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Soil environmental quality assessment traditionally focuses on a single objective. Therefore, related results only reflect the pollution of the assessment objective and ignore the interaction and relationships between soil, ecology, and human health. In this study, we collected and filtered data about heavy metal content (Cr, Pb, Cd, Hg, As, Cu, Zn, and Ni) in city soils from more than 1000 published papers. Spatial multi-criteria decision-making theory was used to establish the combined evaluation model of soil environmental quality using the geochemical accumulation, ecological risk, non-carcinogenic risk, and carcinogenic risk indexes. Our results showed that the pollution degree and elements causing most pollution were significantly different when these different methods were used for assessment. The proposed framework was able to unify the overall pollution trend in regional soil environmental quality assessment and could output more robust and reasonable assessment results of soil, ecology, and human health. The random forest model was used to analyze the potential sources for excessive accumulation of heavy metal elements in soils, and the results showed that the main potential sources were the proportion of secondary industry and urbanization rate, each with an average contribution ratio of 20%. This study provides comprehensive and specific information for the prevention and control of soil heavy metal pollution in China. [ABSTRACT FROM AUTHOR]

Accurate soil organic carbon (SOC) data are very important for management of agricultural production and climate change mitigation. Visible near-infrared diffuse reflectance spectroscopy is an inexpensive, non-destructive, efficient, and reliable technique for monitoring soil properties. Soil spectral libraries can contain large sets of diverse soil data for empirical calibration. In this study, we focused on improving the prediction accuracy of the SOC content at the local field scale in Tibet using field-wet, intact spectra and different spectral libraries. The direct standardization algorithm and piecewise direct standardization algorithm were used to remove the influence of environmental factors from the in situ vis-NIR spectra. These algorithms effectively removed the influence of environment factors from the field-wet, intact spectra. The ratio of performance to deviation values for prediction of the SOC content using the field and laboratory spectra with the local spectral library were 1.57 and 1.98, respectively. The local spectral library models outperformed spiked national spectral library models and had higher ratio of performance to deviation values for shrub meadows, forests, and the total dataset. [ABSTRACT FROM AUTHOR]

Satellite navigation systems are vulnerable. To guarantee the positioning, navigation and timing (PNT) safety of core infrastructure, it is necessary to establish a secure PNT system with hybrid physical principles. In this paper, the augmentations of the BeiDou satellite system (BDS) itself are analysed, namely augmentations through the BDS inter-satellite link, BDS geostationary orbit (GEO) and inclined geostationary orbit (IGSO) satellites, and BDS PNT services supported by low earth orbit (LEO) satellites. Then, taking BDS as the core component, the comprehensive PNT infrastructure seamlessly covering deep space and deep ocean is described, consisting of the deep space PNT constellation, the sea-floor PNT sonar beacon network, and the ground-based low frequency and very low frequency (VLF) long wave radio stations. Moreover, the key technologies of resilient PNT application matching comprehensive PNT and various autonomous perception PNT information are discussed, such as resilient PNT sensor integration, the resilient PNT functional model and the resilient stochastic model. As a future development direction, the key factors of intelligent PNT services are analysed, including the intelligent perception of PNT application scenes, the intelligent optimization of PNT functional and stochastic models and the intelligent fusion of multisource PNT information. [ABSTRACT FROM AUTHOR]

With the gradual promotion and the application of difficult-to-machine materials such as titanium matrix composites in the aerospace field, high-quality hole-making technology has become a major demand in aviation manufacturing. In order to improve the hole-making quality of TiBw/TC4 composites, asynchronous mixed frequency vibration-assisted hole-making (AMFVAHM) method is proposed. The process consists of two steps: ultrasonic vibration-assisted drilling (UVAD) base hole and low-frequency torsional vibration-assisted helical milling (LFTVAHM) target hole. Based on this process, the cutting trajectory modeling is established, and the hole-making experiment on TiBw/TC4 composites is conducted. The experimental data show that during the hole expansion stage, the maximum XY-plane average milling force decreases by 30.96% and the maximum axial average milling force decreases by 24.49% compared with conventional helical milling (HM) when the torsional vibration frequency and the milling frequency are the same in LFTVAHM. The hole-making experiment shows that AMFVAHM can reduce the chip size, tool wear, and some other defects such as entrance/exit burrs, scratches, and fractures of the hole wall. Comparing with HM and UVAD, the verticality of hole wall increases by 71.43% and 86.21%, the inlet damage decreases by 27.98% and 31.60%, the outlet damage decreases by 2.80% and 14.47%, the hole wall roughness (Ra) decreases by 36.29% and 63.43%, and the maximum white layer thickness decreases by 19.99% and 67.66%. Meanwhile, AMFVAHM process not only reduces the cutting force and cutting temperature but also improves the hole-making quality due to the fretting friction effect of LFTVAHM in secondary hole expansion, which meets the need for high-quality hole-making of difficult-to-machine materials in practical engineering applications. [ABSTRACT FROM AUTHOR]

Carbon fiber–reinforced plastics (CFRP)/titanium alloy (Ti) stacks are extensively applied in the aerospace industry due to their excellent mechanical properties. However, their poor machinability poses great challenges. In this study, longitudinal-torsional ultrasonic vibration drilling (LT-UVD) is innovatively introduced to improve the quality of CFRP/Ti drilling. First, the separation mode of LT-UVD is analyzed by kinematic equations. Then, an experimental platform is built based on the LT-UVD vibration actuator to perform CFRP/Ti drilling experiments. The thrust force, interface temperature, hole wall quality, hole defects, Ti chip morphologies, and tool wear in LT-UVD are experimentally compared against conventional drilling (CD) and longitudinal ultrasonic vibration drilling (L-UVD). The experimental results show that, compared with CD and L-UVD, the thrust force of CFRP in LT-UVD decreases by 20.36–40.55% and 2.04–14.61%, while the thrust force of Ti decreases by 19.08–24.83% and 1.95–9.34%. Moreover, a relatively low maximum interface temperature is achieved in LT-UVD. In addition, the hole size accuracy, surface roughness for the hole's inner surface, and delamination factor are improved in LT-UVD. Fiber pullout defects, chip-breaking performance, and tool wear of CFRP are improved due to torsional vibration in LT-UVD. Finally, according to the high-speed camera, damage forms of the interface area are different when drilling CFRP/Ti stacks with various drilling sequences. [ABSTRACT FROM AUTHOR]

Due to the popular trend of combining online and offline interactions among users in event-based social networks (EBSNs), event recommendation which helps users discover their interesting events has become progressively urgent. Different from classic item recommendation, candidate events usually have short life cycle and occur in the future, resulting in severe challenges of data sparsity and cold-start. However, these problems are not well studied by previous works. In this article, we propose a Meta-Graph-based Attention Recommendation (MGAR) model to tackle aforementioned challenges by fully exploring complex semantic information based on meta-graphs extracted from EBSNs. First, we model the interactions between different entities as a heterogeneous information network and construct multiple meta-graphs to characterize the latent semantic preferences of users. Subsequently, we utilize convolutional neural networks and attention mechanisms to learn user and event latent factors by extracting semantic features of meta-graphs. Furthermore, the fused latent features are utilized to predict the ratings of a user to events and the events with top-k scores are recommended to the user. We collect several real-world datasets from a popular EBSN platform and conduct extensive experiments on the datasets. Our proposed model attains superior recommendation performance over several state-of-the-art approaches. Moreover, the results demonstrate that meta-graphs can reveal the semantic properties between users and events and improve event recommendation performance. [ABSTRACT FROM AUTHOR]

Individuals with congenital or acquired prolongation of the QT interval, or long QT syndrome (LQTS), are at risk of life-threatening ventricular arrhythmia. LQTS is commonly genetic in origin but can also be caused or exacerbated by environmental factors. A missense mutation in the L-type calcium channel CaV1.2 leads to LQTS in patients with Timothy syndrome. To explore the effect of the Timothy syndrome mutation on the electrical activity and contraction of human cardiomyocytes, we reprogrammed human skin cells from Timothy syndrome patients to generate induced pluripotent stem cells, and differentiated these cells into cardiomyocytes. Electrophysiological recording and calcium (Ca2+) imaging studies of these cells revealed irregular contraction, excess Ca2+ influx, prolonged action potentials, irregular electrical activity and abnormal calcium transients in ventricular-like cells. We found that roscovitine, a compound that increases the voltage-dependent inactivation of CaV1.2 (refs 6-8), restored the electrical and Ca2+ signalling properties of cardiomyocytes from Timothy syndrome patients. This study provides new opportunities for studying the molecular and cellular mechanisms of cardiac arrhythmias in humans, and provides a robust assay for developing new drugs to treat these diseases. [ABSTRACT FROM AUTHOR]

This paper aims on slicing of monocrystalline silicon wafers using a newly developed diamond multi-wire reciprocating saw under ingot rocking process. A contact wire length model based on ingot rocking was established. The influence of motion parameters of ingot rocking on the surface quality of multi-wire sawn monocrystalline silicon wafers had been experimentally studied. The slicing surface morphology, surface roughness, and surface hardened layer were investigated by using scanning electron microscope, laser scanning microscopy, and microhardness tester. Results show that compared with the multi-wire cutting mode with an ingot rocking amplitude of 0°, ingot rocking (θm ≠ 0) can reduce the contact wire length of sawing by almost half at any time, and realize discontinuous and segmented sawing of large-diameter silicon wafers. By reducing the contact wire length, the cutting mode under ingot rocking can achieve better surface morphologies, and reduce roughness, thickness of the hardened layer and microhardness of the surface in silicon wafer cutting. Compared with the mode of multi-wire reciprocating sawing with an ingot rocking amplitude of 0°, an ingot rocking amplitude of 5°can reduce roughness, thickness of the hardened layer, and microhardness of the surface in silicon wafer cutting about 30.1%, 20.1%, and 11.3%. Though the ingot rocking amplitude did not significantly influence the contact wire length during the cutting process, the ingot rocking motion significantly influences the ingot feed speed, an ingot rocking amplitude of 5°instead of 3° or 7° is suggested for the best surface quality. [ABSTRACT FROM AUTHOR]

After the presentation of second-order correlation ranging principles with quantum entanglement, the concept of quantum measurement is introduced to dynamic satellite precise orbit determination. Based on the application of traditional orbit determination models for correcting the systematic errors within the satellite, corresponding models for quantum orbit determination (QOD) are established. This paper experiments on QOD with the BeiDou Navigation Satellite System (BDS) by first simulating quantum observations of 1 day arc-length. Then the satellite orbits are resolved and compared with the reference precise ephemerides. Subsequently, some related factors influencing the accuracy of QOD are discussed. Furthermore, the accuracy for GEO, IGSO and MEO satellites increase about 20, 30 and 10 times, respectively, compared with the results from the resolution by measured data. Therefore, it can be expected that quantum technology may also bring delightful surprises to satellite orbit determination as have already emerged in other fields. [ABSTRACT FROM AUTHOR]

CeO is one of the most promising materials applied in chemical mechanical polishing industry. However, due to the high hardness of CeO, a further surface modification is usually required, especially when polishing a soft substrate, such as fused quartz and optical disk. In this work, we reported a novel process for the synthesis of CeO/CeF composite powders which showed improved suspension stability and CMP properties. Ce(CO) and HF were employed as the precursor materials for Ce and F, respectively, which were simply milled and annealed at different temperatures to get the composite powders. The results showed that the morphology of the powders changed from microrods to grape-like shapes which had a smaller particle size. And the XRD results confirmed the formation of CeO/CeF composite phases after the HF addition. The suspension stability and CMP property measurements indicated that the change of particle morphologies and the formation of composite structure benefited the polishing process for fused quartz substrate, and a more planar surface was obtained. All these results indicated that the current processing was of great potentials for the synthesis and practical applications of ceria-based CMP slurries. [ABSTRACT FROM AUTHOR]