Tooth anatomy risk factors influencing root canal working length accessibility

The aim of this study was to analyze the specific influence of root canal anatomy on the accessibility of working length during root canal therapy. Four hundred seventy-six root canal therapy cases （amounting to a total of 1 005 root canals） were examined. The anatomy risk factors assessed in each case included： tooth type （tooth location）, root canal curvature, and root canal calcification, as well as endodontic retreatment. The investigation examined the correlation between each of these anatomic factors and the working length, with statistical analysis consisting of Chi-square tests and multiple logistic regression analysis. In an independent factor analysis, tooth type （tooth iocation）, root canal curvature, canal calcification, and endodontic retreatment were determined to be the primary risk factors. In a multiple-factor regression model, root curvature and canal calcification were found to most significantly influence root canal working length accessibility （P〈0.05）. Root canal anatomy increases the difficulty of root canal preparation. Appropriate consideration of tooth anatomy will assist in accurate determination of preparation difficulty before instrumentation. This study alerts clinical therapists to anatomical factors influencing the working length accessibility, and allows for a direct estimate of success rate given in situ measurements of tooth factors during the root canal treatment procedure.

Influence of anchorage length and pretension on the working resistance of rock bolt based on its tensile characteristics

In coal mining roadway support design,the working resistance of the rock bolt is the key factor affecting its maximum support load.Effective improvement of the working resistance is of great significance to roadway support.Based on the rock bolt’s tensile characteristics and the mining roadway surrounding rock deformation,a mechanical model for calculating the working resistance of the rock bolt was established and solved.Taking the mining roadway of the 17102(3)working face at the Panji No.3 Coal Mine of China as a research site,with a quadrilateral section roadway,the influence of pretension and anchorage length on the working resistance of high-strength and ordinary rock bolts in the middle and corner of the roadway is studied.The results show that when the bolt is in the elastic stage,increasing the pretension and anchorage length can effectively improve the working resistance.When the bolt is in the yield and strain-strengthening stages,increasing the pretension and anchorage length cannot effectively improve the working resistance.The influence of pretension and anchorage length on the ordinary and high-strength bolts is similar.The ordinary bolt’s working resistance is approximately 25 kN less than that of the high-strength bolt.When pretension and anchorage length are considered separately,the best pretensions of the high-strength bolt in the middle of the roadway side and the roadway corner are 41.55 and 104.26 kN,respectively,and the best anchorage lengths are 1.54 and 2.12 m,respectively.The best anchorage length of the ordinary bolt is the same as that of the high-strength bolt,and the best pretension for the ordinary bolt in the middle of the roadway side and at the roadway corner is 33.51 and 85.12 kN,respectively.The research results can provide a theoretical basis for supporting the design of quadrilateral mining roadways.

The relationship between length of service and occupational stress in nurses working in an emergency department

Background: Nurses in emergency departments often face department overcrowding with patients, and deal with very ill patients, critical incidents and excessive workloads. Research has indicated that these situations may be associated with work-related stress and the onset of depressive disorders among nursing staff. Aim & Objective: To investigate length of service in relation to occupational stress levels among nurses working in an emergency department, and develop interventions to reduce stress. Methods: A cross-sectional study using a survey was conducted among nurses(N=79) working in the emergency department of one hospital. Occupational stress was measured using the Symptom Checklist 90(SCL-90). Results: Respondents were categorized according to their length of service. Length of service was categorized as follows: group A, <1 year(n=16); group B, between 1 and 5 years(n=31); group C, between 5 and 10 years(n=20); and group D, >10 years(n=12). Group A reported more somatic and anxiety symptoms and a higher total symptom score on the SCL-90 compared with the normal group(p<0.05). Nurses who had worked for longer than 1 year scored above mid-score on all the SCL-90 subscales except on the interpersonal sensitivity and phobic anxiety subscales(p<0.05). There was no difference between groups B, C and D groups for total SCL-90 score. Conclusion: Nurses who had worked for >1 year in the emergency department experienced more work-related stress than the general population. Further research on suitable interventions for the management of occupational stress in nurses working in emergency departments is required.

孤岛工作面长水平深孔全长水力压裂卸压机理及多参量效果分析

为了解决深井孤岛工作面回采巷道面临的强动压问题,分析了孤岛工作面存在的工作面侧向采空区顶板悬顶、后方采空区侧顶板悬顶以及上部高位岩层结构悬顶3种类型,对深孔压裂类型进行了分析,提出了基于长水平孔的全长水力压裂布置方式,在某矿3203孤岛工作面进行了应用;通过在不同层位的目标岩层施工长水平孔压裂,实现了对于孤岛工作面强动压巷道卸压的全长处理。分别在采场和巷道进行矿压观测并选取评价指标,通过多参量、分阶段的分析,可以发现:这种卸压方式能在顶板构筑弱化条带,达到改善本工作面端头和采空区上方顶板空间结构形态、缩短工作面周期来压步距、降低工作面超前支承应力峰值的作用,从时间和空间上优化工作面超前区域应力场的分布状态,转移煤柱与巷道围岩的高应力,减小采动应力的影响,显著降低回采期间的巷道变形量,实现孤岛工作面的安全高效回采。

不同长度的短切玄武岩纤维混杂对磷建筑石膏基复合材料性能的影响

为了探究不同长度的玄武岩纤维(BF)共同作用时对磷建筑石膏基复合材料(PBGCM)的影响,在磷建筑石膏中加入不同长度的混杂BF,得到混杂纤维增强PBGCM。通过正交试验,从直观分析、极差分析、方差分析对其力学性能和工作性能及不同纤维长度的协同作用机理进行了研究。结果表明:3 mm和15 mm BF混掺对PBGCM的力学性能增强效果往往比3 mm和15 mm BF单掺更好;PBGCM的最大绝干抗压强度、绝干抗拉强度、绝干抗折强度分别比未掺纤维的磷建筑石膏高50.10%、122.15%、79.43%;3 mm和15 mm BF混掺对PBGCM的工作性能减弱效果小于15 mm BF单独加入。3 mm BF对PBGCM的力学性能和工作性能都有极显著的影响;15 mm BF除对其绝干抗压强度没有显著影响外,对其他性能均产生极显著的影响,且影响效果比3 mm BF更大。

高速燃油电磁阀电磁特性

高速燃油电磁阀作为航空发动机用叶片调节器的关键控制部件,其电磁特性直接影响叶片调节器的控制精度。首先基于Maxwell建立电磁阀数值模型。其次,深入研究磁路材料和外壳壁厚对电磁阀电磁力的影响规律。然后,对比研究极面形状和工作气隙相对位置对电磁力的影响规律。最后,研制了高速燃油电磁阀样机,进行实验验证。结果表明:磁路材料均为1J22时,电磁力最大;外壳壁厚0.75~1.5 mm时,各工作气隙下电磁力几乎不变;厚度小于0.75 mm时,电磁力随外壳壁厚的减小而下降;工作气隙小时,锥形极面衔铁电磁力小于平面极面,反之,锥形极面衔铁电磁力较大;工作气隙相对位置对电磁力影响有限。实验结果与仿真结果具有较好的吻合度,验证了仿真模型的正确性和研究方法的可行性。研究成果对高速燃油电磁阀电磁性能优化提升,提供了理论基础和数据支撑,具有实践意义。

基于目标定尺的双偏心摆式飞剪机控制参数计算

研究了双偏心摆式飞剪连续定尺剪切原理,建立了目标定尺长度计算模型,形成比较完善的基于目标定尺长度的双偏心摆式飞剪传动控制参数计算方法。设定曲轴转动角速度曲线,建立速度方程式,解析求解得到曲轴转动角速度,从而得到角加速度、加减速时间、匀速转动角速度、匀速运行保持时间等控制参数。并通过某汽车板连续镀锌机组的双偏心摆式飞剪机进行编制程序和控制计算验证,计算速度快,精度高,完全满足工程需要。

阳泉矿区大埋深超长工作面装备适应性研究

验证了数值模拟和现场实测矿压数据,分析了工作面加长后的矿压规律,合理确定了工作面支护强度和液压支架型号;计算了工作面加长带来的刮板机功率、链条破断负荷等,实现工作面装备的升级改造;通过工作面电液控制和矿压监测预警系统,保证了工作面支护质量。解决了阳泉矿区3#煤层采掘接替紧张等难题。

澄合矿区导水裂隙带发育高度多元线性回归方法预测

通过收集澄合矿区多个工作面导水裂隙带高度实测结果,采用多元线性回归分析的方法分析导水裂隙带高度的主控因素,拟合形成导水裂隙带高度与煤层开采厚度、工作面埋深、工作面倾向长度之间的各相关公式。采用拟合公式计算澄合矿区山阳煤矿1503、1506工作面导水裂隙发育高度,计算得到的工作面导水裂隙带发育高度与微震监测结果基本吻合,表明拟合公式获得的导水裂隙带估算值较为准确。在澄合矿区应用性较好,为澄合矿区相似地质条件的工作面导水裂隙带高度预测提供一定的参考依据。

不同长度工作面矿压显现规律及支护强度分析

为了研究不同工作面长度对矿压显现规律的影响以及工作面长度变化时支架合理支护强度的变化规律,结合某矿实际地质条件,对不同工作面长度下的矿压显现进行分析计算。结果表明,当工作面长度一定,沿走向方向开挖距离超过450 m时,煤壁片帮和顶板下沉量处于平稳状态,不再受走向开挖距离的影响;以走向一次性开挖450 m计算,沿工作面长度方向,顶板下沉量中部最大,两端最小,呈拱形。随着工作面长度的增加,顶板下沉拱逐渐增大,工作面每增加30 m,顶板下沉量增加率为5%~8%。顶板下沉量能直接反映工作面顶板压力的大小,根据分析计算,工作面每增加30 m,支架合理支护强度应增加5%~8%。

Stress analysis of full-length grouted bolt under shear deformation of anchor interface

The bolt anchoring force is closely related to the shear properties of the anchor interface. The shear stress distribution of full-length grouted bolts is analyzed based on the stress-strain relationship among the bolt, grout, rock mass and bond interface,considering the shear properties of the grout and contact interface bonding behavior. In this case, the interfacial shear stress of the grout and rock mass and the bolt axial force are obtained under pull-out and normal working conditions. The results show that the peak shear stress of the interface with the shear deformation of the bond interface is significantly lower than that without it when the pull-out force is applied. When designing bolt parameters of grade IV and V rock mass, the relative deformation between the rock mass and anchor should be considered, with a “unimodal” to “bimodal” shear stress distribution.In the case of a low elastic modulus of rock masses,both the shear stress concentration and distribution range are obvious, and the neutral point is near the bolt head. As the elastic modulus increases, the shear stress concentration and distribution range are reduced, and the neutral point moves towards the distal end. As a result, the optimum length of fulllength grouted bolts can be determined by in-situ pull-out tests and decreases with the increased elastic modulus of the rock mass.

Relationship on the Head Deviation Rate and Laying Length of Porous Tubes

To improve the utilization efficiency of water the laying length of porous tubes was analyzed. Considering long porous tubes the irrigation uniformity of porous tubes was studied by analyzing the deviation rate of the working head of porous tubes and through an impact analysis of the deviation ratio of flow rate based on laying length slope pressure head and perforation spacing. Results showed that the deviation ratio of the flow rate could be reduced by decreasing the length of tubes and increasing the slope. The deviation ratio of flow rate was less influenced by pressure head and perforation spacing. A best laid slope resulted in a longer laying length of the porous tubes and they were not constant.

A METHOD OF ADJUSTING BAR-LENGTH OF STATICALLY INDETERMINATE TRUSS FOR INCREASING ITS LOAD CAPACITY

Based on the character of the internal force distribution of the statically indeterminate truss, the elements stresses were changed by adjusting the length of bars to increase load capacity of structure. The efficiency of the method is illustrated by several examples.

矩形凹结构转子磁流变阻尼器的设计与优化

针对传统盘式磁流变阻尼器(magneto-rheological damper,MRD)力矩密度偏低的问题,提出在转子端面构造凹结构以增加有效工作间隙长度,保持结构尺寸紧凑的同时,提高输出力矩密度。分别建立了传统盘式、矩形凹结构和弧形凹结构力矩模型,通过关键尺寸设计和定量对比分析表明,在同等条件下矩形凹结构对提升力矩密度效果更佳。为充分利用矩形凹结构的力矩增益效应,定量地分析了矩形槽位置、槽宽和槽深等关键参数对力矩密度和力矩波动的影响规律,得到了关键参数合理的优化区间。在满足目标设计力矩、线圈功率及确定的参数取值范围前提下,以体积最小为目标函数,对包括矩形凹结构的磁流变阻尼器结构参数进行了优化设计。结果表明,优化后装置力矩密度增幅达23.39%,为矩形凹结构转子阻尼器的实际设计提供了指导。

露天煤矿工作帮过断层参数控制方法

大型露天煤矿在开采境界内常会遇到发育范围、发育程度不同的断层构造。为了对露天煤矿工作帮过断层相关参数进行优化确定,分析了采剥工作线与断层走向相对位置不同时工作帮过断层方式及工作线长度变化情况,确定了断层影响区域煤炭资源回收原则,阐述了工作线与断层走向相交时工作帮推进过程中生产剥采比变化的影响因素。依据露天开采基本原理,建立了工作帮相交断层走向布置工程模型,论述了工作线的组成并给出工作线长度计算方法。构建了以工作线布置方向、工作帮推进方向为轴的三维空间直角坐标系,计算了各工程模型的断面剥离量和原煤量,确定了采煤工作线长度、工作线与断层走向夹角、工作帮推进距离和生产剥采比之间的函数关系。采用控制变量手段分析生产剥采比变化规律,结果显示:采剥工作线与断层走向正交时初始生产剥采比与断层下降盘工作线长度呈正相关关系;工作帮斜交断层走向推进时,初始生产剥采比与断层上升盘工作线长度、工作线与断层走向夹角呈负相关关系,且工作线与断层走向夹角越小,生产剥采比变化越剧烈。给出了露天煤矿工作帮过断层参数优化原则,提出了利用计算机程序循环判断确定参数的方法。以胜利西二号煤矿为工程背景,将上述优化原则及确定方法进行应用研究。结果表明:工作线与断层走向夹角70°,初始下盘采煤工作线长度为1700 m时,工作帮在F13断层区域推进过程中生产剥采比小于经济合理剥采比,工作线长度始终满足设备作业、走行、调配所需的最小工作线长度要求,且东帮扩帮工程量最小。

沉积温度对不同Co含量WC-Co/SiC/Diamond界面结合性能的影响

本文构建了Co质量分数分别为6%、8%、10%和12%的WC-Co/SiC/Diamond金刚石涂层硬质合金界面模型,利用分子动力学方法模拟了不同沉积温度对其界面结合强度的影响,从黏附功及键长分布两个方面进行具体分析。黏附功分析结果表明,与其他三种Co含量界面模型相比,WC-6%Co/SiC/Diamond界面模型在七个沉积温度下所包含的两种界面的黏附功值均为最高值,并且在不同沉积温度下,WC-6%Co/SiC/Diamond界面模型所包含的WC-6%Co/SiC界面、SiC/Diamond界面的黏附功分别在1123、1173 K时最大,为2.468、5.394 J/m^(2)。键长分布概率分析结果表明,与其他三种Co含量界面模型相比,在任一沉积温度下,WC-6%Co/SiC/Diamond界面模型各界面处键长分布范围的最大值较小,且在1123 K时在WC-6%Co基体上沉积SiC中间层,在1173 K时在SiC中间层上沉积Diamond涂层后,该界面模型界面处的键长最短,键能最大,界面结合性能最好。

高延性水泥基复合材料用短切PVA纤维的长度优选研究

为优选高延性水泥基复合材料(HDCC)用短切聚乙烯醇(PVA)纤维的长度,采用6 mm、9 mm、12 mm、18 mm和24 mm五种长度的PVA纤维,在体积掺量为1.0%的情况下制备HDCC,研究PVA纤维长度对HDCC工作性能、力学性能和纤维桥联能力的影响。结果表明:随着纤维长度的增加,HDCC新拌浆体流动性逐渐降低,当纤维长度从6 mm增加到9 mm时浆体流动性显著下降39%;纤维的掺入提升了HDCC的抗压、抗折强度,但其增幅与纤维长度相关性不大;掺入18 mm纤维制备的HDCC展现出最高的弯曲强度,而掺入9 mm纤维制备的HDCC展现出最高的跨中挠度和弯曲耗能;随着纤维长度的增加,纤维桥联应力和桥联余能均增大,但由于纤维断裂效应越显著,纤维桥联应力和桥联余能增幅逐渐变缓。基于HDCC工作性能、力学性能以及纤维桥联能力的试验与计算结果,9 mm长度的PVA纤维是较为合适的选择。

超长工作面支架工作阻力分布及分区增阻特性研究

综采工作面倾向长度的增加,对顶板破断及应力演化产生的影响效应是复杂的,导致工作面支架支护特性存在分区差异。为深入理解超长工作面支架与围岩相互作用关系,以小保当煤矿450 m超长工作面为工程背景,构建弹性基础岩梁力学模型,运用数理统计及均化循环分析方法,对工作面支架实测数据开展循环末阻力、工作阻力分布频率、支架增阻特性分析,明晰不同面长工作面倾向方向顶板运动及支架工作阻力分布特征,探究超长工作面支架倾向分区内支架增阻特性。研究结果表明:工作面倾向长度增加,导致两巷煤体对中部顶板的支承减弱,中部峰值区域向两巷移近,超长工作面支架工作阻力分布趋势呈M型三峰值分布;超长工作面上部、中部、下部三区域支架呈对数型增阻时,其均化曲线仍为对数函数,表现为先急增阻后趋于平缓,此种支架增阻情况反映了来压期间工作面顶板由快速下沉逐渐变为缓慢下沉;呈对数-指数型增阻时,中上部区域支架增阻均化曲线为对数函数,中部及中下部均化曲线为对数-指数型复合函数,表现出先急增阻然后趋于平缓最后急增阻的特征;当支架工作循环时间超过一定值,对数-指数复合增阻型支架会急速增阻,不利于顶板控制,通过优化工作面割煤速度,降低支架工作循环时间,可减小支架增阻量,避免高阻力状态下支架再次瞬时增阻,提升工作面支架支护效果。

开采因素对煤层底板突水影响的数值模拟研究

应用FLAC^(3D)数值模拟软件建立了开滦范各庄矿煤岩层地质力学模型,模拟了开采工作面长度、采煤深度以及采煤方法对煤层底板破坏状态,结合突水系数公式,查明了奥灰含水层上开采因素对底板突水影响的定量关系。研究表明,当工作面长度为100~200 m时,底板破坏深度和突水系数变化起伏小;当工作面长度<100 m或>200 m时,底板破坏深度和突水系数随工作面长度增加而变化加剧。随着煤层开采深度由300 m增加至900 m,煤层底板破坏深度和突水系数加大。分层开采法采煤的煤层底板破坏深度和突水系数比一次采全高法低,因而更安全。模拟结果和矿区实际采掘工作面长度及采煤方法相符合。

大采长工作面高承压水底板注浆改造技术研究

为解决陈四楼煤矿大采长工作面高承压水区域底板水害治理难题,在矿井典型2517大采长工作面采用底板注浆改造技术解放受底板太原组灰岩水威胁的煤层。通过资料调研和数据计算,选取改造层位并进行钻孔设计,基于底板注浆改造钻孔的涌水量和注浆量数据,对各含水层富水性、注浆量、主要可注裂隙、不同级别充水裂隙注浆材料消耗及平均单孔耗浆量规律进行对比分析。结果表明,含水层富水区主要受裂隙、断层和褶皱等构造的影响,L_(10)灰岩和L_(8)灰岩含水层富水性强,分布较均匀,连通性较好,其含水层以中小型和大型裂隙为主且中小型裂隙较多;工作面平均单孔耗浆量约是充水裂隙涌水量的3.4倍。3次物探结果显示,底板注浆改造效果显著,基本解决了陈四楼煤矿高承压水工作面底板突水问题,可为其他矿区矿井水害治理提供借鉴。