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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

In-depth analysis of solar models with high-metallicity abundances and updated opacity tables

Context. As a result of the high-quality constraints available for the Sun, we are able to carry out detailed combined analyses using neutrino, spectroscopic, and helioseismic observations. These studies lay the ground for future improvements of the key physical components of solar and stellar models because ingredients such as the equation of state, the radiative opacities, or the prescriptions for macroscopic transport processes of chemicals are then used to study other stars in the Universe. Aims. We study the existing degeneracies in solar models using the recent high-metallicity spectroscopic abundances by comparing them to helioseismic and neutrino data and discuss the effect on their properties of changes in the micro and macro physical ingredients. Methods. We carried out a detailed study of solar models computed with a high-metallicity composition from the literature based on averaged 3D models that were claimed to resolve the solar modelling problem. We compared these models to helioseismic and neutrino constraints. Results. The properties of the solar models are significantly affected by the use of the recent OPLIB opacity tables and the inclusion of macroscopic transport. The properties of the standard solar models computed using the OPAL opacities are similar to those for which the OP opacities were used. We show that a modification of the temperature gradient just below the base of the convective zone is required to remove the discrepancies in solar models, particularly in the presence of macroscopic mixing. This can be simulated by a localised increase in the opacity of a few percent. Conclusions. We conclude that the existing degeneracies and issues in solar modelling are not removed by using an increase in the solar metallicity, in contradiction to what has been suggested in the recent literature. Therefore, standard solar models cannot be used as an argument for a high-metallicity composition. While further work is required to improve solar models, we note that direct helioseismic inversions indicate a low metallicity in the convective envelope, in agreement with spectroscopic analyses based on full 3D models.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2026

Exploring the connection between compact object mergers and fast X-ray transients

Context. The connection between compact object mergers and some extragalactic fast X-ray transients (FXRTs) has long been hypothesised but never ultimately established. Aims. In this work, we investigate two FXRTs, the LEIA X-ray Transient LXT 240402A and the Einstein Probe EP 250207b, whose precise positions lie close to nearby (z ≲ 0.1) quiescent galaxies with a negligible probability of chance coincidence, identifying them as particularly promising cases of merger-driven explosions in the local Universe. Methods. We used Chandra to derive accurate localisations for both events and secure otherwise ambiguous associations with their optical counterparts. Deep optical and near-infrared observations with VLT, GTC, and LBT were performed to characterise the surrounding environment and search for kilonova emission, the hallmark of neutron star mergers. Complementary early-time X-ray monitoring with Swift and Einstein Probe was used to constrain the non-thermal afterglow. Results. We find that both FXRTs remain compatible with a compact binary merger progenitor, which produced low-mass ejecta and kilonova emission subdominant to the afterglow. However, alternative explanations such as a distant (z ≳ 1) core-collapse supernova cannot be conclusively ruled out.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Enhancement of Raman scattering signal of a few molecules using photonic nanojet mediated SERS technique

Now a days, single molecule surface enhanced Raman spectroscopy (SMSERS) has become a fascinating tool for studying the structural properties, static and dynamic events of single molecules (instead of ensemble average), with the help of efficient plasmonic nanostructures. This is extremely useful in the field of proteomics because the structural properties of protein molecules are heterogeneous. Even though, SMSERS provides wealthy information about single molecules, it demands high quality surface enhanced Raman scattering (SERS) substrates. So far, a very few researchers succeeded in demonstrating the single molecule Raman scattering using conventional SERS technique. However, the experimental S/N of the Raman signal has been found to be very poor. Recently, with the help of photonic nanojet of an optical microsphere, we were able to enhance the SERS signal of a few molecules adsorbed on the SERS substrates (gold symmetric and asymmetric nanodimers and trimers dispersed on a glass slide). Herein, we report a few details about photonic nanojet mediated SERS technique, a few experimental results and a detailed theoretical study on symmetric and asymmetric nanosphere dimers to understand the dependence of localised surface plasmon resonance (LSPR) wavelength of a nanodimer on the nanogap size and polarization of the excitation light.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Synthesis, characterization and properties of L-arginine-passivated silver nanocolloids

We investigate the effect of L-arginine-surface passivation on localised surface plasmon resonance (LSPR), size and stability of colloidal Silver Nanoparticles (AgNPs) synthesized by chemical reduction method. The surface Plasmon resonance absorption peak of AgNPs shows blue shift with the increase in L-arginine concentration. Transmission electron microscopy (TEM) analysis confirmed that the average size of AgNPs reduces from 10 nm to 6 nm as the concentration of L-Arginine increased from 1 to 5 mM. The X-ray diffraction study (XRD) confirmed the formation face-centred cubic (fcc) structured AgNPs. FT-IR studies revealed strong bonding between L-arginine functional groups and AgNPs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Pair correlations of dipole emitters in a finite charged-sheet structure

The pair correlations arising from the cooperative emission from the joint first excited states of two identical dipole emitters localised within a finite ordered charged-sheet structure (FCSS) are investigated. The FCSS consists of a finite number of charged-sheets separating dielectric layers. The rates of de-excitation corresponding to a pair of states, namely the symmetric state and anti-symmetric state, are evaluated. The study of field-matter interactions of this kind in such a context would be useful for the development of quantum-information and the realisation of quantum-computing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Dissipative particle dynamics of diffusion-NMR requires high Schmidt-numbers

We present an efficient mesoscale model to simulate the diffusion measurement with nuclear magnetic resonance (NMR). On the level of mesoscopic thermal motion of fluid particles, we couple the Bloch equations with dissipative particle dynamics (DPD). Thereby we establish a physically consistent scaling relation between the diffusion constant measured for DPD-particles and the diffusion constant of a real fluid. The latter is based on a splitting into a centre-of-mass contribution represented by DPD, and an internal contribution which is not resolved in the DPD-level of description. As a consequence, simulating the centre-of-mass contribution with DPD requires high Schmidt numbers. After a verification for fundamental pulse sequences, we apply the NMR-DPD method to NMR diffusion measurements of anisotropic fluids, and of fluids restricted by walls of microfluidic channels. For the latter, the free diffusion and the localisation regime are considered.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Dissociation of multiply charged ICN by Coulomb explosion

The fragmentations of iodine cyanide ions created with 2 to 8 positive charges by photoionization from inner shells with binding energies from 59 eV (I 4d) to ca. 900 eV (I 3p) have been examined by multi-electron and multi-ion coincidence spectroscopy with velocity map imaging ion capability. The charge distributions produced by hole formation in each shell are characterised and systematic effects of the number of charges and of initial charge localisation are found.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Tornado model for a magnetised plasma

A new analytical model of axially-symmetric magnetic vortices with both a twisted fluid flow and a magnetic field is proposed. The exact solution for the three-dimensional structure of the fluid velocity and the magnetic field is obtained within the framework of the ideal magnetohydrodynamic equations for an incompressible fluid in a gravitational field. A quasi-stationary localised vortex arises when the radial flow that tends to concentrate vorticity in a narrow column around the axis of symmetry is balanced by the vertical vortex advection in the axial direction. The explicit expressions for the velocity and magnetic field components are obtained. The proposed analytic model may be used to parameterise the observed solar tornadoes and can provide a new indirect way for estimating magnetic twist from the observed azimuthal velocity profiles.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Examining the order-of-limits problem and lattice constant performance of the Tao–Mo functional

In their recent communication a semi-local density functional derived from the density matrix expansion of the exchange hole localised by a general coordinate transformation. We show that the order-of-limits problem present in the functional, dismissed as harmless in the original publication, causes severe errors in predicted phase transition pressures. We also show that the claim that lattice volume prediction accuracy exceeds that of existing similar functionals was based on comparison to reference data that misses anharmonic zero-point expansion and consequently overestimates accuracy. Here, by highlighting these omissions, we give a more accurate assessment of the Tao-Mo functional and show a possible direction for resolving the order-of-limits problem.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Near-field focusing of an optical wave by diffraction gratings

We report the investigation results for spatially-localised light structures (photonic nanojets) under near-field optical radiation scattering on phase diffraction gratings. Main parameters of photonic nanojets from gratings with sawtooth, rectangular and hemispherical groove profiles are obtained by numerical electrodynamic simulation. It is found that by varying a period, degree of filling, groove shape and parameters of optically contrast coating of the diffraction grating one can control the characteristics of the produced photonic jets in a wide range. (laser beams)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Third harmonic generation in the short-wavelength UV range by a single plasmonic nanostructure

The nonlinear optical interaction of laser radiation with nanostructures formed in gold and aluminium nanofilms has been experimentally studied. It is shown that, despite the high susceptibility χ{sub 3} of aluminium in comparison with gold, the third-harmonic generation efficiency at a wavelength of 260 nm is much higher for the nanostructures formed in a gold nanofilm because of the efficient excitation of a localised plasmon resonance at the fundamental frequency. (extreme laser radiation: physics and fundamental applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Fractional laser microablation of skin: increasing the efficiency of transcutaneous delivery of particles

We study several regimes of fractional laser microablation using a pulsed Er : YAG laser for producing microchannels of different depth and incisions that allow transcutaneous delivery of particles of different size, namely, Al{sub 2}O{sub 3} (27 μm), ZrO{sub 2} (smaller than 5 μm) and TiO{sub 2} (smaller than 100 nm). The shock wave regime was used both for enhancing the penetration of particles into the ablation zones and as an independent method of particle delivery into the skin. Based on optical coherence tomography we assessed the coherent depth of particle detection in the skin in 2 hours, 3 days and 10 days after the administration. The maximal localisation depth (up to 450 μm) was obtained for TiO{sub 2} nanoparticles in the regime of incisions with enhancement of particle penetration by pulses of a multiple-beam hydrodynamic shock wave. The results of the study can be useful for developing new methods of transcutaneous delivery of micro- and nanocarriers of medicinal preparations. (laser biophotonics)

36 MATERIALS SCIENCE↗
DOE OSTI2016

Post-filamentation propagation of high-power laser pulses in air in the regime of narrowly focused light channels

We report the results of experimental and theoretical studies of the post-filamentation stage of nonlinear propagation of high-power pulsed radiation from a Ti : sapphire laser in air. We have for the first time obtained the experimental dependences of the angular divergence of specific spatially localised high-intensity light structures that are observed in the beam after its multiple filamentation (post-filamentation of channels) when varying the initial focusing of laser radiation and its energy. It is found that the angular divergence of the post-filamentation channels decreases with increasing pulse energy and reducing beam numerical aperture. The experimental dependences are qualitatively interpreted based on the diffraction model of the Bessel – Gaussian beam. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Scanning photoelectron microscopy using a pointed capillary probe

The possibilities of a new type of scanning probe microscopy (SPM) for two different samples are experimentally demonstrated. The method is based on the use of a pointed capillary, which can simultaneously act as a ‘classical’ SPM probe and also as a controlled thin channel for transporting charged particles emitted by the surface to the detector. In the experiment, photoelectrons pass through a dielectric hollow cone probe with an aperture radius of 1 μm and detected by microchannel plates at different points of the investigated conducting surface irradiated by the second harmonic of a femtosecond Ti : sapphire laser. As a result, the sample’s surface profile is visualised with a subwavelength spatial resolution. This method makes it possible to control spatially localised beams of electrons, ions, neutral atoms (molecules) and soft X-ray radiation, as well as opens a possibility for research in the field of nanoscale photodesorption of molecular ions. (electron microscopy)

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Laser frequency stabilisation on narrow resonances of cold magnesium atoms at the {sup 1}S{sub 0} – {sup 3}P{sub 1} transition

Experimental studies aimed at developing an optical frequency standard based on ultracold magnesium atoms with a relative uncertainty of Δν/ν < 10{sup –16} are performed. The frequency of the clock laser system at a wavelength of 457 nm is stabilised to narrow optical resonances (Ramsey fringes) in time-separated laser fields interacting with cold magnesium atoms localised in a magneto-optical trap (MOT). The frequency stability of the laser system is investigated using a femtosecond comb based on a Ti:sapphire laser. Long-term frequency stability (determined by the Allan function) of ∼5 × 10{sup –15} at averaging time τ = 1000 s is obtained. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Self-action of a wave field in one-dimensional system of weakly coupled active optical waveguides

The dynamics of self-action of a wave field in an array of weakly coupled active optical waveguides is studied analytically and numerically. It is shown that the introduction of weak gain in each of the waveguides allows significant reduction of radiation losses and efficient capture of all radiation in a single optical waveguide. The possibility of controlling the radiation localisation in the desired waveguide at the expense of varying the injection angle of the wave field into the considered system is demonstrated. The dependences of the characteristic parameters of the wave field are determined. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

On the nonlocality of the reflection of an electromagnetic wave from a flat surface upon excitation of surface waves

Diffraction phenomena arising due to reflection of a plane electromagnetic wave from a metal film, which are caused by a limited size of the incident beam aperture, are considered in the Kretschmann scheme used to excite a surface plasmon wave. It is shown that the wave reflection occurs nonlocally, that is, the region of the surface on which the wave is incident and the region from which it is reflected do not substantially coincide. The localisation of the maximum field is investigated when a surface plasmon is excited on a silver film. The absolute values of the gain in terms of the amplitude of the field on the free surface of the film are calculated. The proposed theory is applied to explain the Goos – Hänchen effect. (integrated optics)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Thermoplasmonic laser-induced backside wet etching of sapphire

The technology of thermoplasmonic laser-induced backside wet etching is proposed to microstructure such solid and difficult-to-process materials as sapphire. In this technology, the laser absorbing medium is silver nanoparticles obtained from a precursor (AgNO{sub 3}) and providing significant laser radiation absorption due to the presence of plasmonic absorption with the formation of a substantially localised region with extremely high temperatures and pressures. This approach makes it possible to process sapphire both in the ‘gentle’ regime with the formation of nanometre structures and in the ‘strong’ regime to allow for the formation of ‘deep’ structures with etching rates up to several micrometers per pulse and high aspect ratio. The possibility of formation of periodic structures in sapphire in the above-threshold regime is shown. (in memory of professor v.n. bagratashvili (1947 – 2018))

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗