Variation Of Ambient Pressure Research Articles

Ordinary hot-wire/hot-film method for spirography application

Although hot-wire/hot-film has lots of advantages, but some problems like flow direction detection, variation of temperature and ambient pressure and presence of dust particles in the vicinity of the sensor, cause errors in medical application measurement. This paper describes an innovative way for using ordinary hot-wire/hot-film method in spirography. The innovation includes an obstacle between two hot-film sensors and a procedure for data processing considering all hot-wire/hot-film problems. In addition a calibration syringe with definite volume is used to modify the calibration of spirometer under different working conditions.

Minipressure sensor using AlGaN/GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors (HEMTs) with a polarized polyvinylidene difluoride (PVDF) film coated on the gate area exhibited significant changes in channel conductance upon exposure to different ambient pressures. The PVDF thin film was deposited on the gate region with an ink-jet plotter. Next, the PDVF film was polarized with an electrode located 2 mm above the PVDF film at a bias voltage of 10 kV and 70 °C. Variations in ambient pressure induced changes in the charge in the polarized PVDF, leading to a change in surface charges on the gate region of the HEMT. Changes in the gate charge were amplified through the modulation of the drain current in the HEMT. By reversing the polarity of the polarized PVDF film, the drain current dependence on the pressure could be reversed. Our results indicate that HEMTs have potential for use as pressure sensors.

Pressure Sensing with PVDF Gated AlGaN/GaN High Electron Mobility Transistor

AbstractAlGaN/GaN high electron mobility transistors (HEMTs) with a polarized Polyvinylidene difluoride (PVDF) film coated on the gate area exhibited significant changes in channel conductance upon exposure to different ambient pressures. The PVDF thin film was deposited on the gate region with an inkjet plotter. Next, the PDVF film was polarized with an electrode located 2 mm above the PVDF film at a bias voltage of 10 kV and 70 °C. Variations in ambient pressure induced changes in the charge in the polarized PVDF, leading to a change of surface charges on the gate region of the HEMT. Changes in the gate charge were amplified through the modulation of the drain current in the HEMT. By reversing the polarity of the polarized PVDF film, the drain current dependence on the pressure could be reversed. Our results indicate that HEMTs have potential for use as pressure sensors.

Electronic and Local Structures of La1-x SrxCoO3-δ Studied by In-Situ Micro XAS Measurements

Electronic and local structures of the perovskite-type La0.6Sr0.4CoO3-d, which is a promising cathode material for solid oxide fuel cells, were investigated by means of in-situ micro x-ray absorption spectroscopy measurements under working conditions of solid oxide fuel cells, 1073 K of temperature and 10-105 Pa of oxygen partial pressure. It was found that variations of electronic and local structures of La0.6Sr0.4CoO3-d depending on variations of ambient oxygen partial pressure were clearly detected and could be associated with formation/disappearance of oxygen vacancies in the oxide. It was shown that in-situ x-ray absorption spectroscopy measurements could be a useful tool to examine electronic and local structures of high temperature materials in use.

Nonlinear non-spherical oscillations of gas bubble under a periodic variation of ambient liquid pressure

A mathematical model is constructed for the bubble dynamics, in which the interphase surface variation is presented in the form of a series in spherical harmonics, and the equations are written with the accuracy up to the squared amplitude of the distortion of the spherical shape of the bubble. In the oscillation regimes close to periodic sonoluminescence of a single bubble in a standing acoustic wave, the character of air bubble oscillations in water was studied depending on the bubble initial radius and the amplitude of the liquid pressure variation. It was found that non-spherical oscillations of bounded amplitude can take place outside the region of linearly stable spherical oscillations. Both the oscillations with a period equal to one or several periods of the liquid pressure variation and aperiodic oscillations are observed. It is shown that neglecting the distortions in the form of spherical harmonics with large numbers (i > 3) may lead to a change of oscillation regimes. The influence of distortions on the bubble surface shape for the harmonics with i > 8 is insignificant.

Analysis of natural gas by gas chromatography: Reduction of correlated uncertainties by normalisation

The results of gas chromatographic analysis of natural gas mixtures reveal strong correlations (Pearson correlation coefficient of >0.96) between the uncertainty of each component and variations in the ambient pressure. Although correction for ambient pressure variations can reduce this variability, normalisation of the results of each analysis using the assumption that the sum of all component amount fractions is unity provides significantly greater reductions in the uncertainty of each measured component. We show that the uncertainty in normalised components can be estimated approximately using the correlation coefficient as a measure of the correlation present in the measurements, or exactly using a full calculation of the variance/covariance (V/C) structure of the data.

Arterial blood gases during diving in elite apnea divers.

Elite apnea divers have considerably extended the limits of dive depth and duration but the mechanisms allowing humans to tolerate the compression- and decompression-induced changes in alveolar gas partial pressures are still not fully understood. Therefore we measured arterial blood gas tensions and acid-base-status in two elite apnea divers during simulated wet dives lasting 3 : 55 and 5 : 05 minutes, respectively. Arterial pO2 followed the compression-(from 13.8/16.9 kPa before the dive to 30 kPa at the start of the bottom time) and decompression-induced (from 13.7/21.0 kPa to 3.3/4.9 kPa immediately after surfacing) variations of ambient pressure, while the arterial pCO2 remained within the physiologic range (3.0/3.9 kPa before diving vs. 5.7/5.9 kPa at the end of the bottom time), probably due to the CO2 storage capacity of the blood. These findings may help to explain why humans can sustain deep and long apnea dives without major increases in respiratory drive.

Concentration evolution of gas species within a collapsing bubble in a liquid medium

In this study numerical methods are used to investigate the relationship between chemical concentration of gas species within a cavitating bubble, equilibrium radius of the gas bubble and pressure variations in the ambient liquid. For this purpose, governing equations are developed to describe the dynamic equilibrium of a bubble in a flowing fluid and mass transfer between gas and liquid phases, where it was assumed that gases undergo isothermal compression, obey the ideal gas law, Henry law. It is further assumed that the concentration of each phase within the bubble is uniform. The resulting nonlinear equations are solved using implicit Trapezoidal method with Newton iteration. Four gas species are modeled under various initial and ambient pressure variation conditions. These conditions maybe considered to represent typical cavitation events. The numerical results obtained are presented in terms of dimensionless numbers. These results indicate that chemical damage maybe an important component of cavitation surface damage, since high concentration profiles may develop within a collapsing bubble. Proposed formulation and numerical solutions are simple and cost effective to implement. The results presented in this study maybe used to benchmark experimental investigations or other more complex solutions, which are outside the scope of this study.

Physical correlates of the ultrasonic reflectivity of lipid dispersions suitable as diagnostic contrast agents

The objective of this study was to determine the physical basis of ultrasound (US) reflectivity of echogenic lipid dispersions. These dispersions were made using a process previously described involving sonication of the lipid in water, addition of mannitol, freezing, lyophilization and rehydration. The component lipids were egg phosphatidylcholine, dipalmitoylphosphatidylethanolamine, dipalmitoylphosphatidylglycerol and cholesterol in a molar ratio of 69:8:8:15. Ultrasound reflectivity, as assessed with a 20-MHz intravascular US catheter and analyzed using computer-assisted videodensitometry, was found to be sensitive to variations in ambient pressure; echogenicity was greatly reduced by exposure to 0.5 atm vacuum for 10 s or 1.5 atm pressure for 10 s. Pressure changes of the magnitude that obtain in the arterial circulation had little effect on echogenicity. Vacuum treatment resulted in the release of approximately 100 μL air from a standard preparation of 10 mg lipid in 1 mL. Maximum ultrasonic reflectivity required the presence of 0.1–0.2 mol/L mannitol during the lyophilization step; mere addition of mannitol to the lipid lyophilized in the absence of mannitol produced nonreflective dispersions. Inclusion of sodium phosphate or other electrolytes reduced echogenicity. High echogenicity was associated with the presence of large-volume freeze-dried cakes and fusion of liposomes (which led to a 10 times increase in liposome diameters) during freezing before lyophilization. Lyophilization from water led to liposome fusion, but the cakes were small and US reflectivity was weak. Lyophilization from solutions of cryoprotectants such as trehalose produced large cakes, but little liposome fusion and also led to weak US reflectivity. Filtration through defined pores revealed that approximately 50% of the echogenicity originated from particles smaller than 1 μm and about 2/3 from particles smaller than 3 μm. These results indicate that lyophilization from 0.2 mol/L mannitol solution generates a disrupted array of lipid bilayers that, upon rehydration, fuse and trap small amounts of air distributed among liposome-size particles.

Sensitivity Analysis of the USEPA WINS PM2.5Separator

Factors affecting the performance of the USEPA WINS PM2.5 separator have been systematically evaluated. In conjunction with the separator's laboratory calibrated penetration curve, analysis of the governing equation that describes conventional impactor performance was used to predict changes in cutpoint as a function of impactor dimensions, flow rate, uncertainties in ambient temperature and pressure measurement, and the temperature and pressure of the sampled air volume. By integrating the resulting performance curves with three idealized ambient aerosol size distributions, the effect of these parameters on measured PM2.5 concentration was predicted. Results showed that allowable variations in impactor jet width, flow rate, diffusion oil volumes, and ambient temperature and pressure measurement result in relatively minimal PM2.5 mass concentration measurement biases. Loading of the WINS well with previously collected particles slightly reduces the separator's cutpoint and thus slightly reduces expected PM2.5 mass concentrations. Variations in ambient pressure produce negligible changes in the performance of the WINS. While not causing a true measurement bias as defined by the regulations, low ambient temperatures naturally affect the airstream's properties and inherently shifts the WINS' cutpoint to slightly lower values. Laboratory-induced crystallization of the DOW 704 diffusion oil produced no appreciable changes in either the position or shape of the WINS separation curve.

Biomechanical Aspects in Implantable Microphones and Hearing Aids and Development of a Concept with a Hydroacoustical Transmission

The middle ear functions as a sensitive pressure receptor. This implies that it not only transmits sound pressure waves with molecule-sized vibrational amplitudes, but that it also reacts to the million times larger variations of ambient air pressure. This pressure induces movements of the tympanic membrane and of the attached ossicular chain of up to 1,000 microm. Any artificial device that contacts these sound-transporting elements, be it a receiver for an implantable microphone or a transducer for an implantable hearing aid, has to respect these two different modes of biomechanical behavior. A hydroacoustical transmission system has therefore been developed consisting of a water-filled flexible tube, which contacts the ossicular chain with a balloon tip, and which is connected to a piezo-electric transducer at its other end. This soft contact prevents a localized pressure load and does not restrain the free movement of the underlying ossicle during ambient pressure variations. Temporal bone experiments showed that the device transmits vibration energy in good acoustical quality. The device can also be used in a reverse mode, working as a microphone, for example for a totally implantable hearing aid or a cochlear implant. This microphone concept has the advantage that it incorporates the biologic sound receiving components (the tympanic membrane and the ossicular chain micromechanics) into a technical device.

Video investigation of the effects of gravity on single-bubble sonoluminescence

Using NASA’s KC-135 aircraft flying parabolic trajectories, we can observe SBSL as the effective gravity changes from near 0 g to about 1.8 g. A spherical resonator operated at 32.5 kHz is suspended in a constant ambient pressure chamber. Then, a photomultiplier measures light emission while a strobed CCD camera obtains images of the bubble collapse. In normal gravity, buoyancy displaces the bubble from the velocity node of the sound field so that water is flowing past the bubble at the time of collapse. Other gravitational effects include the variation in ambient pressure. During intervals of negligible drift of the SBSL intensity, there can be a rapid intensity rise of between 4% and 20% as the effective gravity decreases. The CCD images are then used to calculate the bubble radius. These measurements were fit to the Rayleigh–Plesset equation to infer the size and pressure conditions by assuming spherical bubble oscillations. These conditions were found to be similar to those reported by other groups for measurements in normal gravity. There are also indications that changes in the effective gravity are accompanied by small changes in the maximum bubble radius. [Work supported by NASA.]

2207 筒内噴射インジェクタの燃料噴霧パターン制御に関する検討 : 第 2 報 L-Step ノズルの微粒化特性

A fuel injector with an L-out orifice (L-Step nozzle) at its tip for controlling fuel spray pattern has been developed for the DI engine. The inclined fuel spray pattern formed by the L-Step nozzle was highly stable against the tested ambient pressure range, from 0.1∿0.6MPa. Moreover, the obtained fuel droplet mean diameter was also stable against ambient pressure variation, with only 5μm increase when the ambient pressure was changed from 0.1 to 0.6 MPa. It was also found that the fuel spray pattern could be controlled by changing the fuel swirl force.

Tympanic pressure gradients and otoacoustic emissions.

The purpose of this study was to investigate the immediate effects of tympanic over- and under-pressure, induced by variations in ambient pressure on click-evoked otoacoustic emissions (CEOAEs) in healthy individuals. It was of particular interest to elucidate whether changes in the CEOAE response in both spectral and time domains could be attributed not only to tympanic, but also to cochlear influence. Nine healthy subjects with normal hearing and middle ear pressure were exposed to ambient pressure changes in a pressure chamber. The pressure was progressively changed in 100 daPa steps to accomplish an increase and a decrease in tympanic pressure. Pressure equilibration of the middle ear was avoided. The relative tympanic over- and under-pressure (+/- 320daPa) was monitored by tympanometry and the CEOAEs recorded at every step of tympanic pressure change. There was a statistically significant reduction of the otoacoustic emission (OAE) response levels and reproducibility already at 100 daPa of ambient pressure change. The OAE response was progressively reduced by increased pressure gradients. The CEOAEs recorded during progressive tympanic over- and under-pressure also had increasingly shorter latencies. These changes of the OAE response characteristics were most pronounced in the 750 to 3000 Hz frequency bands. The progressive attenuation of the OAE response and the concomitant shortening of the OAE response latencies were observed during a combination of altered middle and inner ear pressure. Although the middle and inner ear influence cannot be separated we suggest, based on our findings, that the shortening of latencies may partly be caused by inner ear pressure changes and stiffening of the labyrinthine membranes. Further studies are needed to more specifically clarify the relative contribution of the tympanic and labyrinthine influence, respectively, for the various aspects of pressure influence on the OAE response.

Modeling the Flow of Water on Aircraft in Icing Conditions

A three-dimensional mathematical model that describes the flow of a thin film of water driven by air shear, gravity, surface tension, and ambient pressure variation over a solid substrate is derived. The one-dimensional version is then analyzed and numerical solutions for the fluid film height and velocity obtained. After further simplifying assumptions, a number of formulas that relate film heights and average velocities to the strength of the air shear or gravity effects are also presented

Ambient pressure and single-bubble sonoluminescence

We present a theoretical analysis of the influence of ambient pressure on single-bubble sonoluminescence (SBSL). By combining simulations of gas dynamics, mass diffusion theory, and stability analysis we find a narrow region of the parameter space where stable SBSL is possible. In particular, the theory predicts a 200% increase in SL radiation if ambient pressure is decreased only 5%. The results are compared with preliminary experimental data, and a good agreement is found. Variation of ambient pressure provides a simple and interesting test for the validity of various SL theories, diffusive or nondiffusive mass flow ideas, and stability analyses.

Effects of metabolic rate and ambient vapour pressure on heat strain in protective clothing.

Studies have shown that variations in ambient water vapour pressure from 1.7 to 3.7 kPa have little effect on heat tolerance time at a metabolic rate above 450 W while wearing protective clothing. With lighter exercise, where tolerance times exceed 60 min, variations in vapour pressure have a significant impact on evaporative heat loss and, therefore, heat tolerance. The present study has examined whether these findings extend to conditions with more extreme variations in vapour pressure. Twelve males performed light (L, 350 W) and heavy (H, 500 W) exercise at 40 degrees C in a dry (D, 1.1 kPa) and humid (H, 4.8 kPa) environment while wearing a semi-permeable nuclear, biological and chemical protective clothing ensemble (0.29 m2 x degree C-1.W-1 or 1.88 clo; Woodcock vapour permeability coefficient, im = 0.33). Partitional calorimetry was used to determine the rate of heat storage (S) with evaporative heat loss from the skin (Esk) calculated from changes in dressed mass or the physical properties of the clothing and the vapour pressure gradient between the skin and the environment. Skin vapour pressure was predicted from measurements of water vapour pressure above the skin surface and in the clothing with humidity sensors coupled with thermistors. Final mean skin temperature (Tsk) was higher for the humid trials and averaged 37.4 (0.3) degree C, 38.9 (0.4) degree C, 37.6 (0.5) degree C and 38.5 (0.4) degree C for LD, LH, HD and HH, respectively. Final rectal temperature (Tre) was higher for D with respective values for LD, LH, HD and HH of 39.0 (0.4) degree C, 38.7 (0.4) degree C, 38.8 (0.4) degree C and 38.5 (0.4) degree C. Tolerance time was significantly different among the trials and averaged 120.3 (19.3) min, 54.8 (7.3) min, 63.5 (6.9) min and 36.8 (3.1) min for LD, LH, HD and HH, respectively. Esk was overestimated and, therefore, S was underestimated when the changes in dressed mass were used to determine evaporative heat loss. When skin vapour pressure determined from the humidity sensor data was used to calculate Esk, heat storage was significantly different among the trials and averaged 15.0 (3.0), 13.0 (1.8), 14.2 (2.6) and 12.2 (1.9) kJ.kg-1 for LD, LH, HD and HH, respectively. It was concluded that while wearing the protective clothing all indices of heat strain, including tolerance time, were significantly affected by the change in ambient water vapour pressure from 1.1 to 4.8 kPa during both light and heavy exercise.

An optimized method for airborne peroxyacetyl nitrate (PAN) measurements

In this paper we describe a gas-chromatographic method for PAN measurements in the background atmosphere, which has been adapted to the special requirements of aircraft based campaigns. The instrument is installed in a 1.21 m high, 19 inch rack which has a total weight of 70 kg and a power consumption of 750 VA. The gas chromatograph is equipped with a commercial liquid injector and a valve system for injection of gaseous samples. The gas-inlet system allows automatic injection of samples with defined and constant mass, independent from ambient pressure variations. Two different methods are used for calibration: Liquid PAN calibration samples and a diffusion source for gas-phase calibrations. Both methods have reproducibilities better than 90% and agree with each other to better than 85%. An optimum selectivity of the gas-chromatographic separation is obtained by a combination of two short megabore capillary columns of different polarity. The flow rates are 15 cm3/min, the column temperature is 26°C. For detection an electron-capture detector, operated at 30°C, is used. To allow a reliable control of these relatively low temperatures the instrument is equipped with peltier cooling. To avoid baseline or signal drifts caused by pressure variations in the aircraft cabin an electronic control of the system pressure is integrated into the instrument. The lower limit of detection is better than 15 ppt (3 σ), the time needed for one measurement is less than 4 min. Preliminary results from a flight campaign conducted in June 1994 demonstrate the suitability of the instrument for airborne PAN measurements.

Modelling of Atomization and Vaporization Process in Flash Boiling Spray. 1st Report, Change in Atomization Characteristics with Back Pressure.

In this study, the influence of the flash boiling phenomenon on the fuel spray characteristics was in vestigated using both experiments and model analysis. Pure liquid fuel of n-Pentane or n-Hexane is injected into a vessel under quiescent gaseous atmosphere at room temperature through a pintle-type injector. Fuel sprays are observed by taking photographs for variation of ambient back pressure. In particular, changes in spray characteristics with back pressure are examined in detail. The results show that the saturated vapor pressure of fuel is the most significant factor and the spray characteristics can be varied with the pressure difference between the back pressure and saturated vapor pressure. Furthermore, flow field of the fuel inside the nozzle is estimated with regard to bubble initiation inside the film flow.

Electrical conductivity of tellurium deficient cadmium telluride

The electrical conductivity of polycrystalline cadmium telluride having an impurity content of less than 200 ppm was measured in the temperature range of 675–975 K and in the ambient tellurium pressure varying from 1.0×10−15 atm to 2.0×10−5 atm. The electrical conductivity of polycrystalline CdTe doped with monovalent as well as trivalent cations has also been determined under similar conditions. The conductivity was found to change from predominantly p to predominantly n type at a critical tellurium pressure depending upon the temperature. The electrical conductivity increased with the increase in ambient tellurium pressures reached a maximum, and then decreased with further increase in tellurium pressure. The results have been used to discuss the probable defect structure of CdTe particularly with reference to the variation in ambient tellurium pressure.