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FCS captures fluctuations of the fluorescence due to the motion of single
molecules. Thus, it is necessary to process a large number of data points to ob-
tain a statistically sound simulation of the underlying dynamical process. These
numerical experiments are computing demanding: the motion of each molecule
(data point) must be followed, and the interaction with other molecules (i.e.
reactions) must be solved in every simulated time step.
High Performance Computing (HPC) techniques come to play a key role to
process the needed amount of data points during sucient time steps to cap-
ture the biological process. Using HPC for treating reaction diffusion systems is
presented in previous works like [14,15,16], but the implementation of a specific
application for fluorescence fluctuation analysis based on a volunteer comput-
ing platform is novel at the best of our knowledge. Moreover, the techniques
described in this paper allows the simultaneous analysis of several experiments,
considerably increasing the capability of generation and validation of the pro-
posed models for complex biological phenomena.
In this line of work, the main contribution of the research reported in this arti-
cle is the use of a volunteer computing system to support the ecient execution
of the cases to perform FCS measurements analysis in a realistic scenario.
The article is organized as follows. Section 2 describes the numerical tech-
niques and computing tools to simulate the biological processes. Section 3 intro-
duces the main concepts about distributed computing on volunteer grid/cloud
infrastructures.
The approach using HPC techniques for solving the problem is presented in
Section 4, just before reporting the experimental analysis in Section 5. Section 6
summarizes the main conclusions and lines for future work.
2 Fluorescence Correlation Spectroscopy and Tools
This section describes FCS techniques and the computing tools used to simulate
the underlying biological processes.
2.1 Fluorescence Correlation Spectroscopy
FCS is a well-known technique applied to obtain quantitative information re-
garding the motion of molecules in living cells. It is based on the analysis of
intensity fluctuations caused by fluorescence-labeled molecules moving through
the small detection volume of a confocal or two-photon excitation microscope.
Fig.1showsaschemaofanexperiment: some molecules emit photons when
they are under the observation volume defined by the laser beam. The photon
emission is a stochastic process, its probability is related to the relative position
of the molecule and the beam center, which is the most probable position, while
the probability diminishes when moving out (see Eq. 1),
ˉ
xy
and
ˉ
z
are the radial
and axial waists of the point spread function. Standard values are:
ˉ
xy
=0
.
2
μm
and
ˉ
z
=1
μm
.
g
(
x, y, z
)=exp
−
2(
x
2
+
y
2
)
ˉ
xy
2
z
2
ˉ
z
+
−
(1)
