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At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Metal Halide Perovskites in Quantum Dot Solar Cells: Progress and Prospects

“Go big or go home” could never be a truer statement, especially when it comes to energy. The world population is increasing, the energy use per person is growing more rapidly, and the total electricity use per person is growing even more quickly than that. To handle this demand, energy production must be increased, and it is vital for renewable sources to be used. Currently three quarters of a terawatt of power generated from photovoltaics (PVs) has been installed. At a somewhat optimistic average power-conversion efficiency of 18%, the distributed surface area of high purity optoelectronic grade semiconductor photovoltaic panels pointed at the sun is substantially larger than the area of the whole state of Rhode Island or nearly double the land mass of Luxembourg. While photovoltaic production continues to ramp to immense proportions, perovskite semiconductors are poised to greatly complement existing technology. On the other end of the size spectrum, the study of semiconductor nanocrystals or quantum dots (QDs) has led to advanced structures and deeper understanding within halide perovskite semiconductors. In this article, we show how the development of nanoscale metal halide perovskite semiconductors have gained prominence surpassing all other QD materials in terms of efficiency, and are becoming a platform for further improving technology to solve big energy challenges.

14 SOLAR ENERGY↗
DOE OSTI2020

Wide-angle effects for peculiar velocities

ABSTRACT The line-of-sight peculiar velocities of galaxies contribute to their observed redshifts, breaking the translational invariance of galaxy clustering down to a rotational invariance around the observer. This becomes important when the line-of-sight direction varies significantly across a survey, leading to what are known as ‘wide-angle’ effects in redshift-space distortions. Wide-angle effects will also be present in measurements of the momentum field, i.e. the galaxy density-weighted velocity field, in upcoming peculiar velocity surveys. In this work, we study how wide-angle effects modify the predicted correlation function and power spectrum for momentum statistics, both in autocorrelation and in cross-correlation with the density field. Using both linear theory and the Zel'dovich approximation, we find that deviations from the plane-parallel limit are large and could become important in data analysis for low-redshift surveys. We point out that even multipoles in the cross-correlation between density and momentum are non-zero regardless of the choice of line of sight, and therefore contain new cosmological information that could be exploited. We discuss configuration space, Fourier space, and spherical analyses; providing exact expressions in each case rather than relying on an expansion in small angles. We hope these expressions will be of use in the analysis of upcoming surveys for redshift-space distortions and peculiar velocities.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

The Rest-frame Submillimeter Spectrum of High-redshift, Dusty, Star-forming Galaxies from the SPT-SZ Survey

We present the average rest-frame spectrum of the final catalog of dusty star-forming galaxies (DSFGs) selected from the South Pole Telescope's SPT-SZ survey and measured with Band 3 of the Atacama Large Millimeter/submillimeter Array. This work builds on the previous average rest-frame spectrum, given in Spilker et al. (2014) for the first 22 sources, and is comprised of a total of 78 sources, normalized by their respective apparent dust masses. The spectrum spans 1.9 < z < 6.9 and covers rest-frame frequencies of 240–800 GHz. Combining this data with low-J CO observations from the Australia Telescope Compact Array, we detect multiple bright line features from 12 CO, [Ci], and H 2 O, as well as fainter molecular transitions from 13 CO, HCN, HCO + , HNC, CN, H 2 O + , and CH. We use these detections, along with limits from other molecules, to characterize the typical properties of the interstellar medium (ISM) for these high-redshift DSFGs. We are able to divide the large sample into subsets in order to explore how the average spectrum changes with various galaxy properties, such as effective dust temperature. We find that systems with hotter dust temperatures exhibit differences in the bright 12 CO emission lines, and contain either warmer and more excited dense gas tracers or larger dense gas reservoirs. These observations will serve as a reference point to studies of the ISM in distant luminous DSFGs (L IR > 10 12 L ⊙ ), and will inform studies of chemical evolution before the peak epoch of star formation at z = 2–3.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Canopy spectral reflectance along the NGEE-Arctic tram transect, Utqiagvik (Barrow), Alaska, 2015-2017

Full-spectrum (350-2500 nm) canopy spectral reflectance measured in July 2015, 2016 and 2017 along the NGEE-Arctic tram located on the Barrow Environmental Observatory (BEO), Barrow, Alaska. Measurements were made using a SVC HR1024i spectroradiometer mounted on a manually operated instrument cart. Spectra were collected at 137 stop points at 0.5 m intervals along the tram transect, with each measurement calibrated to variable illumination conditions using a Spectralon white plate. Data were collected in July, 2015-2016, and in June, July and September in 2017. Processed spectral data are presented in .csv and .xlsx files for each year and the complete SVC instrument output (.sig) are also included in .zip files. The data package includes some photographs showing the tram transect and spectroradiometer setup and a written protocol with details of equipment used and methods.The Next-Generation Ecosystem Experiments: Arctic (NGEE Arctic), was a research effort to reduce uncertainty in Earth System Models by developing a predictive understanding of carbon-rich Arctic ecosystems and feedbacks to climate. NGEE Arctic was supported by the Department of Energy's Office of Biological and Environmental Research.The NGEE Arctic project had two field research sites: 1) located within the Arctic polygonal tundra coastal region on the Barrow Environmental Observatory (BEO) and the North Slope near Utqiagvik (Barrow), Alaska and 2) multiple areas on the discontinuous permafrost region of the Seward Peninsula north of Nome, Alaska.Through observations, experiments, and synthesis with existing datasets, NGEE Arctic provided an enhanced knowledge base for multi-scale modeling and contributed to improved process representation at global pan-Arctic scales within the Department of Energy's Earth system Model (the Energy Exascale Earth System Model, or E3SM), and specifically within the E3SM Land Model component (ELM).

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1961

A Threshold Theory for Phase-Locked Loops

A model of a phase-locked loop has been developed which is valid for all signal-to-noise ratios. The model is in the form of a nonlinear feedback system with randomly time-varying parameters. The analysis considers two operating regions. In low signal-to-noise ratio regions, the important consideration is stability. We want to study the asymptotic stability in the mean of a nonlinear system. It follows directly that a necessary condition for asymptotic stability of any nonlinear system is that a linearized model about some equilibrium point be asymptotically stable. By considering all possible equilibrium points, we can find an upper bound on the value of noise density which makes the system unstable. This upper bound represents a threshold value for system operation. In high signal-to-noise ratio regions, our results provide an exact statistical. description of system behavior. Therefore, knowledge of the spectrum of the signal and noise may be used to optimize the system configuration.

Van Trees, H. L.↗
NASA NTRS1976

Thermal model for impact breccia lithification - Manicouagan and the moon

The thermal model of Simonds (1975) is extended to the full spectrum of impact-produced rocks ranging from fragmental breccias to impact melts, with reference to the Manicouagan impact structure in Quebec. This is done by relating the basic textural features of impact-lithified rocks to variations in the mixture of superheated impact-fused material originating near the point of impact and much cooler fragmented debris originating farther from the point of impact.

Simonds, C. H.↗
NASA NTRS1978

Distance limit for a class of model gamma-ray burst sources

It is pointed out that MeV photons have actually been observed in bursts. These observations imply that the nonrelativistic sources cannot be further away than a few kpc from the sun and, therefore, must be galactic. The 27 April 1972 event observed by Apollo 16 shows at higher energies a power law spectrum with a possible line feature around 4 MeV. The optical depth of a homogeneous, isotropic radiation field is estimated with the aid of formulae used by Nikishov (1962) and Jauch and Rohrlich (1955). On the basis of an investigation of the various factors involved, it is tentatively suggested that the gamma-ray bursts which have been detected are galactic, but are in the majority of the cases not connected with unique irreversible star transformation. It appears also unlikely that the gamma-ray bursts are connected with galactic novae.

Schmidt, W. K. H.↗
NASA NTRS1993

Further studies to extend and test the area-time-integral technique applied to satellite data

The principal goal of this project is to establish relationships that would allow application of area-time integral (ATI) calculations based upon satellite data to estimate rainfall volumes. The research has been pursued using two different approaches, which for convenience can be designated as the 'fixed-threshold approach' and the 'variable-threshold approach'. In the former approach, an attempt is made to determine a single temperature threshold in the satellite infrared data that would yield ATI values for identifiable cloud clusters which are most closely related to the corresponding rainfall amounts. Results thus far have indicated that a strong correlation exists between the rain volumes and the satellite ATI values, but the optimum threshold for this relationship seems to differ from one geographic location to another. The difference is probably related to differences in the basic precipitation mechanisms that dominate in the different regions. The average rainfall rate associated with each cloudy pixel is also found to vary across the spectrum of ATI values. Work on the second, or 'variable-threshold', approach for determining the satellite ATI values was essentially suspended during this period due to exhaustion of project funds. Most of the ATI work thus far has dealt with cloud clusters from the Lagrangian or 'floating-target' point of view. For many purposes, however, the Eulerian or 'fixed-target' perspective is more appropriate. For a very large target area encompassing entire cluster life histories, the rain volume-ATI relationship would obviously be the same in either case. The important question for the Eulerian perspective is how small the fixed area can be made while maintaining consistency in that relationship.

Smith, Paul L.↗
NASA NTRS1998

Spectral Irradiance Calibration in the Infrared: Calibrated Stellar Spectra Using Dirbe Radiometry - 9

The absolute calibration of the COBE/DIRBE data in the range 1-25 microns is examined through the in-band fluxes of DIRBE's own set of point-source calibration objects. Using the values of DIRBE fluxes expected for Sirius and for 10 of our published set of absolutely calibrated K and M giants that are in common with DIRBE's own calibration network, I find consistency with the project's formal basis, namely, our published calibrated spectrum of Sirius. This consistency means that one can use the DIRBE radiometry to construct absolutely calibrated "stellar templates" (i.e., continuous calibrated spectra from 1 to 35 microns) on the assumption that the intrinsic stellar spectrum of a star of given spectral class matches the intrinsic spectrum for the star of the same spectral class among the set of K and M giants, the spectrum of which has been absolutely defined. This technique is validated using a set of early M giants with well-characterized ground-based photometry and confirmed with IRAS low-resolution spectra.

Cohen, Martin↗
NASA NTRS2003

A 4 MPC X-Ray Filament Falling into the Cluster A85

We have completed a first paper confirming the ROSAT observation of a merging filamentary structure associated with the rich cluster A85. We detected a portion of the extended 4 Mpc filament first seen by the ROSAT PSPC. We confirm that there is an extended feature, aligned at the same position angle as the major axis of the central cD, the bright cluster galaxies, and nearby groups and clusters. We find that the X-ray emission from the filament is best described by thermal emission with a temperature of approx. 2 keV, which is significantly lower than the ambient cluster medium, but is significantly higher than anticipated for a gas in a weakly bound extended filament. It is not clear whether this is a filament of diffuse emission, a chain of several groups of galaxies, or stripped gas from the infalling south blob. In conclusion, the XMM-Newton observations confirmed that there really is a highly elongated filamentary like structure extending from the the merging south clump to the south east of Abell-85 along the direction defined by all the structures pointed out by Durret et al. (1998b). The fact that the spatial structure of the X-ray filament detected by XMM-Newton cannot be exactly superimposed to that obtained from ROSAT data shows that it is still difficult to determine exactly its nature. However, the X-ray spectrum from this structure is most likely thermal and its temperature is about 2.0 keV, consistent with that of groups. This value is notably cooler than that of the main cluster: the temperature map by Markevitch et al. (1998) shows the presence of gas at about 3-4 keV in the region at a distance from the cluster center at least as far as the northern part of the ellipse. So, we appear to be seeing cool gas as it enters the cluster core. Another possibility is that the filament is associated with the wake of cool stripped gas left behind by the south blob as it falls onto the cluster. In this case, the 'filament', whether it is diffuse or made of groups, would not really be a filament in the large scale structure formation sense. Besides X-ray observations with a much better signal to noise ratio, which probably will have to wait for the next generation of X-ray satellites, optical data can shed light on this question. With this purpose, we intend to perform wide field imaging in various bands to estimate galaxy photometric redshifts and determine how galaxies are distributed in the 'filament' area.

Forman, William↗
NASA NTRS2006

User Interactive Software for Analysis of Human Physiological Data

Ambulatory physiological monitoring has been used to study human health and performance in space and in a variety of Earth-based environments (e.g., military aircraft, armored vehicles, small groups in isolation, and patients). Large, multi-channel data files are typically recorded in these environments, and these files often require the removal of contaminated data prior to processing and analyses. Physiological data processing can now be performed with user-friendly, interactive software developed by the Ames Psychophysiology Research Laboratory. This software, which runs on a Windows platform, contains various signal-processing routines for both time- and frequency- domain data analyses (e.g., peak detection, differentiation and integration, digital filtering, adaptive thresholds, Fast Fourier Transform power spectrum, auto-correlation, etc.). Data acquired with any ambulatory monitoring system that provides text or binary file format are easily imported to the processing software. The application provides a graphical user interface where one can manually select and correct data artifacts utilizing linear and zero interpolation and adding trigger points for missed peaks. Block and moving average routines are also provided for data reduction. Processed data in numeric and graphic format can be exported to Excel. This software, PostProc (for post-processing) requires the Dadisp engineering spreadsheet (DSP Development Corp), or equivalent, for implementation. Specific processing routines were written for electrocardiography, electroencephalography, electromyography, blood pressure, skin conductance level, impedance cardiography (cardiac output, stroke volume, thoracic fluid volume), temperature, and respiration

Cowings, Patricia S.↗
DOE OSTI2025

Joint cosmological fits to DESI-DR1 full-shape clustering and weak gravitational lensing in configuration space

We present a joint $3\times2$-pt cosmological analysis of auto- and cross-correlations between the Dark Energy Spectroscopic Instrument Data Release 1 (DESI-DR1) Bright Galaxy Survey (BGS) and Luminous Red Galaxy (LRG) samples and overlapping shear measurements from the KiDS-1000, DES-Y3 and HSC-Y3 weak lensing surveys. We perform our analysis in configuration space and, in addition to the cosmic shear correlation functions for each weak lensing dataset, we fit the tangential shear of the weak lensing source galaxies around DESI lens galaxies. Finally, we make use of the anisotropic BGS and LRG clustering information by fitting the full shape of the two-point correlation function multipoles measured over the full DESI-DR1 footprint, presenting the first full-shape analysis of DESI measurements in configuration space. We find that the addition of weak lensing information serves to improve, with respect to the clustering-only case, the measurements of the power spectrum amplitude parameters $\ln(10^{10}A_{\rm{s}})$ and $σ_{12}$ by $15\%$ and $36\%$, respectively. It also improves measurements of the linear bias of the lens galaxies by $15-20\%$, depending on the tracer. Our results show excellent consistency, regardless of the weak lensing survey considered, and are furthermore consistent with a companion analysis that fits $3\times2$-pt correlations including DESI projected clustering measurements, as well as the results published by the weak lensing collaborations themselves. Our measured values for weak lensing amplitude are $S_{8}^{\mathrm{DESI\times HSC}}=0.787\pm0.020$, $S_{8}^{\mathrm{DESI\times DES}}=0.791\pm0.016$, $S_{8}^{\mathrm{DESI\times KiDS}}=0.771\pm0.017$, which are $1.9σ-2.9σ$ below the $S_8$ value preferred by Planck. Finally, our clustering-only results are in good agreement with the Fourier space full-shape analysis of all DESI tracers.

Semenaite, A. [Swinburne U., Ctr. Astrophys. Super↗
NASA NTRS2018

SCExAO/CHARIS Near-Infrared Direct Imaging, Spectroscopy, and Forward-Modeling of κ and b: A Likely Young, Low-Gravity Superjovian Companion

We present SCExAO/CHARIS high-contrast imaging/JHK integral field spectroscopy of κ And b, a directly imaged low-mass companion orbiting a nearby B9V star. We detect κ And b at a high signal-to-noise ratio and extract high-precision spectrophotometry using a new forward-modeling algorithm for (A-)LOCI complementary to KLIP-FM developed by Pueyo et al. κ And b’s spectrum best resembles that of a low-gravity L0–L1 dwarf (L0–L1γ). Its spectrum and luminosity are very well matched by 2MASS J0141-4633 and several other 12.5–15 M(sub J) free-floating members of the 40 Myr old Tuc–Hor Association, consistent with a system age derived from recent interferometric results for the primary, a companion mass at/near the deuterium-burning limit (13(sup +12, sub -2) M(sub J)), and a companion-to-primary mass ratio characteristic of other directly imaged planets (q ∼ 0.005(sup +0.005, sub -0.001)). We did not unambiguously identify additional, more closely orbiting companions brighter and more massive than κ And b down to ρ ∼ 0".3 (15 au). SCExAO/CHARIS and complementary Keck/NIRC2 astrometric points reveal clockwise orbital motion. Modeling points toward a likely eccentric orbit: a subset of acceptable orbits include those that are aligned with the star’s rotation axis. However, κ And b’s semimajor axis is plausibly larger than 55 au and in a region where disk instability could form massive companions. Deeper high-contrast imaging of κ And and low-resolution spectroscopy from extreme adaptive optics systems such as SCExAO/CHARIS and higher-resolution spectroscopy from Keck/OSIRIS or, later, IRIS on the Thirty Meter Telescope could help to clarify κ And b’s chemistry and whether its spectrum provides an insight into its formation environment.

Currie, Thayne↗
DOE OSTI2024

Long-term, non-invasive FTIR detection of low-dose ionizing radiation exposure

Non-invasive methods of detecting radiation exposure show promise to improve upon current approaches to biological dosimetry in ease, speed, and accuracy. Here we developed a pipeline that employs Fourier transform infrared (FTIR) spectroscopy in the mid-infrared spectrum to identify a signature of low dose ionizing radiation exposure in mouse ear pinnae over time. Mice exposed to 0.1 to 2 Gy total body irradiation were repeatedly measured by FTIR at the stratum corneum of the ear pinnae. We found significant discriminative power for all doses and time-points out to 90 days after exposure. Classification accuracy was maximized when testing 14 days after exposure (specificity > 0.9 with a sensitivity threshold of 0.9) and dropped by roughly 30% sensitivity at 90 days. Infrared frequencies point towards biological changes in DNA conformation, lipid oxidation and accumulation and shifts in protein secondary structure. Since only hundreds of samples were used to learn the highly discriminative signature, developing human-relevant diagnostic capabilities is likely feasible and this non-invasive procedure points toward rapid, non-invasive, and reagent-free biodosimetry applications at population scales.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2025

A cryogenic white light absorption spectroscopy setup with in situ gamma irradiation and thermo-optical annealing for optical fiber radiation-induced attenuation characterization

Silica optical fiber sensors offer a fast, distributed measurement solution in various cryogenic and radiation environments, such as magnets for fusion power. Under these conditions, light-absorbing point defects limit lifetime via radiation-induced attenuation (RIA). To support RIA kinetics prediction, we present an in situ, broadband absorption spectroscopy setup combining gamma irradiation with liquid nitrogen cooling. The apparatus enables continuous monitoring of narrowband RIA levels and the use of secondary optical annealing light sources, alongside broadband spectrum measurements to characterize RIA defects through spectrum decomposition. Initial results confirm the inevitable photobleaching effect of the probe light source, which must be accounted for. In addition, we report RIA kinetics during cycles of gamma irradiation at 77 K and isochronal thermal annealing steps from liquid nitrogen to room temperature, showcasing the setup’s ability to replicate real fiber operation scenarios. These instruments form an ideal platform to further study the kinetics of RIA coupled with thermal and optical annealing.

Absorption spectroscopy↗
DOE OSTI2022

Optical variability of quasars with 20-yr photometric light curves

ABSTRACT We study the optical gri photometric variability of a sample of 190 quasars within the SDSS Stripe 82 region that have long-term photometric coverage during ∼1998−2020 with SDSS, PanSTARRS-1, the Dark Energy Survey, and dedicated follow-up monitoring with Blanco 4m/DECam. With on average ∼200 nightly epochs per quasar per filter band, we improve the parameter constraints from a Damped Random Walk (DRW) model fit to the light curves over previous studies with 10–15 yr baselines and ≲ 100 epochs. We find that the average damping time-scale τDRW continues to rise with increased baseline, reaching a median value of ∼750 d (g band) in the rest frame of these quasars using the 20-yr light curves. Some quasars may have gradual, long-term trends in their light curves, suggesting that either the DRW fit requires very long baselines to converge, or that the underlying variability is more complex than a single DRW process for these quasars. Using a subset of quasars with better-constrained τDRW (less than 20 per cent of the baseline), we confirm a weak wavelength dependence of τDRW∝λ0.51 ± 0.20. We further quantify optical variability of these quasars over days to decades time-scales using structure function (SF) and power spectrum density (PSD) analyses. The SF and PSD measurements qualitatively confirm the measured (hundreds of days) damping time-scales from the DRW fits. However, the ensemble PSD is steeper than that of a DRW on time-scales less than ∼ a month for these luminous quasars, and this second break point correlates with the longer DRW damping time-scale.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

Identification and yield of carbonic acid and formaldehyde in irradiated ices

Carbonic acid, (OH)2CO, was tentatively identified in the IR spectrum of a proton irradiated CO2 + H2O ice mixture. In this report, we present additional evidence for a more definitive identification of (OH)2CO with (1) the infrared spectrum of a residue obtained by proton irradiation of CO2 + D2O ice mixture, and (2) the IR spectra of solid phases of formaldehyde (H2CO), acetone (CH3)2CO, and dimethyl carbonate (OCH3)2CO, which are structurally similar to (OH)2CO. IR characteristics (peak frequencies and complex refractive indices of the compounds in point 2) are also reported. In particular, the integrated absorption coefficients for the C-O band for the compounds in point 2 do not vary by more than 20 percent. Based on these values, we estimate the yields of H2CO and (OH)2CO by proton irradiation or ice mixtures. Both H2CO and (OH)2CO are possible irradiation products of cometary and planetary ices.

Dellorusso, Neil↗
NASA NTRS2013

Erratum: "Photoionization Modeling of Oxygen K Absorption in the Interstellar Medium, the Chandra Grating Spectra of XTE J1817-330" (2013, Apj, 768, 60)

In the published version of this paper, there are some minor inaccuracies in the absorption-line wavelengths listed in Table 4 as a result of a faulty reduction procedure of the Obs6615 spectrum. The shifts have been detected in a comparison with the wavelengths listed for this spectrum in the Chandra Transmission Grating Catalog and Archive (TGCat8). They are due to incorrect centroid positions of the zero-order image in both reductions as determined by the tgdetect utility which, when disentangled, yield the improved line positions of the amended Table 4 given below. It must also be pointed out that other quantitative findings of the original paper: 1. Table 5, p. 9: the column density (NH), ionization parameter, oxygen abundance of the warmabs model and the normalization and photon index of the power-law model; 2. Table 6, p. 9: the hydrogen column density of the warmabs fit; 3. Table 7, p. 9: the present oxygen equivalent widths of XTE J1817-330; and 4. Table 8, p. 10: the present oxygen column densities of XTE J1817-330 derived from both the curve of growth and warmabs model fit have been revised in the new light and are, within the estimated uncertainty ranges, in good accord with the new rendering.

abundance of the warmabs↗