Event-triggered recording

In principle, the recorded sequence could be triggered with the stimulation event and accumulated. However, in practice there are is a strong variation in the data due to heart beat [197, 502] and respiration. The response of the brain to the stimulation can more reliably be separated from other effects by recording the full sequence over a large number of stimulation events. To record a virtually unlimited sequence the TCSPC channels are operated in the continuous flow mode (see Fig. 3.9, page 36). 

With regard to the data acquisition system (DAS), there are two main problems concerning the A/D conversion and the triggering. Fast A/D units have to be used to ensure that a large number of events are recorded -usually there are A/D converters for each channel of the recording unit. Anti-aliasing (low pass) filters are required so that the signal can be properly transformed to the frequency domain by means of Shannon s Theorem (Rikitake et al. 1987). 

After all four positive scans are completed (typically within 3 s), the polarity is switched and the fifth scan event records a negative-ion full-scan MS. If the expected protonated molecule is not detected in the positive mode, the second, third and fourth scan events are skipped and the fifth (negative-ion-mode) scan event is triggered. Similar to the positive-ion mode, if the expected [M-H]- ion is detected in the full-scan MS, IT data-dependent MS/MS (sixth), FT accurate MS (seventh), and FT MS/MS (eighth) scan events are acquired. Clearly demonstrated here is the ability of the LTQ-FT to handle multiple experiments on a chromatographic time scale. One might question the need for such an elaborate data-dependent scheme when apparently all that is needed is an accurate mass determination followed by a data-dependent accurate mass MS/MS spectmm. Apart from the fact that using the... 

For example, audit trails may be implemented by using database triggers. A trigger is a feature of the Oracle database, which allows code written by the user to be executed based on an event. The concept implies that the edition of a record will produce an event. The event may be defined as an insert, update, or deletion of data from a database table. 

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