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Results for “VISIBLE SPECTRA”

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At least 37 records · Page 2

All sources NASA NTRS DOE OSTI

NASA NTRS1995

The effect of simulated low earth orbit radiation on polyimides (UV degradation study)

UV degradation of polyimide films in air and vacuum were studied using UV-visible, ESR, FTIR, and XPS spectroscopies. The UV-visible spectra of polyimide films showed a blue shift in the absorption compared to Kapton. This behavior was attributed to the presence of bulky groups and kinks along the polymer chains which disrupt the formation of a charge transfer complex. The UV-visible spectra showed also that UV irradiation of polyimides result extensively in surface degradation, leaving the bulk of the polymer intact. ESR spectra of polyimides irradiated in vacuum revealed the formation of stable carbon-centered radicals which give a singlet ESR spectrum, while polyimides irradiated in air produced an asymmetric signal shifted to a lower magnetic field, with a higher g value and line width. This signal was attributed to oxygen-cenetered radicals of peroxy and/or alkoxy type. The rate of radical formation in air was two fold higher than for vacuum irradiation, and reached a plateau after a short time. This suggests a continuous depletion of radicals on the surface via an ablative degradation process. FTIR, XPS, and weight loss studies supported this postulate. An XPS study of the surface indicated a substantial increase in the surface oxidation after irradiation in air. The sharp increase in the C-O binding energy peak relative to the C-C peak was believed to be associated with an aromatic ring opening reaction.

Forsythe, John S.↗

DOE OSTI2017

A Novel Polyester Fabric Treated with Nanoclay/Nano TiO{sub 2}/PAMAM for Discoloration of Reactive Red 4 from Aqueous Solution Under UVA Irradiation

Here, a commercially available absorbent with a high absorbance capacity (Cloisite{sup ®} 15A) together with the high active nano photocatalyst (AEROXIDE{sup ®} TiO{sub 2} P 25) and polyamidoamine based dendrimer (PAMAM) were immobilized on polyester fabric through simple pad-dry-cure method for removing dye from an aqueous solution. Using three components with good activities toward discoloration expected to produce a substrate with an excellent discoloration capacity. FESEM images with EDX patterns and X-ray diffraction spectra revealed the presence of nanoclay and nano TiO{sub 2} on the surface of the fabric. Discoloration of Reactive Red 4 (RR4) was carried out successfully by addition of a piece of the treated fabric in the dye solution under UVA irradiation. UV–visible spectra of the remaining solutions after discoloration indicated complete discoloration of RR4 solution for several times. The photocatalytic properties of the treated fabric was not changed after consecutive discoloration however the fabric surface was colored due to the presence of nanoclay on the surface acting as the dye absorbent. Graphical Abstract: .

36 MATERIALS SCIENCE↗

NASA NTRS1989

Simultaneous infrared and UV-visible absorption spectra of matrix-isolated carbon vapor

Carbon molecules were suggested as possible carriers of the diffuse interstellar bands. In particular, it was proposed that the 443 nm diffuse interstellar band is due to the same molecule which gives rise to the 447 nm absorption feature in argon matrix-isolated carbon vapor. If so, then an associated C-C stretching mode should be seen in the IR. By doing spectroscopy in both the IR and UV-visible regions on the same sample, the present work provides evidence for correlating UV-visible absorption features with those found in the IR. Early data indicates no correlation between the strongest IR feature (1997/cm) and the 447 nm band. Correlation with weaker IR features is being investigated.

Kurtz, Joe↗

DOE OSTI2021

Visible emission spectra of thermographic phosphors under x-ray excitation

Thermographic phosphors have been employed for temperature sensing in challenging environments, such as on surfaces or within solid samples exposed to dynamic heating, because of the high temporal and spatial resolution that can be achieved using this approach. Typically, UV light sources are employed to induce temperature-sensitive spectral responses from the phosphors. However, it would be beneficial to explore x-rays as an alternate excitation source to facilitate simultaneous x-ray imaging of material deformation and temperature of heated samples and to reduce UV absorption within solid samples being investigated. Here, the phosphors BaMgAl 10 O 17 :Eu (BAM), Y 2 SiO 5 :Ce, YAG:Dy, La 2 O 2 S:Eu, ZnGa 2 O 4 :Mn, Mg 3 F 2 GeO 4 :Mn, Gd 2 O 2 S:Tb, and ZnO were excited using incident synchrotron x-ray radiation. These materials were chosen to include conventional thermographic phosphors as well as x-ray scintillators (with crossover between these two categories). X-ray-induced thermographic behavior was explored through the measurement of visible spectral response with varying temperature. The incident x-rays were observed to excite the same electronic energy level transitions in these phosphors as UV excitation. Similar shifts in the spectral response of BAM, Y 2 SiO 5 :Ce, YAG:Dy, La 2 O 2 S:Eu, ZnGa 2 O 4 :Mn, Mg 3 F 2 GeO 4 :Mn, and Gd 2 O 2 S:Tb were observed when compared to their response to UV excitation found in literature. Some phosphors were observed to thermally quench in the temperature ranges tested here, while the response from others did not rise above background noise levels. This may be attributed to the increased probability of non-radiative energy release from these phosphors due to the high energy of the incident x-rays. These results indicate that x-rays can serve as a viable excitation source for phosphor thermometry.

42 ENGINEERING↗

DOE OSTI2016

UTILIZING SYNTHETIC UV SPECTRA TO EXPLORE THE PHYSICAL BASIS FOR THE CLASSIFICATION OF LAMBDA BOÖTIS STARS

Lambda Boo-type stars are a group of late B to early F-type Population I dwarfs that show mild to extreme deficiencies of iron-peak elements (up to 2 dex), but their C, N, O, and S abundances are near solar. This intriguing stellar class has recently regained the spotlight because of the directly imaged planets around a confirmed Lambda Boo star, HR 8799, and a suggested Lambda Boo star, Beta Pictoris. The discovery of a giant asteroid belt around Vega, another possible Lambda Boo star, also suggests hidden planets. The possible link between Lambda Boo stars and planet-bearing stars motivates us to study Lambda Boo stars systematically. Since the peculiar nature of the prototype Lambda Boötis was first noticed in 1943, Lambda Boo candidates published in the literature have been selected using widely different criteria. In order to determine the origin of Lambda Boo stars’ unique abundance pattern and to better discriminate between theories explaining the Lambda Boo phenomenon, a consistent working definition of Lambda Boo stars is needed. We have re-evaluated all published Lambda Boo candidates and their available ultraviolet and visible spectra. In this paper, using observed and synthetic spectra, we explore the physical basis for the classification of Lambda Boo stars, and develop quantitative criteria that discriminate metal-poor stars from bona fide Lambda Boo stars. Based on these stricter Lambda Boo classification criteria, we conclude that neither Beta Pictoris nor Vega should be classified as Lambda Boo stars.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1975

Metal-to-metal charge transfer transitions - Interpretation of visible-region spectra of the moon and lunar materials

Prominent bands in the spectral profiles of Fe-Ti phases in lunar samples have been attributed to charge-transfer transitions between Fe and Ti cations, and a model is presented for calculating charge transfer energies from energy levels computed by the SCF-X(alpha) scattered wave molecular orbital method for isolated MO6 octahedral coordination clusters containing Fe(2+), Fe(3+), Ti(3+), and Ti(4+) cations. The calculated charge transfer energy for the Fe(2+) to Ti(4+) transition correlates well with a measured spectral feature around 0.6 micron in ilmenite, and, since ilmenite is a major constituent of mare basalts and dark-mantling material, the observed darkness and blueness of the regolith in lunar black spots is attributed primarily to this transition. The Ti(3+) to Ti(4+) transition is thought to contribute to some phases.

Loeffler, B. M.↗

NASA NTRS1994

Possible spinel absorption bands in S-asteroid visible reflectance spectra

Minor absorption bands in the 0.55 to 0.7 micron wavelength range of reflectance spectra of 10 S asteroids have been found and compared with those of spinel-group minerals using the modified Gaussian model. Most of these S asteroids are consistently shown to have two absorption bands around 0.6 and 0.67 micron. Of the spinel-group minerals examined in this study, the 0.6 and 0.67 micron bands are most consistent with those seen in chromite. Recently, the existence of spinels has also been detected from the absorption-band features around 1 and 2 micron of two S-asteroid reflectance spectra, and chromite has been found in a primitive achondrite as its major phase. These new findings suggest a possible common existence of spinel-group minerals in the solar system.

Hiroi, T.↗

DOE OSTI2020

Visible Emission Spectra of Thermographic Phosphors under X-ray Excitation.

Abstract not provided.

Westphal, Eric↗

DOE OSTI2016

Final Technical Report - Polymeric Multilayer Infrared Reflecting Mirrors

The goal of this project was to develop a clear, polymeric, multilayer film with an expanded infrared (IR) reflection band which would allow improved rejection of incident IR energy. The IR reflection band is covering the region from about 850 nm to 1830 nm. This film is essentially clear and colorless in the visible portion of the electromagnetic spectra (visible light transmission of about 89%) while reflecting 90-95% of the IR energy over the portion of the spectra indicated above. This film has a nominal thickness of 3 mils, is polymeric in nature (contains no metals, metal oxides, or other material types) and is essentially clear in appearance This film can then be used as a component of other products such as a solar window film, an IR reflecting interlayer for laminated glass, a heat rejecting skylight film, a base film for daylight redirecting products, a greenhouse film, and many more applications. One of the main strengths of this product is that because it is a standalone IR rejecting film, it can be incorporated and retrofitted into many applications that desire or require the transmission of visible light, but want to block other portions of the solar spectra, especially the IR portion. Many of the applications exist in the window glazing product area where this film can provide for substantial energy improvements in applications where visible light is desired.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

NASA NTRS1988

The spectral properties of interplanetary dust particles

The observed spectral and mineralogical properties of interplanetary dust particles (IDP) allows the conclusion that: (1) the majority of IDP infrared spectra are dominated by olivine, pyroxene, or layer lattice silicate minerals, (2) to the first order the emission spectra of comets Halley and Kohoutek can be matched by mixtures of these IDP infrared types, implying that comets contain mixtures of these different crystalline silicates and may vary from comet to comet and perhaps even within a single comet, (3) do not expect to observe a single 20 micron feature in cometary spectra, (4) carbonaceous materials dominate the visible spectra properties of the IDPs even though the mass in these particles consists primarily of silicates, and (5) the particle characteristics summarized need to be properly accounted for in future cometary emission models.

Sandford, Scott A.↗

NASA NTRS1988

The spectral properties of collected interplanetary dust particles

Sandford, S. A.↗

NASA NTRS1993

New K type asteroids

Several new K type asteroids were identified during near infrared spectral observations on July 30, 1992 at NASA's infrared telescope facility (IRTF) at Mauna Kea, Hawaii. These K asteroids are 513 Centesima, 633 Zelima, 1129 Neujmina, 1416 Renauxa, 1799 Koussevitzky, and 1883 Rauma. A K asteroid is an asteroid which possesses a S type spectra in visible wavelengths and a C type spectra visible in near-infrared wavelengths. These objects are usually misclassified as S asteroids on the basis of visible spectra alone. This type was first detected by the 52 infrared color asteroid survey also conducted at the IRTF. Our observations utilized a new seven color infrared asteroid filter system which allows near-infrared data to be collected from asteroids as faint as 16th 5 magnitude.

Granahan, James C.↗

DOE OSTI2016

Synthesis of silver nano-materials from Grevillea robusta A Cunn (Silver-oak tree) leaves extract and shape directing role of cetyltrimethylammonium bromide

Grevillea robusta (Silver-oak tree) tree is a medicinal tree. Conventional UV-visible spectrophotometric and transmission electron microscopic technique were used to determine the morphology of silver nanoplates (AgNP) using Grevillea robusta (Silver-oak tree) aqueous leaves extract for the first time. The visible spectra showed the presence of three well defined surface plasmon absorption (SPR) bands at 500, 550 and 675 nm which was attributed to the anisotropic growth of Ag-nanoplates. Transmission electron microscopic (TEM) analysis of AgNP showed formation of truncated triangular, polyhedral with some irregular shapes nanoplates in the size range 8-20 nm. Cetyltrimethylammonium bromide (CTAB) has no significant effect on the shape of the spectra, position of SPR bands, size and size distribution of AgNP.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2016

CARBON-TO-OXYGEN RATIOS IN M DWARFS AND SOLAR-TYPE STARS

It has been suggested that high C/O ratios (>0.8) in circumstellar disks lead to the formation of carbon-dominated planets. Based on the expectation that elemental abundances in the stellar photospheres give the initial abundances in the circumstellar disks, the frequency distributions of C/O ratios of solar-type stars have been obtained by several groups. The results of these investigations are mixed. Some find C/O > 0.8 in more than 20% of stars, and C/O > 1.0 in more than 6%. Others find C/O > 0.8 in none of the sample stars. These works on solar-type stars are all differential abundance analyses with respect to the Sun and depend on the adopted C/O ratio in the Sun. Recently, a method of molecular line spectroscopy of M dwarfs, in which carbon and oxygen abundances are derived respectively from CO and H{sub 2}O lines in the K band, has been developed. The resolution of the K- band spectrum is 20,000. Carbon and oxygen abundances of 46 M dwarfs have been obtained by this nondifferential abundance analysis. Carbon-to-oxygen ratios in M dwarfs derived by this method are more robust than those in solar-type stars derived from neutral carbon and oxygen lines in the visible spectra because of the difficulty in the treatment of oxygen lines. We have compared the frequency distribution of C/O distributions in M dwarfs with those of solar-type stars and have found that the low frequency of high-C/O ratios is preferred.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

Thickness dependent optical properties of PEMA and (PEMA){sub 0.85}/(ZnO){sub 0.15} nanocomposite films deposited by spray pyrolysis technique on ITO substrate

In this paper, poly (ethyl methacrylate) (PEMA) and (PEMA){sub 0.85}/(ZnO){sub 0.15} nanocomposite films for 2, 3, 4 and 5 minutes have been deposited by spray pyrolysis technique on indium tin oxide (ITO) coated substrate. The effect of thickness of the film on the morphological and optical properties of PEMA and (PEMA){sub 0.85}/(ZnO){sub 0.15} nanocomposite films are studied. The morphological and optical properties of pure PEMA and (PEMA){sub 0.85}/(ZnO){sub 0.15} nanocomposite films are compared. The field emission scanning electron microscopy (FESEM) shows that as the thickness of film increases, uniformity of films increases. It is found from UV-Visible spectra that the energy band gap decreases with increasing the deposition time and refractive index increases with increasing the thickness of the film. The band gap of the nanocomposites is found less than the pure polymer film and opposite trend is observed for refractive index. The optical absorption of PEMA/ZnO nanocomposite films is higher than pure PEMA film. The thickness of the nanocomposite film plays a significant role in the tunability of the optical properties.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2016

THE MISSION ACCESSIBLE NEAR-EARTH OBJECTS SURVEY (MANOS): FIRST PHOTOMETRIC RESULTS

The Mission Accessible Near-Earth Objects Survey aims to physically characterize sub-km near-Earth objects (NEOs). We report the first photometric results from the survey that began in 2013 August. Photometric observations were performed using 1–4 m class telescopes around the world. We present rotational periods and light curve amplitudes for 86 sub-km NEOs, though in some cases only lower limits are provided. Our main goal is to obtain light curves for small NEOs (typically, sub-km objects) and estimate their rotational periods, light curve amplitudes, and shapes. These properties are used for a statistical study to constrain overall properties of the NEO population. A weak correlation seems to indicate that smaller objects are more spherical than larger ones. We also report seven NEOs that are fully characterized (light curve and visible spectra) as the most suitable candidates for a future human or robotic mission. Viable mission targets are objects fully characterized, with Δ v {sup NHATS} ≤ 12 km s{sup −1}, and a rotational period P > 1 hr. Assuming a similar rate of object characterization as reported in this paper, approximately 1230 NEOs need to be characterized in order to find 100 viable mission targets.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2019

Surface coupling of plasma optical emission spectra with bent metal-clad waveguide

We present the design of compact bent metal-clad waveguides to collect the vertically emitted light and to transmit to the horizontal direction. The intention of the design is to collect the plasma optical emission spectra inside the semiconductor etch process chamber to monitor plasma gas phase chemistry resides in the process chamber. Coupler A has been designed for visible spectra range from 748 to 753 nm at which the maximum coupling efficiency is over 52%, while Coupler B operates at the wavelength range from 775 to 780 nm with coupling strength of 62% and Coupler C covers the visible spectrum from 808 to 813 nm with its maximum efficiency of 60%. The surface couplers reveal good spectral characteristics, considerable alignment tolerance and minimal size of 9 × 5 × 1.6 µm{sup 3} each. Relatively simple geometrical structure over conventional grating coupler is advantageous to lower the fabrication cost as well.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2017

0.7–2.5 μ m Spectra of Hilda Asteroids

The Hilda asteroids are primitive bodies in resonance with Jupiter whose origin and physical properties are not well understood. Current models posit that these asteroids formed in the outer solar system and were scattered along with the Jupiter Trojans into their present-day positions during a chaotic episode of dynamical restructuring. In order to explore the surface composition of these enigmatic objects in comparison with an analogous study of Trojans, we present new near-infrared spectra (0.7–2.5 μ m) of 25 Hilda asteroids. No discernible absorption features are apparent in the data. Synthesizing the bimodalities in optical color and infrared reflectivity reported in previous studies, we classify 26 of the 28 Hildas in our spectral sample into the so-called less-red and red sub-populations and find that the two sub-populations have distinct average spectral shapes. Combining our results with visible spectra, we find that Trojans and Hildas possess similar overall spectral shapes, suggesting that the two minor body populations share a common progenitor population. A more detailed examination reveals that while the red Trojans and Hildas have nearly identical spectra, less-red Hildas are systematically bluer in the visible and redder in the near-infrared than less-red Trojans, indicating a putative broad, shallow absorption feature between 0.5 and 1.0 μ m. We argue that the less-red and red objects found in both Hildas and Trojans represent two distinct surface chemistries and attribute the small discrepancy between less-red Hildas and Trojans to the difference in surface temperatures between the two regions.

79 ASTRONOMY AND ASTROPHYSICS↗