The dry-type air filter is made of a paper element.

The sample preparation by the filter paper method and the direct determination of major (thulium)and five neighbouring micro-rare earth element impurities in pure thulium oxide by XRF are described.

In this paper, wavelet is used to erase speckle noise in radar PPI, and the principle of morphology is used for building structure element to filter off the speckle noise and clutter.