Numerical and theoretical study of large-scale failure of strata overlying sublevel caving mines with steeply dipping discontinuities

The deformation and fracture evolution mechanisms of the strata overlying mines mined using sublevel caving were studied via numerical simulations.Moreover,an expression for the normal force acting on the side face of a steeply dipping superimposed cantilever beam in the surrounding rock was deduced based on limit equilibrium theory.The results show the following:(1)surface displacement above metal mines with steeply dipping discontinuities shows significant step characteristics,and(2)the behavior of the strata as they fail exhibits superimposition characteristics.Generally,failure first occurs in certain superimposed strata slightly far from the goaf.Subsequently,with the constant downward excavation of the orebody,the superimposed strata become damaged both upwards away from and downwards toward the goaf.This process continues until the deep part of the steeply dipping superimposed strata forms a large-scale deep fracture plane that connects with the goaf.The deep fracture plane generally makes an angle of 12°-20°with the normal to the steeply dipping discontinuities.The effect of the constant outward transfer of strata movement due to the constant outward failure of the superimposed strata in the metal mines with steeply dipping discontinuities causes the scope of the strata movement in these mines to be larger than expected.The strata in the metal mines with steeply dipping discontinuities mainly show flexural toppling failure.However,the steeply dipping structural strata near the goaf mainly exhibit shear slipping failure,in which case the mechanical model used to describe them can be simplified by treating them as steeply dipping superimposed cantilever beams.By taking the steeply dipping superimposed cantilever beam that first experiences failure as the key stratum,the failure scope of the strata(and criteria for the stability of metal mines with steeply dipping discontinuities mined using sublevel caving)can be obtained via iterative computations from the key stratum,moving downward toward and upwards away from the goaf.

Dipping Process Characteristics Based on Image Processing of Pictures Captured by High-speed Cameras

The dipping process was recorded firstly by high-speed camera system; acceleration time, speed, and dipping time were set by the control system of dipping bed, respectively. By image processing of dipping process based on Otsu's method, it was found that low-viscosity flux glue eliminates the micelle effectively, very low speed also leads to small micelle hidden between the bumps, and this small micelle and hidden phenomenon disappeared when the speed is ≥0.2 cm s-1. Dipping flux quantity of the bump decreases by about 100 square pixels when flux viscosity is reduced from4,500 to 3,500 mpa s. For the 3,500 mpa s viscosity glue, dipping flux quantity increases with the increase of the speed and decreases with the increase of the speed after the speed is up to 0.8 cm s-1. The stable time of dipping glue can be obtained by real-time curve of dipping flux quantity and is only 80–90 ms when dipping speed is from 1.6 to 4.0 cm s-1. Dipping flux quantity has an increasing trend for acceleration time and has a decreasing trend for acceleration. Dipping flux quantity increases with the increase of dipping time, and is becoming saturated when the time is ≥55 ms.

0.87Na_(0.5)Bi_(0.5)TiO_3-0.13PbTiO_3薄膜的MOSD+Dipping制备

采用MOSD+Dipping方法在P型Si(111)衬底上制备了0.87Na0.5Bi0.5TiO3-0.13PbTiO3薄膜。用X射线衍射技术研究了薄膜的结构和结晶性。用原子力显微镜分析了薄膜的表面形貌。同时还研究了薄膜的存储性能。

Structure instability forecasting and analysis of giant rock pillars in steeply dipping thick coal seams

Structure stability analysis of rock masses is essential for forecasting catastrophic structure failure in coal seam mining. Steeply dipping thick coal seams （SDTCS） are common in the Urumqi coalfield, and some dynamical hazards such as roof collapse and mining-induced seismicity occur frequently in the coal mines. The cause of these events is mainly structure instability in giant rock pillars sand- wiched between SDTCS. Developing methods to predict these events is important for safe mining in such a complex environment. This study focuses on understanding the structural mechanics model of a giant rock pillar and presents a viewpoint of the stability of a trend sphenoid fractured beam （TSFB）. Some stability index parameters such as failure surface dips were measured, and most dips were observed to be between 46° and 51°. We used a digital panoramic borehole monitoring system to measure the TSFB＇s height （△H）, which varied from 56.37 to 60.50 m. Next, FLAC^3D was used to model the distribution and evolution of vertical displacement in the giant rock pillars; the results confirmed the existence of a TSFB structure. Finally, we investigated the acoustic emission （AE） energy accumulation rate and observed that the rate commonly ranged from 20 to 40 kJ/min. The AE energy accumulation rate could be used to anticipate impeding seismic events related to structure failure. The results presented provide a useful approach for forecasting catastrophic events related to structure instability and for developing hazard prevention technology for mining in SDTCS.

Monitoring strata behavior due to multi-slicing top coal caving longwall mining in steeply dipping extra thick coal seam

For studying the strata behavior due to multi-slicing top coal caving longwall mining along-the-strike direction in steeply dipping extra thick coal seams,the shield support pressures of the upper and lower slices of panel 37220 in Dongxia Coal Mine were monitored using the KJ513 dynamic monitoring system.The set up rooms adopted the "horizontal line-arc segment-inclined line" form and used different types of shield supports.The results show that the strata pressure of upper slice panel 37220-1 changed slightly along the strike direction,while along the dip direction it exhibited strong to weak pressure from bottom to top.The first weighting interval of lower slice panel 37220-2 was about 60.8 m,and the average periodic weighting interval were about 22.6 m.The strata behavior of panel 37220-2 exhibited a spatiotemporal characteristic in that periodic weighting occurred first in the middle-upper part,followed by the middle and upper parts,arc segment,and finally the lower part.During the periodic weighting,the weighting interval and intensity also exhibited strong space characteristics.The average dynamic load coefficient was 1.48 and the maximum lateral load of the side shield was 20-25 MPa.

Evaluation of the use of sublevel open stoping in the mining of moderately dipping medium-thick orebodies

The flow of blasted ore during mining of moderately dipping medium-thick orebodies is a challenge.Selecting a suitable mining system for such ore bodies is difficult.This paper proposes a diamond layout sublevel open stoping system using fan blastholes with backfilling to mine such orebodies.To evaluate the performance of system the relationships between ore recovery and stope footwall dip angle,footwall surface roughness,drawpoint spacing and production blast ring burden were investigated.An ore recovery data set from 81 laboratory physical model experiments was established from combinations of the listed factors.Various modules in a back propagation neural network structure were compared,and an optimal network structure identified.An ore recovery backpropagation neural network(BPNN)forecast model was developed.Using the model and sensitivity analysis of the factors affecting the proposed open stope mining system,the significance of each factor on ore recovery was studied.The study results were applied to a case study at the Shandong Gold Group Jiaojia Gold Mine.The results showed that the application of a BPNN and sensitivity analysis models for ore recovery prediction in the proposed mining system and field experimental results confirm that the suggested mining method is feasible.

Three-dimensional strata movement around coal face of steeply dipping seam group

Steeply dipping seam group, which has complex occurrence conditions, belongs to the steeply dipping seam. The research on the strata movement around the coal face not only improves safe production technology in practice, but also develops the mining theory. By using physical simulation experiments, numerical simulation and site test, the deformation, failure and movement of surrounding rock in Iongwall working face were analyzed. According to the analysis, characteristics of the seam group were formed which is different from the single seam. Asymmetry mechanics, sequential changes and imbalance of strata movement along the tendency working face were summarized. Furthermore the features of upper and lower seams were different. The mining of the lower seam induced more complex strata movement along the strike. Multi-section mining disturbed surrounding rocks in larger areas than the single section mining did, which had an impact on and dynamic loading function to the support when mining the lower seam, and produced a great influence on the stability of support-rock system.

Breaking and mining-induced stress evolution of overlying strata in the working face of a steeply dipping coal seam

The breaking features and stress distribution of overlying strata in a steeply dipping coal seam(SDCS)differ significantly from those in a near-horizontal one.In this study,the laws governing the evolution of vertical stress release and shear stress concentration in the overlying strata of coal seams with different dip angles are derived via numerical simulation,rock mechanics tests,acoustic emissions,and field measurements.Thus,the stress-driven dynamic evolution of the overlying strata structure,in which a shear stress arch forms,is determined.Upon breaking the lower pari of the overlying strata,the shear stress transfers rapidly to the upper part of the working face.The damaged zone of the overlying strata migrates upward along the dip direction of the working face.The gangue in the lower part of the working face is compacted,leading to an increase in vertical stress.As the dip angle of the coal seam increases,the overlying strata fail suddenly under the action of shear stresses.Finally,the behavioral response of the overlying strata driven by shear stresses in the longwall working face of an SDCS is identified and analyzed in detail.The present research findings reveal the laws governing the behavior of mine pressure in the working face of an SDCS,which in turn can be used to establish the respective on-site guidance.

Structures of ceramics coatings on steel fabricated by hot-dipping and micro-arc oxidation

Firstly, an aluminum coating was produced metallurgically on mild steel by hot-dipping, then an aluminum oxide coating was formed self-growingly from the aluminum coating by micro-arc oxidation treatment. The structures of the composite coatings were investigated by means of SEM, TEM and XRD. The results show that the composite coating consists of three layers which are Fe-Al alloy, aluminum coating and aluminum oxide orderly outward from the steel substrate. There are amorphous phases, k-Al2O3 and θ-Al2O3 mainly in the aluminum oxide.

Preparation of tetrapod-like ZnO whiskers from waste hot dipping zinc

Large and uniform tetrapod-like ZnO whiskers （T-ZnO） were prepared from waste hot dipping zinc by vapor oxidation and examined by means of X-ray diffraction and ICP-AES analysis and scanning electron microscope. The products are pure hexagonal wurtzite crystals with tetrapod shape and edge size of center body 56 μm and needle length of 100130 μm. The size and shape of ZnO particles are fully controlled by the growth conditions and T-ZnO can be obtained only at 8501 000 ℃ and total gas flow rate ranging from 40 to 250 L·h-1 in which the size of the T-ZnO particles varies slightly with temperature. The process of the formation of T-ZnO is that T-ZnO may nucleate at the initial stage with a complete tetrapod shape and develop to the large size, but not the process of （preferential） growth of octahedral nuclei and subsequent growth of the needles. The experiment presents a new method to prepare T-ZnO economically by using the waste hot dipping zinc.

Steeply dipping structural target-oriented viscoacoustic least-squares reverse time migration and its application

Steeply dipping structural imaging is a significant challenge because surface geophones cannot obtain seismic primary reflection wave information from steeply dipping structures.Prismatic waves with a significant amount of steeply dipping information can be used to improve the imaging eff ect on steeply dipping structures.Subsurface attenuation leads to amplitude loss and phase distortion of seismic waves,and ignoring this attenuation during imaging can cause blurring of migration amplitudes.In this study,we proposed a steeply dipping structural target-oriented viscoacoustic least-squares reverse time migration(LSRTM)method with prismatic and primary waves as an objective function based on the viscous wave equation,while deriving Q-compensated wavefield propagation and joint operators of prismatic and primary waves and the Q-compensated demigration operator.Numerical examples on synthetic and field data verified the advantages of the proposed viscoacoustic LSRTM method of joint primary and prismatic waves over conventional viscoacoustic LSRTM and non-compensated LSRTM when using attenuating observed data.

Dipping cells in acidic bath could make stem cells

The discovery that somatic mammalian cells can be epigeneti- cally reprogrammed to induced pluripotent stem cells （iPSCs） through the exogenous expression of the Oct4, Sox2, Klf4 and c-Myc （OSKM） has demonstrated a new way for cell-replace- ment therapy in regenerative medicine （Li et al., 2013; Nishimura and Takahashi, 2013; Takahashi and Yamanaka, 2013）. This novel technology has opened new therapeutic opportunities to gener- ate stem cells in any tissue for cell replacement therapy in a num- ber of disorders （Yamanaka, 2012; Li et al., 2013; Nishimura and Takahashi, 2013; Takahashi and Yamanaka, 2013）. Just last week, two papers published in Nature, describing a surprisingly sim- ple method to turn mature cells into embryonic-like stem ceils by culturing cells in a low pH medium （Obokata et al., 2014a, 2014b）. This method by Obokata and colleagues is truly the sim- plest, cheapest, and fastest method ever achieved for reprogram- min~ somatic cells into multiootent stem cells.

Research on drawing coal effects in the dipping and steep——dipping coal seams

Controllable drawing roof coal mining method is applied either to rently inclined seam or to big dipping seam. This paper sums up four corresponding methods according to conditions of our country, and analyses the coal-recovering effects and proves applicated conditions and measures for improving by "drawing coal theory of the ellipsoid". Its conclusion basically consists with practice. This work is of guiding meaning for designing drawing coal technology.

DRG/DIP融合管理推动公立医院高质量发展的实践探讨

高质量发展是新时期公立医院发展的主旋律。样本医院聚焦DRG/DIP融合管理,通过团队融合、数据融合、系统融合、制度融合等创新实践,实现病种收治难度系数增长、低分值与基层病种收治占比下降、药费占比下降、运行效率提升等成效,有效推动公立医院高质高效发展,助力实现政府、医院、患者多方共赢。

DIP付费对医疗服务项目诊疗强度的影响研究

目的:探索DIP付费对医疗服务项目诊疗强度的影响。方法:收集某市2020年1月至2022年12月330家医疗机构住院患者开展数字化摄影诊疗的数据,利用独立样本t检验比较诊疗强度的变化,采用间断时间序列分析考察DIP付费对诊疗强度的影响。结果:DIP付费后三级医院、一级医院数字化摄影诊疗强度分别增加了0.03和0.04,二级医院下降了0.06;三级医院诊疗强度在短期内增加(β_(2)=0.061),长期却呈现下降趋势(β_(3)=-0.007)。结论:DIP付费对医疗服务项目诊疗强度的政策效应可能与政策预期不一致,异质性和同质性并存;要强化DIP支付方式改革与医疗服务价格改革的协同路径。

DIP医保付费模式下公立医院成本管理常见问题探究

成本管理工作是医院经营管理活动中重要的环节之一。通过成本管理能够提高医院运营效率,实现资源的优化配置。然而,医保支付方式的改革,不仅改变了医保经办单位对医院的支付方式,同时也对医院成本管理工作提出了更高的要求。基于此,本文在DIP医保付费的大背景下,对当前公立医院成本管理工作中需要解决的常见问题进行探讨、研究。

DIP支付方式下医保供给侧政策协同对费用控制的影响研究

目的:本研究旨在探索DIP支付方式与其他医保供给侧政策间的协同效果。方法:以全国DIP改革试点城市A市为处理组,未改革城市B市为对照组进行比较研究。收集2019—2022年共1120个公立医疗机构样本,采用双重差分法对住院医疗总费用及部分费用结构进行分析。结果:A市DIP改革对医疗机构住院医疗总费用、住院检查化验总费用产生显著的抑制效应,对住院药品总费用和住院材料总费用未产生影响。结论:DIP支付方式发挥显著控费效果,住院医疗总费用得到有效控制;单纯采取调价政策与集采政策的控费效果尚有不足;DIP与其他供给侧政策协同,促进医疗费用结构更加合理。建议医保部门注重发挥供给侧政策协同作用,共同推动医保基金使用效率提升。

基于DRG/DIP时代下医院精益运营管理体系构建探讨

新医改深化发展,按照病种诊断进行诊疗分组的DRG/DIP支付手段被广泛应用于各大试点医院,并取得了显著成效。DRG/DIP支付不仅是一种医保结付手段,也是医院规范各科室诊疗行为,提高医疗服务质量的重要管理手段。DRG/DIP时代的到来,引导了医院对“医疗价值”与运营管理模式的思考、对医疗成本控制的需求。本文基于DRG/DIP时代背景下对医院精益运营管理体系构建进行探讨,以期助力医院实现高质量转型与可持续发展。

DIP付费改革背景下公立医院成本精细化管理策略分析

公立医院是我国医疗体系的重要组成部分,肩负着向社会提供公共医疗产品和服务的重要责任。传统按项目支付模式下,医保基金的支付压力逐年增加。随着医药卫生体制改革的逐步深入,医保基金的支付机制也逐步得到了完善。本文着重分析了DIP付费改革对公立医院成本精细化管理的意义和当前公立医院成本精细化管理存在的问题,从多个角度阐述了DIP付费模式下加强成本精细化管理的相关策略。

DIP付费改革实施前后住院费用分析及医疗服务绩效综合评价

目的对比研究医院实施DIP付费改革措施前后住院费用等指标变化,分析和评价医疗服务绩效。方法纳入某院未实施DIP付费改革措施的2023年1季度数据和实施DIP付费改革后的2024年1季度数据,对比住院费用和医疗服务绩效变化。结果DIP付费改革后,患者住院总费用和自付费用均有明显降低,差异有统计学意义(P<0.05),医务性费用占比明显提高,CMI、DRG总量、时间消耗指数、费用消耗指数、低风险死亡率等医疗服务绩效指标均优于改革前。结论DIP付费改革后,医院住院费用控制良好,患者自付费用降低,住院费用结构合理,同时医疗服务绩效水平有明显提高。