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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Mode shape combination in a two-dimensional vibration energy harvester through mass loading structural modification

Mode shapes in the design of mechanical energy harvesters, as a means of performance increase, have been largely overlooked. Currently, the vast majority of energy harvester designs employ some variation of a single-degree-of-freedom cantilever, and the mode shapes of such beams are well known. This is especially true for the first bending mode, which is almost exclusively the chosen vibration mode for energy harvesting. Two-dimensional beam shapes (those which curve, meander, spiral, etc., in a plane) have recently gained research interest, as they offer freedom to modify the vibration characteristics of the harvester beam for achieving higher power density. In this study, the second bending mode shape of the “Elephant” two-dimensional beam shape is examined, and its interaction with the first bending mode is evaluated. A combinatory mode shape created by using mass loading structural modification to lower the second bending modal frequency was found to interact with the first bending mode. This is possible since the first two bending modes do not share common areas of displacement. The combined mode shape is shown to produce the most power of any of the considered mode shapes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Modification of a graphene – copper substrate in vacuum by femtosecond laser radiation

The effect of intense femtosecond laser radiation on single-layer graphene fixed on a copper fine-meshed grid is studied using a compact femtosecond electron diffractometer. A modification of the graphene – copper substrate is found. The composition of the resulting compounds is analysed. It is shown that the main new products are copper oxides. The prospects of using such a substrate in the method of ultrafast electron diffraction and microscopy are analysed. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

C-terminal modification of the insulin B:11–23 peptide creates superagonists in mouse and human type 1 diabetes

A polymorphism at β57 in some major histocompatibility complex class II (MHCII) alleles of rodents and humans is associated with a high risk for developing type 1 diabetes (T1D). However, a highly diabetogenic insulin B chain epitope within the B:9–23 peptide is presented poorly by these alleles to a variety of mouse and human CD4 T cells isolated from either nonobese diabetic (NOD) mice or humans with T1D. We have shown for both species that mutations at the C-terminal end of this epitope dramatically improve presentation to these T cells. Here we present the crystal structures of these mutated peptides bound to mouse IA g7 and human HLA-DQ8 that show how the mutations function to improve T-cell activation. In both peptide binding grooves, the mutation of B:22R to E in the peptide changes a highly unfavorable side chain for the p9 pocket to an optimal one that is dependent on the β57 polymorphism, accounting for why these peptides bind much better to these MHCIIs. Furthermore, a second mutation of the adjacent B:21 (E to G) removes a side chain from the surface of the complex that is highly unfavorable for a subset of NOD mouse CD4 cells, thereby greatly enhancing their response to the complex. These results point out the similarities between the mouse and human responses to this B chain epitope in T1D and suggest there may be common posttranslational modifications at the C terminus of the peptide in vivo to create the pathogenic epitopes in both species.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Characterizing posttranslational modifications in prokaryotic metabolism using a multiscale workflow

Understanding the complex interactions of protein posttranslational modifications (PTMs) represents a major challenge in metabolic engineering, synthetic biology, and the biomedical sciences. In this work, we present a workflow that integrates multiplex automated genome editing (MAGE), genome-scale metabolic modeling, and atomistic molecular dynamics to study the effects of PTMs on metabolic enzymes and microbial fitness. This workflow incorporates complementary approaches across scientific disciplines; provides molecular insight into how PTMs influence cellular fitness during nutrient shifts; and demonstrates how mechanistic details of PTMs can be explored at different biological scales. As a proof of concept, we present a global analysis of PTMs on enzymes in the metabolic network of Escherichia coli. Based on our workflow results, we conduct a more detailed, mechanistic analysis of the PTMs in three proteins: enolase, serine hydroxymethyltransferase, and transaldolase. Finally, application of this workflow identified the roles of specific PTMs in observed experimental phenomena and demonstrated how individual PTMs regulate enzymes, pathways, and, ultimately, cell phenotypes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Modifications to cosmological power spectra from scalar-tensor entanglement and their observational consequences

We consider the effects of entanglement in the initial quantum state of scalar and tensor fluctuations during inflation. We allow the gauge-invariant scalar and tensor fluctuations to be entangled in the initial state and compute modifications to the various cosmological power spectra. We compute the angular power spectra (C{sub l}’s) for some specific cases of our entangled state and discuss what signals one might expect to find in CMB data. This entanglement also can break rotational invariance, allowing for the possibility that some of the large scale anomalies in the CMB power spectrum might be explained by this mechanism.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Tubulin perturbation leads to unexpected cell wall modifications and affects stomatal behaviour in Populus

Cortical microtubules are integral to plant morphogenesis, cell wall synthesis, and stomatal behaviour, presumably by governing cellulose microfibril orientation. Genetic manipulation of tubulins often leads to abnormal plant development, making it difficult to probe additional roles of cortical microtubules in cell wall biogenesis. Here, it is shown that expressing post-translational C-terminal modification mimics of α-tubulin altered cell wall characteristics and guard cell dynamics in transgenic Populus tremula x alba that otherwise appear normal. 35 S promoter-driven transgene expression was high in leaves but unusually low in xylem, suggesting high levels of tubulin transgene expression were not tolerated in wood-forming tissues during regeneration of transformants. Cellulose, hemicellulose, and lignin contents were unaffected in transgenic wood, but expression of cell wall-modifying enzymes, and extractability of lignin-bound pectin and xylan polysaccharides were increased in developing xylem. The results suggest that pectin and xylan polysaccharides deposited early during cell wall biogenesis are more sensitive to subtle tubulin perturbation than cellulose and matrix polysaccharides deposited later. Tubulin perturbation also affected guard cell behaviour, delaying drought-induced stomatal closure as well as light-induced stomatal opening in leaves. Pectins have been shown to confer cell wall flexibility critical for reversible stomatal movement, and results presented here are consistent with microtubule involvement in this process. In conclusion, taken together, the data show the value of growth-compatible tubulin perturbations for discerning microtubule functions, and add to the growing body of evidence for microtubule involvement in non-cellulosic polysaccharide assembly during cell wall biogenesis.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Lysine carboxylation: unveiling a spontaneous post-translational modification

A computational method for the prediction of lysine carboxylation (KCX) in protein structures is described. The method accurately identifies misreported KCXs and predicts previously unknown KCX sites. The carboxylation of lysine residues is a post-translational modification (PTM) that plays a critical role in the catalytic mechanisms of several important enzymes. It occurs spontaneously under certain physicochemical conditions, but is difficult to detect experimentally. Its full impact is unknown. In this work, the signature microenvironment of lysine-carboxylation sites has been characterized. In addition, a computational method called Predictor of Lysine Carboxylation (PreLysCar) for the detection of lysine carboxylation in proteins with available three-dimensional structures has been developed. The likely prevalence of lysine carboxylation in the proteome was assessed through large-scale computations. The results suggest that about 1.3% of large proteins may contain a carboxylated lysine residue. This unexpected prevalence of lysine carboxylation implies an enrichment of reactions in which it may play functional roles. The results also suggest that by switching enzymes on and off under appropriate physicochemical conditions spontaneous PTMs may serve as an important and widely used efficient biological machinery for regulation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Interaction of Long-lived Reactive Species from Cold Atmospheric Pressure Plasma with Polymers: Chemical Modification by Ozone and Reactive Oxygen-Nitrogen Species

Atmospheric pressure plasma (APP) sources are able to generate a variety of reactive species that have different effects on materials, such as functionalization, etching and deposition. In this article, we study the effect of long-lived reactive neutral species on polymers using a model plasma-surface interaction (PSI) system that consists of ultra-thin (~10 nm) polystyrene (PS) films and a surface micro-discharge (SMD) reactor operated with various N 2 /O 2 working gas mixtures. We characterized and quantified the reactive species generated by SMD using IR and UV absorption, and we found that O 3 , N 2 O 5 , N 2 O and HNO 3 are the dominant long-lived reactants near the target surface. When exposing PS films to these reactive species, we observed material responses including film thickness expansion, surface and bulk oxidation, and surface organic nitrate formation. The quantity of these changes varied with the N 2 /O 2 working gas composition. By correlating material response with gas phase species, we find that the chemical modification of PS strongly depends on the density of O 3 in the gas phase, which is indicative of an essential role of O 3 in the remote APP treatment of polymers. Our results show that O 3 causes polymer surface oxidation, participates in the diffusion-reaction process in the polymer bulk, and results in aromatic ring cleavage and the formation of carbonyl groups. In contrast, we did not find a correlation between surface organic nitrate and individual long-lived reactive species mentioned above. This indicates that surface organic nitrate formation on polymer surfaces might result from the interaction of multiple reactive species, including O 3 and nitrogen containing species. A model for the interphase mass transfer of reactive species from gas to solid was also described.

36 MATERIALS SCIENCE↗
DOE OSTI2016

MO-DE-207A-10: One-Step CT Reconstruction for Metal Artifact Reduction by a Modification of Penalized Weighted Least-Squares (PWLS)

Purpose: Metal objects create severe artifacts in kilo-voltage (kV) CT image reconstructions due to the high attenuation coefficients of high atomic number objects. Most of the techniques devised to reduce this artifact utilize a two-step approach, which do not reliably yield the qualified reconstructed images. Thus, for accuracy and simplicity, this work presents a one-step reconstruction method based on a modified penalized weighted least-squares (PWLS) technique. Methods: Existing techniques for metal artifact reduction mostly adopt a two-step approach, which conduct additional reconstruction with the modified projection data from the initial reconstruction. This procedure does not consistently perform well due to the uncertainties in manipulating the metal-contaminated projection data by thresholding and linear interpolation. This study proposes a one-step reconstruction process using a new PWLS operation with total-variation (TV) minimization, while not manipulating the projection. The PWLS for CT reconstruction has been investigated using a pre-defined weight, based on the variance of the projection datum at each detector bin. It works well when reconstructing CT images from metal-free projection data, which does not appropriately penalize metal-contaminated projection data. The proposed work defines the weight at each projection element under the assumption of a Poisson random variable. This small modification using element-wise penalization has a large impact in reducing metal artifacts. For evaluation, the proposed technique was assessed with two noisy, metal-contaminated digital phantoms, against the existing PWLS with TV minimization and the two-step approach. Result: The proposed PWLS with TV minimization greatly improved the metal artifact reduction, relative to the other techniques, by watching the results. Numerically, the new approach lowered the normalized root-mean-square error about 30 and 60% for the two cases, respectively, compared to the two-step method. Conclusion: A new PWLS operation shows promise for improving metal artifact reduction in CT imaging, as well as simplifying the reconstructing procedure.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Modification of the Langmuir–Schaefer method for fabrication of ordered protein films

A modification of the Langmuir–Schaefer method for the fabrication of high-quality protein films on a solid substrate was proposed and applied to lysozyme. The procedure relies on the use of a pre-prepared protein solution, the parameters of which correspond to crystallization conditions. A lysozyme Langmuir monolayer was shown to be formed with the involvement of complexes, namely, dimers and octamers of protein molecules that are present in such protein solutions. These complexes apparently retain the structure after spreading a protein solution onto an aqueous subphase in a Langmuir trough. The thickness of the film after the transfer of the monolayer, which was formed by the proposed procedure, onto a solid substrate corresponds to the diameter of the octamer and this film is dense, continuous, and uniform, as was demonstrated by several methods: X-ray reflectivity, total external reflection X-ray standing wave, and atomic force microscopy. A layer of chloride ions that formed under the Langmuir monolayer was found at the air–protein film interface. This fact confirms an important role of the precipitating agent (chloride ions) in all steps of the formation of lysozyme films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Recrystallization and modification of the stainless-steel surface relief under photonic heat load in powerful plasma discharges

Targets made of ITER-grade 316L(N)-IG stainless steel and Russian-grade 12Cr18Ni10Ti stainless steel with a close composition were exposed at the QSPA-T plasma gun to plasma photonic radiation pulses simulating conditions of disruption mitigation in ITER. After a large number of pulses, modification of the stainless-steel surface was observed, such as the formation of a wavy structure, irregular roughness, and cracks on the target surface. X-ray and optic microscopic analyses of targets revealed changes in the orientation and dimensions of crystallites (grains) over a depth of up to 20 μm for 316L(N)-IG stainless steel after 200 pulses and up to 40 μm for 12Cr18Ni10Ti stainless steel after 50 pulses, which is significantly larger than the depth of the layer melted in one pulse (∼10 μm). In a series of 200 tests of ITER-grade 316L(N)-IG ITER stainless steel, a linear increase in the height of irregularity (roughness) with increasing number of pulses at a rate of up to ∼1 μm per pulse was observed. No alteration in the chemical composition of the stainless-steel surface in the series of tests was revealed. A model is developed that describes the formation of wavy irregularities on the melted metal surface with allowance for the nonlinear stage of instability of the melted layer with a vapor/plasma flow above it. A decisive factor in this case is the viscous flow of the melted metal from the troughs to tops of the wavy structure. The model predicts saturation of the growth of the wavy structure when its amplitude becomes comparable with its wavelength. Approaches to describing the observed stochastic relief and roughness of the stainless-steel surface formed in the series of tests are considered. The recurrence of the melting-solidification process in which mechanisms of the hill growth compete with the spreading of the material from the hills can result in the formation of a stochastic relief.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Defect of the well-known (classical) expression for the ionization rate in gas-discharge plasma and its modification

A critical analysis is given of the well-known expression for the electron-impact ionization rate constant α{sub i} of neutral atoms and ions, derived by linearization of the ionization cross section σ{sub i}(ε) as a function of the electron energy near the threshold I and containing the characteristic factor (I + 2kT). Using the classical Thomson expression for the ionization cross section, it is shown that in addition to the linear slope of σ{sub i}(ε), it is also necessary to take into account the large negative curvature of this function near the threshold. In this case, the second term in parentheses changes its sign, which means that the commonly used expression for α{sub i} (∼4kT/I) already at moderate values of the temperature (kT/I ∼ 0.1). The source of this error lies in a mathematical mistake in the original approach and is related to the incorrect choice of the sequential orders of terms small in the parameter kT/I. On the basis of a large amount of experimental data and considerations similar to the Gryzinski theory, a universal two-parameter modification of the Thomson formula (as well as the Bethe—Born formula) is proposed and a new simple expression for the ionization rate constant for arbitrary values of kT/I is derived.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Reversible electrochemical modification of the surface of a semiconductor by an atomic-force microscope probe

A technique for reversible surface modification with an atomic-force-microscope (AFM) probe is suggested. In this method, no significant mechanical or topographic changes occur upon a local variation in the surface potential of a sample under the AFM probe. The method allows a controlled relative change in the ohmic resistance of a channel in a Hall bridge within the range 20–25%.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Diversity of Properties of Device Structures Based on Group-III Nitrides, Related to Modification of the Fractal-Percolation System

A fractal-percolation system that includes extended defects and random fluctuations in the alloy composition is formed during the growth of device structures based on Group-III nitrides. It is established that the specific features of this system are determined not only by the growth conditions. It is shown that the diversity of the electrical and optical properties of InGaN/GaN LEDs (light-emitting diodes) emitting at wavelengths of 450–460 and 519–530 nm, as well as that of the electrical properties of AlGaN/GaN HEMT (high-electron-mobility transistor) structures, is due to modification of the properties of the fractal-percolation system both during the growth process and under the action of the injection current and irradiation. The influence exerted by these specific features on the service life of light-emitting devices and on the reliability of AlGaN/GaN HEMT structures is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ion Modification of the Field-Emission Properties of Diamond-Graphite Film Structures

The patterns of variation of structure-phase, morphological, and field-emission parameters of nanocomposite diamond-graphite film structures, which were synthesized in microwave plasma of ethanol vapors, with the dose of irradiation with nitrogen ions with an energy of 20 keV are studied. It is found that the morphological parameters of diamond-graphite structures subjected to small-dose irradiation differ only slightly from those of nonirradiated samples. In contrast, the field-emission properties of irradiated samples are altered significantly. The maximum density of field-emission currents increases when the field-emission excitation thresholds are raised. The optimum doses of nitrogen ion implantation resulting in a more than fivefold increase (relative to nonirradiated structures) in the maximum density of field-emission currents are determined. The physical and chemical mechanisms involved in the modification of surface and near-surface properties of diamond-graphite structures subjected to various doses of ion irradiation are examined.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Properties of Optical Ceramics CO1 and CO2 upon Modification of Their Surface by Carbon Nanotubes

The results of a study of the modification of the properties of optical inorganic materials (optical ceramics CO1 (MgF{sub 2}) and CO2 (ZnS)) are presented. It is found that the main characteristics of the studied materials with a surface modified by carbon nanotubes significantly changes when the laser-oriented deposition method is applied. Main features of the carbon nanotubes caused by its developed surface, the strength of C–C bonds, and low value of refraction index are taken into consideration. Analytical, quantum-chemical and experimental results of studies of changes in the spectral and mechanical parameters, as well as the wetting angle of the selected model inorganic matrices, are given.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Enhancing chemical bioproduction with rational control of bacterial post-translational modifications

Efficient conversion of inexpensive feedstocks to valuable chemicals by microbes is critical for a robust bioeconomy, but the ability to rationally design bacteria is hampered by insufficient knowledge of how post translational modifications (PTMs) control bacterial protein function and thus bioproduction phenotypes. Our study will focus on the lysine acetylation, a ubiquitous bacterial PTM that can affect the function of enzymes in central metabolism that are often critical for bioproduction processes, disrupt transcriptional regulation, and reduce translation. However, most lysine acetylation data is observational, which means that we do not know when, how, and what specific acetylated residues affect protein function and bacterial physiology. For our model host, we will use a Pseudomonas putida strain that we previously engineered to convert lignocellulosic feedstocks into chemicals such as itaconic acid (ITA). With this strain, we use a dynamic two-stage bioproduction process in which ITA is produced during a non-growth associated production phase. Production is highest during growth stages when lysine acetylation is low in other organisms (early stationary phase) and stalls in conditions where acetylation is highest (late stationary phase). The switch from high to stalled ITA production is also correlated with an unexpected increase in acetate levels – the precursor to non-enzymatic lysine acetylation. As such, we predict that lysine acetylation plays a substantial role in regulating the metabolic pathways required for ITA production. We will develop a generalizable approach that combines high-throughput genetic screens and cutting-edge genome engineering with state-of-the-art proteomics, metabolomics, and genetic code expansion methods to identify and modulate lysine acetylation patterns in bacteria. Ultimately, these strategies aim to manipulate protein expression and acetylation patterns to enhance bioproduction phenotypes (e.g., sustained ITA production in late stationary phase).

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

RNA-Seq analysis of nine tRNA-Modification deficient mutants in E. coli

We performed an RNA-Seq analysis of nine of E.coli single knockout strains from the Keio collection carrying deletions in tRNA modification genes (dusB, truA, truD, thiI, miaA, rlmN, mnmA, mnmC, mnmG) and wildtype. RNA was isolated from each of the different strains at grown in LB at 37˚C up to mid-exponential phase (OD(A600nm) ~0.6) in three biological replicates.

tRNA modification, transcriptomics, Escherichia co↗