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NASA NTRS2004

An on-board processor for a spaceborne Doppler precipitation radar : requirements and preliminary design

Use of Doppler velocity measurement in spaceborne precipitation radar is highly desirable, since it can allow more accurate retrieval of atmospheric latent heating, which depends on both cloud and rain microphysical processes and on dynamical processes, namely, vertical updrafts and downdrafts. However, if the rain within the antenna beam is very non-uniform, biases can result with conventional pulse-pair processing, and more sophisticated processing is required. The solution is a time-frequency approach, which uses the full Doppler spectrum at each point in time. Since precipitation radars normally operate continuously and collect large amounts of data, real-time, on-board processing of data is needed to reduce the data rate. The objective of this work is to develop an on-board data processor for spaceborne Doppler precipitation radar, using field-programmable gate array (FPGA) technology. This paper describes the simulations and analysis that have been completed during the first year of the project. This includes both analytical calculations and bit-true simulations that allow the effects of finite word length to be explored. Tradeoffs have also been considered between speed and space within the chosen FPGA part. The results of these analyses have been used to develop a complete set of requirements for the processor. Initial design work has begun, based on these requirements. The design is being implemented in Verilog, and a description of this early design effort is also be given.

on-board processing↗

DOE OSTI2024

Semi-Dirac Fermions in a Topological Metal

Topological semimetals with massless Dirac and Weyl fermions represent the forefront of quantum materials research. In two dimensions, a peculiar class of fermions that are massless in one direction and massive in the perpendicular direction was predicted 16 years ago. These highly exotic quasiparticles—the semi-Dirac fermions—ignited intense theoretical and experimental interest but remain undetected. Using magneto-optical spectroscopy, we demonstrate the defining feature of semi-Dirac fermions— B 2 / 3 scaling of Landau levels—in a prototypical nodal-line metal ZrSiS. In topological metals, including ZrSiS, nodal lines extend the band degeneracies from isolated points to lines, loops, or even chains in the momentum space. With calculations and theoretical modeling, we pinpoint the observed semi-Dirac spectrum to the crossing points of nodal lines in ZrSiS. Crossing nodal lines exhibit a continuum absorption spectrum but with singularities that scale as B 2 / 3 at the crossing. Our work sheds light on the hidden quasiparticles emerging from the intricate topology of crossing nodal lines and highlights the potential to explore quantum geometry with linear optical responses. Published by the American Physical Society 2024

Shao, Yinming (ORCID:0000000228910028)↗

NASA NTRS1994

The very soft X-ray emission of X-ray-faint early-type galaxies

A recent reanaylsis of Einstein data, and new ROSAT observations, have revealed the presence of at least two components in the X-ray spectra of X-ray faint early-type galaxies: a relatively hard component (kT greater than 1.5 keV), and a very soft component (kT approximately 0.2-0.3 keV). In this paper we address the problem of the nature of the very soft component and whether it can be due to a hot interstellar medium (ISM), or is most likely originated by the collective emission of very soft stellar sources. To this purpose, hydrodynamical evolutionary sequences for the secular behavior of gas flows in ellipticals have been performed, varying the Type Ia supernovae rate of explosion, and the dark matter amount and distribution. The results are compared with the observational X-ray data: the average Einstein spectrum for six X-ray faint early-type galaxies (among which are NGC 4365 and NGC 4697), and the spectrum obtained by the ROSAT pointed observation of NGC 4365. The very soft component could be entirely explained with a hot ISM only in galaxies such as NGC 4697, i.e., when the depth of the potential well-on which the average ISM temperature strongly depends-is quite shallow; in NGC 4365 a diffuse hot ISM would have a temperature larger than that of the very soft component, because of the deeper potential well. So, in NGC 4365 the softest contribution to the X-ray emission comes certainly from stellar sources. As stellar soft X-ray emitters, we consider late-type stellar coronae, supersoft sources such as those discovered by ROSAT in the Magellanic Clouds and M31, and RS CVn systems. All these candidates can be substantial contributors to the very soft emission, though none of them, taken separately, plausibly accounts entirely for its properties. We finally present a model for the X-ray emission of NGC 4365, to reproduce in detail the results of the ROSAT pointed observation, including the Position Sensitive Proportional Counter (PSPC) spectrum and radial surface brightness distribution. The present data may suggest that the X-ray surface brightness is more extended than the optical profile. In this case, a straightforward explanation in terms of stellar sources could not be satisfactory. The available data can be better explained with three different contributions: a very soft component of stellar origin, a hard component from X-ray binaries, and an approximately 0.6 keV hot ISM. The latter can explain the extended X-ray surface brightness profile, if the galaxy has a dark-to-luminous mass ratio of 9, with the dark matter very broadly distributed, and a SN Ia explosive rate of approximately 0.6 the Tammann rate.

Pellegrini, S.↗

NASA NTRS2010

Vacuum-Compatible Wideband White Light and Laser Combiner Source System

For the Space Interferometry Mission (SIM) Spectrum Calibration Development Unit (SCDU) testbed, wideband white light is used to simulate starlight. The white light source mount requires extremely stable pointing accuracy (<3.2 microradians). To meet this and other needs, the laser light from a single-mode fiber was combined, through a beam splitter window with special coating from broadband wavelengths, with light from multimode fiber. Both lights were coupled to a photonic crystal fiber (PCF). In many optical systems, simulating a point star with broadband spectrum with stability of microradians for white light interferometry is a challenge. In this case, the cameras use the white light interference to balance two optical paths, and to maintain close tracking. In order to coarse align the optical paths, a laser light is sent into the system to allow tracking of fringes because a narrow band laser has a great range of interference. The design requirements forced the innovators to use a new type of optical fiber, and to take a large amount of care in aligning the input sources. The testbed required better than 1% throughput, or enough output power on the lowest spectrum to be detectable by the CCD camera (6 nW at camera). The system needed to be vacuum-compatible and to have the capability for combining a visible laser light at any time for calibration purposes. The red laser is a commercially produced 635-nm laser 5-mW diode, and the white light source is a commercially produced tungsten halogen lamp that gives a broad spectrum of about 525 to 800 nm full width at half maximum (FWHM), with about 1.4 mW of power at 630 nm. A custom-made beam splitter window with special coating for broadband wavelengths is used with the white light input via a 50-mm multi-mode fiber. The large mode area PCF is an LMA-8 made by Crystal Fibre (core diameter of 8.5 mm, mode field diameter of 6 mm, and numerical aperture at 625 nm of 0.083). Any science interferometer that needs a tracking laser fringe to assist in alignment can use this system.

Azizi, Alineza↗

NASA NTRS1991

Weighted slit extraction of low-dispersion IUE spectral data

The weighted slit extraction has been chosen by the IUE project as the standard extraction for low-dispersion spectra in the final IUE archives. In order to properly weight the data within the extraction slit and obtain the optimal evaluation of the true spectrum, a noise model is derived for IUE data. The exclusion of cosmic rays is demonstrated and the improvement in signal-to-noise ratio is quantified for spectra taken with a wide range of flux level. Problematic spectra, such as trailed spectra, multiple spectra, discontinuous spectra, and emission-line spectra, are extracted to demonstrate the robust nature of the method. Comparisons are made between the standard IUE Standard Image Processing System (IUESIPS) extraction, nonstandard narrow slit extraction, trailed IUESIPS extraction, and weighted extraction for these data. Other weighted slit extractions are briefly discussed. The advantages of the weighted slit extraction are: (1) the extraction improves the signal-to-noise ratio of the spectrum while conserving total flux; (2) most of the cosmic rays are automatically removed; (3) the output includes an error estimate for each point in the flux spectrum; and (4) the algorithm can be run in a batch mode that requires no special input parameters.

Kinney, A. L.↗

DOE OSTI2021

First-Principles Study on the Electronic Properties of PDPP-Based Conjugated Polymer via Density Functional Theory

In this study, we focus on computational predictions of the electronic and optical properties of a one-dimensional periodic model of a single chain of a diketopyrrolopyrrole (DPP)-based conjugated polymer (PDPP3T) as a function of electronic configuration changes due to charge injection. Here, we employ density functional theory (DFT) to explore the ground-state and excited-state electronic properties as well as optical properties influenced by charge injection. We utilize both the Heyd–Scuseria–Ernzerhof (HSE06) and Perdew–Burke–Ernzerhof (PBE) functionals to predict the band gap and compute the absorption spectrum. Our DFT results point out that utilizing the HSE06 functional in conjunction with momentum sampling over the Brillouin zone can appropriately predict the band gap and absorption spectrum in good agreement with experimental data. Moreover, we explore the influence of charge-carrier injection on the electronic configuration of the PDPP3T polymer. Our results indicate that the injection of charge carriers into the PDPP3T semiconducting polymer model greatly affects the electrical properties and ends in a low band gap and high mobility of charge carriers in PDPP3T polymers, offering the potential to tailor the material electronic performance for organic photovoltaic and optoelectronic device applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2025

An analytically tractable marked power spectrum

The increasing precision of cosmology data in the modern era is calling for methods to allow the extraction of non-Gaussian information using tools beyond two-point statistics. The marked power spectrum has the potential to extract beyond two-point information in a computationally efficient way while using much of the infrastructure already available for the power spectrum. In this work we explore the marked power spectrum from an analytical perspective. In particular, we explore a low-order polynomial for the mark that allows us to better control the theoretical uncertainties and we show that with minimal new degrees of freedom the analytical results match measurements from N-body simulations for both the matter field and biased tracers in redshift space. Finally, we show that even within the limited forms of mark that we consider, there are degeneracies that can be broken by inclusion of the marked auto-spectrum or the cross-spectrum with the unmarked field. I n conclusion, we discuss future theoretical developments that would enable us to apply this approach to survey data.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1989

Fourier transform methods in local gravity modeling

New algorithms were derived for computing terrain corrections, all components of the attraction of the topography at the topographic surface and the gradients of these attractions. These algoriithms utilize fast Fourier transforms, but, in contrast to methods currently in use, all divergences of the integrals are removed during the analysis. Sequential methods employing a smooth intermediate reference surface were developed to avoid the very large transforms necessary when making computations at high resolution over a wide area. A new method for the numerical solution of Molodensky's problem was developed to mitigate the convergence difficulties that occur at short wavelengths with methods based on a Taylor series expansion. A trial field on a level surface is continued analytically to the topographic surface, and compared with that predicted from gravity observations. The difference is used to compute a correction to the trial field and the process iterated. Special techniques are employed to speed convergence and prevent oscillations. Three different spectral methods for fitting a point-mass set to a gravity field given on a regular grid at constant elevation are described. Two of the methods differ in the way that the spectrum of the point-mass set, which extends to infinite wave number, is matched to that of the gravity field which is band-limited. The third method is essentially a space-domain technique in which Fourier methods are used to solve a set of simultaneous equations.

Harrison, J. C.↗

NASA NTRS2009

Measurement and Characterization of Space Shuttle Solid Rocket Motor Plume Acoustics

Lift-off acoustic environments generated by the future Ares I launch vehicle are assessed by the NASA Marshall Space Flight Center (MSFC) acoustics team using several prediction tools. This acoustic environment is directly caused by the Ares I First Stage booster, powered by the five-segment Reusable Solid Rocket Motor (RSRMV). The RSRMV is a larger-thrust derivative design from the currently used Space Shuttle solid rocket motor, the Reusable Solid Rocket Motor (RSRM). Lift-off acoustics is an integral part of the composite launch vibration environment affecting the Ares launch vehicle and must be assessed to help generate hardware qualification levels and ensure structural integrity of the vehicle during launch and lift-off. Available prediction tools that use free field noise source spectrums as a starting point for generation of lift-off acoustic environments are described in the monograph NASA SP-8072: "Acoustic Loads Generated by the Propulsion System." This monograph uses a reference database for free field noise source spectrums which consist of subscale rocket motor firings, oriented in horizontal static configurations. The phrase "subscale" is appropriate, since the thrust levels of rockets in the reference database are orders of magnitude lower than the current design thrust for the Ares launch family. Thus, extrapolation is needed to extend the various reference curves to match Ares-scale acoustic levels. This extrapolation process yields a subsequent amount of uncertainty added upon the acoustic environment predictions. As the Ares launch vehicle design schedule progresses, it is important to take every opportunity to lower prediction uncertainty and subsequently increase prediction accuracy. Never before in NASA s history has plume acoustics been measured for large scale solid rocket motors. Approximately twice a year, the RSRM prime vendor, ATK Launch Systems, static fires an assembled RSRM motor in a horizontal configuration at their test facility in Utah. The remaining RSRM static firings will take place on elevated terrain, with the nozzle exit plume being mostly undeflected and the landscape allowing placement of microphones within direct line of sight to the exhaust plume. These measurements will help assess the current extrapolation process by direct comparison between subscale and full scale solid rocket motor data.

Kenny, Jeremy↗

NASA NTRS1987

A multiple-time-scale turbulence model based on variable partitioning of turbulent kinetic energy spectrum

A multiple-time-scale turbulence model of a single point closure and a simplified split-spectrum method is presented. In the model, the effect of the ratio of the production rate to the dissipation rate on eddy viscosity is modeled by use of the multiple-time-scales and a variable partitioning of the turbulent kinetic energy spectrum. The concept of a variable partitioning of the turbulent kinetic energy spectrum and the rest of the model details are based on the previously reported algebraic stress turbulence model. Example problems considered include: a fully developed channel flow, a plane jet exhausting into a moving stream, a wall jet flow, and a weakly coupled wake-boundary layer interaction flow. The computational results compared favorably with those obtained by using the algebraic stress turbulence model as well as experimental data. The present turbulence model, as well as the algebraic stress turbulence model, yielded significantly improved computational results for the complex turbulent boundary layer flows, such as the wall jet flow and the wake boundary layer interaction flow, compared with available computational results obtained by using the standard kappa-epsilon turbulence model.

Kim, S.-W.↗

NASA NTRS1989

A multiple-time-scale turbulence model based on variable partitioning of the turbulent kinetic energy spectrum

Kim, S.-W.↗

DOE OSTI2025

2 νββ spectrum in chiral effective field theory

We investigate two-neutrino double beta decay (2νββ) in chiral effective field theory. We find contributions from weak magnetism and double-weak pion-exchange at next-to-leading-order in the chiral power counting. We discuss the impact of the chiral corrections on the electron spectra and find that they should be included in analyses of 2νββ decay that aim to uncover new physics signatures in the electron spectrum. We illustrate this point by revisiting the effect of sterile neutrinos and non-standard charged interactions. We also find that the pion-exchange contributions involve nuclear matrix elements that are related to those appearing in neutrinoless double beta decay (0νββ). We investigate whether the 0νββ nuclear matrix elements can be obtained from detailed measurements of the energy spectrum of the outgoing electrons in 2νββ transitions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS1994

Pressure Sounding of the Middle Atmosphere from ATMOS Solar Occultation Measurements of Atmospheric CO(sub 2) Absorption Lines

A method for retrieving the atmospheric pressure corresponding to the tangent point of an infrared spectrum recorded in the solar occultation mode is described and applied to measurements made by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer. Tangent pressure values are inferred from measurements of isolated CO(sub 2) lines with temperature-insensitive intensities. Tangent pressures are determined with a spectroscopic precision of 1-3%, corresponding to a tangent point height precision, depending on the scale height, of 70-210 meters.

Atmospheric Trace Molecule Spectroscopy ATMOS atmo↗

DOE OSTI2025

Constraining primordial non-Gaussianity from the large scale structure two-point and three-point correlation functions

Surveys of cosmological large-scale structure (LSS) are sensitive to the presence of local primordial non-Gaussianity (PNG), and may be used to constrain models of inflation. Local PNG, characterized by f NL ⁠, the amplitude of the quadratic correction to the potential of a Gaussian random field, is traditionally measured from LSS two-point and three-point clustering via the power spectrum and bi-spectrum. We propose a framework to measure f NL using the configuration space two-point correlation function (2pcf) monopole and three-point correlation function (3pcf) monopole of survey tracers. Our model estimates the effect of the scale-dependent bias induced by the presence of PNG on the 2pcf and 3pcf from the clustering of simulated dark matter haloes. We describe how this effect may be scaled to an arbitrary tracer of the cosmological matter density. The 2pcf and 3pcf of this tracer are measured to constrain the value of f NL ⁠. In LSS surveys, the effect of imaging systematics on two-point statistics is often degenerate with the PNG signal. Our proposed model employs three-point statistics primarily to break this degeneracy. Using simulations of luminous red galaxies observed by the Dark Energy Spectroscopic Instrument (DESI), we demonstrate the accuracy and constraining power of our method. Our forecast indicates the ability to constrain f NL to a precision of σf NL ≈ 22 with one year of DESI survey data, as well as the ability to constrain the imaging systematic weights in situ.

early Universe↗

DOE OSTI2024

Optimal spectral resolution for solids and liquids using FT and other infrared spectrometers: How much resolution do you really need?

In this study we investigate the possibility of using spectral resolutions for infrared measurements of solids and liquids that are not powers of two, e.g. are not at 1, 2, 4, 8, or 16 cm-1 resolution. In almost all reported literature of the last fifty years the resolution used to record for a Fourier transform infrared spectrum has been a power of two. This stems from the fact that 1) the Cooley-Tukey algorithm used to compute such a transform was constructed to use only powers of two and was also driven by 2) the fact that the computing horsepower required to compute the Fourier transform increases as N?log?_2 (N), where N is the number of points in the interferogram (spectrum). For typical spectra, however, the CPU time is no longer a consideration. Our study is based on both liquid and solid spectra, all of which were recorded at 2 cm-1 resolution. There were at total of 70 solids spectra representing 2,472 spectral peaks and 61 liquids spectra (1,765 spectral peaks), each peak being inspected for being singlet / multiplet in nature. Of the 1,765 liquid bands examined, only 27 had widths less than 5 cm-1. Of the 2,472 solid bands examined, only 39 peaks have widths less than 5 cm-1. For liquids, the mean peak width is 24.7 cm-1 but the median peak width is 13.7 cm-1, and, similarly, for solids, the mean peak width is 22.2 cm-1 but the median peak width is 11.2 cm-1. In both cases, solids and liquids, a skewed peak widths distribution was observed, the peak of the distribution representing narrower bands in the 7 to 9 cm-1 FWHM range but displaying a long tail to the very broad bands, with some displaying spectral widths of 100 cm-1 or more. Because one of the most important criteria for successful instrumental design in IR spectroscopy is the spectral resolution, the data were further analyzed showing that a value to resolve 95% of all bands is 5.7 cm-1 for liquids and 5.3 cm-1 for solids; such a resolution would capture the native linewidth (no instrumental broadening) of 95% of all the solids and liquid bands, respectively. Based on the present results we suggest that, when accounting only for intrinsic linewidths an optimized resolution of 6.0 cm-1 will capture 91% of all condensed-phase bands for IR detection of chemical, mineral, and biological materials.

Forland, Brenda M.↗

NASA NTRS1982

Dayglow emissions of the O2 Herzberg bands and the Rayleigh backscattered spectrum of the earth

It is pointed out that numerous fluorescent emissions from the Herzberg bands of molecular oxygen lie in the spectral region 242-300 nm. This coincides with the wavelength range used by orbiting spectrometers that observe the Rayleigh backscattered spectrum of the earth for the purpose of monitoring the vertical distribution of stratospheric ozone. Model calculations suggest that Herzberg band emissions in the dayglow could provide significant contamination of the ozone measurements if the quenching rate of O2(A3Sigma) is sufficiently small. It is noted that this is especially true near 255 nm, where the most intense fluorescent emissions relative to the Rayleigh scattered signal are located and where past satellite measurements have shown a persistent excess radiance above that expected for a pure ozone absorbing and molecular scattering atmosphere. Very small quenching rates, however, are adequate to reduce the dayglow emission to negligible levels. Noting that available laboratory data have not definitely established the quenching on the rate of O2(A3Sigma) as a function of vibration level, it is emphasized that such information is required before the Herzberg band contributions can be evaluated with confidence.

Frederick, J. E.↗

NASA NTRS1976

Real time analysis of voiced sounds

A power spectrum analysis of the harmonic content of a voiced sound signal is conducted in real time by phase-lock-loop tracking of the fundamental frequency, (f sub 0) of the signal and successive harmonics (h sub 1 through h sub n) of the fundamental frequency. The analysis also includes measuring the quadrature power and phase of each frequency tracked, differentiating the power measurements of the harmonics in adjacent pairs, and analyzing successive differentials to determine peak power points in the power spectrum for display or use in analysis of voiced sound, such as for voice recognition.

Hong, J. P.↗

NASA NTRS2000

Chandra Observations of the M31

We report on Chandra observations of the nearest Spiral Galaxy, M3l, The nuclear source seen with previous X-ray observatories is resolved into five point sources. One of these sources is within 1 arc-sec of the M31 central super-massive black hole. As compared to the other point sources in M3l. this nuclear source has an unusually soft spectrum. Based on the spatial coincidence and the unusual spectrum. we identify this source with the central black hole. A bright transient is detected 26 arc-sec to the west of the nucleus, which may be associated with a stellar mass black hole. We will report on a comparison of the x-ray spectrum of the diffuse emission and point sources seen in the central few arcmin

Garcia, Michael↗