Microgravity Science and Technology最新文献

The decrease in orthostatic tolerance due to the deconditioning of cardiovascular system after space flight remains an urgent problem. The effect of longitudinal overloads on a short-arm human centrifuge (SAHC) is believed to be useful in preventing a decrease in orthostatic tolerance in astronauts after spaceflight through regular compensation of hydrostatic blood pressure, which is absent in microgravity. The analysis of adaptive reactions of the autonomic regulation system was carried out by analyzing heart rate variability, blood pressure was used to calculate hemodynamic parameters. These characteristics were analyzed in 6 male subjects (mean age 38 ± 7 (SD) years) during the protocol of training rotations on the SAHC and during a passive orthostatic test with foot support (tilt test). The nonparametric Wilcoxon criterion and Kendall’s rank correlation coefficient were used for statistical analysis. During training rotations, an increase in heart rate (HR), a weakening of high-frequency (HF) and a significant increase in low-frequency (LF) spectral components of the heart rate were observed, indicating the involvement of the sympatho-vagal system with a predominance of sympathetic regulation. It is shown that after a series of rotations on the SAHC, there is a smaller increase in HR in an upright position during a tilt test, which indicates a decrease in excitability and reactivity of the sympathetic nervous system. There was also a decrease in the influence of suprasegmental (higher) autonomic centers on the regulation processes during orthostatic loading. This interval training protocol on the SAHC has a training effect and increases orthostatic stability.

For disclose the effect of nanoparticle shape on flow regime and critical condition of thermocapillary convection, the nanofluid thermocapillary convection with different shaped nanoparticles are investigated in this paper, and the oscillation characteristics of thermocapillary flow are analyzed. The results indicate that, the nanoparticles can significantly alter the oscillatory characteristics of thermocapillary convection instability, and the influence of platelet shaped nanoparticle is the strongest and followed by cylinder, blade, brick, and sphere nanoparticles. The main frequency of oscillatory thermocapillary convection decreases with the increase of sphericity, and the size of hydrothermal wave propagation angle at free surface is as follows: sphere > brick > cylinder > blade > platelet.

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Porous media are widely used for gas–liquid phase separation in micro-gravity, but decreasing pore radius often results in both increased critical pressure for bubble penetration and increased flow resistance through the pores. To address this issue, the present study investigates the bubble dynamics within a hierarchical porous structure to optimize phase separation performance. A theoretical model was developed by analyzing the force balance on an isolated gas bubble to predict critical pressure. The Volume of Fluid (VOF) method was utilized to simulate bubble movement at the pore scale, with critical pressure determined by varying the pressure differential between the inlet and outlet. The effects of bubble radius, pore radius, pore length, and secondary pore location on the critical pressure and critical flow rate were analyzed. Hierarchical pores were found to improve the phase separation performance compared to single stage pores. Specifically, the presence of a secondary pore with pore length and radius of 30 μm increased the critical pressure by 110% and the critical flow rate by 26% compared to a single stage pore with a pore radius of 50 μm.

MiniFix, a syringe-based biological fixation system (SBBFS) is a versatile, fully 3D-printed syringe-driven, stepper motor-operated platform designed for the chemical fixation of biological samples in space-based research. Unlike conventional systems, it leverages additive manufacturing to provide modularity and customizability, enabling manipulation and a chemical fixation of biological samples under altered gravity conditions. MiniFix has performed five successful missions on the MAPHEUS sounding rocket and has demonstrated its reliability and adaptability. The integrated thermal management system uses waste heat from the stepper motors to maintain accurate sample temperature and in turn reduces power consumption and weight. MiniFix is particularly notable for its flexibility, allowing adaptation to diverse biological model systems, from simple organisms to more complex tissue cultures. Its modular design and 3D-printing process enable quick, cost-effective adjustments for different experimental setups. It was successfully printed with three different materials– PLA (Polylactic acid), PETG (Polyethylene terephthalate glycol-modified), and the biodegradable GreenTEC Pro. Its ability to integrate modifications such as illumination further enhances its adaptability for future space missions, for instance with photosynthetic organisms. By offering reliability, modular flexibility, and adaptation to a broad range of biological research goals, the SBBFS represents a new approach to construct flexible hardware for space and gravitational biology.

Thermal energy storage is an efficient way for thermal control of near-earth and deep space detectors, but the melting rate is restricted by low heat transfer performance of phase change material (PCM) and disappearance or suppression of natural convection under micro/low gravity. To accelerate melting of PCM under micro/low gravity, graphene nanoplatelet (GNP)-enhanced PCM with fins are proposed. The effects of fin shape, GNP concentration and gravity level on dynamic melting characteristics considering thermocapillary convection are investigated. The results show that the improvement effect of rectangular fins on melting rate is higher than that of triangular fins under microgravity; with the decrease of gravity level, the melting rate is reduced. The presence of GNP significantly promotes the melting under micro/low gravity. At GNP concentration of 0.03 vol%, the reduction of melting time can reach 58.2%, 49.4% and 51.6% at microgravity, moon’s gravity of 1.625 m s⁻² and Mars’ gravity of 3.711 m s⁻², respectively.

Gas-insulated Metal Transmission Line (GIL) represents a promising alternative to traditional overhead lines for long-distance electric power transmission. The thermal performance of GIL is crucial in determining the dielectric strength of materials, which subsequently affects both transmission capacity and security. In this study, a three-dimensional numerical model is introduced to analyze the coupled relationship between the flow field and temperature field of the environmentally friendly insulating gas perfluoroisobutyronitrile (C₄F₇N). The temperature and flow characteristics of C₄F₇N are analyzed at different Rayleigh numbers. Besides, the effect of GIL geometric size on the flow dynamics and temperature distribution are discussed. The results reveal that the enhancement of buoyancy convection contributes to the temperature drop of conducting body, which enhances the buoyancy convection in return. When the Rayleigh number is below 5 × 10⁵, the flow in GIL is weak and there is only slight variation in temperature of C₄F₇N along the lengthwise direction. However, as the Rayleigh number rises to 5 × 10⁵, the convection become pronounced and distinct variations in temperature distribution along GIL appears. When the Rayleigh number exceeds a threshold value of 1 × 10⁷, the flow instability occurs, leading to an asymmetric temperature distribution as well as the overall temperature drop along GIL. The maximum velocity occurs near the surface of the conduction. As the increase of radius ratio between inner and outer annular surface, both flow intensity strengthens and noticeable reductions in temperature become more apparent. These findings can be utilized for insulation design considerations within GIL systems.

The paper is dedicated to the analysis of medico-biological data obtained during locomotor testing of astronauts. Accurate data interpretation plays a crucial role in locomotion system monitoring, prophylaxis of long-duration spaceflight negative effects and thus in the development of an autonomous medical support system for deep space expeditions. During the locomotor testing the astronaut changes motion modes in accordance with the prescribed training protocol while running on the treadmill, and data such as speed, support pressure, heart rate frequency, etc., are collected simultaneously. The astronaut may follow either an individual protocol developed by specialists or perform his personal protocol at every fourth day of the micro cycle. Our task is to identify unknown motion modes by the means of a posteriori time series segmentation and, specifically, in the presence of various transitional processes as well as signal loss periods. The presence of tricky profiles does not allow for preliminary hypotheses about the distribution pattern of the dataset under study. The article consists of two parts. Firstly, it provides a detailed overview of several modern retrospective (offline) nonparametric multiple changepoint detection methods in multidimensional time series. A change point means an abrupt change in the probability properties of the observed series occurring at an unknown time instant. When describing the algorithms, emphasis is placed on statistics as a measure of data homogeneity, numerical methods for solving optimization problems, and model selection methods. Secondly, the real speed profiles resulting from locomotor testing have been handled through the mentioned algorithms. The validation was performed on three characteristic experimental data samples, allowing for an assessment of the prospects of applying the described methods to the entire dataset.

The work presents the results of numerical simulations of a microdevice designed to concentrate a low-concentration analyte consisting of weakly charged macromolecules. The microdevice consists of a spherical chamber containing an ion-selective sphere located in the center. A gravity-induced pressure-driven flow of an electrolyte solution containing the analyte is established through the chamber. Two electrodes are placed at the input and output of the device to create an external electric field. The properties of the analyte typically differ from those of the ions in the buffer electrolyte solution; for instance, its diffusion coefficient is normally much smaller than those of the electrolyte ions. This asymmetry, combined with a nontrivial electroosmotic flow along the ion-selective sphere, results in significant differences in the analyte behavior compared with the behavior of ions. Several scenarios of analyte concentration, based on both its intrinsic properties (different diffusion coefficients and charges) and external factors such as the intensity of an external electric field and the properties of the flow, are investigated.

To obtain a more accurate gravity field model, gravity field measurement satellites use the drag-free control system to minimize the residual disturbance force of the satellite. To meet the drag-free control accuracy, these tasks propose the requirements of wide continuous throttling ability, low noise, and rapid response for the propulsion system, which acts as the actuator of the control system. This research takes a cusped Hall electric propulsion system as the research object and constructs a component-level propulsion system model based on experimental data. The drag-free control simulation system is designed. And the control simulation results show that the slow thrust response speed of the propulsion system limits the bandwidth of the control system, resulting in the control accuracy not meeting the mission requirements. To solve this problem, a thrust response speed optimization method based on coordinated control of input parameters of the propulsion system is proposed. The results show that the thrust response speed is improved and the bandwidth of the control system is increased after the coordinated control of the flow rate and the voltage, which makes the residual accelerations of the satellite meet the drag-free control requirements of the gravity field measurement satellite.