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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Real-time measurement of parametric influences on the refractive index and length changes in silica optical fibers

In this paper, we present a simple cascaded Fabry-Perot interferometer (FPI) that can be used to measure in real-time the refractive index (RI) and length variation in silica optical fibers caused due to external physical parameters, such as temperature, strain, and radiation. As a proof-of-concept, we experimentally demonstrate real-time monitoring of temperature effects on the RI and length and measure the thermo-optic coefficient (TOC) and thermal expansion coefficient (TEC) by using the cascaded FPI within a temperature range of 21–486°C. The experimental results provide a TEC of 5.53 × 10 −7 /°C and TOC of 4.28 × 10 −6 /°C within the specified temperature range. Such a simple cascaded FPI structure will enable the design of optical sensors to correct for measurement errors by understanding the change in RI and length of optical fiber caused by environment parameters.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

The Aligned Orbit of the Eccentric Warm Jupiter K2-232b

Measuring the obliquity distribution of stars hosting warm Jupiters may help us to understand the formation of close-orbiting gas giants. Few such measurements have been performed due to practical difficulties in scheduling observations of the relatively infrequent and long-duration transits of warm Jupiters. Here, we report a measurement of the Rossiter–McLaughlin effect for K2-232 b, a warm Jupiter on an 11.17 day orbit with an eccentricity of 0.26. The data were obtained with the Automated Planet Finder during two separate transits. The planet’s orbit appears to be well aligned with the spin axis of the host star, with a projected spin–orbit angle of λ = −11.°1 ± 6.°6. Combined with the other available data, we find that high obliquities are almost exclusively associated with planets that either have an orbital separation greater than 10 stellar radii or orbit stars with effective temperatures hotter than 6000 K. This pattern suggests that the obliquities of the closest-orbiting giant planets around cooler stars have been damped by tidal effects.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1979

Chromospheres and coronae of late-type stars

IUE short wavelength (1150-2000 A) spectra of late-type dwarfs, giant, and supergiant stars show a variety of emission features varying in excitation from about 10,000 K to about 3 x 10 to the 5th K. High excitation species are found most strongly in main sequence stars. Dwarf stars with active chromospheres (e.g., Xi Boo) and flare stars (EQ Peg) show enhancement of surface flux as compared to the quiet sun; binary systems of W UMa and RS CVn types show even larger surface fluxes. The enhancement increases with temperature of formation much like a solar active region. The presence of high excitation species in the giant and supergiant stars suggests that parameters other than effective temperature and luminosity are important in establishing a transition region and corona.

Dupree, A. K.↗
NASA NTRS1981

The visual surface brightness relation and the absolute magnitudes of RR Lyrae stars. I - Theory

A theoretical relation analogous to the Barnes-Evans relation between stellar surface brightness and V-R color is derived which is applicable to the temperatures and gravities appropriate to RR Lyrae stars. Values of the visual surface brightness and V-R colors are calculated for model stellar atmospheres with effective temperatures between 6000 and 8000 K, log surface gravities from 2.2 to 3.5, and A/H anbundance ratios from -0.5 to -3.0. The resulting relation is found to be in reasonable agreement with the empirical relation of Barnes, Evans and Moffet (1978), with, however, small sensitivities to gravity and metal abundance. The relation may be used to derive stellar angular diameters from (V,R) photometry and to derive radii, distances, and absolute magnitudes for variable stars when combined with a radial velocity curve. The accuracies of the radii and distances (within 10%) and absolute magnitudes (within 0.25 magnitudes) compare favorably with those of the Baade-Wesselink method currently in use.

Manduca, A.↗
NASA NTRS2003

Physical Studies of Brown Dwarfs and Extrasolar Planets

The primary activities supported under this grant included research into the mid-infrared spectral properties of brown dwarfs, with particular emphasis on the 3-4 micron region, the L band. Several observing trips were made to use facilities on Mauna Kea. The primary discovery was the detection of absorption due to CH4 in several L dwarfs, including one classified as an L5. This is significant since CH4 is usually considered to be the defining characteristic of T dwarfs. The stronger fundamental band at 3.3um, however, makes it possible to observe the emergence of CH4 at hotter temperatures. A secondary result of this work is the surprising weakness of the CH4 nu3 band. This can be interpreted as either an indication that derived effective temperatures are too low, or perhaps, that the equilibrium abundance of CH4 is suppressed due to non-equilibrium processes at work in the atmosphere.

Boyce, Joseph↗
NASA NTRS2023

Thermospheric Temperature and ΣO/N 2 Variations as Observed by GOLD and Compared to MSIS and WACCM-X Simulations During 2019–2020 at Deep Solar Minimum

The ultraviolet-imaging spectrograph that comprises Global-scale Observations of the Limb and Disk (GOLD) mission in geostationary orbit at 47.5°W longitude has taken full disk images at high cadence throughout the deep solar minimum period of 2019–2020. Synoptic (i.e., concurrent and spatially unified and resolved) observations of thermospheric temperature and composition at ∼150 km altitude are made for the first time, allowing GOLD to disambiguate temporal and spatial variations. Here we analyze the daytime effective temperature and column integrated O and N2 density ratio (ΣO/N 2 ) data simultaneously observed by GOLD over 120°W–20°E longitude and 60°S–60°N latitude from 13 October 2019 to 12 October 2020. Daily zonal mean values are calculated for each latitude and compared with NRLMSIS 2.0 and simulations from the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X). On average, the GOLD observations show higher temperatures than Mass Spectrometer Incoherent Scatter radar (MSIS) and WACCM-X by ∼20–60 K (5%–10%) and 80–120 K (12%–18%), respectively. The ΣO/N 2 ratios observed by GOLD are larger than the MSIS results by ∼0.4 (40%) but smaller than the WACCM-X simulations by ∼0.3 (30%). The observed and modeled results are correlated at most latitudes (r = 0.4–0.8), and GOLD, MSIS, and WACCM-X all display a similar seasonal variation and change with latitude. WACCM-X simulates a larger annual variation in ΣO/N 2 , suggesting that the thermospheric circulation is overestimated and atmospheric waves and turbulence transport are not properly represented in the model.

Guiping Liu↗
NASA NTRS2023

Thermospheric Temperature and ΣO/N2 Variations as Observed by GOLD and Compared to MSIS and WACCM-X Simulations During 2019–2020 at Deep Solar Minimum

The ultraviolet-imaging spectrograph that comprises Global-scale Observations of the Limb and Disk (GOLD) mission in geostationary orbit at 47.5°W longitude has taken full disk images at high cadence throughout the deep solar minimum period of 2019–2020. Synoptic (i.e., concurrent and spatially unified and resolved) observations of thermospheric temperature and composition at ∼150 km altitude are made for the first time, allowing GOLD to disambiguate temporal and spatial variations. Here we analyze the daytime effective temperature and column integrated O and N 2 density ratio (ΣO/N 2 ) data simultaneously observed by GOLD over 120°W–20°E longitude and 60°S–60°N latitude from 13 October 2019 to 12 October 2020. Daily zonal mean values are calculated for each latitude and compared with NRLMSIS 2.0 and simulations from the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X). On average, the GOLD observations show higher temperatures than Mass Spectrometer Incoherent Scatter radar (MSIS) and WACCM-X by ∼20–60 K (5%–10%) and 80–120 K (12%–18%), respectively. The ΣO/N2 ratios observed by GOLD are larger than the MSIS results by ∼0.4 (40%) but smaller than the WACCM-X simulations by ∼0.3 (30%). The observed and modeled results are correlated at most latitudes (r = 0.4–0.8), and GOLD, MSIS, and WACCM-X all display a similar seasonal variation and change with latitude. WACCM-X simulates a larger annual variation in ΣO/N 2 , suggesting that the thermospheric circulation is overestimated and atmospheric waves and turbulence transport are not properly represented in the model.

Guiping Liu↗
DOE OSTI2020

Anomalous thermodynamic properties of quantum critical superconductors

Recent high-precision measurements employing different experimental techniques have unveiled an anomalous peak in the doping dependence of the London penetration depth which is accompanied by anomalies in the heat capacity in iron-pnictide superconductors at the optimal composition associated with the hidden antiferromagnetic quantum critical point. Here, we argue that finite temperature effects can be a cause of observed features. Specifically we show that quantum critical magnetic fluctuations under superconducting dome can give rise to a nodal-like temperature dependence of both specific heat and magnetic penetration depth in a fully gapped superconductor. In the presence of line nodes in the superconducting gap fluctuations can lead to the significant renormalization of the relative slope of T-linear penetration depth which is steepest at the quantum critical point. The results we obtain are general and can be applied beyond the model we use.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1972

Investigations of high power problems in space shuttle antenna designs

A study program is discussed which includes a survey of industry and government laboratories and was undertaken to determine the state of the art in dealing with problems of high power levels in reentry antenna design. A laboratory program to develop techniques for testing dielectric materials for effects on RF transmission is also considered, with emphasis on high power applications in space and reentry flights. The study program resulted in a set of guidelines for avoiding breakdown in antenna design. A discussion of temperature effects on dielectric breakdown is also given. From the laboratory program, a description is presented of techniques for (1) heating with a carbon arc image furnace, (2) temperature measurement (using thermocouples and an infrared pyrometer), (3) mass spectrometric monitoring of outgassing, (4) testing for RF breakdown in both heated dielectrics and the dielectric/air and dielectric/plasma interfaces. Data and observations are reported from technique development using candidate shuttle materials falling into three categories: (1) lightweight refractory foams, (2) dense RF window materials, and (3) ablative materials.

Taylor, W. C.↗
NASA NTRS1983

Spectrophotometry of Saturn and its rings from 60 to 180 microns

Comparisons of Saturn observations at far-IR and submillimeter wavelengths, obtained during the earth's March 1980 passage through the plane of Saturn's rings, with spectroscopic observations obtained at an earlier time when the ring plane tilt angle was 21.8 deg, allow a separation of disk and ring contributions to the flux observed in this wavelength range. It is noted that the observed disk emission at 60-180 microns corresponds to a brightness temperature of 104 + or 2 K, and that the brightness temperature of the rings drops 20 K in the 60-80 micron range. An improved estimate of total Saturnian surface brightness is derived which corresponds to an effective temperature of 96.1 + or - 1.6 K.

Melnick, G.↗
NASA NTRS1994

Optical, IUE, and ROSAT observations of the eclipsing nova-like variable V347 Puppis (LB 1800)

Using time-resolved optical spectroscopy and UBVRI and high-speed photometry obtained at Mount Stromlo Observatory, Mount John University Observatory, and the South African Astronomical Observatory; International Ultraviolet Explorer (IUE) ultraviolet spectroscopy; and Roentgen Satellite (ROSAT) survey X-ray fluxes, we present a study of the accretion disk, hot spot, and emission line regions in the bright eclipsing nova-like variable V347 Pup (LB 1800). In the optical and UV, V347 Pup is a strong emission line source with a continuum spectrum which is remarkably red for a high-M cataclysmic variable. Consistent with its high inclination, we interpret the continuum spectrum as the superposition of the spectrum of the cool (T(sub eff) approximately 7000 K) outer edge and the hot (T(sub eff) approximately 100,000 K) inner regions of a self-eclipsed accretion disk. For the assumed parameters, the model matches the level and shape of the observed spectrum for an inclination of approximately 88 and a distance of approximately 300 pc. The prominent hump in the optical and UV light curves just before eclipse manifests the presence of the hot spot where the accretion stream strikes the edge of the disk. The wavelength dependence of the amplitude of the hump is best modeled by a spot having an effective temperature of approximately 25,000 K and an area of approximately 3 x 10(exp 18) sq cm if the spot radiates like a blackbody, or an effective temperatue of approximately 14,000 K and an area of approximately 3 x 10(exp 19) sq cm if it radiates with a stellar spectrum. In either case, the hot spot produces only one-tenth of the predicted luminosity for the assumed mass-transfer rate of 10(exp -8) solar mass/yr. Either the hot spot is 'buried' in the edge of the accretion disk, or a significant fraction of its luminosity is radiated away in lines. The difference in azimuth between the peak of the hump and the dynamically expected location of the hot spot suggests that the spot's emitting surface is rotated forward by approximately 36 deg relative to the edge of the disk.

Mauche, Christopher W.↗
NASA NTRS2001

Remote Sensing of Cloud, Aerosol, and Water Vapor Properties from MODIS

MODIS is an earth-viewing cross-track scanning spectroradiometer launched on the Terra satellite in December 1999. MODIS scans a swath width sufficient to provide nearly complete global coverage every two days from a polar orbiting, sun-synchronous, platform at an altitude of 705 kilometers, and provides images in 36 spectral bands between 0.415 and 14.235 micrometers with spatial resolutions of 250 meters (2 bands), 500 meters (5 bands) and 1000 meters (29 bands). These bands have been carefully selected to enable advanced studies of land, ocean, and atmospheric processes. In this presentation we review the comprehensive set of remote sensing algorithms that have been developed for the remote sensing of atmospheric properties using MODIS data, placing primary emphasis on the principal atmospheric applications of (i) developing a cloud mask for distinguishing clear sky from clouds, (ii) retrieving global cloud radiative and microphysical properties, including cloud top pressure and temperature, effective emissivity, cloud optical thickness, thermodynamic phase, and effective radius, (iii) monitoring tropospheric aerosol optical thickness over the land and ocean and aerosol size distribution over the ocean, (iv) determining atmospheric profiles of moisture and temperature, and (v) estimating column water amount. The physical principles behind the determination of each of these atmospheric products will be described, together with an example of their application using MODIS observations. All products are archived into two categories: pixel-level retrievals (referred to as Level-2 products) and global gridded products at a latitude and longitude resolution of 1 degree (Level-3 products). An overview of the MODIS atmosphere algorithms and products, status, validation activities, and early level-2 and -3 results will be presented.

King, Michael D.↗
NASA NTRS2001

Remote Sensing of Cloud, Aerosol, and Land Properties from MODIS: Applications to the East Asia Region

MODIS is an earth-viewing cross-track scanning spectroradiometer launched on the Terra satellite in December 1999. MODIS scans a swath width sufficient to provide nearly complete global coverage every two days from a polar-orbiting, sun-synchronous platform at an altitude of 705 km, and provides images in 36 spectral bands between 0.415 and 14.235 microns with spatial resolutions of 250 m (two bands), 500 m (five bands) and 1000 m (29 bands). These bands have been carefully selected to enable advanced studies of land, ocean, and atmospheric processes. In this presentation we review the comprehensive set of remote sensing algorithms that have been developed for the remote sensing of atmospheric properties using MODIS data, placing primary emphasis on the principal atmospheric applications of (i) developing a cloud mask for distinguishing clear sky from clouds, (ii) retrieving global cloud radiative and microphysical properties, including cloud top pressure and temperature, effective emissivity, cloud optical thickness, thermodynamic phase, and effective radius, (iii) monitoring tropospheric aerosol optical thickness over the land and ocean and aerosol size distribution over the ocean, (iv) determining atmospheric profiles of moisture and temperature, and (v) estimating column water amount. The physical principles behind the determination of each of these atmospheric products will be described, together with an example of their application using MODIS observations to the east Asian region in Spring 2001. All products are archived into two categories: pixel-level retrievals (referred to as Level-2 products) and global gridded products at a latitude and longitude resolution of 1 degree (Level-3 products). An overview of the MODIS atmosphere algorithms and products, status, validation activities, and early level-2 and -3 results will be presented.

King, Michael D.↗
NASA NTRS2001

Remote Sensing of Cloud, Aerosol, and Water Vapor Properties from MODIS

MODIS is an earth-viewing cross-track scanning spectroradiometer launched on the Terra satellite in December 1999. MODIS scans a swath width sufficient to provide nearly complete global coverage every two days from a polar-orbiting, sun-synchronous, platform at an altitude of 705 km, and provides images in 36 spectral bands from 0.415 to 14.235 microns with spatial resolutions of 250 m (2 bands), 500 m (5 bands) and 1000 m (29 bands). These bands have been carefully selected to enable advanced studies of land, ocean, and atmospheric processes. In this presentation I will review the comprehensive set of remote sensing algorithms that have been developed for the remote sensing of atmospheric properties using MODIS data, placing primary emphasis on the principal atmospheric applications of: (1) developing a cloud mask for distinguishing clear sky from clouds, (2) retrieving global cloud radiative and microphysical properties, including cloud top pressure and temperature, effective emissivity, cloud optical thickness, thermodynamic phase, and effective radius, (3) monitoring tropospheric aerosol optical thickness over the land and ocean and aerosol size distribution over the ocean, (4) determining atmospheric profiles of moisture and temperature, and (5) estimating column water amount. The physical principles behind the determination of each of these atmospheric products will be described, together with an example of their application using MODIS observations. All products are archived into two categories: pixel-level retrievals (referred to as Level-2 products) and global gridded products at a latitude and longitude resolution of 1 deg (Level-3 products). An overview of the MODIS atmosphere algorithms and products, status, validation activities, and early level-2 and -3 results will be presented. Finally, I will present some highlights from the land and ocean algorithms developed for processing global MODIS observations, including: (1) surface reflectance, (2) vegetation indices, leaf area index, and FPAR, (3) albedo and nadir BRDF-adjusted reflectance, (4) normalized water-leaving radiance, (5) chlorophyll-a concentration, and (6) sea surface temperature.

King, Michael D.↗
DOE OSTI2020

Identification of non-Fermi liquid fermionic self-energy from quantum Monte Carlo data

Quantum Monte Carlo (QMC) simulations of correlated electron systems provide unbiased information about system behavior at a quantum critical point (QCP) and can verify or disprove the existing theories of non-Fermi liquid (NFL) behavior at a QCP. However, simulations are carried out at a finite temperature, where quantum critical features are masked by finite-temperature effects. Here, we present a theoretical framework within which it is possible to separate thermal and quantum effects and extract the information about NFL physics at T = 0. We demonstrate our method for a specific example of 2D fermions near an Ising ferromagnetic QCP. We show that one can extract from QMC data the zero-temperature form of fermionic self-energy Σ(ω) even though the leading contribution to the self-energy comes from thermal effects. We find that the frequency dependence of Σ(ω) agrees well with the analytic form obtained within the Eliashberg theory of dynamical quantum criticality, and obeys ω 2/3 scaling at low frequencies. Our results open up an avenue for QMC studies of quantum critical metals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2009

Precise Stabilization of the Optical Frequency of WGMRs

Crystalline whispering gallery mode resonators (CWGMRs) made of crystals with axial symmetry have ordinary and extraordinary families of optical modes. These modes have substantially different thermo-refractive constants. This results in a very sharp dependence of differential detuning of optical frequency on effective temperature. This frequency difference compared with clock gives an error signal for precise compensation of the random fluctuations of optical frequency. Certain crystals, like MgF2, have turnover points where the thermo-refractive effect is completely nullified. An advantage for applications using WGMRs for frequency stabilization is in the possibility of manufacturing resonators out of practically any optically transparent crystal. It is known that there are crystals with negative and zero thermal expansion at some specific temperatures. Doping changes properties of the crystals and it is possible to create an optically transparent crystal with zero thermal expansion at room temperature. With this innovation s stabilization technique, the resultant WGMR will have absolute frequency stability The expansion of the resonator s body can be completely compensated for by nonlinear elements. This results in compensation of linear thermal expansion (see figure). In three-mode, the MgF2 resonator, if tuned at the turnover thermal point, can compensate for all types of random thermal-related frequency drift. Simplified dual-mode method is also available. This creates miniature optical resonators with good short- and long-term stability for passive secondary frequency ethalon and an active resonator for active secondary frequency standard (a narrowband laser with long-term stability).

Savchenkov, Anatoliy↗
DOE OSTI2021

Influence of curing temperature on belite cement hydration: A comparative study with Portland cement

Belite cements (BCs) could be a more sustainable binder than Portland cements (PCs) but adequate knowledge of the hydration features has still to be built. In particular, the mild curing hydration temperature effects have been extensively studied for PCs but not for BCs. This research was triggered by a previous work reporting improved mechanical strengths of BCs at higher curing temperatures. Here, we report the hydration characteristics of a BC at 20, 40 and 60 °C and compared to those of a typical PC. We have corroborated previous findings and used a multi-technique approach including Rietveld phase analysis, thermal analysis, calorimetry, silicon MAS-NMR, mercury intrusion porosimetry and chiefly synchrotron X-ray microtomography, to thoroughly understand the different behavior. In a nutshell, the improved mechanical performances at mild curing temperatures for BCs are mainly due to a much larger belite degree of reaction, with lower porosity coarsening of belite cements also playing a role.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Is there a classical Hyades lithium problem?

The distribution of surface lithium abundances in the Hyades cluster, as a function of effective temperature, has resisted a satisfactory theoretical explanation for more than two decades. Trends in the historically recomputed values of stellar opacity have stimulated a systematic investigation of the effects of larger opacities on lithium depletion during the premain-sequence evolution of low-mass stars. It is shown that the calculated depletion depends quite strongly on the opacities employed, and that both surface and interior opacities play an important role. By performing standard evolutionary calculations with parameterized increments in the opacities, the observed Hyades Li and T(eff) relation for G and K dwarfs have been determined in a manner consistent with the other observational constraints. The solution presented herein requires an increase in interior opacities at about 4 million K over older values by approximately less than 37 percent. Such a change is not incompatible with the historical trends in opacity computations and suggests that the resolution of this problem lies solely in the opacities, without recourse to other physical mechanisms such as turbulent diffusion or 'extra mixing'.

Swenson, Fritz J.↗