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To investigate the effect of nano-metakaolin (NMK) on the early hydration characteristics of cement paste, the electrochemical impedance spectroscopy (EIS) test was executed on the cement pastes containing NMK particles at the early hydration stage (within 48 h). Five NMK contents (0, 1%,3%,5%,7% ) were used to replace ordinary cement. The evolution of electrochemical parameters during the early hydration process of five types of NMK cement paste was compared and analyzed. An equivalent circuit model R1 (Q1R2) Q2, based on a capacitance series circuit, was established to consider both the dispersion effect and double capacitance at the electrode /paste interface. In addition, dielectric constant was employed to characterize the early hydration process of NMK cement paste. The results show that NMK delays the negative capacitance loss time, enhances calcium aluminate reaction, and promotes the early hydration of cement paste. The calculated results by the provided equivalent circuit model show in good agreement with the experimental results. The pore resistance obtained by the equivalent circuit model presents a linear relation with standard consistency water content, while it takes an exponential relation with fluidity. The dielectric constant curve can be used to identify the early hydration process of NMK cement paste. [ABSTRACT FROM AUTHOR]

[Objective] This study utilized remote sensing imagery to classify different croplands accurately to obtain optimal information extraction method and provide basis for improving the quality and efficiency of agricultural production.[Method] This study focused on Fufeng County, Baoji City, Shaanxi Province.Using the Google Earth Engine (GEE) platform, sample points were selected by visual interpretation and field positioning using Sentinel-2 imagery from October 2020 to December 2021.The random forest (RF) algorithm was incorporated with normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), phenological parameters and red-edge bands of remote sensing imagery.The bands calculated based on NDVI were denoted as N, those calculated based on EVI were denoted as E, the inclusion of red edge bands was denoted as 1, and the exclusion was denoted as 2.Based on these parameters, eight different classification models were constructed (NDVI-N1, EVI-E1, N1, E1, NDVI-N2, EVI-E2, N2 and E2) .Four sample segmentation schemes were combined with training to validation ratios of 5:5, 6:4, 7:3 and 8:2, resulting in a total of 32 classification schemes.These schemes were used to classify different types of croplands in Fufeng, and the overall accuracy (Ao) and Kappa coefficient of each scheme were calculated.[Result] (1) After processing with the S-G filtering method, the noises in the NDVI and EVI time series curves of six land cover types were reduced and the curves became smoother.Additionally, the NDVI and EVI curves of the six land cover types showed clear differences. (2) Among 32 classification schemes, only EVI-E1 model and EVI-E2 model with a sample split ratio of 7:3 and E2 model with a sample split ratio of 6:4 had overall accuracies of higher than 90%, indicating that EVI based classification was better in Fufeng. (3) With a sample split ratio of 7:3, the EVI-E1 model had the highest overall accuracy and Kappa coefficient of 91.66% and 89.41%, respectively, making it the optimal classification scheme.However, introducing red-edge band decreased overall accuracy and Kappa coefficient by 1.18% and 1.53%, suggesting that the red edge band should be excluded. (4) The extraction results for wheat, corn and potato fields using the optimal classification scheme were roughly consistent with actual survey results.[Conclusion] This study achieved accurate classification of croplands in Fufeng based on GEE platform and Sentinel-2 data and provided valuable decision support for agricultural production. [ABSTRACT FROM AUTHOR]

A new type of non-orthogonal arc tooth face-gear is designed. The arc tooth cylindrical gear is used as an imaginary tool to envelop the working tooth surface and transition surface of the face gear. The mathematical model of the face-gear is obtained in Matlab. The full tooth surface tooth surface equations of the non-orthogonal arc tooth face-gear is derived，and the realization of tooth surface visualization through Matlab programming which laid the theoretical foundation for the subsequent research on non-orthogonal arc tooth face-gears.

A new approach for mechanical fault diagnosis based on local characteristic- scale decomposition（ LCD） information entropy feature and support vector machine（ SVM） is proposed. Firstly,the fault mechanical vibration signal is decomposed by using the LCD to obtain a certain number of intrinsic scale component（ ISC）. Secondly,combined with information entropy theory,the singular spectrum entropy in time domain,power spectrum entropy in frequency domain,feature space entropy,marginal spectrum entropy and momentary energy entropy in time- frequency domain are defined and used as the feature vector. At last,the feature vectors are put into SVM classifier to recognize different fault type. The results of experiment of bearing fault diagnosis demonstrate that the method based on LCD information entropy feature and SVM is able to identify the bearing faults accurately and effectively,and the diagnosis effect is better than the method based on empirical mode decomposition（ EMD） information entropy and SVM.

It is of great significance to clarify the adsorption law of shale gas under in-situ conditions for the development of deep marine shale gas reservoirs. However, temperature and pressure in deep reservoirs are far higher than those in the range of normal experiments, so the adsorption characteristics of shale gas in the high-pressure section have not been revealed. In this paper, we construct a kerogen model which conforms to the adsorption law of real marine shale samples by using molecular simulation technology, and simulate the methane adsorption at high temperature and high pressure (HTHP) under in-situ conditions. The adsorption characteristics of methane at HTHP under the influence of primary water are comprehensively revealed, and a corresponding reliable isothermal adsorption model is established. The results show that the influence of kerogen molecular number must be fully considered in the construction of kerogen model, otherwise large errors will occur. The shale gas adsorption capacity is stable under the influence of temperature and changes more significantly with the pressure. In kerogen with polar functional group water can significantly reduce methane adsorption, especially under high pressure. The research results can provide a theoretical basis for the adsorption gas evaluation for deep marine shale gas reservoirs. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the value of magnetic resonance imaging (MRI) in the diagnosis of lumbar instability, including the proportion of paravertebral muscle fat infiltration, cross-sectional area and lumbar lordosis. Eighty-seven patients with degenerative lumbar instability were selected as observation group, and 50 healthy subjects were selected as the control group. MRI examination was performed in both groups, the proportion, cross-sectional area and lumbar lordosis of paravertebral muscle fat infiltration were compared between the two groups. The results show that the cross-sectional area of the multifidus muscle and the percentage of fat infiltration in erector spinae in the observation group were significantly lower than those in the control group (P<0.05). The percentage of fat infiltration and lumbar lordosis in the observation group were significantly higher than those in the control group (P<0.05). The MRI parameters of patients with different segmental instability and frymoyer classification in the observation group were statistically significant (P<0.05). The area under the ROC curve of the cross-sectional area and the proportion of fat infiltration of the multifidus muscle in diagnosing multisegment instability were big enough (P<0.05), as well as the fat infiltration proportion in erector spinae and lumbar lordosis. This study confirmed that proportion of fat infiltration and cross-sectional area in paravertebral muscles on MRI have certain application value in the diagnosis of lumbar instability, as well as the lumbar lordosis, which has the highest diagnosis value. [ABSTRACT FROM AUTHOR]