Dilution Effects on Two-Dimensional Heisenberg Antiferromagnets with Non-Magnetic Spin-Gapped Ground State

Dilution effects on spin-1/2 quantum Heisenberg antiferromagnets with a non-magnetic spin-gapped ground state are studied by means of the qunatum Monte Carlo simulation. In the site-diluted system, an antiferromagnetic long-range order (AF-LRO) is induced at an infinitesimal concentration of dilution due to an effective coupling $\tilde{J}_{mn}$ between induced magnetic moments. In the bond-diluted case, on the other hand, the AF-LRO is not induced up to a certain concentration of dilution due to singlet pairs reformed by an AF coupling $\tilde{J}_{\rm af}$ between the edge spins of the diluted bond through the two-dimensional shortest paths. The competition between $\tilde{J}_{mn}$ and $\tilde{J}_{\rm af}$ yields peculiar phenomena in the bond-diluted system.Comment: 6 pages, 3 figures. to appear in Prog. Theor. Phys. Supp

Ground state of antiferromagnetic Heisenberg two-leg ladder in terms of the valence-bond solid picture

We have proposed the plaquette-singlet solid (PSS) ground state for the spin-1 antiferromagnetic Heisenberg two-leg ladder. Based on the PSS picture, we discuss the correspondence of the PSS state to the valence-bond solid (VBS) state of the ground state of spin-2 chain by introducing an appropriate composite spin picture. When the bond alternation is introduced, there occur quantum phase transitions and each phase can be identified with that in the dimerized spin-2 chain. Furthermore, we argue that the VBS picture of spin-2S chain can be applied to the ground state of spin-S two-leg ladder.Comment: 2 pages, 1 eps figure, Proceedings for LT23; Proper citation added, Author list change

Bond-Dilution Effects on Two-Dimensional Spin-Gapped Heisenberg Antiferromagnets

Bond-dilution effects on spin-1/2 spin-gapped Heisenberg antiferromagnets of coupled alternating chains on a square lattice are investigated by means of the quantum Monte Carlo method. It is found that, in contrast with the site-diluted system having an infinitesimal critical concentration, the bond-diluted system has a finite critical concentration of diluted bonds, $x_{c}$, above which the system is in an antiferromagnetic (AF) long-range ordered phase. In the disordered phase below $x_{c}$, plausibly in the concentration region significantly less than $x_{c}$, the system has a spin gap due to singlet pairs of induced magnetic moments reformed by the AF interactions through the two-dimensional shortest paths.Comment: 4 pages, 4 figure

Development of Real Time Storm Surge Forecasting Using Artificial Neural Network

Information Management and Decision Support System

Analysis of Climate Change Effects on Seawall Reliability

Crown heights of seawalls should be designed to suppress overtopping discharge to a permissible level. The permissible level is determined from viewpoints of the structure types of coastal seawalls and hinterland use. It is usually difficult to design the crown heights of seawalls, especially in the present time where climate change due to global warming is expected. This study analyzes climate change effects such as sea level rise (SLR) and increase of waves and surges on the failure probability of seawalls under various conditions of crown height, toe depth and slope by using a Level III reliability analysis. It was found that the difference of SLR trends (fast, medium or low) has less impact on overtopping rates than the differences in wave height change for a seawall at a target location