The nonlinear optical properties of a ͑InP͒ 2 /͑GaP͒ 2 bilayer superlattice structure have been examined with linearly polarized cathodoluminescence spectroscopy. Transmission electron microscopy showed a composition modulation with a period of ϳ800 Å along the ͓110͔ direction, which occurs spontaneously during the growth, resulting in coherently strained quantum wires. The strong excitation dependence of the polarization anisotropy and energy of excitonic luminescence from the quantum wires was found to be consistent with a band-filling model that is based on a k-p and two-dimensional quantum confinement calculation. ͓S0163-1829͑96͒51516-X͔ Nonlinear optical properties of III-V semiconductor nanostructures have attracted a great deal of interest, as they are important for applications in optical communications that involve switching, amplification, and signal processing. An important nonlinear optical property is the change in the emission of light ͑in energy, polarization, and intensity͒ that results from phase-space filling of carriers in one-and twodimensionally confined systems, i.e., quantum wells and wires. 1,2 This property is analogous to the Burstein-Moss band filling which occurs in bulk semiconductors and raises the energy of the unoccupied electron and hole states as the excitation intensity increases. As the dimensionality of the quantum confinement increases from one dimension ͑1D͒ to 2D, the narrowing of the density of states ͑DOS͒ will exhibit a lower excitation threshold for phase-space filling, thereby yielding potentially enhanced nonlinear optical effects. Recently, quantum wires have been fabricated by a straininduced lateral ordering ͑SILO͒ process which occurs spontaneously when (GaP) n /(InP) n and (GaAs) n /(InAs) n shortperiod superlattices are grown on GaAs͑001͒ and InP͑001͒, respectively. 3-7 Previous studies involving transmission electron microscopy ͑TEM͒ and optical measurements such as photoluminescence, electroluminescence, and photoreflectance have shown evidence supporting the existence of quantum wires due to quantum confinement along both the growth direction and the composition modulation direction. 5-8 However, the nature of phase-space filling and the concomitant influence on the polarization properties in these systems have yet to be investigated thoroughly. In this study, we examine the nonlinear optical properties of a ͑InP͒ 2 /͑GaP͒ 2 bilayer superlattice ͑BSL͒ structure using a linearly polarized cathodoluminescence ͑LPCL͒ technique. We demonstrate the existence of an interesting excitation-and temperature-dependent polarization anisotropy in luminescence coming from the SILO quantum wires. A theoretical simulation of the band-filling, luminescence energy shifts and polarization anisotropy changes was performed for the SILO quantum wires using a k-p band-structure calculation, which takes the coherency strain and 2D quantum confine-ment into account, and is compared with the experimental results. Evidence for these strong nonlinear optical effects is a cornerstone in ...

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The eastern woodchuck, Marmota monax, represents a useful animal model to study hepatitis B virus infection in humans. However, immunological studies in this model have been impeded by a lack of basic information about the components of the immune system such as cytokines and chemokines. To clarify the role(s) of interleukin 8 (IL-8) in chronic hepatitis B and hepatocellular carcinoma (HCC) in the woodchuck model, we cloned and characterized the woodchuck IL-8 cDNA and genomic DNA. Sequence analysis revealed that the organization of the wk-IL-8 gene is similar to that of the human IL-8 gene and consists of four exons and three introns. Woodchuck IL-8 protein exhibits the conserved ELRCXC motif of IL-8 and shows 87, 82, 82 and 79% similarity with rabbit, ovine, bovine and human IL-8 proteins, respectively. The biological activity of wk-IL-8 was demonstrated using neutrophil chemotaxis assays. Wk-IL-8 could be readily detected in both tumor and non-tumor tissues with higher expression in the non-tumor tissues in most cases. The results from this study will facilitate the investigation of IL-8 in the immunopathogenesis of hepadnavirus-related diseases by the woodchuck model.