Search Results (100)

In planetary radar observations, accurately scaled inverse synthetic aperture radar (ISAR) images are essential for near-Earth asteroid (NEA) shape reconstruction, rotational-state estimation, and impact risk assessment. However, conventional ISAR cross-range scaling methods typically rely on time–frequency analysis or multidimensional parameter searches, resulting in high computational complexity and limited robustness under the low signal-to-noise ratio (SNR) conditions commonly encountered in NEA observations. To address this challenge, this paper proposes a joint ISAR phase autofocus and cross-range scaling framework based on adaptive phase tracking (APT). The method employs a multi-scale Laplacian of Gaussian (LoG) detector to extract isolated scatterers and reformulates Doppler chirp-rate estimation as a recursive state estimation problem. By adaptively tracking the cross-range Doppler phase of these scatterers, the target’s effective rotation velocity is directly estimated without exhaustive parameter searches. A unified phase compensation function is then constructed to simultaneously achieve range-dependent autofocus and cross-range scaling. Simulation results based on a three-dimensional NEA model with realistic planetary radar imaging parameters demonstrate the effectiveness of the proposed method in near-Earth asteroid imaging scenarios. Experimental results from a UAV turntable setup further verify its capability for cross-range scaling and phase autofocus in a controlled near-field ISAR imaging scenario. These results show that the proposed framework achieves high estimation accuracy and robustness with reduced computational cost, making it an efficient and reliable solution for practical ISAR imaging in challenging radar environments. Full article

We investigate the effects of Lorentz invariance violation (LIV) on the resonance structure of the Z boson in high-energy collider experiments. Building on previous work where resonance line-shape distortions were established, we extend the analysis to include spacelike and lightlike orientations of the LIV vector. The modified dispersion relation induces rapidity-dependent distortions of the resonance profile, with effects growing strongly at large rapidities. In anisotropic scenarios, the signal exhibits characteristic sidereal-time modulation due to the rotation of the Earth relative to the preferred LIV direction. We show that, while global analyses dilute the effect, dedicated studies focusing on high-rapidity bins and sidereal-time dependence can significantly enhance sensitivity. The resulting shifts in reconstructed resonance parameters can reach or exceed current experimental precision for LIV scales as low as ${\delta }_{LIV}\sim {10}^{-8}$. These results demonstrate that collider measurements of unstable gauge bosons provide a complementary and competitive probe of Lorentz violation. Full article

To address the problems of complex influencing factors of chamber pressure and delayed response in manual regulation during shield construction, this study proposes a chamber pressure prediction and parameter-optimization method integrating SSA-RF and PSO based on field tunneling data from 1082 rings. First, on the basis of conventional tunneling parameters, muck improvement parameters, including the cumulative amount of foam mixture in the current ring, the cumulative amount of cutterhead water spray in the current ring, and the cumulative amount of bentonite in the current ring, are introduced. Nine key input variables are then screened by combining Pearson correlation coefficient analysis and distance correlation coefficient analysis. Subsequently, an SSA-RF chamber pressure prediction model is established. The results show that the model achieves an R² of 0.9968 and a MAPE of only 0.34% on the test set, outperforming the other models. Furthermore, with the objective of minimizing the deviation between the predicted chamber pressure and the target value, the PSO algorithm is used to optimize the propulsion speed and the rotation speed of the screw conveyor. The results indicate that, based on the predicted chamber pressure values, the PSO algorithm can output optimized adjustment suggestions for propulsion speed and screw conveyor rotation speed, thus realizing model-assisted regulation of chamber pressure. This study can provide a reference for chamber pressure prediction and auxiliary regulation of tunneling parameters during earth pressure balance shield tunneling. Full article

The global energy demand continues to rise, and increasing harmful emissions from fossil fuel combustion highlight the urgent need for alternative, eco-friendly energy sources. Hydropower stands out as a promising solution, leveraging the fact that 71 % of the Earth’s surface is covered by water, allowing for energy harnessing with minimal environmental impact. Modern hydropower technologies must also be optimized to operate efficiently in low-velocity water, a common condition that typically produces low power output. Savonius turbines have been widely studied, with many efforts focusing on enhancing their performance through design modifications. However, much of this research is limited to numerical simulations only. This study seeks to address this gap by experimentally validating a new optimization process that integrates a deflector into the turbine design, first based on Computational Fluid Dynamics. Both the turbine and deflector were fabricated and tested in our water flume, with a comparative analysis conducted against the standard Savonius turbine. In addition to evaluating key experimental parameters such as torque and rotational speed at various tip speed ratios, Particle Image Velocimetry (PIV) is used to investigate the flow structure around the turbine, proving the validity of our CFD-based optimization under real-world conditions. Full article

Polar motion (PM), a key component of Earth orientation parameters (EOPs), is essential for high-precision satellite orbit determination and deep-space navigation. However, delays in data acquisition and processing limit its availability for real-time applications, necessitating the development of prediction models based on historical observations. Common approaches include least squares extrapolation (LS), autoregressive (AR) models, and their combination (LS + AR), often enhanced by effective angular momentum (EAM) from Earth’s fluid components. This study examines an EAM + LS + AR method for PM prediction, systematically evaluating how different EAM forecast horizons (1–10 days) affect 90-day prediction accuracy for both PM X and Y components. A segmented optimization strategy is proposed and validated against International Earth Rotation and Reference Systems Service (IERS) official predictions using the IERS EOP 14 C04 product. Key findings include: (a) Adjusting the EAM horizon substantially reduces prediction errors. Segmented prediction improves PM X accuracy by 20–30% (1–60 days) and 10–20% (61–90 days) relative to IERS rapid products, while PM Y short-term accuracy improves by 20–40% (1–15 days). (b) The influence of EAM horizon on long-term PM Y prediction gradually weakens, with errors converging to approximately 8 mas by day 90. (c) For 1–10-day forecasts, optimal horizons follow a systematic pattern: day m predictions achieve the highest accuracy using an (m−1)-day EAM horizon, while a 10-day horizon is optimal for long-term forecasts. (d) The proposed method shows clear advantages over IERS forecasts, with 83.5% of PM X predictions (1–90 days) and 50.78% of PM Y predictions (1–15 days), outperforming IERS daily products during the 2024 test period. Full article

To address the strongly nonlinear hydrodynamic coupling and complex maneuvering challenges encountered by large ships during berthing operations in restricted waters, this paper proposes a high-precision autonomous berthing control system incorporating four-quadrant propeller hydrodynamics. Based on an improved Mathematical Maneuvering Group (MMG) framework, a three-degree-of-freedom (3-DOF) dynamic model is established to accurately capture the transient thrust and torque mappings of the propeller over all four quadrants. A dynamic line-of-sight (LOS) guidance system with a nonlinearly decaying acceptance radius is tightly coupled with PD/PI controllers to coordinate and regulate the rudder angle and propeller rotational speed. The numerical solver was rigorously validated against turning-test data for the S-175 container ship, with the errors of the key parameters all controlled within 15%. Subsequently, under the environmental conditions of Yangshan Port, full-condition path-planning and berthing simulations were conducted for the novel B-573 container ship under steady-current disturbances. These simulations evaluated multiple flow directions, namely due south, due north, due west, and due east defined in the Earth-fixed coordinate system, as well as multiple intensity levels ranging from 0 to 1.5 m/s that were specifically tested under the due north current. Quantitative evaluation shows that, under the highly challenging current condition of 1.0 m/s, the dynamic corrective mechanism effectively drives the global mean absolute error (MAE) to converge to 85.50 m, representing a 62% statistical reduction relative to the transient peak value. In addition, a parameter sensitivity analysis based on the cumulative cross-track error confirms that, when subject to variations in the underlying hydrodynamic parameters, the proposed system can suppress fluctuations in trajectory error to a very low level, thereby demonstrating a certain degree of control robustness. During the terminal berthing stage, the vessel smoothly completed an extreme deceleration from an initial speed of 6.4 m/s to a full stop within 588 s, while constraining the maximum astern rotational speed to −2 rps and seamlessly passing through all four propeller quadrants. The results confirm that the proposed autopilot framework possesses a certain degree of engineering feasibility in complex maritime environments. Full article

Local Lorentz Invariance is one of the fundamental postulates of General Relativity, making its experimental verification of paramount importance. Given that various frontier theoretical models predict potential symmetry breaking, the Standard Model Extension framework has been established to systematically study such phenomena. Within the Standard Model Extension gravitational sector, the high-order Lorentz-violating terms with mass dimension $d=6$ exhibit a rapid signal decay with distance, providing a distinct detection advantage in short-range gravity experiments. This work is dedicated to optimizing the testing schemes for $d=6$ Lorentz-violating coefficients. Based on a high-precision torsion balance platform, we propose a novel scheme featuring a comb-stripe design. The improvements are twofold: first, the spatial orientation of the experimental apparatus is optimized to leverage the modulation effects of the Earth’s rotation, thereby enhancing the capability to distinguish and constrain different violation parameters; second, the test and source masses are reconfigured into specifically designed stripe patterns to significantly amplify the fringe-field signals sensitive to Lorentz-violating effects. This paper systematically elaborates on the theoretical foundation and design principles of the new scheme. By performing a detailed comparison of the constraint potentials of various stripe configurations, the five-stripe geometry is identified as the optimal experimental configuration. This study provides a new experimental methodology for exploring physics beyond the Standard Model at higher levels of precision. Full article

The spaceborne full-polarimetric (FP) synthetic aperture radar (SAR) is an advanced sensor for high-resolution Earth observation. However, FP data acquired by such a system are prone to distortions induced by ionospheric Faraday rotation (FR). From the perspective of exploiting these distortions, this enables the estimation of the ionospheric FR angle (FRA), and consequently the total electron content, across most global regions (including the extensive ocean areas) using spaceborne FP SAR measurements. The accuracy of FRA estimation, however, is highly sensitive to noise interference. This study addresses denoising in FRA retrieval based on the Bickel–Bates estimator, with a specific focus on noise reduction methods built upon the adaptive Goldstein filter (AGF) that was originally designed for radar interferometric processing. For the first time, three signal-to-noise ratio (SNR)-based AGFs suitable for FRA estimation are investigated. A key feature of these filters is that their SNRs are all defined using the amplitude of the Bickel–Bates estimator signal rather than the FRA estimates themselves. Accordingly, these AGFs are applied to the estimator signal instead of the estimated FRAs. Two of the three AGFs are developed by adopting the mathematical forms of SNRs and filter parameters consistent with the existing SNR-based AGFs for interferogram. The third AGF is newly proposed by utilizing more general mathematical forms of SNR and filter parameter that differ from the first two. Specifically, its SNR definition aligns with that widely used in image processing, and its filter parameter is derived as a function of the defined SNR plus an additionally introduced adjustable factor. The three SNR-based AGFs tailored for FRA estimation are tested and evaluated against existing AGF variants and classical image denoising methods using three sets of FP SAR Datasets acquired by the L-band ALOS PALSAR sensor, encompassing an ocean-only scene, a plain land–ocean combined scene, and a more complex land–ocean combined scene. Experimental results demonstrate that all three filters can effectively mitigate noise, with the newly proposed AGF achieving the best performance among all denoising methods included in the comparison. Full article

This paper presents a mathematical model that describes the propagation of internal inertia–gravity waves in a stratified atmosphere under the approximations of an incompressible fluid and a traditional β-plane. It demonstrates that, in the incompressible fluid approximation, the temperature field is inconsistent with the heat conduction equation. The system of equations that describes internal inertia–gravity waves is considered in the general case, taking into account the buoyancy force, and reduced to a single equation. The solution is sought in the form of traveling plane waves. A dispersion relation has been obtained in the form of a cubic equation that represents a hypersurface in wave number space, without the assumption of small vertical wavelength. Cross-sections of this surface are plotted, and an extremum study is performed. This shows that a new frequency region appears in the low-frequency spectrum $0<\omega <f_{0z}$ that was not present in the f-plane approximation. Here, $f_{0z}=2{\omega }_0\cdot \sin \phi$ is the Coriolis parameter, and $\phi$ is the latitude. Furthermore, these waves only propagate in the negative direction of the x-axis, i.e., in the opposite direction of the Earth’s rotation. It is also shown that there is a region with a minimum frequency in the “high-frequency” spectrum determined by buoyancy $\omega <f_{0z}$, and that waves propagate in the negative direction as well. Thus, the dispersion surface is shown to have two extremum points. The first is a minimum in the “high-frequency” spectrum ${\omega }_1\approx 0.826f_{0z}$ and the second is a maximum in the “low-frequency” spectrum ${\omega }_2\approx 0.564f_{0z}$. Full article

Regional seismic phases are essential for imaging Earth’s internal structure. Although extensive regional seismic networks are publicly available worldwide, only a small fraction of recorded phase arrivals are picked for constraining earthquake source parameters, leaving most data untapped. Recent deep-learning methods offer powerful tools for automatic phase picking, yet their performance often lags behind that of human experts, particularly at relatively large epicentral distances such as the case of the Pn phase (~200–2000 km). Here, we systematically assess the effect of different test-time augmentation strategies on the Pn phase picking performance using PickNet and PhaseNet, along with the Seis-PnSn dataset containing data worldwide to simulate the out-of-distribution situation. We also propose quality control measures to obtain reliable results when ground truths are unknown. Our experiments show that filter-bank augmentation is more effective than the shift augmentation and the rotation augmentation, improving the proportion of picks within ±0.5/1.0 s errors to 53.87%/70.82% compared with the baseline of 48.98%/66.94% for PickNet and ±0.5/1.0 s errors to 48.45%/67.06% compared with the baseline of 46.32%/64.28% for PhaseNet. After the quality control using the standard deviation of different augmentation results, the proportion is further boosted to 67.39%/78.53% for PickNet and 57.99%/74.72% for PhaseNet. Additionally, we provide the workflow in our study as scripts for real-world data processing. Our work enhances both the accuracy and accessibility of regional seismic phase picking, thereby contributing to the studies of Earth’s internal structure and earthquake source characterization. Full article

For ground-based Celestial Navigation System/Strapdown Inertial Navigation System (CNS/SINS) integrated navigation with arcsecond-level accuracy, the current spatio-temporal transformation model involves a considerable amount of astronomical knowledge, making it difficult for ordinary navigation professionals to quickly master and operate. There has been no strict argumentation on which parameters can be simplified in the calculation process. Under the premise of ensuring that the attitude accuracy of ground integrated navigation meets the requirement of 5 arcseconds, through argumentation and quantitative analysis, the complex links in the spatio-temporal transformation model that contribute minimally to the final attitude measurement accuracy can be eliminated, significantly reducing the complexity of the model and lowering the threshold for its use. The factors considered in this paper include proper motion, annual parallax, light deflection, aberration of light, details of the precession-nutation model, details of the time system, and calibration parameters. Factors contributing less than 0.1 arcsecond to the accuracy during the coordinate transformation process are ignored or approximately simplified. Error analysis shows that the corrections for annual parallax and light deflection have negligible effects on accuracy. Except for the calculation of the Earth’s rotation angle, which requires a relatively precise UT1-UTC time, the time input in the calculation process of other astronomical parameters can directly use UTC time. Experimental measurements show that the calibration parameters obtained by the method in this paper have high robustness, and the parameter accuracy meets the requirements of attitude calculation. The proposed simplified spatio-temporal model reduces the computational load by 90%, can meet the arcsecond-level attitude measurement accuracy requirements of ground-based CNS/INS integrated navigation, and has the potential to be extended to more general dynamic or air/space-based intelligent navigation scenarios. Full article

When relying exclusively on inter-satellite links for autonomous orbit determination, it cannot suppress or eliminate the constellation overall rotation, rendering it incapable of determining its spatial orientation relative to terrestrial and celestial reference frames. To address these limitations, an autonomous orbit determination method for BeiDou Satellites is proposed by integrating satellite-to-ground, inter-satellite, and space-based orientation observations. This study introduces space-based orientation data between navigation satellites to provide inertial frame orientation references for the BeiDou constellation, while utilizing ground-based anchor stations to establish orientation references in the Earth-fixed frame. The results demonstrate that (1) In a 90-day autonomous operation within the inertial frame, the combined use of inter-satellite links and space-based orientation data achieves a 3D orbit position accuracy of 0.45 m. (2) In semi-autonomous operation, with Earth rotation parameter (ERP) updates every three days from ground stations, the 3D orbit determination accuracy reaches the decimeter level; using long-term predicted ERPs in conjunction with satellite-to-ground data, meter-level accuracy is maintained. (3) When the space-based orientation measurement noise is limited to 5 milliarcseconds, the accuracies of polar motion parameters xp and yp reach 2.23 milliarcseconds and 3.55 milliarcseconds, respectively, while the UT1–UTC parameter achieves an accuracy of 0.42 milliseconds. This work provides critical technical support for flexible autonomous navigation of the BeiDou system when the ground control stations are destroyed in the wartime and contributes to the independent determination of ERP within China. Full article

The development of electrocatalysts composed of earth-abundant elements is essential for advancing the commercial application of Proton Exchange Membrane Fuel Cells (PEMFC). Among these, single-atom electrocatalysts, such as Fe-N-C, show great promise for the oxygen reduction reaction (ORR). This study aims to improve the ORR activity and stability of Fe-N-C electrocatalysts by fine-tuning the straightforward 1,10-phenanthroline-iron complexation synthesis method. Key parameters, including iron-to-phenanthroline ratio, carbon powder surface area, and pyrolysis temperature were systematically varied to evaluate their influence on the resulting electrocatalysts. The findings of this study revealed that the electrocatalysts synthesized with 1,10-phenanthroline (Phen) and high-surface-area Black Pearls (BP) possessed much better ORR activity than electrocatalysts prepared by using Vulcan carbon (lower surface area). Interestingly, electrocatalysts prepared with BP, but with a non-bidentate nitrogen-containing ligand molecule, such as imidazole, showed a much poorer activity, as the resulting material predominantly consisted of inactive structures, such as encapsulated iron nanoparticles and iron oxide, as evidenced by HR-TEM, EXAFS, and XRD. Therefore, the results suggest that only the synergistic combination of the bidentate ligand phenanthroline (Phen) and the high-surface-area carbon support (BP) favored the formation of ORR-active Fe-N-C single-atom species upon pyrolysis. The study also unveiled a significant enhancement in electrocatalyst stability during accelerated durability tests (and air storage) as the pyrolysis temperature was increased from 700 to 1300 °C, albeit at the expense of ORR activity, likely resulting from the generation of iron particles. Pyrolysis at 1050 °C yielded the electrocatalyst with the most favorable balance of activity and stability in rotating disk measurements, while maintaining moderate durability under PEM fuel cell operation. The insights obtained in this study may guide the development of more active efficient and durable electrocatalysts, synthesized via a simple method using earth-abundant elements, for application in PEMFC cathodes. Full article

In this study, we present analysis of TESS photometry, spectral energy distribution (SED), high-resolution spectroscopy, and spot modeling of the ${\alpha }^2$ CVn-type star AL Col (HD 46462). The primary objective is to determine its fundamental physical parameters and investigate its surface activity characteristics. Using TESS short-cadence (120 s) SAP flux, we identified a rotational frequency of 0.09655 ${\mathrm{d}}^{-1}$ ($P_{\mathrm{rot}}=10.35733$ d). Wavelet analysis reveals that while the amplitudes of the harmonic components vary over time, the strength of the primary rotational frequency remains stable. A SED analysis of multi-band photometric data yields an effective temperature ($T_{\mathrm{eff}}$) of 11,750 K. High-resolution spectroscopic observations covering wavelengthrange 4500–7000 Å provide refined estimates of $T_{\mathrm{eff}}$ = 13,814 ± 400 K, $logg$ = 4.09 ± 0.08 dex, and $\upsilon sini$ = 16 ± 1 km s⁻¹. Abundance analysis shows solar-like composition of O ii, Mg ii, S ii, and Ca ii, while helium is under-abundant by 0.62 dex. Rare earth elements (REEs) exhibit over-abundances of up to 5.2 dex, classifying the star as an Ap/Bp-type star. AL Col has a radius of $R=3.74\pm 0.48{\mathrm{R}}_{\odot }$, with its H–R diagram position estimating a mass of $M=4.2\pm 0.2{\mathrm{M}}_{\odot }$ and an age of $0.12\pm 0.01$ Gyr, indicating that the star has slightly evolved from the main sequence. The TESS light curves were modeled using a three-evolving-spot configuration, suggesting the presence of differential rotation. This star is a promising candidate for future investigations of magnetic field diagnostics and the vertical stratification of chemical elements in its atmosphere. Full article

The Earth Radiation Budget (ERB), a measure of the difference between incoming solar irradiance and outgoing reflected and emitted radiant energy, is a fundamental property of Earth’s climate system. The Libera satellite mission will measure the ERB’s outgoing components to continue the long-term climate data record established by NASA’s Clouds and the Earth’s Radiant Energy System (CERES) mission. In addition to ensuring data continuity, Libera will introduce a novel split-shortwave spectral channel to quantify the partitioning of the outgoing reflected solar component into visible and near-infrared sub-components. However, converting these split-shortwave radiances into the ERB-relevant irradiances requires the development of split-shortwave Angular Distribution Models (ADMs), which demand extensive angular sampling. Here, we show how Rotating Azimuthal Plane Scan (RAPS) parameters—specifically operational cadence and azimuthal scan rate—affect the observational coverage of a defined scene and angular space. Our results show that for a fixed number of azimuthal rotations, a relatively slow azimuthal scan rate of 0.5° per second, combined with more time spent in the RAPS observational mode, provides a more comprehensive sampling of the desired scene and angular space. We also show that operating the Libera instrument in RAPS mode at a cadence between every fifth day and every other day for the first year of space-based operations will provide sufficient scene and angular sampling for the observations to achieve radiance convergence for the scenes that comprise more than half of the expected Libera observations. Obtaining radiance convergence is necessary for accurate ADMs. Full article