Dynamics of precipitation pattern formation at geothermal hot springs

We formulate and model the dynamics of spatial patterns arising during the precipitation of calcium carbonate from a supersaturated shallow water flow. The model describes the formation of travertine deposits at geothermal hot springs and rimstone dams of calcite in caves. We find explicit solutions for travertine domes at low flow rates, identify the linear instabilities which generate dam and pond formation on sloped substrates, and present simulations of statistical landscape evolution

Metagenomes from High-Temperature Chemotrophic Systems Reveal Geochemical Controls on Microbial Community Structure and Function

The Yellowstone caldera contains the most numerous and diverse geothermal systems on Earth, yielding an extensive array of unique high-temperature environments that host a variety of deeply-rooted and understudied Archaea, Bacteria and Eukarya. The combination of extreme temperature and chemical conditions encountered in geothermal environments often results in considerably less microbial diversity than other terrestrial habitats and offers a tremendous opportunity for studying the structure and function of indigenous microbial communities and for establishing linkages between putative metabolisms and element cycling. Metagenome sequence (14–15,000 Sanger reads per site) was obtained for five high-temperature (>65°C) chemotrophic microbial communities sampled from geothermal springs (or pools) in Yellowstone National Park (YNP) that exhibit a wide range in geochemistry including pH, dissolved sulfide, dissolved oxygen and ferrous iron. Metagenome data revealed significant differences in the predominant phyla associated with each of these geochemical environments. Novel members of the Sulfolobales are dominant in low pH environments, while other Crenarchaeota including distantly-related Thermoproteales and Desulfurococcales populations dominate in suboxic sulfidic sediments. Several novel archaeal groups are well represented in an acidic (pH 3) Fe-oxyhydroxide mat, where a higher O2 influx is accompanied with an increase in archaeal diversity. The presence or absence of genes and pathways important in S oxidation-reduction, H2-oxidation, and aerobic respiration (terminal oxidation) provide insight regarding the metabolic strategies of indigenous organisms present in geothermal systems. Multiple-pathway and protein-specific functional analysis of metagenome sequence data corroborated results from phylogenetic analyses and clearly demonstrate major differences in metabolic potential across sites. The distribution of functional genes involved in electron transport is consistent with the hypothesis that geochemical parameters (e.g., pH, sulfide, Fe, O2) control microbial community structure and function in YNP geothermal springs

Metagenome sequence analysis of filamentous microbial communities obtained from geochemically distinct geothermal channels reveals specialization of three aquificales lineages.

The Aquificales are thermophilic microorganisms that inhabit hydrothermal systems worldwide and are considered one of the earliest lineages of the domain Bacteria. We analyzed metagenome sequence obtained from six thermal ‘filamentous streamer’ communities (~40 Mbp per site), which targeted three different groups of Aquificales found in Yellowstone National Park (YNP). Unassembled metagenome sequence and PCR-amplified 16S rRNA gene libraries revealed that acidic, sulfidic sites were dominated by Hydrogenobaculum (Aquificaceae) populations, whereas the circumneutral pH (6.5 - 7.8) sites containing dissolved sulfide were dominated by Sulfurihydrogenibium spp. (Hydrogenothermaceae). Thermocrinis (Aquificaceae) populations were found primarily in the circumneutral sites with undetectable sulfide, and to a lesser extent in one sulfidic system at pH 8. Phylogenetic analysis of assembled sequence containing 16S rRNA genes as well as conserved protein-encoding genes revealed that the composition and function of these communities varied across geochemical conditions. Each Aquificales lineage contained genes for CO2 fixation by the reverse TCA cycle, but only the Sulfurihydrogenibium populations perform citrate cleavage using ATP citrate lyase (Acl). The Aquificaceae populations use an alternative pathway catalyzed by two separate enzymes, citryl CoA synthetase (Ccs) and citryl CoA lyase (Ccl). All three Aquificales lineages contained evidence of aerobic respiration, albeit due to completely different types of heme Cu oxidases (subunit I) involved in oxygen reduction. The distribution of Aquificales populations and differences among functional genes involved in energy generation and electron transport is consistent with the hypothesis that geochemical parameters (e.g., pH, sulfide, H2, O2) have resulted in niche specialization among members of the Aquificales

Glioma imaging in Europe: A survey of 220 centres and recommendations for best clinical practice

Objectives: At a European Society of Neuroradiology (ESNR) Annual Meeting 2015 workshop, commonalities in practice, current controversies and technical hurdles in glioma MRI were discussed. We aimed to formulate guidance on MRI of glioma and determine its feasibility, by seeking information on glioma imaging practices from the European Neuroradiology community. Methods: Invitations to a structured survey were emailed to ESNR members (n=1,662) and associates (n=6,400), European national radiologists’ societies and distributed via social media. Results: Responses were received from 220 institutions (59% academic). Conventional imaging protocols generally include T2w, T2-FLAIR, DWI, and pre- and post-contrast T1w. Perfusion MRI is used widely (85.5%), while spectroscopy seems reserved for specific indications. Reasons for omitting advanced imaging modalities include lack of facility/software, time constraints and no requests. Early postoperative MRI is routinely carried out by 74% within 24–72 h, but only 17% report a percent measure of resection. For follow-up, most sites (60%) issue qualitative reports, while 27% report an assessment according to the RANO criteria. A minori

Ordered hierarchy versus scale invariance in sequence stratigraphy

200 x 10(6) years) are symmetrical transgressive- regressive cycles. However, the sequence record in the range of 1 x 10(4)-200 x 10(6) years, the principal domain of sequence stratigraphy, shows a rather irregular succession of sequences with variable symmetry and bounded by flooding surfaces or exposure surfaces. For these time scales, scale-invariant models are a good first approximation, particularly because the evidence for scale-invariance and randomness in the stratigraphic record is strong: Frequency spectra of sea-level change as well as rates of sedimentation and rates of accommodation change plotted against length of observation span show basic trends indistinguishable from random walk. These trends, combined with scale-invariant sequence models may be the most efficient tools for across-the-board predictions on sequences and for locating islands of order in the sequence record

Hydraulic evaluation of the design and operation of ancient Rome's Anio Novus aqueduct: hydraulic evaluation of ancient Rome's Anio Novus aqueduct

This paper evaluates conveyance and flow characteristics for the Anio Novus, the aqueduct bringing water from the greatest distance to ancient Rome. Travertine accumulations, deposited from water on floor and walls, were used to reconstruct the flow rate and associated spatial and temporal variations. Hydraulic quantities (e.g., flow depth and velocity) markedly varied over the course of the aqueduct, implying that constraints such as topography and construction techniques were combined with hydraulic considerations to determine the aqueduct layout. Design practices differed along the aqueduct and channel size design was not based exclusively on anticipated carrying capacity, tending towards larger-than-necessary design based on experience

The Role of Calcining and Basal Fluidization in the Long Runout of Carbonate Slides: An Example ftom the Herat Mountain Slide Block, Wyoming and Montana, U.S.A

In order to understand the movement of large rock masses or allochthons on low-angle surfaces, we have studied the 3400-km2 Heart Mountain slide block of northwestern Wyoming and southwestern Montana. The Heart Mountain slide block was initiated on a 2 gradient, with its toe thrust a minimum of 45 km across an early Eocene landscape. The slide block moved on a basal layer that ranges in thickness from a few tens of centimeters to several meters. This basal layer commonly has a concrete-like appearance of rounded, mixed-lithology grains in a fine-grained carbonate matrix, and in some locations it has features similar to sedimentary deposits, including both normal and inverse grading, flow banding, turbidite-like structures, and clastic dikes containing pieces of carbonized wood. Nowhere did we observe crosscutting relationships in the basal layer or overlying clastic dikes, as would be expected from incremental or noncatastrophic emplacement. Results from cathodoluminescence and d18O, d13C, and 87Sr/86Sr isotopic compositions from the basal layer support a single movement event followed by hydrothermal and meteoric fluids percolating through a permeable basal layer. These observations suggest that a catastrophic movement on the detachment resulted in frictional heating at the base of the slide. When the generated heat was at least 800C, calcining of carbonates occurred, yielding calcium and magnesium oxide powders and carbon dioxide gas. The calcium oxide powder became mechanically fluidized by the pressurized carbon dioxide gas, leading to a reduced coefficient of friction at the base of the slide, which in turn permitted the long runout on such a low-angle surface. This mechanism might be applied to explain a wide range of catastrophic sliding events where carbonate rocks are involved