Automation in U.S. longwall coal mining: A state-of-the-art review

This paper reviews the development of U.S. longwall mining from an unknown to became the world standard in the past five decades with emphasis on automation. Large scale longwall face equipment were imported from Germany and United Kingdom to increase production in the 1970 s and great effort was made to improve them to suit U.S. conditions, rather than domestic market. Automation began with the development of electrohydraulic shields in 1984 and continue to present. Introduction of first generation semi-automated longwall system occurred in 1995 and step-to-step improvement continues to present following the development of sensor technology and internet of things(IOT). Since then, emphasis on new development has been concentrated on the improvement of equipment reliability, miner's health and safety as well as production, including dust control techniques, proximity sensor, anti-collision and remote control. Automation is classified into two categories: automation of individual face equipment and automation of longwall system. The automation development of longwall system is divided into three stages: shearer-initiated-shield-advance(SISA), semi-automated longwall system, and remote control shearer.

Underground ground control monitoring and interpretation,and numerical modeling, and shield capacity design

Mine or longwall panel layout is a 3D structure with highly non-uniform stress distribution. Recognition of such fact will facilitate underground problem identification/investigation and solving by numerical modeling through proper model construction. Due to its versatility, numerical modeling is the most popular method for ground control design and problem solving. However numerical modeling results require highly experienced professionals to interpret its validity/applicability to actual mining operations due to complicated mining and geological conditions. Underground ground control monitoring is routinely performed to predict roof behavior such as weighting and weighting interval without matching observation of face mining condition while the mining pressures are being monitored, resulting in unrealistic interpretation of the obtained data on mining pressure. The importance of ground control pressure monitoring and simultaneous observation of mining and geological conditions is illustrated by an example of shield leg pressure monitoring and interpretation in an U.S. longwall coal mine: it was found that the roof strata act like a plate, not an individual block of the size of a shield dimension, as commonly assumed by all researchers and shield capacity is not a fixed property for a longwall panel or a mine or a coal seam. A new mechanism on the interaction between shield's hydraulic leg pressure and roof strata for shield loading is proposed.

Shear Induced Seepage and Heat Transfer Evolution in a Single-Fractured Hot-Dry-Rock

In the enhanced geothermal system(EGS),the injected fluid will induce shear sliding of rock fractures(i.e.,hydroshearing),which consequently,would increase the fracture aperture and improve the heat transfer efficiency of the geothermal reservoir.In this study,theoretical analysis,experimental research and numerical simulation were performed to uncover the permeability and heat transfer enhancement mechanism of the Hot-Dry-Rock(HDR)mass under the impact of shearing.By conducting the direct shear test with the fractured rock samples,the evolution process of fracture aperture during the shearing tests was observed,during which process,cubic law was adopted to depict the rock fracture permeability.To investigate the seepage characteristics and temperature distribution of the fractured HDR under the influence of shearing,a simulation study of shear-seepage-heat transfer in a fractured rock mass has been conducted to validate the observed shear-induced fracture dilation during the direct shear test.The results demonstrate that(1)the hydroshearing increases the dilation of granite fracture and enhances the permeability of the HDR rock mass,while the temperature around the HDR fracture will reduce.(2)Fracture roughness is of vital importance to enhance the permeability during the shearing tests.To be more specific,a rougher fracture always implies a higher permeability and a greater heat extraction efficiency.(3)The shear induced heat extracting efficiency is dominated by the increased fluid flux in the earlier period of the EGS reservoir,and this efficiency is controlled by the outlet water temperature since the fluid flux becomes stable after the shearing test.Therefore,balancing the hydroshearing enhanced heat extraction efficiency and EGS reservoir lifespan would be significant to the sustainable development and utilization of geothermal energy.

Feasibility of sentinel lymph node biopsy omission after integration of ^(18)F-FDG dedicated lymph node PET in early breast cancer: a prospective phase II trial

Objective:Sentinel lymph node biopsy(SLNB)is currently the standard of care in clinically node negative(cN0)breast cancer.The present study aimed to evaluate the negative predictive value(NPV)of 18F-FDG dedicated lymph node positron emission tomography(LymphPET)in cN0 patients.Methods:This was a prospective phase II trial divided into 2 stages(NCT04072653).In the first stage,cN0 patients underwent axillary LymphPET followed by SLNB.In the second stage,SLNB was omitted in patients with a negative preoperative axillary assessment after integration of LymphPET.Here,we report the results of the first stage.The primary outcome was the NPV of LymphPET to detect macrometastasis of lymph nodes(LN-macro).Results:A total of 189 patients with invasive breast cancer underwent LymphPET followed by surgery with definitive pathological reports.Forty patients had LN-macro,and 16 patients had only lymph node micrometastasis.Of the 131 patients with a negative LymphPET result,16 patients had LN-macro,and the NPV was 87.8%.After combined axillary imaging evaluation with ultrasound and LymphPET,100 patients were found to be both LymphPET and ultrasound negative,9 patients had LN-macro,and the NPV was 91%.Conclusions:LymphPET can be used to screen patients to potentially avoid SLNB,with an NPV>90%.The second stage of the SOAPET trial is ongoing to confirm the safety of omission of SLNB according to preoperational axillary evaluation integrating LymphPET.

Authentic Assessment of Compulsory Subjects in Primary Schools:A Case Study in the Western Area of China

This article discusses a case study that explores the relationship between 21st century learning and curriculum alignment.It investigates three compulsory subjects:Chinese,mathematics,and English.By inquiring the survey on individual perspectives on curriculum content and authentic assessment in different schools within the scope of western Chinese primary schools,this article concluded that 21st century learning skills are well developed in primary schools.Although authentic assessment from parents5 perspective is diminutive,it is progressive for some students.Numerous factors can influence the actual practice of authentic assessment as teachers and pedagogies significantly contribute to studentsJ learning outcomes.The authentic assessment in China still has a long way to go in order to boost these learning skills to a higher level.