  The spatially anisotropic triangular antiferromagnet is investigated with the
numerical diagonalization method. As the anisotropy varies, the model changes
into a variety of systems such as the one-dimensional, triangular, and
square-lattice antiferromagnets. Taking into account such a geometrical
character, we impose the screw-boundary condition, which interpolates smoothly
the one- and two-dimensional lattice structures. Diagonalizing the finite
clusters with N=16,20,...,32 spins, we observe an intermediate phase between
the VBS and Neel phases. Suppressing the intermediate phase by applying the
ring exchange, we realize a direct VBS-Neel transition. The simulation data
indicate that the transition is a continuous one with the correlation-length
critical exponent \nu=0.80(15). These features are in agreement with the
deconfinement-criticality scenario advocated by Senthil and coworkers in the
context of the high-temperature superconductivity.
