Showing papers on "Atmospheric pressure published in 2008"
TL;DR: The design and operation of a microfluidic system formed in a synthetic hydrogel captures the main attributes of transpiration in plants: transduction of subsaturation in the vapour phase of water into negative pressures in the liquid phase, stabilization and flow of liquid water at large negative pressures.
Abstract: Plant scientists believe that transpiration-the motion of water from the soil, through a vascular plant, and into the air-occurs by a passive, wicking mechanism. This mechanism is described by the cohesion-tension theory: loss of water by evaporation reduces the pressure of the liquid water within the leaf relative to atmospheric pressure; this reduced pressure pulls liquid water out of the soil and up the xylem to maintain hydration. Strikingly, the absolute pressure of the water within the xylem is often negative, such that the liquid is under tension and is thermodynamically metastable with respect to the vapour phase. Qualitatively, this mechanism is the same as that which drives fluid through the synthetic wicks that are key elements in technologies for heat transfer, fuel cells and portable chemical systems. Quantitatively, the differences in pressure generated in plants to drive flow can be more than a hundredfold larger than those generated in synthetic wicks. Here we present the design and operation of a microfluidic system formed in a synthetic hydrogel. This synthetic 'tree' captures the main attributes of transpiration in plants: transduction of subsaturation in the vapour phase of water into negative pressures in the liquid phase, stabilization and flow of liquid water at large negative pressures (-1.0 MPa or lower), continuous heat transfer with the evaporation of liquid water at negative pressure, and continuous extraction of liquid water from subsaturated sources. This development opens the opportunity for technological uses of water under tension and for new experimental studies of the liquid state of water.
459 citations
TL;DR: In this article, a 2 cm long plasma jet was generated by flowing atmospheric pressure air through a direct current powered microhollow cathode discharge, which was used to eliminate yeast infections of the skin.
Abstract: By flowing atmospheric pressure air through a direct current powered microhollow cathode discharge, we were able to generate a 2cm long plasma jet. With increasing flow rate, the flow becomes turbulent and temperatures of the jet are reduced to values close to room temperature. Utilizing the jet, yeast grown on agar can be eradicated with a treatment of only a few seconds. Conversely, animal studies show no skin damage even with exposures ten times longer than needed for pathogen extermination. This cold plasma jet provides an effective mode of treatment for yeast infections of the skin.
386 citations
TL;DR: In this paper, a room-temperature atmospheric pressure plasma plume generated between a high-voltage electrode and the surrounding room air is reported, which has a peak current of about 360mA.
Abstract: A single electrode room-temperature atmospheric pressure plasma plume generated between a high-voltage electrode and the surrounding room air is reported. The plasma plume has a peak current of about 360mA. This is highest current carried by a room-temperature plasma plume ever reported. The rotational and vibrational temperature of the plasma plume is about 300 and 2950K, respectively. Emission spectra show that excited species, such as O, OH, N2+, etc., are present in the plasma plume.
290 citations
TL;DR: In this article, two types of atmospheric pressure plasma jets are compared in terms of their fundamental properties and their efficiency in etching polymeric materials. And the linear-field jet is shown to drive electron transportation to the downstream application region, thus facilitating more active plasma chemistry there.
Abstract: This letter reports an experimental study of two types of atmospheric pressure plasma jets in terms of their fundamental properties and their efficiency in etching polymeric materials. The first plasma jet has a cross-field configuration with its electric field perpendicular to its gas flow field, whereas the second is a linear-field device having parallel electric and flow fields. The linear-field jet is shown to drive electron transportation to the downstream application region, thus facilitating more active plasma chemistry there. This is responsible for its etching rate of polyamide films being 13-fold that of its cross-field counterpart.
259 citations
TL;DR: In this article, a room temperature atmospheric pressure plasma jet device is reported, which is driven by a kilohertz ac power supply, and is capable of generating a plasma plume up to 11 cm long in the surrounding room air.
Abstract: In this letter, a room temperature atmospheric pressure plasma jet device is reported. The high voltage electrode of the device is covered by a quartz tube with one end closed. The device, which is driven by a kilohertz ac power supply, is capable of generating a plasma plume up to 11cm long in the surrounding room air. The rotational and vibrational temperatures of the plasma plume are 300 and 2300K, respectively. A simple electrical model shows that, when the plasma plume is contacted with a human, the voltage drop on the human is less than 66V for applied voltage of 5kV (rms).
239 citations
TL;DR: In this article, the properties of an atmospheric pressure plasma jet (APPJ) in a single-cell dielectric capillary configuration were examined using spatially and temporally resolved optical diagnostics.
Abstract: The properties of an atmospheric pressure plasma jet (APPJ) are examined in a single-cell dielectric capillary configuration. In contrast to some other flow-driven APPJs, this stable, cold plasma jet is electrically driven, composed of rapidly propagating ionization fronts with speeds of the order of 107cm∕s. Using spatially and temporally resolved optical diagnostics, it is demonstrated that the plasma jet is initiated independent of the dielectric barrier discharge inside the capillary. It is also shown that the properties and dynamics of this APPJ are directly analogous to those of positive corona streamer discharges.
232 citations
TL;DR: The performance of mass spectrometers with limited pumping capacity is shown to be improved through use of a discontinuous atmospheric pressure interface (DAPI), and limits of detection in the low part-per-billion levels were achieved and unit resolution mass spectra were recorded.
Abstract: The performance of mass spectrometers with limited pumping capacity is shown to be improved through use of a discontinuous atmospheric pressure interface (DAPI). A proof-of-concept DAPI interface was designed and characterized using a miniature rectilinear ion trap mass spectrometer. The interface consists of a simple capillary directly connecting the atmospheric pressure ion source to the vacuum mass analyzer region; it has no ion optical elements and no differential pumping stages. Gases carrying ionized analytes were pulsed into the mass analyzer for short periods at high flow rates rather than being continuously introduced at lower flow rates; this procedure maximized ion transfer. The use of DAPI provides a simple solution to the problem of coupling an atmospheric pressure ionization source to a miniature instrument with limited pumping capacity. Data were recorded using various atmospheric pressure ionization sources, including electrospray ionization (ESI), nano-ESI, atmospheric pressure chemical ionization (APCI), and desorption electrospray ionization (DESI) sources. The interface was opened briefly for ion introduction during each scan. With the use of the 18 W pumping system of the Mini 10, limits of detection in the low part-per-billion levels were achieved and unit resolution mass spectra were recorded.
225 citations
TL;DR: In this article, electrical and optical emission properties of non-equilibrium atmospheric air discharges between a metal pin and a tap water anode/cathode are presented and extrapolated scaling laws of low pressure glow discharge support these findings.
Abstract: Electrical and optical emission properties of non-equilibrium atmospheric air discharges between a metal pin and a tap water anode/cathode are presented. With a water anode the discharges are of the glow type as is derived from short-exposure time plasma imaging and electrical characteristics. Additionally, the validity of extrapolated scaling laws of low pressure glow discharge supports these findings.In the case of a water cathode the plasma is filamentary in nature at the water surface. In the case of a water anode, the plasma is diffuse down to 10 ns. The timescales on which the filaments are visible in the near water cathode region and estimates of the electrical field in the cathode layer are consistent with the assumption that these filaments occur due to the electrical instability of the water surface.Spatially resolved rotational temperature measurements and dependence of the rotational temperature on current are discussed in detail. The rotational temperatures of OH and N2 in the positive column of the plasma are identical and equal to 3250 ± 250 K. A 2500 K temperature drop in the near anode region clearly shows that the water anode acts as an effective heat sink for the discharge. This indicates that apart from the electrical stabilization of the discharge by the water electrode due to its distributed resistance, a water anode also thermally stabilizes the discharge. The rotational temperature of nitrogen near the metal anode is typically two times smaller.
190 citations
TL;DR: In this paper, DC glow discharges were experimentally investigated in atmospheric pressure helium, argon, hydrogen, nitrogen and air, and they were characterized by visualization of discharges and voltage and current measurements for current of up to several milliamperes.
Abstract: DC glow discharges were experimentally investigated in atmospheric pressure helium, argon, hydrogen, nitrogen and air. The discharges were characterized by visualization of the discharges and voltage and current measurements for current of up to several milliamperes. Significant differences are seen in the gas temperature; however all the discharges appear to operate as temperature and pressure scaled versions of low pressure discharges. In the normal glow discharges, features such as negative glow, Faraday dark space and positive column regions are clearly observable. In hydrogen and to a lesser degree in helium and argon standing striations of the positive column were visible in the normal glow regime. Normal glow characteristics such as normal current density at the cathode and constant electric field in the positive column are observed although there are some unexplained effects. The emission spectra for each of the discharges were studied. Also the rotational and vibrational temperature of the discharges were measured by adding trace amounts of N2 to the discharge gas and comparing modeled optical emission spectra of the N2 2nd positive system with spectroscopic measurements from the discharge. The gas temperatures for a 3.5 mA normal glow discharge were around 420 K, 680 K, 750 K, 890 K and 1320 K in helium, argon, hydrogen, nitrogen and air, respectively. Measured vibrational and excitation temperatures indicate non-thermal discharge operation. Mixtures of gases achieved intermediate temperatures.
188 citations
TL;DR: The flowing afterglow-atmospheric pressure glow discharge (APGD) ionization source described in part 1 of this study is applied to the direct analysis of condensed-phase samples and the ability of this source to perform spatially resolved analysis is demonstrated.
Abstract: The flowing afterglow-atmospheric pressure glow discharge (APGD) ionization source described in part 1 of this study (in this issue) is applied to the direct analysis of condensed-phase samples. When either liquids or solids are exposed to the ionizing beam of the APGD, strong signals for the molecular ions of substances present on their surfaces can be detected without compromising the integrity of the solid sample structure or sample substrate. As was observed for gas-phase compounds in part 1 of this study, both polar and nonpolar substances can be ionized and detected by mass spectrometry. The parent molecular ion (or its protonated counterpart) is usually the main spectral feature, with little or no fragmentation in evidence. Preliminary quantitative results show that this approach offers very good sensitivity (detection limits in the picogram regime are reported for several test compounds in part 1 of this study) and linear response to the analyte concentration. Examples of the application of this s...
186 citations
TL;DR: The air pollution index (API) sequences in 10 cities in northern China and the synoptic pressure patterns during autumn and winter from 2002 to 2006 were analyzed with diagnostic and statistical methods as discussed by the authors.
TL;DR: In this article, pressure-induced superconductivity in a single crystal of CaFe2As2 has been shown to be superconducting at atmospheric pressure of 0.69 GPa with a transition temperature exceeding 10 K.
Abstract: We report pressure-induced superconductivity in a single crystal of CaFe2As2. At atmospheric pressure, this material is antiferromagnetic below 170 K but under an applied pressure of 0.69 GPa becomes superconducting, with a transition temperature Tc exceeding 10 K. The rate of Tc suppression with applied magnetic field is −0.7 K T−1, giving an extrapolated zero-temperature upper critical field of 10–14 T.
TL;DR: In this article, the DBD is excited by repetitive unipolar nanosecond pulses with a rise time of 15'ns and a full width at half-maximum of 30'ns.
Abstract: Dielectric barrier discharge (DBD) is a typical approach for producing non-thermal plasma at atmospheric pressure. In this experimental study, the DBD is excited by repetitive unipolar nanosecond pulses with a rise time of ~15 ns and a full-width at half-maximum of ~30 ns. With a unipolar pulse voltage of 35 kV, the measured discharge current across the DBD circuit has a positive and negative pulse, and the pulse peak value can be hundreds of amperes. The low-speed camera images of the discharge show that both diffuse 'glow-like' and filamentary discharges can be observed, and the air gap length, barrier variety and applied repetition rate are the important factors influencing the transition of the two discharge modes. According to a known equivalent circuit and measured data of a typical DBD, electrical parameters including voltage, current and instantaneous power across the air gap and dielectric layer are calculated. The calculated results indicate that there are two consecutive discharges in the air gap, and the secondary discharge fires immediately after the primary discharge extinguishes. The power consumption of the secondary discharge is provided by the dielectric layer and deposited during the primary discharge. With the increase in the repetition rate, the energy deposition in the air gap per second is greatly enhanced and can exceed one joule for a repetition rate up to 100 Hz, and the corresponding charge transfer is also increased. The electron temperature and density are estimated to be approximately 5.1 eV and 1.6 × 1012 cm−3, respectively.
TL;DR: The coplanar microscale atmospheric pressure plasma jet (μ-APPJ) is a capacitively coupled radio frequency discharge (13.56 MHz, ~15 W rf power) designed for optimized optical diagnostic access as discussed by the authors.
Abstract: The coplanar microscale atmospheric pressure plasma jet (μ-APPJ) is a capacitively coupled radio frequency discharge (13.56 MHz, ~15 W rf power) designed for optimized optical diagnostic access. It is operated in a homogeneous glow mode with a noble gas flow (1.4 slm He) containing a small admixture of molecular oxygen (~0.5%). Ground state atomic oxygen densities in the effluent up to 2 × 1014 cm−3 are measured by two-photon absorption laser-induced fluorescence spectroscopy (TALIF) providing space resolved density maps. The quantitative calibration of the TALIF setup is performed by comparative measurements with xenon. A maximum of the atomic oxygen density is observed for 0.6% molecular oxygen admixture. Furthermore, an increase in the rf power up to about 15 W (depending on gas flow and mixture) leads to an increase in the effluent's atomic oxygen density, then reaching a constant level for higher powers.
TL;DR: In this article, a composite material for simultaneous luminescent determination of air pressure and temperature is presented, which consists of a fluorinated platinum porphyrin complex (PtTFPP) as an oxygen-sensitive probe, and of the highly temperature-sensitive europium complex Eu(tta)3(dpbt) as temperature probe.
Abstract: A novel kind of composite material for simultaneous luminescent determination of air pressure and temperature is presented. The dual sensor consists of a fluorinated platinum porphyrin complex (PtTFPP) as an oxygen-sensitive probe, and of the highly temperature-sensitive europium complex Eu(tta)3(dpbt) as temperature probe. Both are incorporated into different polymer microparticles to control response characteristics and to avoid interferences. Encapsulation of PtTFPP in poly(styrene-co-acrylonitrile) (PSAN) results in a broad dynamic range from 0.05 to 2.00 bar for pressure measurements. The europium complex was incorporated into poly(vinyl chloride) to reduce the cross sensitivity towards oxygen. This system represents a new class of luminescent sensor system, where the signals are separated via the different luminescence lifetimes of the indicators. It is possible to monitor the emission of the temperature-sensitive probe by means of time-resolved fluorescence imaging without interferences, because the luminescence lifetime of the temperature indicator is tenfold longer than that of the oxygen indicator. The temperature image can then be used to compensate cross sensitivity of the pressure indicator towards temperature. In combination with an appropriate time-resolved measurement technique, this material enables simultaneous imaging of pressure (or oxygen partial pressure) and temperature distributions on surfaces. It is distinguished from other approaches of dual pressure and temperature sensitive paints because it avoids the need of signal separation by application of different cameras or by use of different optical filters or light sources.
TL;DR: In this paper, a molecular gas such as nitrogen at different levels of impurity dominates the ionic composition of an atmospheric pressure noble gas plasma such as in helium, and the positive charge in the discharge is only determined by helium ions if the discharge gas contains less than 1ppm.
Abstract: We present in this letter how a molecular gas such as nitrogen at different levels of impurity dominates the ionic composition of an atmospheric pressure noble gas plasma such as in helium. The positive charge in the discharge is only determined by helium ions if the discharge gas contains less than 1ppm of impurity. Above this impurity level, the positive charge is completely determined by the impurity nitrogen. The higher the relative nitrogen concentration, the more N4+ dominates over N2+. If the impurity level is between 1 and about 20ppm, N2+ is clearly the most abundant positive ion but for higher levels of impurity, N4+ almost completely determines the positive charge.
TL;DR: In this paper, the physicochemical properties such as density, isentropic bulk modulus, heat capacity, and isobaric thermal expansion were calculated in the same temperature and pressure range as the speed of sound was measured.
TL;DR: In this paper, a zero-dimensional global model was developed to calculate the densities of several kinds of species and electron temperature in atmospheric pressure glow discharges (APGDs), and it was shown that even though small fraction of oxygen less than 1% was added to helium or argon, electrons dissipated most of their energy through collisions with oxygen molecules rather than helium and argon atoms.
Abstract: Atmospheric pressure glow discharges (APGDs) have widespread applications, including sterilization, cancer cell treatment, deposition, and surface modification due to their rather simple configurations, thanks to no need for vacuum system and their great capability to generate reactive species such as radical oxygen species. Helium and argon are widely used as feeding gases, achieving stable operations for wide ranges of parameters in atmospheric pressure, and oxygen is added into these gases to generate more reactive oxygen species (ROS), which play a significant role in sterilization. As the measurements of species densities and electron temperature in APGDs are difficult, we have developed the zero-dimensional global model of He/O 2 and Ar/O 2 APGDs to calculate the densities of several kinds of species and electron temperature. It was shown that even though small fraction of oxygen less than 1% was added to helium or argon, electrons dissipated most of their energy through collisions with oxygen molecules rather than helium or argon atoms. The densities of electron, atomic oxygen, and ozone of Ar/O 2 were higher than those of He/ O 2 ; however, the electron temperature of He/O 2 was higher than that of Ar/O 2 . When the pulsed power is applied, the time-averaged electron temperature for the shorter pulse period and the larger duty ratio increased, and the electron density decreased as the duty ratio increased.
TL;DR: In this paper, positive streamers in ambient air at pressures from 0.013 to 1 bar are investigated experimentally, using a slow voltage rise time of 100−180ns, the streamers are intentionally kept thin.
Abstract: Positive streamers in ambient air at pressures from 0.013 to 1 bar are investigated experimentally. The voltage applied to the anode needle ranges from 5 to 45 kV, the discharge gap from 1 to 16 cm. Using a ‘slow’ voltage rise time of 100–180ns, the streamers are intentionally kept thin. For each pressure p, we find a minimal diameter d_min. To test whether streamers at different pressures are similar, the
minimal streamer diameter d_min is multiplied by its pressure p; we find this product to be well approximated by p·d_min = 0.20 ± 0.02mmbar over two decades of air pressure at room temperature. The value also fits diameters of sprite discharges above thunderclouds at an altitude of 80 km when
extrapolated to room temperature (as air density rather than pressure determines the physical behaviour). The minimal velocity of streamers in our measurements is approximately
0.1mmns^(−1) = 105 ms^(−1). The same minimal velocity has been reported for tendrils in sprites. We also investigate the size of the initial ionization cloud at the electrode tip from which the streamers emerge, and the streamer length between branching events. The same quantities are also measured in nitrogen with a purity of approximately 99.9%. We characterize the essential differences with streamers in air and find a minimal diameter of p·d_min = 0.12 ± 0.02mmbar in our nitrogen.
TL;DR: In this article, the authors present the results of their experimental measurements of how variations in the discharge geometry of surface-mounted dielectric barrier discharges (DBDs) affect the force transferred to atmospheric pressure air.
Abstract: We present the results of our experimental measurements of how variations in the discharge geometry of surface-mounted dielectric barrier discharges (DBDs) affect the force transferred to atmospheric pressure air. Our studies include both single barrier plasma actuators (one electrode insulated) and double barrier plasma actuators (both electrodes insulated) operated in quiescent air. Stagnation probe measurements of the induced air flow and direct force measurements using an electronic balance show that, for both actuator types, parallel time-averaged forces increase as the high voltage electrode diameter decreases. For single barrier actuators, this increase is exponential rather than linear as previously reported in the literature. The data from the two measurement techniques are directly proportional to one another. When the variation of velocity and pressure on all sides of an actuator are considered, the techniques show quantitative agreement.
TL;DR: In this article, a mathematical model for the quasi-steady diffusion-limited evaporation of a thin axisymmetric sessile droplet of liquid with a pinned contact line is formulated and solved.
TL;DR: In this article, pressure-induced superconductivity in a single crystal of CaFe2As2 has been shown to be superconducting under applied pressure of 0.69 GPa, with a transition temperature exceeding 10 K.
Abstract: We report pressure-induced superconductivity in a single crystal of CaFe2As2. At atmospheric pressure, this material is antiferromagnetic below 170 K but under an applied pressure of 0.69 GPa becomes superconducting, with a transition temperature Tc exceeding 10 K. The rate of Tc suppression with applied magnetic field is -0.7 K/T, giving an extrapolated zero-temperature upper critical field of 10-14T.
TL;DR: In this article, a model-based control structure is proposed that comprises a multivariable control of the cathode pressure p C and the excess ratio of oxygen λ O 2 using the mass flow controller (MFC) and the outlet throttle as actuators.
TL;DR: In this article, a pure nanocrystalline Zr with a grain size of 30nm and a microhardness of 400 HV has been fabricated by high pressure torsion (HPT) at room temperature using a pressure of 6 GPa and five revolutions in 5min.
TL;DR: In this paper, aramid fiber samples are modified by air dielectric barrier discharge (DBD) plasma at atmospheric pressure, and the surface roughness is improved, the O/C atomic ratio is increased from 15.99% to 27.15% and surface wettability is also enhanced.
Abstract: Aramid fiber (AF) samples are modified by air dielectric barrier discharge (DBD) plasma at atmospheric pressure. Plasma discharge power density and sample treatment time are investigated as the major parameters. Modified AF is characterized by SEM, XPS and wettability tests. It is shown that the surface roughness is improved, the O/C atomic ratio is increased from 15.99% to 27.15%, and the surface wettability is also enhanced significantly. It is also found that the improvements of physical and chemical properties increased with increasing power density and treatment time. The experiment is operated in the case of continuous on-line processing with properly high speed of AF transmission. It is close to industrial production and application.
TL;DR: A plasma-based ambient desorption/ionization mass spectrometry (ADI-MS) source was used to perform molecular mass spectral imaging to analyze several sample surfaces for a wide variety of analytes and with high sensitivity.
Abstract: A plasma-based ambient desorption/ionization mass spectrometry (ADI-MS) source was used to perform molecular mass spectral imaging. A small amount of sample material was ablated by focusing 266 nm laser light onto a spot. The resulting aerosol was transferred by a nitrogen stream to the flowing afterglow of a helium atmospheric pressure glow discharge ionization source; the ionized sample material was analyzed by a Leco Unique time-of-flight mass spectrometer. Two-dimensional mass spectral images were generated by scanning the laser beam across a sample surface. The total analysis time for a 6 mm2 surface, which is limited by the washout of the ablation chamber, was less than 30 min. With this technique, a spatial resolution of ∼20 μm has been achieved. Additionally, the laser ablation configuration was used to obtain depth information of over 2 mm with a resolution of ∼40 μm. The combination of laser ablation with the flowing atmospheric pressure afterglow source was used to analyze several sample surfac...
TL;DR: In this paper, a waveguide-based nozzleless cylinder-type microwave plasma source (MPS) was used to convert methane into hydrogen, and the hydrogen production rate and corresponding energy efficiency in the presented methane reforming were up to 255g[H2]h−1 and 85 g[H 2]kWh−1, respectively.
TL;DR: In this article, the contribution of atmospheric pressure and wind to low frequency (the seasonal cycle and lower) Mediterranean sea level variability has been investigated using the HIPOCAS Project framework, by means of a long-term barotropic run of the HAMSOM model, with a 1/4° × 1/6° spatial resolution.
TL;DR: In this paper, a nonequilibrium atmospheric pressure plasma was produced by applying an alternative current between two electrodes using optical emission spectroscopy (OES) to evaluate the electron density and gas temperature.
Abstract: We produced a nonequilibrium atmospheric pressure plasma by applying an alternative current between two electrodes. The gas temperature and electron density were evaluated using optical emission spectroscopy. It was found that the plasma had gas temperatures from 1800to2150K and ultrahigh electron densities in the order of 1016cm−3. A remarkably high oxygen radical concentration of 1.6×1015cm−3 was obtained at a 1% O2∕Ar gas flow rate of 15slm (standard liters per minute). Contact angles below 10° were obtained in the process of glass cleaning with a plasma exposure time of 23ms.