9 research outputs found
The microbial ferrous wheel in a neutral pH groundwater seep
Evidence for microbial Fe redox cycling was documented in a circumneutral pH ground-water seep near Bloomington, Indiana. Geochemical and microbiological analyses were conducted at two sites, a semi-consolidated microbial mat and a floating puffball structure. In situ voltammetric microelectrode measurements revealed steep opposing gradients of o2 and Fe(I I) at both sites, similar to other groundwater seep and sedimentary environments known to support microbial Fe redox cycling. The puffball structure showed an abrupt increase in dissolved Fed I) just at its surface (~5cm depth), suggesting an internal Fe(I I) source coupled to active Fed 1I) reduction. Most probable number enumerations detected microaerophilic Fe(II)-oxidizing bacteria (FeoB) and dissimilatory Fe(III)-reducing bacteria (FeRB) at densities of 102 to 105 cells ml_~1 in samples from both sites. In vitro Fed 1I) reduction experiments revealed the potential for immediate reduction (no lag period) of native Fe(III) oxides. Conventional full-length 16S rRNA gene clone libraries were compared with high throughput barcode sequencing of theV1, V4, orV6 variable regions of 16S rRNA genes in order to evaluate the extent to which new sequencing approaches could provide enhanced insight into the composition of Fe redox cycling microbial community structure. The composition of the clone libraries suggested a lithotroph-dominated microbial community centered around taxa related to known FeoB (e.g., Gallionella, Sideroxydans, Aquabacterium). Sequences related to recognized FeRB (e.g., Rhodoferax, Aeromonas, Geobacter, Desulfovibrio) were also well-represented. overall, sequences related to known FeoB and FeRB accounted for 88 and 59% of total clone sequences in the mat and puffball libraries, respectively. Taxa identified in the barcode libraries showed partial overlap with the clone libraries, but were not always consistent across different variable regions and sequencing platforms. However, the barcode libraries provided confirmation of key clone library results (e.g., the predominance of Betaproteobacteria) and an expanded view of lithotrophic microbial community composition
Transverse ultrafast laser inscription in bulk silicon
In-volume ultrafast laser direct writing of silicon is generally limited by
strong nonlinear propagation effects preventing the initiation of
modifications. By employing a triple-optimization procedure in the spectral,
temporal and spatial domains, we demonstrate that modifications can be
repeatably produced inside silicon. Our approach relies on irradiation at
-m wavelength with temporally-distorted femtosecond pulses.
These pulses are focused in a way that spherical aberrations of different
origins counterbalance, as predicted by point spread function analyses and in
good agreement with nonlinear propagation simulations. We also establish the
laws governing modification growth on a pulse-to-pulse basis, which allows us
to demonstrate transverse inscription inside silicon with various line
morphologies depending on the irradiation conditions. We finally show that the
production of single-pulse repeatable modifications is a necessary condition
for reliable transverse inscription inside silicon.Comment: 13 pages, 12 figure