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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 OSTI2018

Electrical conductance of near-infrared femtosecond air filaments in the multi-filament regime

Electrical conductive properties of femtosecond laser filaments are of significant interest for applications such as remote arc suppression and discharge guiding. We transmitted electrical current through a DC-biased air plasma channel formed in the wake of an energetic femtosecond laser pulse and observed an increased rate of change of the charge transmitted through the ionized channel with laser energy when crossing from the single- to the multi-filament regime. This behavior is attributed to the confluent effects of greater electron density and increased cross-sectional area of the multifilament plasma structures. As the laser energy is increased, the formation of additional conductive channels in the multi-filamentation regime becomes a significant contributor to the rapid increase of conductivity. Finally, these observations suggest a potential path to attractive applications such as efficient energy transfer in air mediated by femtosecond laser-produced filaments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Alma observations of massive molecular gas filaments encasing radio bubbles in the Phoenix cluster

We report new ALMA observations of the CO(3-2) line emission from the $2.1\pm0.3\times10^{10}\rm\thinspace M_{\odot}$ molecular gas reservoir in the central galaxy of the Phoenix cluster. The cold molecular gas is fuelling a vigorous starburst at a rate of $500-800\rm\thinspace M_{\odot}\rm\; yr^{-1}$ and powerful black hole activity in the form of both intense quasar radiation and radio jets. The radio jets have inflated huge bubbles filled with relativistic plasma into the hot, X-ray atmospheres surrounding the host galaxy. The ALMA observations show that extended filaments of molecular gas, each $10-20\rm\; kpc$ long with a mass of several billion solar masses, are located along the peripheries of the radio bubbles. The smooth velocity gradients and narrow line widths along each filament reveal massive, ordered molecular gas flows around each bubble, which are inconsistent with gravitational free-fall. The molecular clouds have been lifted directly by the radio bubbles, or formed via thermal instabilities induced in low entropy gas lifted in the updraft of the bubbles. These new data provide compelling evidence for close coupling between the radio bubbles and the cold gas, which is essential to explain the self-regulation of feedback. As a result, the very feedback mechanism that heats hot atmospheres and suppresses star formation may also paradoxically stimulate production of the cold gas required to sustain feedback in massive galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1986

Dynamics of solar filaments. VI - Center-to-limb study of H-alpha and C IV velocities in a quiescent filament

The rotation of a stable quiescent filament from near disk center to the limb has been observed. Observations of intensity and velocity were made in H-alpha and C IV, and compared with magnetic field measurements. From the H-alpha observations, it is concluded that the filament is made up of many small scale magnetic features that are not coherently aligned along the neutral line. They are especially convoluted at the apparent 'footpoints'. The measured velocities are of the order of a few kilometers per second in both lines. However, the comparison of the standard deviations of the C IV velocities in and out of the filament as it rotates toward the limb shows that the vertical velocities in the filament are greater than the horizontal velocities. Measurements of velocity do not make it possible to distinguish between the Raadu-Kuperus (1973) or Kippenhahn-Schluter (1957) models for prominences because neither theory is adequately developed for this comparison. However, the observation of the many fine loops brings into question the correctness of either model.

Simon, G.↗
DOE OSTI2020

Long-wavelength-infrared laser filamentation in solids in the near-single-cycle regime

We experimentally demonstrate long-wavelength-infrared (LWIR) femtosecond filamentation in solids. Systematic investigations of supercontinuum (SC) generation and self-compression of the LWIR pulses assisted by laser filamentation are performed in bulk KrS-5 and ZnSe, pumped by ∼ <#comment/> 145 f s , 9 µm, 10 µJ pulses from an optical parametric chirped-pulse amplifier operating at 10 kHz of repetition rate. Multi-octave SC spectra are demonstrated in both materials. While forming stable single filament, 1.5 cycle LWIR pulses with 4.5 µJ output pulse energy are produced via soliton-like self-compression in a 5 mm thick KrS-5. The experimental results quantitatively agree well with the numerical simulation based on the unidirectional pulse propagation equation. This work shows the experimental feasibility of high-energy, near-single-cycle LWIR light bullet generation in solids.

Qu, Shizhen↗
DOE OSTI2018

Duplications and losses of genes encoding known elements of the stress defence system of the Aspergilli contribute to the evolution of these filamentous fungi but do not directly influence their environmental stress tolerance

The contribution of stress protein duplication and deletion events to the evolution of the Aspergilli was studied. We performed a large-scale homology analysis of stress proteins and generated and analysed three stress defence system models based on Saccharomyces cerevisiae , Schizosaccharomyces pombe and Aspergillus nidulans . Although both yeast-based and A. nidulans -based models were suitable to trace evolutionary changes, the A. nidulans -based model performed better in mapping stress protein radiations. The strong Mantel correlation found between the positions of species in the phylogenetic tree on the one hand and either in the A. nidulans -based or S. cerevisiae -based models on the other hand demonstrated that stress protein expansions and reductions contributed significantly to the evolution of the Aspergilli. Interestingly, stress tolerance attributes correlated well with the number of orthologs only for a few stress proteins. Notable examples are Ftr1 iron permease and Fet3 ferro-O 2 -oxidoreductase, elements of the reductive iron assimilation pathway, in the S. cerevisiae -based model, as well as MpkC, a HogA-like mitogen activated protein kinase in the A. nidulans-based model. In the case of the iron assimilation proteins, the number of orthologs showed a positive correlation with H 2 O 2 -induced stress tolerance while the number of MpkC orthologs correlated positively with Congo Red induced cell wall stress, sorbitol induced osmotic stress and H 2 O 2 induced oxidative stress tolerances. For most stress proteins, changes in the number of orthologs did not correlate well with any stress tolerance attributes. As a consequence, stress tolerance patterns of the studied Aspergilli did not correlate with either the sets of stress response proteins in general or with the phylogeny of the species studied. These observations suggest that stress protein duplication and deletion events significantly contributed to the evolution of stress tolerance attributes of Aspergilli. In contrast, there are other processes, which may counterbalance the effects of stress gene duplications or deletions including (i) alterations in the structures of stress proteins leading to changes in their biological activities, (ii) varying biosynthesis of stress proteins, (iii) rewiring stress response regulatory networks or even (iv) acquiring new stress response genes by horizontal gene transfer. As a result, all these multilevel changes are indispensable for the successful adaptation of filamentous fungi to altering environmental conditions, especially when these organisms are entering new ecological niches.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Catastrophic disassembly of actin filaments via Mical-mediated oxidation

Actin filament assembly and disassembly are vital for cell functions. MICAL Redox enzymes are important post-translational effectors of actin that stereo-specifically oxidize actin’s M44 and M47 residues to induce cellular F-actin disassembly. Here we show that Mical-oxidized (Mox) actin can undergo extremely fast (84 subunits/s) disassembly, which depends on F-actin’s nucleotide-bound state. Using near-atomic resolution cryoEM reconstruction and single filament TIRF microscopy we identify two dynamic and structural states of Mox-actin. Modeling actin’s D-loop region based on our 3.9 Å cryoEM reconstruction suggests that oxidation by Mical reorients the side chain of M44 and induces a new intermolecular interaction of actin residue M47 (M47-O-T351). Site-directed mutagenesis reveals that this interaction promotes Mox-actin instability. Moreover, we find that Mical oxidation of actin allows for cofilin-mediated severing even in the presence of inorganic phosphate. Thus, in conjunction with cofilin, Mical oxidation of actin promotes F-actin disassembly independent of the nucleotide-bound state.

Science & Technology - Other Topics↗
DOE OSTI2015

An ammonia spectral map of the L1495-B218 filaments in the Taurus molecular cloud. I. Physical properties of filaments and dense cores

We present deep NH{sub 3} observations of the L1495-B218 filaments in the Taurus molecular cloud covering over a 3° angular range using the K-band focal plane array on the 100 m Green Bank Telescope. The L1495-B218 filaments form an interconnected, nearby, large complex extending over 8 pc. We observed NH{sub 3} (1, 1) and (2, 2) with a spectral resolution of 0.038 km s{sup −1} and a spatial resolution of 31″. Most of the ammonia peaks coincide with intensity peaks in dust continuum maps at 350 and 500 μm. We deduced physical properties by fitting a model to the observed spectra. We find gas kinetic temperatures of 8–15 K, velocity dispersions of 0.05–0.25 km s{sup −1}, and NH{sub 3} column densities of 5 × 10{sup 12} to 1 × 10{sup 14} cm{sup −2}. The CSAR algorithm, which is a hybrid of seeded-watershed and binary dendrogram algorithms, identifies a total of 55 NH{sub 3} structures, including 39 leaves and 16 branches. The masses of the NH{sub 3} sources range from 0.05 to 9.5 M{sub ⊙}. The masses of NH{sub 3} leaves are mostly smaller than their corresponding virial mass estimated from their internal and gravitational energies, which suggests that these leaves are gravitationally unbound structures. Nine out of 39 NH{sub 3} leaves are gravitationally bound, and seven out of nine gravitationally bound NH{sub 3} leaves are associated with star formation. We also found that 12 out of 30 gravitationally unbound leaves are pressure confined. Our data suggest that a dense core may form as a pressure-confined structure, evolve to a gravitationally bound core, and undergo collapse to form a protostar.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Single-shot, multi-signature remote detection of uranium by filament-induced breakdown spectroscopy

Filament-induced breakdown spectroscopy (FIBS) is an attractive remote detection approach that is potentially applicable to nuclear materials, such as uranium (U). Simultaneous detection of atomic U and uranium monoxide features is demonstrated in a single laser shot with detection probabilities of 52.2% and 39.0%, respectively, and with a 1% false-alarm probability. It is shown that a nearly 100% detection probability can be reached with 1% false alarm probability in .1 second when using an 80-Hz laser and data acquisition system. Atomic U and UO signal features are identifiable in the remote measurement with comparable signal-to-background ratios, suggesting that, despite being broader than the U I emission line, the UO band is also suitable for remote detection of uranium by FIBS.

(020.3260) Isotope shifts, (140.3440) Laser-induce↗
NASA NTRS1985

Dynamics of solar filaments. IV - Structure and mass flow of an active region filament

An active region filament near the center of the solar disk was observed on September 29-30, 1980, with the Multichannel Subtractive Double Pass Spectrograph of the Meudon solar tower and the UV Spectrograph and Polarimeter aboard the SMM satellite. H-alpha and C IV measurements are presently used to study brightness and material velocity in the 10,000 and 100,000 K temperature ranges, and photospheric magnetograms are used to investigate the underlying magnetic field. Attention is given to the constraints imposed on possible filament structures by observations, as well as the expected MHD relationships.

Schmieder, B.↗
DOE OSTI2015

H-treatment impact on conductive-filament formation and stability in Ta{sub 2}O{sub 5}-based resistive-switching memory cells

In this article, we evidence the lower formation energy and improved stability of the conductive filament (CF) formed in TiN\Ta{sub 2}O{sub 5}\Ta resistive-switching memory cells treated in NH{sub 3} atmosphere at 400 °C. This annealing treatment results in (i) lower forming voltage, (ii) lower CF resistance, and (iii) longer retention lifetime of the oxygen-vacancy (V{sub o}) chain constituting the CF. Atomistic insights into these processes are provided by ab initio calculations performed for hydrogen (H) species incorporated in non-stoichiometric Ta{sub 2}O{sub 5} supercells: (i) V{sub o} formation energy is reduced by the presence of H, (ii) V{sub o}-chain CF conductivity is increased by V{sub o} + OH complex formation, and (iii) V{sub o}-chain retention is strengthened by the stable V{sub o} + OH complex. As a result, efficient CF formation and excellent state stability are obtained after 15 days at 250 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Initial measurements of two- and three-dimensional ordering, waves, and plasma filamentation in the Magnetized Dusty Plasma Experiment

The Magnetized Dusty Plasma Experiment at Auburn University has been operational for over one year. In that time, a number of experiments have been performed at magnetic fields up to B = 2.5 T to explore the interaction between magnetized plasmas and charged, micron-sized dust particles. This paper reports on the initial results from studies of: (a) the formation of imposed, ordered structures, (b) the properties of dust wave waves in a rotating frame, and (c) the generation of plasma filaments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Consequences of Femtosecond Laser Filament Generation Conditions in Standoff Laser Induced Breakdown Spectroscopy

We investigate the role of femtosecond laser focusing conditions on ablation properties and its implications on analytical merits and standoff detection applications. Femtosecond laser pulses can be used for ablation either by tightly focusing or by using filaments generated during its propagation. We evaluated the persistence of atomic, and molecular emission features as well as time evolution of the fundamental properties (temperature and density) of ablation plumes generated using different methods.

laser ablation (LA)↗