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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Enhanced, continuous, liquid-liquid extraction and in-situ separation of volatile fatty acids from fermentation broth

In 2018 alone, the US landfilled 35.3 million tons of food waste, about 24% of the total landfilled mass. In addition to the negative impacts landfills have demonstrated on the environment and human health, some states have begun to outlaw or dissuade the disposal of food waste and sewage sludge into landfills altogether. An urgent need has thus been created for the development of digestion processes like anaerobic digestion (AD) and arrested methanogenesis (AM) to convert food waste into valuable chemical products. Unfortunately, the buildup of volatile fatty acids (VFAs) during these processes eventually halts the reaction, and energy efficient methodologies for VFA removal are critical for the operation of fermenters. Additionally, VFAs themselves can serve as valuable chemical precursors, and recently AD processes have been modified to increase VFA production during fermentation. However, even with significant research over the past three decades, the separation of VFAs from the fermenter broth has remained expensive. Moreover, the separation of these VFAs from the fermenter broth may cost up to 50% of the entire process budget, hindering the widespread commercial adoption of AD and AM. Here we present a novel liquid-liquid extraction process termed CLEANS (Continuous Liquid-liquid Extraction And iN-situ Separation) as a highly efficient method for continuously separating VFAs from a real fermentation broth solely under gravity. Our optimized process (using an aqueous broth feed pH of 2.5, tri-noctylamine as an extractant, and a 10:1 ratio of aqueous broth to organic extractant), achieved a VFA distribution constant K D = 44.5 ± 7.9, a single-pass recovery = 81.3 ± 2.5%, and an extraction factor = 8.1 ± 0.3. These KD values are over an order of magnitude higher than what has been previously reported for comparable processes. A high aqueous-to-organic flowrate ratio, enabled for the first time by CLEANS, was found to be particularly crucial for achieving optimal extraction. Our separation process demonstrates excellent reproducibility and potential for scalability. The economic and environmental implications of this work are briefly discussed.

42 ENGINEERING↗
DOE OSTI2013

Persistent fibrosis in the liver of choline-deficient and iron-supplemented L-amino acid-defined diet-induced nonalcoholic steatohepatitis rat due to continuing oxidative stress after choline supplementation

Nonalcoholic steatohepatitis (NASH) is characterized by combined pathology of steatosis, lobular inflammation, fibrosis, and hepatocellular degeneration, with systemic symptoms of diabetes or hyperlipidemia, all in the absence of alcohol abuse. Given the therapeutic importance and conflicting findings regarding the potential for healing the histopathologic features of NASH in humans, particularly fibrosis, we investigated the reversibility of NASH-related findings in Wistar rats fed a choline-deficient and iron-supplemented L-amino acid-defined (CDAA) diet for 12 weeks, with a recovery period of 7 weeks, during which the diets were switched to a choline-sufficient and iron-supplemented L-amino acid-defined (CSAA) one. Analysis showed that steatosis and inflammation were significantly resolved by the end of the recovery period, along with decreases in AST and ALT activities within 4 weeks. In contrast, fibrosis remained even after the recovery period, to an extent similar to that in continuously CDAA-fed animals. Real-time reverse transcriptase-polymerase chain reaction, Western blot, and immunohistochemical investigations revealed that expression of some factors indicating oxidative stress (CYP2E1, 4-HNE, and iNOS) were elevated, whereas catalase and SOD1 were decreased, and a hypoxic state and CD34-positive neovascularization were evident even after the recovery period, although the fibrogenesis pathway by activated α-SMA-positive hepatic stellate cells via TGF-β and TIMPs decreased to the CSAA group level. In conclusion, persistent fibrosis was noted after the recovery period of 7 weeks, possibly due to sustained hypoxia and oxidative stress supposedly caused by capillarization. Otherwise, histopathological features of steatosis and inflammation, as well as serum AST and ALT activities, were recovered. - Highlights: ► NASH-like liver lesions are induced in rats by feeding a CDAA diet. ► Steatosis and lobular inflammation are resolved after switching to a CSAA diet. ► Fibrosis is sustained, possibly due to continuing hypoxia and oxidative stress.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Continuous activation of Nrf2 and its target antioxidant enzymes leads to arsenite-induced malignant transformation of human bronchial epithelial cells

Long-term exposure to arsenite leads to human lung cancer, but the underlying mechanisms of carcinogenesis remain obscure. The transcription factor of nuclear factor-erythroid-2 p45-related factor (Nrf2)-mediated antioxidant response represents a critical cellular defense mechanism and protection against various diseases. Paradoxically, emerging data suggest that the constitutive activation of Nrf2 is associated with cancer development, progression and chemotherapy resistance. However, the role of Nrf2 in the occurrence of cancer induced by long-term arsenite exposure remains to be fully understood. By establishing transformed human bronchial epithelial (HBE) cells via chronic low-dose arsenite treatment, we showed that, in acquiring this malignant phenotype, continuous low level of ROS and sustained enhancement of Nrf2 and its target antioxidant enzyme levels were observed in the later-stage of arsenite-induced cell transformation. The downregulation of Keap1 level may be responsible for the over-activation of Nrf2 and its target enzymes. To validate these observations, Nrf2 was knocked down in arsenite-transformed HBE cells by SiRNA transfection, and the levels of Nrf2 and its target antioxidant enzymes, ROS, cell proliferation, migration, and colony formation were determined following these treatments. Results showed that blocked Nrf2 expression significantly reduced Nrf2 and its target antioxidant enzyme levels, restored ROS levels, and eventually suppressed cell proliferation, migration, and colony formation of the transformed cells. In summary, the results of the study strongly suggested that the continuous activation of Nrf2 and its target antioxidant enzymes led to the over-depletion of intracellular ROS levels, which contributed to arsenite-induced HBE cell transformation. - Highlights: • Low level, long term arsenite exposure induces malignant transformation in vitro. • Long term arsenite exposure reduces ROS and MDA levels. • Long term arsenite exposure enhances Nrf2-mediated antioxidant levels. • Knockdown of Nrf2 reduces malignant degree of arsenite-transformed cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

An experimental study on thermo-catalytic pyrolysis of plastic waste using a continuous pyrolyser

Highlights: • Thermo-catalytic pyrolysis of plastic waste in a bench scale continuous feed unit. • Utilizing RDC temperature profile to enhance oil product selectivity towards diesel. • Mesoporosity is a critical factor for coke deposition on catalyst. • Pelletised catalysts, not powder catalysts, provided higher selectivity towards diesel. - Abstract: A bench scale, two-stage, thermo-catalytic reactor equipped with a continuous feeding system was used to pyrolyse pure and waste plastics. Experiments using five zeolitic and clay-based catalysts of different forms (pellet and powders) and different plastic feedstocks – virgin HDPE, HDPE w1aste and mixed plastic waste (MPW) were compared to the control experiments – pyrolysis without catalyst. Results indicated that the two pelletized catalysts were the most promising for the conditions employed. Of these two, one with higher acidity and surface area was highly selective for the gasoline fraction (C{sub 5}–C{sub 11}) giving 80% from the total medium distillate conversion using virgin HDPE as feedstock. It also produced the least amount of olefins (17% for virgin HDPE, 4% for HDPE waste and 2% for MPW) and coke (<1% for virgin HDPE, 3% for HDPE waste and 5% for MPW), and the highest aromatics content (22% for virgin HDPE from un-distilled medium distillate, 5% for HDPE and 13% for MPW both from distilled medium distillate). The second pelletized catalyst exhibited high selectivity for the diesel fraction (C{sub 12}–C{sub 25}) giving 63% from the total medium distillate conversion using virgin HDPE as feedstock. The amount of coke deposited on the catalyst surface depended mainly on the mesopore volume, with less coke deposited as the mesopore volume increased. The variation in catalyst selectivity with acidity strength due to Lewis sites on the catalyst surface controls selectivity towards carbon chain length.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Continuous Fluorescence Assays for Reactions Involving Adenine

5'-Methylthioadenosine phosphorylase (MTAP) and 5'-methylthioadenosine nucleosidase (MTAN) catalyze the phosphorolysis and hydrolysis of 5'-methylthioadenosine (MTA), respectively. Both enzymes have low KM values for their substrates. Kinetic assays for these enzymes are challenging, as the ultraviolet absorbance spectra for reactant MTA and product adenine are similar. We report a new assay using 2-amino-5'-methylthioadenosine (2AMTA) as an alternative substrate for MTAP and MTAN enzymes. Hydrolysis or phosphorolysis of 2AMTA forms 2,6-diaminopurine, a fluorescent and easily quantitated product. We kinetically characterize 2AMTA with human MTAP, bacterial MTANs and use 2,6-diaminopurine as a fluorescent substrate for yeast adenine phosphoribosyltransferase. 2AMTA was used as the substrate to kinetically characterize the dissociation constants for three-transition-state analogue inhibitors of MTAP and MTAN. Kinetic values obtained from continuous fluorescent assays with MTA were in good agreement with previously measured literature values, but gave smaller experimental errors. Chemical synthesis from ribose and 2,6-dichloropurine provided crystalline 2AMTA as the oxalate salt. Chemo-enzymatic synthesis from ribose and 2,6-diaminopurine produced 2-amino-S-adenosylmethionine for hydrolytic conversion to 2AMTA. Interaction of 2AMTA with human MTAP was also characterized by pre-steady-state kinetics and by analysis of the crystal structure in a complex with sulfate as a catalytically inert analogue of phosphate. Furthermore, this assay is suitable for inhibitor screening by detection of fluorescent product, for quantitative analysis of hits by rapid and accurate measurement of inhibition constants in continuous assays, and pre-steady-state kinetic analysis of the target enzymes.

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

54 Mn Radiotracers Demonstrate Continuous Dissolution and Reprecipitation of Vernadite (δ-MnO 2 ) during Interaction with Aqueous Mn(II)

54 Mn radiotracers were used to assess Mn atom exchange between aqueous Mn(II) and vernadite (δ-MnO 2 ) at pH 5.0. Continuous solid–liquid redistribution of 54 Mn atoms occurred, and systems are near isotopic equilibrium after reaction for 3 months. Despite this extensive exchange, X-ray diffraction and X-ray absorption spectroscopy data showed no major changes in vernadite bulk mineralogy. These results demonstrate that the vernadite–Mn(II) interface is dynamic, with the substrate undergoing continuous dissolution and reprecipitation mediated by aqueous Mn(II) without observable impacts on its mineralogy. Interfacial redox reactions between adsorbed Mn(II) and solid-phase Mn(IV) and Mn(III) are proposed as the main drivers of this process. Interaction between aqueous Mn(II) and structural Mn(III) likely involves interfacial electron transfer coupled with Mn atom exchange. Here, the exchange of aqueous Mn(II) and solid-phase Mn(IV) is more complex and is proposed to result from coupled interfacial comproportionation–disproportionation reactions, where electron transfer from adsorbed Mn(II) to lattice Mn(IV) produces transient Mn(III) species that disproportionate to regenerate aqueous Mn(II) and structural Mn(IV). These findings provide further evidence of the importance of Mn(II) (aq) –MnO 2(s) interactions and the attendant production of transient Mn(III) intermediates to the geochemical functioning of phyllomanganates in environments undergoing Mn redox cycling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Self-Evolving Machine: A Continuously Improving Model for Molecular Thermochemistry

Because collecting precise and accurate chemistry data is often challenging, chemistry data sets usually only span a small region of chemical space, which limits the performance and the scope of applicability of data-driven models. To address this issue, we integrated an active learning machine with automatic ab initio calculations to form a self-evolving model that can continuously adapt to new species appointed by the users. In the present work, we demonstrate the self-evolving concept by modeling the formation enthalpies of stable closed-shell polycyclic species calculated at the B3LYP/6-31G(2df,p) level of theory. By combining a molecular graph convolutional neural network with a dropout training strategy, the model we developed can predict density functional theory (DFT) enthalpies for a broad range of polycyclic species and assess the quality of each predicted value. For the species which the current model is uncertain about, the automatic ab initio calculations provide additional training data to improve the performance of the model. For a test set composed of 2858 cyclic and polycyclic hydrocarbons and oxygenates, the enthalpies predicted by the model agree with the reference DFT values with a root-mean-square error of 2.62 kcal/mol. Finally, we found that a model originally trained on hydrocarbons and oxygenates can broaden its prediction coverage to nitrogen-containing species via an active learning process, suggesting that the continuous learning strategy is not only able to improve the model accuracy but is also capable of expanding the predictive capacity of a model to unseen species domains.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Continuously Tunable Pore Size for Gas Separation via a Bilayer Nanoporous Graphene Membrane

We report that pore size is a crucial factor impacting gas separation, but difficult to control for a single-layer nanoporous graphene membrane. Here, we propose a bilayer design of a nanoporous graphene membrane with a continuously tunable effective pore size, by shifting the lateral position of one graphene layer against the other. Molecular dynamics simulations of gas permeation reveal that selective separation of gases, such as CO 2 , N 2 , and CH 4 , of 3–4 Å in kinetic diameter can be achieved for a bilayer membrane from single-layer pores as large as 25 Å in size. Hence, this bilayer design allows both great flexibility of pore sizes in a single layer of graphene and continuous variation of the effective pore size through the bilayer at a sub-ångstrom level.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Ru-Sn/AC for the Aqueous-Phase Reduction of Succinic Acid to 1,4-Butanediol under Continuous Process Conditions

Succinic acid is a biomass-derived platform chemical that can be catalytically converted in the aqueous phase to 1,4-butanediol (BDO), a prevalent building block used in the polymer and chemical industries. Despite significant interest, limited work has been reported regarding sustained catalyst performance and stability under continuous aqueous-phase process conditions. As such, this work examines Ru-Sn on activated carbon (AC) for the aqueous-phase conversion of succinic acid to BDO under batch and flow reactor conditions. Initially, powder Ru-Sn catalysts were screened to determine the most effective bimetallic ratio and provide a comparison to other monometallic (Pd, Pt, Ru) and bimetallic (Pt-Sn, Pd-Re) catalysts. Batch reactor tests determined that a ~1:1 metal weight ratio of Ru to Sn was effective for producing BDO in high yields, with complete conversion resulting in 82% molar yield. Characterization of the fresh Ru-Sn catalyst suggests that the sequential loading method results in Ru sites that are colocated and surface-enriched with Sn. Postbatch reaction characterization confirmed stable Ru-Sn material properties; however, upon a transition to continuous conditions, significant Ru-Sn/AC deactivation occurred due to stainless steel leaching of Ni that resulted in Ru-Sn metal crystallite restructuring to form discrete Ni-Sn sites. Computational modeling confirmed favorable energetics for Ru-Sn segregation and Ni-Sn formation at submonolayer Sn incorporation. To address stainless steel leaching, reactor walls were treated with an inert silica coating by chemical vapor deposition. With leaching reduced, stable Ru-Sn/AC performance was observed that resulted in a molar yield of 71% BDO and 15% tetrahydrofuran for 96 h of time on stream. Postreaction catalyst characterization confirmed low levels of Ni and Cr deposition, although early-stage islanding of Ni-Sn will likely be problematic for industrially relevant time scales (i.e., thousands of hours). Overall, these results (i) demonstrate the performance of Ru-Sn/AC for aqueous phase succinic acid reduction, (ii) provide insight into the Ru-Sn bimetallic structure and deactivation in the presence of leached Ni, and (iii) underscore the importance of compatible reactor metallurgy and durable catalysts.

09 BIOMASS FUELS↗
DOE OSTI2025

Joint Experimental and Computational Characterization of Sum-Frequency Generation between a Continuous Wave Laser and an Ultrafast Frequency Comb Laser for Tunable Laser Development

Ultrafast optical frequency combs allow for both high spectral and temporal resolution in molecular spectroscopy and have become a powerful tool in many areas of chemistry and physics. Ultrafast lasers and frequency combs generated from ultrafast mode-locked lasers often need to be converted to other wavelengths. Commonly used wavelength conversions are optical parametric oscillators, which require an external optical cavity, and supercontinuum generation combined with optical parametric amplifiers. Whether commercial or home-built, these systems are complex and costly. Here, we investigate an alternative, simple, and easy-to-implement approach to tunable frequency comb ultrafast lasers enabled by new continuous-wave laser technology. Sum-frequency generation between an Nd:YAG continuous-wave laser and a Yb:fiber femtosecond frequency comb in a beta-barium borate (BBO) crystal is explored. The resulting sum-frequency beam is a pulsed frequency comb with the same repetition rate as the Yb:fiber source. SNLO simulation software is used to simulate the results and provide benchmarks for designing future systems to achieve wavelength conversion and tunability in otherwise difficult-to-reach spectral regions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Continuous Wave Resonant Photon Stimulated Electron Energy-Gain and Electron Energy-Loss Spectroscopy of Individual Plasmonic Nanoparticles

The unique optical properties of surface plasmon resonances in nanostructured materials have attracted considerable attention, broadly impacting both fundamental research and applied technologies ranging from sensing and optoelectronics to quantum computing. Electron energy-loss spectroscopy (EELS) in the transmission electron microscope has revealed valuable information about the full plasmonic spectrum of these materials with nanoscale spatial resolution. Here, in this study, we report a novel approach for experimentally accessing the photon-stimulated electron energy-gain and stimulated electron energy-loss responses of individual plasmonic nanoparticles via the simultaneous irradiation of a continuous wave laser and continuous current, monochromated electron probe. Stimulated gain and loss probabilities are equivalent and increase linearly in the low-irradiance range of 0.5 × 10 8 to 4 × 10 8 W/m 2 , above which excessive heating reduces the observed probabilities; importantly in our low-irradiance regime, the photon energy must be tuned in resonance with the plasmon energy for the stimulated gain and loss peaks to emerge. Theoretical modeling based on Fermi’s golden rule elucidates how the plasmon resonantly and coherently shuttles energy quanta between the electron probe and the radiation field and vice versa in stimulated electron energy-loss and -gain events. This study opens a fundamentally new approach to explore the quantum physics of excited-state plasmon resonances that does not rely on high-intensity laser pulses or any modification to the EELS detector.

(scanning) transmission electron microscope ((S)TE↗
DOE OSTI2020

Toward Long-Term Accurate and Continuous Monitoring of Nitrate in Wastewater Using Poly(tetrafluoroethylene) (PTFE)–Solid-State Ion-Selective Electrodes (S-ISEs)

Long-term accurate and continuous monitoring of nitrate (NO 3 – ) concentration in wastewater and groundwater is critical for determining treatment efficiency and tracking contaminant transport. Current nitrate monitoring technologies, including colorimetric, chromatographic, biometric, and electrochemical sensors, are not feasible for continuous monitoring. In this work, we addressed this challenge by modifying NO 3 – solid-state ion-selective electrodes (S-ISEs) with poly(tetrafluoroethylene) (PTFE, (C 2 F 4 ) n ). The PTFE-loaded S-ISE membrane polymer matrix reduces water layer formation between the membrane and electrode/solid contact, while paradoxically, the even more hydrophobic PTFE-loaded S-ISE membrane prevents bacterial attachment despite the opposite approach of hydrophilic modifications in other antifouling sensor designs. Specifically, an optimal ratio of 5% PTFE in the S-ISE polymer matrix was determined by a series of characterization tests in real wastewater. Five percent of PTFE alleviated biofouling to the sensor surface by enhancing the negative charge (–4.5 to –45.8 mV) and lowering surface roughness (Ra: 0.56 ± 0.02 nm). It simultaneously mitigated water layer formation between the membrane and electrode by increasing hydrophobicity (contact angle: 104°) and membrane adhesion and thus minimized the reading (mV) drift in the baseline sensitivity (“data drifting”). Long-term accuracy and durability of 5% PTFE-loaded NO 3 – S-ISEs were well demonstrated in real wastewater over 20 days, an improvement over commercial sensor longevity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

A Fully Integrated and Self-Powered Smartwatch for Continuous Sweat Glucose Monitoring

Wearable devices for health monitoring and fitness management have foreseen a rapidly expanding market, especially those for noninvasive and continuous measurements with real-time display that provide practical convenience and eliminated safety/infection risks. In this research, a self-powered and fully integrated smartwatch that consists of flexible photovoltaic cells and rechargeable batteries in the forms of a “watch strap”, electrochemical glucose sensors, customized circuits, and display units integrated into a “dial” platform is successfully fabricated for real-time and continuous monitoring of sweat glucose levels. The functionality of the smartwatch, including sweat glucose sensing, signal processing, and display, can be supported with the harvested/converted solar energy without external charging devices. The Zn-MnO 2 batteries serve as intermediate energy storage units and the utilization of aqueous electrolytes eliminated safety concerns for batteries, which is critical for wearable devices. Such a wearable system in a smartwatch fashion realizes integration of energy modules with self-powered capability, electrochemical sensors for noninvasive glucose monitoring, and in situ and real-time signal processing/display in a single platform for the first time. The as-fabricated fully integrated and self-powered smartwatch also provides a promising protocol for statistical study and clinical investigation to reveal correlations between sweat compositions and human body dynamics.

47 OTHER INSTRUMENTATION↗
DOE OSTI2013

Characterizing Microbial Community and Geochemical Dynamics at Hydrothermal Vents Using Osmotically Driven Continuous Fluid Samplers

Microbes play a key role in mediating all aquatic biogeochemical cycles, and ongoing efforts are aimed at better understanding the relationships between microbial phylogenetic and physiological diversity, and habitat physical and chemical characteristics. Establishing such relationships is facilitated by sampling and studying microbiology and geochemistry at the appropriate spatial and temporal scales, to access information on the past and current environmental state that contributes to observed microbial abundances and activities. A modest number of sampling systems exist to date, few of which can be used in remote, harsh environments such as hydrothermal vents, where the ephemeral nature of venting underscores the necessity for higher resolution sampling. We have developed a robust, continuous fluid sampling system for co-registered microbial and biogeochemical analyses. The osmosis-powered bio-osmosampling system (BOSS) use no electricity, collects fluids with daily resolution or better, can be deployed in harsh, inaccessible environments and can sample fluids continuously for up to five years. Here we present a series of tests to examine DNA, RNA and protein stability over time, as well as material compatability, via lab experiments. We also conducted two field deployments at deep-sea hydrothermal vents to assess changes in microbial diversity and protein expression as a function of the physico-chemical environment. Our data reveal significant changes in microbial community composition co-occurring with relatively modest changes in the geochemistry. These data additionally provide new insights into the distribution of an enigmatic sulfur oxidizing symbiont in its free-living state. Data from the second deployment reveal differences in the representation of peptides over time, underscoring the utility of the BOSS in meta-proteomic studies. In concert, these data demonstrate the efficacy of this approach, and illustrate the value of using this method to study microbial and geochemical phenomena.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2014

Hydrothermal Processing of Macroalgal Feedstocks in Continuous-Flow Reactors

Wet macroalgal slurries have been converted into a biocrude by hydrothermal liquefaction (HTL) in a bench-scale continuous-flow reactor system. Carbon conversion to a gravity-separable oil product of 58.8% was accomplished at relatively low temperature (350 °C) in a pressurized (subcritical liquid water) environment (20 MPa) when using feedstock slurries with a 21.7% concentration of dry solids. As opposed to earlier work in batch reactors reported by others, direct oil recovery was achieved without the use of a solvent, and biomass trace mineral components were removed by processing steps so that they did not cause processing difficulties. In addition, catalytic hydrothermal gasification (CHG) was effectively applied for HTL byproduct water cleanup and fuel gas production from water-soluble organics. Conversion of 99.2% of the carbon left in the aqueous phase was demonstrated. Finally, as a result, high conversion of macroalgae to liquid and gas fuel products was found with low levels of residual organic contamination in byproduct water. Both process steps were accomplished in continuous-flow reactor systems such that design data for process scale-up was generated.

biomass↗
DOE OSTI2022

Achievements and Prospects of Global Broadband Seismographic Networks After 30 Years of Continuous Geophysical Observations

Global seismographic networks (GSNs) emerged during the late nineteenth and early twentieth centuries, facilitated by seminal international developments in theory, technology, instrumentation, and data exchange. The mid- to late-twentieth century saw the creation of the World-Wide Standardized Seismographic Network (1961) and International Deployment of Accelerometers (1976), which advanced global geographic coverage as seismometer bandwidth increased greatly allowing for the recording of the Earth's principal seismic spectrum. The modern era of global observations and rapid data access began during the 1980s, and notably included the inception of the GEOSCOPE initiative (1982) and GSN (1988). Through continual improvements, GEOSCOPE and the GSN have realized near-real time recording of ground motion with state-of-art data quality, dynamic range, and timing precision to encompass 180 seismic stations, many in very remote locations. Data from GSNs are increasingly integrated with other geophysical data (e.g., space geodesy, infrasound and Interferometric Synthetic Aperture Radar). Globally distributed seismic data are critical to resolving crust, mantle, and core structure; illuminating features of the plate tectonic and mantle convection system; rapid characterization of earthquakes; identification of potential tsunamis; global nuclear test verification; and provide sensitive proxies for environmental changes. As the global geosciences community continues to advance our understanding of Earth structure and processes controlling elastic wave propagation, GSN infrastructure offers a springboard to realize increasingly multi-instrument geophysical observatories. Here, we review the historical, scientific, and monitoring heritage of GSNs, summarize key discoveries, and discuss future associated opportunities for Earth Science.

58 GEOSCIENCES↗
DOE OSTI2023

Understanding Subsurface Fracture Evolution Dynamics Using Time‐Lapse Full Waveform Inversion of Continuous Active‐Source Seismic Monitoring Data

Abstract Predicting the behavior, geometry, and flow properties of subsurface fractures remains a challenging problem. Seismic models that can characterize fractures usually suffer from low spatiotemporal resolution. Here, we develop a correlative double‐difference time‐lapse full waveform inversion of continuous active source seismic monitoring data for determining high‐spatiotemporal‐resolution time‐lapse V p models of in‐situ fracture evolution at a shallow contamination site in Wyoming, USA. Assisted by rock physics modeling, we find that (a) rapidly increasing pore pressure initializes and grows the fracture, increasing the porosity slightly (from ∼13.7% to ∼14.6%) in the tight clay formation, thus decreasing V p (∼50 m/s); (b) the fluid injection continues decreasing V p , likely through the introduction of gas bubbles in the injectate; and (c) final V p reductions reach over ∼150 m/s due to a posited ∼4.5% gas saturation. Our results demonstrate that high‐resolution V p changes are indicative of mechanical and fluid changes within the fracture zone during hydrofracturing.

58 GEOSCIENCES↗
DOE OSTI2013

In situ atomic-scale observation of continuous and reversible lattice deformation beyond the elastic limit

The elastic strain sustainable in crystal lattices is usually limited by the onset of inelastic yielding mediated by discrete dislocation activity, displacive deformation twinning and stress-induced phase transformations, or fracture associated with flaws. Here we report a continuous and gradual lattice deformation in bending nickel nanowires to a reversible shear strain as high as 34.6%, which is approximately four times that of the theoretical elastic strain limit for unconstrained loading. The functioning deformation mechanism was revealed on the atomic scale by an in situ nanowire bending experiments inside a transmission electron microscope. The complete continuous lattice straining process of crystals has been witnessed in its entirety for the straining path, which starts from the face-centred cubic lattice, transitions through the orthogonal path to reach a body-centred tetragonal structure and finally to a re-oriented face-centred cubic structure.

36 MATERIALS SCIENCE↗