on alloy composition and pressure

Abstract: Optical absorption studies were performed to investigate the dependence of the fundamental band gap of AlxGa1−xN epitaxial films on Al content and applied hydrostatic pressure The results of absorption measurements performed at atmospheric pressure yielded the variation of the band-gap energy E(x)=343+144x+133x2 eV for the AlxGa1−xN system Optical absorption edge associated with the direct Γ band gap shifts linearly towards higher energy under applied pressure By examining the pressure dependence of the absorption edge in samples with different AlN mole fractions and taking into account the difference of compressibility between the epitaxial films and sapphire substrate, the pressure coefficients for the direct Γ band gaps of AlxGa1−xN were determined

A Tenuous Carbon Dioxide Atmosphere on Jupiter's Moon Callisto

Abstract: An off-limb scan of Callisto was conducted by the Galileo near-infrared mapping spectrometer to search for a carbon dioxide atmosphere. Airglow in the carbon dioxide nu3 band was observed up to 100 kilometers above the surface and indicates the presence of a tenuous carbon dioxide atmosphere with surface pressure of 7.5 x 10(-12) bar and a temperature of about 150 kelvin, close to the surface temperature. A lifetime on the order of 4 years is suggested, based on photoionization and magnetospheric sweeping. Either the atmosphere is transient and was formed recently or some process is currently supplying carbon dioxide to the atmosphere.

Apparatus and method for atmospheric pressure 3-dimensional ion trapping

Abstract: The present invention provides an apparatus for selectively transmitting ions and trapping the ions within a defined 3-dimensional space at atmospheric pressure. The invention is based on the ion focussing principles of high field asymmetric waveform ion mobility spectrometry in which an analyzer region is defined by a space between first and second spaced apart electrodes, the analyzer region having a gas inlet and a gas outlet for providing a flow of gas through the analyzer region. Ions which are introduced into the analyzer region are carried by a gas flow towards a gas outlet. At least one of the electrodes has a curved surface terminus located near the gas outlet and the gas flow is adjusted so that ions are trapped in a defined 3-dimensional space located near the tip of the terminus. Trapping of ions in a defined 3-dimensional space allows a more concentrated flow of desired ions.

Atmospheric pressure matrix assisted laser desorption

Abstract: An Atmospheric Pressure Matrix-Assisted Laser Desorption Ionization (AP-MALDI) apparatus (10) for connecting to a mass spectrometer (100) provides a laser (104) for inducing analyte ions (117) from a matrix sample (115) contained within an atmospheric pressure ionization chamber (102).

Kinetics of radiative species in helium pulsed discharge at atmospheric pressure

Abstract: Time variations of spectral line intensities of a helium dielectric discharge at atmospheric pressure have been analyzed by emission spectroscopy. A dielectric barrier controlled glow discharge with polymer films on the electrodes (O: 0.04 m, interelectrode distance: 0.005 m) is produced with a sinusoidal voltage of ca 800 Vr.m.s. The discharge is characterized by a current peak in each half cycle, its duration is of the order of 5×10 −6 s at 10 4 Hz. The radiative emission species are helium lines and mainly N 2 , N 2 + , CO + , CO 2 and OH bands coming from impurities which were in part desorbed from the polymer surfaces. From the time variations of band emissions, the main kinetic reactions at the origin of radiative species are discussed.

Barometric pressure sensor for use with implantable absolute pressure sensor

Abstract: A barometric pressure sensor (260) for deriving reference pressure data for use in combination with absolute pressure data derived by an implantable medical device (IMD) is disclosed The barometric pressure sensor (260) is located in a sensing module (200) having a module housing (222) enclosing an air chamber (230) which encloses the barometric pressure sensor (260) An air vent (220) extends through the module housing (222) for venting the air chamber (230) to atmospheric pressure outside the housing A protective vent cover (240) extends across the air vent (220) formed of a material capable of air passage and capable of inhibiting passage of moisture, liquids, and particulate contaminants into the air chamber (230) The sensing module (200) is worn or carried by the patient and includes operating circuitry and a power supply for periodically storing sensed atmospheric pressure values as reference pressure data In another embodiment, the sensing module (200) comprises a percutaneous access device (300) which is adapted to be implanted in the skin and subcutaneous tissue layer of the patient

High Pressure Thawing of Fish (Whiting): Influence of the Process Parameters on Drip Losses

Abstract: Atmospheric thawing and pressure-assisted thawing were applied to frozen fish prior to heat treatment (80 °C/20 min). The influence of the pressure level (between atmospheric pressure and 200 MPa), of the freezing rate, of the pressurization rate, and of the pressure holding time was studied in comparison with a thawing process at atmospheric pressure. High freezing rate (0.77 vs.0.14 °C/min), high pressurization rate (100 vs. 42 MPa/min) reduced the thawing drip losses at a given pressure. A decrease in the drip volume for high pressure thawing compared to atmospheric thawing was obtained only by prolonging the pressure holding time. This parameter was most influential in reducing the drip loss. Electrophoresis analysis of thawing drips and of sarcoplasmic proteins of fish fillets showed a modification of the line 48 kDa proteins whose intensity decreased from 150 MPa.

A high accuracy resonant pressure sensor by fusion bonding and trench etching

Abstract: A pressure sensor based upon an electrostatically driven and piezoresistively sensed 'double-shuttle' lateral resonator is presented. The resonator has been designed using simple beam theory and the mode shapes investigated using finite element analysis. The sensor is fabricated using fusion bonding, wafer thinning and trench etching. Measurements of preliminary devices yield a fundamental frequency of = 50 kHz and Q-factor of 1000 in air at atmospheric pressure, rising to over 50,000 in high vacuum (<0.01 mbar). The relative pressure sensitivity of the sensor is measured to be 3.8% bar -1 for a 120 μm thick diaphragm over a pressure range of 10 bar, and 15% bar -1 for a 25 μm thick diaphragm over a pressure range of 3 bar.

Steady-state glow-discharge plasma at atmospheric pressure

Abstract: A plasma treater incorporates a porous metallic layer in one of the electrodes. The porous layer is selected with pores of average size within one order of magnitude of the mean free path of the plasma gas at atmospheric pressure. The plasma gas is injected into the electrode at substantially atmospheric pressure and allowed to diffuse through the porous layer, thereby forming a uniform glow-discharge plasma. The film material to be treated is exposed to the plasma created between this electrode and a second electrode covered by a dielectric layer. Because of the micron size of the pores of the porous metal, each pore also produces a hollow cathode effect that facilitates the ionization of the plasma gas. As a result, a steady-state glow-discharge plasma is produced at atmospheric pressure and at power frequencies as low as 60 Hz.

A method of reducing diffusion losses in a drift spectrometer

Abstract: A method is considered which reduces diffusion losses during analysis of the ions of heavy molecules passed together with a carrier gas through a separation system at atmospheric pressure. Separation takes place under the action of a transverse variable electric field in a way similar to the case of quadrupole mass spectrometers. Instead of the usual uniform-field planar capacitor, it is proposed to employ a cylindrical capacitor with a nonuniform field. It is shown experimentally that a severalfold increase in the output signal is achieved.

Self-contained and portable cryogenic apparatus using carbon dioxide in liquid/solid phases

Abstract: A self-contained portable cryogenic apparatus that operates at the temperature (of the order of -78° C. at atmospheric pressure) reached by reducing the pressure of carbon dioxide (CO 2 ) or equivalent in liquid/solid phase, comprising a reservoir of pressurized liquefied CO 2 , the drawing off head being connected to a liquid/solid CO 2 pressure reduction and ejection system, and comprising a control device, a pressure reduction device and a device for checking the temperature in the area to which it is applied, remarkable in that the top of the CO 2 reservoir is arranged on the apparatus such that during the entire usage period, only the liquid part of the CO 2 inside the reservoir comes into contact with the head so that it is drawn off and forced towards the application area through a pressure reduction and ejection system. The apparatus is particularly suitable for use in sports medicine in the form of a spray gun.

Liquid- and crystallike structures in strongly coupled dusty plasmas

Abstract: Dust particle ordering is discussed in various types of low-temperature plasma, such as thermal plasmas at atmospheric pressure, dc glow discharges, UV- and radioactivity induced plasmas. The investigations of UV-induced dusty plasma were made under microgravity conditions. Experimental data are presented. Properties of ordered structures are discussed and the conditions of formation considered.

Cause of continuous oscillations of the Earth

Abstract: Spheroidal fundamental mode oscillations of the Earth for frequencies between 2 and 7 mHz (millihertz) are observed even on seismically quiet days. Two hypotheses of the cause of these oscillations are investigated: the cumulative effect of small earthquakes and atmospheric pressure variations. The cumulative effect of earthquakes, assuming that earthquakes follow the Gutenberg-Richter law, is shown to be 1–2 orders of magnitude too small. The observed amplitudes of modes require an equivalent earthquake of magnitude 6.0 everyday, which cannot be achieved by summing up contributions from small earthquakes. The hypothesis of atmospheric excitation is favored because of the discovery of seasonal variations in stacked modal amplitudes for spheroidal modes between 0S20 and 0S40. It is also evaluated by comparing observed modal amplitudes with theoretical amplitudes, derived from a stochastic normal mode theory. The source of excitation is atmospheric pressure variations, which indicate turbulent motion of the atmosphere for the frequency range of interest and are estimated by barometer data. The observed modal amplitudes can be matched by the stochastic normal mode theory, indicating that atmospheric pressure variation is large enough to excite solid Earth normal modes up to the observed amplitudes. Therefore two lines of evidence, detection of seasonal variations and approximate match of overall modal amplitudes, support the hypothesis that the continuous background oscillations are excited by atmospheric pressure variations.