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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Numerical solution of singular Lyapunov equations

We consider the numerical solution of large scale singular (continuous-time) Lyapunov equations of the form AX + XA T + BB T = 0, where A is semistable, that is, its spectrum is contained in the left half plane, with the exception of a few semisimple eigenvalues at zero. We also consider the case of a few semisimple eigenvalues on the imaginary axis. We assume that we know these few eigenvalues (zero or imaginary), and that we have or can compute the corresponding invariant subspaces. We use this information to build an appropriate newly proposed subspace on which to project the Lyapunov equations, and then compute a low-rank approximation to the least squares solution. Selected illustrative numerical examples are provided.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

A Fundamentally New Coupled Approach to Contact Mechanics via the Dirichlet‐Neumann Schwarz Alternating Method

Contact phenomena are crucial for understanding the behavior of mechanical systems. However, existing computational approaches for simulating mechanical contact often face numerical challenges, such as inaccurate physical predictions, energy conservation errors, and unwanted oscillations. Here, we introduce an alternative technique for simulating dynamic contact based on the non‐overlapping Schwarz alternating method, originally developed for domain decomposition. In multibody contact scenarios, this method treats each body as a separate, non‐overlapping domain and prevents interpenetration using an alternating Dirichlet–Neumann iterative process. This approach has a strong theoretical foundation, eliminates the need for contact constraints, and offers flexibility, making it ideal for multiscale and multiphysics applications. We conducted a numerical comparison between the Schwarz method and traditional methods, such as the Lagrange multiplier and penalty methods, focusing on a benchmark impact problem. Our results indicate that the Schwarz alternating method outperforms traditional methods in several key areas: it provides more accurate predictions for various measurable quantities and demonstrates exceptional energy conservation capabilities. To address unwanted oscillations in contact velocities and forces, we explored various algorithms and stabilization techniques, ultimately opting for the naïve‐stabilized Newmark scheme for its simplicity and effectiveness. Additionally, we validated the efficiency of the Schwarz method in a three‐dimensional impact problem, highlighting its inherent capacity to accommodate different mesh topologies, time‐integration schemes, and time steps for each interacting body.

Schwarz alternating method↗
DOE OSTI2024

Effect of laminae count and manufacturing methods on mechanical properties of thin‐ply woven composites

Abstract Thin‐ply woven composites exhibit exceptional mechanical performance by delaying the onset of damage, making them suitable for high‐performance structural applications. This study outlines the impact of manufacturing techniques (vacuum bagging and hot pressing), ply count, and fiber waviness on the mechanical properties of aromatic thermosetting copolyester/carbon‐fiber (ATSP/CF) composites. The analysis encompasses several different ply counts, evaluating their effects on the in‐plane elastic modulus (0°–90°) and tensile strength. Results demonstrate that reducing the waviness (or crimp) ratio significantly enhances the in‐plane elastic modulus, with improvements up to 188%, highlighting the importance of fiber alignment. Vacuum bagging produced ply thicknesses from 128 to 58 μm for 1–36 plies, with in‐plane elastic moduli from 30.3 to 87.2 GPa, and 4‐ and 8‐ply samples showed approximately 40% higher stiffness than those made by hot pressing. ATSP resin with high thermal stability (up to 400°C) and recyclability was used. Furthermore, this study highlights the microstructural enhancements achieved through vacuum bagging, as revealed by scanning electron and optical microscopy, and micro‐computed tomography imaging. This paper provides insights into damage mitigation and achieving enhanced mechanical properties by controlling fiber waviness using vacuum bagging and higher ply count in thin‐ply ATSP/CF composites. Highlights Crimp ratio reduction enhances elastic in‐plane elastic modulus up to 188%. Vacuum bagging increases modulus over the hot pressing manufacturing method by 40%. Lowering thickness‐per‐ply increases failure strain from 0.8% to 1.2%. Explored the performance of a novel ATSP matrix with high recyclability and thermal stability.

Kushwaha, Shashank [The Grainger College of Engine↗
DOE OSTI2021

Poly(ether‐block‐amide) membrane with deformability and adjustable surface hydrophilicity for water purification

Abstract Freshwater resources are currently insufficient, and another form of freshwater resources, namely, ice, is very interesting except for the issue of how to use new materials for effective purification during the processing procedure. In this article, a new membrane material with multisize pore structure in the cross‐section and intact thin skin layer on the upper and lower surfaces was successfully prepared by adding porogen, filler and setting heating environment during the phase separation process. The membrane exhibits excellent axial deformability, and its elongation at break can reach to 160% strain. Meanwhile, they all show elastic deformation behavior in the range from −60 to 100°C. Even if high content of hydrophobic filler is compounded into these membranes, that is, 5.7 wt% carbon tube content, water contact angle of membrane's surface is only 72.5°, demonstrating obvious hydrophilicity. In addition, in the water purification process, the adsorption rate constant reached ideal value of 0.26 s −1 , and the equilibrium adsorption capacity was about 2.8 g/g, showing fast and efficient water purification ability. In the mode of external heating source or the membrane's heat dissipation, these prepared membranes can melt the ice to obtain purified water and exhibit a controllable purification ability in this process.

Ge, Chengbiao↗
DOE OSTI2022

Automated detection of photovoltaic cleaning events: A performance comparison of techniques as applied to a broad set of labeled photovoltaic data sets

Extracting accurate soiling loss information from photovoltaic (PV) production data first requires segmenting the time series data per natural or manually occurring cleaning events. Maintenance logs are often incomplete, rain data are often unavailable, and the debate on rain thresholds for cleaning and dew or wind cleanings is still ongoing. The present work aims to overtake these issues by improving automated methods to detect these cleaning events and therefore improve extraction of soiling loss information. Time series power production data from 22 PV inverters were labeled for natural or manually occurring cleaning events. The data sets were carefully selected to include varying degrees of soiling, cleaning events, and noise. Several algorithms, including filtering logic and change point detection, were examined for efficacy at detecting the labeled cleanings. All the methods introduced except for changepoint detection showed significant improvement at detecting the labeled cleaning events per the mean F 1 score. Furthermore, the highest performing cleaning detection algorithm achieved an absolute increase in the mean F 1 score of 43% over the default version of the RdTools stochastic rate and recovery (SRR) algorithm. The highest performing algorithm included irradiance filtering and a cleaning detection threshold, adjusted based on the 40-day centered rolling median of the absolute day-to-day deviations in the daily performance index (PI). Furthermore, these improvements are promising as cleaning detection is an essential step in the automated analysis of PV soiling.

14 SOLAR ENERGY↗
DOE OSTI2023

Effect of isopropanol cosolvent on the rheology and spinnability of aqueous polyacrylic acid solutions

Abstract We investigate the effect of alcohol fraction (isopropanol, IPA) in a binary water‐alcohol solvent mixture on the shear and extensional rheological properties, as well as the role of viscoelasticity on fiber formation of poly(acrylic acid) (PAA) in electrospinning. Comparison of the scaling of both specific viscosities η sp and extensional relaxation times λ E of PAA in water–IPA mixtures, showed stronger scaling compared to salt‐free aqueous polyelectrolyte solutions, except for the η sp in the unentangled regime displaying a polyelectrolyte‐like scaling η sp ~ c 0.5 for all IPA%. Such deviation suggested IPA induces association/aggregation of PAA. However, the trends between η sp and λ E magnitudes as a function of IPA% differ for concentrations compared in the entangled regime. The η sp as well as their elastic moduli exhibit a maximum, whereas λ E increases monotonically with IPA%, suggesting a complex interplay of various interactions are dictating their structure in water‐IPA mixtures, affecting their shear and extensional response differently. Electrospinning experiments showed increasing IPA% reduces the onset of both beaded and uniform fibers. Analysis using dimensionless numbers indicated the enhancement of their elasticity by IPA, and the consequent stabilizing effect on their jets/filaments against break‐up during electrospinning, plays a role in the improvement of their fiber formation.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Second‐ and Third‐Order Elastic Constants of Inert and Energetic Molecular Crystals From Density Functional Theory

Complete tensors of the second- and third-order elastic constants of the organic molecular crystals acetaminophen, pentaerythritol tetranitrate (PETN), cyclotrimethylene trinitramine (RDX), cyclotetramethylene tetranitramine (HMX), 1,1-diamino-2,2-dinitroethylene (FOX-7), hexanitrohexaazaisowurtzitane (CL-20), and erythritol tetranitrate (ETN) have been calculated using dispersion-corrected density functional theory. The sets of second- and third-order elastic constants are expected to provide a more accurate and reliable description of the behavior of these materials under nonhydrostatic loads than pressure- and volume-dependent second-order elastic constants. The tensors of second-order constants have been compared with experimental data and/or other calculations when possible, and with the exception of results for CL-20 from Brillouin scattering experiments, we find good agreement. The calculated third-order elastic constants of PETN are in very good agreement with the subset of third-order constants derived from experimental wave speed measurements. The elastic anisotropies of the crystals have been estimated using the universal elastic anisotropy index, which shows that the crystals fall into three groups with low anisotropy (PETN, RDX, and CL-20), moderate anisotropy (acetaminophen, HMX, and ETN), and high elastic anisotropy (FOX-7).

36 MATERIALS SCIENCE↗
DOE OSTI2025

Contrasting Chemical Kinetic Parameters for Near In‐Service‐Temperature Aging and High‐Temperature Thermal Decomposition of Triaminotrinitrobenzene Formulations

Triaminotrinitrobenzene-based high explosives such as LX-17 offer high energy density and exceptional safety, yet their long-term aging behavior at low temperatures remains poorly understood. In this study, several legacy and new production lots of LX-17 were subjected to accelerated aging experiments below 100°C, during which the formation rate of the initial degradation product, monofurazan (F1), was monitored. Kinetic analysis was performed using a sample-age-aware computational approach, yielding activation energy estimates of 82–91 kJ mol −1 for the low-temperature initiation step—markedly lower than the ∼200 kJ mol −1 associated with high-temperature thermal decomposition. Extrapolation from established cookoff models supports the conclusion that the dominant degradation mechanism at low temperatures differs from that at high temperatures. In conclusion, our results provide a unified kinetic framework that bridges the gap between in-service conditions and high-temperature damage.

Chemistry - Chemical explosives↗
DOE OSTI2020

Solution structure for an Encephalitozoon cuniculi adrenodoxin-like protein in the oxidized state

Encephalitozoon cuniculi is a unicellular, obligate intracellular eukaryotic parasite in the Microsporidia family and one of the agents responsible for microsporidosis infections in humans. Like most Microsporidia, the genome of E. cuniculi is markedly reduced and the organism contains mitochondria-like organelles called mitosomes instead of mitochondria. Here we report the solution NMR structure for a protein physically associated with mitosome-like organelles in E. cuniculi, the 128-residue, adrenodoxin-like protein Ec-Adx (UniProt ID Q8SV19) in the [2Fe-2S] ferredoxin superfamily. Oxidized Ec-Adx contains a mixed four-strand β-sheet, β2-β1-β4-β3 (↓↑↑↓), loosely encircled by three α-helices and two 310-helices. This fold is similar to the structure observed in other adrenodoxin and adrenodoxin-like proteins except for the absence of a fifth anti-parallel β-strand next to β3 and the position of α3. Cross peaks are missing or cannot be unambiguously assigned for 20 amide resonances in the 1 H- 15 N HSQC spectrum of Ec-Adx. These missing residues are clustered primarily in two regions, G48-V61 and L94-L98, containing the four cysteine residues predicted to ligate the paramagnetic [2Fe-2S] cluster. Missing amide resonances in 1 H- 15 N HSQC spectra are detrimental to NMR-based solution structure calculations because 1 H- 1 H NOE restraints are absent (glass half-empty) and this may account for the absent β-strand (β5) and the position of α3 in oxidized Ec-Adx. On the other hand, the missing amide resonances unambiguously identify the presence, and immediate environment, of the paramagnetic [2Fe-2S] cluster in oxidized Ec-Adx (glass half-full).

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Structural characterization and computational analysis of PDZ domains in Monosiga brevicollis

Abstract Identification of the molecular networks that facilitated the evolution of multicellular animals from their unicellular ancestors is a fundamental problem in evolutionary cellular biology. Choanoflagellates are recognized as the closest extant nonmetazoan ancestors to animals. These unicellular eukaryotes can adopt a multicellular‐like “rosette” state. Therefore, they are compelling models for the study of early multicellularity. Comparative studies revealed that a number of putative human orthologs are present in choanoflagellate genomes, suggesting that a subset of these genes were necessary for the emergence of multicellularity. However, previous work is largely based on sequence alignments alone, which does not confirm structural nor functional similarity. Here, we focus on the PDZ domain, a peptide‐binding domain which plays critical roles in myriad cellular signaling networks and which underwent a gene family expansion in metazoan lineages. Using a customized sequence similarity search algorithm, we identified 178 PDZ domains in the Monosiga brevicollis proteome. This includes 11 previously unidentified sequences, which we analyzed using Rosetta and homology modeling. To assess conservation of protein structure, we solved high‐resolution crystal structures of representative M. brevicollis PDZ domains that are homologous to human Dlg1 PDZ2, Dlg1 PDZ3, GIPC, and SHANK1 PDZ domains. To assess functional conservation, we calculated binding affinities for mbGIPC, mbSHANK1, mbSNX27, and mbDLG‐3 PDZ domains from M. brevicollis . Overall, we find that peptide selectivity is generally conserved between these two disparate organisms, with one possible exception, mbDLG‐3. Overall, our results provide novel insight into signaling pathways in a choanoflagellate model of primitive multicellularity.

Gao, Melody↗
DOE OSTI2023

Monomer and dimer structures of cytochrome bo 3 ubiquinol oxidase from Escherichia coli

Abstract The Escherichia coli cytochrome bo 3 ubiquinol oxidase is a four‐subunit heme‐copper oxidase that serves as a proton pump in the E. coli aerobic respiratory chain. Despite many mechanistic studies, it is unclear whether this ubiquinol oxidase functions as a monomer, or as a dimer in a manner similar to its eukaryotic counterparts—the mitochondrial electron transport complexes. In this study, we determined the monomeric and dimeric structures of the E. coli cytochrome bo 3 ubiquinol oxidase reconstituted in amphipol by cryogenic electron microscopy single particle reconstruction (cryo‐EM SPR) to a resolution of 3.15 and 3.46 Å, respectively. We have discovered that the protein can form a dimer with C2 symmetry, with the dimerization interface maintained by interactions between the subunit II of one monomer and the subunit IV of the other monomer. Moreover, the dimerization does not induce significant structural changes in the monomers, except the movement of a loop in subunit IV (residues 67–74).

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Engineering highly stable variants of Corynactis californica green fluorescent proteins

Fluorescent proteins (FPs) are versatile biomarkers that facilitate effective detection and tracking of macromolecules of interest in real time. Engineered FPs such as superfolder green fluorescent protein (sfGFP) and superfolder Cherry (sfCherry) have exceptional refolding capability capable of delivering fluorescent readout in harsh environments where most proteins lose their native functions. Our recent work on the development of a split FP from a species of strawberry anemone, Corynactis californica, delivered pairs of fragments with up to threefold faster complementation than split GFP. We present the biophysical, biochemical, and structural characteristics of five full-length variants derived from these split C. californica GFP (ccGFP). These ccGFP variants are more tolerant under chemical denaturation with up to 8 kcal/mol lower unfolding free energy than that of the sfGFP. It is likely that some of these ccGFP variants could be suitable as biomarkers under more adverse environments where sfGFP fails to survive. A structural analysis suggests explanations of the variations in stabilities among the ccGFP variants.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Prediction of protein assemblies, the next frontier: The CASP14-CAPRI experiment

Here we present the results for CAPRI Round 50, the fourth joint CASP-CAPRI protein assembly prediction challenge. The Round comprised a total of twelve targets, including six dimers, three trimers, and three higher-order oligomers. Four of these were easy targets, for which good structural templates were available either for the full assembly, or for the main interfaces (of the higher-order oligomers). Eight were difficult targets for which only distantly related templates were found for the individual subunits. Twenty-five CAPRI groups including eight automatic servers submitted ~1250 models per target. Twenty groups including six servers participated in the CAPRI scoring challenge submitted ~190 models per target. The accuracy of the predicted models was evaluated using the classical CAPRI criteria. The prediction performance was measured by a weighted scoring scheme that takes into account the number of models of acceptable quality or higher submitted by each group as part of their five top-ranking models. Compared to the previous CASP-CAPRI challenge, top performing groups submitted such models for a larger fraction (70–75%) of the targets in this Round, but fewer of these models were of high accuracy. Scorer groups achieved stronger performance with more groups submitting correct models for 70–80% of the targets or achieving high accuracy predictions. Servers performed less well in general, except for the MDOCKPP and LZERD servers, who performed on par with human groups. In addition to these results, major advances in methodology are discussed, providing an informative overview of where the prediction of protein assemblies currently stands.

protein complexes↗
DOE OSTI2024

Antimicrobial mechanisms of g‐C 3 N 4 @ ZnO against oomycetes Phytophthora capsici: from its metabolism, membrane structures and growth

Abstract BACKGROUND Phytophthora capsici , a refractory and model oomycete plant pathogen, especially threatens multiple vegetable crops. A limited number of chemical pesticides play a vital role in controlling oomycete plant diseases. However, this approach often leads to excessive use of chemical agent, exacerbates environmental issues and more and more drug‐resistant strains of oomycete. Therefore, it is imperative to devise innovative solutions that can effectively address the infection of oomycete while maintaining high levels of environmental sustainability and low toxicity. RESULTS In this study, g‐C 3 N 4 @ZnO heterostructure was synthesized and characterized. The g‐C 3 N 4 @ZnO showed higher toxicity on Phytophthora capsici than graphitic carbon nitride (g‐C 3 N 4 ) nanosheets and zinc oxide (ZnO) nanoparticles in vitro and in vivo . Except the hyphal growth of Phytophthora capsici , their germination rate of spores, sporangium formation and number of spores were all suppressed by g‐C 3 N 4 @ZnO heterostructure. Furthermore, we found that this g‐C 3 N 4 @ZnO heterostructure has higher photocatalytic activity under visible light, which potentially enhanced the reactive oxygen species (ROS) mediated stress on Phytophthora capsici . Ultrastructural morphology, global changes of gene expression and weighted gene co‐expression network analysis all supported that the anti‐oomycete activity of g‐C 3 N 4 @ZnO was manifested in the destruction of membrane system and inhibition of multiple metabolisms of Phytophthora capsici under visible irradiation, which also could be attributed to the ROS and zinc ion (Zn 2+ ) mediated stress. CONCLUSION This works offers a novel oomycete disease management strategy by using g‐C 3 N 4 @ZnO, which were attributed to the ROS stress, destruction of membrane system and inhibition of multiple metabolisms. © 2023 Society of Chemical Industry.

Cai, Lin↗
DOE OSTI2024

The Nonradiative Properties of Self–Trapped Holes in Ultra–Wide Bandgap Gallium Oxide Film

The photoluminescence (PL) of self-trapped holes (STH) in ultra-wide bandgap β-Ga 2 O 3 is commonly its most dominant light emission and is an inherent property. Thus, gaining knowledge of the crystal dynamics that impact the PL properties is vital to sensor and other technologies. The PL, Raman-phonons, and their interactions are studied at an extreme temperature range of 77–622 K. The PL is studied up to the bandgap value of ≈5 eV. It is found that the high-energy Raman modes provide a major route to the nonradiative process of the PL via STH–phonon interaction with an activation energy of 72 meV. This dynamic is modeled with the configurational coordinate scheme at the strong phonon coupling limit. The exceptionally broad Gaussian PL linewidth manifests this coupling. The weak temperature response of the PL energy peak position indicates that the STH has characteristics of a deep-level defect. This contrasts with the large redshift of ≈220 meV of the optical gap of the film, ascertained from transmission. Unlike the temperature response of the high-energy phonons, the behavior of the low-energy phonons is found to follow the Bose–Einstein population increase, indicating no strong interaction with the STH.

Raman↗
DOE OSTI2021

Elastic Properties and Deformation Mechanisms in the van der Waals Single-Crystalline Indium Selenide

The bulk van der Waals (vdW) single-crystalline indium selenide (β-InSe) displays exceptional plasticity in a layered crystalline form at both micro- and macroscale. However, the nanoscale origin of plasticity remains unclear. Herein, an atomic-level study on the deformation mechanisms of InSe by using first-principles calculations is reported. Remarkable anisotropic elasticity is observed in the vdW InSe layered crystal, and the stiffness is dramatically softened because of the vdW gap in the layered structure. The simulations capture the distinct fracture modes in the uniaxial tensile deformation, depending on the loading directions—brittle fracture in the [100] and [110] directions while ductile failure in the [001] direction. The InSe layered crystal structure exhibits superplastic deformability under uniaxial compression. Different transition pathways, including interlayer tangling, amorphization, and cross-linking, are tracked along respective deformation directions. The unprecedented plasticity of InSe layered crystals can be attributed to the phase transition coupled with interlayer gliding and cross-layer dislocation slipping. Here, this study deepens our understanding of the deformation mechanisms of layered materials at the atomistic level and provides insights into tailoring material properties for low-dimensional material design based on its deformation mechanisms.

2D materials↗
DOE OSTI2024

Investigation of Interlayer Dielectric in BaTiO 3 /III–Nitride Transistors

In this paper, the impact of varying the thickness of the Al 2 O 3 interlayer dielectric on the electrical characteristics of BaTiO 3 /III-nitride transistors is investigated. In the findings, it is revealed that a minimum thickness of 8 nm for the Al 2 O 3 layer is crucial to maintain high device performance and protect against sputtering-induced damage during BaTiO 3 deposition. The fabricated BaTiO 3 /Al 2 O 3 /AlGaN/GaN high electron mobility transistors exhibit exceptional electrical properties, including a maximum current density of 700 mA mm –1 , an on-resistance of 5 Ω mm, an I ON /I OFF ratio of 10 7 , a subthreshold slope of 119 mV dec –1 , and significantly reduced gate leakage current. The devices with the optimal 8 nm Al 2 O 3 thickness demonstrates excellent agreement between theoretical and experimental values for effective mobility, achieving a value of 1188 cm 2 V –1 ·s at a 2D electron gas density of 10 13 cm –2 . Furthermore, in the study, it is confirmed that increasing the Al 2 O 3 thickness also improves the quality of interface charge density, as evidenced by the results obtained from capacitance–voltage measurements. In these findings, the critical role of controlling the Al 2 O 3 thickness in optimizing the electrical characteristics and overall performance of BaTiO 3 /III-nitride transistors are highlighted.

42 ENGINEERING↗
DOE OSTI2023

Synthesis of Pyrimidine Modified Seleno–DNA as a Novel Approach to Antisense Candidate

Chemically modified antisense oligonucleotides (ASO) currently in pre–clinical and clinical experiments mainly focus on the 2’–position derivatizations to enhance stability and targeting affinity. Considering the possible incompatibility of 2’–modifications with RNase H stimulation and activity, we have hypothesized that the atom specific modifications on nucleobases can retain the complex structure and RNase H activity, while enhancing ASO's binding affinity, specificity, and stability against nucleases. Herein we report a novel strategy to explore our hypothesis by synthesizing the deoxynucleoside phosphoramidite building block with the seleno–modification at 5–position of thymidine, as well as its Se–oligonucleotides. Via X–ray crystal structural study, we found that the Se–modification was located in the major groove of nucleic acid duplex and didn't cause the thermal and structural perturbations. Surprisingly, our nucleobase–modified Se–DNAs were exceptionally resistant to nuclease digestion, while compatible with RNase H activity. In conclusion, this affords a novel avenue for potential anti–sense modification in the form of Se–antisense oligonucleotides (Se–ASO).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗