Science.gov

Sample records for accretion physics studies

  1. Fundamental Ice Crystal Accretion Physics Studies

    NASA Technical Reports Server (NTRS)

    Currie, Tom; Knezevici, Danny; Fuleki, Dan; Struk, Peter M.; Broeren, Andy P.; Tsao, Jen-ching; Vargas, Mario; Wright, William

    2011-01-01

    Due to numerous engine power-loss events associated with high-altitude convective weather, ice accretion within an engine due to ice-crystal ingestion is being investigated. The National Aeronautics and Space Administration (NASA) and the National Research Council (NRC) of Canada are starting to examine the physical mechanisms of ice accretion on surfaces exposed to ice-crystal and mixed-phase conditions. In November 2010, two weeks of testing occurred at the NRC Research Altitude Facility utilizing a single wedge-type airfoil designed to facilitate fundamental studies while retaining critical features of a compressor stator blade or guide vane. The airfoil was placed in the NRC cascade wind tunnel for both aerodynamic and icing tests. Aerodynamic testing showed excellent agreement compared with CFD data on the icing pressure surface and allowed calculation of heat transfer coefficients at various airfoil locations. Icing tests were performed at Mach numbers of 0.2 to 0.3, total pressures from 93 to 45 kPa, and total temperatures from 5 to 15 C. Ice and liquid water contents ranged up to 20 and 3 grams per cubic meter, respectively. The ice appeared well adhered to the surface in the lowest pressure tests (45 kPa) and, in a particular case, showed continuous leading-edge ice growth to a thickness greater than 15 millimeters in 3 minutes. Such widespread deposits were not observed in the highest pressure tests, where the accretions were limited to a small area around the leading edge. The suction surface was typically ice-free in the tests at high pressure, but not at low pressure. The icing behavior at high and low pressure appeared to be correlated with the wet-bulb temperature, which was estimated to be above 0 C in tests at 93 kPa and below 0 C in tests at lower pressure, the latter enhanced by more evaporative cooling of water. The authors believe that the large ice accretions observed in the low pressure tests would undoubtedly cause the aerodynamic

  2. Fundamental Ice Crystal Accretion Physics Studies

    NASA Technical Reports Server (NTRS)

    Struk, Peter M.; Broeren, Andy P.; Tsao, Jen-Ching; Vargas, Mario; Wright, William B.; Currie, Tom; Knezevici, Danny; Fuleki, Dan

    2012-01-01

    Due to numerous engine power-loss events associated with high-altitude convective weather, ice accretion within an engine due to ice crystal ingestion is being investigated. The National Aeronautics and Space Administration (NASA) and the National Research Council (NRC) of Canada are starting to examine the physical mechanisms of ice accretion on surfaces exposed to ice-crystal and mixed-phase conditions. In November 2010, two weeks of testing occurred at the NRC Research Altitude Facility utilizing a single wedge-type airfoil designed to facilitate fundamental studies while retaining critical features of a compressor stator blade or guide vane. The airfoil was placed in the NRC cascade wind tunnel for both aerodynamic and icing tests. Aerodynamic testing showed excellent agreement compared with CFD data on the icing pressure surface and allowed calculation of heat transfer coefficients at various airfoil locations. Icing tests were performed at Mach numbers of 0.2 to 0.3, total pressures from 93 to 45 kPa, and total temperatures from 5 to 15 C. Ice and liquid water contents ranged up to 20 and 3 g/m3, respectively. The ice appeared well adhered to the surface in the lowest pressure tests (45 kPa) and, in a particular case, showed continuous leading-edge ice growth to a thickness greater than 15 mm in 3 min. Such widespread deposits were not observed in the highest pressure tests, where the accretions were limited to a small area around the leading edge. The suction surface was typically ice-free in the tests at high pressure, but not at low pressure. The icing behavior at high and low pressure appeared to be correlated with the wet-bulb temperature, which was estimated to be above 0 C in tests at 93 kPa and below 0 C in tests at lower pressure, the latter enhanced by more evaporative cooling of water. The authors believe that the large ice accretions observed in the low pressure tests would undoubtedly cause the aerodynamic performance of a compressor component

  3. A Study of Ice Accretion Physics to Improve the Ice Accretion on Airfoils

    NASA Technical Reports Server (NTRS)

    Bragg, Michael B.

    2001-01-01

    This three-year grant began on November 7, 1996 and was no-cost extended to end on October 30, 2000. The objectives of the grant were: (1) To examine the effect of wind tunnel turbulence on ice accretion; (2) To determine the relationship between ice accretion geometry and airfoil performance; and (3) To determine if the wake-survey method was an appropriate experimental technique for iced-airfoil drag measurement. As specified in the grant the primary deliverables for this research were annual reports in the form of AIAA papers presented at national meetings each year. Masters theses and annual oral reports to be given at NASA Lewis (now Glenn) were also deliverables. Six AIAA papers documented the research findings from this study, Mr. Chad Henze's Masters thesis describes the wind tunnel turbulence work in detail, and a summary of the icing wind tunnel turbulence work was published in the archival AIAA Journal of Aircraft. A brief summary of the findings is given. Please refer to the reports for the details of the studies and findings.

  4. AGN Accretion Physics: Insights from K2

    NASA Astrophysics Data System (ADS)

    Vogeley, Michael

    We propose to use Kepler K2 mission observations of 1800 supermassive black holes at the centers of galaxies (Active Galactic Nuclei; AGN) to test models for accretion physics, to study the relationship between variability and other AGN properties such as accretion rate, and to guide methods for detecting and classifying AGN in future time-domain surveys. AGN exhibit optical brightness fluctuations on timescales from below an hour up to many years. These fluctuations are determined by the physics of accretion of matter onto black holes from their galactic environment. By observing variability on timescales down to below an hour, Kepler probes the accretion region on length scales that are too small to be directly imaged using conventional telescopes. These data allow us to test competing models for accretion physics that make different predictions for the statistics of variability. Our previous work provides strong evidence that models of AGN variability that work on long timescale data are not adequate to describe the full range of fluctuation timescales probed by Kepler. We will analyze the light curves of 1800 AGN that have been monitored by Kepler during recent and ongoing K2 campaigns. These objects span a large range of luminosity and AGN type, thus allowing study of the relationship between variability and other physical properties. We will characterize the statistics of AGN variability using state-of-the-art methods of time series analysis that are appropriate for quantifying the stochastic behavior of AGN. This analysis builds on our previous work in which we developed and tested new analysis software that extracts the full information content of these light curves and will enable several key outcomes: (1) Measurement of the relationship between types of AGN and their variability. (2) Tests for dependence of variability on accretion rate. (3) Investigation of changes in variability behavior that point to changes in the mode of accretion. (4) Correlations

  5. Probing Agn Accretion Physics With Kepler

    NASA Astrophysics Data System (ADS)

    Vogeley, Michael

    We propose to use Kepler observations of a sample of ~100 supermassive black holes at the centers of galaxies (Active Galactic Nuclei; AGN) to test models for accretion physics, to study the relationship between variability and other AGN properties, and to guide methods for detecting and classifying AGN in future time-domain surveys. AGN exhibit optical brightness fluctuations on timescales from below an hour up to many years. These fluctuations are determined by the physics of accretion of matter onto black holes from their galactic environment. By observing variability on timescales down to below an hour, Kepler probes the accretion region on length scales that are too small to be directly imaged using conventional telescopes. Data from this unique time- domain telescope now allow us to test competing models for accretion physics that make different predictions for the statistics of variability. Preliminary work provides strong evidence that models of AGN variability that work on long timescale data are not adequate to describe the full range of fluctuation timescales probed by Kepler. We will analyze the light curves of Kepler AGN that span a large range of luminosity and AGN type, thus allowing study of the relationship between variability and other physical properties. Using methods developed and tested by the Kepler team, we will perform custom post-processing of these light curves to remove known systematics. Statistical analyses of the AGN light curves will include estimation of the Structure Function, which quantifies the correlations of brightness fluctuations, and maximum likelihood light curve reconstruction. Competing models for the stochastic behavior of AGN will be tested to evaluate which models best describe variability of AGN over the full range of timescales probed by Kepler. Correlations between the stochastic model parameters and physical parameters will provide new methods for classification of AGN from their variability and aid in

  6. Accreting Millisecond Pulsars and Fundamental Physics

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2005-01-01

    X-ray emission from the surfaces of rapidly rotating neutron stars encodes information about their global properties as well as physical conditions locally. Detailed modelling of, for example, the energy dependent pulse profiles observed from accreting millisecond pulsars and thermonuclear burst oscillations can be used to derive constraints on the masses and radii of neutron stars. These measurements provide direct information on the properties of the dense matter equation of state of the supranuclear density matter in their interiors. Study of absorption lines created in the surface layers can also provide measurements of masses and radii, and may be able to probe aspects of relativistic gravity, such as frame dragging. I will discuss the results of recent efforts to carry out such measurements and their implications for the properties of dense matter.

  7. ACCRETION RATE AND THE PHYSICAL NATURE OF UNOBSCURED ACTIVE GALAXIES

    SciTech Connect

    Trump, Jonathan R.; Impey, Christopher D.; Gabor, Jared M.; Diamond-Stanic, Aleksandar M.; Kelly, Brandon C.; Civano, Francesca; Hao, Heng; Lanzuisi, Giorgio; Merloni, Andrea; Salvato, Mara; Urry, C. Megan; Jahnke, Knud; Nagao, Tohru; Taniguchi, Yoshi; Koekemoer, Anton M.; Liu, Charles; Mainieri, Vincenzo; Scoville, Nick Z.

    2011-05-20

    We show how accretion rate governs the physical properties of a sample of unobscured broad-line, narrow-line, and lineless active galactic nuclei (AGNs). We avoid the systematic errors plaguing previous studies of AGN accretion rates by using accurate intrinsic accretion luminosities (L{sub int}) from well-sampled multiwavelength spectral energy distributions from the Cosmic Evolution Survey, and accurate black hole masses derived from virial scaling relations (for broad-line AGNs) or host-AGN relations (for narrow-line and lineless AGNs). In general, broad emission lines are present only at the highest accretion rates (L{sub int}/L{sub Edd} > 10{sup -2}), and these rapidly accreting AGNs are observed as broad-line AGNs or possibly as obscured narrow-line AGNs. Narrow-line and lineless AGNs at lower specific accretion rates (L{sub int}/L{sub Edd} < 10{sup -2}) are unobscured and yet lack a broad-line region. The disappearance of the broad emission lines is caused by an expanding radiatively inefficient accretion flow (RIAF) at the inner radius of the accretion disk. The presence of the RIAF also drives L{sub int}/L{sub Edd} < 10{sup -2} narrow-line and lineless AGNs to have ratios of radio-to-optical/UV emission that are 10 times higher than L{sub int}/L{sub Edd} > 10{sup -2} broad-line AGNs, since the unbound nature of the RIAF means it is easier to form a radio outflow. The IR torus signature also tends to become weaker or disappear from L{sub int}/L{sub Edd} < 10{sup -2} AGNs, although there may be additional mid-IR synchrotron emission associated with the RIAF. Together, these results suggest that specific accretion rate is an important physical 'axis' of AGN unification, as described by a simple model.

  8. Physics of accretion flows around compact objects

    NASA Astrophysics Data System (ADS)

    Lasota, Jean-Pierre

    2007-01-01

    Several physical and astrophysical problems related to accretion onto black holes and neutron stars are briefly reviewed. I discuss the observed differences between these two types of compact objects in quiescent Soft X-ray Transients. Then I review the status of various non-standard objects suggested as an alternative to black holes. Finally, I present new results and a suggestion about the nature of the jet activity in Active Galactic Nuclei. To cite this article: J.-P. Lasota, C. R. Physique 8 (2007).

  9. Accretion Rate and the Physical Nature of Unobscured Active Galaxies

    NASA Astrophysics Data System (ADS)

    Trump, Jonathan R.; Impey, Christopher D.; Kelly, Brandon C.; Civano, Francesca; Gabor, Jared M.; Diamond-Stanic, Aleksandar M.; Merloni, Andrea; Urry, C. Megan; Hao, Heng; Jahnke, Knud; Nagao, Tohru; Taniguchi, Yoshi; Koekemoer, Anton M.; Lanzuisi, Giorgio; Liu, Charles; Mainieri, Vincenzo; Salvato, Mara; Scoville, Nick Z.

    2011-05-01

    We show how accretion rate governs the physical properties of a sample of unobscured broad-line, narrow-line, and lineless active galactic nuclei (AGNs). We avoid the systematic errors plaguing previous studies of AGN accretion rates by using accurate intrinsic accretion luminosities (L int) from well-sampled multiwavelength spectral energy distributions from the Cosmic Evolution Survey, and accurate black hole masses derived from virial scaling relations (for broad-line AGNs) or host-AGN relations (for narrow-line and lineless AGNs). In general, broad emission lines are present only at the highest accretion rates (L int/L Edd > 10-2), and these rapidly accreting AGNs are observed as broad-line AGNs or possibly as obscured narrow-line AGNs. Narrow-line and lineless AGNs at lower specific accretion rates (L int/L Edd < 10-2) are unobscured and yet lack a broad-line region. The disappearance of the broad emission lines is caused by an expanding radiatively inefficient accretion flow (RIAF) at the inner radius of the accretion disk. The presence of the RIAF also drives L int/L Edd < 10-2 narrow-line and lineless AGNs to have ratios of radio-to-optical/UV emission that are 10 times higher than L int/L Edd > 10-2 broad-line AGNs, since the unbound nature of the RIAF means it is easier to form a radio outflow. The IR torus signature also tends to become weaker or disappear from L int/L Edd < 10-2 AGNs, although there may be additional mid-IR synchrotron emission associated with the RIAF. Together, these results suggest that specific accretion rate is an important physical "axis" of AGN unification, as described by a simple model. Based on observations with the XMM-Newton satellite, an ESA science mission with instruments and contributions directly funded by ESA member states and NASA; the Magellan telescope, operated by the Carnegie Observatories; the ESO Very Large Telescope; and the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian

  10. Accretion physics: It's not U, it's B

    NASA Astrophysics Data System (ADS)

    Miller, Jon

    2017-03-01

    Black holes grow by accreting mass, but the process is messy and redistributes gas and energy into their environments. New evidence shows that magnetic processes mediate both the accretion and ejection of matter.

  11. The Physics of Wind-Fed Accretion

    SciTech Connect

    Mauche, C W; Liedahl, D A; Akiyama, S; Plewa, T

    2008-05-27

    We provide a brief review of the physical processes behind the radiative driving of the winds of OB stars and the Bondi-Hoyle-Lyttleton capture and accretion of a fraction of the stellar wind by a compact object, typically a neutron star, in detached high-mass X-ray binaries (HMXBs). In addition, we describe a program to develop global models of the radiatively-driven photoionized winds and accretion flows of HMXBs, with particular attention to the prototypical system Vela X-1. The models combine XSTAR photoionization calculations, HULLAC emission models appropriate to X-ray photoionized plasmas, improved models of the radiative driving of photoionized winds, FLASH time-dependent adaptive-mesh hydrodynamics calculations, and Monte Carlo radiation transport. We present two- and three-dimensional maps of the density, temperature, velocity, ionization parameter, and emissivity distributions of representative X-ray emission lines, as well as synthetic global Monte Carlo X-ray spectra. Such models help to better constrain the properties of the winds of HMXBs, which bear on such fundamental questions as the long-term evolution of these binaries and the chemical enrichment of the interstellar medium.

  12. The Event Horizon Telescope: exploring strong gravity and accretion physics

    NASA Astrophysics Data System (ADS)

    Ricarte, Angelo; Dexter, Jason

    2015-01-01

    The Event Horizon Telescope (EHT), a global sub-millimetre wavelength very long baseline interferometry array, is now resolving the innermost regions around the supermassive black holes Sgr A* and M87. Using black hole images from both simple geometric models and relativistic magnetohydrodynamical accretion flow simulations, we perform a variety of experiments to assess the promise of the EHT for studying strong gravity and accretion physics during the stages of its development. We find that (1) the addition of the Large Millimeter Telescope (LMT) and Atacama Large Millimeter/submillimeter Array along with upgraded instrumentation in the `Complete' stage of the EHT allow detection of the photon ring, a signature of Kerr strong gravity, for predicted values of its total flux; (2) the inclusion of coherently averaged closure phases in our analysis dramatically improves the precision of even the current array, allowing (3) significantly tighter constraints on plausible accretion models and (4) detections of structural variability at the levels predicted by the models. While observations at 345 GHz circumvent problems due to interstellar electron scattering in line of sight to the galactic centre, short baselines provided by CARMA (Combined Array for Research in Millimeter-wave Astronomy) and/or the LMT could be required in order to constrain the overall shape of the accretion flow. Given the systematic uncertainties in the underlying models, using the full complement of two observing frequencies (230 and 345 GHz) and sources (Sgr A* and M87) may be critical for achieving transformative science with the EHT experiment.

  13. Plasma physics of accreting neutron stars

    NASA Technical Reports Server (NTRS)

    Ghosh, Pranab; Lamb, Frederick K.

    1991-01-01

    Plasma concepts and phenomena that are needed to understand X- and gamma-ray sources are discussed. The capture of material from the wind or from the atmosphere or envelope of a binary companion star is described and the resulting types of accretion flows discussed. The reasons for the formation of a magnetosphere around the neutron star are explained. The qualitative features of the magnetospheres of accreting neutron stars are then described and compared with the qualitative features of the geomagnetosphere. The conditions for stable flow and for angular and linear momentum conservation are explained in the context of accretion by magnetic neutron stars and applied to obtain rough estimates of the scale of the magnetosphere. Accretion from Keplerian disks is then considered in some detail. The radial structure of geometrically thin disk flows, the interaction of disk flows with the neutron star magnetosphere, and models of steady accretion from Keplerian disks are described. Accretion torques and the resulting changes in the spin frequencies of rotating neutron stars are considered. The predicted behavior is then compared with observations of accretion-powered pulsars. Magnetospheric processes that may accelerate particles to very high energies, producing GeV and, perhaps, TeV gamma-rays are discussed. Finally, the mechanisms that decelerate and eventually stop accreting plasma at the surfaces of strongly magnetic neutron stars are described.

  14. Diagnosing the Black Hole Accretion Physics of Sgr A*

    NASA Astrophysics Data System (ADS)

    Fazio, Giovanni; Ashby, Matthew; Baganoff, Frederick; Becklin, Eric; Carey, Sean; Gammie, Charles; Ghez, Andrea; Glaccum, William; Gurwell, Mark; Haggard, Daryl; Hora, Joseph; Ingalls, James; Marrone, Daniel; Meyer, Leo; Morris, Mark; Smith, Howard; Willner, Steven; Witzel, Gunther

    2016-08-01

    The Galactic center offers the closest opportunity for studying accretion onto supermassive black holes. The fluctuating source, Sgr A*, is detected across the electromagnetic spectrum and may originate in the accretion flow or jet. Recent general relativistic magneto-hydrodynamic (GRMHD) models indicate that variability can be produced by a tilted inner disk, gravitational lensing of bright spots in the disk by the hole, or particle acceleration in reconnection events. These models produce different flare characteristics, and in particular better characterization of flares may enable us to distinguish between strong and weakly magnetized disks. Disentangling the power source and emission mechanisms of the flares is a central challenge to our understanding of the Sgr A* accretion flow. Following our successful observations of the variability of Sgr A* with IRAC in 2013 and 2014, we propose simultaneous IRAC (4.5 micron) and Chandra (2-10 keV) observations to (1) probe the accretion physics of Sgr A* on event-horizon scales and (2) detect any effect of the object G2 on Sgr A*. Specifically, we propose six additional epochs of observation, each of 24 uninterrupted hours; four in 2017 July and two in 2018 July. In this proposal we request two 24-hour (86.4 ks) Chandra periods, and are requesting another four through the Chandra TAC to have simultaneous X-ray observations in each of the six Spitzer epochs. Independent of this proposal we will also request NuSTAR (3-79 keV), SMA/ALMA/APEX (0.8 mm), and Keck/Magellan NIR (2.2 micron) observations during the IRAC/Chandra epochs. Only such long-duration, continuous, multi-wavelength observations can achieve a comprehensive view of the dominant emission process(es) and quantify the physical properties near the event horizon. Theoretical models are increasing in physical sophistication, and our study will provide essential constraints for the next generation of models.

  15. Probing AGN Accretion Physics through AGN Variability: Insights from Kepler

    NASA Astrophysics Data System (ADS)

    Kasliwal, Vishal Pramod

    that the DRW is insufficient to characterize AGN variability. We provide a new approach to probing accretion physics with variability by decomposing observed light curves into a set of impulses that drive diffusive processes using C-ARMA models. Applying our approach to Kepler data, we demonstrate how the time-scales reported in the literature can be interpreted in the context of the growth and decay time-scales for flux perturbations and tentatively identify the flux perturbation driving process with accretion disk turbulence on length-scales much longer than the characteristic eddy size. Our analysis technique is applicable to (1) studying the connection between AGN sub-type and variability properties; (2) probing the origins of variability by studying the multi-wavelength behavior of AGN; (3) testing numerical simulations of accretion flows with the goal of creating a library of the variability properties of different accretion mechanisms; (4) hunting for changes in the behavior of the accretion flow by block-analyzing observed light curves; and (5) constraining the sampling requirements of future surveys of AGN variability.

  16. Outflow and Accretion Physics in Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    McGraw, Sean Michael

    This dissertation focuses on placing observational constraints on outflows and accretion disks in active galactic nuclei (AGN) for the purpose of better understanding the physics of super-massive black holes (SMBHs) and their evolution with the host galaxy over cosmic time. Quasar outflows and their importance in SMBH-host galaxy co-evolution can be further understood by analyzing broad absorption lines (BALs) in rest-frame UV spectra that trace a range of wind conditions. We quantify the properties of the flows by conducting BAL variability studies using multiple-epoch spectra acquired primarily from MDM Observatory and from the Sloan Digital Sky Survey. Iron low-ionization BALs (FeLoBALs) are a rare type of outflow that may represent a transient phase in galaxy evolution, and we analyze the variations in 12 FeLoBAL quasars with redshifts between 0.7 ≤ z ≤ 1.9 and rest frame timescales between ˜10 d to 7.6 yr. We investigate BAL variability in 71 quasar outflows that exhibit P V absorption, a tracer of high column density gas (i.e. NH ≥ 1022 cm -2), in order to quantify the energies and momenta of the flows. We also characterize the variability patterns of 26 quasars with mini-BALs, an interesting class of absorbers that may represent a distinct phase in the evolution of outflows. Low-luminosity AGN (LLAGN) are important objects to study since their prominence in the local Universe suggest a possible evolution from the quasar era, and their low radiative outputs likely indicate a distinct mode of accretion onto the SMBH. We probe the accretion conditions in the LLAGN NGC 4203 by estimating the SMBH mass, which is obtained by modeling the 2-dimensional velocity field of the nebular gas using spectra from the Hubble Space Telescope. We detect significant BAL and mini-BAL variability in a subset of quasars from each of our samples, with measured rest-frame variability time-scales from days to years and over multiple years on average. Variable wavelength

  17. A physical understanding of how reionization suppresses accretion on to dwarf haloes

    NASA Astrophysics Data System (ADS)

    Noh, Yookyung; McQuinn, Matthew

    2014-10-01

    We develop and test with cosmological simulations a physically motivated theory for how the interplay between gravity, pressure, cooling, and self-shielding set the redshift-dependent mass scale at which haloes can accrete intergalactic gas. This theory provides a physical explanation for the halo mass scale that can accrete unshocked intergalactic gas, which has been explained with ad hoc criteria tuned to reproduce the results of a few simulations. Furthermore, it provides an intuitive explanation for how this mass scale depends on the reionization redshift, the amplitude of the ionizing background, and the redshift. We show that accretion is inhibited on to more massive haloes than had been thought because previous studies had focused on the gas fraction of haloes rather than the instantaneous mass that can accrete gas. A halo as massive as 1011 M⊙ cannot accrete intergalactic gas at z = 0, even though typically its progenitors were able to accrete gas at higher redshifts. We describe a simple algorithm that can be implemented in semi-analytic models, and we compare the predictions of this algorithm to numerical simulations.

  18. Modeling the optical-X-ray accretion lag in LMC X-3: Insights into black-hole accretion physics

    SciTech Connect

    Steiner, James F.; McClintock, Jeffrey E.; Orosz, Jerome A.; Buxton, Michelle M.; Bailyn, Charles D.; Remillard, Ronald A.; Kara, Erin

    2014-03-10

    The X-ray persistence and characteristically soft spectrum of the black hole X-ray binary LMC X-3 make this source a touchstone for penetrating studies of accretion physics. We analyze a rich, ten-year collection of optical/infrared (OIR) time-series data in conjunction with all available contemporaneous X-ray data collected by the All-Sky Monitor and Proportional Counter Array detectors aboard the Rossi X-ray Timing Explorer. A cross-correlation analysis reveals an X-ray lag of ≈2 weeks. Motivated by this result, we develop a model that reproduces the complex OIR light curves of LMC X-3. The model is comprised of three components of emission: stellar light, accretion luminosity from the outer disk inferred from the time-lagged X-ray emission, and light from the X-ray-heated star and outer disk. Using the model, we filter a strong noise component out of the ellipsoidal light curves and derive an improved orbital period for the system. Concerning accretion physics, we find that the local viscous timescale in the disk increases with the local mass accretion rate; this in turn implies that the viscosity parameter α decreases with increasing luminosity. Finally, we find that X-ray heating is a strong function of X-ray luminosity below ≈50% of the Eddington limit, while above this limit X-ray heating is heavily suppressed. We ascribe this behavior to the strong dependence of the flaring in the disk upon X-ray luminosity, concluding that for luminosities above ≈50% of Eddington, the star lies fully in the shadow of the disk.

  19. Aerodynamics and thermal physics of helicopter ice accretion

    NASA Astrophysics Data System (ADS)

    Han, Yiqiang

    developed based on a set of 82 experimental measurements and also compared to existing predictions tools. Two reference predictions found in the literature yielded 76% and 54% discrepancy with respect to experimental testing, whereas the proposed ice roughness prediction model resulted in a 31% minimum accuracy in prediction. It must be noted that the accuracy of the proposed model is within the ice shape reproduction uncertainty of icing facilities. Based on the new ice roughness prediction model and the CSR heat transfer scaling method, an icing heat transfer model was developed. The approach achieved high accuracy in heat transfer prediction compared to experiments conducted at the AERTS facility. The discrepancy between predictions and experimental results was within +/-15%, which was within the measurement uncertainty range of the facility. By combining both the ice roughness and heat transfer predictions, and incorporating the modules into an existing ice prediction tool (LEWICE), improved prediction capability was obtained, especially for the glaze regime. With the available ice shapes accreted at the AERTS facility and additional experiments found in the literature, 490 sets of experimental ice shapes and corresponding aerodynamics testing data were available. A physics-based performance degradation empirical tool was developed and achieved a mean absolute deviation of 33% when compared to the entire experimental dataset, whereas 60% to 243% discrepancies were observed using legacy drag penalty prediction tools. Rotor torque predictions coupling Blade Element Momentum Theory and the proposed drag performance degradation tool was conducted on a total of 17 validation cases. The coupled prediction tool achieved a 10% predicting error for clean rotor conditions, and 16% error for iced rotor conditions. It was shown that additional roughness element could affect the measured drag by up to 25% during experimental testing, emphasizing the need of realistic ice structures

  20. Theoretical Studies of Accreting Neutron Stars

    NASA Technical Reports Server (NTRS)

    Taam, Ronald E.

    2003-01-01

    Among the newly discovered classes of X-ray sources which have attracted wide attention are close binary systems in which mass is transferred via Roche lobe overflow from a low mass donor star to its neutron star companion. Many of these sources exhibit intense bursts of X-ray radiation as well as periodic and quasi-periodic phenomena. Intensive analysis of these sources as a class has provided insight into the accretion process in binary star systems and into the magnetic field, rotational, and nuclear evolution of the underlying neutron star. In this proposal we have focused on theoretical studies of the hydrodynamical and nuclear processes that take place on the surface of accreting neutron stars in these systems. The investigation of these processes is critical for providing an understanding of a number of outstanding problems related to their transient behavior and evolution.

  1. Physics-Based Spectra of Accretion Disks around Black Holes

    NASA Technical Reports Server (NTRS)

    Krolik, Julian H.

    2005-01-01

    The purpose of this grant was to begin the process of deriving the light output of accretion disks around black holes directly from the actual processes that inject heat into the accreting matter, rather than from guessed dependences of heating rate on physical parameters. At JHU, the effort has focussed so far on models of accretion onto "intermediate mass black holes", a possible class of black holes, examples of which may have recently been discovered in nearby galaxies. There, Krolik and his student (Yawei Hui) have computed stellar atmospheres for uniformly-heated disks around this class of black holes. Their models serve two purposes: they are the very first serious attempts to compute the spectrum from accreting black holes in this mass range; and a library of such models can be used later in this program as contrasts for those computed on the basis of real disk dynamics. The output from these local disk calculations has also been successfully coupled to a program that applies the appropriate relativistic transformations and computes photon trajectories in order to predict the spectrum received by observers located at different polar angles. The principal new result of these calculations is the discovery of potentially observable ionization edges of H-like C and O at frequencies near the peak in flux from these objects. Most of the grant money at UCSB was spent on supporting graduate student Shane Davis. In addition. some money was spent on supporting two other students: Ari Socrates (now a Hubble Fellow at Princeton), and Laura Melling. Davis spent the year constructing stellar atmosphere models of accretion disks appropriate for the high/soft (thermal) state of black hole X-ray binaries. As with AGN models published previously by our collaboration with NASA support. our models include a complete general relativistic treatment of both the disk structure and the propagation of photons from the disk to a distant observer. They also include all important

  2. Diagnosing the Black Hole Accretion Physics of Sgr A*: Spitzer/Chandra Observations

    NASA Astrophysics Data System (ADS)

    Hora, Joseph L.; Fazio, Giovanni G.; Willner, Steven P.; Gurwell, Mark A.; Smith, Howard Alan; Ashby, Matthew; Baganoff, Frederick K.; Witzel, Gunther; Morris, Mark; Ghez, Andrea M.; Meyer, Leo; Becklin, Eric E.; Ingalls, James G.; Glaccum, William J.; Carey, Sean J.; Haggard, Daryl; Marrone, Daniel P.; Gammie, Charles F.

    2017-01-01

    The Galactic center offers the closest opportunity for studying accretion onto a supermassive black hole. The fluctuating source, Sgr A*, is detected across the electromagnetic spectrum and its flux may originate in either the accretion flow or a jet, or both. Disentangling the power source and emission mechanisms of the flares is a central challenge to our understanding of the Sgr A* accretion flow. Recent general relativistic magneto-hydrodynamic (GRMHD) models indicate that variability can be produced by a tilted inner disk, gravitational lensing of bright spots in the disk by the hole, or particle acceleration in reconnection events. These models produce different flare characteristics, and better characterization of flares may enable us to distinguish between strong and weakly magnetized disks. Following our successful Spitzer observations of the variability of Sgr A* in 2013 and 2014, we have undertaken a program of simultaneous IRAC (4.5 micron) and Chandra (2-10 keV) observations to (1) probe the accretion physics of Sgr A* on event-horizon scales and (2) detect any effect of the object G2 on Sgr A*. In addition, several ground-based observatories participated in the campaigns, at wavelengths including radio, sub-mm, and the near-infrared. We will present initial Spitzer/Chandra results from the two 24-hour epochs in 2016 July. Only such long-duration, continuous, multi-wavelength observations can achieve a comprehensive view of the dominant emission process(es) and quantify the physical properties near the event horizon.

  3. Overview of the physics in the accretion column

    NASA Astrophysics Data System (ADS)

    Wolff, Michael Thomas

    2016-04-01

    This talk discusses the current efforts to model the wide array of physical processes that are important when plasma accretes onto the surface of a highly magnetic neutron star. Broad non-thermal power law X-ray continua are observed that can be modeled by Comptonization of bremsstrahlung, cyclotron, and black body contributions. Cyclotron resonance absorption lines are observed, cast against these broad continua, yielding measurements of the magnetic field strengths. Observations show that in some sources the cyclotron line energies can vary with observed luminosity. This observation has lead to significant debate regarding aspects of the cyclotron line formation process. Multiple groups are currently working on modeling the physical processes that affect the behavior of the plasmas, the formation of the X-ray continuum, and the formation of the cyclotron lines. New analysis tools are becoming available to help interpret observations of these systems. In particular, observations by Suzaku and NuSTAR of the X-ray spectra of these binary systems are advancing our searches for the cyclotron lines and our understanding of the physical processes that contribute to the X-ray continuum formation.

  4. A pilot study to Doppler-image an accretion spot

    NASA Astrophysics Data System (ADS)

    Moritz Guenther, Hans

    2009-10-01

    Classical T Tauri stars (CTTS) are young, accreting systems. The accretion is thought to cause a soft X-ray excess and unusual line ratios in the He-like triplets. The accretion spots can also be seen with optical Doppler-imaging; however, the final test to correlate these signatures - simultaneous X-ray and ground-based observations - is still missing. We propose a 15 ks pilot study of MN Lup, the prime target for simultaneous observations from the optical point of view, to confirm its CTTS status and characterize its X-ray properties.

  5. X-Shooter study of accretion in Chamaeleon I

    NASA Astrophysics Data System (ADS)

    Manara, C. F.; Fedele, D.; Herczeg, G. J.; Teixeira, P. S.

    2016-01-01

    We present the analysis of 34 new VLT/X-Shooter spectra of young stellar objects in the Chamaeleon I star-forming region, together with four more spectra of stars in Taurus and two in Chamaeleon II. The broad wavelength coverage and accurate flux calibration of our spectra allow us to estimate stellar and accretion parameters for our targets by fitting the photospheric and accretion continuum emission from the Balmer continuum down to ~700 nm. The dependence of accretion on stellar properties for this sample is consistent with previous results from the literature. The accretion rates for transitional disks are consistent with those of full disks in the same region. The spread of mass accretion rates at any given stellar mass is found to be smaller than in many studies, but is larger than that derived in the Lupus clouds using similar data and techniques. Differences in the stellar mass range and in the environmental conditions between our sample and that of Lupus may account for the discrepancy in scatter between Chamaeleon I and Lupus. Complete samples in Chamaeleon I and Lupus are needed to determine whether the difference in scatter of accretion rates and the lack of evolutionary trends are not influenced by sample selection. This work is based on observations made with ESO Telescopes at the Paranal Observatory under programme ID 084.C-1095 and 094.C-0913.

  6. Exploring mass-scaling physics and outflow geometry in accreting black holes

    NASA Astrophysics Data System (ADS)

    Connors, Riley Michael Thomas

    2017-01-01

    One of the main tasks facing studies of black hole accretion in both black hole X-ray binaries (XRB) and Active Galactic Nuclei (AGN) is to break spectral model-fitting degeneracies. We explore two methods of simultaneous spectral modelling to reduce these degeneracies: (a) simultaneous fitting of XRBs and AGN, and (b) folding in timing properties in a novel way to better understand the outflow evolution of XRBs during outburst.It is a long-standing idea that AGN are scaled up versions of XRBs, such that the physics of accretion cares only about accretion rate, and not the black hole mass. We show that this principle of scale-invariance may provide us with a way to break degeneracies in broadband spectral modelling of both XRBs and AGN, focusing primarily on low-luminosity sources where degeneracies are more prevalent. We simultaneously model the broadband spectra of the two most quiescent (LX ~ 10-9 LEdd) accreting black holes on opposite ends of the mass scale, the XRB A0620-00 and Sgr A*, the Galactic centre supermassive black hole (during bright flaring). We use an outflow-dominated model capable of reproducing the broadband spectrum from radio to X-ray frequencies, co-evolving parameters that are representative of the mass-scaling properties. Such a method reduces the degeneracies in our model parameters, contributing to answering this question regarding the dominant emission mechanisms.We adopt a similar technique to investigate how spatial parameters of an XRB outflow can be better understood by tracking our model parameters as a function of the XRB variability properties during outburst, focusing in particular on GX 339-4. I shall discuss how utilising a novel characterisation of the timing properties of XRBs allows us to do this in a simple, quantitative way.We are currently developing our models further to incorporate the most up-to-date disc reflection routines in order to describe the jet/disc interaction more accurately. I shall briefly discuss this

  7. Multi-wavelength Accretion Studies of Cataclysmic Variable Stars

    NASA Astrophysics Data System (ADS)

    Coppejans, Deanne

    2016-10-01

    Recent developments in the field of Cataclysmic Variable stars (CVs) have highlighted the need for large (more unbiased) samples of CVs with known properties, as well as the need for multi- wavelength studies to determine the accretion-outflow connection. In this thesis I have presented radio observations of non-magnetic CVs, proving them to be significant radio emitters. I have also presented optical follow-up studies of CVs, and developed an algorithm that automatically classifies these objects based on photometric data from large surveys. This was applied to the Catalina Real-time Transient Survey to produce a catalogue of accretion properties for 1031 CVs.

  8. Workshop on Physics of Accretion Disks Around Compact and Young Stars

    NASA Technical Reports Server (NTRS)

    Liang, E (Editor); Stepinski, T. F. (Editor)

    1995-01-01

    The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was to bring together workers on accretion disks in the western Gulf region (Texas and Louisiana). Part 2 presents the workshop program, a list of poster presentations, and a list of workshop participants. Accretion disks are believed to surround many stars. Some of these disks form around compact stars, such as white dwarfs, neutron stars, or black holes that are members of binary systems and reveal themselves as a power source, especially in the x-ray and gamma regions of the spectrum. On the other hand, protostellar disks are believed to be accretion disks associated with young, pre-main-sequence stars and manifest themselves mostly in infrared and radio observations. These disks are considered to be a natural outcome of the star formation process. The focus of this workshop included theory and observations relevant to accretion disks around compact objects and newly forming stars, with the primary purpose of bringing the two communities together for intellectual cross-fertilization. The nature of the workshop was exploratory, to see how much interaction is possible between distinct communities and to better realize the local potential in this subject. A critical workshop activity was identification and documentation of key issues that are of mutual interest to both communities.

  9. Magnetized accretion

    NASA Astrophysics Data System (ADS)

    Heyvaerts, J.

    This lecture reviews in simple terms the general subject of large scale magnetic field coupling to plasma flows in the vicinity of accreting compact stars. The relevant astrophysical phenomenology is summarized. Disk interaction with the magnetosphere of accreting stars is first discussed, in particular the structure of the magnetopause, its stability and plasma ejection in so-called propeller systems. The physics of accretion/ejection is then considered. Acceleration and focusing mechanisms of jets from accretion disks around compact stars or black holes and the question of the self-consistency of accretion and ejection are described. By contrast, small scale MHD turbulence in disks is not discussed, neither are accretion columns near the polar caps of neutron stars or white dwarfs. The reader is only assumed to have some basic knowledge of astrophysics and of fluid mechanics and electromagnetism.

  10. Laboratory Study of Angular Momentum Transport in Astrophysical Accretion Disks

    NASA Astrophysics Data System (ADS)

    Ji, Hantao

    2014-10-01

    Studying astrophysical processes in the lab becomes increasingly possible and exciting, as one of Stirling's favorite subjects throughout his scientific career. In this talk, I will describe experimental efforts to study mechanisms of rapid angular momentum transport required to occur in accretion disks to explain a wide range of phenomena from star formation, energetic activity of cataclysmic variables, to powering quasars, the most luminous steady sources in the Universe. By carefully isolating effects due to artificial boundaries, which are inherent to terrestrial experiments, certain astrophysical questions regarding hydrodynamic and magnetohydrodynamic stabilities are being addressed in the laboratory. Inspirations from Stirling as well as scientific exchanges with him will be mentioned during this talk as part of my scientific journey on this subject.

  11. Characterization of subglacial Lake Vostok as seen from physical and isotope properties of accreted ice.

    PubMed

    Lipenkov, Vladimir Ya; Ekaykin, Alexey A; Polyakova, Ekaterina V; Raynaud, Dominique

    2016-01-28

    Deep drilling at the Vostok Station has reached the surface of subglacial Lake Vostok (LV) twice-in February 2012 and January 2015. As a result, three replicate cores from boreholes 5G-1, 5G-2 and 5G-3 became available for detailed and revalidation analyses of the 230 m thickness of the accreted ice, down to its contact with water at 3769 m below the surface. The study reveals that the concentration of gases in the lake water beneath Vostok is unexpectedly low. A clear signature of the melt water in the surface layer of the lake, which is subject to refreezing on the icy ceiling of LV, has been discerned in the three different properties of the accreted ice: the ice texture, the isotopic and the gas content of the ice. These sets of data indicate in concert that poor mixing of the melt (and hydrothermal) water with the resident lake water and pronounced spatial and/or temporal variability of local hydrological conditions are likely to be the characteristics of the southern end of the lake. The latter implies that the surface water may be not representative enough to study LV's behaviour, and that direct sampling of the lake at different depths is needed in order to move ahead with our understanding of the lake's hydrological regime.

  12. X-Shooter study of accretion in ρ-Ophiucus: very low-mass stars and brown dwarfs

    NASA Astrophysics Data System (ADS)

    Manara, C. F.; Testi, L.; Natta, A.; Alcalá, J. M.

    2015-07-01

    We present new VLT/X-Shooter optical and near-infrared spectra of a sample of 17 candidate young low-mass stars and brown dwarfs located in the ρ-Ophiucus cluster. We derived the spectral type and extinction for all the targets, and then we determined their physical parameters. All the objects but one have M⋆≲0.6 M⊙, and eight have mass below or close to the hydrogen-burning limit. Using the intensity of various permitted emission lines present in their spectra, we determined the accretion luminosity and mass accretion rates (Ṁacc) for all the objects. When compared with previous works targeting the same sample, we find that, in general, these objects are not as strongly accreting as previously reported, and we suggest that the reason is our more accurate estimate of the photospheric parameters. We also compare our findings with recent works in other slightly older star-forming regions, such as Lupus, to investigate possible differences in the accretion properties, but we find that the accretion properties for our targets have the same dependence on the stellar and substellar parameters as in the other regions. This leads us to conclude that we do not find evidence for a different dependence of Ṁacc with M⋆ when comparing low-mass stars and brown dwarfs. Moreover, we find a similar small (≲1 dex) scatter in the Ṁacc-M⋆ relation as in some of our recent works in other star-forming regions, and no significant differences in Ṁacc due to different ages or properties of the regions. The latter result suffers, however, from low statistics and sample selection biases in the current studies. The small scatter in the Ṁacc-M⋆ correlation confirms that mass accretion rate measurements in the literature based on uncertain photospheric parameters and single accretion indicators, such as the Hα width, can lead to a scatter that is unphysically large. Our studies show that only broadband spectroscopic surveys coupled with a detailed analysis of the

  13. Experimental evidence for modifying the current physical model for ice accretion on aircraft surfaces

    NASA Technical Reports Server (NTRS)

    Olsen, W.; Walker, E.

    1986-01-01

    Closeup movies, still photographs, and other experimental data suggest that the current physical model for ice accretion needs significant modification. At aircraft airspeeds there was no flow of liquid over the surface of the ice after a short initial flow, even at barely subfreezing temperatures. Instead, there were very large stationary drops on the ice surface that lose water from their bottoms by freezing and replenish their liquid by catching the microscopic cloud droplets. This observation disagrees with the existing physical model, which assumes there is a thin liquid film continuously flowing over the ice surface. With no such flow, the freezing-fraction concept of the model fails when a mass balance is performed on the surface water. Rime ice does, as the model predicts, form when the air temperature is low enough to cause the cloud droplets to freeze almost immediately on impact. However, the characteristic shapes of horn-glaze ice or rime ice are primarily caused by the ice shape affecting the airflow locally and consequently the droplet catch and the resulting ice shape. Ice roughness greatly increases the heat transfer coefficient, stops the movement of drops along the surface, and may also affect the airflow initially and thereby the droplet catch. At high subreezing temperatures the initial flow and shedding of surface drops have a large effect on the ice shape. At the incipient freezing limit, no ice forms.

  14. Using High Speed Rotating Gas to Study Angular Momentum in Accretion Disks

    NASA Astrophysics Data System (ADS)

    Berrios, William; Greess, Samuel; Merino, Enrique; Ji, Hantao

    2013-10-01

    Accretion disks are a sheet of gas and dust which surrounds black holes and quasars. The angular momentum in accretion disks is one of the biggest mysteries in astrophysics. A machine was recently built to create accretion disks in a closed chamber. In order to study this, there are several important instruments that are used: a fog machine to see the accretion disks form within the chamber, a high speed camera to observe and record the formation of the accretion disks, and Particle Image Velocimetry (PIV) to analyze velocity profile of the rotating gas and better understand this phenomenon. By collecting relevant data and subsequent computational analysis, results from a previous experiment are reproduced, expanded and the new properties observed with this experiment are characterized. A discussion of any modifications done to the machine, technical challenges and preliminary results will be presented.

  15. Using Animations to Study the Formation of Gas Giant Planets via the Core Accretion Model

    NASA Astrophysics Data System (ADS)

    Hubickyj, O.; Lissauer, J. J.; Bodemheimer, P.; D'Angelo, G.

    2009-12-01

    With the ever increasing number of extrasolar planets being discovered (373 as of 8/13/09 quoted by The Extrasolar Planets Encyclopedia: exoplanet.eu) and the recognition of their diverse nature it is very important to understand the formation processes of the gas giant planets. The core accretion model has successfully explained many features of the formation of gas giant planets in the Solar System (Pollack et al. 1996, Hubickyj et al. 2005) and it has provided an explanation of the characteristics of exoplanets. One example is the observed frequency of planets around stars with a high metal content (e.g. Kornet et al. 2005, Valenti and Fischer 2008). Improvements to the input physics to our computer model have resulted in the very important result that gas giant planets (i.e. Jupiter) can form via the core accretion model on a timescale that agrees with observations of protoplanetary disks (Hillenbrand 2008). These observations set the formation time to about 3 to 5 million years. We will present our recent results (Hubickyj et al. 2005,Lissauer et al. 2009) in the form of animations. Our models generate a substantial amount of data. Having published plots of the important values of our study: mass and radius growth, luminosity, and accretion rates as a function of time, we are now ready to study the second tier of information from our recorded data. We examine the energy profiles within the envelope as it evolves, the location and changes of the convective layers, and the location of the mass deposited by the planetesimals in the envelope as the protoplanet evolves. We find that by animating the data we can study the internal processes in the growing envelope of the protoplanet. The qualitative nature of the processes in the protoplanetary envelope is easily discerned in these animations and a deeper insight to the core accretion processes in the gas giant planets is gained. Hillenbrand, L. A. 2008. Disk-dispersal and planet-formation timescales. Physica

  16. Winds of Change: The Physics of Accretion, Ejection, and X-ray Variability in GRS1915+105

    NASA Astrophysics Data System (ADS)

    Neilsen, Joseph

    2013-04-01

    In the last twenty years, even as multiwavelength observations of black hole X-ray binaries have led to major advances, the microquasar GRS 1915+105 has continually challenged our understanding of the physics of accretion and ejection. With its relativistic jets, ionized winds, and myriad states of rapid, extreme variability, this remarkable black hole has been alternately seen as the black sheep of X-ray binaries and a Rosetta stone for black hole astrophysics. In this talk, I will present our efforts to use a decade of high-resolution X-ray spectroscopy of GRS 1915+105 to shed light on the processes that regulate its erratic behavior. I will highlight in particular the role of accretion disk winds on time scales ranging from seconds to years. Drawing on recent results, I will discuss the broader implications of these massive winds for the physics of inflows and outflows around black holes.

  17. A physical interpretation of the variability power spectral components in accreting neutron stars

    NASA Astrophysics Data System (ADS)

    Ingram, Adam; Done, Chris

    2010-07-01

    We propose a physical framework for interpreting the characteristic frequencies seen in the broad-band power spectra from black hole and neutron star binaries. We use the truncated disc/hot inner flow geometry, and assume that the hot flow is generically turbulent. Each radius in the hot flow produces fluctuations, and we further assume that these are damped on the viscous frequency. Integrating over radii gives broad-band continuum noise power between low- and high-frequency breaks which are set by the viscous time-scale at the outer and inner edge of the hot flow, respectively. Lense-Thirring (vertical) precession of the entire hot flow superimposes the low-frequency quasi-periodic oscillation (QPO) on this continuum power. We test this model on the power spectra seen in the neutron star systems (atolls) as these have the key advantage that the (upper) kHz QPO most likely independently tracks the truncation radius. These show that this model can give a consistent solution, with the truncation radius decreasing from 20 to 8Rg while the inner radius of the flow remains approximately constant at ~4.5Rg i.e. 9.2 km. We use this very constrained geometry to predict the low-frequency QPO from Lense-Thirring precession of the entire hot flow from ro to ri. The simplest assumption of a constant surface density in the hot flow matches the observed QPO frequency to within 25 per cent. This match can be made even better by considering that the surface density should become increasingly centrally concentrated as the flow collapses into an optically thick boundary layer during the spectral transition. The success of the model opens up the way to use the broad-band power spectra as a diagnostic of accretion flows in strong gravity.

  18. A numerical study of the stability of radiative shocks. [in accretion flows onto white dwarf stars

    NASA Technical Reports Server (NTRS)

    Imamura, J. N.; Wolff, M. T.; Durisen, R. H.

    1984-01-01

    Attention is given to the oscillatory instability of optically thin radiative shocks in time-dependent numerical calculations of accretion flows onto degenerate dwarfs. The present nonlinear calculations yield good quantitative agreement with the linear results obtained for oscillation frequencies, damping rates, and critical alpha-values. The fundamental mode and the first overtone in the shock radius and luminosity variations can be clearly identified, and evidence is sometimes seen for the second overtone. Time-dependent calculations are also performed which include additional physics relevant to degenerate dwarf accretion, such as electron thermal conduction, unequal electron and ion temperatures, Compton cooling, and relativistic corrections to the bremsstrahlung cooling law. All oscillatory modes are found to be damped, and hence stable, in the case of a 1-solar mass white dwarf accreting in spherical symmetry.

  19. Parametric study of flow patterns behind the standing accretion shock wave for core-collapse supernovae

    SciTech Connect

    Iwakami, Wakana; Nagakura, Hiroki; Yamada, Shoichi

    2014-05-10

    In this study, we conduct three-dimensional hydrodynamic simulations systematically to investigate the flow patterns behind the accretion shock waves that are commonly formed in the post-bounce phase of core-collapse supernovae. Adding small perturbations to spherically symmetric, steady, shocked accretion flows, we compute the subsequent evolutions to find what flow pattern emerges as a consequence of hydrodynamical instabilities such as convection and standing accretion shock instability for different neutrino luminosities and mass accretion rates. Depending on these two controlling parameters, various flow patterns are indeed realized. We classify them into three basic patterns and two intermediate ones; the former includes sloshing motion (SL), spiral motion (SP), and multiple buoyant bubble formation (BB); the latter consists of spiral motion with buoyant-bubble formation (SPB) and spiral motion with pulsationally changing rotational velocities (SPP). Although the post-shock flow is highly chaotic, there is a clear trend in the pattern realization. The sloshing and spiral motions tend to be dominant for high accretion rates and low neutrino luminosities, and multiple buoyant bubbles prevail for low accretion rates and high neutrino luminosities. It is interesting that the dominant pattern is not always identical between the semi-nonlinear and nonlinear phases near the critical luminosity; the intermediate cases are realized in the latter case. Running several simulations with different random perturbations, we confirm that the realization of flow pattern is robust in most cases.

  20. Accretion Shocks in the Laboratory: Using the OMEGA Laser to Study Star Formation

    NASA Astrophysics Data System (ADS)

    Young, R. P.; Kuranz, C. C.; Li, C. K.; Hartigan, P.; Froula, D.; Fiksel, G.; Ross, J. S.; Chang, P. Y.; Klein, S.; Zylstra, A.; Sio, H. W.; Liao, A.; Barnak, D.

    2016-10-01

    We present an on-going series of experiments using the OMEGA laser (Laboratory for Laser Energetics) to study star formation. Spectra of young stars show evidence of hotspots created when streams of accreting material impact at the surface of the star to create accretion shocks. These accretion shocks are poorly understood, as the surfaces of young stars cannot be spatially resolved. Our experiment series creates a scaled ``accretion shock'' on the OMEGA laser by driving a plasma jet (the ``accretion stream'') into a solid block (the ``stellar surface''), in the presence of a parallel magnetic field analogous to the star's local field. Thus far, visible image data from this experimental series either shows very thin accretion shocks forming or does not show them forming at all. We intend to present this data, provide possible explanations for why shocks may not have formed, and discuss potential improvements to the experimental design. This work is funded by the U.S. Department of Energy, through the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, Grant Number DE-NA0002956, and the National Laser User Facility Program, Grant Number DE-NA0002719.

  1. A Study of Scaling for Intercycle Ice Accretion Tests

    NASA Technical Reports Server (NTRS)

    Anderson, David N.; Botura, Galdemir C.; Broeren, Andy P.; Bond, Thomas H. (Technical Monitor)

    2003-01-01

    The Ruff method with matched scale and reference velocity was used to determine appropriate 1/2-scale test conditions to simulate a full-size icing encounter for an NACA 23012 wing section protected with a pneumatic boot deicing system. Intercycle ice accretions were recorded on a 36-in-chord model used to represent 1/2-scale and compared with a hybrid reference model (full-size leading-edge and truncated aft section) representing a 72-in-chord full-size airfoil. The intercycle ice thickness and extent of icing for the scale tests generally compared well with those from the reference model. However, the scale tests did not reproduce the location and number of feather rows seen in the reference tests aft of the main ice shape. Many of the differences observed were believed to result from not scaling the pneumatic boot design along with the model size for these tests.

  2. The accretion history of dark matter haloes - I. The physical origin of the universal function

    NASA Astrophysics Data System (ADS)

    Correa, Camila A.; Wyithe, J. Stuart B.; Schaye, Joop; Duffy, Alan R.

    2015-06-01

    Understanding the universal accretion history of dark matter haloes is the first step towards determining the origin of their structure. We use the extended Press-Schechter formalism to derive the halo mass accretion history from the growth rate of initial density perturbations. We show that the halo mass history is well described by an exponential function of redshift in the high-redshift regime. However, in the low-redshift regime the mass history follows a power law because the growth of density perturbations is halted in the dark energy dominated era due to the accelerated expansion of the Universe. We provide an analytic model that follows the expression {M(z)=M0(1+z)^{af(M0)}e^{-f(M0)z}}, where M0 = M(z = 0), a depends on cosmology and f(M0) depends only on the linear matter power spectrum. The analytic model does not rely on calibration against numerical simulations and is suitable for any cosmology. We compare our model with the latest empirical models for the mass accretion history in the literature and find very good agreement. We provide numerical routines for the model online (available at https://bitbucket.org/astroduff/commah).

  3. Rethinking Black Hole Accretion Discs

    NASA Astrophysics Data System (ADS)

    Salvesen, Greg

    Accretion discs are staples of astrophysics. Tapping into the gravitational potential energy of the accreting material, these discs are highly efficient machines that produce copious radiation and extreme outflows. While interesting in their own right, accretion discs also act as tools to study black holes and directly influence the properties of the Universe. Black hole X-ray binaries are fantastic natural laboratories for studying accretion disc physics and black hole phenomena. Among many of the curious behaviors exhibited by these systems are black hole state transitions -- complicated cycles of dramatic brightening and dimming. Using X-ray observations with high temporal cadence, we show that the evolution of the accretion disc spectrum during black hole state transitions can be described by a variable disc atmospheric structure without invoking a radially truncated disc geometry. The accretion disc spectrum can be a powerful diagnostic for measuring black hole spin if the effects of the disc atmosphere on the emergent spectrum are well-understood; however, properties of the disc atmosphere are largely unconstrained. Using statistical methods, we decompose this black hole spin measurement technique and show that modest uncertainties regarding the disc atmosphere can lead to erroneous spin measurements. The vertical structure of the disc is difficult to constrain due to our ignorance of the contribution to hydrostatic balance by magnetic fields, which are fundamental to the accretion process. Observations of black hole X-ray binaries and the accretion environments near supermassive black holes provide mounting evidence for strong magnetization. Performing numerical simulations of accretion discs in the shearing box approximation, we impose a net vertical magnetic flux that allows us to effectively control the level of disc magnetization. We study how dynamo activity and the properties of turbulence driven by the magnetorotational instability depend on the

  4. Global General Relativistic Magnetohydrodynamic Simulations of Black Hole Accretion Flows: A Convergence Study

    NASA Astrophysics Data System (ADS)

    Shiokawa, Hotaka; Dolence, Joshua C.; Gammie, Charles F.; Noble, Scott C.

    2012-01-01

    Global, general relativistic magnetohydrodynamic (GRMHD) simulations of non-radiative, magnetized disks are widely used to model accreting black holes. We have performed a convergence study of GRMHD models computed with HARM3D. The models span a factor of four in linear resolution, from 96 × 96 × 64 to 384 × 384 × 256. We consider three diagnostics of convergence: (1) dimensionless shell-averaged quantities such as plasma β (2) the azimuthal correlation length of fluid variables; and (3) synthetic spectra of the source including synchrotron emission, absorption, and Compton scattering. Shell-averaged temperature is, except for the lowest resolution run, nearly independent of resolution; shell-averaged plasma β decreases steadily with resolution but shows signs of convergence. The azimuthal correlation lengths of density, internal energy, and temperature decrease steadily with resolution but show signs of convergence. In contrast, the azimuthal correlation length of magnetic field decreases nearly linearly with grid size. We argue by analogy with local models, however, that convergence should be achieved with another factor of two in resolution. Synthetic spectra are, except for the lowest resolution run, nearly independent of resolution. The convergence behavior is consistent with that of higher physical resolution local model ("shearing box") calculations and with the recent non-relativistic global convergence studies of Hawley et al.

  5. Classical Accreting Pulsars with NICER

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.

    2014-01-01

    Soft excesses are very common center dot Lx > 1038 erg/s - reprocessing by optically thick material at the inner edge of the accretion disk center dot Lx < 1036 erg/s - photoionized or collisionally heated diffuse gas or thermal emission from the NS surface center dot Lx 1037 erg/s - either or both types of emission center dot NICER observations of soft excesses in bright X-ray pulsars combined with reflection modeling will constrain the ionization state, metalicity and dynamics of the inner edge of the magnetically truncated accretion disk Reflection models of an accretion disk for a hard power law - Strong soft excess below 3 keV from hot X-ray heated disk - For weakly ionized case: strong recombination lines - Are we seeing changes in the disk ionization in 4U1626-26? 13 years of weekly monitoring with RXTE PCA center dot Revealed an unexpectedly large population of Be/X-ray binaries compared to the Milky Way center dot Plotted luminosities are typical of "normal" outbursts (once per orbit) center dot The SMC provides an excellent opportunity to study a homogenous population of HMXBs with low interstellar absorption for accretion disk studies. Monitoring with NICER will enable studies of accretion disk physics in X-ray pulsars center dot The SMC provides a potential homogeneous low-absorption population for this study center dot NICER monitoring and TOO observations will also provide measurements of spinfrequencies, QPOs, pulsed fluxes, and energy spectra.

  6. Foundations of Black Hole Accretion Disk Theory.

    PubMed

    Abramowicz, Marek A; Fragile, P Chris

    2013-01-01

    This review covers the main aspects of black hole accretion disk theory. We begin with the view that one of the main goals of the theory is to better understand the nature of black holes themselves. In this light we discuss how accretion disks might reveal some of the unique signatures of strong gravity: the event horizon, the innermost stable circular orbit, and the ergosphere. We then review, from a first-principles perspective, the physical processes at play in accretion disks. This leads us to the four primary accretion disk models that we review: Polish doughnuts (thick disks), Shakura-Sunyaev (thin) disks, slim disks, and advection-dominated accretion flows (ADAFs). After presenting the models we discuss issues of stability, oscillations, and jets. Following our review of the analytic work, we take a parallel approach in reviewing numerical studies of black hole accretion disks. We finish with a few select applications that highlight particular astrophysical applications: measurements of black hole mass and spin, black hole vs. neutron star accretion disks, black hole accretion disk spectral states, and quasi-periodic oscillations (QPOs).

  7. Wavelength dependence of polarization and physical mechanisms of magnetic field generation in accretion disks around supermassive black holes in active galactic nuclei

    NASA Astrophysics Data System (ADS)

    Piotrovich, M. Yu.; Gnedin, Yu. N.; Buliga, S. D.; Natsvlishvili, T. M.

    2014-08-01

    Analysis of the wavelength dependence of the polarization of radiation from active galactic nuclei (AGNs) is shown to allow the main physical mechanisms of magnetic field generation in accretion disks around supermassive black holes in these objects to be determined. These main processes include the generation of magnetic fields as a result of the equality between the magnetic and radiation pressures or as a result of the equality between the magnetic and gas pressures. In several cases, the wavelength dependence of polarization is shown to be explained, provided that the Shakura-Sunyaev viscosity parameter depends on the accretion-disk radius.

  8. Accretion Rate: An Axis Of Agn Unification

    NASA Astrophysics Data System (ADS)

    Trump, Jonathan R.; Impey, C. D.; Kelly, B. C.

    2011-01-01

    We show how accretion rate governs the physical properties of broad-line, narrow-line, and lineless active galactic nuclei (AGNs). We avoid the systematic errors plaguing previous studies of AGN accretion rate by using accurate accretion luminosities from well-sampled multiwavelength SEDs from the Cosmic Evolution Survey (COSMOS), and accurate black hole masses derived from virial scaling relations (for broad-line AGNs) or host-AGN relations (for narrow-line and lineless AGNs). In general, broad emission lines are present only at the highest accretion rates (L/L_Edd>0.01), and these rapidly accreting AGNs are observed as broad-line AGNs or possibly as obscured narrow-line AGNs. Narrow-line and lineless AGNs at lower specific accretion rates (L/L_Edd<0.01) are unobscured and yet lack a broad line region. The disappearance of the broad emission lines is caused by an expanding radiatively inefficient accretion flow (RIAF) at the inner radius of the accretion disk. The presence of the RIAF also drives L/L_Edd<0.01 narrow-line and lineless AGNs to be 10-100 times more radio-luminous than broad-line AGNs, since the unbound nature of the RIAF means it is easier to form a radio outflow. The IR torus signature also tends to become weaker or disappear from L/L_Edd<0.01 AGNs, although there may be additional mid-IR synchrotron emission associated with the RIAF. Together these results suggest that specific accretion rate is an important physical "axis" of AGN unification, described by a simple model.

  9. STUDIES OF THERMALLY UNSTABLE ACCRETION DISKS AROUND BLACK HOLES WITH ADAPTIVE PSEUDOSPECTRAL DOMAIN DECOMPOSITION METHOD. II. LIMIT-CYCLE BEHAVIOR IN ACCRETION DISKS AROUND KERR BLACK HOLES

    SciTech Connect

    Xue Li; Lu Jufu; Sadowski, Aleksander; Abramowicz, Marek A. E-mail: lujf@xmu.edu.cn

    2011-07-01

    For the first time ever, we derive equations governing the time evolution of fully relativistic slim accretion disks in the Kerr metric and numerically construct their detailed non-stationary models. We discuss applications of these general results to a possible limit-cycle behavior of thermally unstable disks. Our equations and numerical method are applicable in a wide class of possible viscosity prescriptions, but in this paper we use a diffusive form of the 'standard alpha prescription' that assumes that the viscous torque is proportional to the total pressure. In this particular case, we find that the parameters that dominate the limit-cycle properties are the mass-supply rate and the value of the alpha-viscosity parameter. Although the duration of the cycle (or the outburst) does not exhibit any clear dependence on the black hole spin, the maximal outburst luminosity (in the Eddington units) is positively correlated with the spin value. We suggest a simple method for a rough estimate of the black hole spin based on the maximal luminosity and the ratio of outburst to cycle durations. We also discuss a temperature-luminosity relation for the Kerr black hole accretion disk limit cycle. Based on these results, we discuss the limit-cycle behavior observed in microquasar GRS 1915+105. We also extend this study to several non-standard viscosity prescriptions, including a 'delayed heating' prescription recently addressed by the MHD simulations of accretion disks.

  10. A VLT/X-Shooter study of accretion and photoevaporation in Transitional Disks

    NASA Astrophysics Data System (ADS)

    Manara, Carlo Felice; Testi, Leonardo; Natta, Antonella; Ricci, Luca; Benisty, Myriam; Rosotti, Giovanni; Ercolano, Barbara

    2013-07-01

    Transitional Disks (TDs) are considered to be a late evolutionary stage of optically thick massive disks whose inner regions are being evacuated, leaving behind large holes that can be detected both by modeling the infrared spectral energy distribution (SED) or, in some cases, by mm-interferometry. These holes could be produced by processes of photoevaporation, grain growth, or planet formation. Still, none of these processes alone has been shown to be sufficient to explain all observations. In this context, the combination of inner hole size, mass accretion rate and wind properties is a powerful observational diagnostic of disk evolution models, but the current measurements of mass accretion rates for TDs are mostly based on secondary indicators (such as the 10% Ha width), and very few data on the wind properties for these objects are available. Here we present a detailed study of the accretion and wind properties of TDs carried out with the VLT/X-Shooter spectrograph. Combining new and archival X-Shooter observations, we collected a sample of more than 20 TDs from different nearby star-forming regions. Our sample includes objects with both small (<5-15 AU) and large (>20-30 AU) known inner hole size from the literature (either from mm-observations or infrared SED fitting). We check their stellar parameters (Teff, Lstar, Av, Mstar) and derive their accretion properties (Lacc, Macc) in a self-consistent way, which makes use of the wide wavelength coverage of X-Shooter, and study their wind properties by mean of different forbidden emission lines analysis. Here we present some preliminary results.

  11. Episodic Accretion in Young Stars

    NASA Astrophysics Data System (ADS)

    Audard, M.; Ábrahám, P.; Dunham, M. M.; Green, J. D.; Grosso, N.; Hamaguchi, K.; Kastner, J. H.; Kóspál, Á.; Lodato, G.; Romanova, M. M.; Skinner, S. L.; Vorobyov, E. I.; Zhu, Z.

    In the last 20 years, the topic of episodic accretion has gained significant interest in the star-formation community. It is now viewed as a common, although still poorly understood, phenomenon in low-mass star formation. The FU Orionis objects (FUors) are long-studied examples of this phenomenon. FU Orionis objects are believed to undergo accretion outbursts during which the accretion rate rapidly increases from typically 10-7 to a few 10-4 M⊙ yr-1, and remains elevated over several decades or more. EXors, a loosely defined class of pre-main-sequence stars, exhibit shorter and repetitive outbursts, associated with lower accretion rates. The relationship between the two classes, and their connection to the standard pre-main-sequence evolutionary sequence, is an open question: Do they represent two distinct classes, are they triggered by the same physical mechanism, and do they occur in the same evolutionary phases? Over the past couple of decades, many theoretical and numerical models have been developed to explain the origin of FUor and EXor outbursts. In parallel, such accretion bursts have been detected at an increasing rate, and as observing techniques improve, each individual outburst is studied in increasing detail. We summarize key observations of pre-main-sequence star outbursts, and review the latest thinking on outburst triggering mechanisms, the propagation of outbursts from star/disk to disk/jet systems, the relation between classical EXors and FUors, and newly discovered outbursting sources — all of which shed new light on episodic accretion. We finally highlight some of the most promising directions for this field in the near- and long-term.

  12. Multi-dimensional structure of accreting young stars

    NASA Astrophysics Data System (ADS)

    Geroux, C.; Baraffe, I.; Viallet, M.; Goffrey, T.; Pratt, J.; Constantino, T.; Folini, D.; Popov, M. V.; Walder, R.

    2016-04-01

    This work is the first attempt to describe the multi-dimensional structure of accreting young stars based on fully compressible time implicit multi-dimensional hydrodynamics simulations. One major motivation is to analyse the validity of accretion treatment used in previous 1D stellar evolution studies. We analyse the effect of accretion on the structure of a realistic stellar model of the young Sun. Our work is inspired by the numerical work of Kley & Lin (1996, ApJ, 461, 933) devoted to the structure of the boundary layer in accretion disks, which provides the outer boundary conditions for our simulations. We analyse the redistribution of accreted material with a range of values of specific entropy relative to the bulk specific entropy of the material in the accreting object's convective envelope. Low specific entropy accreted material characterises the so-called cold accretion process, whereas high specific entropy is relevant to hot accretion. A primary goal is to understand whether and how accreted energy deposited onto a stellar surface is redistributed in the interior. This study focusses on the high accretion rates characteristic of FU Ori systems. We find that the highest entropy cases produce a distinctive behaviour in the mass redistribution, rms velocities, and enthalpy flux in the convective envelope. This change in behaviour is characterised by the formation of a hot layer on the surface of the accreting object, which tends to suppress convection in the envelope. We analyse the long-term effect of such a hot buffer zone on the structure and evolution of the accreting object with 1D stellar evolution calculations. We study the relevance of the assumption of redistribution of accreted energy into the stellar interior used in the literature. We compare results obtained with the latter treatment and those obtained with a more physical accretion boundary condition based on the formation of a hot surface layer suggested by present multi

  13. Partial accretion regime of accreting millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Eksi, Kazim

    2016-07-01

    The inner parts of the disks around neutron stars in low mass X-ray binaries may become geometrically thick due to inhibition of accretion at the disk mid-plane when the central object is rotating rapidly. In such a case matter inflowing through the disk may keep accreting onto the poles of the neutron star from the parts of the disk away from the disk mid-plane while the matter is propelled at the disk mid-plane. An important ingredient of the evolution of millisecond pulsars is then the fraction of the inflowing matter that can accrete onto the poles in the fast rotation regime depending on the fastness parameter. This ``soft'' propeller regime may be associated with the rapid decay stage observed in the light curves of several accreting millisecond pulsars. To date only a few studies considered the partial accretion regime. By using geometrical arguments we improve the existing studies and test the model by reproducing the lightcurves of millisecond X-ray pulsars via time dependent simulations of disk evolution. We also present analytical solutions that represent disks with partial accretion.

  14. Using Simulations of Black Holes to Study General Relativity and the Properties of Inner Accretion Flow

    NASA Astrophysics Data System (ADS)

    Hoormann, Janie Katherine

    2016-06-01

    While Albert Einstein's theory of General Relativity (GR) has been tested extensively in our solar system, it is just beginning to be tested in the strong gravitational fields that surround black holes. As a way to study the behavior of gravity in these extreme environments, I have used and added to a ray-tracing code that simulates the X-ray emission from the accretion disks surrounding black holes. In particular, the observational channels which can be simulated include the thermal and reflected spectra, polarization, and reverberation signatures. These calculations can be performed assuming GR as well as four alternative spacetimes. These results can be used to see if it is possible to determine if observations can test the No-Hair theorem of GR which states that stationary, astrophysical black holes are only described by their mass and spin. Although it proves difficult to distinguish between theories of gravity, it is possible to exclude a large portion of the possible deviations from GR using observations of rapidly spinning stellar mass black holes such as Cygnus X-1. The ray-tracing simulations can furthermore be used to study the inner regions of black hole accretion flows. I examined the dependence of X-ray reverberation observations on the ionization of the disk photosphere. My results show that X-ray reverberation and X-ray polarization provides a powerful tool to constrain the geometry of accretion disks which are too small to be imaged directly. The second part of my thesis describes the work on the balloon-borne X-Calibur hard X-ray polarimetry mission and on the space-borne PolSTAR polarimeter concept.

  15. A spectroscopic study of the radial velocity variations and accretion disks found in four dwarf novae

    NASA Astrophysics Data System (ADS)

    Stover, R. J.

    Time resolved spectroscopic observations of the four dwarf novae SS Cyg, EM Cyg, U Gem, and RU Peg are presented. Although these systems were studied previously, all of the spectroscopic studies were done photographically. A linear response, digital detector is employed. Analytic techniques to the study of the radial velocity variations and emission line profiles found in dwarf novae are applied. In the study of SS Cyg cross-correlation techniques were used for the first time to measure the radial velocity variations of the secondary star absorption lines. In the study of U Gem, analysis of the accretion disk emission lines showed that the motion of the material in the disk cannot be described accurately by orbits defined within the three-body approximation. The observations of EM Cyg reveal an unstable accretion disk, with emission lines that vary erratically on timescales of minutes to days. New measurements of the radial velocity variations of the emission and absorption lines found in the spectrum of RU Peg agree with previous measurements but have a higher accuracy.

  16. A Study of Large Droplet Ice Accretions in the NASA-Lewis IRT at Near-Freezing Conditions

    NASA Technical Reports Server (NTRS)

    Miller, Dean R.; Addy, Harold E. , Jr.; Ide, Robert F.

    1996-01-01

    This report documents the results of an experimental study on large droplet ice accretions which was conducted in the NASA-Lewis Icing Research Tunnel (IRT) with a full-scale 77.25 inch chord Twin-Otter wing section. This study was intended to: (1) document the existing capability of the IRT to produce a large droplet icing cloud, and (2) study the effect of various parameters on large droplet ice accretions. Results are presented from a study of the IRT's capability to produce large droplets with MVD of 99 and 160 microns. The effect of the initial water droplet temperature on the resultant ice accretion was studied for different initial spray bar air and water temperatures. The initial spray bar water temperature was found to have no discernible effect upon the large droplet ice accretions. Also, analytical and experimental results suggest that the water droplet temperature is very nearly the same as the tunnel ambient temperature, thus providing a realistic simulation of the large droplet natural icing condition. The effect of temperature, droplet size, airspeed, angle-of attack, flap setting and de-icer boot cycling time on ice accretion was studied, and will be discussed in this report. It was found that, in almost all of the cases studied, an ice ridge formed immediately aft of the active portion of the de-icer boot. This ridge was irregular in shape, varied in location, and was in some cases discontinuous due to aerodynamic shedding.

  17. Promises and Problems of Pebble Accretion

    NASA Astrophysics Data System (ADS)

    Kretke, Katherine A.; Levison, H. F.

    2013-10-01

    Despite the large number of exoplanets indicating that giant planets are a common outcome of the star formation process, theoretical models still struggle to explain how ~10 Earth mass rocky/icy embryos can form within the lifetimes of gaseous circumstellar disks. In recent years, aerodynamic-aided accretion of ``pebbles,'' particles ranging from millimeters to decimeters in size, has been suggested as a potential solution to this long-standing problem. Local simulations, simulations which look at the detailed behavior of these pebbles in the vicinity of a planetary embryo, have shown that the potential planetary growth rates can be surprisingly fast. If one assumes that most of the mass in a protoplanetary disk resides in these pebble-sized particles, a Mars mass core could grow to 10 Earth masses in only a few thousand years. However, these local studies cannot investigate how this accretion process behaves in the more complicated, multi-planet environment. We have incorporated the local accretion physics into LIPAD, a Lagrangian code which can follow the collisional / accretional / dynamical evolution of a planetary system, to investigate the how this pebble accretion will manifest itself in the larger planet formation picture. We present how these more comprehensive models raise challenges to using pebble accretion to form observed planetary systems.

  18. Effects of Ice Accretion on Aircraft Aerodynamics

    NASA Technical Reports Server (NTRS)

    Bragg, Michael B.

    1998-01-01

    The primary objective of this research was to support the development of a new ice accretion model by improving our physical understanding of the ice accretion process through experimental measurements. The focus was on the effect of the initial ice roughness (smooth/rough boundary) on the accretion process. This includes understanding the boundary-layer development over the roughness and especially its effect on the heat transfer which is fundamental to the ice accretion process. The research focused on acquiring the experimental data needed to formulate a new ice accretion physical model. Research was conducted to analyze boundary-layer data taken on a NACA 0012 airfoil with roughness to simulate the smooth/rough boundary. The effect of isolated roughness on boundary-layer transition was studied experimentally to determine if the classical critical roughness Reynolds number criteria could be applied to transition in the airfoil leading-edge area. The effect of simulated smooth/rough boundary roughness on convective heat transfer was studied to complete the study. During the course of this research the effect of free-stream wind tunnel turbulence on the boundary layer was measured. Since this quantity was not well known, research to accurately measure the wind tunnel turbulence in an icing cloud was undertaken. Preliminary results were attained and the final data were acquired, reduced and presented under a subsequent grant.

  19. Numerical and experimental study of magnetized accretion phenomena in young stars

    NASA Astrophysics Data System (ADS)

    Khiar, Benjamin; Ciardi, Andrea; Revet, Guilhem; Vinci, Tommaso; Fuchs, Julien; Orlando, Salvatore; Inaf Team; Luli Team; Lerma Team

    2016-10-01

    Newly formed stars accrete mass from the circumstellar disc via magnetized accretion funnels that connect the inner disc regions to the star. The ensuing impact of this free-falling plasma onto the stellar surface generates a strong shock, whose emission is used as a proxy to determine the accretion rates. Observations show that the X-ray luminosity arising from the shock heated plasma at the base of accretion columns is largelybelow the value expected on the basis of optical/UV observations. As a result, current 2D numerical simulations matching X-ray accretion rates cannot reproduce optical accretion rates. To understand the impact of accretion flows on the stellar surface in the presence of a strong magnetic field we have developed laboratory experiments reproducing crucial aspects of the accretion dynamics in Young Stellar Objects. As a model of accretion columns, we use laser-produced super-Alfvenic magnetically confined jets to collide them on solid targets. Here we present results from these experiments and from multi-dimensional MHD simulations. The authors acknowledge the support from the Ile-de-France DIM ACAV, from the LABEX Plas@par and from the ANR Grant SILAMPA.

  20. Spiral Waves in Accretion Discs - Theory

    NASA Astrophysics Data System (ADS)

    Boffin, H. M. J.

    Spirals shocks have been widely studied in the context of galactic dynamics and protostellar discs. They may however also play an important role in some classes of close binary stars, and more particularly in cataclysmic variables. In this paper, we review the physics of spirals waves in accretion discs, present the results of numerical simulations and consider whether theory can be reconcilied with observations.

  1. On the role of disks in the formation of stellar systems: A numerical parameter study of rapid accretion

    SciTech Connect

    Kratter, Kaitlin M.; Matzner, Christopher D.; Krumholz, Mark R.; Klein, Richard I.

    2009-12-23

    We study rapidly accreting, gravitationally unstable disks with a series of idealized global, numerical experiments using the code ORION. Our numerical parameter study focuses on protostellar disks, showing that one can predict disk behavior and the multiplicity of the accreting star system as a function of two dimensionless parameters which compare the infall rate to the disk sound speed and orbital period. Although gravitational instabilities become strong, we find that fragmentation into binary or multiple systems occurs only when material falls in several times more rapidly than the canonical isothermal limit. The disk-to-star accretion rate is proportional to the infall rate and governed by gravitational torques generated by low-m spiral modes. Furthermore, we also confirm the existence of a maximum stable disk mass: disks that exceed ~50% of the total system mass are subject to fragmentation and the subsequent formation of binary companions.

  2. On the role of disks in the formation of stellar systems: A numerical parameter study of rapid accretion

    DOE PAGES

    Kratter, Kaitlin M.; Matzner, Christopher D.; Krumholz, Mark R.; ...

    2009-12-23

    We study rapidly accreting, gravitationally unstable disks with a series of idealized global, numerical experiments using the code ORION. Our numerical parameter study focuses on protostellar disks, showing that one can predict disk behavior and the multiplicity of the accreting star system as a function of two dimensionless parameters which compare the infall rate to the disk sound speed and orbital period. Although gravitational instabilities become strong, we find that fragmentation into binary or multiple systems occurs only when material falls in several times more rapidly than the canonical isothermal limit. The disk-to-star accretion rate is proportional to the infallmore » rate and governed by gravitational torques generated by low-m spiral modes. Furthermore, we also confirm the existence of a maximum stable disk mass: disks that exceed ~50% of the total system mass are subject to fragmentation and the subsequent formation of binary companions.« less

  3. Recent Observational Progress on Accretion Disks Around Compact Objects

    NASA Astrophysics Data System (ADS)

    Miller, Jon M.

    2016-04-01

    Studies of accretion disks around black holes and neutron stars over the last ten years have made remarkable progress. Our understanding of disk evolution as a function of mass accretion rate is pushing toward a consensus on thin/thick disk transitions; an apparent switching between disk-driven outflow modes has emerged; and monitoring observations have revealed complex spectral energy distributions wherein disk reprocessing must be important. Detailed studies of disk winds, in particular, have the potential to reveal the basic physical processes that mediate disk accretion, and to connect with numerical simulations. This talk will review these developments and look ahead to the potential of Astro-H.

  4. Potential Impacts of ASTRO-H on the Studies of Accreting White Dwarf Binaries

    NASA Astrophysics Data System (ADS)

    Mukai, Koji; Yuasa, Tadayuki; Harayama, Atsushi; Hayashi, Takayuki; Ishida, Manabu; Long, Knox S.; Terada, Yukikatsu; Tsujimoto, Masahiro; ASTRO-H Team

    2015-01-01

    Interacting binaries in which a white dwarf accretes material from a companion - cataclysmic variables (CVs) in which the mass loss is via Roche-lobe overflow, and symbiotic stars in which the white dwarf captures the wind of a late type giant - are important populations of X-ray sources. Accretion onto the white dwarf surface often creates shocks with temperatures in the 10-50 keV range. If the post-shock region stays optically thin, it produces multi-temperature plasma emission over the medium to hard X-ray band (~0.5-50 keV). This makes them well-matched to the capabilities of the upcoming ASTRO-H mission, which will allow high-resolution spectroscopy in the 0.3-10 keV range with the microcalorimeter instrument, Soft X-ray Spectrometer (SXS), and simultaneous imaging spectroscopy in the 5-80 keV range with the Hard X-ray Imager (HXI). We will highlight several areas in which ASTRO-H can make unique contributions to the studies of these binaries. For example, X-ray emitting plasma in many of these systems are expected to have such high densities that only the SXS can provide density diagnostics. The prominent Fe K lines will allow dynamical studies of the X-ray emitting plasma for which velocities of order 1,000 km s-2 are expected. Finally, we discuss the potential of ASTRO-H to study the reflection off the white dwarf surface, both via the continuum bump observable with the HXI and the 6.4 keV fluorescent iron line with the SXS. For near Chandrasekhar-mass white dwarfs, the gravitational redshift of the latter is within reach of the instrumental capability and may provide the best direct measurement of their masses.

  5. Can Oregon Marshes Keep Up With The Rising Tide? A Study of Short and Long Term Marsh Accretion.

    EPA Science Inventory

    More frequent inundation of Oregon coastal marshlands associated with rising sea level threatens these important and diverse habitats. Study plot accretion rates determined by the marker horizon method and longer term peak Cs137 detection in eight marsh systems from Coquille to ...

  6. Massive star formation by accretion. I. Disc accretion

    NASA Astrophysics Data System (ADS)

    Haemmerlé, L.; Eggenberger, P.; Meynet, G.; Maeder, A.; Charbonnel, C.

    2016-01-01

    Context. Massive stars likely form by accretion and the evolutionary track of an accreting forming star corresponds to what is called the birthline in the Hertzsprung-Russell (HR) diagram. The shape of this birthline is quite sensitive to the evolution of the entropy in the accreting star. Aims: We first study the reasons why some birthlines published in past years present different behaviours for a given accretion rate. We then revisit the question of the accretion rate, which allows us to understand the distribution of the observed pre-main-sequence (pre-MS) stars in the HR diagram. Finally, we identify the conditions needed to obtain a large inflation of the star along its pre-MS evolution that may push the birthline towards the Hayashi line in the upper part of the HR diagram. Methods: We present new pre-MS models including accretion at various rates and for different initial structures of the accreting core. We compare them with previously published equivalent models. From the observed upper envelope of pre-MS stars in the HR diagram, we deduce the accretion law that best matches the accretion history of most of the intermediate-mass stars. Results: In the numerical computation of the time derivative of the entropy, some treatment leads to an artificial loss of entropy and thus reduces the inflation that the accreting star undergoes along the birthline. In the case of cold disc accretion, the existence of a significant swelling during the accretion phase, which leads to radii ≳ 100 R⊙ and brings the star back to the red part of the HR diagram, depends sensitively on the initial conditions. For an accretion rate of 10-3M⊙ yr-1, only models starting from a core with a significant radiative region evolve back to the red part of the HR diagram. We also obtain that, in order to reproduce the observed upper envelope of pre-MS stars in the HR diagram with an accretion law deduced from the observed mass outflows in ultra-compact HII regions, the fraction of the

  7. A Preliminary Study of Ice-Accretion Scaling for SLD Conditions

    NASA Technical Reports Server (NTRS)

    Anderson, David N.

    2003-01-01

    Proposed changes to aircraft icing certification rules are being considered by European, Canadian, and American regulatory agencies to include operation in super-cooled large droplet conditions (SLD). This paper reports results of an experimental study in the NASA Glenn Icing Research Tunnel (IRT) to evaluate how well scaling methods developed for Appendix C conditions might apply to SLD conditions. Until now, scaling studies have been confined to the FAA FAR-25 Appendix C envelope of atmospheric cloud conditions. Tests were made in which it was attempted to scale to a droplet MVD of 50 microns from clouds having droplet MVDs of 175, 120, 100, and 70 microns. Scaling was based on the Ruff method with scale velocities found either by maintaining constant Weber number or by using the average of the velocities obtained by maintaining constant Weber number and constant Reynolds number. Models were unswept NACA 0012 wing sections. The reference model had a chord of 91.4 cm. Scale models had chords of 91.4, 80.0, and 53.3 cm. Tests were conducted with reference airspeeds of 100 and 150 kt (52 and 77 m/s) and with freezing fractions of 1.0, 0.6, and 0.3. It was demonstrated that the scaled 50-micron cloud simulated well the non-dimensional ice shapes accreted in clouds with MVD's of 120 microns or less.

  8. Chaotic cold accretion on to black holes

    NASA Astrophysics Data System (ADS)

    Gaspari, M.; Ruszkowski, M.; Oh, S. Peng

    2013-07-01

    Bondi theory is often assumed to adequately describe the mode of accretion in astrophysical environments. However, the Bondi flow must be adiabatic, spherically symmetric, steady, unperturbed, with constant boundary conditions. Using 3D adaptive mesh refinement simulations, linking the 50 kpc to the sub-parsec (sub-pc) scales over the course of 40 Myr, we systematically relax the classic assumptions in a typical galaxy hosting a supermassive black hole. In the more realistic scenario, where the hot gas is cooling, while heated and stirred on large scales, the accretion rate is boosted up to two orders of magnitude compared with the Bondi prediction. The cause is the non-linear growth of thermal instabilities, leading to the condensation of cold clouds and filaments when tcool/tff ≲ 10. The clouds decouple from the hot gas, `raining' on to the centre. Subsonic turbulence of just over 100 km s-1 (M > 0.2) induces the formation of thermal instabilities, even in the absence of heating, while in the transonic regime turbulent dissipation inhibits their growth (tturb/tcool ≲ 1). When heating restores global thermodynamic balance, the formation of the multiphase medium is violent, and the mode of accretion is fully cold and chaotic. The recurrent collisions and tidal forces between clouds, filaments and the central clumpy torus promote angular momentum cancellation, hence boosting accretion. On sub-pc scales the clouds are channelled to the very centre via a funnel. In this study, we do not inject a fixed initial angular momentum, though vorticity is later seeded by turbulence. A good approximation to the accretion rate is the cooling rate, which can be used as subgrid model, physically reproducing the boost factor of 100 required by cosmological simulations, while accounting for the frequent fluctuations. Since our modelling is fairly general (turbulence/heating due to AGN feedback, galaxy motions, mergers, stellar evolution), chaotic cold accretion may be common in

  9. Wind-accretion Disks in Wide Binaries, Second-generation Protoplanetary Disks, and Accretion onto White Dwarfs

    NASA Astrophysics Data System (ADS)

    Perets, Hagai B.; Kenyon, Scott J.

    2013-02-01

    Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured material forms an accretion disk. Here, we study the evolution of wind-accretion disks, using a numerical approach which allows us to follow the long-term evolution. For a broad range of initial conditions, we derive the radial density and temperature profiles of the disk. In most cases, wind accretion leads to long-lived stable disks over the lifetime of the asymptotic giant branch donor star. The disks have masses of a few times 10-5-10-3 M ⊙, with surface density and temperature profiles that follow broken power laws. The total mass in the disk scales approximately linearly with the viscosity parameter used. Roughly, 50%-80% of the mass falling into the disk accretes onto the central star; the rest flows out through the outer edge of the disk into the stellar wind of the primary. For systems with large accretion rates, the secondary accretes as much as 0.1 M ⊙. When the secondary is a white dwarf, accretion naturally leads to nova and supernova eruptions. For all types of secondary star, the surface density and temperature profiles of massive disks resemble structures observed in protoplanetary disks, suggesting that coordinated observational programs might improve our understanding of uncertain disk physics.

  10. RADIATIVELY EFFICIENT MAGNETIZED BONDI ACCRETION

    SciTech Connect

    Cunningham, Andrew J.; Klein, Richard I.; McKee, Christopher F.; Krumholz, Mark R.; Teyssier, Romain

    2012-01-10

    We have carried out a numerical study of the effect of large-scale magnetic fields on the rate of accretion from a uniform, isothermal gas onto a resistive, stationary point mass. Only mass, not magnetic flux, accretes onto the point mass. The simulations for this study avoid complications arising from boundary conditions by keeping the boundaries far from the accreting object. Our simulations leverage adaptive refinement methodology to attain high spatial fidelity close to the accreting object. Our results are particularly relevant to the problem of star formation from a magnetized molecular cloud in which thermal energy is radiated away on timescales much shorter than the dynamical timescale. Contrary to the adiabatic case, our simulations show convergence toward a finite accretion rate in the limit in which the radius of the accreting object vanishes, regardless of magnetic field strength. For very weak magnetic fields, the accretion rate first approaches the Bondi value and then drops by a factor of {approx}2 as magnetic flux builds up near the point mass. For strong magnetic fields, the steady-state accretion rate is reduced by a factor of {approx}0.2 {beta}{sup 1/2} compared to the Bondi value, where {beta} is the ratio of the gas pressure to the magnetic pressure. We give a simple expression for the accretion rate as a function of the magnetic field strength. Approximate analytic results are given in the Appendices for both time-dependent accretion in the limit of weak magnetic fields and steady-state accretion for the case of strong magnetic fields.

  11. The Dripping Handrail Model: Transient Chaos in Accretion Systems

    NASA Technical Reports Server (NTRS)

    Young, Karl; Scargle, Jeffrey D.; Cuzzi, Jeffrey (Technical Monitor)

    1995-01-01

    We define and study a simple dynamical model for accretion systems, the "dripping handrail" (DHR). The time evolution of this spatially extended system is a mixture of periodic and apparently random (but actually deterministic) behavior. The nature of this mixture depends on the values of its physical parameters - the accretion rate, diffusion coefficient, and density threshold. The aperiodic component is a special kind of deterministic chaos called transient chaos. The model can simultaneously exhibit both the quasiperiodic oscillations (QPO) and very low frequency noise (VLFN) that characterize the power spectra of fluctuations of several classes of accretion systems in astronomy. For this reason, our model may be relevant to many such astrophysical systems, including binary stars with accretion onto a compact object - white dwarf, neutron star, or black hole - as well as active galactic nuclei. We describe the systematics of the DHR's temporal behavior, by exploring its physical parameter space using several diagnostics: power spectra, wavelet "scalegrams," and Lyapunov exponents. In addition, we note that for large accretion rates the DHR has periodic modes; the effective pulse shapes for these modes - evaluated by folding the time series at the known period - bear a resemblance to the similarly- determined shapes for some x-ray pulsars. The pulsing observed in some of these systems may be such periodic-mode accretion, and not due to pure rotation as in the standard pulsar model.

  12. On the effects of tidal interaction on thin accretion disks: An analytic study

    NASA Technical Reports Server (NTRS)

    Dgani, R.; Livio, M.; Regev, O.

    1994-01-01

    We calculate tidal effects on two-dimensional thin accretion disks in binary systems. We apply a perturbation expansion to obtain an analytic solution of the tidally induced waves. We obtain spiral waves that are stronger at the inner parts of the disks, in addition to a local disturbance which scales like the strength of the local tidal force. Our results agree with recent calculations of the linear response of the disk to tidal interaction.

  13. Plans and Preliminary Results of Fundamental Studies of Ice Crystal Icing Physics in the NASA Propulsion Systems Laboratory

    NASA Technical Reports Server (NTRS)

    Struk, Peter; Tsao, Jen-Ching; Bartkus, Tadas

    2017-01-01

    This paper describes plans and preliminary results for using the NASA Propulsion Systems Lab (PSL) to experimentally study the fundamental physics of ice-crystal ice accretion. NASA is evaluating whether this facility, in addition to full-engine and motor-driven-rig tests, can be used for more fundamental ice-accretion studies that simulate the different mixed-phase icing conditions along the core flow passage of a turbo-fan engine compressor. The data from such fundamental accretion tests will be used to help develop and validate models of the accretion process. This paper presents data from some preliminary testing performed in May 2015 which examined how a mixed-phase cloud could be generated at PSL using evaporative cooling in a warmer-than-freezing environment.

  14. A Systems-Level Perspective on Engine Ice Accretion

    NASA Technical Reports Server (NTRS)

    May, Ryan D.; Guo, Ten-Huei; Simon, Donald L.

    2013-01-01

    The accretion of ice in the compression system of commercial gas turbine engines operating in high ice water content conditions is a safety issue being studied by the aviation sector. While most of the research focuses on the underlying physics of ice accretion and the meteorological conditions in which accretion can occur, a systems-level perspective on the topic lends itself to potential near-term operational improvements. This work focuses on developing an accurate and reliable algorithm for detecting the accretion of ice in the low pressure compressor of a generic 40,000 lbf thrust class engine. The algorithm uses only the two shaft speed sensors and works regardless of engine age, operating condition, and power level. In a 10,000-case Monte Carlo simulation, the detection approach was found to have excellent capability at determining ice accretion from sensor noise with detection occurring when ice blocks an average of 6.8% of the low pressure compressor area. Finally, an initial study highlights a potential mitigation strategy that uses the existing engine actuators to raise the temperature in the low pressure compressor in an effort to reduce the rate at which ice accretes.

  15. Star formation sustained by gas accretion

    NASA Astrophysics Data System (ADS)

    Sánchez Almeida, Jorge; Elmegreen, Bruce G.; Muñoz-Tuñón, Casiana; Elmegreen, Debra Meloy

    2014-07-01

    Numerical simulations predict that metal-poor gas accretion from the cosmic web fuels the formation of disk galaxies. This paper discusses how cosmic gas accretion controls star formation, and summarizes the physical properties expected for the cosmic gas accreted by galaxies. The paper also collects observational evidence for gas accretion sustaining star formation. It reviews evidence inferred from neutral and ionized hydrogen, as well as from stars. A number of properties characterizing large samples of star-forming galaxies can be explained by metal-poor gas accretion, in particular, the relationship among stellar mass, metallicity, and star-formation rate (the so-called fundamental metallicity relationship). They are put forward and analyzed. Theory predicts gas accretion to be particularly important at high redshift, so indications based on distant objects are reviewed, including the global star-formation history of the universe, and the gas around galaxies as inferred from absorption features in the spectra of background sources.

  16. Accretion Disk Emission Around Kerr Black Holes

    NASA Astrophysics Data System (ADS)

    Campitiello, Samuele; Sbarrato, T.; Ghisellini, G.

    2016-10-01

    Measuring the spin of supermassive Black holes in Active Galactic Nuclei is a further step towards a better understanding of the evolution of their physics. We proposed a new method to estimate the Black hole spin, based on data-fitting. We consider a numerical model called KERRBB, including all relativistic effects (i.e. light-bending, gravitational redshift and Doppler beaming). We found that the same spectrum can be produced by different masses, accretion rates and spins, but that these three quantities are related. In other words, having a robust indipendent estimate on one of these three quantities fixes the other two. By using the Black hole mass, estimated by the virial method, we can pinpoint a narrow range of possible spins and accretion rates for the 32 blazars we have studied. For these objects, we found a lower limit of the spin, that must be a/M > 0.6-0.7

  17. Studies in medium energy physics

    SciTech Connect

    Green, A.; Hoffmann, G.W.; McDonough, J.; Purcell, M.J.; Ray, R.L.; Read, D.E.; Worn, S.D.

    1991-12-01

    This document constitutes the (1991--1992) technical progress report and continuation proposal for the ongoing medium energy nuclear physics research program supported by the US Department of Energy through special Research Grant DE-FG05-88ER40444. The experiments discussed are conducted at the Los Alamos National Laboratory's (LANL) Clinton P. Anderson Meson Physics Facility (LAMPF) and the Alternating Gradient Synchrotron (AGS) facility of the Brookhaven National Laboratory (BNL). The overall motivation for the work discussed in this document is driven by three main objectives: (1) provide hadron-nucleon and hadron-nucleus scattering data which serve to facilitate the study of effective two-body interactions, test (and possibly determine) nuclear structure, and help study reaction mechanisms and dynamics; (2) provide unique, first-of-a-kind exploratory'' hadron-nucleus scattering data in the hope that such data will lead to discovery of new phenomena and new physics; and (3) perform precision tests of fundamental interactions, such as rare decay searches, whose observation would imply fundamental new physics.

  18. Measuring the stellar wind parameters in IGR J17544-2619 and Vela X-1 constrains the accretion physics in supergiant fast X-ray transient and classical supergiant X-ray binaries

    NASA Astrophysics Data System (ADS)

    Giménez-García, A.; Shenar, T.; Torrejón, J. M.; Oskinova, L.; Martínez-Núñez, S.; Hamann, W.-R.; Rodes-Roca, J. J.; González-Galán, A.; Alonso-Santiago, J.; González-Fernández, C.; Bernabeu, G.; Sander, A.

    2016-06-01

    two stars is their terminal velocities (ν∞ = 1500 km s-1 in IGR J17544-2619 and ν∞ = 700 km s-1 in Vela X-1), which have important consequences on the X-ray luminosity of these sources. Conclusions: The donors of IGR J17544-2619 and Vela X-1 have similar spectral types as well as similar parameters that physically characterize them and their spectra. In addition, the orbital parameters of the systems are similar too, with a nearly circular orbit and short orbital period. However, they show moderate differences in their stellar wind velocity and the spin period of their neutron star which has a strong impact on the X-ray luminosity of the sources. This specific combination of wind speed and pulsar spin favors an accretion regime with a persistently high luminosity in Vela X-1, while it favors an inhibiting accretion mechanism in IGR J17544-2619. Our study demonstrates that the relative wind velocity is critical in class determination for the HMXBs hosting a supergiant donor, given that it may shift the accretion mechanism from direct accretion to propeller regimes when combined with other parameters.

  19. Accretion Processes in Astrophysics

    NASA Astrophysics Data System (ADS)

    González Martínez-País, Ignacio; Shahbaz, Tariq; Casares Velázquez, Jorge

    2014-03-01

    List of contributors; List of participants; Preface; Acknowledgments; Abbreviations; 1. Accretion disks Henk Spruit; 2. The evolution of binary systems Philipp Podsiadlowski; 3. Accretion onto white dwarfs Brian Warner; 4. Accretion in X-ray binary systems Robert I. Hynes; 5. X-ray binary populations in galaxies Giuseppina Fabbiano; 6. Observational characteristics of accretion onto black holes I Chris Done; 7. Observational characteristics of accretion onto black holes II Rob Fender; 8. Computing black hole accretion John F. Hawley; Appendix: Piazzi Smyth, the Cape of Good Hope, Tenerife and the siting of large telescopes Brian Warner.

  20. Eclipse Mapping of Accretion Discs

    NASA Astrophysics Data System (ADS)

    Baptista, R.

    The eclipse mapping method is an inversion technique that makes use of the information contained in eclipse light curves to probe the structure, the spectrum and the time evolution of accretion discs. In this review I present the basics of the method and discuss its different implementations. I summarize the most important results obtained to date and discuss how they have helped to improve our understanding of accretion physics, from testing the theoretical radial brightness temperature distribution and measuring mass accretion rates to showing the evolution of the structure of a dwarf novae disc throughout its outburst cycle, from isolating the spectrum of a disc wind to revealing the geometry of disc spiral shocks. I end with an outline of the future prospects.

  1. An experimental and theoretical study of the ice accretion process during artificial and natural icing conditions

    NASA Technical Reports Server (NTRS)

    Kirby, Mark S.; Hansman, R. John

    1988-01-01

    Real-time measurements of ice growth during artificial and natural icing conditions were conducted using an ultrasonic pulse-echo technique. This technique allows ice thickness to be measured with an accuracy of + or - 0.5 mm; in addition, the ultrasonic signal characteristics may be used to detect the presence of liquid on the ice surface and hence discern wet and dry ice growth behavior. Ice growth was measured on the stagnation line of a cylinder exposed to artificial icing conditions in the NASA Lewis Icing Research Tunnel (IRT), and similarly for a cylinder exposed in flight to natural icing conditions. Ice thickness was observed to increase approximately linearly with exposure time during the initial icing period. The ice accretion rate was found to vary with cloud temperature during wet ice growth, and liquid runback from the stagnation region was inferred. A steady-state energy balance model for the icing surface was used to compare heat transfer characteristics for IRT and natural icing conditions. Ultrasonic measurements of wet and dry ice growth observed in the IRT and in flight were compared with icing regimes predicted by a series of heat transfer coefficients. The heat transfer magnitude was generally inferred to be higher for the IRT than for the natural icing conditions encountered in flight. An apparent variation in the heat transfer magnitude was also observed for flights conducted through different natural icing-cloud formations.

  2. How do accretion discs break?

    NASA Astrophysics Data System (ADS)

    Dogan, Suzan

    2016-07-01

    Accretion discs are common in binary systems, and they are often found to be misaligned with respect to the binary orbit. The gravitational torque from a companion induces nodal precession in misaligned disc orbits. In this study, we first calculate whether this precession is strong enough to overcome the internal disc torques communicating angular momentum. We compare the disc precession torque with the disc viscous torque to determine whether the disc should warp or break. For typical parameters precession wins: the disc breaks into distinct planes that precess effectively independently. To check our analytical findings, we perform 3D hydrodynamical numerical simulations using the PHANTOM smoothed particle hydrodynamics code, and confirm that disc breaking is widespread and enhances accretion on to the central object. For some inclinations, the disc goes through strong Kozai cycles. Disc breaking promotes markedly enhanced and variable accretion and potentially produces high-energy particles or radiation through shocks. This would have significant implications for all binary systems: e.g. accretion outbursts in X-ray binaries and fuelling supermassive black hole (SMBH) binaries. The behaviour we have discussed in this work is relevant to a variety of astrophysical systems, for example X-ray binaries, where the disc plane may be tilted by radiation warping, SMBH binaries, where accretion of misaligned gas can create effectively random inclinations and protostellar binaries, where a disc may be misaligned by a variety of effects such as binary capture/exchange, accretion after binary formation.

  3. The Instability in Accretion Flows: GvMRI

    NASA Astrophysics Data System (ADS)

    Yardimci, Melis; Ebru Devlen, Doç.

    2016-07-01

    In this study, we discuss the physical instability defining the expected turbulence in Radiatively Inefficient Accretion Flows (RIAFs) around the supermassive black holes (e.g., Sagittarius A* in the center of our Galaxy). These flows, with a high probability, include weakly collisional hot, optically thin and dilute plasmas. Within these flows, gravitational potential energy brought about by turbulent stresses is trapped as heat energy. Thus, in order accretion to be realized, outward transport of heat as well as angular momentum is required. This outward heat transport may reduce the mass inflow rate on black hole. We solve MHD equations including variation of viscosity coefficients with pressure in the momentum conservation equation. We plot the wave number-frequency diagrams for the wave modes. We show that one of the most probable candidates for definition of mass accretion and the source of excess heat energy in RIAFs is the gyroviscous modified magnetorotational instabilitiy (GvMRI).

  4. An experimental study of the aerodynamics of a NACA0012 airfoil with a simulated glaze ice accretion, volume 2

    NASA Technical Reports Server (NTRS)

    Bragg, Michael B.

    1993-01-01

    This is the second volume of a report documenting the effect of simulated ice accretion on the aerodynamic performance of a NACA 0012 airfoil. Both an experimentally measured and a computer generated ice shape are studied. The purpose of this report is to present the results of the measurements, not an analysis of the data. Surface pressure, integrated lift and pitching moment data are presented as well as drag from a wake survey. A split hot film probe was used to document the flow-field about the airfoil with simulated ice. Data in the separation bubbles, reattached boundary layer and wake are presented. Both tabulated and graphical data are presented in the paper. The data are also available on computer disk for easy access.

  5. Probing the Physics of Narrow-line Regions in Active Galaxies. III. Accretion and Cocoon Shocks in the LINER NGC 1052

    NASA Astrophysics Data System (ADS)

    Dopita, Michael A.; Ho, I.-Ting; Dressel, Linda L.; Sutherland, Ralph; Kewley, Lisa; Davies, Rebecca; Hampton, Elise; Shastri, Prajval; Kharb, Preeti; Jose, Jessy; Bhatt, Harish; Ramya, S.; Scharwächter, Julia; Jin, Chichuan; Banfield, Julie; Zaw, Ingyin; James, Bethan; Juneau, Stéphanie; Srivastava, Shweta

    2015-03-01

    We present Wide Field Spectrograph integral field spectroscopy and Hubble Space Telescope Faint Object Spectrograph spectroscopy for the low-ionization nuclear emission line region (LINER) galaxy NGC 1052. We infer the presence of a turbulent accretion flow forming a small-scale accretion disk. We find a large-scale outflow and ionization cone along the minor axis of the galaxy. Part of this outflow region is photoionized by the active galactic nucleus and shares properties with the extended narrow-line region of Seyfert galaxies, but the inner (R≲ 1.0″) accretion disk and the region around the radio jet appear shock excited. The emission-line properties can be modeled by a “double-shock” model in which the accretion flow first passes through an accretion shock in the presence of a hard X-ray radiation, and the accretion disk is then processed through a cocoon shock driven by the overpressure of the radio jets. This model explains the observation of two distinct densities (˜104 and ˜106 cm-3) and provides a good fit to the observed emission-line spectrum. We derive estimates for the velocities of the two shock components and their mixing fractions, the black hole mass, and the accretion rate needed to sustain the LINER emission and derive an estimate for the jet power. Our emission-line model is remarkably robust against variation of input parameters and hence offers a generic explanation for the excitation of LINER galaxies, including those of spiral type such as NGC 3031 (M81).

  6. Electromagnetic signatures of thin accretion disks in wormhole geometries

    SciTech Connect

    Harko, Tiberiu; Kovacs, Zoltan; Lobo, Francisco S. N.

    2008-10-15

    In this paper, we study the physical properties and characteristics of matter forming thin accretion disks in static and spherically symmetric wormhole spacetimes. In particular, the time averaged energy flux, the disk temperature, and the emission spectra of the accretion disks are obtained for these exotic geometries and are compared with the Schwarzschild solution. It is shown that more energy is emitted from the disk in a wormhole geometry than in the case of the Schwarzschild potential and the conversion efficiency of the accreted mass into radiation is more than a factor of 2 higher for the wormholes than for static black holes. These effects in the disk radiation are confirmed in the radial profiles of temperature corresponding to theses flux distributions, and in the emission spectrum {omega}L({omega}) of the accretion disks. We conclude that specific signatures appear in the electromagnetic spectrum, thus leading to the possibility of distinguishing wormhole geometries by using astrophysical observations of the emission spectra from accretion disks.

  7. Basic Studies in Plasma Physics

    DTIC Science & Technology

    2010-02-17

    ring by Evans, Kafri, Koduvely, and Mukamel, and the weakly asymmetric version was later studied by Clincy, Derrida , and Evans. Here the latter model...Dipole Model, Rev. in Math. Phys., 20, 835-872, 2007 Los Alamos Arxiv:math-ph/0609069 4. B. Derrida , E. Speer and J.L. Lebowitz, Entropy of Open...mat/0612371. 11 14. J.L. Lebowitz, Emergent Phenomena. Physics Journal, 6,1-6, 2007 15. T. Bodineau, B. Derrida and J.L. Lebowitz, Vortices in the

  8. Relativistic shocks in electron-positron plasmas, and polar cap accretion onto neutron stars: Two non-linear problems in astrophysical plasma physics

    SciTech Connect

    Arons, J.

    1988-08-15

    I outline particle simulations and theory of relativistic shock waves in an e/sup +-/ plasma. Magnetic reflection of particles is an essential role in the shock structure. Instability of the reflected particles in the shock front produces intense extraordinary mode radiation. Such shocks are candidates for the particle accelerator in plerions and in extragalactic jets only if the upstream Poynting flux composes no more than 10% of the total. I summarize analytical and numerical studies of radiation dominated accretion onto the magnetic poles of neutron stars. The upper limit to the photon luminosity depends upon magnetic confinement, not upon the dragging of photons into the star. Numerical solutions show the plasma forms large scale ''photon bubbles.'' I suggest the percolative loss of radiation controls the pressure and therefore the limits of magnetic confinement. Loss of magnetic confinement through resistive interchange instability is suggested as a means of generating TeV to PeV voltage drops along the magnetic field. 34 refs., 6 figs., 1 tab.

  9. Chondrule Accretion with a Growing Protoplanet

    NASA Astrophysics Data System (ADS)

    Matsumoto, Yuji; Oshino, Shoichi; Hasegawa, Yasuhiro; Wakita, Shigeru

    2017-03-01

    Chondrules are primitive materials in the solar system. They were formed in about the first 3 Myr of the solar system’s history. This timescale is longer than that of Mars formation, and it is conceivable that protoplanets, planetesimals, and chondrules might have existed simultaneously in the solar nebula. Due to protoplanets’ perturbation on the planetesimal dynamics and chondrule accretion on them, all the formed chondrules are unlikely to be accreted by the planetesimals. We investigate the amount of chondrules accreted by planetesimals in such a condition. We assume that a protoplanet is in oligarchic growth, and we perform analytical calculations of chondrule accretion by both a protoplanet and planetesimals. Through the oligarchic growth stage, planetesimals accrete about half of the formed chondrules. The smallest planetesimals get the largest amount of chondrules, compared with the amount accreted by more massive planetesimals. We perform a parameter study and find that this fraction is not greatly changed for a wide range of parameter sets.

  10. Plans and Preliminary Results of Fundamental Studies of Ice Crystal Icing Physics in the NASA Propulsion Systems Laboratory

    NASA Technical Reports Server (NTRS)

    Struk, Peter; Tsao, Jen-Ching; Bartkus, Tadas

    2016-01-01

    This presentation accompanies the paper titled Plans and Preliminary Results of Fundamental Studies of Ice Crystal Icing Physics in the NASA Propulsion Systems Laboratory. NASA is evaluating whether PSL, in addition to full-engine and motor-driven-rig tests, can be used for more fundamental ice-accretion studies that simulate the different mixed-phase icing conditions along the core flow passage of a turbo-fan engine compressor. The data from such fundamental accretion tests will be used to help develop and validate models of the accretion process. This presentation (and accompanying paper) presents data from some preliminary testing performed in May 2015 which examined how a mixed-phase cloud could be generated at PSL using evaporative cooling in a warmer-than-freezing environment.

  11. Detection of the Impact of Ice Crystal Accretion in an Aircraft Engine Compression System During Dynamic Operation

    NASA Technical Reports Server (NTRS)

    May, Ryan D.; Simon, Donald L.; Guo, Ten-Huei

    2014-01-01

    The accretion of ice in the compression system of commercial gas turbine engines operating in high ice water content conditions is a safety issue being studied by the aviation community. While most of the research focuses on the underlying physics of ice accretion and the meteorological conditions in which accretion can occur, a systems-level perspective on the topic lends itself to potential near-term operational improvements. Here a detection algorithm is developed which has the capability to detect the impact of ice accretion in the Low Pressure Compressor of an aircraft engine during steady flight as well as during changes in altitude. Unfortunately, the algorithm as implemented was not able to distinguish throttle changes from ice accretion and thus more work remains to be done.

  12. Small Seed Black Hole Growth in Various Accretion Regimes

    NASA Astrophysics Data System (ADS)

    Gerling-Dunsmore, Hannalore J.; Hopkins, Philip F.

    2016-03-01

    Observational evidence indicates a population of super massive black holes (SMBHs) (~109 -1010M⊙) formed within 1 Gyr after the Big Bang. One proposed means of SMBH formation is accretion onto small seed black holes (BHs) (~ 100M⊙). However, the existence of SMBHs within 1 Gyr requires rapid growth, but conventional models of accretion fail to grow the seed BHs quickly enough. Super Eddington accretion (Ṁ >ṀEddington) may aid in improving growth efficiency. We study small seed BH growth via accretion in 3D, using the magneto-hydrodynamics+gravity code GIZMO. In particular, we consider a BH in a high density turbulent star-forming cloud, and ask whether or not the BH can capture sufficient gas to grow rapidly. We consider both Eddington-limited and super Eddington regimes, and resolve physics on scales from 0.1 pc to 1 kpc while including detailed models for stellar feedback physics, including stellar winds, supernovae, radiation pressure, and photo-ionization. We present results on the viability of different small seed BHs growing into SMBH candidates.

  13. NUMERICAL SIMULATIONS OF OPTICALLY THICK ACCRETION ONTO A BLACK HOLE. I. SPHERICAL CASE

    SciTech Connect

    Fragile, P. Chris; Gillespie, Anna; Monahan, Timothy; Rodriguez, Marco; Anninos, Peter

    2012-08-01

    Modeling the radiation generated by accreting matter is an important step toward realistic simulations of black hole accretion disks, especially at high accretion rates. To this end, we have recently added radiation transport to the existing general relativistic magnetohydrodynamic code, Cosmos++. However, before attempting to model radiative accretion disks, we have tested the new code using a series of shock tube and Bondi (spherical inflow) problems. The four radiative shock tube tests, first presented by Farris et al., have known analytic solutions, allowing us to calculate errors and convergence rates for our code. The Bondi problem only has an analytic solution when radiative processes are ignored, but it is pertinent because it is closer to the physics we ultimately want to study. In our simulations, we include Thomson scattering and thermal bremsstrahlung in the opacity, focusing exclusively on the super-Eddington regime. Unlike accretion onto bodies with solid surfaces, super-Eddington accretion onto black holes does not produce super-Eddington luminosity. In our examples, despite accreting at up to 300 times the Eddington rate, our measured luminosity is always several orders of magnitude below Eddington.

  14. Gas dynamics for accretion disk simulations

    NASA Technical Reports Server (NTRS)

    Whitehurst, R.

    1994-01-01

    The behavior of accretion disks can largely be understood in terms of the basic physical processes of mass, energy, and momentum conservation. Despite this, detailed modeling of these systems using modern computational techniques is challenging and controversial. Disturbing differences exist between methods used widely in astrophysics, namely Eulerian finite-difference techniques and particle codes such as SPH. Therefore neither technique is fully satisfactory for accretion disk simulations. This paper describes a new fully Lagrangian method designed to resolve these difficulties.

  15. Evolution of Pre-Main Sequence Accretion Disks

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2000-01-01

    The aim of this project was to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, pre-main sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we: (1) Developed detailed calculations of disk structure to study physical conditions and investigate the observational effects of grain growth in T Tauri disks; (2) Studied the dusty emission and accretion rates in older disk systems, with ages closer to the expected epoch of (giant) planet formation at 3-10 Myr, and (3) Began a project to develop much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution.

  16. Accretion of a Small Continental Fragment to a Larger Continental Plate: Mesozoic Ecuador as a Case-Study Area

    NASA Astrophysics Data System (ADS)

    Massonne, H.

    2013-05-01

    Only a few regions on Earth are appropriate to study processes that have happened in deeper crustal levels during the accretion of a microplate to a larger continental plate. Ecuador is one of these regions where in middle Mesozoic times a small continental fragment collided with the South-American plate. Along the suture between both plates, which occurs close to the present volcanic belt of Ecuador, high-pressure (HP) metamorphic rocks developed. These rocks, which are metapelites, metabasites, and metagranitoids, record processes during the microcontinent-continent collision (Massonne and Toulkeridis, 2012, Int. Geol. Rev. 54). The pressures, determined for the HP rocks, were as high as 14 kbar at temperatures somewhat above 500°C. The HP stage was followed by slight heating at the early exhumation. Peak temperatures up to 560°C were reached at pressures ≥10 kbar. This HP metamorphism was caused by the collision of the microplate with the South-American plate resulting in crustal thickening. The ascent of the HP rocks occurred in an exhumation channel. Before the collision, an oceanic basin existed between these plates. Probably, it was narrow as eclogite bodies are lacking in the N-S trending HP belt of Ecuador. Such bodies, especially if the eclogites had experienced pressures in excess of 20 kbar, are markers of a collision of major continental plates in Phanerozoic times with originally extended oceanic basins between these plates. In a more global context, the narrow ocean between the microplate and the South American continent is assumed to have been the westernmost portion of the Neo-Tethys which had extended to completely separate the two major fragments of former Pangaea before the opening of the southern Atlantic Ocean. This opening caused the closure of the narrow Neo-Tethys segment between the colliding microplate and the South American plate. This segment was bordered by E-W trending transform faults. A fault system (La Palma - El Guayabo fault

  17. Theoretical Researches on Hot Accretion Flows around Black Holes

    NASA Astrophysics Data System (ADS)

    Xie, F. G.

    2010-10-01

    Black hole accretion systems, which are widely believed to be harbored in the central regions of active galactic nuclei (AGNs), low-luminosity AGNs (LLAGNs) as well as some X-ray binaries (XRBs), are the key physical processes to understand their observational phenomena, like spectral energy distribution, radiative variability, etc. In this thesis, we focus on the hot accretion flow models, including advection-dominated accretion flow (ADAF) and luminous hot accretion flow (LHAF). These models are the foundations to explain the observations of LLAGNs and XRBs in hard state. In Chapter 1, a detailed description of the background is presented. First the astrophysical black holes and the systems in which they reside are discussed. Then, an extensive discussion on the accretion process is presented. The basic concepts, 4 well-known accretion models and the mechanism of the transition between ADAF and standard thin disk are focused on. After this, we further describe the properties of ADAF - the basic model of this thesis, e.g., the dynamics, the radiative processes and several recent progresses: outflow, direct turbulent heating to the electrons, as well as LHAF at relatively high accretion rate. In Chapter 2, the influences of outflow on the dynamics of inflow are explored. As indicated through observations (e.g., towards the Galactic center), theoretical researches and (magneto-) hydrodynamical simulations, outflow is a common phenomenon in accretion systems. However, most researches in this field, especially when aiming at explaining/fitting observational data, incline to only include the mass loss due to the existence of outflow, while all the other effects like the angular momentum transport are totally neglected. This obviously conflicts with the results from simulations. Since outflow is not fully understood currently, we here parameterize its properties. Our results are shown as follows: (1) under current status of observations and theories, it is acceptable to

  18. The Importance of Rotational Time-scales in Accretion Variability

    NASA Astrophysics Data System (ADS)

    Costigan, Gráinne; Vink, Joirck; Scholz, Aleks; Testi, Leonardo; Ray, Tom

    2013-07-01

    For the first few million years, one of the dominant sources of emission from a low mass young stellar object is from accretion. This process regulates the flow of material and angular moments from the surroundings to the central object, and is thought to play an important role in the definition of the long term stellar properties. Variability is a well documented attribute of accretion, and has been observed on time-scales of from days to years. However, where these variations come from is not clear. Th current model for accretion is magnetospheric accretion, where the stellar magnetic field truncates the disc, allowing the matter to flow from the disc onto the surface of the star. This model allows for variations in the accretion rate to come from many different sources, such as the magnetic field, the circumstellar disc and the interaction of the different parts of the system. We have been studying unbiased samples of accretors in order to identify the dominant time-scales and typical magnitudes of variations. In this way different sources of variations can be excluded and any missing physics in these systems identified. Through our previous work with the Long-term Accretion Monitoring Program (LAMP), we found 10 accretors in the ChaI region, whose variability is dominated by short term variations of 2 weeks. This was the shortest time period between spectroscopic observations which spanned 15 months, and rules out large scale processes in the disk as origins of this variability. On the basis of this study we have gone further to study the accretion signature H-alpha, over the time-scales of minutes and days in a set of Herbig Ae and T Tauri stars. Using the same methods as we used in LAMP we found the dominant time-scales of variations to be days. These samples both point towards rotation period of these objects as being an important time-scale for accretion variations. This allows us to indicate which are the most likely sources of these variations.

  19. Evolution of Pre-Main Sequence Accretion Disks

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2002-01-01

    The aim of this project is to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, pre-main sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we plan to: (1) Develop much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution; (2) Study the dusty emission and accretion rates in these systems, with ages closer to the expected epoch of (giant) planet formation at 3-10 Myr; and (3) Develop detailed model disk structures consistent with observations to infer physical conditions in protoplanetary disks and to constrain possible grain growth as the first stage of planetesimal formation.

  20. Connecting High School Physics Experiences, Outcome Expectations, Physics Identity, and Physics Career Choice: A Gender Study

    ERIC Educational Resources Information Center

    Hazari, Zahra; Sonnert, Gerhard; Sadler, Philip M.; Shanahan, Marie-Claire

    2010-01-01

    This study explores how students' physics identities are shaped by their experiences in high school physics classes and by their career outcome expectations. The theoretical framework focuses on physics identity and includes the dimensions of student performance, competence, recognition by others, and interest. Drawing data from the Persistence…

  1. Holocene reef accretion: southwest Molokai, Hawaii, U.S.A.

    USGS Publications Warehouse

    Engels, Mary S.; Fletcher, Charles H.; Field, Michael E.; Storlazzi, Curt D.; Grossman, Eric E.; Rooney, John J.B.; Conger, Christopher L.; Glenn, Craig

    2004-01-01

    Two reef systems off south Molokai, Hale O Lono and Hikauhi (separated by only 10 km), show strong and fundamental differences in modern ecosystem structure and Holocene accretion history that reflect the influence of wave-induced near-bed shear stresses on reef development in Hawaii. Both sites are exposed to similar impacts from south, Kona, and trade-wind swell. However, the Hale O Lono site is exposed to north swell and the Hikuahi site is not. As a result, the reef at Hale O Lono records no late Holocene net accretion while the reef at Hikauhi records consistent and robust accretion over late Holocene time. Analysis and dating of 24 cores from Hale O Lono and Hikauhi reveal the presence of five major lithofacies that reflect paleo-environmental conditions. In order of decreasing depositional energy they are: (1) coral-algal bindstone; (2) mixed skeletal rudstone; (3) massive coral framestone; (4) unconsolidated floatstone; and (5) branching coral framestone-bafflestone. At Hale O Lono, 10 cores document a backstepping reef ranging from ∼ 8,100 cal yr BP (offshore) to ∼ 4,800 cal yr BP (nearshore). A depauperate community of modern coral diminishes shoreward and seaward of ∼ 15 m depth due to wave energy, disrupted recruitment activities, and physical abrasion. Evidence suggests a change from conditions conducive to accretion during the early Holocene to conditions detrimental to accretion in the late Holocene. Reef structure at Hikauhi, reconstructed from 14 cores, reveals a thick, rapidly accreting and young reef (maximum age ∼ 900 cal yr BP). Living coral cover on this reef increases seaward with distance from the reef crest but terminates at a depth of ∼ 20 m where the reef ends in a large sand field. The primary limitation on vertical reef growth is accommodation space under wave base, not recruitment activities or energy conditions. Interpretations of cored lithofacies suggest that modern reef growth on the southwest corner of Molokai, and by

  2. Basic Studies in Plasma Physics

    DTIC Science & Technology

    2013-01-31

    External Stresses, (with C. Laberge and P. Fratzl), Phys. Rev. Lett., 75:4448-4451, 1995. [15] Shock Profiles for the Asymmetric Simple Exclusoin...Postdoctoral Fellow, Yale University, 1956-57 POSITIONS: Stevens Institute of Technology, Assistant Professor of Physics, 1957-59 Belfer Graduate

  3. Pulsed accretion in a variable protostar

    NASA Astrophysics Data System (ADS)

    Muzerolle, James; Furlan, Elise; Flaherty, Kevin; Balog, Zoltan; Gutermuth, Robert

    2013-01-01

    Periodic increases in luminosity arising from variable accretion rates have been predicted for some pre-main-sequence close binary stars as they grow from circumbinary disks. The phenomenon is known as pulsed accretion and can affect the orbital evolution and mass distribution of young binaries, as well as the potential for planet formation. Accretion variability is a common feature of young stars, with a large range of amplitudes and timescales as measured from multi-epoch observations at optical and infrared wavelengths. Periodic variations consistent with pulsed accretion have been seen in only a few young binaries via optical accretion tracers, albeit intermittently with accretion luminosity variations ranging from zero to 50 per cent from orbit to orbit. Here we report that the infrared luminosity of a young protostar (of age about 105 years) increases by a factor of ten in roughly one week every 25.34 days. We attribute this to pulsed accretion associated with an unseen binary companion. The strength and regularity of this accretion signal is surprising; it may be related to the very young age of the system, which is a factor of ten younger than the other pulsed accretors previously studied.

  4. Pulsed accretion in a variable protostar.

    PubMed

    Muzerolle, James; Furlan, Elise; Flaherty, Kevin; Balog, Zoltan; Gutermuth, Robert

    2013-01-17

    Periodic increases in luminosity arising from variable accretion rates have been predicted for some pre-main-sequence close binary stars as they grow from circumbinary disks. The phenomenon is known as pulsed accretion and can affect the orbital evolution and mass distribution of young binaries, as well as the potential for planet formation. Accretion variability is a common feature of young stars, with a large range of amplitudes and timescales as measured from multi-epoch observations at optical and infrared wavelengths. Periodic variations consistent with pulsed accretion have been seen in only a few young binaries via optical accretion tracers, albeit intermittently with accretion luminosity variations ranging from zero to 50 per cent from orbit to orbit. Here we report that the infrared luminosity of a young protostar (of age about 10(5) years) increases by a factor of ten in roughly one week every 25.34 days. We attribute this to pulsed accretion associated with an unseen binary companion. The strength and regularity of this accretion signal is surprising; it may be related to the very young age of the system, which is a factor of ten younger than the other pulsed accretors previously studied.

  5. Effects of ice accretions on aircraft aerodynamics

    NASA Astrophysics Data System (ADS)

    Lynch, Frank T.; Khodadoust, Abdollah

    2001-11-01

    This article is a systematic and comprehensive review, correlation, and assessment of test results available in the public domain which address the aerodynamic performance and control degradations caused by various types of ice accretions on the lifting surfaces of fixed wing aircraft. To help put the various test results in perspective, overviews are provided first of the important factors and limitations involved in computational and experimental icing simulation techniques, as well as key aerodynamic testing simulation variables and governing flow physics issues. Following these are the actual reviews, assessments, and correlations of a large number of experimental measurements of various forms of mostly simulated in-flight and ground ice accretions, augmented where appropriate by similar measurements for other analogous forms of surface contamination and/or disruptions. In-flight icing categories reviewed include the initial and inter-cycle ice accretions inherent in the use of de-icing systems which are of particular concern because of widespread misconceptions about the thickness of such accretions which can be allowed before any serious consequences occur, and the runback/ridge ice accretions typically associated with larger-than-normal water droplet encounters which are of major concern because of the possible potential for catastrophic reductions in aerodynamic effectiveness. The other in-flight ice accretion category considered includes the more familiar large rime and glaze ice accretions, including ice shapes with rather grotesque features, where the concern is that, in spite of all the research conducted to date, the upper limit of penalties possible has probably not been defined. Lastly, the effects of various possible ground frost/ice accretions are considered. The concern with some of these is that for some types of configurations, all of the normally available operating margins to stall at takeoff may be erased if these accretions are not

  6. Diskoseismology: Probing relativistic accretion disks

    NASA Astrophysics Data System (ADS)

    Nowak, Michael Allen

    1992-08-01

    Helioseismology has provided a wealth of information about the structure of the solar atmosphere. Little is known, however, about the structure of accretion disks that are thought to exist around black holes and neutron stars. In this thesis we present calculations of modes that are trapped in thin Keplerian accretion disks. We hope to use observations of thes modes to elucidate the structure of the inner relativistic regions of accretion disks. Our calculations assume that the thin disk is terminated by an innermost stable orbit, as would occur around a slowly rotating black hole or weakly magnetized compact neutron star. The dominant relativistic effects, which allow modes to be trapped within the inner region of the disk, are approximated via a modified Newtonian potential. Using the Lagrangian formulation of Friedman and Schutz, we develop a general formalism for investigating the adiabatic oscillations of arbitrary unperturbed disk models. First we consider the special case of acoustic waves in disks with isothermal atmospheres. Next we describe the Lagrangian perturbation vectors in terms of the derivatives of a scalar potential, as has been done by Ipser and Lindblom. Using this potential, we derive a single partial differential equation governing the oscillations of a disk. The eigenfunctions and eigenfrequencies of a variety of disk models are found to fall into two main classes which are analogous to the p-modes and g-modes in the sun. Specifically we use the potential formalism to compute the g-modes for disks with isothermal atmospheres. Physical arguments show that both the p-modes and g-modes belong to the same family of modes as the p-modes and g-modes in the sun, just viewed in a different parameter regime. With the aid of the Lagrangian formalism we consider possible growth or damping mechanisms and compute the (assumed) relatively small rates of growth or damping of the modes. Specifically, we consider gravitational radiation reaction and

  7. Some topics in the magnetohydrodynamics of accreting magnetic compact objects

    NASA Technical Reports Server (NTRS)

    Aly, J. J.

    1986-01-01

    Magnetic compact objects (neutron stars or white dwarfs) are currently thought to be present in many accreting systems that are releasing large amounts of energy. The magnetic field of the compact star may interact strongly with the accretion flow and play an essential role in the physics of these systems. Some magnetohydrodynamic (MHD) problems that are likely to be relevant in building up self-consistent models of the interaction between the accreting plasma and the star's magnetosphere are addressed in this series of lectures. The basic principles of MHD are first introduced and some important MHD mechanisms (Rayleigh-Taylor and Kelvin-Helmholtz instabilities; reconnection) are discussed, with particular reference to their role in allowing the infalling matter to penetrate the magnetosphere and mix with the field. The structure of a force-free magnetosphere and the possibility of quasistatic momentum and energy transfer between regions linked by field-aligned currents are then studied in some detail. Finally, the structure of axisymmetric accretion flows onto magnetic compact objects is considered.

  8. ON THE STRUCTURE OF ACCRETION DISKS WITH OUTFLOWS

    SciTech Connect

    Jiao Chengliang; Wu Xuebing E-mail: wuxb@pku.edu.cn

    2011-06-01

    To study the outflows from accretion disks, we solve the set of hydrodynamic equations for accretion disks in spherical coordinates (r{theta}{phi}) to obtain the explicit structure along the {theta}-direction. Using self-similar assumptions in the radial direction, we change the equations to a set of ordinary differential equations about the {theta}-coordinate, which are then solved with symmetrical boundary conditions in the equatorial plane; the velocity field is then obtained. The {alpha} viscosity prescription is applied and an advective factor f is used to simplify the energy equation. The results display thinner, quasi-Keplerian disks for Shakura-Sunyaev disks; thicker, sub-Keplerian disks for advection-dominated accretion flows; and slim disks which are consistent with previous popular analytical models. However, an inflow region and an outflow region always exist, except when the viscosity parameter {alpha} is too large, which supports the results of some recent numerical simulation works. Our results indicate that the outflows should be common in various accretion disks and may be stronger in slim disks, where both advection and radiation pressure are dominant. We also present the structure's dependence on the input parameters and discuss their physical meanings. The caveats of this work and possible improvements for the future are discussed.

  9. Wind-driven Accretion in Transitional Protostellar Disks

    NASA Astrophysics Data System (ADS)

    Wang, Lile; Goodman, Jeremy J.

    2017-01-01

    Transitional protostellar disks have inner cavities that are heavily depleted in dust and gas, yet most of them show signs of ongoing accretion, often at rates comparable to full disks. We show that recent constraints on the gas surface density in a few well-studied disk cavities suggest that the accretion speed is at least transsonic. We propose that this is the natural result of accretion driven by magnetized winds. Typical physical conditions of the gas inside these cavities are estimated for plausible X-ray and FUV radiation fields. The gas near the midplane is molecular and predominantly neutral, with a dimensionless ambipolar parameter in the right general range for wind solutions of the type developed by Königl, Wardle, and others. That is to say, the density of ions and electrons is sufficient for moderately good coupling to the magnetic field, but it is not so good that the magnetic flux needs to be dragged inward by the accreting neutrals.

  10. Can Oregon marshes keep up with the rising tide? A study of short and long term marsh accretion - CERF 2015

    EPA Science Inventory

    More frequent inundation of Oregon coastal marshlands associated with rising sea level threatens these important and diverse habitats. Accretion rates determined by the marker horizon method and longer term peak Cs137 detection in nine marsh systems from Coquille to Tillamook we...

  11. UV variability and accretion dynamics in the young open cluster NGC 2264

    NASA Astrophysics Data System (ADS)

    Venuti, L.; Bouvier, J.; Irwin, J.; Stauffer, J. R.; Hillenbrand, L. A.; Rebull, L. M.; Cody, A. M.; Alencar, S. H. P.; Micela, G.; Flaccomio, E.; Peres, G.

    2015-09-01

    Context. Photometric variability is a distinctive feature of young stellar objects; exploring variability signatures at different wavelengths provides insight into the physical processes at work in these sources. Aims: We explore the variability signatures at ultraviolet (UV) and optical wavelengths for several hundred accreting and non-accreting members of the star-forming region NGC 2264 (~3 Myr). Methods: We performed simultaneous monitoring of u- and r-band variability for the cluster population with CFHT/MegaCam. The survey extended over two full weeks, with several flux measurements per observing night. A sample of about 750 young stars is probed in our study, homogeneously calibrated and reduced, with internally consistently derived stellar parameters. Objects span the mass range 0.1-2 M⊙; about 40% of them show evidence for active accretion based on various diagnostics (Hα, UV, and IR excesses). Results: Statistically distinct variability properties are observed for accreting and non-accreting cluster members. The accretors exhibit a significantly higher level of variability than the non-accretors, in the optical and especially in the UV. The amount of u-band variability is found to correlate statistically with the median amount of UV excess in disk-bearing objects, which suggests that mass accretion and star-disk interaction are the main sources of variability in the u band. Spot models are applied to account for the amplitudes of variability of accreting and non-accreting members, which yields different results for each group. Cool magnetic spots, several hundred degrees colder than the stellar photosphere and covering from 5 to 30% of the stellar surface, appear to be the leading factor of variability for the non-accreting stars. In contrast, accretion spots with a temperature a few thousand degrees higher than the photospheric temperature and that extend over a few percent of the stellar surface best reproduce the variability of accreting objects

  12. An Approach to Detect and Mitigate Ice Particle Accretion in Aircraft Engine Compression Systems

    NASA Technical Reports Server (NTRS)

    May, Ryan D.; Guo, Ten-Huei; Simon, Donald L.

    2013-01-01

    The accretion of ice in the compression system of commercial gas turbine engines operating in high ice water content conditions is a safety issue being studied by the aviation sector. While most of the research focuses on the underlying physics of ice accretion and the meteorological conditions in which accretion can occur, a systems-level perspective on the topic lends itself to potential near-term operational improvements. This work focuses on developing an accurate and reliable algorithm for detecting the accretion of ice in the low pressure compressor of a generic 40,000 lbf thrust class engine. The algorithm uses only the two shaft speed sensors and works regardless of engine age, operating condition, and power level. In a 10,000-case Monte Carlo simulation, the detection approach was found to have excellent capability at determining ice accretion from sensor noise with detection occurring when ice blocks an average of 6.8 percent of the low pressure compressor area. Finally, an initial study highlights a potential mitigation strategy that uses the existing engine actuators to raise the temperature in the low pressure compressor in an effort to reduce the rate at which ice accretes.

  13. An Approach to Detect and Mitigate Ice Particle Accretion in Aircraft Engine Compression Systems

    NASA Technical Reports Server (NTRS)

    May, Ryan D.; Guo, Ten-Huei; Simon, Donald L.

    2013-01-01

    The accretion of ice in the compression system of commercial gas turbine engines operating in high ice water content conditions is a safety issue being studied by the aviation sector. While most of the research focuses on the underlying physics of ice accretion and the meteorological conditions in which accretion can occur, a systems-level perspective on the topic lends itself to potential near-term operational improvements. This work focuses on developing an accurate and reliable algorithm for detecting the accretion of ice in the low pressure compressor of a generic 40,000 lbf thrust class engine. The algorithm uses only the two shaft speed sensors and works regardless of engine age, operating condition, and power level. In a 10,000-case Monte Carlo simulation, the detection approach was found to have excellent capability at determining ice accretion from sensor noise with detection occurring when ice blocks an average of 6.8% of the low pressure compressor area. Finally, an initial study highlights a potential mitigation strategy that uses the existing engine actuators to raise the temperature in the low pressure compressor in an effort to reduce the rate at which ice accretes.

  14. An Ultraviolet Study of Non-periodic Variability in Accreting Pre-Main Sequence Stars: UXors

    NASA Astrophysics Data System (ADS)

    Eaton, N. L.; Herbst, W.

    1994-05-01

    Many earlier type (K0 or hotter) pre-main sequence stars are known to occasionally and irregularly fade by as much as 2-3 magnitudes in V. Such excursions occur on timescales of ten to forty days. They include both G-type T Tauri stars and Herbig Ae/Be stars. We propose UX Ori as a prototype for this class of variable stars and refer to them as UXors. We have used archival IUE spectra and a catalog of UBVRI photometry to study the variations of 5 such objects, namely: RY Lup, RY Tau, CO Ori, BF Ori, and UX Ori. The leading hypothesis for explaining their behavior is variable circumstellar obscuration. Relationships between UV spectral line fluxes and equivalent widths and V magnitude are found and displayed. Some shell features in UX Ori and BF Ori switch from absorption to emission during the minima. The equivalent width of these (emission) features [FeII(1,62,63) and MgII(1)] increases as the star fades. Spectral energy distributions (SEDs) covering the interval of 1200 to 8900 angstroms were constructed for several stars at different V magnitude light levels. A strong depression in the SED around 2200 angstroms, caused by iron lines is quite noticeable in UX Ori and BF Ori when the stars are bright. The source and location of the variable obscuring material is discussed.

  15. An Ultraviolet and Optical Study of Accreting Pre-Main-Sequence Stars: Uxors

    NASA Astrophysics Data System (ADS)

    Eaton, Nancy L.; Herbst, William

    1995-11-01

    UX Ori stars (UXors) are pre-main-sequence stars of both the Herbig Ae/Be and T Tauri type which show aperiodic eclipse-like minima. Their variations have been attributed to occultations by circumstellar material. We use archival IUE spectra and a catalog of UBVRI photometry to study the variations of five such objects, namely, RY Lup, RY Tau, CO Ori, BF Ori, and UX Ori. Relationships between UV spectral line fluxes and equivalent widths and V magnitude are found and displayed. Some shell features in UX Ori and BF Ori switch from absorption to emission during the minima. The equivalent widths of the emission features increase as the star fades. Spectral energy distributions (SEDs) covering the interval of 1200-8900 Å were constructed for several stars at different V magnitude light levels. A strong depression in the SED around 2400 Å, caused primarily by iron absorption lines (the "iron curtain") is quite noticeable in UX Ori and BF Ori when the stars are bright, but is diminished or absent when faint. The data are discussed in the context of the variable circumstellar obscuration hypothesis and provide some additional support for it.

  16. Studies of Accreting Neutron Stars with RXTE Cycle 4 Observations: III: TOO Observations of Atoll Sources

    NASA Technical Reports Server (NTRS)

    Paciesas, William S.

    2002-01-01

    NASA Grant NAG 5-9244 provided funds for the research projects 'ASM-Triggered TOO Observations of Kilohertz Oscillations in Five Atoll Sources' and 'Further Measurements of the Kilohertz Oscillations in 4U 1705-44' approved under the Rossi X-ray Timing Explorer (RXTE) Guest Observer Program Cycle 4 and funded under the 1999 NASA Astrophysics Data Program. The principal investigator of the observing time proposals was Dr. E. C. Ford (U. of Amsterdam). The grant was funded for one year beginning 3/15/2000. The original ADP proposal was submitted by Prof. Jan van Paradijs, who passed away in 1999 before the funds were distributed. Prof. Wilham S. Padesas administered the grant during the period of performance. In spite of a wealth of observational data on the kHz QPO in low-mass X-ray binaries (LMXBs), the interpretation of this phenomenon is currently uncertain because the pairs of kHz QPO peaks and the oscillations seen in some Type I X-ray bursts are almost, but not quite, connected by a simple beat frequency relation. Further systematic studies of systems with known QPOs are required in order to better understand the phenomenon. The proposals were intended to contribute to a solution to this confusion by observing the sources as they vary over a wide range of X-ray flux. RXTE target-of-opportunity observations of six transient atoll sources, 4U 0614+09, KS 1732-260, Ser X-1, 4U 1702-42, 4U 1820-30 and 4U 1705-44 were to be performed at various flux levels based on ASM measurements.

  17. Accretion disks around black holes

    NASA Technical Reports Server (NTRS)

    Abramowicz, M. A.

    1994-01-01

    The physics of accretion flow very close to a black hole is dominated by several general relativistic effects. It cannot be described by the standard Shakura Sunyaev model or by its relativistic version developed by Novikov and Thome. The most important of these effects is a dynamical mass loss from the inner edge of the disk (Roche lobe overflow). The relativistic Roche lobe overflow induces a strong advective cooling, which is sufficient to stabilize local, axially symmetric thermal and viscous modes. It also stabilizes the non-axially-symmetric global modes discovered by Papaloizou and Pringle. The Roche lobe overflow, however, destabilizes sufficiently self-gravitating accretion disks with respect to a catastrophic runaway of mass due to minute changes of the gravitational field induced by the changes in the mass and angular momentum of the central black hole. One of the two acoustic modes may become trapped near the inner edge of the disk. All these effects, absent in the standard model, have dramatic implications for time-dependent behavior of the accretion disks around black holes.

  18. Investigation of surface water behavior during glaze ice accretion

    NASA Technical Reports Server (NTRS)

    Hansman, R. John, Jr.; Turnock, Stephen R.

    1988-01-01

    Microvideo observations of glaze ice accretions on 1-in-diameter cylinders in a closed-loop refrigerated wind tunnel were obtained to study factors controlling the behavior of unfrozen surface water during glaze ice accretion. Three zones of surface water behavior were noted, each with a characteristic roughness. The effect of substrate thermal and roughness properties on ice accretions was also studied. The contact angle and hysteresis were found to increase sharply at temperatures just below 0 C, explaining the high resistance to motion of water beads observed on accreting glaze ice surfaces. Based on the results, a simple multizone modification to the current glaze ice accretion model is proposed.

  19. Fueling galaxy growth through gas accretion in cosmological simulations

    NASA Astrophysics Data System (ADS)

    Nelson, Dylan Rubaloff

    Despite significant advances in the numerical modeling of galaxy formation and evolution, it is clear that a satisfactory theoretical picture of how galaxies acquire their baryons across cosmic time remains elusive. In this thesis we present a computational study which seeks to address the question of how galaxies get their gas. We make use of new, more robust simulation techniques and describe the first investigations of cosmological gas accretion using a moving-mesh approach for solving the equations of continuum hydrodynamics. We focus first on a re-examination of past theoretical conclusions as to the relative importance of different accretion modes for galaxy growth. We study the rates and nature of gas accretion at z=2, comparing our new simulations run with the Arepo code to otherwise identical realizations run with the smoothed particle hydrodynamics code Gadget. We find significant physical differences in the thermodynamic history of accreted gas, explained in terms of numerical inaccuracies in SPH. In contrast to previous results, we conclude that hot mode accretion generally dominates galaxy growth, while cold gas filaments experience increased heating and disruption. Next, we consider the impact of feedback on our results, including models for galactic-scale outflows driven by stars as well as the energy released from supermassive black holes. We find that feedback strongly suppresses the inflow of "smooth" mode gas at all redshifts, regardless of its temperature history. Although the geometry of accretion at the virial radius is largely unmodified, strong galactic-fountain recycling motions dominate the inner halo. We measure a shift in the characteristic timescale of accretion, and discuss implications for semi-analytical models of hot halo gas cooling. To overcome the resolution limitations of cosmological volumes, we simulate a suite of eight individual 1012 solar mass halos down to z=2. We quantify the thermal and dynamical structure of the gas in

  20. Dust Coagulation in Protoplanetary Accretion Disks

    NASA Technical Reports Server (NTRS)

    Schmitt, W.; Henning, Th.; Mucha, R.

    1996-01-01

    The time evolution of dust particles in circumstellar disk-like structures around protostars and young stellar objects is discussed. In particular, we consider the coagulation of grains due to collisional aggregation. The coagulation of the particles is calculated by solving numerically the non-linear Smoluchowski equation. The different physical processes leading to relative velocities between the grains are investigated. The relative velocities may be induced by Brownian motion, turbulence and drift motion. Starting from different regimes which can be identified during the grain growth we also discuss the evolution of dust opacities. These opacities are important for both the derivation of the circumstellar dust mass from submillimeter/millimeter continuum observations and the dynamical behavior of the disks. We present results of our numerical studies of the coagulation of dust grains in a turbulent protoplanetary accretion disk described by a time-dependent one-dimensional (radial) alpha-model. For several periods and disk radii, mass distributions of coagulated grains have been calculated. From these mass spectra, we determined the corresponding Rosseland mean dust opacities. The influence of grain opacity changes due to dust coagulation on the dynamical evolution of a protostellar disk is considered. Significant changes in the thermal structure of the protoplanetary nebula are observed. A 'gap' in the accretion disk forms at the very frontier of the coagulation, i.e., behind the sublimation boundary in the region between 1 and 5 AU.

  1. Electron thermodynamics in GRMHD simulations of low-luminosity black hole accretion

    NASA Astrophysics Data System (ADS)

    Ressler, S. M.; Tchekhovskoy, A.; Quataert, E.; Chandra, M.; Gammie, C. F.

    2015-12-01

    Simple assumptions made regarding electron thermodynamics often limit the extent to which general relativistic magnetohydrodynamic (GRMHD) simulations can be applied to observations of low-luminosity accreting black holes. We present, implement, and test a model that self-consistently evolves an entropy equation for the electrons and takes into account the effects of spatially varying electron heating and relativistic anisotropic thermal conduction along magnetic field lines. We neglect the backreaction of electron pressure on the dynamics of the accretion flow. Our model is appropriate for systems accreting at ≪10-5 of the Eddington accretion rate, so radiative cooling by electrons can be neglected. It can be extended to higher accretion rates in the future by including electron cooling and proton-electron Coulomb collisions. We present a suite of tests showing that our method recovers the correct solution for electron heating under a range of circumstances, including strong shocks and driven turbulence. Our initial applications to axisymmetric simulations of accreting black holes show that (1) physically motivated electron heating rates that depend on the local magnetic field strength yield electron temperature distributions significantly different from the constant electron-to-proton temperature ratios assumed in previous work, with higher electron temperatures concentrated in the coronal region between the disc and the jet; (2) electron thermal conduction significantly modifies the electron temperature in the inner regions of black hole accretion flows if the effective electron mean free path is larger than the local scaleheight of the disc (at least for the initial conditions and magnetic field configurations we study). The methods developed in this work are important for producing more realistic predictions for the emission from accreting black holes such as Sagittarius A* and M87; these applications will be explored in future work.

  2. Studies in theoretical particle physics

    SciTech Connect

    Kaplan, D.B.

    1991-07-01

    This proposal focuses on research on three distinct areas of particle physics: (1) Nonperturbative QCD. I tend to continue work on analytic modelling of nonperturbative effects in the strong interactions. I have been investigating the theoretical connection between the nonrelativistic quark model and QCD. The primary motivation has been to understand the experimental observation of nonzero matrix elements involving current strange quarks in ordinary matter -- which in the quark model has no strange quark component. This has led to my present work on understanding constituent (quark model) quarks as collective excitations of QCD degrees of freedom. (2) Weak Scale Baryogenesis. A continuation of work on baryogenesis in the early universe from weak interactions. In particular, an investigation of baryogenesis occurring during the weak phase transition through anomalous baryon violating processes in the standard model of weak interactions. (3) Flavor and Compositeness. Further investigation of a new mechanism that I recently discovered for dynamical mass generation for fermions, which naturally leads to a family hierarchy structure. A discussion of recent past work is found in the next section, followed by an outline of the proposed research. A recent publication from each of these three areas is attached to this proposal.

  3. AGN Variability: Probing Black Hole Accretion

    NASA Astrophysics Data System (ADS)

    Moreno, Jackeline; O'Brien, Jack; Vogeley, Michael S.; Richards, Gordon T.; Kasliwal, Vishal P.

    2017-01-01

    We combine the long temporal baseline of Sloan Digital Sky Survey (SDSS) for quasars in Stripe 82 with the high precision photometry of the Kepler/K2 Satellite to study the physics of optical variability in the accretion disk and supermassive black hole engine. We model the lightcurves directly as Continuous-time Auto Regressive Moving Average processes (C-ARMA) with the Kali analysis package (Kasliwal et al. 2016). These models are extremely robust to irregular sampling and can capture aperiodic variability structure on various timescales. We also estimate the power spectral density and structure function of both the model family and the data. A Green's function kernel may also be estimated for the resulting C-ARMA parameter fit, which may be interpreted as the response to driving impulses such as hotspots in the accretion disk. We also examine available spectra for our AGN sample to relate observed and modelled behavior to spectral properties. The objective of this work is twofold: to explore the proper physical interpretation of different families of C-ARMA models applied to AGN optical flux variability and to relate empirical characteristic timescales of our AGN sample to physical theory or to properties estimated from spectra or simulations like the disk viscosity and temperature. We find that AGN with strong variability features on timescales resolved by K2 are well modelled by a low order C-ARMA family while K2 lightcurves with weak amplitude variability are dominated by outliers and measurement errors which force higher order model fits. This work explores a novel approach to combining SDSS and K2 data sets and presents recovered characteristic timescales of AGN variability.

  4. Does mass accretion lead to field decay in neutron stars?

    NASA Technical Reports Server (NTRS)

    Shibazaki, N.; Murakami, T.; Shaham, J.; Nomoto, K.

    1989-01-01

    Adopting the hypothesis of accretion-induced magnetic field decay in neutron stars, the consequent evolution of a neutron star's spin and magnetic field are calculated. The results are consistent with observations of binary and millisecond radio pulsars. Thermomagnetic effects could provide a possible physical mechanism for such accretion-induced field decay.

  5. Galaxies in Clusters : Gas Stripping and Accretion

    NASA Astrophysics Data System (ADS)

    O'Dea, Chris; Balsara, Dinshaw; Livio, Mario

    1994-05-01

    We study the process of a galaxy moving through the intercluster gas in a cluster of galaxies, using a high quality hydrocode run at high resolutions. We find that ram pressure stripping occurs in the form of individual events that are separated by about ten million years. In addition we find that the galaxy accretes gas from the downstream side into the core. This accretion process exhibits a radial "pumping" mode, similar to the one found previously in simulations of wind accretion onto compact objects. Some implications of our results for the understanding of a few recent observations are discussed.

  6. Accretion dynamics and disk evolution in NGC 2264: a study based on CoRoT photometric observations

    NASA Astrophysics Data System (ADS)

    Alencar, S. H. P.; Teixeira, P. S.; Guimarães, M. M.; McGinnis, P. T.; Gameiro, J. F.; Bouvier, J.; Aigrain, S.; Flaccomio, E.; Favata, F.

    2010-09-01

    Context. The young cluster NGC 2264 was observed with the CoRoT satellite for 23 days uninterruptedly in March 2008 with unprecedented photometric accuracy. We present the first results of our analysis of the accreting population belonging to the cluster as observed by CoRoT. Aims: We search for possible light curve variability of the same nature as that observed in the classical T Tauri star AA Tau, which was attributed to a magnetically controlled inner disk warp. The inner warp dynamics is supposed to be directly associated with the interaction between the stellar magnetic field and the inner disk region. Methods: We analyzed the CoRoT light curves of 83 previously known classical T Tauri stars that belong to NGC 2264 classifying them according to their light-curve morphology. We also studied the CoRoT light-curve morphology as a function of a Spitzer-based classification of the star-disk systems. Results: The classification derived on the basis of the CoRoT light-curve morphology agrees very well with the Spitzer IRAC-based classification of the systems. The percentage of AA Tau-like light curves decreases as the inner disk dissipates, from 40% ± 10% in systems with thick inner disks to 36% ± 16% in systems with anemic disks and zero in naked photosphere systems. Indeed, 91% ± 29% of the CTTS with naked photospheres exhibit pure spot-like variability, while only 18% ± 7% of the thick disk systems do so, presumably those seen at low inclination and thus free of variable obscuration. Conclusions: AA Tau-like light curves are found to be fairly common, with a frequency of at least ~30 to 40% in young stars with inner dusty disks. The temporal evolution of the light curves indicates that the structure of the inner disk warp, located close to the corotation radius and responsible for the obscuration episodes, varies over a timescale of a few (~1-3) rotational periods. This probably reflects the highly dynamical nature of the star-disk magnetospheric interaction

  7. Dynamics of accretion disks in a constant curvature f(R)-gravity

    NASA Astrophysics Data System (ADS)

    Alipour, N.; Khesali, A. R.; Nozari, K.

    2016-07-01

    So far the basic physical properties of matter forming a thin accretion disc in the static and spherically symmetric space-time metric of the vacuum f(R) modified gravity models (Pun et al. in Phys. Rev. D 78:024043, 2008) and building radiative models of thin accretion disks for both Schwarzschild and Kerr black holes in f(R) gravity (Perez et al. in Astron. Astrophys. 551:4, 2013) were addressed properly. Also von Zeipel surfaces and convective instabilities in f(R)-Schwarzschild(Kerr) background have been investigated recently (Alipour et al. in Mon. Not. R. Astron. Soc. 454:1992, 2015). In this streamline, here we study the effects of radial and angular pressure gradients on thick accretion disks in Schwarzschild geometries in a constant curvature f(R) modified gravity. Since thick accretion disks have high accretion rate, we study configuration and structure of thick disks by focusing on the effect of pressure gradient on formation of the disks. We clarify our study by assuming two types of equation of state: polytropic and Clapeyron equation of states.

  8. Planetary migration, accretion, and atmospheres

    NASA Astrophysics Data System (ADS)

    Dobbs-Dixon, Ian M.

    This dissertation explores three distinct projects in the field of planetary formation and evolution: type I migration, cessation of mass accretion, and the atmospheric dynamics of hot Jupiters. All three of these projects touch on outstanding or unresolved issues in the field. Each attempts to unify analytic and numerical approaches in order to physically motivate solutions while simultaneously probing areas currently inaccessible to purely analytic approaches. The first section, type I migration, explores the outstanding problem of the rapid inward migration of low mass planets embedded in protoplanetary disks. Analytic estimates of migration predict characteristic timescales that are much shorter then either observed disk lifetimes or theoretical core-accretion formation timescales. If migration is actually as efficient as these analytic estimates predict, planet formation across the observed range of masses and semimajor axis' is difficult. Here I introduce several new formalisms to both allow the disk to adiabatically adjust to the presence of a planet and include the effect of axisymmetric disk self-gravity. I find that these modifications increase migration timescales by approximately 4 times. In addition to these numerical improvements, I present simulations of migration in lower sound-speed regions of the disk on the grounds that self shadowing within the disk could yield substantially cooler gas temperatures then those derived by most irradiated disk models. In such regions the planetary perturbation excites a secondary instability, leading to the formation of vortices. These vortices cause a substantial reduction in the net torque, increasing migration timescales by up to approximately 200 times the analytically predicted rate. The second section addresses the mechanism for shutting off accretion onto giant planets. According to the conventional sequential accretion scenario, giant planets acquire a majority of their gas in a runaway phase. Conventional

  9. The Physical Tourist. A European Study Course

    NASA Astrophysics Data System (ADS)

    Kortemeyer, Gerd; Westfall, Catherine

    2010-03-01

    We organized and led a European study course for American undergraduate university students to explore the early history of relativity and quantum theory. We were inspired by The Physical Tourist articles published in this journal on Munich, Bern, Berlin, Copenhagen, and Göttingen. We describe this adventure both for others wishing to teach such a course and for anyone wishing to walk in the footsteps of the physicists who revolutionized physics in the early decades of the twentieth century.

  10. ACCRETION FLOW DYNAMICS OF MAXI J1659-152 FROM THE SPECTRAL EVOLUTION STUDY OF ITS 2010 OUTBURST USING THE TCAF SOLUTION

    SciTech Connect

    Debnath, Dipak; Molla, Aslam Ali; Chakrabarti, Sandip K.; Mondal, Santanu E-mail: aslam@csp.res.in E-mail: santanu@csp.res.in

    2015-04-20

    Transient black hole candidates are interesting objects to study in X-rays as these sources show rapid evolutions in their spectral and temporal properties. In this paper, we study the spectral properties of the Galactic transient X-ray binary MAXI J1659-152 during its very first outburst after discovery with the archival data of RXTE Proportional Counter Array instruments. We make a detailed study of the evolution of accretion flow dynamics during its 2010 outburst through spectral analysis using the Chakrabarti–Titarchuk two-component advective flow (TCAF) model as an additive table model in XSPEC. Accretion flow parameters (Keplerian disk and sub-Keplerian halo rates, shock location, and shock strength) are extracted from our spectral fits with TCAF. We studied variations of these fit parameters during the entire outburst as it passed through three spectral classes: hard, hard-intermediate, and soft-intermediate. We compared our TCAF fitted results with standard combined disk blackbody (DBB) and power-law (PL) model fitted results and found that variations of disk rate with DBB flux and halo rate with PL flux are generally similar in nature. There appears to be an absence of the soft state, unlike what is seen in other similar sources.

  11. Numerical Solution of the Radiative Transfer Equation: X-Ray Spectral Formation from Cylindrical Accretion onto a Magnetized Neutron Star

    NASA Technical Reports Server (NTRS)

    Fairnelli, R.; Ceccobello, C.; Romano, P.; Titarchuk, L.

    2011-01-01

    Predicting the emerging X-ray spectra in several astrophysical objects is of great importance, in particular when the observational data are compared with theoretical models. This requires developing numerical routines for the solution of the radiative transfer equation according to the expected physical conditions of the systems under study. Aims. We have developed an algorithm solving the radiative transfer equation in the Fokker-Planck approximation when both thermal and bulk Comptonization take place. The algorithm is essentially a relaxation method, where stable solutions are obtained when the system has reached its steady-state equilibrium. Methods. We obtained the solution of the radiative transfer equation in the two-dimensional domain defined by the photon energy E and optical depth of the system pi using finite-differences for the partial derivatives, and imposing specific boundary conditions for the solutions. We treated the case of cylindrical accretion onto a magnetized neutron star. Results. We considered a blackbody seed spectrum of photons with exponential distribution across the accretion column and for an accretion where the velocity reaches its maximum at the stellar surface and at the top of the accretion column, respectively. In both cases higher values of the electron temperature and of the optical depth pi produce flatter and harder spectra. Other parameters contributing to the spectral formation are the steepness of the vertical velocity profile, the albedo at the star surface, and the radius of the accretion column. The latter parameter modifies the emerging spectra in a specular way for the two assumed accretion profiles. Conclusions. The algorithm has been implemented in the XPEC package for X-ray fitting and is specifically dedicated to the physical framework of accretion at the polar cap of a neutron star with a high magnetic field (approx > 10(exp 12) G). This latter case is expected to be of typical accreting systems such as X

  12. ASYMMETRIC ACCRETION FLOWS WITHIN A COMMON ENVELOPE

    SciTech Connect

    MacLeod, Morgan; Ramirez-Ruiz, Enrico

    2015-04-10

    This paper examines flows in the immediate vicinity of stars and compact objects dynamically inspiralling within a common envelope (CE). Flow in the vicinity of the embedded object is gravitationally focused, leading to drag and potentially to gas accretion. This process has been studied numerically and analytically in the context of Hoyle–Lyttleton accretion (HLA). Yet, within a CE, accretion structures may span a large fraction of the envelope radius, and in so doing sweep across a substantial radial gradient of density. We quantify these gradients using detailed stellar evolution models for a range of CE encounters. We provide estimates of typical scales in CE encounters that involve main sequence stars, white dwarfs, neutron stars, and black holes with giant-branch companions of a wide range of masses. We apply these typical scales to hydrodynamic simulations of three-dimensional HLA with an upstream density gradient. This density gradient breaks the symmetry that defines HLA flow, and imposes an angular momentum barrier to accretion. Material that is focused into the vicinity of the embedded object thus may not be able to accrete. As a result, accretion rates drop dramatically, by one to two orders of magnitude, while drag rates are only mildly affected. We provide fitting formulae to the numerically derived rates of drag and accretion as a function of the density gradient. The reduced ratio of accretion to drag suggests that objects that can efficiently gain mass during CE evolution, such as black holes and neutron stars, may grow less than implied by the HLA formalism.

  13. Problems and Promises of Pebble Accretion

    NASA Astrophysics Data System (ADS)

    Kretke, Katherine A.; Levison, H. F.

    2013-05-01

    Abstract (2,250 Maximum Characters): Despite the large number of exoplanets indicating that planets are a common outcome of the star formation process, theoretical models still struggle to explain how ~10 Earth mass rocky/icy embryos can form within the lifetimes of gaseous circumstellar disks. Recently, aerodynamic-aided accretion of ``pebbles,'' particles ranging from millimeters to decimeters in size, has been suggested as a potential solution to this long-standing problem. Local simulations, simulations which look at the detailed behavior of these pebbles in the vicinity of a planetary embryo, have shown that the potential planetary growth rates can be surprisingly fast. If one assumes that most of the mass in a protoplanetary disk resides in these pebble-sized particles, a Mars mass core could grow to 10 Earth masses in only a few thousand years. However, these local studies cannot investigate how this accretion process behaves in the more complicated, multi-planet environment. We have incorporated a prescription of this pebble accretion into LIPAD, a Lagrangian code which can follow the collisional/accretional/dynamical evolution of a planetary system, to investigate the how this pebble accretion will manifest itself in the larger planet formation picture. We discuss how these more comprehensive models present challenges for using pebble accretion to form observed planetary systems.

  14. Giant planet formation via pebble accretion

    NASA Astrophysics Data System (ADS)

    Guilera, O. M.

    2016-08-01

    In the standard model of core accretion, the formation of giant planets occurs by two main processes: first, a massive core is formed by the accretion of solid material; then, when this core exceeds a critical value (typically greater than ) a gaseous runaway growth is triggered and the planet accretes big quantities of gas in a short period of time until the planet achieves its final mass. Thus, the formation of a massive core has to occur when the nebular gas is still available in the disk. This phenomenon imposes a strong time-scale constraint in the giant planet formation due to the fact that the lifetimes of the observed protoplanetary disks are in general lower than 10 Myr. The formation of massive cores before 10 Myr by accretion of big planetesimals (with radii 10 km) in the oligarchic growth regime is only possible in massive disks. However, planetesimal accretion rates significantly increase for small bodies, especially for pebbles, particles of sizes between mm and cm, which are strongly coupled with the gas. In this work, we study the formation of giant planets incorporating pebble accretion rates in our global model of planet formation.

  15. The Structure and Evolution of an Accretion Flow Interacting with the Central Star

    NASA Astrophysics Data System (ADS)

    Fujimoto, Masayuki Y.

    1995-09-01

    The mechanical and thermal structure of accretion flows interacting with the central stars via viscous stress is studied by modeling the spatial variation of dynamical viscosity with a simple one-parameter function. The latter assumption has the advantage of yielding the analytical solution of rotation laws, and the thermal balance near the disk-star interface is analyzed by means of a one-zone approximation. Based on these results, a general picture of the evolutionary changes in the accretion process is presented with the spin history of central stars taken into account. Under a constant accretion rate, there exists the maximum rotation rate of the central star which allows the structure of accretion flow in hydrostatic and thermal equilibrium; it is smaller for larger accretion rates and occurs when the inflow rate of angular momentum decreases to the critical value Jdottrn, which takes the values around zero or larger, depending on the physical conditions in the flows. The equilibrium configurations with both the positive and negative inflow rate of angular momentum, as discussed by Paczynski and by Popham & Narayan are possible, in which the stellar rotation rate is no longer accelerated, and hence, the structure of accretion flow remains the same. It is shown, however, that these configurations exchange their thermal stability at this maximum rotation rate; in particular, the structures of mass accretion with the inflow rate of angular momentum below Jdottrn is secularly unstable, and hence, they cannot be realized in the course of the evolution. The evolution of the systems differs according to the stellar response to the mass accretion; corresponding to Jdottrn, there exists the critical value, Scri (≃ -3 or larger), for the changing rate of the stellar radius 5 = d log R*(t)/d log M*(t)(M* and R* being the mass and equator radius of the central star, respectively). If the central star expands or shrinks moderately during accreting mass as 5 ≥ Scri, the

  16. The fate or organic matter during planetary accretion - Preliminary studies of the organic chemistry of experimentally shocked Murchison meteorite

    NASA Technical Reports Server (NTRS)

    Tingle, Tracy N.; Tyburczy, James A.; Ahrens, Thomas J.; Becker, Christopher H.

    1992-01-01

    The fate of organic matter in carbonaceous meteorites during hypervelocity (1-2 km/sec) impacts is investigated using results of experiments in which three samples of the Murchison (CM2) carbonaceous chondrite were shocked to 19, 20, and 36 GPa and analyzed by highly sensitive thermal-desorption photoionization mass spectrometry (SALI). The thermal-desorptive SALI mass spectra of unshocked CM2 material revealed presence of indigenous aliphatic, aromatic, sulfur, and organosulfur compounds, and samples shocked to about 20 GPa showed little or no loss of organic matter. On the other hand, samples shocked to 36 GPa exhibited about 70 percent loss of organic material and a lower alkene/alkane ratio than did the starting material. The results suggest that it is unlikely that the indigenous organic matter in carbonaceous chondritelike planetesimals could have survived the impact on the earth in the later stages of earth's accretion.

  17. FUNDAMENTAL ASPECTS OF EPISODIC ACCRETION CHEMISTRY EXPLORED WITH SINGLE-POINT MODELS

    SciTech Connect

    Visser, Ruud; Bergin, Edwin A.

    2012-07-20

    We explore a set of single-point chemical models to study the fundamental chemical aspects of episodic accretion in low-mass embedded protostars. Our goal is twofold: (1) to understand how the repeated heating and cooling of the envelope affects the abundances of CO and related species; and (2) to identify chemical tracers that can be used as a novel probe of the timescales and other physical aspects of episodic accretion. We develop a set of single-point models that serve as a general prescription for how the chemical composition of a protostellar envelope is altered by episodic accretion. The main effect of each accretion burst is to drive CO ice off the grains in part of the envelope. The duration of the subsequent quiescent stage (before the next burst hits) is similar to or shorter than the freeze-out timescale of CO, allowing the chemical effects of a burst to linger long after the burst has ended. We predict that the resulting excess of gas-phase CO can be observed with single-dish or interferometer facilities as evidence of an accretion burst in the past 10{sup 3}-10{sup 4} yr.

  18. The impact of non-thermal electrons on resolved black hole accretion disk images

    NASA Astrophysics Data System (ADS)

    Mao, Shengkai; Dexter, Jason; Quataert, Eliot

    2015-01-01

    Recent developments in radio astronomy (in particular, the Event Horizon Telescope) allow us for the first time to resolve length scales around the Milky Way's Sgr A* comparable to the event horizon radius. These observations are opening up new opportunities to study strong gravity and accretion physics in the vicinity of a supermassive black hole. However, the processes governing black hole accretion are not well understood. In particular, the electron thermodynamics in black hole accretion disks remain mysterious, and current models vary significantly from each other. The impact of these differences between current electron thermodynamics models on results obtained from EHT images is not well understood. Thus, in this work, we explore the effects of non-thermal electrons on black hole images and radio spectra in the context of both semi-analytic and numerical models of accretion flows. Using general relativistic ray-tracing and radiative transfer code, we simulate images of the accretion disk around Sgr A* and compare our simulations to observed radio data. We estimate the range of electron energy distribution functions permissible by the data. In so doing, we also explore the range and variety of black hole images obtained by varying the distribution function.

  19. Accretion Flow in the inner Accretion Discs of Cataclysmic Variables

    NASA Astrophysics Data System (ADS)

    Balman, Solen; Revnivtsev, Mikhail

    2012-07-01

    We study nature of time variability of brightness of non-magnetic cataclysmic variables. We show that lightcurtves of all analyzed DN systems in UV and X-ray energy bands demonstrate band limited noise, which can be adequately described in the framework of the model of propagating fluctuations. The frequency of the break indicates the inner disc truncation with a range of radii (10-3)e+9 cm. We analyse the RXTE and optical (RTT150) data of SS Cyg in outburst and quiescence which show that during the outburst the inner disk radius moves towards the white dwarf and receeds as the outburst declines to quiescence. Cross-correlations between the simultaneous UV and X-ray light curves find time lags in the X-rays of 90-180 sec consistent with travel time of matter from a truncated inner disc to the white dwarf surface. This suggests that DN and other plausible nonmagnetic systems have truncated accretion discs indicating that the accretion may occur through coronal flows in the disc. We compare and contrast magnetic and nonmagnetic systems in terms of their aperiodic noise characteristics and the model of propagating fluctuations. The comparison of the X-ray/UV time lag observed by us in the case of non-magnetic CVs with those, detected for magnetic CVs allows us to make an rough estimate of the viscosity parameter. Multi band simultaneous observations of coming observattories like ASTROSAT will give us the opportunity to study time variability of brightness variations of accretion disks in cataclysmic variables in quiescence and outburst using LAXPC and UVIT/OPT instruments. We will elaborate on the nature and possible outcomes of such research.

  20. Generalized Similarity for Accretion/Decretion Disks

    NASA Astrophysics Data System (ADS)

    Rafikov, Roman R.

    2016-10-01

    Decretion (or external) disks are gas disks freely expanding to large radii due to their internal stresses. They are expected to naturally arise in tidal disruption events, around Be stars, in mass-losing post-main-sequence binaries, as a result of supernova fallback, etc. Their evolution is theoretically understood in two regimes: when the central object does not exert torque on the disk (a standard assumption for conventional accretion disks) or when no mass inflow (or outflow) occurs at the disk center. However, many astrophysical objects—circumbinary disks, Be stars, neutron stars accreting in a propeller regime, etc.—feature non-zero torque simultaneously with the non-zero accretion (or ejection of mass) at the disk center. We provide a general description for the evolution of such disks (both linear and nonlinear) in the self-similar regime, to which the disk should asymptotically converge with time. We identify a similarity parameter λ, which is uniquely related to the degree, to which the central mass accretion is suppressed by the non-zero central torque. The known decretion disk solutions correspond to the two discrete values of λ, while our new solutions cover a continuum of its physically allowed values, corresponding to either accretion or mass ejection by the central object. A direct relationship between λ and central \\dot{M} and torque is also established. We describe the time evolution of the various disk characteristics for different λ, and show that the observable properties (spectrum and luminosity evolution) of the decretion disks, in general, are different from the standard accretion disks with no central torque.

  1. Accretion dynamics of EX Lupi in quiescence. The star, the spot, and the accretion column

    NASA Astrophysics Data System (ADS)

    Sicilia-Aguilar, Aurora; Fang, Min; Roccatagliata, Veronica; Collier Cameron, Andrew; Kóspál, Ágnes; Henning, Thomas; Ábrahám, Peter; Sipos, Nikoletta

    2015-08-01

    Context. EX Lupi is a young, accreting M0 star and the prototype of EXor variable stars. Its spectrum is very rich in emission lines, including many metallic lines with narrow and broad components. The presence of a close companion has also been proposed, based on radial velocity signatures. Aims: We use the metallic emission lines to study the accretion structures and to test the companion hypothesis. Methods: We analyse 54 spectra obtained during five years of quiescence time. We study the line profile variability and the radial velocity of the narrow and broad metallic emission lines. We use the velocity signatures of different species with various excitation conditions and their time dependency to track the dynamics associated with accretion. Results: We observe periodic velocity variations in the broad and the narrow line components, consistent with rotational modulation. The modulation is stronger for lines with higher excitation potentials (e.g. He II), which are likely produced in a confined area very close to the accretion shock. Conclusions: We propose that the narrow line components are produced in the post-shock region, while the broad components originate in the more extended, pre-shock material in the accretion column. All the emission lines suffer velocity modulation due to the rotation of the star. The broad components are responsible for the line-dependent veiling observed in EX Lupi. We demonstrate that a rotationally modulated line-dependent veiling can explain the radial velocity signature of the photospheric absorption lines, making the close-in companion hypothesis unnecessary. The accretion structure is locked to the star and very stable during the five years of observations. Not all stars with similar spectral types and accretion rates show the same metallic emission lines, which could be related to differences in temperature and density in their accretion structure(s). The contamination of photospheric signatures by accretion

  2. Physics Courses--Some Suggested Case Studies

    ERIC Educational Resources Information Center

    Swetman, T. P.

    1972-01-01

    To communicate the relevance and excitement of science activity to students, the use of more imaginative, and even openly speculative, case studies in physics courses is suggested. Some useful examples are Magnetic Monopoles, Constants, Black Holes, Antimatter, Zero Mass Particles, Tachyons, and the Bootstrap Hypothesis. (DF)

  3. Analytical Study of Physics Education Websites' Content

    ERIC Educational Resources Information Center

    Elayyan, Shaher R.

    2016-01-01

    The current study is compatible with the scientific mobility in dealing with the Internet as a source of knowledge. It aims to introduce the Physics Education Websites (PEWs) and guide their followers toward the most credibility of them by analyzing their content. The sample consisted of (36) websites which were selected according to specific…

  4. Magnetospheric accretion in EX Lupi

    NASA Astrophysics Data System (ADS)

    Abraham, Peter; Kospal, Agnes; Bouvier, Jerome

    2016-08-01

    We propose to observe EX Lup, the prototype of the EXor class of young eruptive stars, in order to understand how the accretion process works in the quiescent system. Here, we request 2.6 hours of telescope time on Spitzer, to carry out a mid-infrared photometric monitoring, which we will supplement with simultaneous ground-based optical and near-infrared data. The multi-wavelength light curves will allow us to reliably separate the effects of fluctuating accretion rate from the rotation of the star. By analyzing the variations of the accretion rate we will determine whether EX Lup accretes through a few stable accretion columns or several short-lived random accretion streams. With this campaign, EX Lup will become one of the T Tauri systems where the accretion process is best understood.

  5. Accretion of southern Alaska

    USGS Publications Warehouse

    Hillhouse, J.W.

    1987-01-01

    Paleomagnetic data from southern Alaska indicate that the Wrangellia and Peninsular terranes collided with central Alaska probably by 65 Ma ago and certainly no later than 55 Ma ago. The accretion of these terranes to the mainland was followed by the arrival of the Ghost Rocks volcanic assemblage at the southern margin of Kodiak Island. Poleward movement of these terranes can be explained by rapid motion of the Kula oceanic plate, mainly from 85 to 43 Ma ago, according to recent reconstructions derived from the hot-spot reference frame. After accretion, much of southwestern Alaska underwent a counterclockwise rotation of about 50 ?? as indicated by paleomagnetic poles from volcanic rocks of Late Cretaceous and Early Tertiary age. Compression between North America and Asia during opening of the North Atlantic (68-44 Ma ago) may account for the rotation. ?? 1987.

  6. Accretion Onto Magnetic Degenerate Stars

    NASA Technical Reports Server (NTRS)

    Frank, Juhan

    2000-01-01

    While the original objectives of this research program included the study of radiative processes in cataclysmic variables and the evolution of neutron star magnetic fields, the scope of the reported research expanded to other related topics as this project developed. This final report therefore describes the results of our research in the following areas: 1) Irradiation-driven mass transfer cycles in cataclysmic variables and low-mass X-ray binaries; 2) Propeller effect and magnetic field decay in isolated old neutron stars; 3) Decay of surface magnetic fields in accreting neutron stars and pulsars; 4) Finite-Difference Hydrodynamic simulations of mass transfer in binary stars.

  7. Matter accreting neutron stars

    NASA Technical Reports Server (NTRS)

    Meszaros, P.

    1981-01-01

    Some of the fundamental neutron star parameters, such as the mass and the magnetic field strength, were experimentally determined in accreting neutron star systems. Some of the relevant data and the models used to derive useful information from them, are reviewed concentrating mainly on X-ray pulsars. The latest advances in our understanding of the radiation mechanisms and the transfer in the strongly magnetized polar cap regions are discussed.

  8. Accretion disk electrodynamics

    NASA Technical Reports Server (NTRS)

    Coroniti, F. V.

    1985-01-01

    Accretion disk electrodynamic phenomena are separable into two classes: (1) disks and coronas with turbulent magnetic fields; (2) disks and black holes which are connected to a large-scale external magnetic field. Turbulent fields may originate in an alpha-omega dynamo, provide anomalous viscous transport, and sustain an active corona by magnetic buoyancy. The large-scale field can extract energy and angular momentum from the disk and black hole, and be dynamically configured into a collimated relativistic jet.

  9. Accretion of the Earth.

    PubMed

    Canup, Robin M

    2008-11-28

    The origin of the Earth and its Moon has been the focus of an enormous body of research. In this paper I review some of the current models of terrestrial planet accretion, and discuss assumptions common to most works that may require re-examination. Density-wave interactions between growing planets and the gas nebula may help to explain the current near-circular orbits of the Earth and Venus, and may result in large-scale radial migration of proto-planetary embryos. Migration would weaken the link between the present locations of the planets and the original provenance of the material that formed them. Fragmentation can potentially lead to faster accretion and could also damp final planet orbital eccentricities. The Moon-forming impact is believed to be the final major event in the Earth's accretion. Successful simulations of lunar-forming impacts involve a differentiated impactor containing between 0.1 and 0.2 Earth masses, an impact angle near 45 degrees and an impact speed within 10 per cent of the Earth's escape velocity. All successful impacts-with or without pre-impact rotation-imply that the Moon formed primarily from material originating from the impactor rather than from the proto-Earth. This must ultimately be reconciled with compositional similarities between the Earth and the Moon.

  10. Studies in medium energy physics: Addendum

    NASA Astrophysics Data System (ADS)

    Green, A.; Hoffmann, G. W.; McDonough, J.; Purcell, M. J.; Ray, R. L.; Read, D. E.; Worn, S. D.

    1991-12-01

    This document constitutes the (1991--1992) technical progress report and continuation proposal for the ongoing medium energy nuclear physics research program supported by the U.S. Department of Energy through special Research Grant DE-FG05-88ER-40444. The experiments discussed are conducted at the Los Alamos National Laboratory's (LANL) Clinton P. Anderson Meson Physics Facility (LAMPF) and the Alternating Gradient Synchrotron (AGS) facility of the Brookhaven National Laboratory (BNL). The overall motivation for the work discussed in this document is driven by three main objectives: (1) provide hadron-nucleon and hadron-nucleus scattering data which serve to facilitate the study of effective two-body interactions, test (and possibly determine) nuclear structure, and help study reaction mechanisms and dynamics; (2) provide unique, first-of-a-kind 'exploratory' hadron-nucleus scattering data in the hope that such data will lead to discovery of new phenomena and new physics; and (3) perform precision tests of fundamental interactions, such as rare decay searches, whose observation would imply fundamental new physics.

  11. GRAVITATIONAL ACCRETION OF PARTICLES ONTO MOONLETS EMBEDDED IN SATURN's RINGS

    SciTech Connect

    Yasui, Yuki; Ohtsuki, Keiji; Daisaka, Hiroshi E-mail: ohtsuki@tiger.kobe-u.ac.jp

    2014-12-20

    Using a local N-body simulation, we examine gravitational accretion of ring particles onto moonlet cores in Saturn's rings. We find that gravitational accretion of particles onto moonlet cores is unlikely to occur in the C ring and probably difficult in the inner B ring as well provided that the cores are rigid water ice. Dependence of particle accretion on ring thickness changes when the radial distance from the planet and/or the density of particles is varied: the former determines the size of the core's Hill radius relative to its physical size, while the latter changes the effect of self-gravity of accreted particles. We find that particle accretion onto high-latitude regions of the core surface can occur even if the rings' vertical thickness is much smaller than the core radius, although redistribution of particles onto the high-latitude regions would not be perfectly efficient in outer regions of the rings such as the outer A ring, where the size of the core's Hill sphere in the vertical direction is significantly larger than the core's physical radius. Our results suggest that large boulders recently inferred from observations of transparent holes in the C ring are not formed locally by gravitational accretion, while propeller moonlets in the A ring would be gravitational aggregates formed by particle accretion onto dense cores. Our results also imply that the main bodies of small satellites near the outer edge of Saturn's rings may have been formed in rather thin rings.

  12. GR-AMRVAC code applications: accretion onto compact objects, boson stars versus black holes

    NASA Astrophysics Data System (ADS)

    Meliani, Z.; Grandclément, P.; Casse, F.; Vincent, F. H.; Straub, O.; Dauvergne, F.

    2016-08-01

    In the close vicinity of a compact object strong gravity imprints its signature onto matter. Systems that contain at least one compact object are observed to exhibit extreme physical properties and typically emit highly energetic radiation. The nature of the compact objects that produce the strongest gravitational fields is to date not settled. General relativistic numerical simulations of fluid dynamics around black holes, neutron stars, and other compact objects such as boson stars (BSs) may give invaluable insights into this fundamental question. In order to study the behavior of fluid in the strong gravity regime of an arbitrary compact object we develop a new general relativistic hydrodynamics code. To this end we extend the existing versatile adaptive mesh refinement code MPI-AMRVAC into a general relativistic hydrodynamics framework and adapt it for the use of numerically given spacetime metrics. In the present article we study accretion flows in the vicinity of various types of BSs whose numerical metrics are calculated by the KADATH spectral solver library. We design specific tests to check the reliability of any code intending to study BSs and compare the solutions with those obtained in the context of Schwarzschild black holes. We perform the first ever general relativistic hydrodynamical simulations of gas accretion by a BS. The behavior of matter at small distances from the center of a BS differs notably from the black hole case. In particular we demonstrate that in the context of Bondi spherical accretion the mass accretion rate onto non-rotating BSs remains constant whereas it increases for Schwarzschild black holes. We also address the scenario of non-spherical accretion onto BSs and show that this may trigger mass ejection from the interior of the BS. This striking feature opens the door to forthcoming investigations regarding accretion-ejection flows around such types of compact objects.

  13. Monitoring Accreting X-ray Pulsars with the GLAST Burst Monitor

    NASA Technical Reports Server (NTRS)

    Wilson, Colleen A.; Finger, Mark H.; Patel, Sandeep K.; Bhat, P. Narayana; Preece, Robert D.; Meegan, Charles A.

    2007-01-01

    Accreting pulsars are exceptionally good laboratories for probing the detailed physics of accretion onto magnetic stars. While similar accretion flows also occur in other types of astrophysical systems, e.g. magnetic CVs, only neutron stars have a small enough moment of inertia for the accretion of angular momentum to result in measurable changes in spin-frequency in a timescale of days. Long-term monitoring of accreting pulsar spin-frequencies and fluxes was demonstrated with the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory. Here we present sample results from BATSE, discuss measurement techniques appropriate for GBM, and estimate the expected GBM sensitivity.

  14. Study of physical interaction mefenamic acid - isonicotinamide

    NASA Astrophysics Data System (ADS)

    Yuyun, Yonelian; Nugrahani, Ilma

    2015-09-01

    Solid-solid interaction in the form of physics and chemistry can occur in a combination of active ingredients with the active ingredient or active ingredients with excipients in a pharmaceutical preparation. Physical interactions can be classified into physical interaction system eutectic, peritectic, and molecular compounds based on the phase diagram of a mixture of two-component systems. The physical interaction between mefenamic acid and isonicotinamide not been reported previously. This study aims to examine the type of interaction of mefenamic acid (MA) with isonicotinamide (INA) and its interaction with the isolation methods by solvent drop grinding as the simplest method and easy to do. PXRD data showed the interaction of MA:INA mixture contained no new peaks, so the indicated MA:INA only form of eutectic interaction. There was founded new endothermic peak for DTA data at 149.5°C (SDG-Ethanol) and 148.4°C (SDG-EtAct). The results of infrared spectroscopy analysis indicated a shift in the NH stretch 3367 cm-1 to 3359 cm-1; and 3185 cm-1 to 3178 cm-1.

  15. Atmospheric cloud physics laboratory project study

    NASA Technical Reports Server (NTRS)

    Schultz, W. E.; Stephen, L. A.; Usher, L. H.

    1976-01-01

    Engineering studies were performed for the Zero-G Cloud Physics Experiment liquid cooling and air pressure control systems. A total of four concepts for the liquid cooling system was evaluated, two of which were found to closely approach the systems requirements. Thermal insulation requirements, system hardware, and control sensor locations were established. The reservoir sizes and initial temperatures were defined as well as system power requirements. In the study of the pressure control system, fluid analyses by the Atmospheric Cloud Physics Laboratory were performed to determine flow characteristics of various orifice sizes, vacuum pump adequacy, and control systems performance. System parameters predicted in these analyses as a function of time include the following for various orifice sizes: (1) chamber and vacuum pump mass flow rates, (2) the number of valve openings or closures, (3) the maximum cloud chamber pressure deviation from the allowable, and (4) cloud chamber and accumulator pressure.

  16. Study of viscosity parameter in accretion disks around black holes with outflows: An analysis of 2010-11 outburst of GX 399-4.

    NASA Astrophysics Data System (ADS)

    Nagarkoti, Shreeram; Chakrabarti, Sandip Kumar

    2016-07-01

    We study axisymmetric steady state viscous accretion flows around Schwarzschild black holes and draw theoretical parameter space of allowed Quasi Periodic Oscillation (QPO) frequencies and viscosity parameter. The low frequency QPOs are considered to be the consequences of resonance of infall and cooling time scales. The outflows are considered to be confined in between the centrifugal barrier and the funnel wall. Comparing the data from TCAF fitting of GX 339-4 outburst in 2010-11, we find that viscosity parameter during the outburst evolved from 0.0005 to 0.04 during the rising phase of the outburst. This range of viscosity parameter has been quoted taking account of outflows and 10% thermal dissipation at the base of the outflow. Also, the maximum amount of outflow ejection possible was found to be ~14% of the inflow.

  17. Physical Chemical Studies on Molecular Composite Compositions

    DTIC Science & Technology

    1993-02-20

    McCrone , L. B., Deity, J. G., Polarized Light Microscopy, McCrone Research Institute, Chicago (1987). 32. Wolfe, W. L., In Handbook of Optics, Optical...are discussed. The rheology of miscible blends of the rodlike chains with flexibie or semiflexible chains is discussed using a model accounting for...vii PHYSICAL- CHEMICAL STUDIES ON RODLIKE POLYMER COMPOSITIONS The following is a final report for work of AFOSR-89--0125, covering the period January

  18. Soft X-Ray Excess from Shocked Accreting Plasma in Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Fukumura, Keigo; Hendry, Douglas; Clark, Peter; Tombesi, Francesco; Takahashi, Masaaki

    2016-08-01

    We propose a novel theoretical model to describe the physical identity of the soft X-ray excess that is ubiquitously detected in many Seyfert galaxies, by considering a steady-state, axisymmetric plasma accretion within the innermost stable circular orbit around a black hole (BH) accretion disk. We extend our earlier theoretical investigations on general relativistic magnetohydrodynamic accretion, which implied that the accreting plasma can develop into a standing shock under suitable physical conditions, causing the downstream flow to be sufficiently hot due to shock compression. We perform numerical calculations to examine, for sets of fiducial plasma parameters, the physical nature of fast magnetohydrodynamic shocks under strong gravity for different BH spins. We show that thermal seed photons from the standard accretion disk can be effectively Compton up-scattered by the energized sub-relativistic electrons in the hot downstream plasma to produce the soft excess feature in X-rays. As a case study, we construct a three-parameter Comptonization model of inclination angle θ obs, disk photon temperature kT in, and downstream electron energy kT e to calculate the predicted spectra in comparison with a 60 ks XMM-Newton/EPIC-pn spectrum of a typical radio-quiet Seyfert 1 active galactic nucleus, Ark 120. Our χ 2-analyses demonstrate that the model is plausible for successfully describing data for both non-spinning and spinning BHs with derived ranges of 61.3 keV ≲ kT e ≲ 144.3 keV, 21.6 eV ≲ kT in ≲ 34.0 eV, and 17.°5 ≲ θ obs ≲ 42.°6, indicating a compact Comptonizing region of three to four gravitational radii that resembles the putative X-ray coronae.

  19. Physics Studies at the University of Havana

    NASA Astrophysics Data System (ADS)

    de Melo Pereira, Osvaldo; Sánchez Colina, María

    The licenciatura en física degree course was created as part of the 1962 University Reform. It started at the Physics School within the Science Faculty of the University of Havana, also including the Schools of Mathematics, Chemistry, Biological Sciences, Geography and Psychology (Henriques Rodríguez, Daisy, R, Revista Cubana de Educación Superior XXI(8), 2001). The degree of licenciado had replaced that of baciller since 1880, but only the physico-mathematical sciences and physico-chemical sciences degree courses existed prior to the 1962 university reform. In this paper, we will analyze some data concerning the undergraduate and graduate studies during the 46 years elapsed since the creation of the physics degree course at the University of Havana. Several related issues, such as the development of scientific research and the influence of international collaboration, are dealt with in other contributions to this volume.

  20. Ice Accretions on Modern Airfoils Investigated

    NASA Technical Reports Server (NTRS)

    Addy, Harold E., Jr.

    2000-01-01

    The Icing Branch at the NASA Glenn Research Center at Lewis Field initiated and conducted the Modern Airfoils Ice Accretions project to identify ice shapes and determine their effects on the aerodynamic performance of aircraft, particularly on lift and drag. Previous aircraft ice shape and performance documentation focused on a few, older airfoils. This permitted more basic studies of the ice accretion process to be undertaken. However, having established both a working data base of ice shapes and the capability to predict these shapes for basic airfoils, questions arose about how ice might accrete differently on airfoils more representative of those being designed and flown on various aircraft today. Similarly, information about how these ice shapes would affect aerodynamic performance was needed.

  1. Galaxies in clusters: Gas stripping and accretion

    NASA Astrophysics Data System (ADS)

    Balsara, Dinshaw; Livio, Mario; O'Dea, Christopher P.

    1994-12-01

    We study the process of a galaxy moving through the intracluster gas in a cluster of galaxies, using two-dimensional hydrodynamic simulations at high resolution. We find that ram pressure stripping occurs in the form of individual events which are separated by a few times 107 yr. In addition, we find that the galaxy accretes gas from the downstream side into the core. This accretion process exhibits a radial 'pumping' mode, similar to the one found previously in simulations of wind accretion onto compact objects. The flow is found to exhibit a complex shock structure around the core. Some implications of our results for the understanding of a few recent observations are discussed.

  2. The accretion of migrating giant planets

    NASA Astrophysics Data System (ADS)

    Dürmann, Christoph; Kley, Wilhelm

    2017-02-01

    Aims: Most studies concerning the growth and evolution of massive planets focus either on their accretion or their migration only. In this work we study both processes concurrently to investigate how they might mutually affect one another. Methods: We modeled a two-dimensional disk with a steady accretion flow onto the central star and embedded a Jupiter mass planet at 5.2 au. The disk is locally isothermal and viscosity is modeled using a constant α. The planet is held on a fixed orbit for a few hundred orbits to allow the disk to adapt and carve a gap. After this period, the planet is released and free to move according to the gravitational interaction with the gas disk. The mass accretion onto the planet is modeled by removing a fraction of gas from the inner Hill sphere, and the removed mass and momentum can be added to the planet. Results: Our results show that a fast migrating planet is able to accrete more gas than a slower migrating planet. Utilizing a tracer fluid we analyzed the origin of the accreted gas originating predominantly from the inner disk for a fast migrating planet. In the case of slower migration, the fraction of gas from the outer disk increases. We also found that even for very high accretion rates, in some cases gas crosses the planetary gap from the inner to the outer disk. Our simulations show that the crossing of gas changes during the migration process as the migration rate slows down. Therefore, classical type II migration where the planet migrates with the viscous drift rate and no gas crosses the gap is no general process but may only occur for special parameters and at a certain time during the orbital evolution of the planet.

  3. Magnetic Field Roles in Black-Holes Accretion Disk's Structure

    NASA Astrophysics Data System (ADS)

    Abbassi, S.; Samadi, M.

    2016-09-01

    We study several factors which play remarkable roles in vertical structure and dynamics of hot accretion flows around black holes. These factors are large-scale magnetic field, thermal conduction, outflow and self-gravity. We consider an axisymmetric, rotating, steady viscous-resistive hot accretion flows.

  4. Turbulent Distortion of Condensate Accretion

    NASA Technical Reports Server (NTRS)

    Hazoume, R.; Orou Chabi, J.; Johnson, J. A., III

    1997-01-01

    When a simple model for the relationship between the density-temperature fluctuation correlation and mean values is used, we determine that the rate of change of turbulent intensity can influence directly the accretion rate of droplets. Considerable interest exists in the accretion rate for condensates in nonequilibrium flow with icing and the potential role which reactant accretion can play in nonequilibrium exothermic reactant processes. Turbulence is thought to play an important role in such flows. It has already been experimentally determined that turbulence influences the sizes of droplets in the heterogeneous nucleation of supersaturated vapors. This paper addresses the issue of the possible influence of turbulence on the accretion rate of droplets.

  5. A Study on Linking High-School Physics and Perfect Teaching Reformation of College Physics

    ERIC Educational Resources Information Center

    Liu, Xiaolai; Li, Qun; Gao, Jiangtao

    2011-01-01

    For the students who have just entered colleges, learning university physics would be a challenge. This paper discusses how to make students who have just finished senior high school physics won't feel difficult in learning university physics and how to guide and cultivate the students' interest in the study of physics so to stimulate the…

  6. Physical model studies of water column separation

    NASA Astrophysics Data System (ADS)

    Autrique, R.; Rodal, E.; Sánchez, A.; Carmona, L.

    2012-11-01

    Results of physical model studies of water column separation following an upstream valve closure in a horizontal pipe are presented, using three dimensionless parameters: the magnitude of the transient, M, or the ratio between the Joukowsky pressure and the initial absolute head; ΔHr, or the ratio between the maximum overpressure and the Joukowsky pressure, and tcr, the duration of the vapor cavity relative to the pipeline period. Conclusions are derived, aiming to a better understanding of water column separation extreme pressures and to the establishment of useful preliminary design guidelines.

  7. Cloud feedback studies with a physics grid

    SciTech Connect

    Dipankar, Anurag; Stevens, Bjorn

    2013-02-07

    During this project the investigators implemented a fully parallel version of dual-grid approach in main frame code ICON, implemented a fully conservative first-order interpolation scheme for horizontal remapping, integrated UCLA-LES micro-scale model into ICON to run parallely in selected columns, and did cloud feedback studies on aqua-planet setup to evaluate the classical parameterization on a small domain. The micro-scale model may be run in parallel with the classical parameterization, or it may be run on a "physics grid" independent of the dynamics grid.

  8. Tokamak physics experiment: Diagnostic windows study

    SciTech Connect

    Merrigan, M.; Wurden, G.A.

    1995-11-01

    We detail the study of diagnostic windows and window thermal stress remediation in the long-pulse, high-power Tokamak Physics Experiment (TPX) operation. The operating environment of the TPX diagnostic windows is reviewed, thermal loads on the windows estimated, and cooling requirements for the windows considered. Applicable window-cooling technology from other fields is reviewed and its application to the TPX windows considered. Methods for TPX window thermal conditioning are recommended, with some discussion of potential implementation problems provided. Recommendations for further research and development work to ensure performance of windows in the TPX system are presented.

  9. Accretion shock geometries in the magnetic variables

    NASA Technical Reports Server (NTRS)

    Stockman, H. S.

    1988-01-01

    The first self consistent shock models for the AM Herculis-type systems successfully identified the dominant physical processes and their signatures. These homogenous shock models predict unpolarized, Rayleigh-Jeans optical spectra with sharp cutoffs and rising polarizations as the shocks become optically thin in the ultraviolet. However, the observed energy distributions are generally flat with intermediate polarizations over a broad optical band. These and other observational evidence support a non-homogenous accretion profile which may extend over a considerable fraction of the stellar surface. Both the fundamental assumptions underlying the canonical 1-D shock model and the extension of this model to inhomogenous accretion shocks were identified, for both radial and linear structures. The observational evidence was also examined for tall shocks and little evidence was found for relative shock heights in excess of h/R(1) greater than or equal to 0.1. For several systems, upper limits to the shock height can be obtained from either x ray or optical data. These lie in the region h/R(1) is approximately 0.01 and are in general agreement with the current physical picture for these systems. The quasi-periodic optical variations observed in several magnetic variables may eventually prove to be a major aid in further understanding their accretion shock geometries.

  10. Spiral-driven accretion in protoplanetary discs . III. Tridimensional simulations

    NASA Astrophysics Data System (ADS)

    Hennebelle, Patrick; Lesur, Geoffroy; Fromang, Sébastien

    2017-03-01

    Context. Understanding how accretion proceeds in proto-planetary discs, and more generally, understanding their dynamics, is a crucial questions that needs to be answered to explain the conditions in which planets form. Aims: The role that accretion of gas from the surrounding molecular cloud onto the disc may have on its structure needs to be quantified. Methods: We performed tridimensional simulations using the Cartesian AMR code RAMSES of an accretion disc that is subject to infalling material. Results: For the aspect ratio of H/R ≃ 0.15 and disc mass Md ≃ 10-2M⊙ used in our study, we find that for typical accretion rates of the order of a few 10-7M⊙ yr-1, values of the α parameter as high as a few 10-3 are inferred. The mass that is accreted in the inner part of the disc is typically at least 50% of the total mass that has been accreted onto the disc. Conclusions: Our results suggest that external accretion of gas at moderate values onto circumstellar discs may trigger prominent spiral arms that are reminiscent of recent observations made with various instruments, and may lead to significant transport through the disc. If confirmed from observational studies, such accretion may therefore influence disc evolution.

  11. Transsonic accretion modes with density jumps

    NASA Astrophysics Data System (ADS)

    Adarchenko, V. A.; Voronin, S. M.

    2015-08-01

    In this study, a class of steady-state solutions of the problem of matter incidence on a gravitating center (accretion), in which the matter jump through a sound barrier is performed at the discontinuity (density jump), is proposed. Substantiation of such solutions is given based on the theory of fast—slow systems. Certain partial solutions are presented as an example.

  12. What Young People Say about Physical Activity: The Children's Sport Participation and Physical Activity (CSPPA) Study

    ERIC Educational Resources Information Center

    Tannehill, Deborah; MacPhail, Ann; Walsh, Julia; Woods, Catherine

    2015-01-01

    The Children's Sport Participation and Physical Activity (CSPPA) study is a unique multi-centre/discipline study undertaken by three Irish institutions, Dublin City University, University of Limerick and University College Cork. The study sought to assess participation in physical activity, physical education and sport (PAPES) among 10-18 year…

  13. Dynamically important magnetic fields near accreting supermassive black holes.

    PubMed

    Zamaninasab, M; Clausen-Brown, E; Savolainen, T; Tchekhovskoy, A

    2014-06-05

    Accreting supermassive black holes at the centres of active galaxies often produce 'jets'--collimated bipolar outflows of relativistic particles. Magnetic fields probably play a critical role in jet formation and in accretion disk physics. A dynamically important magnetic field was recently found near the Galactic Centre black hole. If this is common and if the field continues to near the black hole event horizon, disk structures will be affected, invalidating assumptions made in standard models. Here we report that jet magnetic field and accretion disk luminosity are tightly correlated over seven orders of magnitude for a sample of 76 radio-loud active galaxies. We conclude that the jet-launching regions of these radio-loud galaxies are threaded by dynamically important fields, which will affect the disk properties. These fields obstruct gas infall, compress the accretion disk vertically, slow down the disk rotation by carrying away its angular momentum in an outflow and determine the directionality of jets.

  14. Understanding Physics, First Edition, Study Guide

    NASA Astrophysics Data System (ADS)

    Cummings, Karen; Laws, Priscilla W.; Redish, Edward F.; Cooney, Patrick J.

    2004-04-01

    Built on the foundations of Halliday, Resnick, and Walker's Fundamentals of Physics Sixth Edition, this text is designed to work with interactive learning strategies that are increasingly being used in physics instruction (for example, microcomputer-based labs, interactive lectures, etc. ). In doing so, it incorporates new approaches based upon Physics Education Research (PER), aligns with courses that use computer-based laboratory tools, and promotes Activity Based Physics in lectures, labs, and recitations.

  15. Physical design study of the CEPC booster

    NASA Astrophysics Data System (ADS)

    Zhang, Chuang

    2016-09-01

    A physical design study of the Circular Electron-Positron Collider (CEPC) booster is reported. The booster provides 120 GeV electron and positron beams for the CEPC collider with top-up injection. The booster is mounted above the collider in the same tunnel. To save cost, the energy of the linac injector for the booster is chosen as 6 GeV, corresponding to a magnetic field of 30.7 Gs. In this paper, the booster lattice is described and optimization of the cell length is discussed. A novel scheme of bypass near the detector of the collider is designed. The extremely low magnetic field caused by low injection energy is studied, and a new ideal of wiggling bands is proposed to mitigate the low-field problem. Beam transfer and injection from the linac to the booster are considered.

  16. Ice Accretions on a Swept GLC-305 Airfoil

    NASA Technical Reports Server (NTRS)

    Vargas, Mario; Papadakis, Michael; Potapczuk, Mark; Addy, Harold; Sheldon, David; Giriunas, Julius

    2002-01-01

    An experiment was conducted in the Icing Research Tunnel (IRT) at NASA Glenn Research Center to obtain castings of ice accretions formed on a 28 deg. swept GLC-305 airfoil that is representative of a modern business aircraft wing. Because of the complexity of the casting process, the airfoil was designed with three removable leading edges covering the whole span. Ice accretions were obtained at six icing conditions. After the ice was accreted, the leading edges were detached from the airfoil and moved to a cold room. Molds of the ice accretions were obtained, and from them, urethane castings were fabricated. This experiment is the icing test of a two-part experiment to study the aerodynamic effects of ice accretions.

  17. Inception of ice accretion by ice crystal impact

    NASA Astrophysics Data System (ADS)

    Löwe, Jens; Kintea, Daniel; Baumert, Arne; Bansmer, Stephan; Roisman, Ilia V.; Tropea, Cameron

    2016-09-01

    In this experimental and theoretical study the ice accretion phenomena on a heated cylinder in Braunschweig Icing Wind Tunnel are investigated. The ice crystal size, velocity, the liquid-to-total mass ratio are accurately controlled. The evolution of the cylinder temperature, the time required for the inception of the ice accretion, and the ice accretion rate are measured for various operating conditions. The surface temperature of the solid target is determined by balancing the heating power in the wall and the cooling effect of the stream of ice particles. We have discovered that the inception of the ice crystal accretion is determined by the instant when the surface temperature of the heated target reduces to the freezing temperature. This result will help to model the phenomena of ice crystal accretion.

  18. Mathematical methods of studying physical phenomena

    NASA Astrophysics Data System (ADS)

    Man'ko, Margarita A.

    2013-03-01

    In recent decades, substantial theoretical and experimental progress was achieved in understanding the quantum nature of physical phenomena that serves as the foundation of present and future quantum technologies. Quantum correlations like the entanglement of the states of composite systems, the phenomenon of quantum discord, which captures other aspects of quantum correlations, quantum contextuality and, connected with these phenomena, uncertainty relations for conjugate variables and entropies, like Shannon and Rényi entropies, and the inequalities for spin states, like Bell inequalities, reflect the recently understood quantum properties of micro and macro systems. The mathematical methods needed to describe all quantum phenomena mentioned above were also the subject of intense studies in the end of the last, and beginning of the new, century. In this section of CAMOP 'Mathematical Methods of Studying Physical Phenomena' new results and new trends in the rapidly developing domain of quantum (and classical) physics are presented. Among the particular topics under discussion there are some reviews on the problems of dynamical invariants and their relations with symmetries of the physical systems. In fact, this is a very old problem of both classical and quantum systems, e.g. the systems of parametric oscillators with time-dependent parameters, like Ermakov systems, which have specific constants of motion depending linearly or quadratically on the oscillator positions and momenta. Such dynamical invariants play an important role in studying the dynamical Casimir effect, the essence of the effect being the creation of photons from the vacuum in a cavity with moving boundaries due to the presence of purely quantum fluctuations of the electromagnetic field in the vacuum. It is remarkable that this effect was recently observed experimentally. The other new direction in developing the mathematical approach in physics is quantum tomography that provides a new vision of

  19. Microwave ice accretion meter

    NASA Technical Reports Server (NTRS)

    Magenheim, Bertram (Inventor); Rocks, James K. (Inventor)

    1984-01-01

    A system for indicating ice thickness and rate of ice thickness growth on surfaces is disclosed. The region to be monitored for ice accretion is provided with a resonant surface waveguide which is mounted flush, below the surface being monitored. A controlled oscillator provides microwave energy via a feed point at a controllable frequency. A detector is coupled to the surface waveguide and is responsive to electrical energy. A measuring device indicates the frequency deviation of the controlled oscillator from a quiescent frequency. A control means is provided to control the frequency of oscillation of the controlled oscillator. In a first, open-loop embodiment, the control means is a shaft operated by an operator. In a second, closed-loop embodiment, the control means is a processor which effects automatic control.

  20. He-accreting WDs: AM CVn stars with WD donors

    NASA Astrophysics Data System (ADS)

    Piersanti, L.; Yungelson, L. R.; Tornambé, A.

    2015-09-01

    We study the physical and evolutionary properties of the `white dwarf (WD) family' of AM CVn stars by computing realistic models of interacting double-degenerate systems. We evaluate self-consistently both the mass-transfer rate from the donor, as determined by gravitational wave emission and interaction with the binary companion, and the thermal response of the accretor to mass deposition. We find that, after the onset of mass transfer, all the considered systems undergo a strong non-dynamical He-flash. However, due to the compactness of these systems, the expanding accretors fill their Roche lobe very soon, thus preventing the efficient heating of the external layers of the accreted CO WDs. Moreover, due to the loss of matter from the systems, the orbital separations enlarge and mass transfer comes to a halt. The further evolution depends on the value of dot{M} after the donors fill again their lobe. On one hand, if the accretion rate, as determined by the actual value of (Mdon, Macc), is high enough, the accretors experience several He-flashes of decreasing strength and then quiescent He-burning sets in. Later on, since the mass-transfer rate in IDD is a permanently decreasing function of time, accretors experience several recurrent strong flashes. On the other hand, for intermediate and low values of dot{M} the accretors enter directly the strong flashes accretion regime. As expected, in all the considered systems the last He-flash is the strongest one, even if the physical conditions suitable for a dynamical event are never attained. When the mass accretion rate decreases below (2-3) × 10-8 M⊙ yr-1, the compressional heating of the He-shell becomes less efficient than the neutrino cooling, so that all the accretors in the considered systems evolve into massive degenerate objects. Our results suggest that SNe .Ia or Type Ia Supernovae due to Edge-Lit Detonation in the WD family of AM CVn stars should be much more rare than previously expected.

  1. Accretion and star formation in RQQs

    NASA Astrophysics Data System (ADS)

    White, Sarah; Jarvis, Matt; Häußler, Boris; Maddox, Natasha; Kalfountzou, Eleni; Hardcastle, Martin

    2016-06-01

    Active Galactic Nuclei (AGN) and star-forming galaxies are well-traced in the radio part of the electromagnetic spectrum, due to emission at these wavelengths being unaffected by dust obscuration. The key processes involved in producing the radio emission are black-hole accretion and star formation, both of which are thought to be crucial in determining how galaxies evolve. Disentangling the two contributions requires multi-wavelength data, and this is the approach we use for our work on radio-quiet quasars (RQQs). In contrast to previous studies, we find that accretion-connected radio emission dominates over that due to star formation, even at very low radio flux-densities. The first sample we describe is selected from the VISTA Deep Extragalactic Observations (VIDEO) survey, whose depth allows the study of very low accretion rates and/or lower-mass black holes. A second sample is obtained from the Spitzer-Herschel Active Galaxy Survey, spanning a factor of ~100 in optical luminosity over a narrow redshift range at z ~ 1. This enables evolutionary effects to be decoupled when comparisons are made with the VIDEO sample. Using radio data from the Karl G. Jansky Very Large Array (JVLA), we find further support that the AGN makes a significant contribution to the radio emission in RQQs. In addition, the levels of accretion and star formation appear to be weakly correlated with each other, and with optical luminosity.

  2. Where a Neutron Star's Accretion Disk Ends

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-03-01

    In X-ray binaries that consist of a neutron star and a companion star, gas funnels from the companion into an accretion disk surrounding the neutron star, spiraling around until it is eventually accreted. How do the powerful magnetic fields threading through the neutron star affect this accretion disk? Recent observations provide evidence that they may push the accretion disk away from the neutron stars surface.Truncated DisksTheoretical models have indicated that neutron star accretion disks may not extend all the way in to the surface of a neutron star, but may instead be truncated at a distance. This prediction has been difficult to test observationally, however, due to the challenge of measuring the location of the inner disk edge in neutron-star X-ray binaries.In a new study, however, a team of scientists led by Ashley King (Einstein Fellow at Stanford University) has managed to measure the location of the inner edge of the disk in Aquila X-1, a neutron-star X-ray binary located 17,000 light-years away.Iron line feature detected by Swift (red) and NuSTAR (black). The symmetry of the line is one of the indicators that the disk is located far from the neutron star; if the inner regions of the disk were close to the neutron star, severe relativistic effects would skew the line to be asymmetric. [King et al. 2016]Measurements from ReflectionsKing and collaborators used observations made by NuSTAR and Swift/XRT both X-ray space observatories of Aquila X-1 during the peak of an X-ray outburst. By observing the reflection of Aquila X-1s emission off of the inner regions of the accretion disk, the authors were able to estimate the location of the inner edge of the disk.The authors find that this inner edge sits at ~15 gravitational radii. Since the neutron stars surface is at ~5 gravitational radii, this means that the accretion disk is truncated far from the stars surface. In spite of this truncation, material still manages to cross the gap and accrete onto the

  3. Crossing the Eddington Limit: Examining Disk Spectra at High Accretion Rates

    NASA Astrophysics Data System (ADS)

    Sutton, Andrew D.; Swartz, Douglas A.; Roberts, Timothy P.; Middleton, Matthew J.; Soria, Roberto; Done, Chris

    2017-02-01

    The faintest ultraluminous X-ray sources (ULXs), those with 0.3–10 keV luminosities 1< {L}{{X}}/{10}39< 3 {erg} {{{s}}}-1, tend to have X-ray spectra that are disk-like but broader than expected for thin accretion disks. These “broadened disk (BD)” spectra are thought to indicate near- or mildly super-Eddington accretion onto stellar remnant black holes. Here we report that a sample of bright thermal-dominant black hole binaries, which have Eddington ratios constrained to moderate values, also show BD spectra in the 0.3–10 keV band at an order of magnitude lower luminosities. This broadening would be missed in studies that only look above ∼ 2 {keV}. While this may suggest that BD ULXs could be powered by accretion onto massive stellar remnant black holes with close to maximal spin, we argue in favor of a scenario where they are at close to the Eddington luminosity, such that radiation pressure would be expected to result in geometrically slim, advective accretion disks. However, this implies that an additional physical mechanism is required to produce the observed broad spectra at low Eddington ratios.

  4. Exploring the connection between stellar halo profiles and accretion histories in L * galaxies

    NASA Astrophysics Data System (ADS)

    Amorisco, Nicola C.

    2017-03-01

    I use a library of controlled minor merger N-body simulations, a particle tagging technique and Monte Carlo generated ΛCDM accretion histories to study the highly stochastic process of stellar deposition onto the accreted stellar halos (ASHs) of L * galaxies. I explore the main physical mechanisms that drive the connection between the accretion history and the density profile of the ASH. I find that: i) through dynamical friction, more massive satellites are more effective at delivering their stars deeper into the host; ii) as a consequence, ASHs feature a negative gradient between radius and the local mass-weighed virial satellite-to-host mass ratio; iii) in L * galaxies, most ASHs feature a density profile that steepens towards sharper logarithmic slopes at increasing radii, though with significant halo-to-halo scatter; iv) the ASHs with the largest total ex-situ mass are such because of the chance accretion of a small number of massive satellites (rather than of a large number of low-mass ones).

  5. Tidal marsh accretion processes in the San Francisco Bay-Delta - are our models underestimating the historic and future importance of plant-mediated organic accretion?

    NASA Astrophysics Data System (ADS)

    Windham-Myers, L.; Drexler, J. Z.; Byrd, K. B.; Schile, L. M.

    2012-12-01

    Peat-accreting coastal wetlands have the potential to keep elevational pace with sea-level rise, thus providing both adaptation and mitigation for expected rises in atmospheric concentrations of greenhouse gases (GHGs). Due to oxidation and sedimentation processes, marsh elevations are generally constrained by sea level rise (1-2 mm yr-1). However, the relative importance of mineral vs. organic accretion remain poorly understood. At least four lines of evidence from the brackish-fresh region of California's SFBay-Delta suggest that potential rates of organic accretion may be underestimated in calibration datasets of the last century. First, tidal marsh elevations have been maintained with changing rates of SLR over the past 6700 years even during periods of low sediment availability. Second, the presence of fibric remnants in historic peat cores suggests that millennial preservation of autochtonous material may be greater in the absence of mineral inputs. Third, an experimental restoration of emergent marsh on subsided peat soil has generated new "proto-peat" at average rates of 4 cm y-1, nearly 40-times mean sea level rise, storing an average of 1 kg C m-2 yr-1 since 1997. Fourth, annual measurements of root production of the dominant fresh-brackish marsh species tule (Schoenoplectus acutus) show high productivity and minimal sensitivity to variable tidal range elevations and fresh-brackish salinities. Separating the relative importance of belowground productivity from decomposition in driving rates of organic accretion may be possible by assessment of fibric remnants, as an index of organic "preservation". Using three distinct peat cores from a larger study with calibrated dating and geochemistry data, fibric remnants (particles >2mm) were assessed at 10 cm intervals and compared with physical and associated geochemical down-core variability (n=230 segments). The presence of fibric remnants was reduced in the presence of sediment, as indicated by mineral content

  6. Face-on accretion onto a protoplanetary disc

    NASA Astrophysics Data System (ADS)

    Wijnen, T. P. G.; Pols, O. R.; Pelupessy, F. I.; Portegies Zwart, S.

    2016-10-01

    ) accretion of material with no azimuthal angular momentum. Our study, as well as previous work, suggests that the former, dominant process is mainly caused by numerical, rather than physical effects, while the latter is not. The latter process, as expected theoretically, causes the disc to become more compact and increases the surface density profile considerably at smaller radii. Conclusions: The disc size is determined in the first place by the ram pressure exerted by the flow when it first hits the disc. Further evolution is governed by the decrease in the specific angular momentum of the disc as it accretes material with no azimuthal angular momentum. Even taking into account the uncertainties in our simulations and the result that the loading rate is within a factor two of a simple geometric estimate, the size and lifetime of the disc are probably not sufficient to accrete the amount of mass required in the early disc accretion scenario. An animation of the simulation is available at http://www.aanda.org

  7. Statistical Physics, Neural Networks, Brain Studies

    NASA Astrophysics Data System (ADS)

    Toulouse, Gerard

    1999-01-01

    An overview of some aspects of a vast domain, located at the crossroads of physics, biology and computer science is presented: 1) During the last fifteen years, physicists advancing along various pathways have come into contact with biology (computational neurosciences) and engineering (formal neural nets). 2) This move may actually be viewed as one component in a larger picture. A prominent trend of recent years, observable over many countries, has been the establishment of interdisciplinary centers devoted to the study of: cognitive sciences; natural and artificial intelligence; brain, mind and behaviour; perception and action; learning and memory; robotics; man-machine communication, etc. What are the promising lines of development? What opportunities for physicists? An attempt will be made to address such questions, and related issues.

  8. Effect of Gas Accretion Disc Profile on Orbital Parameters of the Accreted Stars

    NASA Astrophysics Data System (ADS)

    Shukirgaliyev, Bekdaulet T.; Panamarev, Taras P.; Naurzbaeva, Aisha Zh.; Kalambay, Mukhagali T.; Makukov, Maxim A.; Vilkoviskij, Emmanuil Y.; Omarov, Chingis T.; Berczik, Peter; Just, Andreas; Spurzem, Rainer

    2016-10-01

    The results of studies of the effect of the gas disk and its profile on the dynamics of active galactic nuclei are presented. The study was conducted with a numerical model of galactic nucleus based on phiGRAPE+GPU comprising three subsystems - a central supermassive black hole, gaseous accretion disc, and compact stellar cluster. The evolution of the compact stellar cluster is modeled with direct integration (N-body simulation), while the black hole and gaseous disc are represented phenomenologically: the black hole is introduced as an external potential (fixed in space but variable in time due to black hole mass growth), and the gaseous disc is introduced as spatial time-independent density distribution. We examined and compared with each other orbital parameters of accreting stars for model of the galactic nucleus with gas disc of constant and variable thickness, as well as without gas. It was found that in the presence of a gaseous disk almost half of the accreted particles interact strongly with the gas and are captured by the disc before accretion, while more than 85% of particles are affected to some extent by the disc prior to accretion. This suggests that interaction of the stellar cluster with the gas disk in the galactic nucleus might lead to the formation of stellar disk in the central part of the nucleus.

  9. Nuclear physics problems for accreting neutron stars

    SciTech Connect

    Wallace, R.K.; Woosley, S.E.

    1983-01-01

    The importance of p(e/sup -/nu)n and of (p,..gamma..) reactions on /sup 56/Ni during a thermonuclear runaway on a neutron star surface is pointed out. A fast 16-isotope approximate nuclear reaction network is developed that is suitable for use in hydrodynamic calculations of such events.

  10. Coronal Neutrino Emission in Hypercritical Accretion Flows

    NASA Astrophysics Data System (ADS)

    Kawabata, R.; Mineshige, S.; Kawanaka, N.

    2008-03-01

    Hypercritical accretion flows onto stellar mass black holes (BHs) are commonly believed to be as a promising model of central engines of gamma-ray bursts (GRBs). In this model a certain fraction of the gravitational binding energy of accreting matter is deposited to the energy of relativistic jets via neutrino annihilation and/or magnetic fields. However, some recent studies have indicated that the energy deposition rate by neutrino annihilation is somewhat smaller than that needed to power a GRB. To overcome this difficulty, Ramirez-Ruiz and Socrates proposed that high-energy neutrinos from the hot corona above the accretion disk might enhance the efficiency of the energy deposition. We elucidate the disk corona model in the context of hypercritical accretion flows. From the energy balance in the disk and the corona, we can calculate the disk and coronal temperature, Td and Tc, and neutrino spectra, taking into account the neutrino cooling processes by neutrino-electron scatterings and neutrino pair productions. The calculated neutrino spectra consist of two peaks: one by the neutrino emission from the disk and the other by that from the corona. We find that the disk corona can enhance the efficiency of energy release but only by a factor of 1.5 or so, unless the height of the corona is very small, Hll r. This is because the neutrino emission is very sensitive to the temperature of the emitting region, and then the ratio Tc/Td cannot be very large.

  11. Accretion, Outflows, and Winds of Magnetized Stars

    NASA Astrophysics Data System (ADS)

    Romanova, Marina M.; Owocki, Stanley P.

    2015-10-01

    Many types of stars have strong magnetic fields that can dynamically influence the flow of circumstellar matter. In stars with accretion disks, the stellar magnetic field can truncate the inner disk and determine the paths that matter can take to flow onto the star. These paths are different in stars with different magnetospheres and periods of rotation. External field lines of the magnetosphere may inflate and produce favorable conditions for outflows from the disk-magnetosphere boundary. Outflows can be particularly strong in the propeller regime, wherein a star rotates more rapidly than the inner disk. Outflows may also form at the disk-magnetosphere boundary of slowly rotating stars, if the magnetosphere is compressed by the accreting matter. In isolated, strongly magnetized stars, the magnetic field can influence formation and/or propagation of stellar wind outflows. Winds from low-mass, solar-type stars may be either thermally or magnetically driven, while winds from massive, luminous O and B type stars are radiatively driven. In all of these cases, the magnetic field influences matter flow from the stars and determines many observational properties. In this chapter we review recent studies of accretion, outflows, and winds of magnetized stars with a focus on three main topics: (1) accretion onto magnetized stars; (2) outflows from the disk-magnetosphere boundary; and (3) winds from isolated massive magnetized stars. We show results obtained from global magnetohydrodynamic simulations and, in a number of cases compare global simulations with observations.

  12. ACCRETION OUTBURSTS IN CIRCUMPLANETARY DISKS

    SciTech Connect

    Lubow, S. H.; Martin, R. G.

    2012-04-20

    We describe a model for the long-term evolution of a circumplanetary disk that is fed mass from a circumstellar disk and contains regions of low turbulence (dead zones). We show that such disks can be subject to accretion-driven outbursts, analogous to outbursts previously modeled in the context of circumstellar disks to explain FU Ori phenomena. Circumplanetary disks around a proto-Jupiter can undergo outbursts for infall accretion rates onto the disks in the range M-dot{sub infall} approx. 10{sup -9} to 10{sup -7} M{sub Sun} yr{sup -1}, typical of accretion rates in the T Tauri phase. During outbursts, the accretion rate and disk luminosity increases by several orders of magnitude. Most of the planet mass growth during planetary gas accretion may occur via disk outbursts involving gas that is considerably hotter than predicted by steady state models. For low infall accretion rates M-dot{sub infall} {approx}< 10{sup -10} M{sub sun} yr{sup -1} that occur in late stages of disk accretion, disk outbursts are unlikely to occur, even if dead zones are present. Such conditions are favorable for the formation of icy satellites.

  13. Evolution of Pre-Main Sequence Accretion Disks

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2005-01-01

    The aim of this project was to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, premain sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we developed much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution; measured disk accretion rates in these systems; and constructed detailed model disk structures consistent with observations to infer physical conditions such as grain growth in protoplanetary disks.

  14. Evolution of Pre-Main Sequence Accretion Disks

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2003-01-01

    The aim of this project is to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, pre-main sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we are developing much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution; measuring disk accretion rates in these systems; and constructing detailed model disk structures consistent with observations to infer physical conditions such as grain growth in protoplanetary disks.

  15. Evolution of Pre-Main Sequence Accretion Disks

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2004-01-01

    The aim of this project is to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, pre-main sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we are developing much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution; measuring disk accretion rates in these systems; and constructing detailed model disk structures consistent with observations to infer physical conditions such as grain growth in protoplanetary disks.

  16. Using Case Studies in Calculus-based Physics

    NASA Astrophysics Data System (ADS)

    Katz, Debora M.

    2006-12-01

    Do your students believe that the physics only works in your classroom or laboratory? Or do they see that physics underlies their everyday experience? Case studies in physics help students connect physics principles to their everyday experience. For decades, case studies have been used to teach law, medicine and biology, but they are rarely used in physics. I am working on a calculus-based physics textbook for scientists and engineers. Case studies are woven into each chapter. Stop by and get a case study to test out in your classroom. I would love to get your feedback.

  17. Partial accretion in the propeller stage of accreting millisecond X-ray pulsars

    NASA Astrophysics Data System (ADS)

    Gungor, Can; Gogus, Ersin; Eksi, Kazim Yavuz; Guver, Tolga

    2016-07-01

    Accreting millisecond X-ray pulsars (AMXPs) are very important objects for studying the stages of disk - magnetosphere interaction as these objects may show different stages in an observable duration. A typical X-ray light curve of an outburst of AMXP has a fast rise and an exponential decay phases. Most of the outbursts have a knee where the flux goes from the slow decay stage to the rapid decay stage. This knee may be linked to the transition from accretion to propeller stage. Since, after the knee, the X-ray luminosity of the source is still higher than its quiescent level, the accretion from inner disc must be continuing in the propeller stage with a lower fraction than in the accretion stage. The X-ray does not only come from accretion onto the poles but the inner parts of the disk may also contribute to the total X-ray luminosity. To infer what fraction (f) of the inflowing matter accretes onto the star the light curve in the propeller stage, one should first separate the emission originating from the disk and obtain a light curve of X-ray emission only from the magnetic poles. We provide a new method to infer from the observational data the fraction of accreting matter onto the neutron star pole to the mass transferring from outer layers of the disc to the inner disc (f), as a function of the fastness parameter (ω_{*}), assuming the knee is due to the transition from accretion to the propeller stage. We transform X-ray luminosities to the mass fraction, f, and the time scale of outburst to fastness parameter, ω_*. It allows us to compare different types of outbursts of an AMXP in f - ω_* space which is universal for a unique system. We analysed the Rossi X-ray Timing Explorer/Proportional Counter Array (RXTE/PCA) observations of the 2000 and the 2011 outbursts and the Swift Gamma-Ray Burst Mission/X-ray Telescope (SWIFT/XRT) data of the 2013 outburst of the most known AMXP, Aql X-1 using a combination of blackbody representing hot spot, disk blackbody

  18. Dynamics of core accretion

    DOE PAGES

    Nelson, Andrew F.; Ruffert, Maximilian

    2012-12-21

    In this paper, we perform three-dimensional hydrodynamic simulations of gas flowing around a planetary core of mass Mpl = 10M⊕ embedded in a near Keplerian background flow, using a modified shearing box approximation. We assume an ideal gas behaviour following an equation of state with a fixed ratio of the specific heats, γ = 1.42, consistent with the conditions of a moderate-temperature background disc with solar composition. No radiative heating or cooling is included in the models. We employ a nested grid hydrodynamic code implementing the ‘Piecewise Parabolic Method’ with as many as six fixed nested grids, providing spatial resolutionmore » on the finest grid comparable to the present-day diameters of Neptune and Uranus. We find that a strongly dynamically active flow develops such that no static envelope can form. The activity is not sensitive to plausible variations in the rotation curve of the underlying disc. It is sensitive to the thermodynamic treatment of the gas, as modelled by prescribed equations of state (either ‘locally isothermal’ or ‘locally isentropic’) and the temperature of the background disc material. The activity is also sensitive to the shape and depth of the core's gravitational potential, through its mass and gravitational softening coefficient. Each of these factors influences the magnitude and character of hydrodynamic feedback of the small-scale flow on the background, and we conclude that accurate modelling of such feedback is critical to a complete understanding of the core accretion process. The varying flow pattern gives rise to large, irregular eruptions of matter from the region around the core which return matter to the background flow: mass in the envelope at one time may not be found in the envelope at any later time. No net mass accretion into the envelope is observed over the course of the simulation and none is expected, due to our neglect of cooling. Except in cases of very rapid cooling however, as

  19. Dynamics of core accretion

    SciTech Connect

    Nelson, Andrew F.; Ruffert, Maximilian

    2012-12-21

    In this paper, we perform three-dimensional hydrodynamic simulations of gas flowing around a planetary core of mass Mpl = 10M embedded in a near Keplerian background flow, using a modified shearing box approximation. We assume an ideal gas behaviour following an equation of state with a fixed ratio of the specific heats, γ = 1.42, consistent with the conditions of a moderate-temperature background disc with solar composition. No radiative heating or cooling is included in the models. We employ a nested grid hydrodynamic code implementing the ‘Piecewise Parabolic Method’ with as many as six fixed nested grids, providing spatial resolution on the finest grid comparable to the present-day diameters of Neptune and Uranus. We find that a strongly dynamically active flow develops such that no static envelope can form. The activity is not sensitive to plausible variations in the rotation curve of the underlying disc. It is sensitive to the thermodynamic treatment of the gas, as modelled by prescribed equations of state (either ‘locally isothermal’ or ‘locally isentropic’) and the temperature of the background disc material. The activity is also sensitive to the shape and depth of the core's gravitational potential, through its mass and gravitational softening coefficient. Each of these factors influences the magnitude and character of hydrodynamic feedback of the small-scale flow on the background, and we conclude that accurate modelling of such feedback is critical to a complete understanding of the core accretion process. The varying flow pattern gives rise to large, irregular eruptions of matter from the region around the core which return matter to the background flow: mass in the envelope at one time may not be found in the envelope at any later time. No net mass accretion into the envelope is observed over the course of the simulation and none is expected, due to our neglect of cooling. Except in cases of very rapid cooling

  20. To accrete or not accrete, that is the question

    USGS Publications Warehouse

    von, Huene R.

    1986-01-01

    Along modern convergent margins tectonic processes span a spectrum from accretion to erosion. The process of accretion is generally recognized because it leaves a geologic record, whereas the process of erosion is generally hypothetical because it produces a geologic hiatus. Major conditions that determine the dominance of accretion or erosion at modern convergent margins are: 1) rate and direction of plate convergence, 2) sediment supply and type in the trench, and 3) topography of the subducting ocean floor. Most change in structure has been ascribed to plate motion, but both erosion and accretion are observed along the same convergence margin. Thus sediment supply and topography are probably of equivalent importance to plate motion because both erosion and accretion are observed under constant conditions of plate convergence. The dominance of accretion or erosion at a margin varies with the thickness of trench sediment. In a sediment flooded trench, the proportions of subducted and accreted sediment are commonly established by the position of a decollement along a weak horizon in the sediment section. Thus, the vertical variation of sediment strength and the distribution of horizontal stress are important factors. Once deformation begins, the original sediment strength is decreased by sediment remolding and where sediment thickens rapidly, increases in pore fluid pressure can be pronounced. In sediment-starved trenches, where the relief of the subducting ocean floor is not smoothed over, the front of the margin must respond to the topography subducted as well as that accreted. The hypothesized erosion by the drag of positive features against the underside of the upper plate (a high stress environment) may alternate with erosion due to the collapse of a margin front into voids such as graben (a low stress environment). ?? 1986 Ferdinand Enke Verlag Stuttgart.

  1. 40 CFR 792.135 - Physical and chemical characterization studies.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 33 2012-07-01 2012-07-01 false Physical and chemical characterization... A Study § 792.135 Physical and chemical characterization studies. (a) All provisions of the GLPs shall apply to physical and chemical characterization studies designed to determine...

  2. 40 CFR 792.135 - Physical and chemical characterization studies.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 32 2014-07-01 2014-07-01 false Physical and chemical characterization... A Study § 792.135 Physical and chemical characterization studies. (a) All provisions of the GLPs shall apply to physical and chemical characterization studies designed to determine...

  3. 40 CFR 792.135 - Physical and chemical characterization studies.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 31 2010-07-01 2010-07-01 true Physical and chemical characterization... A Study § 792.135 Physical and chemical characterization studies. (a) All provisions of the GLPs shall apply to physical and chemical characterization studies designed to determine...

  4. 40 CFR 792.135 - Physical and chemical characterization studies.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 33 2013-07-01 2013-07-01 false Physical and chemical characterization... A Study § 792.135 Physical and chemical characterization studies. (a) All provisions of the GLPs shall apply to physical and chemical characterization studies designed to determine...

  5. 40 CFR 792.135 - Physical and chemical characterization studies.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 32 2011-07-01 2011-07-01 false Physical and chemical characterization... A Study § 792.135 Physical and chemical characterization studies. (a) All provisions of the GLPs shall apply to physical and chemical characterization studies designed to determine...

  6. Physical Fitness and Physical Activity in Adolescents with Asperger Syndrome: A Comparative Study

    ERIC Educational Resources Information Center

    Borremans, Erwin; Rintala, Pauli; McCubbin, Jeffrey A.

    2010-01-01

    While physical activity is beneficial for youth with developmental disabilities, little is known about those individuals' fitness profile and levels of activity. Therefore the purpose of this study was to investigate the physical fitness profile and physical activity level of 30 adolescents with and without Asperger syndrome (AS). Evaluations were…

  7. A Case Study Objectively Assessing Female Physical Activity Levels within the National Curriculum for Physical Education

    ERIC Educational Resources Information Center

    Hobbs, Matthew; Daly-Smith, Andrew; Morley, David; McKenna, James

    2015-01-01

    The purpose of this study was to assess the impact of the National Curriculum for Physical Education (NCPE) lesson themes and contexts on the profile of moderate-to-vigorous physical activity (MVPA). Fifteen, Year 9 Physical Education (PE) lessons were assessed within the lesson themes of Outwitting Opponents (OO) (delivered through field hockey…

  8. How Physics Instruction Impacts Students' Beliefs about Learning Physics: A Meta-Analysis of 24 Studies

    ERIC Educational Resources Information Center

    Madsen, Adrian; McKagan, Sarah B.; Sayre, Eleanor C.

    2015-01-01

    In this meta-analysis, we synthesize the results of 24 studies using the Colorado Learning Attitudes about Science Survey (CLASS) and the Maryland Physics Expectations Survey (MPEX) to answer several questions: (1) How does physics instruction impact students' beliefs? (2) When do physics majors develop expert-like beliefs? and (3) How do…

  9. Laboratory studies in ultraviolet solar physics

    NASA Technical Reports Server (NTRS)

    Parkinson, W. H.; Kohl, J. L.; Gardner, L. D.; Raymond, J. C.; Smith, P. L.

    1991-01-01

    The research activity comprised the measurement of basic atomic processes and parameters which relate directly to the interpretation of solar ultraviolet observations and to the development of comprehensive models of the component structures of the solar atmosphere. The research was specifically directed towards providing the relevant atomic data needed to perform and to improve solar diagnostic techniques which probe active and quiet portions of the solar chromosphere, the transition zone, the inner corona, and the solar wind acceleration regions of the extended corona. The accuracy with which the physical conditions in these structures can be determined depends directly on the accuracy and completeness of the atomic and molecular data. These laboratory data are used to support the analysis programs of past and current solar observations (e.g., the Orbiting solar Observatories, the Solar Maximum Mission, the Skylab Apollo Telescope Mount, and the Naval Research Laboratory's rocket-borne High Resolution Telescope and Spectrograph). In addition, we attempted to anticipate the needs of future space-borne solar studies such as from the joint ESA/NASA Solar and Heliospheric Observatory (SOHO) spacecraft. Our laboratory activities stressed two categories of study: (1) the measurement of absolute rate coefficients for dielectronic recombination and electron impact excitation; and (2) the measurement of atomic transition probabilities for solar density diagnostics. A brief summary of the research activity is provided.

  10. An in-depth study of a neutron star accreting at low Eddington rate: on the possibility of a truncated disc and an outflow

    NASA Astrophysics Data System (ADS)

    Degenaar, N.; Pinto, C.; Miller, J. M.; Wijnands, R.; Altamirano, D.; Paerels, F.; Fabian, A. C.; Chakrabarty, D.

    2017-01-01

    Due to observational challenges, our knowledge of low-level accretion flows around neutron stars is limited. We present NuSTAR, Swift and Chandra observations of the low-mass X-ray binary IGR J17062-6143, which has been persistently accreting at ≃0.1 per cent of the Eddington limit since 2006. Our simultaneous NuSTAR/Swift observations show that the 0.5-79 keV spectrum can be described by a combination of a power law with a photon index of Γ ≃ 2, a blackbody with a temperature of kTbb ≃ 0.5 keV (presumably arising from the neutron star surface) and disc reflection. Modelling the reflection spectrum suggests that the inner accretion disc was located at Rin ≳ 100 GM/c2 (≳225 km) from the neutron star. The apparent truncation may be due to evaporation of the inner disc into a radiatively-inefficient accretion flow, or due to the pressure of the neutron star magnetic field. Our Chandra gratings data reveal possible narrow emission lines near 1 keV that can be modelled as reflection or collisionally ionized gas, and possible low-energy absorption features that could point to the presence of an outflow. We consider a scenario in which this neutron star has been able to sustain its low accretion rate through magnetic inhibition of the accretion flow, which gives some constraints on its magnetic field strength and spin period. In this configuration, IGR J17062-6143 could exhibit a strong radio jet as well as a (propeller-driven) wind-like outflow.

  11. Azimuthal Stress and Heat Flux In Radiatively Inefficient Accretion Flows

    NASA Astrophysics Data System (ADS)

    Devlen, Ebru

    2016-07-01

    Radiatively Inefficient Accretion Flows (RIAFs) have low radiative efficiencies and/or low accretion rates. The accreting gas may retain most of its binding energy in the form of heat. This lost energy for hot RIAFs is one of the problems heavily worked on in the literature. RIAF observations on the accretion to super massive black holes (e.g., Sagittarius A* in the center of our Galaxy) have shown that the observational data are not consistent with either advection-dominated accretion flow (ADAF) or Bondi models. For this reason, it is very important to theoretically comprehend the physical properties of RIAFs derived from observations with a new disk/flow model. One of the most probable candidates for definition of mass accretion and the source of excess heat energy in RIAFs is the gyroviscous modified magnetorotational instability (GvMRI). Dispersion relation is derived by using MHD equations containing heat flux term based on viscosity in the energy equation. Numerical solutions of the disk equations are done and the growth rates of the instability are calculated. This additional heat flux plays an important role in dissipation of energy. The rates of the angular momentum and heat flux which are obtained from numerical calculations of the turbulence brought about by the GVMRI are also discussed.

  12. Constraining Accreting Binary Populations in Normal Galaxies

    NASA Astrophysics Data System (ADS)

    Lehmer, Bret; Hornschemeier, A.; Basu-Zych, A.; Fragos, T.; Jenkins, L.; Kalogera, V.; Ptak, A.; Tzanavaris, P.; Zezas, A.

    2011-01-01

    X-ray emission from accreting binary systems (X-ray binaries) uniquely probe the binary phase of stellar evolution and the formation of compact objects such as neutron stars and black holes. A detailed understanding of X-ray binary systems is needed to provide physical insight into the formation and evolution of the stars involved, as well as the demographics of interesting binary remnants, such as millisecond pulsars and gravitational wave sources. Our program makes wide use of Chandra observations and complementary multiwavelength data sets (through, e.g., the Spitzer Infrared Nearby Galaxies Survey [SINGS] and the Great Observatories Origins Deep Survey [GOODS]), as well as super-computing facilities, to provide: (1) improved calibrations for correlations between X-ray binary emission and physical properties (e.g., star-formation rate and stellar mass) for galaxies in the local Universe; (2) new physical constraints on accreting binary processes (e.g., common-envelope phase and mass transfer) through the fitting of X-ray binary synthesis models to observed local galaxy X-ray binary luminosity functions; (3) observational and model constraints on the X-ray evolution of normal galaxies over the last 90% of cosmic history (since z 4) from the Chandra Deep Field surveys and accreting binary synthesis models; and (4) predictions for deeper observations from forthcoming generations of X-ray telesopes (e.g., IXO, WFXT, and Gen-X) to provide a science driver for these missions. In this talk, we highlight the details of our program and discuss recent results.

  13. Spectroscopy of Low Mass X-Ray Binaries: New Insights into Accretion. Revised

    NASA Technical Reports Server (NTRS)

    DilVrtilek, Saeqa; Mushotzky, Richard (Technical Monitor)

    2001-01-01

    This project is to observe two low mass X-ray binaries, chosen for their X-ray brightness, low column density, and diversity of accretion behavior. The high spectral resolution of the RGS, the broad energy range and tremendous collecting power of EPIC, and simultaneous optical monitoring with the OM are particularly well-suited to these studies. observation of one of the two objects has taken place and the data were received in late November. The second object is yet to be observed. Over the next year we will: investigate the physical conditions of the emitting gas using emission and recombination line diagnostics to determine temperatures, densities, elemental abundances, and ionization structure; study the behavior of emission features as a function of binary orbit; and test and improve models of X-ray line emission developed by us over the past decade. We will gain insight on both the geometry of the accretion flow and on the evolutionary history of LMXBs.

  14. Spectroscopy of Low Mass X-Ray Binaries: New Insights into Accretion

    NASA Technical Reports Server (NTRS)

    Vrtilek, Saeqa Dil; Mushotzky, Richard F. (Technical Monitor)

    2002-01-01

    This project is to observe two low mass X-ray binaries, chosen for their X-ray brightness, low column density, and diversity of accretion behavior. The high spectral resolution of the RGS, the broad energy range and tremendous collecting power of EPIC, and simultaneous optical monitoring with the OM are particularly well-suited to these studies. The second of two objects was not observed until September of 2002. Data analysis for the new observation is underway. over the next year we will: investigate the physical conditions of the emitting gas using emission and recombination line diagnostics to determine temperatures, densities, elemental abundances, and ionization structure; study the behavior of emission features as a function of binary orbit; and test and improve models of X-ray line emission developed by us over the past decade. We will gain insight on both the geometry of the accretion flow and on the evolutionary history of LMXBs.

  15. Accretion onto Compact Objects Viewed as a Flow in Converging-Diverging Ducts

    NASA Astrophysics Data System (ADS)

    Chakrabarti, K.; Majumdar, M. M.; Chakrabarti, Sandip K.

    Black hole accretion is necessarily transonic and the number of physical sonic points depends on the angular momentum of the flow. We study the properties of such a flow by recasting this idea into an engineering problem in which a flow has a subsonic to supersonic transition when it passes through a de Laval nozzle, i.e. a converging and diverging duct in a flat geometry in the presence of sufficient end pressure difference. Particularly interesting is the case of the centrifugal pressure supported standing shock formation inside an accretion flow, because the flow passes through at least two saddle type sonic points, one before and one after the shock. In this case, the duct itself has two minima and a maximum. We study the properties of such a duct as a function of the inflow parameters and classify all possible types of the flow through this composite nozzle.

  16. Dynamics of continental accretion.

    PubMed

    Moresi, L; Betts, P G; Miller, M S; Cayley, R A

    2014-04-10

    Subduction zones become congested when they try to consume buoyant, exotic crust. The accretionary mountain belts (orogens) that form at these convergent plate margins have been the principal sites of lateral continental growth through Earth's history. Modern examples of accretionary margins are the North American Cordilleras and southwest Pacific subduction zones. The geologic record contains abundant accretionary orogens, such as the Tasmanides, along the eastern margin of the supercontinent Gondwana, and the Altaïdes, which formed on the southern margin of Laurasia. In modern and ancient examples of long-lived accretionary orogens, the overriding plate is subjected to episodes of crustal extension and back-arc basin development, often related to subduction rollback and transient episodes of orogenesis and crustal shortening, coincident with accretion of exotic crust. Here we present three-dimensional dynamic models that show how accretionary margins evolve from the initial collision, through a period of plate margin instability, to re-establishment of a stable convergent margin. The models illustrate how significant curvature of the orogenic system develops, as well as the mechanism for tectonic escape of the back-arc region. The complexity of the morphology and the evolution of the system are caused by lateral rollback of a tightly arcuate trench migrating parallel to the plate boundary and orthogonally to the convergence direction. We find geological and geophysical evidence for this process in the Tasmanides of eastern Australia, and infer that this is a recurrent and global phenomenon.

  17. Dynamics of continental accretion

    NASA Astrophysics Data System (ADS)

    Moresi, L.; Betts, P. G.; Miller, M. S.; Cayley, R. A.

    2014-04-01

    Subduction zones become congested when they try to consume buoyant, exotic crust. The accretionary mountain belts (orogens) that form at these convergent plate margins have been the principal sites of lateral continental growth through Earth's history. Modern examples of accretionary margins are the North American Cordilleras and southwest Pacific subduction zones. The geologic record contains abundant accretionary orogens, such as the Tasmanides, along the eastern margin of the supercontinent Gondwana, and the Altaïdes, which formed on the southern margin of Laurasia. In modern and ancient examples of long-lived accretionary orogens, the overriding plate is subjected to episodes of crustal extension and back-arc basin development, often related to subduction rollback and transient episodes of orogenesis and crustal shortening, coincident with accretion of exotic crust. Here we present three-dimensional dynamic models that show how accretionary margins evolve from the initial collision, through a period of plate margin instability, to re-establishment of a stable convergent margin. The models illustrate how significant curvature of the orogenic system develops, as well as the mechanism for tectonic escape of the back-arc region. The complexity of the morphology and the evolution of the system are caused by lateral rollback of a tightly arcuate trench migrating parallel to the plate boundary and orthogonally to the convergence direction. We find geological and geophysical evidence for this process in the Tasmanides of eastern Australia, and infer that this is a recurrent and global phenomenon.

  18. Bondi-Hoyle Accretion in an Isothermal Magnetized Plasma

    NASA Astrophysics Data System (ADS)

    Lee, Aaron T.; Cunningham, Andrew J.; McKee, Christopher F.; Klein, Richard I.

    2014-03-01

    In regions of star formation, protostars and newborn stars will accrete mass from their natal clouds. These clouds are threaded by magnetic fields with a strength characterized by the plasma β—the ratio of thermal and magnetic pressures. Observations show that molecular clouds have β <~ 1, so magnetic fields have the potential to play a significant role in the accretion process. We have carried out a numerical study of the effect of large-scale magnetic fields on the rate of accretion onto a uniformly moving point particle from a uniform, non-self-gravitating, isothermal gas. We consider gas moving with sonic Mach numbers of up to {\\cal M}\\approx 45; magnetic fields that are either parallel, perpendicular, or oriented 45° to the flow; and β as low as 0.01. Our simulations utilize adaptive mesh refinement in order to obtain high spatial resolution where it is needed; this also allows the boundaries to be far from the accreting object to avoid unphysical effects arising from boundary conditions. Additionally, we show that our results are independent of our exact prescription for accreting mass in the sink particle. We give simple expressions for the steady-state accretion rate as a function of β and {\\cal M} for the parallel and perpendicular orientations. Using typical molecular cloud values of {\\cal M}\\sim 5 and β ~ 0.04 from the literature, our fits suggest that a 0.4 M ⊙ star accretes ~4 × 10-9 M ⊙ yr-1, almost a factor of two less than accretion rates predicted by hydrodynamic models. This disparity can grow to orders of magnitude for stronger fields and lower Mach numbers. We also discuss the applicability of these accretion rates versus accretion rates expected from gravitational collapse, and under what conditions a steady state is possible. The reduction in the accretion rate in a magnetized medium leads to an increase in the time required to form stars in competitive accretion models, making such models less efficient than predicted by

  19. Bondi-Hoyle accretion in an isothermal magnetized plasma

    SciTech Connect

    Lee, Aaron T.; McKee, Christopher F.; Klein, Richard I.; Cunningham, Andrew J.

    2014-03-01

    In regions of star formation, protostars and newborn stars will accrete mass from their natal clouds. These clouds are threaded by magnetic fields with a strength characterized by the plasma β—the ratio of thermal and magnetic pressures. Observations show that molecular clouds have β ≲ 1, so magnetic fields have the potential to play a significant role in the accretion process. We have carried out a numerical study of the effect of large-scale magnetic fields on the rate of accretion onto a uniformly moving point particle from a uniform, non-self-gravitating, isothermal gas. We consider gas moving with sonic Mach numbers of up to M≈45; magnetic fields that are either parallel, perpendicular, or oriented 45° to the flow; and β as low as 0.01. Our simulations utilize adaptive mesh refinement in order to obtain high spatial resolution where it is needed; this also allows the boundaries to be far from the accreting object to avoid unphysical effects arising from boundary conditions. Additionally, we show that our results are independent of our exact prescription for accreting mass in the sink particle. We give simple expressions for the steady-state accretion rate as a function of β and M for the parallel and perpendicular orientations. Using typical molecular cloud values of M∼5 and β ∼ 0.04 from the literature, our fits suggest that a 0.4 M {sub ☉} star accretes ∼4 × 10{sup –9} M {sub ☉} yr{sup –1}, almost a factor of two less than accretion rates predicted by hydrodynamic models. This disparity can grow to orders of magnitude for stronger fields and lower Mach numbers. We also discuss the applicability of these accretion rates versus accretion rates expected from gravitational collapse, and under what conditions a steady state is possible. The reduction in the accretion rate in a magnetized medium leads to an increase in the time required to form stars in competitive accretion models, making such models less efficient than predicted by

  20. Bayesian inference in physics: case studies

    NASA Astrophysics Data System (ADS)

    Dose, V.

    2003-09-01

    This report describes the Bayesian approach to probability theory with emphasis on the application to the evaluation of experimental data. A brief summary of Bayesian principles is given, with a discussion of concepts, terminology and pitfalls. The step from Bayesian principles to data processing involves major numerical efforts. We address the presently employed procedures of numerical integration, which are mainly based on the Monte Carlo method. The case studies include examples from electron spectroscopies, plasma physics, ion beam analysis and mass spectrometry. Bayesian solutions to the ubiquitous problem of spectrum restoration are presented and advantages and limitations are discussed. Parameter estimation within the Bayesian framework is shown to allow for the incorporation of expert knowledge which in turn allows the treatment of under-determined problems which are inaccessible by the traditional maximum likelihood method. A unique and extremely valuable feature of Bayesian theory is the model comparison option. Bayesian model comparison rests on Ockham's razor which limits the complexity of a model to the amount necessary to explain the data without fitting noise. Finally we deal with the treatment of inconsistent data. They arise frequently in experimental work either from incorrect estimation of the errors associated with a measurement or alternatively from distortions of the measurement signal by some unrecognized spurious source. Bayesian data analysis sometimes meets with spectacular success. However, the approach cannot do wonders, but it does result in optimal robust inferences on the basis of all available and explicitly declared information.

  1. ACCRETING CIRCUMPLANETARY DISKS: OBSERVATIONAL SIGNATURES

    SciTech Connect

    Zhu, Zhaohuan

    2015-01-20

    I calculate the spectral energy distributions of accreting circumplanetary disks using atmospheric radiative transfer models. Circumplanetary disks only accreting at 10{sup –10} M {sub ☉} yr{sup –1} around a 1 M{sub J} planet can be brighter than the planet itself. A moderately accreting circumplanetary disk ( M-dot ∼10{sup −8} M{sub ⊙} yr{sup −1}; enough to form a 10 M{sub J} planet within 1 Myr) around a 1 M{sub J} planet has a maximum temperature of ∼2000 K, and at near-infrared wavelengths (J, H, K bands), this disk is as bright as a late-M-type brown dwarf or a 10 M{sub J} planet with a ''hot start''. To use direct imaging to find the accretion disks around low-mass planets (e.g., 1 M{sub J} ) and distinguish them from brown dwarfs or hot high-mass planets, it is crucial to obtain photometry at mid-infrared bands (L', M, N bands) because the emission from circumplanetary disks falls off more slowly toward longer wavelengths than those of brown dwarfs or planets. If young planets have strong magnetic fields (≳100 G), fields may truncate slowly accreting circumplanetary disks ( M-dot ≲10{sup −9} M{sub ⊙} yr{sup −1}) and lead to magnetospheric accretion, which can provide additional accretion signatures, such as UV/optical excess from the accretion shock and line emission.

  2. General Physics, Study Guide, 2nd Edition

    NASA Astrophysics Data System (ADS)

    Sternheim, Morton M.; Kane, Joseph W.

    1991-01-01

    Introduces physics to science students with a wide range of interests. Unlike many other physics texts, the coverage and emphasis here is influenced by the specific needs of science majors, including those in the life sciences, and thus treats topics such as geometric optics, mechanics of fluids and acoustics. The derivative is introduced in Chapter One and integrals are used sparingly until electricity and magnetism are covered. Entire chapters are devoted to applications of physics covering subjects such as nerve conduction, ionizing radiation and nuclear magnetic resonance, demonstrating the widespread utility of physics and the unity of science. To aid in comprehension, calculations involving calculus are carried out with a good deal of detail and discussion. Each chapter features a checklist of terms to define or explain as well as problems and exercises. Additional problems and exercises are located in the Supplementary Topics section.

  3. Migration of accreting giant planets

    NASA Astrophysics Data System (ADS)

    Crida, A.; Bitsch, B.; Raibaldi, A.

    2016-12-01

    We present the results of 2D hydro simulations of giant planets in proto-planetary discs, which accrete gas at a more or less high rate. First, starting from a solid core of 20 Earth masses, we show that as soon as the runaway accretion of gas turns on, the planet is saved from type I migration : the gap opening mass is reached before the planet is lost into its host star. Furthermore, gas accretion helps opening the gap in low mass discs. Consequently, if the accretion rate is limited to the disc supply, then the planet is already inside a gap and in type II migration. We further show that the type II migration of a Jupiter mass planet actually depends on its accretion rate. Only when the accretion is high do we retrieve the classical picture where no gas crosses the gap and the planet follows the disc spreading. These results impact our understanding of planet migration and planet population synthesis models. The e-poster presenting these results in French can be found here: L'e-poster présentant ces résultats en français est disponible à cette adresse: http://sf2a.eu/semaine-sf2a/2016/posterpdfs/156_179_49.pdf.

  4. ACCRETION DISK TEMPERATURES OF QSOs: CONSTRAINTS FROM THE EMISSION LINES

    SciTech Connect

    Bonning, E. W.; Shields, G. A.; Stevens, A. C.; Salviander, S. E-mail: shields@astro.as.utexas.edu E-mail: triples@astro.as.utexas.edu

    2013-06-10

    We compare QSO emission-line spectra to predictions based on theoretical ionizing continua of accretion disks. The observed line intensities do not show the expected trend of higher ionization with theoretical accretion disk temperature as predicted from the black hole mass and accretion rate. Consistent with earlier studies, this suggests that the inner disk does not reach temperatures as high as expected from standard disk theory. Modified radial temperature profiles, taking account of winds or advection in the inner disk, achieve better agreement with observation. The emission lines of radio-detected and radio-undetected sources show different trends as a function of the theoretically predicted disk temperature.

  5. Accretion tori and cones of ionizing radiation in Seyfert galaxies

    NASA Technical Reports Server (NTRS)

    Acosta-Pulido, Jose A.; Perez-Fournon, Ismael; Calvani, Massimo; Wilson, Andrew S.

    1990-01-01

    The photoionization of extended narrow-line regions in Seyfert galaxies by the radiation produced in a thick accretion disk is studied. The emission-line spectrum is calculated for a range of black hole masses, varying the values of the ionization parameter and the disk size. It is found that models with a million solar masses fit observations of very large accretion disk sizes, while models with 10 million solar masses fit them better with smaller disks. The latter models are preferable since they have lower super-Eddington accretion rates.

  6. Circinus X-1: a Laboratory for Studying the Accretion Phenomenon in Compact Binary X-Ray Sources. Ph.D. Thesis - Maryland Univ.

    NASA Technical Reports Server (NTRS)

    Robinson-Saba, J. L.

    1983-01-01

    Observations of the binary X-ray source Circinus X-1 provide samples of a range of spectral and temporal behavior whose variety is thought to reflect a broad continuum of accretion conditions in an eccentric binary system. The data support an identification of three or more X-ray spectral components, probably associated with distinct emission regions.

  7. Terrestrial Planets Accreted Dry

    NASA Astrophysics Data System (ADS)

    Albarede, F.; Blichert-Toft, J.

    2007-12-01

    Plate tectonics shaped the Earth, whereas the Moon is a dry and inactive desert. Mars probably came to rest within the first billion years of its history, and Venus, although internally very active, has a dry inferno for its surface. The strong gravity field of a large planet allows for an enormous amount of gravitational energy to be released, causing the outer part of the planetary body to melt (magma ocean), helps retain water on the planet, and increases the pressure gradient. The weak gravity field and anhydrous conditions prevailing on the Moon stabilized, on top of its magma ocean, a thick buoyant plagioclase lithosphere, which insulated the molten interior. On Earth, the buoyant hydrous phases (serpentines) produced by reactions between the terrestrial magma ocean and the wet impactors received from the outer Solar System isolated the magma and kept it molten for some few tens of million years. The elemental distributions and the range of condensation temperatures show that the planets from the inner Solar System accreted dry. The interior of planets that lost up to 95% of their K cannot contain much water. Foundering of their wet surface material softened the terrestrial mantle and set the scene for the onset of plate tectonics. This very same process may have removed all the water from the surface of Venus 500 My ago and added enough water to its mantle to make its internal dynamics very strong and keep the surface very young. Because of a radius smaller than that of the Earth, not enough water could be drawn into the Martian mantle before it was lost to space and Martian plate tectonics never began. The radius of a planet therefore is the key parameter controlling most of its evolutional features.

  8. H-chondrite parent asteroid: A multistage cooling, fragmentation and re-accretion history constrained by thermometric studies, diffusion kinetic modeling and geochronological data

    NASA Astrophysics Data System (ADS)

    Ganguly, Jibamitra; Tirone, Massimiliano; Chakraborty, Sumit; Domanik, Kenneth

    2013-03-01

    We present a detailed thermometric study and cooling history analysis of selected H-chondrites from the petrologic types 4-6 on the basis of their mineralogical properties, and integrate these data with other available constraints on the cooling rates to develop a comprehensive model for the cooling, fragmentation and re-accretion history of the parent asteroid. Temperatures have been determined on the basis of two-pyroxene (2-Px) and spinel (Spnl)-orthopyroxene (Opx)/olivine (Ol) thermometers using the average of line scans and distributed spot analysis of coexisting pairs in each set. All of these minerals have been found to be compositionally homogeneous from ˜1 to 2 μm from the interface within the resolution of microprobe analysis. The thermometric results for the H5 (Allegan and Richardton) and H6 (Guarena and Kernouvé) samples are very similar. Also, while the 2-Px temperature increases by ˜90 °C from H4 to H5/6, a reverse trend is observed for the Spnl-Opx/Ol temperatures implying compositional resetting of these pairs during cooling. For the H4 sample (Forest Vale) all thermometric results are similar. The cooling rates calculated from numerical modeling of the compositional profiles in Opx-Cpx pairs in H5 and H6, corrected for the spatial averaging or convolution effect in microprobe analysis, are ˜25-100 °C/ky, which are 3-4 orders of magnitude higher than the cooling rates implied by in situ cooling in an onion-shell parent body model. Similar numerical simulation of the compositional profile in Opx-Spnl pair in H4 yields a cooling rate ˜50 °C/ky, which is in very good agreement with recent metallographic cooling rate of this sample and geochronological constraints on the cooling T-t path. Numerical simulation suggests that the slow cooling of the H5/6 samples at a rate of ˜15 °C/My, as deduced by recent metallographic study, could not have commenced at a temperature above ˜700 °C since, otherwise, the simulated compositional profile fails

  9. Accretion, metamorphism, and brecciation of ordinary chondrites - Evidence from petrologic studies of meteorites from Roosevelt County, New Mexico

    NASA Technical Reports Server (NTRS)

    Scott, Edward R. D.; Taylor, G. Jeffrey; Keil, Klaus

    1986-01-01

    The olivines and pyroxenes from twenty-nine ordinary chondrites from Roosevelt County, New Mexico are examined. The mineralogical properties of the chondrites studied are described. Correlations between mineral compositions and petrologic type and between petrologic type and bulk chemistry are analyzed. It is observed that mean CaO concentrations in olivine show significant variations among equilibrated chondrites, but these are not correlated with petrologic type; the degree of heterogeneity of FeO concentrations in olivines of types 4-6 is not correlated with the degree of metamorphism; and mean FeO concentrations of silicates show average increases of 3-5 percent from type 4 to type 6 in each group.

  10. FM6: Summary of Session #5 on Accretion and Feedback in Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Brenneman, Laura

    Focus Meeting 6 of the IAU 2015 Symposium centered around the topic of ``X-ray Surveys of the Hot and Energetic Universe.'' Within this two-day meeting seven sessions (31 total talks) were presented, whose topics included galaxy cluster physics and evolution, cluster cosmological studies, AGN demographics and X-ray binary populations, first quasars, accretion and feedback, large-scale structures, and normal and starburst galaxies. Herein, I summarize the results presented during session #5, which focused on AGN accretion and feedback. Six authors contributed their work to our session: Laura Brenneman, Kazushi Iwasawa, Massimo Gaspari, Michaela Hirschmann, Franz Bauer and Yuan Liu. I provide a brief introduction below, followed by the details of the presentations of each author in the order in which the presentations were given.

  11. Chondrule formation in the radiative accretional shock

    NASA Technical Reports Server (NTRS)

    Ruzmaikina, T. V.; Ip, W.

    1994-01-01

    The physical, mineralogical, and isotopic properties of chondrules strongly indicate that they were formed by the rapid melting and resolidification of preexisting solids composed of primitive material. The chondrule precursors were heated to temperatures of about 1800 K in short high-temperature events, followed by cooling with a rate of 10(exp 2)-10(exp 3) K/hr. A heat input of about 1500 J/g is required to heat chondrule precursors to such a temperature and melt them. Lightning discharges and flares in the solar nebula, and heating of the chondrule precursors by friction with gas decelerated in the accretional shock or in a shock (of unspecified origin) within the solar nebula, have been discussed as possible mechanisms for chondrule formation. One advantage of chondrule formation in large-scale shocks is that a lot of dust material can be processed. An accretional shock, which is produced by infalling gas of the presolar cloud when it collides with the solar nebula, belongs to this type of shock. In 1984 Wood considered the possibility of chondrule formation in the accretional shock by heating of chondrule precursors by gas drag. He concluded that the density in the accreting material is much lower than needed to melt silicates at the distance of the asteroid belt if the accreting matter had the cosmic ratio of dust to gas, and the mass of the solar nebula did not exceed 2 solar mass units. Melting of chondrule precursors is difficult because of their effective cooling by thermal radiation. Suppression of the radiative cooling of individual grains in dust swarms, which are opaque to thermal emission, was considered to be the only possible means of chondrule formation in solar nebula shocks. Previous models of solid grain melting in solar nebula shocks have neglected gas cooling behind the shock front, i.e., they considered adiabatic shocks. In this paper we show that large dust grains could be heated much stronger than was supposed by these authors, because of

  12. SWIFT X-RAY TELESCOPE STUDY OF THE BLACK HOLE BINARY MAXI J1659–152: VARIABILITY FROM A TWO COMPONENT ACCRETION FLOW

    SciTech Connect

    Kalamkar, M.; Klis, M. van der; Heil, L.; Homan, J.

    2015-08-01

    We present an energy dependent X-ray variability study of the 2010 outburst of the black hole X-ray binary MAXI J1659–152 with the Swift X-ray Telescope (XRT). The broadband noise components and the quasi-periodic oscillations (QPO) observed in the power spectra show a strong and varied energy dependence. Combining Swift XRT data with data from the Rossi X-ray Timing Explorer, we report, for the first time, an rms spectrum (fractional rms amplitude as a function of energy) of these components in the 0.5–30 keV energy range. We find that the strength of the low-frequency component (<0.1 Hz) decreases with energy, contrary to the higher frequency components (>0.1 Hz) whose strengths increase with energy. In the context of the propagating fluctuations model for X-ray variability, we suggest that the low-frequency component originates in the accretion disk (which dominates emission below ∼2 keV) and the higher frequency components are formed in the hot flow (which dominates emission above ∼2 keV). As the properties of the QPO suggest that it may have a different driving mechanism, we investigate the Lense–Thirring precession of the hot flow as a candidate model. We also report on the QPO coherence evolution for the first time in the energy band below 2 keV. While there are strong indications that the QPO is less coherent at energies below 2 keV than above 2 keV, the coherence increases with intensity similar to what is observed at energies above 2 keV in other black hole X-ray binaries.

  13. Flow dynamics and sedimentation of lateral accretion packages in sinuous deep-water channels: A 3D seismic case study from the northwestern South China Sea margin

    NASA Astrophysics Data System (ADS)

    Li, Shengli; Gong, Chenglin

    2016-07-01

    The current study uses 3D seismic data to document architectural styles and flow dynamics of lateral accretion packages (LAPs) associated with sinuous deep-water channels, contributing to a better understanding of flow processes and sedimentation associated with LAPs. The documented LAPs underwent three main stages of architectural evolution, including the early incision stages characterized by intense downcutting, active migration stages characterized by active migration and avulsion of the individual channels, and late abandonment stages characterized by the termination of sediment gravity-flows and LAP growth. These three stages of LAP growth repeated through time, yielding a fining-upward pattern from sandy channel-fill turbidites, into sand-mud couplets, all capped by muddy turbidites. A river-reversed helical flow circulation was created by an imbalance, through the flow depth, of inwardly directed pressure gradient forces near the bed and outwardly directed centrifugal forces near the surface. It consists of low-velocity cores near the outer banks and low-velocity cores along the inner banks. Such river-reversed helical flow pattern is evidenced by volumetrically extensive LAPs and toplap and downlap terminations along the gentle banks and by aerially restricted, seismically unresolvable levees and truncation terminations near the steep banks. This river-reversed helical flow circulation favors asymmetric intra-channel deposition characterized by inner bank deposition versus outer bank erosion, and which, in turn, forced individual channels to consistently migrate towards outer banks, resulting in significant asymmetric cross-channel profiles with aerially extensive LAPs along inner banks.

  14. Sedimentological and GPR studies of subglacial deposits in the Joux Valley (Vaud, Switzerland): backset accretion in an esker followed by an erosive jokulhlaup

    USGS Publications Warehouse

    Fiore, J.; Pugin, A.; Beres, N.

    2002-01-01

    During the Wu??rmian glaciation, the Jura ice sheet covered the Joux Valley (Vaud, Switzerland). A geomorphological study reveals many drumlins in this valley. Some are composed of gravels and sand, others of till. Outcrops show that the surface of the sandy-gravel drumlins is a major and sharp erosion surface. Given the lack of shearing structures in sediments below this erosion level, its origin cannot be linked to ice action of the glacier. Very high-energy subglacial meltwater floods (jo??kulhlaups), probably due to the drainage of subglacial or supraglacial lakes, are the more likely cause of the erosion. Results of a ground penetrating radar (GPR) survey show the internal structure of one of these sandy-gravel drumlins to depth of 15 m. These GPR data, together with sedimentological observations, indicate that prior to erosion, subglacial sedimentation occurred in closed conduits (eskers) with strong and rapid flow variations. The sediments contain large chute-and-pool structures (high flow energy backset accretion) with dimensions comparable to the conduit width. Therefore, we interpret these sandy-gravel drumlins as portions of eskers, their present drumlin shape being the result of erosion by one or many jo??kulhlaups. The good preservation of the subglacial meltwater deposits is the result of the closed-basin geometry of the Joux Valley, which limited movement at the base of the glacier. This new contribution to the interpretation of the Joux Valley glacial features underlines the importance of meltwater in sedimentological processes under the Jura ice sheet.

  15. Along-axis variability in crustal accretion at the Mid-Atlantic Ridge: Results from the OCEAN study

    USGS Publications Warehouse

    Henstock, T.J.; White, Robert S.; McBride, J.H.

    1996-01-01

    The OCEAN experiment is an integrated geophysical study of a region of the Cape Verde abyssal plain that formed at 140 Ma. Deep seismic reflection and ocean bottom hydrophone (OBH) refraction data were acquired along lines parallel and perpendicular to the paleoridge axis trend identified from a detailed magnetic anomaly survey. The igneous basement is overlain by about 1.3 km of sediment which enables improved imaging of intracrustal structure beyond that possible near the Mid-Atlantic Ridge axis. We describe the results of a 150-km long profile oriented parallel to magnetic anomalies M15 and M16, along which deep seismic reflection data collected by the British Institutions Reflection Profiling Syndicate are complemented by refraction data constrained by four OBHs. The line spans an entire spreading segment between two fracture zones; the northern of which has an offset of 40 km and the other (central) has an offset of only 10 km. Away from the fracture zones, the mean igneous crustal thickness is 7.2 km; near both fracture zones, thinning of up to 4 km is observed, giving a mean igneous crustal thickness over the whole segment of approximately 6.5 km. Differences are seen between the two fracture zones in their seismic velocity structure, in the associated basement topography, and in the presence of a strong reflection extending into the mantle beneath the northern fracture zone. The boundary between oceanic layers 2 and 3 correlates with variably coherent normal incidence reflections and a change in the character of the reflectivity. A number of planar reflections up to 10 km in length are present within the middle and lower crust, dipping outward from beneath low-amplitude basement highs at ??? 15??; these appear to be present only within layer 3. The Moho has several expressions in the reflection data, including isolated reflection events, a local increase in reflected amplitudes, and a downward decrease in coherent reflections. At the center of the segment

  16. Space manufacturing utilizing the directional electrostatic accretion process

    NASA Technical Reports Server (NTRS)

    Mortensen, A.

    1986-01-01

    The Directional Electrostatic Accretion Process (DEAP) is described with respect to both the physical process and its application to manufacturing in space. This high precision portable manufacturing method will revolutionize current practices in manufacturing and repair of spacecraft and space structures. The cost effectiveness of this process will be invaluable to future space manufacturing projects.

  17. Physics 20-30: Program of Studies.

    ERIC Educational Resources Information Center

    Alberta Dept. of Education, Edmonton. Curriculum Branch.

    Presented in English and French, Physics 20-30 is an academic program that helps students better understand and apply fundamental concepts and skills. The major goals of the program are: (1) to develop in students an understanding of the interconnecting ideas and principles that transcend and unify the natural science disciplines; (2) to provide…

  18. Theoretical Studies in Elementary Particle Physics

    SciTech Connect

    Collins, John C.; Roiban, Radu S

    2013-04-01

    This final report summarizes work at Penn State University from June 1, 1990 to April 30, 2012. The work was in theoretical elementary particle physics. Many new results in perturbative QCD, in string theory, and in related areas were obtained, with a substantial impact on the experimental program.

  19. Characterizing Accreting White Dwarf Pulsators

    NASA Astrophysics Data System (ADS)

    Szkody, Paula; Mukadam, Anjum

    2014-02-01

    Understanding the population, mass distribution, and evolution of accreting white dwarfs impacts the entire realm of binary interaction, including the creation of Type Ia supernovae. We are concentrating on accreting white dwarf pulsators, as the pulsation properties allow us a view of how the accretion affects the interior of the star. Our ground- based photometry on 11 accreting pulsators with corresponding temperatures from HST UV spectra suggest a broad instability strip in the range of 10500 to 16000K. Additionally, tracking a post-outburst heated white dwarf as it cools and crosses the blue edge and resumes pulsation provides an independent method to locate the empirical instability strip. Determining a post-outburst cooling curve yields an estimate of the amount of heating and the accreted mass during the outburst. We request additional photometry of 2 objects that present unique properties: GW Lib which has not yet returned to its pre-outburst pulsation spectrum after 6 yrs, and EQ Lyn which returned to its pre- outburst pulsation after 3 yrs but is now turning on and off without ongoing outbursts. Following the pulsation spectrum changes over stretches of several nights in a row will provide specific knowledge of the stability of the observed modes.

  20. Turbulent Transport In Global Models of Magnetized Accretion Disks

    NASA Astrophysics Data System (ADS)

    Sorathia, Kareem

    The modern theory of accretion disks is dominated by the discovery of the magnetorotational instability (MRI). While hydrodynamic disks satisfy Rayleigh's criterion and there exists no known unambiguous route to turbulence in such disks, a weakly magnetized disk of plasma is subject to the MRI and will become turbulent. This MRI-driven magnetohydrodnamic turbulence generates a strong anisotropic correlation between the radial and azimuthal magnetic fields which drives angular momentum outwards. Accretion disks perform two vital functions in various astrophysical systems: an intermediate step in the gravitational collapse of a rotating gas, where the disk transfers angular momentum outwards and allows material to fall inwards; and as a power source, where the gravitational potential energy of infalling matter can be converted to luminosity. Accretion disks are important in astrophysical processes at all scales in the universe. Studying accretion from first principles is difficult, as analytic treatments of turbulent systems have proven quite limited. As such, computer simulations are at the forefront of studying systems this far into the non-linear regime. While computational work is necessary to study accretion disks, it is no panacea. Fully three-dimensional simulations of turbulent astrophysical systems require an enormous amount of computational power that is inaccessible even to sophisticated modern supercomputers. These limitations have necessitated the use of local models, in which a small spatial region of the full disk is simulated, and constrain numerical resolution to what is feasible. These compromises, while necessary, have the potential to introduce numerical artifacts in the resulting simulations. Understanding how to disentangle these artifacts from genuine physical phenomena and to minimize their effect is vital to constructing simulations that can make reliable astrophysical predictions and is the primary concern of the work presented here. The use

  1. Current Experimental Basis for Modeling Ice Accretions on Swept Wings

    NASA Technical Reports Server (NTRS)

    Vargas, Mario

    2005-01-01

    This work presents a review of the experimental basis for modeling ice accretions on swept wings. Experimental work related to ice accretion physics on swept wings conducted between 1954 and 2004 is reviewed. Proposed models or explanations of scallop formations are singled out and discussed. Special emphasis is placed on reviewing the work done to determine the basic macroscopic mechanisms of scallop formation. The role of feather growth and its connection to scallop growth is discussed. Conceptual steps in modeling scallop formations are presented. Research elements needed for modeling are discussed.

  2. Highlights from the First Ever Demographic Study of Solar Physics, Space Physics, and Upper Atmospheric Physics

    NASA Astrophysics Data System (ADS)

    Moldwin, M.; Morrow, C. A.; White, S. C.; Ivie, R.

    2014-12-01

    Members of the Education & Workforce Working Group and the American Institute of Physics (AIP) conducted the first ever National Demographic Survey of working professionals for the 2012 National Academy of Sciences Solar and Space Physics Decadal Survey to learn about the demographics of this sub-field of space science. The instrument contained questions for participants on: the type of workplace; basic demographic information regarding gender and minority status, educational pathways (discipline of undergrad degree, field of their PhD), how their undergraduate and graduate student researchers are funded, participation in NSF and NASA funded spaceflight missions and suborbital programs, and barriers to career advancement. Using contact data bases from AGU, the American Astronomical Society's Solar Physics Division (AAS-SPD), attendees of NOAA's Space Weather Week and proposal submissions to NSF's Atmospheric, Geospace Science Division, the AIP's Statistical Research Center cross correlated and culled these data bases resulting in 2776 unique email addresses of US based working professionals. The survey received 1305 responses (51%) and generated 125 pages of single space answers to a number of open-ended questions. This talk will summarize the highlights of this first-ever demographic survey including findings extracted from the open-ended responses regarding barriers to career advancement which showed significant gender differences.

  3. Airfoil Ice-Accretion Aerodynamics Simulation

    NASA Technical Reports Server (NTRS)

    Bragg, Michael B.; Broeren, Andy P.; Addy, Harold E.; Potapczuk, Mark G.; Guffond, Didier; Montreuil, E.

    2007-01-01

    NASA Glenn Research Center, ONERA, and the University of Illinois are conducting a major research program whose goal is to improve our understanding of the aerodynamic scaling of ice accretions on airfoils. The program when it is completed will result in validated scaled simulation methods that produce the essential aerodynamic features of the full-scale iced-airfoil. This research will provide some of the first, high-fidelity, full-scale, iced-airfoil aerodynamic data. An initial study classified ice accretions based on their aerodynamics into four types: roughness, streamwise ice, horn ice, and spanwise-ridge ice. Subscale testing using a NACA 23012 airfoil was performed in the NASA IRT and University of Illinois wind tunnel to better understand the aerodynamics of these ice types and to test various levels of ice simulation fidelity. These studies are briefly reviewed here and have been presented in more detail in other papers. Based on these results, full-scale testing at the ONERA F1 tunnel using cast ice shapes obtained from molds taken in the IRT will provide full-scale iced airfoil data from full-scale ice accretions. Using these data as a baseline, the final step is to validate the simulation methods in scale in the Illinois wind tunnel. Computational ice accretion methods including LEWICE and ONICE have been used to guide the experiments and are briefly described and results shown. When full-scale and simulation aerodynamic results are available, these data will be used to further develop computational tools. Thus the purpose of the paper is to present an overview of the program and key results to date.

  4. Dynamics of flux tubes in accretion disks

    NASA Technical Reports Server (NTRS)

    Vishniac, E. T.; Duncan, R. C.

    1994-01-01

    The study of magnetized plasmas in astrophysics is complicated by a number of factors, not the least of which is that in considering magnetic fields in stars or accretion disks, we are considering plasmas with densities well above those we can study in the laboratory. In particular, whereas laboratory plasmas are dominated by the confining magnetic field pressure, stars, and probably accretion disks, have magnetic fields whose beta (ratio of gas pressure to magnetic field pressure) is much greater than 1. Observations of the Sun suggest that under such circumstances the magnetic field breaks apart into discrete flux tubes with a small filling factor. On the other hand, theoretical treatments of MHD turbulence in high-beta plasmas tend to assume that the field is more or less homogeneously distributed throughout the plasma. Here we consider a simple model for the distribution of magnetic flux tubes in a turbulent medium. We discuss the mechanism by which small inhomogeneities evolve into discrete flux tubes and the size and distribution of such flux tubes. We then apply the model to accretion disks. We find that the fibrilation of the magnetic field does not enhance magnetic buoyancy. We also note that the evolution of an initially diffuse field in a turbulent medium, e.g., any uniform field in a shearing flow, will initially show exponential growth as the flux tubes form. This growth saturates when the flux tube formation is complete and cannot be used as the basis for a self-sustaining dynamo effect. Since the typical state of the magnetic field is a collection of intense flux tubes, this effect is of limited interest. However, it may be important early in the evolution of the galactic magnetic field, and it will play a large role in numerical simulations. Finally, we note that the formation of flux tubes is an essential ingredient in any successful dynamo model for stars or accretion disks.

  5. Physical-chemical studies of transuranium elements

    SciTech Connect

    Peterson, J.R.

    1991-01-01

    Major advances in our continuing program to determine, interpret, and correlate the basic chemical and physical properties of the transuranium elements are summarized. Research topics include: Molar enthalpies of formation of BaCmO{sub 3} and BaCfO{sub 3}; luminescence of europium oxychloride at various pressures; and anti-stokes luminescence of selected actinide (III) compounds. 42 refs., 4 figs., 2 tabs.

  6. Dynamical Masses of Accreting White Dwarfs

    NASA Astrophysics Data System (ADS)

    Pala, A. F.; Gänsckie, B. T.

    2017-03-01

    The mass retention efficiency is a key question in both the theoretical and observational study of accreting white dwarfs in interacting binaries, with important implications for their potential as progenitors for type Ia supernovae (SNe Ia). Canonical wisdom is that classical nova eruptions erode the white dwarf mass, and consequently, cataclysmic variables (CVs) have been excluded from the SN Ia progenitor discussion. However the average mass of white dwarfs in CVs is substantially higher (≃ 0.83 M⊙) than that of single white dwarfs (≃ 0.64 M ⊙), in stark contrast to expectations based on current classical nova models. This finding is based on a sample of ≃ 30 CV white dwarfs with accurate mass measurements, most of them in eclipsing systems. Given the fundamental importance of the mass evolution of accreting white dwarfs, it is necessary to enlarge this sample and to diversify the methods used for measuring masses. We have begun a systematic study of 27 CVs to almost double the number of CV white dwarfs with an accurate mass measurement. Using VLT/X-shooter phase-resolved observations, we can measure the white dwarf masses to a few percent, and will be able to answer the question whether accreting CV white dwarfs grow in mass.

  7. Gas accretion from halos to disks: observations, curiosities, and problems

    NASA Astrophysics Data System (ADS)

    Elmegreen, Bruce G.

    2016-08-01

    Accretion of gas from the cosmic web to galaxy halos and ultimately their disks is a prediction of modern cosmological models but is rarely observed directly or at the full rate expected from star formation. Here we illustrate possible large-scale cosmic HI accretion onto the nearby dwarf starburst galaxy IC10, observed with the VLA and GBT. We also suggest that cosmic accretion is the origin of sharp metallicity drops in the starburst regions of other dwarf galaxies, as observed with the 10-m GTC. Finally, we question the importance of cosmic accretion in normal dwarf irregulars, for which a recent study of their far-outer regions sees no need for, or evidence of, continuing gas buildup.

  8. Probing the Environment of Accreting Compact Objects

    NASA Astrophysics Data System (ADS)

    Hanke, Manfred

    2011-04-01

    X-ray binaries are the topic of this thesis. They consist of a compact object -- a black hole or a neutron star -- and an ordinary star, which loses matter to the compact object. The gravitational energy released through this process of mass accretion is largely converted into X-rays. The latter are used in the present work to screen the environment of the compact object. The main focus in the case of a massive star is on its wind, which is not homogeneous, but may display structures in form of temperature and density variations. Since great importance is, in multiple respects, attached to stellar winds in astrophysics, there is large interest in general to understand these structures more thoroughly. In particular for X-ray binaries, whose compact object obtains matter from the wind of its companion star, the state of the wind can decisively influence mass accretion and its related radiation processes. A detailed introduction to the fundamentals of stellar winds, compact objects, accretion and radiation processes in X-ray binaries, as well as to the employed instruments and analysis methods, is given in chapter 1. The focus of this investigation is on Cygnus X-1, a binary system with a black hole and a blue supergiant, which form a persistently very bright X-ray source because of accretion from the stellar wind. It had been known for a long time that this source -- when the black hole is seen through the dense stellar wind -- often displays abrupt absorption events whose origin is suspected to be in clumps in the wind. More detailed physical properties of these clumps and of the wind in general are explored in this work. Observations that were specifically acquired for this study, as well as archival data from different satellite observatories, are analyzed in view of signatures of the wind and its fine structures. These results are presented in chapter 2. In a first part of the analysis, the statistical distribution of the brightness of Cyg X-1, as measured since

  9. Swept wing ice accretion modeling

    NASA Technical Reports Server (NTRS)

    Potapczuk, M. G.; Bidwell, C. S.

    1990-01-01

    An effort to develop a three-dimensional ice accretion modeling method is initiated. This first step toward creation of a complete aircraft icing simulation code builds on previously developed methods for calculating three-dimensional flowfields and particle trajectories combined with a two-dimensional ice accretion calculation along coordinate locations corresponding to streamlines. This work is intended as a demonstration of the types of calculations necessary to predict a three-dimensional ice accretion. Results of calculations using the 3D method for a MS-317 swept wing geometry are projected onto a 2D plane normal to the wing leading edge and compared to 2D results for the same geometry. These results indicate that the flowfield over the surface and the particle trajectories differed for the two calculations. This led to lower collection efficiencies, convective heat transfer coefficients, freezing fractions, and ultimately ice accumulation for the 3D calculation.

  10. Correlation Study of Physics Achievement, Learning Strategy, Attitude and Gender in an Introductory Physics Course

    ERIC Educational Resources Information Center

    Sezgin Selcuk, Gamze

    2010-01-01

    This study investigates the relationship between multiple predictors of physics achievement including reported use of four learning strategy clusters (elaboration, organization, comprehension monitoring and rehearsal), attitudes towards physics (sense of care and sense of interest) and a demographic variable (gender) in order to determine the…

  11. Cosmic dust synthesis by accretion and coagulation

    NASA Technical Reports Server (NTRS)

    Praburam, G.; Goree, J.

    1995-01-01

    The morphology of grains grown by accretion and coagulation is revaled by a new laboratory method of synthesizing cosmic dust analogs. Submicron carbon particles, grown by accretion of carbon atoms from a gas, have a spherical shape with a cauliflower-like surface and an internal micro-structure of radial columns. This shape is probably common for grains grown by accretion at a temperature well below the melting point. Coagulated grains, consisting of spheres that collided to form irregular strings, were also synthesized. Another shape we produced had a bumpy non- spherical morphology, like an interplanetary particle collected in the terrestrial stratosphere. Besides these isolated grains, large spongy aggregates of nanometer-size particles were also found for various experimental conditions. Grains were synthesized using ions to sputter a solid target, producing an atomic vapor at a low temperature. The ions were provided by a plasma, which also provided electrostatic levitation of the grains during their growth. The temporal development of grain growth was studied by extinguishing the plasma after various intervals.

  12. Minidisks in Binary Black Hole Accretion

    NASA Astrophysics Data System (ADS)

    Ryan, Geoffrey; MacFadyen, Andrew

    2017-02-01

    Newtonian simulations have demonstrated that accretion onto binary black holes produces accretion disks around each black hole (“minidisks”), fed by gas streams flowing through the circumbinary cavity from the surrounding circumbinary disk. We study the dynamics and radiation of an individual black hole minidisk using 2D hydrodynamical simulations performed with a new general relativistic version of the moving-mesh code Disco. We introduce a comoving energy variable that enables highly accurate integration of these high Mach number flows. Tidally induced spiral shock waves are excited in the disk and propagate through the innermost stable circular orbit, providing a Reynolds stress that causes efficient accretion by purely hydrodynamic means and producing a radiative signature brighter in hard X-rays than the Novikov–Thorne model. Disk cooling is provided by a local blackbody prescription that allows the disk to evolve self-consistently to a temperature profile where hydrodynamic heating is balanced by radiative cooling. We find that the spiral shock structure is in agreement with the relativistic dispersion relation for tightly wound linear waves. We measure the shock-induced dissipation and find outward angular momentum transport corresponding to an effective alpha parameter of order 0.01. We perform ray-tracing image calculations from the simulations to produce theoretical minidisk spectra and viewing-angle-dependent images for comparison with observations.

  13. University Physics, Study Guide, Revised Edition

    NASA Astrophysics Data System (ADS)

    Benson, Harris

    1996-01-01

    Partial table of contents: Vectors. One-Dimensional Kinematics. Particle Dynamics II. Work and Energy. Linear Momentum. Systems of Particles. Angular Momentum and Statics. Gravitation. Solids and Fluids. Oscillations. Mechanical Waves. Sound. First Law of Thermodynamics. Kinetic Theory. Entropy and the Second Law of Thermodynamics. Electrostatics. The Electric Field. Gauss's Law. Electric Potential. Current and Resistance. The Magnetic Field. Sources of the Magnetic Field. Electromagnetic Induction. Light: Reflection and Refraction. Lenses and Optical Instruments. Wave Optics I. Special Relativity. Early Quantum Theory. Nuclear Physics. Appendices. Answers to Odd-Numbered Exercises and Problems. Index.

  14. Kronos: A Multiwavelength Observatory for Mapping Accretion-Driven Sources

    NASA Technical Reports Server (NTRS)

    Peterson, Bradley M.; Polidan, Ronald S.; Robinson, Edward L.

    2002-01-01

    Kronos is a multiwavelength observatory proposed as a NASA Medium Explorer. Kronos is designed to make use of the natural variability of accreting sources to create microarcsecond-resolution maps of the environments of supermassive black holes in active galaxies and stella-size black holes in binary systems and to characterize accretion processes in Galactic compact binaries. Kronos will obtain broad energy range spectroscopic data with co-aligned X-ray, ultraviolet, and optical spectrometers. The high-Earth orbit of Kronos enables well-sampled, high time-resolution observations, critical for the innovative and sophisticated methods that are used to understand the accretion flows, mass outflows, jets, and other phenomena found in accreting sources. By utilizing reverberation mapping analysis techniques, Kronos produces advanced high-resolution maps of unprecedented resolution of the extreme environment in the inner cores of active galaxies. Similarly, Doppler tomography and eclipse mapping techniques characterize and map Galactic binary systems, revealing the details of the physics of accretion processes in black hole, neutron star, and white dwarf binary systems. The Kronos instrument complement, sensitivity, and orbital environment make it suitable to aggressively address time variable phenomena in a wide range of astronomical objects from nearby flare stars to distant galaxies.

  15. Ubiquitous equatorial accretion disc winds in black hole soft states

    NASA Astrophysics Data System (ADS)

    Ponti, G.; Fender, R. P.; Begelman, M. C.; Dunn, R. J. H.; Neilsen, J.; Coriat, M.

    2012-05-01

    High-resolution spectra of Galactic black holes (GBHs) reveal the presence of highly ionized absorbers. In one GBH, accreting close to the Eddington limit for more than a decade, a powerful accretion disc wind is observed to be present in softer X-ray states and it has been suggested that it can carry away enough mass and energy to quench the radio jet. Here we report that these winds, which may have mass outflow rates of the order of the inner accretion rate or higher, are a ubiquitous component of the jet-free soft states of all GBHs. We furthermore demonstrate that these winds have an equatorial geometry with opening angles of few tens of degrees, and so are only observed in sources in which the disc is inclined at a large angle to the line of sight. The decrease in Fe XXV/Fe XXVI line ratio with Compton temperature, observed in the soft state, suggests a link between higher wind ionization and harder spectral shapes. Although the physical interaction between the wind, accretion flow and jet is still not fully understood, the mass flux and power of these winds and their presence ubiquitously during the soft X-ray states suggest they are fundamental components of the accretion phenomenon.

  16. Accreting neutron stars by QFT

    NASA Astrophysics Data System (ADS)

    Chen, Shao-Guang

    layer with thickness of 1 km then q = 1 (N1S1), the gravity from N1S1 inside and exterior will be completely shielded. Because of net nuν _{0} flux is the medium to produce and transmit gravity, q obstructed by the shielding layer lie on the density of layer matter and the section of single nucleon to electronic neutrino obtained by nuclear physics experiments is about 1.1*10 ({-) 43} cm (2) . The mass inside N1S1 for exterior has not gravity interaction, it equivalent to has not inertia as the mass vanish. The neutron star is as a empty shell thereby may rapidly rotating and has not upper limit of mass and radii by the gravity accretion of N1S1, which will influence the mechanisms of pulsars, quasars and X-rays generated. At N1S1 interior the mass for exterior has not gravity which is just we searching dark matter. The mass each part will each other shielding and gravity decrease to less than the pressure of the degenerate neutron gas. The neutron star cannot collapse into a singular point with infinite density, i.e., the black hole with infinite gravity cannot be formed or the neutron star is jest the black hole in observational meaning. By the gravity accrete of N1S1 the neutron star may enlarge its shell radii but thickness keep. Only a shell gravity may be not less than any a observed value which to be deemed as black hole. The neutron star has powerful gravity certainly accompany with great surface negative charge and it may rapidly to rotate, so that there is a powerful magnetic field surround it. The accreting neutron star is as a slowly expand empty shell with fixed thickness of 1 km, its spin period depend on its radii or total accretion mass.

  17. Testing the Star-Disk Connection: CIV and MGII Maps of Accretion Disks CYC3-MED

    NASA Astrophysics Data System (ADS)

    Horne, Keith

    1992-06-01

    Empirical scaling laws among magnetic activity indicators are well established for the sun and other cool stars. Ground-based studies of Balmer and CaII emission suggest that similar relationships may hold for the accretion disks and tidally-locked secondary stars in cataclysmic variables. We propose to test this star-disk connection by using HST to make Doppler maps of MgII and CIV emission in three quiescent dwarf novae. These lines sensitive to chromospheric and transition region temperature regimes are predicted to scale as radius to the -3/2 and -3 respectively in the Keplerian accretion disk. Our experiment tests the hypothesis that dynamo action powers emission lines from accretion disk chromospheres. The disk and secondary star rotate much faster than the stars for which magnetic activity relations have been previously determined. By expanding the study of magnetic activity to higher rotation rates and different geometries, we expect to gain insights into the basic physics that will advance our understanding of dynamos and magnetic activity in a broad context. NOTE: THE TAC CUT THIS PROPOSAL FROM 3 TO 1 OBJECT.

  18. An Experimental Study of the Flowfield on a Semispan Rectangular Wing with a Simulated Glaze Ice Accretion. Ph.D. Thesis, 1993 Final Report

    NASA Technical Reports Server (NTRS)

    Khodadoust, Abdollah

    1994-01-01

    Wind tunnel experiments were conducted in order to study the effect of a simulated glaze ice accretion on the flowfield of a semispan, reflection-plane, rectangular wing at Re = 1.5 million and M = 0.12. A laser Doppler velocimeter was used to map the flowfield on the upper surface of the model in both the clean and iced configurations at alpha = 0, 4, and 8 degrees angle of attack. At low angles of attack, the massive separation bubble aft of the leading edge ice horn was found to behave in a manner similar to laminar separation bubbles. At alpha = 0 and 4 degrees, the locations of transition and reattachment, as deduced from momentum thickness distributions, were found to be in good agreement with transition and reattachment locations in laminar separation bubbles. These values at y/b = 0.470, the centerline measurement location, matched well with data obtained on a similar but two dimensional model. The measured velocity profiles on the iced wing compared reasonably with the predicted profiles from Navier-Stokes computations. The iced-induced separation bubble was also found to have features similar to the recirculating region aft of rearward-facing steps. At alpha = 0 degrees and 4 degrees, reverse flow magnitudes and turbulence intensity levels were typical of those found in the recirculating region aft of rearward-facing steps. The calculated separation streamline aft of the ice horn at alpha = 4 degrees, y/b = 0.470 coincided with the locus of the maximum Reynolds normal stress. The maximum Reynolds normal stress peaked at two locations along the separation streamline. The location of the first peak-value coincided with the transition location, as deduced from the momentum thickness distributions. The location of the second peak was just upstream of reattachment, in good agreement with measurements of flows over similar obstacles. The intermittency factor in the vicinity of reattachment at alpha = 4 degrees, y/b = 0.470, revealed the time-dependent nature of

  19. On the accretion process in a high-mass star forming region. A multitransitional THz Herschel-HIFI study of ammonia toward G34.26+0.15

    NASA Astrophysics Data System (ADS)

    Hajigholi, M.; Persson, C. M.; Wirström, E. S.; Black, J. H.; Bergman, P.; Olofsson, A. O. H.; Olberg, M.; Wyrowski, F.; Coutens, A.; Hjalmarson, Å.; Menten, K. M.

    2016-01-01

    Aims: Our aim is to explore the gas dynamics and the accretion process in the early phase of high-mass star formation. Methods: The inward motion of molecular gas in the massive star forming region G34.26+0.15 is investigated by using high-resolution profiles of seven transitions of ammonia at THz frequencies observed with Herschel-HIFI. The shapes and intensities of these lines are interpreted in terms of radiative transfer models of a spherical, collapsing molecular envelope. An accelerated Lambda Iteration (ALI) method is used to compute the models. Results: The seven ammonia lines show mixed absorption and emission with inverse P-Cygni-type profiles that suggest infall onto the central source. A trend toward absorption at increasingly higher velocities for higher excitation transitions is clearly seen in the line profiles. The J = 3 ← 2 lines show only very weak emission, so these absorption profiles can be used directly to analyze the inward motion of the gas. This is the first time a multitransitional study of spectrally resolved rotational ammonia lines has been used for this purpose. Broad emission is, in addition, mixed with the absorption in the 10-00 ortho-NH3 line, possibly tracing a molecular outflow from the star forming region. The best-fitting ALI model reproduces the continuum fluxes and line profiles, but slightly underpredicts the emission and absorption depth in the ground-state ortho line 10-00. An ammonia abundance on the order of 10-9 relative to H2 is needed to fit the profiles. The derived ortho-to-para ratio is approximately 0.5 throughout the infalling cloud core similar to recent findings for translucent clouds in sight lines toward W31C and W49N. We find evidence of two gas components moving inwards toward the central region with constant velocities: 2.7 and 5.3 km s-1, relative to the source systemic velocity. Attempts to model the inward motion with a single gas cloud in free-fall collapse did not succeed. Herschel is an ESA space

  20. Impact-induced melting during accretion of the Earth

    NASA Astrophysics Data System (ADS)

    de Vries, Jellie; Nimmo, Francis; Melosh, H. Jay; Jacobson, Seth A.; Morbidelli, Alessandro; Rubie, David C.

    2016-12-01

    Because of the high energies involved, giant impacts that occur during planetary accretion cause large degrees of melting. The depth of melting in the target body after each collision determines the pressure and temperature conditions of metal-silicate equilibration and thus geochemical fractionation that results from core-mantle differentiation. The accretional collisions involved in forming the terrestrial planets of the inner Solar System have been calculated by previous studies using N-body accretion simulations. Here we use the output from such simulations to determine the volumes of melt produced and thus the pressure and temperature conditions of metal-silicate equilibration, after each impact, as Earth-like planets accrete. For these calculations a parameterised melting model is used that takes impact velocity, impact angle and the respective masses of the impacting bodies into account. The evolution of metal-silicate equilibration pressures (as defined by evolving magma ocean depths) during Earth's accretion depends strongly on the lifetime of impact-generated magma oceans compared to the time interval between large impacts. In addition, such results depend on starting parameters in the N-body simulations, such as the number and initial mass of embryos. Thus, there is the potential for combining the results, such as those presented here, with multistage core formation models to better constrain the accretional history of the Earth.

  1. TURBULENT MIXING ON HELIUM-ACCRETING WHITE DWARFS

    SciTech Connect

    Piro, Anthony L.

    2015-03-10

    An attractive scenario for producing Type Ia supernovae (SNe Ia) is a double detonation, where detonation of an accreted helium layer triggers ignition of a C/O core. Whether or not such a mechanism can explain some or most SNe Ia depends on the properties of the helium burning, which in turn is set by the composition of the surface material. Using a combination of semi-analytic and simple numerical models, I explore when turbulent mixing due to hydrodynamic instabilities during the accretion process can mix C/O core material up into the accreted helium. Mixing is strongest at high accretion rates, large white dwarf (WD) masses, and slow spin rates. The mixing would result in subsequent helium burning that better matches the observed properties of SNe Ia. In some cases, there is considerable mixing that can lead to more than 50% C/O in the accreted layer at the time of ignition. These results will hopefully motivate future theoretical studies of such strongly mixed conditions. Mixing also has implications for other types of WD surface explosions, including the so-called .Ia supernovae, the calcium-rich transients (if they arise from accreting WDs), and metal-enriched classical novae.

  2. Observational Tests of the Picture of Disk Accretion

    NASA Astrophysics Data System (ADS)

    Maccarone, Thomas J.

    2014-09-01

    In this chapter, I present a summary of observational tests of the basic picture of disk accretion. An emphasis is placed on tests relevant to black holes, but many of the fundamental results are drawn from studies of other classes of systems. Evidence is discussed for the basic structures of accretion flows. The cases of systems with and without accretion disks are discussed, as is the evidence that disks actually form. Also discussed are the hot spots where accretion streams impact the disks, and the boundary layers in the inner parts of systems where the accretors are not black holes. The nature of slow, large amplitude variability is discussed. It is shown that some of the key predictions of the classical thermal-viscous ionization instability model for producing outbursts are in excellent agreement with observational results. It is also show that there are systems whose outbursts are extremely difficult to explain without invoking variations in the rate of mass transfer from the donor star into the outer accretion disk, or tidally induced variations in the mass transfer rates. Finally, I briefly discuss recent quasar microlensing measurements which give truly independent constraints on the inner accretion geometry around black holes.

  3. Theoretical and experimental studies of elementary physics

    SciTech Connect

    Bodek, A.; Ferbel, T.; Melissinos, A.C.; Olsen, S.; Slattery, P.; Tipton, P.; Das, A.; Hagen, C.R.; Rajeev, S.G.; Okubo, S.

    1992-04-30

    The experimental high energy physics program is directed toward the execution of experiments that probe the basic constituents of matter and the forces between them. These experiments are carried out at national and international accelerator facilities. At the current time, we are primarily concentrating on the following projects: Direct photon production in hadronic reactions (Fermilab E706); Production of hybrid mesons in the nuclear Coulomb field; The D-Zero experiment at the Tevatron collider; Deep inelastic neutrino- and electron-nucleon scattering at FNAL and SLAC; Nonlinear QED at critical field strengths at SLAC; The Experiments at KEK (AMY, 17keV neutrino); The CDF experiment at the Tevatron collider; and SSC-related detector R D on scintillating tile- and diamond-based calorimetry and microstrip tracking detectors.

  4. Daytime physical activity patterns and physical fitness in institutionalized elderly women: an exploratory study.

    PubMed

    Ikezoe, Tome; Asakawa, Yasuyoshi; Shima, Hiroto; Kishibuchi, Kaoru; Ichihashi, Noriaki

    2013-01-01

    This study investigated the relationship between daytime physical activity patterns and physical fitness in elderly women. The subjects comprised 19 elderly women who resided in a nursing home. Time spent lying, sitting, standing and walking and the number of steps taken during the daytime from 10:00 to 16:00 were measured to determine physical activity patterns. Physical fitness measures included muscle strength, balance, flexibility and physical performance. The elderly women spent 18.3% of their daytime walking, 7.31% in a standing position, 56.9% sitting and 17.4% lying down. Our results showed that the time spent in walking or standing positions was significantly associated with balance and physical performance such as walking speed, while the time spent in a sitting position was inversely associated with muscle strength, balance and physical performance. The results of this study suggest that the time the elderly spend on weight-bearing activities and in sedentary behavior are associated with physical fitness.

  5. Using the Case Study Method in Teaching College Physics

    ERIC Educational Resources Information Center

    Burko, Lior M.

    2016-01-01

    The case study teaching method has a long history (starting at least with Socrates) and wide current use in business schools, medical schools, law schools, and a variety of other disciplines. However, relatively little use is made of it in the physical sciences, specifically in physics or astronomy. The case study method should be considered by…

  6. 40 CFR 160.135 - Physical and chemical characterization studies.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 23 2010-07-01 2010-07-01 false Physical and chemical characterization... and chemical characterization studies. (a) All provisions of the GLP standards shall apply to physical and chemical characterization studies designed to determine stability, solubility, octanol...

  7. 40 CFR 160.135 - Physical and chemical characterization studies.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 24 2011-07-01 2011-07-01 false Physical and chemical characterization... and chemical characterization studies. (a) All provisions of the GLP standards shall apply to physical and chemical characterization studies designed to determine stability, solubility, octanol...

  8. 40 CFR 160.135 - Physical and chemical characterization studies.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 24 2014-07-01 2014-07-01 false Physical and chemical characterization... and chemical characterization studies. (a) All provisions of the GLP standards shall apply to physical and chemical characterization studies designed to determine stability, solubility, octanol...

  9. 40 CFR 160.135 - Physical and chemical characterization studies.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 25 2013-07-01 2013-07-01 false Physical and chemical characterization... and chemical characterization studies. (a) All provisions of the GLP standards shall apply to physical and chemical characterization studies designed to determine stability, solubility, octanol...

  10. 40 CFR 160.135 - Physical and chemical characterization studies.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 25 2012-07-01 2012-07-01 false Physical and chemical characterization... and chemical characterization studies. (a) All provisions of the GLP standards shall apply to physical and chemical characterization studies designed to determine stability, solubility, octanol...

  11. Perturbation growth in accreting filaments

    NASA Astrophysics Data System (ADS)

    Clarke, S. D.; Whitworth, A. P.; Hubber, D. A.

    2016-05-01

    We use smoothed particle hydrodynamic simulations to investigate the growth of perturbations in infinitely long filaments as they form and grow by accretion. The growth of these perturbations leads to filament fragmentation and the formation of cores. Most previous work on this subject has been confined to the growth and fragmentation of equilibrium filaments and has found that there exists a preferential fragmentation length-scale which is roughly four times the filament's diameter. Our results show a more complicated dispersion relation with a series of peaks linking perturbation wavelength and growth rate. These are due to gravo-acoustic oscillations along the longitudinal axis during the sub-critical phase of growth. The positions of the peaks in growth rate have a strong dependence on both the mass accretion rate onto the filament and the temperature of the gas. When seeded with a multiwavelength density power spectrum, there exists a clear preferred core separation equal to the largest peak in the dispersion relation. Our results allow one to estimate a minimum age for a filament which is breaking up into regularly spaced fragments, as well as an average accretion rate. We apply the model to observations of filaments in Taurus by Tafalla & Hacar and find accretion rates consistent with those estimated by Palmeirim et al.

  12. Neutrinos from Accreting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Anchordoqui, Luis A.; Torres, Diego F.; McCauley, Thomas P.; Romero, Gustavo E.; Aharonian, Felix A.

    2003-05-01

    The magnetospheres of accreting neutron stars develop electrostatic gaps with huge potential drops. Protons and ions, accelerated in these gaps along the dipolar magnetic field lines to energies greater than 100 TeV, can impact onto the surrounding accretion disk. A proton-induced cascade develops, and charged pion decays produce ν emission. With extensive disk shower simulations using DPMJET and GEANT4, we have calculated the resulting ν spectrum. We show that the spectrum produced out of the proton beam is a power law. We use this result to propose accretion-powered X-ray binaries (with highly magnetized neutron stars) as a new population of pointlike ν sources for kilometer-scale detectors such as ICECUBE. As a particular example, we discuss the case of A0535+26. We show that ICECUBE should find A0535+26 to be a periodic ν source, one for which the formation and loss of its accretion disk can be fully detected. Finally, we comment briefly on the possibility that smaller telescopes such as AMANDA could also detect A0535+26 by folding observations with the orbital period.

  13. Strongly Magnetized Accretion Disks Around Black Holes

    NASA Astrophysics Data System (ADS)

    Salvesen, Greg; Armitage, Philip J.; Simon, Jacob B.; Begelman, Mitchell C.

    2017-01-01

    Recent observations are suggestive of strongly magnetized accretion disks around black holes. Performing local (shearing box) simulations of accretion disks, we investigate how a strong magnetization state can develop and persist. We demonstrate that poloidal flux is a necessary prerequisite for the sustainability of strongly magnetized accretion disks. We also show that black hole spin measurements can become unconstrained if magnetic fields provide a significant contribution to the vertical pressure support of the accretion disk atmosphere.

  14. A comparative study of middle school and high school students' views about physics and learning physics

    NASA Astrophysics Data System (ADS)

    Ding, Lin

    2013-01-01

    Previous studies of student epistemological beliefs about physics and learning physics focused on college and post-college students in Western countries. However, little is known about early-grade students in Asian countries. This paper reports Chinese middle and high school students' views about the nature of physics and learning physics, measured by the Colorado Learning Attitudes Survey about Science (CLASS). Two variables—school level and gender—are examined for a series of comparative analyses. Results show that although middle school students received fewer years of education in physics, they demonstrated more expert-like conceptions about this subject matter than high school students. Also, male students in general exhibited more expert-like views than their female counterparts. While such a gender difference remained constant across both middle and high schools, for the most part it was a small-size difference.

  15. Lessons from accretion disks in cataclysmic variables

    NASA Astrophysics Data System (ADS)

    Horne, Keith

    1998-04-01

    We survey recent progress in the interpretation of observations of cataclysmic variables, whose accretion disks are heated by viscous dissipation rather than irradiation. Many features of standard viscous accretion disk models are confirmed by tomographic imaging studies of dwarf novae. Eclipse maps indicate that steady disk temperature structures are established during outbursts. Doppler maps of double-peaked emission lines suggest disk chromospheres heated by magnetic activity. Gas streams impacting on the disk rim leave expected signatures both in the eclipses and emission lines. Doppler maps of dwarf nova IP Peg at the beginning of an outburst show evidence for tidally-induced spiral shocks. While enjoying these successes, we must still face up to the dreaded ``SW Sex syndrome'' which afflicts most if not all cataclysmic variables in high accretion states. The anomalies include single-peaked emission lines with skewed kinematics, flat temperature-radius profiles, shallow offset line eclipses, and narrow low-ionization absorption lines at phase 0.5. The enigmatic behavior of AE Aqr is now largely understood in terms of a magnetic propeller model in which the rapidly spinning white dwarf magnetosphere expels the gas stream out of the system before an accretion disk can form. A final piece in this puzzle is the realization that an internal shock zone occurs in the exit stream at just the right place to explain the anomalous kinematics and violent flaring of the single-peaked emission lines. Encouraged by this success, we propose that disk-anchored magnetic propellers operate in the high accretion rate systems afflicted by the SW Sex syndrome. Magnetic fields anchored in the Keplerian disk sweep forward and apply a boost that expels gas stream material flowing above the disk plane. This working hypothesis offers a framework on which we can hang all the SW Sex anomalies. The lesson for theorists is that magnetic links appear to be transporting energy and angular

  16. Geometry Modeling and Grid Generation for "Icing Effects" and "Ice Accretion" Simulations on Airfoils

    NASA Technical Reports Server (NTRS)

    Choo, Yung; Vickerman, Mary; Lee, Ki D.; Thompson, David S.

    2000-01-01

    There are two distinct icing-related problems for airfoils that can be simulated. One is predicting the effects of ice on the aerodynamic performance of airfoils when ice geometry is known ("icing effects" study). The other is simulating ice accretion under specified icing conditions ("ice accretion" simulation). This paper will address development of two different software packages for two-dimensional geometry preparation and grid generation for both "icing effects" and "ice accretion" studies.

  17. Spes: Exotic Beams for Nuclear Physics Studies

    NASA Astrophysics Data System (ADS)

    Andrighetto, Alberto; Manzolaro, Mattia; Corradetti, Stefano; Scarpa, Daniele; Vasquez, Jesu; Rossignoli, Massimo; Monetti, Alberto; Calderolla, Michele; Prete, Gianfranco

    2014-02-01

    The SPES project at Laboratori di Legnaro of INFN (Italy) is concentrating on the production of neutron-rich radioactive nuclei for nuclear physics experiments using uranium fission at a rate of 1013 fission/s. The emphasis on neutron-rich isotopes is justified by the fact that this vast territory has been little explored. The Radioactive Ion Beam (RIB) will be produced by the ISOL technique using proton induced fission on a direct target of UCx. The most critical element of the SPES project is the Multi-Foil Direct Target. Up to the present time, the proposed target represents an innovation in terms of its capability to sustain the primary beam power. This talk will present the status of the project financed by INFN, which is actually in the construction phase at Legnaro. In particular, developments related to the target and the ion-source activities using the surface ion source, plasma ion source, and laser ion source techniques will be reported.

  18. Self-consistent evolution of accreting low-mass stars and brown dwarfs

    NASA Astrophysics Data System (ADS)

    Baraffe, I.; Elbakyan, V. G.; Vorobyov, E. I.; Chabrier, G.

    2017-01-01

    We present self-consistent calculations coupling numerical hydrodynamics simulations of collapsing pre-stellar cores and stellar evolution models of accreting objects. We analyse the main impact of consistent accretion history on the evolution and lithium depletion of young low-mass stars and brown dwarfs. These consistent models confirm the generation of a luminosity spread in Herzsprung-Russell diagrams at ages 1-10 Myr. They also confirm that early accretion can produce objects with abnormal Li depletion, as found in a previous study that was based on arbitrary accretion rates. The results strengthen that objects with anomalously high level of Li depletion in young clusters should be extremely rare. We also find that early phases of burst accretion can produce coeval models of similar mass with a range of different Li surface abundances, and in particular with Li-excess compared to the predictions of non-accreting counterparts. This result is due to a subtle competition between the effect of burst accretion and its impact on the central stellar temperature, the growth of the stellar radiative core and the accretion of fresh Li from the accretion disk. Only consistent models could reveal such a subtle combination of effects. This new result could explain the recent, puzzling observations of Li-excess of fast rotators in the young cluster NGC 2264. Present self-consistent accreting models are available in electronic form.

  19. The environmental dependence of gas accretion on to galaxies: quenching satellites through starvation

    NASA Astrophysics Data System (ADS)

    van de Voort, Freeke; Bahé, Yannick M.; Bower, Richard G.; Correa, Camila A.; Crain, Robert A.; Schaye, Joop; Theuns, Tom

    2017-04-01

    Galaxies that have fallen into massive haloes may no longer be able to accrete gas from their surroundings: a process referred to as 'starvation' or 'strangulation' of satellites. We study the environmental dependence of gas accretion on to galaxies using the cosmological, hydrodynamical EAGLE simulation. We quantify the dependence of gas accretion on stellar mass, redshift, and environment, using halo mass and galaxy overdensity as environmental indicators. We find a strong suppression, of many orders of magnitude, of the gas accretion rate in dense environments, primarily for satellite galaxies. This suppression becomes stronger at lower redshift. However, the scatter in accretion rates is very large for satellites. This is (at least in part) due to the variation in the halocentric radius, since gas accretion is more suppressed at smaller radii. Central galaxies are influenced less strongly by their environment and exhibit less scatter in their gas accretion rates. The star formation rates of both centrals and satellites show similar behaviour to their gas accretion rates. The relatively small differences between gas accretion and star formation rates demonstrate that galaxies generally exhaust their gas reservoir somewhat faster at higher stellar mass, lower redshift, and in denser environments. We conclude that the environmental suppression of gas accretion could directly result in the quenching of star formation.

  20. Plastic Deformation of Accreted Planetesimals

    NASA Astrophysics Data System (ADS)

    Kadish, J.

    2005-08-01

    The early stages of planetesimal growth follow an accretion model (Weidenschilling, Icarus 2000), which influences the intrinsic strength of a body and may control how its shape evolves after growth. In previous work we have determined the stress field of an accreted planetesimal accounting for possible variation in the object's spin as it accretes (Kadish et al., IJSS In Press) At the end of growth, these objects are subject to transport mechanisms that can distribute them throughout the solar system. As they are transported these objects can be spun-up by tidal forces (Scheeres et al, Icarus 2000), YORP (Bottke et al., Asteroids III 2002), and collisions (Binzel et al., Asteroids II 1989). Such an increase of spin will cause perturbations to the initial stress field and may lead to failure. We are able to show analytically that failure is initiated on the object's surface and a plastic zone propagates inward as the object's spin is increased. If we model an accreted body as a conglomeration of rocks similar to a gravel or sand, the deformation in the region of failure is characterized using a Mohr-Coulomb failure criterion with negligible cohesion and zero hardening(e.g. Holsapple, Icarus 2001). Such a response is highly non-linear and must be solved using finite elements and iterative methods (Simo and Hughes, Computational Inelasticity 1998). Using the commercial finite element code ABAQUS, we present the shape deformation resulting from an elasto-plastic analysis of a spinning, self-gravitating accreted sphere that is spun-up after growth is complete. The methodology can be extended to model plastic deformation due to local failure for more complex planetesimal shapes, such as for the asteroid Kleopatra. This work has implications for the evolution of planetesimal shapes, the creation of binary and contact binary asteroids, and for the maximum spin rate of small planetary bodies.

  1. Competency Revalidation Study of Specialty Practice in Sports Physical Therapy

    PubMed Central

    Thein-Nissenbaum, Jill; Bartlett, Lynn; Woodall, William R.; Reinking, Mark F.; Wallmann, Harvey W.; Mulligan, Edward P.

    2009-01-01

    Purpose The primary purpose of this study was to revalidate the competencies that define the practice of sports physical therapy. Additionally, the study allowed for the comparison of responses of board certified specialists in sports physical therapy to respondents who were not specialists. Methods A survey instrument based the on American Board of Physical Therapy Specialties practice analysis template and The Guide to Physical Therapist Practice was developed by the Sports Specialty Council and a panel of subject matter experts in sports physical therapy. The instrument was sent to 630 physical therapists, 315 of whom were board certified specialists in sports physical therapy and 315 of whom were randomly selected members of the Sports Physical Therapy Section who were not board certified specialists in sports physical therapy. Two hundred and thirty seven subjects returned completed surveys for a 41% response rate. One hundred and fifty eight respondents were sports specialists Results The survey results were reviewed by the Sports Specialty Council and another panel of subject matter experts. Using a defined decision making process, the results were used to determine the competencies that define the specialty practice of sports physical therapy. Survey results were also used to develop the sports physical therapy specialty board examination blue print. A number of significant comparisons between the specialists and non-specialists were identified. Conclusion The competency revalidation process culminated in the publication of the Sports Physical Therapy Description of Specialty Practice. This document serves to guide the process related to the attainment and maintenance of the board certified clinical specialist in sports physical therapy. PMID:21509106

  2. On the formation of compact planetary systems via concurrent core accretion and migration

    NASA Astrophysics Data System (ADS)

    Coleman, Gavin A. L.; Nelson, Richard P.

    2016-04-01

    We present the results of planet formation N-body simulations based on a comprehensive physical model that includes planetary mass growth through mutual embryo collisions and planetesimal/boulder accretion, viscous disc evolution, planetary migration and gas accretion on to planetary cores. The main aim of this study is to determine which set of model parameters leads to the formation of planetary systems that are similar to the compact low-mass multiplanet systems that have been discovered by radial velocity surveys and the Kepler mission. We vary the initial disc mass, solids-to-gas ratio and the sizes of the boulders/planetesimals, and for a restricted volume of the parameter space we find that compact systems containing terrestrial planets, super-Earths and Neptune-like bodies arise as natural outcomes of the simulations. Disc models with low values of the solids-to-gas ratio can only form short-period super-Earths and Neptunes when small planetesimals/boulders provide the main source of accretion, since the mobility of these bodies is required to overcome the local isolation masses for growing embryos. The existence of short-period super-Earths around low-metallicity stars provides strong evidence that small, mobile bodies (planetesimals, boulders or pebbles) played a central role in the formation of the observed planets.

  3. THE ACCRETION WIND MODEL OF FERMI BUBBLES. II. RADIATION

    SciTech Connect

    Mou, Guobin; Yuan, Feng; Gan, Zhaoming; Sun, Mouyuan

    2015-09-20

    In a previous work, we have shown that the formation of Fermi bubbles can be due to the interaction between winds launched from the hot accretion flow in Sgr A* and the interstellar medium (ISM). In that work, we focus only on the morphology. In this paper we continue our study by calculating the gamma-ray radiation. Some cosmic-ray protons (CRp) and electrons (CRe) must be contained in the winds, which are likely formed by physical processes such as magnetic reconnection. We have performed MHD simulations to study the spatial distribution of CRp, considering the advection and diffusion of CRp in the presence of magnetic field. We find that a permeated zone is formed just outside of the contact discontinuity between winds and the ISM, where the collisions between CRp and thermal nuclei mainly occur. The decay of neutral pions generated in the collisions, combined with the inverse Compton scattering of background soft photons by the secondary leptons generated in the collisions and primary CRe, can well explain the observed gamma-ray spectral energy distribution. Other features such as the uniform surface brightness along the latitude and the boundary width of the bubbles are also explained. The advantage of this “accretion wind” model is that the adopted wind properties come from the detailed small-scale MHD numerical simulation of accretion flows and the value of mass accretion rate has independent observational evidences. The success of the model suggests that we may seriously consider the possibility that cavities and bubbles observed in other contexts such as galaxy clusters may be formed by winds rather than jets.

  4. X-RAYING AN ACCRETION DISK IN REALTIME: THE EVOLUTION OF IONIZED REFLECTION DURING A SUPERBURST FROM 4U 1636-536

    SciTech Connect

    Keek, L.; Ballantyne, D. R.; Kuulkers, E.; Strohmayer, T. E.

    2014-12-20

    When a thermonuclear X-ray burst ignites on an accreting neutron star, the accretion disk undergoes sudden strong X-ray illumination, which can drive a range of processes in the disk. Observations of superbursts, with durations of several hours, provide the best opportunity to study these processes and to probe accretion physics. Using detailed models of X-ray reflection, we perform time resolved spectroscopy of the superburst observed from 4U 1636-536 in 2001 with the Rossi X-Ray Timing Explorer. The spectra are consistent with a blackbody reflecting off a photoionized accretion disk, with the ionization state dropping with time. The evolution of the reflection fraction indicates that the initial reflection occurs from a part of the disk at larger radius, subsequently transitioning to reflection from an inner region of the disk. Even though this superburst did not reach the Eddington limit, we find that a strong local absorber develops during the superburst. Including this event, only two superbursts have been observed by an instrument with sufficient collecting area to allow for this analysis. It highlights the exciting opportunity for future X-ray observatories to investigate the processes in accretion disks when illuminated by superbursts.

  5. REVIEWS OF TOPICAL PROBLEMS: The nature of accretion disks of close binary stars: overreflection instability and developed turbulence

    NASA Astrophysics Data System (ADS)

    Fridman, A. M.; Bisikalo, D. V.

    2008-06-01

    The current status of the physics of accretion disks in close binary stars is reviewed, with an emphasis on the hydrodynamic overreflection instability, which is a factor leading to the accretion disk turbulence. The estimated turbulent viscosity coefficients are in good agreement with observations and explain the high angular momentum transfer rate and the measured accretion rate. Based on the observations, a power-law spectrum for the developed turbulence is obtained.

  6. ON HYDROMAGNETIC STRESSES IN ACCRETION DISK BOUNDARY LAYERS

    SciTech Connect

    Pessah, Martin E.; Chan, Chi-kwan E-mail: ckch@nordita.org

    2012-05-20

    Detailed calculations of the physical structure of accretion disk boundary layers, and thus their inferred observational properties, rely on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. The standard model for turbulent shear viscosity satisfies this assumption by construction. However, this behavior is not supported by numerical simulations of turbulent magnetohydrodynamic (MHD) accretion disks, which show that angular momentum transport driven by the magnetorotational instability (MRI) is inefficient in disk regions where, as expected in boundary layers, the angular frequency increases with radius. In order to shed light on physically viable mechanisms for angular momentum transport in this inner disk region, we examine the generation of hydromagnetic stresses and energy density in differentially rotating backgrounds with angular frequencies that increase outward in the shearing-sheet framework. We isolate the modes that are unrelated to the standard MRI and provide analytic solutions for the long-term evolution of the resulting shearing MHD waves. We show that, although the energy density of these waves can be amplified significantly, their associated stresses oscillate around zero, rendering them an inefficient mechanism to transport significant angular momentum (inward). These findings are consistent with the results obtained in numerical simulations of MHD accretion disk boundary layers and challenge the standard assumption of efficient angular momentum transport in the inner disk regions. This suggests that the detailed structure of turbulent MHD accretion disk boundary layers could differ appreciably from those derived within the standard framework of turbulent shear viscosity.

  7. [Physical activity, physical fitness, and overweight in children and adolescents: evidence from epidemiologic studies].

    PubMed

    Ortega, Francisco B; Ruiz, Jonatan R; Castillo, Manuel J

    2013-10-01

    Physical activity and fitness play a significant role in prevention of overweight and obesity in children and adolescents. Current understanding and evidence from epidemiologic studies provide useful insights to better understand how they relate to each other and how to develop future intervention strategies. This paper summarizes the most relevant information from cross-sectional and longitudinal studies on the relationships between physical activity, physical fitness, and overweight in early life. According to current scientific evidence: (i) High levels of physical activity during childhood and adolescence, particularly vigorous physical activity, are associated to lower total and central adiposity at this age and later in life; (ii) the level of physical fitness, especially aerobic fitness, is inversely related to current and future adiposity levels; (iii) overweight children and adolescents with a high fitness level have a healthier cardiovascular profile than their overweight, low fit peers and a similar profile to their normal weight, low fit peers. This suggests that high fitness levels may counteract the negative consequences attributed to body fat. These findings suggest that increasing physical fitness in overweight children and adolescents may have many positive effects on health, including lower body fat levels.

  8. Numerical simulation of the Hall effect in magnetized accretion disks with the Pluto code

    NASA Astrophysics Data System (ADS)

    Nakhaei, Mohammad; Safaei, Ghasem; Abbassi, Shahram

    2014-01-01

    We investigate the Hall effect in a standard magnetized accretion disk which is accompanied by dissipation due to viscosity and magnetic resistivity. By considering an initial magnetic field, using the PLUTO code, we perform a numerical magnetohydrodynamic simulation in order to study the effect of Hall diffusion on the physical structure of the disk. Current density and temperature of the disk are significantly modified by Hall diffusion, but the global structure of the disk is not substantially affected. The changes in the current densities and temperature of the disk lead to a modification in the disk luminosity and radiation.

  9. Space physics strategy: Implementation study. Volume 2: Program plan

    NASA Technical Reports Server (NTRS)

    1991-01-01

    In June, 1989, the Space Science and Applications Advisory Committee (SSAAC) authorized its Space Physics Subcommittee (SPS) to prepare a plan specifying the future missions, launch sequence, and encompassing themes of the Space Physics Division. The plan, now complete, is the product of a year-long study comprising two week-long workshops - in January and June 1990 - assisted by pre-workshop, inter-workshop, and post-workshop preparation and assessment activities. The workshops engaged about seventy participants, drawn equally from the Division's four science disciplines: cosmic and heliospheric physics, solar physics, magnetosphere physics, and ionosphere-thermosphere-mesospheric physics. An earlier report records the outcome of the first workshop; this is the report of the final workshop.

  10. Using the Case Study Method in Teaching College Physics

    NASA Astrophysics Data System (ADS)

    Burko, Lior M.

    2016-10-01

    The case study teaching method has a long history (starting at least with Socrates) and wide current use in business schools, medical schools, law schools, and a variety of other disciplines. However, relatively little use is made of it in the physical sciences, specifically in physics or astronomy. The case study method should be considered by physics faculty as part of the effort to transition the teaching of college physics from the traditional frontal-lecture format to other formats that enhance active student participation. In this paper we endeavor to interest physics instructors in the case study method, and hope that it would also serve as a call for more instructors to produce cases that they use in their own classes and that can also be adopted by other instructors.

  11. Undergraduate Physical Activity and Depressive Symptoms: A National Study

    ERIC Educational Resources Information Center

    Elliot, Catherine A.; Kennedy, Catherine; Morgan, George; Anderson, Sharon K.; Morris, Debra

    2012-01-01

    Objective: To study the effects of college students' physical activity and gender on depressive and suicidal symptoms. Method: The National College Health Assessment survey was administered to college students nationwide. Data were analyzed with 4x2 ANOVAs and Games-Howell post hoc tests when appropriate. Results: More frequent physical activity…

  12. Phenomenographic Study of Students' Problem Solving Approaches in Physics

    ERIC Educational Resources Information Center

    Walsh, Laura N.; Howard, Robert G.; Bowe, Brian

    2007-01-01

    This paper describes ongoing research investigating student approaches to quantitative and qualitative problem solving in physics. This empirical study was conducted using a phenomenographic approach to analyze data from individual semistructured problem solving interviews with 22 introductory college physics students. The main result of the study…

  13. The Place of Astronomy in the Study of Physics

    ERIC Educational Resources Information Center

    Tricker, R. A. R.

    1973-01-01

    Presents two examples of astronomical problems suitable for use in teaching of Newton's and Kepler's laws of motion in a logical fashion. Indicates that the gratuitous presentation of physical principles may lead to removal of student interests and sense of achievement and satisfaction in the study of physics. (CC)

  14. Chemical Physics: A Subject for Study at University?

    ERIC Educational Resources Information Center

    Dunmur, D. A.

    1982-01-01

    Traces development of chemical physics as a distinct discipline and reviews its position as a subject for study in United Kingdom universities. Reports results of a survey of chemical physics courses and graduates (1975-1980), including employment data on these graduates. (Author/JN)

  15. Telling Physical Education Teacher Education Tales through Pedagogical Case Studies

    ERIC Educational Resources Information Center

    Stolz, Steven A.; Pill, Shane

    2016-01-01

    This paper analyses two pedagogical case studies (PCS) from a multidisciplinary perspective to highlight the problems of theoretical knowledge in tertiary physical education teacher education (PETE) programmes, school-based physical education (PE) practice and continuous professional learning (CPL) in PE. We argue that a critical view of tertiary…

  16. Parsec-Scale Accretion and Winds Irradiated by a Quasar

    NASA Technical Reports Server (NTRS)

    Dorodnitsyn, A.; Kallman, T.; Proga, D.

    2016-01-01

    We present numerical simulations of properties of a parsec-scale torus exposed to illumination by the central black hole in an active galactic nucleus (AGN). Our physical model allows to investigate the balance between the formation of winds and accretion simultaneously. Radiation-driven winds are allowed by taking into account radiation pressure due to UV and IR radiation along with X-ray heating and dust sublimation. Accretion is allowed through angular momentum transport and the solution of the equations of radiative, viscous radiation hydrodynamics. Our methods adopt flux-limited diffusion radiation hydrodynamics for the dusty, infrared pressure driven part of the flow, along with X-ray heating and cooling. Angular momentum transport in the accreting part of the flow is modeled using effective viscosity. Our results demonstrate that radiation pressure on dust can play an important role in shaping AGN obscuration. For example, when the luminosity illuminating the torus exceeds L greater than 0.01 L(sub Edd), where L(sub Edd) is the Eddington luminosity, we find no episodes of sustained disk accretion because radiation pressure does not allow a disk to form. Despite the absence of the disk accretion, the flow of gas to smaller radii still proceeds at a rate 10(exp -4)-10(exp -1)M dot yr(exp -1) through the capturing of the gas from the hot evaporative flow, thus providing a mechanism to deliver gas from a radiation-pressure dominated torus to the inner accretion disk. As L L(sub edd) increases, larger radiation input leads to larger torus aspect ratios and increased obscuration of the central black hole. We also find the important role of the X-ray heated gas in shaping the obscuring torus.

  17. Star-disc interaction in galactic nuclei: orbits and rates of accreted stars

    NASA Astrophysics Data System (ADS)

    Kennedy, Gareth F.; Meiron, Yohai; Shukirgaliyev, Bekdaulet; Panamarev, Taras; Berczik, Peter; Just, Andreas; Spurzem, Rainer

    2016-07-01

    We examine the effect of an accretion disc on the orbits of stars in the central star cluster surrounding a central massive black hole by performing a suite of 39 high-accuracy direct N-body simulations using state-of-the art software and accelerator hardware, with particle numbers up to 128k. The primary focus is on the accretion rate of stars by the black hole (equivalent to their tidal disruption rate for black holes in the small to medium mass range) and the eccentricity distribution of these stars. Our simulations vary not only the particle number, but disc model (two models examined), spatial resolution at the centre (characterized by the numerical accretion radius) and softening length. The large parameter range and physically realistic modelling allow us for the first time to confidently extrapolate these results to real galactic centres. While in a real galactic centre both particle number and accretion radius differ by a few orders of magnitude from our models, which are constrained by numerical capability, we find that the stellar accretion rate converges for models with N ≥ 32k. The eccentricity distribution of accreted stars, however, does not converge. We find that there are two competing effects at work when improving the resolution: larger particle number leads to a smaller fraction of stars accreted on nearly circular orbits, while higher spatial resolution increases this fraction. We scale our simulations to some nearby galaxies and find that the expected boost in stellar accretion (or tidal disruption, which could be observed as X-ray flares) in the presence of a gas disc is about a factor of 10. Even with this boost, the accretion of mass from stars is still a factor of ˜100 slower than the accretion of gas from the disc. Thus, it seems accretion of stars is not a major contributor to black hole mass growth.

  18. Physical activity among the elderly in China: a qualitative study.

    PubMed

    Li, Yanling; Du, Xiaojing; Zhang, Chunfang; Wang, Sibao

    2013-07-01

    The benefits of physical activity are well known, but little is known about the views of elderly Chinese people regarding physical activity, and what factors affect this. This qualitative study aims to explore the experiences and perceptions of the elderly community regarding physical activity and to gain a better understanding of these. A qualitative study of 12 elderly Chinese people was undertaken using the Colaizzi phenomenological approach and using semi-structured interviews to gather data. Three key themes emerged relating to current physical activity status, beliefs about physical activity and factors influencing physical activity. This study provides new knowledge about the elderly community's experiences and perceptions of physical activity. By understanding these, were may show that promoting active lifestyles and building physical activity into and around day-to-day activities are important strategies in increasing levels of activity. Furthermore, the need for appropriate activity facilities, available space, peer motivation and general social support could promote activity beliefs and subsequent adherence among the elderly community.

  19. Unveiling slim accretion disc in AGN through X-ray and Infrared observations

    NASA Astrophysics Data System (ADS)

    Castelló-Mor, Núria; Kaspi, Shai; Netzer, Hagai; Du, Pu; Hu, Chen; Ho, Luis C.; Bai, Jin-Ming; Bian, Wei-Hao; Yuan, Ye-Fei; Wang, Jian-Min

    2017-01-01

    In this work, which is a continuation of Castello-Mor et al. (2016), we present new X-ray and infrared (IR) data for a sample of active galactic nuclei (AGN) covering a wide range in Eddington ratio over a small luminosity range. In particular, we rigorously explore the dependence of the optical-to-X-ray spectral index αOX and the IR-to-optical spectral index on the dimensionless accretion rate, dot{M}=dot{m}/η where dot{m}=LAGN/LEdd and η is the mass-to-radiation conversion efficiency, in low and high accretion rate sources. We find that the SED of the faster accreting sources are surprisingly similar to those from the comparison sample of sources with lower accretion rate. In particular: I) the optical-to-UV AGN SED of slow and fast accreting AGN can be fitted with thin AD models. II) The value of αOX is very similar in slow and fast accreting systems up to a dimensionless accretion rate dot{M}c ˜10. We only find a correlation between αOX and dot{M} for sources with dot{M}>dot{M}c. In such cases, the faster accreting sources appear to have systematically larger αOX values. III) We also find that the torus in the faster accreting systems seems to be less efficient in reprocessing the primary AGN radiation having lower IR-to-optical spectral slopes. These findings, failing to recover the predicted differences between the SEDs of slim and thin ADs within the observed spectral window, suggest that additional physical processes or very special geometry act to reduce the extreme UV radiation in fast accreting AGN. This may be related to photon trapping, strong winds, and perhaps other yet unknown physical processes.

  20. Chondrule Formation via Impact Jetting Triggered by Planetary Accretion

    NASA Astrophysics Data System (ADS)

    Hasegawa, Yasuhiro; Wakita, Shigeru; Matsumoto, Yuji; Oshino, Shoichi

    2016-01-01

    Chondrules are one of the most primitive elements that can serve as a fundamental clue to the origin of our solar system. We investigate a formation scenario of chondrules that involves planetesimal collisions and the resultant impact jetting. Planetesimal collisions are the main agent to regulate planetary accretion that leads to the formation of terrestrial planets and cores of gas giants. The key component of this scenario is that ejected materials can melt when the impact velocity between colliding planetesimals exceeds about 2.5 km s-1. Previous simulations have shown that the process is efficient enough to reproduce the primordial abundance of chondrules. We examine this scenario carefully by performing semi-analytical calculations that are developed based on the results of direct N-body simulations. As found in the previous work, we confirm that planetesimal collisions that occur during planetary accretion can play an important role in forming chondrules. This arises because protoplanet-planetesimal collisions can achieve an impact velocity of about 2.5 km s-1 or higher, as protoplanets approach the isolation mass (Mp,iso). Assuming that the ejected mass is a fraction (Fch) of the colliding planetesimals’ mass, we show that the resultant abundance of chondrules is expressed well by FchMp,iso, as long as the formation of protoplanets is completed within a given disk lifetime. We perform a parameter study and examine how the abundance of chondrules and the timing of their formation change. We find that the impact jetting scenario generally works reasonably well for a certain range of parameters, while more dedicated work would be needed to include other physical processes that are neglected in this work and to examine their effects on chondrule formation.

  1. Neutron Star Seismology with Accreting Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Strohmayer, Tod

    Neutron stars provide natural laboratories for the study of a number of important topics in fundamental physics, including the composition and equation of state (EOS) of cold matter at the highest densities achievable in nature. The physical conditions in their deep interiors cannot be replicated in terrestrial laboratories, and the nature of matter under such extreme conditions remains one of the major unsolved problems in physics. Direct measurement of the mass - radius relationship for neutron stars is very important for constraining the EOS of dense matter, however, since different phases of dense matter can have similar equations of state, mass and radius measurements alone are not very efficient in determining their interior composition. Additional, complementary observables are needed to more definitively probe the composition of neutron star cores. Asteroseismology, the measurement of the characteristic frequencies of the normal modes of oscillation of stars, can provide a powerful probe of their interiors. For example, helioseismology has provided unprecedented insights about the deep interior of the Sun. Comparable capabilities for neutron star seismology have not yet been achieved, but our recent work indicates that sensitive searches for the signatures of neutron star oscillations can be carried out using the high time resolution, pulse timing data obtained by the Rossi X-ray Timing Explorer (RXTE)-and in the case of a single source the XMM-Newton pn camera-from the population of accreting millisecond X-ray pulsars (AMXPs, Strohmayer & Mahmoodifar 2014a), and in some thermonuclear burst sources (Strohmayer & Mahmoodifar 2014b). It is the primary aim of this proposal to carry out the first such comprehensive search for global oscillation modes across this entire source class of neutron stars using approximately 6 M-sec of RXTE and 100 k-sec of XMMNewton archival data, and thereby significantly advance the nascent field of neutron star seismology. We will

  2. Physical organic studies of organometallic reactions

    SciTech Connect

    Bergman, Robert G.

    1981-01-01

    The mechanisms of reactions of organotransition metal complexes have only begun to be understood in detail during the last ten years. The complementary interaction of techniques and concepts developed earlier in studies of organic reaction mechanisms, with those commonly used in inorganic chetnistry, has played a crucial role in helping to elucidate organor.1etall.ic reaction mechanisms. A few systems in which this interaction has proved especially fruitful are discussed in this article.

  3. Comparisons and connections between mean field dynamo theory and accretion disc theory

    NASA Astrophysics Data System (ADS)

    Blackman, E. G.

    2010-01-01

    The origin of large scale magnetic fields in astrophysical rotators, and the conversion of gravitational energy into radiation near stars and compact objects via accretion have been subjects of active research for a half century. Magnetohydrodynamic turbulence makes both problems highly nonlinear, so both subjects have benefitted from numerical simulations.However, understanding the key principles and practical modeling of observations warrants testable semi-analytic mean field theories that distill the essential physics. Mean field dynamo (MFD) theory and alpha-viscosity accretion disc theory exemplify this pursuit. That the latter is a mean field theory is not always made explicit but the combination of turbulence and global symmetry imply such. The more commonly explicit presentation of assumptions in 20th century textbook MFDT has exposed it to arguably more widespread criticism than incurred by 20th century alpha-accretion theory despite complementary weaknesses. In the 21st century however, MFDT has experienced a breakthrough with a dynamical saturation theory that consistently agrees with simulations. Such has not yet occurred in accretion disc theory, though progress is emerging. Ironically however, for accretion engines, MFDT and accretion theory are presently two artificially uncoupled pieces of what should be a single coupled theory. Large scale fields and accretion flows are dynamically intertwined because large scale fields likely play a key role in angular momentum transport. I discuss and synthesize aspects of recent progress in MFDT and accretion disc theory to suggest why the two likely conspire in a unified theory.

  4. Planetary accretion in circumstellar disks

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; Stewart, Glen R.

    1993-01-01

    The formation of terrestrial planets and the cores of Jovian planets is reviewed in the framework of the planetesimal hypothesis, wherein planets are assumed to grow via the pairwise accumulation of small solid bodies. Emphasis is placed on the dynamics of solid body accretion from kilometer size planetesimals to terrestrial type planets. This stage of planetary growth is least dependent on the characteristics of the evolutionary state of the central star. It is concluded that the evolution of the planetesimal size distribution is determined by the gravitationally enhanced collision cross-section, which favors collisions between planetesimals with smaller velocities. Runaway growth of the largest planetesimal in each accretion zone appears to be a likely outcome. The subsequent accumulation of the resulting protoplanets leads to a large degree of radial mixing in the terrestrial planet region, and giant impacts are probable.

  5. Obscured accretion from AGN surveys

    NASA Astrophysics Data System (ADS)

    Vignali, Cristian

    2014-07-01

    Recent models of super-massive black hole (SMBH) and host galaxy joint evolution predict the presence of a key phase where accretion, traced by obscured Active Galactic Nuclei (AGN) emission, is coupled with powerful star formation. Then feedback processes likely self-regulate the SMBH growth and quench the star-formation activity. AGN in this important evolutionary phase have been revealed in the last decade via surveys at different wavelengths. On the one hand, moderate-to-deep X-ray surveys have allowed a systematic search for heavily obscured AGN, up to very high redshifts (z~5). On the other hand, infrared/optical surveys have been invaluable in offering complementary methods to select obscured AGN also in cases where the nuclear X-ray emission below 10 keV is largely hidden to our view. In this review I will present my personal perspective of the field of obscured accretion from AGN surveys.

  6. Analytic models of relativistic accretion disks

    NASA Astrophysics Data System (ADS)

    Zhuravlev, V. V.

    2015-06-01

    We present not a literature review but a description, as detailed and consistent as possible, of two analytic models of disk accretion onto a rotating black hole: a standard relativistic disk and a twisted relativistic disk. Although one of these models is older than the other, both are of topical interest for black hole studies. The treatment is such that the reader with only a limited knowledge of general relativity and relativistic hydrodynamics, with little or no use of additional sources, can gain insight into many technical details lacking in the original papers.

  7. Zircon dating of oceanic crustal accretion.

    PubMed

    Lissenberg, C Johan; Rioux, Matthew; Shimizu, Nobumichi; Bowring, Samuel A; Mével, Catherine

    2009-02-20

    Most of Earth's present-day crust formed at mid-ocean ridges. High-precision uranium-lead dating of zircons in gabbros from the Vema Fracture Zone on the Mid-Atlantic Ridge reveals that the crust there grew in a highly regular pattern characterized by shallow melt delivery. Combined with results from previous dating studies, this finding suggests that two distinct modes of crustal accretion occur along slow-spreading ridges. Individual samples record a zircon date range of 90,000 to 235,000 years, which is interpreted to reflect the time scale of zircon crystallization in oceanic plutonic rocks.

  8. Normal Modes of Black Hole Accretion Disks

    SciTech Connect

    Ortega-Rodriguez, Manuel; Silbergleit, Alexander S.; Wagoner, Robert V.; /Stanford U., Phys. Dept. /KIPAC, Menlo Park

    2006-11-07

    This paper studies the hydrodynamical problem of normal modes of small adiabatic oscillations of relativistic barotropic thin accretion disks around black holes (and compact weakly magnetic neutron stars). Employing WKB techniques, we obtain the eigen frequencies and eigenfunctions of the modes for different values of the mass and angular momentum of the central black hole. We discuss the properties of the various types of modes and examine the role of viscosity, as it appears to render some of the modes unstable to rapid growth.

  9. Formation of primordial supermassive stars by rapid mass accretion

    SciTech Connect

    Hosokawa, Takashi; Yoshida, Naoki; Yorke, Harold W.; Inayoshi, Kohei; Omukai, Kazuyuki E-mail: hosokwtk@gmail.com

    2013-12-01

    Supermassive stars (SMSs) forming via very rapid mass accretion ( M-dot {sub ∗}≳0.1 M{sub ⊙} yr{sup −1}) could be precursors of supermassive black holes observed beyond a redshift of about six. Extending our previous work, here we study the evolution of primordial stars growing under such rapid mass accretion until the stellar mass reaches 10{sup 4–5} M {sub ☉}. Our stellar evolution calculations show that a star becomes supermassive while passing through the 'supergiant protostar' stage, whereby the star has a very bloated envelope and a contracting inner core. The stellar radius increases monotonically with the stellar mass until ≅ 100 AU for M {sub *} ≳ 10{sup 4} M {sub ☉}, after which the star begins to slowly contract. Because of the large radius, the effective temperature is always less than 10{sup 4} K during rapid accretion. The accreting material is thus almost completely transparent to the stellar radiation. Only for M {sub *} ≳ 10{sup 5} M {sub ☉} can stellar UV feedback operate and disturb the mass accretion flow. We also examine the pulsation stability of accreting SMSs, showing that the pulsation-driven mass loss does not prevent stellar mass growth. Observational signatures of bloated SMSs should be detectable with future observational facilities such as the James Webb Space Telescope. Our results predict that an inner core of the accreting SMS should suffer from the general relativistic instability soon after the stellar mass exceeds 10{sup 5} M {sub ☉}. An extremely massive black hole should form after the collapse of the inner core.

  10. A WARM MODE OF GAS ACCRETION ON FORMING GALAXIES

    SciTech Connect

    Murante, Giuseppe; Calabrese, Matteo; De Lucia, Gabriella; Monaco, Pierluigi; Borgani, Stefano; Dolag, Klaus E-mail: monaco@oats.inaf.it E-mail: calabrese@oato.inaf.it E-mail: kdolag@mpa-garching.mpg.de

    2012-04-20

    We present results from high-resolution cosmological hydrodynamical simulations of a Milky-Way-sized halo, aimed at studying the effect of feedback on the nature of gas accretion. Simulations include a model of interstellar medium and star formation, in which supernova (SN) explosions provide effective thermal feedback. We distinguish between gas accretion onto the halo, which occurs when gas particles cross the halo virial radius, and gas accretion onto the central galaxy, which takes place when gas particles cross the inner one-tenth of the virial radius. Gas particles can be accreted through three different channels, depending on the maximum temperature value, T{sub max}, reached during the particles' past evolution: a cold channel for T{sub max} < 2.5 Multiplication-Sign 10{sup 5} K, a hot one for T > 10{sup 6} K, and a warm one for intermediate values of T{sub max}. We find that the warm channel is at least as important as the cold one for gas accretion onto the central galaxy. This result is at variance with previous findings that the cold mode dominates gas accretion at high redshift. We ascribe this difference to the different SN feedback scheme implemented in our simulations. While results presented so far in the literature are based on uneffective SN thermal feedback schemes and/or the presence of a kinetic feedback, our simulations include only effective thermal feedback. We argue that observational detections of a warm accretion mode in the high-redshift circumgalactic medium would provide useful constraints on the nature of the feedback that regulates star formation in galaxies.

  11. PHYSICAL STUDIES OF ISOLATED EUCARYOTIC NUCLEI

    PubMed Central

    Olins, Donald E.; Olins, Ada L.

    1972-01-01

    The degree of chromatin condensation in isolated rat liver nuclei and chicken erythrocyte nuclei was studied by phase-contrast microscopy as a function of solvent pH, K+ and Mg++ concentrations Data were represented as "phase" maps, and standard solvent conditions selected that reproducibly yield granular, slightly granular, and homogeneous nuclei Nuclei in these various states were examined by ultraviolet absorption and circular dichroism (CD) spectroscopy, low-angle X-ray diffraction, electron microscopy, and binding capacity for ethidium bromide Homogeneous nuclei exhibited absorption and CD spectra resembling those of isolated nucleohistone. Suspensions of granular nuclei showed marked turbidity and absorption flattening, and a characteristic blue-shift of a crossover wavelength in the CD spectra. In all solvent conditions studied, except pH < 2 3, low-angle X-ray reflections characteristic of the native, presumably superhelical, nucleohistone were observed from pellets of intact nuclei. Threads (100–200 A diameter) were present in the condensed and dispersed phases of nuclei fixed under the standard solvent conditions, and examined in the electron microscope after thin sectioning and staining Nuclei at neutral pH, with different degrees of chromatin condensation, exhibited similar binding capacities for ethidium bromide. These data suggest a model that views chromatin condensation as a close packing of superhelical nucleohistone threads but still permits condensed chromatin to respond rapidly to alterations in solvent environment. PMID:4554987

  12. Hydrodynamic Viscosity in Accretion Disks

    NASA Astrophysics Data System (ADS)

    Duschl, Wolfgang J.; Strittmatter, Peter A.; Biermann, Peter L.

    We propose a generalized accretion disk viscosity prescription based on hydrodynamically driven turbulence at the critical effective Reynolds number. This approach is consistent with recent re-analysis by Richard & Zahn (1999) of experimental results on turbulent Couette-Taylor flows. This new β-viscosity formulation applies to both selfgravitating and non-selfgravitating disks and is shown to yield the standard α-disk prescription in the case of shock dissipation limited, non-selfgravitating disks.

  13. Accretion of low angular momentum material onto black holes: 2D magnetohydrodynamical case.

    NASA Astrophysics Data System (ADS)

    Proga, D.; Begelman, M. C.

    2003-03-01

    We report on the second phase of our study of slightly rotating accretion flows onto black holes. We consider magnetohydrodynamical (MHD) accretion flows with a spherically symmetric density distribution at the outer boundary, but with spherical symmetry broken by the introduction of a small, latitude-dependent angular momentum and a weak radial magnetic field. We study accretion flows by means of numerical 2D, axisymmetric, MHD simulations with and without resistive heating. Our main result is that the properties of the accretion flow depend mostly on an equatorial accretion torus. Initially, accretion occurs only through the polar funnel, as in the hydrodynamic inviscid case, where material has zero or very low angular momentum. The material that has too much angular momentum to be accreted directly forms a thick torus near the equator. However, in the later phase of the evolution, the transport of angular momentum due to the magnetorotational instability (MRI) facilitates accretion through the torus, too. The torus thickens towards the poles and develops a corona or an outflow or both. Consequently, the mass accretion through the funnel is stopped. The accretion of rotating gas through the torus is significantly reduced compared to the accretion of non-rotating gas (i.e., the Bondi rate). Our results do not change if we switch on or off resistive heating. Overall our simulations are very similar those presented by Stone, Pringle, Hawley and Balbus despite different initial and outer boundary conditions. Thus, we confirm that the MRI is very robust and controls the nature of radiatively inefficient accretion flows. DP acknowledges support from NASA under LTSA grant NAG5-11736 and support provided by NASA through grant AR-09532 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. MB acknowledges support from NSF grant AST-9876887.

  14. Commencement Bay Study. Volume VI. Physical Oceanography.

    DTIC Science & Technology

    1981-12-31

    x C4 N miAnA a)Naaaa a ON .41 0 -N n NCa4aa a U - - 0 MO ~ S M -Mis a a If Ni ŕ 3 iin 0 09 CaI l 1 1 1 ?1 0 ’-NMM.eC% rN waa 0a%0 ; N N inN 0;C inW M ...Birds I.KEY WORDS (Cmnimman m reverse Bdse If .toreewy and Ident’ by Nock number) SloisWetlands Noise Aesthetics Marine Fish Sediments Land and Water...Use Washington Phsialoeaogapy Air Quality and City of Tacoma Baseline WtrQaiyClimate Commencement Bay Studies 2& AISTRCT’ Coniaw M "W SMN R04Aeeee 1011

  15. BOOK REVIEW: Rotation and Accretion Powered Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, V. M.

    2008-03-01

    ever wanted to know about pulsars but were afraid to ask. Chapter 1 begins a brief and interesting account of the discovery of pulsars, followed by an overview of the rotation-powered and accretion-powered populations. The following four chapters are fairly detailed and reasonably quantitative descriptions of neutron star interiors. This is no easy feat, given that a description of the physics of neutron stars demands a deep understanding of all major physical forces, and must include general relativity as well as detailed particle physics. The historical notes at the beginning of Chapter 2 are particularly fascinating, recounting the path to today's understanding of neutron stars in very interesting detail. Chapter 7 presents rotation-powered pulsar radio properties, and a nice description of pulsar timing, including relativistic and non-relativistic binaries and GR tests. The remaining chapters tackle a variety of topics including binary evolution, superfluidity, accretion-powered pulsar properties, magnetospheres and emission mechanisms, magnetic fields, spin evolution and strange stars. The coverage is somewhat uneven, with the strange star chapter, for example, an obvious afterthought. The utility of an encyclopedia lies in its breadth and in how up-to-date it is. Although admirable in its intentions, the Ghosh book does omit some major pulsar topics. This book leaves the impression that rotation-powered pulsars produce only radio emission; hardly (if at all) mentioned is the vast literature on their infrared, optical, and even more importantly, x-ray and gamma-ray emission, the latter being far more relevant to the pulsar 'machine' than the energetically puny radio output. Also absent are pulsar winds; this is particularly puzzling given both the lovely wind nebula that graces the book's cover, and the central role the wind plays as primary sink of the rotation power. One of the most actively pursued topics in pulsar astrophysics in the past decade, magnetars

  16. Factors related to physical activity: a study of adolescents.

    PubMed

    Vilhjalmsson, R; Thorlindsson, T

    1998-09-01

    Although the consequences of physical activity have been carefully documented, less is known about its correlates, particularly among children and youth. Based on a representative national survey of 1131 Icelandic adolescents, the study examined various physical, psychological, social and demographic factors related to physical activity. Male sex, significant others' involvement in physical activity (father, friend and older brother), sociability, perceived importance of sport and of health improvement and satisfaction with mandatory gym classes in school, were all related to more involvement, whereas hours of paid work and TV-viewing were related to less. Furthermore, the data suggested that the influence of friend's participation in physical activity depends on his or her emotional significance. Influential others appeared to affect males and females in the same way. The meaning of the results and their implications for future research are discussed.

  17. Spectral Analysis and Experimental Modeling of Ice Accretion Roughness

    NASA Technical Reports Server (NTRS)

    Orr, D. J.; Breuer, K. S.; Torres, B. E.; Hansman, R. J., Jr.

    1996-01-01

    A self-consistent scheme for relating wind tunnel ice accretion roughness to the resulting enhancement of heat transfer is described. First, a spectral technique of quantitative analysis of early ice roughness images is reviewed. The image processing scheme uses a spectral estimation technique (SET) which extracts physically descriptive parameters by comparing scan lines from the experimentally-obtained accretion images to a prescribed test function. Analysis using this technique for both streamwise and spanwise directions of data from the NASA Lewis Icing Research Tunnel (IRT) are presented. An experimental technique is then presented for constructing physical roughness models suitable for wind tunnel testing that match the SET parameters extracted from the IRT images. The icing castings and modeled roughness are tested for enhancement of boundary layer heat transfer using infrared techniques in a "dry" wind tunnel.

  18. Massive accretion disks in galactic nuclei

    NASA Astrophysics Data System (ADS)

    Scoville, N. Z.

    In the luminous infrared galaxies, very large masses of interstellar matter have been concentrated in the galactic nuclei at radii less than 300 pc as a result of galactic merging, while in lower luminosity systems, this material is probably concentrated by stellar bars and viscous accretion. In both cases, the nuclear region will be highly obscured by dust at visible wavelengths, forcing studies to longer wavelengths where the extinction is reduced. We review recent high resolution near infrared (HST-NICMOS) and mm-interferometric imaging of the dense gas and dust accretion disks in nearby luminous galactic nuclei. Since this nuclear ISM is the active ingredient for both starburst activity and a likely fuel for central AGNs, the nuclear accretion disks are critical to both the activity and the optical appearance of the nucleus. For a sample of 24 luminous galaxies imaged with NICMOS at 1-2μm, approximately 13 show nuclear point sources, indicating the existence of a central AGN or an intense starburst at <= 50 pc radius. Approximately 14 of the sample galaxies have apparent central dust disks. In the best studied ultraluminous IR galaxy, Arp 220, the 2μm imaging shows dust disks in both of the merging galactic nuclei and mm-CO line imaging indicates molecular gas masses ~ 109Msolar for each disk. The two gas disks in Arp 220 are counterrotating and their dynamical masses are ~ 2×109Msolar, that is, only slightly larger than the gas masses. These disks have radii ~ 100 pc and thickness 10-50 pc. The high brightness temperatures of the CO lines indicate that the gas in the disks has area filling factors ~25-50% and mean densities of >= 104 cm-3. Within these nuclear disks, the rate of massive star formation is undoubtedly prodigious and, given the high viscosity of the gas, there will also be high radial accretion rates, perhaps >= 10 Msolar yr-1. If this inflow persists to very small radii, it is enough to feed even the highest

  19. Internal Differentiation in Early-Accreting Planetesimals

    NASA Astrophysics Data System (ADS)

    Elkins-Tanton, Linda; Weiss, B. P.; Zuber, M. T.

    2009-09-01

    Chondritic meteorites are unmelted, variably metamorphosed samples of the earliest solids of the solar system. A recent paleomagnetic study of CV chondrites suggests that though the chondrites themselves were not melted, their parent body was internally differentiated and produced a core magnetic dynamo. Bodies that accreted before 1.3 to 3 Ma after CAIs likely contained sufficient 26Al to melt internally from the insulated cumulative effects of radiogenic heating. These bodies would melt from the interior out, sometimes forming an interior magma ocean under a solid, conductive, undifferentiated shell. This shell would consist of the same chondritic material that made up the bulk accreting body before melting began. Simulations indicate that this model of chondrite meteorite genesis requires specific but reasonable conditions: The chondrites experienced metamorphism in the undifferentiated crust of an internally differentiated body of radius 250 km to 450 km, which likely accreted no later than 2.0 Ma after CAIs. This body could have produced a core dynamo lasting more than 10 Ma that left a thermoremanent magnetization in Allende. Because of the limited lifetime of 26Al and the longer apparent period over which chondrite parent bodies were forming, many other parent bodies likely heated without significant melting. However, bodies that are internally differentiated may well exist undetected in the asteroid belt. The shapes and masses of 1 Ceres and 2 Pallas are consistent with differentiated interiors. Other internally differentiated asteroids may have lost their hydrostatic shapes through later impacts, but their surfaces may be irregular, space-weathered primitive material, perhaps with altered or differentiated material at the bottoms of the largest craters. This scenario can explain the mismatch between the enormous diversity (more than 130) of parent bodies represented by achondrites and the paucity (fewer than 10) of basaltic asteroids. Funded by NSF

  20. Variable Protostellar Accretion with Episodic Bursts

    NASA Astrophysics Data System (ADS)

    Vorobyov, Eduard I.; Basu, Shantanu

    2015-06-01

    We present the latest development of the disk gravitational instability and fragmentation model, originally introduced by us to explain episodic accretion bursts in the early stages of star formation. Using our numerical hydrodynamics model with improved disk thermal balance and star-disk interaction, we computed the evolution of protostellar disks formed from the gravitational collapse of prestellar cores. In agreement with our previous studies, we find that cores of higher initial mass and angular momentum produce disks that are more favorable to gravitational instability and fragmentation, while a higher background irradiation and magnetic fields moderate the disk tendency to fragment. The protostellar accretion in our models is time-variable, thanks to the nonlinear interaction between different spiral modes in the gravitationally unstable disk, and can undergo episodic bursts when fragments migrate onto the star owing to the gravitational interaction with other fragments or spiral arms. Most bursts occur in the partly embedded Class I phase, with a smaller fraction taking place in the deeply embedded Class 0 phase and a few possible bursts in the optically visible Class II phase. The average burst duration and mean luminosity are found to be in good agreement with those inferred from observations of FUors. The model predicts the existence of two types of bursts: the isolated ones, showing well-defined luminosity peaks separated with prolonged periods (˜ {{10}4} yr) of quiescent accretion, and clustered ones, demonstrating several bursts occurring one after another during just a few hundred years. Finally, we estimate that 40%-70% of the star-forming cores can display bursts after forming a star-disk system.

  1. Ice Accretion Measurements on an Airfoil and Wedge in Mixed-Phase Conditions

    NASA Technical Reports Server (NTRS)

    Struk, Peter; Bartkus, Tadas; Tsao, Jen-Ching; Currie, Tom; Fuleki, Dan

    2015-01-01

    This paper describes ice accretion measurements from experiments conducted at the National Research Council (NRC) of Canada's Research Altitude Test Facility during 2012. Due to numerous engine power loss events associated with high altitude convective weather, potential ice accretion within an engine due to ice crystal ingestion is being investigated collaboratively by NASA and NRC. These investigations examine the physical mechanisms of ice accretion on surfaces exposed to ice crystal and mixed phase conditions, similar to those believed to exist in core compressor regions of jet engines. A further objective of these tests is to examine scaling effects since altitude appears to play a key role in this icing process.

  2. Spectrum-luminosity dependence of radiation from the polar emitting regions in accreting magnetized neutron stars

    NASA Astrophysics Data System (ADS)

    Klochkov, Dmitry

    2016-04-01

    The recent progress in observational techniques allowed one to probe the evolution of the X-ray spectrum in accreting pulsars (especially, of the cyclotron absorption line - the key spectral feature of accreting magnetized neutron stars) in great detail on various timescales, from pulse-to-pulse variability to secular trends. Particularly interesting are the discovered spectrum-luminosity correlations which are being used to infer the structure and physical characteristics of the pulsar's polar emitting region. I will present the latest developments in the modeling of the emitting structure (accretion column/mound/spot) aimed at explaining the observed spectrum-luminosity dependences.

  3. Constraints on Bygone Nucleosynthesis of Accreting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Meisel, Zach; Deibel, Alex

    2017-03-01

    Nuclear burning near the surface of an accreting neutron star produces ashes that, when compressed deeper by further accretion, alter the star’s thermal and compositional structure. Bygone nucleosynthesis can be constrained by the impact of compressed ashes on the thermal relaxation of quiescent neutron star transients. In particular, Urca cooling nuclei pairs in nuclear burning ashes that cool the neutron star crust via neutrino emission from {e}--capture/{β }--decay cycles and provide signatures of prior nuclear burning over the ∼century timescales it takes to accrete to the {e}--capture depth of the strongest cooling pairs. Using crust cooling models of the accreting neutron star transient MAXI J0556-332, we show that this source likely lacked Type I X-ray bursts and superbursts ≳120 years ago. Reduced nuclear physics uncertainties in rp-process reaction rates and {e}--capture weak transition strengths for low-lying transitions will improve nucleosynthesis constraints using this technique.

  4. ACCRETION RATES OF MOONLETS EMBEDDED IN CIRCUMPLANETARY PARTICLE DISKS

    SciTech Connect

    Ohtsuki, Keiji; Yasui, Yuki; Daisaka, Hiroshi

    2013-08-01

    We examine the gravitational capture probability of colliding particles in circumplanetary particle disks and accretion rates of small particles onto an embedded moonlet, using analytic calculation, three-body orbital integrations, and N-body simulations. Expanding our previous work, we take into account the Rayleigh distribution of particles' orbital eccentricities and inclinations in our analytic calculation and orbital integration and confirm agreement between them when the particle velocity dispersion is comparable to or larger than their mutual escape velocity and the ratio of the sum of the physical radii of colliding particles to their mutual Hill radius (r-tilde{sub p}) is much smaller than unity. As shown by our previous work, the capture probability decreases significantly when the velocity dispersion is larger than the escape velocity and/or r-tilde{sub p}{approx}>0.7. Rough surfaces of particles can enhance the capture probability. We compare the results of three-body calculations with N-body simulations for accretion of small particles by an embedded moonlet and find agreement at the initial stage of accretion. However, when particles forming an aggregate on the moonlet surface nearly fill the Hill sphere, the aggregate reaches a quasi-steady state with a nearly constant number of particles covering the moonlet, and the accretion rate is significantly reduced compared to the three-body results.

  5. The Effect of Transient Accretion on the Spin-up of Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Sudip; Chakrabarty, Deepto

    2017-01-01

    A millisecond pulsar is a neutron star that has been substantially spun up by accretion from a binary companion. A previously unrecognized factor governing the spin evolution of such pulsars is the crucial effect of nonsteady or transient accretion. We numerically compute the evolution of accreting neutron stars through a series of outburst and quiescent phases, considering the drastic variation of the accretion rate and the standard disk–magnetosphere interaction. We find that, for the same long-term average accretion rate, X-ray transients can spin up pulsars to rates several times higher than can persistent accretors, even when the spin-down due to electromagnetic radiation during quiescence is included. We also compute an analytical expression for the equilibrium spin frequency in transients, by taking spin equilibrium to mean that no net angular momentum is transferred to the neutron star in each outburst cycle. We find that the equilibrium spin rate for transients, which depends on the peak accretion rate during outbursts, can be much higher than that for persistent sources. This explains our numerical finding. This finding implies that any meaningful study of neutron star spin and magnetic field distributions requires the inclusion of the transient accretion effect, since most accreting neutron star sources are transients. Our finding also implies the existence of a submillisecond pulsar population, which is not observed. This may point to the need for a competing spin-down mechanism for the fastest-rotating accreting pulsars, such as gravitational radiation.

  6. Monitoring The Land Accretion Development at Coastal Area of Blanakan, Subang Indonesia

    NASA Astrophysics Data System (ADS)

    Nandi; Meriana, Ginna; Somantri, Lili

    2016-11-01

    A land accretion is formed by deposition in estuaries. Recently, a land development in Subang coastal area has raised an increase. Beside its potential, coastal areas are also threatened with damage including abrasion, accretion, loss of mangrove forests, and sea water intrusion. One of the coastal areas that have been arising in very extensive land is Blanakan coastal in Subang Regency. This study aims to monitor the development of a land accretion that have been arise during the period of 1990 to 2015 and also to examine the use of a land accretion and analyze the impact of a land accretion to the social and economic conditions in the Blanakan Coastal Areas. The method used in this research was descriptive quantitative method. In this research, The Landsat imageries were overlaid came from 1990, 2000, 2010, and 2015 to determine the development of a land accretion. Based on the results of Landsat imagery overlaid over the period 1990-2015. Overall, during the period 1990-2015, accreted land formed was an area of 782.9 hectares and abrasion area of 73.3 hectares with changes in the most far reaching 1580.3 m. The use of land accretion in the Blanakan Coastal mostly used for a fishpond with a key commodity is Milkfish and Bago shrimps. The impact of land accretion to the social and economic conditions was reflected through the five indicators such as livelihoods, income, education, health, and ownership of assets.

  7. Accretion of phantom scalar field into a black hole

    SciTech Connect

    Gonzalez, J. A.; Guzman, F. S.

    2009-06-15

    Using numerical methods we present the first full nonlinear study of a phantom scalar field accreted into a black hole. We study different initial configurations and find that the accretion of the field into the black hole can reduce its area down to 50 percent within time scales of the order of few masses of the initial horizon. The analysis includes the cases where the total energy of the space-time is positive or negative. The confirmation of this effect in full nonlinear general relativity implies that the accretion of exotic matter could be considered an evaporation process. We speculate that if this sort of exotic matter has some cosmological significance, this black hole area reduction process might have played a crucial role in black hole formation and population.

  8. Dynamical structure of magnetized dissipative accretion flow around black holes

    NASA Astrophysics Data System (ADS)

    Sarkar, Biplob; Das, Santabrata

    2016-09-01

    We study the global structure of optically thin, advection dominated, magnetized accretion flow around black holes. We consider the magnetic field to be turbulent in nature and dominated by the toroidal component. With this, we obtain the complete set of accretion solutions for dissipative flows where bremsstrahlung process is regarded as the dominant cooling mechanism. We show that rotating magnetized accretion flow experiences virtual barrier around black hole due to centrifugal repulsion that can trigger the discontinuous transition of the flow variables in the form of shock waves. We examine the properties of the shock waves and find that the dynamics of the post-shock corona (PSC) is controlled by the flow parameters, namely viscosity, cooling rate and strength of the magnetic field, respectively. We separate the effective region of the parameter space for standing shock and observe that shock can form for wide range of flow parameters. We obtain the critical viscosity parameter that allows global accretion solutions including shocks. We estimate the energy dissipation at the PSC from where a part of the accreting matter can deflect as outflows and jets. We compare the maximum energy that could be extracted from the PSC and the observed radio luminosity values for several supermassive black hole sources and the observational implications of our present analysis are discussed.

  9. Investigation of surface water behavior during glaze ice accretion

    NASA Technical Reports Server (NTRS)

    Hansman, R. John, Jr.; Turnock, Stephen R.

    1990-01-01

    A series of experimental investigations that focused on isolating the primary factors that control the behavior of unfrozen surface water during glaze ice accretion were conducted. Detailed microvideo observations were made of glaze ice accretions on 2.54 cm diam cylinders in a closed-loop refrigerated wind tunnel. Distinct zones of surface water behavior were observed; a smooth wet zone in the stagnation region with a uniform water film, a rough zone where surface tension effects caused coalescence of surface water into stationary beads, and a zone where surface water ran back as rivulets. The location of the transition from the smooth to the rough zone was found to migrate towards the stagnation point with time. Comparative tests were conducted to study the effect of the substrate thermal and roughness properties on ice accretion. The importance of surface water behavior was evaluated by the addition of a surface tension reducing agent to the icing tunnel water supply, which significantly altered the accreted glaze ice shape. Measurements were made to determine the contact angle behavior of water droplets on ice. A simple multizone modification to current glaze ice accretion models was proposed to include the observed surface roughness behavior.

  10. Angular momentum transport in thin accretion disks and intermittent accretion.

    PubMed

    Coppi, B; Coppi, P S

    2001-07-30

    The plasma modes, transporting angular momentum in accretion disks, under minimally restrictive conditions when the magnetic energy density is significant relative to the thermal energy density, are shown to be singular if the ideal MHD approximation is adopted. A similarity with the modes producing magnetic reconnection in current carrying plasmas is established. The combined effects of finite plasma temperature, of plasma compressibility, of the gradient of the rotation frequency, and of appropriate transport processes (outside ideal MHD) are involved in the onset of these nonaxisymmetric and locally corotating modes.

  11. Physical therapy rehabilitation strategies for dancers: a qualitative study.

    PubMed

    Sabo, Megin

    2013-01-01

    This was a qualitative study utilizing a phenomenological approach. The purpose was to determine what rehabilitation strategies physical therapists use with dancers and to discuss techniques for implementing these strategies from both the dancer's and the physical therapist's perspectives. Self-administered questionnaires were sent via email to dancers and physical therapists. Purposeful sampling was done through use of a criterion sampling method that required participants to have experienced dancer rehabilitation. Data were correlated to find common strategies and to encourage modification of current approaches. Physical therapists returned 29 surveys, while dancers returned eight. Five themes were identified in the areas of: 1. evaluation, 2. dance modification, 3. interventions, 4. education, and 5. communication. The conclusion of this study was that successful rehabilitative strategies involve ongoing evaluation that incorporates knowledge of dance technique and performance, dance-centered movement modification that is clearly defined, and an understanding of dance lingo.

  12. The 2009 outburst of accretion-powered millisecond pulsar IGR J17511-3057 as observed by Swift and RXTE

    NASA Astrophysics Data System (ADS)

    Ibragimov, Askar; Poutanen, Juri; Kajava, Jari

    Accretion-powered millisecond pulsars (AMPs) are very interesting astrophysical objects. Mat-ter from accretion disk is captured by star's magnetic field and falls along the field lines, creating "hotspots" near magnetic poles of the star. Typical spectrum of an AMP contains a disk emis-sion, blackbody emission of a hotspot and a powerlaw tail, produced by thermal Comptonizaion in accreting shock. Pulse profiles of these sources are modified by relativistic effects and can be used to put geometrical constraints and to understand physical processes near the compact object. IGR J17511-3057 was discovered on September 12, 2009 during the INTEGRAL Galactic Bulge monitoring program. The source has the pulse frequency of 245 Hz. In this work, we study spectral and temporal characheristics of IGR J17511-3057 during the outburst, based on Swift and RXTE data. We analyze its energy spectra in range 0.6-150 keV, phase-resolved spectra, pulse profiles, time lags and discuss physical conditions in the source.

  13. Aerodynamic Simulation of Runback Ice Accretion

    NASA Technical Reports Server (NTRS)

    Broeren, Andy P.; Whalen, Edward A.; Busch, Greg T.; Bragg, Michael B.

    2010-01-01

    This report presents the results of recent investigations into the aerodynamics of simulated runback ice accretion on airfoils. Aerodynamic tests were performed on a full-scale model using a high-fidelity, ice-casting simulation at near-flight Reynolds (Re) number. The ice-casting simulation was attached to the leading edge of a 72-in. (1828.8-mm ) chord NACA 23012 airfoil model. Aerodynamic performance tests were conducted at the ONERA F1 pressurized wind tunnel over a Reynolds number range of 4.7?10(exp 6) to 16.0?10(exp 6) and a Mach (M) number ran ge of 0.10 to 0.28. For Re = 16.0?10(exp 6) and M = 0.20, the simulated runback ice accretion on the airfoil decreased the maximum lift coe fficient from 1.82 to 1.51 and decreased the stalling angle of attack from 18.1deg to 15.0deg. The pitching-moment slope was also increased and the drag coefficient was increased by more than a factor of two. In general, the performance effects were insensitive to Reynolds numb er and Mach number changes over the range tested. Follow-on, subscale aerodynamic tests were conducted on a quarter-scale NACA 23012 model (18-in. (457.2-mm) chord) at Re = 1.8?10(exp 6) and M = 0.18, using low-fidelity, geometrically scaled simulations of the full-scale castin g. It was found that simple, two-dimensional simulations of the upper- and lower-surface runback ridges provided the best representation of the full-scale, high Reynolds number iced-airfoil aerodynamics, whereas higher-fidelity simulations resulted in larger performance degrada tions. The experimental results were used to define a new subclassification of spanwise ridge ice that distinguishes between short and tall ridges. This subclassification is based upon the flow field and resulting aerodynamic characteristics, regardless of the physical size of the ridge and the ice-accretion mechanism.

  14. Physical Activity, Sedentary Time and Physical Capability in Early Old Age: British Birth Cohort Study

    PubMed Central

    Cooper, Andrew J. M.; Simmons, Rebecca K.; Kuh, Diana; Brage, Soren; Cooper, Rachel

    2015-01-01

    Purpose To investigate the associations of time spent sedentary, in moderate-to-vigorous-intensity physical activity (MVPA) and physical activity energy expenditure (PAEE) with physical capability measures at age 60-64 years. Methods Time spent sedentary and in MVPA and, PAEE were assessed using individually calibrated combined heart rate and movement sensing among 1727 participants from the MRC National Survey of Health and Development in England, Scotland and Wales as part of a detailed clinical assessment undertaken in 2006-2010. Multivariable linear regression models were used to examine the cross-sectional associations between standardised measures of each of these behavioural variables with grip strength, chair rise and timed up-&-go (TUG) speed and standing balance time. Results Greater time spent in MVPA was associated with higher levels of physical capability; adjusted mean differences in each capability measure per 1standard deviation increase in MVPA time were: grip strength (0.477 kg, 95% confidence interval (CI): 0.015 to 0.939), chair rise speed (0.429 stands/min, 95% CI: 0.093 to 0.764), standing balance time (0.028 s, 95% CI: 0.003 to 0.053) and TUG speed (0.019 m/s, 95% CI: 0.011 to 0.026). In contrast, time spent sedentary was associated with lower grip strength (-0.540 kg, 95% CI: -1.013 to -0.066) and TUG speed (-0.011 m/s, 95% CI: -0.019 to -0.004). Associations for PAEE were similar to those for MVPA. Conclusion Higher levels of MVPA and overall physical activity (PAEE) are associated with greater levels of physical capability whereas time spent sedentary is associated with lower levels of capability. Future intervention studies in older adults should focus on both the promotion of physical activity and reduction in time spent sedentary. PMID:25961736

  15. How physics instruction impacts students' beliefs about learning physics: A meta-analysis of 24 studies

    NASA Astrophysics Data System (ADS)

    Madsen, Adrian; McKagan, Sarah B.; Sayre, Eleanor C.

    2015-06-01

    In this meta-analysis, we synthesize the results of 24 studies using the Colorado Learning Attitudes about Science Survey (CLASS) and the Maryland Physics Expectations Survey (MPEX) to answer several questions: (1) How does physics instruction impact students' beliefs? (2) When do physics majors develop expert-like beliefs? and (3) How do students' beliefs impact their learning of physics? We report that in typical physics classes, students' beliefs deteriorate or at best stay the same. There are a few types of interventions, including an explicit focus on model-building and (or) developing expertlike beliefs that lead to significant improvements in beliefs. Further, small courses and those for elementary education and nonscience majors also result in improved beliefs. However, because the available data oversamples certain types of classes, it is unclear whether these improvements are actually due to the interventions, or due to the small class size, or student populations typical of the kinds of classes in which these interventions are most often used. Physics majors tend to enter their undergraduate education with more expertlike beliefs than nonmajors and these beliefs remain relatively stable throughout their undergraduate careers. Thus, typical physics courses appear to be selecting students who already have strong beliefs, rather than supporting students in developing strong beliefs. There is a small correlation between students' incoming beliefs about physics and their gains on conceptual mechanics surveys. This suggests that students with more expertlike incoming beliefs may learn more in their physics courses, but this finding should be further explored and replicated. Some unanswered questions remain. To answer these questions, we advocate several specific types of future studies: measuring students' beliefs in courses with a wider range of class sizes, student populations, and teaching methods, especially large classes with very innovative pedagogy and

  16. Accretion and Magnetic Reconnection in the Classical T Tauri Binary DQ Tau

    NASA Astrophysics Data System (ADS)

    Tofflemire, Benjamin M.; Mathieu, Robert D.; Ardila, David R.; Akeson, Rachel L.; Ciardi, David R.; Johns-Krull, Christopher; Herczeg, Gregory J.; Quijano-Vodniza, Alberto

    2017-01-01

    The theory of binary star formation predicts that close binaries (a < 100 au) will experience periodic pulsed accretion events as streams of material form at the inner edge of a circumbinary disk (CBD), cross a dynamically cleared gap, and feed circumstellar disks or accrete directly onto the stars. The archetype for the pulsed accretion theory is the eccentric, short-period, classical T Tauri binary DQ Tau. Low-cadence (∼daily) broadband photometry has shown brightening events near most periastron passages, just as numerical simulations would predict for an eccentric binary. Magnetic reconnection events (flares) during the collision of stellar magnetospheres near periastron could, however, produce the same periodic, broadband behavior when observed at a one-day cadence. To reveal the dominant physical mechanism seen in DQ Tau’s low-cadence observations, we have obtained continuous, moderate-cadence, multiband photometry over 10 orbital periods, supplemented with 27 nights of minute-cadence photometry centered on four separate periastron passages. While both accretion and stellar flares are present, the dominant timescale and morphology of brightening events are characteristic of accretion. On average, the mass accretion rate increases by a factor of five near periastron, in good agreement with recent models. Large variability is observed in the morphology and amplitude of accretion events from orbit to orbit. We argue that this is due to the absence of stable circumstellar disks around each star, compounded by inhomogeneities at the inner edge of the CBD and within the accretion streams themselves. Quasiperiodic apastron accretion events are also observed, which are not predicted by binary accretion theory.

  17. Physical activity for people with dementia: a scoping study

    PubMed Central

    2013-01-01

    Background This scoping study aimed to identify how physical activity may benefit people with dementia; how and/or if current service provide these benefits; and what support they need to do so. Methods Methods included an evidence review using literature; mapping current service provision through a survey; and in-depth interviews with a sample of service providers. Results The 26 studies included in the review indicated the potential effectiveness of physical activity for people with dementia, including improvements in cognition and mood, behaviour and physical condition. Mechanisms of action and the link with outcomes were poorly defined and implemented. The mapping survey and related interviews showed that service providers were delivering a range of services broadly consistent with the scientific evidence. They tended to take a holistic view of possible benefits, and focused on enjoyment and well-being, more than specific cognitive, physical and behavioural outcomes highlighted in literature. Service providers needed more evidence based information and resources to develop services and realise their potential. Conclusion Despite potential benefits demonstrated in literature and practice, there is a need for further research to optimise interventions and to consider some neglected issues including delivery at home and in communities; impacts for carers; physical activities through ADLs; and individual needs. Studies are needed which take a more holistic approach to the effects of physical activity, and outcomes should be broader and include mental health and wellbeing. PMID:24274624

  18. A Wind Accretion Model for HLX-1

    NASA Astrophysics Data System (ADS)

    Miller, M. Coleman; Farrell, Sean A.; Maccarone, Thomas J.

    2014-06-01

    The brightest ultraluminous X-ray source currently known, HLX-1, has been observed to undergo five outburst cycles. The periodicity of these outbursts, and their high inferred maximum accretion rates of ~few × 10-4 M ⊙ yr-1, naturally suggest Roche lobe overflow at the pericenter of an eccentric orbit. It is, however, difficult for the Roche lobe overflow model to explain the apparent trend of decreasing decay times over the different outbursts while the integrated luminosity also drops. Thus, if the trend is real rather than simply being a reflection of the complex physics of accretion disks, a different scenario may be necessary. We present a speculative model in which, within the last decade, a high-mass giant star had most of its envelope tidally stripped by the ~104 - 5 M ⊙ black hole in HLX-1, and the remaining core plus low-mass hydrogen envelope now feeds the hole with a strong wind. This model can explain the short decay time of the disk, and could explain the fast decrease in decay time if the wind speed changes with time. A key prediction of this model is that there will be excess line absorption due to the wind; our analysis does in fact find a flux deficit in the ~0.9-1.1 keV range that is consistent with predictions, albeit at low significance. If this idea is correct, we also expect that within years to dacades the bound material from the original disruption will return and will make HLX-1 a persistently bright source.

  19. More on accreting black hole spacetime in equatorial plane

    NASA Astrophysics Data System (ADS)

    Salahshoor, K.; Nozari, K.; Khesali, A. R.

    2017-02-01

    Spacetime around an accreting black hole is an interesting issue to study. The metric of an isolated black hole (rotating or non-rotating) spacetime has been well-known for decades. Although metrics of some spacetimes containing accreting black holes are known in some situations, the issue has some faces that are not well-known yet and need further investigation. In this paper, we construct a new form of metric which the effect of accretion disk on black hole spacetime is taken into account in the equatorial plane. We study motion and trajectories of massive particles and also photons falling from infinity towards black hole in equatorial plane around the black hole. We use an exponential form for the density profile of the accretion disk in equatorial plane as ρ =ρ0e^{-α r}. We show that with this density profile, the disk is radially stable if α ≤ 3 × 10^{-3} (in units of length inverse). In order to study some important quantities related to the accretion disks such as locations of marginally stable circular orbits (r_{ms} or r_{ISCO}), marginally bounded circular orbits (r_{mb}), and also photon orbits in equatorial plane, we use the effective potential approach. We show that in this spacetime metric the innermost stable circular orbit in equatorial plane is given by r_{ISCO}=4.03 μ (where μ =MG/c 2) which is different, but comparable, with the Schwarzschild spacetime result, r^{(Sch)}_{ISCO}=6 μ . We show that the maximum radiation efficiency of the accretion disk, η , in equatorial plane is 8.6 percent which is greater than the corresponding value for Schwarzschild spacetime. Finally, we show that in this setup photons can have stable circular orbits in equatorial plane unlike the Schwarzschild spacetime.

  20. Accretion-induced variability links young stellar objects, white dwarfs, and black holes.

    PubMed

    Scaringi, Simone; Maccarone, Thomas J; Körding, Elmar; Knigge, Christian; Vaughan, Simon; Marsh, Thomas R; Aranzana, Ester; Dhillon, Vikram S; Barros, Susana C C

    2015-10-01

    The central engines of disc-accreting stellar-mass black holes appear to be scaled down versions of the supermassive black holes that power active galactic nuclei. However, if the physics of accretion is universal, it should also be possible to extend this scaling to other types of accreting systems, irrespective of accretor mass, size, or type. We examine new observations, obtained with Kepler/K2 and ULTRACAM, regarding accreting white dwarfs and young stellar objects. Every object in the sample displays the same linear correlation between the brightness of the source and its amplitude of variability (rms-flux relation) and obeys the same quantitative scaling relation as stellar-mass black holes and active galactic nuclei. We also show that the most important parameter in this scaling relation is the physical size of the accreting object. This establishes the universality of accretion physics from proto-stars still in the star-forming process to the supermassive black holes at the centers of galaxies.

  1. Accretion-induced variability links young stellar objects, white dwarfs, and black holes

    PubMed Central

    Scaringi, Simone; Maccarone, Thomas J.; Körding, Elmar; Knigge, Christian; Vaughan, Simon; Marsh, Thomas R.; Aranzana, Ester; Dhillon, Vikram S.; Barros, Susana C. C.

    2015-01-01

    The central engines of disc-accreting stellar-mass black holes appear to be scaled down versions of the supermassive black holes that power active galactic nuclei. However, if the physics of accretion is universal, it should also be possible to extend this scaling to other types of accreting systems, irrespective of accretor mass, size, or type. We examine new observations, obtained with Kepler/K2 and ULTRACAM, regarding accreting white dwarfs and young stellar objects. Every object in the sample displays the same linear correlation between the brightness of the source and its amplitude of variability (rms-flux relation) and obeys the same quantitative scaling relation as stellar-mass black holes and active galactic nuclei. We also show that the most important parameter in this scaling relation is the physical size of the accreting object. This establishes the universality of accretion physics from proto-stars still in the star-forming process to the supermassive black holes at the centers of galaxies. PMID:26601307

  2. Physics.

    ERIC Educational Resources Information Center

    Bromley, D. Allan

    1980-01-01

    The author presents the argument that the past few years, in terms of new discoveries, insights, and questions raised, have been among the most productive in the history of physics. Selected for discussion are some of the most important new developments in physics research. (Author/SA)

  3. Heavy-ion physics studies for the Future Circular Collider

    NASA Astrophysics Data System (ADS)

    Armesto, N.; Dainese, A.; d'Enterria, D.; Masciocchi, S.; Roland, C.; Salgado, C. A.; van Leeuwen, M.; Wiedemann, U. A.

    2014-11-01

    The Future Circular Collider (FCC) design study is aimed at assessing the physics potential and the technical feasibility of a new collider with centre-of-mass energies, in the hadron-hadron collision mode including proton and nucleus beams, more than seven times larger than the nominal LHC energies. An electron-positron collider in the same tunnel is also considered as an intermediate step, which in the long term would allow for electron-hadron collisions. First ideas on the physics opportunities with heavy ions at the FCC are presented, covering the physics of quark-gluon plasma, gluon saturation, photon-induced collisions, as well as connections with the physics of ultra-high-energy cosmic rays.

  4. Hybrid Numerical Simulations Of Planetesimal Accretion

    NASA Astrophysics Data System (ADS)

    Marzari, Francesco; Weidenschilling, S. J.

    2006-09-01

    The multi-zone simulation code modelling the accretion of planetesimals into planets (Spaute et al. 1991, Icarus 92, 147; Weidenschilling et al. 1997, ICARUS 128, 429) includes a statistical continuum of small bodies in logarithmic mass bins, while large bodies are discrete objects with individual masses and orbits. Formerly, gravitational interactions between large planetary embryos were treated by statistical scattering. The code has now been updated to properly handle the orbits of protoplanets in a deterministic way. The trajectories of the larger bodies are numerically computed with the symplectic integrator SyYMBA. The additional forces acting on the protoplanets due to collisions with smaller planetesimals and their gravitational perturbations, including dynamical friction, as well as gas drag and tidal interaction with the solar nebula, are incorporated in the N-body algorithm by applying a further step in the leap-frog structure of the SyMBA integrator. The changes in the orbital elements of the large bodies, computed in the stochastic part of the code with a Monte Carlo approach, are applied for half a timestep before and after the N-body Hamiltonian propagation as suggested in Lee & Peale (ApJ 567, 596, 2002). With this code we intend to study the effect of dynamical friction on terrestrial planet formation and the accretion of planetary cores in the outer solar system. We will present preliminary results of simulations performed with the updated code.

  5. ECCENTRICITY EVOLUTION THROUGH ACCRETION OF PROTOPLANETS

    SciTech Connect

    Matsumoto, Yuji; Nagasawa, Makiko; Ida, Shigeru E-mail: nagasawa.m.ad@m.titech.ac.jp

    2015-09-10

    Most super-Earths detected by the radial velocity (RV) method have significantly smaller eccentricities than the eccentricities corresponding to velocity dispersion equal to their surface escape velocity (“escape eccentricities”). If orbital instability followed by giant impacts among protoplanets that have migrated from outer regions is considered, it is usually considered that eccentricities of the merged bodies become comparable to those of orbital crossing bodies, which are excited up to their escape eccentricities by close scattering. However, the eccentricity evolution in the in situ accretion model has not been studied in detail. Here, we investigate the eccentricity evolution through N-body simulations. We have found that the merged planets tend to have much smaller eccentricities than escape eccentricities due to very efficient collision damping. If the protoplanet orbits are initially well separated and their eccentricities are securely increased, an inner protoplanet collides at its apocenter with an outer protoplanet at its pericenter. The eccentricity of the merged body is the smallest for such configurations. Orbital inclinations are also damped by this mechanism and planets tend to share a same orbital plane, which is consistent with Kepler data. Such efficient collision damping is not found when we start calculations from densely packed orbits of the protoplanets. If the protoplanets are initially in the mean-motion resonances, which corresponds to well separated orbits, the in situ accretion model well reproduces the features of eccentricities and inclinations of multiple super-Earths/Earth systems discovered by RV and Kepler surveys.

  6. Black hole accretion disks with coronae

    NASA Technical Reports Server (NTRS)

    Svensson, Roland; Zdziarski, Andrzej A.

    1994-01-01

    Observations suggest the existence of both hot and cold dark matter in the centers of active galactic nuclei. Recent spectral models require a major fraction of power to be dissipated in the hot matter. We study the case when the hot matter forms a corona around a standard cold alpha-disk. In particular, we investigate the case when a major fraction, f, of the power released when the cold matter accretes is transported to and dissipated in the corona. This has major effects on the cold disk, making it colder, more geometrically thin, denser, and having larger optical depths. One important consequence is the disappearance of the effectively optically thin zone as well as of the radiation pressure dominated zone for values of f sufficiently closed to unity. The disappearance of the radiation pressure dominated zone will result in a cold disk with only a gas pressure dominated zone that is stable against thermal and viscous instabilities. We also show that the pressure ( and the radiation) from the corona will only affect the surface layers of the cold disk. Our results disagree with those of other recent work on accretion disks with coronae. We find those works to be based on unphysical assumptions.

  7. Theory of protostellar accretion disks

    NASA Technical Reports Server (NTRS)

    Ruden, S.

    1994-01-01

    I will present an overview of the current paradigm for the theory of gaseous accretion disks around young stars. Protostellar disks form from the collapse of rotating molecular cloud cores. The disks evolve via outward angular momentum transport provided by several mechanisms: gravitational instabilities, thermal convective turbulence, and magnetic stresses. I will review the conditions under which these mechanisms are efficient and consistent with the observed disk evolutionary timescales of several million years. Time permitting, I will discuss outbursts in protostellar disks (FU Orionis variables), the effect of planet formation on disk structure, and the dispersal of remnant gas.

  8. Disk tides and accretion runaway

    NASA Technical Reports Server (NTRS)

    Ward, William R.; Hahn, Joseph M.

    1995-01-01

    It is suggested that tidal interaction of an accreting planetary embryo with the gaseous preplanetary disk may provide a mechanism to breach the so-called runaway limit during the formation of the giant planet cores. The disk tidal torque converts a would-be shepherding object into a 'predator,' which can continue to cannibalize the planetesimal disk. This is more likely to occur in the giant planet region than in the terrestrial zone, providing a natural cause for Jupiter to predate the inner planets and form within the O(10(exp 7) yr) lifetime of the nebula.

  9. Velocity-porosity relationships for slope apron and accreted sediments in the Nankai Trough Seismogenic Zone Experiment, Integrated Ocean Drilling Program Expedition 315 Site C0001

    NASA Astrophysics Data System (ADS)

    Hashimoto, Y.; Tobin, H. J.; Knuth, M.

    2010-12-01

    In this study, we focused on the porosity and compressional wave velocity of marine sediments to examine the physical properties of the slope apron and the accreted sediments. This approach allows us to identify characteristic variations between sediments being deposited onto the active prism and those deposited on the oceanic plate and then carried into the prism during subduction. For this purpose we conducted ultrasonic compressional wave velocity measurements on the obtained core samples with pore pressure control. Site C0001 in the Nankai Trough Seismogenic Zone Experiment transect of the Integrated Ocean Drilling Program is located in the hanging wall of the midslope megasplay thrust fault in the Nankai subduction zone offshore of the Kii peninsula (SW Japan), penetrating an unconformity at ˜200 m depth between slope apron sediments and the underlying accreted sediments. We used samples from Site C0001. Compressional wave velocity from laboratory measurements ranges from ˜1.6 to ˜2.0 km/s at hydrostatic pore pressure conditions estimated from sample depth. The compressional wave velocity-porosity relationship for the slope apron sediments shows a slope almost parallel to the slope for global empirical relationships. In contrast, the velocity-porosity relationship for the accreted sediments shows a slightly steeper slope than that of the slope apron sediments at 0.55 of porosity. This higher slope in the velocity-porosity relationship is found to be characteristic of the accreted sediments. Textural analysis was also conducted to examine the relationship between microstructural texture and acoustic properties. Images from micro-X-ray CT indicated a homogeneous and well-sorted distribution of small pores both in shallow and in deeper sections. Other mechanisms such as lithology, clay fraction, and abnormal fluid pressure were found to be insufficient to explain the higher velocity for accreted sediments. The higher slope in velocity-porosity relationship for

  10. Potential flow analysis of glaze ice accretions on an airfoil

    NASA Technical Reports Server (NTRS)

    Zaguli, R. J.

    1984-01-01

    The results of an analytical/experimental study of the flow fields about an airfoil with leading edge glaze ice accretion shapes are presented. Tests were conducted in the Icing Research Tunnel to measure surface pressure distributions and boundary layer separation reattachment characteristics on a general aviation wing section to which was affixed wooden ice shapes which approximated typical glaze ice accretions. Comparisons were made with predicted pressure distributions using current airfoil analysis codes as well as the Bristow mixed analysis/design airfoil panel code. The Bristow code was also used to predict the separation reattachment dividing streamline by inputting the appropriate experimental surface pressure distribution.

  11. Pulsed Accretion onto Eccentric and Circular Binaries

    NASA Astrophysics Data System (ADS)

    Muñoz, Diego J.; Lai, Dong

    2016-08-01

    We present numerical simulations of circumbinary accretion onto eccentric and circular binaries using the moving-mesh code AREPO. This is the first set of simulations to tackle the problem of binary accretion using a finite-volume scheme on a freely moving mesh, which allows for accurate measurements of accretion onto individual stars for arbitrary binary eccentricity. While accretion onto a circular binary shows bursts with period of ˜ 5 times the binary period P b, accretion onto an eccentric binary is predominantly modulated at the period ˜ 1{P}{{b}}. For an equal-mass circular binary, the accretion rates onto individual stars are quite similar to each other, following the same variable pattern in time. By contrast, for eccentric binaries, one of the stars can accrete at a rate 10-20 times larger than its companion. This “symmetry breaking” between the stars, however, alternates over timescales of order 200P b and can be attributed to a slowly precessing, eccentric circumbinary disk. Over longer timescales, the net accretion rates onto individual stars are the same, reaching a quasi-steady state with the circumbinary disk. These results have important implications for the accretion behavior of binary T Tauri stars and supermassive binary black holes.

  12. Neighbourhood perceptions of physical activity: a qualitative study

    PubMed Central

    Burgoyne, Louise N; Woods, Catherine; Coleman, Rosarie; Perry, Ivan J

    2008-01-01

    Background Effective promotion of physical activity in low income communities is essential given the high prevalence of inactivity in this sector. Methods This study explored determinants of engaging in physical activity in two Irish city based neighbourhoods using a series of six focus groups and twenty five interviews with adult residents. Data were analysed using constant comparison methods with a grounded theory approach. Results Study findings centred on the concept of 'community contentment'. Physical activity was related to the degree of contentment/comfort within the 'self' and how the 'self' interacts within the neighbourhood. Contemporary focus on outer bodily appearance and pressure to comply with societal expectations influenced participants' sense of confidence and competence. Social interaction, involvement, and provision of adequate social supports were viewed as positive and motivating. However normative expectations appeared to affect participants' ability to engage in physical activity, which may reflect the 'close knit' culture of the study neighbourhoods. Access to suitable local facilities and amenities such as structured and pleasant walking routes was regarded as essential. Indeed participants considered walking to be their preferred form of physical activity which may relate to the minimal skill requirement, ease of access and low financial costs incurred. Conclusion In the context of physical activity, health promoters need to be conscious of the difficulties that individuals feel in relation to bodily appearance and the pressure to comply with societal standards. This may be particularly relevant in low income settings where insufficient allocation of resources and social supports means that individuals have less opportunity to attend to physical activity than individuals living in higher income settings. PMID:18373842

  13. Studies in chemical physics through high-pressure luminescence

    SciTech Connect

    Drickamer, H.G.

    1981-01-01

    Energy transfer in chelates of Eu/sup 3 +/ with ligands (dibenzylmethane) was studied as a function of pressure. Rate of thermal dissipation of electronic excitation was correlated with viscosity and dielectric constant for indoles in a series of solvents, and with pressure for porphyrins. Effects of medium (dielectric constant, viscosity) on complexes were studied. Studies on 3-hydroxyflavone are also summarized. These studies show the power of high pressure luminescence as a tool in chemical physics. 11 figures. (DLC)

  14. Physical activity and memory functions: an interventional study.

    PubMed

    Ruscheweyh, R; Willemer, C; Krüger, K; Duning, T; Warnecke, T; Sommer, J; Völker, K; Ho, H V; Mooren, F; Knecht, S; Flöel, A

    2011-07-01

    Previous studies have suggested beneficial effects of physical activity on cognition. Here, we asked in an interventional approach if physical activity performed at different intensity levels would differentially affect episodic memory function. Additionally, we tried to identify mechanisms mediating these changes. Sixty-two healthy elderly individuals were assessed for level of physical activity, aerobic fitness, episodic memory score, neurotrophin and catecholamine levels, and received a magnetic resonance image of the brain at baseline and after a six months intervention of medium or low-intensity physical activity or control. Increase in total physical activity was positively associated with increase in memory score over the entire cohort, without significant differences between intensity groups. It was also positively associated with increases in local gray matter volume in prefrontal and cingulate cortex, and BDNF levels (trend). In conclusion, we showed that physical activity conveys the beneficial effects on memory function independently of its intensity, possibly mediated by local gray matter volume and neurotrophic factors. Our findings may carry significant implications for prevention of cognitive decline in the elderly.

  15. LHCf experiment: forward physics at LHC for cosmic rays study

    NASA Astrophysics Data System (ADS)

    Del Prete, M.; Adriani, O.; Berti, E.; Bonechi, L.; Bongi, M.; Castellini, G.; D'Alessandro, R.; Haguenauer, M.; Itow, Y.; Kasahara, K.; Kawade, K.; Makino, Y.; Masuda, K.; Matsubayashi, E.; Menjo, H.; Mitsuka, G.; Muraki, Y.; Okuno, Y.; Papini, P.; Perrot, A.-L.; Ricciarini, S.; Sako, T.; Sakurai, N.; Sugiura, Y.; Suzuki, T.; Tamura, T.; Tiberio, A.; Torii, S.; Tricomi, A.; Turner, W. C.; Zhou, Q. D.

    2016-11-01

    The LHCf experiment, optimized for the study of forward physics at LHC, completes its main physics program in this year 2015, with the proton-proton collisions at the energy of 13 TeV. LHCf gives important results on the study of neutral particles at extreme pseudo-rapidity, both for proton-proton and for proton-ion interactions. These results are an important reference for tuning the models of the hadronic interaction currently used for the simulation of the atmospheric showers induced by very high energy cosmic rays. The results of this analysis and the future perspective are presented in this paper.

  16. System studies for quasi-steady-state advanced physics tokamak

    SciTech Connect

    Reid, R.L.; Peng, Y.K.M.

    1983-11-01

    Parametric studies were conducted using the Fusion Engineering Design Center (FEDC) Tokamak Systems Code to investigate the impact of veriation in physics parameters and technology limits on the performance and cost of a low q/sub psi/, high beta, quasi-steady-state tokamak for the purpose of fusion engineering experimentation. The features and characteristics chosen from each study were embodied into a single Advanced Physics Tokamak design for which a self-consistent set of parameters was generated and a value of capital cost was estimated.

  17. Hyper-Eddington accretion flows on to massive black holes

    NASA Astrophysics Data System (ADS)

    Inayoshi, Kohei; Haiman, Zoltán; Ostriker, Jeremiah P.

    2016-07-01

    We study very high rate, spherically symmetric accretion flows on to massive black holes (BHs; 102 ≲ MBH ≲ 106 M⊙) embedded in dense metal-poor clouds, performing one-dimensional radiation hydrodynamical simulations. We find solutions from outside the Bondi radius at hyper-Eddington rates, unimpeded by radiation feedback when (n∞/105 cm-3) > (MBH/104 M⊙)-1(T∞/104 K)3/2, where n∞ and T∞ are the density and temperature of ambient gas. Accretion rates in this regime are steady, and larger than 5000LEdd/c2, where LEdd is the Eddington luminosity. At lower Bondi rates, the accretion is episodic due to radiative feedback and the average rate is below the Eddington rate. In the hyper-Eddington case, the solution consists of a radiation-dominated central core, where photon trapping due to electron scattering is important, and an accreting envelope which follows a Bondi profile with T ≃ 8000 K. When the emergent luminosity is limited to ≲ LEdd because of photon trapping, radiation from the central region does not affect the gas dynamics at larger scales. We apply our result to the rapid formation of massive BHs in protogalaxies with a virial temperature of Tvir ≳ 104K. Once a seed BH forms at the centre of the galaxy, it can grow to a maximum ˜105(Tvir/104 K) M⊙ via gas accretion independent of the initial BH mass. Finally, we discuss possible observational signatures of rapidly accreting BHs with/without allowance for dust. We suggest that these systems could explain Lyα emitters without X-rays and nearby luminous infrared sources with hot dust emission, respectively.

  18. RINGED ACCRETION DISKS: EQUILIBRIUM CONFIGURATIONS

    SciTech Connect

    Pugliese, D.; Stuchlík, Z. E-mail: zdenek.stuchlik@physics.cz

    2015-12-15

    We investigate a model of a ringed accretion disk, made up by several rings rotating around a supermassive Kerr black hole attractor. Each toroid of the ringed disk is governed by the general relativity hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. Properties of the tori can then be determined by an appropriately defined effective potential reflecting the background Kerr geometry and the centrifugal effects. The ringed disks could be created in various regimes during the evolution of matter configurations around supermassive black holes. Therefore, both corotating and counterrotating rings have to be considered as being a constituent of the ringed disk. We provide constraints on the model parameters for the existence and stability of various ringed configurations and discuss occurrence of accretion onto the Kerr black hole and possible launching of jets from the ringed disk. We demonstrate that various ringed disks can be characterized by a maximum number of rings. We present also a perturbation analysis based on evolution of the oscillating components of the ringed disk. The dynamics of the unstable phases of the ringed disk evolution seems to be promising in relation to high-energy phenomena demonstrated in active galactic nuclei.

  19. Nonlinear variations in axisymmetric accretion

    NASA Astrophysics Data System (ADS)

    Bose, Soumyajit; Sengupta, Anindya; Ray, Arnab K.

    2014-05-01

    We subject the stationary solutions of inviscid and axially symmetric rotational accretion to a time-dependent radial perturbation, which includes nonlinearity to any arbitrary order. Regardless of the order of nonlinearity, the equation of the perturbation bears a form that is similar to the metric equation of an analogue acoustic black hole. We bring out the time dependence of the perturbation in the form of a Liénard system by requiring the perturbation to be a standing wave under the second order of nonlinearity. We perform a dynamical systems analysis of the Liénard system to reveal a saddle point in real time, whose implication is that instabilities will develop in the accreting system when the perturbation is extended into the nonlinear regime. We also model the perturbation as a high-frequency traveling wave and carry out a Wentzel-Kramers-Brillouin analysis, treating nonlinearity iteratively as a very feeble effect. Under this approach, both the amplitude and the energy flux of the perturbation exhibit growth, with the acoustic horizon segregating the regions of stability and instability.

  20. PROPERTIES OF GRAVITOTURBULENT ACCRETION DISKS

    SciTech Connect

    Rafikov, Roman R.

    2009-10-10

    We explore the properties of cold gravitoturbulent accretion disks-non-fragmenting disks hovering on the verge of gravitational instability (GI)-using a realistic prescription for the effective viscosity caused by gravitational torques. This prescription is based on a direct relationship between the angular momentum transport in a thin accretion disk and the disk cooling in a steady state. Assuming that opacity is dominated by dust we are able to self-consistently derive disk properties for a given M-dot assuming marginal gravitational stability. We also allow external irradiation of the disk and account for a non-zero background viscosity, which can be due to the magneto-rotational instability. Spatial transitions between different co-existing disk states (e.g., between irradiated and self-luminous or between gravitoturbulent and viscous) are described and the location of the boundary at which the disk must fragment is determined in a variety of situations. We demonstrate in particular that at low enough M-dot external irradiation stabilizes the gravitoturbulent disk against fragmentation to very large distances thus providing means of steady mass transport to the central object. Implications of our results for the possibility of planet formation by GI in protoplanetary disks and star formation in the Galactic center and for the problem of feeding supermassive black holes in galactic nuclei are discussed.

  1. Urinary loss of tricarboxylic acid cycle intermediates as revealed by metabolomics studies: an underlying mechanism to reduce lipid accretion by whey protein ingestion?

    PubMed

    Lillefosse, Haldis H; Clausen, Morten R; Yde, Christian C; Ditlev, Ditte B; Zhang, Xumin; Du, Zhen-Yu; Bertram, Hanne C; Madsen, Lise; Kristiansen, Karsten; Liaset, Bjørn

    2014-05-02

    Whey protein intake is associated with the modulation of energy metabolism and altered body composition both in human subjects and in animals, but the underlying mechanisms are not yet elucidated. We fed obesity-prone C57BL/6J mice high-fat diets with either casein (HF casein) or whey (HF whey) for 6 weeks. At equal energy intake and apparent fat and nitrogen digestibility, mice fed HF whey stored less energy as lipids, evident both as lower white adipose tissue mass and as reduced liver lipids, compared with HF-casein-fed mice. Explorative analyses of 48 h urine, both by (1)H NMR and LC-MS metabolomic platforms, demonstrated higher urinary excretion of tricarboxylic acid (TCA) cycle intermediates citric acid and succinic acid (identified by both platforms), and cis-aconitic acid and isocitric acid (identified by LC-MS platform) in the HF whey, relative to in the HF-casein-fed mice. Targeted LC-MS analyses revealed higher citric acid and cis-aconitic acid concentrations in fed state plasma, but not in liver of HF-whey-fed mice. We propose that enhanced urinary loss of TCA cycle metabolites drain available substrates for anabolic processes, such as lipogenesis, thereby leading to reduced lipid accretion in HF-whey-fed compared to HF-casein-fed mice.

  2. A NEW NETWORK FOR HIGHER-TEMPERATURE GAS-PHASE CHEMISTRY. I. A PRELIMINARY STUDY OF ACCRETION DISKS IN ACTIVE GALACTIC NUCLEI

    SciTech Connect

    Harada, Nanase; Herbst, Eric; Wakelam, Valentine

    2010-10-01

    We present a new interstellar chemical gas-phase reaction network for time-dependent kinetics that can be used for modeling high-temperature sources up to {approx}800 K. This network contains an extended set of reactions based on the Ohio State University (OSU) gas-phase chemical network. The additional reactions include processes with significant activation energies, reverse reactions, proton exchange reactions, charge exchange reactions, and collisional dissociation. Rate coefficients already in the OSU network are modified for H{sub 2} formation on grains, ion-neutral dipole reactions, and some radiative association reactions. The abundance of H{sub 2}O is enhanced at high temperature by hydrogenation of atomic O. Much of the elemental oxygen is in the form of water at T {>=} 300 K, leading to effective carbon-rich conditions, which can efficiently produce carbon-chain species such as C{sub 2}H{sub 2}. At higher temperatures, HCN and NH{sub 3} are also produced much more efficiently. We have applied the extended network to a simplified model of the accretion disk of an active galactic nucleus.

  3. Cosmological evolution of supermassive black holes and AGN: a synthesis model for accretion and feedback .

    NASA Astrophysics Data System (ADS)

    Merloni, A.

    The growth of supermassive black holes (SMBH) through accretion is accompanied by the release of enormous amounts of energy which can either be radiated away, as happens in quasars, advected into the black hole, or disposed of in kinetic form through powerful jets, as is observed, for example, in radio galaxies. Here, I will present new constraints on the evolution of the SMBH mass function and Eddington ratio distribution, obtained from a study of AGN luminosity functions aimed at accounting for both radiative and kinetic energy output of AGN in a systematic way. First, I discuss how a refined Soltan argument leads to joint constraints on the mass-weighted average spin of SMBH and of the total mass density of high redshift (z˜ 5) and ``wandering'' black holes. Then, I will show how to describe the ``downsizing'' trend observed in the AGN population in terms of cosmological evolution of physical quantities (black hole mass, accretion rate, radiative and kinetic energy output). Finally, the redshift evolution of the AGN kinetic feedback will be briefly discussed and compared with the radiative output of the evolving SMBH population, thus providing a robust physical framework for phenomenological models of AGN feedback within structure formation.

  4. The accretion environment in Vela X-1 during a flaring period using XMM-Newton

    NASA Astrophysics Data System (ADS)

    Martínez-Núñez, S.; Torrejón, J. M.; Kühnel, M.; Kretschmar, P.; Stuhlinger, M.; Rodes-Roca, J. J.; Fürst, F.; Kreykenbohm, I.; Martin-Carrillo, A.; Pollock, A. M. T.; Wilms, J.

    2014-03-01

    We present analysis of 100 ks contiguous XMM-Newton data of the prototypical wind accretor Vela X-1. The observation covered eclipse egress between orbital phases 0.134 and 0.265, during which a giant flare took place, enabling us to study the spectral properties both outside and during the flare. This giant flare with a peak luminosity of 3.92+0.42-0.09 × 1037 erg s-1 allows estimates of the physical parameters of the accreted structure with a mass of ~1021 g. We have been able to model several contributions to the observed spectrum with a phenomenological model formed by three absorbed power laws plus three emission lines. After analysing the variations with orbital phase of the column density of each component, as well as those in the Fe and Ni fluorescence lines, we provide a physical interpretation for each spectral component. Meanwhile, the first two components are two aspects of the principal accretion component from the surface of the neutron star, the third component seems to be the X-ray light echo formed in the stellar wind of the companion.

  5. [Physical anthropology studies at Keijo Imperial University Medical School].

    PubMed

    Kim, Ock-Joo

    2008-12-01

    Medical research during the Japanese Colonial Period became systematic and active after the Keijo Imperial University Medical School was established in 1926. Various kinds of research were conducted there including pharmacological, physiological, pathological and parasitological research. The Keijo Imperial University was give a mission to study about Korea. Urgent topics for medical research included control of infectious diseases, hygiene and environmental health that might have affected colonizing bodies of the Japanese as well as the colonized. The bodies of Koreans had been studied by Japanese even before the establishment of the University. The Keijo Imperial University research team, however, organized several field studies for physical anthropology and blood typing research at the national scale to get representative sampling of the people from its north to its south of the Korean peninsula. In the filed, they relied upon the local police and administrative power to gather reluctant women and men to measure them in a great detail. The physical anthropology and blood typing research by the Japanese researchers was related to their eagerness to place Korean people in the geography of the races in the world. Using racial index R.I.(= (A%+AB%)/(B%+AB%)), the Japanese researchers put Koreans as a race between the Mongolian and the Japanese. The preoccupation with constitution and race also pervasively affected the medical practice: race (Japanese, Korean, or Japanese living in Korea) must be written in every kind of medical chart as a default. After the breakout of Chinese-Japanese War in 1937, the Keijo Imperial University researchers extended its physical anthropology field study to Manchuria and China to get data on physics of the people in 1940. The Japanese government and research foundations financially well supported the Keijo Imperial University researchers and the field studies for physical anthropology in Korea, Manchuria and China. The physical

  6. [Predicting Spectra of Accretion Disks Around Galactic Black Holes

    NASA Technical Reports Server (NTRS)

    Krolik, Julian H.

    2004-01-01

    The purpose of this grant was to construct detailed atmosphere solutions in order to predict the spectra of accretion disks around Galactic black holes. Our plan of action was to take an existing disk atmosphere code (TLUSTY, created by Ivan Hubeny) and introduce those additional physical processes necessary to make it applicable to disks of this variety. These modifications include: treating Comptonization; introducing continuous opacity due to heavy elements; incorporating line opacity due to heavy elements; adopting a disk structure that reflects readjustments due to radiation pressure effects; and injecting heat via a physically-plausible vertical distribution.

  7. Luminosity limit for alpha-viscosity accretion disks

    NASA Technical Reports Server (NTRS)

    Liang, Edison P.; Wandel, Amri

    1991-01-01

    The existence of a luminosity limit for alpha-viscosity physically thin accretion disks around black holes is established, using a new formulation of the radiation equation bridging optically thick and thin regimes. For alpha close to unity, this limit can be lower than the Eddington limit. Physically, this limit is due to the combined effects of gas and radiation pressure which become too large to satisfy vertical hydrostatic balance at intermediate optical depths for sufficiently high luminosities. This effect was overlooked in previous treatments using only the optically thin or thick limits of the radiative equation.

  8. Physical Education and Physical Activity: Results from the School Health Policies and Programs Study 2006

    ERIC Educational Resources Information Center

    Lee, Sarah M.; Burgeson, Charlene R.; Fulton, Janet E.; Spain, Christine G.

    2007-01-01

    Background: Comprehensive school-based physical activity programs consist of physical education and other physical activity opportunities including recess and other physical activity breaks, intramurals, interscholastic sports, and walk and bike to school initiatives. This article describes the characteristics of school physical education and…

  9. CSI 2264: Accretion process in classical T Tauri stars in the young cluster NGC 2264

    NASA Astrophysics Data System (ADS)

    Sousa, A. P.; Alencar, S. H. P.; Bouvier, J.; Stauffer, J.; Venuti, L.; Hillenbrand, L.; Cody, A. M.; Teixeira, P. S.; Guimarães, M. M.; McGinnis, P. T.; Rebull, L.; Flaccomio, E.; Fürész, G.; Micela, G.; Gameiro, J. F.

    2016-02-01

    Context. NGC 2264 is a young stellar cluster (~3 Myr) with hundreds of low-mass accreting stars that allow a detailed analysis of the accretion process taking place in the pre-main sequence. Aims: Our goal is to relate the photometric and spectroscopic variability of classical T Tauri stars to the physical processes acting in the stellar and circumstellar environment, within a few stellar radii from the star. Methods: NGC 2264 was the target of a multiwavelength observational campaign with CoRoT, MOST, Spitzer, and Chandra satellites and photometric and spectroscopic observations from the ground. We classified the CoRoT light curves of accreting systems according to their morphology and compared our classification to several accretion diagnostics and disk parameters. Results: The morphology of the CoRoT light curve reflects the evolution of the accretion process and of the inner disk region. Accretion burst stars present high mass-accretion rates and optically thick inner disks. AA Tau-like systems, whose light curves are dominated by circumstellar dust obscuration, show intermediate mass-accretion rates and are located in the transition of thick to anemic disks. Classical T Tauri stars with spot-like light curves correspond mostly to systems with a low mass-accretion rate and low mid-IR excess. About 30% of the classical T Tauri stars observed in the 2008 and 2011 CoRoT runs changed their light-curve morphology. Transitions from AA Tau-like and spot-like to aperiodic light curves and vice versa were common. The analysis of the Hα emission line variability of 58 accreting stars showed that 8 presented a periodicity that in a few cases was coincident with the photometric period. The blue and red wings of the Hα line profiles often do not correlate with each other, indicating that they are strongly influenced by different physical processes. Classical T Tauri stars have a dynamic stellar and circumstellar environment that can be explained by magnetospheric

  10. Computer simulations of planetary accretion dynamics: Sensitivity to initial conditions

    NASA Technical Reports Server (NTRS)

    Isaacman, R.; Sagan, C.

    1976-01-01

    The implications and limitations of program ACRETE were tested. The program is a scheme based on Newtonian physics and accretion with unit sticking efficiency, devised to simulate the origin of the planets. The dependence of the results on a variety of radial and vertical density distribution laws, the ratio of gas to dust in the solar nebula, the total nebular mass, and the orbital eccentricity of the accreting grains was explored. Only for a small subset of conceivable cases are planetary systems closely like our own generated. Many models have tendencies towards one of two preferred configurations: multiple star systems, or planetary systems in which Jovian planets either have substantially smaller masses than in our system or are absent altogether. But for a wide range of cases recognizable planetary systems are generated - ranging from multiple star systems with accompanying planets, to systems with Jovian planets at several hundred AU, to single stars surrounded only by asteroids.

  11. Where do Accretion Disks Around Black Holes End?

    NASA Astrophysics Data System (ADS)

    Asmus, D.; Duschl, W. J.

    2010-10-01

    Accretion disks around (supermassive) black holes act as "machines" which extract gravitational energy. In fact, the observed radiation allows to sample the physical conditions very close to the event horizon. For a test particle, the innermost stable circular orbit (ISCO) is located at 3 rS for a non-rotating hole (Schwarzschild metrics; at smaller radii for a rotating black hole). This ISCO is usually identified with the inner edge of the accretion disk. For a given black hole mass, it allows, in principle, to determine the Kerr parameter. In "real life," however, we deal not with test particles but with a viscous flow, which introduces additional forces. We have calculated the location of the inner edge in a more realistic environment. The results show that the true inner edge of the disk is no longer located at the ISCO, when radial advection of energy is taken into account with a careful treatment of the transonic nature of the flow.

  12. Numerical Modeling of Tidal Effects in Polytropic Accretion Discs

    NASA Technical Reports Server (NTRS)

    Godon, P.

    1996-01-01

    A two-dimensional time-dependent hybrid Fourier-Chebyshev method of collocation is developed and used for the study of tidal effects in accretion discs, under the assumption of a polytropic equation of state and a standard alpha viscosity prescription.

  13. Measuring physical activity with sensors: a qualitative study.

    PubMed

    Dias, André; Fisterer, Bernhard; Lamla, Gregor; Kuhn, Klaus; Hartvigsen, Gunnar; Horsch, Alexander

    2009-01-01

    Long term wearing of motion and heart rate sensors are essential aspects for longitudinal studies on physical activity measurement studies. We conducted a qualitative study with seven subjects in a total of 13 test sessions to identify usability and handling problems associated with Stayhealth RT3, Actigraph GT1M and Polar RS800 sensors. We found that battery life limitation is the most recurrent technical problem and long term wear of heart rate sensors produces discomfort and skin irritation.

  14. A School-Based Study on Situational Interest of Investigative Study in Senior Physics

    ERIC Educational Resources Information Center

    Leung, Yat-yin

    2015-01-01

    This paper reports the findings from the interview data of a research aiming at studying how to trigger students' situational interest in physics and its implications on learning and teaching in the New Senior Secondary (NSS) physics curriculum. 49 students from a boys' school were invited to write one to three learning experiences in physics that…

  15. Self-Image and Physical Education--A Phenomenological Study

    ERIC Educational Resources Information Center

    Perrin-Wallqvist, Renee; Carlsson, Eva Segolsson

    2011-01-01

    In this study our aim was to investigate (a) how the awareness of one's self-image reveals itself as a phenomenon, and (b) if self-image is influenced by physical education in a social context with teachers and pupils. Six pupils, aged 15 and 16 years, attending compulsory school were interviewed with the use of an empirical phenomenological…

  16. A Descriptive Study of Cooperative Problem Solving Introductory Physics Labs

    ERIC Educational Resources Information Center

    Knutson, Paul Aanond

    2011-01-01

    The purpose of this study was to determine the ways in which cooperative problem solving in physics instructional laboratories influenced the students' ability to provide qualitative responses to problems. The literature shows that problem solving involves both qualitative and quantitative skills. Qualitative skills are important because those…

  17. Incorporating Active Learning with Videos: A Case Study from Physics

    ERIC Educational Resources Information Center

    Lee, Kester J.; Sharma, Manjula D.

    2008-01-01

    Watching a video often results in passive learning and does not actively engage students. In this study, a class of 20 HSC Physics students were introduced to a teaching model that incorporated active learning principles with the watching of a video that explored the Meissner Effect and superconductors. Students would watch short sections of the…

  18. Physical Education Studies (Years 9 & 10): Teachers Guide.

    ERIC Educational Resources Information Center

    Tasmanian Education Dept., Hobart (Australia).

    This guide provides an outline of possible course content for a 2-year physical education studies program during years 9 and 10. Teachers will need to supplement the ideas and materials presented in the guide with ideas and information of their own, using the guide as a starting point and resource for developing their own programs. Most of the…

  19. Strategies for Equality: Guidance, Social Studies, Physical Education.

    ERIC Educational Resources Information Center

    Rutgers, The State Univ., New Brunswick, NJ. Training Inst. for Sex Desegregation of the Public Schools.

    This document contains descriptions of projects in guidance, physical education and social studies which were developed by participants in workshops for nondiscriminatory curriculum development training. Projects and appendices in the guidance section include plans for field trips and open houses in nontraditional careers for men and women; for…

  20. Perceptions of Physical Activity by Older Adults: A Qualitative Study

    ERIC Educational Resources Information Center

    Jancey, Jonine M.; Clarke, Ann; Howat, Peter; Maycock, Bruce; Lee, Andy H.

    2009-01-01

    Objective: To identify issues and perceptions concerning physical activity in older adults. Design: Qualitative study. Setting: Perth, Western Australia. Methods: Sixteen adults aged 65 to 74 years were interviewed in their own homes using a semi-structured interview schedule. Data were analysed using a descriptive qualitative methodology.…

  1. Study Guide for TCT in Health and Physical Education.

    ERIC Educational Resources Information Center

    Mullan, Marie R.

    This study guide is designed for those individuals preparing to take the Georgia Teacher Certification Test (TCT) in health and physical education. The test covers nine broad subareas: (1) health, body systems, disease; (2) tennis, handball, fencing, bowling, track, and recreational games; (3) development, hygiene, safety, nutrition; (4) softball,…

  2. A Longitudinal Study of Relational and Physical Aggression in Preschool

    ERIC Educational Resources Information Center

    Crick, Nicki R.; Ostrov, Jamie M.; Burr, Jean E.; Cullerton-Sen, Crystal; Jansen-Yeh, Elizabeth; Ralston, Peter

    2006-01-01

    To understand the development of relational aggression during early childhood, 91 girls and boys ("M" age=39.0; "SD"=7.6 months) and their teachers participated in an 18-month longitudinal study. Children were observed for relational and physical aggression during free play in four time periods. Individually administered interviews were conducted…

  3. Accretion Disks in Algols: Progenitors and Evolution

    NASA Astrophysics Data System (ADS)

    van Rensbergen, W.; de Greve, J. P.

    2017-02-01

    There are only a few Algols with derived accretion disk parameters. These measurements provide additional constraints for tracing the origin of individual systems. With a modified binary evolution code, series of close binary evolution were calculated. For six Algols with accretion disks we found initial systems that evolve closely into the presently observed system parameters and disk characteristics.

  4. Laboratory experiments on Radiative Shocks relevant to Stellar Accretion

    NASA Astrophysics Data System (ADS)

    Chaulagain, Uddhab

    2015-08-01

    Radiative shocks are strong shocks which are characterized by a plasma at high temperatures emitting an important fraction of its energy as radiation. Radiative shocks are found in many astrophysical systems, including stellar accretion shocks, supernovae remnants, jet driven shocks, etc. In the case of stellar accretion, matter is funneled into accretion columns by the stellar magnetic field, and falls at several hundreds km/s from the circumstellar envelope onto the stellar photosphere. This generates a strong radiative shock with x-ray spectral signatures that are a key ingredient to quantify the mass accretion rate. The physical structure and dynamics of such plasmas is complex, and experimental benchmarks are needed to provide a deeper understanding of the physics at play.Recently, radiative shocks have also been produced experimentally using high energy lasers. We discuss the results of an experiment performed on the Prague Asterix Laser System (PALS) facility. Shocks are generated by focusing the PALS Infrared laser beam on millimetre-scale targets filled with xenon gas at low pressure. The shock that is generated then propagates in the gas with a sufficiently high velocity such that the shock is in a radiative flux dominated regime. We will present the first instantaneous imaging of a radiative shock at 21.2 nm which is characterized by the presence of both the radiative precursor and the post shock structure. These results are complemented with time-and-space resolved XUV plasma self-emission measurements using fast diodes. Interpretation of the data, supported by numerical simulations using the 2-D radiative-hydrodynamics code ARWEN, will be presented showing the importance of radiative processes from atomic to larger scales.

  5. Accretion in the galactic halo

    NASA Astrophysics Data System (ADS)

    Stephens, Alex Courtney

    2000-10-01

    The Milky Way disk is enveloped in a diffuse, dynamically-hot collection of stars and star clusters collectively known as the ``stellar halo''. Photometric and chemical analyses suggest that these stars are ancient fossils of the galaxy formation epoch. Yet, little is known about the origin of this trace population. Is this system merely a vestige of the initial burst of star formation within the decoupled proto-Galaxy, or is it the detritus of cannibalized satellite galaxies? In an attempt to unravel the history of the Milky Way's stellar halo, I performed a detailed spectroscopic analysis of 55 metal-poor stars possessing ``extreme'' kinematic properties. It is thought that stars on orbits that either penetrate the remote halo or exhibit large retrograde velocities could have been associated with assimilated (or ``accreted'') dwarf galaxies. The hallmark of an accreted halo star is presumed to be a deficiency (compared with normal stars) of the α-elements (O, Mg, Si, Ca, Ti) with respect to iron, a consequence of sporadic bursts of star formation within the diminutive galaxies. Abundances for a select group of light metals (Li, Na, Mg, Si, Ca, Ti), iron-peak nuclides (Cr, Fe, Ni), and neutron-capture elements (Y, Ba) were calculated using line-strengths measured from high-resolution, high signal-to-noise spectral observations collected with the Keck I 10-m and KPNO 4-m telescopes. The abundances extracted from the spectra reveal: (1)The vast majority of outer halo stars possess supersolar [α/Fe] > 0.0) ratios. (2)The [α/Fe] ratio appears to decrease with increasing metallicity. (3)The outer halo stars have lower ratios of [α/Fe] than inner halo stars at a given metallicity. (4)At the largest metallicities, there is a large spread in the observed [α/Fe] ratios. (5)[α/Fe] anti-correlates with RAPO. (6)Only one star (BD+80° 245) exhibits the peculiar abundances expected of an assimilated star. The general conclusion extracted from these data is that the

  6. Child physical abuse and adult mental health: a national study.

    PubMed

    Sugaya, Luisa; Hasin, Deborah S; Olfson, Mark; Lin, Keng-Han; Grant, Bridget F; Blanco, Carlos

    2012-08-01

    This study characterizes adults who report being physically abused during childhood, and examines associations of reported type and frequency of abuse with adult mental health. Data were derived from the 2000-2001 and 2004-2005 National Epidemiologic Survey on Alcohol and Related Conditions, a large cross-sectional survey of a representative sample (N = 43,093) of the U.S. population. Weighted means, frequencies, and odds ratios of sociodemographic correlates and prevalence of psychiatric disorders were computed. Logistic regression models were used to examine the strength of associations between child physical abuse and adult psychiatric disorders adjusted for sociodemographic characteristics, other childhood adversities, and comorbid psychiatric disorders. Child physical abuse was reported by 8% of the sample and was frequently accompanied by other childhood adversities. Child physical abuse was associated with significantly increased adjusted odds ratios (AORs) of a broad range of DSM-IV psychiatric disorders (AOR = 1.16-2.28), especially attention-deficit hyperactivity disorder, posttraumatic stress disorder, and bipolar disorder. A dose-response relationship was observed between frequency of abuse and several adult psychiatric disorder groups; higher frequencies of assault were significantly associated with increasing adjusted odds. The long-lasting deleterious effects of child physical abuse underscore the urgency of developing public health policies aimed at early recognition and prevention.

  7. Particle Physics in High School: A Diagnose Study.

    PubMed

    Tuzón, Paula; Solbes, Jordi

    2016-01-01

    The science learning process improves when the contents are connected to students' lives. Particle physics has had a great impact in our society in the last years and has changed the theoretical picture about matter fundamental dynamics. Thus, we think that academic contents about matter components and interactions should be updated. With this study we aim to characterize the level of knowledge of high school students about this topic. We built a test with questions about classical atomic models, particle physics, recent discoveries, social implications and students opinions about it. Contrary to our first suspicion, students' answers show a high variability. They have new physics ideas and show a great interest towards modern concepts. We suggest including an updated view of this topic as part of the curriculum.

  8. Particle Physics in High School: A Diagnose Study

    PubMed Central

    Solbes, Jordi

    2016-01-01

    The science learning process improves when the contents are connected to students’ lives. Particle physics has had a great impact in our society in the last years and has changed the theoretical picture about matter fundamental dynamics. Thus, we think that academic contents about matter components and interactions should be updated. With this study we aim to characterize the level of knowledge of high school students about this topic. We built a test with questions about classical atomic models, particle physics, recent discoveries, social implications and students opinions about it. Contrary to our first suspicion, students’ answers show a high variability. They have new physics ideas and show a great interest towards modern concepts. We suggest including an updated view of this topic as part of the curriculum. PMID:27253377

  9. Physical restraint usage at a teaching hospital: a pilot study.

    PubMed

    Barton-Gooden, Antoinette; Dawkins, Pauline E; Bennett, Joanna

    2015-02-01

    This mixed method study examines the prevalence of restraint usage; perception of nurses and doctors about the practice and whether they were trained to apply physical restraints. The physical restraint prevalence tools were used to observe 172 adult patients and conduct 47 chart audits in the medical-surgical wards and a psychiatric unit in November 2011. Focus group discussions with nurses and doctors were conducted. Quantitative data were analyzed using the SPSS and focus group discussions thematically analyzed. The prevalence of physical restraints between the medical-surgical wards was 75%. Nurses and medical doctors were not formally trained to apply restraint, and had learnt from peer observation. They expressed sadness, guilt, and fear when restraints are used and identified that inadequate institutional support existed. Restraint usage was high, and nurses and doctors experienced moral dilemma when they perceived that lack of formal training and inadequate institutional support may contribute to patient injury.

  10. Accretion flows onto supermassive black holes

    NASA Technical Reports Server (NTRS)

    Begelman, Mitchell C.

    1988-01-01

    The radiative and hydrodynamic properties of an angular momentum-dominated accretion flow onto a supermassive black hole depend largely on the ratio of the accretion rate to the Eddington accretion rate. High values of this ratio favor optically thick flows which produce largely thermal radiation, while optically thin 'two-temperature' flows may be present in systems with small values of this ratio. Observations of some AGN suggest that thermal and nonthermal sources of radiation may be of comparable importance in the 'central engine'. Consideration is given to the possibilities for coexistence of different modes of accretion in a single flow. One intriguing possibility is that runaway pair production may cause an optically thick 'accretion annulus' to form at the center of a two-temperature inflow.

  11. Studies of visual attention in physics problem solving

    NASA Astrophysics Data System (ADS)

    Madsen, Adrian M.

    The work described here represents an effort to understand and influence visual attention while solving physics problems containing a diagram. Our visual system is guided by two types of processes -- top-down and bottom-up. The top-down processes are internal and determined by ones prior knowledge and goals. The bottom-up processes are external and determined by features of the visual stimuli such as color, and luminance contrast. When solving physics problems both top-down and bottom-up processes are active, but to varying degrees. The existence of two types of processes opens several interesting questions for physics education. For example, how do bottom-up processes influence problem solvers in physics? Can we leverage these processes to draw attention to relevant diagram areas and improve problem-solving? In this dissertation we discuss three studies that investigate these open questions and rely on eye movements as a primary data source. We assume that eye movements reflect a person's moment-to-moment cognitive processes, providing a window into one's thinking. In our first study, we compared the way correct and incorrect solvers viewed relevant and novice-like elements in a physics problem diagram. We found correct solvers spent more time attending to relevant areas while incorrect solvers spent more time looking at novice-like areas. In our second study, we overlaid these problems with dynamic visual cues to help students' redirect their attention. We found that in some cases these visual cues improved problem-solving performance and influenced visual attention. To determine more precisely how the perceptual salience of diagram elements influenced solvers' attention, we conducted a third study where we manipulated the perceptual salience of the diagram elements via changes in luminance contrast. These changes did not influence participants' answers or visual attention. Instead, similar to our first study, the time spent looking in various areas of the

  12. PHOTOMETRIC DETERMINATION OF THE MASS ACCRETION RATES OF PRE-MAIN-SEQUENCE STARS. I. METHOD AND APPLICATION TO THE SN 1987A FIELD

    SciTech Connect

    De Marchi, Guido; Panagia, Nino; Romaniello, Martino E-mail: panagia@stsci.ed

    2010-05-20

    We have developed and successfully tested a new self-consistent method to reliably identify pre-main-sequence (PMS) objects actively undergoing mass accretion in a resolved stellar population, regardless of their age. The method does not require spectroscopy and combines broadband V and I photometry with narrowband H{alpha} imaging to (1) identify all stars with excess H{alpha} emission, (2) convert the excess H{alpha} magnitude into H{alpha} luminosity L(H{alpha}), (3) estimate the H{alpha} emission equivalent width, (4) derive the accretion luminosity L{sub acc} from L(H{alpha}), and finally (5) obtain the mass accretion rate M-dot{sub acc} from L{sub acc} and the stellar parameters (mass and radius). By selecting stars with an accuracy of 15% or better in the H{alpha} photometry, the statistical uncertainty on the derived M-dot{sub acc} is typically {approx_lt}17% and is dictated by the precision of the H{alpha} photometry. Systematic uncertainties, of up to a factor of 3 on the value of M-dot{sub acc}, are caused by our incomplete understanding of the physics of the accretion process and affect all determinations of the mass accretion rate, including those based on a spectroscopic H{alpha} line analysis. As an application of our method, we study the accretion process in a field of 9.16 arcmin{sup 2} around SN 1987A, using existing Hubble Space Telescope photometry. We identify as bona fide PMS stars a total of 133 objects with a H{alpha} excess above the 4{sigma} level and a median age of 13.5 Myr. Their median mass accretion rate of 2.6 x 10{sup -8} M{sub sun} yr{sup -1} is in excellent agreement with previous determinations based on the U-band excess of the stars in the same field, as well as with the value measured for G-type PMS stars in the Milky Way. The accretion luminosity of these PMS objects shows a strong dependence on their distance from a group of hot massive stars in the field and suggests that the ultraviolet radiation of the latter is rapidly

  13. Stability of stagnation via an expanding accretion shock wave

    NASA Astrophysics Data System (ADS)

    Velikovich, A. L.; Murakami, M.; Taylor, B. D.; Giuliani, J. L.; Zalesak, S. T.; Iwamoto, Y.

    2016-05-01

    Stagnation of a cold plasma streaming to the center or axis of symmetry via an expanding accretion shock wave is ubiquitous in inertial confinement fusion (ICF) and high-energy-density plasma physics, the examples ranging from plasma flows in x-ray-generating Z pinches [Maron et al., Phys. Rev. Lett. 111, 035001 (2013)] to the experiments in support of the recently suggested concept of impact ignition in ICF [Azechi et al., Phys. Rev. Lett. 102, 235002 (2009); Murakami et al., Nucl. Fusion 54, 054007 (2014)]. Some experimental evidence indicates that stagnation via an expanding shock wave is stable, but its stability has never been studied theoretically. We present such analysis for the stagnation that does not involve a rarefaction wave behind the expanding shock front and is described by the classic ideal-gas Noh solution in spherical and cylindrical geometry. In either case, the stagnated flow has been demonstrated to be stable, initial perturbations exhibiting a power-law, oscillatory or monotonic, decay with time for all the eigenmodes. This conclusion has been supported by our simulations done both on a Cartesian grid and on a curvilinear grid in spherical coordinates. Dispersion equation determining the eigenvalues of the problem and explicit formulas for the eigenfunction profiles corresponding to these eigenvalues are presented, making it possible to use the theory for hydrocode verification in two and three dimensions.

  14. Constraining models of accretion outbursts in low-mass YSOs}

    NASA Astrophysics Data System (ADS)

    Ninan, J. P.; Ojha, D. K.; Ghosh, S. K.; Bhatt, B. C.

    Young low-mass stars, which are still undergoing accretion, have been found to undergo sudden outbursts in short period of time. They are believed to be due to sudden increase of typically ˜2 orders of magnitude in mass infall rate. Classically these objects are classified as FUors and EXors. FUors undergo long duration outbursts for several decades of typical magnitude δ m ˜ 4-5, while EXors undergo short duration outbursts for few months to years of typical magnitude δ m ˜ 2-3 and they might occur repeatedly. From the number count of FUors, it is estimated that every low-mass stars, on a minimum, undergo FUors kind of outburst in its early life. We present our study on three such rare outbursts in optical and near-infrared wavebands using long-term observations with 2-m Himalayan Chandra Telescope and 2-m IUCAA Girawali Observatory telescope. Using the current available models and the constrains on it, we can deduce to understand the physical process driving the outburst.

  15. Physical and dynamical studies of planet-crossing asteroids.

    NASA Astrophysics Data System (ADS)

    Hahn, G.

    This thesis is a summary of the following papers: 1. A data base of observing conditions for Aten-Apollo-Amor objects during the 20th century, 1986. 2. A data base of observing conditions for Aten-Apollo-Amor objects during the 20th century. II. First update (through February 1988), 1988. 3. UBVRI and JHK photometry of the near-Earth asteroid 1862 Apollo, 1983. 4. Physical studies of Apollo-Amor asteroids: UBVRI photometry of 1036 Ganymed and 1627 Ivar, 1988. 5. Physical studies of asteroids XVII: JHK photometry of selected main-belt and near-Earth asteroids, 1988. 6. Asteroids in cometary orbits, 1985. 7. Orbital studies of 1982 YA, 1983 VA and 1984 BC, 1986. 8. Orbital evolution studies of planet-crossing asteroids, 1988.

  16. Chondrule formation during planetesimal accretion

    NASA Astrophysics Data System (ADS)

    Asphaug, Erik; Jutzi, Martin; Movshovitz, Naor

    2011-08-01

    We explore the idea that most chondrules formed as a consequence of inefficient pairwise accretion, when molten or partly molten planetesimals ~ 30-100 km diameter, similar in size, collided at velocities comparable to their two-body escape velocity ~ 100 m/s. Although too slow to produce shocks or disrupt targets, these collisions were messy, especially after ~ 1 Ma of dynamical excitation. In SPH simulations we find that the innermost portion of the projectile decelerates into the target, while the rest continues downrange in massive sheets. Unloading from pre-collision hydrostatic pressure P0 ~ 1-100 bar into the nebula, the melt achieves equilibrium with the surface energy of chondrule-sized droplets. Cooling is regulated post collision by the expansion of the optically thick sheets. on a timescale of hours-days. Much of the sheet rains back down onto the target to be reprocessed; the rest is dispersed.

  17. Shocks in the low angular momentum accretion flow

    NASA Astrophysics Data System (ADS)

    Suková, Petra; Janiuk, Agnieszka

    2015-04-01

    We address the variability of low luminous galactic nuclei including the Sgr A* or other transient accreting systems, e.g. the black hole X-ray binaries, such as GX 339-4 or IGR J17091. These sources exhibit bright X-ray flares and quasi-periodical oscillations and are theoretically interpreted as the quasi-spherical accretion flows, formed instead of or around Keplerianaccretion disks. In low angular momentum flows the existence of shocks for some range of leading parameters (energy, angular momentum and adiabatic constant of the gas) was studied semi-analytically. The possible hysteresis effect, caused by the fact that the evolution of the flow and the formation of the shock depends on its own history, was discovered. The presence of the shock in the accreted material is important for the observable properties of the out-coming radiation. In the shocked region the gas is dense and hot, thus much more luminous than in the other case. We study the appearance of standing shocks in low angular momentum gas accreting onto a black hole with numerical hydrodynamicalsimulations, using the ZEUS code with Paczynski-Wiitapseudo-Newtonian potential.

  18. Accretion Discs Show Their True Colours

    NASA Astrophysics Data System (ADS)

    2008-07-01

    Quasars are the brilliant cores of remote galaxies, at the hearts of which lie supermassive black holes that can generate enough power to outshine the Sun a trillion times. These mighty power sources are fuelled by interstellar gas, thought to be sucked into the hole from a surrounding 'accretion disc'. A paper in this week's issue of the journal Nature, partly based on observations collected with ESO's Very Large Telescope, verifies a long-standing prediction about the intensely luminous radiation emitted by these accretion discs. Uncovering the disc ESO PR Photo 21/08 Uncovering the inner disc "Astronomers were puzzled by the fact that the best models of these discs couldn't quite be reconciled with some of the observations, in particular, with the fact that these discs did not appear as blue as they should be," explains lead-author Makoto Kishimoto. Such a discrepancy could be the signal that there was something very wrong with the models. With his colleagues, he investigated this discrepancy by studying the polarised light from six quasars. This enabled them to demonstrate that the disc spectrum is as blue as predicted. "The crucial observational difficulty here has been that the disc is surrounded by a much larger torus containing hot dust, whose light partly outshines that of the disc," says Kishimoto. "Because the light coming from the disc is scattered in the disc vicinity and thus polarised, by observing only polarised light from the quasars, one can uncover the buried light from the disc." In a similar way that a fisherman would wear polarised sunglasses to help get rid of the glare from the water surface and allow him to see more clearly under the water, the filter on the telescope allowed the astronomers to see beyond surrounding clouds of dust and gas to the blue colour of the disc in infrared light. The observations were done with the FORS and ISAAC instruments on one of the 8.2-m Unit Telescopes of ESO's Very Large Telescope, located in the Atacama

  19. Magnetised accretion discs in Kerr spacetimes

    NASA Astrophysics Data System (ADS)

    Ranea-Sandoval, Ignacio F.; García, Federico

    2015-01-01

    Context. Observational data from X-ray binary systems provide strong evidence of astronomical objects that are too massive and compact to be explained as neutron or hybrid stars. When these systems are in the thermal (high/soft) state, they emit mainly in the 0.1-5 keV energy range. This emission can be explained by thin accretion discs that formed around compact objects like black holes. The profile of the fluorescent iron line is useful to obtain insight into the nature of the compact object. General relativity does not ensure that a black hole must form after the complete gravitational collapse of very massive stars, and other theoretical models such as naked singularities cannot be discarded. The cosmic censorship conjecture was proposed by Penrose to avoid these possibilities and is yet to be proven. Aims: We study the effect caused by external magnetic fields on the observed thermal spectra and iron line profiles of thin accretion discs formed around Kerr black holes and naked singularities. We aim to provide a tool that can be used to estimate the presence of magnetic fields in the neighbourhood of a compact object and to probe the cosmic censorship conjecture in these particular astrophysical environments. Methods: We developed a numerical scheme able to calculate thermal spectra of magnetised Page-Thorne accretion discs formed around rotating black holes and naked singularities as seen by an arbitrary distant observer. We incorporated two different magnetic field configurations: uniform and dipolar, using a perturbative scheme in the coupling constant between matter and magnetic field strength. Under the same assumptions, we obtained observed synthetic line profiles of the 6.4 keV fluorescent iron line. Results: We show that an external magnetic field produces potentially observable modifications on the thermal energy spectrum and the fluorescent iron line profile. Thermal energy spectra of naked singularities are harder and brighter than those from black

  20. Modeling Gas Distribution in Protoplanetary Accretion Disks

    NASA Astrophysics Data System (ADS)

    Kronberg, Martin; Lewis, Josiah; Brittain, Sean

    2010-07-01

    Protoplanetary accretion disks are disks of dust and gas which surround and feed material onto a forming star in the earliest stages of its evolution. One of the most useful methods for studying these disks is near infrared spectroscopy of rovibrational CO emission. This paper presents the methods in which synthetically generated spectra are modeled and fit to spectral data gathered from protoplanetary disks. This paper also discussed the methods in which this code can be improved by modifying the code to run a Monte Carlo analysis of best fit across the CONDOR cluster at Clemson University, thereby allowing for the creation of a catalog of protoplanetary disks with detailed information about them as gathered from the model.

  1. Galactic warps induced by material accretion

    NASA Astrophysics Data System (ADS)

    Shen, J.; Sellwood, J. A.

    2003-12-01

    The outer regions of many edge-on disk galaxies appear noticeably warped with an integral-sign shape. The ubiquity of warps suggests that they are either long-lived or repeatedly regenerated. One of the promising methods to generate warps is by accretion of material with misaligned angular momentum (Jiang & Binney 1999). We study this process using grid-based N-body methods that allow large numbers of particles to be employed but introduce a preferred plane. We present tests that show that the grid effects are under control. Our simulations include the random motions of disk stars and explore disk-halo coupling in more detail. We pay particular attention to whether or not the resultant warps follow Briggs's rules of warp behavior.

  2. Musculoskeletal injuries in physical education versus non-physical education teachers: a prospective study.

    PubMed

    Goossens, Lennert; Vercruysse, Sien; Cardon, Greet; Haerens, Leen; Witvrouw, Erik; De Clercq, Dirk

    2016-01-01

    Physical education (PE) teachers have a physically demanding job, putting them at a considerable risk for musculoskeletal injuries. To structurally develop tailored injury prevention programmes for PE teachers, a clear understanding of the extent, characteristics and underlying factors of their musculoskeletal injuries compared to referents is necessary. Therefore, the current study prospectively followed 103 PE teachers and 58 non-PE teachers, who registered musculoskeletal injuries and time of exposure to sports participation during one school year. Pearson χ(2)-tests and independent samples t-tests determined significant differences between PE and non-PE teachers regarding demographics and variables possibly related to injury occurrence. PE teachers had 1.23 and non-PE teachers 0.78 injuries/teacher/school year. This difference was significantly different after adjustment for hours spent weekly on intracurricular teaching during the career and for injury history during the preceding six months (P = 0.009; OR = 0.511; 95% CI = 0.308-0.846). PE teachers' most affected body parts were the knee and the back. PE teachers had a more extensive injury history (P < 0.001), a higher work- (P < 0.001) and sport index (P < 0.001), practiced more sports (P < 0.002) and taught more extracurricular sports (P = 0.001). Future injury prevention programmes should take account for the great injury history and heavy physical load in PE teachers.

  3. A study of student perceptions of physics teacher behavior

    NASA Astrophysics Data System (ADS)

    Brekelmans, Mieke; Wubbels, Theo; Créton, Hans

    This study investigates student perceptions of the behavior of physics teachers in relation to some other variables in the classroom situation. The research was carried out as a Dutch option of the Second International Science Study. Data were gathered in 65 classrooms of physics teachers with pupils 15 years old. Some of the teachers (21) used the new PLON curriculum and the others a traditional one. Student perceptions of teacher behavior were measured with a questionnaire based on the interpersonal theory of Leary (1957). The aspect of behavior measured is called interactional teacher behavior. We found remarkably high correlations between student perceptions of teacher behavior and affective outcomes such as appreciation of the lessons and motivation for the subject matter. Also, the correlations with cognitive outcomes measured with a standardized international test were significant. It appears that some differences exist between teacher behaviors that are favorable for high cognitive outcomes and behaviors favorable for high affective outcomes in physics lessons. Hardly any differences were found in teacher behavior between teachers using the traditional and the new physics curriculum.

  4. Analytic solutions to the accretion of a rotating finite cloud towards a central object - I. Newtonian approach

    NASA Astrophysics Data System (ADS)

    Mendoza, S.; Tejeda, E.; Nagel, E.

    2009-02-01

    We construct a steady analytic accretion flow model for a finite rotating gas cloud that accretes material to a central gravitational object. The pressure gradients of the flow are considered to be negligible, and so the flow is ballistic. We also assume a steady flow and consider the particles at the boundary of the spherical cloud to be rotating as a rigid body, with a fixed amount of inwards radial velocity. This represents a generalization to the traditional infinite gas cloud model described by Ulrich. We show that the streamlines and density profiles obtained deviate largely from the ones calculated by Ulrich. The extra freedom in the choice of the parameters on the model can naturally account for the study of protostars formed in dense clusters by triggered mechanisms, where a wide variety of external physical mechanisms determine the boundary conditions. Also, as expected, the model predicts the formation of an equatorial accretion disc about the central object with a radius different from the one calculated by Ulrich.

  5. Emission of gravitational waves by precession of slim accretion disks dynamically driven by the Bardeen-Petterson effect

    NASA Astrophysics Data System (ADS)

    Alfonso, W. D.; Sánchez, L. A.; Mosquera, H. J.

    2015-11-01

    The electromagnetic radiation emitted from some astrophysical objects such as active galactic nuclei (AGN), micro-quasars (M-QSRs), and central engines of gamma-ray burst (GRBs), seems to have a similar physical origin: a powerful jet of plasma ejected from a localized system, presumably composed of an accretion disk encircling a compact object. This radiation is generally beamed in the polar directions and in some cases, it appears to have a spiral-like structure that could be explained if the central system itself precesses. In this work, we use the slim disk accretion model, presented by Popham et al. (1999), to studying the gravitational waves (GWs) emitted by the precession of the accretion disk around a solar-mass Kerr black hole (KBH). For practical purposes, this model describes the central engine of a class of GRBs when some astrophysical constrains are fulfilled. The induced precession considered here is driven by the Bardeen-Petterson effect, which results from the combination of viscous effects in such disks and the relativistic frame-dragging effect. We evaluate the feasibility of direct detection of the GWs computed for such a model and show that the precession of this kind of systems could be detected by gravitational wave observatories like DECIGO, ultimate-DECIGO, and BBO, with higher probability if such a class of sources are placed at distances less than 1 Mpc.

  6. Runaway gas accretion and gap opening versus type I migration

    NASA Astrophysics Data System (ADS)

    Crida, A.; Bitsch, B.

    2017-03-01

    Growing planets interact with their natal protoplanetary disc, which exerts a torque onto them allowing them to migrate in the disc. Small mass planets do not affect the gas profile and migrate in the fast type-I migration. Although type-I migration can be directed outwards for planets smaller than 20 - 30M⊕ in some regions of the disc, planets above this mass should be lost into the central star long before the disc disperses. Massive planets push away material from their orbit and open a gap. They subsequently migrate in the slower, type II migration, which could save them from migrating all the way to the star. Hence, growing giant planets can be saved if and only if they can reach the gap opening mass, because this extends their migration timescale, allowing them to eventually survive at large orbits until the disc itself disperses. However, most of the previous studies only measured the torques on planets with fixed masses and orbits to determine the migration rate. Additionally, the transition between type-I and type-II migration itself is not well studied, especially when taking the growth mechanism of rapid gas accretion from the surrounding disc into account. Here we use isothermal 2D disc simulations with FARGO-2D1D to study the migration behaviour of gas accreting protoplanets in discs. We find that migrating giant planets always open gaps in the disc. We further show analytically and numerically that in the runaway gas accretion regime, the growth time-scale is comparable to the type-I migration time-scale, indicating that growing planets will reach gap opening masses before migrating all the way to the central star in type-I migration if the disc is not extremely viscous and/or thick. An accretion rate limited to the radial gas flow in the disc, in contrast, is not fast enough. When gas accretion by the planet is taken into account, the gap opening process is accelerated because the planet accretes material originating from its horseshoe region. This

  7. Black-Hole Accretion Disks --- Towards a New Paradigm ---

    NASA Astrophysics Data System (ADS)

    Kato, S.; Fukue, J.; Mineshige, S.

    2008-03-01

    Part I: Concepts of Accretion Disks: Chap. 1: Introduction, 1.1 Accretion Energy - Historical Origin, { Accretion-Disk Paradigm - Active Universe, 1.3 Accretion-Powered Objects - Observational Reviews, 1.4 X-Ray Binaries and Ultra-Luminous X-Ray Sources, 1.5 Active Galactic Nuclei, 1.6 Present Paradigm, Chap. 2: Physical Processes Related to Accretion, 2.1 Eddington Luminosity, 2.2 Bondi Accretion, 2.3 Viscous Process, 2.4 Magnetic Instabilities, 2.5 Relativistic Effects Part II: Classical Picture: Chap. 3: Classical Models, 3.1 Viscous Accretion Disks, 3.2 Standard Disks, 3.3 Optically Thin Disks, 3.4 Accretion Disk Coronae, 3.5 Relativistic Standard Disks, 3.6 Relativistic Tori Chap. 4: Secular and Thermal Instabilities, 4.1 Secular Instability, 4.2 Thermal Instability, 4.3 Stability Examination on dot{M}-Σ and T-Σ Planes, 4.4 Mathematical Derivation of the Stability Criterion, Chap. 5: Dwarf-Nova Type Instability, 5.1 Thermal-Ionization Instability, 5.2 Time Evolution of Disks in X-Ray Novae Chap. 6: Observability of Relativistic Effects, 6.1 Ray Tracing, 6.2 Imaging - Black Hole Silhouette, 6.3 Spectroscopy - Continuum and Line, 6.4 Photometry - Light Curve Diagnosis, 6.5 Other Effects - Lensing and Jets, Part III: Modern Picture: Chap. 7: Equations to Construct Generalized Models, 7.1 Basic Equations and Importance of Advection, 7.2 One-Temperature Disks, 7.3 Two-Temperature Disks, 7.4 Time-Dependent Equations Chap. 8: Transonic Nature of Accretion Flows, 8.1 Topology of Black-Hole Accretion, 8.2 Regularity Condition at a Critical Radius, 8.3 Topology around the Critical Radius in Isothermal Disks, 8.4 Numerical Examples of Transonic Flows, 8.5 Transonic Flows with Standing Shocks Chap. 9: Radiatively Inefficient Accretion Flows, 9.1 Advection-Dominated Accretion Flow, 9.2 Radial Structure of Advection-Dominated Flow, 9.3 Radiation Spectra of Advection-Dominated Flow, 9.4 Stability of Advection-Dominated Flow, 9.5 Multi-Dimensional Effects, Chap. 10: Slim

  8. Fundamental movement skills and physical fitness as predictors of physical activity: A 6-year follow-up study.

    PubMed

    Jaakkola, T; Yli-Piipari, S; Huotari, P; Watt, A; Liukkonen, J

    2016-01-01

    The purpose of this study was to examine the extent to which fundamental movement skills and physical fitness scores assessed in early adolescence predict self-reported physical activity assessed 6 years later. The sample comprised 333 (200 girls, 133 boys; M age = 12.41) students. The effects of previous physical activity, sex, and body mass index (BMI) were controlled in the main analyses. Adolescents' fundamental movement skills, physical fitness, self-report physical activity, and BMI were collected at baseline, and their self-report energy expenditure (metabolic equivalents: METs) and intensity of physical activity were collected using the International Physical Activity Questionnaire 6 years later. Results showed that fundamental movement skills predicted METs, light, moderate, and vigorous intensity physical activity levels, whereas fitness predicted METs, moderate, and vigorous physical activity levels. Hierarchical regression analyses also showed that after controlling for previous levels of physical activity, sex, and BMI, the size of the effect of fundamental movement skills and physical fitness on energy expenditure and physical activity intensity was moderate (R(2) change between 0.06 and 0.15), with the effect being stronger for high intensity physical activity.

  9. Modeling of surface roughness effects on glaze ice accretion

    NASA Technical Reports Server (NTRS)

    Hansman, R. John, Jr.; Yamaguchi, Keiko; Berkowitz, Brian M.; Potapczuk, Mark

    1990-01-01

    A series of experimental investigations focused on studying the cause and effect of roughness on accreting glaze ice surfaces were conducted. Detailed microvideo observations were made of glaze ice accretions on 1 to 4 inch diameter cylinders in three icing wind tunnels (the Data Products of New England six inch test facility, the NASA Lewis Icing Research Tunnel, and the B. F. Goodrich Ice Protection Research Facility). Infrared thermal video recordings were made of accreting ice surfaces in the Goodrich facility. Distinct zones of surface water behavior were observed; a smooth wet zone in the stagnation region with a uniform water film; a rough zone where surface tension effects caused coalescence of surface water into stationary beads; a horn zone where roughness elements grow into horn shapes; a runback zone where surface water ran back as rivulets; and a dry zone where rime feathers formed. The location of the transition from the smooth to the rough zone was found to migrate with time towards the stagnation point. The behavior of the transition appeared to be controlled by boundary layer transition and bead formation mechanisms at the interface between the smooth and rough zones. Regions of wet ice growth and enhanced heat transfer were clearly visible in the infrared video recordings of glaze ice surfaces. A simple multi-zone modification to the current glaze ice accretion model was proposed to include spatial variability in surface roughness.

  10. Black Hole Accretion and Feedback Driven by Thermal Instability

    NASA Astrophysics Data System (ADS)

    Gaspari, M.; Ruszkowski, M.; Oh, S. P.; Churazov, E.; Brighenti, F.; Ettori, S.; Sharma, P.; Temi, P.

    2013-03-01

    Multiwavelength data indicate that the cores of several galaxy clusters are moderately cooling, though not catastrophically, showing signs of filamentary extended multiphase gas. Through 3D AMR hydrodynamic simulations, we study the impact of thermal instability in the evolution of the intracluster medium. Common moderate turbulence of just over 100 km/s leads to the growth of nonlinear thermal instability within the central few tens kpc. In the presence of a global counterbalancing heating, the condensation of extended filamentary cold gas is violent, occurring when the cooling time falls below 10 times the free-fall time. The frequent stochastic collisions, fragmentations and shearing motions between the cold clouds, filaments and the central torus, efficiently reduce angular momentum. Tracking the accreting gas with a dynamical range of 10 million, we find that the accretion rate is boosted up to 100 times with respect to the Bondi rate. In a commonly turbulent and quasi-stable atmosphere, the mode of black accretion is cold and chaotic, substantially different from the classic idealized scenario. Only in the transonic regime, turbulent dissipation starts to inhibit thermal instability. On sub-parsec scales the cold phase is channeled via a funnel, triggering the black hole feedback likely linked to mechanical jets/outflows. As shown by long-term self-regulated simulations, the interplay of chaotic cold accretion and AGN feedback is crucial in order to avoid the cooling catastrophe and to reproduce the key thermodynamical features of observed clusters.

  11. Influence of Hatha yoga on physical activity constraints, physical fitness, and body image of breast cancer survivors: a pilot study.

    PubMed

    Van Puymbroeck, Marieke; Schmid, Arlene; Shinew, Kimberly J; Hsieh, Pei-Chun

    2011-01-01

    Breast cancer survivors often experience changes in their perception of their bodies following surgical treatment. These changes in body image may increase self-consciousness and perceptions of physical activity constraints and reduce participation in physical activity. While the number of studies examining different types of yoga targeting women with breast cancer has increased, studies thus far have not studied the influence that Hatha yoga has on body image and physical activity constraints. The objective of this study was to explore the changes that occur in breast cancer survivors in terms of body image, perceived constraints, and physical fitness following an 8-week Hatha yoga intervention. This study used a nonrandomized two-group pilot study, comparing an 8-week Hatha yoga intervention with a light exercise group, both designed for women who were at least nine months post-treatment for breast cancer. Both quantitative and qualitative data were collected in the areas of body image, physical activity constraints, and physical fitness. Findings indicated that quantitatively, yoga participants experienced reductions in physical activity constraints and improvements in lower- and upper-body strength and flexibility, while control participants experienced improvements in abdominal strength and lower-body strength. Qualitative findings support changes in body image, physical activity constraints, and physical fitness for the participants in the yoga group. In conclusion, Hatha yoga may reduce constraints to physical activity and improve fitness in breast cancer survivors. More research is needed to explore the relationship between Hatha yoga and improvements in body image.

  12. MN Lup: X-RAYS FROM A WEAKLY ACCRETING T TAURI STAR

    SciTech Connect

    Guenther, H. M.; Wolk, S. J.; Wolter, U.; Robrade, J.

    2013-07-01

    Young T Tauri stars (TTS) are surrounded by an accretion disk, which over time disperses due to photoevaporation, accretion, and possibly planet formation. The accretion shock on the central star produces an UV/optical veiling continuum, line emission, and X-ray signatures. As the accretion rate decreases, the impact on the central star must change. In this article we study MN Lup, a young star where no indications of a disk are seen in IR observations. We present XMM-Newton and VLT/UVES observations, some of them taken simultaneously. The X-ray data show that MN Lup is an active star with L{sub X} /L{sub bol} close to the saturation limit. However, we find high densities (n{sub e} > 3 Multiplication-Sign 10{sup 10} cm{sup -3}) in the X-ray grating spectrum. This can be well fitted using an accretion shock model with an accretion rate of 2 Multiplication-Sign 10{sup -11} M{sub Sun} yr{sup -1}. Despite the simple H{alpha} line profile which has a broad component, but no absorption signatures as typically seen on accreting TTS, we find rotational modulation in Ca II K and in photospheric absorption lines. These line profile modulations do not clearly indicate the presence of a localized hot accretion spot on the star. In the H{alpha} line we see a prominence in absorption about 2R{sub *} above the stellar surface-the first of its kind on a TTS. MN Lup is also the only TTS where accretion is seen, but no dust disk is detected that could fuel it. We suggest that MN Lup presents a unique and short-lived state in the disk evolution. It may have lost its dust disk only recently and is now accreting the remaining gas at a very low rate.

  13. Supermassive star formation via episodic accretion: protostellar disc instability and radiative feedback efficiency

    NASA Astrophysics Data System (ADS)

    Sakurai, Y.; Vorobyov, E. I.; Hosokawa, T.; Yoshida, N.; Omukai, K.; Yorke, H. W.

    2016-06-01

    The formation of supermassive stars (SMSs) is a potential pathway to seed supermassive black holes in the early universe. A critical issue for forming SMSs is stellar UV feedback, which may limit the stellar mass growth via accretion. In this paper, we study the evolution of an accreting SMS and its UV emissivity with realistic variable accretion from a circumstellar disc. First we conduct a 2D hydrodynamical simulation to follow the protostellar accretion until the stellar mass exceeds 104 M⊙. The disc fragments by gravitational instability, creating many clumps that migrate inward to fall on to the star. The resulting accretion history is highly time-dependent: short episodic accretion bursts are followed by longer quiescent phases. We show that the disc for the direct collapse model is more unstable and generates greater variability than normal Pop III cases. Next, we conduct a stellar evolution calculation using the obtained accretion history. Our results show that, regardless of the variable accretion, the stellar radius monotonically increases with almost constant effective temperature at Teff ≃ 5000 K as the stellar mass increases. The resulting UV feedback is too weak to hinder accretion due to the low flux of stellar UV photons. The insensitivity of stellar evolution to variable accretion is attributed to the fact that time-scales of variability, ≲103 yr, are too short to affect the stellar structure. We argue that this evolution will continue until the SMS collapses to produce a black hole by the general relativistic instability after the mass reaches ≳105 M⊙.

  14. Glancing through the accretion column of EXO 2030+375

    NASA Astrophysics Data System (ADS)

    Ferrigno, Carlo; Pjanka, Patryk; Bozzo, Enrico; Klochkov, Dmitry; Ducci, Lorenzo; Zdziarski, Andrzej A.

    2016-09-01

    Context. The current generation of X-ray instruments progressively reveals more and more details about the complex magnetic field topology and the geometry of the accretion flows in highly magnetized accretion-powered pulsars. Aims: We took advantage of the large collecting area and good timing capabilities of the EPIC cameras onboard XMM-Newton to investigate the accretion geometry onto the magnetized neutron star hosted in the high-mass X-ray binary EXO 2030+375 during the rise of a source type I outburst in 2014. Methods: We carried out a timing and spectral analysis of the XMM-Newton observation as a function of the neutron star spin phase. We used a phenomenological spectral continuum model comprising the required fluorescence emission lines. Two neutral absorption components are present: one covering the source fully, one only partially. The same analysis was also carried out on two Suzaku observations of the source performed during outbursts in 2007 and 2012, to search for possible spectral variations at different luminosities. Results: The XMM-Newton data caught the source at an X-ray luminosity of 2 × 1036 erg s-1 and revealed a narrow dip-like feature in its pulse profile that was never reported before. The width of this feature corresponds to about one hundredth of the neutron star spin period. Based on the results of the phase-resolved spectral analysis we suggest that this feature can be ascribed to the self-obscuration of the accretion stream passing in front of the observer line of sight. We inferred from the Suzaku observation carried out in 2007 that the self-obscuration of the accretion stream might produce a significantly wider feature in the neutron star pulsed profile at higher luminosities (≳2 × 1037 erg s-1). Conclusions: This discovery allowed us to derive additional constraints on the physical properties of the accretion flow in this object at relatively small distances from the neutron star surface. The narrow dip-like feature in the

  15. Accretion and ejection in black-hole X-ray transients

    NASA Astrophysics Data System (ADS)

    Kylafis, N. D.; Belloni, T. M.

    2015-02-01

    Context. A rich phenomenology has been accumulated over the years regarding accretion and ejection in black-hole X-ray transients (BHTs) and it needs an interpretation. Aims: Here we summarize the current observational picture of the outbursts of BHTs, based on the evolution traced in a hardness-luminosity diagram (HLD), and we offer a physical interpretation. Methods: The basic ingredient in our interpretation is the Poynting-Robertson cosmic battery (PRCB), which provides locally the poloidal magnetic field needed for the ejection of the jet. In addition, we make two assumptions, easily justifiable. The first is that the mass-accretion rate to the black hole in a BHT outburst has a generic bell-shaped form, whose characteristic time scale is much longer than the dynamical or the cooling ones. This is guaranteed by the observational fact that all BHTs start their outburst and end it at the quiescent state, i.e., at very low accretion rate, and that state transitions take place over long time scales (hours to days). The second assumption is that at low accretion rates the accretion flow is geometrically thick, ADAF-like, while at high accretion rates it is geometrically thin. Last, but not least, we demonstrate that the previous history of the system is absolutely necessary for the interpretation of the HLD. Results: Both, at the beginning and the end of an outburst, the PRCB establishes a strong poloidal magnetic field in the ADAF-like part of the accretion flow, and this explains naturally why a jet is always present in the right part of the HLD. In the left part of the HLD, the accretion flow is in the form of a thin disk, and such a disk cannot sustain a strong poloidal magnetic filed. Thus, no jet is expected in this part of the HLD. Finally, the counterclockwise traversal of the HLD is explained as follows: all outbursts start from the quiescent state, in which the inner part of the accretion flow is ADAF-like, threaded by a poloidal magnetic field. As the

  16. Nucleosynthesis in the accretion disks of Type II collapsars

    NASA Astrophysics Data System (ADS)

    Banerjee, Indrani; Mukhopadhyay, Banibrata

    2013-09-01

    We investigate nucleosynthesis inside the gamma-ray burst (GRB) accretion disks formed by the Type II collapsars. In these collapsars, the core collapse of massive stars first leads to the formation of a proto-neutron star. After that, an outward moving shock triggers a successful supernova. However, the supernova ejecta lacks momentum and within a few seconds the newly formed neutron star gets transformed to a stellar mass black hole via massive fallback. The hydrodynamics of such an accretion disk formed from the fallback material of the supernova ejecta has been studied extensively in the past. We use these well-established hydrodynamic models for our accretion disk in order to understand nucleosynthesis, which is mainly advection dominated in the outer regions. Neutrino cooling becomes important in the inner disk where the temperature and density are higher. The higher the accretion rate (dot M) is, the higher the density and temperature are in the disks. We deal with accretion disks with relatively low accretion rates: 0.001 Msolar s-1 ≲ dot M ≲ 0.01 Msolar s-1 and hence these disks are predominantly advection dominated. We use He-rich and Sirich abundances as the initial condition of nucleosynthesis at the outer disk, and being equipped with the disk hydrodynamics and the nuclear network code, we study the abundance evolution as matter inflows and falls into the central object. We investigate the variation in the nucleosynthesis products in the disk with the change in the initial abundance at the outer disk and also with the change in the mass accretion rate. We report the synthesis of several unusual nuclei like 31P, 39K, 43Sc, 35Cl and various isotopes of titanium, vanadium, chromium, manganese and copper. We also confirm that isotopes of iron, cobalt, nickel, argon, calcium, sulphur and silicon get synthesized in the disk, as shown by previous authors. Much of these heavy elements thus synthesized are ejected from the disk via outflows and hence they

  17. Herschel-ATLAS: the link between accretion luminosity and star formation in quasar host galaxies

    NASA Astrophysics Data System (ADS)

    Bonfield, D. G.; Jarvis, M. J.; Hardcastle, M. J.; Cooray, A.; Hatziminaoglou, E.; Ivison, R. J.; Page, M. J.; Stevens, J. A.; de Zotti, G.; Auld, R.; Baes, M.; Buttiglione, S.; Cava, A.; Dariush, A.; Dunlop, J. S.; Dunne, L.; Dye, S.; Eales, S.; Fritz, J.; Hopwood, R.; Ibar, E.; Maddox, S. J.; Michałowski, M. J.; Pascale, E.; Pohlen, M.; Rigby, E. E.; Rodighiero, G.; Serjeant, S.; Smith, D. J. B.; Temi, P.; van der Werf, P.

    2011-09-01

    We use the science demonstration field data of the Herschel Astrophysical Terahertz Large Area Survey to study how star formation, traced by the far-infrared Herschel data, is related to both the accretion luminosity and redshift of quasars selected from the Sloan Digital Sky Survey (SDSS) and the 2dF-SDSS luminous red galaxy (LRG) and Quasar Spectroscopic Catalogue survey. By developing a maximum-likelihood estimator to investigate the presence of correlations between the far-infrared and optical luminosities, we find evidence that the star formation in quasar hosts is correlated with both redshift and quasar accretion luminosity. Assuming a relationship of the form LIR∝LθQSO(1 +z)ζ, we find θ= 0.22 ± 0.08 and ζ= 1.6 ± 0.4, although there is substantial additional uncertainty in ζ of the order of ±1, due to uncertainties in the host galaxy dust temperature. We find evidence for a large intrinsic dispersion in the redshift dependence, but no evidence for intrinsic dispersion in the correlation between LQSO and LIR, suggesting that the latter may be due to a direct physical connection between star formation and black hole accretion. This is consistent with the idea that both the quasar activity and star formation are dependent on the same reservoir of cold gas, so that they are both affected by the influx of cold gas during mergers or heating of gas via feedback processes. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  18. The Planetary Accretion Shock. I. Framework for Radiation-hydrodynamical Simulations and First Results

    NASA Astrophysics Data System (ADS)

    Marleau, Gabriel-Dominique; Klahr, Hubert; Kuiper, Rolf; Mordasini, Christoph

    2017-02-01

    The key aspect determining the postformation luminosity of gas giants has long been considered to be the energetics of the accretion shock at the surface of the planet. We use one-dimensional radiation-hydrodynamical simulations to study the radiative loss efficiency and to obtain postshock temperatures and pressures and thus entropies. The efficiency is defined as the fraction of the total incoming energy flux that escapes the system (roughly the Hill sphere), taking into account the energy recycling that occurs ahead of the shock in a radiative precursor. We focus in this paper on a constant equation of state (EOS) to isolate the shock physics but use constant and tabulated opacities. While robust quantitative results will have to await a self-consistent treatment including hydrogen dissociation and ionization, the results presented here show the correct qualitative behavior and can be understood from semianalytical calculations. The shock is found to be isothermal and supercritical for a range of conditions relevant to the core accretion formation scenario (CA), with Mach numbers { M }≳ 3. Across the shock, the entropy decreases significantly by a few times {k}{{B}}/{{baryon}}. While nearly 100% of the incoming kinetic energy is converted to radiation locally, the efficiencies are found to be as low as roughly 40%, implying that a significant fraction of the total accretion energy is brought into the planet. However, for realistic parameter combinations in the CA scenario, we find that a nonzero fraction of the luminosity always escapes the Hill sphere. This luminosity could explain, at least in part, recent observations in the young LkCa 15 and HD 100546 systems.

  19. An XMM-Newton Monitoring Campaign of the Accretion Flow in IGRJ16318-4848

    NASA Technical Reports Server (NTRS)

    Mushotzky, Richard (Technical Monitor); Nicastro, Fabrizio

    2005-01-01

    This grant is associated to a successful XMM-Newton-AO3 observational proposal to monitor the spectrum of the X-ray loud component of the recently discovered binary system IGR J16138-4848, to study the conditions of the accretion flows (and their evolution) in binary system. All four EPIC-PN and MOS observations of the target have now been performed (the last one of the 4, only 3 months ago). The four observations were logarithmically spaced, so to cover timescales from days to months. Data from all four pointings have now been reduced, using the XMM-Newton data reduction pipeline, and spectra and lightcurves from the target have been extracted. For the first three observations we have already performed the observation-by-observation data analysis, by fitting the single EPIC spectra with spectral models that include an intrinsic continuum power law (reduced at low energy by neutral absorption), a 6.4 keV iron emission line (detected in all spectra with varying intensity) and a Compton-reflection component. A Compton reflection component is also detected in all spectra, although at lower significance. The analysis of the fourth and last observation of our monitoring campaign has just recently begun. Next, we will (1) stack together the four observations of IGR J16138-4848, to obtain high-accuracy estimates of the average spectral parameters of this object; and then (2) proceed to the time-evolving analysis, of the three spectral parameters: (a) Gamma (the slope of the intrinsic continuum), (b) W(FeK), the equivalent width of the 6.4 keV Iron emission line, and (c) R, the relative amount of Compton reflection. Through this time-resolved spectroscopic analysis we hope to constrain (a) the physical state of the accreting matter and its relation with the X-ray output, and (b) the evolution of the accretion flow geometry, distribution and covering factor.

  20. On the X-ray spectra of luminous, inhomogeneous accretion flows

    NASA Astrophysics Data System (ADS)

    Merloni, A.; Malzac, J.; Fabian, A. C.; Ross, R. R.

    2006-08-01

    We discuss the expected X-ray spectral and variability properties of black hole accretion discs at high luminosity, under the hypothesis that radiation-pressure-dominated discs are subject to violent clumping instabilities and, as a result, have a highly inhomogeneous two-phase structure. After deriving the full accretion disc solutions explicitly in terms of the parameters of the model, we study their radiative properties both with a simple two-zone model, treatable analytically, and with radiative transfer simulations which account simultaneously for energy balance and Comptonization in the hot phase, together with reflection, reprocessing, ionization and thermal balance in the cold phase. We show that, if not only the density, but also the heating rate within these flows is inhomogeneous, then complex reflection-dominated spectra can be obtained for a high enough covering fraction of the cold phase. In general, large reflection components in the observed X-ray spectra should be associated with strong soft excesses, resulting from the combined emission of ionized atomic emission lines. The variability properties of such systems are such that, even when contributing to a large fraction of the hard X-ray spectrum, the reflection component is less variable than the power-law-like emission originating from the hot Comptonizing phase, in agreement with what is observed in many Narrow Line Seyfert 1 galaxies and bright Seyfert 1. Our model falls within the family of those trying to explain the complex X-ray spectra of bright AGN with ionized reflection, but presents an alternative, specific, physically motivated, geometrical set-up for the complex multiphase structure of the inner regions of near-Eddington accretion flows.

  1. On the physical nature of halogen bonds: a QTAIM study.

    PubMed

    Syzgantseva, Olga A; Tognetti, Vincent; Joubert, Laurent

    2013-09-12

    In this article, we report a detailed study on halogen bonds in complexes of CHCBr, CHCCl, CH2CHBr, FBr, FCl, and ClBr with a set of Lewis bases (NH3, OH2, SH2, OCH2, OH(-), Br(-)). To obtain insight into the physical nature of these bonds, we extensively used Bader's Quantum Theory of Atoms-in-Molecules (QTAIM). With this aim, in addition to the examination of the bond critical points properties, we apply Pendás' Interacting Quantum Atoms (IQA) scheme, which enables rigorous and physical study of each interaction at work in the formation of the halogen-bonded complexes. In particular, the influence of primary and secondary interactions on the stability of the complexes is analyzed, and the roles of electrostatics and exchange are notably discussed and compared. Finally, relationships between QTAIM descriptors and binding energies are inspected.

  2. Physics validation studies for muon collider detector background simulations

    SciTech Connect

    Morris, Aaron Owen; /Northern Illinois U.

    2011-07-01

    Within the broad discipline of physics, the study of the fundamental forces of nature and the most basic constituents of the universe belongs to the field of particle physics. While frequently referred to as 'high-energy physics,' or by the acronym 'HEP,' particle physics is not driven just by the quest for ever-greater energies in particle accelerators. Rather, particle physics is seen as having three distinct areas of focus: the cosmic, intensity, and energy frontiers. These three frontiers all provide different, but complementary, views of the basic building blocks of the universe. Currently, the energy frontier is the realm of hadron colliders like the Tevatron at Fermi National Accelerator Laboratory (Fermilab) or the Large Hadron Collider (LHC) at CERN. While the LHC is expected to be adequate for explorations up to 14 TeV for the next decade, the long development lead time for modern colliders necessitates research and development efforts in the present for the next generation of colliders. This paper focuses on one such next-generation machine: a muon collider. Specifically, this paper focuses on Monte Carlo simulations of beam-induced backgrounds vis-a-vis detector region contamination. Initial validation studies of a few muon collider physics background processes using G4beamline have been undertaken and results presented. While these investigations have revealed a number of hurdles to getting G4beamline up to the level of more established simulation suites, such as MARS, the close communication between us, as users, and the G4beamline developer, Tom Roberts, has allowed for rapid implementation of user-desired features. The main example of user-desired feature implementation, as it applies to this project, is Bethe-Heitler muon production. Regarding the neutron interaction issues, we continue to study the specifics of how GEANT4 implements nuclear interactions. The GEANT4 collaboration has been contacted regarding the minor discrepancies in the neutron

  3. Limiting Accretion onto Massive Stars by Fragmentation-Induced Starvation

    SciTech Connect

    Peters, Thomas; Klessen, Ralf S.; Mac Low, Mordecai-Mark; Banerjee, Robi; /ZAH, Heidelberg

    2010-08-25

    Massive stars influence their surroundings through radiation, winds, and supernova explosions far out of proportion to their small numbers. However, the physical processes that initiate and govern the birth of massive stars remain poorly understood. Two widely discussed models are monolithic collapse of molecular cloud cores and competitive accretion. To learn more about massive star formation, we perform simulations of the collapse of rotating, massive, cloud cores including radiative heating by both non-ionizing and ionizing radiation using the FLASH adaptive mesh refinement code. These simulations show fragmentation from gravitational instability in the enormously dense accretion flows required to build up massive stars. Secondary stars form rapidly in these flows and accrete mass that would have otherwise been consumed by the massive star in the center, in a process that we term fragmentation-induced starvation. This explains why massive stars are usually found as members of high-order stellar systems that themselves belong to large clusters containing stars of all masses. The radiative heating does not prevent fragmentation, but does lead to a higher Jeans mass, resulting in fewer and more massive stars than would form without the heating. This mechanism reproduces the observed relation between the total stellar mass in the cluster and the mass of the largest star. It predicts strong clumping and filamentary structure in the center of collapsing cores, as has recently been observed. We speculate that a similar mechanism will act during primordial star formation.

  4. LIMITING ACCRETION ONTO MASSIVE STARS BY FRAGMENTATION-INDUCED STARVATION

    SciTech Connect

    Peters, Thomas; Klessen, Ralf S.; Banerjee, Robi; Low, Mordecai-Mark Mac

    2010-12-10

    Massive stars influence their surroundings through radiation, winds, and supernova explosions far out of proportion to their small numbers. However, the physical processes that initiate and govern the birth of massive stars remain poorly understood. Two widely discussed models are monolithic collapse of molecular cloud cores and competitive accretion. To learn more about massive star formation, we perform and analyze simulations of the collapse of rotating, massive, cloud cores including radiative heating by both non-ionizing and ionizing radiation using the FLASH adaptive-mesh refinement code. These simulations show fragmentation from gravitational instability in the enormously dense accretion flows required to build up massive stars. Secondary stars form rapidly in these flows and accrete mass that would have otherwise been consumed by the massive star in the center, in a process that we term fragmentation-induced starvation. This explains why massive stars are usually found as members of high-order stellar systems that themselves belong to large clusters containing stars of all masses. The radiative heating does not prevent fragmentation, but does lead to a higher Jeans mass, resulting in fewer and more massive stars than would form without the heating. This mechanism reproduces the observed relation between the total stellar mass in the cluster and the mass of the largest star. It predicts strong clumping and filamentary structure in the center of collapsing cores, as has recently been observed. We speculate that a similar mechanism will act during primordial star formation.

  5. Simultaneous Spectral and Timing Observations of Accreting Neuron Stars

    NASA Technical Reports Server (NTRS)

    Kaaret, P.; Oliversen, Ronald J. (Technical Monitor)

    2002-01-01

    The goal of this proposal is to perform simultaneous x-ray spectral and millisecond timing observations of accreting neutron stars to further our understanding of their accretion dynamics and in the hope of using these systems as probes of the physics of strong gravitational fields. NAG5-9104 is the successor grant to NAG5-8408. Observations using the Rossi X-Ray Timing Explorer (RXTE) and BeppoSAX were performed of 4U1702-429, 4U1735-44, and Cyg X-2. Unfortunately, only a small fraction of the approved observing time was obtained for the first two targets and the data are of limited scientific value. Data analysis has been completed on the observations of Cyg X-2. We discovered a correlation between the frequency of the horizontal branch oscillations (HBO) and a soft, thermal component of the x-ray spectrum likely associated with emission from the accretion disk. This correlation may place constraints on models of the oscillations. A paper based on these results appeared in the Astrophysical Journal.

  6. Is math anxiety in the secondary classroom limiting physics mastery? A study of math anxiety and physics performance

    NASA Astrophysics Data System (ADS)

    Mercer, Gary J.

    This quantitative study examined the relationship between secondary students with math anxiety and physics performance in an inquiry-based constructivist classroom. The Revised Math Anxiety Rating Scale was used to evaluate math anxiety levels. The results were then compared to the performance on a physics standardized final examination. A simple correlation was performed, followed by a multivariate regression analysis to examine effects based on gender and prior math background. The correlation showed statistical significance between math anxiety and physics performance. The regression analysis showed statistical significance for math anxiety, physics performance, and prior math background, but did not show statistical significance for math anxiety, physics performance, and gender.

  7. Accretion in Saturn's F Ring

    NASA Astrophysics Data System (ADS)

    Meinke, B. K.; Esposito, L. W.; Stewart, G.

    2012-12-01

    Saturn's F ring is the solar system's principal natural laboratory for direct observation of accretion and disruption processes. The ring resides in the Roche zone, where tidal disruption competes with self-gravity, which allows us to observe the lifecycle of moonlets. Just as nearby moons create structure at the B ring edge (Esposito et al. 2012) and the Keeler gap (Murray 2007), the F ring "shepherding" moons Prometheus and Pandora stir up ring material and create observably changing structures on timescales of days to decades. In fact, Beurle et al (2010) show that Prometheus makes it possible for "distended, yet gravitationally coherent clumps" to form in the F ring, and Barbara and Esposito (2002) predicted a population of ~1 km bodies in the ring. In addition to the observations over the last three decades, the Cassini Ultraviolet Imaging Spectrograph (UVIS) has detected 27 statistically significant features in 101 occultations by Saturn's F ring since July 2004. Seventeen of those 27 features are associated with clumps of ring material. Two features are opaque in occultation, which makes them candidates for solid objects, which we refer to as Moonlets. The 15 other features partially block stellar signal for 22 m to just over 3.7 km along the radial expanse of the occultation. Upon visual inspection of the occultation profile, these features resemble Icicles, thus we will refer to them as such here. The density enhancements responsible for such signal attenuations are likely due to transient clumping of material, evidence that aggregations of material are ubiquitous in the F ring. Our lengthy observing campaign reveals that Icicles are likely transient clumps, while Moonlets are possible solid objects. Optical depth is an indicator of clumping because more-densely aggregated material blocks more light; therefore, it is natural to imagine moonlets as later evolutionary stage of icicle, when looser clumps of material compact to form a feature that appears

  8. Cyclotron Lines in Accreting Neutron Star Spectra

    NASA Astrophysics Data System (ADS)

    Wilms, Jörn; Schönherr, Gabriele; Schmid, Julia; Dauser, Thomas; Kreykenbohm, Ingo

    2009-05-01

    Cyclotron lines are formed through transitions of electrons between discrete Landau levels in the accretion columns of accreting neutron stars with strong (1012 G) magnetic fields. We summarize recent results on the formation of the spectral continuum of such systems, describe recent advances in the modeling of the lines based on a modification of the commonly used Monte Carlo approach, and discuss new results on the dependence of the measured cyclotron line energy from the luminosity of transient neutron star systems. Finally, we show that Simbol-X will be ideally suited to build and improve the observational database of accreting and strongly magnetized neutron stars.

  9. Impact of physical activity domains on subsequent physical activity in youth: a 5-year longitudinal study.

    PubMed

    Hardie Murphy, Michelle; Rowe, David A; Woods, Catherine B

    2017-02-01

    This study evaluates how domains of physical activity (PA) in youth predict later PA and assesses factors influencing changes in sports participation. Young people from the Children's Sport Participation and Physical Activity study (n = 873; baseline age 10-18 years; 30.4% male) completed self-report surveys in 2009 and 2014. In a multiple linear regression analysis, participation frequency in club sport (β = 0.18) and extracurricular sport (β = 0.13) significantly predicted PA 5 years later, adjusted for age, sex and urban/rural classification (P < 0.01). Overall, rates of regular (at least once per week) youth sports participation were high (males 79.3-85.5%; females 74.8-83.2%). Uptake and dropout of specific sports varied widely. Despite high levels of migration into and out of Gaelic games, they remained popular at follow-up. Weight training was the only sport that increased in both sexes (P < 0.05). Fitness, friends and enjoyment were top motivations for taking up a new sport. Other commitments, a lack of interest and time were important factors leading to sports dropout. PA promotion strategies should include youth sport, take into consideration what sports are attractive to young people and address reasons for uptake and dropout.

  10. X-ray deficiency on strongly accreting T Tauri stars. Comparing Orion with Taurus

    NASA Astrophysics Data System (ADS)

    Bustamante, I.; Merín, B.; Bouy, H.; Manara, C. F.; Ribas, Á.; Riviere-Marichalar, P.

    2016-03-01

    Context. Depending on whether a T Tauri star accretes material from its circumstellar disk or not, different X-ray emission properties can be found. The accretion shocks produce cool heating of the plasma, contributing to the soft X-ray emission from the star. Aims: Using X-ray data from the Chandra Orion Ultra-deep Project and accretion rates that were obtained with the Hubble Space Telescope/WFPC2 photometric measurements in the Orion Nebula Cluster (ONC), we studied the relation between the accretion processes and the X-ray emissions of a coherent sample of T Tauri sources in the region. Methods: We performed regression and correlation analyses of our sample of T Tauri stars between the X-ray parameters, stellar properties, and the accretion measurements. Results: We find that a clear anti-correlation is present between the residual X-ray luminosity and the accretion rates in our samples in Orion that is consistent with that found on the XMM-Newton Extended Survey of the Taurus molecular cloud (XEST) study. A considerable number of classified non-accreting sources show accretion rates comparable to those of classical T Tauri Stars (CTTS). Our data do not allow us to confirm the classification between classical and weak-line T Tauri stars (WTTS), and the number of WTTS in this work is small compared to the complete samples. Thus, we have used the entire samples as accretors in our analysis. We provide a catalog with X-ray luminosities (corrected from distance) and accretion measurements of an ONC T Tauri stars sample. Conclusions: Although Orion and Taurus display strong differences in their properties (total gas and dust mass, star density, strong irradiation from massive stars), we find that a similar relation between the residual X-ray emission and accretion rate is present in the Taurus molecular cloud and in the accreting samples from the ONC. The spread in the data suggests dependencies of the accretion rates and the X-ray luminosities other than the

  11. Accretion onto the first stellar mass black holes

    SciTech Connect

    Alvarez, Marcelo A.; Wise, John H.; Abel, Tom

    2009-08-05

    The first stars, forming at redshifts z > 15 in minihalos with M {approx} 10{sup 5-6} M{sub {circle_dot}} may leave behind remnant black holes, which could conceivably have been the 'seeds' for the supermassive black holes observed at z {approx}< 7. We study remnant black hole growth through accretion, including for the first time the radiation emitted due to accretion, with adaptive mesh refinement cosmological radiation-hydrodynamical simulations. The effects of photo-ionization and heating dramatically affect the large-scale inflow, resulting in negligible mass growth. We compare cases with accretion luminosity included and neglected to show that accretion radiation drastically changes the environment within 100 pc of the black hole, increasing gas temperatures by an order of magnitude. Gas densities are reduced and further star formation in the same minihalo is prevented for the two hundred million years we followed. Without radiative feedback included most seed black holes do not gain mass as efficiently as has been hoped for in previous theories, implying that black hole remnants of Pop III stars in minihalos are not likely to be miniquasars. Most importantly, however, our calculations demonstrate that if these black holes are indeed accreting close to the Bondi-Hoyle rate with ten percent radiative efficiency they have a dramatic local effect in regulating star formation in the first galaxies. This suggests a novel mechanism for massive black hole formation - stellar-mass black holes may have suppressed fragmentation and star formation after falling into halos with virial temperatures {approx} 10{sup 4} K, facilitating intermediate mass black hole formation at their centers.

  12. ROTATING ACCRETION FLOWS: FROM INFINITY TO THE BLACK HOLE

    SciTech Connect

    Li, Jason; Ostriker, Jeremiah; Sunyaev, Rashid

    2013-04-20

    Accretion onto a supermassive black hole of a rotating inflow is a particularly difficult problem to study because of the wide range of length scales involved. There have been broadly utilized analytic and numerical treatments of the global properties of accretion flows, but detailed numerical simulations are required to address certain critical aspects. We use the ZEUS code to run hydrodynamical simulations of rotating, axisymmetric accretion flows with Bremsstrahlung cooling, considering solutions for which the centrifugal balance radius significantly exceeds the Schwarzschild radius, with and without viscous angular momentum transport. Infalling gas is followed from well beyond the Bondi radius down to the vicinity of the black hole. We produce a continuum of solutions with respect to the single parameter M-dot{sub B}/ M-dot{sub Edd}, and there is a sharp transition between two general classes of solutions at an Eddington ratio of M-dot{sub B}/M-dot{sub Edd}{approx}few Multiplication-Sign 10{sup -2}. Our high inflow solutions are very similar to the standard Shakura and Sunyaev results. But our low inflow results are to zeroth order the stationary Papaloizou and Pringle solution, which has no accretion. To next order in the small, assumed viscosity they show circulation, with disk and conical wind outflows almost balancing inflow. These solutions are characterized by hot, vertically extended disks, and net accretion proceeds at an extremely low rate, only of order {alpha} times the inflow rate. Our simulations have converged with respect to spatial resolution and temporal duration, and they do not depend strongly on our choice of boundary conditions.

  13. Physics, AP Student Study Guide, 6th Edition

    NASA Astrophysics Data System (ADS)

    Cutnell, John D.; Johnson, Kenneth W.

    2003-11-01

    This Sixth Edition helps readers understand the interrelationships among basic physics concepts and how they fit together to describe our physical world. Throughout the book, the authors emphasize the relevance of physics to our everyday lives. Real-world physics applications, including many biomedical applications, show how physics principles come into play over and over again in our lives. Problem Solving Insights explain each calculation in detail, guiding readers through the quantitative process Includes a CD containing physics simulations

  14. RECONSTRUCTING THE ACCRETION HISTORY OF THE GALACTIC STELLAR HALO FROM CHEMICAL ABUNDANCE RATIO DISTRIBUTIONS

    SciTech Connect

    Lee, Duane M.; Johnston, Kathryn V.; Sen, Bodhisattva; Jessop, Will

    2015-03-20

    Observational studies of halo stars during the past two decades have placed some limits on the quantity and nature of accreted dwarf galaxy contributions to the Milky Way (MW) stellar halo by typically utilizing stellar phase-space information to identify the most recent halo accretion events. In this study we tested the prospects of using 2D chemical abundance ratio distributions (CARDs) found in stars of the stellar halo to determine its formation history. First, we used simulated data from 11 “MW-like” halos to generate satellite template sets (STSs) of 2D CARDs of accreted dwarf satellites, which are composed of accreted dwarfs from various mass regimes and epochs of accretion. Next, we randomly drew samples of ∼10{sup 3–4} mock observations of stellar chemical abundance ratios ([α/Fe], [Fe/H]) from those 11 halos to generate samples of the underlying densities for our CARDs to be compared to our templates in our analysis. Finally, we used the expectation-maximization algorithm to derive accretion histories in relation to the STS used and the sample size. For certain STSs used we typically can identify the relative mass contributions of all accreted satellites to within a factor of two. We also find that this method is particularly sensitive to older accretion events involving low-luminosity dwarfs, e.g., ultra-faint dwarfs—precisely those events that are too ancient to be seen by phase-space studies of stars and too faint to be seen by high-z studies of the early universe. Since our results only exploit two chemical dimensions and near-future surveys promise to provide ∼6–9 dimensions, we conclude that these new high-resolution spectroscopic surveys of the stellar halo will allow us to recover its accretion history—and the luminosity function of infalling dwarf galaxies—across cosmic time.

  15. The power of relativistic jets is larger than the luminosity of their accretion disks.

    PubMed

    Ghisellini, G; Tavecchio, F; Maraschi, L; Celotti, A; Sbarrato, T

    2014-11-20

    Theoretical models for the production of relativistic jets from active galactic nuclei predict that jet power arises from the spin and mass of the central supermassive black hole, as well as from the magnetic field near the event horizon. The physical mechanism underlying the contribution from the magnetic field is the torque exerted on the rotating black hole by the field amplified by the accreting material. If the squared magnetic field is proportional to the accretion rate, then there will be a correlation between jet power and accretion luminosity. There is evidence for such a correlation, but inadequate knowledge of the accretion luminosity of the limited and inhomogeneous samples used prevented a firm conclusion. Here we report an analysis of archival observations of a sample of blazars (quasars whose jets point towards Earth) that overcomes previous limitations. We find a clear correlation between jet power, as measured through the γ-ray luminosity, and accretion luminosity, as measured by the broad emission lines, with the jet power dominating the disk luminosity, in agreement with numerical simulations. This implies that the magnetic field threading the black hole horizon reaches the maximum value sustainable by the accreting matter.

  16. The power of relativistic jets is larger than the luminosity of their accretion disks

    NASA Astrophysics Data System (ADS)

    Ghisellini, G.; Tavecchio, F.; Maraschi, L.; Celotti, A.; Sbarrato, T.

    2014-11-01

    Theoretical models for the production of relativistic jets from active galactic nuclei predict that jet power arises from the spin and mass of the central supermassive black hole, as well as from the magnetic field near the event horizon. The physical mechanism underlying the contribution from the magnetic field is the torque exerted on the rotating black hole by the field amplified by the accreting material. If the squared magnetic field is proportional to the accretion rate, then there will be a correlation between jet power and accretion luminosity. There is evidence for such a correlation, but inadequate knowledge of the accretion luminosity of the limited and inhomogeneous samples used prevented a firm conclusion. Here we report an analysis of archival observations of a sample of blazars (quasars whose jets point towards Earth) that overcomes previous limitations. We find a clear correlation between jet power, as measured through the γ-ray luminosity, and accretion luminosity, as measured by the broad emission lines, with the jet power dominating the disk luminosity, in agreement with numerical simulations. This implies that the magnetic field threading the black hole horizon reaches the maximum value sustainable by the accreting matter.

  17. Constraints on the temperature inhomogeneity in quasar accretion discs from the ultraviolet-optical spectral variability

    NASA Astrophysics Data System (ADS)

    Kokubo, Mitsuru

    2015-05-01

    The physical mechanisms of the quasar ultraviolet (UV)-optical variability are not well understood despite the long history of observations. Recently, Dexter & Agol presented a model of quasar UV-optical variability, which assumes large local temperature fluctuations in the quasar accretion discs. This inhomogeneous accretion disc model is claimed to describe not only the single-band variability amplitude, but also microlensing size constraints and the quasar composite spectral shape. In this work, we examine the validity of the inhomogeneous accretion disc model in the light of quasar UV-optical spectral variability by using five-band multi-epoch light curves for nearly 9 000 quasars in the Sloan Digital Sky Survey (SDSS) Stripe 82 region. By comparing the values of the intrinsic scatter σint of the two-band magnitude-magnitude plots for the SDSS quasar light curves and for the simulated light curves, we show that Dexter & Agol's inhomogeneous accretion disc model cannot explain the tight inter-band correlation often observed in the SDSS quasar light curves. This result leads us to conclude that the local temperature fluctuations in the accretion discs are not the main driver of the several years' UV-optical variability of quasars, and consequently, that the assumption that the quasar accretion discs have large localized temperature fluctuations is not preferred from the viewpoint of the UV-optical spectral variability.

  18. A spectroscopic survey of Herbig Ae/Be stars with X-Shooter - II. Accretion diagnostic lines

    NASA Astrophysics Data System (ADS)

    Fairlamb, J. R.; Oudmaijer, R. D.; Mendigutia, I.; Ilee, J. D.; van den Ancker, M. E.

    2017-02-01

    The Herbig Ae/Be stars (HAeBes) allow an exploration of the properties of pre-main-sequence(PMS) stars above the low-mass range (<2 M_{⊙}) and those bordering the high-mass range (>8 M_{⊙}). This paper is the second in a series exploring accretion in 91 HAeBes with Very Large Telescope/X-shooter spectra. Equivalent width measurements are carried out on 32 different lines, spanning the UV (ultraviolet) to NIR (near infrared), in order to obtain their line luminosities. The line luminosities were compared to accretion luminosities that were determined directly from measurements of a UV excess. When detected, emission lines always demonstrate a correlation with the accretion luminosity, regardless of detection frequency. The average relationship between accretion luminosity and line luminosity is found to be L_acc ∝ L_line1.16 ± 0.15. This is in agreement with the findings in Classical T Tauri stars, although the HAeBe relationship is generally steeper, particularly towards the Herbig Be mass range. Since all observed lines display a correlation with the accretion luminosity, all of them can be used as accretion tracers. This has increased the number of accretion diagnostic lines in HAeBes 10-fold. However, questions still remain on the physical origin of each line, which may not be due to accretion.

  19. Constraining the initial conditions and final outcomes of accretion processes around young stars and supermassive black holes

    NASA Astrophysics Data System (ADS)

    Stone, Jordan M.

    relative proximity to the center of our own Galaxy, provides the opportunity to study a low-luminosity accretion mode that would be difficult or impossible to observe in more remote galaxies. Variable emission from the accretion flow arises from very deep within the flow and could be used to reveal the physics of the accretion process. Characterizing the variability is challenging because all wavelength regimes from radio through X-ray are affected by the process(es) that gives rise to the variations. I report observations of variability at wavelengths that are difficult or challenging to observe from the ground using the SPIRE instrument onboard the Herschel Space Observatory. My work provides the first constraints on the flux of the accretion flow at 250mum. Variations at 500, 350, and 250mum observed with Herschel exhibit typical amplitudes similar to the variations observed at 1300mum from the ground, but the amplitude distribution of flux variations observe with Herschel does not exhibit a tail to large amplitudes that is seen at 1300mum. This could suggest a connection between large-amplitude mm/submillimeter variations and X-ray activity, since no increased X-ray activity was observed during our Herschel monitoring.

  20. Relationship between physical activity, physical fitness and multiple metabolic risk in youths from Muzambinho's study.

    PubMed

    Barbosa, João Paulo Dos Anjos Souza; Basso, Luciano; Seabra, André; Prista, Antonio; Tani, Go; Maia, José António Ribeiro; Forjaz, Cláudia Lúcia De Moraes

    2016-08-01

    Negative associations between physical activity (PA), physical fitness and multiple metabolic risk factors (MMRF) in youths from populations with low PA are reported. The persistence of this association in moderately-to highly active populations is not, however, well established. The aim of the present study was to investigate this association in a Brazilian city with high frequency of active youths. We assessed 122 subjects (9.9 ± 1.3 years) from Muzambinho city. Body mass index, waist circumference, glycaemia, cholesterolaemia, systolic and diastolic blood pressures were measured. Maximal handgrip strength and one-mile walk/run test were used. Leisure time PA was assessed by interview. Poisson regression was used in the analysis. The model explained 11% of the total variance. Only relative muscular strength and one-mile walk/run were statistically significant (p < .05). Those who needed more time to cover the one-mile walk/run test had an increased in metabolic risk of 11%, and those with greater strength reduced the risk by about 82%. In conclusion, children and youths from an active population who need less time to cover the one-mile walk/run test or who had greater muscular strength showed a reduced metabolic risk. These results suggest that even in children and youths with high leisure time PA, a greater aerobic fitness and strength might help to further reduce their MMRF.

  1. The beaming of subhalo accretion

    NASA Astrophysics Data System (ADS)

    Libeskind, Noam I.

    2016-10-01

    We examine the infall pattern of subhaloes onto hosts in the context of the large-scale structure. We find that the infall pattern is essentially driven by the shear tensor of the ambient velocity field. Dark matter subhaloes are preferentially accreted along the principal axis of the shear tensor which corresponds to the direction of weakest collapse. We examine the dependence of this preferential infall on subhalo mass, host halo mass and redshift. Although strongest for the most massive hosts and the most massive subhaloes at high redshift, the preferential infall of subhaloes is effectively universal in the sense that its always aligned with the axis of weakest collapse of the velocity shear tensor. It is the same shear tensor that dictates the structure of the cosmic web and hence the shear field emerges as the key factor that governs the local anisotropic pattern of structure formation. Since the small (sub-Mpc) scale is strongly correlated with the mid-range (~ 10 Mpc) scale - a scale accessible by current surveys of peculiar velocities - it follows that findings presented here open a new window into the relation between the observed large scale structure unveiled by current surveys of peculiar velocities and the preferential infall direction of the Local Group. This may shed light on the unexpected alignments of dwarf galaxies seen in the Local Group.

  2. Accretion Timescales from Kepler AGN

    NASA Astrophysics Data System (ADS)

    Kasliwal, Vishal P.; Vogeley, Michael S.; Richards, Gordon T.

    2015-01-01

    We constrain AGN accretion disk variability mechanisms using the optical light curves of AGN observed by Kepler. AGN optical fluxes are known to exhibit stochastic variations on timescales of hours, days, months and years. The excellent sampling properties of the original Kepler mission - high S/N ratio (105), short sampling interval (30 minutes), and long sampling duration (~ 3.5 years) - allow for a detailed examination of the differences between the variability processes present in various sub-types of AGN such as Type I and II Seyferts, QSOs, and Blazars. We model the flux data using the Auto-Regressive Moving Average (ARMA) representation from the field of time series analysis. We use the Kalman filter to determine optimal mode parameters and use the Akaike Information Criteria (AIC) to select the optimal model. We find that optical light curves from Kepler AGN cannot be fit by low order statistical models such as the popular AR(1) process or damped random walk. Kepler light curves exhibit complicated power spectra and are better modeled by higher order ARMA processes. We find that Kepler AGN typically exhibit power spectra that change from a bending power law (PSD ~ 1/fa) to a flat power spectrum on timescales in the range of ~ 5 - 100 days consistent with the orbital and thermal timescales of a typical 107 solar mass black hole.

  3. Combining N-body accretion simulations with partitioning experiments in a statistical model of terrestrial planet accretion and core formation

    NASA Astrophysics Data System (ADS)

    Fischer, R. A.; Ciesla, F.; Campbell, A. J.

    2014-12-01

    's feeding zone. The model can reveal the relative importance of various accretionary processes, highlighting targets for future experimental and numerical studies. For example, changing the depth of partitioning to 70% of the CMB pressure leads to an increase of 1.7 ± 2.8 wt% Si and 2.2 ± 3.5 wt% O in Earth analogue cores, comparable to variations due to accretion history.

  4. Accreting pre-main-sequence models and abundance anomalies in globular clusters

    NASA Astrophysics Data System (ADS)

    Tognelli, E.; Prada Moroni, P. G.; Degl'Innocenti, S.

    2015-12-01

    We investigated the possibility of producing helium-enhanced stars in globular clusters by accreting polluted matter during the pre-main-sequence phase. We followed the evolution of two different classes of pre-main-sequence accreting models, one which neglects and the other that takes into account the protostellar evolution. We analysed the dependence of the final central helium abundance, of the tracks position in the HR diagram and of the surface lithium abundance evolution on the age at which the accretion of polluted material begins and on the main physical parameters that govern the protostellar evolution. The later is the beginning of the late accretion and the lower are both the central helium and the surface lithium abundances at the end of the accretion phase and in Zero Age Main Sequence (ZAMS). In order to produce a relevant increase of the central helium content the accretion of polluted matter should start at ages lower than 1 Myr. The inclusion of the protostellar evolution has a strong impact on the ZAMS models too. The adoption of a very low seed mass (i.e. 0.001 M⊙) results in models with the lowest central helium and surface lithium abundances. The higher is the accretion rate and the lower is the final helium content in the core and the residual surface lithium. In the worst case - i.e. seed mass 0.001 M⊙ and accretion rate ≥10-5 M⊙ yr-1 - the central helium is not increased at all and the surface lithium is fully depleted in the first few million years.

  5. Spectroscopic Signatures Of Magnetospheric Accretion In Herbig Ae/Be Stars

    NASA Astrophysics Data System (ADS)

    Järvinen, Silva P.; Schöller, Markus; Pogodin, Michail A.; Cahuasqui, Andres; Drake, Natalia A.; Hubrig, S.; Petr-Gotzens, Monika; Savanov, Igor S.; Ilyin, Ilya; Stelzer, Beate

    2016-07-01

    Important diagnostics of the star/circumstellar interaction region of HerbigAe/Be stars are accessible by examining the temporal behavior of thenear-IR spectral lines He I λ10830 and Paschen gamma. We reduced andanalyzed 30 spectra of the strongly magnetic Herbig Ae star HD101412,acquired with the CRIRES and X-shooter spectrographs installed at theVLT (ESO, Chile). We found that the temporal behavior of these diagnosticlines in the near-infrared spectra can be explained by rotational modulationof line profiles generated by accreting gas with a period P = 20.53d.This period is about half of the magnetic rotation period P = 42.76dpreviously determined from measurements of the mean longitudinal magneticfield. Our finding indicates that the accreted matter falls onto the star in regions close to the magnetic poles intersecting the line-of-sight twiceduring the rotation cycle. The results of our study clearly demonstratethe power of such an analysis to diagnose the physical properties ofaccretion flows onto pre-main sequence stars.

  6. How surface density of galaxy disks affects metallicity? Outflow and Accretion

    NASA Astrophysics Data System (ADS)

    Wu, Po-Feng; Kudritzki, Rolf-Peter; Tully, R. Brent; Neill, J. D.

    2015-08-01

    The surface density of disk is considered as a second parameter affecting the evolution of disk galaxies other than mass. Several physical and chemical properties of galaxies are found to be correlated with surface density of disk galaxies. However, the surface density, or surface brightness, is also strongly correlated with mass. It's not clear whether surface density really plays a role, or those correlations simply reflect the effect from stellar mass. To ask the question properly, one should take away the dependence on mass of galaxies, i.e., compare galaxies with the same mass but different surface densities.In this study, we ask, besides stellar mass, whether the surface density of disks also affects chemical evolution of galaxies. We demonstrate that, after removing the dependence on stellar mass and gas mass, the metallicity of galaxy still correlates with surface density of the galaxy disk. At the same stellar and gas mass, higher surface brightness galaxies on average possess both higher stellar and gas-phase metallicity, inferred from broadband color and spectrosopy of HII regions, respectively.We use an analytical model of chemical evolution involving gas outflow and accretion to explore possible reasons causing the difference in metallicity. Accroding to the model, at the same mass, lower metallicity galaxies should have experienced severer mass loss during star-formation events, and/or be inert to gas accretion. Both scenarios are consistent with general expections from properties of low surface density disks of shallow potential wells and dynamical stability.

  7. Modeling High-resolution Spectra from X-ray Illuminated Accretion Disks

    NASA Astrophysics Data System (ADS)

    Garcia, Javier; Kallman, T.

    2010-01-01

    This work is focused on the study of X-ray illuminated accretion disks around compact objects by modeling their structure and reprocessed spectra. Use of low-accuracy and incomplete atomic data is a key limitation in models which have been calculated so far. We remedy this situation by incorporating data for line energies, transition probabilities and photoionization cross sections taken from various sources, most notably calculations using the R-matrix suite of codes. We also implement a self-consistent approach for the radiative transfer of X-rays and the heating and ionization of the gas. These promise to lead to significant improvements in the understanding of the X-ray observations of active galactic nuclei (AGN), X-ray binaries and galactic black holes. By performing detailed radiative transfer calculations we have computed the reflected spectra from constant density slabs for different input parameters (e.g., density, strength of incident X-rays, iron abundance), including the redistribution of photons due to Compton scattering. Although broad and skewed iron emission lines observed in many accreting systems are often attributed to the Doppler effect and gravitational redshift, our results show that Comptonization can be responsible for a significant fraction of the line broadening. By analyzing simulated Suzaku observations from our models, we provide equivalent and physical widths and line centroid energies for atomic lines, absorption edges and recombination continua (among other features). These are provided in tabular and graphical form that can be used directly in the interpretation of observational data.

  8. Accretion-ejection models for AGN jets

    NASA Astrophysics Data System (ADS)

    Zanni, C.

    2008-10-01

    It is likely that jets from Active Galactic Nuclei derive their energy from accretion onto the central black hole. It is actually possible to fuel the jets by extracting energy and angular momentum from the accretion disk and/or the rotating black hole via the action of large-scale magnetic fields. In this talk I will first present results of analytical and numerical models of the launching process of jets from magnetized accretion disks: I will show that, although a sizeable fraction of the accretion power goes into the jets, these outflows are presumably only mildly relativistic. In the second place, I will therefore suggest that the strongly relativistic components observed at the VLBI scales are accelerated in the innermost parts of the AGNs by Blandford-Znajek and/or Compton-rocket processes. Nonetheless, the non-relativistic disk-wind is needed to collimate the relativistic component and to reproduce the total power of extragalactic jets.

  9. Planetary science: Iron fog of accretion

    DOE PAGES

    Anderson, William W.

    2015-03-02

    Here, pinpointing when Earth's core formed depends on the extent of metal–silicate equilibration in the mantle. Vaporization and recondensation of impacting planetesimal cores during accretion may reconcile disparate lines of evidence.

  10. Time lag in transient cosmic accreting sources

    NASA Astrophysics Data System (ADS)

    Bisnovatyi-Kogan, G. S.; Giovannelli, F.

    2017-02-01

    Context. We develop models for time lag between the maxima of the source brightness in different wavelengths during a transient flash of luminosity that is connected with a short-period increase of the mass flux onto the central compact object. Aims: We derive a simple formula for finding the time delay among events in different wavelengths which is valid in general for all disk-accreting cosmic sources. We quantitatively also discuss a model for time-lag formation in active galactic nuclei (AGNs). Methods: In close binaries with accretion disks, the time lag is connected with effects of viscosity that define a radial motion of matter in the accretion disk. In AGN flashes, the infalling matter has a low angular momentum, and the time lag is defined by the free-fall time to the gravitating center. Results: We show the validity of these models by means of several examples of galactic and extragalactic accreting sources.

  11. Spectroscopy of Low Mass X-Ray Binaries: New Insights into Accretion

    NASA Technical Reports Server (NTRS)

    DilVrtilek, Saeqa; Mushotsky, Richard (Technical Monitor)

    2004-01-01

    This project is to observe two low mass X-ray binaries, chosen for their X-ray brightness, low column density, and diversity of accretion behavior. The high spectral resolution of the RGS, the broad energy range and tremendous collecting power of EPIC, and simultaneous optical monitoring with the OM are particularly well-suited to these studies. The second of two objects was observed on September of 2002. Data analysis for both observation has been completed: an investigation of the physical conditions of the emitting gas using emission and recombination line diagnostics to determine temperatures, densities, elemental abundances, and ionization structure. A study of behavior of the emission features as a function of binary orbit shows modulated behavior in one of the systems. A paper on "High-resolution observations of low-mass X-ray binaries" is near completion. The paper includes observations with the Chandra HETG that are not yet completed.

  12. 43 CFR 3110.5-4 - Accreted lands.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 43 Public Lands: Interior 2 2013-10-01 2013-10-01 false Accreted lands. 3110.5-4 Section 3110.5-4 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT... Accreted lands. Where an offer includes any accreted lands, the accreted lands shall be described by...

  13. 43 CFR 3110.5-4 - Accreted lands.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 2 2014-10-01 2014-10-01 false Accreted lands. 3110.5-4 Section 3110.5-4 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT... Accreted lands. Where an offer includes any accreted lands, the accreted lands shall be described by...

  14. 43 CFR 3110.5-4 - Accreted lands.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false Accreted lands. 3110.5-4 Section 3110.5-4 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT... Accreted lands. Where an offer includes any accreted lands, the accreted lands shall be described by...

  15. 43 CFR 3110.5-4 - Accreted lands.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 43 Public Lands: Interior 2 2012-10-01 2012-10-01 false Accreted lands. 3110.5-4 Section 3110.5-4 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT... Accreted lands. Where an offer includes any accreted lands, the accreted lands shall be described by...

  16. Transonic disk accretion onto black holes

    NASA Technical Reports Server (NTRS)

    Liang, E. P. T.; Thompson, K. A.

    1980-01-01

    The solution for the radial drift velocity of thin disk accretion onto black holes must be transonic, and is analogous to the critical solution in spherical Bondi accretion, except for the presence of angular momentum. The transonic requirement yields a correct treatment of the inner region of the disk not found in the conventional Keplerian models and may lead to significantly different overall disk structures. Possible observational consequences, relevant to the black hole hypothesis for Cyg X-1 and other candidates, are discussed.

  17. Implementation of Physics Education in Nature; A Pioneer Rescue Team Study: An Explanation by Physics

    NASA Astrophysics Data System (ADS)

    Gürel, Zeynep; Ergen, Hüseyin; Gürel, Atilla

    2007-04-01

    Within this research, it is generally aimed at constituting a sample implementation which shapes the contents of physics course together with its social facet and at forming a platform and starting debates for the contents. Within that purpose, we have conglomerated the students, their professor and the volunteers from the public body responsible for civil services such as the protection and maintenance of factories, power plants, rescue of civilians, and etc. to call on duty in instances of war or extra-ordinary circumstances, named civilian defence. Two camping activities in which various performances were fulfilled were held together with the students. The study focuses on sampling one of the performances which is the crossing a steam and a pond by a rope tied to trees in each ends. The focused study neither orients for nor goals any inspiration for civilian defence purposes. Civilian defence purposes are side-products and they have not been covered in the study. The main aims of this study are monitoring the instances of critical awareness in the students and presenting the samples of the process as a case study.

  18. A Particular Appetite: Cosmological Hydrodynamic Simulations of Preferential Accretion in the Supermassive Black Holes of Milky Way Size Galaxies

    NASA Astrophysics Data System (ADS)

    Sanchez, Natalie; Bellovary, Jillian M.; Holley-Bockelmann, Kelly

    2016-01-01

    With the use of cosmological hydrodynamic simulations of Milky Way-type galaxies, we identify the preferential source of gas that is accreted by the supermassive black holes (SMBHs) they host. We examine simulations of two Milky Way analogs, each distinguished by a differing merger history. One galaxy is characterized by several major mergers and the other has a more quiescent history. By examining and comparing these two galaxies, which have a similar structure at z=0, we asses the importance of merger history on black hole accretion. This study is an extension of Bellovary et. al. 2013, which studied accretion onto SMBHs in massive, high redshift galaxies. Bellovary found that the fraction of gas accreted by the galaxy was proportional to that which was accreted by its SMBH. Contrary to Bellovary's previous results, we found that though the gas accreted by a quiescent galaxy will mirror the accretion of its central SMBH, a galaxy that is characterized by an active merger history will have a SMBH that preferentially accretes gas gained through mergers. We move forward by examining the angular momentum of the gas accreted by these Milky Way-type galaxies to better understand the mechanisms fueling their central SMBH.

  19. Neighbourhood green space, physical function and participation in physical activities among elderly men: the Caerphilly Prospective study

    PubMed Central

    2014-01-01

    Background The built environment in which older people live plays an important role in promoting or inhibiting physical activity. Most work on this complex relationship between physical activity and the environment has excluded people with reduced physical function or ignored the difference between groups with different levels of physical function. This study aims to explore the role of neighbourhood green space in determining levels of participation in physical activity among elderly men with different levels of lower extremity physical function. Method Using data collected from the Caerphilly Prospective Study (CaPS) and green space data collected from high resolution Landmap true colour aerial photography, we first investigated the effect of the quantity of neighbourhood green space and the variation in neighbourhood vegetation on participation in physical activity for 1,010 men aged 66 and over in Caerphilly county borough, Wales, UK. Second, we explored whether neighbourhood green space affects groups with different levels of lower extremity physical function in different ways. Results Increasing percentage of green space within a 400 meters radius buffer around the home was significantly associated with more participation in physical activity after adjusting for lower extremity physical function, psychological distress, general health, car ownership, age group, marital status, social class, education level and other environmental factors (OR = 1.21, 95% CI 1.05, 1.41). A statistically significant interaction between the variation in neighbourhood vegetation and lower extremity physical function was observed (OR = 1.92, 95% CI 1.12, 3.28). Conclusion Elderly men living in neighbourhoods with more green space have higher levels of participation in regular physical activity. The association between variation in neighbourhood vegetation and regular physical activity varied according to lower extremity physical function. Subjects reporting poor lower extremity

  20. Magnetorotational dynamo chimeras. The missing link to turbulent accretion disk dynamo models?

    NASA Astrophysics Data System (ADS)

    Riols, A.; Rincon, F.; Cossu, C.; Lesur, G.; Ogilvie, G. I.; Longaretti, P.-Y.

    2017-02-01

    In Keplerian accretion disks, turbulence and magnetic fields may be jointly excited through a subcritical dynamo mechanisminvolving magnetorotational instability (MRI). This dynamo may notably contribute to explaining the time-variability of various accreting systems, as high-resolution simulations of MRI dynamo turbulence exhibit statistical self-organization into large-scale cyclic dynamics. However, understanding the physics underlying these statistical states and assessing their exact astrophysical relevance is theoretically challenging. The study of simple periodic nonlinear MRI dynamo solutions has recently proven useful in this respect, and has highlighted the role of turbulent magnetic diffusion in the seeming impossibility of a dynamo at low magnetic Prandtl number (Pm), a common regime in disks. Arguably though, these simple laminar structures may not be fully representative of the complex, statistically self-organized states expected in astrophysical regimes. Here, we aim at closing this seeming discrepancy by reporting the numerical discovery of exactly periodic, yet semi-statistical "chimeral MRI dynamo states" which are the organized outcome of a succession of MRI-unstable, non-axisymmetric dynamical stages of different forms and amplitudes. Interestingly, these states, while reminiscent of the statistical complexity of turbulent simulations, involve the same physical principles as simpler laminar cycles, and their analysis further confirms the theory that subcritical turbulent magnetic diffusion impedes the sustainment of an MRI dynamo at low Pm. Overall, chimera dynamo cycles therefore offer an unprecedented dual physical and statistical perspective on dynamos in rotating shear flows, which may prove useful in devising more accurate, yet intuitive mean-field models of time-dependent turbulent disk dynamos. Movies associated to Fig. 1 are available at http://www.aanda.org

  1. X-ray observations of the accreting Be/X-ray binary pulsar A 0535+26 in outburst

    NASA Astrophysics Data System (ADS)

    Caballero, I.

    2009-04-01

    Neutron stars are compact objects, characterized by R~10-14 km radius, M~1.4Msun and extremely high central densities ~10e15 g/cm^3. If they are part of a binary system, a flow of matter can take place from the companion star onto the neutron star. The accretion of matter onto neutron stars is one of the most powerful sources of energy in the universe. The accretion of matter takes place under extreme physical conditions, with magnetic fields in the range B~10^(8-15)G, which are impossible to reproduce on terrestrial laboratories. Therefore, accreting neutron stars are unique laboratories to study the matter under extreme conditions. In this thesis, X-ray observations of the accreting Be/X-ray binary A 0535+26 during a normal (type I) outburst are presented. In this system, the neutron star orbits around the optical companion HDE 245770 in an eccentric orbit, and sometimes presents X-ray outbursts (giant or normal) associated with the passage of the neutron star through the periastron. After more than eleven years of quiescence, A 0535+26 showed outbursting activity in 2005. The normal outburst analyzed in this work took place in August/September 2005, and reached a maximum X-ray flux of ~400 mCrab in the 5-100 kev range. The outburst, which lasted for ~30 days, was observed with the RXTE and INTEGRAL observatories. We have measured the spectrum of the source. In particular, two absorption-like features, interpreted as fundamental and first harmonic cyclotron resonant scattering features, have been detected at E~46 kev and E~102 kev with INTEGRAL and RXTE. Cyclotron lines are the only direct way to measure the magnetic field of a neutron star. Our observations have allowed to confirm the magnetic field of A 0535+26 at the site of the X-ray emission to be B~5x10^12 G. We studied the luminosity dependence of the cyclotron line in A 0535+26, and contrary to other sources, we found no significant variation of the cyclotron line energy with the luminosity. Changes of

  2. Magnetohydrodynamic Accretion Around Supermassive Black Holes : Short-Length Disc for Stronger Field

    NASA Astrophysics Data System (ADS)

    Biswas, Ritabrata

    2016-07-01

    Thin accretion flow, i.e., geometrically thin accretion disc was first studied by Shakura and Sunyaev. Relativistic fluid flows around a black hole produce enormous energy on the cost of permanent lost of the gravitational potential due to the fall into a infinitely sloped gravitational well or to be specific, into a space time singularity. This energy is actually observed in different wavelengths and we specify the source as Active Galactic Nuclei, quasars, Gamma-ray burst sources etc. Eventually, two popular kind of accretion disc models are there. The first one is advection dominated, known as geometrically thin optically thick accretion disc. The other is geometrically thick but optically thin as it does not capture photons inside! The jets formed by accretion phenomena are still not well explained. Size of the accretion disc, power of the jets can be powered by magnetic fields generated by the ionized particles of the accretion flow. We show the exact dependency of the disc size upon the magnetic field present along with the quantity of the central gravitating mass.

  3. MEASURING THE STELLAR ACCRETION RATES OF HERBIG Ae/Be STARS

    SciTech Connect

    Donehew, Brian; Brittain, Sean E-mail: sbritt@clemson.edu

    2011-02-15

    The accretion rate of young stars is a fundamental characteristic of these systems. While accretion onto T Tauri stars has been studied extensively, little work has been done on measuring the accretion rate of their intermediate-mass analogs, the Herbig Ae/Be stars. Measuring the stellar accretion rate of Herbig Ae/Bes is not straightforward both because of the dearth of metal absorption lines available for veiling measurements and the intrinsic brightness of Herbig Ae/Be stars at ultraviolet wavelengths where the brightness of the accretion shock peaks. Alternative approaches to measuring the accretion rate of young stars by measuring the luminosity of proxies such as the Br {gamma} emission line have not been calibrated. A promising approach is the measurement of the veiling of the Balmer discontinuity. We present measurements of this veiling as well as the luminosity of Br {gamma}. We show that the relationship between the luminosity of Br {gamma} and the stellar accretion rate for classical T Tauri stars is consistent with Herbig Ae stars but not Herbig Be stars. We discuss the implications of this finding for understanding the interaction of the star and disk for Herbig Ae/Be stars.

  4. Phantom Accretion onto the Schwarzschild AdS Black Hole with Topological Defect

    NASA Astrophysics Data System (ADS)

    Amani, Ali R.; Farahani, H.

    2012-09-01

    In this paper, we have studied phantom energy accretion of prefect fluid onto the Schwarzschild AdS black hole with topological defect. We have obtained critical point during the accretion of fluid on the black hole where the speed of flow is equal speed of sound (Sharif and Abbas in Phantom accretion onto the Schwarzschild de-Sitter black hole, 2011, arXiv:1109.1043 [gr-qc]). The critical velocities have been computed so that the speed of fluid into the black hole is less than speed of sound. Finally, we have found that the critical point is near the black hole horizon.

  5. Crustal accretion at fast spreading ridges and implications for hydrothermal circulation

    NASA Astrophysics Data System (ADS)

    Theissen-Krah, S.; Rupke, L.; Hasenclever, J.

    2015-12-01

    Oceanic crust is continuously created at mid-ocean ridges, but the location of lower crust crystallization continues to be debated since the proposal of the gabbro glacier and many sills end-member models. Geophysical and geochemical studies find evidence for either of the models. The crust is cooled by a combination of heat diffusion and advection, and hydrothermal circulation is thought to play a key role in distinguishing between both models. We use our numerical model for joint modeling of crustal accretion and hydrothermal circulation1 to test different accretion and hydrothermal cooling scenarios. The results match the seismic and structural observations from the East Pacific Rise2 and the Oman Ophiolite3, with a shallow melt lens at the correct location overlaying a narrow volume of partially molten rocks. Our results show that no more than 25-50% of the lower crust crystallizes in situ and that deep circulation is likely to occur at fast and intermediate spreading ridges. The occurrence of deep hydrothermal cooling however does not rule out that a major portion of the lower crust is formed in the shallow melt lens; our simulations rather suggest that it is necessary independent of where in the lower crust crystallization takes place. 1 Theissen-Krah, S., Iyer, K., Rupke, L. H. & Morgan, J. P. Coupled mechanical and hydrothermal modeling of crustal accretion at intermediate to fast spreading ridges. Earth and Planetary Science Letters 311, 275-286, doi:10.1016/j.epsl.2011.09.018 (2011). 2 Dunn, R. A., Toomey, D. R. & Solomon, S. C. Three-dimensional seismic structure and physical properties of the crust and shallow mantle beneath the East Pacific Rise at 9 degrees 30'N. Journal of Geophysical Research-Solid Earth 105, 23537-23555 (2000). 3 Nicolas, A. & Boudier, F. Structural contribution from the Oman ophiolite to processes of crustal accretion at the East Pacific Rise. Terra Nova 27, 77-96, doi:10.1111/ter.12137 (2015).

  6. A gender study investigating physics self-efficacy

    NASA Astrophysics Data System (ADS)

    Sawtelle, Vashti

    The underrepresentation of women in physics has been well documented and a source of concern for both policy makers and educators. My dissertation focuses on understanding the role self-efficacy plays in retaining students, particularly women, in introductory physics. I use an explanatory mixed methods approach to first investigate quantitatively the influence of self-efficacy in predicting success and then to qualitatively explore the development of self-efficacy. In the initial quantitative studies, I explore the utility of self-efficacy in predicting the success of introductory physics students, both women and men. Results indicate that self-efficacy is a significant predictor of success for all students. I then disaggregate the data to examine how self-efficacy develops differently for women and men in the introductory physics course. Results show women rely on different sources of self-efficacy than do men, and that a particular instructional environment, Modeling Instruction, has a positive impact on these sources of self-efficacy. In the qualitative phase of the project, this dissertation focuses on the development of self-efficacy. Using the qualitative tool of microanalysis, I introduce a methodology for understanding how self-efficacy develops moment-by-moment using the lens of self-efficacy opportunities. I then use the characterizations of self-efficacy opportunities to focus on a particular course environment and to identify and describe a mechanism by which Modeling Instruction impacts student self-efficacy. Results indicate that the emphasizing the development and deployment of models affords opportunities to impact self-efficacy. The findings of this dissertation indicate that introducing key elements into the classroom, such as cooperative group work, model development and deployment, and interaction with the instructor, create a mechanism by which instructors can impact the self-efficacy of their students. Results from this study indicate that

  7. Obscured AGN Accretion Across Cosmic Time

    NASA Astrophysics Data System (ADS)

    Coil, Alison

    We propose to combine data from XMM-Newton, the Chandra X-ray Observatory, and the Spitzer Space Telescope with ground-based optical spectroscopy from Keck and Magellan to measure the relationship between AGN obscuration and accretion activity over the bulk of cosmic history. This work will establish the prominence of both obscured and unobscured growth phases of black holes and shed light on the processes that trigger and fuel AGN as a function of time. We will complete three complementary projects that focus on a) understanding the completeness and biases of AGN selection at mid-IR versus X-ray wavelengths, b) tracing optical obscuration as a function of luminosity and redshift, and c) measuring the distribution and evolution of X-ray absorption of AGN. We will undertake a study of AGN demographics comparing selection techniques at three different wavelengths: mid-IR selection using data from the Spitzer Space Telescope, X- ray selection using data from the XMM-Newton and Chandra satellites, and broad-line optical selection using PRIMUS spectroscopy. We will determine the overlap and uniqueness of samples created using each method, to quantify the completeness and biases inherent in AGN selection at each wavelength. This will lead to a constraint on the fraction of heavily obscured, Compton-thick AGN to z~1. To study the optical obscuration of AGN, we will use three recently-completed spectroscopic surveys -- PRIMUS, DEEP2, and our own Keck program -- to robustly determine the ratio of unobscured (broad-line) to obscured (non--broad-line) X-ray selected AGN as a function of luminosity from z~0.2 to z~3. We will utilize the well- understood selection functions and characterize the AGN completeness of each survey as a function of redshift, magnitude, and obscuration properties. This will allow us to correct for a variety of observational effects to measure the underlying joint redshift- and luminosity-dependence of optical obscuration, which has direct implications

  8. Accretion Disks around Young Stars

    NASA Astrophysics Data System (ADS)

    D'Alessio, Paola

    1996-04-01

    A method to calculate the structure and brightness distribution of accretion disks surrounding low and intermediate mass young stars is introduced and discussed. The method includes a realistic treatment of the energy transport mechanisms and disk heating by radiation from external sources. The disk is assumed steady, geometrically thin and in vertical hydrostatic equilibrium. The turbulent viscosity coefficient is expressed using the α prescription and the α parameter and the mass accretion rate are assumed to be constant through the disk. Energy is transported in the vertical direction by: (a) a turbulent flux, computed self-consistently with the viscosity coefficient used to describe the viscous energy dissipation, (b) radiation, using the first moments of the transfer equation, the Eddington approximation, and the Rosseland and Planck Mean Opacities, and (c) convection, taking into account that the convective elements, not necessarily optically thick, lose energy by radiation and turbulent flux. This treatment of the energy transport mechanisms differs from previous work in this field, allowing one to extend, with confidence, the calculation of the disk structure to optically thin regimes. The heating mechanisms considered, which affect the disk's structure and emission, are stellar radiation and a circumstellar envelope which reprocesses and scatters radiation from the star and from the disk itself. In addition to a detailed numerical calculation, an analytical self-consistent formulation of the irradiation of the disk is given. This analytical formulation allows one to understand and extend the numerical results. To evaluate the potential of the method presented in this thesis, a set of models of viscous non-irradiated and irradiated disks are computed. Their predictions are compared with observations of young stellar sources likely to have disks. Given the disk structure and specifying its orientation with respect to the line of sight, the specific

  9. CONSTRAINTS ON THE VISCOSITY AND MAGNETIC FIELD IN HOT ACCRETION FLOWS AROUND BLACK HOLES

    SciTech Connect

    Liu, B. F.; Taam, Ronald E. E-mail: r-taam@northwestern.edu

    2013-07-15

    The magnitude of the viscosity and magnetic field parameters in hot accretion flows is investigated in low luminosity active galactic nuclei (LLAGNs). Theoretical studies show that a geometrically thin, optically thick disk is truncated at mass accretion rates less than a critical value by mass evaporated vertically from the disk to the corona, with the truncated region replaced by an advection dominated accretion flow (ADAF). The critical accretion rate for such a truncation is a function of the viscosity and magnetic field. Observations of X-ray photon indices and spectral fits of a number of LLAGNs published in the literature provide an estimate of the critical rate of mass accretion and the truncation radius, respectively. By comparing the observational results with theoretical predictions, the viscosity and magnetic field parameters in the hot accretion flow region are estimated. Specifically, the mass accretion rates inferred in different sources constrain the viscosity parameter, whereas the truncation radii of the disk, as inferred from spectral fits, further constrain the magnetic field parameter. It is found that the value of the viscosity parameter in the corona/ADAF ranges from 0.17 to 0.5, with values clustered about 0.2-0.3. Magnetic pressure is required by the relatively small truncation radii for some LLAGNs and is found to be as high as its equipartition value with the gas pressure. The inferred values of the viscosity parameter are in agreement with those obtained from the observations of non-stationary accretion in stellar mass black hole X-ray transients. This consistency provides support for the paradigm that a geometrically thin disk is truncated by means of a mass evaporation process from the disk to the corona at low mass accretion rates.

  10. PHOTOMETRIC DETERMINATION OF THE MASS ACCRETION RATES OF PRE-MAIN-SEQUENCE STARS. II. NGC 346 IN THE SMALL MAGELLANIC CLOUD

    SciTech Connect

    De Marchi, Guido; Sirianni, Marco; Panagia, Nino; Sabbi, Elena; Romaniello, Martino; Prada Moroni, Pier Giorgio; Degl'Innocenti, Scilla E-mail: panagia@stsci.edu

    2011-10-10

    We have studied the properties of the stellar populations in the field of the NGC 346 cluster in the Small Magellanic Cloud, using a novel self-consistent method that allows us to reliably identify pre-main-sequence (PMS) objects actively undergoing mass accretion, regardless of their age. The method does not require spectroscopy and combines broadband V and I photometry with narrowband H{alpha} imaging to identify all stars with excess H{alpha} emission and derive the accretion luminosity L{sub acc} and mass accretion rate M-dot{sub acc} for all of them. The application of this method to existing Hubble Space Telescope (HST)/Advanced Camera for Surveys photometry of the NGC 346 field has allowed us to identify and study 680 bona fide PMS stars with masses from {approx}0.4 M{sub sun} to {approx}4 M{sub sun} and ages in the range from {approx}1 Myr to {approx}30 Myr. Previous investigations of this region, based on the same data, had identified young ({approx}3 Myr old) candidate PMS stars on the basis of their broadband colors. In this study, we show that there are at least two, almost equally numerous, young populations with distinct ages of, respectively, {approx}1 and {approx}20 Myr. We provide accurate physical parameters for all of them. We take advantage of the unprecedented size of our PMS sample and of its spread in mass and age to study the evolution of the mass accretion rate as a function of stellar parameters. We find that, regardless of stellar mass, the mass accretion rate decreases with roughly the square root of the age, or about three times slower than predicted by current models of viscous disk evolution, and that more massive stars systematically have a higher mass accretion rate in proportion to their mass. A multivariate linear regression fit reveals that log M-dot{sub acc}{approx_equal}-0.6 log t + log m + c, where t is the age of the star, m is its mass, and c is a quantity that is higher at lower metallicity. This result is consistent with

  11. The PISA Pre-Main Sequence accreting models

    NASA Astrophysics Data System (ADS)

    Tognelli, Emanuele; Prada Moroni, Pier Giorgio; Degl'Innocenti, Scilla

    2013-07-01

    The poster investigates the effect of accretion processes on the evolution of stellar models computed by means of the well tested and updated PROSECCO evolutionary code, under the hypothesis of thin-disk accretion. We analysed the effect on the evolution of the adoption of different parameters as the accretion rate, accretion history, seed mass, and the fraction of the infalling matter energy (alpha_acc) deposed in to the star (accretion energy). We confirm that the most critical parameter is the accretion energy. We show that, depending on alpha_acc the evolution of accreting and non-accreting objects can be completely different, confirming that the adoption of small alpha_acc value (i.e. small accretion energy, cold accretion) produces fainter and more compact models with respect to the ones predicted from non-accreting structures at the same mass and age, models that can not be reconciled with the data available for young objects (i.e. position in the HR diagram, lithium abundances). On the contrary, if a large part of the accretion luminosity is deposed into the star (alpha_acc = 1, hot accretion), at least during the fisrt stages of the accretion phase or during bursts episodes, large radii and luminosities are achievable, with resulting structures much more similar to the non-accreting ones.

  12. A Study of the Effect Introductory Physical Science Produces in Students' Abilities in Selected Areas of Physics.

    ERIC Educational Resources Information Center

    Robertson, Harold Frederick, Jr.

    This study, conducted at Northeast Catholic High School for Boys in Philadelphia, was designed to determine if a significant difference existed between ninth-grade students experienced in Introductory Physical Science and ninth-grade students experienced in conventional General Science in ability to manipulate basic physics laboratory equipment,…

  13. Factors Associated with Adolescent Physical Activity during Middle School Physical Education: A One-Year Case Study

    ERIC Educational Resources Information Center

    Senne, Terry; Rowe, David; Boswell, Boni; Decker, James; Douglas, Shaun

    2009-01-01

    The purpose of this descriptive component of a larger, exploratory case study was to examine associations among lesson contexts, teacher behaviors, and adolescent physical activity over a year of physical education (PE) at one school. Middle school students (n = 206) and their PE teachers (n = 4) were observed twice-weekly across one academic…

  14. Ice Accretion Prediction on Wind Turbines and Consequent Power Losses

    NASA Astrophysics Data System (ADS)

    Yirtici, Ozcan; Tuncer, Ismail H.; Ozgen, Serkan

    2016-09-01

    Ice accretion on wind turbine blades modifies the sectional profiles and causes alteration in the aerodynamic characteristic of the blades. The objective of this study is to determine performance losses on wind turbines due to the formation of ice in cold climate regions and mountainous areas where wind energy resources are found. In this study, the Blade Element Momentum method is employed together with an ice accretion prediction tool in order to estimate the ice build-up on wind turbine blades and the energy production for iced and clean blades. The predicted ice shapes of the various airfoil profiles are validated with the experimental data and it is shown that the tool developed is promising to be used in the prediction of power production losses of wind turbines.

  15. Fractionation and Accretion of Meteorite Parent Bodies

    NASA Technical Reports Server (NTRS)

    Weidenschilling, Stuart J.

    2005-01-01

    Senior Scientist Stuart J. Weidenschilling presents his final administrative report for the research program on which he was the Principal Investigator. The research program resulted in the following publications: 1) Particle-gas dynamics and primary accretion. J. N. Cuzzi and S. J . Weidenschilling. To appear in Meteorites and the Early Solar System 11 (D. Lauretta et a]., Eds.), Univ. Arizona Press. 2005; 2) Timescales of the solar protoplanetary disk. S. Russell, L. Hartmann, J . N. Cuzzi, A. Krot, M. Gounelle and S. J. Weidenschilling. To appear in Meteorites and the Early Solar System II (D. Lauretta et al., Eds.), Univ. Arizona Press, 2005; 3) Nebula evolution of thermally processed solids: Reconciling astrophysical models and chondritic meteorites. J. N. Cuzzi, F. J. Ciesla, M. I. Petaev, A. N. Krot, E. R. D. Scott and S . J. Weidenschilling. To appear in Chondrites and the Protoplanetary Disk (A. Krot et a]., Eds.), ASP Conference Series, 2005; 4) Possible chondrule formation in planetesimal bow shocks: Physical processes in the near vicinity of the planetesimal. L. L. Hood, F. J. Ciesla and S. J. Weidenschilling. To appear in Chondrites and the Protoplanetary Disk (A. Krot et al., Eds.), ASP Conference Series, 2005; 5) From icy grains to comets. In Comets II (M. Festou et al., Eds.), Univ. Arizona Press, pp. 97- 104, 2005; 6) Evaluating planetesimal bow shocks as sites for chondrule formation. F. J . Ciesla, L. L. Hood and S. J. Weidenschilling. Meteoritics & Planetary Science 39, 1809-1 821, 2004; and 7) Radial drift of particles in the solar nebula: Implications for planetesimal formation. Icarus 165, 438-442, 2003.

  16. Pouring 'Cold Water' on Hot Accretion

    NASA Astrophysics Data System (ADS)

    Rubin, A. E.

    1995-09-01

    The extensive recrystallization of type-6 OC has been interpreted as having resulted either from prograde thermal metamorphism of initially cold, unequilibrated material [1,2] or from autometamorphism due to slow cooling of material that accreted while still hot (1000-1200 K). Although the physical implausibility of hot accretion has been addressed [3], no comprehensive evaluation has been made of arguments in its favor. As shown below, these arguments are based on incomplete data, flawed experiments or improbable interpretations. Correlation between petrologic type and Ca in low-Ca pyroxene. Models of prograde metamorphism assume that, with increasing temperature, opx acquires Ca at the expense of diopside. Analyses of pyroxene in 10 H chondrites showed no correlation between Ca in pyroxene cores and increasing petrologic type [4], but more extensive data sets show such correlations [1,5,6]. A review of data for 51 OC [7] shows a progressive increase in the Wo content of low-Ca pyroxene with petrologic type: Wo 0.4-1.2 in type-3 and -4; Wo 1.2-1.6 in type-5; and Wo 1.6-2.2 in type-6. Striated opx. Undeformed striated opx were interpreted as having formed from inverted protopyroxene during slow cooling [8]; striated opx from H4 Quenggouk were found to convert into normal opx within 1 week during annealing at 1100 K [9]. Because prograde metamorphism probably lasted ~60 Ma [10], there should be no striated opx remaining in type-4 or -5 OC. However, samples of 99% twinned clinopyroxene (analogous to that in chondrules in type-3 OC) annealed for >3 weeks at <=1250 K exhibited only very minor inversion to opx [11-13]. These experiments are consistent with prograde metamorphism; it seems likely that Quenggouk pyroxene probably had a substantial proportion of opx lamellae to begin with. Spinodal decomposition textures and cooling rates. Spinodal decomposition textures in pyroxene in type 4-5 OC were observed to have the same periodicities as those in type-3 OC [14]; it

  17. Problem roulette: Studying introductory physics in the cloud

    NASA Astrophysics Data System (ADS)

    Evrard, August E.; Mills, Michael; Winn, David; Jones, Kathryn; Tritz, Jared; McKay, Timothy A.

    2015-01-01

    We introduce Problem Roulette (PR), a web-based study service at the University of Michigan that offers random-within-topic access to a large library of past exam problems in introductory physics courses. Built on public-private cloud infrastructure, PR served nearly 1000 students during Fall 2012 term, delivering more than 60,000 problem pages. The service complements that of commercial publishing houses by offering problems authored by local professors and by explicitly aligning topics with exam content. We describe the service architecture, including reporting and analytical capabilities, and present an initial evaluation of the impact of its use. Among roughly 500 students studying electromagnetism, we find that the 229 students who worked fifty or more problems over the term outperformed their complement by 0.40 grade points (on a 4.0 scale). This improvement partly reflects a selection bias that academically stronger students used the service more frequently. Adjusting for this selection bias, we find a grade point improvement of 0.22, significantly above the random noise level of 0.04. The simple message to students is that working five or more additional problems per week can lead to a quarter-letter grade improvement in introductory physics. Student comments emphasize the importance of randomness in helping them to synthesize concepts. The PR source code is publicly available.

  18. H line; a beam line for fundamental physics study

    NASA Astrophysics Data System (ADS)

    Kawamura, Naritoshi; Toyoda, Akihisa; Aoki, Masaharu; Shimomura, Koichiro; Mibe, Tsutomu; Nakatsugawa, Yohei; Otani, Masashi; Saito, Naohito; Miyake, Yasuhiro

    2014-12-01

    The muon facility, J-PARC (Muon Science Establishment; MUSE), has been operating since the first beam in 2008. Starting with a 200 kW proton beam, a beam intensity of 3 × 106 muons/s was reached in 2009 which was the most intense pulsed muon beam in the world. From the 2 cm thick graphite target, four secondary muon beam lines are designed to be extracted. Three beam lines currently exist, the first being operational and the other two undergoing commissioning. The fourth and the last beam line, the H line, is planned to be constructed. This new beam line is designed to have a large acceptance, provides the ability to tune the momentum, and use a kicker magnet and/or a Wien filter. The H line is designed to provide an intense beam of 108 surface muons/s for fundamental physics studies to observe new physics beyond the standard model. Such studies require high statistics and they need to occupy the experimental areas for a relatively long period.

  19. Accretion onto Fast X-Ray Pulsars

    NASA Technical Reports Server (NTRS)

    Rappaport, S. A.; Fregeau, J. M.; Spruit, H.

    2004-01-01

    The recent emergence of a new class of accretion-powered, transient, millisecond X-ray pulsars presents some difficulties for the conventional picture of accretion onto rapidly rotating magnetized neutron stars and their spin behavior during outbursts. In particular, it is not clear that the standard paradigm can accommodate the wide range in M(i.e., approx. greater than a factor of 50) over which these systems manage to accrete and the high rate of spindown that the neutron stars exhibit in at least a number of cases. When the accretion rate drops sufficiently, the X-ray pulsar is said to become a "fast rotator," and in the conventional view, this is accompanied by a transition from accretion to "propellering," in which accretion ceases and the matter is ejected from the system. On the theoretical side, we note that this scenario for the onset of propellering cannot be entirely correct because it is not energetically self-consistent. We show that, instead, the transition is likely to take place through disks that combine accretion with spindown and terminate at the corotation radius. We demonstrate the existence of such disk solutions by modifying the Shakura-Sunyaev equations with a simple magnetic torque prescription. The solutions are completely analytic and have the same dependence on M and a (the viscosity parameter) as the original Shakura-Sunyaev solutions, but the radial profiles can be considerably modified, depending on the degree of fastness. We apply these results to compute the torques expected during the outbursts of the transient millisecond pulsars and find that we can explain the large spin-down rates that are observed for quite plausible surface magnetic fields of approx. 10(exp 90 G.

  20. Accretion onto Pre-Main-Sequence Stars

    NASA Astrophysics Data System (ADS)

    Hartmann, Lee; Herczeg, Gregory; Calvet, Nuria

    2016-09-01

    Accretion through circumstellar disks plays an important role in star formation and in establishing the properties of the regions in which planets form and migrate. The mechanisms by which protostellar and protoplanetary disks accrete onto low-mass stars are not clear; angular momentum transport by magnetic fields is thought to be involved, but the low-ionization conditions in major regions of protoplanetary disks lead to a variety of complex nonideal magnetohydrodynamic effects whose implications are not fully understood. Accretion in pre-main-sequence stars of masses ≲1M⊙ (and in at least some 2-3-M⊙ systems) is generally funneled by the stellar magnetic field, which disrupts the disk at scales typically of order a few stellar radii. Matter moving at near free-fall velocities shocks at the stellar surface; the resulting accretion luminosities from the dissipation of kinetic energy indicate that mass addition during the T Tauri phase over the typical disk lifetime ˜3 Myr is modest in terms of stellar evolution, but is comparable to total disk reservoirs as estimated from millimeter-wave dust emission (˜10-2 M⊙). Pre-main-sequence accretion is not steady, encompassing timescales ranging from approximately hours to a century, with longer-timescale variations tending to be the largest. Accretion during the protostellar phase—while the protostellar envelope is still falling onto the disk—is much less well understood, mostly because the properties of the central obscured protostar are difficult to estimate. Kinematic measurements of protostellar masses with new interfometric facilities should improve estimates of accretion rates during the earliest phases of star formation.

  1. Guest investigator program study: Physics of equatorial plasma bubbles

    NASA Technical Reports Server (NTRS)

    Tsunoda, Roland T.

    1994-01-01

    Plasma bubbles are large-scale (10 to 100 km) depletions in plasma density found in the night-time equatorial ionosphere. Their formation has been found to entail the upward transport of plasma over hundreds of kilometers in altitude, suggesting that bubbles play significant roles in the physics of many of the diverse and unique features found in the low-latitude ionosphere. In the simplest scenario, plasma bubbles appear first as perturbations in the bottomside F layer, which is linearly unstable to the gravitationally driven Rayleigh-Taylor instability. Once initiated, bubbles develop upward through the peak of the F layer into its topside (sometimes to altitudes in excess of 1000 km), a behavior predicted by the nonlinear form of the same instability. While good general agreement has been found between theory and observations, little is known about the detailed physics associated with plasma bubbles. Our research activity centered around two topics: the shape of plasma bubbles and associated electric fields, and the day-to-day variability in the occurrence of plasma bubbles. The first topic was pursued because of a divergence in view regarding the nonlinear physics associated with plasma bubble development. While the development of perturbations in isodensity contours in the bottomside F layer into plasma bubbles is well accepted, some believed bubbles to be cylinder-like closed regions of depleted plasma density that floated upward leaving a turbulent wake behind them (e.g., Woodman and LaHoz, 1976; Ott, 1978; Kelley and Ott, 1978). Our results, summarized in a paper submitted to the Journal of Geophysical Research, consisted of incoherent scatter radar measurements that showed unambiguously that the depleted region is wedgelike and not cylinderlike, and a case study and modeling of SM-D electric field instrument (EFI) measurements that showed that the absence of electric-field perturbations outside the plasma-depleted region is a distinct signature of wedge

  2. Propagation of tidal disturbance in gaseous accretion disks

    NASA Technical Reports Server (NTRS)

    Lin, D. N. C.; Papaloizou, J. C. B.; Savonije, G. J.

    1990-01-01

    Linear wave propagation is studied in geometrically thin accretion disks where the equilibrium variables, such as density and temperature, are stratified in the direction normal to the plane of the disk; i.e., the vertical direction. It is shown, due to refraction effects, that waves excited by tidal disturbances induced by a satellite or a companion of the central object are not expected to reach the interior regions of the disk with a significant amplitude.

  3. Particle simulation for accretion sheets in narrow double stars

    NASA Astrophysics Data System (ADS)

    Geyer, F.; Herold, H.; Ruder, H.

    1988-11-01

    Development and behavior of accretion sheets in double stars systems are studied by particle simulation calculations. Numerical analysis considers the following parameters in the binary system: primary and secondary components, path period of the system, and mass flow rates. Mass behavior is described by Roche-potential. The particle motion equation in the double star system is solved by the Leap-Frog procedure. Velocity friction simulation is obtained by viscous interaction considerations.

  4. Baseline Assessment of Net Calcium Carbonate Accretion Rates on U.S. Pacific Reefs

    PubMed Central

    Vargas-Ángel, Bernardo; Richards, Cristi L.; Vroom, Peter S.; Price, Nichole N.; Schils, Tom; Young, Charles W.; Smith, Jennifer; Johnson, Maggie D.; Brainard, Russell E.

    2015-01-01

    This paper presents a comprehensive quantitative baseline assessment of in situ net calcium carbonate accretion rates (g CaCO3 cm-2 yr-1) of early successional recruitment communities on Calcification Accretion Unit (CAU) plates deployed on coral reefs at 78 discrete sites, across 11 islands in the central and south Pacific Oceans. Accretion rates varied substantially within and between islands, reef zones, levels of wave exposure, and island geomorphology. For forereef sites, mean accretion rates were the highest at Rose Atoll, Jarvis, and Swains Islands, and the lowest at Johnston Atoll and Tutuila. A comparison between reef zones showed higher accretion rates on forereefs compared to lagoon sites; mean accretion rates were also higher on windward than leeward sites but only for a subset of islands. High levels of spatial variability in net carbonate accretion rates reported herein draw attention to the heterogeneity of the community assemblages. Percent cover of key early successional taxa on CAU plates did not reflect that of the mature communities present on surrounding benthos, possibly due to the short deployment period (2 years) of the experimental units. Yet, net CaCO3 accretion rates were positively correlated with crustose coralline algae (CCA) percent cover on the surrounding benthos and on the CAU plates, which on average represented >70% of the accreted material. For foreeefs and lagoon sites combined CaCO3 accretion rates were statistically correlated with total alkalinity and Chlorophyll-a; a GAM analysis indicated that SiOH and Halimeda were the best predictor variables of accretion rates on lagoon sites, and total alkalinity and Chlorophyll-a for forereef sites, demonstrating the utility of CAUs as a tool to monitor changes in reef accretion rates as they relate to ocean acidification. This study underscores the pivotal role CCA play as a key benthic component and supporting actively calcifying reefs; high Mg-calcite exoskeletons makes CCA

  5. Baseline Assessment of Net Calcium Carbonate Accretion Rates on U.S. Pacific Reefs.

    PubMed

    Vargas-Ángel, Bernardo; Richards, Cristi L; Vroom, Peter S; Price, Nichole N; Schils, Tom; Young, Charles W; Smith, Jennifer; Johnson, Maggie D; Brainard, Russell E

    2015-01-01

    This paper presents a comprehensive quantitative baseline assessment of in situ net calcium carbonate accretion rates (g CaCO3 cm(-2) yr(-1)) of early successional recruitment communities on Calcification Accretion Unit (CAU) plates deployed on coral reefs at 78 discrete sites, across 11 islands in the central and south Pacific Oceans. Accretion rates varied substantially within and between islands, reef zones, levels of wave exposure, and island geomorphology. For forereef sites, mean accretion rates were the highest at Rose Atoll, Jarvis, and Swains Islands, and the lowest at Johnston Atoll and Tutuila. A comparison between reef zones showed higher accretion rates on forereefs compared to lagoon sites; mean accretion rates were also higher on windward than leeward sites but only for a subset of islands. High levels of spatial variability in net carbonate accretion rates reported herein draw attention to the heterogeneity of the community assemblages. Percent cover of key early successional taxa on CAU plates did not reflect that of the mature communities present on surrounding benthos, possibly due to the short deployment period (2 years) of the experimental units. Yet, net CaCO3 accretion rates were positively correlated with crustose coralline algae (CCA) percent cover on the surrounding benthos and on the CAU plates, which on average represented >70% of the accreted material. For foreeefs and lagoon sites combined CaCO3 accretion rates were statistically correlated with total alkalinity and Chlorophyll-a; a GAM analysis indicated that SiOH and Halimeda were the best predictor variables of accretion rates on lagoon sites, and total alkalinity and Chlorophyll-a for forereef sites, demonstrating the utility of CAUs as a tool to monitor changes in reef accretion rates as they relate to ocean acidification. This study underscores the pivotal role CCA play as a key benthic component and supporting actively calcifying reefs; high Mg-calcite exoskeletons makes CCA

  6. MAGNETOSPHERIC ACCRETION IN CLOSE PRE-MAIN-SEQUENCE BINARIES

    SciTech Connect

    Ardila, David R.; Jonhs-Krull, Christopher; Herczeg, Gregory J.; Mathieu, Robert D.; Quijano-Vodniza, Alberto

    2015-10-01

    The transfer of matter between a circumbinary disk and a young binary system remains poorly understood, obscuring the interpretation of accretion indicators. To explore the behavior of these indicators in multiple systems, we have performed the first systematic time-domain study of young binaries in the ultraviolet. We obtained far- and near-ultraviolet HST/COS spectra of the young spectroscopic binaries DQ Tau and UZ Tau E. Here we focus on the continuum from 2800 to 3200 Å and on the C iv doublet (λλ1548.19, 1550.77 Å) as accretion diagnostics. Each system was observed over three or four consecutive binary orbits, at phases ∼0, 0.2, 0.5, and 0.7. Those observations are complemented by ground-based U-band measurements. Contrary to model predictions, we do not detect any clear correlation between accretion luminosity and phase. Further, we do not detect any correlation between C iv flux and phase. For both stars the appearance of the C iv line is similar to that of single Classical T Tauri Stars (CTTSs), despite the lack of stable long-lived circumstellar disks. However, unlike the case in single CTTSs, the narrow and broad components of the C iv lines are uncorrelated, and we argue that the narrow component is powered by processes other than accretion, such as flares in the stellar magnetospheres and/or enhanced activity in the upper atmosphere. We find that both stars contribute equally to the narrow component C iv flux in DQ Tau, but the primary dominates the narrow component C iv emission in UZ Tau E. The C iv broad component flux is correlated with other accretion indicators, suggesting an accretion origin. However, the line is blueshifted, which is inconsistent with its origin in an infall flow close to the star. It is possible that the complicated geometry of the region, as well as turbulence in the shock region, are responsible for the blueshifted line profiles.

  7. Physical Structure of Four Symbiotic Binaries

    NASA Technical Reports Server (NTRS)

    Kenyon, Scott J. (Principal Investigator)

    1997-01-01

    Disk accretion powers many astronomical objects, including pre-main sequence stars, interacting binary systems, and active galactic nuclei. Unfortunately, models developed to explain the behavior of disks and their surroundings - boundary layers, jets, and winds - lack much predictive power, because the physical mechanism driving disk evolution - the viscosity - is not understood. Observations of many types of accreting systems are needed to constrain the basic physics of disks and provide input for improved models. Symbiotic stars are an attractive laboratory for studying physical phenomena associated with disk accretion. These long period binaries (P(sub orb) approx. 2-3 yr) contain an evolved red giant star, a hot companion, and an ionized nebula. The secondary star usually is a white dwarf accreting material from the wind of its red giant companion. A good example of this type of symbiotic is BF Cygni: our analysis shows that disk accretion powers the nuclear burning shell of the hot white dwarf and also manages to eject material perpendicular to the orbital plane (Mikolajewska, Kenyon, and Mikolajewski 1989). The hot components in other symbiotic binaries appear powered by tidal overflow from a very evolved red giant companion. We recently completed a study of CI Cygni and demonstrated that the accreting secondary is a solar-type main sequence star, rather than a white dwarf (Kenyon et aL 1991). This project continued our study of symbiotic binary systems. Our general plan was to combine archival ultraviolet and optical spectrophotometry with high quality optical radial velocity observations to determine the variation of line and continuum sources as functions of orbital phase. We were very successful in generating orbital solutions and phasing UV+optical spectra for five systems: AG Dra, V443 Her, RW Hya, AG Peg, and AX Per. Summaries of our main results for these systems appear below. A second goal of our project was to consider general models for the

  8. Psychosocial Factors and Theory in Physical Activity Studies in Minorities

    PubMed Central

    Mama, Scherezade K.; McNeill, Lorna H.; McCurdy, Sheryl A.; Evans, Alexandra E.; Diamond, Pamela M.; Adamus-Leach, Heather J.; Lee, Rebecca E.

    2015-01-01

    Objectives To summarize the effectiveness of interventions targeting psychosocial factors to increase physical activity (PA) among ethnic minority adults and explore theory use in PA interventions. Methods Studies (N = 11) were identified through a systematic review and targeted African American/Hispanic adults, specific psychosocial factors, and PA. Data were extracted using a standard code sheet and the Theory Coding Scheme. Results Social support was the most common psychosocial factor reported, followed by motivational readiness, and self-efficacy, as being associated with increased PA. Only 7 studies explicitly reported using a theoretical framework. Conclusions Future efforts should explore theory use in PA interventions and how integration of theoretical constructs, including psychosocial factors, increases PA. PMID:25290599

  9. AS ABOVE, SO BELOW: EXPLOITING MASS SCALING IN BLACK HOLE ACCRETION TO BREAK DEGENERACIES IN SPECTRAL INTERPRETATION

    SciTech Connect

    Markoff, Sera; Silva, Catia V.; Nowak, Michael A.; Gallo, Elena; Plotkin, Richard M.; Hynes, Robert; Wilms, Jörn; Maitra, Dipankar; Drappeau, Samia E-mail: C.V.DeJesusSilva@uva.nl E-mail: egallo@umich.edu E-mail: joern.wilms@sternwarte.uni-erlangen.de E-mail: samia.drappeau@irap.omp.eu

    2015-10-20

    Over the past decade, evidence has mounted that several aspects of black hole (BH) accretion physics proceed in a mass-invariant way. One of the best examples of this scaling is the empirical “fundamental plane of BH accretion” relation linking mass, radio, and X-ray luminosity over eight orders of magnitude in BH mass. The currently favored theoretical interpretation of this relation is that the physics governing power output in weakly accreting BHs depends more on relative accretion rate than on mass. In order to test this theory, we explore whether a mass-invariant approach can simultaneously explain the broadband spectral energy distributions from two BHs at opposite ends of the mass scale but that are at similar Eddington accretion fractions. We find that the same model, with the same value of several fitted physical parameters expressed in mass-scaling units to enforce self-similarity, can provide a good description of two data sets from V404 Cyg and M81*, a stellar and supermassive BH, respectively. Furthermore, only one of several potential emission scenarios for the X-ray band is successful, suggesting it is the dominant process driving the fundamental plane relation at this accretion rate. This approach thus holds promise for breaking current degeneracies in the interpretation of BH high-energy spectra and for constructing better prescriptions of BH accretion for use in various local and cosmological feedback applications.

  10. A Study of Physics First Curricula in Pennsylvania

    ERIC Educational Resources Information Center

    Dreon, Oliver, Jr.

    2005-01-01

    Physics First has gained momentum across the country. Providing a radically different paradigm to teaching science at the high school level, the Physics First movement inverts the traditional science sequence by teaching physics to ninth grade students. One of the benefits of this change, supporters claim, is that it provides a foundation to teach…

  11. Accreting Binary Populations in the Earlier Universe

    NASA Technical Reports Server (NTRS)

    Hornschemeier, Ann

    2010-01-01

    It is now understood that X-ray binaries dominate the hard X-ray emission from normal star-forming galaxies. Thanks to the deepest (2-4 Ms) Chandra surveys, such galaxies are now being studied in X-rays out to z approximates 4. Interesting X-ray stacking results (based on 30+ galaxies per redshift bin) suggest that the mean rest-frame 2-10 keV luminosity from z=3-4 Lyman break galaxies (LBGs), is comparable to the most powerful starburst galaxies in the local Universe. This result possibly indicates a similar production mechanism for accreting binaries over large cosmological timescales. To understand and constrain better the production of X-ray binaries in high-redshift LBGs, we have utilized XMM-Newton observations of a small sample of z approximates 0.1 GALEX-selected Ultraviolet-Luminous Galaxies (UVLGs); local analogs to high-redshift LBGs. Our observations enable us to study the X-ray emission from LBG-like galaxies on an individual basis, thus allowing us to constrain object-to-object variances in this population. We supplement these results with X-ray stacking constraints using the new 3.2 Ms Chandra Deep Field-South (completed spring 2010) and LBG candidates selected from HST, Swift UVOT, and ground-based data. These measurements provide new X-ray constraints that sample well the entire z=0-4 baseline

  12. A LAGRANGIAN INTEGRATOR FOR PLANETARY ACCRETION AND DYNAMICS (LIPAD)

    SciTech Connect

    Levison, Harold F.; Duncan, Martin J.; Thommes, Edward

    2012-10-01

    We present the first particle-based Lagrangian code that can follow the collisional/accretional/dynamical evolution of a large number of kilometer-sized planetesimals through the entire growth process of becoming planets. We refer to it as the Lagrangian Integrator for Planetary Accretion and Dynamics or LIPAD. LIPAD is built on top of SyMBA, which is a symplectic N-body integrator. In order to handle the very large number of planetesimals required by planet formation simulations, we introduce the concept of a tracer particle. Each tracer is intended to represent a large number of disk particles on roughly the same orbit and size as one another and is characterized by three numbers: the physical radius, the bulk density, and the total mass of the disk particles represented by the tracer. We developed statistical algorithms that follow the velocity and size evolution of the tracers due to close gravitational encounters and physical collisions with one another. The tracers mainly dynamically interact with the larger objects (planetary embryos) in the normal N-body way. LIPAD's greatest strength is that it can accurately model the wholesale redistribution of planetesimals due to gravitational interaction with the embryos, which has recently been shown to significantly affect the growth rate of planetary embryos. We verify the code via a comprehensive set of tests that compare our results with those of Eulerian and/or direct N-body codes.

  13. 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.

  14. No collective neutrino flavor conversions during the supernova accretion phase.

    PubMed

    Chakraborty, Sovan; Fischer, Tobias; Mirizzi, Alessandro; Saviano, Ninetta; Tomàs, Ricard

    2011-10-07

    We perform a dedicated study of the supernova (SN) neutrino flavor evolution during the accretion phase, using results from recent neutrino radiation hydrodynamics simulations. In contrast to what was expected in the presence of only neutrino-neutrino interactions, we find that the multiangle effects associated with the dense ordinary matter suppress collective oscillations. The matter suppression implies that neutrino oscillations will start outside the neutrino decoupling region and therefore will have a negligible impact on the neutrino heating and the explosion dynamics. Furthermore, the possible detection of the next galactic SN neutrino signal from the accretion phase, based on the usual Mikheyev-Smirnov-Wolfenstein effect in the SN mantle and Earth matter effects, can reveal the neutrino mass hierarchy in the case that the mixing angle θ(13) is not very small.

  15. Thin accretion discs are stabilized by a strong magnetic field

    NASA Astrophysics Data System (ADS)

    Sądowski, Aleksander

    2016-07-01

    By studying three-dimensional, radiative, global simulations of sub-Eddington, geometrically thin (H/R ≈ 0.15) black hole accretion flows we show that thin discs which are dominated by magnetic pressure are stable against thermal instability. Such discs are thicker than predicted by the standard model and show significant amount of dissipation inside the marginally stable orbit. Radiation released in this region, however, does not escape to infinity but is advected into the black hole. We find that the resulting accretion efficiency (5.5 ± 0.5 per cent for the simulated 0.8dot{M}_Edd disc) is very close to the predicted by the standard model (5.7 per cent).

  16. The Accretion Process in Extremely High Magnetic Field Polars

    NASA Astrophysics Data System (ADS)

    Vogel, Justus

    2009-10-01

    We propose a triggered observation of one of the highest magnetic field polars known which escaped XMM-Newton so far. Utilizing the broad spectral range covered by XMM-Newton including the OM, we will simultaneously determine the energy content of the three cooling channels of the post-shock accretion plasma: cyclotron radiation in the UV, plasma radiation in hard X-rays and re-processed radiation in soft X-rays. We will confront our observations with state-of-art models and study quantitatively the energy balance of the cooling plasma as a function of white dwarf mass, accretion rate and magnetic field strength. Our targets, all with magnetic fields in excess of 100 MG give access to a rather unexplored parameter regime.

  17. Properties of Accretion Flows Irradiated by a Quasar

    NASA Astrophysics Data System (ADS)

    Proga, Daniel

    2008-03-01

    I present results from recent time-dependent hydrodynamical calculations of flows that are under the influence of supermassive black hole gravity and radiation from an accretion disk surrounding the hole. The calculations take into account radiation heating/cooling and the radiation force due to electron scattering and spectral lines. I show how the mass accretion and outflow rates, and the flow dynamics respond to thermal effects and effects of radiation pressure and gas rotation. The main focus of this work is to gain insights into the problem of AGN feedback which is studie