面向制造的弧齿圆柱齿轮建模及强度分析

在分析弧齿圆柱齿轮加工原理和数学建模的基础上,提出一种面向制造的弧齿圆柱齿轮建模新方法,解决长期以来弧齿圆柱齿轮3维造型和实际加工不一致的问题,保证后续分析、加工等工序的正确性。基于UG的二次开发,采用齿坯滚动进给、刀具旋转切削的方法,实现面向制造的弧齿圆柱齿轮的3维造型和快速原型制造,在此基础上深入分析刀具半径对弧齿圆柱齿轮的接触应力分布的影响,得出不同曲率下齿轮强度的变化规律。有限元分析结果表明同等条件下弧齿圆柱齿轮的接触强度较直齿轮有显著提高,其最大齿根应力仅为直齿圆柱齿轮的27%,弧齿圆柱齿轮齿根应力与弧齿线半径有明显的关系。此方法为弧齿圆柱齿轮在高速重载等工况下的工业应用提供理论依据和工程应用价值。     

儿童牙釉质中自由基含量与照射剂量的关系

本文用电子自旋共振（ＥＳＲ）技术,对２５个儿童恒牙和３５个乳牙釉质样品中的自由基含量进行了测定,研究了牙釉质中自由基含量与辐射剂量的关系。在２５个儿童恒牙样品中,有１２个男性样品,１３个女性样品;在３５个乳牙样品中,有２０个男性样品,１５个女性样品。将恒牙和乳牙各分成４和５个剂量组,用＾６０Ｃｏγ射线照射各组样品,剂量率为０．４８Ｇｙ／ｍｉｎ,各组累积剂量分别为０．３０（只对乳牙）、０．５０、１．     

Fiber optic displacement sensor for imaging of tooth surface roughness

A simple and inexpensive method using fiber optic displacement sensor is proposed for measurements of tooth surface roughness based on the intensity modulation technique. A light beam was launched onto a tooth surface via a bundled fiber. The reflected light from the surface was collected and measured as a function of lateral distance to estimate the roughness of the surface. The system’s roughness measurement capability was successfully tested on teeth surfaces of varying surface texture. In the measurement, the average surface roughness, R_a for the canine, molar, hybrid composite resin and artificial teeth surfaces were estimated to be approximately 121, 62.6, 39 and 37.6 μm, respectively. The experimental results indicated the capability of implementation of the displacement sensor for the imaging of the tooth surface profile as well as a micron-size roughness estimator with a measurement error of less than 2.35%.     

Strontium in 19th century Australian children''s teeth

The enamel of teeth from 57 children, who died in the mid to late 1800s, were analysed to investigate strontium (Sr) concentrations in historic teeth. Teeth were analysed using proton induced X-ray emission at the Australian Nuclear Science and Technology Organisation (ANSTO). Where available, multiple teeth were analysed for each individual including permanent (molars and premolars) and deciduous teeth (molars). Preliminary results show that Sr does not appear to be affected by the postmortem environment. Sr levels in permanent molars strongly correlate with levels in the premolars but not with the deciduous molars. Concerns are raised over the large variation seen in Sr levels and the effect it would have on the interpretation of Sr levels in studies with small sample sizes.     

基于VFP的计算机辅助机床齿轮变速组的齿数确定

对计算机辅助机床齿轮变速组的齿数确定方法做出了讨论；采用VISUAL FOXPRO编制计算机程序,解决了机床传动系统变速组齿轮齿数的计算机辅助确定问题;建立了计算机辅助机床传动系统设计中的一个重要模块;以实例说明计算机辅助齿轮齿数的确定过程,得到更为高效的设计过程.     

用图表法设计齿轮传动

介绍一种设计齿轮传动的图表法,利用这种方法,能够在同时满足最小传动中心距和最大承载能力的条件下,直接确定齿轮传动的模数和齿数。     

Teeth as biomonitors of selenium concentrations in tissues of beluga whales (Delphinapterus leucas)

Selenium (Se) is an essential element which has been shown to play an important role in protecting marine mammals against the toxic effects of mercury (Hg) and other metals. It has been suggested that metal concentration in marine mammal teeth can potentially be used as bioindicators for body burden. The objective of this study was to investigate the relationship between Se concentrations in beluga (Delphinapterus leucas) teeth and those previously measured in soft tissues (liver, kidney, muscle and muktuk). Tooth Hg concentrations are also measured, and the relationships between Se and Hg in teeth and soft tissues are examined. Se in the teeth of beluga was measured using hydride generation atomic fluorescence spectrometry (HG-AFS) and Hg in beluga teeth was measured by cold-vapour atomic absorption. Tooth Se concentrations ranged from 108 ng/g to 245 ng/g dry weight, and tooth Hg concentrations ranged from 10 to 189 ng/g dry weight. In the soft tissues, Se concentrations were highest in the liver, followed by kidney, muktuk, and muscle. There were significant correlations between tooth Se concentrations and animal age, tooth Se and liver and muscle Se, and between liver Se and animal age. The molar ratio of Hg:Se in the liver was found to be 0.70. This study is the first to measure Se in the teeth of a marine mammal species, and HG-AFS is found to be an effective technique for determining Se in beluga teeth. Tooth Se can be used as predictor for liver and muscle Se, although these relationships may be strongly influenced by the association of Se with Hg in marine mammal tissues. This study contributes to an increased understanding of the storage and metabolism of Se in marine mammals.     

An evaluation of teeth of ringed seals (Phoca hispida) from Greenland as a matrix to monitor spatial and temporal trends of mercury and stable isotopes

Total mercury (Hg) concentrations were measured in teeth of ringed seals from Qeqertarsuaq, central West Greenland (1982 to 2006) and Ittoqqortoormiit, central East Greenland (1986 to 2006). Stable isotopic ratios of carbon (¹³C/¹²C) and nitrogen (¹⁵N/¹⁴N) were determined as well to provide insights into diet variations between regions or through time. Mercury concentrations decreased the first years of life of the animals suggesting that Hg had been transferred from the mother to the foetus and newborn. The Hg concentrations in teeth were significantly lesser in ringed seals from central West Greenland compared to those from central East Greenland. Carbon and nitrogen stable isotopic values measured in the animals differed also significantly between the two regions. Increasing temporal trends of dental Hg concentrations between 1994 and 2006 were observed in ringed seals from both central West Greenland and central East Greenland. These increases were attributed to global changes in environmental Hg levels since no temporal trends in δ¹⁵N values were found to support the hypothesis of a diet shift over time. Furthermore, a decreasing temporal trend in δ¹³C values was observed in the teeth of seals from central East Greenland, and explained by a likely change over time towards more pelagic feeding habits; alternatively, the so-known Seuss effect was thought to be responsible for this decrease. Finally, it was concluded that the tooth of ringed seal was a good monitoring tissue to assess Hg trends.     

Recognition and segmentation of teeth and mandibular nerve canals in panoramic dental X-rays by Mask RCNN

This study proposes a method based on the instance segmentation algorithm Mask RCNN for recognizing and segmenting 32 teeth and 2 mandibular nerve canals in panoramic dental X-rays. Compared with Faster RCNN, Mask RCNN has an additional semantic segmentation branch, which could directly obtain the position of teeth and the information about mandibular nerve canals in this study. At the same time, Mask RCNN introduces ROI Align, making Mask segmentation more accurate. A total of 120 training sets, 40 validation sets, and 120 test sets were used in the training and testing process. Forty of the test sets were used to test the full-tooth panoramic dental X-rays, and 40 were used for the edentulous panoramic dental X-rays, with 40 for the mandibular canals. The average precision, recall, and F1-score values of the full teeth were 96.59 %, 96.4 %, and 96.5 %, respectively. The P_m value of the defined edentulous panoramic dental X-rays was 95.41 %, and the average precision, recall, and F1-score values of mandibular canals were 76.05 %, 83.70 %, and 78.10 %, respectively. The results showed that the algorithm could effectively identify each tooth, including missing teeth and mandibular nerve canals in panoramic dental X-rays, solving the problem of too many oral structures in panoramic dental X-rays, which makes it difficult to determine the overall oral state. This study will help other researchers promote the research on artificial intelligence-assisted diagnosis in the oral field.