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At least 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

A Simple Model of the Energy Threshold for Snowball Chambers

Cloud and bubble chambers have historically been used for particle detection, capitalizing on supersaturation and superheating, respectively. Here, we present new results from a prototype snowball chamber, in which an incoming particle triggers the crystallization of a purified, supercooled liquid. We demonstrate, for the first time, simulation agreement with our first results from 5 years ago: the higher temperature of the freezing of water and significantly shorter time spent supercooled compared to the control in the presence of a Cf-252 fission neutron source. This is accomplished by combining Geant4 modeling of neutron interactions with the Seitz nucleation model used in superheated bubble chambers, including those seeking dark matter. We explore the possible implications of using this new technology for GeV-scale WIMP searches, especially in terms of spin-dependent proton coupling, and report the first supercooling of WbLS (water-based liquid scintillator).

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

A Hydro-based MCMC Analysis of SNR 0509–67.5: Revealing the Explosion Properties from Fluid Discontinuities Alone

Using Hubble Space Telescope/ACS Hα images of SNR 0509–67.5 taken ~10 yr apart, we measure the forward shock (FS) proper motions (PMs) at 231 rim locations. The average shock radius and velocity are 3.66 ± 0.036 pc and 6315 ± 310 km s –1 . Hydrodynamic simulations, recast as similarity solutions, provide models for the supernova remnant’s expansion into a uniform ambient medium. These are coupled to a Markov chain Monte Carlo (MCMC) analysis to determine explosion parameters, constrained by the FS measurements. For our baseline model, the MCMC posteriors yield an age of 315.5 ± 1.8 yr, a dynamical explosion center at 5 h 09 m 31. s 16, $-67^\circ 31^{\prime} 17\buildrel{\prime\prime}\over{.} 1$ and ambient medium densities at each azimuth ranging over 3.7–8.0 × 10 –25 g cm –3 . The age uncertainty can be an order of magnitude larger when considering other models, or subsets of the data. We detect stellar PMs corresponding to speeds in the Large Magellanic Cloud ≥ 770 km s –1 . Five stars in the remnant show measurable PMs but none are moving radially from the dynamical center. There are four stars 1."4 from the center, including three faint, previously unidentified ones. Using coronal [Fe XIV ] λ5303 emission as a proxy for the reverse shock location, we constrain the explosion energy (for a compression factor of 4) to a value of E = (1.30 ± 0.41) × 10 51 erg for the first time from shock kinematics alone. Higher compression factors (7 or more) are strongly disfavored based on multiple criteria, arguing for inefficient particle acceleration in the Balmer shocks of SNR 0509–67.5.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1973

Use of ERTS data for mapping Arctic sea ice

This investigation is to evaluate the application of ERTS data for detecting and mapping Arctic sea ice. The specific objectives are to determine the spectral bands most suitable for detecting ice, to measure the scale and types of ice features that can be detected, and to develop interpretive techniques for differentiating ice from clouds and for mapping ice concentrations. The ERTS data are being analyzed primarily for three Arctic areas, the eastern Beaufort Sea, Baffin Bay, and the Greenland Sea.

Barnes, J. C.↗
NASA NTRS1972

An upper limit on the OH abundance in the intercloud medium.

A search for weak OH emission at 1665 and 1667 MHz was carried out in three high-latitude directions containing no compact clouds of H I or dust. No OH emission was detected down to low limits, and the comparison of our upper limits with the known H I and dust-column densities reinforces the suggestion that OH tends to be concentrated to regions of high dust or gas density.

Knapp, G. R.↗
NASA NTRS1978

The atmospheres of the Jovian satellites

Observational data on the atmospheres of the Galilean satellites of Jupiter, primarily Io, are reviewed. Io's sodium and hydrogen clouds are discussed along with searches for other species associated with Io. The supply and loss of neutral species to and from Io's clouds are considered, and models for the ionosphere of Io detected by Pioneer 10 are examined. Information and speculation concerning possible atmospheres of Europa, Ganymede, and Callisto are briefly summarized. The suggestion is noted that Ganymede could conceivably maintain a significant (of the order of 1 microbar) atmosphere consisting in large part of oxygen.

Johnson, T. V.↗
NASA NTRS1982

Morphology and movements of polarization features on Venus

Ground and spacecraft based polarization observations of Venus detected the signature of the so called 1-micron radius cloud particles that constitute the main cloud deck on Venus, as well as that of sub-micron sized particles that form a haze above this main cloud layer. Whether such observations showed any local clustering or organization in the polarimetry data remained uncertain until the relatively high resolution observations from the Pioneer Venus Orbiter Cloud Photopolarimeter (OCPP) became available. The available polarization data from this instrument was studied to see whether local organization was present, to study the morphology of such features or polarization clouds, and finally, to see if they can be followed in a sequence of observations to study their motions.

Limaye, S. S.↗
NASA NTRS1985

Spectra of simulated lightning on Venus, Jupiter, and Titan

Laser-induced plasmas in various gas mixtures were used to simulate lightning in other planetary atmospheres. This method of simulation has the advantage of producing short-duration, high-temperature plasmas free from electrode contamination. The laser-induced plasma discharges in air are shown to accurately simulate terrestrial lightning and can be expected to simulate lightning spectra in other planetary atmospheres. Spectra from 240 to 880 nm are presented for simulated lightning in the atmospheres of Venus, earth, Jupiter, and Titan. The spectra of lightning on the other giant planets are expected to be similar to that of Jupiter because the atmospheres of these planets are composed mainly of hydrogen and helium. The spectra of Venus and Titan show substantial amounts of radiation due to the presence of carbon atoms and ions and show CN Violet radiation. Although small amounts of CH4 and NH3 are present in the Jovian atmosphere, only emission from hydrogen and helium is observed. Most differences in the spectra can be understood in terms of the elemental ratios of the gas mixtures. Consequently, observations of the spectra of lightning on other planets should provide in situ estimates of the atmospheric and aerosol composition in the cloud layers in which lightning is occurring. In particular, the detection of inert gases such as helium should be possible and the relative abundance of these gases compared to major constituents might be determined.

Borucki, W. J.↗
NASA NTRS1994

Probing the galactic disk and halo. 1: The NGC 3783 sight line

We report a study of Galactic disk and halo absorption toward the Seyfert galaxy NGC 3783 which has Galactic coordinates l = 287.46 and b = +22.95. The data were obtained with the Goddard High Resolution Spectrograph operating at medium resolution with the Large Science Aperture, which produces a line spread function having a sharp core (full width at half maximum (FWHM) approximately 20 km/s) and broad wings extending to +/- 70 km/s. Ion species detected in absorption near zero LSR velocity include C IV and N V for high ions, and C I, Mg II, Si II, and S II for low ions. Absorption from a high-velocity cloud (HVC) at a velocity of +240 km/s along the sight line is also detected in the ion species of S II, Si II, and probably C I. This is the first reported case where S II and C I absorption has been detected in a HVC. The S II lines are especially useful since metal abundance estimates based on S are largely unaffected by dust grains. The study is aided by the availability of 21 cm emission data.

Lu, Limin↗
NASA NTRS1994

Observations of the Small Magellanic Cloud by the Vela 5B X-ray monitor

We present Vela 5B observations of the Small Magellanic Cloud (SMC) region obtained during the years 1969 - 1979. We detect the 3.89 day orbital modulation of SMC X-1 with a false alarm probability of 4.3 x 10(exp -3) and observe a high state beginning in 1970 September and lasting approximately 100 days. We also detect three outbursts by a transient source consistent with the position of the candidate Be-neutron star system H0107-750 (= 1H 0103-762). These events occur roughly 100 days apart and last for approximately 35 days. No detections of SMC X-2 or SMC X-3 are apparent above a limit of approximately 7 x 10(exp 37) ergs/s.

Whitlock, L.↗
NASA NTRS1993

Small-scale structure of O2(+) and proton hydrates in a Noctilucent Cloud and polar mesospheric summer echo of August 9/10 1991 above Kiruna

A novel mass spectrometer designed to measure simultaneously positive ion composition in the mesosphere, was successfully launched during the NLC-91 project. Instruments supporting the mass spectrometer were a probed to measure both electrons and positive ions as well as a wave propagation experiment. The location of the Noctilucent Clouds (NLC) was determined by a particle impact sensor to detect secondary electrons and ions from the impact of NLC particle. The density of proton hydrates and of the related total ions is depleted in the NLC region at 83 km. An improved detection limit of 5 x 10(exp 4)/cu m for positive ions and improved height resolution revealed for the first time large gradients in the O2(+), H(+)(H2O)2 and H(+)(H2O)6 densities within a small height range of the order of 50 m. Such gradients at the altitude of NLC and Polar Mesospheric Summer Echoes (PMSE) are associated with strong variability of mesospheric water vapor, temperature and neutral air density.

Balsiger, F.↗
NASA NTRS1995

The Caltech airborne submillimeter SIS receiver

We have constructed a sensitive submillimeter receiver for the NASA Kuiper Airborne Observatory (KAO) which at present operates in the 500-750 GHz band. The DSB receiver noise temperature is about 5 h nu/k(sub B) over the 500-700 GHz range. This receiver has been used to detect H2O(18)O, HCl, and CH in interstellar molecular clouds, and also to search for C(+) emission from the highly redshifted galaxy (z = 2.3) IRAS 10214.

Zmuidzinas, Jonas↗
NASA NTRS1998

Observations of Total Lightning Associated with Severe Convection During the Wet Season in Central Florida

This paper will discuss findings of a collaborative lightning research project between National Aeronautics and Space Administration, the Massachusetts Institute of Technology and the National Weather Service office In Melbourne Florida. In August 1996, NWS/MLB received a workstation which incorporates data from the KMLB WSR-88D, Cloud to Ground (CG) stroke data from the National Lightning Detection Network (NLDN), and 3D volumetric lightning data collected from the Kennedy Space Centers' Lightning Detection And Ranging (LDAR) lightning system. The two primary objectives of this lightning workstation, called Lightning Imaging Sensor Data Applications Display (USDAD), are to: observe how total lightning relates to severe convective storm morphology over central Florida, and compare ground based total lightning data (LDAR) to a satellite based lightning detection system. This presentation will focus on objective #1. The LISDAD system continuously displays CG and total lighting activity overlaid on top of the KMLB composite reflectivity product. This allows forecasters to monitor total lightning activity associated with convective cells occurring over the central Florida peninsula and adjacent coastal waters. The LISDAD system also keeps track of the amount of total lightning data, and associated KMLB radar products with individual convective cells occurring over the region. By clicking on an individual cell, a history table displays flash rate information (CG and total lightning) in one minute increments, along with radar parameter trends (echo tops, maximum dBz and height of maximum dBz) every 5 minutes. This history table Is updated continuously, without user intervention, as long as the cell is identified. Reviewing data collected during the 1997 wet season (21 cases) revealed that storms which produced severe weather (hall greater or = 0.75 in. or wind damage) typically showed a rapid rise In total lightning prior to the onset of severe weather. On average, flash rate increases of 25 FPM per minute over a time scale of approximately 5 minutes were common. These pulse severe storms typically reached values of 150 to 200 FPM with some cells exceeding 400 FPM. One finding which could have a direct application to the warning process is that the rapid increase in lightning typically occurred in advance of the warning issuance time. Comparisons between the ending time of the rapid rate increase and the time of when the warning was issued by NWS/MLB meteorologist exhibited a lead time of 8 minutes. It is conceivable that if close monitoring of the LISDAD system by operational meteorologist is routinely performed, warnings for pulse severe storms could be issued up to 4 to 6 minutes earlier than what is issued currently.

Sharp, D.↗
NASA NTRS2000

Science Writers' Guide to TERRA

The launch of NASA's Terra spacecraft marks a new era of comprehensive monitoring of the Earth's atmosphere, oceans, and continents from a single space-based platform. Data from the five Terra instruments will create continuous, long-term records of the state of the land, oceans, and atmosphere. Together with data from other satellite systems launched by NASA and other countries, Terra will inaugurate a new self-consistent data record that will be gathered over the next 15 years. The science objectives of NASAs Earth Observing System (EOS) program are to provide global observations and scientific understanding of land cover change and global productivity, climate variability and change, natural hazards, and atmospheric ozone. Observations by the Terra instruments will: provide the first global and seasonal measurements of the Earth system, including such critical functions as biological productivity of the land and oceans, snow and ice, surface temperature, clouds, water vapor, and land cover; improve our ability to detect human impacts on the Earth system and climate, identify the "fingerprint" of human activity on climate, and predict climate change by using the new global observations in climate models; help develop technologies for disaster prediction, characterization, and risk reduction from wildfires, volcanoes, floods, and droughts, and start long-term monitoring of global climate change and environmental change.

Source record↗
NASA NTRS1995

Thermal Balance in Dense Molecular Clouds: Radiative Cooling Rates and Emission-Line Luminosities

We consider the radiative cooling of fully shielded molecular astrophysical gas over a wide range of temperatures ( 10 K < T < 2500 K) and H2 densities ( 10(exp 3)/cc < n(H2) < 10(exp 10)/cc). Our model for the radiative cooling of molecular gas includes a detailed treatment of the interstellar chemistry that determines the abundances of important coolant molecules, and a detailed treatment of the excitation of the species H2, CO, H2O, HCl, O2, C, O, and their isotopic variants where important. We present results for the total radiative cooling rate and for the cooling rate due to individual coolant species, as a function of the gas temperature, density, and optical depth. We have also computed the individual millimeter, submillimeter, and far-infrared line strengths that contribute to the total radiative cooling rate, and we have obtained example spectra for the submillimeter emission expected from molecular cloud cores. Many of the important cooling lines will be detectable using the Infrared Space Observatory and the Submillimeter Wave Astronomy Satellite.

Neufeld, David A.↗
NASA NTRS2007

Phototransistors Development and their Applications to Lidar

Custom-designed two-micron phototransistors have been developed using Liquid Phase Epitaxy (LPE), Molecular Beam Epitaxy (MBE) and Metal-Organic Chemical Vapor Deposition (MOCVD) techniques under Laser Risk Reduction Program (LRRP). The devices were characterized in the Detector Characterization Laboratory at NASA Langley Research Center. It appears that the performance of LPE- and MBE-grown phototransistors such as responsivity, noise-equivalent-power, and gain, are better than MOCVD-grown devices. Lidar tests have been conducted using LPE and MBE devices under the 2-micrometer CO2 Differential Absorption Lidar (DIAL) Instrument Incubator Program (IIP) at the National Center for Atmospheric Research (NCAR), Boulder, Colorado. The main focus of these tests was to examine the phototransistors performances as compared to commercial InGaAs avalanche photodiode by integrating them into the Raman-shifted Eye-safe Aerosol Lidar (REAL) operating at 1.543 micrometers. A simultaneous measurement of the atmospheric backscatter signals using the LPE phototransistors and the commercial APD demonstrated good agreement between these two devices. On the other hand, simultaneous detection of lidar backscatter signals using MBE-grown phototransistor and InGaAs APD, showed a general agreement between these two devices with a lower performance than LPE devices. These custom-built phototransistors were optimized for detection around 2-micrometer wavelength while the lidar tests were performed at 1.543 micrometers. Phototransistor operation at 2-micron will improve the performance of a lidar system operating at that wavelength. Measurements include detecting hard targets (Rocky Mountains), atmospheric structure consisting of cirrus clouds and boundary layer. These phototransistors may have potential for high sensitivity differential absorption lidar measurements of carbon dioxide and water vapor at 2.05-micrometers and 1.9-micrometers, respectively.

Abedin, M. N.↗
NASA NTRS2013

Ground and Space-Based Measurement of Rocket Engine Burns in the Ionosphere

On-orbit firings of both liquid and solid rocket motors provide localized disturbances to the plasma in the upper atmosphere. Large amounts of energy are deposited to ionosphere in the form of expanding exhaust vapors which change the composition and flow velocity. Charge exchange between the neutral exhaust molecules and the background ions (mainly O+) yields energetic ion beams. The rapidly moving pickup ions excite plasma instabilities and yield optical emissions after dissociative recombination with ambient electrons. Line-of-sight techniques for remote measurements rocket burn effects include direct observation of plume optical emissions with ground and satellite cameras, and plume scatter with UHF and higher frequency radars. Long range detection with HF radars is possible if the burns occur in the dense part of the ionosphere. The exhaust vapors initiate plasma turbulence in the ionosphere that can scatter HF radar waves launched from ground transmitters. Solid rocket motors provide particulates that become charged in the ionosphere and may excite dusty plasma instabilities. Hypersonic exhaust flow impacting the ionospheric plasma launches a low-frequency, electromagnetic pulse that is detectable using satellites with electric field booms. If the exhaust cloud itself passes over a satellite, in situ detectors measure increased ion-acoustic wave turbulence, enhanced neutral and plasma densities, elevated ion temperatures, and magnetic field perturbations. All of these techniques can be used for long range observations of plumes in the ionosphere. To demonstrate such long range measurements, several experiments were conducted by the Naval Research Laboratory including the Charged Aerosol Release Experiment, the Shuttle Ionospheric Modification with Pulsed Localized Exhaust experiments, and the Shuttle Exhaust Ionospheric Turbulence Experiments.

Bernhardt, P. A.↗
NASA NTRS2017

The Diffuse Interstellar Bands: Solving a Century Old Problem

The Diffuse Interstellar Bands (DIBs) are a set of apporoximately 500 absorption bands that are seen in the spectra of reddened stars (i.e., stars obscured by the presence of interstellar clouds in their line of sight). The first DIBs were detected in the visible over a century ago. Diffuse Interstellar Bands are now detected from the near ultraviolet to the near infrared in the spectra of reddened stars spanning a variety of interstellar environments in our local, and in other galaxies. Although DIB carriers are a significant part of the interstellar chemical inventory as they account for a noticeable fraction of the interstellar extinction, the nature of their carriers is still unknown over a century after the detection of the first bands. DIB carriers are stable and ubiquitous in a broad variety of interstellar environments and play a unique role in interstellar physics and chemistry. It has long been realized that the solving of the DIB problem requires a strong synergy between astronomical observations, laboratory astrophysics and astrochemistry, quantum chemistry calculations and astrophysical modeling of line-of-sights. In this review, we'll present and discuss the current state of this perplexing problem. We'll review the progress and the failures that have been encountered in the long quest for the identification of the carriers of these ubiquitous interstellar bands.

Molecules in Space↗
DOE OSTI2025

Enhancing Cluster Identification in Atom Probe Tomography Data Using Transfer Learning

Atom Probe Tomography (APT) is a powerful technique for visualizing the atomic-scale distribution of solutes in materials, but quantitative cluster analysis of APT datasets remains a challenge due to the need for subjective parameter selection in clustering algorithms. While distance-based and density-based methods such as HDBSCAN are widely used, their performance is highly sensitive to user-defined parameters, which undermines reproducibility and accuracy. This study proposes an image-based, deep learning-aided workflow for automating parameter selection and cluster detection in APT data analysis. By projecting 3D APT point clouds onto 2D planes, we leverage pretrained convolutional neural networks (ConvNeXt-Tiny and ResNet-50) through transfer learning to predict the number of clusters present in synthetic datasets. The output is used to guide K-means clustering and estimate HDBSCAN parameters, specifically minimum cluster size and minimum sample points. This approach reduces reliance on manual parameter tuning, improving consistency and scalability. The methodology demonstrates the feasibility of using image-based deep learning for interpreting complex spatial patterns in APT data, enabling faster and more objective analysis. The complete workflow and code are made publicly available to support reproducibility and future research.

Density-based clustering↗