Influence of abnormal stress under a residual bearing coal pillar on the stability of a mine entry

Mine entries close to residual bearing coal pillars(RBCPs) will suffer large deformation that may cause rock burst. To better understand the deformation mechanism and develop safe and practical guidelines for entry design, most studies focus on the absolute size of the stress field in and around the pillar. In this paper, we present a new approach to analyze the abnormal stress field close to a RBCP that uses the stress concentration coefficient(SCC), stress gradient(SG), and coefficient of lateral pressure(CLP) to describe the stress state induced by the RBCP. Based on elastic theory and a mathematical model for the abutment stress in the RBCP, an analytical solution for the abnormal stress in the strata below the RBCP was derived and the characteristics of the abnormal stress for a case study of a coal mine in China were analyzed. The results show that the abnormal stress field around the pillar is characterized by four distinct zones: a zone of high SCC, high SG, and CLP less than 1, a zone of high SCC, low SG, and CLP less than 1, a zone of low SCC, SG close to 0, and CLP greater than 1, and a zone of SCC close to 1, SC close to 0, and CLP close to 1. Based on this zoning pattern, a numerical model was established to study the combined effects of the abnormal stress on the stability of the entry. The most stable zone was determined based on a model of the Xinrui coal mine and verified by field measurements at the mine. Our conclusions can be used as guidelines for designing safe entry layouts in similar geological and mining settings.

Feasibility analysis of gob-side entry retaining on a working face in a steep coal seam

Based on the decline in exploitation of coal resources, steep coal seam mining and mining face tensions continue to explore the feasibility analysis of steeply inclined faces in the gob. One of the key factors in utilizing the technology of gob-side entry retaining in steep coal seams is to safely and effectively prevent caving rock blocks from rushing into the gob-side entry by sliding downwards along levels. Using theoretical analysis and field methods, we numerically simulated the mining process on a fully-mechanized face in a steep coal seam. The stress and deformation process of roof strata has been analyzed, and the difficulty of utilizing the technology is considered and combined with practice in a steep working face in Lvshuidong mine. The feasibility of utilizing the technology of gob-side entry retaining in a steep coal seam has been recognised. We propose that roadways along the left lane offshoot body use a speciallymade reinforced steel dense net to build a dense rock face at the lower head. The results show that the lane offshoot branch creates effective roof control, safe conditions for roadway construction workers, and practical application of steeply inclined gob.

Stability analysis and control technology of gob‑side entry retaining with double roadways by flling with high‑water material in gently inclined coal seam

To ameliorate the defects of insufcient support resistance of traditional roadside flling bodies for gob-side entry retaining(GER),overcome the inability to adapt to the deformation of surrounding rock,and isolate the goaf efectively,a new type of high-water material as a roadside flling body for GER technology with double roadways was proposed.The instability analysis and control technology of GER with double roadways by flling high-water material into a gently inclined coal seam were studied.The basic mechanical properties of the new high-water material were investigated through laboratory experiments,and their main advantages were identifed.The reasonable width of the roadside flling wall of a high-water material was obtained by combining ground pressure observation and theoretical calculations.The distribution characteristics of the stress and plastic zone of surrounding rock of GER after being stabilized by the disturbance of the working face were studied using numerical simulations,and the failure range of GER by flling with high-water material was revealed.Based on this,a coupling control technology of anchor cables and bolts+single props+metal mesh+anchor bolts is proposed.Through the coupling methods of arranging borehole peeping and observing the convergences of surrounding rock,the results demonstrate that GER with double roadways by flling with a 1.8-m-wide high-water material has a good control efect.The above research will play an active role in promoting the application of high-water materials in GER roadside flling.

Three-dimensional analysis of pedicle screw channel,screw entry point and lateral surface of cervical vertebral body

Objective To explore three-dimensional relations of pedicle screw channel (PSC) ,screw entry point and lateral surface of cervical vertebral body by digital techniques. Methods CT scan images of cervical

INFLUENCES OF CASTING SPEED AND SEN DEPTH ON FLUID FLOW IN THE FUNNEL TYPE MOLD OF A THIN SLAB CASTER

In recent years, thin slab continuous casting technology has been widely used to improve the quality of the product and to reduce the cost. One of the challenges faced by this technology is to design reasonable flow patterns, which strongly affect the surface and inner properties of the final slab in the mold. With the fixed scales and complex geometrical structures of nozzle and funnel type mold, a series of numerical simulations are made to analyze the flow patterns in melt steel using finite volume method based on structured body fitted coordinate grids. The CFD （computational fluid dynamics） package is validated first using one typical case described in previously published studies, and then it is developed to study the effect of operational parameters on fluid flow in thin slab caster. Two operational parameters, casting speed and SEN （submerged entry nozzle） depth, are mainly considered for numerical analysis. On the basis of present simulations, the reasonable SEN submergence depths corresponding to different casting speeds are suggested according to fluid flow characteristics like, flow jet impingement on the narrow side of the mold, flow speed of the melt steel beneath the meniscus and the recirculation region. This is the first stage of study on the numerical analysis of the whole thin slab casting process with electromagnetic brake.

Vasoactive-Ventilation-Renal Score Predicts Cardiac Care Unit Length of Stay in Patients Undergoing Re-Entry Sternotomy: A Derivation Study

Background: The vasoactive-ventilation-renal (VVR) score includes pulmonary and renal dysfunctions not previously addressed by the vasoactive inotrope score (VIS) and may be a better predictor of cardiac care unit (CCU) length of stay (LOS) in patients undergoing re-entry sternotomy (defined as no earlier than 30 days after previous sternotomy) for congenital heart disease (CHD). Methods: Patients undergoing re-entry sternotomy for CHD from August 1, 2009 to June 30, 2016 were studied retrospectively. A total of 96 patients undergoing 133 re-entry procedures were identified. VVR scores were calculated on CCU admission post-procedure (at 0 hour), 24-hour, and 48-hour after admission to the CCU. The response variable was CCU LOS.? Recursive partition analysis identified variables predicting LOS. Results: 133 re-entry sternotomies in 96 patients made up the samples of the database;11 samples were removed due to incomplete data or placement on ECMO. Of the initial 25 features, 5 were removed for near zero variance and 3 categorical features were removed for non-information. Covariance analysis did not demonstrate any significant correlation amongst the remaining features. Initial recursive tree regression using ANOVA, cross validation and conditional predictive p-value (cp) = 0.01 produced 3 trees. The tree with lowest cross validation error was selected. The resulting 2 split trees with ventilator days less than 20 days and VVR score at 48 hours greater than 23 identified three CCU LOS groups with mean CCU LOS of 77.6, 55.1, and 9.5 days. Conclusions: Recursive partition analysis identified ventilator days greater than 20 days and the sub-population VVR at 48 hours as predictive of CCU LOS in patients undergoing re-entry sternotomy for CHD.

Epidata Entry-Epidata Analysis软件联用在医院处方分析评价中的应用

目的探讨不合格处方分析评价的新技术、新方法。方法运用Epidata Entry软件进行数据录入,通过编写check文件,对录入数据和流程进行控制,联用Epidata Analysis软件对不合格处方进行分析。结果 Epidata Entry软件便于不合格处方的录入和管理,Epidata Analysis软件便于不合格处方的分析,两软件联用可实现不合格处方数字化管理,方法可靠。结论该方法应用于医院处方分析评价,具有简单、易学、方便、实用、几乎不需任何费用等优点。

EXPERIMENTAL AND THEORETICAL STUDY ON THE HIGH-SPEED HORIZONTAL WATER ENTRY BEHAVIORS OF CYLINDRICAL PROJECTILES

In this article,the horizontal water-entry of flat-nose projectiles of two different lengths at impact velocities of 400 m/s-600 m/s is studied experimentally and theoretically.Based on the solution of the Rayleigh-Besant problem,a set of projectile dynamic equations are derived and a cavity model is built to describe the projectile＇s water entry dynamics.A parameter in the cavity model is determined by employing the principle of energy conservation.The results indicate that the flat-nose projectiles enjoy a good stability of trajectory,the drag coefficient and the velocity decay coefficient are dependent on the cavitation number,and increase along the penetration distance but with a relatively small variation.The maximum cavity radius decreases monotonically with the penetration distance.Projectiles with the same nose shapes at different initial velocities have a basically consistent cavity dimension before the deep pinching off phenomenon occurs.Good agreements are observed between results obtained by the analytical model and the experimental results.

空投方舱入水静力分析研究

针对降落伞空投方舱入水问题进行了静力分析,以得到典型载况下的最佳入水角.确定了方舱主尺度及船型参数.首先,假定入水角,计算不同吃水深度下的静水力特性;然后,假定重心高度,计算艏部和艉部入水时的复原力矩,得到复原力矩曲面图谱;最后,通过计算超载、满载和空载3种典型载况下的倾覆力矩,进一步确定入水静力平衡曲线,得出3种典型载况下的最佳入水角.结果表明:在艏部入水时,超载下最佳入水角为38°,满载下最佳入水角在10°~90°,空载下最佳入水角为12°;在艉部入水时,超载下最佳入水角为58°,满载下最佳入水角为55°,空载下最佳入水角为51°.并可将结果用于约束其他载况下的最佳入水角.通过空投方舱入水角要求可约束某一载况下重心高度可行域,为后续设计和空投入水提供技术参考数据.

深埋矿井沿空留巷切顶卸压底板变形控制

目前有关巷道底鼓的研究与实践主要探讨巷道底板的变形机理及控制技术,对沿空留巷切顶卸压前后底板力学分析不全面。针对该问题,基于煤体分区破坏特征构建了切顶前后巷道围岩和底板力学模型,分析实体煤、巷旁支护及采空区对底板的作用,获得切顶前后巷道底鼓解析解,得出巷旁煤帮弹塑性区、巷道支护体及顶板下沉区底板所受载荷共同影响巷道底鼓量大小。采用数值模拟验证切顶卸压前后沿空留巷围岩破坏特征、应力分布及底鼓量变化,结果表明:切顶卸压技术可有效缩小巷道实体煤侧面及顶部的破坏区域,维持巷道围岩结构稳定;巷道底板最大应力、巷旁支护阻力、巷道底鼓量均下降,平均降幅分别为25.78%,56.14%,54.07%。现场应用结果表明,厚硬顶板沿空留巷底鼓量由709.3451 mm降至320.9658 mm,切顶卸压技术可以优化巷道围岩应力结构,抑制巷道底鼓,有效改善底板破坏情况。

集体经营性建设用地入市案例分析与优化对策

集体经营性建设用地入市试点改革的主要任务是通过完善集体经营性建设用地产权制度,理顺入市途径,建立城乡统一交易市场和监管体系,以达到与国有建设用地同地同权、农民集体收益共享、土地流转顺畅的目的。本研究从集体经营性建设用地入市改革制度的演变入手,通过对北京开展的由镇村主导,解决城市“夹心层”租房难的集租房建设和福州、永泰集体建设用地入市试点案例和成效分析,剖析当前入市试点中存在的城乡用地同地同权机制未形成、收益分配制度不明确和集体建设用地零散化、碎片化等方面的问题,提出明晰产权完善主体职能、完善收益分配机制和优化规划管控盘活土地资源等优化对策,进一步完善集体经营性建设用地出让制度和服务监管。

2017—2022年厦门口岸出入境人员传染病流行特征分析

目的本文旨在通过对2017—2022年在厦门口岸接受传染病监测的出入境人员的传染病感染情况进行统计分析,揭示其分布规律和流行趋势,进一步为口岸传染病监测和防控工作提供科学依据。方法对2017—2022年在厦门口岸进行传染病监测体检的39168名出入境人员的乙肝、丙肝、梅毒和艾滋病的监测结果进行统计分析,并研究其流行病学特征。结果2017—2022年期间,在厦门口岸共计39168名出入境人员接受了传染病监测体检,总共检出4种2344例传染病,总检出率为5.98%。其中乙肝表面抗原(HBsAg)阳性2092例,丙型肝炎抗体阳性35例,梅毒螺旋体抗体阳性197例,人类免疫缺陷病毒(HIV)抗体阳性20例。不同年份之间的传染病总检出率差异具有统计学意义(P<0.05),其中HBsAg阳性检出率和梅毒阳性检出率在不同年份间差异具有统计学意义。男性传染病总检出率(7.10%)明显高于女性(2.71%),男性传染病检出率呈现出逐年下降的趋势。女性在不同年份之间的检出率存在显著的统计学差异(P<0.05)。结论为有效开展口岸传染病防控工作,本口岸应重点加强对梅毒和乙肝的监测,同时关注丙肝、艾滋等近年来明显呈上升趋势的疾病以及年龄在40岁以上男性人群。开展有针对性的宣传教育和行为干预措施,以提高效率和影响力。

沿空留巷工作面复用巷道大面积悬顶水力压裂治理研究

针对榆家梁煤矿52306沿空留巷工作面复用巷道上覆岩层普遍坚硬致密,难以自然垮落,易形成悬顶灾害问题,分析复用巷道顶板悬顶形成原因,建立复用巷道顶板悬顶区域水力压裂数值模拟模型,研究复用巷道侧砼墙应力演化规律,并对比分析水力压裂前后液压支架压力分布特征、巷道围岩变形量、钻孔超声波监测数据及其窥视结果,研究结果表明:坚硬顶板悬顶灾害的主控因素为悬顶跨度;坚硬顶板水力压裂技术可有效降低复用巷道侧砼墙应力集中程度,减小复用巷道围岩变形量,得出砼墙上部悬顶长度的合理切顶范围在2~5 m之间;对复用巷道采用顶板水力压裂措施后,液压支架整体平均工作阻力降低约12%,巷道变形大幅减小;钻孔窥视结果表明钻孔内部裂隙显著扩展,致裂效果显著;通过采取顶板水力压裂措施,削弱各岩层之间的黏聚力,弱化坚硬顶板,降低上覆岩层抗拉强度,实现缩短悬顶跨度和降低矿压显现程度。榆家梁煤矿52306沿空留巷工作面复用巷道从原长距离悬顶控制到目前的采空区顶板明显下沉、断裂和垮落,保障矿井安全高效生产。

船舶进出港报告制度差异性分析

通过对船舶进出港报告涉及的相关法律规定以及实践进行对比分析,找到不同层级的法律规定对于船舶进出港报告内容上的不同,对有冲突的部分进行着重对比分析,指出可能存在的法律问题,最后结合目前进出港报告的操作实践,就法律修订和实践操作给出相关建议,以期完善统一当前的法律规定中船舶进出港报告的要求,让船舶进出港报告制度的实施更加顺畅、监管更加高效。

常熟口岸出入境人员腹部B超检查结果分析

目的通过对出入境人员腹部B超检查结果进行分析,掌握这一人群的健康状况,有针对性地进行医学指导。方法对2018年1月至2022年12月经常熟口岸出入境的3302名体检人员的腹部B超检查结果进行分析。结果检出疾病种类24种,阳性病例共1478例,检出率为44.76%。肝脏患病最多,为961例,占总阳性病例的65.02%;其次是胆道系统疾病268例,占阳性病例的18.13%;肾脏疾病227例,占阳性病例的15.36%;脾脏21例,占阳性病例的1.42%;胰腺1例,占阳性病例的0.07%。男性疾病检出率为58.47%,女性疾病检出率为19.98%,男性检出率高于女性。结论根据统计结果,了解这一人群的疾病谱,为保健中心科学有效的制定防治措施提供依据。

杜儿坪煤矿72908面回风巷煤柱宽度设计

针对杜儿坪矿72908工作面回风巷沿空掘巷煤柱留设问题,采用理论计算、数值模拟分析的方法得到合理宽度应为7 m。

CSP连铸浸入式水口结瘤案例研究

研究了CSP连铸浸入式水口结瘤两种案例。案例曲线表明,塞棒开度和结晶器液面波动是钢水浇铸过程中最重要的特征参数。薄板坯连铸铝镇静钢中间包水口结瘤是高熔点夹杂在水口内壁的聚集。生产不稳,积压钢水在LF多次处理,产生细小的高熔点夹杂难以去除;软吹钢水“露眼”和开浇烧氧再生高熔点夹杂来不及去除都会导致水口结瘤。钙处理主要是球化夹杂,改善钢水可浇性。即使Ca/Als(钙/酸溶铝)和Ca/Alin(钙/酸不溶铝)都合适,夹杂物绝对量大,钢水可浇性仍较差,水口容易结瘤。

2012~2013年中国进境植物疫情截获情况分析

本文对2012~2013年中国进境植物疫情截获情况进行统计分析,重点分析不同检疫业务类型、有害生物类别、来源国(地区)植物疫情截获数据和全国首次截获检疫性有害生物情况,以期为今后植物检疫工作的针对性和有效性提供参考。

急进高原前后士兵心理应激与焦虑、抑郁情绪的交叉滞后分析

目的了解士兵急进高原前后应激与焦虑抑郁情绪的变化及相互预测作用。方法急进高原前后1周,分别采用心理应激自评问卷（psychological stress self-evaluation test,PSET）、焦虑自评量表（self-rating anxiety scale,SAS）和抑郁自评量表（self-rating depression scale,SDS）对1 342名驻平原部队士兵进行调查。结果士兵的应激总分、焦虑总分和抑郁总分在急进高原后1周均显著增高（P〈0.01）。年龄〉20-25岁组士兵在急进高原前后的焦虑情绪低于其他分组（P〈0.05）,在急进高原前的抑郁情绪低于其他分组（P〈0.05）,在急进高原后抑郁情绪显著低于≤18岁组和〉25岁组（P〈0.05）;在急进高原前,军龄〉2-5年组的焦虑情绪显著低于军龄〉1-2及〉5年组（P〈0.05）,抑郁情绪显著低于〉5年组（P〈0.05）,在急进高原后,军龄〉2-5年组焦虑情绪显著低于其他分组（P〈0.05）。交叉滞后相关分析表明,在同步相关一致性的前提下,急进高原前士兵的焦虑情绪（β=0.210,P〈0.01）和抑郁情绪（β=0.257,P〈0.01）能有效的预测急进高原后的应激水平。结论部队进驻高原前的焦虑、抑郁情绪影响进驻高原后的应激水平。

RLV再入混合制导方法研究(英文)

提出可重复使用跨大气层飞行器(RLV)再入混合制导方法,该方法将再入轨道在线生成技术、基于阻力加速度飞行剖面的跟踪制导技术和数值预测制导技术有机结合。其中再入轨道在线生成能够向轨道预测制导算法提供初值,以加快轨道预测制导算法收敛速度;轨道跟踪控制器控制再入吸热,使再入轨道满足再入走廊约束;而数值预测制导算法则对再入轨道进行快速预报,生成合适的制导指令,将RLV导向目标。给出了RLV再入混合制导的具体算法,并对Marshall航天中心先进制导与控制项目所提出的九种再入情况进行了初步仿真,结果表明所提出的RLV再入混合制导方案是可行的。