Goldbach数的例外集合

我们把能表成二个奇素数之和的偶数称为Goldbach数,以E(x)记作不超过x的非Goldbach数的数目,本文证明了E(x)=O(x^9.99).     

An investigation of the spatial resolution requirements for two-point correlation measurements using LDV

The spatial resolution requirements for accurate two-point correlation measurements at small separations are investigated. Practical guidelines in terms of characteristic measuring volume sizes and estimated Kolmogorov length scales are given. Sample measurements of two-point one-component longitudinal correlations on the centerline of a turbulent jet are presented.Financial support from NUTEK, the Swedish National Board for Industrial and Technical Development, is acknowledged.     

Gamma-gamma directional correlation measurements in192Os

E2/M1 mixing ratios of transitions in¹⁹²Os have been determined by the gammagamma directional correlation technique. The results are: δ(484.5 keV)= ?10±1, δ(283.3 keV)= ?3.8± 0.7 and δ(201.3 keV)= ?4.6±1.     

高压覆膜制样X射线荧光光谱法测定土壤和水系沉积物中的氯研究

氯是化探样品分析中的重要元素,而X射线荧光光谱法是测定卤族元素的重要技术手段.已有研究表明,X射线荧光光谱法在测定氯时,同一样片中氯的测定值随重复测定次数的增加而逐渐增大或减小.采用高压覆膜制样技术制片,测定土壤和水系沉积物中的氯,氯(24～40000μg·g-1)校准曲线的相关系数明显改善,RM S(均方根)由未贴膜...     

Structure and properties of niobium-doped potassium titanyl phosphate crystals

A series of potassium titanyl phosphate crystals, KTiOPO₄, with various concentrations of niobium dopant has been grown, and some of their physical properties and structural characteristics have been studied. The incorporation of a small amount of niobium results in considerable changes in the electrical conductivity of KTP: Nb crystals and the temperature of the ferroelectric phase transition. Thus, the presence of 3–4 at. % of niobium results in an increase of conductivity by more than an order of magnitude, whereas T _C decreases from 930 to 620°C. The X-ray diffraction study of the crystals has been performed at room temperature; the neutron diffraction analysis was made at temperatures of 20, 330, and 730°C. It was revealed that two crystallographically independent positions are statistically (by 90%) occupied by potassium cations, which results in the concentration of potassium atoms in the structure higher than it was expected from the condition of preservation of crystal electroneutrality. At high niobium concentrations, the monoclinic compound of the composition K₂TiNb₂P₂O₃ is formed.     

CVD样品台旋转对沉积金刚石涂层的影响

以CH3COCH3和H2为反应气源,利用热丝化学气相沉积(HFCVD)方法,通过改变样品台的旋转频率在YG6硬质合金(WC-6wt; Co)基体上沉积金刚石涂层.利用X射线衍射分析YG6硬质合金表面沉积金刚石涂层物相,通过扫描电子显微镜和压痕试验机分析金刚石涂层的表面形貌、沉积厚度和膜基结合性能,考察了样品台旋转频率对沉积金刚石涂层结构与性能的影响,以确定最佳的样品台旋转频率.结果 表明,在固定沉积工艺参数条件下,当样品台的旋转频率为2次/h时,在YG6硬质合金基体上沉积的金刚石涂层具有较优的晶粒和更均匀致密的聚晶结构以及更高的膜-基结合力.