A signal can be detected based on a level slice system and detection delay time can be reduced by setting the recording density of a header field in a linear direction lower than that of a user data recording field. The method relies on elevated levels of the ratio of A40A42 associated with lipoproteins in the cerebrospinal fluid of individuals at risk as compared to this ratio in the overall population. Such metal nanowires are useful for electronics applications. Preferably, the determined time is towards the end of the flush cycle.