Flat Low-Loss Silicon Gradient Index Lens for Millimeter and Submillimeter Wavelengths

We present the design, simulation, and planned fabrication process of a flat high resistivity silicon gradient index (GRIN) lens for millimeter and submillimeter wavelengths with very low absorption losses. The gradient index is created by sub wavelength holes whose size increases with the radius of the lens. The effective refractive index created by the subwavelength holes is constant over a very wide bandwidth, allowing the fabrication of achromatic lenses up to submillimeter wavelengths. The designed GRIN lens was successfully simulated and shows an expected efficiency better than that of a classic silicon plano-concave spherical lens with approximately the same thickness and focal length. Deep reactive ion etching (DRIE) and wafer-bonding of several patterned wafers will be used to realize our first GRIN lens prototype

Early Agriculture in the Maya Lowlands

Wetland research in northern Belize provides the earliest evidence for development of agriculture in the Maya Lowlands. Pollen data confirm the introduction of maize and manioc before 3000 B.C. Dramatic deforestation, beginning ca. 2500 B.C. and intensifying in wetland environments ca. 1500-1300 B.C., marks an expansion of agriculture, which occurred in the context of a mixed foraging economy. By 1000 B.C. a rise in groundwater levels led farmers to construct drainage ditches coeval with the emergence of Maya complex society ca. 1000-400 B.C. Field manipulations often involved minor modifications of natural hummocks. Canal systems are not as extensive in northern Belize as previously reported, nor is there evidence of artificially raised planting platforms. By the Classic period, wetland fields were flooded and mostly abandoned