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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Localised nanoscale resistive switching in GaP thin films with low power consumption

Nanoscale localisation of the electroforming-free resistive switching (RS) behaviour in polycrystalline GaP thin films has been observed for the first time. A combination of conductive atomic force microscopy and first-order reversal curve current–voltage measurements indicated that the grain boundaries are the preferred sites for the formation of the conductive switching filaments. It is proposed, based on TEM and XPS results, that local electrochemical migration of Ga ions along the grain boundaries plays a critical role in the switching mechanism. In the low-resistance (ON) state, the conduction mechanism was found to be the space-charge-limited current mechanism, while the high-resistance (OFF) state was governed by the Frenkel–Poole mechanism. Here, a high OFF/ON resistance ratio (~10 4 ) and lower power consumption than current RS devices, in addition to the easy integration of GaP with silicon substrates, make these GaP films promising for future applications in future non-volatile resistive random access memory (RRAM).

36 MATERIALS SCIENCE↗
DOE OSTI2017

Generation of giant spatially localised Gaussian wave packets in active fibres with saturable inertial nonlinearity

The dynamics of wave packets in an active fibre with saturable inertial nonlinearity of logarithmic type is considered. The possibility of forming spatially localised Gaussian wave packets (TEM{sub 00} mode) with a large (significantly exceeding 100 μm{sup 2}) mode area and a large (above 1 TW) peak power in such structures is shown. (nonlinear-optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Displacement and localisation of a transparent nanosphere by light-pressure forces in the field of a focused laser beam

We report the results of a numerical simulation of the Langevin equation describing the motion of a transparent nanosphere under the action of a resulting light-pressure force in the field of a continuous focused Gaussian laser beam. The conditions for the localisation of the nanosphere near the focal waist of the beam focused by the lens are determined. An analytical solution of the approximate (truncated) equation of motion is found, which almost exactly coincides with the results of the numerical simulation of the initial equation. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Localisation of intense sound produced by an optical pulsating discharge in the air

It is shown that the localisation radius and the spectrum of intense sound produced by an optical pulsating discharge in the air depend on the power and repetition rate of the repetitively pulsed laser radiation, which is associated with a manifestation of the wave merging mechanism and sound absorption in the air. The experiment makes use of a CO2 laser with a power of ∼1.5 kW and a repetition rate of microsecond pulses of ∼50 kHz. (interaction of laser radiation with matter. laser plasma)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Localised plasmons in sphere-like fullerenes and nanoparticles with conducting shells: Classical electrodynamic approach

Based on the classical electrodynamic approach, we consider localised plasmons in fullerenes and small particles with metal layers and shells. At low energies of the radiation quantum, models of fullerenes as conducting shells are used taking into account the contribution of only π electrons, and at high energies, of both π and σ electrons. The obtained maxima of the scattering cross sections correspond to the values of 20 and 27 eV that were determined experimentally and in quantum models for the maxima of the photoionisation cross sections of fullerenes C{sub 60} and C{sub 28}, respectively. Approximate analytical results are presented for resonant frequencies, Q factors, radiation patterns, scattering and absorption cross sections for sphere-like particles and fullerenes, as well as integral equations and functionals for dielectric particles with a conducting shell of arbitrary shape. Analysis relies on the use of effective surface conductivity. (plasmons)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Stimulated emission, photoluminescence, and localisation of nonequilibrium charge carriers in ultrathin (monolayer) GaN/AlN quantum wells

The stimulated emission and photoluminescence of ultrathin GaN quantum wells with a nominal thickness of 1.5 – 2 monolayers (MLs) and AlN barrier layers 4 – 6.66 ML thick, obtained by plasma-activated molecular beam epitaxy on c-sapphire substrates, are studied. The stimulated emission of TE polarisation in ultrathin GaN/AlN quantum wells is obtained under pumping directly into quantum wells. The wavelength of stimulated emission varied from 262 to 290 nm, depending on the thickness of the wells and barriers. It is shown that stimulated emission is achieved on localised GaN states with a thickness of 2 and 3 ML in ultrathin quantum wells with a nominal thickness of 1.5 and 2 ML, respectively. The minimum excitation threshold of stimulated emission was 700 kW cm{sup −2} at λ = 270 nm. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Localised electromagnetic waves in a rhombic waveguide array with competing nonlinearities

We consider a model of a discrete photonic system representing a quasi-one-dimensional rhombic array of waveguides, where, in addition to the positive cubic nonlinearity, the negative quintic nonlinearity is taken into account for the material of which the central chain of the waveguides is made. The other two waveguide chains are made of an optically linear material. A continual approximation is used to obtain a solution for a system of coupled waves, which describes a wave localised in the transverse direction. In a certain special case, the competition of nonlinearities leads to the formation of a step-shaped distribution of the field intensities over the waveguides. (integrated optics)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

A Physics-Aligned Multi-Domain Machine Learning Framework for Time-Localised Diagnosis of Power Electronics Faults

This paper presents a physics-aligned framework for fault diagnosis in multi-phase power-electronic systems using cycle-synchronous windowing and multi-domain features derived from Fourier, wavelet, and Hilbert–Huang representations. While both logistic regression and multilayer perceptron (MLP) models achieve perfect performance under standard evaluation, blind unseen testing reveals a critical failure in a baseline MLP. This is shown to arise from model selection based on validation accuracy. Using validation-loss-based selection restores correct unseen performance and improves confidence. Feature ablation shows that Fourier and wavelet features dominate, while computational analysis indicates that feature extraction, particularly HHT, governs runtime.

Kumar, Praveen [ORNL] (ORCID:0000000291877857)↗
DOE OSTI2022

Super-localisation of a point-like emitter in a resonant environment: Correction of the mirage effect

In this paper, we show that it is possible to overcome one of the fundamental limitations of super-resolution microscopy: the necessity to be in an optically homogeneous environment. Using recent modal approximation results from [ 10 , 7 ], we show, as a proof of concept, that it is possible to recover the position of a single point-like emitter in a known resonant environment from far-field measurements, with a precision two orders of magnitude below the classical Rayleigh limit. The procedure does not involve solving any partial differential equation, is computationally light (optimisation in \begin{document}$ \mathbb{R}^d $\end{document} with \begin{document}$ d $\end{document} of the order of \begin{document}$ 10 $\end{document} ) and is therefore suited for the recovery of a very large number of single emitters.

Mathematics↗
DOE OSTI2018

Oxidative stress promotes redistribution of TRPM2 channels to the plasma membrane in hepatocytes

Highlights: • In hepatocytes, TRPM2 channels are mainly localised in intracellular organelles. • Oxidative stress increases the number of TRPM2 channels in the plasma membrane. • TRPM2 trafficking to the PM may contribute to positive Ca{sup 2+}-dependent feedback. Transient Receptor Potential Melastatin (TRPM) 2 is a non-selective Ca{sup 2+} permeable cation channel and a member of the Transient Receptor Potential (TRP) channel family. TRPM2 has unique gating properties; it is activated by intracellular ADP-ribose (ADPR), whereas Ca{sup 2+} plays a role of an important co-factor in channel activation, increasing TRPM2 sensitivity to ADPR. TRPM2 is highly expressed in rat and mouse hepatocytes, where it has been shown to contribute to oxidative stress-induced cell death and liver damage due to paracetamol-overdose. The mechanisms regulating the activity of TRPM2 channels in hepatocytes, however, are not well understood. In this paper, we investigate the localisation of TRPM2 protein in hepatocytes. The presented results demonstrate that in rat hepatocytes under normal conditions, most of the TRPM2 protein is localised intracellularly. This was determined by confocal microscopy using TRPM2-and plasma membrane (PM)-specific antibodies and immunofluorescence, and biotinylation studies followed by western blotting. Interestingly, in hepatocytes treated with either H{sub 2}O{sub 2} or paracetamol, the amount of TRPM2 co-localised with PM is significantly increased, compared to the untreated cells. It is concluded that trafficking of TRPM2 to the PM could potentially contribute to a positive feedback mechanism mediating Ca{sup 2+} overload in hepatocytes under conditions of oxidative stress.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Nucleocytoplasmic trafficking of Nipah virus W protein involves multiple discrete interactions with the nuclear import and export machinery

Paramyxoviruses replicate in the cytoplasm with no obvious requirement to interact with the nucleus. Nevertheless, the W protein of the highly lethal bat-borne paramyxovirus Nipah virus (NiV) is known to undergo specific targeting to the nucleus, mediated by a single nuclear localisation signal (NLS) within the C-terminal domain. Here, we report for the first time that additional sites modulate nucleocytoplasmic localisation of W. We show that the N-terminal domain interacts with importin α1 and contributes to nuclear accumulation of W, indicative of a novel N-terminal NLS. We also find that W undergoes exportin-1 mediated nuclear export, dependent on a leucine at position 174. Together, these data enable significant revision of the generally accepted model of W trafficking, with implications for understanding of the mechanisms of NiV immune evasion. - Highlights: • A new model for Nipah virus W protein nucleocytoplasmic trafficking is proposed. • Nipah W protein is shown to undergo active nuclear export via exportin-1. • Nipah W nuclear import is mediated by multiple nuclear localisation signals.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

N-terminal nesprin-2 variants regulate β-catenin signalling

The spatial compartmentalisation of biochemical signalling pathways is essential for cell function. Nesprins are a multi-isomeric family of proteins that have emerged as signalling scaffolds, herein, we investigate the localisation and function of novel nesprin-2 N-terminal variants. We show that these nesprin-2 variants display cell specific distribution and reside in both the cytoplasm and nucleus. Immunofluorescence microscopy revealed that nesprin-2 N-terminal variants colocalised with β-catenin at cell-cell junctions in U2OS cells. Calcium switch assays demonstrated that nesprin-2 and β-catenin are lost from cell-cell junctions in low calcium conditions whereas emerin localisation at the NE remained unaltered, furthermore, an N-terminal fragment of nesprin-2 was sufficient for cell-cell junction localisation and interacted with β-catenin. Disruption of these N-terminal nesprin-2 variants, using siRNA depletion resulted in loss of β-catenin from cell-cell junctions, nuclear accumulation of active β-catenin and augmented β-catenin transcriptional activity. Importantly, we show that U2OS cells lack nesprin-2 giant, suggesting that the N-terminal nesprin-2 variants regulate β-catenin signalling independently of the NE. Together, these data identify N-terminal nesprin-2 variants as novel regulators of β-catenin signalling that tether β-catenin to cell-cell contacts to inhibit β-catenin transcriptional activity. - Highlights: • N-terminal nesprin-2 variants display cell specific expression patterns. • N-terminal spectrin repeats of nesprin-2 interact with β-catenin. • N-terminal nesprin-2 variants scaffold β-catenin at cell-cell junctions.. • Nesprin-2 variants play multiple roles in β-catenin signalling.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Phase contrast imaging measurements and numerical simulations of turbulent density fluctuations in gas-fuelled ECRH discharges in Wendelstein 7-X

The fundamental nature of turbulent density fluctuations in standard Wendelstein 7-X (W7-X) stellarator discharges is investigated experimentally via phase contrast imaging (PCI) in combination with gyrokinetic simulations with the code GENE. We find that density fluctuations are ion-temperature-gradient-driven and radially localised in the outer half of the plasma. It is shown that the line-integrated PCI measurements cover the right range of wavenumbers and a favourable toroidal and poloidal location to capture some of the strongest density fluctuations in W7-X. Due to the radial localisation of fluctuations, measured wavenumber–frequency spectra exhibit a dominant phase velocity, which can be related to the E × B rotation velocity at the radial position of a well in the neoclassical radial electric field. The match is robust against variations of heating power and line-integrated density, which is partly due to the localisation of fluctuations and partly due to effects of the radial gradient in the E × B velocity profile on the wavenumber–frequency spectrum. The latter effect is studied with a newly built synthetic PCI diagnostic and global gyrokinetic simulations with GENE-3D.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Multiplexed CRISPR/Cas9 editing of the long-chain acyl-CoA synthetase family in the diatom Phaeodactylum tricornutum reveals that mitochondrial ptACSL3 is involved in the synthesis of storage lipids

Long-chain acyl-CoA synthetases (LACS) play diverse and fundamentally important roles in lipid metabolism. While their functions have been well established in bacteria, yeast and plants, the mechanisms by which LACS isozymes regulate lipid metabolism in unicellular oil-producing microalgae, including the diatom Phaeodactylum tricornutum , remain largely unknown. In P. tricornutum , a family of five genes ( ptACSL1 – ptACSL5 ) encodes LACS activities. For this work, we generated single lacs knockout/knockdown mutants using multiplexed CRISPR/Cas9 method, and determined their substrate specificities towards different fatty acids (FAs) and subcellular localisations. ptACSL3 is localised in the mitochondria and its disruption led to compromised growth and reduced triacylglycerol (TAG) content when cells were bubbled with air. The ptACSL3 mutants showed altered FA profiles in two galactoglycerolipids and phosphatidylcholine (PC) with significantly reduced distribution of 16:0 and 16:1. ptACSL5 is localised in the peroxisome and its knockdown resulted in reduced growth rate and altered molecular species of PC and TAG, indicating a role in controlling the composition of acyl-CoAs for lipid synthesis. Our work demonstrates the potential of generating gene knockout mutants with the mutation of large fragment deletion using multiplexed CRISPR/Cas9 and provides insight into the functions of LACS isozymes in lipid metabolism in the oleaginous microalgae.

59 BASIC BIOLOGICAL SCIENCES↗