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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Mo-N-co-doped mesoporous TiO{sub 2} microspheres with enhanced visible light photocatalytic activity

Highlights: • The Mo-N-co-doped mesoporous TiO{sub 2} microspheres were synthesized via a solvothermal method and further nitriding treatment. • The properties of TiO{sub 2} microspheres can be tuned by Mo-N-co-doping. • Photocatalytic rate is much higher than Pure TiO{sub 2} catalyst powder and Mo doped TiO{sub 2} microspheres. • The higher activity is attributed to the large BET surface area, narrow band gap and intense light absorbance in visible region. - Abstract: Mo-N-co-doped mesoporous TiO{sub 2} microspheres were synthesized via a solvothermal method, followed by nitriding treatment under ammonia gas flow. The efficiency of the samples was investigated by monitoring the degradation of Rhodamine-B under visible light irradiation. The experimental results revealed that Mo-N-co-doped mesoporous TiO{sub 2} microspheres showed better performances than Mo-TiO{sub 2} microspheres. It was observed that; 0.1% molar quantity of Mo doped on TiO{sub 2} at 500 °C for 2 h under nitriding conditions gave highest photocatalytic activities. The nitridation under ammonia gas of Mo-TiO{sub 2} samples created oxygen vacant sites and led to incorporation of substitutional and interstitial Nitrogen. The enhanced visible light photocatalytic activities of Mo-N-co-doped TiO{sub 2} photocatalyst was attributed to the large surface areas, narrow band gap and intense light absorbance in visible region. This study may create a promising and eco-friendly method towards synthesis of metal and non-metals co-doped on semiconductor materials to improve their photocatalytic activities and applications.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Pt-TiO{sub 2} microspheres with exposed {001} facets for degradation of formaldehyde in air: Formation mechanism and enhanced visible light photocatalytic activity

Highlights: • TiO{sub 2} microspheres with exposed {001} facets were successfully synthesized. • Pt-TiO{sub 2} catalyst combined the properties of Pt nanoparticles and TiO{sub 2} {001} facet. • The catalyst exhibited an enhanced visible-light photocatalytic activity. • The formation mechanism of TiO{sub 2} microspheres with exposed {001} facets was studied. - Abstract: In this study, TiO{sub 2} microspheres with exposed {001} facets were successfully synthesized by a low-temperature hydrothermal method without using any organic solvents as morphology controlling agent. Furthermore, an active Pt-TiO{sub 2} catalyst was prepared by impregnation and deposition-precipitation methods with reduction processes. The photocatalytic activity of the samples was evaluated by degradation of formaldehyde in air under visible light irradiation at room temperature. After modification with Pt, the optical absorption property of the Pt-TiO{sub 2} microspheres was extended to visible light range. More importantly, the Pt-TiO{sub 2} microspheres exhibited excellent photocatalytic performance for formaldehyde degradation under visible light irradiation, being superior to pure TiO{sub 2} microspheres and even Pt-P25. The formation mechanism of the TiO{sub 2} microspheres with exposed {001} facets was studied. Moreover, the proper photocatalytic mechanism was also proposed. This work provided new insight into the improvement of photocatalytic activity by special high-energy facet exposing and noble metal depositing.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Novel synthesis of plasmonic Bi{sub 2}Sn{sub 2}O{sub 7}/Ag-AgCl nanocomposite with enhanced visible light photocatalytic property

Highlights: • Stable Bi{sub 2}Sn{sub 2}O{sub 7}/Ag/AgCl composite is prepared by an easy-completing method for the first time. • The Bi{sub 2}Sn{sub 2}O{sub 7}/Ag/AgCl composite has remarkably enhanced photocatalytic activity under visible light irradiation. • The enhanced photocatalytic activity is attributed to enhanced visible-light absorption and high separation efficiency of electron-hole pairs. • The possible mechanism of photocatalysis enhancement is investigated and illustrated. - Abstract: We report a novel Bi{sub 2}Sn{sub 2}O{sub 7}/Ag-AgCl photocatalysts with excellent visible-light-driven photocatalytic properties. The crystalline Bi{sub 2}Sn{sub 2}O{sub 7} was synthesized by solid-state reaction at 550 °C. Then Bi{sub 2}Sn{sub 2}O{sub 7}/Ag-AgCl was prepared using deposition-precipitation technique followed by photo-reduction of partial Ag{sup +} to Ag{sup 0} nanoparticles on surface of AgCl. The photocatalysis were evaluated by degrading organic dyes under controlled conditions. The Bi{sub 2}Sn{sub 2}O{sub 7}/Ag-AgCl composite exhibited a much improved photocatalysis, approximately 7 times stronger than that of pure Bi{sub 2}Sn{sub 2}O{sub 7}, primarily due to its enhanced visible-light absorption and high separation efficiency of charge. On the basis of band structure analysis, a possible mechanism of photocatalysis enhancement for Bi{sub 2}Sn{sub 2}O{sub 7}/Ag-AgCl is proposed. The strong photocatalytic capability, together with simplicity of fabrication suggests Bi{sub 2}Sn{sub 2}O{sub 7}/Ag-AgCl composite provided in this study may have certain practical applications in water treatments. Additionally, the study implies a novel but simple methodology that may be also applicable in construction of other types of single semiconductor/plasmonic composite photocatalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Synthesis of black TiO2 with efficient visible-light photocatalytic activity by ultraviolet light irradiation and low temperature annealing

Highlights: • In this work, we have prepared black titanium dioxide (B-TiO{sub 2}) nanoparticals in combination with ultraviolet light and low temperature annealing. This method is simple, efficient and environmentally friendly. • The synthesis mechanism of the black B-TiO{sub 2} nanomaterials was analyzed by combining the different characterization data with the first-principles calculation results. • The Ti-O lattice and structure of the B-TiO{sub 2} sample did not change after low-temperature annealing. • The process of H-doping results in a reduction of the localized Ti{sup 3+} states, that are also the recombination centers of excited electrons and holes. • These nanoparticles can absorb a amount of visible light and degrade the organic pollution. - Abstract: Herein, a simple, efficient, and environmentally friendly strategy to prepare black TiO{sub 2} nanoparticles has been reported; the procedure combines the ultraviolet light irradiation and low-temperature annealing (300 °C) with continuous N{sub 2} flow under atmospheric pressure. The samples were characterized by the various techniques, such as X-ray diffraction, high resolution transmission electron microcopy, Raman spectroscopy, X-ray photoelectron spectroscopy. The photocatalytic degradation of the organic contaminant Rhodamine B was investigated when black TiO{sub 2} nanoparticles was irradiaed with ultraviolet light and visible light. The black TiO{sub 2} material possesses an anatase phase and is able to absorb a high amount of photon energy in the visible light region, effectively driving photochemical degradation reactions. The enhancement of the photocatalytic activity can be attributed to the following: first, the hydrogen ions decrease the localized Ti{sup 3+} states (which are also the e{sup −}-h{sup +} recombination centers) leading to a more efficient separation of the electron-hole pairs; secondly, the conduction band electrons in black TiO{sub 2} nanoparticles are responsible for strong absorption of visible light. Consequently, the photocatalytic degradation of Rhodamine B can be significantly enhanced using black TiO{sub 2} nanoparticles. This work proves that hydrogenated black TiO{sub 2} promotes the absorption of the entire electromagnetic spectrum and exhibits high photocatalytic activity under solar light irradiation.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

An in situ annealing route to [Bi6O6(OH)2](NO3)4·2H2O/g-C3N4 heterojunction and its visible-light-driven photocatalytic performance

Highlights: • The heterojunction (BBN-g-C{sub 3}N{sub 4}) was synthesized by in situ calcination route. • The baked Bi(NO{sub 3}){sub 3}·5H{sub 2}O as raw material is crucial to obtain highly crystalline BBN-g-C{sub 3}N{sub 4}. • BBN-g-C{sub 3}N{sub 4} exhibited better visible-light-driven photocatalytic activity than Bi{sub 2}O{sub 3}-g-C{sub 3}N{sub 4}. • BBN-g-C{sub 3}N{sub 4} prepared by calcining route possessed better photocatalytic activity than by mechanical mixing method. - Abstract: Known as incomplete hydrolysis products of Bi(NO{sub 3}){sub 3}·5H{sub 2}O, basic bismuth nitrates (BBN), were commonly obtained via a solution route. Herein, BBN-CN ([Bi{sub 6}O{sub 6}(OH){sub 2}](NO{sub 3}){sub 4}·2H{sub 2}O/g-C{sub 3}N{sub 4}) and Bi{sub 2}O{sub 3}-g-C{sub 3}N{sub 4} heterojunctions were prepared in situ by mixing g-C{sub 3}N{sub 4} with baked Bi(NO{sub 3}){sub 3}·5H{sub 2}O and subsequent calcining at 250 °C and 550 °C, respectively. The baked Bi(NO{sub 3}){sub 3}·5H{sub 2}O as a bismuth source was crucial to the formation of highly crystalline BBN, and otherwise, the product was poor-crystalline and low photoactive. The as-prepared BBN-CN exhibited better photocatalytic activity for rhodamine B (RhB) degradation under visible light irradiation than BBN, g-C{sub 3}N{sub 4}, and Bi{sub 2}O{sub 3}-g-C{sub 3}N{sub 4}, although Bi{sub 2}O{sub 3} is more visible-light-active. These could be attributed to higher surface areas and more negative conduction band potentials of BBN, which benefits for capturing the photogenerated electrons to form active O{sub 2}{sup −} radicals. Furthermore, the presence of g-C{sub 3}N{sub 4} plays a crucial role in enlarging visible light response.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

A construction of Ag-modified raspberry-like AgCl/Ag2WO4 with excellent visible-light photocatalytic property and stability

Highlights: • The Ag-modified raspberry-like AgCl/Ag{sub 2}WO{sub 4} photocatalysts were prepared by a facile solvent-free method. • Ag and AgCl were easily deposited on the Ag{sub 2}WO{sub 4} by one-step solid-sate reaction between Ag{sub 2}WO{sub 4} and HONH{sub 3}Cl. • The morphology of raspberry-like can facilitate the contact of dye molecules and composite photocatalysts. • The photocatalysts exhibit an effective separation of the photoinduced electron-hole pairs. • The photocatalysts show excellent photocatalytic activity and photo-stability under visible light irradiation. - Abstract: A novel multiphase photocatalyst of Ag-modified raspberry-like AgCl/Ag{sub 2}WO{sub 4} composite was successfully fabricated via a facile solvent-free reaction technique, in which the Ag and AgCl were subtlely generated from the one-step reaction between Ag{sub 2}WO{sub 4} particles and HONH{sub 3}Cl as reductant and chlorine source at room temperature. The as-obtained ternary Ag-modified raspberry-like AgCl/Ag{sub 2}WO{sub 4} composites can facilitate the contact of dye molecules and photocatalysts, exhibiting superior photocatalytic property and good recycling ability towards the decomposition of organic dye under the visible-light irradiation. The reductant addition amounts greatly affect the performance of Ag{sub 2}WO{sub 4} photocatalyst. The optimum composite ratio of Ag-modified AgCl/Ag{sub 2}WO{sub 4} samples show significant enhancement of visible-light photocatalytic activities and the degradation rate constant is about 16 times greater than that of pure Ag{sub 2}WO{sub 4}. The highly improved performance of Ag-modified raspberry-like AgCl/Ag{sub 2}WO{sub 4} structure can be ascribed to the surface plasma resonance (SPR) effects of metal Ag and the synergistic effect among composites, accordingly effectively promote the separation of photoinduced electron-hole pairs, widen the absorbance range in the visible light and increase surface area. The h{sup +} and ·OH degraded mechanism for the improved photocatalytic activity of Ag-modified AgCl/Ag{sub 2}WO{sub 4} is proposed based on radical-trapping experiments and ESR spectra records.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Easily separable N-doped ZnO microspheres with high photocatalytic activity under visible light

Highlights: • N-doped ZnO microspheres are successfully prepared for environmental photocatalysis. • N doping is responsible for the highly improved photocatalytic activity. • The microspheres are easily separated from the suspension system by sedimentation. - Abstract: Here, two strategies are simultaneously applied to ZnO for easy separation of the photocatalyst particles by forming micron-sized spheres and for extension of the spectral response into the visible region by nitrogen doping. The prepared nitrogen-doped ZnO microspheres show highly improved photocatalytic activity for the degradation of humic acid (HA), a complex refractory organic compound, under visible light. Substitutional and interstitial doping of nitrogen are behind the improved visible light absorption and photocatalytic activity. Using 1 g/L of N-doped ZnO with urea/Zn molar ratio of 3, 95.4% of HA with an initial concentration of 5 mg/L can be degraded within 80 min of visible light irradiation of 122 mW/cm{sup 2}. Under identical experimental conditions, almost complete mineralization of HA is achieved within 12 h. Holes and hydroxyl radicals are mainly responsible for the degradation of HA. Significant reduction of toxicity of the photocatalytically treated HA solution is realized within 9 h.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

CdS quantum dots/Ti3+-TiO2 nanobelts heterojunctions as efficient visible-light-driven photocatalysts

Highlights: • A novel CdS QDs/Ti{sup 3+}-TiO{sub 2} nanobelts heterojunction photocatalyst is prepared. • It narrows the bandgap and extends the photoresponse to visible light region. • It exhibits excellent visible-light-driven photocatalytic performance. • It is due to synergistic effect of CdS QDs, Ti{sup 3+} self-doping and heterojunction. - Abstract: CdS quantum dots (QDs)/Ti{sup 3+}-TiO{sub 2} nanobelts heterojunctions as 0D/1D architectures are fabricated through hydrothermal-chemical bath deposition combine with in-situ solid-state chemical reduction approach. The CdS QDs of ∼7 nm are loaded on TiO{sub 2} nanobelts with width of 50–300 nm and several micrometers long, and the heterojunctions are formed efficiently. The prepared heterojunctions exhibit excellent photocatalytic performance for complete removal of methylene blue (∼99%) and hydrogen production efficiency (∼480.6 μmol h{sup −1}) under visible light irradiation, which are as high as 2 and 23 times than that of pristine TiO{sub 2} nanobelts. The enhancement is attributed to the Ti{sup 3+} self-doping and CdS QDs extend the photoresponse to visible light region and the formation of heterojunctions favor the spatial separation of photogenerated charge carriers. Therefore, the high-efficient 0D/1D heterojunction composites have potential applications in the field of environment and energy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Decoration of Fe3O4 and CoWO4 nanoparticles over graphitic carbon nitride: Novel visible-light-responsive photocatalysts with exceptional photocatalytic performances

Highlights: • g-C{sub 3}N{sub 4}/Fe{sub 3}O{sub 4}/CoWO{sub 4} nanocomposites as efficient photocatalysts are reported. • The g-C{sub 3}N{sub 4}/Fe{sub 3}O{sub 4}/NiWO{sub 4} (10%) nanocomposite exhibited the highest activity. • Activity was 12.5-folds greater than g-C{sub 3}N{sub 4} in RhB degradation under visible light. • The nanocomposite is magnetically separated from the treated solution. - Abstract: In this work, nanoparticles of Fe{sub 3}O{sub 4} and CoWO{sub 4} were decorated over graphitic carbon nitride (g-C{sub 3}N{sub 4}) to fabricate very efficient visible-light-responsive photocatalysts through a facile refluxing-calcination method. Among the fabricated photocatalysts, the g-C{sub 3}N{sub 4}/Fe{sub 3}O{sub 4}/CoWO{sub 4} (10%) nanocomposite displayed superior activity in degradation of RhB, which is 12.5 and 11.5 times superior than the pristine g-C{sub 3}N{sub 4} and g-C{sub 3}N{sub 4}/Fe{sub 3}O{sub 4} photocatalysts, respectively. Additionally, exceptional performance of the ternary photocatalyst was confirmed in degradations of three organic pollutants under visible light. Higher harvesting ability of visible light and effective separation of electron/hole pairs from recombination are two main factors responsible for the observed exceptional photocatalytic activity of the ternary nanocomposite. Due to enough saturation magnetization of the ternary nanocomposite, the photocatalyst was entirely separated from the degradation system by a conventional magnet. Finally, photostability of the ternary photocatalyst during four successive runs was confirmed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microwave-assistant hydrothermal synthesis of SnO2@ZnO hierarchical nanostructures enhanced photocatalytic performance under visible light irradiation

Highlights: • A photocatalyst of SnO{sub 2}@ZnO HNSs is prepared via a microwave-assistant hydrothermal method. • Enhanced photodegradation of methylene blue under the visible light irradiation has been observed. • The defect in photocatalyst is the main photocatalytic mechanism under the visible light irradiation. • The superoxide radical is the main photoactive species. - Abstract: In this paper, for the first time, SnO{sub 2}@ZnO hierarchical nanostructures (HNSs) were synthesized by a simple two-step microwave-assistant hydrothermal method. Systematical characterization of the SnO{sub 2}@ZnO HNSs revealed that the rutile SnO{sub 2} nanowires (NWs) were uniformly and tightly grown on the entire surface of each ZnO nanoflowers (NFs). The photocatalytic performance of the SnO{sub 2}@ZnO HNSs showed a remarkably enhanced photocatalytic performance under visible light irradiation (400 nm≤λ ≤ 800 nm). The photoluminescence (PL) spectrum results indicated that the defect related energy level is the main mechanism of the photocatalytic performance under the visible light irradiation. The unique morphology and heterojunction structures in SnO{sub 2}@ZnO HNSs were the core enhanced mechanism in photodegradation process. The advantage endowed with the microwave-assistant hydrothermal method can result in the efficient spatial charge separation between ZnO nanorods (NRs) and SnO{sub 2} NWs and reduce the charge recombination along the heterojunction, which makes SnO{sub 2}@ZnO HNSs a highly promising for photocatalytic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Te-doped perovskite NaTaO3 as a promising photocatalytic material for hydrogen production from water splitting driven by visible light

Highlights: • S, Se and Te-doped NaTaO{sub 3} is a promising material for photocatalytic water splitting. • Enhanced absorption coefficient in the visible light range is identified for Te-doped NaTaO{sub 3}. • Te-doped NaTaO{sub 3} exhibits higher electron and hole mobility than pristine NaTaO{sub 3}. - Abstract: The photocatalytic hydrogen production from water splitting can be achieved by using the pristine NaTaO{sub 3} experimentally, but the reaction cannot be driven by the visible light because of the wide band gap of NaTaO{sub 3}. The present work focuses on tuning the photocatalytic performance of NaTaO{sub 3} into the visible light range by doping S, Se, and Te elements. The obvious decrease in band energy gaps (E{sub g}s) and noticeable red-shift of the absorption edges are observed for the doped structures. The valence band maximum and conduction band minimum of the doped structures satisfy the requirement of the water splitting. Moreover, a significant enhancement of absorption coefficient in the visible light range is observed for the doped structure of Te@O. The calculated carrier mobility is used to evaluate the charge spatial separation of Te@O and the unusual increases and the obvious differences of the mobility of the electrons and holes are observed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Facile synthesis and size dependent visible light photo catalytic properties of bio-compatible silver nanoclusters

Highlights: • Facile synthetic methodology to prepare biocompatible silver nanoclusters ligated with glutathione. • Controlled size and composition of AgNC was achieved and fully characterized. • Visible light photo catalytic performances AgNCs are observed to be size dependent. • Catalytic efficiency was found to be enhanced upon reduction in size of AgNCs in visible photo-Fenton like processes. - Abstract: Recently tremendous research efforts have been carried out to synthesize metal nanocluster owing to their wide applications in bio-imaging, nonlinear optical materials and catalysis. To explore such applications a precise control of size and composition of the metal nanoclusters are highly desirable. Here we report controlled synthesis and characterization of water soluble silver nanocluster ligated with glutathione. We have developed facile methodologies to prepare nanoclusters with distinct optical and catalytic properties. To achieve tunable size, optical property and chemical composition, here we mainly modulate the nature of metallic salt precursor, reducing agent and reaction conditions. Catalytic properties of as synthesized nanoclusters are explored in visible light induced photo-Fenton like processes for the degradation of model water pollutants such as methyl orange (MO) and Rhodamine B (RhB). The present research work investigates the influence of size of silver nanoclusters (Ag NCs) on photo Fenton like processes under visible light.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Visible-active photocatalytic behaviors observed in nanostructured lead chalcogenides PbX (X = S, Se, Te)

Nanostructured lead chalcogenides (PbX, X = Te, Se, S) were prepared via a simple hydrothermal method. The powder samples were characterized by XRD, SEM, SAED and DRS. Phase composition and microstructure analysis indicate that these samples are pure lead chalcogenides phases and have similar morphologies. These lead chalcogenides display efficient absorption in the UV-visible light range. The photocatalytic properties of lead chalcogenides nanoparticles were evaluated by the photodegradation of Congo red under UV-visible light irradiation in air atmosphere. The Congo red solution can be efficiently degraded under visible light in the presence of lead chalcogenides nanoparticles. The photocatalytic activities of lead chalcogenides generally increase with increasing their band gaps and shows no appreciable loss after repeated cycles. Our results may be useful for developing new photocatalyst systems responsive to visible light among narrow band gap semiconductors.

36 MATERIALS SCIENCE↗
DOE OSTI2013

PROSPECTING IN LATE-TYPE DWARFS: A CALIBRATION OF INFRARED AND VISIBLE SPECTROSCOPIC METALLICITIES OF LATE K AND M DWARFS SPANNING 1.5 dex

Knowledge of late K and M dwarf metallicities can be used to guide planet searches and constrain planet formation models. However, the determination of metallicities of late-type stars is difficult because visible wavelength spectra of their cool atmospheres contain many overlapping absorption lines, preventing the measurement of equivalent widths. We present new methods, and improved calibrations of existing methods, to determine metallicities of late K and M dwarfs from moderate resolution (1300 < R < 2000) visible and infrared spectra. We select a sample of 112 wide binary systems that contain a late-type companion to a solar-type primary star. Our sample includes 62 primary stars with previously published metallicities, as well as 50 stars with metallicities determined from our own observations. We use our sample to empirically determine which features in the spectrum of the companion are best correlated with the metallicity of the primary. We find {approx_equal}120 features in K and M dwarf spectra that are useful for predicting metallicity. We derive metallicity calibrations for different wavelength ranges, and show that it is possible to get metallicities reliable to <0.10 dex using either visible, J-, H-, or K-band spectra. We find that the most accurate metallicities derived from visible spectra requires the use of different calibrations for early-type (K5.5-M2) and late-type (M2-M6) dwarfs. Our calibrations are applicable to dwarfs with metallicities of -1.04 < [Fe/H] <+0.56 and spectral types from K7 to M5. Lastly, we use our sample of wide binaries to test and refine existing calibrations to determine M dwarf metallicities. We find that the {zeta} parameter, which measures the ratio of TiO can CaH bands, is correlated with [Fe/H] for super-solar metallicities, and {zeta} does not always correctly identify metal-poor M dwarfs. We also find that existing calibrations in the K and H bands are quite reliable for stars with [Fe/H] >-0.5, but are less useful for more metal-poor stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A SEMI-ANALYTICAL MODEL OF VISIBLE-WAVELENGTH PHASE CURVES OF EXOPLANETS AND APPLICATIONS TO KEPLER- 7 B AND KEPLER- 10 B

Kepler has detected numerous exoplanet transits by measuring stellar light in a single visible-wavelength band. In addition to detection, the precise photometry provides phase curves of exoplanets, which can be used to study the dynamic processes on these planets. However, the interpretation of these observations can be complicated by the fact that visible-wavelength phase curves can represent both thermal emission and scattering from the planets. Here we present a semi-analytical model framework that can be applied to study Kepler and future visible-wavelength phase curve observations of exoplanets. The model efficiently computes reflection and thermal emission components for both rocky and gaseous planets, considering both homogeneous and inhomogeneous surfaces or atmospheres. We analyze the phase curves of the gaseous planet Kepler- 7 b and the rocky planet Kepler- 10 b using the model. In general, we find that a hot exoplanet’s visible-wavelength phase curve having a significant phase offset can usually be explained by two classes of solutions: one class requires a thermal hot spot shifted to one side of the substellar point, and the other class requires reflective clouds concentrated on the same side of the substellar point. Particularly for Kepler- 7 b, reflective clouds located on the west side of the substellar point can best explain its phase curve. The reflectivity of the clear part of the atmosphere should be less than 7% and that of the cloudy part should be greater than 80%, and the cloud boundary should be located at 11° ± 3° to the west of the substellar point. We suggest single-band photometry surveys could yield valuable information on exoplanet atmospheres and surfaces.

79 ASTRONOMY AND ASTROPHYSICS↗
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↗
DOE OSTI2016

SU-F-T-166: On the Nature of the Background Visible Light Observed in Fiber Optic Dosimetry of Proton Beams

Purpose: The nature of the background visible light observed during fiber optic dosimetry of proton beams, whether it is due to Cherenkov radiation or not, has been debated in the literature recently. In this work, experimentally and by means of Monte Carlo simulations, we shed light on this problem and investigated the nature of the background visible light observed in fiber optics irradiated with proton beams. Methods: A bare silica fiber optics was embedded in tissue-mimicking phantoms and irradiated with clinical proton beams with energies of 100–225 MeV at Roberts Proton Therapy Center. Luminescence spectroscopy was performed by a CCD-coupled spectrograph to analyze in detail the emission spectrum of the fiber tip across the visible range of 400–700 nm. Monte Carlo simulation was performed by using FLUKA Monte Carlo code to simulate Cherenkov light and ionizing radiation dose deposition in the fiber. Results: The experimental spectra of the irradiated silica fiber shows two distinct peaks at 450 and 650 nm, whose spectral shape is different from that of Cherenkov radiation. We believe that the nature of these peaks are connected to the point defects of silica including oxygen-deficiency center (ODC) and non-bridging oxygen hole center (NBOHC). Monte Carlo simulations confirmed the experimental observations that Cherenkov radiation cannot be solely responsible for such a signal. Conclusion: We showed that Cherenkov radiation is not the dominant visible signal observed in bare fiber optics irradiated with proton beams. We observed two distinct peaks at 450 and 650 nm whose nature is connected with the point defects of silica fiber including oxygen-deficiency center and non-bridging oxygen hole center.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

A Contrast Calibration Protocol for X-ray Speckle Visibility Spectroscopy

X-ray free electron lasers, with their ultrashort highly coherent pulses, opened up the opportunity of probing ultrafast nano- and atomic-scale dynamics in amorphous and disordered material systems via speckle visibility spectroscopy. However, the anticipated count rate in a typical experiment is usually low. Therefore, visibility needs to be extracted via photon statistics analysis, i.e., by estimating the probabilities of multiple photons per pixel events using pixelated detectors. Considering the realistic X-ray detector responses including charge cloud sharing between pixels, pixel readout noise, and gain non-uniformity, speckle visibility extraction relying on photon assignment algorithms are often computationally demanding and suffer from systematic errors. In this paper, we present a systematic study of the commonly-used algorithms by applying them to an experimental data set containing small-angle coherent scattering with visibility levels ranging from below 1% to ∼60%. We also propose a contrast calibration protocol and show that a computationally lightweight algorithm can be implemented for high-speed correlation evaluation.

47 OTHER INSTRUMENTATION↗