The determination of the relative permittivity of periodic stratified media based on the iterative time-reversal method

In this paper, we present a new method to determine the relative permittivity of periodic stratified media using the iterative time-reversal method. Based on transmission line theory, the focal peak value of iterative time-reversal electro- magnetic waves, which contain information about the periodic stratified medium, is computed in pulse-echo mode. Using the relationship between the focal peak value and the relative permittivity of the periodic stratified medium, the relative permittivity can be obtained by measuring the focal peak value. Numerical simulations are conducted, and the results demonstrate the feasibility of the proposed approach to the measurement of the relative permittivity of a periodic stratified medium.     

负载CeO_2的活化粉煤灰的制备及对酸性红B的脱色

采用H2SO4对粉煤灰进行活化处理,再经液相沉淀法负载CeO2,制得活化粉煤灰/CeO2复合材料.EDS分析结果证实了活化粉煤灰/CeO2复合材料的形成.利用活化粉煤灰/CeO2复合材料对酸性红B模拟染料废水进行脱色处理,研究了各种反应条件对脱色效果的影响,并对脱色机理进行了探讨.实验结果表明:粉煤灰经质量分数为50%的H2SO4活化后,1g活化粉煤灰负载CeO20.25g,焙烧温度为500℃,投加灰量为10g/L,搅拌反应120min,对于初始质量浓度为20mg/L,pH=1的酸性红B模拟废水,在日光照射下脱色率达93.2%,在紫外光照射下脱色率可达97.5%.说明活化粉煤灰/CeO2复合材料对染料废水有很好的脱色效果,在造纸废水、纺织印染废水的处理上有良好的应用前景.     

重视老年人口腔保健

人口老龄化现象在我国已成为日益突出问年人口腔保健工作势在必行。随着年龄的增长，口腔组织器官逐渐产生退行性变化，一些带有老年人特征的口腔疾病，如根面龋、磨损、牙周病、口腔粘膜病、牙列缺损、缺失等病症，时常影响老年人的正常生活，应特别引起重视，并注意以下预防保健方法：