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NASA NTRS2014

ALMA Observations of α Centauri First Detection of Main-Sequence Stars at 3 mm Wavelength

The precise mechanisms that provide the non-radiative energy for heating the chromosphere and the corona of the Sun and those of other stars constitute an active field of research. By studying stellar chromospheres one aims at identifying the relevant physical processes. Defining the permittable extent of the parameter space can also serve as a template for the Sun-as-a-star. This feedback will probably also help identify stars that potentially host planetary systems that are reminiscent of our own. Earlier observations with Herschel and APEX have revealed the temperature minimum of Alpha Cen, but these were unable to spatially resolve the binary into individual components. With the data reported in this Letter, we aim at remedying this shortcoming. Furthermore, these earlier data were limited to the wavelength region between 100 and 870 um. In the present context, we intend to extend the spectral mapping (SED) to longer wavelengths, where the contrast between stellar photospheric and chromospheric emission becomes increasingly evident. The Atacama Large Millimeter submillimeter Array (ALMA) is particularly suited to point sources, such as unresolved stars. ALMA provides the means to achieve our objectives with both its high sensitivity of the collecting area for the detection of weak signals and the high spatial resolving power of its adaptable interferometer for imaging close multiple stars. This is the first detection of main-sequence stars at a wavelength of 3 mm. Furthermore, the individual components of the binary Alpha CenAB are clearly detected and spatially well resolved at all ALMA wavelengths. The high signal-to-noise ratios of these data permit accurate determination of their relative flux ratios, i.e., S(sub y(sup B)) / S(sub y(sup A))> = 0.54 +/- 0.04 at 440 μm, = 0.46 +/- 0.01 at 870 μm, and = 0.47 +/- 0.006 at 3.1 mm, respectively.. The previously obtained flux ratio of 0.44+/-0.18, which was based on measurements in the optical and at 70 μm, is consistent with the present ALMA results, albeit with a large error bar. The observed 3.1 mm emission greatly exceeds what is predicted from the stellar photospheres, and undoubtedly arises predominantly as free-free emission in the ionized chromospheric plasmas of both stars. Given the distinct difference in their cyclic activity, the similarity of their submm SEDs appears surprising.

Herschel↗

NASA NTRS1983

Failure detection with uncertain models

In this paper the author considers the issue of robust failure detection. In one way or another all failure detection methods generate signals which tend to highlight the presence of particular failures if they have actually occurred. However, if any model uncertainties have effects on the observables which are at all like those of one or more of the failure modes, these will also be accentuated. Consequently the problem of robust failure detection is concerned with generating signals which are maximally sensitive to some effects (failures) and minimally sensitive to other (model errors). Previously announced in STAR as N83-32417

Lou, X.-C.↗

NASA NTRS2021

Quantitative Investigation of Radiometric Interactions between Snowfall, Snow Cover, and Cloud Liquid Water over Land

Falling snow alters its own microwave signatures when it begins to accumulate on the ground, making retrieval of snowfall challenging. This paper investigates the effects of snow-cover depth and cloud liquid water content on microwave signatures of terrestrial snowfall using reanalysis data and multi-annual observations by the Global Precipitation Measurement (GPM) core satellite with particular emphasis on the 89 and 166 GHz channels. It is found that over shallow snow cover (snow water equivalent (SWE) ≤100 kg/sq. m) and low values of cloud liquid water path (LWP 100–150 g/sq. m), the scattering of light snowfall (intensities ≤0.5 mm/ h) is detectable only at frequency 166 GHz, while for higher snowfall rates, the signal can also be detected at 89 GHz. However, when SWE exceeds 200 kg/sq. m and the LWP is greater than 100–150 g/sq. m, the emission from the increased liquid water content in snowing clouds becomes the only surrogate microwave signal of snowfall that is stronger at frequency 89 than 166 GHz. The results also reveal that over high latitudes above 60°N where the SWE is greater than 200 kg/sq. m and LWP is lower than 100–150 g/sq. m, the snowfall microwave signal could not be detected with GPM without considering a priori data about SWE and LWP. Our findings provide quantitative insights for improving retrieval of snowfall in particular over snow-covered terrain.

Zeinab Takbiri↗

NASA NTRS1998

Evidence for Phyllosilicates near the Lunar South Pole

While theoretically water ice could be stable in permanently shadowed areas near the lunar poles, there is conflicting observational evidence for the existence of water ice at either pole. Clementine's bistatic radar resumed a weak signal commensurate with water ice in the South Pole Aitken Basin; however, groundbased radar searches have not detected such a signal at either pole. Lunar Prospector measured large amounts of H (attributed to water) at both poles; however, Galileo near-infrared spectral measurements of the north polar region did not detect the prominent 3.0 micron absorption feature due to interlayer and adsorbed water in phyllosilicates. Evidence for the existence of water at the lunar poles is still ambiguous and controversial. We present evidence, based on the analysis of Galileo SSI images, for the presence of phyllosilicates near the lunar south pole. Using the color image sequence (560 nm, 670 nm, 756 nm, and 889 nm) of Lunmap 14 taken during the Galileo Earth-Moon pass I, we have identified areas that show evidence for a 0.7 microns absorption feature present in Fe-bearing phyllosilicates.

Vilas, Faith↗

DOE OSTI2024

New limit on dark photon kinetic mixing in the 0.2 – 1.2 μ eV mass range from the Dark E-field Radio experiment

We report new limits on the kinetic mixing strength of the dark photon spanning the mass range 0.21 − 1.24 μ eV corresponding to a frequency span of 50–300 MHz. The Dark E-field Radio experiment is a wideband search for dark photon dark matter. In this paper we detail changes in calibration and upgrades since our proof-of-concept pilot run. Our detector employs a wide-bandwidth E-field antenna moved to multiple positions in a shielded room, a low noise amplifier, wideband analog-to-digital converter, followed by a 2 24 -point fast Fourier transform. An optimal filter searches for signals with Q ≈ 10 6 . In nine days of integration, this system is capable of detecting dark photon signals corresponding to a kinetic mixing strength ε several orders of magnitude lower than previous limits. We find a 95% exclusion limit on ε over this mass range between 6 × 10 − 15 and 6 × 10 − 13 , tracking the complex resonant mode structure in the shielded room. Published by the American Physical Society 2024

Astronomy & Astrophysics↗

NASA NTRS2006

Performance of Dispersed Fringe Sensor in the Presence of Segmented Mirror Aberrations: Modeling and Simulation

Dispersed Fringe Sensing (DFS) is an efficient and robust method for coarse phasing of a segmented primary mirror such as the James Webb Space Telescope (JWST). In this paper, modeling and simulations are used to study the effect of segmented mirror aberrations on the fringe image, DFS signals and DFS detection accuracy. The study has shown due to the pixilation spatial filter effect from DFS signal extraction the effect of wavefront error is reduced and DFS algorithm will be more robust against wavefront aberration by using multi-trace DFS approach. We also studied the JWST Dispersed Hartmann Sensor (DHS) performance in presence of wavefront aberrations caused by the gravity sag and we use the scaled gravity sag to explore the JWST DHS performance relationship with the level of the wavefront aberration. This also includes the effect from line-of-sight jitter.

segmented mirrors↗

DOE OSTI2022

Circular Trajectory Approach for Online Sinusoidal Signal Distortion Monitoring and Visualization

The increasing complexity and uncertainties of modern power systems are placing significant demands on signal monitoring techniques. This work proposes the Circular Trajectory Approach (CTA) for online sinusoidal signal distortion monitoring and visualization. CTA can detect distortions of a sinusoidal signal. Compared with existing waveform anomaly detection techniques, CTA is faster in detection and less computation intensive. It thus supports edge devices and online applications. CTA also offers a new means of sinusoidal signal distortion visualization. It can reveal the distorted sections in a sinusoidal cycle and clearly display the distortions. The proposed approach is tested on real data from an open source EPRI dataset.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

NASA NTRS1993

Effects of atmospheric variations on acoustic system performance

Acoustic propagation over medium to long ranges in the atmosphere is subject to many complex, interacting effects. Of particular interest at this point is modeling low frequency (less than 500 Hz) propagation for the purpose of predicting ranges and bearing accuracies at which acoustic sources can be detected. A simple means of estimating how much of the received signal power propagated directly from the source to the receiver and how much was received by turbulent scattering was developed. The correlations between the propagation mechanism and detection thresholds, beamformer bearing estimation accuracies, and beamformer processing gain of passive acoustic signal detection systems were explored.

Nation, Robert↗

NASA NTRS1999

The LISA Mission Design

The proposed Laser Interferometer Space Antenna (LISA) is designed to observe gravitational radiation from galactic binaries and massive black holes in other galaxies. LISA will observe waves in the frequency range 0.1 mHz to 1 Hz, which can never be observed on Earth due to background noise. The three LISA spacecraft will be located at the vertices of an equilateral triangle with side length 5 million km. The orbits are chosen so that the triangle formation trails the Earth by 20 degrees. Each spacecraft will contain two independent instruments containing a proof mass, laser and 30 cm diameter telescope for the transmission and reception of laser signals. Two independent Michelson interferometers will be formed, allowing both polarizations of gravitational waves to be detected. The observed signals will yield unique information about the formation of massive black holes and the nature of gravity in the high-field limit.

Folkner, W. M.↗

DOE OSTI2020

Extending light WIMP searches to single scintillation photons in LUX

© 2020 American Physical Society. We present a novel analysis technique for liquid xenon time projection chambers that allows for a lower threshold by relying on events with a prompt scintillation signal consisting of single detected photons. The energy threshold of the LUX dark matter experiment is primarily determined by the smallest scintillation response detectable, which previously required a twofold coincidence signal in its photomultiplier arrays, enforced in data analysis. The technique presented here exploits the double photoelectron emission effect observed in some photomultiplier models at vacuum ultraviolet wavelengths. We demonstrate this analysis using an electron recoil calibration dataset and place new constraints on the spin-independent scattering cross section of weakly interacting massive particles (WIMPs) down to 2.5 GeV/c2 WIMP mass using the 2013 LUX dataset. This new technique is promising to enhance light WIMP and astrophysical neutrino searches in next-generation liquid xenon experiments.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1972

A study of FM threshold extension techniques

The characteristics of three postdetection threshold extension techniques are evaluated with respect to the ability of such techniques to improve the performance of a phase lock loop demodulator. These techniques include impulse-noise elimination, signal correlation for the detection of impulse noise, and delta modulation signal processing. Experimental results from signal to noise ratio data and bit error rate data indicate that a 2- to 3-decibel threshold extension is readily achievable by using the various techniques. This threshold improvement is in addition to the threshold extension that is usually achieved through the use of a phase lock loop demodulator.

Arndt, G. D.↗

NASA NTRS1992

Detecting Lamb waves with broad-band acousto-ultrasonic signals in composite structures

Lamb waves can be produced and detected in ceramic matrix composites (CMC) and metal matrix composites (MMC) plates using the acousto-ultrasonic configuration employing broadband transducers. Experimental dispersion curves of lowest symmetric and antisymmetric modes behave in a manner analogous to the graphite/polymer theoretical curves. In this study a basis has been established for analyzing Lamb wave velocities for characterizing composite plates. Lamb wave dispersion curves and group velocities were correlated with variations in axial stiffness and shear stiffness in MMC and CMC. For CMC, interfacial shear strength was also correlated with the first antisymmetric Lamb mode.

Kautz, Harold E.↗

NASA NTRS2007

R.F Microphotonics for NASA Space Communications Applications

An RF microphotonic receiver has-been developed at Ka-band. The receiver consists of a lithium niobate micro-disk that enables RF-optical coupling to occur. The modulated optical signal (- 200 THz) is detected by the high-speed photonic signal processing electronics. When compared with an electronic approach, the microphotonic receiver technology offers 10 times smaller volume, smaller weight, and smaller power consumption; greater sensitivity; and optical isolation for use in extreme environments. The status of the technology development will be summarized, and the potential application of the receiver to NASA space communications systems will be described.

Pouch, John↗

NASA NTRS1986

An infrared search for extraterrestrial laser signals

The focus of project SETI is on microwave frequencies, where receivers fundamentally have the best sensitivity for the detection of narrow band signals. Such receivers, when coupled to existing radio telescopes, form an optimum system for broad area searches over the sky. Detection of narrow band infrared signals is best done with a laser heterodyne reciever similar in function to a microwave spectral line receiver. A receiver was built for astrophysical observations at 30 THz (10 microns) and the spectrometer is being adapted for SETI work. The receiver uses a small CO2 laser as the local oscillator, a HgCdTe diode as the photomixer, and a multichannel intermediate frequency (IF) filterbank. An advanced multichannel IF processor is now being built to detect infrared line radiation in 1000 spectral channels each 1 MHz wide. When completed this processor will be used with a ground based telescope next year for a survey of several hundred selected stars for narrow band CO2 laser signals at 30 THz.

Betz, A.↗

NASA NTRS1973

Detection of S02 and N02 in Stack Plume by Raman Scattering and Fluorescence

We have been studying laser-Raman radar which can be used as the remote detector of sulfur dioxide concentration in the stack plume of boiler exhaust gas, and some results have been published. In this paper, we report the interference of nitrogen dioxide fluorescence against sulfur dioxide Raman scattering and the measuring method of sulfur dioxide and nitrogen dioxide concentration. In a stack plume, high density dust and high concentration carbon dioxide are included, therefore very strong Mie back-scattering and carbon dioxide Raman scattering are observed. The separation of these scattering signals from sulfur dioxide Raman signal was the first problem for the laser-Raman radar. But, this problem was solved by using the filter which have high resolving power. It is well known that nitrogen dioxide can be excited to emit fluorescence of broad spectrum by blue-green light. The light source of the laser-Raman radar is SH of Nd:YAG laser, and boiler exhaust gas includes several tens ppm of nitrogen dioxide, then the interference of nitrogen dioxide fluorescence brings the error to sulfur dioxide measurement. 'rhe rejection of the interference can be achieved by the subtraction of the nitrogen dioxide fluorescence contribution from detected signal at sulfur dioxide Raman scattering wavelength. The nitrogen dioxide fluorescence contribution can be measured by two methods. The first is to convert the nitrogen dioxide fluorescence intensity which is measured at a different wavelength from sulfur dioxide Raman line into the one at sulfur dioxide Raman line. The second is to convert the detected signal intensity, which is obtained when the range gate is set just behind the plume, into the one obtained at the range of the plume using the difference of the time dependence between sulfur dioxide Raman scattering and nitrogen dioxide fluorescence. Nitrogen dioxide fluorescence has lifetime of about 300nS, while Raman scattering has none. By either of the two methods, the contribution of nitrogen dioxide fluorescence is determined. Then, we can measure the nitrogen dioxide and sulfur dioxide concentration.The minimum detectable concentration and the experimental results of the remote sensing of sulfur dioxide and nitrogen dioxide in stack plume will be discussed in detail.

Nakahara, S.↗

NASA NTRS1988

DS/LPI autocorrelation detection in noise plus random-tone interference

The authors present and analyze a frequency-noncoherent two-lag autocorrelation statistic for the wideband detection of random BPSK signals in noise-plus-random-multitone interference. It is shown that this detector is quite robust to the presence or absence of interference and its specific parameter values, contrary to the case of an energy detector. The rule assumes knowledge of the data rate and the active scenario under H0. It is concluded that the real-time autocorrelation domain and its samples (lags) are a viable approach for detecting random signals in dense environments.

Hinedi, S.↗

DOE OSTI2021

Quantitative analysis method for multi-color microscopy

We developed an analysis framework for quantitatively interpreting results from multi-color fluorescence microscopy data. When the emission signal from fluorescent probes (i.e. from biological microscopy or in single-particle microscopy) is spectrally separated before detection, the resulting signals contain information about the strengths of each probe. We built a model to deconvolve the raw data into quantitative descriptions of either of the wavelength of a single probe or the relative strengths among multiple probes. This approach requires only spectrally separating the image data into two or more channels, as opposed to fully resolving the spectral profile, thus allowing other microscopy techniques to be used simultaneously. Our analysis framework incorporates the response features of the optical and imaging elements used to produce the spectral separation, yielding highly quantitative interpretations of the underlying behaviors that give rise to the data.

Ryan, Duncan↗

NASA NTRS1999

Laser Optogalvanic Spectroscopy pf Neon and Argon in a Discharge Plasma and its Significance for Microgravity Combustion

A detailed study of combustion mechanisms in flames, employing laser-based diagnostics, has provided good knowledge and understanding of the physical phenomena, and led to better characterization of the dynamical and chemical combustion processes, both under low-gravity (in space) and normal gravity (in ground based facilities, e.g. drop towers). Laser induced fluorescence (LIF), laser-induced incandescence (LII) and LIF thermometry have been widely used to perform nonintrusive measurements and to better understand combustion phenomena. Laser optogalvanic (LOG) spectroscopy has well-established applications in ion mobility measurements, atomic and molecular spectroscopy, ionization rates, recombination rates, velocity measurements and as a combustion probe for trace element detection. Absorption spectra of atomic and molecular species in flames can be obtained via LOG spectroscopy by measuring the voltage and current changes induced by laser irradiation. There are different kinds of processes that contribute to a discharge current, namely: (1) electron impact ionization, (2) collisions among the excited atoms of the discharge species and (3) Penning ionization. In general, at higher discharge currents, the mechanism of electron impact ionization dominates over Penning ionization, whereby the latter is hardly noticeable. In a plasma, whenever the wavelength of a laser coincides with the absorption of an atomic or molecular species, the rate of ionization of the species momentarily increases or decreases due to laser-assisted acceleration of collisional ionization. Such a rate of change in the ionization is monitored as a variation in the transient current by inserting a high voltage electrode into the plasma. Optogalvanic spectroscopy in discharges has been useful for characterizing laser line-widths and for providing convenient calibration lines for tunable dye lasers in the ultraviolet, visible and infrared wavelength regions. Different kinds of quantitative information, such as the electron collisional ionization rate, can be extracted from the complex processes occurring within the discharge. In the optogalvanic effect (OGE), there is no problem of overlap from background emissions, and hence even weak signals can be detected with a high signal-to-noise ratio, which makes the optogalvanic effect sensitive enough to resolve vibrational changes in molecular bonds and differences in energy levels brought about by different electron spins. For calibration purposes, neon and argon gaseous discharges have been employed most extensively, because these gases are commonly used as buffer gases within hollow-cathode lamps and provide an acceptable density of calibration lines. In the present work, our main aim has been to understand the dominant physical processes responsible for the production of the OGE signal, based on the extensive time resolved optogalvanic waveforms recorded, and also to extract quantitative information on the rates of excited state collisional processes.

Misra, Prabhakar↗