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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Substrate-Controlled Electronic Properties of Perovskite Layer in Lateral Heterojunction Configuration

In this work, we fabricated halide perovskite-based lateral heterojunction devices with nickel oxide/titanium oxide all back contacts, allowing us to access the perovskite surface directly for analysis with various advanced techniques, including ultraviolet and X-ray photoemission spectroscopy (UPS/XPS), Kelvin probe force microscopy (KPFM), and surface photovoltage (SPY), to discern the role of selective contacts. Specifically, by tuning of the selectivity of the contacts, e.g., through varying the level of nickel oxidation, we show that the selectivity of the contacts induces a gradient in carrier concentration across the surface of the active layer that is connected to carrier extraction at the buried interface and hence to device functionality.

carrier concentration↗
DOE OSTI2023

Electrolytic Etching of Germanium Substrates with Hydrogen Peroxide

Anodic electrolytic etching of germanium has been performed in hydrogen peroxide etchants with controlled external conditions. In-situ current and ex-situ etch-depths were measured and tracked with respect to etchant composition and stir rates. Gas bubbles formed during the etching process were found to cause non-uniformity in etch-current and surface quality. The effects were minimized in specific composition spaces. Quantitative analysis revealed a linear correlation of the number of electrons transferred during germanium oxidation with the number of surface atoms removed. Experimental results of 2.77 electrons/atom deviate significantly from 4 electrons/atom previously reported for silicon. The conclusion is that etching mechanisms for germanium are sufficiently different from those for silicon which invalidates the direct transfer of processing techniques between the two materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1999

High-Performance Bipropellant Engine

TRW, under contract to the NASA Lewis Research Center, has successfully completed over 10 000 sec of testing of a rhenium thrust chamber manufactured via a new-generation powder metallurgy. High performance was achieved for two different propellants, N2O4- N2H4 and N2O4 -MMH. TRW conducted 44 tests with N2O4-N2H4, accumulating 5230 sec of operating time with maximum burn times of 600 sec and a specific impulse Isp of 333 sec. Seventeen tests were conducted with N2O4-MMH for an additional 4789 sec and a maximum Isp of 324 sec, with a maximum firing duration of 700 sec. Together, the 61 tests totalled 10 019 sec of operating time, with the chamber remaining in excellent condition. Of these tests, 11 lasted 600 to 700 sec. The performance of radiation-cooled rocket engines is limited by their operating temperature. For the past two to three decades, the majority of radiation-cooled rockets were composed of a high-temperature niobium alloy (C103) with a disilicide oxide coating (R512) for oxidation resistance. The R512 coating practically limits the operating temperature to 1370 C. For the Earth-storable bipropellants commonly used in satellite and spacecraft propulsion systems, a significant amount of fuel film cooling is needed. The large film-cooling requirement extracts a large penalty in performance from incomplete mixing and combustion. A material system with a higher temperature capability has been matured to the point where engines are being readied for flight, particularly the 100-lb-thrust class engine. This system has powder rhenium (Re) as a substrate material with an iridium (Ir) oxidation-resistant coating. Again, the operating temperature is limited by the coating; however, Ir is capable of long-life operation at 2200 C. For Earth-storable bipropellants, this allows for the virtual elimination of fuel film cooling (some film cooling is used for thermal control of the head end). This has resulted in significant increases in specific impulse performance (15 to 20 sec). To determine the merits of a powder rhenium thrust chamber, Lewis On-Board Propulsion Branch directed TRW (under the Space Storable Rocket Technology Program and the High Pressure Earth Storable Rocket Technology Program) to design, fabricate, and test an engineering model to serve as a technology demonstrator.

Biaglow, James A.↗
DOE OSTI2024

Machine learning-driven descriptions of protein dynamics at solid-liquid interfaces

This chapter has described how ML has enabled quantitative analysis of HS-AFM data to discover the physical phenomena governing protein dynamics and ordering at solid-liquid interfaces. The research detailed in this chapter modeled the rotation models of protein nanorods, the discovery of which would otherwise not be possible. By tracking the trajectories of individual protein rods from frame to frame, it was possible to model Brownian type motion and behaviors and Levy-flight dynamics that had not previously been shown. We also described the application of the Python package AtomAI, which has been developed specifically to analyze and extract physical phenomena, providing exemplar code for training an ensemble of deep neural networks to produce the semantic segmentation of AFM data and functions for encoding and decoding local environments. We last described a combinatorial approach to analyze very noisy data with a densely covered substrate where the emergence of order for the protein liquid crystals could be elucidated. By combining the methods from Case 1 and 2, it was possible to obtain the center of mass and angle for each rod in the images and track the assembly of the rods over time into a 2D liquid crystal array on the surface of mica.

protein dynamics, solid-liquid interfaces, atomic ↗
DOE OSTI2019

Mechanism of the α-Zr to hexagonal-ZrO transformation and its impact on the corrosion performance of nuclear Zr alloys

Displacive transformations have been widely reported in metals, alloys and ceramics, but rarely reported to be important in the aqueous corrosion of alloys. We report here our analysis of the formation of the hexagonal-ZrO suboxide during the aqueous corrosion of α-Zr alloys and propose this to be a paraequilibrium displacive transformation with the rate controlled by oxygen diffusion. Two orientation relationships were identified between α-Zr and hexagonal-ZrO, ( 0002 ) α − Z r ∥ ( 1 ¯ 011 ) h − Z r O and [ 2 ¯ 110 ] α - Z r ∥ [ 10 1 ¯ 2 ] h - Z r O or ( 0002 ) α − Z r ∥ ( 22 4 ¯ 1 ¯ ) h − Z r O and [ 2 ¯ 110 ] α − Z r ∥ [ 1 1 ¯ 01 ] h − Z r O , with the first one more commonly observed. No specific orientation relationships between either hexagonal-ZrO and monoclinic-ZrO 2 or α-Zr and monoclinic-ZrO 2 were identified, which suggests that the formation of often-reported bulk oxide texture during aqueous corrosion is not related directly to the texture of the metallic substrate. In conclusion, these results provide a guideline for understanding the mechanisms of crystallographic evolution during oxide growth on commercial zirconium alloys, and also demonstrate the capability of transmission Kikuchi diffraction to investigate orientation relationships in nano-scale materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Characterization of a selective, zero power sensor for distributed sensing of hydrogen in energy applications

The use of hydrogen as a clean and renewable energy source is increasing rapidly for both vehicle and stationary applications. There are safety concerns for the locations in which hydrogen is made, used, and transported (i.e., pipelines and tanker trucks). Sensors are needed to comply with safety regulations and to enable a smooth and safe rollout of hydrogen as an alternative energy. However, hydrogen sensors do not yet exist that have the combined features of small size and low power for easy deployment coupled with high-volume manufacturability and low cost. This is necessary to accommodate the emerging fixed and mobile markets while retaining critical metrological metrics, including measurement range, detection limits, selectivity, fast response, stability, and long lifetime. An amperometric gas sensor for hydrogen (AGS) has been developed using an innovative manufacturing method. The sensor was designed using scalable fabrication strategies based on “Printed Electronics” (PE) methodology which are compatible with large-scale production. Prototype sensors were batch fabricated with multiple individual elements on a substrate compatible in size with a standard 8-inch wafer to enable high-volume, low-cost manufacturing, thereby leveraging PE and semiconductor fabrication infrastructure. This novel AGS was instrumented with control circuitry and evaluated for hydrogen detection in the range of 0–5000 ppmv H2 in air. Specific performance evaluations included assessment of the sensor measurement range, repeatability, and selectivity.

08 HYDROGEN↗
DOE OSTI2024

Reconceptualizing the Ir III Role in Metallaphotoredox Catalysis: From Strong Photooxidant to Potent Energy Donor

Dual Ir III /L n Ni II metallaphotoredox catalyzed C(sp 3 )–C(sp 2 ) cross-coupling reactions are widely assumed to proceed by photoinduced single electron transfer steps due to the highly oxidizing Ir III * excited state (Ir III = [Ir(dF(CF 3 )ppy) 2 (dtbbpy)] + [PF 6 ] – ; dF(CF 3 )ppy = 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine; L n = dtbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine). Using time-resolved absorption and emission spectroscopy, we reveal that energy transfer between Ir III * and various LnNi II precatalysts and intermediates with k q ≥ 10 8 M –1 s –1 also drives catalysis. Specifically, the excited states of L n Ni II dihalide precatalysts/organometallic intermediates accessible by energy transfer appear to drive bond homolysis, halogen radical elimination, and reductive elimination reactions that facilitate formation of cross-coupled products. Energy transfer dynamics consequently circumvent the need for photoinduced electron transfer, thereby extending substrate scopes to coupling partners that cannot be oxidized by Ir III *. Within a cross-electrophile coupling model reaction between 4-bromobenzotrifluoride and bromocyclohexane, energy transfer activates the L n Ni II precatalyst at early reaction times before nucleophilic reductants are present. In the absence of Ir III , direct excitation of L n Ni II (Br) 2 also activates the precatalyst to form a L n Ni II (Br)(Aryl) intermediate. To compare energy transfer and electron transfer kinetics, we determined rate constants for reductive quenching by Br – (k SET = 4.1 × 10 8 M –1 s –1 ) and for the subsequent electron transfer from reduced Ir III•– to L n Ni II (Br) 2 (k SET = 4.1 × 10 7 M –1 s –1 ) using Stern-Volmer analysis and pulse radiolysis, respectively. Energy transfer rate constants are competitive with the electron transfer rate constants and energy transfer is a parallel pathway within metallaphotoredox catalysis. Exploiting the energy transfer mechanism, we demonstrate highly selective cross-electrophile coupling between 4-chlorobenzotrifluoride and bromocyclohexane to form exclusively cross-coupled product. Here, with alkyl-trifluoroborate nucleophiles that do not reductively quench IrIII* emission, transmetalation with L n Ni II (Br/Cl)(Aryl) followed by energy transfer also drives excited state reductive elimination to form C(sp 3 )–C(sp 2 ) cross-coupled product. Similarly, energy transfer rather than Ni II oxidation drives C(sp 2 )–OR reductive elimination, despite the strongly oxidizing ability of Ir III *. In total, these reactions demonstrate energy transfer processes from Ir III * to L n Ni II in metallaphotoredox catalysis that can unlock alternative reactive pathways.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Multi-level regulation of the chloroplast ATP synthase: the chloroplast NADPH thioredoxin reductase C (NTRC) is required for redox modulation specifically under low irradiance

The chloroplast ATP synthase is known to be regulated by redox modulation of a disulfide bridge on thec-subunit through the ferredoxin–thioredoxin regulatory system. We show that a second enzyme, therecently identified chloroplast NADPH thioredoxin reductase C (NTRC), plays a role specifically at low irradi-ance. Arabidopsis mutants lacking NTRC (ntrc) displayed a striking photosynthetic phenotype in which feed-back regulation of the light reactions was strongly activated at low light, but returned to wild-type levels asirradiance was increased. This effect was caused by an altered redox state of the c-subunit under low, butnot high, light. The low light-specific decrease in ATP synthase activity in ntrc resulted in a buildup of thethylakoid proton motive force with subsequent activation of non-photochemical quenching and downregu-lation of linear electron flow. We conclude that NTRC provides redox modulation at low light using the rela-tively oxidizing substrate NADPH, whereas the canonical ferredoxin–thioredoxin system can take over athigher light, when reduced ferredoxin can accumulate. Based on these results, we reassess previous modelsfor ATP synthase regulation and propose that NTRC is most likely regulated by light. We also find that ntrcis highly sensitive to rapidly changing light intensities that probably do not involve the chloroplast ATP syn-thase, implicating this system in multiple photosynthetic processes, particularly under fluctuating environ-mental conditions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Advanced QPSK Optical Modulators Using Lithium Niobate Thin Films (Final Scientific Report)

Lithium niobate thin film based optical modulator devices have been produced using this SBIR award. A bonding apparatus was developed that was used to bond lithium niobate to silicon at room temperature. The bonding apparatus was designed, assembled and qualified for production of thin film substrates. The optical properties of ion sliced thin films produced using this bonding apparatus was optimized to achieve low loss optical waveguides. Optical grating coupler and other component of the proposed optical modulator were designed. Preliminary results show the proposed method for making optical modulator meets the required customer specifications. All the required process steps for manufacturing of the devices were developed and optimized. Further funding is required to make a final prototype device that can be provided to customers.

36 MATERIALS SCIENCE↗
DOE OSTI2023

GaN MOCVD Growth on Native substrates for High Voltage (15-20 KV) Vertical Power Devices

This project aims to develop metalorganic chemical vapor deposition (MOCVD) homoepitaxy of GaN on native substrates with fast growth rate (15-20 μm/hr), low background doping (low-10 15 cm -3 ) and smooth surface morphology via comprehensive understanding of the crystal growth process including high quality GaN substrate development and surface preparation, impurity and native defects control, and their impacts on the breakdown field. The team successfully developed a new growth process by introducing the laser-assisted MOCVD (LA-MOCVD) process to address the limited growth rates of GaN in the traditional MOCVD process. Specifically, the use of the CO2 laser with lasing wavelength of 9.219 μm, the strong coupling between the laser beam with the ammonia (GaN MOCVD precursor) leads to efficient decomposition of NH3 which significantly increases the effective group V/III molar ratio and thus suppresses C impurity incorporation in MOCVD GaN. The reduction in C incorporation in LA-MOCVD GaN is especially prominent when the GaN growth rate is fast (> 10 μm/hr), which allows to develop thick GaN films with high crystalline quality and low controllable doping needed for vertical high power device applications. The results of this project lead to the demonstration of vertical GaN PN diodes with record breakdown voltage of ~ 8kV with high Baliga’s figure of merit.

24 POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS1995

The control of stoichiometry in Epitaxial semiconductor structures. Interfacial Chemistry: Property relations. A workshop review

A workshop on the control of stoichiometry in epitaxial semiconductor structures was held on August 21-26, 1995 in the hotel Stutenhaus at Vesser in Germany. The secluded location of the workshop in the forest of Thuringia and its informal style stimulated extensive private discussions among the participants and promoted new contacts between young scientists from Eastern and Western Europe and the USA. Topics addressed by the presentations were interactions of precursors to heteroepitaxy and doping with the substrate surface, the control of interfacial properties under the conditions of heteroepitaxy for selected materials systems, methods of characterization of interfaces and native point defects in semiconductor heterostructures and an in depth evaluation of the present status of the control and characterization of the point defect chemistry for one specific semiconductor (ZnGeP2), including studies of both heterostructures and bulk single crystals. The selected examples of presentations and comments given here represent individual choices - made by the author to highlight major points of the discussions.

Bachmann, Klaus J.↗
DOE OSTI2016

Electrodeposition of Fe{sub 2}O{sub 3} nanoparticles and its supercapacitive properties

Fe{sub 2}O{sub 3} metal oxide nanoparticles are synthesized by electrodeposition method on stainless steel substrate. The crystal structure and surface morphological studies of the obtained metal oxide thin film are carried out by using X-ray diffraction (XRD) technique and Scanning Electron Microscopy (SEM) respectively. The electrochemical properties of Fe{sub 2}O{sub 3} thin film like Cyclic Voltammetry (CV), Galvonostatic Charge-Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS) are studied in a bath of 0.5 M Na{sub 2}SO{sub 4} as electrolyte. The observed specific capacitance shows improved values 135 Fg{sup −1} at 5 mVs{sup −1} scan rate. The electrochemical stability of Fe{sub 2}O{sub 3} electrode is investigated using cyclic voltammetry for 1000 cycles at a scan rate 50 mVs{sup −1}. The Fe{sub 2}O{sub 3} electrode exhibits superior cycling stability with only 4-5% capacitance loss after one thousand cycles. The values of specific power and specific energy of Fe{sub 2}O{sub 3} electrode obtained from Galvonostatic charge discharge studies are 2250 W.kg{sup −1} and 63.15 Wh.kg{sup −1} respectively at current density 1 A/g. From all the electrochemical properties of Fe{sub 2}O{sub 3} electrode, it indicates that it will be promising electrode material for supercapacitor application.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Advanced low-cost intermetallic coatings for molten salt pump impeller. Final report

1.0 INTRODUCTION The use of solar energy to produce steam for the generation of electricity is an established technology, with multiple designs for concentrating solar power (CSP) steam generators available commercially and a number of such units currently operating. As part of the effort to improve the overall efficiency of this technology, designers have developed thermal energy storage (TES) mechanisms that employ molten salt to capture a portion of the solar energy available during the day-time hours and make that energy available for steam generation during periods when the sun’s energy is not available. In current TES systems, nitrate salts are used extensively as the medium of energy exchange. However, due to the chemical instability of these salts at temperatures above 600ºC, they are not being considered for use in the next more efficient generation of CSP plants, in which the energy exchange fluids will be required to operate in the range 600ºC to 800ºC. At these higher temperatures, molten chloride salts, such as KCl-MgCl2, are viewed as promising alternatives to the nitrate salts, but, of course, these chloride-based salts are highly corrosive to the engineering alloys commonly used in the construction of pressure vessels, heat exchangers, pumps and piping at high temperatures. Hence, a solution to the problem of material degradation is essential if the next generation of CSP plants is to be commercially viable (Ref 1). In order to effectively address the problem of molten chloride salt corrosion at high temperatures (≥ 750ºC) and thereby to reduce the cost of molten salt tanks and related apparatus, various options have been considered, with one of the most promising being an innovative coatings system developed and applied onto low alloy ferritic or austenitic stainless material. Development of such a coating system would reduce the capital costs of thermal energy storage (TES) and increase the overall efficiency of the concentrating solar power (CSP) system. Although high strength nickel base alloys are well suited for many high temperature applications, they have significant limitations when exposed to molten chloride salt conditions and they are very expensive. Monolithic materials such as the austenitic stainless steels (e.g., SS310 and SS347) and the more common nickel base alloys (e.g., IN625 and IN800H) have exhibited high corrosion rates in molten chloride salt environments (Ref1). Molten salt corrosion of IN625 in salts containing chlorides showed a catastrophic corrosion rate of 1.111”/year at 800ºC (Ref1). Hence, an innovative coatings solution to mitigate molten chloride salt corrosion is needed. Of the many coating techniques available in the market, no one technique appears to be capable of producing effective protection from molten salt corrosion at a relatively low cost. There are thermal spray coating techniques, in particular the twin wire-arc technology, that are attractive when considering the coating of large molten salt tanks because the coatings application rate is high, the overall application cost is low and repairs to the coating can readily be made either in the shop or in the field. However, the twin wire arc coating materials currently available in the market have certain inherent limitations, including porosity and mechanical bonding to the substrate, which limit their effectiveness in providing protection against molten chloride salt corrosion at high temperatures. What is required is an approach that combines the economy and versatility of thermal spray wire-arc technology with the superior resistance of advanced alloys to effectively combat molten chloride salt corrosion at elevated temperatures. Applied Thermal Coatings, Inc. (ATC) has investigated an innovative coatings technology to produce dual layer cermet/ceramic coatings that will be dense and impervious to any corrosive molten salts/fluids, thereby resisting the effects of molten salt corrosion. Development of coatings using this technology will make it possible to fabricate the molten salt systems using a relatively low-cost base material, which will reduce the overall cost of the power generating system and enhance the commercial viability of solar power. 2.0 PROJECT OVERVIEW Of the coating technologies available for the production of a cost-effective method of protection from the effects of high-temperature chloride attack, there are two that offer specific advantages for the CSP/TES application, particularly when used in a way that effectively complements the strengths of each coating method. The first of these is electroless nickel plating, through which a nickel-rich layer is produced on the surface of a component through chemical reduction. The second coating technology is aluminizing, in which aluminum is diffused into the surface of a component and, depending on the composition of the substrate, aluminides are formed. The objective of this project has been to demonstrate the feasibility of a low- cost coating for the protection of pump impellers used for the inductive transport of molten salts. Initial interest focused on an inter-metallic nickel aluminide coating and subsequently, for economic reasons, consideration also was given to a coating composed of iron aluminides. Applying such coatings to low alloy or austenitic stainless-steel substrates will provide the superior resistance to molten chloride salt corrosion and blade tip erosion that normally can be achieved only through the use of more highly alloyed – and, therefore, more expensive - nickel-base materials and it will do so at a substantially lower cost. The coating systems evaluated were designed to take advantage either of the combined strengths of the electroless nickel plating process and the aluminizing process to produce a nickel-aluminide intermetallic coating or to rely solely on the aluminizing process to produce, in conjunction with iron from the substrate, a protective layer consisting of iron aluminides. With respect to the nickel aluminide protection, this has been achieved by first depositing a layer of nickel-rich alloy onto an austenitic stainless substrate using the electroless nickel plating process and then aluminizing the nickel- coated surface to produce the nickel aluminide coating. With respect to the iron aluminide protection, this has been achieved by aluminizing bare austenitic stainless steel. Testing has supported the conclusion that the developed coatings will resist attack by molten chloride salts at high temperatures (550°C to 750°C) and have sufficient hardness to resist blade tip erosion.The steps taken to develop either a low-cost intermetallic nickel aluminide coating using electroless nickel plating and aluminizing or a low-cost iron aluminide coating using aluminizing only, and to demonstrate the quality of the coatings and their effectiveness against molten chloride salt corrosion and erosion at high temperatures (≤ 750ºC) have been as follows: 1. Design of the optimum electroless nickel plating and aluminizing mixtures using advanced thermodynamic analysis; 2. Development of processing parameters for the electroless nickel plating and aluminizing processes, to be used either together or separately; 3. Production of specimens coated using the designated electroless nickel plating process; 4. Production of samples with intermetallic nickel aluminide coating or iron aluminide coating; 5. Investigation of the performance of the intermetallic nickel aluminide coating and the iron aluminide coating when subjected to molten chloride salts corrosion at high temperatures (≥ 750ºC); and, 6. Metallurgical characterization of the microstructure of the coatings, both prior to and after exposure to molten salt environments at elevated temperatures.

14 SOLAR ENERGY↗
DOE OSTI2015

Structural, Functional, and Immunogenic Insights on Cu,Zn Superoxide Dismutase Pathogenic Virulence Factors from Neisseria meningitidis and Brucella abortus

ABSTRACT Bacterial pathogens Neisseria meningitidis and Brucella abortus pose threats to human and animal health worldwide, causing meningococcal disease and brucellosis, respectively. Mortality from acute N. meningitidis infections remains high despite antibiotics, and brucellosis presents alimentary and health consequences. Superoxide dismutases are master regulators of reactive oxygen and general pathogenicity factors and are therefore therapeutic targets. Cu,Zn superoxide dismutases (SODs) localized to the periplasm promote survival by detoxifying superoxide radicals generated by major host antimicrobial immune responses. We discovered that passive immunization with an antibody directed at N. meningitidis SOD (NmSOD) was protective in a mouse infection model. To define the relevant atomic details and solution assembly states of this important virulence factor, we report high-resolution and X-ray scattering analyses of NmSOD and of SOD from B. abortus (BaSOD). The NmSOD structures revealed an auxiliary tetrahedral Cu-binding site bridging the dimer interface; mutational analyses suggested that this metal site contributes to protein stability, with implications for bacterial defense mechanisms. Biochemical and structural analyses informed us about electrostatic substrate guidance, dimer assembly, and an exposed C-terminal epitope in the NmSOD dimer. In contrast, the monomeric BaSOD structure provided insights for extending immunogenic peptide epitopes derived from the protein. These collective results reveal unique contributions of SOD to pathogenic virulence, refine predictive motifs for distinguishing SOD classes, and suggest general targets for antibacterial immune responses. The identified functional contributions, motifs, and targets distinguishing bacterial and eukaryotic SOD assemblies presented here provide a foundation for efforts to develop SOD-specific inhibitors of or vaccines against these harmful pathogens. IMPORTANCE By protecting microbes against reactive oxygen insults, SODs aid survival of many bacteria within their hosts. Despite the ubiquity and conservation of these key enzymes, notable species-specific differences relevant to pathogenesis remain undefined. To probe mechanisms that govern the functioning of Neisseria meningitidis and Brucella abortus SODs, we used X-ray structures, enzymology, modeling, and murine infection experiments. We identified virulence determinants common to the two homologs, assembly differences, and a unique metal reservoir within meningococcal SOD that stabilizes the enzyme and may provide a safeguard against copper toxicity. The insights reported here provide a rationale and a basis for SOD-specific drug design and an extension of immunogen design to target two important pathogens that continue to pose global health threats.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Carbonate Minerals and Dissimilatory Iron-Reducing Organisms Trigger Synergistic Abiotic and Biotic Chain Reactions under Elevated CO 2 Concentration

Increasing CO 2 emission has resulted in pressing climate and environmental issues. While abiotic and biotic processes mediating the fate of CO 2 have been studied separately, their interactions and combined effects have been poorly understood. To explore this knowledge gap, an iron-reducing organism, Orenia metallireducens, was cultured under 18 conditions that systematically varied in headspace CO 2 concentrations, ferric oxide loading, and dolomite (CaMg(CO 3 ) 2 ) availability. The results showed that abiotic and biotic processes interactively mediate CO 2 acidification and sequestration through "chain reactions", with pH being the dominant variable. Specifically, dolomite alleviated CO 2 stress on microbial activity, possibly via pH control that transforms the inhibitory CO 2 to the more benign bicarbonate species. The microbial iron reduction further impacted pH via the competition between proton (H + ) consumption during iron reduction and H + generation from oxidization of the organic substrate. Under Fe(III)-rich conditions, microbial iron reduction increased pH, driving dissolved CO 2 to form bicarbonate. Spectroscopic and microscopic analyses showed enhanced formation of siderite (FeCO 3 ) under elevated CO 2 , supporting its incorporation into solids. In conclusion, the results of these CO 2 -microbe-mineral experiments provide insights into the synergistic abiotic and biotic processes that alleviate CO 2 acidification and favor its sequestration, which can be instructive for practical applications (e.g., acidification remediation, CO 2 sequestration, and modeling of carbon flux).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Frontal polymerization of thermosets to enable vacuum-formed structural electronics

Material design and accessible manufacturing are often at odds with each other, calling for creative solutions to adapt high-performance materials to available processes. This challenge is represented well by in-mold electronics, an innovative approach to the manufacture of 3D circuitry and electronic components that offers game-changing advantages. In-mold electronics relies on vacuum forming processes, which are historically limited to thermoplastics. Extending these methods to include thermosets would enable manufacturing of robust components with desirable properties. Here, we provide a solution to make thermoset materials amenable to vacuum forming. Specifically, an ambient polymerization is used to transition a liquid monomeric solution to an elastomeric gel. These free-standing gels can then be vacuum formed, and the reaction can be completed via frontal polymerization. Thermoset materials produced with this method have properties that provide benefits over traditionally employed thermoplastic substrates and enable 3D device integration into environmentally demanding architectural, automotive, and extraterrestrial structures.

Fowler, Hayden Elise [Sandia National Laboratories↗
DOE OSTI2014

Raman spectroscopy of GaP/GaNP core/shell nanowires

Raman spectroscopy is employed to characterize structural and phonon properties of GaP/GaNP core/shell nanowires (NWs) grown by molecular beam epitaxy on Si substrates. According to polarization-dependent measurements performed on single NWs, the dominant Raman modes associated with zone-center optical phonons obey selection rules in a zinc-blende lattice, confirming high crystalline quality of the NWs. Two additional modes at 360 and 397 cm{sup −1} that are specific to the NW architecture are also detected in resonant Raman spectra and are attributed to defect-activated scattering involving zone-edge transverse optical phonons and surface optical phonons, respectively. It is concluded that the formation of the involved defect states are mainly promoted during the NW growth with a high V/III ratio.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Crystal Structures of the SpoIID Lytic Transglycosylases Essential for Bacterial Sporulation

Bacterial spores are the most resistant form of life known on Earth and represent a serious problem for (i) bioterrorism attack, (ii) horizontal transmission of microbial pathogens in the community, and (iii) persistence in patients and in a nosocomial environment. Stage II sporulation proteinD(SpoIID) is a lytic transglycosylase (LT) essential for sporulation. The LT superfamily is a potential drug target because it is active in essential bacterial processes involving the peptidoglycan, which is unique to bacteria. However, the absence of structural information for the sporulation-specific LT enzymes has hindered mechanistic understanding of SpoIID. In this paper, we report the first crystal structures with and without ligands of the SpoIID family from two community relevant spore-forming pathogens, Bacillus anthracis and Clostridium difficile . The structures allow us to visualize the overall architecture, characterize the substrate recognition model, identify critical residues, and provide the structural basis for catalysis by this new family of enzymes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗