Limited Angle Research Articles

Macroscopic and Mesoscopic Damage Characteristics and Energy Evolution Laws of Rock Mass With Double Arcuate Fractures Under Uniaxial Compression

ABSTRACTIn order to reveal the influence of double arc‐shaped fissure dip angles on the macro‐micro failure and energy evolution laws of rock masses, a numerical model of red sandstone was firstly established using the PFC2D. Moreover, mesoscopic parameters of the numerical model were calibrated based on the uniaxial compression tests on intact and single straight fissure red sandstone specimens. Then, particle flow simulation tests of red sandstone with different arc‐shaped fissure dip angles were carried out. The results show that the peak strength and elastic modulus both increase with the increase of arc‐shaped fissure dip angle α, exhibiting an oblique shear‐tensile failure pattern. Six types of cracks evolved during the instability and rupture of the rock mass with double arc‐shaped fissures. The macroscopic fissures in the rock mass ultimately penetrate along the extension direction of the arc‐shaped fissures. As the arc‐shaped fissure dip angle α increases, the crack evolution is positively correlated with the acoustic emission (AE) of the specimen. When approaching instability failure, the AE ringing count rapidly increases. There is a critical angle limit inflection point for the total energy absorbed by the rock between 60° and 75°, with a total energy increase of about 54%. During instability failure, it is dominated by dissipative energy, with elastic energy as a supplement. This article derived a damage constitutive model of red sandstone with different arc‐shaped fissure dip angles, revealing the damage laws of red sandstone under different arc‐shaped fissure dip angles.

Enhancing System Capacity Through Joint Space‐Ground Multi‐Beam Coordination for LEO Satellite Systems

ABSTRACTDue to the long transmission distance of the constellation network represented by the low‐orbit satellite system, the satellite‐to‐ground link is subject to large path loss and limited communication performance. This paper uses multi‐satellite and multi‐beam joint transmission technology to form a virtual multiplex network with ground multi‐antenna terminals (Multiple‐Input Multiple‐Output [MIMO] system). However, due to the high‐speed movement of satellites, the topology of the MIMO system is unstable, which in turn affects the stability of the system throughput. This article proposes two inter‐satellite cooperation modes to improve the stability of MIMO system capacity. The first method is to optimize the channel capacity by rationally allocating the beam power of the gateway station so that the gateway station can achieve transparent forwarding through satellites. The second method rotates the angle of the user's receiving antenna to combat channel changes caused by changes in satellite position. Simulation results show that both methods can effectively improve the minimum channel capacity. Transparent forwarding can increase the capacity by about 22.7%, while the rotating antenna can still improve the performance gain by at least 36.3% even with a limited rotation angle. This research contributes to the development of stable and efficient communication systems in satellite‐ground cooperative networks.

Phase transformation and texture evolution during micro-incremental forming of ultra-thin SS316 sheets

Size effects present significant challenges in micro-scale manufacturing, compounded by the complexities of tooling and fixture design. However, Micro-incremental Sheet Forming (µ-ISF) has emerged as an innovative die-less forming technique for producing miniature products, effectively addressing some of these challenges. This study focuses on the formability analysis of annealed SS316 foils of various thicknesses. Trapezoids with different aspect ratios were produced using three different tool diameters (Td). It was observed that an increase in Td led to a decrease in both surface roughness and wall angle limit. This reduction in formability was thoroughly investigated through microstructural analysis, revealing that deformation-induced phase transformation (DIPT) is one of the key factors contributing to the decreased formability of SS316 foils.

Improving Treatment Quality of Gynecologic Cancers with Online Adaptive Brachytherapy Using Deep Learning-Based CT Imaging

This study proposes a framework for online adaptive three-dimensional (3D) brachytherapy, a type of radiation therapy used to treat gynecological cancers such as cervical and endometrial cancers. Intracavitary brachytherapy is used to deliver a high dose of radiation directly to the tumor, while minimizing exposure to the surrounding normal tissue. Maintaining accurate reproducibility of radiation dose delivery during each treatment session is important. The proposed framework uses a C-arm-based integrated online imaging system for computed tomography (CT) and single-photon emission computed tomography (SPECT) to detect changes in the treatment conditions and improve treatment quality. The C-arm CT system acquires 3D images by obtaining two-dimensional image data at limited rotation angles, which are less than the complete 360° range of rotation. However, images obtained with limited angular rotation have poor image quality and many artifacts. To overcome this limitation, a deep learning technique was applied to eliminate these artifacts and improve image quality. This study evaluated the auto-segmentation performance of ground truth (GT) images, limited-angle C-arm cone-beam CT images, and C-arm CT images corrected using deep learning. We used the Dice similarity coefficient and Hausdorff distance to quantitatively evaluate the auto-segmentation performance of major organs in the pelvic region. Although slight differences were observed in certain areas, the auto-segmentation results demonstrated an overall high performance, similar to that of the GT image. The results showed that the proposed framework can establish an optimal treatment plan by quickly and accurately calculating the patient's internal radiation dose distribution. This study demonstrates the potential of deep learning-based high-quality CT imaging techniques and auto-contouring techniques for major organs within images to improve the treatment quality of intracavitary brachytherapy.

Advancing 3D dental scanning: The use of photogrammetry with light detection and ranging for edentulous arches

The advent of computer-aided design and computer-aided manufacturing (CAD-CAM) has necessitated the acquisition of digital scans. However, there are limitations and problems with acquiring accurate 3-dimensional (3D) casts from edentulous patients, especially in the presence of saliva. The purpose of this in vitro study was to develop a novel approach for obtaining 3D casts of edentulous arches by using 2-dimensional (2D) images as an alternative to traditional 3D scanners with and without light detection and ranging (LiDAR). This study comprised 6 groups, each consisting of 10 specimens. For the control group, 3D casts were generated by scanning edentulous mandibular molds using a dental laboratory scanner. Experimental groups included photogrammetry with and without LiDAR under various conditions (Groups PG360, PG120, LPG120, PG360S, LPG120S). For Groups PG120, LPG120, and LPG120S, a custom-made manikin was used. In all photogrammetry groups, images of each mold were captured with a mobile phone (iPhone 14 Pro Max). The casts from the experimental groups were superimposed onto those from the control group using the Blender Foundation software program (Version 3.6.1). The mean distances were calculated and statistically analyzed using 1-way ANOVA followed by the post hoc Tukey test (α=.05). The mean distances between the experimental groups and the control group varied significantly. The PG360 and PG120 groups showed a statistically significant difference from the control group (P<.001, 95% CI), with mean distances of 1.54 ±0.31 mm and 4.54 ±1.65 mm, respectively. The LPG120S group, which combined photogrammetry with LiDAR in the presence of artificial saliva, achieved a mean distance of 2.03 ±0.46mm, which was not significantly different from the control group (P=.501, 95% CI). The successful scanning of edentulous mandibular molds using a mobile phone was achieved through a combination of 2D images and LiDAR, covering a limited access angle of 120 degrees. Compared with other techniques, the method developed the most accurate 3D casts and was less susceptible to interference from saliva, a significant issue for intraoral scanners.

Advancing Forest Plot Surveys: A Comparative Study of Visual vs. LiDAR SLAM Technologies

Forest plot surveys are vital for monitoring forest resource growth, contributing to their sustainable development. The accuracy and efficiency of these surveys are paramount, making technological advancements such as Simultaneous Localization and Mapping (SLAM) crucial. This study investigates the application of SLAM technology, utilizing LiDAR (Light Detection and Ranging) and monocular cameras, to enhance forestry plot surveys. Conducted in three 32 × 32 m plots within the Tibet Autonomous Region of China, the research compares the efficacy of LiDAR-based and visual SLAM algorithms in estimating tree parameters such as diameter at breast height (DBH), tree height, and position, alongside their adaptability to forest environments. The findings revealed that both types of algorithms achieved high precision in DBH estimation, with LiDAR SLAM presenting a root mean square error (RMSE) range of 1.4 to 1.96 cm and visual SLAM showing a slightly higher precision, with an RMSE of 0.72 to 0.85 cm. In terms of tree position accuracy, the three methods can achieve tree location measurements. LiDAR SLAM accurately represents the relative positions of trees, while the traditional and visual SLAM systems exhibit slight positional offsets for individual trees. However, discrepancies arose in tree height estimation accuracy, where visual SLAM exhibited a bias range from −0.55 to 0.19 m and an RMSE of 1.36 to 2.34 m, while LiDAR SLAM had a broader bias range and higher RMSE, especially for trees over 25 m, attributed to scanning angle limitations and branch occlusion. Moreover, the study highlights the comprehensive point cloud data generated by LiDAR SLAM, useful for calculating extensive tree parameters such as volume and carbon storage and Tree Information Modeling (TIM) through digital twin technology. In contrast, the sparser data from visual SLAM limits its use to basic parameter estimation. These insights underscore the effectiveness and precision of SLAM-based approaches in forestry plot surveys while also indicating distinct advantages and suitability of each method to different forest environments. The findings advocate for tailored survey strategies, aligning with specific forest conditions and requirements, enhancing the application of SLAM technology in forestry management and conservation efforts.

Dealing with Missing Angular Sections in NanoCT Reconstructions of Low Contrast Polymeric Samples Employing a Mechanical In Situ Loading Stage.

While in situ experiments are gaining importance for the (mechanical) assessment of metamaterials or materials with complex microstructures, imaging conditions in such experiments are often challenging. The lab-based computed tomography system Xradia 810 Ultra allows for the in situ (time-lapsed) mechanical testing of samples. However, the in situ loading setup of this system limits the image acquisition angle to 140°. For low contrast polymeric materials, this limited acquisition angle leads to regions of low information gain, thus preventing an accurate reconstruction of the data using a filtered back projection algorithm resulting in erroneous microstructures. Here, we demonstrate how the information gain can be improved by selecting an appropriate position of the sample. A low contrast polymeric tetrahedral microlattice sample and a structured sample with specific markers, both scanned over 140° and 180°, demonstrate that the missing structural details in the 140° reconstruction are limited to an angular wedge of about 20°. Depending on the sample geometry and microstructure, applying simple strategies for the in situ experiments allows accurate reconstruction of the data. For the tetrahedral microlattice, a simple rotation of the sample by 90° rotates all relevant surfaces by about 30° to the original illumination direction, creating a more even X-ray illumination for all the projections, thus providing enough X-ray absorption for an accurate reconstruction of the geometry.

Angular Kinematics at Minimum Toe Clearance in People With Transtibial Amputation Using Articulated and Nonarticulated Prosthesis.

Subjects with unilateral transtibial amputation exhibit altered minimum toe clearance (MTC) depending on the ankle prosthesis used. It has been suggested that a limited prosthetic ankle angle could be the cause of the change. The aim of this study was to investigate the alterations in kinematics in the joints responsible for the changes in MTC when using an articulating hydraulic ankle (AHA) prosthesis compared to a nonarticulating ankle (NAA) prosthesis. Twelve participants with unilateral transtibial amputation walked at their self-selected speed on a 10 m pathway. They used both the same AHA and NAA prosthetic models and the prosthetic characteristics were unchanged except for the ankle mechanisms and, consequently, its mass. Data from MTC and hip, knee, and ankle angles in the sagittal, frontal, and transversal plane at the time of MTC were statistically analyzed with a paired sample t-test. The AHA prosthesis showed significantly higher MTC mean (AHA=24.7 ± 9.6 mm versus NAA=17.4 ± 5.2 mm, P<0.01) and variability (13.4 ± 9.6 mm versus 6.7 ± 4.2 mm, P=0.03) on the prosthetic limb than the NAA. A higher mean MTC could be explained by an increase in ankle angle dorsiflexion (AHA=-1.2 ± 2.6 deg versus NAA=-2.9 ± 1.5 deg, P=0.01), while the variability of the prosthetic MTC appears to be influenced by changes in prosthetic mass. The results of this study suggest that ankle dorsiflexion during swing and the mass of the prosthesis have a direct influence in mean MTC and its variability, respectively.

Source-detector trajectory optimization for FOV extension in dental CBCT imaging

In dental imaging, Cone Beam Computed Tomography (CBCT) is a widely used imaging modality for diagnosis and treatment planning. Small dental scanning units are the most popular due to their cost-effectiveness. However, these small systems have the limitation of a small field of view (FOV) as the source and detector move at a limited angle in a circular path. This often limits the FOV size. In this study, we addressed this issue by modifying the source-detector trajectory of the small dental device. The main goal of this study was to extend the FOV algorithmically by acquiring projection data with optimal projection angulation and isocenter location rather than upgrading any physical parts of the device. A novel algorithm to implement a Volume of Interest (VOI) guided trajectory is developed in this study based on the small dental imaging device's geometry. In addition, this algorithm is fused with a previously developed off-axis scanning method which uses an elliptical trajectory, to compensate for the existing constraints and to further extend the FOV. A comparison with standard circular trajectory is performed. The FOV of such a standard trajectory is a circle of 11 cm diameter in the axial plane. The proposed novel trajectory extends the FOV significantly and a maximum FOV of 19.5 cm is achieved with the Structural Similarity Index Measure (SSIM) score ranging between (≈98-99%) in different VOIs. The study results indicate that the proposed source-detector trajectory can extend dental imaging FOV and increase imaging performance, which ultimately results in more precise diagnosis and enhanced patient outcomes.

Impurities with a cusp: general theory and 3d Ising

In CFTs, the partition function of a line defect with a cusp depends logarithmically on the size of the line with an angle-dependent coefficient: the cusp anomalous dimension. In the first part of this work, we study the general properties of the cusp anomalous dimension. We relate the small cusp angle limit to the effective field theory of defect fusion, making predictions for the first couple of terms in the expansion. Using a concavity property of the cusp anomalous dimension we argue that the Casimir energy between a line defect and its orientation reversal is always negative (“opposites attract”). We use these results to determine the fusion algebra of Wilson lines in N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{N} $$\\end{document} = 4 SYM as well as pinning field defects in the Wilson-Fisher fixed points. In the second part of the paper we obtain nonperturbative numerical results for the cusp anomalous dimension of pinning field defects in the Ising model in d = 3, using the recently developed fuzzy-sphere regularization. We also compute the pinning field cusp anomalous dimension in the O(N) model at one-loop in the ε-expansion. Our results are in agreement with the general theory developed in the first part of the work, and we make several predictions for impurities in magnets.

Numerical and experimental study of three-layered Al 1050/Mg AZ31B/ Al 1050 sheets formability considering strain and stress conditions through single point incremental forming

This article examines the formability of 3-layer Al 1050/Mg-AZ31B /Al 1050 sheets experimentally and numerically. Mg AZ31B, with its high strength-to-weight ratio, and Al 1050, with its formability and lightweight, are attractive industrial metals. In the experimental method, the forming limit diagram (FLD), the Forming limit angle (FLA), and the fracture depth were investigated for the 3-layer and base samples with two pyramid and cone geometries. The results showed that the ductility in the cone geometry is higher than that of the pyramid. Also, by comparing the FLD of the 3-layer sample to the base sample, the results showed that the formability of the 3-layer sample increased compared to the Mg-AZ31B base sample. In contrast, the formability decreased compared to the base sample of Al 1050. Numerical studies for predicting the FLD using the SPIF method were carried out using Abaqus software. The numerical techniques considered the second deviation minor strain (SDMIS), second deviation effect strain (SDEF), second deviation thickness (SDT), and second deviation major strain (SDMS). The results showed that the highest accuracy occurred for the SDT method compared to other numerical methods. To remove the effect of the strain path on the numerical analysis for predicting the FLD (from the stress analysis method), a second deviation of von Mises stress (SDVMS) was used. By examining the results, it was found that the results of numerical methods considering stress could be highly accurate.

Partial state-constrained integrated guidance and control for an STT missile with self-adjusting prescribed performance via non-barrier Lyapunov function method

A state-constrained guidance and control law is vital to the flight safety of an aerial interceptor against a maneuvering target. Taking the flight angle limitations, manipulation saturation, and terminal constraints into consideration, a novel integrated guidance and control (IGC) schema with a self-adjusting prescribed performance is proposed. To avoid the feasibility condition via the conventional barrier Lyapunov function-based method, a new state-dependent nonlinear mapping function is designed, based on which the state-constrained IGC system is converted into a constrained-free model. A novel prescribed performance with a self-tuning mechanism is proposed to guarantee satisfied transit and steady guidance performances. The backstepping technique combined with super-twisting integral sliding modes and newly defined predefined-time disturbance observers is implemented to generate state-constrained virtual command signals. All the signals in the closed-loop system are strictly proven to be bounded by Lyapunov stability theory. The simulation results show the effectiveness of the proposed IGC schema.

Comparison between Flexible Ureteroscopy by Using Uretral Access Sheath and Flexible Ureterosopy without Using Ureteral Access Sheath in Cases of Upper Ureteric and Pelvic Stones

Abstract Background Ureteral access sheath use has been widely accepted by urologists since older ureteroscopes were difficult to insert into the ureter due to their stiffness, width and limited deflection angles. However, with advancing technology and design improvement, new generation ureteroscopes are thinner and built with lighter and more flexible materials than their older counterparts. This in turn has produced devices that are easier to maneuver, meaning that procedures can be performed without needing UAS thus the actual benefit of UAS was under question. Aim of the Work to compare the usage of UAS versus not using the UAS during FURS regard operative time, intra operative, postoperative complications and patient satisfaction. Patients and Methods This randomized controlled clinical trial was conducted in Urology Department, Ain Shams, University Hospitals and included 50 upper ureteric stone disease patients. They were divided into 2 comparative groups (each group 25 patients) by closed envelop method. One of these groups underwent FURS with ureteral access sheath and the second group underwent FURS without ureteral access sheath. Results there was no significant difference between the 2 groups regarding demographic or clinical data. Moreover, no significant difference was detected between the 2 groups regarding intra or post-operative complications, stone free rate or duration of hospital stay. However, statistically significant longer operative time was recorded in UAS group compared to no UAS group. Conclusion our study showed that flexible ureterenoscopy without ureteral access sheath Seems to be safe as flexible ureterenoscopy with ureteral access sheath regards intraoperative, post- operative complications, patient satisfaction, stone free rate and duration of hospital stay, an additional advantage is shorter operative time without using of ureteral access sheath

Impact of Ureteral Access Sheath during Flexible Ureteroscopy as Regard Complication and Stone Free Rate

Abstract Background Ureteral access sheath use has been widely accepted by urologists since older ureteroscopes were difficult to insert into the ureter due to their stiffness, width and limited deflection angles. However, with advancing technology and design improvement, new generation ureteroscopes are thinner and built with lighter and more flexible materials than their older counterparts. This in turn has produced devices that are easier to maneuver, meaning that procedures can be performed without needing UAS thus the actual benefit of UAS was under question. Objective To compare the usage of UAS versus not using the UAS during FURS regard operative time, intra operative, postoperative complications and patient satisfaction. Patients and Methods 120 patients with symptomatic upper ureteric and renal pelvic stone disease were enrolled, they were divided into 2 equal groups one underwent FURS with UAS and the second group underwent FURS without UAS. Results There was a statistically significant higher frequency of postoperative complications in No UAS comparing to UAS group with p-value (p &amp;lt; 0.05) in the form of Postoperative fever and Postoperative sepsis. While, there is no statistically significant difference between groups according to OR time (min.), Stone free rate, Hospital stay (hrs.) and Postoperative pain. Conclusion In the current study we aimed to compare the usage of UAS versus not using the UAS during FURS regard operative time, intra operative, postoperative complications and patient satisfaction. In the included patients, There was a statistically significant higher frequency of postoperative sepsis and fever in No UAS comparing to UAS group, with p-value (p &amp;lt; 0.05). While, there is no statistically significant difference between groups according to operative time “min”, Stone free rate, Hospital stay (hrs.) and Postoperative pain. Moreover, significant association of postoperative sepsis and fever with residual stones in included patients. UAS has superior advantage over no-UAS due to lower incidence of sepsis and fever in the current study.

Ultra-wide viewing angle holographic display system based on spherical diffraction

In the field of holographic displays, achieving a large viewing angle (LVA) has long been an essential and formidable challenge due to the limited diffraction angle of planar spatial light modulators (SLMs). Spherical holography, which allows observation from all perspectives, represents a practical approach to achieve the LVA. However, the physical limitations of commercial SLMs constrain direct implementation, making the realization of spherical holographic displays almost impractical and thus hindering technological advancement. This paper introduces an optical solution for spherical holographic display system, enabling the accurate reproduction of ultra-wide viewing angles and large objects. Our system utilizes a novel technique involving a convex parabolic mirror to convert an incident plane wave into a spherical wave. This innovative strategy permits the use of a planar SLM to create a 360°spherical holographic display. Additionally, we address the sampling issue for generating spherical holograms by constraining the point spread function (PSF), reducing the number of samples, and adapting it for visible light. Numerical simulations and optical experiments validate our success in achieving an ultra-wide viewing angle with a 360°horizontal angle and an 80°zenith angle range. Our system outperforms the state-of-the-art holographic-optical-elements approach both in computation speed and object size. We believe that our work significantly advances spherical holographic displays and offers a practical solution with vast potential applications in medicine, geology, and astronomy.

Prospect for detecting magnetism in two-dimensional perovskite oxides by electron magnetic circular dichroism

Two-dimensional (2D) magnets, especially strongly correlated 2D transition-metal perovskite oxides, have attracted significant attention due to their intriguing electromagnetic properties for potential applications in spintronic devices. Potentially electron magnetic circular dichroism (EMCD) under zone axis conditions can provide three-dimensional components of magnetic moments in 2D materials, but the collection efficiency and the signal-to-noise ratio for out-of-plane (OOP) components is limited due to the limited collection angle. Here we conducted a comprehensive computational simulation to optimize the experimental setting of EMCD for detecting the OOP components of magnetic moments in three beam conditions (3BCs) on 2D perovskite oxides La1-xSrxMnO3 (LSMO) in a TEM. The key parameters are sample thickness, accelerating voltage, Sr doping concentration, collection semi-angle and position, and sample orientation including systematic reflections excited and tilt angle. Our simulation results demonstrate that the relative dynamical diffraction coefficients of Mn OOP EMCD of LaMnO3 with a thickness ranging from 1 unit cell (uc) to 4 uc can be optimized in a 3BC with (110) systematic reflections excited and a relatively large collection semi-angle of 19 mrad at the relatively low accelerating voltage of 80 kV. In most cases, the relative dynamic diffraction coefficients for La1-xSrxMnO3 with the thickness ranging from 1 uc to 4 uc decrease with the increase of the Sr doping concentrations. The optimal tilt angle from a zone axis to a 3BC is 18° for the cases of the LSMO thickness of 2 uc, 3 uc and 4 uc, and 22° for the monolayer LSMO. Our work provides the theoretical simulation foundation for optimized EMCD experiments for measuring OOP components of magnetic moments in 2D transition-metal perovskite oxides.

Bimodal distribution of inter-individual distance in free-ranging narrow-ridged finless porpoises

Inter-individual distance (IID) is an important indicator of social organisation because solitary species are spatially intolerant towards conspecifics, whereas group-living species are usually gregarious with collective behaviour. Therefore, by examining the relationship between the distribution of IIDs and the active space of cues or signals, and behaviours, we can predict their social organisation. The narrow-ridged finless porpoises (NRFPs) have been described as a solitary species; however, recent studies described NRFPs tend to live in groups more than alone. To resolve the inconsistency, the present study investigated IIDs, the active spaces of sounds, and behaviours. The distribution of IIDs measured using drone was classified into three distributions. The close and intermediate distributions were significantly shorter than the distribution predicted by the angle of drone camera, whereas the far distributions were not. The far distributions were thus a random distribution within the limited angle of the camera. The close distributions were shorter than the active space, exhibiting a high proportion of collective behaviours, while intermediate distributions did not. These results suggest that NRFPs have both solitary- and group-living characteristics. Specifically, the intermediate distribution suggests a solitary aspect to maintain IIDs from others, while the close distribution indicates a group-living aspect with social interactions.

Position Servo Control of Electromotive Valve Driven by Centralized Winding LATM Using a Kalman Filter Based Load Observer

The exhaust gas recirculation (EGR) valve plays an important role in improving engine fuel economy and reducing emissions. In order to improve the positioning accuracy and robustness of the EGR valve under uncertain dynamics and external disturbances, this paper proposes a positioning servo system design for an electromotive (EM) EGR valve based on the Kalman filter. Taking a novel valve driven by a central winding limited angle torque motor (LATM) as the object, we have fully considered the influence of the motor rotor position and load current, as well as the magnetic field saturation and cogging effect, improved the existing LTAM model, and derived accurate torque expression. The parameter uncertainty of the above internal model and the external stochastic disturbance were unified as “total disturbance”, and a Kalman filter-based observer was designed for disturbance estimations and real-time feed-forward compensation. Furthermore, using non-contact magnetic angle measurements to obtain accurate valve position information, a position control model with real-time response and high accuracy was established. Numerous simulated and experimental data show that in the presence of ± 25% plant model parameter fluctuations and random shock-type disturbances, the servo system scheme proposed in this paper achieves a maximum position deviation of 0.3 mm, a repeatability of positioning accuracy after disturbances of 0.01 mm, and a disturbance recovery time of not more than 250 ms. In addition, the above performance is insensitive to the duration of the disturbance, which demonstrates the strong robustness, high accuracy, and excellent dynamic response capability of the proposed design.

Enhanced Second-Harmonic Generation in Thin-Film Lithium Niobate Circular Bragg Nanocavity.

Second-order nonlinearity gives rise to many distinctive physical phenomena, e.g., second-harmonic generation, which play an important role in fundamental science and various applications. Lithium niobate, one of the most widely used nonlinear crystals, exhibits strong second-order nonlinear effects and electro-optic properties. However, its moderate refractive index and etching sidewall angle limit its capability in confining light into nanoscales, thereby restricting its application in nanophotonics. Here, we exploit nanocavities formed by second-order circular Bragg gratings, which support resonant anapole modes, to achieve a 42 000-fold enhanced second-harmonic generation in thin-film lithium niobate. The nanocavity exhibits a record-high normalized conversion efficiency of 1.21 × 10-2 cm2/GW under the pump intensity of 1.9 MW/cm2. Besides, we also show s- and p-polarization-independent second-harmonic generation in elliptical Bragg nanocavities. This work could inspire the study of nonlinear optics at the nanoscale on thin-film lithium niobate, as well as other novel photonic platforms.

Study of hydrogen fuel cell unmanned surface vehicle crane collision avoidance control by using an improved artificial potential field

ABSTRACT In this paper, a collision avoidance control strategy based on an enhanced Artificial Potential Field (APF) is proposed to overcome stationary and dynamic surface obstacles for Unmanned Surface Vehicle Crane (USVC) powered by hydrogen fuel cells. The proposed collision avoidance control relies on the gravitational and repulsive potential field functions. An angle limitation and speed optimisation design strategies are derived to enhance the path planning performance and guarantee the safety of the system. Finally, the simulation and experiment of USVC platform equipped with hydrogen fuel cells are developed to confirmed the effectiveness and reliability of the collision avoidance control strategy based on a novel APF under several obstacles.