Additional error is introduced by freezing artifacts, which are difficult to avoid, and non-specific background signal.

The four-wave mixing processes (which provide the unwanted background signal), however, don't interfere with each other.

There is therefore always a background signal present in the chromatogram.

Both these factors lead to a high background fluorescent signal from these membrane slides.

However, occasionally there occur extremely large lightning flashes which produce distinctive signatures that stand out from the background signals.

The sections reacted with the sense probe served as a control for non-specific background signal.

As the bar goes up, more and more of the dashed curve (which represents expected background signals) will fall below it.

The background signal, or noise, was one of the links in this complex relationship.

Due to the multiphoton absorption the background signal is strongly suppressed.

In this way, it resembles "noise", the background signal that pervades every instrument used for astronomy.