deletions | additions       diff --git a/Concepts.tex b/Concepts.tex  index d4382eb..55f765a 100644  --- a/Concepts.tex  +++ b/Concepts.tex 
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The recorded stream of timestamps is the result of two processes: one characterized  by a high count rate, due to fluorescence photons of single molecules crossing the  excitation volume, and another characterized by a lower count rate, due to “background  counts” "background  counts"  originating from detector dark counts, afterpulsing, out-of-focus molecules and sample scattering and/or impurities~\cite{Gopich_2008}.  % Gopich provides a theoretical expression for out-of-focus counts, but ignores scattering, impurities, dcr and afterpulsing (which you do not mention). For this reason, I would rather cite an original experimental paper going back to the early FCS works (dealing with exactly the same issues.   The signature of these two types of processes can be 
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Experimentally, we found that when the background is not constant,  it usually varies  on time scales of tens of seconds (see figure~\ref{fig:bg_timetrace}).  FRETBursts divides the data set acquisition  in constant duration constant-duration  time windows called \textit{background periods} and computes the background rates for  each of these windows (see section~\ref{sec:bg_calc}).  Note that FRETBursts uses the same definitions of constant these local  background period windows rates also  during burst search, in order to compute time-dependent burst detection thresholds   and for background correction of burst data (see section~\ref{sec:burstsearch}).