Variation Of Ambient Pressure Research Articles

Meteorological factors and risk of ischemic stroke, intracranial hemorrhage, and subarachnoid hemorrhage: A time-stratified case-crossover study.

Stroke risks associated with rapid climate change remain controversial due to a paucity of evidence. To examine the risk of subarachnoid hemorrhage (SAH), intracranial hemorrhage (ICH), and ischemic stroke (IS) associated with meteorological parameters. In this time-stratified case-crossover study, adult patients hospitalized for their first stroke between 2011 and 2020 from the insurance claims data in Taiwan were identified. The hospitalization day was designated as the case period, and three or four control periods were matched by the same day of the week and month of each case period. Daily mean and 24-h variations in ambient temperature, relative humidity, air pressure, and apparent temperature were measured. Conditional logistic regression models were applied to assess the risk of stroke associated with exposure to weather variables, using the third quintile as a reference, controlling for air pollutant levels. There were 7161 patients with SAH, 40,426 patients with ICH, and 107,550 patients with IS. There was an inverse linear relationship between mean daily temperature and apparent temperature with ICH. Elevated mean daily atmospheric pressure was associated with an increased risk of ICH. A greater decrease in apparent temperature over a 24-h period was associated with increased risk of ICH but decreased risk of IS (odds ratio (95% confidence interval) for the first vs. third quintile of changes in apparent temperature, 1.141 (1.053-1.237) and 0.946 (0.899-0.996), respectively). There were considerable differences in short-term associations between meteorological parameters and three main pathological types of strokes. The authors have no permission to share the data.

An expanding mechanical role for the tiny mammalian endolymphatic duct: 1. Modification of Békésy model is specifically needed to cope with ambient pressure variation—with weather, altitude or ocean depth

von Békésy’s pioneering work and two-chamber model with basilar membrane (BM) separating the perilymph chambers was a first-pass assumption which worked to explain basic frequency-band analysis. Yet it did not cover psychoacoustical phenomena. Nor did it cover the repeated demonstrations by this author of baseline displacements of the BM, nor mysterious changes in the volume of the tiny endolymphatic duct—even in human ears with normal thresholds. Since 2009 the duct has been shown to possess all the necessary characteristics of a pressure vessel, viz., it is lined with aquaporins and tight junctions while the cells of the stria vascularis maintain a strict osmotic gradient. We submit that such evolutionary change was necessary because ambient pressure changes are too large to be corrected by passive equalization and need to be actively eliminated to preserve hearing sensitivity. Any theory must cover marine mammals which have adapted to ocean pressures measured in megapascals. In this case, infrasound is modelled as a varying pressure pedestal which must be cancelled. This video presentation covers one possible mechanical configuration for how such a cancelation might be achieved—a hypothesized feedback control system utilizing outer hair cell somatic motility plus our previously-modelled otolith-based pressure transducer.

Ethanol Blend Effects on The Spray Properties of a Biodiesel Fuel by Ambient Pressure Variation

Diesel engine spray nozzles are crucial to pollutant generation and engine efficiency. Nozzle performance can be enhanced by adjusting the nozzle's internals. A successful demonstration of the nozzle would be one in which the spray's outcome was uniformly dispersed throughout a wide area, with the grains scattered similarly. The purpose of this research was to examine how a diesel-ethanol characteristic under normal atmospheric pressure (spray tip penetration, the velocity of spray, and spray angle) and, in general, to assess the performance of biodiesel fuel on diesel engines, a substantial amount of biodiesel and operational expenses for the engine are necessary. It was an experimental approach to the study. The research involved recording spray fuel at the nozzle. Using a 480 fps high-speed camera, we tested BD20, BD20E5, and BD20E10 fuel at three different ambient pressures (1 bar, 2 bar, and 3 bar). The injection pressure was 15 MPa, and the fuel temperature was 28.2 degrees Celsius. Spray tip penetration and spray velocity decreased and spray angle increased after ethanol was added to the mixture, consistent with the studies' findings. Lowered spray tip penetration, slower spray speeds, and a complete spray angle result from the increased ambient pressure.

Advanced Pressure Compensation in High Accuracy NDIR Sensors for Environmental Studies

Measurements of atmospheric gas concentrations using of NDIR gas sensors requires compensation of ambient pressure variations to achieve reliable result. The extensively used general correction method is based on collecting data for varying pressures for a single reference concentration. This one-dimensional compensation approach is valid for measurements carried out in gas concentrations close to reference concentration but will introduce significant errors for concentrations further away from the calibration point. For applications, requiring high accuracy, collecting, and storing calibration data at several reference concentrations can reduce the error. However, this method will cause higher demands on memory capacity and computational power, which is problematic for cost sensitive applications. We present here an advanced, but practical, algorithm for compensation of environmental pressure variations for relatively low-cost/high resolution NDIR systems. The algorithm consists of a two-dimensional compensation procedure, which widens the valid pressure and concentrations range but with a minimal need to store calibration data, compared to the general one-dimensional compensation method based on a single reference concentration. The implementation of the presented two-dimensional algorithm was verified at two independent concentrations. The results show a reduction in the compensation error from 5.1% and 7.3%, for the one-dimensional method, to -0.02% and 0.83% for the two-dimensional algorithm. In addition, the presented two-dimensional algorithm only requires calibration in four reference gases and the storing of four sets of polynomial coefficients used for calculations.

Effect of relative humidity on the long-term operation of a single mask triple GEM chamber

The characteristic studies of a Single Mask (SM) triple Gas Electron Multiplier (GEM) detector are carried out using Ar/CO2 gas mixture in 70/30 volume ratio in continuous flow mode. A 55Fe X-ray source is used for this work. The gain and energy resolution are studied from the 5.9 keV X-ray energy spectra. After correcting the effects of ambient temperature and pressure variation, the effect of ambient relative humidity on the gain and energy resolution of the chamber is investigated. The details of the experimental setup, measurement methods and results are presented in this article.

Quantifying antisite defect concentrations in yttrium aluminum garnet by high-precision density analysis

Quantifying the nature and density of lattice defects in high-quality crystals is often difficult or impossible with commonly employed material characterization techniques. In many cases, even the density of intentionally doped impurities present in a grown crystal must be inferred indirectly using methods such as mapping spatial variations in crystal properties or, when the defects are optically active, interpreting optical absorption with imprecisely known oscillator strengths. In this work we explore gravimetric techniques to obtain absolute defect densities in crystals, a powerful approach often overlooked in modern materials science. A hydrostatic weighing apparatus based on Archimedes’ principle was constructed, tested, and refined to enable high-precision density measurements of small crystal samples. Application of this system is illustrated by determining the density of Yttrium Aluminum Garnet (YAG) relative to a high-purity silicon crystal density reference, minimizing traditional difficulties in correcting for the variations in surface tension and the water and air density due to small changes in ambient temperature, pressure, and solution composition. This method, using a relatively simple apparatus and small samples, is effective in measuring the intrinsic concentration of Y–Al antisite lattice defects in YAG, agreeing with results from far more elaborate high-resolution optical laser spectroscopy at cryogenic temperatures. Furthermore, we quantitatively analyze the effects of several potential sources for error, including natural variations in isotope distributions, residual surface contamination, and ambient temperature or pressure variations. Subsequently, we find that the density analysis method is a promising technique for characterizing new and modified materials being developed for applications ranging from solid-state lasers and scintillators to quantum information.

Gas turbine off-design behavior modelling and operation windows analysis under different ambient conditions

As a core equipment for energy conversion and clean utilization, gas turbines are utilized in many areas under various ambient conditions. Ambient conditions can vary with seasons and time of a year, even in the same location. Ambient conditions also have significant impacts on gas turbine performances at part-load. In this paper, we proposed an off-design behavior mechanism model of gas turbines, which aims at quantifying impacts of ambient conditions on gas turbine performances. Impacts of key parameters are considered, including compressor geometry, staged combustion in a combustor and turbine cooling. Moreover, an operation windows analysis is presented. In order to illustrate variation logics of NOx emissions, load regulating capacity with variations of ambient temperature, pressure and relative humidity, case studies are performed considering twelve parameters, four regions and seven ambient conditions. Results show that the ambient temperature has the most significant impacts on the gas turbine performances. The output power, gas turbine efficiency and load regulation capacity are improved at base-load as well as part-load. When the ambient temperature drops from 15 °C to −15 °C at base-load, the efficiency and the power increase by 2.1% and 13.9%, respectively, whilst the regulation range of which increases from 46.4% to 51.4%.

Effect of sub-atmospheric pressure on the characteristics of concurrent/upward flame spread over a thin solid

The variation of ambient pressure is a potential tool for studying the driving parameters of fire dynamics and heat release in low-pressure environments such as high-altitude locations, aircraft, and spacecraft. The study of upward flame spread over a solid fuel has direct implications on material flammability and fire development, and low pressure environments have recently gained more attention for the possible comparison with the reduced gravity conditions encountered during space missions. In this work, we consider upward spreading flames over thin acrylic sheets in ambient pressures between 30 and 100 kPa. A forced flow velocity of 20 cm/s is added to the naturally-driven buoyant flow, creating a mixed flow field (natural and forced) that varies with pressure. Flame characteristics such as spread rate and standoff distance are measured from the video analysis of the experiments. It is observed that the former decreases with pressure while the latter increases. The larger flame stand-off distance at low pressures partially explains the decrease of the flame spread rate since the convective heat flux from the flame to the solid decreases. Additionally, volumetric concentrations of the combustion products are measured during the experiments. The results show lower O2 consumption and CO2 production rates at lower pressures. Based on these rates, we could calculate the heat release rate from upward spreading flames at low pressure, providing fundamental information for better understanding pressure-gravity correlations. According to the results, the volumetric heat release rate is proportional to pressure, which is consistent with previous studies on pressure modeling of fires. This suggests that chemical kinetics is not a constraint for the conditions tested in this study, which could help make future flammability tests comparable to low gravity ones.

Understanding the influence of unsteady and convection terms in heat transfer model on the predicted heat flux in engines operated under different combustion modes

The aim of current research is to develop an enhanced heat transfer model to accurately predict the heat flux through the cylinder walls during the working process of internal combustion engines operated under different loads and combustion modes. Two enhanced models, i.e., the unsteady model and the steady convective contribution (SCC) model were respectively constructed based on the thermal wall function. The effects of the transient ambient gas temperature and pressure variations, as well as the chemical reaction source term, were included in the unsteady model. Then the contributions of the unsteady terms, such as the temporal derivative of gas temperature, the pressure work, and the chemical heat source in the energy equation were analyzed in detail. The results indicate that the mechanism of the unsteady heat transfer process is different in the engine operated under motored conditions and different combustion modes, including conventional diesel combustion (CDC), homogeneous charge compression ignition (HCCI), and reactivity controlled compression ignition (RCCI). Afterward, the influence of the gas velocity and the pressure difference perpendicular to the walls were included in the SCC model to consider their contributions to the heat fluxes near the chamber walls. It is found that the heat fluxes predicted by the SCC model are in better agreement with the experimental data, especially in the CDC mode under different swirl ratios and loads. The peak of the heat flux predicted by the SCC model shows superiority to that of the previous steady heat transfer models and the unsteady heat transfer model.

Pressure Sensitivity of Electron Emission from SiOx Tunneling Diodes and their Outstanding Emission Performance under Rough Vacuum

AbstractOn‐chip electron sources with low pressure‐sensitivity and outstanding emission performances under rough vacuum are highly desired for developing miniature fully encapsulated vacuum electronic devices. Here, the sensitivity of electron emission from SiOx tunneling diodes formed in electroformed SiOx to the variation of ambient vacuum pressure from ≈10−4 to ≈102 Pa is explored. Electron emission from SiOx tunneling diodes is found to be insensitive to pressure variation when the pressure is lower than ≈10−1 Pa and exhibits fast degradation above the pressure, showing much lower pressure sensitivity than field emission sources. Despite emission current degradation above ≈10−1 Pa, SiOx tunneling diodes exhibit stable and reproducible electron emission under fixed rough vacuum up to 8 Pa, and good restorability after being repeatedly exposed to air pressure. By analyzing transport current of SiOx tunneling diodes under varying ambient vacuum pressure, the degradation of emission current above ≈10−1 Pa is attributed to the widening of insulating SiOx channel in the diode due to the transformation of Si conducting filament to SiOx with increasing oxygen partial pressure.

Design and Development of a Cold-Flow Test-Bench for Study of Advanced Nozzles in Subsonic Counter-Flows

As advanced nozzles may offer alternative solutions to conventional nozzles for the future class of reusable launch vehicles, a critical aspect is to tailor these novel technologies to current recovery strategies, more specifically to vertical landing sustained by retro-propulsion. Researchers at Technische Universität Dresden have developed a dedicated test-bench for the vacuum wind tunnel facility, where Advanced Nozzle Concepts (ANCs), such as aerospike and dual-bell nozzles, are tested in cold-gas configuration while invested by subsonic counter-flows. The main objective of the test campaign is to evaluate the performance and altitude–compensation characteristics of such ANCs by simulating a vertical landing manoeuvre through the variation of ambient pressure experienced during the landing burn. A detailed description of design and development of the test-bench, together with preliminary results from the commissioning activities, are here offered to the reader. The force measurements, together with pressure and temperature data, contribute to evaluate thrust levels and coefficients, as well as the monitoring of the interaction between the nozzle cold-flow and the opposing free-stream. A background-oriented schlieren system allows to visualise the external flow-field. In conclusion, an outline of the upcoming test campaign and a description of the expected results is offered.

Impact of Air Density Variation on a Simulated Earth-to-Air Heat Exchanger’s Performance

Due to their simple design and reliable operation, earth-to-air heat exchangers (EAHE) are used in modern buildings to reduce ventilation heat losses. EAHE operation in atmospheric conditions results in variation in ambient air temperature and pressure affecting air density. The paper presents the study on the impact of ambient air density variation on the calculated hourly air temperature at the EAHE outlet and the resulting energy use for space heating and cooling of an exemplary residential building. The ground temperature was computed from the model given in EN 16798-5-1. Then, air density was obtained using five various methods. Energy use for space heating and cooling of the building was computed using the 5R1C thermal network model of EN ISO 13790. Depending on the chosen method and concerning the base case without EAHE, a reduction in annual heating and cooling needs was obtained from 7.5% to 8.8% in heating and from 15.3% to 19% in cooling. Annual heating and cooling gain from EAHE were 600.9 kWh and 628.3 kWh for heating and 616.9 kWh and 603.5 kWh for cooling for the Typical Meteorological Years (TMY) and International Weather for Energy Calculation (IWEC) files, respectively. Unit heating and cooling gains per heat exchanger area were from 34.9 kWh/m2 to 36.8 kWh/m2 and from −35.1 kWh/m2 to −36.3 kWh/m2. Density variation with temperature from the relevant typical Polish meteorological year at constant pressure, in comparison to the method of EN 16798-5-1, resulted in an hourly difference of that unit gain up to 4.3 W/m2 and 2.0 W/m2 for heating and cooling, respectively. The same was true inthe case of IWEC files that resulted in differences of 5.5 W/m2 and 1.1 W/m2.

Numerical Simulation of Decompression Process of a Mars Rover in the Launch Phase

This paper performs numerical simulation on the decompression process of a Mars rover using FLUENT. The pressure differential between the inside and outside of the Mars rover resulting from changes in ambient pressure of the rocket fairing is investigated. In terms of numerical simulation, PROFILE outlet boundary conditions are developed and the impacts of ambient pressure settings, time steps, and mesh density are investigated to improve the accuracy of simulation results. The decompression process of the separate large module, large and small modules under two types of ambient pressures are simulated. The results show that the largest pressure differential between the inside and outside of the module body is less than 2200 Pa. Because of the small size of the small module, the results for the separate large module and the large/small modules are consistent. The pressure differential between the inside and outside of the rover is mainly influenced by the variation in ambient pressure.

Efectos de la variación en la presión de oxígeno ambiental sobre el movimiento dentario ortodóntico.

Objective: To evaluate the effects of variation in ambient oxygen pressure on orthodontic tooth movement in guinea pigs. Material and Methods: Seventy-two guinea pigs randomly distributed into two groups (A and B) were evaluated in the study. All specimens were fitted with orthodontic appliances to distalize maxillary incisors. Group A was controlled under conditions of oxygen pressures at sea level (150 masl, 157 mm Hg) and Group B under conditions of oxygen pressures at altitude (3405 masl, 107 mm Hg). The clinical (distance between the distal-incisal angles of the maxillary incisors), biochemical (serum alkaline phosphatase), and histopathological characteristics (osteoblast and osteocyte count) were evaluated before placing the orthodontic devices and after 24 and 72 hours. Results: In the clinical evaluation, the distance between the distal-incisal angles of the maxillary incisors, on day one and three, was significantly higher in group B compared to group A (p=0.002 and p=0.001, respectively). In the biochemical evaluation, the level of serum alkaline phosphatase on the first and third days was significantly higher in group B compared to group A (p=0.001 and p=0.001, respectively). In the histopathological evaluation, the osteoblasts and osteocytes count on day one and three was significantly higher in group B compared to group A (p<0.05). Conclusion: Oxygen pressure at high altitude positively influenced orthodontic tooth movement in guinea pigs, improving its clinical, biochemical, and histopathological characteristics.

White light-emitting ZnO nanoparticles exhibiting color temperature tunability with near UV excitation and high color rendering

The development of high-quality white-light phosphor for lighting and their facile synthesis is highly desired. Achieving white-light emission in undoped metal-oxides is in great demand, and hence ZnO being a potential phosphor was explored. However, tailoring defect-oriented emissions that mainly depend on processing conditions is challenging. Annealing effects on ZnO to obtain white-light with completely diminished near band-edge emission is detailed here. A systematic variation of processing temperature, ambient pressure, and ambient gas helped tailor the white-light emission. Optimized ZnO nanophosphors emitted white-light with the near-ideal Commission International de l’Eclairage (CIE) coordinates (x = 0.32, y = 0.33 at λex = 325 nm) and correlated color temperature (CCT) of 6200 K (corresponding to day white-light). Optimized processing conditions achieved neutral white-light (x = 0.33, y = 0.33 at λex = 340 nm) and CCT 5645 K. ZnO nanoparticles exhibit excellent color rendering index (CRI) of >90 and high R9 values up to 97%, essential in efficiently rendering object colors compared to that under sunlight. Phosphor-converted white light-emitting diodes (pc-WLEDs) were fabricated on commercial LEDs using the prepared ZnO nanophosphors. pc-WLEDs emitted neutral and day white-light, well-suited for indoor solid-state lighting devices.

Entropy image analysis of primary atomization for a coaxial airwater jet submitted to acoustics at variable ambient pressure.

Entropy image analysis of primary atomization for a coaxial airwater jet submitted to acoustics at variable ambient pressure.

Selective Laser Melting under Variable Ambient Pressure: A Mesoscopic Model and Transport Phenomena

Recent reports on the selective laser melting (SLM) process under a vacuum or low ambient pressure have shown fewer defects and better surface quality of the as-printed products. Although the physical process of SLM in a vacuum has been investigated by high-speed imaging, the underlying mechanisms governing the heat transfer and molten flow are still not well understood. Herein, we first developed a mesoscopic model of SLM under variable ambient pressure based on our recent laser-welding studies. We simulated the transport phenomena of SLM 316L stainless steel powders under atmospheric and 100 Pa ambient pressure. For typical process parameters (laser power: 200 W; scanning speed: 2 m∙s −1 ; powder diameter: 27 μm), the average surface temperature of the cavity approached 2800 K under atmospheric pressure, while it came close to 2300 K under 100 Pa pressure. More vigorous fluid flow (average speed: 4 m∙s −1 ) was observed under 100 Pa ambient pressure, because the pressure difference between the evaporation-induced surface pressure and the ambient pressure was relatively larger and drives the flow under lower pressure. It was also shown that there are periodical ripple flows (period: 14 μs) affecting the surface roughness of the as-printed track. Moreover, the molten flow was shown to be laminar because the Reynolds number is less than 400 and is far below the critical value of turbulence; thus, the viscous dissipation is significant. It was demonstrated that under a vacuum or lower ambient pressure, the ripple flow can be dissipated more easily by the viscous effect because the trajectory length of the ripple is longer; thus, the surface quality of the tracks is improved. To summarize, our model elucidates the physical mechanisms of the interesting transport phenomena that have been observed in independent experimental studies of the SLM process under variable ambient pressure, which could be a powerful tool for optimizing the SLM process in the future.

On simulating the effect of gravity on concurrent flame spread over thin paper through variations in ambient pressure

The environment inside a spacecraft, or a space habitat, can greatly differ from those on earth, affecting the burning behavior of solid fuels. Because in a gravity field there is a flame-induced buoyancy, it is very difficult to reproduce on Earth the environmental conditions of a spacecraft, or a habitat in the Moon or Mars, thus making fire testing and burning predictions harder. A potential alternative approach to overcome this problem is to reduce buoyancy effects by using reduced ambient pressure in normal gravity. The objective of this work is to explore the possibility of simulating the effect of gravity, and in turn buoyancy, through changes in ambient pressure, on upward/concurrent flame spread over a thin combustible solid. Comparisons with available data at different gravity levels are used to determine the extent to which low-pressure can be used to replicate flame spread characteristics at different gravities. Experiments of the upward/concurrent flame spread over thin Kimwipe paper sheets were conducted in normal gravity inside a pressure chamber with ambient pressures ranging between 100 and 30 kPa and a forced flow velocity of 10 cm/s. Results show that reductions of pressure slow down the flame spread over the paper surface, and also reduces flame intensity. Comparison with published partial gravity data shows that as the pressure is reduced, the normal gravity flame spread rate approaches that observed at different gravity levels. The data presented is correlated in terms of a mixed convection non-dimensional number that describes the convective heat transferred from the flame to the solid, and that also describes the primary mechanism controlling the spread of the flame. The correlation provides information about the similitudes of the flame spread process in variable pressure, flow velocity and gravity environments, providing guidance for potential ground-based testing for fire safety design in spacecraft.

Vacuum laser beam welding characteristics for aluminum alloys and its effects on plasma plume generation and laser weldability

The laser weldability of aluminum alloy is unstable due to low laser beam absorption rate, low viscosity, and high thermal diffusivity. As a result, defects such as porosity and sagging are easily formed in the fusion zone. Vacuum laser beam welding (VLBW) has been introduced to ensure better weldability by using a relatively low ambient pressure. This allows for deep penetration depth and stable keyhole behavior compared to welding under atmospheric conditions. To evaluate the effects of ambient pressure on laser welding characteristics, VLBW was performed with similar and dissimilar aluminum alloys. Varying the pressure inside the vacuum chamber affected the welding characteristics. It is inferred that variation in ambient pressure changes the interactions between the laser source and substrate, such as the laser energy transfer, plasma plume generation, and the behavior of keyhole and molten pool. The penetration depth increased with decreasing ambient pressure for the same heat input conditions. Also, decreasing the ambient pressure reduced the formation of defects such as sagging, underfill, and porosity. Plasma plume generation was also varied depending on the ambient pressure, and plasma plume height and intensity were compared using a CCD camera. In this experiment, an ambient pressure of 10 mbar was sufficient to ensure good welding properties and stability. Below 10 mbar, the VLBW system is considered an effective alternative to processes that require high vacuum environments.

Effect of ambient pressure on gas adsorption characteristics of residual coal in abandoned underground coal mines

To study the influence of ambient pressure on gas adsorption of residual coal and provide a basis for establishing a reasonable calculation model of gas resource adsorbed in residual coal in abandoned underground coal mines, the residual coal was divided into loose-type residual coal and column-type residual coal after an analysis on the ambient gas pressure variation process. Then the gas adsorption experiments were conducted under adsorption equilibrium pressure range of 0.5–2.5 MPa using a self-made experimental device. The results show that (1) In the range of 0.5–2.5 MPa, the amount of methane adsorption in the loose-type residual coal under the intense replenishment condition can be 19.5% less than that under the gradual replenishment condition. (2) With a continuous decrease in ambient pressure, the methane adsorption amount in the column-type coal is reduced. The adsorption capacity at a unit pressure drop gradually increases from a minimum of 0.24 mL▪g-1 × 0.1 MPa−1 to a maximum of 2.375 mL▪g-1× 0.1 MPa−1. The initial adsorption equilibrium pressure shows little effect on the methane adsorption in column-type residual coal. (3) The bigger difference of the methane adsorption amount, with a maximum of 2.347 mL▪g-1, between the loose-type residual coal and column-type residual coal under the intense replenishment condition can be observed in the pressure range of 0.8–1.2 MPa. Therefore, the coal type should be considered to establish a gas storage model of residual coal in abandoned coal mines.