Microgravity Science and Technology最新文献

To investigate the effects of different gravity conditions on the solution flow fields and crystal growth rates during the dissolution and growth processes of InGaSb crystals utilizing the vertical gradient freezing (VGF) methods, two-dimensional numerical simulations were conducted. Nine numerical simulations were performed under a range of gravity conditions, including microgravity: 1 × 10^− 4 G, 0.01 G; small gravity: 0.1 G, 0.17 G (lunar gravity), 0.38 G (Mars); normal gravity: 1.0 G, and high gravity: 2.0 G, 5.0 G, and 10.0 G. The results demonstrated that the natural convection induced by gravity significantly affects the growth rates of InGaSb crystals. The growth rates were highly sensitive to variations in gravity, decreasing as gravity increased within the range of 0.01 to 2.0 G. Under microgravity conditions (no larger than 0.01 G), growth rates values were very similar, indicating that under microgravity the InGaSb growth process is diffusion-dominant. When gravity exceeds 2.0 G, the growth rates of InGaSb stabilize, but larger non-uniform areas develop as gravity increases, compromising the quality of the grown crystals.

This study employs two-dimensional numerical simulation to characterize droplet migration and collision dynamics on unidirectional and symmetrical multi-level wettability gradient (WG) surfaces under Earth (g₀), Martian (0.38 g₀), and microgravity (10⁻⁶g₀). Parametric analysis reveals WG = -15/2°/mm optimizes single-droplet migration time in microgravity, exhibiting minimal sensitivity to gravity reduction, while WG = -20/2°/mm maximizes efficiency under g₀. Larger droplets (D = 3 mm) accelerate terrestrial transport but severely impede microgravity migration, where smaller droplets (D = 2 mm) excel. Peak velocity (> 0.3 m/s), governed by WG and D independent of gravity, dictates acceleration capability. Final equilibrium morphology mainly depends on WG. For dual droplets, microgravity collision requires WG = ∓ 15/2& ∓ 20/2°/mm and D = 2 mm; lower gradients or larger diameters prevent collision. The results demonstrate that reduced gravity disrupts mirror-synchronized droplet motion observed under g₀, delaying collision initiation. These findings provide critical guidelines for designing passive capillary fluidic systems in variable-gravity environments, particularly space applications.

Microgravity environments significantly impact soot formation and flame stability in laminar diffusion flames, yet the underlying mechanisms remain poorly understood, especially in high-pressure combustion systems. This study utilizes a hybrid moment method (HMOM) coupled with P1 radiation modeling to investigate the radiation-induced modifications to temperature fields, flow structures, and soot evolution in ethylene-air co-flow flames under elevated pressures (1–8 bar), comparing normal gravity and microgravity conditions. Results show that microgravity environments amplify soot volume fractions by 200–300% compared to normal gravity, due to extended reactant residence times. Radiative heat losses lower peak flame temperatures by 20–150 K, with this reduction becoming more pronounced at higher pressures due to increased radiation from both gases and soot. At critical pressure thresholds in microgravity, a transition from closed-tip to open-tip flame structures occurs in co-flow laminar diffusion flames, driven by radiative heat losses approaching 45%–60% of total chemical energy. Unlike spherical flame extinction, laminar diffusion flames experience local extinction triggered by heat release rate (HRR) decay at the flame tip, followed by the opening of the hydroxyl radical (OH) zone. This structural modification creates an oxidative boundary discontinuity, preventing the OH zone from fully encapsulating soot particles, thus allowing soot to escape oxidation pathways.

As a zero-carbon fuel, ammonia (NH(_3)) has attracted great interests recently. Due to its slow propagation speed, NH(_3) flames are strongly affected by gravity and radiation. This study investigates the propagation of spherically expanding NH(_3)/air flames under the combined effects of gravity and radiation using two-dimensional simulations with detailed chemistry and transport models. The results show that gravity significantly deforms the flame front, leading to a mushroom-shaped structure in which the local flame displacement speed varies along the front due to local stretch effects. This phenomenon becomes more pronounced at lower equivalence ratios as a result of the reduced flame speed. Overall, gravity enhances the global flame propagation speed. On the other hand, radiation slows the flame propagation by lowering the flame temperature and inducing an inward flow velocity. This makes the flame more susceptible to the influence of gravity and amplifies the deformation of the flame front. Finally, the performance of various approaches for determining the unstretched laminar flame speed from spherically expanding flames under gravitational and radiational conditions is assessed. It is found that when both gravity and radiation effects are significant, the spherically expanding flame method using flame radius history is not applicable, regardless of the definition of equivalent radius, and the surface-averaged method is the only reliable approach. This study provides insights into the understanding and accurate measurement of NH(_3)/air flame propagation characteristics.

The article proposes a theoretical model of EWOD (electrowetting–on–dielectric) taking into account the saturation of the dynamic contact angle using the example of forced oscillations of an electrolyte droplet in a spatially inhomogeneous alternating electric field. This droplet is clamped between two plates, which are electrodes. The inhomogeneity of the plate surface is described by an individual function, which is a wetting parameter and a proportionality coefficient between the contact line velocity and the contact angle deviation. It is shown that the surface inhomogeneity leads to the excitation of additional modes, the spectrum of which is determined by the function describing this inhomogeneity. It is found that the surface inhomogeneity can change the saturation angle. Qualitative agreement with experiments is shown.

This study comprehensively investigates the effects of gravitational variations and throughflow of convection in anisotropic porous media under LTNE (local thermal non-equilibrium conditions). By using a normal mode analysis, the linear stability analyses are analyzed. The gravitational force is modelled in three forms- linear, parabolic, and exponential- all oriented along the spatial configuration’s vertical axis. The critical Rayleigh number for convection onset is approximated through the Galerkin approximation. The results show that the throughflow constraint consistently stabilizes the system, regardless of direction. Additionally, an increase in the thermal and mechanical conductivities leads to enhanced system stability, while greater mechanical anisotropy weakens the convection onset. Notably, the system demonstrates the highest stability under exponential gravity variations, compared to linear and parabolic variations. The initiation and consistency of convection in these systems play a crucial role in: Forecasting thermal extraction performance, reservoir temperature reduction, and crafting eco-friendly energy harvesting approaches.

The influence of simulated microgravity on cellular processes has attracted growing interest due to its relevance in space biology and medical research. This study investigates the impact of simulated microgravity on Caco-2 cells, a widely used human epithelial colorectal adenocarcinoma cell line, co-cultured with the pathogenic enterohemorrhagic E. coli O157:H7 strain. The experiment explored cells lipids alterations and metabolic changes under microgravity conditions compared to terrestrial gravity. Using a lipidomics approach under simulated microgravity we observed an upregulation of lysophosphatidylcholines LysoPC 14:0, LysoPC 16:0, LysoPC 16:1, LysoPC 17:0, LysoPC 18:0, LysoPC 18:1, LysoPC 20:1 as well as ceramides Cer 18:1;O₂/16:0, Cer 18:1;O₂/24:0, Cer 18:2;O₂/24:0. Conversely, we detected a downregulation of phosphatidylcholines PC 14:0/14:0, PC 14:0/16:1, PC 16:0/16:1 and PC 18:0/18:1 and sphingomyelins SM 18:1;O₂/16:0, SM 18:1;O₂/24:0, and SM 18:2;O₂/24:0, and the betaine lipids of microbial origin diacylglyceryl-trimethylhomoserine DGTS 16:0/19:1 and DGTS 19:1/19:1. These findings provide insights into the molecular adaptations of human epithelial cells in response to microgravity and offer a foundation for future studies on microbiome-host dynamics in spaceflight environments.

Microgravity anaemia is a significant physiological issue in space travel, characterized by a decrease in red blood cell mass and haematological parameters. The history of spaceflights, from the Gemini and Apollo to the International Space Station, demonstrates repeated decreases in RBC mass and haemoglobin upon exposure to microgravity. The intrinsic pathophysiology includes enhanced hemolysis, fluid shift with disturbed plasma volume, and an imbalance in erythropoietin signaling and erythropoiesis. Microgravity not only enhances RBC breakdown by as much as 54% compared to Earth conditions but also causes rapid fluid redistribution, with effects on cardiovascular and renal function. This is further influenced by changes in erythropoietin regulation and the process of neo-cytolysis, whereby repressed erythropoietin causes the selective elimination of neocytes, thereby precisely regulating RBC mass in response to environmental changes. A clear understanding of these processes will be crucial for maximizing crew health and designing effective countermeasures to prevent microgravity-induced anemia.

During interplanetary flights, hypomagnetic conditions (HMC) may be one of the specific factors affecting the astronaut’s body. Their combined effect with other factors of flight beyond low Earth orbit will greatly enhance the damaging effect on the body, including on the structural and functional state of the cardiovascular system (CVS). Our study was performed during a 12-month simulated isolation. It was attended by 6 healthy volunteers (2 men and 4 women). HMC (0.113 ± 0.062 µT) was modeled on -(2–4) days before the volunteers were placed in a hermetic facility and at the final stage of isolation (346–350) days of stay in a hermetic facility. Two 4-hour exposures with GMU exposure and background studies were conducted. Throughout their stay in the facility, each volunteer underwent continuous electrocardiogram (ECG) recording. The main indicators characterizing the autonomic modulating effects on the cardiovascular system changed in the HMC as follows: compared with the background, both women and men had higher heart rate in the HMC, VLF(mc²) and LF(mc²), as well as in men, the total power of the spectrum increased and prevailed in both exposures. When viewing ECG recordings in women, episodes of tachycardia were detected in the isolation exposure, as well as cardiac arrhythmias in the form of extrasystoles of ventricular and atrial origin, no cardiac arrhythmias were detected before isolation. In general, the strongest response of regulatory mechanisms associated with autonomic influences on the CVS in the HMC after 12 months of isolation was observed in women compared to men.

The functioning of gastrocnemius-soleus (G-S) muscle complex aids in stabilizing and controlling major bony joints, it also provides the primary coordination of the foot and body mass support. Geometric positioning of the foot and transferring of plantar loads can be adversely impacted in human musculature system because of the inactivity of muscles in microgravity environment. Differential activation of the G-S muscles can be analyzed to learn more about their roles during movement, performance and injury prevention. Therefore, the aim of this study was to analyze G-S muscle activity during on velcroid (V) and nonvelcroid (NV) sloping surfaces during slope walking, standing and calf raise in human Body. In the present study, it was hypothesized that muscle activity of G-S muscle complex enhances during slope walking, standing and calf raise on V sloping surface. 10 volunteers performed above activities on predefined slope angles of 0° ± 6°, ± 12° and ± 18° for both NV and V sloping surfaces. Biopac^® data acquisition system was used to obtain EMG signals to analyze the muscular activities in time and frequency domains. It was observed that soleus muscle activity was increased by 22% for 0 ° to 18 ° inclination and 21% for 0 ° to -18 ° declination on V-surface. Similarly, for gastrocnemius muscle the muscle activity was enhanced on V sloping surface by 20% for 0 ° to 18 ° inclination and 15% for 0 ° to -18 ° declination respectively. ANOVA results demonstrate the muscle activity increased substantially (p < 0.05) during these tasks being performed on V sloping surface. Further analysis indicates that muscle activity is stronger for soleus muscle as compared to gastrocnemius muscle. Also, there is no other similar work reported previously, that has been done for this purpose. This information about enhanced muscle activity is envisaged to have important clinical implications as it will play an important role in training and rehabilitation activities along with creating a countermeasures solution necessary when G-S muscle experience disuse.