Variation Of Ambient Pressure Research Articles

Asymmetric droplet splashing

Asymmetric droplet splashing is observed during oblique impacts and under variable ambient pressure. These two effects are viewed as symmetry breaking factors which lead to new forms of splashing, including upward-only splashing and wing splashing.

Single-step, DC thermal plasma-assisted synthesis of Ag-C nanocomposites with less than 10 nm sizes for antibacterial applications

A single-step, thermal plasma-assisted technique is reported for size-controlled synthesis of silver-carbon (Ag-C) nanocomposites, to be used for antibacterial applications. Silver nanoparticles of sizes less than 10 nm can directly penetrate into the core of the bacteria, while stiff, nanocrystalline carbon may rupture the microorganisms with their sharp edges. Experiments demonstrated that silver nanoparticles nucleate anchoring tightly on carbon sheets, which can inhibit their aggregation and growth in size and becomes more effective as crystallinity of the carbon enhances further. Nanocomposite samples were synthesized using a hot graphite nozzle and with variation of ambient pressure in the sample collection chamber. The Ag-C sample synthesized at 190 mbar chamber pressure demonstrated the best antibacterial activities. The zone of inhibition was measured for this sample as 18 mm for the gram-positive E. hirae and 15 mm for the gram-negative E. coli bacteria at their corresponding minimum inhibitory values of 0.54 mg ml−1 and 0.9 mg ml−1 respectively. The crystallinity of the carbon nanosheets was measured to be the best for this particular sample and the average size of the silver nanoparticles remaining entangled on them was measured as 4.6 nm, which to our knowledge is the smallest ever synthesized by a plasma-assisted method. The gas temperature at the injection section was measured using the C2 Swan band system, (0, 0) vibrational transition located at 516.5 nm, which confirms temperature enhanced substantially in presence of the graphite nozzle, which had led to the enhanced material crystallinity and synthesis of particles with the smallest sizes.

On the Problem of Taking into Account the Effect of Meteorological Factors on Large Precision Systems: A Case Study of the Baksan Large-Base Laser Interferometer

Variations in ambient temperature and atmospheric pressure coincide with the wave train of the lunar–solar tide in the diurnal and semidiurnal frequency ranges, where they have the greatest influence on deformation measurements by laser interferometers. Based on data from the Baksan laser interferometer of the Sternberg Astronomical Institute of Moscow University over a 15-year observation period, it is shown that the response of large measuring systems to these variations has a pronounced frequency dependence. Using the constructed mathematical model the problem of taking into account how meteorological factors influence measurements is solved in the frequency domain with the aid of images of deformation time series and meteorological factors, obtained by Fourier transform. A transient function is constructed in the form of the so-called aperiodic link, which takes into account the frequency dependence and delay of thermoelastic deformation of the measuring system on the variation in ambient temperature. The converted temperature and pressure images are subtracted from the deformation image using the corresponding transient functions. As a result, the new deformation image bears virtually no influence of meteorological factors; inverse transform yields a new deformation time series.

Optical coherence elastography by ambient pressure modulation for high-resolution strain mapping applied to patterned cross-linking.

The purpose of this study was to develop a novel non-contact optical coherence elastography (OCE) approach to measure laterally and axially highly resolved corneal strain distribution at different stages of patterned corneal cross-linking (CXL). Freshly enucleated rat eyes were obtained and prepared for accelerated patterned CXL treatment with distinct ultraviolet (UV) patterns (central, peripheral, bow-tie irradiation). Each cornea was measured repeatedly, in three different conditions: (i) virgin, (ii) after epithelial debridement and 0.5% hypo-osmolar riboflavin instillation for 30 min, and (iii) after patterned CXL at 9 mW cm-2 for 10 min. For biomechanical assessment, the corneal deformation response to an ambient pressure variation of -2 mmHg was recorded by OCE. Strain maps were obtained from phase and magnitude changes in the complex optical coherence tomography signal. Virgin corneas presented negative strain (-2.7 ± 1.1‰) in the anterior cornea and positive strain (1.9 ± 1.3‰) in the posterior cornea. A pronounced shift towards positive strains in the anterior cornea (particularly in UV-irradiated regions) was observed after CXL. Patterned UV irradiation induced localized strain alterations closely matching the geometry of the irradiation pattern. This study demonstrates the possibility of non-contact OCE by ambient pressure modulation, which could substantially improve the early diagnosis of corneal degeneration, advance research in small-animal eyes and refine in vitro mechanical investigation.

An experimental study on explosive boiling of superheated droplets in vacuum spray flash evaporation

Spray flash evaporation is an effective desalination method, which increases specific surface area of salty water by liquid atomization, thereby improving desalination performance and maximising low-grade heat source utilization. During evaporation, explosive boiling phenomenon occurs inside superheated droplets on a heated surface. In order to understand the mechanism of explosive boiling, spray flash evaporation of distilled water and 3.5 wt% salty water in a high vacuum vessel was observed visually. Meanwhile, a parametric study was carried out to scrutinize the impacts of the variation of ambient pressure, heat flux, and surface superheat degree. The experiment data indicates that nucleate site is located in the upper layer of a droplet due to internal superheated liquid and Marangoni convection. In different operating conditions, bubble fragmentation process or crown fragmentation process happens at nucleate site. The fragmentation time of pure water, which is mainly influenced by heat flux and surface superheat degree, shrinks with higher heat flux and higher surface superheat degree. The fragmentation time of 3.5 wt% salty water decreases with ambient pressure drops and superheat degree increments.

Magnetic levitation and guidance performance of Y–Ba–Cu–O and Gd–Ba–Cu–O bulk superconductors under low ambient pressure

The high-temperature superconducting Maglev-evacuated tube transport (HTS Maglev-ETT) system has significant potential for practical applications. In order to employ HTS bulks in an ETT system, it is necessary to study the magnetic levitation and guidance performance of bulk superconductors under low ambient pressure conditions that are representative of those inside the tube. As a result, we have investigated the Maglev performance of Y–Ba–Cu–O (YBCO) and Gd–Ba–Cu–O (GdBCO) single grain, bulk superconductors under different ambient pressures of 100 kPa, 60 kPa and 20 kPa using a bespoke pressure-controlling platform, in which the superconductors were positioned above a Halbach permanent magnet guideway. The levitation forces under conditions of field-cooling (FC) and zero-field-cooling (ZFC) have been measured and analyzed. The guidance force for the FC case and the levitation force relaxation for the ZFC case were also measured. It was found from the experimental results that the Maglev performance of both types of bulk superconductor improves significantly by reducing the ambient pressure in their immediate working environment. The levitation forces of YBCO and GdBCO bulk superconductors were observed to increase by 11.6% and 4.4% in the case of FC, and by 20.3% and 13.7% in the case of ZFC, respectively, as the ambient pressure changed from 100 kPa to 20 kPa. An improvement of the guidance force and an inhibition of the levitation force relaxation were also observed for these materials. The supercooled liquid nitrogen cryogen in the low-pressure environment further reduces the temperature, which, in turn, increases the critical current density Jc of the bulk superconductors and improves their levitation performance. These results provide further evidence of the significant advantages of combining HTS Maglev with evacuated tube technologies as a key enabling feature of the HTS Maglev-ETT system. The data further indicate that YBCO bulk superconductors tend to be more sensitive to ambient pressure and temperature variation than GdBCO bulk superconductors. This difference essentially reflects the dependence of Maglev performance of HTS bulk superconductors on Jc when operating in a low-pressure environment.

Buoyancy Effect on Downward Flame Spread Over PMMA Cylinders

Understanding material flammability at different gravity levels is important for fire safety applications in space facilities where the environments may include microgravity, low velocity flows, low pressure and elevated oxygen concentration. One possible approach to simulate on-earth the burning behavior inside spacecraft environments, and facilitate testing, is to reduce buoyancy effects by decreasing ambient pressure. The objective of this work is to study the effect of pressure, and consequently buoyancy and indirectly gravity, on downward flame spread rate over cylindrical samples of polymethyl-methacrylate (PMMA), and by comparison with reduced gravity data, observe up to what point low-pressure can be used to replicate flame spread in space facilities. Experiments in normal gravity are conducted using pressures ranging between 100 kPa and 30 kPa and oxygen concentrations between 19% and 23%, with a forced flow velocity of 100 mm/s. The low-pressure data is compared with microgravity data obtained aboard the International Space Station during the BASS-II experiments. Results show that reductions of ambient pressure slow down the flame spread process approaching that expected at low gravity. The normal gravity and microgravity data are correlated in terms of a mixed convection parameter that describes the main controlling mechanisms of heat transferred. Although the correlation works well for the normal gravity data it does not work as well for the microgravity data. However, it provides information about what is to be expected in environments of variable ambient pressure, oxygen concentration, and reduced gravity, providing an insight for future designs when considering fire safety in spacecrafts.

Fabrication of dual-parameter fiber-optic sensor by cascading FBG with FPI for simultaneous measurement of temperature and gas pressure

A dual-parameter fiber-optic sensor based on fiber Bragg grating (FBG) cascaded with Fabry–Pérot interferometer (FPI) structure is described and demonstrated to measure temperature and gas pressure simultaneously. The proposed sensing structure consists of an extrinsic FPI in the form of hemispherical ultraviolet (UV) curing glue capped on a FBG end face. The spectral interference peak produced by the UV glue FPI is sensitive to ambient temperature and gas pressure variations, whereas the reflection spectrum of FBG only depends on temperature and insensitive to pressure change, therefore, the temperature and gas pressure can be simultaneously measured by this cascaded sensor. Experimental results show that the sensor has higher temperature and gas pressure sensitivities of 223.4 pm/° C and 24.99 nm/MPa in a range from 30 ∘C to 110 ∘C and from 0.1 MPa to 0.7 MPa. Utilizing the temperature-dependent sensitivity of FBG, a constructed sensitivity matrix is used to distinguish measurement of temperature and gas pressure, and the measurement resolutions are determined to be 0.086 ∘C and 0.730 KPa. This sensing architecture is not only an effective method for single-point multi-parameter measurement, but also has merits of high sensitivity, compactness, ease of fabrication and low cost, which make it valuable for biosensors and medical applications.

On the functional compartmentalization of the normal middle ear. Morpho-histological modelling parameters of its mucosa

BackgroundMiddle ear physiology includes both sound pressure transmission and homeostasis of its static air pressure. Pressure gradients are continuously created by gas exchange over the middle ear mucosa as well as by ambient pressure variations. Gas exchange models require actual values for regional mucosa thickness, blood vessel density, and diffusion distance. Such quantitative data have been scarce and limited to few histological samples from the tympanic cavity (TC) and the antrum. However, a detailed regional description of the morphological differences of the TC and mastoid air cell system (MACS) mucosa has not been available. The aim of the present study was to provide such parameters. MethodsThe study included sets of three histological H&E-slides from 15 archived healthy temporal bones. We performed a comparison of the mucosa morphology among the following regions: (1) anterior TC; (2) inferior TC; (3) posterior TC; (4) superior TC; (5) MACS antrum; (6) superior MACS; (7) central MACS; (8) inferior MACS. ResultsRegions (1)–(3), situated below the inter-attico-tympanic diaphragm, had the largest proportion of high respiratory epithelium, cilia and loose lamina propria within the mucosa, as well as the thickest mucosa and the largest diffusion distance. Regions (6)–(8), situated above the diaphragm, had the thinnest mucosa, the shortest distance to the blood vessels, together with the largest proportion of flat epithelium and very few cilia. Regions (4)–(5), still supradiaphragmatic, had intermediary values for these parameters, but generally closer to regions (6)–(8). The blood vessel density and the proportion of active mucosa were not significantly different among the regions. ConclusionMucosa of regions (1), (2) and (3) represented a predominantly clearance-specific morphology, whereas in regions (4)–(8) it seemed adapted to gas exchange. However, the lack of statistically significant differences in blood vessel density and proportion of active mucosa indicated that all regions could be involved in gas exchange with the highest adaptation in the superior MACS. This pattern divides the middle ear functionally along the inter-attico-tympanic diaphragm rather than the anatomical division into TC and MACS.

Improvement of Detection Sensitivity of Microbubbles as Sensors to Detect Ambient Pressure.

Microbubbles are considered a promising tool for noninvasive estimation of local blood pressure. It is reported that the subharmonic scattering amplitude of microbubbles decreases by 9 to 12 dB when immersed in the media under an ambient pressure variation from 0 to 180 mmHg. However, the pressure sensitivity still needs to be improved to satisfy clinical diagnostic requirements. Here, we investigated the effects of acoustic parameters on the pressure sensitivity of microbubbles through measuring the acoustic attenuation and scattering properties of commercially available SonoVue microbubbles. Our results showed that the first harmonic, subharmonic, and ultraharmonic amplitudes of microbubbles were reduced by 6.6 dB, 10.9 dB, and 9.3 dB at 0.225 mechanical index (MI), 4.6 dB, 19.8 dB, and 12.3 dB at 0.25 MI, and 18.5 dB, 17.6 dB, and 12.6 dB at 0.3 MI, respectively, when the ambient pressure increased from 0 to 180 mmHg. Our finding revealed that a moderate MI (0.25–0.4) exciting microbubbles could significantly improve their sensitivities to detect ambient pressure.

Numerical analysis of bubble dynamics in the diffuser of a jet pump under variable ambient pressure

Recent studies have shown that the collapse of cavitation bubbles in a jet pump can generate an extremely high pressure with many potential applications. The dynamics of the bubble is governed by the Rayleigh-Plesset equation. With the bubble dynamics equation and the heat and mass transfer model solved with the Runge-Kutta fourth order adaptive step size method, the oscillations of the bubble in the diffuser of the jet pump are assessed under varied conditions. To obtain the pressure variation along the diffuser, the Bernoulli equation and the pressure measured in experiment are coupled. The results of simulation show that a transient motion of the bubbles can be obtained in the diffuser quantitatively, to obtain the pressure and temperature shock in the bubble. Moreover, increasing the outlet pressure coefficient would result in a more intense bubble collapsing process, which can be used in the subsequent studies of the cavitation applications. The predictions are compared with experiments with good agreement.

Accounting for Uncontrolled Variations in Low-Speed Turbine Experiments

It is common to assume that the performance of low-speed turbines depends only on the flow coefficient and Reynolds number. As such, the required operating point is achieved by controlling the values of these two nondimensional quantities by, for example, appropriate choices for the mass flow rate and applied brake torque. However, when the turbine has an atmospheric inlet and uses unconditioned air, variations in ambient pressure, temperature, and humidity are introduced. While it is still possible to maintain the required values for the flow coefficient and Reynolds number, the ambient variations affect additional nondimensional quantities which are related to the blade speed and gas properties. Generally, the values of these additional nondimensional quantities cannot be controlled and, consequently, they affect the turbine performance. In addition, thermal effects, which are exacerbated by the use of plastic blades, can cause changes in the blade row seal clearance and these also affect the performance. Therefore, to obtain measurements with greater accuracy and repeatability, the changes in the uncontrolled nondimensional quantities must be accounted. This paper contains four parts. First, it is described how suitable data acquisition parameters can be determined to eliminate short time scale facility unsteadiness within the measurements. Second, by the analysis of models, the most appropriate forms for the additional nondimensional quantities that influence turbine performance are obtained. Since the variations in the uncontrolled nondimensional quantities affect repeatability, the size of the effect on the turbine performance is quantified. Third, a best-fit accounting methodology is described, which reduces the effects of the uncontrolled nondimensional quantities on turbine performance, provided sufficient directly related measurements are available. Finally, the observations are generalized to high-speed turbomachines.

Influencia de la presión de oxígeno ambiental sobre la regeneración ósea guiada

ObjectiveTo evaluate the influence of the variation in ambient oxygen pressure on guided bone regeneration in guinea pigs. Material and methodA total of 32 male guinea pigs weighing 750±50g were assigned into two groups of 16 (group A: studied at 150 metres above sea level in the city of Lima and oxygen pressure of 157mmHg; group B: was at 3230 meters above sea level in the city of Jauja and an oxygen pressure of 107mmHg). Bone defects of 5×6mm were induced in the jaw in both groups through extra-oral surgical access. The defect in 8 guinea pigs of each group were covered with a porcine resorbable collagen membrane, but not in the other animals. The osteoblast and osteocyte cell counts were evaluated at 15 and 30 days post-operatively. ResultsAt 15 and 30 days, in the groups studied at height and with the membrane applied, the osteoblast count was 71±12.1 cells/field, and 83±7.2 cells/field, respectively, and an osteocyte count of 34.5±6.6 cells/field, and 25±7.6 cells/field, respectively. These groups had a higher number of bone cells in all the comparisons, but there were no statistically significant differences (P>.05). ConclusionThere was a tendency to form a greater amount of bone cells was found in the samples treated with bone regeneration and exposed to altitude compared to those at sea level.

Numerical simulation of the internal flow of swirl atomizer under ambient pressure

This paper presents the simulation study of internal flow of open-end swirl injectors under steady and oscillating ambient pressures. A two-dimensional swirl axisymmetric model based on the volume of fluid method was developed to study the effect of ambient pressure on the internal flow of open-end swirl injectors. The response of injector flow to the ambient pressure oscillation was investigated by superimposing periodical oscillation of ambient pressure at the spout outlet. The results show that the variation of ambient pressure affects the liquid phase volumetric fraction within the gas–liquid shear layer. The spray angle near the wall remains constant independent of the ambient pressure. The velocity distribution on different axial sections rarely varies with ambient pressure. When the ambient pressure oscillated, the ambient pressure oscillation would cause the flow rate oscillation at the spout. The phase delay between the flow rate oscillation at spout and the ambient pressure oscillation is proportional to the oscillation frequency.

Experimental investigation of the important influence of pretreatment process of thermally exfoliated graphene on their microstructure and supercapacitor performance

Thermal exfoliation is a popular approach to prepare thin-layered graphene in large scale. Generally believed that the microstructure and surface chemistry of the products could tailored by the variation of ambient gas pressure, temperature, acid and organic substances during thermal exfoliation of graphite oxide (GO). In this work, we investigated the effect of physical pre-treatment process and acid assisting on the texture, surface state and electrochemical performance of the resulting thermal exfoliated graphene, and found that the different physical pre-treatment process had great influence on the microstructure and specific surface area of graphene. Especially the graphene formed by sonication treatment consisted by thin layers with lots of wrinkles delivered the highest specific surface area of 678m2/g. Adding volatile acid in the process of pre-treatment could decrease their specific surface area. But the graphene obtained with acid assisting was possessed of larger pore volume and improved conductivity which promoted their electrochemical performance effectively. The important role of physical pre-treatment process and acid assisting process in expansion-exfoliation of GO was discussed in detail in this work.

Two-wavelength interferometer based on sinusoidal phase modulation with an acetylene stabilized laser and a second harmonic generation.

A two-wavelength interferometer (TWI) based on a sinusoidal-phase-modulation method with an acetylene stabilized laser and a second harmonic generation (SHG) was developed. The periodic non-linearity error for the TWI was estimated to be ± 0.1 µm at a dead path of 0.32 m. A long-term measurement showed that the TWI stability was ± 3 × 10(-7) at a dead path of 1.00 m for 12 hours with an ambient pressure variation of 3 hPa under controlled conditions of ambient temperature and humidity. Finally, we confirmed that the TWI has substantially better stability than a single-wavelength interferometer by comparing both interferometers with large temporal and spatial temperature variations.

Explanation of penetration depth variation during laser welding under variable ambient pressure

It has been observed that the penetration depth during laser welding (LW) under vacuum or reduced ambient pressure could be significantly greater than that during welding under atmospheric pressure. Previous explanations of this phenomenon usually limit to specific wavelength laser welding and have difficulties in explaining why the variation will disappear, as the welding speed increases. Here, we propose that this variation is caused by the temperature difference of keyhole wall under variable ambient pressure based on a correct physical description of related processes. A new surface pressure model, dependent on ambient pressure, is proposed for describing the evaporation process during laser material interaction under variable ambient pressure. For laser welding of a 304 stainless steel with 2.0 kW laser power and 3 m/min welding speed, it is shown that the average keyhole wall temperature is around 2900 K under atmospheric pressure, and only around 2300 K under vacuum, which results in significant penetration depth variations. Interestingly, it is also shown that as the welding speed increases, the average temperature of the front keyhole wall gradually rises due to the reduction of the mean incident angle of laser, and the magnitude of this increase is larger in welding under vacuum than under atmospheric pressure. It allows us to explain why the penetration depth improvement decreases to zero with the increase of welding speed.

Self-Powered Piezo-Floating-Gate Smart-Gauges Based on Quasi-Static Mechanical Energy Concentrators and Triggers

Changes in physical processes like ambient temperature or pressure variations occur at frequencies that are significantly lower than 1 Hz. This poses a challenge for designing self-powered sensors that monitor these quasi-static physical processes and at the same time scavenge operational energy for sensing, computation, and storage from the signal being monitored. In this paper, we present a novel paradigm for designing a self-powered sensor/data logger that exploits the physics of negative-stiffness mechanical energy concentrators with the physics of our previously reported piezoelectricity driven impact ionized hot-electron injection (p-IHEI)-based sensors. The operational principle is based on the sudden transitions from unstable mode branch switching during the elastic postbuckling response of slender columns, which are used to generate high-frequency deformations as an input to the p-IHEI-based sensor. The experimental results demonstrate that the proposed self-powered sensor based on an integrated circuit fabricated in a 0.5-μm CMOS technology can count and record the number of quasi-static input events with frequencies spanning less than 1 Hz.

Effect of magnetic field on single-bubble in water

In this paper, we extend the Rayleigh-Plesset model by considering the effect of a magnetic field on the nonlinear response of an oscillating spherical air bubble in water. Water molecules in motion, derived by a time varying ultrasound pressure field, suffer a torque from the magnetic field by Lorentz force. The rotational energy and the translational energy together constitute the kinetic energy of the water molecule. The work done by the pressure during the contraction and expansion of bubble is equal to the total kinetic energy of the water molecule in liquid. According to energy conservation, we establish a modified control equation of the bubble motion under the action of an applied external magnetic field. The integration of the nonlinear differential equation governing the bubble motion is performed analytically by using a regular expansion, and is solved numerically by using a fourth-order Runge-Kutta method. It is shown that the variation of ambient pressure changes the bubble dynamics when the magnetic field is off. The ambient pressure is increased due to the effect of external magnetic field. The pressure induced by magnetic field increases linearly with the increase of magnetic field intensity and the coefficient is about 103 times. The bubble expansion rate, maximum radius, and the velocity of the collapsing bubble decrease as the magnetic field increases. It is predicted that the applying of a magnetic field can widen the pressure range and modify bubble dynamics.

Lung injury related to extreme environments.

As extreme sports become more popular, related respiratory injury may compromise the athlete’s performance and result in morbidity and even mortality. In this article we will discuss different lung injuries in relation to performing different activities in an extreme environment. The evolution of fish to amphibians, reptiles to endothermic birds and mammals has been accompanied by a progressively thinner pulmonary blood gas barrier, to accommodate the constraint of increased oxygen uptake and carbon dioxide output [1]. Accordingly, pulmonary circulation has evolved as a separate high flow–low pressure system. In humans, mean pulmonary artery pressures (PAP) are 8–20 mmHg, pulmonary wedge pressures are 5–14 mmHg and pulmonary capillary pressures are 8–12 mmHg [2]. A low-pressure regimen preserves the integrity of an alveolar capillary membrane only 0.3 μm thick. However, this structure is vulnerable to increased pressures during strenuous exercise or environmental hypoxic exposure as a cause of stress failure of the pulmonary capillaries and accumulation of extravascular lung water [3]. Reports of lung injury related to extremes of exercise and variations in ambient pressure and altitude confirm this vulnerability. The resulting lung injury takes the form of noncardiogenic pulmonary oedema. The occurrence of noncardiogenic pulmonary oedema and pulmonary haemorrhage has been described in relation to a variety of disorders related to auto- and exogenous immunological reactions, infections and certain inhalants. However, numerous reports of lung injury manifesting as pulmonary oedema with associated haemorrhage have been described more recently in relation to immersion underwater, swimming, extreme exercise and exposure to altitude. In addition, pulmonary oedema resulting from negative intra-alveolar pressure has been described in the anaesthesia literature and may play a role in exercise- and immersion-induced pulmonary oedema. A single mechanism responsible for production of noncardiogenic pulmonary oedema related to immersion, altitude and exercise has not …