Principal Point Research Articles

A new procedure for onboard calibration of star sensors installed on low Earth orbit satellite

This paper suggests a new onboard calibration procedure for star sensors installed on low Earth orbit satellites. In this procedure, all the error factors are investigated, and an accurate model of the star sensor is presented. Then, a new scenario is proposed for producing real data from a star sensor installed on a satellite while the satellite is moving in orbit. These sensor data are entered into the unscented Kalman filter as measurement data, and the sensor parameters, including focal length and principal point, are estimated. In the following, the estimated parameters are entered into the linear Kalman filter, and the misalignment error is estimated. Finally, the proposed procedure is simulated, and its performance is checked. The simulation results show the high accuracy and convergence speed of the suggested algorithm.

Multi-method comparison and multi-index evaluation of cracking characteristics of asphalt mixture

The micro crack inside asphalt pavement are potential and antecedent factors for macroscopic cracking of the pavement. The position and quantity of micro cracks have a significant impact on the service life and failure mode of asphalt pavement. The purpose of this study was to conduct multi-scale analysis and multi-index evaluation on the whole process of generation, expansion, and transformation of micro-crack inside asphalt pavement (asphalt mixture) based on multiple testing methods. Firstly, synchronous tests were conducted on the cracking process of asphalt mixture by using three-point bending loading method, acoustic emission (AE) monitoring method, and digital image correlation (DIC) analysis method. Secondly, a three-dimensional finite element model of the asphalt mixture beam was established for AE source location simulation. Finally, the advantages and limitations of multi-methods were compared and analyzed. The principal strain points with different sizes were randomly distributed in the tensile area of the asphalt mixture beam bottom at the initial loading stage, and the number of the principal strain points increased with the decrease of the loading rate. The macroscopic main crack of the asphalt mixture beam generated and expanded from the maximum principal strain point (P1) at the later loading stage. The AE dominant-frequency distribution ranges of micro-crack expanding process, macro-crack generating process, and failure process of asphalt mixture beam were 78.125–156.25 kHz, 234.375–312.5 kHz, and 0–78.125 kHz, respectively. Four stages of damage evolution and cracking process inside the asphalt mixture beam were obtained by the AE source location simulation. A comprehensive and systematic evaluation of bending cracking characteristics of asphalt mixture beam was realized by obtaining multiple indexes from multiple scales with multiple methods.

The bearings and distances isolines combinations of the navigational landmarks pair for the vessel fixed position determination

The issues of applying basic navigation parameters (bearing and distance), and their isolines traditionally used in navigation practice in coastal waters are studied in the paper. A new distinctive feature is the use of isolines combinations (three distance arcs, two isoazimuths, a hyperbola and an ellipse) based on measured bearings and distances to the pair of landmarks to obtain the vessel fixed positions with high precision. The traditional navigation methods (the theory of isolines, the generalized method of lines position, the method of least squares) are involved as a mathematical framework. The mathematical argumentation and the isolines characteristics of bearings and distances, their combinations (difference and sum of distances, difference of bearings) are given. The solutions of the surplus equations of the lines position under random error influence by the least squares method and the accuracy assessment of the vessel fix position by the radial error including the reduced variant to compensate the systematic errors are suggested. The principal points of the research are supported by the graphic interpretation, and the given expressions are adjusted to the practical application and navigation systems software development. The computer simulation that shows the radial error of the fixed position by seven position lines is at least two times less than by any pair of position lines has been carried out. The formalization of the proposed methods in the automatic navigation systems or in autonomous ship control systems will enable the navigator on board or at operating the vessel remotely to solve the problems of the navigation information processing in coastal and congested waters on a new level.

Propagation of uncertainty for an epipole-dependent model for convergent stereovision structure computation

An analytic model incorporating stereo epipoles is proposed for structure computation using a convergent stereovision setup. The developed model is predicated on the image parameters of both CCD camera sensors, together with two extrinsic parameters, namely the stereo baseline distance and the stereo projection angle of the scene point of interest. In the model, the points on the image planes are measured relative to the principal points, stereo epipoles are featured, and only focal length-normalized camera sensor coordinates are required for structure computation. The reconstruction model could be employed in active vision-based metrology in which the stereo imaging cameras are systematically rotated about their vertical axes relative to each other. The performance of the model is studied, and its accuracy tested by comparing the 3-space coordinates it predicted to the those obtained by a gold standard triangulation and to the ground truth results. In terms of execution speed the proposed reconstruction model exhibited a computation time of 0.6 ms compared to 6.2 ms and 9.9 ms recorded for the direct linear transformation and gold standard triangulation algorithms respectively. The coordinate measurement uncertainties determined by experimental methods are subsequently compared with those obtained by a theoretical approach based on the analytic reconstruction model. Strong correlations were found to exist between the two sets of uncertainty values obtained.

The Design and Control of a Biomimetic Binocular Cooperative Perception System Inspired by the Eye Gaze Mechanism.

Research on systems that imitate the gaze function of human eyes is valuable for the development of humanoid eye intelligent perception. However, the existing systems have some limitations, including the redundancy of servo motors, a lack of camera position adjustment components, and the absence of interest-point-driven binocular cooperative motion-control strategies. In response to these challenges, a novel biomimetic binocular cooperative perception system (BBCPS) was designed and its control was realized. Inspired by the gaze mechanism of human eyes, we designed a simple and flexible biomimetic binocular cooperative perception device (BBCPD). Based on a dynamic analysis, the BBCPD was assembled according to the principle of symmetrical distribution around the center. This enhances braking performance and reduces operating energy consumption, as evidenced by the simulation results. Moreover, we crafted an initial position calibration technique that allows for the calibration and adjustment of the camera pose and servo motor zero-position, to ensure that the state of the BBCPD matches the subsequent control method. Following this, a control method for the BBCPS was developed, combining interest point detection with a motion-control strategy. Specifically, we propose a binocular interest-point extraction method based on frequency-tuned and template-matching algorithms for perceiving interest points. To move an interest point to a principal point, we present a binocular cooperative motion-control strategy. The rotation angles of servo motors were calculated based on the pixel difference between the principal point and the interest point, and PID-controlled servo motors were driven in parallel. Finally, real experiments validated the control performance of the BBCPS, demonstrating that the gaze error was less than three pixels.

Measurement Modeling and Performance Analysis of a Bionic Polarimetric Imaging Navigation Sensor Using Rayleigh Scattering to Generate Scattered Sunlight.

The bionic polarimetric imaging navigation sensor (BPINS) is a navigation sensor that provides absolute heading, and it is of practical engineering significance to model the measurement error of BPINS. The existing BPINSs are still modeled using photodiode-based measurements rather than imaging measurements and are not modeled systematically enough. This paper proposes a measurement performance analysis method of BPINS that takes into account the geometric and polarization errors of the optical system. Firstly, the key error factors affecting the overall measurement performance of BPINS are investigated, and the Stokes vector-based measurement error model of BPINS is introduced. Secondly, based on its measurement error model, the effect of the error source on the measurement performance of BPINS is quantitatively analyzed using Rayleigh scattering to generate scattered sunlight as a known incident light source. The numerical results show that in angle of E-vector (AoE) measurement, the coordinate deviation of the principal point has a greater impact, followed by grayscale response inconsistency of CMOS and integration angle error of micro-polarization array, and finally lens attenuation; in degree of linear polarization (DoLP) measurement, the grayscale response inconsistency of CMOS has a more significant impact. This finding can accurately guide the subsequent calibration of BPINS, and the quantitative results provide an important theoretical reference for its optimal design.

ANALYSIS OF CALIBRATION ERRORS IN AUTOMOBILE CONTROL TELEVISION SYSTEM

Camera calibration is a critical method for 3D measurement applications based on 2D images. During calibration, internal camera parameters such as principal point and focal length are determined. The principal point is the intersection of the camera's optical axis and the image plane, while the focal length is measured from the lens center to the principal point.This article theoretically investigates calibration errors in two reference planes considering various conditions, such as shifts in the reference plane and changes in focal lengths. Errors in determining the coordinates of reference points in images were used to evaluate these calibration errors.The error in estimating the focal length and principal point is formulated using analytical equations, and the results are compared with simulation outcomes to validate the effectiveness of the proposed formulas. The research reveals that calibration errors arise due to shifts in the reference plane and changes in focal lengths. The obtained results are crucial for enhancing camera calibration methods and improving the accuracy of 3D measurements based on 2D images.This article extends the understanding of camera calibration errors and provides new theoretical approaches for their assessment. The research findings may be beneficial for scientists and practitioners working in the fields of computer vision, image processing, and 3D measurements.Further research in this area may contribute to the development of new calibration methods and approaches that will improve the performance of automotive systems and ensure high accuracy and reliability in the future.

Attitude Correlated Frames Based Calibration Method for Star Sensors.

Star sensors undergo laboratory calibration before they leave the factory. In addition, recalibration is necessary after they experience vibration, deformation, etc. Using the analysis of attitude-dependent and attitude-independent interstar angular invariance calibration methods (IAICMs) as a reference, an attitude-correlated frame-based calibration method (ACFCM) is proposed in this work, which combines the advantages of both methods. Using outdoor star observations, the ACFCM correlates star image frames obtained at different times via a strapdown gyro unit. As a result, the number of efficient star images for calibration increases rapidly and the distribution of star images becomes much more uniform, thus improving the calibration accuracy of the star sensor. A simulation and experimental tests were designed and carried out. Both the simulation and experimental results verify the feasibility of the proposed ACFCM method. Furthermore, by comparing our method with the IAICMs, the repeatability and reliability of the principal point obtained from the calibration with the ACFCM method proposed in this work were significantly improved.

Cardiovascular Safety of Azithromycin in Patients Hospitalized With COVID-19: A Prespecified Pooled Analysis of the COALITION I and COALITION II Randomized Clinical Trials

The cardiovascular safety from azithromycin in the treatment of several infectious diseases has been challenged. In this prespecified pooled analysis of 2 multicenter randomized clinical trials, we aimed to assess whether the use of azithromycin might lead to corrected QT (QTc) interval prolongation or clinically relevant ventricular arrhythmias. In the COALITION COVID Brazil I trial, 667 patients admitted with moderate COVID-19 were randomly allocated to hydroxychloroquine, hydroxychloroquine plus azithromycin, or standard of care. In the COALITION COVID Brazil II trial, 447 patients with severe COVID-19 were randomly allocated to hydroxychloroquine alone versus hydroxychloroquine plus azithromycin. The principal end point for the present analysis was the composite of death, resuscitated cardiac arrest, or ventricular arrhythmias. The addition of azithromycin to hydroxychloroquine did not result in any prolongation of the QTc interval (425.8 ± 3.6 ms vs 427.9 ± 3.9 ms, respectively, mean difference -2.1 ms, 95% confidence interval -12.5 to 8.4 ms, p = 0.70). The combination of azithromycin plus hydroxychloroquine compared with hydroxychloroquine alone did not result in increased risk of the primary end point (proportion of patients with events at 15 days 17.2% vs 16.0%, respectively, hazard ratio 1.08, 95% confidence interval 0.78 to 1.49, p = 0.65). In conclusion, in patients hospitalized with COVID-19 already receiving standard-of-care management (including hydroxychloroquine), the addition of azithromycin did not result in the prolongation of the QTc interval or increase in cardiovascular adverse events. Because azithromycin is among the most commonly prescribed antimicrobial agents, our results may inform clinical practice. Clinical Trial Registration: NCT04322123, NCT04321278.

Adaptive Drilling of Film Cooling Holes of Turbine Vanes Based on Registration of Point Clouds

The manufacture of film cooling holes on turbine guide vanes of an aero engine suffers from the contour errors resulting from a casting process. It is therefore necessary to adjust positions and orientations of cooling holes for each vane. This paper proposes an adaptive compensation machining method based on a combination of a principal component analysis iterative closest point (PCA-ICP) registration method and an orthocenter mapping method. Firstly, a registration is carried out between an ideal point cloud and a measured point cloud by a laser measurement machine to obtain a transformation matrix. Then, the exit center of a cooling hole is obtained by an orthocenter mapping method. Simulation results show that the machining errors of vanes can be improved from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 0.1 mm to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 0.03 mm. Machining tests show that with a combination of the PCA-ICP registration and orthocenter mapping methods, the cooling holes are drilled adaptively to meet the machining requirements.

Micro bi-prism bi-telecentric single lens Stereo-DIC system using one-step calibration method

In recent years, the bi-prism bi-telecentric single lens stereo digital image correlation (BBSL Stereo-DIC) system has emerged as a viable approach for measuring stereo surface deformation. However, the reliance on a bi-prism that needs to be precisely aligned perpendicular to the optical axis of the bi-telecentric lens using a laser beam, as well as the need to remove the bi-prism during the calibration phase, impose limitations on the practical application of the existing method. To overcome these challenges, we propose a convenient one-step calibration method that eliminates the positional dependence on the bi-prism. This method incorporates the bi-prism’s attitude parameter and principal point coordinates as additional intrinsic parameters. Similar to traditional binocular calibration, the calibration process involves capturing a series of images of a calibration target at various positions and orientations, making it convenient and straightforward for DIC users. A numerical simulation calibration experiment is performed to illustrate the difference between the proposed method and the existing method. The result shows that the bi-prism’s attitude parameter has a significant impact on 3D reconstruction. A rigid-body translation experiment and a tensile experiment of an 800H alloy micro-specimen with a notch are conducted on a micro BBSL Stereo-DIC system. The results and the comparison with finite element simulation prove the accuracy of the proposed method, which demonstrates that the one-step calibration method can be easily employed for micro stereo surface deformation measurement.

Aspirin and Hemocompatibility Events With a Left Ventricular Assist Device in Advanced Heart Failure

Left ventricular assist devices (LVADs) enhance quality and duration of life in advanced heart failure. The burden of nonsurgical bleeding events is a leading morbidity. Aspirin as an antiplatelet agent is mandated along with vitamin K antagonists (VKAs) with continuous-flow LVADs without conclusive evidence of efficacy and safety. To determine whether excluding aspirin as part of the antithrombotic regimen with a fully magnetically levitated LVAD is safe and decreases bleeding. This international, randomized, double-blind, placebo-controlled study of aspirin (100 mg/d) vs placebo with VKA therapy in patients with advanced heart failure with an LVAD was conducted across 51 centers with expertise in treating patients with advanced heart failure across 9 countries. The randomized population included 628 patients with advanced heart failure implanted with a fully magnetically levitated LVAD (314 in the placebo group and 314 in the aspirin group), of whom 296 patients in the placebo group and 293 in the aspirin group were in the primary analysis population, which informed the primary end point analysis. The study enrolled patients from July 2020 to September 2022; median follow-up was 14 months. Patients were randomized in a 1:1 ratio to receive aspirin (100 mg/d) or placebo in addition to an antithrombotic regimen. The composite primary end point, assessed for noninferiority (-10% margin) of placebo, was survival free of a major nonsurgical (>14 days after implant) hemocompatibility-related adverse events (including stroke, pump thrombosis, major bleeding, or arterial peripheral thromboembolism) at 12 months. The principal secondary end point was nonsurgical bleeding events. Of the 589 analyzed patients, 77% were men; one-third were Black and 61% were White. More patients were alive and free of hemocompatibility events at 12 months in the placebo group (74%) vs those taking aspirin (68%). Noninferiority of placebo was demonstrated (absolute between-group difference, 6.0% improvement in event-free survival with placebo [lower 1-sided 97.5% CI, -1.6%]; P < .001). Aspirin avoidance was associated with reduced nonsurgical bleeding events (relative risk, 0.66 [95% confidence limit, 0.51-0.85]; P = .002) with no increase in stroke or other thromboembolic events, a finding consistent among diverse subgroups of patient characteristics. In patients with advanced heart failure treated with a fully magnetically levitated LVAD, avoidance of aspirin as part of an antithrombotic regimen, which includes VKA, is not inferior to a regimen containing aspirin, does not increase thromboembolism risk, and is associated with a reduction in bleeding events. ClinicalTrials.gov Identifier: NCT04069156.

A detailed study of short fatigue crack directions for carbon steel specimens with circular holes subject to cyclic biaxial loads

The effect of notches and biaxial fatigue loading on the crack paths was studied in detail for thin-walled tube specimens with a passing-through hole, paying special attention to the short-crack period. The study was focused on the high cycle fatigue regime. The material was a carbon steel and the tests were under load control, at Rσ=−1. The crack initiation point on the notch surface and the crack direction were studied with an optical microscope on the specimen outer surface and with a scanning electron microscope and a non-contact 3D optical profilometer on the fracture surface. The crack direction was analyzed for several crack lengths, ranging from the length of one average grain to the length of twenty average grains, all lengths within the short-crack regime, in order to carefully observe the evolution of the crack direction in the Stage I and during the transition from Stage I to Stage II. A statistical analysis of the crack initiation point and the experimental crack directions was carried out. In general, the crack initiation point was close to the maximum principal stress point. The crack direction during the first grains was approximately the Mode I direction. There was no initiation in Mode II. The crack continued in the Mode I direction as it got longer, within the short-crack period. The experimental fatigue limits were compared with the predictions calculated with two models from the literature. The direction of the straight lines used by the models to make the predictions were compared with the average crack directions measured experimentally. The goodness of the models, not only from the point of view of the fatigue limit value prediction but also from the closeness of the direction of the line used for the prediction to the experimental crack direction, was discussed.

Asymmetric Folded Plate with Parallel Edges in Validation of their Static Behavior by Combining Vlasov Torsion Theory with Bernoulli Bending Theory

Aims: A new hybrid procedure that combines the Vlasov torsion theory with the Bernoulli bending theory is presented herein, to demonstrate qualitatively and quantitatively the operation of asymmetric folded plates with parallel edges, which are loaded with gravity static loads. Background: A recently proposed technique based on Vlasov torsion theory is used for the exact calculation of the Principal Elastic Reference System in a reinforced concrete folded plate having an asymmetric thin-walled open cross-section with parallel edges. Moreover, the warping moment (or bi-moment) concept of the Vlasov theory is combined with the pure-bending around two axes, according to the Bernoulli bending theory, to determine the normal stresses along the longitudinal dimension of the folded plate. Methods: Τhe warping properties of a thin-walled open cross-section are determined by calculating: (a) the elastic characteristics (elastic center, principal axes) of the section, (b) the principal start point, the sectorial coordinates, the wrapping moment of inertia and the wrapping stiffness of the section. Finally, the normal stresses along the longitudinal dimension are calculated considering the bi-axes flexure with the bi-moment phenomenon. Results: Τhe exact solution of normal stresses at the middle section of an examined folded plate along the longitudinal dimension is found by combining the Bernoulli bending theory for prismatic beams and the Vlasov torsion theory for thin-walled open sections. Conclusion: The current procedure can be used as a benchmark analysis method of asymmetric folded plates in order to evaluate the reliability of the results of various analysis F.E.M. software, covering an open issue of the structural analysis of special structures.

Principles of self-calibration and visual effects for digital camera distortion

Abstract Producing accurate spatial data with stereo photogrammetric techniques is a challenging task, and the central projection of the space needs to be defined as closely as possible to its real form in each image taken for the relevant production. Interior camera parameters that define the exact imaging geometry of the camera and the exterior orientation parameters that locate and rotate the imaging directions in a coordinate system have to be known accurately for this correct definition. All distortions sourcing from lens and sensor planes and their recording geometry are significant as they are not suitable for detection with manual measurements. It is of vital importance to clearly understand the camera self-calibration concept with respect to the lens and the sensor plane geometry and include every possible distortion source as an unknown parameter in the calibration adjustments as they are all modellable systematic errors. In this study, possible distortion sources and self-calibration adjustments are explained in detail with a recently developed visualization software. The distortion sources investigated in the study are radial, tangential, differential scale, and axial skewing distortion. Thanks to the developed software, image center point, distorted grids, undistorted grids, and principal points were visualized. As a result, the most important element of obtaining accurate and precise photogrammetric productions is the correct definition of the central projection of the space for each image, and therefore, the study explains an accurate and robust procedure with the correct definition and use of correct camera internal parameters.

An improved camera model for oblique-viewing laparoscopes: high reprojection accuracy independent of telescope rotation

Objective. Oblique-viewing laparoscopes are popular in laparoscopic surgeries where the target anatomy is located in narrow areas. Their viewing direction can be shifted by telescope rotation without changing the laparoscope pose. This rotation also changes laparoscope camera parameters that are estimated by camera calibration to be able to reproject an anatomical model onto the laparoscopic view, creating augmented reality (AR). The aim of this study was to develop a camera model that accounts for these changes, achieving high reprojection accuracy for any telescope rotation. Approach. Camera parameters were acquired by calibrations encompassing a wide telescope rotation range. For those parameters showing periodic changes upon rotation, interpolation models were created and used to establish an updatable camera model. With this model, corner points of a tracked checkerboard were reprojected onto the checkerboard laparoscopic images, at random rotation angles. Root-mean-square reprojection errors (RMSEs) were calculated between the reprojected and imaged corner points. Main results. Reprojection RMSEs were low and approximately independent on telescope rotation angle, over a wide rotation range of 320°. The mean reprojection RMSE was 2.8 0.7 pixels for a conventional laparoscope and 3.6 0.7 pixels for a chip-on-the-tip (COTT) laparoscope, corresponding to 0.3 0.1 mm and 0.4 0.1 mm in world coordinates respectively. Worst-case reprojection errors were about 9 pixels (0.8 mm) for both laparoscopes. Significance. The camera model developed in this study improves on existing models for oblique-viewing laparoscopes because it provides high reprojection accuracy independent of the telescope rotation angle and is applicable for conventional and chip-on-a-tip oblique-viewing laparoscopes. The work presented here is an important step towards creating accurate AR in image-guided interventions where oblique-viewing laparoscopes are used while simultaneously providing the surgeon the flexibility to rotate the telescope to any desired rotation angle. Acronyms. CC: camera coordinates; CCToolbox: camera calibration toolbox; COTT: chip-on-the-tip; CS: camera sensor; DD: decentering distortion; FL: focal length; OTS: optical tracking system; PP: principal point; RD: radial distortion; SI: supplementary information; hand-eye translation component

IMPROVING CAMERA POSE ESTIMATION USING SWARM PARTICLE ALGORITHMS

Abstract. Most computer vision and photogrammetry applications rely on accurately estimating the camera pose, such as visual navigation, motion tracking, stereo photogrammetry, and structure from motion. The Essential matrix is a well-known model in computer vision that provides information about the relative orientation between two images, including the rotation and translation, for calibrated cameras with a known camera matrix. To estimate the Essential matrix, the camera calibration matrices, which include focal length and principal point location must be known, and the estimation process typically requires at least five matching points and the use of robust algorithms, such as RANSAC to fit a model to the data as a robust estimator. From the usually large number of matched points, choosing five points, the Essential matrix can be determined based on a simple solution, which could be good or bad. Obtaining a globally optimal and accurate camera pose estimation, however, requires additional steps, such as using evolutionary algorithms (EA) or swarm algorithms (SA), to prevent getting trapped in local optima by searching for solutions within a potentially huge solution space.This paper aims to introduce an improved method for estimating the Essential matrix using swarm particle algorithms that are known to efficiently solve complex problems. Various optimization techniques, including EAs and SAs, such as Particle Swarm Optimization (PSO), Gray Wolf Optimization (GWO), Improved Gray Wolf Optimization (IGWO), Genetic Algorithm (GA), Salp Swarm Algorithm (SSA) and Whale Optimization Algorithm (WOA), are explored to obtain the global minimum of the reprojection error for the five-point Essential matrix estimation based on using symmetric geometric error cost function. The experimental results on a dataset with known camera orientation demonstrate that the IGWO method has achieved the best score compared to other techniques and significantly speeds up the camera pose estimation for larger number of point pairs in contrast to traditional methods that use the collinearity equations in an iterative adjustment.

Error suppression method of SINS/CNS integrated navigation based on diametrical stargazing

The strap-down inertial navigation system (SINS)/celestial navigation system (CNS) integrated navigation system has been extensively employed in the aerospace field owing to its unique advantages. The internal parameter errors of the star sensor constitute one of the primary factors that affect the navigation accuracy. In this paper, an error suppression method based on diametrical stargazing has been designed to suppress the navigation errors caused by the internal parameter errors of the star sensor. First, a SINS/CNS integrated navigation model based on Kalman filter has been established. Then the influence of the principal point error, image-plane tilt error, and distortions of the optical system on the measurement accuracy of the star sensor have been analyzed. Further, the process of introducing the errors into the measurement equation has been obtained. Finally, for multiple errors, two stargazing methods have been designed to suppress the impact of these errors on the navigation accuracy, whereas the constant errors of the inertial device can be modulated. The simulation results demonstrate that the proposed method can improve the positioning accuracy of the system, and verify the effectiveness of the algorithm.

Calculation Method of Earth Pressure Considering Wall Displacement and Axial Stress Variations

Current earth pressure calculation methods suffer from certain limitations because they do not consider the effect of retaining wall displacement. In this study, the soil behind the wall is assumed to be in a plane strain state, and drawing upon nonlinear elastic constitutive theory, an earth pressure calculation method is proposed, capable of considering both axial stress and wall displacement. To account for changes in soil modulus with confining pressure, the tangent modulus from the Duncan-Chang nonlinear model is introduced. Depending on the direction of the principal stress behind the retaining wall, the static earth pressure point, the major principal stress inflection point, and the minor principal stress second inflection point are determined. The conditions for the existence of the second inflection point are also given. These specific points, together with the limit earth pressure point, divide the earth pressures acting on the wall into six regions. The study provides earth pressure calculation formulas for T (translation) mode, RBT (rotation about a point below the base) mode, and RTT (rotation about a point above the top) mode based on the characteristics of wall displacement distribution in each mode. The proposed method exhibits good agreement with the test results, offering an effective approach for accurately calculating earth pressures related to displacement.

Meconium-stained amniotic fluid and neonatal morbidity in nulliparous patients with prolonged pregnancy.

Our objective was to study the strength of the association between meconium-stained amniotic fluid and severe morbidity among neonates of nulliparas with prolonged pregnancies. This was a secondary analysis of the NOCETER randomized trial that took place between 2009 and 2012 in which 11 French maternity units included 1373 nulliparas at 41+0 weeks of gestation onwards with a single live fetus in cephalic presentation. This analysis excluded patients with a cesarean delivery before labor and those with bloody amniotic fluid or of unreported consistency. The principal end point was a composite criterion of severe neonatal morbidity (neonatal death, 5-minute Apgar <7, convulsions in the first 24 h, meconium aspiration syndrome, mechanical ventilation ≥24 h, or neonatal intensive care unit admission for 5 days or more). The neonatal outcomes of pregnancies with thin or thick meconium-stained amniotic fluid were compared with those with normal amniotic fluid. The association between the consistency of the amniotic fluid and neonatal morbidity was tested by univariate and then multivariate analysis adjusted for gestational age at birth, duration of labor, and country of birth. This study included 1274 patients: 803 (63%) in the group with normal amniotic fluid, 196 (15.4%) in the thin amniotic fluid group, and 275 (21.6%) in the thick amniotic fluid group. The neonates of patients with thick amniotic fluid had higher rates of neonatal morbidity than those of patients with normal amniotic fluid (7.3% vs. 2.2%; p < 0.001; adjusted relative risk [aRR] 3.3, 95% confidence interval [CI] 1.7-6.3), but those of patients with thin amniotic fluid did not (3.1% vs. 2.2%; p = 0.50; aRR 1.0, 95% CI, 0.4-2.7). Among nulliparas at 41+0 weeks onwards, only thick meconium-stained amniotic fluid is associated with a higher rate of severe neonatal morbidity.