Constellations matched to the Rayleigh fading channel

We introduce a new technique for designing signal sets matched to the Rayleigh fading channel, In particular, we look for n-dimensional (n⩾2) lattices whose structure provides nth-order diversity. Our approach is based on a geometric formulation of the design problem which in turn can be solved by using a number-geometric approach. Specifically, a suitable upper bound on the pairwise error probability makes the design problem tantamount to the determination of what is called a critical lattice of the body S={x=(x₁, ···, x_n)∈Rⁿ, |Π_i=1ⁿx_i|⩽1}. The lattices among which we search for an optimal solution are the standard embeddings in R ⁿ of the number ring of some totally real number field of degree n over Q. Simulation results confirm that this approach yields lattices with considerable coding gains     

Hydraulic Conductivity of Soil Sorptive Zones Created by In Situ Injection of a Cationic Surfactant

The sorptive capabilities of soils for organic contaminants can be greatly enhanced by treatment with cationic surfactants, and this has been suggested as a potential in situ approach for contaminant plume management. The hydraulic properties of soils modified by injection of hexadecyltrimethylammonium (HDTMA) were investigated using soil columns and a fixed-ring consolidometer. Oshtemo soil (87% sand, 10.5% clay, 2.5% silt) under two different effective stresses, was equilibrated with 1?mM NaCl and treated by recirculation of two different HDTMA soil concentrations, one above and one below the cation exchange capacity. No statistically significant changes in hydraulic conductivity occurred as a result of HDTMA treatment at any of the experimental conditions studied. These results suggest that sorptive zones created in situ with HDTMA may be hydraulically feasible.