Search Results (329)

This paper designs a statistical channel state information-based pinching antenna system for short-packet communication (SPC). To maximize the average maximal achievable rate (MAR) under physical collision-avoidance constraints, we formulate a highly non-convex geometry optimization problem, which is solved by our proposed novel phase-domain proximal policy optimization (PPO) framework. Unlike conventional coordinate-based approaches, the agent operates in a dual-component trigonometric phase domain, and the generated phase actions are mapped to feasible antenna positions via a customized phase-domain action mapping, which fundamentally avoids the $0/2\pi$ phase discontinuity and ensures stable learning. To evaluate the reliability of SPC, we derive a tractable statistical characterization of the received signal-to-noise ratio based on a mixture Gamma approximation over spatially correlated Rician fading channels, leading to a closed-form approximation for the average block error rate (BLER). A bisection search algorithm is further developed to minimize the required blocklength under the target reliability constraint. Simulation results demonstrate that the proposed phase-domain PPO scheme significantly outperforms the conventional algorithms in terms of average MAR, average BLER, and blocklength efficiency, with the performance gain becoming more pronounced as the number of antennas per waveguide increases. Full article

Structural static testing is paramount for validating the structural integrity of critical aerospace components. However, conventional test rigs are often constrained to fixed loading axes and frequently induce parasitic torques. Accurate reproduction of aero-engine pylon flight loads therefore requires a mechanism that combines omnidirectional vector loading, high stiffness, and efficient force transmission. Achieving these coupled requirements is primarily a geometric synthesis problem, yet the associated workspace, stiffness, and load–capacity indices are nonlinear, mutually coupled, and expensive to evaluate over dense pose samples. To address this optimization bottleneck, this work develops a task-specific 6-UPS loading mechanism and a bio-inspired sensitivity-weighted NSGA-II algorithm for its geometric synthesis. Inspired by gene/locus-specific heterogeneity in biological evolution, the algorithm assigns variable-wise search intensities according to design-variable sensitivities, which are estimated using Multivariate Adaptive Regression Splines (MARS). In this way, influential design genes receive stronger local exploitation, whereas less sensitive ones retain broader exploration. Numerical simulations demonstrate that the proposed approach reduces computation time from about 30 h to 3 h relative to direct optimization with the baseline NSGA-II, while simultaneously improving workspace, stiffness, and load-carrying capacity. A hybrid physical prototype was further tested under 240 loaded pose conditions; the system maintained force magnitude errors below 0.64% (63.42 N) and directional deviations below 1.15°. These results support the efficacy of the proposed bio-inspired optimization-based design methodology for high-fidelity static testing of aero-engine pylons under the adopted hybrid setup. Full article

The chemical evolution of simple molecules into higher-order structures, such as amino acids, is a fundamental process occurring throughout the cosmos. Methane (CH₄) serves as a key precursor in this evolutionary sequence and is prevalent on planetary bodies like Mars and Saturn. In these environments, CH₄ is frequently ionized by cosmic radiation, forming the methane radical cation (CH₄⁺). In this study, the ion-molecule reactions between CH₄⁺ and neutral CH₄ (CH₄⁺ + CH₄ → products) were investigated using direct ab initio molecular dynamics (AIMD) simulations to elucidate the underlying reaction mechanisms. Our calculations demonstrate that proton transfer (PT) occurs efficiently, yielding the methanium ion (CH₅⁺) and the highly reactive methyl radical (CH₃): CH₄⁺ + CH₄ → CH₅⁺ + CH₃. Furthermore, the reaction outcomes exhibit a strong dependence on the impact parameter (b). Collisions at very low impact parameters (b = 0–0.2 Å) resulted in non-reactive, billiard-ball-like scattering. Within the range of b = 0.2–3.0 Å, the formation of a long-lived complex, [CH₅-CH₃]⁺, was observed. In the intermediate range of b = 3.0–5.0 Å, a proton-stripping mechanism predominated in PT channel, while collisions at b > 5.0 Å were exclusively non-reactive. The reaction mechanism was qualitatively discussed. These findings provide a detailed atomistic picture of the collision dynamics governing methane-derived molecular evolution in celestial environments. Full article

Background: Missing data, particularly progression-driven dropout, introduces substantial bias in longitudinal oncology studies, directly impacting response classification based on RECIST criteria. While machine learning-based imputation methods are increasingly used, their performance is rarely evaluated in a clinically interpretable framework centered on patient-level endpoints such as Best Overall Response (BOR). Methods: We propose a clinically grounded evaluation framework based on RECIST 1.1 focused on patient-level Best Overall Response classification. Longitudinal tumor trajectories were simulated for 270 patients (1:1, HER2+ and HER2−) across nine follow-up visits using both Gompertz and Stein–Fojo growth models, resulting in 2700 patient-visit observations. Realistic missingness was introduced through a combination of random mechanisms and progression-driven dropout. Three machine learning imputation models, long short-term memory (LSTM), MissForest, and Multiple Imputation (MI) were evaluated under both direct (MAR-based) and non-responder imputation strategies. Performance was assessed using BOR classification metrics, including accuracy and Cohen’s kappa. Result: Across both simulation frameworks, imputation substantially improved BOR classification performance. Under the Gompertz model, accuracy increased from 0.84–0.89 with direct imputation to 0.94–0.99 with non-responder imputation, with corresponding kappa improvements from 0.73–0.82 to 0.90–0.99. Similar trends were observed under the Stein–Fojo model (accuracy: 0.82–0.84 vs. 0.91–0.96; kappa: 0.69–0.72 vs. 0.86–0.94). Across all evaluated methods, NRI improved classification performance by approximately 10 percentage points in accuracy and up to 17 percentage points in kappa. The improvement was observed consistently across both tumor growth models and different missingness scenarios, demonstrating the robustness of the findings. Conclusions: This study demonstrates that successful handling of missing data depends not only on the imputation method itself, but also on the choice of a clinically meaningful endpoint and appropriate estimand strategies aligned with the underlying missing data assumptions. In the METABRIC-derived simulations, clinically informed handling of progression-related missingness substantially improved RECIST-based BOR classification across all evaluated methods, suggesting that appropriate endpoint selection and the corresponding estimand strategy for missing data handling may have a greater influence on classification performance than the choice among the imputation models applied. Full article

This paper develops a unified asymptotic theory for conditional single-index U-statistics and the associated conditional U-processes in the setting of locally stationary functional time series subject to missing-at-random response mechanisms. The proposed framework addresses, within a single nonparametric inferential architecture, three major sources of complexity in modern functional data analysis: infinite-dimensional covariates, smoothly time-varying stochastic dynamics, and incomplete response observations. The methodology is based on a class of kernel-type estimators combining temporal localization, functional single-index smoothing, and inverse-propensity correction. Temporal localization captures the gradual evolution of the underlying regression structure, the single-index projection provides an effective dimension-reduction mechanism for functional covariates, and the propensity adjustment restores the target conditional functional under the MAR sampling scheme. The principal contribution of the paper is the establishment of weak convergence, in a suitable space of bounded functions, for the resulting propensity-adjusted conditional U-process indexed by a general class of measurable kernels. Under absolute regularity conditions, local stationarity assumptions, small-ball probability requirements, entropy restrictions of VC type, and uniform consistency of the propensity-score estimator, the normalized process is shown to converge weakly to a tight centered Gaussian process. The limiting covariance structure explicitly reflects the interaction between temporal smoothing, functional concentration, dependence, and the random loss of responses. In parallel, uniform convergence rates are derived for the associated conditional single-index U-statistic estimators, thereby quantifying the respective contributions of smoothing bias, stochastic fluctuation, local-stationarity approximation error, and missingness-induced variance inflation. A substantial part of the analysis is devoted to the technical difficulties created by the simultaneous presence of dependence, nonstationarity, functional covariates, and incomplete observations. The proofs combine Hoeffding-type decompositions adapted to weighted incomplete data, blocking and coupling arguments for absolutely regular triangular arrays, refined entropy bounds for kernel-indexed function classes, and small-ball probability techniques for functional covariates. The MAR mechanism is incorporated via inverse-propensity weighting, and its effects on the effective sample size, asymptotic variance, and bias structure are made explicit. The theory also provides a rigorous foundation for bandwidth selection through blocked, propensity-adjusted cross-validation and clarifies its relation to the corresponding oracle risk. The proposed framework encompasses a broad class of statistical learning and inference problems involving pairwise or higher-order functionals of functional time series. In particular, it applies to conditional Kendall-type functionals, discrimination problems, metric learning with incomplete labels, and conditional independence testing under local stationarity. A simulation study illustrates the finite-sample behavior of the proposed estimators and supports the theoretical findings across varying regimes of temporal nonstationarity, serial dependence, functional concentration, and response missingness. Overall, the results provide a mathematically rigorous and methodologically flexible foundation for inference from evolving functional data when dependence, infinite dimensionality, and incomplete observation are present simultaneously. Full article

The complex composition and extremely harsh, uncertain surface conditions on Mars impose stringent requirements on the coring performance and fault tolerance of a coring sampler. To satisfy the drilling and coring requirements of Martian soil–rock composite strata, a coring sampler capable of multiple repeated sampling operations is designed, which enables reliable acquisition and preservation of core samples. Drilling and coring experiments are conducted on simulated Martian soil with different particle size distributions and relative densities, as well as basalt specimens. The coring efficiency of the developed bit for Martian soil and rock under diverse working conditions, together with its wear characteristics during repeated coring, is systematically investigated. The results indicate that the proposed coring sampler structure is well adaptable to Martian soil–rock composite drilling. The coring mass of simulated Martian soil increases with increasing advance-to-rotation ratio and relative density, as well as decreasing median particle size. The coring mass of specimens with 91.7% relative density is significantly higher than that of 72.8%, and the maximum single coring mass of fine-grained pure regolith specimens reaches 19.32 g. During basalt coring, higher rotational speeds lead to more severe bit wear and more pronounced temperature elevation, with a peak temperature of 372.4 °C at 120 r/min. A rotational speed of 110 r/min achieves the best compromise between core integrity and bit service life, exhibiting excellent long-term operational stability and favorable cutting–rock-breaking matching performance. The results of this research provide a reference scheme and data support for future Martian soil–rock composite coring and drilling exploration missions. Full article

To improve the accuracy and stability of X-ray pulsar time-delay estimation for multi-scenario celestial remote sensing and navigation, this paper proposes a time-delay estimation method based on a waterfall-plot multi-criteria framework and develops an end-to-end simulation framework for multi-scenario applications. First, a pulsar profile waterfall-plot model is built, and principal component analysis is performed to characterize candidate periodic structures. The contribution rate of the principal eigenvalue is used to describe the overall significance of the candidate period, and the projection variance of the first principal component is used to measure the prominence of the candidate pattern in the principal subspace. Second, support vector regression is used to fit the peak track of the waterfall plot, and a regression slope is used to describe the geometric stability of the candidate period. These three indicators are fused for pulsar period and time-delay estimation. Tests based on Insight-HXMT satellite observation data show that, compared with the ${\chi }^2$ and $Z^2$ test methods, our method improves time-delay estimation accuracy by 68.68% and 50.43%, respectively. Multi-scenario navigation simulations indicate positioning improvements of approximately 0.83 km, 3.04 km, and 1.05 km in the Earth-orbiting, Earth–Moon transfer, and Mars approach scenarios, respectively. These results suggest that the proposed framework can improve pulsar time-delay estimation and may provide useful measurement support for celestial remote sensing and navigation. Full article

Mars Sample Return Program planning includes a series of spacecraft staged both on the Martian surface and in low-Mars-orbit (LMO). During the transfer of samples into orbit, external spacecraft surfaces might be exposed to Mars dust carried on the sample container exterior and possibly extant microbiota (if present). This study was designed to characterize the synergistic effects of LMO ultraviolet irradiation, vacuum, and solar heating on the survival of two UV-resistant and heat-tolerant bacteria, one yeast, and one fungus. The species tested were Bacillus pumilus SAFR-032 spores, Geobacillus stearothermophilus ATCC 12980 spores, Naganishia onofrii DBVPG 5303 cells, and Aspergillus fumigatus ISSFT-021-30 spores, respectively. Spores of A. fumigatus ISSFT-021-30 and B. pumilus were also exposed to LMO conditions with and without a Mojave Mars Simulant (MMS) dust layer. Based on the data, the time required to reach the desired Sterility Assurance Level (SAL; dose-defined to yield a −12 log reduction) was 2.0 h for A. fumigatus ISSFT-021-30 and 76.6 min for B. pumilus SAFR-032 if exposed directly to the solar UV beam under LMO conditions. With the MMS present, predicted times to reach one SAL were extended to 22 h and 1.72 h, respectively. Analysis of UV transmittance through cell stacks of up to 12 µm thick was performed for A. fumigatus ISSFT-021-30. Results indicated that ~4–5% of UVC photons can penetrate through 12 µm stacked aggregates of spores. These findings indicate that (1) the LMO environment can be used to attain the mandated levels of spacecraft surface bioburden reductions and (2) dust shielding and microbial aggregation attenuate UV irradiation, leading to extended orbital residence times to achieve mandated bioburden reductions. Full article

Future long-duration human space missions will expose astronauts to chronically reduced gravitational loading, a condition associated with oxidative stress and epithelial barrier dysfunction. The intestinal epithelial barrier depends on tight junctions (TJs), yet the impact of partial gravity on TJ composition, assembly, and claudin organization remains poorly defined. Here, we show that differentiated intestinal epithelial monolayers exposed to simulated Mars gravity undergo TJ ultrastructural remodeling, characterized by loss of apical membrane “kissing points” and widening of the paracellular space, accompanied by impaired barrier function. Simulated Mars gravity also induces oxidative stress and accumulation of cytoplasmic and nuclear lipid droplets, consistent with altered membrane and lipid homeostasis. At the molecular level, simulated Mars gravity promotes selective TJ changes, with significant downregulation—but not mislocalization—of barrier-forming claudins CLDN1 and CLDN3 and the scaffolding protein ZO-1, while CLDN2, CLDN4, CLDN7, CLDN12, CLDN23, and OCLN remain unchanged. STAT3 activation, but not ERK or NF-κB signaling, may be associated with these alterations and is consistent with a stress-adaptive remodeling response to oxidative stress under simulated Mars gravity. Overall, these findings identify simulated Mars gravity as a disruptor of intestinal barrier homeostasis and highlight TJ remodeling as a target for countermeasures to preserve gut integrity during deep-space missions. Full article

Underwater Wireless Sensor Networks (UWSNs) play a vital role in ocean monitoring and exploration. However, harsh underwater conditions and frequent topology changes caused by node and sink mobility pose significant challenges for reliable routing. Conventional routing protocols that depend on global route reconstruction and static paths generate excessive control overhead and degrade performance in large-scale underwater environments. In this paper, we propose an energy-efficient virtual cell-based mobile-sink adaptive routing (VC-MAR) protocol for UWSNs. The sensing field is logically partitioned into a three-dimensional grid of virtual cells, where a cell-gateway is elected in each cell to construct a low-overhead routing backbone. To support sink mobility, VC-MAR introduces a localized route-adjustment mechanism that updates only the affected backbone segments rather than reconstructing the entire routing structure. By confining routing updates to neighboring cells influenced by sink movement, the proposed protocol significantly reduces control packet exchanges while ensuring stable and reliable data delivery. Simulation results show that the proposed VC-MAR improves the packet delivery ratio by up to 20% and reduces routing control overhead by about 34% compared with traditional grid-based routing methods. These results confirm the suitability of VC-MAR for dynamic and realistic underwater sensing scenarios. Full article

This paper presents a theoretical engineering feasibility analysis of the RK-X photocatalytic process for In Situ Resource Utilisation (ISRU) on Mars. Experimental validation under simulated Martian conditions is the essential next step before any mission deployment claim can be made. The RK-X process converts the two most abundant Martian resources, atmospheric carbon dioxide (CO₂) and subsurface water ice (H₂O), into formic acid (HCOOH) and oxygen (O₂) through a fulvic acid-based photocatalytic cycle validated at the industrial scale in Hungary. A reference module processing 10 tonnes of CO₂ per Earth year yields 10.459 tonnes of formic acid and 3.636 tonnes of oxygen, sufficient to sustain a six-person crew for approximately two Earth years with a 198% safety margin over nominal respiratory demand. The economic analysis indicates that importing equivalent oxygen from Earth costs $1.82–$3.64 million per year; equivalent energy storage (Li-ion) costs $30.5–$61 million for one-time use. Formic acid stores 15.25 MWh of energy in ambient-stable liquid form at a round-trip efficiency of 68.64% without cryogenic infrastructure. A photovoltaic array of 55.37 m² provides the primary energy source; a kilowatt-class nuclear fission reactor constitutes the strategic opportunity for continuous, dust-storm-immune operation with free thermal co-generation. Three critical research gaps have been identified requiring laboratory validation before Mars deployment: (i) catalyst performance at the Martian CO₂ partial pressure (p(CO₂) < 10 mbar, T = 15 °C); (ii) water ice and dry ice extraction at an operational scale; and (iii) integrated closed-loop system demonstration. Built on Earth-proven chemistry with identified, addressable development pathways, the RK-X process theoretically resolves the problems of oxygen supply, seasonal energy storage, water management, and cryogenic infrastructure within a single closed-loop chemical cycle. Full article

The X-ray occultation technique has emerged as a novel remote sensing method for probing planetary neutral atmospheres, complementing traditional radio and ultraviolet stellar occultations. This study evaluates the feasibility and effective altitude range of X-ray occultation for retrieving Martian atmospheric density. Using the Mars Climate Database (MCD) for atmospheric number density profiles and the XrayDB database for photoabsorption cross-sections, we calculate the X-ray transmittance as a function of tangent altitude for photon energies ranging from 0.25 keV to 20 keV. An onion-peeling ray-tracing model is employed to simulate the line-of-sight optical depth. The results indicate that X-ray photons in the soft to hard X-ray band (0.25–20 keV) are sensitive to the Martian atmosphere at altitudes between approximately 50 km and 160 km, bridging the gap between accelerometer measurements (surface to ∼50 km) and extreme ultraviolet (EUV) remote sensing (>100 km). This forward modeling framework provides a theoretical baseline for future X-ray occultation-based density retrieval in the Martian mid-atmosphere. Full article

The minimum fuel transfer problem in low-thrust trajectory optimization remains a major challenge and is typically addressed using bang-bang control. A novel methodology integrating Adaptive Multiresolution Collocation (AMRC) and Sequential Convex Programming (SCP) to solve the minimum-fuel low-thrust trajectory optimization problem is proposed. First, the approach employs the cubic spline wavelet-like transform for mesh refinement, where wavelet coefficients serve as error indicators to dynamically concentrate nodes in regions of rapid state variation. Then, the nonlinear programming problem is convexified via control variable relaxation and small-perturbation linearization, reformulated as a second-order cone programming (SOCP) problem, and efficiently solved using convex optimization tools. Subsequently, progressive selection of the location points ensures rapid and accurate convergence to the optimal trajectory. Finally, numerical simulations of Earth–Mars and Earth–Venus transfer validate the effectiveness and accuracy of the AMRC-based method. Compared with conventional approaches, the proposed method achieves comparable optimality while markedly improving computational efficiency, precisely localizing switching times, and improving numerical precision, requiring only 29.7% of the nodes and 14.7% of the computation time of uniform-grid convex optimization, achieving fuel-optimal deviations within 0.07% of the indirect method and demonstrating accuracy improvements of 2–3 orders of magnitude over GPOPS. Full article

Climate change is increasingly affecting groundwater resources in the Carpathian Basin, while rising temperatures are likely to increase irrigation demand and pressure on aquifers. We assessed climate- and pumping-driven impacts on the Nyírség recharge–discharge system (north-eastern Hungary) by combining shallow groundwater monitoring (1970–2022) with hydroclimate indicators from CHIRPS precipitation and ERA5-Land air temperature and snow depth (1981–2024). Using these datasets, we developed and calibrated a MODFLOW groundwater-flow model for representative wet (2010) and dry (2022) conditions, incorporating permitted abstraction and scenario-based estimates of unregistered pumping. We then ran scenario simulations to evaluate mid-century (2050) conditions and managed aquifer recharge (MAR) options. Precipitation exhibits strong interannual variability, but the region shows marked warming and a pronounced decline in snow storage, implying reduced cold-season buffering and higher evaporative demand. Simulations reproduce the observed post-2010 decline in shallow groundwater, with the largest decreases in higher-elevation recharge areas, whereas increased pumping mainly intensifies localized drawdown near major well fields. Scenario results indicate that climate-driven reductions in recharge dominate basin-scale declines by 2050, while MAR provides primarily local benefits; direct subsurface injection performs best among the tested options. These findings support practical groundwater management by prioritizing measurable and enforceable abstraction (including unregistered withdrawals), demand-side irrigation efficiency and adaptive caps in recharge areas, and targeted subsurface MAR where source water and infrastructure are available. Full article

High-concentration carbon monoxide (CO) produced by incomplete methane combustion in underground explosions is the primary cause of post-explosion fatalities, with typical concentrations (2–4%) far exceeding human tolerance limits. Unsupported Co₃O₄ catalysts were synthesized via a hydrothermal route and evaluated for post-explosion CO elimination under realistic mine-atmosphere conditions. The phase-pure spinel catalyst (crystallite size ~18 nm, S_BET = 68.5 m²/g) exhibited exceptional low-temperature activity with T₅₀ = 43 °C and T₉₀ = 59 °C under 10% O₂, and an apparent activation energy of 63 kJ/mol, substantially outperforming commercial Hopcalite (T₅₀ = 95 °C). In 20 L explosion vessel tests simulating 11% CH₄ combustion at a catalyst loading of 200 g/m³, CO was reduced from 2.85% to 0.32% (89% reduction), extending the escape time factor to k_es = 1.62. Continuous operation at 70 °C for 120 h maintained CO conversion above 96%, and three consecutive explosion cycles produced only a modest ~2% decline in activity, with post-test XRD confirming retention of the spinel phase. Mechanistic studies combining in situ DRIFTS and CO-TPD identify a Mars–van Krevelen pathway driven by surface Co³⁺ sites and reactive lattice oxygen. Full article