Microgravity Science and Technology最新文献

The authors present an analytical solution of equations describing the diffusion transfer and recombination of positive lithium ions and negative benzoate ions in benzoic acid after their injection from the surface of a protonated lithium niobate substrate. In the course of the solving one-dimensional stationary problem, the profiles of ions concentrations and electric potential distribution have obtained, corresponding to different values of governing parameters. The benzoate ions form thin boundary layer, while the ions of lithium completely fill considered region and have relatively uniform distribution. The comparison of analytical solution with numerical results permits to estimate the degree of the influence of electric field on the final distributions, which is formed due to the difference of ions concentrations. The expression, which determines the thickness of boundary layer, is obtained by the multiple scales method.

The effects of a ground-based model of microgravity on executive functions (namely, inhibition) were investigated in this study. Volunteers participated in so-called dry immersion (DI), during which they spent 21 days in a water-filled tub in the supine position. During this period, they performed an auditory Go/NoGo task while multichannel EEG activity was recorded. The Go/NoGo task was performed one time outside of the DI and two times during the stay in the DI. ERPs were computed on correct NoGo and Go trials. While no behavioral deterioration of the Go/NoGo task was found during their stay in the DI, a significant difference was found in amplitudes between NoGo N2 ERP peaks before DI and during DI. The N2 peak was smaller on the 17th day of DI, indicating a potentially lower level of inhibitory control during simulated microgravity conditions. The amplitudes of the N1 and P3 peaks did not change significantly. The dry immersion procedure reproduces some of the important physiological factors of real space flights (support withdrawal, bodily liquid redistribution), thus our results hint at possible brain and behavioral alterations in real space flight that have so far been unnoticed.

This paper presents data from large, isolated n-dodecane droplets burning in microgravity on the International Space Station, along with preliminary comparisons with numerical and analytic predictions indicating general agreement in trends. The tests involved were primarily in air (a few in reduced oxygen) at ambient pressures ranging from 0.50 to 5.0 atm. After ignition, the droplets burn with a hot flame that extinguishes when the radiant energy loss causes the flame temperature to drop below the hot-flame-required value. The total flame radiative loss at extinction is nearly independent of pressure, while the peak flame diameter prior to hot-flame extinction decreases with increasing pressure. The maximum hot-flame temperature, inferred from fiber-support radiative emisssions, decreases with increasing pressure, and the hot flames become dimmer with increasing pressure. At 1.0 atm and below there is a prolonged period of coolflame burning that ends with cool-flame extinction at a finite droplet size; the cool-flame-extinction droplet diameter increases and the cool-flame burning rate decreases with decreasing ambient pressure. Above 1.25 atm warm-flame burning and hot-flame re-ignitions become prevalent. At 5.0 atm, there is no abrupt hot-flame extinction with transition to a cool flame; the flame gradually gets dimmer, and the flame temperature decreases over a much longer time, the transition between hot-flame and warm-flame burning becoming almost undiscernible.

The pool boiling heat transfer (phase-change immersion cooling) phenomenon holds significant importance in the energy consumption management of large-power electronics. However, the optimization of surface structure for achieving stable and efficient heat transfer during boiling process remains a significant challenge. Herein, we propose a simplified and direct hybrid surface strategy that combines crossed mini channels and a capillary wick to address the cooling issues faced by high-performance power devices. The copper capillary wick is combined with the crossed mini channel to form a hybrid surface by a simple integrated sintering method. This study investigates the combined effects of different parameters of the capillary wick (average diameter size and powder addition) and minichannels (depth and width) on enhancing the nucleate boiling performance on these hybrid surfaces. The working fluid used in this investigation is HFE-7100. At ΔT_sub = 30 K, the CHF achieved by the hybrid surfaces combining capillary wicks and minichannels can reach 131 W/cm², while the highest HTC is measured at 2.32 W/(cm²·K), both CHF and HTC achieve multiplicative enhancement compared to smooth surfaces. Furthermore, we have developed a CHF prediction model for the hybrid surfaces, which exhibits a prediction error of less than 15%.

The phenomenon of solidified suspended hollow droplets is often run into industry and nature. In this study, we focus on the containerless solidification process of a hollow droplet undergoing a forcing flow. We found that when the radius ratio (R_io) varied with different growth angles, it changes the trend of the solidification rate of the solidifying front over time. Specifically, with the growth angle of 5° (i.e., Φ_gr = 5°), the suspended hollow droplets finished solidification in almost the same time for R_io in the range of 0.2–0.7. When we increase the growth angle by 5°, i.e., Φ_gr = 10°, the solidification time increases with the increase of R_io. Also following the increase of R_io, this increase in the solidification time is even higher for the growth angle Φ_gr = 15°. The inlet temperature is also considered. Obviously, increasing the inlet temperature increases the solidification time of the hollow droplets. In addition, when the Reynolds number increases, the solidification time of the droplets also tends to increase. However, the increment of this trend is different under different temperatures of the forcing flow.

The examination of the impact of microgravity on biological systems has gained considerable attention owing to its potential implications for health and disease. Simulated microgravity serves as a valuable methodology for elucidating the intricate cellular responses to altered gravitational conditions. This study investigates the effects of simulated microgravity on cellular DNA, employing four distinct cell lines—breast, brain, and esophageal cancer cells, in conjunction with normal cells for comparative analysis. The experiment utilized the comet assay test to quantitatively assess DNA damage. The results revealed a discernible disparity in the response to simulated microgravity, notably with cancer cells exhibiting a significant increase in DNA damage compared to the relatively minimal effects observed in both control and normal cells. Furthermore, within the cancer cell lines, significant variations in the extent of DNA damage were evident, implying a cell type-dependent response to simulated microgravity. These findings illuminate the potential differential susceptibility of cancerous and normal cells to microgravity-induced DNA damage. Consequently, this research substantially contributes to our comprehension of microgravity-induced cellular responses and unveils promising avenues for targeted interventions in cancer therapy.

This paper delves into the dynamics of surface-active bubbles under low-frequency acoustic waves, with a focus on the stability effect and basic principle of rupture. The Rayleigh-Plesset equation is extended and modified based on real biological data, resulting in a model of surface-active bubbles with nonlinear surface tension. Using the Runge-Kutta method for numerical calculations, it is observed that larger acoustic wave amplitudes lead to larger bubble amplitudes. The acoustic wave frequency only affects the bubble vibration frequency in the low-frequency range, but at the resonance frequency, the bubble oscillations are violent. To further explain bubble rupture, the stress-strain relationship of the surface active layer of the bubble is studied, with the stress on the wall increasing sharply with the bubble radius. The stability of the non-spherical interface of the surface-active bubbles reveals a critical radius value, with bubbles in a stable state when the radius is smaller than this value. Through simulation, it is observed that bubbles vibrate in a steady state under stable conditions, but when the radius exceeds the critical value, a non-spherical interface appears ultimately resulting in inward depression and rupture.

Repeated jumping has been demonstrated as a feasible exercise countermeasure in microgravity and has been shown to reduce deconditioning in head down bed rest studies. However, varying landing stiffness may provide greater contribution of both axial and medio-lateral bone strain and muscle loading at greater muscle lengths, which may help minimize bone and muscle deconditioning. Therefore, this study investigated the effect of different landing styles on the force profile and ground contact time during repeated jumping using HIFIm in microgravity. Two participants performed repeated jumping on the HIFIm jump sled in microgravity during a parabolic flight campaign. ‘Ground’ forces and ground contact time were compared between landing styles where increased landing stiffness was instructed to the jumper, and increased spring resistance. The results show that the forces experienced when performing repeated jumps in microgravity are sensitive to the landing style employed. As greater stiffness was instructed, peak forces increased, and ground contact time decreased significantly. Peak forces and ground contact time also significantly increased when spring resistance increased. These results highlight that landing instructions and spring configurations could be used as training variables when developing an astronaut training program, which can use different jump styles to minimize bone and muscle deconditioning. Further research using bed rest analogs and repeated jumping using HIFIm is needed to demonstrate varied repeated jumping interventions as an effective exercise method for minimizing deconditioning in astronauts.