The object is to enable cipher communication even when a cipher key in a one-time pad cipher is running short. The present invention also provides for determining a drug metabolite level of a subject during therapy and measuring periodically the drug metabolite level of a subject on maintenance therapy to ensure treatment compliance and continued therapeutic response by measuring minimal clinical important differences in the drug metabolite levels. A second image feature vector conversion device converts an images-to-be-retrieved feature vector into a second image feature vector for use in a similarity computation according to the similarity computation image feature vector configuration information. One embodiment of a method for forming the write pole includes depositing non-magnetic gap material on the write pole and trailing step. The method to prepare low reflective surface can provide a low reflective surface structure that can be applied to photovoltaic device surface or various display surface as a surface able to reduce reflection significantly by absorbing wavelengths in the range of visible and infrared ray through internally total reflection with simple, low cost, and ecofriendly process.