Beijing experienced a period of severe atmospheric particulate pollution from 2015 to 2016. In order to acquire the characteristics of polycyclic aromatic hydrocarbons (PAHs) under heavy polluting ...status, one year sampling campaign was carried out. We selected PM2.5 samples which had the highest concentrations or suffered serious haze-fog weathers in each month. Through the analysis of data from heavily polluting phase, the mean concentrations of PM2.5 and PAHs in winter (369.63 μg m−3 and 223.60 ng m−3) were obviously higher than that in other seasons. The concentration of Σ16PAHs ranged from 3.22 to 297.01 ng m−3, with a mean value of 77.48 ng m−3. In winter, 4-ring PAH congeners (52.33%) contributed the most in PM2.5, followed by 5-rings (27.05%), 6-rings (11.55%) and 2∼3-rings (9.06%). Summertime measurements showed the highest decline in PAHs concentrations for 3∼5-ring congeners. The diagnostic ratios and PCA analysis manifest that vehicle and combustion emission were major sources and totally occupied 88.57% under heavy polluting stage. Moreover, exponential relationship between LWM/HWM (light/high weight molecule-PAHs) and combustion-derived PAHs, as well as linear relationship between BghiP and ∑PAHs verified that the pollution sources mentioned above affected local atmosphere environment as major sources. The highest total BaP equivalent concentration suggested that toxicity potency under heavy polluting phase was mainly attributed to 5-ring PAHs. Through analysis of carcinogenic-PAHs, potency risk to adults was significantly higher than that to children. BaP, BbF and DahA, which belong to 5-ring congeners, contributed the highest potency carcinogenic risk. BbF in winter, BaP in spring and winter may cause potential risk to local residents.
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•Characteristics of PAHs under heavy polluting phase were studied in urban Beijing.•4-ring PAH congeners (52.33%) contributed the most in PM2.5 in winter.•Diesel-fuelled vehicle emission and coal combustion were major sources under heavy polluting stage.•Toxicity potency was mainly influenced by 5-ring PAH congeners, such as BaP, BbF and DahA.•BbF in winter, BaP in spring and winter may cause potential risk to citizen.
High-precision positioning with low-cost global navigation satellite systems (GNSS) in urban environments remains a significant challenge due to the significant multipath effects, non-line-of-sight ...(NLOS) errors, as well as poor satellite visibility and geometry. A GNSS system is typically implemented with a least-square (LS) or a Kalman-filter (KF) estimator, and a proper weight scheme is vital for achieving reliable navigation solutions. The traditional weight schemes are based on the signal-in-space ranging errors (SISRE), elevation and C/N0 values, which would be less effective in urban environments since the observation quality cannot be fully manifested by those values. In this paper, we propose a new multi-feature support vector machine (SVM) signal classifier-based weight scheme for GNSS measurements to improve the kinematic GNSS positioning accuracy in urban environments. The proposed new weight scheme is based on the identification of important features in GNSS data in urban environments and intelligent classification of line-of-sight (LOS) and NLOS signals. To validate the performance of the newly proposed weight scheme, we have implemented it into a real-time single-frequency precise point positioning (SFPPP) system. The dynamic vehicle-based tests with a low-cost single-frequency u-blox M8T GNSS receiver demonstrate that the positioning accuracy using the new weight scheme outperforms the traditional C/N0 based weight model by 65.4% and 85.0% in the horizontal and up direction, and most position error spikes at overcrossing and short tunnels can be eliminated by the new weight scheme compared to the traditional method. It also surpasses the built-in satellite-based augmentation systems (SBAS) solutions of the u-blox M8T and is even better than the built-in real-time-kinematic (RTK) solutions of multi-frequency receivers like the u-blox F9P and Trimble BD982.
•Imbibition experiments with/without surfactant were conducted using a novel cell.•Mechanistic model of spontaneous imbibition for tight oil was built and validated.•The model includes the impacts of ...surfactant and media properties on imbibition.•The effects of fracture, rock size, IFT, wettability, and temperature were studied.
Spontaneous imbibition has become a role on the development of tight oil reservoirs. Many oilfield cases have confirmed the validity of soaking to produce oil depending on imbibition. Considerable yield has been recovered from soaking for a period of time after hydraulic fracturing by fracturing fluid. In order to study the spontaneous imbibition and its influencing factors in tight oil reservoir with stimulated reservoir volume (SRV), we first conducted wettability and imbibition experiments with/without surfactant treatment using different tight cores. Then, we established a mechanism model of imbibition including the influencing factors in tight oil reservoirs based on the experiments. The model was also validated using the published results. After that, numerical simulation was employed to study the impacts of some essential factors on the effects of spontaneous imbibition. The results indicate that no matter mixed-wet or water-wet tight cores, water can be spontaneously imbibed into the tight cores, and consequently expel the oil. The wettability alteration agent has slight influence on contact angle and imbibition recovery for the water-wet core, but it has a distinct influence on those of the mixed-wet or oil-wet core. Natural fractures in tight rock can promote the imbibition. The size of the tight rock after hydraulic fracturing is a significant factor of imbibition recovery. Interfacial tension is crucial to imbibition in tight reservoir because capillary force becomes more significant in tight rocks than that in conventional reservoirs. Wettability intensely decides the imbibition recovery, and it is indispensable to add modifying agents to enhance imbibition for mix-wet or oil-wet rocks. The reduction of temperature in tight oil reservoir due to fracturing and huff-n-puff may decrease the recovery by more than 1% after 5–6 cycles.
We present a fresh perspective on the Landau level quantization rule; that is, by successively including zero-field magnetic response functions at zero temperature, such as zero-field magnetization ...and susceptibility, the Onsager’s rule can be corrected order by order. Such a perspective is further reinterpreted as a quantization of the semiclassical electron density in solids. Our theory not only reproduces Onsager’s rule at zeroth order and the Berry phase and magnetic moment correction at first order but also explains the nature of higher-order corrections in a universal way. In applications, those higher-order corrections are expected to curve the linear relation between the level index and the inverse of the magnetic field, as already observed in experiments. Our theory then provides a way to extract the correct value of Berry phase as well as the magnetic susceptibility at zero temperature from Landau level fan diagrams in experiments. Moreover, it can be used theoretically to calculate Landau levels up to second-order accuracy for realistic models.
To study the effect of periodic water circulation on rock mass, chlorite–amphibolite rocks from the slope of Nanfen open-pit iron mine in Liaoning province were chosen as the engineering samples and ...were investigated using uniaxial compressive experiment and scanning electron microscopy. The effect of different wetting and drying cycles on the mechanical properties and microstructure of the rocks was investigated. The characteristics of pore parameters from the SEM images were obtained by Image Pro Plus image processing software. The results show that with the increase in number of wetting and drying cycles, the uniaxial compressive strength of the rock decreases and the porosity increases significantly. The weakening of macroscopic mechanical properties of rocks is closely related to the changes in microstructures of rocks. The water–rock interaction changes the size, shape and porosity of the rock pores and then affects its mechanical properties. Based on the combination of macro and micro, quantitative analysis of the weakening process of rocks subjected to wet and dry cycles can provide a better reference index for evaluating the stability of geotechnical engineering.
Electronic skins (e‐skins) have been widely investigated as important platforms for healthcare monitoring, human/machine interfaces, and soft robots. However, mask‐free formation of patterned active ...materials on elastomer substrates without involving high‐cost and complicate processes is still a grand challenge in developing e‐skins. Here, SiC‐based strain sensor arrays are fabricated on elastomer for e‐skins by a laser direct writing (LDW) technique, which is mask‐free, highly efficient, and scalable. The direct synthesis of active material on elastomer is ascribed to the LDW‐induced conversion of siloxanes to SiC. The SiC‐based devices own a highest sensitivity of ≈2.47 × 105 achieved at a laser power of 0.8 W and a scanning velocity of 1.25 mm s−1. Moreover, the LDW‐developed device provides a minimum strain detection limit of 0.05%, a small temperature drift, and a high mechanical durability for over 10 000 cycles. When it is mounted onto human skins, the SiC‐based device is able to monitor external stimuli and human health conditions, with the capability of wireless data transmission. Its potential application in e‐skins is further proved by an LDW‐fabricated device having 3 × 3 SiC sensor array for tactile sensing.
SiC‐based strain sensor arrays are fabricated on elastomers for electronic skins by laser direct writing, which is mask‐free, highly efficient, and scalable. The device displays the highest sensitivity of ≈2.47 × 105 achieved at a laser power of 0.8 W and scanning velocity of 1.25 mm s−1, applicable for monitoring external stimuli and human health conditions, with the capability of wireless data transmission.
The pseudo-amino acid composition has been widely used to convert complicated protein sequences with various lengths to fixed length digital feature vectors while keeping considerable sequence order ...information. However, so far the only software available to the public is the web server PseAAC (http://www.csbio.sjtu.edu.cn/bioinf/PseAAC), which has some limitations in dealing with large-scale datasets. Here, we propose a new cross-platform stand-alone software program, called PseAAC-Builder (http://www.pseb.sf.net), which can be used to generate various modes of Chou’s pseudo-amino acid composition in a much more efficient and flexible way. It is anticipated that PseAAC-Builder may become a useful tool for studying various protein attributes.
Despite the wide use of aryl radicals in organic synthesis, current methods to prepare them from aryl halides, carboxylic acids, boronic acids, and diazonium salts suffer from limitations. Aryl ...triflates, easily obtained from phenols, are promising aryl radical progenitors but remain elusive in this regard. Inspired by the single electron transfer process for aryl halides to access aryl radicals, we developed a simple and efficient protocol to convert aryl triflates to aryl radicals. Our success lies in exploiting sodium iodide as the soft electron donor assisted by light. This strategy enables the scalable synthesis of two types of important organic molecules, i.e., aryl boronates and aryl iodides, in good to high yields, with broad functional group compatibility in a transition-metal-free manner at room temperature. This protocol is anticipated to find potential applications in other aryl-radical-involved reactions by using aryl triflates as aryl radical precursors.
For high-precision positioning applications, various GNSS errors need to be mitigated, including the tropospheric error, which remains a significant error source as it can reach up to a few meters. ...Although some commercial GNSS correction data providers, such as the Quasi-Zenith Satellite System (QZSS) Centimeter Level Augmentation Service (CLAS), have developed real-time precise regional troposphere products, the service is available only in limited regional areas. The International GNSS Service (IGS) has provided precise troposphere correction data in TRO format post-mission, but its long latency of 1 to 2 weeks makes it unable to support real-time applications. In this work, a real-time troposphere prediction method based on the IGS post-processing products was developed using machine learning techniques to eliminate the long latency problem. The test results from tropospheric predictions over a year using the proposed method indicate that the new method can achieve a prediction accuracy (RMSE) of 2 cm, making it suitable for real-time applications.
Summary
Plant health is intricately linked to crop quality, food security and agricultural productivity. Obtaining accurate plant health information is of paramount importance in the realm of ...precision agriculture. Wearable sensors offer an exceptional avenue for investigating plant health status and fundamental plant science, as they enable real‐time and continuous in‐situ monitoring of physiological biomarkers. However, a comprehensive overview that integrates and critically assesses wearable plant sensors across various facets, including their fundamental elements, classification, design, sensing mechanism, fabrication, characterization and application, remains elusive. In this study, we provide a meticulous description and systematic synthesis of recent research progress in wearable sensor properties, technology and their application in monitoring plant health information. This work endeavours to serve as a guiding resource for the utilization of wearable plant sensors, empowering the advancement of plant health within the precision agriculture paradigm.
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