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Rolling bearings are an important part of problems that often occur in rotating machinery. Their fault conditions are complex and difficult to diagnose. Aiming at the problem that small sample learning has a large difference between the true feature value and the target feature value and the generalization ability is weak, this paper proposes a small sample learning model that combines semi-supervised variational autoencoder and LightGBM classification model. The Bayesian optimization and improvement algorithm based on Gaussian process is used to optimize the LightGBM hyperparameters, thus effectively solving the defects such as unstable performance, weak ability of extracting features, and overfitting in small sample learning. Comparative verification on the bearing experimental data set released by the Western Reserve University in the United States shows that the method has better diagnostic accuracy when facing small sample data space. [ABSTRACT FROM AUTHOR]

In order to study the effects of different atmospheres ( nitrogen and air) and temperature ranges (300 ~ 500 °C, 300 ~ 700 °C and 300 ~ 900 °C ) on the composition and amount of pyrolysis products in paper-making reconstituted tobacco substrates, solid phase microextraction, adsorption-desorption and gas chromatography-mass spectrometry methods were used for analysis. The results showed that under the nitrogen and air atmospheres, the pyrolysis products of substrates at the range of 300 ~ 700 °C and 300 ~ 900 °C obviously increased when compared with those at the range of 300 ~500 °C . A large number of polycyclic aromatic hydrocarbons and olefins were produced in these two temperature ranges. Nicotine was only found in the pyrolysis products of substrates at the range of 300 ~ 500 °C. The contents of furfural and phytadiene were higher at these three temperature ranges. In the same temperature range,under the air atmosphere,the release amount of important cleavage products such as crotonaldehyde, 2-methyl-furan and furfural with relatively low molecular weight was higher than that under nitrogen atmosphere. The relative release of alcohols increased, and the presence of oxygen in air promoted the full combustion of substrates, thereby resulting in the reduction of total pyrolysis products. [ABSTRACT FROM AUTHOR]

Aimed to the issues of limitation of packet transmission with low priority and single-hop environment of enhanced distribution channel access (EDCA) in 802. lie-based wireless Mesh networks (WMNs), this paper designed a cross-layer mechanism based on pure EDCA named CL-EDCA. By taking packet's end-to-end forwarding delay and hops bound requirement, CL-EDCA could dynamically adjust packet's priority level in each flow at network layer based on per access category delay(PACD) and queue length, which were gathered from link and mac layer, to effectively adjust the utilization of access category (AC) and EDCA. Simulation results show CL-EDCA can provide excellent end-to-end delay assurance while achieving much higher fairness of data transmission, compared to the pure EDCA scheme. [ABSTRACT FROM AUTHOR]

In IEEE802. 11e-based wireless mesh networks, the parameters (eg., contention windows, transmission opportunity) used in 802. 11e's mechanism is statically assigned in order to guarantee the quality of service, which is more suitable to the communication nodes in one hop transmission with environment and not to the wireless multi-hop environment. In view of the problem that data flows with long delay bound may consume more channel time than data flows with short one so as to cause packet loss and networks performance degradation, a fair share scheme based on the residual packet delay bound, which is equally distributed among data packet, is proposed to alleviate the retransmission number and promote the fairness between data flows. Simulation results show that the proposed scheme is more effective than the original 802. 11e protocol. [ABSTRACT FROM AUTHOR]

In order to study the control effect of different anchoring lengths on surrounding rock in roadways, the stress distribution laws of holt were deduced, and the mechanical analysis model concerning different anchoring lengths was established through theoretical method. Different factors, such as bolt diameter, surrounding rock strength, anchorage length, pre-tightening force, bolt spacing, etc., were analyzed, engineering measures on bolt designing were also recommended, and the correctness of theoretical results was verified through filed test. The results show that the inner force of rock bolt concentrates in the 1/3 range of anchoring section mainly, and damps to the root along the length of bolt. In softer rock mass, anchorage effect is better to be exerted. Adopting high pre-tightening force and setting a certain length of free-segment can help pre-tightening force to spread in surrounding rock, form effective bearing structure in anchored rock mass, and achieve a supporting potential of bolt. When bolt spacing increases, a better control effect of surrounding rock can be achieved through applying high pre-tightening force and reducing anchorage length appropriately. [ABSTRACT FROM AUTHOR]

Using a self-developed triaxial gas seepage experiment system, the seepage characteristics of coalbed gas has been investigated for the Klinkenberg effect of gas seepage. With experimental data analysis and theoretical derivation, a method considering Klinkenberg effect for evaluating the permeability of coalbed gas had been developed, synthesizing the influence of gas dynamic viscosity and gas compressibility factor. The method considering Klinkenberg effect is more reasonable and more precise than the tradition pseudo pressure method through comparing the calculation results. The results show that; (1) The Klinkenberg effect has an obvious effect on the seepage of coalbed gas. The permeability results assessed by the method considering Klinkenberg effect are valid and can fully reflect the true state of gas flow. (2) The effect of adsorption and desorption has a certain impact on the coal seam gas permeability and can lead to the reduction of absolute permeability in a coal seam. (3) The effect of dynamic viscosity and compressibility factor on gas permeability can be ignored in a close vicinity of the standard state. However, the effect of dynamic viscosity and compressibility factor on gas permeability cannot be ignored far away from the standard state. Research results are useful for correctly understanding the Klinkenberg effect and selecting more accurate calculation method for the permeability assessment on coalbed gas. [ABSTRACT FROM AUTHOR]

In order to solve the problem in deep high-stress rock roadway and roadway with structural fracture zone, a new support system--square-type steel confined concrete (SQCC) was developed. And the important component of it, square-type steel confined concrete arch centering was further studied. The inner force expressions of straight wall semicircle arch was deduced with the force method, and combined with the engineering practice to calculate the inner force distribution of four section arch, which is the field application, under uniformly loads. From the inner force distribution of arch centering, that arch legs and vault is the key position of the arch centering failure is confirmed. Through the strength analysis of the SQCC component to check the key parts of the possible, get that first failure part is arch leg and the ultimate bearing capacity of SQCC arch centering is 1 315 kN. The mechanics experiment of SQCC arch centering are carried out by using designed 1 : 1 mechanics test system of confined concrete arch centering. Meanwhile combined with the results of numerical experiments on SQCC arch centering by using ABAQUS software. Through the analysis on the error rate of ultimate bearing capacity, ... = -7. 1%, ... = - 1. 1%, the key position, the inner force, deformation and stress, research the mechanical properties and faileure mechanism of SQCC arch centering, and verify the conclusion based on the theoretical arithmetic and laboratory experiment is right. [ABSTRACT FROM AUTHOR]

To study the surrounding rock stress evolution laws and deformation features of deep roadway with thick top coal, a large-scale geomechanical model test system was newly developed. This test system mainly consists of counter-force device, flexible uniform pressure loading device, digital intelligent hydraulic control system and high precision pluralistic real-time monitoring system. This flexible assembled system has large space for simulating, can provide high and uniform loading which can increase test precision. Taking 3302 working face of Zhaolou Coal Mine as engineering background, according to a large number of similar meterial compounding tests, two kinds of similar materials belong to different series were determined to simulate sandstone and coal respectively. Similar supporting components such as prestressed bolt(cable), box supporting beam, steel strip, and steel tray were designed and manufactured; the large-scale model test research was carried out on pressure relief anchor box beam support system, and the surrounding rock stress evolution and deformation laws in excavating and supporting of deep roadway with thick top coal was obtained. Results show this system can be preferably used for excavate-support model test of deep coal roadways and other large scale chambers. [ABSTRACT FROM AUTHOR]