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At least 1,135 records · Page 63

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DOE OSTI2023

Real-time latent heat emission during dynamic-compression freezing of water

Abstract Dynamic compression studies have been used to study the nucleation kinetics of water to ice VII for decades. Diagnostics such as photon Doppler velocimetry, transmission loss, and imaging have been used to measure pressure/density, and phase fraction, while temperature has remained the difficult thermodynamic property to quantify. In this work, we measured pressure/density and implemented a diagnostic to measure the temperature. In doing so the temperature shows quasi-isentropically compressed liquid water forms ice at pressures below the previously defined metastable limit, and the liquid phase is not hypercoooled as previously thought above that limit. Instead, the latent heat raises the temperature to the liquid-ice-VII melt line, where it remains with increasing pressure. We propose a hypothesis to corroborate these results with previous work on dynamic compression freezing. These results provide constraints for nucleation models, and suggest this technique be used to investigate phase transitions in other materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS1972

Early-type stars and the mean-square electron density in the galactic disk.

An assessment is made of the total supply of ionizing photons from hot stars, within several hundred parsecs of the sun. The resulting photoionized H II regions probably contribute an average emission measure of the order of 5 pc per cm to the 6th power, through the galactic disk; this is smaller than other recent estimates.

Richstone, D. O.↗

NASA NTRS1973

X-ray spectrum of the entire Cygnus Loop.

The spectrum of the entire Cygnus Loop has been obtained using gas-filled proportional counters and filters flown on a Nike-Aerobee rocket. The results indicate an average spectral temperature of (2.8 plus or minus 0.2) x 1,000,000 K and the presence of excess emission in the energy range from 0.530 to 0.693 keV. If the excess emission originates in a single line at 0.658 keV, the intensity at the earth corresponds to 1.8 plus or minus 0.7 photons per sq cm per sec, or about 10% of the total energy received from the Loop. The spectrum of the entire Loop is found to be attenuated by an average of (4.8 plus or minus 0.2) x 10 to the 20th hydrogen atoms per sq cm.

Stevens, J. C.↗

NASA NTRS1977

Ultraviolet observations of 3C 273 by the ANS

Five-band spectrophotometry between rest wavelengths of 1340 A and 2850 A is presented. The 2200-A absorption feature seems to be present in 3C 273 with a depth appropriate for an internal reddening of E(B-V) = 0.13. The dereddened ultraviolet flux distribution can be described by a power law of spectral index 1.21. This power law can account for the observed flux in X-rays. It provides more photons than needed to excite the observed H-beta by photoionization and Fe II lines by resonance fluorescence. The emission-line flux ratios, Ly-alpha/C IV/ semiforbidden C III/H-beta are 100/80/60/10.

Wu, C.-C.↗

NASA NTRS1978

The acceleration of high-velocity clouds in supernova remnants

Interstellar clouds passed by blast waves emanating from supernova explosions will be accelerated by the ram pressure of the expanding interior shocked gas. We present numerical and analytical solutions for cloud acceleration in this environment, comparing the results with recent observations of faint, high-velocity (greater than 100 km/sec) filaments observed in Cygnus and Vela. Photons from the conductive interface between the clouds and the surrounding medium can provide the ionizing flux necessary for observable optical emission. Several predictions are made, the most important of which is that fast clouds of neutral hydrogen with column densities of about 10 quintillion per sq cm should be observable in 21 cm studies of SNRs.

Mckee, C. F.↗

NASA NTRS1978

Extreme ultraviolet spectrum of a hot interstellar plasma

The EUV (100-1000 A) spectrum of an optically thin plasma over the temperature range 100,000-10 million K is calculated, and the effects of free-free, free-bound, and two-photon continuum radiation are considered. The resulting spectra are presented in graphical form, with a separate tabulation of intensities for the emission lines. Results in the 100-200 A region are compared with those of other workers, and the major sources of uncertainty in this type of calculation are discussed. The applicability of the results to EUV observations of the interstellar medium are also mentioned.

Stern, R.↗

NASA NTRS1979

Thin-film scintillators for extended ultraviolet /UV/ response silicon detectors

The preparation and radiometric properties of silicon detectors coated with fluorescent thin films are described. The films are deposited from solutions of clear plastics, such as acrylic resins, polyvinyl toluene or polystyrene, and of organic laser dyes in a common solvent. They are optically clear, mechanically and chemically stable, yet easily applied and removed. Multiple doped films of a few microns thickness exhibit broad-band absorption from less than 250 nm to about 450 nm and narrow band emissions with peaks ranging from 380 nm to 600 nm. Internal quantum efficiencies are close to 100 percent and fluorescence decay times are in the nanosecond range. When deposited on optically denser media, a large fraction of the fluorescent emission is trapped in the substrate. Silicon photodiodes coated with multiple doped films exhibit high external quantum efficiencies and virtually flat photon response in the near UV.

Viehmann, W.↗

NASA NTRS1980

Atmospheric Emission Photometric Imaging on Spacelab (AEPI)

Two parallel detector systems are used for atmospheric emission photometric emission. The top system is a TV system using the image intensified S.E.C. tube as the detector. The bottom system, the photon counting array (P.C.A.), uses a microchannel plate intensified anode array tube and is equivalent to a 100 channel photomultiplier. For the television, the filters are selected by means of a filter wheel set. The field of view of the is interchangeable between 20 and 6 degrees, by means of a moveable prism. The quartz window mu channel plate intensifier is fiber optically coupled to a 40-25 demagnifying tube which is in turn coupled to the S.E.C. tube. The PCA channel has a fixed field of view of 4 deg and a remote control interchangeable photometric converter optics which converts the imaging array into a multichannel photometer. The mu channel plate array tube amplifies the photons into detectable counts for the PCA electronics. The entire system is pointed by a two axis gimbal. The flight equipment to be acquired consists of a gyro package and an interactive flight control unit panel. The gyro package is necessary because of the inadequate attitude reference supplied by the current Spacelab systems.

Mende, S. B.↗

NASA NTRS1984

CN and C2H in IRC +10216

The effects of the production of the radicals CN and C2H from the dissociation of HCN and C2H2 by ambient UV photons in the outer envelope of IRC +10216 are investigated. The spatial distribution of the radicals and their observable millimeter emission-line characteristics are calculated from the inferred abundances of the progenitor species in the envelope of IRC +10216 using photochemical and radiative transfer models. These are compared with available observations to examine whether photoproduction is a possible explanation of the observed emission from these species. The results suggest that the variable abundances induced by photodestruction of their progenitors do affect the observed emission from the radicals.

Huggins, P. J.↗

NASA NTRS1986

A two-dimensional intensified photodiode array for imaging spectroscopy

The Johns Hopkins University is currently developing an instrument to fly aboard NASA's Space Shuttle as a Spartan payload in the late 1980s. This Spartan free flyer will obtain spatially resolved spectra of faint extended emission line objects in the wavelength range 750-1150 A at about 2-A resolution. The use of two-dimensional photon counting detectors will give simultaneous coverage of the 400 A spectral range and the 9 arc-minute spatial resolution along the spectrometer slit. The progress towards the flight detector is reported here with preliminary results from a laboratory breadboard detector, and a comparison with the one-dimensional detector developed for the Hopkins Ultraviolet Telescope. A hardware digital centroiding algorithm has been successfully implemented. The system is ultimately capable of 15-micron resolution in two dimensions at the image plane and can handle continuous counting rates of up to 8000 counts/s.

Tennyson, P. D.↗

NASA NTRS1990

Imaging other planetary systems from the moon

This paper studies the problem of using a telescope like the HST, only larger and sensitive to a wider range of wavelengths, to image systems of planets like the solar system around other stars. Both reflected starlight and thermal radiation from the planets are treated. The instrumental effects of aperture diffraction, scattering due to the power spectral density of telescope mirror surface errors, and telescope thermal emission are included. The integration time required to achieve a signal-to-noise ratio is computed at 5 for photon-statistical random errors only, which is a necessary but not sufficient criterion for detection at a confidence level of five standard deviations. A cold telescope on the moon with 16m aperture and the optical quality of HST could detect and characterize planets around nearby stars.

Brown, Robert A.↗

NASA NTRS1993

Pulsed high-energy gamma rays from PSR 1055-52

The Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory has detected a high-energy gamma-ray source at a position coincident with that of the radio pulsar PSR 1055-52. Analysis of the EGRET data at the radio pulsar period of 197 ms has revealed pulsed gamma-radiation at energies above 300 MeV, making PSR 1055-52 the fifth detected high-energy gamma-ray pulsar. The pulsed radiation from PSR 1055-52 has a very hard photon spectral index of -1.18 +/- 0.16 and a high efficiency for converting its rotational energy into gamma-rays. No unpulsed emission was observed.

Fierro, J. M.↗

NASA NTRS1999

A Direct Comparison Between EUV Coronal Flux and Helium Resonance Line Photon Flux from SOHO/CDS Data

In the wealth of EUV spectroscopic and imaging data gathered by the SOHO and TRACE missions, a prominent role is played by the helium resonance emission. For example, He I lines are among the most intense features in CDS/NIS spectra, while the EIT 304 waveband (dominated by He II emission) is routinely employed to map the structure of the solar chromosphere and transition region. However, no 'standard' model has emerged so far that is able to interpret observed He spectra/images to a satisfactory degree of self-consistency. Recent research on the problem of the formation of the solar helium spectrum tends to rule out a dominant role of coronal radiation in exciting He resonance lines. However, while evidence for this result is strong, it is based on indirect tests. Here we present a preliminary assessment of this issue based on a more direct approach, which involves a measure with CDS/GIS of the photoionizing EUV radiation. This measure can be directly compared with the observed flux in the main He I and He II resonance lines observed with CDS/NIS2.

Andretta, V.↗

NASA NTRS2001

First Astronomical Use Of Multiplexed Transition Edge Bolometers

We present performance results based on the first astronomical use of multiplexed superconducting bolometers. The Fabry-Perot Interferometer Bolometer Research Experiment (FIBRE) is a broadband submillimeter spectrometer that achieved first light in June 2001 at the Caltech Submillimeter Observatory (CSO). FIBRE's detectors are superconducting transition edge sensor (TES) bolometers read out by a SQUID multiplexer. The Fabry-Perot uses a low resolution grating to order sort the incoming light. A linear bolometer array consisting of 16 elements detects this dispersed light, capturing five orders simultaneously from one position on the sky. With tuning of the Fabry-Perot over one free spectral range, a spectrum covering delta-lamda/lamda = 1/7 at a resolution of delta-lamda/lamda = 1/1200 can be acquired. This spectral resolution is sufficient to resolve doppler broadened line emission from external galaxies. FIBRE operates in the 350 micrometer and 450 micrometer bands. These bands cover line emission from the important PDR tracers neutral carbon [CI] and carbon monoxide (CO). We have verified that the multiplexed bolometers are photon noise limited even with the low power present in moderate resolution spectrometry.

Benford, D. J.↗

NASA NTRS2003

Strategies for Studying the Sources of Gamma Ray Bursts

The study of gamma ray bursts (GRBs) has rapidly evolved in recent years with the discovery of their cosmological nature and with BATSE, BeppoSAX, HETE and the IPN enabling a wide variety of associated . afterglow measurements. Multiwavelength observations ranging through the radio, optical, soft and hard x-ray, and gamma-ray regimes have exploded the field of GRB interpretation. Also, the Amanda, Milagro and LIGO experiments can search for related neutrino, cosmic-ray photon, and gravitational radiation events, even with the delayed alerts, such as from the IPN. The infrared region, where the optical emissions from sources at the extreme distances may be shifted, will become important but is undersubscribed. The soon-to-be launched Swift mission will greatly broaden the GRB discipline, and a strategy for associated ground-based measurements is outlined. The need for the improved global distribution of all instruments, in particular, robotic infrared detectors, is cited.

Cline, T. L.↗

NASA NTRS2013

Iodine Tagging Velocimetry and Mechanism in the Hypersonic Near Wake of a MultiPurpose Crew Vehicle

This study demonstrates a new molecular tagging velocimetry (MTV) method for velocity measurements of high speed flow. It demonstrates offbody Iodine Tagging Velocimetry (ITV) in the hypersonic near wake of a MultiPurpose Crew Vehicle (MPCV) model. Experiments are performed in the NASA-Langley 31-inch Mach 10 air wind tunnel. A 0.5% I2 / N2 mixture is seeded on the leeward backshell of the model using a pressure tap. I2 laser-induced fluorescence is excited along a 5.5 mm line using an ArF excimer laser near 193 nm. Results indicate I2 absorbs at least 2 photons to produce iodine ions and electrons. These recombine as the tagged region is displaced downstream to produce I (2P3/2) whose emission is monitored at 206 nm. Results at P0 = 2.41 MPa (350 psi), T0 = 990K, and 10 micro-sec transit times produce velocities from 630-820 m/sec across the I2 seeded jet at a distance of 38.2 mm (25.5 jet diameters) downstream from the jet orifice. Maximum wake jet velocities near the shear layer are 59% of freestream velocity.

Balla, R. Jeffrey↗

DOE OSTI2022

Refractory solar selective coatings

Selective receiver coatings provide high performance for concentrated solar power applications. The solar selective coating provides high solar absorptivity (90% or greater) with low IR emissivity (0.1 or less) while maintaining stability at temperatures greater than 700° C. The coating comprises a composite of a mesoporous photonic matrix with a conformal optical coating. One example composite coating includes a mesoporous photonic coating comprising a plurality of particles having sizes between 100 nm and 2000 nm, and a conformal optical coating formed by Atomic Layer Deposition (ALD) that infiltrates the mesoporous structure of the photonic coating and comprises metal nanoparticles and an amorphous dielectric matrix.

14 SOLAR ENERGY↗

DOE OSTI2023

A Leptonic Model for Neutrino Emission From Active Galactic Nuclei

It is often stated that the observation of high-energy neutrinos from an astrophysical source would constitute a smoking gun for the acceleration of hadronic cosmic rays. Here, we point out that there exists a purely leptonic mechanism to produce TeV-scale neutrinos in astrophysical environments. In particular, very high-energy synchrotron photons can scatter with X-rays, exceeding the threshold for muon-antimuon pair production. When these muons decay, they produce neutrinos without any cosmic-ray protons or nuclei being involved. In order for this mechanism to be efficient, the source in question must produce very high-energy photons which interact in an environment that is dominated by keV-scale radiation. As an example, we consider the active galaxy NGC 1068, which IceCube has recently detected as a source of TeV-scale neutrinos. We find that the neutrino emission observed from this source could potentially be generated through muon pair production for reasonable choices of physical parameters.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗