Preparation of MoS2 nanosheets in isopropanol with salt as assistant.
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Here, we report a facile salt-assisted direct liquid-phase exfoliation method for mass production of MoS2 ...nanosheets. We choose organic solvent isopropanol (IPA) as exfoliation media and potassium ferrocyanide, potassium sodium tartrate, or sodium tartrate as salt, the assistant. The selected salts show universal and efficient assistant effect for the exfoliation of MoS2 in IPA. Especially, potassium ferrocyanide (K4Fe(CN)6) can enhance the exfoliation efficiency up to 73 times and a dispersion of MoS2 nanosheets with concentration as high as 0.240 mg mL−1 can be easily obtained in IPA-K4Fe(CN)6 system. Transmission electron microscopy, atomic force microscopy (AFM), and Raman spectroscopy show that bulk MoS2 has been successfully exfoliated into mono- to few-layer MoS2 nanosheets. AFM analysis indicates that nearly 60% flakes are monolayer in MoS2 dispersion.
Ultrasonic guided wave monitoring is regularly used for monitoring the structural health of industrial pipes, but small defects are difficult to identify owing to the influence of the environment and ...pipe structure on the guided wave signal. In this paper, a high-sensitivity monitoring algorithm based on adaptive principal component analysis (APCA) for defects of pipes is proposed, which calculates the sensitivity index of the signals and optimizes the process of selecting principal components in principal component analysis (PCA). Furthermore, we established a comprehensive damage index (K) by extracting the subspace features of signals to display the existence of defects intuitively. The damage monitoring algorithm was tested by the dataset collected from several pipe types, and the experimental results show that the APCA method can monitor the hole defect of 0.075% cross section loss ratio (SLR) on the straight pipe, 0.15% SLR on the spiral pipe, and 0.18% SLR on the bent pipe, which is superior to conventional methods such as optimal baseline subtraction (OBS) and average Euclidean distance (AED). The results of the damage index curve obtained by the algorithm clearly showed the change trend of defects; moreover, the contribution rate of the K index roughly showed the location of the defects.
Mechanically interlocked molecules (MIMs) with discrete molecular components linked through a mechanical bond in space can be harnessed for the operation of molecular switches and machines, which ...shows huge potential to imitate the dynamic response of natural enzymes. In this work, rotaxane compounds were adopted as building monomers for the synthesis of a crown-ether ring mechanically intercalated covalence organic framework (COF). This incorporation of MIMs into open architecture implemented large amplitude motions, whose wheel slid along the axle in response to external stimulation. After impregnation with Zn2+ ions, the relative locations of two zinc active sites (crown-ether coordinated Zn(II) and bipyridine coordinated Zn(II)) are endowed with great flexibility to fit the conformational transformation of an organophosphorus agent during the hydrolytic process. Notably, the resulting self-adaptive binuclear zinc center in a crown-ether-threaded COF network is endowed with a record catalytic ability, with a rate over 85.5 μM min–1 for organophosphorus degradation. The strategy of synthesis for porous artificial enzymes through the introduction of mechanically bound crown ether will enable significant breakthroughs and new synthetic concepts for the development of advanced biomimetic catalysts.
The methodology based on reflected guided-wave by a reflector associated with an increase or a decrease in the cross-sectional area has the challenge of determining their location and identity. This ...paper presents a numerical investigation of a method for locating and identifying the reflector based on guided-wave circumferential scanning and phase characteristics. To determine the axial and circumferential positions of the reflector within the pipeline, the procedures of the guided wave-based circumferential scanning were presented, including data preprocessing, median filter, image smoothing and binary processing. Through theoretical analysis, we obtained the phase relationship between the guided-wave excitation signal and reflection signals generated by a reflector, such as corrosion, crack, weld and support, which caused the change in the cross-sectional area. Consequently, an algorithm based on the phase characteristics was proposed to determine the change and type of reflector. The spatial distances were calculated between the guided wave excitation signals with different phases and the concerned reflection signals, subsequently identifying the change and type of the reflector by comparing the distance values. An identification index named the reliable index for the character of the reflector (RICR) was defined to evaluate the reliability of the predicted results. Numerical and finite element simulation validations of the proposed method were performed. It has been found that if RICR was larger than 1.05, the results predicting the reflector type were reliable. The proposed method was found to be superior relative to the conventional correlation coefficient method according to the numerical results. Finally, the simulation results demonstrated that the proposed method could be potentially applied for locating and identifying reflectors in pipelines.
A highly crystalline perylene imide polymer (Urea‐PDI) photocatalyst is successfully constructed. The Urea‐PDI presents a wide spectrum response owing to its large conjugated system. The Urea‐PDI ...performs so far highest oxygen evolution rate (3223.9 µmol g−1 h−1) without cocatalysts under visible light. The performance is over 107.5 times higher than that of the conventional PDI supramolecular photocatalysts. The strong oxidizing ability comes from the deep valence band (+1.52 eV) which is contributed by the covalent‐bonded conjugated molecules. Besides, the high crystallinity and the large molecular dipoles of the Urea‐PDI contribute to a robust built‐in electric field promoting the separation and transportation of photogenerated carriers. Moreover, the Urea‐PDI is very stable and has no performance attenuation after 100 h continuous irradiation. The Urea‐PDI polymer photocatalyst provides with a new platform for the use of photocatalytic water oxidation, which is expected to contribute to clean energy production.
A crystalline perylene imide polymer photocatalyst with the highest oxygen evolution performance is achieved. The polymer can be reused over 100 h without any decrease in performance overcoming the poor stability of the organic photocatalysts. The superior photocatalytic performance comes from the suitable energy band and the robust built‐in electric field contributed by the highly crystallinity and large molecular dipole.
Non-invasive glucose monitoring has emerged as a new opportunity in medical diagnostics and health. Non-invasive glucose monitoring technology are evolving rapidly as the new medical monitoring ...devices which demand more compactness, comfort and accuracy, among other characteristics. This review examines two distinct approaches to non-invasive glucose monitoring based on the physiological parameters monitored: breath acetone and body surface monitoring. The review summarizes breath acetone monitoring, which analyzes a compound produced during human respiration, focusing on the use of advanced chromatography, mass spectrometry, and portable gas biosensors to improve convenience and mobility. Focusing on glucose monitoring through body surface secretions or electrical signals, the review discusses several promising methods, such as optical and electrochemical techniques. Given special emphasis are methods involving interstitial fluid (ISF), which are noted for their significant potential to enhance the practicality and accuracy of glucose monitoring. Despite the persistent challenges pertaining to the accuracy and standardization of non-invasive testing devices, we maintain the belief that with ongoing research and innovation, it is possible to attain enhanced accuracy, reliability, and convenience in non-invasive glucose monitoring technology in the future.
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•Divided non-invasive blood glucose monitoring techniques into two aspects: breath detection and body surface monitoring.•Detailed elaboration on the applications of optical methods and electrochemical methods in two aspects.•Summarized the characteristics of numerous composite nanomaterials.•Emphasized the extraction methods and analytical methods of interstitial fluids.
High‐efficiency photocatalysts based on metal‐organic frameworks (MOFs) are often limited by poor charge separation and slow charge‐transfer kinetics. Herein, a novel MOF photocatalyst is ...successfully constructed by encapsulating C60 into a nano‐sized zirconium‐based MOF, NU‐901. By virtue of host‐guest interactions and uneven charge distribution, a substantial electrostatic potential difference is set‐up in C60@NU‐901. The direct consequence is a robust built‐in electric field, which tends to be 10.7 times higher in C60@NU‐901 than that found in NU‐901. In the catalyst, photogenerated charge carriers are efficiently separated and transported to the surface. For example, photocatalytic hydrogen evolution reaches 22.3 mmol g−1 h−1 for C60@NU‐901, which is among the highest values for MOFs. Our concept of enhancing charge separation by harnessing host‐guest interactions constitutes a promising strategy to design photocatalysts for efficient solar‐to‐chemical energy conversion.
Isolated C60 molecules are encapsulated in a Zr‐based NU‐901 metal‐organic framework (MOF) to obtain a C60@NU‐901 composite. Host‐guest interactions amplify the irregular charge distribution of the system, giving rise to an enhanced built‐in electric field that promotes efficient charge separation and transportation of carriers. The composite mediates photocatalytic H2 production under visible light.
•Proposing a new type of concept drift group concept drift that commonly exists in multiple data streams.•A group concept drift detection method is proposed through detecting the change of error ...rate.•A new test statistic, free for any distributions with any dimension p, is proposed.•A novel online hypothesis testing based on our proposed test statistic is developed.
Concept drift may lead to a sharp downturn in the performance of streaming in data-based algorithms, caused by unforeseeable changes in the underlying distribution of data. In this paper, we are mainly concerned with concept drift across multiple data streams, and in situations where the drift of each data stream cannot be detected in time, due to slight underlying distribution drifts. We call this group concept drift. When compared to the detection of concept drift for a single data stream, the challenges of detecting group concept drift arise from three aspects: first, the training data become more complex; second, the underlying distribution becomes more complex; and third, the correlations between data streams become more complex. To address these challenges, the key idea of our method is to construct a distribution free test statistic, free from any underlying distribution in multiple data streams. Then, for streaming data, we design an online learning algorithm to obtain this test statistic, thereby determining the concept drift caused by the hypothesis test. The experiment evaluations with both synthetic and real-world datasets prove that our method can accurately detect concept drift from multiple data streams.
Switch rails are weak but essential components in a high-speed rail track system, which have an urgent non-destructive testing requirement due to aging and associated fatigue damage accumulation. ...They are settled under sophisticated operation environments, which causes them to have unpredictable damages, such as abrasion, exfoliation, and cracks. Our goal is to propose a reliable system to detect structural damages of switch rails. Using ultrasonic guided waves to examine the health status of switch rails makes it possible to continuously evaluate the health status of switch rails when they are in use. Conventional damage detection methods with ultrasonic guided waves such as baseline signal subtraction, independent component analysis-based methods cannot always make reliable detection results. These methods are either lack of powerful abilities to capture the characteristics of damaged signals or time-consuming to be operated in real damage detection tasks. In this paper, a convolutional neural network-based system is proposed to solve both of the above challenges simultaneously. The proposed model employs multiple convolutional layers to extract deep features of ultrasonic guided wave signals. These features are then fed into a classifier to predict whether they are damaged signals or not. To evaluate the proposed model performance, we collected ultrasonic guided wave signals from two different switch rails. The proposed model achieved more than 91% testing accuracy and outperformed other relevant methods. It also demonstrated the proposed model had strong generalization abilities to make it capable in practical switch rail structural damage detection tasks.
Temperature changes are a major challenge in outdoor guided wave structural health monitoring of rails. Temperature variations greatly impact the waveform of guided wave signals, making it ...challenging to diagnose and characterize defects. Traditional temperature compensation methods, such as signal stretch and scale transform, are restricted to use in regular structures, such as plates and pipes. To solve the temperature compensation problem in long rails with serious mode conversion and complex structure echo, we propose a temperature compensation and defect monitoring method, namely, sliding window dynamic time-series warping (SWDTW), which overcomes the challenges of mass computation and overcompensation of dynamic time-series warping (DTW). The basic idea of SWDTW is to utilize sliding windows to accelerate the computation and identify defects from subsequence scales. Then, an index, window subsequence Teager energy (WSTE), is used to indicate the local abnormality of guided wave signals, and a sliding window net (SWnet) is devised to monitor the occurrence of defects automatically. Outdoor monitoring of turnout rails showed that the proposed method can effectively reduce the temperature noise and recognize an artificial defect with 1.16% and 0.36% cross-sectional change rates (CSCRs) on the switch and stock rails, respectively, at different temperatures; moreover, the defect signals processed by SWDTW showed better defect identification performance than those processed by scale transform and DTW.
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