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Results for “VISIBLE SPECTRA”

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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Study on fabrication of TiO{sub 2} thin films by spin – coating and their optical properties

Study on fabrication of TiO{sub 2} thin films and their optical properties in UV-VIS spectrum has been conducted. TiO{sub 2} nanopowders were prepared by co-precipitation method with varying mixing duration for 5, 10 and 25 hours using TiCl{sub 3} as precursor. The as-synthesized TiO{sub 2} phase is anatase having crystalline size of 14.25 nm, 13.75 nm and 12.62, respectively for the corresponding mixing duration. Thin films of TiO{sub 2} were fabricated by spin coating method and then checked by XRD diffractometer and UV-Vis Spectrophotometer to examine their structure and band gap energy. The prepared films also contain anatase phase of TiO{sub 2} with respective band gap of 3.70 eV, 3.74 eV and 3.76 eV, depending on the powders and their treatment.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Edge and defect luminescence of powerful ultraviolet InGaN/GaN light-emitting diodes

The spectrum of ultraviolet (UV) InGaN/GaN light-emitting diodes and its dependence on the current flowing through the structure are studied. The intensity of the UV contribution to the integrated diode luminescence increases steadily with increasing density of current flowing through the structure, despite a drop in the emission quantum efficiency. The electroluminescence excitation conditions that allow the fraction of UV emission to be increased to 97% are established. It is shown that the nonuniform generation of extended defects, which penetrate the active region of the light-emitting diodes as the structures degrade upon local current overheating, reduces the integrated emission intensity but does not affect the relative intensity of diode emission in the UV (370 nm) and visible (550 nm) spectral ranges.

36 MATERIALS SCIENCE↗
NASA NTRS2009

Visible and Near-IR Reflectance Spectra for Smectite, Sulfate And Perchlorate under Dry Conditions for Interpretation of Martian Surface Mineralogy

Visible and near-IR (VNIR) spectral data for the martian surface obtained from orbit by the MRO-CRISM and OMEGA instruments are interpreted as having spectral signatures of H2O/OH-bearing phases, including smectites and other phyllosilicates, sulfates, and high-SiO2 phases [e.g., 1-4]. Interpretations of martian spectral signatures are based on and constrained by spectra that are obtained in the laboratory on samples with known mineralogical compositions and other physicochemical characteristics under, as appropriate, Mars-like environmental conditions (e.g., temperature, pressure, and humidity). With respect to environmental conditions, differences in the absolute concentration of atmospheric H2O can effect the hydration state and therefore the spectra signatures of smectite phyllosilicates (solvation H2O) and certain sulfates (hydration H2O) [e.g., 5-7]. We report VNIR spectral data acquired under humid (laboratory air) and dry (dry N2 gas) environments for two natural smectites (nontronite API-33A and saponite SapCa-1) to characterize the effect of solvation H2O on spectral properties. We also report spectral data for the thermal dehydration products of (1) melanterite (FeSO4.7H2O) in both air and dry N2 gas and (2) Mg-perchlorate (Mg(ClO4)2.6H2O) in dry N2 environments. Spectral measurements for samples dehydrated in dry N2 were made without exposing them to humid laboratory air.

Morris, R.V.↗
DOE OSTI2017

Influence of induced colour centres on the frequency – angular spectrum of a light bullet of mid-IR radiation in lithium fluoride

The influence of the occurrence of a structure consisting of long-lived colour centres, formed in an LiF crystal upon filamentation of femtosecond mid-IR radiation, on the supercontinuum characteristics is investigated. With an increase in the number of incident pulses, the length and transverse size of the structure of colour centres induced in LiF increase, and the supercontinuum spectrum in the short-wavelength region is markedly transformed due to the occurrence of the waveguide propagation regime, absorption, and scattering of radiation from the newly formed structure of colour centres. Under these conditions, the intensity of the anti-Stokes wing decreases by two orders of magnitude after several tens of pulses. Spectral components arise in the visible range, the angular divergence of which increases with increasing wavelength. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1990

Combined infrared and ultraviolet-visible spectroscopy matrix-isolated carbon vapor

Infrared and UV-visible absorption spectra have been measured on the same sample of matrix-isolated carbon vapor in order to establish correlations between absorption intensities of vibrational and electronic transitions as a function of sample annealing. A high degree of correlation has been found between the IR feature at 1998/cm recently assigned to C8 and a UV absorption feature at about 3100 A. Thus, for the first time, direct evidence is given for the assignment of one of the unknown UV-visible features of the long-studied matrix-isolated carbon vapor spectrum.

Kurtz, Joe↗
NASA NTRS1985

Hibonite: Crystal Chemistry and Origin of Blue Coloration in Meteoritic Assemblages

The blue color and optical spectra of hibonite, a common constituent of refractory inclusions in carbonaceous chondrites, are discussed. Because they may be manifestations of exotic cation species stabilized in unusual coordination sites in the hibonite crystalstructure. Hibonite, ideally CaAl12O19, is conducive to atomic substitution of host Ca2+ and Al3+ ions by a variety of lanthanide and first series transition elements. The latter cations are responsible for the colors of many rock-forming minerals as a result of intraelectronic or intervalence transitions. The visible-region spectra of most oxide and silicate minerals are generally well understood. Assignments of absorption bands in meteoritic hibonite optical spectra due to uncertainties of cation valencies and complexities in the crystal structure are examined. The crystal chemistry of hibonite is reviewed, Mossbauer spectral measurements of iron-bearing hibonite and electronic transitions that may be responsible for the blue coloration of meteoritic hibonites are discussed.

Burns, R. G.↗
DOE OSTI2017

Uncertainty in the visibility mask of a survey and its effects on the clustering of biased tracers

The forecasted accuracy of upcoming surveys of large-scale structure cannot be achieved without a proper quantification of the error induced by foreground removal (or other systematics like 0-point photometry offset). Because these errors are highly correlated on the sky, their influence is expected to be especially important at very large scales, at and beyond the first Baryonic Acoustic Oscillation (BAO). In this work we quantify how the uncertainty in the visibility mask of a survey, that gives the survey depth in a specific sky area, influences the measured power spectrum of a sample of tracers of the density field and its covariance matrix. We start from a very large set of 10,000 catalogs of dark matter (DM) halos in periodic cosmological boxes, produced with the PINOCCHIO approximate method. To make an analytic approach feasible, we assume luminosity-independent halo bias and an idealized geometry for the visibility mask, that is constant in square tiles of physical length l ; this should be interpreted as the projection, at the observation redshift, of the angular correlation scale of the foreground residuals. We find that the power spectrum of these biased tracers can be expressed as the sum of a cosmological term, a mask term and a term involving their convolution. The mask and convolution terms scale like P ∝ l {sup 2}σ {sub A} {sup 2}, where σ {sub A} {sup 2} is the variance of the uncertainty on the visibility mask. With l = 30−100 Mpc/ h and σ {sub A} = 5−20%, the mask term can be significant at k ∼ 0.01−0.1 h /Mpc, and the convolution term can amount to ∼ 1−10% of the total. The influence of mask uncertainty on power spectrum covariance is more complicated: the coupling of the convolution term with the other two gives rise to several mixed terms, that we quantify by difference using the mock catalogs. These are found to be of the same order of the mask covariance, and to introduce non-diagonal terms at large scales. As a consequence, the power spectrum covariance matrix cannot be expressed as the sum of a cosmological and of a mask term. More realistic settings (realistic foregrounds, luminosity-dependent bias) make the analytical approach not feasible, and the problem requires on the one hand usage of extended sets of mock catalogs, on the other hand detailed knowledge of the correlations among errors in the visibility masks. Our results lie down the theoretical bases to quantify the impact that uncertainties in the mask calibration have on the derivation of cosmological constraints from large spectroscopic surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1982

Do comets evolve into asteroids - Evidence from physical studies

Physical observations of low-activity periodic comets and asteroids in distant and peculiar orbits are reviewed. In particular, magnitude studies and reflection spectra at visible and infrared wavelengths are discussed. While it may never be possible to prove unambiguously that a cometary nucleus has been observed, the fainter a given comet is, the more likely it is that some light reflected from a solid surface will be observed. Studies of magnitudes obtained by Roemer suggest that at certain periods the nuclei of P/Arend-Rigaux and P/Neujmin 1 may be photometrically resolved. It is shown that this may also be the case for P/Schwassmann-Wachmann 1, but that it is less likely for P/Tempel 2. At times of minimum activity, the optical spectra of P/Arend-Rigaux and P/Schwassmann-Wachmann 1 resemble those of RD-type asteroids like 944 Hidalgo. In order to progress with physical studies of cometary nuclei, an increased effort should be made to obtain magnitudes and other physical observations of comets during stages of minimal activity.

Degewij, J.↗
DOE OSTI2018

Facile preparation of CuO/g-C3N4 with enhanced photocatalytic degradation of salicylic acid

Highlights: • CuO /g-C{sub 3}N{sub 4} sheets were prepared by using a novel one-pot method. • CuO/g-C{sub 3}N{sub 4} exhibited higher catalytic activity than the parent g-C{sub 3}N{sub 4} material. • The increased photocatalytic activity was proposed. - Abstract: CuO particles supported on graphitic carbon nitride (g-C{sub 3}N{sub 4}) nanosheeets were prepared using a novel one-pot method. In the presence of ammonium nitrate, different mass ratios of copper nitrate/melamine were used to fabricate these catalysts, which were characterized using XRD, N{sub 2}-physisorption, FT-IR, TEM, XPS and UV–vis analysis. The catalytic performance of CuO/g-C{sub 3}N{sub 4} was evaluated by photodegrading salicylic acid under visible-light irradiation. Among these novel catalysts, CuO(1.0)/g-C{sub 3}N{sub 4} was found to exhibit the highest catalytic activity, which was more than 100% greater than the parent g-C{sub 3}N{sub 4} material. The improved photocatalytic properties of CuO/g-C{sub 3}N{sub 4} may be ascribed to the formation of p-n heterojunctions between CuO and g-C{sub 3}N{sub 4}, resulting in the effective separation of photogenerated electron-hole pairs and the enhanced absorption of visible light. Furthermore, the CuO/g-C{sub 3}N{sub 4} composites had excellent stability and reused for five times without obvious loss of activity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

An Effect of Internal Structure of Bimetallic Nanoparticles on Optical Properties for AuAg/Glass Material

Optical extinction spectra calculated via multisphere T-matrices for nanoparticles with different concentrations of metals and different architectures (core–shell, inverse core–shell, or alloy) are considered. A method is proposed for determination of architecture of nanoparticles (core–shell or alloy) from only data on the position of plasmon resonance and composition of components. The use of an optical spectrum fitting technique to the spectra of monodisperse noninteracting bimetallic nanoparticles with a predetermined structure appeared to be effective for the determination of the internal structure of nanoparticles, except large nanoparticles with a radius of more than 60 nm containing less than ∼25% silver atoms.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Detecting Sub-Micron Space Weathering Effects in Lunar Grains With Synchrotron Infrared Nanospectroscopy

Space weathering processes induce changes to the physical, chemical, and optical properties of space-exposed soil grains. For the Moon, space weathering causes reddening, darkening, and diminished contrast in reflectance spectra over visible and near-infrared wavelengths. The physical and chemical changes responsible for these optical effects occur on scales below the diffraction limit of traditional far-field spectroscopic techniques. Recently developed super-resolution spectroscopic techniques provide an opportunity to understand better the optical effects of space weathering on the sub-micrometer length scale. This paper uses synchrotron infrared nanospectroscopy to examine depth-profile samples from two mature lunar soils in the mid-infrared, 1,500 –700 cm -1 (6.7–14.3 μm). Overall, our findings are broadly consistent with prior bulk observations and theoretical models of space weathered spectra of lunar materials. These results provide a direct spatial link between the physical/chemical changes in space-exposed grain surfaces and spectral changes of space weathered bodies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The metal abundances across cosmic time (MACT) Survey. I. Optical spectroscopy in the subaru deep field

Deep rest-frame optical spectroscopy is critical for characterizing and understanding the physical conditions and properties of the ionized gas in galaxies. Here, we present a new spectroscopic survey called “Metal Abundances across Cosmic Time” or MACT, which will obtain rest-frame optical spectra for ∼3000 emission-line galaxies. This paper describes the optical spectroscopy that has been conducted with MMT/Hectospec and Keck/DEIMOS for ≈1900 z = 0.1–1 emission-line galaxies selected from our narrowband and intermediate-band imaging in the Subaru Deep Field. In addition, we present a sample of 164 galaxies for which we have measured the weak [O iii]λ4363 line (66 with at least 3σ detections and 98 with significant upper limits). This nebular emission line determines the gas-phase metallicity by measuring the electron temperature of the ionized gas. This paper presents the optical spectra, emission-line measurements, interstellar properties (e.g., metallicity, gas density), and stellar properties (e.g., star formation rates, stellar mass). Paper II of the MACT survey (Ly et al.) presents the first results on the stellar mass–gas metallicity relation at z ≲ 1 using the sample with [O iii]λ4363 measurements.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2004

Lunar and Planetary Science XXXV: Asteroids, Meteors, Comets

Reports included:Long Term Stability of Mars Trojans; Horseshoe Asteroids and Quasi-satellites in Earth-like Orbits; Effect of Roughness on Visible Reflectance Spectra of Planetary Surface; SUBARU Spectroscopy of Asteroid (832) Karin; Determining Time Scale of Space Weathering; Change of Asteroid Reflectance Spectra by Space Weathering: Pulse Laser Irradiation on Meteorite Samples; Reflectance Spectra of CM2 Chondrite Mighei Irradiated with Pulsed Laser and Implications for Low-Albedo Asteroids and Martian Moons; Meteorite Porosities and Densities: A Review of Trends in the Data; Small Craters in the Inner Solar System: Primaries or Secondaries or Both?; Generation of an Ordinary-Chondrite Regolith by Repetitive Impact; Asteroid Modal Mineralogy Using Hapke Mixing Models: Validation with HED Meteorites; Particle Size Effect in X-Ray Fluorescence at a Large Phase Angle: Importance on Elemental Analysis of Asteroid Eros (433); An Investigation into Solar Wind Depletion of Sulfur in Troilite; Photometric Behaviour Dependent on Solar Phase Angle and Physical Characteristics of Binary Near-Earth-Asteroid (65803) 1996 GT; Spectroscopic Observations of Asteroid 4 Vesta from 1.9 to 3.5 micron: Evidence of Hydrated and/or Hydroxylated Minerals; Multi-Wavelength Observations of Asteroid 2100 Ra-Shalom: Visible, Infrared, and Thermal Spectroscopy Results; New Peculiarities of Cometary Outburst Activity; Preliminary Shape Modeling for the Asteroid (25143) Itokawa, AMICA of Hayabusa Mission; Scientific Capability of MINERVA Rover in Hayabusa Asteroid Mission; Characteristics and Current Status of Near Infrared Spectrometer for Hayabusa Mission; Sampling Strategy and Curation Plan of Hayabusa Asteroid Sample Return Mission; Visible/Near-Infrared Spectral Properties of MUSES C Target Asteroid 25143 Itokawa; Calibration of the NEAR XRS Solar Monitor; Modeling Mosaic Degradation of X-Ray Measurements of 433 Eros by NEAR-Shoemaker; Scattered Light Remediation and Recalibration of near Sheomaker s NIS Global Dataaset at 433 Eros; Evaluation of Preparation and Measuring Techniques for Interplanetary Dust Particles for the MIDAS Experiment on Rosetta; Chiron: a Proposed Remote Sensing Prompt Gamma Ray Activation Analysis Instrument for a Nuclear Powered Prometheus Mission;From Present Surveying to Future Prospecting of the Asteroid Belt; Asteroid Physical Properties Probe Microgravity Testing of a Surface Sampling System for Sample Return from Small Solar System Bodies;and Penetrator Coring Apparatus for Cometary Surfaces.

Source record↗
DOE OSTI2016

CHANDRA ACIS SURVEY OF X-RAY POINT SOURCES: THE SOURCE CATALOG

The Chandra archival data is a valuable resource for various studies on different X-ray astronomy topics. In this paper, we utilize this wealth of information and present a uniformly processed data set, which can be used to address a wide range of scientific questions. The data analysis procedures are applied to 10,029 Advanced CCD Imaging Spectrometer observations, which produces 363,530 source detections belonging to 217,828 distinct X-ray sources. This number is twice the size of the Chandra Source Catalog (Version 1.1). The catalogs in this paper provide abundant estimates of the detected X-ray source properties, including source positions, counts, colors, fluxes, luminosities, variability statistics, etc. Cross-correlation of these objects with galaxies shows that 17,828 sources are located within the D {sub 25} isophotes of 1110 galaxies, and 7504 sources are located between the D {sub 25} and 2 D {sub 25} isophotes of 910 galaxies. Contamination analysis with the log N –log S relation indicates that 51.3% of objects within 2 D {sub 25} isophotes are truly relevant to galaxies, and the “net” source fraction increases to 58.9%, 67.3%, and 69.1% for sources with luminosities above 10{sup 37}, 10{sup 38}, and 10{sup 39} erg s{sup −1}, respectively. Among the possible scientific uses of this catalog, we discuss the possibility of studying intra-observation variability, inter-observation variability, and supersoft sources (SSSs). About 17,092 detected sources above 10 counts are classified as variable in individual observation with the Kolmogorov–Smirnov (K–S) criterion ( P {sub K–S} < 0.01). There are 99,647 sources observed more than once and 11,843 sources observed 10 times or more, offering us a wealth of data with which to explore the long-term variability. There are 1638 individual objects (∼2350 detections) classified as SSSs. As a quite interesting subclass, detailed studies on X-ray spectra and optical spectroscopic follow-up are needed to categorize these SSSs and pinpoint their properties. In addition, this survey can enable a wide range of statistical studies, such as X-ray activity in different types of stars, X-ray luminosity functions in different types of galaxies, and multi-wavelength identification and classification of different X-ray populations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

THE NATURE AND FREQUENCY OF THE GAS OUTBURSTS IN COMET 67P/CHURYUMOV–GERASIMENKO OBSERVED BY THE ALICE FAR-ULTRAVIOLET SPECTROGRAPH ON ROSETTA

ALICE is a far-ultraviolet imaging spectrograph on board Rosetta that, among multiple objectives, is designed to observe emissions from various atomic and molecular species from within the coma of comet 67P/Churyumov–Gerasimenko. The initial observations, made following orbit insertion in 2014 August, showed emissions of atomic hydrogen and oxygen spatially localized close to the nucleus and attributed to photoelectron impact dissociation of H{sub 2}O vapor. Weaker emissions from atomic carbon were subsequently detected and also attributed to electron impact dissociation, of CO{sub 2}, the relative H i and C i line intensities reflecting the variation of CO{sub 2} to H{sub 2}O column abundance along the line of sight through the coma. Beginning in 2015 mid-April, Alice sporadically observed a number of outbursts above the sunward limb characterized by sudden increases in the atomic emissions, particularly the semi-forbidden O i λ 1356 multiplet, over a period of 10–30 minutes, without a corresponding enhancement in long-wavelength solar reflected light characteristic of dust production. A large increase in the brightness ratio O i λ 1356/O i λ 1304 suggests O{sub 2} as the principal source of the additional gas. These outbursts do not correlate with any of the visible images of outbursts taken with either OSIRIS or the navigation camera. Beginning in 2015 June the nature of the Alice spectrum changed considerably with CO Fourth Positive band emission observed continuously, varying with pointing but otherwise fairly constant in time. However, CO does not appear to be a major driver of any of the observed outbursts.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

On the Theory of Plasmon–Excitons: An Estimate of the Coupling Constant and the Optical Spectrum

The structure of the optical spectra related to the resonant interaction of quasi-two-dimensional excitons and localized plasmons is investigated theoretically. The constant of plasmon–exciton coupling is estimated in a model considering a semiconductor quantum well close to a layer of metal nanoparticles in an adjacent dielectric medium. Numerical calculations carried out for GaAs/Ag and ZnO/Al nanosystems indicate that near the plasmon–exciton resonance the spectrum features a double-peak structure which exhibits the plasmon-excitonic anticrossing behavior upon detuning from exact resonance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Biodegradable Tragacanth Gum Based Silver Nanocomposite Hydrogels and Their Antibacterial Evaluation

In this article, biodegradable tragacanth gum (TG) biopolymer based silver nanocomposite hydrogels (SNCHs) were prepared with acrylamide as monomer using a simple redox polymerization method. TG acts as stabilizer to produce uniform and large silver nanoparticles (Ag-NPs) in presence of Terminalia chebula (TC) leaf extract in the hydrogel network. Forier transform infrared spectroscopy demonstrated the structural units of functional groups of polymeric backbone of the hydrogels. The formation of Ag-NPs in TG based hydrogels was confirmed by UV–Vis spectra. The morphology of homogeneously dispersed Ag-NPs throughout hydrogel networks was confirmed by scanning electron microscopy. TEM analysis indicates that Ag-NPs with average diameters of around 5 nm formed within the hydrogel networks. The evaluation of antibacterial activity of Ag-NPs performed against gram-negative Escherichia coli and gram-positive Bacillus subtilis bacteria and obtained results proved that these newly developed hydrogels have great potential for use in wound healing as well as water purification applications.

36 MATERIALS SCIENCE↗
DOE OSTI2016

NLTE ANALYSIS OF HIGH-RESOLUTION H -BAND SPECTRA. I. NEUTRAL SILICON

We investigated the reliability of our silicon atomic model and the influence of non-local thermodynamical equilibrium (NLTE) on the formation of neutral silicon (Si i) lines in the near-infrared (near-IR) H -band. We derived the differential Si abundances for 13 sample stars with high-resolution H -band spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), as well as from optical spectra, both under local thermodynamical equilibrium (LTE) and NLTE conditions. We found that the differences between the Si abundances derived from the H -band and from optical lines for the same stars are less than 0.1 dex when the NLTE effects are included, and that NLTE reduces the line-to-line scatter in the H -band spectra for most sample stars. These results suggest that our Si atomic model is appropriate for studying the formation of H -band Si lines. Our calculations show that the NLTE corrections of the Si i H -band lines are negative, i.e., the final Si abundances will be overestimated in LTE. The corrections for strong lines depend on surface gravity, and tend to be larger for giants, reaching ∼−0.2 dex in our sample, and up to ∼−0.4 dex in extreme cases of APOGEE targets. Thus, the NLTE effects should be included in deriving silicon abundances from H -band Si i lines, especially for the cases where only strong lines are available.

79 ASTRONOMY AND ASTROPHYSICS↗