  Using the theory of diffusion in graphs, we propose a model to study
mesoscopic transport through a diffusive quantum dot. The graph consists of
three quasi-1D regions: a central region describing the dot, and two identical
left- and right- wires connected to leads, which mimic contacts of a real
system. We find the exact solution of the diffusion equation for this graph and
evaluate the conductance including quantum corrections. Our model is
complementary to the RMT-models describing quantum dots. Firstly, it reproduces
the universal limit at zero temperature. But the main advantage compared to
RMT-models is that it allows one to take into account interaction-induced
dephasing at finite temperatures. Besides, the crossovers from open to almost
closed quantum dots and between different regimes of dephasing can be described
within a single framework. We present results for the temperature dependence of
the weak localization correction to the conductance for the experimentally
relevant parameter range and discuss the possibility to observe the elusive
0D-regime of dephasing in different mesoscopic systems.
