Search Results (103)

Infrared cameras used in radio telescopes often suffer image degradation in complex optical and thermal environments. Solar radiation, convergent reflected light, and thermal emission from support structures can substantially impair imaging performance. To address this problem, this paper proposes a split reflective ellipsoidal baffle for suppressing infrared imaging degradation. Unlike conventional baffles, which mainly rely on structural occlusion and surface absorption, the proposed design functions as an upstream stray light regulation unit. It also establishes a computational framework integrating ellipsoidal vane geometry, realistic edge microtopography modelling, ray-tracing simulation, and detector plane irradiance response analysis. First, the reflective properties of the ellipsoidal surface are used to construct an off-axis stray light propagation constraint model. Under this model, incident stray radiation is redirected away from the effective imaging path or guided into light-trapping regions between adjacent vanes. Second, a laser confocal microscope is used to capture the true three-dimensional edge morphology of vanes with different materials and machining angles. This strategy addresses the limitations of the conventional 0.02 mm rounded edge approximation, which cannot accurately represent real scattering behaviour. The measured morphologies are then converted into high-fidelity computational models compatible with ray-tracing analysis. Furthermore, stray light suppression performance is evaluated using point source transmittance, detector plane irradiance distribution, and grey scale response in experimental images. Simulation and darkroom experiments show that the proposed baffle suppresses residual stray light more effectively than conventional absorptive baffles. The results demonstrate a computable, manufacturable, and experimentally verifiable strategy for front-end stray light control and baffle optimisation. This strategy can also support image quality enhancement in infrared imaging systems operating under complex optical and thermal environments. Full article

Surface roughness of woven fabrics plays a key role in tactile comfort and skin–textile interaction, particularly in medical applications involving prolonged contact with human skin. This study focuses on the surface roughness of woven fabrics in plain and twill (1/3 S) weaves intended for hospital bed sheets and bedding applications. Plain weave represents a structurally symmetric system, while twill weave exhibits a pronounced diagonal structure. Roughness was evaluated using the Fabric Touch Tester (FTT) and further analyzed through amplitude (Rq), height distribution (Rku), and frequency-related parameters (linear peak density) obtained by signal processing and peak analysis in OriginPro 2026. The results showed that weave structure is the dominant factor influencing surface topography. Plain weave fabrics exhibited higher amplitude roughness and more uniform height distribution, while twill fabrics showed lower global roughness but stronger directional dependence, particularly in diagonal directions. Linear peak density was not significantly affected by laundering cycles, fiber composition, or finishing, but was strongly dependent on weave type. The findings demonstrate that due to the orthotropic nature of woven fabrics, surface roughness, derived from surface topography, cannot be adequately described by a single parameter, and that a combined analysis of amplitude and spatial descriptors is required, with the surface being evaluated not only along the principal symmetry directions (warp and weft) but also in off-axis directions. These results provide valuable insight for the design of hospital textiles with improved tactile comfort and reduced risk of skin irritation. Full article

Rod ends are critical structural components primarily designed to sustain axial loads in mechanical and aeronautical assemblies. However, operational conditions may involve transverse loading, which induces significant bending stresses concentrated in the threaded shank region. This research presents an experimental investigation aimed at characterizing the elastoplastic bending behavior of the threaded portion of rod ends subjected to such off-axis loads. Specimens manufactured from precipitation-hardened stainless steel 17-4 PH were tested under both displacement and force control strategies. Each specimen was subjected to incremental loading until failure to determine the elastic limit, yield point, ultimate bending strength and fracture mode. The experimental results enabled a preliminary assessment of the static resistance of the threaded region; furthermore, a comparison with analytical formulations and empirical estimation methods available in the literature revealed promising agreement. These findings highlight the importance of accounting for non-axial loading in the design of threaded joints for critical applications. This study establishes a baseline for broader experimental campaigns aimed at validating these results and exploring fatigue behavior under cyclic transverse loads. Full article

Based on vector wave aberration theory, this paper analyzes the relative positions of the third-order coma node and astigmatism nodes under pupil decenter and proposes an initial structure selection criterion in which the coma node coincides with the geometric midpoint of the two astigmatism nodes. Using this criterion, an F/6 off-axis catadioptric telephoto optical system with a focal length of 900 mm and an entrance pupil diameter of 150 mm was designed. The measured on-axis RMS wavefront error was better than 0.025λ at 632.8 nm. The results demonstrate that the system meets the requirements for high-resolution long-focal-length imaging. Full article

Carbon fiber textile-reinforced engineered cementitious composite (CTR-ECC) is widely utilized in structural strengthening applications due to its advantages of low weight and high strength. A comprehensive understanding of its mechanical behavior under off-axis tension is crucial for addressing the prevalent off-axis stress states in engineering practice. This paper presents an experimental investigation on the off-axis tensile properties of CTR-ECC. Specimens were fabricated with four off-axis angles: 0°, 15°, 30°, and 45°. The study revealed three main findings: (1) Under axial (0°) loading, failure is characterized by yarn fracture and interface slip, whereas off-axis tension induces a stable progressive delamination failure in textile-reinforced ECC systems. (2) While CTR-ECC exhibits higher tensile strength than plain ECC at all angles, its strength decreases significantly as the off-axis angle increases (e.g., a 27.1% reduction at 15°). Off-axis layouts, however, substantially improve energy absorption, with strain energy density increasing by up to 368.4% at 30°. (3) A phenomenological constitutive model was developed, which can adequately capture the stress–strain response of CTR-ECC under various off-axis angles, with coefficients of determination (R²) exceeding 0.9 in all cases. These results provide important insights into the failure mechanisms and performance design of CTR-ECC under off-axis tension conditions. Full article

We introduce the two-point propagation field (TPPF)—a real-valued, phase-sensitive quantity defined as the functional derivative of the single-photon detection probability with respect to an infinitesimal opaque perturbation placed between the source and detection slits. The TPPF is analytically derived and shown to exhibit a stable, high-frequency sinusoidal structure with periods of 4~7 nm near the X-ray detection slit. This structure enables shot-noise-limited displacement detection with ∼200 pm precision for 6 keV X-rays using total photon counts on the order of 1 × ${10}^7$ and detector photon counting as low as 287. Beyond displacement detection, the TPPF physically performs a Fourier–Radon transformation of the projection data, providing a pathway to non-iterative frequency-domain tomography. Two conceptual strategies—a central blocker and off-axis multi-slit arrays—are estimated to lower the required incident photon budget by more than one order of magnitude each, yielding combined reductions of two to three orders of magnitude with near-term detector development. The TPPF concept, originally developed in a perturbative study of single-particle propagation, bridges quantum measurement questions with practical high-resolution X-ray physics. This work provides the foundational physics required for future discrete sampling and 3D numerical reconstruction algorithms. Full article

This study presents a flight-envelope-based methodology for aerodynamic load assessment and composite material selection applied to a hybrid fixed-wing tri-rotor VTOL (Vertical Take-Off and Landing) unmanned aerial vehicle (UAV). A certification-oriented maneuver and gust envelope was established to define the critical load cases. Reynolds-averaged Navier–Stokes (RANS) simulations of the full aircraft at nominal cruise were performed to determine global aerodynamic coefficients and distributed pressure fields, including interference effects from the fuselage and externally mounted VTOL system. A complementary wing-only angle-of-attack study was used to characterize lift, drag, and chordwise pressure distributions over the relevant incidence range. Critical envelope points were mapped to equivalent aerodynamic states in terms of lift coefficient and angle of attack, enabling a quasi-steady correlation between certification loads and CFD (Computational Fluid Dynamics) results. In parallel, carbon fiber-reinforced polymer (CFRP) laminates were experimentally evaluated under tensile, open-hole tensile, and flexural loading. The results indicate that, within the two investigated laminate configurations, the [0°/90°] CFRP laminate provides the more suitable strength and stiffness for primary wing structures, while off-axis laminates are better suited for secondary regions. The proposed workflow links flight-envelope definition, aerodynamic analysis, and material selection, providing a basis for preliminary structural design. Full article

The crystallinity of cubic silicon carbide (3C-SiC) epilayers is improved through the use of a novel wafer bonding and regrowth technique resulting in a reduction in planar defects. The process involves the epitaxial growth of a 3–6 µm thick 3C-SiC seed on silicon (Si), which is polished and bonded to a new handle wafer before the original substrate and defective interface region of the 3C-SiC epilayer are removed. Further epitaxial growth on this Bonded Switchback template results in higher quality 3C-SiC epilayers through the reduction in crystal mosaicity, stacking fault defects, and elimination of interface voids. The process could be applied to 3C-SiC grown on both on- and off-axis substrates, and the form of the new handle has no impact on the growth process, enabling this technology to be applied to sapphire or hexagonal 4H-SiC substrates. The use of such substrates would overcome the thermal budget limitations of Si substrates for 3C-SiC heteroepitaxy and ion implantation. Bonded Switchback can improve material quality for applications in power electronics, as well as see the heterogeneous integration of 3C-SiC into other device structures, potentially leading to a new range of hybrid 3C-SiC/Si devices without the high density of defects observed at the interface between these two materials. Full article

This paper addresses the chromatic aberration and off-axis collimation issues in the laser–lens–fiber coupling system by proposing a chromatic aberration-corrected Meta-lens design based on a particle swarm optimization algorithm and structural interleaving method. By establishing an optimization model that includes wavelength-dependent phase factors, achromatic performance with a focal length standard deviation of less than 0.4 μm is achieved in the 1260–1360 nm band. Innovatively, the structural interleaving technique is adopted to integrate multiple different phase distributions into a single meta-surface, keeping the coupling efficiency fluctuation within 8% over a ±1 μm off-axis displacement range. The research results demonstrate that this method effectively solves the phase quantization and dispersion matching challenges of large-scale meta-lens, achieving a phase matching efficiency of 95.2%, providing a feasible path for the engineering application of highly robust meta-lens in high-precision optical systems. Full article

Compared with the conventional push-broom imaging mode, conical scanning extends the imaging swath through rotational scanning and is suitable for high-resolution, wide-swath remote sensing. To achieve continuous full-coverage imaging, the camera must be mounted at a certain tilt angle and employ an off-axis optical system with a sufficiently large field of view (FOV). However, the tilted installation causes nonuniform irradiance and increased off-axis distortion, while wide-field off-axis imaging also introduces radiometric consistency problems in focal-plane multi-detector stitching. To address these issues, this study investigates the optical design of a tilted off-axis camera for conical-scan imaging. Under the constraints of full coverage and swath requirements, key optical parameters were jointly determined, and a lightweight wide-coverage off-axis three-mirror system was designed, optimized, and evaluated. The final system has a focal length of 1545 mm, an F-number of 8.4, and a full FOV of 23.4° × 11.7°. The modulation transfer function is greater than 0.41 at the Nyquist frequency, and the maximum distortion is less than 2.5446%. In addition, for the focal-plane optical stitching structure, the coupled effects of local structural vignetting and global geometric vignetting induced by the tilted installation were analyzed. The results show that the gray-level difference in the adjacent detector overlap regions is only 0.31–0.53 digital numbers (DN), and the full focal plane shows a smooth gray-level attenuation rate of 5.39–6.77%. These results indicate that vignetting has no significant effect on focal-plane stitching. The proposed camera is well suited for conical-scan imaging. Full article

Strong light interference severely degrades imaging system performance. This paper presents a novel digital micromirror device (DMD)-based imaging system for robust, strong light suppression and long-distance detection. Our design strategically places the DMD at the primary image plane, utilizing a large F-number objective for extended depth of field. The relay imaging system employs a tilted image plane in a near-symmetric configuration to effectively balance DMD-induced aberrations, which avoids the off-axis layout and overall tilt of the relay system itself and greatly simplifies system alignment. Stray light analysis verifies the rationality of the structural design, and MTF tests confirm that the assembly performance of the prototype meets the design requirements. The system can achieve clear imaging of buildings at 1 km, which demonstrates its long-distance imaging capability. With an entrance pupil power density of 4.68 × 10⁻⁴ W/cm², strong light interference suppression has been successfully achieved via the DMD regional flipping method. This system offers an efficient solution for long-range imaging in strong light environments. Full article

The jet structure plays an important role in both the prompt and afterglow emission phases of gamma-ray bursts (GRBs). Whether GRB jets are better described by uniform (top-hat) or structured models remains an open question. We use the afterglowpy Python package to numerically model the late X-ray afterglow light curves of a large sample of long and short GRBs, and apply the Bayesian Information Criterion (BIC) to compare the performance of top-hat and Gaussian structured jet models. Within our adopted modeling framework, we find that the top-hat model is preferred by the BIC for ∼78.9% (150/190) of long GRBs and 70% (7/10) of short GRBs. GRB 180205A and GRB 140515A exhibit $\Delta$BIC < 2 for all three model comparisons, indicating that top-hat, Gaussian, and power-law jets provide equivalent fits to their afterglow light curves. This large-sample analysis suggests that uniform jets may be more common than structured jets in the observed GRB population, although this conclusion is subject to the limitations of our model assumptions and the BIC-based model selection criterion. Furthermore, we find that the best-fit distributions of observer angle ${\theta }_{\mathrm{obs}}$, electron energy fraction ${ϵ}_e$, and isotropic equivalent energy $E_0$ differ significantly between the top-hat and Gaussian jet models, with ${\theta }_{\mathrm{obs}}$ showing the most pronounced distinction. Full article

Off-axis reflective telescopes are prone to component misalignment due to external environmental factors and mechanical vibrations. This misalignment introduces low-order aberrations, which severely degrade imaging quality. Thus, active misalignment correction is crucial for maintaining the imaging performance of off-axis reflective telescopes. Current computer-aided alignment technologies for optical systems mostly rely on wavefront sensors to acquire aberrations at multiple fixed fields of view (FOVs) or even the full FOV. This significantly increases system complexity and hinders practical engineering applications. To address this issue, this study first conducts sensitivity analysis of misaligned degrees of freedom (DOFs) using a mode truncation algorithm based on singular value decomposition (SVD). A compensation strategy is proposed to avoid the aberration coupling effect. Furthermore, two novel misalignment aberration compensation methods for off-axis reflective telescopes are presented. These methods require only a single focal spot image and eliminate the need for aberration detection and iterative calculations. One method directly solves component misalignment errors using a convolutional neural network (CNN) based on the system’s point spread function (PSF). To further improve compensation performance, an improved method fusing spot images and Zernike coefficients is proposed. In practical misalignment correction, both methods input a single acquired focal spot image into a well-trained model to obtain the misalignment compensation amount. Simulation experiments demonstrate that the improved method, which uses Zernike polynomial coefficients as an intermediate feature bridge, effectively establishes the mapping relationship between spot images and misalignment amounts. It achieves higher solution accuracy and better aberration compensation effect compared to the direct CNN method. This verifies the necessity of extracting Zernike polynomial coefficient features from spot images. Comparative experiments with the traditional sensitivity matrix method show that the two proposed methods outperform the sensitivity matrix method in aberration compensation accuracy over a large misalignment range. Comprehensive simulation results confirm the feasibility and effectiveness of the proposed methods. They overcome the limitations of existing methods, such as complex structure, high cost, and low efficiency, to a certain extent. Full article

Methane (CH₄) is a potent greenhouse gas, with livestock rumination being a significant contributor to global emissions. This study developed a real-time monitoring system utilizing Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) to simultaneously track rumination behavior and CH₄ concentrations in cattle breath. By optimizing the off-axis integrated cavity structure and implementing a specialized environmental control system, we enhanced stability and detection accuracy, achieving a rapid 3 s response time to dynamic concentration changes. Laboratory stability tests and Allan deviation analysis demonstrated a minimum detection limit of 0.07 ppm. Continuous field monitoring of Simmental cattle revealed a daily methane production of approximately 311.83 L. The emission rates exhibited a distinct double-peak pattern heavily influenced by feeding schedules. Furthermore, a positive correlation was observed between the time elapsed post feeding and both the frequency and intensity of methane emission peaks. This method enables highly dynamic, stable, long-term monitoring of greenhouse gas emissions from ruminants, providing a robust tool for quantifying emissions and informing scientific feeding practices. Full article

The aerodynamic behavior of small-scale UAV propellers operating under non-axial inflow conditions poses a significant prediction challenge due to the presence of strong azimuthal asymmetries, inherently unsteady flow phenomena, and Reynolds number effects that dominate forward flight conditions. Although numerical models based on the Moving Reference Frame (MRF) formulation combined with steady RANS solvers are widely used in engineering practice because of their low computational cost, the precise limits of their applicability in crossflow configurations remain poorly defined. This work conducts a comprehensive numerical investigation that systematically compares steady RANS–MRF predictions against time-accurate URANS simulations across a wide range of advanced ratios and rotor tilt angles. Rigorous validation of the computational framework against experimental data in axial and near-axial regimes demonstrates excellent agreement, with deviations below 5% in propulsive efficiency. The results clearly identify the operational envelope within which MRF-based steady models remain valid under non-axial inflow. In particular, the steady approach exhibits robust performance for low-to-moderate advance ratios, where global errors in thrust and power remain below 10% for $\mu =0.40$. However, the fidelity of the method deteriorates sharply under extreme edgewise-flight conditions ($\mu =0.70)$, in which the crossflow component dominates the aerodynamic field, the “frozen-rotor” assumption progressively loses mathematical consistency, and the solver may converge toward steady solutions that no longer represent a physically meaningful flow state. The URANS analysis further reveals two critical phenomena that cannot be captured by steady-state models. First, at high advance ratios, the retreating blade encounters an extensive region of reverse flow, which induces negative sectional thrust and strongly anharmonic load waveforms. This behavior has direct implications for structural design: the peak-to-peak amplitude of thrust oscillation in edgewise flight can exceed the mean thrust level, implying extreme cyclic loading and a high risk of high-cycle fatigue. Second, the simulations quantify the emergence of off-axis parasitic moments (pitching and rolling), which are negligible in vertical flight but reach magnitudes comparable to the total aerodynamic torque in forward-flight conditions. Taken together, these findings highlight the need for a hybrid-fidelity strategy in UAV propulsion analysis: employing steady RANS–MRF within the validated domain for energetic assessments, while relying on time-accurate URANS for mandatory evaluation of structural loading, vibration, and control logic in critical high-speed regimes. Full article