  Heat conduction phenomena are studied theoretically using computer
simulation. The systems are crystal with nonlinear interaction, and fluid of
hard-core particles. Quasi-one-dimensional system of the size of $L_x\times
L_y\times L_z(L_z\gg L_x,L_y)$ is simulated. Heat baths are put in both end:
one has higher temperature than the other. In the crystal case, the interaction
potential $V$ has fourth-order non-linear term in addition to the harmonic
term, and Nose-Hoover method is used for the heat baths. In the fluid case,
stochastic boundary condition is charged, which works as the heat baths.
Fourier-type heat conduction is reproduced both in crystal and fluid models in
three-dimensional system, but it is not observed in lower dimensional system.
Autocorrelation function of heat flux is also observed and long-time tails of
the form of $\sim t^{-d/2}$, where $d$ denotes the dimensionality of the
system, are confirmed.
