Search NASA⌕ Search

Engineering topics

Li, Chun

Publications and source records attributed to Li, Chun.

17 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Discovery of GuaB inhibitors with efficacy against Acinetobacter baumannii infection

ABSTRACT Guanine nucleotides are required for growth and viability of cells due to their structural role in DNA and RNA, and their regulatory roles in translation, signal transduction, and cell division. The natural antibiotic mycophenolic acid (MPA) targets the rate-limiting step inde novoguanine nucleotide biosynthesis executed by inosine-5´-monophosphate dehydrogenase (IMPDH). MPA is used clinically as an immunosuppressant, but whetherin vivoinhibition of bacterial IMPDH (GuaB) is a valid antibacterial strategy is controversial. Here, we describe the discovery of extremely potent small molecule GuaB inhibitors (GuaBi) specific to pathogenic bacteria with a low frequency of on-target spontaneous resistance and bactericidal efficacyin vivoagainstAcinetobacter baumanniimouse models of infection. The spectrum of GuaBi activity includes multidrug-resistant pathogens that are a critical priority of new antibiotic development. Co-crystal structures ofA. baumannii, Staphylococcus aureus, andEscherichia coliGuaB proteins bound to inhibitors show comparable binding modes of GuaBi across species and identifies key binding site residues that are predictive of whole-cell activity across both Gram-positive and Gram-negative clades of Bacteria. The clearin vivoefficacy of these small molecule GuaB inhibitors in a model ofA. baumanniiinfection validates GuaB as an essential antibiotic target. IMPORTANCE The emergence of multidrug-resistant bacteria worldwide has renewed interest in discovering antibiotics with novel mechanism of action. For the first time ever, we demonstrate that pharmacological inhibition ofde novoguanine biosynthesis is bactericidal in a mouse model ofAcinetobacter baumanniiinfection. Structural analyses of novel inhibitors explain differences in biochemical and whole-cell activity across bacterial clades and underscore why this discovery may have broad translational impact on treatment of the most recalcitrant bacterial infections.

Microbiology↗
DOE OSTI2022

Real-World Subsynchronous Oscillation Events in Power Grids with High Penetrations of Inverter-Based Resources

This paper presents a survey of real-world sub-synchronous oscillation events associated with inverter-based resources (IBR) over the past decade. The focus is on those oscillations in the subsynchronous frequency range known to be influenced by power grid characteristics, e.g., series compensation or low system strength. A brief overview of the historical events is presented followed by detailed descriptions of a series of events. This paper also examines causation mechanisms and proposes future research directions to meet grid needs worldwide.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2021

Genomic characterization of three marine fungi, including Emericellopsis atlantica sp. nov. with signatures of a generalist lifestyle and marine biomass degradation

ABSTRACT Marine fungi remain poorly covered in global genome sequencing campaigns; the 1000 fungal genomes (1KFG) project attempts to shed light on the diversity, ecology and potential industrial use of overlooked and poorly resolved fungal taxa. This study characterizes the genomes of three marine fungi: Emericellopsis sp. TS7, wood-associated Amylocarpus encephaloides and algae-associated Calycina marina. These species were genome sequenced to study their genomic features, biosynthetic potential and phylogenetic placement using multilocus data. Amylocarpus encephaloides and C. marina were placed in the Helotiaceae and Pezizellaceae (Helotiales) , respectively, based on a 15-gene phylogenetic analysis. These two genomes had fewer biosynthetic gene clusters (BGCs) and carbohydrate active enzymes (CAZymes) than Emericellopsis sp. TS7 isolate. Emericellopsis sp. TS7 ( Hypocreales , Ascomycota ) was isolated from the sponge Stelletta normani . A six-gene phylogenetic analysis placed the isolate in the marine Emericellopsis clade and morphological examination confirmed that the isolate represents a new species, which is described here as E. atlantica . Analysis of its CAZyme repertoire and a culturing experiment on three marine and one terrestrial substrates indicated that E. atlantica is a psychrotrophic generalist fungus that is able to degrade several types of marine biomass. FungiSMASH analysis revealed the presence of 35 BGCs including, eight non-ribosomal peptide synthases (NRPSs), six NRPS-like, six polyketide synthases, nine terpenes and six hybrid, mixed or other clusters. Of these BGCs, only five were homologous with characterized BGCs. The presence of unknown BGCs sets and large CAZyme repertoire set stage for further investigations of E. atlantica . The Pezizellaceae genome and the genome of the monotypic Amylocarpus genus represent the first published genomes of filamentous fungi that are restricted in their occurrence to the marine habitat and form thus a valuable resource for the community that can be used in studying ecological adaptions of fungi using comparative genomics.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Synchronized Waveforms – A Frontier of Data-Based Power System and Apparatus Monitoring, Protection, and Control

Voltage and current waveforms contain the most authentic and granular information on the behaviors of power systems. In recent years, it has become possible to synchronize waveform data measured from different locations. Thus large-scale coordinated analyses of multiple waveforms over a wide area are within our reach. This development could unleash a set of new concepts, strategies, and tools for monitoring, protecting, and controlling power systems and apparatuses. This paper presents an in-depth review and analysis of the advancements in synchronized waveform data, including measurement devices, data characteristics, use cases, and comparisons with synchrophasor data. Based on the findings, five strategies are proposed to discover and develop synchronized waveform based applications over multiple application areas. The paper also presents three complementary measurement platforms and two data screening algorithms for application implementation. It further discusses committee activities and standard developments useful to explore the full potential of the data.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2020

Anti‐adhesive effects of sialic acid and Lactobacillus plantarum on Staphylococcus aureus in vitro

Abstract Staphylococcus aureus (S. aureus) is a common food‐borne pathogen that causes severe diseases after adhesion to epithelial cells. Lactobacillus inhibits pathogenic bacterial adhesion and infection. In addition, sialic acid (SA) is widely known for its beneficial biological functions. A new way of reducing the occurrence of diseases and curbing the overuse of antibiotics is ingesting prebiotics and probiotics that regulate the intestinal flora. In this study, we first evaluated the anti‐adhesive effects of several strains of Lactobacillus on S. aureus . The study revealed that the S. aureus adhesion was inhibited by all the strains of Lactobacillus . Besides, the rate of inhibition by L. plantarum Z‐4 was significantly higher than other Lactobacillus species . We then investigated the effects of different SA concentrations (40, 100, 150, 200, and 260 μg/ml) on the growth and adhesion characteristics of L. plantarum and S. aureus . The results showed that SA influences bacterial adhesion by regulating the bacteria's growth characteristics. Finally, the effects of SA combined with Lactobacillus on the adhesion of S. aureus were assessed by competition, exclusion and displacement methods. SA with a concentration of 260 μg/mL combined with L. plantarum had the highest inhibition effect on the competition assays. In addition, the expression of S. aureus adhesion‐related genes was reduced. This provides a new perspective on the application of SA and/or L. plantarum and its potential to resist adhesion of S. aureus .

Lu, Yingying↗
DOE OSTI2020

Tuning Irreversible Magnetoresistance in Pr 0.67 Sr 0.33 MnO 3 Film via Octahedral Rotation

Herein, the oxygen octahedral rotation around the out-of-plane axis is explored to study its effect on metastable status, magnetic cluster glass in manganite. The antiphase rotation around the out-of-plane axis (TiO 6 α Ο α Ο c – ) of SrTiO 3 enhances the Mn–O bond anisotropy along in-plane and out-of-plane directions and weakens the ferromagnetic interactions in a 12 nm Pr 0.67 Sr 0.33 MnO 3 film on the (001) SrTiO 3 substrate, which together promote the formation of magnetic cluster-glassiness and enlarges the irreversible magnetoresistance (MR) effect with enhanced relaxation time of charge carriers. The effect of TiO 6 α Ο α Ο c – in the SrTiO 3 substrate on material properties is obvious with a large irreversible MR effect for thin films, which fades away with the increase in film thickness. At 10 K, the irreversible MR is 0.91 for the 12 nm film and 0.22 for the 30 nm film. This work extends current understanding on interfacial coupling to metastable status and could help explore other systems in the perovskite structure with octahedral rotation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Direct Spectroscopy for Probing the Critical Role of Partial Covalency in Oxygen Reduction Reaction for Cobalt-Manganese Spinel Oxides

Nanocrystalline multivalent metal spinels are considered as attractive non-precious oxygen electrocatalysts. Identifying their active sites and understanding their reaction mechanisms are essential to explore novel transition metal (TM) oxides catalysts and further promote their catalytic efficiency. Here we report a systematic investigation, by means of soft X-ray absorption spectroscopy (sXAS), on cubic and tetragonal Co x Mn 3-x O 4 (x = 1, 1.5, 2) spinel oxides as a family of highly active catalysts for the oxygen reduction reaction (ORR). We demonstrate that the ORR activity for oxide catalysts primarily correlates to the partial covalency of between O 2p orbital with Mn 4+ 3d t 2g -down/e g -up, Mn 3+ 3d e g -up and Co 3+ 3d e g -up orbitals in octahedron, which is directly revealed by the O K-edge sXAS. Our findings propose the critical influences of the partial covalency between oxygen 2p band and specific metal 3d band on the competition between intermediates displacement of the ORR, and thus highlight the importance of electronic structure in controlling oxide catalytic activity.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Role of CTGF in sensitivity to hyperthermia in ovarian and uterine cancers

Even though hyperthermia is a promising treatment for cancer, the relationship between specific temperatures and clinical benefits and predictors of sensitivity of cancer to hyperthermia is poorly understood. Ovarian and uterine tumors have diverse hyperthermia sensitivities. Integrative analyses of the specific gene signatures and the differences in response to hyperthermia between hyperthermia-sensitive and -resistant cancer cells identified CTGF as a key regulator of sensitivity. CTGF silencing sensitized resistant cells to hyperthermia. CTGF small interfering RNA (siRNA) treatment also sensitized resistant cancers to localized hyperthermia induced by copper sulfide nanoparticles and near-infrared laser in orthotopic ovarian cancer models. Lastly, CTGF silencing aggravated energy stress induced by hyperthermia and enhanced apoptosis of hyperthermia-resistant cancers.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Electrically tunable superconducting terahertz metamaterial with low insertion loss and high switchable ratios

With the emergence and development of artificially structured electromagnetic materials, active terahertz (THz) metamaterial devices have attracted significant attention in recent years. Tunability of transmission is desirable for many applications. For example, short-range wireless THz communications and ultrafast THz interconnects require switches and modulators. However, the tunable range of transmission amplitude of existing THz metamaterial devices is not satisfactory. In this article, we experimentally demonstrate an electrically tunable superconducting niobium nitride metamaterial device and employ a hybrid coupling model to analyze its optical transmission characteristics. The maximum transmission coefficient at 0.507 THz is 0.98 and decreases to 0.19 when the applied voltage increases to 0.9 V. A relative transmittance change of 80.6% is observed, making this device an efficient narrowband THz switch. Additionally, the frequency of the peak is red shifted from 0.507 to 0.425 THz, which means that the device can be used to select the frequency. This study offers an alternative tuning method to existing optical, thermal, magnetic-field, and electric-field tuning, delivering a promising approach for designing active and miniaturized THz devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗