Search Results (960)

This paper investigates the optimal control problem of orbital rendezvous for spacecraft in near-circular orbits with a low-thrust propulsion system. Two optimality criteria are considered: time-optimal and motor-time-optimal control. A linearized mathematical model of relative motion between the active and passive spacecraft is employed, which is formulated in dimensionless variables that characterize secular, periodic, and lateral motion components of the relative motion. By applying Pontryagin’s Maximum Principle, the equations governing the optimal relative motion of the spacecraft are derived. To address the discontinuities associated with the bang–bang switching function inherent in the motor-time-optimal problem, and the lack of a suitable initial guess, a homotopy method is adopted, in which the solution to the rendezvous time-optimal problem is used as an initial guess and is gradually deformed into the motor-time-optimal control. Considering the errors introduced by the linearization of the relative motion model, the obtained control law is validated via numerical simulations based on the original nonlinear dynamics of the system. Simulation results demonstrate that the proposed trajectory optimization methodology achieves high success rates and rapid convergence, providing valuable theoretical support and practical guidance for mission scenarios with similar trajectory design requirements. Full article

Stochastically forced nonlinear wave systems are commonly associated with complex dynamical behavior, although little is known about the general interaction of nonlinear dispersion, irrational forcing frequencies, and multiplicative noise. To fill this gap, we consider a generalized stochastic SIdV equation and examine the effects of deterministic and stochastic influences on the long-term behavior of the equation. The PDE was modeled using a stochastic traveling-wave transformation that simplifies it into a planar system, which was studied using Darboux-seeded constructions, Poincaré maps, bifurcation patterns, Lyapunov exponents, recurrence plots, and sensitivity diagnostics. We discovered that natural, implicit, and unique seeds produce highly diverse transformed wave fields exhibiting both irrational and golden-ratio forcing, controlling the transition from quasi-periodicity to chaos. Stochastic perturbation is demonstrated to suppress as well as to amplify chaotic states, based on noise levels, altering attractor geometry, predictability, and multistability. Meanwhile, OGY control is demonstrated to be able to stabilize chosen unstable periodic orbits of the double-well regime. A stochastic bifurcation analysis was performed with respect to noise strength $\sigma$, revealing that the attractor structure of the system remains robust under stochastic excitation, with noise inducing only bounded fluctuations rather than qualitative dynamical transitions within the investigated parameter regime. These findings demonstrate that the emergence, deformation, and controllability of complex oscillatory patterns of stochastic nonlinear wave models are jointly controlled by nonlinear structure, external forcing, and noise. Full article

Low-thrust propulsion systems have become mainstream for Low Earth Orbit (LEO) satellites due to their superior propellant efficiency, yet conventional low-thrust transfer strategies suffer from high computational costs and failure to achieve full orbital element convergence. To address these drawbacks, this paper proposes a novel semi-analytical three-phase low-thrust transfer strategy that leverages $J_2$ gravitational precession to realize convergence of all orbital elements for circular orbits. The core of the method lies in the design of two symmetric thrust arcs and an intermediate coasting period that utilizes $J_2$ precession. By solving the resulting polynomial equation, the strategy achieves simultaneous controlled convergence of the Right Ascension of the Ascending Node (RAAN) and the argument of latitude (AOL). Simulation results demonstrate that the proposed method achieves significant fuel savings compared to direct transfer strategies, while simultaneously achieving superior computational speed. Extensive validation via 100,000 Monte Carlo simulations confirms the method’s scope of applicability, and the sufficient conditions for the existence of a solution are provided. It is further found that the proposed method is particularly well-suited for missions involving medium-to-high inclination orbits and large RAAN gaps, such as constellation deployment. In conclusion, this strategy provides a fuel-efficient and computationally fast solution for low-thrust transfer, establishing the basis for the operational management of future large-scale space systems equipped with low-thrust propulsion. Full article

Background: Mucormycosis, an invasive fungal infection with high morbidity and mortality rates, requires prompt surgical and antifungal therapies; however, the role of antifungal susceptibility testing (AFST) in clinical management of mucormycosis remains underexplored. We aimed to describe the experience of using AFST in the clinical management of mucormycosis. Methods: We conducted a retrospective study from 1 October 2017 to 8 February 2023. We included non-pregnant patients aged ≥ 18 years old with a positive culture for Mucorales and with proven or probable mucormycosis. We collected clinical and microbiological data using a chart review. Results: Over the study period, a total of 119 patients were included, with 36 (30%) undergoing AFST. Of all patients, the median age was 54 years, with 80 (67%) being White and not Hispanic and 73 (61%) being male. Fifty-three (45%) patients had DM, 27 (23%) had hematological malignancy, 15 (13%) had SOT, and 23 (19%) had COVID-19. Half of the cases met the criteria of proven invasive mucormycosis, with pulmonary involvement being the most common presentation (46, 39%), followed by rhino-cerebral-orbital involvement (35, 29%). The majority of Mucorales isolates were Rhizopus species (79, 66%). Among the 36 who underwent AFST, posaconazole minimal inhibitory concentrations (MICs) were lower than isavuconazole (range 0.03 to 2 µg/mL versus 0.1 to 16 µg/mL, respectively). AFST resulted in a change in antifungal therapy from isavuconazole to posaconazole in 3/36 (8%) cases. There was no statistically significant difference in the mortality between the patients whose isolates received AFST versus those who did not have AFST performed. Conclusions: AFST led to a change in antifungal therapy in a minority of mucormycosis cases. Further studies to understand the epidemiological range of antifungal MICs and the effect of AFST-informed antifungal therapy are needed. Full article

Circuit implementation is a widely accepted method for validating theoretical insights observed in chaotic systems. It also serves as a basis for numerous chaos-based engineering applications, including data encryption, random number generation, secure communication, neuromorphic computing, and so forth. To get feasible, compact, and cost-effective circuit implementations of chaotic systems, the underlying mathematical model may be simplified while preserving all rich nonlinear behaviors. In this framework, this manuscript presents a simplified Hopfield Neural Network (HNN) capable of generating a broad spectrum of complex behaviors using a minimal number of electronic elements. Based on Shil’nikov’s theorem for heteroclinic orbits, the number of non-zero synaptic connections in the matrix weights is reduced, while simultaneously using only one nonlinear activation function. As a result of these simplifications, we obtain the most compact electronic implementation of a tri-neuron HNN with the lowest component count but retaining complex dynamics. Comprehensive theoretical and numerical analyses by equilibrium points, density-colored continuation diagrams, basin of attraction, and Lyapunov exponents, confirm the presence of periodic oscillations, spiking, bursting, and chaos. Such chaotic dynamics range from single-scroll chaotic attractors to double-scroll chaotic attractors, as well as coexisting attractors to transient chaos. A brief security application of an S-Box utilizing the presented HNN is also given. Finally, a physical implementation of the HNN is given to confirm the proposed approach. Experimental observations are in good agreement with numerical results, demonstrating the usefulness of the proposed approach. Full article

The Eocene fourth member of the Shahejie formation (Es4x) in the Bonan Depression, Bohai Bay Basin, records syn-rift sedimentation under alternating arid and humid climates. It provides insight into how orbital-scale climatic fluctuations influenced tectonics, facies patterns, and reservoir distribution. This study integrates 406 m of core data, 92 thin sections, 450 km² of 3D seismic data, and multiple geochemical proxies, leading to the recognition of five facies associations (LFA): (1) alluvial fans, (2) braided rivers, (3) floodplain mudstones, (4) fan deltas, and (5) saline lacustrine evaporites. Three major depositional cycles are defined within the Es4x. Seismic reflections, well-log patterns, and thickness trends suggest that these cycles represent fourth-order lake-level fluctuations (0.8–1.1 Myr) rather than short 21-kyr precession rhythms. This implies long-term climate and tectonic modulation, likely linked to eccentricity-scale monsoon variability. Hyperarid phases are marked by Sr/Ba > 4, δ¹⁸O > +4‰, and thick evaporite accumulations. In contrast, Sr/Ba < 1 and δ¹⁸O < −8‰ reflect humid conditions with larger lakes and enhanced fluvial input. During wet periods, rivers produced sand bodies nearly 40 times thicker than in dry intervals. Reservoir quality is highest in braided-river sandstones (LFA 2) with 12%–19% porosity, preserved by chlorite coatings that limit quartz cement. Fan-delta sands (LFA 4) have <8% porosity due to calcite cementation, though fractures (10–50 mm) improve permeability. Floodplain mudstones (LFA 3) and evaporites (LFA 5) act as seals. This work presents a predictive depositional and reservoir model for arid–humid rift systems and highlights braided-river targets as promising exploration zones in climate-sensitive basins worldwide. Full article

The FY-4B satellite, launched in June 2021 as China’s new-generation geostationary meteorological satellite, carries three identical High-Energy Particle Detectors (HEPDs) that enable multi-directional, wide-spectral measurements of energetic electrons. The three units are mounted in the zenith (−Z), flight (+X with a +Y offset of 30°), and anti-flight (−X with a −Y offset of 30°) directions, allowing simultaneous observations from nine look directions over a field of view close to 180° in the 0.4–4 MeV energy range (eight energy channels). This paper systematically presents the design principles of the HEPD electron detector, the ground calibration scheme, and preliminary in-orbit validation results. The probe employs a multi-layer silicon semiconductor telescope technique to achieve high-precision measurements of electron energy spectra, fluxes, and directional anisotropy in the 0.4–4 MeV range. Ground synchrotron calibration shows that the energy resolution is better than 16% for energies above 1 MeV, and the angular resolution is about 20°, providing a solid basis for subsequent quantitative inversion. During in-orbit operation, HEPD remains stable under both quiet conditions and strong geomagnetic storms: the measured electron fluxes, differential energy spectra, and directional distributions show good agreement with GOES-16 observations in the same energy bands during quiet periods and for the first time provide from geostationary orbit pitch-angle-resolved images of the minute-scale evolution of electron enhancement events. These results demonstrate that HEPD is capable of long-term monitoring of the geostationary radiation environment and can supply high-quality, continuous, and reliable data to support studies of radiation-belt particle dynamics, data assimilation in space weather models, and radiation warnings for satellites in orbit. Full article

Benthic δ¹⁸O and δ¹³C values, as well as the mean grain size (MS) of sortable silt (SS), were used to construct the records of deep-water ventilation during the last 300 ka, at core GC02. This core is located at 4430 m water depth on the Madagascar basin near the Southwest Indian Ocean mid-ridge (SWIR). Decreased values of MS of SS reveal a weakened Antarctic Bottom Water (AABW) in the glacial periods, while increased values indicate enhanced AABW in the interglacial periods. The MS of SS record in GC02 exhibited a particularly good synchronization with a record based on the δ¹³C gradient between the North Atlantic and tropical Pacific Ocean, indicating that AABW is dominated by the overturning strength of the Atlantic meridional overturning circulation (AMOC), and showed a higher generation rate in the early stages of the glacial periods. A rapid reduction in δ¹³C occurred in MIS 2, 4, and 6; the MS values in GC02 and winter sea ice (WSI) also exhibited significant decreases and increases, respectively. By controlling the transport of ventilated water mass to deep waters and polar heat transport, in the Indian Ocean, both the change in AABW intensity and the Southern Ocean ice volume result from changes in the AMOC under the orbital modulation background. In the Southwest Indian Ocean, AMOC has a larger effect on ice volume during glacial periods, while its effect on AABW is relatively strong during interglacial periods. Full article

Background/Objectives: Mucormycosis is a rapidly progressive invasive fungal infection that commonly involves the sinonasal region and skull base in patients with systemic comorbidities, yet robust ENT data from middle-income settings are scarce. Methods: We performed a single-center retrospective review of all patients with histopathologically confirmed mucormycosis treated in the Otorhinolaryngology Department of Dicle University between 2010 and 2023, covering a 14-year period. Eligible patients had paranasal sinus computed tomography at presentation and received surgical and/or systemic antifungal therapy. Demographic data, comorbidities, disease subtype, radiological extent, treatment modality and survival were extracted from records. Survival was estimated using Kaplan–Meier analysis, and group differences were tested with chi-square statistics (p ≤ 0.05). Results: Fifty-two patients met the inclusion criteria (mean age 56.5 ± 15.2 years; 57.7% male); 73.1% had at least one systemic comorbidity, most frequently diabetes mellitus (65.4%) and hematological malignancy (19.2%). Disease was sinonasal in 42.3%, rhino-orbital in 28.8% and rhino-orbito-cerebral in 28.8%. Baseline CT showed intracranial extension in 26.9%. Overall survival was 59.6% and differed markedly by subtype, highest in isolated sinonasal disease (81.8%) and lowest in rhino-orbito-cerebral disease (26.7%). Intracranial extension was associated with higher mortality (71.4% vs. 28.9%). Combined surgical debridement plus systemic antifungal therapy, used in 84.6% of patients, yielded lower mortality than antifungal therapy alone (31.8% vs. 87.5%). Conclusions: In this ENT cohort, prognosis was mainly determined by anatomical extent and treatment strategy. Our findings suggest that timely combined surgical and antifungal management, when feasible and in appropriately selected patients, is associated with improved survival outcomes. Full article

The performance of the MADOCA-PPP (Multi-GNSS Orbit and Clock Augmentation-Precise Point Positioning) wide-range ionospheric correction requires further investigation during periods of high ionospheric activity, particularly regarding its impact on the convergence time and positioning accuracy of both PPP and PPP with Ambiguity Resolution (PPP-AR). Thus, the present study selects the month with the highest average Kp index between January 2023 and May 2025 and conducts positioning analyses at nine stations. Results indicate that applying wide-range ionospheric corrections reduces PPP convergence time by 47% in static mode and 54% in kinematic mode. When these corrections are integrated into PPP-AR, they shorten the convergence time by 69% in static mode and 72% in kinematic mode. Moreover, PPP-AR enhanced with wide-range ionospheric corrections achieves the highest positioning accuracy across both modes: in static mode, the horizontal and vertical root mean square errors (RMSEs) are approximately 5.2 cm and 6.9 cm, respectively, while in kinematic mode, these values are 5.6 cm and 8.0 cm. These findings demonstrate that the wide-range ionospheric corrections provided by the MADOCA-PPP service effectively enhance PPP performance during periods of heightened ionospheric activity. Full article

Current passive microwave satellites like SMAP still face limitations in observational frequency and responsiveness in regions with frequent cloud cover, dense vegetation, or complex terrain, making it difficult to achieve continuous global monitoring with high spatio-temporal resolution. To enhance global high-frequency monitoring capabilities, this study utilizes global reflectivity data provided by the Tianmu-1 (TM-1) constellation since 2023, combined with multiple auxiliary variables, including NDVI, VWC, precipitation, and elevation, to develop a 9 km resolution soil moisture retrieval model. Several spatial clustering and temporal partitioning strategies are incorporated for systematic evaluation. Additionally, since the publicly available TM-1 L1 reflectivity data does not provide separable polarization channels, this study uses DDM/specular point reflectivity as the primary observable quantity for modeling and mitigates non-soil factor interference by introducing multi-source priors such as NDVI, VWC, precipitation, terrain, and roughness. Unlike SMAP’s “single orbit daily fixed local time” observation mode, TM-1, leveraging multi-constellation and multi-orbit reflection geometry, offers more balanced temporal sampling and availability in cloudy, rainy, and mid-to-high latitude regions. This enables temporal gap filling and rapid event response (such as moisture transitions within hours after precipitation events) during periods of SMAP’s quality masking or intermittent data loss. Results indicate that the model combining LC-cluster with seasonal partitioning delivers the best performance at the cluster level, achieving a correlation coefficient (R) of 0.8155 and an unbiased RMSE (ubRMSE) of 0.0689 cm³/cm³, with a particularly strong performance in barren and shrub ecosystems. Comparisons with SMAP and ISMN datasets show that TM-1 is consistent with mainstream products in trend tracking and systematic error control, providing valuable support for global and high-latitude studies of dynamic hydrothermal processes due to its more balanced mid- and high-latitude orbital coverage. Full article

Invasive Mucormycosis (IM) is an extremely rare infection with a high mortality rate, caused by a group of fungi classified as Mucorales moulds. Rhizomucor pusillus is a saprophitic, thermophilic, and angioinvasive microorganism that grows and lives at about 45 °C and is usually found in different environmental spaces such as soil, air, water, food, and other organic matter. These features predispose the infection to wide dissemination, especially in immunocompromised patients and most often in children after chemotherapy for hematological malignancies (HMs). Mucormycosis in patients with hematologic malignancies and neutropenia represents between 0.07% and 4.29% of the concomitant diseases. IM can develop into an infection in different sites, but its most common manifestation is pulmonary, followed by rhino-orbital–cerebral and disseminated forms. In recent years, an increased morbidity rate has been associated with the ongoing COVID-19 pandemic, as cited in the literature. There are many publications with COVID-19-associated mucormycosis (CAM) cases. The present treatment protocol includes extensive and radical surgical debridement and systemic antifungal therapy with Liposomal Amphotericin B (L-AmB), Posaconazole, and Isavuconazole, either combined or as monotherapy. Despite these new treatment modalities, the mortality rate remains over 50%. We present a rare case of a 3-year-old child with acute lymphoblastic leukemia (ALL) and systemic Rhizomucor pusillus infection, diagnosed on the occasion of lung and brain abscesses. The patient underwent lung and brain surgery and is recovering well with no further complications. The two-year follow-up period shows no signs of recurrence of the disease. Full article

The coffee leaf miner (Leucoptera coffeella) is a major pest of coffee crops and can cause significant economic losses. Early monitoring is essential to support decision-making for its control. This study aimed to evaluate the potential of fuzzy logic for detecting leaf miner infestation using a 2.5-year historical series of Sentinel-2A satellite images processed on the Google Earth Engine platform. Field monitoring of coffee leaf miner infestation was carried out at the EPAMIG Experimental Field, located in São Sebastião do Paraíso, Minas Gerais, Brazil. The period evaluated was from September 2022 to April 2025. Vegetation indices were calculated using the Google Earth Engine platform, and a database was built with eight indices (NDVI, EVI, GNDVI, SR, IPVI, NDMI, MCARI, and CLMI) along with coffee leaf miner infestation data. Principal Component Analysis (PCA) was applied to reduce data dimensionality and identify the most relevant indices for distinguishing infested from healthy plants, explaining 90.9% of the total variance in the first two components (PC1 and PC2). The indices CLMI, IPVI, GNDVI, and MCARI showed the greatest contribution to class separation. A fuzzy inference model was implemented based on the mean index values and validated through performance metrics. The results indicated an overall accuracy of 79.1%, a sensitivity (recall) of 86.6%, a specificity of 66.6%, an F1-score of 0.838, a Kappa coefficient of 0.545, and an area under the curve (AUC) of 0.766. These findings confirm the potential of integrating orbital spectral data via Google Earth Engine with fuzzy logic analysis as an efficient tool, contributing to the adoption of more sustainable monitoring practices in coffee farming. The fuzzy logic system received as input the spectral values derived from Sentinel-2A imagery, specifically the indices identified as most relevant by the PCA (CLMI, IPVI, GNDVI, and MCARI). These indices were computed and integrated into the inference model through processing routines developed in the Google Earth Engine platform, enabling a direct connection between satellite-derived spectral patterns and the detection of coffee leaf miner infestation. Full article

This study presents a comprehensive analysis of pre- and co-seismic ionospheric disturbances associated with the 2023 Ms6.2 Jishishan earthquake by leveraging the unique observational strengths of BDS, particularly its high-orbit satellites. A multi-parameter space weather index was employed to effectively isolate seismogenic signals from geomagnetic disturbances, confirming that the main shock occurred during geomagnetically quiet conditions. Statistical analysis of 41 historical earthquakes (Mw ≥ 5.5) reveals that 47.2% were associated with detectable Total Electron Content (TEC) anomalies. An inverse correlation between earthquake magnitude and anomaly detectability within a 31-day window suggests prolonged precursor durations for larger events may produce longer-duration precursory signals, which challenge conventional detection methods. The synergistic capabilities of BDS Geostationary Earth Orbit (GEO) and Inclined Geosynchronous Orbit (IGSO) satellites were demonstrated: GEO satellites provide unprecedented temporal stability for continuous TEC monitoring, while IGSO satellites enable high-resolution spatial mapping of Co-seismic Ionospheric Disturbances (CIDs). The detected CIDs propagated at velocities below 1.6 km/s, consistent with acoustic gravity wave (AGW) mechanisms. A case study during a geomagnetically active period further reveals modulated CID propagation characteristics, indicating potential coupling between seismic forcing and space weather. Our findings validate BDS as a powerful and precise tool for ionospheric seismology and provide critical insights into Lithosphere–Atmosphere–Ionosphere Coupling (LAIC) dynamics. Full article

This study presents multi-band photometric observations and detailed period analysis of a totally eclipsing binary system exhibiting low photometric amplitude. The system exhibits characteristic W Ursae Majoris (EW)-type light curves with complete eclipses. In our light curve modeling, we tested two setups: one excluding third light and the other including it as a free parameter (accounting for a potential tertiary component). Photometric analysis reveals that ASASSN-V J171815.10+450432.9 (hereafter J171815) represents a marginal contact binary system with an extreme mass ratio (the more massive component is designated as the primary star), approaching the theoretical lower limit for stable contact configurations. Furthermore, our investigation of orbital period variations uncovers a long-term period increase at a rate of ${\displaystyle \frac{dP}{dt}}=(1.08\pm 0.05)\times {10}^{-6}\mathrm{day}{\mathrm{yr}}^{-1}$, which is likely attributable to ongoing mass transfer between components. This interpretation aligns with the system’s geometric configuration and observed light curve asymmetries. The unique characteristics presented by this binary system serve as a rare opportunity for in-depth research on the mass ratio theory, and also provide an important opportunity for testing the Thermal Relaxation Oscillation (TRO) theory. Full article