Search Results (477)

Spaceflight induces a wide array of effects on the human body, notably including pathological changes mediated by alterations in gravity. Abnormalities in the formation of primary cilia (ciliogenesis) can lead to cell cycle arrest and decreased epithelial cell proliferation, thereby delaying wound healing. To investigate the effect of microgravity on ciliogenesis in bronchial epithelial cells, we used a 3D clinostat to generate simulated microgravity (SMG) conditions. When BEAS-2B bronchial epithelial cells were exposed to SMG for 72 h, their proliferation was significantly reduced. The expression of Ki-67, which is not expressed in the G0 phase, decreased under SMG. Conversely, the expression of p27, which is expressed in the G0 and G1 phases, increased under SMG. These results suggest that SMG led to an increase in the number of cells in the quiescent phase. When the mRNA expressions of ARL13B (a marker of cilia assembly) and disassembly-related genes (Aurora A, NDE1, HDAC6, and DVL2) were evaluated, SMG upregulated ciliary assembly markers and downregulated disassembly markers. In addition, SMG increased the cilia length and number of ciliated cells. These findings suggest that SMG contributes to reduced cell proliferation through cell cycle arrest by disrupting normal ciliogenesis. Our findings indicate that SMG could delay lung injury by decreasing cell proliferation. Full article

This study investigated the influence of spatial orientation on bead morphology and molten pool dynamics during cold metal transfer wire arc additive manufacturing (CMT-WAAM). Experiments in horizontal, transverse, vertical-down, and vertical-up orientations under varying wire feed speeds revealed that increasing the feed rate improved bead uniformity and reduced defects in horizontal deposition, while gravity-induced asymmetry dominated non-horizontal orientations. Transverse cladding produced tilted, uneven beads with reduced penetration; vertical-down enhanced lateral spreading but resulted in the shallowest weld depth; vertical-up limited spreading, yielding narrow beads with higher reinforcement. Optimal cladding quality was achieved at a wire feed speed of 6.7 m/min for the first layer, with a reduced heat input applied for subsequent layers to minimize residual stress and deformation. Numerical simulations further elucidated transient temperature and flow fields. Heat accumulation and dissipation varied with orientation and layer sequence: horizontal deposition formed deep, symmetric pools; transverse deposition generated asymmetric vortices and uneven solidification; vertical-up deposition caused upward counterflow with restricted spreading; vertical-down promoted rapid spreading and faster solidification. A detailed comparison between simulated and experimental temperature distributions and cross-sectional profiles demonstrated excellent agreement, thereby validating the accuracy and predictive capability of the developed model. This integrated experimental-numerical approach provided a comprehensive understanding of orientation-dependent molten pool behavior and offered a robust framework for optimizing process parameters, enhancing dimensional accuracy, and controlling defects in CMT additive manufacturing. Full article

Atom interferometer (AI)-based dynamic gravimeters enable high-precision absolute gravity measurements, which are crucial for applications in geophysics, navigation, resource exploration, and metrology. Understanding their underlying mechanisms and minimizing measurement noise is essential for enhancing performance. This work investigates gravity-measurement noise in AI-based systems induced by the dead time of the classical accelerometer. Using actual dynamic gravity-measurement data, we demonstrate that a dead time of 0.12 s introduces significant gravity-measurement noise, reaching 8 mGal. To elucidate the mechanism of this noise, we derive a frequency-domain formula, identifying high-frequency aliasing as its source. Analysis of the derived expressions indicates that reducing the dead-time duration and suppressing the acceleration’s high-frequency noise are effective strategies for mitigating this noise. This work provides significant insights into noise analysis and the future design of AI-based dynamic gravimeters. Full article

I revisit some arguments that motivate infrared/ultraviolet (IR/UV) mixing, a mechanism such that ultraviolet quantum-gravity structures produce novel features also in a far-infrared regime. On the conceptual side, I highlight in particular an apparently general connection between IR/UV mixing and departures from the standard relativistic symmetries of classical spacetimes. In addition to its conceptual appeal, interest in IR/UV mixing has also been driven by the availability of some opportunities for experimental testing, and my main focus is on phenomenological models of IR/UV mixing that can provide guidance to the experimental efforts. While usually each formulation of IR/UV mixing is investigated within an isolated research program, some parts of my analysis point to possible connections among different formulations and with other quantum-gravity studies. Full article

To address the performance degradation of large deployable antennas mounted on floating offshore platforms, this paper presents a systematic investigation into their dynamic response and surface precision evolution under typical sea-based excitations. A high-fidelity finite element model of a truss-type deployable antenna is established, with the root mean square (RMS) error serving as the primary metric for the quantitative assessment of surface precision. Through a comparative analysis of structural behaviors under static loads (e.g., gravity and wind) and dynamic excitations (e.g., heave and roll motions), the antenna’s response characteristics under complex loading conditions are revealed. The results indicate that the peak surface precision error induced by dynamic excitation occurs during the initial transient phase, rather than the steady-state phase. Furthermore, the structure exhibits high sensitivity to roll motion parameters, with a 90° roll azimuth identified as the worst-case scenario. The RMS value of the surface error is also found to increase linearly with motion amplitude. This study successfully quantifies the influence of the marine environment on antenna performance, providing a theoretical basis for the optimization design and performance evaluation of offshore antenna structures. Full article

We investigate the effect of general relativity on the Sitnikov problem. The Sitnikov problem is one of the simplest three-body problems, in which the two primary bodies (a binary system) have equal mass m and orbit their barycenter, while the third body is treated as a test particle under Newtonian gravity. The trajectory of the test particle is perpendicular to the orbital plane of the binary (along z-axis) and passes through the barycenter of the two primaries. To study the general relativistic contributions, we first derive the equations of motion for both the binary and the test particle based on the first post-Newtonian Einstein–Infeld–Hoffmann equation, and integrate these equations numerically. We examine the behavior of the test particle (third body) as a function of the orbital eccentricity of the central binary e, the dimensionless gravitational radius $\lambda$, which characterizes the strength of general relativistic effect, and the initial position of the test particle ${\overline{z}}_0$. Our numerical calculations reveal the following; as general relativistic effects $\lambda$ increase and the eccentricity e of the binary orbit grows, the distance $\overline{r}$ between the test particle and the primary star undergoes complicated oscillations over time. Consequently, the gravitational force acting on the test particle also varies in a complex manner. This leads to a resonance state between the position $\overline{z}$ of the test particle and the distance $\overline{r}$, causing the energy E of the test particle to become $E\ge 0$. This triggers the effective ejection of the test particle due to the gravitational slingshot effect. In this paper, we shall refer to this ejection mechanism of test particle as the “Sitnikov mechanism.” As a concrete phenomenon that becomes noticeable, the increase in general relativistic effects and the eccentricity of the binary orbit leads to the following: (a) ejection of test particles from the system in a shorter time, and (b) increasing escape velocity of the test particle from the system. As an astrophysical application, we point out that the high-velocity ejection of test particles induced by the Sitnikov mechanism could contribute to elucidating the formation processes of astrophysical jets and hyper-velocity stars. Full article

The rational utilization of cultivated land resources is central to ensuring both ecological and food security in the Yangtze River Economic Belt (YREB), holding strategic significance for regional sustainable development. Using panel data from 2010 to 2023 for 130 cities in the YREB, this study examines a spatial correlation network (SCN) for non-grain land use (NGLU) and its driving forces via a modified gravity model, social network analysis (SNA), and quadratic assignment procedure regression. The results show the following: (1) The risk of NGLU continues to increase, with the spatial pattern evolving from a “single-peak right deviation” pattern to a “multi-peak coexistence” pattern featuring three-level polarization and gradient transmission, primarily driven by economic potential disparities. (2) The SCN has increased in density, but its pathways are relatively singular. Node functions exhibit significant differentiation, with high-degree nodes forming “control poles”, high-intermediate nodes dominating cross-regional risk transmission, and low-proximity nodes experiencing “protective marginalization”. Node centrality distribution is highly connected with the regional development gradient. (3) The formation of the spatial network is jointly driven by multiple factors. Geographical proximity, economic potential differences, comparative benefit differences, non-agricultural employment differences, and factor mobility all positively contribute to the spillover effect. Conversely, implementing cultivated land protection policies and the regional imbalance in local industrial development path dependence significantly inhibit the non-grain trend. This study further reveals that a synergistic governance system characterized by “axial management, node classification, and edge support” should be recommended to prevent the gradient risk transmission induced by economic disparities, providing a scientific basis for achieving sustainable use of regional cultivated land resources and coordinated governance of food security. Full article

Modified gravity theories with a nonminimal coupling between curvature and matter offer a compelling alternative to dark energy and dark matter by introducing an explicit interaction between matter and curvature invariants. Two of the main consequences of such an interaction are the emergence of an additional force and the non-conservation of the energy–momentum tensor, which can be interpreted as an energy exchange between matter and geometry. By adopting this interpretation, one can then take advantage of many different approaches in order to investigate the phenomenon of gravitationally induced particle creation. One of these approaches relies on the so-called irreversible thermodynamics of open systems formalism. By considering the scalar–tensor formulation of one of these theories, we derive the corresponding particle creation rate, creation pressure, and entropy production, demonstrating that irreversible particle creation can drive a late-time de Sitter acceleration through a negative creation pressure, providing a natural alternative to the cosmological constant. Furthermore, we demonstrate that the generalized second law of thermodynamics holds: the total entropy, from both the apparent horizon and enclosed matter, increases monotonically and saturates in the de Sitter phase, imposing constraints on the allowed particle production dynamics. Furthermore, we present brief reviews of other theoretical descriptions of matter creation processes. Specifically, we consider approaches based on the Boltzmann equation and quantum-based aspects and discuss the generalization of the Klein–Gordon equation, as well as the problem of its quantization in time-varying gravitational fields. Hence, gravitational theories with nonminimal curvature–matter couplings present a unified and testable framework, connecting high-energy gravitational physics with cosmological evolution and, possibly, quantum gravity, while remaining consistent with local tests through suitable coupling functions and screening mechanisms. Full article

The fabrication of support-free structures in pellet additive manufacturing (PAM) is severely limited by gravity-induced sagging, a phenomenon lacking predictive, physics-based models. This study introduces and validates a numerical model for the thermofluid dynamics of sagging, aiming to correlate process parameters with filament deflection. A predictive finite element (FE) model incorporating temperature-dependent non-Newtonian material properties and heat transfer dynamics has been developed. This was validated via a systematic experimental study on a desktop-scale PAM 3D printer investigating nozzle temperature, printhead speed, screw speed and fan cooling, using polylactic acid (PLA) as a printing material. Findings show that process parameter optimization can reduce bridge deflection by 64.91%, with active fan cooling being the most dominant factor due to accelerated solidification. Increased printhead speed reduced sagging, whereas higher screw speeds and extrusion temperature showed the opposite effect. The FE model accurately replicated these results and further revealed that sagging ceases once the filament cools below its minimum flow temperature (approximately 150–160 °C for PLA). This validated model provides a robust foundation for tuning process parameters, unlocking effective support-free 3D printing in PAM. Full article

Surface subsidence and seepage damage in surrounding soils induced by leakage from municipal water supply pipelines pose significant risks to urban infrastructure. To clarify how leakage water diffuses in unsaturated soils and to assess seepage damage potential, this study established a numerical model based on the Richards equation combined with the van Genuchten (VG) model. The model was validated against physical model tests using remolded Q3 loess, ensuring consistency in soil parameters and leakage conditions. Simulation results reveal that soil saturation evolution follows three stages—initial, rising, and stable—with preferential flow paths forming above the leakage point before gradually evolving into radial diffusion controlled by both pressure and gravity. The extent of the saturated zone increases with pipeline pressure, but the enhancement effect diminishes as pressure rises, reflecting the nonlinear water-retention characteristics of loess. Seepage damage risk was evaluated using the Terzaghi critical hydraulic gradient criterion. The results show that higher pressures enlarge the critical zone more rapidly, yet its ultimate radius stabilizes within approximately 2.3 m around the leakage point. Moreover, this study proposes that potential seepage damage may occur once effective saturation reaches about 85%, corresponding to the air-entry value of loess, thus providing a more conservative criterion for engineering risk assessment. Overall, the validated Richards-based numerical model reproduces the key features of leakage-induced unsaturated diffusion and offers practical guidance for identifying seepage-prone zones and mitigating subsidence hazards in municipal water supply systems. Full article

Sediment erosion under turbulent wave action is a highly dynamic process shaped by the interaction between wave properties and sediment characteristics. Despite extensive empirical research, the underlying mechanisms of wave-induced erosion remain insufficiently understood, particularly regarding the threshold energy required for particle mobilization and the factors governing displacement patterns. This study employed a custom-built wave flume and a 3D-printed sampler to examine sediment behavior under controlled wave conditions. Rounded glass beads, chosen to eliminate the influence of particle shape, were used as sediment analogs with a similar specific gravity to natural sand. Ten experiments were conducted to systematically assess the effects of particle size, particle number, input voltage (wave power), and water depth on sediment response. The results revealed that (1) only a fraction of particles were mobilized, with the remainder forming stable interlocking structures; (2) the number of displaced particles increased with particle size, particle count, and water depth; (3) a threshold wave power is required to initiate erosion, though buoyancy under shallow conditions reduces this threshold; and (4) wave steepness, rather than voltage or wave height alone, provided the strongest predictor of sediment displacement. These findings highlight the central role of wave steepness in erosion modeling and call for its integration into predictive frameworks. The study concludes with methodological limitations and proposes future research directions, including expanded soil types, large-scale flume testing, and advanced flow field measurements. Full article

Cryogenic propellant sloshing presents significant challenges in aerospace systems, inducing vehicle instability, structural fatigue, energy losses, and complex thermal management issues. This review synthesizes experimental, analytical, and numerical advances with an emphasis on energy dissipation and conversion efficiency in propellant storage and transfer. Recent developments in computational fluid dynamics (CFD) and AI-driven digital-twin frameworks are critically examined alongside the influences of tank materials, baffle configurations, and operating conditions. Unlike conventional fluids, cryogenic propellants in microgravity and within composite overwrapped pressure vessels (COPVs) exhibit unique thermodynamic and dynamic couplings that remain only partially characterized. Prior reviews have typically treated these factors in isolation; here, they are unified through an integrated perspective linking cryogenic thermo-physics, reduced-gravity hydrodynamics, and fluid–structure interactions. Persistent research limitations are identified in the areas of data availability, model validation, and thermo-mechanical coupling fidelity, underscoring the need for scalable multi-physics approaches. This review’s contribution lies in consolidating these interdisciplinary domains while outlining a roadmap toward experimentally validated, AI-augmented digital-twin architectures for improved energy efficiency, reliability, and propellant stability in next-generation aerospace missions. Full article

To overcome the production bottleneck induced by the high viscosity of extra-heavy oil and resolve the issues of limited efficiency in traditional thermal oil recovery methods (including cyclic steam stimulation (CSS), steam flooding, and steam-assisted gravity drainage (SAGD)) as well as the fragmentation of existing viscosity reducer evaluation systems, this study establishes a multi-dimensional evaluation system for the effectiveness of viscosity reducers, with stage-averaged remaining oil saturation as the core benchmarks. A “1D static → 2D dynamic → 3D synergistic” progressive sequential experimental design was adopted. In the 1D static experiments, multi-gradient concentration tests were conducted to analyze the variation law of the viscosity reduction rate of viscosity reducers, thereby screening out the optimal adapted concentration for subsequent experiments. For the 2D dynamic experiments, sand-packed tubes were used as the experimental carrier to compare the oil recovery efficiencies of ultimate steam flooding, viscosity reducer flooding with different concentrations, and the composite process of “steam flooding → viscosity reducer flooding → secondary steam flooding”, which clarified the functional value of viscosity reducers in dynamic displacement. In the 3D synergistic experiments, slab cores were employed to simulate the SAGD development process after multiple rounds of cyclic steam stimulation, aiming to explore the regulatory effect of viscosity reducers on residual oil distribution and oil recovery factor. This novel evaluation system clearly elaborates the synergistic mechanism of viscosity reducers, i.e., “chemical empowerment (emulsification and viscosity reduction, wettability alteration) + thermal amplification (steam carrying and displacement, steam chamber expansion)”. It fills the gap in the existing evaluation chain, which previously lacked a connection from static performance to dynamic displacement and further to multi-process synergistic adaptation. Moreover, it provides quantifiable and implementable evaluation criteria for steam–chemical composite flooding of extra-heavy oil, effectively releasing the efficiency-enhancing potential of viscosity reducers. This study holds critical supporting significance for promoting the efficient and economical development of extra-heavy oil resources. Full article

Although hypergravity may influence cardiac mechanosensitivity, the effects on specific ion channels remain inadequately understood. This research examined the effects of long-term hypergravity on the functional activity and transcriptional expression of mechanosensitive channels (MSCs) in rat ventricular cardiomyocytes. After 14 days of exposure to 4g, rats were subjected to molecular and electrophysiological analyses. Significant remodeling of MSC-encoding genes was revealed by RNA-seq. Trpm7 (+41.23%, p = 0.0073) and Trpc1 (+68.23%, p = 0.0026) were significantly upregulated among non-selective cation channels, while Trpv2 (−62.19%, p = 0.0044) and Piezo2 (−57.58%, p = 0.0079) were significantly downregulated. Kcnmb1 (−47.84%, p = 0.0203) was suppressed, whereas Traak/K2P4.1 showed a strong increase (+239.48%, p = 0.0092), among K⁺-selective MSCs. Furthermore, Kir6.1 was significantly downregulated (−75.8%, p = 0.0085), whereas Kir6.2 was significantly upregulated (+38.58%, p = 0.0317). These results suggest targeted transcriptional reprogramming that suppresses pathways associated with maladaptive Ca²⁺ influx while enhancing Ca²⁺-permeable mechanosensitive channels alongside stabilized K⁺ conductance. At the structural level, cardiomyocytes from hypergravity exposure showed a 44% increase in membrane capacitance, consistent with hypertrophic remodeling, and sarcomere elongation (p < 0.001). Functionally, stretch-activated current (I_SAC) was markedly hypersensitive in patch-clamp analysis: currents were induced at very small displacements (1–2 µm) and were significantly larger under 4–10 µm stretch (222–107% of control values). These findings indicate that chronic hypergravity induces coordinated molecular, structural, and functional remodeling of cardiomyocytes, characterized by increased membrane excitability, compensatory stabilizing mechanisms, and enhanced Ca²⁺ signaling. This demonstrates the flexibility of cardiac mechanotransduction under prolonged gravitational stress, with potential implications for understanding cardiovascular risks, arrhythmias, and hypertrophy associated with altered gravity environments. Full article

Travel policies during crises strongly reshape mobility patterns, raising the challenge of protecting public health while minimizing socio-economic disruption—an essential concern for sustainable development. Most evaluations quantify changes in travel volume, which hampers cross-city comparison and policy monitoring. This study proposes a distance-based sustainability metric—distance equivalence (DE)—that translates policy-induced mobility frictions into interpretable “added distance” within a gravity framework, enabling consistent measurement and monitoring of policy impacts. Using inter-city flows for 358 Chinese cities during the Stay-in-Place for Lunar New Year (SIP) guidance, we map DE, test spatial dependence (Moran’s I; LISA), and apply fuzzy-set Qualitative Comparative Analysis (fsQCA) to identify city-level configurations associated with high DE. DE exhibits significant spatial clustering, concentrating east of the Hu line, where dense urban networks amplify advisory checks. Three recurrent configurations—combining case counts, health-care capacity (hospital beds), and average inter-city distance—are linked to high DE. As a sustainability assessment tool, DE supports adaptive management, region-differentiated strategies, and ex-ante risk assessment for governments, public-health authorities, and transport agencies. The framework generalizes to short-term mobility interventions under crisis conditions, advancing the quantification of policy impacts on sustainable mobility and urban resilience. Full article