Analysis of coal face stability of lower coal seam under repeated mining in close coal seams group

Aiming at the problem of coal face failure of lower coal seam under the influence of repeated mining in close coal seams, with the working face 17,101 as a background, the coal samples mechanics test clarified the strength characteristics of the coal face under repeated mining, through similar simulation experiments, the development of stable roof structure and surrounding rock cracks under repeated mining of close coal seams are further explored. And based on this, establish a coal face failure mechanics model to comprehensively analyze the influence of multiple roof structural instabilities on the stability of the coal face. Finally, numerical simulation is used to further supplement and verify the completeness and rationality of similar simulation experiment and theoretical analysis results. The results show that: affected by repeated mining disturbances, the cracks in the coal face are relatively developed, the strength of the coal body is reduced, and the coal face is more prone to failure under the same roof pressure; During the mining of coal seam 17#, the roofs of different layers above the stope form two kinds of "arch" structures and one kind of “voussoir beam” structure, and there are three different degrees of frequent roof pressure phenomenon, which is easy to cause coal face failure; Under repeated mining of close coal seams, the roof pressure acting on the coal face is not large. The main controlling factor of coal face failure is the strength of the coal body, and the form of coal face failure is mostly the shear failure of soft coal. The research results can provide a theoretical basis for coal face failure under similar conditions.

Finite Volume Method for the Launch Safety of Energetic Materials

It is important to examine the ignition of energetic materials for launch safety. Given that there is a paucity of experimental tests, numerical simulations are important for analysing energetic materials. A computer program based on the finite volume method and viscoelastic statistical crack mechanics model is developed to study the ignition of energetic materials. The trends of temperature and stress of energetic materials subjected to projectile base pressure are studied by numerical examples. The results are compared with those in an extant study, which verified the correctness of the proposed method. Additionally, the relationships between the temperature increase and nonimpact ignition of energetic materials were analysed. The results show that when the temperature at the bottom of the explosive rises to a certain value, it will cause the explosive to ignite. This research has significance to the study of the base gap of explosives, and it provides a reference for launch safety evaluation of energetic materials.

Multiscale mechanical models of DNA nanotubes: A theoretical basis for the design and tuning of DNA nanocarriers

DNA nanostructures are one of potential candidates for drug carriers due to their good biocompatibility and non-specificity in vivo. A reliable prediction about mechanical properties of artificial DNA structures is desirable to improve the efficiency of DNA drug carriers, however there is only a handful of information on mechanical functionalities of DNA nanotubes (DNTs). This paper focuses on quantifying the multiscale correlations among DNT deformation, packaging conditions and surrounding factors to tune mechanical properties of DNTs. By combining WLC statistical mechanics model, Parsegian's mesoscopic liquid crystal model and Euler's continuum beam theory, we developed a multiscale DNA-frame model; then theoretically characterize the initial packed states of DNTs for the first time, and reveal the diversity mechanism in mechanical properties of DNTs induced by interchain interactions and initial packed states. Moreover, the study of parameters, such as packaging conditions and environmental factors, provides a potential control strategy for tuning mechanical properties of DNTs. These conclusions provide a theoretical basis for accurately controlling the property and deformation of DNT in various DNT dynamic devices, such as DNA nanocarriers.

Logistic Regression via Excel Spreadsheets: Mechanics, Model Selection, and Relative Predictor Importance

Logistic regression is one of the most fundamental tools in predictive analytics. Graduate business analytics students are often familiarized with implementation of logistic regression using Python, R, SPSS, or other software packages. However, an understanding of the underlying maximum likelihood model and the mechanics of estimation are often lacking. This paper describes two Excel workbooks that can be used to enhance conceptual understanding of logistic regression in several respects: (i) by providing a clear formulation and solution of the maximum likelihood estimation problem; (ii) by showing the process for testing the significance of logistic regression coefficients; (iii) by demonstrating different methods for model selection to avoid overfitting, specifically, all possible subsets ordinary least squares regression and l1-regularized logistic regression (lasso); and (iv) by illustrating the measurement of relative predictor importance using all possible subsets.

An efficient, localised approach for the simulation of elastic blood vessels using the lattice Boltzmann method

Many numerical studies of blood flow impose a rigid wall assumption due to the simplicity of its implementation compared to a full coupling with a solid mechanics model. In this paper, we present a localised method for incorporating the effects of elastic walls into blood flow simulations using the lattice Boltzmann method implemented by the open-source code HemeLB. We demonstrate that our approach is able to more accurately capture the flow behaviour expected in elastic walled vessels than ones with rigid walls. Furthermore, we show that this can be achieved with no loss of computational performance and remains strongly scalable on high performance computers. We finally illustrate that our approach captures the same trends in wall shear stress distribution as those observed in studies using a rigorous coupling between fluid dynamics and solid mechanics models to solve flow in personalised vascular geometries. These results demonstrate that our model can be used to efficiently and effectively represent flows in elastic blood vessels.