PIXE detection limits for dental enamel from some human teeth by excitation with protons and He ions from a 3 MeV Van der Graaff accelerator

A technique has been developed to measure elemental content in human teeth using H⁺ and ⁴He²⁺ ion beam analysis. Teeth of Oradea inhabitants were sampled in two stomatological clinics in Oradea in the period of 2004 and 2005 years. Tooth samples were irradiated in vacuum with 2 MeV proton and 3 MeV alpha beams from a Van der Graaff electrostatic accelerator of EG-5 experimental facility in FLNP, JINR. The particle induced X-ray emission (PIXE) analysis, apart from determination of Ca, allowed an optimised detection of Cr, Cu, Fe and Zn above the detection limits by the use of Al and Mylar filters. The detection limits for K_α X-rays using proton and alpha beams are determined and discussed.     

预压层叠式钻齿型孕镶金刚石钻头的研制

分析了高品质钻头的应用需求,指明了高品质钻头的研究方向。设计了一种层叠式结构钻齿,采用预冷压工艺进行压制后,再经过装模热压烧结的新型孕镶金刚石钻头。给出了此类钻头的原材料选择和制作工艺参数,分析了钻探试验结果。结果表明：预压层叠式钻齿型孕镶金刚石钻头,有利于改善钻进条件,提高钻进效率,有效地实现钻头制造过程中节能降耗,是一种广谱性应用前景的孕镶金刚石钻头新型式。     

Lead contents in the surface enamel of primary and permanent teeth, whole blood, serum, and saliva of 6- to 8-year-old children

This study aimed to evaluate associations of Pb-enamel values determined in two successive enamel microbiopsies taken from a primary and a permanent tooth, and to assess how Pb-enamel correlates with Pb-blood and Pb-serum as well as whole (Pb-whole-saliva), submandibular/sublingual (Pb-sub-saliva) and parotid saliva (Pb-parotid-saliva). The study population included 444 children aged 6 to 8 years attending 4 government schools in the district of Campos Eliseos, in Ribeirao Preto, Sao Paulo State, Brazil. Whole blood, serum, parotid, submandibular/sublingual (“sub-saliva”), and whole saliva were collected in trace element-free tubes. Two successive microbiopsies were taken from the surface of a primary and a permanent tooth of each child. Lead concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS). There was a significant correlation between primary and permanent teeth in terms of Pb-enamel, for both the first and the second microbiopsies. When the median Pb-enamel values were compared between the two genders using only the highest 10th percentile Pb-enamel, there was a significant difference between girls and boys for both primary (474.2 vs 910.0 μg/g, respectively; p = 0.02) and permanent teeth (739.5 vs 1325 μg/g, respectively; p = 0.04). There were no significant correlations between Pb-enamel and Pb-blood or between Pb-enamel and lead in the 3 different salivas. However, there was a statistically significant correlation between Pb-enamel and Pb-serum when only the highest 10th percentile Pb-enamel was analyzed (r = 0.57 and p = 0.0002 for primary teeth; r = 0.56 and p < 0.0001, for permanent teeth). In conclusion, our findings have demonstrated a significant correlation between Pb-enamel found in primary and permanent teeth, as well as a significant correlation between Pb-serum and lead in primary and permanent tooth enamel. Boys presented higher Pb-enamel than girls. Our study also suggests that Pb-enamel has no correlation with Pb-blood or with lead in the 3 different salivas.     

JM2—14型回柱绞车的改进设计

分析了JM—14型回柱绞车的结构特点,设计出新型少齿差传动的 JHX—14型回柱绞车。JHX—14型回柱绞车具有结构紧凑、重量轻、传 动效率高和或本低等优点,可作为设计及用户选型之参考。     

牙质粘接剂与含Pheny1-P磷化预处理剂结合的功效

α-甲基丙烯酰氧乙基苯基磷酰氯或α－甲基丙烯酰氧乙基苯基磷酸酯（Pheny1-P）是在苯环位置具有取代基团的新功能单体。对于粘接剂的组成，在使用情况下，证明对于牙齿粘接是良好的。牛牙与这些含磷的甲基丙烯酸酯之间已经评价，对于牙本质的粘接强度取决于取代基团，而对珐琅无粘接。     

双圆弧齿轮在离心式压缩机增速箱中的应用

介绍空压站离心式压缩机硬齿面双圆弧齿轮的技改方案以及齿轮副的制造、安装、现场测试。采用新研制的齿轮副，其噪声、振动及运转平稳性较之技改前有显著改善，在生产中应用良好，在行业中具有推广价值。     

链轮齿形数控铣削加工的工艺研究

使用圆柱立铣刀数控铣削加工链轮,采用直角坐标系(直线轴)附加旋转轴的控制方式:应用直线轴控制多段曲线的连接,完成链轮轮齿轨迹的数控加工,使用数控回转工作台完成链轮零件的分齿运动,利用子程序来循环重复上述运动。此加工方式相比二维坐标轴数控加工链轮的控制方式,具有更为理想的加工效果。此加工方式,在保证零件设计基准、装夹定位基准和装配基准重合的基础上,应用子程序,有效地保证了链轮各齿形尺寸精度的一致性;使用旋转坐标控制,有效地保证和降低了了链轮轮齿的分齿误差。在数控铣床上使用普通圆盘工作台,利用暂停指令手动进行链轮齿形分齿运动的做法,更加完善和拓宽了数控技术具体应用的实用性。     

谐波齿轮传动齿面润滑计算的研究

本文将摩擦学理论应用到谐波齿轮传动中,针对谐波齿轮传动的啮合原理、运动关系、载荷分布、柔轮及轮齿受载后产生弹性变形等特点,建立了可行的齿面最小油膜厚度计算公式,为谐波齿轮传动齿面润滑状态的分析奠定了基础。     

Long-term changes of mercury levels in ringed seal (Phoca hispida) from Amundsen Gulf, and beluga (Delphinapterus leucas) from the Beaufort Sea, western Canadian Arctic

Mercury (Hg) concentrations were determined in the canine teeth of ringed seals (Phoca hispida) harvested during the 13th–14th, late 19th and early 21st Centuries in Amundsen Gulf, Northwest Territories, Canada. Most historical and pre-industrial teeth contained undetectable Hg levels (i.e. < 1.0 ng/g DW), whereas samples from 2001–03 contained up to 12 ng/g DW in an age-dependent pattern. Assuming a median [Hg] value in 13th–14th Century teeth of half the detection limit (i.e. 0.5 ng/g DW), geometric means of Hg in modern teeth were 9–17 times those of seals in the 14th Century, equivalent to an anthropogenic input of 89–94% of total Hg in modern seals. These results corroborate a previous study of beluga (Delphinapterus leucas) in the nearby Beaufort Sea. While the seals' trophic position (inferred from δ¹⁵N values) did not change over time, modern δ¹³C values were lower by about 2‰ than in the 14th and 19th Centuries. This could be due to increased dissolution of anthropogenically derived CO₂ in the ocean from the atmosphere, but could also indicate more offshore pelagic feeding by modern seals, which might be a factor in their Hg exposure. New tooth [Hg] data are also presented for the Beaufort Sea beluga, using recently-discovered museum samples collected in 1960/61, which showed that most of the anthropogenic contribution to beluga Hg had already taken effect by 1960 (reaching  75% of total Hg). Taken together, the long-term seal and beluga data indicate that whereas Hg levels in the marine ecosystems of the western Canadian Arctic were probably unchanged from pre-industrial times up to the late 19th Century, there was a significant, many-fold increase in the early to mid-20th Century, but little or no change after about the early 1960s.     

截锥形齿坯渐开线四齿差行星减速器齿轮承载能力的计算

在截锥形齿坯渐开线少齿差行星减速器内啮合传动中,与直齿圆柱齿轮少齿差行星减速器相比,除了都存在齿廓变形使得多对齿同时啮合外,前者由于截锥形可以减小啮合角,便可以降低载荷、提高传动能力.而与此同时,截锥形却产生了齿面和棱线啮合的情况,从而导致应力集中,降低了传动能力.通过有限元对比计算表明,正负相抵并与后者相比,截锥形齿坯渐开线少齿差行星减速器降低了传动能力.