Teeth segmentation of dental periapical radiographs based on local singularity analysis

Teeth segmentation for periapical raidographs is one of the most critical tasks for effective periapical lesion or periodontitis detection, as both types of anomalies usually occur around tooth boundaries and dental radiographs are often subject to noise, low contrast, and uneven illumination. In this paper, we propose an effective scheme to segment each tooth in periapical radiographs. The method consists of four stages: image enhancement using adaptive power law transformation, local singularity analysis using Hölder exponent, tooth recognition using Otsu's thresholding and connected component analysis, and tooth delineation using snake boundary tracking and morphological operations. Experimental results of 28 periapical radiographs containing 106 teeth in total and 75 useful for dental examination demonstrate that 105 teeth are successfully isolated and segmented, and the overall mean segmentation accuracy of all 75 useful teeth in terms of (TP, FP) is (0.8959, 0.0093) with standard deviation (0.0737, 0.0096), respectively.     

An effective classification and numbering system for dental bitewing radiographs using teeth region and contour information

We propose a dental classification and numbering system to effectively segment, classify, and number teeth in dental bitewing radiographs. An image enhancement method that combines homomorphic filtering, homogeneity-based contrast stretching, and adaptive morphological transformation is proposed to improve both contrast and illumination evenness of the radiographs simultaneously. Iterative thresholding and integral projection are adapted to isolate teeth to regions of interest (ROIs) followed by contour extraction of the tooth and the pulp (if available) from each ROI. A binary linear support vector machine using the skew-adjusted relative length/width ratios of both teeth and pulps, and crown size as features is proposed to classify each tooth to molar or premolar. Finally, a numbering scheme that combines a missing teeth detection algorithm and a simplified version of sequence alignment commonly used in bioinformatics is presented to assign each tooth a proper number. Experimental results show that our system has accuracy rates of 95.1% and 98.0% for classification and numbering, respectively, in terms of number of teeth tested, and correctly classifies and numbers the teeth in four images that were reported either misclassified or erroneously numbered, respectively.     

关于渐开线标准齿轮最少齿数的分析

通过理论分析，给出了范式法加工渐开线标准齿轮避免根切的最少齿数的一般公式，该公式适用于渐开线齿轮根切、干涉的分析，可作为标准齿轮传动设计中齿数选择和是否采用变位齿轮传动的依据。     

弧齿锥齿轮刮削刀盘工作角度的分析（上）

弧齿锥齿轮刮削刀盘采用了斜角切削，在刮削过程中工作角度发生了变化。这种变化涉及到刮削机理的研究和刮削过程中几何参数的选择。本文对刮削过程中工作角度问题进行了探讨，并对工作刃倾角、工作前角和工作后角进行了具体计算，得到了一些变化规律。     

渐开线标准直齿圆柱齿轮基本参数的一种速定法

针对目前渐开线直齿圆柱齿轮设计中齿数、模数较难初定的问题，提出了一种简便可行的方法。通过采用最小二乘法拟合方式，逐步拟定相应的经验公式。给出了一个实例，并指出了本文方法确定渐开线直齿圆柱齿轮基本参数的特点。     

变圆弧齿轮的形成原理及特性

提出了一类变圆弧齿轮。利用偏差函数法,给出了齿廓的完整构造过程,证明了它满足齿廓啮合基本定律;推导了齿廓方程等基本公式,讨论了变圆弧齿轮的特性,给出了变圆弧齿廓的实例;这种齿轮具有较高的承载能力,特别便于高速、高精度数控加工,它将在重载传动场合得到应用。     

偏心轮推杆行星传动内齿圈齿廓修形的研究

提出了偏心轮推杆行星传动内齿圈齿廓修形的原则和修形方法;分别建立了齿廓分段修形的齿廓中段、齿顶段和齿根段的修形增量函数,证明了修形后的齿廓在连接点处具有连续且光滑的特性.建立了修形后同时参与啮合的活齿数计算公式,讨论了齿廓修形基本参数的确定方法及步骤,给出了偏心轮推杆行星传动内齿圈齿廓修形的实例.试验研究表明,齿廓修形后,传动的性能得到了明显改善.     

Nanohybrid scratch resistant coatings for teeth and bone viscoelasticity manifested in tribology

We cover teeth surfaces with nanohybrid coatings containing an inorganic ceramic and an organic copolymer constituents. We report the first ever values of scratch penetration depth and scratch recovery for bare and coated teeth. We find that uncoated teeth undergo viscoelastic recovery (healing) after microscratching – the first manifestation of bone viscoelasticity in tribology. The coatings fill "valleys" in teeth surfaces. In each case a large improvement in the scratch resistance as compared to uncoated teeth is seen. The extent of the improvement depends on the inorganic/organic component ratios in the nanohybrids. Electronic Publication     

渐开线齿轮传动润滑效应的理论分析

建立了渐开线直齿轮传动模型,通过对于中、重载两种不同的载荷进行50余组热弹流润滑数值计算,分析了润滑油黏度与齿面卷吸速度的乘积对齿轮传动接触疲劳寿命的影响。研究结果表明:在齿面卷吸速度固定的情况下,改变润滑油黏度,二次压力峰在中载和重载的工况下都是单调增大的;其X的位置也都单调减小,即向入口区方向移动;次表面剪应力最大值在中载时先减小,再增大,而重载时却单调减小;次表面剪应力最大值的X的位置中载时向出口方向移动,Z位置逐渐向轮齿的表层移动;当重载时X方向是逐渐向出口区移动的,在Z方向是恒定在轮齿固体内部的。     

少齿差行星齿轮齿根弯曲应力计算方法研究

少齿差齿轮副在啮合时由于轮齿受载产生变形可能引发多对齿同时接触承载的情况[1],啮合齿对实际承担的载荷将下降。少齿差齿轮副啮合时存在多对齿同时接触承载的现象,且由于内外齿轮齿廓的凹凸曲率非常接近,啮合时齿面接触面积较大,接触力为分布力,在计算齿根弯曲应力时不宜按集中力处理,这些情况使得准确计算少齿差齿轮副的齿根弯曲应力变得复杂。现以大量有限元计算分析为基础,综合考虑多对齿同时接触承载这一情况,建立了适用于少齿差齿轮副齿根弯曲应力的计算方法,并进行了实验验证。