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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.

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At least 1,189 records · Page 66
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Application of THz probe radiation in low-coherent tomographs based on spatially separated counterpropagating beams

A principle of designing a high-resolution low-coherent THz tomograph, which makes it possible to investigate media with a high spatial resolution (in the range λ{sub 0} – 2λ{sub 0}, where λ{sub 0} is the average probe wavelength) is considered. The operation principle of this tomograph implies probing a medium by radiation with a coherence length of 8λ{sub 0} and recording a hologram of a focused image of a fixed layer of this medium using spatially separated counterpropagating object and reference beams. Tomograms of the medium studied are calculated using a temporal approach based on application of the time correlation function of probe radiation. (terahertz radiation)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Effect of the laser spot shape on spatial distribution of the ion bunch accelerated in a superstrong field

We have investigated the effect of the laser spot shape on the spatial distribution of accelerated ions on the front and back sides of a thin target irradiated by a picosecond laser pulse having the intensity of (3 – 4) × 10{sup 18} W cm{sup -2}. Experimental data are compared with numerical calculations. It is shown that the spatial structure of the ion bunch on the front side of the target resembles the laser spot structure rotated by 90°. (interaction of laser radiation with matter. laser plasma)

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

X-ray optical system for imaging laser plumes with a spatial resolution of up to 70 nm

We consider an X-ray optical system which permits obtaining laser plume images at a wavelength of 13.5 nm with a resolution of up to 70 nm. The X-ray optical system comprises an X-ray Schwarzschild objective made up of two aspherical multilayer mirrors, a scintillator (YAG : Ce ceramics), which converts X-rays to the visible radiation, and a visible-optical system, which images the scintillator surface onto a CCD camera. The spatial resolution of the system is limited by the resolution of the optical system (0.7 μm) and the magnification (10{sup ×}) of the X-ray objective and is as high as 70 nm. The effect of Schwarzschild objective mirror shapes on the spatial resolution is analysed. The profile of concave mirror aspherisation is considered, which provides the attainment of the diffraction-limited quality of the objective. Data are given for the quantum efficiency of the system at a wavelength of 13.5 nm. We describe the experimental test bench intended for studying the developed X-ray optical system and outline the first experimental data which illustrate its efficiency. Owing to the natural division into the 'X-ray' and 'visible' parts, the optical system under discussion permits an easy change of the magnification and the field of view without realigning the X-ray optical elements. The wavelength may be varied in a range between 3 and 40 nm by changing the multilayer mirrors. (extreme laser radiation: physics and fundamental applications)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Measurement accuracy and spatial resolution of a distributed temperature sensor based on a two-pulse differential coherent reflectometer

We present a model and numerical simulation of a distributed temperature sensor based on a two-pulse differential coherent optical time-domain reflectometer (COTDR). The differential phase measured using a phase-sensitive Rayleigh reflectometer is shown to have a regular component, which is a linear function of temperature, and a random component, which is related to a random distribution of scattering centres in the fibre and restricts the accuracy of measurements of variations in temperature. Measurement accuracy can be improved by reducing the relative contribution of the random component via a decrease in pulse duration and/or an increase in the time delay between pulses. The spatial resolution of a differential two-pulse phase-sensitive reflectometer is shown to be determined by the time delay between pulses and to vary little with pulse duration. At a typical pulse duration (200 ns) and delay time (300 ns), the accuracy in measurements of variations in temperature in the 0.1-K range is 2 % and the spatial resolution is about 30 m. (fibre-optic sensors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Recent Studies on the Asymptotic Convergence of the Spatial Discretization for Two-Dimensional Discrete Ordinates Solutions

In this paper, four types of quadrature schemes are used to define discrete directions in the solution of a two-dimensional fixed-source discrete ordinates problem in Cartesian geometry. Such schemes enable generating numerical results for averaged scalar fluxes over specified regions of the domain with high number (up to 105) of directions per octant. Two different nodal approaches, the ADO and AHOT-N0 methods, are utilized to obtain the numerical results of interest. The AHOT-N0 solutions on a sequence of refined meshes are then used to develop an asymptotic analysis of the spatial discretization error in order to derive a reference solution. It was more clearly observed that the spatial discretization error converges asymptotically with second order for the source region with all four quadratures employed, while for the other regions refined meshes along with tighter convergence criterion must be applied to evidence the same behavior. Although, in that case, some differences among the four quadrature schemes results were found.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2013

THE MASSIVE STAR POPULATION IN M101. I. THE IDENTIFICATION AND SPATIAL DISTRIBUTION OF THE VISUALLY LUMINOUS STARS

An increasing number of non-terminal giant eruptions are being observed by modern supernova and transient surveys. But very little is known about the origin of these giant eruptions and their progenitors, many of which are presumably very massive, evolved stars. Motivated by the small number of progenitors positively associated with these giant eruptions, we have begun a survey of the evolved massive star populations in nearby galaxies. The nearby, nearly face-on, giant spiral M101 is an excellent laboratory for studying a large population of very massive stars. In this paper, we present BVI photometry obtained from archival HST/ACS Wide Field Camera images of M101. We have produced a catalog of luminous stars with photometric errors <10% for V < 24.5 and 50% completeness down to V ∼ 26.5 even in regions of high stellar crowding. Using color and luminosity criteria, we have identified candidate luminous OB-type stars and blue supergiants, yellow supergiants, and red supergiants for future observation. We examine their spatial distributions across the face of M101 and find that the ratio of blue to red supergiants decreases by two orders of magnitude over the radial extent of M101 corresponding to 0.5 dex in metallicity. We discuss the resolved stellar content in the giant star-forming complexes NGC 5458, 5453, 5461, 5451, 5462, and 5449 and discuss their color-magnitude diagrams in conjunction with the spatial distribution of the stars to determine their spatio-temporal formation histories.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Spatial structure of sunspot oscillations observed with SDO/AIA

The spatial structure of sunspot oscillations and its variation with frequency and height have been studied using data from SDO/AIA for two well-developed sunspots observed in 2010. Computation of potential magnetic fields together with line-of-sight and vector magnetograms from SDO/HMI allowed us to interpret discovered features of spatial structure. Namely, we have found that (1) expansion of the magnetic field lines above the sunspot causes a gradual broadening of the area occupied by the 3 minute oscillations with height, and (2) variation of magnetic field inclination across the sunspot causes a decrease in the pulsation frequency with distance from the center of the umbra. We have shown that the transformation from 3 minute umbral oscillations to 5 minute penumbral waves can be explained by variation of the acoustic cutoff frequency across the sunspot.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

THE SPATIAL DISTRIBUTION OF DUST AND STELLAR EMISSION OF THE MAGELLANIC CLOUDS

We study the emission by dust and stars in the Large and Small Magellanic Clouds, a pair of low-metallicity nearby galaxies, as traced by their spatially resolved spectral energy distributions. This project combines Herschel Space Observatory PACS and SPIRE far-infrared photometry with other data at infrared and optical wavelengths (the data were obtained as part of the HERschel Inventory of The Agents of Galaxy Evolution survey; PI: M. Meixner). We build maps of dust, stellar luminosity, and mass of both Magellanic Clouds, and analyze the spatial distribution of dust/stellar luminosity and mass ratios. These ratios vary considerably throughout the galaxies, generally between the range 0.01 {<=} L{sub dust}/L{sub *} {<=} 0.6 and 10{sup -4} {<=} M{sub dust}/M{sub *} {<=} 4 Multiplication-Sign 10{sup -3}. We observe that the dust/stellar ratios depend on the interstellar medium environment, such as the distance from currently or previously star-forming regions, and on the intensity of the interstellar radiation field. In addition, we construct star formation rate (SFR) maps, and find that the SFR is correlated with the dust/stellar luminosity and dust temperature in both galaxies, demonstrating the relation between star formation, dust emission, and heating, though these correlations exhibit substantial scatter.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

RESOLVED DEPLETION ZONES AND SPATIAL DIFFERENTIATION OF N{sub 2}H{sup +} AND N{sub 2}D{sup +}

We present a study on the spatial distribution of N{sub 2}D{sup +} and N{sub 2}H{sup +} in 13 protostellar systems. Eight of thirteen objects observed with the IRAM 30 m telescope show relative offsets between the peak N{sub 2}D{sup +} (J = 2 {yields} 1) and N{sub 2}H{sup +} (J = 1 {yields} 0) emission. We highlight the case of L1157 using interferometric observations from the Submillimeter Array and Plateau de Bure Interferometer of the N{sub 2}D{sup +} (J = 3 {yields} 2) and N{sub 2}H{sup +} (J = 1 {yields} 0) transitions, respectively. Depletion of N{sub 2}D{sup +} in L1157 is clearly observed inside a radius of {approx}2000 AU (7'') and the N{sub 2}H{sup +} emission is resolved into two peaks at radii of {approx}1000 AU (3.''5), inside the depletion region of N{sub 2}D{sup +}. Chemical models predict a depletion zone in N{sub 2}D{sup +} and N{sub 2}H{sup +} due to destruction of H{sub 2}D{sup +} at T {approx} 20 K and the evaporation of CO off dust grains at the same temperature. However, the abundance offsets of 1000 AU between the two species are not reproduced by chemical models, including a model that follows the infall of the protostellar envelope. The average abundance ratios of N{sub 2}D{sup +} to N{sub 2}H{sup +} have been shown to decrease as protostars evolve by Emprechtinger et al., but this is the first time depletion zones of N{sub 2}D{sup +} have been spatially resolved. We suggest that the difference in depletion zone radii for N{sub 2}H{sup +} and N{sub 2}D{sup +} is caused by either the CO evaporation temperature being above 20 K or an H{sub 2} ortho-to-para ratio gradient in the inner envelope.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Fast and Furious: Shock heated gas as the origin of spatially resolved hard X-ray emission in the central 5 kpc of the galaxy merger NGC 6240

We have obtained a deep, subarcsecond resolution X-ray image of the nuclear region of the luminous galaxy merger NGC 6240 with Chandra, which resolves the X-ray emission from the pair of active nuclei and the diffuse hot gas in great detail. We detect extended hard X-ray emission from kT ∼ 6 keV (∼70 MK) hot gas over a spatial scale of 5 kpc, indicating the presence of fast shocks with a velocity of ∼2200 km s{sup –1}. For the first time, we obtain the spatial distribution of this highly ionized gas emitting Fe XXV, which shows a remarkable correspondence to the large-scale morphology of H{sub 2}(1-0) S(1) line emission and Hα filaments. Propagation of fast shocks originating in the starburst-driven wind into the ambient dense gas can account for this morphological correspondence. With an observed L {sub 0.5-8} {sub keV} = 5.3 × 10{sup 41} erg s{sup –1}, the diffuse hard X-ray emission is ∼100 times more luminous than that observed in the classic starburst galaxy M82. Assuming a filling factor of 1% for the 70 MK temperature gas, we estimate its total mass (M {sub hot} = 1.8 × 10{sup 8} M {sub ☉}) and thermal energy (E {sub th} = 6.5 × 10{sup 57} erg). The total iron mass in the highly ionized plasma is M {sub Fe} = 4.6 × 10{sup 5} M {sub ☉}. Both the energetics and the iron mass in the hot gas are consistent with the expected injection from the supernovae explosion during the starburst that is commensurate with its high star formation rate. No evidence for fluorescent Fe I emission is found in the CO filament connecting the two nuclei.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The two-dimensional spatial distributions of the globular clusters and low-mass X-ray binaries of NGC 4649

We report significant anisotropies in the projected two-dimensional (2D) spatial distributions of globular clusters (GCs) of the giant Virgo elliptical galaxy NGC 4649 (M60). Similar features are found in the 2D distribution of low-mass X-ray binaries (LMXBs), both associated with GCs and in the stellar field. Deviations from azimuthal symmetry suggest an arc-like excess of GCs extending north at 4-15 kpc galactocentric radii in the eastern side of major axis of NGC 4649. This feature is more prominent for red GCs, but still persists in the 2D distribution of blue GCs. High- and low-luminosity GCs also show some segregation along this arc, with high-luminosity GCs preferentially located in the southern end and low-luminosity GCs in the northern section of the arc. GC-LMXBs follow the anisotropy of red GCs, where most of them reside; however, a significant overdensity of (high-luminosity) field LMXBs is present to the south of the GC arc. These results suggest that NGC 4649 has experienced mergers and/or multiple accretions of less massive satellite galaxies during its evolution, of which the GCs in the arc may be the fossil remnant. We speculate that the observed anisotropy in the field LMXB spatial distribution indicates that these X-ray binaries may be the remnants of a star formation event connected with the merger, or maybe be ejected from the parent red GCs, if the bulk motion of these clusters is significantly affected by dynamical friction. We also detect a luminosity enhancement in the X-ray source population of the companion spiral galaxy NGC 4647. We suggest that these may be younger high mass X-ray binaries formed as a result of the tidal interaction of this galaxy with NGC 4649.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The next generation Virgo cluster survey. VIII. The spatial distribution of globular clusters in the Virgo cluster

We report on a large-scale study of the distribution of globular clusters (GCs) throughout the Virgo cluster, based on photometry from the Next Generation Virgo Cluster Survey (NGVS), a large imaging survey covering Virgo's primary subclusters (Virgo A = M87 and Virgo B = M49) out to their virial radii. Using the g{sub o}{sup ′}, (g' – i') {sub o} color-magnitude diagram of unresolved and marginally resolved sources within the NGVS, we have constructed two-dimensional maps of the (irregular) GC distribution over 100 deg{sup 2} to a depth of g{sub o}{sup ′} = 24. We present the clearest evidence to date showing the difference in concentration between red and blue GCs over the full extent of the cluster, where the red (more metal-rich) GCs are largely located around the massive early-type galaxies in Virgo, while the blue (metal-poor) GCs have a much more extended spatial distribution with significant populations still present beyond 83' (∼215 kpc) along the major axes of both M49 and M87. A comparison of our GC maps to the diffuse light in the outermost regions of M49 and M87 show remarkable agreement in the shape, ellipticity, and boxiness of both luminous systems. We also find evidence for spatial enhancements of GCs surrounding M87 that may be indicative of recent interactions or an ongoing merger history. We compare the GC map to that of the locations of Virgo galaxies and the X-ray intracluster gas, and find generally good agreement between these various baryonic structures. We calculate the Virgo cluster contains a total population of N {sub GC} = 67, 300 ± 14, 400, of which 35% are located in M87 and M49 alone. For the first time, we compute a cluster-wide specific frequency S {sub N,} {sub CL} = 2.8 ± 0.7, after correcting for Virgo's diffuse light. We also find a GC-to-baryonic mass fraction ε {sub b} = 5.7 ± 1.1 × 10{sup –4} and a GC-to-total cluster mass formation efficiency ε {sub t} = 2.9 ± 0.5 × 10{sup –5}, the latter values slightly lower than but consistent with those derived for individual galactic halos. Taken as a whole, our results show that the production of the complex structures in the unrelaxed Virgo cluster core (including the production of the diffuse intracluster light) is an ongoing and continuing process.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Spatially resolving the kinematics of the ≲100 μas quasar broad-line region using spectroastrometry

The broad-line region (BLR) of luminous active galactic nuclei (AGNs) is a prominent observational signature of the accretion flow around supermassive black holes, which can be used to measure their masses (M{sub BH}) over cosmic history. Due to the ≲100 μas angular size of the BLR, current direct constraints on BLR kinematics are limited to those provided by reverberation mapping studies, which are most efficiently carried out on low-luminosity (L) and low-redshift (z) AGNs. We analyze the possibility of measuring the BLR size and study its kinematic structure using spectroastrometry, whereby one measures the spatial position centroid of emission-line photons as a function of velocity. We calculate the expected spectroastrometric signal of a rotation-dominated BLR for various assumptions about the ratio of random to rotational motions and the radial distribution of the BLR gas. We show that for hyper-luminous quasars at z<2.5, the size of the low-ionization BLR can already be constrained with existing telescopes and adaptive optics systems, thus providing a novel method to spatially resolve the kinematics of the accretion flow at 10{sup 3}–10{sup 4} gravitational radii and measure M{sub BH} at the high-L end of the AGN family. With a 30 m class telescope, BLR spectroastrometry should be routinely detectable for much fainter quasars out to z∼6, and for various emission lines. This will enable kinematic M{sub BH} measurements as a function of luminosity and redshift, providing a compelling science case for next-generation telescopes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Spatially resolved dense molecular gas and star formation rate in M51

We present the spatially resolved observations of HCN J = 1−0 emission in the nearby spiral galaxy M51 using the IRAM 30 m telescope. The HCN map covers an extent of 4{sup ′}×5{sup ′}, which is, so far, the largest in M51 with a spatial resolution of 28{sup ′′}. There is a correlation between infrared emission (an indication of star formation rate (SFR)) and HCN (1–0) emission (a dense gas tracer) on a kiloparsec scale in M51, a natural extension of the proportionality between the SFR and the dense gas mass established globally in galaxies. Within M51, the relation appears to be sub-linear (with a slope of 0.74 ± 0.16) as L{sub IR} rises less quickly than L{sub HCN}. We attribute this to a difference between center and outer disk such that the central regions have stronger HCN (1–0) emission per unit star formation. The IR–HCN correlation in M51 is further compared with global ones from the Milky Way to high-z galaxies and bridges the gap between giant molecular clouds and galaxies. Like the centers of nearby galaxies, the L{sub IR}/L{sub HCN} ratio measured in M51 (particularly in the central regions) is slightly lower than what is measured globally in galaxies, yet is still within the scatter. This implies that though the L{sub IR}/L{sub HCN} ratio varies as a function of physical environment in the different positions of M51, IR, and HCN indeed show a linear correlation over 10 orders of magnitude.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE INFLUENCE OF SPATIAL RESOLUTION ON NONLINEAR FORCE-FREE MODELING

The nonlinear force-free field (NLFFF) model is often used to describe the solar coronal magnetic field, however a series of earlier studies revealed difficulties in the numerical solution of the model in application to photospheric boundary data. We investigate the sensitivity of the modeling to the spatial resolution of the boundary data, by applying multiple codes that numerically solve the NLFFF model to a sequence of vector magnetogram data at different resolutions, prepared from a single Hinode/Solar Optical Telescope Spectro-Polarimeter scan of NOAA Active Region 10978 on 2007 December 13. We analyze the resulting energies and relative magnetic helicities, employ a Helmholtz decomposition to characterize divergence errors, and quantify changes made by the codes to the vector magnetogram boundary data in order to be compatible with the force-free model. This study shows that NLFFF modeling results depend quantitatively on the spatial resolution of the input boundary data, and that using more highly resolved boundary data yields more self-consistent results. The free energies of the resulting solutions generally trend higher with increasing resolution, while relative magnetic helicity values vary significantly between resolutions for all methods. All methods require changing the horizontal components, and for some methods also the vertical components, of the vector magnetogram boundary field in excess of nominal uncertainties in the data. The solutions produced by the various methods are significantly different at each resolution level. We continue to recommend verifying agreement between the modeled field lines and corresponding coronal loop images before any NLFFF model is used in a scientific setting.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The spatial distribution of the young stellar clusters in the star-forming galaxy NGC 628

We present a study of the spatial distribution of the stellar cluster populations in the star-forming galaxy NGC 628. Using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey), we have identified 1392 potential young (≲100 Myr) stellar clusters within the galaxy using a combination of visual inspection and automatic selection. We investigate the clustering of these young stellar clusters and quantify the strength and change of clustering strength with scale using the two-point correlation function. We also investigate how image boundary conditions and dust lanes affect the observed clustering. The distribution of the clusters is well fit by a broken power law with negative exponent α. We recover a weighted mean index of α∼−0.8 for all spatial scales below the break at 3.″3 (158 pc at a distance of 9.9 Mpc) and an index of α∼−0.18 above 158 pc for the accumulation of all cluster types. The strength of the clustering increases with decreasing age and clusters older than 40 Myr lose their clustered structure very rapidly and tend to be randomly distributed in this galaxy, whereas the mass of the star cluster has little effect on the clustering strength. This is consistent with results from other studies that the morphological hierarchy in stellar clustering resembles the same hierarchy as the turbulent interstellar medium.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Spatial profile of argon (1s 5 ) metastables in an electron beam generated plasma

Electron beams with an applied magnetic field generate a secondary cold plasma with a selective chemical composition, featuring low-energy ions and metastable species in the discharge periphery, ideal for low-damage plasma treatment of material substrates. In this work, we studied the plasma generated by an e-beam using a 4 kV voltage in a pure argon gas environment under a magnetic field of 150 G and in the pressure range of 25–90 mTorr. We measured the absolute spatial density profile of argon (1 s 5 ) metastables in an electron beam generated plasma by laser-induced fluorescence and found it to be of the order of 10 16 m −3 . The electron temperature and the electron density measured by a Langmuir probe were of the order of 10 16 m −3 and less than an eV respectively. Electron-impact quenching was identified as a significant loss mechanism for the Ar(1s 5 ) state, leading to the saturation of the metastable density at higher pressures. Outside the primary ionization region, the spatial distribution of argon metastables followed a linear diffusion profile, indicating negligible additional production in those regions.

EEDF↗
DOE OSTI2018

Areal density and spatial resolution of high energy electron radiography

Ultrafast imaging tools are of great importance for determining the dynamic density distribution in high energy density (HED) matter. In this work, we designed a high energy electron radiography (HEER) system based on a linear electron accelerator to evaluate its capability for imaging HED matter. 40 MeV electron beams were used to image an aluminum target to study the density resolution and spatial resolution of HEER. The results demonstrate a spatial resolution of tens of micrometers. The interaction of the beams with the target and the beam transport of the transmitted electrons are further simulated with EGS5 and PARMELA codes, with the results showing good agreement with the experimental resolution. Furthermore, the experiment can be improved by adding an aperture at the Fourier plane.

areal density resolution↗