Weightlessness Research Articles

Continuous and Controllable Preparation of Sodium Alginate Hydrogel Tubes Guided by the Soft Cap Inspired by the Apical Growth of the Plant.

Hydrogel tubes made of sodium alginate (SA) have potential applications in drug delivery, soft robots, biomimetic blood vessels, tissue stents, and other fields. However, the continuous preparation of hollow SA hydrogel tubes with good stability and size control remains a huge challenge for chemists, material scientists, and medical practitioners. Inspired by the plant apical growth strategy, a new method named soft cap-guided growth was proposed to produce SA hydrogel tubes. Due to the introduction of inert low gravity substances, such as air and heptane, into the extrusion needle in front of calcium chloride solution to form a soft cap, the SA hydrogel tubes with controllable sizes were fabricated rapidly and continuously without using a template through a negative gravitropism mechanism. The SA hydrogel tubes had good tensile strength, high burst pressure, and good cell compatibility. In addition, hydrogel tubes with complex patterns were conveniently created by controlling the motion path of a soft cap, such as a rotating SA bath or magnetic force. Our research provided a simple innovative technique to steer the growth of hydrogel tubes, which made it possible to mass produce hydrogel tubes with controllable sizes and programmable patterns.

Sustaining Hydrothermal Circulation With Gravity Relevant to Ocean Worlds

AbstractSome ocean worlds may sustain active, seafloor hydrothermal systems, but the characteristics and controls on fluid‐heat transport in these systems are not well understood. We developed three‐dimensional numerical simulations, using a ridge‐flank hydrothermal system on Earth as a reference, to test the influence of ocean world gravity on fluid and heat transport. Simulations represented the upper ∼4–5 km below the seafloor and explored ranges of: heat input at the base, aquifer thickness, depth, and permeability, and gravity values appropriate for Earth, Europa, and Enceladus. We tested when a hydrothermal siphon could be sustained and quantified consequent circulation temperatures, flow rates, and advective heat output. Calculations illustrate a trade‐off in energy between the reduction of buoyancy at lower gravity, which tends to reduce the primary forces driving fluid circulation, and the concomitant reduction in secondary convection, which consumes available energy. When a siphon was sustained under lower gravity, circulation temperatures tended to increase modestly (which should lead to more extensive geochemical reactions), whereas mass flow rates and advective heat output tended to be reduced. Deeper subseafloor circulation resulted in higher temperatures and flow rates, with a deeper, thin aquifer being more efficient in removing heat from the rocky interior. Water‐rock ratios were lower when gravity was lower, as was the efficiency of heat extraction, whereas the time required to circulate the volume of an ocean‐world's ocean through the seafloor increased. This may help to explain how small ocean worlds could sustain hydrothermal circulation for a long time despite limited heat sources.

Laboratory studies on the mechanical properties of sulphur-based construction material at simulated Martian temperatures

Mars is the next destination for further exploration and the hypothetical establishment of humanity's frontier. However, the planet offers very harsh environmental conditions particularly the very cold temperature in the Martian environment. Knowing that the sulphur-based construction material is perceived as one of the ideal Martian construction materials based on the identified abundant source of sulphur on Mars, its behaviour when subjected to the very cold Martian temperature is yet to be fully clarified. Therefore, this study intends to investigate the behaviour of the Martian sulphur-based construction material subjected to the simulated very cold Martian temperature whilst being compared with the simulated hot Martian temperature. Two mixture compositions of 50/50 and 60/40 comprising of sulphur and Mojave Mars simulant 1 (MMS-1) respectively were fabricated in this study characterising the simulated Martian temperature. The workability at 50 % and 60 % sulphur content was initially investigated. Subsequently, the overall mechanical properties characterising the sulphur content and simulated Martian temperature were investigated via unconfined compression, three-point bending and tensile splitting tests. Necessary factors that influence the overall mechanical properties including the internal structure and microstructural characteristics were also performed via ultrasonic pulse velocity (UPV) and scanning electron microscopy (SEM) respectively. X-ray diffraction (XRD) was also conducted to identify the chemical composition of the end product. The comparisons between this study and other previous related studies within the state-of-the-art Martian sulphur-based construction materials were also outlined. Prospects for future construction on Mars are also presented. It was found that the 60 % sulphur content exhibited higher workability due to the high amount of unreactive sulphur. The 50 % sulphur content recorded the optimal overall mechanical properties under the simulated hot and very cold Martian temperatures. The simulated very cold Martian temperature triggered non-uniform interparticle distribution and larger cavities thus dramatically reducing its overall strength and triggering higher volumetric inconsistency. The very brittle nature of unreactive crystallised sulphur binder at excessive thickness particularly at 60 % sulphur content in between filler particles also triggered volumetric inconsistency which further worsened at the simulated very cold Martian temperature. The iron sulphate hydrate found was almost in agreement with the related works and another new compound, potassium calcium magnesium sulphate was identified as well. The overall mechanical properties are comparable with the other previous related studies and the residual strength when subjected to the simulated very cold Martian temperature remains adequate in the Martian environment of low gravity. The 60 % sulphur content is suggested for structural elements built internally whereas the 50 % sulphur content demonstrated a high potential in adapting to the harsh Martian environmental conditions. The findings of this study hoped to act as the initial outlook on how such Martian sulphur-based construction material would react upon fabrication on Mars.

Erosion rate of lunar soil under a landing rocket, part 1: Identifying the rate-limiting physics

Multiple nations are planning activity on the Moon's surface, and to deconflict lunar operations we must understand the sandblasting damage from rocket exhaust blowing soil. Prior research disagreed over the scaling of the erosion rate, which determines the magnitude of the damage. Reduced gravity experiments and two other lines of evidence now indicate that the erosion rate scales with the kinetic energy flux at the bottom of the laminar sublayer of the gas. Because the rocket exhaust is so fast, eroded particles lifted higher in the boundary layer do not impact the surface for kilometers (if at all; some leave the Moon entirely), so there is no saltation in the vicinity of the gas. As a result, there is little transport of gas kinetic energy from higher in the boundary layer down to the surface, so the emission of soil into the gas is a surprisingly low energy process. In low lunar gravity, a dominant source of resistance to this small energy flux turns out to be the cohesive energy density of the lunar soil, which arises primarily from particles in the 0.3 to 3 μm size range. These particles constitute only a tiny fraction of the mass of lunar soil and have been largely ignored in most studies, so they are poorly characterized.

Investigating combined effects of varying gravity and heat flux direction on the melting dynamics of phase change material in space

The present work investigates the combined effect of varying gravity and heat flux direction with respect to gravity on the melting dynamics of Phase Change Material. Similar conditions are relevant to applications in space, at different space infrastructures, such as orbiting satellites, as well as various extraterrestrial surface assets, landers, and rovers. The numerical simulations are performed to study the melting dynamics of a paraffin-based phase change material with Prandtl number Pr ≈ 71 and Stefan number Ste ≈ 0.33 inside a differentially heated square enclosure. The mathematical model employs a control volume-based enthalpy porosity approach to simulate the melting process inside enclosure. The direction of the incoming heat flux relative to the gravity vector is defined in terms of an orientation angle, which is varying circularly with a step of 45°, whereas the gravity level is ranging from the terrestrial surface value g to 0.2g to analyze the melting process over a wide range of Rayleigh number 100 ≤ Ra ≤ 107. The study provides a detailed insight into the attributes of heat transfer, flow dynamics, and energy storage, along with a quantitative analysis of the transition between various melting regimes and temporal fluctuations in the performance parameters. The findings demonstrate that the mutual orientation between the directions of incoming heat flux and gravity, as well as the value of the latter, significantly affect features of the convective motion in the liquid phase, as well as the entire thermally driven heat transfer within the domain. In particular, for the oppositely directed gravity and heat flux, the melted fluid closely resembles Rayleigh-Bénard convection with the presence of multicellular flow structures, while at other orientation angles, except for a co-directed gravity and heat flux case, a circular convective motion of the melted fluid takes place. The results of numerical simulations reveal declining melting rates as the mutual orientation of gravity and heat flux changes from opposite to co-directed and vice versa. The low gravity conditions delay the onset of convection-driven melting, reducing the melting rate significantly.

Liquid hydrogen tank chill and no-vent fill prediction using computational fluid dynamics

Cryogenic tank chill and fill is an important cryogenic fluid management technology that supports and enables many of NASA’s long-duration space missions. For no-vent fill, the receiver tank pressure remains below the supply tank pressure during the entire duration of the fill so that the tank does not require venting. This is especially advantageous for tank fill operations in low gravity where the position of the liquid is not always known and venting the tank may cause loss of propellant by venting liquid. In lieu of expensive tests conducted on-orbit, accurate computational models capable of predicting receiver tank pressure during cryogenic propellant tank fill may be used to reduce system and propellant mass as well as mission risk. However, these numerical models must be validated or anchored to test data. This study presents computational fluid dynamics (CFD) models with conjugate heat transfer that are used to predict a liquid hydrogen tank chill and no-vent fill ground test conducted at Lewis Research Center (now Glenn Research Center) in 1991. The specific test case chosen for model validation implemented an upward-facing jet near the bottom of a cylindrical 34 liter tank. CFD predictions are compared to experimental measurements of tank pressure, fill level, and wall temperature. The CFD results show reasonable agreement to the test data but overpredict the pressure collapse near the end of the fill despite the liquid jet penetrating the liquid-vapor interface.

Horizontal running inside circular walls of Moon settlements: a comprehensive countermeasure for low-gravity deconditioning?

Long-lasting exposure to low gravity, such as in lunar settlements planned by the ongoing Artemis Program, elicits muscle hypotrophy, bone demineralization, cardio-respiratory and neuro-control deconditioning, against which optimal countermeasures are still to be designed. Rather than training selected muscle groups only, 'whole-body' activities such as locomotion seem better candidates, but at Moon gravity both 'pendular' walking and bouncing gaits like running exhibit abnormal dynamics at faster speeds. We theoretically and experimentally show that much greater self-generated artificial gravities can be experienced on the Moon by running horizontally inside a static 4.7 m radius cylinder (motorcyclists' 'Wall of Death' of amusement parks) at speeds preventing downward skidding. To emulate lunar gravity, 83% of body weight was unloaded by pre-tensed (36 m) bungee jumping bands. Participants unprecedentedly maintained horizontal fast running (5.4-6.5 m s-1) for a few circular laps, with intense metabolism (estimated as 54-74 mlO2 kg-1 min-1) and peak forces during foot contact, inferred by motion analysis, of 2-3 Earth body weight (corresponding to terrestrial running at 3-4 m s-1), high enough to prevent bone calcium resorption. A training regime of a few laps a day promises to be a viable countermeasure for astronauts to quickly combat whole-body deconditioning, for further missions and home return.

Comparative Studies on Effects of Simulated Microgravity on Growth and Photosynthetic Parameters in Rice and Mungbean

Microgravity or low gravity environment of space can be simulated on Earth by using clinorotation with appropriate speed of rotation. Previous reports show that microgravity environment (real or simulated) affects growth, chlorophyll content and photosynthetic performance in different plants. However, most of the reports showed variation in results. Earlier studies carried out on simulated microgravity (SMG) using clinorotation in our laboratory showed increase in growth, chlorophyll content and various yield attributes in case of laboratory and field grown rice. Subsequent studies were carried out on mungbean seedlings. In the present work, comparative aspects of these studies are reported. Results of the present study showed increase in growth, chlorophyll content and chlorophyll fluorescence parameters in SMG samples as compared to control samples in rice and mungbean seedlings. Interestingly, percentage of enhancement in growth, chlorophyll content and chlorophyll fluorescence parameters of SMG samples is significantly higher in rice (monocotyledonous) seedlings as compared to mungbean (dicotyledonous).

One-dimensional modelling of air injection into abandoned oil fields for heat generation

With the global drive for net-zero emissions, it has never been more important to find clean energy sources. There are thousands of abandoned oilfields worldwide with the potential to be reactivated to produce clean energy with air injection and subsequent waste fluid sequestration. Air injection, and the development of a fire-front, may be used with enhanced geothermal systems by taking advantage of the inherent increase in heat and pressure. Conventionally used as an enhanced oil recovery technique, air injection has gained the reputation of being a high-risk intervention due to the many failures in its history. Knowledge of how petrophysical rock properties and oil physical and chemical properties control the consequences of air injection is key to optimzing the selection of late-life, or even abandoned oilfields for use in such systems. Here we use one-dimensional modelling to test the effect of varying porosity, permeability, oil viscosity and API gravity on the success of air injection. Modelling shows that the most important factor controlling temperature is the porosity of the reservoir, followed by the API gravity and then the viscosity of the oil. The most important factors controlling velocity of the fire-front are API gravity followed by oil viscosity. We show that reservoirs with high porosity and low permeability with high viscosity and low API gravity oil reach the highest fire-front temperatures. The significance of this work is that it provides several geoscience-related criteria to rank possible candidate reservoirs for reactivation and clean energy generation via air injection: the best candidates will have the highest total porosity, relatively low permeability, highest oil viscosity and lowest API gravity, such fields can then move on to bespoke and more complex simulations.

Aligned fractures on asteroid Ryugu as an indicator of thermal fracturing

Context. Asteroid and comet surfaces are exposed to a complex environment that includes low gravity, high temperature gradients, and a bombardment of micrometeorites and cosmic rays. Surface material exposed to this environment evolves in a specific way depending on various factors such as the bodies’ size, heliocentric distance, and composition. Fractures in boulders, as seen on asteroid Ryugu, can help to determine and constrain the dominant processes eroding small-body surface materials. It is also possible to estimate fracture growth timescales based on the abundance and length of fractures in boulders. Aims. We analyse the number, orientation, and length of fractures on asteroid Ryugu to establish the relation between the fractures and the processes that may have formed them. We also compare our results to similar investigations conducted on other small bodies and estimate the timescale of fracture growth. Methods. 198 high-resolution Hayabusa2 images of asteroid Ryugu suitable for our fracture analysis were selected and map-projected. Within these images, fractures in boulders were manually mapped using the QGIS software. The fracture coordinates were extracted and the fractures’ orientation and length were computed for 1521 identified fractures. Results. Fractures in boulders on asteroid Ryugu are found to be preferentially north-south aligned, suggesting a formation through thermal erosion. Modeling the fracture length indicates a fracture growth timescale of 30 000 to 40 000 yr, slightly younger than ages found previously for asteroid Bennu. The errors in these ages, due to uncertainties about the thermophysical parameters used in this model, are substantial (−33 000 yr +250 000 yr). However, even with these large errors, the model suggests that thermal fracturing is a geologically fast process. These times are not too dissimilar to those quoted in the literature for Ryugu and Bennu, since similar thermophysical material parameters for Ryugu and Bennu seem likely.

Fully Endoscopic Minimally Invasive Trans-Eyebrow Supraorbital Translaminar Approach to Third Ventricle Craniopharyngiomas: Technical Nuances and Stepwise Illustrative Description

BackgroundTraditional microsurgical approaches for addressing intraventricular craniopharyngioma pose limited access to the retrochiasmatic area and tumors with significant lateral or rostrocaudal extensions. Extended endoscopic endonasal approaches can effectively overcome many of limitations, yet they require a favorable angle between the optic chiasm and pituitary gland, as well as the involvement of the third ventricle floor by the tumor. MethodsHerein, the authors describe the surgical nuances of a keyhole technique for resecting third ventricle craniopharyngiomas via a fully endoscopic minimally-invasive trans-eyebrow supraorbital translaminar approach (ESOTLA). A case description detailing the approach’s application is provided, along with a series of cadaveric photographs to highlight the relevant anatomy and step-by-step dissection process. ResultsThe patient is a 44-year-old man who presented with polyuria, low urine specific gravity, hypogonadism, and hypopituitarism. Brain MRI revealed a solid-cystic heterogeneous-enhanced retrochiasmatic mass within the third ventricle, consistent with craniopharyngioma. A one-stage ESOTLA was indicated based on the narrow corridor between the pituitary gland and optic chiasm and the high functional status of the patient. Near-total resection was achieved, and no new postoperative neurologic or endocrine deficit was observed. Targeted therapy was implemented based on the histologic result, and the most recent surveillance MRI showed no evidence of the residual tumor. ConclusionsBy combining a keyhole approach with variable-angle endoscopic visualization through a smaller bony and soft tissue exposure, ESOTLA can provide enhanced illumination within the third ventricle, potentially addressing cosmetic concerns and limited exposure area and angle of freedom associated with its conventional microsurgical counterpart.

Development of Composite Materials Using Magnesium Matrix with Variations in the Addition of Volume Fractions of Nano-Al2O3 Reinforcement Results of the Stir Casting Method

Magnesium matrix composites were developed as a form of material selection that can save fuel use due to excess magnesium, which has very low specific gravity and still has good mechanical properties. In this study, a magnesium matrix composite with nano-Al2O3 reinforcement was successfully fabricated using the stir casting method. When compared with magnesium monolithic, the addition of nano-Al2O3 particles of 0.05, 0.10, 0.15, 0.20, and 0.25 %Vf in magnesium composite casting was investigated to improve the mechanical properties of Mg/nano-Al2O3 composites. Magnesium composites with 0.20% Vf reinforcement were found to be the best composition of impact price, wear rate, density, and porosity. This is because the more reinforcement given, the more mechanical properties increase, but the agglomeration tendency of nano-Al2O3 particles is higher so that at a composition of 0.25 %Vf, there is a mechanism anomaly because the reinforcement carried out is less homogeneous. In addition to the number of amplifiers, the improvement of mechanical properties is influenced by the fabrication process, i.e. stir casting. This study uses chemical characterization of OES, EDS, and XRD, hard damage, impact, wear, density and porosity testing, and metallographic observations using OM and SEM.

Direct ink writing of viscous inks in variable gravity regimes using parabolic flights

Additive manufacturing (AM) has significant utility for off-planet fabrication where dedicated infrastructure is severely limited, weight reduction and in situ resource utilization is desirable, and demands for complex systems are high. Direct ink writing (DIW) is a useful AM technique since it enables the deposition of a broad set of materials and the co-printing of multiple materials simultaneously. This allows for the fabrication of complex functional devices and systems in addition to structural objects. To evaluate this technique for space applications, this study characterized DIW in low gravity environments. Parabolic flights were used to simulate Martian, Lunar, and Micro gravity, and the effects that these 3 gravity regimes have on two critical print performance parameters, drooping and slumping, was evaluated using viscous paste inks deposited with an auger-driven extrusion head. In the drooping case, bridging structures were printed across gaps without support material, and the deformation was monitored. In the slumping case, a wall was printed through sequential layer deposition, and the vertical displacement of each layer under reduced gravity was explored. As expected, we found that a reduction in apparent gravity led to a decrease in the droop of a printed line, and as apparent gravitational acceleration is decreased its impact on the magnitude of drooping becomes less significant. For wall structures printed in simulated Lunar or Martian gravity regimes, the total structure height was found to be similar to that of a structure printed under Earth's gravitational conditions. In contrast, for prints performed in microgravity, it was found that slumping was significantly reduced and structure height was larger. These results provide experimental data to enable the design and optimization of appropriate structures and tool paths for printing objects using DIW for off-planet manufacturing.

Study on the mechanical model of footpad-terrain for walking robot moving in low gravity environment

Due to the low gravity environment and the influence of complex terrain condition in deep space exploration, wheeled mobile systems are prone to meet motion abnormalities. The excellent motion performance of walking robot is more suitable for the future deep space exploration, but the robots are prone to occur large sinkage in soft terrain. A mechanical model is built to describe a gait cycle of a walking robot under soft terrain and low gravity environment. The force on the footpad during actual movement in a gait cycle is obtained through a single-legged test bench under the simulated planet terrain. The effects of sizes of footpads, sinkage and other factors are explored. The results indicate that the larger the size of the footpad, the greater the horizontal force on the footpad, the better the motion performance is. But as the size of footpad increase, the vertical force decreases which indicates poor support performance. By comparing and analyzing the model values with the experimental values, for the horizontal force FT, the average errors for the average force and peak force are 10.05% and 7.76%. The average errors for average force and peak force are 5.19% and 5.86% for vertical force FN. The values are not significantly different from the model values and experimental values which indicates that the mechanical model has high accuracy. The obtained mechanical model can provide a reference for the motion of walking robots in complex low gravity environment.

Изучение влияния содержания гафния и эрбия на формирование микроструктуры при литье алюминиевого сплава 1590 в медный кокиль

Introduction. High-magnesium aluminum alloys are widely used in the automotive, building and aerospace industries due to its low specific gravity and high strength. The characteristics of such alloys can be improved by small additions of scandium and zirconium. However, scandium is very expensive, so in new generation alloys its amount is tended to be reduced. In the recently developed 1590 aluminum alloy, this was achieved by addition of erbium and hafnium. The objective of the paper is to study the effect of erbium and hafnium concentrations on the modification of the cast structure in 1590 aluminum alloy at high solidification rates. Research Methods. The paper investigates the microstructure, chemical composition and size of intermetallic compounds in specimens from ten alloy 1590 modifications with different hafnium and erbium contents cast into a copper chill mold with a solidification rate of 10 °C/sec. The grain structure was studied using an optical microscope. The chemical composition and size of the intermetallic phases were studied using a Tescan Vega 3 scanning electron microscope. Results and discussion. It is established that as the amount of hafnium and erbium increases, the cast structure is modified. In general, grain refinement with the addition of hafnium and erbium can be explained by a higher degree of supercooling between the solid and liquid phases. At a hafnium content of 0.16 %, the dendritic structure begins to transform into an equiaxed grain structure. This transformation can be explained by the appearance of primary intermetallic compounds of the Al3Sc type in the liquid phase. Such intermetallic compounds are identified at a concentration of erbium and hafnium equal to 0.16 %. Moreover, in all alloys eutectic intermetallic compounds are identified that contained manganese and iron and had no effect on the cast structure. Comparison with previously obtained results on the grain size of specimens cast into a steel mold shows that with higher solidification rate, the structure modification in 1590 alloy is getting less efficient. This is explained by an increase in the concentration of transition elements in the solid solution, primarily scandium, necessary for the formation of primary intermetallic particles.

Experimental Study on the Performance of Frictional Drag Reducer with Low Gravity Solids

Reducing energy consumption during drilling operations is beneficial to both the environment and economy. Frictional drag reducers (FDR) are widely used to reduce the energy loss caused by turbulent flow. FDR plays an important role in flow lines as they can reduce the frictional pressure drop effectively, and benefit the selection of circulating fluid and pump. However, several factors can influence the performance of FDR, including fluid additives and incorporated solids, such as drill solids. Thus, the main objective of this paper is to study the influence of low gravity solids (LGS) on the performance of the FDR. This paper is mainly based on experimental study. The experimental work contains two parts: rheology characterization and flow loop tests. Rheology characterization tests were performed to calculate the flow consistency index (K) and flow behavior index (n). Flow loop experiments were conducted for two geometry (0.457 inch and 0.797 inch diameter). Xanthan gum was used as a fractional drag reducer. Bentonite and quartz sand were added as low gravity solids. Three designed water-based mud systems are tested for drag reduction efficiency of Xanthan gum. Flow rate of the mud varied from 3 gpm to 16 gpm. Concentration of Xanthan ranged from 0.1 lbm/bbl to 0.6 lbm/bbl. Low weight solids were added with weight percentage of 0.5%, 1%, 2% and 2.5%. The result shows that xanthan gum is an efficient drag reducer for adequate reasons. Firstly, even at al low concentration, xanthan gum shows high resistance to degradation. Secondly, the maximum drag reduction with xanthan gum is up to 70.54% with a concentration of 0.6 lbm/bbl. However, the existence of different low gravity solids influence the efficiency of xanthan gum in different styles. Experiment results indicate that the higher the weight percentage of bentonite, the lower the drag reduction effectiveness. While with the increasing concentration of quartz sand, the drag reduction does not show an intense change. This study intents to give an instructive guidance on usage of frictional drag reducers in drilling mud system design. Removal of low gravity solids from the mud is difficult, which pose a danger to the drilling fluid. By understanding the effectiveness of FDR, we can reduce energy consumption when irremovable low gravity solids exist. FDR can be used for modifying the mud contents to develop a lower pressure gradient under turbulent flow condition. In the same scenario, adding FDR can suppress turbulent at a constant pressure gradient but with a higher flow rate.

Simulation of Human Movement in Zero Gravity.

In the era of expanding manned space missions, understanding the biomechanical impacts of zero gravity on human movement is pivotal. This study introduces a novel and cost-effective framework that demonstrates the application of Microsoft's Azure Kinect body tracking technology as a motion input generator for subsequent OpenSim simulations in weightlessness. Testing rotations, locomotion, coordination, and martial arts movements, we validate the results' realism under the constraints of angular and linear momentum conservation. While complex, full-body coordination tasks face limitations in a zero gravity environment, our findings suggest possible approaches to device-free exercise routines for astronauts and reveal insights into the feasibility of hand-to-hand combat in space. However, some challenges remain in distinguishing zero gravity effects in the simulations from discrepancies in the captured motion input or forward dynamics calculations, making a comprehensive validation difficult. The paper concludes by highlighting the framework's practical potential for the future of space mission planning and related research endeavors, while also providing recommendations for further refinement.

Müller cells are activated in response to retinal outer nuclear layer degeneration in rats subjected to simulated weightlessness conditions.

JOURNAL/nrgr/04.03/01300535-202507000-00032/figure1/v/2024-09-09T124005Z/r/image-tiff A microgravity environment has been shown to cause ocular damage and affect visual acuity, but the underlying mechanisms remain unclear. Therefore, we established an animal model of weightlessness via tail suspension to examine the pathological changes and molecular mechanisms of retinal damage under microgravity. After 4 weeks of tail suspension, there were no notable alterations in retinal function and morphology, while after 8 weeks of tail suspension, significant reductions in retinal function were observed, and the outer nuclear layer was thinner, with abundant apoptotic cells. To investigate the mechanism underlying the degenerative changes that occurred in the outer nuclear layer of the retina, proteomics was used to analyze differentially expressed proteins in rat retinas after 8 weeks of tail suspension. The results showed that the expression levels of fibroblast growth factor 2 (also known as basic fibroblast growth factor) and glial fibrillary acidic protein, which are closely related to Müller cell activation, were significantly upregulated. In addition, Müller cell regeneration and Müller cell gliosis were observed after 4 and 8 weeks, respectively, of simulated weightlessness. These findings indicate that Müller cells play an important regulatory role in retinal outer nuclear layer degeneration during weightlessness.

Along-strike break-up variations of the continent–ocean transition zone in the northern South China Sea

We analyse how the potential field and deep structures of the continent–ocean transition (COT) zone in the northern South China Sea vary along-strike with the aim of understanding the break-up styles and synrift magmatism in this region. The high free-air gravity anomaly and the accompanying basement structures are evidence of significant mantle upwelling and serpentinization in the northeastern COT zone. The top-basement of the COT is uplifted and rough, but gradually retrogrades into a relatively flat and low relief towards the mid-northern margin, where the reduced gravity anomaly reflects subdued mantle upwelling, but perhaps stronger synrift magmatism. On the northwestern margin, the low gravity anomaly suggests fairly limited mantle upwelling, but more synrift magmatic intrusions in the crust; the top-basement of the COT zone is smooth and slightly deepened. The width of the COT zone is mostly <30 km and the oldest legible magnetic anomaly (C11r) within the zone is related to the final continental break-up. The seaward limit of the COT should be relocated further south beyond anomaly C11r, pointing to a very narrow zone of true oceanic lithosphere in the NW Sub-basin. The coexistence of mantle upwelling/serpentinization, magmatic underplating and volcanism on top of the COT during continental break-up characterizes a typical intermediate rifted margin, although there are significant along-strike variations. Thematic collection: This article is part of the Emerging knowledge on the tectonics of the South China Sea collection available at: https://www.lyellcollection.org/topic/collections/south-china-sea

Fates of a Nonwetting Slug in Tapered Microcapillaries under Gravity and Zero Gravity Conditions: Dynamics, Asymptotic Equilibrium Analysis, and Computational Fluid Dynamics Verifications.

It has been determined experimentally and numerically that a nonwetting slug in a tapered capillary tube, under the sole action of capillary force, self-propels itself toward the wider end of the tube until an equilibrium state is reached. The aim of this work is to highlight the state of the slug at equilibrium in terms of configuration and location. Furthermore, it turns out that gravity adds richness to this phenomenon, and more fates become possible. A modified Bond number is developed that determines the relative importance of gravity and capillarity for this system. According to the magnitude of the Bond number, three more fates are possible. Therefore, in a tapered capillary tube held vertically upward with its wider end at the top, in the absence of gravity or under microgravity conditions, the nonwetting slug moves upward toward the wider end of the tube until it reaches equilibrium with the two menisci part of a single sphere. The location of the slug at equilibrium in this case represents the farthest fate among the other fates. When gravity exists yet capillarity dominates, the slug still moves upward toward the wider end. However, in this case, the two menisci become parts of two different spheres of different curvatures. For this scenario, the slug climbs upward but reaches a lower level compared to the previous scenario. On the other hand, when gravity dominates, the slug experiences a net downward pull toward the narrower end of the tube and starts to move in the direction of gravity until capillary force establishes a balance, then it stops. When gravity sufficiently dominates, it pulls the slug downward until it completely drains off the tube. A computational fluid dynamics (CFD) analysis is conducted in order to build a framework for verification exercises. Excellent agreements between the results of the developed model and the CFD analysis are obtained. A fate map and a scheme are developed to identify these four fates based on two Bond numbers; namely, the initial Bond number and that associated with the slug when it is at the exit.