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Showing papers on "Atmospheric pressure published in 2001"


Journal ArticleDOI
Han Ju Lee1, Sang Yong Lee1
TL;DR: In this article, the two-phase frictional multiplier was expressed using the Lockhart-Martinelli type correlation but with the modification on parameter C. The correlations with the modified C successfully cover wide ranges of the Martinelli parameter (X=0.303-79.4) and the all-liquid Reynolds number (ReLo=175-17700) based on the hydraulic diameter within the deviation of ±10%.

342 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used spatio-temporal cross-correlation spectroscopy (CCS) to carry out diagnostic measurements of barrier discharge (BD) in air at atmospheric pressure.
Abstract: The technique of spatially resolved cross-correlation spectroscopy (CCS) is used to carry out diagnostic measurements of the barrier discharge (BD) in air at atmospheric pressure. Quantitative estimates for electric field strength E(x,t) and for relative electron density ne(x,t)/nemax are derived from the experimentally determined spatio-temporal distributions of the luminosity for the spectral bands of the 0-0 transitions of the second positive system of N2 (λ = 337.1 nm) and the first negative system of N2+ (λ = 391.5 nm). These results are used to test the validity of some physical models of electrical breakdown in a BD. The influence of the spatio-temporal structure of the discharge on the chemical kinetics of ozone synthesis is studied by means of a semi-empirical method based on the results of spatially resolved CCS measurements.

323 citations


Journal ArticleDOI
TL;DR: In this paper, an atmospheric pressure plasma jet (APPJ) operates using rf power and produces a stable homogeneous discharge at atmospheric pressure, which is divided into two regimes, a "normal" operating mode when the discharge is stable and homogeneous, and a "failure" mode when it converts into a filamentary arc.
Abstract: Discharge phenomena of a nonthermal atmospheric pressure plasma source have been studied. An atmospheric pressure plasma jet (APPJ) operates using rf power and produces a stable homogeneous discharge at atmospheric pressure. After breakdown, the APPJ operation is divided into two regimes, a “normal” operating mode when the discharge is stable and homogeneous, and a “failure” mode when the discharge converts into a filamentary arc. Current and voltage (I–V) characteristics and spatially resolved emission intensity profiles have been measured during the normal operating mode. These measurements show that the APPJ produces an alpha (α) mode rf capacitive discharge. Based upon a dimensional analysis using the observed I–V characteristics, a rough estimate is made for plasma density of 3×1011 cm−3 and an electron temperature of 2 eV. In addition, the gas temperature of 120 °C has been spectroscopically measured inside the discharge. These plasma parameters indicate that the APPJ shows promise for various mater...

311 citations


Journal ArticleDOI
TL;DR: An atmospheric pressure non-equilibrium plasma (APNEP) has been developed in the UK by EA Technology Ltd and is currently being investigated in collaboration with the University of Surrey as mentioned in this paper.
Abstract: An atmospheric pressure non-equilibrium plasma (APNEP) has been developed in the UK by EA Technology Ltd and is currently being investigated in collaboration with the University of Surrey. The main focus is the use of atmospheric pressure plasmas to modify the surfaces of commercially important polymers including polyolefins, poly(ethylene terephthalate) and poly(methyl methacrylate). These surface modifications include surface cleaning and degreasing, oxidation, reduction, grafting, cross-linking (carbonization), etching and deposition. When trying to achieve targeted surface engineering, it is vital to gain an understanding of the mechanisms that cause these effects, for example, surface functionalization, adhesion promotion or multi-layer deposition. Hence comparisons between vacuum plasma treated surfaces have also been sought with a view to using the extensive vacuum plasma literature to gain further insight. In this paper, we will introduce the APNEP and compare the key characteristics of the plasma with those of traditional vacuum plasma systems before highlighting some of the surface modifications that can be achieved by using atmospheric plasma. Data from the analysis of treated polymers (by spectroscopy, microscopy and surface energy studies) and from direct measurements of the plasma and afterglow will be presented. Finally, our current understanding of the processes involved will be given, particularly those that are important in downstream surface treatments which take place remote from the plasma source.

270 citations


Journal ArticleDOI
TL;DR: In this article, the authors illustrate the use of an atmospheric plasma to enhance the adhesion characteristics of low-density polyethylene (LDPE) and poly(ethylene terephthalate) (PET).
Abstract: An atmospheric pressure non-equilibrium plasma (APNEP) developed in the UK by EA Technology Ltd is currently being investigated in collaboration with the University of Surrey. Of the many applications of surface modification that can be induced using plasmas, adhesion enhancement is one of the most commercially important. In this paper, we illustrate the use of an atmospheric plasma to enhance the adhesion characteristics of low-density polyethylene (LDPE) and poly(ethylene terephthalate) (PET). The polymers were treated in the remote afterglow region of an atmospheric pressure plasma to avoid the thermal effects that can cause degradation for thermally sensitive materials when placed in direct contact with the plasma. Reactive (oxygen containing) and inert (oxygen free) atmospheric plasmas rapidly impart adhesion enhancement by a factor of two to ten as measured by 180° peel tests. However, extended exposure to the atmospheric plasma does not impart additional adhesion enhancement as the surface is ablated revealing the underlying polymer with poor adhesive characteristics. In contrast, vacuum plasma treated LDPE and PET show increased adhesion with extended plasma treatment. An adhesion enhancement in excess of two to three orders of magnitude was found to be achievable for vacuum plasma treatment times greater than 10 min.

269 citations


Journal ArticleDOI
TL;DR: In this paper, the kinetics of the gas phase reaction between atomic mercury and hydroxyl radical has been determined at room temperature and atmospheric pressure of air by relative rate technique, and the rate coefficient obtained was k(Hg 0 + · OH )=(8.7±2.8)×10 −14 cm 3 s −1 leading to natural lifetimes of mercury at global mean conditions of 4-7 month due to this reaction.

220 citations


Journal ArticleDOI
TL;DR: In this article, the products of the gas phase reactions of OH radicals with the n-alkanes n-pentane through n-octane at 298 ± 2 K and atmospheric pressure of air have been investigated using gas chromatography with flame ionization detection (GC-FID), combined GC-MS, and in situ atmospheric pressure ionization tandem mass spectrometry.
Abstract: Products of the gas-phase reactions of OH radicals with the n-alkanes n-pentane through n-octane at 298 ± 2 K and atmospheric pressure of air have been investigated using gas chromatography with flame ionization detection (GC-FID), combined gas chromatography−mass spectrometry (GC-MS), and in situ atmospheric pressure ionization tandem mass spectrometry. The formation yields of alkyl nitrates from n-hexane, n-heptane, and n-octane were measured by GC-FID, with the sum of the isomeric alkyl nitrates being 0.141 ± 0.020, 0.178 ± 0.024, and 0.226 ± 0.032, respectively. These alkyl nitrate yields are ∼35% lower than previous data reported from this laboratory in the early 1980s. Using negative ion atmospheric pressure chemical ionization with the addition of pentafluorobenzyl alcohol to study the n-pentane through n-octane reactions and those of the fully deuterated n-alkanes, hydroxyalkyl nitrate products were identified from the n-pentane, n-heptane, and n-octane reactions for the first time and the presenc...

203 citations


Journal ArticleDOI
TL;DR: In this article, gas breakdown in an atmospheric pressure rf capacitive plasma source developed for materials applications is studied, and the breakdown voltage is largely a function of the product of the pressure and the discharge gap spacing, approximating the Paschen curve.
Abstract: Gas breakdown is studied in an atmospheric pressure rf capacitive plasma source developed for materials applications. At a rf frequency of 13.56 MHz, breakdown voltage is largely a function of the product of the pressure and the discharge gap spacing, approximating the Paschen curve. However, breakdown voltage varies substantially with rf frequency due to a change in the electron loss mechanism. A large increase in breakdown voltage is observed when argon, oxygen, or nitrogen is added to helium despite their lower ionization potential. Discussion is given for optimal breakdown conditions at atmospheric pressure.

199 citations


Journal ArticleDOI
TL;DR: Silicon dioxide films were grown using an atmospheric-pressure plasma jet that was produced by flowing oxygen and helium between two coaxial metal electrodes that were driven by 13.56 MHz radio frequency power as discussed by the authors.
Abstract: Silicon dioxide films were grown using an atmospheric-pressure plasma jet that was produced by flowing oxygen and helium between two coaxial metal electrodes that were driven by 13.56 MHz radio frequency power. The plasma exiting from between the electrodes was mixed with tetraethoxysilane (TEOS), and directed onto a silicon substrate held at 115-350 °C. Silicon dioxide films were deposited at rates ranging from 20±2 to 300±25 nm min-1. The deposition rate increased with decreasing temperature and increasing TEOS pressure, oxygen pressure and RF power. For the latter two variables, the rate increased as follows: Rd∝P0.3O2(RF)1.4. Films grown at 115 °C were porous and contained adsorbed hydroxyl groups, whereas films grown at 350 °C were smooth, dense and free of impurities. These results suggest that the mechanism in the atmospheric pressure plasma is the same as that in low-pressure plasmas.

193 citations


Journal ArticleDOI
TL;DR: In this article, a model for the drying of weakly permeable materials is presented, which is based upon macroscopic thermodynamic considerations. But the model assumes that the gas pressure cannot remain constant because no significant convective Darcean transport of the gas can actually occur, and the diffusion of vapor becomes rapidly nonactive as a driving force of moisture transport.
Abstract: Modeling of the drying of porous materials is often approached by assuming that the gas pressure of the vapor-air mixture remains constantly equal to the outer atmospheric pressure. Use of both experimental and theoretical results reveals that such an assumption is inadequate to account for the weight loss observed during the drying of weakly permeable materials. For such materials, the gas pressure cannot remain constant because no significant convective Darcean transport of the gas can actually occur. In contrast, the evaporation coupled with the diffusion of dry air generates a gas overpressure that propagates within the material and works actively toward a uniform vapor molar concentration. As a consequence, the diffusion of vapor becomes rapidly nonactive as a driving force of moisture transport. Paradoxically, the drying of weakly permeable materials is eventually achieved by the transport of moisture in its liquid form and its evaporation at the sample boundary in contact with the surrounding air. The analysis is carried out through a modeling of which the formulation is based upon macroscopic thermodynamic considerations. It involves a dry-air component and a water component, the liquid and the water-vapor phases being addressed separately.

190 citations


Journal ArticleDOI
TL;DR: Dielectric barrier discharges (DBDs) at atmospheric pressure are obtained using mixtures of He and Ar as carrier gasses and various reactive additives such as hydrocarbons, hydrogen and nitrogen as discussed by the authors.
Abstract: Dielectric barrier discharges (DBDs) at atmospheric pressure are obtained using mixtures of He and Ar as carrier gasses and various reactive additives such as hydrocarbons, hydrogen and nitrogen. These DBDs are used in three applications: deposition of polymer films; cleaning of Ag and Cu substrates; and activation of polyurethane and steel surfaces. In the case of the film deposition, several process conditions are investigated and the resulting films are analysed by scanning electron microscope, Fourier transform infrared spectroscopy and NMR. In another series of experiments Ag and Cu surfaces, covered with sulfide and oxide layers, are treated by means of a DBD in helium or argon with hydrogen added. The surfaces are analysed with X-ray photoelectron spectroscopy. Finally, a He–N2 plasma is used as an activator of polyurethane.

Book
01 Jan 2001
TL;DR: In this paper, the authors discuss the composition and structure of the atmosphere, and present a model of the current and future climate changes, as well as the current, past and future conditions of the world.
Abstract: I. ENERGY AND MASS. 1. Composition and Structure of the Atmosphere. 2. Solar Radiation and the Seasons. 3. Energy Balance and Temperature. 4. Atmospheric Pressure and Wind. II. WATER IN THE ATMOSPHERE. 5. Atmospheric Moisture. 6. Cloud Development and Forms. 7. Precipitation Processes. III. DISTRIBUTION AND MOVEMENT OF AIR. 8. Atmospheric Circulation and Pressure Distributions. 9. Air Masses and Fronts. IV. DISTURBANCES. 10. Mid-Latitude Cyclones. 11. Lightning, Thunder, and Tornadoes. 12. Tropical Storms and Hurricanes. V. HUMAN ACTIVITIES AND SPECIAL TOPICS. 13. Weather Forecasting and Analysis. 14. Human Effects: Air Pollution and Heat Islands. VI. CURRENT, PAST AND FUTURE CLIMATES. 15. Earth's Climates. 16. Climate Changes: Past and Future. VII. SPECIAL TOPICS AND APPENDICES. 17. Atmospheric Optics. Appendix A: Unit of Measurement and Conversions. Appendix B: The Standard Atmosphere. Appendix C: Weather Map Symbols. Appendix D: Weather Extremes. Glossary. Index.

15 Dec 2001
TL;DR: In this paper, the surface growth rate of premixed ethylene/air flames with C/O ratios of 0.78-0.98 was found to be due to reduced H atom concentrations as temperatures decrease as a result of radiative heat losses.
Abstract: Abstract Soot formation was studied within laminar premixed ethylene/air flames (C/O ratios of 0.78–0.98) stabilized on a flat-flame burner operating at atmospheric pressure. Measurements included soot volume fractions by both laser extinction and gravimetric methods, temperatures by multiline emission, soot structure by thermophoretic sampling and transmission electron microscopy, major gas species concentrations by sampling and gas chromatography, concentrations of condensable hydrocarbons by gravimetric sampling, and velocities by laser velocimetry. These data were used to find soot surface growth rates and primary soot particle nucleation rates along the axes of the flames. Present measurements of soot surface growth rates were correlated successfully by predictions based on typical hydrogen-abstraction/carbon-addition (HACA) mechanisms of Frenklach and co-workers and Colket and Hall. These results suggest that reduced soot surface growth rates with increasing residence time seen in the present and other similar flames were mainly caused by reduced rates of surface activation due to reduced H atom concentrations as temperatures decrease as a result of radiative heat losses. Primary soot particle nucleation rates exhibited variations with temperature and acetylene concentrations that were similar to recent observations for diffusion flames; however, nucleation rates in the premixed flames were significantly lower than in the diffusion flames for reasons that still must be explained. Finally, predictions of yields of major gas species based on mechanisms from both Frenklach and co-workers and Leung and Lindstedt were in good agreement with present measurements and suggest that H atom concentrations (relevant to HACA mechanisms) approximate estimates based on local thermodynamic equilibrium in the present flames.

Journal ArticleDOI
TL;DR: Results show that negative ion IS with an eluent system consisting of acidic ammonium acetate buffer provides the best conditions for detection of flavonoids in mass spectrometry mode, their LODs being between 0.8 and 13 microM for an injection volume of 20 microl.
Abstract: The effect of nine different eluent compositions on the ionization efficiency of five flavonoids was studied using ion spray (IS), atmospheric pressure chemical ionization (APCI), and the novel atmospheric pressure photoionization (APPI), in positive and negative ion modes. The eluent composition had a great effect on the ionization efficiency, and the optimal ionization conditions were achieved in positive ion IS and APCI using 0.4% formic acid (pH 2.3) as a buffer, and in negative ion IS and APCI using ammonium acetate buffer adjusted to pH 4.0. For APPI work, the eluent of choice appeared to be a mixture of organic solvent and 5 mM aqueous ammonium acetate. The limits of detection (LODs) were determined in scan mode for the analytes by liquid chromatography/mass spectrometry using IS, APCI and APPI interfaces. The results show that negative ion IS with an eluent system consisting of acidic ammonium acetate buffer provides the best conditions for detection of flavonoids in mass spectrometry mode, their LODs being between 0.8 and 13 microM for an injection volume of 20 microl.

Journal ArticleDOI
TL;DR: The design, fabrication, and operation of this new technique of generating on-chip air pressure, used for metering and pumping nanoliter discrete drops in microchannels, are described.
Abstract: A class of “lab-on-a-chip” devices use external air pressure for pumping discrete drops in a microchannel network. External air connectors can be cumbersome and are real-estate intensive. We have developed an on-chip technique to generate pressures required for metering and pumping of nanoliter-volume discrete drops. This is achieved by heating of trapped air in a pressure-generating chamber. The pressure-generating chamber is connected to the point of pressure application in the liquid-conveying microchannel through an air-delivery channel. The trapped air volume on the order of 100 nL is heated by resistive metal heaters by tens of degrees celcius to generate air pressures on the order of 7.5 kN/m2. The rate of discrete drop pumping is electronically controlled in the microchannel device by controlling the rate of air heating. Flow rates on the order of 20 nL/s are obtained in the microchannel (300 μm × 30 μm) by heating the air chamber at the rate of ∼6 °C/s. In this paper, we describe the design, fabr...

Journal ArticleDOI
TL;DR: In this paper, the influence of the filament properties on the deposition of organosilicon on planar aluminium substrates has been studied using dielectric barrier discharges (DBD) at atmospheric pressure.
Abstract: Dielectric barrier discharges (DBD) at atmospheric pressure are presented as a tool to create organosilicon deposits on technical planar aluminium substrates (up to 15 × 8 cm2) by admixing small amounts of hexamethyldisiloxane (HMDSO) and tetraethoxysilane (TEOS) to the carrier gas of the discharges. Using barrier materials of different specific capacities (2.6 × 104 and 3.2 pF/cm2) in two electrode arrangements operated at less than 1 W, the influence of the filament properties on the deposition is studied. In comparison to these arrangements, a third electrode setup with a barrier of the specific capacity of 2.9 pF/cm2 is operated at approximately 50 W to study the influence of the specific energy of the plasma (energy per molecule) on the deposition process. The plasma chemical process was studied qualitatively by Gas Chromatography, and properties of the plasma-treated substrates were examined by means of X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared (FTIR) spectroscopy, as well as visually.

Journal ArticleDOI
TL;DR: An atmospheric pressure nanosampling interface for mass spectrometry based on near-field laser ablation and a spatial resolution of less than 200 nm and a sensitivity below 2 amol is demonstrated.
Abstract: We describe an atmospheric pressure nanosampling interface for mass spectrometry based on near-field laser ablation. Pulsed laser radiation is delivered to the sample surface through a near-field optical probe, and the ablation plume is sampled through a capillary orifice and analyzed by standard MS methods. A spatial resolution of less than 200 nm and a sensitivity below 2 amol is demonstrated.

Journal ArticleDOI
TL;DR: In this paper, the thermal decomposition of polytetrafluoroethylene (PTFE) has been studied using dynamic TG-DTG at heating rates between 1 and 25°C/min at atmospheric pressure.
Abstract: The kinetics of the thermal decomposition of polytetrafluoroethylene (PTFE) have been studied using dynamic TG-DTG at heating rates between 1 and 25°C/min at atmospheric pressure. Two different atmospheres were used: on the one hand, an inert atmosphere (N 2 ) in order to study the pyrolysis of the material, and on the other hand an oxidative atmosphere (synthetic air) to study the combustion of the polymer. The same kinetic model has been applied simultaneously to runs performed at different heating rates and different atmospheres allowing a good correlation of the weight loss data. The kinetic model considers that the overall decomposition of the PTFE is done via two different parallel processes. Dynamic measurements were performed by combined thermogravimetry mass spectrometry (TG-MS) in order to determine the decomposition products. The evolution of C 2 F 4 , CF 4 , COF 2 , HF, hydrocarbons, benzene and some other compounds has been also analyzed.

Journal ArticleDOI
TL;DR: In this article, the authors describe several variations of this unique plasma source and some of its potential applications, including high pressure and low temperature plasma processes with high selectivity, minimal ion densities, and low surface damage.
Abstract: Processing materials at atmospheric pressure provides clear advantages over traditional, vacuum-based plasma processing: in addition to reduction in the capital cost of equipment and the elimination of constraints imposed by vacuum-compatibility, high pressure and low temperature plasma processes offer unprecedented improvements for generation of active chemical species, high chemical selectivity, minimal ion densities resulting in low surface damage and surface treatment methods unattainable by other means. We describe several variations of this unique plasma source and some of its potential applications.

Patent
25 May 2001
TL;DR: In this article, the plasmas are generated using a RF power source and a rectangular waveguide, which can be used for applications such as materials processing and carrying out chemical reactions.
Abstract: Plasma processing is carried out at pressures of about atmospheric pressure, at pressures below atmospheric pressure, or at pressures above atmospheric pressure. The plasmas are generated using a RF power source and a rectangular waveguide. The plasmas can be used for applications such as materials processing and carrying out chemical reactions.

Journal ArticleDOI
TL;DR: A liquid sampling-atmospheric pressure glow discharge (LS-APGD) optical emission spectroscopy source is described in this article, which utilizes an electrolytic solution containing the analyte specimen as one of the discharge electrodes.
Abstract: A liquid sampling–atmospheric pressure glow discharge (LS-APGD) optical emission spectroscopy source is described. This device utilizes an electrolytic solution containing the analyte specimen as one of the discharge electrodes. The passage of an electrical current (either electrons or positive ions) across the solution/gas phase interface causes local heating and the volatilization of the analyte species. Collisions in the negative glow region of the plasma result in optical emission, which is characteristic of the analyte elements. Operation of this device with the analyte solution acting as either the cathode or anode is demonstrated. Typical discharge conditions include currents of 80 mA, potentials of up to 1000 V, with the i-V characteristics exhibiting ‘abnormal’ glow discharge behavior. The analyte-containing electrolyte solution is not limited to hydronium ions, as other salts (e.g., Li+ and Na+) also provide sufficient conductivity to sustain the discharge. Spatial maps of analyte emission and spectral background provide insights into the basic operation mechanism of the discharge. The use of a coaxial gas flow around the stainless-steel capillary outlet permits stable plasma operation at low liquid flow rates (0.1–0.3 mL min−1) where pulsation present in the liquid delivery system makes the discharge itself quite unstable. Analytical response curves for Hg, Mg, Na and Pb are demonstrated to have good linearity, with preliminary limits of detection determined to be in the range of 1.1–2.0 ppm (≈10 ng) for 5 µL sample volumes.

Journal ArticleDOI
TL;DR: In this paper, the atmospheric pressure glow discharge (APGD) was studied in neon at atmospheric pressure and it was found that the APGD can also be generated in neon under specific conditions.
Abstract: The dielectric barrier discharge burning at atmospheric pressure usually has a filamentary non-homogeneous form. However, it was found that uniform dielectric barrier discharge can be generated in helium, nitrogen and in the mixture of argon with acetone under specific conditions. Such uniform discharge is called atmospheric pressure glow discharge (APGD). We studied dielectric barrier discharge burning in neon at atmospheric pressure and we found that the APGD can also be generated in neon. We measured the electrical characteristics of APGD in neon for different voltages and frequencies of power supply and different gas flows. We found that higher gas flow stabilizes the APGD and we determined the area of parameters in which the APGD burns. The images of discharges were recorded by a video camera and emission optical spectra were measured by a spectrometer. The properties of the discharges in neon were compared with the properties of discharges burning in argon and in the mixture of neon with argon.

Patent
20 Mar 2001
TL;DR: A pump assembly provides direct replacement of volumes of liquid from a reservoir with equal volumes of air preferably at substantially atmospheric pressure, the same pressure or with pressure equalization to be at least equal to atmospheric pressure as discussed by the authors.
Abstract: A pump assembly provides for direct replacement of volumes of liquid from a reservoir with equal volumes of air preferably at substantially atmospheric pressure, the same pressure or with pressure equalization to be at least equal to atmospheric pressure. A slide arrangement preferably positively displaces liquid from the reservoir and air into the reservoir. The pump draws air from the atmosphere into a chamber from which the air either is available for passage to replace liquid from the reservoir or is pressurized to assist dispensing liquid, preferably, admixing with the liquid to provide foaming. Gravity separation of air and liquid to be dispensed is used to replace liquid with air in the reservoir and to selectively place air and liquid into communication with passageways for ejection.

Journal ArticleDOI
TL;DR: Energy distribution and heat transfer mechanisms in atmospheric pressure non-equilibrium plasmas were investigated extensively through energy balance analysis, emission spectroscopy of the rotational band of CH (A2??X2?), and gas chromatographic analysis as mentioned in this paper.
Abstract: Energy distribution and heat transfer mechanisms in atmospheric pressure non-equilibrium plasmas were investigated extensively through energy balance analysis, emission spectroscopy of the rotational band of CH (A2??X2?), and gas chromatographic analysis. Two plasma sources were examined: methane-fed dielectric barrier discharge (DBD) and atmospheric pressure glow-discharge (APG). The DBD features filamentary microdischarges accompanied by surface discharge along a dielectric barrier. As a result, 60% of the input power was measured as heat transfer to the dielectric electrode, whereas 20% was to the metallic electrode. Consequently, feed gas average temperature was increased only by 20-40?K. On the other hand, rotational temperature of the corresponding emission region exceeded average gas temperature by 100?K. In APG, heat transfer to electrodes was dominated by formation of negative glow regardless of whether the electrode was covered by a dielectric. However, negative glow tended to be thinner and more intense when it formed on a metallic electrode, leading to slightly higher metallic heating. Rotational temperature in APG was close to average gas temperature since APG does not show radial localization of plasma. Energy efficiency for methane decomposition process to produce ethane, ethylene, and hydrogen was about 1% regardless of the plasma source. Energy distribution and heat transfer mechanisms depend strongly on the plasma spatial structure rather than flow fields or feed gas physical properties.

Journal ArticleDOI
TL;DR: In this article, the formation of silicon powder by pyrolysis of silane diluted in argon at different concentrations has been studied, where a hot wall gas-phase reactor was used for the thermal decomposition of SiH 4 at 1000°C and atmospheric pressure.
Abstract: The formation of silicon powder by pyrolysis of silane diluted in argon at different concentrations has been studied. A hot wall gas-phase reactor was used for the thermal decomposition of SiH 4 at 1000°C and atmospheric pressure. The composition, morphology, size, and shape of the particles produced has been studied utilizing electron microscopy, X-ray diffraction, infrared spectroscopy, and BET gas adsorption. Depending on the experimental conditions, agglomerates of polycrystalline, sintered particles have been obtained, which are composed of nanocrystallites of about 25 nm in size.

Journal ArticleDOI
TL;DR: A detection sensitivity of at least 8 parts in 10(9) of TNT vapor with a signal-to-noise ratio of approximately 10 has been experimentally verified for an unfocused approximately 5-mJ laser beam, measured at a distance of approximately 15 cm from the TNT sample.
Abstract: A unique scheme has been applied for sensitive remote detection of 2,4,6-trinitrotoluene (TNT) vapor trace amounts at atmospheric pressure and 24 degrees C. The detection concept is based on a single laser beam inducing a tandem process: photodissociation of TNT vapor followed by highly selective detection of its photofragments vibrationally excited NO, utilizing laser-induced fluorescence with the A2Sigma+(v' = 0) <-- X2Pi(v'' = 2) transition. A detection sensitivity of at least 8 parts in 10(9) of TNT vapor with a signal-to-noise ratio of approximately 10 has been experimentally verified for an unfocused approximately 5-mJ laser beam, measured at a distance of approximately 15 cm from the TNT sample.

Journal ArticleDOI
TL;DR: In this paper, the authors estimate errors in analyzed pressure fields and the impact of those errors on GRACE surface mass estimates by comparing analyzed fields with barometric surface pressure measurements in the United States and North Africa/Arabian peninsula.
Abstract: The Gravity Recovery and Climate Experiment (GRACE) satellite mission will resolve temporal variations in gravity orders of magnitude more accurately and with considerably higher resolution than any existing satellite. Effects of atmospheric mass over land will be removed prior to estimating the gravitational field, using surface pressure fields generated by global weather forecast centers. To recover the continental hydrological signal with an accuracy of 1 cm of equivalent water thickness down to scales of a few hundred kilometers, atmospheric pressure must be known to an accuracy of 1 mbar or better. We estimate errors in analyzed pressure fields and the impact of those errors on GRACE surface mass estimates by comparing analyzed fields with barometric surface pressure measurements in the United States and North Africa/Arabian peninsula. We consider (1) the error in 30-day averages of the pressure field, significant because the final GRACE product will average measurements collected over 30-day intervals, and (2) the short-period error in the pressure fields which would be aliased by GRACE orbital passes. Because the GRACE results will average surface mass over scales of several hundred kilometers, we assess the pressure field accuracy averaged over those same spatial scales. The atmospheric error over the 30-day averaging period, which will map directly into GRACE data, is generally <0.5 mbar. Consequently, analyzed pressure fields will be adequate to remove the atmospheric contribution from GRACE hydrological estimates to subcentimeter levels. However, the short-period error in the pressure field, which would alias into GRACE data, could potentially contribute errors equivalent to 1 cm of water thickness. We also show that given sufficiently dense barometric coverage, an adequate surface pressure field can be constructed from surface pressure measurements alone.

Journal ArticleDOI
TL;DR: In this paper, a theoretical model was developed and applied to the experimental results presented in this paper, and the model correctly predicts the inverse square root dependence of the film growth rate on sample area and it predicts that it will be difficult to process long samples, such as tapes, in simple reactor geometries.
Abstract: YBa2Cu3O7 films were fabricated on SrTiO3 substrates using the BaF2 ex situ process. Precursor films 1, 3 and 5 μm thick were processed in an atmospheric pressure reactor using a gas mixture of oxygen, nitrogen and water vapor. The films were processed at different water vapor pressures and it was observed that the film growth rate was independent of film thickness and proportional to the square root of the water vapor pressure. The dependence of the film growth rate on film area was also investigated for film areas varying from 10 to 160 mm2. Surprisingly, it was observed that the growth rate was inversely proportional to square root of the area of the film. A theoretical model is developed and applied to the experimental results presented in this paper. The model correctly predicts the inverse square root dependence of the film growth rate on sample area. In addition, it predicts that it will be difficult to process long samples, such as tapes, in simple reactor geometries.

Journal ArticleDOI
TL;DR: In this paper, the authors examined high-frequency sea level variations forced by changes in surface atmospheric pressure and wind and their sensitivity to different forcing mechanisms, bottom topography resolution, and amount of friction in a barotropic ocean model.
Abstract: This study examines high-frequency sea level variations forced by changes in surface atmospheric pressure and wind and their sensitivity to different forcing mechanisms, bottom topography resolution, and amount of friction in a barotropic ocean model. Optimal model performance, defined in terms of the explained variance in satellite altimeter and bottom pressure data, is found when using relatively strong friction, equivalent to a damping timescale of only a few days over the deep ocean, and topography with minimal smoothing. Spatial variations of the optimal friction parameter seem to reflect the roughness of bottom topography. The model demonstrates skill in simulating the wind-driven response as well as the nonequilibrium response to atmospheric pressure variations.

Journal ArticleDOI
TL;DR: Vibrational sum frequency generation (SFG) spectroscopy has been developed to a stage of surface sensitivity that is comparable to the classical surface science methods and has been successfully employed to study a variety of adsorbate-substrate interfaces and due to its surface-specificity it allows the study of ads absorbates from submonolayer coverages up to atmospheric gas pressure as mentioned in this paper.
Abstract: Vibrational sum frequency generation (SFG) spectroscopy has been developed to a stage of surface sensitivity that is comparable to the classical surface science methods. SFG has been successfully employed to study a variety of adsorbate–substrate interfaces and due to its surface-specificity it allows the study of adsorbates from submonolayer coverages up to atmospheric gas pressure. A number of case studies is presented including adsorption, co-adsorption and reactions on single crystal surfaces and supported nanoparticles. Studies of CO adsorption on Pt(111) and Pd(111) from 10−7 to 1000 mbar have shown that the high pressure adsorbate structures were comparable with saturation structures obtained at low temperature in ultrahigh vacuum. No evidence for pressure-induced surface rearrangements was found. However, pronounced differences in the CO adsorbate structure on supported Pd nanoparticles and on Pd(111) were detected. It is further shown how polarization dependent SFG can be employed to determine molecular orientations of CO and NO and how SFG is carried out during ethylene hydrogenation. Broadband techniques allow the performance of time-resolved pump–probe SFG experiments and to take “snapshots” of the transient vibrational spectrum.