A comparison between the diffusivity of gases in soil cores and in soil aggregates

Gas diffusivity was measured in duplicate soil cores (10 cm long and 6 cm diameter) from depths of 0–10, 10–20 and 20–30 cm, and in beds of 1–2 mm aggregates taken from the same site at the same depths. A steady state method was used, with ethane as the diffusing gas. As the samples dried, the fractional air-filled pore space increased, from 0. 1 to 0.45 for the cores and from 0.35 to 0.65 for the aggregates. The maximum relative diffusivity of the aggregate samples (0.38) was approximately twice that of the core samples, reflecting the difference in pore space. Equations are presented for calculating the solid, air and water fractions of the samples and for calculating the diffusivity within peds and aggregates. These calculations allowed a comparison of the diffusion/porosity relationship within aggregates and peds.     

Synthesis of Novel Thin-Film Materials by Pulsed Laser Deposition

Pulsed laser deposition (PLD) is a conceptually and experimentally simple yet highly versatile tool for thin-film and multilayer research. Its advantages for the film growth of oxides and other chemically complex materials include stoichiometric transfer, growth from an energetic beam, reactive deposition, and inherent simplicity for the growth of multilayered structures. With the use of PLD, artificially layered materials and metastable phases have been created and their properties varied by control of the layer thicknesses. In situ monitoring techniques have provided information about the role of energetic species in the formation of ultrahard phases and in the doping of semiconductors. Cluster-assembled nanocrystalline and composite films offer opportunities to control and produce new combinations of properties with PLD.