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This paper investigates the failure mechanism of nonuniform large geotextile-reinforced cofferdam under seepage and excavation effects on soft sediments. A numerical model is established and validated with available testing results. Then, parametric studies are carried out to investigate the potential influence factors. This study found that the difference between the upstream and downstream water levels and the excavation depth both have significant influences on the stability of cofferdams, where excavation is the key influence factor affecting the stability of the cofferdam. Numerical results revealed that the safety factor could reduce by about 20% with excavation of about 1.5 m. An empirical equation is proposed for quantitative prediction of the stability of geotextile-reinforced cofferdams. A thorough understanding about the failure mechanisms of cofferdams as well as an empirical formula for predicting the stability is concluded in this study, which could provide engineering guide for flexible foundations reinforced by geotextiles. [ABSTRACT FROM AUTHOR]

Battery swapping stations effectively address the challenges of long charging times, lack of charging stations, and safety hazards for electric two-wheelers. With the rapid development of shared electric bicycles and takeaways, the scale of electric two-wheeler users is expanding while generating a huge demand for battery swapping. The research on the planning and operation of battery swapping stations (BSSs) for electric two-wheelers has yet to be widely discussed. This study developed a data-driven optimization model based on machine learning algorithms using Beijing's battery swapping stations and point of interest (POI) dataset. First, through the spatial features of BSS analyzed by ArcGIS, we found that the coverage of BSSs was mainly concentrated within the fifth ring road, and the utilization rate was unbalanced. Then, on a 3000 m grid scale, a prediction model of BSS quantity with random forest, support vector regression, and gradient-boosting decision tree algorithm was built. The final stacking model was constructed by strengthening three single models with an accuracy of 86.21%. Compared with the original BSSs layout, the machine-learning algorithm proposed in this study can cover more factors and avoid the subjectivity of site selection. Finally, the queuing model for BSSs based on the Monte Carlo simulation was proposed. Through two scenarios, we found that the key parameters m (the number of charging slots) and λ (the user arrival rate) were influential to the outputs of service capability. [ABSTRACT FROM AUTHOR]

• A LarkMNet is proposed for weak-feature crack recognition in high-resolution images. • A Perception Large Kernel Convolutional Network is designed to expand the sensory field. • LarkMNet's accuracy in detecting weak feature cracks exceeds existing methods. • Experiments and applications demonstrate the effectiveness and robustness of LarkMNet. Weak feature crack detection is crucial for dam structural health. Existing methods for detecting weak feature cracks in high-resolution images continue to pose challenges. This paper proposes a Perception Large Kernel-based Multi-level Gather-and-Distribute Network (LarkMNet) for weak-feature crack detection in high-resolution images. The construction of a Perception Large-Kernel ConvNet (LarkNet) enables feature extraction and expansion of the receptive field in high-resolution images. The design of the Multi-level Gather-and-Distribute Network (MGDNet) aims to enhance the critical characteristics of weak cracks. Introducing a Shared Detection Head and an Inner-SCYLLA-Intersection over Union further enhances the model's detection accuracy. Experimental results demonstrate that LarkMNet's detection accuracy in high-resolution image datasets surpasses that of mainstream detection models, achieving an F1 score and mAP of 89.4% and 93.3%, respectively. Furthermore, the method's validity has been confirmed through high-resolution image testing and UAV on-site inspections, efficiently and accurately detecting weak feature cracks in high-resolution images. [ABSTRACT FROM AUTHOR]

Bioinspired composites, capable of tailoring mechanical properties by the strategy of making full use of their advantages and bypassing their drawbacks, are vital for numerous engineering applications such as lightweight ultrahigh-strength, enhanced toughness, improved low-/high- velocity impact resistance, wave filtering, and energy harvesting. Helicoidal composites are examples of them. However, how to optimize the geometric structure to maximize the low-velocity impact resistance of helicoidal composites has been ignored, which is vital to the lightweight and high strength for aerospace, defense, ship, bridge, dam, vessel, and textile industries. Here, we combined experiments and numerical simulations to report the dynamic response of helicoidal composites subjected under low-velocity impact (0–10 m/s). Our helicoidal structures, inspired by the Stomatopod Dactyl club, are fabricated using polylactic acid (PLA) by FFF in a single-phase way. The helicoidal strategy aims to exploit, to a maximum extent, the axial tensile strength of filaments and simultaneously make up the shortage of inter-filament contact strength. We demonstrate experimentally that the low-velocity impact resistance has been enhanced efficiently as the helicoidal angle varies, and that the 15° helicoidal plate is better than others, which has also been confirmed by the numerical simulations. The findings reported here provide a new routine to design composites systems with enhanced impact resistance, offering a method to improve impact performance and expand the application of 3D printing. [ABSTRACT FROM AUTHOR]

Motivated by the practical supply chain management of the automobile industry, we study the car sequencing problem (CSP) that minimizes the conflicts occur when sequentially manufacturing cars on an assembly line. The CSP is a well-established problem, subject to the paint batching constraints to decrease the energy consumption for color changeovers and production rate constraints in the assembly shop to ensure a smooth usage of car options. However, the existing solution algorithms to this problem do not take into account the block batches, which desires a consecutive production batch of cars requiring a certain option. This requirement often occurs when specialized labor time window is short in the customized car production scenario, and renders additional complexities to the traditional car sequencing problem. In this paper, we present a novel model to deal with these constraints and simultaneously generate the sequencing and replenishment decisions. Besides, we develop two math-heuristic algorithms to solve the proposed large-scale CSP. The presented heuristics are on the basis of relax-and-fix procedures, fix-and-optimize procedures and adaptive variable neighborhood search. To solve the large-sized instances (commercial solvers, i.e., Cplex, cannot obtain a feasible result within 1 h), we design and implement a reinforced parameter tuning mechanism to dynamically select the parameter values, so as to speed up the search process. The proposed models and heuristics are tested on representative instances generated from the benchmark in the literature (CSPLib), as well as large-sized instances generated from real-world cases. We report on extensive computational experiments and provide basic managerial insights into the planning process. [ABSTRACT FROM AUTHOR]

Concrete age is the time since the moment water is added to the cement, and the age of concrete comprehensively reflects the physical properties of the concrete when curing under standard conditions. For concrete under nonstandard conditions, its physical properties are directly related to both its age and temperature history. The equivalent age of concrete is the time at which concrete under nonstandard conditions reaches the same state as concrete under standard conditions. Most equivalent methods, such as the Nurse-Saul function and the Arrhenius function, are based on a maturity index. However, the accuracy of these methods breaks down when the curing temperature range is wide. In this paper, the electrical resistivity of concrete is used as the index to determine the equivalent age of concrete. This method is based on the assumption that concrete with the same mixture proportions has the same electrical resistivity when the maturity of the concrete is the same, regardless of the curing history. The proposed method is advantageous because it can be performed in real time and is nondestructive. To constantly measure the electrical resistivity of concrete, an automatic data acquisition system is developed to monitor the electrical resistivity of concrete and reduce the error caused by polarization as much as possible. Then, a model for predicting the electrical resistivity of concrete under different curing temperatures is proposed to conveniently calculate the equivalent coefficient. Finally, the results calculated by the proposed equivalent method are compared with those of the standard method (Nurse-Saul equation), and the results of the proposed model are found to be more reasonable. [ABSTRACT FROM AUTHOR]

With the rapid development of high-precision positioning service applications, there is a growing demand for accurate and seamless positioning services in indoor and outdoor (I/O) scenarios. To address the problem of low localization accuracy in the I/O transition area and the difficulty of achieving fast and accurate I/O switching, a Kalman filter based on the salp swarm algorithm (SSA) for seamless multi-source fusion positioning of global positioning system/inertial navigation system/smartphones (GPS/INS/smartphones) is proposed. First, an Android smartphone was used to collect sensor measurement data, such as light, magnetometer, and satellite signal-to-noise ratios in different environments; then, the change rules of the data were analyzed, and an I/O detection algorithm based on the SSA was used to identify the locations of users. Second, the proposed I/O detection service was used as an automatic switching mechanism, and a seamless indoor–outdoor localization scheme based on improved Kalman filtering with K-L divergence is proposed. The experimental results showed that the SSA-based I/O switching model was able to accurately recognize environmental differences, and the average accuracy of judgment reached 97.04%. The localization method achieved accurate and continuous seamless navigation and improved the average localization accuracy by 53.79% compared with a traditional GPS/INS system. [ABSTRACT FROM AUTHOR]

Thermal conductivity of concrete greatly influences the heat transfer of buildings and affected by many factors. This paper presents a prediction model for thermal conductivity of concrete by adopting the theory of Wiener bounds and considering concrete to have four components (water, air, aggregate, and cement mortar). The proposed model considers the combined effects of porosity, water saturation, and the volume fraction of aggregate on the thermal conductivity of concrete by weighting parameters of η 1 , η 2 , η 3 , respectively. By adjusting the weighting parameters of each component, the model can consider the influence of various factors on the thermal conductivity of concrete more comprehensively. Thermal conductivity of each component and expression of weighting parameters are determined by literature and experiments. The proposed model has been verified by the measured thermal conductivity of concrete under different porosities, water content, and volume fractions of aggregate with the prediction accuracy of ± 12 % . Finally, the regularity of the change in the thermal conductivity of concrete with porosity, water saturation, the volume fraction of aggregate, and temperature is analyzed. [ABSTRACT FROM AUTHOR]

Strong earthquakes have an impact on the regional thermal radiation background, which has been both observed and confirmed. This effect produces anomalies in the thermal radiation background (TRBA) and increases the difficulty of extracting a thermal radiation anomaly (TRA) that is associated with an earthquake occurring during the same time period. The extraction and identification of such anomalies has been ignored by previous studies. In this study, we investigate the time-frequency analysis (TFA) method, together with the wavelet filtering of the Daubechies method and the relative power spectrum analysis of the Fourier Welch method to extract and analyse the TRBA caused by the 2008 Wenchuan Ms 8.0 earthquake and the TRA of the 2013 Minxian-Zhangxian Ms 6.6 earthquake using data concerning the brightness temperature of a black body (TBB) from the Fengyun-2 series of geostationary meteorological satellites developed by China. The result showed that this method can effectively extract and analyse the TRBA caused by the Wenchuan earthquake and the TRA of the Minxian-Zhangxian earthquake form a complex background environment. Furthermore, we discussed the impact of the earthquake on the TRBA and segmented the process. The impact is mainly reflected by three aspects; the characteristic period of the TRBA changes, the TRBA occurs at the same time every year, which is identical to the time at which the earthquake anomaly occurred, and the impact process is in stages. We also summarized the correlation between the characteristic parameters of a TRA and the regional thermal radiation background, geography, and climatic factors. [ABSTRACT FROM AUTHOR]

Highlights • Morphology engineering on iron oxides is carried out via an electrochemical method. • Morphology transition from zero-dimension to one-dimension is realized. • Iron oxide electrode delivers a high capacity of 184 mAh g−1 at 2 A g−1 (∼6C rate). • The Ni/Fe full cell exhibits a good energy density of 82.3 Wh kg−1. Abstract Aqueous rechargeable Ni/Fe batteries possess potential advantages for large-scale energy storage applications due to their low cost, high safety and fast ion diffusions in electrolyte. However, the electrochemical performance of the iron-based anode is still far from ideal due to particle aggregations. Herein, we carry out the morphology engineering on the iron oxide active materials via a facile electrochemical method to improve its charge storage capability. The morphology transition from zero-dimensional particles to one-dimensional nanorods is realized by tuning the electrolyte composition, while subsequent annealing treatment results in further morphology modification into 3D interconnected nanoparticles (10–20 nm). The hierarchical structure allows facile ion and electron transfers, and the large surface provides various active sites for the charge storage conversion reaction. As a result, even at the high current density of 2 A g−1 (∼6C rate), the iron oxide electrode can still deliver a high specific capacity of 184 mAh g−1. At the same time, the morphology integrity and stability of the electrode leads to a good cycle life, with 87.5% capacity retained upon 5000 cycles. The Ni/Fe full cell assembled with the iron oxide anode and a Ni-Co double hydroxide cathode exhibits a good energy density of 82.3 Wh kg−1 at the power density of 3.3 kW kg−1. Our fundamental study would provide new insights for the electro-deposition of iron-based materials and endow new opportunities for the fabrication of high-performance iron-based electrodes for energy storage systems. [ABSTRACT FROM AUTHOR]

Thermodynamic equations are derived for physical adsorption of gases and vapors on fractal surfaces of heterogeneous microporous solids. The influence of surface geometry on gas adsorption on a microporous solid is studied by analyzing the dependence of the differential molar enthalpy ΔH, the immersion enthalpy ΔHim, and the differential molar entropy ΔS on the fractal dimension D, which is used to characterize the surface irregularity. It is shown that -ΔH, -ΔHim, -ΔS, and the average adsorption potential A increase as the fractal dimension of the surface accessible for adsorption increases. The dependence of these thermodynamic quantities on the fractal dimension D is attributed to the fact that the fraction of small micropores in microporous solids increases as the fractal dimension D increases. [ABSTRACT FROM AUTHOR]

TRANSPARENT TESTA1 (TT1) is a zinc finger protein that contains a WIP domain. It plays important roles in controlling differentiation and pigmentation of the seed coat endothelium, and can affect the expression of early biosynthetic genes and late biosynthetic genes of flavonoid biosynthesis in Arabidopsis thaliana. In Brassica napus (AACC, 2 n = 38), the functions of BnTT1 genes remain unknown and few studies have focused on their roles in fatty acid (FA) biosynthesis. In this study, BnTT1 family genes were silenced by RNA interference, which resulted in yellow rapeseed, abnormal testa development (a much thinner testa), decreased seed weight, and altered seed FA composition in B. napus . High-throughput sequencing of genes differentially expressed between developing transgenic B. napus and wild-type seeds revealed altered expression of numerous genes involved in flavonoid and FA biosynthesis. As a consequence of this altered expression, we detected a marked decrease of oleic acid (C18:1) and notable increases of linoleic acid (C18:2) and α-linolenic acid (C18:3) in mature transgenic B. napus seeds by gas chromatography and near-infrared reflectance spectroscopy. Meanwhile, liquid chromatography–mass spectrometry showed reduced accumulation of flavonoids in transgenic seeds. Therefore, we propose that BnTT1s are involved in the regulation of flavonoid biosynthesis, and may also play a role in FA biosynthesis in B. napus . [ABSTRACT FROM AUTHOR]

B Correction to: J Wireless Com Network (2022) 2022:26 b https://doi.org/10.1186/s13638-022-02113-7 Following publication of the original article [[1]], the authors flagged that Wenchao Wei had been erroneously affiliated with affiliation 3 instead of affiliation 2. Reference 1 Yu Y, Lu X, Zhao T, Cheng M, Liu L, Wei W. Heuristic approaches for the car sequencing problems with block batches. [Extracted from the article]

The Sarez Dam, currently recognized as the world's highest natural dam, holds immense economic significance, necessitating the reliable monitoring and early detection of potential deformations. This study utilizes the Beidou high-precision deformation monitoring system for the dam. Employing baseline network solutions, precise point positioning, and real-time kinematic positioning, the monitoring data from October 2021 to March 2023 were meticulously processed and comparatively analyzed. The results reveal varied degrees of displacement deformation at all sites, with horizontal deformation towards the lake center and vertical deformation showing subsidence. The three-dimensional vector average displacement is 29.1 mm, with an average monthly rate of 4.3 mm/month, and the maximum deformation is 41.4 mm. The cause of the horizontal deformation towards the lake center may be a slow collapse of the coastal soil and rock towards the lake center. Additionally, the monitoring detected a 7.2-magnitude earthquake on 23 February 2023, 52 km from the dam, causing an average displacement of 22.5 mm towards the south, which is 20 times the monthly deformation rate. In summary, deformation is present within the dam monitoring area, with a relatively stable deformation rate, warranting continued tracking and monitoring. Furthermore, earthquakes significantly impact dam deformation, necessitating heightened attention to the potential for seismic-induced dam damage in the future. [ABSTRACT FROM AUTHOR]

• To magnify the frequency ranges of vibration suppression, phononic bandgaps are tuned three times by adjusting stiffness contrast. • Transmission testing and simulations validate triply tunable phononic bandgaps. • Extra 37.5% phononic band gaps are obtained. Sound and vibration pollution is ubiquitous in urban areas. How to alleviate the pollution has been concerned because of their broad frequency range. Currently, phononic crystals (PCs) are potential candidates for solutions. However, specific geometry, mass, and stiffness of PCs produce only fixed narrow bandgaps. Many PCs can only be tuned from one bandgap to the other. Here, in order to realize triply or multiply tunable phononic bandgaps, we introduce the three-dimensional (3D) printed hollow sphere lattice metamaterials. Utilizing the reversible temperature-dependent stiffness of the glassy polymer and discontinuity of stable thermal field in the lattice structure, we soften triply the binders between hollow spheres, keep hollow spheres hard, and attain triple modulation of the phononic bandgaps, which was validated by conducting low-amplitude transmission testing and numerical simulations. The results show that phononic bandgaps can be magnified by 37.5%. The findings reported here provide a path for designing phononic lattices with controllable and broad band gaps, offering extensive potential applications in acoustic and vibration suppression, wave guiding or filtering, and non-destructive testing. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we will present a motion pattern recognition based Kalman filter (PRKF), and apply it to the time difference of arrival (TDOA) algorithm of indoor localization. The state matrix in Kalman filter (KF) is determined by the motion pattern which the target node is supposed to act, and this will bring new system error if the assumption is not correct. Considering this, we first create three fuzzy sets using three KFs whose state matrix stand for different motion patterns, then linearly combined the memberships of a target node of the fuzzy sets. Finally, simulation results show that the PRKF can enhance the localization accuracy about more than 20%. [Copyright &y& Elsevier]

The phosphorus uptake 1 ( Pup1) locus was identified as a major quantitative trait locus (QTL) for tolerance of phosphorus deficiency in rice. Near-isogenic lines with the Pup1 region from tolerant donor parent Kasalath typically show threefold higher phosphorus uptake and grain yield in phosphorus-deficient field trials than the intolerant parent Nipponbare. In this study, we report the fine mapping of the Pup1 locus to the long arm of chromosome 12 (15.31–15.47 Mb). Genes in the region were initially identified on the basis of the Nipponbare reference genome, but did not reveal any obvious candidate genes related to phosphorus uptake. Kasalath BAC clones were therefore sequenced and revealed a 278-kbp sequence significantly different from the syntenic regions in Nipponbare (145 kb) and in the indica reference genome of 93-11 (742 kbp). Size differences are caused by large insertions or deletions (INDELs), and an exceptionally large number of retrotransposon and transposon-related elements (TEs) present in all three sequences (45%–54%). About 46 kb of the Kasalath sequence did not align with the entire Nipponbare genome, and only three Nipponbare genes (fatty acid α-dioxygenase, dirigent protein and aspartic proteinase) are highly conserved in Kasalath. Two Nipponbare genes (expressed proteins) might have evolved by at least three TE integrations in an ancestor gene that is still present in Kasalath. Several predicted Kasalath genes are novel or unknown genes that are mainly located within INDEL regions. Our results highlight the importance of sequencing QTL regions in the respective donor parent, as important genes might not be present in the current reference genomes. [ABSTRACT FROM AUTHOR]

The popularity of electric vehicles has been limited by factors such as range, long charging times and fast power failure in winter. In order to overcome these challenges, battery swapping stations (BSS) have been constructed and greatly promoted in recent years. In this paper, the related literature on electric vehicle service is reviewed and the co-occurrence of keywords is analyzed using CiteSpace. The literature is classified according to clustering results and recurring themes, such as the location of BSS, inventory decisions, charging strategies and BSS assignment. In each topic, typical optimization models and algorithms proposed in previous studies are summarized. Then, this paper gives a case about the business model and revenue capacity calculation of BSS. Finally, it points out the future research direction of battery swapping stations for electric vehicles. [ABSTRACT FROM AUTHOR]

Abstract: This study aims to assess the risk of high intensity focused ultrasound (HIFU) therapy on the incidence of distant metastases and to investigate its association with HIFU-elicited anti-tumor immunity in a murine melanoma (B16-F10) model. Tumor-bearing legs were amputated immediately after or 2 days following HIFU treatment to differentiate the contribution of the elicited anti-tumor immunity. In mice undergoing amputation immediately after mechanical, thermal, or no HIFU treatment, metastasis rates were comparable (18.8%, 13.3%, and 12.5%). In contrast, with a 2-day delay in amputation, the corresponding metastasis rates were 6.7%, 11.8%, and 40%, respectively. Animal survival rate was higher and CTL activity was enhanced in the HIFU treatment groups. Altogether, our results suggest that HIFU treatment does not increase the risk of distant metastasis. Instead, HIFU treatment can elicit an anti-tumor immune response that may be harnessed to improve the overall effectiveness and quality of cancer therapy. [Copyright &y& Elsevier]

• A new method for mass concrete temperature control is proposed and proved. • Mass concrete temperature change has great effect on the surface layer moisture. • Coupled heat and moisture transfer is considered in control system design. In this paper, a new method for hydraulic mass concrete temperature control to reduce temperature stress is proposed. Based on dam temperature distribution characteristics, an external heating and cooling source is used to make the water circulate in the pre-embedded pipe net in the concrete surface layer to control the concrete temperature. The minimum adverse strain principle is used to design the key parameters of the control system, and the strain caused by temperature and moisture is considered because of the porousness of concrete. The feasibility of the new method is studied via a mass concrete (1 m × 1 m × 1 m) experiment with pre-embedded temperature and moisture sensors under cold environmental conditions. The temperature and moisture evolutions in the control process show that the concrete temperature can be effectively controlled by the new method, but temperature control also has a great effect on the moisture in the surface layer concrete. Considering that the decreasing moisture of surface layer concrete in the temperature control process can also lead to adverse strain, based on the coupled heat and moisture transfer theory, the key parameters of the control system in the experiment are studied and optimized via simulations to reduce adverse strain. [ABSTRACT FROM AUTHOR]

Hydraulic concrete is often scoured by sediment-laden flow, resulting in wear damage on the surface of concrete. This study, used a homemade scouring device to explore mainly the effect of sand characteristics on mortar surface erosion. A 3D scanner was used to digitally reconstruct the damage contours on the specimen surface. The effects of various influencing factors on the scouring damage were investigated by analyzing the morphology and the characteristics of the scouring pits. Results indicate that impact angle and sand particle size greatly influence the morphology of the scour pit. Smaller sand particles cause more scouring damage to the mortar than larger ones. The abrasion volume is greatest at 90° impact when the sand particle size is large (0.4–2 mm) and at 20° impact when the sand particle size is small (0.1–0.2 mm). Gray correlation analysis shows that impact angle exerts the greatest effect on abrasion volume, whereas the sand content has the least effect. In addition, a mathematical model was proposed for predicting mortar abrasion volume taking into account the characteristics of sand particles. This study can provide a reference for the life prediction and durability design of concrete runners. • The effects of sediment characteristics on the wear damage of mortar were investigated in detail. • A new wear measurement method is proposed. A homemade test setup was used for the scouring test, and a 3D scanner was used to digitally reconstruct the damage profile on the specimen surface. • By analyzing the morphology and characteristics of the scour pits, the scour damage mechanism is investigated. • A mathematical prediction model for the abrasion volume prediction is deduced on the basis of experimental data. The model also takes into account the effect of sand properties. [ABSTRACT FROM AUTHOR]

Low-Earth orbit (LEO) satellites have fast motion and thus provide rapid geometric change relation to the ground stations in a short period of time, which are expected to improve the positioning performance. In this study, a LEO constellation of 160 LEO satellites was simulated and simulated LEO observation data at global, European, and American stations were used to estimate the uncalibrated phase delays (UPDs) and achieve static and kinematic precise point positioning (PPP) ambiguity resolution (AR). The quality of the estimated UPD products were evaluated. More than 89 % and 96 % of the wide- and narrow-lane UPDs had a posteriori residual of less than 0.15 and 0.25 cycles, respectively. In static PPP, all ambiguity fixing rates were larger than 63 %. Compared with float solutions, the average convergence time of the fix solutions at the global, European and American stations was accelerated by 8 %, 6 % and 7 %, respectively; the average root-mean-square errors (RMSEs) in the east, north, and up components at the global, European and American stations were decreased by (22 %, 20 %, 15 %), (36 %, 34 %, 28 %) and (44 %, 31 %, 29 %), respectively. In kinematic PPP, all ambiguity fixing rates were larger than 40 %. Compared with float solutions, the average convergence time of the fix solutions at the global, European and American stations was accelerated by 4 %, 19 % and 14 %, respectively; the average RMSEs in the east, north, and up components at the global, European and American stations were decreased by (10 %, 10 %, 7 %), (27 %, 22 %, 11 %) and (32 %, 20 %, 10 %), respectively. In both static and kinematic PPP, AR accelerated the convergence time and improved the positioning accuracy. [ABSTRACT FROM AUTHOR]

The Global Navigation Satellite System (GNSS) can be utilized for long-distance and high-precision time transmission. With the ongoing development of low Earth orbit (LEO) satellites and the rapidly changing geometric relationships between them, the convergence rate of ambiguity parameters in Precise Point Positioning (PPP) algorithms has increased, enabling fast and reliable time transfer. In this paper, GPS is used as an experimental case, the LEO satellite constellation is designed, and simulated LEO observation data are generated. Then, using the GPS observation data provided by IGS, a LEO-enhanced PPP model is established. The LEO-augmented PPP model is employed to facilitate faster and more reliable high-precision time transfer. The application of the LEO-augmented PPP model to time transfer is examined and discussed through experimental examples. These examples show multiple types of time transfer links, and the experimental outcomes are uniform. GPS + LEO is compared with exclusive GPS time transfer schemes. The clock offset of the time transfer link for the GPS + LEO scheme converges more swiftly, meaning that the time required for the clock offset to reach a stable level is the briefest. In this paper, standard deviation is employed to assess stability, and Allan deviation is utilized to assess frequency stability. The results show that the clock offset stability and frequency stability achieved by the GPS + LEO scheme are superior within the convergence time range. Controlled experiments with different numbers of satellites for LEO enhancement indicate that time transfer performance can be improved by increasing the number of satellites. As a result, augmenting GPS tracking data with LEO observations enhances the time transfer service compared to GPS alone. [ABSTRACT FROM AUTHOR]

Precision point positioning (PPP) utilizing the Global Navigation Satellite System (GNSS) is a traditional and widely employed technology. Its performance is susceptible to observation discontinuities and unfavorable geometric configurations. Consequently, the integration of the Inertial Navigation System (INS) and GNSS makes full use of their respective advantages and effectively mitigates the limitations of GNSS positioning. However, the GNSS/INS integration faces significant challenges in complex and harsh urban environments. In recent years, the geometry between the user and the satellite has been effectively improved with the advent of lower-orbits and faster-speed Low Earth Orbit (LEO) satellites. This enhancement provides more observation data, opening up new possibilities and opportunities for high-precision positioning. Meanwhile, in contrast to the traditional extended Kalman filter (EKF) approach, the performance of the LEO-enhanced GNSS/INS tightly coupled integration (TCI) can be significantly improved by employing the factor graph optimization (FGO) method with multiple iterations to achieve stable estimation. In this study, LEO data and the FGO method were employed to enhance the GNSS/INS TCI. To validate the effectiveness of the method, vehicle data and simulated LEO observations were subjected to thorough analysis. The results suggest that the integration of LEO data significantly enhances the positioning accuracy and convergence speed of the GNSS/INS TCI. In contrast to the FGO GNSS/INS TCI without LEO enhancement, the average enhancement effect of the LEO is 22.16%, 7.58%, and 10.13% in the north, east, and vertical directions, respectively. Furthermore, the average root mean square error (RMSE) of the LEO-enhanced FGO GNSS/INS TCI is 0.63 m, 1.21 m, and 0.85 m in the north, east, and vertical directions, respectively, representing an average improvement of 41.91%, 13.66%, and 2.52% over the traditional EKF method. Meanwhile, the simulation results demonstrate that LEO data and the FGO method effectively enhance the positioning and convergence performance of GNSS/INS TCI in GNSS-challenged environments (tall buildings, viaducts, underground tunnels, and wooded areas). [ABSTRACT FROM AUTHOR]

This study proposes a model using 5G time-of-arrival data to assist global navigation satellite system precise point positioning ambiguity resolution. Specifically, the model addresses the problem of PPP requiring a long convergence time in partially satellite-occluded GNSS environments, such as urban canyons. First, we apply the ionosphere-free PPP model to estimate uncalibrated phase delays. Next, we combine real 5G data with GNSS data to determine whether introducing 5G observations will decrease the convergence time of the PPP solution. Experimental results reveal that the 5G-assisted PPP model can effectively improve the convergence efficiency of the float solution, lower the fixed time, and achieve greater positional reliability. Notably, the combination of GPS, BDS, and 5G with a sampling interval of 1 s obtains a fixed solution in an average of 1.12 min. Moreover, 5G-assisted GNSS positioning effectively compensates for partial satellite occlusion, optimizes the PDOP value, and speeds up ambiguity fixing. The introduction of three and more 5G base stations helps to obtain fixed solutions within 9 min when it is difficult to obtain fixed solutions relying only on GNSS. Our findings have important implications for improving the widespread applicability and effectiveness of satellite-based navigation systems in light of increasing urbanization and the rise of signal-occluding environments. [ABSTRACT FROM AUTHOR]

In order to improve the effective guidance of martial arts movements, a decomposition method of martial arts movements based on image recognition is proposed. First of all, visual image target sampling of martial arts action is performed, and most of the noise background is eliminated through morphological gradient operation. Then, the contour edge of the human body is obtained, the contour edge of each frame of the video is extracted, and the accumulation is realized in the same image. Using accumulation, the edge image calculates the grid-based HOG to obtain the image action feature vector. Secondly, using the improved dynamic time warping theory combined with the characteristics of the angle change of each joint under the action time sequence, the joint change sequence among various martial arts movements can be identified in order to realize the decomposition process of martial arts actions based on image recognition. The experimental results show that the use of image recognition can effectively decompose martial arts movements. [ABSTRACT FROM AUTHOR]

The team sports game video features complex background, fast target movement, and mutual occlusion between targets, which poses great challenges to multiperson collaborative video analysis. This paper proposes a video semantic extraction method that integrates domain knowledge and in-depth features, which can be applied to the analysis of a multiperson collaborative basketball game video, where the semantic event is modeled as an adversarial relationship between two teams of players. We first designed a scheme that combines a dual-stream network and learnable spatiotemporal feature aggregation, which can be used for end-to-end training of video semantic extraction to bridge the gap between low-level features and high-level semantic events. Then, an algorithm based on the knowledge from different video sources is proposed to extract the action semantics. The algorithm gathers local convolutional features in the entire space-time range, which can be used to track the ball/shooter/hoop to realize automatic semantic extraction of basketball game videos. Experiments show that the scheme proposed in this paper can effectively identify the four categories of short, medium, long, free throw, and scoring events and the semantics of athletes' actions based on the video footage of the basketball game. [ABSTRACT FROM AUTHOR]

The objective of this study is to examine the role of disorder eating in athlete performance. To examine the role of disorder eating in athlete performance, the role of disorder eating, energy deficiency, negative eating behavior and demotivation is also considered. Therefore, the relationship between disorder eating, energy deficiency, negative eating behavior, demotivation and athlete performance has been examined through the course of the present study. To this end, a total of nine hypotheses are proposed in this study including six direct hypotheses and three indirect hypotheses. Data is collected from a population of athletes in China and a questionnaire is used the main instrument for data collection wherein a Like rt scale is used on account of its suitability for collecting the opinion and views of individuals. After analyzing the data using a statistical tool, it is observed that disorder eating has an important role in athlete performance. It is found that; disorder eating has a positive effect on energy deficiency. It also has positive effect on negative eating behavior. Disorder eating is found to have a positive effect on demotivation. Furthermore, energy deficiency has negative effects on athlete performance. Negative eating behavior has a negative effect on athlete performance. Finally, demotivation also has negative effect on athlete performance. [ABSTRACT FROM AUTHOR]

Sustained load is a common type of load for concrete structures during service. It may affect the pore structure of mortar, thereby affecting the transmission characteristics of water and the durability of concrete. In this paper, the pore structure and transport properties of mortars at low- stress levels were investigated. Non-destructive axial tensile and compressive loads were applied to the mortar to study the permeability and water absorption of the mortar under different loads. In addition, the mortar's pore structure was analyzed under varying sustained loads using the RapidAir 457 pore structure analyzer and micro-CT scans. Results show that within the stress levels of the experimental design, compressive loads tend to reduce the water transmission rate in mortar, whereas tensile loads have a positive effect on water transmission. The pore-size distribution of mortars with different water-cement ratios is affected differently by load. Finally, seepage simulation was carried out using the three-dimensional model established by CT scanning. The results show that the simulated values and experimental test values were consistent with the changing trend of the load. With increasing compressive load, the water seepage path is obstructed, resulting in decreased permeability. Conversely, under tensile loads, the number and density of streamlines increase, facilitating water penetration. • The effect of sustained loading on the pore structure was studied. • The effect of sustained loading on the permeability of mortar was studied. • Three-dimensional pore models of mortar was established based on CT scan results. • Seepage simulation was performed using a three-dimensional model. [ABSTRACT FROM AUTHOR]

Satellite navigation systems enable long‐distance and high‐precision time transfers. The authors proposed an undifferenced precise time transfer method with information constraints in this study. A more accurate receiver clock offset can be obtained by constraining the station coordinate parameters and receiver clock offset parameters to achieve a precise time transfer. In this example, the research object is the time transfer link established by the Global Positioning System observation station using a caesium clock, rubidium clock, and hydrogen clock. The clock difference sequence of the time‐transfer link was calculated by combining the observation data and precise products. Following analysis of the examples, the following conclusions were reached. The undifferenced precise time transfer method based on information constraints can effectively be used to smooth the clock difference sequence of the receiver and the clock difference sequence of the time transfer link. To some extent, this method can also be used to reflect the performance of atomic clocks at Global Positioning System stations and is better suited for the precise time transfer of the equal‐clock long‐baseline time transfer link. Simultaneously, the frequency stability of this method is improved significantly in the short term compared to the traditional scheme without any constraints. The improvement of frequency stability is helpful to improve the accuracy of time transfer. [ABSTRACT FROM AUTHOR]

Establishing an ultra-high-precision link for time–frequency comparisons between satellites and ground stations is critically important. This endeavor is fundamental to the advancement of pioneering space science exploration and the development of a robust space-based time–frequency system featuring ultra-high-precision space atomic clocks. In response to the requirements for assessing the long-term stability of high-precision space atomic clocks, we have designed and implemented a satellite–ground microwave time–frequency comparison system and method based on a three-frequency mode. Ground-based experimental results demonstrate that the equipment layer can achieve a satellite–ground time comparison accuracy better than 0.4 ps (RMS), with the equipment delay stability (ADEV) for all three frequencies being better than 8 × 10−18 at 86,400. By leveraging the ground-based experimental results, we constructed a satellite–ground time–frequency comparison simulation and verification platform. This platform realizes ultra-high-precision satellite–ground time–frequency comparison based on the China Space Station (CSS). After correcting various transmission delay errors, the satellite–ground time comparison achieved an accuracy better than 0.8 ps and an ADEV better than 2 × 10−17 at 86,400. This validation of our novel satellite–ground time–frequency comparison system and method, capable of achieving an 10−17 magnitude stability, is not only a significant contribution to the field of space time–frequency systems but also paves the way for future advancements and applications in space science exploration. [ABSTRACT FROM AUTHOR]

Deep penetrating sealer (DPS) is a general term for a class of waterproofing agent that can fill the internal pores of concrete; it is produced by mixing an alkali metal silicate solution as the base material with catalysts and additives. The objective of this study was to investigate the characteristics and mechanism of the effect of different amounts of DPS sprayed on concrete. The water absorption, hydrophilicity, permeability, microhardness, abrasion erosion resistance and pore structure of concrete were tested at different water/cement ratios and amounts of sprayed DPS. The test and analysis results showed that, compared with a control concrete, concrete absorbed less water and exhibited less permeability after being sprayed with DPS. Moreover, the hydrophilicity, microhardness and abrasion erosion resistance improved, while the pore volume significantly decreased. The effect was more evident when the amount of sprayed DPS was higher. This study provides a reference for practical engineering applications by demonstrating the variation in concrete surface properties after spraying different amounts of DPS. [ABSTRACT FROM AUTHOR]

Specific emitter identification (SEI) is a professional technology to recognize different emitters by measuring the unique features of received signals. It has been widely used in both civilian and military fields. Recently, many SEI methods based on deep learning have been proposed, most of which assume that the training set and testing set have the same data distribution. However, in reality, the testing set is generally used later than the training set and lacks labels. The long time span may change the signal transmission environment and fingerprint features. These changes result in considerable differences in data distribution between the training and testing sets, thereby affecting the recognition and prediction abilities of the model. Therefore, the existing works cannot achieve satisfactory results for a long time span SEI. To address this challenge and obtain stable fingerprints, we transform the long time span SEI problem into a domain adaptive problem and propose an unsupervised domain adaptive method called LTS-SEI. Noteworthily, LTS-SEI uses a multilayer convolutional feature extractor to learn feature knowledge and confronts a domain discriminator to generate domain-invariant shallow fingerprints. The classifier of LTS-SEI applies feature matching to source domain samples and target domain samples to achieve the domain alignment of deep fingerprints. The classifier further reduces the intraclass diversity of deep features to alleviate the misclassification problem of edge samples in the target domain. To confirm the effectiveness and reliability of LTS-SEI, we collect multiple sets of real satellite navigation signals using two antennas with 13 m- and 40 m-large apertures, respectively, and construct two available datasets. Numerous experiments demonstrate that LTS–SEI can considerably increase the recognition accuracy of the long time span SEI and is superior to the other existing methods. [ABSTRACT FROM AUTHOR]

In this paper we propose an enhanced fireworks algorithm for locating the critical slip surface giving the minimum safety factor in slope stability analysis, and we employ a concise algorithm of the Morgenstern and Price method to calculate the safety factor. To demonstrate its applicability and to illustrate the reliability and effectiveness of the proposed method, we present three benchmark examples with varying complex slopes. By comparing the minimum safety factor and the total number of iterations, the proposed method is proved to be highly competitive in terms of efficiency and accuracy. [ABSTRACT FROM AUTHOR]

• The temperature and humidity inside the mass concrete were measured. • The results of numerical simulation and field tests are compared. • A model was proposed and solved for coupled heat – moisture-force transport in concrete. • Changes in temperature, humidity and stress can be predicted by establishing a coupled numerical analysis model. Hydraulic mass concrete has been in a temperature and humidity cycle environment for a long time, reducing the performance and service life of its structure. Under the premise of temperature control, we use the Soret effect as the basis of heat- humidity coupling, and then use thermal conductivity, diffusion coefficient and elastic modulus to evaluate the coupling effect between temperature, relative humidity, and stress of mass concrete, and establish a thermal – humidity -force coupling model. Using the embedded temperature and humidity sensor to conduct experiments on mass concrete, this study explores the temperature control pipeline's influence on the temperature and relative humidity distribution inside the concrete and the feasibility of the coupling model. Through experimental results and model analysis, this study found that, under temperature control, the prediction results of the coupled model are more consistent with the experimental results, and its accuracy is higher than that of the uncoupled model. In the process of temperature control, temperature has a significant effect on surface water diffusion, whereas humidity has little effect on temperature conduction, and temperature conduction is mainly affected by temperature gradient. Temperature control can effectively reduce the temperature amplitude inside the concrete, reducing the stress inside the concrete. Moreover, the coupled thermal-moisture-force model can accurately predict the variation trend of temperature, relative humidity, and stress with time at each point inside the concrete under temperature control. The theoretical results of this study can provide a reference for the design, construction, and maintenance of hydraulic engineering structures in the future and better grasp the internal temperature, relative humidity, and stress of hydraulic concrete in different environments and the change law. [ABSTRACT FROM AUTHOR]

• A new method was proposed for determining the maximum paste coating thickness. • Digital models of pervious concrete were created. • Influence of maximum paste coating thicknesses on the pore characteristics and seepage flow was investigated. • An empirical formula was proposed to determine the Kozeny–Carman constant. The determination of the maximum paste coating thickness on aggregate (MPCT) without void clogging is essential for effectively controlling the permeability of a pervious concrete (PC). The main objective of this study is to investigate the influence of varying MPCTs on the pore characteristics and seepage flow of PC. A new method was proposed for determining the MPCT of PC, and the relationships between the MPCT and the rheological properties of cement paste were established. Subsequently, digital models of PC with varying MPCTs were created, and the connected pore was extracted for analysis of pore characteristics. Seepage flow simulations were conducted to analyze the permeability characteristics of PCs under varying MPCTs. The results indicate that the pore characteristics are directly influenced by the MPCT, in which the effective porosity, specific surface, and tortuosity show linear correlations with the MPCT. When the MPCT ranges from 0.44 to 0.99 mm, the pore size of the PCs exhibits a single-peak distribution ranging from 1.4 to 13.5 mm, while the coordination number of the pores is distributed within the range of 1 to 14. Additionally, the permeability coefficient of PC decreases as the MPCT increases. When the MPCT exceeds 0.85 mm, the permeability coefficient drops to less than 1 mm/s, and the rate of decrease slows down. An empirical formula was proposed to determine the Kozeny–Carman (KC) constant, which improves the accuracy of the KC equation in predicting the permeability of PC. The findings presented in this study serve as a reference for the design of mixture proportions and the optimization of permeability in PC. [ABSTRACT FROM AUTHOR]

To investigate the cold response mechanism and low temperature regulation of flowering in tulips, this study identified 32 MADS-box transcription factor family members in tulips based on full-length transcriptome sequencing, named TgMADS1-TgMADS32. Phylogenetic analysis revealed that these genes can be divided into two classes: type I and type II. Structural analysis showed that TgMADS genes from different subfamilies have a similar distribution of conserved motifs. Quantitative real-time PCR results demonstrated that some TgMADS genes (e.g., TgMADS3, TgMADS15, TgMADS16, and TgMADS19) were significantly upregulated in buds and stems under cold conditions, implying their potential involvement in the cold response of tulips. In summary, this study systematically identified MADS family members in tulips and elucidated their evolutionary relationships, gene structures, and cold-responsive expression patterns, laying the foundation for further elucidating the roles of these transcription factors in flowering and the cold adaptability of tulips. [ABSTRACT FROM AUTHOR]

Accuracy and reliability are determining factors when selecting where to place a global navigation satellite system (GNSS) receiver for landslide monitoring and early warning in real time. Previous studies have revealed that surface occlusion models (SOMs) are beneficial to reduce the multipath error of satellite observation when the satellite line of sight is near the ground and improve the accuracy and reliability of GNSS monitoring. This paper investigates fitting functions to determine appropriate SOMs for GNSS stations located in different spatial environments. Based on their similarity to terrain patterns, Gaussian, Fourier, and sum of sine functions were chosen to build SOMs for the rover sites with different occlusions; the performance of fitting accuracy and application on the positioning were analyzed. The results indicate that the three functions present a similar performance considering the goodness of fit, but the Fourier and sum of sine functions can significantly improve the efficacy of SOMs and enhance performance in positioning for landslide monitoring. Therefore, these two functions can effectively support accurate and reliable GNSS landslide monitoring in real time. [ABSTRACT FROM AUTHOR]

As a basic task and key link of space situational awareness, space target recognition has become crucial in threat analysis, communication reconnaissance and electronic countermeasures. Using the fingerprint features carried by the electromagnetic signal to recognize is an effective method. Because traditional radiation source recognition technologies are difficult to obtain satisfactory expert features, automatic feature extraction methods based on deep learning have become popular. Although many deep learning schemes have been proposed, most of them are only used to solve the inter-class separable problem and ignore the intra-class compactness. In addition, the openness of the real space may invalidate the existing closed-set recognition methods. In order to solve the above problems, inspired by the application of prototype learning in image recognition, we propose a novel method for recognizing space radiation sources based on a multi-scale residual prototype learning network (MSRPLNet). The method can be used for both the closed- and open-set recognition of space radiation sources. Furthermore, we also design a joint decision algorithm for an open-set recognition task to identify unknown radiation sources. To verify the effectiveness and reliability of the proposed method, we built a set of satellite signal observation and receiving systems in a real external environment and collected eight Iridium signals. The experimental results show that the accuracy of our proposed method can reach 98.34% and 91.04% for the closed- and open-set recognition of eight Iridium targets, respectively. Compared to similar research works, our method has obvious advantages. [ABSTRACT FROM AUTHOR]

In this study, 22 maneuvering events of C59 and C60 geostationary equatorial orbit (GEO) satellites of the BeiDou global navigation satellite system (BDS-3) in 2021 were detected and analyzed based on a time-differenced carrier phase velocity measurement algorithm combined with a broadcast ephemeris and station data. We set different empirical thresholds to analyze the effect of threshold selection on the maneuvering detection sensitivity. The sensitivity and consistency of this algorithm for GEO satellite maneuvering detection were analyzed by combining BDS-3 with other Global navigation satellite systems (GNSS) and selecting different geographic stations. The results demonstrate that changing the threshold significantly affects the maneuvering detection of C60, with the optimal maneuvering thresholds of C59 and C60 being 0.045 and 0.02, respectively. A combination of BDS-3 and GPS with equal weights was identified to be most suitable for maneuvering detection of GEO satellites. For any specific maneuver, the difference between the maneuvering time detection of C59 by stations at different geographical locations was no more than 1 min. During the maneuvering detection of C60, the start time of maneuvering detected by African stations was 4.26–8.61 min earlier than that detected by the Chinese and Australian stations, and the end time of maneuvering detected by the African stations was consistent with that detected by the Chinese and Australian stations. [ABSTRACT FROM AUTHOR]

The BeiDou navigation satellite system (BDS) comprises geostationary earth orbit (GEO) satellites as well as inclined geosynchronous orbit (IGSO) and medium earth orbit (MEO) satellites. Owing to their special orbital characteristics, GEO satellites require frequent orbital maneuvers to ensure that they operate in a specific orbital window. The availability of the entire system is affected during the maneuver period because service cannot be provided before the ephemeris is restored. In this study, based on the conventional dynamic orbit determination method for navigation satellites, multiple sets of instantaneous velocity pulses parameters which belong to one of pseudo-stochastic parameters were used to simulate the orbital maneuver process in the orbital maneuver arc and establish the observed and predicted orbits of the maneuvered and non-maneuvered satellites of BeiDou regional navigation satellite system (BDS-2) and BeiDou global navigation satellite system (BDS-3). Finally, the single point positioning (SPP) technology was used to verify the accuracy of the observed and predicted orbits. The orbit determination accuracy of maneuvered satellites can be greatly improved by using the orbit determination method proposed in this paper. The overlapping orbit determination accuracy of maneuvered GEO satellites of BDS-2 and BDS-3 can improve 2–3 orders of magnitude. Among them, the radial orbit determination accuracy of each maneuvered satellite is basically better than 1 m. simultaneously, the combined orbit determination of the maneuvered and non-maneuvered satellites does not have a great impact on the orbit determination accuracy of the non-maneuvered satellites. Compared with the multi GNSS products (indicated by GBM) from the German Research Centre for Geosciences (GFZ), the impact of adding the maneuvered satellites on the orbit determination accuracy of BDS-2 satellites is less than 9 %. Furthermore, the orbital recovery time and the service availability period are significantly improved. When the node of the predicted orbit is traversed approximately 3 h after the maneuver, the accuracy of the predicted orbit of the maneuvered satellite can reach that of the observed orbit. The SPP results for the BDS reached a normal level when the node of the predicted orbit was 2 h after the maneuver. [ABSTRACT FROM AUTHOR]

An abstract of the article "Restoration of Impaired Myocardial Contractility by Overexpressing Sarcoplasmic Reticulum Calcium ATPase through Recombinant Adeno-Associated," by Xiachum Lu and colleagues is presented.

Several global navigation satellite systems (GNSS) broadcast overlapping frequencies to enhance interoperability, allowing tight integration with only one reference satellite for every system with the same frequency. The key to realizing tight integration is estimating and utilizing differential intersystem biases, which allows the integer characteristic of the differenced ambiguity of two satellites from different systems to be retrieved. In this study, a detailed algorithm flow of a tight integration kinematic uncalibrated phase delay (UPD)-based PPP ambiguity resolution (PPP-AR) method, which includes multiple parts, is introduced. Subsequently, PPP-AR numerical experiments were conducted in a high-shade observation environment to determine the performance. In comparison with traditional methods, our results indicate that the average success fix rate improves from 83% to 100% after using the tight integration method in an environment where only three satellites are observed for each system. Moreover, for fewer than nine satellites, the tight integration method can still consistently maintain a fixed state. However, for comparison, the traditional loose integration method could no longer be implemented. [ABSTRACT FROM AUTHOR]

Traditional PPP-RTK algorithm research has focused on users in a reference station network. However, if a proper PPP-RTK user algorithm can be designed for out-of-network users to achieve accurate and rapid positioning, the effective service area of existing reference station networks can be markedly expanded. To address the problem of extrapolating atmospheric corrections for out-of-network users, this study presents a single-reference-station (SRS) PPP-RTK model to address atmospheric delay corrections, by ensuring that only corrections from the closest reference station are used. Several numerical experiments were designed and conducted to compare the performance of the presented model and a widely used interpolation model. The extrapolation error distribution, mean and the maximum of absolute values of errors, and standard deviation of errors were selected as indicators. The results show that the SRS PPP-RTK model is significantly more accurate than the interpolation model. Thus, for out-of-network users, we suggest that the presented SRS PPP-RTK model should be used, and the residual atmospheric delays are needed to be estimated. [ABSTRACT FROM AUTHOR]

Freeze–thaw cycles (FTCs) and steel bar corrosion (SBC) are the most common service conditions of hydraulic concrete and have significant impacts on its durability. Using pullout and microscopic tests of different FTC and SBC rates, we selected the mass loss rate, ultrasonic velocity, bond strength and bond slip in order to describe the changes in the macro-properties, and also selected the porosity and pore size distribution as micro-parameters in order to explore the influence of FTCs and SBC on the mechanical properties of hydraulic concrete. The results showed that the bond strength decreased as the FTCs increased due to the microstructure damage caused by FTC and SBC, which affects the mechanical properties. A corrosion rate of ≤3% offset the damage caused by 50 FTCs. FTCs and SBC resulted in superimposed damage effects on the concrete. In addition, we established a bond strength damage model based on the joint FTCs and SBC and quantitatively described the degradation law of the macro-mechanical properties. The analysis shows that the influence of FTCs on the bond strength was greater than that of the SBC. These research results can provide a reference and experimental support for the frost-resistant design and durability prediction of hydraulic concrete structures in cold environments. [ABSTRACT FROM AUTHOR]

The Chinese BeiDou global satellite system (BDS-3) and regional system (BDS-2) are predicted to coexist over the next decade. Intersystem biases (ISBs) in BDS-2/BDS-3 play a key role in maintaining the consistency and continuity from the BDS-2 to BDS-3 time transfer. Here, we discuss the temporal characteristics, parameter composition, generation mechanism, and the effect of ISBs in BDS-2/BDS-3 on time and frequency transfer. The satellite orbits and clock products from three international GNSS service analysis centers, namely Wuhan University (WUM, China), GeoForschungsZentrum Potsdam (GFZ, Germany), and the Center for Orbit Determination in Europe (CODE), were employed to investigate the time-transfer stability of ISBs when BDS-2 and BDS-3 were used in combination. We analyzed the intrinsic characteristics of ISBs, the receiver types, antennas, and frequency standards. Our first results showed that ISBs are stable for different analysis center products, although the mean values of daily results differed markedly for the three analysis centers. With respect to the relationship between station attribution and ISB difference for a time link, the receiver type, antenna, and frequency standard influence the ISB differences in time and frequency transfer. The effect of three ISB stochastic models was evaluated with respect to time and frequency transfer. The "walk" and "constant" schemes were slightly superior to "noise", with the improvement in their frequency stability being approximately 5% compared with that of "noise". [ABSTRACT FROM AUTHOR]

In PPP-RTK, obtaining accurate atmospheric delay information for the user through interpolation is one of the keys to achieving high-precision real-time positioning. The ionospheric delay that is extracted by a reference network based on uncalibrated phase delay (UPD) products is often difficult to separate from errors such as receiver code hardware delay and UPD reference error. Inter-satellite single-difference (SD) ionospheric delay information is typically provided to the user. This paper proposes an interpolation model that uses the atmospheric delay coefficient to represent the SD ionospheric delay, based on the mean position of the ionospheric pierce point (IPP) of each satellite pair and the center position of the network, which is called the differenced surface model (DSM). We chose four scenarios to compare the interpolation accuracy of the proposed model with the inverse distance-based linear interpolation method (DIM) and USM based on the difference between the longitude and latitude of the reference and ionospheric pierce point (IPP) of every satellite (here, we call it USM for short). The four scenarios involve a medium-scale reference network with an average distance to the reference station of 41 km, a large-scale reference network with an average distance to the reference station of 98 km, and out-of-network users, and a network with a common minimum of three reference stations. The results show that the root mean square (RMS) of the SD residuals of ionospheric delay for DSM were 1.4, 3.2, 2.2, and 1.4 cm, respectively, for the four scenarios that were considered, which are slightly better delay values than those that were achieved using DIM and USM. For the scenario with three reference stations, the interpolation accuracies of DIM and DSM were no different from those for four reference stations, indicating that the server can still try to provide ionospheric correction service under the condition of fewer reference stations. In contrast, USM could not provide service because it lacked the sufficient number of reference stations. DSM was used as the ionospheric delay interpolation model to analyze GPS and Galileo dual-system PPP-RTK positioning performance. In addition, the atmospheric parameter constraint method of users was used in PPP-RTK in reference networks of different scales. For the 41-km and 98-km reference networks, the time to first fix (TTFF) were 14.5 s and 33.1 s, respectively, and the mean RMS values for the east (E), north (N), and up (U) directions were 0.80, 0.93, and 2.72 cm, respectively, and 1.0, 1.1, and 4.0 cm, respectively, for a period of 5 min after convergence. The fixing rate and positioning accuracy of DSM during the 5-min period were better than those of DIM when the same empirical model was used to determine the mean square error of atmospheric delay. [ABSTRACT FROM AUTHOR]

Precise point positioning (PPP) technology is one of the core technologies in the field of GNSS high-precision positioning. It is used widely because it can realize centimeter-level positioning in outdoor environments by using only a single receiver. However, its convergence is time-consuming, particularly in urban areas where satellite occlusion is more severe. A combined BeiDou Navigation Satellite System (BDS) and fifth generation mobile communication technology (5G) PPP observation model is proposed, in which the two kinds of observations are combined and solved at the original observation level. The impact of different numbers and geometries of 5G base stations on the convergence time of PPP is analyzed from both static and dynamic perspectives. The results confirm that PPP technology combining BDS and 5G can effectively accelerate convergence while improving the accuracy of positioning. [ABSTRACT FROM AUTHOR]