Low-pressure Environment Research Articles

Equilibrium Shapes of Ag, Ni, and Ir Nanoparticles under CO Conditions

Metal nanoparticles are widely used in catalysis by virtue of their excellent physicochemical properties, which are closely related to their morphology. In this work, we predict the reshaping of Ag, Ni, and Ir metal nanoparticles under a CO atmosphere using the recently proposed multiscale structure reconstruction model. In the low-pressure environment, temperature has little effect on the structures of Ag nanoparticles. However, the structures of Ag nanoparticles will change significantly in high- and low-temperature environments. Ni and Ir nanoparticles are greatly affected by the environment due to their stronger interactions with CO. This study demonstrates the structural changes of Ag, Ni, and Ir nanoparticles under different pressures and temperatures, providing theoretical guidance for in situ experiments and the rational design of nanocatalysts.

Numerical Study of Heat Transfer in a Two-Dimensional Rarefied Hydrogen Gas Moved Jet Impingement Using Direct Simulation Monte Carlo-Finite Difference Coupled Method

Temperature control is an important indicator for the lithography. However, the factors causing temperature fluctuation in lithography remain unclear under a low-pressure environment. In this work, in order to study the jet impingement heat transfer of hydrogen under rarefied conditions, the direct simulation Monte Carlo (DSMC) method and the finite difference method (FDM) are coupled. The heat exchange capacity in the jet impingement obtained using DSMC method is treated as a boundary condition for substrate. The difference of impingement heat transfer of rarefied hydrogen jet under different conditions of inlet absolute pressure, impingement distance and jet aperture are studied. The temperature of substrate is calculated by FDM. Results show that heat exchange capacity of the jet impingement rises with an increasing the inlet absolute pressure and pipe diameter, drops with reducing impact distance. The temperature control requirements can be met when the heat exchange capacity exceeds 380 W/(m2·K), the structural parameters satisfying the temperature control requirement are demarcated. The aforementioned findings can provide design ideas for high-precision temperature control devices.

Propagation characteristics of blast shock waves in low-pressure environment

Propagation characteristics of blast shock waves in low-pressure environment

ALTERAÇÕES FISIOLÓGICAS DOS ATLETAS DE ARTES MARCIAIS EM TREINOS DE ALTITUDE

ABSTRACT Introduction: Recent studies have shown that altitude training can significantly improve hemoglobin content in athletes. This allows for greater oxygen transport to the muscles and, consequently, greater load capacity during training. However, there is no confirmed evidence of athlete-specific training in martial arts. Objective: Explore the load capacity and ability changes caused by high altitude training in athletes. Methods: The research selected ten high-level martial arts athletes as volunteers to compare the functional changes caused by high-altitude training. Physical and functional data were collected before the beginning of the experiment and at its conclusion after three weeks. Results: Measured abilities were significantly improved after 11 days of altitude physical training. After 21 days of altitude training, these abilities improved significantly. The urea nitrogen and creatine kinase values increased rapidly with increasing load intensity in the first stage, peaked in the second stage, and decreased in the third stage. Conclusion: Training in the low-pressure hypoxic environment at high altitude, using dual stimulation of hypoxia and exercise to make the athletes stress response, can stimulate the physical potential to achieve a range of physiological abilities to improve the body’s resistance to hypoxia. Level of evidence II; Therapeutic studies - investigation of treatment outcomes.

Design and analysis of integrated environmental control system for Plateau cold chain transport vehicles

Plateaus, one of the most important terrain types in China, contain high-quality agricultural and livestock resources. However, due to their natural conditions, they host major deficiencies in cold chain logistics. Existing studies have focused on improving the temperature regulation capabilities of cold chain vehicle refrigeration or air conditioning systems, but have neglected the unique low-pressure environment faced by the Plateau cold chain transport vehicles. Using zoning design, air and vapor cycle refrigeration technologies, this study proposed a bootstrap-type integrated environmental control system (BIECS) and simple-type integrated environmental control system (SIECS) to realize vehicle “micro-environmental control.” The analytical solution of the thermal characteristics of the system was obtained based on the scaling-endoreversible thermodynamic analysis model. Moreover, the influence of ambient humidity on the thermal performance of the system was evaluated based on the enthalpy method. According to the typical working conditions, the system performances using different refrigerants, R404A, R448A, and R452A, were analyzed at different trailer temperatures, cooling capacities, and altitudes. Our results showed that, under the same design requirements, the coefficient of performance (COP) of the BIECS was slightly higher than that of the SIECS. Higher the trailer temperature and cooling capacity, higher is the COP of the system. Comparing the three refrigerants under the same working conditions, compared with R404A, the COP of the BIECS and SIECS increased by 13.4% and 10.9%, respectively, using R484A, and increased by 6.1% and 5.0%, respectively, using R452A. The performance of the systems that used R448A was the best. The system could ensure a 2.4-km cab pressure altitude at an ambient altitude of 5 km, but the COP could decrease by 31.8–35.6%, compared to that on the plains. This study provides and comprehensively evaluates a new technical solution for the environmental control of Plateau cold chain transportation vehicles. It also provides comprehensive health protection measures for drivers and technical support for the promotion and development of Plateau cold chains.

A Reevaluation of Cryolava Flow Evolution: Assumptions, Physical Properties, and Conceptualization.

Cryovolcanism has been invoked to explain numerous features observed on icy bodies. Many of these features show similar morphologies to volcanic features observed on Earth suggesting similar physics involved in their formation. Cryovolcanism lies at the intersection of volcanology and hydrology but as such, no one model from either discipline satisfactorily represents cryolava flow emplacement. We produced a new model for cryolava flow evolution that draws from both disciplines to track the physical, chemical, and thermal states of a hypothetical H2O-NaCl flow on a Europa-like body as it evolves away from the vent. This model is currently restricted to compositions on the water-rich side of this chemical system and only predicts emplacement up to the turbulent to laminar transition. Modeling the laminar regime and a broader compositional space will be dealt with separately. Concentrations between 5 and 23wt% (H2O-NaCl eutectic) and initial flow thicknesses of 0.1, 1, 10, and 100m were set as initial conditions. Model results suggest that flow may reach 40-60vol% solids before transitioning to laminar flow. The thermal budget for these flows is dominated by the heat loss from vaporization in the low-pressure environment. This model produces length to thickness aspect ratios, for the given compositions, that are broadly consistent with candidate cryovolcanic features on Ceres and Titan. These first-order comparisons are not ideal and suggest the need for future modeling of cryovolcanic features in at least two dimensions.

Corrosion Behavior of P110 Steel in Simulated CO<sub>2</sub> and Formation Water Environment

The corrosion behavior and mechanism of P110 steel tubing in in low CO2 particle pressure and high salinity formation water environment was investigated through high temperature and high pressure dynamic immersion tests, macro-morphology analysis, scanning electron microscopy(SEM) inspection, energy disperse spectroscopy(EDS) analysis and X-ray diffraction(XRD) analysis. The Results showed that the increasing of CO2 partial pressure accelerated the corrosion process of P110 tubing steel, and the corrosion rates of P110 tubing decreased with the increasing of temperature. Furthermore, the high content of Ca2+ in the formation water also had a big influence on the corrosion behavior of P110 tubing steel, for it could affect the precipitation quantity and morphology of CaCO3 at different temperature and CO2 particle pressure.

Durability effect of nano-SiO2/Al2O3 on cement mortar subjected to sulfate attack under different environments

Ambient humidity and air pressure have significant effects on the durability of cement-based materials subjected to sulfate attack. This paper investigated the durability performance of cement paste and cement mortar containing nano-SiO2 (NS) and nano-Al2O3 (NA) attacked by Na2SO4 solution under low air pressure (60 kPa, LP) and normal air pressure (101 kPa, NP) environments. The results showed that supersaturated Na2SO4 solution could crystallize in the pores of mortar and deposit on the surface of mortar, accompaning by the transformation from Na2SO4∙10H2O with fibrous to Na2SO4 with powder. The presence of low air pressure environment exacerbated the capillary transport rate and the water evaporation rate, resulting in a severer salt efflorescence. However, the incorporation of NS/NA could reduce the adsorption height of the salt solution on the surface of the mortar and thus alleviate the Na2SO4-induced damage. Moreover, the flexural/compressive strength of nano-modified mortar subjected to Na2SO4 attack under NP and LP environments were enhanced due to the nucleation effect and chemical activity of NS and NA. Furthermore, the addition of nanomaterials decreased the porosity and the amount of harmful pores above 50 nm in the samples and increased the consumption the erodible Ca(OH)2, reducing the generation of Na2SO4-induced corrosion products. Among them, the system containing NA at 0.5 wt% performed better, which is of great significance for the protection of concrete components exposed to sulfate attack in the practical engineering.

A comparative study on high pulse energy femtosecond laser drilling of high-aspect-ratio holes under different pressure conditions

Laser drilling of high-aspect-ratio holes is gradually on the agenda in the field of aerospace manufacturing. We present a comparative study of high pulse energy femtosecond laser micro-hole machining of thermal barrier coated superalloys under different pressure conditions. The ablation results showed that severe contaminative ablation patterns occurred near the geometric focus position, which is related to the remarkable refraction of the plasma near the geometric focus. Adopting negative defocus positions can restrain the plasma defocusing effect and eliminate these ablation defects. As compared to the case in the atmospheric pressure condition, the drilled holes had good retention in diameters, and the aperture size as small as 30 μm can be achieved in the low-pressure environment, which is attributed to a good suppression of the plasma defocusing effect. The drilled samples have convergent and divergent shapes struck within the hole in the low-pressure condition while the hole profiles show good collimation along the thickness direction in the atmospheric pressure environment. This can be attributed to the fact that the pulse energy can be well dispersed to the hole sidewall because of the plasma defocusing effect in the atmospheric pressure environment, and the sidewall materials can be effectively removed. The maximum aspect ratio of the hole can reach 15.7 based on the drilling results. The presented results provide some guidance for the machining of micro-holes with high aspect ratios on other occasions.

Experimental study on spreading and burning characteristics of continuous spill fire under low pressure

To investigate the influence of low ambient pressure on spill fire, the methanol spill fire experiments on fireproof glass with discharge rates ranging from 60 to 180 mL/min were conducted in a low-pressure chamber. The spread radius, burning rate, and heat transfer process between liquid layer and glass of spill fire were analyzed in-depth under low ambient pressure of 60 kPa and atmospheric pressure of 101 kPa. The results showed the entire spread process of spill fire and found that the spreading radius under atmospheric pressure was slightly smaller than that under low-pressure environment. The burning rate of spill fire under atmospheric pressure is lower than low pressure which the relation between pressure and burning rate can be expressed as m⋅∝P0.32. With respect to the heat transfer process, the heat loss including radiation penetration and heat convection under 60 kPa was lower than under 101 kPa, and the heat convection loss was dominant under two pressures. Finally, a semi-theoretical model was developed to estimate the burning rate in the quasi-steady stage by considering the spreading radius and heat transfer process. The model was validated with the experimental data and showed reasonable accuracy.

Rheology and air entrainment of fresh Portland cement mortars in simulated low air pressure environments

Air entrainment in cement-based materials is believed to be affected by low air pressure (AP) which is the atmospheric characteristic in high plateaus, and thus the rheology may be affected. This paper attempts to study rheology and air entrainment of fresh Portland cement mortar in simulated low APs. The results indicate that the rheological responses with the varying AP gradients are relevant to the air entrainments in fresh mortar mixtures. The volume changes of air voids in fresh mortars are linearly related to the varying APs, which is owing to not only the AP difference between the inside and outside air voids but also the additional pressure on the liquid films of air voids stemming from the surface tension changes. Moreover, the Bingham capillary number is calculated to account for the air void deformability. Then rheological parameters are correlated to the content and deformability of air voids in fresh mortars.

Study on Effect of Decompression and Near-Freezing Storage on Preservation of Fresh-Cut Fruits

To explore the effects of pressure, temperature, precooling and use of plastic bags on the preservation effect of mixed fresh-cut fruits and vegetables. In this Paper, apples, strawberries and potatoes are taken as the research objects. After fresh cutting, an appropriate amount of them is mixed, and the near-freezing point is set as -1°C. Seven control groups are set up: group A (normal pressure, normal temperature); Group B (atmospheric pressure, 4°C); Group C (10 kPa, -1°C); Group D (vacuum precooling, 10 kPa, -1°C); Group E (10 kPa, 4°C); Group F (vacuum precooling, 10 kPa, 4°C); Group G (without fresh bag, normal pressure, normal temperature) studied its preservation effect under different storage conditions within 9 days. Through the analysis and comprehensive evaluation of various indicators, the suitable storage and preservation methods of mixed fresh-cut fruits and vegetables are obtained. The results show that the preservation effect is more obvious at the later stage of the storage experiment, the final sensory score is the highest, the weight loss rate is the lowest, and the weight loss rate is reduced by 4.91% compared with the low pressure environment at 4°C. The use of plastic bags have the greatest impact on the weight loss rate and appearance of fruits and vegetables. Using plastic bags can reduce the weight loss by 48.48% on average compared with the same period, and the sensory score increases by 1 to 3 points. In the low pressure and high humidity environment, the weight of apple increases, and the final weight increases by 0.46% to 1.55%. The weight loss rate of strawberry is the highest, which can reach 22.54%. The vacuum pre-cooling process can reduce the weight of fruits and vegetables by 0.76% to 1.15%. When the low-pressure near-ice temperature storage is adopted to avoid the surge of weight loss rate, the average weight loss rate will be reduced by 7.8%.

IEEE EMBS International Student Conferences -Insights From 2022 Editions.

Student members within IEEE Engineering in Medicine and Biology Society (EMBS) are one of the most active segments among all other membership levels. Student-led initiatives all around the world have shown the necessity to give students the opportunity to present solutions to educational challenges, aiming to make the learning of young people an enriching and continuous experience while honing their organizational skills. IEEE EMBS SAC [1], formed under vice president for member and student activities, has taken the responsibility to initiate and implement programs for undergraduate and graduate student members of the society. One of these programs, IEEE EMBS ISC, is the flagship event under the oversight of the Professional Development Portfolio. The purpose of the ISCs is to help students learn to manage an IEEE-style conference in a low-pressure environment and improve on their soft skills like leadership, communication, teamwork, and project management. Moreover, it gives them a platform to practice giving and receiving peer feedback on scientific writing and presentations, as well as making international connections which could turn into future collaborations.

A multi-process coupling study of scavenging pressure effect on gas exchange of a linear engine

The linear engine is expected to operate with new gas exchange characteristics due to its unconstrained and adaptive dynamics. This study develops a simulation method that mutually transfers the coupling parameters between the piston motion model, generating model, combustion model, and scavenging model, and it iterates the calculation results of motion, combustion and scavenging for gas exchange predication. Then, the coupling effect of scavenging pressure fluctuation on gas exchange in a two-stroke linear engine is also investigated. The results indicate that unlike conventional engine systems, the linear engine reciprocation and compression ratio both increase first and then decrease with the enhancing scavenging pressure, namely the duration of gas exchange is shortened or prolonged, while the linear engine also provides high in-cylinder gas pressure for gas exchange, but the in-cylinder gas temperature reverses. The intake quality and escape amount of the cylinder both vary in positive correlation with the scavenging pressure, which leads to low trapping efficiency, although it cleans more exhaust. The results also find that high scavenging efficiency and fresh charge trapping efficiency can be obtained synchronously at an appropriately low scavenging pressure environment due to its adaptive motion.

Characteristics of electron evolution during initial low-pressure discharge stage upon microwave circuits

High-power microwave-induced low-pressure discharges seriously threaten the reliability of space payload systems. Under extremely low-pressure conditions, the evolution of ionized and secondary electrons at the initial stage of discharge is crucial to figure out the discharge process. Therefore, this paper investigates the development of multiple electrons in the discharge process under a highly low-pressure environment using numerical simulation. A three-dimensional simulation model based on the Monte Carlo algorithm is established by considering various electron-gas collisions and secondary electron emissions from different material surfaces. The evolution characteristics of various electrons' populations, energy, and distribution patterns during the discharge process are analyzed. In addition, the influence of the critical conditions at different air pressures on the electron evolution during the discharge process and the intrinsic causes are also investigated. This study is significant in revealing the transition characteristics between multipactor and low-pressure discharge and exploring their inherent mechanisms.

Gather: An Innovative Tool for Residency Pre-Interview Events

INTRODUCTION: General surgery residency interviews have been conducted virtually for the past two years to accommodate social distancing restrictions. The financial benefits of interviewing from home have motivated calls for a permanent move towards virtual interviews. However, the pre-interview meet-and-greet—the best opportunity for applicants to interact with residents in a low pressure environment—has been notoriously difficult to recreate in this format. Here, we present our experience using the novel digital platform Gather. METHODS: Gather is a video communication platform in which each user controls an avatar that can move within a virtual space. The platform creates a group chat limited to individuals who are near each other within the virtual space, facilitating small group conversations within a larger group. This better reapproximates the small group mingling that occurs within a traditional pre-interview event. We custom designed a virtual environment simulating the bar at which our meet-and-greet was held pre pandemic, and designated resident chaperones to help users adjust to this new format. Applicant and resident attitudes were measured using post-event surveys. RESULTS: Overall qualitative feedback from applicants and current residents was positive. The format was more enjoyable and interactive than traditional Zoom breakout rooms and more closely captured the ethos of an in-person meet-and-greet event. Applicants were able to adjust to the format and navigate the map without difficulty. Quantitative evaluation via applicant-based surveys is pending. CONCLUSION: The Gather platform represents a novel opportunity to improve pre-interview events. This and similar innovative technologies may significantly improve the virtual interview process.

The Influence of Airflow Rate on the Thermal Runaway Propagation Characteristics of Lithium-Ion Batteries in a Low-Pressure Environment

The Influence of Airflow Rate on the Thermal Runaway Propagation Characteristics of Lithium-Ion Batteries in a Low-Pressure Environment

An improved high altitude ultrasonic anemometer

This paper describes a sonic anemometer for low pressure (∼10mbar) environments. The technology is being developed as a high accuracy 3-D wind measurement system for the surface of Mars and stratospheric balloons. Applications include climate research, balloon navigation, and detection of energetic events through infrasonic atmospheric gravity waves. The device was constructed from an ST 32 bit Nucleo microcontroller and a custom daughter board that interface with high performance application specific amplifiers and multiplexers. Total power draw is 1.5 W. The sensor head uses narrowband commercial ultrasound transducers operating near 40 kHz at voltages below 30 Vpp. The total mass of the head is 180 g with a volume 15 cm on a side. The resulting system can take speed of sound and 3-axis flow velocity data at 0.4 Hz with 10 cm/s RMS fluctuation. Bell jar testing demonstrated operation to −5 oC and 10 mbar. A balloon launch to 32 km will occur before the meeting and will result in the first wind measurements at this altitude with a digital sonic anemometer. We will report on results and compare to inertial and GPS. [Work supported by NASA-NNX16AJ24G and NASA-80NSSC20M0007. Thanks to the NASA Wallops Balloon Programs Office for technical support.]

Drift characteristics and the multi-field coupling stress mechanism of the pantograph-catenary arc under low air pressure

The fault caused by a pantograph-catenary arc is the main factor that threatens the stability of high-speed railway energy transmission. Pantograph-catenary arc vertical drift is more severe than the case under normal pressure, as it is easy to develop the rigid busbar, which may lead to the flashover occurring around the support insulators. We establish a pantograph-catenary arc experiment and diagnosis platform to simulate low pressure and strong airflow environment. Meanwhile, the variation law of arc drift height with time under different air pressures and airflow velocities is analyzed. Moreover, arc drift characteristics and influencing factors are explored. The physical process of the arc column drifting to the rigid busbar with the jumping mechanism of the arc root on the rigid busbar is summarized. In order to further explore the mechanism of the above physical process, a multi-field stress coupling model is built, as the multi-stress variation law of arc is quantitatively evaluated. The dynamic action mechanism of multi-field stress on arc drifting characteristics is explored, as the physical mechanism of arc drifting under low pressure is theoretically explained. The research results provide theoretical support for arc suppression in high-altitude areas.

Effects of sleep insufficiency on spatial working memory in low-pressure and hypoxic environments.

Background:This study aimed to investigate the effects of sleep insufficiency on spatial working memory in low-pressure and hypoxic environments.Methods:We selected 58 insufficient sleepers and 27 normal sleepers among the college students living in high-altitude areas for a long time to receive a spatial 2-back working memory task, while collecting behavioral and electroencephalograph data. We adopted an independent sample t-test and repeated measures analysis of variance to compare the differences in response time and accuracy, P2 and late positive potential components, and theta band energy values in the spatial working memory task between insufficient and normal sleepers.Results:We found no significant differences in response time and accuracy between the insufficient sleep group and the normal sleep group; however, the P2 peak value and the early theta band energy value were higher in the insufficient sleep group than in the normal sleep group.Conclusions:These results suggest that the spatial working memory ability of individuals with sleep insufficiency was weakened under low-pressure and low-oxygen environment.