2,276 research outputs found
Low-temperature hydrogen production and consumption in partially-hydrated peridotites in Oman: implications for stimulated geological hydrogen production
No full textThe Samail Ophiolite in Oman, the largest exposed body of ultramafic rocks at the Earth’s surface, produces a continuous flux of hydrogen through low-temperature water/rock reactions. In turn, the scale of the subsurface microbial biosphere is sufficient to consume much of this hydrogen, except where H2 is delivered to surface seeps via faults. By integrating data from recent investigations into the alteration history of the peridotites, groundwater dynamics, and the serpentinite-hosted microbial communities, we identify feasible subsurface conditions for a pilot demonstration of stimulated geological hydrogen production. A simple technoeconomic analysis shows that the stimulation methods to be used must increase the rate of net hydrogen production at least 10,000-fold compared to the estimated natural rate to economically produce hydrogen from engineered water/rock reactions in the peridotite formations. It may be possible to meet this challenge within the upper 1–2 km, given the projected availability of reactive Fe(II)-bearing phases and the lower drilling costs associated with shallower operations. Achieving ≥10,000-fold increases in the H2 production rate will require a combination of stimuli. It will likely be necessary to increase the density of fracturing in the reaction volume by at least two orders of magnitude. Then, the H2-production rates must also be increased by another two orders of magnitude by increasing the water/rock ratio and modifying the chemistry of the injected fluids to optimize formation of Fe(III)-bearing secondary phases. These fluid modifications must be designed to simultaneously minimize microbial consumption of H2 within the stimulation volume. In contrast, preserving the high potentials for biological H2 consumption in the shallow groundwaters replete with oxidants such as nitrate, sulfate and dissolved inorganic carbon will reduce the potential for any inadvertent leaks of hydrogen to the atmosphere, where it acts as an indirect greenhouse gas
Reductions to the set of random strings: The resource-bounded case
No full textThis paper is motivated by a conjecture that BPP can be characterized in terms of polynomial-time nonadaptive reductions to the set of Kolmogorov-random strings. In this paper we show that an approach laid out in [ADF+13] to settle this conjecture cannot succeed without significant alteration, but that it does bear fruit if we consider time-bounded Kolmogorov complexity instead.
We show that if a set A is reducible in polynomial time to the set of time-t-bounded Kolmogorov-random strings (for all large enough time bounds t), then A is in P/poly, and that if in addition such a reduction exists for any universal Turing machine one uses in the definition of Kolmogorov complexity, then A is in PSPACE.Peer reviewe
Molecular evidence for an active microbial methane cycle in subsurface serpentinite-hosted groundwaters in the Samail Ophiolite, Oman
No full textSerpentinization can generate highly reduced fluids replete with hydrogen (H
2) and methane (CH
4), potent reductants capable of driving microbial methanogenesis and methanotrophy, respectively. However, CH
4 in serpentinized waters is thought to be primarily abiogenic, raising key questions about the relative importance of methanogens and methanotrophs in the production and consumption of CH
4 in these systems. Herein, we apply molecular approaches to examine the functional capability and activity of microbial CH
4 cycling in serpentinization-impacted subsurface waters intersecting multiple rock and water types within the Samail Ophiolite of Oman. Abundant 16S rRNA genes and transcripts affiliated with the methanogenic genus Methanobacterium were recovered from the most alkaline (pH, >10), H
2- and CH
4-rich subsurface waters. Additionally, 16S rRNA genes and transcripts associated with the aerobic methanotrophic genus Methylococcus were detected in wells that spanned varied fluid geochemistry. Metagenomic sequencing yielded genes encoding homologs of proteins involved in the hydrogenotrophic pathway of microbial CH
4 production and in microbial CH
4 oxidation. Transcripts of several key genes encoding methanogenesis/methanotrophy enzymes were identified, predominantly in communities from the most hyperalkaline waters. These results indicate active methanogenic and methanotrophic populations in waters with hyperalkaline pH in the Samail Ophiolite, thereby supporting a role for biological CH
4 cycling in aquifers that undergo low-temperature serpentinization. IMPORTANCE Serpentinization of ultramafic rock can generate conditions favorable for microbial methane (CH
4) cycling, including the abiotic production of hydrogen (H
2) and possibly CH
4. Systems of low-temperature serpentinization are geobiological targets due to their potential to harbor microbial life and ubiquity throughout Earth's history. Biomass in fracture waters collected from the Samail Ophiolite of Oman, a system undergoing modern serpentinization, yielded DNA and RNA signatures indicative of active microbial methanogenesis and methanotrophy. Intriguingly, transcripts for proteins involved in methanogenesis were most abundant in the most highly reacted waters that have hyperalkaline pH and elevated concentrations of H
2 and CH
4. These findings suggest active biological methane cycling in serpentinite-hosted aquifers, even under extreme conditions of high pH and carbon limitation. These observations underscore the potential for microbial activity to influence the isotopic composition of CH
4 in these systems, which is information that could help in identifying biosignatures of microbial activity on other planets.
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Reply to “Methane origin in the Samail ophiolite: Comment on ‘Modern water/rock reactions in Oman hyperalkaline peridotite aquifers and implications for microbial habitability’” [Geochim. Cosmochim. Acta 179 (2016) 217–241]
No full textModern water/rock reactions in Oman hyperalkaline peridotite aquifers and implications for microbial habitability
No full textThe Samail ophiolite in Oman is undergoing modern hydration and carbonation of peridotite and may host a deep subsurface biosphere. Previous investigations of hyperalkaline fluids in Oman have focused on fluids released at surface seeps, which quickly lose their reducing character and precipitate carbonates upon contact with the O2/CO2-rich atmosphere. In this work, geochemical analysis of rocks and fluids from the subsurface provides new insights into the operative reactions in serpentinizing aquifers. Serpentinite rock and hyperalkaline fluids (pH > 10), which exhibit millimolar concentrations of Ca2+, H2 and CH4, as well as variable sulfate and nitrate, were accessed from wells situated in mantle peridotite near Ibra and studied to investigate their aqueous geochemistry, gas concentrations, isotopic signatures, mineralogy, Fe speciation and microbial community composition.The bulk mineralogy of drill cuttings is dominated by olivine, pyroxene, brucite, serpentine and magnetite. At depth, Fe-bearing brucite is commonly intermixed with serpentine, whereas near the surface, olivine and brucite are lost and increased magnetite and serpentine is detected. Micro-Raman spectroscopy reveals at least two distinct generations of serpentine present in drill cuttings recovered from several depths from two wells. Fe K-edge X-ray absorption near-edge spectroscopy (XANES) analysis of the lizardite shows a strong tetrahedral Fe coordination, suggesting a mixture of both Fe(II) and Fe(III) in the serpentine. Magnetite veins are also closely associated with this second generation serpentine, and 2–10 ?m magnetite grains overprint all minerals in the drill cuttings. Thus we propose that the dissolved H2 that accumulates in the subsurface hyperalkaline fluids was evolved through low temperature oxidation and hydration of relict olivine, as well as destabilization of pre-existing brucite present in the partially serpentinized dunites and harzburgites. In particular, we hypothesize that Fe-bearing brucite is currently reacting with dissolved silica in the aquifer fluids to generate late-stage magnetite, additional serpentine and dissolved H2.Dissolved CH4 in the fluids exhibits the most isotopically heavy carbon in CH4 reported in the literature thus far. The CH4 may have formed through abiotic reduction of dissolved CO2 or through biogenic pathways under extreme carbon limitation. The methane isotopic composition may have also been modified by significant methane oxidation. 16S rRNA sequencing of DNA recovered from filtered hyperalkaline well fluids reveals an abundance of Meiothermus, Thermodesulfovibrionaceae (sulfate-reducers) and Clostridia (fermenters). The fluids also contain candidate phyla OP1 and OD1, as well as Methanobacterium (methanogen) and Methylococcus sp. (methanotroph). The composition of these microbial communities suggests that low-temperature hydrogen and methane generation, coupled with the presence of electron acceptors such as nitrate and sulfate, sustains subsurface microbial life within the Oman ophiolite
Series "T" Transporter, Lt8 17725
No full textArtist's rendering of a LeTourneau Series "T" Transporter, used to haul off-road equipment, timber and pipe, according to author Eric Orlemann. Total production for all transporter types and variations was about 25 units
Low‐Temperature Hydrogen Formation During Aqueous Alteration of Serpentinized Peridotite in the Samail Ophiolite
No full textSerpentinized peridotite is reacting with groundwater in the subsurface of the Samail ophiolite in Oman. Although these rocks are partially to completely serpentinized, they interact with a groundwater aquifer containing hyperalkaline fluids rich in H2 and CH4. Since the mechanisms by which H2 production may continue at low temperatures (<50°C) are not fully understood, core recovered during the Oman Drilling Project provides an excellent opportunity to study the mineralogy and Fe speciation in highly serpentinized harzburgite recording multiple stages of water/rock interaction. In Hole BA3A, early hydration of olivine and pyroxene, which likely occurred at temperatures of ∼100°C–200°C, produced serpentine, Fe-rich brucite, awaruite, and little magnetite. Notably, Fe-rich brucite is only preserved at >∼100 m depth in the core. Fe-rich brucite is nearly absent within two near-surface reaction zones where later stages of reaction are recorded, which include replacement of Fe-rich brucite by Fe(III)-bearing serpentine, and increases in the proportion of other Fe(III)-bearing phases such as magnetite and hydroandradite. Thus, Fe-rich brucite at depth represents substantial stored capacity for H2 production that can continue at low temperature, even after primary olivine and pyroxene are exhausted, thereby sustaining habitable conditions for microbial life
Applications of Time-Bounded Kolmogorov Complexity in Complexity Theory
No full text. This paper presents one method of using time-bounded Kolmogorov complexity as a measure of the complexity of sets, and outlines a number of applications of this approach to different questions in complexity theory. Connections will be drawn among the following topics: NE predicates, ranking functions, pseudorandom generators, and hierarchy theorems in circuit complexity. 1 Introduction Complexity theory provides a setting in which one can associate to any recursive set L a function t L on the natural numbers, and with justification claim that t L is a measure of the complexity of L; namely L can be accepted by exactly those machines that run in time\Omega (t L (n)). In this paper, we will consider a means of using time-bounded Kolmogorov complexity to define a function KL , that measures a different aspect of the complexity of L. We will argue that this is a useful measure by presenting a number of applications of this measure to questions in complexity theory. 1.1 Complexity of St..
2015 Kansas Performance Tests with Soybean Varieties
No full textSoybean performance tests are conductd each year to provide information on the relative performance of new and established varieties and brands at several locations in Kansas. Main Station, Manhattan: Jane Lingenfelser, Assistant Agronomist; William T. Schapaugh, Jr., Professor (Senior Author); Brent Christenson, Research Assistant; Cheyenne Stephens, Research Assistant; Research Centers: Patrick Evans, Colby; Lonnie Mengarelli, Parsons; Monty Spangler, Garden City; Josh Coltrain, Crawford County Extension; Experiment Fields: Eric Adee, Topeka; Gary Cramer, Hutchinson; Andrew Esser, Scandia; James Kimball, Ottawa; Cooperators: Vernon Egbert, McCune; Lance Rezac, Onaga; Dale Roberds, Pittsburg; Clayton Short, Assaria
Expanding the Vision for Blueberry Extension
No full textCooperative Extension programs are in a state of flux as new methods of information delivery are adopted by agents, specialists, and clientele. Online methods are crucial tools as the number of Extension specialists with specialization in blueberries shrink. Therefore, increased communications to develop collaborations among Extension personnel should be a priority. The All About Blueberries (AAB) Community of Practice (CoP) launched in 2010 and was motivated by six goals: (1) to improve insect and disease identification; (2) to improve blueberry production efficiency and productivity; (3) to educate about blueberry cultivation; (4) to improve grower profit margins; (5) to hasten adoption of new innovations and technologies; and (6) to improve the safe handling of fresh produce by emphasizing the importance of food safety in the consumer section and harvesting in the grower section. The AAB portal and its 36 contributing authors represent an ideal venue to showcase nationwide blueberry consumer and producer research and educational efforts. The AAB CoP can provide a platform for enhanced and strategic coordination among blueberry Extension specialists nationwide. Better coordination can lead to positive outcomes that result in more recognition of Extension as a critical aspect of the research-to-end user continuum. Pursuing online methods meets clientele needs and strengthens Extension’s reach to all stakeholders and audiences, nationally and internationally. Support and expansion of the blueberry eXtension portal has great potential to be a leader in developing efficient and effective Extension methods to reach existing clientele and new audiences.Paper presented at NABREW Conference, Paper Session II:Blueberry Extension, on June 25, 2014, Atlantic City, N.J
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