Soft Roof Failure Mechanism and Supporting Method for Gob-Side Entry Retaining

To study the soft roof failure mechanism and the supporting method for a gateway in a gently inclined coal seam with a dip angle of 16° kept for gob-side entry retaining, and through the methodology of field investigation and numerical and analytical modeling, this paper analyzed the stress evolution law of roof strata at the working face end and determined that the sharp horizontal stress unloading phenomenon along the coal wall side did not appear after the working face advanced. Conversely, the horizontal stress along the gob side instantly decreased and the tensile stress produced, and the vertical stress in the central part of the roof had a higher reduction magnitude as well. An in-depth study indicates that the soft roof of the working face end subsided and seriously separated due to the effect of the front abutment pressure and the roof hanging length above the gob line, as well as certain other factors, including the rapid unloading of the lateral stress, tension and shear on the lower roof rock layer and dynamic disturbance. Those influencing factors also led to rapid crack propagation on a large scale and serious fracturing in the soft roof of the working face end. However, in the gob stress stabilized zone, the soft roof in the gob-side entry retaining has a shearing failure along the filling wall inside affected by the overburden pressure, rock bulking pressure, and roof gravity. To maintain the roof integrity, decrease the roof deformation, and enable the control of the working face end soft roof and the stabilization of the gob-side entry retaining roof, this study suggests that the preferred bolt installation angle for the soft roof situation is 70° based on the rock bolt extrusion strengthening theory

Mesomechanics coal experiment and an elastic-brittle damage model based on texture features

To accurately describe damage within coal, digital image processing technology was used to determine texture parameters and obtain quantitative information related to coal meso-cracks. The relationship between damage and mesoscopic information for coal under compression was then analysed. The shape and distribution of damage were comprehensively considered in a defined damage variable, which was based on the texture characteristic. An elastic-brittle damage model based on the mesostructure information of coal was established. As a result, the damage model can appropriately and reliably replicate the processes of initiation, expansion, cut-through and eventual destruction of microscopic damage to coal under compression. After comparison, it was proved that the predicted overall stress-strain response of the model was comparable to the experimental result. Keywords: Mesomechanics experiment, Image processing, Texture feature, Damage variable, Damage mode

Random pruning: channel sparsity by expectation scaling factor

Pruning is an efficient method for deep neural network model compression and acceleration. However, existing pruning strategies, both at the filter level and at the channel level, often introduce a large amount of computation and adopt complex methods for finding sub-networks. It is found that there is a linear relationship between the sum of matrix elements of the channels in convolutional neural networks (CNNs) and the expectation scaling ratio of the image pixel distribution, which is reflects the relationship between the expectation change of the pixel distribution between the feature mapping and the input data. This implies that channels with similar expectation scaling factors ( $\delta _{E}$δE ) cause similar expectation changes to the input data, thus producing redundant feature mappings. Thus, this article proposes a new structured pruning method called EXP. In the proposed method, the channels with similar $\delta _{E}$δE are randomly removed in each convolutional layer, and thus the whole network achieves random sparsity to obtain non-redundant and non-unique sub-networks. Experiments on pruning various networks show that EXP can achieve a significant reduction of FLOPs. For example, on the CIFAR-10 dataset, EXP reduces the FLOPs of the ResNet-56 model by 71.9% with a 0.23% loss in Top-1 accuracy. On ILSVRC-2012, it reduces the FLOPs of the ResNet-50 model by 60.0% with a 1.13% loss of Top-1 accuracy. Our code is available at: https://github.com/EXP-Pruning/EXP_Pruning and DOI: 10.5281/zenodo.8141065

Simulation Methods for MEMS S&A Devices for 2D Fuze Overload Loading

An experimental testing system for the two-dimensional (2D) fuze overload loading process was designed to address the loading issues of recoil overload and centrifugal overload in fuze safety and arming (S&A) device. By incorporating centrifuge rotation energy storage, impact acceleration simulation, and equivalent centrifugal rotation simulation, a block equipped with a fuze S&A device accelerated instantly upon having impact from a centrifuge-driven impact hammer, simulating recoil overload loading. The impact hammer was retracted instantaneously by adopting an electromagnetic brake, which resulted in the centrifugal rotation of the block around its track, to simulate the centrifugal overload loading. The dynamic equations of the experimental testing system and the equations of impact hammer motions were established, whereby the rotation speed of the centrifuge and the braking force of the electromagnetic brake were calculated and selected. A dynamic model of the collision between the impact hammer and block was established using ANSYS/LS-DYNA software for simulation analysis. The acceleration curves of the recoil overload and centrifugal overload with variations in the centrifuge speed, cushion material, and buffer thickness were obtained, which verified the feasibility of the proposed loading simulation method. Two-dimensional overload loading simulation tests were performed using the developed experimental testing system, and the acceleration curves of the recoil overload and centrifugal overload were measured. The test results indicated that the proposed system can accomplish 2D overload loading simulations for a recoil overload of several 10,000× g and centrifugal overload of several 1000× g

Microstructure and electric characteristics of AETiO3 (AE=Mg, Ca, Sr) doped CaCu3Ti4O12 thin films prepared by the sol–gel method

This paper focuses on the effects of alkline-earth metal titante AETiO3 (AE=Mg, Ca, Sr) doping on the microstructure and electric characteristics of CaCu3Ti4O12 thin films prepared by the sol–gel method. The results showed that the grain size of CCTO thin films could be increased by MgTiO3 doping. The movement of the grain boundaries was impeded by the second phases of CaTiO3 and SrTiO3 concentrating at grain boundaries in CaTiO3 and SrTiO3 doped CCTO thin films. Rapid ascent of dielectric constant could be observed in 0.1Mg TiO3 doped CCTO thin films, which was almost as three times high as pure CCTO thin film and the descent of the dielectric loss at low frequency could also be observed. In addition, the nonlinear coefficient (α), threshold voltage (VT) and leakage current (IL) of AETiO3 doped CCTO thin films (AE=Mg, Ca, Sr) showed different variation with the increasing content of the MgTiO3, CaTiO3 and SrTiO3

Preparation and characterization of antibacterial oxide film with deposited silver on Al alloy

Aluminum (Al) alloy products are widely used in people’s lives, while the existence and breeding of microorganisms on their surface cannot meet the health criteria and even may harm human health. In the present study, we successfully prepared the antibacterial oxide film on the 6063 Al alloy specimens by direct-current anodizing followed by Ag element depositing and the hole sealing process. The results suggested that compared with the Al substrate, the wear resistance of the obtained film was increased to 0.79, and the corrosion resistance was significantly improved. The antibacterial rate against Escherichia coli could be achieved as 94.38 ± 3.23%, and the adhesion force between the film and substrate was about 11 N. With the increase of the deposition time, the surface color of samples was gradually darkened, and meanwhile, the surface became uniform again without particles eventually. Energy dispersive spectroscopy (EDS) results showed the silver element was deposited on the surface and at the bottom of the porous oxide layer, and the amount of silver also increased with prolonging the deposition time. Moreover, x-ray photoelectron spectroscopy (XPS) analysis results on the surface showed the deposited silver element existed in the form of the ion and elemental substance, which indicated that reduction reaction of Ag ^+ appeared on the oxide film surface

Gravity flow sedimentary characteristics and sedimentary model of the 1 member of the Tengger formation in Saihantala depression (Erlian Basin, China)

Based on core, well-logging and seismic data, the gravity flow characteristics and sedimentary model of the 1st member of the Tengger formation in the eastern steep slope belt of the Sai-4 tectonic belt in the Saihantala depression (Erlian Basin, China) have been systematically studied; further, the sublacustrine fan sedimentary model in the study area has been established. The main types of gravity flow identified in the study area are sandy debris flow deposits and turbidity flow deposition. Affected by paleo-geomorphology, provenance and other factors, sublacustrine fans in the eastern steep slope zone are formed by gravity flows from different periods. The sublacustrine fan is divided into three subfacies: inner-fan, mid-fan and outer-fan. The subfacies can be subdivided into six types of microfacies: main channel, levee of main channel, distributary channel, inter-channel, levee of distributary channel and terminals. The formation of the sublacustrine fan is caused by steep slopes and triggered by earthquakes. The sedimentary model of the sublacustrine fan and its sedimentary characteristics provide a foundation for exploring and developing oil and gas in the study area