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We review some of the recent development in quantum Monte Carlo (QMC) methods for models of strongly correlated electron systems. QMC is a promising general theoretical tool to study many-body systems, and has been widely applied in areas spanning condensed-matter, high-energy, and nuclear physics. Recent progress has included two new methods, the ground-state and finite-temperature constrained path Monte Carlo methods. These methods significantly improve the capability of numerical approaches to lattice models of correlated electron systems. They allow calculations without any decay of the sign, making possible calculations for large system sizes and low temperatures. The methods are approximate. Benchmark calculations show that accurate results on energy and correlation functions can be obtained. This chapter gives a pedagogical introduction to quantum Monte Carlo, with a focus on the constrained path Monte Carlo methods.
A geometric approach in the design of codebooks for OR frequency-hopping multiple-access (FHMA) channels is developed by treating a signal matrix as a finite set of distinct points. The relationship among the parameters of an interference-free j-distinguishable-point codebook, j>or=1, is established by using coordinate-free arguments. Geometry induced by such a codebook is characterized, and the design of a well-structured j-distinguishable-point codebook is related to a block design problem. It is shown that a well-structured 1-distinguishable-point codebook implies the axiom system of a finite affine plane. >