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目的探讨死髓牙根管治疗诊间急症(IAE)发生的临床相关因素.方法对101例临床病人103颗根管治疗的死髓牙进行临床观察.结果 27颗牙(26.21%)发生了IEA,其中后牙IAE的发生率高于前牙.结论根管预备时,对不同牙位在IAE发生中的特点应予以重视. 相似文献
3.
利用自主研制的大型土工试验装置,在考虑桩长和桩尖角度影响的情况下,开展了静压桩的沉桩以及静载荷试验,以研究试验过程中桩端阻力的变化规律。试验结果表明:沉桩过程中,桩端阻力随沉桩深度的增加而非线性增大,也随桩长和桩尖角度的增加而增大,沉桩深度为25D时,桩端阻力基本达到极值,同一沉桩深度处桩端阻力在沉桩阻力中的占比随桩长(20D~30D范围内)的增加而减小,随桩尖角度的增加而增大;静载荷试验过程中,桩端阻力随沉降量的增加而非线性增大,也随桩长和桩尖角度的增加而增大,同一沉降量处桩端阻力在桩顶荷载中的占比随桩长的增加而减小,随桩尖角度的增加而增大。 相似文献
4.
Yee-Meng Chiew 《天津大学学报(英文版)》2008,14(4):289-295
This paper examines scour and scour countermeasures at bridge piers and abutments. Abutment scour is by far more complex than its counterpart associated with piers because of the possibility of the presence of a floodplain. Notwithstanding this, the mechanism of scour at both piers and abutments is very similar; moreover, the failure mechanisms associated with both armoring and flow-altering countermeasures are not very different. In rivers with a floodplain, abutment scour becomes much more complex. In cases where the abutment ends at or near to the floodplain, it can initiate bank erosion, which clearly is an important erosion problem that is quite distinct from the customary scour at either an abutment in rivers without a floodplain or a pier. For this reason, abutment scour can be very site-specific while pier-scour is more generic in nature. To this end, the ability to identify the type of abutment scour that may form in a particular channel is closely related to an engineer＇s ability to propose devices for effective scour countermeasure.By summarizing research efforts on using riprap as a pier or abutment countermeasure over the past few decades, this paper highlights the deficiencies of riprap in arresting pier scour. To this end, different failure mechanisms are identified. They are shear failure, winnowing failure, edge failure, bedform-induced failure and bed-degradation induced failure. Each failure mechanism can singly or, more likely, combine to cause the eventual breakdown of the riprap layer. The study shows that a riprap layer is vulnerable to other failure mechanisms even though it is adequately designed against shear failure, rendering it ineffective in arresting scour. 相似文献
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With the terms of the exact series solution taken as trial functions, the method of point collocation was used to calculate the large deflection of a circular plate. The axisymmetrical bending formulae were developed for the calculation of a circular plate subjected to polynomial distributed loads, a concentrated load at the center, uniform radial forces and moments along the edge or their combinations. The support may be elastic. The buckling load was calculated. Under action of uniformly distributed load, central load or their compound load, solutions were compared with those obtained by other methods, Buckling beyond critical thrust was compared with that calculated by the power series method. The method presented in this paper has advantages of wide convergent range, high precision and short computing time. Moreover, the computing time is nearly independent of the complexity of the loads. 相似文献
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Wen Sun Hongyu Chen Yi Zhong Wei Zhang Fengqing Chu Lin Li Yue Chen Xiang Wang Qirui Wang Yuxin Wang Yongyue Wei Laikui Liu Yan Xu 《Anatomical sciences education》2022,15(3):566-575
Dental anatomy is an integrated, core fundamental dental course, which prepares students for all future clinical dental courses. This study aimed to build up an online dental learning platform of micro-computed tomography-based three-dimensional (3D) tooth models with pulp cavity, and to further evaluate its effectiveness for dental anatomy education using a cohort study. First, ninety-six extracted permanent teeth were scanned by micro-computed tomography and the enamel, dentine, and pulp cavity of each was distinguished by different grey-scale intensities using Mimics software. Three-dimensional images allowed further discrimination and insights into permanent three-rooted premolars, central tip, and dental diseases including deep caries and wedge-shaped defects. Furthermore, a second mesiobuccal canal (MB2) in maxillary permanent molar teeth and Vertucci type III root canal configuration in mandibular anterior teeth could be detected using the 3D analytical tool. A digitized 3D tooth model learning platform was implemented. Last, two groups of dental students were assessed to evaluate the effect of 3D models on dental anatomy education. Participants in the Digital group were allowed to use the online dental learning platform freely after class, while the participants in the Traditional group were not. Assessment quizzes showed that participants' scores improved in the Digital group with the use of the learning platform compared with scores in the Traditional group. A questionnaire survey indicated that the participants had a positive attitude toward the 3D models. Thus, adding digital 3D resources to a traditional curriculum may have a positive effect on academic achievements. 相似文献
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《天津大学学报(英文版)》2018,(6)
To locate and quantify local damage in a simply supported bridge, in this study, we derived a rotational-angle influence line equation of a simply supported beam model with local damage. Using the diagram multiplication method, we introduce an analytical formula for a novel damage-identification indicator, namely the diff erence of rotational-angle influence linescurvature(DRAIL-C). If the initial stiff ness of the simply supported beam is known, the analytical formula can be effectively used to determine the extent of damage under certain circumstances. We determined the effectiveness and anti-noise performance of this new damage-identification method using numerical examples of a simply supported beam, a simply supported hollow-slab bridge, and a simply supported truss bridge. The results show that the DRAIL-C is directly proportional to the moving concentrated load and inversely proportional to the distance between the bridge support and the concentrated load and the distance between the damaged truss girder and the angle measuring points. The DRAIL-C indicator is more sensitive to the damage in a steel-truss-bridge bottom chord than it is to the other elements. 相似文献
8.
Xu Jianming 《大连大学学报》1992,(1)
本研究对238名(男110女128)年令在18～43周岁,国人辽宁地区青、中年的上颌磨牙1070颗,其中第一磨牙(M_1)476颗.第二磨牙(M_2)476颗,第三磨牙(M_3)118颗进行了观测。测出了上颌磨牙的牙尖型在各类磨牙的分布状态及牙冠的二种退化形式各自表现的特征,取得了各项有关数据;测出了上颌磨牙中各类磨牙的卡氏征阳性率及卡氏征出现各形的频率。讨论中以国人活体牙各项数值与国内、外各有关数值进行了比较,得出活体牙与尸牙的异同及人种间的差异,并对磨牙形态及卡氏征的形态学进行了扼要地探讨。 相似文献
9.
三维重建法测量中国北方成人股骨膝外翻角(英文) 总被引：1，自引：0，他引：1
Tong LIU ;Chen-yu WANG ;Jian-lin XIAO ;Lan-yu ZHU ;Xue-zhou LI ;Yan-guo QIN ;Zhong-li GAO 《Journal of Zhejiang University. Science. B》2014,15(8):720-726
研究目的:利用三维重建影像模型获取膝外翻角,并通过使用这种方法来测量中国北方成人膝外翻角的平均估计值。创新要点:本研究所获取的膝外翻角平均值对于在中国北方人群进行膝关节置换术时有着重要的参考意义,新的三维重建测量法使得膝外翻角的术前个体化测量更加精确。研究方法:利用64名患者的CT血管造影(CTA)的DICOM数据获取共128件股骨三维重建模型。在重建的股骨模型上分别定位髁间凹最高点(点A)、膝关节线上20 cm截面的髓腔中点(点B)和股骨头旋转中心(点C)。之后膝关节外翻角即由股骨远端解剖轴(线AB)与股骨机械轴(线AC)所围成(上述定位过程详见图5)。经统计分析后,128件股骨的平均外翻角值为6.20°±1.20°。统计分析还发现,膝外翻角与个体年龄呈显著性正相关,同一个体的左右侧外翻角呈显著性正相关。重要结论:在对北方成年人群进行膝关节置换术时,选取外翻角为6°可会在重建人体下肢力线上获得更好的术后效果。在对年长患者进行手术时应选用更大的外翻角。 相似文献
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采用ABAQUS有限元软件建立桩承加筋路基和桩基桥台模型,系统研究桩基桥台－路基－地基的相互作用性状,包括桥台桩基水平位移、桥头路面沉降、桥台桩弯矩等的变化规律,分析深厚软土地基的超孔压固结,并提出若干施工建议。 相似文献
11.
受堆载超载影响下的桩基性状分析研究 总被引：5，自引：0，他引：5
地面大面积堆载超载常常使地基软弱土体产生侧向变形，从而挤压邻近桩基，因而对桩基上部的构筑物不利。将桩体等效成板桩，用梁单元模拟，以一现场试验为依据，章采用平面有限元分析了堆载超载影响下的相邻桩基性状。 相似文献
12.
Yun-feng Liu Russell Wang Dale A. Baur Xian-feng Jiang 《Journal of Zhejiang University. Science. B》2018,19(1):38-48
Objective
To investigate the stress distribution to the mandible, with and without impacted third molars (IM3s) at various orientations, resulting from a 2000-Newton impact force either from the anterior midline or from the body of the mandible.Materials and methods
A 3D mandibular virtual model from a healthy dentate patient was created and the mechanical properties of the mandible were categorized to 9 levels based on the Hounsfield unit measured from computed tomography (CT) images. Von Mises stress distributions to the mandibular angle and condylar areas from static impact forces (Load I-front blow and Load II left blow) were evaluated using finite element analysis (FEA). Six groups with IM3 were included: full horizontal bony, full vertical bony, full 450 mesioangular bony, partial horizontal bony, partial vertical, and partial 450 mesioangular bony impaction, and a baseline group with no third molars.Results
Von Mises stresses in the condyle and angle areas were higher for partially than for fully impacted third molars under both loading conditions, with partial horizontal IM3 showing the highest fracture risk. Stresses were higher on the contralateral than on the ipsilateral side. Under Load II, the angle area had the highest stress for various orientations of IM3s. The condylar region had the highest stress when IM3s were absent.Conclusions
High-impact forces are more likely to cause condylar rather than angular fracture when IM3s are missing. The risk of mandibular fracture is higher for partially than fully impacted third molars, with the angulation of impaction having little effect on facture risk.13.
Ran Cheng Hui Yang Mei-ying Shao Tao Hu Xue-dong Zhou 《Journal of Zhejiang University. Science. B》2009,10(5):395-399
Soft drinks have many potential health problems. The inherent acids and sugars have both acidogenic and cariogenic potential, resulting in dental caries and potential enamel erosion. In this report we present a 25-year-old man complaining with the severe worn-out of the front teeth during the past 3 years. He had a history of drinking cola for more than 7 years and had a poor oral hygiene. Severe decays were present in the incisors and the canines, while less severe lesions were noted on the premolars and the molars. The review is to show the relationship between dental erosion and caries and soft drinks. Some efforts have been taken to reduce the harmful effect of soft drinks. 相似文献
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用不同浓度的亚硒酸钠（se^4 ），分别处理洋葱根尖，结果表明随浓度的增加和染毒时间的延长，有丝分裂指数逐渐下降，且在此过程中还出现微核、染色体滞后、染色体桥等畸变现象。 相似文献
15.
为了提高篮球投篮的准确性,提出基于粒子滤波的篮球旋转投射最优角度分析计算方法。构建篮球旋转投射的动力学和运动学模型,结合动态差分模型进行篮球旋转投射的基元轨迹方程建模,采用最大似然估计方法进行篮球旋转投射最优角度的优化计算,并采用自适应的轨迹修正方法进行篮球旋转投射过程中的力学控制,实现篮球旋转投射最优角度分析。仿真结果表明,采用该方法进行篮球旋转投射最优角度计算的准确度较高,运动力学控制能力较好,具有较好的角度修正和轨迹跟踪能力,在篮球旋转投射运动学建模中具有很好的应用价值。 相似文献
16.
以四川雅泸高速公路干海子特大桥为工程背景,采用Midas Civil有限元软件建立三跨一联钢管混凝土格构式高墩连续弯梁桥结构。进行E1弹性地震响应分析,探讨了该类新型梁桥结构的动力特性、内力分布规律,以及地震波激励角度参数对全桥各个指标的影响规律,研究结果表明:钢管混凝土格构式高墩连续弯梁桥结构刚度较柔、周期长,不可忽视弯扭耦合效应。上部主梁弯矩值控制截面位于固定支座位置处,扭矩峰值出现在梁端位置处;下部格构墩弯矩和轴力控制截面均出现在固底墩墩底,墩顶为桥墩位移控制截面。支座中心连线和与之垂直的方向均为最不利激励角度。 相似文献
17.
Zhen-zhen Peng Xin-min Chen Jun Wang Ai-jie Li Zu-jie Xu 《Journal of Zhejiang University. Science. B》2013,14(6):526-532
Objective
This study investigated the effect of proximal contact strength on the three-dimensional displacements of cantilever fixed partial denture (CFPD) under vertically concentrated loading with digital laser speckle (DLS) technique.Methods
Fresh mandible of beagle dog was used to establish the implant-supported CFPD for specimen. DLS technique was employed for measuring the three-dimensional displacement of the prosthesis under vertically concentrated loading ranging from 200 to 3 000 g. The effect of the contact tightness on the displacement of CFPD was investigated by means of changing the contact tightness.Results
When an axial concentrated loading was exerted on the pontic of the implant-supported CFPD, the displacement of the CFPD was the greatest. The displacement of the prosthesis decreased with the increase of contact strength. When the contact strength was 0, 0.95, and 3.25 N, the displacement of the buccolingual direction was smaller than that of the mesiodistal direction but greater than that of the occlusogingival direction. When the force on the contact area was 6.50 N, the mesiodistal displacement of the prosthesis was the biggest while the buccolingual displacement was the smallest.Conclusions
The implant-supported CFPD is an effective therapy for fully or partially edentulous patients. The restoration of the contact area and the selection of the appropriate contact strength can reduce the displacement of the CFPD, and get a better stress distribution. The most appropriate force value is 3.25 N in this study. 相似文献18.
Motion of a tiny tool thrown by an astronaut inside a spinning space vehicle in a state of free fall
S N Maitra 《Resonance》2007,12(4):80-84
One of two astronauts, while conducting an experiment inside a spinning space vehicle in a state of free fall neglecting all
gravitational effects, throws a tiny tool at the other with a velocity perpendicular to its axis of rotation. Considering
the motion of the tool with respect to the rotating frame rigidly fixed to the vehicle, we can obtain the position of the
tool at a subsequent time by use of rotational kinematics and geometry without involving the concepts of coriolis and centripetal
forces. 相似文献
19.
李秀云 《石家庄铁路工程职业技术学院学报》2014,(1):53-57
四川雅砻江卡拉至杨房沟水电站交通专用公路洪水沟大桥由于地形限制,在桥墩施工时,施工便道无法修至各桥墩处。要在比桥墩承台高96 m的0#桥台附近开挖施工平台,安装混凝土拌和设备,采取特殊措施将混凝土输送到桥墩附近的施工平台,再用高压混凝土输送泵泵送混凝土到桥墩上。项目采用混凝土输送泵结合缓冲溜管,成功解决混凝土垂直向下、水平、向上输送问题,保证工程质量,加快施工进度。该技术对其他类似工程具有借鉴作用。 相似文献
20.
黄国凯 《福建工程学院学报》2019,(3):242-246
以某主跨85m钢管混凝土拱桥为研究对象,采用ANSYS建立局部精细化模型,对拱座进行受力分析。研究表明:拱梁组合体系拱桥拱座的结构刚度比较大,在拱脚最大弯矩工况下,最大变形出现在哑铃型拱肋加载截面下缘,变形值仅为4.3mm;拱座整体应力分析表明,结构受力以纵桥向受压为主,整体应力值不大,拱肋与拱座节点交界面因刚度突变出现了较大的应力变化,存在不大于1MPa的主拉应力;除了端横梁预应力锚固处压应力在10MPa左右,其他部位应力绝对值均在1MPa以下,满足要求;为了进一步优化结构受力,避免局部应力集中,应在结构中增加加腋、倒角等。 相似文献