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Contents of this presentation include: Advanced Subsonic Technology (AST) goals and general information; Nozzle nomenclature; Nozzle schematics; Photograph of all baselines; Configurations tests and types of data acquired; and Engine cycle and plug geometry impact on EPNL.
This work studied the feasibility of using Helmholtz resonator cavities embedded in low-pressure-turbine (LPT) airfoils to (1) reduce core noise by damping acoustic modes; (2) use the synthetic jets produced by the liner hole acoustic oscillations to improve engine efficiency by maintaining turbulent attached flow in the LPT at low-Reynolds-number cruise conditions; and (3) reduce engine nitrogen oxide emissions by lining the internal cavities with materials capable of catalytic conversion. Flat plates with embedded Helmholtz resonators, designed to resonate at either 3000 or at 400 Hz, were simulated using computational fluid dynamics. The simulations were conducted for two inlet Mach numbers, 0.25 and 0.5, corresponding to Reynolds numbers of 90 000 and 164 000 based on the effective chordwise distance to the resonator orifice. The results of this study are (1) the region of acoustic treatment may be large enough to have a benefit; (2) the jets may not possess sufficient strength to reduce flow separation (based on prior work by researchers in the flow control area); and (3) the additional catalytic surface area is not exposed to a high velocity, so it probably does not have any benefit.
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Abstract Clay minerals impart important chemical properties to soils, in part, by virtue of changes in the redox state of Fe in their crystal structures. Therefore, measurement of Fe(III)/Fe(II) and partitioning of Fe(II) in different reactive sites in clay minerals (during biological and chemical Fe(III) reduction) is essential to understand their role and their relative reactivity in terms of reduction and immobilization of heavy metal contaminants such as technetium. This study had three objectives: (1) to understand the degree of dissolution of nontronite (Fe-rich smectite) as a result of chemical and biological reduction of Fe(III) in the structure; (2) to quantify partitioning of chemically and biologically produced Fe(II) into different reactive sites in reduced nontronite, including aqueous Fe 2+ , ammonium chloride-extractable Fe(II) (mainly from the ion-exchangeable sites, denoted as Fe ( II ) NH 4 Cl ${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$ ), sodium acetate-extractable Fe(II) (mainly from the surface complexation sites, denoted as Fe(II) acetate ), and structural Fe(II) (denoted as Fe(II) str ); and (3) to evaluate the reactivity of these Fe(II) species in terms of Tc(VII) reduction. Chemical and biological reduction of Fe(III) in nontronite (NAu-2) was performed, and reduced nontronite samples with different extents of Fe(III) reduction (1.2–71%) were prepared. The extent of reductive dissolution was measured as a function of the extent of Fe(III) reduction. Our results demonstrated that chemically and biologically produced Fe(II) in NAu-2 may be accommodated in the NAu-2 structure if the extent of Fe(III) reduction is small (< ∼30%). When the extent of reduction was >∼30%, dissolution of nontronite occurred with a corresponding decrease in crystallinity of residual nontronite. The Fe(II) produced was available for partitioning into four species: Fe ( ab ) 2 + ${\rm{Fe}}_{\left( {{\rm{ab}}} \right)}^{2 + }$ , Fe(II) acetate , Fe ( II ) NH 4 Cl ${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$ , and Fe(II) str . The increase in Fe(II) acetate during the early stages of Fe(III) reduction indicated that the Fe(II) released had the greatest affinity for the surface-complexation sites, but this site had a limited capacity (∼60 µmol of Fe(II)/g of NAu-2). The subsequent increase in Fe ( II ) NH 4 Cl ${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$ indicated that the released Fe(II) partitioned into the exchangeable sites once the amount of Fe at the surface-complexation sites reached half of its maximum site capacity. The fraction of Fe(II) str decreased concomitantly, as a result of Fe(II) release from the NAu-2 structure, from 100% when the extent of Fe(III) reduction was <30% to nearly 65% when the extent of Fe(III) reduction reached 71%. The Fe(II) acetate and Fe(II) str exhibited greater reactivity in terms of Tc(VII) reduction than the Fe ( II ) NH 4 Cl ${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$ . Clearly, the surface-complexed and structural Fe(II) are the desirable species when reduced clay minerals are used to reduce and immobilize soluble heavy metals in contaminated groundwater and soils. These results have important implications for understanding microbe—clay mineral interactions and heavy metal immobilization in clay-rich natural environments.
Three known nitrogenase isozymes, Mo-, V-, and Fe-, catalyze biological reduction of dinitrogen (N 2 ) to ammonia (NH 3 ). All three utilize the same reductive elimination mechanism: an intermediate with two metal-bound hydrides reductively-eliminates hydrogen gas (H 2 ) in a reaction coupled to binding and activation of N 2 . Nonetheless, the three isozymes show dramatically different relative rates of H 2 formation and N 2 reduction, revealing important differences in reactivity with substrates. Carbon monoxide (CO) has been characterized as both an inhibitor and substrate for Mo- and V-nitrogenases, but not for the Fe-nitrogenase. In this work, we present a comparative study of the reactivity of the three isozymes with CO, examining CO both as a substrate and as an inhibitor of proton (H + ) reduction under steady-state conditions. For Mo-nitrogenase, there is neither detectable reduction of CO nor inhibition of H + reduction. Fe- and V-nitrogenase show CO reduction and inhibition of H + reduction that depends on the CO partial pressure. For V-nitrogenase, ethylene (C 2 H 4 ) is the major reduction product with a maximum specific activity of ~7.5 nmol C 2 H 4 /nmol VFe protein/min at 1 atm CO. The major product of CO reduction for Fe-nitrogenase is methane (CH 4 ) with a maximum specific activity of ~4.8 nmol CH 4 /nmol FeFe protein/min at 0.05 atm CO. The rate of CH 4 production by Fe-nitrogenase progressively increases to a maximum at 0.05 atm CO and then declines to ~10% with increasing CO partial pressure up to 1 atm. CO does not inhibit proton reduction in Mo-nitrogenase but shows 16% inhibition for V-nitrogenase and 35% for Fe-nitrogenase.
The reduction of Hg II to Hg I or Hg 0 can lead to significant changes in Hg toxicity and mobility in the environment. Photochemical reduction is the primary process for the reduction of Hg II to Hg 0 in sunlit environments; however, dark reduction of HgII can occur via microbial metabolic processes and/or reduction by reduced natural organic matter, Fe II mineral phases, Fe II sorbed to minerals, or aqueous Fe II . Here, in this study, we demonstrate a novel Hg II reduction pathway involving another environmentally relevant reductant, Mn II . Abiotic reduction of Hg II O by Mn II was studied as a function of pH and anion environment (perchlorate, sulfate, chloride) using X-ray absorption spectroscopy to characterize the solid-phase Hg and Mn species. At circumneutral pH of 7.5, about 70% of Hg II was reduced to elemental Hg 0 within 2 h. In contrast, 12 h were needed to achieve the same extent of reduction at pH 6.9. In the presence of sulfate and chloride, Hg I species were formed. Hg II reduction was initially rapid and coupled with the oxidation of soluble Mn II -oxides to insoluble Mn IV -oxides, followed by a significantly slower reduction of Hg II during the Mn II -catalyzed transformation of the Mn IV -oxides to hydroxide and oxyhydroxide minerals. The observed reduction of Hg II by Mn II at circumneutral pH could be an important transformation pathway for environmental Hg, affecting its bioavailability and mobility under mildly reducing conditions.
An investigation is conducted in 2019 under the NASA Ames Center Innovation Funds (CIF) project entitled “Anti-Phase Vortex Reduction Control for Rotor Noise Suppression“ to experimentally validate an anti-phase rotor noise suppression concept. The first objective of the investigation is to conduct computational fluid dynamics (CFD) simulations to investigate the noise characteristics of several anti-phase rotor designs. The second objective is to conduct a series of acoustic tests of anti-phase rotors in an anechoic chamber at Pennsylvania State University (PSU) to evaluate the merit of the anti-phase rotor concept. The CFD investigation seeks to optimize the anti-phase alternating trailing edge patterns for rotor noise suppression. The design objective is to maximize the noise reduction while maintaining the aerodynamic thrust. The investigation is performed using a three-dimensional (3D) Unsteady Reynolds-Averaged Navier-Stokes (URANS) commercial solver STAR-CCM+ together with the Ffowcs-Williams and Hawkings (FW-H) formula to obtain the aerodynamic thrust and far-field noise level. An acoustic study is conducted for 13 anti-phase design candidates based on a proprietary rotor design. The CAD geometry of the rotor is furnished by PSU. These design candidates include different alternating trailing edge (TE) waveforms, TE segment lengths, TE deflection amplitudes, and transition characteristics. The best design candidate among those explored is an anti-phase rotor that has a four-period TE waveform which results in a reduction in far-field noise level of 2.1 dB in the hover condition and a reduction of 1.1 dB in the forward flight condition at 9.7 m/s. A further acoustic study is conducted for a different rotor manufactured by APC. Five APC rotor design candidates are simulated. The best anti-phase design candidate for the APC rotor results in a reduction in far-field noise level of 4.0 dB in the hover condition. An in-phase design candidate is also studied. This in-phase design provides a noise reduction of 2.5 dB. A series of acoustic experiments in the PSU anechoic chamber have been conducted in July 2019 and October 2019. Both anti-phase and in-phase rotors fabricated for the left-hand and right-hand rotations are tested. In the hover condition, all the rotors do not provide sufficient evidence of improved acoustic performance. However, the experimental data in the hover condition are deemed to be inconclusive due to the flow recirculation in the anechoic chamber caused by the rotor downwash. In the forward flight condition at 9.7 m/s, the anti-phase right-hand rotor produces a noise reduction by as much as 6.5 dB in the frequency range of 2000-4000 Hz, while the in-phase right-hand rotor produces a noise reduction by as much as 5 dB in the same frequency range. Both the anti-phase and in-phase left hand rotors offer no evidence of noise reduction. The difference in the acoustic performance of the left-hand and right-hand rotors could be explained by the location of the microphone array which is placed to the left side of the rotors. This microphone array location could create a bias in the sound pressure level in favor of the right-hand rotor. Using the average noise reduction values, the anti-phase 4H rotor could offer a noise reduction by as much as 3.25 dB while the in-phase 4I rotor could produce up to a 2.5 dB noise reduction. Both the computational and experimental results have provided sufficient evidence to support the noise suppression capability of the proposed anti-phase rotor concepts.
Iron reduction and sulfate reduction often occur simultaneously in anoxic systems, and where that is the case, the molar ratio between the reactions (i.e., Fe/SO 4 2- reduced) influences their impact on water quality and carbon storage. Previous research has shown that pH and the supply of electron donors and acceptors affect that ratio, but it is unclear how their influences compare and affect one another. This study examines impacts of pH and the supply of acetate, sulfate, and goethite on the ratio of iron to sulfate reduction in semi-continuous sediment bioreactors. We examined which parameter had the greatest impact on that ratio and whether the parameter influences depended on the state of each other. Results show that pH had a greater influence than acetate supply on the ratio of iron to sulfate reduction, and that the impact of acetate supply on the ratio depended on pH. In acidic reactors (pH 6.0 media), the ratio of iron to sulfate reduction decreased from 3:1 to 2:1 as acetate supply increased (0-1 mM). In alkaline reactors (pH 7.5 media), iron and sulfate were reduced in equal proportions, regardless of acetate supply. Secondly, a comparison of experiments with and without sulfate shows that the extent of iron reduction was greater if sulfate reduction was occurring and that the effect was larger in alkaline reactors than acidic reactors. Thus, the influence of sulfate supply on iron reduction extent also depended on pH and suggests that iron reduction grows more dependent on sulfate reduction as pH increases. Our results compare well to trends in groundwater geochemistry and provide further evidence that pH is a major control on iron and sulfate reduction in systems with crystalline (oxyhydr)oxides. pH not only affects the ratio between the reactions but also the influences of other parameters on that ratio.
Reduction of mobile aqueous uranyl complexes can be hindered by the strength of the uranyl-ligand complex and the resistivity of the complexes to electron transfer. Semiconducting solids, such as magnetite (Fe 3 O 4 ) and ilmenite (FeTiO 3 ), can facilitate otherwise-slow electron transfer between the reductant and oxidant, especially if these species are adsorbed on their surfaces as inner-sphere complexes. Electrons can then be shuttled through the surface or the structure. This process can be facilitated by either finding a new electron transfer path or by weakening or destroying the ligand-uranyl complex. Using in situ electrochemical atomic force microscopy (EC-AFM), we imaged reduction products of uranyl as mediated by magnetite and ilmenite in the absence or presence of the organic ligands, ethylenediaminetetraacetate (EDTA) and oxalate. In situ images of uranyl reduction show gradual nucleation and growth of reduced uranium on the mineral surfaces with decreasing reduction potentials. X-ray photoelectron spectroscopy (XPS) measurements indicate pentavalent uranium as the dominant uranium species resulting from uranyl reduction mediated by magnetite and ilmenite. The reduction potentials of uranyl-organic species relevant to our reaction system, (U VI O 2 ∙oxalate) 0 and (U VI O 2 ∙HEDTA) - , are derived using quantum–mechanical modeling and compared with the midpoint potentials obtained from cyclic voltammetry measurements. The spectroscopic, electrochemical, and computational data suggest that the catalysis of Fe-bearing minerals facilitates the reduction of uranyl-organic complexes. U(VI)-oxalate complexes are redox-active and participate directly in the reduction mediated by magnetite. In the presence of EDTA, reduction of uranyl may proceed in concert with ligand exchange between metals (i.e., U and Fe) on the mineral surface. Finally, the proposed mechanism is the breaking of uranyl-organic bonds upon interaction with the mineral surface followed by the formation of Fe-organic bonds, thereby allowing the reduction of hexavalent uranyl to pentavalent one.
This paper evaluates a set of contrail reduction strategies based on the flight range of aircraft as contrail reduction strategies have different impacts on aircraft depending on how they plan to fly. In general, aircraft with longer flight distances cruise at the altitudes where contrails are more likely to form. The concept of the contrail frequency index is used to quantify contrail impacts. The strategy for reducing the persistent contrail formation is to minimize the contrail frequency index by altering the aircraft's cruising altitude. A user-defined factor is used to trade off between contrail reduction and extra CO2 emissions. A higher value of tradeoff factor results in more contrail reduction and extra CO2 emissions. Results show that contrail reduction strategies using various tradeo factors behave differently from short-range flights to long-range ights. Analysis shows that short-distance flights (less than 500 miles) are the most frequent flights but contribute least to contrail reduction. Therefore these aircraft have the lowest priority when applying contrail reduction strategies. Medium-distance flights (500 to 1000 miles) have a higher priority if the goal is to achieve maximum contrail reduction in total; long-distance flights (1000 to 1500 miles) have a higher priority if the goal is to achieve maximum contrail reduction per flight. The characteristics of transcontinental flights (greater than 1500 miles) vary with different weather days so the priority of applying contrail reduction strategies to the group needs to be evaluated based on the locations of the contrail areas during any given day. For the days tested, medium-distance ights contribute up to 42.6% of the reduction among the groups during a day. The contrail frequency index per 1,000 miles for medium-distance, long-distance, and transcontinental flights can be reduced by an average of 75%. The results provide a starting point for developing operational policies to reduce the impact of aviation on climate based on aircraft flight distances.
A study is presented for the noise and fuel burn reduction potential of an innovative double deck concept aircraft with two three-shaft direct-drive turbofan engines. The engines are mounted from the fuselage so that the engine inlet is over the main wing. It is shown that such an aircraft can achieve a cumulative Effective Perceived Noise Level (EPNL) about 28 dB below the current aircraft noise regulations of Stage 4. The combination of high bypass ratio engines and advanced wing design with laminar flow control technologies provide fuel burn reduction and low noise levels simultaneously. For example, the fuselage mounted engine position provides more than 4 EPNLdB of noise reduction by shielding the inlet radiated noise. To identify the potential effect of noise reduction technologies on this concept, parametric studies are presented to reveal the system level benefits of various emerging noise reduction concepts, for both engine and airframe noise reduction. These concepts are discussed both individually to show their respective incremental noise reduction potential and collectively to assess their aggregate effects on the total noise. Through these concepts approximately about 8 dB of additional noise reduction is possible, bringing the cumulative noise level of this aircraft to 36 EPNLdB below Stage 4, if the entire suite of noise reduction technologies would mature to practical application. In a final step, an estimate is made for this same aircraft concept but with higher bypass ratio, geared, turbofan engines. With this geared turbofan propulsion system, the noise is estimated to reach as low as 40-42 dB below Stage 4 with a fuel burn reduction of 43-47% below the 2005 best-in-class aircraft baseline. While just short of the NASA N+2 goals of 42 dB and 50% fuel burn reduction, for a 2025 in service timeframe, this assessment shows that this innovative concept warrants refined study. Furthermore, this design appears to be a viable potential future passenger aircraft, not only in meeting the regulatory requirements, but also in competing with aircraft of different advanced designs within this N+2 timeframe and goal framework.
Microbial iodate (IO 3 – ) reduction is a major component of the iodine biogeochemical reaction network in anaerobic marine basins and radioactive iodine-contaminated subsurface environments. Alternative iodine remediation technologies include microbial reduction of IO 3 – to iodide (I – ) and microbial methylation of I – to volatile gases. The metal reduction pathway is required for anaerobic IO 3 – respiration by the gammaproteobacterium Shewanella oneidensis . However, the terminal IO 3 – reductase and additional enzymes involved in the S. oneidensis IO 3 – electron transport chain have not yet been identified. In this study, gene deletion mutants deficient in four extracellular electron conduits (EECs; Δ mtrA , Δ mtrA -Δ mtrDEF , Δ mtrA -Δ dmsEF , Δ mtr A-ΔSO4360) and DMSO reductase (Δ dmsB ) of S. oneidensis were constructed and examined for anaerobic IO 3 – reduction activity with either 20 mM lactate or formate as an electron donor. IO 3 – reduction rate experiments were conducted under anaerobic conditions in defined minimal medium amended with 250 μM IO 3 – as anaerobic electron acceptor. Only the Δ mtrA mutant displayed a severe deficiency in IO 3 – reduction activity with lactate as the electron donor, which suggested that the EEC-associated decaheme cytochrome was required for lactate-dependent IO 3 – reduction. The Δ mtrA -Δ dmsEF triple mutant displayed a severe deficiency in IO 3 – reduction activity with formate as the electron donor, whereas Δ mtrA -Δ mtrDEF and Δ mtr A-ΔSO4360 retained moderate IO 3 – reduction activity, which suggested that the EEC-associated dimethylsulfoxide (DMSO) reductase membrane-spanning protein DmsE, but not MtrA, was required for formate-dependent IO 3 – reduction. Furthermore, gene deletion mutant Δ dmsB (deficient in the extracellular terminal DMSO reductase protein DmsB) and wild-type cells grown with tungsten replacing molybdenum (a required co-factor for DmsA catalytic activity) in defined growth medium were unable to reduce IO 3 – with either lactate or formate as the electron donor, which indicated that the DmsAB complex functions as an extracellular IO 3 – terminal reductase for both electron donors. Results of this study provide complementary genetic and phenotypic evidence that the extracellular DMSO reductase complex DmsAB of S. oneidensis displays broad substrate specificity and reduces IO 3 – as an alternate terminal electron acceptor.
Chromium stable isotope ratios are used to trace the reduction of Cr(VI) to Cr(III) in both ancient and modern systems. However, quantitative interpretation of Cr isotopic signatures has been stymied by the large variability in isotopic fractionation factors for Cr(VI) reduction by different reductants. Here we determine Cr isotope fractionation factors during Cr(VI) reduction by Fe(II/III)-bearing clay minerals, which are abundant in subsurface environments. Several variables were tested: pH, total Fe content of the clay, and the fraction of reduced Fe within the clay (Fe(II)/Fe(total)). The latter controls the standard reduction potential of the clay. Our results demonstrate that neither pH nor total Fe content of the clay have major effects on isotopic fractionation. In contrast, as the effective standard reduction potential of the clay and thus the standard free energy of Cr(VI) reduction become more negative, Cr isotope fractionation factors decrease in magnitude from - 4.9 to -1.3‰ according to a linear free energy relationship. This linear free energy relationship can be predicted from Marcus electron transfer theory and allows first-order predictions of Cr isotope fractionation factors to be made from the standard reduction potential or Fe(II)/Fe(total) of a clay, potentially improving our ability to model Cr isotope signatures in geochemical systems. Chromium is the first isotope system to show such a linear free energy relationship over a diverse range of reductants, including both aqueous and solid-phase reductants, and may provide a model for determining other redox-driven kinetic isotope effects in environmentally important isotope systems.
The importance of size reduction to the commercial deployment of biomass utilization technologies cannot be overemphasized. Size reduction is necessary to create good flowing, easily digestible lignocellulosic biomass. However, inefficiencies and inconsistencies have not been well addressed for the process of size reduction. This has motivated quite a few research studies, some of which have reported the influence of process variables and pretreatment on the size reduction performance as well as the development of novel size reduction equipment and empirical mathematical models. In this Perspective, we present a systematic and critical evaluation of the state of lignocellulosic biomass size reduction research to provide insights for engineers and scientists for future development and investigation. We first briefly discuss the structural biology and failure mode of lignocellulosic biomass. Then, we present a comprehensive, data-driven picture of the interactions among lignocellulosic biomass attributes, size reduction process variables, pretreatment processes, and size reduction process performance (as defined by product characteristics and size reduction energy consumption). The sizing equipment tool wear issues are also summarized. Finally, we highlight some existing gaps and future research opportunities for lignocellulosic biomass size reduction to inform the development of newer technologies that could effectively produce high-value lignocellulosic biomass particles.
Mo-nitrogenase catalyzes the reduction of dinitrogen (N 2 ) to two ammonia (NH 3 ) at the active-site FeMo-cofactor. Substrate activation requires the accumulation of three or four electrons and protons as two Fe-bound hydrides and is coupled to obligatory H 2 release through reductive hydride elimination. Subsequent delivery of four or five additional electrons and protons to the bound N 2 yields two NH 3 molecules. Increasing evidence suggests that at least one belt sulfide within FeMo-cofactor is dynamically involved in the catalytic cycle. A recent report further proposed that sulfite (SO 3 2− ) is required for N 2 reduction, with sulfite binding required for NH 3 release and a subsequent six-electron reduction of the bound sulfite to regenerate the resting cofactor. To test this proposal, we conducted turnover studies of Mo-nitrogenase under sulfite-free conditions using a reduced viologen as reductant and protein preparations devoid of dithionite or sulfite. Under these conditions, nitrogenase effectively catalyzed both N 2 reduction and proton reduction, exhibiting steady-state turnover under N 2 for 6 min, with a turnover number exceeding 150, approaching that observed with dithionite as reductant. The same H 2 -formed/N 2 -reduced ratio was observed whether dithionite or the viologen species was used as reductant. Further, EPR spectroscopic analyses showed that the FeMo-cofactor returned to its resting state after multiple catalytic cycles in the absence of sulfite. Finally, physiological bypass of sulfite formation does not affect the capacity for diazotrophic growth of the model nitrogen-fixing organism Azotobacter vinelandii . Finally, these results demonstrate that sulfite is not required for Mo-nitrogenase-catalyzed N 2 reduction either in vitro or in vivo .
Pyrite (FeS 2 ) has a very low solubility and therefore has historically been considered a sink for iron (Fe) and sulfur (S) and unavailable to biology in the absence of oxygen and oxidative weathering. Anaerobic methanogens were recently shown to reduce FeS 2 and assimilate Fe and S reduction products to meet nutrient demands. However, the mechanism of FeS 2 mineral reduction and the forms of Fe and S assimilated by methanogens remained unclear. Thermodynamic calculations described herein indicate that H 2 at aqueous concentrations as low as 10 –10 M favors the reduction of FeS 2 , with sulfide (HS – ) and pyrrhotite (Fe 1–x S) as products; abiotic laboratory experiments confirmed the reduction of FeS 2 with dissolved H 2 concentrations greater than 1.98 × 10 –4 M H 2 . Growth studies of Methanosarcina barkeri provided with FeS 2 as the sole source of Fe and S resulted in H 2 production but at concentrations too low to drive abiotic FeS 2 reduction, based on abiotic laboratory experimental data. A strain of M. barkeri with deletions in all [NiFe]-hydrogenases maintained the ability to reduce FeS 2 during growth, providing further evidence that extracellular electron transport (EET) to FeS 2 does not involve H 2 or [NiFe]-hydrogenases. Physical contact between cells and FeS 2 was required for mineral reduction but was not required to obtain Fe and S from dissolution products. The addition of a synthetic electron shuttle, anthraquinone-2,6-disulfonate, allowed for biological reduction of FeS 2 when physical contact between cells and FeS 2 was prohibited, indicating that exogenous electron shuttles can mediate FeS 2 reduction. Here, transcriptomics experiments revealed upregulation of several cytoplasmic oxidoreductases during growth of M. barkeri on FeS 2 , which may indicate involvement in provisioning low potential electrons for EET to FeS 2 . Collectively, the data presented herein indicate that reduction of insoluble FeS 2 by M. barkeri occurred via electron transfer from the cell surface to the mineral surface resulting in the generation of soluble HS – and mineral-associated Fe 1–x S. Solubilized Fe(II), but not HS – , from mineral-associated Fe 1–x S reacts with aqueous HS – yielding aqueous iron sulfur clusters (FeS aq ) that likely serve as the Fe and S source for methanogen growth and activity. FeS aq nucleation and subsequent precipitation on the surface of cells may result in accelerated EET to FeS 2 , resulting in positive feedback between cell activity and FeS 2 reduction.
The electrolytic reduction of TiO2 in LiCl–Li2O (1 wt.%) at 650 °C was investigated under a series of cathodic reduction potentials and applied charges to provide a mechanistic understanding of the electrochemical characteristics of the system. The optimal cathodic reduction potential was determined as being −0.3 V vs. Li/Li+. Li2TiO3 and LiTiO2 were structurally identified as intermediate and partial reduction products of the TiO2 electrolytic reduction. The reduction of LiTiO2 was extremely slow and reversible due to its high stability and the detrimental effect of Li2O accumulation within the solid particles. The most reduced product obtained in this study was LiTiO2, which was achieved when using 150% of the theoretical charge under the optimal reduction potential. The highest reduction extent obtained in this study was 25%. Based on theoretical DFT modeling, a detailed multistep reduction mechanism and scheme were proposed for TiO2 electrolytic reduction in LiCl–Li2O (1 wt.%) at 650 °C.
School buildings have a great potential for carbon emission reduction since their annual emission is about 72 million metric tons. Currently, more than 30% of school buildings were built before 1960 and are underperforming. To effectively reduce carbon emissions via school building retrofits, it is critical for policymakers to understand the carbon intensity reduction potential of retrofitting school buildings in different regions. Hence, this study develops a method to comprehensively assess the long-term carbon intensity reduction potential of aggregated commercial buildings on a county-by-county basis in the continental U.S. We apply this method to the K-12 school buildings including primary and secondary school buildings. Here, this paper predicts the carbon intensity reduction potential of K-12 school buildings with eight building retrofit measures from 2022 to 2050 in the continental U.S. The results reveal several interesting findings: (1) In the approximately 3,000 counties of the U.S. from 2022 to 2050, the carbon intensity reduction potential of retrofitting K-12 school buildings in each county ranges from 0.41 kg/m 2 to 40.00 kg/m 2 . (2) Even in the same climate zone, the trends of carbon intensity reduction potential from 2022 to 2050 are different depending on their electricity sources. For example, in a hot and humid climate zone, the carbon intensity reduction potential in Florida will decrease from 2044 to 2048. However, in Mississippi, the carbon intensity reduction potential from 2044 to 2046 will increase due to the termination of the nuclear energy usage. (3) Generally, reducing lighting power density leads to more carbon intensity reduction in most states, but it might not be applicable for states with high clean energy penetration, such as Washington.