SEARCH · Engineering Papers

Results for “Flux Measurement”

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.

SourceResearch connectionFrom yearThrough year

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

At least 649 records · Page 36

All sources NASA NTRS DOE OSTI

NASA NTRS1980

Light ion concentrations and fluxes in the polar regions during magnetically quiet times

Ion concentrations, flow velocities, and fluxes, measured by the ion mass spectrometer on the Isis 2 satellite for periods around the solstices and equinoxes of 1971 and 1972, have been used in a study of the polar wind morphology during magnetically quiet times. The results confirm the major tenets of polar wind theories; namely, that an upward flow of both H(+) and He(+) ions exists at all times over the entire polar region; H(+) fluxes are of the order of 10 to the 8th ions/sq cm s in both summer and winter polar regions. O(+) is the dominant ion specie at 1400-km altitude in regions of strong H(+) flows, and H(+) is depleted over the entire region where the polar wind flows. H(+) fluxes tend to be lower in winter than in summer, whereas He(+) fluxes are a factor of 10 higher in winter and tend to follow the neutral helium concentration near the F2 maximum. The latter agree well with model calculations of flux in the winter but lie above the model values by a factor of 2 in the summer. H(+) fluxes also agree well with ion flow models.

Hoffman, J. H.↗

NASA NTRS1985

Energetic solar particle fluxes out to 3 AU during the 7 May 1978 flare event

Simultaneous solar proton flux measurements on IMP 7 and by the world wide neutron monitor network during the May 7, 1978 flare event led to conclusions that in the energy range from 50 MeV to 10 GeV: (1) the propagation of the flare particles in the interplanetary magnetic field (IMF) between the Sun and the Earth was nearly scatter free; and (2) therefore, the intensity time (IT) profiles of the solar proton fluxes observed at Earth for about one hour after onset represent the solar injection profiles even to energies as low as 50 MeV. Observations of the IMF at Helios A indicate that the IMF was undisturbed between the Sun and Helios A at the time of the May 7, 1978 flare event; and, therefore, the solar particle propagation was also scatter free from the Sun to Helios A.

Lockwood, J. A.↗

NASA NTRS1983

Adiabatic expansion of cosmic ray sources and the consequences for secondary antiprotons

The low-energy antiproton flux measurement of Buffinton et al. (1981) is more than an order of magnitude higher than can be explained by interstellar production. It has been suggested that the excess antiprotons may be created by supernovae in very dense regions of ISM. These sources would provide the additional target material necessary to produce the excess cosmic ray antiprotons; in addition, adiabatic energy losses due to supernova expansion will increase the flux of low-energy antiprotons. The antiproton flux from such sources is examined here, with attention given to the energy loss effects of the adiabatic and collisional losses of both the primary and secondary cosmic ray fluxes. Ionization losses of the antiprotons are also considered.

Mauger, B. G.↗

NASA NTRS2001

Evolution of Iron K Alpha Line Emission in the Black Hole Candidate GX 339-4

GX 339-4 was regularly monitored with the Rossi X-Ray Timing Explorer during a period (in 1999) when its X-ray flux decreased significantly (from 4.26 x 10(exp -10) to 7.6 x 10(exp -12) ergs in the 3-20 keV band), as the source settled into the 'off state.' Our spectral analysis revealed the presence of a prominent iron K alpha line in the observed spectrum of the source for all observations. The line shows an interesting evolution: it is centered at approx. 6.4 keV when the measured flux is above 5 x 10(exp -1) ergs per sq cm/s but is shifted to approx. 6.7 keV at lower fluxes. The equivalent width of the line appears to increase significantly toward lower fluxes, although it is likely to be sensitive to calibration uncertainties. While the fluorescent emission of neutral or mildly ionized iron atoms in the accretion disk can perhaps account for the 6.4 keV line, as is often invoked for black hole candidates, it seems difficult to understand the 6.7 keV line with this mechanism because the disk should be less ionized at lower fluxes (unless its density changes drastically). On the other hand, the 6.7 keV line might be due to a recombination cascade of hydrogen- or helium-like iron ions in an optically thin, highly ionized plasma. We discuss the results in the context of proposed accretion models.

Feng, Y. X.↗

DOE OSTI2024

Interactions Between Climate and Species Drive Future Forest Carbon and Water Balances

Global change is altering forest carbon and water balances; however, the extent to which tree species shape ecosystem‐scale responses to climate, particularly in biodiverse forests, remains unclear. To address this, we simulated the effects of an envelope of future climate conditions on watershed carbon and water balances and quantified the contributions of tree species based on their xylem anatomy. We accomplished this by incorporating species‐level transpiration calculations into a landscape‐scale ecosystem process model. Our revised model linked the effects of forest succession, species composition, and climate change on water and carbon. Calibration of forest water fluxes using sap flux measurements and catchment water balances captured variability in species transpiration and interannual ET in biodiverse, humid temperate forest catchments in the southern Blue Ridge Mountains, USA. Across wet and dry future climate projections, ET increased, and streamflow and net carbon uptake decreased, particularly under a scenario of increasing drought. Despite accounting for just 30% of current biomass, diffuse‐porous tree species were the main driver of carbon and water flux responses now and in the future, thus intensifying the increase in ET and decline in streamflow. As diffuse‐porous biomass continues to increase, these forests will be increasingly sensitive to drought, amplifying losses of carbon sequestration and freshwater delivery.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1979

Observations of the diffuse interstellar EUV radiation field

Results are reported for observations and a preliminary theoretical analysis of the diffuse interstellar EUV radiation field exhibiting positive measurable fluxes in the wavelength range from 912 to 1150 A. The observations were made with the UV spectrometers on the two Voyager spacecraft, and a spectral half-width of 30 A was obtained. The procedures used in the analysis are described in detail, particularly those relating to the elimination of thermal and cosmic-ray noise, internal instrumental scattering from bright lines, and possible contributions from direct starlight. Measurements in several directions reveal diffuse intensities at 975 A ranging from a maximum of about 10 to the -7th erg/sq cm per (sec sr A) near the galactic plane to an upper limit of 10 to the -8th erg/sq cm per (sec sr A). A comparison of the present measurements with various theoretical predictions and previous measurements indicates reasonable agreement with some theoretical predictions of the interstellar EUV intensity.

Sandel, B. R.↗

NASA NTRS1986

Atmospheric methane sources - Alaskan tundra bogs, an alpine fen, and a subarctic boreal marsh

Methane (CH4) flux measurements from Alaska tundra bogs, an alpine fen, and a subarctic boreal marsh were obtained at field sites ranging from Prudhoe Bay on the coast of the Arctic Ocean to the Alaskan Range south of Fairbanks during August 1984. In the tundra, average CH4 emission rates varied from 4.9 mg CH4 per sq m per day (moist tundra) to 119 mg CH4 per sq m per day (waterlogged tundra). Fluxes averaged 40 mg CH4 per sq m per day from wet tussock meadows in the Brooks Range and 289 mg Ch4 per sq m per day from an alpine fen in the Alaskan Range. The boreal marsh had an average CH4 emission rate of 106 mg CH4 per sq m per day. Significant emissions were detected in tundra areas where peat temperatures were as low as 4 C, and permafrost was only 25 cm below the ground surface. Emission rates from the 17 sites sampled were found to be logarithmically related to water levels at the sites. Extrapolation of the data to an estimate of the total annual CH4 emission from all arctic and boreal wetlands suggests that these ecosystems are a major source of atmospheric CH4 and could account for up to 23 percent of global CH4 emissions from wetlands.

Sebacher, D. I.↗

NASA NTRS1990

Long-term monitoring of the earth's radiation budget; Proceedings of the Meeting, Orlando, FL, Apr. 17, 18, 1990

The uses of the broadband flux measurements as well as the improvements in the Earth Radiation Budget Experiment in instrumentation and data reduction are summarized. Scientific uses of earth-radiation budget data are discussed, along with a perspective on the instrumentation giving a new foundation for studies of the radiation budget, with emphasis on calibration and long-term stability. Cloud identification and angular modeling are covered including angular dependence models for radiance to flux conversion and the pattern recognition of clouds and ice in polar regions. The surface-radiation budget and atmospheric radiative flux divergence from the Clouds and Earth Radiant Energy System are covered, and time dependence of the earth's radiation fields, determination of the outgoing longwave radiation and its diurnal variations are considered.

Barkstrom, Bruce R.↗

DOE OSTI2022

Constraining the charge-, time-, and rigidity-dependence of cosmic-ray solar modulation with AMS-02 observations during Solar Cycle 24

Our basic theoretical understanding of the sources of cosmic rays and their propagation through the interstellar medium is hindered by the Sun, that through the solar wind affects the observed cosmic-ray spectra. This effect is known as solar modulation. Recently released cosmic-ray observations from the Alpha Magnetic Spectrometer (AMS-02) and publicly available measurements of the solar wind properties from the Advanced Composition Explorer and the Wilcox observatory allow us to test the analytical modeling of the time-, charge- and rigidity-dependence of solar modulation. We rely on associating measurements on the local heliospheric magnetic field and the heliospheric current sheet’s tilt angle, to model the time-dependence and amplitude of cosmic-ray solar modulation. We find evidence for the solar modulation’s charge- and rigidity-dependence during the era of solar cycle 24. Our analytic prescription to model solar modulation can explain well the large-scale time evolution of positively charged cosmic-ray fluxes in the range of rigidities from 1 GV to 10 GV. Here, we also find that cosmic-ray electron fluxes measured during the first years of cycle 24 are less trivial to explain, due to the complex and rapidly evolving structure of the heliosphere’s magnetic field that they experienced as they propagated inwards.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS1992

Time-averaged heat transfer and pressure measurements and comparison with prediction for a two-stage turbine

Time-averaged Stanton number and surface-pressure distributions are reported for the first-stage vane row and the first-stage blade row of the Rocketdyne Space Shuttle Main Engine two-stage fuel-side turbine. These measurements were made at 10 percent, 50 percent, and 90 percent span on both the pressure and suction surfaces of the component. Stanton-number distributions are also reported for the second-stage vane at 50 percent span. A shock tube is used as a short-duration source of heated and pressurized air to which the turbine is subjected. Platinum thin-film gages are used to obtain the heat-flux measurements and miniature silicone-diaphragm pressure transducers are used to obtain the surface pressure measurements. The first-stage vane Stanton number distributions are compared with predictions obtained using a quasi-3D Navier-Stokes solution and a version of STAN5. This same N-S technique was also used to obtain predictions for the first blade and the second vane.

Dunn, M. G.↗

NASA NTRS1983

Selective nonresonant acceleration of He-3(2+) and heavy ions by H(+) cyclotron waves

The model advanced by Fisk (1978) to explain the anomalous enhancements in the abundance of some ionic species in energetic solar particle flux measurements at about 1 AU is revised by including the proper nonlinear physics of particle energization by electrostatic ion cyclotron (EIC) waves. The revised model contains two basic concepts by Fisk: the energization by EIC waves and the need for a second stage acceleration. There is no need for exciting He-4(2+) cyclotron waves, since the dominant process is nonresonant and can be accomplished by hydrogen cyclotron waves. The A/Q selectivity in the flux available for energization in the second stage process enters through the nonlinear saturation level, which in conventional theories depends on the current that drives the instabilities.

Varvoglis, H.↗

NASA NTRS1981

Stagnation region gas film cooling: Spanwise angled injection from multiple rows of holes

The stagnation region of a cylinder in a cross flow was used in experiments conducted with both a single row and multiple rows of spanwise angled (25 deg) coolant holes for a range of the coolant blowing ratio with a freestream to wall temperature ratio approximately equal to 1.7 and R(eD) = 90,000. Data from local heat flux measurements are presented for injection from a single row located at 5 deg, 22.9 deg, 40.8 deg, 58.7 deg from stagnation using a hole spacing ratio of S/d(o) = 5 and 10. Three multiple row configurations were also investigated. Data are presented for a uniform blowing distribution and for a nonuniform blowing distribution simulating a plenum supply. The data for local Stanton Number reduction demonstrated a lack of lateral spreading by the coolant jets. Heat flux levels larger than those without film cooling were observed directly behind the coolant holes as the blowing ratio exceeded a particular value. The data were spanwise averaged to illustrate the influence of injection location, blowing ratio and hole spacing. The large values of blowing ratio for the blowing distribution simulating a plenum supply resulted in heat flux levels behind the holes in excess of the values without film cooling. An increase in freestream turbulence intensity from 4.4 to 9.5 percent had a negligible effect on the film cooling performance.

Luckey, D. W.↗

NASA NTRS1993

Streamwise vorticity generation and mixing enhancement in free jets by delta-tabs

The effect of triangular tabs, placed at the nozzle exit, on the evolution of free jets is investigated. The effect, a large distortion of the jet cross section and a resultant increase in mixing downstream, has been inferred before to be due to a pair of streamwise vortices originating from each tab. In this paper, the generation mechanism of the stream wise vorticity (omega sub x) is considered first. Two sources are postulated. One is the upstream 'pressure hill', produced by the tab, which appears to be the dominant source. Another is due to vortex filaments shed from the sides of the tab and reoriented downstream by the mean shear of the mixing layer. In the case of a 'delta-tab', a triangular tab with its apex leaning downstream, vorticity from the two sources explain the stronger effect in that configuration. Data on the vorticity evolution for the effect of two delta-tabs are presented, up to twelve jet diameters from the exit, which show that the streamwise vortices persist even at the farthest measurement station. The magnitude of omega sub x-maximum decays continually with distance from the nozzle, its ratio to azimuthal vorticity maximum is found to be about 1/5 everywhere. The relative effect of a delta-tab on jets from an axisymmetric nozzle and a 8:1 rectangular nozzle is also studied. The mixing layer distortion is found to be less pronounced in the rectangular case. The jet mixing, as manifested by the mass flux measured at a downstream station, is increased in the axisymmetric jet but it is decreased in the rectangular jet under consideration by the delta-tab.

Zaman, K. B. M. Q.↗

NASA NTRS1993

Streamwise vorticity generation and mixing enhancement in free jets by 'delta-tabs'

The effect of triangular tabs, placed at the nozzle exit, on the evolution of free jets is investigated. The effect, a large distortion of the jet cross section and a resultant increase in mixing downstream, has been inferred before to be due to a pair of streamwise vortices originating from each tab. In this paper, the generation mechanism of the streamwise vorticity (omega sub x) is considered first. Two sources are postulated. One is the upstream 'pressure hill', produced by the tab, which appears to be the dominant source. Another is due to vortex filaments shed from the sides of the tab and reoriented downstream by the mean shear of the mixing layer. In the case of a 'delta-tab', a triangular tab with its apex leaning downstream, vorticity from the two sources explain the stronger effect in that configuration. Data on the vorticity evolution for the effect of two delta-tabs are presented, up to twelve jet diameters from the exit, which show that the streamwise vortices persist even at the farthest measurement station. The magnitude of omega sub x-maximum decays continually with distance from the nozzle, its ratio to azimuthal vorticity maximum is found to be about 1/5 everywhere. The relative effect of a delta-tab on jets from an axisymmetric nozzle and a 8:1 rectangular nozzle is also studied. The mixing layer distortion is found to be less pronounced in the rectangular case. The jet mixing, as manifested by the mass flux measured at a downstream station, is increased in the axisymmetric jet but it is decreased in the rectangular jet under consideration by the delta-tab.

Zaman, K. B. M. Q.↗

DOE OSTI2024

Coordinated JWST Imaging of Three Distance Indicators in a Supernova Host Galaxy and an Estimate of the Tip of the Red Giant Branch Color Dependence

Boasting a 6.5 m mirror in space, JWST can increase by several times the number of supernovae (SNe) to which a redshift-independent distance has been measured with a precision distance indicator (e.g., tip of the red giant branch (TRGB) or Cepheids); the limited number of such SN calibrators currently dominates the uncertainty budget in distance ladder Hubble constant (H 0 ) experiments. JWST/NIRCAM imaging of the Virgo Cluster galaxy NGC 4536 is used here to preview JWST program GO-1995, which aims to measure H 0 using three stellar distance indicators (Cepheids, TRGB, and J-branch asymptotic giant branch/carbon stars). Each population of distance indicator was here successfully detected—with sufficiently large number statistics, well-measured fluxes, and characteristic distributions consistent with ingoing expectations—so as to confirm that we can acquire distances from each method precise to about 0.05 mag (statistical uncertainty only). We leverage overlapping Hubble Space Telescope imaging to identify TRGB stars, crossmatch them with the JWST photometry, and present a preliminary constraint on the slope of the TRGB's F115W versus (F115W – F444W) relation equal to -0.99 ± 0.16 mag mag -1 . This slope is consistent with prior slope measurements in the similar Two Micron All-Sky Survey J band, as well as with predictions from the BaSTI isochrone suite. We use the new TRGB slope estimate to flatten the 2D TRGB feature and measure a (blinded) TRGB distance relative to a set of fiducial TRGB colors, intended to represent the absolute fiducial calibrations expected from geometric anchors such as NGC 4258 and the Magellanic Clouds. In doing so, we empirically demonstrate that the TRGB can be used as a standardizable candle at the IR wavelengths accessible with JWST.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2024

AmeriFlux Measurement Component Instrument Handbook

An AMC system was installed at the Atmospheric Radiation Measurement (ARM) Climate Research Facility’s North Slope Alaska (NSA) Barrow site, also known as NSA C1 at the ARM Data Archive, in August 2012. A second AMC system was installed at the third ARM Mobile Facility deployment at Oliktok Point, also known as NSA M1. This in situ system consists of 12 combination soil temperature and volumetric water content (VWC) reflectometers and one set of upwelling and downwelling PAR sensors, all deployed within the fetch of the Eddy Correlation Flux Measurement System. Soil temperature and VWC sensors placed at two depths (10 and 30 cm below the vegetation layer) at six locations (or microsites) allow soil property inhomogeneity to be monitored across a landscape. The soil VWC and temperature sensors used at NSA C1 are the Campbell Scientific CS650L and the sensors at NSA M1 use the Campbell Scientific CS655. The two sensors are nearly identical in function, and vendor specifications are based on the CS650 unless otherwise stated.

47 OTHER INSTRUMENTATION↗

NASA NTRS1991

Anode power deposition in an applied-field segmented anode MPD thruster

Anode heat flux measurements of a water cooled segmented anode applied-field MPD thruster were made to investigate anode heat transfer phenomena. Pure argon and argon-hydrogen mixtures were used as propellants for a variety of thruster currents, propellant mass flow rates, and axial applied magnetic field strengths. The thruster was operated in two modes; with all four segments active, and with two of the segments floating. In addition, thrust and specific impulse were determined for each operating condition. The results show that the heat flux to the anode increases monotonically with axial magnetic field strength and thruster current. Between 50 and 75 percent of the anode heat flux is transported by the current carrying electrons. Convective and radiative heat transfer account for the remaining portion of the power deposited in the anode. The addition of hydrogen to the argon propellant results in the reduction of the fraction of anode power deposited by the anode fall to a level equivalent to that deposited by convection and radiation.

Myers, R. M.↗

DOE OSTI2024

Data Acquisition System Selection and Calibration of Resistive Moisture Content Measurements for Large-Scale Field Studies in Cold Climate Residential Building Envelope Performance

The residential building stock built before the energy codes were enforced has several significant inefficiency problems in terms of insulation and air leakage. To decrease these inefficiencies, building retrofits are necessary. However, if the envelope is not appropriately designed, excessive accumulation of moisture content and thus mold formation and decay inside the envelope layers can be a vital problem. This risk becomes higher, especially in extreme climate conditions such as cold winters and hot and humid summers as in some northern regions of the U.S. Field studies are essential to test the long-term hygrothermal performance of building envelopes. Although in-situ temperature, RH, and heat flux measurements are straightforward, moisture content measurements are cumbersome. Mainly, because of the heterogeneous nature of the wood materials, deviations and nonuniformities within the materials are unavoidable. Resistance measurements are one of the oldest methods used to measure the moisture content of wood and other building materials. In large-scale studies, it is commonly preferred to use multi-purpose data acquisition systems (DAQ) and custom-made or prefabricated moisture pins to measure the electrical resistance (and thus moisture content) of critical building materials. These multi-purpose DAQ systems generally provide lower costs and offer more flexibility. However, these systems require calibration and fine-tuning to achieve accurate moisture content measurements. A large-scale, two-year-long field study was conducted in northern Minnesota to monitor the hygrothermal performance of residential retrofit wall systems in cold climates. Two base case walls and sixteen different wall treatments were tested. Moisture contents were measured at various layers in each wall treatment using 85 sets of moisture pins. This paper focuses on the overall approach, fabrication, and calibration methodology for the combination of custom-made moisture pins and a multi-purpose DAQ. The aim is to directly use the low-excitation multi-purpose DAQ without any extra voltage regulator. A half-bridge circuit is used to measure wood resistance with 4V excitation voltage and 100 kΩ and 500 kΩ reference resistors. The system is calibrated for four different materials: Douglas fir, lodgepole pine, western red cedar, and oriented strand board (OSB). Calibration experiments were done under controlled conditions in 50% and 65% RH test chambers. Resistance-based moisture content calibration curves are obtained for each species. Results show that higher reference resistors provided better calibration curves for lower excitation voltages.

Desjarlais, Andre Omer↗