Explore the vast range of titles available.

Accurate and timely misfire fault diagnosis is of vital significance for diesel engines. However, existing algorithms are prone to fall into model over-fitting and adopt low energy-concentrated features. This paper presents a novel extreme gradient boosting-based misfire fault diagnosis approach utilizing the high-accuracy time–frequency information of vibration signals. First, diesel engine misfire tests were conducted under different spindle speeds, and the corresponding vibration signals were acquired via a triaxial accelerometer. The time-domain features of signals were extracted by using a time-domain statistics method, while the high-accuracy time–frequency domain features were obtained via the high-resolution multisynchrosqueezing transform. Thereafter, considering the nonlinearity and high dimensionality of the original characteristic data sets, the locally linear embedding method was employed for feature dimensionality reduction. Eventually, to avoid model overfitting, the extreme gradient boosting algorithm was utilized for diesel engine misfire fault diagnosis. Experiments under different spindle speeds and comprehensive comparisons with other evaluation methods were conducted to demonstrate the effectiveness of the proposed extreme gradient boosting-based misfire diagnosis method. The results verify that the highest classification accuracy of the proposed extreme gradient boosting-based algorithm is up to 99.93%. Simultaneously, the classification accuracy of the presented approach is approximately 24.63% higher on average than those of algorithms that use wavelet packet-based features. Moreover, it is shown that it obtains the minimum root mean squared error and can effectively prevent the model from falling into overfitting.

In this letter, we propose an indoor visible light positioning technique using a Modified Momentum Back-Propagation (MMBP) algorithm based on received signal strength (RSS) with sparse training data set. Unlike other neural network algorithms that require a large number of training data points to locate accurately, we have realized high-precision positioning for 100 test points with only 20 training points in a 1.8 m × 1.8 m × 2.1 m localization area. In order to verify the adaptability of the MMBP algorithm, we experimentally demonstrate two different training data acquisition methods adopting either even or arbitrary training sets. In addition, we also demonstrate the positioning accuracy of the traditional RSS algorithm. Experimental results show that the average localization accuracy optimized by our proposed algorithm is only 1.88 cm for the arbitrary set and 1.99 cm for the even set, while the average positioning error of the traditional RSS algorithm reaches 14.34 cm. Comparison indicates that the positioning accuracy of our proposed algorithm is 7.6 times higher. Results also show that the performance of our system is higher than some previous reports based on RSS and RSS fingerprint databases using complex machine learning algorithms trained by a large amount of training points.

The Galileo High Accuracy Service (HAS), aiming at providing a Precise Point Positioning (PPP) service worldwide, will soon transmit precise orbits, clocks and biases, for both Galileo and GPS, in the signal-in-space and through a ground channel. This will be complemented in the future with precise ionosphere corrections and HAS data authentication. This work provides an overview of Galileo initial HAS, focusing on its overall message structure, architecture, and early performance. The initial HAS is strictly based on the existing Galileo monitoring and uplink capabilities already available for the other Galileo services. This contribution assesses the service coverage, the accuracy of the broadcast corrections, and the user PPP performance of Galileo HAS for the first time. The results show that Galileo HAS can provide broad coverage with few-centimeter broadcast correction accuracy and fulfill the targeted two-decimeter user horizontal accuracy in the evaluated conditions even in its initial phase.

GNSS has become ubiquitous in high-precision applications, although the cost of high-end GNSS receivers remains a major obstacle for many applications. Recent advances in GNSS receiver technology have led to the development of low-cost GNSS receivers, making high-precision positioning available to a wider range of users. One such technique for achieving high-precision positioning is Precise Point Positioning-Real Time Kinematic (PPP-RTK). It is a GNSS processing technique that combines the PPP and RTK approaches to provide high-precision positioning in real time without the need for a base station. In this work, we aim to assess the performance of the low-cost u-blox ZED-F9P GNSS module in PPP-RTK mode using the low-cost u-blox ANN-MB antenna. The experiment was designed to investigate both the time it takes the receiver to resolve the phase ambiguity and to determine the positioning accuracies achievable. Results showed that the u-blox ZED-F9P GNSS module could achieve centimeter-level positioning accuracy in about 60 s in PPP-RTK mode. These results make the PPP-RTK technique a good candidate to fulfill the demand for mass-market accurate and robust navigation since uses satellite-based corrections to provide accurate positioning information without the need for a local base station or network. Furthermore, due to its rapid acquisition capabilities and accurate data georeferencing, the technique has the potential to serve as a valuable method to improve the accuracy of the three-S techniques (GIS, remote sensing, and GPS/GNSS).

A method is proposed to improve two aspects of numerical simulations for a model of two fluids coupled across a flat interface. This problem is motivated by atmosphere-ocean interaction. A deferred correction approach lifts the numerical order of accuracy formally from first order (very common in applications) to second order in terms of the time interval of communication between the fluid code components. This is accomplished in a two-step predictor-corrector-type method. In the second step, a further defect correction is included as well. The \"defect\" represents artificial diffusion used in the fluid solvers, which is often included to control numerical noise or to model subscale mixing processes. The addition of the defect correction adds only marginally to the expense, but in exchange may provide a significant reduction of overdiffusive effects. The defect and deferred correction approaches are combined into a so-called defect-deferred correction (DDC) method. A full DDC algorithm is studied using finite elements in space, including an analysis of the stability and convergence. The method is unconditionally stable and optimally convergent, and also enforces a formal reduction in artificial diffusion effects. A computational example using a known (manufactured) solution illustrates the theoretical predictions. We observe a computational benefit in this example even for coarse time steps and over a wide range of artificial viscosity values. Some discussion is provided regarding the possibility to generalize the approach for application codes. Briefly, legacy atmosphere and ocean codes may be used as-is over a coupling time interval for a predictor computation. The corrector step would then potentially be implemented as a straightforward modification of the predictor step that leverages the existing code structure.

Crystal monochromators are indispensable optical components for the majority of beamlines at synchrotron radiation facilities. Channel‐cut monochromators are sometimes chosen to filter monochromatic X‐ray beams by virtue of their ultrahigh angular stability. Nevertheless, high‐accuracy polishing on the inner diffracting surfaces remains challenging, thus hampering their performance in preserving the coherence or wavefront of the photon beam. Herein, a magnetically controlled chemical–mechanical polishing (MC‐CMP) approach has been successfully developed for fine polishing of the inner surfaces of channel‐cut crystals. This MC‐CMP process relieves the constraints of narrow working space dictated by small offset requirements and achieves near‐perfect polishing on the surface of the crystals. Using this method, a high‐quality surface with roughness of 0.614 nm (root mean square, r.m.s.) is obtained in a channel‐cut crystal with 7 mm gap designed for beamlines at the High Energy Photon Source, a fourth‐generation synchrotron radiation source under construction. On‐line X‐ray topography and rocking‐curve measurements indicate that the stress residual layer on the crystal surface was removed. Firstly, the measured rocking‐curve width is in good agreement with the theoretical value. Secondly, the peak reflectivity is very close to theoretical values. Thirdly, topographic images of the optics after polishing were uniform without any speckle or scratches. Only a nearly 2.5 nm‐thick SiO2 layer was observed on the perfect crystalline matrix from high‐resolution transmission electron microscopy photographs, indicating that the structure of the bulk material is defect‐ and dislocation‐free. Future development of MC‐CMP is promising for fabricating wavefront‐preserving and ultra‐stable channel‐cut monochromators, which are crucial to exploit the merits of fourth‐generation synchrotron radiation sources or hard X‐ray free‐electron lasers. The novel magnetically controlled chemical–mechanical polishing technique features simplicity in mechanical components and compatibility with almost all kinds of surface shapes, and is able to fabricate high‐accuracy inner‐wall surfaces without damaging layers.

Aerosol jet printing (AJP) is a promising direct writing (DW) technology based on the gas‐driven aerosol. However, the pressure within printhead is hard to be controlled in real time, leading to obvious jet relaxation phenomenon during AJP, which is the critical determinant affecting dimensional accuracy and conformity of printed patterns. In this work, a shuttering system based on an internal mechanical switching valve with special flow channels is proposed to modulate the pressure distribution within printhead, thereby controlling the aerosol jet stream's flow direction in real time to enable faster ON‐OFF responsivity and higher printing accuracy. By designing the flow channel geometry of valve, the pressure is maintained constant during ON‐OFF switching, fundamentally eliminating jet relaxation time from > 35 s, improving morphological uniformity along entire printed lines, permitting parameter‐independent characteristics. With this strategy, the ON‐OFF delay due to the dimensions of the two dead zones in AJP system is eliminated by precompensation. Moreover, the stability and universality of this approach are analyzed by repeatedly printing short‐line arrays at ON‐OFF frequency F = 0.2–50 Hz, aligned endpoints demonstrate the stable high‐responsivity ON‐OFF control characteristics, which confirms great application prospects of this strategy in high‐accuracy manufacturing of complex functional patterns. This work demonstrates ultra‐high ON‐OFF responsivity of AJP by mechanical switching valve assisted shuttering. The jet relaxation and ON‐OFF delay are substantially eliminated from greater than 35 s, maintaining patterning quality independent of the variations of printing parameters, permitting excellent process stability and universality. This leads to significant improvement in manufacturing accuracy of AJP for complex functional devices.

Smoothed particle hydrodynamics (SPH), as one of the earliest meshfree methods, has broad prospects in modeling a wide range of problems in engineering and science, including extremely large deformation problems such as explosion and high velocity impact. This paper aims to provide a comprehensive overview on the recent advances of SPH method in the fields of fluid, solid, and biomechanics. First, the theory of SPH is described, and improved algorithms of SPH with high accuracy are summarized, such as the finite particle method (FPM). Techniques used in SPH method for simulating fluid, solid and biomechanics problems are discussed. The δ -SPH method and Godunov SPH (GSPH) based on the Riemann model are described for handling instability issues in fluid dynamics. Next, the interface contact algorithm for fluid-structure interaction is also discussed. The common algorithms for improving the tensile instability and the framework of total Lagrangian SPH are examined for challenging tasks in solid mechanics. In terms of biomechanics, the governing equations and the coupling forces based on SPH method are exemplified. Then, various typical engineering applications and recent advances are elaborated. The application of fluid mainly depicts the interaction between fluid and rigid body as well as elastomer, while some complicated fluid-structure interaction ocean engineering problems are also presented. In the aspect of solid dynamics, galaxy, geotechnical mechanics, explosion and impact, and additive manufacturing are summarized. Furthermore, the recent advancements of SPH method in biomechanics, such as hemodynamically and gut health, are discussed in general. In addition, to overcome the limitations of computational efficiency and computational scale, the multiscale adaptive resolution, the parallel algorithm and the automated mesh generation are addressed. The development of SPH software in China and abroad is also summarized. Finally, the challenging task of SPH method in the future is summarized. In future research work, the establishment of multi-scale coupled SPH model and deep learning technology in solid and biodynamics will be the focus of expanding the engineering applications of SPH methods.

The Galileo High Accuracy Service (HAS) is a GNSS augmentation that provides precise satellite corrections to users worldwide for free directly through Galileo’s E6 signal. The HAS service provides free PPP corrections from the Galileo constellation and the Internet, with targeted real-time 95% positioning performance of better than 20 cm horizontal and 40 cm vertical error after 5 min of convergence time globally and shorter in Europe. The HAS initial service, under validation at the time of writing, provides these capabilities with a reduced performance (based on the current Galileo stations network). Live HAS test signals broadcasted from the Galileo satellites during summer 2022 have been decoded and analyzed. Corrections include Galileo and GPS orbit, clock, and code bias corrections, with SISRE of 10.6 cm and 11.8 cm for Galileo and GPS, respectively. Code bias corrections showed good performance as well, with rms of 0.28 ns, 0.26 ns, and 0.22 ns for Galileo C1C–C5Q, C1C–C7Q, and C1C–C6C, respectively, and 0.20 ns for GPS C1C–C2L. Float PPP positioning performance results show that the combined Galileo and GPS solution can already achieve the HAS full service accuracy performance target and is close in terms of convergence time, with 95% rms of 13.1 cm and 18.6 cm horizontally and vertically, respectively, in kinematic mode, and with a 95% convergence time of 7.5 min. The latter is expected to be improved with the inclusion of satellite phase bias and local atmospheric corrections. With these early Galileo HAS test signals, this preliminary analysis indicates that the HAS full service targets are attainable. Finally, a correction latency analysis is performed, showing that even with latency of up to 60 s, positioning can remain within the targeted HAS accuracy performance.

We compare the performance of dual-band (GPS L1/L2 and Galileo E1/E5a) real-time kinematic (RTK) positioning in an open sky and urban scenarios in southern Finland using two different authentication schemes: one using only satellites authenticated by Galileo’s open service navigation message authentication (OSNMA) service (which at the moment of our tests led to using only authenticated Galileo satellites) and the other with no authentication. The results show the actual trade-off between accuracy and availability vs. authenticity associated with using only OSNMA-authenticated satellites, while the authentication of only Galileo satellites is possible (e.g., a drop of RTK positioning availability from 96.67 to 86.01% in our open sky and from 73.55 to 18.65% in our urban scenarios, respectively), and an upper bound of the potential performance that could be reached in similar experimental conditions had the authentication of GPS satellites been supported (e.g., an overall 14 cm and 10.20 m 95% horizontal accuracy in our open sky and urban scenarios, with below 30, 20 and 10 cm during 97.39, 96.03 and 92.43% of the time in the open sky and 49.12, 45.96 and 39.63% in the urban scenarios, respectively).