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Sample records for closely spaced quasar

  1. Close companions to two high-redshift quasars

    SciTech Connect

    McGreer, Ian D.; Fan, Xiaohui; Bian, Fuyan; Strauss, Michael A.; Haiman, Zoltàn; Richards, Gordon T.; Jiang, Linhua; Schneider, Donald P.

    2014-10-01

    We report the serendipitous discoveries of companion galaxies to two high-redshift quasars. SDSS J025617.7+001904 is a z = 4.79 quasar included in our recent survey of faint quasars in the SDSS Stripe 82 region. The initial MMT slit spectroscopy shows excess Lyα emission extending well beyond the quasar's light profile. Further imaging and spectroscopy with LBT/MODS1 confirms the presence of a bright galaxy (i {sub AB} = 23.6) located 2'' (12 kpc projected) from the quasar with strong Lyα emission (EW{sub 0} ≈ 100 Å) at the redshift of the quasar, as well as faint continuum. The second quasar, CFHQS J005006.6+344522 (z = 6.25), is included in our recent HST SNAP survey of z ∼ 6 quasars searching for evidence of gravitational lensing. Deep imaging with ACS and WFC3 confirms an optical dropout ∼4.5 mag fainter than the quasar (Y {sub AB} = 25) at a separation of 0.''9. The red i {sub 775} – Y {sub 105} color of the galaxy and its proximity to the quasar (5 kpc projected if at the quasar redshift) strongly favor an association with the quasar. Although it is much fainter than the quasar, it is remarkably bright when compared to field galaxies at this redshift, while showing no evidence for lensing. Both systems may represent late-stage mergers of two massive galaxies, with the observed light for one dominated by powerful ongoing star formation and for the other by rapid black hole growth. Observations of close companions are rare; if major mergers are primarily responsible for high-redshift quasar fueling then the phase when progenitor galaxies can be observed as bright companions is relatively short.

  2. Quasar Astrophysics with the Space Interferometry Mission

    NASA Technical Reports Server (NTRS)

    Unwin, Stephen; Wehrle, Ann; Meier, David; Jones, Dayton; Piner, Glenn

    2007-01-01

    Optical astrometry of quasars and active galaxies can provide key information on the spatial distribution and variability of emission in compact nuclei. The Space Interferometry Mission (SIM PlanetQuest) will have the sensitivity to measure a significant number of quasar positions at the microarcsecond level. SIM will be very sensitive to astrometric shifts for objects as faint as V = 19. A variety of AGN phenomena are expected to be visible to SIM on these scales, including time and spectral dependence in position offsets between accretion disk and jet emission. These represent unique data on the spatial distribution and time dependence of quasar emission. It will also probe the use of quasar nuclei as fundamental astrometric references. Comparisons between the time-dependent optical photocenter position and VLBI radio images will provide further insight into the jet emission mechanism. Observations will be tailored to each specific target and science question. SIM will be able to distinguish spatially between jet and accretion disk emission; and it can observe the cores of galaxies potentially harboring binary supermassive black holes resulting from mergers.

  3. Low-redshift quasars in the SDSS Stripe 82. Host galaxy colours and close environment

    NASA Astrophysics Data System (ADS)

    Bettoni, D.; Falomo, R.; Kotilainen, J. K.; Karhunen, K.; Uslenghi, M.

    2015-12-01

    We present a photometrical and morphological multicolour study of the properties of low-redshift (z < 0.3) quasar hosts based on a large and homogeneous data set of quasars derived from the Sloan Digital Sky Survey (DR7). We used quasars that were imaged in the SDSS Stripe82 that is up to 2 mag deeper than standard Sloan images. This sample is part of a larger data set of ˜400 quasars at z < 0.5 for which both the host galaxies and their galaxy environments were studied. For 52 quasars, we undertake a study of the colour of the host galaxies and of their close environments in the u, g, r, i and z bands. We are able to resolve almost all the quasars in the sample in the filters g, r, i and z and also in u for about 50 per cent of the targets. We found that the mean colours of the QSO host galaxy (g - i = 0.82 ± 0.26; r - i = 0.26 ± 0.16 and u - g = 1.32 ± 0.25) are very similar to the values of a sample of inactive galaxies matched in terms of redshift and galaxy luminosity with the quasar sample. There is a suggestion that the most massive QSO hosts have bluer colours. Both quasar hosts and the comparison sample of inactive galaxies have candidates of close (<50 kpc) companion galaxies for ˜30 per cent of the sources with no significant difference between active and inactive galaxies. We do not find significant correlation between the central black hole (BH) mass and the quasar host luminosity that appears to be extra luminous at a given BH mass with respect to the local relation (MBH - Mhost) for inactive galaxies. This confirms previous suggestion that a substantial disc component, not correlated with the BH mass, is present in the galaxies hosting low-z quasars. These results support a scenario where the activation of the nucleus has negligible effects on the global structural and photometrical properties of the hosting galaxies.

  4. Hubble Space Telescope Images of Nearby Luminous Quasars. 2; Results for Eight Quasars and Tests of the Detection Sensitivity

    NASA Technical Reports Server (NTRS)

    Bahcall, John N.; Kirhakos, Sofia; Schneider, Donald P.

    1995-01-01

    Observations with the Wide-Field Camera of the Hubble Space Telescope (HST) are presented for eight intrinsically luminous quasars with redshifts between 0.16 and 0.29. These observations, when combined with a similar HST study of the quasar PKS 2349-014, show that luminous nearby quasars exist in a variety of environments. Seven companion galaxies brighter than M(V) = 16.5 (H(sub 0) = 100 km s(sup -1) Mpc(sup -1), Omega(sub 0) = 1.0) lie within a projected distance of 25 kpc of the quasars; three of the companions are located closer than 3'' (6 kpc projected distance) from the quasars, well within the volume that would be enclosed by a typical L* host galaxy. The observed association of quasars and companion galaxies is statistically significant and may he an important element in the luminous-quasar phenomenon. Apparent host galaxies are detected for three of the quasars: PG 1116+215, 3C 273, and PG 1444+407; the hosts have an average absolute magnitude of about 0.6 mag brighter than L*. The agreement between the previously published major-axis directions in ground-based images and in the present HST images of 3C 273 and PG 1444+407 constitutes important evidence supporting the reality of these candidate host galaxies. Upper limits are placed on the visual-band brightnesses of representative galactic hosts for all the quasars. These limits are established by placing galaxy images obtained with HST underneath the quasars and measuring at what faintness level the known galaxies are detected. On average, the HST spirals would have been detected if they were as faint as 1 mag below L*, and the early-type galaxies could have been detected down to a brightness level of about L*, where L* is the Schechter characteristic luminosity of field galaxies. Smooth, featureless galaxy models (exponential disks or de Vaucouleurs profiles) are fitted to the residual light after a best-fitting point source is subtracted from the quasar images. The results show that smooth spiral

  5. HUBBLE SPACE TELESCOPE IMAGING OF POST-STARBURST QUASARS

    SciTech Connect

    Cales, S. L.; Brotherton, M. S.; Shang Zhaohui; Bennert, Vardha Nicola; Canalizo, G.; Stoll, R.; Ganguly, R.; Vanden Berk, D.; Paul, C.; Diamond-Stanic, A. E-mail: mbrother@uwyo.edu E-mail: bennert@physics.ucsb.edu E-mail: stoll@astronomy.ohio-state.edu E-mail: daniel.vandenberk@email.stvincent.edu E-mail: aleks@ucsd.edu

    2011-11-10

    We present images of 29 post-starburst quasars (PSQs) from a Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) Wide Field Channel Snapshot program. These broadlined active galactic nuclei (AGNs) possess the spectral signatures of massive (M{sub burst} {approx} 10{sup 10} M{sub sun}), moderate-aged stellar populations (hundreds of Myr). Thus, their composite nature provides insight into the AGN-starburst connection. We measure quasar-to-host galaxy light contributions via semi-automated two-dimensional light profile fits of point-spread-function-subtracted images. We examine the host morphologies and model the separate bulge and disk components. The HST/ACS-F606W images reveal an equal number of spiral (13/29) and early-type (13/29) hosts, with the remaining three hosts having indeterminate classifications. AGNs hosted by early-type galaxies have on average greater luminosity than those hosted by spiral galaxies. Disturbances such as tidal tails, shells, star-forming knots, and asymmetries are seen as signposts of interaction/merger activity. Disturbances like these were found in 17 of the 29 objects and are evenly distributed among early-type and spiral galaxies. Two of these systems are clearly merging with their companions. Compared to other AGNs of similar luminosity and redshift, these PSQs have a higher fraction of early-type hosts and disturbances. Our most luminous objects with disturbed early-type host galaxies appear to be consistent with merger products. Thus, these luminous galaxies may represent a phase in an evolutionary scenario for merger-driven activity. Our less luminous objects appear to be consistent with Seyfert galaxies not requiring triggering by major mergers. Many of these Seyferts are barred spiral galaxies.

  6. Hubble Space Telescope Imaging of Post-starburst Quasars

    NASA Astrophysics Data System (ADS)

    Cales, S. L.; Brotherton, M. S.; Shang, Zhaohui; Bennert, Vardha Nicola; Canalizo, G.; Stoll, R.; Ganguly, R.; Vanden Berk, D.; Paul, C.; Diamond-Stanic, A.

    2011-11-01

    We present images of 29 post-starburst quasars (PSQs) from a Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) Wide Field Channel Snapshot program. These broadlined active galactic nuclei (AGNs) possess the spectral signatures of massive (M burst ~ 1010 M sun), moderate-aged stellar populations (hundreds of Myr). Thus, their composite nature provides insight into the AGN-starburst connection. We measure quasar-to-host galaxy light contributions via semi-automated two-dimensional light profile fits of point-spread-function-subtracted images. We examine the host morphologies and model the separate bulge and disk components. The HST/ACS-F606W images reveal an equal number of spiral (13/29) and early-type (13/29) hosts, with the remaining three hosts having indeterminate classifications. AGNs hosted by early-type galaxies have on average greater luminosity than those hosted by spiral galaxies. Disturbances such as tidal tails, shells, star-forming knots, and asymmetries are seen as signposts of interaction/merger activity. Disturbances like these were found in 17 of the 29 objects and are evenly distributed among early-type and spiral galaxies. Two of these systems are clearly merging with their companions. Compared to other AGNs of similar luminosity and redshift, these PSQs have a higher fraction of early-type hosts and disturbances. Our most luminous objects with disturbed early-type host galaxies appear to be consistent with merger products. Thus, these luminous galaxies may represent a phase in an evolutionary scenario for merger-driven activity. Our less luminous objects appear to be consistent with Seyfert galaxies not requiring triggering by major mergers. Many of these Seyferts are barred spiral galaxies.

  7. A census of quasar-intrinsic absorption in the Hubble Space Telescope archive: systems from high-resolution echelle spectra

    NASA Astrophysics Data System (ADS)

    Ganguly, Rajib; Lynch, Ryan S.; Charlton, Jane C.; Eracleous, Michael; Tripp, Todd M.; Palma, Christopher; Sembach, Kenneth R.; Misawa, Toru; Masiero, Joseph R.; Milutinovic, Nikola; Lackey, Benjamin D.; Jones, Therese M.

    2013-10-01

    We present a census of zabs ≲ 2 intrinsic (those showing partial coverage) and associated (zabs ˜ zem) quasar absorption-line systems detected in the Hubble Space Telescope archive of Space Telescope Imaging Spectrograph echelle spectra. This work complements the Misawa et al. survey of 2 < zem < 4 quasars that selects systems using similar techniques. We confirm the existence of so-called strong N V intrinsic systems (where the equivalent width of H I Lyα is small compared to N V λ1238) presented in that work, but find no convincing cases of `strong C IV' intrinsic systems at low redshift/luminosity. Moreover, we also report on the existence of `strong O VI' systems. From a comparison of partial coverage results as a function of ion, we conclude that systems selected by the N V ion have the highest probability of being intrinsic. By contrast, the C IV and O VI ions are poor selectors. Of the 30 O VI systems tested, only two of the systems in the spectrum on 3C 351 show convincing evidence for partial coverage. However, there is an ˜3σ excess in the number of absorbers near the quasar redshift (|Δv| ≤ 5000 km s-1) over absorbers at large redshift differences. In at least two cases, the associated O VI systems are known not to arise close to the accretion disc of the quasar.

  8. The Hubble Space Telescope Quasar Absorption Line Key Project. 10: Galactic H I 21 centimeter emission toward 143 quasars and active Galactic nuclei

    NASA Technical Reports Server (NTRS)

    Lockman, Felix J.; Savage, Blair D.

    1995-01-01

    Sensitive H I 21 cm emission line spectra have been measured for the directions to 143 quasars and active galactic nuclei (AGNs) chosen from the observing lists for the Hubble Space Telescope (HST) Quasar Absorption Line Key Project. Narrow-band and wide-band data were obtained with the National Radio Astronomy Observatory (NRAO) 43 m radio telescope for each object. The narrow-band data have a velocity resolution of 1 km/s, extend from -220 to +170 km/s, and are corrected for stray 21 cm radiation. The wide-band data have a resolution of 4 km/s and extend from -1000 to +1000 km/s. The data are important for the interpretation of ultraviolet absorption lines near zero redshift in Key Project spectra. Twenty-two percent of the quasars lie behind Galactic high-velocity H I clouds with absolute value of V(sub LSR) greater than 100 km/s whose presence can increase the equivalent width of interstellar absorption lines significantly. This paper contains the emission spectra and measures of the H I velocities and column densities along the sight line to each quasar. We discuss how the measurements can be used to estimate the visual and ultraviolet extinction toward each quasar and to predict the approximate strength of the strong ultraviolet resonance lines of neutral gas species in the HST Key Project spectra.

  9. HUBBLE SPACE TELESCOPE NARROWBAND SEARCH FOR EXTENDED Ly{alpha} EMISSION AROUND TWO z > 6 QUASARS

    SciTech Connect

    Decarli, Roberto; Walter, Fabian; Yang Yujin; Hennawi, Joseph F.; Rix, Hans-Walter; Venemans, Bram P.; Carilli, Chris L.; Fan Xiahoui; Kurk, Jaron; Riechers, Dominik; Strauss, Michael A.

    2012-09-10

    We search for extended Ly{alpha} emission around two z > 6 quasars, SDSS J1030+0524 (z = 6.309) and SDSS J1148+5251 (z = 6.419) using Wide Field Camera 3 narrowband filters on board the Hubble Space Telescope. For each quasar, we collected two deep, narrowband images, one sampling the Ly{alpha} line+continuum at the quasar redshifts and one of the continuum emission redward of the line. After carefully modeling the point-spread function, we find no evidence for extended Ly{alpha} emission. These observations set 2{sigma} limits of L(Ly{alpha}, extended) <3.2 Multiplication-Sign 10{sup 44} erg s{sup -1} for J1030+0524 and L(Ly{alpha}, extended) <2.5 Multiplication-Sign 10{sup 44} erg s{sup -1} for J1148+5251. Given the star formation rates typically inferred from (rest-frame) far-infrared measurements of z {approx} 6 quasars, these limits are well below the intrinsic bright Ly{alpha} emission expected from the recombination of gas photoionized by the quasars or by the star formation in the host galaxies, and point toward significant Ly{alpha} suppression or dust attenuation. However, small extinction values have been observed along the line of sight to the nuclei, thus reddening has to be coupled with other mechanisms for Ly{alpha} suppression (e.g., resonance scattering). No Ly{alpha} emitting companions are found, down to a 5{sigma} sensitivity of {approx}1 Multiplication-Sign 10{sup -17} erg s{sup -1} cm{sup -2} arcsec{sup -2} (surface brightness) and {approx}5 Multiplication-Sign 10{sup -17} erg s{sup -1} cm{sup -2} (assuming point sources).

  10. A Long-Term Space Astrophysics Research Program: The Evolution of the Quasar Continuum

    NASA Technical Reports Server (NTRS)

    Elvis, M.; Oliversen, Ronald K. (Technical Monitor)

    2001-01-01

    Four papers have been written. One reports on the major study funded by this grant: a pan-chromatic study of the quasar continuum at redshift 3. Two others make use of the quasar continuum shapes to find the minimum total accretion luminosity of the Universe, and hence the efficiency and spin of supermassive black holes; the second shows that the reemission of absorbed quasar radiation alleviates a major problem with galaxy formation and the FIR background. The last paper recognizes the role quasars may play in the initial formation of dust in the early Universe. The major study of a sample of z=3 and its comparison with a sample of z=0.l quasars across the whole X-ray to radio spectrum was completed and accepted for publication in ApJ Supplements. This study comprises the thesis work of Olga Kuhn. The two samples are matched in evolved luminosity, and so should be sampling the same black hole population at different z, and in different accretion states. Despite this no strong differences were found between the samples, except in the 'small bump' region of the optical/UV. This region is dominated by FeII emission, and may indicate abundance evolution in quasars. The lack of overall spectral changes argues strongly against a single population of quasars fading over cosmic time, and for a multiple generation, or multiple outburst model for quasars. A study of the total luminosity absorbed from quasars and re-emitted in the infrared produced two results (reported in two papers): The minimum intrinsic luminosity/Gpc(3) from AGN compared with the measured mass density in supermassive black holes [Gpc(-3)] requires a conversion efficiency of accreted mass into luminosity of greater than 15%. Non-rotating black holes cannot exceed 5% efficiency, while rapidly rotating black holes can reach 47%. Hence our result requires that most supermassive black holes must be rapidly rotating. The second result comes from considering the contribution that the re-radiated quasar

  11. Early Fermi Gamma-ray Space Telescope Observations of the Quasar 3C454.3

    SciTech Connect

    Abdo, A

    2009-05-07

    This is the first report of Fermi Gamma-ray Space Telescope observations of the quasar 3C 454.3, which has been undergoing pronounced long-term outbursts since 2000. The data from the Large Area Telescope (LAT), covering 2008 July 7-October 6, indicate strong, highly variable {gamma}-ray emission with an average flux of {approx} 3 x 10{sup -6} photons cm{sup -2} s{sup -1}, for energies > 100 MeV. The {gamma}-ray flux is variable, with strong, distinct, symmetrically-shaped flares for which the flux increases by a factor of several on a time scale of about three days. This variability indicates a compact emission region, and the requirement that the source is optically thin to pair-production implies relativistic beaming with Doppler factor {delta} > 8, consistent with the values inferred from VLBI observations of superluminal expansion ({delta} {approx} 25). The observed {gamma}-ray spectrum is not consistent with a simple power-law, but instead steepens strongly above {approx} 2 GeV, and is well described by a broken power-law with photon indices of {approx} 2.3 and {approx} 3.5 below and above the break, respectively. This is the first direct observation of a break in the spectrum of a high luminosity blazar above 100 MeV, and it is likely direct evidence for an intrinsic break in the energy distribution of the radiating particles. Alternatively, the spectral softening above 2GeV could be due to -ray absorption via photonphoton pair production on the soft X-ray photon field of the host AGN, but such an interpretation would require the dissipation region to be located very close ({approx}< 100 gravitational radii) to the black hole, which would be inconsistent with the X-ray spectrum of the source.

  12. A possible close supermassive black-hole binary in a quasar with optical periodicity.

    PubMed

    Graham, Matthew J; Djorgovski, S G; Stern, Daniel; Glikman, Eilat; Drake, Andrew J; Mahabal, Ashish A; Donalek, Ciro; Larson, Steve; Christensen, Eric

    2015-02-01

    Quasars have long been known to be variable sources at all wavelengths. Their optical variability is stochastic and can be due to a variety of physical mechanisms; it is also well-described statistically in terms of a damped random walk model. The recent availability of large collections of astronomical time series of flux measurements (light curves) offers new data sets for a systematic exploration of quasar variability. Here we report the detection of a strong, smooth periodic signal in the optical variability of the quasar PG 1302-102 with a mean observed period of 1,884 ± 88 days. It was identified in a search for periodic variability in a data set of light curves for 247,000 known, spectroscopically confirmed quasars with a temporal baseline of about 9 years. Although the interpretation of this phenomenon is still uncertain, the most plausible mechanisms involve a binary system of two supermassive black holes with a subparsec separation. Such systems are an expected consequence of galaxy mergers and can provide important constraints on models of galaxy formation and evolution. PMID:25561176

  13. Quasars, Redshifts and Controversies

    NASA Astrophysics Data System (ADS)

    Arp, Halton C.

    1988-09-01

    Introduction; 1. Distance of quasars; 2. The battle over statistics; 3. Galaxies visibly connected to quasars; 4. Certain galaxies with many quasars; 5. Distribution of quasars in space; 6. Galaxies with excess redshift; 7. Small excess redshifts, the local group of galaxies, and quantization of redshifts; 8. Correcting intrinsic redshifts and identifying hydrogen clouds within nearby groups of galaxies; 9. Ejection from galaxies; 10. The sociology of the controversy; 11. Interpretations; Glossary; Index.

  14. 46 CFR 72.15-15 - Ventilation for closed spaces.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 3 2010-10-01 2010-10-01 false Ventilation for closed spaces. 72.15-15 Section 72.15-15... ARRANGEMENT Ventilation § 72.15-15 Ventilation for closed spaces. (a) All enclosed spaces within the vessel... spaces and for closing all doorways, ventilators and annular spaces around funnels and other openings...

  15. 46 CFR 72.15-15 - Ventilation for closed spaces.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 3 2013-10-01 2013-10-01 false Ventilation for closed spaces. 72.15-15 Section 72.15-15... ARRANGEMENT Ventilation § 72.15-15 Ventilation for closed spaces. (a) All enclosed spaces within the vessel... spaces and for closing all doorways, ventilators and annular spaces around funnels and other openings...

  16. 46 CFR 72.15-15 - Ventilation for closed spaces.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 3 2012-10-01 2012-10-01 false Ventilation for closed spaces. 72.15-15 Section 72.15-15... ARRANGEMENT Ventilation § 72.15-15 Ventilation for closed spaces. (a) All enclosed spaces within the vessel... spaces and for closing all doorways, ventilators and annular spaces around funnels and other openings...

  17. 46 CFR 72.15-15 - Ventilation for closed spaces.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 3 2014-10-01 2014-10-01 false Ventilation for closed spaces. 72.15-15 Section 72.15-15... ARRANGEMENT Ventilation § 72.15-15 Ventilation for closed spaces. (a) All enclosed spaces within the vessel... spaces and for closing all doorways, ventilators and annular spaces around funnels and other openings...

  18. 46 CFR 72.15-15 - Ventilation for closed spaces.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 3 2011-10-01 2011-10-01 false Ventilation for closed spaces. 72.15-15 Section 72.15-15... ARRANGEMENT Ventilation § 72.15-15 Ventilation for closed spaces. (a) All enclosed spaces within the vessel... spaces and for closing all doorways, ventilators and annular spaces around funnels and other openings...

  19. 78 FR 53497 - Commercial Space Transportation Advisory Committee; Closed Session

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-29

    ... Federal Aviation Administration Commercial Space Transportation Advisory Committee; Closed Session AGENCY: Federal Aviation Administration (FAA), DOT. ACTION: Notice of Commercial Space Transportation Advisory... closed session of the Commercial Space Transportation Advisory Committee (COMSTAC). The special...

  20. The Hubble Space Telescope quasar absorption line key project. II - Data calibration and absorption-line selection

    NASA Technical Reports Server (NTRS)

    Schneider, Donald P.; Hartig, George F.; Jannuzi, Buell T.; Kirhakos, Sofia; Saxe, David H.; Weymann, Ray J.; Bahcall, John N.; Bergeron, Jacqueline; Boksenberg, Alec; Sargent, W. L. W.

    1993-01-01

    We present the observational and data processing aspects of the Hubble Space Telescope Quasar Absorption Line Key Project. Topics discussed include the observational technique, calibration of the data, software that simulates the data, the automated procedure used to identify and characterize the absorption features, and the determination of the sensitivity limits of the survey.

  1. Controlled Microbial Cenoses in Closed Spaces

    NASA Astrophysics Data System (ADS)

    Somova, Lydia; Mikheeva, Galina

    Controlled microbial cenoses have good prospects in closed spaces: for air treatment in LSS and cellars industrial premises; for sewage treatment in LSS; for increase of productivity and protect of plants from infections in LSS. Possible methods of formation of microbiocenoses are: selection, autoselection, artificial formation taking into account their biochemical properties and metabolic interactions. Experimental microbiocenoses, has been produced on the basis of natural association of microorganisms by long cultivation on specially developed medium. Dominating groups are bacteria of genera: Lactobacillus, Streptococcus, Leuconostoc, Bidobac-terium, Rhodopseudomonas and yeast of genera: Kluyveromyces, Saccharomyces and Torulop-sis. Microbiocenoses do not contain pathogenic and conditionally pathogenic microorganisms, they possess opposing and probiotic properties. Different examples of microbial cenoses actions are to be presented in the paper.

  2. A NEW METHOD TO DIRECTLY MEASURE THE JEANS SCALE OF THE INTERGALACTIC MEDIUM USING CLOSE QUASAR PAIRS

    SciTech Connect

    Rorai, Alberto; Hennawi, Joseph F.; White, Martin

    2013-10-01

    Although the baryons in the intergalactic medium (IGM) trace dark matter fluctuations on megaparsec scales, on smaller scales ∼100 kpc, fluctuations are suppressed because the finite temperature gas is pressure supported against gravity, analogous to the classical Jeans argument. This Jeans filtering scale, which quantifies the small-scale structure of the IGM, has fundamental cosmological implications. First, it provides a thermal record of heat injected by ultraviolet photons during cosmic reionization events, and thus constrains the thermal and reionization history of the universe. Second, the Jeans scale determines the clumpiness of the IGM, a critical ingredient in models of cosmic reionization. Third, it sets the minimum mass scale for gravitational collapse from the IGM, and hence plays a pivotal role in galaxy formation. Unfortunately, it is extremely challenging to measure the Jeans scale via the standard technique of analyzing purely longitudinal Lyα forest spectra, because the thermal Doppler broadening of absorption lines along the line-of-sight, is highly degenerate with Jeans smoothing. In this work, we show that the Jeans filtering scale can be directly measured by characterizing the coherence of correlated Lyα forest absorption in close quasar pairs, with separations small enough ∼100 kpc to resolve it. We present a novel technique for this purpose, based on the probability density function (PDF) of phase angle differences of homologous longitudinal Fourier modes in close quasar pair spectra. A Bayesian formalism is introduced based on the phase angle PDF, and Markov Chain Monte Carlo techniques are used to characterize the precision of a hypothetical Jeans scale measurement, and explore degeneracies with other thermal parameters governing the IGM. A semi-analytical model of the Lyα forest is used to generate a large grid (500) of thermal models from a dark matter only simulation. Our full parameter study indicates that a realistic sample of

  3. A Long-Term Space Astrophysics Research Program. The Evolution of the Quasar Continuum

    NASA Technical Reports Server (NTRS)

    Elvis, M.

    1998-01-01

    The grant "The Evolution of the Quasar Continuum" resulted in over 53 published referred papers and conference proceedings. The more significant of these papers are listed below, and abstracts are attached. The papers address a wide range of issues involving the evolution of quasars, their electromagnetic emissions, and their environment, from nearby low luminosity Seyfert galaxies to quasars at the highest redshifts. Primarily observational in content the work nonetheless included theoretical studies of quasar accretion disks that attempt to explain the observed time variability of quasars, and the overall 'demographics' of the quasar population. The work carried out under this grant has laid a strong foundation for ongoing and future research with AXAF, HST and other new facilities.

  4. A Long-Term Space Astrophysics Research Program: The Evolution of the Quasar Continuum

    NASA Technical Reports Server (NTRS)

    Elvis, M.; Oliversen, Ronald K. (Technical Monitor)

    2002-01-01

    Four papers have been written. One reports on the major study funded by this grant: a pan-chromatic study of the quasar continuum at redshift 3. Two others make use of the quasar continuum shapes to find the minimum total accretion luminosity of the Universe, and hence the efficiency and spin of supermassive black holes; the second shows that the reemission of absorbed quasar radiation alleviates a major problem with galaxy formation and the FIR background. The last paper recognizes the role quasars may play in the initial formation of dust in the early Universe.

  5. 46 CFR 190.15-10 - Ventilation for closed spaces.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 7 2010-10-01 2010-10-01 false Ventilation for closed spaces. 190.15-10 Section 190.15... CONSTRUCTION AND ARRANGEMENT Ventilation § 190.15-10 Ventilation for closed spaces. (a) All enclosed spaces... chemical laboratories, scientific laboratories, chemical storerooms, and machinery spaces and for...

  6. 46 CFR 190.15-10 - Ventilation for closed spaces.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 7 2013-10-01 2013-10-01 false Ventilation for closed spaces. 190.15-10 Section 190.15... CONSTRUCTION AND ARRANGEMENT Ventilation § 190.15-10 Ventilation for closed spaces. (a) All enclosed spaces... chemical laboratories, scientific laboratories, chemical storerooms, and machinery spaces and for...

  7. 46 CFR 190.15-10 - Ventilation for closed spaces.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 7 2014-10-01 2014-10-01 false Ventilation for closed spaces. 190.15-10 Section 190.15... CONSTRUCTION AND ARRANGEMENT Ventilation § 190.15-10 Ventilation for closed spaces. (a) All enclosed spaces... chemical laboratories, scientific laboratories, chemical storerooms, and machinery spaces and for...

  8. 46 CFR 190.15-10 - Ventilation for closed spaces.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 7 2012-10-01 2012-10-01 false Ventilation for closed spaces. 190.15-10 Section 190.15... CONSTRUCTION AND ARRANGEMENT Ventilation § 190.15-10 Ventilation for closed spaces. (a) All enclosed spaces... chemical laboratories, scientific laboratories, chemical storerooms, and machinery spaces and for...

  9. 46 CFR 190.15-10 - Ventilation for closed spaces.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 7 2011-10-01 2011-10-01 false Ventilation for closed spaces. 190.15-10 Section 190.15... CONSTRUCTION AND ARRANGEMENT Ventilation § 190.15-10 Ventilation for closed spaces. (a) All enclosed spaces... chemical laboratories, scientific laboratories, chemical storerooms, and machinery spaces and for...

  10. Weak bump quasars

    NASA Technical Reports Server (NTRS)

    Wilkes, B. J.; Mcdowell, J.

    1994-01-01

    Research into the optical, ultraviolet and infrared continuum emission from quasars and their host galaxies was carried out. The main results were the discovery of quasars with unusually weak infrared emission and the construction of a quantitative estimate of the dispersion in quasar continuum properties. One of the major uncertainties in the measurement of quasar continuum strength is the contribution to the continuum of the quasar host galaxy as a function of wavelength. Continuum templates were constructed for different types of host galaxy and individual estimates made of the decomposed quasar and host continua based on existing observations of the target quasars. The results are that host galaxy contamination is worse than previously suspected, and some apparent weak bump quasars are really normal quasars with strong host galaxies. However, the existence of true weak bump quasars such as PHL 909 was confirmed. The study of the link between the bump strength and other wavebands was continued by comparing with IRAS data. There is evidence that excess far infrared radiation is correlated with weaker ultraviolet bumps. This argues against an orientation effect and implies a probable link with the host galaxy environment, for instance the presence of a luminous starburst. However, the evidence still favors the idea that reddening is not important in those objects with ultraviolet weak bumps. The same work has led to the discovery of a class of infrared weak quasars. Pushing another part of the envelope of quasar continuum parameter space, the IR-weak quasars have implications for understanding the effects of reddening internal to the quasars, the reality of ultraviolet turnovers, and may allow further tests of the Phinney dust model for the IR continuum. They will also be important objects for studying the claimed IR to x-ray continuum correlation.

  11. 46 CFR 92.15-10 - Ventilation for closed spaces.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 4 2010-10-01 2010-10-01 false Ventilation for closed spaces. 92.15-10 Section 92.15-10... CONSTRUCTION AND ARRANGEMENT Ventilation § 92.15-10 Ventilation for closed spaces. (a) Except as noted in paragraph (c) of this section, all enclosed spaces within the vessel shall be properly vented or...

  12. 46 CFR 92.15-10 - Ventilation for closed spaces.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 4 2014-10-01 2014-10-01 false Ventilation for closed spaces. 92.15-10 Section 92.15-10... CONSTRUCTION AND ARRANGEMENT Ventilation § 92.15-10 Ventilation for closed spaces. (a) Except as noted in paragraph (c) of this section, all enclosed spaces within the vessel shall be properly vented or...

  13. 46 CFR 92.15-10 - Ventilation for closed spaces.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 4 2012-10-01 2012-10-01 false Ventilation for closed spaces. 92.15-10 Section 92.15-10... CONSTRUCTION AND ARRANGEMENT Ventilation § 92.15-10 Ventilation for closed spaces. (a) Except as noted in paragraph (c) of this section, all enclosed spaces within the vessel shall be properly vented or...

  14. 46 CFR 92.15-10 - Ventilation for closed spaces.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 4 2013-10-01 2013-10-01 false Ventilation for closed spaces. 92.15-10 Section 92.15-10... CONSTRUCTION AND ARRANGEMENT Ventilation § 92.15-10 Ventilation for closed spaces. (a) Except as noted in paragraph (c) of this section, all enclosed spaces within the vessel shall be properly vented or...

  15. 46 CFR 92.15-10 - Ventilation for closed spaces.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 4 2011-10-01 2011-10-01 false Ventilation for closed spaces. 92.15-10 Section 92.15-10... CONSTRUCTION AND ARRANGEMENT Ventilation § 92.15-10 Ventilation for closed spaces. (a) Except as noted in paragraph (c) of this section, all enclosed spaces within the vessel shall be properly vented or...

  16. A long-term space astrophysics research program: The evolution of the quasar continuum

    NASA Technical Reports Server (NTRS)

    Elvis, M.

    1993-01-01

    The research program supported by this grant now has great momentum. Numerous papers are in progress, and a strong multi-wavelength observing program is rapidly accumulating data on samples of high redshift quasars across the spectrum. ROSAT spectra of quasars continue to yield surprises. Of four z = 3 quasars with X-ray spectra, three show strong absorption. This contrasts strongly with the situation for luminous AGN at low redshifts where fewer than 1 in 20 show X-ray absorption. A new site for this absorption is probably needed, either around the quasar (e.g. in a cluster cooling flow) or along the line of sight (e.g. in a Damped Lyman-alpha system). The unabsorbed quasar allows limits on the physical conditions in a damped Lyman-alpha cloud to be calculated, and will allow a X-ray Gunn-Peterson test to be applied that will limit the fraction of the closure mass in an intergalactic medium. The X-ray spectral indices of these z = 3 quasars show no change from those of similar objects at low z, suggesting that 'short-lifetime' models apply. Eight other z = 3-4 quasars have been detected and their energy distributions from X-rays to Infrared (using new infrared spectrographs) have been compiled. These are now being compared with the low z continua from the 'Atlas of Quasar Energy Distributions' to search for evolutionary changes. The discovery of a likely warm absorber in 3C351 made recognition of another example simple. Also, modeling of the conditions in the absorber in 3C351 using the OVI absorption line from HST and the high ionization emission lines, suggests that the broad line region is indeed the origin of the warm absorber in this quasar, and by extension, others. Warm absorbers can now be used as a new diagnostic of this region. The X-ray spectrum of a 'Red Quasar', 3C212, has a cut-off spectrum, which could be fitted by an absorbed power-law, or more remarkably, by an unabsorbed black body. Using our quasi-simultaneous optical data and photoionization

  17. Hubble Space Telescope Close to Capture

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The Hubble Space Telescope (HST), with its normal routine temporarily interrupted, is about to be captured by the Space Shuttle Columbia prior to a week of servicing and upgrading by the STS-109 crew. The telescope was captured by the shuttle's Remote Manipulator System (RMS) robotic arm and secured on a work stand in Columbia's payload bay where 4 of the 7-member crew performed 5 space walks completing system upgrades to the HST. Included in those upgrades were: The replacement of the solar array panels; replacement of the power control unit (PCU); replacement of the Faint Object Camera (FOC) with a new advanced camera for Surveys (ACS); and installation of the experimental cooling system for the Hubble's Near-Infrared Camera and Multi-object Spectrometer (NICMOS), which had been dormant since January 1999 when its original coolant ran out. The Marshall Space Flight Center had the responsibility for the design, development, and construction of the the HST, which is the most complex and sensitive optical telescope ever made, to study the cosmos from a low-Earth orbit. Launched March 1, 2002, the STS-109 HST servicing mission lasted 10 days, 22 hours, and 11 minutes. It was the 108th flight overall in NASA's Space Shuttle Program.

  18. A transformer of closely spaced pulsed waveforms

    NASA Technical Reports Server (NTRS)

    Niedra, J.

    1970-01-01

    Passive circuit, using diodes, transistors, and magnetic cores, transforms the voltage of repetitive positive or negative pulses. It combines a pulse transformer with switching devices to effect a resonant flux reset and can transform various pulsed waveforms that have a nonzero average value and are relatively cosely spaced in time.

  19. Dust in the Quasar Wind (Artist Concept)

    NASA Technical Reports Server (NTRS)

    2007-01-01

    Dusty grains -- including tiny specks of the minerals found in the gemstones peridot, sapphires and rubies -- can be seen blowing in the winds of a quasar, or active black hole, in this artist's concept. The quasar is at the center of a distant galaxy.

    Astronomers using NASA's Spitzer Space Telescope found evidence that such quasar winds might have forged these dusty particles in the very early universe. The findings are another clue in an ongoing cosmic mystery: where did all the dust in our young universe come from?

    Dust is crucial for efficient star formation as it allows the giant clouds where stars are born to cool quickly and collapse into new stars. Once a star has formed, dust is also needed to make planets and living creatures. Dust has been seen as far back as when the universe was less than a tenth of its current age, but how did it get there? Most dust in our current epoch forms in the winds of evolved stars that did not exist when the universe was young.

    Theorists had predicted that winds from quasars growing in the centers of distant galaxies might be a source of this dust. While the environment close to a quasar is too hot for large molecules like dust grains to survive, dust has been found in the cooler, outer regions. Astronomers now have evidence that dust is created in these outer winds.

    Using Spitzer's infrared spectrograph instrument, scientists found a wealth of dust grains in a quasar called PG2112+059 located at the center of a galaxy 8 billion light-years away. The grains - including corundum (sapphires and rubies); forsterite (peridot); and periclase (naturally occurring in marble) - are not typically found in galaxies without quasars, suggesting they might have been freshly formed in the quasar's winds.

  20. Twin Quasars Tango And It's No Mirage

    NASA Astrophysics Data System (ADS)

    2002-03-01

    image of a single quasar into an apparent double has proved fruitless. This led to the speculation that the gravitation light-bending might be caused by a new type of cluster that contained hot gas and dark matter, but failed to ever make stars or galaxies. Such a "dark cluster" would be invisible to optical and ultraviolet telescopes, but would be detectable in X-rays. The Chandra images, the most sensitive ever taken for this type of search, showed no evidence for a massive dark cluster. Further, the X-ray spectra of the two quasars were distinctly different. "This may mean that the pair Q2345+007A,B actually consists of two separate quasars," said Green. "However, a mystery remains. How can two quasars have identical optical spectra - every bump and wiggle? The coincidence seems improbable." One possible explanation is that the quasars are formed close by each other grow up to look alike at optical wavelengths, but that X-rays which probe closer to their central black holes, bring out the individual differences. Chandra observed Q2345+007 on May 26, 2000, for 65,000 seconds using the Advanced CCD Imaging Spectrometer instrument. Scientists from the Harvard-Smithsonian Center for Astrophysics and the National Optical Astronomy Observatory were also members of the research team. The ACIS camera was developed for NASA by Pennsylvania State University, University Park, Pa., and the Massachusetts Institute of Technology, Cambridge, Mass. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program. TRW, Inc., Redondo Beach, Calif., is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge. The National Optical Astronomy Observatory is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation.

  1. Quasars Candidates in the Hubble Deep Field

    NASA Astrophysics Data System (ADS)

    Conti, A.; Kennefick, J. D.; Martini, P. L.; Omser, P. S.

    1996-12-01

    The Hubble Deep Field gives us an unprecedented view of our universe and an opportunity to study a wide range of questions in galaxy evolution and cosmology. Here, we will focus on the search for faint quasars and AGN in the crude combined images using a multicolor imaging analysis that has proven very successful in recent years. To produce a catalog of objects in the field, we used the FOCAS package for object detection with particular care to the set of input parameters used to minimize spurious detections. For each detected source we measured aperture magnitudes in several different apertures using the IRAF PHOT routine. For object classification we have chosen not to use the built in FOCAS routines, instead we have developed classification schemes that closely resemble those of Flynn at al. (1996) to distinguish resolved from unresolved objects in the Hubble Deep Field. We generated synthetic quasar spectra in the range 2.0quasar colors.These colors are used to identify areas of the multicolor space where quasars might be expected. A quasar candidate list is being formed. Routines were developed to determine the completeness of our data to point sources in the observed bands. The data are 50 % complete at 27.0(m) , 28.9(m) ,29.1(m) , 28.2(m) in the F300W (U), F450W (B), F606W (V) and F814W (I) filter respectively. These completeness limits closely approximate the 3sigma detection limit. We will present a list of quasars candidates and compare the results to expectations from previous surveys and extrapolations from current models. Our initial extrapolations, based on the luminosity function of Boyle (1991) and Warren at al. (1994), suggest the Hubble Deep Field may contain of order 10 quasars.

  2. Towards a comprehensive picture of powerful quasars, their host galaxies and quasar winds at z ˜ 0.5

    NASA Astrophysics Data System (ADS)

    Wylezalek, Dominika; Zakamska, Nadia L.; Liu, Guilin; Obied, Georges

    2016-03-01

    Luminous type-2 quasars in which the glow from the central black hole is obscured by dust are ideal targets for studying their host galaxies and the quasars' effect on galaxy evolution. Such feedback appears ubiquitous in luminous obscured quasars where high-velocity-ionized nebulae have been found. We present rest-frame yellow-band (˜5000 Å) observations using the Hubble Space Telescope (HST) for a sample of 20 luminous quasar host galaxies at 0.2 < z < 0.6 selected from the Sloan Digital Sky Survey. For the first time, we combine host galaxy observations with geometric measurements of quasar illumination using blue-band HST observations and [O III] integral field unit observations probing the quasar winds. The HST images reveal bright merger signatures in about half the galaxies; a significantly higher fraction than in comparison inactive ellipticals. We show that the host galaxies are primarily bulge-dominated, with masses close to M*, but belong to <30 per cent of elliptical galaxies that are highly star forming at z ˜ 0.5. Ionized gas signatures are uncorrelated with faint stellar discs (if present), confirming that the ionized gas is not concentrated in a disc. Scattering cones and [O III] ionized gas velocity field are aligned with the forward scattering cones being co-spatial with the blue-shifted side of the velocity field, suggesting the high-velocity gas is indeed photo-ionized by the quasar. Based on the host galaxies' high star formation rates and bright merger signatures, we suggest that this low-redshift outbreak of luminous quasar activity is triggered by recent minor mergers. Combining these novel observations, we present new quasar unification tests, which are in agreement with expectations of the orientation-based unification model for quasars.

  3. A hybrid genetic algorithm for resolving closely spaced objects

    NASA Technical Reports Server (NTRS)

    Abbott, R. J.; Lillo, W. E.; Schulenburg, N.

    1995-01-01

    A hybrid genetic algorithm is described for performing the difficult optimization task of resolving closely spaced objects appearing in space based and ground based surveillance data. This application of genetic algorithms is unusual in that it uses a powerful domain-specific operation as a genetic operator. Results of applying the algorithm to real data from telescopic observations of a star field are presented.

  4. Heat Transfer Analysis of a Closed Brayton Cycle Space Radiator

    NASA Technical Reports Server (NTRS)

    Juhasz, Albert J.

    2007-01-01

    This paper presents a mathematical analysis of the heat transfer processes taking place in a radiator for a closed cycle gas turbine (CCGT), also referred to as a Closed Brayton Cycle (CBC) space power system. The resulting equations and relationships have been incorporated into a radiator sub-routine of a numerical triple objective CCGT optimization program to determine operating conditions yielding maximum cycle efficiency, minimum radiator area and minimum overall systems mass. Study results should be of interest to numerical modeling of closed cycle Brayton space power systems and to the design of fluid cooled radiators in general.

  5. Galaxy Clustering Around Nearby Luminous Quasars

    NASA Technical Reports Server (NTRS)

    Fisher, Karl B.; Bahcall, John N.; Kirhakos, Sofia; Schneider, Donald P.

    1996-01-01

    We examine the clustering of galaxies around a sample of 20 luminous low redshift (z approx. less than 0.30) quasars observed with the Wide Field Camera-2 on the Hubble Space Telescope (HST). The HST resolution makes possible galaxy identification brighter than V = 24.5 and as close as 1 min or 2 min to the quasar. We find a significant enhancement of galaxies within a projected separation of approx. less than 100 1/h kpc of the quasars. If we model the QSO/galaxy correlation function as a power law with a slope given by the galaxy/galaxy correlation function, we find that the ratio of the QSO/galaxy to galaxy/galaxy correlation functions is 3.8 +/- 0.8. The galaxy counts within r less than 15 1/h kpc of the quasars are too high for the density profile to have an appreciable core radius (approx. greater than 100 1/h kpc). Our results reinforce the idea that low redshift quasars are located preferentially in groups of 10-20 galaxies rather than in rich clusters. We see no significant difference in the clustering amplitudes derived from radio-loud and radio-quiet subsamples.

  6. Hubble space telescope/cosmic origins spectrograph observations of the quasar Q0302–003: Probing the He II reionization epoch and QSO proximity effects

    SciTech Connect

    Syphers, David; Shull, J. Michael

    2014-03-20

    Q0302–003 (z = 3.2860 ± 0.0005) was the first quasar discovered that showed a He II Gunn-Peterson trough, a sign of incomplete helium reionization at z ≳ 2.9. We present its Hubble Space Telescope/Cosmic Origins Spectrograph far-UV medium-resolution spectrum, which resolves many spectral features for the first time, allowing study of the quasar itself, the intergalactic medium, and quasar proximity effects. Q0302–003 has a harder intrinsic extreme-UV spectral index than previously claimed, as determined from both a direct fit to the spectrum (yielding α{sub ν} ≈ –0.8) and the helium-to-hydrogen ion ratio in the quasar's line-of-sight proximity zone. Intergalactic absorption along this sightline shows that the helium Gunn-Peterson trough is largely black in the range 2.87 < z < 3.20, apart from ionization due to local sources, indicating that helium reionization has not completed at these redshifts. However, we tentatively report a detection of nonzero flux in the high-redshift trough when looking at low-density regions, but zero flux in higher-density regions. This constrains the He II fraction to be about 1% in the low-density intergalactic medium (IGM) and possibly a factor of a few higher in the IGM as a whole, suggesting helium reionization has progressed substantially by z ∼ 3.1. The Gunn-Peterson trough recovers to a He II Lyα forest at z < 2.87. We confirm a transmission feature due to the ionization zone around a z = 3.05 quasar just off the sightline, and resolve the feature for the first time. We discover a similar such feature possibly caused by a luminous z = 3.23 quasar further from the sightline, which suggests that this quasar has been luminous for >34 Myr.

  7. Modal vector estimation for closely spaced frequency modes

    NASA Technical Reports Server (NTRS)

    Craig, R. R., Jr.; Chung, Y. T.; Blair, M.

    1982-01-01

    Techniques for obtaining improved modal vector estimates for systems with closely spaced frequency modes are discussed. In describing the dynamical behavior of a complex structure modal parameters are often analyzed: undamped natural frequency, mode shape, modal mass, modal stiffness and modal damping. From both an analytical standpoint and an experimental standpoint, identification of modal parameters is more difficult if the system has repeated frequencies or even closely spaced frequencies. The more complex the structure, the more likely it is to have closely spaced frequencies. This makes it difficult to determine valid mode shapes using single shaker test methods. By employing band selectable analysis (zoom) techniques and by employing Kennedy-Pancu circle fitting or some multiple degree of freedom (MDOF) curve fit procedure, the usefulness of the single shaker approach can be extended.

  8. Rationale for evaluating a closed food chain for space habitats

    NASA Technical Reports Server (NTRS)

    Modell, M.; Spurlock, J. M.

    1980-01-01

    Closed food cycles for long duration space flight and space habitation are examined. Wash water for a crew of six is economically recyclable after a week, while a total closed loop water system is effective only if the stay exceeds six months' length. The stoichiometry of net plant growth is calculated and it is shown that the return of urine, feces, and inedible plant parts to the food chain, along with the addition of photosynthesis, closes the food chain loop. Scenarios are presented to explore the technical feasibility of achieving a closed loop system. An optimal choice of plants is followed by processing, waste conversion, equipment specifications, and control requirements, and finally, cost-effectiveness.

  9. Hubble Space Telescope Faint Object Spectrograph and ground-based observations of the broad absorption line quasar 0226-1024

    NASA Technical Reports Server (NTRS)

    Korista, Kirk T.; Weymann, Ray J.; Morris, Simon L.; Kopko, Michael, Jr.; Turnshek, David A.; Hartig, George F.; Foltz, Craig B.; Burbidge, E. M.; Junkkarinen, Vesa T.

    1992-01-01

    Faint Object Spectrograph data from the Hubble Space Telescope of the broad absorption line quasar 0226-1024 have revealed the presence of 8-10 absorbing ions between 680 and 1000 A (restframe): C III, N III, N IV, O III, O IV, O VI, S V, S VI, possibly Ne VIII, and possibly O V* arising from a metastable excited state. We also present ground-based optical observations of the broad line troughs for the following ions: H I, C IV, N V, Si IV, and possibly Fe III, S IV, P V, and C III* (also arising from a metastable excited state). The results of this fit are used to estimate the absorbing ionic column densities. There is evidence that the broad absorption line clouds are optically thick and either do not completely cover the continuum source or narrow unresolved lines are present.

  10. Hubble Space Telescope ultraviolet spectroscopy of the highly polarized but quiescent quasar OI 287

    NASA Technical Reports Server (NTRS)

    Antonucci, Robert; Kinney, Anne L.; Hurt, Todd

    1993-01-01

    The quasar OI 287 has a unique combination of properties, including a high and constant optical polarization oriented parallel to the radio axis, a quiescent optical flux, and a lobe-dominant radio source. Previous studies have led to the picture of an edge-on thin dusty torus occulting a featureless continuum (FC) source and a broad line region (BLR) in this object. The FC source and the BLR are seen only in reflected (polarized) light. In the unified models, this makes OI 287 a 'quasar 2', analogous to the type 2 Seyfert galaxies and the narrow-line radio galaxies. Our UV spectrum adds two bits of information consistent with the above ideas. First, the spectrum neither turns up in the UV, as expected for optically thin dust scattering, nor turns down as expected for polarization by dust transmission. It is consistent with reflection by free electrons or optically thick dust. Second, there are in fact blueshifted absorption troughs associated with the C IV 1549 A line, supporting the analogy with BALs, as well as the idea that the BALs are objects which present a nearly edge-on view of a disk structure.

  11. Glycosylation of closely spaced acceptor sites in human glycoproteins

    PubMed Central

    Shrimal, Shiteshu; Gilmore, Reid

    2013-01-01

    Summary Asparagine-linked glycosylation of proteins by the oligosaccharyltransferase (OST) occurs when acceptor sites or sequons (N-x≠P-T/S) on nascent polypeptides enter the lumen of the rough endoplasmic reticulum. Metazoan organisms assemble two isoforms of the OST that have different catalytic subunits (STT3A or STT3B) and partially non-overlapping cellular roles. Potential glycosylation sites move past the STT3A complex, which is associated with the translocation channel, at the protein synthesis elongation rate. Here, we investigated whether close spacing between acceptor sites in a nascent protein promotes site skipping by the STT3A complex. Biosynthetic analysis of four human glycoproteins revealed that closely spaced sites are efficiently glycosylated by an STT3B-independent process unless the sequons contain non-optimal sequence features, including extreme close spacing between sequons (e.g. NxTNxT) or the presence of paired NxS sequons (e.g. NxSANxS). Many, but not all, glycosylation sites that are skipped by the STT3A complex can be glycosylated by the STT3B complex. Analysis of a murine glycoprotein database revealed that closely spaced sequons are surprisingly common, and are enriched for paired NxT sites when the gap between sequons is less than three residues. PMID:24105266

  12. Developing closed life support systems for large space habitats

    NASA Technical Reports Server (NTRS)

    Phillips, J. M.; Harlan, A. D.; Krumhar, K. C.

    1978-01-01

    In anticipation of possible large-scale, long-duration space missions which may be conducted in the future, NASA has begun to investigate the research and technology development requirements to create life support systems for large space habitats. An analysis suggests the feasibility of a regeneration of food in missions which exceed four years duration. Regeneration of food in space may be justified for missions of shorter duration when large crews must be supported at remote sites such as lunar bases and space manufacturing facilities. It is thought that biological components consisting principally of traditional crop and livestock species will prove to be the most acceptable means of closing the food cycle. A description is presented of the preliminary results of a study of potential biological components for large space habitats. Attention is given to controlled ecosystems, Russian life support system research, controlled-environment agriculture, and the social aspects of the life-support system.

  13. Approximating the Generalized Voronoi Diagram of Closely Spaced Objects

    SciTech Connect

    Edwards, John; Daniel, Eric; Pascucci, Valerio; Bajaj, Chandrajit

    2015-06-22

    We present an algorithm to compute an approximation of the generalized Voronoi diagram (GVD) on arbitrary collections of 2D or 3D geometric objects. In particular, we focus on datasets with closely spaced objects; GVD approximation is expensive and sometimes intractable on these datasets using previous algorithms. With our approach, the GVD can be computed using commodity hardware even on datasets with many, extremely tightly packed objects. Our approach is to subdivide the space with an octree that is represented with an adjacency structure. We then use a novel adaptive distance transform to compute the distance function on octree vertices. The computed distance field is sampled more densely in areas of close object spacing, enabling robust and parallelizable GVD surface generation. We demonstrate our method on a variety of data and show example applications of the GVD in 2D and 3D.

  14. Approximating the Generalized Voronoi Diagram of Closely Spaced Objects

    PubMed Central

    Edwards, John; Daniel, Eric; Pascucci, Valerio; Bajaj, Chandrajit

    2016-01-01

    We present an algorithm to compute an approximation of the generalized Voronoi diagram (GVD) on arbitrary collections of 2D or 3D geometric objects. In particular, we focus on datasets with closely spaced objects; GVD approximation is expensive and sometimes intractable on these datasets using previous algorithms. With our approach, the GVD can be computed using commodity hardware even on datasets with many, extremely tightly packed objects. Our approach is to subdivide the space with an octree that is represented with an adjacency structure. We then use a novel adaptive distance transform to compute the distance function on octree vertices. The computed distance field is sampled more densely in areas of close object spacing, enabling robust and parallelizable GVD surface generation. We demonstrate our method on a variety of data and show example applications of the GVD in 2D and 3D. PMID:27540272

  15. Multi-wavelength Monitoring of Lensed Quasars: Deciphering Quasar Structure at Micro-arcseconds Scales

    NASA Astrophysics Data System (ADS)

    Mosquera, Ana; Morgan, Christopher W.; Kochanek, Christopher S.; Dai, Xinyu; Chen, Bin; MacLeod, Chelsea Louise; Chartas, George

    2016-01-01

    Microlensing in multiply imaged gravitationally lensed quasars provides us with a unique tool to zoom in on the structure of AGN and explore their physics in more detail. Microlensing magnification, caused primarily by stars and white dwarfs close to the line of sight towards the lensed quasar images, is seen as uncorrelated flux variations due to the relative motions of the quasar, the lens, its stars, and the observer, and it depends on the structural and dynamical properties of the source and the lens. Since the magnification depends upon the size of the source, we can use microlensing to measure the size of quasar emission regions. In essence, the amplitude of the microlensing variability encodes the source size, with smaller sources showing larger variability amplitudes. Using state of the art microlensing techniques, our team has performed pioneering research in the field based on multi-wavelength space and ground-based observations. Among the most remarkable results, using Chandra observations we have set the first quantitative constraints on the sizes of the X-ray emission regions of quasars. In this work l briefly describe the methodology, the results from our previous multi-wavelength monitoring programs, and the next frontier of exploring the dependence of the structure of the X-ray emission regions on black hole mass and X-ray energy.

  16. Dusty Quasars at High Redshifts

    NASA Astrophysics Data System (ADS)

    Weedman, Daniel; Sargsyan, Lusine

    2016-09-01

    A population of quasars at z ˜ 2 is determined based on dust luminosities νL ν (7.8 μm) that includes unobscured, partially obscured, and obscured quasars. Quasars are classified by the ratio νL ν (0.25 μm)/νL ν (7.8 μm) = UV/IR, assumed to measure obscuration of UV luminosity by the dust that produces IR luminosity. Quasar counts at rest-frame 7.8 μm are determined for quasars in the Boötes field of the NOAO Deep Wide Field Survey using 24 μm sources with optical redshifts from the AGN and Galaxy Evolution Survey (AGES) or infrared redshifts from the Spitzer Infrared Spectrograph. Spectral energy distributions are extended to far-infrared wavelengths using observations from the Herschel Space Observatory Spectral and Photometric Imaging Receiver (SPIRE), and new SPIRE photometry is presented for 77 high-redshift quasars from the Sloan Digital Sky Survey. It is found that unobscured and obscured quasars have similar space densities at rest-frame 7.8 μm, but the ratio L ν (100 μm)/L ν (7.8 μm) is about three times higher for obscured quasars than for unobscured, so that far-infrared or submillimeter quasar detections are dominated by obscured quasars. We find that only ˜5% of high-redshift submillimeter sources are quasars and that existing 850 μm surveys or 2 mm surveys should already have detected sources at z ˜ 10 if quasar and starburst luminosity functions remain the same from z = 2 until z = 10.

  17. SPITZER OBSERVATIONS OF YOUNG RED QUASARS

    SciTech Connect

    Urrutia, Tanya; Lacy, Mark; Spoon, Henrik; Glikman, Eilat; Petric, Andreea; Schulz, Bernhard E-mail: mlacy@nrao.edu E-mail: eilat.glikman@yale.edu E-mail: bschulz@ipac.caltech.edu

    2012-10-01

    We present mid-infrared spectra and photometry of 13 redshift 0.4 < z < 1 dust reddened quasars obtained with Spitzer IRS and MIPS. We compare properties derived from their infrared spectral energy distributions (intrinsic active galactic nucleus (AGN) luminosity and far-infrared luminosity from star formation) to the host luminosities and morphologies from Hubble Space Telescope imaging, and black hole masses estimated from optical and/or near-infrared spectroscopy. Our results are broadly consistent with models in which most dust reddened quasars are an intermediate phase between a merger-driven starburst triggering a completely obscured AGN, and a normal, unreddened quasar. We find that many of our objects have high accretion rates, close to the Eddington limit. These objects tend to fall below the black hole mass-bulge luminosity relation as defined by local galaxies, whereas most of our low accretion rate objects are slightly above the local relation, as typical for normal quasars at these redshifts. Our observations are therefore most readily interpreted in a scenario in which galaxy stellar mass growth occurs first by about a factor of three in each merger/starburst event, followed sometime later by black hole growth by a similar amount. We do not, however, see any direct evidence for quasar feedback affecting star formation in our objects, for example, in the form of a relationship between accretion rate and star formation. Five of our objects, however, do show evidence for outflows in the [O III]5007 A emission line profile, suggesting that the quasar activity is driving thermal winds in at least some members of our sample.

  18. Hilbert-space localization in closed quantum systems

    NASA Astrophysics Data System (ADS)

    Cohen, Doron; Yukalov, Vyacheslav I.; Ziegler, Klaus

    2016-04-01

    Quantum localization within an energy shell of a closed quantum system stands in contrast to the ergodic assumption of Boltzmann, and to the corresponding eigenstate thermalization hypothesis. The familiar case is the real-space Anderson localization and its many-body Fock-space version. We use the term Hilbert-space localization in order to emphasize the more general phase-space context. Specifically, we introduce a unifying picture that extends the semiclassical perspective of Heller, which relates the localization measure to the probability of return. We illustrate our approach by considering several systems of experimental interest, referring in particular to the bosonic Josephson tunneling junction. We explore the dependence of the localization measure on the initial state and on the strength of the many-body interactions using a recursive projection method.

  19. Underwater acoustic source localization using closely spaced hydrophone pairs

    NASA Astrophysics Data System (ADS)

    Sim, Min Seop; Choi, Bok-Kyoung; Kim, Byoung-Nam; Lee, Kyun Kyung

    2016-07-01

    Underwater sound source position is determined using a line array. However, performance degradation occurs owing to a multipath environment, which generates incoherent signals. In this paper, a hydrophone array is proposed for underwater source position estimation robust to a multipath environment. The array is composed of three pairs of sensors placed on the same line. The source position is estimated by performing generalized cross-correlation (GCC). The proposed system is not affected by a multipath time delay because of the close distance between closely spaced sensors. The validity of the array is confirmed by simulation using acoustic signals synthesized by eigenrays.

  20. Predicting Space Weather Effects on Close Approach Events

    NASA Astrophysics Data System (ADS)

    Newman, L.; Besser, R.; Hejduk, M.

    The NASA Robotic Conjunction Assessment Risk Analysis (CARA) team sends ephemeris data to the Joint Space Operations Center (JSpOC) for screening against the high accuracy catalog, then assesses risk posed to protected assets from predicted close approaches. Since most spacecraft supported by the CARA team are located in LEO orbits, atmospheric drag is a primary source of state estimate uncertainty, and drag is directly governed by space weather. At present the actual effect of space weather on atmospheric density cannot be accurately predicted because most atmospheric density models are empirical in nature. The Jacchia-Bowman-HASDM 2009 atmospheric density model used at the JSpOC employs a solar storm active compensation feature that predicts storm sizes and arrival times, and thus the resulting neutral density alterations. With this feature, estimation errors can occur in either direction (i.e., over- or under-estimation of density and thus drag), giving rise to several questions. Does a change in space weather make a close approach safer or riskier? Might performing a maneuver make the approach worse due to uncertainty in predicted location at a given time? What if there are errors in the predicted timing or magnitude of the space weather event? Although the exact effect of a solar storm on atmospheric drag cannot be determined, one can explore the effects of drag perturbations on conjuncting objects' trajectories to determine if a conjunction can become riskier or less risky. The CARA team has constructed a Space Weather Trade-Space tool that systematically alters the drag coefficient of the conjuncting objects and recalculates the probability of collision for each case to determine the effect is likely to have on the collision risk. In addition to a review of the theory and the particulars of the tool, all of the observed output will be explained, along with statistics of their frequency.

  1. The Hubble Space Telescope Quasar Absorption Line Key Project: The Unusual Absorption-Line System in the Spectrum of PG 2302+029--Ejected or Intervening?

    NASA Technical Reports Server (NTRS)

    Jannuzi, B. T.; Hartig, G. F.; Kirhakos, S.; Sargent, W. L. W.; Turnshek, D. A.; Weymann, R. J.; Bahcall, J. N.; Bergeron, J.; Boksenberg, A.; Savage, B. D.; Schneider, D. P.; Wolfe, A. M.

    1996-01-01

    We report the discovery of a high-ionization broad absorption line system at a redshift of z(sub abs) = 0.695 in the spectrum of the z(sub em) = 1.052 radio-quiet quasar PG 2302+029. Broad absorption with FWHM from 3000 to 5000 km/s is detected from C iv, N v, and O vi in Hubble Space Telescope (HST) Faint Object Spectrograph spectra of the quasar. A narrow-line system (FWHM approx. 250 km/s) at z(sub abs) = 0.7016 is resolved from the broad blend and includes absorption by Ly alpha and the C iv, N v, and O vi doublets. No absorption by low-ionization metal species (e.g., Si II and Mg II) is detected in the HST or ground-based spectra for either the broad or the narrow system. The centroids of the broad system lines are displaced by approx. 56,000 km/s to the blue of the quasar's broad emission lines. The reddest extent of the broad-line absorption is more than 50,000 km/s from the quasar. The properties of this system are unprecedented, whether it is an intervening or an ejected system.

  2. Close-up of Shuttle Thermal Tiles in Space

    NASA Technical Reports Server (NTRS)

    2005-01-01

    Launched on July 26, 2005 from the Kennedy Space Center in Florida, STS-114 was classified as Logistics Flight 1. Among the Station-related activities of the mission were the delivery of new supplies and the replacement of one of the orbital outpost's Control Moment Gyroscopes (CMGs). STS-114 also carried the Raffaello Multi-Purpose Logistics Module and the External Stowage Platform-2. A major focus of the mission was the testing and evaluation of new Space Shuttle flight safety, which included new inspection and repair techniques. Upon its approach to the International Space Station (ISS), the Space Shuttle Discovery underwent a photography session in order to assess any damages that may have occurred during its launch and/or journey through Space. The mission's third and final Extra Vehicular Activity (EVA) included taking a close-up look and the repair of the damaged heat shield. Gap fillers were removed from between the orbiter's heat-shielding tiles located on the craft's underbelly. Never before had any repairs been done to an orbiter while still in space. This particular photo was taken by astronaut Stephen K. Robinson, STS-114 mission specialist, whose shadow is visible on the thermal protection tiles, and a portion of the Canadian built Remote Manipulator System (RMS) robotic arm and the Nile River is visible at the bottom.

  3. Hubble Space Telescope faint object spectrograph Quasar Absorption System Snapshot Survey (AbSnap). 1: Astrometric optical positions and finding charts of 269 bright QSO

    NASA Technical Reports Server (NTRS)

    Bowen, David V.; Osmer, Samantha J.; Blades, J. Chris; Tytler, David; Cottrell, Lance; Fan, Xiao-Ming; Lanzetta, Kenneth M.

    1994-01-01

    We present finding charts and optical positions accurate to less than 1 arcsec for 269 bright (V less than or = 18.5) Quasi-Stellar Objects (QSOs). These objects were selected as candidates for the Hubble Space Telescope (HST) Quasar Absorption System Snapshot Survey (AbSnap), a program designed to use the Faint Object Spectrograph (FOS) to obtain short exposure ultraviolet (UV) spectra of bright QSOs. Many quasars were included because of their proximity to bright, low redshift galaxies and positions of these QSOs are measured accurately for the first time. Data were obtained using the digitized sky survey produced by the Space Telescope Science Institute's Guide Stars Selection System Astrometric Support Program.

  4. Heat transfer from cylinders having closely spaced fins

    NASA Technical Reports Server (NTRS)

    Biermann, Arnold E

    1937-01-01

    The heat-transfer coefficients have been determined for five steel cylinders having fins 1.22 inches wide and the spacing between the fins ranging from 0.022 to 0.131 inch. The cylinders were tested with and without baffles in a wind tunnel; they were also tested enclosed in jackets with the cooling air supplied by a blower. A maximum heat transfer was reached at a fin space of about 0.45 inch for the cylinders tested with each of the three methods of cooling investigated. The rise in temperature of the air passing between the fins and the change in flow pattern were found to be important factors limiting the heat transfer that may be obtained by decreasing the fin space. The use of baffles for directing the air around the cylinders with closely spaced fins proved very effective in increasing the over-all heat-transfer coefficient, provided that the spacing was not appreciably less than that for maximum heat transfer.

  5. 78 FR 70093 - Commercial Space Transportation Advisory Committee-Closed Session

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-11-22

    ... Federal Aviation Administration Commercial Space Transportation Advisory Committee--Closed Session AGENCY: Federal Aviation Administration (FAA), DOT. ACTION: Notice of Commercial Space Transportation Advisory... closed session of the Commercial Space Transportation Advisory Committee (COMSTAC). The special...

  6. A Hungry Quasar Caught in the Act

    NASA Astrophysics Data System (ADS)

    2001-05-01

    interaction with the quasar host galaxy. Quasar activity is believed to be triggered by such dramatic events. Since some time, astronomers have therefore been searching for clear evidence for a connection between gravitational interaction and the quasar phenomenon. However, quasars are very bright objects and their light easily outshines all nearby objects. Any companion galaxies and structural features that may indicate interaction are therefore hard to detect. While observations with the Hubble Space Telescope (HST) have much improved our knowledge of the interaction-activity connection in some relatively nearby quasars, it has been difficult to probe the same phenomenon in more distant quasar environments. Such studies clearly require larger telescopes. The observations of the quasar HE 1013-2136 presented here result from a new programme that addresses this issue at earlier cosmic epochs. This 17-mag object is seen in the southern constellation Hydra (The Water Snake) and is located at a distance of about 10 billion light years (the redshift is z = 0.785) PR Photo 20a/01 shows an image of HE 1013-2136 and its immediate surroundings, obtained with the FORS2 multi-mode instrument at the 8.2-m VLT KUEYEN telescope under very good seeing conditions. The image resolution is about 0.6 arcsec, or about 10,000 light-years at the distance of the quasar. The image has been further sharpened by means of image processing software (the Lucy algorithm) in PR Photo 20b/01 , now also showing the distribution of objects very close to the bright quasar image. This impressively illustrates the light gathering and resolution power of the VLT. Tidal forces at HE 1013-2136 The quasar is the point-like object at the center of the images. It is embedded within a complex structure that mainly consists of two arc-like and knotty tails extending in different directions. Such tails are well-known from nearby galaxy interactions, cf. NGC 6872/IC4970 and are a consequence of tidal forces in the

  7. A closed life-support system for space colonies

    NASA Technical Reports Server (NTRS)

    Johnson, R. D.; Jebens, H. J.; Sweet, H. C.

    1977-01-01

    In 1975, a system design study was performed to examine a completely self-contained system for a permanent colony of 10,000 inhabitants in space. Fundamental to this design was the life support system. Since resupply from earth is prohibitive in transportation costs, it was decided to use a closed system with the initial supply of oxygen coming from processing of lunar ores, and the supply of carbon, nitrogen and hydrogen from earth. The problem of life support was treated starting with the nutritional and metabolic requirements for the human population, creating a food and water chain sufficient to supply these demands, adding the additional requirements for the animal and plant sources in the food chain, feeding back useful waste products, supplying water as required from different sources, and closing the loop by processing organic wastes into CO2. This concept places the burden of the system upon plants for O2 generation and waste processing the CO2 generation.

  8. Accumulation of Raman gain between closely spaced pulse pairs.

    PubMed

    Marshall, L R; Piper, J A

    1990-12-01

    The short-pulse conversion efficiency of stimulated Raman scattering in Pb vapor is increased from 15% to 35% by using a novel technique that employs a closely spaced pair of pump pulses. The second pulse scatters off the coherent excitation induced in the medium by the first pulse, with a resultant enhancement in efficiency. To our knowledge these results give the first observation of such long-lived cooperative phenomena in stimulated Raman scattering. We have also observed this phenomenon in H(2) and show that this technique is readily applicable to other Raman-active media. PMID:19771085

  9. NASA Research For Instrument Approaches To Closely Spaced Parallel Runways

    NASA Technical Reports Server (NTRS)

    Elliott, Dawn M.; Perry, R. Brad

    2000-01-01

    Within the NASA Aviation Systems Capacity Program, the Terminal Area Productivity (TAP) Project is addressing airport capacity enhancements during instrument meteorological condition (IMC). The Airborne Information for Lateral Spacing (AILS) research within TAP has focused on an airborne centered approach for independent instrument approaches to closely spaced parallel runways using Differential Global Positioning System (DGPS) and Automatic Dependent Surveillance-Broadcast (ADS-B) technologies. NASA Langley Research Center (LaRC), working in partnership with Honeywell, Inc., completed in AILS simulation study, flight test, and demonstration in 1999 examining normal approaches and potential collision scenarios to runways with separation distances of 3,400 and 2,500 feet. The results of the flight test and demonstration validate the simulation study.

  10. Close Up of Space Shuttle External Tank's Intertank Flange Area

    NASA Technical Reports Server (NTRS)

    2004-01-01

    In NASA's Michoud Assembly Facility in New Orleans, the Space Shuttle External Tank 120 is in position for its new foam application process on the liquid hydrogen tank-to-inter tank flange area, a tank structural connection point. This image is a close-up of the inter tank flange area. The foam will be applied with an enhanced finishing procedure that requires two technicians, one for a new mold-injection procedure to the intertank's ribbing and one for real-time videotaped surveillance of the process. The 120 tank is slated for launch on the Orbiter Discovery scheduled for next Spring. Marshall Space Flight Center played a significant role in the development of the new application process designed to replace the possible debris shedding source previously used. (Lockheed Martin/NASA Michoud)

  11. A Closed Ecological System in a Space Experiment

    NASA Astrophysics Data System (ADS)

    Strauch, S. M.; Schuster, M.; Lebert, M.; Richter, P.; Schmittnagel, M.; Hader, D.-P.

    2008-06-01

    The Russian FOTON-M3 mission, a satellite for mid-length experiments in space and recovery afterwards, included a closed artificial ecosystem (OMEGAHAB for Oreochromis Mossambicus-Euglena Gracilis-Aquatic HABitat) with the photosynthetic flagellate Euglena gracilis as oxygen producer and larvae of Oreochromis mossambicus, a Tilapia species, as consumer. During the 12-day orbital flight the algae were observed 10 minutes per day by means of a miniaturized microscope to analyse their swimming behavior. The fishes were also filmed to monitor their development and movement. An identical experiment was carried out as ground control. A data downlink provided the measured temperature values of the space experiment every day to readjust the temperature of the ground reference in order to eliminate the influence of the different temperature on the velocity of the development of the fishes. The system worked very well and confirmed the design in principle. OMEGAHAB was the most successful German experiment of that kind as yet.

  12. The Extremes of Quasar Variability

    NASA Astrophysics Data System (ADS)

    Stern, Daniel

    2016-04-01

    Variability is one of the key observational properties of quasars, and it can be used as a probe of their fueling, physics, and evolution. A new generation of synoptic sky surveys, in combination with the novel data analytics tools, offers unprecedented data sets for the studies of quasars in the time domain. I will illustrate this with examples from the Catalina Real-Time Transient Survey (CRTS), which has an open and growing archive of 500 million light curves, including 350,000 spectroscopically confirmed quasars, with the time baselines ranging from 10 minutes to 10 years. I will discuss a new approach to discover quasars using a combination of variability and mid-IR colors from WISE, which results in a catalog of over a million quasar candidates. I will then discuss quasars with extreme, anomolous light curves, including quasars that have gone through extreme brightening events over the past decade with concordant large changes in their spectroscopic properties. I will also discuss a small subset of quasars with periodic light curves which we interpret as a signature of close (milliparsec scale) supermassive black hole (SMBH) binaries.

  13. CFD simulation of boundary effects on closely spaced jets

    NASA Astrophysics Data System (ADS)

    Shrivastava, Ishita; Adams, Eric

    2015-11-01

    In coastal areas characterized by shallow water depth, industrial effluents are often diluted using multiple closely spaced jets. Examples of such effluents include brine from desalination plants, treated wastewater from sewage treatment plants and heated water from thermal power plants. These jets are arranged in various orientations, such as unidirectional diffusers and rosette groups, to maximize mixing with ambient water. Due to effects of dynamic pressure, the jets interact with each other leading to mixing characteristics which are quite different from those of individual jets. The effect of mutual interaction is exaggerated under confinement, when a large number of closely spaced jets discharge into shallow depth. Dilution through an outfall, consisting of multiple jets, depends on various outfall and ambient parameters. Here we observe the effects of shoreline proximity, in relation to diffuser length and water depth, on the performance of unidirectional diffusers discharging to quiescent water. For diffusers located closer to shore, less dilution is observed due to the limited availability of ambient water for dilution. We report on the results of Computational Fluid Dynamics (CFD) simulations and compare the results with experimental observations.

  14. HUBBLE'S 100,000TH EXPOSURE CAPTURES IMAGE OF DISTANT QUASAR

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The Hubble Space Telescope achieved its 100,000th exposure June 22 with a snapshot of a quasar that is about 9 billion light-years from Earth. The Wide Field and Planetary Camera 2 clicked this image of the quasar, the bright object in the center of the photo. The fainter object just above it is an elliptical galaxy. Although the two objects appear to be close to each other, they are actually separated by about 2 billion light-years. Located about 7 billion light-years away, the galaxy is almost directly in front of the quasar. Astronomer Charles Steidel of the California Institute of Technology in Pasadena, Calif., indirectly discovered the galaxy when he examined the quasar's light, which contained information about the galaxy's chemical composition. The reason, Steidel found, was that the galaxy was absorbing the light at certain frequencies. The astronomer is examining other background quasars to determine which kinds of galaxies absorb light at the same frequencies. Steidel also was somewhat surprised to discover that the galaxy is an elliptical, rather than a spiral. Elliptical galaxies are generally believed to contain very little gas. However, this elliptical has a gaseous 'halo' and contains no visible stars. Part of the halo is directly in front of the quasar. The bright object to the right of the quasar is a foreground star. The quasar and star are separated by billions of light-years. The quasar looks as bright as the star because it produces a tremendous amount of light from a compact source. The 'disturbed-looking' double spiral galaxy above the quasar also is in the foreground. Credit: Charles Steidel (California Institute of Technology, Pasadena, CA) and NASA. Image files in GIF and JPEG format and captions may be accessed on Internet via anonymous ftp from ftp.stsci.edu in /pubinfo.

  15. Predicting Space Weather Effects on Close Approach Events

    NASA Technical Reports Server (NTRS)

    Hejduk, Matthew D.; Newman, Lauri K.; Besser, Rebecca L.; Pachura, Daniel A.

    2015-01-01

    The NASA Robotic Conjunction Assessment Risk Analysis (CARA) team sends ephemeris data to the Joint Space Operations Center (JSpOC) for conjunction assessment screening against the JSpOC high accuracy catalog and then assesses risk posed to protected assets from predicted close approaches. Since most spacecraft supported by the CARA team are located in LEO orbits, atmospheric drag is the primary source of state estimate uncertainty. Drag magnitude and uncertainty is directly governed by atmospheric density and thus space weather. At present the actual effect of space weather on atmospheric density cannot be accurately predicted because most atmospheric density models are empirical in nature, which do not perform well in prediction. The Jacchia-Bowman-HASDM 2009 (JBH09) atmospheric density model used at the JSpOC employs a solar storm active compensation feature that predicts storm sizes and arrival times and thus the resulting neutral density alterations. With this feature, estimation errors can occur in either direction (i.e., over- or under-estimation of density and thus drag). Although the exact effect of a solar storm on atmospheric drag cannot be determined, one can explore the effects of JBH09 model error on conjuncting objects' trajectories to determine if a conjunction is likely to become riskier, less risky, or pass unaffected. The CARA team has constructed a Space Weather Trade-Space tool that systematically alters the drag situation for the conjuncting objects and recalculates the probability of collision for each case to determine the range of possible effects on the collision risk. In addition to a review of the theory and the particulars of the tool, the different types of observed output will be explained, along with statistics of their frequency.

  16. Performance of a simple closed aquatic ecosystem (CAES) in space

    NASA Astrophysics Data System (ADS)

    Wang, G.-H.; Li, G.-B.; Hu, C.-X.; Liu, Y.-D.; Song, L.-R.; Tong, G.-H.; Liu, X.-M.; Cheng, E.-T.

    2004-01-01

    A simple Closed Aquatic Ecosystem (CAES) consisting of single-celled green algae ( Chlorella pyrenoidosa, producer), a spiral snail ( Bulinus australianus, consumer) and a data acquisition and control unit was flown on the Chinese Spacecraft SHENZHOU-II in January 2001 for 7 days. In order to study the effect of microgravity on the operation of CAES, a 1 g centrifuge reference group in space, a ground 1 g reference group and a ground 1 g centrifuge reference group (1.4 g group) were run concurrently. Real-time data about algae biomass (calculated from transmission light intensity), temperature, light and centrifugation of the CAES were logged at minute intervals. It was found that algae biomass of both the microgravity group and the ground 1 g centrifuge reference group (1.4 g) fluctuated during the experiment, but the algae biomass of the 1 g centrifuge reference group in space and the ground 1 g reference group increased during the experiment. The results may be attributable to influences of microgravity and 1.4 g gravity on the algae and snails metabolisms. Microgravity is the main factor to affect the operation of CAES in space and the contribution of microgravity to the effect was also estimated. These data may be valuable for the establishment of a complex CELSS in the future.

  17. Quasars Probing Quasars. VI. Excess H I Absorption within One Proper Mpc of z ~ 2 Quasars

    NASA Astrophysics Data System (ADS)

    Prochaska, J. Xavier; Hennawi, Joseph F.; Lee, Khee-Gan; Cantalupo, Sebastiano; Bovy, Jo; Djorgovski, S. G.; Ellison, Sara L.; Lau, Marie Wingyee; Martin, Crystal L.; Myers, Adam; Rubin, Kate H. R.; Simcoe, Robert A.

    2013-10-01

    With close pairs of quasars at different redshifts, a background quasar sightline can be used to study a foreground quasar's environment in absorption. We use a sample of 650 projected quasar pairs to study the H I Lyα absorption transverse to luminous, z ~ 2 quasars at proper separations of 30 kpc < R < 1 Mpc. In contrast to measurements along the line-of-sight, regions transverse to quasars exhibit enhanced H I Lyα absorption and a larger variance than the ambient intergalactic medium, with increasing absorption and variance toward smaller scales. Analysis of composite spectra reveals excess absorption characterized by a Lyα equivalent width profile W = 2.3 Å (R /100 kpc)-0.46. We also observe a high (sime 60%) covering factor of strong, optically thick H I absorbers (H I column N_{H\\,\\scriptsize{I}}>10^{17.3}\\, cm^{-2}) at separations R < 200 kpc, which decreases to ~20% at R ~= 1 Mpc, but still represents a significant excess over the cosmic average. This excess of optically thick absorption can be described by a quasar-absorber cross-correlation function ξQA(r) = (r/r 0)γ with a large correlation length r_0=12.5^{+2.7}_{-1.4}\\, h^{-1}\\ Mpc (comoving) and \\gamma =1.68^{+0.14}_{-0.30}. The H I absorption measured around quasars exceeds that of any previously studied population, consistent with quasars being hosted by massive dark matter halos M halo ≈ 1012.5 M ⊙ at z ~ 2.5. The environments of these massive halos are highly biased toward producing optically thick gas, and may even dominate the cosmic abundance of Lyman limit systems and hence the intergalactic opacity to ionizing photons at z ~ 2.5. The anisotropic absorption around quasars implies the transverse direction is much less likely to be illuminated by ionizing radiation than the line-of-sight.

  18. 3. A Closed Aquatic System for Space and Earth Application

    NASA Astrophysics Data System (ADS)

    Slenzka, K.; Duenne, M.; Jastorff, B.; Ranke, J.; Schirmer, M.

    Increased durations in space travel as well as living in extreme environments are requiring reliable life support systems in general and bioregenerative ones in detail. Waste water management, air revitalization and food production are obviously center goals in this research, however, in addition a potential influence by chemicals, drugs etc. released to the closed environment must be considered. On this basis ecotoxicological data become more and more important for CELSS (Closed Ecological Life Support System) development and performance. The experiences gained during the last years in our research group lead to the development of an aquatic habitat, called AquaHab (formerly CBRU), which is a closed, self-sustaining system with a total water volume of 9 liters. In the frame program of a R&D project funded by the state of Bremen and OHB System, AquaHab is under adaptation to become an ecotoxicological research unit containing for example Japanese Medaka or Zebra Fish, amphipods, water snails and water plants. Test runs were standardized and analytical methods were developed. Beside general biological and water chemical parameters, activity measurements of biotransforming enzymes (G6PDH, CytP450-Oxidase, Peroxidase) and cell viability tests as well as residual analysis of the applied substance and respective metabolites were selected as evaluation criteria. In a first series of tests low doses effects of TBT (Tributyltin, 0.1 to 20 μgTBT/l nominal concentration) were analyzed. The AquaHab and data obtained for applied environmental risk assessment will be presented at the assembly.

  19. Hubble Space Telescope Observations of the Luminous IRAS Source FSC 10214+4724: A Gravitationally Lensed Infrared Quasar

    NASA Technical Reports Server (NTRS)

    Eisenhardt, Peter R.; Armus, Lee; Hogg, David W.; Soifer, B. T.; Neugebauer, G.; Werner, Michael W.

    1996-01-01

    With a redshift of 2.3, the IRAS source FSC 10214+4724 is apparently one of the most luminous objects known in the universe. We present an image of FSC 10214+4724 at 0.8 pm obtained with the Hubble Space Telescope (HST) WFPC2 Planetary Camera. The source appears as an unresolved (less then 0.06) arc 0.7 long, with significant substructure along its length. The center of curvature of the arc is located near an elliptical galaxy 1.18 to the north. An unresolved component 100 times fainter than the arc is clearly detected on the opposite side of this galaxy. The most straightforward interpretation is that FSC 10214+4724 is gravitationally lensed by the foreground elliptical galaxy, with the faint component a counter-image of the IRAS source. The brightness of the arc in the HST image is then magnified by approx. 100, and the intrinsic source diameter is approx. 0.0l (80 pc) at 0.25 microns rest wavelength. The bolometric luminosity is probably amplified by a smaller factor (approx. 30) as a result of the larger extent expected for the source in the far-infrared. A detailed lensing model is presented that reproduces the observed morphology and relative flux of the arc and counterimage and correctly predicts the position angle of the lensing galaxy. The model also predicts reasonable values for the velocity dispersion, mass, and mass-to-light ratio of the lensing galaxy for a wide range of galaxy redshifts. A redshift for the lensing galaxy of -0.9 is consistent with the measured surface brightness profile from the image, as well as with the galaxy's spectral energy distribution. The background lensed source has an intrinsic luminosity approx. 2 x 10(exp 13) L(solar mass) and remains a highly luminous quasar with an extremely large ratio of infrared to optical/ultraviolet luminosity.

  20. Various Approaches for Targeting Quasar Candidates

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Zhao, Y.

    2015-09-01

    With the establishment and development of space-based and ground-based observational facilities, the improvement of scientific output of high-cost facilities is still a hot issue for astronomers. The discovery of new and rare quasars attracts much attention. Different methods to select quasar candidates are in bloom. Among them, some are based on color cuts, some are from multiwavelength data, some rely on variability of quasars, some are based on data mining, and some depend on ensemble methods.

  1. Active galactic nucleus and quasar science with aperture masking interferometry on the James Webb Space Telescope

    SciTech Connect

    Ford, K. E. Saavik; McKernan, Barry; Sivaramakrishnan, Anand; Martel, André R.; Koekemoer, Anton; Lafrenière, David; Parmentier, Sébastien

    2014-03-10

    Due to feedback from accretion onto supermassive black holes (SMBHs), active galactic nuclei (AGNs) are believed to play a key role in ΛCDM cosmology and galaxy formation. However, AGNs extreme luminosities and the small angular size of their accretion flows create a challenging imaging problem. We show that the James Webb Space Telescope's Near Infrared Imager and Slitless Spectrograph (JWST-NIRISS) Aperture Masking Interferometry (AMI) mode will enable true imaging (i.e., without any requirement of prior assumptions on source geometry) at ∼65 mas angular resolution at the centers of AGNs. This is advantageous for studying complex extended accretion flows around SMBHs and in other areas of angular-resolution-limited astrophysics. By simulating data sequences incorporating expected sources of noise, we demonstrate that JWST-NIRISS AMI mode can map extended structure at a pixel-to-pixel contrast of ∼10{sup –2} around an L = 7.5 point source, using short exposure times (minutes). Such images will test models of AGN feedback, fueling, and structure (complementary with ALMA observations), and are not currently supported by any ground-based IR interferometer or telescope. Binary point source contrast with NIRISS is ∼10{sup –4} (for observing binary nuclei in merging galaxies), significantly better than current ground-based optical or IR interferometry. JWST-NIRISS's seven-hole non-redundant mask has a throughput of 15%, and utilizes NIRISS's F277W (2.77 μm), F380M (3.8 μm), F430M (4.3 μm), and F480M (4.8 μm) filters. NIRISS's square pixels are 65 mas per side, with a field of view ∼2' × 2'. We also extrapolate our results to AGN science enabled by non-redundant masking on future 2.4 m and 16 m space telescopes working at long-UV to near-IR wavelengths.

  2. Possibility of graphene growth by close space sublimation.

    PubMed

    Sopinskyy, Mykola V; Khomchenko, Viktoriya S; Strelchuk, Viktor V; Nikolenko, Andrii S; Olchovyk, Genadiy P; Vishnyak, Volodymyr V; Stonis, Viktor V

    2014-01-01

    Carbon films on the Si/SiO2 substrate are fabricated using modified method of close space sublimation at atmospheric pressure. The film properties have been characterized by micro-Raman and X-ray photoelectron spectroscopy and monochromatic ellipsometry methods. Ellipsometrical measurements demonstrated an increase of the silicon oxide film thickness in the course of manufacturing process. The XPS survey spectra of the as-prepared samples indicate that the main elements in the near-surface region are carbon, silicon, and oxygen. The narrow-scan spectra of C1s, Si2p, O1s regions indicate that silicon and oxygen are mainly in the SiOx (x ≈ 2) oxide form, whereas the main component of C1s spectrum at 284.4 eV comes from the sp2-hybridized carbon phase. Micro-Raman spectra confirmed the formation of graphene films with the number of layers that depended on the distance between the graphite source and substrate. PMID:24731549

  3. Close-spaced vapor transport of II-VI semiconductors

    NASA Astrophysics Data System (ADS)

    Perrier, Gerard

    1991-12-01

    The close spaced vapor transport (CSVT) is an efficient and cost-effective technique that allows the growth of polycrystalline as well as epitaxial thin layers of semiconductors. It has been applied to II-VI materials, especially to zinc and cadmium chalcogenides. A summary table including the deposition parameters, i.e., the nature of the ambient gas, the temperature of the source, the temperature difference between source and substrate, and the values of the growth rates measured on various substrates is presented for ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe. Experimental results concerning the growth of ZnSe on GaAs substrates are also reported. The CSVT system uses an Ar atmosphere and the working temperature is ca. 825 degree(s)C. The temperatures of source and substrate are measured during deposition and growth rates of the ZnSe films are studied as a function of the reciprocal temperature of the substrate surface for GaAs and quartz (inert) substrates. The measured values of the growth rate are compared to the theoretical ones given by the reaction-limited model and the diffusion-limited model. The validity of the models is discussed in terms of the nature of the molecules participating in the transport.

  4. Insulators and Materials for Closed-Spaced Thermoelectric Modules

    SciTech Connect

    Donald P. Snowden

    2003-07-20

    The primary goal of this Phase I program has been accomplished: to demonstrate a ceramic, injection-molded eggcrate which will form the support structure for a close-spaced thermoelectric module which can operate at significantly higher temperatures than presently possible with such modules. It has been shown that yttria-stabilized zirconia is compatible at high temperatures with typical thermoelectric materials (TAGS, SnTE and PbTe) and that it can serve as a barrier between them to preclude cross-contamination and doping of the constituents of one leg type by those from the other. Using a 2 x 2 ceramic eggcrate, thermally sprayed molybdenum electrodes have been deposited on a test module which effectively seal each pocket, further reducing the possibility of migration of elements. Based on these results the next tasks are to refine the design of the injection tool and the injection parameters to produce consistent results and to allow increase in the size of the module to that on which commercial, high-temperature thermoelectric modules can be based. In addition, development of the fabrication techniques for segmented thermoelectric legs for use with these ceramic eggcrates at high temperatures must be continued.

  5. A DISTANT QUASAR'S BRILLIANT LIGHT

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The arrow in this image, taken by a ground-based telescope, points to a distant quasar, the brilliant core of an active galaxy residing billions of light-years from Earth. As light from this faraway object travels across space, it picks up information on galaxies and the vast clouds of material between galaxies as it moves through them. The Space Telescope Imaging Spectrograph aboard NASA's Hubble Space Telescope decoded the quasar's light to find the spectral 'fingerprints' of highly ionized (energized) oxygen, which had mixed with invisible clouds of hydrogen in intergalactic space. The quasar's brilliant beam pierced at least four separate filaments of the invisible hydrogen laced with the telltale oxygen. The presence of oxygen between the galaxies implies there are huge quantities of hydrogen in the universe. Credits: WIYN Telescope at Kitt Peak National Observatory in Arizona. The telescope is owned and operated by the University of Wisconsin, Indiana University, Yale University, and the National Optical Astronomy Observatories.

  6. Locating star-forming regions in quasar host galaxies

    NASA Astrophysics Data System (ADS)

    Young, J. E.; Eracleous, M.; Shemmer, O.; Netzer, H.; Gronwall, C.; Lutz, Dieter; Ciardullo, R.; Sturm, Eckhard

    2014-02-01

    We present a study of the morphology and intensity of star formation in the host galaxies of eight Palomar-Green quasars using observations with the Hubble Space Telescope. Our observations are motivated by recent evidence for a close relationship between black hole growth and the stellar mass evolution in its host galaxy. We use narrow-band [O II]λ3727, Hβ, [O III]λ5007 and Paα images, taken with the Wide Field Planetary Camera 2 and NICMOS instruments, to map the morphology of line-emitting regions, and, after extinction corrections, diagnose the excitation mechanism and infer star-formation rates. Significant challenges in this type of work are the separation of the quasar light from the stellar continuum and the quasar-excited gas from the star-forming regions. To this end, we present a novel technique for image decomposition and subtraction of quasar light. Our primary result is the detection of extended line-emitting regions with sizes ranging from 0.5 to 5 kpc and distributed symmetrically around the nucleus, powered primarily by star formation. We determine star-formation rates of the order of a few tens of M⊙ yr-1. The host galaxies of our target quasars have stellar masses of the order of 1011 M⊙ and specific star-formation rates on a par with those of M82 and luminous infrared galaxies. As such they fall at the upper envelope or just above the star-formation mass sequence in the specific star formation versus stellar mass diagram. We see a clear trend of increasing star-formation rate with quasar luminosity, reinforcing the link between the growth of the stellar mass of the host and the black hole mass found by other authors.

  7. 76 FR 4412 - Commercial Space Transportation Advisory Committee-Closed Session

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-01-25

    ... TRANSPORTATION Federal Aviation Administration Commercial Space Transportation Advisory Committee--Closed Session AGENCY: Federal Aviation Administration (FAA), DOT. ACTION: Notice of Commercial Space Transportation... 102-3.160, notice is hereby given of a special closed session of the Commercial Space...

  8. NEAR-INFRARED IMAGING OF A z = 6.42 QUASAR HOST GALAXY WITH THE HUBBLE SPACE TELESCOPE WIDE FIELD CAMERA 3

    SciTech Connect

    Mechtley, M.; Windhorst, R. A.; Cohen, S. H.; Jansen, R. A.; Scannapieco, E.; Ryan, R. E.; Koekemoer, A. M.; Schneider, G.; Fan, X.; Hathi, N. P.; Keel, W. C.; Roettgering, H.; Schneider, D. P.; Strauss, M. A.; Yan, H. J.

    2012-09-10

    We report on deep near-infrared F125W (J) and F160W (H) Hubble Space Telescope Wide Field Camera 3 images of the z = 6.42 quasar J1148+5251 to attempt to detect rest-frame near-ultraviolet emission from the host galaxy. These observations included contemporaneous observations of a nearby star of similar near-infrared colors to measure temporal variations in the telescope and instrument point-spread function (PSF). We subtract the quasar point source using both this direct PSF and a model PSF. Using direct subtraction, we measure an upper limit for the quasar host galaxy of m{sub J} > 22.8 and m{sub H} > 23.0 AB mag (2 {sigma}). After subtracting our best model PSF, we measure a limiting surface brightness from 0.''3 to 0.''5 radius of {mu}{sub J} > 23.5 and {mu}{sub H} > 23.7 AB mag arcsec{sup -2} (2 {sigma}). We test the ability of the model subtraction method to recover the host galaxy flux by simulating host galaxies with varying integrated magnitude, effective radius, and Sersic index, and conducting the same analysis. These models indicate that the surface brightness limit ({mu}{sub J} > 23.5 AB mag arcsec{sup -2}) corresponds to an integrated upper limit of m{sub J} > 22-23 AB mag, consistent with the direct subtraction method. Combined with existing far-infrared observations, this gives an infrared excess log (IRX) > 1.0 and corresponding ultraviolet spectral slope {beta} > -1.2 {+-} 0.2. These values match those of most local luminous infrared galaxies, but are redder than those of almost all local star-forming galaxies and z {approx_equal} 6 Lyman break galaxies.

  9. Paired quasars near NGC 2639 - Evidence for quasars in superclusters

    NASA Technical Reports Server (NTRS)

    Ford, H.; Ciardullo, R.; Harms, R.

    1983-01-01

    Arp (1979, 1980) has found quasars with similar redshifts which appear to be paired across low-redshift galaxies. Arp concludes that the pairings provide evidence for an association between high-redshift quasars and a small, low-redshift galaxy. Oort et al. (1981) suggested an alternative hypothesis to explain the close redshift pairs. They proposed that the two closest pairs are in superclusters at the cosmological distances implied by the quasars' redshifts. The low-redshift quasar pair U7/U10 (0.303/0.305) is close enough to allow detection of any associated clusters of galaxies on deep red photographs. The present investigation had originally the objective to test the supercluster hypothesis by searching for faint clusters which might comprise a supercluster at z approximately 0.3. Unfortunately, the disappearance of the pairs makes it impossible to test the hypothesis in this field. The search for a supercluster at z = 0.30 revealed a faint rich cluster of galaxies near the quasar U10 (z = 0.305). It was found that U10 is not associated with the cluster.

  10. OH maser observations using the Russian interferometric network ``Quasar'' in preparation for scientific observations with the space mission RadioAstron.

    NASA Astrophysics Data System (ADS)

    Litovchenko, I. D.; Alakoz, A. V.; Kostenko, V. I.; Lihachev, S. F.; Finkelstein, A. M.; Ipatov, A. V.

    2012-07-01

    We present results of a VLBI experiment at a wavelength of 18 cm, which simulates the ground-space interferometer with space link to RadioAstron. An array of five antennas was used, four of them are located in the Russian Federation, plus the the 32-m radio telescope in Medicine (Italy). The 22-m radio telescope in Pushchino (Moscow Region) acted in place of the space arm. It has an effective area of 100 square meters. The three other Russian 32-m antennas are operated by the Institute of Applied Astronomy RAS; they are located at Badary, Svetloe and Zelenchukskaya (interferometer network ``Quasar''). The maximum base-line, Badary-Svetloe, was about 4402 km, providing an angular resolution of about 0.009 arc seconds at a wavelength of 18 cm. The duration of the experiment was 10 hours on 02/03 February 2011. The program of observations included quasars 3C273, 3C279, 3C286 and the maser source - W3(OH). W3(OH) was observed only by the Russian telescopes and was investigated at the frequency of the 1665 MHz main line. The data were recorded on the MK5 recorder (32-m radio telescopes) and the RDR system (RadioAstron Digital Recorder) in Pushchino. The low SEFD (system equivalence of flux density) of Pushchino emulated the RadioAstron antenna. Correlation was performed with the universal software correlator of the AstroSpace Center of Lebedev Physical Institute. The correlator output format is compatible with that used by the AIPS package, which was used for data analysis. After analyzing the correlated data we obtained relative coordinates of the maser components. The main results are tabulated and presented in the figures. The data quality is sufficient for astrophysical analysis and comparison with previous observations of maser source W3(OH) on VLBI networks EVN and VLBA.

  11. Space ecosynthesis: An approach to the design of closed ecosystems for use in space

    NASA Technical Reports Server (NTRS)

    Macelroy, R. D.; Averner, M. M.

    1978-01-01

    The use of closed ecological systems for the regeneration of wastes, air, and water is discussed. It is concluded that such systems, if they are to be used for the support of humans in space, will require extensive mechanical and physico-chemical support. The reason for this is that the buffering capacity available in small systems is inadequate, and that natural biological and physical regulatory mechanisms rapidly become inoperative. It is proposed that mathematical models of the dynamics of a closed ecological system may provide the best means of studying the initial problems of ecosystem closure. A conceptual and mathematical model of a closed ecosystem is described which treats the biological components as a farm, calculates the rates of flow of elements through the system by mass-balance techniques and control theory postulates, and can evaluate the requirements for mechanical buffering activities. It is suggested that study of the closure of ecosystems can significantly aid in the establishment of general principles of ecological systems.

  12. The Hubble Space Telescope quasar absorption line key project. 6: Properties of the metal-rich systems

    NASA Technical Reports Server (NTRS)

    Bergeron, Jacqueline; Petitjean, Patrick; Sargent, W. L. W.; Bahcall, John N.; Boksenberg, Alec; Hartig, George F.; Jannuzi, Buell T.; Kirhakos, Sofia; Savage, Blair D.; Schneider, Donald P.

    1994-01-01

    We present an analysis of the properties of a sample of 18 metal-rich, low-redshift z(sub abs) much less than z(sub em) absorbers seen in low- and medium-resolution spectra obtained for the Quasar Absorption Line Key Project with the Hubble Space Telescope Faint Object Spectrograph (HST/FOS). For most of the C IV and Lyman-limit systems, observations in the optical wavelength range of the expected associated Mg II absorption are available. As at high redshift (z approximately 2), there are two subclasses of absorbers which are characterized by the presence or absence of MG II absorption. However, some low-redshift Mg II and Fe absorptions originate from regions optically thin to UV ionizing photons and thus, at low redshift, the low-ionization systems do not always trace high opacities, as is the case at high redshift. This implies that the mean ionization state of metal-rich, optically thin absorbing clouds falls with decreasing redshift, which is consistent with the hypothesis that the gas is photoionized by the metagalactic UV background radiation field. Two main constraints are derived from the analysis of the Lyman-limit sample, assuming photoionization models are valid. First, a low opacity to ionizing photons (tau(sub LL) approximately less than 1), as observed for several Mg II-Fe II systems at z approximately 0.5, sets limits on the ionization level of hydrogen, thus on the total hydrogen column density and the heavy element abundances, (Z/H) approximately -0.5 to -0.3. Second, the dimensions of individual Mg II clouds are smaller than at high redshift by a factor 3-10. At z approximately greater than 0.6, the O VI absorption doublet is detected in four of the five z(sub abs) much less than z(sub em) systems for which the O VI wavelength range has been observed, whereas the associated N V doublet is detected in only two cases. This suggests that the presence of a high-ionization O VI phase is a general property of z approximately 0.6-1 absorption systems

  13. Information for Lateral Aircraft Spacing Enabling Closely-Spaced Runway Operations During Instrument-Weather Conditions

    NASA Technical Reports Server (NTRS)

    Thrush, Trent; Pritchett, Amy; Johnson, Eric; Hansman, R. John; Shafto, Michael (Technical Monitor)

    1994-01-01

    In an effort to increase airport capacity, the U.S. plans on investing nearly $6 billion a year to properly maintain and improve the nation's major airports. Current FAA standards however, require a reduction in terminal operations during instrument-weather conditions at many airports, causing delays and reducing airport capacity. NASA, in cooperation with the FAA, has developed the Terminal Area Productivity Program to achieve clear-weather capacity in instrument- weather conditions for all phases of flight. This paper describes a series of experiments planned to investigate the conceptual design of different systems that provide information to flight crews regarding nearby traffic during the approach phase of flight. The purpose of this investigation is to identify and evaluate different display and auditory interfaces to the crew for use in closely-spaced parallel runway operations. Three separate experiments are planned for the investigation. The first two experiments will be conducted using part-task flight simulators located at the MIT Aeronautical Systems Laboratory and at NASA Ames. The third experiment will be conducted in the Advanced Concepts Flight Simulator, a generic "glass-cockpit" simulator at NASA Ames. Subjects for each experiment will be current glass-cockpit pilots from major U.S. air carriers. Subject crews will fly several experimental scenarios in which pseudo-aircraft are "blundered" into the subject aircraft simulation. Runway spacing, longitudinal aircraft separation, aircraft performance and traffic information will be varied. Analyses of the subject reaction times in evading the blundering aircraft and the resulting closest points of approach will be conducted. This paper presents a preliminary examination of the data recorded during the part-task experiments. The impact of traffic information on closely-spaced parallel runway operations is discussed, cockpit displays to aid these operations are examined, and topics for future research

  14. The Hubble Space Telescope quasar absorption line key project. v. redshift evolution of lyman limit absorption in the spectra of a large sample of quasars

    NASA Astrophysics Data System (ADS)

    Stengler-Larrea, Erik A.; Boksenberg, Alec; Steidel, Charles C.; Sargent, W. L. W.; Bahcall, John N.; Bergeron, Jacqueline; Hartig, George F.; Jannuzi, Buell T.; Kirhakos, Sofia; Savage, Blair D.; Schneider, Donald P.; Turnshek, David A.; Weymann, Ray J.

    1995-05-01

    Using a sample of 119 QSOs, containing objects we have selected having previously available high quality ground-based and IUE spectral observations, together with Hubble Space Telescope (HST) observations of 26 QSOs from Bahcall et al. (1993, 1995) and Impey et al. (1995) and new optical observations of 41 objects by Steidel & Sargent (1995), we study the redshift evolution of Lyman limit absorption systems (LLSs; tau greater than 1.0) over the reshift range 0.32 less than or equal to zLLS less than or equal to 4.11. The HST observations significantly improve the determination of the low redshift (0.4 less than or equal to zLLS less than or equal to 1.4) distribution. We find the effect which may have been responsible for the apparent strong evolution at aLLS greater than or equal to 2.5 found by Lanzetta (1991), which led him to consider a broken, not single power law as a better description of the redshift distribution of LLSs. After removing objects which may bias our sample, leaving a total of 169 QSOs, we find the distribution is well described by a single power law, and obtain for the number density as a function of redshift the form N(z) = N0(1 + z)gamma with gamma = 1.50 =/- 0.39 and N0 = 0.25-0.10+0.17, consistent with a constant comoving density of absorbers in a Firedmann universe with q0 = 0 but indicating evolution if q0 = 1/2.

  15. The Hubble Space Telescope quasar absorption line key project. v. redshift evolution of lyman limit absorption in the spectra of a large sample of quasars

    NASA Technical Reports Server (NTRS)

    Stengler-Larrea, Erik A.; Boksenberg, Alec; Steidel, Charles, C.; Sargent, W. L. W.; Bacall, John N.; Bergeron, Jacqueline; Hartig, George F.; Jannuzi, Buell T.; Kirhakos, Sofia; Savage, Blair D.

    1995-01-01

    Using a sample of 119 QSOs, containing objects we have selected having previously available high quality ground-based and IUE spectral observations, together with Hubble Space Telescope (HST) observations of 26 QSOs from Bahcall et al. (1993, 1995) and Impey et al. (1995) and new optical observations of 41 objects by Steidel & Sargent (1995), we study the redshift evolution of Lyman limit absorption systems (LLSs; tau greater than 1.0) over the reshift range 0.32 less than or equal to z(sub LLS) less than or equal to 4.11. The HST observations significantly improve the determination of the low redshift (0.4 less than or equal to z(sub LLS) less than or equal to 1.4) distribution. We find the effect which may have been responsible for the apparent strong evolution at a(sub LLS) greater than or equal to 2.5 found by Lanzetta (1991), which led him to consider a broken, not single power law as a better description of the redshift distribution of LLSs. After removing objects which may bias our sample, leaving a total of 169 QSOs, we find the distribution is well described by a single power law, and obtain for the number density as a function of redshift the form N(z) = N(sub 0)(1 + z)(exp gamma) with gamma = 1.50 =/- 0.39 and N(sub 0) = 0.25(sup -0.10)(sub +0.17), consistent with a constant comoving density of absorbers in a Firedmann universe with q(sub 0) = 0 but indicating evolution if q(sub 0) = 1/2.

  16. Plants for space plantations. [crops for closed life support systems

    NASA Technical Reports Server (NTRS)

    Nikishanova, T. I.

    1978-01-01

    Criteria for selection of candidate crops for closed life support systems are presented and discussed, and desired characteristics of candidate higher plant crops are given. Carbohydrate crops, which are most suitable, grown worldwide are listed and discussed. The sweet potato, ipomoea batatas Poir., is shown to meet the criteria to the greatest degree, and the criteria are recommended as suitable for initial evaluation of candidate higher plant crops for such systems.

  17. Ultra Reliable Closed Loop Life Support for Long Space Missions

    NASA Technical Reports Server (NTRS)

    Jones, Harry W.; Ewert, Michael K.

    2010-01-01

    Spacecraft human life support systems can achieve ultra reliability by providing sufficient spares to replace all failed components. The additional mass of spares for ultra reliability is approximately equal to the original system mass, provided that the original system reliability is not too low. Acceptable reliability can be achieved for the Space Shuttle and Space Station by preventive maintenance and by replacing failed units. However, on-demand maintenance and repair requires a logistics supply chain in place to provide the needed spares. In contrast, a Mars or other long space mission must take along all the needed spares, since resupply is not possible. Long missions must achieve ultra reliability, a very low failure rate per hour, since they will take years rather than weeks and cannot be cut short if a failure occurs. Also, distant missions have a much higher mass launch cost per kilogram than near-Earth missions. Achieving ultra reliable spacecraft life support systems with acceptable mass will require a well-planned and extensive development effort. Analysis must determine the reliability requirement and allocate it to subsystems and components. Ultra reliability requires reducing the intrinsic failure causes, providing spares to replace failed components and having "graceful" failure modes. Technologies, components, and materials must be selected and designed for high reliability. Long duration testing is needed to confirm very low failure rates. Systems design should segregate the failure causes in the smallest, most easily replaceable parts. The system must be designed, developed, integrated, and tested with system reliability in mind. Maintenance and reparability of failed units must not add to the probability of failure. The overall system must be tested sufficiently to identify any design errors. A program to develop ultra reliable space life support systems with acceptable mass should start soon since it must be a long term effort.

  18. Noncontact Friction and Force Fluctuations between Closely Spaced Bodies

    SciTech Connect

    Stipe, B. C.; Mamin, H. J.; Stowe, T. D.; Kenny, T. W.; Rugar, D.

    2001-08-27

    Noncontact friction between a Au(111) surface and an ultrasensitive gold-coated cantilever was measured as a function of tip-sample spacing, temperature, and bias voltage using observations of cantilever damping and Brownian motion. The importance of the inhomogeneous contact potential is discussed and comparison is made to measurements over dielectric surfaces. Using the fluctuation-dissipation theorem, the force fluctuations are interpreted in terms of near-surface fluctuating electric fields interacting with static surface charge.

  19. Closely Spaced MEG Source Localization and Functional Connectivity Analysis Using a New Prewhitening Invariance of Noise Space Algorithm

    PubMed Central

    Zhang, Junpeng; Cui, Yuan; Deng, Lihua; He, Ling; Zhang, Junran; Zhang, Jing; Zhou, Qun; Liu, Qi; Zhang, Zhiguo

    2016-01-01

    This paper proposed a prewhitening invariance of noise space (PW-INN) as a new magnetoencephalography (MEG) source analysis method, which is particularly suitable for localizing closely spaced and highly correlated cortical sources under real MEG noise. Conventional source localization methods, such as sLORETA and beamformer, cannot distinguish closely spaced cortical sources, especially under strong intersource correlation. Our previous work proposed an invariance of noise space (INN) method to resolve closely spaced sources, but its performance is seriously degraded under correlated noise between MEG sensors. The proposed PW-INN method largely mitigates the adverse influence of correlated MEG noise by projecting MEG data to a new space defined by the orthogonal complement of dominant eigenvectors of correlated MEG noise. Simulation results showed that PW-INN is superior to INN, sLORETA, and beamformer in terms of localization accuracy for closely spaced and highly correlated sources. Lastly, source connectivity between closely spaced sources can be satisfactorily constructed from source time courses estimated by PW-INN but not from results of other conventional methods. Therefore, the proposed PW-INN method is a promising MEG source analysis to provide a high spatial-temporal characterization of cortical activity and connectivity, which is crucial for basic and clinical research of neural plasticity. PMID:26819768

  20. Quantum field theory in spaces with closed timelike curves

    NASA Astrophysics Data System (ADS)

    Boulware, David G.

    1992-11-01

    Gott spacetime has closed timelike curves, but no locally anomalous stress energy. A complete orthonormal set of eigenfunctions of the wave operator is found in the special case of a spacetime in which the total deficit angle is 2π. A scalar quantum field theory is constructed using these eigenfunctions. The resultant interacting quantum field theory is not unitary because the field operators can create real, on-shell, particles in the noncausal region. These particles propagate for finite proper time accumulating an arbitrary phase before being annihilated at the same spacetime point as that at which they were created. As a result, the effective potential within the noncausal region is complex, and probability is not conserved. The stress tensor of the scalar field is evaluated in the neighborhood of the Cauchy horizon; in the case of a sufficiently small Compton wavelength of the field, the stress tensor is regular and cannot prevent the formation of the Cauchy horizon.

  1. The Hubble Space Telescope quasar absorption line key project. III - First observational results on Milky Way gas

    NASA Technical Reports Server (NTRS)

    Savage, Blair D.; Lu, Limin; Bahcall, John N.; Bergeron, Jacqueline; Boksenberg, Alec; Hartig, George F.; Jannuzi, Buell T.; Kirhakos, Sofia; Lockman, Felix J.; Sargent, W. L. W.

    1993-01-01

    Absorption lines found near zero redshift due to Milky Way disk and halo gas in the spectra of 15 quasars observed with the Faint Object Spectrograph (FOS) of the HST at a resolution of about 230 km/s are reported. Results show that Milky Way absorption lines comprise about 44 percent of all absorption lines seen in the first group of Key Project FOS spectra. Milky Way lines were observed for 3C 273 and H1821 + 643. Limits to the Mg-to-H abundance ratio obtained for very high velocity Mg II absorption detections imply gas-phase Mg abundances for the very high velocity gas ranging from more than 0.059 to more than 0.32 times the solar abundance. In all cases where high-velocity H I emission is seen, corresponding high-velocity metal-line absorption is observed.

  2. Nutritional criteria for closed-loop space food systems

    NASA Technical Reports Server (NTRS)

    Rambaut, P. C.

    1980-01-01

    The nutritional requirements for Skylab crews are summarized as a data base for long duration spaceflight nutrient requirements. Statistically significant increases in energy consumption were detected after three months, along with CO2/O2 exhalation during exercise and thyroxine level increases. Linoleic acid amounting to 3-4 g/day was found to fulfill all fat requirements, and carbohydrate and protein (amino acid) necessities are discussed, noting that vigorous exercise programs avoid deconditioning which enhances nitrogen loss. Urinary calcium losses continued at a rate 100% above a baseline figure, a condition which ingestion of vitamin D2 did not correct. Projections are given that spaceflights lasting more than eight years will necessitate recycling of human waste for nutrient growth, which can be processed into highly efficient space food with a variety of tastes.

  3. Nanoscale Engineering of Closely-Spaced Electronic Spins in Diamond.

    PubMed

    Scarabelli, Diego; Trusheim, Matt; Gaathon, Ophir; Englund, Dirk; Wind, Shalom J

    2016-08-10

    Numerous theoretical protocols have been developed for quantum information processing with dipole-coupled solid-state spins. Nitrogen vacancy (NV) centers in diamond have many of the desired properties, but a central challenge has been the positioning of NV centers at the nanometer scale that would allow for efficient and consistent dipolar couplings. Here we demonstrate a method for chip-scale fabrication of arrays of single NV centers with record spatial localization of about 10 nm in all three dimensions and controllable inter-NV spacing as small as 40 nm, which approaches the length scale of strong dipolar coupling. Our approach uses masked implantation of nitrogen through nanoapertures in a thin gold film, patterned via electron-beam lithography and dry etching. We verified the position and spin properties of the resulting NVs through wide-field super-resolution optically detected magnetic resonance imaging. PMID:27428077

  4. XMM-Newton closes in on space's exotic matter

    NASA Astrophysics Data System (ADS)

    2002-11-01

    With ESA's space telescope XMM-Newton, they are now closer to testing this idea. For the first time, XMM-Newton has been able to measure the influence of the gravitational field of a neutron star on the light it emits. This measurement provides much better insight into these objects. Neutron stars are among the densest objects in the Universe. They pack the mass of the sun inside a sphere 10 kilometres across. A sugar cube-sized piece of neutron star weighs over a billion tonnes. Neutron stars are the remnants of exploding stars up to eight times more massive than our Sun. They end their life in a supernova explosion and then collapse under their own gravity. Their interiors may therefore contain a very exotic form of matter. Scientists believe that in a neutron star, the density and the temperatures are similar to those existing a fraction of a second after the Big Bang. They assume that when matter is tightly packed as it is in a neutron star, it goes through important changes. Protons, electrons, and neutrons - the components of atoms - fuse together. It is possible that even the building-blocks of protons and neutrons, the so-called quarks, get crushed together, giving rise to a kind of exotic plasma of 'dissolved' matter. How to find out? Scientists have spent decades trying to identify the nature of matter in neutron stars. To do this, they need to know some important parameters very precisely: if you know a star’s mass and radius, or the relationship between them, you can obtain its compactness. However,no instrument has been advanced enough to perform the measurements needed, until now. Thanks to ESA's XMM-Newton observatory, astronomers have been able for the first time to measure the mass-to-radius ratio of a neutron star and obtain the first clues to its composition. These suggest that the neutron star contains normal, non-exotic matter, although they are not conclusive. The authors say this is a “key first step” and they will keep on with the

  5. Investigations in Time and of Space Using the FIRST Survey: Radio Source Variability and the Evolution of FR II Quasars

    NASA Astrophysics Data System (ADS)

    Thyagarajan, Nithyanandan

    The FIRST survey covered ∼10,000 deg2 of the sky over a decade, providing unprecedented levels of flux density sensitivity (∼ 1 mJy) at 1.4 GHz, uniformity to within 15% (at ∼0.15 mJy rms), 5.4" angular resolution, astrometric accuracy to better than 1" and has cataloged ≳ 800,000 sources. It has made enormous contributions to diverse scientific ends including such subjects as radio source populations, quasars, large-scale structure and clustering of radio sources, gravitational lensing, cosmology, etc. I present the motivation, analysis and results of two projects also intended to demonstrate the power and expand the scope of the FIRST survey's scientific reach. A comprehensive search for variable and transient radio sources has been conducted using the ∼55,000 snapshot images of the FIRST survey. An analysis leading to the discovery of 1,651 variable and transient objects down to mJy levels over a wide range of timescales (few minutes to years) is presented. The multi-wavelength matching for counterparts reveals the diverse classes of objects exhibiting variability. Interestingly, ∼ 60% of the objects in the sample have either no classified counterparts or no corresponding sources at any other wavelength and require multi-wavelength follow-up observations. I discuss these classes of variables and speculate on the identity of objects that lack multi-wavelength counterparts. Thus, the FIRST survey has yielded the largest sample by far of radio variables and transients to date to unprecedented levels of sensitivity and sky coverage and demonstrates the promise of future radio instruments which have transient-detection as one of their key science projects. For decades, radio astronomers have attempted to use double-lobed radio sources to constrain the angular size-redshift (θ - z ) relation and to derive cosmological parameters therefrom. Most of the early attempts have, embarrassingly, shown general consistency with a static Euclidean universe rather

  6. Constraining Sub-parsec Binary Supermassive Black Holes in Quasars with Multi-epoch Spectroscopy. I. The General Quasar Population

    NASA Astrophysics Data System (ADS)

    Shen, Yue; Liu, Xin; Loeb, Abraham; Tremaine, Scott

    2013-09-01

    We perform a systematic search for sub-parsec binary supermassive black holes (BHs) in normal broad-line quasars at z < 0.8, using multi-epoch Sloan Digital Sky Survey (SDSS) spectroscopy of the broad Hβ line. Our working model is that (1) one and only one of the two BHs in the binary is active; (2) the active BH dynamically dominates its own broad-line region (BLR) in the binary system, so that the mean velocity of the BLR reflects the mean velocity of its host BH; (3) the inactive companion BH is orbiting at a distance of a few R BLR, where R BLR ~ 0.01-0.1 pc is the BLR size. We search for the expected line-of-sight acceleration of the broad-line velocity from binary orbital motion by cross-correlating SDSS spectra from two epochs separated by up to several years in the quasar rest frame. Out of ~700 pairs of spectra for which we have good measurements of the velocity shift between two epochs (1σ error ~40 km s-1), we detect 28 systems with significant velocity shifts in broad Hβ, among which 7 are the best candidates for the hypothesized binaries, 4 are most likely due to broad-line variability in single BHs, and the rest are ambiguous. Continued spectroscopic observations of these candidates will easily strengthen or disprove these claims. We use the distribution of the observed accelerations (mostly non-detections) to place constraints on the abundance of such binary systems among the general quasar population. Excess variance in the velocity shift is inferred for observations separated by longer than 0.4 yr (quasar rest frame). Attributing all the excess to binary motion would imply that most of the quasars in this sample must be in binaries, that the inactive BH must be on average more massive than the active one, and that the binary separation is at most a few times the size of the BLR. However, if this excess variance is partly or largely due to long-term broad-line variability, the requirement of a large population of close binaries is much weakened

  7. QUASARS PROBING QUASARS. IV. JOINT CONSTRAINTS ON THE CIRCUMGALACTIC MEDIUM FROM ABSORPTION AND EMISSION

    SciTech Connect

    Hennawi, Joseph F.; Prochaska, J. Xavier

    2013-03-20

    We have constructed a sample of 29 close projected quasar pairs where the background quasar spectrum reveals absorption from optically thick H I gas associated with the foreground quasar. These unique sightlines allow us to study the quasar circumgalactic medium (CGM) in absorption and emission simultaneously, because the background quasar pinpoints large concentrations of gas where Ly{alpha} emission, resulting from quasar-powered fluorescence, resonant Ly{alpha} scattering, and/or cooling radiation, is expected. A sensitive search (1{sigma} surface-brightness limits of SB{sub Ly{alpha}}{approx_equal}3 Multiplication-Sign 10{sup -18} erg s{sup -1} cm{sup -2} arcsec{sup -2}) for diffuse Ly{alpha} emission in the environments of the foreground (predominantly radio-quiet) quasars is conducted using Gemini/GMOS and Keck/LRIS slit spectroscopy. We fail to detect large-scale {approx}100 kpc Ly{alpha} emission, either at the location of the optically thick absorbers or in the foreground quasar halos, in all cases except a single system. We interpret these non-detections as evidence that the gas detected in absorption is shadowed from the quasar UV radiation due to obscuration effects, which are frequently invoked in unified models of active galactic nuclei. Small-scale R {approx}< 50 kpc extended Ly{alpha} nebulosities are detected in 34% of our sample, which are likely the high-redshift analogs of the extended emission-line regions (EELRs) commonly observed around low-redshift (z < 0.5) quasars. This may be fluorescent recombination radiation from a population of very dense clouds with a low covering fraction illuminated by the quasar. We also detect a compact high rest-frame equivalent width (W{sub Ly{alpha}} > 50 A) Ly{alpha}-emitter with luminosity L{sub Ly{alpha}} = 2.1 {+-} 0.32 Multiplication-Sign 10{sup 41} erg s{sup -1} at small impact parameter R = 134 kpc from one foreground quasar, and argue that it is more likely to result from quasar-powered fluorescence

  8. HUBBLE CAPTURES MERGER BETWEEN QUASAR AND GALAXY

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This NASA Hubble Space Telescope image shows evidence fo r a merger between a quasar and a companion galaxy. This surprising result might require theorists to rethink their explanations for the nature of quasars, the most energetic objects in the universe. The bright central object is the quasar itself, located several billion light-years away. The two wisps on the (left) of the bright central object are remnants of a bright galaxy that have been disrupted by the mutual gravitational attraction between the quasar and the companion galaxy. This provides clear evidence for a merger between the two objects. Since their discovery in 1963, quasars (quasi-stellar objects) have been enigmatic because they emit prodigious amounts of energy from a very compact source. The most widely accepted model is that a quasar is powered by a supermassive black hole in the core of a galaxy. These new observations proved a challenge for theorists as no current models predict the complex quasar interactions unveiled by Hubble. The image was taken with the Wide Field Planetary Camera-2. Credit: John Bahcall, Institute for Advanced Study, NASA.

  9. Weak bump quasars

    NASA Technical Reports Server (NTRS)

    Mcdowell, Jonathan C.; Elvis, Martin; Wilkes, Belinda J.; Willner, Steven P.; Oey, M. S.

    1989-01-01

    The recent emphasis on big bumps dominating the UV continuum of quasars has obscured the facts that bump properties vary widely and that there are objects in which no such component is evident. As part of a survey of quasar continuum spectra, a class of quasars is identified in which the optical-UV continuum big bump feature appears to be weak or absent, relative to both IR and X-ray. These weak bump quasars are otherwise normal objects and constitute a few percent of the quasar population.

  10. Solving Quasars (Part 1)

    SciTech Connect

    Elvis, Martin

    2003-10-29

    Quasars are a frustratingly unsolved problem in astrophysics. For 40 years quasars and AGN have presented an ever-proliferating list of diverse and confusing phenomenology from optical to X-ray wavelengths. The result has been that despite being the most powerful objects in the universe, quasars have been increasingly sidelined in astrophysics. This is unfortunate, as quasars pose major physics, as well as astrophysics puzzles, and should be important in cosmology. The problem, I believe, is not that we do not know enough physics, but rather that we do not have the right geometry. I have proposed a simple geometric and kinematic model that allows all of the quasar diversity to be understood as part of a single structure, the 'Quasar Atmosphere'. This structure suggests a natural physical interpretation, that builds on our understanding of stars (the only fully solved problem in astrophysics), and offers the prospect that we can use quasars for cosmology at last.

  11. GALACTIC-SCALE ABSORPTION OUTFLOW IN THE LOW-LUMINOSITY QUASAR IRAS F04250-5718: HUBBLE SPACE TELESCOPE/COSMIC ORIGINS SPECTROGRAPH OBSERVATIONS

    SciTech Connect

    Edmonds, Doug; Borguet, Benoit; Arav, Nahum; Dunn, Jay P.; Penton, Steve; Kriss, Gerard A.; Korista, Kirk; Bautista, Manuel; Costantini, Elisa; Kaastra, Jelle; Steenbrugge, Katrien; Ignacio Gonzalez-Serrano, J.; Benn, Chris; Aoki, Kentaro; Behar, Ehud; Micheal Crenshaw, D.; Everett, John; Gabel, Jack; Moe, Maxwell; Scott, Jennifer

    2011-09-20

    We present absorption line analysis of the outflow in the quasar IRAS F04250-5718. Far-ultraviolet data from the Cosmic Origins Spectrograph on board the Hubble Space Telescope reveal intrinsic narrow absorption lines from high ionization ions (e.g., C IV, N V, and O VI) as well as low ionization ions (e.g., C II and Si III). We identify three kinematic components with central velocities ranging from {approx}-50 to {approx}-230 km s{sup -1}. Velocity-dependent, non-black saturation is evident from the line profiles of the high ionization ions. From the non-detection of absorption from a metastable level of C II, we are able to determine that the electron number density in the main component of the outflow is {approx}<30 cm{sup -3}. Photoionization analysis yields an ionization parameter log U{sub H} {approx} -1.6 {+-} 0.2, which accounts for changes in the metallicity of the outflow and the shape of the incident spectrum. We also consider solutions with two ionization parameters. If the ionization structure of the outflow is due to photoionization by the active galactic nucleus, we determine that the distance to this component from the central source is {approx}>3 kpc. Due to the large distance determined for the main kinematic component, we discuss the possibility that this outflow is part of a galactic wind.

  12. NEAR-INFRARED PHOTOMETRIC PROPERTIES OF 130,000 QUASARS: AN SDSS-UKIDSS-MATCHED CATALOG

    SciTech Connect

    Peth, Michael A.; Ross, Nicholas P.; Schneider, Donald P.

    2011-04-15

    We present a catalog of over 130,000 quasar candidates with near-infrared (NIR) photometric properties, with an areal coverage of approximately 1200 deg{sup 2}. This is achieved by matching the Sloan Digital Sky Survey (SDSS) in the optical ugriz bands to the UKIRT Infrared Digital Sky Survey (UKIDSS) Large Area Survey (LAS) in the NIR YJHK bands. We match the {approx}1 million SDSS DR6 Photometric Quasar catalog to Data Release 3 of the UKIDSS LAS (ULAS) and produce a catalog with 130,827 objects with detections in one or more NIR bands, of which 74,351 objects have optical and K-band detections and 42,133 objects have the full nine-band photometry. The majority ({approx}85%) of the SDSS objects were not matched simply because these were not covered by the ULAS. The positional standard deviation of the SDSS Quasar to ULAS matches is {delta}{sub R.A.} = 0.''1370 and {delta}{sub decl.} = 0.''1314. We find an absolute systematic astrometric offset between the SDSS Quasar catalog and the UKIDSS LAS, of |R.A.{sub offset}| = 0.''025 and |decl.{sub offset}| = 0.''040; we suggest the nature of this offset to be due to the matching of catalog, rather than image, level data. Our matched catalog has a surface density of {approx}53 deg{sup -2} for K {<=} 18.27 objects; tests using our matched catalog, along with data from the UKIDSS Deep Extragalactic Survey, imply that our limiting magnitude is i {approx} 20.6. Color-redshift diagrams, for the optical and NIR, show a close agreement between our matched catalog and recent quasar color models at redshift z {approx}< 2.0, while at higher redshifts, the models generally appear to be bluer than the mean observed quasar colors. The gJK and giK color spaces are used to examine methods of differentiating between stars and (mid-redshift) quasars, the key to currently ongoing quasar surveys. Finally, we report on the NIR photometric properties of high, z > 4.6, and very high, z > 5.7, redshift previously discovered quasars.

  13. Near-infrared Photometric Properties of 130,000 Quasars: An SDSS-UKIDSS-matched Catalog

    NASA Astrophysics Data System (ADS)

    Peth, Michael A.; Ross, Nicholas P.; Schneider, Donald P.

    2011-04-01

    We present a catalog of over 130,000 quasar candidates with near-infrared (NIR) photometric properties, with an areal coverage of approximately 1200 deg2. This is achieved by matching the Sloan Digital Sky Survey (SDSS) in the optical ugriz bands to the UKIRT Infrared Digital Sky Survey (UKIDSS) Large Area Survey (LAS) in the NIR YJHK bands. We match the ≈1 million SDSS DR6 Photometric Quasar catalog to Data Release 3 of the UKIDSS LAS (ULAS) and produce a catalog with 130,827 objects with detections in one or more NIR bands, of which 74,351 objects have optical and K-band detections and 42,133 objects have the full nine-band photometry. The majority (~85%) of the SDSS objects were not matched simply because these were not covered by the ULAS. The positional standard deviation of the SDSS Quasar to ULAS matches is δR.A. = 0farcs1370 and δdecl. = 0farcs1314. We find an absolute systematic astrometric offset between the SDSS Quasar catalog and the UKIDSS LAS, of |R.A.offset| = 0farcs025 and |decl.offset| = 0farcs040; we suggest the nature of this offset to be due to the matching of catalog, rather than image, level data. Our matched catalog has a surface density of ≈53 deg-2 for K <= 18.27 objects; tests using our matched catalog, along with data from the UKIDSS Deep Extragalactic Survey, imply that our limiting magnitude is i ≈ 20.6. Color-redshift diagrams, for the optical and NIR, show a close agreement between our matched catalog and recent quasar color models at redshift z <~ 2.0, while at higher redshifts, the models generally appear to be bluer than the mean observed quasar colors. The gJK and giK color spaces are used to examine methods of differentiating between stars and (mid-redshift) quasars, the key to currently ongoing quasar surveys. Finally, we report on the NIR photometric properties of high, z > 4.6, and very high, z > 5.7, redshift previously discovered quasars.

  14. Quasar Rain

    NASA Astrophysics Data System (ADS)

    Elvis, Martin

    2015-01-01

    Velocity resolved reverberation mapping (VRRM) has shown clear evidence for inflows in the broad emission line (BEL) region of active galactic nuclei: redshifted BELs at zero lag (AGNs, e.g. Arp 151, Bentz et al. 2010; Grier et al. 2013). While radiative transfer in rotating disks can give shorter red side lags than blue, a zero lag has to be along our line of sight, so it is hard to escape infall. The BEL region is normally considered to be rotating or in outflow so this result is a surprise. Infalling BEL gas cannot fall far without the need to lose angular momentum for accreting gas producing an accretion disk.I suggest that quasar continuum irradiation induced cooling instabilities (Chakravorty et al 2009; Krolik, McKee & Tarter 1981) lead to dense BEL clouds condensing out of the semi-ubiquitous warm absorber (WA) outflows found in AGNs and that these clouds may produce a VRRM inflow signature.Unlike WA gas, dense high column density BEL clouds are hard to accelerate with radiation pressure (Risaliti & Elvis 2010; Mushotzky, Solomon & Strittmatter 1972). BEL clouds will thus stall in the outflow and begin to fall back toward the central black hole after a dynamical time, 'raining out' of the WA medium. If these BEL clouds condense out before these outflows reach escape velocity [v(esc)] then this inflow can potentially produce the observed VRRM signature. As the clouds fall back in they will be moving on elliptical orbits supersonically through the WA gas with Mach number ~(2000 km/s)/(100km/s) ~20. This will produce comet-like structures with narrow opening angles, as seen in asymmetric X-ray absorbing 'eclipses' (Maiolino et al. 2010). They will survive only a few months, as required to avoid forming a disk. For this picture to work the condensation time must be less than the acceleration time to v(esc) and the destruction time must be longer than the dynamical time.

  15. A state-space dynamical representation for multibody mechanical systems. II - Systems with closed loops

    NASA Astrophysics Data System (ADS)

    Schwertassek, R.; Roberson, R. E.

    1984-05-01

    The dynamical equations of motion of a multibody system are reduced to state-space equations in the computer-oriented multibody formalism of Roberson and Wittenberg (1966), extending the analysis of Schwertassek and Roberson (1983) to systems with closed loops. The multibody spacecraft model of Kane and Levinson (1980) and Schiehlen and Kreuzer (1977) is analyzed as an example. The closed-loop equations permit the use of the MULTIBODY computer code (Schwertassek, 1978) to treat such more general systems.

  16. Merging Galaxies Create a Binary Quasar

    NASA Astrophysics Data System (ADS)

    2010-02-01

    Observatory in California indicated that the object was likely a binary quasar in the midst of a galaxy merger. Carnegie's Mulchaey then used the 6.5 meter Baade-Magellan telescope at the Las Campanas observatory in Chile to obtain deeper images and more detailed spectroscopy of the merging galaxies. "Just because you see two galaxies that are close to each other in the sky doesn't mean they are merging," says Mulchaey. "But from the Magellan images we can actually see tidal tails, one from each galaxy, which suggests that the galaxies are in fact interacting and are in the process of merging." Thomas Cox, now a fellow at the Carnegie Observatories, corroborated this conclusion using computer simulations of the merging galaxies. When Cox's model galaxies merged, they showed features remarkably similar to what Mulchaey observed in the Magellan images. "The model verifies the merger origin for this binary quasar system," he says. "It also hints that this kind of galaxy interaction is a key component of the growth of black holes and production of quasars throughout our universe." * The authors of the paper published in the Astrophysical Journal are Paul J. Green of the Harvard-Smithsonian Center for Astrophysics, Adam D. Myers of the University of Illinois at Urbana-Champaign, Wayne A. Barkhouse of the University of North Dakota, John S. Mulchaey of the Observatories of the Carnegie Institution for Science, Vardha N. Bennert of the Department of Physics, University of California, Santa Barbara, Thomas J. Cox of the Observatories of the Carnegie Institution for Science, Thomas L. Aldcroft of the Harvard-Smithsonian Center for Astrophysics, and Joan M. Wrobel of National Radio Astronomy Observatory, Socorro, NM. More information, including images and other multimedia, can be found at: http://chandra.harvard.edu and http://chandra.nasa.gov

  17. Closed Crawl Space Performance: Proof of Concept in the Production Builder Marketplace

    SciTech Connect

    Malkin-Weber, Melissa; Dastur, Cyrus; Mauceri, Maria; Hannas, Benjamin

    2008-10-30

    This overview is intended to be a very concise, limited summary of the key project activities discussed in the detailed report that follows. Due to the large scope of this project, the detailed report is broken into three individually titled sections. Each section repeats key background information, with the goal that the sections will eventually stand alone as complete reports on the major activities of the project. The information presented herein comes from ongoing research, so please note that all observations, findings and recommendations presented are preliminary and subject to change in the future. We invite and welcome your comments and suggestions for improving the project. Advanced Energy completed its first jointly-funded crawl space research project with the Department of Energy in 2005. That project, funded under award number DE-FC26-00NT40995 and titled 'A Field Study Comparison of the Energy and Moisture Performance Characteristics of Ventilated Versus Sealed Crawl Spaces in the South' demonstrated the substantial energy efficiency and moisture management benefits that result from using properly closed crawl space foundations for residential construction instead of traditional wall vented crawl space foundations. Two activities of this first project included (1) an assessment of ten existing homes to document commonly observed energy and moisture failures associated with wall-vented crawl space foundations and (2) a detailed literature review that documented both the history of closed crawl space research and the historical lack of scientific justification for building code requirements for crawl space ventilation. The most valuable activity of the 2005 project proved to be the field demonstration of various closed crawl space techniques, which were implemented in a set of twelve small (1040 square feet), simply designed homes in eastern North Carolina. These homes had matched envelope, mechanical and architectural designs, and comparable performance

  18. Probabilistic Analysis of Impact of Wake Vortices on Closely-Spaced Parallel Approaches

    NASA Technical Reports Server (NTRS)

    Hardy, Gordon H.; Rossow, Vernon J.; Meyn, Larry A.

    2005-01-01

    One of the primary constraints on the capacity of the nation's air transportation system is the landing capacity of its largest airports. Many airports with closely spaced parallel runways suffer a severe runway acceptance rate when the weather conditions do not allow full utilization of these parallel runways. The present requirement for simultaneous independent landings in Instrument Meteorological Conditions, IMC, is at least 4300 feet of lateral runway spacing (as close as 3000 feet for runways with a Precision Runway Monitor). Operations in Visual Meteorological Conditions, VMC, to Closely Spaced Parallel Approaches only require a lateral runway spacing greater than 750 feet. A study by Hardy and Lewis integrated and extended earlier studies and concepts in lateral traffic separation, longitudinal station keeping, wake prediction, wake display, and the concepts of R N P into a preliminary system concept for Closely Spaced Parallel Approaches in IMC. This system allows IMC airport acceptance rates to approach those for VMC. The system concept that was developed, presented traffic and wake information on the NAVigation Display, NAV, and developed operational procedures for a mix of conventional and Runway Independent Aircraft with different approach speeds to Closely Spaced Parallel Runways. This paper first describes some improvements made on the technology needed to better predict and formulate a probabilistic representation for the time-dependent motion and spreading of the hazardous region associated with the lift-generated vortex wakes of preceding aircraft. In this way, the time at which the vortex wakes of leading aircraft intrude into the airspace of adjacent flight-corridor/runway combinations can be more reliably predicted. Such a prediction is needed because it determines restraints to be placed on in-trail separation distances; or, the allowable time intervals between aircraft executing nearly simultaneous landings or takeoffs on very closely-spaced

  19. Strong associated C 4 absorption in low redshift quasars

    NASA Technical Reports Server (NTRS)

    Tytler, David

    1990-01-01

    IUE spectra of quasars were used to determine the frequency of occurrence of strong associated C 4 absorption systems at low red shifts. Four systems are found with rest frame equivalent width (REW) greater than 5 angstroms in the spectra of 38 quasars. This rate of occurrence of 0.12 is not significantly different from the rate of 0.064 determined for high red shift quasars. The detected strong associated systems are all in low red shift quasars which have been imaged from the ground. One of the quasars is unusual, having two nuclei, a close companion and distorted isotopes. Two of the others also have close companion galaxies at projected distances of under 100 kpc. The conclusion was made that a much larger sample is needed.

  20. Infrared weak quasars

    NASA Technical Reports Server (NTRS)

    Mcdowell, J. C.; Elvis, M.; Wilkes, B. J.

    1992-01-01

    Examples of quasars with anomalously weak IR emission are presented, and the effects of starlight subtraction on estimates of the UV and IR component strengths are discussed. Inferred model parameters are very sensitive to the position of the peak of the UV energy distribution. In many low redshift objects the peak is not seen; even in those objects where the turnover is clear, the turnover may not be intrinsic but instead due to reddening within the quasar host galaxy. The small number of unusual quasars with weak IR emission will be of utility as a probe of the quasar phenomenon in the absence of dominant dust reprocessing.

  1. Pilot Non-Conformance to Alerting System Commands During Closely Spaced Parallel Approaches

    NASA Technical Reports Server (NTRS)

    Pritchett, Amy R.; Hansman, R. John

    1997-01-01

    Pilot non-conformance to alerting system commands has been noted in general and to a TCAS-like collision avoidance system in a previous experiment. This paper details two experiments studying collision avoidance during closely-spaced parallel approaches in instrument meteorological conditions (IMC), and specifically examining possible causal factors of, and design solutions to, pilot non-conformance.

  2. Characterizing Quasar Outflows I: Sample, Spectral Measurements

    NASA Astrophysics Data System (ADS)

    Ganguly, Rajib; Christenson, D. H.; Richmond, J. M.; Derseweh, J. A.; Robbins, J. M.; Townsend, S. L.; Stark, M. A.

    2012-05-01

    Galaxy evolution models have shown that quasars are a crucial ingredient in the evolution of massive galaxies. Outflows play a key role in the story of quasars and their host galaxies, by helping regulate the accretion process, the star-formation rate and mass of the host galaxy (i.e., feedback). The prescription for modeling outflows as a contributor to feedback requires knowledge of the outflow velocity, geometry, and column density. In particular, we need to understand how these depend on physical parameters and how much is determined stochastically (and with what distribution). For this purpose, we are examining a sample of 11000 z=1.7-2.0 quasars from the Sloan Digital Sky Survey. This redshift range permits the following from the SDSS spectra: (1) separation of objects that do and do not exhibit outflows; (2) classification/measurement of outflow properties (ionization, velocity, velocity width); and (3) measurements of UV emission line and continuum parameters. In this poster, we subjectively divide these quasars into four categories: broad absorption-line quasars (2700 objects), associated absorption-line quasars (1700 objects), reddened quasars (160 objects), and unabsorbed/unreddened quasars (6300 objects). We present measurements of the absorption (velocities, velocity widths, equivalent widths), composite spectral profiles of outflows as a function of velocity, as well as measurements of the continuum and CIV, MgII, and FeII emission-line properties. In accompanying posters, we add photometry from the rest-frame X-ray (ROSAT and Chandra), EUV (GALEX), optical (2MASS), and infrared (WISE) bands to complete the SED. The continuum and emission-line measurements from the SDSS spectra and accompanying photometry provides estimates on the black hole masses, bolometric luminsosities, and SED. We consider empirically how these affect the outflow properties. This material is based upon work supported by the National Aeronautics and Space Administration under

  3. A Constraint on Quasar Clustering at z = 5 from a Binary Quasar

    NASA Astrophysics Data System (ADS)

    McGreer, Ian D.; Eftekharzadeh, Sarah; Myers, Adam D.; Fan, Xiaohui

    2016-03-01

    We report the discovery of a quasar pair at z = 5 separated by 21″. Both objects were identified as quasar candidates using simple color selection techniques applied to photometric catalogs from the Canada-France-Hawaii Telescope (CFHT) Legacy Survey (CFHTLS). Spectra obtained with the MMT present no discernible offset in redshift between the two objects; on the other hand, there are clear differences in the emission line profiles and in the multiwavelength spectral energy distributions that strongly disfavor the hypothesis that they are gravitationally lensed images of a single quasar. Both quasars are surprisingly bright given their proximity (a projected separation of ˜135 kpc), with i = 19.4 and i = 21.4. Previous measurements of the luminosity function demonstrate that luminous quasars are extremely rare at z = 5 the existence of this pair suggests that quasars have strong small-scale clustering at high redshift. Assuming a real-space correlation function of the form ξ(r) ∝ (r/r0)-2, this discovery implies a correlation length of r0 ≳ 20h-1 Mpc, consistent with a rapid strengthening of quasar clustering at high redshift as seen in previous observations and predicted by theoretical models where feedback effects are inefficient at shutting down black hole growth at high redshift. Observations reported here were obtained at the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona.

  4. Negative Pressure Wound Therapy on Closed Surgical Wounds With Dead Space

    PubMed Central

    Suh, Hyunsuk; Lee, A-Young; Park, Eun Jung; Hong, Joon Pio

    2016-01-01

    Background Closed incisional wound surgery frequently leaves dead space under the repaired skin, which results in delayed healing. The purpose of this study was to evaluate the effect of negative pressure wound therapy (NPWT) on incisional wounds with dead space after primary closure by evaluating the fluid volume through the suction drain, blood flow of the skin, tensile strength, and histology of the wounds. Methods Bilateral 25-cm-long incisional wounds with dead space were created on the back of 6 pigs by partially removing the back muscle and then suturing the skin with nylon sutures. NPWT (experimental group) or gauze dressing (control group) was applied over the closed incision for 7 days. Analysis of the wound included monitoring the amount of closed suction drain, blood perfusion unit, tensile strength of the repaired skin, and histology of the incision site. Results The drainage amount was significantly reduced in the experimental group (49.8 mL) compared to the control group (86.2 mL) (P = 0.046). Skin perfusion was increased in the experimental group with statistical significance compared to the control group (P = 0.0175). Collagen staining was increased in the experimental group. The tensile strength of the incision site was significantly higher in the experimental group (24.6 N at 7 days, 61.67 N at 21 days) compared to the control group (18.26 N at 7 days, 50.05 N at 21 days) (P = 0.02). Conclusion This study explains some of the mechanism for using NPWT in closed incision wounds with dead space. It demonstrates that NPWT significantly reduces drainage amount, increases skin perfusion, increases tensile strength, and has the tendency to promote collagen synthesis for closed wound with dead space indicating enhanced healing. PMID:25003432

  5. Quantum field theory in spaces with closed time-like curves. [Gott space

    SciTech Connect

    Boulware, D.G.

    1992-01-01

    Gott spacetime has closed timelike curves, but no locally anomalous stress-energy. A complete orthonormal set of eigenfunctions of the wave operator is found in the special case of a spacetime in which the total deficit angle is 27[pi]. A scalar quantum field theory is constructed using these eigenfunctions. The resultant interacting quantum field theory is not unitary because the field operators can create real, on-shell, particles in the acausal region. These particles propagate for finite proper time accumulating an arbitrary phase before being annihilated at the same spacetime point as that at which they were created. As a result, the effective potential within the acausal region is complex, and probability is not conserved. The stress tensor of the scalar field is evaluated in the neighborhood of the Cauchy horizon; in the case of a sufficiently small Compton wavelength of the field, the stress tensor is regular and cannot prevent the formation of the Cauchy horizon.

  6. QUASARS PROBING QUASARS. VI. EXCESS H I ABSORPTION WITHIN ONE PROPER Mpc OF z ∼ 2 QUASARS

    SciTech Connect

    Prochaska, J. Xavier; Cantalupo, Sebastiano; Lau, Marie Wingyee; Bovy, Jo; Djorgovski, S. G.; Ellison, Sara L.; Martin, Crystal L.; Simcoe, Robert A.

    2013-10-20

    With close pairs of quasars at different redshifts, a background quasar sightline can be used to study a foreground quasar's environment in absorption. We use a sample of 650 projected quasar pairs to study the H I Lyα absorption transverse to luminous, z ∼ 2 quasars at proper separations of 30 kpc < R < 1 Mpc. In contrast to measurements along the line-of-sight, regions transverse to quasars exhibit enhanced H I Lyα absorption and a larger variance than the ambient intergalactic medium, with increasing absorption and variance toward smaller scales. Analysis of composite spectra reveals excess absorption characterized by a Lyα equivalent width profile W = 2.3 Å (R /100 kpc){sup –0.46}. We also observe a high (≅ 60%) covering factor of strong, optically thick H I absorbers (H I column N{sub H{sub I}}>10{sup 17.3} cm{sup -2}) at separations R < 200 kpc, which decreases to ∼20% at R ≅ 1 Mpc, but still represents a significant excess over the cosmic average. This excess of optically thick absorption can be described by a quasar-absorber cross-correlation function ξ{sub QA}(r) = (r/r{sub 0}){sup γ} with a large correlation length r{sub 0} = 12.5{sup +2.7}{sub -1.4} h{sup -1} Mpc (comoving) and γ=1.68{sup +0.14}{sub -0.30}. The H I absorption measured around quasars exceeds that of any previously studied population, consistent with quasars being hosted by massive dark matter halos M{sub halo} ≈ 10{sup 12.5} M{sub ☉} at z ∼ 2.5. The environments of these massive halos are highly biased toward producing optically thick gas, and may even dominate the cosmic abundance of Lyman limit systems and hence the intergalactic opacity to ionizing photons at z ∼ 2.5. The anisotropic absorption around quasars implies the transverse direction is much less likely to be illuminated by ionizing radiation than the line-of-sight.

  7. The Combination Application of Space Filling and Closed Irrigation Suction in Reconstruction of Sacral Decubitus Ulcer

    PubMed Central

    Weizhong, Liang; Zuojun, Zhao; Junling, Wu; Hongmei, Ai

    2014-01-01

    Dead space and poor drainage are the main reasons for intractable sacral decubitus ulcers. The objective of this study was to investigate the effects of treatment for sacral decubitus ulcer using space filling through muscle flap and closed irrigation. A total of 22 patients with serious sacral decubitus ulcer were treated with space filling through muscle flap and closed irrigation. After debridement of the decubitus ulcer, the infected areas over the bony prominence and osseous prominences were debrided. We elevated biceps femoris long head or semitendinosus and semimembranosus muscle. Pedicled by proximal part of muscle, the muscle flap was elevated to cover the ischial tuberosity. Transfusion systems of inflow and outflow drainage were placed between the muscle flap and ischial tuberosity. Wound healing and complications were observed. One wound dehiscence healed after secondary suturing. One wound gradually healed by dressing change after 3 weeks. The other cases had good results. Space filling and closed irrigation were complementary. The use of these two methods simultaneously is useful for the management of sacral decubitus ulcers. PMID:25216432

  8. THE EXTREME ULTRAVIOLET DEFICIT AND MAGNETICALLY ARRESTED ACCRETION IN RADIO-LOUD QUASARS

    SciTech Connect

    Punsly, Brian

    2014-12-20

    The Hubble Space Telescope composite quasar spectra presented in Telfer et al. show a significant deficit of emission in the extreme ultraviolet for the radio-loud component of the quasar population (RLQs) compared to the radio-quiet component of the quasar population. The composite quasar continuum emission between 1100 Å and ∼580 Å is generally considered to be associated with the innermost regions of the accretion flow onto the central black hole. The deficit between 1100 Å and 580 Å in RLQs has a straightforward interpretation as a missing or a suppressed innermost region of local energy dissipation in the accretion flow. It is proposed that this can be the result of islands of large-scale magnetic flux in RLQs that are located close to the central black hole that remove energy from the accretion flow as Poynting flux (sometimes called magnetically arrested accretion). These magnetic islands are natural sites for launching relativistic jets. Based on the Telfer et al. data and the numerical simulations of accretion flows in Penna et al., the magnetic islands are concentrated between the event horizon and an outer boundary of <2.8 M (in geometrized units) for rapidly rotating black holes and <5.5 M for modestly rotating black holes.

  9. Embedded coupled microrings with high-finesse and close-spaced resonances for optical signal processing.

    PubMed

    Souza, Mario C M M; Barea, Luis A M; Vallini, Felipe; Rezende, Guilherme F M; Wiederhecker, Gustavo S; Frateschi, Newton C

    2014-05-01

    Single microring resonators have been used in applications such as wavelength multicasting and microwave photonics, but the dependence of the free spectral range with ring radius imposes a trade-off between the required GHz optical channel spacing, footprint and power consumption. We demonstrate four-channel all-optical wavelength multicasting using only 1 mW of control power, with converted channel spacing of 40-60 GHz. Our device is based on a compact embedded microring design fabricated on a scalable SOI platform. The coexistence of close resonance spacing and high finesse (205) in a compact footprint is possible due to enhanced quality factors (30,000) resulting from the embedded configuration and the coupling-strength dependence of resonance spacing, instead of ring size. In addition, we discuss the possibility of achieving continuously mode splitting from a single-notch resonance up to 40 GHz. PMID:24921744

  10. Properties of closely spaced independently addressable lasers fabricated by impurity-induced disordering

    SciTech Connect

    Thornton, R.L.; Mosby, W.J.; Donaldson, R.M.; Paoli, T.L. )

    1990-04-23

    We describe the fabrication and characteristics of closely spaced (10 {mu}m) dual-beam laser sources by the process of impurity-induced disordering. We present data demonstrating that these devices are capable of high efficiency and reliable operation when operated in a {ital p}-side up configuration. We also show that these devices can be placed in close proximity with a minimal amount of thermal and electrical interaction between devices. These features have significant implications for the realization of high-density arrays of independently addressable lasers for optical interconnection of integrated circuits and optical imaging systems.

  11. PHOTOMETRIC OBSERVATIONS OF SELECTED, OPTICALLY BRIGHT QUASARS FOR SPACE INTERFEROMETRY MISSION AND OTHER FUTURE CELESTIAL REFERENCE FRAMES

    SciTech Connect

    Ojha, Roopesh E-mail: nz@usno.navy.mil E-mail: rgaume@usno.navy.mil

    2009-09-15

    Photometric observations of 235 extragalactic objects that are potential targets for the Space Interferometry Mission (SIM) are presented. Mean B, V, R, I magnitudes at the 5% level are obtained at 1-4 epochs between 2005 and 2007 using the 1 m telescopes at Cerro Tololo Inter-American Observatory and the Naval Observatory Flagstaff Station. Of the 134 sources that have V magnitudes in the Veron and Veron-Cetty catalog, a difference of over 1.0 mag is found for the observed-catalog magnitudes for about 36% of the common sources, and 10 sources show over 3 mag difference. Our first set of observations presented here form the basis of a long-term photometric variability study of the selected reference frame sources to assist in mission target selection and to support QSO multicolor photometric variability studies in general.

  12. Wake Encounter Analysis for a Closely Spaced Parallel Runway Paired Approach Simulation

    NASA Technical Reports Server (NTRS)

    Mckissick,Burnell T.; Rico-Cusi, Fernando J.; Murdoch, Jennifer; Oseguera-Lohr, Rosa M.; Stough, Harry P, III; O'Connor, Cornelius J.; Syed, Hazari I.

    2009-01-01

    A Monte Carlo simulation of simultaneous approaches performed by two transport category aircraft from the final approach fix to a pair of closely spaced parallel runways was conducted to explore the aft boundary of the safe zone in which separation assurance and wake avoidance are provided. The simulation included variations in runway centerline separation, initial longitudinal spacing of the aircraft, crosswind speed, and aircraft speed during the approach. The data from the simulation showed that the majority of the wake encounters occurred near or over the runway and the aft boundaries of the safe zones were identified for all simulation conditions.

  13. THE HISTORY AND ENVIRONMENT OF A FADED QUASAR: HUBBLE SPACE TELESCOPE OBSERVATIONS OF HANNY'S VOORWERP AND IC 2497

    SciTech Connect

    Keel, William C.; Manning, Anna; Lintott, Chris J.; Schawinski, Kevin; Bennert, Vardha N.; Thomas, Daniel; Chojnowski, S. Drew; Van Arkel, Hanny; Lynn, Stuart

    2012-08-15

    We present Hubble Space Telescope imaging and spectroscopy, along with supporting Galaxy Evolution Explorer and ground-based data, for the extended high-ionization cloud known as Hanny's Voorwerp, near the spiral galaxy IC 2497. Wide Field Camera 3 images show complex dust absorption near the nucleus of IC 2497. The galaxy core in these data is, within the errors, coincident with the very long baseline interferometry core component marking the active nucleus. Space Telescope Imaging Spectrograph (STIS) optical spectra show the active galactic nucleus (AGN) to be a type 2 Seyfert galaxy of rather low luminosity. The derived ionization parameter log U = -3.5 is in accordance with the weak X-ray emission from the AGN. We find no high-ionization gas near the nucleus, adding to the evidence that the AGN is currently at a low radiative output (perhaps with the central black hole having switched to a mode dominated by kinetic energy). The nucleus is accompanied by an expanding ring of ionized gas Almost-Equal-To 500 pc in projected diameter on the side opposite Hanny's Voorwerp. Where sampled by the STIS slit, this ring has Doppler offset Almost-Equal-To 300 km s{sup -1} from the nucleus, implying a kinematic age <7 Multiplication-Sign 10{sup 5} years. Narrowband [O III] and H{alpha}+[N II] Advanced Camera for Surveys images show fine structure in Hanny's Voorwerp, including limb-brightened sections suggesting modest interaction with a galactic outflow and small areas where H{alpha} is strong. We identify these latter regions as regions ionized by recent star formation, in contrast to the AGN ionization of the entire cloud. These candidate 'normal' H II regions contain blue continuum objects, whose colors are consistent with young stellar populations; they appear only in a 2 kpc region toward IC 2497 in projection, perhaps meaning that the star formation was triggered by compression from a narrow outflow. The ionization-sensitive ratio [O III]/H{alpha} shows broad bands

  14. A Sample of Quasars with Strong Nitrogen Emission Lines from the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Jiang, Linhua; Fan, Xiaohui; Vestergaard, M.

    2008-06-01

    We report on 293 quasars with strong N IV] λ1486 or N III] λ1750 emission lines (rest-frame equivalent width >3 Å) at 1.7 < z < 4.0 selected from the Sloan Digital Sky Survey (SDSS) Fifth Data Release. These nitrogen-rich (N-rich) objects comprise ~1.1% of the SDSS quasars. The comparison between the N-rich quasars and other quasars shows that the two quasar subsets share many common properties. We also confirm previous results that N-rich quasars have much stronger Lyα and N V λ1240 emission lines. Strong nitrogen emission in all ionization states indicates high overall nitrogen abundances in these objects. We find evidence that the nitrogen abundance is closely related to quasar radio properties. The radio-loud fraction in the N III]-rich quasars is 26% and in the N IV]-rich quasars is 69%, significantly higher than ~8% measured in other quasars with similar redshift and luminosity. Therefore, the high nitrogen abundance in N-rich quasars could be an indicator of a special quasar evolution stage, in which the radio activity is also strong.

  15. BINARY QUASARS AT HIGH REDSHIFT. I. 24 NEW QUASAR PAIRS AT z {approx} 3-4

    SciTech Connect

    Hennawi, Joseph F.; Myers, Adam D.; Shen, Yue; Strauss, Michael A.; Djorgovski, S. G.; Glikman, Eilat; Mahabal, Ashish; Fan Xiaohui; Martin, Crystal L.; Richards, Gordon T.; Schneider, Donald P.; Shankar, Francesco

    2010-08-20

    The clustering of quasars on small scales yields fundamental constraints on models of quasar evolution and the buildup of supermassive black holes. This paper describes the first systematic survey to discover high-redshift binary quasars. Using color-selection and photometric redshift techniques, we searched 8142 deg{sup 2} of Sloan Digital Sky Survey imaging data for binary quasar candidates, and confirmed them with follow-up spectroscopy. Our sample of 27 high-redshift binaries (24 of them new discoveries) at redshifts 2.9 < z < 4.3 with proper transverse separations 10 kpc < R{sub perpendicular} < 650 kpc increases the number of such objects known by an order of magnitude. Eight members of this sample are very close pairs with R{sub perpendicular} < 100 kpc, and of these close systems four are at z>3.5. The completeness and efficiency of our well-defined selection algorithm are quantified using simulated photometry and we find that our sample is {approx}50% complete. Our companion paper uses this knowledge to make the first measurement of the small-scale clustering (R < 1 h {sup -1} Mpc comoving) of high-redshift quasars. High-redshift binaries constitute exponentially rare coincidences of two extreme (M {approx}> 10{sup 9} M {sub sun}) supermassive black holes. At z {approx} 4, there is about one close binary per 10 Gpc{sup 3}, thus these could be the highest sigma peaks, the analogs of superclusters, in the early universe.

  16. Causes and effects of the first quasars.

    PubMed Central

    Rees, M J

    1993-01-01

    The light we observe from the most distant known quasars set out when the Universe was about 200 times denser than it is now and less than one-tenth of its present age. The existence of these objects implies that galaxy formation had already, at that early epoch, proceeded to the stage when massive (>10(8)M[symbol, see text]) objects had accumulated in the centers of at least some young galaxies. A specific model is presented to show that the evolution and luminosity function of quasars are compatible with the cold dark matter cosmogony. Most big galaxies probably passed through a quasar phase; the remnant black holes in nearby galaxies may reveal themselves via the flares that occur whenever a star passes too close to them and gets tidally disrupted. The rich absorption spectra of quasars serve as a probe of the intervening medium. The gas responsible for the Lyman alpha absorption lines may be due to primordial gas gravitationally confined in minihalos of dark matter--shallow potential wells whose evolution and relation to dwarf galaxies are briefly discussed. The patchy heat input into the intergalactic medium from early quasars could modulate the environment in which galaxies form, leading to large-scale spatial correlations in the galaxy distribution. This review concludes with general comments on the prospects for a fully quantitative understanding of galaxy formation. PMID:11607397

  17. Leveraging Spitzer's Legacy: Quasars and Feedback at High Redshift

    NASA Astrophysics Data System (ADS)

    Richards, Gordon; Anderson, Scott; Bauer, Franz; Deo, Rajesh; Fan, Xiaohui; Gallagher, Sarah; Myers, Adam; Strauss, Michael; Zakamska, Nadia

    2009-04-01

    Recent research efforts to understand the evolution of galaxies and quasars are beginning to form a consistent picture. Galaxies and their supermassive black holes grow through mergers, but with decreasing characteristic mass scales over time. Much less, however, is known about the evolution of galaxies at high redshifts and the role played by energy injection from the onset of active black hole growth. Understanding these events requires investigating a statistically significant number of high-redshift quasars and crossing the L* boundary in luminosity. To construct an appropriate data set requires both relatively wide-areas (to find these rare objects) and moderate-depth imaging (to probe below L* in luminosity). Unfortunately, existing optical and MIR surveys fail to meet both of these requirements. Furthermore, both optical and MIR quasar selection are blindest at the most crucial redshifts. Here we propose to address these gaps with targeted IRAC observations of a few hundred high-redshift quasars from the Sloan Digital Sky Survey. Such a sample will enable the construction of a proper training set for the discovery of 2.5quasars through combined optical+MIR (from IRAC channels 1 and 2) selection methods that overcome the limitations inherent to optical and MIR selection alone. By concentrating on SDSS Stripe 82, with sensitivity of i~23, we will learn how to identify high-redshift quasars in other fields over a large range in luminosity. With this knowledge, we will crack open the high-z quasar discovery space within existing IRAC legacy surveys (SWIRE, XFLS, Bootes, COSMOS). With a large sample of high-redshift quasars spanning a large range in luminosity, we can turn the quasar luminosity function and quasar clustering analysis into tools for distinguishing between different evolutionary models and feedback prescriptions. In all, we will observe 330 SDSS quasars using 307 pointings/AORs, totaling 48.5 hours of IRAC time.

  18. Giant scattering cones in obscured quasars

    NASA Astrophysics Data System (ADS)

    Obied, Georges; Zakamska, Nadia L.; Wylezalek, Dominika; Liu, Guilin

    2016-03-01

    We analyse Hubble Space Telescope observations of scattering regions in 20 luminous obscured quasars at 0.24 < z < 0.65 (11 new observations and nine archival ones) observed at rest frame ˜3000 Å. We find spectacular 5-10 kpc-scale scattering regions in almost all cases. The median scattering efficiency at this wavelength (the ratio of observed to estimated intrinsic flux) is 2.3, and 73 per cent of the observed flux at this wavelength is due to scattered light, which if unaccounted for may strongly bias estimates of quasar hosts' star formation rates. Modelling these regions as illuminated dusty cones, we estimate the radial density distributions of the interstellar medium as well as the geometric properties of circumnuclear quasar obscuration - inclinations and covering factors. Small derived opening angles (median half-angle and standard deviation 27° ± 9°) are inconsistent with a 1:1 type 1/type 2 ratio. We suggest that quasar obscuration is patchy and that the observer has an ˜40 per cent chance of seeing a type 1 source even through the obscuration. We estimate median density profile of the scattering medium to be nH = 0.04-0.5 (1 kpc/r)2 cm-3, depending on the method. Quasars in our sample likely exhibit galaxy-wide winds, but if these consist of optically thick clouds then only a small fraction of the wind mass ( ≲ 10 per cent) contributes to scattering.

  19. The Significant Incidents and Close Calls in Human Space Flight Chart: Lessons Learned Gone Viral

    NASA Technical Reports Server (NTRS)

    Wood, Bill; Pate, Dennis; Thelen, David

    2010-01-01

    This presentation will explore the surprising history and events that transformed a mundane spreadsheet of historical spaceflight incidents into a popular and widely distributed visual compendium of lessons learned. The Significant Incidents and Close Calls in Human Space Flight Chart (a.k.a. The Significant Incidents Chart) is a popular and visually captivating reference product that has arisen from the work of the Johnson Space Center (JSC) Safety and Mission Assurance (S&MA) Flight Safety Office (FSO). It began as an internal tool intended to increase our team s awareness of historical and modern space flight incidents. Today, the chart is widely recognized across the agency as a reference tool. It appears in several training and education programs. It is used in familiarization training in the JSC Building 9 Mockup Facility and is seen by hundreds of center visitors each week. The chart visually summarizes injuries, fatalities, and close calls sustained during the continuing development of human space flight. The poster-sized chart displays over 100 total events that have direct connections to human space flight endeavors. The chart is updated periodically. The update process itself has become a collaborative effort. Many people, spanning multiple NASA organizations, have provided suggestions for additional entries. The FSO maintains a growing list of subscribers who have requested to receive updates. The presenters will discuss the origins and motivations behind the significant incidents chart. A review of the inclusion criteria used to select events will be offered. We will address how the chart is used today by S&MA and offer a vision of how it might be used by other organizations now and in the future. Particular emphasis will be placed on features of the chart that have met with broad acceptance and have helped spread awareness of the most important lessons in human spaceflight.

  20. High Redshift Quasars

    NASA Technical Reports Server (NTRS)

    Elvis, Martin S.

    1996-01-01

    The report for this period includes three papers: 'Associated Absorption at Low and High Redshift'; 'Strong X-ray Absorption in a Broad Absorption Line Quasar: PHL5200'; and 'ASCA and ROSAT X-ray Spectra of High-Redshift Radio-Loud Quasars'. The first gives examples from both low and high redshift for combining information on absorbing material in active galactic nuclei from both x-ray and the UV. The second presents ASCA observations of the z = 1.98 prototype broad absorption line quasar (BALQSO): PHL 5200, detected with both the solid-state imaging spectrometers and the gas imaging spectometers. The third paper presents results on the x-ray properties of 9 high-redshift radio-loud quasars observed by ASCA and ROSAT, including ASCA observations of S5 0014+81 (z = 3.38) and S5 0836+71 (z = 2.17) and ROSAT observations of PKS 2126-158.

  1. Observed Quasar Structure

    NASA Astrophysics Data System (ADS)

    Schild, Rudolph E.

    2011-05-01

    With the introduction of microlensing (nano-lensing) and reverberation analysis, understanding of the luminous structure surrounding quasars has gone from theoretical speculation to an observer's sport. Micro-lensing with day timescale has demonstrated that quasars have structure on scales of 1 R_G which we attribute to the inner edge of the accretion disc, at central distance 70 R_G in lo-hard state (radio loud) Q0957 quasar, indicated by reverberation. Reverberation of the dominant optical continuum has been detected in all 55 hi-soft quasars with brightness data, originating in the dusty torus observed in UV-optical and IR reverberation. Microlensing simulation compared to brightness monitoring shows that 2/3 of the UV-optical continuum originates in the outer torus. The observed color effects observed in the microlensing support the existence of inner and outer luminous structure.

  2. Quasars: A Progress Report.

    ERIC Educational Resources Information Center

    Weedman, Daniel

    1988-01-01

    Reports on some of the discoveries over the last quarter century regarding quasars including spectra and energy sources, formation and evolution, and cosmological probes. Describes some of the fundamental mysteries that remain. (CW)

  3. Finding Quasars with SNAP

    NASA Astrophysics Data System (ADS)

    Brondel, B. J.; Mufson, S. L.

    2005-12-01

    The Supernova / Acceleration Probe (SNAP) is a planned satellite observatory that will investigate the dark energy by producing imaging data over a large (several square-degree) field of sky that will rival or exceed the Hubble Ultra Deep Field in photometric quality and depth. As such, SNAP is ideally suited for deep surveys as auxiliary science. We discuss application of quasar science techniques to SNAP photometry. Based on a simple photometric quasar / Lyman forest model, we simulate the population of quasars that SNAP will observe and compare the resulting photometry with a population of model stellar photometry. We examine the effectiveness of identifying quasars based only on photometric data by a variety of techniques, most of which were first developed for use with Sloan Digital Sky Survey. Exclusion of the stellar locus in the style of Newberg & Yanni, statistical mapping, and machine learning with neural networks are among the techniques we explore. A photometric redshift calculus is also presented.

  4. Aeroelastic dynamics of mistuned blade assemblies with closely spaced blade modes

    NASA Technical Reports Server (NTRS)

    Pierre, Christophe; Murthy, Durbha V.

    1993-01-01

    The aeroelastic characteristics of tuned and randomly mistuned blade assemblies which possess two blade-alone natural modes with close frequencies are studied. Modal interactions among the two blade modes are shown to be come extremely significant for small frequency separation. The two distinct loci of the aeroelastic eigenvalues, which characterize an assembly with well separated modes, fully merge into a single root locus as the blade-mode frequency separation vanishes. Also, while in the case of well separated blade modes the introduction of random mistuning into one blade mode affects only the assembly modes which are predominantly of that blade-mode type, mistuning results in the localization of all the assembly modes when the blade-alone natural frequencies are close. Results indicate that in the case of closely-spaced blade modes a single-degree of freedom blade model yields qualitatively erroneous results and that an N-blade assembly with two close blade modes behaves like an equivalent 2Nb-blade assembly with a single blade mode.

  5. Closed Cycle Magnetohydrodynamic Nuclear Space Power Generation Using Helium/Xenon Working Plasma

    NASA Technical Reports Server (NTRS)

    Litchford, R. J.; Harada, N.

    2005-01-01

    A multimegawatt-class nuclear fission powered closed cycle magnetohydrodynamic space power plant using a helium/xenon working gas has been studied, to include a comprehensive system analysis. Total plant efficiency was expected to be 55.2 percent including pre-ionization power. The effects of compressor stage number, regenerator efficiency, and radiation cooler temperature on plant efficiency were investigated. The specific mass of the power generation plant was also examined. System specific mass was estimated to be 3 kg/kWe for a net electrical output power of 1 MWe, 2-3 kg/kWe at 2 MWe, and approx.2 kg/KWe at >3 MWe. Three phases of research and development plan were proposed: (1) Phase I-proof of principle, (2) Phase II-demonstration of power generation, and (3) Phase III-prototypical closed loop test.

  6. Evaluating Nextgen Closely Spaced Parallel Operations Concepts with Validated Human Performance Models: Flight Deck Guidelines

    NASA Technical Reports Server (NTRS)

    Hooey, Becky Lee; Gore, Brian Francis; Mahlstedt, Eric; Foyle, David C.

    2013-01-01

    The objectives of the current research were to develop valid human performance models (HPMs) of approach and land operations; use these models to evaluate the impact of NextGen Closely Spaced Parallel Operations (CSPO) on pilot performance; and draw conclusions regarding flight deck display design and pilot-ATC roles and responsibilities for NextGen CSPO concepts. This document presents guidelines and implications for flight deck display designs and candidate roles and responsibilities. A companion document (Gore, Hooey, Mahlstedt, & Foyle, 2013) provides complete scenario descriptions and results including predictions of pilot workload, visual attention and time to detect off-nominal events.

  7. Experimental Studies Of Pilot Performance At Collision Avoidance During Closely Spaced Parallel Approaches

    NASA Technical Reports Server (NTRS)

    Pritchett, Amy R.; Hansman, R. John

    1997-01-01

    Efforts to increase airport capacity include studies of aircraft systems that would enable simultaneous approaches to closely spaced parallel runway in Instrument Meteorological Conditions (IMC). The time-critical nature of a parallel approach results in key design issues for current and future collision avoidance systems. Two part-task flight simulator studies have examined the procedural and display issues inherent in such a time-critical task, the interaction of the pilot with a collision avoidance system, and the alerting criteria and avoidance maneuvers preferred by subjects.

  8. Close-spaced vapor transport and photoelectrochemistry of gallium arsenide for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Ritenour, Andrew J.

    The high balance-of-system costs of photovoltaic installations indicate that reductions in absorber cost alone are likely insufficient for photovoltaic electricity to reach grid parity unless energy conversion efficiency is also increased. Technologies which both yield high-efficiency cells (>25%) and maintain low costs are needed. GaAs and related III--V semiconductors are used in the highest-efficiency single- and multi-junction photovoltaics, but the technology is too expensive for non-concentrated terrestrial applications. This is due in part to the limited scalability of traditional syntheses, which rely on expensive reactors and employ toxic and pyrophoric gas-phase precursors such as arsine and trimethyl gallium. This work describes GaAs films made by close-spaced vapor transport, a potentially scalable technique which is carried out at atmospheric pressure and requires only bulk GaAs, water vapor, and a temperature gradient to deposit crystalline films with similar electronic properties to GaAs prepared using traditional syntheses. Although close-spaced vapor transport of GaAs was first developed in 1963, there were few examples of GaAs photovoltaic devices made using this method in the literature at the onset of this project. Furthermore, it was unclear whether close-spaced vapor transport could produce GaAs films appropriate for use in photovoltaics. The goal of this project was to create and study GaAs devices made using close-spaced vapor transport and determine whether the technique could be used for production of grid-connected GaAs photovoltaics. In Chapter I the design of the vapor transport reactor, the chemistry of crystal growth, and optoelectronic characterization techniques are discussed. Chapter II focuses on compositional measurements, doping, and improved electronic quality in CSVT GaAs. Chapter III describes several aspects of the interplay between structure and electronic properties of photoelectrochemical devices. Chapter IV addresses

  9. Induced Recrystallization of CdTe Thin Films Deposited by Close-Spaced Sublimation

    SciTech Connect

    Moutinho, H. R.; Dhere, R. G.; Al-Jassim, M. M.; Levi, D. H.; Kazmerski, L. L.; Mayo, B.

    1998-10-29

    We have deposited CdTe thin films by close-spaced sublimation at two different temperature ranges. The films deposited at the lower temperature partially recrystallized after CdCl{sub 2} treatment at 350 C and completely recrystallized after the same treatment at 400 C. The films deposited at higher temperature did not recrystallize at these two temperatures. These results confirmed that the mechanisms responsible for changes in physical properties of CdTe films treated with CdCl{sub 2} are recrystallization and grain growth, and provided an alternative method to deposit CSS films using lower temperatures.

  10. Induced Recrystallization of CdTe Thin Films Deposited by Close-Spaced Sublimation

    SciTech Connect

    Moutinho, H. R.; Dhere, R. G.; Al-Jassim, M. M.; Levi, D. H.; Kazmerski, L. L.; Mayo, B.

    1998-10-26

    We have deposited CdTe thin films by close-spaced sublimation at two different temperature ranges. The films deposited at the lower temperature partially recrystallized after CdCl2 treatment at 350 C and completely recrystallized after the same treatment at 400 C. The films deposited at higher temperature did not recrystallize at these two temperatures. These results confirmed that the mechanisms responsible for changes in physical properties of CdTe films treated with CdCl2 are recrystallization and grain growth, and provided an alternative method to deposit CSS films using lower temperatures.

  11. Issues in Airborne Systems for Closely-Spaced Parallel Runway Operations

    NASA Technical Reports Server (NTRS)

    Pritchett, A.; Carpenter, B.; Asari, K.; Kuchar, J.; Hansman, R. J.

    1995-01-01

    Efforts to increase airport capacity include studies of aircraft systems that would enable simultaneous approaches to closely spaced parallel runways in Instrument Meteorological Conditions (IMC). The time-critical nature of a parallel approach results in key design issues for current and future collision avoidance systems. These issues are being studied in two ways. First, a part-task flight simulator study has examined the procedural and display issues inherent in such a time-critical task. Second, a prototype collision avoidance logic capable of generating this maneuver guidance has been designed using a recently developed methodology.

  12. Time-resolved photoluminescence of polycrystalline CdTe grown by close-spaced sublimation

    SciTech Connect

    Keyes, B.; Dhere, R.; Ramanathan, K. )

    1994-06-30

    Polycrystalline CdTe has shown great promise as a low-cost material for thin-film, terrestrial photovoltaic applications, with efficiencies approaching 16% achieved with close-spaced sublimation (CSS)-grown CdTe. Due to the inherent complexities of polycrystalline material, much of the progress in this area has occurred through a slow trial-and-error process. This report uses time-resolved photoluminescence (TRPL) to characterize the CdTe material quality as a function of one basic growth parameter---substrate temperature. This characterization is done for two different glass substrate materials, soda-lime silicate and borosilicate.

  13. Carbon-Carbon Recuperators in Closed-Brayton-Cycle Nuclear Space Power Systems: A Feasibility Assessment

    NASA Technical Reports Server (NTRS)

    Barrett, Michael J.; Johnson, Paul K.

    2004-01-01

    The feasibility of using carbon-carbon recuperators in closed-Brayton-cycle (CBC) nuclear space power conversion systems (PCS) was assessed. Recuperator performance expectations were forecast based on projected thermodynamic cycle state values for a planetary mission. Resulting thermal performance, mass and volume for a plate-fin carbon-carbon recuperator were estimated and quantitatively compared with values for a conventional offset-strip-fin metallic design. Material compatibility issues regarding carbon-carbon surfaces exposed to the working fluid in the CBC PCS were also discussed.

  14. Quasar counts from variability and color selected samples

    NASA Astrophysics Data System (ADS)

    Andrews, Peter Arthur

    Quasars are among the brightest and most distant objects known, making them intrinsically interesting as well as ideal probes of the history of the universe. Over 23,000 quasars have been found since their discovery four decades ago, but most were identified by various redshift-limited ultraviolet excess methods which excluded extended sources. This prohibits the use of the global quasar sample in a statistical manner for quasar lensing studies. To improve on this situation, the QUEST survey was born, with the goal of finding large numbers of quasars and gravitational lenses using a uniform selection method for cosmology studies. To date, we have completed three years of driftscan imaging observations using the QUEST 16 CCD camera on the 1m Schmidt telescope at Llano del Hato in Venezuela. Presented here are descriptions of the equipment, data, software and selection methods used, our discovered quasar candidates, a list of confirmed quasars, measured quasar surface densities and comparisons with published results. Ten nights of UBUV filter data covering 155 square degrees are analyzed using the traditional UV-excess color-selection method to find low-redshift quasars. From the candidates where we obtained spectroscopy, we measured a low-redshift quasar surface density of 5 +/- 1 per square degree to a B magnitude limit of 19.4. Twenty-five nights of RBRV data taken over three years and covering 250 square degrees are analyzed to find quasars by their variability. To our knowledge the variability portion of our survey is the largest of its kind, using over a dozen nights fully covering most of the huge survey area. Because variability can be used to find quasars uniformly over all redshifts and extended or close groupings of objects are properly treated by our survey, the results here may be less biased with respect to lensed quasars than other selection methods. From the variability candidates where we obtained spectroscopy, we measured a quasar surface density of

  15. Visualizing plasmon coupling in closely spaced chains of Ag nanoparticles by electron energy-loss spectroscopy.

    PubMed

    Song, Fengqi; Wang, Tingyu; Wang, Xuefeng; Xu, Changhui; He, Longbing; Wan, Jianguo; Van Haesendonck, Christian; Ringer, Simon P; Han, Min; Liu, Zongwen; Wang, Guanghou

    2010-02-01

    Anisotropic plasmon coupling in closely spaced chains of Ag nanoparticles is visualized using electron energy-loss spectroscopy in a scanning transmission electron microscope. For dimers as the simplest chain, mapping the plasmon excitations with nanometer spatial resolution and an energy resolution of 0.27 eV intuitively identifies two coupling plasmons. The in-phase mode redshifts from the ultraviolet region as the interparticle spacing is reduced, reaching the visible range at 2.7 eV. Calculations based on the discrete-dipole approximation confirm its optical activeness, where the longitudinal direction is constructed as the path for light transportation. Two coupling paths are then observed in an inflexed four-particle chain. PMID:20077517

  16. Optimizing surface-enhanced Raman scattering by template guided assembling of closely spaced silver nanocluster arrays

    NASA Astrophysics Data System (ADS)

    Xu, C. H.; Xie, B.; Liu, Y. J.; He, L. B.; Han, M.

    2009-04-01

    We present an easy approach to synthesize closely spaced regular arrays of silver nanoclusters, which are self-assembled by depositing gas-phase synthesized metal nanoclusters onto pre-patterned triblock copolymer templates. The array has a high particle density of about 2 ×103 particles per μm2, and an average interparticle space of about 20 nm. The surface plasmon resonance wavelength of the array is tuned due to the interparticle plasmon coupling. High SERS sensitivity for less than one layer trans-1,2-bi-(4-pyridyl) ethylene (BPE) molecule detection, with an enhancement factor of 2.6 ×106, has been demonstrated for a substrate with this array. The enhanced Raman signal was found to be 5 times higher than that measured from the substrate with randomly distributed silver nanoparticles.

  17. Advances in defining a closed Brayton conversion system for future ARIANE 5 space nuclear power applications

    SciTech Connect

    Tilliette, Z.P.

    1987-01-01

    The present European ARIANE space program will expand into the large ARIANE 5 launch vehicle from 1995. It is assumed that important associated missions would require the generation of 200 kWe or more in space during several years at the very beginning of the next century. For this reason, in 1983, the French C.N.E.S. (Centre National d'Etudes Spatiales) and C.E.A. (Commissariat a l'Energie Atomique) have initiated preliminary studies of a space nuclear power system. The currently selected conversion system is a closed Brayton cycle. Reasons for this choice are given: high efficiency of a dynamic system; monophasic, inert working fluid; extensive turbomachinery experience, etc. A key aspect of the project is the adaptation to heat rejection conditions, namely to the radiator geometry which depends upon the dimensions of the ARIANE 5 spacecraft. In addition to usual concepts already studied for space applications, another cycle arrangement is being investigated which could offer satisfactory compromises among many considerations, increase the efficiency of the system, and make it more attractive as far as the specific mass (kg/lWe), the specific radiator area (m/sup 2//kWe), and various technological aspects are concerned. Comparative details are presented.

  18. OBSCURATION BY GAS AND DUST IN LUMINOUS QUASARS

    SciTech Connect

    Usman, S. M.; Murray, S. S.; Hickox, R. C.; Brodwin, M.

    2014-06-10

    We explore the connection between absorption by neutral gas and extinction by dust in mid-infrared (IR) selected luminous quasars. We use a sample of 33 quasars at redshifts 0.7 < z ≲ 3 in the 9 deg{sup 2} Boötes multiwavelength survey field that are selected using Spitzer Space Telescope Infrared Array Camera colors and are well-detected as luminous X-ray sources (with >150 counts) in Chandra observations. We divide the quasars into dust-obscured and unobscured samples based on their optical to mid-IR color, and measure the neutral hydrogen column density N {sub H} through fitting of the X-ray spectra. We find that all subsets of quasars have consistent power law photon indices Γ ≈ 1.9 that are uncorrelated with N {sub H}. We classify the quasars as gas-absorbed or gas-unabsorbed if N {sub H} > 10{sup 22} cm{sup –2} or N {sub H} < 10{sup 22} cm{sup –2}, respectively. Of 24 dust-unobscured quasars in the sample, only one shows clear evidence for significant intrinsic N {sub H}, while 22 have column densities consistent with N {sub H} < 10{sup 22} cm{sup –2}. In contrast, of the nine dust-obscured quasars, six show evidence for intrinsic gas absorption, and three are consistent with N {sub H} < 10{sup 22} cm{sup –2}. We conclude that dust extinction in IR-selected quasars is strongly correlated with significant gas absorption as determined through X-ray spectral fitting. These results suggest that obscuring gas and dust in quasars are generally co-spatial, and confirm the reliability of simple mid-IR and optical photometric techniques for separating quasars based on obscuration.

  19. Multiport well design for sampling of ground water at closely spaced vertical intervals

    SciTech Connect

    Delin, G.N.; Landon, M.K.

    1996-11-01

    Detailed vertical sampling is useful in aquifers where vertical mixing is limited and steep vertical gradients in chemical concentrations are expected. Samples can be collected at closely spaced vertical intervals from nested wells with short screened intervals. However, this approach may not be appropriate in all situations. An easy-to-construct and easy-to-install multiport sampling well to collect ground-water samples from closely spaced vertical intervals was developed and tested. The multiport sampling well was designed to sample ground water from surficial sand-and-gravel aquifers. The device consists of multiple stainless-steel tubes within a polyvinyl chloride (PVC) protective casing. The tubes protrude through the wall of the PVC casing at the desired sampling depths. A peristaltic pump is used to collect ground-water samples form the sampling ports. The difference in hydraulic head between any two sampling ports can be measured with a vacuum pump and a modified manometer. The usefulness and versatility of this multiport well design was demonstrated at an agricultural research site near Princeton, Minnesota where sampling ports were installed to a maximum depth of about 12 m below land surface. Trace experiments were conducted using potassium bromide to document the degree to which short-circuiting occurred between sampling ports. Samples were successfully collected for analysis of major cations and anions, nutrients, selected herbicides, isotopes, dissolved gases, and chlorofluorocarbon concentrations.

  20. Synthesis of Ga 2O 3 chains with closely spaced knots connected by nanowires

    NASA Astrophysics Data System (ADS)

    Dai, L.; You, L. P.; Duan, X. F.; Lian, W. C.; Qin, G. G.

    2004-07-01

    Chains of closely spaced metal or semiconductor particles have potential applications in optoelectronics and single electron devices. We report, for the first time, the synthesis of Ga 2O 3 chains with closely spaced knots connected by nanowires using the thermal evaporation method with a specially designed quartz boat. The Ga 2O 3 chains grew only on the Si substrates where Au catalyst or Ga droplets were coated. The average diameter of the knots is about 450 nm and that of the nanowires is about 50 nm. The selected area electron diffraction of either a knot or a connecting nanowire includes two sets of overlapped single crystal electron diffraction patterns which belong to the [1 0 2] and [1 0 1¯] crystal zone axes of the monoclinic β-Ga 2O 3 phase, respectively. The knot and its neighbor nanowire have the common ( 2¯ 0 1) growth planes at their interface. A mechanism model for the Ga 2O 3 chains synthesis based on the vapor-liquid-solid mechanism is discussed.

  1. Multiport well design for sampling of ground water at closely spaced vertical intervals

    USGS Publications Warehouse

    Delin, G.N.; Landon, M.K.

    1996-01-01

    Detailed vertical sampling is useful in aquifers where vertical mixing is limited and steep vertical gradients in chemical concentrations are expected. Samples can be collected at closely spaced vertical intervals from nested wells with short screened intervals. However, this approach may not be appropriate in all situations. An easy-to-construct and easy-to-install multiport sampling well to collect ground-water samples from closely spaced vertical intervals was developed and tested. The multiport sampling well was designed to sample ground water from surficial sand-and-gravel aquifers. The device consists of multiple stainless-steel tubes within a polyvinyl chloride (PVC) protective casing. The tubes protrude through the wall of the PVC casing at the desired sampling depths. A peristaltic pump is used to collect ground-water samples from the sampling ports. The difference in hydraulic head between any two sampling ports can be measured with a vacuum pump and a modified manometer. The usefulness and versatility of this multiport well design was demonstrated at an agricultural research site near Princeton, Minnesota where sampling ports were installed to a maximum depth of about 12 m below land surface. Tracer experiments were conducted using potassium bromide to document the degree to which short-circuiting occurred between sampling ports. Samples were successfully collected for analysis of major cations and anions, nutrients, selected herbicides, isotopes, dissolved gases, and chlorofluorcarbon concentrations.

  2. Detecting Space-Time Alternating Biological Signals Close to the Bifurcation Point

    PubMed Central

    Jia, Zhiheng; Bien, Harold; Entcheva, Emilia

    2011-01-01

    Time-alternating biological signals, i.e., alternans, arise in variety of physiological states marked by dynamic instabilities, e.g., period doubling. Normally, a sequence of large–small–large transients, they can exhibit variable patterns over time and space, including spatial discordance. Capture of the early formation of such alternating regions is challenging because of the spatiotemporal similarities between noise and the small-amplitude alternating signals close to the bifurcation point. We present a new approach for automatic detection of alternating signals in large noisy spatiotemporal datasets by exploiting quantitative measures of alternans evolution, e.g., temporal persistence, and by preserving phase information. The technique specifically targets low amplitude, relatively short alternating sequences and is validated by combinatorics-derived probabilities and empirical datasets with white noise. Using high-resolution optical mapping in live cardiomyocyte networks, exhibiting calcium alternans, we reveal for the first time early fine-scale alternans, close to the noise level, which are linked to the later formation of larger regions and evolution of spatially discordant alternans. This robust method aims at quantification and better understanding of the onset of cardiac arrhythmias and can be applied to general analysis of space-time alternating signals, including the vicinity of the bifurcation point. PMID:19695992

  3. CONSTRAINING SUB-PARSEC BINARY SUPERMASSIVE BLACK HOLES IN QUASARS WITH MULTI-EPOCH SPECTROSCOPY. I. THE GENERAL QUASAR POPULATION

    SciTech Connect

    Shen, Yue; Liu, Xin; Loeb, Abraham; Tremaine, Scott

    2013-09-20

    We perform a systematic search for sub-parsec binary supermassive black holes (BHs) in normal broad-line quasars at z < 0.8, using multi-epoch Sloan Digital Sky Survey (SDSS) spectroscopy of the broad Hβ line. Our working model is that (1) one and only one of the two BHs in the binary is active; (2) the active BH dynamically dominates its own broad-line region (BLR) in the binary system, so that the mean velocity of the BLR reflects the mean velocity of its host BH; (3) the inactive companion BH is orbiting at a distance of a few R{sub BLR}, where R{sub BLR} ∼ 0.01-0.1 pc is the BLR size. We search for the expected line-of-sight acceleration of the broad-line velocity from binary orbital motion by cross-correlating SDSS spectra from two epochs separated by up to several years in the quasar rest frame. Out of ∼700 pairs of spectra for which we have good measurements of the velocity shift between two epochs (1σ error ∼40 km s{sup –1}), we detect 28 systems with significant velocity shifts in broad Hβ, among which 7 are the best candidates for the hypothesized binaries, 4 are most likely due to broad-line variability in single BHs, and the rest are ambiguous. Continued spectroscopic observations of these candidates will easily strengthen or disprove these claims. We use the distribution of the observed accelerations (mostly non-detections) to place constraints on the abundance of such binary systems among the general quasar population. Excess variance in the velocity shift is inferred for observations separated by longer than 0.4 yr (quasar rest frame). Attributing all the excess to binary motion would imply that most of the quasars in this sample must be in binaries, that the inactive BH must be on average more massive than the active one, and that the binary separation is at most a few times the size of the BLR. However, if this excess variance is partly or largely due to long-term broad-line variability, the requirement of a large population of close

  4. High Velocity Outflows in Quasars

    NASA Astrophysics Data System (ADS)

    Hamann, Fred; Rodriguez Hidalgo, Paola; Nestor, Daniel

    2006-02-01

    High velocity (HV) outflows are important components of SMBH growth and evolution. The ability of SMBHs to accrete matter and light up as AGN probably requires that outflows are present to carry away angular momentum. Outflows during the luminous AGN phase might also play a critical role in ``unveiling" young dust-enshrouded AGN and in ``polluting" the intergalactic medium with metals at high redshifts. Nonetheless, AGN outflows remain poorly understood. We have begun a program to study a nearly unexplored realm of AGN outflow parameter space: HV winds with v> 10,000 km/s up to v~ 0.2c but small velocity dispersions (narrow absorption lines), such that v/(Delta) v ≫ 1. These extreme outflows have been detected so far in just a few quasars, but they might be ubiquitous if, as expected, the flows subtend a small solid angle as seen from the central engine. Narrow-line HV flows merit specific attention because they pose unique challenges for theoretical models of the wind acceleration, mass loss rates, launch radii, etc. They might also comprise a significant fraction of absorbers previously attributed to unrelated (interveinng) gas or galaxies. We have compiled a list of bright quasars with candidate HV outflow lines (CIV 1550 A) in existing SDSS spectra. We now propose to observe ~50 of these candidates with the 2.1m GoldCam to i) identify/confirm some of the true outflow systems (based on line variability), ii) place a firm lower limit on the fraction of quasars with narrow-line HV outflows, iii) compile a short list of confirmed HV outflow sources for future study, and iv) use the combined SDSS and GoldCam data to measure or constrain basic outflow properties, such as the kinematics, locations, and physical conditions.

  5. Ultraviolet (UV) From Quasars - Skylab Student Experiment ED-23

    NASA Technical Reports Server (NTRS)

    1973-01-01

    This chart describes the Skylab student experiment Ultraviolet (UV) from Quasars, proposed by John C. Hamilton of Aiea, Hawaii. This experiment utilized Skylab's Ultraviolet Stellar Astronomy equipment to photograph quasars in the UV spectrum and compare those images to existing radio and visible data. In March 1972 NASA and the National Science Teachers Association selected 25 experiment proposals for flight on Skylab. Science advisors from the Marshall Space Flight Center aided and assisted the students in developing the proposals for flight on Skylab.

  6. Quasar Absorption Studies

    NASA Technical Reports Server (NTRS)

    Mushotzky, Richard (Technical Monitor); Elvis, Martin

    2004-01-01

    The aim of the proposal is to investigate the absorption properties of a sample of inter-mediate redshift quasars. The main goals of the project are: Measure the redshift and the column density of the X-ray absorbers; test the correlation between absorption and redshift suggested by ROSAT and ASCA data; constrain the absorber ionization status and metallicity; constrain the absorber dust content and composition through the comparison between the amount of X-ray absorption and optical dust extinction. Unanticipated low energy cut-offs where discovered in ROSAT spectra of quasars and confirmed by ASCA, BeppoSAX and Chandra. In most cases it was not possible to constrain adequately the redshift of the absorber from the X-ray data alone. Two possibilities remain open: a) absorption at the quasar redshift; and b) intervening absorption. The evidences in favour of intrinsic absorption are all indirect. Sensitive XMM observations can discriminate between these different scenarios. If the absorption is at the quasar redshift we can study whether the quasar environment evolves with the Cosmic time.

  7. DISCOVERY OF THE DISTURBED RADIO MORPHOLOGY IN THE INTERACTING BINARY QUASAR FIRST J164311.3+315618

    SciTech Connect

    Kunert-Bajraszewska, Magdalena; Janiuk, Agnieszka

    2011-08-01

    We report the high-resolution radio observations and the subsequent analysis of the radio-loud compact steep spectrum quasar FIRST J164311.3+315618, one of the members of a binary system. The second component of the system is a radio-quiet active galactic nucleus. The projected separation of this pair is 2.''3 (15 kpc); it is one of the smallest-known-separation binary quasars. The multi-band images of this binary system made with the Hubble Space Telescope show that the host galaxy of the radio-loud quasar is highly disturbed. The radio observations presented here were made with the Multi-Element Radio-Linked interferometer network (MERLIN) at 1.66 GHz and 5 GHz. We show that the radio morphology of FIRST J164311.3+315618 is complex on both frequencies and exhibits four components that indicate the intermittent activity with a possible rapid change of the jet direction and/or restarting of the jet due to the interaction with the companion. The radio components that are no longer powered by the jet can quickly fade away. We suggest that this makes the potential distortions of the radio structure short-lived phenomena. Our numerical simulations show that the influence of the companion can lead to prolonged current and future activities. FIRST J164311.3+315618 is an unusual and statistically very rare low redshift binary quasar wherein the first close encounter is probably just taking place.

  8. Distributions of Quasar Hosts on the Galaxy Main Sequence Plane

    NASA Astrophysics Data System (ADS)

    Zhang, Zhoujian; Shi, Yong; Rieke, George H.; Xia, Xiaoyang; Wang, Yikang; Sun, Bingqing; Wan, Linfeng

    2016-03-01

    The relation between star formation rates (SFRs) and stellar masses, i.e., the galaxy main sequence, is a useful diagnostic of galaxy evolution. We present the distributions relative to the main sequence of 55 optically selected PG and 12 near-IR-selected Two Micron All Sky Survey (2MASS) quasars at z ≤ 0.5. We estimate the quasar host stellar masses from Hubble Space Telescope or ground-based AO photometry, and the SFRs through the mid-infrared aromatic features and far-IR photometry. We find that PG quasar hosts more or less follow the main sequence defined by normal star-forming galaxies while 2MASS quasar hosts lie systematically above the main sequence. PG and 2MASS quasars with higher nuclear luminosities seem to have higher specific SFRs (sSFRs), although there is a large scatter. No trends are seen between sSFRs and SMBH masses, Eddington ratios, or even morphology types (ellipticals, spirals, and mergers). Our results could be placed in an evolutionary scenario with quasars emerging during the transition from ULIRGs/mergers to ellipticals. However, combined with results at higher redshift, they suggest that quasars can be widely triggered in normal galaxies as long as they contain abundant gas and have ongoing star formation.

  9. A Closed Brayton Power Conversion Unit Concept for Nuclear Electric Propulsion for Deep Space Missions

    NASA Astrophysics Data System (ADS)

    Joyner, Claude Russell; Fowler, Bruce; Matthews, John

    2003-01-01

    In space, whether in a stable satellite orbit around a planetary body or traveling as a deep space exploration craft, power is just as important as the propulsion. The need for power is especially important for in-space vehicles that use Electric Propulsion. Using nuclear power with electric propulsion has the potential to provide increased payload fractions and reduced mission times to the outer planets. One of the critical engineering and design aspects of nuclear electric propulsion at required mission optimized power levels is the mechanism that is used to convert the thermal energy of the reactor to electrical power. The use of closed Brayton cycles has been studied over the past 30 or years and shown to be the optimum approach for power requirements that range from ten to hundreds of kilowatts of power. It also has been found to be scalable to higher power levels. The Closed Brayton Cycle (CBC) engine power conversion unit (PCU) is the most flexible for a wide range of power conversion needs and uses state-of-the-art, demonstrated engineering approaches. It also is in use with many commercial power plants today. The long life requirements and need for uninterrupted operation for nuclear electric propulsion demands high reliability from a CBC engine. A CBC engine design for use with a Nuclear Electric Propulsion (NEP) system has been defined based on Pratt & Whitney's data from designing long-life turbo-machines such as the Space Shuttle turbopumps and military gas turbines and the use of proven integrated control/health management systems (EHMS). An integrated CBC and EHMS design that is focused on using low-risk and proven technologies will over come many of the life-related design issues. This paper will discuss the use of a CBC engine as the power conversion unit coupled to a gas-cooled nuclear reactor and the design trends relative to its use for powering electric thrusters in the 25 kWe to 100kWe power level.

  10. TacSat-2: Path finder for a Close Space Support Asset

    NASA Astrophysics Data System (ADS)

    Bhopale, A.; Finley, C.

    2008-08-01

    With th e launch of TacSat-2, the Oper ationally Responsive Sp ace (O RS) commun ity had its f irst on- orbit asset and opportunity to prove or disprove the premise that small, in expensiv e, and quickly constructed spacecraf t could perform useful operation al missions when needed and for as long as need ed. All of the components of the comp lex TacSat-2 system had to work together to answer the basic questions, "In a crisis, can a lab-developed spacecraf t and ground architecture competen tly p erform th e mission of systems that cost twen ty times the price and tak e four times as long to develop? Mor eover, can th is system actu ally improve on the responsiveness of Nation al Systems to a certain set of underserv ed Oper ational customers?" When all w as said and done, TacSat-2 was a sp acecraf t that h ad to: 1) Carry th irteen tactical and scientific payloads to orbit, many of which doubled as essen tial, non-redundant subsystems; 2) Launch from an unproven launch base on a last minute "rep lacement" launch vehicle; and 3) Fulfill about 140 on-orbit mission requirements. It had tactical sensors, two unproven communication links, numerous next-gen eration single- string componen ts (e.g., h igh-efficiency propulsion system, thin-film so lar arrays, low-power versatile star camera) , and autonomous softw are to mak e the system more friendly and familiar to Tactical, rather than Spacecraf t Op erators. However, the mission was as mu ch about the implementation as it w as about the components. TacSat-2 was designed for and emp loyed with a different concept of operations ( CONOPS) than tradition al N ational Operational Assets. It w as designed to be th e fir st-ev er Clo se Space Support platform and operated in a manner more analogous to Close Air Support aircraf t than to tr aditional spacecraft. Therefore, th e primary objective of the TacSat-2 mission was to use th e TacSat-2 system to id entify those parts of the spacecr aft, ground system, and CON OPS

  11. Homojunction GaAs solar cells grown by close space vapor transport

    SciTech Connect

    Boucher, Jason W.; Ritenour, Andrew J.; Greenaway, Ann L.; Aloni, Shaul; Boettcher, Shannon W.

    2014-06-08

    We report on the first pn junction solar cells grown by homoepitaxy of GaAs using close space vapor transport (CSVT). Cells were grown both on commercial wafer substrates and on a CSVT absorber film, and had efficiencies reaching 8.1%, open circuit voltages reaching 909 mV, and internal quantum efficiency of 90%. The performance of these cells is partly limited by the electron diffusion lengths in the wafer substrates, as evidenced by the improved peak internal quantum efficiency in devices fabricated on a CSVT absorber film. Unoptimized highly-doped n-type emitters also limit the photocurrent, indicating that thinner emitters with reduced doping, and ultimately wider band gap window or surface passivation layers, are required to increase the efficiency.

  12. Performance and Mass Modeling Subtleties in Closed-Brayton-Cycle Space Power Systems

    NASA Technical Reports Server (NTRS)

    Barrett, Michael J.; Johnson, Paul K.

    2006-01-01

    A number of potential NASA missions could benefit from closed-Brayton-cycle (CBC) power conversion systems. The human and robotic mission power applications include spacecraft, surface base, and rover scenarios. Modeling of CBC subsystems allows system engineers, mission planners and project managers to make informed decisions regarding power conversion system characteristics and capabilities. To promote thorough modeling efforts, a critical review of CBC modeling techniques is presented. Analysis of critical modeling elements, component influences and cycle sensitivities is conducted. The analysis leads to quantitative results addressing projections on converter efficiency and overall power conversion system mass. Even moderate modeling errors are shown to easily over-predict converter efficiencies by 30% and underestimate mass estimates by 20%. Both static and dynamic modeling regimes are evaluated. Key considerations in determining model fidelity requirements are discussed. Conclusions and recommendations are presented that directly address ongoing modeling efforts in solar and nuclear space power systems.

  13. Performance and Mass Modeling Subtleties in Closed-Brayton-Cycle Space Power Systems

    NASA Technical Reports Server (NTRS)

    Barrett, Michael J.; Johnson, Paul K.

    2005-01-01

    A number of potential NASA missions could benefit from closed-Brayton-cycle (CBC) power conversion systems. The human and robotic mission power applications include spacecraft, surface base, and rover scenarios. Modeling of CBC subsystems allows system engineers, mission planners and project managers to make informed decisions regarding power conversion system characteristics and capabilities. To promote thorough modeling efforts, a critical review of CBC modeling techniques is presented. Analysis of critical modeling elements, component influences and cycle sensitivities is conducted. The analysis leads to quantitative results addressing projections on converter efficiency and overall power conversion system mass. Even moderate modeling errors are shown to easily over-predict converter efficiencies by 30 percent and underestimate mass estimates by 20 percent. Both static and dynamic modeling regimes are evaluated. Key considerations in determining model fidelity requirements are discussed. Conclusions and recommendations are presented that directly address ongoing modeling efforts in solar and nuclear space power systems.

  14. Growth of CdTe thin films on graphene by close-spaced sublimation method

    SciTech Connect

    Jung, Younghun; Yang, Gwangseok; Kim, Jihyun; Chun, Seungju; Kim, Donghwan

    2013-12-02

    CdTe thin films grown on bi-layer graphene were demonstrated by using the close-spaced sublimation method, where CdTe was selectively grown on the graphene. The density of the CdTe domains was increased with increasing the number of the defective sites in the graphene, which was controlled by the duration of UV exposure. The CdTe growth rate on the bi-layer graphene electrodes was 400 nm/min with a bandgap energy of 1.45–1.49 eV. Scanning electron microscopy, micro-Raman spectroscopy, micro-photoluminescence, and X-ray diffraction technique were used to confirm the high quality of the CdTe thin films grown on the graphene electrodes.

  15. Induced recrystallization of CdTe thin films deposited by close-spaced sublimation

    SciTech Connect

    Moutinho, H.R.; Dhere, R.G.; Al-Jassim, M.M.; Levi, D.H.; Kazmerski, L.L.; Mayo, B.

    1999-03-01

    We have deposited CdTe thin films by close-spaced sublimation at two different temperature ranges. The films deposited at the lower temperature partially recrystallized after CdCl{sub 2} treatment at 350&hthinsp;{degree}C and completely recrystallized after the same treatment at 400&hthinsp;{degree}C. The films deposited at higher temperature did not recrystallize at these two temperatures. These results confirmed that the mechanisms responsible for changes in physical properties of CdTe films treated with CdCl{sub 2} are recrystallization and grain growth, and provided an alternative method to deposit CSS films using lower temperatures. {copyright} {ital 1999 American Institute of Physics.}

  16. Adaptive Filtering for Large Space Structures: A Closed-Form Solution

    NASA Technical Reports Server (NTRS)

    Rauch, H. E.; Schaechter, D. B.

    1985-01-01

    In a previous paper Schaechter proposes using an extended Kalman filter to estimate adaptively the (slowly varying) frequencies and damping ratios of a large space structure. The time varying gains for estimating the frequencies and damping ratios can be determined in closed form so it is not necessary to integrate the matrix Riccati equations. After certain approximations, the time varying adaptive gain can be written as the product of a constant matrix times a matrix derived from the components of the estimated state vector. This is an important savings of computer resources and allows the adaptive filter to be implemented with approximately the same effort as the nonadaptive filter. The success of this new approach for adaptive filtering was demonstrated using synthetic data from a two mode system.

  17. Carbon-Carbon Recuperators in Closed-Brayton-Cycle Space Power Systems

    NASA Technical Reports Server (NTRS)

    Barrett, Michael J.; Johnson, Paul K.

    2006-01-01

    The use of carbon-carbon (C-C) recuperators in closed-Brayton-cycle space power conversion systems was assessed. Recuperator performance was forecast based on notional thermodynamic cycle state values for planetary missions. Resulting thermal performance, mass and volume for plate-fin C-C recuperators were estimated and quantitatively compared with values for conventional offset-strip-fin metallic designs. Mass savings of 40-55% were projected for C-C recuperators with effectiveness greater than 0.9 and thermal loads from 25-1400 kWt. The smaller thermal loads corresponded with lower mass savings; however, at least 50% savings were forecast for all loads above 300 kWt. System-related material challenges and compatibility issues were also discussed.

  18. Carbon-Carbon Recuperators in Closed-Brayton-Cycle Space Power Systems

    NASA Technical Reports Server (NTRS)

    Barrett, Michael J.; Johnson, Paul K.; Naples, Andrew G.

    2006-01-01

    The feasibility of using carbon-carbon (C-C) recuperators in conceptual closed-Brayton-cycle space power conversion systems was assessed. Recuperator performance expectations were forecast based on notional thermodynamic cycle state values for potential planetary missions. Resulting thermal performance, mass and volume for plate-fin C-C recuperators were estimated and quantitatively compared with values for conventional offset-strip-fin metallic designs. Mass savings of 30 to 60 percent were projected for C-C recuperators with effectiveness greater than 0.9 and thermal loads from 25 to 1400 kWt. The smaller thermal loads corresponded with lower mass savings; however, 60 percent savings were forecast for all loads above 300 kWt. System-related material challenges and compatibility issues were also discussed.

  19. Comparison of Procedures for Dual and Triple Closely Spaced Parallel Runways

    NASA Technical Reports Server (NTRS)

    Verma, Savita; Ballinger, Deborah; Subramanian Shobana; Kozon, Thomas

    2012-01-01

    A human-in-the-loop high fidelity flight simulation experiment was conducted, which investigated and compared breakout procedures for Very Closely Spaced Parallel Approaches (VCSPA) with two and three runways. To understand the feasibility, usability and human factors of two and three runway VCSPA, data were collected and analyzed on the dependent variables of breakout cross track error and pilot workload. Independent variables included number of runways, cause of breakout and location of breakout. Results indicated larger cross track error and higher workload using three runways as compared to 2-runway operations. Significant interaction effects involving breakout cause and breakout location were also observed. Across all conditions, cross track error values showed high levels of breakout trajectory accuracy and pilot workload remained manageable. Results suggest possible avenues of future adaptation for adopting these procedures (e.g., pilot training), while also showing potential promise of the concept.

  20. Principles for RNA metabolism and alternative transcription initiation within closely spaced promoters.

    PubMed

    Chen, Yun; Pai, Athma A; Herudek, Jan; Lubas, Michal; Meola, Nicola; Järvelin, Aino I; Andersson, Robin; Pelechano, Vicent; Steinmetz, Lars M; Jensen, Torben Heick; Sandelin, Albin

    2016-09-01

    Mammalian transcriptomes are complex and formed by extensive promoter activity. In addition, gene promoters are largely divergent and initiate transcription of reverse-oriented promoter upstream transcripts (PROMPTs). Although PROMPTs are commonly terminated early, influenced by polyadenylation sites, promoters often cluster so that the divergent activity of one might impact another. Here we found that the distance between promoters strongly correlates with the expression, stability and length of their associated PROMPTs. Adjacent promoters driving divergent mRNA transcription support PROMPT formation, but owing to polyadenylation site constraints, these transcripts tend to spread into the neighboring mRNA on the same strand. This mechanism to derive new alternative mRNA transcription start sites (TSSs) is also evident at closely spaced promoters supporting convergent mRNA transcription. We suggest that basic building blocks of divergently transcribed core promoter pairs, in combination with the wealth of TSSs in mammalian genomes, provide a framework with which evolution shapes transcriptomes. PMID:27455346

  1. The Pan-STARRS1 z>6 quasar survey: More than 100 quasars within the first Gyr of the universe

    NASA Astrophysics Data System (ADS)

    Walter, Fabian; Banados, Eduardo; Venemans, Bram; Decarli, Roberto; Farina, Emanuele; Mazzucchelli, Chiara; Fan, Xiaohui; Chambers, Kenneth C.

    2016-01-01

    Quasars are the most luminous non-transient sources in the Universe. As such, they are ideal probes of the redshift range z=6-7, a critical phase in cosmic history, when the Universe is emerging from the dark ages. Over the last three years we have exploited the Pan-STARRS1 survey, more than doubling the number of known z>5.5 quasars (tripling the number of z>6 quasars in the southern sky, and discovering 4 of the 9 quasars known at z>6.5). This seach significantly extended the sampled parameter space in terms of quasar luminosities and redshift coverage. Pioneering studies already demostrate the intrumental role of QSOs in probing the very early phases of galaxy formation and black hole growth within 1 Gyr from the Big Bang: a) billion solar masses black holes are already in place, b) they are surrounded by massive reservoirs of cold gas, and c) the neutral fraction of the intergalactic medium rapidly drops after z~6, thus marking the end of the epoch of reionization. Our significantly enlarged sample marks the transition phase from studies of individual sources to statistical studies of the high-z quasar population. We present some of the comprehensive multiwavelength characterization of the high-z quasar population and their environment (our on-going efforts include deep NIR spectroscopy, ALMA, NOEMA, HST, Spitzer, and JVLA observations).

  2. Tunneling spectroscopy of close-spaced dangling-bond pairs in Si(001):H

    PubMed Central

    Engelund, Mads; Zuzak, Rafał; Godlewski, Szymon; Kolmer, Marek; Frederiksen, Thomas; García-Lekue, Aran; Sánchez-Portal, Daniel; Szymonski, Marek

    2015-01-01

    We present a combined experimental and theoretical study of the electronic properties of close-spaced dangling-bond (DB) pairs in a hydrogen-passivated Si(001):H p-doped surface. Two types of DB pairs are considered, called “cross” and “line” structures. Our scanning tunneling spectroscopy (STS) data show that, although the spectra taken over different DBs in each pair exhibit a remarkable resemblance, they appear shifted by a constant energy that depends on the DB-pair type. This spontaneous asymmetry persists after repeated STS measurements. By comparison with density functional theory (DFT) calculations, we demonstrate that the magnitude of this shift and the relative position of the STS peaks can be explained by distinct charge states for each DB in the pair. We also explain how the charge state is modified by the presence of the scanning tunneling microscopy (STM) tip and the applied bias. Our results indicate that, using the STM tip, it is possible to control the charge state of individual DBs in complex structures, even if they are in close proximity. This observation might have important consequences for the design of electronic circuits and logic gates based on DBs in passivated silicon surfaces. PMID:26404520

  3. Multi-MW Closed Cycle MHD Nuclear Space Power Via Nonequilibrium He/Xe Working Plasma

    NASA Technical Reports Server (NTRS)

    Litchford, Ron J.; Harada, Nobuhiro

    2011-01-01

    Prospects for a low specific mass multi-megawatt nuclear space power plant were examined assuming closed cycle coupling of a high-temperature fission reactor with magnetohydrodynamic (MHD) energy conversion and utilization of a nonequilibrium helium/xenon frozen inert plasma (FIP). Critical evaluation of performance attributes and specific mass characteristics was based on a comprehensive systems analysis assuming a reactor operating temperature of 1800 K for a range of subsystem mass properties. Total plant efficiency was expected to be 55.2% including plasma pre-ionization power, and the effects of compressor stage number, regenerator efficiency and radiation cooler temperature on plant efficiency were assessed. Optimal specific mass characteristics were found to be dependent on overall power plant scale with 3 kg/kWe being potentially achievable at a net electrical power output of 1-MWe. This figure drops to less than 2 kg/kWe when power output exceeds 3 MWe. Key technical issues include identification of effective methods for non-equilibrium pre-ionization and achievement of frozen inert plasma conditions within the MHD generator channel. A three-phase research and development strategy is proposed encompassing Phase-I Proof of Principle Experiments, a Phase-II Subscale Power Generation Experiment, and a Phase-III Closed-Loop Prototypical Laboratory Demonstration Test.

  4. Einstein spectra of quasars

    NASA Technical Reports Server (NTRS)

    Wilkes, Belinda J.

    1988-01-01

    The results of the initial stage of the CfA survey of quasar energy distributions are reviewed. Einstein imaging proportional counter spectra of 33 quasars have been studied by fitting a single power law slope and absorption by an equivalent column density of neutral hydrogen. Comparison with the higher energy HEAO-A2 data leads to a two-component model for the X-ray spectrum. The X-ray column density is systematically lower than the 21-cm measured Galactic column density along the same line of sight.

  5. THE COLOR VARIABILITY OF QUASARS

    SciTech Connect

    Schmidt, Kasper B.; Rix, Hans-Walter; Knecht, Matthias; Hogg, David W.; Shields, Joseph C.; Maoz, Dan; Bovy, Jo

    2012-01-10

    We quantify quasar color variability using an unprecedented variability database-ugriz photometry of 9093 quasars from Sloan Digital Sky Survey (SDSS) Stripe 82, observed over 8 years at {approx}60 epochs each. We confirm previous reports that quasars become bluer when brightening. We find a redshift dependence of this blueing in a given set of bands (e.g., g and r), but show that it is the result of the flux contribution from less-variable or delayed emission lines in the different SDSS bands at different redshifts. After correcting for this effect, quasar color variability is remarkably uniform, and independent not only of redshift, but also of quasar luminosity and black hole mass. The color variations of individual quasars, as they vary in brightness on year timescales, are much more pronounced than the ranges in color seen in samples of quasars across many orders of magnitude in luminosity. This indicates distinct physical mechanisms behind quasar variability and the observed range of quasar luminosities at a given black hole mass-quasar variations cannot be explained by changes in the mean accretion rate. We do find some dependence of the color variability on the characteristics of the flux variations themselves, with fast, low-amplitude, brightness variations producing more color variability. The observed behavior could arise if quasar variability results from flares or ephemeral hot spots in an accretion disk.

  6. Hubble Space Telescope View of Comet C/Siding Spring during its Close Encounter with Mars

    NASA Astrophysics Data System (ADS)

    Li, J. Y.; Samarasinha, N. H.; Kelley, M. S. P.; Farnham, T. L.; Bodewits, D.; A'Hearn, M. F.; Lisse, C. M.; Delamere, W. A.; Mutchler, M. J.

    2014-12-01

    Comet C/2013 A1 (Siding Spring) is a dynamically new comet whose physical and chemical status should be the least evolved since the formation of cometesimals during the planetary system formation processes. Its close encounter with Mars on October 19, 2014 at a distance of 131,000 km allows for imaging its nucleus and inner coma by MRO/HiRISE at 140 m/pix resolution. Such an encounter offers us the opportunity to do cometary flyby science for a dynamically new comet for the first time ever. Those observations have the potential to advance our understanding of comets in ways similar to previous flyby missions to periodic comets. An extensive observing campaign from many ground- and space-based platforms is supporting the "flyby" observations from Mars spacecraft. We will monitor the comet with Hubble Space Telescope for >24 hrs total observing time around the encounter, to obtain images of the inner coma at ~46 km/pix at the comet. These observations will allow us to perform detailed studies of the morphology of the dust and gas coma of C/Siding Spring, and to connect the observations performed from various platforms at various spatial resolutions and over a long time baseline. The ultimate goal is to correlate large-scale coma behaviors to the nucleus as resolved by MRO/HiRISE. We will report the HST observations and the preliminary results.

  7. Theoretical analysis of surface-plasmon-polariton resonators in free space and close to an interface

    NASA Astrophysics Data System (ADS)

    Jung, Jesper; Søndergaard, Thomas

    2008-04-01

    Surface-plasmon-polariton (SPP) resonators consisting of metal strips in free space, and gap plasmon polariton resonators consisting of a metal strip close to either a block of metal or a metal surface, are studied as optical resonators. The analysis is performed using the Green's function surface integral equation method. For strips in free space, we show how the scattering resonances can be understood, by thinking of the strips as optical resonators for short-range SPPs. The two gap resonator configurations, strip-block and strip-surface, have different structure terminations as the width of the strip and the block are identical whereas the surface is infinite. In the strip-surface configuration, the scattering resonances are broader and red-shifted, compared to the strip-block configuration. This is explained as a consequence of the effective length of the resonator being larger in the strip-surface configuration. By varying the gap size, we study the transition from a SPP resonator to a gap plasmon polariton resonator. In the strip-surface configuration, light can be scattered into both out-of-plane propagating waves and into SPPs that propagate along the surface. For small gaps of a few tens of nanometers, a large enhancement in the scattering cross section is seen due to strong scattering into SPPs.

  8. Phase space matching and finite lifetime effects for top-pair production close to threshold

    SciTech Connect

    Hoang, Andre H.; Reisser, Christoph J.; Ruiz-Femenia, Pedro

    2010-07-01

    The top-pair tt production cross section close to threshold in e{sup +}e{sup -} collisions is strongly affected by the small lifetime of the top quark. Since the cross section is defined through final states containing the top decay products, a consistent definition of the cross section depends on prescriptions of how these final states are accounted for the cross section. Experimentally, these prescriptions are implemented, for example, through cuts on kinematic quantities such as the reconstructed top quark invariant masses. As long as these cuts do not reject final states that can arise from the decay of a top and an antitop quark with a small off-shellness compatible with the nonrelativistic power counting, they can be implemented through imaginary phase space matching conditions in nonrelativistic QCD. The prescription-dependent cross section can then be determined from the optical theorem using the e{sup +}e{sup -} forward scattering amplitude. We compute the phase space matching conditions associated to cuts on the top and antitop invariant masses at next-to-next-to-leading logarithmic order and partially at next-to-next-to-next-to-leading logarithmic order in the nonrelativistic expansion accounting also for higher order QCD effects. Together with finite lifetime and electroweak effects known from previous work, we analyze their numerical impact on the tt cross section. We show that the phase space matching contributions are essential to make reliable nonrelativistic QCD predictions, particularly for energies below the peak region, where the cross section is small. We find that irreducible background contributions associated to final states that do not come from top decays are strongly suppressed and can be neglected for the theoretical predictions.

  9. THE ULTRAVIOLET-TO-MID-INFRARED SPECTRAL ENERGY DISTRIBUTION OF WEAK EMISSION LINE QUASARS

    SciTech Connect

    Lane, Ryan A.; Shemmer, Ohad; Diamond-Stanic, Aleksandar M.; Fan Xiaohui; Anderson, Scott F.; Brandt, W. N.; Schneider, Donald P.; Plotkin, Richard M.; Richards, Gordon T.; Strauss, Michael A. E-mail: ohad@unt.edu

    2011-12-20

    We present Spitzer Space Telescope photometry of 18 Sloan Digital Sky Survey (SDSS) quasars at 2.7 {<=} z {<=} 5.9 which have weak or undetectable high-ionization emission lines in their rest-frame ultraviolet (UV) spectra (hereafter weak-lined quasars, or WLQs). The Spitzer data are combined with SDSS spectra and ground-based, near-infrared (IR) photometry of these sources to produce a large inventory of spectral energy distributions (SEDs) of WLQs across the rest-frame {approx}0.1-5 {mu}m spectral band. The SEDs of our sources are inconsistent with those of BL Lacertae objects which are dominated by synchrotron emission due to a jet aligned close to our line of sight, but are consistent with the SED of ordinary quasars with similar luminosities and redshifts that exhibit a near-to-mid-IR 'bump', characteristic of hot dust emission. This indicates that broad emission lines in WLQs are intrinsically weak, rather than suffering continuum dilution from a jet, and that such sources cannot be selected efficiently from traditional photometric surveys.

  10. An Automated Search for Gravitationally Lensed Quasars in the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Sivakumar, Pranav; Sivakumar, Janani N.; Nebres, Paul J.

    2016-01-01

    Quasar lensing is a powerful tool in deciphering the characteristics of dark matter and dark energy. Given the availability of "big data" on quasars, including the SDSS DR12 and the recently released DES data set, a robust automated algorithm for the detection of lensed quasars is rapidly becoming a necessity. We report results from an automated search for lensed quasars consisting of two complementary algorithms: a morphological algorithm directed at finding wide-separation lens candidates and a PSF-difference-based algorithm aimed at identifying close-separation lens candidates. This research started with a baseline data set of over 450,000 quasars and 996,317 spatial neighbors within 16 arcseconds of each quasar in the SDSS DR12. This threshold can identify quasars lensed by galaxy-scale to cluster-scale matter concentrations. The first part of the automated method matched redshift and color characteristics of images and compared key emission lines in the spectrum of the quasars and their neighbors. The second portion applied image segmentation techniques to deblend close-separation candidates identified as one photometric object by SDSS. Cross-matching with observations of the same targets across other bands of the electromagnetic spectrum and elimination of confirmed binary quasars increased the confidence level of the resulting candidate list. The automated search efficiently produced output consistent with results reported in the literature. In addition, the algorithms identified many new lens candidates not yet reported in the literature which warrant detailed follow-up observations.

  11. Metallicity and Quasar Outflows

    NASA Astrophysics Data System (ADS)

    Wang, Huiyuan; Zhou, Hongyan; Yuan, Weimin; Wang, Tinggui

    2012-06-01

    Correlations of the outflow strength of quasars, as measured by the blueshift and asymmetry index (BAI) of the C IV line, with intensities and ratios of broad emission lines, based on composite quasar spectra built from the Sloan Digital Sky Survey, are investigated. We find that most of the line ratios of other ions to C IV increase prominently with BAI. These behaviors can be well understood in the context of increasing metallicity with BAI. The strength of the dominant coolant, C IV line, decreases, and weak collisionally excited lines increase with gas metallicity as a result of the competition between different line coolants. Using Si IV+O IV]/C IV as an indicator of gas metallicity, we present, for the first time, a strong correlation between the metallicity and the outflow strength of quasars over a wide range of 1.7-6.9 times solar abundance. Our result implies that metallicity plays an important role in the formation of quasar outflows, likely by affecting outflow acceleration. This effect may have a profound impact on galaxy evolution via momentum feedback and chemical enrichment.

  12. METALLICITY AND QUASAR OUTFLOWS

    SciTech Connect

    Wang, Huiyuan; Zhou, Hongyan; Wang, Tinggui; Yuan, Weimin

    2012-06-01

    Correlations of the outflow strength of quasars, as measured by the blueshift and asymmetry index (BAI) of the C IV line, with intensities and ratios of broad emission lines, based on composite quasar spectra built from the Sloan Digital Sky Survey, are investigated. We find that most of the line ratios of other ions to C IV increase prominently with BAI. These behaviors can be well understood in the context of increasing metallicity with BAI. The strength of the dominant coolant, C IV line, decreases, and weak collisionally excited lines increase with gas metallicity as a result of the competition between different line coolants. Using Si IV+O IV]/C IV as an indicator of gas metallicity, we present, for the first time, a strong correlation between the metallicity and the outflow strength of quasars over a wide range of 1.7-6.9 times solar abundance. Our result implies that metallicity plays an important role in the formation of quasar outflows, likely by affecting outflow acceleration. This effect may have a profound impact on galaxy evolution via momentum feedback and chemical enrichment.

  13. Quasar feedback revealed by giant molecular outflows

    NASA Astrophysics Data System (ADS)

    Feruglio, C.; Maiolino, R.; Piconcelli, E.; Menci, N.; Aussel, H.; Lamastra, A.; Fiore, F.

    2010-07-01

    In the standard scenario for galaxy evolution young star-forming galaxies transform into red bulge-dominated spheroids, where star formation has been quenched. To explain this transformation, a strong negative feedback generated by accretion onto a central super-massive black hole is often invoked. The depletion of gas resulting from quasar-driven outflows should eventually stop star-formation across the host galaxy and lead the black hole to “suicide” by starvation. Direct observational evidence for a major quasar feedback onto the host galaxy is still missing, because outflows previously observed in quasars are generally associated with the ionized component of the gas, which only accounts for a minor fraction of the total gas content, and typically occurrs in the central regions. We used the IRAM PdB Interferometer to observe the CO(1-0) transition in Mrk 231, the closest quasar known. Thanks to the wide band we detected broad wings of the CO line, with velocities of up to 750 km s-1 and spatially resolved on the kpc scale. These broad CO wings trace a giant molecular outflow of about 700 M_⊙/year, far larger than the ongoing star-formation rate (~200 M_⊙/year) observed in the host galaxy. This wind will totally expel the cold gas reservoir in Mrk 231 in about 107 yrs, therefore halting the star-formation activity on the same timescale. The inferred kinetic energy in the molecular outflow is ~1.2 × 1044 erg/s, corresponding to a few percent of the AGN bolometric luminosity, which is very close to the fraction expected by models ascribing quasar feedback to highly supersonic shocks generated by radiatively accelerated nuclear winds. Instead, the contribution by the SNe associated with the starburst fall short by several orders of magnitude to account for the kinetic energy observed in the outflow. The direct observational evidence for quasar feedback reported here provides solid support to the scenarios ascribing the observed properties of local massive

  14. Kinematic Modeling of Separation Compression for Paired Approaches to Closely-Spaced Parallel Runways

    NASA Technical Reports Server (NTRS)

    Madden, Michael M.

    2014-01-01

    In a simultaneous paired approach to closely-spaced parallel runways, a pair of aircraft flies in close proximity on parallel approach paths. The longitudinal separation between the aircraft must be maintained within a range that avoids wake encounters and, if one of the aircraft blunders, avoids collision. To increase operational availability, the approach procedure must accommodate a mixture of aircraft sizes and, consequently, approach speeds. In these procedures, the slower aircraft is placed in the lead position. The faster aircraft maintains separation from the slow aircraft in a dependent operation until final approach and flies independently afterward. Due to the higher approach speed of the fast aircraft, longitudinal separation will decrease during final approach. Therefore, the fast aircraft must position itself before the final approach so that it will remain within the safe range of separation as separation decreases. Given the approach geometry and speed schedule for each aircraft, one can use kinematics to estimate the separation loss between a pair of aircraft. A kinematic model can complement fast-time Monte-Carlo simulations of the approach by enabling a tailored reduction in the variation of starting position for the fast aircraft. One could also implement the kinematic model in ground-based or on-board decision support tools to compute the optimal initial separation for a given pair of aircraft. To better match the auto-coupled flight of real aircraft, the paper derives a kinematic model where the speed schedule is flown using equivalent airspeed. The predicted time of flight using the equivalent airspeed kinematic model compares well against a high-fidelity aircraft simulation performing the same approach. This model also demonstrates a modest increase in the predicted loss of separation when contrasted against a kinematic model that assumes the scheduled speed is true airspeed.

  15. The luminosity function of quasars

    NASA Technical Reports Server (NTRS)

    Pei, Yichuan C.

    1995-01-01

    We propose a new evolutionary model for the optical luminosity function of quasars. Our analytical model is derived from fits to the empirical luminosity function estimated by Hartwick and Schade and Warren, Hewett, and Osmer on the basis of more than 1200 quasars over the range of redshifts 0 approximately less than z approximately less than 4.5. We find that the evolution of quasars over this entire redshift range can be well fitted by a Gaussian distribution, while the shape of the luminosity function can be well fitted by either a double power law or an exponential L(exp 1/4) law. The predicted number counts of quasars, as a function of either apparent magnitude or redshift, are fully consistent with the observed ones. Our model indicates that the evolution of quasars reaches its maximum at z approximately = 2.8 and declines at higher redshifts. An extrapolation of the evolution to z approximately greater than 4.5 implies that quasars may have started their cosmic fireworks at z(sub f) approximately = 5.2-5.5. Forthcoming surveys of quasars at these redshifts will be critical to constrain the epoch of quasar formation. All the results we derived are based on observed quasars and are therefore subject to the bias of obscuration by dust in damped Ly alpha systems. Future surveys of these absorption systems at z approximately greater than 3 will also be important if the formation epoch of quasars is to be known unambiguously.

  16. Importance of closely spaced vertical sampling in delineating chemical and microbiological gradients in groundwater studies

    USGS Publications Warehouse

    Smith, R.L.; Harvey, R.W.; LeBlanc, D.R.

    1991-01-01

    Vertical gradients of selected chemical constituents, bacterial populations, bacterial activity and electron acceptors were investigated for an unconfined aquifer contaminated with nitrate and organic compounds on Cape Cod, Massachusetts, U.S.A. Fifteen-port multilevel sampling devices (MLS's) were installed within the contaminant plume at the source of the contamination, and at 250 and 2100 m downgradient from the source. Depth profiles of specific conductance and dissolved oxygen at the downgradient sites exhibited vertical gradients that were both steep and inversely related. Narrow zones (2-4 m thick) of high N2O and NH4+ concentrations were also detected within the contaminant plume. A 27-fold change in bacterial abundance; a 35-fold change in frequency of dividing cells (FDC), an indicator of bacterial growth; a 23-fold change in 3H-glucose uptake, a measure of heterotrophic activity; and substantial changes in overall cell morphology were evident within a 9-m vertical interval at 250 m downgradient. The existence of these gradients argues for the need for closely spaced vertical sampling in groundwater studies because small differences in the vertical placement of a well screen can lead to incorrect conclusions about the chemical and microbiological processes within an aquifer.Vertical gradients of selected chemical constituents, bacterial populations, bacterial activity and electron acceptors were investigated for an unconfined aquifer contaminated with nitrate and organic compounds on Cape Cod, Massachusetts, USA. Fifteen-port multilevel sampling devices (MLS's) were installed within the contaminant plume at the source of the contamination, and at 250 and 2100 m downgradient from the source. Depth profiles of specific conductance and dissolved oxygen at the downgradient sites exhibited vertical gradients that were both steep and inversely related. Narrow zones (2-4 m thick) of high N2O and NH4+ concentrations were also detected within the contaminant plume

  17. Broad-line region physical conditions along the quasar eigenvector 1 sequence

    NASA Astrophysics Data System (ADS)

    Marziani, P.; Sulentic, J. W.; Negrete, C. A.; Dultzin, D.; Zamfir, S.; Bachev, R.

    2010-12-01

    We compare broad emission-line profiles and estimate line ratios for all major emission lines between Lyα and Hβ in a sample of six quasars. The sources were chosen with two criteria in mind: the existence of high-quality optical and ultraviolet spectra and the possibility of sampling the spectroscopic diversity in the 4D eigenvector 1 (4DE1) context. In the latter sense, each source occupies a region (bin) in the full width at half-maximum (FWHM)(Hβ) versus Fe IIopt strength plane that is significantly different from the others. High signal-to-noise ratio Hβ emission-line profiles are used as templates for modelling the other lines (Lyα, C IV λ1549, He II λ1640, Al III λ1860, Si III] λ1892 and Mg II λ2800). We can adequately model all broad lines assuming the existence of three components distinguished by blueshifted, unshifted and redshifted centroids [indicated as a blue component (BLUE), broad component (BC) and very broad component (VBC), respectively]. BC (electron density ne˜ 1012 cm-3, ionization parameter U˜ 10-2 and column density Nc≳ 1023 cm-2) is present in almost all type-1 quasars and therefore corresponds most closely to the classical broad-line emitting region (the reverberating component). The bulk of Mg II λ2800 and Fe II emission also arises in this region. The BLUE emission (log ne˜ 10, log U˜-1 and log Nc < 23) arises in less optically thick gas; it is often thought to arise in an accretion disc wind. The least understood component involves the VBC (high ionization and large column density), which is found in no more than half (but almost all radio-loud) type-1 quasars and luminous Seyfert nuclei. It is perhaps the most distinguishing characteristic of quasars with FWHM (Hβ) ≳ 4000 km s-1 that belong to the so-called population B of our 4DE1 space. Population A quasars [FWHM (Hβ) ≲ 4000 km s-1] are dominated by BC emission in Hβ and BLUE component emission in C IV λ1549 and other high ionization lines. 4DE1 appears to

  18. Heat transport through plasmonic interactions in closely spaced metallic nanoparticle chains

    NASA Astrophysics Data System (ADS)

    Ben-Abdallah, Philippe; Joulain, Karl; Drevillon, Jérémie; Le Goff, Clément

    2008-02-01

    We report a numerical investigation on the heat transfer through one-dimensional arrays of metallic nanoparticles closely spaced in a host material. Our simulations show that the multipolar interactions play a crucial role in the heat transport via collective plasmons. Calculations of the plasmonic thermal conductance and of the thermal conductivity in ballistic and diffusive regimes, respectively, have been carried out. (a) Using the Landauer-Buttiker formalism, we have found that, when the host material dielectric constant takes positive values, the multipolar interactions drastically enhance by several orders of magnitude the ballistic thermal conductance of collective plasmons compared with that of a classical dipolar chain. On the contrary, when the host material dielectric constant takes negative values, we have demonstrated the existence of nonballistic multipolar modes which annihilate the heat transfer through the chains. (b) Using the kinetic theory, we have also examined the thermal behavior of chains in the diffusion approximation. We have shown that the plasmonic thermal conductivity of metallic nanoparticle chains can reach 1% of the bulk metal thermal conductivity. This result could explain the anomalously high thermal conductivity observed in many colloidal suspensions, the so-called nanofluids.

  19. A Preliminary and Simplified Closed Brayton Cycle Modeling for a Space Reactor Application

    SciTech Connect

    Guimaraes, Lamartine Nogueira Frutuoso; Camillo, Giannino Ponchio

    2008-01-21

    The Nuclear Energy Division (ENU) of the Institute for Advanced Studies (IEAv) has started a preliminary design study for a Closed Brayton Cycle Loop (CBCL) aimed at a space reactor application. The main objectives of the study are: 1) to establish a starting concept for the CBCL components specifications, and 2) to build a demonstrative simulator of CBCL. This preliminary design study is developing the CBCL around the NOELLE 60290 turbo machine. The actual nuclear reactor study is being conducted independently. Because of that, a conventional heat source is being used for the CBCL, in this preliminary design phase. This paper describes the steady state simulator of the CBCL operating with NOELLE 60290 turbo machine. In principle, several gases are being considered as working fluid, as for instance: air, helium, nitrogen, CO{sub 2} and gas mixtures such as helium and xenon. However, for this first application pure helium will be used as working fluid. Simplified models of heat and mass transfer were developed to simulate thermal components. Future efforts will focus on implementing a graphical interface to display the thermal process variables in steady state and to keep track of the modifications being implemented at the NOELLE 60290 turbo machine in order to build the CBCL.

  20. Parallel Operation of Multiple Closely Spaced Small Aspect Ratio Rod Pinches

    DOE PAGESBeta

    Harper-Slaboszewicz, Victor J.; Leckbee, Joshua; Bennett, Nichelle; Madrid, Elizabeth A.; Rose, David V.; Thoma, Carsten; Welch, Dale R.; Lake, Patrick W.; McCourt, Andrew L.

    2014-12-10

    A series of simulations and experiments to resolve questions about the operation of arrays of closely spaced small aspect ratio rod pinches has been performed. Design and post-shot analysis of the experimental results are supported by 3D particle-in-cell simulations. Both simulations and experiments support these conclusions. Penetration of current to the interior of the array appears to be efficient, as the current on the center rods is essentially equal to the current on the outer rods. Current loss in the feed due to the formation of magnetic nulls was avoided in these experiments by design of the feed surface ofmore » the cathode and control of the gap to keep the electric fields on the cathode below the emission threshold. Some asymmetry in the electron flow to the rod was observed, but the flow appeared to symmetrize as it reached the end of the rod. Interaction between the rod pinches can be controlled to allow the stable and consistent operation of arrays of rod pinches.« less

  1. Parallel Operation of Multiple Closely Spaced Small Aspect Ratio Rod Pinches

    SciTech Connect

    Harper-Slaboszewicz, Victor J.; Leckbee, Joshua; Bennett, Nichelle; Madrid, Elizabeth A.; Rose, David V.; Thoma, Carsten; Welch, Dale R.; Lake, Patrick W.; McCourt, Andrew L.

    2014-12-10

    A series of simulations and experiments to resolve questions about the operation of arrays of closely spaced small aspect ratio rod pinches has been performed. Design and post-shot analysis of the experimental results are supported by 3D particle-in-cell simulations. Both simulations and experiments support these conclusions. Penetration of current to the interior of the array appears to be efficient, as the current on the center rods is essentially equal to the current on the outer rods. Current loss in the feed due to the formation of magnetic nulls was avoided in these experiments by design of the feed surface of the cathode and control of the gap to keep the electric fields on the cathode below the emission threshold. Some asymmetry in the electron flow to the rod was observed, but the flow appeared to symmetrize as it reached the end of the rod. Interaction between the rod pinches can be controlled to allow the stable and consistent operation of arrays of rod pinches.

  2. Design of a Simplified Closed Brayton Cycle for a Space Reactor Application

    SciTech Connect

    Guimaraes, Lamartine N. F.; Camillo, Giannino Ponchio; Placco, Guilherme Moreira

    2009-03-16

    The Nuclear Energy Division (ENU) of the Institute for Advanced Studies (IEAv) has started a preliminary design study for a Closed Brayton Cycle Loop (CBCL) aimed at a space reactor application. The main objectives of the study are: 1) to establish a starting concept for the CBCL components specifications, and 2) to build a demonstrative simulator of CBCL. This preliminary design study is been developed around the NOELLE 60290 turbo machine. The actual nuclear reactor study is being conducted independently. Because of that, a conventional heat source is being used for the CBCL, in this preliminary design phase. This paper describes details of the CBCL mechanical design and the steady state simulator of the CBCL operating with NOELLE 60290 turbo machine. In principle, several gases are being considered as working fluid, as for instance: air, helium, nitrogen, CO2 and gas mixtures such as helium and xenon. However, for this first application pure helium will be used as working fluid. Simplified models of heat and mass transfer were developed to simulate thermal components. A new graphical interface was developed for the simulator to display the thermal process variables in steady state and to keep track of the modifications being implemented at the NOELLE 60290 turbo machine in order to build the CBCL. A set of new results are being produced. These new results help to establish the hot and cold source geometry allowing for price estimating costs for building the actual device. These fresh new results will be presented and discussed.

  3. Native Defect Control of CdTe Thin Film Solar Cells by Close-Spaced Sublimation

    NASA Astrophysics Data System (ADS)

    Okamoto, Tamotsu; Kitamoto, Shinji; Yamada, Akira; Konagai, Makoto

    2001-05-01

    The control of native defects in the CdTe thin film solar cells was investigated using a novel source for close-spaced sublimation (CSS) process which was prepared by vacuum evaporation with elemental Cd and Te (evaporated source). The evaporated sources were prepared on glass substrates at room temperature, and the Cd/Te ratio was controlled by varying the Cd and Te beam equivalent pressures. In the cells using the Te-rich source, the conversion efficiency was less than 0.2% because of the extremely low shunt resistance. On the other hand, a conversion efficiency above 15% was obtained by using the Cd-rich source. Capacitance-voltage (C-V) characteristics revealed that the acceptor concentration in the CdTe layer increased with increasing Cd/Te ratio of the evaporated source. Furthermore, photoluminescence spectra implied that the formation of the Cd vacancies in the CdTe layer was suppressed using the Cd-rich source.

  4. Simulated Wake Characteristics Data for Closely Spaced Parallel Runway Operations Analysis

    NASA Technical Reports Server (NTRS)

    Guerreiro, Nelson M.; Neitzke, Kurt W.

    2012-01-01

    A simulation experiment was performed to generate and compile wake characteristics data relevant to the evaluation and feasibility analysis of closely spaced parallel runway (CSPR) operational concepts. While the experiment in this work is not tailored to any particular operational concept, the generated data applies to the broader class of CSPR concepts, where a trailing aircraft on a CSPR approach is required to stay ahead of the wake vortices generated by a lead aircraft on an adjacent CSPR. Data for wake age, circulation strength, and wake altitude change, at various lateral offset distances from the wake-generating lead aircraft approach path were compiled for a set of nine aircraft spanning the full range of FAA and ICAO wake classifications. A total of 54 scenarios were simulated to generate data related to key parameters that determine wake behavior. Of particular interest are wake age characteristics that can be used to evaluate both time- and distance- based in-trail separation concepts for all aircraft wake-class combinations. A simple first-order difference model was developed to enable the computation of wake parameter estimates for aircraft models having weight, wingspan and speed characteristics similar to those of the nine aircraft modeled in this work.

  5. Quasars in the COSMOS Field

    NASA Astrophysics Data System (ADS)

    Prescott, M. K. M.; Impey, C. D.; Cool, R. J.; Scoville, N. Z.

    2006-06-01

    We obtained medium-resolution spectra of 336 quasar candidates in the COSMOS HST Treasury field using the MMT 6.5 m telescope and the Hectospec multiobject spectrograph. Candidates were drawn from the Sloan Digital Sky Survey (SDSS) DR1 catalog using quasar flags set by the SDSS multicolor quasar target selection algorithm. In this paper we present our discovery spectra from 1.39 deg2 (69.5% of the COSMOS field) and a discussion of the selection method and yields. We confirmed 95 quasars, including at least two BAL quasars; 80 of these are new quasars that do not appear in previous quasar confirmation follow-up studies. The candidates additionally included 184 compact emission-line galaxies, a third of which are likely type 2 AGNs, and 12 stars. The quasars span a range in magnitude of 18.3quasar surface density from SDSS color selection of 102 deg-2 down to g=22.5 over the entire COSMOS field. This work is the first step toward the eventual goal of setting up a grid of quasar absorption line probes of the 2 deg2 field and of conducting a complete census of supermassive black holes in this well-studied survey region. The total quasar count at the conclusion of this study is 139, making COSMOS one of the most densely sampled regions of sky where a grid of quasar sight lines can be used to probe the intervening volume.

  6. Fifty Years of Quasars: Physical Insights and Potential for Cosmology

    NASA Astrophysics Data System (ADS)

    Sulentic, J. W.; Marziani, P.; Dultzin, D.; D'Onofrio, M.; del Olmo, A.

    2014-12-01

    Last year (2013) was more or less the 50th anniversary of the discovery of quasars. It is an interesting time to review what we know (and don't know) about them both empirically and theoretically. These compact sources involving line emitting plasma show extraordinary luminosities extending to one thousand times that of our Milky Way in emitting volumes of a few solar system diameters (log Lboi= 44.0 - 48.0 erg s-1: D=1-3 light months ~ 103 - 104 gravitational radii). The advent of 8-10 meter class telescopes enables us to study them spectroscopically in ever greater detail. In 2000 we introduced a 4D Eigenvector 1 parameters space involving optical, UV and X- ray measures designed to serve as a 4D equivalent of the 2D H-R diagram so important for depicting the diversity of stellar types and evolutionary states. This diagram has revealed a principal sequence of quasars distinguished by Eddington ratio (proportional to the accretion rate per unit mass). Thus while stellar differences are primarily driven by the mass of a star, quasar differences are apparently driven by the ratio of luminosity-to-mass. Out of this work has emerged the concept of two quasars populations A and B separated at Eddington ratio around 0.2 which maximizes quasar multispectral differences. The mysterious 8% of quasars that are radio-loud belong to population B which are the lowest accretors with the largest black hole masses. Finally we consider the most extreme population A quasars which are the highest accretors and in some cases are among the youngest quasars. We describe how these sources might be exploited as standard candles for cosmology.

  7. Orbital stability of systems of closely-spaced planets, II: configurations with coorbital planets

    NASA Astrophysics Data System (ADS)

    Smith, Andrew W.; Lissauer, Jack J.

    2010-08-01

    We numerically investigate the stability of systems of 1 {M_{oplus}} planets orbiting a solar-mass star. The systems studied have either 2 or 42 planets per occupied semimajor axis, for a total of 6, 10, 126, or 210 planets, and the planets were started on coplanar, circular orbits with the semimajor axes of the innermost planets at 1 AU. For systems with two planets per occupied orbit, the longitudinal initial locations of planets on a given orbit were separated by either 60° (Trojan planets) or 180°. With 42 planets per semimajor axis, initial longitudes were uniformly spaced. The ratio of the semimajor axes of consecutive coorbital groups in each system was approximately uniform. The instability time for a system was taken to be the first time at which the orbits of two planets with different initial orbital distances crossed. Simulations spanned virtual times of up to 1 × 108, 5 × 105, and 2 × 105 years for the 6- and 10-planet, 126-planet, and 210-planet systems, respectively. Our results show that, for a given class of system (e.g., five pairs of Trojan planets orbiting in the same direction), the relationship between orbit crossing times and planetary spacing is well fit by the functional form log( t c / t 0) = b β + c, where t c is the crossing time, t 0 = 1 year, β is the separation in initial orbital semimajor axis (in terms of the mutual Hill radii of the planets), and b and c are fitting constants. The same functional form was observed in the previous studies of single planets on nested orbits (Smith and Lissauer 2009). Pairs of Trojan planets are more stable than pairs initially separated by 180°. Systems with retrograde planets (i.e., some planets orbiting in the opposite sense from others) can be packed substantially more closely than can systems with all planets orbiting in the same sense. To have the same characteristic lifetime, systems with 2 or 42 planets per orbit typically need to have about 1.5 or 2 times the orbital separation as

  8. Physiological Disorders in Closed Environment-Grown Crops for Space Life Support

    NASA Astrophysics Data System (ADS)

    Wheeler, Raymond; Morrow, Robert

    Crop production for life support systems in space will require controlled environments where temperature, humidity, CO2, and light might differ from natural environments where plants evolved. Physiological disorders, i.e., abnormal plant growth and development, can occur under these controlled environments. Among the most common of these disorders are Ca deficiency injuries such as leaf tipburn (e.g., lettuce), blossom-end-rot in fruits (e.g., tomato and pepper), and internal tissue necrosis in fruits or tubers (e.g., cucumber and potato). Increased Ca nutrition to the plants typically has little effect on these disorders, but slowing overall growth or providing better air circulation to increase transpiration can be effective. A second common disorder is oedema or intumescence, which appears as callus-like growth or galls on leaves (e.g., sweetpotato, potato, pepper, and tomato). This disorder can be reduced by increasing the near UV radiation ( 300-400 nm) to the plants. Leaf injury and necrosis can occur under long photoperiods (e.g., tomato, potato, and pepper) and at super-elevated (i.e., ¿ than 4000 mol mol-1) CO2 concentrations (e.g., soybean, potato, and radish), and these can be managed by reducing the photoperiod and CO2 concentration, respectively. Lack of blue light in the spectrum (e.g., under red LEDs or LPS lamps) can result in leggy growth and/or leaves lacking in chlorophyll (e.g., wheat, bean, and radish). Volatile organic compounds (VOCs), most commonly ethylene, can accumulate in tightly closed systems and result in a variety of negative responses. Most of these disorders can be mitigated by altering the environmental set-points or by using more resistant cultivars.

  9. Pilot Non-Conformance to Alerting System Commands During Closely Spaced Parallel Approaches

    NASA Technical Reports Server (NTRS)

    Pritchett, Amy Ruth; Hansman, R. John; Corker, Kevin (Technical Monitor)

    1997-01-01

    Cockpit alerting systems monitor potentially hazardous situations, both inside and outside the aircraft. When a hazard is projected to occur, the alerting system displays alerts and/or command decisions to the pilot. However, pilots have been observed to not conform to alerting system commands by delaying their response or by not following the automatic commands exactly. This non-conformance to the automatic alerting system can reduce its benefit. Therefore, a need exists to understand the causes and effects of pilot non-conformance in order to develop automatic alerting systems whose commands the pilots are more likely to follow. These considerations were examined through flight simulator evaluations of the collision avoidance task during closely spaced parallel approaches. This task provided a useful case-study because the effects of non-conformance can be significant, given the time-critical nature of the task. A preliminary evaluation of alerting systems identified non-conformance in over 40% of the cases and a corresponding drop in collision avoidance performance. A follow-on experiment found subjects' alerting and maneuver selection criteria were consistent with different strategies than those used by automatic systems, indicating the pilot may potentially disagree with the alerting system if the pilot attempts to verify automatic alerts and commanded avoidance maneuvers. A final experiment found supporting automatic alerts with the explicit display of its underlying criteria resulted in more consistent subject reactions. In light of these experimental results, a general discussion of pilot non-conformance is provided. Contributing factors in pilot non-conformance include a lack of confidence in the automatic system and mismatches between the alerting system's commands and the pilots' own decisions based on the information available to them. The effects of non-conformance on system performance are discussed. Possible methods of reconciling mismatches are

  10. Experimental Study of Collision Detection Schema Used by Pilots During Closely Spaced Parallel Approaches

    NASA Technical Reports Server (NTRS)

    Pritchett, Amy R.; Hansman, R. John

    1996-01-01

    An experimental flight simulator study was conducted to examine the mental alerting logic and thresholds used by subjects to issue an alert and execute an avoidance maneuver. Subjects flew a series of autopilot landing approaches with traffic on a closely-spaced parallel approach; during some runs, the traffic would deviate towards the subject and the subject was to indicate the point when they recognized the potential traffic conflict, and then indicate a direction of flight for an avoidance maneuver. A variety of subjects, including graduate students, general aviation pilots and airline pilots, were tested. Five traffic displays were evaluated, with a moving map TCAS-type traffic display as a baseline. A side-task created both high and low workload situations. Subjects appeared to use the lateral deviation of the intruder aircraft from its approach path as the criteria for an alert regardless of the display available. However, with displays showing heading and/or trend information, their alerting thresholds were significantly lowered. This type of range-only schema still resulted in many near misses, as a high convergence rate was often established by the time of the subject's alert. Therefore, the properties of the intruder's trajectory had the greatest effect on the resultant near miss rate; no display system reliably caused alerts timely enough for certain collision avoidance. Subjects' performance dropped significantly on a side-task while they analyzed the need for an alert, showing alert generation can be a high workload situation at critical times. No variation was found between subjects with and with out piloting experience. These results suggest the design of automatic alerting systems should take into account the range-type alerting schema used by the human, such that the rationale for the automatic alert should be obvious to, and trusted by, the operator. Although careful display design may help generate pilot/automation trust, issues such as user non

  11. CdZnS thin films sublimated by closed space using mechanical mixing: A new approach

    NASA Astrophysics Data System (ADS)

    Mahmood, Waqar; Shah, Nazar Abbas

    2014-06-01

    Cadmium sulfide (CdS) is a prominent material for its tunable band gap used as a window layer in II-VI semiconductor solar cells. The light trapping capability of window layer is one of the powerful tools to enhance the efficiency of the cell. CdS and zinc (Zn) powders were mixed mechanically with different weight percents to make CdZnS (CZS) powder. CZS was deposited onto an ultrasonically cleaned glass substrate using close spaced sublimation (CSS) technique. CZS as-deposited thin films were characterized for structural, surface morphology with energy dispersive X-rays (EDX) and optical properties for the use of window layer in CdS/CdTe based solar cells. The different Zn concentrations in CZS played a vital role on crystallite size in structural analysis and optical properties e.g. transmission, absorption coefficient and energy band gap, etc. The crystallite size of as-deposited CZS thin films were increased as Zn concentration was increased up to certain value. The energy band gap varies from 2.42 eV to 2.57 eV for as-deposited CZS thin films with increasing Zn concentrations and surface morphology changes also. These changes were occurred due to zinc diffusion in CdS thin films. An angle resolved transmission data was taken to check the behavior of CdS and CZS thin film at different angles. A comparative study was carried out between CdS thin films and CZS thin films for the use of good window layer material.

  12. Behind the Photos and the Tears: Media Images, Neoliberal Discourses, Racialized Constructions of Space and School Closings in Chicago

    ERIC Educational Resources Information Center

    Allweiss, Alexandra; Grant, Carl A.; Manning, Karla

    2015-01-01

    This critical article provides insights into how media frames influence our understandings of school reform in urban spaces by examining images of students during the 2013 school closings in Chicago. Using visual framing analysis and informed by framing theory and critiques of neoliberalism we seek to explore two questions: (1) What role do media…

  13. The ecology of microorganisms in a small closed system: Potential benefits and problems for space station

    NASA Technical Reports Server (NTRS)

    Rodgers, E. B.

    1986-01-01

    The inevitble presence on the space station of microorganisms associated with crew members and their environment will have the potential for both benefits and a range of problems including illness and corrosion of materials. This report reviews the literature presenting information about microorganisms pertinent to Environmental Control and Life Support (ECLS) on the space station. The perspective of the report is ecological, viewing the space station as an ecosystem in which biological relationships are affected by factors such as zero gravity and by closure of a small volume of space. Potential sites and activities of microorganisms on the space station and their environmental limits, microbial standards for the space station, monitoring and control methods, effects of space factors on microorganisms, and extraterrestrial contamination are discussed.

  14. DISCOVERING THE MISSING 2.2 < z < 3 QUASARS BY COMBINING OPTICAL VARIABILITY AND OPTICAL/NEAR-INFRARED COLORS

    SciTech Connect

    Wu Xuebing; Wang Ran; Bian Fuyan; Jiang Linhua; Fan Xiaohui; Schmidt, Kasper B.

    2011-09-15

    The identification of quasars in the redshift range 2.2 < z < 3 is known to be very inefficient because the optical colors of such quasars are indistinguishable from those of stars. Recent studies have proposed using optical variability or near-infrared (near-IR) colors to improve the identification of the missing quasars in this redshift range. Here we present a case study combining both methods. We select a sample of 70 quasar candidates from variables in Sloan Digital Sky Survey (SDSS) Stripe 82, which are non-ultraviolet excess sources and have UKIDSS near-IR public data. They are clearly separated into two parts on the Y - K/g - z color-color diagram, and 59 of them meet or lie close to a newly proposed Y - K/g - z selection criterion for z < 4 quasars. Of these 59 sources, 44 were previously identified as quasars in SDSS DR7, and 35 of them are quasars at 2.2 < z < 3. We present spectroscopic observations of 14 of 15 remaining quasar candidates using the Bok 2.3 m telescope and the MMT 6.5 m telescope, and successfully identify all of them as new quasars at z = 2.36-2.88. We also apply this method to a sample of 643 variable quasar candidates with SDSS-UKIDSS nine-band photometric data selected from 1875 new quasar candidates in SDSS Stripe 82 given by Butler and Bloom based on the time-series selections, and find that 188 of them are probably new quasars with photometric redshifts at 2.2 < z < 3. Our results indicate that the combination of optical variability and optical/near-IR colors is probably the most efficient way to find 2.2 < z < 3 quasars and is very helpful for constructing a complete quasar sample. We discuss its implications for ongoing and upcoming large optical and near-IR sky surveys.

  15. On the alignment of quasars

    NASA Astrophysics Data System (ADS)

    Zhu, X.-F.

    1986-06-01

    Taking the two Savage-Bolton 5 deg x 5 deg regions of optical quasar patrol as samples, a systematic analysis of the number of aligned quasars was made and compared with the random data generated by Monte Carlo method. The statistical result is that, at least for these two samples, there is no clear evidence for alignment.

  16. On the alignment of quasars

    NASA Astrophysics Data System (ADS)

    Zhu, Xing-fen

    1986-06-01

    Taking the two Savage-Bolton 5° × 5° regions of optical quasar patrol as samples, I made a systematic analysis of the number of aligned quasars and compared with the random data generated by Monte Carlo method. The statistical result is that, at least for these two samples, there is no clear evidence for alignment.

  17. The Circumgalactic Medium of Quasars

    NASA Astrophysics Data System (ADS)

    Hennawi, Joe

    2014-07-01

    I will argue that observations of the diffuse gas in the outskirts of quasar host galaxies, or the so called circumgalactic medium, are essential for understanding how luminous quasars evolve in a cosmological context. Such observations also provide a fruitful comparison to theory, because hydrodynamics at moderate overdensities is much easier to simulate than the complicated processes which trigger quasar activity. A novel technique will be introduced, whereby a foreground quasar can be studied in absorption against a background quasar, resolving scales as small as 30 kpc. This experiment reveals a rich absorption spectrum which contains a wealth of information about the physical conditions of diffuse gas around quasars. Hydrodynamical simulations of the massive dark matter halos which host luminous quasars under predict the amount of cool gas observed in quasar environs by a large factor, challenging our understanding of how massive galaxies form. I will also discuss a very sensitive search for Ly-alpha emission from the same gas which we study in absorption.

  18. QUASAR PG1115+080 AND GRAVITATIONAL LENS

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Left: The light from the single quasar PG 1115+080 is split and distorted in this infrared image. PG 1115+080 is at a distance of about 8 billion light years in the constellation Leo, and it is viewed through an elliptical galaxy lens at a distance of 3 billion light years. The NICMOS frame is taken at a wavelength of 1.6 microns and it shows the four images of the quasar (the two on the left are nearly merging) surrounding the galaxy that causes the light to be lensed. The quasar is a variable light source and the light in each image travels a different path to reach the Earth. The time delay of the variations allows the distance scale to be measured directly. The linear streaks on the image are diffraction artifacts in the NICMOS instrument (NASA/Space Telescope Science Institute). Right: In this NICMOS image, the four quasar images and the lens galaxy have been subtracted, revealing a nearly complete ring of infrared light. This ring is the stretched and amplified starlight of the galaxy that contains the quasar, some 8 billion light years away. (NASA/Space Telescope Science Institute). Credit: Christopher D. Impey (University of Arizona)

  19. Photometric Monitoring of Quasars with Kepler

    NASA Astrophysics Data System (ADS)

    Unwin, Stephen C.; Wehrle, A. E.; Wiita, P. J.; Revalski, M.; Silano, D.; Sprague, D.; Di Lorenzo, P.

    2013-01-01

    We have observed the photometric variability of four flat-spectrum radio quasars, and one radio galaxy (Cyg A) with Kepler, since mid-2010. Kepler’s ability to observe uninterrupted for very extended durations provides a unique opportunity to obtain very long time sequences on active galactic nuclei, something that is hard to do even with dedicated ground-based telescope networks. It allows us to examine these light curves for variability on timescales from hours to weeks, and to probe the physical processes involved in accretion around the central black hole and the organization of some of that energy into jets that ultimately power double-lobed radio sources. Kepler was designed to detect exoplanet transits of stars, and the data analysis pipeline is highly optimized for that purpose. We cannot use the standard analysis tools for the quasi-random variability in quasars, so we re-analysed the raw data, and overcame some of the challenges in calibrating these light curves. We briefly discuss some of the issues in producing calibrated light curves for long timescales. For each quasar we computed power spectra, and found power-law slopes of around -2 for most. Although sensitive to quasi-periodic variations, we did not find any convincing evidence for periodicity in any of our targets. This research was carried out, in part, at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Copyright 2012. California Institute of Technology. Government sponsorship acknowledged.

  20. CONSTRAINTS ON THE FAINT END OF THE QUASAR LUMINOSITY FUNCTION AT z {approx} 5 IN THE COSMOS FIELD

    SciTech Connect

    Ikeda, H.; Matsuoka, K.; Kajisawa, M.; Nagao, T.; Taniguchi, Y.; Shioya, Y.; Enoki, M.; Capak, P.; Masters, D.; Scoville, N. Z.; Civano, F.; Koekemoer, A. M.; Morokuma, T.; Salvato, M.; Schinnerer, E.

    2012-09-10

    We present the result of our low-luminosity quasar survey in the redshift range of 4.5 {approx}< z {approx}< 5.5 in the COSMOS field. Using the COSMOS photometric catalog, we selected 15 quasar candidates with 22 < i' < 24 at z {approx} 5 that are {approx}3 mag fainter than the Sloan Digital Sky Survey quasars in the same redshift range. We obtained optical spectra for 14 of the 15 candidates using FOCAS on the Subaru Telescope and did not identify any low-luminosity type-1 quasars at z {approx} 5, while a low-luminosity type-2 quasar at z {approx} 5.07 was discovered. In order to constrain the faint end of the quasar luminosity function at z {approx} 5, we calculated the 1{sigma} confidence upper limits of the space density of type-1 quasars. As a result, the 1{sigma} confidence upper limits on the quasar space density are {Phi} < 1.33 Multiplication-Sign 10{sup -7} Mpc{sup -3} mag{sup -1} for -24.52 < M{sub 1450} < -23.52 and {Phi} < 2.88 Multiplication-Sign 10{sup -7} Mpc{sup -3} mag{sup -1} for -23.52 < M{sub 1450} < -22.52. The inferred 1{sigma} confidence upper limits of the space density are then used to provide constraints on the faint-end slope and the break absolute magnitude of the quasar luminosity function at z {approx} 5. We find that the quasar space density decreases gradually as a function of redshift at low luminosity (M{sub 1450} {approx} -23), being similar to the trend found for quasars with high luminosity (M{sub 1450} < -26). This result is consistent with the so-called downsizing evolution of quasars seen at lower redshifts.

  1. Being a Closely Spaced Second Child Is Not So Bad. Child-Spacing Effects on Intelligence, Personality, and Social Competence.

    ERIC Educational Resources Information Center

    Nuttall, Ronald L.; Nuttall, Ena Vazquez

    This study focuses on the effects of family size and spacing on intellectual, social, and personality development of children. The sample consisted of 533 suburban, middle class, large family (five or more) and small two child family children. The children, 233 boys and 300 girls, were teenagers attending either junior or senior high school.…

  2. Characterizing Quasar Outflows III: SEDs, and Bolometric Luminosity Estimates

    NASA Astrophysics Data System (ADS)

    Richmond, Joseph; Robbins, J. M.; Ganguly, R.; Stark, M. A.; Christenson, D. H.; Derseweh, J. A.; Townsend, S. L.

    2012-05-01

    Galaxy evolution models have shown that quasars are a crucial ingredient in the evolution of massive galaxies. Outflows play a key role in the story of quasars and their host galaxies, by helping regulate the accretion process, the star-formation rate and mass of the host galaxy (i.e., feedback). The prescription for modeling outflows as a contributor to feedback requires knowledge of the outflow velocity, geometry, and column density. In particular, we need to understand how these depend on physical parameters and how much is determined stochastically (and with what distribution). For this purpose, we are examining a sample of 11000 z=1.7-2.0 quasars from the Sloan Digital Sky Survey. This redshift range permits the following from the SDSS spectra: (1) separation of objects that do and do not exhibit outflows; (2) classification/measurement of outflow properties (ionization, velocity, velocity width); and (3) measurements of UV emission line and continuum parameters. In this poster, we add photometry from both the Two Micron All-Sky Survey (2MASS) and from the Wide-Field Infrared Survey Explorer (WISE). 2MASS photometry covers the rest-frame optical regime of these qusars, while the WISE W1, W2, and W3 bands cover the rest-frame wavelength ranges 0.9-1.27 micron, 1.35-1.75 micron, and 2.52-5.51 micron, respectively. The preliminary release of WISE data cover 3800 of our quasars. In an accompnying poster, we have subjectively divided these quasars into four categories: broad absorption-line quasars (2700 objects), associated absorption-line quasars (1700 objects), reddened quasars (160 objects), and unabsorbed/unreddened quasars (6300 objects). Here, we present average SEDs for these subsamples, estimates of bolometric luminosity, and explore changes in SED based on both outflow properties and quasar physical properties. This material is based upon work supported by the National Aeronautics and Space Administration under Grant No. 09-ADP09-0016 issued through the

  3. Studies of Quasar Outflows

    NASA Technical Reports Server (NTRS)

    Arav, Nahum

    2002-01-01

    The main aim of this research program is to determine the ionization equilibrium and abundances in quasar outflows. Especially in the broad absorption line QSO PG 0946+301. We find that the outflow's metalicity is consistent with being solar, while the abundance ratio of phosphorus to other metals is at least ten times solar. These findings are based on diagnostics that are not sensitive to saturation and partial covering effects in the BALs (Broad Adsorption Lines), which considerably weakened previous claims for enhanced metalicity. Ample evidence for these effects is seen in the spectrum.

  4. Difference Imaging of Lensed Quasar Candidates in the Sloan Digital Sky Survey Supernova Survey Region

    NASA Astrophysics Data System (ADS)

    Lacki, Brian C.; Kochanek, Christopher S.; Stanek, Krzysztof Z.; Inada, Naohisa; Oguri, Masamune

    2009-06-01

    Difference imaging provides a new way to discover gravitationally lensed quasars because few nonlensed sources will show spatially extended, time variable flux. We test the method on the fields of lens candidates in the Sloan Digital Sky Survey (SDSS) Supernova Survey region from the SDSS Quasar Lens Search (SQLS) and one serendipitously discovered lensed quasar. Starting from 20,536 sources, including 49 SDSS quasars, 32 candidate lenses/lensed images, and one known lensed quasar, we find that 174 sources including 35 SDSS quasars, 16 candidate lenses/lensed images, and the known lensed quasar are nonperiodic variable sources. We can measure the spatial structure of the variable flux for 119 of these variable sources and identify only eight as candidate extended variables, including the known lensed quasar. Only the known lensed quasar appears as a close pair of sources on the difference images. Inspection of the remaining seven suggests they are false positives, and only two were spectroscopically identified quasars. One of the lens candidates from the SQLS survives our cuts, but only as a single image instead of a pair. This indicates a false positive rate of order ~1/4000 for the method, or given our effective survey area of order 0.82 deg2, ~5 per deg2 in the SDSS Supernova Survey. The fraction of quasars not found to be variable and the false positive rate would both fall if we had analyzed the full, later data releases for the SDSS fields. While application of the method to the SDSS is limited by the resolution, depth, and sampling of the survey, several future surveys such as Pan-STARRS, LSST, and SNAP will significantly improve on these limitations.

  5. The Hubble Space Telescope Quasar Absorption Line Key Project. XIV. The Evolution of Lyα Absorption Lines in the Redshift Interval z = 0-1.5

    NASA Astrophysics Data System (ADS)

    Weymann, Ray J.; Jannuzi, Buell T.; Lu, Limin; Bahcall, John N.; Bergeron, Jacqueline; Boksenberg, Alec; Hartig, George F.; Kirhakos, Sofia; Sargent, W. L. W.; Savage, Blair D.; Schneider, Donald P.; Turnshek, David A.; Wolfe, Arthur M.

    1998-10-01

    either line misidentification or incomplete spectral coverage. Considering the insensitivity of the equivalent width to large changes in the column density for saturated lines, we suggest that this result is probably attributable to rapid evolution of the very highest column density systems, rather than real differences in metallicity. We find evidence that the rate of evolution increases with increasing equivalent width. We compare our results for the variation of line density with redshift to recent numerical simulations of Lyα absorbers, in particular, to those of Riediger, Petitjean, & Mucket, which extend to zero redshift. We find fairly good agreement between these simulations and our results, though the rapid evolution we find in the Lyα systems containing heavy element ions is not predicted in their models. We speculate that these heavy element-containing Lyα systems involve those clouds closely associated with galaxies, whose column densities are too high and whose sizes are too small to be included in the Riediger et al. simulations. Our results for Lyα lines at the high end of our equivalent width distribution are compatible with the recent analysis of the absorber-galaxy correlation by Chen et al. For the weaker lines, however, our results suggest that whatever association exists between absorbers and galaxies is different from that for the stronger lines. We conclude with some suggestions for further observations. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  6. Potential Sedimentary Evidence of Two Closely Spaced Tsunamis on the West Coast of Aceh, Indonesia

    NASA Astrophysics Data System (ADS)

    Monecke, Katrin; Meilianda, Ella; Rushdy, Ibnu; Moena, Abudzar; Yolanda, Irvan P.

    2016-04-01

    Recent research in the coastal regions of Aceh, Indonesia, an area that was largely affected by the 2004 Sumatra Andaman earthquake and ensuing Indian Ocean tsunami, suggests the possibility that two closely spaced tsunamis occurred at the turn of the 14th to 15th century (Meltzner et al., 2010; Sieh et al., 2015). Here, we present evidence of two buried sand layers in the coastal marshes of West Aceh, possibly representing these penultimate predecessors of the 2004 tsunami. We discovered the sand layers in an until recently inaccessible area of a previously studied beach ridge plain about 15 km North of Meulaboh, West Aceh. Here, the 2004 tsunami left a continuous, typically a few cm thick sand sheet in the coastal hinterland in low-lying swales that accumulate organic-rich deposits and separate the sandy beach ridges. In keeping with the long-term progradation of the coastline, older deposits have to be sought after further inland. Using a hand auger, the buried sand layers were discovered in 3 cores in a flooded and highly vegetated swale in about 1 km distance to the shoreline. The pair of sand layers occurs in 70-100 cm depth and overlies 40-60 cm of dark-brown peat that rests on the basal sand of the beach ridge plain. The lower sand layer is only 1-6 cm thick, whereas the upper layer is consistently thicker, measuring 11-17 cm, with 8-14 cm of peat in between sand sheets. Both layers consist of massive, grey, medium sand and include plant fragments. They show very sharp upper and lower boundaries clearly distinguishing them from the surrounding peat and indicating an abrupt depositional event. A previously developed age model for sediments of this beach ridge plain suggest that this pair of layers could indeed correlate to a nearby buried sand sheet interpreted as tsunamigenic and deposited soon after 1290-1400AD (Monecke et al., 2008). The superb preservation at this new site allows the clear distinction of two depositional events, which, based on a first

  7. Neutrinos from flat-spectrum radio quasars

    NASA Technical Reports Server (NTRS)

    Mannheim, K.; Stanev, T.; Biermann, P. L.

    1992-01-01

    The GRO observation (Hartman et al., 1992) of a very strong flux of gamma rays with an energy index close to 2 from the distant quasar 3C279 and other extragalactic flat-spectrum radio sources is in very good agreement with models that advocate the important role of very high energy protons and nuclei in the energy transport in AGN. Protons and nuclei cool by interactions on the nonthermal fields in the nuclear jet of the AGN and generate gamma ray and neutrino fluxes. Ultra high energy neutrinos could be observed with sensitive air shower experiments in outbursts as powerful as the one seen by GRO.

  8. A Wealth of Dust Grains in Quasar Winds

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Click on image for larger poster version

    This plot of data captured by NASA's Spitzer Space Telescope reveals dust entrained in the winds rushing away from a quasar, or growing black hole. The quasar, called PG2112+059, is located deep inside a galaxy 8 billion light-years away. Astronomers believe the dust might have been forged in the winds, which would help explain where dust in the very early universe came from.

    The data were captured by Spitzer's infrared spectrograph, an instrument that splits apart light from the quasar into a spectrum that reveals telltale signs of different minerals. Each type of mineral, or dust grain, has a unique signature, as can be seen in the graph, or spectrum, above.

    The strongest features are from the mineral amorphous olivine, or glass (purple); the mineral forsterite found in sand (blue); and the mineral corundum found in rubies (light blue). The detection of forsterite and corundum is highly unusual in galaxies without quasars. Therefore, their presence is a key clue that these grains might have been created in the quasar winds and not by dying stars as they are in our Milky Way galaxy. Forsterite is destroyed quickly in normal galaxies by radiation, so it must be continually produced to be detected by Spitzer.

    Corundum is hard, and provides a seed that softer, more common minerals usually cover up. As a result, corundum is usually not seen in spectra of galaxies. Since Spitzer did detect the mineral, it is probably forming in a clumpy environment, which is expected in quasar winds. All together, the signatures of the unusual minerals in this spectrum point towards dust grains forming in the winds blowing away from quasars.

  9. Do quasars evolve over cosmological time scales?

    NASA Astrophysics Data System (ADS)

    Wampler, E. J.; Ponz, D.

    Systematic biases that are redshift dependent can influence the optical discovery of quasars and the evolution laws derived from counts of quasars. New data and their interpretation for quasars brighter than MB = -24 in the Palomar Bright Quasar Survey (BQS) (Schmidt and Green, 1983) are consistent with no evolution. A comparison of BQS quasars with the brightest quasars from the CTIO Schmidt Telescope Survey (Osmer and Smith, 1980) shows that if q(0) is near zero, the comoving density of bright quasars in a Friedmann cosmology is about 15 times higher for the CTIO survey quasars (mean z of about 2.8) than for the BQS quasars (mean z of about 1.8). In this case spectral evolution is also required since the CTIO quasars have stronger CIV 1548 A lines than the BQS quasars of similar luminosity. Alternatively, if q(0) is taken to be near 1, the CTIO survey quasars would then have a lower luminosity than the BQS quasars and these data would be consistent with no evolution. Strong CIV 1548 A lines for the CTIO quasars would then fit the general correlation between absolute quasar luminosity and emission line strength (Wampler, Gaskell, Burke and Baldwin, 1984).

  10. Effects of a Closed Space Environment on Gene Expression in Hair Follicles of Astronauts in the International Space Station.

    PubMed

    Terada, Masahiro; Seki, Masaya; Takahashi, Rika; Yamada, Shin; Higashibata, Akira; Majima, Hideyuki J; Sudoh, Masamichi; Mukai, Chiaki; Ishioka, Noriaki

    2016-01-01

    Adaptation to the space environment can sometimes pose physiological problems to International Space Station (ISS) astronauts after their return to earth. Therefore, it is important to develop healthcare technologies for astronauts. In this study, we examined the feasibility of using hair follicles, a readily obtained sample, to assess gene expression changes in response to spaceflight adaptation. In order to investigate the gene expression changes in human hair follicles during spaceflight, hair follicles of 10 astronauts were analyzed by microarray and real time qPCR analyses. We found that spaceflight alters human hair follicle gene expression. The degree of changes in gene expression was found to vary among individuals. In some astronauts, genes related to hair growth such as FGF18, ANGPTL7 and COMP were upregulated during flight, suggesting that spaceflight inhibits cell proliferation in hair follicles. PMID:27029003

  11. Effects of a Closed Space Environment on Gene Expression in Hair Follicles of Astronauts in the International Space Station

    PubMed Central

    Terada, Masahiro; Seki, Masaya; Takahashi, Rika; Yamada, Shin; Higashibata, Akira; Majima, Hideyuki J.; Sudoh, Masamichi; Mukai, Chiaki; Ishioka, Noriaki

    2016-01-01

    Adaptation to the space environment can sometimes pose physiological problems to International Space Station (ISS) astronauts after their return to earth. Therefore, it is important to develop healthcare technologies for astronauts. In this study, we examined the feasibility of using hair follicles, a readily obtained sample, to assess gene expression changes in response to spaceflight adaptation. In order to investigate the gene expression changes in human hair follicles during spaceflight, hair follicles of 10 astronauts were analyzed by microarray and real time qPCR analyses. We found that spaceflight alters human hair follicle gene expression. The degree of changes in gene expression was found to vary among individuals. In some astronauts, genes related to hair growth such as FGF18, ANGPTL7 and COMP were upregulated during flight, suggesting that spaceflight inhibits cell proliferation in hair follicles. PMID:27029003

  12. VTOL in ground effect flows for closely spaced jets. [to predict pressure and upwash forces on aircraft structures

    NASA Technical Reports Server (NTRS)

    Migdal, D.; Hill, W. G., Jr.; Jenkins, R. C.

    1979-01-01

    Results of a series of in ground effect twin jet tests are presented along with flow models for closely spaced jets to help predict pressure and upwash forces on simulated aircraft surfaces. The isolated twin jet tests revealed unstable fountains over a range of spacings and jet heights, regions of below ambient pressure on the ground, and negative pressure differential in the upwash flow field. A separate computer code was developed for vertically oriented, incompressible jets. This model more accurately reflects fountain behavior without fully formed wall jets, and adequately predicts ground isobars, upwash dynamic pressure decay, and fountain lift force variation with height above ground.

  13. Automation of closed environments in space for human comfort and safety

    NASA Technical Reports Server (NTRS)

    1991-01-01

    The results of the second year of a three year design project on the automation of the Environmental Control and Life Support System (ECLSS) of the Space Station Freedom (SSF) are presented. The results are applicable to other space missions that require long duration space habitats. A description of conceptual controls which are developed for the Water Recovery and Management (WRM) Subassembly is given. Mathematical modeling of the Air Revitalization (AR) Subassembly is presented. The work done by the Kansas State University NASA/USRA interdisciplinary student design team is concluded with a discussion of the expert system which was developed for the AR Subassembly.

  14. Quasar variability limits on cosmological density of cosmic strings

    SciTech Connect

    Tuntsov, A. V.; Pshirkov, M. S.

    2010-03-15

    We put robust upper limits on the average cosmological density {Omega}{sub s} of cosmic strings based on the variability properties of a large homogeneous sample of Sloan Digital Sky Survey quasars. We search for an excess of characteristic variations of quasar brightness that are associated with string lensing and use the observed distribution of these variations to constrain the density of strings. The limits obtained do not invoke any clustering of strings. They apply to both open segments and closed loops of strings, usefully extend over a wide range of tensions 10{sup -13}quasar intrinsic variability rather than a mere increase in the volume of data.

  15. Towards an ALHAMBRA quasar catalogue

    NASA Astrophysics Data System (ADS)

    Chaves-Montero, J.; Bonoli, S.

    2015-05-01

    We present the steps towards the identification of quasars in the ALHAMBRA fields using only the ALHAMBRA photospectra. The ALHAMBRA survey (Moles et al. 2005, 2008) uses a set of 20 contiguous optical filters and three infrared filtes (J, H, and Ks). The entire coverage of the optical range and the width of the filters (˜ 300 Å) allowed us to detect emission line quasars and to compute their accurate redshifts. Starting from ˜430 000 sources we ended up with a catalogue of 524 quasar candidates with z>0.8 in an area of 2.79 deg^2. To determine the level of galaxy contamination in our sample and the accuracy of the photo-z we performed a crossmatch between spectroscopically identified objects in another surveys and the ALHAMBRA sources, detecting 1 058 galaxies and 205 quasars. After applying our algorithm none of the galaxies was classified as quasar, the accuracy of the quasar photo-z was σ_{NMAD}=0.010, and the level of quasars with photo-z significantly different to their spec-z (outliers) was 3.12 %.

  16. Selective Growth of CdTe on Nano-patterned CdS via Close-Space Sublimation

    NASA Astrophysics Data System (ADS)

    Aguirre, Brandon A.; Zubia, David; Ordonez, Rafael; Anwar, Farhana; Prieto, Heber; Sanchez, Carlos A.; Salazar, Maria T.; Pimentel, Alejandro. A.; Michael, Joseph R.; Zhou, Xiaowang; Mcclure, John C.; Nielson, Gregory N.; Cruz-Campa, Jose L.

    2014-07-01

    Selective-area deposition of CdTe on CdS via close-space sublimation is used to study the effect of window size (2 μm and 300 nm) on grain growth. The basic fabrication procedures for each of the layers (CdS, SiO2, and CdTe) and for achieving selective-area growth are presented. Selective-area growth of both micro- and nano-scale CdTe islands on CdS substrates using close-spaced sublimation is demonstrated. Scanning electron microscopy and electron backscatter diffraction microstructure analysis show that the micro-scale CdTe islands remain polycrystalline. However, when the island size is reduced to 300 nm, single crystal CdTe can be achieved within the windows. The CdTe grains were most often in the (101) orientation for both the micro- and nano-sized CdTe islands.

  17. Differences in Ambient Polycyclic Aromatic Hydrocarbon Concentrations between Streets and Alleys in New York City: Open Space vs. Semi-Closed Space

    PubMed Central

    Lovinsky-Desir, Stephanie; Miller, Rachel L.; Bautista, Joshua; Gil, Eric N.; Chillrud, Steven N.; Yan, Beizhan; Camann, David; Perera, Frederica P.; Jung, Kyung Hwa

    2016-01-01

    Background: Outdoor ambient polycyclic aromatic hydrocarbon (PAH) concentrations are variable throughout an urban environment. However, little is known about how variation in semivolatile and nonvolatile PAHs related to the built environment (open space vs. semi-closed space) contributes to differences in concentrations. Methods: We simultaneously collected 14, two-week samples of PAHs from the outside of windows facing the front (adjacent to the street) open side of a New York City apartment building and the alley, semi-closed side of the same apartment unit between 2007 and 2012. We also analyzed samples of PAHs measured from 35 homes across Northern Manhattan and the Bronx, 17 from street facing windows with a median floor level of 4 (range 2–26) and 18 from alley-facing windows with a median floor level of 4 (range 1–15). Results: Levels of nonvolatile ambient PAHs were significantly higher when measured from a window adjacent to a street (an open space), compared to a window 30 feet away, adjacent to an alley (a semi-closed space) (street geometric mean (GM) 1.32 ng/m3, arithmetic mean ± standard deviation (AM ± SD) 1.61 ± 1.04 ng/m3; alley GM 1.10 ng/m3, AM ± SD 1.37 ± 0.94 ng/m3). In the neighborhood-wide comparison, nonvolatile PAHs were also significantly higher when measured adjacent to streets compared with adjacent to alley sides of apartment buildings (street GM 1.10 ng/m3, AM ± SD 1.46 ± 1.24 ng/m3; alley GM 0.61 ng/m3, AM ± SD 0.81 ± 0.80 ng/m3), but not semivolatile PAHs. Conclusions: Ambient PAHs, nonvolatile PAHs in particular, are significantly higher when measured from a window adjacent to a street compared to a window adjacent to an alley, despite both locations being relatively close to street traffic. This study highlights small-scale spatial variations in ambient PAH concentrations that may be related to the built environment (open space vs. semi-closed space) from which the samples are measured, as well as the relative distance

  18. A new apparatus for multilayer growth by chemical vapor deposition: The sliding-boat close-spaced technique

    NASA Astrophysics Data System (ADS)

    Yoshikawa, Akihiko; Yoshihara, Seiji; Kasai, Haruo; Nishimaki, Masao

    1980-10-01

    A new apparatus for multilayer growth by chemical vapor deposition, the sliding-boat close-spaced tecnique (SBCST), is presented. The structure of the SBCST growth apparatus is quite similar to that of the conventional liquid phase epitaxy sliding-boat. The possibility of obtaining thin multilayer films by SBCST is shown. Preliminary experimental results for its application to the growth of n-CdS/p-InP heterojunction solar cells are also shown.

  19. The optical variability of the quasar 3C 446

    SciTech Connect

    Barbieri, C.; Vio, R.; Cappellaro, E; Turatto, M Padova Osservatorio Astronomico, Padua )

    1990-08-01

    The optical variability of the quasar 3C 446 is investigated using power spectrum and structure function analysis along with a new set of observations that extend the available data till 1989. No contradiction is found between the PS and SF analyses. The presence of the 1540-day periodicity is strengthened by the occurrence of the 1988 luminosity peak, suggesting that the next burst will occur in the northern spring of 1992. The time series of the quasar is nonstationary. The light variations are determined by a sequence of luminosity bursts, mostly regularly spaced in time and lasting up to 2 yr. 25 refs.

  20. A Hubble Diagram for Quasars

    NASA Astrophysics Data System (ADS)

    Risaliti, Guido; Lusso, Elisabeta

    2015-09-01

    We present a new method to test the cosmological model at high z, and measure the cosmological parameters, based on the non-linear correlation between UV and X-ray luminosity in quasars. While the method can be successfully tested with the data available today, a deep X-ray survey matching the future LSST and Euclid quasar catalogs is needed to achieve a high precision. Athena could provide a Hubble diagram for quasar analogous to that available today for supernovae, but extending up to z>6.

  1. HST/COS OBSERVATIONS OF THIRTEEN NEW He II QUASARS

    SciTech Connect

    Syphers, David; Anderson, Scott F.; Zheng Wei; Meiksin, Avery; Schneider, Donald P.; York, Donald G.

    2012-04-15

    The full reionization of intergalactic helium was a major event in the history of the intergalactic medium (IGM), and UV observations of the He II Gunn-Peterson trough allow us to characterize the end of this process at z {approx} 3. Due to intervening hydrogen absorption, quasars allowing such study are rare, with only 33 known in the literature, and most of those are very recent discoveries. We expand on our previous discovery work, and present 13 new He II quasars with redshifts 2.82 < z < 3.77, here selected with {approx}80% efficiency, and including several that are much brighter than the vast majority of those previously known. This is the largest sample of uniformly observed He II quasars covering such a broad redshift range, and they show evidence of IGM opacity increasing with redshift, as expected for the helium reionization epoch. No evidence of He II Ly{alpha} quasar emission is seen in individual or averaged spectra, posing a problem for standard models of the broad-line region. The current rapid advance in the study of He II quasars has been greatly facilitated by the Cosmic Origins Spectrograph on the Hubble Space Telescope, and we discuss the instrumental and other subtleties that must be taken into account in IGM He II observations.

  2. Performance and Mass Modeling Subtleties in Closed-Brayton-Cycle Space Power Systems

    NASA Technical Reports Server (NTRS)

    Barrett, Michael J.; Johnson, Paul K.

    2005-01-01

    Contents include the following: 1. Closed-Brayton-cycle (CBC) thermal energy conversion is one available option for future spacecraft and surface systems. 2. Brayton system conceptual designs for milliwatt to megawatt power converters have been developed 3. Numerous features affect overall optimized power conversion system performance: Turbomachinery efficiency. Heat exchanger effectiveness. Working-fluid composition. Cycle temperatures and pressures.

  3. Opening and Closing Interactive Spaces: Shaping Four-Year-Old Children's Participation in Two English Settings

    ERIC Educational Resources Information Center

    Payler, Jane

    2007-01-01

    This paper draws on an ESRC-funded study (Payler, 2005) of the sociocultural influences on learning processes of 10 four-year-old children in their second year of the Foundation Stage in England (DfEE, 2000). The children, very close in age, were in one of two early years settings: a pre-school playgroup with a largely invisible pedagogy…

  4. Probability distributions for the magnification of quasars due to microlensing

    NASA Technical Reports Server (NTRS)

    Wambsganss, Joachim

    1992-01-01

    Gravitational microlensing can magnify the flux of a lensed quasar considerably and therefore possibly influence quasar source counts or the observed quasar luminosity function. A large number of distributions of magnification probabilities due to gravitational microlensing for finite sources are presented, with a reasonable coverage of microlensing parameter space (i.e., surface mass density, external shear, mass spectrum of lensing objects). These probability distributions were obtained from smoothing two-dimensional magnification patterns with Gaussian source profiles. Different source sizes ranging from 10 exp 14 cm to 5 x 10 exp 16 cm were explored. The probability distributions show a large variety of shapes. Coefficients of fitted slopes for large magnifications are presented.

  5. FAR-INFRARED PROPERTIES OF TYPE 1 QUASARS

    SciTech Connect

    Hanish, D. J.; Teplitz, H. I.; Capak, P.; Desai, V.; Armus, L.; Brinkworth, C.; Brooke, T.; Colbert, J.; Fadda, D.; Noriega-Crespo, A.; Paladini, R.; Frayer, D.; Huynh, M.; Lacy, M.; Murphy, E.; Scarlata, C.; Shenoy, S.

    2013-05-01

    We use the Spitzer Space Telescope Enhanced Imaging Products and the Spitzer Archival Far-InfraRed Extragalactic Survey to study the spectral energy distributions (SEDs) of spectroscopically confirmed type 1 quasars selected from the Sloan Digital Sky Survey (SDSS). By combining the Spitzer and SDSS data with the Two Micron All Sky Survey, we are able to construct a statistically robust rest-frame 0.1-100 {mu}m type 1 quasar template. We find that the quasar population is well-described by a single power-law SED at wavelengths less than 20 {mu}m, in good agreement with previous work. However, at longer wavelengths, we find a significant excess in infrared luminosity above an extrapolated power-law, along with significant object-to-object dispersion in the SED. The mean excess reaches a maximum of 0.8 dex at rest-frame wavelengths near 100 {mu}m.

  6. Application of Closed Loop Optimal Guidance for a Constant Thrust Space Vehicle

    NASA Astrophysics Data System (ADS)

    Rezaei Darestani, Mahdy; Abbasi Mahale, Mahdi

    2016-01-01

    This research presents derivation and implementation of the explicit guidance problem to steer a space vehicle into exo atmospheric phase of flight to develop three-dimensional optimal trajectory. The proposed guidance algorithm is in association with continuous powered flight of the space vehicle in ascent manoeuvre. Stability, accuracy and simplicity of this approach are the improved developments in comparison with the IGM approach. This algorithm uses the calculus of variation method for the two boundary-value injection problem to generate an optimal trajectory of space vehicle with online generation of steering command to inject to any desired orbit. Here the end conditions have been determined as the orbital height, inclination and eccentricity where the initial conditions are fixed. The simulation results are considered which shows the accuracy and simplicity of this method to reach to the desired orbit in minimum fuel.

  7. Automation of closed environments in space for human comfort and safety

    NASA Technical Reports Server (NTRS)

    1990-01-01

    The results are presented of the first year of a three year project on the automation of the Environmental Control and Life Support System (ECLSS) of the Space Station Freedom (SSF). The results are applicable to other future space mission. The work was done by the Kansas State University NASA/USRA interdisciplinary student design team. The six ECLSS subsystems and how they interact are discussed. Proposed control schemes and their rationale are discussed for the Atmosphere Revitalization (AR) subsystem. Finally, a description of the mathematical models for many components of the ECLSS control system is given.

  8. Through BAL Quasars Brightly

    NASA Technical Reports Server (NTRS)

    Chartas, George

    2003-01-01

    We report on an observation of the broad absorption line (BAL) quasar PG 1115+080 performed with the XMM-Newton observatory. Spectral analysis reveals the second case of a relativistic X-ray-absorbing outflow in a BAL quasar. The first case was revealed in a recent observation of APM 08279+5255 with the Chandra X-Ray Observatory. As in the case of APM 08279+5255, the observed flux of PG 1115+080 is greatly magnified by gravitational lensing. The relatively high redshift (z=1.72) of the quasar places the redshifted energies of resonant absorption features in a sensitive portion of the XMM- Newton spectral response. The spectrum indicates the presence of complex low-energy absorption in the 0.2-0.6 keV observed energy band and high-energy absorption in the 2-5 keV observed energy band. The high-energy absorption is best modeled by two Gaussian absorption lines with rest-frame energies of 7.4 and 9.5 keV. Assuming that these two lines axe produced by resonant absorption due to Fe XXV, we infer that the X-ray absorbers are outflowing with velocities of approx. 0.10c and approx. 0.34c respectively. We have detected significant variability of the energies and widths of the X-ray BALs in PG 1115+080 and APM 08279+5255 over timescales of 19 and 1.8 weeks (proper time), respectively. The BAL variability observed from APM 08279+5255 supports our earlier conclusion that these absorbers are most likely launched at relatively small radii of less than 10(exp 16)(Mbh/M8)(sup 1/2) cm. A comparison of the ionization properties and column densities of the low-energy and high-energy absorbers indicates that these absorbers are likely distinct; however, higher spectral resolution is needed to confirm this result. Finally, we comment on prospects for constraining the kinematic and ionization properties of these X-ray BALs with the next generation of X-ray observatories.

  9. Tropospheric gravity waves observed by three closely-spaced ST radars

    NASA Technical Reports Server (NTRS)

    Carter, D. A.; Eriddle, A. C. AFGARELLO, R.ly stable thro; Eriddle, A. C. AFGARELLO, R.ly stable thro

    1985-01-01

    During a 6 week period in 1982, 3 ST (Stratosphere-Troposphere) radars measured horizontal and vertical wavelengths of small scale tropospheric gravity waves. These 50 MHz, vertically-directed radars were located in a trianglar network with approximately 5 km spacing on the southern coast of France at the mouth of the Rhone River during the ALPEX (Alpine Experiment) program.

  10. How big and how close? Habitat patch size and spacing to conserve a threatened species

    EPA Science Inventory

    We present results of a spatially-explicit, individual-based stochastic dispersal model (HexSim) to evaluate effects of size and spacing of patches of habitat of Northern Spotted Owls (NSO; Strix occidentalis caurina) in Pacific Northwest, USA, to help advise USDI Fish and Wildli...

  11. Closely spaced nanomagnets by dual e-beam exposure for low-energy nanomagnet logic

    SciTech Connect

    Shah, Faisal A.; Csaba, Gyorgy; Butler, Katherine; Bernstein, Gary H.

    2013-05-07

    The effect of nanomagnet spacing on required clock field has been studied by micromagnetic simulation for supermalloy (Ni{sub 79}Fe{sub 16}Mo{sub 5}) dots with dimensions 90 Multiplication-Sign 60 Multiplication-Sign 20 nm{sup 3} and 120 Multiplication-Sign 60 Multiplication-Sign 20 nm{sup 3}. Reduction of the inter-magnet spacing for both dimensions has resulted in reduction of the required clock field in the simulation. A dual e-beam exposure technique has been developed to allow fabrication of ultra dense features using conventional poly(methylmethacrylate) e-beam resist. Nanomagnet logic (NML) datalines of supermalloy dots with {approx}10 nm and {approx}15 nm spacing have been fabricated using dual e-beam exposure with a 3{sigma} overlay accuracy of {approx}4 nm. Fabricated NML datalines have been characterized using magnetic force microscopy for various clock fields. Datalines of both spacing have shown proper NML functionality with a clock field as low as 60 mT.

  12. Quasar candidates near 1057 + 01

    SciTech Connect

    Crampton, D.; Cartledge, S.; Cowley, A.P.; Hartwick, F.D.A. Arizona State Univ., Tempe Victoria Univ. )

    1991-04-01

    Positions and magnitudes are given for 143 quasar candidates and three white dwarf candidates discovered with the CFHT blue grens in a 2.7 square degree area in the direction 1057 + 01. The goal of this survey is to provide complete samples of quasars to study the large scale distribution of matter at moderate to high (z less than 3.4) redshifts. Part of the region surveyed in this paper was previously studied by Crampton and Parmar (1983), allowing a comparison of the search and measurements accuracies. Redshifts, derived from MMT spectroscopy, for 27 of the candidates are also presented. One quasar, 1058.1 + 0052, displays strong broad absorption lines characteristic of BAL quasars. 5 refs.

  13. Solving close-coupling equations in momentum space without singularities II

    NASA Astrophysics Data System (ADS)

    Bray, A. W.; Abdurakhmanov, I. B.; Kadyrov, A. S.; Fursa, D. V.; Bray, I.

    2016-06-01

    The implementation of the convergent close-coupling method, whereby the principal-value singularity is treated analytically (Bray et al., 2015), has been extended to non-zero angular momenta. Its utility is demonstrated through application to proton scattering on excited states of positronium at incident energies spanning six orders of magnitude. It is shown that the analytic treatment is necessary in the case of highly excited positronium states.

  14. Asteroids to Quasars

    NASA Astrophysics Data System (ADS)

    Lugger, Phyllis M.

    2004-12-01

    Asteroid dedication; William Liller: Biographical Sketch; William Liller: Autobiographical Meanderings; Preface; List of Participants; Conference Photo; Part I. 1. Solar System Astronomy: Asteroids Joseph Veverka; 2. Sixteen years of stellar occultations James Elliott; 3. Comets to Quasars: Surface photometry from standard stars and the morphology of the galaxy-quasar interface Peter Usher; 4. Observing Solar Eclipses Jay Pasachoff; Part II. 5. Planetary Nebulae: new insights and opportunities Lawrence Aller; 6. Studies of planetary nebulae at radio wavelengths Yervant Terzian; 7. Optical identifications of compact galactic X-ray sources: Liller Lore Jonathan Grindlay; 8. Ages of globular clusters derived from BVRI CCD photometry Gonzalo Alcaino; 9. Stellar spectrum synthesis Jun Jugaku; 10. Mass exchange and stellar abundance anomalies Benjamin Peery; Part III. Extragalactic Astronomy: 11. The M31 globular cluster system John Huchra; 12. Spiral structure and star formation in galaxies Debra Elmegreen; 13. The discovery of hot coronae around early type galaxies William Forman and Christine Jones; 14. The morphology of clusters of galaxies, the formation efficiency of galaxies and the origin of the intracluster medium Christine Jones and William Forman; 15. Testing models for the dynamical evolution of clusters of galaxies Phyllis Lugger; 16. What is in the X-ray sky? Rudolph Schild; 17. Einstein deep surveys Stephen Murray, Christine Jones and William Forman; Part IV. History, Lore and Archaeoastronomy: 18. Robert Wheeler Willson: His Life and Legacy Barbara Welther; 19. The great mnemonics contest Owen Gingerich; 20. Hetu'u Rapanui: The archaeoastronomy of Easter Island William Liller; Indexes; Names; Objects; Subjects.

  15. Automation of closed environments in space for human comfort and safety

    NASA Technical Reports Server (NTRS)

    Cogley, Allen C.; Tucker, Nathan P.

    1992-01-01

    For prolonged missions into space and colonization outside the Earth's atmosphere, development of Environmental Control and Life Support Systems (ECLSS) are essential to provide astronauts with habitable environments. The Kansas State University Advanced Design Team have researched and designed a control system for an ECLSS like that on Space Station Freedom. The following milestones have been accomplished: (1) completed computer simulation of the CO2 Removal Assembly; (2) created a set of rules for the expert control system of the CO2 Removal Assembly; (3) created a classical controls system for the CO2 Removal Assembly; (4) established a means of communication between the mathematical model and the two controls systems; and (5) analyzed the dynamic response of the simulation and compared the two methods of control.

  16. Analysis of the enhancement of thermal radiation between closely-spaced surfaces due to microscale phenomena

    SciTech Connect

    Whale, M.D.; Cravalho, E.G.

    1997-07-01

    In the past several decades, there have been numerous attempts to develop a general formalism that accounts for the effects of wave interference and radiation tunneling (far-field and near-field effects) on the net radiative transfer between surfaces. In their most general form, these approaches yield correct results, which are in agreement. However, the practical application to particular materials has required various simplifications, which are not generally applicable and cannot be compared directly. The authors explore the basis of the assumptions used to make these approximations, clarify their limitations, and offer a set of regimes delineating their applicability. They derive proximity functions (in the strongly-absorbing and weakly-absorbing limits) that incorporate all the transport-enhancing effects of the general formalism, but show the details of the spacing effect across all frequency and spacing regimes. These functions provide a simple and elegant means to account for the far- and near-field effects of thermal radiation.

  17. Closing the gap in systems engineering education for the space industry

    NASA Technical Reports Server (NTRS)

    Carlisle, R.

    1986-01-01

    The education of system engineers with emphasis on designing systems for space applications is discussed. System engineers determine the functional requirements, performance needs, and implementation procedures for proposed systems and their education is based on aeronautics and mathematics. Recommendations from industry for improving the curriculum of system engineers at the undergraduate and graduate levels are provided. The assistance provided by companies to the education of system engineers is examined.

  18. Disclosing the Radio Loudness Distribution Dichotomy in Quasars: An Unbiased Monte Carlo Approach Applied to the SDSS-FIRST Quasar Sample

    NASA Astrophysics Data System (ADS)

    Baloković, M.; Smolčić, V.; Ivezić, Ž.; Zamorani, G.; Schinnerer, E.; Kelly, B. C.

    2012-11-01

    We investigate the dichotomy in the radio loudness distribution of quasars by modeling their radio emission and various selection effects using a Monte Carlo approach. The existence of two physically distinct quasar populations, the radio-loud and radio-quiet quasars, is controversial and over the last decade a bimodal distribution of radio loudness of quasars has been both affirmed and disputed. We model the quasar radio luminosity distribution with simple unimodal and bimodal distribution functions. The resulting simulated samples are compared to a fiducial sample of 8300 quasars drawn from the SDSS DR7 Quasar Catalog and combined with radio observations from the FIRST survey. Our results indicate that the SDSS-FIRST sample is best described by a radio loudness distribution which consists of two components, with (12 ± 1)% of sources in the radio-loud component. On the other hand, the evidence for a local minimum in the loudness distribution (bimodality) is not strong and we find that previous claims for its existence were probably affected by the incompleteness of the FIRST survey close to its faint limit. We also investigate the redshift and luminosity dependence of the radio loudness distribution and find tentative evidence that at high redshift radio-loud quasars were rarer, on average louder, and exhibited a smaller range in radio loudness. In agreement with other recent work, we conclude that the SDSS-FIRST sample strongly suggests that the radio loudness distribution of quasars is not a universal function, and that more complex models than presented here are needed to fully explain available observations.

  19. DISCLOSING THE RADIO LOUDNESS DISTRIBUTION DICHOTOMY IN QUASARS: AN UNBIASED MONTE CARLO APPROACH APPLIED TO THE SDSS-FIRST QUASAR SAMPLE

    SciTech Connect

    Balokovic, M.; Smolcic, V.; Ivezic, Z.; Zamorani, G.; Schinnerer, E.; Kelly, B. C.

    2012-11-01

    We investigate the dichotomy in the radio loudness distribution of quasars by modeling their radio emission and various selection effects using a Monte Carlo approach. The existence of two physically distinct quasar populations, the radio-loud and radio-quiet quasars, is controversial and over the last decade a bimodal distribution of radio loudness of quasars has been both affirmed and disputed. We model the quasar radio luminosity distribution with simple unimodal and bimodal distribution functions. The resulting simulated samples are compared to a fiducial sample of 8300 quasars drawn from the SDSS DR7 Quasar Catalog and combined with radio observations from the FIRST survey. Our results indicate that the SDSS-FIRST sample is best described by a radio loudness distribution which consists of two components, with (12 {+-} 1)% of sources in the radio-loud component. On the other hand, the evidence for a local minimum in the loudness distribution (bimodality) is not strong and we find that previous claims for its existence were probably affected by the incompleteness of the FIRST survey close to its faint limit. We also investigate the redshift and luminosity dependence of the radio loudness distribution and find tentative evidence that at high redshift radio-loud quasars were rarer, on average louder, and exhibited a smaller range in radio loudness. In agreement with other recent work, we conclude that the SDSS-FIRST sample strongly suggests that the radio loudness distribution of quasars is not a universal function, and that more complex models than presented here are needed to fully explain available observations.

  20. Parametric thermodynamic analysis of closed-cycle gas-laser operation in space

    NASA Technical Reports Server (NTRS)

    Burns, R. K.

    1974-01-01

    Cycle efficiency and radiator area required were calculated for thermally and electrically pumped lasers operating in closed cycles with a compressor and the required heat exchangers. A thermally pumped laser included within a Brayton cycle was also analyzed. Performance of all components, including the laser, was parametrically varied. For the thermally pumped laser the cycle efficiencies range below 10 percent and are very sensitive to the high-pressure losses associated with the supersonic diffuser required at the laser cavity exit. The efficiencies predicted for the electrically pumped laser cycles range slightly higher, but radiator area also tends to be larger.

  1. SDSS J0246-0825: A New Gravitationally Lensed Quasar from the Sloan Digital Sky Survey

    SciTech Connect

    Inada, N; Burles, S; Gregg, M D; Becker, R H; Schechter, P L; Eisenstein, D J; Oguri, M; Castander, F J; Hall, P B; Johnston, D E; Pindor, B; Richards, G T; Schneider, D P; White, R L; Brinkmann, J; Szalay, A; York, D G

    2005-11-10

    We report the discovery of a new two-image gravitationally lensed quasar, SDSS J024634.11-082536.2 (SDSS J0246-0825). This object was selected as a lensed quasar candidate from the Sloan Digital Sky Survey (SDSS) by the same algorithm that was used to discover other SDSS lensed quasars (e.g., SDSS J0924+0219). Multicolor imaging with the Magellan Consortium's Walter Baade 6.5-m telescope and the spectroscopic observations using the W. M. Keck Observatory's Keck II telescope confirm that SDSS J0246-0825 consists of two lensed images ({Delta}{theta} = 1''.04) of a source quasar at z = 1.68. Imaging observations with the Keck telescope and the Hubble Space Telescope reveal an extended object between the two quasar components, which is likely to be a lensing galaxy of this system. From the absorption lines in the spectra of quasar components and the apparent magnitude of the galaxy, combined with the expected absolute magnitude from the Faber-Jackson relation, we estimate the redshift of the lensing galaxy to be z = 0.724. A highly distorted ring is visible in the Hubble Space Telescope images, which is likely to be the lensed host galaxy of the source quasar. Simple mass modeling predicts the possibility that there is a small (faint) lensing object near the primary lensing galaxy.

  2. Automation of closed environments in space for human comfort and safety

    NASA Technical Reports Server (NTRS)

    1991-01-01

    The development of Environmental Control and Life Support Systems (ECLSS) for Space Station Freedom, future colonization of the Moon, and Mars missions presents new challenges for present technologies. ECLSS that operate during long-duration missions must be semi-autonomous to allow crew members environmental control without constant supervision. A control system for the ECLSS must address these issues as well as being reliable. The Kansas State University Advanced Design Team is in the process of researching and designing controls for the automation of the ECLSS for Space Station Freedom and beyond. The ECLSS for Freedom is composed of six subsystems. The temperature and humidity control (THC) subsystem maintains the cabin temperature and humidity at a comfortable level. The atmosphere control and supply (ACS) subsystem insures proper cabin pressure and partial pressures of oxygen and nitrogen. To protect the space station from fire damage, the fire detection and suppression (FDS) subsystem provides fire-sensing alarms and extinguishers. The waste management (WM) subsystem compacts solid wastes for return to Earth, and collects urine for water recovery. The atmosphere revitalization (AR) subsystem removes CO2 and other dangerous contaminants from the air. The water recovery and management (WRM) subsystem collects and filters condensate from the cabin to replenish potable water supplies, and processes urine and other waste waters to replenish hygiene water supplies. These subsystems are not fully automated at this time. Furthermore, the control of these subsystems is not presently integrated; they are largely independent of one another. A fully integrated and automated ECLSS would increase astronauts' productivity and contribute to their safety and comfort.

  3. Automation of closed environments in space for human comfort and safety

    NASA Technical Reports Server (NTRS)

    1990-01-01

    The Environmental Control and Life Support System (ECLSS) for the Space Station Freedom and future colonization of the Moon and Mars presents new challenges for present technologies. Current plans call for a crew of 8 to live in a safe, shirt-sleeve environment for 90 days without ground support. Because of these requirements, all life support systems must be self-sufficient and reliable. The ECLSS is composed of six subsystems. The temperature and humidity control (THC) subsystem maintains the cabin temperature and humidity at a comfortable level. The atmosphere control and supply (ACS) subsystem insures proper cabin pressure and partial pressures of oxygen and nitrogen. To protect the space station from fire damage, the fire detection and suppression (FDS) subsystem provides fire sensing alarms and extinguishers. The waste management (WM) subsystem compacts solid wastes for return to Earth, and collects urine for water recovery. Because it is impractical, if not impossible, to supply the station with enough fresh air and water for the duration of the space station's extended mission, these elements are recycled. The atmosphere revitalization (AR) subsystem removes CO2 and other dangerous contaminants from the air. The water recovery and management (WRM) subsystem collects and filters condensate from the cabin to replenish potable water supplies, and processes urine and other waste waters to replenish hygiene water supplies. These subsystems are not fully automated at this time. Furthermore, the control of these subsystems is not presently integrated; they are largely independent of one another. A fully integrated and automated ECLSS would increase astronauts' productivity and contribute to their safety and comfort. The Kansas State University Advanced Design Team is in the process of researching and designing controls for the automation of the ECLSS for Space Station Freedom and beyond. The approach chosen to solve this problem is to divide the design into three

  4. The Environments of Obscured Quasars

    NASA Astrophysics Data System (ADS)

    Jones, Kristen M.; Lacy, Mark; Nielsen, Danielle

    2016-01-01

    Supermassive Black Hole (SMBH) feedback is prescribed for driving the high-end shape of the galaxy luminosity function, clearing the circumnuclear environment during the end stages of mergers, and eventually turning off its own accretion. Yet the dominant processes and characteristics of active galactic nuclei are indistinct. Chief among this confusion is how significant the role of dust is in each galaxy. Orientation of the dusty torus is attributed to causing the differences between Sy1 and Sy2, but whether obscured quasars are found in particularly dusty host galaxies, if they exist at a different stage in the merger process (early on, before the dust is blown out), or if they are merely oriented differently than optical quasars is not yet so well distinguished. With obscured quasars now observed to make up 50% or greater of the population of quasars, the question of what causes obscuration becomes vital to address. With this in mind, I study matched samples of obscured and unobscured quasars to characterize their environments, with the intent of addressing what contribution environment has to obscuration levels. I investigate the megaparsec-scale environments of SIRTF Wide-field Infra-Red Extragalactic Survey (SWIRE) quasars at z ˜ 1-3 by cross-correlating the sample with 3.8 million galaxies from the Spitzer Extragalactic Representative Volume Survey (SERVS). Optically obscured quasars are compared to a control sample of optically-bright quasars via selection in the mid-infrared. Environments were observed at 3.6 and 4.5 μm to a depth of ≈ 2 μJy (AB = 23.1). Recent work has found diverse results in such studies, with dependence of environmental richness on both redshift and level of obscuration. I find that, within reasonable error, on average there is no distinct difference between the level of clustering for obscured and normal quasars, and that there is no dependence on redshift of this result within the range of 1.3 < z < 2.5. I compare our results

  5. Bayesian High-redshift Quasar Classification from Optical and Mid-IR Photometry

    NASA Astrophysics Data System (ADS)

    Richards, Gordon T.; Myers, Adam D.; Peters, Christina M.; Krawczyk, Coleman M.; Chase, Greg; Ross, Nicholas P.; Fan, Xiaohui; Jiang, Linhua; Lacy, Mark; McGreer, Ian D.; Trump, Jonathan R.; Riegel, Ryan N.

    2015-08-01

    We identify 885,503 type 1 quasar candidates to i≲ 22 using the combination of optical and mid-IR photometry. Optical photometry is taken from the Sloan Digital Sky Survey-III: Baryon Oscillation Spectroscopic Survey (SDSS-III/BOSS), while mid-IR photometry comes from a combination of data from the Wide-field Infrared Survey Explorer (WISE) “AllWISE” data release and several large-area Spitzer Space Telescope fields. Selection is based on a Bayesian kernel density algorithm with a training sample of 157,701 spectroscopically confirmed type 1 quasars with both optical and mid-IR data. Of the quasar candidates, 733,713 lack spectroscopic confirmation (and 305,623 are objects that we have not previously classified as photometric quasar candidates). These candidates include 7874 objects targeted as high-probability potential quasars with 3.5\\lt z\\lt 5 (of which 6779 are new photometric candidates). Our algorithm is more complete to z\\gt 3.5 than the traditional mid-IR selection “wedges” and to 2.2\\lt z\\lt 3.5 quasars than the SDSS-III/BOSS project. Number counts and luminosity function analysis suggest that the resulting catalog is relatively complete to known quasars and is identifying new high-z quasars at z\\gt 3. This catalog paves the way for luminosity-dependent clustering investigations of large numbers of faint, high-redshift quasars and for further machine-learning quasar selection using Spitzer and WISE data combined with other large-area optical imaging surveys.

  6. Characterizing Quasar Outflows II: The Incidence of the Highest Velocity Outflows

    NASA Astrophysics Data System (ADS)

    Stark, Michele A.; Ganguly, R.; Christenson, D. H.; Richmond, J. M.; Derseweh, J. A.; Robbins, J. M.; Townsend, S. L.

    2012-05-01

    Galaxy evolution models have shown that quasars are a crucial ingredient in the evolution of massive galaxies. Outflows play a key role in the story of quasars and their host galaxies, by helping regulate the accretion process, the star-formation rate and mass of the host galaxy (i.e., feedback). The prescription for modeling outflows as a contributor to feedback requires knowledge of the outflow velocity, geometry, and column density. In particular, we need to understand how these depend on physical parameters and how much is determined stochastically (and with what distribution). For this purpose, we are examining a sample of 11000 z=1.7-2.0 quasars from the Sloan Digital Sky Survey. This redshift range permits the following from the SDSS spectra: (1) separation of objects that do and do not exhibit outflows; (2) classification/measurement of outflow properties (ionization, velocity, velocity width); and (3) measurements of UV emission line and continuum parameters. In an accompanying poster, we subjectively divide these quasars into four categories (broad absorption-line quasars, associated absorption-line quasars, reddened quasars, and unabsorbed/unreddened quasars). This subjective scheme is limited with regard to classifying narrow absorption-line systems (NALs). With single epoch, low dispersion SDSS spectra, we cannot distinguish between cosmologically intervening NALs, and intrinsic NALs that appear at large velocity offsets. In this poster, we tackle this uncertainty statistically by considering the incidence of both CIV and MgII NALs as a function of velocity, and how this distribution changes with quasar properties. We expect that absorption by intervening structures should not vary with quasar property. Other accompanying posters add photometry from rest-frame X-ray through the infrared (WISE) to complete the SED, which we utilize in these efforts. This material is based upon work supported by the National Aeronautics and Space Administration under

  7. Quantum field theory in spaces with closed time-like curves

    SciTech Connect

    Boulware, D.G.

    1992-12-31

    Gott spacetime has closed timelike curves, but no locally anomalous stress-energy. A complete orthonormal set of eigenfunctions of the wave operator is found in the special case of a spacetime in which the total deficit angle is 27{pi}. A scalar quantum field theory is constructed using these eigenfunctions. The resultant interacting quantum field theory is not unitary because the field operators can create real, on-shell, particles in the acausal region. These particles propagate for finite proper time accumulating an arbitrary phase before being annihilated at the same spacetime point as that at which they were created. As a result, the effective potential within the acausal region is complex, and probability is not conserved. The stress tensor of the scalar field is evaluated in the neighborhood of the Cauchy horizon; in the case of a sufficiently small Compton wavelength of the field, the stress tensor is regular and cannot prevent the formation of the Cauchy horizon.

  8. Quantum field theory in spaces with closed time-like curves

    NASA Astrophysics Data System (ADS)

    Boulware, D. G.

    Gott spacetime has closed timelike curves, but no locally anomalous stress-energy. A complete orthonormal set of eigenfunctions of the wave operator is found in the special case of a spacetime in which the total deficit angle is 27(pi). A scalar quantum field theory is constructed using these eigenfunctions. The resultant interacting quantum field theory is not unitary because the field operators can create real, on-shell, particles in the acausal region. These particles propagate for finite proper time accumulating an arbitrary phase before being annihilated at the same spacetime point as that at which they were created. As a result, the effective potential within the acausal region is complex, and probability is not conserved. The stress tensor of the scalar field is evaluated in the neighborhood of the Cauchy horizon; in the case of a sufficiently small Compton wavelength of the field, the stress tensor is regular and cannot prevent the formation of the Cauchy horizon.

  9. Preliminary Human-in-the-Loop Assessment of Procedures for Very-Closely-Spaced Parallel Runways

    NASA Technical Reports Server (NTRS)

    Verma, Savita; Lozito, Sandra C.; Ballinger, Deborah S.; Trot, Greg; Hardy, Gordon H.; Panda, Ramesh C.; Lehmer, Ronald D.; Kozon, Thomas E.

    2010-01-01

    Demand in the future air transportation system concept is expected to double or triple by 2025 [1]. Increasing airport arrival rates will help meet the growing demand that could be met with additional runways but the expansion airports is met with environmental challenges for the surrounding communities when using current standards and procedures. Therefore, changes to airport operations can improve airport capacity without adding runways. Building additional runways between current ones, or moving them closer, is a potential solution to meeting the increasing demand, as addressed by the Terminal Area Capacity Enhancing Concept (TACEC). TACEC requires robust technologies and procedures that need to be tested such that operations are not compromised under instrument meteorological conditions. The reduction of runway spacing for independent simultaneous operations dramatically exacerbates the criticality of wake vortex incursion and the calculation of a safe and proper breakout maneuver. The study presented here developed guidelines for such operations by performing a real-time, human-in-the-loop simulation using precision navigation, autopilot-flown approaches, with the pilot monitoring aircraft spacing and the wake vortex safe zone during the approach.

  10. Ozone concentration in leaf intercellular air spaces is close to zero

    SciTech Connect

    Laisk, A.; Moldau, H. ); Kull, O. )

    1989-07-01

    Transpiration and ozone uptake rates were measured simultaneously in sunflower leaves at different stomatal openings and various ozone concentrations. Ozone uptake rates were proportional to the ozone concentration up to 1500 nanoliters per liter. The leaf gas phase diffusion resistance (stomatal plus boundary layer) to water vapor was calculated and converted to the resistance to ozone multiplying it by the theoretical ratio of diffusion coefficients for water vapor and ozone in air (1.67). The ozone concentration in intercellular air spaces calculated from the ozone uptake rate and diffusion resistance to ozone scattered around zero. The ozone concentration in intercellular air spaces was measured directly bu supplying ozone to the leaf from one side and measuring the equilibrium concentration above the other side, and it was found to be zero. The total leaf resistance to ozone was proportional to the gas phase resistance to water vapor with a coefficient of 1.68. It is concluded that ozone enters the leaf by diffusion through the stomata, and is rapidly decomposed in cell walls and plasmalemma.

  11. Space-Bounded Church-Turing Thesis and Computational Tractability of Closed Systems

    NASA Astrophysics Data System (ADS)

    Braverman, Mark; Schneider, Jonathan; Rojas, Cristóbal

    2015-08-01

    We report a new limitation on the ability of physical systems to perform computation—one that is based on generalizing the notion of memory, or storage space, available to the system to perform the computation. Roughly, we define memory as the maximal amount of information that the evolving system can carry from one instant to the next. We show that memory is a limiting factor in computation even in lieu of any time limitations on the evolving system—such as when considering its equilibrium regime. We call this limitation the space-bounded Church-Turing thesis (SBCT). The SBCT is supported by a simulation assertion (SA), which states that predicting the long-term behavior of bounded-memory systems is computationally tractable. In particular, one corollary of SA is an explicit bound on the computational hardness of the long-term behavior of a discrete-time finite-dimensional dynamical system that is affected by noise. We prove such a bound explicitly.

  12. High redshift quasars and high metallicities

    NASA Technical Reports Server (NTRS)

    Ferland, Gary J.

    1997-01-01

    A large-scale code called Cloudy was designed to simulate non-equilibrium plasmas and predict their spectra. The goal was to apply it to studies of galactic and extragalactic emission line objects in order to reliably deduce abundances and luminosities. Quasars are of particular interest because they are the most luminous objects in the universe and the highest redshift objects that can be observed spectroscopically, and their emission lines can reveal the composition of the interstellar medium (ISM) of the universe when it was well under a billion years old. The lines are produced by warm (approximately 10(sup 4)K) gas with moderate to low density (n less than or equal to 10(sup 12) cm(sup -3)). Cloudy has been extended to include approximately 10(sup 4) resonance lines from the 495 possible stages of ionization of the lightest 30 elements, an extension that required several steps. The charge transfer database was expanded to complete the needed reactions between hydrogen and the first four ions and fit all reactions with a common approximation. Radiative recombination rate coefficients were derived for recombination from all closed shells, where this process should dominate. Analytical fits to Opacity Project (OP) and other recent photoionization cross sections were produced. Finally, rescaled OP oscillator strengths were used to compile a complete set of data for 5971 resonance lines. The major discovery has been that high redshift quasars have very high metallicities and there is strong evidence that the quasar phenomenon is associated with the birth of massive elliptical galaxies.

  13. Toward a Prescription for Feedback from Quasar Outflows

    NASA Astrophysics Data System (ADS)

    Ganguly, Rajib; Bourjaily, M.; Munsell, J.; Brotherton, M. S.; Bhattacharjee, A.; Runnoe, J.; Charlton, J. C.; Eracleous, M.

    2011-01-01

    Models have shown that quasars are a crucial ingredient in the evolution of massive galaxies. Outflows play a key role in the story of quasars and their host galaxies, by helping regulate the accretion process, the star-formation rate and mass of the host galaxy (i.e., feedback). The prescription for modeling outflows as a contributor to feedback requires knowledge of the outflow velocity, distance, geometry, and column density. In particular, we need to understand how these depend on physical parameters and how much is determined stochastically (and with what distribution). For this purpose, we are examining a sample of 14000 z=1.7-2.0 quasars from the Sloan Digital Sky Survey. This redshift range permits the following from the SDSS spectra: (1) separation of objects that do and do not exhibit outflows; (2) classification/measurement of outflow properties (ionization, velocity, velocity width); and (3) estimates of the quasar black hole mass. To this, we are adding photometry from GALEX, 2MASS, and ROSAT in an effort to characterize more fully the quasar SEDs. ROSAT photometry provides estimates of the level of soft X-ray absorption, which helps regulate the velocity of outflows. GALEX photometry samples the extreme ultraviolet range where several high ionization species, that may be present in the outflows, absorb light. 2MASS photometry samples the rest-frame optical, where the effects of absorption and dust reddening are minimal, yield better estimates of the bolometric luminosity (hence, Eddington ratio). In this poster, we will present preliminary measurements of the amount of absorption in the soft X-ray and extreme ultraviolet bands as a function of both outflow properties and quasar physical properties. This material is based upon work supported by the National Aeronautics and Space Administration under Grant No. 09-ADP09-0016 issued through the Astrophysics Data Analysis Program.

  14. The Closed Aquatic System AquaHab® as part of a CELSS for Exploration, Space and Earth Application

    NASA Astrophysics Data System (ADS)

    Slenzka, Klaus

    AquaHab R is a small, self-sustaining closed microcosm, based on the former space shuttle payload C.E.B.A.S. (Closed Equilibrated Biological Aquatic System). AquaHab R contains on laboratory scale within 8 liters of water volume different groups of organisms (fish, snails, amphipods, plants). During the last years, it was developed to a system for the risk assessment of chemicals as well as an early warning tool for air and water contamination, major concerns during long-term stays in closed habitats for example on Earth's subsurface (deep sea) or later on the Moon or Mars. AquaHab R is now enhanced developed for exploratory missions having implemented an algae reactor system for biomass production etc.. During first tests, the transport of oxygen from the algae reactor into the AquaHab R was demonstrated successfully. In the common AquaHab R - bioreactor system, the different subsystems will serve for several tasks. In the AquaHab R - tank, the removal of waste water (mainly nutrients) as well as the production of some higher plants and fish as food source will be most beneficial; additionally the AquaHab R -tank is supporting astronauts psychological health recovery (home aquaria effect, taking care for pets). The beneficially output of the algae reactors will e.g. be the increased delivery of oxygen and metabolic products with application potential for humans (as e.g. vitamins, drug like acting substances) as well as being a food source in general and also the removal of carbon dioxide. Furthermore, specialized algae can also serve as early warning tool, as all the organisms in the AquaHab R do, or producing energy equivalents. The different subsystems will interact with each other to treat the products of humans being in the closed habitat in the most effective way. This new life support subsystem will be bioregenerative and sustainable in the meaning, that no material transport into the system is needed, and non-usable and maybe toxic end products won‘t be

  15. Automation of closed environments in space for human comfort and safety

    NASA Technical Reports Server (NTRS)

    1992-01-01

    This report culminates the work accomplished during a three year design project on the automation of an Environmental Control and Life Support System (ECLSS) suitable for space travel and colonization. The system would provide a comfortable living environment in space that is fully functional with limited human supervision. A completely automated ECLSS would increase astronaut productivity while contributing to their safety and comfort. The first section of this report, section 1.0, briefly explains the project, its goals, and the scheduling used by the team in meeting these goals. Section 2.0 presents an in-depth look at each of the component subsystems. Each subsection describes the mathematical modeling and computer simulation used to represent that portion of the system. The individual models have been integrated into a complete computer simulation of the CO2 removal process. In section 3.0, the two simulation control schemes are described. The classical control approach uses traditional methods to control the mechanical equipment. The expert control system uses fuzzy logic and artificial intelligence to control the system. By integrating the two control systems with the mathematical computer simulation, the effectiveness of the two schemes can be compared. The results are then used as proof of concept in considering new control schemes for the entire ECLSS. Section 4.0 covers the results and trends observed when the model was subjected to different test situations. These results provide insight into the operating procedures of the model and the different control schemes. The appendix, section 5.0, contains summaries of lectures presented during the past year, homework assignments, and the completed source code used for the computer simulation and control system.

  16. QUANTIFYING QUASAR VARIABILITY AS PART OF A GENERAL APPROACH TO CLASSIFYING CONTINUOUSLY VARYING SOURCES

    SciTech Connect

    Kozlowski, Szymon; Kochanek, Christopher S.; Udalski, A.; Wyrzykowski, L.; Soszynski, I.; Szymanski, M. K.; Kubiak, M.; Pietrzynski, G.; Szewczyk, O.; Ulaczyk, K.; Poleski, R. E-mail: ckochanek@astronomy.ohio-state.ed

    2010-01-10

    Robust fast methods to classify variable light curves in large sky surveys are becoming increasingly important. While it is relatively straightforward to identify common periodic stars and particular transient events (supernovae, novae, microlensing events), there is no equivalent for non-periodic continuously varying sources (quasars, aperiodic stellar variability). In this paper, we present a fast method for modeling and classifying such sources. We demonstrate the method using approx86, 000 variable sources from the OGLE-II survey of the LMC and approx2700 mid-IR-selected quasar candidates from the OGLE-III survey of the LMC and SMC. We discuss the location of common variability classes in the parameter space of the model. In particular, we show that quasars occupy a distinct region of variability space, providing a simple quantitative approach to the variability selection of quasars.

  17. Cosmic evolution of Quasar radio structure

    NASA Technical Reports Server (NTRS)

    Hutchings, J. B.; Neff, S. G.

    1991-01-01

    We discuss the results of a survey of Quasar radio structures over redshifts from 0.6 to 3.7. There are clear evolutionary trends in size and luminosity, which suggest that the duty cycle of individual Quasars has increased over cosmic time. This affects source count statistics and gives clues on the evolution of Quasar environments.

  18. Tunable Lattice Coupling of Multipole Plasmon Modes and Near-Field Enhancement in Closely Spaced Gold Nanorod Arrays

    PubMed Central

    Huang, Yu; Zhang, Xian; Ringe, Emilie; Hou, Mengjing; Ma, Lingwei; Zhang, Zhengjun

    2016-01-01

    Considering the nanogap and lattice effects, there is an attractive structure in plasmonics: closely spaced metallic nanoarrays. In this work, we demonstrate experimentally and theoretically the lattice coupling of multipole plasmon modes for closely spaced gold nanorod arrays, offering a new insight into the higher order cavity modes coupled with each other in the lattice. The resonances can be greatly tuned by changes in inter-rod gaps and nanorod heights while the influence of the nanorod diameter is relatively insignificant. Experimentally, pronounced suppressions of the reflectance are observed. Meanwhile, the near-field enhancement can be further enhanced, as demonstrated through surface enhanced Raman scattering (SERS). We then confirm the correlation between the near-field and far-field plasmonic responses, which is significantly important for maximizing the near-field enhancement at a specific excitation wavelength. This lattice coupling of multipole plasmon modes is of broad interest not only for SERS but also for other plasmonic applications, such as subwavelength imaging or metamaterials. PMID:26983501

  19. System Mass Variation and Entropy Generation in 100-kWe Closed-Brayton-Cycle Space Power Systems

    SciTech Connect

    Barrett, Michael J.; Reid, Bryan M.

    2004-02-04

    State-of-the-art closed-Brayton-cycle (CBC) space power systems were modeled to study performance trends in a trade space characteristic of interplanetary orbiters. For working-fluid molar masses of 48.6, 39.9 and 11.9 kg/kmol, peak system pressures of 1.38 and 3.0 MPa and compressor pressure ratios ranging from 1.6 to 2.4, total system masses were estimated. System mass increased as peak operating pressure increased for all compressor pressure ratios and molar mass values examined. Minimum mass point comparison between 72% He at 1.38 MPa peak and 94% He at 3.0 MPa peak showed an increase in system mass of 14%. Converter flow loop entropy generation rates were calculated for 1.38 and 3.0 MPa peak pressure cases. Physical system behavior was approximated using a pedigreed NASA-Glenn modeling code, Closed Cycle Engine Program (CCEP), which included realistic performance prediction for heat exchangers, radiators and turbomachinery.

  20. System Mass Variation and Entropy Generation in 100-kWe Closed-Brayton-Cycle Space Power Systems

    NASA Astrophysics Data System (ADS)

    Barrett, Michael J.; Reid, Bryan M.

    2004-02-01

    State-of-the-art closed-Brayton-cycle (CBC) space power systems were modeled to study performance trends in a trade space characteristic of interplanetary orbiters. For working-fluid molar masses of 48.6, 39.9 and 11.9 kg/kmol, peak system pressures of 1.38 and 3.0 MPa and compressor pressure ratios ranging from 1.6 to 2.4, total system masses were estimated. System mass increased as peak operating pressure increased for all compressor pressure ratios and molar mass values examined. Minimum mass point comparison between 72% He at 1.38 MPa peak and 94% He at 3.0 MPa peak showed an increase in system mass of 14%. Converter flow loop entropy generation rates were calculated for 1.38 and 3.0 MPa peak pressure cases. Physical system behavior was approximated using a pedigreed NASA-Glenn modeling code, Closed Cycle Engine Program (CCEP), which included realistic performance prediction for heat exchangers, radiators and turbomachinery.

  1. An echolocation model for range discrimination of multiple closely spaced objects: Transformation of spectrogram into the reflected intensity distribution

    NASA Astrophysics Data System (ADS)

    Matsuo, Ikuo; Kunugiyama, Kenji; Yano, Masafumi

    2004-02-01

    Using frequency-modulated echolocation, bats can discriminate the range of objects with an accuracy of less than a millimeter. However, bats' echolocation mechanism is not well understood. The delay separation of three or more closely spaced objects can be determined through analysis of the echo spectrum. However, delay times cannot be properly correlated with objects using only the echo spectrum because the sequence of delay separations cannot be determined without information on temporal changes in the interference pattern of the echoes. To illustrate this, Gaussian chirplets with a carrier frequency compatible with bat emission sweep rates were used. The delay time for object 1, T1, can be estimated from the echo spectrum around the onset time. The delay time for object 2 is obtained by adding T1 to the delay separation between objects 1 and 2 (extracted from the first appearance of interference effects). Further objects can be located in sequence by this same procedure. This model can determine delay times for three or more closely spaced objects with an accuracy of about 1 μs, when all the objects are located within 30 μs of delay separation. This model is applicable for the range discrimination of objects having different reflected intensities and in a noisy environment (0-dB signal-to-noise ratio) while the cross-correlation method is hard to apply to these problems.

  2. Tunable Lattice Coupling of Multipole Plasmon Modes and Near-Field Enhancement in Closely Spaced Gold Nanorod Arrays

    NASA Astrophysics Data System (ADS)

    Huang, Yu; Zhang, Xian; Ringe, Emilie; Hou, Mengjing; Ma, Lingwei; Zhang, Zhengjun

    2016-03-01

    Considering the nanogap and lattice effects, there is an attractive structure in plasmonics: closely spaced metallic nanoarrays. In this work, we demonstrate experimentally and theoretically the lattice coupling of multipole plasmon modes for closely spaced gold nanorod arrays, offering a new insight into the higher order cavity modes coupled with each other in the lattice. The resonances can be greatly tuned by changes in inter-rod gaps and nanorod heights while the influence of the nanorod diameter is relatively insignificant. Experimentally, pronounced suppressions of the reflectance are observed. Meanwhile, the near-field enhancement can be further enhanced, as demonstrated through surface enhanced Raman scattering (SERS). We then confirm the correlation between the near-field and far-field plasmonic responses, which is significantly important for maximizing the near-field enhancement at a specific excitation wavelength. This lattice coupling of multipole plasmon modes is of broad interest not only for SERS but also for other plasmonic applications, such as subwavelength imaging or metamaterials.

  3. System Mass Variation and Entropy Generation in 100-kWe Closed-Brayton-Cycle Space Power Systems

    NASA Technical Reports Server (NTRS)

    Barrett, Michael J.; Reid, Bryan M.

    2004-01-01

    State-of-the-art closed-Brayton-cycle (CBC) space power systems were modeled to study performance trends in a trade space characteristic of interplanetary orbiters. For working-fluid molar masses of 48.6, 39.9, and 11.9 kg/kmol, peak system pressures of 1.38 and 3.0 MPa and compressor pressure ratios ranging from 1.6 to 2.4, total system masses were estimated. System mass increased as peak operating pressure increased for all compressor pressure ratios and molar mass values examined. Minimum mass point comparison between 72 percent He at 1.38 MPa peak and 94 percent He at 3.0 MPa peak showed an increase in system mass of 14 percent. Converter flow loop entropy generation rates were calculated for 1.38 and 3.0 MPa peak pressure cases. Physical system behavior was approximated using a pedigreed NASA Glenn modeling code, Closed Cycle Engine Program (CCEP), which included realistic performance prediction for heat exchangers, radiators and turbomachinery.

  4. System Mass Variation and Entropy Generation in 100k We Closed-Brayton-Cycle Space Power Systems

    NASA Technical Reports Server (NTRS)

    Barrett, Michael J.; Reid, Bryan M.

    2004-01-01

    State-of-the-art closed-Brayton-cycle (CBC) space power systems were modeled to study performance trends in a trade space characteristic of interplanetary orbiters. For working-fluid molar masses of 48.6, 39.9, and 11.9 kg/kmol, peak system pressures of 1.38 and 3.0 MPa and compressor pressure ratios ranging from 1.6 to 2.4, total system masses were estimated. System mass increased as peak operating pressure increased for all compressor pressure ratios and molar mass values examined. Minimum mass point comparison between 72 percent He at 1.38 MPa peak and 94 percent He at 3.0 MPa peak showed an increase in system mass of 14 percent. Converter flow loop entropy generation rates were calculated for 1.38 and 3.0 MPa peak pressure cases. Physical system behavior was approximated using a pedigreed NASA Glenn modeling code, Closed Cycle Engine Program (CCEP), which included realistic performance prediction for heat exchangers, radiators and turbomachinery.

  5. Tunable Lattice Coupling of Multipole Plasmon Modes and Near-Field Enhancement in Closely Spaced Gold Nanorod Arrays.

    PubMed

    Huang, Yu; Zhang, Xian; Ringe, Emilie; Hou, Mengjing; Ma, Lingwei; Zhang, Zhengjun

    2016-01-01

    Considering the nanogap and lattice effects, there is an attractive structure in plasmonics: closely spaced metallic nanoarrays. In this work, we demonstrate experimentally and theoretically the lattice coupling of multipole plasmon modes for closely spaced gold nanorod arrays, offering a new insight into the higher order cavity modes coupled with each other in the lattice. The resonances can be greatly tuned by changes in inter-rod gaps and nanorod heights while the influence of the nanorod diameter is relatively insignificant. Experimentally, pronounced suppressions of the reflectance are observed. Meanwhile, the near-field enhancement can be further enhanced, as demonstrated through surface enhanced Raman scattering (SERS). We then confirm the correlation between the near-field and far-field plasmonic responses, which is significantly important for maximizing the near-field enhancement at a specific excitation wavelength. This lattice coupling of multipole plasmon modes is of broad interest not only for SERS but also for other plasmonic applications, such as subwavelength imaging or metamaterials. PMID:26983501

  6. Voltage breakdown between closely spaced electrodes over polymeric insulator surfaces in air

    NASA Astrophysics Data System (ADS)

    Gray, Eoin W.; Harrington, Daniel J.

    1982-01-01

    Voltage breakdowns of some narrow gap electrodes [2-10 mil (0.05-0.25 mm)] on polymeric insulator surfaces (epoxy-glass and triazine) have been examined over the pressure range from atmospheric pressure to 127 Torr and are shown to be an air breakdown modified by the presence of the insulator. Breakdown values as a function of the number of the breakdown and discharge energy level were also examined. In the worst case the breakdown voltage was observed to decrease by approximately 1300 V after about five successive breakdowns. The breakdown voltage between narrowly spaced metallic contacts on dielectric surfaces has been assumed to exhibit a Gaussian distribution. Non-Gaussian, bimodal distributions have been observed in the present work. These bimodal distributions, found on fine line epoxy-glass and triazine printed wiring boards, and attempts for explanation in terms of the flashover discharge initiating mechanisms, including the effects of ultraviolet radiation and a negative-ion flux on breakdown, are described. Negative ions appear to reduce the standard deviation but do not reduce the breakdown voltage. Ultraviolet radiation reduces both the standard deviation and the breakdown voltage. Increasing the conductor overlap distance (line length) reduced the breakdown voltage.

  7. a Glimpse Into the Time Before Quasars were Born

    NASA Astrophysics Data System (ADS)

    1996-11-01

    According to the widely accepted Big Bang theory, the first galaxies formed by gravitational accretion from slight irregularities in a primordial sea of matter, a process that required considerable time. Hence it would be expected that there would be a delay between the Big Bang and the appearance of the first galaxies. Or, looking back in time from the present, we would expect to find an epoch in the distant past when galaxies had not yet come into being. The space density of quasars An international group of astronomers 1 has now performed observations that seem to offer a glimpse into this very early period. They show that, when looking further and further into space and therefore successively farther back in time, the space density of quasars, after first increasing towards a maximum, then declines rapidly towards zero. Quasars are thought to be the nuclei of active galaxies , that is galaxies in the process of formation or undergoing violent interactions with other galaxies. Such objects are extremely bright and they can be seen across the Universe. That is the reason why quasars, rather than the much fainter normal galaxies , have been used to study the distant Universe. The possible existence of a rapid decline in the number of quasars as we look into the very distant Universe has been suspected for many years. Recent searches for distant quasars by means of optical telescopes observing their visible light have provided the strongest evidence. However, it has also been suggested that this decline could be merely due to obscuration caused by material in intervening galaxies - the distant Universe may be hidden from view. Observations of radio sources Radio waves are unaffected by dust, however, and many quasars are strong radio sources. Therefore, the group of astronomers from Germany, Great Britain, and the United States recently undertook a search for very distant quasars based on their radio emission. This involved measuring accurate positions of hundreds

  8. The Walk on Floor Eyes Closed Tandem Step Test as a Quantitative Measure of Ataxia After Space Flight

    NASA Technical Reports Server (NTRS)

    Fisher, E. A.; Reschke, M. F.; Kofman, I. S.; Cerisano, J. M.; Lawrence, E. L.; Peters, B. T.; Bloomberg, J. J.; Harm, D. L.

    2010-01-01

    INTRODUCTION Posture and locomotion are among the functions most affected by space flight. Postflight ataxia can be quantified easily by using the walk on the floor line test with the eyes closed (WOFEC). Data from a modified WOFEC were obtained as part of an ongoing interdisciplinary pre- and postflight study (Functional Task Test, FTT) designed to evaluate both postflight functional performance of astronauts and related physiological changes. METHODS Five astronauts with flight durations of 12 to 16 days participated in this study. Performance measurements were obtained in 2 preflight sessions, on landing day, and 1, 6, and 30 days after landing. The WOFEC test consisted of walking with the feet placed heel to toe in tandem, arms folded across the chest and eyes closed, for 10 steps. A trial was initiated after the eyes were closed and the front foot was aligned with the rear foot. The performance metric was the average percentage of correct steps completed over 3 trials. A step was not counted as correct if the crewmember sidestepped, opened eyes, or paused for more than 3 seconds between steps. Step accuracy was scored independently by 3 examiners. RESULTS Immediately after landing subjects seemed to be unaware of their foot position relative to their body or the floor. The percentage of correct steps was significantly decreased on landing day. Partial recovery was observed the next day, and full recovery to baseline on the sixth day post landing. CONCLUSION These data clearly demonstrate the sensorimotor challenges facing crewmembers after they return from space flight. Although this simple test is intended to complement the FTT battery of tests, it has some stand-alone value as it provides investigators with a means to quantify vestibular ataxia as well as provide instant feedback on postural stability without the use of complex test equipment.

  9. Closely Spaced Pregnancies Are Associated With Increased Odds of Autism in California Sibling Births

    PubMed Central

    Liu, Kayuet; Bearman, Peter S.

    2011-01-01

    OBJECTIVE: To determine whether the interpregnancy interval (IPI) is associated with the risk of autism in subsequent births. METHODS: Pairs of first- and second-born singleton full siblings were identified from all California births that occurred from 1992 to 2002 using birth records, and autism diagnoses were identified by using linked records of the California Department of Developmental Services. IPI was calculated as the time interval between birth dates minus the gestational age of the second sibling. In the primary analysis, logistic regression models were used to determine whether odds of autism in second-born children varied according to IPI. To address potential confounding by unmeasured family-level factors, a case-sibling control analysis determined whether affected sibling (first versus second) varied with IPI. RESULTS: An inverse association between IPI and odds of autism among 662 730 second-born children was observed. In particular, IPIs of <12, 12 to 23, and 24 to 35 months were associated with odds ratios (95% confidence intervals) for autism of 3.39 (3.00–3.82), 1.86 (1.65–2.10), and 1.26 (1.10–1.45) relative to IPIs of ≥36 months. The association was not mediated by preterm birth or low birth weight and persisted across categories of sociodemographic characteristics, with some attenuation in the oldest and youngest parents. Second-born children were at increased risk of autism relative to their firstborn siblings only in pairs with short IPIs. CONCLUSIONS: These results suggest that children born after shorter intervals between pregnancies are at increased risk of developing autism; the highest risk was associated with pregnancies spaced <1 year apart. PMID:21220394

  10. Heavily reddened type 1 quasars at z > 2 - I. Evidence for significant obscured black hole growth at the highest quasar luminosities

    NASA Astrophysics Data System (ADS)

    Banerji, Manda; Alaghband-Zadeh, S.; Hewett, Paul C.; McMahon, Richard G.

    2015-03-01

    We present a new population of z > 2 dust-reddened, type 1 quasars with 0.5 ≲ E(B - V) ≲ 1.5, selected using near-infrared (NIR) imaging data from the UKIDSS-LAS (Large Area Survey), ESO-VHS (European Southern Obseratory-VISTA Hemisphere Survey) and WISE surveys. NIR spectra obtained using the Very Large Telescope for 24 new objects bring our total sample of spectroscopically confirmed hyperluminous (>1013 L⊙), high-redshift dusty quasars to 38. There is no evidence for reddened quasars having significantly different Hα equivalent widths relative to unobscured quasars. The average black hole masses (˜109-1010 M⊙) and bolometric luminosities (˜1047 erg s-1) are comparable to the most luminous unobscured quasars at the same redshift, but with a tail extending to very high luminosities of ˜1048 erg s-1. 66 per cent of the reddened quasars are detected at >3σ at 22 μm by WISE. The average 6-μm rest-frame luminosity is log10(L6 μm/ erg s-1) = 47.1 ± 0.4, making the objects among the mid-infrared brightest active galactic nuclei (AGN) currently known. The extinction-corrected space density estimate now extends over three magnitudes (-30 < Mi < -27) and demonstrates that the reddened quasar luminosity function is significantly flatter than that of the unobscured quasar population at z = 2-3. At the brightest magnitudes, Mi ≲ -29, the space density of our dust-reddened population exceeds that of unobscured quasars. A model where the probability that a quasar becomes dust reddened increases at high luminosity is consistent with the observations and such a dependence could be explained by an increase in luminosity and extinction during AGN-fuelling phases. The properties of our obscured type 1 quasars are distinct from the heavily obscured, Compton-thick AGN that have been identified at much fainter luminosities and we conclude that they likely correspond to a brief evolutionary phase in massive galaxy formation.

  11. A Snapshot Survey for Gravitational Lenses among z>=4.0 Quasars. II. Constraints on the 4.0Quasar Population

    NASA Astrophysics Data System (ADS)

    Richards, Gordon T.; Haiman, Zoltán; Pindor, Bartosz; Strauss, Michael A.; Fan, Xiaohui; Eisenstein, Daniel; Schneider, Donald P.; Bahcall, Neta A.; Brinkmann, J.; Fukugita, Masataka

    2006-01-01

    We report on i-band snapshot observations of 157 Sloan Digital Sky Survey quasars at 4.0Space Telescope (HST) to search for evidence of gravitational lensing of these sources. None of the quasars appear to be strongly lensed and multiply imaged at the angular resolution (~0.1") and sensitivity of HST. The nondetection of strong lensing in these systems constrains the z=4-5 luminosity function to an intrinsic slope of β>-3.8 (3 σ), assuming a break in the quasar luminosity function at M*1450~-24.5. This constraint is considerably stronger than the limit of β>-4.63 obtained from the absence of lensing in four z>5.7 quasars. Such constraints are important to our understanding of the true space density of high-redshift quasars and the ionization state of the early universe. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program 9472.

  12. On the Triggering of Quasars During First Passage

    NASA Astrophysics Data System (ADS)

    da Silva, Robert

    2011-10-01

    Merger induced quasar {QSO} activity is commonly invoked as a principal mechanism responsible for the growth of central super-massive black holes {SMBHs} and concurrent evolution of their host galaxies. Despite the apparent successes of such models in reproducing global populations and distributions, fundamental questions surrounding the fueling of SMBHs remain untested. In particular, theoretical treatments predict that the the evolution of the BHs during a merger is determined by their host galaxy's bulge component. We will test this observationally by imaging 10 early-stage merging pairs of galaxies where one galaxy is in a quasar phase and the other is not. By selecting a sample of merging galaxies after first close passage but before final coalescence, we may study the early stages of the merger and precisely determine the properties of the progenitors. This allows a unique 1-to-1 comparison of the QSO-host and companion galaxy that cannot be attained with any other sample. In this manner, we will establish whether quasar triggering is sensitive to the host galaxy morphology. Analysis of the morphologies and stellar masses will also equip us to tackle other key questions related to quasar evolution and triggering. The proposed imaging will constrain the stellar masses of each galaxy to characterize the merger mass ratios that trigger QSO activity. Lastly, comparisons of the SMBH to the host bulge mass, at this intermediate stage, will offer new insights into the path SMBHs take on their way to the Magorrian relation.

  13. False periodicities in quasar time-domain surveys

    NASA Astrophysics Data System (ADS)

    Vaughan, S.; Uttley, P.; Markowitz, A. G.; Huppenkothen, D.; Middleton, M. J.; Alston, W. N.; Scargle, J. D.; Farr, W. M.

    2016-09-01

    There have recently been several reports of apparently periodic variations in the light curves of quasars, e.g. PG 1302-102 by Graham et al. Any quasar showing periodic oscillations in brightness would be a strong candidate to be a close binary supermassive black hole and, in turn, a candidate for gravitational wave studies. However, normal quasars - powered by accretion on to a single, supermassive black hole - usually show stochastic variability over a wide range of time-scales. It is therefore important to carefully assess the methods for identifying periodic candidates from among a population dominated by stochastic variability. Using a Bayesian analysis of the light curve of PG 1302-102, we find that a simple stochastic process is preferred over a sinusoidal variation. We then discuss some of the problems one encounters when searching for rare, strictly periodic signals among a large number of irregularly sampled, stochastic time series, and use simulations of quasar light curves to illustrate these points. From a few thousand simulations of steep spectrum (`red noise') stochastic processes, we find many simulations that display few-cycle periodicity like that seen in PG 1302-102. We emphasize the importance of calibrating the false positive rate when the number of targets in a search is very large.

  14. The dust emission of high-redshift quasars

    NASA Astrophysics Data System (ADS)

    Leipski, C.; Meisenheimer, K.

    2012-07-01

    The detection of powerful near-infrared emission in high redshift (z > 5) quasars demonstrates that very hot dust is present close to the active nucleus also in the very early universe. A number of high-redshift objects even show significant excess emission in the rest frame NIR over more local AGN spectral energy distribution (SED) templates. In order to test if this is a result of the very high luminosities or redshifts, we construct mean SEDs from the latest SDSS quasar catalogue in combination with MIR data from the WISE preliminary data release for several redshift and luminosity bins. Comparing these mean SEDs with a large sample of z > 5 quasars we could not identify any significant trends of the NIR spectral slope with luminosity or redshift in the regime 2.5 < z lesssim 6 and 1045 < νLν (1350Å) lesssim 1047 erg/s. In addition to the NIR regime, our combined Herschel and Spitzer photometry provides full infrared SED coverage of the same sample of z > 5 quasars. These observations reveal strong FIR emission (LFIR gtrsim 1013 Lodot) in seven objects, possibly indicating star-formation rates of several thousand solar masses per year. The FIR excess emission has unusally high temperatures (T~65K) which is in contrast to the temperature typically expected from studies at lower redshift (T~45K). These objects are currently being investigated in more detail.

  15. VSOP Monitoring of the Quasar 1928+738

    NASA Technical Reports Server (NTRS)

    Murphy, D. W.

    1999-01-01

    One limitation of the VSOP (VLBI Space Observatory Program) mission is that several famous superluminal sources such as 3C273 cannot be monitored with good uv-coverage throughout the lifetime of the VSOP Mission at regular intervals that are spaced closely enough to follow the evolution in the fine-scale source-structure. The reason for this is that the HALCA spacecraft cannot#observe sources outside certain restricted ranges of sun angle, defined to be the time variable angle between the source and the sun. However sources that lie within 10 degrees of the ecliptic poles can be observed throughout the year and observations are not restricted to narrow temporal windows. Furthermore, the best ground-based uv-coverages are obtained for circumpolar sources and consequently these will be the sources for which the maximum amount of space VLBI data will be obtained with a given ground array. We have began a VSOP monitoring campaign at 5 GHz on the relatively low redshift (z=0.3) superluminal quasar 1928+738 which is both a circumpolar source and lies 10 degrees away from the ecliptic pole. 1928+738 is in the S5 polar cap sample and has been well studied both on the arsecond-scale and mas-scale. 22 GHz observations have shown that the motion of the VLBI components in 1928+738 is inconsistent with simple linear expansion along a fixed position angle (PA) for all components. Indeed, 1928+738 was one of the first sources for which helical jet motion was proposed and it has been further proposed that a massive binary black hole (MBBH) system is responsible for the sinusoidal jet ridge line observed at 22 GHz over a S year period. our VSOP observations are designed to check this proposal.

  16. The Geometry of Quasar Outflows

    NASA Astrophysics Data System (ADS)

    Ganguly, Rajib

    2012-10-01

    Quasar outflows are important for understanding the accretion and growth processes of the central black hole, but also potentially play a role in feedback to the galaxy, halting star formation and infall of gas. A big uncertainty lies in the geometry and density of these outflows, especially as a function of ionization and velocity. We aim to tackle this using the archival COS M grating spectra of 266 quasars. We separate the geometry of outflows into two parts: the solid angle subtended around the black hole, and the distance of the outflow from the central engine. Large numbers of quasars with high resolution spectra are required for each aspect of this statistical investigation. First, we will determine which/how many absorption-line systems are intrinsic through both partial covering methods and statistical assessments. Second, we will consider the incidence of intrinsic absorbers as a function of quasar property {e.g., radio-loudness, SED shape, black hole mass, bolometric luminosity}. This will reveal what determines the solid angle. This can only be done at moderate redshifts where quasars with a larger range of properties are observable, and hence requires HST/COS. Third, we will use the wide range of diagnostic lines to constrain the physical conditions of the absorbers. We will target the CIII*1175 complex and apply photoionization models to constrain the densities and ionization parameters. This will provide the largest set yet of intrinsic absorbers with systematic distance constraints. In tandem with the solid angles, this work will inform models regarding the geometry of quasar outflows.

  17. Quasar Accretion Disks are Strongly Inhomogeneous

    NASA Astrophysics Data System (ADS)

    Dexter, Jason; Agol, Eric

    2011-01-01

    Active galactic nuclei have been observed to vary stochastically with 10%-20% rms amplitudes over a range of optical wavelengths where the emission arises in an accretion disk. Since the accretion disk is unlikely to vary coherently, local fluctuations may be significantly larger than the global rms variability. We investigate toy models of quasar accretion disks consisting of a number of regions, n, whose temperatures vary independently with an amplitude of σ T in dex. Models with large fluctuations (σ T = 0.35-0.50) in 102-103 independently fluctuating zones for every factor of two in radius can explain the observed discrepancy between thin accretion disk sizes inferred from microlensing events and optical luminosity while matching the observed optical variability. For the same range of σ T , inhomogeneous disk spectra provide excellent fits to the Hubble Space Telescope quasar composite without invoking global Compton scattering atmospheres to explain the high levels of observed UV emission. Simulated microlensing light curves for the Einstein cross from our time-varying toy models are well fit using a time-steady power-law temperature disk and produce magnification light curves that are consistent with current microlensing observations. Deviations due to the inhomogeneous, time-dependent disk structure should occur above the 1% level in the light curves, detectable in future microlensing observations with millimagnitude sensitivity.

  18. Incidence of strong Mg II absorbers towards different types of quasars

    NASA Astrophysics Data System (ADS)

    Joshi, Ravi; Chand, Hum; Gopal-Krishna

    2013-10-01

    We report the first comparative study of strong Mg II absorbers (Wr ≥ 1.0 Å) seen towards radio-loud quasars of core-dominated (CDQ) and lobe-dominated (LDQ) types and normal quasars (QSOs). The CDQ and LDQ samples were derived from the Sloan Digital Sky Survey Data Release 7 after excluding known `broad-absorption-line' quasars and blazars. The Mg II associated absorption systems having a velocity offset v < 5000 km s-1 from the systemic velocity of the background quasar were also excluded. Existing spectroscopic data for redshift-matched sightlines of 3975 CDQs and 1583 LDQs, covering an emission redshift range 0.39-4.87, were analysed and 864 strong Mg II absorbers were found, covering the redshift range 0.45-2.17. The conclusions reached using this well-defined large data set of strong Mg II absorbers are (i) the number density, dN/dz, towards CDQs shows a small, marginally significant excess (˜9 per cent at 1.5σ significance) over the estimate available for QSOs; (ii) in the redshift space, this difference is reflected in terms of a 1.6σ excess of dN/dz over the QSOs, within the narrow redshift interval 1.2-1.8; (iii) the dN/dβ distribution (with β = v/c) for CDQs shows a significant excess (at 3.75σ level) over the distribution found for a redshift- and luminosity-matched sample of QSOs, at β in the range 0.05-0.1. This leads us to infer that a significant fraction of strong Mg II absorption systems seen in this offset velocity range are probably associated with the CDQs and might be accelerated into the line of sight by their powerful jets and/or due to the accretion-disc outflows close to our direction. Support to this scenario comes from a consistency check in which we consider only the spectral range corresponding to β > 0.2. The computed redshift distribution for strong Mg II absorbers towards CDQs now shows excellent agreement with that known for QSOs, as indeed is expected for purely intervening absorption systems. Thus, it appears that for

  19. Origin of regularities in the redshift distributions of distant galaxies and quasars

    SciTech Connect

    Ozernoy, L.M.

    1990-01-01

    A model in which inhomogeneities originated during inflation and transformed eventually into density peaks with maximum wavelength equal to the horizon size at the decoupling epoch (z{sub dec} {approx} 10{sup 3}) would give at the present for very large scale structure a periodic distribution: 1n (1 + z) (approx) 0.04n + 0.04, n = 0,1,2,{hor ellipsis}. This formula in which the true phase is replaced by its characteristic value fits the data on redshift distribution of distant galaxies fairly well. Some relevant implications are discussed in the paper, such as difference between the constants of periodicity C {equivalent to} {Delta}1n (1 + z): C{sub G} for distant galaxies and C{sub Q} for quasars, and a recent finding that quasars close on the sky to low redshifted galaxies shot a higher concentration toward peaks in the quasar redshift distribution than do quasars in general. 17 refs.

  20. Early Star Formation and High-Redshift Quasars

    NASA Astrophysics Data System (ADS)

    Dietrich, Matthias; Peterson, B. M.

    2007-12-01

    We are investigating for a sample of about 30 high-redshift quasars, with redshifts up to z=6, the gas chemical metallicity based on emission line ratios and employing the FeII UV/MgII line ratio, we probe the differential metal enrichment timescale between iron and alpha-elements at these early epochs. The quasars show enhanced solar metallicities ( 5 times solar) in their broad emission-line region and no indication of a metallicity evolution up to redshifts z=6. The measured FeII UV/MgII ratios range from 3 to 5, typical for high redshift quasars, with a weighted mean of about 4. However, there is a weak tendency for a lower mean ratio at z>4.7. For the first time, we will compare the gas metallicity and the FeII UV/MgII ratio for high redshift quasars. In concert, the gas metallicity, the FeII UV/MgII ratio, and model-based estimated time scales for enriching the gas and building up the super-massive black holes suggest that a violent episode of star formation and the main growth of the black hole occur roughly contemporaneously beginning at redshifts z = 8 to 13. Support for this work was provided by NASA through grant HST-GO-10792 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

  1. PHOTOMETRIC REDSHIFTS AND QUASAR PROBABILITIES FROM A SINGLE, DATA-DRIVEN GENERATIVE MODEL

    SciTech Connect

    Bovy, Jo; Hogg, David W.; Weaver, Benjamin A.; Myers, Adam D.; Hennawi, Joseph F.; McMahon, Richard G.; Schiminovich, David; Sheldon, Erin S.; Brinkmann, Jon; Schneider, Donald P.

    2012-04-10

    We describe a technique for simultaneously classifying and estimating the redshift of quasars. It can separate quasars from stars in arbitrary redshift ranges, estimate full posterior distribution functions for the redshift, and naturally incorporate flux uncertainties, missing data, and multi-wavelength photometry. We build models of quasars in flux-redshift space by applying the extreme deconvolution technique to estimate the underlying density. By integrating this density over redshift, one can obtain quasar flux densities in different redshift ranges. This approach allows for efficient, consistent, and fast classification and photometric redshift estimation. This is achieved by combining the speed obtained by choosing simple analytical forms as the basis of our density model with the flexibility of non-parametric models through the use of many simple components with many parameters. We show that this technique is competitive with the best photometric quasar classification techniques-which are limited to fixed, broad redshift ranges and high signal-to-noise ratio data-and with the best photometric redshift techniques when applied to broadband optical data. We demonstrate that the inclusion of UV and NIR data significantly improves photometric quasar-star separation and essentially resolves all of the redshift degeneracies for quasars inherent to the ugriz filter system, even when included data have a low signal-to-noise ratio. For quasars spectroscopically confirmed by the SDSS 84% and 97% of the objects with Galaxy Evolution Explorer UV and UKIDSS NIR data have photometric redshifts within 0.1 and 0.3, respectively, of the spectroscopic redshift; this amounts to about a factor of three improvement over ugriz-only photometric redshifts. Our code to calculate quasar probabilities and redshift probability distributions is publicly available.

  2. Photometric redshifts and quasar probabilities from a single, data-driven generative model

    SciTech Connect

    Bovy, Jo; Myers, Adam D.; Hennawi, Joseph F.; Hogg, David W.; McMahon, Richard G.; Schiminovich, David; Sheldon, Erin S.; Brinkmann, Jon; Schneider, Donald P.; Weaver, Benjamin A.

    2012-03-20

    We describe a technique for simultaneously classifying and estimating the redshift of quasars. It can separate quasars from stars in arbitrary redshift ranges, estimate full posterior distribution functions for the redshift, and naturally incorporate flux uncertainties, missing data, and multi-wavelength photometry. We build models of quasars in flux-redshift space by applying the extreme deconvolution technique to estimate the underlying density. By integrating this density over redshift, one can obtain quasar flux densities in different redshift ranges. This approach allows for efficient, consistent, and fast classification and photometric redshift estimation. This is achieved by combining the speed obtained by choosing simple analytical forms as the basis of our density model with the flexibility of non-parametric models through the use of many simple components with many parameters. We show that this technique is competitive with the best photometric quasar classification techniques—which are limited to fixed, broad redshift ranges and high signal-to-noise ratio data—and with the best photometric redshift techniques when applied to broadband optical data. We demonstrate that the inclusion of UV and NIR data significantly improves photometric quasar-star separation and essentially resolves all of the redshift degeneracies for quasars inherent to the ugriz filter system, even when included data have a low signal-to-noise ratio. For quasars spectroscopically confirmed by the SDSS 84% and 97% of the objects with Galaxy Evolution Explorer UV and UKIDSS NIR data have photometric redshifts within 0.1 and 0.3, respectively, of the spectroscopic redshift; this amounts to about a factor of three improvement over ugriz-only photometric redshifts. Our code to calculate quasar probabilities and redshift probability distributions is publicly available.

  3. Relativistic Motion in Quasars

    NASA Astrophysics Data System (ADS)

    Cohen, M. H.

    1986-02-01

    This is a summary of an article which will appear in "Highlights of Modern Astrophysics" (Cohen, 1985). The majority of strong core-dominated radio sources show superluminal motion and rapid variations in flux density. Some of them also have X-rays which are weaker than the amount predicted by the inverse-Compton effect. All these characteristics can be explained by rela tivistic motion. The superluminal motion and the unusual rapidity of the variations are kinematic effects. The radiating source nearly keeps up with its own radiation, with a consequent reduction in time scales. The weak X-rays are an artifact introduced when the inverse-Compton cal culation is based on the spectrum measured in the terrestrial coordinate system. When allowance is made for motion towards the observer,the measurements give a lower limit to the Doppler factor of the moving source. The common model uses a narrow jet pointed at angle θ to the line of sight, and carrying luminous blobs moving at Lorentz factor y. This model can explain all the above effects, and also the common core-jet radio morphology. Application of the model gives values of y between 5 and 10, and values of θ less than 200. The Doppler effect boosts t e flux density of those jets which are pointed nearly at us. The strong sources we see must therefore form a small subset of a large population of sources most of which are misdi rected and weak. It is likely that the parent population consists of the "classical double" quasars. Nearly all of the superluminal sources have low surface brightness halos, which could be the outer double radio lobes seen end-on.

  4. Differential tolerance to biological and subjective effects of four closely spaced doses of N,N-dimethyltryptamine in humans.

    PubMed

    Strassman, R J; Qualls, C R; Berg, L M

    1996-05-01

    Tolerance of the behavioral effects of the short-acting, endogenous hallucinogen, N,N-dimethyltryptamine (DMT) is seen inconsistently in animals, and has not been produced in humans. The nature and time course of responses to repetitive, closely spaced administrations of an hallucinogenic dose of DMT were characterized. Thirteen experienced hallucinogen users received intravenous 0.3 mg/kg DMT fumarate, or saline placebo, four times, at 30 min intervals, on 2 separate days, in a randomized, double-blind, design. Tolerance to "psychedelic" subjective effects did not occur according to either clinical interview or Hallucinogen Rating Scale scores. Adrenocorticotropic hormone (ACTH), prolactin, cortisol, and heart rate responses decreased with repeated DMT administration, although blood pressure did not. These data demonstrate the unique properties of DMT relative to other hallucinogens and underscore the differential regulation of the multiple processes mediating the effects of DMT. PMID:8731519

  5. Low-Cost Growth of III-V Layers on Si Using Close-Spaced Vapor Transport

    SciTech Connect

    Boucher, Jason W.; Greenaway, Ann L.; Ritenour, Andrew J.; Davis, Allison L.; Bachman, Benjamin F.; Aloni, Shaul; Boettcher, Shannon W.

    2015-06-14

    Close-spaced vapor transport (CSVT) uses solid precursors to deposit material at high rates and with high precursor utilization. The use of solid precursors could significantly reduce the costs associated with III-V photovoltaics, particularly if growth on Si substrates can be demonstrated. We present preliminary results of the growth of GaAs1-xPx with x ≈ 0.3 and 0.6, showing that CSVT can be used to produce III-V-V’ alloys with band gaps suitable for tandem devices. Additionally, we have grown GaAs on Si by first thermally depositing films of Ge and subsequently depositing GaAs by CSVT. Patterning the Ge into islands prevents cracking due to thermal mismatch and is useful for potential tandem structures.

  6. The role of oxygen in CdS/CdTe solar cells deposited by close-spaced sublimation

    SciTech Connect

    Rose, D.H.; Levi, D.H.; Matson, R.J.

    1996-05-01

    The presence of oxygen during close-spaced sublimation (CSS) of CdTe has been previously reported to be essential for high-efficiency CdS/CdTe solar cells because it increases the acceptor density in the absorber. The authors find that the presence of oxygen during CSS increases the nucleation site density of CdTe, thus decreasing pinhole density and grain size. Photoluminescence showed that oxygen decreases material quality in the bulk of the CdTe film, but positively impacts the critical CdS/CdTe interface. Through device characterization the authors were unable to verify an increase in acceptor density with increased oxygen. These results, along with the achievement of high-efficiency cells (13% AM1.5) without the use of oxygen, led the authors to conclude that the use of oxygen during CSS deposition of CdTe can be useful but is not essential.

  7. Heat transfer from combustion gases to a single row of closely spaced tubes in a swirl crossflow Stirling engine heater

    NASA Technical Reports Server (NTRS)

    Bankston, C. P.; Back, L. H.

    1982-01-01

    This paper describes an experimental program to determine the heat-transfer characteristics of a combustor and heat-exchanger system in a hybrid solar receiver which utilizes a Stirling engine. The system consists of a swirl combustor with a crossflow heat exchanger composed of a single row of 48 closely spaced curved tubes. In the present study, heat-transfer characteristics of the combustor/heat-exchanger system without a Stirling engine have been studied over a range of operating conditions and output levels using water as the working fluid. Nondimensional heat-transfer coefficients based on total heat transfer have been obtained and are compared with available literature data. The results show significantly enhanced heat transfer for the present geometry and test conditions. Also, heat transfer along the length of the tubes is found to vary, the effect depending upon test condition.

  8. Epitaxial Growth of High-Resistivity CdTe Thick Films Grown Using a Modified Close Space Sublimation Method

    NASA Astrophysics Data System (ADS)

    Jiang, Quanzhong; Brinkman, Andy W.; Veeramani, Perumal; Sellin, Paul. J.

    2010-02-01

    This paper reports the growth of high-resistivity CdTe thick epitaxial films of single crystal nature using a modified close space sublimation method (MCSS) in a Te-rich environment. We propose that the high Te2 partial pressure results in an increased concentration of TeCd antisites acting as deep donors to produce the high-resistivity CdTe, as well as improved quality of thick films. This is in agreement with the deep-donor model introduced by Fiderele et al. [Cryst. Res. Technol. 38 (2003) 588]. The thick films have a µeτe value in the order 10-4 cm2 V-1 and as expected, the TeCd antisites appeared not to act as electron traps.

  9. A three-dimensional phase space dynamical model of the Earth{close_quote}s radiation belt

    SciTech Connect

    Boscher, D.M.; Beutier, T.; Bourdarie, S.

    1996-07-01

    A three dimensional phase space model of the Earth{close_quote}s radiation belt is presented. We have taken into account the magnetic and electric radial diffusions, the pitch angle diffusions due to Coulomb interactions and interactions with the plasmaspheric hiss, and the Coulomb drag. First, a steady state of the belt is presented. Two main maxima are obtained, corresponding to the inner and outer parts of the belt. Then, we have modelled a simple injection at the external boundary. The particle transport seems like what was measured aboard satellites. A high energy particle loss is found, by comparing the model results and the measurements. It remains to be explained. {copyright} {ital 1996 American Institute of Physics.}

  10. Mid-infrared luminous quasars in the GOODS-Herschel fields: a large population of heavily obscured, Compton-thick quasars at z ≈ 2

    NASA Astrophysics Data System (ADS)

    Del Moro, A.; Alexander, D. M.; Bauer, F. E.; Daddi, E.; Kocevski, D. D.; McIntosh, D. H.; Stanley, F.; Brandt, W. N.; Elbaz, D.; Harrison, C. M.; Luo, B.; Mullaney, J. R.; Xue, Y. Q.

    2016-02-01

    We present the infrared (IR) and X-ray properties of a sample of 33 mid-IR luminous quasars (νL6 μm ≥ 6 × 1044 erg s-1) at redshift z ≈ 1-3, identified through detailed spectral energy distribution analyses of distant star-forming galaxies, using the deepest IR data from Spitzer and Herschel in the GOODS-Herschel fields. The aim is to constrain the fraction of obscured, and Compton-thick (CT, NH > 1.5 × 1024 cm-2) quasars at the peak era of nuclear and star formation activities. Despite being very bright in the mid-IR band, ≈30 per cent of these quasars are not detected in the extremely deep 2 and 4 Ms Chandra X-ray data available in these fields. X-ray spectral analysis of the detected sources reveals that the majority (≈67 per cent) are obscured by column densities NH > 1022 cm-2; this fraction reaches ≈80 per cent when including the X-ray-undetected sources (9 out of 33), which are likely to be the most heavily obscured, CT quasars. We constrain the fraction of CT quasars in our sample to be ≈24-48 per cent, and their space density to be Φ = (6.7 ± 2.2) × 10-6 Mpc-3. From the investigation of the quasar host galaxies in terms of star formation rates (SFRs) and morphological distortions, as a sign of galaxy mergers/interactions, we do not find any direct relation between SFRs and quasar luminosity or X-ray obscuration. On the other hand, there is tentative evidence that the most heavily obscured quasars have, on average, more disturbed morphologies than the unobscured/moderately obscured quasar hosts, which preferentially live in undisturbed systems. However, the fraction of quasars with disturbed morphology amongst the whole sample is ≈40 per cent, suggesting that galaxy mergers are not the main fuelling mechanism of quasars at z ≈ 2.

  11. ZFP57 recognizes multiple and closely spaced sequence motif variants to maintain repressive epigenetic marks in mouse embryonic stem cells

    PubMed Central

    Anvar, Zahra; Cammisa, Marco; Riso, Vincenzo; Baglivo, Ilaria; Kukreja, Harpreet; Sparago, Angela; Girardot, Michael; Lad, Shraddha; De Feis, Italia; Cerrato, Flavia; Angelini, Claudia; Feil, Robert; Pedone, Paolo V.; Grimaldi, Giovanna; Riccio, Andrea

    2016-01-01

    Imprinting Control Regions (ICRs) need to maintain their parental allele-specific DNA methylation during early embryogenesis despite genome-wide demethylation and subsequent de novo methylation. ZFP57 and KAP1 are both required for maintaining the repressive DNA methylation and H3-lysine-9-trimethylation (H3K9me3) at ICRs. In vitro, ZFP57 binds a specific hexanucleotide motif that is enriched at its genomic binding sites. We now demonstrate in mouse embryonic stem cells (ESCs) that SNPs disrupting closely-spaced hexanucleotide motifs are associated with lack of ZFP57 binding and H3K9me3 enrichment. Through a transgenic approach in mouse ESCs, we further demonstrate that an ICR fragment containing three ZFP57 motif sequences recapitulates the original methylated or unmethylated status when integrated into the genome at an ectopic position. Mutation of Zfp57 or the hexanucleotide motifs led to loss of ZFP57 binding and DNA methylation of the transgene. Finally, we identified a sequence variant of the hexanucleotide motif that interacts with ZFP57 both in vivo and in vitro. The presence of multiple and closely located copies of ZFP57 motif variants emerges as a distinct characteristic that is required for the faithful maintenance of repressive epigenetic marks at ICRs and other ZFP57 binding sites. PMID:26481358

  12. Dynamics and adaptive control of a dual-arm space robot with closed-loop constraints and uncertain inertial parameters

    NASA Astrophysics Data System (ADS)

    Jia, Ying-Hong; Hu, Quan; Xu, Shi-Jie

    2014-02-01

    A dynamics-based adaptive control approach is proposed for a planar dual-arm space robot in the presence of closed-loop constraints and uncertain inertial parameters of the payload. The controller is capable of controlling the position and attitude of both the satellite base and the payload grasped by the manipulator end effectors. The equations of motion in reduced-order form for the constrained system are derived by incorporating the constraint equations in terms of accelerations into Kane's equations of the unconstrained system. Model analysis shows that the resulting equations perfectly meet the requirement of adaptive controller design. Consequently, by using an indirect approach, an adaptive control scheme is proposed to accomplish position/attitude trajectory tracking control with the uncertain parameters being estimated on-line. The actuator redundancy due to the closed-loop constraints is utilized to minimize a weighted norm of the joint torques. Global asymptotic stability is proven by using Lyapunov's method, and simulation results are also presented to demonstrate the effectiveness of the proposed approach. [Figure not available: see fulltext.

  13. Atlas of quasar energy distributions

    NASA Technical Reports Server (NTRS)

    Elvis, Martin; Wilkes, Belinda J.; Mcdowell, Jonathan C.; Green, Richard F.; Bechtold, Jill; Willner, S. P.; Oey, M. S.; Polomski, Elisha; Cutri, Roc

    1994-01-01

    We present an atlas of the spectral energy distributions (SEDs) of normal, nonblazar, quasars over the whole available range (radio to 10 keV X-rays) of the electromagnetic spectrum. The primary (UVSX) sample includes 47 quasars for which the spectral energy distributions include X-ray spectral indices and UV data. Of these, 29 are radio quiet, and 18 are radio loud. The SEDs are presented both in figures and in tabular form, with additional tabular material published on CD-ROM. Previously unpublished observational data for a second set of quasars excluded from the primary sample are also tabulated. The effects of host galaxy starlight contamination and foreground extinction on the UVSX sample are considered and the sample is used to investigate the range of SED properties. Of course, the properties we derive are influenced strongly by the selection effects induced by quasar discovery techniques. We derive the mean energy distribution (MED) for radio-loud and radio-quiet objects and present the bolometric corrections derived from it. We note, however, that the dispersion about this mean is large (approximately one decade for both the infrared and ultraviolet components when the MED is normalized at the near-infrared inflection). At least part of the dispersion in the ultraviolet may be due to time variability, but this is unlikely to be important in the infrared. The existence of such a large dispersion indicates that the MED reflects only some of the properties of quasars and so should be used only with caution.

  14. Discovery of three z > 6.5 quasars in the VISTA kilo-degree infrared galaxy (VIKING) survey

    SciTech Connect

    Venemans, B. P.; Findlay, J. R.; Sutherland, W. J.; De Rosa, G.; McMahon, R. G.; González-Solares, E. A.; Lewis, J. R.; Simcoe, R.; Kuijken, K.

    2013-12-10

    Studying quasars at the highest redshifts can constrain models of galaxy and black hole formation, and it also probes the intergalactic medium in the early universe. Optical surveys have to date discovered more than 60 quasars up to z ≅ 6.4, a limit set by the use of the z-band and CCD detectors. Only one z ≳ 6.4 quasar has been discovered, namely the z = 7.08 quasar ULAS J1120+0641, using near-infrared imaging. Here we report the discovery of three new z ≳ 6.4 quasars in 332 deg{sup 2} of the Visible and Infrared Survey Telescope for Astronomy Kilo-degree Infrared Galaxy (VIKING) survey, thus extending the number from 1 to 4. The newly discovered quasars have redshifts of z = 6.60, 6.75, and 6.89. The absolute magnitudes are between –26.0 and –25.5, 0.6-1.1 mag fainter than ULAS J1120+0641. Near-infrared spectroscopy revealed the Mg II emission line in all three objects. The quasars are powered by black holes with masses of ∼(1-2) × 10{sup 9} M {sub ☉}. In our probed redshift range of 6.44 < z < 7.44 we can set a lower limit on the space density of supermassive black holes of ρ(M {sub BH} > 10{sup 9} M {sub ☉}) > 1.1 × 10{sup –9} Mpc{sup –3}. The discovery of three quasars in our survey area is consistent with the z = 6 quasar luminosity function when extrapolated to z ∼ 7. We do not find evidence for a steeper decline in the space density of quasars with increasing redshift from z = 6 to z = 7.

  15. A SIMPLE MODEL FOR QUASAR DEMOGRAPHICS

    SciTech Connect

    Conroy, Charlie; White, Martin

    2013-01-10

    We present a simple model for the relationship between quasars, galaxies, and dark matter halos from 0.5 < z < 6. In the model, black hole (BH) mass is linearly related to galaxy mass, and galaxies are connected to dark matter halos via empirically constrained relations. A simple 'scattered' light bulb model for quasars is adopted, wherein BHs shine at a fixed fraction of the Eddington luminosity during accretion episodes, and Eddington ratios are drawn from a lognormal distribution that is redshift independent. This model has two free, physically meaningful parameters at each redshift: the normalization of the M {sub BH}-M {sub gal} relation and the quasar duty cycle; these parameters are fit to the observed quasar luminosity function (LF) over the interval 0.5 < z < 6. This simple model provides an excellent fit to the LF at all epochs and also successfully predicts the observed projected two-point correlation of quasars from 0.5 < z < 2.5. It is significant that a single quasar duty cycle at each redshift is capable of reproducing the extant observations. The data are therefore consistent with a scenario wherein quasars are equally likely to exist in galaxies, and therefore dark matter halos, over a wide range in masses. The knee in the quasar LF is a reflection of the knee in the stellar-mass-halo-mass relation. Future constraints on the quasar LF and quasar clustering at high redshift will provide strong constraints on the model. In the model, the autocorrelation function of quasars becomes a strong function of luminosity only at the very highest luminosities and will be difficult to observe because such quasars are so rare. Cross-correlation techniques may provide useful constraints on the bias of such rare objects. The simplicity of the model allows for rapid generation of quasar mock catalogs from N-body simulations that match the observed LF and clustering to high redshift.

  16. The diversity of quasars unified by accretion and orientation.

    PubMed

    Shen, Yue; Ho, Luis C

    2014-09-11

    Quasars are rapidly accreting supermassive black holes at the centres of massive galaxies. They display a broad range of properties across all wavelengths, reflecting the diversity in the physical conditions of the regions close to the central engine. These properties, however, are not random, but form well-defined trends. The dominant trend is known as 'Eigenvector 1', in which many properties correlate with the strength of optical iron and [O III] emission. The main physical driver of Eigenvector 1 has long been suspected to be the quasar luminosity normalized by the mass of the hole (the 'Eddington ratio'), which is an important parameter of the black hole accretion process. But a definitive proof has been missing. Here we report an analysis of archival data that reveals that the Eddington ratio indeed drives Eigenvector 1. We also find that orientation plays a significant role in determining the observed kinematics of the gas in the broad-line region, implying a flattened, disk-like geometry for the fast-moving clouds close to the black hole. Our results show that most of the diversity of quasar phenomenology can be unified using two simple quantities: Eddington ratio and orientation. PMID:25209799

  17. The diversity of quasars unified by accretion and orientation

    NASA Astrophysics Data System (ADS)

    Shen, Yue; Ho, Luis C.

    2014-09-01

    Quasars are rapidly accreting supermassive black holes at the centres of massive galaxies. They display a broad range of properties across all wavelengths, reflecting the diversity in the physical conditions of the regions close to the central engine. These properties, however, are not random, but form well-defined trends. The dominant trend is known as `Eigenvector 1', in which many properties correlate with the strength of optical iron and [O III] emission. The main physical driver of Eigenvector 1 has long been suspected to be the quasar luminosity normalized by the mass of the hole (the `Eddington ratio'), which is an important parameter of the black hole accretion process. But a definitive proof has been missing. Here we report an analysis of archival data that reveals that the Eddington ratio indeed drives Eigenvector 1. We also find that orientation plays a significant role in determining the observed kinematics of the gas in the broad-line region, implying a flattened, disk-like geometry for the fast-moving clouds close to the black hole. Our results show that most of the diversity of quasar phenomenology can be unified using two simple quantities: Eddington ratio and orientation.

  18. Discovery of a narrow line quasar

    NASA Technical Reports Server (NTRS)

    Stocke, J.; Liebert, J.; Maccacaro, T.; Griffiths, R. E.; Steiner, J. E.

    1982-01-01

    A stellar object is reported which, while having X-ray and optical luminosities typical of quasars, has narrow permitted and forbidden emission lines over the observed spectral range. The narrow-line spectrum is high-excitation, the Balmer lines seem to be recombinational, and a redder optical spectrum than that of most quasars is exhibited, despite detection as a weak radio source. The object does not conform to the relationships between H-beta parameters and X-ray flux previously claimed for a large sample of the active galactic nuclei. Because reddish quasars with narrow lines, such as the object identified, may not be found by the standard techniques for the discovery of quasars, the object may be a prototype of a new class of quasars analogous to high-luminosity Seyfert type 2 galaxies. It is suggested that these objects cannot comprise more than 10% of all quasars.

  19. A Hubble Diagram for Quasars

    NASA Astrophysics Data System (ADS)

    Risaliti, G.; Lusso, E.

    2015-12-01

    We present a new method to test the ΛCDM cosmological model and to estimate cosmological parameters based on the nonlinear relation between the ultraviolet and X-ray luminosities of quasars. We built a data set of 1138 quasars by merging several samples from the literature with X-ray measurements at 2 keV and SDSS photometry, which was used to estimate the extinction-corrected 2500 Å flux. We obtained three main results: (1) we checked the nonlinear relation between X-ray and UV luminosities in small redshift bins up to z˜ 6, confirming that the relation holds at all redshifts with the same slope; (2) we built a Hubble diagram for quasars up to z˜ 6, which is well matched to that of supernovae in the common z = 0-1.4 redshift interval and extends the test of the cosmological model up to z˜ 6; and (3) we showed that this nonlinear relation is a powerful tool for estimating cosmological parameters. Using the present data and assuming a ΛCDM model, we obtain {{{Ω }}}M = 0.22{}-0.08+0.10 and {{{Ω }}}{{Λ }} = 0.92{}-0.30+0.18 ({{{Ω }}}M = 0.28 ± 0.04 and {{{Ω }}}{{Λ }} = 0.73 +/- 0.08 from a joint quasar-SNe fit). Much more precise measurements will be achieved with future surveys. A few thousand SDSS quasars already have serendipitous X-ray observations from Chandra or XMM-Newton, and at least 100,000 quasars with UV and X-ray data will be made available by the extended ROentgen Survey with an Imaging Telescope Array all-sky survey in a few years. The Euclid, Large Synoptic Survey Telescope, and Advanced Telescope for High ENergy Astrophysics surveys will further increase the sample size to at least several hundred thousand. Our simulations show that these samples will provide tight constraints on the cosmological parameters and will allow us to test for possible deviations from the standard model with higher precision than is possible today.

  20. Discovery of low-redshift X-ray selected quasars - New clues to the QSO phenomenon

    NASA Technical Reports Server (NTRS)

    Grindlay, J. E.; Forman, W. R.; Steiner, J. E.; Canizares, C. R.; Mcclintock, J. E.

    1980-01-01

    The identification of six X-ray sources discovered by the Einstein Observatory with X-ray quasars is reported, and the properties of these X-ray selected quasars are discussed. The four high-latitude fields of 1 sq deg each in which the Einstein imaging proportional counter detected serendipitous X-ray sources at intermediate exposures of 10,000 sec were observed by 4-m and 1.5-m telescopes, and optical sources with uv excesses and emission line spectra typical of many low-redshift quasars and Seyfert 1 galaxies were found within the 1-arcsec error boxes of the X-ray sources. All six quasars identified were found to be radio quiet, with low redshift and relatively faint optical magnitudes, and to be similar in space density, colors and magnitude versus redshift relation to an optically selected sample at the same mean magnitude. X-ray luminosity was found to be well correlated with both continuum and broad-line emission luminosities for the known radio-quiet quasars and Seyfert 1 galaxies, and it was observed that the five objects with the lowest redshifts have very similar X-ray/optical luminosity ratios despite tenfold variations in X-ray luminosity. It is concluded that photoionization by a continuum extending to X-ray energies is the dominant excitation mechanism in radio-quiet quasars.

  1. The Far-Infrared Emission of Radio Loud and Radio Quiet Quasars

    NASA Technical Reports Server (NTRS)

    Polletta, M.; Courvoisier, T. J.-L.; Wilkes, B. J.; Hooper, E. J.

    2000-01-01

    Continuum observations at radio, millimeter, infrared and soft X-ray energies are presented for a sample of 22 quasars, consisting of flat and steep spectrum radio loud, radio intermediate and radio quiet objects. The primary observational distinctions, among the different kinds of quasars in the radio and IR energy domains are studied using large observational datasets provided by ISOPHOT on board the Infrared Space Observatory, by the IRAM interferometer, by the sub-millimetre array SCUBA on JCMT, and by the European Southern Observatory (ESO) facilities IRAC1 on the 2.2 m telescope and SEST. The spectral energy distributions of all quasars from radio to IR energies are analyzed and modeled with non-thermal and thermal spectral components. The dominant mechanism emitting in the far/mid-IR is thermal dust emission in all quasars, with the exception of flat spectrum radio loud quasars for which the presence of thermal IR emission remains rather uncertain, since it is difficult to separate it from the bright non-thermal component. The dust is predominantly heated by the optical/ultraviolet radiation emitted from the external components of the AGN. A starburst contributes to the IR emission at different levels, but always less than the AGN (<= 27%). The distribution of temperatures, sizes, masses, and luminosities of the emitting dust are independent of the quasar type.

  2. Toward a Complete Picture of Quasar Outflows: from BALs to mini-BALs

    NASA Astrophysics Data System (ADS)

    Moravec, Emily; Hamann, Fred; Capellupo, Daniel M.; McGraw, Sean; Shields, Joseph C.; Rodriguez Hidalgo, Paola

    2016-01-01

    Accretion disk outflows are important for galaxy evolution and an integral part of the quasar phenomenon, but they remain poorly understood. In order to construct a more complete picture of the quasar phenomenon, we need to understand the full range of different types of quasar outflows and how they correlate with one another. We examine seven SDSS quasars with CIV 1548,1551 Å outflow lines that span a range from strong BALs to weak mini-BALs. They have moderate redshifts (1.68 < z < 1.91) to minimize contamination from the Lyα forest while still allowing measurements of CIV from the ground and other important lines like OVI 1031,1038 Å and PV 1118,1128 Å with HST. We use archival SDSS and BOSS spectra in combination with HST COS G230L observations and multi-epoch ground-based spectra obtained at the MDM and Kitt Peak observatories to measure a variety of ions across the rest UV wavelength range. Our preliminary analysis shows OVI is present and stronger than CIV in all seven quasars. In one case, we detect an OVI mini-BAL with no accompanying CIV, requiring a highly-ionized outflow. In the strongest BAL quasar, we detect resolved PV doublet absorption that requires PV optical depths > 3 and in outflow gas with a line-of-sight covering fraction of only 0.27. Thus, the total column density in this outflow component might exceed N_H > 1023 cm-2 which has important consequences for the outflow kinetic energies and feedback. The multi-epoch CIV data reveal CIV outflow variability in all seven quasars; four become weaker, one becomes stronger, and two become both stronger and weaker over the different epochs. This variability happens across time scales of ~1-12 years in the quasar rest frames which is consistent with outflow locations close to the central quasar engines. We use these and other results to constrain the ionization, column density, and location of the absorbers with the broader goals of understanding accretion physics, the integrated structure of

  3. Unsteady Reynolds averaged Navier-Stokes simulation of the post-critical flow around a closely spaced group of silos

    NASA Astrophysics Data System (ADS)

    Hillewaere, J.; Dooms, D.; Van Quekelberghe, B.; Degroote, J.; Vierendeels, J.; De Roeck, G.; Lombaert, G.; Degrande, G.

    2012-04-01

    During a storm in October 2002, wind induced ovalling vibrations were observed on several empty silos of a closely spaced group (pitch-to-diameter ratio of 1.05) consisting of 8 by 5 silos in the port of Antwerp (Belgium). Numerical simulations of the turbulent wind flow are performed to clarify the occurrence of the observed ovalling vibrations near the lee side corner of the group by studying the dynamic wind pressures on the silo surfaces and linking to the dynamic properties of the silo structures. As the orientation of the group largely affects the pressure distribution around the cylinders of the group, the influence of the angle of incidence of the wind flow on these ovalling vibrations is examined while other parameters, such as spacing ratio and Reynolds number are unchanged. To achieve results within a reasonable computation time, 2D unsteady Reynolds averaged Navier-Stokes (URANS) equations using Menter's shear stress transport turbulence model were performed. In order to elucidate the influence of the applied turbulence model and to qualitatively validate the spatial and temporal discretization of the 2D highly turbulent post-critical (Re=1.24×107) flow simulations for the silo group, single cylinder simulations were used. The geometric resemblance of the group arrangement with rectangular cylinders on the one hand and of the interstitial spaces with tube arrays (e.g. heat exchangers) on the other hand is used to qualitatively compare the observed flow phenomena. The simulations show that the silo group can be treated neither as a tube array nor as a solid bluff body. Subsequent linking of dynamic wind pressures to dynamic properties of the silo structures reveals strong narrow band frequency peaks in the turbulent pressure coefficient spectra of the silos near the lee side corners of the group that match the structural natural frequencies of the third and fourth ovalling mode shape of the silos. This match indicates a forced, resonant response which

  4. On the statistics of quasar absorption lines

    NASA Astrophysics Data System (ADS)

    Zuiderwijk, E. J.

    1984-12-01

    The distribution of absorption lines in 13 quasar spectra is analyzed and shown to be fully consistent with the hypothesis of randomly, but not uniformly, distributed absorption features. The analysis by Libby et al. (1984), in which it is claimed that the number of wavelength coincidences among absorption lines in different quasar spectra (as measured in the rest frame of the quasars) is much larger than expected, implying absorbers in the quasars themselves, is totally invalid. Instead, the number of these coincidences is fully commensurate with the expected one on the assumption of randomness.

  5. Quasars and Active Galaxies: A Reading List.

    ERIC Educational Resources Information Center

    Fraknoi, Andrew

    1988-01-01

    Contains the annotated bibliographies of introductory books and sections of books, recent introductory articles, more advanced articles, and more advanced books dealing with quasars and active galaxies. (CW)

  6. Growth, surface treatment and characterization of polycrystalline lead iodide thick films prepared using close space deposition technique

    NASA Astrophysics Data System (ADS)

    Zhu, Xinghua; Sun, Hui; Yang, Dingyu; Zheng, Xiaolin

    2012-11-01

    Lead iodide (PbI2) polycrystalline thick films were fabricated on glass substrates with a conductive indium-tin-oxide layer using a close space deposition technique. The morphology of the as-deposited PbI2 films is typically and highly oriented polycrystalline structure, made up of microcrystal platelets upright on the substrate plane. Two techniques including the surface mechanical cutting and after-growth cadmium telluride coating were employed to improve the films' surface properties. It was shown that both of the film surface treatment methods markedly decreased the dark current of PbI2 films. The photo-to-dark current ratio of about 2.05 under 241Am γ-ray source with activity of 2.78 μCi irradiation was obtained from the film treated using both surface cutting and after-growth CdTe coating. Charge transport characteristics of these films were measured and the hole mobility 7.7×10-2-1.67×10-1 cm2/V s was estimated.

  7. The Space Operations Simulation Center (SOSC) and Closed-Loop Hardware Testing for Orion Rendezvous System Design

    NASA Technical Reports Server (NTRS)

    Milenkovic, Zoran; DSouza, Christopher; Huish, David; Bendle, John; Kibler, Angela

    2012-01-01

    The exploration goals of Orion / MPCV Project will require a mature Rendezvous, Proximity Operations and Docking (RPOD) capability. Ground testing autonomous docking with a next-generation sensor such as the Vision Navigation Sensor (VNS) is a critical step along the path of ensuring successful execution of autonomous RPOD for Orion. This paper will discuss the testing rationale, the test configuration, the test limitations and the results obtained from tests that have been performed at the Lockheed Martin Space Operations Simulation Center (SOSC) to evaluate and mature the Orion RPOD system. We will show that these tests have greatly increased the confidence in the maturity of the Orion RPOD design, reduced some of the latent risks and in doing so validated the design philosophy of the Orion RPOD system. This paper is organized as follows: first, the objectives of the test are given. Descriptions of the SOSC facility, and the Orion RPOD system and associated components follow. The details of the test configuration of the components in question are presented prior to discussing preliminary results of the tests. The paper concludes with closing comments.

  8. Performance Expectations of Closed-Brayton-Cycle Heat Exchangers in 100-kWe Nuclear Space Power Systems

    NASA Technical Reports Server (NTRS)

    Barrett, Michael J.

    2003-01-01

    Performance expectations of closed-Brayton-cycle heat exchangers to be used in 100-kWe nuclear space power systems were forecast. Proposed cycle state points for a system supporting a mission to three of Jupiter s moons required effectiveness values for the heat-source exchanger, recuperator and rejection exchanger (gas cooler) of 0.98,0.95 and 0.97, respectively. Performance parameters such as number of thermal units (Nm), equivalent thermal conductance (UA), and entropy generation numbers (Ns) varied from 11 to 19,23 to 39 kWK, and 0.019 to 0.023 for some standard heat exchanger configurations. Pressure-loss contributions to entropy generation were significant; the largest frictional contribution was 114% of the heat-transfer irreversibility. Using conventional recuperator designs, the 0.95 effectiveness proved difficult to achieve without exceeding other performance targets; a metallic, plate-fin counterflow solution called for 15% more mass and 33% higher pressure-loss than the target values. Two types of gas-coolers showed promise. Single-pass counterflow and multipass cross-counterflow arrangements both met the 0.97 effectiveness requirement. Potential reliability-related advantages of the cross-countefflow design were noted. Cycle modifications, enhanced heat transfer techniques and incorporation of advanced materials were suggested options to reduce system development risk. Carbon-carbon sheeting or foam proved an attractive option to improve overall performance.

  9. Characterization of CdMnTe films deposited from polycrystalline powder source using closed-space sublimation method

    SciTech Connect

    Lai, Jianming; Wang, Junnan; Wang, Lin; Ji, Huanhuan; Xu, Run; Zhang, Jijun; Huang, Jian; Shen, Yue; Min, Jiahua; Wang, Linjun Xia, Yiben

    2015-09-15

    CdMnTe films were prepared on quartz substrates by closed-space sublimation of polycrystalline Cd{sub 0.74}Mn{sub 0.26}Te powders. This was performed at different substrate temperatures (T{sub s} = 200, 300, 350, and 400 °C). The interfacial adhesion strength between the films and substrates, when fabricated from polycrystalline powders, was greater than that of films grown using a bulk source. X-ray diffraction studies revealed that the as-deposited films had a zinc blende structure with a preferential (111) orientation. Precipitation of Te occurred in the films deposited at T{sub s} = 200 °C, as confirmed using scanning electron microscopy, x-ray diffraction, and Raman spectroscopy. The growth mode and re-evaporation dependence on the value of T{sub s} of the films were investigated. Our results suggested that materials suitable for radiation detection can be grown from a powder source at lower substrate temperatures then when grown from a bulk source.

  10. Level sequence and splitting identification of closely spaced energy levels by angle-resolved analysis of fluorescence light

    NASA Astrophysics Data System (ADS)

    Wu, Z. W.; Volotka, A. V.; Surzhykov, A.; Dong, C. Z.; Fritzsche, S.

    2016-06-01

    The angular distribution and linear polarization of the fluorescence light following the resonant photoexcitation is investigated within the framework of density matrix and second-order perturbation theory. Emphasis has been placed on "signatures" for determining the level sequence and splitting of intermediate (partially) overlapping resonances, if analyzed as a function of photon energy of incident light. Detailed computations within the multiconfiguration Dirac-Fock method have been performed, especially for the 1 s22 s22 p63 s ,Ji=1 /2 +γ1→(1s22 s 2 p63 s ) 13 p3 /2,J =1 /2 ,3 /2 →1 s22 s22 p63 s ,Jf=1 /2 +γ2 photoexcitation and subsequent fluorescence emission of atomic sodium. A remarkably strong dependence of the angular distribution and linear polarization of the γ2 fluorescence emission is found upon the level sequence and splitting of the intermediate (1s22 s 2 p63 s ) 13 p3 /2,J =1 /2 ,3 /2 overlapping resonances owing to their finite lifetime (linewidth). We therefore suggest that accurate measurements of the angular distribution and linear polarization might help identify the sequence and small splittings of closely spaced energy levels, even if they cannot be spectroscopically resolved.

  11. Analysis of targeting method for closed-loop guidance of a multi-stage space launch vehicle

    NASA Astrophysics Data System (ADS)

    Song, Eun-Jung; Cho, Sangbum; Roh, Woong-Rae

    2016-04-01

    This study considers the orbit insertion targeting problem for guidance of a multi-stage space launch vehicle. To design guidance algorithm for a particular mission target, the orbit designation method should be determined first, as the target orbit of closed-loop guidance during the upper stage flight is usually specified at the end of the final stage. We investigate some advantages of this single target approach over the one with intermediate targets in addition to the final target by comparing them in various flight conditions using an explicit guidance algorithm. We notice that in some cases application of the single targeting can be rather tricky and thus propose here an extended version of the single targeting algorithm that can be applied to problems where the target orbit plane has to be changed during the upper stages flight. We also demonstrate that this pseudo-single target method can be applied to these kinds of problems smoothly in contrast to the conventional single target algorithms by conducting numerical simulations for disturbed off-nominal conditions as well as for the nominal condition.

  12. Optical and electrical characterizations of highly efficient CdTe thin film solar cells prepared by close-spaced sublimation

    NASA Astrophysics Data System (ADS)

    Okamoto, T.; Yamada, A.; Konagai, M.

    2000-06-01

    The effects of the Cu diffusion on the optical and electrical properties of CdTe thin film solar cells prepared by close-spaced sublimation (CSS) were investigated by capacitance-voltage ( C- V) measurement and low-temperature photoluminescence (PL) measurement. C- V measurement revealed that the net acceptor concentration in the CdTe layer was independent of the heat treatment after screen printing of the Cu-doped graphite electrode for Cu diffusion into the CdTe layer, although it greatly affected the solar cell performance. Furthermore, the depth profile of PL spectrum of CdTe layer implies that the heat treatment for Cu diffusion facilitates the formation of low-resistance contact to CdTe through the formation of a heavily doped (p +) region in the CdTe adjacent to the back electrode, but Cu atoms do not act as effective acceptors in the CdTe layer except the region near the back electrode.

  13. Performance Expectations of Closed-Brayton-Cycle Heat Exchangers in 100-kWe Nuclear Space Power Systems

    NASA Technical Reports Server (NTRS)

    Barrett, Michael J.

    2003-01-01

    Performance expectations of closed-Brayton-cycle heat exchangers to be used in 100-k We nuclear space power systems were forecast. Proposed cycle state points for a system supporting a mission to three of Jupiter's moons required effectiveness values for the heat-source exchanger, recuperator and rejection exchanger (gas cooler) of 0.98, 0.95, and 0.97, respectively. Performance parameters such as number of thermal units (Ntu), equivalent thermal conductance (UA), and entropy generation numbers (Ns) varied from 11 to 19, 23 to 39 kW/K, and 0.019 to 0.023 for some standard heat exchanger configurations. Pressure-loss contributions to entropy generation were significant; the largest frictional contribution was 114% of the heat transfer irreversibility. Using conventional recuperator designs, the 0.95 effectiveness proved difficult to achieve without exceeding other performance targets; a metallic, plate-fin counterflow solution called for 15% more mass and 33% higher pressure-loss than the target values. Two types of gas-coolers showed promise. Single-pass counterflow and multipass cross-counterflow arrangements both met the 0.97 effectiveness requirement. Potential reliability-related advantages of the cross-counterflow design were noted. Cycle modifications, enhanced heat transfer techniques and incorporation of advanced materials were suggested options to reduce system development risk. Carbon-carbon sheeting or foam proved an attractive option to improve overall performance.

  14. Tracking a large number of closely spaced objects based on the particle probability hypothesis density filter via optical sensor

    NASA Astrophysics Data System (ADS)

    Lin, Liangkui; Xu, Hui; An, Wei; Sheng, Weidong; Xu, Dan

    2011-11-01

    This paper presents a novel approach to tracking a large number of closely spaced objects (CSO) in image sequences that is based on the particle probability hypothesis density (PHD) filter and multiassignment data association. First, the particle PHD filter is adopted to eliminate most of the clutters and to estimate multitarget states. In the particle PHD filter, a noniterative multitarget estimation technique is introduced to reliably estimate multitarget states, and an improved birth particle sampling scheme is present to effectively acquire targets among clutters. Then, an integrated track management method is proposed to realize multitarget track continuity. The core of the track management is the track-to-estimation multiassignment association, which relaxes the traditional one-to-one data association restriction due to the unresolved focal plane CSO measurements. Meanwhile, a unified technique of multiple consecutive misses for track deletion is used jointly to cope with the sensitivity of the PHD filter to the missed detections and to eliminate false alarms further, as well as to initiate tracks of large numbers of CSO. Finally, results of two simulations and one experiment show that the proposed approach is feasible and efficient.

  15. Heavily obscured quasar host galaxies at z ∼ 2 are discs, not major mergers

    NASA Astrophysics Data System (ADS)

    Schawinski, Kevin; Simmons, Brooke D.; Urry, C. Megan; Treister, Ezequiel; Glikman, Eilat

    2012-09-01

    We explore the nature of heavily obscured quasar host galaxies at z˜ 2 using deep Hubble Space Telescope Wide Field Camera 3/infrared imaging of 28 dust-obscured galaxies (DOGs) to investigate the role of major mergers in driving black hole growth. The high levels of obscuration of the quasars selected for this study act as a natural coronagraph, blocking the quasar light and allowing a clear view of the underlying host galaxy. The sample of heavily obscured quasars represents a significant fraction of the cosmic mass accretion on supermassive black holes as the quasars have inferred bolometric luminosities around the break of the quasar luminosity function. We find that only a small fraction (4 per cent, at most 11-25 per cent) of the quasar host galaxies are major mergers. Fits to their surface brightness profiles indicate that 90 per cent of the host galaxies are either disc dominated, or have a significant disc. This disc-like host morphology, and the corresponding weakness of bulges, is evidence against major mergers and suggests that secular processes are the predominant driver of massive black hole growth. Finally, we suggest that the coincidence of mergers and active galactic nucleus activity is luminosity dependent, with only the most luminous quasars being triggered mostly by major mergers. a MUSYC catalogue ID, see Cardamone et al. (2010). Objects with X-ray detections are marked with *. b See images shown in Fig. 1. c The ratio of the host luminosity to the point source luminosity, reported only when GALFIT requires an unresolved object to yield a physical fit. This may be due to an AGN point source (in the case of the X-ray-detected DOGs) or an unresolved bulge or central concentration, i.e. a central bulge. d See Fig. 2.

  16. OPTOPUS observations of quasar candidates.

    NASA Astrophysics Data System (ADS)

    Cristiani, S.

    1987-06-01

    OPTOPUS is a fiber-optic instrument for multiple-object spectroscopy with the Boiler & Chivens spectrograph and a CCD detector at the 3.6-m telescope. The system has been described in detail by the Optical Instrumentation Group (1985, The Messenger 41,25). Its application for observing Halley's comet has been reported by Lund and Surdej (1986, The Messenger 43, 1). Here another "classical" use of multiple-object spectroscopy is presented: followup observations of quasar candidates.

  17. Quasar redshifts: the intrinsic component

    NASA Astrophysics Data System (ADS)

    Hansen, Peter M.

    2016-09-01

    The large observed redshift of quasars has suggested large cosmological distances and a corresponding enormous energy output to explain the brightness or luminosity as seen at earth. Alternative or complementary sources of redshift have not been identified by the astronomical community. This study examines one possible source of additional redshift: an intrinsic component based on the plasma characteristics of high temperature and high electron density which are believed to be present.

  18. Quasar microlensing and dark matter

    NASA Technical Reports Server (NTRS)

    Rix, Hans-Walter; Hogan, Craig J.

    1988-01-01

    The amplification of quasar brightness due to gravitational lensing by foreground objects is discussed. It is shown that a recently published sample of X-ray-selected quasars behind foreground galaxies shows a statistically significant brightening compared to a control sample. Correlations with galaxy redshift and impact parameter predicted by microlensing are also demonstrated. A technique is described to measure the mean density of the lenses from a small number of identified cases of microlensing. It is shown that, in this sample, amplification bias is important in determining the mean intensity enhancement and must be included in the density estimate. Assuming that at least two of the four intrinsically brightest quasars behind galaxies are indeed microlensed, the present data yield a formal lower limit on the mean density parameter of lenses Omega(l) greater than 0.25 at 95 percent confidence. These data also imply that a considerable quantity of dark matter exists in macroscopic objects outside the visible parts of galaxies but is still highly correlated with them.

  19. Quasar target selection fiber efficiency

    SciTech Connect

    Newberg, H.; Yanny, B.

    1996-05-01

    We present estimates of the efficiency for finding QSOs as a function of limiting magnitude and galactic latitude. From these estimates, we have formulated a target selection strategy that should net 80,000 QSOs in the north galactic cap with an average of 70 fibers per plate, not including fibers reserved for high-redshift quasars. With this plan, we expect 54% of the targets to be QSOs. The North Galactic Cap is divided into two zones of high and low stellar density. We use about five times as many fibers for QSO candidates in the half of the survey with the lower stellar density as we use in the half with higher stellar density. The current plan assigns 15% of the fibers to FIRST radio sources; if these are not available, those fibers would be allocated to lower probability QSO sources, dropping the total number of QSOs by a small factor (5%). We will find about 17,000 additional quasars in the southern strips, and maybe a few more at very high redshift. Use was made of two data sets: the star and quasar simulated test data generated by Don Schneider, and the data from UJFN plate surveys by Koo (1986) and Kron (1980). This data was compared to results from the Palomar-Green Survey and a recent survey by Pat Osmer and collaborators.

  20. Insights into quasar UV spectra using unsupervised clustering analysis

    NASA Astrophysics Data System (ADS)

    Tammour, A.; Gallagher, S. C.; Daley, M.; Richards, G. T.

    2016-06-01

    Machine learning techniques can provide powerful tools to detect patterns in multidimensional parameter space. We use K-means - a simple yet powerful unsupervised clustering algorithm which picks out structure in unlabelled data - to study a sample of quasar UV spectra from the Quasar Catalog of the 10th Data Release of the Sloan Digital Sky Survey (SDSS-DR10) of Paris et al. Detecting patterns in large data sets helps us gain insights into the physical conditions and processes giving rise to the observed properties of quasars. We use K-means to find clusters in the parameter space of the equivalent width (EW), the blue- and red-half-width at half-maximum (HWHM) of the Mg II 2800 Å line, the C IV 1549 Å line, and the C III] 1908 Å blend in samples of broad absorption line (BAL) and non-BAL quasars at redshift 1.6-2.1. Using this method, we successfully recover correlations well-known in the UV regime such as the anti-correlation between the EW and blueshift of the C IV emission line and the shape of the ionizing spectra energy distribution (SED) probed by the strength of He II and the Si III]/C III] ratio. We find this to be particularly evident when the properties of C III] are used to find the clusters, while those of Mg II proved to be less strongly correlated with the properties of the other lines in the spectra such as the width of C IV or the Si III]/C III] ratio. We conclude that unsupervised clustering methods (such as K-means) are powerful methods for finding `natural' binning boundaries in multidimensional data sets and discuss caveats and future work.

  1. Quasar Variability in the Mid-Infrared

    NASA Astrophysics Data System (ADS)

    Kozłowski, Szymon; Kochanek, Christopher S.; Ashby, Matthew L. N.; Assef, Roberto J.; Brodwin, Mark; Eisenhardt, Peter R.; Jannuzi, Buell T.; Stern, Daniel

    2016-02-01

    The Decadal IRAC Boötes Survey is a mid-IR variability survey of the ˜9 sq. deg. of the NDWFS Boötes Field and extends the time baseline of its predecessor, the Spitzer Deep, Wide-Field Survey (SDWFS), from 4 to 10 years. The Spitzer Space Telescope visited the field five times between 2004 and 2014 at 3.6 and 4.5 μm. We provide the difference image analysis photometry for a half a million mostly extragalactic sources. In mid-IR color-color plane, sources with quasar colors constitute the largest variability class (75%), 16% of the variable objects have stellar colors and the remaining 9% have the colors of galaxies. Adding the fifth epoch doubles the number of variable active galactic nuclei (AGNs) for the same false positive rates as in SDWFS, or increases the number of sources by 20% while decreasing the false positive rates by factors of 2-3 for the same variability amplitude. We quantify the ensemble mid-IR variability of ˜1500 spectroscopically confirmed AGNs using single power-law structure functions (SFs), which we find to be steeper (index γ ≈ 0.45) than in the optical (γ ≈ 0.3), leading to much lower amplitudes at short time-lags. This provides evidence for large emission regions, smoothing out any fast UV/optical variations, as the origin of infrared quasar variability. The mid-IR AGN SF slope γ seems to be uncorrelated with both the luminosity and rest-frame wavelength, while the amplitude shows an anti-correlation with the luminosity and a correlation with the rest-frame wavelength.

  2. The luminosity function of quasars and its evolution: A comparison of optically selected quasars and quasars found in radio catalogs

    NASA Technical Reports Server (NTRS)

    Petrosian, V.

    1973-01-01

    The luminosity function of quasars and its evolution are discussed, based on comparison of available data on optically selected quasars and quasars found in radio catalogs. It is assumed that the red shift of quasars is cosmological and the results are expressed in the framework of the Lambda = 0, Q sub Q = 1 cosmological model. The predictions of various density evolution laws are compared with observations of an optically selected sample of quasars and quasar samples from radio catalogs. The differences between the optical luminosity functions, the red shift distributions and the radio to optical luminosity ratios of optically selected quasars and radio quasars rule out luminosity functions where there is complete absence of correlation between radio and optical luminosities. These differences also imply that Schmidt's (1970) luminosity function, where there exists a statistical correlation between radio and optical luminosities, although may be correct for high red shift objects, disagrees with observation at low red shifts. These differences can be accounted for by postulating existence of two classes (1 and 2) of objects.

  3. Cadmium sulfide thin films deposited by close spaced sublimation and cadmium sulfide/cadmium telluride solar cells

    NASA Astrophysics Data System (ADS)

    Marinskiy, Dmitriy Nikolaevich

    1998-12-01

    One of the applications of CdS films is as a window layer in CdTe and Cu(In,Ga)Sesb2 solar cells. The study of the optical and structural properties of CdS films deposited by close spaced sublimation as well as their influence on CdS/CdTe solar cell performance is part of the CdTe solar cell program at the University of South Florida. CdS films have been deposited by the close-spaced sublimation technique. The influence of the main process parameters, the substrate and source temperatures, and the ambient in the deposition chamber has been investigated. As-deposited films have been subjected to heat treatments in Hsb2 ambient, in CdClsb2 atmosphere, and in atmosphere with small amounts of oxygen. A special annealing chamber was built to carry out the annealing experiments in the presence of CdClsb2 vapor and oxygen. Several CSS chambers were assembled to study the influence of various process parameters simultaneously and validate the results. Results of scanning electron microscopy and photoluminescence measurements have been used as the primary characterization techniques. X-ray diffraction, electron microprobe analysis, and transmission measurements have also been carried out. It was found that as deposited CdS films have a hexagonal structure independent of the process parameters used. The presence of a CdO phase was detected in the samples grown with the highest oxygen concentration in the ambient. The resistivity of CdS films is controlled by intergrain barriers. Photoluminescence measurements showed the presence of oxygen-acceptor transition and a wide variation in the intensity of deep emission bands. The variation in the intensities was correlated with the variation in the deposition and annealing conditions. However, no correlation was found between the PL intensities of defect bands and cell performance. CdS/CdTe junctions have been fabricated using standard deposition and postgrowth techniques developed in the USF solar cells laboratory. All cells have

  4. Chandra Observations of 12 Luminous Red Quasars

    SciTech Connect

    Urrutia, T; Lacy, M; Gregg, M D; Becker, R H

    2005-03-11

    The authors present results of a study of 12 dust-reddened quasars with 0.4 < z < 2.65 and reddenings in the range 0.15 < E(B-V) < 1.7. They obtained ACIS-S X-ray spectra of these quasars, estimated the column densities towards them, and hence obtained the gas:dust ratios in the material obscuring the quasar. They detect all but one of the red quasars in the X-rays. Even though there is no obvious correlation between the X-ray determined column densities of the sources and their optical color or reddening, all of the sources show absorbed X-ray spectra. When they correct the luminosity for absorption, they can be placed among luminous quasars; therefore their objects belong to the group of high luminosity analogues of the sources contributing to the X-ray background seen in deep X-ray observations. Such sources are also found in serendipitous shallow X-ray surveys. There is a hint that the mean spectral slope of the red quasar is higher than that of normal, unobscured quasars, which could be an indication for higher accretion rates and/or an evolutionary effect. They investigate the number density of these sources compared to type 2 AGN based on the X-ray background and estimate how many moderate luminosity red quasars may be found in deep X-ray fields.

  5. Quasars as very-accurate clock synchronizers

    NASA Technical Reports Server (NTRS)

    Hurd, W. J.; Goldstein, R. M.

    1975-01-01

    Quasars can be employed to synchronize global data communications, geophysical measurements, and atomic clocks. It is potentially two to three orders of magnitude better than presently-used Moon-bounce system. Comparisons between quasar and clock pulses are used to develop correction or synchronization factors for station clocks.

  6. LBQS 0103-2753: A BINARY QUASAR IN A MAJOR MERGER

    SciTech Connect

    Shields, G. A.; Rosario, D. J.; Junkkarinen, V.; Chapman, S. C.; Bonning, E. W.; Chiba, T. E-mail: rosario@mpe.mpg.de E-mail: schapman@ast.cam.ac.uk E-mail: tamara.chiba@yale.edu

    2012-01-10

    We present Hubble Space Telescope (HST) and United Kingdom Infrared Telescope spectra and images of the 2 kpc (0.''3) binary quasar LBQS 0103-2753 (z = 0.858). The HST images (V and I bands) show tidal features demonstrating that this system is a major galaxy merger in progress. A two-color composite image brings out knots of star formation along the tidal arc and elsewhere. The infrared spectrum shows that both objects are at the same redshift and that the discrepant redshift of C IV in component A is not representative of the true systemic redshift of this component. LBQS 0103-2753 is one of the most closely spaced binary QSOs known and is one of the relatively few dual active galactic nuclei showing confirmed broad emission lines from both components. While statistical studies of binary QSOs suggest that simultaneous fueling of both black holes during a merger may be relatively rare, LBQS 0103-2753 demonstrates that such fueling can occur at high luminosity at a late stage in the merger at nuclear spacing of only a few kpc, without severe obscuration of the nuclei.

  7. Extreme Red Quasars in SDSS-BOSS

    NASA Astrophysics Data System (ADS)

    Hamann, Fred; Zakamska, Nadia; Paris, Isabelle; Herbst, Hanna; Villforth, Carolin; Alexandroff, Rachael; Ross, Nicholas; Greene, Jenny; Strauss, Michael

    2015-08-01

    Red quasars are believed to mark a critical transition stage of massive galaxy evolution when a blowout of gas and dust truncates the initial starburst and provides our first visible views of a luminous central AGN. Red quasars could therefore have unusual properties associated with a young evolution stage, such as higher accretion rates, higher rates of mergers and interactions, and more common or more powerful outflows capable of driving a galaxy-wide blowout (e.g., compared to normal blue quasars in presumably more evolved galaxy hosts). The recently completed Baryon Oscillation Spectroscopy Survey (BOSS) of SDSS-III has discovered many more faint quasars with higher redshifts and redder colors than any previous large survey. We combine BOSS spectra with SDSS and Wide-Field Infrared Survey Explorer (WISE) photometry of nearly 100,000 quasars to identify and characterize the red quasar population at redshifts >2. We find a number of strong trends with the amount of reddening/obscuration. For example, red quasars are 5 to 8 times more likely to have broad absorption lines and other "intrinsic" absorption lines that identify quasar-driven outflows. Perhaps most interesting is that extreme red quasars (ERQs), selected via rest-frame UV to near-IR colors similar to Dust Obscured Galaxies (DOGs), have uniquely exotic emission line properties that include extreme velocity shifts between lines and the broadest and most blueshifted [OIII] lines yet discovered (with FWHMs reaching >3000 km/s). We will discuss the implications of these results for models of the structure and evolution of quasars and their host galaxy environments.

  8. A direct measurement of the mean occupation function of quasars: Breaking degeneracies between halo occupation distribution models

    SciTech Connect

    Chatterjee, Suchetana; Nguyen, My L.; Myers, Adam D.; Zheng, Zheng

    2013-12-20

    Recent work on quasar clustering suggests a degeneracy in the halo occupation distribution constrained from two-point correlation functions. To break this degeneracy, we make the first empirical measurement of the mean occupation function (MOF) of quasars at z ∼ 0.2 by matching quasar positions with groups and clusters identified in the MaxBCG sample. We fit two models to the MOF, a power law and a four-parameter model. The number distribution of quasars in host halos is close to Poisson, and the slopes of the MOF obtained from our best-fit models (for the power-law case) favor an MOF that monotonically increases with halo mass. The best-fit slopes are 0.53 ± 0.04 and 1.03 ± 1.12 for the power-law model and the four-parameter model, respectively. We measure the radial distribution of quasars within dark matter halos and find it to be adequately described by a power law with a slope –2.3 ± 0.4. We measure the conditional luminosity function (CLF) of quasars and show that there is no evidence that quasar luminosity depends on host halo mass, similar to the inferences drawn from clustering measurements. We also measure the conditional black hole mass function (CMF) of our quasars. Although the results are consistent with no dependence on halo mass, we observe a slight indication of downsizing of the black hole mass function. The lack of halo mass dependence in the CLF and CMF shows that quasars residing in galaxy clusters have characteristic luminosity and black hole mass scales.

  9. Evidence for the alignment of quasar radio polarizations with large quasar group axes

    NASA Astrophysics Data System (ADS)

    Pelgrims, V.; Hutsemékers, D.

    2016-05-01

    Recently, evidence has been presented for the polarization vectors from quasars to preferentially align with the axes of the large quasar groups (LQG) to which they belong. This report was based on observations made at optical wavelengths for two LQGs at redshift ~1.3. The correlation suggests that the spin axes of quasars preferentially align with their surrounding large-scale structure that is assumed to be traced by the LQGs. Here, we consider a large sample of LQGs built from the Sloan Digital Sky Survey DR7 quasar catalogue in the redshift range 1.0-1.8. For quasars embedded in this sample, we collected radio polarization measurements with the goal to study possible correlations between quasar polarization vectors and the major axis of their host LQGs. Assuming the radio polarization vector is perpendicular to the quasar spin axis, we found that the quasar spin axis is preferentially parallel to the LQG major axis inside LQGs that have at least 20 members. This result independently supports the observations at optical wavelengths. We additionally found that when the richness of an LQG decreases, the quasar spin axis becomes preferentially perpendicular to the LQG major axis and that no correlation is detected for quasar groups with fewer than 10 members.

  10. QUART: Quasar hosts Unveiled by high Angular Resolution Techniques

    NASA Astrophysics Data System (ADS)

    Vayner, Andrey; Wright, Shelley; Murray, Norman W.; Armus, Lee; Larkin, James E.

    2016-06-01

    We present results from the new QUART survey that aims to resolve high-redshift (z = 1.5 - 2.5) radio-quiet and radio-loud quasi stellar object (QSO) host galaxies using the integral field spectrograph (IFS) OSIRIS, and the Keck Adaptive Optics (AO) system. The combination of AO and IFS provides the necessary contrast to disentangle the bright-unresolved QSO from the underlying faint host galaxy with unprecedented sensitivity. We study the ionized gas in these systems to sub-kiloparsec scales, yielding essential constraints on the resolved host galaxies dynamics, morphologies, star formation rates, metallicities, and nebular emission diagnostics. We combine OSIRIS and AO observations with multi-wavelength data sets from Atacama Large Millimeter/submillimeter Array, Hubble Space Telescope, and Very Large Array to better understand the multiple phases of the ISM and stellar population properties of the hosts. Radio-quiet QSOs have shown little-to-no star formation and no evidence of extended QSO narrow line emission. In contrast, our latest OSIRIS results of radio-loud z~1.5-2 quasars have revealed evidence for both concurrent star formation and extended quasar narrow line emission with strong outflows. These outflows are co-spatial with structure observed in the radio data, typically with the path of the quasar jet and/or lobe structure. These winds are highly extended (8-12 kpc) and show broad emission line profiles (extending up to 2,500 km/s), indicating strong evidence of quasar “feedback” in their host galaxies.

  11. The Subaru High-z Quasar Survey: Discovery of Faint z ~ 6 Quasars

    NASA Astrophysics Data System (ADS)

    Kashikawa, Nobunari; Ishizaki, Yoshifumi; Willott, Chris J.; Onoue, Masafusa; Im, Myungshin; Furusawa, Hisanori; Toshikawa, Jun; Ishikawa, Shogo; Niino, Yuu; Shimasaku, Kazuhiro; Ouchi, Masami; Hibon, Pascale

    2015-01-01

    We present the discovery of one or two extremely faint z ~ 6 quasars in 6.5 deg2 utilizing a unique capability of the wide-field imaging of the Subaru/Suprime-Cam. The quasar selection was made in (i'-zB ) and (zB -zR ) colors, where zB and zR are bandpasses with central wavelengths of 8842 Å and 9841 Å, respectively. The color selection can effectively isolate quasars at z ~ 6 from M/L/T dwarfs without the J-band photometry down to zR < 24.0, which is 3.5 mag deeper than the Sloan Digital Sky Survey (SDSS). We have selected 17 promising quasar candidates. The follow-up spectroscopy for seven targets identified one apparent quasar at z = 6.156 with M 1450 = -23.10. We also identified one possible quasar at z = 6.041 with a faint continuum of M 1450 = -22.58 and a narrow Lyα emission with HWHM =427 km s-1, which cannot be distinguished from Lyman α emitters. We derive the quasar luminosity function at z ~ 6 by combining our faint quasar sample with the bright quasar samples by SDSS and CFHQS. Including our data points invokes a higher number density in the faintest bin of the quasar luminosity function than the previous estimate employed. This suggests a steeper faint-end slope than lower z, though it is yet uncertain based on a small number of spectroscopically identified faint quasars, and several quasar candidates still remain to be diagnosed. The steepening of the quasar luminosity function at the faint end does increase the expected emission rate of the ionizing photon; however, it only changes by a factor of approximately two to six. This was found to still be insufficient for the required photon budget of reionization at z ~ 6.

  12. Quasars in the Time Domain: Supermassive Black Hole Binaries and Extreme Objects

    NASA Astrophysics Data System (ADS)

    Graham, Matthew; Djorgovski, Stanislav G.; Stern, Daniel; Drake, Andrew J.; Mahabal, Ashish A.; Glikman, Eilat

    2016-01-01

    Quasar variability can offer insights into the physics of AGN, as it is driven by the variations in the accretion rate, changes in obscuration, and/or instabilities and propagation effects of the relativistic jets. Large synoptic sky surveys such as CRTS (crts.caltech.edu) offer new possibilities in this domain.We use the data set of CRTS light curves of ~335,000 known, spectroscopically confirmed quasars. They have up to a few hundred data points each, with baselines of up to 10 years. This is an unprecedented data set for the studies of quasar variability.We have previously identified a characteristic time scale of stochastic quasar variability, ~54 days (restframe), which anticorrelates with luminosity and black hole mass. While the origin of this phenomenon is not yet understood, it may lead to new insights into the physics of AGN accretion disks and quasars in general. While most quasars show such a characteristic time scale and trends, a subset exhibit a time scale that is significantly different than expected given their physical parameters. We have also found a number of other objects that show extreme variability (in RMS amplitude, or other measures). For a number of these objects we have now detected significant spectroscopic changes that correlate with the photometric variability. We will describe some of the more interesting cases.An even more interesting is the recent detection of periodically variable quasars, which are interpreted as a signature of close (milliparsec scale) supermassive black hole binaries (SMBH) en route to a merger. This population may offer new insights into the assembly of SMBH and their physics in the gravitational wave regime. We have initiate a spectroscopic monitoring program of these objects, and have already detected some spectroscopic changes for some of them. We will describe these results and their possible interpretations.

  13. Anomaly distribution of quasar magnitudes: a test of lensing by a hypothetic supergiant molecular cloud in the Galactic halo

    NASA Astrophysics Data System (ADS)

    Giraud, E.

    2012-07-01

    Context. An anomaly in the distribution of quasar magnitudes based on the Sloan Digital Sky survey, was reported by Longo. The angular size of this quasar anomaly is on the order of ±15° on the sky. A smooth low surface brightness structure detected in γ-rays and at 408 MHz, coincides with the sky location and extent of the anomaly, and is close to the northern component of a pair of γ-ray bubbles discovered in the Fermi Gamma-ray Space Telescope survey. Molecular clouds are thought to be illuminated by cosmic rays. Molecular gas in the Galaxy, in the form of cold H2, may be a significant component of dark matter as suggested by Pfenniger et al. Aims: I test the hypothesis that the magnitude anomaly in the quasar distribution, is due to lensing by a hypothetical supergiant molecular cloud (SGMC) either in or falling into the Galactic halo. Methods: A series of grid lens models are built by assuming that a SGMC is a fractal structure constructed with clumps of 10-3 M⊙, 10 AU in size, and considering various fractal dimensions. Local amplifications are computed by using the single-plane approximation. Results: A complex network of caustics due to the clumpy structure is present. Our best single plane lens model capable of explaining Longo's effect, at least in sparse regions, requires a mass (1.5-4.1) × 1010 M⊙ within 8.7 × 8.7 × (5-8.6) kpc3 at a lens plane distance of 20 kpc, and is constructed from a molecular-cloud building-block of 5 × 105 M⊙ within a scale of 30 pc expanded by fractal scaling with dimension D = 1.8-2 out to 5-8.6 kpc for the SGMC. The mass budget depends on the cloud depth and on the fractal dimension. Conclusions: If such a SGMC were found to exist, it may provide at least part of a lensing explanation for the luminous anomaly discovered in quasars and red galaxies.

  14. Diverse lavas from closely spaced volcanoes drawing from a common parent: Emmons Lake Volcanic Center, Eastern Aleutian Arc

    USGS Publications Warehouse

    Mangan, M.; Miller, T.; Waythomas, C.; Trusdell, F.; Calvert, A.; Layer, P.

    2009-01-01

    Emmons Lake Volcanic Center (ELVC) on the lower Alaskan Peninsula is one of the largest and most diverse volcanic centers in the Aleutian Arc. Since the Middle Pleistocene, eruption of ~ 350 km3 of basalt through rhyolite has produced a 30 km, arc front chain of nested calderas and overlapping stratovolcanoes. ELVC has experienced as many as five major caldera-forming eruptions, the most recent, at ~ 27 ka, produced ~ 50 km3 of rhyolitic ignimbrite and ash fall. These violent silicic events were interspersed with less energetic, but prodigious, outpourings of basalt through dacite. Holocene eruptions are mostly basaltic andesite to andesite and historically recorded activity includes over 40 eruptions within the last 200 yr, all from Pavlof volcano, the most active site in the Aleutian Arc. Geochemical and geophysical observations suggest that although all ELVC eruptions derive from a common clinopyroxene + spinel + plagioclase fractionating high-aluminum basalt parent in the lower crust, magma follows one of two closely spaced, but distinct paths to the surface. Under the eastern end of the chain, magma moves rapidly and cleanly through a relatively young (~ 28 ka), hydraulically connected dike plexus. Steady supply, short magma residence times, and limited interaction with crustal rocks preserve the geochemistry of deep crustal processes. Below the western part of the chain, magma moves haltingly through a long-lived (~ 500 ka) and complex intrusive column in which many generations of basaltic to andesitic melts have mingled and fractionated. Buoyant, silicic melts periodically separate from the lower parts of the column to feed voluminous eruptions of dacite and rhyolite. Mafic lavas record a complicated passage through cumulate zones and hydrous silicic residues as manifested by disequilibrium phenocryst textures, incompatible element enrichments, and decoupling of REEs and HFSEs ratios. Such features are absent in mafic lavas from the younger part of the chain

  15. A Validated Set of MIDAS V5 Task Network Model Scenarios to Evaluate Nextgen Closely Spaced Parallel Operations Concepts

    NASA Technical Reports Server (NTRS)

    Gore, Brian Francis; Hooey, Becky Lee; Haan, Nancy; Socash, Connie; Mahlstedt, Eric; Foyle, David C.

    2013-01-01

    The Closely Spaced Parallel Operations (CSPO) scenario is a complex, human performance model scenario that tested alternate operator roles and responsibilities to a series of off-nominal operations on approach and landing (see Gore, Hooey, Mahlstedt, Foyle, 2013). The model links together the procedures, equipment, crewstation, and external environment to produce predictions of operator performance in response to Next Generation system designs, like those expected in the National Airspaces NextGen concepts. The task analysis that is contained in the present report comes from the task analysis window in the MIDAS software. These tasks link definitions and states for equipment components, environmental features as well as operational contexts. The current task analysis culminated in 3300 tasks that included over 1000 Subject Matter Expert (SME)-vetted, re-usable procedural sets for three critical phases of flight; the Descent, Approach, and Land procedural sets (see Gore et al., 2011 for a description of the development of the tasks included in the model; Gore, Hooey, Mahlstedt, Foyle, 2013 for a description of the model, and its results; Hooey, Gore, Mahlstedt, Foyle, 2013 for a description of the guidelines that were generated from the models results; Gore, Hooey, Foyle, 2012 for a description of the models implementation and its settings). The rollout, after landing checks, taxi to gate and arrive at gate illustrated in Figure 1 were not used in the approach and divert scenarios exercised. The other networks in Figure 1 set up appropriate context settings for the flight deck.The current report presents the models task decomposition from the tophighest level and decomposes it to finer-grained levels. The first task that is completed by the model is to set all of the initial settings for the scenario runs included in the model (network 75 in Figure 1). This initialization process also resets the CAD graphic files contained with MIDAS, as well as the embedded

  16. The large-scale quasar-Lyman α forest cross-correlation from BOSS

    SciTech Connect

    Font-Ribera, Andreu; Arnau, Eduard; Miralda-Escudé, Jordi E-mail: edu.arnau.lazaro@gmail.com; and others

    2013-05-01

    We measure the large-scale cross-correlation of quasars with the Lyα forest absorption in redshift space, using ∼ 60000 quasar spectra from Data Release 9 (DR9) of the Baryon Oscillation Spectroscopic Survey (BOSS). The cross-correlation is detected over a wide range of scales, up to comoving separations r of 80 h{sup −1}Mpc. For r > 15 h{sup −1}Mpc, we show that the cross-correlation is well fitted by the linear theory prediction for the mean overdensity around a quasar host halo in the standard ΛCDM model, with the redshift distortions indicative of gravitational evolution detected at high confidence. Using previous determinations of the Lyα forest bias factor obtained from the Lyα autocorrelation, we infer the quasar bias factor to be b{sub q} = 3.64{sup +0.13}{sub −0.15} at a mean redshift z = 2.38, in agreement with previous measurements from the quasar auto-correlation. We also obtain a new estimate of the Lyα forest redshift distortion factor, β{sub F} = 1.1±0.15, slightly larger than but consistent with the previous measurement from the Lyα forest autocorrelation. The simple linear model we use fails at separations r < 15h{sup −1}Mpc, and we show that this may reasonably be due to the enhanced ionization due to radiation from the quasars. We also provide the expected correction that the mass overdensity around the quasar implies for measurements of the ionizing radiation background from the line-of-sight proximity effect.

  17. Selection of quasar candidates from combined radio and optical surveys using neural networks

    NASA Astrophysics Data System (ADS)

    Carballo, R.; Cofiño, A. S.; González-Serrano, J. I.

    2004-09-01

    The application of supervised artificial neural networks (ANNs) for quasar selection from combined radio and optical surveys with photometric and morphological data is investigated, using the list of candidates and their classification from the work of White et al. Seven input parameters and one output, evaluated to 1 for quasars and 0 for non-quasars during the training, were used, with architectures 7: 1 and 7: 2: 1. Both models were trained on samples of ~800 sources and yielded similar performance on independent test samples, with reliability as large as 87 per cent at 80 per cent completeness (or 90 to 80 per cent for completeness from 70 to 90 per cent). For comparison, the quasar fraction from the original candidate list was 56 per cent. The accuracy is similar to that found by White et al. using supervised learning with oblique decision trees and training samples of similar size. In view of the large degree of overlapping between quasars and non-quasars in the parameter space, this performance probably approaches the maximum value achievable with this data base. Predictions of the probabilities for the 98 candidates without spectroscopic classification in White et al. are presented and compared with the results from their work. The values obtained for the two ANN models and the decision trees are found to be in good agreement. This is the first analysis of the performance of ANNs for the selection of quasars. Our work shows that ANNs provide a promising technique for the selection of specific object types in astronomical data bases.

  18. The SDSS view of the Palomar-Green Bright Quasar Survey

    NASA Astrophysics Data System (ADS)

    Jester, S.; Richards, G. T.; Schneider, D. P.; Stoughton, C.; Green, R. F.; Gunn, J. E.; Hall, P. B.; Kron, R. G.; Schmidt, M.; Vanden Berk, D. E.

    2004-12-01

    We compare the properties of UV excess-selected PG quasars to the ``PG-like'' subset of SDSS multicolor-selected quasars. We find no statistically significant differences in the distributions of optical colors, redshift, or radio properties taken from the FIRST survey (radio flux, power, and radio-optical flux ratio). Comparing the PG quasars to the entire SDSS quasar sample, we find that the PG UV excess selection criterion does not remove any objects from the PG that are not already removed by the B-band brightness limit. Thus, PG quasars constitute a representative sample of quasars which are bright in the B-band. However, the i-band limited SDSS sample includes objects with a much wider range of colors at i-band magnitudes similar to those of the PG objects. Thus, the PG sample is not fully representative of today's fainter quasar samples and may be biased in important ways (e.g., its X-ray properties). Funding for the Sloan Digital Sky Survey (SDSS) has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho, and the Max Planck Society. The SDSS is managed by the Astrophysical Research Consortium (ARC) for the Participating Institutions. The Participating Institutions are The University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, the Korean Scientist Group, Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, University of Pittsburgh, Princeton University, the United States Naval Observatory, and the University of Washington.

  19. The Composite Spectrum of BOSS Quasars Selected for Studies of the Lyα Forest

    NASA Astrophysics Data System (ADS)

    Harris, David W.; Jensen, Trey W.; Suzuki, Nao; Bautista, Julian E.; Dawson, Kyle S.; Vivek, M.; Brownstein, Joel R.; Ge, Jian; Hamann, Fred; Herbst, H.; Jiang, Linhua; Moran, Sarah E.; Myers, Adam D.; Olmstead, Matthew D.; Schneider, Donald P.

    2016-06-01

    The Baryon Oscillation Spectroscopic Survey (BOSS) has collected more than 150,000 2.1 ≤ z ≤ 3.5 quasar spectra since 2009. Using this unprecedented sample, we create a composite spectrum in the rest-frame of 102,150 quasar spectra from 800–3300 Å at a signal-to-noise ratio close to 1000 per pixel (Δv of 69 km s‑1). Included in this analysis is a correction to account for flux calibration residuals in the BOSS spectrophotometry. We determine the spectral index as a function of redshift of the full sample, warp the composite spectrum to match the median spectral index, and compare the resulting spectrum to Sloan Digital Sky Survey (SDSS) photometry used in target selection. The quasar composite matches the color of the quasar population to 0.02 mag in g ‑ r, 0.03 mag in r ‑ i, and 0.01 mag in i ‑ z over the redshift range 2.2 < z < 2.6. The composite spectrum deviates from the imaging photometry by 0.05 mag around z = 2.7, likely due to differences in target selection as the quasar colors become similar to the stellar locus at this redshift. Finally, we characterize the line features in the high signal-to-noise composite and identify nine faint lines not found in the previous composite spectrum from SDSS.

  20. The FIRST-2MASS Red Quasar Survey

    SciTech Connect

    Glikman, E; Helfand, D J; White, R L; Becker, R H; Gregg, M D; Lacy, M

    2007-06-28

    Combining radio observations with optical and infrared color selection--demonstrated in our pilot study to be an efficient selection algorithm for finding red quasars--we have obtained optical and infrared spectroscopy for 120 objects in a complete sample of 156 candidates from a sky area of 2716 square degrees. Consistent with our initial results, we find our selection criteria--J-K > 1.7,R-K > 4.0--yield a {approx} 50% success rate for discovering quasars substantially redder than those found in optical surveys. Comparison with UVX- and optical color-selected samples shows that {approx}> 10% of the quasars are missed in a magnitude-limited survey. Simultaneous two-frequency radio observations for part of the sample indicate that a synchrotron continuum component is ruled out as a significant contributor to reddening the quasars spectra. We go on to estimate extinctions for our objects assuming their red colors are caused by dust. Continuum fits and Balmer decrements suggest E(B-V) values ranging from near zero to 2.5 magnitudes. Correcting the K-band magnitudes for these extinctions, we find that for K {le} 14.0, red quasars make up between 25% and 60% of the underlying quasar population; owing to the incompleteness of the 2MASS survey at fainter K-band magnitudes, we can only set a lower limit to the radio-detected red quasar population of > 20-30%.

  1. Probing the Luminosity Function of Young Quasars

    NASA Astrophysics Data System (ADS)

    Urrutia, Tanya; Glikman, E.; Lacy, M.

    2010-01-01

    In the last year, we have been using the Triple Spec Near-Infrared spectrograph on the Palomar Observatory to identify candidate dust-reddened quasars using the FIRST radio survey, the UKIDSS near-infrared survey and the SDSS optical survey. A previous campaign using the shallow near-infrared 2MASS survey, was very successful in finding dust obscured quasars by finding very red (R-K > 4, J-K > 1.7) radio sources (Glikman et al. 2007). Among them are many young, interacting galaxies (Urrutia, Lacy & Becker 2008) and a large fraction of Low Ionization Broad Absorption Line Quasars (Urrutia et al. 2009), implying that the red quasar population probes a young phase in the lifetime of an AGN. By using the same color criteria on the deeper UKIDSS survey, we are able to probe into higher redshifts and lower luminosity red quasars. This is a first step to build a luminosity function for dust-obscured quasars. We then will be able to answer the question if young quasars are more generally more luminous as their older counterparts, perhaps because of higher accretion efficiency.

  2. What BOSS has taught us about Quasars.

    NASA Astrophysics Data System (ADS)

    Ross, Nicholas; SDSS-III BOSS Quasar Science Working Group

    2015-01-01

    This talk presents science highlights from the SDSS-III BOSS Quasar Survey, which has obtained spectra for over 300,000 quasars, 200,000 of which are at redshift z>2. Using this dataset, new measurements of the luminosity function have been made, with the faint end of the luminosity function now measured to z~5. New clustering results from DR12 are presented, and the weak luminosity dependence of quasar clustering at z~0.5 is also discussed.New studies of the broad absorption line (BAL) quasar population have also been performed, with a sample of BAL quasars from the original SDSS being re-observed. These new data have shown the disappearance of CIV BAL troughs and indeed the transformation of BAL QSOs to non-BAL QSOs. BAL disappearance, and emergence, events appear to be extremes of general BAL variability, and have shed light on accretion-disk wind models.We highlight the discovery of new classes of quasars including: a population of broad-line Mg II emitters found in a passive galaxy sample; objects with extremely red optical-to-mid infrared colors; objects with very curious UV line (LyA:NV) ratios and potentially the long-sought after high-redshift Type 2 Quasar population.Finally, we describe two new dedicated programs, one focusing on reverberation mapping, the other on X-ray selected quasars.A full list of papers connected to the BOSS Quasar Survey is given at: http://www.sdss3.org/science/publications.php

  3. The quasar mass-luminosity plane

    NASA Astrophysics Data System (ADS)

    Steinhardt, Charles Louis

    2010-11-01

    This thesis investigates the quasar mass-luminosity plane, as a new tool to explore the relationship between black hole mass and quasar luminosity over time. Previous techniques used quasar luminosity function and mass functions, which are one-dimensional projections of the mass-luminosity plane. The M --- L plane contains information that cannot be seen in these projections. We use 62,185 quasars from the Sloan Digital Sky Survey DR5 sample to develop several new constraints on quasar accretion. Black hole masses, based on the widths of their Hbeta, Mg II, and C IV lines and adjacent continuum luminosities, were used assuming using standard virial mass estimate scaling laws. In each redshift interval over the range 0.2 < z < 4.0, low-mass quasars reach at their Eddington luminosity, but high-mass quasars fall short, even by a factor of ten or more at 0.2 < z < 0.6. We examine several potential sources of measurement uncertainty or bias and show that none of them can account for this effect. We also show the statistical uncertainty in virial mass estimation to have an upper bound of ˜ 0.2 dex, smaller than the 0.4 dex previously reported. The maximum mass of quasars at each redshift is sharp and evolving. High-mass black holes turn off their luminous accretion at higher redshift than lower-mass black holes. Further, turnoff for quasars at any given mass is synchronized to within 0.7--3 Gyr, tighter than would be expected given the dynamics of their host galaxies. We find potential signatures of the quasar turnoff mechanism, including a dearth of high-mass quasars at low Eddington ratio, low CIV/MgII emission line ratio, and a red spectral tilt. Finally, we use these new constraints to analyze models for the evolution of individual quasars over time. We find a restricted family of tracks that lie within the M --- L plane at all redshifts, suggesting that a single, constant feedback mechanism between all supermassive black holes and their host galaxies might apply

  4. The Backlit Universe: How Distant Quasars Illuminate the Large Scale Structure

    NASA Astrophysics Data System (ADS)

    Slosar, An&{Caron; Z.}E.

    2011-04-01

    The Lyman-α forest is a series of absorption features in the spectra of distant quasars, blue-ward of the Lyman-α emission line. These features arise as the light from the quasar is absorbed by the intervening neutral hydrogen. This gives one-dimensional information about the fluctuations in the neutral hydrogen density along the line of sight to the quasar. When spectra of many quasars are combined, it allows one to build a three-dimensional image of the fluctuations in the neutral hydrogen density and thus infer the corresponding fluctuations in the matter density. This makes the Lyman-α forest a unique probe of the distant Universe, opening a novel window on understanding dark energy, dark matter, neutrino properties and inflation. Using the 14,000 quasars from the first year data, the BOSS experiment has detected, for the first time, three-dimensional correlations in the Lyman-alpha forest fluctuations to cosmological distances. The signal has thhe expected amplitude and redshift-space distortions and we find no evidence for overwhelming instrumental or astrophysical contamination. The BOSS experiment was projected to measure the distance to the redshift of z ˜2.5 with a better than 2% precision through detection of baryonic acoustic signature in the flux correlations. The present results give these forecasts new credibility.

  5. A Bayesian Method For Finding Galaxies That Cause Quasar Absorption Lines

    NASA Astrophysics Data System (ADS)

    Shoemaker, Emileigh Suzanne; Laubner, David Andrew; Scott, Jennifer E.

    2016-01-01

    We present a study of candidate absorber-galaxy pairs for 39 low redshift quasar sightlines (0.06 < z < 0.85) using a statistical approach to match absorbers with galaxies near the quasar lines of sight. Of the 75 quasars observed with HST/Cosmic Origins Spectrograph (COS) and archived on the Mikulski Archive for Space Telescopes (MAST), 39 overlap with the footprint of the Sloan Digital Sky Survey (SDSS). We downloaded the COS linelists for these quasar spectra from MAST and queried the SDSS DR12 database for photometric data on all galaxies within 1 Mpc of each of these quasar lines of sight. We calculated photometric redshifts for all the SDSS galaxies using the Bayesian Photometric Redshift code. We used all these absorber and galaxy data as input into an absorber-galaxy matching code which also employs a Bayesian scheme, along with known statistics of the intergalactic medium and circumgalactic media of galaxies, for finding the most probable galaxy match for each absorber. We compare our candidate absorber-galaxy matches to existing studies in the literature and explore trends in the absorber and galaxy properties among the matched and non-matched populations. This method of matching absorbers and galaxies can be used to find targets for follow up spectroscopic studies.

  6. Connecting the Silicate Dust and Gas Properties of Distant Galaxies Using Quasar Absorption Systems

    NASA Astrophysics Data System (ADS)

    Aller, Monique C.; Kulkarni, Varsha P.; York, Donald G.; Welty, Daniel E.; Vladilo, Giovanni; Som, Debopam; Lackey, Kyle; Dwek, Eli; Beiranvand, Nassim; Morrison, Sean

    2016-01-01

    We present recent results from our program investigating the silicate dust properties in distant galaxies using quasar absorption systems. The dust and gas properties of distant galaxies can be characterized by studying the absorption features produced by them along the sightlines to luminous background quasars. Based on our prior finding that silicate dust absorption in z<1.5 quasar absorption systems exhibits a range of optical depths and absorption feature substructures, suggestive of silicate grain property variations, we are investigating silicate dust absorption in quasar absorption systems toward quasars with archival Spitzer Space Telescope Infrared Spectrograph (IRS) spectra. We present our measurements of the 10 and/or 18 micron silicate dust absorption feature(s) in these systems, and discuss constraints on the grain properties, such as composition and crystallinity, based on the shape and substructure present in these features. We also investigate the correlations between the silicate dust properties and the reddening. Connections between the silicate dust and gas phase metal absorption properties can also be probed for some of our targets with archival ground-based spectra. These relationships will yield valuable insights into the star formation history and evolution of metals and dust. This work is supported by NASA through ADAP grant NNX14AG74G and by an award issued by JPL/Caltech, and from US-NSF grant AST-1108830 to the University of South Carolina.

  7. Ecology of micro-organisms in a small closed system - Potential benefits and problems for Space Station

    NASA Technical Reports Server (NTRS)

    Rodgers, E. B.; Seale, D. B.; Boraas, M. E.; Sommer, C. V.

    1989-01-01

    The probable sources and implications of microbial contamination on the proposed Space Station are discussed. Because of the limited availability of material, facilities and time on the Space Station, we are exploring the feasibility of replacing traditional incubation methods for assessing microbial contamination with rapid, automated methods. Some possibilities include: ATP measurement, microscopy and telecommunications, and molecular techniques such as DNA probes or monoclonal antibodies. Some of the important ecological factors that could alter microbes in space include microgravity, exposure to radiation, and antibiotic resistance.

  8. Chandra Observes Cosmic Traffic Pile-Up In Energetic Quasar Jet

    NASA Astrophysics Data System (ADS)

    2000-11-01

    Using the unrivaled high resolution of NASA's Chandra X-ray Observatory, astronomers have seen important new details in the powerful jet shooting from the quasar 3C273. This research, coupled with optical and radio data, may reveal how these very high velocity jets are driven from the supermassive black holes that scientists believe lurk in the center of quasars. "For the first time, Chandra has given us an X-ray view into the area between 3C273's core and the beginning of the jet," says MIT's Herman Marshall, lead author on the paper submitted to Astrophysical Journal Letters. "Instead of being void of X-ray emission, Chandra has enabled us to detect a faint, but definite, stream of energy." The high-powered jets driven from quasars, often at velocities very close to the speed of light, have long been perplexing for scientists. Instead of seeing a smooth stream of material driven from the core of the quasar, most optical, radio, and earlier X-ray observations have revealed inconsistent, "lumpy" clouds of gas. This newly discovered continuous X-ray flow in 3C273 from the core to the jet may reveal insight on the physical processes that power these jets. Scientists would like to learn why matter is violently ejected from the quasar's core, then appears to suddenly slow down. "If there is a slower car in front on a highway, a faster one from behind will eventually catch up and maybe cause a wreck," says Marshall. "If the jet flow velocity changes, then gas shocks may result, which are akin to car collisions. These gigantic clouds of high-energy electrons, now seen in X rays with Chandra, may indeed be the result of some sort of cosmic traffic pile-up." The X-ray power produced in one of these pile-ups is tremendous. For example, the X-ray output of the first knot in the jet is greater than that of most Seyfert galaxies, which are thought to be powered by supermassive black holes. The abundance of X-ray emission suggests that large amounts of energy may also be

  9. The use of cortical screw anchorage for closing a space resulting from the loss of a lower molar--a case report.

    PubMed

    Janiszewska-Olszowska, Joanna; Socha, Alina; Bińczak, Paulina

    2013-01-01

    Orthodontic microscrews are temporary implants providing skeletal anchorage, which may be used for en-masse incisor retraction, as well as for the protraction of posterior segments in order to close spaces without retracting anterior teeth. A patient, aged 16 was reported in whom a miniscrew of 9.5 mm length and 2 mm dimension was inserted distal to the lower left second premolar 2 months after extracting the first molar with periapical bone lesion after failed endodontic treatment. The lower third molar was mesialised using direct anchorage and a power arm to minimize mesial tipping. The space closed within 20 months, followed by a spontaneous eruption of the adjacent third molar. This treatment method constitutes a good alternative to third molar autotransplantation, allowing the avoidance of the risk of surgical procedure. PMID:25026758

  10. INTERSTELLAR SILICATE DUST IN FIVE QUASAR ABSORPTION SYSTEMS

    SciTech Connect

    Kulkarni, Varsha P.; Torres-Garcia, Legna M.; Som, Debopam; York, Donald G.; Welty, Daniel E.; Vladilo, Giovanni

    2011-01-01

    We report on a study of interstellar silicate dust in five quasar absorption systems at 0.44 < z{sub abs} < 1.31 toward quasars Q0235+164, 3C196, Q0852+3435, Q0937+5628, and Q1203+0634, using data from the Infrared Spectrograph on board the Spitzer Space Telescope. In the absorbers toward Q0235+164, 3C196, Q0852+3435, and Q0937+5628, the 9.7 {mu}m silicate feature is detected in absorption at {approx}5{sigma}-10{sigma} significance, with rest-frame equivalent widths of {approx}0.2-0.5 {mu}m. For Q1203+0634, the noisy data allow us to make only a 3.6{sigma} detection of absorption at 10 {mu}m. Fits to the redshifted 9.7 {mu}m features with four possible template profiles indicate that the laboratory amorphous olivine profile generally provides the best fit, with inferred peak optical depths of {tau}{sub 9.7} {approx} 0.08-0.18. For three of the quasars with optical spectra available from the Sloan Digital Sky Survey, the Large Magellanic Cloud supershell extinction curve provides the best formal fits, with E(B - V) of 0.34-0.54 mag. A 2175 A extinction bump at the absorber redshift (known to exist in Q0235+164) appears to be present at >2.8{sigma} level in Q0852+3435, >2.5{sigma} level in Q1203+0634, and marginally at nearly 2{sigma} level in Q0937+5628. We briefly explore possible correlations between {tau}{sub 9.7} and the color excess, the strength of the 2175 A bump, and the metallicity (which appears to be relatively high for these absorbers, in the range of {approx}>0.1 solar to supersolar). While our measurements are consistent with a linear relation between {tau}{sub 9.7} and E(B - V), the {tau}{sub 9.7}/E(B - V) ratios for these quasar absorbers appear to be higher than those for diffuse interstellar clouds in the Milky Way, closer to values observed for the Galactic center. Some of these quasar sightlines may trace regions in the bulges of the galaxies responsible for the absorption systems.

  11. Remarks of Ruth Bates Harris, Deputy Assistant Administrator, National Aeronautics and Space Administration at summer institute closing activity

    NASA Technical Reports Server (NTRS)

    1975-01-01

    Applications of experience and knowledge gained from aeronautical and space research and exploration are discussed briefly. Spinoffs are presented which improve the quality of life by contributing to advances in health, transportation, foods, communications, energy, safety, and manufacturing.

  12. A closed-cycle dilution refrigerator with free-space and fiber optical access for quantum optomechanics experiments at 25mK

    NASA Astrophysics Data System (ADS)

    Groeblacher, Simon; Wieczorek, Witlef; Christ, Peter; Buehler, Matthias; Wernicke, Doreen; Hoehne, Jens; Aspelmeyer, Markus

    2011-03-01

    We report on the operation of a closed-cycle dilution refrigerator for quantum optomechanics experiments at 25mK. The dilution fridge is accessible both via free-space as well as fiber coupling, allowing us to perform a variety of optical experiments at low temperatures. It is designed to vibrationally isolate the experiment allowing for stable operation of a high-finesse optical cavity. This enables us to perform cavity-optomechanics experiments at ultra-low temperatures.

  13. Quasars, pulsars, black holes and HEAO's

    NASA Technical Reports Server (NTRS)

    Doolitte, R. F.; Moritz, K.; Whilden, R. D. C.

    1974-01-01

    Astronomical surveys are discussed by large X-ray, gamma ray, and cosmic ray instruments carried onboard high-energy astronomy observatories. Quasars, pulsars, black holes, and the ultimate benefits of the new astronomy are briefly discussed.

  14. Quasars as Probes of Cosmological Reionization

    NASA Astrophysics Data System (ADS)

    Mortlock, Daniel

    Quasars are the most luminous non-transient sources in the epoch of cosmological reionization (which ended a billion years after the Big Bang, corresponding to a redshift of z ≃ 5), and are powerful probes of the inter-galactic medium at that time. This review covers current efforts to identify high-redshift quasars and how they have been used to constrain the reionization history. This includes a full description of the various processes by which neutral hydrogen atoms can absorb/scatter ultraviolet photons, and which lead to the Gunn-Peterson effect, dark gap and dark pixel analyses, quasar near zones and damping wing absorption. Finally, the future prospects for using quasars as probes of reionization are described.

  15. Black-Hole Feedback in Quasars

    NASA Video Gallery

    This animation illustrates how black-hole feedback works in quasars. Dense gas and dust in the center simultaneously fuels the black hole and shrouds it from view. The black-hole wind propels large...

  16. Characterizing Quasar Outflows IV: Regulating Outflows Through X-ray and EUV Absorption

    NASA Astrophysics Data System (ADS)

    Derseweh, Jeffrey; Ganguly, R.; Richmond, J. M.; Stark, M. A.; Christenson, D. H.; Robbins, J. M.; Townsend, S. L.

    2012-05-01

    Galaxy evolution models have shown that quasars are a crucial ingredient in the evolution of massive galaxies. Outflows play a key role in the story of quasars and their host galaxies, by helping regulate the accretion process, the star-formation rate and mass of the host galaxy (i.e., feedback). The prescription for modeling outflows as a contributor to feedback requires knowledge of the outflow velocity, geometry, and column density. In particular, we need to understand how these depend on physical parameters and how much is determined stochastically (and with what distribution). For this purpose, we are examining a sample of 11000 z=1.7-2.0 quasars from the Sloan Digital Sky Survey. This redshift range permits the following from the SDSS spectra: (1) separation of objects that do and do not exhibit outflows; (2) classification/measurement of outflow properties (ionization, velocity, velocity width); and (3) measurements of UV emission line and continuum parameters. In this poster, we add photometry from the GALEX All-sky imaging survey, as well as the Chandra and ROSAT archives. These provide coverage of the rest-frame extreme ultraviolet, and soft X-ray bands. In an accompanying poster, we have subjectively divided these quasars into four categories: broad absorption-line quasars (2700 objects), associated absorption-line quasars (1700 objects), reddened quasars (160 objects), and unabsorbed/unreddened quasars (6300 objects). We are interested in testing the radiative-driving hypothesis that requires a suppression of X-ray flux in order to transfer momentum efficiently to the UV-absorbing gas. Hence, we explore how absorption in both the extreme ultraviolet and the soft X-ray bands correlate with properties of the UV outflows, quasar property, and changes in SED shape. This material is based upon work supported by the National Aeronautics and Space Administration under Grant No. 09-ADP09-0016 issued through the Astrophysics Data Analysis Program and by Chandra

  17. Quasar x-ray spectra revisited

    NASA Technical Reports Server (NTRS)

    Shastri, P.; Wilkes, B. J.; Elvis, M.; Mcdowell, J.

    1992-01-01

    A sample of 45 quasars observed by the Imaging Proportional Counter (IPC) on the Einstein satellite is used to re-examine the relationship between the soft (0.2-3.5 keV) X-ray energy index and radio-loudness. We found the following: (1) the tendency for radio-loud quasars to have systematically flatter X-ray slopes than radio-quiet quasars (RQQ's) is confirmed with the soft X-ray excess having negligible effect; (2) there is a tendency for the flatness of the X-ray slope to correlate with radio core-dominance for radio-loud quasars, suggesting that a component of the X-ray emission is relativistically beamed; (3) for the RQQ's the soft X-ray slopes, with a mean of approximately 1.0, are consistent with the slopes found at higher energies (2-10 keV) although steeper than those observed for Seyfert 1 galaxies (also 2-10 keV) where the reflection model gives a good fit to the data; (4) the correlation of FeII emission line strength with X-ray energy index is confirmed for radio-quiet quasars using a subset of 18 quasars. The radio-loud quasars show no evidence for a correlation. This relation suggests a connection between the ionizing continuum and the line emission from the broad emission line region (BELR) of radio-quiet quasars, but in the opposite sense to that predicted by current photoionization models; and (5) the correlations of X-ray slope with radio core dominance and FeII equivalent width within the radio-loud and radio-quiet sub-classes respectively imply that the observed wide range of X-ray spectral slopes is real rather than due to the large measuring uncertainties for individual objects.

  18. Quasar X-ray spectra revisited

    NASA Technical Reports Server (NTRS)

    Shastri, P.; Wilkes, B. J.; Elvis, M.; Mcdowell, J.

    1993-01-01

    A sample of 45 quasars observed by the IPC on the Einstein satellite is used to reexamine the relationship of the soft X-ray energy index with radio properties and the optical Fe II emission. The tendency for radio-loud quasars to have systematically flatter X-ray energy indices than radio-quiet quasars is confirmed with the soft X-ray excess having negligible effect. There is a tendency for the flatness of the X-ray slope to correlate with radio core dominance for radio-loud quasars, suggesting that a component of the X-ray emission is relativistically beamed. For the radio-quiet quasars, the soft X-ray energy indices with a mean of about 1.0 are consistent with the indices found at higher energies, although steeper than those observed for Seyfert 1 galaxies where the reflection model gives a good fit to the data. The correlation of Fe II emission line strength with X-ray energy index is confirmed for radio-quiet quasars using a subset of 18 objects. The radio-loud quasars show no evidence for a correlation. This relation suggests a connection between the ionizing continuum and line emission from the broad emission-line region (BELR) of radio-quiet quasars, but in the opposite sense to that predicted by current photoionization models. The correlations of X-ray slope with radio core dominance and Fe II equivalent width within the radio-loud and radio-quiet subclasses, respectively, imply that the observed wide range of X-ray energy indices is real rather than due to the large measuring uncertainties for individual objects.

  19. Quasar clustering in a galaxy and quasar formation model based on ultra high-resolution N-body simulations

    NASA Astrophysics Data System (ADS)

    Oogi, Taira; Enoki, Motohiro; Ishiyama, Tomoaki; Kobayashi, Masakazu A. R.; Makiya, Ryu; Nagashima, Masahiro

    2016-02-01

    We investigate clustering properties of quasars using a new version of our semi-analytic model of galaxy and quasar formation with state-of-the-art cosmological N-body simulations. In this study, we assume that a major merger of galaxies triggers cold gas accretion on to a supermassive black hole and quasar activity. Our model can reproduce the downsizing trend of the evolution of quasars. We find that the median mass of quasar host dark matter haloes increases with cosmic time by an order of magnitude from z = 4 (a few 1011 M⊙) to z = 1 (a few 1012 M⊙), and depends only weakly on the quasar luminosity. Deriving the quasar bias through the quasar-galaxy cross-correlation function in the model, we find that the quasar bias does not depend on the quasar luminosity, similar to observed trends. This result reflects the fact that quasars with a fixed luminosity have various Eddington ratios and thus have various host halo masses that primarily determine the quasar bias. We also show that the quasar bias increases with redshift, which is in qualitative agreement with observations. Our bias value is lower than the observed values at high redshifts, implying that we need some mechanisms that make quasars inactive in low-mass haloes and/or that make them more active in high-mass haloes.

  20. Simultaneous Estimation of Time Delays and Quasar Structure

    NASA Astrophysics Data System (ADS)

    Morgan, Christopher W.; Eyler, Michael E.; Kochanek, C. S.; Morgan, Nicholas D.; Falco, Emilio E.; Vuissoz, C.; Courbin, F.; Meylan, G.

    2008-03-01

    We expand our Bayesian Monte Carlo method for analyzing the light curves of gravitationally lensed quasars to simultaneously estimate time delays and the sizes of quasar continuum emission regions including their mutual uncertainties. We apply the method to HE1104-1805 and QJ0158-4325, two doubly imaged quasars with microlensing and intrinsic variability on comparable timescales. For HE1104-1805 the resulting time delay of Δ tAB = tA - tB = 162.2-5.9+6.3 days and accretion disk size estimate of log {(rs/cm) [cos (i)/0.5]1/2} = 15.7-0.5+0.4 at 0.2 μm in the rest frame and for inclination i are consistent with earlier estimates but suggest that existing methods for estimating time delays in the presence of microlensing underestimate the uncertainties. We are unable to measure a time delay for QJ0158-4325, but the accretion disk size is log {(rs/cm) [cos (i)/0.5]1/2} = 14.9 +/- 0.3 at 0.3 μm in the rest frame. Based on observations obtained with the Small and Moderate Aperture Research Telescope System (SMARTS) 1.3 m, which is operated by the SMARTS Consortium, and observations made with the NASA/ESA Hubble Space Telescope for program HST-GO-9744 of the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  1. The Gaia Initial Quasar Catalog

    NASA Astrophysics Data System (ADS)

    Andrei, H.; Antón, S.; Taris, F.; Bourda, G.; Souchay, J.; Bouquillon, J.; Barache, C.; Pereira Osorio, J. J.; Charlot, P.; Vieira Martins, R.; Lambert, S.; Camargo, J. I.; da Silva Neto, D. N.; Assan, M.; le Campion, J.-F.

    2014-12-01

    We present the latest, updated, and fully corrected version of the Gaia Initial QSO Catalog (GIQC), produced by the CU3 GWP-S-335-13000. It contains 1 248 372 objects, of which 191 802 are considered and marked as Defining ones, because of their observational history and existence of spectroscopic redshift. Also objects with strong, calibrator-like radio emission are included in this category. The Defining objects represent a clean sample of quasars. The remaining objects aim to bring completeness to the GIQC at the time of its compilation. For the whole GIQC the average density is 30.3 sources per sq.deg., practically all sources have an indication of magnitude and of morphological indexes, and 90% of the sources have an indication of redshift and of variability indexes.

  2. Balmer line shifts in quasars

    NASA Astrophysics Data System (ADS)

    Sulentic, J. W.; Marziani, P.; Del Olmo, A.; Zamfir, S.

    2016-02-01

    We offer a broad review of Balmer line phenomenology in type 1 active galactic nuclei, briefly summarising luminosity and radio loudness effects, and discussing interpretation in terms of nebular physics along the 4D eigenvector 1 sequence of quasars. We stress that relatively rare, peculiar Balmer line profiles (i.e., with large shifts with respect to the rest frame or double and multiple peaked) that start attracted attentions since the 1970s are still passable of multiple dynamical interpretation. More mainstream objects are still not fully understood as well, since competing dynamical models and geometries are possible. Further progress may come from inter-line comparison across the 4D Eigenvector 1 sequence.

  3. A multicolour search for quasars

    NASA Astrophysics Data System (ADS)

    Mitchell, Paul Simon

    The Edinburgh Multicolour Survey is a data set of approximately 1.3 million images covering a contiguous area of 0.1 steradians at high Galactic latitudes. These data are derived from 130 UK Schmidt photographic plates taken in passbands U, B, V, R, and I in two strips at declinations -5 degrees and 0 degrees, comprising the standard United Kingdom Schmidt Telescope (UKST) fields 789-794 and 861-867 respectively. The aim of the survey is to produce a dataset containing accurate UBVRI information and morphological classification for every image detected in any waveband in the measured area, enabling the discrimination of intrinsically rare populations of objects with non-stellar colours from the foreground of normal Galactic stars. The development of the dataset from its initiation as raw plate material through to the production of the final five-band catalogues, and the selection of quasars over a wide range in redshift are discussed.

  4. X-ray properties of quasars

    NASA Technical Reports Server (NTRS)

    Ku, W. H.-M.; Helfand, D. J.; Lucy, L. B.

    1980-01-01

    The X-ray properties of 111 catalogued quasars have been examined with the imaging proportional counter on board the Einstein Observatory. Thirty-five of the objects, of redshift between 0.064 and 3.53, were detected as X-ray sources. The 0.5-4.5-keV X-ray properties of these quasars are correlated with their optical and radio continuum properties and with their redshifts and variability characteristics. The X-ray luminosity of quasars tends to be highest for those objects which are bright in the optical and radio regimes and which exhibit optically violent variability. These observations suggest that quasars should be divided into two classes on the basis of radio luminosities, spectra, evolution and underlying morphology and that quasars can make up a significant portion of the diffuse soft X-ray background only if the slope of the optical quasar log N-log S relation is steeper than 2 to m sub b of about 21.5.

  5. THE HALO OCCUPATION DISTRIBUTION OF SDSS QUASARS

    SciTech Connect

    Richardson, Jonathan; Chatterjee, Suchetana; Nagai, Daisuke; Zheng Zheng; Shen Yue

    2012-08-10

    We present an estimate of the projected two-point correlation function (2PCF) of quasars in the Sloan Digital Sky Survey (SDSS) over the full range of one- and two-halo scales, 0.02 h{sup -1} Mpc < r{sub p} < 120 h{sup -1} Mpc. This was achieved by combining data from SDSS DR7 on large scales and Hennawi et al. (with appropriate statistical corrections) on small scales. Our combined clustering sample is the largest spectroscopic quasar clustering sample to date, containing {approx}48, 000 quasars in the redshift range 0.4 {approx}< z {approx}< 2.5 with median redshift 1.4. We interpret these precise 2PCF measurements within the halo occupation distribution (HOD) framework and constrain the occupation functions of central and satellite quasars in dark matter halos. In order to explain the small-scale clustering, the HOD modeling requires that a small fraction of z {approx} 1.4 quasars, f{sub sat} = (7.4 {+-} 1.4) Multiplication-Sign 10{sup -4}, be satellites in dark matter halos. At z {approx} 1.4, the median masses of the host halos of central and satellite quasars are constrained to be M{sub cen} = 4.1{sup +0.3}{sub -0.4} Multiplication-Sign 10{sup 12} h{sup -1} M{sub Sun} and M{sub sat} = 3.6{sup +0.8}{sub -1.0} Multiplication-Sign 10{sup 14} h{sup -1} M{sub Sun }, respectively. To investigate the redshift evolution of the quasar-halo relationship, we also perform HOD modeling of the projected 2PCF measured by Shen et al. for SDSS quasars with median redshift 3.2. We find tentative evidence for an increase in the mass scale of quasar host halos-the inferred median mass of halos hosting central quasars at z {approx} 3.2 is M{sub cen} = 14.1{sup +5.8}{sub -6.9} Multiplication-Sign 10{sup 12} h{sup -1} M{sub Sun }. The cutoff profiles of the mean occupation functions of central quasars reveal that quasar luminosity is more tightly correlated with halo mass at higher redshifts. The average quasar duty cycle around the median host halo mass is inferred to be f{sub q

  6. THE PROPERTIES OF QUASAR HOSTS AT THE PEAK OF THE QUASAR ACTIVITY

    SciTech Connect

    Kotilainen, Jari K.; Falomo, Renato; Decarli, Roberto; Treves, Aldo; Uslenghi, Michela; Scarpa, Riccardo E-mail: renato.falomo@oapd.inaf.i E-mail: aldo.treves@uninsubria.i E-mail: riccardo.scarpa@gtc.iac.e

    2009-10-01

    We present near-infrared imaging obtained with ESO VLT/ISAAC of a sample of 16 low luminosity radio-quiet quasars (RQQs) at the epoch around the peak of the quasar activity (2 < z < 3), aimed at investigating their host galaxies. For 11 quasars, we are able to detect the host galaxies and derive their properties, while for the other 5 quasars, upper limits to the host luminosity are estimated. The luminosities of the host galaxies of RQQs at high redshift are in the range of those of massive inactive elliptical galaxies. This work complements our previous systematic study of quasar hosts aimed to trace the cosmological luminosity evolution of the host galaxies up to z approx 2 and extends our pilot study of a few luminous quasars at z > 2. The luminosity trend with a cosmic epoch resembles that observed for massive inactive galaxies, suggesting a similar star formation history. In particular, both quasar host galaxies and massive inactive galaxies appear mostly assembled already at the peak age of the quasar activity. This result is of key importance for testing the models of joint formation and evolution of galaxies and their active nuclei.

  7. Close women, distant men: line bisection reveals sex-dimorphic patterns of visuomotor performance in near and far space.

    PubMed

    Stancey, Helen; Turner, Mark

    2010-05-01

    The mid-points of a series of lines which were positioned both within hand-reach (near space) and beyond hand-reach (far space) were estimated by 24 women and 24 men. When using a laser pointer to perform estimations, women were more accurate in the near condition than the far, whereas men were more accurate in the far condition than the near. When using a stick pointer for the far condition, women were more accurate than when using the laser, whereas men were more accurate using the laser pointer than the stick for the far condition. There was no difference between near and far accuracy scores for either sex using the stick. These results suggest that use of a tool which provides proprioceptive feedback causes the brain to remap far-space stimuli as if situated in near space. Possible origins and neural bases for these differences are considered. Finally, the study found evidence for pseudoneglect, but no evidence for pseudoneglect shift. PMID:19646327

  8. Shielding of longitudinal magnetic fields with thin, closely, spaced concentric cylindrical shells with applications to atomic clocks

    NASA Technical Reports Server (NTRS)

    Wolf, S. A.; Gubser, D. U.; Cox, J. E.

    1978-01-01

    A general formula is given for the longitudinal shielding effectiveness of N closed concentric cylinders. The use of these equations is demonstrated by application to the design of magnetic shields for hydrogen maser atomic clocks. Examples of design tradeoffs such as size, weight, and material thickness are discussed. Experimental results on three sets of shields fabricated by three manufacturers are presented. Two of the sets were designed employing the techniques described. Agreement between the experimental results and the design calculations is then demonstrated.

  9. Red Quasars: Hunting For Hidden Rubies in the Sky

    NASA Astrophysics Data System (ADS)

    Calapa, Marie; Gregg, M.; West, M.

    2014-01-01

    Energetic galactic nuclei, known as quasars, have typically been thought of as blue objects. Over the past decade, however, the existence of a population of red quasars has emerged, revealing a new frontier in the study of these objects. Techniques for efficiently finding red quasars are needed, and we are exploring various selection methods for identifying them in large photometric surveys. Combining IR and optical photometry from UKIDSS and SDSS, we have found a way to separate red quasar candidates from most other sources more effectively than using optical data alone. After our technique proved successful with known red quasars, we applied it to a sample of random objects chosen from a small patch of sky. Investigating those objects that qualified as likely candidates, we found that a large fraction, approaching 50%, were red quasars. This selection technique was then used to make a list of red quasar candidates for further investigation with SpeX at IRTF. Our method for effectively identifying red quasars, using only photometric data, will improve statistics of the red population of quasars. In our small sample area alone, we were able to find over a 1,000 red quasar candidates, implying their numbers may be a significant fraction of all quasars in the universe, perhaps even the majority. Developing a reliable method to find these objects will increase our understanding of the relation between red and blue quasars and the quasar phenomenon in general.

  10. HOST GALAXIES OF LUMINOUS TYPE 2 QUASARS AT z {approx} 0.5

    SciTech Connect

    Liu Xin; Greene, Jenny E.; Strauss, Michael A.; Zakamska, Nadia L.; Krolik, Julian H.; Heckman, Timothy M.

    2009-09-10

    We present deep Gemini GMOS optical spectroscopy of nine luminous quasars at redshifts z {approx} 0.5, drawn from the Sloan Digital Sky Survey type 2 quasar sample. Our targets were selected to have high intrinsic luminosities (M{sub V} < -26 mag) as indicated by the [O III] {lambda}5007 A emission-line luminosity (L[{sub OIII}]). Our sample has a median black hole mass of {approx}10{sup 8.8} M{sub sun} inferred assuming the local M {sub BH}-{sigma}{sub *} relation and a median Eddington ratio of {approx}0.7, using stellar velocity dispersions {sigma}{sub *} measured from the G band. We estimate the contamination of the stellar continuum from scattered quasar light based on the strength of broad H{beta}, and provide an empirical calibration of the contamination as a function of L {sub [OIII]}; the scattered-light fraction is {approx}30% of L{sub 5100} for objects with L {sub [OIII]} = 10{sup 9.5} L{sub sun}. Population synthesis indicates that young poststarburst populations (<0.1 Gyr) are prevalent in luminous type 2 quasars, in addition to a relatively old population (>1 Gyr) which dominates the stellar mass. Broad emission complexes around He II {lambda}4686 A with luminosities up to 10{sup 8.3} L{sub sun} are unambiguously detected in three out of the nine targets, indicative of Wolf-Rayet (WR) populations. Population synthesis shows that {approx}5 Myr poststarburst populations contribute substantially to the luminosities (>50% of L{sub 5100}) of all three objects with WR detections. We find two objects with double cores and four with close companions. Our results may suggest that luminous type 2 quasars trace an early stage of galaxy interaction, perhaps responsible for both the quasar and the starburst activity.

  11. INFRARED SPECTRA AND PHOTOMETRY OF COMPLETE SAMPLES OF PALOMAR-GREEN AND TWO MICRON ALL SKY SURVEY QUASARS

    SciTech Connect

    Shi, Yong; Rieke, G. H.; Su, K. Y. L.; Ogle, P. M.; Balog, Z.

    2014-10-01

    As a step toward a comprehensive overview of the infrared (IR) diagnostics of the central engines and host galaxies of quasars at low redshift, we present Spitzer Space Telescope spectroscopic (5-40 μm) and photometric (24, 70, and 160 μm) measurements of all Palomar-Green (PG) quasars at z < 0.5 and Two Micron All Sky Survey (2MASS) quasars at z < 0.3. We supplement these data with Herschel measurements at 160 μm. The sample is composed of 87 optically selected PG quasars and 52 near-IR-selected 2MASS quasars. Here we present the data, measure the prominent spectral features, and separate emission due to star formation from that emitted by the dusty circumnuclear torus. We find that the mid-IR (5-30 μm) spectral shape for the torus is largely independent of quasar IR luminosity with scatter in the spectral energy distribution (SED) shape of ≲0.2 dex. Except for the silicate features, no large difference is observed between PG (unobscured—silicate emission) and 2MASS (obscured—silicate absorption) quasars. Only mild silicate features are observed in both cases. When in emission, the peak wavelength of the silicate feature tends to be longer than 9.7 μm, possibly indicating effects on grain properties near the active galactic nucleus. The IR color is shown to correlate with the equivalent width of the aromatic features, indicating that the slope of the quasar mid- to far-IR SED is to first order driven by the fraction of radiation from star formation in the IR bands.

  12. Quasar energy distributions. I - Soft X-ray spectra of quasars

    NASA Technical Reports Server (NTRS)

    Wilkes, Belinda J.; Elvis, Martin

    1987-01-01

    As the initial stage of a study of quasar energy distributions (QEDs), Einstein IPC spectra of 24 quasars are presented. These are combined with previously reported IPC spectra to form a sample of 33 quasars with well-determined soft X-ray slopes. A correlation analysis shows that radio loudness, rather than redshift or luminosity, is fundamentally related to the X-ray slope. This correlation is not followed by higher energy spectra of active galaxies. Two components are required to explain both sets of results. The best-fit column densities are systematically smaller than the Galactic values. The same effect is not present in a sample of BL Lac objects, implying that the effect is intrinsic to the quasars and is caused by a low-energy turnup in the quasar spectra.

  13. Heavily reddened quasars at z ˜ 2 in the UKIDSS Large Area Survey: a transitional phase in AGN evolution

    NASA Astrophysics Data System (ADS)

    Banerji, Manda; McMahon, Richard G.; Hewett, Paul C.; Alaghband-Zadeh, Susannah; Gonzalez-Solares, Eduardo; Venemans, Bram P.; Hawthorn, Melanie J.

    2012-12-01

    We present a new sample of purely near-infrared-selected KVega < 16.5 [KAB < 18.4] extremely red [(J - K)Vega > 2.5] quasar candidates at z ˜ 2 from ≃900 deg2 of data in the UKIDSS Large Area Survey (LAS). Five of these are spectroscopically confirmed to be heavily reddened type 1 active galactic nuclei (AGN) with broad emission lines bringing our total sample of reddened quasars from the UKIDSS-LAS to 12 at z = 1.4-2.7. At these redshifts, Hα (6563 Å) is in the K band. However, the mean Hα equivalent width of the reddened quasars is only 10 per cent larger than that of the optically selected population and cannot explain the extreme colours. Instead, dust extinction of AV ˜ 2-6 mag is required to reproduce the continuum colours of our sources. This is comparable to the dust extinctions seen in submillimetre galaxies at similar redshifts. We argue that the AGN are likely being observed in a relatively short-lived breakout phase when they are expelling gas and dust following a massive starburst, subsequently turning into UV-luminous quasars. Some of our quasars show direct evidence for strong outflows (v ˜ 800-1000 km s-1) affecting the Hα line consistent with this scenario. We predict that a larger fraction of reddened quasar hosts are likely to be submillimetre bright compared to the UV-luminous quasar population. We use our sample to place new constraints on the fraction of obscured type 1 AGN likely to be missed in optical surveys. Taken at face value our findings suggest that the obscured fraction depends on quasar luminosity. The space density of obscured quasars is approximately five times that inferred for UV-bright quasars from the Sloan Digital Sky Survey (SDSS) luminosity function at Mi < -30 but seems to drop at lower luminosities even accounting for various sources of incompleteness in our sample. We find that at Mi ˜ -28 for example, this fraction is unlikely to be larger than ˜20 per cent although these fractions are highly uncertain at

  14. Joint-space adaptive control of a 6 DOF end-effector with closed-kinematic chain mechanism

    NASA Technical Reports Server (NTRS)

    Nguyen, Charles C.; Zhou, Zhen-Lei

    1989-01-01

    The development is presented for a joint-space adaptive scheme that controls the joint position of a six-degree-of-freedom (DOF) robot end-effector performing fine and precise motion within a very limited workspace. The end-effector was built to study autonomous assembly of NASA hardware in space. The design of the adaptive controller is based on the concept of model reference adaptive control (MRAC) and Lyapunov direct method. In the development, it is assumed that the end-effector performs slowly varying motion. Computer simulation is performed to investigate the performance of the developed control scheme on position control of the end-effector. Simulation results manifest that the adaptive control scheme provides excellent tracking of several test paths.

  15. Closed-cell foams produced from sputter-deposited aluminum. [experiments on earth and in space environment

    NASA Technical Reports Server (NTRS)

    Patten, J. W.; Greenwell, E. N.

    1977-01-01

    Sputter deposited aluminum containing argon was melted to produce foam, both in the earth's gravitational field and in a zero-gravity space environment. Experiments leading to trapping of up to 270 ppm argon sputtering gas in pure aluminum during high-rate dc triode sputter deposition are discussed. Conduct of the melting experiments and design of the furnace used are described. Metallography; an analysis of bubble size, distribution, and morphology; and a preliminary description of the kinetics are also presented.

  16. Quasar emission lines, radio structures and radio unification

    NASA Astrophysics Data System (ADS)

    Jackson, Neal; Browne, I. W. A.

    2013-02-01

    Unified schemes of radio sources, which account for different types of radio active galactic nucleus in terms of anisotropic radio and optical emission, together with different orientations of the ejection axis to the line of sight, have been invoked for many years. Recently, large samples of optical quasars, mainly from the Sloan Digital Sky Survey (SDSS), together with large radio samples, such as Faint Images of the Radio Sky at Twenty cm (FIRST), have become available. These hold the promise of providing more stringent tests of unified schemes but, compared to previous samples, lack high-resolution radio maps. Nevertheless, they have been used to investigate unified schemes, in some cases yielding results which appear inconsistent with such theories. Here we investigate using simulations how the selection effects to which such investigations are subject can influence the conclusions drawn. In particular, we find that the effects of limited resolution do not allow core-dominated radio sources to be fully represented in the samples, that the effects of limited sensitivity systematically exclude some classes of sources and the lack of deep radio data make it difficult to decide to what extent closely separated radio sources are associated. Nevertheless, we conclude that relativistic unified schemes are entirely compatible with the current observational data. For a sample selected from SDSS and FIRST which includes weak-cored triples we find that the equivalent width of the [O III] emission line decreases as core dominance increases, as expected, and also that core-dominated quasars are optically brighter than weak-cored quasars.

  17. Beacons in Time: Maarten Schmidt and the Discovery of Quasars.

    ERIC Educational Resources Information Center

    Preston, Richard

    1988-01-01

    Tells the story of Maarten Schmidt and the discovery of quasars. Discusses the decomposition of light, crucial observations and solving astronomical mysteries. Describes spectroscopic analysis used in astronomy and its application to quasars. (CW)

  18. THE SUBARU HIGH-z QUASAR SURVEY: DISCOVERY OF FAINT z ∼ 6 QUASARS

    SciTech Connect

    Kashikawa, Nobunari; Furusawa, Hisanori; Niino, Yuu; Ishizaki, Yoshifumi; Onoue, Masafusa; Toshikawa, Jun; Ishikawa, Shogo; Willott, Chris J.; Im, Myungshin; Shimasaku, Kazuhiro; Ouchi, Masami; Hibon, Pascale

    2015-01-01

    We present the discovery of one or two extremely faint z ∼ 6 quasars in 6.5 deg{sup 2} utilizing a unique capability of the wide-field imaging of the Subaru/Suprime-Cam. The quasar selection was made in (i'-z{sub B} ) and (z{sub B} -z{sub R} ) colors, where z{sub B} and z{sub R} are bandpasses with central wavelengths of 8842 Å and 9841 Å, respectively. The color selection can effectively isolate quasars at z ∼ 6 from M/L/T dwarfs without the J-band photometry down to z{sub R} < 24.0, which is 3.5 mag deeper than the Sloan Digital Sky Survey (SDSS). We have selected 17 promising quasar candidates. The follow-up spectroscopy for seven targets identified one apparent quasar at z = 6.156 with M {sub 1450} = –23.10. We also identified one possible quasar at z = 6.041 with a faint continuum of M {sub 1450} = –22.58 and a narrow Lyα emission with HWHM =427 km s{sup –1}, which cannot be distinguished from Lyman α emitters. We derive the quasar luminosity function at z ∼ 6 by combining our faint quasar sample with the bright quasar samples by SDSS and CFHQS. Including our data points invokes a higher number density in the faintest bin of the quasar luminosity function than the previous estimate employed. This suggests a steeper faint-end slope than lower z, though it is yet uncertain based on a small number of spectroscopically identified faint quasars, and several quasar candidates still remain to be diagnosed. The steepening of the quasar luminosity function at the faint end does increase the expected emission rate of the ionizing photon; however, it only changes by a factor of approximately two to six. This was found to still be insufficient for the required photon budget of reionization at z ∼ 6.

  19. Quasars: a supermassive rotating toroidal black hole interpretation

    NASA Astrophysics Data System (ADS)

    Spivey, R. J.

    2000-08-01

    A supermassive rotating toroidal black hole (TBH) is proposed as the fundamental structure of quasars and other jet-producing active galactic nuclei. Rotating protogalaxies gather matter from the central gaseous region leading to the birth of massive toroidal stars, the internal nuclear reactions of which proceed very rapidly. Once the nuclear fuel is spent, gravitational collapse produces a slender ring-shaped TBH remnant. Transitory electron and neutron degeneracy stabilized collapse phases, although possible, are unlikely owing to the large masses involved thus these events are typically the first supernovae of the host galaxies. Given time, the TBH mass increases through continued accretion by several orders of magnitude, the event horizon swells whilst the central aperture shrinks. The difference in angular velocities between the accreting matter and the TBH induces a magnetic field that is strongest in the region of the central aperture and innermost ergoregion. Owing to the presence of negative energy states when such a gravitational vortex is immersed in an electromagnetic field, circumstances are near ideal for energy extraction via non-thermal radiation including the Penrose process and superradiant scattering. This establishes a self-sustaining mechanism whereby the transport of angular momentum away from the quasar by relativistic bi-directional jets reinforces both the modulating magnetic field and the TBH/accretion disc angular velocity differential. Continued mass-capture by the TBH results in contraction of the central aperture until the TBH topology transitions to being spheroidal, extinguishing quasar behaviour. Similar mechanisms may be operating in microquasars, supernovae and sources of repeating gamma-ray bursts when neutron density or black hole tori arise. Long-term TBH stability seems to require either a negative cosmological constant, a non-stationary space-time resulting from the presence of accreting matter or the intervention of quantum

  20. Quasar Spectral Energy Distributions As A Function Of Physical Property

    NASA Astrophysics Data System (ADS)

    Townsend, Shonda; Ganguly, R.; Stark, M. A.; Derseweh, J. A.; Richmond, J. M.

    2012-05-01

    Galaxy evolution models have shown that quasars are a crucial ingredient in the evolution of massive galaxies. Outflows play a key role in the story of quasars and their host galaxies, by helping regulate the accretion process, the star-formation rate and mass of the host galaxy (i.e., feedback). The prescription for modeling outflows as a contributor to feedback requires knowledge of the outflow velocity, geometry, and column density. In particular, we need to understand how these depend on physical parameters and how much is determined stochastically (and with what distribution). In turn, models of outflows have shown particular sensitivity to the shape of the spectral energy distribution (SED), depending on the UV luminosity to transfer momentum to the gas, the X-ray luminosity to regulate how efficiently that transfer can be, etc. To investigate how SED changes with physical properties, we follow up on Richards et al. (2006), who constructed SEDs with varying luminosity. Here, we construct SEDs as a function of redshift, and physical property (black hole mass, bolometric luminosity, Eddington ratio) for volume limited samples drawn from the Sloan Digital Sky Survey, with photometry supplemented from 2MASS, WISE, GALEX, ROSAT, and Chandra. To estimate black hole masses, we adopt the scaling relations from Greene & Ho (2005) based on the H-alpha emission line FWHM. This requires redshifts less than 0.4. To construct volume-limited subsamples, we begin by adopting g=19.8 as a nominal limiting magnitude over which we are guaranteed to detect z<0.4 quasars. At redshift 0.4, we are complete down to Mg=-21.8, which yields 3300 objects from Data Release 7. At z=0.1, we are complete down to Mg=-18.5. This material is based upon work supported by the National Aeronautics and Space Administration under Grant No. 09-ADP09-0016 issued through the Astrophysics Data Analysis Program.

  1. Biodiversity and Ecology of Amphibians and Reptiles of the Kennedy Space Center: 1998 Close-Out Report to NASA

    NASA Technical Reports Server (NTRS)

    Sigel, Richard A.

    1999-01-01

    Since 1992, there have been researchers have been studying the population ecology and conservation biology of the amphibians and reptiles of the Kennedy Space Center (KSC) This research is an outgrowth of my Master's work in the late 1970's under Lew Ehrhart at UCF. The primary emphasis of our studies are (1) examination of long-term changes in the abundance of amphibians and reptile populations, (2) occurrence and effects of Upper Respiratory Tract Disease (URTD) in gopher tortoises (Gopherus polyphemus), and (3) ecological studies of selected species.

  2. Systems efficiency and specific mass estimates for direct and indirect solar-pumped closed-cycle high-energy lasers in space

    NASA Technical Reports Server (NTRS)

    Monson, D. J.

    1978-01-01

    Based on expected advances in technology, the maximum system efficiency and minimum specific mass have been calculated for closed-cycle CO and CO2 electric-discharge lasers (EDL's) and a direct solar-pumped laser in space. The efficiency calculations take into account losses from excitation gas heating, ducting frictional and turning losses, and the compressor efficiency. The mass calculations include the power source, radiator, compressor, fluids, ducting, laser channel, optics, and heat exchanger for all of the systems; and in addition the power conditioner for the EDL's and a focusing mirror for the solar-pumped laser. The results show the major component masses in each system, show which is the lightest system, and provide the necessary criteria for solar-pumped lasers to be lighter than the EDL's. Finally, the masses are compared with results from other studies for a closed-cycle CO2 gasdynamic laser (GDL) and the proposed microwave satellite solar power station (SSPS).

  3. SIX MORE QUASARS AT REDSHIFT 6 DISCOVERED BY THE CANADA-FRANCE HIGH-z QUASAR SURVEY

    SciTech Connect

    Willott, Chris J.; Crampton, David; Hutchings, John B.; Schade, David; Delorme, Philippe; Delfosse, Xavier; Forveille, Thierry; Reyle, Celine; Albert, Loic; Bergeron, Jacqueline; Omont, Alain; McLure, Ross J.

    2009-03-15

    We present imaging and spectroscopic observations for six quasars at z {>=} 5.9 discovered by the Canada-France High-z Quasar Survey (CFHQS). The CFHQS contains subsurveys with a range of flux and area combinations to sample a wide range of quasar luminosities at z {approx} 6. The new quasars have luminosities 10-75 times lower than the most luminous Sloan Digital Sky Survey quasars at this redshift. The least luminous quasar, CFHQS J0216-0455 at z = 6.01, has absolute magnitude M {sub 1450} = -22.21, well below the likely break in the luminosity function. This quasar is not detected in a deep XMM-Newton survey showing that optical selection is still a very efficient tool for finding high-redshift quasars.

  4. 3C 57 as an atypical radio-loud quasar: implications for the radio-loud/radio-quiet dichotomy

    NASA Astrophysics Data System (ADS)

    Sulentic, J. W.; Martínez-Carballo, M. A.; Marziani, P.; del Olmo, A.; Stirpe, G. M.; Zamfir, S.; Plauchu-Frayn, I.

    2015-06-01

    Lobe-dominated radio-loud (LD RL) quasars occupy a restricted domain in the 4D Eigenvector 1 (4DE1) parameter space which implies restricted geometry/physics/kinematics for this subclass compared to the radio-quiet (RQ) majority of quasars. We discuss how this restricted domain for the LD RL parent population supports the notion for a RQ-RL dichotomy among type 1 sources. 3C 57 is an atypical RL quasar that shows both uncertain radio morphology and falls in a region of 4DE1 space where RL quasars are rare. We present new radio flux and optical spectroscopic measures designed to verify its atypical optical/UV spectroscopic behaviour and clarify its radio structure. The former data confirms that 3C 57 falls off the 4DE1 quasar `main sequence' with both extreme optical Fe II emission (R_{Fe II} ˜ 1) and a large C IV λ1549 profile blueshift (˜-1500 km s-1). These parameter values are typical of extreme Population A sources which are almost always RQ. New radio measures show no evidence for flux change over a 50+ year time-scale consistent with compact steep-spectrum (or young LD) over core-dominated morphology. In the 4DE1 context where LD RL are usually low L/LEdd quasars, we suggest that 3C 57 is an evolved RL quasar (i.e. large blackhole mass) undergoing a major accretion event leading to a rejuvenation reflected by strong Fe II emission, perhaps indicating significant heavy metal enrichment, high bolometric luminosity for a low-redshift source and resultant unusually high Eddington ratio giving rise to the atypical C IV λ1549.

  5. Indications and counterindications for applying different versions of closed ecosystems for space and terrestrial problems of life support.

    PubMed

    Mezhevikin, V V; Okhonin, V A; Bartsev, S I; Gitelson, J I

    1994-11-01

    Different versions of manned closed ecosystems (CES) based on photosynthesis of unicellular and/or higher plants and chemosynthesis or bacteria are considered. Different versions of CES have been compared for applying them on Earth, Moon, Mars and Venus orbital stations, for Mars missions and planetary stations as well as to provide high-quality life in extreme conditions on the Earth. In microgravity [correction of mycrogravity] we recommend CES with unicellular organisms based on photosynthesis or chemosynthesis (depending of the availability of the light or electric energy). For the planetary stations with Moon gravity and higher CES with higher plants are recommended. Improvement of indoor air quality by CES biotechnology is considered. PMID:11540175

  6. Evolution of Quasar Spectral Energy Distributions

    NASA Astrophysics Data System (ADS)

    Schilling, Amanda; Kennefick, J.; Mahmood, A.

    2012-05-01

    A common practice when formulating quasar luminosity functions (QLF) has been to adopt an average spectral index, $\\alpha$, for the sample even though it is well known that quasars exhibit a broad range of spectral energy distributions (SED.) We have investigated the possible evolution of $\\alpha$ as a function of redshift, as any evolution in this parameter would introduce or mask evolution in the QLF. We imaged 103 Sloan Digital Sky Survey (SDSS) quasars in the optical and near-infrared bands, near in time to mitigate the effects of variability, in three redshift bins centered at $z\\approx 1.9$, $2.7$, and $4.0$, corresponding to look-back times of 10-12 billion years. We present restframe UV-optical SED’s and spectral indices and discuss possible evolution in our sample. We also use single epoch spectra of the quasars to estimate the mass of the central black hole and discuss possible correlations of quasar properties such as mass, luminosity, and spectral shape.

  7. Relativistic redshifts in quasar broad lines

    SciTech Connect

    Tremaine, Scott; Shen, Yue; Liu, Xin; Loeb, Abraham E-mail: yshen@obs.carnegiescience.edu E-mail: aloeb@cfa.harvard.edu

    2014-10-10

    The broad emission lines commonly seen in quasar spectra have velocity widths of a few percent of the speed of light, so special- and general-relativistic effects have a significant influence on the line profile. We have determined the redshift of the broad Hβ line in the quasar rest frame (determined from the core component of the [O III] line) for over 20,000 quasars from the Sloan Digital Sky Survey Data Release 7 quasar catalog. The mean redshift as a function of line width is approximately consistent with the relativistic redshift that is expected if the line originates in a randomly oriented Keplerian disk that is obscured when the inclination of the disk to the line of sight exceeds ∼30°-45°, consistent with simple active galactic nucleus unification schemes. This result also implies that the net line-of-sight inflow/outflow velocities in the broad-line region are much less than the Keplerian velocity when averaged over a large sample of quasars with a given line width.

  8. Exploring the Quasar Luminosity Function with Quasars Selected by both Color and Variability

    NASA Astrophysics Data System (ADS)

    Peters, Christina M.; Richards, Gordon T.

    2016-01-01

    Using a Bayesian selection algorithm, we determine the optimal combination of color and variability information to identify quasars in current and future multi-epoch optical surveys. The color analysis is based on SDSS photometry, and the variability parameters are calculated from power-law fits to the structure functions. Simultaneous color and variability classification improves classification over either color or variability selection alone, with particular improvement in the selection of quasars with colors similar to stars. This method identifies 22,867 new type 1 quasar candidates in SDSS Stripe 82, which can be combined with the WISE and SDSS photometric quasar candidate catalogs. The redshifts of the candidate quasars were estimated using all available bands, weighting each band by smoothing the PDF. We show how to correct the candidate quasar luminosity function (QLF) for the completeness fraction and systematic errors in redshifts. The corrected QLF is comparable to those determined by spectroscopic investigations, suggesting that LSST and other next-generation surveys will be able to accurately determine the QLF in the absence of spectra. Finally, the quasars are divided into high and low Eddington fractions, using delta(g-i) and CIV blueshift as proxies. The candidate QLFs for the two populations are compared to look for changes as a function of redshift. This work was supported in part by NSF grant 1411773.

  9. Closed-form solution for the Wigner phase-space distribution function for diffuse reflection and small-angle scattering in a random medium.

    PubMed

    Yura, H T; Thrane, L; Andersen, P E

    2000-12-01

    Within the paraxial approximation, a closed-form solution for the Wigner phase-space distribution function is derived for diffuse reflection and small-angle scattering in a random medium. This solution is based on the extended Huygens-Fresnel principle for the optical field, which is widely used in studies of wave propagation through random media. The results are general in that they apply to both an arbitrary small-angle volume scattering function, and arbitrary (real) ABCD optical systems. Furthermore, they are valid in both the single- and multiple-scattering regimes. Some general features of the Wigner phase-space distribution function are discussed, and analytic results are obtained for various types of scattering functions in the asymptotic limit s > 1, where s is the optical depth. In particular, explicit results are presented for optical coherence tomography (OCT) systems. On this basis, a novel way of creating OCT images based on measurements of the momentum width of the Wigner phase-space distribution is suggested, and the advantage over conventional OCT images is discussed. Because all previous published studies regarding the Wigner function are carried out in the transmission geometry, it is important to note that the extended Huygens-Fresnel principle and the ABCD matrix formalism may be used successfully to describe this geometry (within the paraxial approximation). Therefore for completeness we present in an appendix the general closed-form solution for the Wigner phase-space distribution function in ABCD paraxial optical systems for direct propagation through random media, and in a second appendix absorption effects are included. PMID:11140505

  10. Quasar feedback and the origin of radio emission in radio-quiet quasars

    NASA Astrophysics Data System (ADS)

    Zakamska, Nadia L.; Greene, Jenny E.

    2014-07-01

    We analyse Sloan Digital Sky Survey spectra of 568 obscured luminous quasars. The [O III] λ5007 Å emission line shows blueshifts and blue excess, indicating that some of the narrow-line gas is undergoing an organized outflow. The velocity width containing 90 per cent of line power ranges from 370 to 4780 km s-1, suggesting outflow velocities up to ˜2000 km s-1, and is strongly correlated with the radio luminosity among the radio-quiet quasars. We propose that radio emission in radio-quiet quasars is due to relativistic particles accelerated in the shocks within the quasar-driven outflows; star formation in quasar hosts is insufficient to explain the observed radio emission. The median radio luminosity of the sample of νLν[1.4 GHz] = 1040 erg s-1 suggests a median kinetic luminosity of the quasar-driven wind of Lwind = 3 × 1044 erg s-1, or about 4 per cent of the estimated median bolometric luminosity Lbol = 8 × 1045 erg s-1. Furthermore, the velocity width of [O III] is positively correlated with mid-infrared luminosity, which suggests that outflows are ultimately driven by the radiative output of the quasar. Emission lines characteristic of shocks in quasi-neutral medium increase with the velocity of the outflow, which we take as evidence of quasar-driven winds propagating into the interstellar medium of the host galaxy. Quasar feedback appears to operate above the threshold luminosity of Lbol ˜ 3 × 1045 erg s-1.

  11. The UV-bright Quasar Survey (UVQS): DR1

    NASA Astrophysics Data System (ADS)

    Monroe, TalaWanda R.; Prochaska, J. Xavier; Tejos, Nicolas; Worseck, Gabor; Hennawi, Joseph F.; Schmidt, Tobias; Tumlinson, Jason; Shen, Yue

    2016-07-01

    We present the first data release (DR1) from our UV-bright Quasar Survey for new z ∼ 1 active galactic nuclei (AGNs) across the sky. Using simple GALEX UV and WISE near-IR color selection criteria, we generated a list of 1450 primary candidates with FUV < 18.5 mag. We obtained discovery spectra, primarily on 3 m-class telescopes, for 1040 of these candidates and confirmed 86% as AGNs, with redshifts generally at z > 0.5. Including a small set of observed secondary candidates, we report the discovery of 217 AGNs with FUV < 18 mag that previously had no reported spectroscopic redshift. These are excellent potential targets for UV spectroscopy before the end of the Hubble Space Telescope mission. The main data products are publicly available through the Mikulski Archive for Space Telescopes.

  12. 3D Position and Velocity Vector Computations of Objects Jettisoned from the International Space Station Using Close-Range Photogrammetry Approach

    NASA Technical Reports Server (NTRS)

    Papanyan, Valeri; Oshle, Edward; Adamo, Daniel

    2008-01-01

    Measurement of the jettisoned object departure trajectory and velocity vector in the International Space Station (ISS) reference frame is vitally important for prompt evaluation of the object s imminent orbit. We report on the first successful application of photogrammetric analysis of the ISS imagery for the prompt computation of the jettisoned object s position and velocity vectors. As post-EVA analyses examples, we present the Floating Potential Probe (FPP) and the Russian "Orlan" Space Suit jettisons, as well as the near-real-time (provided in several hours after the separation) computations of the Video Stanchion Support Assembly Flight Support Assembly (VSSA-FSA) and Early Ammonia Servicer (EAS) jettisons during the US astronauts space-walk. Standard close-range photogrammetry analysis was used during this EVA to analyze two on-board camera image sequences down-linked from the ISS. In this approach the ISS camera orientations were computed from known coordinates of several reference points on the ISS hardware. Then the position of the jettisoned object for each time-frame was computed from its image in each frame of the video-clips. In another, "quick-look" approach used in near-real time, orientation of the cameras was computed from their position (from the ISS CAD model) and operational data (pan and tilt) then location of the jettisoned object was calculated only for several frames of the two synchronized movies. Keywords: Photogrammetry, International Space Station, jettisons, image analysis.

  13. Clustering of High Redshift (z>2.9) Quasars from the Sloan Digital Sky Survey

    SciTech Connect

    Shen, Yue; Strauss, Michael A.; Oguri, Masamune; Hennawi, Joseph F.; Fan, Xiaohui; Richards, Gordon T.; Hall, Patrick B.; Schneider, Donald P.; Szalay, Alexander S.; Thakar, Anirudda R.; Berk, Daniel E.Vanden; Anderson, Scott F.; Bahcall, Neta A.; /KIPAC, Menlo Park

    2006-11-30

    We study the two-point correlation function of a uniformly selected sample of 4,428 optically selected luminous quasars with redshift 2.9 {le} z {le} 5.4 selected over 4041 deg{sup 2} from the Fifth Data Release of the Sloan Digital Sky Survey. We fit a power-law to the projected correlation function w{sub p}(r{sub p}) to marginalize over redshift space distortions and redshift errors. For a real-space correlation function of the form {zeta}(r) = (r/r{sub 0}){sup -{gamma}}, the fitted parameters in comoving coordinates are r{sub 0} = 15.2 {+-} 2.7 h{sup -1} Mpc and {gamma} = 2.0 {+-} 0.3, over a scale range 4 {le} r{sub p} {le} 150 h{sup -1} Mpc. Thus high-redshift quasars are appreciably more strongly clustered than their z {approx} 1.5 counterparts, which have a comoving clustering length r{sub 0} {approx} 6.5 h{sup -1} Mpc. Dividing our sample into two redshift bins: 2.9 {le} z {le} 3.5 and z {ge} 3.5, and assuming a power-law index {gamma} = 2.0, we find a correlation length of r{sub 0} = 16.9 {+-} 1.7 h{sup -1} Mpc for the former, and r{sub 0} = 24.3 {+-} 2.4 h{sup -1} Mpc for the latter. Strong clustering at high redshift indicates that quasars are found in very massive, and therefore highly biased, halos. Following Martini & Weinberg, we relate the clustering strength and quasar number density to the quasar lifetimes and duty cycle. Using the Sheth & Tormen halo mass function, the quasar lifetime is estimated to lie in the range 4 {approx} 50 Myr for quasars with 2.9 {le} z {le} 3.5; and 30 {approx} 600 Myr for quasars with z {ge} 3.5. The corresponding duty cycles are 0.004 {approx} 0.05 for the lower redshift bin and 0.03 {approx} 0.6 for the higher redshift bin. The minimum mass of halos in which these quasars reside is 2-3 x 10{sup 12} h{sup -1} M{sub {circle_dot}} for quasars with 2.9 {le} z {le} 3.5 and 4-6 x 10{sup 12} h{sup -1} M{sub {circle_dot}} for quasars with z {ge} 3.5; the effective bias factor b{sub eff} increases with redshift, e.g., b

  14. Subnanosecond GPS-based clock synchronization and precision deep-space tracking

    NASA Technical Reports Server (NTRS)

    Dunn, C. E.; Lichten, S. M.; Jefferson, D. C.; Border, J. S.

    1992-01-01

    Interferometric spacecraft tracking is accomplished by the Deep Space Network (DSN) by comparing the arrival time of electromagnetic spacecraft signals at ground antennas separated by baselines on the order of 8000 km. Clock synchronization errors within and between DSN stations directly impact the attainable tracking accuracy, with a 0.3-nsec error in clock synchronization resulting in an 11-nrad angular position error. This level of synchronization is currently achieved by observing a quasar which is angularly close to the spacecraft just after the spacecraft observations. By determining the differential arrival times of the random quasar signal at the stations, clock offsets and propagation delays within the atmosphere and within the DSN stations are calibrated. Recent developments in time transfer techniques may allow medium accuracy (50-100 nrad) spacecraft tracking without near-simultaneous quasar-based calibrations. Solutions are presented for a worldwide network of Global Positioning System (GPS) receivers in which the formal errors for DSN clock offset parameters are less than 0.5 nsec. Comparisons of clock rate offsets derived from GPS measurements and from very long baseline interferometry (VLBI), as well as the examination of clock closure, suggest that these formal errors are a realistic measure of GPS-based clock offset precision and accuracy. Incorporating GPS-based clock synchronization measurements into a spacecraft differential ranging system would allow tracking without near-simultaneous quasar observations. The impact on individual spacecraft navigation-error sources due to elimination of quasar-based calibrations is presented. System implementation, including calibration of station electronic delays, is discussed.

  15. Intergalactic Helium Absorption toward High-Redshift Quasars

    NASA Technical Reports Server (NTRS)

    Giroux, Mark L.; Fardal, Mark A.; Shull, J. Michael

    1995-01-01

    The recent Hubble Space Telescope (HST) observations of the z(q) = 3.286 quasar Q0302-003 (Jakobsen et at. 1994) and the z(q) = 3.185 quasar Q1935-67 by Tytler (1995) show absorption edges at the redshifted wavelength of He II 304 A. A key goal is to distinguish between contributions from discrete Ly-alpha forest clouds and a smoothly distributed intergalactic medium (IGM). We model the contributions from each of these sources of He II absorption, including the distribution of line Doppler widths and column densities, the 'He II proximity effect' from the quasar, and a self-consistent derivation of the He II opacity of the universe as a function of the spectrum of ionizing sources, with the assumption that both the clouds and the IGM are photoionized. The He II edge can be fully accounted for by He II line blanketing for reasonable distributions of line widths and column densities in the Ly-alpha forest, provided that the ionizing sources have spectral index alpha(s) greater than 1.5, and any He II proximity effect is neglected. Even with some contribution from a diffuse IGM, it is difficult to account for the edge observed by Jakobsen et al. (1994) with a 'hard' source spectrum (alpha(s) less than 1.3). The proximity effect modifies the relative contributions of the clouds and IGM to tau(He II) near the quasar (z approx. less than z(q)) and markedly increases the amount of He II absorption required. This implies, for example, that to account for the He II edge with line blanketing alone, the minimum spectral index alpha(s) must be increased from 1.5 to 1.9. We demonstrate the need for higher resolution observations that characterize the change in transmission as z approaches z(q) and resolve line-free gaps in the continuum. We set limits on the density of the diffuse IGM and suggest that the IGM and Ly-alpha clouds are likely to be a significant repository for dark baryons.

  16. Conceptual Design Study of a Closed Brayton Cycle Turbogenerator for Space Power Thermal-To-Electric Conversion System

    NASA Technical Reports Server (NTRS)

    Hansen, Jeff L.

    2000-01-01

    A conceptual design study was completed for a 360 kW Helium-Xenon closed Brayton cycle turbogenerator. The selected configuration is comprised of a single-shaft gas turbine engine coupled directly to a high-speed generator. The engine turbomachinery includes a 2.5:1 pressure ratio compression system with an inlet corrected flow of 0.44 kg/sec. The single centrifugal stage impeller discharges into a scroll via a vaned diffuser. The scroll routes the air into the cold side sector of the recuperator. The hot gas exits a nuclear reactor radiator at 1300 K and enters the turbine via a single-vaned scroll. The hot gases are expanded through the turbine and then diffused before entering the hot side sector of the recuperator. The single shaft design is supported by air bearings. The high efficiency shaft mounted permanent magnet generator produces an output of 370 kW at a speed of 60,000 rpm. The total weight of the turbogenerator is estimated to be only 123 kg (less than 5% of the total power plant) and has a volume of approximately 0.11 cubic meters. This turbogenerator is a key element in achieving the 40 to 45% overall power plant thermal efficiency.

  17. INFRARED CLASSIFICATION AND LUMINOSITIES FOR DUSTY ACTIVE GALACTIC NUCLEI AND THE MOST LUMINOUS QUASARS

    SciTech Connect

    Weedman, Daniel; Sargsyan, Lusine; Houck, James; Barry, Donald; Lebouteiller, Vianney

    2012-12-20

    Mid-infrared spectroscopic measurements from the Infrared Spectrometer (IRS) on Spitzer are given for 125 hard X-ray active galactic nuclei (AGNs; 14-195 keV) from the Swift Burst Alert Telescope (BAT) sample and for 32 AGNs with black hole masses (BHMs) from reverberation mapping. The 9.7 {mu}m silicate feature in emission or absorption defines an infrared AGN classification describing whether AGNs are observed through dust clouds, indicating that 55% of the BAT AGNs are observed through dust. The mid-infrared dust continuum luminosity is shown to be an excellent indicator of intrinsic AGN luminosity, scaling closely with the hard X-ray luminosity, log {nu}L{sub {nu}}(7.8 {mu}m)/L(X) = -0.31 {+-} 0.35, and independent of classification determined from silicate emission or absorption. Dust luminosity scales closely with BHM, log {nu}L{sub {nu}}(7.8 {mu}m) = (37.2 {+-} 0.5) + 0.87 log BHM for luminosity in erg s{sup -1} and BHM in M{sub Sun }. The 100 most luminous type 1 quasars as measured in {nu}L{sub {nu}}(7.8 {mu}m) are found by comparing Sloan Digital Sky Survey (SDSS) optically discovered quasars with photometry at 22 {mu}m from the Wide-Field Infrared Survey Explorer (WISE), scaled to rest frame 7.8 {mu}m using an empirical template determined from IRS spectra. The most luminous SDSS/WISE quasars have the same maximum infrared luminosities for all 1.5 < z < 5, reaching total infrared luminosity L{sub IR} = 10{sup 14.4} L{sub Sun }. Comparing with dust-obscured galaxies from Spitzer and WISE surveys, we find no evidence of hyperluminous obscured quasars whose maximum infrared luminosities exceed the maximum infrared luminosities of optically discovered quasars. Bolometric luminosities L{sub bol} estimated from rest-frame optical or ultraviolet luminosities are compared to L{sub IR}. For the local AGN, the median log L{sub IR}/L{sub bol} = -0.35, consistent with a covering factor of 45% for the absorbing dust clouds. For the SDSS/WISE quasars, the median log L

  18. A Ly{alpha} HALO AROUND A QUASAR AT REDSHIFT z = 6.4

    SciTech Connect

    Willott, Chris J.; Chet, Savironi; Hutchings, John B.; Bergeron, Jacqueline

    2011-12-15

    We present long-slit spectroscopic data that reveal extended Ly{alpha} emission around the z = 6.417 radio-quiet quasar CFHQS J2329-0301. The Ly{alpha} emission is extended over 15 kpc and has a luminosity of >8 Multiplication-Sign 10{sup 36} W, comparable to the most luminous Ly{alpha} halos known. The emission has complex kinematics, in part due to foreground absorption, which only partly covers the extended nebula. The velocity ranges from -500 km s{sup -1} to +500 km s{sup -1}, with a peak remarkably close to the systemic velocity identified by broad Mg II emission of the quasar. There is no evidence for infall or outflow of the halo gas. We speculate that the Ly{alpha} emission mechanism is recombination after quasar photoionization of gas sitting within a high-mass dark matter halo. The immense Ly{alpha} luminosity indicates a higher covering factor of cold gas compared with typical radio-quiet quasars at lower redshift.

  19. Continuum energy distributions of quasars in the Palomar-Green Survey

    SciTech Connect

    Neugebauer, G.; Matthews, K.; Schmidt, M.; Soifer, B.; Green, R.F.

    1987-03-01

    Nearly simultaneous observations, from 0.3 to 2.2 microns, of the complete set of quasars found in the Palomar-Green survey are presented, along with 3.7 and 10.1 microns observations of a limited number of the quasars. The majority of the continua at rest frequencies between 10 to the 13.8th and 10 to the 15.3rd Hz are consistent with fits by two power-law slopes plus a 3000 A bump. The spectral indices representing the lower frequency observations have a median value of -1.4, while those describing the higher frequencies have a median value of -0.2. The transition frequency between these slopes is close to 10 to the 14.5th Hz in the rest frame; the dispersion around this frequency is about one octave. A significant fraction of the low-redshift quasars show evidence of nebulosity within 5 arcsec of the quasar. 19 references.

  20. Detecting the First Quasars with ALMA

    NASA Astrophysics Data System (ADS)

    Schleicher, Dominik R. G.; Spaans, Marco; Klessen, Ralf S.

    2010-05-01

    We show that ALMA is the first telescope that can probe the dust-obscured central region of quasars at z > 5 with a maximum resolution of ~ 30 pc employing the 18 km baseline. We explore the possibility of detecting the first quasars with ALMA (Schleicher, Spaans, & Klessen 2009). For this purpose, we adopt the Seyfert 2 galaxy NGC 1068 as a reference system and calculate the expected fluxes if this galaxy were placed at high redshift. This choice is motivated by the detailed observations available for this system and the absence of any indication for an evolution in metallicity in high-redshift quasars. It is a conservative choice due to the moderate column densities in NGC 1068, leading to moderate fluxes.

  1. Determining Orientation in Radio-Quiet Quasars

    NASA Astrophysics Data System (ADS)

    Brotherton, Michael S.; Singh, Vikram; Runnoe, Jessie C.

    2016-01-01

    We present further steps developing an orientation indicator based on optical parameters that can be used for radio-quiet quasars. We recently demonstrated that the ratio of orientation-biased black hole mass calculated using the velocity width of Hbeta to the orientation-unbiased black hole mass calculated using the stellar velocity dispersion correlates with radio-loud orientation indicators, albeit with significant scatter. Our new work eliminates or reduces some sources of scatter to improve the significance of the correlation and to produce a better predictive prescription. Beyond biasing some mass measurements, orientation also affects luminosity determinations, and in turn estimates of the Eddington fraction, as well as luminosity functions, and other quasar properties. A practical radio-quiet orientation indicator for quasars is overdue.

  2. THE SUDDEN DEATH OF THE NEAREST QUASAR

    SciTech Connect

    Schawinski, Kevin; Virani, Shanil; Megan Urry, C.; Natarajan, Priyamvada; Coppi, Paolo; Evans, Daniel A.; Keel, William C.; Manning, Anna; Lintott, Chris J.; Kaviraj, Sugata; Bamford, Steven P.; Jozsa, Gyula I. G.; Garrett, Michael; Van Arkel, Hanny; Gay, Pamela; Fortson, Lucy

    2010-11-20

    Galaxy formation is significantly modulated by energy output from supermassive black holes at the centers of galaxies which grow in highly efficient luminous quasar phases. The timescale on which black holes transition into and out of such phases is, however, unknown. We present the first measurement of the shutdown timescale for an individual quasar using X-ray observations of the nearby galaxy IC 2497, which hosted a luminous quasar no more than 70,000 years ago that is still seen as a light echo in 'Hanny's Voorwerp', but whose present-day radiative output is lower by at least two, and more likely by over four, orders of magnitude. This extremely rapid shutdown provides new insight into the physics of accretion in supermassive black holes and may signal a transition of the accretion disk to a radiatively inefficient state.

  3. A computational model of echolocation: Transformation of spectrogram into the reflected intensity distribution for range discrimination of multiple closely spaced objects

    NASA Astrophysics Data System (ADS)

    Matsuo, Ikuo; Kunugiyama, Kenji; Yano, Masafumi

    2001-05-01

    Using frequency-modulated echolocation, bats can discriminate the range of objects with an accuracy of less than a millimeter. However, the echolocation mechanism is not well understood. The delay separation of three or more closely spaced objects can be determined through analysis of the echo spectrum. However, delay times cannot be properly correlated with objects using only the echo spectrum because the sequence of delay separations cannot be determined without information on temporal changes in the interference pattern of the echoes. To illustrate this, Gaussian chirplets with a carrier frequency compatible with bat emission sweep rates were used. The delay time for object 1, T1, can be estimated from the echo spectrum around the onset time. The delay time for object 2 is obtained by adding T1 to the delay separation between objects 1 and 2 (extracted from the first appearance of interference effects). Further objects can be located in sequence by this same procedure. This model can determine delay times for multiple closely spaced objects with an accuracy of about 1 microsecond, when all the objects are located within 30 microseconds of delay separation. This accuracy is possible even with objects having different reflected intensities and in a noisy environment.

  4. Doping and electronic properties of GaAs grown by close-spaced vapor transport from powder sources for scalable III–V photovoltaics

    SciTech Connect

    Ritenour, Andrew J.; Boucher, Jason W.; DeLancey, Robert; Greenaway, Ann L.; Aloni, Shaul; Boettcher, Shannon W.

    2014-09-01

    We report the use of a simple close-spaced vapor transport technique for the growth of high-quality epitaxial GaAs films using potentially inexpensive GaAs powders as precursors. The free carrier type and density (1016 to 1019 cm–3) of the films were adjusted by addition of Te or Zn powder to the GaAs source powder. We show using photoelectrochemical and electron beam-induced current analyses that the minority carrier diffusion lengths of the n- and p-GaAs films reached ~3 μm and ~8 μm, respectively. Hall mobilities approach those achieved for GaAs grown by metal–organic chemical vapor deposition, 1000–4200 cm2 V–1 s–1 for n-GaAs and 50–240 cm V–1 s–1 for p-GaAs depending on doping level. We conclude that the electronic quality of GaAs grown by close-spaced vapor transport is similar to that of GaAs made using conventional techniques and is thus sufficient for high-performance photovoltaic applications.

  5. Doping and electronic properties of GaAs grown by close-spaced vapor transport from powder sources for scalable III–V photovoltaics

    DOE PAGESBeta

    Ritenour, Andrew J.; Boucher, Jason W.; DeLancey, Robert; Greenaway, Ann L.; Aloni, Shaul; Boettcher, Shannon W.

    2014-09-01

    We report the use of a simple close-spaced vapor transport technique for the growth of high-quality epitaxial GaAs films using potentially inexpensive GaAs powders as precursors. The free carrier type and density (1016 to 1019 cm–3) of the films were adjusted by addition of Te or Zn powder to the GaAs source powder. We show using photoelectrochemical and electron beam-induced current analyses that the minority carrier diffusion lengths of the n- and p-GaAs films reached ~3 μm and ~8 μm, respectively. Hall mobilities approach those achieved for GaAs grown by metal–organic chemical vapor deposition, 1000–4200 cm2 V–1 s–1 for n-GaAsmore » and 50–240 cm V–1 s–1 for p-GaAs depending on doping level. We conclude that the electronic quality of GaAs grown by close-spaced vapor transport is similar to that of GaAs made using conventional techniques and is thus sufficient for high-performance photovoltaic applications.« less

  6. Rapid, Single-Molecule Assays in Nano/Micro-Fluidic Chips with Arrays of Closely Spaced Parallel Channels Fabricated by Femtosecond Laser Machining

    PubMed Central

    Canfield, Brian K.; King, Jason K.; Robinson, William N.; Hofmeister, William H.; Davis, Lloyd M.

    2014-01-01

    Cost-effective pharmaceutical drug discovery depends on increasing assay throughput while reducing reagent needs. To this end, we are developing an ultrasensitive, fluorescence-based platform that incorporates a nano/micro-fluidic chip with an array of closely spaced channels for parallelized optical readout of single-molecule assays. Here we describe the use of direct femtosecond laser machining to fabricate several hundred closely spaced channels on the surfaces of fused silica substrates. The channels are sealed by bonding to a microscope cover slip spin-coated with a thin film of poly(dimethylsiloxane). Single-molecule detection experiments are conducted using a custom-built, wide-field microscope. The array of channels is epi-illuminated by a line-generating red diode laser, resulting in a line focus just a few microns thick across a 500 micron field of view. A dilute aqueous solution of fluorescently labeled biomolecules is loaded into the device and fluorescence is detected with an electron-multiplying CCD camera, allowing acquisition rates up to 7 kHz for each microchannel. Matched digital filtering based on experimental parameters is used to perform an initial, rapid assessment of detected fluorescence. More detailed analysis is obtained through fluorescence correlation spectroscopy. Simulated fluorescence data is shown to agree well with experimental values. PMID:25140634

  7. Rapid, single-molecule assays in nano/micro-fluidic chips with arrays of closely spaced parallel channels fabricated by femtosecond laser machining.

    PubMed

    Canfield, Brian K; King, Jason K; Robinson, William N; Hofmeister, William H; Davis, Lloyd M

    2014-01-01

    Cost-effective pharmaceutical drug discovery depends on increasing assay throughput while reducing reagent needs. To this end, we are developing an ultrasensitive, fluorescence-based platform that incorporates a nano/micro-fluidic chip with an array of closely spaced channels for parallelized optical readout of single-molecule assays. Here we describe the use of direct femtosecond laser machining to fabricate several hundred closely spaced channels on the surfaces of fused silica substrates. The channels are sealed by bonding to a microscope cover slip spin-coated with a thin film of poly(dimethylsiloxane). Single-molecule detection experiments are conducted using a custom-built, wide-field microscope. The array of channels is epi-illuminated by a line-generating red diode laser, resulting in a line focus just a few microns thick across a 500 micron field of view. A dilute aqueous solution of fluorescently labeled biomolecules is loaded into the device and fluorescence is detected with an electron-multiplying CCD camera, allowing acquisition rates up to 7 kHz for each microchannel. Matched digital filtering based on experimental parameters is used to perform an initial, rapid assessment of detected fluorescence. More detailed analysis is obtained through fluorescence correlation spectroscopy. Simulated fluorescence data is shown to agree well with experimental values. PMID:25140634

  8. Structural-acoustic optimum design of shell structures in open/closed space based on a free-form optimization method

    NASA Astrophysics Data System (ADS)

    Shimoda, Masatoshi; Shimoide, Kensuke; Shi, Jin-Xing

    2016-03-01

    Noise reduction by structural geometry optimization has attracted much attention among designers. In the present work, we propose a free-form optimization method for the structural-acoustic design optimization of shell structures to reduce the noise of a targeted frequency or frequency range in an open or closed space. The objective of the design optimization is to minimize the average structural vibration-induced sound pressure at the evaluation points in the acoustic field under a volume constraint. For the shape design optimization, we carry out structural-acoustic coupling analysis and adjoint analysis to calculate the shape gradient functions. Then, we use the shape gradient functions in velocity analysis to update the shape of shell structures. We repeat this process until convergence is confirmed to obtain the optimum shape of the shell structures in a structural-acoustic coupling system. The numerical results for the considered examples showed that the proposed design optimization process can significantly reduce the noise in both open and closed spaces.

  9. Spectroscopy of quasar candidates from SDSS commissioning data

    SciTech Connect

    Fan, Xiaohui; Strauss, Michael A.; Gunn, James E.; Ivezic, Zeljko; Knapp, Gillian; Lupton, Robert H. Hennessy, Gregory S. Munn, Jeffrey A.; Newberg, Heidi J.; Yanny, Brian Schneider, Donald P.

    1999-04-01

    The Sloan Digital Sky Survey has obtained images in five broad-band colors for several hundred square degrees. We present color-color diagrams for stellar objects, and demonstrate that quasars are easily distinguished from stars by their distinctive colors. Follow-up spectroscopy in less than ten nights of telescope time has yielded 22 new quasars, 9 of them at z{gt}3.65, and one with z=4.75, the second highest-redshift quasar yet known. Roughly 80{percent} of the high-redshift quasar candidates selected by color indeed turn out to be high-redshift quasars. {copyright} {ital 1999 American Institute of Physics.}

  10. Nine optically selected quasars with redshifts larger than 3

    NASA Technical Reports Server (NTRS)

    Schmidt, Maarten; Schneider, Donald P.; Gunn, James E.

    1987-01-01

    The detection of nine quasars with redshifts between 3.0 and 3.8 is reported. The quasars were all found in a grism survey from their Lyman-alpha emission line. The r magnitudes of the quasars range from 18.5 to 21.7. The strengths of the Lyman-alpha lines are comparable to the values observed in other quasars (rest equivalent widths from 40 to 160 A). The spectrum of one of the objects possesses complex broad absorption features, similar to those seen in PHL 5200. A preliminary evaluation of these findings suggests that the comoving quasar density declines gradually beyond z = 3.

  11. The Space Operations Simulation Center (SOSC) and Closed-loop Hardware Testing for Orion Rendezvous System Design

    NASA Technical Reports Server (NTRS)

    D'Souza, Christopher; Milenkovich, Zoran; Wilson, Zachary; Huich, David; Bendle, John; Kibler, Angela

    2011-01-01

    The Space Operations Simulation Center (SOSC) at the Lockheed Martin (LM) Waterton Campus in Littleton, Colorado is a dynamic test environment focused on Autonomous Rendezvous and Docking (AR&D) development testing and risk reduction activities. The SOSC supports multiple program pursuits and accommodates testing Guidance, Navigation, and Control (GN&C) algorithms for relative navigation, hardware testing and characterization, as well as software and test process development. The SOSC consists of a high bay (60 meters long by 15.2 meters wide by 15.2 meters tall) with dual six degree-of-freedom (6DOF) motion simulators and a single fixed base 6DOF robot. The large testing area (maximum sensor-to-target effective range of 60 meters) allows for large-scale, flight-like simulations of proximity maneuvers and docking events. The facility also has two apertures for access to external extended-range outdoor target test operations. In addition, the facility contains four Mission Operations Centers (MOCs) with connectivity to dual high bay control rooms and a data/video interface room. The high bay is rated at Class 300,000 (. 0.5 m maximum particles/m3) cleanliness and includes orbital lighting simulation capabilities.

  12. Closing the Confidence Gap in Aerosol Contributions to Direct Radiative Forcing Using Space-based and Suborbital Resources

    NASA Astrophysics Data System (ADS)

    Kahn, R. A.

    2009-12-01

    As expected, the aerosol data products from the NASA Earth Observing System’s MISR and MODIS instruments provide significant advances in regional and global aerosol optical depth (AOD) mapping, aerosol type measurement, and source plume characterization from space. Although these products have been and are being used for many applications, ranging from regional air quality assessment, to aerosol air mass type evolution, to aerosol injection height and aerosol transport model validation, uncertainties still limit the quantitative constraints these satellite data place on global-scale direct aerosol radiative forcing. Some further refinement of the current aerosol products is possible, but a major advance in this area seems to require a different paradigm, involving the integration of satellite and suborbital data with models. This presentation will briefly summarize where we stand, and what incremental advances we can expect, with the current aerosol products, and will then elaborate on some initial steps aimed at the necessary integration. Many other AGU presentations, covering parts of the community’s emerging efforts in this direction, will be referenced, and key points from the recently released CCSP-SAP (US Climate Change Program - Synthesis and Assessment Product) 2.3 - Atmospheric aerosols: Properties and Climate Impacts, will be included in the discussion.

  13. Unexpected spatial intensity distributions and onset timing of solar electron events observed by closely spaced STEREO spacecraft

    NASA Astrophysics Data System (ADS)

    Klassen, A.; Dresing, N.; Gómez-Herrero, R.; Heber, B.; Müller-Mellin, R.

    2016-09-01

    We present multi-spacecraft observations of four solar electron events using measurements from the Solar Electron Proton Telescope (SEPT) and the Electron Proton Helium INstrument (EPHIN) on board the STEREO and SOHO spacecraft, respectively, occurring between 11 October 2013 and 1 August 2014, during the approaching superior conjunction period of the two STEREO spacecraft. At this time the longitudinal separation angle between STEREO-A (STA) and STEREO-B (STB) was less than 72°. The parent particle sources (flares) of the four investigated events were situated close to, in between, or to the west of the STEREO's magnetic footpoints. The STEREO measurements revealed a strong difference in electron peak intensities (factor ≤12) showing unexpected intensity distributions at 1 AU, although the two spacecraft had nominally nearly the same angular magnetic footpoint separation from the flaring active region (AR) or their magnetic footpoints were both situated eastwards from the parent particle source. Furthermore, the events detected by the two STEREO imply a strongly unexpected onset timing with respect to each other: the spacecraft magnetically best connected to the flare detected a later arrival of electrons than the other one. This leads us to suggest the concept of a rippled peak intensity distribution at 1 AU formed by narrow peaks (fingers) superposed on a quasi-uniform Gaussian distribution. Additionally, two of the four investigated solar energetic particle (SEP) events show a so-called circumsolar distribution and their characteristics make it plausible to suggest a two-component particle injection scenario forming an unusual, non-uniform intensity distribution at 1 AU.

  14. Cowpeas and pinto beans: yields and light efficiency of candidate space crops in the Laboratory Biosphere closed ecological system

    NASA Astrophysics Data System (ADS)

    Nelson, M.; Dempster, W. F.; Silverstone, S.; Alling, A.; Allen, J. P.; van Thillo, M.

    An experiment utilizing cowpeas Vigna unguiculata pinto beans Phaseolus vulgaris L and Apogee ultra-dwarf wheat was conducted in the soil-based closed ecological facility Laboratory Biosphere from February to May 2005 The lighting regime was 13 hours light 11 hours dark at a light intensity of 960 mu mol m -2 s -1 45 moles m -2 day -1 supplied by high-pressure sodium lamps The pinto beans and cowpeas were grown at two different plant densities The pinto bean produced 710 g m -2 total aboveground biomass and 341 g m -2 at 33 5 plants per m 2 and at 37 5 plants per m 2 produced 1092 g m -2 total biomass and 537 g m -2 of dry seed an increase of almost 50 Cowpeas at 28 plants m -2 yielded 1060 g m -2 of total biomass and 387 g seed m -2 outproducing the less dense planting by more than double 209 in biomass and 86 more seed as the planting of 21 plants m -2 produced 508 g m-2 of total biomass and 209 g m-2 of seed Edible yield rate EYR for the denser cowpea bean was 4 6 g m -2 day -1 vs 2 5 g m -2 day -1 for the less dense stand average yield was 3 5 g m -2 day -1 EYR for the denser pinto bean was 8 5 g m -2 day -1 vs 5 3 g m -2 day -1 average EYR for the pinto beans was 7 0 g m -2 day -1 Yield efficiency rate YER the ratio of edible to non-edible biomass was 0 97 for the dense pinto bean 0 92 for the less dense pinto bean and average 0 94 for the entire crop The cowpeas

  15. Possible evolution of supermassive black holes from FRI quasars

    NASA Astrophysics Data System (ADS)

    Kim, Matthew I.; Christian, Damian J.; Garofalo, David; D'Avanzo, Jaclyn

    2016-08-01

    We explore the question of the rapid buildup of black hole mass in the early universe employing a growing black hole mass-based determination of both jet and disk powers predicted in recent theoretical work on black hole accretion and jet formation. Despite simplified, even artificial assumptions about accretion and mergers, we identify an interesting low probability channel for the growth of one billion solar mass black holes within hundreds of millions of years of the Big Bang without appealing to super Eddington accretion. This result is made more compelling by the recognition of a connection between this channel and an end product involving active galaxies with FRI radio morphology but weaker jet powers in mildly sub-Eddington accretion regimes. While FRI quasars have already been shown to occupy a small region of the available parameter space for black hole feedback in the paradigm, we further suggest that the observational dearth of FRI quasars is also related to their connection to the most massive black hole growth due to both these FRIs high redshifts and relative weakness. Our results also allow us to construct the AGN luminosity function at high redshift, that agree with recent studies. In short, we produce a connection between the unexplained paucity of a given family of active galactic nuclei and the rapid growth of supermassive black holes, two heretofore seemingly unrelated aspects of the physics of active galactic nuclei.

  16. Possible evolution of supermassive black holes from FRI quasars

    NASA Astrophysics Data System (ADS)

    Kim, Matthew I.; Christian, Damian J.; Garofalo, David; D'Avanzo, Jaclyn

    2016-08-01

    We explore the question of the rapid buildup of black hole mass in the early universe employing a growing black hole mass-based determination of both jet and disc powers predicted in recent theoretical work on black hole accretion and jet formation. Despite simplified, even artificial assumptions about accretion and mergers, we identify an interesting low probability channel for the growth of one billion solar mass black holes within hundreds of millions of years of the big bang without appealing to super Eddington accretion. This result is made more compelling by the recognition of a connection between this channel and an end product involving active galaxies with FRI radio morphology but weaker jet powers in mildly sub-Eddington accretion regimes. While FRI quasars have already been shown to occupy a small region of the available parameter space for black hole feedback in the paradigm, we further suggest that the observational dearth of FRI quasars is also related to their connection to the most massive black hole growth due to both these FRIs high redshifts and relative weakness. Our results also allow us to construct the AGN (active galactic nucleus) luminosity function at high redshift, that agree with recent studies. In short, we produce a connection between the unexplained paucity of a given family of AGNs and the rapid growth of supermassive black holes, two heretofore seemingly unrelated aspects of the physics of AGNs.

  17. The contribution of quasar outflows to cosmological structure formation

    NASA Astrophysics Data System (ADS)

    Arav, Nahum

    2011-10-01

    A vast new discovery space is opened up by the high sensitivity of COS in the far UV. These new capabilities are ushering a revolution in the study of AGN outflows. We now have the ability to obtain high quality data on objects up to a redshift of about 1, providing access to ten times more {and better} diagnostic absorption lines than was possible with STIS {which could only observe outflows at z<0.05 with sufficient S/N}. These diagnostics will allow us to quantify how much do quasar outflow contribute to AGN feedback. On the way to this lofty goal, we'll be able to resolve important questions in the study of these outflows: Where are they situated within the host galaxy? What is their ionization equilibrium and chemical abundances? Unlike ground-based observations, COS data can yield the answers to all these questions for the most ubiquitous outflows, and therefore connect them to our developing understanding of cosmological structure formation.Our analysis of recent archived COS observations gives a concrete example for the above claims; including the first determination of the distance from the central source for a high-ionization outflow. Here we propose an archive program to look through the 520 COS G130M and G160M orbits of AGN archive observations, identify quasar outflows and publish the analyses of the best cases.

  18. Einstein observations of active galaxies and quasars

    NASA Technical Reports Server (NTRS)

    Schreier, E. J.

    1979-01-01

    The radio galaxies Centaurus A and Signus B are discussed. In both these sources, a comparison of the radio and imaged X-ray flux is allowed for the measurement of the magnetic fields. Einstein observations of quasars are discussed. The number of known X-ray emitting QSO's was increased from 3 to 22 and the distances where these QSO's were seen to correspond to an age of 15 billion years. It was shown that these quasars contributed significantly to the X-ray background.

  19. The black hole spins of quasars

    NASA Astrophysics Data System (ADS)

    You, Bei; Cao, Xinwu

    2016-02-01

    We present the estimates of the black hole spins of five quasars. The peaks of the spectra of the accretion discs surrounding massive black holes in quasars are in the far-UV or soft X-ray band, which are usually not observed. However, in the disc corona model, the soft photons from the disc are Comptonized to high energy in the hot corona, and the hard X-ray spectra (luminosity and spectral shape) contain the information of the incident spectra from the disc. The values of black hole spin parameter a are inferred from the spectral fitting, which spread over a large range, ~ -0.94 to 0.998.

  20. Blue outliers among intermediate redshift quasars

    NASA Astrophysics Data System (ADS)

    Marziani, P.; Sulentic, J. W.; Stirpe, G. M.; Dultzin, D.; Del Olmo, A.; Martínez-Carballo, M. A.

    2016-01-01

    [OIII]λ 5007 "blue outliers"—that are suggestive of outflows in the narrow line region of quasars—appear to be much more common at intermediate z (high luminosity) than at low z. About 40~% of quasars in a Hamburg ESO intermediate z sample of 52 sources qualify as "blue outliers" (i.e., quasars with [OIII]λλ 4959,5007 lines showing large systematic blueshifts with respect to rest frame). We discuss major findings on what has become an intriguing field in active galactic nuclei research and stress the relevance of "blue outliers" to feedback and host galaxy evolution.

  1. Radio frequency interference at QUASAR Network Observatories

    NASA Astrophysics Data System (ADS)

    Ilin, Gennadii

    2011-07-01

    Different sources of radio frequency interference (RFI) at Quasar-network observatories and their affect on VLBIsessions are discussed. For example, the stronger of them registered last time are UMTS mobile phone base stations which were built not far from Quasar-network observatories location. These stations emit signals near 2100MHz and produce RFI of critical level. To control RFI level regular spectral measurements of the intermediate frequency signals at the outputs of the receivers are conducted. As a result, real spread of RFI sources, including DORIS, have to be taken into account in planning of VLBI observation sessions and especially it is concerned VLBI 2010 project realization.

  2. Low-Cost Blast Wave Generator for Studies of Hearing Loss and Brain Injury: Blast Wave Effects in Closed Spaces

    PubMed Central

    Newman, Andrew J.; Hayes, Sarah H.; Rao, Abhiram S.; Allman, Brian L.; Manohar, Senthilvelan; Ding, Dalian; Stolzberg, Daniel; Lobarinas, Edward; Mollendorf, Joseph C.; Salvi, Richard

    2015-01-01

    Background Military personnel and civilians living in areas of armed conflict have increased risk of exposure to blast overpressures that can cause significant hearing loss and/or brain injury. The equipment used to simulate comparable blast overpressures in animal models within laboratory settings is typically very large and prohibitively expensive. New Method To overcome the fiscal and space limitations introduced by previously reported blast wave generators, we developed a compact, low-cost blast wave generator to investigate the effects of blast exposures on the auditory system and brain. Results The blast wave generator was constructed largely from off the shelf components, and reliably produced blasts with peak sound pressures of up to 198 dB SPL (159.3 kPa) that were qualitatively similar to those produced from muzzle blasts or explosions. Exposure of adult rats to 3 blasts of 188 dB peak SPL (50.4 kPa) resulted in significant loss of cochlear hair cells, reduced outer hair cell function and a decrease in neurogenesis in the hippocampus. Comparison to existing methods Existing blast wave generators are typically large, expensive, and are not commercially available. The blast wave generator reported here provides a low-cost method of generating blast waves in a typical laboratory setting. Conclusions This compact blast wave generator provides scientists with a low cost device for investigating the biological mechanisms involved in blast wave injury to the rodent cochlea and brain that may model many of the damaging effects sustained by military personnel and civilians exposed to intense blasts. PMID:25597910

  3. Using quasar physics to improve the celestial reference frame

    NASA Astrophysics Data System (ADS)

    Shabala, Stanislav; Plank, Lucia; McCallum, Jamie; Boehm, Johannes

    2015-08-01

    Radio-loud quasars making up the International Celestial Reference Frame (ICRF) are dynamic objects with significant structure that changes on timescales of months and years. This is a problem for reference frame stability, as realised through the geodetic and astrometric Very Long Baseline Interferometry (VLBI) technique, which has so far largely treated quasars as point sources in analysis. I will describe the source structure simulator recently implemented in the Vienna VLBI Software (VieVS) package, and quantify the effects of various levels of source structure on the celestial and terrestrial reference frames, and Earth Orientation Parameters linking these two frames. We find that even relatively modest levels of quasar structure can produce systematic effects that affect derived quasar positions significantly in excess of the noise floor of the present ICRF realisation, ICRF2.I will also discuss the observed relationship between astrophysical properties of quasars, their structure and geodetic stability. By simulating quasar structure and evolution in VieVS, we have devised various quasar mitigation strategies. These include: (1) astrophysically-based quasar selection techniques; (2) scheduling sources by taking into account quasar structure; and (3) analyzing geodetic and astrometric VLBI observations using knowledge of quasar structure. I will describe our simulation results, and outline promising quasar structure mitigation strategies.

  4. Dust-free quasars in the early Universe.

    PubMed

    Jiang, Linhua; Fan, Xiaohui; Brandt, W N; Carilli, Chris L; Egami, Eiichi; Hines, Dean C; Kurk, Jaron D; Richards, Gordon T; Shen, Yue; Strauss, Michael A; Vestergaard, Marianne; Walter, Fabian

    2010-03-18

    The most distant quasars known, at redshifts z approximately 6, generally have properties indistinguishable from those of lower-redshift quasars in the rest-frame ultraviolet/optical and X-ray bands. This puzzling result suggests that these distant quasars are evolved objects even though the Universe was only seven per cent of its current age at these redshifts. Recently one z approximately 6 quasar was shown not to have any detectable emission from hot dust, but it was unclear whether that indicated different hot-dust properties at high redshift or if it is simply an outlier. Here we report the discovery of a second quasar without hot-dust emission in a sample of 21 z approximately 6 quasars. Such apparently hot-dust-free quasars have no counterparts at low redshift. Moreover, we demonstrate that the hot-dust abundance in the 21 quasars builds up in tandem with the growth of the central black hole, whereas at low redshift it is almost independent of the black hole mass. Thus z approximately 6 quasars are indeed at an early evolutionary stage, with rapid mass accretion and dust formation. The two hot-dust-free quasars are likely to be first-generation quasars born in dust-free environments and are too young to have formed a detectable amount of hot dust around them. PMID:20237563

  5. Some observations on colocated and closely spaced strong ground-motion records of the 1999 Chi-Chi, Taiwan, earthquake

    USGS Publications Warehouse

    Wang, G.-Q.; Boore, D.M.; Igel, H.; Zhou, X.-Y.

    2003-01-01

    information regarding the permanent displacements is lost. The causative mechanisms of the baseline offsets are unknown presently. Hence, it is very difficult to recover the permanent displacements from the modern digital records, although for records close to large earthquakes, the signal-to-noise ratio should theoretically be adequate to obtain ground motions with periods of hundreds of seconds. This study reinforces our conclusion from previous studies that the sources of baseline offsets occurring in digital strong-motion records are very complex and often unpredictable, and that, therefore, it is difficult to remove the baseline effects to maximize the information content of the record. The baseline offsets only affect very long period motions (e.g., >20 sec), however, and therefore are of little or no engineering concern.

  6. Vegetable production facility as a part of a closed life support system in a Russian Martian space flight scenario

    NASA Astrophysics Data System (ADS)

    Berkovich, Yu. A.; Smolyanina, S. O.; Krivobok, N. M.; Erokhin, A. N.; Agureev, A. N.; Shanturin, N. A.

    2009-07-01

    A Manned Mars Mission scenario had been developed in frame of the Project 1172 supported International Science & Technology Center in Moscow. The Mars transit vehicle (MTV) supposed to have a crew of 4-6 with Pilot Laboratory compartment volume of 185 m 3 and with inner diameter of 4.1 m. A vegetable production facility with power consumption up to 10 kW is being considered as a component of the life support system to supply crew members by fresh vegetables during the mission. Proposed design of conveyor-type plant growth facility (PGF) comprised of 4-modules. Each module has a cylindrical planting surface and spiral cylindrical LED assembly to provide a high specific productivity relative to utilized onboard resources. Each module has a growth chamber that will be from 0.7 m to 1.5 m in length, and a crop illuminated area from 1.7 m 2 to 4.0 m 2. Leafy crops (cabbage, lettuce, spinach, chard, etc.) have been selected for module 1, primarily because of the highest specific productivity per consumed resources. Dietitians have recommended also carrot crop for module 2, pepper for module 3 and tomato for module 4. The maximal total PGF light energy estimated as 1.16 kW and total power consumption as about 7 kW. The module 1 characteristics have been calculated using own experimental data, information from the best on ground plant growth experiments with artificial light were used to predict crop productivity and biomass composition in the another modules. 4-module PGF could produce nearly 0.32 kg per crew member per day of fresh edible biomass, which would be about 50% of recommended daily vegetable supplement. An average crop harvest index is estimated as 0.75. The MTV food system could be entirely closed in terms of vitamins C and A with help of the PGF. In addition the system could provide 10-25% of essential minerals and vitamins of group B, and about 20% of food fibers. The present state of plant growth technology allows formulating of requirements specification

  7. Cowpeas and pinto beans: Performance and yields of candidate space crops in the laboratory biosphere closed ecological system

    NASA Astrophysics Data System (ADS)

    Nelson, M.; Dempster, W. F.; Allen, J. P.; Silverstone, S.; Alling, A.; Thillo, M. van

    An experiment utilizing cowpeas ( Vigna unguiculata L.), pinto beans ( Phaseolus vulgaris L.) and Apogee ultra-dwarf wheat ( Triticum sativa L.) was conducted in the soil-based closed ecological facility, Laboratory Biosphere, from February to May 2005. The lighting regime was 13 h light/11 h dark at a light intensity of 960 μmol m -2 s -1, 45 mol m -2 day -1 supplied by high-pressure sodium lamps. The pinto beans and cowpeas were grown at two different planting densities. Pinto bean production was 341.5 g dry seed m -2 (5.42 g m -2 day -1) and 579.5 dry seed m -2 (9.20 g m -2 day -1) at planted densities of 32.5 plants m -2 and 37.5 plants m -2, respectively. Cowpea yielded 187.9 g dry seed m -2 (2.21 g m -2 day -1) and 348.8 dry seed m -2 (4.10 g m -2 day -1) at planted densities of 20.8 plants m -2 and 27.7 plants m -2, respectively. The crop was grown at elevated atmospheric carbon dioxide levels, with levels ranging from 300-3000 ppm daily during the majority of the crop cycle. During early stages (first 10 days) of the crop, CO 2 was allowed to rise to 7860 ppm while soil respiration dominated, and then was brought down by plant photosynthesis. CO 2 was injected 27 times during days 29-71 to replenish CO 2 used by the crop during photosynthesis. Temperature regime was 24-28 °C day/deg 20-24 °C night. Pinto bean matured and was harvested 20 days earlier than is typical for this variety, while the cowpea, which had trouble establishing, took 25 days more for harvest than typical for this variety. Productivity and atmospheric dynamic results of these studies contribute toward the design of an envisioned ground-based test bed prototype Mars base.

  8. The Host Galaxies of High-Luminosity Obscured Quasars at 2.5

    NASA Astrophysics Data System (ADS)

    Ross, Nicholas; Strauss, M. A.; Greene, J. E.; Zakamska, N. L.; Brandt, W. N.; Alexandroff, R.; Liu, G.; Smith, P. S.; The SDSS-III BOSS Quasar Working Group

    2014-01-01

    Active Galactic Nuclei play a key role in the evolution of galaxies. However, very little is known about the host galaxies of the most luminous quasars at redshift 2.5, the epoch when massive black hole growth peaked. The brightness of the quasar itself, which can easily outshine a galaxy by a large factor, makes it very difficult to study emission from extended gas or stars in the host galaxy. However, we have imaged the extended emission from the host galaxies of a unique sample of six optically extinguished (Type II) luminous quasars with 2.5, with the Hubble Space Telescope (Cycle 20, GO 13014) using ACS/F814W to access the rest-frame near-ultraviolet, and WFC3/F160W for the rest-frame optical longward of 4000A. These objects are selected from the spectroscopic database of the SDSS/Baryon Oscillation Spectroscopic Survey to have strong, narrow emission lines and weak continua. With these images, we have quantified the luminosity, morphology, and dynamical state of the host galaxies, and searched for extended scattered light from the obscured central engine. These observations are the first comprehensive study of both host galaxy light and scattered light in high-luminosity quasars at the epoch of maximum black hole growth, and give insights into the relationship between host galaxies and black holes during this important, and yet largely unexplored period.

  9. A rapid energetic X-ray flare in the quasar PKS0558 - 504

    NASA Technical Reports Server (NTRS)

    Remillard, R. A.; Grossan, B.; Bradt, H. V.; Ohashi, T.; Hayashida, K.

    1991-01-01

    A recent observation from the Ginga satellite of the quasar PKS0558 - 504 is reported during which the X-ray flux increased by 67 percent in the space of only three minutes. There was no significant change in the spectrum. Comprehensive analysis of the data strongly indicates that this was a genuine X-ray flare originating in the quasar. The implied rate of change in luminosity in the 2-10 keV range, assuming a Hubble constant of 70 km/s/Mpc, and a cosmological deceleration parameter q0 = 0.5, is 3.2 x 10 to the 42nd erg/sq s, the highest value measured for a quasar. When photon scattering is considered, this is about 16 times greater than could be produced, with a three-minute rise time, in an isotropically emitting plasma. It is argued that the apparent luminosity must be enhanced by relativistic beaming. This is the first indication of beaming in an 'ordinary' unpolarized quasar.

  10. Interstellar Silicate Dust Grain Properties in Distant Galaxies Probed by Quasar Absorption Systems

    NASA Astrophysics Data System (ADS)

    Aller, Monique C.; Kulkarni, Varsha P.; York, Donald G.; Welty, Daniel E.; Vladilo, Giovanni; Som, Debopam

    2015-01-01

    Dust grains are a fundamental component of the interstellar medium, and significantly impact many of the physical processes driving galaxy evolution, including star formation, and the heating, cooling and ionization of interstellar material. Using the absorption features produced by dust in the spectra of luminous background quasars, it is possible to study the properties of extragalactic interstellar dust grains. We will present results from an ongoing program utilizing existing Spitzer Space Telescope infrared quasar spectra to probe silicate dust grain properties in z<1.4 quasar absorption systems. In combination with complementary ground-based data on associated gas-phase metal absorption lines, we explore connections between the interstellar dust and gas in the quasar absorption systems. Our project yields clear detections of the 10 micron silicate dust absorption feature in the studied systems, as well as detections of the 18 micron silicate dust absorption feature in sources with adequate spectral coverage. Based on measured variations in the breath, peak wavelength, and substructure of the 10 micron absorption features, there appear to be differences in the silicate dust grain properties from system-to-system. We also show indications of trends between the gas-phase metal properties, such as metallicity and gas velocity spread, with the silicate dust grain absorption properties. Support for this work is provided by NASA through an award issued by JPL/Caltech and through NASA grant NNX14AG74G, and from National Science Foundation grants AST-0908890 and AST-1108830 to the University of South Carolina.

  11. Using quasars as standard clocks for measuring cosmological redshift.

    PubMed

    Dai, De-Chang; Starkman, Glenn D; Stojkovic, Branislav; Stojkovic, Dejan; Weltman, Amanda

    2012-06-01

    We report hitherto unnoticed patterns in quasar light curves. We characterize segments of the quasar's light curves with the slopes of the straight lines fit through them. These slopes appear to be directly related to the quasars' redshifts. Alternatively, using only global shifts in time and flux, we are able to find significant overlaps between the light curves of different pairs of quasars by fitting the ratio of their redshifts. We are then able to reliably determine the redshift of one quasar from another. This implies that one can use quasars as standard clocks, as we explicitly demonstrate by constructing two independent methods of finding the redshift of a quasar from its light curve. PMID:23003944

  12. CLUSTERING OF OBSCURED AND UNOBSCURED QUASARS IN THE BOOeTES FIELD: PLACING RAPIDLY GROWING BLACK HOLES IN THE COSMIC WEB

    SciTech Connect

    Hickox, Ryan C.; Alexander, David M.; Goulding, Andrew D.; Myers, Adam D.; Brodwin, Mark; Forman, William R.; Jones, Christine; Murray, Stephen S.; Eisenstein, Daniel; Caldwell, Nelson; Brown, Michael J. I.; Cool, Richard J.; Kochanek, Christopher S.; Dey, Arjun; Jannuzi, Buell T.; Assef, Roberto J.; Eisenhardt, Peter R.; Gorjian, Varoujan; Stern, Daniel; Le Floc'h, Emeric

    2011-04-20

    We present the first measurement of the spatial clustering of mid-infrared-selected obscured and unobscured quasars, using a sample in the redshift range 0.7 < z < 1.8 selected from the 9 deg{sup 2} Booetes multiwavelength survey. Recently, the Spitzer Space Telescope and X-ray observations have revealed large populations of obscured quasars that have been inferred from models of the X-ray background and supermassive black hole evolution. To date, little is known about obscured quasar clustering, which allows us to measure the masses of their host dark matter halos and explore their role in the cosmic evolution of black holes and galaxies. In this study, we use a sample of 806 mid-infrared-selected quasars and {approx}250,000 galaxies to calculate the projected quasar-galaxy cross-correlation function w{sub p} (R). The observed clustering yields characteristic dark matter halo masses of log(M{sub halo} [h {sup -1} M{sub sun}]) = 12.7{sup +0.4}{sub -0.6} and 13.3{sup +0.3}{sub -0.4} for unobscured quasars (QSO-1s) and obscured quasars (Obs-QSOs), respectively. The results for QSO-1s are in excellent agreement with previous measurements for optically selected quasars, while we conclude that the Obs-QSOs are at least as strongly clustered as the QSO-1s. We test for the effects of photometric redshift errors on the optically faint Obs-QSOs, and find that our method yields a robust lower limit on the clustering; photo-z errors may cause us to underestimate the clustering amplitude of the Obs-QSOs by at most {approx}20%. We compare our results to previous studies, and speculate on physical implications of stronger clustering for obscured quasars.

  13. Gravitational lensing in quasar samples

    NASA Astrophysics Data System (ADS)

    Claeskens, Jean-François; Surdej, Jean

    The first cosmic mirage was discovered approximately 20 years ago as the double optical counterpart of a radio source. This phenomenon had been predicted some 70 years earlier as a consequence of General Relativity. We present here a summary of what we have learnt since. The applications are so numerous that we had to concentrate on a few selected aspects of this new field of research. This review is focused on strong gravitational lensing, i.e. the formation of multiple images, in QSO samples. It is intended to give the reader an up-to-date status of the observations and to present an overview of its most interesting potential applications in cosmology and astrophysics, as well as numerous important results achieved so far. The first section follows an intuitive approach to the basics of gravitational lensing and is developed in view of our interest in multiply imaged quasars. The astrophysical and cosmological applications of gravitational lensing are outlined in Sect. 2 and the most important results are presented in Sect. 5. Sections 3 and 4 are devoted to the observations. Finally, conclusions are summarized in the last section. We have tried to avoid duplication with existing (and excellent) introductions to the field of gravitational lensing. For this reason, we did not concentrate on the individual properties of specific lens models, as these are already well presented in Narayan and Bartelmann (1996) and on a more intuitive ground in Refsdal and Surdej (1994). Wambsganss (1998) proposes a broad view on gravitational lensing in astronomy; the reviews by Fort and Mellier (1994) and Hattori et al. (1999) deal with lensing by galaxy clusters; microlensing in the Galaxy and the local group is reviewed by Paczynski (1996) and a general panorama on weak lensing is given by Bartelmann and Schneider (1999) and Mellier (1999). The monograph on the theory of gravitational lensing by Schneider, Ehlers and Falco (1992) also remains a reference in the field.

  14. The Large Sky Area Multi-object Fiber Spectroscopic Telescope Quasar Survey: Quasar Properties from the First Data Release

    NASA Astrophysics Data System (ADS)

    Ai, Y. L.; Wu, Xue-Bing; Yang, Jinyi; Yang, Qian; Wang, Feige; Guo, Rui; Zuo, Wenwen; Dong, Xiaoyi; Zhang, Y.-X.; Yuan, H.-L.; Song, Y.-H.; Wang, Jianguo; Dong, Xiaobo; Yang, M.; -Wu, H.; Shen, S.-Y.; Shi, J.-R.; He, B.-L.; Lei, Y.-J.; Li, Y.-B.; Luo, A.-L.; Zhao, Y.-H.; Zhang, H.-T.

    2016-02-01

    We present preliminary results of the quasar survey in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) first data release (DR1), which includes the pilot survey and the first year of the regular survey. There are 3921 quasars reliably identified, among which 1180 are new quasars discovered in the survey. These quasars are at low to median redshifts, with a highest z of 4.83. We compile emission line measurements around the Hα, Hβ, Mg ii, and C iv regions for the new quasars. The continuum luminosities are inferred from SDSS photometric data with model fitting, as the spectra in DR1 are non-flux-calibrated. We also compile the virial black hole mass estimates, with flags indicating the selection methods, and broad absorption line quasars. The catalog and spectra for these quasars are also available. Of the 3921 quasars, 28% are independently selected with optical-infrared colors, indicating that the method is quite promising for the completeness of the quasar survey. LAMOST DR1 and the ongoing quasar survey will provide valuable data for studies of quasars.

  15. The quasar mass-luminosity plane - I. A sub-Eddington limit for quasars

    NASA Astrophysics Data System (ADS)

    Steinhardt, Charles L.; Elvis, Martin

    2010-03-01

    We use 62185 quasars from the Sloan Digital Sky Survey Data Release 5 sample to explore the relationship between black hole mass and luminosity. Black hole masses were estimated based on the widths of their Hβ, MgII and CIV lines and adjacent continuum luminosities using standard virial mass estimate scaling laws. We find that, over the range 0.2 < z < 4.0, the most luminous low-mass quasars are at their Eddington luminosity, but the most luminous high-mass quasars in each redshift bin fall short of their Eddington luminosities, with the shortfall of the order of 10 or more at 0.2 < z < 0.6. We examine several potential sources of measurement uncertainty or bias and show that none of them can account for this effect. We also show the statistical uncertainty in virial mass estimation to have an upper bound of ~0.15 dex, smaller than the 0.4 dex previously reported. We also examine the highest mass quasars in every redshift bin in an effort to learn more about quasars that are about to cease their luminous accretion. We conclude that the quasar mass-luminosity locus contains a number of new puzzles that must be explained theoretically.

  16. Identification of wind turbine testing practices and investigation of the performance benefits of closely-spaced lateral wind farm configurations

    NASA Astrophysics Data System (ADS)

    McTavish, Sean

    -field blockage effect and is analogous to the increase in wind speed caused by blockage in a closed

  17. Ionized Absorbers in Active Galactic Nuclei and Very Steap Soft X-Ray Quasars

    NASA Technical Reports Server (NTRS)

    Fiore, Fabrizio; White, Nicholas (Technical Monitor)

    2000-01-01

    Steep soft X-ray (0.1-2 keV) quasars share several unusual properties: narrow Balmer lines, strong Fe II emission, large and fast X-ray variability, and a rather steep 2-10 keV spectrum. These intriguing objects have been suggested to be the analogues of Galactic black hole candidates in the high, soft state. We present here results from ASCA observations for two of these quasars: NAB 0205 + 024 and PG 1244 + 026. Both objects show similar variations (factor of approximately 2 in 10 ks), despite a factor of approximately 10 difference in the 0.5-10 keV luminosity (7.3 x 10(exp 43) erg/s for PG 1244 + 026 and 6.4 x 10(exp 44) erg/s for NAB 0205 + 024, assuming isotropic emission, H(sub 0) = 50.0 and q(sub 0) = 0.0). The X-ray continuum of the two quasars flattens by 0.5-1 going from the 0.1-2 keV band towards higher energies, strengthening recent results on another half-dozen steep soft X-ray active galactic nuclei. PG 1244 + 026 shows a significant feature in the '1-keV' region, which can be described either as a broad emission line centered at 0.95 keV (quasar frame) or as edge or line absorption at 1.17 (1.22) keV. The line emission could be a result of reflection from a highly ionized accretion disc, in line with the view that steep soft X-ray quasars are emitting close to the Eddington luminosity. Photoelectric edge absorption or resonant line absorption could be produced by gas outflowing at a large velocity (0.3-0.6 c).

  18. The Optical-UV Emissivity of Quasars: Dependence on Black Hole Mass and Radio Loudness

    NASA Astrophysics Data System (ADS)

    Shankar, Francesco; Calderone, Giorgio; Knigge, Christian; Matthews, James; Buckland, Rachel; Hryniewicz, Krzysztof; Sivakoff, Gregory; Dai, Xinyu; Richardson, Kayleigh; Riley, Jack; Gray, James; La Franca, Fabio; Altamirano, Diego; Croston, Judith; Gandhi, Poshak; Hönig, Sebastian; McHardy, Ian; Middleton, Matthew

    2016-02-01

    We analyzed a large sample of radio-loud and radio-quiet quasar spectra at redshift 1.0 ≤ z ≤ 1.2 to compare the inferred underlying quasar continuum slopes (after removal of the host galaxy contribution) with accretion disk models. The latter predict redder (decreasing) α3000 continuum slopes ({L}ν \\propto {ν }α at 3000 Å) with increasing black hole mass, bluer α3000 with increasing luminosity at 3000 Å, and bluer α3000 with increasing spin of the black hole, when all other parameters are held fixed. We find no clear evidence for any of these predictions in the data. In particular, we find the following. (i) α3000 shows no significant dependence on black hole mass or luminosity. Dedicated Monte Carlo tests suggest that the substantial observational uncertainties in the black hole virial masses can effectively erase any intrinsic dependence of α3000 on black hole mass, in line with some previous studies. (ii) The mean slope α3000 of radio-loud sources, thought to be produced by rapidly spinning black holes, is comparable to, or even redder than, that of radio-quiet quasars. Indeed, although quasars appear to become more radio loud with decreasing luminosity, we still do not detect any significant dependence of α3000 on radio loudness. The predicted mean α3000 slopes tend to be bluer than in the data. Disk models with high inclinations and dust extinction tend to produce redder slopes closer to empirical estimates. Our mean α3000 values are close to the ones independently inferred at z < 0.5, suggesting weak evolution with redshift, at least for moderately luminous quasars.

  19. Quasar Host Galaxies/Neptune Rotation/Galaxy Building Blocks/Hubble Deep Field/Saturn Storm

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Computerized animations simulate a quasar erupting in the core of a normal spiral galaxy, the collision of two interacting galaxies, and the evolution of the universe. Hubble Space Telescope (HST) images show six quasars' host galaxies (including spirals, ellipticals, and colliding galaxies) and six clumps of galaxies approximately 11 billion light years away. A false color time lapse movie of Neptune displays the planet's 16-hour rotation, and the evolution of a storm on Saturn is seen though a video of the planet's rotation. A zoom sequence starts with a ground-based image of the constellation Ursa major and ends with the Hubble Deep Field through progressively narrower and deeper views.

  20. Astrometric and Photometric Variability in Quasars

    NASA Astrophysics Data System (ADS)

    Andrei, A. H.; Bouquillon, S.; Penna, J. L.; Taris, F.; Anton, S.; Souchay, J.; Camargo, J. I. B.; da Silva Neto, D. N.; Vieira Martins, R.; Assafin, M.; Pinto, S. dos Reis Carvalho

    2010-05-01

    Quasars are the choicest objects to define a quasi-inertial reference frame. At the same time, they are active galactic nuclei powered by a massive black hole. As the astrometric precision of ground-based optical observations approaches the limit set by the forthcoming GAIA mission, astrometric stability can be investigated. Though the optical emission from the core region usually exceeds the other components by a factor of a hundred, the variability of those components must surely imply some measure of variability of the astrometric baricenter. Whether this is confirmed or not, it puts important constraints on the relationship of the quasar's central engine to the surrounding distribution of matter. To investigate the correlation between long-term optical variability and what is dubbed as the “random walk” of the astrometric center, a program is being pursued at the WFI/ESO 2.2m. The sample was selected from quasars known to undergo large-amplitude and long-term optical variations (Smith et al. 1993; Teerikorpi 2000). The observations are typically made every two months. The treatment is differential, comparing the quasar position and brightness against a sample of selected stars for which the average relative distances and magnitudes remain constant. The provisional results for four objects bring strong support to the hypothesis of a relationship between astrometric and photometric variability. A full account is provided by Andrei et al. (2009).

  1. The Physics Program for the QUASAR facility

    NASA Astrophysics Data System (ADS)

    Gates, D. A.; Lazerson, S. A.; Neilson, G. H.; Zarnstorff, M.; Schmitz, O.; Frerichs, H.

    2014-10-01

    The QUASi-Axisymmetric Research (QUASAR) stellarator is a new facility which can solve two critical problems for fusion, disruptions and steady-state, and which provides new insights into the role of symmetry in plasma confinement. The principle of quasi-axisymmetry will be used in QUASAR to study how tokamak-like systems can be made disruption-free and steady-state with low recirculating power, while also improving upon features of tokamaks, such as; stable at high pressure with high confinement, and scalable to a compact reactor. The two large stellarator experiments - LHD and W7-X - are pioneering facilities capable of developing 3D physics understanding at large scale and for very long pulses. The QUASAR design is unique in being QA and optimized for confinement, stability, and moderate aspect ratio (4.5). Important elements of the physics program for QUASAR are: establishing the physics basis of the design by demonstrating stable operation at high- β simultaneous with good neoclassical confinement, understanding the concomitant turbulent transport, and understanding the dependence of the underlying transport on magnetic geometry. An additional important element of the program will be understanding the physics characteristics of a QA stellarator with an high flux expansion ergodic edge. This work supported by DoE Contract No. DEAC02-76CH03073.

  2. Measuring Distances to Remote Galaxies and Quasars.

    ERIC Educational Resources Information Center

    McCarthy, Patrick J.

    1988-01-01

    Describes the use of spectroscopy and the redshift to measure how far an object is by measuring how fast it is receding from earth. Lists the most distant quasars yet found. Tables include "Redshift vs. Distance" and "Distances to Celestial Objects for Various Cosmologies." (CW)

  3. A SPECTACULAR OUTFLOW IN AN OBSCURED QUASAR

    SciTech Connect

    Greene, Jenny E.; Zakamska, Nadia L.; Smith, Paul S.

    2012-02-10

    SDSS J1356+1026 is a pair of interacting galaxies at redshift z = 0.123 that hosts a luminous obscured quasar in its northern nucleus. Here we present two long-slit Magellan LDSS-3 spectra that reveal a pair of symmetric {approx}10 kpc size outflows emerging from this nucleus, with observed expansion velocities of {approx}250 km s{sup -1} in projection. We present a kinematic model of these outflows and argue that the deprojected physical velocities of expansion are likely {approx}1000 km s{sup -1} and that the kinetic energy of the expanding shells is likely 10{sup 44-45} erg s{sup -1}, with an absolute minimum of >10{sup 42} erg s{sup -1}. Although a radio counterpart is detected at 1.4 GHz, it is faint enough that the quasar is considered to be radio quiet by all standard criteria, and there is no evidence of extended emission due to radio lobes, whether aged or continuously powered by an ongoing jet. We argue that the likely level of star formation is insufficient to power the observed energetic outflow and that SDSS J1356+1026 is a good case for radio-quiet quasar feedback. In further support of this hypothesis, polarimetric observations show that the direction of quasar illumination is coincident with the direction of the outflow.

  4. Quasar H II Regions During Cosmic Reionization

    SciTech Connect

    Alvarez, Marcelo A.; Abel, Tom; /KIPAC, Menlo Park

    2007-03-30

    Cosmic reionization progresses as HII regions form around sources of ionizing radiation. Their average size grows continuously until they percolate and complete reionization. We demonstrate how this typical growth can be calculated around the largest, biased sources of UV emission such as quasars by further developing an analytical model based on the excursion set formalism. This approach allows us to calculate the sizes and growth of the HII regions created by the progenitors of any dark matter halo of given mass and redshift with a minimum of free parameters. Statistical variations in the size of these pre-existing HII regions are an additional source of uncertainty in the determination of very high redshift quasar properties from their observed HII region sizes. We use this model to demonstrate that the transmission gaps seen in very high redshift quasars can be understood from the radiation of only their progenitors and associated clustered small galaxies. The fit requires the epoch of overlap to be at z = 5.8 {+-} 0.1. This interpretation makes the transmission gaps independent of the age of the quasars observed. If this interpretation were correct it would raise the prospects of using radio interferometers currently under construction to detect the epoch of reionization.

  5. Gravitational lensing size scales for quasars

    NASA Astrophysics Data System (ADS)

    Chartas, G.; Rhea, C.; Kochanek, C.; Dai, X.; Morgan, C.; Blackburne, J.; Chen, B.; Mosquera, A.; MacLeod, C.

    2016-05-01

    We review results from our monitoring observations of several lensed quasars performed in the optical, UV, and X-ray bands. Modeling of the multi-wavelength light curves provides constraints on the extent of the optical, UV, and X-ray emission regions. One of the important results of our analysis is that the optical sizes as inferred from the microlensing analysis are significantly larger than those predicted by the theoretical-thin-disk estimate. In a few cases we also constrain the slope of the size-wavelength relation. Our size constraints of the soft and hard X-ray emission regions of quasars indicate that in some objects of our sample the hard X-ray emission region is more compact than the soft and in others the soft emission region is smaller. This difference may be the result of the relative strengths of the disk-reflected (harder and extended) versus corona-direct (softer and compact) components in the quasars of our sample. Finally, we present the analysis of several strong microlensing events where we detect an evolution of the relativistic Fe line profile as the magnification caustic traverses the accretion disk. These caustic crossings are used to provide constraints on the innermost stable circular orbit (ISCO) radius and the accretion disk inclination angle of the black hole in quasar RX J1131-1231.

  6. THE RADIO PROPERTIES OF TYPE 2 QUASARS

    SciTech Connect

    Lal, Dharam Vir; Ho, Luis C.

    2010-03-15

    This paper presents the first high-resolution and high-sensitivity study of the radio properties of optically selected type 2 quasars. We used the Very Large Array at 8.4 GHz to observe 59 sources drawn from the Sloan Digital Sky Survey sample of Zakamska et al.. The detection rate of our survey is 59% (35/59), comparable to the detection rate in FIRST at 1.4 GHz. Ongoing star formation, although present, contributes negligible radio emission at the current sensitivity limit. Comparing the radio powers with the [O III] {lambda}5007 luminosities, we find that roughly 15% {+-} 5% of the sample can be considered radio loud. Intriguingly, the vast majority of the detected sources in our sample fall in a region intermediate between those traditionally occupied by radio loud and radio quiet quasars. Moreover, most of these 'radio intermediate' sources tend to have flat or inverted radio spectra, which we speculate may be caused by free-free absorption by ionized gas in the narrow-line region. The incidence of flat-spectrum sources in type 2 quasars appears to be much higher than in type 1 quasars, in apparent violation of the simple orientation-based unified model for active galaxies.

  7. Re-examining the case for neutral gas near the redshift 7 quasar ULAS J1120+0641

    NASA Astrophysics Data System (ADS)

    Bosman, Sarah E. I.; Becker, George D.

    2015-09-01

    Signs of damping-wing absorption attenuating the Lyman α emission line of the first known z ˜ 7 quasar, ULAS J1120+0641, recently provided exciting evidence of a significantly neutral intergalactic medium (IGM). This long-awaited signature of reionization was inferred, in part, from a deficit of flux in the quasar's Lyman α emission line based on predictions from a composite of lower redshift quasars. The composite sample was chosen based on its C IV emission line properties; however, as the original study by Mortlock et al. noted, the composite contained a slight velocity offset in C IV compared to ULAS J1120+0641. Here we test whether this offset may be related to the predicted strength of the Lyman α emission line. We confirm the significant (˜10 per cent at rms) scatter in Lyman α flux for quasars of a given C IV velocity and equivalent width found by Mortlock et al. We further find that among lower redshift objects chosen to more closely match the C IV properties of ULAS J1120+0641, its Lyman α emission falls within the observed distribution of fluxes. Among lower redshift quasars chosen to more closely match in C IV velocity and equivalent width, we find that ULAS J1120+0641 falls within the observed distribution of Lyman α emission line strengths. This suggests that damping-wing absorption may not be present, potentially weakening the case for neutral gas around this object. Larger samples of z > 7 quasars may therefore be needed to establish a clearer picture of the IGM neutral fraction at these redshifts.

  8. Definition of the metric on the space clos{sub ∅}(X) of closed subsets of a metric space X and properties of mappings with values in clos{sub ∅}(R{sup n})

    SciTech Connect

    Zhukovskii, E S; Panasenko, E A

    2014-09-30

    The paper is concerned with the extension of tests for superpositional measurability, Filippov's implicit function lemma and the Scorza Dragoni property to set-valued (and, as a corollary, to single-valued) mappings that fail to satisfy the Carathéodory conditions (the upper Carathéodory conditions) and are not continuous (upper semicontinuous) in the phase variable. The corresponding results depend on the introduction of the space clos{sub ∅}(X) of all closed subsets (including the empty set) of an arbitrary metric space X; a metric on clos{sub ∅}(X) is proposed; the space clos{sub ∅}(X) is shown to be complete whenever the original space X is; a criterion for convergence of a sequence is put forward; mappings with values in clos{sub ∅}(X) are studied. Some results on set-valued mappings satisfying the Carathéodory conditions and having compact values in R{sup n} are shown to hold for mappings with values in clos{sub ∅}(R{sup n}), measurable in the first argument, and continuous in the proposed metric in the second argument. Bibliography: 22 titles.

  9. Cross-Correlations in Quasar Radio Emission

    NASA Astrophysics Data System (ADS)

    Nefedyev, Yuri; Panischev, Oleg; Demin, Sergey

    The main factors forming the complex evolution of the accretive astrophysical systems are nonlinearity, intermittency, nonstationarity and also collective phenomena. To discover the dynamic processes in these objects and to detain understanding their properties we need to use all the applicable analyzing methods. Here we use the Flicker-Noise Spectroscopy (FNS) as a phenomenological approach to analyzing and parameterizing the auto- and cross-correlations in time series of astrophysical objects dynamics. As an example we consider the quasar flux radio spectral density at frequencies 2.7 GHz and 8.1 GHz. Data have been observed by Dr. N. Tanizuka (Laboratory for Complex Systems Analysis, Osaka Prefecture University) in a period of 1979 to 1988 (3 309 days). According to mental habits quasar is a very energetic and distant active galactic nucleus containing a supermassive black hole by size 10-10,000 times the Schwarzschild radius. The quasar is powered by an accretion disc around the black hole. The accretion disc material layers, moving around the black hole, are under the influence of gravitational and frictional forces. It results in raising the high temperature and arising the resonant and collective phenomena reflected in quasar emission dynamics. Radio emission dynamics of the quasar 0215p015 is characterized by three quasi-periodic processes, which are prevalent in considering dynamics. By contrast the 1641p399's emission dynamics have not any distinguish processes. It means the presence of high intermittency in accretive modes. The second difference moment allows comparing the degree of manifesting of resonant and chaotic components in initial time series of the quasar radio emission. The comparative analysis shows the dominating of chaotic part of 1641p399's dynamics whereas the radio emission of 0215p015 has the predominance of resonant component. Analyzing the collective features of the quasar radio emission intensity demonstrates the significant

  10. Flickering Quasar Helps Chandra Measure the Expansion Rate of the universe

    NASA Astrophysics Data System (ADS)

    2000-11-01

    Astronomers using the Chandra X-ray Observatory have identified a flickering, four-way mirage image of a distant quasar. A carefully planned observation of this mirage may be used to determine the expansion rate of the universe as well as to measure the distances to extragalactic objects, arguably two of the most important pursuits in modern astronomy. quasar RX J0911.4+0551 This figure is a composite of the X-ray image of the gravitational lens RX J0911.4+551 (top panel) and the light curves of the lensed images A2 (left panel) and A1 (right panel). Credit: NASA George Chartas, senior research associate at The Pennsylvania State University (Penn State) and Marshall W. Bautz, principal research scientist at the Massachusetts Institute of Technology (MIT) Center for Space Research, present their findings today at the meeting of the High Energy Astrophysics Division of the American Astronomical Society in Honolulu, Hawaii. "With a carefully planned follow-up, the Chandra observation of quasar RX J0911.4+0551 may lead to a measurement of the Hubble constant, the expansion rate of the universe, in less than a day," said Chartas. The observation would be done not with mirrors but with mirages--four images of a single quasar that capture the quasar's light at different moments of time due to the speed of light and the location of the mirages. Quasars are extremely distant galaxies with cores that glow with the intensity of 10 trillion Suns, a phenomenon likely powered by a supermassive black hole in the heart of the galaxy. This single "point source" image of a quasar may appear as four or five sources when the quasar--from our vantage point on Earth--is behind a massive intervening deflector, such as a dim galaxy. A mirage of images form when the gravity of the intervening deflector forces light rays to bend and take different paths to reach us. The time it takes for light to reach us from the distant object will depend on which path a ray decides to take. "An

  11. Enhanced performance of CdS/CdTe thin-film devices through temperature profiling techniques applied to close-spaced sublimation deposition

    SciTech Connect

    Xiaonan Li; Sheldon, P.; Moutinho, H.; Matson, R.

    1996-05-01

    The authors describe a methodology developed and applied to the close-spaced sublimation technique for thin-film CdTe deposition. The developed temperature profiles consisted of three discrete temperature segments, which the authors called the nucleation, plugging, and annealing temperatures. They have demonstrated that these temperature profiles can be used to grow large-grain material, plug pinholes, and improve CdS/CdTe photovoltaic device performance by about 15%. The improved material and device properties have been obtained while maintaining deposition temperatures compatible with commercially available substrates. This temperature profiling technique can be easily applied to a manufacturing environment by adjusting the temperature as a function of substrate position instead of time.

  12. Investigation of induced recrystallization and stress in close-spaced sublimated and radio-frequency magnetron sputtered CdTe thin films

    SciTech Connect

    Moutinho, H.R.; Dhere, R.G.; Al-Jassim, M.M.; Levi, D.H.; Kazmerski, L.L.

    1999-07-01

    We have induced recrystallization of small grain CdTe thin films deposited at low temperatures by close-spaced sublimation (CSS), using a standard CdCl{sub 2} annealing treatment. We also studied the changes in the physical properties of CdTe films deposited by radio-frequency magnetron sputtering after the same post-deposition processing. We demonstrated that the effects of CdCl{sub 2} on the physical properties of CdTe films are similar, and independent of the deposition method. The recrystallization process is linked directly to the grain size and stress in the films. These studies indicated the feasibility of using lower-temperature processes in fabricating efficient CSS CdTe solar cells. We believe that, after the optimization of the parameters of the chemical treatment, these films can attain a quality similar to CSS films grown using current standard conditions. {copyright} {ital 1999 American Vacuum Society.}

  13. [Life support of the Mars exploration crew. Control of a zeolite system for carbon dioxide removal from space cabin air within a closed air regeneration cycle].

    PubMed

    Chekov, Iu F

    2009-01-01

    The author describes a zeolite system for carbon dioxide removal integrated into a closed air regeneration cycle aboard spacecraft. The continuous operation of a double-adsorbent regeneration system with pCO2-dependable productivity is maintained through programmable setting of adsorption (desorption) semicycle time. The optimal system regulation curve is presented within the space of statistical performance family obtained in quasi-steady operating modes with controlled parameters of the recurrent adsorption-desorption cycle. The automatically changing system productivity ensures continuous intake of concentrated CO2. Control of the adsorption-desorption process is based on calculation of the differential adsorption (desorption) heat from gradient of adsorbent and test inert substance temperatures. The adaptive algorithm of digital control is implemented through the standard spacecraft interface with the board computer system and programmable microprocessor-based controllers. PMID:19621802

  14. Influence of substrate temperature on structural and optical properties of bismuth oxide thin films deposited by close-spaced vacuum sublimation

    NASA Astrophysics Data System (ADS)

    Ivashchenko, M. M.; Buryk, I. P.; Latyshev, V. M.; Stepanenko, A. O.; Levchenko, K. S.

    2015-12-01

    Bi2O3 thin films were deposited on ultrasonically-cleaned glass and mica substrates by close-spaced vacuum sublimation technique. Films surface morphology was studied using scanning electron microscopy (SEM). Structural study based on the transmission-electron microscopy (TEM) and selected-area electron diffraction (SAED) analysis has been shown that deposited films were polycrystalline with face-centered cubic structure. Optical study was carried out by spectral photometry analysis in the wavelengths range λ = 320-900 nm using the optical transmittance and absorbance measurements. For determination optical band gap Eg the Tauc plot was used and the band gap energy Eg is determined in the range of 3.50-3.62 eV, respectively. Fourier-transform infra-red (FTIR) analysis shown that obtained films are well-crystalline and have a good optical quality.

  15. X-ray spectral evolution of high redshift quasars

    NASA Technical Reports Server (NTRS)

    Bechtold, Jill; Elvis, Martin; Fiore, Fabrizio; Kuhn, Olga; Cutri, Roc M.; Mcdowell, Jonathan C.; Rieke, Marcia; Siemiginowska, Aneta; Wilkes, Belinda J.

    1994-01-01

    At z approx. equals 3, the x-ray spectra of radio-loud and radio-quiet quasars are different. High-redshift radio-quiet quasars either have large absorbing columns, N(sub H), and steeper power law spectral indices, alpha(sub epsilon), than low redshift quasars, or no absorption and similar alpha(sub epsilon)'s. In contrast, the radio-loud quasars at high redshift have substantial absorption and similar alpha(sub epsilon)'s to low redshift quasars. Implications for the interpretation of the evolution of the luminosity function of quasars are discussed. If the absorption arises outside the central engine for both radio-loud and radio-quiet quasars, then radio-quiet quasars differ from the radio-loud quasars in that their emitted power law spectrum has evolved with redshift. We argue that this favors models where quasars are numerous and short-lived, rather than rare and long-lived.

  16. A Systematic Meta-Survey of High Redshift Quasars Probing their Environments and Evolution

    NASA Astrophysics Data System (ADS)

    Gobeille, Doug B. P.

    We have constructed a meta-survey of 298 quasars in the window from 7 to 17.5 hours in right ascension and 0 to 65 degrees in declination. These quasars span three decades of total power and redshifts from 0.158 to 5.284. All sources had a flux density of greater than 70 mJy at 1.4 GHz. At redshifts z > 2.5 our sample is complete. It is also complete for z < 1 and P Tot1:4 > 1027.55 W/Hz. Our quasar sample is built from archival Very Large Array (VLA) observations, as well as three observations in 2007 and 2008. This sample represents one of the most complete meta-surveys to date of the high redshift universe. In the 1980's, two competing groups (Ne, Gower and Hutchings, and Barthel, Miley, and Lonsdale) investigated the high redshift universe, seeking to investigate the dependence of largest linear size (LLS) and bending angles on redshift, core power, and extended power. Using our sample we test the differing results of these groups and build our own model of source evolution with redshift and power. We also seek a relationship between bending angles and core dominance, modeling this dependence on the thoughts of Orr & Browne showing that projected bending angles grow as the angle to the line of sight approaches the intrinsic bending angle of the quasar. We will also present an additional component of our high redshift quasar observations seeking arcsecond scale jets to be observed with the space based Chandra x-ray telescope. These observations will be used to investigate the nature of x-ray emission from the knots of kiloparsec jets in the high redshift universe.

  17. Natural convection mass transfer at a vertical array of closely-spaced horizontal cylinders with special reference to electrochemical reactor design

    SciTech Connect

    Sedahmed, G.H.; Nirdosh, I.

    1995-06-01

    Many industrial electrochemical processes such as electrowinning of metals, electrochemical pollution control, and electroorganic and electroinorganic syntheses are diffusion-controlled processes whose rates depend on the geometry of the working electrode as well as the prevailing hydrodynamic conditions. Recently much work has been done to develop new electrochemical reactors which are more efficient than the traditional parallel plate electrochemical reactor used in conducting such processes. In line with this, the object of the present work was to study the natural convection mass transfer behavior of a new electrode geometry, namely an array of closely-spaced horizontal tubes. Natural convection mass transfer at a vertical array of closely-spaced horizontal cylinders was studied by an electrochemical technique involving the measurement of the limiting current of the cathodic deposition of copper from acidified copper sulfate solution. Various combinations of solution concentration, cylinder diameter, and number of cylinders per array were used including experiments on single cylinders. The mass transfer coefficient at the array was found to decrease with increasing number of cylinders, pass through a minimum, and then increase with further increase in the number of cylinders per array; the mass transfer coefficient increased with increasing cylinder diameter in the array. Mass transfer data for different arrays were correlated for the range 6.3 {times} 10{sup 9} < ScGr < 3.63 {times} 10{sup 10} by the equation Sh = 0.455(ScGr){sup 0.25} and for the range 6.3 {times} 10{sup 10} < ScGr < 3.63 {times} 10{sup 12} by the equation Sh = 0.0064(ScGr){sup 0.42}. The characteristic length used in the above correlations was obtained by dividing the array area by the perimeter projected onto a horizontal plane. Practical implications of the present results in designing electrochemical reactors with heat transfer facilities are highlighted.

  18. Similarity of ionized gas nebulae around unobscured and obscured quasars

    NASA Astrophysics Data System (ADS)

    Liu, Guilin; Zakamska, Nadia L.; Greene, Jenny E.

    2014-08-01

    Quasar feedback is suspected to play a key role in the evolution of massive galaxies, by removing or reheating gas in quasar host galaxies and thus limiting the amount of star formation. In this paper, we continue our investigation of quasar-driven winds on galaxy-wide scales. We conduct Gemini Integral Field Unit spectroscopy of a sample of luminous unobscured (type 1) quasars, to determine the morphology and kinematics of ionized gas around these objects, predominantly via observations of the [O III] λ5007 Å emission line. We find that ionized gas nebulae extend out to ˜13 kpc from the quasar, that they are smooth and round, and that their kinematics are inconsistent with gas in dynamical equilibrium with the host galaxy. The observed morphological and kinematic properties are strikingly similar to those of ionized gas around obscured (type 2) quasars with matched [O III] luminosity, with marginal evidence that nebulae around unobscured quasars are slightly more compact. Therefore, in samples of obscured and unobscured quasars carefully matched in [O III] luminosity, we find support for the standard geometry-based unification model of active galactic nuclei, in that the intrinsic properties of the quasars, of their hosts and of their ionized gas appear to be very similar. Given the apparent ubiquity of extended ionized regions, we are forced to conclude that either the quasar is at least partially illuminating pre-existing gas or that both samples of quasars are seen during advanced stages of quasar feedback. In the latter case, we may be biased by our [O III]-based selection against quasars in the early `blow-out' phase, for example due to dust obscuration.

  19. The Faint End of the Quasar Luminosity Function at z ~ 4

    NASA Astrophysics Data System (ADS)

    Glikman, Eilat; Bogosavljević, Milan; Djorgovski, S. G.; Stern, Daniel; Dey, Arjun; Jannuzi, Buell T.; Mahabal, Ashish

    2010-02-01

    The evolution of the quasar luminosity function (QLF) is one of the basic cosmological measures providing insight into structure formation and mass assembly in the universe. We have conducted a spectroscopic survey to find faint quasars (-26.0 < M 1450 < -22.0) at redshifts z = 3.8-5.2 in order to measure the faint end of the QLF at these early times. Using available optical imaging data from portions of the NOAO Deep Wide-Field Survey and the Deep Lens Survey, we have color-selected quasar candidates in a total area of 3.76 deg2. Thirty candidates have R <= 23 mag. We conducted spectroscopic follow-up for 28 of our candidates and found 23 QSOs, 21 of which are reported here for the first time, in the 3.74 < z < 5.06 redshift range. We estimate our survey completeness through detailed Monte Carlo simulations and derive the first measurement of the density of quasars in this magnitude and redshift interval. We find that the binned luminosity function (LF) is somewhat affected by the K-correction used to compute the rest-frame absolute magnitude at 1450 Å. Considering only our R <= 23 sample, the best-fit single power law (Φ vprop L β) gives a faint-end slope β = -1.6 ± 0.2. If we consider our larger, but highly incomplete sample going 1 mag fainter, we measure a steeper faint-end slope -2 < β < -2.5. In all cases, we consistently find faint-end slopes that are steeper than expected based on measurements at z ~ 3. We combine our sample with bright quasars from the Sloan Digital Sky Survey to derive parameters for a double-power-law LF. Our best fit finds a bright-end slope, α = -2.4 ± 0.2, and faint-end slope, β = -2.3 ± 0.2, without a well-constrained break luminosity. This is effectively a single power law, with β = -2.7 ± 0.1. We use these results to place limits on the amount of ultraviolet radiation produced by quasars and find that quasars are able to ionize the intergalactic medium at these redshifts. The data presented herein were obtained at the

  20. Photometric redshift techniques of quasars in big-data era

    NASA Astrophysics Data System (ADS)

    Zhang, Yanxia

    2015-08-01

    With the availability of the huge amounts of data from ground- and space-based large multiband photometric surveys, photometric redshifts provide an estimate for the distance of an astronomical object and have become a crucial tool for extragalactic astronomy and cosmology. Various phtometric redshift approaches are in bloom. Their performance and efficiency not only depend on completeness and quality of data, but also on the volume of data. The increase of data volume lead to different choice of techniques. We present various data mining methods used for photometric redshift estimation of quasars and compare their advantages and disadvantages. In the big-data era, the methods fit for large-scale data are in great requirement.

  1. Colors of 2625 Quasars at 0

    NASA Astrophysics Data System (ADS)

    Richards, Gordon T.; Fan, Xiaohui; Schneider, Donald P.; Vanden Berk, Daniel E.; Strauss, Michael A.; York, Donald G.; Anderson, John E., Jr.; Anderson, Scott F.; Annis, James; Bahcall, Neta A.; Bernardi, Mariangela; Briggs, John W.; Brinkmann, J.; Brunner, Robert; Burles, Scott; Carey, Larry; Castander, Francisco J.; Connolly, A. J.; Crocker, J. H.; Csabai, István; Doi, Mamoru; Finkbeiner, Douglas; Friedman, Scott D.; Frieman, Joshua A.; Fukugita, Masataka; Gunn, James E.; Hindsley, Robert B.; Ivezić, Željko; Kent, Stephen; Knapp, G. R.; Lamb, D. Q.; Leger, R. French; Long, Daniel C.; Loveday, Jon; Lupton, Robert H.; McKay, Timothy A.; Meiksin, Avery; Merrelli, Aronne; Munn, Jeffrey A.; Newberg, Heidi Jo; Newcomb, Matt; Nichol, R. C.; Owen, Russell; Pier, Jeffrey R.; Pope, Adrian; Richmond, Michael W.; Rockosi, Constance M.; Schlegel, David J.; Siegmund, Walter A.; Smee, Stephen; Snir, Yehuda; Stoughton, Chris; Stubbs, Christopher; SubbaRao, Mark; Szalay, Alexander S.; Szokoly, Gyula P.; Tremonti, Christy; Uomoto, Alan; Waddell, Patrick; Yanny, Brian; Zheng, Wei

    2001-05-01

    We present an empirical investigation of the colors of quasars in the Sloan Digital Sky Survey (SDSS) photometric system. The sample studied includes 2625 quasars with SDSS photometry: 1759 quasars found during SDSS spectroscopic commissioning and SDSS follow-up observations on other telescopes, 50 matches to FIRST quasars, 573 matches to quasars from the NASA Extragalactic Database, and 243 quasars from two or more of these sources. The quasars are distributed in a 2.5d wide stripe centered on the celestial equator covering ~529 deg2. Positions (accurate to 0.2") and SDSS magnitudes are given for the 898 quasars known prior to SDSS spectroscopic commissioning. New SDSS quasars, which range in brightness from i*=15.39 to the photometric magnitude limit of the survey, represent an increase of over 200% in the number of known quasars in this area of the sky. The ensemble average of the observed colors of quasars in the SDSS passbands are well represented by a power-law continuum with αν=-0.5 (fν~να) and are close to those predicted by previous simulations. However, the contributions of the ``small blue (or λ3000) bump'' and other strong emission lines have a significant effect upon the colors. The color-redshift relation exhibits considerable structure, which may be of use in determining photometric redshifts for quasars from their colors alone. The range of colors at a given redshift can generally be accounted for by a range in the optical spectral index with a distribution αν=-0.5+/-0.65 (95% confidence), but there is a red tail in the distribution. This tail may be a sign of internal reddening, especially since fainter objects at a given redshift tend to exhibit redder colors than the average. Finally, we show that there is a continuum of properties between quasars and Seyfert galaxies, and we test the validity of the traditional dividing line (MB=-23) between the two classes of active galactic nuclei. Based on observations obtained with the Sloan Digital

  2. X-Ray Spectra of Quasars from the ROSAT Public Archive

    NASA Technical Reports Server (NTRS)

    Elvis, Martin S.; West, Donald (Technical Monitor)

    2000-01-01

    This has been a most productive proposal. We have: (1) Found many new X-ray absorbed quasars at z>2; (2) Determined that all of these are radio-loud, favoring an intrinsic origin for the absorption; (3) Found that the one radio-quiet exception lay close to a nearby galaxy, so initiating the X-ray study of the ISM of normal galaxies via X-ray spectroscopy; (4) Discovered a class of 'red quasars', probably the tip of a large obscured population; and (5) Discovered a class of 'blank field X-ray sources'. These are a heterogeneous collection but probably include several peculiar types of active galactic nuclei (AGN). Follow-up of the 'blanks' is being undertaken under a separate ADP program. Chandra and XMM-Newton observing time for these objects has been approved. This program has produced six refereed papers and six published conference proceedings.

  3. An ultraviolet atlas of quasar and blazar spectra

    NASA Technical Reports Server (NTRS)

    Kinney, A. L.; Bohlin, R. C.; Blades, J. C.; York, D. G.

    1991-01-01

    An atlas is presented which provides a uniformly extracted and calibrated set of over 1000 UV spectra of the highest possible SNR for quasars and blazars observed with the IUE. The spectra show that quasars and blazars vary more in the UV than in the optical, and show increasing variability toward shorter wavelengths. The low-redshift quasars have Ly-alpha emission lines dominated by strong, narrow components, while high-redshift quasars seem to lack such narrow components. Absorption by gas in the Galaxy is ubiquitous in strong interstellar lines of C II, O I, Si II, Mg II, and Fe II. Of special note is the detection of Fe II and Mg II absorption due to gas associated with NGC3067 in the quasar 3C 232. Over 20 percent of the combined quasar and Seyfert 1 sample show either associated absorption or absorption just shortward of the emission redshift.

  4. Observational limitations of the Doppler theory of quasars

    NASA Astrophysics Data System (ADS)

    Narlikar, J. V.; Subramanian, K.

    1982-09-01

    The viability of the hypothesis that the redshift of a quasar is due entirely to the Doppler effect which arises from its high ejection speed in a nearby center of explosion is examined in light of data on the aligned triplets of quasars discovered by Arp and Hazard (1980). In view of a physical association of the quasars in a triplet, the computation of the various parameters of the Doppler problem is illustrated and constraints are placed on quasar ejection scenarios in order to critically examine Holyle's recent (1980) hypothesis that quasars emit the bulk of their radiation in a specified backward cone. It is found that the four triplets provide prima facie evidence for such a hypothesis, and further checks on the Doppler model are suggested. A very small, but nonzero fraction of blueshifted quasars is predicted by the model.

  5. SPECTROPOLARIMETRY OF RADIO-SELECTED BROAD ABSORPTION LINE QUASARS

    SciTech Connect

    DiPompeo, M. A.; Brotherton, M. S.; Becker, R. H.; Gregg, M. D.; Tran, H. D.; White, R. L.; Laurent-Muehleisen, S. A.

    2010-07-15

    We report spectropolarimetry of 30 radio-selected broad absorption line (BAL) quasars with the Keck Observatory, 25 from the sample of Becker et al. Both high- and low-ionization BAL quasars are represented, with redshifts ranging from 0.5 to 2.5. The spectropolarimetric properties of radio-selected BAL quasars are very similar to those of radio-quiet BAL quasars: a sizeable fraction (20%) shows large continuum polarization (2%-10%) usually rising toward short wavelengths; emission lines are typically less polarized than the continuum; and absorption line troughs often show large polarization jumps. There are no significant correlations between polarization properties and radio properties, including those indicative of system orientation, suggesting that BAL quasars are not simply normal quasars seen from an edge-on perspective.

  6. Optical variability of radio-intermediate quasars

    NASA Astrophysics Data System (ADS)

    Goyal, Arti; Gopal-Krishna; Joshi, S.; Sagar, R.; Wiita, Paul J.; Anupama, G. C.; Sahu, D. K.

    2010-02-01

    We report the results of our intensive intranight optical monitoring of eight optically bright `radio-intermediate quasars' (RIQs) having flat or inverted radio spectra. The monitoring was carried out in R band on 25 nights during 2005-2009. On each night only one RIQ was monitored for a minimum duration of ~4h (the average being 5.2h per night). Using the CCD as an N-star photometer, an intranight optical variability (INOV) detection threshold of ~1-2 per cent was achieved for the densely sampled differential light curves derived from our data. These observations amount to a large increase over those reported hitherto for this rare and sparsely studied class of quasars which can, however, play an important role in understanding the link between the dominant varieties of powerful active galactic nucleus, namely the radio-quiet quasars (RQQs), radio-loud quasars (RLQs) and blazars. Despite the probable presence of relativistically boosted nuclear jets, inferred from their flat/inverted radio spectra, clear evidence for INOV in our extensive observations was detected only on one night. Furthermore, flux variation between two consecutive nights was clearly seen for one of the RIQs. These results demonstrate that as a class, RIQs are much less extreme in nuclear activity compared to blazars. The availability in the literature of INOV data for another two RIQs conforming to our selection criteria allowed us to enlarge the sample to 10 RIQs (monitored on a total of 42 nights for a minimum duration of ~4h per night). The absence of large amplitude INOV (ψ >= 3 per cent) persists in this enlarged sample. This extensive data base have enabled us to arrive at the first estimate for the INOV duty cycle (DC) of RIQs. The DC is found to be small (~9 per cent), increasing to ~14 per cent if the two cases of `probable' INOV are included. The corresponding value is known to be ~60 per cent for BLLacs and ~15 per cent for both RLQs and RQQs, if they too are monitored for >~4-6h in

  7. Double Lobed Radio Quasars from the Sloan Digital Sky Survey

    SciTech Connect

    de Vries, W H; Becker, R H; White, R L

    2005-11-10

    We have combined a sample of 44 984 quasars, selected from the Sloan Digital Sky Survey (SDSS) Data Release 3, with the FIRST radio survey. Using a novel technique where the optical quasar position is matched to the complete radio environment within 450'', we are able to characterize the radio morphological make-up of what is essentially an optically selected quasar sample, regardless of whether the quasar (nucleus) itself has been detected in the radio. About 10% of the quasar population have radio cores brighter than 0.75 mJy at 1.4 GHz, and 1.7% have double lobed FR2-like radio morphologies. About 75% of the FR2 sources have a radio core (> 0.75mJy). A significant fraction ({approx}40%) of the FR2 quasars are bent by more than 10 degrees, indicating either interactions of the radio plasma with the ICM or IGM. We found no evidence for correlations with redshift among our FR2 quasars: radio lobe flux densities and radio source diameters of the quasars have similar distributions at low (mean 0.77) and high (mean 2.09) redshifts. Using a smaller high reliability FR2 sample of 422 quasars and two comparison samples of radio-quiet and non-FR2 radio-loud quasars, matched in their redshift distributions, we constructed composite optical spectra from the SDSS spectroscopic data. Based on these spectra we can conclude that the FR2 quasars have stronger high-ionization emission lines compared to both the radio quiet and non-FR2 radio loud sources. This is consistent with the notion that the emission lines are brightened by ongoing shock ionization of ambient gas in the quasar host as the radio source expands.

  8. Magnified Views of Relativistic Outflows in Gravitationally Lensed Quasars

    NASA Astrophysics Data System (ADS)

    Chartas, G.; Cappi, M.; Hamann, F.; Eracleous, M.; Strickland, S.; Vignali, C.; Dadina, M.; Giustini, M.; Saez, C.; Misawa, T.

    2016-06-01

    We presents results from X-ray observations of relativistic outflows in lensed quasars. The lensing magnification of the observed objects provides high signal-to-noise X-ray spectra of quasars showing the absorption signatures of relativistic outflows at redshifts near a crucial phase of black hole growth and the peak of cosmic AGN activity. We summarise the properties of the wide-angle relativistic outflow of the z = 1.51 NAL quasar HS 0810 detected in recent deep XMM-Newton and Chandra observations of this object. We also present preliminary results from a mini-survey of gravitationally lensed mini-BAL quasars performed with XMM-Newton.

  9. Red Galaxy Structures Toward a Large Quasar Group Field

    NASA Astrophysics Data System (ADS)

    Williger, Gerard M.; Feil, E. C.; Haberzettl, L.; Clowes, R.; Campusano, L.; Haines, C. P.; Valls-Gabaud, D.; Lehnert, M.; Nesvadba, N.; LQG Team

    2014-01-01

    We present data from deep FUV-NUV-griz images toward a 2 sq degree region in the Clowes-Campusano Large Quasar Group field, which contains structures of quasars on the >100 Mpc scale at 0.8 and 1.2. Large Quasar Groups may be the signal posts for galaxy structures analogous to superclusters at high redshift. Using the six band photometry, we calculate photometric redshifts for red-selected galaxies to identify supercluster-size structures, and compare their locations with the quasars in the field.

  10. Role of Erosion on Closely-Spaced Fault Scarps: High-resolution Laser Scanning Data and Scarp Diffusion Modelling of the Rex Hills Flower Structure, Nevada

    NASA Astrophysics Data System (ADS)

    Baran, R.; Guest, B.; Friedrich, A. M.

    2007-12-01

    Flower structures are often associated with strike-slip faults. Their subsurface geometry is well known but additional information about their geometry and kinematics is also contained in their surface expression, especially in surfaces exhibiting closely-spaced fault scarps. However, detailed surface descriptions of flower structures are rare. Here, we present for the first time topographic profiles extracted from high-resolution digital elevation model (DEM) data using a ground-based laser scanner (Riegl company) to examine the surface expression of a flower structure in great detail. Our study site, the Rex Hills flower structure (40 m high, ~1 km long), is located on the transpressional left-bend between the Pahrump and Amargosa segments of the dextral Stateline fault system (Guest et al., 2007, GSAB). The southern Rex Hills slope exhibits three reverse fault- scarp generations related to three reverse fault branches, respectively. The basal scarp is the youngest and most continuous one. It exhibits five fault segments with an approximately constant displacement along the scarp. The upper two fault-scarp generations are less continuous, and older. The topography of the southern Rex Hills slope also is characterized by alternating valleys and ridges (each ~100 m long) extending perpendicular to the main ridge crest. Our analysis shows that fault scarp morphology varies laterally along this slope. Scarps exposed on ridge crests are typically more numerous (up to 4-5 scarps) and smaller (on average 5 m high), whereas adjacent valleys often exhibit single large (>10 m high) scarps. The larger valley-scarps did not result from the offset across a single fault branch, but resulted from merging of the three scarps mentioned above by enhanced scarp degradation. The preservation potential of small, individual scarps is therefore better on ridge crests relative to adjacent valleys. Assuming a known age of 2 kyrs (Menges et al., 2003, AGU), we examined the spatial

  11. Formation and Signatures of the First Stars and Quasars

    NASA Astrophysics Data System (ADS)

    Haiman, Zoltan

    1998-11-01

    Although direct detection of the very first stars and quasars in the universe is beyond the capabilities of current instruments, there is substantial evidence for the existence of these objects. Observations of the intergalactic medium (IGM) reveal that it was highly ionized, and enriched with heavy elements, before redshift z~ 5. Standard cold dark matter (CDM) cosmological models predict that the first clouds indeed condensed prior to this redshift, around 10/ ~< z/ ~< 30. In this thesis, we study several questions related to the formation and observational signatures of the first generation of astrophysical objects in CDM cosmologies. Using one-dimensional simulations, we study the effects of gas pressure and H2 cooling on the sizes of the first collapsed systems. We find that the H2 abundance reaches high enough values to permit efficient cooling and collapse in the central, shock-heated regions of clouds with virial temperatures T vir/ ~> 100oK. Still smaller clouds (~103Msolar) are able to collapse by z~ 10, due to the gravitational potential of collisionless dark matter. We then examine the effect of ultraviolet (UV) photons on the H2 abundance in these clouds, and find that H2 is universally photodissociated by the low UV flux from the first few stars. This imposes a high minimum mass (~108Msolar) for typical halos that can cool and harbor astrophysical objects. Using phenomenologically calibrated semi-analytical methods, we calculate several indirect consequences of the first stars, including the reionization history of the IGM and the resulting suppression of the cosmic microwave background (CMB) anisotropies; or the optical depth of dust from high redshift Type I supernovae and the resulting spectral distortion of the CMB. Both of these effects will be observable with forthcoming satellites, such as MAP or Planck, while the Next Generation Space Telescope could directly image numerous z>10 star-clusters. Similarly, we extrapolate the observed quasar

  12. The compact radio structure of the high-redshift quasar OQ172

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Jiang, D. R.; Gu, M.; Gurvits, L. I.

    2016-02-01

    The GHz-Peaked Spectrum (GPS) quasar OQ172 (J1445+0958) has an extremely high rest-frame rotation measure (RM > 20 000 rad m-2) and an RM gradient in its inner nucleus. Its jet observed with Very Long Baseline Interferometry (VLBI) is strongly bent along an arc spanning > 100 pc. Near infrared (NIR) spectra reveal an unusually large [O III] line width which suggests a large mass within the NLR and/or strong interactions between the emerging jet and the dense material therein. We present our VLBI Space Observatory Programme (VSOP) and Multi-frequency Very Long Baseline Array (VLBA) observation of the GPS quasar OQ172. The observations will help us to explore the VLBI radio properties and to better understand the circumnuclear environment of OQ172.

  13. The evolution of the quasar continuum

    NASA Technical Reports Server (NTRS)

    Elvis, M.

    1992-01-01

    We now have in hand a large data base of Roentgen Satellite (ROSAT), optical, and IR complementary data. We are in the process of obtaining a large amount of the International Ultraviolet Explorer (IUE) data for the same quasar sample. For our complementary sample at high redshifts, where the UV was redshifted into the optical, we have just had approved large amounts of observing time to cover the quasar continuum in the near-IR using the new Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) array spectrographs. Ten micron, optical, and VLA radio, data also have approved time. An ISO US key program was approved to extend this work into the far-IR, and the launch of ASTRO-D (early in 1993) promises to extend it to higher energy X-rays.

  14. Microlensing of quasar ultraviolet iron emission

    SciTech Connect

    Guerras, E.; Mediavilla, E.; Kochanek, C. S.; Muñoz, J. A.; Falco, E.; Motta, V.; Rojas, K.

    2013-12-01

    We measure the differential microlensing of the UV Fe II and Fe III emission line blends between 14 quasar image pairs in 13 gravitational lenses. We find that the UV iron emission is strongly microlensed in four cases with amplitudes comparable to that of the continuum. Statistically modeling the magnifications, we infer a typical size of r{sub s}∼4√(M/M{sub ⊙}) light-days for the Fe line-emitting regions, which is comparable to the size of the region generating the UV continuum (∼3-7 light-days). This may indicate that a significant part of the UV Fe II and Fe III emission originates in the quasar accretion disk.

  15. Quasars as probes of the intergalactic medium

    NASA Technical Reports Server (NTRS)

    Green, R. F.; Bechtold, J.

    1984-01-01

    Spectral energy distributions for 10 high red shift quasars in the wavelength range 1250 to 10,000 A were obtained by IUE. A pronounced steepening is detected shortward of 1200 A, which correlates well with quasar red shift, but poorly with luminosity. The observed slope change is explained by Lyman continuum absorption from the strongest 5% of the Lyman alpha forest lines, identified with the low column density metal containing systems. Reddening may also contribute to the steepening, but a much lower neutral gas to dust ratio than that found in the Galaxy is required. Optically thick Lyman limit discontinuities are seen with zabs zem. These systems are metal containing, constant in comoving density with epoch, and require in L* galaxy to have a cross section of 5 to 10 Holmberg radii.

  16. A Bayesian reanalaysis of the quasar dataset

    NASA Astrophysics Data System (ADS)

    Cameron, E.; Pettitt, A. N.

    We investigate recent claims of spatial variation in the fine structure constant on cosmic distance scales based on estimates of its extra-galactic-to-on-Earth ratio recovered from ``many multiplet'' fitting of quasar absorption spectra. To overcome the limitations of previous analyses requiring the assumption of a strictly unbiased and Normal distribution for the ``unexplained errors'' of this quasar dataset we employ a Bayesian model selection strategy with prior-sensitivity analysis. A particular strength of the hypothesis testing methodology advocated herein is that it can handle both parametric and semi-parametric models self-consistently through a combination of recursive marginal likelihood estimation and importance sample reweighting. We conclude from the presently-available data that the observed trends are more likely to arise from biases of opposing sign in the two telescopes used to undertake these measurements than from a genuine large-scale trend in this fundamental ``constant''.

  17. The 3000 A bump in quasars

    NASA Technical Reports Server (NTRS)

    Oke, J. B.; Shields, G. A.; Korycansky, D. G.

    1984-01-01

    New observations of the 3000 A bump in quasars are presented and some simple considerations regarding its physical origin are addressed. Absolute spectrophotometry of 30 quasars with redshifts between 0.53 and 0.70 was obtained with the multichannel spectrometer on the 5 m Hale telescope with a rest wavelength coverage of 2000-5000 A. The continuum observations are well represented by a single power law plus a smooth, broad bump and superposed Fe II multiplets. The strength of the bump correlates fairly well with that of H-beta but poorly with those of the Mg II and Fe II lines. Models consisting of a power law and optically thick hydrogen continua with temperatures of about 12,000 K, and Balmer-edge optical depths equal to three fit the observed energy distributions well. The physical conditions and continuum emission of a dense slab of hydrogen heated by gamma rays are analyzed.

  18. Mining for Dust in Type 1 Quasars

    NASA Astrophysics Data System (ADS)

    Krawczyk, Coleman M.; Richards, Gordon T.; Gallagher, S. C.; Leighly, Karen M.; Hewett, Paul C.; Ross, Nicholas P.; Hall, P. B.

    2015-06-01

    We explore the extinction/reddening of ˜35,000 uniformly selected quasars with 0\\lt z≤slant 5.3 in order to better understand their intrinsic optical/ultraviolet (UV) spectral energy distributions. Using rest-frame optical-UV photometry taken from the Sloan Digital Sky Survey’s (SDSS) 7th data release, cross-matched to WISE in the mid-infrared, 2MASS and UKIDSS in the near-infrared, and GALEX in the UV, we isolate outliers in the color distribution and find them well described by an SMC-like reddening law. A hierarchical Bayesian model with a Markov Chain Monte Carlo sampling method was used to find distributions of power law indices and E(B-V) consistent with both the broad absorption line (BAL) and non-BAL samples. We find that, of the ugriz color-selected type 1 quasars in SDSS, 2.5% (13%) of the non-BAL (BAL) sample are consistent with E(B-V)\\gt 0.1 and 0.1% (1.3%) with E(B-V)\\gt 0.2. Simulations show both populations of quasars are intrinsically bluer than the mean composite, with a mean spectral index ({{α }λ }) of -1.79 (-1.83). The emission and absorption-line properties of both samples reveal that quasars with intrinsically red continua have narrower Balmer lines and stronger high-ionization emission lines, the latter indicating a harder continuum in the extreme-UV and the former pointing to differences in black hole mass and/or orientation.

  19. Optical microvariability of bright type 2 quasars

    NASA Astrophysics Data System (ADS)

    Polednikova, Jana; Ederoclite, Alessandro; Cepa, Jordi; de Diego Onsurbe, José Antonio; González-Serrano, José Ignacio

    2014-07-01

    We present results from a project focused on searching optical microvariabilty (also known as ``intra-night'' variability) in type 2 - obscured - quasars. Optical microvariability can be described as very small changes in the flux, typically in the order of hundredths of magnitude, which can be observed on timescales of hours. Such studies have been so far conducted for samples of blazars and type 1, unobscured, AGNs, where the optical microvariability was detected with success. We have focused on obscured targets which would pose a challenge to the AGN standard model. In the present work, however, we have observed a sample of three bright (g mag < 17) type 2 quasar, based on the catalog of type 2 quasars from SDSS of Reyes et al. (2008). The observations were carried out with the 1.5 meter telescope at San Pedro Martir observatory in Mexico. The sample was observed during an observation period of four days in Johnsons V filter, resulting in at least two continuous intervals of observations per target during the observational run. We have obtained differential light curves for our sources as well as for the comparison stars. They were analyzed using one-way analysis of variance statistical test (ANOVA), which has been repeatedly used in the past for studies of unobscured targets. Based on the results from the statistical analysis, we show that at least two out of three observed targets appear to be variable on time scales of hours. So far, this is the first study which confirmed existence of optical microvariability in type 2 quasars.

  20. Quasar X-Ray Spectra Revisited: Erratum

    NASA Astrophysics Data System (ADS)

    Shastri, P.; Wilkes, B. J.; Elvis, M.; McDowell, J.

    1994-08-01

    In the paper "Quasar X-Ray Spectra Revisited " by P. Shastri, B. J. Wilkes, M. Elvis, and J. McDowell (ApJ, 410,29 [1993]), there is an error in the flux density levels in Figures 4a and 4b. As a result of an error during rebinning of the optical spectrophotometry data, the flux density levels in those two figures are a factor of 5 lower then their actual value.