Biofi lms living on gold (Au) grains play a key role in the biogeochemical cycle of Au by promoting the dispersion of Au via the formation of Au nanoparticles as well as the formation of secondary biomorphic Au. Gold grains from Queensland, Australia, are covered by a polymorphic, organic-inorganic layer that is up to 40 µm thick. It consists of a bacterial biofi lm containing Au nanoparticles associated with extracellular polymeric substances as well as bacterioform Au. Focused ion beam (FIB) sectioning through the biofi lm revealed that aggregates of nanoparticulate Au line open spaces beneath the active biofi lm layer. These aggregates (bacterioform Au type 1) resulted from the reprecipitation of dissolved Au, and their internal growth structures provide direct evidence for coarsening of the Au grains. At the contact between the polymorphic layer and the primary Au, bacterioform Au type 2 is present. It consists of solid rounded forms into which crystal boundaries of underlying primary Au extend, and is the result of dealloying and Ag dissolution from the primary Au. This study demonstrates that (1) microbially driven dissolution, precipitation, and aggregation lead to the formation of bacterioform Au and contribute to the growth of Au grains under supergene conditions, and (2) the microbially driven mobilization of coarse Au into nanoparticles plays a key role in mediating the mobility of Au in surface environments, because the release of nanoparticulate Au upon biofi lm disintegration greatly enhances environmental mobility compared to Au complexes only.

The first electromagnetic metamaterials (EM3) produced by microfabrication are reported. They are based on the rod-split-ring-resonator design as proposed by Pendry et al. [IEEE Trans. Microwave Theory Tech. 47, 2075 (1999)] and experimentally confirmed by Smith et al. [Phys. Rev. Lett. 84, 4184 (2000)] in the GHz frequency range. Numerical simulation and experimental results from far infrared (FIR) transmission spectroscopy support the conclusion that the microfabricated composite material is EM3 in the range 1-2.7 THz. This extends the frequency range in which EM3 are available by about 3 orders of magnitude well into the FIR, thereby widely opening up opportunities to verify the unusual physical implications on electromagnetic theory as well as to build novel electromagnetic and optical devices.

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The angular asymmetry parameter β fl of the photon-induced fluorescence radiation of Ar + (4p-4s) fine-structure resolved satellite lines was measured from threshold up to 38.4 eV. It is well known that the cross sections of these valence shell satellites are dominated by the decay of aligned doubly excited states leading to an extremely complicated energy dependence. In contrast, we observe that the β fl parameter becomes less structured with increasing total angular momentum J of the photoion. The β fl measurements can be interpreted by a partialwave analysis of the photofragmentation products. For the population of the 4p 2 F 7/2 ion state only d 5/2 photoelectrons are emitted on all resonances. For the population of the 4p 2 D 5/2 and the 4p 4 P 5/2 ion states the emission of the parity-unfavoured d 5/2 photoelectrons dominates.

The absolute cross sections for the 3s-photoionization and the 3p-photoionization of the Ar atom and the Ar-like ions K+ and Ca2+ are calculated. The calculation is performed within the configuration-interaction technique using the Pauli-Fock atomic orbitals. The simultaneous analysis of the calculated and measured total and partial cross sections yields the interpretation of the prominent resonances observed in a recent experiment on Ar above the 3s-threshold.

Articles you may be interested inLaser induced fluorescence measurements of microwave stimulated OH molecules from H2O photodissociation Lymanα, Lymanα coincidence detection in the photodissociation of doubly excited molecular hydrogen into two H(2p) atoms J. Chem. Phys. 88, 3016 (1988); 10.1063/1.453943 H Lymanα emission from photodissociation of H2OThe polarization of the Lyman-␣ fluorescence following photodissociation of H 2 and D 2 into fragments in the 1s and 2l states has been determined as a function of the excess energy of the fragments. The predicted oscillations of the polarization as a function of excess energy were clearly observed. In addition, the theoretical polarization was recalculated including the stronger B -BЈ coupling scheme as well as collisional effects on the polarization. The collisional effects include the quenching processes for H(2s) and H(2p) and disaligning collisions. The calculations reproduced the experimental data quite well giving a cross section for the disaligning collisions of ͑1.0Ϯ0.2͒•10 Ϫ14 cm 2 for H 2 and D 2 at a gas temperature of 137 K in the relative velocity range of 2 to 7 km s Ϫ1 . This can be considered as a proof of the theoretical predictions on the interference effects between the continua excited coherently.

The alignment of Kr II 4p 4 5p (EJ ) states after the Auger decay of the Kr I 3d 9 5/2 5p (J = 1) resonance was measured using photon-induced fluorescence spectroscopy (PIFS) and the alignment parameters A 20 were calculated within the stepwise decay model. Using the same wavefunctions, the angular distribution parameters of the Auger electrons were also calculated. Good agreement with the measured A 20 value and with published experimental and calculated values for β Aug is obtained.