Search NASA⌕ Search

SEARCH · Search NASA

Results for “LIGHT EMISSION”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Relationship of EUV Irradiance Coronal Dimming Slope and Depth to Coronal Mass Ejection Speed and Mass

Extreme ultraviolet (EUV) coronal dimmings are often observed in response to solar eruptive events. These phenomena can be generated via several different physical processes. For space weather, the most important of these is the temporary void left behind by a coronal mass ejection (CME). Massive, fast CMEs tend to leave behind a darker void that also usually corresponds to minimum irradiance for the cooler coronal emissions. If the dimming is associated with a solar are, as is often the case, the are component of the irradiance light curve in the cooler coronal emission can be isolated and removed using simultaneous measurements of warmer coronal lines. We apply this technique to 37dimming events identified during two separate two-week periods in 2011, plus an event on 2010 August 7 analyzed in a previous paper, to parameterize dimming in terms of depth and slope. We provide statistics on which combination of wavelengths worked best for the flare-removal method, describe the fitting methods applied to the dimming light curves, and compare the dimming parameters with corresponding CME parameters of mass and speed. The best linear relationships found are nu(sub CME) [km/s] approx. equals 2.36 x 10 6 [km/%] x s(sub dim) [%/s] m(sub CME) [g] approx. equals 2.59 x 10(exp.15 [g/%] x the square root of d(sub dim) [%].These relationships could be used for space weather operations of estimating CME mass and speed using near-real-time irradiance dimming measurements.

Mason, James Paul↗
NASA NTRS1976

Effect of air temperature and relative humidity at various fuel-air ratios on exhaust emissions on a per-mode basis of an Avco Lycoming 0-320 DIAD light aircraft engine. Volume 2: Individual data points

A carbureted four cylinder air cooled 0-320 DIAD Lycoming aircraft engine was tested to establish the effects of air temperature and humidity at various fuel-air ratios on the exhaust emissions on a per-mode basis. The test conditions included carburetor lean-out at air temperatures of 50, 59, 80, and 100 F at relative humidities of 0, 30, 60, and 80 percent. Temperature-humidity effects at the higher values of air temperature and relative humidity tested indicated that the HC and CO emissions increased significantly, while the NOx emissions decreased. Even at a fixed fuel-air ratio, the HC emissions increase and the NOx emissions decrease at the higher values of air temperature and humidity. Volume II contains the data taken at each of the individual test points.

Skorobatckyi, M.↗
NASA NTRS1978

Effect of Air Temperature and Relative Humidity at Various Fuel-Air Ratios on Exhaust Emissions on a Per-Mode Basis of an AVCO Lycoming 0-320 Diad Light Aircraft Engine: Volume 1: Results and Plotted Data

A carbureted four cylinder air cooled 0-320 DIAD Lycoming aircraft engine was tested to establish the effects of air temperature and humidity at various fuel-air ratios on the exhaust emissions on a per-mode basis. The test conditions include carburetor lean out at air temperatures of 50, 59, 80, and 100 F at relative humidities of 0, 30, 60, and 80 percent. Temperature humidity effects at the higher values of air temperature and relative humidity tested indicated that the HC and CO emissions increased significantly, while the NOx emissions decreased. Even at a fixed fuel air ratio, the HC emissions increase and the NOx emissions decrease at the higher values of air temperature and humidity.

Skorobatckyi, M.↗
NASA NTRS2004

Subsurface Sampling and Sensing Using Burrowing Moles

Finding evidence for life on Mars will likely require accessing the subsurface since the Martian surface is both hostile to life and to preservation of biosignatures due to the cold dry conditions, the strong W environment, and the presence of strong oxidants. Systems are needed to probe beneath the sun and oxidant baked surface of Mars and return samples to the surface for analysis or to bring the instrument sensing underground. Recognizing this need, the European Space Agency incorporated a small subsurface penetrometer or Mole onto the Beagle 2 Mars lander. Had the 2003 landing been successful, the Mole would have collected samples from 1-1.5 m depth and delivered them to an organic analysis instrument on the surface. The de- vice called the Planetary Underground Tool (PLUTO), also measured soil mechanical and thermophysical properties. Constrained by the small mass and volume allowance of the Beagle lander, the PLUTO mole was a slender cylinder only 2 cm diameter and 28 cm long equipped with a small sampling device designed to collect samples and bring them to the surface for analysis by other instrument. The mass of the entire system including deployment mechanism and tether was 1/2 kg. sensor package underground to make in situ measurements. The Mars Underground Mole (MUM) is a larger Mole based on the PLUTO design but incorporating light collection optics that interface to a fiber optic cable in the tether that transmits light to a combined stimulated emission Raman Spectrometer and Short Wave Infrared (SWIR) reflectance Spectrometer with sensitivity from 0.7 to 2.5 micrometers. This instrument is called the Dual Spectral Sensor and uses a Digital Array Scanning Interferometer as the sensor technology, a type of fourier transform interferometer that uses fixed element prisms and thus is highly rugged compared to a Michaelson interferometer. Due to the size limitations of an on-Mole instrument compartment, and the availability of a tether, the sensor head, light sources, and control electronics for the instrument are on the surface. The DSS sensor is capable of sensing a wide range of minerals relevant to Mars Astrobiology objectives including hydrated minerals, clays, carbonates, sulfates, and ice. Additionally, Raman spectroscopy is effective for detecting organics. The MUM is designed to achieve a maximum depth of penetration of 5 m in Mars regolith and can be repeatedly deployed and retrieved. The ability to perform repeated sampling, combined with the low mass and power requirements, means that Moles could be incorporated into a rover mission as well as used on a stationary platform. The Mole mechanism is a pointed slender cylinder that advances into soil by way of an internal sliding hammer mechanism. Part of the energy released by the spring-loaded hammer with each shock is transferred to the Mole casing and from there to the soil, resulting in penetration by displacing and compressing the surrounding soil. A backwards-directed impulse as a re- action to each forward shock is transferred via a suppressor mass against a second weaker spring allowing forward motion without requiring reactive forces provided by the lander. The Mole tip can be opened to collect soil samples. The Mole casing is tethered to a supporting mechanism that supplies power. Components supporting the Mole on the surface include a launch tube, tether reel and winch for pulling in tether, in addition to the tether itself.

Stoker, C. R.↗
NASA NTRS1997

The Environmental Impact of Intra-Cluster Medium on the Interstellar Medium in Early Type Galaxies

High resolution X-ray images of three early type galaxies observed with the ROSAT HRI are presented. Data for NGC 1553 and NGC 5846 indicate that the emission is highly irregular, with interesting features on scales from a few arcsec to a few arcmin. The gas temperatures also vary both with the galactocentric radius and in correspondence to regions of higher emission and denser material. Strikingly similar features are observed in the X-ray and H(alpha) morphologies of NGC 1553 and NGC 5846, while smoother, more regular isophotes are observed in NGC 4649 at both wavelengths. A connection between these two kinds of emission therefore seems likely. In the light of our observations we discuss possible scenarios that can and account for the connection between X-ray and H(alpha) emissions.

Trinchieri, Ginevra↗
NASA NTRS1988

Infrared supernova light curves and asymmetric stellar mass loss

Infrared dust emission echos from Type II supernovae are a natural consequence of the heating of circumstellar dust by the supernova light. Red supergiants, the likely progenitors of most Type II supernovae, are known in some cases to have asymmetric circumstellar envelopes. It is noted that an asymmetric dust distribution can have a substantial effect on the evolution of an infrared echo and results are presented for an ellipsoidal dust distribution. The angle between the symmetry axis and the line of sight is unknown in any particular case so that detailed observations of a number of supernovae will be necessary to test for asymmetries. Asymmetries may also be observable in the radio structure of supernovae and in a possible scattered-light echo.

Emmering, Robert T.↗
NASA NTRS2012

Modeling Phase-Aligned Gamma-Ray and Radio Millisecond Pulsar Light Curves

Since the discovery of the first eight gamma-ray millisecond pulsars (MSPs) by the Fermi Large Area Telescope, this population has been steadily expanding. Four of the more recent detections, PSR J00340534, PSR J1939+2134 (B1937+21; the first MSP ever discovered), PSR J1959+2048 (B1957+20; the first discovery of a black widow system), and PSR J2214+3000, exhibit a phenomenon not present in the original discoveries: nearly phase-aligned radio and gamma-ray light curves (LCs). To account for the phase alignment, we explore models where both the radio and gamma-ray emission originate either in the outer magnetosphere near the light cylinder or near the polar caps. Using a Markov Chain Monte Carlo technique to search for best-fit model parameters, we obtain reasonable LC fits for the first three of these MSPs in the context of altitude-limited outer gap (alOG) and two-pole caustic (alTPC) geometries (for both gamma-ray and radio emission). These models differ from the standard outer gap (OG)/two-pole caustic (TPC) models in two respects: the radio emission originates in caustics at relatively high altitudes compared to the usual conal radio beams, and we allow both the minimum and maximum altitudes of the gamma-ray and radio emission regions to vary within a limited range (excluding the minimum gamma-ray altitude of the alTPC model, which is kept constant at the stellar radius, and that of the alOG model, which is set to the position-dependent null charge surface altitude). Alternatively, phase-aligned solutions also exist for emission originating near the stellar surface in a slot gap scenario (low-altitude slot gap (laSG) models). We find that the alTPC models provide slightly better LC fits than the alOG models, and both of these give better fits than the laSG models (for the limited range of parameters considered in the case of the laSG models). Thus, our fits imply that the phase-aligned LCs are likely of caustic origin, produced in the outer magnetosphere, and that the radio emission for these pulsars may come from close to the light cylinder. In addition, we were able to constrain the minimum and maximum emission altitudes with typical uncertainties of 30% of the light cylinder radius. Our results therefore describe a third gamma-ray MSP subclass, in addition to the two previously found by Venter et al.: those with LCs fit by standard OG/TPC models and those with LCs fit by pair-starved polar cap models.

Venter, C.↗
NASA NTRS1993

Variations of the ultraviolet Fe II and Balmer continuum emission in the Seyfert galaxy NGC 5548

We present measurements of the Balmer continuum/Fe II emission blend between 2160 and 4130 A in the Seyfert galaxy NGC 5548. The measurements are from spectra obtained as part of the combined space-based and ground-based monitoring program of this object in 1988-1989. An iterative scheme is used to determine and subtract the continuum emission underlying the emission blend so as to obtain a light curve sampled once every four days. The small blue bump is an important component of the emission-line cooling, constituting about one third of the line flux in this object. Its flux varies with an amplitude of approximately +/- 20 percent about the mean, similar to the amplitude of the Balmer line variations during the same period. Its light curve resembles that of Ly-alpha, with a lag of about 10 days behind the continuum variations. The bump variation amplitude is independent of the wavelength interval where it is measured, which indicates that both the Balmer continuum and Fe II emission have comparable variation amplitudes. These results suggest that the Fe II UV multiplets and the Balmer continuum are emitted in the same parts of the broad-line region as most other broad emission lines in this object.

Maoz, D.↗
NASA NTRS1987

Chromospheric-coronal activity at saturated levels

High-resolution IUE observations of Mg II emission lines in W Ursae Majoris were obtained. In addition, estimates of the Mg II emission for other F-type contact binaries were obtained using archival high-resolution k line spectra and some nonstandard methods; the available data were compiled for Mg II, C IV, and X-ray emission in main-sequence F, G, K, and M dwarfs in order to determine the upper levels of radiation from their chromospheric-coronal plasma. The high-resolution IUE observations of Mg II h and k emission lines in W UMa indicate that both components of the contact binary have similar chromospheres, confirming the many earlier low-resolution light curve studies. The Mg II emission (L Mg II)/Lbol) of contact binaries correlates with the Rossby number (R0), forming an extension of single G-K dwarfs.

Vilhu, Osmi↗
NASA NTRS2009

Zinc Alloys for the Fabrication of Semiconductor Devices

ZnBeO and ZnCdSeO alloys have been disclosed as materials for the improvement in performance, function, and capability of semiconductor devices. The alloys can be used alone or in combination to form active photonic layers that can emit over a range of wavelength values. Materials with both larger and smaller band gaps would allow for the fabrication of semiconductor heterostructures that have increased function in the ultraviolet (UV) region of the spectrum. ZnO is a wide band-gap material possessing good radiation-resistance properties. It is desirable to modify the energy band gap of ZnO to smaller values than that for ZnO and to larger values than that for ZnO for use in semiconductor devices. A material with band gap energy larger than that of ZnO would allow for the emission at shorter wavelengths for LED (light emitting diode) and LD (laser diode) devices, while a material with band gap energy smaller than that of ZnO would allow for emission at longer wavelengths for LED and LD devices. The amount of Be in the ZnBeO alloy system can be varied to increase the energy bandgap of ZnO to values larger than that of ZnO. The amount of Cd and Se in the ZnCdSeO alloy system can be varied to decrease the energy band gap of ZnO to values smaller than that of ZnO. Each alloy formed can be undoped or can be p-type doped using selected dopant elements, or can be n-type doped using selected dopant elements. The layers and structures formed with both the ZnBeO and ZnCdSeO semiconductor alloys - including undoped, p-type-doped, and n-type-doped types - can be used for fabricating photonic and electronic semiconductor devices for use in photonic and electronic applications. These devices can be used in LEDs, LDs, FETs (field effect transistors), PN junctions, PIN junctions, Schottky barrier diodes, UV detectors and transmitters, and transistors and transparent transistors. They also can be used in applications for lightemitting display, backlighting for displays, UV and visible transmitters and detectors, high-frequency radar, biomedical imaging, chemical compound identification, molecular identification and structure, gas sensors, imaging systems, and for the fundamental studies of atoms, molecules, gases, vapors, and solids.

Ryu, Yungryel↗
NASA NTRS1993

Optical and Hubble Space Telescope ultraviolet spectropolarimetry of 3C 273 and PG 1114+445

New optical spectropolarimetry and broad-band measurements, made during periods when the linear polarization of the quasar 3C 273 was no greater than 1 pct, are combined with ultraviolet polarization measurements made with the Faint Object Spectrograph of the Hubble Space Telescope. Very weak UV polarization during the time of observation is seen in the HST measurements, which is consistent with the completely unpolarized UV continuum and emission lines. Optical spectropolarimetry, however, reveals polarized light, the source of which is consistent with a nonthermal component, diluted by other unpolarized emission sources, such as the 'big blue bump'. Optical spectropolarimetry of the radio-quiet quasar PG 1114+445 is also presented. The polarization of this QSO is thought to result from scattering by dust external to the narrow-line region. 3C 273 and PG 1114+445 are useful in illustrating the range of polarizing mechanisms which can operate in low-polarization QSOs.

Smith, Paul S.↗
NASA NTRS1995

Extreme ultraviolet light curves of UZ Fornacis: Evidence for accretion stream absorption and vertical extent of the accretion spot

We report on two pointed observations of UZ For carried out by the imaging photometers aboard the Extreme Ultraviolet Explorer (EUVE), one as part of the EUVE Right Angle Program and one as an off-axis source during a guest observation. Both observations lasted approximately 3 days and covered a total of 72 orbits of the UZ For binary providing multiple coverage of all the orbital phases of UZ For. The resulting high signal-to-noise phase-folded light curve strongly constrains the emission and absorption geometry of UZ For. We have detected a narrow absorption dip that we attribute to the accretion stream at the location of the stagnation region many white dwarf radii away from the accretion spot and have also detected a broad dip caused by absorption much closer to the white dwarf surface. Both absorption effects are variable in time and phase. Based on the timescales of M-star eclipse ingress and egress, the angular spot size is constrained to be less than 5 deg; thus the ratio of spot area to white dwarf surface area is less than or equal to 0.0005. To explain the light curve phase duration given this small angular spot size, the extreme-ultraviolet (EUV) accretion spot must be raised vertically by approximately 5% of the white dwarf radius.

Warren, John K.↗
NASA NTRS1989

Observations of the diffuse UV radiation field

Spectra are presented for the diffuse UV radiation field between 1250 to 3100 A from eight different regions of the sky, which were obtained with the Johns Hopkins UVX experiment. UVX flew aboard the Space Shuttle Columbia (STS-61C) in January 1986 as part of the Get-Away Special project. The experiment consisted of two 1/4 m Ebert-Fastie spectrometers, covering the spectral range 1250 to 1700 A at 17 A resolution and 1600 to 3100 A at 27 A resolution, respectively, with a field of view of 4 x .25 deg, sufficiently small to pick out regions of the sky with no stars in the line of sight. Values were found for the diffuse cosmic background ranging in intensity from 300 to 900 photons/sq cm/sec/sr/A. The cosmic background is spectrally flat from 1250 to 3100 A, within the uncertainties of each spectrometer. The zodiacal light begins to play a significant role in the diffuse radiation field above 2000 A, and its brightness was determined relative to the solar emission. Observed brightnesses of the zodiacal light in the UV remain almost constant with ecliptic latitude, unlike the declining visible brightnesses, possibly indicating that those (smaller) grains responsible for the UV scattering have a much more uniform distribution with distance from the ecliptic plane than do those grains responsible for the visible scattering.

Murthy, Jayant↗
NASA NTRS2008

Observation of Solar Wind Charge Exchange Emission from Exospheric Material in and Outside Earth's Magnetosheath

A long XMM-Newton exposure is used to observe solar wind charge exchange (SWCX) emission from exospheric material in and outside Earth s magnetosheath. The light curve of the O VII (0.5-0.62 keV) band is compared with a model for the expected emission, and while the emission is faint and the light curve has considerable scatter, the correlation is significant to better than 99.9%. This result demonstrates the validity of the geocoronal SWCX emission model for predicting a contribution to astrophysical observations to a scale factor of order unity (1.36). The results also demonstrate the potential utility of using X-ray observations to study global phenomena of the magnetosheath which currently are only investigated using in situ measurements.

Snowden, S. L.↗
NASA NTRS2009

Observation of Solar Wind Charge Exchange Emission From Exospheric Material in and Outside Earth's Magnetosheath 2008 September 25

A long XMM-Newton exposure is used to observe solar wind charge exchange (SWCX) emission from exospheric material in and outside Earth's magnetosheath. The light curve of the O vii (0.5-0.62 keV) band is compared with a model for the expected emission, and while the emission is faint and the light curve has considerable scatter, the correlation is significant to better than 99.9%. This result demonstrates the validity of the geocoronal SWCX emission model for predicting a contribution to astrophysical observations to a scale factor of order unity (1.5). In addition, an average value of the SWCX O vii emission from the magnetosheath over the observation of 2.6 +/- 0.5 LU is derived. The results also demonstrate the potential utility of using X-ray observations to study global phenomena of the magnetosheath which currently are only investigated using in situ measurements.

Snowden, S. L.↗
NASA NTRS2015

Testing Dissipative Magnetosphere Model Light Curves and Spectra with Fermi Pulsars

We explore the emission properties of a dissipative pulsar magnetosphere model introduced by Kalapotharakos et al. comparing its high-energy light curves and spectra, due to curvature radiation, with data collected by the Fermi LAT. The magnetosphere structure is assumed to be near the force-free solution. The accelerating electric field, inside the light cylinder (LC), is assumed to be negligible, while outside the LC it rescales with a finite conductivity (sigma). In our approach we calculate the corresponding high-energy emission by integrating the trajectories of test particles that originate from the stellar surface, taking into account both the accelerating electric field components and the radiation reaction forces. First, we explore the parameter space assuming different value sets for the stellar magnetic field, stellar period, and conductivity. We show that the general properties of the model are in a good agreement with observed emission characteristics of young gamma-ray pulsars, including features of the phase-resolved spectra. Second, we find model parameters that fit each pulsar belonging to a group of eight bright pulsars that have a published phase-resolved spectrum. The sigma values that best describe each of the pulsars in this group show an increase with the spin-down rate (E˙ ) and a decrease with the pulsar age, expected if pair cascades are providing the magnetospheric conductivity. Finally, we explore the limits of our analysis and suggest future directions for improving such models.

acceleration of particles↗
NASA NTRS1990

Ground-based studies of emission-line variability: Recent results for NGC 5548 and future plans

Ever since emission-line variability was first detected in AGNs, it has been clearly understood that light-travel time effects in the broadline region (BLR) afford a tool for studying the structure of these spatially unresolved regions. However, only within the last few years has the observational problem become well defined in terms of the sampling rates and quality of data necessary to address the problem correctly. The amount of data required to extract structural information about the BLR from the continuum and emission-line light curves is so considerable that the most promising approach seemed to be to combine the observational efforts. The goal was to work together to produce a large, high-quality database which would then be released to individual investigators for more complete analysis. The cornerstone of this effort, was a joint NASA/ESA/SERC program to monitor the spectrum of NGC 5548 every four days with IUE from December 1988 through August 1988. A concurrent ground-based program was organized in an effort to enhance the scientific return on the project by extending the wavelength coverage and providing higher spectral resolution and signal to noise ratios than would be possible with IUE. It also turned out that the temporal resolution of the ground-based program was somewhat better than the temporal resolution of the IUE program, and the temporal baseline is longer and continues to grow. The database and initial results are presented by Peterson et al., (1991). The important results of the ground-based program are summarized, some additional applications of the existing data are described, and a few comments are made on what can be done in the future to expand on this work.

Peterson, Bradley M.↗
NASA NTRS1995

Simultaneous UV, optical and radio monitoring of the BL Lac object OJ 287 in March 1993

The BL Lacertae object OJ 287 was intensively monitored with the IUE satellite from 1993 March 15 to 20 in the 2000-3000 A wavelength region. The very low emission state of the source hampered the detection during part of the 23 performed exposures. The light curve at 2650 A constructed with the 11 best images exhibits a variable trend with a factor is less than or approximately 2 enhancement of the flux in about 3 hours. Simultaneous ground based observations show an optical flux variability of smaller amplitude, but correlated with the UV light curve without any apparent lag. The radio light curve is nearly constant. The UV emission state is the weakest observed in 15 years for this flaring blazard, being a factor of less than orapproximately 20 lower than the maximum recorded one.

Pian, E.↗