Dental survey at school with the purpose to select children with no actual need of dental treatment

The purpose of this study was to develop an examination method to select children without from children with need of dental treatment. Furthermore the objective was that these examinations could be performed as a survey at school, without utilizing an expensive and fully equipped dental clinic but still maintain the certainty for the individual not to be at increased risk to be declared false caries-free, in comparison with ordinary examination at a dental clinic. The material comprised 88 children 10-13 years old. The children were subject to a survey-examination at school and a few weeks later at a dental clinic by the same examiner. Initially the children were examined at school by two examiners in order to measure the inter-examiner variability. The results showed that 2 of the 88 examined children (2.3%) were judged false healthy at school examination with respect to caries. The inter-examiner variability in diagnosing caries was greater than the intra-examiner variability between survey at school and examination at the dental clinic.     

石英砂的塑性机理研究

研究了石英砂的塑性并对其进行改善,得出石英砂颗粒大小、砖坯含水率、砖坯p H值和增塑剂含量对砖坯塑性的影响规律及机理,并且为利用石英砂而采用可塑成型去制备高性能的烧结砖探索出了合适的成型工艺条件:球磨时间24h、含水率为29%、坯料p H=9和增塑剂含量为5%。     

高速机床进给系统的发展趋势

在明确了高速加工对机床进给进给系统要求的基础上，比较和分析了滚珠丝杠、直线电机和并联虚拟轴机构等三种高速进给系统的性能、特点、存在问题及其解决办法，指出了它们各自的适用范围和应用前景。     

高速机床电主轴过盈配合量的计算

电主轴是高速机床的核心部件,电机转子与机床主轴间过盈配合量的大小是影响主轴性能的重要因素。本文根据材料力学和弹性力学理论,对电主轴的配合特性进行了分析,分别推导出电主轴在静态和高速运转条件下,主轴过盈量和应力分布的理论公式。最后,根据理论公式计算出ＧＤ－Ⅱ型电主轴的过盈配合量,研究结果表明,采用理论公式设计的过盈配合能较好地满足高速电主轴的需要。     

基于Pandora 观测的OMI 全球臭氧产品精度验证

臭氧是大气中一种重要的微量气体, 是影响对流层与平流层大气运动的重要成分之一, 臭氧的高精度探测 对于环境和气候具有重要的意义。OMI 传感器是目前具备探测全球臭氧含量的主要遥感传感器之一。利用地基 Pandora 观测网全球范围内44 个臭氧观测站点数据对OMI 卫星数据产品进行了精度验证。结果表明: OMI 臭氧产品 与Pandora 地基测量结果之间具有很好的线性相关性, 相关系数达到0.948, 但精度结果存在区域差异。在南半球地区, 相关系数为0.915; 在北半球低纬度地区, 其相关系数为0.932, 中纬度地区相关系数为0.948, 而在高纬度地区, 相关系 数达到了0.957。此外, 验证精度还与臭氧柱总量存在相关性, 在臭氧柱总量低于220 Du (对应臭氧空洞条件) 时, OMI 卫星产品存在高估现象, 高估约13%; 而在臭氧柱总量高于400 Du 时, OMI 的臭氧产品低于Pandora 地基测量结果, 且 随着臭氧柱总量增加, 低估情况也越严重, 在臭氧柱总量达到500 Du 时, OMI 臭氧产品低估约4%。     

超声冲击诱发表面纳米化及其对表面完整性的影响

采用不同超声冲击参数处理SMA490BW钢,研究了冲击后试样在低、高倍下的微观组织特征、残余应力及硬度分布等表面完整性能的变化。实验结果表明,经过超声冲击表面处理后,样品表面层晶粒细化为纳米晶,平均晶粒尺寸约为30nm;并在试样表层引入残余压应力,数值最大约为255.5MPa;超声冲击对SMA490BW钢表面能够起到明显的强化作用,与未经处理的试样相比,处理后试样表面硬度最大提高了约66.7%。超声冲击强化处理改善SMA490BW钢的表面完整性的效果与冲击电流、冲击时间之间的关系不遵循单调变化规律,超声冲击参数为20min/1.5A时,试样具有较好的表面完整性,冲击影响层深度约为320μm。     

超声冲击对高速列车转向架焊接十字接头超高周疲劳性能的影响

针对高速列车转向架在实际运用中出现的疲劳问题,利用HJ-Ⅲ型超声冲击处理装置,对高速列车转向架用SAM490BW钢十字接头焊趾进行超声冲击处理,并对处理后接头的超高周疲劳性能进行研究。结果表明,原始焊态试样和超声冲击态试样的S-N曲线均出现了传统意义上的水平段。超声冲击处理试样的疲劳强度相比于未处理试样提高了25%。经过超声冲击处理后,疲劳裂纹源的数量由多个变为单个,焊接接头焊趾处的应力集中系数下降了32.4%,降低了裂纹萌生概率;超声冲击降低了焊趾区域的残余拉应力,并诱发产生残余压应力,高达-255.5 MPa;焊趾表层晶粒得到细化,晶粒平均尺寸小于100nm;裂纹在塑性变形区扩展路径变长。     

The lactulose breath hydrogen test and small intestinal bacterial overgrowth

OBJECTIVES: To i) document the sensitivity and specificity of a combined scintigraphic/lactulose breath hydrogen test for small intestinal bacterial overgrowth and ii) investigate the validity of currently accepted definitions of an abnormal lactulose breath hydrogen test based on "double peaks" in breath hydrogen concentrations. METHODS: Twenty-eight subjects were investigated with culture of proximal small intestinal aspirate and a 10-g lactulose breath hydrogen test combined with scintigraphy. Gastroduodenal pH, the presence or absence of gastric bacterial overgrowth, and the in vitro capability of overgrowth flora to ferment lactulose were determined. RESULTS: Sensitivity (16.7%) and specificity (70.0%) of the lactulose breath hydrogen test alone for small intestinal bacterial overgrowth were poor. Combination with scintigraphy resulted in 100% specificity, because double peaks in serial breath hydrogen concentrations may occur as a result of lactulose fermentation by cecal bacteria. Sensitivity increased to 38.9% with scintigraphy, because a single rise in breath hydrogen concentrations, commencing before the test meal reaches the cecum, may occur in this disorder. Sensitivity remained suboptimal irrespective of the definition of small intestinal bacterial overgrowth used, the nature of the overgrowth flora, favorable luminal pH, the presence of concurrent gastric bacterial overgrowth, or the in vitro ability of the overgrowth flora to ferment lactulose. CONCLUSIONS: Definitions of an abnormal lactulose breath hydrogen test based on the occurrence of double peaks in breath hydrogen concentrations are inappropriate. Not even the addition of scintigraphy renders this test a clinically useful alternative to culture of aspirate for diagnosing small intestinal bacterial overgrowth.     

增强战斗力的有效途径:虚拟战争

在军事领域中,随着军事斗争的复杂性的不断增加,人们一直在寻求一种能在实验条件下“预先实践战争”的方法,来深入地研究未来战争的规律。现代科学技术的飞速发展,使得人们这一愿望得以实现。在虚拟现实技术基础上发展起来的“虚拟战争”方法,正是研究增强军队战斗力的有效途径。本文对这一课题作了概要的阐述。     

新铌酸盐化合物K4CuNb8O23及其Cu^2＋与Nb^5＋的类质同象代换

1986年Wanklyn等曾报道存在化合物K_5Cu_2Nb_(11)O_(31),并给出其X射线粉晶谱线,但未见进一步指标化和确定其所属晶系及晶胞参数的报道。本研究表明,存在一种新铌酸盐晶体K_4CuNb_8O_(23),其成分及X射线谱异于K_5Cu_2Nb_(11)O_(31)。 用分析纯K_2CO_3、Nb_2O_5及CuSO_4·5H_O按一定比例配制并于1100—1300℃间烧成,