Grain size effect on rock strength is a topic of great interest in geotechnical engineering. A consensus obtained from earlier laboratory tests is that rock strength generally decreases with the increase of grain size for both silicate and carbonate rocks; however, some recent numerical results conflict with such laboratory test results. To address this intriguing issue, the effect of grain size on strength of polymineralic crystalline rock with low porosity is investigated numerically using the grain-based modeling (GBM) approach in discrete element method (DEM) by interpreting micro-cracking process in response to loading. In agreement with some previous DEM simulation results, the simulated rock strength is found to increase with increasing grain size for both homogeneous and heterogeneous models, even when the number of assembled disks in one mineral grain changes. The mechanism of strength increase with increasing grain size is mainly associated with the number of assembled smooth-joint contacts along grain interfaces and the generation of grain boundary cracks in response to loading. The grain interfaces significantly weaken the integrity of the rock model, which is similar to effects of inherent defects in real rock. As the grain size increases, fewer grain interfaces are built in the model and the rock strength becomes much higher. Hence, by solely changing the mineral grain size in a model, the mechanism of grain size effect as observed in laboratory tests cannot be replicated. To address this issue, a method of degradation of grain boundary strength parameters is used to mimic the possible mechanism of grain size effect. The simulated strength using the method becomes comparable with those obtained from laboratory tests when the heterogeneity in the rock is considered. Degradation of grain boundary parameters with increasing grain size provides a plausible explanation for the grain size effect on rock strength.
Since the model of hypersonic missile cannot be built accurately and it can change unpredictably, traditional design method is not very effective.A synchronizing control method is introduced in this paper.A synchronizing system that has the similar structures with the controlled system is constructed, then a control law is design to make the synchronizing system trace the controlled system.So the controlled system can be controlled by controlling the synchronizing system.Finally, detailed numerical simulation was done and it showed that the synchronous control method is proved to be more effective than PID control method.
Understanding human activity and behavior, particularly real-time understanding in video feeds, is one of the most active areas of research in Computer Vision (CV) and Artificial Intelligence (AI) nowadays. To advance the topic of integrating learning engagement research with university teaching practice, accurate and efficient assessment, and analysis of students’ classroom learning behavior engagement is very important. The recently proposed classroom behavior recognition algorithms have some limitations, such as the inability to quickly and accurately identify students’ classroom behaviors because they do not consider the motion information of students between consecutive frames. In recent years, action recognition algorithms based on Convolutional Neural Networks (CNN) have improved significantly. To address the limitations of existing algorithms, in this study, a 3D-CNN is selected as a network model for classroom student behavior recognition, which increases information multisourcing and classroom student localization with high accuracy and robustness. For better analysis of human behavior in videos, the 3D convolution extends the 2D convolution to the spatial–temporal domain. In the proposed system, first of all, a real-time picture stream of each student is obtained by combining real-time target detection and tracking. Then, a deep spatiotemporal residual CNN is used to learn the spatiotemporal features of each student’s behavior, so, as to achieve real-time recognition of classroom behaviors for multistudent targets in classroom teaching scenarios. To verify the effectiveness of the proposed model, different experiments are conducted using the labeled classroom behavior dataset. The experimental results demonstrate that the proposed model exhibits better performance in classroom behavior recognition. The accurate recognition of classroom behaviors can assist the teachers and students to understand the classroom learning situation and help to promote the development of smart classroom.
In the way of teamwork development,using version control software has become a must.This article describes how to deploy VSS in the software development for version control,in order to achieve the entire software development process for effective management.
A high current proton RFQ accelerator has been constructed in China for the basic study of Accelerator Driven Subcritical System. A new beam line will be set up for the 3.54MeV, 50mA proton beam from the RFQ in order to study beam halo phenomenon. Therefore, 18 wire scanners consist of a thin carbon wire and two scrapers will be installed on the beam line to traverse the entire beam cross-section. So we can experimentally study the beam loss and beam halo. Some simulations results of the heat on the devices by using finite element method software—ANSYS are presented. The electronics interface will also be discussed.
Weibo platform is an indispensable transmission channel in education policy release and dissemination. The events and sentiments contained in education policies microblogs include the public sentiment and support the general management and guidance scientifically and efficiently. This study constructs a dataset based on the “Double Reduction Policy” relevant microblogs and comments. The policy events are extracted by Latent Dirichlet Allocation (LDA) model and Language Technology Platform (LTP). Based on the emotion dictionary, an attention-based BiLSTM model is constructed to classify the public sentiments. The experimental results reveal four themes: “industry impact,” “institutional supervision,” “public feedback,” and “policy implementation.” The distribution conforms to the development trend of online public sentiments.
Space-charge forces acting in mismatched beams have been identified as a major cause of beam halo. In this paper, we describe the beam halo experimental results in a FODO beam line at IHEP. With this beam transport line, experiments are firstly carried out to determine the main beam parameters at the exit of a RFQ with intense beams, and then the measured beam profiles at different positions are compared with the multi-particle simulation profiles to study the formation of beam halo. The maximum measured amplitudes of the matched and mismatched beam profiles agreed well with simulations. Details of the experiment will be presented.
The novel notion of a `generalized realization' for asynchronous sequential machines with critical races is presented as a tool for the design of output feedback controllers that eliminate the uncertainty caused by critical races. A generalized realization helps represent the uncertainty induced by critical races and creates a deterministic relationship between input-output data and the generalized state. This makes it possible to use deterministic techniques to design output feedback controllers for non-deterministic asynchronous sequential machines.
The China Spallation Neutron Source(CSNS) accelera-tor systems is designed to deliver a 1.6GeV, 100kW pro-ton beam to a solid metal target for neutron scattering research. It consists of a 50keV H⁻ Ion Source, a 3MeV Radio Frequency Quadrupole (RFQ), an 80MeV Drift Tube Linac (DTL), and a 1.6GeV Rapid-cycling Synchro-tron (RCS). The DTL consists of four tanks. In 2017, three of four tanks have been commissioned successfully, and beam has been accelerated to 61MeV with nearly 100% transmission. However, in July 2017, one quadrupole contained in the drift tube was found fault, the beam transmission decreased to 80%. A new lattice has been designed and the 100% transmission has recovered. In January 2018, the last tank of the DTL has been commissioned and accelerated the H⁻ beam to the design energy of 80MeV for the first time. The commissioning progress and the measurement results before and after lattice adjustment will be presented.
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